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采用SHRIMP锆石微区U-Pb测年及角闪石40Ar-39Ar测年对冈底斯成矿带东段工布江达县沙让斑岩钼矿区的角闪石闪长岩体进行了年代学研究。对角闪石闪长岩中单颗粒锆石11个样品点分析,其206Pb/238U年龄范围在(45.39±0.77)～(52.7±3.3)Ma之间,加权平均值为(47.17±0.41)Ma,(n=11,MSWD=2.0)。对角闪石样品采用40Ar-39Ar阶段升温测年,年龄谱呈马鞍形,说明角闪石样品存在过剩氩,加权平均年龄(55.10±0.79)Ma不具地质意义,最低坪年龄(53.25±0.60)Ma接近但大于角闪石的结晶年龄。综合前人研究结果,笔者认为:①角闪石闪长岩体形成年龄为(53.25±0.60)Ma,属于喜马拉雅期,相当于始新世,岩体侵入时间早于含矿主岩体斜长花岗斑岩的形成时间。②受后期花岗斑岩体侵入热事件的影响,锆石的蜕晶化作用导致年龄偏小,角闪石Ar-Ar法最低坪年龄基本代表成岩年龄。③斑岩钼矿的形成与主碰撞期岩浆底侵作用有关,始新世早期,冈底斯成矿带的地壳已经增厚到可以产生地壳熔融的厚度,形成斑岩钼矿。④冈底斯成矿带存在40～65Ma的主碰撞期,显示出念青唐古拉成矿带具有良好的寻找斑岩型钼矿-矽卡岩型多金属矿的潜力。
The SHRIMP Zircon U-Pb dating and the 40Ar-39Ar dating of amphibole were used to study the chronology of amphibole-diorite bodies in the Sharang porphyry molybdenum deposit area in the eastern section of the Gangdese metallogenic belt . The eleven samples of single zircon from the amphibole-dickite were analyzed. The 206Pb / 238U ages ranged from (45.39 ± 0.77) to (52.7 ± 3.3) Ma and the weighted average was (47.17 ± 0.41) Ma , (n = 11, MSWD = 2.0). The amphibole samples are dated by 40Ar-39Ar temperature stage, and the age spectrum is saddle-shaped, indicating that there is excess argon in the amphibole samples. The weighted mean age (55.10 ± 0.79) Ma is not geologically significant, and the minimum age is 53.25 ± 0.60. Ma is close to but greater than the crystalline age of amphibole. Based on the results of previous studies, the author thinks: ① The age of the amphibole-diorite body is (53.25 ± 0.60) Ma, belonging to the Himalayan period, which is equivalent to the Eocene. The intrusion time of the amphibolite is earlier than that of the host rock Granite porphyry formation time. (2) Influenced by the invaded thermal event of granitic porphyry in the later stage, the degeneratization of zircon led to the younger age. The lowest plateau age of Ar-Ar method of amphibole basically represented diagenetic age. (3) The formation of porphyry molybdenum ore is related to the magmatic underplating in the main collision period. In the early Eocene, the crust of the Gangdese metallogenic belt has been thickened to the thickness that can produce the crustal melting and form porphyry molybdenum ore. ④ The main collision period of Gangdese metallogenic belt is 40-65Ma, indicating that the Nyainqentanglha metallogenic belt has good potential for finding porphyry molybdenum-skarn-type polymetallic ore.