摘要
北祁连黑石山地区的基性—酸性火山岩中,从南向北依次产出郝泉沟、白马洼、黑石山沟、放符崖等花岗岩体,其中在郝泉沟斜长花岗岩体中发现了郝泉沟金矿床。采用LA-ICP-MS同位素测定技术,获得白马洼英云闪长岩和郝泉沟斜长花岗岩的锆石U-Pb年龄分别为(440.2±2.4)Ma和(431.8±2.4)Ma,表明岩体形成时代为晚奥陶世末—早志留世;同时测定白马洼花岗岩体的全岩Rb-Sr和Sm-Nd同位素组成,计算的(87Sr/86Sr)i值为0.70535,εNd(t)值为1.11,推断其源于增厚的下地壳。本次研究表明,在早古生代晚期,随着祁连洋盆闭合,中祁连地块与北祁连奥陶纪岛弧发生碰撞,导致地壳加厚,引起下地壳玄武质岩石部分重熔,黑石山地区的花岗岩体形成于这一背景下。
The Haoquangou, Baimawa, Heishishangou and Fangfuya granite bodies are exposed from the south to the north in the ba- sic-acidic volcanic rocks of Heishishan area of north Qilian, and the Haoquangou gold deposit was found in the Haoquangou pla giogranite body. Based on LA-ICP-MS zircon U-Pb geochronologic study, the authors obtained the age of （440.2±2.4）Ma （MSWD=0.052） for Baimawa tonalite and the age of （431.8±2.4）Ma （MSWD=0.042） for Haoquangou plagiogranite, suggesting that these intrusive bodies were formed in late Ordovician-early Silurian period. Based on the whole rock Rb-Sr and Sm-Nd isotope composition of Baimawa tonalite, the authors calculated the （87Sr/86Sr）; value and the εNd（t） value, which are 0.70535 and 1.11 respec- tively. These data show that Baimawa granite body might have originated in the thickened lower crust. This study has revealed that the north Qilian probably experienced the tectonic evolution of the closure of the Qilian Ocean, the collision of the central Qilian block with the north Qilian Ordovician island arc, the thickening of the crust, and then the partial remelting of basaltic rocks in the lower crust during the late Early Paleozoic; as a result, the granite bodies of Heishishan area were formed.
出处
《地质通报》
CAS
CSCD
北大核心
2013年第10期1575-1583,共9页
Geological Bulletin of China
基金
中国地质调查局项目(编号:1212011085083
12120113047300)
