Application of geochemistry to the petrogenesis and geodynamics of komatiites and leucogranites

地球化学在科马提岩和淡色花岗岩岩石成因和地球动力学中的应用

• 批准号: 3782-2006
• 负责人: Dostal, Jaroslav
• 金额: $ 2.21万
• 依托单位: Saint Mary's University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2006
• 资助国家: 加拿大
• 起止时间: 2006-01-01 至 2007-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=332476
• 关键词: Application; geochemistry; petrogenesis; geodynamics; komatiites

Two research projects will be undertaken with the aim of adding to our knowledge of how the Earth's mantle and crust evolved and how and where economic mineral deposits might have been formed. The first project deals with MgO-rich volcanic rocks, komatiites, which provide a window on the composition and thermal regime of the Archean mantle. Komatiites are assumed to represent plumes of unusually hot rock that were ejected from a great depth (plume model). Recently, however, researchers have suggested an alternative model whereby komatiites were formed by the melting of mantle at a relatively shallow depth and at considerably lower temperatures (subduction model). The purpose of this project is to test these two contradictory models by investigating the chemical composition of komatiites in two locations where komatiitic rocks show a wide compositional range. However, as komatiites are usually altered, the focus is to utilize "in situ" analyses of fresh clinopyroxene (major and trace elements) and of pristine melt inclusions trapped in relict primary minerals (major and trace elements, water, Pb and Li isotopes).  From these data, the nature of the magma sources as well as the melting processes can be inferred and used to test the mantle plume komatiite vs. subduction zone komatiite controversy. The second project will focus on granitic rocks that are rich in lithium and fluorine, elements that can help concentrate valuable metals. In some areas, these rocks host deposits of tin, tungsten and uranium. The study will look at granitic rocks of similar ages from Atlantic Canada and Europe. Determining the trace element and isotope compositions of these rocks and their constituent minerals will provide critical information on how the rocks and their deposits formed and will show if the granites could have originally been part of a large geological province enriched in metallic mineral deposits. Thus, this study can improve mineral exploration models.

将开展两个研究项目，目的是增加我们对地球地幔和地壳如何演变以及经济矿藏如何和在何处形成的知识。第一个项目涉及富含MgO的火山岩，科马提岩，它提供了一个窗口的组成和太古代地幔的热状态。科马提岩被认为是从很深的地方喷出的异常热的岩石柱（柱模型）。然而，最近，研究人员提出了另一种模型，即科马提岩是由地幔在相对较浅的深度和相当低的温度下熔融形成的（俯冲模型）。该项目的目的是通过调查科马提岩的化学成分来测试这两个矛盾的模型，其中科马提岩的化学成分范围很广。然而，由于科马提岩通常是蚀变的，重点是利用新鲜单斜辉石的“原位”分析（主量元素和微量元素）和残留原生矿物中捕获的原始熔融包裹体（主要和微量元素、水、铅和锂同位素）。从这些数据来看，可以推断岩浆来源的性质以及熔融过程，并用于检验地幔柱科马提岩与俯冲带科马提岩争议第二个项目将侧重于富含锂和氟的花岗岩，这些元素可以帮助浓缩有价值的金属。在某些地区，这些岩石承载着锡、钨和铀的矿床。这项研究将着眼于来自大西洋加拿大和欧洲的类似年龄的花岗岩。确定这些岩石及其组成矿物的微量元素和同位素组成将提供有关岩石及其矿床如何形成的关键信息，并将显示花岗岩最初是否可能是富含金属矿床的大型地质省的一部分。因此，该研究可以改进矿产勘查模型。