Metamorphism and tectonic evolution of the Lhasa terrane, Central Tibet
Metamorphism and tectonic evolution of the Lhasa terrane, Central Tibet
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DOI：
10.1016/j.gr.2012.08.024
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发表时间：
2014
影响因子：
6.1
通讯作者：
Z. Zhang;X. Dong;M. Santosh;Guochun Zhao
中科院分区：
文献类型：
--
作者：
Z. Zhang;X. Dong;M. Santosh;Guochun Zhao
藏南拉萨地体由前寒武纪结晶基底、古生代-中生代沉积地层和古生代-新生代岩浆岩组成。长期以来，该地体一直被认为是在新生代与向北漂移的印度大陆碰撞之前与欧亚大陆发生碰撞之前与欧亚大陆碰撞的最后一个地壳块体。因此，拉萨地体是揭示喜马拉雅-藏期造山带起源和演化史的关键。尽管以往的造山带构造演化模型有很多来自拉萨地体的证据，但很少考虑该地体的变质历史。本文主要根据本课题组的最新研究成果，综述了拉萨地体变质作用的时空特征，并对其地球动力学背景和构造意义进行了评价。拉萨地体经历了大洋俯冲带的新元古代和晚古生代高压变质作用，陆陆碰撞带的早古生代和早中生代MP变质作用，大洋中脊俯冲带的晚白垩世HT/MP变质作用，以及大陆俯冲带上方增厚地壳中的两期新生代MP变质作用。这些变质和伴生的岩浆事件揭示了拉萨地体从新元古代到新生代经历了复杂的构造演化。主要结论如下：(1)拉萨地块由拉萨南北地体组成，由古特提斯洋及其后的晚古生代缝合带隔开。(2)拉萨地体北部结晶基底中含有新元古代洋壳岩石，可能是罗迪尼亚超大陆裂解形成的莫桑比克洋的残留物。(3)拉萨北部洋壳基底经历了低温世晚期(~650M a)的高压变质作用和早古生代(~485M a)的MP变质作用，并伴随着莫桑比克洋的闭合和东西冈瓦那的最终融合，表明拉萨北部地体可能部分来源于东非造山带北段。(4)印度大陆北缘，包括拉萨南北地体和羌塘地体，经历了早古生代岩浆作用，表明冈瓦那末次融合后原特提斯洋俯冲形成的安第斯型造山作用。(5)拉萨、羌塘地体经历了中古生代(~360 Ma)的岩浆活动，表明古特提斯洋俯冲形成了安第斯式的造山作用。(6)拉萨南北地体之间古特提斯洋的闭合和随后的地体碰撞形成了晚二叠世(约260 Ma)高压变质带和三叠纪(220 Ma)MP变质带。(7)拉萨南部地体经历了晚白垩世(约90 Ma)安第斯型造山作用，其特征是新特提斯洋向北俯冲过程中区域的HT/MP变质作用和大量冈底斯岩基的同时代侵位。(8)早新生代(55-45 Ma)，陆陆碰撞造山作用导致拉萨南部地体增厚的地壳经历了MP角闪岩相变质作用和同碰撞岩浆作用。(9)随着大陆的不断汇聚，拉萨南部地体在…期间也经历了MP变质作用
The Lhasa terrane in southern Tibet is composed of Precambrian crystalline basement, Paleozoic to Mesozoic sedimentary strata and Paleozoic to Cenozoic magmatic rocks. This terrane has long been accepted as the last crustal block to be accreted with Eurasia prior to its collision with the northward drifting Indian continent in the Cenozoic. Thus, the Lhasa terrane is the key for revealing the origin and evolutionary history of the Himalayan–Tibetan orogen. Although previous models on the tectonic development of the orogen have much evidence from the Lhasa terrane, the metamorphic history of this terrane was rarely considered. This paper provides an overview of the temporal and spatial characteristics of metamorphism in the Lhasa terrane based mostly on the recent results from our group, and evaluates the geodynamic settings and tectonic significance. The Lhasa terrane experienced multistage metamorphism, including the Neoproterozoic and Late Paleozoic HP metamorphism in the oceanic subduction realm, the Early Paleozoic and Early Mesozoic MP metamorphism in the continent–continent collisional zone, the Late Cretaceous HT/MP metamorphism in the mid-oceanic ridge subduction zone, and two stages of Cenozoic MP metamorphism in the thickened crust above the continental subduction zone. These metamorphic and associated magmatic events reveal that the Lhasa terrane experienced a complex tectonic evolution from the Neoproterozoic to Cenozoic. The main conclusions arising from our synthesis are as follows: (1) The Lhasa block consists of the North and South Lhasa terranes, separated by the Paleo-Tethys Ocean and the subsequent Late Paleozoic suture zone. (2) The crystalline basement of the North Lhasa terrane includes Neoproterozoic oceanic crustal rocks, representing probably the remnants of the Mozambique Ocean derived from the break-up of the Rodinia supercontinent. (3) The oceanic crustal basement of North Lhasa witnessed a Late Cryogenian (~ 650 Ma) HP metamorphism and an Early Paleozoic (~ 485 Ma) MP metamorphism in the subduction realm associated with the closure of the Mozambique Ocean and the final amalgamation of Eastern and Western Gondwana, suggesting that the North Lhasa terrane might have been partly derived from the northern segment of the East African Orogen. (4) The northern margin of Indian continent, including the North and South Lhasa, and Qiangtang terranes, experienced Early Paleozoic magmatism, indicating an Andean-type orogeny that resulted from the subduction of the Proto-Tethys Ocean after the final amalgamation of Gondwana. (5) The Lhasa and Qiangtang terranes witnessed Middle Paleozoic (~ 360 Ma) magmatism, suggesting an Andean-type orogeny derived from the subduction of the Paleo-Tethys Ocean. (6) The closure of Paleo-Tethys Ocean between the North and South Lhasa terranes and subsequent terrane collision resulted in the formation of Late Permian (~ 260 Ma) HP metamorphic belt and Triassic (220 Ma) MP metamorphic belt. (7) The South Lhasa terrane experienced Late Cretaceous (~ 90 Ma) Andean-type orogeny, characterized by the regional HT/MP metamorphism and coeval intrusion of the voluminous Gangdese batholith during the northward subduction of the Neo-Tethyan Ocean. (8) During the Early Cenozoic (55–45 Ma), the continent–continent collisional orogeny has led to the thickened crust of the South Lhasa terrane experiencing MP amphibolite-facies metamorphism and syn-collisional magmatism. (9) Following the continuous continent convergence, the South Lhasa terrane also experienced MP metamorphism during …