High-grade complexes record the late Permian-Middle Triassic arc metamorphism in the southernmost Altaids: Implications for the final closure of the Paleo-Asian Ocean
High-grade complexes record the late Permian-Middle Triassic arc metamorphism in the southernmost Altaids: Implications for the final closure of the Paleo-Asian Ocean
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DOI：
10.1016/j.lithos.2023.107054
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发表时间：
2023-02
期刊：
影响因子：
3.5
通讯作者：
Hao Wang;W. Xiao;Rui Li;Hongxu Chen;Zhou Tan;Q. Mao;Meng-Yan Shi
中科院分区：
文献类型：
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作者：
Hao Wang;W. Xiao;Rui Li;Hongxu Chen;Zhou Tan;Q. Mao;Meng-Yan Shi
造山带中的高级变质杂岩或地体具有多构造热记录能力，在重建地球过去的造山动力学和构造史方面起着至关重要的作用。赤金杂岩位于阿尔泰山脉最南端，由强烈变形的中-高级变质火山岩组成，包括(含石榴石)云母-石英片岩、长英片麻岩和角闪片岩和片麻岩，对古亚洲洋(PAO)末端演化的激烈争议的时间和构造构造施加了关键的限制。长期以来，在构造重建中，该杂岩一直被解释为微大陆的前寒武纪基底。我们对赤金杂岩进行了详细的野外调查、地球化学研究和碎屑年龄谱分析，揭示了构造-岩性-地球化学与起源于大陆弧区的火山-岩浆喷发的相似性。经热力学模拟和地温压测量重建的逆时针P-T路径和高/P地温梯度(∼24-37°C/Km)，揭示了热侵入和有限弧形地壳增厚至原地等压冷却引起的进行性“热”T/P变质作用的岩浆底侵机制。角闪石和黑云母~(40)Ar/~(39)Ar~(39)Ar和锆石U单键铅测年表明，晚二叠世至中三叠世(∼252~237M a)，由于PAO继续向南俯冲，大陆弧系仍处于活动状态，从而制约了阿尔泰期至晚三叠世的最终融合。这项研究提出了一种新的视角，将阿尔泰最南端的高级岩石重新定义为弧形变质杂岩，而不是所谓的古代微大陆，并为识别全球造山带中具有不同成因的相似变质杂岩或地体的构造性质提供了一个潜在的模板范例。
High-grade metamorphic complexes or terranes in orogens play a vital role in reconstructing orogenic dynamics and tectonic history of Earth's past owing to their multi-tectono-thermal recording capacity. The Chijin Complex, located in the southernmost Altaids and composed of intensely deformed medium- to high-grade meta-volcanic rocks including (garnet-bearing) mica-quartz schists, felsic gneisses, and amphibolitic schists and gneisses, imposes crucial constraints on the fiercely disputed timing and tectonic architecture of the Paleo-Asian Ocean's (PAO) terminal evolution. This Complex has long been interpreted as the Precambrian basement of a microcontinent in tectonic reconstructions. Our detailed field investigations, geochemical research, and detrital age spectrum analyses of the Chijin Complex reveal structural-lithological-geochemical affinities to volcanic-magmatic extrusions originating from a continental arc regime. Anti-clockwiseP-Tpaths and highT/Pgeothermal gradients (∼24–37 °C/km), reconstructed by thermodynamic modeling and geothermobarometry for the Complex, reveal magmatic underplating mechanism from prograde “hot”T/Pmetamorphism resulting from thermal intrusion and finite arc crustal thickening toin-situretrograde isobaric cooling. Hornblende and biotite40Ar/39Ar and zircon Usingle bondPb dating demonstrates that the continental arc system was still active as during the Late Permian to Middle Triassic (∼252–237 Ma) as a result of continuing southward subduction of the PAO, thereby constraining the final amalgamation of the Altaids to the Late Triassic. This study proposes a new perspective for redefining high-grade rocks at the southernmost Altaids as arc-metamorphic complexes rather than “reputed” ancient microcontinent, as well as a potential template example for discerning tectonic nature of semblable metamorphic complexes or terranes with distinct origins in global orogens.