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|Title:||Metasomatized lithospheric mantle beneath the Western Qinling, central China: insight into carbonatite melts in the mantle|
|Citation:||Journal of Geology, 2012; 120(6):671-681|
|Publisher:||University of Chicago Press|
|Ben-Xun Su, Hong-Fu Zhang, Ji-Feng Ying, Yan-Jie Tang, Yan Hu and M. Santosh|
|Abstract:||Mantle xenoliths from the Western Qinling, central China, are dominated by lherzolites, which can be divided into four subgroups—namely, garnet-facies, coexisting spinel-garnet, spinel-facies, and carbonate-bearing ones. All these rocks display light rare earth element enrichment, positive Sr and Ba anomalies, carbonatite-like trace element patterns, and Sr-Nd-Pb isotopic mixing between depleted mantle and enriched mantle type II end members, consistent with the geochemical features resulting from carbonatite metasomatism. The garnet-facies lherzolites show high trace element concentrations but low LaN/YbN ratios, and they show high Sr and Pb isotopic ratios that are similar to those of carbonatites, suggesting that they were highly metasomatized. The spinel-facies group has the lowest trace element concentrations but higher LaN/YbN ratios than the garnet-facies group; their lowest Sr and Pb isotopic ratios are closer to those of the depleted mantle end member, implying low-degree metasomatism. Geochemical variation of the coexisting spinel-garnet sample lies between that of the garnet and spinel groups. The elevated and highly variable trace element concentrations and Sr-Pb isotopic values of the carbonate-bearing lherzolite group are most likely related to the modal content of carbonate minerals. Collectively, these geochemical features indicate a rising front of carbonatite metasomatism in the lithospheric mantle beneath the Western Qinling. Combining experimental and empirical data, the positive Pb, Y, and high-field strength element anomalies in the peridotites might be ascribed to the involvement of a subduction component in the carbonatite melts. On the basis of the data presented in this article, we propose a general model for carbonatite metasomatism in the lithospheric mantle to interpret the different signatures recorded in the garnet-facies peridotites (chemical imprint) and spinel-facies peridotites (occurrence of carbonate minerals), which has potential application to other regions that have undergone carbonatite metasomatism.|
|Rights:||© 2012 by The University of Chicago. All rights reserved.|
|Appears in Collections:||Geology & Geophysics publications|
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