Noble gas composition of Patagonian subcontinental lithospheric mantle

JALOWITZKI TIAGO; SUMINO HIROCHIKA; CONCEIÇÃO ROMMULO V.; ORIHASHI YUJI; NAGAO KEISUKE; BERTOTTO GUSTAVO W.; BALBINOT EDUARDO; SCHILLING MANUEL; GERVASONI FERNANDA

Congreso; Goldschmidt Conference 2016; 2016

Noble gas composition of mantle xenoliths from Pali-Aike Volcanic Field and Gobernador Gregores, Patagonian subcontinental lithospheric mantle(SCLM), reflects three-component mixing between air, SCLM and MORB-like. Pali-Aike mantle xenoliths represent the intrinsic local SCLM reservoirwith higher (U+Th+K)/(3He, 22Ne, 36Ar) ratios compared to MORB source. This mantle reservoir is characterized by radiogenic 3He/4HeAVERAGE = 6.87 ±0.04 RA and nucleogenic mantle neon with 21Ne/22Ne average of 0.090, with 3He/22Ne ratios (up to 13.66 ± 0.37) higher than depleted MORBs (8.31?9.75).40Ar/36Ar ratios range from near?atmospheric ratio (510) up to 16400, with mantle 40Ar/36Ar reaching 54000. Mantle 129Xe/132Xe reach up to 1.11, whereas136Xe/132Xe up to 0.40. Gobernador Gregores mantle xenoliths represent the SCLM metasomatized by MORB-like component with 3He/4HeAVERAGE = 7.24 ± 0.09 RA, slightly less nucleogenic mantle neon with 21Ne/22Ne = 0.065, 3He/22Ne = 8.39 ± 0.14, and 40Ar/36Ar ratios usually less than 4000. The MORBlike component is related to asthenospheric mantle upwelling in response to the opening of a slabwindow, which is consequence of South Chile Ridge subduction. Although Pali-Aike SCLM displays MORB-like metasomatism, it could have been homogenized during the last 14 Ma, after rapid passage and northward migration of the Chile Triple Junction and its slab window at this latitude.