西准噶尔石炭纪洋中脊俯冲岩浆活动:以玛里雅蛇绿岩为例  

Magmatism of mid-oceanic ridge subduction during Carboniferous in western Junggar:Evidence from Maliya ophiolite

作　　者：张继恩[1,2] 肖文交[1] 韩春明[1] 郭谦谦[1,2] 毛启贵[3] 敖松坚[1,2] 

机构地区：[1]中国科学院地质与地球物理研究所岩石圈演化国家重点实验室,北京100029 [2]中国科学院研究生院,北京100049 [3]北京矿产地质研究院,北京100012

出　　处：《岩石学报》2010年第11期3272-3282,共11页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(2007CB411307);国家重点基础研究发展规划项目(2001CB409801)资助;国家杰出青年基金项目(40725009)

摘　　要：玛里雅蛇绿岩位于新疆准噶尔西缘达拉布特断裂东侧的弧前增生楔内,形成于石炭纪,出露岩石类型齐全,其中硅质岩与火山岩相间出露,多表现为非构造接触。地球化学特征表明,它们大致可以分为四个系列:(1)A系列为岛弧英安岩,Th强烈富集,可能有洋壳沉积物参与,高场强元素Nb亏损,与洋壳的俯冲有关;(2)M系列与典型洋中脊玄武岩的稀土元素配分模式一致,不过Ba强烈富集,可能受到俯冲流体的影响;(3)E系列位于地幔序列N-MORB和E-MORB之间,表明它可能是地幔岩浆的混合产物,未受到地幔岩浆源区之外物质的影响;(4)O系列与典型的洋岛玄武岩基本一致,只是Ta、La和Th含量略偏低,但都处于地幔序列范围内,可能与其他岩浆源有轻微的混合。这种岩浆特征与智利洋中脊俯冲环境下所产生的岩浆特征一致;由于西准噶尔晚古生代仍然发生俯冲消减,因此推测玛里雅蛇绿岩可能形成于洋中脊俯冲环境。Maliya ophiolite occurs in a fore-arc accretionary prism,southeast of Dalabute ophiolitic belt in western Junggar. The ages of basalt and fossil indicate that it was formed during Carboniferous. Volcano and chert,the main lithologies of this ophiolite,outcropping in lenses,with non-tectonic contact,indicate they are contemporaneous products. Geochemical characteristics show their magmatic sources are complex that can be subdivided into four series:(1) A-series is dacite,with highly enriched in Th,indicating involvements of oceanic sediments,and depleted in Nb,which means they may be formed under subduction setting; (2) The REE patterns of M-series are much similar with that of N-MORB,with except of Ba,which is highly enriched because of the influence of fluids released from subducted oceanic slab; (3) E-series,locating between the mantle array of N-MORB and E-MORB,indicates it may be the mixture of mantle magmas,with no influence of other magmas; (4) The characteristics of O-series consist with that of OIB. All are located in the line of mantle sequence,except Ta,La and Th,which are slightly lower than typical OIB value. This may indicate mild mixture of other magmatic sources. The magmatic characteristics of the Maliya ophiolite mentioned above are very similar to that of the rocks formed during mid-oceanic ridge subduction in Chile. Combined with subducting at Late Paleozoic in western Junggar,we suppose the Maliya ophiolite may be generated during mid-oceanic ridge subduction.

关 键 词：蛇绿岩 石炭纪 洋中脊俯冲 玛里雅 西准噶尔 

分 类 号：P588.14[天文地球—岩石学]