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

将进行两个研究项目，目的是增加我们对地幔和地壳如何演变以及经济矿藏可能如何和在何处形成的认识。第一个项目涉及富氧化镁的火山岩，科马地岩，它为太古代地幔的组成和热状态提供了一个窗口。科马地岩被认为代表了从很深的地方喷出的异常热的岩石羽状体（羽状体模型）。然而，最近研究人员提出了另一种模型，即科马地岩是在相对较浅的深度和相当低的温度下由地幔融化形成的（俯冲模型）。这个项目的目的是通过在两个地方调查科马提岩的化学成分来检验这两个相互矛盾的模型，这些地方的科马提岩显示出广泛的成分范围。然而，由于科马长岩通常是蚀变的，因此重点是利用“原位”分析新鲜斜辉石（主要元素和微量元素）和残留原生矿物（主要元素和微量元素、水、铅和锂同位素）中捕获的原始熔融包裹体。根据这些数据，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之争。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，这些岩石中蕴藏着锡、钨和铀。这项研究将研究来自加拿大大西洋和欧洲的年龄相仿的花岗岩。测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关于岩石及其矿床如何形成的关键信息，并将表明这些花岗岩最初是否可能是一个富含金属矿床的大型地质省的一部分。因此，本研究可以完善矿产勘查模型。

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.