Abstract The porphyry copper mineralization at the Zaldívar deposit is confined to a NE-striking corridor of early- and late-intermineral granodioritic and dacitic porphyry intrusions and associated magmatic-hydrothermal breccia bodies. Country rocks comprise Early Permian rhyolite and andesite of La Tabla Formation plus comagmatic granitoids and Late Triassic andesite dikes. Middle Eocene andesitic rocks are common but of ill-defined distribution. Hydrothermal alteration consists of centrally located, magnetite-bearing potassic assemblages that are partially to completely overprinted by chlorite-epidote and sericitic alteration zones. The bulk of the hypogene metal resource was introduced synchronously with potassic alteration and A- and B-type veinlets during emplacement and evolution of multiple centers of biotite-bearing, early-intermineral porphyry and breccia bodies. Late-intermineral, hornblende-bearing dacite porphyry phases and associated breccia centers were emplaced later than the A- and B-veinlets but prior to multiple D-type veinlet generations and contributed additional, although lower grade, mineralization. Late-mineral dacite dikes are barren. Extensions to the east and northeast connect Zaldívar with Escondida Norte, and both can be considered as separate, coalescing porphyry copper deposits. Two discrete porphyry copper systems coexist at Zaldívar: Early Permian and late Eocene. The minor, copper-only Early Permian event (~290–285 Ma) was associated with an evolved, end-stage rhyolite porphyry phase of the La Tabla magmatism. The major late Eocene event (38.6–36.1 Ma) produced copper in addition to gold, molybdenum, and silver. Protracted Eocene porphyry copper alteration and mineralization, over ~2.5 m.y. as constrained by numerous U-Pb (zircon) and Re-Os (molybdenite) ages, was coincident with the high rates of uplift and denudation synchronous with contractional Incaic deformation. Earliest-stage porphyry intrusions at 39–38 Ma were probably associated with the terminal stages of a volcanic edifice, likely a dome complex, whose erosion products were deposited in contiguous, synorogenic basins. District-wide precursor magmatism of intermediate composition was active between 45 and 41 Ma. Oxidation and enrichment were active between ~17 and 15 Ma (supergene alunite), consistent with the chronology of supergene activity throughout the district and wider region.

Abstract Deep-water channel-levee complexes of the middle to upper Eocene Brito Formation are extensively exposed along the Pacific coast of southwestern Nicaragua across a distance of more than 70 km (43 mi) and a total thickness of approximately 2500 m (8200 ft). The Brito Formation forms part of an up-to-13-km (≤8-mi)-thick sedimentary infill of the Sandino forearc basin consisting of Late Cretaceous to Holocene deep- to shallow-marine and continental pyroclastic deposits. Coastal outcrops parallel and perpendicular to bed trends allow the reconstruction of laterally and vertically stacked channel-levee complexes. Each channel-levee complex consists of several (one to seven) probably shingled, channel-levee systems with a feeder or distributary channel near the center. Individual channel-levee complexes are 80–120 m (262–393 ft) thick and 5–11 km (3–7 mi) wide. Levee deposits are mainly sheetlike and have been interpreted on the basis of bed thickness, grain size, occurrence of CCC elements (climbing ripples, convolute lamination, and rip-up clasts, Walker, 1984 ), lateral facies changes, variations in the local paleoslope, and locally intercalated crevasse deposits. The Playa Las Tablas section documents a coarse-grained channel-levee system with synsedimentary faulting along the channel margins. The system consists of three offset-stacked channel fills with relatively low aspect ratios that are flanked by finer grained, sandy, levee deposits. The channels are mainly filled with pebble- to boulder-sized pebbly sandstones (diameter of the ten largest clasts, D10 = 32 cm [12.6 in.]) deposited from high-density turbidity flows. The levee deposits consist of sheetlike, thin- to thick-bedded sandstones with interbedded siltstones.

ABSTRACT The Upper Cretaceous Las Tablas unit of the Franciscan Complex, a conglomerate-breccia containing a diverse array of clasts, is located in the central California Coast Ranges. The Las Tablas unit was originally deposited in southern California, where significant amounts of the western half of the Sierra Nevada batholith and coeval Great Valley forearc basin and basement are missing. The most likely explanation for this absence is that forearc and western arc assemblages were removed through a combination of surface and tectonic erosion that accompanied Laramide shallow subduction. Petrographic analysis of rounded to subrounded gabbro, quartz diorite, tonalite, granodiorite, and andesite clasts from the Las Tablas unit reveals a prehnite-pumpellyite–grade overprint of primary igneous textures. Furthermore, zircon grains derived from these clasts yield generally Late Jurassic to Early Cretaceous U-Pb ages and positive Hf isotopic values, with one sample yielding a Late Cretaceous age and a negative Hf value. These relations strongly suggest that the analyzed clasts experienced subduction zone metamorphism and were derived principally from the western and axial Sierra Nevada batholith, with possible additional input from forearc basement (the Coast Range ophiolite). The presence of western arc–derived detritus in the Las Tablas unit suggests that surface plus tectonic erosion removed a significant amount of these units and incorporated them into the subduction complex. Granitic clasts of the Las Tablas unit were likely introduced into previously subducted and exhumed Franciscan materials by sedimentary rather than tectonic processes.

