大陆洪积玄武岩(CFB)熔岩的结晶:纹理研究的启示

IF 3.5 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Aristle Monteiro, Tushar Mittal, Raymond Duraiswami, Stephen Self
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引用次数: 0

摘要

大陆洪积玄武岩群是地球上已知体积最大的喷发(约104立方公里)的产物,单个流场的面积通常远远超过1万平方公里,平均熔岩厚度超过5米。对这类熔岩流的喷发方式的研究广泛依赖于形态观察以及与现代熔岩流和实验类似物的比较。在本研究中,我们利用从已有文献中收集到的数据,将洪积玄武岩熔岩的质地与世界各地不同喷发环境下的熔岩进行比较,以详细了解喷发的风格。晶体尺寸分布(CSD)数据的比较表明,CFB 的喷发方式与现代裂隙喷发(如冰岛)的喷发方式相似。这与基于形态观测的推断相吻合。我们还使用一维热模型来估算单个熔岩裂隙内随深度变化的冷却率,并检验这些模型的假设是否有效。结果显示,平均而言,洪积玄武岩熔岩的传导冷却速度要比我们预期的快得多(快达约102倍),才能与纹理观测结果相吻合。该模型还经常无法复制观测到的 CFB 熔岩长度随深度的相对变化。此外,根据晶体形状计算出的冷却速度与根据晶体长度计算出的冷却速度也不一致,这表明对于大面积的CFB流场,冷却流模型的假设条件需要修改。鉴于 CFB 流场的面积很大,而且推断单个流场的喷发时间相对较长,我们推测,裂片的膨胀和通过断裂形成新裂片以及喷发速率的变化是这些流场冷却模型中缺少的关键过程。考虑到这些过程对于得出准确的冷却率至关重要,而准确的冷却率对于更好地了解 CFB 在喷发时对环境的影响非常重要。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
The crystallization of continental flood basalt (CFB) lavas: insights from textural studies
Continental flood basalts provinces are the product of the largest known volumetric eruptions on Earth (~104 km3), with individual flow fields commonly covering well over 10 000 km2 with a mean lava thickness of over 5 m. Studies focusing on the emplacement style of such lava flows have relied extensively on morphological observations and comparisons with modern lava flows and experimental analogs. In the present study, we compare the textures of flood basalt lavas with those from different eruption settings all over the world using data collected from pre-existing literature to gain detailed insights into the style of eruption. Comparison of crystal size distribution (CSD) data indicates that the eruption style of CFBs is similar to those of modern-day fissure eruptions (e.g. Iceland). This matches inferences based on observations of morphology. We also use a 1D thermal model to estimate the depth dependent cooling rates within a single lava lobe and test the validity of assumptions built into the formulation of these models. The results reveal that, on average, flood basalt lavas need to conductively cool much faster than we would expect (up to order of ~102 times faster) to match the textural observations. The model is also frequently unable to replicate the observed depth-wise relative variations in length with depth for CFB lavas. Furthermore, the calculated cooling rates from crystal shapes also do not match those calculated from crystal lengths, indicating the assumptions in cooling flow models need to be modified for large CFB flow fields. Given the large areas of CFB flow-fields and the relatively long eruption times inferred for the emplacement of individual flow fields, we hypothesize that inflation of lobes and formation of new lobes via breakouts combined with variable eruption rates are key processes that are missing when modeling the cooling of these flow fields. Accounting for these processes is essential to derive accurate cooling rates, which is important to better understand the environmental impact CFBs have at the time of emplacement.
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来源期刊
Journal of Petrology
Journal of Petrology 地学-地球化学与地球物理
CiteScore
6.90
自引率
12.80%
发文量
117
审稿时长
12 months
期刊介绍: The Journal of Petrology provides an international forum for the publication of high quality research in the broad field of igneous and metamorphic petrology and petrogenesis. Papers published cover a vast range of topics in areas such as major element, trace element and isotope geochemistry and geochronology applied to petrogenesis; experimental petrology; processes of magma generation, differentiation and emplacement; quantitative studies of rock-forming minerals and their paragenesis; regional studies of igneous and meta morphic rocks which contribute to the solution of fundamental petrological problems; theoretical modelling of petrogenetic processes.
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