EMPLACEMENT OF THE LONGMEN-SHAN THRUST-NAPPE BELT ALONG THE EASTERN MARGIN OF THE TIBETAN PLATEAU

The topographic descent from the eastern margin of the Tibetan Plateau to the Sichuan Basin passes through the Longmen Shan Thrust-Nappe Bel t, which is sub-divided by six NW-dipping, major listric thrusts, with accompanying duplexes and imbricate fans, into five large-scale nappe s. Each nappe has its own stratigraphic and deformational features. In the inner Longmen Shan (Longmen Mountains), allochthonous nappe units have incorporated both Mesoproterozoic basement and Sinian (Neoproter ozoic) to Triassic cover sequences as 'thick-skinned' horses; whereas in the frontal Longmen Shan, Sinian-Cretaceous cover sediments have be en stripped from the basement as 'thin-skinned' fold and thrust sheets , including the extensively distributed klippen structures. Pre-thrust ing extension during Devonian to middle late Triassic times resulted i n syn-depositional normal faults. Structural inversion of these faults initiated the 'Peng Xian-Guan Xian Basement Complex', Jiuding Shan an d Tangwangzhai nappes during the early episode of the Indosinian oroge ny (Norian to Rhaetian). This was followed by episodic thrusting durin g latest Triassic to Early Cretaceous times to develop the Guan Xian-A n Xian and Southeastern Marginal nappes that have incorporated sedimen ts from the neighbouring foreland basin into the frontal part of the T hrust-Nappe Belt. During a late Miocene reactivation of the pre-existi ng thrusts, differential thrusting occurred across the Thrust-Nappe Be lt.