The authors conducted a combined study of petrologic, geochemical, geochronological, and Lu-Hf isotopic analysis of the plutons from the Darongshan-Shiwandashan granitoids. Igneous zircons from the Taima granite porphyry yielded a weighted 206Pb/238U age of (243±3) Ma, consistent with ages of other plutons of the granitoids. All these plutons are mainly composed of granite, granite porphyry and charnockite, and contain granulite enclaves. They are all strongly peraluminous, high-K calc-alkaline granites and show negative Eu anomalies with Eu/Eu* ratios being 0.30~0.54. They are enriched in Rb, Th and U, and depleted in Nb, Ta, P, Ti. They have high total REE content and display enrichment in LREE. These geochemical features are consistent well with the S-type characteristics of the granitoids. In situ zircon Hf analyses show negative εHf(t) values from-16 to-6, and have the depleted mantle two-stage Hf model ages (TDM2) of 1.6~2.3 Ga. The authors hold that the S-type granites were formed by melting of the Paleoproterozoic to Mesoproterozoic meta-sedimentary rocks in an extensional tectonic setting. Heat input associated with the asthenosphere mantle upwelling might have played an important role in crustal melting and crystallization of the granitoids. Geodynamically, the formation of the S-type granitoids was related to the subduction of the Paleo-Pacific plate.%本文对大容山—十万大山花岗岩带南西段的浦北、旧州、台马、大寺、那垌岩体进行了岩石学、地球化学、年代学及Lu-Hf同位素研究.台马岩体花岗斑岩LA-ICP-MS锆石U-Pb年龄为(243±3) Ma, 与其它岩体同属早三叠世花岗岩.所有这些岩体均主要由花岗岩和花岗斑岩组成, 部分含麻粒岩包体.它们均属强过铝质花岗岩, 明显富集大离子亲石元素 Rb、Th、U, 亏损 Nb、Ta、P、Ti 等高场强元素.同时, 它们稀土元素总量较高, 相对富集轻稀土, Eu负异常明显(Eu/Eu* = 0.30~0.54), 具典型的S-型花岗岩特征.岩体的锆石εHf(t)值均为负值,集中在-16~-6之间,二阶段模式年龄(TDM2)集中在1.6~2.3 Ga之间.综合上述结果推测,大容山—十万大山 S-型花岗岩, 为地壳减压松弛的构造背景下, 地幔或软流圈物质上涌, 诱发地壳中的中元古—古元古代变质沉积岩发生高温熔融作用的结果, 其成因可能与古太平洋板块俯冲作用相关.
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