首页> 外文期刊>Proceedings of the Indian Academy of Sciences. Earth and Planetary Sciences >Late Devonian and Triassic basalts from the southern continental margin of the East European Platform, tracers of a single heterogeneous lithospheric mantle source
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Late Devonian and Triassic basalts from the southern continental margin of the East European Platform, tracers of a single heterogeneous lithospheric mantle source

机译:来自东欧平台南部大陆边缘的晚泥盆世和三叠纪玄武岩,是单一非均质岩石圈地幔源的示踪剂

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摘要

In Late Devonian and Early-to-Late Triassic times, the southern continental margin of the Eastern European Platform was the site of a basaltic volcanism in the Donbas and Fore-Caucasus areas respectively. Both volcanic piles rest unconformably upon Paleoproterozoic and Late Paleozoic units respectively, and emplaced during continental rifting periods some 600 km away from expected locations of active oceanic subduction zones. This paper reports a comparative geochemical study of the basaltic rocks, and views them as the best tracers of the involved mantle below the Eastern European Platform. The Late Devonian alkaline basic rocks differ from the calc-alkaline Triassic basic rocks by their higher alkali-silica ratio, their higher TiO_2, K_2O, P_2O_5 and FeO contents, their higher trace element contents, a higher degree of fractionation between the most and the least incompatible elements and the absence of Ta-Nb negative anomalies. These general features, clearly distinct from those of partial melting and fractional crystallization, are due to mantle source effects. With similar Nd and Sr isotopic signatures indicating mantle-crust mixing, both suites would originate from the melting of a same but heterogeneous continental mantle lithosphere (refertilized depleted mantle). Accordingly the Nd model ages, the youngest major event associated with mantle metasomatism occurred during Early Neoproterozoic times (~650 Ma).
机译:在泥盆纪晚期和晚三叠世早期,东欧平台的南部大陆边缘分别是顿巴斯地区和前高加索地区的玄武质火山活动的地点。两座火山桩分别不一致地停留在古元古代和晚古生代单元上,并在大陆裂谷期被放置,距活跃的海洋俯冲带的预期位置约600 km。本文报道了对玄武岩的比较地球化学研究,并将其视为东欧平台以下相关地幔的最佳示踪剂。泥盆纪晚期碱性基岩与钙碱性三叠纪基岩的不同之处在于其较高的碱硅比,较高的TiO_2,K_2O,P_2O_5和FeO含量,较高的痕量元素含量,最大和最大的分馏程度。最少的不相容元素,以及不存在Ta-Nb负异常。这些一般特征明显不同于部分熔融和部分结晶的特征,是由于地幔源效应所致。具有相似的Nd和Sr同位素特征,表明地幔与地壳混合,这两个套件都来自相同但异质的大陆地幔岩石圈(简称枯竭地幔)的融化。因此,Nd模型年龄变大,与地幔交代作用有关的最年轻的主要事件发生在新元古代早期(〜650 Ma)。

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