藏北羌塘比隆错一带新生代火山岩的成因:壳幔过渡带局部熔融的地球化学证据  

Cenozoic volcanic rocks in the Bêlog Co area, Qiangtang, northern Tibet, China: Petrochemical evidence for partial melting of the mantle-crust transition zone.

作　　者：赖绍聪[1] 秦江锋[1] 李永飞[1] 刘鑫[1] 

机构地区：[1]西北大学大陆动力学教育部重点实验室西北大学地质学系,陕西西安710069

出　　处：《地质通报》2006年第1期64-69,共6页Geological Bulletin of China

基　　金：国家自然科学基金项目(批准号:40572050);高等学校优秀青年教师教学科研奖励计划资助。

摘　　要：羌塘比隆错新近纪火山岩主要岩石类型为安粗岩—粗面岩,为一套中基性—中性的碱性系列岩石组合,SiO2含量介于52%～62%之间,Al2O3>15%,Na2O/K2O>1,MgO<3.30%。岩石轻稀土元素较强富集,LREE/HREE=10～13,(La/Yb)N=15～19,弱负Eu异常,δEu=0.71～0.89。Mg#与SiO2的相关关系和La/Sm-La、Cr-Tb等亲岩浆元素与超亲岩浆元素协变关系表明,该套岩石为共源岩浆分离结晶的产物。岩石组合类型和低的Sm/Yb值(3.23～3.97)表明,它们应来源于岩石圈地幔尖晶石二辉橄榄岩的局部熔融;弱的负Eu异常和Nb、Ta、Ti的相对亏损,又反映了陆源岩浆的特征,可见,比隆错新近纪碱性火山岩应为青藏高原特殊的壳幔过渡带局部熔融的产物。Neogene volcanic rocks in the Belog Co area, Qiangtang, northern Tibet, are represented by a typical intermediatebasic and intermediate alkaline rock association and the main rock type is latite-trachyte, Their chemical composition is characterized by SIO2=52-62%, Al2O3〉15%, Na2O/K2O〉1 and MgO 〈3.30%. In addition, the volcanic rocks are LREE-enriched with LREE/HREE=10-13 and （La/Yb）N=15-19 and show a weak negative Eu anomaly with δEu=0.71-0.89. The close relationship between Mg# and SiO2 and co-variation of the magmatophile elements and ultra-magmatophile elements such as La/Sm-La and Cr-Tb indicate that this association of volcanic rocks is the product of comagmatic fractional crystallization. The rock association type and lower Sm/Yb values （Sm/Yb=3.23-3.97） imply that this association of volcanic rocks should originate from partial melting of spinel lherzolite in the lithospheric mantle. On the other hand, the weak negative Eu anomaly and relative depletion in Nb, . Ta and Ti reflect the features of terrigenous magma. So the Neogene Belog Co alkaline volcanic rocks should be the production of partial melting of the special crust-mantle transition zone on the Qinghai-Tibet Plateau.

关 键 词：常量和微量元素 新生代火山岩 壳幔过渡带 青藏高原 

分 类 号：P534.6[天文地球—古生物学与地层学] P588.14[天文地球—地质学]