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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Towards the reconstruction of the shallow plumbing system of the Barombi Mbo Maar (Cameroon) Implications for diatreme growth processes of a polygenetic maar volcano
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Towards the reconstruction of the shallow plumbing system of the Barombi Mbo Maar (Cameroon) Implications for diatreme growth processes of a polygenetic maar volcano

机译：致力于重建Barombi Mbo Maar（喀麦隆）的浅层管道系统对多基因Maar火山的极端生长过程的影响

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Understanding the mechanisms involved in the formation of maars and their diatreme growth processes has been a subject of contention. While there is no direct evidence of the presence of diatremes beneath most of the young maars, their existence is inferred based on the amount and type of country rocks excavated at different depths and deposited as pyroclastic ejecta around their craters. Properly tracing fragmented country rocks in ejecta to interpret their depths of origin and thus the depths of phreatomagmatic explosions require good and detailed information on the substrate geology that is generally lacking at many maars. As an alternative, this paper explores the role of juvenile components in deposits of a maar for understanding the cratering and growth of diatremes during maar-forming eruptions. Based on field investigations, pyroclast distribution, componentry and grain morphology examinations this study reports on the eruptive mechanisms that led to the formation of the Barombi Mbo Maar (BMM), a polygenetic maar volcano in Cameroon. The BMM consists of three diatremes that formed during distinct eruptive events and coalesced to produce an "amalgamated maar-diatreme". Two end-member types of eruption styles from the "dry" magmatic to the "wet" phreatomagmatic explosions governed the formation of the mar. In total, a minimum of similar to 0.0658 km(3) of magma (Dense Rock Equivalent corrected) was ejected based on calculation by applying interpolation techniques on digital elevation models obtained from SRTM30m data corrected by rock textural data collected from the field. The distribution of juvenile clasts throughout the stratigraphic sequence suggests a complex subsurface eruptive process, which originated probably within the uppermost part of the diatreme. From the distribution and morphology of juvenile clasts in the deposits, it is inferred that cratering and country rock excavation during the growth of each of the small diatremes developed mainly from shallow level explosions, sometimes with lateral and vertical variations in the position of the explosion loci. A prospective juvenile-based conceptual model is proposed for the formation of the BMM. The model suggests that, during maar-forming eruptions, explosions taking place at a deeper position might entrain extensive amount of lithics from the mostly lithic-dominated upper crater infill to deposit juvenile-poor (<10 vol.%) tephra beds. Layers with a juvenile content of 10-60 vol.% for example, might result from deep to shallow-seated explosions, with a common entrainment of lithics from the crater infill region, and with much of the remobilized tephra being transported to the ejecta ring sequence. In contrast explosions occurring at shallower positions will produce mainly juvenile-rich beds (juvenile > 90 vol.%). (C) 2015 Elsevier B.V. All rights reserved.
机译：理解形成毛虫及其异常生长过程的机制一直是争论的主题。尽管没有直接的证据表明大多数年轻的玛尔石下面都存在杀虫剂，但它们的存在是根据在不同深度开挖并以火山碎屑喷出物沉积在火山口周围的乡村岩石的数量和类型来推断的。正确地追踪喷出物中破碎的乡村岩石以解释其起源深度，因此，岩浆爆炸的深度需要许多基质上通常缺乏的关于基质地质的良好而详细的信息。作为替代方案，本文探讨了马氏矿床中的青少年成分的作用，以了解马雷形成喷发期间百灵药的火山口和生长。根据野外调查，火山碎屑分布，成分和颗粒形态检查，本研究报告了导致喀麦隆多基因马阿尔火山Barombi Mbo Maar（BMM）形成的喷发机制。 BMM由在不同的爆发事件期间形成并合并产生“融合的玛尔-钻石”的三个异常组成。从“干”岩浆岩到“湿”岩浆岩爆发有两种末端类型的喷发类型控制了火星的形成。总的来说，在通过对基于SRTM30m数据的数字高程模型中应用插值技术而获得的插值技术，通过计算得出了至少约0.0658 km（3）的岩浆（密实的岩石等效物校正），该喷射量是由从现场采集的岩石纹理数据校正而来的。整个地层层序中的幼岩碎屑的分布表明了一个复杂的地下喷发过程，该过程可能起源于该异常的最上部。从矿床中的幼岩碎屑的分布和形态可以推断出，每个小径的生长过程中的火山口和乡村岩石开挖主要是由浅水准爆炸产生的，有时爆炸地点的位置在横向和垂直方向都有变化。提出了一种基于青少年的前瞻性概念模型，用于BMM的形成。该模型表明，在形成麻石的喷发过程中，在更深的位置发生爆炸可能会从大部分以石块为主的上火山口夹杂物夹带大量石块，以沉积贫瘠（小于10％（体积））的特菲拉床。例如，幼虫含量为10％至60％（体积）的层可能是由深部到浅部爆炸产生的，通常是从火山口填充区夹带石屑，并且大部分已移动的特非拉被运输到弹射环序列。相反，在较浅位置发生的爆炸将主要产生富含少年的床（少年> 90％（体积））。 （C）2015 Elsevier B.V.保留所有权利。

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