Skip to Main Content

Abstract

The southern Patagonian Cordillera south of the present location of the Chile Triple Junction (46.5°S) preserves distinctive deformational and backarc magmatic features that are a consequence of a series of northward-propagating ridge collision events that started at ca. 14 Ma. An abrupt increase of ~2000 m of topographic elevation and the exhumation and uplift of mid-Miocene to Pliocene plutons within the cordillera south of the Chile Triple Junction is accomplished by horizontal compressive deformation (both thin- and thick-skinned) within the Patagonian fold-thrust belt. Ridge-trench collisions have formed asthenospheric slab windows beneath the southern Patagonian Cordillera. Backarc magmatism associated with slab window formation includes a distinctive suite of adakites and extensive outpourings of oceanic island basalt (OIB)-like plateau basalts. The adakites formed from the partial melting of the young, hot trailing edge of the Nazca plate that preceded slab window opening, whereas the OIB-like plateau basalts formed from dynamic asthenospheric flow as the slab windows opened up beneath the backarc.

Introduction

The purpose of this field trip is to examine the geologic features associated with the process of ridge-trench collision along a partial transect across the southern Patagonian Cordillera near the latitude of the present location of the Chile Triple Junction at 46.5°S latitude (Fig. 1). The effects of the northward-propagating ridge collision events starting at ca. 14 Ma at 54°S latitude are well documented by ophiolite emplacement and forearc subduction erosion (Bourgois et al., 1996; Mpodozis et al., 1985; Guivel et al., 1999), anomalous forearc felsic and mid-oceanic ridge basalt (MORB)-like magmatism (Mpodozis et al., 1985; Forsythe et al., 1986; Lagabrielle et al., 1994; Le Moigne et al., 1996), production of a gap in the Quaternary volcanic arc (Stern et al., 1990), rapid uplift and reactivation of deformation in the fold-and-thrust belt (Ramos, 1989; Coutand et al., 1999; Kraemer et al., 2002), and adakitic and OIB-like basaltic magmatism in the backarc (Gorring et al., 1997; Ramos et al., 2004). All of these well-documented effects, coupled with the relatively simple and well-constrained plate convergence geometry, make southern Patagonia one of the best places on Earth to investigate geo dynamic processes associated with ridge collision.

Figure 1.

Tectonic setting of southern South America showing the distribution of Neogene plateau lavas, adakites, the Patagonian fold-and-thrust belt, and the Southern (SVZ) and Austral Volcanic Zones (AVZ). Ridge collision times are shown in bold numbers (Cande and Leslie, 1986).

Figure 1.

Tectonic setting of southern South America showing the distribution of Neogene plateau lavas, adakites, the Patagonian fold-and-thrust belt, and the Southern (SVZ) and Austral Volcanic Zones (AVZ). Ridge collision times are shown in bold numbers (Cande and Leslie, 1986).

However, due to the geography, difficult access, and long distances, this trip will concentrate on features that are most easily accessible from the Argentine foreland basin and backarc side, into the hinterland of the cordillera in Chile, but not as far as the forearc region in the Taitao Peninsula area. The main highlights of this trip will include spectacular, “whole mountain-side” exposures of the hinterland and foreland portions of the Patagonian fold-thrust belt and examples of the Late Miocene to Pleistocene adakitic and basaltic magmatism that occurred in the backarc. Along the way, we will also observe other classic geologic features of the southern Patagonian Andes including the Miocene Fitz Roy pluton, Jurassic rhyolites, late Paleozoic low-grade metamorphic basement, Cretaceous granitoids of Patagonian Batholith, well-exposed Cretaceous and Tertiary sedimentary sections, and Pleistocene moraine complexes and geomorphology.

Users of this guide should keep in mind that this area presents particular challenges in terms of logistics. Air access, vehicle rental, and availability of modern amenities are generally limited to the three major towns and cities in the region (El Calafate, Comodoro Rivadavia in Argentina, and Coyhaique in Chile). Outside of these major towns, fuel is generally available in the small towns and outposts, but distances are deceptively great and the region desolate. Therefore, one must stop at every available gas station to fuel up and carefully plan for adequate supplies of food and water. Lodging is generally not an issue, but don't expect modern facilities outside of the major towns. The majority of the roads are gravel but are well maintained. Gravel eventually will take its toll on the vehicle, thus one must have at least two “real” spare tires and an array of essential tools (heavy-duty jack, assorted wrenches, shovel, etc.) to deal with problems on the road. Groceries and lodging are generally quite limited outside the major towns.

The Southern Patagonian Cordillera

The Andean Cordillera lines the entire 7000-km-long western margin of South America where subduction of oceanic plates has occurred beneath the continent. They are the result of crustal thickening due to horizontal shortening and magmatic addition since the Late Cretaceous. The southern Patagonian Cordillera is defined here as the segment of the Andes, south of the latitude of the Chile Triple Junction at 46.5°S and north of 53°S where the more E-W–trending Fueguian Cordillera approximately begins. From east to west, the southern Patagonian Cordillera can be divided into four distinctive zones (e.g., Kraemer, 1993; Diraison et al., 2000; Ramos, 2005).

  1. The Magallanes (or Austral) foreland basin, containing relatively undeformed early Cretaceous to Tertiary sediments reaching a maximum thickness of 8000 m.

  2. The Patagonian fold-and-thrust belt, where late Paleozoic sedimentary and metamorphic rocks, Jurassic volcanics, and early Cretaceous to Tertiary sediments form belts of thick-and thin-skinned deformation.

  3. The central main cordillera, where late Paleozoic sedimentary and metamorphic rocks, Jurassic volcanics, and Mesozoic to Miocene calc-alkaline granitoids of the Patagonian Batholith are characterized mainly by thick-skinned, high-angle reverse and thrust deformation.

  4. The western coastal belt, where a highly deformed, accretionary prism complex of late Paleozoic meta sedimentary rocks are intruded by granitoids of the Patagonian Batholith.

Late Paleozoic

Paleozoic basement rocks are widely exposed in the southern Patagonian Cordillera and record evidence for a major episode of crustal shortening along the margin of the supercontinent Gondwana. They consist of two different units: (1) low-grade metasedimentary rocks of the Rio Lacteo Formation and (2) the thick sedimentary sequence of the Bahia La Lancha Formation. Rocks of the Rio Lacteo Formation are found to the north, between 45° and 48°S, and are dominated by quartzites, mica schists, and phyllites with minor greenstones and marbles (Leanza, 1972; Hervé, 1988; Hervé et al., 1998; Bell and Suárez, 2000). The Bahia La Lancha Formation is a typical flysch sequence of graywacke, quartz sandstones, and shale up to 2000 m thick that is exposed to the south between 48° and 51°S (Riccardi, 1971). Time constraints for the Rio Lacteo Formation are derived from K-Ar ages of intrusive tonalitic rocks of Late Carboniferous–Early Permian at various locations (Halpern, 1973; Niemeyer et al., 1984; Ramos, 1989; Bell and Suárez, 2000). Bahia La Lancha rocks contain fossils of Late Devonian–Carboniferous age (Riccardi, 1971). Main deformation and metamorphism of both units is thought to be related to the docking of various allochthonous terranes that collided with the active Pacific margin of Gondwana in the latest Paleozoic (Gondwanide Orogeny) (Ramos, 1988).

Triassic to Middle Jurassic

Following the period of terrane accretion in the late Paleozoic, the southwestern margin of Gondwana appears to have experienced widespread extension and crustal thinning that preceded the eventual breakup of the supercontinent (Dalziel, 1981). From the late Triassic to mid-Jurassic, a system of NNW-oriented rift basins were formed, and vast quantities of silicic volcanics (mainly rhyolite and associated volcaniclastics) covered more than 106 km2 of Patagonia (Gust et al., 1985; Pankhurst et al., 1998). This important suite of volcanics in southern South America is known as the Chon Aike province (Kay et al., 1989; Pankhurst et al., 1998). Locally these rocks have various formation names such as Tobifera Formation (Thomas, 1949), El Quemado Complex (Riccardi, 1971), and Ibáñez Formation (Niemeyer et al., 1974). Chon Aike volcanics were deposited unconformably over the late Paleozoic basement and locally attain thicknesses of >2000 m (Biddle et al., 1986).

Cretaceous

The Cretaceous heralds the start of the “Andean” tectonic cycle as subduction along the western margin of South America began and was characterized by initial uplift of the Patagonian Cordillera, development of the Magallanes foreland basin, and emplacement of the majority of the Patagonian Batholith (Katz, 1972; Suárez and Pettigrew, 1976; Winslow, 1981, 1982). During the latest Jurassic and early Cretaceous, erosion of the Chon Aike volcanics provided clastic material for the fluvial and marginal marine sands that eventually formed the basal unit of the Magallanes basin, called the Springhill Formation (Riccardi, 1988). The Springhill is an important unit because it is the primary reservoir for hydrocarbon exploration in Magallanes basin. Subsequently, a thick sequence of early to middle Cretaceous black marine shales (the Rio Mayer and Rio Belgrano Formations), were deposited in an anoxic environment across the entire basin and provided the main source for hydrocarbons (Pittion and Gouadain, 1992). Uplift and deformation in the southern Patagonian Cordillera started in the middle to late Cretaceous and is marked by a peak in plutonic activity in the eastern margin of the Patagonian Batholith and by a change to coarse clastic sediments delivered to the Magallanes basin (e.g., the El Alamo, La Anita, Chorillo, Cerro Fortaleza, and Lago Sofia Formations; Winslow, 1982). From this point onward, the Magallanes basin developed as a true foreland basin as deformation progressed eastward toward the craton, producing the Patagonian fold-thrust belt (Winslow, 1981, 1982; Ramos, 1989; Kraemer, 1993; Klepeis, 1994; Coutand et al., 1999). Plate reorganization and/or an increase in plate convergence rates along the Patagonian margin are thought to have been responsible.

Early Cenozoic

In the Paleogene, continued uplift and deformation occurred within the southern Patagonian Cordillera (see reviews in Diraison et al., 2000; Ramos, 2005) as relatively rapid and steady convergence along the margin was maintained (Minster and Jordan, 1978; Pardo-Casas and Molnar, 1987; Gripp and Gordon, 1990). Paleogene uplift and deformation in the southern Patagonian Cordillera is marked by changing sedimentation patterns and deepening of the Magallanes basin westward toward the main cordillera with as much as 5000 m of sediment infill in the axial part of the basin (Biddle et al., 1986). Foreland basin sedimentation was dominated by continental and shallow marine sediments that are interpreted as synorogenic molasse deposits based on the presence of growth strata and prominent regional angular unconformities (Biddle et al., 1986; Malumián, 2002; Kraemer et al., 2002; Suárez et al., 2000). These sediments are youngest and record maximum deformation in the Fuegian Cordillera where the NNE convergence vector was more orthogonal to the margin (see Ramos, 2005). Unlike the Cretaceous, widespread subduction zone magmatism in the main cordillera is not observed (Ramos, 1982). Instead, large volumes of alkaline, OIB-like basalts erupt in the foreland basin and backarc regions, represented by the Posadas basalt. Peak magmatic activity for the Posadas basalts occurred at ca. 49 Ma, but they also show a broad southward younging age progression from north to south between 53 and 43 Ma (Ramos and Kay, 1992; Kay et al., 2002).

Punctuating the overall steady convergence is the collision of the Farallon-Aluk spreading ridge system (Cande and Leslie, 1986). According to plate reconstructions by Cande and Leslie (1986), this ridge collision proceeded southward along the margin from ~42°S to the tip of Tierra del Fuego between ca. 60 and 40 Ma. Thus, there appears to be a close temporal and spatial correlation between the timing of ridge collision and deformation in the fold-and-thrust belt, cessation of arc magmatism, and the eruption of OIB-like alkaline basalts in the backarc (e.g., Ramos and Kay, 1992; Ramos, 2005).

Late Cenozoic

A new round of intense uplift and deformation occurred within the southern Patagonian Cordillera throughout the Neogene as the modern convergence geometry is established along the margin at ca. 25 Ma. The initial stage of Neogene uplift and deformation is marked by the deposition synorogenic molasse of the Rio Frias and Santa Cruz Formations in the early to middle Miocene that unconformably overly deformed Cretaceous and Paleogene sedimentary rocks. Superimposed on this relatively rapid convergence is the collision of the Chile Ridge spreading system beginning ca. 15 Ma (Cande and Leslie, 1986) and is thought to be responsible for the climax of Neogene uplift and deformation (Ramos, 2005). This ridge collision caused arc magmatism to shut down and shift eastward with the eruption of OIB-like alkaline basalts (Ramos and Kay, 1992; Gorring et al., 1997) and slab-melt adakites in the backarc (Kay et al., 1993; Ramos et al., 2004) and the emplacement of synorogenic granitoids on the eastern side of the main cordillera. A unique suite of forearc volcanics and granitoids was also emplaced along the western coastal belt on the Taitao Peninsula (Mpodozis et al., 1985; Forsythe et al., 1986; Lagabrielle et al., 1994; Le Moigne et al., 1996; Guivel et al., 1999; Lagabrielle et al., 2000). Neogene topographic uplift is also thought to have contributed to intense glaciation of the southern Patagonian Cordillera, starting around 6 Ma (Mercer, 1976) and continuing into the Holocene (Ivins and James, 1999).

Late Cenozoic Tectonic Framework

The current tectonic framework of the southern Andean Cordillera involves a relatively complex interaction between the oceanic Nazca, Antarctic, and Scotia plates and the continental South American plate (Fig. 1). The Nazca plate subducts rapidly beneath the South American plate at a relative velocity of 9 cm/yr, whereas the Antarctic plate subducts more slowly at 2 cm/yr. The Nazca and Antarctic plates are separated by the Chile Ridge system. At the southernmost tip of the Andes, the Scotia and South American plates form a large-scale, left-lateral transcurrent boundary. The current plate motion vectors and relative convergence rates were established ca. 25 Ma, when the Nazca plate vector changed from highly oblique (010°E) to approximately orthogonal (080°E) with respect to the continental margin of South America (Minster and Jordan, 1978; Pardo-Casas and Molnar, 1987; Gripp and Gordon, 1990).

