【作者】 吴新伟；

【导师】 刘正宏；

【作者基本信息】 吉林大学 ， 构造地质学， 2018， 博士

【摘要】 本文以扎兰屯南部晚古生代地质体为研究对象,利用古生物年代学和锆石LA-ICP-MS U-Pb定年技术,确定了研究区晚古生代沉积地层的沉积时限、环境和物源以及岩浆岩的形成时代;利用岩浆岩的主量元素和微量元素特征,讨论了研究区火成岩岩石组合的时空变异、岩浆源区性质及其形成的构造背景。最终结合区域地质资料,探讨了研究区晚古生代区域构造演化历史。通过对扎兰屯南部大民山组、红水泉组、宝力高庙组、格根敖包组、大石寨组和哲斯组砂岩中碎屑锆石的U-Pb年代学研究,结合古生物化石证据和与上覆地层的接触关系,认为研究区内大民山组形成于晚泥盆世;红水泉组形成于早石炭世;宝力高庙组和格根敖包组形成于晚石炭世;大石寨组形成于早二叠世,哲斯组形成于中二叠世。晚泥盆世大民山组为一套海相沉积地层组合,碎屑锆石年龄主要为321-359Ma,此外含有少量前寒武纪锆石,说明大民山组沉积物源主要来自同时期的火山弧,其前寒武纪锆石可能来自松嫩地块古老基底,结合大民山组古生物特征和硅质岩成因特征,大民山组应沉积于活动陆缘环境下的弧前盆地。早石炭世红水泉组为一套复理石建造组合,碎屑锆石年龄主要为336-488Ma,并含有前寒武纪锆石年龄,其沉积物源主要来自于早古生代和晚古生代岩浆弧,而古老锆石应来自于松嫩地块古老基底,结合古生物特征,红水泉组应沉积于弧后-弧间盆地。晚石炭世宝力高庙组为一套陆缘沉积组合,碎屑锆石年龄集中在298-358Ma,此外还有少量早古生代锆石,沉积物源区主要来自晚古生代火山弧,较为单一,宝力高庙组应沉积于弧后盆地。晚石炭世格根敖包组为一套海陆交互相沉积岩组合,碎屑锆石年龄主要集中在337-412Ma,其物源主要为晚古生代火山弧,少量早古生代和前寒武纪锆石的存在表明该区可能有来自早期火山弧和古老基底的物质,综合古生物和岩相学特征,格根敖包组应形成于弧后盆地边缘。早二叠世大石寨组和中二叠世哲斯组为浅海相沉积,其碎屑锆石年龄为270Ma-390Ma,其主要来源于晚古生代岩浆弧,应沉积于伸展裂陷盆地。对扎兰屯南部晚古生代岩浆岩进行了锆石LA-ICP-MS U-Pb定年,其锆石均为半自形-自形,具有典型的岩浆震荡生长环带,结合高的Th/U比值,暗示其为岩浆成因。锆石U-Pb结果显示,研究区晚古生代岩浆活动可以分为四期:晚泥盆世、早石炭世、晚石炭世、早-中二叠世。扎兰屯南部晚泥盆世岩浆岩以大民山组火山岩为代表,具有较高的Ti O2含量和Fe O含量,富集Ti、Zr和亏损Y、Sr,具有典型的洋岛拉斑玄武岩特征,其Ti/Yb、Zr/Yb和La/Nb值也与洋岛玄武岩相似,说明大民山组碱性玄武岩形成于与俯冲有关的大洋板内洋岛环境。早石炭世岩浆岩以花岗质岩石为主,具有较高的Si O2含量、Al2O3含量和低的Mg#、Ni和Co含量,富集轻稀土元素和高场强元素,亏损重稀土元素和大离子亲石元素,表明早石炭世花岗质岩石起源于下地壳的部分熔融,应形成与同碰撞到晚造山的构造环境。晚石炭世岩浆活动包括了基性侵入岩和酸性火山岩。基性侵入岩具有较低的Si O2含量,高的Mg O、Fe O、Fe2O3以及较高的Sc、Co、Ni等含量,表明其原始岩浆起源于地幔物质的部分熔融。晚石炭世基性岩较高的Nb/U和Ta/U值说明原始岩浆受到了大规模陆壳物质的混染。晚石炭世格根敖包组酸性火山岩具有较低Y和Yb含量和较高的Sr含量,富集轻稀土元素,亏损重稀土元素,并具有微弱的Eu异常,具有埃达克岩石的特点,应是板块碰撞作用的产物。早二叠世岩浆活动主要为A型花岗质侵入岩和中基性侵入岩,两者从岩石组合特征上构成了类双峰式岩浆岩组合,可能代表了一种伸展环境。岩浆岩地球化学、沉积建造和物源综合分析表明:内蒙古扎兰屯南部地区晚泥盆世处于活动陆缘构造背景,并在弧前沉积盆地中形成了海相碎屑沉积岩建造和碱性玄武岩;早石炭世处于俯冲-碰撞环境并继续沉积海相沉积岩建造,钙碱性-高钾钙碱性的中-酸性弧岩浆岩发育,并在弧后伸展环境形成A型火山岩;晚石炭世进入陆-陆碰撞和碰撞后环境,形成了一套海陆交互相建造和具有埃达克质岩石特征的酸性火山岩;早二叠世研究区进入了造山后伸展阶段,形成了海相沉积建造、A型花岗岩以及类双峰式岩浆岩。更多还原

