南秦岭东段构造热事件与地壳演化

发布时间：2018-05-25 10:36

  本文选题：造山带 + 南秦岭　； 参考：《中国科学技术大学》2016年博士论文

【摘要】：南秦岭构造带是秦岭造山带的重要组成部分,前人的研究结果表明南秦岭和扬子板块有很大的相似性,因此,南秦岭地体是理解秦岭两阶段碰撞造山过程的关键因素,记录两个相邻地体裂解而后又拼合的历史。本文研究了南秦岭相关岩石单元的三个主要内容。其一,研究了南秦岭结晶基底陡岭杂岩两类主要的岩石类型,厘定了形成时代和经历的主要演化历史,并与扬子板块前寒武的演化历史对比,探讨两个相邻板块的不同演化历程。其二,研究了侵入陡岭杂岩的新元古侵入岩的不同源区和岩石成因,结合广泛分布于扬子北缘的新元古构造事件,探讨其形成构造背景。其三,研究了侵入到南秦岭过渡型基底中的镁铁质岩墙群,准确限定其形成年龄以及岩石成因,并探讨其动力学背景和秦岭造山活动的关系。陡岭杂岩主要由副片麻岩以及花岗质正片麻岩构成。三个正片麻岩的岩浆成因的锆石显示年龄为～2.5 Ga,表明为太古代和古元古代交界的岩浆活动。Nd-Hf同位素证明壳幔分异发生在～3.0 Ga。这一期的岩浆活动在扬子板块没有发现,暗示了南秦岭和扬子板块不同的早期演化历史。副片麻岩中包含不同成因的复杂来源的碎屑锆石,锆石的主要的年龄峰值集中在2.5 Ga,2.0 Ga,1.5 Ga和800 Ma,其中2.0 Ga和800 Ma的锆石Th/U比值很低,没有环带,表明存在两次变质叠加。其中2.5 Ga的碎屑锆石与正片麻岩中的锆石年龄和Hf同位素相似,并与扬子板块新元古沉积岩中2.5 Ga的锆石特征类似,表明陡岭杂岩正片麻岩可能是这些沉积岩的重要源区。古元古晚期的变质作用在扬子板块也广泛分布,证明了南秦岭和扬子的密切联系,而800 Ma的角闪岩相的变质作用也制约了南秦岭和扬子板块由挤压转向伸展环境的的时间,与Rodinia超大陆的聚合和裂解过程可能密切相关。侵入到陡岭杂岩的新元古侵入体,未显示变质变形的特征,虽然包含从辉长岩到花岗岩的多种岩石类型,形成时代却集中在750-720 Ma。所研究的侵入岩具有不同的源区,其中镁铁质岩石分为两类,一类是高Ti的辉长岩,岩浆系列为碱性或拉斑质,具有高Fe含量,较低的Mg“,没有明显的Nb-Ta亏损,同位素特征显示亏损的特征,表明为软流圈地幔部分熔融的产物；另外一类为钙碱性辉长岩和辉长闪长岩,具有较高的MgO含量以及Mg#,微量元素具有典型的岛弧岩浆特征,如富集轻稀土,大离子亲石元素,亏损高场强元素特征,Nd同位素显示较大的范围,εNd(t)为-3.0到6.2,表明来自不均一交代的岩石圈地幔熔融的产物。长英质岩石也分为两类,一类是Ⅰ型花岗岩,Nd-Hf同位素表明来自于幔源岩浆和壳源岩浆混合成因,另一类是S型花岗岩,源区主要是类似于陡岭杂岩变沉积岩的地壳岩石部分熔融形成。地幔到地壳岩石发生广泛熔融,表明南秦岭新元古中晚期处于伸展背景。结合扬子北缘的新元古构造活动,将新元古的演化历史可以归纳如下：800 Ma之前的加积俯冲阶段,-800 Ma的弧陆碰撞阶段,800-700 Ma的裂谷活动阶段以及700-620 Ma大陆裂解阶段。南秦岭武当地区存在大量的基性岩墙群,锆石U-Pb定年表明存在两期不同的侵位时代,-460Ma以及～220Ma,远小于前人的获得的～680-650Ma的结果。两期基性岩脉表现为相似的主量元素特征,但是截然不同的微量元素和同位素特征。早古生代的岩浆富集LREEs, LILEs以及HFSEs,具有EMⅡ型地幔同位素特征,显示来自于类似OIB的富集地幔源区。早中生代的基性岩脉分为两类,其中一类亏损LREEs, LILEs以及HFSEs,具有DM型地幔同位素特征,表明来自于软流圈地幔源区,第二类相比于第一类岩脉有更高的Rb, Ba, K含量,同时具有EMI型同位素特征,表明它们的源区包含了显著的扬子板块下地壳岩石贡献。这些镁铁质岩浆记录了南秦岭显生宙漫长的演化历史,古生代的基性岩脉可能与分隔南秦岭和扬子板块的勉略洋的形成相关,而早中生代的基性岩脉来源于两者碰撞拼合后伸展阶段软流圈上涌部分熔融,俯冲的大洋板片断离模型不仅可以来用解释中生代武当地区的镁铁质岩脉成因,也可以解释秦岭中生代造山东西两侧的差异。在东侧的大别苏鲁地区,板块断裂的深度较大,没有明显的同造山岩浆活动,而在东秦岭地区,板片断离的深度较小,软流圈上涌至较浅位置,引起地壳广泛熔融,形成大量的花岗质岩浆活动。武当地区的基性岩脉记录了勉略洋从形成到闭合的历史。
[Abstract]:The southern Qinling Mountains tectonic belt is an important part of the Qinling Mountains orogenic belt. The results of previous studies show that the southern Qinling Mountains and the Yangtze plate are very similar. Therefore, the southern Qinling Mountains earth body is the key factor in understanding the two stage of the collision orogenic process in Qinling Mountains, and records the history of the splitting and splitting of the two adjacent areas. In this paper, the related rocks in southern Qinling Mountains are studied. Three main contents of the stone unit. First, we studied two main types of rock types of the crystalline basement dling complex in southern Qinling Mountains, determined the main evolution history of the formation time and experience, compared with the evolution history of the Precambrian of the Yangtze plate, and discussed the different evolution course of the two adjacent plates. Secondly, the new elements of the intrusion of the dash complex were studied. The non homologous region and petrogenesis of the paleo intrusive rocks are combined with the Neoproterozoic tectonic