Water content difference between continental lower crust and lithospheric mantle: granulite and peridotite xenoliths hosted in basalts from Junan, Shandong Province
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    Abstract:

    The deep continental lithosphere, which includes the lower crust and the lithospheric mantle, is a very important layer in the earth's interior. The minerals comprise lower continental crust and lithospheric mantle are mainly nominally anhydrous minerals (NAMs) such as clinopyroxene, orthopyroxene, feldspar, olivine and garnet, and could contain very small and variable amounts of water in the structure as hydrogen-related minor defects; nevertheless, such trace amounts of water can disproportionally affect many physical and chemical properties and play a vital role in geodynamical processes. Knowledge of water distribution in the deep earth may help us understand the interior processes and the evolution of the earth. In this study, using Fourier transform infrared spectrometer (FTIR) analysis, the authors obtained the water content of such minerals as clinopyroxene, orthopyroxene and plagioclase in continental lower crustal granulite xenoliths and mantle peridotite xenoliths hosted by alkali basalts in Junan, Shandong Province. H2O content ranges from 300×10-6 to 1 180×10-6 for clinopyroxene, 80×10-6 to 169×10-6 for orthopyroxene, 717×10-6 to 1 239×10-6 for plagioclase, and 525 ×10-6 to 855×10-6 for bulk rock in continental lower crustal granulite xenoliths; and from 466×10-6 to 746×10-6 for clinopyroxene, 187×10-6 to 304×10-6 for orthopyroxene, 6×10-6 to 15×10-6 for olivine, and 81×10-6 to 245×10-6 for bulk rock in mantle peridotite xenoliths. The measured water concentrations of the minerals and bulk rock can roughly reflect the distribution of water in its sources, as evidenced by the following observations: ① EMP and FTIR measurements show no inter- and intra-grain heterogeneities for individual minerals in each sample; ② the cores of the clean, crack-and inclusion-free grains of relatively larger sizes were selected for FTIR measurements; ③ the studied samples were usually fresh and subjected to no alteration. In agreement with previous investigations of similar samples from Hannuoba and Nushan in North China Craton, water content of the continental lower crust is obviously higher than that of the underlying lithospheric mantle.

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杨贵才,杨晓志,郝艳涛,夏群科,2012,大陆下地壳和岩石圈地幔含水性的差异——山东莒南玄武岩中深源包体的初步观察[J].岩石矿物学杂志,31(5):691~700. YANG Gui-cai, YANG Xiao-zhi, HAO Yan-tao, XIA Qun-ke,2012,Water content difference between continental lower crust and lithospheric mantle: granulite and peridotite xenoliths hosted in basalts from Junan, Shandong Province[J]. Acta Petrologica et Mineralogica,31(5):691~700.

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  • Received:June 13,2011
  • Revised:May 25,2012
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