西藏西南部三叠系穷果群的地层学与岩相
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摘要
在区域地质调查、实测地层剖面和区域对比基础上,对西藏西南部雅鲁藏布江缝合带西段的穷果群进行了研究,认为穷果群仅分布于萨嘎以西的仲巴微地体,萨嘎以东雅鲁藏布江缝合带中过去识别的穷果群实为构造混杂岩(三叠系—古近系)修康岩群的大型外来岩块;与下伏二叠系曲嘎群呈(侵蚀)假整合接触,上未见顶,与修康岩群之间可能不存在直接的整合/不整合接触关系;时代为三叠纪Induan期—Carnian期。依据岩相、层位差异,穷果群由下向上可划分为屯具场组、屯具日组和尼多曲组3个地层单元。屯具场组以石英砂岩为特征,向上夹含岩屑砂岩、粉砂岩和板岩或互层,厚30~550m,顶与屯具日组整合接触,时代暂置于早三叠世早期的Induan期,大多分布于霍尔巴—仲巴地区,其下部沉积环境为(可含障壁)滨岸,向上演变为为浅表海;屯具日组以晶粒灰岩为特征夹板岩/页岩、粉砂岩,或与之互层,产较为丰富的菊石、双壳类、牙形石等化石,厚200~800m,上未见顶或与尼多曲组整合接触,广泛分布于仲巴微地体,依据Claraia和Eumorphotis双壳动物群、Flemingites和Meekoceras菊石动物群、Neospathodus牙形石动物群,其时代可归属于早三叠世晚期的Olenekian期—中三叠世,沉积于较深陆表海环境;尼多曲组以黑色、深灰色碳质板岩为特征,厚300~500m,与下伏地层整合或假整合或断层接触,上未见顶,分布于仲巴地区,牙形石Metapolygnathus cf.polygnathiformis指示其时代为晚三叠世早期的Carnian期,沉积于深表海。
On the basis of 1/50 000 regional geological mapping and stratigraphic investigation,we analyzed the stratigraphy and lithofacies of the shallow marine Triassic Qiongguo Group in southwestern Tibet,which belongs to the Zhongba microterrane,the western part of the famous Yarlung Zangbo Suture Zone.Its spatial distribution and stratigraphic relationship with other strata are revised.It is proposed that the Qiongguo Group only occurs in the Zhongba microterrane to the west of the Saga area.Strata previously described as the Qiongguo Group to the east of the Saga area represent large olistoliths of the tectonic mélange Xiukang Lithic Unit(i.e.the so-called Xiukang Group).The Qiongguo Group overlies unconformably the Permian Quga Group.Fossil ammonites,bivalves and conodonts indicate that the Qiongguo Group ranges in age from the Induan to the Carnian of the Triassic.The Qiongguo Group can be divided into three formations,including,in ascending order,Tunjuchang Formation,Tunjuri Formation,and Niduoqu Formation.The Tunjuchang Formation is 30-50 min thickness,characterized by quartz arenite that transitions upsection into lithic sandstones,siltstones and slates deposited in shallow-water near-shore environments on an epicontinental sea.It unconformably overlies Permian strata and conformably underlies the Tunjuri Formation in the Zhongba area.It is tentatively regarded as early Triassic Induan in age.The overlying Tunjuri Formation is 200-800 min thickness in the Zhongba microterrane and composed of crystalline limestones intercalated with slates,shales,and siltstones.It may be conformably overlain by the Niduoqu Formation.The occurrence of bivalves(e.g.,Claraia and Eumorphotis),ammonites(e.g.,Flemingites and Meekoceras),conodonts(e.g.,Neospathodus)suggests that the Tunjuri Formation is likely Olenekian-Ladinian in age and was deposited in deeper environments in an epicontinental sea.The Niduoqu Formation is 300-500 mthick in the Zhongba area,featured by dark gray-black carbonaceous slates.It conformably overlies the Tunjuri Formation or is in a fault contact with Permian strata.The occurrence of the conodont fossil Metapolygnathuscf.polygnathiformis indicates that this formation was deposited in the Carnian in a deeper epicontinental sea.
