Miocene felsic magmatic rocks with high Sr/Y ratios are widely distributed throughout the Gangdese belt of southern Tibet. These provide a good opportunity to explore the magmatic process and deep dynamic mechanisms that occurred after collision between the Indo and the Asian plates. In this paper, felsic volcanic rocks from the Zongdangcun Formation in the Wuyu Basin in the central part of the southern Gangdese belt are used to disclose their origin. Zircon U-Pb geochronology analysis shows that the felsic magmatism occurred at ca. 10.3 ± 0.2 Ma, indicating that the Zongdangcun Formation formed during the Miocene. Most of these felsic magmatic rocks plot in the rhyolite area in the TAS diagram. The rhyolite specimens from the Zongdangcun Formation have the characteristics of high SiO₂ (>64%), K₂O, SiO₂, and Sr contents, a low Y content and a high Sr/Y ratio, and the rocks are rich in LREE and depleted in HREE, showing geochemical affinity to adakitic rocks. The rocks have an enriched Sr-Nd isotopic composition (εNd(t) = −6.76 to −6.68, (⁸⁷Sr/⁸⁶Sr)_i = 0.7082–0.7088), which is similar to the mixed product of the juvenile Lhasa lower continental crust and the ancient Indian crust. The Hf isotopes of zircon define a wide compositional range (εHf(t) = −4.19 to 6.72) with predominant enriched signatures. The Miocene-aged crustal thickness in southern Tibet, calculated on the basis of the Sr/Y and (La/Yb)_N ratios was approximately 60–80 km, which is consistent with the thickening of the Qinghai-Tibet Plateau. The origin of Miocene felsic magmatic rocks with high Sr/Y ratios in the middle section of the Gangdese belt likely involved a partial melting of the thickened lower crust, essentially formed by the lower crust of the Lhasa block, with minor contribution from the ancient Indian crust. After comprehensively analyzing the post-collisional high Sr/Y magmatic rocks (33–8 Ma) collected from the southern margin of the Gangdese belt, we propose that the front edge tearing and segmented subduction of the Indian continental slab may be the major factor driving the east-west trending compositional changes of the Miocene adakitic rocks in southern Tibet.

中文翻译：

---

青藏高原南冈底斯带乌榆盆地中新世长英质岩浆岩成因及地球动力学意义

中新世长英质岩浆岩广泛分布于藏南冈底斯带。这些为探索印度板块与亚洲板块碰撞后发生的岩浆过程和深部动力机制提供了很好的机会。本文以冈底斯带南部中段乌榆盆地纵党村组长英质火山岩为例，揭示其成因。锆石 U-Pb 年代学分析表明，长英质岩浆作用发生在约 10.3±0.2 Ma，表明纵党村组形成于中新世。这些长英质岩浆岩大多分布在 TAS 图中的流纹岩区。纵党村组流纹岩标本具有高SiO ₂ (>64%)、K ₂O、SiO ₂、Sr 含量低，Y 含量低，Sr/Y 比值高，岩石富含轻稀土，贫重稀土，对埃达克岩具有地球化学亲和性。岩石具有富集的Sr-Nd同位素组成(εNd(t) = -6.76 to -6.68, ( ⁸⁷ Sr/ ⁸⁶ Sr) _i = 0.7082-0.7088)，类似于幼年拉萨下陆地壳的混合产物和古印度地壳。锆石的 Hf 同位素定义了广泛的成分范围（εHf(t) = -4.19 至 6.72），具有主要的富集特征。基于Sr/Y和(La/Yb) _N计算的藏南中新世地壳厚度比率约为 60-80 公里，这与青藏高原的增厚一致。冈底斯带中段具有高 Sr/Y 比率的中新世长英质岩浆岩的成因可能涉及加厚的下地壳的部分熔融，该地壳主要由拉萨地块的下地壳形成，古印度的贡献较小脆皮。综合分析冈底斯带南缘采集的碰撞后高Sr/Y岩浆岩（33~8 Ma），我们认为印度大陆板块前缘撕裂和分段俯冲可能是驱动它的主要因素。藏南中新世埃达克岩东西走向的成分变化.