ABSTRACT We generated low-temperature thermochronological data on crystalline rocks from the Chiapas Massif in southern Mexico to constrain the complex relationship among tectonics, exhumation, and sedimentation in the region. Our data show that the first recorded cooling event occurred at ca. 40–25 Ma due to denudation of the sedimentary cover of the Chiapas Massif at slow rates of ~0.1 km/m.y. This was followed by a period of tectonic quiescence from ca. 25 to 14 Ma. Between ca. 14 and 7 Ma, cooling implying exhumation of the massif at rates of up to ~0.7 km/m.y. was renewed, and this was associated with, and possibly responsible for, the Miocene “Chiapanecan” deformational event observed in the Chiapas fold-and-thrust belt to the northeast of the massif. This younger uplift was also accompanied by the onset of arc-related magmatism beneath the massif, between ca. 13 and 9 Ma, along the Tonalá shear zone at the Pacific coast. Since ca. 7 Ma, additional but slower cooling and exhumation are indicated along the length of the Chiapas Massif, and arc magmatism has jumped north by ~125 km from the Tonalá shear zone into the Chiapas fold-and-thrust belt. Concurrently, subsidence and sedimentation have persisted along the offshore Tehuantepec Shelf to the south, suggesting that the Tonalá shear zone has been recently active (despite no magnitude 4 or larger earthquakes), with up-to-the-north vertical displacement. We interpret the exhumation at ca. 40–25 Ma to pertain to displacement of the Chortis block along the paleo–Motagua fault zone, either as a northward propagation of a basement thrust beneath the massif within a regional transpressional setting, or as a deep, ductile crustal thickening and attendant isostatic uplift of the southern flank of the massif during the transpressional passage of the Chortis block. The ensuing quiescence (25–14 Ma) coincided, we believe, with the passage of the “western tail” of Chortis, which is internally deformed and perhaps transferred compressive stress less effectively than had the central, continental core of the Chortis block earlier. Renewed uplift and exhumation of the region began by ca. 14–10 Ma. An onset at ca. 10 Ma is probably the best estimate for the beginning of exhumation of the northwestern and central portions of the Chiapas Massif, whereas the present-day southeastern tip of the massif (potentially an allochthonous sliver belonging to the Chortis block) started to exhume earlier, at ca. 14 Ma. By ca. 13 Ma, arc magmatism had moved into the western Tehuantepec area, marking the onset of subduction of the Cocos plate beneath the Chiapas Massif. Hence, we interpret the main period of uplift of the Chiapas Massif and primary shortening of the Chiapas fold-and-thrust belt (ca. 14–7 Ma) as being driven by the establishment of Cocos subduction beneath the area.

Abstract The structural evolution of southern Mexico is described in the context of its plate tectonic evolution and illustrated by two restored crustal scale cross-sections through Cuicateco and the Veracruz Basin and a third across Chiapas. We interpret the Late Jurassic–Early Cretaceous opening of an oblique hyper-stretched intra-arc basin between the Cuicateco Belt and Oaxaca Block of southern Mexico where Lower Cretaceous deep-water sediments accumulated. These rocks, together with the hyper-stretched basement beneath them and the Oaxaca Block originally west of them, were thrust onto the Cretaceous platform of the Cuicateco region during a Late Cretaceous–Eocene orogenic event. The mylonitic complex of the Sierra de Juárez represents this hyper-stretched basement, perhaps itself an extensional allochthon. The Chiapas fold-and-thrust belt is mainly Neogene in age. Shallowing of the subduction angle of the Cocos Plate in the wake of the Chortis Block, suggested by seismicity and migrating arc volcanism, is thought to play an important role in the development of the Chiapas fold-and-thrust belt itself, helping to explain the structural dilemma of a vertical transcurrent plate boundary fault (the Tonalá Fault) at the back of an essentially dip-slip fold-and-thrust belt.