Beginning at ca. 14–15 Ma, the Chile ridge system collided with the southernmost tip of the Patagonian Andes, in the western part of Tierra del Fuego (Cande and Leslie, 1986). The Chile Triple Junction (the triple point between Nazca, Antarctica, and South America) has since migrated northward along the margin in a series of ridge collision events to its present location near the Taitao Peninsula at 46.5°S (Cande and Leslie, 1986). Thus, since the middle Miocene, the tectonics along the margin of the southern Patagonian Cordillera south of Chile Triple Junction has changed from rapid (9 cm/yr), slightly oblique (075°E) convergence associated with subduction of the Nazca plate to slow (2 cm/yr), orthogonal (090°E) convergence associated with Antarctic plate subduction. Because the Chile Ridge system is segmented with individual ridge axes oriented NNW-SSE, the ridge collision is only slightly oblique to the margin. This relatively simple collision geometry coupled with the rapid (7 cm/yr) westward absolute plate motion vector of the South American plate is likely responsible for the complete subduction of the Chile Ridge system without any trace of internal deformation in either the Nazca or Antarctic plates.

Consequences of Ridge Collision

The primary, large-scale geodynamic consequence of the ridge-trench collision is the formation of asthenospheric slab windows beneath the southern Patagonian Cordillera (Cande and Leslie, 1986; Ramos and Kay, 1992; Gorring et al., 1997) (see Fig. 2). Slab windows form because of the large differential convergence velocities (~7 cm/yr) between the Nazca and Antarctic plates (Gorring et al., 1997). In theory, the opening of slab window allows relatively hot, asthenospheric mantle to flow upward between plates (e.g., Thorkelson, 1996), and this process has been linked to profound effects on the late Cenozoic magmatic and deformational history of the southern Patagonian Cordillera (Ramos and Kay, 1992; Gorring et al., 1997; Ramos, 2005). The unique geodynamics of ridge collision and slab window formation, in theory, should have profound, observable effects on the geologic evolution of a mountain belt. In the southern Patagonian Cordillera, the following features are thought to be related (either directly or indirectly) to the late Cenozoic ridge-trench collision:

Figure 2.

Schematic cross sections (no vertical exaggeration) showing the Patagonian slab window model (Gorring et al., 1997), highlighting mantle source regions and petrogenetic processes involved in the genesis of Neogene slab window lavas erupted northeast of where a Chile Ridge segment collided with the Chile Trench at ca. 12 Ma. Abbreviations: OIB—oceanic island basalt; SSVZ—southern Southern Volcanic Zone.

Figure 2.

Schematic cross sections (no vertical exaggeration) showing the Patagonian slab window model (Gorring et al., 1997), highlighting mantle source regions and petrogenetic processes involved in the genesis of Neogene slab window lavas erupted northeast of where a Chile Ridge segment collided with the Chile Trench at ca. 12 Ma. Abbreviations: OIB—oceanic island basalt; SSVZ—southern Southern Volcanic Zone.

This field trip will focus on the last two items on the bulleted list above, and these items are described in further detail below.

Patagonian Fold-and-Thrust Belt

Basic Structure

The Patagonian fold-and-thrust belt is a classic foreland fold-thrust belt that extends for ~1000 km along the eastern foothills of the southern Andes between 46° and 55°S along the southwestern margin of the Magallanes basin (Winslow, 1982; Ramos, 1989; Klepeis, 1994; Kraemer, 2003) (Fig. 1). The belt is ~40–100 km wide and can be generally split into two along-strike segments, an eastern foreland zone and a western hinterland zone (Ramos, 1989; Kraemer, 1993) (Fig. 3). In the sector north of 51°S, deformation in the eastern foreland zone is characterized by gentle, kilometer-scale folding and thin-skinned, west-verging backthrusts in Cretaceous and Tertiary sedimentary rocks (Ramos, 1989; Kraemer, 1993; Coutand et al., 1999). Deformation gradually increases westward toward the hinterland, where deformation is characterized by mostly thick-skinned, east-verging imbricate thrust sheets that uplift late Paleozoic basement and Mesozoic volcanic rocks (Fig. 4). A triangle zone marks the transition between the foreland and hinterland zones, which is particularly well developed north of Lago San Martin (~49°S; Ramos, 1989) (Figs. 3 and 4). Major décollements are recognized to occur near the base of the Rio Mayer Formation and within the late Paleozoic metasedimentary basement where much of the shortening is accommodated. Fault kinematic analysis and the N-S to NNW trend of folds and thrusts both indicate dominant E-W compression with a component of right-lateral wrenching along strike in this sector of the Patagonian fold-and-thrust belt (Coutand et al., 1999).

Figure 3.

Major structures of the Patagonian fold-and-thrust belt. Figure from Ramos (1989).

Figure 3.

Major structures of the Patagonian fold-and-thrust belt. Figure from Ramos (1989).

Figure 4.

(on this and following page). Structural cross sections of the Patagonian fold-and-thrust belt. Lines of section are in Figure 3. Figure from Ramos (1989).

Figure 4.

(on this and following page). Structural cross sections of the Patagonian fold-and-thrust belt. Lines of section are in Figure 3. Figure from Ramos (1989).

Topography and Timing of Deformation in Relation to Late Cenozoic Ridge Collision

The timing of deformation in the southern Patagonian Cordillera and the development of the Patagonian fold-and-thrust belt is broadly constrained by important changes in sedimentation and the presence of unconformities in the Cretaceous and Tertiary section. There is general consensus that the initial formation of the fold-and-thrust belt started during the middle to late Cretaceous and was followed by major contractional events that took place during the latest Cretaceous, Eocene, and Miocene times (e.g., Ramos, 1989; Suárez et al., 2000). These major deformational events have been linked to periods of rapid orthogonal convergence at ca. 80 Ma, ca. 50–40 Ma, and 25–10 Ma (e.g., Suárez et al., 2000), but were also enhanced by ridge collisions events during these times (e.g., Ramos and Kay, 1992; Ramos, 2005).

With respect to the late Cenozoic event, the beginning of deformation is constrained by synorogenic molasse deposits of the Rio Frias and Santa Cruz Formations that contain interbedded ash layers with maximum Ar/Ar ages of ca. 19 Ma (Feagle et al., 1995). An angular unconformity exists between the Santa Cruz Formation and the overlying main plateau basalts, the oldest of which are ca. 14–12 Ma (Gorring et al., 1997), and constrains the minimum age of significant foreland basin sedimentation. Additional evidence for latest Oligocene to mid-Miocene deformation comes from apatite fission track data, which suggest that rapid uplift and denudation started ca. 30–23 Ma along the Pacific coast and subsequently migrated 200 km eastward until ca. 12–8 Ma (Thomson et al., 2001). New age data and structural information from the Torres del Paine region (51°S) suggest significant late Oligocene to mid-Miocene compressional deformation constrained by the deformed “external gabbros” dated at ca. 30 Ma and the undeformed Torres del Paine pluton with a minimum age of ca. 12 Ma (Altenburger et al., 2003). Oxygen isotope data from paleosols from the Santa Cruz Formation indicate that the present-day orographic rain shadow across the southern Patagonian Cordillera was established between ca. 17 and 14 Ma and can be attributed to rapid topographic uplift of >1 km (Blisniuk et al., 2005). The above data clearly indicate that uplift and deformation was well under way prior to collision of the Chile ridge system and is linked to more orthogonal and increased convergence rates at ca. 25 Ma (e.g., Ramos, 1989; Suárez et al., 2000; Thomson et al., 2001).

However, there is also evidence that final uplift and deformation in the eastern main cordillera and the Patagonian fold-thrust belt is linked to the late Cenozoic ridge collision along the southern Patagonian margin. Ramos and Kay (1992) and Ramos (2005) pointed out the drastic change in the topography and style of deformation that occurs at the latitude of the modern Chile Triple Junction (46.5°S). There is an abrupt uplift of >2000 m of elevation along the crest of the Patagonian Cordillera from north to south at 46.5°S (Fig. 5). To the north, the average elevation of the highest peaks of the Patagonian Cordillera is ~2000 m, whereas to the south of the Chile Triple Junction, average elevations increase suddenly to >4000 m (Cerro San Valentin, 4078 m) and remain relatively high at >3000 m (Cerro San Lorenzo, 3706 m; Cerro Fitz Roy, 3405 m; Cerro Paine Grande, 3050 m; among others) until 53°S, where once again maximum average peak heights are ~2000 m. This difference in topography is spatially correlated with a significant difference in the style of deformation north and south of the Chile Triple Junction and the development of the southern Patagonian fold-thrust belt (Ramos, 2005).

Figure 5.

North-south topographic section of the Patagonian Andes in which maximum elevation is indicated at each latitude. Present Chile Ridge collision is taking place at 46.5°S. Figure from Ramos (2005).

Figure 5.

North-south topographic section of the Patagonian Andes in which maximum elevation is indicated at each latitude. Present Chile Ridge collision is taking place at 46.5°S. Figure from Ramos (2005).

South of the Chile Triple Junction, uplift of the southern Patagonian Cordillera is accomplished by crustal stacking that involves substantial amounts of shortening taken up by both thin-skinned (foreland) and thick-skinned deformation (main cordillera). North of the Chile Triple Junction, there is only a modest amount of shortening, with crustal stacking taking place primarily through mild tectonic inversion of Mesozoic normal faults coupled with significant dextral transpressional deformation taken up on the Liquine-Ofqui Fault (Fig. 6). Further evidence for Late Cenozoic ridge collision-related uplift and deformation comes from isotopic ages (mostly K/Ar and 40Ar/39Ar) of granitoid plutons from the eastern edge of the main cordillera. Ages range between 18 and 3 Ma and include the following:

Figure 6.

Schematic cross sections highlighting major structural differences of the Patagonian Cordillera north (A) and south (B) of the present Chile Triple Junction. Figure from Ramos (2005).

Figure 6.

Schematic cross sections highlighting major structural differences of the Patagonian Cordillera north (A) and south (B) of the present Chile Triple Junction. Figure from Ramos (2005).

The mid-Miocene to Pliocene ages coupled with the present elevation of >2000–4000 m of the Cerro Fitz Roy, Cerro San Lorenzo, and Torres del Paine plutons clearly require significant post-middle to late Miocene exhumation and erosion of cover rocks (e.g., Skarmeta and Castelli, 1997; Suárez et al., 2000; Ramos, 2005). Coutand et al. (1999) cited evidence for Pliocene shortening in Patagonian fold-thrust belt along the north shore of Lago Viedma (49.5°S) that includes gentle tilting of Pliocene plateau basalts and feeder dikes that cut Early Cretaceous sediments that are offset with top to the east (reverse) sense of motion. In the Lago Buenos Aires region (~46.5°S), Lagabrielle et al. (2004) cited geomorphic evidence for post– late-Miocene uplift, including uplift and dissection of relict late Miocene-Pliocene paleosurfaces, stream capture, and transpressional strike-slip faults that cut late Miocene plateau basalts.

Backarc Magmatism Related to Ridge Collision

Perhaps the most unequivocal affects of ridge collision in the southern Patagonian Cordillera are the backarc magmatic affects. Suites of distinctive igneous rocks are well characterized geochemically and are well constrained by radiometric dating and thus can be correlated in both and time and space with the sequential collision of segments of the Chile Ridge along the southern Patagonian margin since the middle Miocene (Gorring et al., 1997; Ramos et al., 2004).

Adakites

The term “adakite” was coined by Defant and Drummond (1990) for a geochemically distinctive type of silicic volcanic rocks from Adak Island in the Aleutians. These rocks were originally discovered and interpreted by Kay (1978) as being generated by partial melting of oceanic crust (e.g., “slab melting”). Since 1990, the term adakite has been applied (controversially) to a variety of volcanic rocks with “adakitic” geo chemical characteristics that may have formed from distinctly different processes other than direct slab melting, namely forearc subduction erosion and partial melting of thickened mafic lower continental crust (see Kay and Kay, 2002). Thus, the origin of many adakites via direct slab melting has been vigorously debated (see Yogodzinski et al., 2001).

Perhaps the best remaining candidates for a slab-melt origin are those from southern Patagonia that erupted in the backarc region east of the modern volcanic arc gap between the Austral Volcanic Zone and Southern Volcanic Zone and where ridge subduction has occurred over the past ca. 12 Ma (Kay et al., 1993; Ramos et al., 2004). Adakites from three separate localities have been recognized: these are the Chaltén (49.2°S), Puesto Nuevo (48.6°S), and Cerro Pampa (47.6°S) adakites. Outcrops at all three localities are relatively small (~100–200 m diameter), pluglike, subvolcanic (?) bodies of porphyritic dacite with large (up to 4–5 cm long), acicular phenocrysts of hornblende ± plagioclase. Convincing geochemical evidence for a slab-melt origin for these hornblende dacites comes from high Sr (1330–2300 ppm), Cr (80–100 ppm), and Ni (40–75) at 63%–68% SiO2, MORB-like 87Sr/86Sr (0.7028–0.7033), 143Nd/144Nd >0.51289, and steep rare earth element (REE) patterns (La/Yb = 28–38, heavy rare earth element [HREE]-depleted) (Kay et al., 1993; Ramos et al., 2004) (Table 1). New 40Ar/39Ar laser ablation dates on hornblende for Chaltén, Puesto Nuevo, and Cerro Pampa adakites show a systematic northward decrease in age from ca. 14.5, ca. 13.1, to ca. 11.5 Ma, respectively (Ramos et al., 2004). The geochemistry and timing of these adakites is consistent with partial melting of the young, hot trailing edge of the Nazca plate associated with the ca. 12 Ma ridge collision event that preceded slab window opening and the eruption of extensive OIB-like basalts (Fig. 2).

TABLE 1.

