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Oxygen isotopic heterogeneity of Pali Aike basaltic magmas from southernPatagonia as evidenced by oxygen isotope compositions of olivines

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Title
Oxygen isotopic heterogeneity of Pali Aike basaltic magmas from southernPatagonia as evidenced by oxygen isotope compositions of olivines
Other Titles
남부 파타고니아 팔리아이케 현무암질 마그마의 산소 동위원소 조성의 불균질성
Authors
Choo, Mi Kyung
Park, Kye-Hun
Sung Hi Choi
Lee, Mi Jung
Lee, Jong Ik
Kyu Han Kim
Subject
Geochemistry & Geophysics
Keywords
HIMU; Oxygen isotope; Pali Aike olivine; Patagonia; laser Fluorination
Issue Date
2015
Citation
Choo, Mi Kyung, et al. 2015. "Oxygen isotopic heterogeneity of Pali Aike basaltic magmas from southernPatagonia as evidenced by oxygen isotope compositions of olivines". GEOCHEMICAL JOURNAL, 49(1): 83-101.
Abstract
Oxygen isotope ratios were determined using laser fluorination methods on 15 olivines and seven matrix samples separated from the Pali Aike alkali basalt of southern Patagonia. The δ18O values were measured in ranges of 4.23 to 5.23‰ and 4.64 to 5.26‰ for olivine and matrix, respectively. The δ18O values of Pali Aike olivines are lower and have a wider range than those of normal upper mantle (5.0?5.4‰). We considered that the heterogeneity of the oxygen isotope compositions of Pali Aike olivine provides evidence of assimilation at a shallow level and the presence of recycled material. The differences between olivine and matrix δ18O values indicate that Δ18O(melt-ol) (0.14 to 0.50) was within equilibrium fractionation for some and in disequilibrium for most samples at magmatic temperature. Oxygen isotope compositions in disequilibrium indicate that the lower δ18O for the melt is explained by interaction with low δ18O hydrothermally altered rocks. The low δ18Oolivine values for low forsterite (Fo) contents of Pali Aike lavas can be explained by the effect of shallow-level assimilation. The oxygen isotope values for the olivine of high-MgO (or high-Fo) compositions are thought to represent oxygen isotope variation in the mantle source region. The low and variable δ18O signature of Pali Aike olivine can be explained by crustal recycling, such as a contribution from the hydrothermally altered oceanic crustal melt. These heterogeneous oxygen isotope compositions indicate that Pali Aike olivines require both assimilation at a shallow level and a component of the high-μ end-members (HIMU) mantle derived from recycled mantle lithologies in the form of pyroxenite or eclogite.
URI
http://repository.kopri.re.kr/handle/201206/6083
DOI
http://dx.doi.org/10.2343/geochemj.2.0333
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