Abstract

First data on oxygen isotopic composition in phenocrysts in volcanic rocks from Okhotsk–Chukotka volcanic belt (106–78 Ma, North-Eastern Russia) together with Sr and Nd isotopic data gives additional geochemical evidence on belt segmentation. Calculated δ¹⁸O_melt in calc-alkaline magmas of belt vary from normal-δ¹⁸O (from +5.2 to +6.9‰) consistent with mantle-like signatures of radiogenic isotopes. Low-δ¹⁸O (from +4.7 to +4.8‰) silicic magmas were found in Western–Okhotsk segment of the belt interpreted as assimilation of hydrothermally altered rocks from pre-caldera rifted basement. The highest δ¹⁸O values were obtained for Chukotka segment of the belt reaching +10.8‰ and these are correlated with elevated ⁸⁷Sr/⁸⁶Sr due to assimilation of relatively mature high-δ¹⁸O continental crust. Comparison with Kamchatka volcanic belt is performed.

中文翻译：

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鄂霍次克-楚科奇火山带岩浆氧同位素组成变化

摘要

鄂霍次克-楚科奇火山带（106-78 Ma，俄罗斯东北部）火山岩斑晶中氧同位素组成的第一个数据以及 Sr 和 Nd 同位素数据为带分割提供了额外的地球化学证据。计算得出的带钙碱性岩浆中的δ ¹⁸ O_熔体与正常-δ ¹⁸ O（从 +5.2 到 +6.9‰）不同，与放射性同位素的地幔样特征一致。在该带的西-鄂霍次克段发现了低 δ ¹⁸ O（从 +4.7 到 +4.8‰）硅质岩浆，解释为同化来自火山口前裂谷基底的热液蚀变岩石。最高的 δ ¹⁸ O 值在该带的楚科奇段获得，达到 +10.8‰，这些值与升高的⁸⁷ Sr/ ⁸⁶ Sr 由相对成熟的高δ ¹⁸ O 大陆地壳同化作用形成。与堪察加火山带进行比较。