龙首山地块的构造属性--来自U-Pb锆石年龄的约束

摘要

The samples were collected from Jinchuan continental scientific drilling core of 1 000 meters below.The geochemical analysis of variational basalts show that the distribution patterns of the rare-earth element(REE) were rich in light REE and the light and heavy REE fractionation significantly right mode. Trace elements show Rb,Ba,La,Ce,Nd,Sm,Nb,Ta are relative enrichment and Sr,Zr ,Hf are deficit. High Nb/Yb ratio,Th/Ta=1.7~5.63,Ta/Hf=0.10~0.21 ,which shows that the characteristics of continental rift basalt in the early time. We can conclude that Paleoproterozoic Longshoushan block is in the initial stage of continental block cracking. Zircon U-Pb isotopic ages indicate that the Longshoushan Block Baijiazuizi Group experienced at least three intense tectonic magmatic metamorphism event,period of peak events are respectively 2.1 Ga,1.9 Ga and 1.85 Ga. Contrast of the tectonic evolution and stratigraphic structure of the Longshoushan block and North China plate,Yang Zi plate,Tarim plate and Western China Craton,we know that Longshoushan block has most similarities with Western China Craton. So the prospecting orientation for the Cu-Ni sulfide deposit in the future should be put in the whole Western China Craton.%在金川矿集区大陆科学钻探岩芯中采集到1000 m以下的样品，岩石地球化学分析显示，变玄武岩的稀土元素配分模式呈轻稀土富，轻、重稀土分馏明显的右倾型模式，微量元素显示Rb、Ba、La、Ce、Nd、Sm相对富集，Nb、Ta、Sr、Zr、Hf亏损。Nb/Yb比值高，Th/Ta=1.7~5.63，Ta/Hf=0.10~0.21，具有大陆裂谷初期的玄武岩特征。由此推断，古元古代龙首山地块为一个正处于初期裂解的大陆块。锆石U-Pb同位素测年显示，龙首山地块白家嘴子组至少经历了三期强烈的构造岩浆变质事件，主峰期分别为2.1 Ga、1.9 Ga和1.85 Ga。对比龙首山地块与华北板块、杨子板块、塔里木板块和西域板块的地层结构与构造演化特征，龙首山地块与西域板块有诸多相似性，今后的找矿方向应着眼于整个西域板块。