events widely distributed in the northern margin of the Yangtze River, and the formation of its tectonic setting is discussed. Thirdly, the mafic rock wall group invading into the transitional basement of South Qinling Mountains is studied, the age of formation and the cause of rock formation are accurately defined, and its dynamic background and Qinling Mountains orogenic activities are discussed. The dling complex is mainly composed of paraplastic gneiss and granitic positive gneiss. The magmatic zircon of three positive magma shows a age of ~ 2.5 Ga, indicating that the magmatism.Nd-Hf isotopes at the junction of Archaean and Palaeoproterozoic showed that the magmatic activity of the crust and mantle differentiation occurred in the period of ~ 3 Ga., and that there was no hair in the Yangtze plate. It is suggested that the early evolution history of southern Qinling Mountains and Yangzi plate is different. Parisneis contains complex sources of detrital zircon from different origins. The main peak age of zircon is 2.5 Ga, 2 Ga, 1.5 Ga and 800 Ma, of which 2 Ga and 800 Ma zircon Th/U ratio is very low, and there is no belt, indicating that there is two metamorphic superposition. 2.5 of them. The detrital zircon of Ga is similar to the zircon age and Hf isotopes in the ortho Proterozoic, similar to the zircon features of the 2.5 Ga in the Neoproterozoic sedimentary rocks of the Yangtze plate, indicating that the dling complex is probably an important source of these sedimentary rocks. The metamorphic action of the late Proterozoic was also widely distributed in the Yangtze plate, proving that southern Qinling Mountains and the Yangtze were also proved. The metamorphism of the 800 Ma amphibolite facies also restricts the time of the southern Qinling Mountains and the Yangtze plate from the extrusion to the extensional environment, which is closely related to the process of polymerization and cracking of the Rodinia supercontinent. The Neoproterozoic intrusions into the dling complex have not shown the characteristics of metamorphic deformation, although it contains from gabbro to granite. A variety of rock types, the formation age is concentrated in 750-720 Ma., the intrusive rocks have different source areas, of which mafic rocks are divided into two types, one is high Ti gabbro, the magma series is alkaline or pulla, with high Fe content, low Mg ", no obvious Nb-Ta loss, isotopic characteristics show loss characteristics, isotopic characteristics show loss characteristics, the isotope characteristics show loss characteristics. The latter is the product of partial melting of the asthenosphere mantle; the other is calc alkaline gabbro and gabbro, with high MgO content and Mg#. The trace elements have typical island arc magma characteristics, such as the enrichment of light rare earth, large ion lithopite elements, the loss of high field and strong elements, Nd isotopes showing a larger range, and the Nd (T) of -3.0 to 6.2 It shows the product of the melting of the lithosphere