| The destruction of the North China Craton(NCC)is one of up-to-date research fields in Geosciences.At present,the study has basically believed that the eastern NCC(ENCC)was destructed in the Meso-Cenozoic,and the lithosphere is obviously thinned.In contrast,the Ordos Basin,located in the western NCC(WNCC),has a great dispute over whether the craton has been destructed or not.Especially,it is not clear about the evolution rule of the lithosphere since the late Mesozoic.Based on the current geothermal field characteristics,thermal history and thermal structure of the basin,we can obtain a large number of deep information of the lithosphere,which can provide some evidence for the evolution and dynamic mechanism of the lithosphere in the WNCC.In this paper,we reconstructed the Meso-Cenozoic thermal history by method of Easy%Ro and fission track,and summarize the thermal history evolution of different tectonic units in the Ordos basin.Combining with crust structure and thermal parameters,the Meso-Cenozoic lithospheric thermal structure of different tectonic units is calculated,and the relationships between thermal structure and rheological structure,tectonics and magmatic activity are further discussed.Eventually,we initially propose lithospheric dynamic mechanism in the Meso-Cenozoic in Ordos Basin.The results show that the Moho depth is between 39km~46km(average 43km),which is generally characterized by shallow depth in the southeast,and gradually increasing toward the west.In current,the thickness of seismic lithosphere in the basin is between 130km~200km and thickening toward the west.In addition,the thickness of seismic lithosphere is relatively thin(70km~100km)in the Cenozoic graben basin surrounding the Ordos basin.The current terrestrial heat flux is distributed at 46 m W/m~2~70 m W/m~2,with an average of 62 m W/m~2,which indicates that the Ordos basin belongs to the middle temperature basin.The isoline of terrestrial heat flux is distribution in the north-south direction.The heat flow is larger in the east,north and south,gradually decreasing toward the west.The Meso-Cenozoic thermal history of different tectonic units shows a similar evolution trend.Since the Mesozoic,the heat flux gradually increased,and it had reached to highest value within the range of 81 m W/m~2~103m W/m~2 in the early Cretaceous.Correspondingly,the lithosphere occurred on a large scale thinning,and it can be characterized by the thin lithosphere,less than 1 ratio of crust and mantle heat flow,a typical lithosphere structure with ?cold crust and hot mantle?.After the early Cretaceous,the heat flow began to decrease rapidly,and it was reduced to 63 m W/m~2~73m W/m~2 in the early Paleogene.Since the Neogene,the heat flux decreased slowly.Nowadays,the thermal lithosphere thickness in the Ordos basin is 82.77km~162.06 km,less than 100 km in the east,more than 140 km in the Tianhuan depression and the western margin thrust belt.The present-day mantle heat flux distributes between 21.79 m W/m~2~38.76 m W/m~2 in the eastern region,and the ratio of crust and mantle heat flow is less than 1,which suggest the mantle is relatively hot.In the western region,the ratios of crust and mantle heat flow(1.40~1.51)reflect a typical lithosphere structure with ?hot crust and cold mantle?.The lithosphere has been reformed to some extent in Ordos Basin rather than destruction since the Meso-Cenozoic.The dynamic evolution of the lithosphere is mainly influenced by the early Cretaceous mantle plume and the interaction of Pacific and Eurasian plate. |
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