GEOCHEMICAL AND AGE DATA FOR PATAGONIAN SLAB WINDOW VOLCANICS

Cerro PampaPuesto NuevoChalténPost-plateauMain-plateau
SampleRB5RB7RB8PNA1FVRLC-7LC-21
Latitude (°S)47°54.5′47°54.5′47°54.5′48°56.0′49°25.5′49°11.4′48°18.3′
Longitude (°W)71°25.4′71°25.4′71°25.4′72°12.5′72°59.5′71°20.7′70°58.2′
SiO2 (wt%)62.5567.8863.2265.6764.9747.8953.22
TiO20.620.510.840.680.662.961.60
Al2O317.2716.2616.5316.5615.2115.1115.96
FeO3.132.243.783.023.3211.408.70
MnO0.090.110.110.100.060.170.13
MgO3.622.482.922.923.427.226.21
CaO7.124.506.724.404.517.898.14
Na2O4.664.564.314.253.664.074.02
K2O1.221.701.882.703.701.770.48
P2O5N.D.N.D.N.D.0.250.241.020.22
Total100.3100.2100.3100.699.899.598.7
La (ppm)2721402730499
Ce61459764649319
Nd30205229274313
Sm4.43.27.64.95.08.83.8
Eu1.160.771.931.161.192.631.34
Tb0.340.270.630.380.431.060.66
Yb0.720.691.200.960.991.721.50
Lu0.090.080.160.120.130.210.23
Sr18861334229414391369925452
Ba306391356320381523135
Cs0.300.300.603.201.000.600.20
RbN.D.N.D.N.D.N.D.N.D.N.D.7.3
U1.002.601.802.003.101.750.54
Th5.06.77.57.014.96.41.1
PbN.D.N.D.N.D.N.D.N.D.N.D.1.5
YN.D.N.D.N.D.N.D.N.D.N.D.20
ZrN.D.N.D.N.D.N.D.N.D.N.D.108
Hf3.23.25.05.45.75.82.4
NbN.D.N.D.N.D.N.D.N.D.N.D.13
Ta0.701.800.700.500.804.390.84
Sc8611991718
Cr978581100102159218
Ni7647435468116133
Co1591514134840
87Sr/86Sr0.702900.703090.702850.703210.70330N.D.0.70358
eNd+5.7+5.5+6.9+4.9~+5N.D.N.D.
Ar/Ar age (Ma)N.D.N.D.11.4 ± 0.613.1 ± 0.614.5 ± 0.3<6 (?)ca. 12
Cerro PampaPuesto NuevoChalténPost-plateauMain-plateau
SampleRB5RB7RB8PNA1FVRLC-7LC-21
Latitude (°S)47°54.5′47°54.5′47°54.5′48°56.0′49°25.5′49°11.4′48°18.3′
Longitude (°W)71°25.4′71°25.4′71°25.4′72°12.5′72°59.5′71°20.7′70°58.2′
SiO2 (wt%)62.5567.8863.2265.6764.9747.8953.22
TiO20.620.510.840.680.662.961.60
Al2O317.2716.2616.5316.5615.2115.1115.96
FeO3.132.243.783.023.3211.408.70
MnO0.090.110.110.100.060.170.13
MgO3.622.482.922.923.427.226.21
CaO7.124.506.724.404.517.898.14
Na2O4.664.564.314.253.664.074.02
K2O1.221.701.882.703.701.770.48
P2O5N.D.N.D.N.D.0.250.241.020.22
Total100.3100.2100.3100.699.899.598.7
La (ppm)2721402730499
Ce61459764649319
Nd30205229274313
Sm4.43.27.64.95.08.83.8
Eu1.160.771.931.161.192.631.34
Tb0.340.270.630.380.431.060.66
Yb0.720.691.200.960.991.721.50
Lu0.090.080.160.120.130.210.23
Sr18861334229414391369925452
Ba306391356320381523135
Cs0.300.300.603.201.000.600.20
RbN.D.N.D.N.D.N.D.N.D.N.D.7.3
U1.002.601.802.003.101.750.54
Th5.06.77.57.014.96.41.1
PbN.D.N.D.N.D.N.D.N.D.N.D.1.5
YN.D.N.D.N.D.N.D.N.D.N.D.20
ZrN.D.N.D.N.D.N.D.N.D.N.D.108
Hf3.23.25.05.45.75.82.4
NbN.D.N.D.N.D.N.D.N.D.N.D.13
Ta0.701.800.700.500.804.390.84
Sc8611991718
Cr978581100102159218
Ni7647435468116133
Co1591514134840
87Sr/86Sr0.702900.703090.702850.703210.70330N.D.0.70358
eNd+5.7+5.5+6.9+4.9~+5N.D.N.D.
Ar/Ar age (Ma)N.D.N.D.11.4 ± 0.613.1 ± 0.614.5 ± 0.3<6 (?)ca. 12

Note: Adakite data from Kay et al. (1993) and Ramos et al. (2004); slab window basalt data from Gorring and Kay (2001). N.D.—not determined.

OIB-Like Slab Window Basalts

Large volumes of mafic slab window magmas erupted over vast areas of the southern Patagonian backarc southeast of the modern Chile Triple Junction following a series of ridge collisions along the Chile Trench during the mid- to late Miocene (Gorring et al., 1997). Slab window lavas are most abundant between 46.5° and 49.5°S, northeast of two ridge segments that collided at ca. 12 Ma and ca. 6 Ma and are located 100–400 km east of the volcanic arc gap between the Southern Volcanic Zone and Austral Volcanic Zone (Fig. 1). K/Ar and 40Ar/39Ar ages (Ramos and Kay, 1992; Gorring et al., 1997) suggest two periods of magmatism: (1) an older (12–5 Ma) voluminous, tholeiitic (48%–55% SiO2; 4%–5% Na2O + K2O) main-plateau sequence and (2) a younger (7 to <0.1 Ma), less voluminous, alkaline (43%–49% SiO2; 5%–8% Na2O + K2O) post-plateau sequence (Fig. 7). The main-plateau lavas form large, elevated plateaus of the Mesetas de la Muerte, Belgrano, del Lago Buenos Aires, Central, and the smaller mesetas in the northeast region. The main-plateau lavas have a maximum total thickness of 100–200 m, and their total eruptive volume is estimated at 1000–2000 km3. The post-plateau lava sequence includes small scoria cones, lava flows, and pyroclastic deposits capping the main-plateau sequence with a total eruptive volume estimated at 100 km3. Both main- and post-plateau lavas have strong OIB-like geochemical signatures (La/Ta < 20; Ba/La < 20; 87Sr/86Sr = 0.7035–0.7049; 143Nd/144Nd = 0.51290–0.51261) (Table 1) and, in the backarc segment opposite the 12 Ma ridge collision, systematically young to the northeast (Fig. 7B).

Figure 7.

(A) Map showing the distribution of Neogene main-plateau and post-plateau lavas, and the location of the Cerro Pampa adakite. AVZ— Austral Volcanic Zone; SSVZ—southern Southern Volcanic Zone. (B) Plot of slab window plateau lavas ages projected onto the SW-NE transect in (A) showing the northeastward younging trend of the main- and post-plateau lavas. Arrow shows predicted age progression for a mantle hotspot track based on a 2.5 cm/yr absolute plate motion vector for South America. Gray zone shows the predicted time when the trailing edge of the Nazca plate passed beneath the backarc. Both figures modified from Gorring et al. (1997).

Figure 7.

(A) Map showing the distribution of Neogene main-plateau and post-plateau lavas, and the location of the Cerro Pampa adakite. AVZ— Austral Volcanic Zone; SSVZ—southern Southern Volcanic Zone. (B) Plot of slab window plateau lavas ages projected onto the SW-NE transect in (A) showing the northeastward younging trend of the main- and post-plateau lavas. Arrow shows predicted age progression for a mantle hotspot track based on a 2.5 cm/yr absolute plate motion vector for South America. Gray zone shows the predicted time when the trailing edge of the Nazca plate passed beneath the backarc. Both figures modified from Gorring et al. (1997).

A slab window tectonic model has been developed by Gorring et al. (1997) to explain the sequence of magmatic events occurring along a SW-NE transect opposite the Chile Ridge segment that collided at ca. 12 Ma as shown in Figure 2. Normal arc volcanism, similar to that in the modern Andean Southern Volcanic Zone, is assumed to have occurred in the modern arc gap prior to ridge collision in the early Miocene. By 12 Ma, the ridge had collided, causing volcanism in the former arc region to cease and shift into the backarc. Partial melting of the young, hot, Nazca Plate produced the southern Patagonian adakites. Contemporaneous eruptions of minor volumes of mafic backarc lavas are best related to melting in the supraslab mantle wedge that preceded the opening of the slab window. From 10 to 2 Ma, mafic lavas with strong OIB-like chemical signatures derived from the subslab asthenospheric mantle erupted across the backarc above a developing slab window. Main-plateau lavas represent relatively large-degree partial melts (10%–15%) associated with strong asthenospheric flow around the trailing Nazca plate edge, whereas post-plateau lavas are small-degree melts (1%–4%) generated by weak asthenospheric flow through a wide slab window. A simple one-stage melting model of a pristine OIB-like subslab asthenospheric source can explain most post-plateau lavas. Main-plateau lavas from the western backarc are also dominated by the OIB-like subslab asthenospheric mantle, but clearly have evidence for arc and crustal components (relatively low Nb/U and Ce/Pb and high Sr/La) derived from interaction with slab-melt and fluid-contaminated mantle wedge and continental lithosphere. Finally, backarc magmatism ends and the locus magmatic activity shifts westward to form the arc volcanism in the Austral Volcanic Zone above the leading edge of the Antarctic plate (Stern and Kilian, 1996). Farther north, opposite the ridge segment that collided at 6 Ma, a similar dynamic slab window model can explain abundant Plio-Pleistocene (5–0.2 Ma), main- and post-plateau lavas that occur in the Meseta del Lago Buenos Aires region.

Road Log

Day 1—El Calafate to El Chaltén

We will drive east out of Calafate on Provincial Route 11. On the south side of the valley, one can observe (from a distance) the beautifully exposed (glacially carved), upper Cretaceous and Tertiary foreland basin sedimentary section. We then turn north on the famous “Ruta Cuarenta” or National Route 40 and soon pass over the Rio Santa Cruz and cross over the Rio La Leona. After ~70 km, turn left onto Provincial Route 23 and travel west toward the cordillera along the north side of Lago Viedma. We will make several stops along this road to examine the large-scale structure of the Patagonian fold-and-thrust belt as we drive west into the town of El Chaltén.

On the north side of the valley, Late Cretaceous and Tertiary sediments are unconformably overlain by flat-lying basalts that form high plateaus (Mesetas Basaltica, Chica, and del Viento). These plateau basalts have early Pliocene K/Ar whole-rock ages of ca. 3.5 Ma (Mercer, 1976). In this area, we are located near the eastern edge of the deformation front in the foreland basin where the Cretaceous sediments are only mildly deformed and fold wavelengths are large (km scale) and amplitudes are small.

Stop 1-1: Patagonian Fold-Thrust Belt

Once west of the Rio Cangrejo, deformation intensity noticeably increases as we pass a section of the late Cretaceous La Anita and Pari Aike Formations that are moderately east dipping beneath the western edge of the Meseta Chica. The first stop(s) will be at or near the bridge over the Rio Blanco, where we can observe (from a distance) structures associated with surface exposure of the easternmost, thin-skinned thrusts faults (both east and west verging) (Figs. 8 and 9). Folds in the marine sandstones of the Cerro Toro Formation beneath the Bardas de Kaiken Aike are of chevron, kink, and concentric styles, typical of flexural slip in rhythmically layered, turbidite sequences.

Figure 8.

Geologic and structural map of the northern shore of Lago Viedma, with location of the structural section in Figure 9. Figure from Coutand et al. (1999).

Figure 8.

Geologic and structural map of the northern shore of Lago Viedma, with location of the structural section in Figure 9. Figure from Coutand et al. (1999).

Figure 9.

Structural cross section partly controlled by seismic data. Black bars indicate approximate location of seismic lines. No vertical exaggeration. Figure from Coutand et al. (1999).

Figure 9.

Structural cross section partly controlled by seismic data. Black bars indicate approximate location of seismic lines. No vertical exaggeration. Figure from Coutand et al. (1999).

Stop 1-2: Patagonian Fold-Thrust Belt

The second major stop will be on the east side of the bridge across the Rio de las Vueltas. Along the gorge walls, there are very nice exposures of the early Cretaceous black shales of the Rio Mayer Formation cut by several small basaltic(?) dikes and capped by glacial deposits. The black shales of the Rio Mayer Formation form the basal décollement for the thin-skinned part of the Patagonian fold-and-thrust belt. On the south-facing flanks of Cerro Faldeo there are spectacular folds (and thrusts) within the Rio Mayer Formation.

Stop 1-3: Patagonian Fold-Thrust Belt

The third stop will be a few kilometers to the west at a formal scenic viewpoint just within the national park boundary. This vantage point, on a clear day, affords a spectacular view of the granitic spires of Cerro Fitz Roy (3405 m) and Cerro Torre (3102 m) and an overview of the thick-skinned portion of the Patagonian fold-and-thrust belt. At this location, we are only a few kilometers east of the first of several east-verging, steeply dipping, thick-skinned thrusts that uplift and bring to the surface late Paleozoic marine metasediments (low-grade Bahia La Lancha Formation, which forms the basal décolle ment), Jurassic volcanics of the El Quemado Complex, early Cretaceous shales of the Rio Mayer Formation, and the Miocene Cerro Fitz Roy pluton (Figs. 8 and 9). Depending on weather conditions and time, several stops will be made near the town of El Chaltén or in the Lago Desierto region to observe the general geology of the area. Overnight is in El Chaltén at the Hotel Fitz Roy.

Day 2—El Chaltén to Estancia La Angostura

Stop 2-1: Cerro Fitz Roy Pluton

Weather permitting, we will take a short trek (~6 km round-trip; ~200 m elevation change) up to the first good, relatively close viewpoint of the Cerro Fitz Roy pluton. On the way, we will be walking over and around outcrops of the Jurassic El Quemado Formation, which is a thick series of rhyolitic volcanics. The Miocene Cerro Fitz Roy pluton is a composite calc-alkaline pluton made up of mostly coarse-grained quartz monzonite and diorite and has an imprecise K/Ar age of 18 ± 3 Ma (Nullo et al., 1978). The pluton intrudes the Jurassic El Quemado Complex and the late Paleozoic Bahia La Lancha Formation and generally has steep, sharp contacts that can be seen in the high col between Aguja Saint Exupery and Mojon Rojo and the high col between southeast flank of Cerro Torre and the Cordon Adela. To the south of Cerro Fitz Roy, Coutand et al. (1999) identified an associated granitic sheet that has been thrust over intensely deformed Rio Mayer shales indicating that the Cerro Fitz Roy pluton is a syntectonic intrusion.

