大别造山带毗邻新生代盆地物质平衡分析

Mass Balance Analysis of the Dabie Orogenic Belt and Its Adjacent Cenozoic Sedimentary Basins

沉积盆地的地层往往保留着源区构造演化的重要信息。本文利用物质平衡的方法,通过大别山周边十个沉积盆地的新生界地层信息,计算这些盆地中沉积物的堆积量和堆积速率,研究了新生代以来大别山的剥蚀过程和剥蚀速率。结果显示,大别造山带毗邻盆地在第四纪、新近纪和古近纪的平均总堆积速率分别为9.85×105～1.96×106m3/a、4.48×105～8.27×105m3/a和1.62×106～2.31×106m3/a。十个盆地的大部分沉积物源自大别山,且大别山的大部分剥蚀物被沉积到了这十个盆地中。在估算中,我们假设这两个“大部分”在量上相等,即等效于盆地的沉积物全部源于大别山,且大别山的剥蚀物全部沉积于所计算的盆地之中,则大别造山带在新生代的平均剥蚀厚度为2.1～2.95km,平均剥蚀速率为32～49mm/ka。新生代以来大别造山带剥露速率与剥蚀速率相近,表明大别造山带在新生代已经总体处于剥露稳态。

Sedimentary records from adjacent basins can provide valuable information about evolution of orogenic belt. Mass balance analysis is an effective way for the estimation of provenance erosion and basin accumulation. Ten Cenozoic sedimentary basins adjacent to Dabie orogen are analyzed in this study. According to the mass balance principle, the solid volumes of erosion material from orogen equal to the solid volumes of sediments accumulated in basins. Based on strata information such as thickness, area and porosity, the sedimentary volumes for the ten sedimentary basins are calculated by considering factors such as compaction, basin erosion depth and changes in sediment area. At last, the calculated volumes are recompacted to a porosity equivalent to the source rock. The sediment volumes are separated into three stratigraphic units （i. e. , Quarternary, Neogene and Paleogene） to achieve better time resolution. The results show that the average sediment accumulation rate into the ten basins in Quarternary, Neogene and Paleogene are 9. 85×10^5-1. 96×10^6m^3/a, 4.48×10^5-8.27×10^5m^3/a and 1.62×1066-2. 31×10^6m^3/a. Considering the coupling relations between Dabie oregon and its adjacent Cenozoic basins, we assume that all the sediments are from the Dabie orogen and all the material eroded from Dabie orogen are deposited in the ten basins. Then the average eroded depth of Dabie orogen since Cenozoic is 2. 1 - 2. 95km. The average erosion rate is 32 - 49mm/ka in Cenozoic. The erosion rate of Dabie oreogen is approximately equivalent to the exhumation rate based on low temperature thermalchronological data, showing that the Dabie orogen has reached the steady state in Cenozoic.