ABSTRACT We present a summary of information on seismically active faulting in Chiapas, Mexico, related to North America–Caribbean plate-boundary zone deformation. We collected data from published works, and we also present new data collected from reporting agencies. Several active structures were identified as part of the deformation of the plate-boundary zone in the states of Chiapas and Veracruz, including 18 large (up to 175-km-long) strike-slip faults belonging to three tectonic realms: the Tonalá realm, the Depresión Central, and the strike-slip fault province. Available fault-plane solutions indicate left-lateral, strike-slip displacement along these faults. The reverse-fault province is also found to be part of the plate-boundary zone and seismically active, with thrust-faulting fault-plane solutions. Deformation extends to the northwest, along the Veracruz coastal plains region, which is also seismically active.

ABSTRACT We redefine the “Chontal arc” of the southern Isthmus of Tehuantepec, Mexico, as the Chontal allochthon. The Chontal assemblage is composed of Upper Cretaceous low-grade metavolcanic and metasedimentary rocks included in the Chivela lithodeme. By means of field observations, laser-ablation detrital zircon geochronology, and trace-element geochemistry, we constrained the provenance and tectonic setting of these rocks. We concluded that they form an allochthon emplaced during a Paleogene transpressive event. Basement structure in the greater Oaxaca-Chiapas area was assessed by qualitative interpretation of Mexican State aeromagnetic maps. Chivela lithodeme sediments include a contribution from Albian–Turonian volcanic arc rocks no longer present in the region, likely sourced from the Chortís block or from the Greater Antilles Arc as it collided with southern Yucatan. Maastrichtian basic intrusive units, basalt flows, and pillow lavas with pelagic sediments in the Chontal are subalkaline, plotting in the normal mid-ocean-ridge basalt (N-MORB) field of discrimination diagrams. The igneous rocks are interpreted as pertaining either to the inception of the paleo–Motagua fault zone (left step in the fault trace), or to local backarc extension behind the Chortís block just before it began to migrate eastward, in a basin we call the Chontal basin. The Chontal allochthon was thrust northward onto parautochthonous strata flanking the Mixtequita and Chiapas Massif basements. Chontal allochthon rocks were later intruded by Miocene granitoids related to the inception of Cocos plate subduction arc magmatism. Rocks of the Chontal allochthon have been previously linked to the Cuicateco belt of eastern Oaxaca, but this is challenged here on the basis of lithologic type, chronology, tectonic associations, structural styles, and discontinuous anomaly trends in aeromagnetic maps.

Abstract New structural, geochronological, and petrological data highlight which crustal sections of the North American–Caribbean Plate boundary in Guatemala and Honduras accommodated the large-scale sinistral offset. We develop the chronological and kinematic framework for these interactions and test for Palaeozoic to Recent geological correlations among the Maya Block, the Chortís Block, and the terranes of southern Mexico and the northern Caribbean. Our principal findings relate to how the North American–Caribbean Plate boundary partitioned deformation; whereas the southern Maya Block and the southern Chortís Block record the Late Cretaceous–Early Cenozoic collision and eastward sinistral translation of the Greater Antilles arc, the northern Chortís Block preserves evidence for northward stepping of the plate boundary with the translation of this block to its present position since the Late Eocene. Collision and translation are recorded in the ophiolite and subduction–accretion complex (North El Tambor complex), the continental margin (Rabinal and Chuacús complexes), and the Laramide foreland fold–thrust belt of the Maya Block as well as the overriding Greater Antilles arc complex. The Las Ovejas complex of the northern Chortís Block contains a significant part of the history of the eastward migration of the Chortís Block; it constitutes the southern part of the arc that facilitated the breakaway of the Chortís Block from the Xolapa complex of southern Mexico. While the Late Cretaceous collision is spectacularly sinistral transpressional, the Eocene–Recent translation of the Chortís Block is by sinistral wrenching with transtensional and transpressional episodes. Our reconstruction of the Late Mesozoic–Cenozoic evolution of the North American–Caribbean Plate boundary identified Proterozoic to Mesozoic connections among the southern Maya Block, the Chortís Block, and the terranes of southern Mexico: (i) in the Early–Middle Palaeozoic, the Acatlán complex of the southern Mexican Mixteca terrane, the Rabinal complex of the southern Maya Block, the Chuacús complex, and the Chortís Block were part of the Taconic–Acadian orogen along the northern margin of South America; (ii) after final amalgamation of Pangaea, an arc developed along its western margin, causing magmatism and regional amphibolite–facies metamorphism in southern Mexico, the Maya Block (including Rabinal complex), the Chuacús complex and the Chortís Block. The separation of North and South America also rifted the Chortís Block from southern Mexico. Rifting ultimately resulted in the formation of the Late Jurassic–Early Cretaceous oceanic crust of the South El Tambor complex; rifting and spreading terminated before the Hauterivian ( c . 135 Ma). Remnants of the southwestern Mexican Guerrero complex, which also rifted from southern Mexico, remain in the Chortís Block (Sanarate complex); these complexes share Jurassic metamorphism. The South El Tambor subduction–accretion complex was emplaced onto the Chortís Block probably in the late Early Cretaceous and the Chortís Block collided with southern Mexico. Related arc magmatism and high- T /low- P metamorphism (Taxco–Viejo–Xolapa arc) of the Mixteca terrane spans all of southern Mexico. The Chortís Block shows continuous Early Cretaceous–Recent arc magmatism. Supplementary material: Analytical methods and data, and sample description are available at http://www.geolsoc.org.uk/SUP18360.

