西准噶尔白杨河地区早二叠世闪长岩的年代学和地球化学:岩石成因和构造意义  

Age and geochemical characteristics of Early Permian diorite in the Baiyanghe region,West Junggar:Petrogenesis and tectonic implication

作　　者：尹继元[1,2] 陈文[1] 龙晓平 袁超[2] 张运迎[2] 王毓婧[2] 关义立[2] 

机构地区：[1]中国地质科学院地质研究所大陆构造与动力学国家重点实验室同位素热年代学实验室,北京100037 [2]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

出　　处：《地球化学》2013年第4期361-372,共12页Geochimica

基　　金：国家自然科学基金(41203026;41073031;41273012;41173005);中国地质科学院地质研究所基本科研业务费项目(J1209);国土资源部公益性行业专项经费(201211074-05);地质矿产调查评价专项(12120113015600)

摘　　要：西准噶尔白杨河地区的莫合台西北岩体是一个以闪长岩为主的小岩体。该闪长岩由斜长石(65%～70%)、角闪石(10%～15%)和辉石(10%～15%)组成,其全岩SiO2含量在55.1%～57.0%之间。该闪长岩富集大离子亲石元素(LILE)(如Ba、K、Rb和U)和轻稀土元素(LREE),相对亏损Nb、Ta、Ti等高强场元素,显示了与俯冲带相关的岩浆特征。这些闪长岩可能是由俯冲的板片流体/沉积物交代的地幔楔部分熔融而成。全岩Ar-Ar测年获得了(283±3)Ma的坪年龄,显示其形成于早二叠世,在321 Ma,西准噶尔地区开始洋脊俯冲活动,其至少持续到292 Ma;在283 Ma时,西准噶尔处于正常的俯冲体系或后碰撞环境。Ar-Ar dating on Mohetaixibei dioritic rock chips from Baiyanghe region, westem Junggar, has yielded a plateau age of （283±3） Ma, i.e., Early Permian. The diorite mainly contains plagioclase （65%-70%）, pyroxene （10%,15%） and hornblende （10%,15%）. The SiO2 contents vary between 55.1%,57.0% suggesting that they are diorite rather than gabbro or dolerite as marked in the geological map （1 ： 200000） of Baiyanghe, Xinjiang. The diorites are characterized by enrichments in large ion lithophile elements （LILE） （e.g., Ba, K, Rb and U） and light rare earth elements （LREE） and depletions in high field strength elements （HFSE） （e.g., Nb, Ta and Ti）, which are consistent with geochemical characteristics of subduction-related magmas. The diorites can be generated by partial melting of the mantle wedge metasomatized by slab released fluid/sediment melts. High temperature magmatism in the West Junggar likely began at 321 Ma. Therefore, ridge subduction in the western Junggar likely occurred between 321-292 Ma. At 283 Ma, the western Junggar was in a normal subduction system or post-collisional setting.

关 键 词：闪长岩 Ar—Ar年代学 早二叠世 地球化学 西准噶尔 

分 类 号：P59[天文地球—地球化学] P597[天文地球—地质学]