闪锌矿^(40)Ar/^(39)Ar真空击碎与阶段加热定年技术  

Sphalerite ^(40)Ar-^(39)Ar dating by crushing in vacuum and stepwise heating on crushed powders

作　　者：蒋映德[1] 邱华宁[1] 云建兵[1] 王强[1] 

机构地区：[1]中国科学院广州地球化学研究所同位素年代学与地球化学重点实验室

出　　处：《地球化学》2007年第5期448-456,共9页Geochimica

基　　金：国家自然科学基金(40472048)

摘　　要：凡口铅锌矿闪锌矿样品40Ar/39Ar真空击碎实验释出较高的39ArK,电子探针分析证实了闪锌矿中含有丰富的钾矿物微晶,因此对该闪锌矿真空击碎分析后的固体粉末继续进行40Ar/39Ar阶段加热分析。真空击碎分析获得了两条明显分开的等时线,对应的等时线年龄～235Ma和～270Ma分别代表了次生、原生流体包裹体的形成年龄。固体粉末阶段加热分析获得了闪锌矿中钾矿物微晶的年龄为～271Ma,与该闪锌矿原生包裹体年龄一致,代表了闪锌矿的成矿年龄。真空击碎和阶段加热实验得到截然不同的K/Ca比值,表明真空击碎法提取的气体主要来自流体包裹体,而加热法释出的气体则主要来自钾矿物微晶。闪锌矿40Ar/39Ar真空击碎与阶段加热分析技术将为探索铅锌矿床直接定年提供新的技术手段。Sphalerite 04FK-02Sp from the Fankou Pb-Zn deposit, northern Guangdong Province, is analyzed using ^40 Ar/^39 Ar crushing technique. The high concentration of 39ARK supposes the presence of some K-rich microlites inside the sphalerite, which is confirmed by subsequent EPMA analyses. In order to obtain the age of the K-rich mierolites, the crushed powders are further analyzed by stepwise heating with an external furnace. The crushing experiment defines two distinct isochron lines corresponding to ages of （234.5_＋5.7） Ma （lo-）and （269.7 _＋ 6. 2） Ma which are interpreted as the ages of the secondary and primary fluid inclusions, respectively. The results of the crushed powders by stepwise heating yield a fiat age spectrum with a plateau age of （267.2 ± 2.5） Ma （from 400 to 800 ℃ ）, and defines a good isochron line with age of （271.3 ±5.4） Ma. The concordant ages of the K-rich microlites by heating and the primary fluid inclusions by crushing clearly indicate that a mineralization epoch took place in the middle Permian. Sphalerite ^40 Ar/^39 Ar progressive crushing and stepwise heating techniques provide a promising approach to directly determine the mineralization ages of Pb-Zn deposits. The ability to date sulfides directly, rather than associated K-bearing hydrothermal phases, is very important for obtaining accurate ages of ore deposits. Remarkable differences of K/Ca rations between crushing and heating experiments suggest that the gases should come from different sources, that is, the gases by crushing are mainly from the fluid inclusions and those by heating from the solid K-rich microlites. Argon within the solid phase of K-rich microlites is hardly released by crushing.

关 键 词：^40 Ar/^39 Ar法 真空击碎 阶段加热 K/Ca比值 凡口铅锌矿 

分 类 号：P597[天文地球—地球化学]