Abstract The Chiapas Fold and Thrust Belt (CFTB) of southern Mexico underwent widespread contraction during the well-documented middle Miocene ‘Chiapanecan’ Orogeny. However, earlier phases of folding have been documented in the region and might have affected the belt before the Miocene. We carried out a stratigraphic review and a structural analysis of the belt, complemented by 40 Ar– 39 Ar dating of synorogenic illite to identify the successive pulses of deformation. Reliable radiometric ages were obtained in three folds from the southern portion of the belt, and in one thrust gouge near the front of the belt. Authigenic illite-rich samples were located in Upper Cretaceous limestone successions that experienced bed-parallel shear during folding and thrusting. They yielded ages ranging from 35 to 40 Ma in the folds and 54.5 ± 7 Ma in the thrust, documenting thin-skinned folding and thrusting in the belt mostly in Eocene time. Some of the basement faults of the belt may have been active during this phase. However, most of the pervasive lateral faults that cross-cut the regional folds in the belt were mostly active from the Miocene onwards, causing transpression and fold amplification.

Abstract The Miocene Nanchital conglomerate of the western Chiapas Foldbelt is the coarsest terrigenous clastic depositional Cenozoic unit of the region, probably comprising more proximal sections of hydrocarbon-rich slope-fan reservoirs found in the more distal Sureste Basin of the southern Gulf of Mexico fringe. Traditionally, the felsic igneous and metamorphic components of the conglomerate were assumed to derive from the Permian basement of the nearby Chiapas Massif. However, zircon U–Pb dating of five Nanchital conglomerate clasts from the Chiapas Foldbelt as well as several igneous exposures in SW Tehuantepec indicates that the Nanchital conglomerate's catchment area included the western Isthmus of Tehuantepec for late Middle Miocene and possibly early Late Miocene time, after which the more proximal Chiapas Massif and Chiapas Foldbelt likely became dominant. This study suggests that traditional concerns over the limited extent of quartz-rich clastic source areas feeding terrigenous clastic reservoirs in the Sureste Basin might be overly pessimistic. We propose a temporal framework for viewing Neogene and Quaternary clastic supply to the southern Gulf of Mexico.

