SHRIMP zircon U–Pb evidence for extended Mesozoic magmatism in the Patagonian Batholith and assimilation of Archean crustal components

Abstract

The Patagonian Batholith forms the core of the southern Andes for about 1900km. We investigated the ages of magmatic evolution of this major granitic batholith with SHRIMP, or sensitive high mass-resolution ion microprobe. Zircons from four samples were dated near 45°S along a profile from the core of the batholith in Chile to pre-Andean Patagonia in Argentina, yielding ages of 191Ma±3,107Ma±2,96.3Ma±1.3, and 81.7Ma±1.3. An unexpected result is the presence of Precambrian zircon xenocrysts in the pre-Andean batholith apophyses, concentrated near 3.40–3.00, 2.75–2.50, and 2.15–1.95Ga. This demonstrates the presence of rocks derived from a Paleoproterozoic–Archean basement, which contaminated the gabbro and two granitoids.