Multistage anatexis during tectonic evolution from oceanic subduction to continental collision: A review of the North Qaidam UHP Belt, NW China
Multistage anatexis during tectonic evolution from oceanic subduction to continental collision: A review of the North Qaidam UHP Belt, NW China
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从大洋俯冲到大陆碰撞的构造演化过程中的多期深熔作用：柴北缘超高压带的回顾
DOI：
10.1016/j.earscirev.2019.02.016
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发表时间：
2019-04
影响因子：
12.1
通讯作者：
Li Yan
中科院分区：
文献类型：
--
作者：
Yu Shengyao;Li Sanzhong;Zhang Jianxin;Peng Yinbiao;Somerville Ian;Liu Yongjiang;Wang Zhengyi;Li Zhuofan;Yao Yong;Li Yan
由于柴达木地块早古生代俯冲到祁连地块之下，青藏高原北部柴达木超高压变质带被认为是典型的高山型超高压变质带。柴达木超高压变质带北部保存完好的古生代变质岩混合岩、闪长岩混合岩、长英质岩席/岩墙和深成花岗岩为研究地壳熔体的产生、迁移和归宿以及与造山作用有关的地球动力学过程提供了良好的机会。根据构造关系、岩石学、年代学、全岩地球化学和锶单键Nd同位素资料，将柴北超高压变质带早古生代俯冲-大陆碰撞过程中的深熔作用进一步划分为3个发展阶段：470 Ma、446~428 Ma和432~420 Ma。第一期花岗岩类亮粒体富K，贫Na，低Sr/Y，富大离子亲石元素(LILES)，可能源于大洋俯冲过程中大陆弧环境下古长英质片麻岩的部分熔融。二期富钠亮砂体和英云闪长岩具有高Na、Sr、Sr/Y、La/Yb和低重稀土元素(HREE)的特征，其εNd(T)为0.1~4.3，锆石εHf(T)为8.3~10.2，与典型的英云闪长花岗闪长岩(TTGs)相似。这些类TTG岩浆是在大陆碰撞增厚的下地壳高压麻粒岩相条件下，新侵位的具有弧形亲和性的辉长岩部分熔融而成的。从类TTG熔体演化出的体积显著的迁移深成岩将成为陆壳的一部分，并有助于地壳的生长，部分残留的HP麻粒岩和/或石榴石辉石岩通过拆沉作用进入地幔。锡铁山地体和吕梁山地体的混合超高压片麻岩和榴辉岩中均保存有第三期深熔作用。第三期超高压片麻岩中富KFS的长英质白云母具有高碱、低镁组分的特征，FeOt+ 、MgO、 + 、TiO2%。在微量元素分布图上，这些富含KFS的白质体具与其寄主片麻岩平行的模式，但元素含量较低，Eu和Sr呈轻微正异常。退变榴辉岩中富Pl的亮体具有如下特征：(1)富CaO、Na2O，贫K2O，Na2O/K2O比值约为2.0；(2)高La/Yb、Sr/Y，低Y、HREE；(3)高Al_2O_3，低Mg#值；(4)富Lile(如Rb、Ba、K、Sr、Pb)，贫高场强元素(HFSe)。超高压榴辉岩和长英质片麻岩在退变初期部分熔融，形成富Pl和富KFS的白云母体，主要是由脱水熔融引起的，其中以榴辉石和白云母为主。深俯冲超高压片麻岩部分熔融形成的深熔熔体以同碰撞深成岩体的形式聚集并迁移到深俯冲地壳片外。柴达木超高压变质带从早期折返阶段产生的亮体熔体向后期折返阶段产生的同碰撞花岗岩类的熔体演化，可能对柴达木北超高压变质带从地幔深处向下地壳水平折返具有重要意义。
The North Qaidam ultra-high pressure (UHP) metamorphic belt in the northern Tibetan Plateau is considered as a typical Alpine-type UHP metamorphic belt due to the Early Paleozoic subduction of the Qaidam Block beneath the Qilian Block. The well-preserved Paleozoic metatexite migmatite, diatexite migmatite, felsic sheet/dyke and anatectic granite in the North Qaidam UHP metamorphic belt provide us with an excellent opportunity to study the generation, transport and final fate of crustal melt and geodynamic processes associated with orogenesis. Based on structural relationships, petrology, geochronology, whole-rock geochemistry and Srsingle bondNd isotope data, the Early Paleozoic anatexis during oceanic subduction to continental collision in the North Qaidam UHP metamorphic belt can be further divided into three stages of development ~470 Ma, 446–428 Ma and 432–420 Ma. The first-stage granitic leucosomes are rich in K, poor in Na with low Sr/Y and enrichment of large ion lithophile elements (LILEs), which were probably derived from partial melting of ancient felsic gneiss in continental arc circumstances during oceanic subduction. The second-stage Na-rich leucosomes and tonalite plutons are characterized by high Na, Sr, Sr/Y and La/Yb and low heavy rare earth elements (HREEs), with positive εNd(t) values of 0.1–4.3 and zircon εHf(t) values of 8.3–10.2, similar to typical tonalite-trondhjemite-granodiorites (TTGs). These TTG-like magmas were produced through partial melting of newly emplaced gabbroic rocks with arc affinity under high-pressure (HP) granulite-facies conditions in a thickened lower crust during continental collision. The volumetrically significant migrated plutons evolved from TTG-like melt will become segments of continental crust and contribute to crustal growth, with partial residual products of HP granulite and/or garnet pyroxenite to the mantle by delamination. The third stage of anatexis was preserved in both migmatitic UHP gneiss and eclogite in the Xitieshan and Luliangshan terranes. The Kfs-rich felsic leucosomes inside UHP gneisses in the third stage are characterized by high alkali contents and low mafic component with FeOT+ MgO + TiO2<2%. In trace element distribution diagrams, these Kfs-rich leucosomes exhibit parallel patterns to their host gneisses but lower element contents and slightly positive Eu and Sr anomalies. The Pl-rich leucosomes within the retrograde eclogite have geochemical features as follows: (1) rich in CaO, Na2O and poor in K2O, with Na2O/K2O ratios >2.0; (2) high La/Yb and Sr/Y, and low Y and HREEs; (3) high Al2O3and low Mg# values; and (4) enriched in LILEs(e.g., Rb, Ba, K, Sr, Pb) and poor in high field strength elements (HFSEs). Partial melting of UHP eclogite and felsic gneiss during the initial retrogression stage with Pl-rich and Kfs-rich leucosome formation was triggered by dehydration melting involving predominant zoisite and muscovite. The anatectic melts from partial melting of deeply subducted UHP gneiss have accumulated and migrated outside the deeply subducted crustal slice in the form ofsyn-collisional plutons. The melt evolution from the leucosomes produced at the early exhumation stage to syn-collisional granitoids produced at the late exhumation, might contribute greatly to the exhumation of the North Qaidam UHP metamorphic belt from mantle depths to the lower crustal levels.
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作者：
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通讯作者：
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影响因子：
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作者：
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柴北缘超高压地体折返过程中超高压榴辉岩的深熔作用：来自岩石学、锆石U-Pb定年和地球化学的制约
影响因子：
4.9
作者：
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通讯作者：
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影响因子：
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作者：
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通讯作者：
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