西藏中冈底斯成矿带晚三叠世铍铷稀有金属矿化:独居石U-Pb年代学证据

在西藏南木林县北部地区新发现了Be-Rb±（Nb-Ta）稀有金属找矿线索，但由于含矿岩体中锆石U含量过高，导致对其进行U-Pb年代学研究不能获得可靠的岩浆结晶年龄.采用LA-ICP-MS方法对赋矿岩体的独居石进行了U-Pb年代学研究，获得了207.0±0.7 Ma（n=22，MSWD=0.101）的独居石206Pb/238U加权平均年龄和207.0±0.8 Ma（MSWD=0.107）的下交点年龄，能够更加可靠地代表赋矿岩浆岩的结晶年龄.该独居石U-Pb年龄表明，含矿岩体结晶于晚三叠世，晚于区内的花岗闪长岩形成年龄，可能代表了尚未能完全识别出的冈底斯印支期造山活动晚期一次重要的成岩事件.该期赋存稀有金属岩体的发现进一步丰富了中冈底斯成矿带的矿种和矿床类型，对更加深入地认识冈底斯成矿带中生代构造－岩浆演化与成矿作用，丰富和完善与青藏高原多岛弧盆演化有关的造山与成矿理论有重要意义. 

Late Triassic Beryllium and Rubidium Rare Metals Mineralization in the Central Gangdise Metallogenic Belt,Tibet, China: Evidence from Monazite U-Pb Geochronology

Beryllium and rubidium mineralization is newly found in northern Namling, Tibet, China. However, the U-Pb ages are not reliable representation of magmatic emplacement age since U concentration in zircons from the mineralized pegmatitic muscovite monzogranite is too high. LA-ICP-MS is taken on monazites from this pyrogenic rock using 24 μm spot 193 nm laser, yielding reliable age. The weighted average age of 206Pb/238U is 207.0±0.7 Ma (n=22, MSWD=0.101), and the lower intercepted age is 207.0±0.8 Ma (MSWD=0.107). These ages obtained by LA-ICP-MS analysis show the mineralized pegmatitic muscovite monzogranite emplaced in Late Triassic and later than granodiorite in this region. It may represent an important diagenetic event that has not yet been fully identified in the late stage of Indosinian orogeny in Paleo-Gangdise. This new discovery may expand minerals and deposit types for further regional prospecting in the central Gangdise metallogenic belt. Furthermore, this discovery also has great importance for the re-understanding of the Mesozoic tectonic evolution, magmatic evolution and mineralization in this belt. And further enhances the orogenic and metallogenic theories related to the evolution of multi-island-arc-basin in the Qinghai-Tibet Plateau.