Las Tablas de Daimiel, Spain, is one of the scarce, freshwater wetlands areas still preserved in southern Europe. The wetland is fed by surface and groundwater. We studied the Quaternary sedimentary record of Las Tablas in a drill hole that penetrated 38.5 m of shallow-lake and fluvial deposits. Differences in the dominantly micritic muds indicate three main stages of development. In the lowest stage, unit A, (Lower? to Middle Pleistocene) the slightly saline wetland developed under a relatively arid climate that favored slow flow movement of the fluvial system and the disconnection of the ponded areas. In the intermediate stage, unit B, (Middle to Upper Pleistocene) extensive peat developed during wetter conditions. Biosiliceous sediments (diatoms and sponge spicules) also accumulated in this swampy setting. In the latter stage, unit C, (Upper Pleistocene to Holocene) palustrine carbonates formed in a freshwater environment with desiccation events, followed by fluvial reworking of the lake margins. Lithification of these deposits was relatively fast (<10,000 yr). The studies of the core, including mineralogy, petrography, stables isotopes, and pollen analyses, indicate that these sediments are similar to those of ancient palustrine sequences. Therefore, Las Tablas can be considered as a recent analogue for freshwater palustrine systems that have no marine influence. These systems are very sensitive to changes in climate or base level, and their study is needed to better understand the terrestrial sedimentary record. Study is needed also to determine how to preserve these wetlands. Las Tablas de Daimiel constituyen uno de los escasos humedales de agua dulce que aún se conservan en el sur de Europa, concretamente en España. El humedal está abastecido por aguas superficiales y subterráneas. El registro sedimentario Cuaternario de Las Tablas, se ha estudiado mediante un sondeo en el que se cortaron 38.5 m de depósitos lacustres someros y fluviales, esencialmente carbonatos micríticos. Las características de los sedimentos permiten diferenciar tres principales etapas de sedimentación. En la primera etapa, unidad A, (Pleistoceno Inferior? a Medio) el humedal era ligeramente salino y se desarrolló bajo un clima relativamente árido que favoreció el flujo más lento del sistema fluvial, permitiendo la desconexión de las zonas encharcadas. En la etapa intermedia, unidad B, (Pleistoceno Medio a Superior) el amplio desarrollo de turberas indica condiciones más húmedas, en las que dentro de las áreas pantanosas también se depositaron sedimentos biosilíceos (diatomeas y espículas de esponjas). En la última etapa, unidad C, (Pleistoceno Superior a Holoceno) los sedimentos característicos son carbonatos palustres formados en un ambiente de agua dulce con eventos de desecación seguidos de posterior retrabajamiento de los márgenes lacustres por canales fluviales. La litificación de estos depósitos fue relativamente rápida (<10000 años). El estudio llevado a cabo en el sondeo (mineralogía, petrografía, isótopos estables, análisis polínicos) indica que estos sedimentos son similares a las secuencias palustres del registro geológico. Por tanto, Las Tablas de Daimiel pueden considerarse como un análogo reciente para sistemas palustres de agua dulce que no tengan influencia marina. Estos sistemas son muy sensibles a cambios climáticos y/o del nivel de base, por lo que su estudio es necesario para conocer mejor el registro sedimentario continental, pero también para preservar estos humedales.

