GEOCHEMISTRY OF UPPER PALEOZOIC LOWER TRIASSIC GRANITOIDS OF THE CENTRAL FRONTAL CORDILLERA (33-DEGREES-10-33-DEGREES-45), ARGENTINA

New petrographic and chemical data from Upper Palaeozoic-Triassic gran itoids from the Frontal Cordillera of Argentina (33 degrees 10 to 33 d egrees 45) are presented. Five stocks with ages from Early Carbonifero us to Late Permian were sampled. The rocks are all calc alkaline with the mineralogy of each stock comprising essential plagioclase, alkali- feldspar and quartz with monor biotite and hornblende. Chemically, the rocks are similar to granitoids from the Frontal Cordillera of Chile, although the Argentinian stocks have generally higher K/Rb ratios. RE E chondrite-normalized patterns and overall abundances, along with oth er petrological and geochemical similarities, suggest a common mode of origin for the granitoid stocks. The absence of systematic and wide v ariations in abundance of compatible trace elements suggest that the s tocks represent magmas largely unaffected by extensive high-level frac tional crystallization, and that their compositions are controlled pri marily at source. Their age, tectonic setting and geochemical trends a re consistent with magma pulses generated during crustal extension. Th e magma source region is considered to be relatively mafic lower crust . Copyright (C) 1996 Elsevier Science Ltd & Earth Sciences & Resources Institute