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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.

虽然地球上地幔的大部分被认为是由橄榄石为主的超镁铁质岩石，有证据表明，从地幔捕虏体和钻石中的包裹体的镁铁质岩石成分，如榴辉岩和辉石的存在。榴辉岩可能是洋壳俯冲的结果，但许多辉石岩也可能是地幔熔融或交代过程的结果。由于它们为地幔作用提供了证据，因此研究它们并解释它们的起源深度以及它们对地幔地震性质的影响是非常重要的。一些关于地震性质的研究甚至提出对流地幔可能包括超镁铁岩和镁铁岩的机械混合物。在这项研究中，这种榴辉岩/辉石岩的相关系将被研究到地球过渡带的条件下，主要是在这些岩石主要由单斜辉石和石榴石组成的范围内。使用这些关系，两个地质压力计将被校准;一个采用的比例，铝托管在单斜辉石硅网站共存的石榴石和其他采用的镁铁质组合内的镁橄榄石-石榴石过渡。由于高的化学变化和少量的阶段，在这样的组合的矿物成分强烈依赖于散装组合物。在这项研究中，相关系在一个广泛的范围内合理的榴辉岩和辉石岩的组合物将进行研究，并保持内部一致性，多个样品室将采用许多散装组合物将在相同的压力和温度下同时平衡。此外，还将进行进一步的实验，以评估氧逸度和H2O对这些气压计平衡的影响。这些气压计对于确定钻石中矿物包裹体的形成深度至关重要。人们越来越认识到，许多这样的包裹体是在地球对流地幔的岩石圈下条件下形成的。钻石研究的这一日益增长的领域为研究地幔深部的过程提供了一个非凡的机会。利用这些结果，将对一系列金刚石包裹体和捕虏体的成因条件进行研究。此外，通过将镁铁质岩石相关系的热力学模型与弹性数据相结合，将计算俯冲洋壳成分的地震速度，并与地震观测结果进行比较。