Deformation in the orogen-foreland system of the southern Central Andes between 33° and 36° S varies in style, locus, and amount of shortening. The controls that determine these spatially variable characteristics have largely remained unknown, yet both the subduction of the oceanic Nazca plate and the strength of the South American plate have been invoked to play a major role. While the parameters governing the subduction processes are similar between 33° and 36° S, the lithospheric strength of the upper plate is spatially variable due to structures inherited from past geodynamic regimes and associated compositional differences in the South American plate. Regional Mesozoic crustal horizontal extension generated a < 40-km-thick crust with a more mafic composition in the lower crust south of 35°S; north of this latitude, however, a more felsic lower crust is inferred from geophysical data. To assess the influence of different structural and compositional heterogeneities on the style of deformation in the southern Central Andes, we developed a suite of geodynamic models of intraplate lithospheric shortening for two E–W transects (33° 40′ S and 36° S) across the Andes. The models are constrained by local geological and geophysical information. Our results demonstrate a decoupled shortening mode between the brittle upper crust and the ductile lower crust in those areas characterized by a mafic lower crust (36° S transect). In contrast, a more felsic lower crust, such as in the 33° 40′ S transect, results in a coupled shortening mode. Furthermore, we find that differences in lithospheric thickness and the asymmetry of the lithosphere–asthenosphere boundary may promote the formation of a crustal-scale, west-dipping detachment zone that drives the overall deformation and lateral expansion of the orogen. Our study represents the first geodynamic modeling effort in the southern Central Andes aimed at understanding the roles of heterogeneities (crustal composition and thickness) at the scale of the entire lithosphere as well as the geometry of the lithosphere–asthenosphere boundary with respect to mountain building.

中部安第斯山脉中部南部造山带-前陆系统在33°至36°S之间的形变在样式，轨迹和缩短量上都不同。决定这些空间变化特征的控制方法很大程度上仍是未知的，但是海洋纳斯卡板块的俯冲作用和南美板块的强度都被发挥了重要作用。尽管控制俯冲过程的参数在33°S和36°S之间相似，但由于过去的地球动力学模式所继承的结构以及南美板块的相关组成差异，上板块的岩石圈强度在空间上是可变的。区域中生界地壳水平延伸在35°S以南的下地壳中形成了厚度小于40 km的地壳，其铁素体成分更多。但是，在这个纬度以北 从地球物理数据可以推断出地壳的下部长得多。为了评估安第斯中部南部不同结构和成分的非均质性对变形样式的影响，我们开发了一套板内岩石圈缩短的地球动力学模型，用于两个横断面（33°40′S和36°S）安第斯山脉。这些模型受当地地质和地球物理信息的约束。我们的结果表明，在以镁铁质下地壳（横断面为36°S）为特征的区域中，脆性上地壳和韧性下地壳之间的解耦缩短模式是不相关的。相反，诸如33°40'S断面的较稀疏的下地壳则导致了一种缩短的耦合模式。此外，我们发现岩石圈厚度的差异和岩石圈-软流圈边界的不对称性可能会促进地壳尺度的西倾脱离带的形成，从而推动造山带的整体变形和横向扩张。我们的研究代表了安第斯中部南部地区的首次地球动力学建模工作，旨在了解异质性（地壳成分和厚度）在整个岩石圈范围内的作用以及岩石圈-软流圈边界的几何形状对山区建筑的影响。