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The Patagonian intraplate basalts: A reflection of the South Atlantic convection cell
Gondwana Research ( IF 6.1 ) Pub Date : 2021-03-01 , DOI: 10.1016/j.gr.2020.12.008
Nina Søager , Paul Martin Holm , Gabriela Isabel Massaferro , Miguel Haller , Marie Katrine Traun

Abstract Based on an extensive literature dataset on Cenozoic intraplate basalts from Patagonia, Argentina, we provide a revised interpretation of the mantle sources of volcanism and suggest a relation to the South Atlantic hotspots and mantle flow. Furthermore, we present 16 elemental analyses of North Patagonian basalts as well as 12 Sr, Nd and Pb-isotopes. The new data reveal that the North Patagonian basanite-nephelinite rocks with HIMU OIB-type trace element patterns do not have highly radiogenic Pb-isotopes and are unrelated to the South Patagonian HIMU-type Pali Aike source. Instead, they were formed within the lifetime of the South Atlantic Ocean by metasomatism of the local lithospheric mantle (SCLM) by carbonatitic melts from the ambient South Atlantic asthenosphere. Thus, they are an example of a very young HIMU source supporting that the HIMU OIB-type signature was formed by carbonate metasomatism of lithospheric mantle and not by recycling of oceanic crust. In contrast, the EM1-type basalts dominating in Central Patagonia have significantly elevated FeOT/MnO (up to 79) and low CaO contents (mostly between 8 and 9 wt%). This indicates derivation from a pyroxenitic source, which presumably formed by melt metasomatism of the SCLM. In isotopic space, the Patagonian basalts can be modelled by mixing of depleted South Atlantic MORB mantle (representing the SCLM) with 2–7% Discovery and Bouvet hotspot melts in varying proportions (representing the metasomatizing agents). The latitudinal variation in isotopic compositions of the Patagonian basalts is a mirror image of the variation at the mid-Atlantic Ridge. This observation is consistent with the westward direction of the mantle flow and drift of South America and suggests that the hotspot locations and flow direction of the South Atlantic convection cell has been stable for a significant part of the lifetime of the South Atlantic ocean bringing plume influenced asthenosphere westwards beneath Patagonia.

中文翻译:

巴塔哥尼亚板内玄武岩:南大西洋对流单元的反映

摘要 基于阿根廷巴塔哥尼亚新生代板内玄武岩的大量文献数据集,我们对火山活动的地幔来源进行了修订解释,并提出了与南大西洋热点和地幔流的关系。此外,我们还提供了北巴塔哥尼亚玄武岩的 16 种元素分析以及 12 种 Sr、Nd 和 Pb 同位素。新数据表明,具有HIMU OIB型微量元素模式的北巴塔哥尼亚玄武岩-霞石岩没有高放射性Pb同位素,与南巴塔哥尼亚HIMU型帕里艾克源无关。相反,它们是在南大西洋的生命周期内通过来自南大西洋周围软流圈的碳酸盐岩熔体交代局部岩石圈地幔 (SCLM) 形成的。因此,它们是非常年轻的 HIMU 源的一个例子,支持 HIMU OIB 型特征是由岩石圈地幔的碳酸盐交代作用形成的,而不是由海洋地壳的再循环形成的。相比之下,在巴塔哥尼亚中部占主导地位的 EM1 型玄武岩具有显着升高的 FeOT/MnO(高达 79)和低 CaO 含量(主要在 8 至 9 wt% 之间)。这表明源自辉石源,它可能是由 SCLM 的熔体交代形成的。在同位素空间中,巴塔哥尼亚玄武岩可以通过将耗尽的南大西洋 MORB 地幔(代表 SCLM)与不同比例的 2-7% 发现和布韦热点熔体(代表交代剂)混合来建模。巴塔哥尼亚玄武岩同位素组成的纬度变化是大西洋中脊变化的镜像。
更新日期:2021-03-01
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