Origins of layers in layered mafic intrusions

层状镁铁质岩体中层的起源

• 批准号: RGPIN-2018-05327
• 负责人: Mungall, James
• 金额: $ 5.25万
• 依托单位: Carleton University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=751167
• 关键词: Origins; layers; layered; mafic; intrusions

Large igneous provinces represent events during which millions of cubic km of extremely hot magma passed through the Earth's crust and were either emplaced as collections of intrusions or erupted as voluminous lava flows. Intrusions within large igneous provinces are dominated by magnesium- and iron-rich (i.e., mafic) rocks and display layering that superficially resembles the layering in some sedimentary rocks, hence the general term "layered mafic intrusions" (LMI). LMI contain the world's most important reserves of important metals including chromium and platinum; they are also important sources of copper, nickel, palladium, phosphorus, iron, titanium, vanadium, and niobium. The origins of mineralized layers in LMI remain a matter of intense research activity and controversy. The LMI research community tends to favor the concept of magma chambers as large as ten km deep and hundreds of km wide within which crystals accumulate along the base to form an upward-aggrading series of layers. However, the study of layered rocks in granitic intrusions and of layered mafic intrusions at mid-ocean ridge settings has shown that in many cases layering results from the repeated intrusion of separate thin horizontal sheets of magma to produce a layered stack of sills. The difference is critical for guiding mineral exploration strategies in newly discovered deposit groups like the Ring of Fire deposits of northwestern Ontario. My group and a few others have recently suggested that the magma chamber hypothesis for very large sill-shaped LMI should be replaced by the idea of sequential emplacement of stacks of sills in many examples. The objective of the proposed research is to develop rigorous tests of the sill hypothesis for LMI and some of its competing hypotheses. Some key questions to be answered will include: "How can we recognize the margins of sills intruded into older sills that remain very hot themselves?"; "Can we detect evidence for short, intense periods of heating of rocks adjacent to sills within LMI?"; "What sequence of rocks is expected to be produced if a magma solidifies without having sills emplaced within it?" We will use four examples of LMI as natural field laboratories; the iconic Bushveld Complex of South Africa and Stillwater Complex of Montana, which are candidates for the sill hypothesis, the Sudbury Igneous Complex of Ontario, which is known to have been a classical magma chamber, and the Kyak Bay Intrusion of Quebec, whose geology is poorly known but exceptionally well-exposed. The work will involve mapping, sampling and measurement of rock and mineral composition and textures. The field observations will be compared with the predictions that can be made using thermodynamic and numerical models of igneous processes such as chemical diffusion, crystal nucleation and growth, maturation of igneous textures, magma flow and emplacement, and heat flow within magmas and their solid host rocks.

大火成岩省代表事件，在此期间，数百万立方公里的极热的岩浆经过地球的地壳，要么被作为侵入集的集合或作为大量熔岩流爆发而爆发。 大火成岩省内的入侵以镁和铁富含镁（即镁铁质）岩石为主导，并显示出表面上与某些沉积岩石中的分层相似的分层，因此，一般的术语“分层的镁铁质侵入”（LMI）（LMI）。 LMI包含世界上最重要的重要金属储量，包括铬和铂；它们也是铜，镍，钯，磷，铁，钛，钒和niobium的重要来源。 LMI中矿化层的起源仍然是激烈的研究活动和争议的问题。 LMI研究界倾向于偏爱岩浆腔室的概念，深十公里，宽度为数百公里，晶体沿着底部积聚，形成了一系列向上的层。 然而，对中山脊环境中花岗岩侵入和分层的镁铁质侵入的研究的研究表明，在许多情况下，分层的岩浆的薄薄水平水平板反复入侵产生了分层的纹状体。 差异对于指导新发现的矿床集团（如安大略省西北部的火环）等新发现的矿产勘探策略至关重要。 我的小组和其他一些人最近提出，在许多示例中，应该将岩浆形的LMI的岩浆腔室假设取代。 拟议的研究的目的是开发对LMI及其一些竞争假设的SILL假设的严格检验。 要回答的一些关键问题将包括：“我们如何认识到侵入自己仍然很热的旧窗台的窗台的边缘？” “我们可以检测到LMI内部与基座附近的岩石的短暂加热时期的证据吗？”； “如果岩浆在没有凹痕的情况下凝固而固化，预计将产生哪些岩石序列？”我们将以四个LMI的例子为天然现场实验室。南非的标志性灌木丛和蒙大拿州的斯蒂尔沃特建筑群，它们是基林假设的候选者，安大略省的萨德伯里火成岩综合体，已知是经典的岩浆室，而Quebec的Kyak Bay入侵，Quebec的地质学众所周知，但异常良好。 这项工作将涉及岩石以及矿物组成和纹理的映射，采样和测量。 将使用热力学和数值模型进行的预测，将现场观察结果进行比较，例如化学扩散过程，例如化学扩散，晶体成核和生长，火成岩质地的成熟，岩浆流量和增强的成熟，岩浆中的热量以及岩浆中的热流及其固体宿主岩石。