Mantle-derived Archaean monozodiorites and trachyandesites
Mantle-derived Archaean monozodiorites and trachyandesites
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DOI：
10.1038/310222a0
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发表时间：
1984-07
期刊：
影响因子：
64.8
通讯作者：
S. Shirey;G. Hanson
中科院分区：
文献类型：
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作者：
S. Shirey;G. Hanson
在北美上级省的安大略雨湖地区和明尼苏达州的朱红区及其附近，2680 - 2750-Myr的1 - 5侵入花岗岩-绿岩带6 - 8包括各种各样的火山岩和侵入岩，其初始Pb、Sr和Nd同位素比值接近地幔4，5，9-12。同位素制约要求在1亿~ 2亿年内从硅质不饱和地幔中产生大量硅质过饱和岩浆。本文介绍了雨湖地区强烈富集大离子亲石元素的二长闪长岩和粗安岩的地球化学资料。我们的结论是，它们是由地幔直接熔融深度小于50公里的无水或含水条件下。稀土元素丰度和143 Nd/144 Nd初始值表明，地幔源区在熔融前不久富集大离子亲石元素。二长闪长岩-粗安岩及其花岗闪长岩衍生物可能占雨湖地区和朱红地区出露火成岩的20%。如果这些岩石在其他大陆板块中同样丰富，那么早期大陆地壳的很大一部分可能是由富含LILE的地幔直接熔融形成的。
The 2,680–2,750-Myr old1–5intrusive granite–greenstone terranes6–8in the Rainy Lake region, Ontario, and in, and adjacent to, the Vermilion District, Minnesota, of the Superior Province in North America, include a wide variety of volcanic and intrusive rocks with initial Pb, Sr and Nd isotope ratios close to those for the mantle4,5,9–12. The isotopic constraints require the production of large volumes of silica-oversaturated magmas from silica-undersaturated mantle within 100–200 Myr. We present here geochemical data on monzodiorites and trachyandesites from the Rainy Lake area which are strongly enriched in large-ion-lithophile elements (LILE). We conclude that they are derived by direct melting of the mantle at depths of <50km in either anhydrous or hydrous conditions. Their rare-earth element (REE) abundances and initial143Nd/144Nd ratios suggest that their mantle sources were enriched in LILE shortly before melting. The monzodiorites-trachyandesites and their granodioritic derivatives may comprise up to 20% of the exposed igneous rocks in the Rainy Lake region and Vermilion District. If these rocks are as abundant in other Archaean terranes, a significant part of the early continental crust could have formed by direct melting of LILE-enriched mantle.