Special Issue "Mineral Textural and Compositional Variations as a Tool for Understanding Magmatic Processes"

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Geochemistry and Geochronology".

Deadline for manuscript submissions: 31 December 2019

Special Issue Editor

Guest Editor
Prof. Silvio Mollo

Department of Earth Sciences, Sapienza – University of Rome, Italy
Website | E-Mail
Interests: igneous and experimental petrology

Special Issue Information

Dear Colleagues,

Magma chamber processes and eruption dynamics are recognized as the most important mechanisms controlling the final textures and compositions of minerals and their host rocks. During crystallization and solidification phenomena, the physicochemical state of the system shifts from equilibrium to dynamic conditions under the effect of variable pressures, temperatures, oxygen fugacities, and volatile contents. In this scenario, magmas crystallize at different depths, evolve, degas, mix with new magma, and interact with the country rock. The solidification of magmas may also occur along kinetic or time-dependent pathways, where rapid cooling and decompression exert a primary influence on the nucleation and growth of phenocrysts, microphenocrysts and microlites characterizing the volcanic units. Understanding these different aspects over the temporal and spatial scales at which the crystallization and solidification processes occur in magmatic reservoirs, volcanic conduits and subaerial/submarine eruptions is essential to interpret correctly the variable environmental conditions recorded in igneous minerals. The main goal for this Special Issue is to collect different scientific contributions denoting how magma chamber processes and eruption dynamics studied either in laboratory or in nature can ultimately affect the evolutionary histories and petrographic complexities of igneous rocks.

The first round submission deadline is 31 December 2018.

Prof. Dr. Silvio Mollo
Guest Editor

Manuscript Submission Information

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Keywords

  • magma chamber processes
  • eruption dynamics
  • magma crystallization
  • magma degassing
  • magma mixing
  • magma-crust interaction
  • magma cooling and decompression
  • mineral textural evolutions
  • bulk rock and mineral compositional changes

Published Papers (4 papers)

