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大火成岩省(LIPs)作为地质记录中一类特殊的岩浆活动,以短时间内(1~5Ma)喷发的岩浆体积占整个火山活动岩浆体积的75%为特征(Coffin et al., 1994; Ernst et al., 2005),其一般由大陆溢流玄武岩组成,并含有少量的酸性岩(Bryan et al., 2002; Bryan, 2007; Ernst et al., 2013)。华南西部地区在晚二叠世—中三叠世期间沉积了大量陆源碎屑岩(Zeng Yunfu et al., 1995; Yang Jianghai et al., 2012b; Du Yuansheng et al., 2013),其中晚二叠世的碎屑物源分析揭示了从峨眉山大火成岩省(LIP)到右江盆地的“源-汇”沉积体系(He Bin et al., 2007; Yang Jianghai et al., 2014, 2015; Lehrmann et al., 2015; Yu Xin et al., 2017; Deng Xusheng et al., 2020)。陆源碎屑沉积物/岩来源于陆地表层岩石的风化剥蚀,其物质组成可直接反映地球表层的岩石组成和风化剥蚀状态(Taylor et al., 1995; Nesbitt et al., 1996),是地表地貌演化、造山作用、海-陆变迁、水系分布和气候变化的重要信息载体(Weltje et al., 2004; Liu Shaofeng et al., 2010; Hu Xiumian et al., 2015; Schachtman et al., 2019)。在华南西南地区晚二叠世的源-汇沉积体系中,碎屑沉积物来源于峨眉山LIP火山岩的风化剥蚀(He Bin et al., 2007; Yang Jianghai et al., 2012a),自北西向南东依次沉积于右江盆地北部的河流-湖泊、滨-浅海和深水盆地环境(He Bin et al., 2007; Shao Longyi et al., 2013; Yang Jianghai et al., 2014, 2015; Yu Xin et al., 2017; Deng Xusheng et al., 2020)。详细的沉积物源分析表明,该源-汇沉积体系中的源岩以峨眉山LIP高-Ti玄武质火山岩为主,并含少量酸性火山岩(Yang Jianghai et al., 2015; Deng Xusheng et al., 2020);碎屑锆石的U-Pb年龄、化学成分和Hf同位素研究表明,峨眉山LIP在晚二叠世剥蚀的火山岩具有特定的岩浆演化序列(Yang Jianghai et al., 2015; Deng Xusheng et al., 2020),即在峨眉山LIP晚期岩浆演化过程中地壳对其贡献逐渐减小。已有研究显示,峨眉山LIP在早三叠世仍为剥蚀区,为周缘的陆相和海相沉积盆地提供了陆源碎屑沉积物(He et al., 2007; Yang Jianghai et al., 2014; Lehrmann et al., 2015; Zhang Yingli et al., 2016; Zhu Min et al.,2016),但是对峨眉山LIP在早三叠世剥蚀的火山岩石属性及其与晚二叠世剥蚀的火山岩在组成上的差异还不清楚,对剥蚀的火山岩所记录的岩浆演化过程未有深入研究。
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本文对右江盆地北缘下三叠统下部的飞仙关组开展了详细的沉积物源分析,并与该地区已报道的晚二叠世沉积物源数据进行对比,进一步明确了峨眉山LIP在晚二叠世到早三叠世早期剥蚀的火山岩石序列,探讨了其可能的岩浆演化趋势。
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1 区域地质概况
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峨眉山LIP和右江盆地均位于华南西缘 (图1a),两者在空间上毗邻。该LIP主体呈菱形展布于川、滇、黔交界地区,出露面积约2.5×105~3.0×105 km2(Chung Sunlin et al., 1995; Xu Yigang et al., 2001, 2004),主要由溢流玄武质火山岩和同时期的镁铁质、长英质侵入体以及少量的酸性火山岩、火山碎屑岩及超基性岩构成(Chung Sunlin et al., 1995; Xu Yigang et al., 2001; Xiao Long et al., 2004; Ali et al., 2005; Wang Xiaolei et al., 2007; Zhang Zhaochong et al., 2009)。峨眉山火山岩序列多以平行不整合覆盖在中二叠统茅口组碳酸盐岩之上,其顶部则以平行不整合与晚二叠世—三叠纪的碎屑沉积岩接触(Xu Yigang et al., 2001, 2004; He Bin et al., 2007; Zhu Jiang et al., 2021)。现存的峨眉山火山岩序列在西部厚度可达~5000m,向东减薄至几十米。玄武质火山岩在组成上可分成高-Ti和低-Ti两种类型。前者在该大火成岩省地区分布广泛,而后者则仅出现于大火成岩省的西部且位于高-Ti玄武岩序列之下(Xu Yigang et al., 2001; Zhou Meifu et al., 2002; Zhang Zhaochong et al., 2006, 2008)。前人通过同位素定年、磁性地层学和生物地层学研究,将峨眉山大火成岩省的主体喷发期限制在中—晚二叠世之交,即~260Ma (Ali et al., 2002; Zhou Meifu et al., 2002; He Bin et al., 2007; Zheng Liandi et al., 2010; Zhong Hong et al., 2011; Shellnutt et al., 2012, 2014; Huang Hu et al., 2016; Sun Yadong et al., 2017; Li Youjuan et al., 2018; Liu Junping et al., 2020)。现存的酸性火山岩主要分布于少数几个火山序列的顶部。Zhong Yuting et al.(2014)和Yang Jianghai et al.(2018)分别对宾川和普安地区的酸性火山岩开展高精度锆石U-Pb同位素定年,获得了259.1±0.5Ma和259.5±0.2Ma两个年龄,约束了峨眉山LIP玄武岩火山活动终止的时代。最新的锆石U-Pb同位素年代学研究认为,峨眉山大火成岩省的酸性火山喷发可持续至~257Ma(Zhong Yuting et al., 2020; Shellnutt et al., 2020)。峨眉山LIP自形成之后,其以玄武岩为主的火山岩在晚二叠世—早三叠世遭受了强烈的风化剥蚀,为邻近的右江盆地、盐源盆地、会泽盆地等提供了大量的陆源碎屑沉积物(He Bin et al., 2007, 2010; Yang Jianghai et al., 2012a, 2012b, 2015; Zhu Min et al.,2016; Zhang Yingli et al., 2016, 2019, 2021)。
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右江盆地位于峨眉山LIP东南部的华南大陆西南缘 (图1)。华南大陆由扬子地块和华夏地块在新元古代早期碰撞拼贴而成,并随Rodinia超大陆的裂解在新元古代晚期发生了大规模的构造、岩浆和盆地沉积活动(Li Zhengxiang et al., 1995; Wang Xiaolei et al., 2007; Zheng Yongfei et al., 2007; Shu Liangshu et al., 2011; Zhao Guochun et al., 2012; Cawood et al., 2013),随后在早古生代又经历了广泛的褶皱、挤压造山,造成早古生代晚期地层的普遍缺失(Shu Liangshu et al., 2008; Wang Yuejun et al., 2013; Zhang Qiao et al., 2015; Li Sanzhong et al., 2016)。伴随泥盆纪的拉张裂陷作用,华南开始接受晚古生代的海相沉积,其中在其西南地区形成了右江盆地(Guo Feng et al., 2004; Lehrmann et al., 2007; Du Yuansheng et al., 2013; Qiu Liang et al., 2017)。该盆地发育有泥盆纪到早三叠世的深水盆地相碳酸盐岩、浊积岩、硅-泥质岩夹火山岩和孤立碳酸盐岩台地沉积序列,在中三叠世出现巨厚的碎屑浊流沉积而趋于淹没消亡(Yang Jianghai et al., 2012a; Du Yuansheng et al., 2013; Duan Liang et al., 2018)。右江盆地在中—晚二叠世之交发生了重大的沉积和古地理变革,在局部地区伴随有玄武岩的喷发(Fan Weiming et al., 2008;Lai Shaocong et al., 2012),发生较显著的盆地裂陷作用(Huang Hu et al., 2014)。盆地北部位于He et al.(2003)所划分的峨眉山LIP外带地区,自晚二叠世初期开始接受大量源自峨眉山LIP山岩剥蚀的陆源碎屑沉积物(He Bin et al., 2007; Yang Jianghai et al., 2012b, 2014, 2015; Yu Xin et al., 2017; Deng Xusheng et al., 2020; Zhu Jiang et al., 2020)。这些沉积岩含有高的玄武质火山岩岩屑、低的Al2O3/TiO2值、~260Ma的碎屑锆石年龄峰值等特征,主要分布于晚二叠世的宣威组、晒瓦组、龙潭组等和早三叠世早期的罗楼组下部、拔杆组、石炮组和飞仙关组等地层(He Bin et al., 2007; Yang Jianghai et al., 2014; Huang Hu et al., 2014; Lehrmann et al., 2015; Yu Xin et al., 2017)。
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图1 华南西南部峨眉山大火成岩省和右江盆地分布图(a)(据Yang Jianghai et al., 2018修改) 及华南地区早三叠世印度期古地理图(b)(据Liu Baojun et al., 1994修改)
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Fig.1 Schematic for the Emeishan large igneous province and Youjiang basin in western South China (a) (revised from Yang Jianghai et al., 2018) and Early Triassic Induan paleogeographic map of South China (b) (according to Liu Baojun et al., 1994)