On the basis of 1/50 000 regional geological mapping and stratigraphic investigation,we analyzed the stratigraphy and lithofacies of the shallow marine Triassic Qiongguo Group in southwestern Tibet,which belongs to the Zhongba microterrane,the western part of the famous Yarlung Zangbo Suture Zone.Its spatial distribution and stratigraphic relationship with other strata are revised.It is proposed that the Qiongguo Group only occurs in the Zhongba microterrane to the west of the Saga area.Strata previously described as the Qiongguo Group to the east of the Saga area represent large olistoliths of the tectonic mélange Xiukang Lithic Unit(i.e.the so-called Xiukang Group).The Qiongguo Group overlies unconformably the Permian Quga Group.Fossil ammonites,bivalves and conodonts indicate that the Qiongguo Group ranges in age from the Induan to the Carnian of the Triassic.The Qiongguo Group can be divided into three formations,including,in ascending order,Tunjuchang Formation,Tunjuri Formation,and Niduoqu Formation.The Tunjuchang Formation is 30-50 min thickness,characterized by quartz arenite that transitions upsection into lithic sandstones,siltstones and slates deposited in shallow-water near-shore environments on an epicontinental sea.It unconformably overlies Permian strata and conformably underlies the Tunjuri Formation in the Zhongba area.It is tentatively regarded as early Triassic Induan in age.The overlying Tunjuri Formation is 200-800 min thickness in the Zhongba microterrane and composed of crystalline limestones intercalated with slates,shales,and siltstones.It may be conformably overlain by the Niduoqu Formation.The occurrence of bivalves(e.g.,Claraia and Eumorphotis),ammonites(e.g.,Flemingites and Meekoceras),conodonts(e.g.,Neospathodus)suggests that the Tunjuri Formation is likely Olenekian-Ladinian in age and was deposited in deeper environments in an epicontinental sea.The Niduoqu Formation is 300-500 mthick in the Zhongba area,featured by dark gray-black carbonaceous slates.It conformably overlies the Tunjuri Formation or is in a fault contact with Permian strata.The occurrence of the conodont fossil Metapolygnathuscf.polygnathiformis indicates that this formation was deposited in the Carnian in a deeper epicontinental sea.
引文
河北省地质调查院.2005.中华人民共和国区域地质调查报告和地质图,1/25万《日新幅》(H44C001001)、《札达县幅》(H44C001002)、《姜叶马幅》(H44C002002).
河北省地质调查院.2006.中华人民共和国区域地质调查报告,1/25万《亚热幅》、《普兰县幅》(国内部分).
河北省区域地质调查研究所,石家庄经济学院.2002.中华人民共和国区域地质调查报告,1/25万《萨嘎县幅》(H45C003001)、《吉隆县幅》(H45C004001)(国内部分).
河北省区域地质调查研究所,石家庄经济学院.2003.中华人民共和国区域地质调查报告,1/25万《桑桑区幅》(H45C003002).
河北省区域地质调查研究院.2005.中华人民共和国区域地质调查报告,1/25万《霍尔巴幅》(H44C002004)和《巴巴扎东幅》(H44C003004)(国内部分).
湖北省地质调查研究院.2003.中华人民共和国区域地质调查报告,1/25万《拉孜县幅》(H45C003003).
黄圭成,莫宣学,徐德明,雷义均,李丽娟.2006.西藏西南部达巴-休古嘎布蛇绿岩带的形成与演化.华南地质与矿产,3:1-9.
李文忠,沈树忠.2005.西藏雅鲁藏布江缝合带二叠纪灰岩体的动物群及其古地理意义.地质论评,51(3):225-234.
李祥辉,王成善,李亚林,魏玉帅,陈曦.2014a.仲巴微地体之定义及构成.地质学报,88(8):1372-1381.
李祥辉,王成善,李亚林,魏玉帅,陈曦.2014b.西藏仲巴地区曲嘎组的拆解.地质通报,33(5):614-628.
梁定益,张宜智,聂泽同,奚成德.1991.西藏阿里地区地层//郭铁鹰,梁定益,张宜智等.西藏阿里地质.武汉:中国地质大学出版社.1-109.
罗凯,李祥辉,王成善,李亚林,葛玉魁,张宝森,李龙.2012.西藏仲巴地区早古生代鹦鹉螺化石的发现及地质意义.地质通报,31(4):36-39.
盛怀斌,曲景川.1991.西藏仲巴地区的一个晚泥盆世菊石动物群.中国地质科学院院报,22:179-189.
孙高远,胡修棉.2012.仲巴地体的板块亲缘性:来自碎屑锆石U-Pb年代学和Hf同位素的证据.岩石学报,28(5):1635-1646.
孙立新,张振利,范永贵,贾建称,李金和.2002.西藏仲巴晚白垩世硅质岩放射虫化石的发现.地质通报,21(3):172-174.
