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青海省沱沱河地区开心岭一带中二叠世—早三叠世构造背景是影响该区成矿规律和找矿方向分析的重要因素。对开心岭一带中二叠世诺日巴尕日保组玄武岩地球化学及侵入其中的辉长岩进行年代学研究,以期对该区中二叠世—早三叠世成矿构造背景提供一定的约束。采用LA-ICP-MS技术测得的辉长岩中锆石206Pb/238U年龄加权平均值为247.0±1.7Ma,属于早三叠世,该期岩浆事件可能是龙木错—双湖缝合带和可可西里—金沙江缝合带在此阶段发生俯冲的产物。地球化学特征表明,中二叠世玄武岩具有高镁、富铁、贫碱的特征,属于拉斑系列玄武岩;富集LREE和部分HFSE,REE表现为轻、重稀土元素分馏明显的右倾型配分型式。具有相对高的Zr含量(平均含量大于70×10-6)和Zr/Y值(5.2~7.0),Nb、Ta、Zr、Hf和Ti相对亏损,Nb/La值(0.1~0.3)较低,总体具有大陆玄武岩的特征,但受到不同程度陆壳或岩石圈地幔的混染。综合多种判别图解分析认为,该套玄武岩形成于大陆裂谷环境。
The Middle Permian-Early Triassic tectonic setting of Kaixingling area in Tuotuohe area of Qinghai Province is an important factor that influences the metallogenic regularity and prospecting direction in this area. The geochronology of basalt geochemistry and intrusive gabbro in the No.2 Permian Norgesbaiga Gambo Formation in Kaixingling area is studied by geochronology in order to provide some information on the tectonic setting of the Middle Permian-Early Triassic ore-forming structure in the area constraint. The weighted average 206Pb / 238U ages of zircons from gabbro, measured by LA-ICP-MS technique, are 247.0 ± 1.7Ma and belongs to the Early Triassic. The magmatic event may be the Longmucuo-Shuanghu suture The Hoh Xil-Jinsha River suture was the product of subduction at this stage. The geochemical characteristics show that the Middle Permian basalts are characterized by high magnesium, iron-rich and low-alkali. They belong to the basalt series. The enrichment of LREE and some HFSE shows that the REE is characterized by light fraction and heavy fractionation of REE. . With relatively high Zr content (average content over 70 × 10-6) and Zr / Y values (5.2-7.0), relative loss of Nb, Ta, Zr, Hf and Ti, and lower value of Nb / La , Generally have the characteristics of continental basalts, but are contaminated by crust or lithospheric mantle to varying degrees. Comprehensive analysis of a variety of discrimination diagram that the set of basalts formed in the continental rift environment.