The Mesozoic basins in Yanshan, China underwent several important tectonic transformations, including changes from a pre-Late Triassic marginal cratonic basin to a Late Triassic-Late Jurassic flexural basin and then to a late Late Jurassic-Early Cretaceous rift basin. In response to two violent intraplate deformation at Late Triassic and Late Jurassic, coarse fluvial depositional systems in Xingshikou and Tuchengzi Formations were deposited in front of thrust belts. Controlled by transform and extension faulting, fan deltas and lacustrine systems were deposited in Early Cretaceous basins. The composition of clastic debris in Late Triassic and Late Jurassic flexural basins respectively represents unroofing processes from Proterozoic to Archean and from early deposited, overlying pyroclastic rocks to basement rocks in provenance areas. Restored protobasins were gradually migrated toward nearly NEE to EW-trending from Early Jurassic to early Late Jurassic. The Early Cretaceous basins with a NNE-trending crossed over early-formed basins. The Early-Late Jurassic and Early Cretaceous basins were respectively controlled by different tectonic mechanisms.

[1] The Dabieshan orogenic belt is a zone of longlived shortening with late-stage extension that formed during Mesozoic time in central China. Regional basin analysis coupled with structural cross sections provides a means of reconstructing the paleogeography of the region from Triassic continental collision through early Tertiary extension. The overall distribution of different basin types in the orogenic belt indicates that there was a prolonged period of shortening throughout the Mesozoic that became less intense over time. Meanwhile, extension became more common from Jurassic into Tertiary time. Either compression or extension was isochronous but limited to different geographic regions and/or crustal levels or alternated repeatedly orogen-wide through time. Nonetheless, the orogen underwent gradual transition from overall shortening and crustal thickening to dominantly extension and rift basin formation although these events overlapped in time from the Jurassic through Early Cretaceous. Penecontemporaneous compression and extension across the orogen may reflect long-term (>100 m.y.) shortening and crustal thickening leading to gravitational spreading of the resultant thick crustal welt. We suspect that this prolonged history of shortening across two nearby (100 km apart) suture zones played some role in the exhumation of ltrahighpressure rocks from beneath the Dabieshan.

通过对金寨县三尖铺组和凤凰台组沉积剖面中花岗岩砾石岩石化学和同位素年代学分析证明，作为合肥盆地主要物源区的大别山或北淮阳地区原始存在同碰撞造山后的花岗岩砾石样品错石U-Pb不一致性下交点年龄为214Ma左右、白云母40Ar/39Ar年龄为196Ma左右、钾长石K-Ar年龄为181Ma左右。前者可能为花岗岩的成岩年龄，后两者为样品中白云母和钾长石的同位素封闭年龄，而沉积剖面中大量出现花岗岩砾石的沉积岩年龄应代表了岩体剥露于地表的最小年龄值，取166Ma。由此，计算出岩体自214Ma形成后，晚三叠世至中侏罗世初期经历了早期缓慢隆升和后期快速隆升，隆升速率分别为0.08和0.4～0.3km/Ma。这些结果与大别超高压变质岩带、北淮阳逆冲带隆升时期基本一致。

During the Late Triassic and Jurassic, three structural belts developed in the western Ordos Basin and adjacent regions of China: the Alxa compressive wedge, the Helanshan struc-tural belt and the Liupanshan fold and thrust belt. Three types of basin also developed: a Late Triassic composite basin with a northwestern Ordos rift sub-basin and a southwestern Ordos fore-land sub-basin; an Early-Middle Jurassic intracratonic basin; and a Late Jurassic foreland-type molasse wedge. It is suggested that these basins resulted from Late Triassic unconstrained lateral extrusion and Jurassic constrained lateral extrusion. The Alxa region is interpreted as an extru-sional wedge bounded by strike-slip deformation which escaped laterally from the indentation of the Liupanshan thrust belt from the south. During the Late Triassic the Sino-Korean Block to the east of Helanshan was controlled by a stress state with nearly E-W trending extension. At this stage extrusion was unconstrained. The Helanshan developed as a rift sub-basin due to trans-tensional tectonics at the lateral margin of the wedge. At this time, a foreland sub-basin was formed in front of the Liupanshan thrust belt. During the Jurassic, the Sino-Korean Block to the east of the Helanshan was gradually compressed westwards and the extrusion structure became constrained. The Early-Middle Jurassic shows a transitional stage from unconstrained to con-strained extrusion, and the Ordos Basin developed as an intracratonic basin. From the latest Middle Jurassic: to the Late Jurassic, intense lateral escape and opposite compression led to the formation of the Helanshan fold and thrust belt and its frontal foreland molasse wedge. At the same time another foreland molasse wedge was developed in front of the Liupanshan thrust belt. The switch from rifting to thrusting in the Helanshan is a result of the changing stress field at theCircum-Pacific plate boundary, the clockwise rotation of the Sino-Korean Block to the east ofthe Helanshan and the anticlockwise rotation of the Alxa Block.