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(a)中黑色方块为前人研究的上二叠统—下三叠统露头和岩芯剖面位置,包括哲觉(He Bin et al., 2007)、四大寨(Yang Jianghai et al., 2015)、西林(Lehrmann et al., 2015)、普安(Deng Xusheng et al., 2020)、八渡(Yang Jianghai et al., 2014)、会泽(Zhang Yingli et al., 2016)和盐源(Zhu Min et al., 2016)
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Black squares in (a) indicate the locations of outcrop or core sections previously studied at Zhejue (He Bin et al., 2007), Sidazhai (Yang Jianghai et al., 2015), Pu'an (Deng Xusheng et al., 2020), Badu (Yang Jianghai et al., 2014), Huize (Zhang Yingli et al., 2016) and Yanyuan (Zhu Min et al., 2016)
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2 采样剖面和分析方法
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研究样品采自黔西南贞丰地区的两个钻孔岩芯剖面(ZK-11和ZK-12)。在该区,下三叠统飞仙关组整合于上二叠统龙潭组之上和下三叠统永宁镇组之下,在岩性上主要以交替出现的紫红色、灰绿色粉砂质泥岩夹有泥质灰岩、碎屑灰岩为特征, 具条带构造和缝合线构造, 可见细粒、微细粒黄铁矿星点状、浸染状、结核状分布(图2)。
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飞仙关组发育小型交错层理、波状和透镜状层理、双黏土层等沉积构造,灰岩中可见有双壳、腕足类等化石碎片,泥岩中可见有少量植物碎片等。岩性组合、沉积构造和生物化石表明,飞仙关组沉积于受潮汐作用影响的三角洲平原环境(图1b,Liu Baojun et al., 1994)。
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本文从飞仙关组上部共采集泥岩样品22件,其中12件采自钻孔ZK-11,10件采自钻孔ZK-12。对采集的22件泥岩样品首先去除样品表层,然后在澳实分析检测(广州)有限公司进行样品细粉碎(＜200目),随后采用X荧光质谱(XRF)方法对主量元素含量进行测定,其分析检测精度优于3%,误差为2%。在中国地质大学(武汉)地质过程与矿产资源国家重点实验室(GPMR),利用等离子电感耦合质谱分析仪(ICP-MS)对样品进行微量元素含量分析,其测定精度优于5%,不确定度小于5%。全岩矿物组成分析测试在中国地质大学(武汉)地质过程与矿产资源国家重点实验室完成,利用X'Pert Pro X射线粉末衍射(XRD)对钻孔ZK-11的11件样品进行矿物成分和含量分析,分析误差约为5%。
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从钻孔ZK-11剖面采集了4件粉砂质泥岩样品,利用淘洗和重液分选重矿物,在双目镜下挑选出碎屑锆石颗粒。碎屑锆石颗粒经制靶并抛光后,在GPMR实验室利用激光剥蚀等离子电感耦合质谱(LA-ICP-MS) 对其进行了U-Pb同位素和微量元素分析。激光剥蚀系统使用GeoLas2005,束斑直径选用32 μm。采用ICPMSDataCal进行了背景和信号的离线选择和集成,以及微量元素分析和U-Pb测年的时间漂移校正和定量校准(Liu Yongsheng et al., 2008),用Si做内标利用NIST610玻璃对锆石微量元素进行校正。U-Pb同位素定年采用标准锆石91500作为外标进行同位素分析矫正(Wiedenbeck et al., 2004)。在获得的U-Pb年龄数据中,小于1000Ma的锆石年龄按照206Pb/238U年龄计算,而大于1000Ma的锆石年龄按照207Pb/206Pb年龄计算。
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图2 贞丰地区飞仙关组岩芯照片(左)和上二叠统—下三叠统地层格架和采样岩芯柱状图(右)
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Fig.2 Drilling core photos of the Lower Triassic Feixianguan Formation (left) and the Upper Permian-Lower Triassic stratigraphic framework and the sampled drilling core successions in Zhenfeng region (right)
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3 结果
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3.1 飞仙关组泥岩的矿物和地球化学组成
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飞仙关组泥岩样品主要由长石(5%~22%)、石英(7%~15%)、黏土矿物(平均54.4%)和碳酸盐矿物(1%~4%)等组成。少数样品中也检测到赤铁矿 (平均为4.38%)、黄铁矿(平均为3%)和锐钛矿(平均为1%)等富铁矿物(表1)。黏土矿物包括大量的伊利石和少量的绿泥石。对比中生代以来泥岩的矿物组成(Shaw et al., 1965),飞仙关组泥岩具有更低的石英/长石含量比值(0.5~1.88)。
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在主量元素组成上,泥岩样品具有相对低的SiO2含量(31.6%~54.3%)、高的TiO2 (1.80%~3.00%)和Fe2O3 (6.1~14.6%) 含量等特征(表2)。样品的Al2O3/TiO2值为4.8~6.4,显著低于平均大陆上地壳的相应值(30.4,Taylor et al., 1995)。泥岩样品的稀土元素(REE)总含量为2002×10-6~3271×10-6 (表2),具有中等的La/Sm值(4.83~5.31)、低的Th/Nb、Th/Sc和Zr/Sc值(分别为0.19~0.25、0.41~0.53和13.1~16.1)。在稀土元素(REE)球粒陨石标准化图上 (图3a),泥岩样品显示出轻REE富集、重REE亏损和弱负Eu异常(Eu/Eu*=0.84~0.89)的特征,(La/Yb)N值为8.89~11.47。在原始地幔标准化的微量元素蛛网图上 (图3b),泥岩样品显示出显著的Ba和Sr负异常和微小的Ti负异常,而Nb、Ta表现为轻微的负异常(图3b), La/NbN值为1.86~2.56。
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3.2 碎屑锆石U-Pb年龄及微量元素组成
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飞仙关组的碎屑锆石多为无色或淡粉红色、棱角状—次棱角状,在CL图像上显示出振荡环带、核边结构和弱分带或无分带三种不同的内部形态 (图4)。对4件泥岩样品的112颗碎屑锆石进行了112个分析(表3),其中98个U-Pb年龄数据具有较高的谐和度(＞90%)。在碎屑锆石的U-Pb年龄频率直方图上,4件样品具有相对一致的碎屑锆石U-Pb年龄分布 (图5),形成了约280~240Ma和约1100~500Ma的两个主要年龄组,此外也含有少量的古元古代—新太古代年龄。其中,最年轻的主要年龄组形成了259±4Ma的年龄峰值。
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对~260Ma年龄组的碎屑锆石开展了微量元素分析。结果表明,除少数颗粒外均具有从La到Lu逐渐富集和正Ce异常(Ce/Ce*=1.1~118)及负Eu异常(Eu/Eu*=0.013~0.43)的球粒陨石标准化模式,为典型的中—酸性岩浆锆石的稀土元素配分特征(Hoskin et al., 2000; Wu Yuanbao et al., 2004)。这些锆石的Nb、Hf、Yb和Th含量分别为0.90×10-6~17.00×10-6、6261×10-6~11857×10-6、129×10-6~1080×10-6和44×10-6~1065×10-6,具有较大的Nb/Hf、Th/Nb、U/Yb和Nb/Yb值变化范围,分别为0.0002~0.002、4.5~227.8、0.37~2.96和0.004~0.017。
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注:n代表矿物含量低于XRD检测标准。
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图3 贞丰下三叠统飞仙关组泥岩球粒陨石标准化稀土元素配分模式图(a)和原始地幔标准化微量元素蛛网图(b)
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Fig.3 Chondrite-normalized REE distributions (a) and primitive-mantle normalized spider diagram (b) for the mudstone of the Lower Triassic Feixianguan Formation at Zhenfeng
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数据来源: 球粒陨石据Taylor et al.(1995);原始地幔数据Sun et al.(1989); 峨眉山大火成岩省的平均高Ti玄武岩(Xu Yigang et al.2001, 2007; Xiao Long et al., 2004; Qi Liang et al., 2008; Lai Shaocong et al., 2012); 平均粗面岩(Shellnutt et al., 2010; Xu Yigang et al., 2010) 和平均流纹岩(Xu Yigang et al., 2010)也投在图中用以比较
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Data sources: normalized values for chondrite are from Taylor et al.(1995) and primitive mantle are from Sun et al.(1989); the average high-Ti baslts (Xu Yigang et al.2001, 2007, Xiao Long et al., 2004; Qi Liang et al., 2008; Lai Shaocong et al., 2012), trachytes (Shellnutt et al., 2010; Xu Yigang et al., 2010) and rhyolites (Xu Yigang et al., 2010) from ELIP basalts are also shown for comparison
