合肥盆地中生界沉积物物源分析及构造意义

Provenance Analysis of Mesozoic Hefei Basin and Tectonic Significance

应用砂岩端元组分、重矿物成分变化等方法对合肥盆地及其南缘的中生界沉积物物源研究表明:合肥盆地大致以六安断裂为界分为南带和北带,其物源有显著差异。北带沉积物主要来源于华北板块,特别是早、中侏罗世,从晚侏罗世到早白垩世,大别造山带大规模的剥露开始,其母岩物质已经完全参与了盆地主体区的沉积;南带中、晚侏罗世沉积的物源来自北淮阳带,但大别造山带也有相当程度的贡献,凤凰台组沉积时期是大别造山带隆升最快、幅度最大的时期。早白垩世盆地的充填物质主要来自大别高压变质岩带,指示其俯冲、折返已经到达地表并持续遭受剥蚀,自中晚侏罗世到早白垩世早期剥蚀程度逐渐加大。从源区看,北带侏罗系样品的源区更接近于被动大陆边缘,南带多为主动大陆边缘。而白垩系样品无论北带还是南带多落入或靠近主动大陆边缘,说明早白垩世滨太平洋构造域已经占主导作用,南北差异减弱,早白垩世早期是南北向区域挤压特提斯构造域向北东向伸展的滨太平洋构造域转换的关键时期。此外值得注意的是中生界少数样品反映了岛弧区背景,许多样品具有混合源区的明显特征。

Based on sandstone extremity ingredient and heavy mineral component, the paper analyses sediments provenance and structure significance of Mesozoic Hefei Basin and its southern edge. The results indicate that the basin is generally divided into the north and south belts bordered by Liu＇an fault, which contain noticeably different sediment provenance. The sediments in the north basin mainly come from North China Plate especially from Early-Late Jurassic, middle-Jurassic, Late Jurassic to Early Cretaceous, when Dabie orogen was uplifted and denudated on a great scale and the main body of the whole basin was deposited with the source rock clasts. In contrast, the Middle and Late Jurassic source rocks of the south basin were originated from northern Huaiyang belt, while Dabie orogen also had considerable contribution. For the orogen experienced the uplifting with the fastest speed and greatest scale. The filling materials in Early Cretaceous basin were mainly derived from the highly metamorphosed Dabie orogen belt, which showed the subduction and the return of the area and the continuation of the denudation of the parent rock. Denudation quantity increased from Middle-Late Jurassic to Early Cretaceous. Viewed from its source areas, the south zone of the basin is close to active continent margin, while the north zone is close to the passive continent margin. The result also indicates that forepart of Early Cretaceous should be the key period for the tectonic change from Tethy regime（extrution/N-S direction） to Pacific regime（ N-E direction/extend）.