Provenance and compositional variations of intra-caldera lake sediments at La Primavera, Jalisco, Western Mexico

摘要

The multi-proxy provenance analyses carried out in the Upper Pleistocene sediments of the La Primavera intracaldera paleolake in western Mexico document the evolution of source areas. This lake formed a few thousand years after the caldera collapse (similar to 95 ka) and lasted until the intra-caldera resurgence process that ended 75 ka ago. Between 93.8 and 71 ka the sedimentary succession that filled the lake was affected by the extrusion of domes at its central part and the constant influx of volcaniclastic debris. Ring-fault domes and extra-caldera activity sourced at San Miguel volcano provided additional volcanic debris into the lake. Based on our multiproxy studies and recent age determinations of the post-caldera activity is likely that the paleolake was coggled at 78 ka in the central sector of the caldera, synchronously with the caldera resurgence. The resulting deposits (volcaniclastic debris) are tuffaceous sands characterized by lithoarenites rich in neo-volcanic grains, mainly vitrophyric and felsitic volcanic fragments with similar characteristics to the rocks of the Ixtahuantonte, El Nejahuete composite dome, Cerro Alto, Las Pilas, and Dos Coyotes domes. Geochemically, the sediments of the La Primavera caldera exhibit concentrations and elemental relationships of major and trace elements similar to the average of the upper continental crust. However, the high concentrations of some elements, such as La, Th, Ti, and Zr are related to the hyperalkaline nature of the magmatism that originated this volcanic caldera. The concentrations of SiO2/Al2O3, Na2O/K2O, Th, Sc, and Zr/10 indicate a passive margin tectonic setting deposition under low weathering conditions.