mantle melt from the inhomogeneous metasomatism. The felsic rocks are also divided into two types, one is type I granite, and the Nd-Hf isotopes indicate that the mixture of mantle derived magma and crust source magma and the other type is S type granite. The source area is mainly formed by partial melting of the crustal rocks similar to the dling complex sedimentary rocks. The extensive melting of the mantle to the crustal rocks indicates that the middle late Neoproterozoic in southern Qinling Mountains is in extensional background. In combination with the Neoproterozoic tectonic activities of the northern margin of the Yangtze, the evolutionary history of the Neoproterozoic can be summed up as follows: the accretion subduction stage before 800 Ma, the arc collision stage of the -800 Ma, the rift stage of the 800-700 Ma and the 700-620 Ma continental fissure. There are a large number of basic rock wall groups in the Wudang region of southern Qinling Mountains. The zircon U-Pb dating shows that there are two different emplacement times, -460Ma and 220Ma, far less than the results obtained by the predecessors to 680-650Ma. The two phases of the basic rock veins are characterized by similar principal elements, but are distinct trace elements and isotopes. The magma of the Palaeozoic was enriched in LREEs, LILEs and HFSEs, characterized by EM II mantle isotopes, showing the origin of the rich mantle derived from similar OIB. The early Mesozoic basic rock veins were divided into two types, including a loss of LREEs, LILEs and HFSEs, with the DM type mantle isotopic characteristics, indicating that the second types were compared to the asthenosphere mantle source region. The first type of vein has a higher Rb, Ba, K content and EMI isotopic characteristics, indicating that their source area contains significant contribution to the lower crust rock of the Yangtze plate. These mafic magma records the long history of the protracted evolution of the southern Qinling Mountains, and the Paleozoic vein may be associated with the delimited ocean of the southern Qinling Mountains and the Yangtze plate. The formation of the early Mesozoic basic rocks originated from the partial melting of the asthenosphere in the extension stage after the collision and combination. The subduction of the oceanic plate fragments from the model can not only explain the genesis of the mafic veins in the Mesozoic Wudang region, but also explain the difference between the two sides of the Mesozoic orogenic East and West in Qinling Mountains. In the region of Shandong, the depth of the plate fracture is larger, and there is no obvious same orogenic magmatic activity. In East Qinling Mountains, the depth of the plate fragment is smaller and the soft flow circle flows to a relatively shallow position, causing extensive melting of the crust and forming a large number of granitic magma activities.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P548
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本文编号：1933122