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图4 贞丰下三叠统飞仙关组碎屑锆石阴极发光图像
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Fig.4 Cathodoluminescence images of detrital zircons from the Lower Triassic Feixianguan Formation at Zhenfeng
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4 讨论
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4.1 飞仙关组的沉积物源
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飞仙关组泥岩样品表现出长石、石英含量低而黏土矿物含量高的特征,且黏土矿物主要由伊利石所组成,仅有少量的绿泥石。但其Al2O3/TiO2值仍较后太古代平均泥岩显著偏低,反映了高的TiO2含量。Al2O3和TiO2相对于其他主要元素具有较高的稳定性,在风化剥蚀过程中更加不易受影响,因此沉积物中的Al2O3/TiO2值通常被用作物源指标(He Bin et al., 2007; Yang Jianghai et al., 2015)。飞仙关组样品的Al2O3/TiO2值与黔西南哲觉、八渡和桂西北天峨等地的早三叠世碎屑岩的Al2O3/TiO2值具有很好的一致性,同时也与黔南四大寨上二叠统晒瓦组砂岩(Yang Jianghai et al., 2012, 2015)、桂西北天峨上二叠统领薅组粉砂岩(Yang Jianghai et al., 2012, 2014)和黔西南灰家堡上二叠统龙潭组泥岩和粉砂岩(Yu Xin et al., 2017; Deng Xusheng et al., 2020)的Al2O3/TiO2值范围非常相似(图6)。样品的Al2O3/TiO2值也与峨眉山LIP高Ti玄武岩的Al2O3/TiO2值(集中于2.5~4.5之间,Xu Yigang et al., 2001; Xiao Long et al., 2004; He Bin et al., 2007; Lai Shaocong et al., 2012)较为接近,但远低于峨眉山酸性火山岩(流纹岩为20.52~22.50, 粗面岩为15.54~19.52)和平均大陆上地壳的Al2O3/TiO2值(图6)。同时,研究的飞仙关组泥岩显示出与峨眉山火山岩(Xu Yigang et al., 2001, 2007, 2010; Shellnutt et al., 2010; Lai Shaocong et al., 2012)相似的稀土元素和微量元素组成,相对于峨眉山高-Ti玄武岩表现出Eu、Sr、Ti的相对亏损, 而相对于峨眉山酸性火山岩则表现出Eu、Sr和Ti的相对富集 (图3)。在Al2O3/TiO2-La/Sm双变量图中,研究的飞仙关组泥岩与邻区的下三叠统下部碎屑岩和上二叠统碎屑岩的投点区具有很大的重叠性 (图6),表明了在源岩组成上的继承性。两端元的混合计算结果显示,晚二叠世—早三叠世早期的主要源岩可由~70%峨眉山高-Ti玄武岩和~30%酸性火山岩混合而成 (Yang Jianghai et al., 2015)。
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图5 贞丰下三叠统飞仙关组泥岩碎屑锆石的U-Pb年龄频率分布图
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Fig.5 Frequency distribution of detrital zircon U-Pb ages from mudstone of the Lower Triassic Feixianguan Formation at Zhenfeng
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上述关于峨眉山LIP火山岩是飞仙关组主要物源的认识与碎屑锆石~260Ma的主要年龄组是一致的。飞仙关组样品含有峰值为~260Ma的主要碎屑锆石年龄组,这与峨眉山LIP的主要火山活动发生于中—晚二叠世之交相吻合(Zhou Meifu et al., 2002; Zhong Yuting et al.,2014; Huang Hu et al.,2016; Li Youjuan et al.,2018; Yang Jianghai et al., 2018)。更为重要的是,这些~260Ma的碎屑锆石与岛弧/造山型或大陆弧型岩浆结晶锆石在微量元素组成具有较大差异,在Th/Nb-Hf/Th和Nb/Yb-U/Yb图解上主体落在或靠近板内/非造山或洋岛环境(图7),支持主要物源来自于地幔柱成因的峨眉山LIP (Xu Yigang et al., 2001, 2004, 2007; Xiao Long et al., 2004)。需要注意,碎屑锆石中检测到一些230~250Ma的U-Pb年龄,它们比实际的地层沉积时代(印度阶251.9~251.2Ma, Tong Jinnan et al., 2019)还要年轻,但是在峨眉山LIP火山序列顶部的凝灰岩中,Yang Jianghai et al.(2018) 发现,二次离子探针(SIMS)分析确定为240~250Ma的锆石经化学剥蚀-热电离质谱(CA-TIMS)分析后,均给出了~260Ma的高精度U-Pb年龄。考虑到化学剥蚀可以较有效地去除放射性Pb丢失的锆石区域(Zhong Yuting et al., 2014; Yang Jianghai et al., 2018),因此之前获得三叠纪U-Pb年龄实际是放射性成因Pb丢失的结果,而非真实的锆石结晶年龄。基于这一认识,本文推测飞仙关组样品中的一些碎屑锆石也很可能受到放射性成因Pb丢失的影响,在没有经过化学剥蚀处理的情况给出了显著偏小的U-Pb年龄,不能作为指示其他可能火山岩源区的有效依据。此外,在Th/Nb-Hf/Th和U/Yb-Nb/Yb图中确实有~260Ma碎屑锆石落在岩浆弧/造山带环境,但仍处在前人研究的上二叠统~260Ma碎屑锆石的投点范围内。若有火山弧碎屑物质加入必然会导致全岩地球化学组成的变化,这与观察到的全岩地球化学特征不符,因此火山弧不可能作为所研究的飞仙关组的重要物源。
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图6 贞丰下三叠统飞仙关组泥岩样品与可能源岩峨眉山大火成岩省高Ti玄武岩(Xu Yigang et al., 2001, 2007; Xiao Long et al., 2004)、粗面岩(Shellnutt and Jahn, 2010; Xu Yigang et al., 2010)和流纹岩(Xu Yigang et al., 2010) 的La/Sm-Al2O3/TiO2图解
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Fig.6 Bivariate plot of La/Sm-Al2O3/TiO2 for the mudstone of Lower Triassic Feixianguan Formation in Zhenfeng region and potential source rocks in ELIP, including the high-Ti basalts (Xu Yigang et al., 2001, 2007; Xiao Long et al., 2004), trachytes (Shellnutt and Jahn, 2010; Xu Yigang et al., 2010) and rhyolites (Xu Yigang et al., 2010)
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八渡 (Yang Jianghai et al., 2014) 和哲觉 (He Bin et al., 2007) 剖面下三叠统下部碎屑岩、四大寨剖面 (Yang Jianghai et al., 2015) 上二叠统碎屑岩和平均大陆上地壳 (Taylor et al., 1995) 也投在图中用以比较
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The clastic rocks of the lowerpart of the Lower Triassic from Badu (Yang Jianghai et al., 2014) and Zhejue (He Bin et al., 2007) sections, the Upper Permian clastic rocks from Sidazha (Yang Jianghai et al., 2015) section and the average UCC (Taylor et al., 1995) are also shown for comparison
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续表3
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图7 贞丰下三叠统飞仙关组~260Ma锆石与上二叠统龙潭组下部 (Deng Xusheng et al., 2020)和上部 (Yu Xin et al., 2017; Deng Xusheng et al.,2020) 以及下三叠统下部拔杆组(Yang Jianghai et al., 2014)碎屑锆石的Hf/Th-Th/Nb (据Yang Jianghai et al., 2012)与U/Yb-Nb/Yb (据Grimes et al., 2015)图解
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Fig.7 Diagrams of Hf/Th vs.Th/Nb (modified after Yang et al., 2012) and U/Yb vs.Nb/Yb (modified after Grimes et al., 2015) for detrital zircons with ages of~260Ma from the Lower Triassic Feixianguan Formation at Zhenfeng.Also plotted are detrital zircons with ages of~260Ma from the Upper Permian Longtan Formation (after Yu Xin et al., 2017; Deng Xusheng et al., 2020) and the Lower Triassic Bagan Formation (after Yang Jianghai et al., 2014)
