Detrital-zircon U-Pb geochronology of the Quebrada del Carrizo Metamorphic Complex and El Jardin Schists and spatially-related granitoids of the Sierra Castillo Batholith

Abstract

U-Pb detrital-zircon geochronology of two discrete outcrops of mica schists of the western border of the Domeyko Cordillera in the Region of Atacama, northern Chile, indicates that the maximum age of sedimentation of their protolith corresponds to the Late Carboniferous to Early Permian. The Early Permian granitoids of the Sierra Castillo Batholith that intruded the metamorphic rocks show ductile deformation and were emplaced within hot crust not much later than the greenschist-facies metamorphism peak that affected their host rocks. Therefore, the metamorphism of the Quebrada del Carrizo Metamorphic Complex and El Jardin Schists is constrained temporarily between the maximum age of sedimentation of detrital zircons (314 +/- 11 to 291 +/- 5 Ma) and the crystallization of Early Permian intrusions (292.2 +/- 6.6 to 278.3 +/- 5.8 Ma), thus pointing to Early Permian metamorphic peak. Concentration of U-Pb ages between 400 and 600 Ma indicate eastern detrital input sources, such as the Pampean and Brasiliano orogenies and the Ordovician-Silurian Famatinian magmatic arc of northwestern Argentina. Other concentration of detrital-zircon U-Pb ages between 900 to 1,200 Ma reflect contributions of magmatic rocks of age of the Proterozoic Sunsas orogeny (Grenville). Whereas, only few grains of zircon with U-Pb ages older than 1,200 Ma occur and these may correspond to a minor contribution zircon from South American cratonic areas. Zircon grains of Devonian age are scarce in populations of zircons analyzed, consistent with a passive margin and a lull of magmatic activity during this period in the paleo-Pacific border of Gondwana. The U-Pb detrital zircon data from the Quebrada del Carrizo Metamorphic Complex and El Jardin Schists coincide with detritalzircon U-Pb data previously published for other metamorphic complexes of central-northern Chile, which are part of a Late Paleozoic subduction complex or accretionary wedge developed in the western edge of Gondwana. Consequently, the Quebrada del Carrizo Metamorphic Complex and El Jardin Schists are relics of the same Paleozoic accretionary wedge, which constituted the substratum for the emplacement of the Permian plutons of the Sierra Castillo Batholith.