【摘要】 滇西特提斯构造域广泛发育中—新生代岩浆作用,是长期复杂的造山作用的结果。出露于腾冲地块的坡仑山花岗岩体锆石U-Pb年龄和地球化学特征显示,坡仑山岩体主要岩石类型为斑状花岗闪长岩,以全碱含量高为特征,属于高钾钙碱性系列,富集大离子亲石元素、亏损高场强元素(Nb、Ta、Ti和P)。锆石U-Pb定年结果指示岩体的侵位时代为66~63 Ma,是新特提斯洋汇聚过程的产物。部分锆石颗粒或晶区具有高的U和Th含量特征,其U-Pb年龄集中在35~30 Ma,明显年轻于岩体侵位时代,而与高黎贡山变质带变质—变形时代吻合,可能反映高U-Th锆石同位素体系遭受热事件重置。全岩Sr-Nd同位素组成显示富集特征,初始87Sr/86Sr比值介于0.7158和0.7164之间,初始εNd值为-14.5至-15.3,对应Nd模式年龄值为2.04~2.10 Ga,推测岩浆源区可能以古元古代地壳物质为主。更多还原

【Abstract】 Mesozoic to Cenozoic magmatic activities, widely distributed in the Tethyan belt of western Yunnan, are induced by the long-time complicated orogenic processes. Zircon U-Pb age data and geochemical characteristics of the Polunshan granite, exposed in the Tenchong block, are reported in this study. The Polunshan granite pluton is composed mainly of porphyritic coarse-grained granodiorites. Geochemically, this granite is characterized by high alkali contents and belongs to the high-potassic calc-alkaline rock type. It enriches in large-ion lithosphile elements and depletes in high field-strength elements(Nb, Ta, Ti and P). Results of the zircon U-Pb dating suggest emplacement ages of 66~63 Ma for the magma(s) of the Polunshan granite, pointing to a magmatic product related to the closure of the Neo-Tethys Ocean. Many analysed zircon grains or crystal domains have high contents of U and Th. They yield U-Pb ages of about 35~30 Ma, significantly younger than emplacement time of the granite, but similar to the age of deformation or metamorphism of the Gaoligongshan metamorphic belt. This phanomenon implies that the U-Pb isotopic system of those zircons of high Th-U-contents was reset during the late thermal event. The Polunshan granite exhibits entrenchment feature in Sr-Nd isotopic composition, with initial87Sr/86 Srratios of 0.7158 to 0.7164 and initial εNdvalues of-14.5 to-15.3, corresponding to Nd modal ages of2.04~2.10 Ga, suggesting that Paleoproterozoic crustal material as a major source of the magma(s).更多还原