四川盆地地表剥蚀量恢复及其意义

磷灰石裂变径迹(AFT)热隆升史模拟能够定量恢复盆地四维动态热隆升剥蚀过程.根据四川盆地93件磷灰石裂变径迹样品定量热史模拟表明,晚白垩世以来盆地发生了广泛的阶段式抬升剥蚀作用,即晚白垩世(～65 Ma前)快速隆升剥蚀、古近纪(65～23 Ma前左右)缓慢隆升剥蚀、新近纪(23 Ma前至今)快速隆升剥蚀.晚白垩世至今盆地范围内隆升剥蚀总厚度普遍大于2.5 km,新近纪快速隆升剥蚀幅度普遍大于1 km.进一步结合31组镜质体反射率反演校正剥蚀量数据,编绘阶段性(晚白垩世以来和新近纪)四川盆地地表剥蚀量等厚图,综合表明晚白垩世以来四川盆地隆升剥蚀量等值线展布格局发生根本变化,即早期主要以NE向展布格局为主(具近NE向和E-W向特征),新近纪则主要以近E-W向展布格局、盆地南北分异(北部地区隆升剥蚀量普遍小于2 km,南部地区普遍大于2 km)为主.四川盆地大中型油气田空间分布与晚中生代-新生代低剥蚀量具有密切联系.

Restoration of exhumation thickness and its significance in Sichuan Basin,China

The inversion model of temperature-time depending on apatite fission track (AFT) can reconstruct 4-D dynamical uplift and exhumation history in sedimentary basins. The inversion of 93 AFT samples indicates that there has been a regional episodic cooling (＜110℃) since Late Cretaceous in Sichuan Basin. Sichuan Basin was quickly uplifted and exhumed during Late Cretaceous (～65 Ma B.P.) and Neogene (23 Ma B.P.～), but did slowly during Paleogene. The exhumation thickness in Sichuan Basin is generally more than 2.5 km since Late Cretaceous, while more than 1 km in Neogene. Comparing with 31 inversion and Easy-Ro(vitrinite reflectance) corrected data of erosion from Ro, this paper compiles the isopach map of the exhumation thickness during Neogene and since Late Cretaceous in Sichuan Basin. The total exhumation thickness has spread through NE-SW strike since Late Cretaceous, but E-W strike in Neogene. There has been a change of the tectonic background from Late Cretaceous to Neogene, resulting in multistage uplift and exhumation in Sichuan basin. There is a close relationship between the distribution of large to medium-sized oil and gas fields and the lower surface erosion thickness in Sichuan Basin.