南岭地区温公岩体的岩石成因及其构造指示  

The Petrogenesis and Tectonic Implication of Wengong Intrusion in the Nanling Range

作　　者：甘成势 王岳军[2] 蔡永丰[4] 刘汇川[2] 张玉芝[1,2] 宋菁菁[1,3] 郭小飞[1,3] 

机构地区：[1]中国科学院广州地球化学研究所同位素地球化学国家重点实验室,广东广州510640 [2]中山大学地球科学与地质工程学院,广东省地质过程与矿产资源勘查重点实验室,广东广州510275 [3]中国科学院大学,北京100049 [4]桂林理工大学地球科学学院,广西桂林541004

出　　处：《地球科学（中国地质大学学报）》2016年第1期17-34,共18页Earth Science-Journal of China University of Geosciences

基　　金：国家重点基础研究发展计划项目(No.2014CB440901);国家自然科学基金项目(Nos.41372198,41402165);中山大学中央高校基本事业费

摘　　要：南岭构造带处于古特提斯构造域与古太平洋构造域的复合部位,是研究古特提斯构造域向古太平洋构造域转换的理想地区.温公岩体位于广东省梅州兴宁地区的南岭构造带东段.该岩体LA-ICP-MS锆石U-Pb年代学定年结果为196.9±4.4Ma,具A型花岗岩的典型地球化学特征,如富硅(69.22%~76.33%)、高Zr+Nb+Ce+Y含量、高FeO_t/MgO和10 000×Ga/Al比值、亏损高场强元素和Eu负异常明显等.样品具高钾低镁、准铝质到弱过铝质的特征,其K_2O含量为3.81%~4.43%,MgO为0.20%~0.82%,A/CNK比值为0.95~1.10,属于高钾钙碱性花岗岩.样品具相对亏损的Sr-Nd-Hf同位素组成,其ε_(Nd)(t)为-2.7^-0.5,ε_(Hf)(t)为+2.1^+7.7.传统观点认为华南地区缺少205~180Ma的岩浆记录,而本文温公岩体的精确定年结果说明华南东南部地区存在早侏罗世(~197Ma)岩浆活动.结合区域相关地质资料,我们认为温公岩体形成于陆内伸展的构造背景,主要是基性下地壳部分熔融的产物,并在成岩过程中发生了分离结晶作用.~197Ma的温公A型花岗岩体是目前华南东南部燕山期识别出的最老A型花岗岩体,结合区域内196~156Ma的A型花岗岩的特征,指示华南东南部从古特提斯构造域向古太平洋构造域转换的时限应晚于早侏罗世.The early Yanshanian geology of southeastern China is characterized by widespread igneous rocks, especially granites. However, the petrogenesis and tectonic implication of these granites in South China remain highly controversial. The A-type granites are the important carrier for better understanding the tectonic evolution of the South China block since the formation is commonly related to extensional tectonic setting. In this study, a set of new zircon U-Pb geochronological, elemental and Sr- Nd-Hf isotopic data is presented for the Wengong A-type granite in eastern Nanling range in northern Guangdong Province. Laser zircon U-Pb dating for the Wengong granitic sample give a weighted mean age of 196.9 ± 4.4 Ma and in-situ zircon εHf （t） values ranging from ＋ 2.1 to ＋ 7.7. Their whole rock e Na （t） values range from - 2.7 to - 0.5. The Wengong granites are en- riched in SiO2 （69.22%-76.33%） and total alkalis （7.77%-8.35%）. They are metaluminous-peraluminous with A/CNK values ranging from 0.95 to 1.10. These samples have high rare earth element contents, FeOt/MgO （4.40-9.75） and 10 000X Ga/Al ratios （2.9-3,3）, as well as significant Sr, Ti and Eu negative anomalies. Based on these geochemical data, it is proposed that the Wengong granites originated from mafic lower crust in response to the earliest Jurassic extensional setting. In combination with available data, it is inferred that the A-type granites in the Nanling range predominantly formed at 196- 156 Ma, suggesting an early Yanshanian extensional event in SE China. These A-type granites probably formed in intra-plated extensional environment, indicating the transformation from Paleotethyan to Paleopacific domain after earliest Jurassic.

关 键 词：温公A型花岗岩 南岭构造带 锆石U-PB年代学 SR-ND-HF同位素 岩石学 

分 类 号：P548[天文地球—构造地质学]