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

大陆碰撞带的跨走向不连续性和沿走向变异性

• 批准号: RGPIN-2014-06209
• 负责人: Godin, Laurent
• 金额: $ 3.13万
• 依托单位: Queen's University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2015
• 资助国家: 加拿大
• 起止时间: 2015-01-01 至 2016-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=588870
• 关键词: Cross; strike; discontinuities; along; variability

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.

尽管山地带是我们理解造山作用（造山过程）的关键，但大多数山地带仅在一个方向上进行研究：与构造运动平行。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，并导致造山模型的突破性进展，但淡化了在大多数造山带内观察到的显着的沿走向变化。同样未被充分认识到的事实是，继承的（造山前）结构无可否认地影响着整个造山带周期中造山结构的发展。因此，为了充分了解造山过程，有必要通过对碰撞板块的前造山构造的清晰描述来补充对造山系统的理解。喜马拉雅系统被选为天然实验室，是因为其壮观且未解开的保存、公认的前喜马拉雅基底交叉结构、已知的构造板块配置、收敛速度和最近的演化，以及因此有限的构造叠印，使得喜马拉雅和前喜马拉雅变形之间的区别成为可能。 喜马拉雅系统通常被认为是横向连续的。尽管地形和地形、造山带结构和收敛速度沿走向存在显着变化，但其主要地质分区在整个长度上被认为是不间断的。在这个资助周期中，我的具体目标是识别和分析喜马拉雅造山带的横向变化，并阐明这些变化如何与冲撞板块碰撞前的内部构造联系起来。在该提议中，假设埋藏在喜马拉雅山锋逆冲断层以南印度恒河平原下方的北东向前寒武纪基底山脊继续延伸至喜马拉雅造山带下方，并可能促成了这些沿走向的变化。最重要的是，这些山脊与可能随着时间的推移而反复重新激活的深层结构之间可能存在的联系尚未确定。如果这些山脊在造山带演化的早期与造山带相互作用，这可能会导致造山带平行的应变划分，在变质核内表现为横向延性应变变化，在前陆褶皱逆冲带中表现为横向坡道、横向差异折返和/或沉积物厚度变化，甚至在当今的地震活动沿走向划分中。 这些潜在的相互作用将通过 HQP 领导的几个项目进行探索，包括： 使用地震数据对前陆褶皱冲断带进行 3D 重建；现场和实验室调查，以评估应变的沿走向变化、变质峰条件和喜马拉雅变质核的折返；连接当今地震活动、应力轨迹和交叉走向基底山脊的数值应力模型；以及变形的动态缩放离心机模拟建模。预计该计划最终将提供关键的动态链接，以了解阿巴拉契亚山脉、加拿大科迪勒拉山脉和格伦维尔造山带等较古老山脉带演化中的基底交叉结构。这种横向不连续性被解释为控制地震破裂，影响横向沉积厚度变化和褶皱逆冲带几何形状，并且可能与可以定位矿化流体并控制油气通过前陆盆地运移的深层结构有关，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。