【作者】 王超；

【导师】 刘良；

【作者基本信息】 西北大学 ， 矿物学、岩石学、矿床学， 2011， 博士

【摘要】 前寒武纪占据了目前为止整个地球地质发展时期的90%,认识该时期的地球演化历史是我们探索地球乃至行星的形成与发展规律的基本前提。塔里木克拉通为中国三大克拉通之一,其前寒武纪地质研究程度远低于我国的华北克拉通和扬子克拉通,其现有的研究成果不能系统刻画该地区完整的前寒武纪地质演化历史。本文通过对塔里木盆地南缘(铁克里克和阿尔金地区)各前寒武纪沉积地层和侵入体进行精确的锆石年代学、地球化学和变质岩石学分析,系统厘定了塔里木盆地南缘各前寒武纪地质体的形成时代、性质和变质历史；在对沉积地层同位素年代学分析的基础上,建立了各单元的碎屑锆石谱系图,分析其物源和古地理环境,为重建塔里木克拉通前寒武纪地质演化历史和全球超大陆复原提供约束资料；通过锆石Hf同位素分析,对塔里木盆地南缘前寒武纪地壳演化作用进行了初步讨论。本论文主要取得了以下几方面成果：1、进一步获得塔里木盆地南缘新太古代—古元古代地质体与2.0-1.8 Ga变质作用的新证据。获得阿尔金拉配泉地区的米兰岩群形成时代为新太古代(2.7-2.6 Ga),并经历了-2.0-1.8 Ga的变质作用；黑山地区的米兰岩群的原岩时代为古元古代,约2.0 Ga,也经历了-1.8 Ga的变质作用；获得铁克里克地区赫罗斯坦岩群角闪斜长片麻岩形成时代为2.27 Ga,经历了1.83Ga的变质作用。铁克里克地区古元古代赫罗斯坦岩群和阿尔金地区米兰岩群锆石年代学研究表明塔里木盆地南缘存在一次广泛的2.0-1.8 Ga的区域变质作用,说明塔里木陆块南缘存在与全球Columbia超大陆汇聚事件一致的地质记录。2、对铁克里克和阿尔金地区的前寒武纪地层时代和岩浆作用时代进行了系统工作,许多地层时代被重新厘定,发现并确定了大量新元古代地层和岩浆作用。在铁克里克地区,确定原划为古元古代的埃连卡特岩群和卡拉喀什岩群、长城纪的塞拉加兹塔格岩群、青白口纪苏库罗克组和南华纪的恰克马克力克组主体应形成于新元古代,为青白口纪—南华纪。其中发育780—789 Ma火山岩和787—845 Ma的花岗质岩浆作用。在阿尔金地区,确定原划为太古代—古元古代的阿尔金岩群、红柳沟蓟县纪塔昔达坂群和部分原划为长城纪的巴什库尔干岩群应为新元古代地层。阿尔金岩群中发育900—930 Ma的花岗质岩浆作用。3、分析确定了塔里木盆地南缘新元古代岩浆作用的性质和期次。确定南阿尔金地区存在900—930 Ma碰撞汇聚型花岗岩,可能与Grenvillian造山事件相关的记录,代表一古老的活动大陆边缘；在新元古代晚期700-800Ma,阿尔金和铁克里克地区均表现为造山后的伸展裂解,指示塔里木板块南缘前寒武记基底存在新元古代Rodinia超大陆裂解事件4、针对南阿尔金超高压石榴子石橄榄岩和淡水泉含石榴石蓝晶长英质高压麻粒岩,开展了变质演化的深入研究,首次确定其经历了顺时针型的P-T-t轨迹,揭示其是新元古代的岩浆岩在早古生代发生陆壳深俯冲后折返的产物,结合前人的研究成果,进一步确定阿尔金岩群经历了早古生代(-500Ma)的高压—超高压变质作用,分析提出它们代表新元古代地壳在早古生代的地壳再造。阿尔金岩群的变质岩石学研究表明,阿尔金南缘淡水泉—带出露的含石榴石蓝晶长英质片麻岩的峰期矿物组合为Grt+Ky+Per+Qz+Rut,利用三相长石温度计及GASP压力计,获得峰期变质温压条件为T=9501000℃,P=2.42-2.49Gpa,属长英质高压麻粒岩。根据温压估算和实验岩石学资料,阿尔金石榴子石橄榄岩经历了早期尖晶石橄榄岩相→石榴子石橄榄岩相(峰期变质P、T为4.2-6.0 GPa、920-990℃)→角闪石石榴子石橄榄岩相→尖晶石橄榄岩相的转变。岩石地球化学特征和主要矿物低的Cr2O3含量说明英尕利萨依石榴子石橄榄岩的具有Fe-Ti型橄榄岩或“壳源”橄榄岩特征。结合钻石U-Pb年龄和Hf同位素特征分析,石榴子石橄榄岩和石榴子石辉石岩的原岩为早期新元古代幔源岩浆侵入地壳后的堆晶杂岩,随后该岩石发生陆壳深俯冲(＞100km),在约500 Ma经历超高压变质,然后折返到地面。5、通过对塔里木盆地南缘新元古代岩浆作用和地层碎屑锆石年代学研究,首次对铁克里克和阿尔金地区的新元古代沉积地层的沉积物源和古地理进行了分析,揭示塔里木盆地南缘在新元古代晚期主体为伸展背景,表现为断陷伸展盆地或拉张沉陷陆表海盆地。阿尔金地区新元古代地层中碎屑锆石年龄构成了多期峰值：1750-1850 Ma、1550Ma、1300-1400 Ma、900-925 Ma、777-834 Ma、648 Ma和500 Ma。其中阿尔金岩群主要年龄峰值为800 Ma、1350 Ma和1480Ma,不具有米兰岩群和侵入米兰岩群的古侵入体年代学信息,说明米兰岩群未对阿尔金岩群形成物源,也进一步说明阿尔金中新元古代时期米兰岩群未隆升或者在二者之间存在地理上的屏障限制了古老克拉通物质的进入。巴什库尔干岩群具有多期年龄峰值：647 Ma、770 Ma、843 Ma,905 Ma、1350 Ma、1900 Ma和2600 Ma等年龄,显示其具有米兰岩群、侵入米兰岩群古元古代侵入体和阿尔金岩群的物源信息,并且巴什库尔干岩群沉积时代较晚(647 Ma),说明巴什库尔干岩群是在新元古代晚期的一个断陷盆地,受到南北两侧物源的供给。铁克里克地区新元古代地层中碎屑锆石主要峰值为：2500-2700 Ma,2200-2300 Ma,1800-1950 Ma,835-850 Ma,787-800 Ma。铁克里克北部的苏库罗克组和恰克马克组具有相似的年龄谱系(840Ma、1900Ma和2600Ma),且该地层沉积最大时代为830 Ma；南部的塞拉加兹塔格岩群和埃连卡特岩群沉积时代介于744-780 Ma,它们均存在古元古代的碎屑锆石信息(1900 Ma和2600 Ma),说明它们均存在赫罗斯坦岩群和其中的侵入体物源信息,铁克里克南部后期未对北部提供物源,结合铁克里克南缘的板内火山岩特征,该时期铁克里克总体表现为向南变深的拉张沉陷陆表海盆地。6、研究发现在铁克里克地区古元古代存在新生地壳生长和太古宙地壳的再造作用,而新元古代地壳主要为古元古代地壳活化再造的产物。阿尔金地区新元古代地壳主要为中元古代地壳再造,新元古代地壳在古生代又遭受了改造。因此,地壳再造过程贯穿整个前寒武纪地质演化历史。锆石Hf同位素分析表明赫罗斯坦岩群中的角闪斜长片麻岩(2.33 Ga)为太古代陆壳物质(2.86 Ga)在2.33 Ga时再循环的产物,2.27-2.21 Ga和1.83 Ga时的深熔变质事件代表了地壳物质古元古代的再造；锆石Hf同位素分析表明,新元古代塞拉加兹塔格岩群主体(787 Ma左右)是由古元古代的地壳物质(约1900 Ma)经历岩浆重熔再沉积形成的,表现为古老地壳的再造,而-1986 Ma的古元古代年龄锆石源区两阶段模式年龄介于2241-2813 Ma,具有正和负的εHf(t)值,说明这类锆石的母岩可能分别对应古元古代的新生地壳和太古宙地壳再造。更多还原

