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首页> 外文期刊>Contributions to Mineralogy and Petrology >Deciphering petrogenic processes using Pb isotope ratios from time-series samples at Bezymianny and Klyuchevskoy volcanoes, Central Kamchatka Depression
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Deciphering petrogenic processes using Pb isotope ratios from time-series samples at Bezymianny and Klyuchevskoy volcanoes, Central Kamchatka Depression

机译：使用堪察加半岛中部Bezymianny和Klyuchevskoy火山的时间序列样本中的Pb同位素比率来解释成岩过程

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摘要

The Klyuchevskoy group of volcanoes in the Kamchatka arc erupts compositionally diverse magmas (high-Mg basalts to dacites) over small spatial scales. New high-precision Pb isotope data from modern juvenile (1956-present) erupted products and hosted enclaves and xenoliths from Bezymianny volcano reveal that Bezymianny and Klyuchevskoy volcanoes, separated by only 9 km, undergo varying degrees of crustal processing through independent crustal columns. Lead isotope compositions of Klyuchevskoy basalts-basaltic andesites are more radiogenic than Bezymianny andesites (~(208)Pb/~(204)Pb=37.850-37.903, ~(207)Pb/~(204)Pb = 15.468-15.480, and ~(206)Pb/~(204)Pb= 18.249-18.278 at Bezymianny; ~(208)Pb/~(204)Pb=37.907-37.949, ~(207)Pb/~(204)Pb= 15.478- 15.487, and ~(206)Pb/~(204)Pb = 18.289-18.305 at Klyuchevskoy). A mid-crustal xenolith with a crystallization pressure of 5.2 ± 0.6 kbars inferred from two-pyroxene geobarom-etry and basaltic andesite enclaves from Bezymianny record less radiogenic Pb isotope compositions than their host magmas. Hence, assimilation of such lithologies in the middle or lower crust can explain the Pb isotope data in Bezymianny andesites, although a component of magma mixing with less radiogenic mafic recharge magmas and possible mantle heterogeneity cannot be excluded. Lead isotope compositions for the Klyuchevskoy Group are less radiogenic than other arc segments (Karymsky-Eastern Volcanic Zone; Shiveluch-Northern Central Kamchatka Depression), which indicate increased lower-crastal assimilation beneath the Klyuchevskoy Group. Decadal timescale Pb isotope variations at Klyuchevskoy demonstrate rapid changes in the magnitude of assimilation at a volcanic center. Lead isotope data coupled with trace element data reflect the influence of crustal processes on magma compositions even in thin mafic volcanic arcs.
机译：堪察加弧线的Klyuchevskoy火山群在较小的空间尺度上喷出了组成多样的岩浆（高镁玄武岩到伏安岩）。来自现代幼年（1956-至今）爆发产物的新高精度Pb同位素数据以及来自Bezymianny火山的飞地和异质岩显示，仅9 km的Bezymianny和Klyuchevskoy火山通过独立的地壳柱经历了不同程度的地壳加工。 Klyuchevskoy玄武岩-玄武安山岩的铅同位素组成比Bezymianny安山岩更具有放射源性（〜（208）Pb /〜（204）Pb = 37.850-37.903，〜（207）Pb /〜（204）Pb = 15.468-15.480，〜 （206）Pb /〜（204）Pb = 18.249-18.278 at Bezymianny;〜（208）Pb /〜（204）Pb = 37.907-37.949，〜（207）Pb /〜（204）Pb = 15.478- 15.487，和〜（206）Pb /〜（204）Pb = 18.289-18.305，在Klyuchevskoy）。从贝塞米尼的二py地质重金属和玄武质安山岩飞地推断出的中壳硬壳异质岩的放射成因铅同位素比其宿主岩浆少，其结晶压力为5.2±0.6 kbar。因此，尽管不能排除岩浆混合与低放射性镁铁质充注岩浆和可能的地幔异质性的成分，但在中下地壳中这类岩性的同化可以解释贝兹米尼安山岩中的铅同位素数据。与其他弧段（Karymsky-东部火山带; Shiveluch-Northern Kamchatka凹陷）相比，Klyuchevskoy组的铅同位素组成的放射性较低，这表明Klyuchevskoy组下的下地壳同化作用增加。 Klyuchevskoy的年代际时标Pb同位素变化表明，火山中心的同化幅度迅速变化。铅同位素数据与痕量元素数据相结合，反映了地壳过程对岩浆成分的影响，即使在薄的铁镁质火山弧中也是如此。

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