滇西地区富碱斑岩中地幔流体作用踪迹及其成矿作用意义  

Actual traces of mantle fluid from alkali-rich porphyries in western Yunnan,and associated implications to metallogenesis

作　　者：刘显凡[1,2] 蔡永文[1] 卢秋霞[1] 陶专[1] 赵甫峰[1] 蔡飞跃[1] 李春辉[1] 宋祥峰[1] 

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]中国地质大学(武汉)地质过程与矿产资源国家重点实验室,湖北武汉430074

出　　处：《地学前缘》2010年第1期114-136,共23页Earth Science Frontiers

基　　金：国家自然科学基金项目(40773031;40473027);中国地质大学(武汉)地质过程与矿产资源国家重点实验室开放基金项目(GPMR2007;GPMR0509);成都理工大学矿物学;岩石学;矿床学国家重点(培育)学科建设项目(SZD0407)

摘　　要：滇西地区大量产出的富碱斑岩及其包体岩石的形成和演化与该区新生代陆内变形、构造作用、幔源岩浆和深源流体活动,及其与此有关而广泛发育的内生多金属矿产存在必然的联系。本文通过岩相学、岩石化学、电子探针、扫描电镜和能谱分析,较为系统地分析论证了这一关联的内在统一制约和联系的纽带即深部地质过程和由此相伴的含矿地幔流体作用,初步揭示了这种深部过程和地幔流体作用的微观踪迹和方式可以直接表现为:(1)呈脉状和浸染状穿插于深源包体岩石中的富钠玻璃,透光镜下呈微晶和雏晶,颜色随成分差异而不均匀,化学成分以高硅、铝、钠、铁,低钾、钙、镁为特征,矿物成分以钠长石、角闪石、磁铁矿(镜铁矿)、钛铁矿组合为特征,是富碱岩浆携带包体岩石之前即已存在的上地幔流体;(2)呈脉状、团块状和浸染状穿插于主岩和各类包体岩石的富铁玻璃;(3)呈独立包体产出于霓辉正长斑岩中的富铁熔浆包体。后两者物质在透光镜下无光性,呈黑色不透明,反光镜下不反光,但在电子显微镜下呈显微晶质结构,化学成分以高硅、铝、铁,低钙、镁、钠、钾为特征,矿物组成上以硅酸盐和石英为主,含有碳硅石、含铬自然铁、钛铁矿、磷灰石等地幔标志矿物,其中微晶金属和非金属矿物之间呈熔离结构交生,反映了地幔流体的熔浆性质及其与富碱岩浆不混溶的特征;由地幔流体对岩石的交代浸染作用,引起主岩和包体岩石中普遍发育各种蚀变作用,如角闪石化、硅化和绿泥石化等,并导致矿物组合总体上表现为暗色矿物由辉石→角闪石→黑云母→绿泥石的退变序列。该地幔流体微观踪迹的三种表现形式与富碱岩浆共存,并共同运移,但两者由于组成和性质的差异而互不混溶;结合透岩浆流体成矿作用理论和本文论证的综合分析认为,当富碱岩浆和地幔�The formation and evolution of plentiful alkali-rich porphyries with deep-xenoliths have an inevitable connection to the Cenozoic continental deformations,tectonisms,mantle magmas,anatectic fluids,and associated abundant polymetallic deposits. By the petrographical and petrochemical studies and the analyses using electron microprobe,scanning electron microscopy and energy spectroscopy,we confirmed that the connection was brought about by the deep geological processes and the action of ore-bearing mantle fluids. Microscopic traces and existing modalities of the processes and the action can be directly manifested as the following：（1）Na-rich glasses,which show as microlites and embryonic crystals under optical microscope,interpenetrated among deep-xenoliths in a veined or disseminated manner. The colour of the glass changes with its composition and it is not uniform. The chemical composition of the glass is characterized by high Si,Al,Na and Fe,and low K,Ca,and Mg; the mineral composition is characterized by the assemblage of albite,amphibole,magnetite （specularite） and ilmenite. The microlite glass was formed from the upper mantle fluid before the xenoliths having been caught by the alkali-rich magma.（2）Fe-rich glasses interpenetrated in a veined,agglomerated or disseminated manner among the host rocks and various xenoliths.（3）Black microcrystalline iron-rich melt xenoliths as independent xenoliths existed in aegerine syenite porphyry. Both the above （2） and （3） entities are of submicroscopic crystalline texture under electron microscope,but almost no any demonstration of optical properties under transmitted or reflected light,only appeared as black opaque materials under optical microscope. Their chemical compositions are characterized as high Si,Al and Fe,and low Ca,Mg,Na and K. Their main mineral compositions are silicate and quartz,as well as moissanite,native iron with chromium,specularite with titanium,ilmenite,apatite etc. The unmixing texture,which is assumed to be caused by the un

关 键 词：富碱斑岩 富铁熔浆包体 富钠与富铁玻璃 地幔流体与岩浆不混溶作用 流体交代蚀变成矿 滇西地区 

分 类 号：P588.12[天文地球—岩石学] P611[天文地球—地质学]