东昆仑造山带早中生代幔源岩浆事件及其地质意义

东昆仑造山带早中生代幔源岩浆底侵不仅为花岗岩类的广泛发育提供了能量和物质基础,也为厘定区域构造环境提供了新的约束。本文对区域上发育的小尖山岩体、拉陵高里沟脑2、3号岩体开展了精确的锆石U-Pb年代学研究,并与区域上镁铁质岩体做了对比。LA-ICP-MS U-Pb定年结果表明,小尖山岩体磁黄铁矿化辉长岩锆石~(206)Pb/~(238)U-~(207)Pb/~(235)U谐和年龄为247.1±1.1Ma,与前人获得的中细粒辉长岩年龄相差20Ma,暗示该岩体为多期岩浆活动的产物。拉陵高里沟脑2号和3号岩体辉长岩锆石~(206)Pb/~(238)U-~(207)Pb/~(235)U谐和年龄分别为(244.9±1.6)Ma和(238.4±4.1)Ma,二者年龄在测试误差范围内一致,为同期岩浆作用的产物。结合区域上已知镁铁质岩体的形成时代及地球化学特征,认为早中生代幔源岩浆形成于后碰撞伸展环境,活动时限为251~221Ma。该期幔源岩浆与地壳物质发生了广泛的物质与能量交换,是今后该区铜镍矿勘查的重要对象之一。

Early Mesozoic mantle-derived magmatic events and their geological significance in the East Kunlun orogenic belt

The Early Mesozoic mantle-derived magmatic underplating in the East Kunlun orogenic belt provides not only energy and material for the extensive development of granites, but also a new constraint on determination of regional tectonic environments. In this paper, an accurate zircon U-Pb chronology study is carried out on the Xiaojianshan and Lalinggaoligounao intrusion, and a comparison is made with the mafic rock in the study area. The resultsofLA-ICP-MSU-Pbdatingshowthattheconcordiaageofzircon206Pb / 238U-207Pb /235Uis(247.1 ±1.1)Ma,whichis20Maolderthan the age of gabbro in previous work, indicating that the intrusion is the product of multi-stage magmatic activities. The zircon ages of the 206 Pb / 238 U-207 Pb/235 U for No. 2 and No. 3 intrusions are (244. 9 ± 1. 6) Ma and (238. 4 ± 4. 1) Ma, respectively. Based on the ages and geochemical character-istics of the known mafic rocks in the area, we suggest that the Early Mesozoic mantle magma was formed in the post-collision extensional environment with a time limit of 251~221 Ma. The mantle-derived magma of this period has experienced a wide material and energy exchange with crust, which is one of the important objects of copper-nickel exploration in the future.