北部湾涠洲岛橄榄岩中熔体包裹体——大陆岩石圈地幔交代作用的新证据  

Melt inclusions of peridotites in Weizhou Island,Northern Bay:New evidence of mantle metasomatism in subcontinentle lithospheric mantle.

作　　者：樊祺诚[1] 隋建立[1] 孙谦[1] 李霓[1] 赵勇伟[1] 杜星星[1] 

机构地区：[1]中国地震局地质研究所,北京100029

出　　处：《岩石学报》2008年第11期2495-2500,共6页Acta Petrologica Sinica

基　　金：国家自然科学基金(40572044;40772038)

摘　　要：根据北部湾涠洲岛晚更新世火山岩中尖晶石二辉橄榄岩的矿物化学和形成条件推测,它们是来自地下约40km～50 km 的大陆岩石圈地幔样品。涠洲岛地幔橄榄岩中同时出现高硅(64%～68%)和低硅(49%～57%)两种熔体成分,它们普遍富碱、Al_2O_3和 H_2O、CO_2等挥发组分(2%～5%)。研究认为,两种熔体存在不同的成因机制。高硅熔体可能与软流圈上升的玄武质岩浆和斜方辉石反应或下地壳物质循环进入地幔后的部分熔融有关。低硅熔体直接提供了富硅熔体与橄榄石发生交代作用的证据。这可以用富 SiO_2熔体+Ol→贫 SiO_2熔体+Opx 反应解释,其结果是消耗橄榄石生成斜方辉石。涠洲岛橄榄岩中两种熔体的发现,进一步提供了发生在大陆岩石圈地幔流(熔)体与橄榄岩交代作用的普遍性、复杂性,以及地幔熔体多样性的新证据。Peridotite xeonliths and enclosed melt inclusions （MIs） record information of geodynamic evolution of subcontinental lithospheric mantle. Small xenoliths, mainly spinel lherzolites in size of several um, were discovered in the late Pleistocene basalts in Weizhou Island, Northern Bay. Mineral geochemistry indicates that the xenoliths are segments of the lithospheric mantle from 40km - 50 km depth. Two types of MIs, high-silicon MIs （64% - 68% ） and low-silicon（49% - 57% ） MIs, occur in the peridotites, and both types of the MIs are eventually rich in SiO2, Al2O3 , H2O, CO2 and other volatile （2% -5% ）. Our research indicates that the origins of the MIs are different. High-silicon MIs are derived from the reaction of basaltic magma from upwelling asthenosphere with orthopyroxene, or partial melting of recycled lower crust into the upper mantle. Low-silicon MIs are derived from metasomatism, and the reaction can be described as, high-silicon melts ＋ Olivine→Opx ＋ low-silicon melts. This reaction consumes SiO2 and olivine, produces orthopyroxene. The facts provide evidences of the occurrence and diversity of metasomatism reactions between fluid （melt） and peridotite in the subcontinental lithosphere, and also provide a new case of diversity of melt inclusions.

关 键 词：熔体包裹体 橄榄岩捕虏体 地幔交代作用 大陆岩石圈地幔 北部湾涠洲岛 

分 类 号：P588.125[天文地球—岩石学]