Cross-strike discontinuities and along-strike variability in continental collision zones

虽然山脉带是我们理解造山作用(造山过程)的熔炉，但大多数山脉带只从一个方向进行研究：平行于构造运输。这种方法揭示了从变质腹地到前陆逆冲系统的重要跨走向变化，并导致造山模式取得突破性进展，但淡化了在大多数造山带中观察到的重大沿走向变化。同样被忽视的是，不可否认的是，继承的(造山前)构造在整个造山带的旋回中影响着造山构造的发展。因此，为了充分了解造山过程，有必要通过清楚地描述碰撞板块的造山前构造来补充对造山系统的理解。喜马拉雅系之所以被选为天然实验室，是因为它保存了壮观而未解体的遗迹，承认了前喜马拉雅基底的交叉构造，已知的构造板块配置、汇聚速度和最近的演化，因此有限的构造叠加使喜马拉雅和前喜马拉雅变形得以区分。 喜马拉雅系统通常被认为是横向连续的；它的主要地质分区在整个长度上被认为是不间断的，尽管沿走向在地形和地貌、造山带结构和会聚速度方面存在显著差异。在这个赠款周期中，我的具体目标是识别和分析喜马拉雅造山带的横向变化，并阐明这种变化如何与碰撞前俯冲板块的内部构造联系起来。在这个方案中，假设喜马拉雅前缘逆冲南侧印度-恒河平原下埋藏的北东向前寒武纪基底脊在喜马拉雅造山带下继续存在，并可能对这些沿走向的变化起到了作用。最重要的是，这些海脊和深层结构之间的可能联系尚未确定，这些结构可能随着时间的推移而被反复激活。如果这些山脊在造山带演化早期与造山带相互作用，这可能导致造山带平行应变分配，在变质核内表现为侧向韧性应变变化，在前陆褶皱冲断带表现为侧向斜坡、侧向差异折返和/或沉积物厚度变化，甚至导致今天的地震活动沿走向的分配。 这些潜在的相互作用将通过HQP领导的几个项目来探索，这些项目包括：使用地震数据重建前陆褶皱冲断带；现场和实验室调查，以评估沿走向的应变变化、变质峰值条件和喜马拉雅变质核的折返；将现代地震活动、应力轨迹和跨走向基底隆起联系起来的数值应力模拟；以及动态规模的离心机变形模拟模拟。预计该项目最终将提供关键的动态链接，以了解阿巴拉契亚山脉、加拿大科迪莱拉山脉和格伦维尔造山带等老山带演化中的基底交叉构造。这种横向不连续被解释为控制地震破裂，影响横向沉积厚度变化和褶皱冲断带几何结构，并可能与深部构造有关，这些构造可以定位成矿流体并控制通过前陆盆地的油气运移，例如在加拿大西部沉积盆地中观察到的情况。就喜马拉雅系统而言，这种隐藏的地质灾害控制可能会对地球上人口最稠密的地区之一产生巨大影响。

Although mountain belts are the crucible of our understanding of orogenesis (mountain building processes), most mountain belts are only studied in one direction: parallel to the tectonic transport. This approach has revealed important across-strike variations from metamorphic hinterlands towards foreland thrust systems and led to ground-breaking advancements in orogenic models, but downplayed significant along-strike variations observed within most orogens. Equally underappreciated is the fact that inherited (pre-orogenic) structures undeniably influence the development of the orogenic architecture throughout the orogen’s cycle. To fully understand mountain building processes, it is therefore necessary to complement the understanding of the orogenic system with a clear depiction of the pre-orogenic configuration of the colliding plates. The Himalayan system is chosen as a natural laboratory because of its spectacular and unravelled preservation, recognized pre-Himalayan basement cross-structures, known tectonic plate configuration, convergence rates and recent evolution, and consequently limited tectonic overprinting enabling the distinction between Himalayan and pre-Himalayan deformation. The Himalayan system is commonly perceived as laterally continuous; its main geological subdivisions have been viewed as uninterrupted along its entire length, despite significant along-strike variation in topography and relief, orogen structure, and convergence rates. In this grant cycle, I specifically aim to identify and analyse lateral variations in the Himalayan orogen, and to elucidate how such variations may be linked with the pre-collision internal configuration of the underthrusting plate. In this proposal, it is hypothesized that NE-trending Precambrian basement ridges buried beneath the Indo-Gangetic Plain south of the Himalayan Frontal thrust continue beneath the Himalayan orogen and may have contributed to these along-strike changes. Most importantly, the possible link between these ridges and deep-seated structures that may have been repeatedly reactivated through time has yet to be established. If these ridges interacted with the orogen early in its evolution, this may have lead to orogen-parallel strain partitioning, expressed within the metamorphic core as lateral ductile strain variations, in the foreland fold-thrust belt as lateral ramps, lateral differential exhumation, and/or sediment thickness variations, or even in the present-day along-strike partitioning of seismicity. These potential interactions will be explored through several HQP-led projects involving: 3D reconstruction of the foreland fold-thrust belt using seismic data; field and lab investigations to assess along-strike variation in strain, metamorphic peak conditions, and exhumation of the Himalayan metamorphic core; numerical stress modelling linking present-day seismicity, stress trajectories, and cross-strike basement ridges; and dynamically-scaled centrifuge analogue modelling of deformation. It is anticipated that this program will ultimately provide key dynamic links to understand basement cross-structures in the evolution of older mountain belts, such as the Appalachians, the Canadian Cordillera, and the Grenville orogen. Such lateral discontinuities have been interpreted to control earthquake ruptures, influence lateral sedimentary thickness variations and fold-thrust belt geometry, and may be related to deep-seated structures that can localize mineralizing fluids and control hydrocarbon migration through the foreland basin, such as what is observed in the Western Canadian sedimentary basin. In the case of the Himalayan system, such hidden geohazard controls can have tremendous repercussions for one of the most densely-populated regions on Earth.