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GEOCHRONOLOGY, SR-ND ISOTOPE GEOCHEMISTRY AND PHASE EQUILIBRIA MODELING: INSIGHTS INTO PETROGENESIS OF CHIMO-YELAPA METAMORPHIC COMPLEX, MEXICO
U-Pb zircon ages from three paragneisses suggest a maximum depositional age of c. 280–180 Ma. Late Jurassic magmatism is evidenced by U-Pb zircon ages from biotite-orthogneiss sample. The U-Pb zircon ages from an amphibole-orthogneiss and an amphibolite indicate the emplacement of their protolith at c. 135 Ma. The age range, c. 120–112 Ma, in these samples indicate a tectono-thermal event at Albian-Cenomanian, similarly, one paragneiss yield monazite U-Pb ages of ~120-117, supporting this hypothesis. Finally, new geochronological data from PVB yields an igneous crystallization of ~83 Ma.
The Nd-Sr geochemistry of CYMC show εNdi = -8.36 to -5.45 and εSri = 67.72-125.28 in paragneisses, εNdi = -4.74-5.64 and εSri = -10.66-81.79 Ma in orthogneisess, εNdi = 3.91-8.09 and εSri -10.73-80.64 in amphibolites, and εNdi = -1.87 to -1.03 and εSri = 3.83-10.24 for PVB. Phase equilibria modelling was performed in two sillimanite-bearing paragneisses. Our pseudosections indicate that mineral assemblage sillimanite + garnet + biotite formed at ~6–7.5 kbar and ~710–730 °C, which are the first thermobarometrical data in the region.
Our new data suggest a tectonic evolution for the Chimo-Yelapa Metamorphic Complex as a transition from a passive continental margin regime (c. 280–180 Ma) to a continental arc setting (c. 135 Ma.), with regional metamorphism at c.120-112 Ma. Finally, the crystallization of Puerto Vallarta Batholith was during the Late Cretaceous. These events were associated to the convergence of the Farallon and North America plates during the Jurassic to the Late Cretaceous in the NW of Mexico.