Facies architecture and origin of a submarine rhyolitic lava flow‐dome complex, Ponza, Italy
Facies architecture and origin of a submarine rhyolitic lava flow‐dome complex, Ponza, Italy
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意大利庞扎海底流纹质熔岩流穹顶复合体的相结构和起源
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
D. Rita
中科院分区：
文献类型：
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作者：
C. Scutter;R. Cas;C. Moore;D. Rita
蓬扎岛和加维岛（意大利庞廷群岛西部）保留了部分水下高硅（75-77% SiO2）流纹岩熔岩流，覆盖了三个古老圆顶的边缘。仅熔岩暴露面积就达24 km2，而悬崖上暴露的厚度为150 m，熔岩流的保存体积为3.6 km3，原始体积很可能已超过7 km3。熔岩流由连贯的黑曜石和几种玻璃碎屑岩相组成，包括原位角砾岩和碎屑旋转角砾岩和砂岩，它们都表现出级配关系。连贯黑曜石以单独的区域出现，并且通常呈流带状。尽管存在流动褶皱，但带状结构通常是近水平的，轻轻地向北北东方向倾斜。玻璃碎屑占熔岩体积的 90%，具有厚度从 0.5 到 2 m 不等的扩散层。这种分层也轻轻地向北北东方向倾斜，并在某些地方以一些连贯的层位、粗碎和细碎的原位透明碎屑岩、浮石质透明碎屑岩和碎屑旋转的透明碎屑岩的交替为标志。在庞扎 13 公里长度的大部分地区，分层是横向连续的且方向一致：流带的近水平方向和层序上部存在的再沉积沉积物表明该单元是熔岩流。再沉积物包括由熔岩流上部和边缘部分的重力不稳定性引发的泥石流和浊流的近端和远端沉积物，并包括层状单晶黑曜岩角砾岩和层状玻璃质粉砂岩和砂岩。熔岩流被不同时代的流纹岩体侵入和横切，包括不一致的、连贯的内部断裂的同生流纹岩体，以及具有玻璃边缘和蚀变晕的晚期准同生岩脉。
The Islands of Ponza and Gavi (western Pontine Archipelago, Italy) preserve parts of a subaqueously emplaced, high-silica (75–77% SiO2) rhyolitic lava flow that overlies the margins of three older domes. Exposures of the lava alone cover 24 km2, and with a thickness of 150 m exposed in the cliffs, the preserved volume of the lava flow is 3.6 km3, and the original volume is likely to have exceeded 7 km3. The lava flow consists of coherent obsidian and several hyaloclastite facies, including in situ and clast-rotated breccias and sandstones, which all exhibit gradational relationships. The coherent obsidian occurs as separate domains and is often flow banded. Although flow folds occur, the banding is generally subhorizontal, dipping gently to the NNE. The hyaloclastite, representing 90% of the lava by volume, has a diffuse layering varying from 0.5 to 2 m in thickness. This layering also dips gently to the NNE and is marked in places by alternation of some coherent horizons, coarse and finely fragmented in situ hyaloclastite, pumiceous hyaloclastite, and clast-rotated hyaloclastite. The layering is laterally continuous and consistent in orientation over most of the 13 km length of Ponza: the subhorizontal orientation of the flow banding and presence of resedimented deposits in the upper parts of the sequence indicate that the unit is a lava flow. The resedimented deposits comprise both proximal and distal deposits of debris flows and turbidity currents initiated by gravitational instability of the upper and marginal parts of the lava flow and include stratified monomictic obsidian breccias and bedded vitric siltstones and sandstones. The lava flow has been intruded and crosscut by rhyolitic bodies of various ages, including discordant, coherent to internally fractured contemporaneous rhyolite bodies, and late, penecontemporaneous dikes with glassy margins and alteration haloes.