前陆褶皱冲断带厚皮缩短盐构造运动的物理模拟

Physical Models of Thick-Skinned Contractional Salt Tectonics in a Foreland Fold-and-Thrust Belt

尺度物理实验用干石英砂和聚合硅树脂为实验材料 ,模拟了前陆褶皱冲断带厚皮缩短盐构造 ,并与薄皮缩短盐构造及无盐层的褶皱冲断带构造模型进行了对比。实验表明 ,由于塑性盐层的存在 ,厚皮缩短盐构造呈 3层式结构模式。盐上层主要形成敞开褶皱、箱状褶皱、前冲和背冲断层以及冲垒构造 ,盐下层形成逆冲断层及冲垒构造 ,断层通常都终止于盐层中。尽管盐层局部变薄或增厚 ,但不形成刺穿型盐构造。褶皱冲断带不具构造指向特征 ,其楔形库仑锥剖面呈平台与斜坡两段式形态。模型对比表明 ,厚皮缩短与薄皮缩短所产生的盐上层构造形态相似 ,不易区分 ;但二者的库仑锥剖面有所不同。厚皮前陆褶皱冲断盐构造与无盐层的褶皱冲断构造无论是其几何形态、还是库仑锥剖面都有极大的差别 ,极易区分。实验结果对解释前陆褶皱冲断构造和寻找盐下油气圈闭都有着重要的指导意义。

Scaled physical modeling investigated structures formed during thick-skinned contractional salt tectonics in a foreland fold-and-thrust belt. Dry quartz sand simulated brittle sedimentary rocks, and viscous silicon polymer simulated viscous rock salt. During the shortening, the salt layer strongly decoupled deformation in the suprasalt overburden from that in the subsalt strata. Overburden structures mainly comprised box folds, fore- and back-thrusts, and pop-ups, whereas subsalt structures comprised fore- and back-thrusts and pop-ups. Faults did not propagate across the salt layer and were confined within either the overburden or the subsalt strata. Structures in the fold-and-thrust belt showed no consistent vergence. The profile of the Coulomb wedge of the deformation belt comprised a flat segment and a forward-sloping segment; the flat part corresponded to the area where the subsalt pop-up had uplifted the overlying salt and overburden layers. No diapiric salt structures were formed during the shortening. Comparative modeling showed that thin-skinned contractional salt tectonics created similar structures in the suprasalt overburden to those in the thick-skinned models. However, the overall profile of the Coulomb wedge in the thin-skinned model had a lower taper. On the other hand, a model lacking a salt layer created an entirely different structural style. In the model lacking the salt, fore-thrusts and tight folds dominated the fold-and-thrust belt, and the structures showed a very strong and consistent basinward vergence. Among all the models, the model lacking the salt had the highest Coulomb wedge taper.