三江北段纳日贡玛斜长花岗斑岩的年代学及地质意义

Chronological and Geological Significance of Narigongma Plagiogranite Porphyry in the North Part of the Sanjiang Region

纳日贡玛斑岩产于三江北段，由大小不同的6个斑岩体组成，岩石化学显示属于高钾钙碱性系列岩石；稀土配分型式为几乎不具负Eu异常的轻稀土富集型。笔者利用锆石U—Pb方法首次测得纳日贡玛斜长花岗斑岩的生成年龄为41．0±0．18Ma，属喜马拉雅早期。从区域构造演化的角度来看，三江北段大部分花岗质岩体的形成都与喜马拉雅造山作用过程中的岩浆侵位相关，表现为多数同位素年龄都集中在21～66Ma。鉴于纳日贡玛铜钼矿产于纳日贡玛斑岩体中，属于斑岩型，花岗斑岩体为纳日贡玛铜钼矿提供了成矿物质来源。同时三江北段发育较多的中酸性岩体，纳日贡玛铜钼矿床成岩年龄的确定对于在该区寻找斑岩型铜钼矿有重要的理论和现实意义。

Located in the north part of the Sanjiang Region and composed of 6 small porphyry bodies, Narigongma porphyry belongs to high-K calc-alkaline series in petrochemistry. The REE diagram shows that the rock is enriched in LREE with rarely negative Eu anomaly. Zircon U-Pb dating method has determined for the first time that the diagenetic age of Narigongma plagioclase porphyry is about 41. 0 0. 18Ma in the Early Himalayan epoch. From the view of regional tectonic evolution, the formation of most granite ore bodies in the north part of the Sanjiang Region are closely related to the magmatic emplacement of Himalayan orogeny, as most of the isotopic ages concentrate in 21-66 Ma. Because Narigongma Cu-Mo deposit occurred in porphyry bodies, the granite porphyry has provided mineral sources for the deposit mineralization. Meanwhile, due to abundant occurrence of intermediate-acid magmatic bodies in the north part of the Sanjiang Region, the diagenetic age determination of Narigongma porphyry Cu-Mo deposit is of great theoretical and practical importance in porphyry Cu-Mo deposit ProsPecting.