五河杂岩凤阳群白云山组的源区特征及沉积时代:来自锆石U-Pb年龄和Lu-Hf同位素的证据
发布时间：2018-12-30 16:13
【摘要】：华北克拉通东部陆块内的胶-辽-吉带是一条古元古代构造活动带,其是否向南西穿越郯庐断裂带延伸至徐州-蚌埠一带还存在着争议。蚌埠地区早前寒武纪变质基底主要包括晚太古代早期的霍邱群、古元古代五河群、凤阳群以及少量的古元古代花岗(片麻)岩。其中低绿片岩相变质的凤阳群自下而上被分为白云山组、青石山组和宋集组,原始沉积物分别为石英砂岩-砂、粉砂泥质及富镁碳酸盐岩交替-粉砂泥质、泥质和少量泥灰质。本次研究对采自凤阳群底部白云山组的2个石英岩和1个长石石英岩样品的碎屑锆石U-Pb年龄及Lu-Hf同位素研究表明,3个样品的碎屑锆石年龄图谱十分相似,最重要的年龄区间为2.57~2.46Ga,峰值年龄约为2.52Ga,εHf(t)值在-7.39到+7.37之间,其中有大约90%具有正值,来源于蚌埠地区的晚太古代末期的花岗质岩石。另一个重要的年龄区间是2.98~2.66Ga,峰值为2.94Ga和2.69Ga,εHf(t)值在-11.8到+7.24之间,其中超过90%为正值,来源于蚌埠地区的霍邱群以及晚太古代早期花岗质岩体。此外,还有少量具有负εHf(t)值的3.61~3.34Ga的古太古代碎屑锆石被发现。这些古太古代碎屑锆石的εHf(t)值(-6.34~-1.05)以及两阶段模式年龄(3.75~4.07Ga)与华北克拉通南缘邻近地区(登封、焦作、信阳以及胶东)发现的古太古代锆石特征相似,说明华北克拉通南缘可能存在过古太古代,甚至冥古宙古老陆壳。5颗最年轻的锆石可以将凤阳群白云山组的最大沉积年龄限定在2.37Ga左右,而前人报到的白云母K-Ar年龄1878Ma与蚌埠地区1.88~1.80Ga的主期变质时代为其形成时代的上限做出了限制。结合胶-辽-吉带老岭群和北辽河群大石桥组中具有相似碎屑锆石年龄图谱的变质沉积岩,我们认为在2.3~2.1Ga裂谷发育早期活动带内沉积了海相碳酸盐岩及新太古代陆壳来源的碎屑岩。
[Abstract]:The Jiao-Liao-Ji belt in the eastern North China Craton is an ancient tectonic active belt of Gu Yuan. Whether it extends southward through the Tanlu fault zone to Xuzhou-Bengbu is controversial. The early Precambrian metamorphic basement in Bengbu area mainly includes Huoqiu Group in early late Archean, Wuhe Group in Paleoproterozoic, Fengyang Group and a small amount of Paleoproterozoic granitic (schneiss) rocks. The Fengyang Group with low greenschist facies metamorphism is divided into Baiyunshan formation, Qingshishan formation and Songji formation from bottom to top. The original sediments are quartz sandstone sand, silty clay and mafic rich carbonate rock alternately silty muddy, argillaceous and a little shaly. The U-Pb age and Lu-Hf isotopic study of two quartz and one feldspar quartz samples collected from Baiyunshan formation at the bottom of Fengyang Group show that the age profiles of three samples are very similar. The most important age range is 2.57 ~ 2.46Ga, the peak age is about 2.52Ga, and the 蔚 Hf (t) value is -7.39-7.37, about 90% of which are positive, derived from the granitic rocks of late Archean in Bengbu area. Another important age range is 2.98 / 2.66Ga.The peak values are 2.94Ga and 2.69Ga. the 蔚 Hf (t) values range from -11.8 to 7.24, of which more than 90% are positive. It comes from Huoqiu group in Bengbu area and early late Archean granitic rock mass. In addition, a small amount of paleoArchean clastic zircon with negative 蔚 Hf (t) value of 3.61~3.34Ga has been found. The 蔚 Hf (t) values of these PaleoArchean clastic zircons (-6.34 ~ 1.05) and the two-stage model age (3.75~4.07Ga) are close to the southern margin of the North China Craton (Dengfeng, Jiaozuo, Jiaozuo). The characteristics of PaleoArchean zircon found in Xinyang and Jiaodong are similar, indicating that there may have been PaleoArchean on the southern margin of North China Craton. Five of the youngest zircons can limit the maximum sedimentary age of the Baiyunshan formation of the Fengyang group to about 2.37Ga. The age of Muscovite K-Ar 1878Ma and the main stage metamorphism of 1.88~1.80Ga in Bengbu area are limited by the upper limit of the age of Muscovite. Combined with metamorphic sedimentary rocks of the Laoling Group and the Dashiqiao formation of the North Liaohe Group, which have similar age maps of clastic zircons, We believe that marine carbonate rocks and clastic rocks from NeoArchean continental crust were deposited in the early active zone of the 2.3~2.1Ga rift.
