The structure of the Central Andes forearc of northern Chile has been an enigma for many years. Along this region, the preservation of a long pediplain constituted by gravels and unconsolidated sediments has hidden the structure of the region, making it difficult to understand its tectonic evolution. The traditional and regional-scale structural models are mainly supported by outcrop-scale and local observations. To unravel the structure of this Andes region, we carried out a regional-scale study based on local and regional observations, geological mapping, and the elaboration of local and regional balanced cross-sections, thereby illustrating the geometry and distribution of the first-order structural styles. We examined four specific sectors along a regional transect: the Loa and San Salvador rivers (parallel to each other), Sierra de Limón Verde, and Cerros de Tuina. Three structural styles were identified in the hybrid thick- and thin-skinned and doubly verging fold-and-thrust belt. These styles comprise partially inverted Permian to Jurassic normal faults, thick-skinned reverse faults affecting Paleozoic crystalline basement blocks, and shallow and thin-skinned fault-related folds. The shallow and thin-skinned fault-related folds usually result from the propagation of large, thick-skinned thrust ramps into stratigraphic successions. The restoration of a regionally balanced cross section constrained by field data and the previously interpreted two-dimensional (2-D) seismic profiles suggest that much of the crustal shortenings are accommodated by the reverse reactivation of Triassic and Jurassic normal faults bounding half-graben structures. It is also accommodated by blind thrust faults, whose geometry, kinematic, and depth are debatable. However, we have proposed a large, thick-skinned thrust ramp as the structure responsible for the greater shortening in the region, along which a significant thick- to thin-skinned transition occurs. The age of the synorogenic deposits identified here is unknown, specially those exposed at the Loa and San Salvador rives, however, the basal successions exposed at the Tuina sector reported Upper Cretaceous ages, thus suggesting that the orogeny in the forearc could have started during this time spam. Regional correlations with similar synorogenic deposits recognized in neighboring regions (e.g., Salar de Atacama Basin and Coastal Cordillera) also affirm an Upper Cretaceous–Paleocene age for the initiation of the crustal contraction in the region.

多年来，智利北部安第斯山脉中部前弧的结构一直是个谜。沿该地区保存有由砾石和松散沉积物构成的长陆平原，隐藏了该地区的结构，使其难以理解其构造演化。传统和区域尺度的结构模型主要由露头尺度和局地观测支持。为了弄清这个安第斯地区的结构，我们根据当地和区域观测、地质测绘进行了区域尺度研究，以及局部和区域平衡横截面的详细说明，从而说明一阶结构样式的几何形状和分布。我们检查了沿区域样带的四个特定区域：Loa 河和 San Salvador 河（彼此平行）、Sierra de Limón Verde 和 Cerros de Tuina。在混合厚皮和薄皮和双折褶皱推力带中确定了三种结构样式。这些样式包括部分倒置的二叠纪至侏罗纪正断层、影响古生代结晶基底块的厚层逆断层以及与断层相关的浅层和薄层褶皱。与断层有关的浅而薄的褶皱通常是由大而厚的逆冲斜坡延伸到地层序列中产生的。三叠纪和侏罗纪正断层以半地堑结构为界的反向重新激活适应了地壳缩短。它也被盲逆冲断层所容纳，其几何形状、运动学和深度是有争议的。然而，我们提出了一个大的、厚皮推力斜坡作为该区域更大缩短的结构，沿着该斜坡发生明显的厚皮向薄皮过渡。这里确定的同成因沉积物的年龄未知，特别是那些出露在罗亚河和圣萨尔瓦多河的沉积物，然而，在推拿区出露的基底层序报告了上白垩纪年龄，因此表明前弧的造山运动可能是在这段时间垃圾邮件中开始的。与在邻近地区（例如，Salar de Atacama 盆地和沿海科迪勒拉）发现的类似同成因沉积物的区域相关性也证实了该地区地壳收缩开始的上白垩统 - 古新世时代。