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: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=708344
• 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造山带的形成和崩塌过程中物质和能量的重新分配以及矿床的形成起着重要作用。在大型山脉的形成过程中，地壳增厚使地壳深部的温度和压力升高。大量的流体流入山带下方的深部热地壳，促进了部分熔融，从而大大削弱了大片大陆地壳。这些熔融弱化的区域可能充当大规模的剪切带，促进山脉的形成，或者可能横向流向造山带前缘，导致高海拔高原的形成。例如，地球物理成像表明，喜马拉雅山带下方存在大面积的部分熔融地壳，这种熔融弱化物质的横向运动被认为在青藏高原的发展中起着一级作用。虽然广泛的流体流动的部分熔融可能有重要的构造后果，这些流体的来源，成分和运输途径的约束不足。这部分是由于缺乏进入现代山脉带之下的地壳深部的途径。 位于安大略西南部的格伦维尔省代表了古老的喜马拉雅山脉带被严重侵蚀的核心。这一地区是一个天然的实验室，可以用来研究现代山脉地带（如亚洲的喜马拉雅山脉和南美洲的安第斯山脉）下发生的过程。该研究计划将利用地质野外测绘和地球化学实验室工作，调查流体渗透和部分熔融对古代山脉带构造演化的作用。野外工作将限制流体在安大略暴露的地壳深部的传输路径。实验室工作将在滑铁卢大学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。这一研究项目的结果将有助于深入了解地壳深部流体渗透对现代和古代山区构造演化的作用。 流体在从地壳深部清除具有经济价值的元素（如金、铀和锡）并将其输送到地壳浅层产生矿床方面发挥着重要作用。然而，我们对地壳深部流体-岩石相互作用的认识仍然是初步的。因此，这项研究计划的更广泛的意义是提高对现代和古代山区地下流体-岩石相互作用的理解，这可用于改进含金属矿床的成因模型，并优先考虑在加拿大和世界各地勘探这些矿床。