Review of the oldest (4400-3600 Ma) geological and mineralogical record: Glimpses of the beginning
Review of the oldest (4400-3600 Ma) geological and mineralogical record: Glimpses of the beginning
复制标题
DOI：
10.18814/epiiugs/2001/v24i2/003
复制
发表时间：
2001-06
期刊：
影响因子：
3.1
通讯作者：
A. Nutman;C. Friend;V. Bennett
中科院分区：
文献类型：
--
作者：
A. Nutman;C. Friend;V. Bennett
地幔橄榄岩的Re-Os同位素特征为研究深部化学储集和地幔演化提供了新的视角。这是由于该体系与以亲石元素为基础的Rb-Sr和Sm-Nd同位素体系相比，具有不同的特征，对橄榄岩中的次生蚀变相对不敏感。在Itsaq片麻岩杂岩中，对整个岩石及其橄榄石和铝尖晶石的Os同位素研究将其与保存完好的约3800 Ma深海橄榄岩的稀有残余分离开来，这些橄榄岩在约3800 Ma时被困在地壳中（Friend等人，在审查中）提供了第一个直接制约的Os同位素演化的早期地幔（班尼特审查）。新的结果表明，高度亲铁元素Re和Os存在于3800 Ma地幔中的近似南极丰度。一般认为，硅酸盐地球中高度亲铁的成分是在地核形成后通过添加流星“晚期饰面”（例如，Chou，1978），早期橄榄岩的结果限制了这一成分的时间，因为它必须在3800 Ma前加入地球并均匀化到地幔中，并可用于取样。此外，始太古代橄榄岩的Os同位素组成没有提供证据表明在早古生代地幔中存在大量储存的镁铁质地壳。
The Re-Os isotopic characteristics of mantle peridotites are providing a new perspective on deep chemical reservoirs and mantle evolution. This is due to the contrasting behaviour of this system and its relative insensitivity to secondary alteration in peridotites compared with the lithophile element based Rb-Sr and Sm-Nd isotopic sys-tems. Within the Itsaq Gneiss Complex, Os isotopic study of whole rocks and their olivine and aluminous spinel separates from rare relicts of well preserved ~3800 Ma abyssal peridotites trapped in the crust at ~3800 Ma (Friend et al., in review) are providing the first direct constraints on the Os isotopic evolution of the early mantle (Bennett in review). The new results indicate that the highly siderophile elements Re and Os were present in the 3800 Ma mantle at approximately chondritic abundances. As it is generally considered that the highly siderophile component of the silicate Earth was emplaced post-core formation by the addition of a meteoric "late veneer" (e.g., Chou, 1978), the results from the early peridotites constrain the timing of this component in that it must have been added to the Earth and homogenised into the mantle and be available for sam-pling by 3800 Ma. Additionally, the Os isotopic compositions of the Eoarchaean peridotites provide no evidence for the presence of large amounts of stored mafic crust in the early Archaean mantle.