Geology of the coastal Chiapas (Mexico) Miocene plutons and the Tonalá shear zone: Syntectonic emplacement and rapid exhumation during sinistral transpression

Abstract

Late Miocene plutons in coastal Chiapas, Mexico, represent the roots of an extinct magmatic arc. Miocene granitoids of calc-alkaline composition and arc chemistry intruded into and were deformed within the Tonalá mylonite belt in the middle to upper crust. The mylonite belt is a crustal-scale shear zone extending along the western margin of the Chiapas Massif for ~150 km. Deformation is characterized by a dominantly subhorizontal lineation and subvertical foliation along a strikingly linear zone that trends ~310°. Mylonitic fabrics contain ambiguous but dominantly sinistral shear indicators. Intrusions are interpreted as syntectonic on the basis of similar U-Pb zircon crystallization age estimates (ca. 10 Ma) and the cooling age estimates obtained on neoformed micas in the mylonite. The plutons are elongated, their long axis is parallel to shear zone, and some plutons show markedly asymmetric outcrop patterns, with sheared tails that trail behind the intrusions and that are consistent with sinistral displacement. Parts of plutons were mylonitized by continuous deformation in the Tonalá shear zone, locally developing intricate pseudotachylyte and cataclasite veins slightly oblique to the mylonite foliation. Outside of the shear zone, plutons preserve magmatic fabrics. These observations are consistent with features common to syntectonic granites interpreted to have been emplaced along strike-slip shear zones in a transpressional setting. We interpret the Tonalá mylonites as representing a relict transform boundary that was slightly oblique to the Polochic-Motagua fault system, which accommodated over 100 km of sinistral displacement between the Chortis block (on the Caribbean plate) and Chiapas (on the North America plate) in late Miocene time.

Geomorphic analysis of transient landscapes in the Sierra Madre de Chiapas and Maya Mountains (northern Central America): implications for the North American–Caribbean–Cocos plate boundary

“…Our results and those of Authemayou et al (2011) also provide evidence for vertical motions along the Tonalá shear zone. There are evidence for a Miocene sinistral motions along the Tonalá shear zone and for the Tuxtla and Malpaso faults (Guzmán-Speziale and Meneses-Rocha, 2000;Witt et al, 2012b;Molina-Garza et al, 2015). However, the GPS data suggest a presentday ∼ 2.5 mm yr −1 extension along the Tonalá shear zone and a similar amount of compression along the Tuxtla Fault (Fig.…”

“…The western flank of the Chiapas Massif is bounded by the left-lateral Tonalá shear zone, which connects to the south to the western termination of the Polochic Fault (Wawrzyniec et al, 2005;Weber et al, 2005). The displacement along the Tonalá shear zone is synchronous with Miocene magmatic intrusions and could have reached 100 km (Molina-Garza et al, 2015). The Central Valley is a ∼ 170 km long and ∼ 30 km wide depression corresponding to a NW-trending synclinorium with superimposed smaller folds (Witt et al, 2012b).…”

“…The Chiapas Massif mostly consists of Permian igneous rocks affected by medium-to high-grade metamorphism and middle to late Miocene intrusions related to the subduction of the Cocos Plate (Damon and Montesinos, 1978;Weber et al, 2007;Molina-Garza et al, 2015). The western flank of the Chiapas Massif is bounded by the left-lateral Tonalá shear zone, which connects to the south to the western termination of the Polochic Fault (Wawrzyniec et al, 2005;Weber et al, 2005).…”

Caracterización granulométrica de los depósitos de abanicos aluviales en la Cuenca de Motozintla, Chiapas, México: un peligro geológico latente por eventos de inundación

“…Este desplazamiento de 130 km, también coincide con el modelo presentado por Authemayou et al (2011) en el que define a la triple unión como la interacción de las placas Norte América-Cocos-Caribe en un arreglo subducción-subducción-transformante (SST). Molina-Garza et al (2015) también proponen que la falla Tonalá-Motozintla constituye la sutura que forma esta triple unión y que tiene una migración hacia el sur, asumiendo que presenta una componente de empuje cercano a la intersección con el sistema de fallas Polochic. Lyon-Caen et al (2006) y Franco et al (2012 realizaron estudios detallados sobre la cinemática de fallas en el norte de América Central y su conexión con la zona de subducción de la placa de Cocos en la región de Chiapas, Guatemala y El Salvador.…”

“…Lo anterior concuerda con Weber et al (2002), quien menciona que la Sierra de Chiapas está compuesta en su mayor parte por rocas ígneas del batolito chiapaneco y que representa uno de los complejos ígneos más grandes de México. Molina-Garza et al (2015) concluyeron que el macizo de Chiapas está constituido por un complejo plutónico y metamórfico de edad predominantemente Pérmico, sobre el que yacen rocas sedimentarias de edad Jurásico-Cretácico. También mencionan que el plutón de la costa chiapaneca está sobreyacido por una sucesión Jurásica de lechos rojos (red beds).…”