Osmium isotope compositions of detrital Os-rich alloys from the Rhine River provide evidence for a global late Mesoproterozoic mantle depletion event
Osmium isotope compositions of detrital Os-rich alloys from the Rhine River provide evidence for a global late Mesoproterozoic mantle depletion event
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DOI：
10.1016/j.epsl.2016.07.047
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发表时间：
2016-10-15
影响因子：
5.3
通讯作者：
Pearson, D. Graham
中科院分区：
文献类型：
--
作者：
Dijkstra, Arjan H.;Dale, Christopher W.;Pearson, D. Graham
本文报道了在莱茵河含金和铂族矿物的砂矿中发现的297个地幔源碎屑Ru-Os-Ir合金颗粒的锇同位素组成。这些合金可能是对流地幔高度熔融的结果，来自中欧阿尔卑斯地区残余的古生代地幔橄榄岩，这些橄榄岩是在瓦里斯坎造山运动之前作为冈瓦纳衍生的“阿莫里亚”地体拼合的一部分而增加的。富os合金的1870 /1880同位素比值分布较广，有0.1244和0.1205两种模式。这两种模式对应于铼耗尽年龄，解释为对应于0.5 Ga和类似于1.1 Ga的高程度地幔熔融事件。这些数据证实了海洋地幔保存古代融化事件证据的能力。我们的新数据，结合已发表的乌拉尔和塔斯马尼亚富os合金的数据，以及深海橄榄岩的数据，表明在古生代海洋地幔岩石中，有一个主要的全球晚中元古代（1.0-1.2 Ga）高度熔融事件的地理广泛记录。这个模式年龄峰值在中欧和西欧的地壳记录中基本上是不存在的，但与当时全球大陆地壳锆石年龄的明显峰值相吻合。因此，在1.0-1.2 Ga区间达到峰值的高度地幔融化可能影响了大部分地幔。这个间隔发生在一个相对的超大陆稳定时期，在海洋领域可能伴随着海底的快速扩张和广泛的俯冲，以及异常高的地幔柱活动，形成了两个活跃的地幔超井。Elsevier B.V.版权所有
We report osmium isotopic compositions for 297 mantle-derived detrital Ru-Os-Ir alloy grains found in gold and platinum-group mineral bearing placers of the Rhine River. These alloys were likely formed as a result of high degree melting in the convective mantle and derived from residual Paleozoic mantle peridotites in the Alps of Central Europe that were accreted as part of a collage of Gondwana-derived 'Armorican' terranes before the Variscan Orogeny. The 1870s/1880s isotope ratios of the Os-rich alloys show a wide distribution, with two modes at 0.1244 and 0.1205. These two modes correspond to rhenium depletion ages, interpreted to correspond with episodes of high-degree mantle melting, at 0.5 and similar to 1.1 Ga. The data confirm the ability of the oceanic mantle to preserve evidence of ancient melting events. Our new data, in combination with published data on Os-rich alloys from the Urals and Tasmania and with data for abyssal peridotites, indicate a geographically widespread record of a major global Late Mesoproterozoic (1.0-1.2 Ga) high-degree melting event in Paleozoic oceanic mantle rocks. This model age peak is essentially absent from the crustal record of Central-Western Europe, but does coincide with the apparent peak in global continental crust zircon ages at this time. Thus, high-degree mantle melting peaking in the 1.0-1.2 Ga interval may have affected a large part of Earth's mantle. This interval occurred during a period of relative super-continental stability, which may have been accompanied in the oceanic realm by rapid seafloor spreading and extensive subduction, and by unusually high activity of mantle plumes forming two active mantle superswells. Crown Copyright (C) 2016 Published by Elsevier B.V. All rights reserved.