摘要
在褶皱冲断带的构造变形中,滑脱层是影响变形的主要控制因素之一。塔里木盆地北缘的乌什和库车褶皱冲断带的构造变形主要受到深浅两套滑脱层的控制,且浅部滑脱层沿走向存在厚度和性质差异。本文采用物理模拟研究方法,结合乌什和库车褶皱冲断带的地质背景,设计了4组实验模型,研究双滑脱层模型中浅部滑脱层沿走向的厚度与性质差异对褶皱冲断带变形的影响。实验中用微玻璃珠模拟页岩、泥岩等脆性滑脱层,用硅胶模拟盐岩、膏盐岩等韧性滑脱层。实验模型共铺设两套滑脱层,其中基底滑脱层为均匀分布的脆性滑脱层,而浅部滑脱层沿走向存在厚度和性质差异。实验结果表明:在双滑脱层模型中,浅部滑脱层沿走向的厚度与性质差异对褶皱冲断带的构造变形及楔体坡度值具有重要的控制作用。具体表现为:①当浅部滑脱层沿走向存在厚度差异时,浅部滑脱层较薄一侧的变形制约较厚一侧的变形传递,导致模型整体变形前锋的传递距离较近,且模型两侧的变形前锋的扩展范围基本一致。较薄一侧的断层发育数量明显比较厚一侧的数量多、间距小,且楔体坡度值自较薄一侧向较厚一侧逐渐减小。②当浅部滑脱层沿走向存在性质差异时,浅部脆性滑脱层一侧表现为上下一体的变形,而韧性滑脱层一侧表现为上下分层变形。在两侧浅部滑脱层厚度一致的情况下,韧性滑脱层一侧的传播速度总体快于脆性滑脱层一侧,但两者的最终传递距离趋于一致,楔体坡度值从脆性滑脱层一侧向韧性滑脱层一侧逐渐减小;当浅部脆性滑脱层的厚度减小时,随着缩短量的持续增加,模型两侧变形前锋的传递距离仍然具有趋于一致特点,且模型的楔体坡度值整体偏大,但脆性滑脱层一侧的楔体坡度值始终大于韧性滑脱层一侧。此外,模拟结果验证了在乌什和库车褶皱冲断带中,浅部滑脱层沿走向的性质差异是造成构造样式差异的主要控制因素,但并不一定是造成该冲断带变形前锋发生大规模偏转的根本原因。
Décollement is one of the main controlling factors affecting structural deformation of fold and thrust belts.The structural deformation of the Wushi and Kuqa fold and thrust belts in the northern margin of the Tarim Basin was mainly controlled by two sets of basal and shallow décollement,between which are differences in thickness and property along the strike.In this paper,with the objective of studying the influence of these"along the strike differences"on the structural deformation of the Wushi and Kuqa fold and thrust belts,four sets of experimental models were designed based on the analogue modeling method and the geological background of these belts.In the sandbox models,glass microbeads are used to simulate brittle décollement such as in shales and mudstones,and silicone gel is used to simulate the ductile décollement such as in salt rocks and gypsum salt rocks.There are two sets of décollements in the experimental models,in which the basal one is a uniformly distributed brittle décollement,and the shallow one has differences in thickness and property along the strike.The experimental results show that in the sandbox model with double décollements,thickness and property differences of the shallow décollement along the strike play a very important role in controlling the structural deformation and wedge taper of the fold and thrust belts.The specific results are as follows:①when the thickness of the shallow décollement is variable along the strike,deformation on the thinner side of the shallow décollement restricts the deformation transfer to the thicker side.This results in a relatively short transfer distance of the deformation front of the model and the extension range of the deformation front on both sides of the model is basically the same.The number of faults on the thinner side is obviously larger than that on the thicker side,and the interval between them is smaller.The wedge taper gradually decreases from the thinner to the thicker side.②When there is a difference in the property of the shallow décollement along the strike,the brittle side shows up-and-down deformation,while ductile side shows up-and-down layered deformation.Under the condition that both sides of the shallow décollement have the same thickness,the propagation speed of the ductile side is generally faster than the brittle side,but the extension range of deformation front on both sides of the final model is basically the same,and the wedge taper decreases gradually from the side of the brittle décollement to the side of the ductile décollement.When the thickness of the shallow brittle décollement decreases,the transfer distance of the deformation front on both sides of the model still tends to be consistent with the continuous increase of the shortening distance,and the overall wedge taper is larger,but the wedge taper on the brittle side is always larger than the one on the ductile side.In addition,the analogue modelling results verify that in the Wushi and Kuqa fold and thrust belts,the difference in the property of the shallow décollement along the strike is the main controlling factor that causes the structural style differences,but it is not the primary reason for the large-scale deflection of the deformation front of the fold and thrust belts.
作者
龙毅
陈汉林
程晓敢
林秀斌
张耀
成亚
LONG Yi;CHEN Hanlin;CHENG Xiaogan;LIN Xiubin;ZHANG Yao;CHENG Ya(School of Earth Sciences,Zhejiang University Hangzhou,310027;Structural Research Center of Oil&Gas Bearing Basin of Ministry of Education,Hangzhou,310027;Earthquake Administration of Zhejiang Province,Hangzhou,310013)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2020年第6期1763-1779,共17页
Acta Geologica Sinica
基金
国家重点研发计划(2016YFC0601004)
国家科技重大专项(2017ZX05008001,2016ZX05003001)
国家自然科学基金(41720104003)资助的成果。
关键词
物理模拟
浅部滑脱层
厚度差异
性质差异
褶皱冲断带
analogue modeling
shallow décollement
thickness difference
property difference
fold and thrust belts
