四川盆地早古生代构造热演化特征

何丽娟+黄方+刘琼颖+李春荣+汪集旸

基金项目：中国石油化工股份有限公司海相前瞻性研究项目(YPH08101)

摘要：四川盆地位于扬子板块西缘,是中国重要的含油气盆地之一，在震旦纪—早奥陶世处于裂陷特征的被动大陆边缘阶段。利用地球动力学理论在岩石圈尺度探讨盆地构造热演化特征，恢复早古生代热历史，为盆地生烃状态、生烃期次等研究提供重要热参数。首先，利用回剥技术得到盆地构造沉降史，并作为构造热演化模拟的目标函数；然后，基于二维多期拉张模型，分别与晚震旦世、寒武纪和奥陶纪等3个时期构造沉降量拟合得到3期拉张系数，揭示岩石圈底界和温度场的演化以及基底热流随时间的演化特征。模拟结果显示：在岩石圈拉张作用下，软流圈上涌形成热扰动，震旦纪时期基底热流值略有升高，其中高值主要分布在盆地西北与西南，而川东北受到的影响最小；热扰动在寒武纪有所减弱，至奥陶纪时期基本消失，盆地热流值呈缓慢下降趋势；盆地基底热流在早古生代始终在52~59 mW·m-2范围内。

关键词：构造热演化；多期拉张模型；早古生代；基底热流；岩石圈尺度；数值模拟；四川盆地

中图分类号：P314.2文献标志码：A

Tectonothermal Evolution of Sichuan Basin in Early Paleozoic

HE Lijuan, HUANG Fang, LIU Qiongying, LI Chunrong, WANG Jiyang

(Key Laboratory of Petroleum Resources Research of Chinese Academy of Sciences, Institute of Geology

and Geophysics, Chinese Academy of Sciences, Beijing 100029, China)

Abstract: Sichuan Basin, located in the western margin of Yangtze Plate, is one of the important oilgasbearing basins in China. The basin is in the passive continental margin stage with rift in SinianOrdovician. The tectonothermal evolution of basin was simulated by a geodynamical method in the lithospheric scale, and the thermal history of Early Paleozoic was obtained in order to provide important thermal parameters for assessment of hydrocarbon generation of basin. The tectonic subsidence of basin was firstly calculated by backstripping technique to provide objective function for the tectonothermal modeling; secondly, based on twodimensional multiphase extensional model, three episode extensional coefficients were estimated through fitting with the tectonic subsidences of Late Sinian, Cambrian and Ordovician in order to reveal the evolution of lithospheric base and temperature, as well as the basal heat flow. The modeling results show that the thermal disturbance, which is induced due to lithospheric extension and upwelling of asthenosphere, increases the basal heat flow in Late Sinian, and the effects are high in the northwest and southwest of basin and little in the northeast; the thermal disturbance weakens in Cambrian and disappears gradually in Ordovician, and consequently the basal heat flow decreases slowly; the basal heat flow of basin is still 5259 mW·m-2 in Early Paleozoic.

Key words: tectonothermal evolution; multiphase extensional model; Early Paleozoic; basal heat flow; lithospheric scale; numerical modeling; Sichuan Basin

0引言

盆地热历史控制着油气的生成、运移、聚集以及保存等过程，是含油气盆地分析的重要环节。热历史的恢复可以利用岩石圈尺度的构造热演化方法或盆地尺度的古温标方法［15］进行。四川盆地现今大地热流值平均为53 mW·m-2,具有典型克拉通型盆地中低热流特征［6］。……