Stop 2-2: Chaltén Adakite

After the trek, we will drive east out of El Chaltén back along Provincial Route 23. The second stop of the day will be the Chaltén adakite (Ramos et al., 2004), located ~10 km east of El Chaltén, just inside the national park boundary. The outcrop forms a low hill on the north side of Route 23 that is partially covered by glacial till. The Chaltén adakite is a coarse-grained, porphyritic dacite with abundant acicular to prismatic hornblende phenocrysts (2–3 cm) in a matrix of fine-grained plagioclase and clino pyroxene. The Chaltén adakite has all the classic geochemical characteristics of a slab-melt adakite (high SiO2, Sr, Cr, Ni, steep REE patterns, and MORB-like 87Sr/86Sr and 143Nd/144Nd ratios) (Table 1, sample FVR; Fig. 10). Ramos et al. (2004), obtained 40Ar/39Ar laser ablation ages on hornblende phenocrysts that yielded a step-heated plateau age of 14.5 ± 0.29 Ma. This age predates ridge collision by ca. 2.5 Ma and is consistent with partial melting of the young portion of the Nazca plate that would have been subducting beneath backarc at this time (see model in Fig. 2).

Figure 10.

Geochemical plots showing the strong oceanic island basalt (OIB)-like characteristics of Neogene Patagonian main-plateau (filled symbols) and post-plateau (open symbols) slab window lavas. Data and fields from Kay et al. (1993), Gorring and Kay (2001), and Ramos et al. (2004). BSE—bulk silicate earth; HIMU—high U/Pb mantle; MORB—mid-oceanic ridge basalt; NMORB—normal mid-oceanic ridge basalt; OIB—oceanic island basalt; SSVZ—southern Southern Volcanic Zone.

Figure 10.

Geochemical plots showing the strong oceanic island basalt (OIB)-like characteristics of Neogene Patagonian main-plateau (filled symbols) and post-plateau (open symbols) slab window lavas. Data and fields from Kay et al. (1993), Gorring and Kay (2001), and Ramos et al. (2004). BSE—bulk silicate earth; HIMU—high U/Pb mantle; MORB—mid-oceanic ridge basalt; NMORB—normal mid-oceanic ridge basalt; OIB—oceanic island basalt; SSVZ—southern Southern Volcanic Zone.

Stop 2-3: Slab Window Plateau Basalts

Continue eastward on Route 23 and then turn north on National Route 40 toward the small town of Tres Lagos. Continue north on Route 40 from the gas station at Tres Lagos. About 20 km north of Tres Lagos, the road begins to enter an increasingly narrower valley with basalt plateaus on both sides. These are late Miocene to Pliocene alkali basalts of the post-plateau sequence of the Meseta La Siberia and are dated at ca. 5–7 Ma (Gorring et al., 1997). The road gradually climbs in elevation and then comes over a pass a few kilometers north of the Estancia La Lucia. The third major stop will be along National Route 40 ~50 km north of Tres Lagos and 2–3 km north of Estancia La Lucia. At this locality, several flows from a young, monogenetic cinder cone complex (Cerro Cordon) located 1–2 km to the east are exposed in several nice roadcuts. Stern et al. (1990) reported small (<5 cm diameter) spinel lherzolite xenoliths in some of the lavas from this locality. These lavas belong to the latest Miocene to Pleistocene post-plateau sequence of Gorring et al. (1997). The lavas are highly alkaline basalts with strong OIB-like characteristics, typical of southern Patagonian slab window plateau lavas (Table 1, sample LC-7; Fig. 10). This locality has not been dated, but other post-plateau lavas from the area clearly postdate the timing of ridge collision by at least 5 Ma and erupted when the slab window beneath this part of the backarc was fully developed (Fig. 2).

Stop 2-4: Lago Cardiel Overview

Continue north on Route 40 for another ~50 km and stop along the road at overlook of Lago Cardiel. From this vantage point looking west, one can see the inverted topographic relations of the older, higher, mid-Miocene main-plateau lavas (10–12 Ma) of the Mesetas la Siberia and de la Muerte and the early Pliocene (4–5 Ma) post-plateau lavas that cap the low elevation surfaces that form peninsulas on the north and south sides of the lake. Continue north on Route 40 for another ~80 km. Overnight is at the Estancia La Angostura.

Day 3—Estancia La Angostura to Lago Posadas

Stop 3-1: Rio Chico Overview; Main Plateau Lavas

Continue north on Route 40 in the valley of the Rio Chico. The first stop will be above the bridge over the Rio Chico. Here we can obtain good views of mid-Miocene main-plateau lavas to the west (Meseta de la Muerte) and to the north and east (Meseta Central). Pliocene post-plateau lavas can be observed at distinctly lower elevation on the east side of the Rio Chico valley. Beautiful examples of alluvial terrace levels are exposed from the active downcutting of the river. The terraces are composed of the famous “Patagonian gravel,” which forms a more or less continuous sheet (on average a few meters thick, but up to 50–100 m thick in places) across Patagonia. Originally noted and interpreted (more or less correctly) by Charles Darwin, the gravels represent the huge quantities of glacial outwash shed off of the southern Patagonian Cordillera during peak Plio-Pleistocene glaciations.

Stop 3-2: Slab Window Plateau Basalts

Continue northwestward on Route 40 for ~35 km. The second stop will be at the road maintenance facility at Tamel Aike. Nice exposures on the north side of the road, behind the buildings, allow us to examine a representative example of the mid-Miocene main-plateau basalts. These lavas are tholeiitic basalts, with flat REE patterns (low La/Yb ratios) and relatively low concentrations of incompatible elements. Although dominantly OIB-like, they have geochemical evidence for contamination with both arc and crustal components (Table 1, sample LC-21; Fig. 10). This particular locality has not been dated, but main-plateau lavas in the immediate vicinity have 40Ar/39Ar total fusion ages of ca. 12 Ma (Gorring et al., 1997) and erupted at about the same time as the ridge collision, and thus, technically are not “slab window lavas” senso stricto.

Stop 3-3: Glacial Geomorphology

Continue north on Route 40 for ~120 km, until we reach the small hamlet of Bajo Caracoles at the head of the glacial valley of Lago Puyrredón. This desolate place sits on top of a moraine that affords spectacular, long distance views of the cordillera crowned by Cerro San Lorenzo (3706 m) and the high, Miocene basalt-capped plateaus to the north (Meseta del Lago Buenos Aires) and south (Meseta Belgrano). Follow Provincial Road 39 west, toward the town of Lago Posadas (also known as Hipólito Yrigoyen). We will cross several prominent moraine complexes with intervening outwash plains. The Lagos Puyreddon and Buenos Aires valleys (the next one to the north) contain a complete record of at least 16 glacial advances since the Greatest Patagonian Glaciation that occurred at ca. 1.1 Ma (Singer et al., 2004). These are some of the best preserved moraine complexes on Earth, let alone in the Southern Hemisphere. Our third stop of the day will be ~35 km west of Bajo Caracoles on Route 39 at the prominent roadcut on the crest of a moraine complex in order to examine its internal structure.

Stop 3-4: Patagonian Fold-Thrust Belt

As we approach the town of Lago Posadas, we will again see spectacular, glacially carved, continuous, mountainside exposure of the eastern deformation front of the Patagonian fold-and-thrust belt. At the fourth stop, just southeast of the town of Lago Posadas, a complete Cretaceous to early Miocene sedimentary section is exposed on the north flank of the Meseta Belgrano. The entire section is gently tilted to the east into a frontal monocline and marks the eastern limit of deformation (see cross section A–A′ on Fig. 4; section D–D′ on Fig. 11). It is capped by undeformed, mid-Miocene, main-plateau lavas that have been dated ca. 10 Ma (Gorring et al., 1997). From this location, the main peak of Cerro San Lorenzo (3706 m) is also visible, if weather permits. Cerro San Lorenzo is the second highest peak in the Patagonian Cordillera. It is an oval-shaped (130 km2), calc-alkaline granitoid pluton. Recent K/Ar and 40Ar/39Ar radiometric age dates on various rock types within the pluton have yielded latest Miocene ages ranging from 6.2 ± 0.2 Ma to 6.6 ± 0.5 Ma (Welkner, 2000). Depending on weather conditions and time, additional stops will be made west of the Lago Posadas, in particular a glacially scoured outcrop of Jurassic volcanics, a Younger Dryas(?) moraine that cuts across Lago Puyrredón, and an overlook of the “Garganta del Diablo” on the Rio Oro. Overnight is in Lago Posadas.

Figure 11.

Geologic cross sections of the Patagonian fold-and-thrust belt near Lago Posadas at ~47°S. Figure from Giacosa et al. (1999).

Figure 11.

Geologic cross sections of the Patagonian fold-and-thrust belt near Lago Posadas at ~47°S. Figure from Giacosa et al. (1999).

Day 4—Lago Posadas to Puerto Bertrand via Los Antiguos and Chile Chico

Drive east out of Lago Posadas and then north onto the secondary road heading north toward Paso Roballos. This road traverses across the Sierra Colorado, which is a block of the Jurassic rhyolitic volcanics (mostly ignimbrites) of the El Quemado Complex uplifted on east-verging thrust faults (section C–C′ on Fig. 11).

Stop 4-1: Zeballos Complex and Tertiary Sediments

The first stop of the day will be at the pass at ~1500 m elevation at a place called the “El Portezuelo” or sometimes referred to as Paso Zeballos. Early to middle Miocene Rio Zeballos Group fluvial sandstones and conglomerates (equivalent to the Santa Cruz Formation) that represent foreland basin molasse deposits are well exposed in the canyons of the Rio Zeballos and Rio Jeinimeni (Figs. 12 and 13). Conspicuous meter-wide dikes intrude the Zeballos Group in several localities. On the east side of the valley, middle Miocene to Pleistocene slab window basalts of the Meseta del Lago Buenos Aires unconformably overly the Rio Zeballos Group. The prominent Monte Zeballos (2743 m), the sharp spire of Cerro Zeballos (2073 m), and an unnamed, light-colored dome (2648 m, 40Ar/39Ar age = 3.3 ± 0.3 Ma; Brown et al., 2004) dominate the eastern skyline on the western edge of the Meseta del Lago Buenos Aires. Recent reconnaissance mapping and geochemical analyses (DaSilva et al., 2006) indicate that this a highly alkaline volcanic complex (informally named the “Zeballos Complex”) that contains rare trachyandesitic and trachydacitic lavas and intrusives that are typically of Neogene slab window-related plateau sequences. The Sierra Chacabuco on the west side of the valley is composed of Jurassic volcanics that are uplifted along a N-S east-vergent thrust fault that lies roughly within the axis of the valley (section B–B′ on Fig. 11). This thrust dies out to the north of Lago Buenos Aires as deformation style changes to the mild tectonic inversion characteristic of the foreland north of the Chile Triple Junction.

Figure 12.

Geologic map of the Lago General Carrera–Buenos Aires area. Figure from Lagabrielle et al. (2004).

Figure 12.

Geologic map of the Lago General Carrera–Buenos Aires area. Figure from Lagabrielle et al. (2004).

Figure 13.

Geologic cross section along line of section in Figure 12. Figure from Lagabrielle et al. (2004).

Figure 13.

Geologic cross section along line of section in Figure 12. Figure from Lagabrielle et al. (2004).

West of Chile Chico, the main road follows the southern shore of Lago General Carrera and traverses through mostly Jurassic rhyolitic volcanics. About ~50 km west of Chile Chico, the road crosses a prominent river valley at Puerto Fachinal. On the west side of the river there are excellent roadcuts through glacial sediments and the road climbs up onto the Fachinal Moraine (Younger Dryas?). About 25 km west of Fachinal, the road cuts through the ca. 10 Ma Paso Las Llaves granite pluton. Another ~40 km west, just east of the Rio Las Duñas, outcrops of northernmost Cosmelli Basin can be seen in the low craggy hills to the south. The Cosmelli Basin (see map in Fig. 12) succession consists of late Paleocene to early middle Miocene marine and fluvial molasse sediments that are equivalent to the Centinela and Santa Cruz Formations in Argentina. The basin is deformed and shows evidence of synsedimentary contractional tectonics interpreted to be related to the same early to late Miocene deformation that affected the Patagonian fold-and-thrust belt in the Argentine foreland (Flint et al., 1994).

Finally, west of Puerto Guadal to Puerto Bertrand, there are numerous roadcuts of the late Paleozoic metasedimentary rocks of the Rio Lacteo Formation, which form the metamorphic basement of the southern Patagonian Cordillera. These rocks represent metamorphosed marine turbidites, limestones, and pyroclastics rocks that were intensely deformed and subjected to medium-grade greenschist facies metamorphism during pre-late Carboniferous times (Bell and Suárez, 2000). Stay overnight in cabins along the Rio Baker a few kilometers south of Puerto Bertrand.

Day 5—Puerto Bertrand to Coyhaique

Drive back north along the Carretera Austral (Chilean National Route 7). The late Paleozoic Rio Lacteo Formation is exposed along many roadcuts between Puerto Bertrand and Puerta Murta, a distance of ~100 km. Along this stretch of road there are many excellent viewpoints of the high peaks to the west, especially the San Valentin massif (4078 m), the highest peak in the Patagonian Cordillera. The Cretaceous Patagonian Batholith underlies these peaks, and the high topography supports the Northern Patagonian Ice Cap. There are also superb vistas looking southwest across Lago General Carrera. Near Puerto Murta there are roadcut exposures of Cretaceous granitoids of the batholith and the young (<1 Ma) Murta basalts to examine. The road continues northeastward and then west following the Rio Ibáñez to the town of Villa Castillo. The picturesque Cordón Castillo dominates the view and is made up of a roof pendant (?) of Jurassic ignimbrites overlying granitoids of the Patagonian Batholith.

