摘要
华南中生代构造由早期的挤压转为晚期的拉张,确定这种构造转折时期对认识华南大地构造演化具有重要意义。花岗岩的多期次侵入往往是不同构造环境的产物,不同构造环境花岗岩表现出岩石地球化学组成上的差别。本文对湘东北望湘花岗岩体不同期次岩石地球化学研究后,认为257～165 Ma,151～144 Ma,135～128 Ma 3个侵入期的花岗质岩石分别在TiO_2,K/Rb,Rb/Sr,∑REE,δEu及微量元素组成上存在较大的差异,反映为不同的产出构造环境,分别代表印支期的挤压构造环境、燕山早期的剪切—走滑环境和燕山晚期的伸展—滑脱环境。J_3—K_1(140 Ma±)是挤压—剪切与伸展—拉张构造环境的转折期,前者表现为岩石圈增厚,后者表现为岩石圈减薄,湘东南大规模金属及铀矿的形成多与岩石圈减薄期花岗质小岩体有成因联系。
In Southeast China, the tectonic setting changed from the early compressional structure to the late exten-sional structure in the Mesozoic. The definition of this period of tectonic conversion is important in understanding the tectonic evolution in Southeast China. As the multi-phase intrusion was the product of different tectonic settings, the granites showed differences in lithochemical compositions. Accordingly, the Wangxiang granitic intrusion can be divided into three phases; 257~160 Ma, 155~140 Ma and 137~128 Ma. The granitic rocks of these phases show great differences in the contents of TiO2, P2O5, K/Rb, ∑REE, δEu and trace elements, reflecting different tectonic settings in which they were formed. For the Indo-Chinese intrusion, the contents of TiO2, P2O5, K/Rb and 2REE are high, the ratios of Rb/Sr are low, and the negative Eu anomalies are not remarkable (δEu = 0. 78~0. 83). The contents of major and trace element show a compression-nappe structure setting. The early Yanshanian intrusion has medium values of TiO2, P2O5, K/Rb,∑REE and δEu. The contents of the major and trace elements show a shear-slide setting. The late Yanshanian intrusion has low contents in TiO2, P2O5, K/Rb and ∑REE; negative Eu anomalies are obvious, δEu =0. 19~0. 40; and the ratios of (La/Yb)N are low (averaging 6. 8). The contents of major and elements show an extension decollement setting. J3-K1(~140 Ma) was the epoch of tectonic conversion from compression-shearing to extension-decolle-ment. The tectonic movement caused lithosphere thickening before -140 Ma and lithosphere thinning after ~ 140 Ma. The large-scale mineralization in southeastern Hunan has genetic relations with the small granitic intrusions in the extension-decollement tectonic setting.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2003年第1期98-103,共6页
Acta Geologica Sinica
基金
国家杰出青年基金(编号49925309)
中国科学院知识创新工程项目(编号KZCXZ-102)
中国科学院矿床地球化学开放研究实验室基金项目(2000)联合资助的成果
关键词
构造环境
岩石地球化学
花岗岩
中生代
微量元素
岩石圈
tectonic setting
epoch of tectonic conversion
lithogeochemistry
Wangxiang granitic intrusion
