冈底斯西北缘晚白垩世石英二长岩的年代学、地球化学、构造环境及成矿意义  

Geochronology, Geochemistry, Tectonic Setting and Metallogenetic Significance of the Late Cretaceous Quartz Monzonite in the Northwestern Gangdise Terrane

作　　者：李华亮[1,2] 杨绍 李德威[1,2,3] 张硕[1,2] 吕志伟[1,2] 陈桂凡[1,2] 

机构地区：[1]中国地质大学(武汉)地质调查研究院,湖北武汉430074 [2]中国地质大学(武汉)地球科学学院,湖北武汉430074 [3]中国地质大学(武汉)青藏高原研究中心,湖北武汉430074

出　　处：《大地构造与成矿学》2014年第3期694-705,共12页Geotectonica et Metallogenia

基　　金：中国地质调查局西藏1:5万聂拉木等4幅区域地质调查(编号:1212011121242);西藏1:5万日土县卡易错地区4幅区域地质调查(编号:1212011121246)

摘　　要：85-90 Ma是班公湖-怒江构造带一个重要的成矿期。目前对该期矿床的形成环境和矿床成因还存在争议,而且该带西段的研究比较薄弱。通过区域地质矿产调查,我们在班公湖-怒江构造带西段日土县西侧扎隆琼娃发现与近南北走向的伸展构造和晚白垩世富镁石英二长岩密切相关的富铁矿。通过锆石LA-ICP-MS U-Pb测年法获得石英二长岩的成岩年龄和成矿年龄分别为85.60±0.48 Ma和85.51±0.77 Ma。地球化学特征显示石英二长岩类似埃达克质花岗岩,却具有较高的Mg#（52.9-56.8）、Cr（106.8×10^-6-597.1×10^-6）、Ni（60.6×10^-6-78.2×10^-6）,岩石富集轻稀土和大离子亲石元素Rb、Th、U等,亏损重稀土和高场强元素Nb、Ta、Ti等。据此初步认为：晚白垩世中期班公湖-怒江构造带在陆内地幔软流圈底辟及相关的地壳热隆伸展构造背景下,通过壳幔相互作用形成了富镁石英二长岩及其相关的富铁矿。85-90 Ma is an important metallogenic period for the Bangong Lake-Nujiang River tectonic zone. So far, the metallogenic geological background and genesis of this period are still controversial, and the western part of the tectonic zone is less well documented. Based on the regional geological and mineral investigations, we found a high-grade iron deposit at Zhalongqiongwa in the west of Ritu County, west part of the Bangong Lake-Nujiang River tectonic zone. The deposit is closely associated with the nearly north-south extensional tectonics and the late Cretaceous magnesium-rich quartz monzonite. The diagenetic age and mineralization age are 85.60±0.48 Ma and 85.51±0.77 Ma, respectively, using LA-ICP-MS zircon U-Pb dating method. Geochemical characteristics show that the quartz monzonite is suspected to be adakitic granite, with high SiO2（62.09%-65.54%）, Al2O3（15.08%-15.92%）, Sr（385×10^-6-453×10^-6） and low Y（14.8×10^-6-17.9×10^-6）, Yb（1.40×10^-6-1.70×10^-6）, LREE enrichment（19.56〈（La/Yb）N〈N26.69）, weak negative Eu anomaly（0.72〈δEu〈0.81）. However, the quartz monzonite has high contents of Mg#（52.9-56.8）, Cr（107×10^-6 -597×10^-6）, Ni（60.6×10^-6-78.2×10^-6） and is rich in LREE and LILE（e.g. Rb, Th, U） and poor in HREE and HFSE, such as Nb, Ta, Ti. It is suggested that under the background of asthenosphere diapirism and related thermal-uplift extensional tectonics in the crust, the crust-mantle interaction led to the formation of the magnesium-rich quartz monzonite and the relevant magnetite deposit.

关 键 词：石英二长岩 伸展构造 壳幔作用 陆内成矿 班公湖-怒江构造带西段 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]