A geotraverse across two paleo-subduction zones in Tien Shan, Tajikistan
A geotraverse across two paleo-subduction zones in Tien Shan, Tajikistan
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DOI：
10.1016/j.gr.2016.09.010
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发表时间：
2017-07
影响因子：
6.1
通讯作者：
D. Konopelko;R. Seltmann;Yunus Mamadjanov;R. Romer;Y. Rojas‐Agramonte;Y. Rojas‐Agramonte;T. Jeffries;D. Fidaev;A. Niyozov
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文献类型：
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作者：
D. Konopelko;R. Seltmann;Yunus Mamadjanov;R. Romer;Y. Rojas‐Agramonte;Y. Rojas‐Agramonte;T. Jeffries;D. Fidaev;A. Niyozov
本文首次对塔吉克斯坦Mogol-Tau和Kurama山脉的Chatkal-Kurama地块以及天山造山带的Gissar段收集的14块岩浆岩进行了LA-ICP-MS U-Pb锆石年龄、地球化学和Sr-Nd-Pb同位素数据。这些来自两个晚古生代活动边缘的超俯冲和后碰撞岩浆岩的新资料，约束了一个跨越两个古俯冲带的大地运动的构造模型：(1)mogoll - tau山脉的425 Ma Muzbulak花岗岩形成于突厥斯坦洋北缘的超俯冲环境。北倾板块从早志留世俯冲至早中泥盆世。此后，直到早石炭世，突厥斯坦洋的北侧仍然是一个被动的边缘。(2)早石炭世，突厥斯坦洋北缘俯冲恢复，315 ~ 305 Ma古卡拉-基亚、穆兹别克和卡拉马扎侵入体形成于莫格尔陶和库拉马山脉的超俯冲环境。(3)与此同时，早石炭世，突厥斯坦海南被动边缘的裂谷作用形成了短暂的Gissar盆地，Gissar微大陆将其与突厥斯坦海隔开。315 Ma Kharangon斜长花岗岩和321 ~ 312 Ma安第斯型超俯冲Gissar岩基记录了Gissar盆地的北倾俯冲作用。Gissar山脉南部的Kharangon和Khanaka辉长斜花岗岩体的地球化学和Sr-Nd同位素组成（87Sr/86Sr(t) 0.7047 ~ 0.7056， εNd为+ 1.5 ~ + 2.3）与蛇绿岩伴生斜花岗岩体的典型幔源相适应。Gissar基和mogola - tau Kurama山脉的超俯冲岩石具有不同程度的Sr-Nd-Pb混合同位素特征（87Sr/86Sr(t) 0.7057 ~ 0.7064， εNd为- 2.1 ~ - 5.0），是幔源岩浆与大陆地壳相互作用的大陆弧的典型特征。(4)晚石炭世，突厥斯坦洋与吉萨尔盆地处于封闭状态。早二叠世Chinorsay （288 Ma）和Dara-i-pioz （267 Ma）碰撞后岩体，位于Gissar微大陆北部，经过长期岩浆演化，具有板内地球化学亲和性，其同位素Sr-Nd-Pb同位素组成（87Sr/86Sr(t) 0.7074 ~ 0.7086， εNd为- 5.5 ~ - 7.4）表明其源自前寒武纪大陆地壳，并得到了古Nd模式年龄（1.5和1.7 Ga）的支持。中国赛花岗闪长岩中存在850 ~ 500 Ma的继承锆石颗粒。在Gissar南部和Mogol-Tau和Kurama山脉（297-286 Ma）的碰撞后侵入体，直接位于超俯冲岩浆系列之后，具有弧相关岩浆的地球化学和同位素特征。Mogol-Tau和Kurama山脉的碰撞后侵入岩体具有明显的玄武岩亲和性，这可以用软流圈热物质与碰撞后板块断裂引起的岩石圈地幔俯冲富集楔块的相互作用来解释。尽管形成于不同的构造环境，但所有岩浆岩的Nd模式年龄都相对较老（1.7 ~ 1.0 Ga），表明其来源中含有大量古元古代或更古老的地壳物质，其模式年龄与南天山的Alai段和Kokshaal段碰撞后岩体的模式年龄相似。
We present first LA-ICP-MS U–Pb zircon ages as well as geochemical and Sr–Nd–Pb isotope data for 14 magmatic rocks collected along ca. 400 km profile across the Chatkal-Kurama terrane in the Mogol-Tau and Kurama ranges and the Gissar Segment of the Tien Shan orogen in Tajikistan. These new data from supra-subduction and post-collisional magmatic rocks of two Late Paleozoic active margins constrain a tectonic model for terrane motions across two paleo-subduction zones: (1) The 425 Ma old Muzbulak granite of the Mogol-Tau range formed in a supra-subduction setting at the northern margin of the Turkestan Ocean. The north-dipping plate was subducted from the Early Silurian to the earliest Middle Devonian. Thereafter the northern side of the Turkestan Ocean remained a passive margin until the