| aleogeographic features in the south part of North China in the Late ermian-Early Triassic show that the sedimentary environment changes a lot from transitional facies inclined to the south to inland fluvial-lacustrine facies,with high terrain in the southeast and northwest low.The dynamic mechanism of this transition should be closely related to the subduction of Mianlue Ocean the collision orogeny between the North Qinling Orogenic Belt and the Southern of North China Block.However,the research about sedimentary characteristics and provenance in the south part of North China Basin in response to Qinling orogeny in the Early-Middle Triassic,and basin-mountain interaction was relatively low.Meanwhile,the transition process and pattern of the southern North China Basin from an inland craton basin to foreland basin was still unclear.Based on this,we analyzed the provenance of the Lower-Middle Triassic in Jiyuan area in detail with the method of sedimentary petrology,geochemistry of elements,and detrital zircon geochronology.In addition,investigated the basin-mountain tectonic evolution between the southern of North China Basin and the North Qinling Orogenic Belt,including the development and evolution process of foreland basin system in primary,combined with strata sedimentary features and Qinling orogeny.The main achievements were listed as follows:(1)Lower Triassic in Jiyuan area was deposited mainly in the environment of lacustrine delta,which transformed into shore-shallow lake in the upper part of Heshanggou Formation,with dry and hot climatic conditions.Ermaying Formation in the Middle Triassic was deposited in the environment of lacustrine delta,shore-shallow lake and meandering river respectively from bottom to top,and weather conditions turn into warm and moist.(2)The provenance of Liujiagou Formation in the Lower Triassic in study area was mainly derived from the ermian sedimentary covers of the Southern of North China Block and the North Qinling Orogenic Belt.The sediments deposited in Heshanggou Formation was provided mainly by the North Qinling Orogenic Belt.The provenance of Ermaying Formation in the Middle Triassic was derived from sedimentary covers of the Southern of North China Block.The characteristics of detrital zircon ages suggest that the North Qinling Orogenic Belt should be higher in topography in the sedimentary period of Liujiagou Formation.The provenance from Qinling orogenic belt in Heshanggou Formation increased,which should be the result of weakened squeezing and the basement of the basin rebound.The Southern of North China Block should be thrust and uplifted in the period of Ermaying Formation deposited,which made it further denudated and provided abundant sediments to Jiyuan area,and blocked the provenance input from the Qinling orogenic belt at the same time.(3)In the Early Triassic,the southern of North China Basin was a part of giant inland sedimentary basin in north China,which still be the evolutionary phases of inland craton basin.In the Middle-Late Triassic,the Southern of North China Block was thrust and uplifted,fast denudation and slow thrust caused limited loading,sedimentary rate exceeded subsiding rate,which result in fluvial-delta overcompensated deposit,in corresponding to the initial stage of foreland basin forming.In the late Late Triassic,slower denudation and faster thrust rate result in the sediments supply reduced and the loading of orogenic belt enhanced gradually,the settlement of the basin accelerated,lead to the formation of deep-water deposition in the foredeep along the orogenic belt.Since then,the south part of north China fully steeped into the evolutionary stage of foreland basin.The sedimentary strata in the Middle Triassic in Jiyuan area recorded the initial change of the southern of North China Basin from an inland craton basin to foreland basin,which is significant for understanding the transition process of the basin and its sedimentary characteristics in response. |
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