DISCUSSION ON FORMATION AND EVOLUTION OF JURASSIC BASIN-PROTOTYPE OF QAIDAM BASIN

Qaidam Basin evolution has come down in one continuous line with Qaidam Massif development. Before and in Triassic period, the main part of Qaidam Massif rose stably, but rift zones developed and received marine rift-typed sediments only at southern and northern borderland. At the end of Triassic period, the marine sedimentation on Qaidam Massif (including its surroundings) has ended, and interior basin started to develop in Qaidam area. In the light of the plate-tectonic mechanism to form the nappe structural zones at southern and northern borders of Qaidam Basin, the two continental foreland-basins which developed separately at southern and northern borders of Chaidamu Basin have similar characters and unified formation cause though their scale is different. And the foreland-basins appeared piggyback model and developed gradually towards inside basin. In addition, a series of pull-apart basins have formed at western border of Qaidam Massif. Therefore, Jurassic basin-prototype of Qaidam Massif is a superimposed basin of foreland-basin and full-apart basin. From Cretaceous Period to Paleocene-Eocene, subsidence and sedimentation area migrated gradually towards inside basin because the major thrust belts were piggyback and developed towards inside basin. After Oligocene, the natures of foreland-basin and pull-apart basin were on longer evident due to intensive compression and inside basin flexure caused by collision of Indian plate with Eurasian plate. And the former foreland-basin and pull-apart basin turned into intensive structural deformation zone and local sedimentary area for Neogene and Quaternary.