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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Subaqueous eruption and emplacement of OT2 in the Middle Miocene Iizuka Formation, Noto Peninsula, Japan
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Subaqueous eruption and emplacement of OT2 in the Middle Miocene Iizuka Formation, Noto Peninsula, Japan

机译：日本能登半岛中新世饭冢中段的OT2水下喷发和定位

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摘要

OT2 (Okada Tuff 2) is one of six rhyolitic tuff beds that occur in a Middle Miocene marine diatomite (lower lizuka Formation) and are known as the Okada Tuff. OT2 is well-sorted, and thins and thickens infilling channels 1-3 m across and 0-30 cm deep with a thickness up to 30 cm. Small channels 10-30 cm across and 1-10 cm deep are commonly superimposed within wider channels. A thin diatomite layer is ripped from the substrate up to a level immediately above the small channels. The basal part beneath the ripped-up diatomite layer is dominated by ash components with vague wavy stratifications. Above the ripped-up diatomite layer, diatomite clasts are dispersed, and pumice lapilli increase upward in amount and size with local interruption at a middle lower level by a poorly defined, pumice lapilli poor thin layer. Many glass and pumice shards are blocky with curviplanar surfaces and jigsaw cracks, presumably produced by phreatomagmatic explosions. The poorly defined two layers of OT2 are interpreted to be ash turbidites individually produced by discrete phreatomagmatic explosions. Lenticular bedforms and channels indicate that the currents were fully turbulent and unsteady, fed by the submarine eruptions. Upward coarsening of pumice probably represents settling lag of hot pumice. OT2 perhaps provides potential diagnostic features to identify eruption-fed turbidites.
机译：OT2（冈田凝灰岩2）是中新世海相硅藻土（下利祖卡组）中出现的六个流纹凝灰岩床之一，被称为冈田凝灰岩。 OT2的分类非常好，可对1-3 m跨度和0-30 cm深的填充通道进行变薄和增厚，厚度可达30 cm。通常将宽10-30厘米，深1-10厘米的小通道叠加在较宽的通道内。从基材上剥离出一层薄薄的硅藻土层，直至紧接在小通道上方。剥落的硅藻土层下面的基础部分主要是灰分成分，具有模糊的波浪状分层。在被剥落的硅藻土层上方，硅藻土碎屑被分散，浮石悬垂石的数量和大小向上增加，并且在中间较低的位置被定义不清的浮石悬垂薄的薄层中断。许多玻璃和浮石碎片呈块状，表面呈曲线状，并存在锯齿状的裂纹，可能是由岩浆爆炸引起的。 OT2的定义不明确的两层被认为是由离散的岩浆爆破单独产生的灰浊物。透镜状的床形和水道表明，由于海底爆发，洋流完全湍流且不稳定。浮石的向上粗化可能表示热浮石的沉降滞后。 OT2可能提供潜在的诊断功能，以识别喷发的浊质。

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