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Li L.,No 1 Institute Of Geological And Mineral Resources Survey | Li L.,Key Laboratory Au Ag Polymetallic Deposit Ser And Deep Seated Metallogenic P Henan Pro | Sun W.,No 1 Institute Of Geological And Mineral Resources Survey | Meng X.,No 1 Institute Of Geological And Mineral Resources Survey | And 3 more authors.
Acta Petrologica Sinica | Year: 2013

Systematic and comprehensive petrological and geochemical study investigates the formation of eight northeastern Yanshanian granites in the southern margin of North China Block in Xiaoshan Mountain area, China. Petrologically, adamellite is domain. Geochemically, according to major elements, eight granites are silicate and belong to high K-shoshonite series; all granites have similar trace element patterns (including REE), obvious partition of LREE from HREE (La/Yb)N =9.52 ∼ 41. 21 (avg. 26. 16), and weakly abnormal Eu (δ5Eu =0. 82 ∼ 1. 35), and enrich in Rb, Ba, Th, K, Pb, Hf and Y, and deplete in Ta, Nb, Zr, P and Ti. High Sr (392. 8×10-6 ∼. 9×10-6, avg. 678. 8×10-6), low Y (8. 12×10-6 -21.34 × 10-6, avg. 14. 86×10-6) and Yb (0. 503 × 10-6 ∼ 1. 756 × 10-6, avg. 1. 26 × 10 -6) characterize a garnet-bearing magma source in a thick lower crust under North China Block. Initial isotopic Sr ratio (ISr = 0. 70645 ∼ 0. 71022, avg. 0. 70828) and initial epsilon Nd (εnd(t) = - 19. 7 ∼ -3.4, avg. - 14.6) disclose a crustal magma source. The proterozoic Nd depleted mantle model ages (t2DM) of the granites are concentrated in 1827 ∼2372Ma, and present high radiogenic Pb and initial Pb ratios (206 Pb/204 Pb = 17. 728 ∼ 18. 720 (avg. 17. 905); 207Pb/204Pb = 15. 444 ∼ 15. 656 (avg. 15. 544); 208Pb/204Pb = 37. 519 ∼ 38. 707 (avg. 38.187). All isotopic data suggest that the batholith was problebly formed by partial melting of the South Qinling crystalline basement with the participatioin of Taihua Group, Xiong' er Group and mantle materials. When extension environment substitute compression conditions caused by subduction of Yangtze Block with Qinling micro-block under North China Block, delamination of thick garnet-bearing crust and asthenosphere upwelling provide heat to melt the thick bottom crust, and forward, to form magma. This suggests that the crystalline basement under South Qinlin Orogen through detachment in north direction into the crystalline basement of Xiaoshan Mountain area, and the north of Xiaoshan Mountain area probably s the northern margin of East Qinling Orogen. Source

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