Felsic volcanism in the Kermadec arc, SW Pacific: crustal recycling in an oceanic setting
Felsic volcanism in the Kermadec arc, SW Pacific: crustal recycling in an oceanic setting
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DOI：
10.1144/gsl.sp.2003.219.01.05
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
I. Smith;T. Worthington;R. Stewart;R. Price;J. Gamble
中科院分区：
文献类型：
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作者：
I. Smith;T. Worthington;R. Stewart;R. Price;J. Gamble
摘要大型长英质火山岩系统是大陆环境中火山弧系统的常见特征，但不是无处不在的。大洋火山弧喷发物质以玄武岩和玄武岩安山岩为主，中间成分较少，英安岩和流纹岩较少见。Kermadec弧是西南太平洋的一个洋内辐合系。火山以连续弧形出现，主要是海底弧形。尽管构造环境简单，但长英质岩浆活动广泛存在。在克尔马德克群岛，麦考利火山是一座玄武岩火山，在大约6000年前产生了一次大型长英质火山喷发。在邻近的拉乌尔火山上也可以看到类似的岩浆演化模式，玄武岩活动建造了火山的主要建筑，在过去3000年里，那里的活动以不同规模的长英质喷发为特征。在克尔马德克弧及其向北延伸的汤加弧的其他地方，记录到了30座火山中有11座火山的长英质喷发，这些火山有岩相学信息，在许多情况下是最近的一次喷发。长英质岩浆活动是该弧广泛存在的近期特征，这种岩浆活动的规模和程度对于一个构造简单的大洋俯冲系统来说似乎是不寻常的。对长英质岩浆作用起源的一种解释是母玄武岩成分的长期分离结晶，但对长英质岩石化学成分的模拟不支持这一点。第二种解释是地壳深熔作用，尽管显然与海洋环境不符。克尔马德克弧长英质喷发的一个重要特征是，每个盖夫拉序列或产状都有独特的化学成分，尽管它们都表现出相同的一般特征。我们认为，这一特征支持地壳深熔作用的模式，而不是一系列母岩浆的分馏作用。我们还认为，在大洋弧系的热演化过程中，底侵过程与连续的岩浆(和热)通量一起，可以产生一个地壳厚度，在这个厚度内，底板弧质的脱水熔融产生长英质岩浆。此外，这种情况可以代表一个正在发展的洋弧中的一个独特的“青少年”阶段，因为一旦长英质熔体被提取出来，下地壳就变成了一个贫瘠的残留物。
Abstract Large-scale felsic volcanic systems are a common, but not ubiquitous, feature of volcanic arc systems in continental settings. However, in oceanic volcanic arcs the erupted materials are dominated by basalts and basaltic andesites, whereas intermediate compositions are rare and dacites and rhyolites relatively uncommon. The Kermadec arc is an intraoceanic convergent system in the SW Pacific. Volcanoes occur as a continuous arc that is mainly submarine. Despite its simple tectonic setting, felsic magmatism is widespread. In the Kermadec Islands, Macauley Volcano is a basaltic volcano that produced a large felsic eruption about 6000 years ago. A comparable pattern of magmatic evolution is seen on adjacent Raoul Volcano, where basaltic activity built the main edifice of the volcano and where activity during the last 3000 years has been characterized by felsic eruptions of varying size. Elsewhere in the Kermadec arc and in its northward extension, the Tonga arc, felsic eruptions are recorded from 11 of the 30 volcanoes for which petrographic information is available, and in many cases these are the most recent eruptions. Felsic europtions are a widespread recent feature of the arc, and the scale and extent of this magmatism appears to be unusual for a tectonically simple oceanic subduction system. One explanation of the origin of the felsic magmatism is prolonged fractional crystallization from a parental basalt composition, but modelling of the chemical compositions of the felsic rocks does not support this. A second explanation, albeit apparently at odds with the oceanic setting, is crustal anatexis. An important feature of the felsic eruptives from the Kermadec arc is that each tephra sequence or occurrence has a unique chemical composition, although all show the same generalized characteristics. We suggest that this feature supports a model of crustal anatexis rather than fractionation of a range of parental magmas. We also suggest that in the thermal evolution of an oceanic arc system the processes of underplating, together with the continuous magmatic (and thermal) flux, can generate a crustal thickness in which dehydration melting of underplated arc material generates felsic magmas. Further, this condition can represent a unique ‘adolescent’ stage in a developing oceanic arc, as once the felsic melts are extracted the lower crust becomes an infertile residue.