地质通报
地質通報
지질통보
GEOLOGICAL BULLETIN OF CHINA
2014年
7期
1061-1066
,共6页
徐梦婧%李才%吴彦旺%解超明
徐夢婧%李纔%吳彥旺%解超明
서몽청%리재%오언왕%해초명
西藏%果芒错蛇绿混杂岩%硅质岩%地球化学%形成环境
西藏%果芒錯蛇綠混雜巖%硅質巖%地毬化學%形成環境
서장%과망착사록혼잡암%규질암%지구화학%형성배경
Tibet%Guomangco ophiolitic mélange%siliceous rocks%geochemistry%origin
果芒错蛇绿混杂岩位于狮泉河-永珠-嘉黎蛇绿混杂岩带中段,是该带中保存较好的一套蛇绿混杂岩,其形成环境是确定狮泉河-永珠-嘉黎蛇绿混杂岩带构造属性的重要依据。对果芒错蛇绿混杂岩中的硅质岩进行了地球化学分析,为判断蛇绿混杂岩的形成环境提供新的约束条件。硅质岩通常呈几十厘米夹层产于玄武岩中,含有大量晚三叠世-白垩纪放射虫化石。硅质岩SiO2含量为71.38%~77.67%,Al2O3含量为8.62%~11.51%,MnO/TiO2值为0.28~0.35,(Ce/Ce*)SN值为0.92~0.94,(La/Ce)SN值为1.13~1.17,反映了陆源物质的影响,而V、Ni、Cu和V/Y值高于大陆边缘硅质岩,与洋中脊和大洋盆地硅质岩相似,说明果芒错硅质岩可能形成于受陆源物质影响且与大陆边缘有一定距离的环境中。结合变质橄榄岩、镁铁质岩墙和玄武岩的地球化学特征,初步认为果芒错蛇绿混杂岩的形成环境为靠近大陆边缘的弧后盆地。
果芒錯蛇綠混雜巖位于獅泉河-永珠-嘉黎蛇綠混雜巖帶中段,是該帶中保存較好的一套蛇綠混雜巖,其形成環境是確定獅泉河-永珠-嘉黎蛇綠混雜巖帶構造屬性的重要依據。對果芒錯蛇綠混雜巖中的硅質巖進行瞭地毬化學分析,為判斷蛇綠混雜巖的形成環境提供新的約束條件。硅質巖通常呈幾十釐米夾層產于玄武巖中,含有大量晚三疊世-白堊紀放射蟲化石。硅質巖SiO2含量為71.38%~77.67%,Al2O3含量為8.62%~11.51%,MnO/TiO2值為0.28~0.35,(Ce/Ce*)SN值為0.92~0.94,(La/Ce)SN值為1.13~1.17,反映瞭陸源物質的影響,而V、Ni、Cu和V/Y值高于大陸邊緣硅質巖,與洋中脊和大洋盆地硅質巖相似,說明果芒錯硅質巖可能形成于受陸源物質影響且與大陸邊緣有一定距離的環境中。結閤變質橄欖巖、鎂鐵質巖牆和玄武巖的地毬化學特徵,初步認為果芒錯蛇綠混雜巖的形成環境為靠近大陸邊緣的弧後盆地。
과망착사록혼잡암위우사천하-영주-가려사록혼잡암대중단,시해대중보존교호적일투사록혼잡암,기형성배경시학정사천하-영주-가려사록혼잡암대구조속성적중요의거。대과망착사록혼잡암중적규질암진행료지구화학분석,위판단사록혼잡암적형성배경제공신적약속조건。규질암통상정궤십전미협층산우현무암중,함유대량만삼첩세-백성기방사충화석。규질암SiO2함량위71.38%~77.67%,Al2O3함량위8.62%~11.51%,MnO/TiO2치위0.28~0.35,(Ce/Ce*)SN치위0.92~0.94,(La/Ce)SN치위1.13~1.17,반영료륙원물질적영향,이V、Ni、Cu화V/Y치고우대륙변연규질암,여양중척화대양분지규질암상사,설명과망착규질암가능형성우수륙원물질영향차여대륙변연유일정거리적배경중。결합변질감람암、미철질암장화현무암적지구화학특정,초보인위과망착사록혼잡암적형성배경위고근대륙변연적호후분지。
The Guongmangco ophiolitic mélange is well developed in the middle part of Shiquanhe-Yongzhu-Jiali ophiolitic mélange belt, and its formational environment can provide important evidence for investigating the tectonics of the Shiquanhe-Yong-zhu-Jiali ophiolitic mélange belt. In this paper, the geochemistry of siliceous rocks was studied to judge the formational environment of the Guomangco ophiolitic mélange. Siliceous rocks occur as intercalated beds in basalt and have abundant Late Triassic-Early Cre-taceous radiolarite. The siliceous rocks have SiO2 content of 71.38%~77.67%, high Al2O3 content of 8.62%~11.51%, MnO/TiO2 ra-tios of 0.28~0.35, (Ce/Ce*)SN ratios of 0.92~0.94 and (La/Ce)SN ratios of 1.13~1.17, implying the influence of the input of terrigenous components. However, they have higher V, Ni and Cu content and V/Y ratios than the siliceous rocks in epicontinental settings, sim-ilar to things of siliceous rocks in ocean mid-ridge and basin. Guomangco siliceous rocks were probably formed in an ocean basin rel-atively far away from the continent and mainly affected by the input of terrigenous components. In combination with the geochemis-try of metamorphic peridotite, mafic dike and basalt, the authors hold that the Guomangco ophiolitic mélange was probably formed in a back-arc basin close to the continental margin.