川西同德和沙坝麻粒岩及其退变质岩石之间的元素迁移  

Migration of Elements between Granulites and Their Retrograded Metamorphic Rocks in Tongde and Shaba Area, Western Sichuan Province

作　　者：于航波[1] 徐士进[1] 王汝成[1] 孙海婷[1] 刘文中[1] 方中[1] 

机构地区：[1]南京大学内生金属成矿作用国家重点实验室,地球科学系南京210093

出　　处：《高校地质学报》2004年第4期634-648,共15页Geological Journal of China Universities

基　　金：国家自然科学基金资助项目 (4 9972 0 6 2 ) ;教育部科技项目 (10 4 0 89)

摘　　要：利用川西麻粒岩的全岩化学组成与岩石中特征矿物的化学性质 ,研究了麻粒岩退变质作用的元素迁移。对紫苏辉石、普通辉石和普通角闪石的电子探针分析表明 ,随着麻粒岩退变质作用程度的加深 ,矿物的化学组成与全岩的元素迁移同步变化。由于矿物组合和岩相的转变以及地壳流体的作用 ,同德二辉麻粒岩在退变质至黑云角闪斜长片麻岩过程中 ,K ,Rb ,Cs,K/Na ,Fe3+ 和Fe3+ /Fe2 + 增加 ,Fe2 + ,V ,Co ,Ba ,Sr和Pb降低 ;在沙坝二辉麻粒岩退变质为含绿帘石角闪斜长片麻岩过程中 ,Na ,Ca ,Fe3+ ,Zr,Hf,Nb ,Ta ,Rb ,U ,Th ,REE和Fe3+ /Fe2 + 增加 ,Fe2 + ,Mg ,K ,Co ,Zn ,Cs ,Pb和K/Na降低。麻粒岩退变质过程中制约不同元素迁移的主要矿物相是普通角闪石等退变质新生矿物。同德和沙坝两个麻粒岩块退变质作用中 ,个别元素迁移性状并不相同 ,这可能与原岩的性质和变质流体的成分等环境地质条件有关。A geochemical study of elemental migration from granulite-facies rocks to amphibolite-facies rocks during retrograde metamorphism has been carried out through the analyses both of petrochemical data for whole rocks and electronic microprobe data for essential minerals (e.g. hypersthene, augite and hornblende) in the rocks. The removal variations of compositions for major elements in the whole rocks and their essential minerals are similar, which suggests that such changes were most likely controlled by the transformation of main mineralogical phases and the fluid/rock interaction during the retrograde metamorphism. Abundances of K, Rb, Cs, Fe^(3+), Ti, LREE of whole rocks are gradually increased from Tongde granulites to biotite-hornblende plagiogneisses,while abundances of Li, Ca, Mg, Fe^(2+), V, Co, Pb, P and HREE decreased. In addition, the elements such as Na, Be, Rb, Y, Nb, Ta, Th, U, Cr, Ni, REE are increased from Shaba granulites to epidote-hornblende plagiogneisses, while Li, K, Ti, Fe, Mn, Mg, V, Co, Zn, Pb decreased. Many lithophile elements and LREE are enriched and some transitional elements are depleted in the highly retrograded rocks from granulites, therefore the authors suppose that the metamorphic fluids in the retrograde metamorphic process could be derived from upper-crust reservoirs. Due to the fluid/rock interaction many chemical elements in granulites including REE were activated and migrated in the prolonged duration of retrograde metamorphism.

关 键 词：麻粒岩 退变质作用 元素迁移 四川省西部 

分 类 号：P588.3[天文地球—岩石学] P595[天文地球—地质学]