Chinese Acad Sci, Inst Geol & Geophys, Beijing 100029, Peoples R China
; Tianjin Inst Geol & Mineral Resources, Tianjin 300170, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Beijing 100039, Peoples R China
The boundary of the East China Plateau (ECP) is mainly definited on the distribution of adakites. It has already known that the northernmost adakites of the plateau during the Mesozoic Era were distributed in the western Liaoning Province, northern Hebei Province and southern Inner Mongolia. The reliable adakites were dated between the early of Early Cretaceous and Late Jurassic period (such as Anjiayingzi granite in 132 +/- 5Ma). The present data show the adakites are roughly separated from non adakite by the Chifeng-Kaiyuan fault, is distributed on the south of. These imply that the northern boundary of the ECP is along the Chifeng-Kaiyuan zone and it represents the plateau border during Jurassic Period. The Yixian Formation in the western Liaoning lies within the plateau. As is known that the second section of Yixian Formation (124 similar to 127Ma) is the same as the stage of the Jehol Biota development, it means the climate at that time is warm and humid, luxuriant plant, the sumptuous pasture, low elevation, lacustrine lake. So it was unlikely belong to the barren and cold mountain, where is lack of animals and plants. The volcanic rock research of Yixian Formation shows that Yixian Formation during the Early Cretaceous(135 similar to 120Ma) is mainly composed by basalt and sanukite (high magnesium andesite) which are non adakite. So at least about 127Ma ago there is not plateau distributed in the Jehol Biota areas, the plateau boundary shift southward. It may be along Xuanhua-Luanping-Jinzhou zone to the south of the Jehol Biota district. No contemporary sediment, or the very thin sediment in the basin is directly result from plateau uplift. There was no basin in plateau during the middle-late Jurassic period, which is lack of Cretaceous stratum, implies that the plateau is generally on the uplifting stage. The ice raft and the glacier mud rock flow deposited along the northern and northwest edge of the plateau during early Cretaceous, implies that the northern edge of the plateau may be of the suitable height, may be similar to presents Himalaya Mountain. The Mesozoic structural characteristics indicate that there are enormous differences between the Jurassic Period and early Cretaceous: The tectonics characteristics behave mainly the NS compression during Jurassic Period, especially late Jurassic Period, and change into extension tectonics in the middle stage of Early Cretaceous, obviously change the Paleo environment and geography. Studies have shown that the Mesozoic adakite have roughly limited the plateau initial and extinction duration in the eastern China, according to the data published recently, the adakite's ages distribute from 170 to 120Ma, indicate that the ECP appears before 170Ma, probably reach the summit during the late Jurassic, disappear during the middle stage of early Cretaceous (120Ma). The tectonics, stratagraphy and volcanic rock data in western Liaoning and the northern Hebei indicate the ECP district was experienced the compression, and uplifted during the Jurassic Period, then changed into extension background during the Early Cretaceous (from 127Ma), The Fuxin-Yixian-Chaoyang-Fengning areas with abundant Jehol Biota has already depressed. These imply that the ECP may start collapsing from the northern edge, finally collapses wholly about 120Ma.