The High-temperature Garnet-pyroxenite Enclaves in the Spinel-bearing Peridotite: Evidence for Partial Melting of the Upper Mantle in Northern Dabie Mountain, China
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P542.5

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    Abstract:

    The spinel-bearing peridotite massif occurring near Raobazhai, Huoshan County of northern Dabie Mountain, is the largest upper mantle relict slab in the Dabie Mountain area. The massif was emplaced as a rootless lenticular intrusion of solid state into the plutonic gneiss complex of Dabie Mountain. The eclogite and garnet pyroxenite enclaves are of high-temperature genesis and are products of partial melting of the upper mantle. In the PI-CIPW versus A12O3 diagram the high-temperature eclogites are plotted into the tholeiite field rather than that of calc-alkaline basalts. The REE distributions of the garnet pyroxenite and the spinel-bearing peridotite are of similar flat patterns, only the total REE of the latter are lower than those of the high temperature eclogites. The plots in the Ni-Co-Sc ternary diagram show that the eclogite and garnet pyroxenites are plotted close to the trend line of deep-seated basalts, while the spinel-bearing peridotites are plotted along the trend of ultramafic relics, which clearly reveals the partial melting of the upper mantle in northern Dabie Mountain. The spinel in the peridotite is defined as pleonaste, the Cr# of which is rather low (Cr# = 12~21), while the associated olivine are Fo-rich (Fo=92~93), indicating that the partial melting was just at its initial stage, estimated at 15%. The low content of TiO2 in spinel suggests a low oxygen fugacity during the melting of the mantle. The occurrence of the Raobazhai spinel-bearing peridotite massif shows that accompanying the exhumation and uplift of the UHP rock units there must be some upper mantle fragments being carried up to the shallower levels. Due to the upwelling of the asthenosphere or the break-off of the subducting slabs, the extruded rock slab could maintain a high temperature regime. This had caused the earlier deep-seated granulite-facies retrometamorphism, which was later shifted to high amphibolite-facies retrometamorphism during the subsequent uplift.

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YOU Zhendong, ZHONG Zengqiu, SUO Shutian, ZHOU HanwenChina University of Geosciences, Wuhan,.2004. The High-temperature Garnet-pyroxenite Enclaves in the Spinel-bearing Peridotite: Evidence for Partial Melting of the Upper Mantle in Northern Dabie Mountain, China[J]. Acta Geologica Sinica,78(1):89-96

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  • Revised:June 24,2003
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