Tectonic implications of the Nan Suture zone and its relationship to the Sukhothai Fold Belt, northern Thailand

The Nan Suture and the Sukhothai Fold Belt reflect the processes associated with the collision between the Shan-Thai and Indochina Terranes in southea st Asia. The Shan-Thai Terrane rifted from Gondwana in the Early Permian. A s it drifted north a subduction complex developed along its northern margin . The Nan serpentinitic melange is a thrust slice within the Pha Som Metamo rphic Complex and in total this unit is a Late Permian accretionary complex containing offscraped blocks from subducted oceanic crust of Carboniferous and Permian age. The deformational style within the Pha Som Metamorphic Co mplex supports a west-dipping subduction zone. The Late Permian to Late Tri assic fore-are basin sediments are preserved in the Sukhothai Fold Belt and include a near continuous sedimentary record, at least locally. The whole sequence was folded and complexly thrust in the Late Triassic as a result o f the collision. Late syn- to post-kinematic granites place an upper limit of 200 Ma on the time of collision. Post-orogenic sediments prograded acros s the suture in the Jurassic. (C) 2000 Elsevier Science Ltd. All rights res erved.