湖南道县虎子岩碱性玄武岩及其基性捕虏体成因和地质意义  

Petrogenesis and implications for alkali olivine basalts and its basic xenoliths from Huziyan in Dao County,Hunan Province

作　　者：杨金豹[1] 赵志丹[1] 莫宣学[1] 盛丹[2] 丁聪[1] 王丽丽[1] 侯青叶[1] 李红进 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,地球科学与资源学院,北京100083 [2]湖南省国土资源规划院,长沙410007 [3]延长石油集团研究院,西安710077

出　　处：《岩石学报》2015年第5期1421-1432,共12页Acta Petrologica Sinica

基　　金：深部探测技术与实验研究专项课题(Sinoprobe-04-02);科技部国际合作基金(2011DFA22460);111计划(B07011)联合资助

摘　　要：本文在湖南道县虎子岩地区采集了碱性玄武岩、橄榄辉长岩和基性麻粒岩捕虏体。碱性玄武岩的斑晶为橄榄石（10%～15%）,岩石K2O含量为2.88%～3.51%,Mg#值为80,具有洋岛玄武岩的微量元素特征,岩石具有富集的氧同位素组成（7.8‰～11.0‰）,可能是其上升到地表后由碳酸盐岩组分的加入及后期风化蚀变作用造成的,其相对均一且为负的εNd（t）值和靠近EMⅡ地幔端员的特点,指示了该玄武岩是拉张构造环境下富集地幔部分熔融的产物。橄榄辉长岩具有弱富集的LREE（La/Yb）N=2.5～3.0）、弱的Eu正异常（δEu=1.03～1.06）,其Sr-Nd同位素组成更靠近EMⅡ地幔端员,87Sr/86Sr比值、εNd（t）值及Nd模式年龄均高于碱性玄武岩,说明橄榄辉长岩是先形成的上述玄武岩浆在未到达地表之前局部发生结晶作用后形成的。基性麻粒岩捕虏体具较强的正Eu异常（δEu=1.42～4.41）,其重稀土元素含量出现明显的分组特征,强烈亏损U、Th和Nb、Ta、Zr、Hf、Ti等高场强元素,同时Sr-Nd同位素组成显示其具有壳幔混合的特征。本文结合已有研究结果,探讨了岩浆起源和演化,以及与古太平洋板片俯冲有关的构造环境转换。We collected alkali basalts,gabbro xenoliths and basic granulite xenoliths from Huziyan,Hunan Province. The alkali basalts contain 10% ～ 15% phenocrysts of olivine,with high K2O content（ 2. 88% ～ 3. 51%） and high Mg#values and OIB-like REE compositions（（ La / Yb）N= 16 ～ 26）. They have relatively homogeneous and negative εNd（ t） values,and the tendency toward to EMⅡ end member,which indicate that it is derived from an enriched mantle partial melting under the extensional tectonic setting. Their high O isotopic values（ 7. 8‰ ～ 11. 0‰） maybe resulted from the contamination of carbonate rock after the ascent of magma or due to posterior weathering alteration. The olivine gabbro xenoliths slightly enriched LREE（（ La / Yb）N= 2. 5 ～ 3. 0） have almost subtle Eu anomaly（ δEu = 1. 03 ～ 1. 06）,with Sr-Nd isotopic composition close to that of the EMⅡ end member. Their 87 Sr /86 Sr ratios,εNd（ t）values,and Nd model ages are lower than the above basalts,which suggest that the olivine gabbro is formed by the local crystallization of previous basaltic magma before reaching the surface. The basic granulite xenoliths have high Eu anomaly（ δEu = 1. 42 ～ 4. 41） and are grouped under HREE content,and strongly depleted in U,Th and HFSEs（ Nb,Ta,Zr,Hf and Ti）. Meanwhile,their Sr-Nd isotopic composition indicate that they are typified of crust-mantle mixing signature. The processes of magmatic origin and evolution are relevant to the tectonic setting transformation in the eastern of South China,which was controlled by the subduction of Paleo-Pacific slab.

关 键 词：碱性玄武岩 基性麻粒岩捕虏体 富集地幔 构造环境 华南 

分 类 号：P588.124[天文地球—岩石学] P588.145[天文地球—地质学]