Subduction-related metasomatism at convergent margins is a crucial process for the lithosphere evolution of the overriding plate. In the central Tibetan Plateau, tectonic transitions and related mantle metasomatism history of the oceanic subduction beneath the South Qiangtang terrane (SQT) remain ambiguous, which impeded understanding the geological evolution of the SQT during the Mesozoic and interpreting the geodynamic process responsible for the Cenozoic post-collisional magmatism. This paper integrated the new and published geochronological and geochemical data from the Jurassic-Cretaceous magmatic rocks in the western part of the SQT to explore the variations of magmatism and processes of mantle modifications. The Jurassic arc magmatism is characterized by the southward younging migration with increasing zircon εHf (t) values and the east–west linear distribution of ca. 155–150 Ma slab-derived adakites. After a magmatic gap at ca. 145–130 Ma, the Early Cretaceous magmatism (130–100 Ma) with distinct juvenile isotopic compositions reinitiated firstly in the south of the Jurassic magmatic belt. In comparison, a younger phase of felsic rocks (120–100 Ma) spatially and geochemically overlaps the northern Jurassic granitoids with ancient crustal sources. These spatial–temporal-geochemical covariations of magmatism could be best explained by the southward transference of oceanic subduction at the earliest Cretaceous that was induced by the Jurassic accretion of an oceanic plateau onto the SQT. Under such subduction regimes, several high-Nb mafic rocks in the northern and southern magmatic belts which were formed by partial melting of the slab-melts-metasomatized lithospheric mantle respectively recorded the Jurassic and Cretaceous mantle metasomatism beneath the SQT, based on their spatial and geochemical relationships with two phases of the adakites. Combined with other geological evidence, these results contribute to elucidating the Mesozoic geodynamic evolution of the oceanic subduction beneath the SQT, which further has implications on the deep dynamic processes responsible for post-collisional magmatism.

中文翻译：

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南强塘地层下两阶段中生代海洋俯冲作用及相关地幔交代作用及其对碰撞后岩浆作用的影响


收敛边缘的俯冲相关交代作用是覆盖板块岩石圈演化的关键过程。在青藏高原中部，南强塘地层 （SQT） 下海洋俯冲的构造过渡和相关的地幔交代历史仍然不明确，这阻碍了理解中生代 SQT 的地质演化和解释导致新生代碰撞后岩浆作用的地球动力学过程。本文整合了 SQT 西部侏罗纪—白垩纪岩浆岩中新发表的地质年代学和地球化学数据，以探索岩浆作用的变化和地幔改性过程。侏罗纪弧岩浆作用的特点是向南年轻迁移，锆石 εHf （t） 值增加，以及约 155-150 马 板生的亚石的东西线性分布。在大约 145-130 马 的岩浆间隙之后，具有独特幼年同位素组成的早白垩世岩浆作用（130-100 马）首先在侏罗纪岩浆带南部重新开始。相比之下，长英质岩石的年轻阶段（120-100 马）在空间和地球化学上与北部侏罗纪花岗岩与古老的地壳来源重叠。岩浆作用的这些空间-时间-地球化学协变可以用最早白垩纪海洋俯冲的南移来最好地解释，这是由侏罗纪海洋高原吸积到 SQT 上引起的。 在这种俯冲状态下，由板状熔融交代化岩石圈地幔部分熔融形成的南北岩浆带中数块高 Nb 镁铁质岩石分别记录了 SQT 下的侏罗纪和白垩纪地幔交代作用，基于它们与亚达晶两相的空间和地球化学关系。结合其他地质证据，这些结果有助于阐明 SQT 下方海洋俯冲的中生代地球动力学演化，这进一步对导致碰撞后岩浆作用的深部动力学过程产生了影响。