Early Carboniferous. (2) In the Early Carboniferous, subduction under the northern margin of the Turkestan Ocean resumed and the 315 to 305 Ma old Kara-Kiya, Muzbek, and Karamazar intrusions formed in a supra-subduction setting in the Mogol-Tau and Kurama ranges. (3) At the same time, in the Early Carboniferous, rifting of the southern passive margin of the Turkestan Ocean formed the short-lived Gissar Basin, separated from the Turkestan Ocean by the Gissar micro-continent. North-dipping subduction in the Gissar Basin is documented by the 315 Ma Kharangon plagiogranite and the voluminous ca. 321–312 Ma Andean-type supra-subduction Gissar batholith. The Kharangon and Khanaka gabbro-plagiogranite intrusions of the southern Gissar range have geochemical and Sr–Nd isotopic compositions (87Sr/86Sr(t) 0.7047–0.7056, εNd of + 1.5 to + 2.3) compatible with mantle-derived origin typical for plagiogranites associated with ophiolites. The supra-subduction rocks from the Gissar batholith and from the Mogol-Tau Kurama ranges have variably mixed Sr–Nd–Pb isotopic signatures (87Sr/86Sr(t) 0.7057–0.7064, εNd of − 2.1 to − 5.0) typical for continental arcs where mantle-derived magmas interact with continental crust. (4) In the latest Carboniferous, the Turkestan Ocean and the Gissar Basin were closed. The Early Permian Chinorsay (288 Ma) and Dara-i-pioz (267 Ma) post-collisional intrusions, emplaced in the northern part of the Gissar micro-continent after a long period of amagmatic evolution, have intraplate geochemical affinities and isotopic Sr–Nd–Pb isotopic compositions (87Sr/86Sr(t) 0.7074–0.7086, εNd of − 5.5 to − 7.4) indicating derivation from Precambrian continental crust which is supported by old Nd model ages (1.5 and 1.7 Ga), and by the presence of inherited zircon grains with ages 850–500 Ma in the Chinorsay granodiorite. The post-collisional intrusions in the southern Gissar and in the Mogol-Tau and Kurama ranges (297–286 Ma), emplaced directly after supra-subduction magmatic series, have geochemical and isotopic signatures of arc-related magmas. The distinct shoshonitic affinities of post-collisional intrusions in the Mogol-Tau and Kurama ranges are explained by the interaction of hot asthenospheric material with subduction-enriched wedge of lithospheric mantle due to slab break-off at post-collisional stage. Despite origination from different tectonic environments, all magmatic rocks have relatively old Nd model ages (1.7–1.0 Ga) indicating a significant proportion of Paleoproterozoic or older crustal material in their sources and their model ages are similar to those of post-collisional intrusions from the Alai and Kokshaal Segments of the South Tien Shan.