SHRIMP U-Pb zircon age of tuff from the Kunyang Group in central Yunnan： Evidence for Grenvillian orogeny in South China
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因为， Grenvillian 造山运动是否发生在华南，仍然保持高度争论高质量，区别数据正在缺乏，因此，解决这件事的钥匙是发现与 Grenvillianorogeny 有关的可确定时代的暴烈或沉积的岩石。如此的岩石在从在中央云南的降低中间的部分 ofKunyang 组的 Fuliangpeng 成员是显然在场的；在这里，单位是厚的超过 100 m 并且由 andesiticignimbrite， tuffite， terrigeous 棒麴霉素和碳酸盐组成。这些暴烈的岩石， Sibao 褶层戳的发达南方系上带子，从中央云南在晚前寒武纪的时间代表最早计算碱的暴烈的活动并且与两个是同时代的在到碳酸盐和在其它地方的 seismite 开发的开始的从岩屑的沉积外形的一个变化。为 SHRIMPanalysis 的二件样品从这个暴烈的单位被收集。从 FuliangpengMember 的底部，样品 G3-29-2 是 ignimbrite，并且从它恢复的大约 100 锆石晶体有 euhedral 形状并且在 cathodoluminescent (CL ) 下面显示相对简单的部门带状配列成像，建议 amagmatogenic 起源。25 锆石被分析， 1032 ± 9 妈的称平均数的 U-Pb 年龄被获得。样品 G3-29-3 从最高 Fuliangpeng 成员的部分是 tuffite，并且许多绕行显然由岩屑形成的锆石被恢复。九这些锆石被分析，并且最旧的单个谷物的 U-Pb 锆石变老，暗示 6 妈在 Cathaysia 开发了的那个 Paleoproterozoic 地下室是 1938 ± 2。标明日期的结果，与关于 FuliangpengMember 的大地构造的研究结合了，导致我们结束那迟了的 Mesoproterozoic orogenic 暴烈的活动发生在华南的西方的部分，并且 Yangtze 和 Cathaysian cratons 的相关碰撞是 Rodinia 的集会的不可分的部分。Keywords:
Rodinia
Orogeny
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Abstract The Qingbaikouan System is the lowest unit of the Neoproterozoic Erathem in Chinese stratigraphic succession, and it now provides a precise geochronological framework and geological time scale for mapping and stratal correlation in China. However, a sensitive high‐resolution ion microprobe (SHRIMP) U‐Pb zircon age date (1368±12 Ma) obtained from a bentonite in the Qingbaikouan Xiamaling Formation indicates that it belongs to the Mesoproterozoic Erathem instead. This change is a milestone in understanding the Precambrian Stratigraphic Time Scale in China, and it has had great influence on Precambrian correlations in Asia. Otherwise, a large amount of geochronological work has been done in the “Jiangnan Orogen Belt” of South China, and new isotopic data have redefined the traditional recognition of metamorphosed Mesoproterozoic strata from the Sibao orogeny to the Neoproterozoic Erathem. Based on SHRIMP zircon U‐Pb age data, the authors regard the Sibao orogeny (equal to the Willing orogeny) as a movement at ca 820 Ma, meaning that the Sibao orogeny was not equivalent to the Grenvillian orogeny. Finally, we report here the first SHRIMP U‐Pb age of the boundary between the top of the Qingbaikouan Gongdong Formation (786.8±5.6 Ma) and the bottom of the Chang'an (diamictite) Formation (778.4±5.2 Ma), which is the age of the lowest diamictite of the Nanhuan System in China.
