地幔地球化学:洋岛玄武岩制约

发布时间：2018-03-12 20:25

本文选题：地幔结构　切入点：地幔成分　出处：《中国科学:地球科学》2017年10期 　论文类型：期刊论文

【摘要】：对地幔的地球化学研究为理解地球的形成和演化、其内部结构以及地幔动力学提供了重要制约.全地球的成分是通过由地幔岩石与球粒陨石对比所得到,并由此引出了球粒陨石质地球模型.这个模型认为地球难熔元素比例与球粒陨石相同,但挥发份相对亏损.洋岛玄武岩可能是源于地幔柱深部成因,进而成为研究深部地球的独特途径.洋岛玄武岩同位素组成变化可用有限几个地幔端元(例如,DMM、EM1、EM2和HIMU)来描述,由此用来解译重要的地幔过程.地壳物质通过俯冲和拆沉进入深部地幔,对地幔不均一的形成起到了重要作用.然而,这些地壳物质如何由部分熔融所提取,例如洋岛玄武岩成因中贫橄榄石岩石的作用,仍是热点争论话题.高~3He/~4He地幔的位置和成因仍有争议,存在从下地幔未演化(或弱演化)的原始物质到浅部成因的高程度演化物质的看法,后者包括古老熔融残留、弧下镁铁质堆晶和再循环含水矿物.可能存在的核幔相互作用被假定为洋岛玄武岩中诸如放射成因~(186)Os以及Fe和Ni的富集之类地球化学特征形成的原因.诸如~(142)Nd、~(182)W和Xe同位素之类的短寿命核素的微小但重要的变化在古老和现代岩石中均有报道,这暗示地幔必须在地球形成后100Myr内即发生分异,而且地幔并未被对流所有效均一化.
[Abstract]:Geochemical studies of the mantle provide important constraints for understanding the formation and evolution of the Earth, its internal structure and mantle dynamics. The composition of the whole Earth is derived from the comparison of mantle rocks with chondrites. The chondrite-like earth model is derived. The model holds that the ratio of refractory elements to chondrites is the same as that of chondrites, but the volatiles are relatively depleted. The oceanic island basalts may have originated from the deep mantle plume. The variations in isotopic composition of oceanic basalts can be described by a limited number of mantle end elements (such as DMMMU EM1 EM2 and HIMU). This is used to interpret important mantle processes. Crustal matter enters the deep mantle through subduction and deconvolution, which plays an important role in the formation of mantle heterogeneity. However, how these crustal materials are extracted by partial melting, For example, the role of olivine rocks in the genesis of oceanic basalts is still a hot topic of debate. There is a perception of a high level of evolution from unevoluted (or weakly evolved) primitive matter in the lower mantle to a highly evolved material of shallow origin, which includes ancient molten residues, Subarc magnesia-ferrite heaps and recycled water-bearing minerals. The possible core-mantle interaction is assumed to be the cause of the formation of geochemical characteristics in oceanic island basalts, such as the enrichment of radiogenic basalts such as 186Os and Fe and Ni. Minor but important changes in short-lived nuclides such as Xe isotopes have been reported in both ancient and modern rocks. This implies that the mantle must be differentiated within 100 Myr after the formation of the Earth and that the mantle is not effectively homogenized by convection.
【作者单位】： Department
【基金】：美国国家科学基金会项目(编号:NSF EAR-1524387) 国家自然科学基金项目(批准号:41590620)资助
【分类号】：P542.5;P588.145

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