U-Pb age of a late Cenozoic ultra-high temperature metamorphic event under Central Mexico, as inferred from granulite xenoliths from Cerro El Toro, Mexico

Cerro El Toro, a Pliocene scoria cone that carried abundant lower crust xenoliths to the surface, is located in Mesa Central (MC), Mexico, where mafic alkalic intra-plate volcanism has occurred since early Miocene (end of Sierra Madre Occidental volcanism). Early studies Toro showed feldspathic granulite equilibrated at P = 0.9–1.4 GPa and T 900−1100°C under anhydrous conditions (ternary feldspars calculations). A young (Oligocene-Quaternary?) pulse ultra-high temperature (UHT) metamorphism was thus proposed for region, without strict age constrain.Zircon crystals recovered from set nine (7 Grt-Sil bearing metapelites, Px-bearing meta-quartz diorite, Grt-Opx orthogneiss) were selected LA-(MC)-ICPMS U-Pb geochronology. Palaeozoic Neoproterozoic zircon are scant, whereas Mesozoic Cenozoic ages more abundant. Based on their chondrite-normalized REEs all zircons interpreted as igneous, those late Oligocene (ca. 27–6 Ma) mostly metamorphic grew during protracted UHT crust. The presence metasediments indicative action subducted Farallon plate, coupled with tectonic erosion continentally derived sediments, either forearc basin and/or an accretionary prism relaminated by sediment diapirism. Similarities among xenolith modern sediments belonging Mexico Pacific coast point towards NW-SE 100 km long stretch across Zihuatanejo possible source.The paucity Grenville-age detrital grains suggests area not underlain Proterozoic basement, implying substantial reduction Oaxaquia extension beneath younger Guerrero terrane.