The phase relations of mafic rocks within the Earths mantle and geobarometers for eclogite and pyroxenite rocks to conditions of the Earths transition zone.

地幔内镁铁质岩石的相关系以及榴辉岩和辉石岩岩石的地质气压计与地球过渡带条件的关系。

基本信息

批准号：
264531645
负责人：
Professor Dr. Daniel J. Frost
金额：
--
依托单位：
Bayerisches Forschungsinstitut für Experimentelle Geochemie und Geophysik (BGI)
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2014
资助国家：
德国
起止时间：
2013-12-31 至 2015-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/264531645?language=en
关键词：
phase relations mafic rocks within

项目摘要

While the bulk of the Earths upper mantle is considered to be comprised of olivine dominated ultramafic rocks, there is evidence from mantle xenoliths and inclusions in diamonds for the presence of mafic rock compositions such as eclogites and pyroxenites. Eclogites are likely present in the mantle as a result of subduciton of oceanic crust, however, many pyroxenite rocks may also be present as a result of melting or metasomatic processes occurring in the mantle. As they provide evidence for mantle processes, studying these rocks and interpreting their depth of origin and also their influence on mantle seismic properties is of great importance. Some studies on seismic properties have even proposed that the convecting mantle may comprise a mechanical mixture of ultramafic and mafic rocks. In this study the phase relations of such eclogitic/pyroxenitic rocks will be studied up to conditions of the Earths transition zone, and mainly in the range where these rocks are composed principally of clinopyroxene and garnet. Using these relations, two geobarometers will be calibrated; one that employs the proportion of Al hosted in the clinopyroxene Si-site coexisting with garnet and the other that employs the majorite-garnet transition within such mafic assemblages. Due to the high chemical variance and small number of phases, the mineral compositions within such assemblages are strongly dependent on bulk compositions. In this study phase relations over a wide range of plausible eclogite and pyroxenite compositions will be studied and to maintain internal consistency multiple sample chambers will be employed so many bulk compositions will be equilibrated at the same pressure and temperature simultaneously. In addition further experiments will be performed to asses the effects of oxygen fugacity and H2O on these barometer equilibria. These barometers are essential for determining the depth of formation of mineral inclusions in diamonds. It is increasingly recognised that many such inclusions are formed at sublithospheric conditions in the Earths convecting mantle. This growing field of diamond study presents a remarkable opportunity to investigate processes in the deep mantle. Using the results the conditions of origin of a range of diamond inclusions and xenoliths will be investigated. In addition by combining a thermodynamic model for mafic rock phase relations with elasticity data, the seismic velocity of subducted oceanic crust compositions will be calculated and compared with seismic observations.

虽然大部分地球上地幔被认为由橄榄石主导的超镁铁质岩石组成，但有来自地幔异种石的证据和钻石中的夹杂物，表明存在米菲岩石组成，例如粘岩和pyroxenite。由于海洋壳的细胞尺寸，可能存在地幔中的叶绿树，但是，由于地幔中发生的融化或代理过程，许多辉石岩也可能存在。当他们提供地幔过程的证据，研究这些岩石并解释其起源深度以及对地幔地震特性的影响非常重要。一些关于地震特性的研究甚至提出，对流地幔可能包括超镁铁质和镁铁质岩石的机械混合物。在这项研究中，将研究这种偶氮/去成为岩石岩石的相位关系，直到地球过渡区的条件，主要是这些岩石主要由clinopyroxene和Garnet组成的范围。使用这些关系，将校准两个Geobarometer。一种采用了在Clinopyroxene Si位置与石榴石共存的Al比例，另一个是在此类镁铁质组合中采用大多数Garnet转变的比例。由于化学方差较高和相数较少，因此这种组合中的矿物组成很大程度上取决于散装组成。在这一研究阶段，将研究各种合理的叶绿树和辉石组成的范围内的关系，并保持内部一致性，将采用多个样品室，因此在相同的压力和温度同时，将在相同的压力和温度下平衡。另外，将进行进一步的实验，以评估氧气和H2O对这些晴雨表平衡的影响。这些气压计对于确定钻石中矿物质夹杂物的深度至关重要。越来越多地认识到，许多此类夹杂物是在对流地幔的地球上跨层条件下形成的。这项不断增长的钻石研究领域为研究深层地幔过程中的过程提供了一个了不起的机会。使用结果，将研究一系列钻石夹杂物和异种石的起源条件。另外，通过将用于镁铁质岩石相关关系的热力学模型与弹性数据相结合，将计算俯冲的海洋外壳组成的地震速度，并将其与地震观测结果进行比较。