Seeking Evidence for Reactive Assimilation in a Hybrid Pluton

寻找混合冥王星反应同化的证据

• 批准号: 0808725
• 负责人: James Beard
• 金额: $ 4.46万
• 依托单位: Virginia Museum of Natural History Foundation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-07-01 至 2010-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0808725&HistoricalAwards=false
• 关键词: Seeking; Evidence; Reactive; Assimilation; Hybrid

The PI seeks funding to identify source components in hybrid mixed plutonic rocks and to understand the mechanisms by which they are incorporated. He proposes that the fundamental process involves assimilation by disaggregation and reaction of crystalline materials with silicate melts. In particular, wholesale melting of assimilant may not be required. Instead, solids formed during partial melting (e.g. dehydration melting) of the assimilant are incorporated into the magma as the xenolith disaggregates. Reactions during assimilation and crystallization promote both chemical mixing and physical disintegration of xenoliths and are largely responsible for the cryptic character of bulk assimilation. The goal of this project is to identify mesoscale and microscale regions within igneous rocks that reflect varying degrees of crust vs. mantle input. The work will focus on petrographic and mineralogical heterogeneities that may preserve evidence of fine-scale, cryptic mixing even if original textures and mineralogy have been modified by reactive processes during assimilation and crystallization. The work is specifically aimed at the identification and characterization of minerals - either phenocrysts or xenocrysts - that predate the hybridization event as well as reactant minerals that carry a hybrid signature. The PI proposes to investigate these processes in the Martinsville Igneous Complex (MIC) in southern Virginia, a gabbro-diorite complex with a hybrid isotopic signature. The MIC is well-suited for this study because; 1) isotope chemistry is strongly correlated with major and trace element chemistry within the MIC; 2) the system (a basaltic intrusion into pelitic rocks) is geologically well-characterized, highly contrasting, and simple and; 3) minerals and mineral clots have been identified in the pluton that are tentatively interpreted as being derived from the country rocks. Additionally, petrographically distinctive phases, including zoned, dusty plagioclase in the pluton and blue quartz in the country rocks provide obvious analytical targets. Data to be acquired unclude a suite of whole rock analyses, and mineral chemical and zoning data including major and trace elements and oxygen isotopes.Broader impacts: The PI will incorporate information from this study into his ongoing program of K-12 teacher training, which already includes a large component on the origin and composition of granitic magmas. If this proposal is supported, additional support will be sought to create an inquiry-based exhibit on igneous rocks that emphasizes the results of the proposed research. This museum is a focal point for school visitation and alternative learning in an economically depressed region (Enterprise Zone) where approximately 50% of the school-age population is African-American and Hispanic.

PI寻求资金，以确定混合混合深成岩中的来源成分，并了解它们被合并的机制。他提出，基本过程包括通过解聚结晶物质和硅酸盐熔体的反应进行同化。特别是，可能不需要大规模熔化同化剂。相反，在同化物的部分熔融(例如脱水熔融)过程中形成的固体随着捕虏体的解体而并入岩浆。同化和结晶过程中的反应促进了包体的化学混合和物理解体，并在很大程度上导致了整体同化的隐蔽性。该项目的目标是确定火成岩内反映地壳与地幔输入不同程度的中尺度和微尺度区域。这项工作将侧重于岩相学和矿物学的不均一性，即使原始结构和矿物学在同化和结晶过程中被反应过程改变了，也可能保存细微、神秘混合的证据。这项工作的具体目的是识别和表征杂交事件之前的矿物--斑晶或捕虏晶--以及带有杂交特征的反应性矿物。PI建议在弗吉尼亚州南部的马丁斯维尔火成岩杂岩(MIC)中研究这些过程，马丁斯维尔火成岩杂岩是一种具有混合同位素特征的辉长闪长岩杂岩。MIC非常适合于这项研究，因为：1)同位素化学与MIC内的主要和微量元素化学密切相关；2)该系统(侵入泥质岩的玄武岩)地质特征良好，对比强烈，结构简单；3)在岩体中发现了矿物和矿块，初步解释为来自围岩。此外，岩石学上的独特相，包括岩体中的带状、尘土飞扬的斜长石和围岩中的蓝色石英，提供了明显的分析目标。将获得的数据不包括一套全岩分析，以及包括常量和微量元素以及氧同位素在内的矿物化学和分带数据。广泛的影响：PI将把这项研究的信息纳入他正在进行的K-12教师培训计划中，该计划已经包括了关于花岗岩岩浆的起源和组成的很大一部分。如果这项提议得到支持，将寻求更多的支持，以创建一个以调查为基础的火成岩展览，强调拟议研究的结果。在经济不景气的地区(企业区)，这个博物馆是学校参观和替代学习的焦点，那里大约50%的学龄人口是非裔美国人和西班牙裔。