ABSTRACT New low-temperature thermochronological data analyses (apatite fission track and apatite and zircon [U-Th]/He) on rocks from the southern (Pacific) margin of Mexico between Acapulco and the western Gulf of Tehuantepec, where pre–middle Eocene arc and forearc complexes are expected but missing, show that this continental margin was subjected to an important Tertiary exhumational event. Exhumation is constrained to ca. 32–20 Ma in the west (Acapulco) and to ca. 19–11 Ma in the east (Puerto Angel) and was thus eastwardly diachronous. The diachroneity is interpreted as relating to the migration of the Chortis block, representing the western end of the Caribbean plate. The amount of exhumation along the trend is constrained to roughly 4–5 km (~0.3–0.6 km/m.y.). These magnitudes and rates are much less than previous estimates of 2.5–4 km/m.y. during the Oligocene, which are likely overestimated. These faster rates have been employed in a competing model for arc removal by orthogonal subduction erosion (i.e., Chortis block not involved), which is accordingly questioned. The exhumation was not due to shearing or fault-related uplift as the Chortis block migrated, but rather to the inception of subduction along Mexico in the wake of Chortis block migration. A four-part history applies to southern Mexico that is eastwardly diachronous: (1) inception of arc magmatism as the Chortis block first moved over the ~150 km depth contour of the Farallon/Cocos Benioff zone; (2) uplift and exhumation of basement as southern Mexico encountered and overrode the site of the Farallon/Cocos Benioff zone; (3) northward migration of arc magmatism as the Chortis block left the cross section and North America continued to advance further onto the Cocos plate, producing flat slab subduction geometry; and (4) resumption of forearc subsidence once the Mexican margin had acquired a subduction zone hanging-wall geometry. The missing arc terrane along southern Mexico is the Chortis block.

Abstract We present an updated synthesis of the widely accepted ‘single-arc Pacific-origin’ and ‘Yucatán-rotation’ models for Caribbean and Gulf of Mexico evolution, respectively. Fourteen palaeogeographic maps through time integrate new concepts and alterations to earlier models. Pre-Aptian maps are presented in a North American reference frame. Aptian and younger maps are presented in an Indo-Atlantic hot spot reference frame which demonstrates the surprising simplicity of Caribbean–American interaction. We use the Müller et al. ( Geology 21 : 275–278, 1993) reference frame because the motions of the Americas are smoothest in this reference frame, and because it does not differ significantly, at least since c. 90 Ma, from more recent ‘moving hot spot’ reference frames. The Caribbean oceanic lithosphere has moved little relative to the hot spots in the Cenozoic, but moved north at c. 50 km/Ma during the Cretaceous, while the American plates have drifted west much further and faster and thus are responsible for most Caribbean–American relative motion history. New or revised features of this model, generally driven by new data sets, include: (1) refined reconstruction of western Pangaea; (2) refined rotational motions of the Yucatán Block during the evolution of the Gulf of Mexico; (3) an origin for the Caribbean Arc that invokes Aptian conversion to a SW-dipping subduction zone of a trans-American plate boundary from Chortís to Ecuador that was part sinistral transform (northern Caribbean) and part pre-existing arc (eastern, southern Caribbean); (4) acknowledgement that the Caribbean basalt plateau may pertain to the palaeo-Galapagos hot spot, the occurrence of which was partly controlled by a Proto-Caribbean slab gap beneath the Caribbean Plate; (5) Campanian initiation of subduction at the Panama–Costa Rica Arc, although a sinistral transform boundary probably pre-dated subduction initiation here; (6) inception of a north-vergent crustal inversion zone along northern South America to account for Cenozoic convergence between the Americas ahead of the Caribbean Plate; (7) a fan-like, asymmetric rift opening model for the Grenada Basin, where the Margarita and Tobago footwall crustal slivers were exhumed from beneath the southeast Aves Ridge hanging wall; (8) an origin for the Early Cretaceous HP/LT metamorphism in the El Tambor units along the Motagua Fault Zone that relates to subduction of Farallon crust along western Mexico (and then translated along the trans-American plate boundary prior to onset of SW-dipping subduction beneath the Caribbean Arc) rather than to collision of Chortis with Southern Mexico; (9) Middle Miocene tectonic escape of Panamanian crustal slivers, followed by Late Miocene and Recent eastward movement of the ‘Panama Block’ that is faster than that of the Caribbean Plate, allowed by the inception of east–west trans-Costa Rica shear zones. The updated model integrates new concepts and global plate motion models in an internally consistent way, and can be used to test and guide more local research across the Gulf of Mexico, the Caribbean and northern South America. Using examples from the regional evolution, the processes of slab break off and flat slab subduction are assessed in relation to plate interactions in the hot spot reference frame.