Revisiting Oaxaquia-Laurentia connections during Rodinia assembly: Insights from u-pb dating and geochemistry of massif-type anorthosite intrusions and associated rocks from the northern Oaxacan Complex, southern Mexico

Abstract

Oaxaquia is a fundamental piece of the Mexican geological record. This Proterozoic crustal block evolved throughout the Calymmian-Tonian and has been traditionally included within the Rodinian realm. However, several aspects, such as its paleoposition and the occurrence of AMCG magmatism during the final stages of Rodinia’s consolidation, are still a matter of debate. In this work, we present new whole-rock geochemical and LA-ICP-MS U-Pb zircon geochronological data for the Huitzo suite from the northern Oaxacan Complex, one of the most extensive outcrops of AMCG rocks in Oaxaquia. This information allowed us to reinterpret the tectonic evolution of Oaxaquia during the Stenian-Tonian interval and refine its role in the amalgamation process of Rodinia. The massif-type anorthosite intrusions under study are alkalic, Ba-Sr-rich, devoid of olivine, and exhibit antiperthitic feldspars. These features resemble several anorthosite complexes exposed in present-d ay southeastern Laurentia. The U-Pb geochronological data demonstrate the existence of AMCG pulses between 1015–960 Ma that are contemporary to the late- to post-orogenic Laurentian anorthositic-granitic activity. These new insights suggest a space–time relationship between Oaxaquia and Laurentia that challenges the traditional Amazonia-Oaxaquia-Baltica link. We propose that Oaxaquia was caught in the collision zone between Laurentia and Amazonia as Rodinia was being assembled. During this process, Oaxaquia was positioned near the easternmost part of the Grenville Province, a region with a similar magmatic and metamorphic history. This area experienced orogenic relaxation and magmatism associated with lithospheric delamination after the main orogenic phase (∼1020 Ma), thus generating the oldest alkalic anorthosite intrusions along the core of the orogen. Once the collisional orogenesis ended (∼978 Ma), a post-orogenic extensional regime was established, favoring the generation of the youngest AMCG intrusions.