References Cited

Altenburger
,
U.
Oberhansli
,
R.
Putlitz
,
B.
Wemmer
,
K.
,
2003
,
Tectonic controls and Cenozoic magmatism at the Torres del Paine, southern Andes (Chile, 51°10′S)
:
Revista Geológica de Chile
 , v.
30
, no.
1
, p.
65
81
.
Bell
,
M.
Suárez
,
M.
,
2000
,
The Rio Lacteo Formation of southern Chile: Late Paleozoic orogeny in the Andes of southernmost South America
:
Journal of South American Earth Sciences
 , v.
13
, p.
133
145
,
doi: 10.1016/S0895-9811(00)00005-5
.
Biddle
,
K.T.
Uliana
,
M.A.
Mitchum
,
R.M.
Fitzgerald
,
M.G.
Coutand
,
I.
Diraison
,
M.
Cobbold
,
P.R.
Gapais
,
D.
Rossello
Wright
,
R.C.
,
1986
,
The stratigraphic and structural evolution of the central and eastern Magallanes basin, South America
, in
Allen
,
P.A.
Homewood
,
P.
, eds.,
Foreland basins
 :
International Association of Sedimentologists, Special Publication
, v.
8
, p.
41
61
.
Blisniuk
,
P.M.
Stem
,
L.A.
Chamberlain
,
C.P.
Idleman
,
B.
Zeitler
,
P.K.
,
2005
,
Climatic and ecologic changes during Miocene surface uplift in the Southern Patagonian Andes
:
Earth and Planetary Science Letters
 , v.
230
, p.
125
142
,
doi: 10.1016/j.epsl.2004.11.015
.
Bourgois
,
J.
Martin
,
H.
Le Moigne
,
J.
Frutos
,
J.
,
1996
,
Subduction erosion related to spreading-ridge subduction: Taitao peninsula (Chile margin triple junction area)
:
Geology
 , v.
24
, p.
723
726
,
doi: 10.1130/ 0091-7613(1996)024<0723:SERTSR>2.3.CO;2
.
Brown
,
L.L.
Singer
,
B.S.
Gorring
,
M.
,
2004
,
Paleomagnetic and geochronologic results from Meseta del Lago Buenos Aires, Patagonia
:
Geochemistry Geophysics Geosystems
 , v.
5
, p.
Q01H04
,
doi: 10.1029/ 2003GC000526
.
Cande
,
S.C.
Leslie
,
R.B.
,
1986
,
Late Cenozoic tectonics of the Southern Chile Trench
:
Journal of Geophysical Research
 , v.
91
, p.
471
496
.
Coutand
,
I.
Diraison
,
M.
Cobbold
,
P.R.
Gapais
,
D.
Rossello
,
E.A.
Miller
,
M.
,
1999
,
Structure and kinematics of a foothills transect, Lago Viedma, southern Andes (49°30′S)
:
Journal of South American Earth Sciences
 , v.
12
, p.
1
15
,
doi: 10.1016/S0895-9811(99)00002-4
.
Dalziel
,
I.W.D.
,
1981
,
Backarc extension in the southern Andes: A review and critical reappraisal
:
Philosophical Transactions of the Royal Society of London, Series A
 , v.
300
, p.
319
335
,
doi: 10.1098/rsta.1981.0067
.
DaSilva
,
M.
Gorring
,
M.L.
Singer
,
B.
Brown
,
L.
,
2006
,
Ridge subduction volcanism in the Zeballos Complex, southern Patagonian Andes: Backbone of the Americas, Patagonia to Alaska, Mendoza, Argentina, April 3–7, 2006
:
Geological Society of America Abstracts with Programs
 , v.
2
, p.
49
.
Defant
,
M.J.
Drummond
,
M.S.
,
1990
,
Derivation of some modern arc magmas by melting of young subducted lithosphere
:
Nature
 , v.
347
, p.
662
665
,
doi: 10.1038/347662a0
.
Diraison
,
M.
Cobbold
,
P.R.
Gapais
,
D.
Rosello
,
E.
,
2000
,
Cenozoic crustal thickening, wrenching and rifting in the foothills of the southernmost Andes
:
Tectonophysics
 , v.
316
, p.
91
119
,
doi: 10.1016/S0040-1951(99)00255-3
.
Feagle
,
J.G.
Bown
,
T.M.
Swisher
,
C.
Buckley
,
G.A.
,
1995
,
Age of the Pinturas and Santa Cruz Formations
:
VI Congreso Argentino de Paleontología y Bioestratigrafía (Trelew), Actas
 , p.
129
135
.
Flint
,
S.S.
Prior
,
D.J.
Agar
,
S.M.
Turner
,
P.
,
1994
,
Stratigraphic and structural evolution of the Tertiary Cosmelli Basin and its relationship to the Chile triple junction
:
Journal of the Geological Society
 , v.
151
, p.
251
268
,
doi: 10.1144/gsjgs.151.2.0251
.
Forsythe
,
R.D.
Nelson
,
E.P.
Carr
,
M.J.
Kaeding
,
M.E.
Hervé
,
M.
Mpodozis
,
C.
Soffia
,
J.M.
Harambour
,
S.
,
1986
,
Pliocene near-trench magmatism in southern Chile: A possible manifestation of ridge collision
:
Geology
 , v.
14
, p.
23
27
,
doi: 10.1130/0091-7613(1986)14<23:PNMISC> 2.0.CO;2
.
Giacosa
,
R.E.
Franchi
,
M.
Genini
,
A.
,
1999
,
Hoja Geológica 4772-III Lago Belgrano, Hoja Geológica 4772-IV Lago Posadas, Provincia de Santa Cruz
:
Buenos Aires, Servicio Geológico Minero Argentina
 , v.
256
,
scale: 1:250,000
.
Gorring
,
M.L.
Kay
,
S.M.
,
2001
,
Mantle sources and processes of Neogene slab window magmas from southern Patagonia, Argentina
:
Journal of Petrology
 , v.
42
, p.
1067
1094
,
doi: 10.1093/petrology/42.6.1067
.
Gorring
,
M.L.
Kay
,
S.M.
Zeitler
,
P.K.
Ramos
,
V.A.
Rubiolo
,
D.
Fernandez
,
M.L.
Panza
,
J.L.
,
1997
,
Neogene Patagonian plateau lavas: Continental magmas associated with ridge collision at the Chile Triple Junction
:
Tectonics
 , v.
16
, p.
1
17
,
doi: 10.1029/96TC03368
.
Gripp
,
A.E.
Gordon
,
R.G.
,
1990
,
Current plate velocities relative to the hotspots incorporating the NUVEL-1 global plate motion model
:
Geophysical Research Letters
 , v.
17
, p.
1109
1112
.
Guivel
,
C.
Lagabrielle
,
Y.
Bourgois
,
J.
Maury
,
R.C.
Fourcade
,
S.
Martin
,
H.
Arnaud
,
N.
,
1999
,
New geochemical constraints for the origin of ridge subduction-related plutonic and volcanic suites from the Chile Triple Junction (Taitao Peninsula and Site 862, LEG ODP on the Taitao Ridge)
:
Tectonophysics
 , v.
311
, p.
83
111
,
doi: 10.1016/S0040-1951(99)00160-2
.
Gust
,
D.A.
Biddle
,
K.T.
Phelps
,
D.W.
Uliana
,
M.A.
,
1985
,
Associated middle to late Jurassic volcanism and extension in southern South America
:
Tectonophysics
 , v.
116
, p.
223
253
,
doi: 10.1016/0040-1951(85)90210-0
.
Halpern
,
M.
,
1973
,
Regional geochronology of Chile south of 50° latitude
:
Geological Society of America Bulletin
 , v.
84
, p.
2407
2422
,
doi: 10.1130/ 0016-7606(1973)84<2407:RGOCSO>2.0.CO;2
.
Hervé
,
F.
,
1988
,
Late Paleozoic subduction and accretion in southern Chile
:
Episodes
 , v.
11
, p.
183
188
.
Hervé
,
F.
Aguirre
,
L.
Godoy
,
E.
Massone
,
H.
Morata
,
D.
Pankhurst
,
R.J.
Ramirez
,
E.
Sepulveda
,
V.
Willner
,
A.
,
1998
,
Nuevos antecedentes acerca de la edad y las condiciones P-T de los complejos metamorficos en Aysen, Chile
:
Buenos Aires, Actas X Congreso Latinoamericano de Geólogo, VI Congreso Nacional de Geología y Economica
 , v.
2
, p.
134
137
.
Ivins
,
E.R.
James
,
T.S.
,
1999
,
Simple models for late Holocene and present-day Patagonian glacier fluctuations and predictions of a geodetically detectable isostatic response
:
Geophysical Journal International
 , v.
138-3
, p.
601
624
.
Katz
,
H.R.
,
1972
,
Plate tectonics-orogenic belts in the southeast Pacific
:
Nature
 , v.
237
, p.
331
,
doi: 10.1038/237331a0
.
Kay
,
R.W.
,
1978
,
Aleutian magnesian andesites: Melts from subducted Pacific ocean crust
:
Journal of Volcanology and Geothermal Research
 , v.
4
, p.
117
132
,
doi: 10.1016/0377-0273(78)90032-X
.
Kay
,
R.W.
Kay
,
S.M.
,
2002
,
Andean adakites: Three ways to make them
:
Acta Petrologica Cínica
 , v.
18-3
, p.
303
311
.
Kay
,
S.M.
Ramos
,
V.A.
Mpodozis
,
C.
Sruoga
,
P.
,
1989
,
Late Paleozoic to Jurassic silicic magmatism at the Gondwana margin: Analogy to the Middle Proterozoic in North America?
:
Geology
 , v.
17
, p.
324
328
,
doi: 10.1130/0091-7613(1989)017<0324:LPTJSM>2.3.CO;2
.
Kay
,
S.M.
Ramos
,
V.A.
Marquez
,
M.
,
1993
,
Evidence in Cerro Pampa volcanic rocks for slab-melting prior to ridge-collision in southern South America
:
The Journal of Geology
 , v.
101
, p.
703
714
.
Kay
,
S.M.
Ramos
,
V.A.
Gorring
,
M.L.
,
2002
,
Geochemistry of Eocene plateau basalts related to ridge collision in southern Patagonia
 , in
Cabaleri
,
N.
Cingolani
,
C.A.
Linares
,
E.
López de Luchi
,
M.G.
Ostera
,
H.A.
Panarello
,
H.O.
, eds.:
XV Congreso Geológico Argentino Actas
, v.
3
, p.
60
65
.
Klepeis
,
K.A.
,
1994
,
The Magallanes and Deseado fault zones: Major segments of the South American-Scoria transform plate boundary in southernmost South America
:
Journal of Geophysical Research
 , v.
99
, p.
22,001
22,014
,
doi: 10.1029/94JB01749
.
Kraemer
,
P.E.
,
1993
,
Perfil estructural de la Cordillera Patagonica Austral a los 50°S, Santa Cruz
:
XII Congreso Geológico Argentino Actas
 , v.
3
, p.
119
125
.
Kraemer
,
P.E.
,
2003
,
Orogenic shortening and the origin of the Patagonian orocline (56° S. Lat)
:
Journal of South American Earth Sciences
 , v.
15
, p.
731
745
,
doi: 10.1016/S0895-9811(02)00132-3
.
Kraemer
,
P.E.
Ploszkiewicz
,
J.V.
Ramos
,
V.A.
,
2002
,
Estructura de la Cordillera Patagonica Austral entre los 46° y 52°S, provincial de Santa Cruz, Argentina
, in
Haller
,
M.J.
, ed.,
Geología y recursos naturales de Santa Cruz
 :
Relatorio del XV Congreso Geológico Argentino
, p.
353
364
.
Lagabrielle
,
Y.
Le Moigne
,
J.
Maury
,
R.C.
Cotten
,
J.
Bourgois
,
J.
,
1994
,
Volcanic record of the subduction of an active spreading ridge, Taitao Peninsula (southern Chile)
:
Geology
 , v.
22
, p.
515
518
,
doi: 10.1130/ 0091-7613(1994)022<0515:VROTSO>2.3.CO;2
.
Lagabrielle
,
Y.
Guivel
,
C.
Maury
,
R.
Bourgois
,
J.
Fourcade
,
S.
Martin
,
H.
,
2000
,
Magmatic-tectonic effects of high thermal regime at the site of active spreading ridge subduction: The Chile Triple Junction model
:
Tectonophysics
 , v.
326
, p.
255
268
,
doi: 10.1016/S0040-1951(00)00124-4
.
Lagabrielle
,
Y.
Suárez
,
M.
Rosello
,
E.A.
Hérail
,
G.
Martinod
,
J.
Réginer
,
M.
de la Cruz
,
R.
,
2004
,
Neogene to Quaternary tectonic evolution of the Patagonian Andes at the latitude of the Chile Triple Junction
:
Tectonophysics
 , v.
385
, p.
211
241
.
Leanza
,
A.
,
1972
,
Andes Patagonicos australes
, in
Leanza
,
A.
, ed.,
Geología a regional Argentina
 :
Cordoba
,
Academia Nacional Ciencias
, p.
689
706
.
Le Moigne
,
J.
Lagabrielle
,
Y.
Whitechurch
,
H.
Girardeau
,
J.
Bourgois
,
J.
Maury
,
R.C.
,
1996
,
Petrography and geochemistry of the ophiolitic and volcanic suites of the Taitao Peninsula-Chile triple junction area
:
Journal of South American Earth Sciences
 , v.
9
, p.
43
58
,
doi: 10.1016/0895-9811(96)00026-0
.
Malumián
,
N.
,
2002
,
El terciario marino: Sus relaciones con el eustatismo
, in
Haller
,
M.J.
, ed.,
Geología y recursos naturales de Santa Cruz
 :
Relatorio del XV Congreso Geológico Argentino
, v.
1
, p.
237
244
.
Mercer
,
J.H.
,
1976
,
Glacial history of southernmost South America
:
Quaternary Research
 , v.
6
, p.
125
166
,
doi: 10.1016/0033-5894(76)90047-8
.
Michael
,
P.J.
,
1983
,
Emplacement and differentiation of Miocene plutons in the foothills of the southernmost Andes
 
