江南古陆南缘四堡群地质年代学研究的最新进展  

NEW ADVANCE lN THE GEOCHRONICAL STVDIES oF SIBAO GROUP IN THESOUTHERN MARGIN OF JIANGNAN OLD CONTINENT

作　　者：韩发 沈建忠 聂凤军 李世朝 杨开泰 杨淳 丁孝石 

机构地区：[1]地矿部矿床所 [2]广西区调队 [3]广西石油地质队 [4]地矿部地质所

出　　处：《中国地质》1994年第6期25-26,共2页Geology in China

基　　金：地矿部同位素开放实验研究室资助项目

摘　　要：四堡群主要分布于桂北九万大山一带,是华南最古老地层单元之一.与四堡群在岩石一地层学上可咨对比的相应火山一沉积岩系,在我国南方广大地区均有出露,但对这套地层的时代归属一直没有定论,是南方悬而未决重大基础地质问题之一.多年来,一些研究者根据侵入于四堡群而被丹洲群不整合覆盖的本洞英云闪长岩体年龄(1063土95Ma)而将其与北方蓟县系相对比(伍实。Sibao Group, one of the oldest volcano-sedimentary sequence in South China, mainly occurs in Jiuwan Mountains, Guibai district, and can be compared with corresponding volcano -sedimentary sequences in this region. But controversy exists about its forming age for a long time. Pillowed basalts have been sampled from Wentong Formation in Lubu mountain, Wudi mining district in order to obtain zircon separates for single-particle 207Pb/206Pb determination. The results show that two groups of primary zircon gave the ages of 1734Ma and 1864Ma respectively, implying that Sibao Group formed in the early Mesoproterozoic or later Paleoproterozoic time, another group of zircon gave a older age with relatively large errors which may represents the forming age of older basement under Sibao Group, combined with the crystal properties of zircon. In addition, seven samples of mafic-ultramafic rocks from Wentong Formation have been selected and gave a Sm-Nd isochronical age of 1852 + 270Ma(2σ), similar to 207Pb/206Pb ages of zircon, which greatly enhanced the credibility of this study, and has a great significance in tectonic and metallogenic studies in South China.

关 键 词：地质年代学 四堡群 古陆壳 江南 

分 类 号：P533[天文地球—古生物学与地层学]