Zircon and Titanite U-Pb SHRIMP dating of unexposed basement units of the Buenos Aires region, southeastern Rio de La Plata Craton, Argentina

摘要

We present U-Pb Sensitive High Mass Resolution Ion MicroProbe (SHRIMP) data of unexposed igneous-metamorphic basement rocks from two areas of the southeastern Rio de la Plata craton (RPC; Buenos Aires city) located within the Buenos Aires-Piedra Alta (BAPA) terrane - and the Tapalque area (Buenos Aires province) - located within the Tandilia terrane, and discuss the tectonic evolution of that portion of the craton based on both the new data and previous work. The newly obtained geochronological data of drill cores indicate that: (a) arc magmatism occurred at 2164-2186Ma corresponding to early Trans-Amazon' (early Rhyacian) arc magmatism; (b) the age of collision between the BAPA and Tandilia terranes is inferred to have commenced at ca. 2110Ma; (c) peak metamorphism occurred at ca. 2069Ma; and (d) the presence of rocks related to the RPC is confirmed under Cenozoic sediments in a large area between Martin Garcia Island and Tandil. We envisage an early Rhyacian divergent double subduction scheme between the BAPA and Tandilia terranes - i.e. N-dipping towards BAPA and S-dipping towards Tandilia - prior to the late Rhyacian collision between these two terranes.