新疆阿尔泰东部新生代玄武岩的地球化学特征与地质意义  

Geochemical characteristics and geologic implications of Cenozoic basalts, east Altai, Xinjiang.

作　　者：张元元[1] 郭召杰[1] 刘畅[1] 许文骞[1] 

机构地区：[1]北京大学地球与空间科学学院造山带和地壳演化教育部重点实验室,北京100871

出　　处：《岩石学报》2007年第7期1730-1738,共9页Acta Petrologica Sinica

基　　金：国家重点基础研究规划项目课题(2007CB411305和2001CB409804);国家自然科学基金项目(40572123)的资助。

摘　　要：新疆阿尔泰东部哈拉乔拉出露有新生代玄武岩,K-Ar 法测得玄武岩的年龄在10～20Ma,地球化学分析结果表明哈拉乔拉玄武岩具有高 TiO_2含量、高钾富碱的特点,属于典型的橄榄玄粗岩系列;强烈富集不相容元素和轻稀土元素,显示出源区富集的特点。(^(87)Sr/^(86)Sr)_i 为0.704432～0.704538,(^(143)Nd/^(144)Nd)_i 为0.512641～0.512779,ε_(Nd)(t)为0.29～1.03,其 Sr-Nd 同位素特征和地球化学特征都与洋岛玄武岩(OIB)相似。La/Nb(0.765～0.823)、Nb/U(35.02～52.01)等不相容元素的比值指示了源区中可能存在少量循环地壳物质。综合对比南天山托云等地区新生代玄武岩,中亚地区的地球化学性质相似的新生代火山岩分布零星,空间上与大型断裂相对应,不应是前人地幔柱成因的观点。本文结合中亚地区古生代地壳的演化特点,提出中亚地区的新生代类 OIB 型玄武岩来源于中亚地区已被改造的富集地幔。The K-Ar dating indicates that Cenozoic Basalts in Halaqiaola area,eastern Altai in north Xinjiang, were emplaced at 10 20Ma. And the Basalts are belonging to shoshonite, which have high concentration of TiO2, high K and alkali, and characterized by enrichment in light rare earth elements and compatible elements, indicating an enriched mantle source. Their geochemical characters and Sr-Nd isotopic composition are similar to those of oceanic island basalts （OIB）, which has the isotopic results of （^87 Sr/^86Sr）i = 0.704432 - 0.704538, （ ^143 Nd/^144 Nd）j = 0. 512641 - 0.512779, εNd （t） = 0.29 - 1.03. The ratios of La/Nb （0. 765 - 0. 823 ） and Nb/U （35.02 -52.01 ） shows that some recycled crust material might be interfused into the enriched source. Analyzing integrally with the Cenozoic basalts in the adjacent areas such as Tuoyun basin, we find that the Cenozoic volcanic rocks in central Asia are scatteredly distributed and developed along the major strike slip faults, which cannot be the results of typical plumes. So this article, combining with the crust evolution in Central Asia, points out that the Cenozoic basalts similar to OIB were originated from the modified enriched mantle which were derived from subducted oceanic crusts during Late Paleozoic.

关 键 词：阿尔泰 新生代玄武岩 地球化学 构造背景 富集地幔 

分 类 号：P588.145[天文地球—岩石学]