Late Mesozoic Subduction-Accretion in the southern Qiangtang: Insights from the Sumxi Igneous Complex of west-central Tibet

Knowledge of the time of the closure of the Bangong-Nujiang Tethyan Ocean (BNTO) is critical for understanding the Mesozoic tectonics of the Tibetan Plateau. This study investigated the ca. 110–106 Ma Sumxi igneous complex (high-Nb basalts, magnesian andesites, and adakitic granites) in westernmost part of the Qiangtang terrane. Detailed studies imply strong slab-mantle interactions and arc affinities of Sumxi lavas, indicating that oceanic subduction may have lasted at least until ca. 105 Ma. Moreover, geochronological and geochemical data compilation of magmatic rocks in southern Qiangtang reveal episodic features, with two main high-flux events (~180–145 Ma and ~125–100 Ma) separated by magmatic lulls (~145–125 Ma). The episodic arc activity contributed greatly to the crustal thickening and surface uplift of the central Tibet before the onset of Lhasa-Qiangtang continental collision. The supporting information Text S1 describes the methods for zircon U–Pb dating, Hf isotopes, whole-rock major- and trace-element and Sr–Nd isotope analyses. The figures consist of trace elements versus Nb correlation diagrams for Sumxi basalts and basaltic andesites (Figure S1), and U/Yb vs. Nb/Yb (ratios in log10) and U/Yb vs Y diagrams of zircons from the Sumxi igneous rocks (Figure S2). The Tables S1-S4 show the data of zircon U–Pb isotope (Table S1), trace element data of zircons from the Sumxi Igneous Complex (Table S2), zircon Lu–Hf isotope (Table S3), and whole-rock major (wt. %), trace (ppm) elements and Sr–Nd isotopes (Table S4).明确班公湖-怒江特提斯洋（Bangong-Nujiang Tethyan Ocean, BNTO）的闭合时间，对于解析青藏高原中生代构造演化格局至关重要。本研究针对羌塘地体最西端的约110~106 Ma松西火成杂岩（高Nb玄武岩、镁安山岩与埃达克质花岗岩）开展了系统研究。详细研究结果显示，松西熔岩具备显著的板片-地幔相互作用特征与弧亲和性，指示大洋俯冲作用至少持续至约105 Ma。此外，通过对羌塘南部岩浆岩的年代学与地球化学数据进行汇编分析，发现其岩浆活动具有幕式演化特征：存在两个主要的高通量岩浆事件（分别为~180~145 Ma与~125~100 Ma），两事件之间被岩浆平静期（~145~125 Ma）分隔。幕式弧岩浆活动在拉萨-羌塘陆陆碰撞启动前，对西藏中部的地壳增厚与地表抬升起到了关键的促进作用。 支持信息文本S1详细阐述了锆石U-Pb定年、Hf同位素分析、全岩主量与微量元素分析以及Sr-Nd同位素分析的实验方法。 附图包含松西玄武岩与玄武安山岩的微量元素-Nb相关图解（图S1），以及松西火成岩锆石的U/Yb vs. Nb/Yb（比值以log₁₀计）与U/Yb vs Y图解（图S2）。 附表S1~S4分别刊载了松西火成杂岩的相关数据：表S1为锆石U-Pb同位素数据，表S2为锆石微量元素数据，表S3为锆石Lu-Hf同位素数据，表S4为全岩主量元素（质量分数wt.%）、微量元素（ppm）与Sr-Nd同位素数据。