攀枝花镁铁质层状岩体磷灰石中的熔融包裹体：岩浆不混熔的证据  

Liquid immiscibility in the Panzhihua mafic layered intrusion: Evidence from melt inclusions in apatite

作　　者：王坤[1,2] 邢长明[1,2] 任钟元[3] 王焰[1] 

机构地区：[1]中国科学院广州地球化学研究所、中国科学院矿物学与成矿学重点实验室,广州510640 [2]中国科学院大学,北京100049 [3]中国科学院广州地球化学研究所、同位素地球化学国家重点实验室,广州510640

出　　处：《岩石学报》2013年第10期3503-3518,共16页Acta Petrologica Sinica

基　　金：科技部973项目(2011CB808903);国家自然科学基金项目(41172064、41072063、41073030)联合资助

摘　　要：攀西（攀枝花-西昌）地区出露一系列赋含大型钒钛磁铁矿矿床的镁铁-超镁铁质层状岩体（例如：攀枝花、红格、白马和太和岩体），它们是～260Ma峨眉山大火成岩省的重要组成部分。显微岩相学研究显示，攀枝花岩体中部带浅色辉长岩磷灰石中存在深色和浅色两类熔融包裹体：深色熔融包裹体为深棕色或黑色，大小约10～60txm，外形呈圆形或磷灰石负晶形。主要由单斜辉石、角闪石、斜长石、磁铁矿等子矿物以及微粒结晶物质组成；浅色熔融包裹体为白色或淡绿色，大小约5～60Nm，外形呈圆形或磷灰石负晶形，由斜长石、角闪石、单斜辉石、少量磁铁矿和石英等子矿物以及微粒结晶物质组成。我们将熔融包裹体加热至1080～1200℃，浅色熔融包裹体完全均一，其平均成分为69．7％Si02、0．24％Ti02、14．5％A120”2．76％FeO、0．64％MgO、5．14％CaO、2．82％Na：O、2．26％K20和O．25％P205，为富Si相；深色熔融包裹体未完全均一，结合电子探针分析以及质量平衡估算，可得其平均成分为42．4％SiO2、1．43％TiO2、8．83％AL2O3、20．5％FeO、5．46％MgO、16．3％CaO、1．11％Na2O、0．30％K：O和1．41％P2O5，为富Fe相。这一结果说明，在攀枝花层状岩体形成过程中，岩浆房中可能同时存在富Fe和富si两种熔体，暗示演化的玄武质岩浆曾发生了不混熔作用。岩浆不混熔及重力分异共同作用导致了岩浆房硅酸盐熔体成分分层，下部的富Fe硅酸盐岩浆层演化形成了岩体下部巨厚的钒钛磁铁矿矿体和暗色辉长岩，上部的富si硅酸盐岩浆层演化形成了岩体上部的长英质岩脉、透镜体和浅色辉长岩。The Panzhihua, Hongge and Baima mafic-ultramafic layered intrusions in Panzhihua-Xichang region host large Fe-Ti-V oxide deposits and are parts of the ～ 260Ma Emeishan large igneous province. Two types of melt inclusions can be identified in apatite from the leucogabbro in the middle zone of Panzhihua intrusion in terms of color： dark and light ones. Dark melt inclusions are dark brown or black in color and range in sizes from 10um to 60um. They commordy behave as circular or negative crystal shapes. Daughter minerals within the dark inelusions include clinopyroxene, hornblende, plagioclase and magnetite. Light inclusions are white or slightly green and range in size from 51xm to 60um. Daughter minerals in the light inclusions include plagioclase, hornblende, elinopyroxene and minor magnetite and Quartz. After being heated to 1080 ～ 1200℃, light inclusions become homogenous glasses. The glasses are Sirich, with an average composition of 69.7% SiO2, 0. 24% TiO2, 14. 5% Al2O3 , 2. 76% FeO, 0. 64% MgO, 5.14% CaO, 2. 82% Na2O, 2. 26% K20 and 0. 25% P205. Dark inclusions are not homogenized after heating. Their averaged compositions that are estimated based on electron probe analysis and mass balance calculation are Fe-rich, with 42.4% SiO2 , 1.43% TiO2, 8. 83% A1203 , 20. 5% FeO, 5.46% MgO, 16. 3% CaO, 1.11% Na2O, 0. 30% K20 and 1.41% P2Os. Coexistence of Fe-rich and Si-rich melt in the apatite of the leucogabbro unit of the Panzhihua intrusion indicates that liquid immiscibility may have occurred in the evolved magmas. Layering of minerals may be contributed to the liquid immiscibility and gravitational differentiation. In this fashion, Fe-rich melts settled down to form the thick Fe-Ti-V oxide ore body and melagabbro in the lower part of the Panzhihua intrusion, whereas Sirich melts move upwards to form the felsic vein, lens and leucogabbro in the upper part.

关 键 词：攀枝花层状岩体 磷灰石 熔融包裹体 岩浆不混熔 钒钛磁铁矿床 

分 类 号：P611.11[天文地球—矿床学]