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飞仙关组样品除含有~260Ma的碎屑锆石外,还见有大量＞300Ma的老锆石颗粒。沉积于云南会泽地区的陆相下三叠统(Zhang Yingli et al., 2016)和广西西北地区的深水相下三叠统(Yang Jianghai et al., 2014; Lehrmann et al., 2015)的碎屑锆石均呈现相似的U-Pb年龄组成特征,也含有大量＞300Ma的碎屑锆石颗粒 (图8a~c)。这些老年龄的锆石颗粒显然不能由峨眉山LIP的岩浆结晶而来。比较发现,这些老锆石的U-Pb年龄组成与滇黔桂地区基底岩石(Liu Yuping et al., 2009)的锆石U-Pb年龄谱具有很高的相似性 (图8e),似乎指示了区域的变质基底也为下三叠统提供了重要的物源区。但是,从华南印支期古地理图(图1b)中可以看出,在早三叠世早期,右江盆地周缘由深水海槽与其他剥蚀区相隔;详细的沉积物源分析也支持碎屑沉积物主要来源于峨眉山大火成岩省的风化剥蚀区。若存在另一物源区的假设成立,考虑到＞300Ma的碎屑锆石在全部定年的飞仙关组碎屑锆石组分中占有的比例高达76%,则可以推测全岩地球化学组成也应体现这一基底物源区的贡献,但这与样品的低Al2O3/TiO2值和弱的Eu、Nb负异常等地球化学特征相矛盾。此外,在地层序列中,峨眉山低-Ti玄武岩上覆于中二叠世茅口组之上,下伏于高-Ti玄武岩和酸性岩之下(Xu Yigang et al., 2004; Yang Jianghai et al., 2018),而峨眉山低-Ti玄武岩和其下伏的茅口组碳酸盐岩现在仍有保存,因此可以推测在晚二叠世—早三叠世的剥蚀过程中,变质基底并未参与剥蚀、为右江盆地提供物源。值得注意的是,前人在峨眉山LIP岩浆岩中也报道有大量的前二叠纪年龄的老锆石颗粒(图8d, Zhou Meifu et al., 2002; Fan Weiming et al., 2008; Zhong Hong et al., 2009; Shellnutt et al., 2014, 2015; Tang Qingyan et al., 2015; Usuki et al., 2015)。因此,综合全岩地球化学数据,可以推测所研究的下三叠统中＞300Ma的碎屑锆石颗粒很可能也应来源于峨眉山大火成岩省,很可能是玄武质岩浆上升过程中从基底岩石捕获而来的。需要指出,玄武岩中锆石含量极低,确定玄武质的沉积物源区应多从矿物学、岩相学和全岩地球化学的角度来思考,碎屑锆石物源分析仅可作为一个参考。
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图8 右江盆地北部陆相(a, Zhang Yingli et al., 2016)、滨-浅海相(b, 本文)和深水相(c, Yang Jianghai et al., 2014; Lehrmann et al., 2015)早三叠世早期碎屑岩锆石U-Pb年龄谱与峨眉山大火成岩省岩浆岩＞300Ma锆石年龄 (d, Fan Weiming et al., 2008; Zhong Hong et al., 2009; Shellnutt et al., 2014, 2015; Tang Qingyan et al., 2015; Usuki et al.,2015)和滇黔桂地区变质基底岩石(e, Liu Yuping et al., 2009)锆石年龄谱对比图
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Fig.8 Detrital zircon U-Pb age spectrum of the Early Triassic clastic rocks from the terrestrial (a, Zhang Yingli et al., 2016), littoral (b, this article) and deep-water facies (c, Yang Jianghai et al., 2014; Lehrmann et al., 2015) in the northern Youjiang basin compared with the ＞300Ma zircon age spectrum from the Emeishan large igneous province (d, Fan Weiming et al., 2008; Zhong Hong et al., 2009; Shellnutt et al., 2014, 2015; Tang Qingyan et al., 2015; Usuki et al., 2015) and zircon U-Pb age distribution of metamorphic basement rocks in SW South China (e, Liu Yuping et al., 2009)
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4.2 峨眉山大火成岩省晚二叠世—早三叠世的火山剥蚀序列
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本文的物源数据显示,黔西南地区下三叠统滨海相飞仙关组与同期的陆相和深水盆地相碎屑岩具有相同的主要物源区(Yang Jianghai et al., 2014; Lehrmann et al., 2015;Zhang Yingli et al, 2016),共同记录了峨眉山LIP在早三叠世早期的风化剥蚀。研究区早三叠世与晚二叠世在源-汇沉积体系上具有明显的继承性,尽管两个时期的全球海平面、区域海陆分布和局部的沉积环境都发生了变化,但碎屑沉积物产生、搬运和堆积的沉积系统没有发生本质变化。从上二叠统到下三叠统,碎屑岩均含有大量的火山岩岩屑和少量的长石颗粒,在地球化学上均具有低Al2O3/TiO2值和弱Eu、Nb负异常的特征,也都具有~260Ma的主要碎屑锆石年龄组。基于详细的碎屑锆石U-Pb年龄、微量元素及Hf同位素组成对比分析,Yang Jianghai et al.(2015)将上二叠统深水相晒瓦组分为上、下两部分,Deng Xusheng et al.(2020)将上二叠统滨-浅海相龙潭组也分为上、下两部分,两者具有很好的空间对比关系(Yu Xin et al., 2017)。上二叠统的上部较下部具有更多的＞300Ma的碎屑锆石颗粒,且上部与下部相比,其~260Ma的碎屑锆石整体上具有相对较高的Th/Nb和U/Yb值(图9)。本文研究的下三叠统飞仙关组整合于上二叠统龙潭组之上(图2),获得的98个有效锆石U-Pb年龄中有75个年龄大于300Ma,且~260Ma碎屑锆石的Th/Nb值集中于20~121,平均为50.34,对应的U/Yb值范围为0.36~2.52,平均为0.92。因此,与龙潭组上部的碎屑锆石数据相比,飞仙关组样品中＞300Ma碎屑锆石颗粒的比重更大,~260Ma碎屑锆石整体上具有更高的Th/Nb和U/Yb值(图9)。考虑到研究区上二叠统和下三叠统的碎屑岩都来自于峨眉山LIP源区,且源岩均由大量高-Ti玄武岩和少量酸性火山岩构成(图6),因此观察到的碎屑锆石年龄和微量元素组成在垂向上的显著变化应反映了峨眉山LIP在晚二叠世—早三叠世的火山剥蚀序列。
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图9 右江盆地晚二叠世龙潭组—早三叠世飞仙关组碎屑锆石年龄分布图及微量元素变化趋势图
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Fig.9 Detrital zircon U-Pb age distributions and trace element characters of the sedimentary rocks from the Late Permian to Early Triassic successions (Longtan and Feixianguan formations) in northern Youjiang basin
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(a)—上二叠统龙潭组和下三叠统下部飞仙关组中＜300Ma的碎屑锆石U-Pb年龄频率分布图;(b)— ＞300Ma的碎屑锆石直方分布图及其所占百分含量变化趋势;(c)—~260Ma碎屑锆石的Th/Nb直方图及箱装图;(d)—~260Ma碎屑锆石的U/Yb直方图及箱装图;箱装图的左右边界分别为25%和75%,其中黑线代表中位值。晚二叠世龙潭组下部数据来自于Deng Xusheng et al.(2020), 其上部数据来自于Yu Xin et al.(2017)和Deng Xusheng et al.(2020)
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(a)—U-Pb age frequency distribution diagrams of detrital zircons with ages of ＜300Ma from the Upper Permian Longtan Formation and Lower Triassic Feixianguan Formation; (b)—the U-Pb age histograms of detrital zircons with ages of ＞300Ma and their percentages in all detrital zircons; (c, d)—histograms and box plots of Th/Nb and U/Yb ratios for the~260Ma zircons in the Late Permian to Early Triassic successions respectively.Box's left and right boundaries are set at 25%and 75%.Black lines in the box represent the median values.Zircon U-Pb ages and trace element data for the Late Permian Longtan Formation are from Yu Xin et al.(2017) and Deng Xusheng et al.(2020)
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根据这一火山剥蚀序列可知: ① 晚二叠世早期剥蚀的峨眉山LIP火山岩中发育有大量新结晶的~260Ma锆石,基本不含有从围岩捕获的老锆石;② 晚二叠世晚期剥蚀的峨眉山LIP火山岩中也发育有大量新结晶的~260Ma锆石,但从围岩捕获的老锆石数量明显增多;③ 早三叠世剥蚀的峨眉山LIP火山岩中发育有少量新结晶的~260Ma锆石,而含有大量从围岩中捕获的老锆石。同时,不同时期剥蚀的峨眉山LIP火山岩在~260Ma锆石的化学组成上也存在变化,即越早剥蚀的火山岩所含的~260Ma锆石其Th/Nb和U/Yb比值越低。利用岩浆锆石Th/Nb、U/Yb等比值对母岩浆化学组成和演化的指示作用(Grimes et al., 2007, 2015; Yang Jianghai et al., 2012),峨眉山LIP火山剥蚀序列中~260Ma锆石Th/Nb、U/Yb比值的增大表明,华南陆壳基底对LIP岩浆的同化混染作用增强,这与老锆石颗粒数量的相应增多是一致的。下三叠统飞仙关组对应于峨眉山LIP晚二叠世—早三叠世火山剥蚀序列中最底部火山岩的风化剥蚀,其碎屑锆石物源数据符合前人提出的有关峨眉山LIP后期岩浆演化的模型,即随着地幔岩浆活动的减弱,玄武质岩浆逐步在地壳中形成岩浆房而发生日益增强的分异结晶作用,大陆地壳物质参与的同化混染作用不断减弱(Yang Jianghai et al., 2015; Deng Xusheng et al., 2020)。
