Characterization of the End-Stages of Fractional Crystallization

Stillwater杂岩是由玄武岩岩浆分离结晶形成的一大堆层状镁铁质火成岩，玄武岩岩浆是地球上最常见的岩浆类型。随着矿物的生长和从结晶的玄武岩岩浆中分离出来，其成分变得越来越丰富，不包括在矿物中的元素，称为不相容元素。在火成岩研究中使用不相容元素来记录构造环境、源区的熔融程度和分离结晶的程度。这项研究将通过检查最后结晶的岩石的分布、丰度和组成来记录不相容元素在斯蒂尔沃特杂岩结晶的最后阶段的行为。Stillwater复合体既具有经济价值，又具有学术价值，因为它拥有美国大部分的铂储量，是了解玄武岩液态结晶的天然实验室。了解这一侵入过程中分离结晶的结束阶段将为解释火成岩系统中不相容元素的总体浓度提供更可靠的基础。这也将有助于理解铂是如何在该侵入岩的矿化部分浓缩到正常水平的1000倍以上的。

MeurerEAR-0229702The Stillwater complex is a large body of layered mafic igneous rock formed by fractional crystallization of a basaltic magma--the most common type of magma generated in the Earth. As minerals grow and separate from a crystallizing basaltic magma, its composition becomes increasingly enriched in elements not included in the minerals, termed incompatible elements. Incompatible elements are used in the study of igneous rocks to document tectonic settings, extents of melting of a source region, and extents of fractional crystallization. This study will document the behavior of incompatible elements during the final stages of the crystallization of the Stillwater complex by examining the distribution, abundance, and composition of the last rocks to have crystallized. The Stillwater complex is of both economic and academic interest, as it hosts the bulk of the platinum reserves of the US and is a natural laboratory for understanding basaltic liquid crystallization. An understanding of the end stages of fractional crystallization in this intrusion will provide a more reliable basis for interpreting incompatible elements concentrations in igneous systems in general. It will also help in understanding how platinum was concentrated to more than 1000 times normal in the mineralized parts of this intrusion.