Tuff rings: Examples from the Fort Rock-Christmas Lake Valley Basin, south-central Oregon
Tuff rings: Examples from the Fort Rock-Christmas Lake Valley Basin, south-central Oregon
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凝灰岩环：俄勒冈州中南部罗克堡-圣诞湖谷盆地的例子
DOI：
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发表时间：
1971
期刊：
影响因子：
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通讯作者：
G. Heiken
中科院分区：
文献类型：
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作者：
G. Heiken
凝灰岩环是在位于湖泊、沿海地区、沼泽和地下水丰富地区的火山口周围建造的玻璃质碎屑的宽而低的层状堆积。岩石堡-圣诞湖流域内的凝灰岩环在上新世-更新世时期喷发，形成一个占据该盆地的湖泊。在湖盆之外是相关的锥和流。凝灰岩锥和凝灰岩环沿着穿过盆地和邻近高地的断层分布。凝灰岩环的形状和高度似乎部分取决于当上升的岩浆与地下水或地表水接触时爆炸性蒸汽产生的深度（蒸汽岩浆喷发）。湖内的喷发产生了水下泥石流，沉积了大量的凝灰岩角砾岩，现在暴露在凝灰岩环的底部。当环突破表面时，大部分火山灰从空气中沉积下来，形成薄层，显示出床面凹陷（炸弹凹陷）。一些陆上岩层是由底潮沉积的（如1965年和1966年在菲律宾的Taal），这些底潮形成了放射状沙丘和丰富的交错层理，并在45°至90°的坡面上形成了灰泥灰。当火山喷发停止之前，水流进入喷口停止，他们充满了同心，垂直凝灰岩床和大量的凝灰岩角砾岩。当火山口的水流在喷发停止前停止时，火山口部分被煤渣、飞溅物和小熔岩湖填满。玄武质成分的玻璃质火山灰构成凝灰岩环喷出物的约95%。火山灰主要由透明、浅棕色至中棕色的玻璃碎片组成，除了斑晶外，只含有少量的微晶。一般来说，颗粒具有块状形状和低泡性，与湖泊盆地外与凝灰岩环同时代的曲形、高度泡状的液滴、弹状和火山灰形成对比。玻璃陨石颗粒形态是岩浆遇水迅速冷却时收缩和破碎的结果。
Tuff rings are wide, low-rimmed, well-bedded accumulations of hyaloclastic debris built around volcanic vents located in lakes, coastal areas, marshes, and areas of abundant ground water. Tuff rings within the Fort Rock-Christmas Lake Valley basin were erupted during Pliocene-Pleistocene time into a lake that occupied the basin. Outside the lake basin are related cinder cones and flows. The cinder cones and tuff rings occur along faults that cross the basin and adjacent highland. The shape and height of the tuff rings appear to be partly dependent on the depth of explosive steam generation when rising magma came in contact with ground or surface water (phreatomagmatic eruptions). Eruptions within the lake produced underwater debris flows that deposited massive tuff breccia now exposed at the bases of the tuff rings. When the rings breached the surface, much of the ash was deposited from the air to form thin beds showing bedding-plane sags (bomb sags). Some of the subaerial beds were deposited by base surges (as at Taal, Philippines, 1965 and 1966) that formed radial dunes and abundant cross bedding and plastered ash onto slope surfaces of 45° to 90°. When eruptions ceased before the flow of water into a vent stopped, they were filled with concentric, vertical tuff beds and massive tuff breccia. When the flow of water into the vent ceased before the eruption stopped, craters were partly filled with cinders, spatter, and small lava lakes. Hyaloclastic ash of basaltic composition constitutes approximately 95% of the ejecta in the tuff rings. The ash consists mostly of clear, light-brown to medium-brown glass fragments, containing only a few microlites in addition to phenocrysts. Generally, the grains have a blocky shape and low vesicularity, in contrast with the curved, highly vesicular droplets, bombs, and cinders of the cinder cones outside of the lake basin that were contemporary with the tuff rings. The hyaloclastic grain morphology is the result of contraction and shattering when the magma was rapidly chilled on contact with water.