scholarly journals What lies beneath? Reconstructing the primitive magmas fueling voluminous silicic volcanism using olivine-hosted melt inclusions

Geology ◽  
2020 ◽  
Vol 48 (5) ◽  
pp. 504-508 ◽  
Author(s):  
Simon J. Barker ◽  
Michael C. Rowe ◽  
Colin J.N. Wilson ◽  
John A. Gamble ◽  
Shane M. Rooyakkers ◽  
...  
Keyword(s):  
Melt Inclusions ◽  
Melt Inclusion ◽  
Taupo Volcanic Zone ◽  
Mantle Dynamics ◽  
Silicic Volcanism ◽  
Depleted Mantle ◽  
Basaltic Magmas ◽  
Show Evidence ◽  
Basaltic Melts ◽  
Eruptive Centers

Abstract Understanding the origins of the mantle melts that drive voluminous silicic volcanism is challenging because primitive magmas are generally trapped at depth. The central Taupō Volcanic Zone (TVZ; New Zealand) hosts an extraordinarily productive region of rhyolitic caldera volcanism. Accompanying and interspersed with the rhyolitic products, there are traces of basalt to andesite preserved as enclaves or pyroclasts in caldera eruption products and occurring as small monogenetic eruptive centers between calderas. These mafic materials contain MgO-rich olivines (Fo79–86) that host melt inclusions capturing the most primitive basaltic melts fueling the central TVZ. Olivine-hosted melt inclusion compositions associated with the caldera volcanoes (intracaldera samples) contrast with those from the nearby, mafic intercaldera monogenetic centers. Intracaldera melt inclusions from the modern caldera volcanoes of Taupō and Okataina have lower abundances of incompatible elements, reflecting distinct mantle melts. There is a direct link showing that caldera-related silicic volcanism is fueled by basaltic magmas that have resulted from higher degrees of partial melting of a more depleted mantle source, along with distinct subduction signatures. The locations and vigor of Taupō and Okataina are fundamentally related to the degree of melting and flux of basalt from the mantle, and intercaldera mafic eruptive products are thus not representative of the feeder magmas for the caldera volcanoes. Inherited olivines and their melt inclusions provide a unique “window” into the mantle dynamics that drive the active TVZ silicic magmatic systems and may present a useful approach at other volcanoes that show evidence for mafic recharge.

Contrasts in gem corundum characteristics, eastern Australian basaltic fields: trace elements, fluid/melt inclusions and oxygen isotopes

2006 ◽  
Vol 70 (6) ◽  
pp. 669-687 ◽  
Author(s):  
Khin Zaw ◽  
F. L. Sutherland ◽  
F. Dellapasqua ◽  
C. G. Ryan ◽  
Tzen-Fu Yui ◽  
...  
Keyword(s):  
Fluid Inclusions ◽  
Melt Inclusions ◽  
Melt Inclusion ◽  
New South ◽  
Alkaline Basalt ◽  
South Wales ◽  
Basaltic Melt ◽  
Isotope Studies ◽  
Alkaline Fluid ◽  
Basaltic Melts

AbstractCorundum xenocrysts from alkaline basalt fields differ in characteristics and hence lithospheric origins. Trace element, fluid/melt inclusion and oxygen isotope studies on two eastern Australian corundum deposits are compared to consider their origins. Sapphires from Weldborough, NE Tasmania, are magmatic (high-Ga, av. 200 ppm) and dominated by Fe (av. 3300 ppm) and variable Ti (av. 400 ppm) as chromophores. They contain Cl, Fe, Ga, Ti and CO2-rich fluid inclusions and give δ18O values (5.1–6.2‰) of mantle range. Geochronology on companion zircons suggests several sources (from 290 Ma to 47 Ma) were disrupted by basaltic melts (47 ± 0.6 Ma). Gem corundums from Barrington, New South Wales, also include magmatic sapphires (Ga av. 170 ppm; δ18O (4.6–5.8‰), but with more Fe (av. 9000 ppm) and less Ti (av. 300 ppm) as chromophores. Zircon dating suggests that gem formation preceded and was overlapped by Cenozoic basaltic melt generation (59–4 Ma). In contrast, a metamorphic sapphire-ruby suite (low-Ga, av. 30 ppm) here incorporates greater Cr into the chromophores (up to 2250 ppm). Fluid inclusions are CO2-poor, but melt inclusions suggest some alkaline melt interaction. The δ18O values (5.1–6.2‰) overlap magmatic sapphire values. Interactions at contact zones (T = 780–940°C) between earlier Permian ultramafic bodies and later alkaline fluid activity may explain the formation of rubies.

scholarly journals Plagioclase archives of depleted melts in the oceanic crust

2021 ◽  
Author(s):  
David Neave ◽  
Olivier Namur
Keyword(s):  
Oceanic Crust ◽  
Upper Mantle ◽  
Incompatible Element ◽  
Melt Inclusions ◽  
Melt Inclusion ◽  
Ocean Island Basalts ◽  
Depleted Mantle ◽  
Ocean Ridge ◽  
High Degree ◽  
Lower Crustal

