Abstract Fold and thrust belts (FTBs) accommodate tectonic convergence through folding and faulting of crustal rocks during a collisional event between two continental plates. Although evidence of distributed deformation is common in FTBs that usually leads to continuous foliations and regionally occurring ductile structures of multiple orders, it has rarely been given much attention assuming that zones of localized deformation, like shear zones and brittle faults, accommodate the entire amount of tectonic convergence. This study presents 3D laboratory-scale models, using viscous thin sheet as crustal layers, to understand the evolution of ductile strain in a tectonic wedge. We varied the degree of mechanical coupling at the basal decollement (i.e., weak versus strong) to investigate this issue at constant convergence velocity in all experiments to avoid the influence of rate-dependence on viscous rheology. Our results reveal that the strength of basal decollement controls the mode of wedge growth and hence, the strain pattern particularly towards the hinterland. The weak decollement models yield a zone of constriction towards the central part of hinterland, explaining the occurrence of isolated patches of L-tectonites and cross-folds in FTBs; while the strong decollement condition allows gravity driven flow to be active in the hinterland, leading to orogen-parallel recumbent folds. In contrast, both weak and strong decollement models produce deformation that characterises the commonness of pervasive, hinterland dipping ductile fabrics towards the mountain front. We correlate our findings to show that spatio-temporal variations in basal coupling are responsible for varying occurrence of ductile structures in FTBs.

中文翻译：

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褶皱冲断带韧性应变的空间变化：从模型到自然

摘要 褶皱逆冲带 (FTBs) 在两个大陆板块之间的碰撞事件中通过地壳岩石的褶皱和断层来适应构造收敛。虽然分布变形的证据在 FTB 中很常见，通常会导致连续的叶理和区域性发生的多阶韧性结构，但假设局部变形带，如剪切带和脆性断层，容纳全部构造收敛。本研究展示了 3D 实验室规模模型，使用粘性薄片作为地壳层，以了解构造楔中延性应变的演变。我们改变了基底脱臼处的机械耦合程度（即，弱与强）在所有实验中以恒定收敛速度研究这个问题，以避免速率依赖性对粘性流变学的影响。我们的结果表明，基底脱垂的强度控制着楔形生长的模式，因此，特别是对腹地的应变模式。弱解滑模型在腹地中部产生一个收缩带，解释了 FTB 中 L 构造岩的孤立斑块和交叉褶皱的出现；而强烈的退缩条件允许重力驱动的流动在腹地活跃，导致与造山带平行的斜卧褶皱。相比之下，弱和强脱模模型都会产生变形，这种变形表征了普遍的、腹地向山前倾斜的延展性织物。