Supplementary Datasets for Focused mid-crustal magma intrusion during continental break-up in Ethiopia'
K.C. WongDavid FergusonPenny WieserD. J. MorganMarie EdmondsAmdemichael Zafu TadesseGezahegn YirguJason HarveySamantha J. Hammond
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Abstract:
Supplementary Datasets for Focused mid-crustal magma intrusion during continental break-up in Ethiopia', including geochemical analyses (standards, secondary standards, and data) Dataset S1: Full dataset of all standards, secondary standards, and data.Dataset S2: High resolution calibrated transmitted and reflected light microscope images of analysed melt inclusions.
A mechanism is examined which allows an intrusive body to melt its way upward in the earth's crust. Due to the increase in melting temperature with depth the melt temperature at the base of an intrusion may be considerably greater than the melt temperature at the top. This temperature difference can drive rapid convection in the intrusion; as a result heat is rapidly transferred to the top of the intrusion. This heat transport can cause melting of the country rock above the intrusion as solidification occurs at the base; the magma zone migrates upwards. Calculations show that this effect can become important in intrusions with a height greater than about 1 km; the effect is also more important when the temperature difference between the country rock and the intrusion is small and if the magma viscosity is low.
Country rock
Layered intrusion
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The location of gold veins, due to a slanting magma dike intrusion in a cold rock, considering earth surface effects is determined. The 400°C and 500°C isotherm evolution resulting from this magma intrusion are studied considering a 2-D model. In this analysis, it is shown that the isotherm envelopes are the most important surfaces. Analytic solutions have been found as a function of the angle a between the dike and the vertical planes. The present results are more general than previous ones in the contest of vertical dikes. Magma convection has been considered in a simplified way. The agreement found that the results in the work the actual vein sites at the gold mine, called Colombia, in the auriferous area of El Callao, located 180 Km south of Ciudad Guayana in Bolivar state, Venezuela, are much better than in previous works.
Dike
Magma chamber
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Made an attempt of reconstruction structure of the Monchegorsk layered intrusion, assessing the composition of the original magma and the conditions of its kristallization. The problem was solved by simply comparing the structure of the Monchegorsk Intrusive with a similar analog (for this purpose, the Kivakka layered Intrusive was chosen), as well as using model constructions using the COMAGMAT software package.
Software package
Layered intrusion
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The Tertiary Austurhorn intrusive complex in SE Iceland represents an exhumed magma chamber that has recorded an extensive history of magma mixing and mingling. The basal part of the intrusion consists predominantly of granophyres that have been intensively and repeatedly intruded by more mafic magma. This association of granophyres, basic and hybrid rocks at Austurhorn is referred to in the literature as a 'net-veined' complex, but field relations suggest a much more complex emplacement history. Here we present petrological and physical constraints on the various processes that resulted in magma mixing and mingling and the formation of different generations of hybrid rocks at Austurhorn. The complexity of the mixing and mingling processes increases towards the inferred centre of the intrusion, where chaotic hybrid rocks dominate the exposed lithology. Complex cross-cutting relations between different hybrid generations strongly suggest multiple magma injection and reheating events in the basal part of the shallow magma chamber. Model calculations employing distribution coefficients based on rare earth element concentrations reveal that early stage hybrid magma generations formed by pure endmember mixing between felsic and mafic magma with about 10% mafic fraction in the hybrids. With repeated injections of mafic magma into the base of the magma chamber, the intruding magma interacted to a greater extent with pre-existing hybrids. This led to the formation of hybrid magma compositions that are shifted towards the mafic endmember over time, with up to 30% of the mafic fraction in the hybrids. These mixing processes are recorded in the zonation patterns of clinopyroxene and plagioclase phenocrysts; the latter have been divided into four main groups by cross-correlation analysis. Melt viscosity calculations were performed to constrain the possible conditions of magma mixing and the results indicate that the interaction of the contrasting magmas most probably occurred at temperatures of approximately 1000°C up to 1120°C. This suggests that the initiation of effective magma mixing requires local superheating of the felsic magmas, thereby confining the process to areas of localized, substantial mafic magma injection.
Igneous differentiation
Magma chamber
Basal (medicine)
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Sills and dykes are commonplace items frequently seen in the field and rarely given a second glance. The mechanism of intrusion of sills and dykes is a relatively simple concept, readily taught to students, and rarely given a second thought. This book, however, is full of second thoughts, insights and models about the intrusion of magma and the formation of many different types of high-level sub-volcanic or plutonic body. It is a volume that makes you think about old …
Sill
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