Geochemical and Sr-Nd-Pb Isotopic Characteristics of the Granitoids of Xiaoshan Mountain Area on the Southern Margin of North China Block and Its Geological Significance
详细信息
- 责任者：Li Lei (No.1 Institute of Geological and Mineral Resources Survey ; Development of Geology and Mineral Resources of Henan Province ; Luoyang 471000 ; China) ; Sun Weizhi
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(8)
- 关键词：花岗岩类 ; granitoid ; 华北板块 ; North China Plate
- 页码：p.2635-2652
- 图表：10 illus., 3 tables, 71 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
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 (δEu = 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 ～ 916. 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 (206Pb/204Pb = 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 is the northern margin of East Qinling Orogen.
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