晚白垩世以来川东北地区的剥蚀历史——多类低温热年代学数据综合剖面的制约

低温热年代学数据是一个与热历史过程紧密相关的资料类型,与高温年代学不同,低温热年代学表观年龄本身在很多情况下没有直接的地质意义.当且仅当样品线性持续冷却的情况下,表观年龄才可以被直接解释为样品经过其封闭温度的大致时间.因此,只有结合地质约束通过对低温热年代学数据进行热历史模拟才能更好地揭示其所蕴含的地质信息.对川东北地...

Post-Early Cretaceous denudation history Of the northeastern Sichuan Basin: constraints from low-temperature thermochronology profiles

Previously reported apatite fission track (AFT) data from surface samples of the northeastern Sichuan Basin yield apparent ages range between 60~80 Ma, which as is often the case, cannot be linked directly to any obvious geological events. Thermal modeling based on those data; however, provide some constraints on the cooling history of the northeastern Sichuan Basin. However, the details of the reconstructed cooling histories reported, vary significantly, especially with regard to the timing of the latest episode of cooling. This variation can be attributed to the lack of geological constraints for modeling purposes and the limited thermal resolution of AFT thermochronology in the lower temperature range (<~60℃). To address these issues, we have acquired new borehole AFT and apatite (U-Th)/He (AHe) data, which when combined with previously reported AFT surface and borehole data, allows synthetic AFT and AHe age and AFT length profiles for the basin to be constructed, and improves thermal history modeling to be carried out. This strategy includes, forward modeling based on candidate thermal histories to obtain predicted low-temperature thermochronology profiles and achieving a good match between the predicted and observed results. Using this strategy, we tested three possible cooling histories for the northeastern Sichuan Basin: linear cooling since 100 Ma, enhanced cooling since 40 Ma following slow cooling since 100 Ma and enhanced cooling since 30 Ma following slow cooling since 100 Ma. Results suggest that the most likely post-Early Cretaceous cooling history for the basin is - cooling at a rate of ~0.57 ℃/Ma between ~100 and 30 Ma, followed by a rate of ~1.67 ℃/Ma since ~30 Ma. Assuming that cooling resulted from denudation (as suggested from previous work) and occurred under a constant paleothermal gradient of ~20 ℃/km (similar to that of the present day), the denudation history of the basin is calculated - denudation at rate of ~29 m/Ma between ~100 Ma and ~30Ma and at ~83 m/Ma since ~30 Ma. The total post Early Cretaceous denudation for the northeastern Sichuan Basin is estimated at ~5 km.