南天山高钾钙碱性花岗岩年代学、岩石成因及其地质意义

J4 ›› 2014, Vol. 20 ›› Issue (1): 58-.

南天山高钾钙碱性花岗岩年代学、岩石成因及其地质意义

毛友亮,樊双虎,陈淑娥,苏春乾,职荣军,芮婷,王江伟,刘明

出版日期:2014-03-20 发布日期:2014-04-19

Geochronology, Petrogenesis and Geological Significance of the High-K Calc-alkaline Granites in the South Tianshan

MAO Youliang,FAN Shuanghu,CHEN Shue,SU Chunqian,ZHI Rongjun, RUI Ting,WANG Jiangwei,LIU Ming

Online:2014-03-20 Published:2014-04-19

摘要/Abstract

摘要： 南天山北缘乌什塔拉地区东泉戈壁岩体岩石类型为似斑状二长花岗岩及少量的镁铁质包体,锆石SHRIMP U-Pb定年结果显示,其形成时代为 305±1 Ma。岩石富碱(K2O + Na2O=7.58%~ 8.44%),富钾(K2O/Na2O=1.09~1.33),高 Mg(# 51.6~58.5), A/CNK 为 0.92~1.00 之间,属于准铝质高 Mg# 高钾钙碱性系列;富集轻稀土(LREE)、大离子亲石元素(Rb,K,Th,U), 亏损重稀土(HREE)、高场强元素(Nb,P,Ti),强烈亏损 Y(10.17×10-6~14.84×10-6)及 Yb(1.054×10-6~1.374×10-6), 弱—无的负 Eu 异常(0.60~0.99),总体表明东泉戈壁岩体为壳 - 幔岩浆混合成因,具有碰撞晚期花岗岩类的地球化学特点。结合区域地质资料,东泉戈壁岩体的侵位表明在塔里木板块与伊犁—中天山板块碰撞造山作用晚期的挤压环境中,由于幔源岩浆的底侵作用,使得下地壳底部物质发生部分熔融,并与幔源岩浆发生混合作用,指示南天山晚古生代残余海盆的闭合。东泉戈壁壳 - 幔岩浆混合型花岗岩的确立表明晚石炭世南天山地区一次重要的地壳垂向生长事件。

关键词: 高钾钙碱性花岗岩;锆石U-Pb年代学;岩浆混合;碰撞晚期;南天山

Abstract: The Dongquangebi pluton is located in the Wushitala area of the northern margin of the South Tianshan, and is comprised mainly of porphyraceous monzonitic granite and a small amount of mafic microgranular enclaves. SHRIMP zircon U-Pb dating of porphyraceous monzonitic granite indicates that the weighted mean 206Pb/238U age is 305±1 Ma. These rocks are characterized by high-alkali (K2O+Na2O=7.58%~8.44%) and high-K (K2O/Na2O=1.09~1.33) and high Mg number (Mg#=51.6~58.5), with the A/CNK values between 0.92 and 1.00, which fall into the metaluminous high-Mg# and high-K calc- alkaline series. These rocks are also characterized by enrichment of LREE and LILE (Rb, K, Th and U) and depletion of HREE and HFSE (Nb, P and Ti), with slightly negative Eu anomaly (0.60~0.99) and strong depletion of Y (10.17×10-6~14.84×10-6) and Yb (1.054×10-6~1.374×10-6). These features suggest that the petrogenesis of the Dongquangebi pluton is magma mixing and the geochemical features of the Dongquangebi pluton belong to granitic rocks formed in the late-stage of a collisional orogeny. Combined with regional geological data, it is concluded that the Dongquangebi granitic pluton was derived from partial melting of the lower crust,with minor mixing with mantle-derived magma,due to the underplating of mantle-derived magma during the late-stage collision between the Tarim plate and Yili-Central Tianshan plate. The collisional magmatism in the South Tianshan indicates that the South Tianshan Late Paleozoic residual basin was closed in the Late Carboniferous, and the establishment ofmagma mixing of the Dongquangebi pluton indicates an important event of vertical growth of the continental crust in the South Tianshan.

Key words: high-K calc-alkaline granite;zircon SHRIMP U-Pb age;magma mixture;late-stage of collisional orogeny;South Tianshan

毛友亮,樊双虎,陈淑娥,苏春乾,职荣军,芮婷,王江伟,刘明. 南天山高钾钙碱性花岗岩年代学、岩石成因及其地质意义[J]. J4, 2014, 20(1): 58-.

MAO Youliang,FAN Shuanghu,CHEN Shue,SU Chunqian,ZHI Rongjun, RUI Ting,WANG Jiang. Geochronology, Petrogenesis and Geological Significance of the High-K Calc-alkaline Granites in the South Tianshan[J]. J4, 2014, 20(1): 58-.