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首页> 外文期刊>Contributions to Mineralogy and Petrology >Geochemical evidence for melting of carbonated peridotite on Santa Maria Island, Azores
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Geochemical evidence for melting of carbonated peridotite on Santa Maria Island, Azores

机译：地球化学证据表明亚速尔群岛圣玛丽亚岛上的碳酸盐橄榄岩熔融

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摘要

The islands of the Azores archipelago emerge from an oceanic plateau built on lithosphere increasing in age with distance from the Mid-Atlantic Ridge from 10 to 45 Ma. Here, we present the first comprehensive major and trace element and Sr–Nd–Pb isotope data from Santa Maria, the easternmost island of the archipelago, along with published data from the other Azores islands situated much closer to the Mid-Atlantic Ridge axis. We can show that the distinctively more variable and more enriched trace element ratios at Santa Maria combined with a relatively small range in Sr–Nd–Pb isotope ratios are the result of low degrees of partial melting of a common Azores mantle plume source underneath thicker lithosphere. This implies that melt extraction processes and melting dynamics may be able to better preserve the trace element mantle source variability underneath thicker lithosphere. These conclusions may apply widely for oceanic melts erupted on relatively thick lithosphere. In addition, lower Ti/Sm and K/La ratios and SiO2 contents of Santa Maria lavas imply melting of a carbonated peridotite source. Mixing of variable portions of deep small-degree carbonated peridotite melts and shallow volatile-free garnet peridotite could explain the geochemical variability underneath Santa Maria in agreement with the volatile-rich nature of the Azores mantle source. However, Santa Maria is the Azores island where the CO2-rich nature of the mantle source is more evident, reflecting a combination of a smaller extent of partial melting and the positioning at the edge of the tilted Azores mantle plume.
机译：亚速尔群岛的群岛从建立在岩石圈上的一个海洋高原出现，随着距中大西洋海脊的距离从10Ma到45Ma的增加，年龄逐渐增加。在这里，我们展示了来自群岛最东端的圣塔玛丽亚的第一份综合性主要元素和微量元素以及Sr-Nd-Pb同位素数据，以及来自更接近大西洋中脊轴线的其他亚速尔群岛的公开数据。我们可以证明，圣玛丽亚地区痕量元素的变化更大，更富集，而Sr-Nd-Pb同位素的变化范围相对较小，这是较厚岩石圈下常见的亚速尔群岛地幔羽流源部分熔融程度较低的结果。 。这意味着在较厚的岩石圈下，熔体提取过程和熔体动力学可能能够更好地保留痕量元素地幔源的可变性。这些结论可能广泛适用于相对较厚的岩石圈爆发的海洋熔体。此外，较低的Ti / Sm和K / La比以及圣玛丽亚熔岩的SiO2含量意味着碳酸钙橄榄岩源的熔融。深层的小规模碳酸盐橄榄岩熔体和浅层无挥发石榴石橄榄岩的可变部分的混合可以解释亚速尔群岛地幔源的富挥发分性质，从而解释了圣玛丽亚下面的地球化学变异性。但是，圣玛丽亚岛是亚速尔群岛，那里的地幔来源富含CO2的性质更加明显，这反映了部分融化程度较小和倾斜的亚速尔群岛地幔柱边缘处的结合。

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