【Abstract】 Precambrian time covers approximately 90% of geologic time of the Earth’s history, starting with the Earth’s creation about 4.5 billion years ago and ending with the initial formation to the beginning of life almost four billion years later. During this time range, the Earth, Sun and Moon formed. As the Earth cooled, it developed its initial atmosphere and ocean, and life in the end period. Studies on early stage of the evolution of the Earth are important for us to implore the formation and evolution of earth and its planetary neighbours.In China, there are three old cratons:the North China craton, the Yangtze craton and the Tarim craton. Tarim craton is located in the northwest of China. In the past time, lesser work of Precambrian research has been done on the Tarim craton than that of the North China craton and the Yangtze, owning to the adverse environmental and poor traffic conditions.In this paper we subject previously proposed correlations for Precambrian terrains (Tiekelike and Altyn) of south margin of Tarim to a series of rigorous geochronological, geochemical and metamorphic petrology tests, based on new LA-ICP-MS U-Pb ages on granites, volcanics and sedimentary successions. This study provides insight into the timing nature of the magmatism of the Tarim during the Precambrian. Base on the detrital provenance study from clastic sedimentary rocks in the Tiekelike and Altyn, I hope to infer the Neoproterozoic tectonic evolution and palaeogeography of the south margin of Tarim relative the formation and the break-up of Rodinia. Additionally, I hope to clarify the crust evolution of the south margin of Tarim and its nature, whether by juvenile accretion, or by reworking of the rocks involved in the Precambrian.The main viewpoints and conclusions in this thesis are as follows:(1) Five U-Pb zircon age groups from South margin of Tarim show the Archaean-Palaeoproterozoic evolutionary history between 2.7 and 1.8 Ga:ca.3.6 and 2.7 Ga continental growth events at ca. Archean; the cratonization at ca.2.6-2.4 Ga; and the 2.0-1.83 Ga metamorphic event, suggest that the remnants of Paleoproterozoic orogens relative to the assembly of Columbia supercontinent.