王成善,夏代祥,周祥,陈建平,陆彦,王根厚,何政伟,李祥辉,万晓樵,曾庆高,普布次仁,刘志飞.1996.雅鲁藏布江缝合带与喜马拉雅地质.北京:地质出版社.1-72.
王玉净,杨群,松冈笃,小林健太,武井雅彦,曾庆高.2002.藏南泽当雅鲁藏布缝合带中的三叠纪放射虫.微体古生物学报,3:1-13.
吴新国,吕继东.2006.雅鲁藏布江缝合带内构造岩片划分及形成---以仲巴-桑桑段为例.大地构造与成矿学,30(3):320-325.
西藏自治区地质矿产局.1993.西藏自治区区域地质志.北京:地质出版社.1-707.
西藏自治区地质矿产局.1997.西藏自治区岩石地层.武汉:中国地质大学出版社.1-302.
西藏自治区地质调查院.2002.中华人民共和国区域地质调查报告和地质图,1/25万《日喀则市幅》(H45C003004).
西藏自治区地质矿产局区域地质调查大队.1983.中华人民共和国区域地质调查报告,1/100万《日喀则幅》(H-45)和《亚东幅》(G-45),地质部分.
西藏自治区地质矿产局区域地质调查大队.1987.中华人民共和国区域地质调查报告,1/100万《噶大克幅》(H-44)地质部分.
杨群,松冈笃,王玉净.2002.西藏南部放射虫微体古生物研究进展.微体古生物学报,19(2):105-111.
余光明,王成善.1990.西藏特提斯沉积地质.北京:地质出版社.1-197.
张振利,专少鹏,李广栋,张计东,孙肖,李先,汪立军,刘鸿章.2007.藏南仲巴地层分区才巴弄组变质玄武质火山岩的发现及其意义.地质通报,26(4):410-416.
中国地质大学(北京).2013.中华人民共和国区域地质调查报告和地质图,1/5万西藏仲巴县城北(拉果错)地区《江木那幅(H44E014024)、《格绒松多幅》(H45E013002)、《岗珠淌幅》(H45E014001)、《穷果公社幅》(H45E014002).
中国地质大学(北京).2014.中华人民共和国区域地质调查报告和地质图,1/5万西藏仲巴县城西地区《归桑幅》(H44E012022)、《郭雅幅》(H44E013022)、《岗久幅》(H44E013023)、《朔幅》(H44E013024)、《直那地布幅》(H44E014022)、《巴巴扎东幅》(H44E014023).
An W,Hu X M&Garzanti E.2016.Sandstone provenance and tectonic evolution of the Xiukang Mélange from Neotethyan subduction to India-Asia collision(Yarlung-Zangbo suture,south Tibet).Gondwana Research(in press).http://dx.doi.org/10.1016/j.gr.2015.08.010.
Dai Jing-en,Wang Cheng-shan,Hébert R,Santosh M,Li Ya-lin&Xu Jun-yi.2011.Petrology and geochemistry of peridotites in the Zhongba ophiolite.Yarlung Zangbo Suture Zone:implications for the Early Cretaceous intra-oceanic subduction zone within the Neo-Tethys.Chemical Geology,288:133-148.
Jadoul F,Berra F&Garzanti E.1998.The Tethys Himalayan passive margin from Late Triassic to Early Cretaceous(South Tibet).Journal of Asian Earth Sciences,16:173-194.
河北省地质调查院.2006.中华人民共和国区域地质调查报告,1/25万《亚热幅》、《普兰县幅》(国内部分).
河北省区域地质调查研究所,石家庄经济学院.2002.中华人民共和国区域地质调查报告,1/25万《萨嘎县幅》(H45C003001)、《吉隆县幅》(H45C004001)(国内部分).
河北省区域地质调查研究所,石家庄经济学院.2003.中华人民共和国区域地质调查报告,1/25万《桑桑区幅》(H45C003002).
河北省区域地质调查研究院.2005.中华人民共和国区域地质调查报告,1/25万《霍尔巴幅》(H44C002004)和《巴巴扎东幅》(H44C003004)(国内部分).
湖北省地质调查研究院.2003.中华人民共和国区域地质调查报告,1/25万《拉孜县幅》(H45C003003).
黄圭成,莫宣学,徐德明,雷义均,李丽娟.2006.西藏西南部达巴-休古嘎布蛇绿岩带的形成与演化.华南地质与矿产,3:1-9.
李文忠,沈树忠.2005.西藏雅鲁藏布江缝合带二叠纪灰岩体的动物群及其古地理意义.地质论评,51(3):225-234.
李祥辉,王成善,李亚林,魏玉帅,陈曦.2014a.仲巴微地体之定义及构成.地质学报,88(8):1372-1381.
