Knowledge of the timing of the closure of the Meso-Tethys Ocean as represented by the Bangong–Nujiang Suture Zone, i.e., the timing of the Lhasa-Qiangtang collision, is critical for understanding the Mesozoic tectonics of the Tibetan Plateau. But this timing is hotly debated; existing suggestions vary from the Middle Jurassic (ca. 166 Ma) to Late Cretaceous (ca. 100 Ma). In this study, we describe the petrology of the Zhonggang igneous–sedimentary rocks in the middle segment of the Bangong–Nujiang Suture Zone and present results of zircon U–Pb geochronology, whole-rock geochemistry, and Sr–Nd isotope analysis of the Zhonggang igneous rocks. The Zhonggang igneous–sedimentary rocks have a thick basaltic basement (>2 km thick) covered by limestone with interbedded basalt and tuff, trachyandesite, chert, and poorly sorted conglomerate comprising limestone and basalt debris. There is an absence of terrigenous detritus (e.g., quartz) within the sedimentary and pyroclastic rocks. These observations, together with the typical exotic blocks-in-matrix structure between the Zhonggang igneous–sedimentary rocks and the surrounding flysch deposits, lead to the conclusion that the Zhonggang igneous–sedimentary rocks are remnants of an ocean island within the Meso-Tethys Ocean. This conclusion is consistent with the ocean island basalt-type geochemistry of the Zhonggang basalts and trachyandesites, which are enriched in light rare earth elements (LaN/YbN = 4.72–18.1 and 5.61–13.7, respectively) and have positive Nb–Ta anomalies (NbPM/ThPM > 1, TaPM/UPM > 1), low initial 87Sr/86Sr ratios (0.703992–0.705428), and positive mantle εNd(t) values (3.88–5.99). Zircon U–Pb dates indicate that the Zhonggang ocean island formed at 141–135 Ma; therefore, closure of the Meso-Tethys Ocean and collision of the Lhasa and Qiangtang terranes must have happened after ca. 135 Ma.

中文翻译：

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中特提斯洋闭合时间：青藏高原班公-怒江缝合带内141-135 Ma洋岛残余的约束

了解以班公-怒江缝合带为代表的中特提斯洋闭合时间，即拉萨-羌塘碰撞的时间，对于理解青藏高原中生代构造至关重要。但这个时间点引起了激烈的争论。现有的建议从中侏罗世（约 166 Ma）到晚白垩世（约 100 Ma）不等。在这项研究中，我们描述了班公-怒江缝合带中段中港火成岩-沉积岩的岩石学，并展示了中港的锆石 U-Pb 年代学、全岩地球化学和 Sr-Nd 同位素分析结果。火成岩。中港火成岩-沉积岩具有厚厚的玄武质基底（>2 km 厚），被石灰岩与玄武岩和凝灰岩、粗长安岩、燧石、以及由石灰石和玄武岩碎片组成的分选不良的砾岩。沉积岩和火山碎屑岩中没有陆源碎屑（例如石英）。这些观察结果，加上中港火成岩-沉积岩与周围复理石矿床之间典型的奇异块状基质结构，得出结论：中港火成岩-沉积岩是中特提斯洋中一个洋岛的残余。 . 该结论与富含轻稀土元素（LaN/YbN分别为4.72-18.1和5.61-13.7）并具有Nb-Ta正异常（ NbPM/ThPM > 1，TaPM/UPM > 1)，低初始 87Sr/86Sr 比率 (0.703992–0.705428)，正地幔 εNd(t) 值 (3.88–5.99)。锆石U-Pb测年表明中港洋岛形成于141-135 Ma；因此，中特提斯洋的闭合和拉萨和羌塘地体的碰撞一定发生在大约 10 年前。135 马。