Exposed sections of accretionary orogens allow reconstruction of their tectonic evolution. Most commonly, orogens are characterized by two‐dimensional shortening perpendicular to the orogenic front. We describe the midcrustal section of the backarc of the early Paleozoic Famatinian accretionary orogen, exposed in the Sierra de Quilmes. Here crustal deformation evolved from a typical two‐dimensional shortening with tectonic transport toward the west, to a noncoaxial constrictional strain with a southward tectonic transport parallel to the orogen. During the early phase of deformation, high‐temperature and low‐pressure (HT‐LP) metamorphic complexes were juxtaposed by west directed thrusting on remarkably thick shear zones forming a thrust duplex. Deformation of the buried footwall complex continued after the exhumed hanging wall ceased to deform. We suggest that the thermally weakened footwall complex responded by initiating a phase of south verging thrusting, parallel to the orogen, associated with strong constriction, associated with L‐tectonites, and sheath folds. This late phase of deformation defines a noncoaxial constrictional regime characterized by simultaneous east‐west and vertical shortening and strong north‐south, orogen‐parallel stretching. Titanite ages and Zr‐in‐titanite thermometry demonstrate that this backarc remained above 700°C for 120 Myr between 500 and 380 Ma. Combined with regional geology, the new data suggest that west verging thrusting interrupted an early, back‐arc extensional phase, and lasted from ~470 to 440 Ma and that footwall constriction and south verging thrusting continued for another 40 to 60 Ma. The Famatinian backarc exposed in Sierra de Quilmes thus is an example of how shortening and orogenic growth in a hot orogen was counterbalanced by lateral flow.

中文翻译：

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从地壳增厚到造山带平行逃逸：钛铁矿在阿根廷西北部古生代法马蒂尼察Backarc中记录的120毫米长的HT-LP演化

增生造山带的裸露部分可以重建其构造演化。最常见的造山带特征是垂直于造山带锋面的二维缩短。我们描述了早古生代法马汀增生造山带的后弧中壳中部，暴露于Sierra de Quilmes。在这里，地壳变形从典型的二维构造缩短向构造运动向西方向发展，成为非同轴的压缩应变，构造运动向南平行于造山带。在变形的早期，高温和低压（HT-LP）变质复合体被西向推力并置在非常厚的剪切带上，形成了一个双重推力。在挖掘出的悬墙停止变形后，埋藏的底墙复合体继续变形。我们认为热弱的底盘复合体是通过发起一个与造山带平行的南向冲断作用的阶段来响应的，该阶段与造山带平行，伴有强烈的收缩，与L-构造体和鞘褶有关。变形的后期定义了一个非同轴的收缩状态，其特征是东西向和垂直向同时缩短，南北向强烈，造山带平行伸展。钛铁矿的年龄和锆钛矿的测温法表明，在500至380 Ma之间，该弧度在120 Myr时仍保持在700°C以上。结合区域地质，新数据表明，西向冲断作用中断了一个早期的弧后扩张阶段，持续时间约为470Ma至440Ma，而下盘面收缩和南向冲断作用又持续了40Ma至60Ma。