Stenian Arc-Magmatism and Early Tonian Medium-To High-Grade Metamorphism Along the Northern Border of Amazonia During the Rodinia Assembly: The Pochotepec Suite in Southern Mexico

The Precambrian basement of Mexico is composed of crustal blocks linked to northern Amazonia during the assembly of the Rodinia supercontinent. In this paper, we examine an extensive basement block known as the Sierra de Juárez Complex (SJC) in southern Mexico by integrating fieldwork, in situ zircon U-Pb geochronology by LA-ICPMS and whole-rock geochemistry. The results provide1 evidence for a continuous middle-to-high-grade metamorphic succession here re-defined as the Pochotepec suite (PS), which comprises an upper lithodeme with volcanosedimentary precursors and a lower lithodeme that includes intermediate to mafic orthogneisses and migmatites. The analytical results suggest that the PS protoliths originated in a continental-arc tectonic setting ca. 1080-1050 Ma along the northern edge of Amazonia before the consolidation of Rodinia. In addition, xenocrystic zircon U-Pb analyses indicate the presence of a recycled older crust of ca. 1200-1300 Ma. Finally, U-Pb data of recrystallized zircon-rims and new metamorphic zircon grains recorded the timing of metamorphism and anatexis of the PS during the early Tonian (954-933 Ma). The crystallization ages of two trondhjemitic leucosomes of 954 and 933 Ma strongly support the migmatization age. The Tonian metamorphic/anatectic episode of the PS differs in grade and age from the typical metamorphism related to the amalgamation of Rodinia reported in Mexico and Colombia (granulite-facies at ca. 990 Ma). Therefore, we interpret this event as either produced by post-orogenic crustal collapse or late contractive tectonics.