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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Contrasting eruption styles of the 147 Kimberlite, Fort a la Corne, Saskatchewan, Canada
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Contrasting eruption styles of the 147 Kimberlite, Fort a la Corne, Saskatchewan, Canada

机译：加拿大萨斯喀彻温省Fort a la Corne 147 Kimberlite的喷发风格对比

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摘要

The Cretaceous Fort a la Corne (FALC) kimberlite field was active over a time span of ~20 Ma with contemporaneous terrestrial (Mannville Group) to marine (Lower Colorado Group) background sedimentation. Steep-sided pipes, craters and positive landform volcanoes such as scoria or tuff cones are thought to have formed during that period. The 147 Kimberlite is located in the SE section of the field's main cluster and is part of the large (～377.5 ha) Orion North volcanic complex. Based on logging of 25 drill cores, the morphology of the country rock/kimberlite interface suggests excavation of a complex crater field down to the upper portion of the Mannville Group sedimentary deposits. At least two types of volcaniclastic deposits are identified: a main kimberlite unit that is typically characterized by crustal xenolith-poor (1-2%), normal graded beds possibly deposited as turbidites in a subaqueous environment, originating from the nearby 148 tephra cone and infilling the adjacent 147 crater, and a second unit, located on the NE margin of the 147 Kimberlite, that represents a thick (～60 m) sequence of large (up to 22 m) sedimentary country rock blocks located at least 60 m above their original stratigraphic position. We suggest the following time sequence of events: Crater excavation as a consequence of a shallow magma fragmentation level within the uppermost country rock sequences, together with several closely spaced eruptive centres initially formed the complex, intercalated crater field. Subsequently, ongoing eruptions with a fragmentation level above the country rock produced the lithic fragment poor main infill of the 148 Kimberlite. Resedimentation from the outer flanks of the 148 tephra cone resulted in the deposition of turbidites in the 147 area. A consolidation phase solidified the lowermost portion of the main infill in 147. A subsequent explosion(s) occurred within the Mannville Group in the 147 area, ejecting large blocks of sedimentary country rocks and fracturing the overlying volcaniclastic main infill. Finally, blocks of the main infill tilted and possibly slumped into the subsidence structure developed above the emptied explosion chamber of 147. The different volcanic deposits reflect a change in eruption style and fragmentation level from highly explosive to spatter activity with little fragmentation potential. Cap rocks to build up the volatile overpressure necessary to blast the craters were not present at the time of emplacement. No diatremes were observed in the study area. Assuming that the magma properties remained constant over time, the change in eruption style has to be attributed to external factors, such as water access to the rising magma. The volcanic behaviour of the kimberlite magma appears to be comparable to that of other magmatic systems, both in eruptive style and production rate. No evidence was found for a high, possibly Plinian production rate or dispersion.
机译：白垩纪Fort a la Corne（FALC）金伯利岩场活跃在约20 Ma的时间范围内，同时期是陆相（Mannville组）到海洋（Lower Colorado组）背景沉积。在此期间，形成了陡峭的管道，火山口和火山岩或凝灰岩锥等正面地形火山。 147号金伯利岩位于该油田主群的东南部，是大型（约377.5公顷）猎户座北部火山群的一部分。基于对25个钻芯的测井，乡村岩石/金伯利岩界面的形态表明，一个复杂的火山口场的开挖一直到曼维尔群沉积沉积的上部。至少确定了两种类型的火山碎屑沉积物：主要为金刚砂岩的主要特征为地壳异岩体贫乏（1-2％），可能在附近的水下环境中以浊石形式沉积的正常梯度床，其起源于附近的148 tephra锥和填充相邻的147火山口，第二个单元位于147金伯利岩的东北边缘，代表一个厚的（〜60 m）序列的大型（至22 m）沉积性乡村岩石块，位于其上方至少60 m原始地层位置。我们建议以下事件发生的时间顺序：由于最上面的乡村岩石序列内的浅层岩浆破碎水平而导致的火山口开挖，加上几个紧密间隔的喷发中心，最初形成了复杂的，交错的火山口场。随后，持续不断的喷发，其碎石水平超过了乡村岩石，从而导致了148金伯利岩的碎石碎屑较弱的主要填充物。来自148个特非拉锥外侧面的再沉积导致浊积石沉积在147个区域中。固结阶段在147年固化了主要填充物的最下部。随后在147区的Mannville组内部发生了爆炸，喷出了大块沉积性乡村岩石并使上伏的火山碎屑性主要填充物破裂。最后，主充填物的块体倾斜并可能塌陷到空的147爆炸室上方形成的沉降结构中。不同的火山沉积物反映了喷发类型和碎裂程度的变化，从高度爆炸性变为飞溅活动，碎裂可能性很小。进驻时没有盖岩来建立炸破弹坑所需的挥发性超压。在研究区域未观察到任何危害。假设岩浆性质随时间保持不变，则喷发方式的变化必须归因于外部因素，例如水进入上升的岩浆。金伯利岩岩浆的火山活动在喷发方式和生产率上似乎与其他岩浆系统相当。没有证据表明可能有较高的普利尼生产速度或分散率。

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