盆山地壳横向变化对挤压构造变形的影响——来自砂箱模拟实验的启示

前陆克拉通与造山带增生楔在地壳结构、力学性质等方面有明显的差异。挤压作用使盆山地壳横向变化通过构造变形表现出来。本文设计了具有深浅两个滑脱层"克拉通"与不同能干性的"造山楔"接触砂箱模型,通过模拟实验分析了盆山地壳横向差异变化对挤压构造变形的影响。实验结果表明,端部的挤压收缩位移由刚性的"克拉通"推挤相对软弱的"造山楔"使之形成挤压"冲起构造",而"造山楔"发生收缩变形的同时也斜向推挤刚性的"克拉通",并通过克拉通内部的滑脱层将收缩应变向克拉通内部传递。受不同深度滑脱层发育的影响,"克拉通"发育分层不协调收缩变形。在挤压作用下,随着"造山楔"与"克拉通"地壳在横向上能干性差异的增加,"造山楔"收缩形成的"冲起构造"幅度减小,而向"克拉通"侧向(斜向)挤压形成的"反冲构造"幅度增加,"造山楔"通过深层滑脱层向"克拉通"传递收缩应变的调节能力减弱,通过浅层滑脱层向"克拉通"传递收缩应变的调节能力增强。"造山楔"由深层过渡至浅层形成强变形带,由"克拉通"边缘至内部形成的深层冲断褶皱与浅层褶皱冲断组合过渡为深层褶皱与浅层的褶皱冲断组合,"克拉通"边缘的冲断带由深层的前展式楔状逆冲叠瓦扇构造向"克拉通"内部的浅层褶皱组合过渡。实验结果为理解中国西北部复杂山前冲断带构造的形成机制具有启示作用。

The impact of lateral variation between the crust of basin and mountain to the contractional structural deformation: Insights from sandbox experiments

There are significant differences between the foreland craton and the incretionary wedge of "orogenic zone" in crustal structure, mechanical property, et al. Compression makes the lateral variation of basin-mountain crust manifested by tectonic deformation. We set the sandbox modeling experiments of "craton" with two detachment layers directly contacting with "orogenic zone" with different competence, analyzing the impact of lateral variation between the crust of basin and mountain to the contractional structural deformation. The result indicates that, the relative rigid "craton" squeezes the relative weak "orogenic wedge", leading to the pop-up of "orogenic wedge". The "orogenic wedge" forms contractional deformation as well as abducting laterally(obliquely)to the "craton" and transmits contractional deformation to the interior of "craton" through the detachment layers of "craton". The detachment layers in different depth of "craton" result in the development of uncoordinated delaminate contractional structural deformation. With the lateral competency variation between the lithosphere "orogenic wedge" and "craton" increases, the amplitude of pop-up structure formed by the contraction of "orogenic wedge" decreases while the amplitude of recoil structure formed by "orogenic wedge" compressing "craton" obliquely increases, the adjustment capacity of the deep attachment layer of "craton" to the oblique thrust displacement of "orogenic wedge" weakened, while the adjustment capacity of the shallow attachment layer to which strengthened, the "orogenic wedge" transits from deep layer to shallow layer forming strong deformation belt, the contractional deformation of the edge to the interior of "craton" transits from the combination of thrust-fold in deep layer and fold-thrust in shallow layer to the combination of fold deformation in deep layer and fold-thrust in shallow layer, the structural deformation of foreland thrust belt in frontal zone transits from the "front distributed wedge imbricated fanshaped tectonic" in deep layer to the fold deformation in shallow layer. The experimental results could enlighten the interpretation of the complicated formation mechanism of the piedmont fault belt in northwest China.