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5 结论
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黔西南地区下三叠统飞仙关组泥岩的矿物学、地球化学和碎屑锆石U-Pb年龄及微量元素组成数据表明,峨眉山LIP火山岩提供了主要的碎屑沉积物源。综合前人有关上二叠统和下三叠统的沉积物源研究结果,飞仙关组的物源分析揭示峨眉山LIP火山岩在晚二叠世—早三叠世经历了持续的风化剥蚀,为邻近从陆到海的沉积体系提供了大量陆源碎屑沉积物。基于上二叠统龙潭组和下三叠统飞仙关组的碎屑锆石U-Pb年龄和锆石微量元素组成,我们重建了峨眉山LIP晚二叠世—早三叠世的火山剥蚀序列,是峨眉山LIP晚期岩浆活动的重要物质记录。下三叠统下部、上二叠统上部和下部的沉积分别对应于这一火山剥蚀序列的下部、中部和上部,其碎屑锆石U-Pb年龄和锆石微量元素组成的对比分析显示,峨眉山LIP晚期地幔来源岩浆受地壳物质混染的影响趋于减弱,而发生了广泛的分异结晶作用。
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参考文献
-
Ali J R, Thompson G M, Song Xieyan, Wang Yunliang. 2002. Emeishan basalts (SW China) and the “end-Guadalupian” crisis: magnetobiostratigraphic constraints. Journal of the Geological Society, 159(1): 21~29.
-
Ali J R, Thompson G M, Zhou Meifu, Song Xieyan. 2005. Emeishan large igneous province, SW China. Lithos, 79(3): 475~489.
-
Bryan S E. 2007. Silicic large igneous provinces. Episodes, 30(1): 20~31.
-
Bryan S E, Riley T R, Jerram D A, Stephens C J, Leat P T. 2002. Silicic volcanism: an undervalued component of large igneous provinces and volcanic rifted margins. Special Paper of the Geological Society of America, 362: 97~118.
-
Cawood P A, Wang Yuejun, Xu Yajun, Zhao Guochun. 2013. Locating South China in Rodinia and Gondwana: a fragment of greater India lithosphere?. Geology, 41(8): 903~906.
-
Chung Sunlin, Jahn B. 1995. Plume-lithosphere interaction in generation of the Emeishan flood basalts at the Permian-Triassic boundary. Geology, 23(10): 889~892.
-
Coffin M F, Eldholm O. 1994. Large Igneous Provinces: Crustal structure, dimensions, and external consequences. Reviews of Geophysics, 32(1): 1~36.
-
Deng Xusheng, Yang Jianghai, Cawood P A, Wang Xuance, Du Yuansheng, Huang Yan, Lu Shufan, He Ben. 2020. Detrital record of late-stage silicic volcanism in the Emeishan large igneous province. Gondwana Research, 79: 197~208.
-
Du Yuansheng, Huang Hu, Yang Jianghai, Huang Hongwei, Tao Ping, Huang Zhiqiang, Hu Lisha, Xie Chunxia. 2013. The basin translation from late Paleozoic to Triassic of the Youjiang basin and its tectonic signification. Geological Review, 59(1): 1~11 (in Chinese with English abstract).
-
Duan Liang, Meng Qinren, Christie-Blick N, Wu Guoli. 2018. New insights on the Triassic tectonic development of South China from the detrital zircon provenance of Nanpanjiang turbidites. Geological Society of America Bulletin, 130(1-2): 24~34.
-
Ernst R E, Buchan K L, Campbell Ian H. 2005. Frontiers in Large Igneous Province research. Lithos, 79(3~4): 271~297.
-
Ernst R E, Jowitt S M. 2013. Large igneous provinces (LIPs) and metallogeny. Society of Econmic Geologists Special Publication. 17: 17~51.
-
Fan Weiming, Zhang Chunhong, Wang Yuejun, Guo Feng. 2008. Geochronology and geochemistry of Permian basalts in western Guangxi Province, Southwest China: evidence for plume-lithosphere interaction. Lithos, 102(1-2): 218~236.
-
Grimes C B, John B E, Kelemen P B, Mazdab F K, Schwartz J J. 2007. Trace element chemistry of zircons from oceanic crust: a method for distinguishing detrital zircon provenance. Geology, 35(7): 643~646.
-
Grimes C B, Wooden J L, Cheadle M J, John B E. 2015. “Fingerprinting” tectono-magmatic provenance using trace elements in igneous zircon. Contrib. Mineral. Petrol. , 170(5-6), DOI: https: //doi. org/10. 1007/s00410-015-1199-3.
-
Guo Feng, Fan Weiming, Wang Yuejun, Li Chaowen. 2004. Upper Paleozoic basalts in the southern Yangtze Block: geochemical and Sr-Nd isotopic evidence for asthenosphere-lithosphere interaction and opening of the Paleo-Tethyan ocean. International Geology Review, 46(4): 332~346.
-
He Bin, Xu Yigang, Chung Sunlin, Xiao Long, Wang Yamei. 2003. Sedimentary evidence for a rapid, kilometer-scale crustal doming prior to the eruption of the Emeishan flood basalts. Earth and Planetary Science Letters, 213(3): 391~405.
-
He Bin, Xu Yigang, Huang Xiaolong, Luo Zhenyu, Shi Yuruo, Yang Qijun, Yu Songyue. 2007. Age and duration of the Emeishan glood volcanism, SW China: geochemistry and SHRIMP zircon U-Pb dating of silicic ignimbrites, post-volcanic Xuanwei Formation and clay tuff at the Chaotian section. Earth and Planetary Science Letters, 255(3): 306~323.
-
He Bin, Xu Yigang, Zhong Yutingt, Guan Junpeng. 2010. The Guadalupian-Lopingian boundary mudstones at Chaotian (SW China) are clastic rocks rather than acidic tuffs: implication for a temporal coincidence between the end-Guadalupian mass extinction and the Emeishan volcanism. Lithos, 119(1): 10~19.
-
Hoskin P W O, Ireland T R. 2000. Rare earth element chemistry of zircon and its use as a provenance indicator. Geology, 28(7): 627~630.
-
Hu Xiumian, Garzanti E, Moore T, Raffi I. 2015. Direct stratigraphic dating of India-Asia collision onset at the Selandian (middle Paleocene, 59±1 Ma). Geology, 43(10): 859~862.
-
Huang Hu, Du Yuansheng, Yang Jianghai, Zhou Lian, Hu Lisha, Huang Hongwei, Huang Zhiqiang. 2014. Origin of Permian basalts and clastic rocks in Napo, Southwest China: implications for the erosion and eruption of the Emeishan Large Igneous Province. Lithos, 208-209: 324~338.
