Alternating Trench Advance and Retreat: Insights From Paleozoic Magmatism in the Eastern Tianshan, Central Asian Orogenic Belt
Alternating Trench Advance and Retreat: Insights From Paleozoic Magmatism in the Eastern Tianshan, Central Asian Orogenic Belt
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海沟进退交替：中亚造山带东天山古生代岩浆作用的启示
DOI：
10.1029/2018tc005051
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发表时间：
2018
期刊：
影响因子：
4.2
通讯作者：
Du Long
中科院分区：
文献类型：
--
作者：
Zhang Yunying;Sun Min;Yuan Chao;Long Xiaoping;Jiang Yingde;Li Pengfei;Huang Zongying;Du Long
增生造山带一般涉及海沟进退，认识海沟进退对于了解岩石圈的热演化和地球动力学至关重要。对中国东天山大南湖-哈尔里克弧志留纪至石炭纪火山岩进行了系统研究。已识别出三个不同的火山活动幕：晚志留世正常安山岩、高Sr/Y安山岩和红柱岩，晚泥盆世双峰高铝玄武岩和英安岩，以及早石炭世高铝玄武岩。这些岩浆作用经历了贫化的地幔楔体和俯冲的板片/沉积物衍生的流体/熔体之间不同程度的相互作用。结合前人的地质资料，我们认为达南湖-哈尔里克弧是由北天山洋向北俯冲形成的，不同于传统的准噶尔洋向南俯冲，可能是向北俯冲形成的东准噶尔弧系。大南湖-哈尔里克弧玄武岩的Ce/Y和长英质岩石的Ho/Yb的时间变化表明，弧壳经历了幕式增厚和减薄，可能反映了海沟的进退过程。晚奥陶世至泥盆纪和晚石炭世的高Ce/Y和Ho/Yb比值对应着两个海沟推进阶段。相反，早石炭世低的Ce/Y和Ho/Yb比值记录了一段海沟退缩时期，导致了达南湖-哈尔利克弧的裂解和博格达弧后盆地的形成。同时，沿NTO南缘开始向南俯冲，形成雅曼苏弧。晚石炭世NTO的两极俯冲导致其最终闭合。
Accretionary orogens generally involve trench advance and retreat, recognition of which is critical to understand the thermal evolution and geodynamics of the lithosphere. A systematic study has been conducted on the Silurian to Carboniferous volcanic rocks from the Dananhu‐Harlik arc in the Chinese eastern Tianshan. Three distinct episodes of volcanism have been recognized: Late Silurian normal andesite, high Sr/Y andesite and sanukitoid, Late Devonian bimodal high‐alumina basalt and dacite, and Early Carboniferous high‐alumina basalt. These magmatism experienced variable degrees of interaction between a depleted mantle wedge and subducting slab‐/sediment‐derived fluid/melt. Combining with previous geological data, we propose that the Dananhu‐Harlik arc was formed by the northward subduction of the North Tianshan Ocean (NTO), different from the traditional southward subduction of the Junggar Ocean, which was likely subducted northward to account for the East Junggar arc system. Temporal changes in Ce/Y of basalts and Ho/Yb of felsic rocks in the Dananhu‐Harlik arc imply that the arc crust underwent episodic thickening and thinning, which probably reflect the trench advance/retreat processes. The high Ce/Y and Ho/Yb ratios in the Late Ordovician to Devonian and Late Carboniferous correspond to two phases of trench advance. Conversely, the low Ce/Y and Ho/Yb ratios in the Early Carboniferous record a period of trench retreat, which caused the splitting of the Dananhu‐Harlik arc and formation of the Bogda back‐arc basin. Meanwhile, a southward subduction initiated along the south margin of the NTO, producing the Yamansu arc. Late Carboniferous bipolar subduction of the NTO led to its final closure.