The nature and timing of post-collisional crustal thickening and its link to surface uplift in the eastern Lhasa block of the southern Tibetan plateau remain controversial. Here we report on Cenozoic magmatism in the Wuyu area of the eastern Lhasa block. The Eocene (ca. 46 Ma) trachyandesites and trachydacites show slight fractionation of rare earth elements (REE), slightly negative Eu and Sr anomalies, and relatively homogeneous Sr-Nd and zircon Hf isotopes (87Sr/86Sr(i) = 0.7050–0.7063, εNd(t) = −0.92 to −0.03, εHf(t) = +2.6 to +4.8). Previous studies have suggested Neo-Tethys oceanic slab break-off at 50–45 Ma; thus, the Wuyu Eocene magmatism could represent a magmatic response to this slab break-off and originate from relatively juvenile Lhasa crust. The Miocene (ca. 15–12 Ma) dacites and rhyolites have adakitic affinities, e.g., high Sr (average 588 ppm), Sr/Y (29–136), and La/Yb (30–76) values, low Y (4–12 ppm) and Yb (0.4–0.9 ppm) contents, and variable Sr-Nd and zircon Hf isotopes (87Sr/86Sr(i) = 0.7064–0.7142, εNd(t) = −11.7 to −3.7, εHf(t) = −3.2 to +4.5). Their more enriched Sr-Nd-Hf isotopes relative to the Eocene lavas indicate that they should be derived from mixed Lhasa lower crust comprising juvenile crust, ultrapotassic rocks, and probably Indian lower crust-derived rocks. This study has also revealed the transformation from Eocene juvenile and thin crust with a thickness of <40 km to Miocene mixed and thickened crust with a thickness of >50 km. Combined with published tectonic data, we suggest that both lithospheric shortening and magma underplating contributed to eastern Lhasa block post-collisional crustal thickening. Given the spatial-temporal distribution of eastern Lhasa block magmatism and regional geology, we invoke a post-collisional tectonic model of steep subduction of the Indian plate and subsequent westward-propagating plate break-off beneath the eastern Lhasa block, which caused the surface uplift.

中文翻译：

---

藏南碰撞后地壳增厚与高原隆升——从拉萨地块东部乌峪地区新生代岩浆活动的认识

碰撞后地壳增厚的性质和时间及其与青藏高原南部拉萨地块东部地表隆升的联系仍存在争议。在这里，我们报道了拉萨地块东部乌峪地区的新生代岩浆活动。始新世（约 46 Ma）粗面长岩和粗面英岩显示出稀土元素（REE）的轻微分馏，Eu 和 Sr 的轻微负异常，以及相对均质的 Sr-Nd 和锆石 Hf 同位素（87Sr/86Sr(i) = 0.7050-0.7063） , εNd(t) = -0.92 到 -0.03，εHf(t) = +2.6 到 +4.8)。先前的研究表明，新特提斯洋板块在 50-45 Ma 断裂；因此，乌榆始新世岩浆活动可以代表对这次板块断裂的岩浆响应，并且起源于相对年轻的拉萨地壳。中新世（约 15-12 Ma）英安岩和流纹岩具有埃达克岩亲和性，例如，高 Sr（平均 588 ppm）、Sr/Y (29–136) 和 La/Yb (30–76) 值，低 Y (4–12 ppm) 和 Yb (0.4–0.9 ppm) 含量，以及可变的 Sr- Nd 和锆石 Hf 同位素（87Sr/86Sr(i) = 0.7064–0.7142，εNd(t) = -11.7 至 -3.7，εHf(t) = -3.2 至 +4.5）。它们相对于始新世熔岩更富集的 Sr-Nd-Hf 同位素表明它们应该来自混合的拉萨下地壳，包括幼年地壳、超钾质岩和可能来自印度下地壳的岩石。该研究还揭示了从始新世厚度<40 km的幼年薄地壳向厚度>50 km的中新世混合增厚地壳的转变。结合已发表的构造数据，我们认为岩石圈缩短和岩浆底侵都促成了拉萨地块东部碰撞后地壳增厚。