[Ph.D. thesis]
:
New York
,
Columbia University
,
367
p.
Minster
,
J.B.
Jordan
,
T.H.
,
1978
,
Present day plate motions
:
Journal of Geophysical Research
 , v.
83
, p.
5331
5354
.
Morata
,
D.
Barbero
,
L.
Suárez
,
M.
de la Cruz
,
R.
,
2002
,
Early Pliocene magmatism and high exhumation rates in the Patagonian Cordillera (46°40'S) K-Ar and fission track data
:
Toulouse, France
,
Fifth International Symposium on Andean Geodynamics (ISAG)
, p.
433
436
.
Mpodozis
,
C.
Hervé
,
M.
Nasi
,
C.
Soffia
,
J.
Forsythe
,
R.
Nelson
,
E.
,
1985
,
El magmatismo plioceno de Península Tres Montes y su relación con la evolución del Punto Triple de Chile Austral
:
Revista Geológica de Chile
 , v.
25–26
, p.
13
28
.
Niemeyer
,
H.
Skarmeta
,
J.
Fuenzalida
,
R
Espinosa
,
W.
,
1984
,
Hojas Península de Taitao y Puerto Aisen, Region de Aisen del General Carlos Ibáñez del Campo
 :
Carta Geológica de Chile, Servicio Nacional de Geología y Mineria
,
Chile
, p.
60
61
, scale: 1:500,000.
Nullo
,
F.E.
Proserpio
,
C.
Ramos
,
V.A.
,
1978
,
Estratigrafía y tectónica de la vertiente este Hielo Continental Patagónico, Argentina, Chile
:
VII Congreso Geológico Argentino Actas
 , v.
1
, p.
455
470
.
Pankhurst
,
R.J.
Leat
,
P.T.
Sruoga
,
P.
Rapela
,
C.W.
Marquez
,
M.
Storey
,
B.C.
Riley
,
T.R.
,
1998
,
The Chon Aike province of Patagonia and related rocks in west Antarctica: A silicic large igneous province
:
Journal of Volcanology and Geothermal Research
 , v.
81
, p.
113
136
,
doi: 10.1016/ S0377-0273(97)00070-X
.
Pankhurst
,
R.J.
Weaver
,
S.D.
Hervé
,
F.
Larrondo
,
P.
,
1999
,
Mesozoic-Cenozoic evolution of the North Patagonian Batholith in Aysen, southern Chile
:
Journal of the Geological Society
 , v.
156
, p.
673
694
.
Panza
,
J.L.
Nullo
,
F.E.
,
1994
,
Mapa geológico de la provincia de Santa Cruz, Republica de Argentina
:
Buenos Aires, Servicio Geológico de Argentina
 , v.
1
,
scale: 1:750,000
.
Pardo-Casas
,
F.
Molnar
,
P.
,
1987
,
Relative motion of the Nazca (Farallon) and South American Plates since Late Cretaceous time
:
Tectonics
 , v.
6
, p.
233
248
.
Petford
,
N.
Turner
,
P.
,
1996
,
Reconnaissance 40Ar/39Ar age and paleomagnetic study of igneous rocks around Coyhaique, S. Chile
:
Saint Malo, France
,
Third International Symposium on Andean Geology (ISAG)
, p.
625
627
.
Pittion
,
J.-L.
Gouadain
,
J.
,
1992
,
Source rocks and oil generation in the Austral Basin
:
Buenos Aires
,
Proceedings of Thirteenth World Petroleum Congress
, p.
113
120
.
Ramos
,
V.A.
,
1988
,
Late Proterozoic-Early Paleozoic of South America: A collisional history
:
Episodes
 , v.
11
, p.
168
174
.
Ramos
,
V.A.
,
1989
,
Foothills structure in Northern Magallanes Basin, Argentina
:
AAPG Bulletin
 , v.
73
, p.
887
903
.
Ramos
,
V.A.
,
2005
,
Seismic ridge subduction and topography: Foreland deformation in the Patagonian Andes
:
Tectonophysics
 , v.
399
, p.
73
86
,
doi: 10.1016/j.tecto.2004.12.016
.
Ramos
,
V.A.
Kay
,
S.M.
,
1992
,
Southern Patagonian plateau basalts and deformation: Backarc testimony of ridge collision
:
Tectonophysics
 , v.
205
, p.
261
282
,
doi: 10.1016/0040-1951(92)90430-E
.
Ramos
,
V.A.
Kay
,
S.M.
Singer
,
B.S.
,
2004
,
Las adakitas de la Cordillera Patagónica: Nuevas evidencias geoquímicas y geocronológicas
:
Revista de la Associación Geológica Argentina
 , v.
59
, p.
693
706
.
Riccardi
,
A.C.
,
1971
,
Estratigrafía en el oriente de la Bahía de la Lancha, Lago San Martin, Santa Cruz, Argentina
:
Museo de la Plata Revista (Geología)
 , v.
7
, p.
245
318
.
Riccardi
,
A.C.
,
1988
,
The Cretaceous system of southern South America
:
Geological Society of America Memoirs
 
168
,
161
p.
Singer
,
B.S.
Ackert
,
R.P.
, Jr.
Guillou
,
H.
,
2004
,
40Ar/39Ar and K-Ar chronol ogy of Pleistocene glaciations in Patagonia
:
Geological Society of America Bulletin
 , v.
116
, p.
434
450
,
doi: 10.1130/B25177.1
.
Skarmeta
,
J.
Castelli
,
J.C.
,
1997
,
Intrusión sintectónica del Granito de Las Torres del Paine, Andes Patagónicos de Chile
:
Revista Geológica de Chile
 , v.
24
, p.
55
74
.
Stern
,
C.R.
Kilian
,
R.
,
1996
,
Role of the subducted slab, mantle wedge, and continental crust in the generation of adakites from the Andean Austral Volcanic Zone
:
Contributions to Mineralogy and Petrology
 , v.
123
, p.
263
281
,
doi: 10.1007/s004100050155
.
Stern
,
C.R.
Frey
,
F.A.
Futa
,
K.
Zartman
,
R.E.
Peng
,
Z.
Kyser
,
T.K.
,
1990
,
Trace element and Sr, Nd, Pb, and O isotopic composition of Pliocene and Quaternary alkali basalts of the Patagonian Plateau lavas of southernmost South America
:
Contributions to Mineralogy and Petrology
 , v.
104
, p.
294
308
,
doi: 10.1007/BF00321486
.
Suárez
,
M.
de la Cruz
,
R.
,
2001
,
Jurassic to Miocene K-Ar dates from eastern central Patagonian Cordillera plutons, Chile (45°–48°S)
:
Geological Magazine
 , v.
138
, p.
53
66
,
doi: 10.1017/S0016756801004903
.
Suárez
,
M.
Pettigrew
,
T.H.
,
1976
,
An upper Mesozoic island arc-back-arc system in the southern Andes and South Georgia
:
Geological Magazine
 , v.
113
, p.
305
328
.
Suárez
,
M.
de la Cruz
,
R.
Bell
,
C.M.
,
2000
,
Timing and origin of deformation along the Patagonian fold and thrust belt
:
Geological Magazine
 , v.
137
, p.
345
353
,
doi: 10.1017/S0016756800004192
.
Thomas
,
C.R.
,
1949
,
Geology and petroleum exploration in the Magallanes Province, Chile
:
AAPG Bulletin
 , v.
33
, p.
1553
1578
.
Thomson
,
S.N.
Hervé
,
F.
Stockhert
,
B.
,
2001
,
Mesozoic-Cenozoic denudation history of the Patagonian Andes (southern Chile) and its correlation to different subduction processes
:
Tectonics
 , v.
20
, p.
693
711
,
doi: 10.1029/2001TC900013
.
Thorkelson
,
D.J.
,
1996
,
Subduction of diverging plates and the principles of slab window formation
:
Tectonophysics
 , v.
255
, p.
47
63
,
doi: 10.1016/0040-1951(95)00106-9
.
Welkner
,
D.
,
1999
,
Geología del area del Cerro de San Lorenzo
:
Cor dillera Patagónica oriental, XI Región de Aysén, Chile (47°25′–47°50′S)
 
[M.S. thesis]
:
Santiago
,
Departamento de Geología, Universidad de Chile
,
148
p.
Welkner
,
D.R.
,
2000
,
Geocronología de los plutones del área de del Cerro San Lorenzo, XI Región de Aysén
:
IX Congreso Geológica de Chile (Puerto Varas) Actas
 , v.
2
, p.
269
273
.
Winslow
,
M.A.
,
1981
,
Mechanisms for basement shortening in the Andean foreland fold belt of southern South America
, in
McClay
,
K-.R.
Price
,
N.J.
, eds.,
Thrust and nappe tectonics
 :
Geological Society of London, Blackwell Scientific Publications
, p.
513
528
.
Winslow
,
M.A.
,
1982
,
The structural evolution of the Magallanes Basin and neotectonics in the southernmost Andes
, in
Cradock
,
C.
, ed.,
Antarctic geoscience
 :
Madison
,
University of Wisconsin
, p.
143
154
.
Yogodzinski
,
G.M.
Lees
,
J.M.
Churikova
,
T.G.
Dorendorf
,
F.
Woerner
,
G.
Volynets
,
O.N.
,
2001
,
Geochemical evidence for the melting of subducting oceanic lithosphere at plate edges
:
Nature
 , v.
409
, p.
500
504
,
doi: 10.1038/35054039
.

Figures & Tables

Figure 1.

Tectonic setting of southern South America showing the distribution of Neogene plateau lavas, adakites, the Patagonian fold-and-thrust belt, and the Southern (SVZ) and Austral Volcanic Zones (AVZ). Ridge collision times are shown in bold numbers (Cande and Leslie, 1986).

Figure 1.

Tectonic setting of southern South America showing the distribution of Neogene plateau lavas, adakites, the Patagonian fold-and-thrust belt, and the Southern (SVZ) and Austral Volcanic Zones (AVZ). Ridge collision times are shown in bold numbers (Cande and Leslie, 1986).

Figure 2.

Schematic cross sections (no vertical exaggeration) showing the Patagonian slab window model (Gorring et al., 1997), highlighting mantle source regions and petrogenetic processes involved in the genesis of Neogene slab window lavas erupted northeast of where a Chile Ridge segment collided with the Chile Trench at ca. 12 Ma. Abbreviations: OIB—oceanic island basalt; SSVZ—southern Southern Volcanic Zone.

Figure 2.

Schematic cross sections (no vertical exaggeration) showing the Patagonian slab window model (Gorring et al., 1997), highlighting mantle source regions and petrogenetic processes involved in the genesis of Neogene slab window lavas erupted northeast of where a Chile Ridge segment collided with the Chile Trench at ca. 12 Ma. Abbreviations: OIB—oceanic island basalt; SSVZ—southern Southern Volcanic Zone.

Figure 3.

Major structures of the Patagonian fold-and-thrust belt. Figure from Ramos (1989).

Figure 3.

Major structures of the Patagonian fold-and-thrust belt. Figure from Ramos (1989).

Figure 4.

(on this and following page). Structural cross sections of the Patagonian fold-and-thrust belt. Lines of section are in Figure 3. Figure from Ramos (1989).

Figure 4.

(on this and following page). Structural cross sections of the Patagonian fold-and-thrust belt. Lines of section are in Figure 3. Figure from Ramos (1989).

Figure 5.

North-south topographic section of the Patagonian Andes in which maximum elevation is indicated at each latitude. Present Chile Ridge collision is taking place at 46.5°S. Figure from Ramos (2005).

Figure 5.

North-south topographic section of the Patagonian Andes in which maximum elevation is indicated at each latitude. Present Chile Ridge collision is taking place at 46.5°S. Figure from Ramos (2005).

Figure 6.

Schematic cross sections highlighting major structural differences of the Patagonian Cordillera north (A) and south (B) of the present Chile Triple Junction. Figure from Ramos (2005).

Figure 6.

Schematic cross sections highlighting major structural differences of the Patagonian Cordillera north (A) and south (B) of the present Chile Triple Junction. Figure from Ramos (2005).

Figure 7.

(A) Map showing the distribution of Neogene main-plateau and post-plateau lavas, and the location of the Cerro Pampa adakite. AVZ— Austral Volcanic Zone; SSVZ—southern Southern Volcanic Zone. (B) Plot of slab window plateau lavas ages projected onto the SW-NE transect in (A) showing the northeastward younging trend of the main- and post-plateau lavas. Arrow shows predicted age progression for a mantle hotspot track based on a 2.5 cm/yr absolute plate motion vector for South America. Gray zone shows the predicted time when the trailing edge of the Nazca plate passed beneath the backarc. Both figures modified from Gorring et al. (1997).

Figure 7.

(A) Map showing the distribution of Neogene main-plateau and post-plateau lavas, and the location of the Cerro Pampa adakite. AVZ— Austral Volcanic Zone; SSVZ—southern Southern Volcanic Zone. (B) Plot of slab window plateau lavas ages projected onto the SW-NE transect in (A) showing the northeastward younging trend of the main- and post-plateau lavas. Arrow shows predicted age progression for a mantle hotspot track based on a 2.5 cm/yr absolute plate motion vector for South America. Gray zone shows the predicted time when the trailing edge of the Nazca plate passed beneath the backarc. Both figures modified from Gorring et al. (1997).

Figure 8.

Geologic and structural map of the northern shore of Lago Viedma, with location of the structural section in Figure 9. Figure from Coutand et al. (1999).

Figure 8.

Geologic and structural map of the northern shore of Lago Viedma, with location of the structural section in Figure 9. Figure from Coutand et al. (1999).

Figure 9.

Structural cross section partly controlled by seismic data. Black bars indicate approximate location of seismic lines. No vertical exaggeration. Figure from Coutand et al. (1999).

Figure 9.

Structural cross section partly controlled by seismic data. Black bars indicate approximate location of seismic lines. No vertical exaggeration. Figure from Coutand et al. (1999).

Figure 10.

Geochemical plots showing the strong oceanic island basalt (OIB)-like characteristics of Neogene Patagonian main-plateau (filled symbols) and post-plateau (open symbols) slab window lavas. Data and fields from Kay et al. (1993), Gorring and Kay (2001), and Ramos et al. (2004). BSE—bulk silicate earth; HIMU—high U/Pb mantle; MORB—mid-oceanic ridge basalt; NMORB—normal mid-oceanic ridge basalt; OIB—oceanic island basalt; SSVZ—southern Southern Volcanic Zone.

Figure 10.

Geochemical plots showing the strong oceanic island basalt (OIB)-like characteristics of Neogene Patagonian main-plateau (filled symbols) and post-plateau (open symbols) slab window lavas. Data and fields from Kay et al. (1993), Gorring and Kay (2001), and Ramos et al. (2004). BSE—bulk silicate earth; HIMU—high U/Pb mantle; MORB—mid-oceanic ridge basalt; NMORB—normal mid-oceanic ridge basalt; OIB—oceanic island basalt; SSVZ—southern Southern Volcanic Zone.

Figure 11.

Geologic cross sections of the Patagonian fold-and-thrust belt near Lago Posadas at ~47°S. Figure from Giacosa et al. (1999).

Figure 11.

Geologic cross sections of the Patagonian fold-and-thrust belt near Lago Posadas at ~47°S. Figure from Giacosa et al. (1999).

Figure 12.

Geologic map of the Lago General Carrera–Buenos Aires area. Figure from Lagabrielle et al. (2004).

Figure 12.

Geologic map of the Lago General Carrera–Buenos Aires area. Figure from Lagabrielle et al. (2004).

