Exhumation History And Paleotopography Reconstruction In Southern Margin Of Altay Mountains Since The Cretaceous

Altai is an important part of the Central Asian Orogenic Belt,and the largest proliferation orogen all over the world.At present,for Altai studies domestic and foreign scholars focus on evolution of the various-stages of orogenic,and geochemical and geochronological for the time limit for determining the orogenic.In contrast,study of the Mesozoic-Cenozoic cooling history is relatively small.To carry out the Altai orogen-orogenic uplift of the cooling and exhumation history of research,for in-depth understanding of the formation of a large mountain range after the evolutionary history is important.It is important to carry out research of the Post-orogenic uplift of the cooling and exhumation history about Altai orogen,it will make us having in-depth understanding of the formation of a large mountain range after the evolutionary history.With the fission track analysis technology improved,fission-track thermochronology as represented by apatite has become the effective means of revealing the exhumation age and speed of orogenic,and the evolution of tectonic,topographic and thermal history.Low chronology records rock movement information of the upper crust within a few kilometers,million-year scale,it offers a good choice for the quantitative recovery of ancient orogenic terrain.This paper discuss about uplifting-exhumation history and paleotopography reconstruction of this region based on fission track technology.AFT data from 51 samples show that the AFTA range from 29 Ma to 110 Ma.The average exhumation rate is 0.045 mm/ma since Late Cretaceous.Thermal history modeling results show that there are multi-times cooling and exhumation since the Cretaceous period in south margin of the Altai Mountains.In Early Cretaceous to Late Cretaceous(about 120?85-75 Ma),the exhumation rate is 0.058 mm/a,and in Late Cretaceous to Eocene(about 85-75?60-50 Ma),the exhumation rate is 0.063 mm/a.Since the Miocene(about 20-15 Ma?Present),the exhumation rate is 0.081 mm/a(the exhumation rate get from three method of age-closure temperature method,the cooling curve simulation and age-elevation method).Early Cretaceous tectonic uplift of the Altai Mountains is contemporaneous with the final closure of the Mongol-Okhotsk Ocean,and convergence and eventual collision of the Siberian and North Chinese(Sino-Korean)/Mongolian continents.Tectonic activities from Late Cretaceous to Eocene is affected by long range effects of Lhasa block and Kohistan-Dras arc hyperplasia.Rapid uplift since the Miocene may be related to distant effects of India-Eurasia convergence.Low-temperature thermochronology can be used to paleotopography reconstruction,and specific process are shown below:First,remodeling the rock samples's cooling history.Then,estimate corresponding the amount of strata erosion through temperature gradient.Finally,considering affect factors of balance role,climate,tectonics.The paper try to give image of paleotopography reconstruction in study region since Late Cretaceous(90 Ma).