【Abstract】 This thesis studies the deposition ages and provenance of the Late Paleozoic sedimentary strata and the geochronology and geochemistry of the Late DevonianMiddle Permian igneous rocks in Southern of Zhalantun area with the method of LA-ICP-MS zircon U-Pb dating.Furthermor,this thesis discusses the spatial-temporal variation of igneous rocks associations,nature of magma sources and their tectonic settings based on major and trace elements for these igneous rocks.These chronological and geochemical data,together with regional geological data,provide constraints on the Late Paleozoic tectonic evolution of Southern of Zhalantun area.The dating results of detrital zircons from quartz sandstones in Daminshan,Hongshuiquan,Baoligaomiao,Gegen`aobao,Dashizhai and Zhesi,together with paleontological evidences,the contact relationship of the overlying strata and their dating results,indicate that the sedimentary ages of the Formations mentioned above are respectively the Late Devonian(Daminshan),the Early Carboniferou(Hongshuiquan)the Late Carboniferous(Baoligaomiao and Gegen`aobao),the Early Permian(Dashizhai)and the middle Permian(Zhesi).The Late Devonian Daminshan Formation is composed mainly of marine clastic formations,the dating results of detrital zircons from sandstone indicate the sediments predominantly came from the Paleozoic igneous arc and minor older basement of Songnen massif.Associated with the features of fossils and geochemistry of siliceous rocks in Daminshan Formation,the Daminshan Formation may represented forearc sediments.The early Carboniferous Hongshuiquan Formation is composed mainly of flysch formation,the dating results of detrital zircons from sandstone indicate the sediments predominantly came from the Paleozoic igneous arc and a few older basement of Songnen massif.Associated with the features of fossils in Hongshuiquan Formation,the Formation may represented backarc-interarc basin sediments.The Late Carboniferous Baoligaomiao Formation is composed mainly of terrigenous deposit formation,the dating results of detrital zircons from sandstone indicate the sedimental source is single and predominantly came from the Late Paleozoic igneous arc and a few older basement of Songnen massif.Associated with the features of fossils in Baoligaomiao Formation,the Baoligaomiao Formation may represented backarc basin sediments.The Late Carboniferous Gegen`aobao Formation is composed mainly of marine terrigenous deposit formation,the dating results of detrital zircons from sandstone indicate the sediments predominantly came from the Paleozoic igneous arc and a few igneous arc of Early Paleozoic and older basement of Songnen massif.Associated with the features of fossils and rock association in Gegen`aobao Formation,the Formation may represented backarc basin sediments.The early Permian Dashizhai and Shoushangou Formation and middle Permian Zhesi Formation are composed mainly of neritic marine deposit formation,the dating results of detrital zircons from sandstone indicate the sediments predominantly came from the Late Paleozoic igneous arc,the Formation may represented rifted basin sediments.Zircons from the igneous rocks in the southern of zhalantun area display fine-scale oscillatory growth zoning and are euhedral-subhedral in shape in CL images,together with their high Th/U ratios,implying their magmatic origin.LA-ICP-MS zircon U-Pb dating results indicate that the magmatic events can be subdivided into four stages: The Late Devonian,early Carboniferous,Late Carboniferou,early-middle Permian.The Late Devonian magmatism in the study area is dominated by volcanic rock in Daminshan Formation.They are characterized by high Ti O2,Fe O,Ti and Zr concentrations,low Y and Sr concentrations,and have similar values of Ti/Yb,Zr/Yb and La/Nb,suggesting that they formed in an ocean island environment within the oceanic plate.The early Carboniferous granitoids are characterized by high Si O2 and Al2O3 concentrations and low Mg#,Ni and Co concentrations,enrichments in LREES and LILES,and depletion in HREEs and HFSEs,suggesting that their primary magmas could form by partial melting of lower crust.Taken together,we conclude that they formed in syn-collision to late orogenic setting.The Late Carboniferous basic rocks are characterized by low Si O2,Sc,Co and Ni concentrations and High Mg O,Fe O,Fe2O3 concentrations,,suggesting that their primary magmas could form by partial melting of mantle.The values of Nb/U and Ta/U indicate the primary magmas have been significantly contaminated by crustal components.The volcanic rocks in Gegen`aobao Formation are characterized by low Y and Yb concentrations and high Sr,enrichment in LREEs and depletion in HREEs and weakly negative Eu anomaly.The volcanic rocks are being an affinity to adakitic rocks.Taken together,we conclude that The Late Carboniferous igneous rocks formed in a thickened lower continental crust accreted in Neoproterozoic.The early Permian granitoids and middle-basic intrusive rocks constitute a bimodal igneous rock association,suggesting that they could form under a post-collisional extensional environment related to collapse of thickened crust caused by collision between the Songnen massif and Xing`an massif.The Late Paleozoic sedimentary formations and the provenance analysis indicate that the Late Devonian marine sedimentary formations and alkali basalt reveal that an active continental margin forearc basin setting,and that early Carboniferous marine sedimentary formations indicate a subduction-collison setting,consistent with the occurrence of calc-alkaline to high-k calc-alkaline arc magma suites and A-style rhyolite in backarc basin,the Late Carboniferous neritic terrigenous clastic and adakitic volcanic rocks suggest that they formed in an collision and rapidly uplift environment.The early Permian A-style and similar bimodal igneous rocks represent a post-orogenic extensional environment and form a marine sedimentary.更多还原