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Isotopic evolution of prehistoric magma sources of Mt. Etna, Sicily: Insights from the Valle Del Bove
Contributions to Mineralogy and Petrology ( IF 3.5 ) Pub Date : 2021-06-25 , DOI: 10.1007/s00410-021-01804-6
P. D. Kempton , A. Spence , H. Downes , J. Blichert-Toft , J. G. Bryce , E. Hegner , P. Z. Vroon

Mount Etna in NE Sicily occupies an unusual tectonic position in the convergence zone between the African and Eurasian plates, near the Quaternary subduction-related Aeolian arc and above the down-going Ionian oceanic slab. Magmatic evolution broadly involves a transition from an early tholeiitic phase (~ 500 ka) to the current alkaline phase. Most geochemical investigations have focussed on either historic (> 130-years old) or recent (< 130-years old) eruptions of Mt. Etna or on the ancient basal lavas (ca. 500 ka). In this study, we have analysed and modelled the petrogenesis of alkalic lavas from the southern wall of the Valle del Bove, which represent a time span of Mt. Etna’s prehistoric magmatic activity from ~ 85 to ~ 4 ka. They exhibit geochemical variations that distinguish them as six separate lithostratigraphic and volcanic units. Isotopic data (143Nd/144Nd = 0.51283–0.51291; 87Sr/86Sr = 0.70332–0.70363; 176Hf/177Hf = 0.28288–0.28298; 206Pb/204Pb = 19.76–20.03) indicate changes in the magma source during the ~ 80 kyr of activity that do not follow the previously observed temporal trend. The oldest analysed Valle del Bove unit (Salifizio-1) erupted basaltic trachyandesites with variations in 143Nd/144Nd and 87Sr/86Sr ratios indicating a magma source remarkably similar to that of recent Etna eruptions, while four of the five subsequent units have isotopic compositions resembling those of historic Etna magmas. All five magma batches are considered to be derived from melting of a mixture of spinel lherzolite and pyroxenite (± garnet). In contrast, the sixth unit, the main Piano Provenzana formation (~ 42–30 ka), includes the most evolved trachyandesitic lavas (58–62 wt% SiO2) and exhibits notably lower 176Hf/177Hf, 143Nd/144Nd, and 206Pb/204Pb ratios than the other prehistoric Valle del Bove units. This isotopic signature has not yet been observed in any other samples from Mt. Etna and we suggest that the parental melts of the trachyandesites were derived predominantly from ancient pyroxenite in the mantle source of Etna.



中文翻译:

富士山史前岩浆源的同位素演化 西西里岛埃特纳火山:Valle Del Bove 的见解

位于西西里岛东北部的埃特纳火山在非洲板块和欧亚板块之间的会聚带中占据了一个不寻常的构造位置,靠近第四纪俯冲相关的风成弧并位于下降的爱奥尼亚大洋板块之上。岩浆演化广泛涉及从早期拉斑岩相(~ 500 ka)到当前碱性相的转变。大多数地球化学调查都集中在历史上(> 130 年)或最近(< 130 年)的火山喷发。埃特纳火山或古老的基底熔岩(约 500 ka)。在这项研究中,我们分析并模拟了 Valle del Bove 南壁碱性熔岩的岩石成因,它代表了 Mt. 的时间跨度。埃特纳火山的史前岩浆活动从~85 到~4 ka。它们表现出地球化学变化,将它们区分为六个独立的岩石地层和火山单元。143 Nd/ 144 Nd = 0.51283–0.51291;87 Sr/ 86 Sr = 0.70332–0.70363;176 Hf/ 177 Hf = 0.28288–0.28298;206 Pb/ 204 Pb = 19.76–20.03) 表明在大约 80 kyr 的活动期间岩浆源的变化不遵循先前观察到的时间趋势。经分析的最古老的 Valle del Bove 单元 (Salifizio-1) 喷发了玄武质粗安岩,其中143 Nd/ 144 Nd 和87 Sr/ 86Sr 比率表明岩浆来源与最近的埃特纳火山喷发非常相似,而随后的五个单元中有四个具有与历史上埃特纳火山岩浆相似的同位素组成。所有五个岩浆批次都被认为是由尖晶石二长沸石和辉石(± 石榴石)的混合物熔融产生的。相比之下,第六个单元,主要的 Piano Provenzana 地层(~ 42-30 ka),包括最进化的粗斜纹岩熔岩(58-62 wt% SiO 2),并表现出明显较低的176 Hf/ 177 Hf、143 Nd/ 144 Nd , 和206 Pb/ 204铅比高于其他史前 Valle del Bove 单位。在 Mt. 的任何其他样品中尚未观察到这种同位素特征。埃特纳火山和我们认为粗安岩的母体熔体主要来自埃特纳火山地幔源中的古代辉石岩。

更新日期:2021-06-28
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