云南宾川-永胜-丽江地区低钛玄武岩和苦橄岩的岩石成因与源区性质  

Petrogenesis and source characteristics of low-Ti basalts and picrites at Binchuan-Yongsheng-Lijiang region,Yunnan,China

作　　者：姜常义[1] 钱壮志[1] 姜寒冰[1] 唐冬梅[1] 张蓬勃[2] 朱士飞[3] 

机构地区：[1]长安大学地球科学与国土资源学院,西安710054 [2]西安石油大学,西安710065 [3]中国矿业大学,徐州221008

出　　处：《岩石学报》2007年第4期777-792,共16页Acta Petrologica Sinica

基　　金：国家自然科学基金重点项目40534020;云南省自然科学基金项目2003D0016Z联合资助的成果

摘　　要：云南宾川-永胜-丽江地区是峨眉山玄武岩厚度最大、喷发最早的地区,最主要的岩石类型是低钛和高钛玄武岩,并有少量摘要云南宾川—永胜—丽江地区是峨眉山玄武岩厚度最大、喷发最早的地区,最主要的岩石类型是低钛和高钛玄武岩,并有少量的苦橄质玄武岩、苦橄岩和麦美奇岩。大部分火山岩的岩石化学组成属于拉斑玄武岩系列,少数低钛玄武岩属碱性玄武岩系列。它们不同程度地富集大离子亲石元素和轻稀土元素,相对亏损重稀土元素,稀土元素分馏明显,显著亏损相容元素(Co,V,Cr,Ni)。陆壳物质对低钛玄武岩浆的混染程度明显大于对苦橄质岩浆的影响程度。而且混染作用对于Sr同位素和大离子亲石元素的影响程度明显大于对Nd同位素和稀土元素的影响程度。Nd和Sr同位素证明,混染物主要是下地壳变质岩,也有少量上部陆壳物质。未受混染的样品具有适度亏损的Nd、Sr同位素组成。低钛玄武岩和苦橄岩类岩石是不同原生岩浆分异演化的产物。低钛玄武岩的原生岩浆是高镁拉斑玄武岩浆,原生苦橄质岩浆以EM-55为代表(MgO= 16.56%)。此外,还有一种比EM-55更富镁的原生岩浆。高镁拉斑玄武岩浆分异过程中的主要分离结晶相/堆晶相是单斜辉石,并有少量斜长石。苦橄岩浆分异过程中的主要分离结晶相/堆晶相是橄榄石,并有少量单斜辉石。参考相关的实验岩石学成果,可以证明,地幔柱源区由两种岩石组成:一种是50%榴辉岩和50%橄榄岩反应形成的石榴石辉石岩,另一种是橄榄岩。在地幔柱绝热上升过程中,位于其轴部的石榴石辉石岩的熔融作用始于≈165km,主要的熔融作用发生于165～128km,持续到66km,熔融产物为苦橄岩浆。橄榄岩的部分熔融始于≈150km,持续到66km,熔融产物是比EM-55更富镁的岩浆。地幔柱头部的熔融作用始于≈100km,终止于66km,主要的熔融作用发生于�At Binchuan-Yongsheng-Lijiang region, NW Yunnan province, thickness of volcanic rock stratum are largest and volcanic lava began to earliest among the Emeishan flood basalts. Main rock types are low-Ti and high-Ti basalts, also have a small amount of picritic basalts, picrites and meimechites. The petrochemical compositions of most volcanic rocks belong to the tholeiitic series, but a little low-Ti basalts to the alkali-basalt series. They enrich in LILEs and LREEs at different degrees, and deplete HREEs, REEs fractionate evidently, compatible elements （Co, V, Cr, Ni） deplete significantly. Low-Ti basalt magma was contaminated by continent crust, at a larger extent than picritic magma. And influences of contamination on Sr isotope and LILEs are more evident than Nd isotope and REEs. Nd and Sr isotope prove that rocks that were assimilated by magma are mainly metamorphic rocks of lower continent crust, but also have minor rocks of upper continent crust. The samples were not contaminated show Nd and Sr isotopic compositions of moderately depleted mantle. The primary magma of low-Ti basalts is high-Mg tholeiitic magma, therefore primary picritic magma is represented by sample EM-55 （MgO = 16. 56% ）. In addition, a more Mg-enriched primary magma than EM-55 exist also. Clinopyroxenes are main fractional crystallization phases/ accumulation phases, plagioclases are minor in differentiation processes of high-Mg tholeiitic magma. However, olivines are main fractional crystallization phases/ accumulation phases of picritic magma. Refer to result of relatent experiment petrology, it can be proved that the mantle plume source exist two kind rocks, a kind rock is garnet pyroxenite, it was formed by reaction between 50% elogite - 50% peridotite; other rock is peridotite. When mantle plume shifted toward upper adiabatically, garnet pyroxenites in axis position of mantle plume began to melting at ≈165km, important melting occurred between 165 -128km, and continued to 66km, the product of melting was picritic magma. Bu

关 键 词：火山岩 岩石学 地球化学 岩石成因 源区性质 P-T条件 云南 

分 类 号：P588.145[天文地球—岩石学]