南岭大东山花岗岩的形成时代与成因——SHRIMP锆石 U-Pb年龄、元素和Sr-Nd-Hf同位素地球化学

南岭大东山花岗岩的形成时代与成因——SHRIMP锆石 U-Pb年龄、元素和Sr-Nd-Hf同位素地球化学

黄会清1, 2，李献华3, 1，李武显1，刘颖1

1. 中国科学院广州地球化学研究所同位素年代学和地球化学重点实验室，广州 510640； 2. 中国科学院研究生院，北京，100049； 3. 中国科学院地质与地球物理研究所岩石圈演化国家重点实验室，北京 100029

收稿日期:2008-09-20 修回日期:2008-09-20 出版日期:2008-09-20 发布日期:2008-09-20

Age and Origin of the Dadongshan Granite from the Nanling Range: SHRIMP U-Pb Zircon Age, Geochemistry and Sr-Nd-Hf Isotopes

HUANG Hui-qing1,2, LI Xian-hua3,1*, LI Wu-xian1, LIU Ying1

1. Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; 2. Graduate School of Chinese Academy of Sciences, Beijing 100039, China; 3. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

Received:2008-09-20 Revised:2008-09-20 Online:2008-09-20 Published:2008-09-20

摘要/Abstract

摘要： 中国东南部南岭地区广泛出露以弱过铝质黑云母二长花岗岩和黑云母钾长花岗岩为主的燕山早期花岗质岩石，其成因有待进一步研究。大东山岩体岩性主要为黑云母二长花岗岩和黑云母钾长花岗岩，两个样品的SHRIMP锆石U-Pb 年龄为165±2 Ma 和159±2 Ma，与区域南岭系列的黑云母花岗岩的主要形成时代一致。花岗岩样品以高硅（SiO2 > 72%）、高钾（K2O/Na2O > 1.6）、富碱（K2O + Na2O = 7.36% ~ 9.31%）和弱过铝质（集中于ASI = 1.00 ~ 1.11）为特征。微量和稀土元素组成上，岩体富Rb, Th 和LREE，贫Ba, Nb, Sr, P 和Ti, Eu 负异常显著（δEu = 0.06 ~ 0.34）。多数样品的Zr，Ce, Nb 和Y 含量总和小于350×10-6，10 000 × Ga/Al 值低于典型的A 型花岗岩。同位素组成上，样品具有高I sr（ 0.7123 ~ 0.7193）和低εN（d t）（-9.3~ -11.5）的特点，两阶段Nd 模式年龄为1.70~1.89 Ga ；与全岩εNd（t）不同，岩浆锆石的εHf（t）具有较大的变化范围（-3.5~ -11.8）。矿物学及地球化学结果表明大东山是一个高分异的I 型花岗岩岩体。岩体岩浆很可能是由元古代火成岩石部分熔融形成，并伴随有少量年轻或新生幔源物质的加入，岩浆上升侵位的过程中发生混合、结晶分异作用。

Abstract: Early Yanshanian (Jurassic) granites, which are dominated by weakly peraluminous biotite monzogranite and K-feldspar granite, are ubiquitous in Nanling Range in Southeast China. However, the petrogenesis of the granites remains controversial.The Dadongshan pluton consists of biotite monzogranite and biotite-bearing K-feldspar granite. SHRIMP U-Pb zircon dating of two samples yield ages of 165 ± 2 Ma and 159 ± 2 Ma, consistent with the major formation time of the“ Nanling-series” biotite granites in the neighboring region. The granites are silica-rich (SiO2 > 72%), potassic (K2O/Na2O > 1.6), weakly peraluminous (most have ASI=1.00 ~ 1.11) and enriched in alkalies (K2O+Na2O = 7.4% ~ 9.3%). Samples are invariably enriched in Rb, Th and LREE, yet depleted in Ba, Nd, Sr, P and Ti, with distinct negative europium anomaly (δEu=0.06 ~ 0.34). Low contents of Zr+Ce+Nb+Y (< 350 ppm) and low 10000 × Ga/Al rule out their A-type affinity. Isotopically, samples show high and variable initial Sr ratios (0.7123 ~ 0.7193), yet low and constantεNd(t) (-9.3 ~ -11.5), corresponding to T2DM age of 1.70 ~ 1.89 Ga.However, their zircon Hf isotopes show large variations, withεHf(t) values between -3.5 and -11.8. Mineralogical and geochemical features suggest that the Dadongshan granites are highly fractionated I-type granites. They were probably derived from partial melting of the Proterozoic igneous protoliths with minor addition of juvenile crust or newly mantle-derived magmas, accompanied by assimilation and fractional crystallization.

黄会清, ，李献华, ，李武显，刘颖. 南岭大东山花岗岩的形成时代与成因——SHRIMP锆石 U-Pb年龄、元素和Sr-Nd-Hf同位素地球化学[J]. J4.

HUANG Hui-qing1,2, LI Xian-hua3,1*, LI Wu-xian1, LIU Ying1. Age and Origin of the Dadongshan Granite from the Nanling Range: SHRIMP U-Pb Zircon Age, Geochemistry and Sr-Nd-Hf Isotopes[J]. J4.