Quantifying the late stage topographic evolution of orogenic belts by Fast Fourier Transform spectral analysis:Applications in the Dabie and Micang Shan, China and Sierra Nevada, U.S.A
Su Zhe1,2 Liu Jing3 Zhang Luxin2,4 Wang Erchei1,5
1.State Key Laboratory of Lithospheric Evolution|Institute of Geology and Geophysics|Chinese Academy of Sciences|Beijing 100029； 2.Graduate University of Chinese Academy of Science|Beijing 100049； 3.Key Laboratory of Continetal Collision and Plateau Uplift|Institute of Tibetan Plateau Research|Chinese Academy of Sciences|Beijing 100085； 4.Key Laboratory of Earth Deep Interior|Institute of Geology and Geophysics| Chinese Academy of Sciences|Beijing 100029； 5.State Key Laboratory of Loess and Quaternary Geology|Institute of Earth Environment|Chinese Academy of Sciences|Xi'an 710075
Recent advances in lowtemperature thermochronology and its applications have shed lights on the detailed processes in the shallowest crustal depth(1～6 km)，such as uplift，exhumation and cooling.However，in practice，much information is lost by imperfect sampling locations due to difficulties in geographic accessibility.In addition，assumptions of the unkown subsurface isotherms，which for instance are topographicallydependent and thus can be nonhorizontal，bring more uncertainties in interpretations.This article introduces a method of the Fast Fourier Transform(FFT)spectral analysis which is produced by Braun(2002b)，combined with the fractual thought to take the elevation(h)and AHe age(a)of samples as the input(I) and output signals(F)，then make a transformation from the time domain to spatial one by the FFT.Through it，we could inverse the laststage of relief change of topography in the orogenic belt.Synthetically，this method considers the influence from the surface topographic fluctuation which could cause the isotherm to be curved.We succeed to apply the method into the Dabie Shan region and the Micang Shan Mt.in China and the Sierra Nevada range，the U.S.A.We find that in the Dabie Shan，the relief has decreased by～40％ ～50％（ β ≈-0.45）in the core since 35 Ma and reduced by～70％（ β≈-0.33）on the flank of the range since 50 Ma.In the Micang Shan，the relief keeps its relief stable（ β ≈-1）since 90 Ma； the Sierra Nevada range has experienced relief reduction by more than 50％ since～65 Ma.
. Quantifying the late stage topographic evolution of orogenic belts by Fast Fourier Transform spectral analysis:Applications in the Dabie and Micang Shan, China and Sierra Nevada, U.S.A[J]. Chinese Journal of Geology, 2011, 46(03): 743-762.