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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >~(210)Pb-~(226)Ra radioactive disequilibria in recent lavas and radon degassing: inferences on the magma chamber dynamics at Stromboli and Merapi volcanoes
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~(210)Pb-~(226)Ra radioactive disequilibria in recent lavas and radon degassing: inferences on the magma chamber dynamics at Stromboli and Merapi volcanoes

机译：〜（210）Pb-〜（226）Ra在最近的熔岩和de脱气中的放射性失衡：对斯特龙博利火山和默拉皮火山的岩浆腔动力学的推断

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摘要

U-series and especially ~(210)Pb-~(226)Ra disequilibria have been measured in recently erupted lavas from the Stromboli (Aeolian Islands, Italy) and Merapi (Java, Indonesia) volcanoes. Both volcanoes display ~(230)Th-~(238)U disequilibria (with a Th enrichment for Stromboli and a U enrichment for Merapi, respectively), strong ~(226)Ra enrichments over ~(230)Th (whereas ~(228)Ra-~(232)Th equilibrium is ubiquitous), and a contrasted evolution of their (~(210)Pb/~(226)Ra) activity ratios calculated at the time of eruption. While these ratios are always close to the equilibrium value of 1 at Stromboli, they show significant variations at Merapi (from 0.75 to 1). It is suggested that the low (~(210)Pb/~(226)Ra) activity ratios result from continuous degassing of ~(222)Rn, the precursor of ~(210)Pb in the decay series, from a shallow magma chamber. A model assuming a physical steady-state of the shallow magma reservoir is proposed, linking the (~(210)Pb/~(226)Ra) ratio of the magma to the fraction of ~(222)Rn lost and to the renewal rate (or residence time) of the magma in the shallow reservoir. The near equilibrium (~(210)Pb/~(226)Ra) ratios at Stromboli imply a high renewal rate of the shallow reservoir (in the range 0.7-3 yr~(-1)) in agreement with its persistent explosive activity. The volume of the reservoir is estimated at 1.3 +- 1.2 * 10~7 m~3. In contrast, the variability of (~(210)Pb/~(226)Ra) ratios at Merapi is interpreted by successive phases of nearly closed-system evolution of the shallow magma chamber (with continuous Rn degassing) and episodes of reinjections and mixing of a deep undegassed magma in this reservoir. Its volume is estimated at 1.6 * 10~7 m~3.
机译：在最近爆发的斯特龙博利火山（意大利风神群岛）和默拉皮火山（印度尼西亚爪哇）的熔岩中，测量到了U系列，尤其是〜（210）Pb-〜（226）Ra不平衡。两座火山均表现出〜（230）Th-〜（238）U不平衡（分别对Stromboli和Th富集，对Stromboli具有Th富集和对Merapi对U具有富集作用），在〜（230）Th上具有〜（226）Ra富集（而〜（228） Ra-〜（232）Th平衡无处不在），并且在喷发时计算出它们的（〜（210）Pb /〜（226）Ra）活性比的对比变化。尽管这些比率在Stromboli始终接近平衡值1，但在Merapi处却显示出显着变化（从0.75到1）。提示较低的（〜（210）Pb /〜（226）Ra）活度比是由于从浅层岩浆室对〜（222）Pb的前驱体〜（222）Rn进行连续脱气而造成的。 。提出了一个假设浅岩浆储层处于物理稳态的模型，将岩浆的（〜（210）Pb /〜（226）Ra）比与〜（222）Rn的损失比例和更新率相关联（或停留时间）在浅水库中的岩浆。 Stromboli处的接近平衡（〜（210）Pb /〜（226）Ra）比表明浅水库的高更新速率（在0.7-3 yr〜（-1）范围内）与其持久的爆炸活性相符。储层的体积估计为1.3 +-1.2 * 10〜7 m〜3。相比之下，Merapi处（〜（210）Pb /〜（226）Ra）比的变异性由浅层岩浆腔室近乎密闭系统演化的连续阶段（连续Rn脱气）以及回注和混合事件来解释。储层中深层不脱盐的岩浆。它的体积估计为1.6 * 10〜7 m〜3。

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