新疆准噶尔盆地西北部二叠纪玄武岩浆作用流体介质条件：流体化学组成及碳同位素制约  

The volatile conditions of Permian basaltic magmatism in northwestern Junggar basin of Xinjiang,China:Constraints from chemical and carbon isotopic compositions of volatiles in basalts

作　　者：张铭杰[1] 余明[1] 汤庆艳[1] 杨扬[1] 陈思童[1] 李中平[2] 史基安[2] ZHANG MingJie YU Ming TANG QingYan YANG Yang CHEN SiTong LI ZhongPing SHI JiAn(Key Laboratory of Mineral Resources in Western China （ Gansu） , School of Earth Seienees, Lanzhou University, Lanzhou 730000, China Gansu key Laboratory of Petroleum Resources, Institute of Geology and Geophysics, CAS, Lanzhou 730000, China)

机构地区：[1]兰州大学地质科学与矿产资源学院、甘肃省西部矿产资源重点实验室,兰州730000 [2]中国科学院地质与地球物理研究所、甘肃省油气资源研究重点实验室,兰州730000

出　　处：《岩石学报》2017年第1期93-103,共11页Acta Petrologica Sinica

基　　金：国土资源部公益性行业科研专项(201511020);国家自然科学基金项目(41472070、41372095);兰州大学中央高校基本科研业务费(lzujbky-2015-64);高等学校博士学科点专项科研基金项目(20120211110023);甘肃省西部矿产资源重点实验室开放基金(WCRMGS-2014-04);中国地质调查局项目(12120114044401)联合资助

摘　　要：准噶尔盆地西北部深层分布着大量的二叠纪玄武岩,其发育的流体介质条件缺乏系统研究。本文采用二叠纪玄武岩岩心样品,对基质中的流体化学组成和碳同位素组成进行分步加热质谱法分析,结果表明二叠纪玄武岩的流体组成中H_2O的含量极高(平均13789mm3.STP/g),次要组分为CO_2、O_2、H_2S和N2等,CO_2和CH_4的δ^(13)C值(分别为-28.9‰^-15.8‰和-36.8‰^-21.9‰)位于地壳与甲烷氧化来源组分的范围内;CH_4、C_2H_6、C_3H_8和C_4H_(10)等甲烷同系物的碳同位素组成随碳数增高总体具有正序分布特征,400~800℃温度段释出CH_4的δ^(13)C值(-25‰左右)明显重于200~400℃的(-35‰左右),部分样品400~800℃的CH_4-C_3H_8存在碳同位素反序分布的特征,显示幔源流体挥发份特征,其中混入大量的沉积有机质热裂解成因烃类气体,应为俯冲蚀变大洋板片的沉积物脱出流体挥发份。大量的H_2O指示岛弧俯冲的再循环流体的加入,甲烷氧化来源特征的CO_2和CH_4碳同位素组成揭示经历了长期的风化过程,表明相关岩浆作用后遭受长期的抬升。The Carboniferous-Permian basalts are occurred in deep part of northwestern Junggar basin, Xinjiang, China. The volatile conditions of the Permian basaltic magmatism had not been studied. The chemical and carbon isotopic compositions of volatiles in the matrix of Permian basalt cores were measured by stepwise heating mass spectrometer. The results showed that the volatiles in Permian basalts from northwestern Junggar basin were composed of dominated H2O with an average of 13789mm3.STP/g （STP-standard tempeture and pressure）, with minor CO2, O2, H2S and N2. The δ13C values of CO2 （-28.9‰ to -15.8‰） and δ13CCH4 （-36.8‰^-21.9‰） were plotted in the δ13C ranges of crust and methane oxidation. The CH4, C2H6, C3H8 and C4H10 etc. methane homologues showed the normal distribution pattern of carbon isotopic compositions among CH4 to C4H10, which are the carbon isotopic features of thermogenic hydrocarbon gases of organic materials in oceanic sedimentary. The δ13C values of CH4 released at 400~800℃ （about -25‰） are heavier than those at 200~400℃ （about -35‰）, and some samples showed partial reversal pattern in CH4 to C3H8 released at 400~800℃, suggested that volatiles originated from mantle could be mixed by hydrocarbons from thermally cracked by sedimentary organic materials, which should be volatiles degassed from alterated subducted oceanic sedimentary. Large quatity of H2O indicated the addition of recycled volatiles in arc. The chemical and carbon isotopic compositions of CO2 and CH4 reveal long time alteration of organic materials, and imply long time uplifting after basaltic magmatism.

关 键 词：来源 碳同位素 流体挥发份 二叠纪玄武岩 准噶尔盆地西北部 

分 类 号：P588.145[天文地球—岩石学] P597.2[天文地球—地质学]