New U-Pb and Hf isotopes data from Jurassic Cañadón Asfalto rift basin, Chubut, Argentina: implications on the crustal evolution of Central Patagonia

HAUSER, N.; MATTEINI, M.; CABALERI, N.; VOLKHEIMER, W.; SILVA NIETO, D.; GALLEGO, O.F.; MONFERRAN, M.D.; PIMENTEL, M.

San Pablo

Simposio; 9th South American Symposium of Isotope Geology; 2014

Universidad de São Paulo

The Jurassic Cañadón Asfalto basin, located in Patagonia between the Somún Cura and Deseado Massifs, is one of the several basins formed during the Mesozoic coeval with the opening of the Atlantic Ocean. This extensional basin records a continental volcanic-sedimentary sequence represented by Cañadón Asfalto formation (CAF). New U-Pb and Hf isotopes date on the basement of the pre-rift-stage, acid volcanic and sedimentary sequences of CAF of the syn-rift stage and sedimentary rocks from the Sierra de La Manea area of the post-rift stage were obtained in order to constrain the crustal evolution of this sector of Patagonia between 0.460 and 0.156 Ga. New U-Pb and Hf isotopes date on the basement of the pre-rift-stage, acid volcanic and sedimentary sequences of CAF of the syn-rift stage and sedimentary rocks from the Sierra de La Manea area of the post-rift stage were obtained in order to constrain the crustal evolution of this sector of Patagonia between 0.460 and 0.156 Ga. The analyses were carried out using a Thermo-Fisher Neptune MC-ICPMS coupled with a Nd:YAG UP213 New Wave laser ablation system at the Laboratory of Geochronology of the University of Brasilia. The U-Pb data obtained on block and ash flow from Lonco Trapial Formation (LTF) considered the basement of the CA rift indicate an age of 169±1 Ma.The Hf data set highlight three main magmatic events during the evolution of Patagonia. The first event (0.156-0.20 Ga) in part represented by the volcano sedimentary sequence of CAF, yielded εHf values between -16 and +4 and Hf TDM between 1.96 and 0.83. The second event (~0.30 Ga) yielded εHf values between -6 and -3.45 and Hf TDM between 1.49 and 1.36 Ga. The third event (0.36-0.42 Ga) yielded εHf values between -4.77 and +0.30 and Hf TDM between 1.52 and 1.19 Ga. The new U-Pb age of 169 Ma for the LTF suggests that it is contemporaneous with CAF. The Hf isotopes data indicate a general reworking of paleo to mesoproterozoic crust during Paleozoic to Mesozoic time with an important mantle contribution for the youngest magmatic event, related with an extensional regime that generated the CA basin.