(2) Our study also places tight constraints on the age of Precambrian sedimentation. The youngest zircon population would represent a good approximation of the maximum age of sedimentation. In this studies, the Precambrian sequences in Tieleleke, the namely Paleoproterozoic-Mesoproterozoic Ailiankete Group, Kalakashi Group and Sailajiazitage Group, Mesoproterozoic-Neoproterozoic Sukuluoke Formation and Nanhua System Qiakemakelike Formation were defined to the Neoproterozoi strata. These strata are mainly composed by the clastic rocks deposited at ca.834-849 Ma and volcanic rocks emplaced between 780 and 789 Ma. Granitoids were intruded at different times during 787-845 Ma in Tieleleke. In Altyn Tagh, the namely Archean-Paleoproterozoic Altyn Group. Jixian System Taxidaban Group and Changcheng System Bashikuergan Group were defined to Neoproterozoic sequences by new detail LA-ICP-MS zircon dating. In this region, the Precambrian granitoids yielded mainly 900-930 Ma ages.(3) The nature and time of Neoproterozoic (930-700 Ma) mamgamtic rocks in the south margin of Tarim Block were identified. This study presents data for ca.787 Ma intraplate volcanic rocks and A-type granites in Tiekeleke. In Altyn, there are syn-collision granites at 900-930 Ma and post-collision granites at ca.703 Ma. These mamgatism probably reflect supercontinent Rodinia assembly and break-up in the south margin of Tarim Block.(4) Danshuiquan Ky-Grt-bearing felsic HP granulite and Jianggelesayi UHP Grt peridotites suggest the Altyn Group underwent the HP-UHP metamorphism. The Altyn Group represents the Neoproterozoic crust exprenced Early Paleozoic reworking at-500 Ma related to the subduction and exhumation.The peak metamorphic mineral assemblage in garnet-kyanite-bearing felsic gneiss from Altyn Group of Danshuiquan, indicates that the gneiss is a suit of high-pressure granulite, and the metamorphic condition is T=950-1000℃, P=2.42-2.49 Gpa according to the GASP barometers. Petrology and P-T estimations of the Yinggelesayi garnet peridotites recorded the transformation from early spinel peridotite into garnet peridotite (peak stage at 4.2-6.0 GPa and 920-990℃) into amphibole garnet peridotite stage into spinel peridotite stage. The P-T evolution is interpreted as a result of subduction and exhumation processes. Combined with information on compositions of whole rocks and minerals, P-T estimations and field relationships, the UHP garnet peridotites from the South Altyn Tagh is assumed to have been formed as cumulates crystallized from a mantle-derived magma intruded the continental crust, and was then subducted to depths of more than 100 km, and then metamorphosed in ultra-high-pressure conditions at-500 Ma.