Giant Dykes and Deep Time Tectonics; the Role of Dyke Swarms in Shaping the Early Earth

巨型堤坝和深层构造；

• 批准号: 2598928
• 金额: --
• 依托单位: University of St Andrews
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2598928
• 关键词: Giant; Dykes; Deep; Time; Tectonics

Magma plumbing systems are commonly dominated by vertical dykes, which deliver magma from depth into shallow-level reservoirs or to be erupted at the surface (Magee et al., 2018a). In active volcanic settings, we track subsurface dyke intrusions to monitor and assess volcano hazards. We also analyse the petrology and chemistry of erupted rocks to shed light on the processes within magma reservoirs that control eruption and hazard style; these processes can also drive the formation of economically important ore deposits. However, within these systems, dykes are typically assumed to be relatively simple pathways that link areas of magma storage to eruption sites. Yet there is a growing awareness that physical and chemical magma processes within dykes can very over small-scales in time and space, giving rise to domains within dykes where magma behaves differently (e.g., Magee et al., 2016; Holness et al., 2017). For example, dykes may be expected to convect, focusing magma ascent in some areas (Holness et al., 2017), whereas other parts of dykes may stagnate and allow layering to occur (Upton & Thomas, 1980). Magma processes within dykes are therefore more complex than many previous studies and models consider. Critically, we do not know how such complexity within dykes could impact the location of eruption sites, the distribution of minerals (including ore deposits), or the evolution and rheology of magma during transport. Addressing this knowledge gap in our understanding of dyking will provide fundamental insights crucial to volcano hazard assessment and mineral exploration. This project will examine the ~1.1 billion year old Tugtutôq Giant Dykes of SE Greenland, which represent a voluminous phase of Proterozoic rift magmatism (Upton & Blundell, 1978). Giant dykes, like those in Tugtutôq, are extremely wide (10's-100's m) and often contain zones of mineral layering (e.g., Upton & Thomas, 1980), which are known to form important mineral and metal ore deposits (e.g., Chaumba & Musa, 2020). These giant dykes represent an excellent natural laboratory to study magma processes within dykes because they contain discrete domains (e.g. layered pods and areas of presumed flow), where magma behaved differently, which can be easily sampled. Previous mineralogical and geochemical studies provide a broad understanding of the Tugtutôq Giant Dykes petrogenic history and associated Ti-Fe deposits (see Steenfelt et al., 2016). However, the mechanics of dyke injection, the formation of pristine mineral layering, and the interaction between domains within these intrusions remain unstudied. This PhD will specifically examine physical and chemical records of magma movement and crystallisation within the Tugtutôq Giant Dykes, in order to determine the controls on the: (1) localisation of magma flow, which may represent a key influence on the location and distribution of eruption sites; and (2) accumulation and evolution of minerals within stagnating magma, which will shed light on how magma chemistry is modified during dyking and formation of associated ore deposits. The resulting data will help the community to pinpoint how magma moves through and stalls within dykes, and how these processes impact magma evolution, mineralisation, and eruption style.

岩浆管道系统通常以垂直岩墙为主，它们将岩浆从深处输送到浅层水库或在地表喷发(Magee等人，2018a)。在活跃的火山环境中，我们跟踪地下堤坝的侵入，以监测和评估火山危害。我们还分析了喷发岩石的岩石学和化学，以揭示控制喷发和灾害类型的岩浆储集层内的过程；这些过程也可以驱动经济上重要的矿床的形成。然而，在这些系统中，岩墙通常被认为是连接岩浆储存区域和喷发地点的相对简单的路径。然而，人们越来越意识到，岩浆在岩墙内的物理和化学作用可以在时间和空间上非常小的尺度上进行，从而在岩墙内产生岩浆行为不同的区域(例如，Magee等人，2016；Holness等人，2017)。例如，堤坝可能会对流，使某些地区的岩浆集中上升(Holness等人，2017年)，而堤坝的其他部分可能会停滞，从而发生分层(Upton&Thomas，1980)。因此，岩浆在岩墙内的过程比许多以前的研究和模型所认为的要复杂得多。关键的是，我们不知道岩墙内的这种复杂性如何影响喷发地点的位置、矿物(包括矿床)的分布，或者岩浆在运输过程中的演化和流变学。解决我们对堤防理解中的这一知识差距将提供对火山危险评估和矿产勘探至关重要的基本见解。该项目将研究格陵兰岛东南部有11亿年历史的图格图克巨型岩墙，它代表了元古界裂谷岩浆活动的巨大阶段(Upton&Blundell，1978)。巨型岩脉，如图格图托克的那些，非常宽(10‘S-100’S米)，通常包含矿物分层带(例如厄普顿和托马斯，1980年)，这是众所周知的形成重要的矿物和金属矿床(例如昌巴和穆萨，2020年)。这些巨型岩墙是研究岩墙内岩浆作用的极好的天然实验室，因为它们包含离散的区域(例如，分层的豆荚和假定流动的区域)，在那里岩浆表现不同，很容易取样。以前的矿物学和地球化学研究使人们对图格图托Q巨型岩脉的成岩历史和相关的钛-铁矿床有了广泛的了解(见SteenFeet等人，2016)。然而，岩脉注入的机制、原始矿物分层的形成以及这些侵入体中各区域之间的相互作用仍未得到研究。本博士学位论文将专门研究图格图托克巨型岩墙内岩浆运动和结晶的物理和化学记录，以确定对以下方面的控制：(1)岩浆流动的局部化，这可能对喷发点的位置和分布产生关键影响；以及(2)停滞的岩浆中矿物的积累和演化，这将有助于揭示岩浆化学在岩脉形成和相关矿床形成过程中的变化。由此产生的数据将帮助该社区准确地确定岩浆如何在岩墙中流动和停滞，以及这些过程如何影响岩浆的演化、矿化和喷发方式。