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暗岩和玄武岩的安山岩在 greenschist 变形了外形在 Wutai 山区在 Paleoproterozoic Hutuo 组的底部与集团企业层发生，诺思中国 Craton。详细说明的地质的调查证实这些暴烈的岩石在附近的沉积岩石以内是一致的。玄武岩的安山岩上的虾结果被划分成二个组。在一个组， 207Pb/206Pb 年龄来自 2433 ～ 2558 妈，它与地下室一致在 Fuping 和 Wutai 区域的外壳的年龄。在另外的组， 13 谷物产出 2140 的加权的吝啬的 207Pb/206Pb 年龄
Basaltic andesite
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巨大的辉绿岩发生在以内原生地，在北方中国的南部的边缘的阶层堵住，地理上在安徽和江苏省的北部分，在比 Neoproterozoic 年轻的阶层都没被发现的地方。从辉绿岩的锆石从 cathodoluminesecence 显示出三不同结构成像，而是他们都具有 magmatic 起源。虾 U-Pbdating 产出 ~(206 ) 的一个范围从 2600 ～ 124 妈的 Pb/~(238 ) U 年龄，而是二个地质的事件能清楚地从一致、不和的年龄被识别。一个人给二加权的mean~( 207 ) 976 +-的Pb/~( 206 ) Pb 年龄 24 和 1038 +-作为辉绿岩结晶化预定被解释的 26 妈，并且其它有Pb/~( 206 ) Pb 2523 +-变老的加权的吝啬的~( 207 )从旧外壳代表继承锆石的形成时间的 52 妈。标明日期的结果显示 mafic magmatic 事件从最近的 Mesoproterozoic 发生在一个转变时期到最早的 Neoproterozoic，与到在 superconti-nent Rodinia 的集会的结果的 Grenvill 海洋外壳的全球 subduction 一致。因此，当重建时，北方中国块需要被考虑在 Rodiniasupercontinent 的框架以内的中国大陆的位置。
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Zircon dating age of tuff bedding from the Sibao Group in Guangxi and Guizhou provinces is firstly reported in this paper.Integrating the zircon SHRIMP U-Pb dating of the granite which intruded into the Sibao Group,the group is thus determined to be Neoproterozoic.The Sibao Group(same as the Fanjingshan,Lengjiaxi and Shuangqiaoshan groups) and the Danzhou Group(same as the Xiajiang,Banxi and Heshangzhen groups),which are slightly metamorphosed rocks are well developed in the Jiangnan Orogen,formed a metamorphosed basement of the Jiangnan old land.Many years ago,the Sibao Group was categorized into Mesoproterozoic,and it was main part of the Sibao Movement.The age of Sibao Group is still influencing the strata subdivision and correlation for the metamorphosed rocks in whole Jiangnan old land and has restricted the Chinese geologists to resolve the geological background and mineralization condition of the Jiangnan Orogen.In zircon study from bentonite in the Sibao Group,we've accurately determined the zircon dating of 841.7 Ma±5.9 Ma in the group and intruded granite zircon dating of 826.8 Ma ± 5.9 Ma from the Mt.Motianling.
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In the zircon study of bentonite from the Danzhou Group and overlying strata of the Nanhua System, the authors accurately determined the age of(801±3) Ma for zircon from the Hedong Formation and(778±6) Ma for zircon from the Gongdong Formation.(778±5) Ma is the age of zircon from the Chang'an Formation, which is the bottom of the Nanhuan System, and(661 ±7) Ma is the age of zircon from Datangpo Formation of the intraglacial period. Some zircon ages of tuff bedding were reported for the first time from the Sibao and Xiajia Groups in Guangxi and Guizhou. In combination of the SHRIMP U-Pb age of the granite(834 ±4 Ma) which intruded into the Sibao Group(842±13 Ma) and the SHRIMP U-Pb age of(837±7) Ma of Bendong granite, the authors hold that the Sibao Group is Late Neoproterozoic strata below the strata of 820 Ma. These isotopic data are very important for us to redefine the age of the Sibao Group and to conduct regional correlation of strata of the corresponding period as well as to study tectonic evolution. There is an angle unconformity between the Sibao Group and overlying Danzhou Group and a nonconformity between the Danzhou Group and the Nanhuan System, suggesting the existence of three levels of tectonic factor. The revised age column will influence the whole metamorphosed basement in the Jiangnan Orogen and the constraints on the relationship of the cover strata in South China.
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Rodinia
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