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: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=567659
• 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.

虽然造山带是我们理解造山作用（造山过程）的熔炉，但大多数造山带只在一个方向上进行研究：与构造运动平行。这种方法揭示了重要的跨走向的变化，从变质的前陆冲断系统，并导致了突破性的进展，造山模型，但淡化显着的沿走向变化观察到的大多数造山带。同样被低估的事实是，继承（前造山）结构必然影响整个造山带的周期造山构造的发展。因此，为了充分理解造山过程，有必要对碰撞板块的前造山构造进行清楚的描述，以补充对造山系统的理解。选择喜马拉雅系统作为天然实验室，是因为其壮观而松散的保存，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变，因此有限的构造叠加使喜马拉雅和前喜马拉雅变形之间的区别。喜马拉雅体系通常被认为是横向连续的;其主要的地质分区被认为是不间断的沿着其整个长度，尽管显着沿走向变化的地形和起伏，造山带结构，收敛速度。在这个授权周期中，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下板块碰撞前的内部配置联系起来。在这个建议中，它是假设东北走向的前寒武纪基底脊下的喜马拉雅前锋冲断南部的印度-恒河平原下继续喜马拉雅造山带，并可能有助于这些沿走向的变化。最重要的是，这些海脊与可能随着时间的推移而一再恢复活动的深层结构之间可能存在的联系尚未确定。如果这些脊相互作用的造山带在其演化的早期，这可能会导致造山带平行应变分区，表示在变质核的横向韧性应变变化，在前陆褶皱冲断带的横向斜坡，横向差异折返，和/或沉积物厚度的变化，甚至在今天的地震活动沿走向分区。这些潜在的相互作用将通过几个HQP主导的项目进行探索，包括：利用地震数据对前陆褶皱冲断带进行三维重建;进行现场和实验室调查，以评估应变、变质峰条件和喜马拉雅变质核的折返的沿走向变化;建立联系当今地震活动、应力轨迹和交叉走向基底脊的数值应力模型;和变形的动态缩放离心模拟模型。预计这一计划将最终提供关键的动态链接，以了解在老山区带，如阿巴拉契亚山脉，加拿大科迪勒拉，和格伦维尔造山带的演变基底交叉结构。这种横向不连续性已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的几何形状，并可能与深部结构，可以本地化成矿流体和控制油气运移通过前陆盆地，如在加拿大西部沉积盆地中观察到的。在喜马拉雅系统的情况下，这种隐藏的地质灾害控制可能对地球上人口最稠密的地区之一产生巨大影响。