Petrology and U–Pb geochronology of high-grade metavolcano-sedimentary rocks from central Xolapa Complex, southern Mexico

Abstract

The Xolapa Complex (XC) is a high-grade metamorphic belt exposed along the southern margin of the North American plate in Mexico. Its evolution includes an episode of widespread anatexis related to crustal thickening and uplift from middle to lower crustal levels during the Paleocene.On the basis of field and petrographic work, this study integrates a petrological modelling approach with zircon and monazite LA-ICP-MS U-Pb geochronology to elucidate the tectonothermal evolution of the central region of this belt. The study area includes a sequence of alternating migmatitic paragneiss and garnet-bearing mafic schist, which is interpreted to represent an Early-Cretaceous (Valanginian-Hauterivian) meta-volcano-sedimentary succession.Petrographic evidence and phase equilibria calculations demonstrate that a staurolite-kyanite grade metamorphism occurred at ~640-670 °C and 8-9 kbar before to widespread migmatization took place. Differential anatexis of fertile and refractory layers occurred progressively via biotite and amphibole dehydration-melting reactions, and continued during peak metamorphism at granulite-facies conditions of ~800-820 °C and ~5-7 kbar. Melt generation/mobilization progressed during cooling until crystallize at ~700 °C, according to Ti-in zircon-thermometry. In order to link U-Pb ages to metamorphic stages, zircon and monazite from different migmatite components were analyzed and chemical fingerprints were used. The age of prograde metamorphism is poorly constrained due to limited preservation of zircon and monazite, but likely occurred during the mid-to Late Cretaceous. Cooling and melt crystallization recorded by leucosome zircon occurred at 61.8±0.6 Ma. Both zircon and low-Y monazite from whole rock 2 and melanosome portions, respectively, are consistent with an episode of growth around 60.9±0.5Ma, but monazite continued to grow/recrystallize for a period of ca. 10 Ma. Thin Oligocene (~34-26 Ma) zircon and high-Y monazite rims are interpreted to reflect a stage of reheating by magmatic advection related to arc plutonism in the region. The results suggest the affinity of the central XC with other Early-Cretaceous volcano-sedimentary basins of central-southern Mexico.A period of crustal thickening would have buried the sequence at depths of ~30 km, causing Barrovian-type metamorphism during mid-to Late Cretaceous time and, eventually, anatexis that evolved at granulite-facies conditions during orogenic collapse in the Paleocene (≥62 Ma). The time span from leucosome crystallization to late-stage reheating in central XC would imply a protracted high-temperature evolution indicating middle-to upper crust residence time of at least ca. 30 Ma.

Detecting the Laramide event in southern Mexico by means of apatite fission-track thermochronology

“…2) (Maldonado et al . 2020). Therefore, the possible influence of movement of the Chortis Block on the development of the Sierra Madre del Sur cannot be ruled out (Nieto-Samaniego et al .…”

“…part of the Chatino terrane; Fig. 2) (Maldonado et al 2020). Therefore, the possible influence of movement of the Chortis Block on the development of the Sierra Madre del Sur cannot be ruled out (Nieto-Samaniego et al 2006;Maldonado et al 2020) (see simplified reconstruction in Fig.…”