T176 Petrochronology: Advances and Applications to Petrogenesis and Tectonics (Posters)

Monday, 23 October 2017
9:00 AM - 6:30 PM
Halls 4EF

ORIGIN AND EVOLUTION OF THE SW-MEXICAN CONTINENTAL CRUST: EVIDENCES FROM DETRITAL ZIRCON U-PB AGES AND HF ISOTOPIC EVOLUTION

Paper number: T176-12
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Arc magmatism in Mexico has been a continuous phenomenon at least since the Lower Jurassic, but it remains unclear how much of the continental mass represents juvenile additions or reworking of pre-existent crust. In order to elucidate the tectono-magmatic evolution of the Mexican continental crust through time, here we report U-Pb geochronology and Hf isotopic data on modern detrital zircons from river-mouth sediments draining to the coastal plain; from San Blás, Nayarít to Zihuatanejo, Guerrero.

The detrital zircons record passive sedimentation and cyclic magmatism during the Mesozoic and Cenozoic. The oldest zircon populations (> 200 Ma) are sourced in the metasediments of the Arteaga complex, a passive basin that received Archaean, Grenvillian, Pan-African and Permo-Triassic detritus from western Pangea during the Upper Triassic (Centeno-García et al., 2011, GSA Bull). The first autochthonous magmatic pulse occurred in the Upper Jurassic (~158 Ma) and is characterized by highly variable ƐHf (-10 to +12), probably indicating reworking of Arteaga metasediments at the initial stages of eastward subduction during the progressive fragmentation of Pangea. An important magmatic pulse with highly juvenile ƐHf (+3 to +15) was established by the Lower Cretaceous (~112 Ma), in the context of tectonic extension and slab rollback that governed the evolution of the Guerrero Terrane (Martini et al., 2014, Geosphere). A third pulse occurred in the Upper Cretaceous (~83 Ma), and is distinguished by the bimodal compositions of the Puerto Vallarta (ƐHf = -5 to 5) and Manzanillo (ƐHf ~ 10) batholiths, generated as a response to gradual slab flattening and arc migration to the continental interior (Ferrari, et al., 2017, ESR). Later on, an Eocene magmatic pulse (~50 Ma) with variably positive ƐHf (+1 to +10) is identified to the SE, associated with two major left-lateral shear zones (Martini et al., 2009, GSA). The final magmatic stage recorded by zircons is the Oligocene-Miocene (~24 Ma) Sierra Madre Occidental (SMO). Zircons from the SMO display ƐHf (-2.5 to 6) that become more juvenile with time, presumably as a response to escalating crustal extension. Our study shows that juvenile additions are favored during periods of extension and rollback, whereas crustal reworking is enhanced during slab flattening and tectonic compression.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-307590

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