-
Huang Hu, Cawood P A, Hou Mingcai, Yang Jianghai, Ni Shijun, Du Yuansheng, Yan Zhaokun, Wang Jun. 2016. Silicic ash beds bracket Emeishan large igneous province to ＜ 1 my. At ~260 Ma. Lithos, 264: 17~27.
-
Lai Shaocong, Qin Jiangfeng, Li Yongfei, Li Sanzhong. 2012. Permian high Ti/Y basalts from the eastern part of the Emeishan large igneous province, southwestern China: petrogenesis and tectonic implications. Journal of Asian Earth Sciences, 47: 216~230.
-
Lehrmann D J, Pei Donghong, Enos P, Minzoni M, Ellwood B B, Orchard M J, Zhang Jiyan, Wei Jiayong, Dillett P, Koenig J, Steffen K, Druke D, Druke J, Kessel B, Newkirk T. 2007. Impact of differential tectonic subsidence on isolated carbonate-platform evolution: Triassic of the Nanpanjiang basin, South China. American Association of Petroleum Geologists Bulletin, 91(3): 287~320.
-
Lehrmann D J, Chaikin D H, Enos P, Minzoni M, Payne J, Yu Meiyi, Goers A, Wood T, Richter p, Kelley B M, Li Xiaowei, Qin Yanjiao, Liu Lingyun, Lu Gang. 2015. Patterns of basin fill in Triassic turbidites of the Nanpanjiang basin: implications for regional tectonics and impacts on carbonate-platform evolution. Basin Research, 27(5): 587~612.
-
Li Sanzhong, Li Xiyao, Zhao Shujuan, Zhao Yang, Liu Xin, Guo Lingli, Wang Yongming, Hao Yi, Zhang Jian, Hu Mengying. 2016. Global early Paleozoic orogens (Ⅲ): intracontinental orogen in South China. Journal of Jilin University (Earth Science Edition), 46(4): 1005~1025 (in Chinese with English abstract).
-
Li Youjuan, He Huaiyu, Ivanov A V, Demomterova E I. 2018. 40Ar/39Ar age of the onset of high-Ti phase of the Emeishan volcanism strengthens the link with the end-Guadalupian mass extinction. International Geology Review, 60(15): 1906~1917.
-
Li Zhengxiang, Zhang Linghua, Powell C M. 1995. South China in Rodinia: part of the missing link between Australia-East Antarctica and Laurentia? Geology, 23(5): 407~410.
-
Liu Baojun, Xu Xiaosong. 1994. Atlas of Lithofacies Palaeogeography of South China. Beijing: Science Press, 1~188.
-
Liu Junping, Wang Xiaofeng, Wang Xiaohu, Yang Aiping, Song Donghu, Tian Sumei, Xia Caixiang, Zhang Kun, Yang Shipan. 2020. Characteristics of the late Middle Permian mafic-ultramafic rocks in Dianzhong area, central Yunnan, and their relationship with the Emei mantle plume—evidence from zircon U-Pb age and petrogeochemistry. Geological Review, 66(5): 1284~1298 (in Chinese with English abstract).
-
Liu Yuping, Su Wenchao, Pi Daohui, Jiang Shaoyongm, Ye Lin, Zhang Qian, Zhou Liqin. 2009. Zircon chronology of basement rocks in the low-temperature metallogenic region of Yunnan, Guizhou and Guangxi. Progress in Natural Science, 19(12): 1319~1325 (in Chinese with English abstract).
-
Liu Yongsheng, Hu Zhaochu, Gao Shan, Günther D, Xu Juan, Gao Changgui, Chen Haihong. 2008. In situ analysis of maior and trace elements of anhydrous minerals by LA-ICP-MS without applying an internal standard. Chemical Geology, 257(1): 34~43.
-
Liu Shaofeng, Zhang Guowei, Ritts B D, Zhang Huiping, Gao Mingxing, Qian Cunchao. 2010. Tracing exhumation of the Dabie Shan ultrahigh-pressure metamorphic complex using the sedimentary record in the Hefei basin, China. Geological Society of America Bulletin, 122(1-2): 198~218.
-
Nesbitt H W, Young G M, Mclennan S M, Keays R R. 1996. Effects of chemical weathering and sorting on the petrogenesis of siliciclastic sediments, with implications for provenance studies. The Journal of Geology, 104(5): 525~542.
-
Qi Liang, Wang Christina Yan, Zhou Meifu. 2008. Controls on the PGE distribution of Permian Emeishan alkaline and peralkaline volcanic rocks in Longzhoushan, Sichuan Province, SW China. Lithos, 106(3): 222~236.
-
Qiu Liang, Yan Danping, Yang Wenxin, Wang Jibin, Tang Xiangli, Ariser S. 2017. Early to middle Triassic sedimentary records in the Youjiang basin, South China: implications for Indosinian orogenesis. Journal of Asian Earth Sciences, 141: 125~139.
-
Schachtman N S, Roering J J, Marshall J A, Gavin D, Granger D E. 2019. The interplay between physical and chemical erosion over glacial-interglacial cycles. Geology, 47(7): 613~616.
-
Shao Longyi, Gao Caixia, Zhang Chao, Wang Hao, Guo Lijun, Gao Caihong. 2013. Sequence-Palaeogeography and coal accumulation of late Permian in southwestern China. Acta Sedimentologica Sinica, 31(5): 856~866 (in Chinese with English abstract).
-
Shaw D B, Weaver C E. 1965. The mineralogical composition of shales. Journal of Sedimentary Research, 35(1): 213~222.
-
Shellnutt J G, Jahn B M, Dostal J. 2010. Elemental and Sr-Nd isotope geochemistry of microgranular enclaves from peralkaline A-type granitic plutons of the Emeishan large igneous province, SW China. Lithos, 119(1-2): 34~46.
-
Shellnutt J G, Denyszyn S W, Mundil R. 2012. Precise age determination of mafic and felsic intrusive rocks from the Permian Emeishan large igneous province (SW China). Gondwana Research, 22(1): 118~126.
-
Shellnutt J G, Wang K L. 2014. An ultramafic primary magma for a low Si, high Ti-Fe gabbro in the Panxi region of the Emeishan large igneous province, SW China. Journal of Asian Earth Sciences, 79: 329~344.
-
Shellnutt J G, Usuki T, Kennedy A K, Chiu H Y. 2015. A lower crust origin of some flood basalts of the Emeishan large igneous province, SW China. Journal of Asian Earth Sciences, 109: 74~85.
-
Shellnutt J G, Pham T T, Denyszyn S W, Yeh Mengwan, Anh T T. 2020. Magmatic duration of the Emeishan large igneous province: insight from northern Vietnam. Geology, 48(5): 457~461.
-
Shu Liangshu, Yu Jinhai, Jia Dong, Wang Bo, Shen Weizhou, Zhang Yueqiao. 2008. Early Paleozoic orogenic belt in the eastern segment of South China. Geological Bulletin of China, 27(10): 1581~1593 (in Chinese with English abstract).
-
Shu Liangshu, Faure M, Yu Jinhai, Jahn B M. 2011. Geochronological and geochemical features of the Cathaysia Block (South China): new evidence for the Neoproterozoic breakup of Rodinia. Precambrian Research, 187(3-4): 263~276.
-
Sun Weidong, McDonough W F. 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. Geological Society London Special Publications, 42(1): 313-345.
-
Sun Yadong, Liu X T, Yan Jiaxin, Chen B, Bond D P G, Joachimski M M, Wignall P B. 2017. Permian (Artinskian to Wuchapingian) conodont biostratigraphy in the Tieqiao section, Laibin area, South China. Palaeogeogr Palaeoclimatol Palaeoecol. , 465: 42~63.
-
Tang Qingyan, Li Chusi, Zhang Mingjie, Yao Lin. 2015. U-Pb age and Hf isotopes of zircon from basaltic andesite and geochemical fingerprinting of the associated picrites in the Emeishan large igneous province, SW China. Miner. Petrol. , 109: 103~114.
-
Taylor S R, Mclennan S M. 1995. The geochemical evolution of the continental crust. Reviews of Geophysics, 33(2): 241~265.
-
Tong Jinnan, Chu Daoliang, Liang Lei, Shu Wenchao, Song Haijun, Song Ting, Song Huyue, Wu Yuyang. 2019. Triassic integrative stratigraphy and timescale of China. Science China Earth Sciences, 49(1): 194~226 (in Chinese with English abstract).