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Research

Open AccessArticle
Modeling the Crystallization and Emplacement Conditions of a Basaltic Trachyandesitic Sill at Mt. Etna Volcano
Minerals 2019, 9(2), 126; https://doi.org/10.3390/min9020126
Received: 9 January 2019 / Revised: 18 February 2019 / Accepted: 19 February 2019 / Published: 21 February 2019
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Abstract
This study documents the compositional variations of phenocrysts from a basaltic trachyandesitic sill emplaced in the Valle del Bove at Mt. Etna volcano (Sicily, Italy). The physicochemical conditions driving the crystallization and emplacement of the sill magma have been reconstructed by barometers, oxygen [...] Read more.
This study documents the compositional variations of phenocrysts from a basaltic trachyandesitic sill emplaced in the Valle del Bove at Mt. Etna volcano (Sicily, Italy). The physicochemical conditions driving the crystallization and emplacement of the sill magma have been reconstructed by barometers, oxygen barometers, thermometers and hygrometers based on clinopyroxene, feldspar (plagioclase + K-feldspar) and titanomagnetite. Clinopyroxene is the liquidus phase, recording decompression and cooling paths decreasing from 200 to 0.1 MPa and from 1050 to 940 °C, respectively. Plagioclase and K-feldspar cosaturate the melt in a lower temperature interval of ~1000–870 °C. Cation exchanges in clinopyroxene (Mg-Fe) and feldspar (Ca-Na) indicate that magma ascent is accompanied by progressive H2O exsolution (up to ~2.2 wt. %) under more oxidizing conditions (up to ΔNNO + 0.5). Geospeedometric constraints provided by Ti–Al–Mg cation redistributions in titanomagnetite indicate that the travel time (up to 23 h) and ascent velocity of magma (up to 0.78 m/s) are consistent with those inferred for other eruptions at Mt. Etna. These kinetic effects are ascribed to a degassing-induced undercooling path caused principally by H2O loss at shallow crustal conditions. Rare earth element (REE) modeling based on the lattice strain theory supports the hypothesis that the sill magma formed from primitive basaltic compositions after clinopyroxene (≤41%) and plagioclase (≤12%) fractionation. Early formation of clinopyroxene at depth is the main controlling factor for the REE signature, whereas subsequent degassing at low pressure conditions enlarges the stability field of plagioclase causing trace element enrichments during eruption towards the surface. Full article
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Open AccessArticle
Unravelling the Crustal Architecture of Cape Verde from the Seamount Xenolith Record
Minerals 2019, 9(2), 90; https://doi.org/10.3390/min9020090
Received: 30 December 2018 / Revised: 28 January 2019 / Accepted: 29 January 2019 / Published: 1 February 2019
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Abstract
The Cape Verde oceanic plateau hosts 10 islands and 11 seamounts and provides an extensive suite of alkaline lavas and pyroclastic rocks. The volcanic rocks host a range of crustal and mantle xenoliths. These xenoliths provide a spectrum of lithologies available to interact [...] Read more.
The Cape Verde oceanic plateau hosts 10 islands and 11 seamounts and provides an extensive suite of alkaline lavas and pyroclastic rocks. The volcanic rocks host a range of crustal and mantle xenoliths. These xenoliths provide a spectrum of lithologies available to interact with magma during transport through the lithospheric mantle and crust. We explore the origin and depth of formation of crustal xenoliths to develop a framework of magma-crust interaction and a model for the crustal architecture beneath the Cape Verde oceanic plateau. The host lavas are phononephelinites to phonolites and the crustal xenoliths are mostly mafic plutonic assemblages with one sedimentary xenolith. REE profiles of clinopyroxene in the host lavas are light rare-earth element (LREE) enriched whereas clinopyoxene from the plutonic xenoliths are LREE depleted. Modelling of REE melt compositions indicates the plutonic xenoliths are derived from mid-ocean ridge basalt (MORB)-type ocean crust. Thermobarometry indicates that clinopyroxene in the host lavas formed at depths of 17 to 46 km, whereas those in the xenoliths formed at 5 to 20 km. This places the depth of origin of the plutonic xenoliths in the oceanic crust. Therefore, the xenoliths trace magma-crust interaction to the MORB oceanic crust and overlying sediments located beneath the Cape Verde oceanic plateau. Full article
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Open AccessArticle
Impulsive Supply of Volatile-Rich Magmas in the Shallow Plumbing System of Mt. Etna Volcano
Minerals 2018, 8(11), 482; https://doi.org/10.3390/min8110482
Received: 18 September 2018 / Revised: 17 October 2018 / Accepted: 22 October 2018 / Published: 25 October 2018
Cited by 1 | PDF Full-text (2336 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Magma dynamics at Mt. Etna volcano are frequently recognized as the result of complex crystallization regimes that, at shallow crustal levels, unexpectedly change from H2O-undersaturated to H2O-saturated conditions, due to the impulsive and irregular arrival of volatile-rich magmas from [...] Read more.
Magma dynamics at Mt. Etna volcano are frequently recognized as the result of complex crystallization regimes that, at shallow crustal levels, unexpectedly change from H2O-undersaturated to H2O-saturated conditions, due to the impulsive and irregular arrival of volatile-rich magmas from mantle depths. On this basis, we have performed hydrous crystallization experiments for a quantitative understanding of the role of H2O in the differentiation of deep-seated trachybasaltic magmas at the key pressure of the Moho transition zone. For H2O = 2.1–3.2 wt %, the original trachybasaltic composition shifts towards phonotephritic magmas never erupted during the entire volcanic activity of Mt. Etna. Conversely, for H2O = 3.8–8.2 wt %, the obtained trachybasalts and basaltic trachyandesites reproduce most of the pre-historic and historic eruptions. The comparison with previous low pressure experimental data and natural compositions from Mt. Etna provides explanation for (1) the abundant release of H2O throughout the plumbing system of the volcano during impulsive ascent of deep-seated magmas; (2) the upward acceleration of magmas feeding gas-dominated, sustained explosive eruptions; (3) the physicochemical changes of gas-fluxed magmas ponding at shallow crustal levels; and (4) the huge gas emissions measured at the summit craters and flank vents which result in a persistent volcanic gas plume. Full article
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Open AccessArticle
The Merensky Cyclic Unit, Bushveld Complex, South Africa: Reality or Myth?
Minerals 2018, 8(4), 144; https://doi.org/10.3390/min8040144
Received: 21 February 2018 / Revised: 26 March 2018 / Accepted: 28 March 2018 / Published: 3 April 2018
Cited by 1 | PDF Full-text (6183 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The Merensky Unit, Bushveld Complex, is commonly described using genetic terms such as “cyclic unit”, typically without careful consideration of the connotations. We suggest that this contributes to the debate on processes forming the unit. This study integrates an extensive field study with [...] Read more.
The Merensky Unit, Bushveld Complex, is commonly described using genetic terms such as “cyclic unit”, typically without careful consideration of the connotations. We suggest that this contributes to the debate on processes forming the unit. This study integrates an extensive field study with detailed petrographic and textural analyses of the Merensky Unit to determine whether it is a “cyclic unit” sensu stricto. The study indicates that the bulk of the platinum-bearing chromitite-feldspathic orthopyroxenite developed through heterogeneous nucleation and in situ growth during multiple replenishment events. The overlying leuconorite developed above a gradational boundary, reflecting mixing following replenishment by a relatively more evolved magma. The bulk of this unit also formed in situ. The uppermost poikilitic anorthosite formed above a distinct boundary through a subsequent injection of a plagioclase-saturated magma, which crystallised in situ. Processes of gravitational settling and local remobilisation of crystals cannot be discounted from contributing to the development of the unit. The final textures throughout the unit developed through pervasive textural equilibration, with extensive fluid-mediated textural equilibration forming the megacrystic feldspathic orthopyroxenite. The evidence for at least five replenishment events indicates that the Merensky Unit is not a cyclic unit; therefore, the genetic term, “Merensky Cyclic Unit”, is misleading and its use should be carefully considered in future work. Full article
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Graphical abstract

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