甘肃花牛山东钾长花岗岩^(40)Ar/^(39)Ar同位素年龄及其地质意义  

^(40)Ar/^(39)Ar ISOTOPIC AGE DATING ON K-FELDSPAR SEPARATES FROM EASTERN HUANIUSHAN GRANITE, GANSU PROVINCE, AND ITS GEOLOGICAL SIGNIFICANCE

作　　者：聂凤军[1] 江思宏[1] 刘妍[1] 陈文[2] 刘新宇[2] 张思红[2] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]中国地质科学院地质研究所,北京100037

出　　处：《地质科学》2002年第4期415-422,共8页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金项目 (编号 :40 0 73 0 1 5 );国家地质调查项目 (编号 :K1 3 3 2 )资助

摘　　要：对甘肃花牛山东复式花岗岩体中钾长花岗岩的钾长石进行了详细的4 0 Ar 39Ar同位素年龄测定 ,1 1个加热阶段所获数据构成一条相关关系非常好的直线 ,其对应的等时线年龄为 1 94 2 5± 1 96Ma( 2σ)。4 0 Ar 36 Ar初始值为 2 88 87± 2 1 7( 2σ) ,接近于尼尔值 ( 2 95 5 )。鉴于该岩体形成之后未受到明显的构造—岩浆活动或其它热事件的影响 ,因此 ,1 94Ma代表了钾长花岗岩钾长石的形成时代。花牛山东钾长花岗岩是燕山早期构造—岩浆活动的产物。由此推断 ,花牛山地区构造—岩浆活动时间不是印支期 ,更不是海西期 。Located at southeastern margin of the Kazakhstan plate, Huaniushan was one of the most important Mo, Pb\|Zn\|Ag and Au metallogenic district, and was considered as one of the key parts of the Beishan orogenic belt. The Precambrian and Phanerozoic granitoid intrusives and the related Mo, Pb\|Zn\|Ag and Au deposits (prospects) were widely distributed. Geochronological study of these granitoids attracted geologists' attention both at home and abroad. The 40 Ar/ 39 Ar isotope data for K feldspar separates from the potassium granite of the eastern Huaniushan granitoid intrusive, northwestern Gansu province, were presented in this paper. Eleven stepwise heating Ar data of the K feldspar separates gave an 40 Ar/ 39 Ar isochron age of 194 25±1 96 Ma (2σ) and 40 Ar/ 36 Ar initial value of 288 87±2 17 (2σ), which was obviously close to Nier's value. This age might represent the crystallization time of the K feldspar of the potassium granite from the eastern Huaniushan granitoid intrusive, and was considered as the youngest age of tectono magmatic events occurring within the Huaniushan district. Although no clear correlation existed in between the 40 Ar/ 39 Ar age of the K feldspar from the potassium granite and lead isotopic model age of the sulfide separates from the Mo, Pb Zn Ag and Au ore veins, some of these galena separates had modal age of 126～180 Ma, which was lower than that of the 40 Ar/ 39 Ar isochron age of the K feldspar. The molybdenum, lead zinc silver and gold deposits (prospects) showed a clear temporal relation to the Yanshanian high K granite. The isotopic age data and field petrological observation indicated that the latest emplacement event of the granitoid magma occurred during the Mesozoic Yanshanian orogeny, and was genetically associated with Mo, Pb Zn Ag and Au mineralization.

关 键 词：^40AR/^39AR同位素年龄 燕山期 钾长花岗岩 花牛山 甘肃 形成时代 中生代 岩浆活动 

分 类 号：P588.121[天文地球—岩石学]