The Tengchong Block within the Sanjiang Tethys belt in the southeastern part of the Tibetan plateau experienced a widespread intrusion of a felsic magmatic suite of granites in its central domain during Late Cretaceous times. Here, we investigate the Guyong and Xiaolonghe plutons from this suite in terms of their petrological, geochemical, and Sr–Nd, zircon U–Pb and Lu–Hf–O isotopic features to gain insights into the evolution of the Neo-Tethys. The Guyong pluton (76 Ma) is composed of metaluminous monzogranites, and the Xiaolonghe pluton (76 Ma) is composed of metaluminous to peraluminous medium- and fine-grained syenogranite. A systematic decrease in Eu, Ba, Sr, P and Ti concentrations; a decrease in Zr/Hf and LREE/HREE ratios; and an increase in the Rb/Ba and Ta/Nb ratios from the Guyong to Xiaolonghe plutons suggest fractional crystallization of biotite, plagioclase, K-feldspar, apatite, ilmenite and titanite. They also show the characteristics of I-type granites. The negative zircon εHf(t) isotopic values (−10.04 to −5.22) and high δ18O values (6.69 to 8.58 ‰) and the negative whole-rock εNd(t) isotopic values (−9.7 to −10.1) and high initial 87Sr/86Sr ratios (0.7098–0.7099) of the Guyong monzogranite suggest that these rocks were generated by partial melting of the Precambrian basement without mantle input. The zircon εHf(t) isotopic values (−10.63 to −3.04) and δ18O values (6.54 to 8.69 ‰) of the Xiaolonghe syenogranite are similar to the features of the Guyong monzogranite, and this similarity suggests a cogenetic nature and magma derivation from the lower crust that is composed of both metasedimentary and meta-igneous rocks. The Xiaolonghe fine-grained syenogranite shows an obvious rare earth element tetrad effect and lower Nb/Ta ratios, which indicate its productive nature with respect to ore formation. In fact, we discuss that the Sn mineralization in the region was possible due to Sn being scavenged from these rocks by exsolved hydrothermal fluids. We correlate the Late Cretaceous magmatism in the central Tengchong Block with the northward subduction of the Neo-Tethys beneath the Burma–Tengchong Block.

中文翻译：

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滇西腾冲地块晚白垩世长英质岩浆组：地球化学和同位素综合调查及其对锡成矿的意义

青藏高原东南部三江特提斯带内的腾冲地块在晚白垩世中域经历了长英质岩浆岩套的广泛侵入。在这里，我们从岩石学、地球化学以及 Sr-Nd、锆石 U-Pb 和 Lu-Hf-O 同位素特征等方面研究了该套件中的古永和小龙河岩体，以深入了解新特提斯的演化。古永岩体(76 Ma)由超铝质二长花岗岩组成，小龙河岩体(76 Ma)由超铝质至过铝质中细粒正长花岗岩组成。Eu、Ba、Sr、P 和 Ti 浓度系统性降低；Zr/Hf 和 LREE/HREE 比率降低；从古永到小龙河岩体的 Rb/Ba 和 Ta/Nb 比值的增加表明黑云母、斜长石、钾长石、磷灰石、钛铁矿和钛铁矿的分级结晶。它们还显示出I型花岗岩的特征。负锆石εHf(吨) 同位素值（-10.04 至 -5.22）和高 δ18O 值（6.69 至 8.58 ‰）和负全岩 εNd(吨) 同位素值（-9.7 到 -10.1）和高初始87锶/86固永二长花岗岩的 Sr 比值（0.7098-0.7099）表明，这些岩石是由前寒武纪基底部分熔融而没有地幔输入产生的。锆石εHf(吨) 同位素值（-10.63 至 -3.04）和 δ18小龙河正长花岗岩的O值（6.54～8.69‰）与古永二长花岗岩的特征相似，这种相似性表明下地壳由变沉积岩和变火成岩组成，具有共生性质和岩浆来源。小龙河细粒正长花岗岩表现出明显的稀土元素四联体效应和较低的Nb/Ta比值，这表明其在成矿方面具有生产性。事实上，我们讨论了该地区的 Sn 矿化是可能的，因为 Sn 被溶出的热液从这些岩石中清除。我们将腾冲地块中部的晚白垩世岩浆作用与缅甸-腾冲地块下方的新特提斯向北俯冲联系起来。