【摘要】 探讨了西藏甲玛中新世花岗斑岩的地球化学特征及意义。通过对岩体(脉)进行的野外地质调查、岩相学研究、全岩地球化学分析及同位素分析,结果表明甲玛花岗斑岩表现过铝质花岗岩的特征,整体表现为:Na2O/K2O<1,A/CNK>1.1,刚玉标准分子(w(C-norm))>1%;轻稀土元素富集,重稀土元素亏损,负Eu、Ce异常不明显,高Sr,低Y、Yb,但Sr/Y值相对较低,不具有埃达克岩的地球化学特征;此外,富集大离子亲石元素,尤其是Rb、Cs、Th、U、K等元素,而高场强元素,尤其是Sc、Ti则强烈亏损;Pb-Sr-Nd同位素均显示其下地壳的物质来源,并受到地幔物质(EMⅡ)的混染。甲玛过铝质花岗斑岩形成于亚洲-印度大陆"后碰撞"造山运动早期阶段的构造活动。更多还原

【Abstract】 This paper studies the geochemical characteristics and their implications of the Miocene granite porphyry in the Jiama deposit,Tibet.The results are obtained by means of field geological investigations,petrographic study,bulk rock analysis and isotopic analysis.These results indicate that the Jiama granite porphyry has the characteristics of peraluminous granite.Na2O/K2O is less than 1 and A/CNK is more than 1.1.Corundum standard molecule(w(C-norm)) is more than 1%.Light REE are rich,while heavy REE are scarce.Negative Eu and Ce are extremely inconspicuous.Sr is high,Y and Yb are low,and Sr/Y value is relatively low.It doesnot possess the geochemical characteristics of adakite rock.It is rich in LILE,especially Rb,Cs,Th,U and K,while its HFSE are scarce,especially Sc and Ti.The Pb-Sr-Nd isotopes reveal about the source of materials from the lower crust,which is mixed with the mantle materials(EMⅡ).It is concluded that the Jiama peraluminous granite porphyry is a product of tectonic movements in the early period of the "post-collision" orogenesis of Asia-India Continent.更多还原