Pb isotopes data from La Modesta Formation, Deseado Massif, Argentina

MOREIRA, P.; GONZALEZ, P.; FERNÁNDEZ, R.; ROLANDO, P.

Punta del Este, Uruguay

Simposio; V South America Symposium on Isotope Geology; 2006

In this contribution we present the first preliminary results of Pb isotopes on meta-volcanic rocks and tourmalinites of the La Modesta Formation.The Pb isotopic composition of metavolcanite are 206Pb/204Pb= 18.593, 207Pb/204Pb= 15.648 and 208Pb/204Pb= 38.371 and the turmalines from the turmalinite have an average ratios of 206Pb/204Pb: 18.721, 207Pb/204Pb: 15.681 and 208Pb/204Pb: 38.652. These Pb isotope ratios are similar and suggest a possible genetic connection, with a common source, between the meta-volcanic rocks and exhalative tourmalinites. These preliminary results provide evidence that the main lead source of the volcanic and exhalative protolites of La Modesta Formation were upper crust rocks. We interpret that probably these rocks could be in part some of the Rio Deseado Complex units (Late Proterozoic-Mid Paleozoic orogenic belt) which are the basement of the forearc basin where the protolites of La Modesta Formation were deposited.