Submarine eruption-fed and resedimented pumice-rich facies: the Dogashima Formation (Izu Peninsula, Japan)
Submarine eruption-fed and resedimented pumice-rich facies: the Dogashima Formation (Izu Peninsula, Japan)
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海底喷发和再沉积的富含浮石相：堂岛组（日本伊豆半岛）
DOI：
10.1007/s00445-014-0867-x
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发表时间：
2014
影响因子：
3.5
通讯作者：
S. Allen
中科院分区：
文献类型：
--
作者：
M. Jutzeler;J. McPhie;S. Allen
在伊豆半岛（日本），上新世富含浮石的Dogashima组（4.55 ± 0.87 Ma）显示出在浪基面以下海洋环境中喷发和沉积的火山岩相的特殊保存。它包括高浓度的密度电流存款，其中包含的碎屑是侵位热，表明一个喷发美联储的起源。Dogashima 2单元的下部由一个非常厚的灰色安山岩角砾岩序列（<12 m）组成，局限于海底水道的底部，逐渐被浮岩角砾岩覆盖，浮岩角砾岩分布广泛，但在漫滩环境中更薄更细。这两个角砾岩具有相似的矿物学和晶体成分，被认为是共同岩浆，来自爆炸性的浮石形成喷发对海底圆顶的破坏。这两个角砾岩沉积从一个单一的，爆炸性的爆发，美联储，持续，海底拥抱，水支持，高浓度密度电流的碎屑根据其密度进行排序。在边缘的通道，局部良好的水力分选的碎屑和分层的浮石角砾岩被解释为反映当地的电流扩张和不稳定，而不是从海底喷发柱和/或伞羽下降过程中的碎屑水力分选的结果。覆盖在角砾岩上的双峰粗（>1 m）浮岩和火山灰富集层可能来自悬浮液中火山碎屑的延迟沉降。在Dogashima 1和2中，由次圆形浮石碎屑组成的厚的交叉和平坦层状相与喷发相交错，这意味着海底火山侧翼的喷发间质量浪费，以及在波底环境下由高能牵引流进行的改造和再沉积。
In the Izu Peninsula (Japan), the Pliocene pumice-rich Dogashima Formation (4.55 ± 0.87 Ma) displays exceptional preservation of volcaniclastic facies that were erupted and deposited in a below wave-base marine setting. It includes high-concentration density current deposits that contain clasts that were emplaced hot, indicating an eruption-fed origin. The lower part of the Dogashima 2 unit consists of a very thick sequence (<12 m) of massive grey andesite breccia restricted to the base of a submarine channel, gradationally overlain by pumice breccia, which is widespread but much thinner and finer in the overbank setting. These two breccias share similar mineralogy and crystal composition and are considered to be co-magmatic and derived from the destruction of a submarine dome by an explosive, pumice-forming eruption. The two breccias were deposited from a single, explosive eruption-fed, sustained, sea floor-hugging, water-supported, high-concentration density current in which the clasts were sorted according to their density. At the rim of the channel, localised good hydraulic sorting of clasts and stratification in the pumice breccia are interpreted to reflect local current expansion and unsteadiness rather than to be the result of hydraulic sorting of clasts during fall from a submarine eruption column and/or umbrella plume. A bimodal coarse (>1 m) pumice- and ash-rich bed overlying the breccias may be derived from delayed settling of pyroclasts from suspension. In Dogashima 1 and 2, thick cross- and planar-bedded facies composed of sub-rounded pumice clasts are intercalated with eruption-fed facies, implying inter-eruptive mass-wasting on the flank of a submarine volcano, and reworking and resedimentation by high-energy tractional currents in a below wave-base environment.