A Laser Ablation ICPMS-Based Study of Postcumulus Processes in Hydrous and Dry Mafic Cumulates

智力优势：矿物在分步结晶过程中聚集形成的火成岩分布广泛，蕴藏着经济矿产资源，并提供了岩浆室物理和化学过程的记录。积云记录了积云（形成晶体堆的那些）和积云后（改变晶体堆的那些）过程的化学和结构证据。拟议的研究将使用激光烧蚀ICP-MS （LA-ICPMS）原位微量元素分析来记录积云后过程的重要性，并对矿物磷灰石进行分析，以了解这些系统中挥发性成分的演化。这项研究将对由玄武岩液体形成的堆积物进行研究，并将对比来自蒙大拿斯蒂尔沃特（Stillwater）杂岩的岩石，这些岩石是由相对干燥的液体结晶而成的，而来自瑞典rymen和Eriksberg辉长岩的岩石是由潮湿的液体结晶而成的。对斯蒂尔沃特斜辉石和Eriksberg角闪洞的浮晶的初步研究表明，微量元素的变化多达三个数量级。通过绘制微晶的成分变化图，可以记录微晶间液的成分演化和空间分布。间隙磷灰石的卤素含量已被证明对了解积积物中挥发物的后期演化和析出有价值。磷灰石的LA-ICPMS分析将提供一种将这些体系的痕量元素演化与其挥发演化联系起来的方法。更广泛的影响：这项工作将提供对部分熔融岩石中运作过程的基本理解。了解这些过程对于了解重要矿石资源的成因至关重要，这些矿石资源包括贵金属（铂和钯）和贱金属（尤其是铬和镍）。了解这些过程对于解释这些岩石及其组成矿物的化学性质也至关重要。考虑到几乎所有来自月球和火星的样本都与要研究的岩石相似，这项工作很可能也会促进我们对这些天体的理解。这项工作还将有助于建立一种经验理解，即在单晶的长时间生长历史中，微量元素是如何在结晶岩浆和生长晶体之间分配的。

Intellectual Merit: Igneous rocks formed by the accumulation of minerals during fractional crystallization (cumulates) are widely distributed, host economic mineral resources, and provide a record of the physical and chemical processes in magma chambers. Cumulates record chemical and textural evidence of both cumulus (those that build the crystal pile) and postcumulus (those that modify the crystal pile) processes. The proposed study will use in situ trace-element analyses by laser ablation ICP-MS (LA-ICPMS) to document the importance of postcumulus processes and analyses of the mineral apatite to understand the evolution of volatile components in these systems. The research will be conducted on cumulates formed from basaltic liquids and will contrast rocks from the Stillwater complex, Montana that crystallized from a relatively dry liquid with those from the Rymmen and Eriksberg gabbros, Sweden that crystallized from a wet liquid. Preliminary studies of oikocrysts of clinopyroxene from the Stillwater and amphibole from the Eriksberg reveal as much as three orders of magnitude variation in trace elements. By mapping the compositional variation in oikocrysts the compositional evolution and spatial distribution of the interstitial liquid can be documented. The halogen content of interstitial apatite has proven to be valuable for understanding the late-stage evolution and exsolution of volatiles in cumulates. LA-ICPMS analyses of apatite will provide a means of relating the trace-element evolution of these systems to their volatile evolution.Broader Impacts: This work will provide a fundamental understanding of the processes that operate in a partially molten rock. Knowledge of these processes is essential for understanding the genesis of important ore resources that host precious (platinum and palladium) and base metal (especially chromium and nickel). Understanding these processes is also central to interpreting the chemistry of these rocks and their constituent minerals. Given that nearly all of our samples from the Moon and Mars are similar to the rocks to be studied, the work is likely to advance our understanding of these bodies as well. The work will also help to establish an empirical understanding of how trace elements are partitioned between crystallizing magmas and growing crystals over an extended growth history for a single crystal.