前陆盆地构造-热演化:以龙门山前陆盆地为例

摘要

The foreland basin is rich in oil and gas resources,but the structural deformation is very complex,which makes the tectono-thermal modeling of the foreland basin a challenge.During the evolution of the foreland basin,the tectono-thermal coupling is reflected in many aspects:the temporal and spatial variations of the lithospheric strength caused by the thermal evolution of the lithosphere and its effects on the lithospheric flexure;the thermal effect of the thrust;and the effect of the rapid deposition on the temperature field of the basin.Firstly,the initial thermal background of the lithosphere and the varied lithospheric thermal-rheological structure and strength has a profound impact on the formation and evolution of the foreland basin.And the thermal disturbance induced by the former thermal event may also superimpose on the subsequent tectonothermal evolution of the foreland basin,exerting a series of influence on the basin evolution.Secondly,more attention should be paid to the thermal coupling between the deep lithosphere and near surface structure.Thrust,uplift and denudation of orogenic belts are important processes related to the formation of the foreland basin and result in thermal convection,which thence greatly influence the orogenic thermal structure and temperature field distribution of the thrust belt and fore deep area.Finally,the rapid deposition during the formation and evolution of the foreland basin may depress strongly the basin temperature field and surface heat flow.Overall,the combined effects of the shallow thermal evolution (including the thrust and rapid deposition) and flexure and thermal evolution of the deep mantle lithosphere resulted in complexity of the tectono-thermal evolution as well as difficulty on the tectono-thermal modeling of the foreland basin.%前陆盆地油气资源丰富但构造变形十分复杂,使得前陆盆地构造-热演化模拟面临挑战.前陆盆地演化过程中构造与热的耦合体现在多个层面:岩石圈热演化对岩石圈强度时空分布及其挠曲的影响;逆冲推覆作用的浅部温度效应;快速沉积作用对盆地温度场的影响等.首先,前陆盆地形成时的岩石圈热背景及其造成的岩石圈强度空间变化对盆地后期的演化具有重要影响.同时早期热事件的热扰动也会叠加在前陆盆地的构造-热演化过程中,并不断衰减,影响岩石圈的流变结构,从而带来一系列的影响.热与构造演化相耦合在前陆盆地定量模拟中非常重要.其次,还需特别关注岩石圈深部过程与近地表构造过程的耦合.造山带逆冲推覆、抬升和剥蚀是与前陆盆地形成相关的重要构造活动,这种运动引起的热对流对造山带的热结构、前陆逆冲带以及前渊地区的温度场的分布有着重要影响.最后,前陆盆地形成演化过程中的快速沉积作用对盆地温度场和地表热流产生强烈的压制作用,对前陆盆地浅部热演化的影响不容忽视.因此,在浅部热演化(包括造山带逆冲推覆、快速沉积压实等)与盆地下伏岩石圈挠曲、深部热演化的联合作用下,使得前陆盆地构造-热演化颇为复杂,二者的耦合使得前陆盆地构造-热演化模拟颇具挑战.