【摘要】：華北克拉通東部陸塊內(nèi)的膠-遼-吉帶是一條古元古代構(gòu)造活動帶,其是否向南西穿越郯廬斷裂帶延伸至徐州-蚌埠一帶還存在著爭議。蚌埠地區(qū)早前寒武紀(jì)變質(zhì)基底主要包括晚太古代早期的霍邱群、古元古代五河群、鳳陽群以及少量的古元古代花崗(片麻)巖。其中低綠片巖相變質(zhì)的鳳陽群自下而上被分為白云山組、青石山組和宋集組,原始沉積物分別為石英砂巖-砂、粉砂泥質(zhì)及富鎂碳酸鹽巖交替-粉砂泥質(zhì)、泥質(zhì)和少量泥灰質(zhì)。本次研究對采自鳳陽群底部白云山組的2個石英巖和1個長石石英巖樣品的碎屑鋯石U-Pb年齡及Lu-Hf同位素研究表明,3個樣品的碎屑鋯石年齡圖譜十分相似,最重要的年齡區(qū)間為2.57~2.46Ga,峰值年齡約為2.52Ga,εHf(t)值在-7.39到+7.37之間,其中有大約90%具有正值,來源于蚌埠地區(qū)的晚太古代末期的花崗質(zhì)巖石。另一個重要的年齡區(qū)間是2.98~2.66Ga,峰值為2.94Ga和2.69Ga,εHf(t)值在-11.8到+7.24之間,其中超過90%為正值,來源于蚌埠地區(qū)的霍邱群以及晚太古代早期花崗質(zhì)巖體。此外,還有少量具有負(fù)εHf(t)值的3.61~3.34Ga的古太古代碎屑鋯石被發(fā)現(xiàn)。這些古太古代碎屑鋯石的εHf(t)值(-6.34~-1.05)以及兩階段模式年齡(3.75~4.07Ga)與華北克拉通南緣鄰近地區(qū)(登封、焦作、信陽以及膠東)發(fā)現(xiàn)的古太古代鋯石特征相似,說明華北克拉通南緣可能存在過古太古代,甚至冥古宙古老陸殼。5顆最年輕的鋯石可以將鳳陽群白云山組的最大沉積年齡限定在2.37Ga左右,而前人報到的白云母K-Ar年齡1878Ma與蚌埠地區(qū)1.88~1.80Ga的主期變質(zhì)時代為其形成時代的上限做出了限制。結(jié)合膠-遼-吉帶老嶺群和北遼河群大石橋組中具有相似碎屑鋯石年齡圖譜的變質(zhì)沉積巖,我們認(rèn)為在2.3~2.1Ga裂谷發(fā)育早期活動帶內(nèi)沉積了海相碳酸鹽巖及新太古代陸殼來源的碎屑巖。
[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.
【作者單位】： 中國地質(zhì)科學(xué)院地質(zhì)研究所;
【基金】：國家自然科學(xué)基金重點項目(41430210) 優(yōu)秀青年科學(xué)基金項目(41622203) 中國地質(zhì)調(diào)查局地質(zhì)調(diào)查項目(DD20160121)聯(lián)合資助
【分類號】：P56;P597

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