内蒙古四子王旗地区侵入白云鄂博群辉长岩的年龄及其对白云鄂博群时代的约束  

Zircon ages of gabbros in the Siziwangqi,Inner Mongolia and its constrain on the formation time of the Bayan Obo Group

作　　者：周志广[1] 王果胜[1] 张达[1] 谷永昌[2] 朱卫平[3] 柳长峰[1] 赵孝旗 胡萌萌[1] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]中国地质调查局天津地调中心,天津300170 [3]中国国土资源航空物探遥感中心,北京100083

出　　处：《岩石学报》2016年第6期1809-1822,共14页Acta Petrologica Sinica

基　　金：中国地质调查项目(1212011220465;1212011085490;1212011120700)资助

摘　　要：内蒙古四子王旗大井坡一带发育的中新元古代白云鄂博群是白云鄂博矿区的东延部分。野外调查过程中在该地区新发现了两个侵入白云鄂博群的辉长岩体,其同位素年龄可很好地约束存在争议的白云鄂博群时代。将侵入都拉哈拉组的辉长岩体称为吉生太辉长岩,将侵入比鲁特组的辉长岩体称为大井坡辉长岩。采用LA-ICPMS法进行锆石U-Pb同位素定年,获得了吉生太辉长岩的侵位年龄为1670±14Ma(MSWD=1.6),大井坡辉长岩的侵位年龄为1342±9Ma(MSWD=0.94)。依据辉长岩的同位素年龄,通过与燕辽裂陷槽元古代地层与岩浆事件对比,厘定了白云鄂博群的形成时代,建议将都拉哈拉组与尖山组划归古元古界长城系,即国际地层表的固结系;将哈拉霍圪特组划归中元古界蓟县系,即国际地层表的盖层系;将比鲁特组划归中国地层表的待建系下部,即国陆地层表的中元代延展系;将白音宝拉格组的时代划归青白口纪。通过对比发现白云鄂博裂陷槽经历的岩浆事件与华北板块及燕辽裂陷槽基本一致,其形成可能与哥伦比亚超大陆裂解有关。The Bayan Obo Group outcropped in the Dajingpo,Siziwangqi,Inner Mongolia,is the eastern extension of Bayan Obo ore deposit. Two gabbro plutons intruded into Bayan Obo Group were discovered through geological survey,whose zircon ages will provide new clues to constrain the controversial formation time of the Bayan Obo Group. The gabbro intruded into Dulahala Formation is named Jishengtai pluton,while the one intruded into Bilute Formation is termed Dajingpo pluton. LA-ICP-MS U-Pb dating yielded ages of 1670 ± 14Ma（ MSWD = 1. 6） for Jishengtai pluton and 1342 ± 9Ma（ MSWD = 0. 94） for Dajingpo pluton,respectively. Based on the new ages,together with published data of Proterozoic strata and magmatic events in Yanliao rift,we suggest that Dulahala and Jianshan formations should belong to Paleoproterzoic Changchengian System, equivalent to Statherian in International Chronostratigraphic Chart（ ICC）; Halahuogete Formation should be Mesoproterozoic Jixianian System,equivalent to Calymmian in ICC; Bilute Formation should be Mesoproterozoic lower part of an awaiting build System,the same to Ectasian in ICC,and the Baiyinbaolage Formation should be Neoproterozoic Qingbaikouian System,which referred as Tonian in ICC. The magmatic events in the North China Craton, Bayan Obo and Yanliao rifts are comparable, which probably related to the breakup of the Columbia suppercontinent.

关 键 词：同位素年龄 辉长岩 白云鄂博群 四子王旗 内蒙古 

分 类 号：P588.124[天文地球—岩石学] P597.3[天文地球—地质学]