李祥辉,王成善,李亚林,魏玉帅,陈曦.2014b.西藏仲巴地区曲嘎组的拆解.地质通报,33(5):614-628.
梁定益,张宜智,聂泽同,奚成德.1991.西藏阿里地区地层//郭铁鹰,梁定益,张宜智等.西藏阿里地质.武汉:中国地质大学出版社.1-109.
罗凯,李祥辉,王成善,李亚林,葛玉魁,张宝森,李龙.2012.西藏仲巴地区早古生代鹦鹉螺化石的发现及地质意义.地质通报,31(4):36-39.
盛怀斌,曲景川.1991.西藏仲巴地区的一个晚泥盆世菊石动物群.中国地质科学院院报,22:179-189.
孙高远,胡修棉.2012.仲巴地体的板块亲缘性:来自碎屑锆石U-Pb年代学和Hf同位素的证据.岩石学报,28(5):1635-1646.
孙立新,张振利,范永贵,贾建称,李金和.2002.西藏仲巴晚白垩世硅质岩放射虫化石的发现.地质通报,21(3):172-174.
王成善,夏代祥,周祥,陈建平,陆彦,王根厚,何政伟,李祥辉,万晓樵,曾庆高,普布次仁,刘志飞.1996.雅鲁藏布江缝合带与喜马拉雅地质.北京:地质出版社.1-72.
王玉净,杨群,松冈笃,小林健太,武井雅彦,曾庆高.2002.藏南泽当雅鲁藏布缝合带中的三叠纪放射虫.微体古生物学报,3:1-13.
吴新国,吕继东.2006.雅鲁藏布江缝合带内构造岩片划分及形成---以仲巴-桑桑段为例.大地构造与成矿学,30(3):320-325.
西藏自治区地质矿产局.1993.西藏自治区区域地质志.北京:地质出版社.1-707.
西藏自治区地质矿产局.1997.西藏自治区岩石地层.武汉:中国地质大学出版社.1-302.
西藏自治区地质调查院.2002.中华人民共和国区域地质调查报告和地质图,1/25万《日喀则市幅》(H45C003004).
西藏自治区地质矿产局区域地质调查大队.1983.中华人民共和国区域地质调查报告,1/100万《日喀则幅》(H-45)和《亚东幅》(G-45),地质部分.
西藏自治区地质矿产局区域地质调查大队.1987.中华人民共和国区域地质调查报告,1/100万《噶大克幅》(H-44)地质部分.
杨群,松冈笃,王玉净.2002.西藏南部放射虫微体古生物研究进展.微体古生物学报,19(2):105-111.
余光明,王成善.1990.西藏特提斯沉积地质.北京:地质出版社.1-197.
张振利,专少鹏,李广栋,张计东,孙肖,李先,汪立军,刘鸿章.2007.藏南仲巴地层分区才巴弄组变质玄武质火山岩的发现及其意义.地质通报,26(4):410-416.
中国地质大学(北京).2013.中华人民共和国区域地质调查报告和地质图,1/5万西藏仲巴县城北(拉果错)地区《江木那幅(H44E014024)、《格绒松多幅》(H45E013002)、《岗珠淌幅》(H45E014001)、《穷果公社幅》(H45E014002).
中国地质大学(北京).2014.中华人民共和国区域地质调查报告和地质图,1/5万西藏仲巴县城西地区《归桑幅》(H44E012022)、《郭雅幅》(H44E013022)、《岗久幅》(H44E013023)、《朔幅》(H44E013024)、《直那地布幅》(H44E014022)、《巴巴扎东幅》(H44E014023).
An W,Hu X M&Garzanti E.2016.Sandstone provenance and tectonic evolution of the Xiukang Mélange from Neotethyan subduction to India-Asia collision(Yarlung-Zangbo suture,south Tibet).Gondwana Research(in press).http://dx.doi.org/10.1016/j.gr.2015.08.010.
Dai Jing-en,Wang Cheng-shan,Hébert R,Santosh M,Li Ya-lin&Xu Jun-yi.2011.Petrology and geochemistry of peridotites in the Zhongba ophiolite.Yarlung Zangbo Suture Zone:implications for the Early Cretaceous intra-oceanic subduction zone within the Neo-Tethys.Chemical Geology,288:133-148.
Jadoul F,Berra F&Garzanti E.1998.The Tethys Himalayan passive margin from Late Triassic to Early Cretaceous(South Tibet).Journal of Asian Earth Sciences,16:173-194.