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首页> 外文期刊>Contributions to Mineralogy and Petrology >Os isotope systematics of komatiitic basalts from the Vetreny belt, Baltic Shield: evidence for a chondritic source of the 2.45 Ga plume
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Os isotope systematics of komatiitic basalts from the Vetreny belt, Baltic Shield: evidence for a chondritic source of the 2.45 Ga plume

机译：Vetreny带，波罗的海盾构的玄武岩的Os同位素系统：2.45 Ga羽状孔的软骨来源

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摘要

The Vetreny belt in the southeast Baltic Shield is a large volcano-sedimentary basin containing a 4- to 8-km-thick sequence of basaltic to komatiitic lavas, which were erupted ~2.45 Ga ago in a continental rift setting during the interaction of a mantle plume and the Archean continental crust of the Karelian granite–greenstone terrane. Re–Os isotope data for olivine cumulate samples and chromite separates from Victoria's lava lake and Golets flow 3 define isochrons with ages of 2387±57 and 2432±34 Ma, respectively. These ages are in good agreement with the previously reported, and new, Nd–Pb and U–Pb zircon ages. These data, coupled with the evidence for immobile behavior of the Re and Os, indicate that the Re–Os system remained closed since the lava eruption. The weighted average initial γ187Os values range between –0.43±0.10 for Golets flow 3 and –0.07±0.13 for the lava lake. A single chromite separate from Golets flow 1 has a γ187Os(T) of –0.06±0.15. Nd–Pb isotope and lithophile trace element data for the Vetreny belt komatiitic basalts were used to monitor the effect of crustal contamination on the Os isotope system and to estimate the initial Os isotope composition of the Vetreny plume source to be approximately chondritic with a γ187Os(T) of –0.9. This implies that the mantle source evolved with a long-term nearly chondritic Re/Os ratio. The data provide further evidence that, by the end of the late Archean, the Earth's upper mantle was well homogenized with respect to the highly siderophile elements, added during the accretion of a late veneer, on a time scale of ~1 Ga.
机译：东南波罗的海盾的Vetreny带是一个大型的火山沉积盆地，包含4至8 km厚的玄武岩至科马蒂奇熔岩序列，这些熔岩是在约2.45 Ga之前在地幔相互作用期间在大陆裂谷中喷发的羽和卡累利阿花岗岩-绿岩地层的太古宙大陆壳。维多利亚的熔岩湖和Golets流3的橄榄石累积样品和亚铬铁矿的Re-Os同位素数据分别定义了等时线，年龄分别为2387±57和2432±34 Ma。这些年龄与以前报道的以及新的Nd-Pb和U-Pb锆石年龄高度吻合。这些数据，加上Re和Os不可移动的证据，表明自熔岩喷发以来，Re-Os系统一直处于封闭状态。 Golets流3的加权平均初始γ187Os值在–0.43±0.10和熔岩湖的–0.07±0.13之间。与Golets流1分离的单个亚铬铁矿的γ187Os（T）为–0.06±0.15。 Vetreny带Komatiitic玄武岩的Nd-Pb同位素和嗜石微量元素数据用于监测地壳污染对Os同位素系统的影响，并估计Vetreny羽流源的初始Os同位素组成大致为软骨形，γ187< / sup> Os（T）为–0.9。这意味着地幔源以长期接近于软骨的Re / Os比演化。数据提供了进一步的证据，表明到太古宙晚期，地球上地幔在晚期单板生长过程中相对于高度亲铁性元素而言已达到均一化，时间尺度约为1 Ga。

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  • 来源
    《Contributions to Mineralogy and Petrology》 |2001年第5期|588-599|共12页
  • 作者

    I. Puchtel; G. Brügmann; A. Hofmann; V. Kulikov; V. Kulikova;

  • 作者单位

    Department of the Geophysical Sciences The University of Chicago 5734 S. Ellis Avenue Chicago IL 60637 USA;

    Max-Planck Institut für Chemie Abteilung Geochemie Postfach 3060 55020 Mainz Germany;

    Max-Planck Institut für Chemie Abteilung Geochemie Postfach 3060 55020 Mainz Germany;

    Institute of Geology Karelian Research Center RAS Pushkinskaya 11 185610 Petrozavodsk Russia;

    Institute of Geology Karelian Research Center RAS Pushkinskaya 11 185610 Petrozavodsk Russia;

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