The link between volcanism and deglaciation in Iceland
The link between volcanism and deglaciation in Iceland
复制标题
冰岛火山活动与冰川消融之间的联系
DOI：
10.1029/2001gc000282
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发表时间：
2002
期刊：
影响因子：
3.7
通讯作者：
K. Grönvold
中科院分区：
文献类型：
--
作者：
John Maclennan;M. Jull;Dan McKenzie;L. Slater;K. Grönvold
冰岛裂谷带喷发速率和熔岩成分的时间变化与冰川消退有关。末次冰期结束后（约12000年前）的平均喷发速率比冰期和近期（<5000年前）的喷发速率高出多达100倍。这种火山活动高峰在冰川消退结束后不到2000年就结束了。来自泰斯塔雷基尔（Theistareykir）和克拉夫拉（Krafla）火山系统的约80个玄武岩和苦橄岩样本的新地球化学数据表明，喷发的主量元素和微量元素成分都存在时间变化。冰后期早期喷发的氧化镁含量范围比其他时期的喷发更大，并且在固定的氧化镁含量下，冰下喷发中不相容元素的浓度高于冰后期早期喷发。克拉夫拉系统近期的喷发成分与冰下喷发相似。冰后期早期熔岩中的高喷发速率和低稀土元素（REE）浓度可归因于冰盖卸载导致的浅地幔熔体生成速率增加。如果存在石榴石，岩浆房过程如结晶和同化作用可导致稀土元素含量的时间变化。然而，石榴石未被观察到作为斑晶或捕虏晶相，并且对于匹配在克拉夫拉和泰斯塔雷基尔观察到的主量元素含量变化也不是必需的。如果喷发速率的增加反映了地幔中熔体产生速率的增加，那么冰川消退的相对时间和喷发速率的爆发可用于估计地幔中熔体的运移速率。如果垂直熔体抽取速度>50米/年，就可以重现冰川消退后喷发速率增强的观测持续时间。
Temporal variation in the eruption rate and lava composition in the rift zones of Iceland is associated with deglaciation. Average eruption rates after the end of the last glacial period, ∼12 kyr BP, were up to 100 times higher than those from both the glacial period and recent times (<5 kyr BP). This peak in volcanic activity finished less than 2 kyr after the end of deglaciation. New geochemical data from ∼80 basalt and picrite samples from the Theistareykir and Krafla volcanic systems show that there is a temporal variation in both the major and trace element composition of the eruptions. Early postglacial eruptions show a greater range in MgO contents than eruptions from other times, and at a fixed MgO content, the concentration of incompatible elements in subglacial eruptions is higher than that in early postglacial eruptions. Recent eruptions from the Krafla system have similar compositions to subglacial eruptions. The high eruption rates and low rare earth element (REE) concentrations in the lava from early postglacial times can be accounted for by increased melt generation rates in the shallow mantle caused by unloading of an ice sheet. Magma chamber processes such as crystallization and assimilation can produce the temporal variation in REE contents if garnet is present. However, garnet is not observed as a phenocryst or xenocryst phase and is not required to match the variation in major element contents observed at Krafla and Theistareykir. If the increase in eruption rates reflects increased melt production rates in the mantle, then the relative timing of deglaciation and the burst in eruption rates can be used to estimate the rate of melt transport in the mantle. The observed duration of enhanced eruption rates after deglaciation can be reproduced if the vertical melt extraction velocity is >50 m yr−1.