Emplacement age of leucogranite in the Kampa Dome, southern Tibet
Emplacement age of leucogranite in the Kampa Dome, southern Tibet
复制标题
藏南康巴穹窿淡色花岗岩的侵位年龄
DOI：
10.1016/j.tecto.2015.12.001
复制
发表时间：
2016
期刊：
影响因子：
2.9
通讯作者：
Wang J.-G.
中科院分区：
文献类型：
--
作者：
Liu X.-C.;Wu F.-Y.;Yu L.-J.;Liu Z.-C.;Ji W.-Q.;Wang J.-G.
喜马拉雅浅花岗岩是破译喜马拉雅造山带造山演化的重要岩石。人们已经认识到，在喜马拉雅山脉内，浅色花岗岩是两个独立但平行的带。北带浅色花岗岩主要暴露于片麻岩穹隆内的侵入成分。本文采用激光烧蚀技术，对坎帕浅花岗岩体进行了U(-Th) -Pb锆石、单氮石、xenotime测年和微量元素组成分析，以确定其侵位年龄和岩性。片麻岩锆石以岩浆为主，确定原岩年龄约498 Ma，未见新生代记录。浅花岗岩体锆石显示继承了由细暗边缘覆盖的岩浆岩心，其年龄偶有明显下降，为27.7±1.0 Ma。而淡花岗石中独居石的Th-Pb年龄为25.7±0.5 Ma ~ 26.8±0.4 Ma，与xenotimes的U-Pb年龄24.8±0.4 Ma相当。白花岗岩体侵入的花岗质片麻岩中，独居石和杂生岩的年龄分别为25.8±0.6 ~ 26.6±0.8 Ma和25.0±0.4 ~ 26.0±1.0 Ma。这些年龄与白花岗岩体的年龄相当，表明白花岗岩体侵位期间形成了变质的独居石和片麻岩色光石。微量元素分析表明，浅花岗岩锆石具有较高的P和REE含量（最高可达3721 ppm），而Th/U比值较低（0.04 ~ 0.16）。同样，来自浅色花岗岩的独居石普遍表现出极端的HREE耗损和显著的负Eu异常，部分表现出明显的四分体效应。这些地球化学特征表明，坎帕浅花岗岩在演化过程中具有高度分馏性。
Himalayan leucogranite is an important rock to decipher the orogenic evolution of the Himalayan orogen. It has been recognized that the leucogranite occurred as two separate, but parallel belts within Himalaya. Leucogranite in the north belt is mainly exposed an intrusion component within the gneissic dome. Although most domes have been intensively studied, the Kampa Dome, located in the east of Southern Tibet, is less investigated due to its inaccessibility. In this study, we conducted a comprehensive set of U(–Th)–Pb zircon, monazite and xenotime dating and trace element composition analyses using laser ablation technique, in order to constrain the emplacement age and lithological nature of the Kampa leucogranite. Zircons from gneiss are mainly magmatic and define a protolith age of ca. 498 Ma, but no Cenozoic age is documented. Zircons from leucogranite display inherited magmatic core overgrown by thin dark rim, which occasionally gives a much younger age of 27.7 ± 1.0 Ma. However, monazites from leucogranite yield a Th–Pb age of 25.7 ± 0.5 Ma to 26.8 ± 0.4 Ma, which is comparable to the U–Pb age of 24.8 ± 0.4 Ma obtained from xenotimes. For the granitic gneiss into which the leucogranite intruded, monazites and xenotimes give ages of 25.8 ± 0.6 Ma to 26.6 ± 0.8 Ma and 25.0 ± 0.4 Ma to 26.0 ± 1.0 Ma, respectively. These ages are comparable to those obtained from the leucogranite, and suggest that the metamorphic monazite and xenotime from gneiss formed during the leucogranite emplacement. Trace element analyses indicated that zircons from leucogranite have high P (up to 3721 ppm) and REE concentrations, but have low in Th/U ratios (0.04–0.16). Similarly, monazites from leucogranite generally show extreme HREE depletion and significant negative Eu anomaly with some displaying significantly tetrad effect. These geochemical features indicated that the Kampa leucogranite was highly fractionated during its evolution.