Figure 13.

Geologic cross section along line of section in Figure 12. Figure from Lagabrielle et al. (2004).

Figure 13.

Geologic cross section along line of section in Figure 12. Figure from Lagabrielle et al. (2004).

TABLE 1.

GEOCHEMICAL AND AGE DATA FOR PATAGONIAN SLAB WINDOW VOLCANICS

Cerro PampaPuesto NuevoChalténPost-plateauMain-plateau
SampleRB5RB7RB8PNA1FVRLC-7LC-21
Latitude (°S)47°54.5′47°54.5′47°54.5′48°56.0′49°25.5′49°11.4′48°18.3′
Longitude (°W)71°25.4′71°25.4′71°25.4′72°12.5′72°59.5′71°20.7′70°58.2′
SiO2 (wt%)62.5567.8863.2265.6764.9747.8953.22
TiO20.620.510.840.680.662.961.60
Al2O317.2716.2616.5316.5615.2115.1115.96
FeO3.132.243.783.023.3211.408.70
MnO0.090.110.110.100.060.170.13
MgO3.622.482.922.923.427.226.21
CaO7.124.506.724.404.517.898.14
Na2O4.664.564.314.253.664.074.02
K2O1.221.701.882.703.701.770.48
P2O5N.D.N.D.N.D.0.250.241.020.22
Total100.3100.2100.3100.699.899.598.7
La (ppm)2721402730499
Ce61459764649319
Nd30205229274313
Sm4.43.27.64.95.08.83.8
Eu1.160.771.931.161.192.631.34
Tb0.340.270.630.380.431.060.66
Yb0.720.691.200.960.991.721.50
Lu0.090.080.160.120.130.210.23
Sr18861334229414391369925452
Ba306391356320381523135
Cs0.300.300.603.201.000.600.20
RbN.D.N.D.N.D.N.D.N.D.N.D.7.3
U1.002.601.802.003.101.750.54
Th5.06.77.57.014.96.41.1
PbN.D.N.D.N.D.N.D.N.D.N.D.1.5
YN.D.N.D.N.D.N.D.N.D.N.D.20
ZrN.D.N.D.N.D.N.D.N.D.N.D.108
Hf3.23.25.05.45.75.82.4
NbN.D.N.D.N.D.N.D.N.D.N.D.13
Ta0.701.800.700.500.804.390.84
Sc8611991718
Cr978581100102159218
Ni7647435468116133
Co1591514134840
87Sr/86Sr0.702900.703090.702850.703210.70330N.D.0.70358
eNd+5.7+5.5+6.9+4.9~+5N.D.N.D.
Ar/Ar age (Ma)N.D.N.D.11.4 ± 0.613.1 ± 0.614.5 ± 0.3<6 (?)ca. 12
Cerro PampaPuesto NuevoChalténPost-plateauMain-plateau
SampleRB5RB7RB8PNA1FVRLC-7LC-21
Latitude (°S)47°54.5′47°54.5′47°54.5′48°56.0′49°25.5′49°11.4′48°18.3′
Longitude (°W)71°25.4′71°25.4′71°25.4′72°12.5′72°59.5′71°20.7′70°58.2′
SiO2 (wt%)62.5567.8863.2265.6764.9747.8953.22
TiO20.620.510.840.680.662.961.60
Al2O317.2716.2616.5316.5615.2115.1115.96
FeO3.132.243.783.023.3211.408.70
MnO0.090.110.110.100.060.170.13
MgO3.622.482.922.923.427.226.21
CaO7.124.506.724.404.517.898.14
Na2O4.664.564.314.253.664.074.02
K2O1.221.701.882.703.701.770.48
P2O5N.D.N.D.N.D.0.250.241.020.22
Total100.3100.2100.3100.699.899.598.7
La (ppm)2721402730499
Ce61459764649319
Nd30205229274313
Sm4.43.27.64.95.08.83.8
Eu1.160.771.931.161.192.631.34
Tb0.340.270.630.380.431.060.66
Yb0.720.691.200.960.991.721.50
Lu0.090.080.160.120.130.210.23
Sr18861334229414391369925452
Ba306391356320381523135
Cs0.300.300.603.201.000.600.20
RbN.D.N.D.N.D.N.D.N.D.N.D.7.3
U1.002.601.802.003.101.750.54
Th5.06.77.57.014.96.41.1
PbN.D.N.D.N.D.N.D.N.D.N.D.1.5
YN.D.N.D.N.D.N.D.N.D.N.D.20
ZrN.D.N.D.N.D.N.D.N.D.N.D.108
Hf3.23.25.05.45.75.82.4
NbN.D.N.D.N.D.N.D.N.D.N.D.13
Ta0.701.800.700.500.804.390.84
Sc8611991718
Cr978581100102159218
Ni7647435468116133
Co1591514134840
87Sr/86Sr0.702900.703090.702850.703210.70330N.D.0.70358
eNd+5.7+5.5+6.9+4.9~+5N.D.N.D.
Ar/Ar age (Ma)N.D.N.D.11.4 ± 0.613.1 ± 0.614.5 ± 0.3<6 (?)ca. 12

Note: Adakite data from Kay et al. (1993) and Ramos et al. (2004); slab window basalt data from Gorring and Kay (2001). N.D.—not determined.

Contents

References

References Cited

Altenburger
,
U.
Oberhansli
,
R.
Putlitz
,
B.
Wemmer
,
K.
,
2003
,
Tectonic controls and Cenozoic magmatism at the Torres del Paine, southern Andes (Chile, 51°10′S)
:
Revista Geológica de Chile
 , v.
30
, no.
1
, p.
65
81
.
Bell
,
M.
Suárez
,
M.
,
2000
,
The Rio Lacteo Formation of southern Chile: Late Paleozoic orogeny in the Andes of southernmost South America
:
Journal of South American Earth Sciences
 , v.
13
, p.
133
145
,
doi: 10.1016/S0895-9811(00)00005-5
.
Biddle
,
K.T.
Uliana
,
M.A.
Mitchum
,
R.M.
Fitzgerald
,
M.G.
Coutand
,
I.
Diraison
,
M.
Cobbold
,
P.R.
Gapais
,
D.
Rossello
Wright
,
R.C.
,
1986
,
The stratigraphic and structural evolution of the central and eastern Magallanes basin, South America
, in
Allen
,
P.A.
Homewood
,
P.
, eds.,
Foreland basins
 :
International Association of Sedimentologists, Special Publication
, v.
8
, p.
41
61
.
Blisniuk
,
P.M.
Stem
,
L.A.
Chamberlain
,
C.P.
Idleman
,
B.
Zeitler
,
P.K.
,
2005
,
Climatic and ecologic changes during Miocene surface uplift in the Southern Patagonian Andes
:
Earth and Planetary Science Letters
 , v.
230
, p.
125
142
,
doi: 10.1016/j.epsl.2004.11.015
.
Bourgois
,
J.
Martin
,
H.
Le Moigne
,
J.
Frutos
,
J.
,
1996
,
Subduction erosion related to spreading-ridge subduction: Taitao peninsula (Chile margin triple junction area)
:
Geology
 , v.
24
, p.
723
726
,
doi: 10.1130/ 0091-7613(1996)024<0723:SERTSR>2.3.CO;2
.
Brown
,
L.L.
Singer
,
B.S.
Gorring
,
M.
,
2004
,
Paleomagnetic and geochronologic results from Meseta del Lago Buenos Aires, Patagonia
:
Geochemistry Geophysics Geosystems
 , v.
5
, p.
Q01H04
,
doi: 10.1029/ 2003GC000526
.
Cande
,
S.C.
Leslie
,
R.B.
,
1986
,
Late Cenozoic tectonics of the Southern Chile Trench
:
Journal of Geophysical Research
 , v.
91
, p.
471
496
.
Coutand
,
I.
Diraison
,
M.
Cobbold
,
P.R.
Gapais
,
D.
Rossello
,
E.A.
Miller
,
M.
,
1999
,
Structure and kinematics of a foothills transect, Lago Viedma, southern Andes (49°30′S)
:
Journal of South American Earth Sciences
 , v.
12
, p.
1
15
,
doi: 10.1016/S0895-9811(99)00002-4
.
Dalziel
,
I.W.D.
,
1981
,
Backarc extension in the southern Andes: A review and critical reappraisal
:
Philosophical Transactions of the Royal Society of London, Series A
 , v.
300
, p.
319
335
,
doi: 10.1098/rsta.1981.0067
.
DaSilva
,
M.
Gorring
,
M.L.
Singer
,
B.
Brown
,
L.
,
2006
,
Ridge subduction volcanism in the Zeballos Complex, southern Patagonian Andes: Backbone of the Americas, Patagonia to Alaska, Mendoza, Argentina, April 3–7, 2006
:
Geological Society of America Abstracts with Programs
 , v.
2
, p.
49
.
Defant
,
M.J.
Drummond
,
M.S.
,
1990
,
Derivation of some modern arc magmas by melting of young subducted lithosphere
:
Nature
 , v.
347
, p.
662
665
,
doi: 10.1038/347662a0
.
Diraison
,
M.
Cobbold
,
P.R.
Gapais
,
D.
Rosello
,
E.
,
2000
,
Cenozoic crustal thickening, wrenching and rifting in the foothills of the southernmost Andes
:
Tectonophysics
 , v.
316
, p.
91
119
,
doi: 10.1016/S0040-1951(99)00255-3
.
Feagle
,
J.G.
Bown
,
T.M.
Swisher
,
C.
Buckley
,
G.A.
,
1995
,
Age of the Pinturas and Santa Cruz Formations
:
VI Congreso Argentino de Paleontología y Bioestratigrafía (Trelew), Actas
 , p.
129
135
.
Flint
,
S.S.
Prior
,
D.J.
Agar
,
S.M.
Turner
,
P.
,
1994
,
Stratigraphic and structural evolution of the Tertiary Cosmelli Basin and its relationship to the Chile triple junction
:
Journal of the Geological Society
 , v.
151
, p.
251
268
,
doi: 10.1144/gsjgs.151.2.0251
.
Forsythe
,
R.D.
Nelson
,
E.P.
Carr
,
M.J.
Kaeding
,
M.E.
Hervé
,
M.
Mpodozis
,
C.
Soffia
,
J.M.
Harambour
,
S.
,
1986
,
Pliocene near-trench magmatism in southern Chile: A possible manifestation of ridge collision
:
Geology
 , v.
14
, p.
23
27
,
doi: 10.1130/0091-7613(1986)14<23:PNMISC> 2.0.CO;2
.
Giacosa
,
R.E.
Franchi
,
M.
Genini
,
A.
,
1999
,
Hoja Geológica 4772-III Lago Belgrano, Hoja Geológica 4772-IV Lago Posadas, Provincia de Santa Cruz
:
Buenos Aires, Servicio Geológico Minero Argentina
 , v.
256
,
scale: 1:250,000
.
Gorring
,
M.L.
Kay
,
S.M.
,
2001
,
Mantle sources and processes of Neogene slab window magmas from southern Patagonia, Argentina
:
Journal of Petrology
 , v.
42
, p.
1067
1094
,
doi: 10.1093/petrology/42.6.1067
.
Gorring
,
M.L.
Kay
,
S.M.
Zeitler
,
P.K.
Ramos
,
V.A.
Rubiolo
,
D.
Fernandez
,
M.L.
Panza
,
J.L.
,
1997
,
Neogene Patagonian plateau lavas: Continental magmas associated with ridge collision at the Chile Triple Junction
:
Tectonics
 , v.
16
, p.
1
17
,
doi: 10.1029/96TC03368
.
Gripp
,
A.E.
Gordon
,
R.G.
,
1990
,
Current plate velocities relative to the hotspots incorporating the NUVEL-1 global plate motion model
:
Geophysical Research Letters
 , v.
17
, p.
1109
1112
.
Guivel
,
C.
Lagabrielle
,
Y.
Bourgois
,
J.
Maury
,
R.C.
Fourcade
,
S.
Martin
,
H.
Arnaud
,
N.
,
1999
,
New geochemical constraints for the origin of ridge subduction-related plutonic and volcanic suites from the Chile Triple Junction (Taitao Peninsula and Site 862, LEG ODP on the Taitao Ridge)
:
Tectonophysics
 , v.
311
, p.
83
111
,
doi: 10.1016/S0040-1951(99)00160-2
.
Gust
,
D.A.
Biddle
,
K.T.
Phelps
,
D.W.
Uliana
,
M.A.
,
1985
,
Associated middle to late Jurassic volcanism and extension in southern South America
:
Tectonophysics
 , v.
116
, p.
223
253
,
doi: 10.1016/0040-1951(85)90210-0
.
Halpern
,
M.
,
1973
,
Regional geochronology of Chile south of 50° latitude
:
Geological Society of America Bulletin
 , v.
84
, p.
2407
2422
,
doi: 10.1130/ 0016-7606(1973)84<2407:RGOCSO>2.0.CO;2
.
Hervé
,
F.
,
1988
,
Late Paleozoic subduction and accretion in southern Chile
:
Episodes
 , v.
11
, p.
183
188
.
Hervé
,
F.
Aguirre
,
L.
Godoy
,
E.
Massone
,
H.
Morata
,
D.
Pankhurst
,
R.J.
Ramirez
,
E.
Sepulveda
,
V.
Willner
,
A.
,
1998
,
Nuevos antecedentes acerca de la edad y las condiciones P-T de los complejos metamorficos en Aysen, Chile
:
Buenos Aires, Actas X Congreso Latinoamericano de Geólogo, VI Congreso Nacional de Geología y Economica
 , v.
2
, p.
134
137
.
Ivins
,
E.R.
James
,
T.S.
,
1999
,
Simple models for late Holocene and present-day Patagonian glacier fluctuations and predictions of a geodetically detectable isostatic response
:
Geophysical Journal International
 , v.
138-3
, p.
601
624
.
Katz
,
H.R.
,
1972
,
Plate tectonics-orogenic belts in the southeast Pacific
:
Nature
 , v.
237
, p.
331
,
doi: 10.1038/237331a0
.
Kay
,
R.W.
,
1978
,
Aleutian magnesian andesites: Melts from subducted Pacific ocean crust
:
Journal of Volcanology and Geothermal Research
 , v.
4
, p.
117
132
,
doi: 10.1016/0377-0273(78)90032-X
.
Kay
,
R.W.
Kay
,
S.M.
,
2002
,
Andean adakites: Three ways to make them
:
Acta Petrologica Cínica
 , v.
18-3
, p.
303
311
.
Kay
,
S.M.
Ramos
,
V.A.
Mpodozis
,
C.
Sruoga
,
P.
,
1989
,
Late Paleozoic to Jurassic silicic magmatism at the Gondwana margin: Analogy to the Middle Proterozoic in North America?
:
Geology
 , v.
17
, p.
324
328
,
doi: 10.1130/0091-7613(1989)017<0324:LPTJSM>2.3.CO;2
.
Kay
,
S.M.
Ramos
,
V.A.
Marquez
,
M.
,
1993
,
Evidence in Cerro Pampa volcanic rocks for slab-melting prior to ridge-collision in southern South America
:
The Journal of Geology
 , v.
101
, p.
703
714
.
Kay
,
S.M.
Ramos
,
V.A.
Gorring
,
M.L.
,
2002
,
Geochemistry of Eocene plateau basalts related to ridge collision in southern Patagonia
 , in
Cabaleri
,
N.
Cingolani
,
C.A.
Linares
,
E.
López de Luchi
,
M.G.
Ostera
,
H.A.
Panarello
,
H.O.
, eds.:
XV Congreso Geológico Argentino Actas
, v.
3
, p.
60
65
.
Klepeis
,
K.A.
,
1994
,
The Magallanes and Deseado fault zones: Major segments of the South American-Scoria transform plate boundary in southernmost South America
:
Journal of Geophysical Research
 , v.
99
, p.
22,001
22,014
,
doi: 10.1029/94JB01749
.
Kraemer
,
P.E.
,
1993
,
Perfil estructural de la Cordillera Patagonica Austral a los 50°S, Santa Cruz
:
XII Congreso Geológico Argentino Actas
 , v.
3
, p.
119
125
.
Kraemer
,
P.E.
,
2003
,
Orogenic shortening and the origin of the Patagonian orocline (56° S. Lat)
:
Journal of South American Earth Sciences
 , v.
15
, p.
731
745
,
doi: 10.1016/S0895-9811(02)00132-3
.
Kraemer
,
P.E.
Ploszkiewicz
,
J.V.
Ramos
,
V.A.
,
2002
,
Estructura de la Cordillera Patagonica Austral entre los 46° y 52°S, provincial de Santa Cruz, Argentina
, in
Haller
,
M.J.
, ed.,
Geología y recursos naturales de Santa Cruz
 :
Relatorio del XV Congreso Geológico Argentino
, p.
353
364
.
Lagabrielle
,
Y.
Le Moigne
,
J.
Maury
,
R.C.
Cotten
,
J.
Bourgois
,
J.
,
1994
,
Volcanic record of the subduction of an active spreading ridge, Taitao Peninsula (southern Chile)
:
Geology
 , v.
22
, p.
515
518
,
doi: 10.1130/ 0091-7613(1994)022<0515:VROTSO>2.3.CO;2
.
Lagabrielle
,
Y.
Guivel
,
C.
Maury
,
R.
Bourgois
,
J.
Fourcade
,
S.
Martin
,
H.
,
2000
,
Magmatic-tectonic effects of high thermal regime at the site of active spreading ridge subduction: The Chile Triple Junction model
:
Tectonophysics
 , v.
326
, p.
255
268
,
doi: 10.1016/S0040-1951(00)00124-4
.
Lagabrielle
,
Y.
Suárez
,
M.
Rosello
,
E.A.
Hérail
,
G.
Martinod
,
J.
Réginer
,
M.
de la Cruz
,
R.
,
2004
,
Neogene to Quaternary tectonic evolution of the Patagonian Andes at the latitude of the Chile Triple Junction
:
Tectonophysics
 , v.
385
, p.
211
241
.
Leanza
,
A.
,
1972
,
Andes Patagonicos australes
, in
Leanza
,
A.
, ed.,
Geología a regional Argentina
 :
Cordoba
,
Academia Nacional Ciencias
, p.
689
706
.
Le Moigne
,
J.
Lagabrielle
,
Y.
Whitechurch
,
H.
Girardeau
,
J.
Bourgois
,
J.
Maury
,
R.C.
,
1996
,
Petrography and geochemistry of the ophiolitic and volcanic suites of the Taitao Peninsula-Chile triple junction area
:
Journal of South American Earth Sciences
 , v.
9
, p.
43
58
,
doi: 10.1016/0895-9811(96)00026-0
.
Malumián
,
N.
,
2002
,
El terciario marino: Sus relaciones con el eustatismo
, in
Haller
,
M.J.
, ed.,
Geología y recursos naturales de Santa Cruz
 :
Relatorio del XV Congreso Geológico Argentino
, v.
1
, p.
237
244
.
Mercer
,
J.H.
,
1976
,
Glacial history of southernmost South America
:
Quaternary Research
 , v.
6
, p.
125
166
,
doi: 10.1016/0033-5894(76)90047-8
.
Michael
,
P.J.
,
1983
,
Emplacement and differentiation of Miocene plutons in the foothills of the southernmost Andes
 
