Rift‐Related Low‐Pressure–High‐Temperature Granulite Facies Metamorphism Generates Widespread Peraluminous Crustal Melts: Evidence From the Early Jurassic Mexican Crust

Abstract High heat fluxes occurring in rift settings are expected to generate partially melted low‐pressure–high‐temperature granulites (LP–HTG). Therefore, studying these rocks can offer valuable insights into crustal reworking during extension. However, our interpretations are limited by the rarity of LP–HTG in the metamorphic record. To better assess the genesis of partially melted LP–HTG, it is relevant to identify their protolith and associated melt as well as to characterize their P‐T evolution. We study the Tejupilco area in Mexico to present the case of the Pepechuca metapelitic xenoliths and the Tizapa metagranite, the latter belonging to the Nazas Igneous Province (NIP). This site serves as an excellent location to outline the partial melting history of the eastern and southern regions of the Mexican crust during the Jurassic. Geochemical and geochronological data, combined with thermodynamic modeling, show that the mid‐ to upper‐crustal protoliths of the Pepechuca xenoliths—a metamorphosed portion of Triassic turbidite sequences—experienced anomalously high T/P (>1700°C/GPa) regional prograde metamorphism and hydrate‐breakdown partial melting during the Early Jurassic (182.2 ± 2.4 Ma). A combination of isotopic, geochronological, and modeling data demonstrates that the Tizapa metagranite originated from the melting of rocks akin to the Pepechuca xenoliths. We also show that the LP–HTG metamorphism occurred in a rift setting during the breakup of Western Pangea. Hence, our results demonstrate that rifting is a viable mechanism for crustal reworking during LP–HTG metamorphism and for the generation of peraluminous felsic igneous rocks, such as those found in the anatectic Jurassic NIP.