Petrogenetic and tectonic implications of Oligocene - Miocene volcanic rocks from the Sierra de San Miguelito complex, central Mexico

Paleogene - Neogene volcanic complexes are commonly found in the southern part of the Mesa Central province (MC), Mexico. The Sierra de San Miguelito Complex (SSMC) is located in the southeastern part of the MC and consists of two main phases of Oligocene and Miocene units as follows: (1) basaltic group of porphyritic texture of basalt/trachybasalt compositions; and (2) rhyolite-ignimbrite group of porphyritic texture of trachydacite/trachyte compositions. Chondrite-normalized rare-earth element patterns for the basaltic group display enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), whereas the rhyolite-ignimbrite group shows enrichment in LREE and high field strength elements (HFSE). The Eu anomalies within the SSMC become progressively more negative from the basaltic group to the rhyolite-ignimbrite group (Eu/Eu* = 1.13 to 0.02) suggest upper crust (crustal contamination) participates during magma generation. Trace element modelling reveals that the basaltic group evolved through a mixing process between mafic and felsic end - members. In contrast, chondrite-normalized and multi-element models reveal that the rhyolite-ignimbrite group evolved by partial melting of the upper continental crust. New multi-dimensional discrimination diagrams along with the Nb-Ta anomalies reveal that the SSMC volcanic rocks were generated in an extensional environment.