Journal of Petrology Advance Access originally published online on February 13, 2006
Journal of Petrology 2006 47(5):965-990; doi:10.1093/petrology/egi102
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Ca-rich GarnetClinopyroxene Rocks at Hujialin in the SuLu Terrane (Eastern China): Deeply Subducted Arc Cumulates?
1 STATE KEY LABORATORY OF LITHOSPHERIC EVOLUTION, INSTITUTE OF GEOLOGY AND GEOPHYSICS, CHINESE ACADEMY OF SCIENCES, P.O. BOX 9825, BEITUCHENG XILU 19, BEIJING 100029, P.R. CHINA
2 THE KEY LABORATORY OF CONTINENTAL DYNAMICS, DEPARTMENT OF GEOLOGY, NORTHWEST UNIVERSITY, XI'AN 710069, P.R. CHINA
RECEIVED APRIL 1, 2005; ACCEPTED DECEMBER 28, 2005
Layers of Ca-rich garnetclinopyroxene rocks enclosed in a serpentinite body at Hujialin, in the SuLu terrane of eastern China, preserve igneous textures, relict spinel in garnet, and exsolution lamellae of Ca-rich garnet, ilmenite/magnetite, Fe-rich spinel, and also amphibole in clinopyroxene. In terms of their major and trace element compositions, the studied samples form a trend from arc cumulates towards FeTi gabbros. Reconstructed augite compositions plot on the trend for clinopyroxene in arc cumulates. These data suggest that the rocks crystallized from mantle-derived magmas differentiated to various extents beneath an arc. The Ca-rich garnet + diopside assemblage is inferred to have formed by compressing Ca-rich augite, whereas the relatively Mg-rich cores of garnet porphyroblasts may have formed at the expense of spinel. The protolith cumulates were subducted from near the crustmantle boundary (c. 1 GPa) deep into the upper mantle (4·8 ± 0·6 GPa and 750 ± 50°C). Negatively sloped PT paths for the garnetclinopyroxene rocks and the corollary of corner flow induced subduction of mantle wedge peridotite are not supported by the available data. Cooling with, or without, decompression of the cumulates after the igneous stage probably occurred prior to deep subduction.
KEY WORDS: arc cumulates; Ca-rich garnet; garnetclinopyroxene rocks; SuLu terrane; UHP metamorphism
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