柴达木盆地北缘反S形褶皱冲断带变形机制的物理模拟研究

A PHYSICAL MODELING ON MECHANISM OF REVERSE S-SHAPED FOLD-AND-THRUST BELTS IN THE NORTHERN QAIDAM BASIN

阿尔金断裂走滑变形的侧向传递十分有限,难以解释柴达木盆地北缘反S形褶皱冲断带的形成。本文设计的一组具有不同性质基底条件的弧形边界砂箱实验表明:刚性块体边界形态控制了褶皱冲断带走向和构造格局,同时基底力学性质也有部分影响作用,因而可用“刚性块体弧形边界联合作用”来解释其形成,即:1)冷湖反S形褶皱冲断带的形成是赛什腾山前弧形边界与昆特依凹陷弧形边界联合作用的结果;2)鄂博梁反S形褶皱冲断带的形成是昆特依凹陷与一里坪凹陷弧形边界联合作用的结果;3)位于一里坪凹陷南侧、与阿尔金断裂左行走滑变形呈反牵引关系的褶皱冲断带则与该凹陷西南侧向南西突出的弧形边界有关。

The reverse S-shaped fold-and-thrust belts in the northern Qaidam Basin were interpreted as a result of lateral traction by sinistral strike slip of the Altyn fault in the north edge of the basin. However, the deformation features of the Qaidam Basin indicated that the area influenced by strike slipping of the Altyn fault was very narrow. To further study the mechanism of the reverse S-shaped fold-and-thrust belts, a set of sandbox models of arcuate boundaries with different substrate were designed according to the actual geological conditions. The experimental resuits showed that the strikes and structural patterns of fold-and-thrust belts were mainly controlled by the boundary geometry of rigid blocks and partially by the mechanical properties of substrates. Based on analyses of the experiments and deformation characteristics of the northern Qaidam Basin, it was proposed that the reverse S-shaped fold-and-thrust belts there could be simply interpreted as the ＂combination effect of arcuate boundaries of rigid blocks＂, namely, 1 ） the Lenghu reverse S-shaped fold-and-thrust belt being a combination effect of arcuate block boundaries of the Saishiteng Mountains and the Kunteyi Sag ; 2） the Eboliang reverse S-shaped fold-and-thrust belt being a combination effect of arcuate block boundaries of the Kunteyi Sag and Yiliping Sag ; 3 ） the fold-and-thrust belt, along southwest edge of the Yiliping Sag and with a reverse traction relation to sinistral strike slipping of the Altyn, being related to the southwestward curved boundary of the sag.