Recycling of subducted crustal components into carbonatite melts revealed by boron isotopes
Recycling of subducted crustal components into carbonatite melts revealed by boron isotopes
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DOI：
10.1038/ngeo2831
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发表时间：
2016-12-01
影响因子：
18.3
通讯作者：
Hemming, N. Gary
中科院分区：
文献类型：
--
作者：
Hulett, Samuel R. W.;Simonetti, Antonio;Hemming, N. Gary
全球硼地球化学循环与地球数十亿年历史上发生的俯冲过程中地质物质的循环密切相关。碳酸盐岩是来自上地幔富碳和富碳酸盐地区的独特熔体，其起源与各种与地幔有关的过程有关，包括俯冲和岩石圈-羽流相互作用。在这里，我们介绍了世界各地碳酸盐岩的硼同位素(增量B-11)组成，这些地点跨越了广泛的侵位年龄范围(类似于40 Ma到类似于2,600 Ma)。因此，它们提供了对近26亿年地球历史中地幔来源的时间演变的洞察。硼同位素值变化很大，范围在-8.6‰到+5.5‰之间，所有年轻的碳酸盐岩样品都是如此(-4.0‰)，而大多数年代较早的碳酸盐岩样品记录的B同位素值较低。考虑到软流圈地幔的B-11值为-7+/-1‰，年轻碳酸盐岩的B同位素组成需要富集(地壳)组分的参与。再循环的地壳成分可能由与主要构造事件重合的地幔热柱活动有关的碳酸盐岩熔体取样，并与过去与超大陆形成有关的重大俯冲事件有关。
The global boron geochemical cycle is closely linked to recycling of geologic material via subduction processes that have occurred over billions of years of Earth's history. The origin of carbonatites, unique melts derived from carbon-rich and carbonate-rich regions of the upper mantle, has been linked to a variety of mantle-related processes, including subduction and plume-lithosphere interaction. Here we present boron isotope (delta B-11) compositions for carbonatites from locations worldwide that span a wide range of emplacement ages (between similar to 40 and similar to 2,600 Ma). Hence, they provide insight into the temporal evolution of their mantle sources for similar to 2.6 billion years of Earth's history. Boron isotope values are highly variable and range between -8.6 parts per thousand and +5.5 parts per thousand, with all of the young (-4.0 parts per thousand), whereas most of the older carbonatite samples record lower B isotope values. Given the delta B-11 value for asthenospheric mantle of -7 +/- 1 parts per thousand, the B isotope compositions for young carbonatites require the involvement of an enriched (crustal) component. Recycled crustal components may be sampled by carbonatite melts associated with mantle plume activity coincident with major tectonic events, and linked to past episodes of significant subduction associated with supercontinent formation.