Abstract The giant Escondida district in northern Chile, discovered in 1981, includes the major porphyry copper deposits at Escondida-Escondida Este, Escondida Norte-Zaldívar, Pampa Escondida, and two small deposits (the Escondida cluster), besides the Chimborazo deposit. The district contains at least 144 million metric tons (Mt) of copper. The Escondida district is part of the middle Eocene to early Oligocene porphyry copper belt, which follows the trench-parallel Domeyko fault system, a product of the Incaic transpressional tectonic phase. At the district scale, the major N-striking Portezuelo-Panadero oblique-reverse fault juxtaposes latest Carboniferous to Early Permian igneous basement with an andesitic volcanic sequence of late Paleocene to early Eocene age, both of which host the porphyry copper mineralization. Immediately before and during porphyry copper formation, a thick siliciclastic sequence with andesitic volcanic products intercalated toward the top (San Carlos strata) filled a deep basin, generated by clockwise rigid-block rotation, within the confines of the Escondida cluster. The presence of these volcanic rocks suggests that an eruptive center was still active within the confines of the Escondida cluster when deposit formation began. The deposits are all centered on multiphase biotite granodiorite porphyry stocks, which were predated by dioritic to monzodioritic precursors and closely associated with volumetrically minor, but commonly high-grade, magmatic-hydrothermal breccias. The earliest porphyry phases consistently host the highest grade mineralization. Alteration-mineralization zoning is well developed: potassic and overprinted gray sericite assemblages containing chalcopyrite and bornite at depth; more pyritic chlorite-sericite and sericitic zones at intermediate levels; and shallow advanced argillic developments, the remnants of former lithocaps that could have attained 200 km 2 in total extent. The latter are associated with high-sulfidation, copper-bearing sulfide mineralization, much of it in enargite-rich, massive sulfide veins. The Escondida and Escondida Norte-Zaldí-var deposits, formed at ∼ 38 to 36 Ma, are profoundly telescoped, whereas the earlier (∼ 41 Ma) Chimborazo and later (∼ 36–34 Ma) Escondida Este and Pampa Escondida deposits display only minor telescoping, suggesting that maximal Incaic uplift and erosion took place from 38 to 36 Ma. The Portezuelo-Panadero and subsidiary longitudinal faults in the district—inverted normal structures that formerly delimited the eastern side of a Mesozoic backarc basin—were subjected to sinistral transpression prior to deposit formation (pre-41 Ma), which gave rise to the clockwise block rotation responsible for generation and initial synorogenic filling of the San Carlos depocenter. The Escondida district was then subjected to transient dextral transpression during emplacement of the NNE- to NE-oriented porphyry copper intrusions and associated alteration and mineralization (∼ 38–34.5 Ma). This dextral regime had waned by the time that a N-trending, late mineral rhyolite porphyry was emplaced at Escondida Este and was replaced by transient sinistral transpression during end-stage formation of NW-striking, high and intermediate sulfidation, massive sulfide veins and phreatic breccia dikes. Since 41 Ma, the faults in the district have undergone no appreciable displacement because none of the porphyry copper deposits shows significant lateral or vertical offset. Renewed uplift and denudation characterized the late Oligocene to early Miocene, during which the extensive former lithocap was largely stripped and incorporated as detritus in a thick piedmont gravel sequence. Development of hematitic leached capping and attendant chalcocite enrichment zones, along with subsidiary oxide copper ore, was active beneath the topographic prominences at Escondida, Escondida Norte-Zaldívar, and, to a lesser degree, Chimborazo from ∼ 18 to 14 Ma, but supergene activity was much less important at the topographically lower, gravel-covered Pampa Escondida deposit. After ∼ 14 Ma, supergene processes were soon curtailed by the onset of hyperaridity throughout much of northern Chile.

Abstract This paper presents a new kinematic model for the structure and tectonic evolution of part of the northern Andes of Colombia based on detailed geologic mapping, strain analysis, seismic interpretation, and 3-D forward modeling. This model indicates that the oblique convergence vector imposed by the Caribbean Plate is not fully partitioned in space, but instead must be distributed in a diffuse zone of transpressional deformation spanning the Cordilleras Oriental and Central. The Piedras-Girardot fold belt, located between the two cordilleras, contains the termination of two regional scale structures of the northern Andes: the Ibagué fault and the Guaduas syncline. The Ibagué fault, with a minimum dextral displacement of 30 km, is the southern boundary of a rigid indenter that was inserted to the east-northeast, causing contrasting deformation styles in the Mesozoic sedimentary sequence to the east and to the south of it. South of the rigid indenter, a complex array of diverging north- to northeast-trending faults and folds delineate a sigmoidal stepover to the left with faults verging outwardly in opposite directions that define the Piedras-Girardot fold belt. The kinematics of deformation indicate that this fold belt is a dextral transpressional system where oblique contraction is accommodated along north-and northwest-trending segments of faults, dextral strike-slip along their northeast-trending segments, and extension along the east-trending faults. This doubly vergent system has northwest-verging thrust faults with oblique displacements approximately parallel to the Ibagué fault (17-km Cambao fault; 7-km Camaito fault), as well as a southeast-verging roof thrust with approximately 8 km of oblique displacement to the east-northeast (Cotomal fault). A geometric fit constrained with a stratigraphic piercing point also requires counterclockwise rotation of the easternmost two thrust sheets by 7° and 138. A three-dimensionally admissible and valid palinspastic restoration of this fold belt requires approximately 52% east-northeast contraction (about 32 km), which is consistent with the minimum displacement of the Ibagué fault and other estimates of shortening in the eastern margin of the Cordillera Oriental. This component of deformation had not been previously identified and quantified in the northern Andes.