辽宁建昌杜杖子岩体年代学、地球化学特征及其构造环境与成矿关系

Geochronological and Geochemical Characteristics of Duzhangzi Pluton in Jianchang, Liaoning Province, and Its Relationship to Tectonic Environment and Mineralization

辽西地区的五指山-虹螺山多金属成矿带上分布有大量的花岗岩侵入体,杜杖子岩体位于成矿带中段,岩石类型为黑云母二长花岗岩。为厘定岩体的形成时代、构造环境和对成矿的影响,对黑云母二长花岗岩进行LA-ICP-MS锆石U-Pb年代学、岩相学和主微量元素研究。研究结果表明,杜杖子岩体成岩年龄为168.5 Ma±0.24 Ma,时代属中侏罗世。岩石具富Si、Al、Na、K,贫Mg、Ca特征,属于岩浆晚期高分异形成的铝质-过铝质高钾钙碱性I型花岗岩。轻稀土富集,重稀土亏损,轻重稀土分馏较大,大离子亲石元素Rb、Ba和K富集,高场强元素Nb、Ta、Zr亏损,铕呈轻微负异常。结合区域构造事件认为,古太平洋板块向华北克拉通东部俯冲形成幔源岩浆,幔源岩浆底侵为地壳发生部分熔融提供热量,且与熔融的壳源岩浆混合,岩浆物质成分由中性逐渐向酸性过渡。受岩浆分异程度、酸度和碱度的制约,富含矿质的热液在岩浆期后结晶分异形成Au、Cu-Pb、Zn-Mo成矿系列,矿液通过岩浆上拱造成的围岩裂隙带上升、减压、降温,当达到合适的条件时,矿质析出富集成矿。

A large number of granite intrusions are distributed in Wuzhishan-Hongluoshan polymetallic metallogenic belt in western Liaoning. Duzhangzi rock mass is located in the middle of the metallogenic belt, and the rock type is biotite monzogranite. LA-ICP-MS zircon U-Pb chronology, petrography and major elements and trace elements of biotite monzogranite were studied in order to determine the formation age, tectonic environment and its influence on mineralization. The results show that the diagenetic age of Duzhangzi pluton is 168.49±0.24 Ma, belonging to the Middle Jurassic. The rock is rich in Si, Al, Na, K and poor in Mg and Ca, belonging to aluminous peraluminous high potassium calcalkaline I-type granite formed by high differentiation in the late magmatic period. LREE is enriched, HREE is depleted, light and heavy rare earth fractionation is large. Large ion lithophile elements Rb, Ba and K are enriched, high field strength elements Nb, Ta and Zr are depleted, and europium presents a slight negative anomaly. Combined with regional tectonic events, it is considered that the ancient Pacific plate subducted to the east of the North China Craton to form mantle derived magma, which provided heat for the partial melting of the crust and mixed with the molten crust derived magma, and the composition of magmatic material gradually transited from neutral to acidic. Restricted by the degree of magmatic differentiation, acidity and alkalinity, the mineral rich hydrothermal solution crystallizes and differentiates after the magmatic period to form Au, Cu-Pb and Zn-Mo metallogenic series. The ore solution rose, decompressed and cooled through the surrounding rock fracture zone caused by magmatic arching. When the appropriate conditions were reached, the mineral precipitated and enriched for mineralization.