Continental orogenesis from ocean subduction, continent collision/subduction, to orogen collapse, and orogen recycling: The example of the North Qaidam UHPM belt, NW China
Continental orogenesis from ocean subduction, continent collision/subduction, to orogen collapse, and orogen recycling: The example of the North Qaidam UHPM belt, NW China
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从海洋俯冲、大陆碰撞/俯冲到造山带塌陷和造山带再造的大陆造山作用：以柴北缘超高压强磁场带为例
DOI：
10.1016/j.earscirev.2013.11.010
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发表时间：
2014
影响因子：
12.1
通讯作者：
Lifei Zhang
中科院分区：
文献类型：
--
作者：
Shuguang Song;Yaoling Niu;Li Su;Cong Zhang;Lifei Zhang
青藏高原北方柴北缘超高压变质带记录了新元古代至古生代大陆造山带从早期海底俯冲到大陆碰撞俯冲再到最终造山带崩溃的完整演化历史。该超高压变质带的岩石主要由长英质片麻岩组成，其中含有榴辉岩和橄榄岩块体。1120-900 Ma的花岗质和砂质/泥质片麻岩构成了该超高压变质带的大部分，并与格伦维尔时代的前一个造山旋回有成因联系。而HUPM榴辉岩的原岩既有850-820 Ma的大陆溢流玄武岩（CFB），也有540-500 Ma的洋壳（蛇绿岩）。早期石英稳定榴辉岩相变质作用发生在445-473 Ma，与北祁连洋缝合带高压岩石的时代相同，是最早被发掘和保存的俯冲期海底岩石。变质岩和榴辉岩中的柯石英锆石和石榴橄榄岩中的金刚石锆石，将超高压变质年龄限定在438-420 Ma，代表了100-200 km，10-20 m.y.早于祁连山海底俯冲的早期。因此，陆壳深俯冲应是大洋俯冲的继续，是大洋岩石圈下沉拉下或上覆板块推下的结果，是被动大陆边缘的必然结果。435 Ma左右，俯冲洋壳发生部分熔融，420 Ma左右，北祁连地区超高压变质岩石开始出露，伴随着造山运动和早泥盆世糖蜜沉积。大洋俯冲带与大陆超高压变质带的退耦可能是由于俯冲洋壳与大陆壳的折返路径和机制不同，或俯冲带的后滚。超高压变质板片和陆壳在折返过程中的减压熔融作用是埃达克质熔体和S型花岗岩形成的主要原因。400-360 Ma发生山体崩塌和岩石圈伸展，形成闪长岩-花岗岩侵入体，标志着一个完整的造山旋回的结束，是新元古代格林威尔造山作用和早古生代加里东造山作用复合的多期构造旋回的典型代表。
The North Qaidam ultra-high pressure metamorphic (UHPM) belt in the northern Tibetan Plateau records a complete history of the evolution of a continental orogen from prior seafloor subduction, to continental collision and subduction, and to the ultimate orogen collapse in the time period from the Neoproterozoic to the Paleozoic. Lithologies in this UHPM belt consist predominantly of felsic gneisses containing blocks of eclogite and peridotite.The 1120–900 Ma granitic and psammitic/pelitic gneisses compose the majority of the UHPM belt and is genetically associated with the previous orogenic cycle of Grenville-age, whereas protoliths of the HUPM eclogites are of both the 850–820 Ma continental flood basalts (CFBs) and the 540–500 Ma oceanic crust (ophiolite). The early stage of quartz-stable eclogite-facies metamorphism took place at ~ 445–473 Ma, the same age as that of the HP rocks in the North Qilian oceanic suture zone, representing the earliest subducting seafloor rocks exhumed and preserved. Coesite-bearing zircons from the metapelite and eclogite, diamond-bearing zircons from garnet peridotites constrain the UHP metamorphic age of ~ 438–420 Ma, which represents the timing of continental subduction at depths of 100–200 km, ~ 10–20 m.y. younger than the early stage of the Qilian seafloor subduction. Therefore, deep subduction of continental crust should be the continuation of oceanic subduction that is pulled down by the sinking oceanic lithosphere or pushed down by the overriding upper plate, which is an expected and inevitable consequence for the scenario of passive continental margins. Partial melting of subducted ocean crust might occur in response to continental subduction at ~ 435 Ma.The UHPM rocks started to exhume accompanied by mountain building and deposition of Early Devonian molasses in the North Qilian region at ~ 420 Ma. Decoupling of oceanic subduction zone and continent UHPM terranes may be attributed to the different exhumation path and mechanism between the subducted oceanic and continent crusts, or rollback of subduction zone. Decompression melting of UHP metamorphosed slab and continental crust during exhumation is responsible for the generation of adakitic melts and S-type granite. Mountain collapse and lithosphere extension happened in the period of ~ 400–360 Ma and formed diorite–granite intrusions in the UHPM belt, which marked the end of a complete orogenic cycle.This UHP metamorphic belt presents an example of multi-epoch tectonic recycles, represented by recombination of the Neoproterozoic Grenvillian orogenesis and the Early Paleozoic Caledonian orogenesis.