RESIDENCE TIME ANALYSIS OF GEOCHEMICAL FLUCTUATIONS IN VOLCANIC SERIES
RESIDENCE TIME ANALYSIS OF GEOCHEMICAL FLUCTUATIONS IN VOLCANIC SERIES
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DOI：
10.1016/0016-7037(93)90372-4
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发表时间：
1993-02-01
影响因子：
5
通讯作者：
ALBAREDE, F
中科院分区：
文献类型：
--
作者：
ALBAREDE, F
建立了由元素和同位素时间序列估算岩浆在火山岩储层中停留时间的模型。同位素或不相容元素比更适合于浓缩数据，因为它们对熔岩中斑晶的丰度不太敏感。岩浆储集层被认为是一个搅拌良好的反应堆，由来自不同来源的岩浆混合并分离晶体。通过做一些假设，可以从比率的变化率中恢复停留时间的一阶估计。1752年至1882年维苏威火山喷发的熔岩中的锶同位素比值表明，岩浆停留时间短于1000年。另一种方法是对被岩浆储集层抑制和延迟的地球化学信号进行傅立叶分析。留尼汪岛Piton de la Fourneise熔岩(留尼汪岛)在1931-1986年期间Ce/Yb波动的衰减使岩浆停留时间在10-30年之间。根据埃特纳火山(西西里岛)上的锶同位素数据，可以确定岩浆在该火山管道系统中的停留时间为14-80年。这些数字与渗漏率相结合表明，这些火山下实际被挖掘的岩浆室的最大尺寸可能几乎不会超过1立方公里。对火山产物的地球化学变化负责的过程所在的岩浆室很可能与地球物理识别的岩浆体截然不同。
A model to estimate magma residence times in volcanic reservoirs from time series of elemental and isotopic data is developed. Isotopic or incompatible element ratios are preferred to concentration data as they are much less sensitive to the phenocryst abundance in the lavas. A magma reservoir is considered as a well-stirred reactor fed by magmas from distinct sources which mix and fractionate crystals. By making a few assumptions, a first-order estimate of residence times can be retrieved from the rate of change of ratios. Strontium isotope ratios in the lavas erupted by Vesuvius from 1752 to 1882 suggest a magma residence time shorter than 1000 years. An alternative method involves a Fourier analysis of the geochemical signal damped and delayed by the magma reservoir. The damping of the Ce/Yb fluctuations in the Piton de la Fournaise lavas (Reunion Island) over the 1931-1986 period brackets the magma residence time between 10 and 30 years. From Sr isotope data on Mount Etna (Sicily), the residence time of magmas in the plumbing system of this volcano can be bracketed between 14 and 80 years. These figures combined with effusion rates suggest that the maximum size of actually tapped magma chambers under these volcanoes may hardly exceed one cubic kilometer. The magma chambers in which the processes responsible for the geochemical variability of volcanic products take place are likely to be distinct from the geophysically identified magma bodies.