【作者单位】： 中国地质科学院地质研究所;
【基金】：国家自然科学基金重点项目(41430210) 优秀青年科学基金项目(41622203) 中国地质调查局地质调查项目(DD20160121)联合资助
【分类号】：P56;P597
本文编号：2395808
[Abstract]:The Jiao-Liao-Ji belt in the eastern North China Craton is an ancient tectonic active belt of Gu Yuan. Whether it extends southward through the Tanlu fault zone to Xuzhou-Bengbu is controversial. The early Precambrian metamorphic basement in Bengbu area mainly includes Huoqiu Group in early late Archean, Wuhe Group in Paleoproterozoic, Fengyang Group and a small amount of Paleoproterozoic granitic (schneiss) rocks. The Fengyang Group with low greenschist facies metamorphism is divided into Baiyunshan formation, Qingshishan formation and Songji formation from bottom to top. The original sediments are quartz sandstone sand, silty clay and mafic rich carbonate rock alternately silty muddy, argillaceous and a little shaly. The U-Pb age and Lu-Hf isotopic study of two quartz and one feldspar quartz samples collected from Baiyunshan formation at the bottom of Fengyang Group show that the age profiles of three samples are very similar. The most important age range is 2.57 ~ 2.46Ga, the peak age is about 2.52Ga, and the 蔚 Hf (t) value is -7.39-7.37, about 90% of which are positive, derived from the granitic rocks of late Archean in Bengbu area. Another important age range is 2.98 / 2.66Ga.The peak values are 2.94Ga and 2.69Ga. the 蔚 Hf (t) values range from -11.8 to 7.24, of which more than 90% are positive. It comes from Huoqiu group in Bengbu area and early late Archean granitic rock mass. In addition, a small amount of paleoArchean clastic zircon with negative 蔚 Hf (t) value of 3.61~3.34Ga has been found. The 蔚 Hf (t) values of these PaleoArchean clastic zircons (-6.34 ~ 1.05) and the two-stage model age (3.75~4.07Ga) are close to the southern margin of the North China Craton (Dengfeng, Jiaozuo, Jiaozuo). The characteristics of PaleoArchean zircon found in Xinyang and Jiaodong are similar, indicating that there may have been PaleoArchean on the southern margin of North China Craton. Five of the youngest zircons can limit the maximum sedimentary age of the Baiyunshan formation of the Fengyang group to about 2.37Ga. The age of Muscovite K-Ar 1878Ma and the main stage metamorphism of 1.88~1.80Ga in Bengbu area are limited by the upper limit of the age of Muscovite. Combined with metamorphic sedimentary rocks of the Laoling Group and the Dashiqiao formation of the North Liaohe Group, which have similar age maps of clastic zircons, We believe that marine carbonate rocks and clastic rocks from NeoArchean continental crust were deposited in the early active zone of the 2.3~2.1Ga rift.
【作者单位】： 中国地质科学院地质研究所;
【基金】：国家自然科学基金重点项目(41430210) 优秀青年科学基金项目(41622203) 中国地质调查局地质调查项目(DD20160121)联合资助
【分类号】：P56;P597
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1 马智,田毅,龚全胜;甘肃北山奥陶纪白云山组的沉积层序及地质意义[J];甘肃科技;2005年09期
，本文编号：2395808
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