Mafic Plinian volcanism and ignimbrite emplacement at Tofua volcano, Tonga
Mafic Plinian volcanism and ignimbrite emplacement at Tofua volcano, Tonga
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DOI：
10.1007/s00445-011-0477-9
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发表时间：
2011-11-01
影响因子：
3.5
通讯作者：
Cooper, L. B.
中科院分区：
文献类型：
--
作者：
Caulfield, J. T.;Cronin, S. J.;Cooper, L. B.
托夫亚岛是西南太平洋汤加托夫亚弧内最大的紧急镁铁质火山。这座火山由一个平均直径4公里的独特火山口主导，在南部和东部有一个淡水湖。最新的爆发火山作用(VEI 5-6)包括两个阶段的活动，每个阶段都埋藏着一种高品位的褐沸石。产物为玄武岩安山岩，二氧化硅含量在52wt%至57wt%之间。第一次也是最大的一次喷发导致一座层状火山向内坍塌，并在岛中心西北方向产生了‘Tofua’燃料岩和一个亚圆形火山口。这种褐沸石以放射状的方式在整个岛屿上沉积，在40公里外的岛屿上伴随着厚达0.5米的普林尼亚瀑布沉积。在整个褐沸岩中，常见的亚圆形和经常是杆状的渣粒炸弹证实了少量边缘岩浆-水的相互作用。然而，粗粒喷发产物的普遍强烈焊接表明，大多数喷发的岩浆是热的、水不饱和的，以较高的速度供应，破碎效率中等较低，与外部水的相互作用程度较低。我们认为，在浅层(<；6千米)的水饱和英安岩体的发育导致了洞室顶板的破坏，导致物质的突然排出，产生了普林尼安喷发柱。在短暂的静止期之后，岛屿东南部的大规模断裂产生了第二个爆炸相，据信是由于化学上不同的岩浆在不相容元素中枯竭而重新注入。这次类似的但规模较小的喷发，将“Hokula”Ignimbrite冰盖侵位在岛的东北部。这些事件喷发了最大总体积为8公里(3)的幼年物质。据估计，主喷发柱的高度约为12公里，并产生了一次主要的大气喷发，在以东40-80公里(沿区域对流层上层风方向)的珊瑚岛上发现的广泛的秋季沉积中记录了火山灰。对Tofua沸石下的木炭和相关秋季单元下的有机物质进行的放射性碳测年表明，这一喷发序列发生在距今1000年之后。我们估计这次喷发的震级为2.24x10(13)kg，硫的释放量为12Tg，并初步将这次喷发归因于南极冰盖记录中记录的公元1030年的硫酸盐火山尖峰。
Tofua Island is the largest emergent mafic volcano within the Tofua arc, Tonga, southwest Pacific. The volcano is dominated by a distinctive caldera averaging 4 km in diameter, containing a freshwater lake in the south and east. The latest paroxysmal (VEI 5-6) explosive volcanism includes two phases of activity, each emplacing a high-grade ignimbrite. The products are basaltic andesites with between 52 wt.% and 57 wt.% SiO2. The first and largest eruption caused the inward collapse of a stratovolcano and produced the 'Tofua' ignimbrite and a sub-circular caldera located slightly northwest of the island's centre. This ignimbrite was deposited in a radial fashion over the entire island, with associated Plinian fall deposits up to 0.5 m thick on islands > 40 km away. Common sub-rounded and frequently cauliform scoria bombs throughout the ignimbrite attest to a small degree of marginal magma-water interaction. The common intense welding of the coarse-grained eruptive products, however, suggests that the majority of the erupted magma was hot, water-undersaturated and supplied at high rates with moderately low fragmentation efficiency and low levels of interaction with external water. We propose that the development of a water-saturated dacite body at shallow (< 6 km) depth resulted in failure of the chamber roof to cause sudden evacuation of material, producing a Plinian eruption column. Following a brief period of quiescence, largescale faulting in the southeast of the island produced a second explosive phase believed to result from recharge of a chemically distinct magma depleted in incompatible elements. This similar, but smaller eruption, emplaced the 'Hokula' Ignimbrite sheet in the northeast of the island. A maximum total volume of 8 km(3) of juvenile material was erupted by these events. The main eruption column is estimated to have reached a height of similar to 12 km, and to have produced a major atmospheric injection of gas, and tephra recorded in the widespread series of fall deposits found on coral islands 40-80 km to the east (in the direction of regional upper-tropospheric winds). Radiocarbon dating of charcoal below the Tofua ignimbrite and organic material below the related fall units imply this eruption sequence occurred post 1,000 years BP. We estimate an eruption magnitude of 2.24x10(13) kg, sulphur release of 12 Tg and tentatively assign this eruption to the AD 1030 volcanic sulphate spike recorded in Antarctic ice sheet records.