-
Usuki T, Lan Chingying, Tran T H, Pham T D, Wang Kuolung, Shellnutt G J, Chung Sunlin. 2015. Zircon U-Pb ages and Hf isotopic compositions of alkaline silicic magmatic rocks in the Phan Si Pan-Tu Le region, northern Vietnam: identification of a displaced western extension of the Emeishan Large Igneous Province. Journal of Asian Earth Sciences, 97: 102~124.
-
Wang Xiaolei, Zhou Jincheng, Griffin W L, Wang Rucheng, Qiu Jiansheng, O'Reilly S Y, Xu Xisheng, Liu Xiaoming, Zhang Guilin. 2007. Detrital zircon geochronology of Precambrian basement sequences in the Jiangnan orogen: dating the assembly of the Yangtze and Cathaysia Blocks. Precambrian Research, 159(1-2): 117~131.
-
Wang Yuejun, Zhang Aimei, Fan Weiming, Zhang Yanhua, Zhang Yuzhi. 2013. Origin of paleosubduction-modified mantle for silurian gabbro in the Cathaysia Block: geochronological and geochemical evidence. Lithos, 160-161: 37~54.
-
Weltje G J, Eynatten H V. 2004. Quantitative provenance analysis of sediments: review and outlook. Sediment Geology, 171(1-4): 1~11.
-
Wiedenbeck M, Hanchar J M, Peck W H, Paul S, John V, Martin W, Andreas K, Yuichi M, Lutz N, Fiebig J, Franchi I, Girard J P, Greenwood R C, Hinton R, Kita N, Mason P R D, Norman M, Ogasawara M, Piccoli P M, Rhede D, Satoh H, Schulz-Dobrick B, Skår O, Spicuzza M J, Terada K, Tindle A, Togashi S, Vennemann T, Xie Q, Zheng Y F. 2004. Further characterisation of the 91500 zircon crystal. Geostandards and Geoanalytical Research, 28(1): 9~39.
-
Wu Yuanbao, Zheng Yongfei. 2004. Genesis of zircon and its constraints on interpretation of U-Pb age. Science Bulletin, 49(15): 1554~1569.
-
Xiao Long, Xu Yigang, Mei Huajin, Zheng Yongfei, He Bin, Pirajno F. 2004. Distinct mantle sources of low-Ti and high-Ti basalts from the western Emeishan large igneous province, SW China: implications for plume-lithosphere interaction. Earth and Planetary Science Letters, 228(3-4): 525~546.
-
Xu Yigang, Chung Sunlin, Jahn B M, Wen Genyao. 2001. Petrologic and geochemical constraints on the petrogenesis of Permian-Triassic Emeishan flood basalts in southwestern China. Lithos, 58(3-4): 145~168.
-
Xu Yigang, He Bin, Chung Sunlin, Menzies M, Frey F A. 2004. Geologic, geochemical, and geophysical consequences of plume involvement in the Emeishan flood-basalt province. Geology, 32(10): 917~920.
-
Xu Yigang, Luo Zhenyu, Huang Xiaolong, He Bin, Xiao Long, Xie Liewen, Shi Yuruo. 2007. Zircon U-Pb and Hf isotope constraints on crustal melting associated with the Emeishan mantle plume. Geochimica et Cosmochimica Acta, 72(13): 3084~3104.
-
Xu Yigang, Chung Sunlin, Shao Hui, He Bin. 2010. Silicic magmas from the Emeishan large igneous province, Southwest China: petrogenesis and their link with the end-Guadalupian biological crisis. Lithos, 119(1-2): 47~60.
-
Yang Jianghai, Cawood P A, Du Yuansheng, Huang Hu, Huang Hongwei, Tao Ping. 2012a. Large igneous province and magmatic arc sourced Permian-Triassic volcanogenic sediments in China. Sedimentary Geology, 261-262: 120~131.
-
Yang Jianghai, Cawood P A, Du Yuansheng, Huang Hu, Hu Lisha. 2012b. Detrital record of Indosinian mountain building in SW China: provenance of the middle Triassic turbidites in the Youjiang basin. Tectonophysics, 574-575: 105~117.
-
Yang Jianghai, Cawood P A, Du Yuansheng, Huang Hu, Hu Lisha. 2014. A sedimentary archive of tectonic switching from Emeishan plume to Indosinian orogenic sources in SW China. Journal of the Geological Society, 171: 269~280.
-
Yang Jianghai, Cawood P A, Du Yuansheng. 2015. Voluminous silicic eruptions during late Permian Emeishan igneous province and link to climate cooling. Earth and Planetary Science Letters, 432: 166~175.
-
Yang Jianghai, Cawood P A, Du Yuansheng, Condon D J, Yan Jiaxin, Liu Jianzhong, Huang Yan, Yuan Dongxun. 2018. Early Wuchiapingian cooling linked to Emeishan basaltic weathering? Earth and Planetary Science Letters, 492: 102~111.
-
Yu Xin, Yang Jianghai, Liu Jianzhong, Du Yuansheng, Chai Rong. 2017. Provenance of late Permian Longtan Formation in SW Guizhou Province and implication for reconstruction of regional sedimentation and paleogeography. Acta Geologica Sinica, 91(6): 1374~1385 (in Chinese with English abstract).
-
Zeng Yunfu, Liu Wenjun, Cheng Hongde, Zheng Rongcai, Zhang Jinquan, Li Xiaoquan, Jiang Tingcao. 1995. Evolution of sedimentation and tectonics of the Youjiang composite basin, South China. Acta Geologica Sinica, 69(2): 113~124 (in Chinese with English abstract).
-
Zhang Qiao, Jiang Yaohui, Wang Guochang, Liu Zheng, Ni Chunyu, Qing Long. 2015. Origin of Silurian gabbros and I-type granites in central Fujian, SE China: implications for the evolution of the early Paleozoic orogen of South China. Lithos, 216-217: 285~297.
-
Zhang Yingli, Wang Zongqi, Wang Gang, Li Qian, Lin Jianfei. 2016. Chromian spinel, zircon age constraints on the provenance of early Triassic Feixianguan Formation sandstones from Huize area, upper Yangtze region. Geological Review, 62(1): 54~72 (in Chinese with English abstract).
-
Zhang Yingli, Jia Xiaotong, Wang Zongqi, Wang Kunming, Chen Muyin. 2019. Provenance analysis and tectonic setting of Early Triassic Jialingjiang Formation in the southwestern Upper Yangtze area: evidence from sedimentology, heavy mineral electron probe microanalysis and U-Pb dating. Acta Geologica Sinica, 93(12): 3197~3222 (in Chinese with English abstract).
-
Zhang Yingli, Jia Xiaotong, Wang Kunming, Wang Zongqi, Chen Muyin. 2021. Provenance analysis of Triassic sediments in the Yingjing area on the western margin of the Yangtze Craton. Geological Review, 67(3): 1~15 (in Chinese with English abstract).
-
Zhang Zhaochong, Mahoney J J, Mao Jingwen, Wang Fusheng. 2006. Geochemistry of picritic and associated basalt flows of the western Emeishan flood basalt province, China. Journal of Petrology, 47(10): 1997~2019.
-
Zhang Zhaochong, Zhi Xiachen, Chen Lei, Saunders A, Reichow M. 2008. Re-Os isotopic compositions of picrites from the Emeishan flood basalt province, China. Earth and Planetary Science Letters, 276(1-2): 30~39.
-
Zhang Zhaochong, Mao Jingwen, Saunders A, Ai Yu, Li Ying, Zhao Li. 2009. Petrogenetic modeling of three mafic-ultramafic layered intrusions in the Emeishan large igneous province, SW China, based on isotopic and bulk chemical constraints. Lithos, 113(3-4): 369~392
-
Zhao Guochun, Cawood P A. 2012. Precambrian geology of China. Precambrian Research, 222-223: 13~54.
-
Zheng Liandi, Yang Zhenyu, Tong Yabo, Yuan Wei. 2010. Magnetostratigraphic constraints on two-stage eruptions of the Emeishan continental flood basalts. Geochemistry Geophysics Geosystems, 11(12): Q12014.
-
Zheng Yongfei, Zhang Shaobing. 2007. Formation and evolution of the Precambrian continental crust in South China. Chinese Science Bulletin, 52(1): 1~10 (in Chinese with English abstract).
-
Zhong Hong, Zhu Weiguang, Hu Ruizhong, Xie Liewen, He Defeng, Liu Feng, Chu Zhuyin. 2009. Zircon U-Pb age and Sr-Nd-Hf isotope geochemistry of the Panzhihua A-type syenitic intrusion in the Emeishan large igneous province, Southwest China and implications for growth of juvenile crust. Lithos, 110(1-4): 109~128.
