岩石学报
巖石學報
암석학보
ACTA PETROLOGICA SINICA
2009年
9期
2271-2280
,共10页
西南天山%独居石%低压麻粒岩%双变质带%等时线年龄%古南天山洋
西南天山%獨居石%低壓痳粒巖%雙變質帶%等時線年齡%古南天山洋
서남천산%독거석%저압마립암%쌍변질대%등시선년령%고남천산양
Southwest Tianshan%Monazite%Low-P pelitic granulite%Paired metamorphic zone%Isochron age%South Tianshan Paleo-Ocean
古南天山洋闭合过程中,由于洋壳俯冲产生的岛弧岩浆作用加热大陆地壳,在新疆西南天山木扎尔特一带形成了一套低压高温泥质麻粒岩相变质岩石.本文用Theriak-Domino热力学软件对该套岩石中的堇青石榴夕线石黑云母片麻岩和含夕线石堇青石榴黑云母片麻岩进行了岩石学相平衡计算研究,得到它们峰期变质的温压条件分别是：T=630～674℃,P=5.2～5.5kbar和T=645～684℃,P=5.4～5.7kbar.并采用独居石Th-U-Pb电子探针定年方法,对样品WQ006中的3颗独居石进行了原位年龄测定(38个分析点),得到2组等时线年龄,分别是376±8Ma和280σ8Ma(2σ).结合独居石的岩相学特征,提出了新疆西南天山低压高温麻粒岩相峰期变质作用的时代为280±8Ma,而376±8Ma(2σ)可能为原沉积岩的原岩/成岩年龄.表明西南天山洋壳开始俯冲发生在晚古生代,进一步证明了西南天山造山带俯冲碰撞发生在晚二叠纪之后的观点.
古南天山洋閉閤過程中,由于洋殼俯遲產生的島弧巖漿作用加熱大陸地殼,在新疆西南天山木扎爾特一帶形成瞭一套低壓高溫泥質痳粒巖相變質巖石.本文用Theriak-Domino熱力學軟件對該套巖石中的堇青石榴夕線石黑雲母片痳巖和含夕線石堇青石榴黑雲母片痳巖進行瞭巖石學相平衡計算研究,得到它們峰期變質的溫壓條件分彆是：T=630～674℃,P=5.2～5.5kbar和T=645～684℃,P=5.4～5.7kbar.併採用獨居石Th-U-Pb電子探針定年方法,對樣品WQ006中的3顆獨居石進行瞭原位年齡測定(38箇分析點),得到2組等時線年齡,分彆是376±8Ma和280σ8Ma(2σ).結閤獨居石的巖相學特徵,提齣瞭新疆西南天山低壓高溫痳粒巖相峰期變質作用的時代為280±8Ma,而376±8Ma(2σ)可能為原沉積巖的原巖/成巖年齡.錶明西南天山洋殼開始俯遲髮生在晚古生代,進一步證明瞭西南天山造山帶俯遲踫撞髮生在晚二疊紀之後的觀點.
고남천산양폐합과정중,유우양각부충산생적도호암장작용가열대륙지각,재신강서남천산목찰이특일대형성료일투저압고온니질마립암상변질암석.본문용Theriak-Domino열역학연건대해투암석중적근청석류석선석흑운모편마암화함석선석근청석류흑운모편마암진행료암석학상평형계산연구,득도타문봉기변질적온압조건분별시：T=630～674℃,P=5.2～5.5kbar화T=645～684℃,P=5.4～5.7kbar.병채용독거석Th-U-Pb전자탐침정년방법,대양품WQ006중적3과독거석진행료원위년령측정(38개분석점),득도2조등시선년령,분별시376±8Ma화280σ8Ma(2σ).결합독거석적암상학특정,제출료신강서남천산저압고온마립암상봉기변질작용적시대위280±8Ma,이376±8Ma(2σ)가능위원침적암적원암/성암년령.표명서남천산양각개시부충발생재만고생대,진일보증명료서남천산조산대부충팽당발생재만이첩기지후적관점.
During the closure of the South Tianshan Paleo-Ocean, a suite of low-pressure pelitic granulite-facies Crd-Grt-Sil-Bt gneiss was formed by the intrusion of arc magma into the landward continental margin of Muzhaerte River in South Tianshan, Xinjiang. Using the thermodynamic software of Theriak-Domino, we performed the NCKFMASH phase equilibria calculation on the Crd-Grt-Sil-Bt gneiss (WQ003) and the sillimanite-bearing Crd-Grt-Bt gneiss (WQ006) , and gained that their peak metamorphic conditions are T = 630 ～674℃ ,P = 5. 2～5.5kbar and T = 645 ～684℃ ,P = 5. 4 ～5. 7kbar, respectively. Moreover, we carried out the geochronological research on three monazite grains in sample WQ006 with the technique of U-Th-Pb chemical monazite dating by electron microprobe and got two characteristic isochron ages, 376 ±8Ma and 280 ±8Ma (2σ). Based on the petrographic study of monazite, 280 ±8Ma can be explained as the age of peak granulite-facies metamorphism, whereas 376 ± 8Ma (2σ) maybe represent the age of detrital or diagenesis, and we conclude that the subduction of South Tianshan oceanic crust began in Late Paleozoic and confirm the opinion that the subduction-collision of Southwest Tianshan orogen occurred after Late-Permian.
