川西江浪穹窿二叠纪大理岩微量元素与碳、氧同位素组成:对古沉积环境的指示  

Trace element and C-O isotopic constraints on the ancient depositional environment of Permian marble in the Jianglang dome,western Sichuan Province

作　　者：代堰锫[1] 朱玉娣[2] 张惠华[1] 李同柱[1] 沈战武[1] DAI Yan-pei;ZHU Yu-di;ZHANG Hui-hua;LI Tong-zhu;SHEN Zhan-wu(Chengdu Center, China Geological Survey, Chengdu 610081, China;School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, China)

机构地区：[1]中国地质调查局成都地质调查中心,四川成都610081 [2]西南石油大学地球科学与技术学院,四川成都610500

出　　处：《地球化学》2017年第3期231-239,共9页Geochimica

基　　金：成都地质调查中心青年科学基金项目(所控基[2015]-05);西南石油大学青年教师"过学术关"项目(201499010083);科研启航计划项目(2015QHZ009);四川省教育厅科研项目(15ZB0058)

摘　　要：江浪穹窿位于松潘-甘孜造山带南缘,其二叠纪地层主要由一套大理岩组成。为精确恢复大理岩的原岩性质及古沉积环境,对微量元素(包括稀土元素)与C、O同位素进行了研究。元素地球化学分析表明,样品具有明显的Ce负异常(δCe 0.60~0.32)以及La(δLa 1.90~1.45)、Eu(δEu 1.67~1.02)、Gd(δGd 2.52~1.35)和Y(δY 1.98~1.38)正异常,Y/Ho值为54.1~38.9,Sr/Ba值介于81.7~23.0之间,V/Cr值为1.20~0.50。同位素测试结果显示,大理岩δ^(13)CV-PDB值为+4.0‰^-0.1‰,δ^(18)OV-SMOW值介于16.3‰~13.6‰之间,计算获得的δ^(18)OV-PDB值为-14.2‰^-16.8‰。综合分析,认为江浪穹窿二叠纪大理岩的原岩为海相碳酸盐岩,其原始O同位素组成受后期成岩作用影响而显著降低;岩石沉积于富含氧气的古海水,并且沉积过程中有少量(<5%)海底高温热液的摄入。结合该套地层还发育顺层变玄武岩和超基性岩的事实,认为松潘-甘孜造山带南缘的二叠纪变质岩石组合可能是古特提斯洋的洋壳残余。The Jianglang dome is located on the southern margin of the Songpan-Garze orogenic belt,and its Permian strata are dominated by a set of marbles.Trace element(including rare-earth elements)and carbon-oxygen isotopes were analyzed to explore the protolith and ancient depositional environment of the marble.Elemental geochemical analyses show apparent negative Ce anomaly(δCe0.60?0.32)and positive La(δLa1.90?1.45),Eu(δEu1.67?1.02),Gd(δGd2.52?1.35),Y(δY1.98?1.38)anomalies,with Y/Ho ratios of54.1to38.9,Sr/Ba ratios of81.7to23.0,and V/Cr ratios of1.20to0.50.Isotopic analyses indicate thatδ13CV-PDB values range from4.0‰to?0.1‰,δ18OV-SMOW values from16.3‰to13.6‰and the calculatedδ18OV-PDB values from?14.2‰to?16.8‰.It is argued that the protolith of the Permian marble in the Jianglang dome was marine carbonate rock,which was deposited from an oxygen-rich paleo-seawater environment.Its primary oxygen isotopic composition was declined by later diagenetic processes.During their precipitation process,a small amount of submarine high-temperature hydrothermal solution(<5%)was added.Considering the occurrences of interbedded metabasalt and ultrabasic rocks,we further proposed that the Permian metamorphic rock assembles were most likely a remnant of the Paleo-Tethys oceanic crust.

关 键 词：二叠纪 大理岩 微量元素 碳同位素 氧同位素 古沉积环境 松潘-甘孜造山带 

分 类 号：P597[天文地球—地球化学]