Fluid-present melting of the deep crust: implications for the tectonics of large convergent orogens

深部地壳的流体熔融：对大型聚合造山带构造的影响

• 批准号: RGPIN-2015-04040
• 负责人: Yakymchuk, Christopher
• 金额: $ 1.75万
• 依托单位: University of Waterloo
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=679736
• 关键词: Fluid; present; melting; deep; crust

The interaction of fluids with rocks in the deep continental crust plays a critical role in the redistribution of mass and energy during the buildup and collapse of mountain belts and the genesis of ore deposits. During the construction of large mountain belts, crustal thickening generates elevated temperatures and pressures in the deep crust. Widespread fluid influx into the deep hot crust beneath mountain belts promotes partial melting, which drastically weakens large regions of continental crust. These melt-weakened regions may act as large-scale shear zones that facilitate mountain buildup or may flow laterally towards orogenic fronts resulting in the formation of high-elevation plateaux. For example, geophysical imaging suggests that large regions of partially molten crust are present beneath the Himalayan mountain belt and the lateral movement of this melt-weakened material is proposed to play a first-order role in the development of the Tibetan Plateau. While widespread fluid-fluxed partial melting may have important tectonic consequences, the sources, compositions and transport pathways of these fluids are poorly constrained. This is due, in part, to the lack of access to the deep crust beneath modern mountain belts.*** The Grenville Province of southwestern Ontario represents the deeply eroded core of an ancient Himalayan-scale mountain belt. This region represents a natural laboratory to investigate the processes that are occurring beneath modern mountain belts - such as the Himalaya in Asia and the Andes in South America. This research program will investigate the role of fluid infiltration and partial melting on the tectonic evolution of an ancient mountain belt using both geological field mapping and geochemical laboratory work. Fieldwork will constrain the transport pathways for fluids in the deep crust exposed in Ontario. Laboratory work will evaluate the source and compositions of the fluids as well as the timing of fluid infiltration using modern geochemical techniques at the University of Waterloo. The results of this research program will provide insights into the role of fluid infiltration in the deep crust on the tectonic evolution of modern and ancient mountain belts. *** Fluids play an important role in scavenging elements of economic interest (e.g. gold, uranium, and tin) from the deep crust and transporting them to the shallower crust where they generate mineral deposits. However, our understanding of fluid-rock interaction in the deep crust is still rudimentary. Therefore, a broader implication of this research program is an improved understanding of fluid-rock interaction beneath modern and ancient mountain belts, which can be used to improve genetic models of metalliferous ore deposits and to prioritize exploration for these deposits in Canada and around the world.**

陆壳深部流体与岩石的相互作用对山带的造山带和崩塌过程中的质量和能量的重新分配以及矿床的成因起着至关重要的作用。在建造大型山脉带的过程中，地壳增厚会导致地壳深层的温度和压力升高。广泛的流体流入山脉下的深热地壳促进了部分熔融，这极大地削弱了大陆地壳的大片区域。这些熔融减弱的地区可能起到促进造山的大规模剪切带的作用，也可能向造山前缘横向流动，从而形成高海拔高原。例如，地球物理成像表明，喜马拉雅山脉下存在大片部分熔融的地壳，这种熔融减弱的物质的横向运动被认为在青藏高原的发展中起到了一级作用。虽然广泛的流体熔融部分熔融可能具有重要的构造后果，但这些流体的来源、成分和输送路径受到的约束很差。这在一定程度上是由于缺乏进入现代山脉下的深层地壳的途径。*安大略省西南部的格伦维尔省代表着古代喜马拉雅山规模的山脉带被深度侵蚀的核心。这一地区代表着一个天然的实验室，可以研究现代山脉下发生的过程--例如亚洲的喜马拉雅山脉和南美洲的安第斯山脉。这项研究计划将利用地质野外填图和化探实验室工作，研究流体渗透和部分熔融在古山带构造演化中的作用。野外工作将限制安大略省暴露的深部地壳中流体的运输路径。滑铁卢大学的实验室工作将利用现代地球化学技术评估流体的来源和成分，以及流体渗透的时间。这一研究计划的结果将为深入了解地壳深部流体渗透对现代和古代山带构造演化的作用提供依据。*流体在从深部地壳中清除有经济价值的元素(如金、铀和锡)并将它们输送到浅层地壳并在那里形成矿藏方面发挥着重要作用。然而，我们对地壳深部流体-岩石相互作用的了解仍处于初级阶段。因此，这项研究计划的一个更广泛的含义是更好地理解现代和古代山脉带下的流体-岩石相互作用，这可以用来改进金属矿床的成因模型，并优先在加拿大和世界各地勘探这些矿床。