[Ph.D. thesis]
:
New York
,
Columbia University
,
367
p.
Minster
,
J.B.
Jordan
,
T.H.
,
1978
,
Present day plate motions
:
Journal of Geophysical Research
 , v.
83
, p.
5331
5354
.
Morata
,
D.
Barbero
,
L.
Suárez
,
M.
de la Cruz
,
R.
,
2002
,
Early Pliocene magmatism and high exhumation rates in the Patagonian Cordillera (46°40'S) K-Ar and fission track data
:
Toulouse, France
,
Fifth International Symposium on Andean Geodynamics (ISAG)
, p.
433
436
.
Mpodozis
,
C.
Hervé
,
M.
Nasi
,
C.
Soffia
,
J.
Forsythe
,
R.
Nelson
,
E.
,
1985
,
El magmatismo plioceno de Península Tres Montes y su relación con la evolución del Punto Triple de Chile Austral
:
Revista Geológica de Chile
 , v.
25–26
, p.
13
28
.
Niemeyer
,
H.
Skarmeta
,
J.
Fuenzalida
,
R
Espinosa
,
W.
,
1984
,
Hojas Península de Taitao y Puerto Aisen, Region de Aisen del General Carlos Ibáñez del Campo
 :
Carta Geológica de Chile, Servicio Nacional de Geología y Mineria
,
Chile
, p.
60
61
, scale: 1:500,000.
Nullo
,
F.E.
Proserpio
,
C.
Ramos
,
V.A.
,
1978
,
Estratigrafía y tectónica de la vertiente este Hielo Continental Patagónico, Argentina, Chile
:
VII Congreso Geológico Argentino Actas
 , v.
1
, p.
455
470
.
Pankhurst
,
R.J.
Leat
,
P.T.
Sruoga
,
P.
Rapela
,
C.W.
Marquez
,
M.
Storey
,
B.C.
Riley
,
T.R.
,
1998
,
The Chon Aike province of Patagonia and related rocks in west Antarctica: A silicic large igneous province
:
Journal of Volcanology and Geothermal Research
 , v.
81
, p.
113
136
,
doi: 10.1016/ S0377-0273(97)00070-X
.
Pankhurst
,
R.J.
Weaver
,
S.D.
Hervé
,
F.
Larrondo
,
P.
,
1999
,
Mesozoic-Cenozoic evolution of the North Patagonian Batholith in Aysen, southern Chile
:
Journal of the Geological Society
 , v.
156
, p.
673
694
.
Panza
,
J.L.
Nullo
,
F.E.
,
1994
,
Mapa geológico de la provincia de Santa Cruz, Republica de Argentina
:
Buenos Aires, Servicio Geológico de Argentina
 , v.
1
,
scale: 1:750,000
.
Pardo-Casas
,
F.
Molnar
,
P.
,
1987
,
Relative motion of the Nazca (Farallon) and South American Plates since Late Cretaceous time
:
Tectonics
 , v.
6
, p.
233
248
.
Petford
,
N.
Turner
,
P.
,
1996
,
Reconnaissance 40Ar/39Ar age and paleomagnetic study of igneous rocks around Coyhaique, S. Chile
:
Saint Malo, France
,
Third International Symposium on Andean Geology (ISAG)
, p.
625
627
.
Pittion
,
J.-L.
Gouadain
,
J.
,
1992
,
Source rocks and oil generation in the Austral Basin
:
Buenos Aires
,
Proceedings of Thirteenth World Petroleum Congress
, p.
113
120
.
Ramos
,
V.A.
,
1988
,
Late Proterozoic-Early Paleozoic of South America: A collisional history
:
Episodes
 , v.
11
, p.
168
174
.
Ramos
,
V.A.
,
1989
,
Foothills structure in Northern Magallanes Basin, Argentina
:
AAPG Bulletin
 , v.
73
, p.
887
903
.
Ramos
,
V.A.
,
2005
,
Seismic ridge subduction and topography: Foreland deformation in the Patagonian Andes
:
Tectonophysics
 , v.
399
, p.
73
86
,
doi: 10.1016/j.tecto.2004.12.016
.
Ramos
,
V.A.
Kay
,
S.M.
,
1992
,
Southern Patagonian plateau basalts and deformation: Backarc testimony of ridge collision
:
Tectonophysics
 , v.
205
, p.
261
282
,
doi: 10.1016/0040-1951(92)90430-E
.
Ramos
,
V.A.
Kay
,
S.M.
Singer
,
B.S.
,
2004
,
Las adakitas de la Cordillera Patagónica: Nuevas evidencias geoquímicas y geocronológicas
:
Revista de la Associación Geológica Argentina
 , v.
59
, p.
693
706
.
Riccardi
,
A.C.
,
1971
,
Estratigrafía en el oriente de la Bahía de la Lancha, Lago San Martin, Santa Cruz, Argentina
:
Museo de la Plata Revista (Geología)
 , v.
7
, p.
245
318
.
Riccardi
,
A.C.
,
1988
,
The Cretaceous system of southern South America
:
Geological Society of America Memoirs
 
168
,
161
p.
Singer
,
B.S.
Ackert
,
R.P.
, Jr.
Guillou
,
H.
,
2004
,
40Ar/39Ar and K-Ar chronol ogy of Pleistocene glaciations in Patagonia
:
Geological Society of America Bulletin
 , v.
116
, p.
434
450
,
doi: 10.1130/B25177.1
.
Skarmeta
,
J.
Castelli
,
J.C.
,
1997
,
Intrusión sintectónica del Granito de Las Torres del Paine, Andes Patagónicos de Chile
:
Revista Geológica de Chile
 , v.
24
, p.
55
74
.
Stern
,
C.R.
Kilian
,
R.
,
1996
,
Role of the subducted slab, mantle wedge, and continental crust in the generation of adakites from the Andean Austral Volcanic Zone
:
Contributions to Mineralogy and Petrology
 , v.
123
, p.
263
281
,
doi: 10.1007/s004100050155
.
Stern
,
C.R.
Frey
,
F.A.
Futa
,
K.
Zartman
,
R.E.
Peng
,
Z.
Kyser
,
T.K.
,
1990
,
Trace element and Sr, Nd, Pb, and O isotopic composition of Pliocene and Quaternary alkali basalts of the Patagonian Plateau lavas of southernmost South America
:
Contributions to Mineralogy and Petrology
 , v.
104
, p.
294
308
,
doi: 10.1007/BF00321486
.
Suárez
,
M.
de la Cruz
,
R.
,
2001
,
Jurassic to Miocene K-Ar dates from eastern central Patagonian Cordillera plutons, Chile (45°–48°S)
:
Geological Magazine
 , v.
138
, p.
53
66
,
doi: 10.1017/S0016756801004903
.
Suárez
,
M.
Pettigrew
,
T.H.
,
1976
,
An upper Mesozoic island arc-back-arc system in the southern Andes and South Georgia
:
Geological Magazine
 , v.
113
, p.
305
328
.
Suárez
,
M.
de la Cruz
,
R.
Bell
,
C.M.
,
2000
,
Timing and origin of deformation along the Patagonian fold and thrust belt
:
Geological Magazine
 , v.
137
, p.
345
353
,
doi: 10.1017/S0016756800004192
.
Thomas
,
C.R.
,
1949
,
Geology and petroleum exploration in the Magallanes Province, Chile
:
AAPG Bulletin
 , v.
33
, p.
1553
1578
.
Thomson
,
S.N.
Hervé
,
F.
Stockhert
,
B.
,
2001
,
Mesozoic-Cenozoic denudation history of the Patagonian Andes (southern Chile) and its correlation to different subduction processes
:
Tectonics
 , v.
20
, p.
693
711
,
doi: 10.1029/2001TC900013
.
Thorkelson
,
D.J.
,
1996
,
Subduction of diverging plates and the principles of slab window formation
:
Tectonophysics
 , v.
255
, p.
47
63
,
doi: 10.1016/0040-1951(95)00106-9
.
Welkner
,
D.
,
1999
,
Geología del area del Cerro de San Lorenzo
:
Cor dillera Patagónica oriental, XI Región de Aysén, Chile (47°25′–47°50′S)
 
[M.S. thesis]
:
Santiago
,
Departamento de Geología, Universidad de Chile
,
148
p.
Welkner
,
D.R.
,
2000
,
Geocronología de los plutones del área de del Cerro San Lorenzo, XI Región de Aysén
:
IX Congreso Geológica de Chile (Puerto Varas) Actas
 , v.
2
, p.
269
273
.
Winslow
,
M.A.
,
1981
,
Mechanisms for basement shortening in the Andean foreland fold belt of southern South America
, in
McClay
,
K-.R.
Price
,
N.J.
, eds.,
Thrust and nappe tectonics
 :
Geological Society of London, Blackwell Scientific Publications
, p.
513
528
.
Winslow
,
M.A.
,
1982
,
The structural evolution of the Magallanes Basin and neotectonics in the southernmost Andes
, in
Cradock
,
C.
, ed.,
Antarctic geoscience
 :
Madison
,
University of Wisconsin
, p.
143
154
.
Yogodzinski
,
G.M.
Lees
,
J.M.
Churikova
,
T.G.
Dorendorf
,
F.
Woerner
,
G.
Volynets
,
O.N.
,
2001
,
Geochemical evidence for the melting of subducting oceanic lithosphere at plate edges
:
Nature
 , v.
409
, p.
500
504
,
doi: 10.1038/35054039
.

Related

Citing Books via

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal