Rutile_zircon_melt assemblages, key to understand processes in mafic layered intrusions: examples from the Bushveld Complex, South Africa

本文通过对Bushveld杂岩的Rustenburg层状套（RLS）及其相关卫星侵入物（Uitkomst岩浆管）中金红石、锆石及其相关熔融包裹体的系统研究，旨在了解这些组合在（超）基性岩石中的形成和组成系统，并获得岩浆室演化过程的新信息。这包括母岩浆的来源和成分，以及结晶过程中的物理化学条件（p -t- x -t-冷却速率），从最早的积云结晶（由铬铁矿中的金红石熔体包裹体反映）到非常晚的积云内熔融阶段（由金红石-锆石对和锆石中相关的熔体包裹体反映）。此外，还将研究接触变质岩中的锆石和金红石，以获得由于Bushveld加热引起的流体诱导hfse动员和-均质化的信息，以及这些元素可能被吸收到RLS中的信息。在这方面，将研究锆石和金红石的结构背景、分带模式、微量元素组成、矿物包裹体和U-Pb-Hf-O同位素。此外，还将研究锆石中的熔体包裹体和铬铁矿中含金红石的熔体包裹体，以量化RLS结晶过程中的熔体分馏，并估计锆石、金红石和熔体之间的分配系数。

This study focus on the systematic investigation of rutile, zircon, and associated melt inclusions in rocks of the Rustenburg Layered Suite (RLS) of the Bushveld Complex, and a related satellite intrusion (Uitkomst magma conduit) with the aim to understand the systematics of the formation and composition of these assemblages in (ultra)mafic rocks, and to obtain new information about processes during magma chamber evolution. This comprises information about the source(s) and composition(s) of the parental magma(s), and physical-chemical conditions (P-T-X-t-cooling rates) during crystallisation from the earliest cumulus crystallisation (reflected by rutile-melt inclusions in chromite), to the very late intra-cumulus melt stage (reflected by rutile-zircon pairs and related melt inclusions in zircon). In addition, zircon and rutile from contact metamorphic rocks will be studied, in order to gain information about fluid induced HFSE-mobilization and -homogenization due to Bushveld heating, and about a possible uptake of these elements into the RLS. In this respect zircon and rutile will be investigated for their textural context, zoning patterns, trace element compositions, mineral inclusions, and U-Pb-Hf-O isotopes. Melt inclusions in zircon, and rutile-bearing melt inclusions in chromite will additionally be studied in order to quantify melt fractionation during RLS crystallisation, and to estimate partitioning coefficients between zircon, rutile and melt.