-
Zhong Hong, Campbell I H, Zhu Weiguang, Allen C M, Hu Ruizhong, Xie Liewen, He Defeng. 2011. Timing and source constraints on the relationship between mafic and felsic intrusions in the Emeishan large igneous province. Geochimica et Cosmochimica Acta, 75(5): 1374~1395.
-
Zhong Yuting, He Bin, Mundil R, Xu Yigang. 2014. CA-TIMS zircon U-Pb dating of felsic ignimbrite from the Binchuan section: implications for the termination age of Emeishan large igneous province. Lithos, 204: 14~19.
-
Zhong Yuting, Mundil R, Chen Jun, Yuan Dongxun, Denyszyn S W, Jost A B, Payne J L, He Bin, Shen Shuzhong, Xu Yigang. 2020. Geochemical, biostratigraphic, and high-resolution geochronological constraints on the waning stage of Emeishan large igneous province. Geological Society of America Bulletin, 132(9-10): 1969~1986.
-
Zhou Meifu, Malpas J, Song Xieyan, Robinson P T, Sun Min, Kennedy A K, Lesher C M, Keays R R. 2002. A temporal link between the Emeishan large igneous province (SW China) and the end-Guadalupian mass extinction. Earth and Planetary Science Letters, 196(3-4): 113~122.
-
Zhu Jiang, Zhang Zhaochong, Santosh M, Jin Ziliang. 2020. Carlin-style gold province linked to the extinct Emeishan plume. Earth and Planetary Science Letters, 530: 115940.
-
Zhu Jiang, Zhang Zhaochong, Santosh M, Tan Shucheng, Jin Ziliang. 2021. Submarine basaltic eruptions across the Guadalupian-Lopingian transition in the Emeishan large igneous province: implication for end-Guadalupian extinction of marine biota. Gondwana Research, 92: 228~238.
-
Zhu Min, Chen Hanlin, Zhou Jing, Yang Shufeng. 2016. Provence of early Triassic in Yanyuan basin, upper Yangtze and its implication for the tectnoic evolution. Earth Science, 41(8): 1309~1321 (in Chinese with English abstract).
-
杜远生, 黄虎, 杨江海, 黄宏伟, 陶平, 黄志强, 胡丽莎, 谢春霞. 2013. 晚古生代—中三叠世右江盆地的格局和转换. 地质论评, 59(1): 1~11.
-
李三忠, 李玺瑶, 赵淑娟, 杨朝, 刘鑫, 郭玲莉, 王永明, 郝义, 张剑, 胡梦颖. 2016. 全球早古生代造山带(Ⅲ): 华南陆内造山. 吉林大学学报(地球科学版), 46(4): 1005~1025.
-
刘宝珺, 许效松. 1994. 中国南方岩相古地理图集. 北京: 科学出版社, 1~188.
-
刘军平, 王晓峰, 王小虎, 杨爱平, 宋冬虎, 田素梅, 夏彩香, 张坤, 杨仕潘. 2020. 滇中甸中地区中二叠世晚期镁铁—超镁铁质岩体特征及其与峨眉地幔柱关系——来自锆石U-Pb年龄及岩石地球化学证据. 地质论评, 66(5): 1284~1298.
-
刘玉平, 苏文超, 皮道会, 蒋少涌, 叶霖, 张乾, 周丽芹. 2009. 滇黔桂低温成矿域基底岩石的锆石年代学研究. 自然科学进展, 19(12): 1319~1325.
-
邵龙义, 高彩霞, 张超, 汪浩, 郭立君, 高彩红. 2013. 西南地区晚二叠世层序—古地理及聚煤特征. 沉积学报, 31(5): 856~866.
-
舒良树, 于津海, 贾东, 王博, 沈渭洲, 张岳桥. 2008. 华南东段早古生代造山带研究. 地质通报, 27(10): 1581~1593.
-
童金南, 楚道亮, 梁蕾, 舒文超, 宋海军, 宋婷, 宋虎跃, 吴玉样. 2019. 中国三叠纪综合地层和时间框架. 中国科学: 地球科学, 49(1): 194~226.
-
于鑫, 杨江海, 刘建中, 杜远生, 柴嵘. 2017. 黔西南晚二叠世龙潭组物源分析及区域沉积古地理重建. 地质学报, 91(6): 1374~1385.
-
曾允孚, 李孝全. 1995. 华南右江复合盆地的沉积构造演化. 地质学报, 69(2): 113~124.
-
张英利, 王宗起, 王刚, 李谦, 林健飞. 2016. 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. 地质论评, 62(1): 54~72.
-
张英利, 贾晓彤, 王宗起, 王坤明, 陈木银. 2019. 上扬子西南缘早三叠世嘉陵江组物源分析和构造环境: 沉积学, 重矿物电子探针和U-Pb年龄的限定. 地质学报, 93(12): 3197~3222.
-
张英利, 贾晓彤, 王坤明, 王宗起, 陈木银. 2021. 扬子西缘荥经地区三叠纪碎屑物源分析. 地质论评, 67(3), 1~15.
-
郑永飞, 张少兵. 2007. 华南前寒武纪大陆地壳的形成和演化. 科学通报, 52(1): 1~10.
-
朱民, 陈汉林, 周静, 杨树锋. 2016. 上扬子西南盐源盆地早三叠世物源体系及构造意义. 地球科学, 41(8): 1309~1321.
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摘要
峨眉山大火成岩省在形成后遭受了强烈的风化剥蚀,与右江盆地构成了独特的源-汇沉积体系,相关的碎屑沉积记录是重建峨眉山大火成岩省晚期火山序列、揭示大火成岩省岩浆演化的关键。本文对黔西南地区右江盆地北缘下三叠统下部飞仙关组开展了详细的沉积物源研究。飞仙关组泥岩由长石、石英和黏矿物等组成,具有低SiO2、高TiO2含量和低Al2O3/TiO2值的特征,具Eu的弱负异常,微弱的Nb、Ta负异常。基于Al2O3/TiO2和La/Sm物源图解分析,研究样品的主要物源由峨眉山大火成岩省的高-Ti玄武岩和少量酸性火山岩构成,这与右江盆地晚二叠世的碎屑沉积物源组成一致。碎屑锆石具有~260 Ma 的年龄峰值,对应锆石具有较低的Th/Nb和较高的Nb/Hf值,均支持峨眉山大火成岩省作为主要的沉积物源区,而同时存在的＞400 Ma的碎屑锆石则对应于峨眉山玄武质岩浆上升时所捕获的华南地壳物质。与上二叠统的碎屑锆石U-Pb年龄组成和锆石化学组成对比分析表明,峨眉山大火成岩省在晚二叠世到早三叠世早期剥蚀的火山岩构成了一定的火山序列,反映了该大火成岩省晚期从强烈地壳混染到分异结晶为主的岩浆演化过程。
Abstract
The Emeishan large igneous province (LIP) suffered intense weathering and denudation after its formation, and formed a unique source-sink depositional system with the Youjiang basin. The relevant clastic sedimentary records are the key to reconstruct the late volcanic sequence and reveal the Emeishan LIP magmatic evolution. In this paper, a detailed study on the provenance of the Lower Triassic Feixianguan Formation in the northern margin of the Youjiang basin in southwestern Guizhou Province was carried out. The mudstones of the Feixiaguan Formation are composed of feldspar, quartz and clay minerals. It is characterized by low SiO2, high TiO2 content and low Al2O3/TiO2 ratio. It shows weak negative Eu anomalies on the REE distribution patterns, and weak negative Nb-Ta anomalies on the primitive-mantle normalized trace element spider diagram. Based on Al2O3/TiO2 and La/Sm ratios analysis, the main provenance of the samples is composed of high-Ti basalts and a small amount of silicic volcanic rocks from the Emeishan large igneous province, which is consistent with the Late Permian clastic provenance in the Youjiang basin. Detrital zircons have a peak age of ~260 Ma, and the corresponding zircons have lower Th/Nb and higher Nb/Hf ratios, which support the Emeishan LIP as the main sediment source area. The detrital zircons with ages of＞400 Ma correspond to the crustal materials captured during the ascent of the ELIP basaltic magma. Compared with the U-Pb age and geochemical composition of detrital zircons from the Upper Permian, the volcanic rocks denuded from Late Permian to Early Triassic formed a certain volcanic sequence, reflecting the magmatic evolution process from strong crustal assimilation to fractional crystallization in the late-stage of the ELIP.
