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首页> 外文期刊>Geoscience Canada >Oceanic Lithosphere 3. The Origin and Evolution of Oceanic Lithosphere: The Geochemistry and Origin of Oceanic Lavas
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Oceanic Lithosphere 3. The Origin and Evolution of Oceanic Lithosphere: The Geochemistry and Origin of Oceanic Lavas

机译：大洋岩石圈3.大洋岩石圈的起源与演化：大洋熔岩的地球化学和起源

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摘要

Oceanic lavas are the most voluminous volcanic products on Earth. Between 15 and 20 km 3 of new oceanic crust is created every year by eruption of mid-ocean ridge basalt (MORB) along sea-floor spreading axes. MORB lavas are olivine- and hypersthene-normative tholeiites highly depleted in incompatible trace elements such as Rb, Sr, Ba,K, Zr, Y and the light rare earth elements. Isotopically, they are characterised by low radiogenic Sr and Pb and high radiogenic Nd. They are formed by decompressional melting of shallow mantle material as it rises beneath spreading axes. This upper mantle source was previously depleted in incompatible elements by extraction of continental crustal material early in Earth history. On a global scale MORB lavas are remarkably uniform, but relatively enriched varieties (E-MORB) are known from all ridge segments. These enriched lavas are transitional in composition to ocean island basalts (OIB) which have much higher contents of incompatible elements and much more varied isotopic compositions than typical MORB lavas. Ocean island basalts are believed to form by partial melting of mantle plumes that rise from near the core-mantle boundary. These plumes entrain mantle material that has been relatively enriched by recycled crustal materials in subduction zones. Mixing of plume mantle and depleted MORB mantle on a variety of scales can explain the occurrence of E-MORB lavas. Large-scale super plumes are believed to be responsible for the formation of oceanic plateaus, which are built by voluminous eruptions of ocean island basalts.
机译：海洋熔岩是地球上数量最多的火山产品。每年，中海脊玄武岩（MORB）沿海底扩张轴线喷发，会形成15至20 km 3的新大洋壳。 MORB熔岩是富含不相容的痕量元素（如Rb，Sr，Ba，K，Zr，Y和轻稀土元素）的橄榄石型和超硫化钠规范型冲孔岩。同位素上，它们的特征是低放射性Sr和Pb和高放射性Nd。它们是由浅层地幔物质在扩散轴下方升起时，通过减压熔融而形成的。上地幔源以前是在地球历史早期通过提取大陆地壳物质而耗尽不相容元素的。在全球范围内，MORB熔岩非常均匀，但是从所有山脊段中都可以找到相对丰富的熔岩（E-MORB）。与典型的MORB熔岩相比，这些富集的熔岩的成分过渡为大洋洲玄武岩（OIB），其中不溶元素的含量高得多，同位素组成也多得多。据认为，大洋玄武岩是通过从地幔边界附近升起的地幔柱部分融化而形成的。这些羽状带夹带着被俯冲带中的循环地壳物质相对丰富的地幔物质。羽状地幔和贫化的MORB地幔在各种尺度上的混合可以解释E-MORB熔岩的发生。人们认为，大型超级羽流是海洋高原形成的原因，海洋高原是由大面积的玄武岩喷发形成的。

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