Early Paleozoic high-Mg granodiorite from the Erlangping unit, North Qinling orogen, central China: Partial melting of metasomatic mantle during the initial back-arc opening
Early Paleozoic high-Mg granodiorite from the Erlangping unit, North Qinling orogen, central China: Partial melting of metasomatic mantle during the initial back-arc opening
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DOI：
10.1016/j.lithos.2017.07.016
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Saihong Yang
中科院分区：
文献类型：
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作者：
Mohammed I.M. Abdallsamed;Yuan-BaoWu;Wenxiang Zhang;Guangyan Zhou;Hao Wang;Saihong Yang
This study discussed the petrological classification, petrogenesis, and tectonic significance of early Paleozoic high Mg granodiorite from the Erlangping unit, in the North Qinling orogen. To achieve this target, we conducted integrated investigation of in situ zircon U-Pb dating, whole-rock geochemical, as well as Sr-Nd-Hf-O isotopic compositions for the Kanfenggou pluton from the Erlangping unit. LA-ICP-MS zircon dating for the Kanfenggou samples yields U-Pb ages of 442.9 +/- 6.2.and 438.0 +/- 6.7 Ma, suggesting that the pluton was emplaced at ca. 440 Ma. Whole-rock geochemical compositions of the samples display intermediate SiO2 (60.48-64.67 wt%) and K2O (1.21 to 2.10 wt%), but high Al2O3 (15.44 to 16.51 wt) and Na2O (4.01 to 4.81 wt%) contents. The granodiorite samples are characterized by elevated MgO ranging from 2.30 to 3.44 wt% and Mg# values of 53.35to 56.66, implying they are high-Mg granodiorites. They are characterized by very high Ba (524-1132 ppm) and Sr (684-980 ppm) contents, but depleted in HREE, and high (La/Yb)(N) ratios of 6.34 to 16.5 and slightly negative to weak positive Eu anomalies (Eu/Eu* = 0.68-1.09). These evidence that the Kanfenggou pluton belongs to the sanukitoid series. The high-Mg granodiorite samples exhibit a mantle signature with high Mg# values (53.35-56.66), Cr (45.8 to 93.3 ppm) and Ni (282 to 48.2 ppm) contents, but enriched in LILE, pointing to an enriched mantle source. The samples show relatively depleted radiogenic isotopic compositions with initial Sr-87/Sr-86 ratios varying from 0.7044 to 0.7047, epsilon(Nd)(t) values from 0.31 to 421, and zircon epsilon(Hf) (t) values from 7.3 to 83. The zircons have a mean delta O-18 value of 5.20 +/- 0.17 parts per thousand. Based on the trace element geochemical features, the metasomatic agent was suggested to be the fluids generated from dehydration of subducted slab. Therefore, we suggest two-stage processes for the formation of the Erlangping high-Mg granodiorites: (1) interaction between slab fluids and mantle peridotite; (2) partial melting of metasomatized mantle peridotite caused by the asthenosphere mantle upwelling and the initial back-arc opening resulted from the oceanic slab rollback.
