塔里木板块东北部柳园粗面玄武岩带:软流圈地幔减压熔融的产物  

Liuyuan trachybasalt belt in the northeastern Tarim Plate: Products of asthenosphere mantle decompressional melting.

作　　者：姜常义[1] 夏明哲[1] 余旭[1] 逯东霞[1] 魏巍[1] 叶书锋[1] 

机构地区：[1]长安大学地球科学与国土资源学院,西安710054

出　　处：《岩石学报》2007年第7期1765-1778,共14页Acta Petrologica Sinica

基　　金：国家自然科学基金重点项目40534020;国家重点基础研究发展规划项目2001CB409800联合资助的成果.

摘　　要：在塔里木东北部,甘肃省西部敦煌市柳园镇南侧,有一条近东西向展布的粗面玄武岩带,长度约150km,宽度达10km,厚度为1900m。这条粗面石玄武岩带属下二叠统哲斯群,岩浆喷发方式以裂隙式溢流为主,枕状构造特别发育。在玄武岩层间夹有很薄的酸性凝灰岩和沉凝灰岩层,属典型的双峰式火山岩组合。按照岩石化学组成的 TAS 分类命名,主要岩石类型为玄武岩、夏威夷岩和橄榄粗安岩。主要造岩矿物为钠长石(Ab 91～100)和普通辉石。普通辉石斑晶、钠长石斑晶和部分基质中的钠长石具有中空结构,并被层状硅酸盐微晶充填。这些岩石基本属碱性玄武岩系列和过渡型系列,大部分属演化的岩浆。演化程度较低的样品具有轻稀土元素亏损型配分曲线,微量元素地球化学具有 MORB 亲和性,ε_(Nd)(t)=+10.14～10.89。玄武质岩浆与陆壳物质之间有较轻的同化混染作用。普通辉石、铁钛氧化物的分离结晶作用是岩浆演化的主要机制。玄武质岩浆源区属于软流圈地幔,部分熔融发生于尖晶石稳定域,是软流圈地幔减压(上涌)熔融的产物。A Trachybasalt belt occurs at the northeastern part of Tarim plate, southern part of Liuyuan town in Dunhuang city, Western Gansu Province. It is 150km long, 10km wide and 1900m thick, trending in a nearly westeastem direction. This trachybasalt belt belongs to Zbesi group of Lower Permian series, the way of magma eruption is mainly effusion of fissure type, pillow structure develops well. Much thin acid tuff and sedimentary tuff layers are intercalated among basalt layers, which are typical bimodal volcanic rock assemblage. Basalt, hawaiite and mugearite are the main rock types based on pertrochemical diagram. The main rock-forming minerals are albite （Ab 91 - 100） and augite. The augite phenocryst, albite phenocryst and some albite in matrix have hollow texture, and it is filled by layered silicate microlite. These rocks belong to alkali basalt series and transitional type series. The samples at low degree comparatively have the LREE-depleted pattern, and the geochemistry character of trace elements shows affine with MORB, εNd（t） = ＋ 10. 14 - ＋ 10. 89. There is less assimilation-contamination between basaltic magma and continental crust matter. The augite and Fe-Ti oxides fractional crystallization is the main mechanism of the magma evolution. Basaltic magma source is situated in asthenosphere mantle, partial melting happens in the spinel stability field. It is the products of asthenosphere mantle decompressional （upwelling） melting.

关 键 词：粗面玄武岩带 早二叠世 岩石地球化学 岩浆源区 减压熔融 塔里木板块 

分 类 号：P588.125[天文地球—岩石学]