上扬子会泽地区早三叠世飞仙关组砂岩物源特征：来自重矿物铬尖晶石和碎屑锆石的限定  

Chromian Spinel,Zircon Age Constraints on the Provenance of Early Triassic Feixianguan Formation Sandstones from Huize Area,Upper Yangtze Region

作　　者：张英利[1] 王宗起[1] 王刚[1] 李谦[2] 林健飞[3] 

机构地区：[1]中国地质科学院矿产资源研究所,国土资源部成矿作用与矿产资源评价重点实验室,北京100037 [2]中国石油勘探开发研究院,北京100083 [3]中国地质大学(北京),北京100083

出　　处：《地质论评》2016年第1期54-72,共19页Geological Review

基　　金：国家自然基金(编号:41302080);中国地质调查局地质调查项目(编号:12120114009401)资助成果~~

摘　　要：上扬子会泽地区早三叠世飞仙关组主要为河流相的紫红色砂岩,物源主要来自于西部和西北部。碎屑重矿物组合表明物源主要来自于岩浆岩,且重矿物中发现大量碎屑铬尖晶石和锆石。本文运用电子探针微区成分分析和碎屑锆石U-Pb测年方法,对上扬子早三叠世飞仙关组砂岩中铬尖晶石和碎屑锆石进行分析。铬尖晶石电子探针化学成分分析显示,其具有高铬、低Fe^(3+)和高TiO_2含量的特征,源岩分析指示这些铬尖晶石来源于与洋岛/板内、岛弧以及大火成岩省相关的火成岩。同时,碎屑锆石LA-ICP-MS U-Pb年龄测定表明,飞仙关组的物源主要来自于248~272Ma和715~997Ma的岩浆岩。铬尖晶石和碎屑锆石综合分析表明,248~272Ma的物源岩石具有大火成岩省玄武岩特征,主要为峨眉山玄武岩及同期基性侵入岩;715~997M的物源为洋岛/板内玄武岩类,主要为研究区周缘与新元古代苏雄组及其同期的岩浆岩;铬尖晶石指示的岛弧性质物源则可能源自1000~1100Ma的岩浆岩。同时,碎屑锆石还指示古元古代和早寒武世发育岩浆作用,且存在古老的新太古代结晶基底。这些资料为上扬子地区构造演化提供了沉积学的证据。Objectives： Huize area is situated between the Kanddian Oldland and Sichuan basin with well-preserved sedimentary records. Achievements were mainly on sedimentary environments and lithofacies palaeogeography of the Feixianguan Formation. Its provenance and tectonic setting are not well understood. Based on sedimentary successions, we focus on the heavy mineral analysis to evaluate their sources. Methods ： Heavy mineral fractions from approximately l0 kg sample No. 10HLS2 and 10HLS16 of silieiclastie rock were concentrated and separated into 100, 150 and 250 p,m size fractions by standard techniques of density and magnetic separation at the Langfang Institute of Regional Geological and Mineral Resource Survey, Hebei Province, China. Detrital heavy minerals （ehromian spinel and zircon） were separated from sample No. IOHLS2 for electron probe microanalysis （EPMA） and LA-ICP-MS U-Pb dating. Two mineral fractions above of roughly 300 grains were randomly handpicked in alcohol under a binocular microscope, mounted in epoxy along with known standards, and polished to expose grain centers for backseattered electron （BSE） imaging and EPMA analysis. Distinct domains within the heavy minerals were selected for analysis based on the BSE images. Determination of the major element compositions of detrital chromian spinel was performed by wavelength-- dispersive spectrometry using an EPMA-1600 electron probe microanalyzer at the China University of Geoscicence （Beijing）. The operating conditions were： accelerating voltage 15kV, beam current 10 nA and beam diameter l lxm. We used as standars： magnetite （Fe）, albite （Si, Na, A1）, apatite （Ca, P）, rutile （Ti）, rhodonite （Mn）, sanidine （K）, olivine （Mg）, fluorite （F）, monazite （La, Ce, Pr, Nd, Th）, zircon （Y, Zr, Hf）, pollucite （Rb, Cs） and single mineral （U, Ta, Nb）. The calculation are based on the CALCMIN excel program. Results： Feixianguan Formation is mainly purple red fluvial sandstone in Huize area

关 键 词：上扬子 碎屑重矿物 铬尖晶石 碎屑锆石年代学 物源分析 

分 类 号：P534.51[天文地球—古生物学与地层学] P588.212.5[天文地球—地质学]