川西喜马拉雅期碰撞造山带岩浆碳酸岩的地幔源区特征——Pb-Sr-Nd同位素证据  

Mantle source characteristics of magmatic carbonatites from the Himalayan Collision Zone in western Sichuan,SW China:Evidence of Pb-Sr-Nd isotopes.

作　　者：田世洪[1] 侯增谦[2] 袁忠信[1] 谢玉玲[3] 费红彩[1] 尹淑苹[3] 衣龙升[3] 杨志明[4] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]国土资源部同位素地质开放重点实验室,北京100037 [3]北京科技大学土木与环境工程学院,北京100083 [4]中国地质科学院地质研究所,北京100037

出　　处：《岩石学报》2006年第3期669-677,共9页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(编号:2002CG412610);国家杰出青年基金(编号:40425014);中国地质科学院重点开放实验室专项资金(编号:KL05-9);中国地质大学(北京)地质过程与矿产资源国家重点实验室资金(编号:GPMR0548)联合资助。

摘　　要：对形成于大陆碰撞带内的川西碳酸岩进行了详细的Pb-Sr-Nd同位素分析。结果表明,川西碳酸岩具有非常负的ε_(Nd)值(-3．2～-18．7)和高的(^(87)Sr/^(86)Sr)_i值(0．706020～0．707923),以及较宽的^(207)Pb/^(204)Pb值(15．362～15．679)和^(208)Pb/^(204)Pb值(38．083～39．202)的特征,明显不同于世界上由非造山作用形成的碳酸岩。它们的Sr-Nd、Pb-Pb、Sr-Pb和Nd-Pb同位素特征表明大多数碳酸岩来源于EMⅠ与EMⅡ之间的一种混合地幔,与元古宙不同质量比的深海/陆源沉积物和下覆的似MORB由俯冲作用引起的洋壳的再循环有关,而少数碳酸岩则受到地壳物质混染的结果。此外,通过动力学背景分析可以得出,富集地幔EMⅠ与EMⅡ之间的熔融产生了川西碳酸岩以及同时代的富钾岩浆岩,这种熔融可能是由于印度大陆板片与扬子大陆板片俯冲引起的新生代软流圈物质的上涌产生的,并发生于青藏高原东缘始新世—渐新世分界线的从转换压扭变形向转换张扭变形的转变过渡的构造背景下。Pb-Sr-Nd isotopes of the Cenozoic carbonatites （WSC） in western Sichuan , east Tibet, China, are presented in this paper. The WSC develop in the eastern Indo-Asian collision zone. The results show that the WSC have extremely low εNd （t） of -3.2 - -18.7 and relative high （^87Sr/^86Sr）; of 0. 706020 - 0, 707923, as well as a wide range of ^207pb/^204Pb （15. 362 - 15. 679） and ^208Pb/^204pb ratios （38. 083 - 39. 202）, distinguished from most carbonatites around the world, generated by anorogenie processes. Their Sr-Nd, Pb-Pb, Sr-Pb and Nd-Pb isotopic signatures indicate that most carbonatites were derived from a transitional source between EMI and EMIl components, related to recycling of the pelagic/terrigenous sediments with various mass ratios and underlying MORB-like oceanic crust by subduction process in Proterozoic times, whereas some carbonatites underwent Sr-Nd-Pb contamination by crustal materials, Melting of an enriched EMI-EMII mantle source for generating the WSC with coeval potassium-rich magmas was most likely triggered by a Cenozoic asthenospheric mantle diapir formed by subduction of the Indian and Yangtze continental slabs, and took place in the tectonic regime of the transition from transpression to transtension at Eocene/Oligocene boundary in the eastern Indo-Asian collision zone.

关 键 词：岩浆碳酸岩 喜马拉雅期碰撞造山带 Pb—Sr—Nd同位素 地幔源区特征 动力学背景 四川西部 

分 类 号：P588.15[天文地球—岩石学] P597.3[天文地球—地质学]