(5) U-Pb ages of detrital zircons from the new defined Neoproterozoic part of Tiekelike and Altyn were used to constrain the palaeogeography and provenance on the southern margin of Tarim during the Neoproterozoic. At the Late Neoproterozoic, the southern margin of Tarim representing an extension rift basin or extension continental sea basin. There are some significant differences in zircon age populations have been found in the sequences of the two tectonic units, although they show the same dominant age populations and even the same minor peaks in the late Neoproterozoic input.The Altyn Group deposits with a large input of early Paleozoic, early Neoproterozoic and Mesoproterozoic zircons while no peaks of cratonic Paloproterozoic ages, and records the Grenvillian magmatism and age surce, suggesting an active margin arc setting. The Bashikuergan Group, with the age peaks of 647 Ma、770 Ma、843Ma,905Ma、1350 Ma、1900Ma和2600Ma, show the older detritus from the cratonic Paloproterozoic Milan Group and the relative proportions of early Neoproterozoic and late Mesoproterozoic zircons from the Altyn Group. The Bashikuergan Group are preserved may have been located at the back-arc basin, attached to the arc-system.The sediments preserved in Tiekelike show the same dominant age populations: 2500-2700 Ma,2200-2300 Ma,1800-1950 Ma,835-850,787-800 Ma. But the Sukuluoke Formation and Qiakemake Formation from the northern of Tiekelike have its youngest detrital zircon population is 830 Ma, however the southern of Tiekelike has a younger depositional age constraint of 744-780 Ma which is younger than northern units of Tiekelike. Combined with the extensional magmanism in Tiekelike, we interpreted the Tiekelike as an south-ward deeping extension continental sea basin at Neoproterozoic.(6) Zircon Hf isotope analyses indicate that the Paleoproterozoic basement of Tiekeleke is a consequence of juvenile addition and Archean crust-reworking; And the Neoproterozoic crust display a contribution of Paleoproterozoic components reworking.Heluositan Group indicates the gneisses formed by melting of Archean crust (2.8 Ga) at 2.33 Ga. The second and third stage at ca.2.27-2.21 Ga and 2.08 Ga represent the reworked crust during compressive stresses. Zircon Hf isotopic data from Sailajiazitage Group show that older zircons (-1994 Ma) have crustal model ages are 2272-2784 Ma, suggesting an ancient crustal growth and reworking. The-787 Ma zircons have-2000 Ma crustal model ages, suggesting derivations from recycled Paleoproterozoic material.更多还原