Continental fold‐thrust belts display a variety of structural styles, ranging from thin‐skinned thrusts following weak lithologic contacts to thick‐skinned thrusts that deform mechanical basement. The common practice of splitting fold‐thrust belts into thin‐ and thick‐skinned map domains has not yielded a predictive model of the primary controls on structural style. Within the Mesozoic‐Paleogene Idaho‐Montana fold‐thrust belt (44–45°N, 112–114°W), we identify crosscutting thin‐ and thick‐skinned thrusts within an otherwise thin‐skinned map domain. This transition occurs within a thin (∼2.5 km) portion of the western Laurentian passive margin, where lower strata pinch out over a prominent basement high (Lemhi arch). Early fold‐thrust belt shortening of sedimentary cover rocks was accommodated through detachment folding, followed by east‐directed, thin‐skinned thrusting along regional‐scale faults (Thompson Gulch and Railroad Canyon thrusts). Later, basement and cover rocks were tilted toward the southeast and a basement‐involved normal fault was reactivated during thick‐skinned thrusting (Radio Tower‐Baby Joe Gulch‐Italian Gulch thrusts), which accommodated shortening at an oblique angle to and truncated the basal detachment of the older thin‐skinned thrusts. This progression from thin‐ to thick‐skinned thrusting occurred >50 km from the foreland, coincident with a regional basement high. Thus, the Idaho‐Montana fold‐thrust belt is a double‐decker system, with upper thin‐ and lower thick‐skinned domains. This double‐decker model is applicable to other fold‐thrust belts and predicts that the transition from thin‐ to thick‐skinned thrusting occurs where the growing critically‐tapered wedge can no longer fit within the sedimentary cover rocks and the basal detachment steps down into structurally lower mechanical basement.

中文翻译：

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从薄到厚皮结构样式过渡的前冲断层地层控制：以爱达荷州-蒙大拿州双层褶皱冲断带为例

大陆架褶皱冲断带表现出多种构造样式，范围从因弱岩性接触而产生的薄皮推力到使机械基底变形的厚皮推力。将褶皱冲断带分为薄型和厚型地图域的常规做法并未得出结构样式主要控制的预测模型。在中生代爱达荷州-蒙大拿州的褶皱冲断带（北纬44-45°，西经112-114°）内，我们确定了在原本薄皮的地图区域内横切薄皮厚的逆冲。这种过渡发生在劳伦斯西部被动边缘的一小段（约2.5公里）内，较低的地层被夹在突出的地下高处（Lemhi拱）上。沉积盖岩的早期褶皱冲断带缩短是通过分离褶皱进行的，随后是东向，沿区域尺度断层（汤普森峡谷和铁路峡谷逆冲）的薄皮逆冲。后来，基底和覆盖岩向东南倾斜，并且在厚皮逆冲作用下（由无线电塔-Baby Joe Gulch-Italian Gulch逆冲）重新激活了基底相关的正断层，该断层以与斜基成一定角度的斜度缩短并截断了基岩。分离较旧的薄皮推力。这种从薄到厚的逆冲运动发生在距前陆> 50 km的地方，与区域基底高度较高相吻合。因此，爱达荷州-蒙大拿州的褶皱冲断带是一个双层系统，具有上，下厚皮层区域。