V11B-3064
H2O contents and geochemistry of peridotite xenoliths from the Anyuan: Nature and evolution of lithospheric mantle beneath the west Cathaysia block，SE China
Monday, 14 December 2015
Poster Hall (Moscone South)
Hui Zhang1, Jianping Zheng1, Jianggu Lu1 and Zhaohui Tang2, (1)State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan, China, (2)Faculty of Engineering, China University of Geosciences, Faculty of Engineering, Wuhan, China
Abstract:
The major-, trace-elements and H2O contents of minerals from peridotite xenoliths hosted in the Mesozoic lamprophyres of Anyuan area (SE China) were analyzed by electron microprobe, LA-ICPMS and Fourier transform infrared spectroscopy, respectively. The xenoliths include spinel harzburgites, lherzolites with or without spinel. The harzburgites and lherzolites with spinels are moderately refractory (Mg#Ol=90.2–91.2), whereas lherzolites without spinels are fertile (Mg#Ol=89.1–89.9). The REE patterns of clinopyroxenes in these xenoliths vary from LREE-depleted, through flat, to LREE-enriched patterns, and commonly exhibit negative U, Pb and Ti anomalies. The results suggest that the xenoliths mostly experienced 1–10% partial melting and subsequently silicate metasomatism. Water contents of clinopyroxene (cpx), orthopyroxene (opx), and olivine (ol) range from 330 to 404 ppm, 126 to 279 ppm, and 11 to 33 ppm, respectively. No correlations between H2O content and melting index (i.e., YbN in cpx, Cr# in spinel) and metasomatic index ((La/Yb)N in cpx) show that extent of partial melting and mantle metasomatism did not modify the initial H2O contents. Most water contents of the mantle source are largely preserved in pyroxenes. The whole-rock water contents range from 67 to 124 ppm, similar to that of the MORB source. Therefore, we suggest that the Cenozoic lithospheric mantle of the Cathaysia block is accreted from the upwelled and cooled asthenospheric mantle. On the other hand, the widespread refractory lithospheric mantle ever existed in the western Cathaysia. The coexistence of fertile mantle and refractory-transitional mantle beneath the west Cathaysia block might be attributed to the refertilization of the lithospheric mantle by the upwelling asthenospheric materials and eventually replacement resulting from the cooling of the upwelled asthenosphere.