Mid-ocean ridge and ocean island basalts provide vital but incomplete insights into the chemical structure of Earth’s mantle. For example, high-anorthite plagioclase carried by these basalts is generally too primitive and incompatible-element depleted to have crystallized from them. Moreover, erupted basalts rarely preserve the strong isotopic and incompatible-element depletions found in some melt inclusions and mantle residua represented by abyssal peridotites. By integrating experimental observations with published analyses of natural crystals and glasses, we demonstrate that high-anorthite plagioclase is in equilibrium with melts generated by high-degree melting of depleted mantle sources. Although such melts seldom erupt, their imprints on crystal and melt inclusion records nonetheless suggest that high-anorthite plagioclase grows from endmember but essentially unexotic magmas. The widespread occurrence of high-anorthite plagioclase in both oceanic basalts and the oceanic crust hence indicates that depleted melts are pervasive in the upper mantle and lower crust despite rarely reaching the surface. Plagioclase archives therefore imply that depleted melts play much a greater role in lower crustal accretion than typically recognized and that the upper mantle may also be more depleted than previously thought.

scholarly journals Constraints on the behaviour and content of volatiles in Galápagos magmas from melt inclusions and nominally anhydrous minerals

2021 ◽  
Author(s):  
Matthew Gleeson ◽  
Sally Gibson ◽  
Michael Stock
Keyword(s):  
Melt Inclusions ◽  
Melt Inclusion ◽  
Careful Consideration ◽  
Volatile Content ◽  
The South ◽  
Nominally Anhydrous Minerals ◽  
South Eastern ◽  
Galapagos Archipelago ◽  
Wide Range ◽  
Basaltic Magmas

Despite their relatively low concentration in most oceanic basalts, volatile species (e.g. H2O, CO2 and S) have a disproportionately large influence on a wide range of mantle and magmatic processes. However, constraining the concentration of H2O (and other volatiles) in basaltic magmas is not straightforward as submarine glass analyses are influenced by assimilation of hydrothermal brines, and the melt inclusion record is often reset by post-entrapment processes. Nevertheless, in this study we show that it is possible to reconstruct a detailed history of the volatile content of basaltic magmas through integration of multiple discreet volatile records and careful consideration of secondary processes. We present new analyses of volatiles in olivine-hosted melt inclusions, melt embayments and nominally anhydrous minerals (NAMS, clinopyroxene and orthopyroxene) found in basalts erupted on Floreana Island in the south-eastern Galápagos Archipelago. Our results indicate that the Floreana magmas, which are characterised by the most radiogenic Pb and Sr isotope signatures in the Galápagos Archipelago, contain H2O concentrations between 0.4 and 0.8 wt% (at a melt Mg# of 0.65, where Mg# = Mg/(Mg + Fe) molar). These are marginally greater than the H2O contents of magmas beneath Fernandina in the western Galápagos Archipelago (cf. 0.2–0.7 wt% H2O at Mg# = 0.65). While the volatile content of magmas from the western archipelago follow trends defined by concurrent mixing and crystallisation, NAMs from Floreana reveal the presence of rare, volatile-rich magmas (~2 wt% H2O) that form as a consequence of reactive porous flow in mush-dominated magmatic systems beneath the south-eastern Galápagos. Furthermore, the Floreana magmas have similar H2O/light Rare Earth Element ratios to basalts from the western Galápagos but contain F/Nd and Cl/K ratios that are ~2 – 3 times greater, indicating that the mantle source of the Floreana lavas might represent an important halogen reservoir in the Galápagos mantle plume.

Basaltic melts in olivine from alkaline pumice of Primor’e: Evidence from the study of melt inclusions

2011 ◽  
Vol 438 (1) ◽  
pp. 656-660 ◽  
Author(s):  
O. A. Andreeva ◽  
V. B. Naumov ◽  
I. A. Andreeva ◽  
V. I. Kovalenko
Keyword(s):  
Melt Inclusions ◽  
Basaltic Melts

A myriad of melt inclusions: a synchrotron microtomography study of melt inclusions and vapour bubbles from Colli Albani (Italy)

2021 ◽  
Author(s):  
Corin Jorgenson ◽  
Luca Caricchi ◽  
Michael Stueckelberger ◽  
Giovanni Fevola ◽  
Gregor Weber
Keyword(s):  
Melt Inclusions ◽  
Melt Inclusion ◽  
Fluid Phase ◽  
Volcanic Eruptions ◽  
Mineral Chemistry ◽  
Magma Ascent ◽  
Vapour Bubble ◽  
Electron Synchrotron ◽  
Colli Albani ◽  
Synchrotron Microtomography

<p>Melt inclusions provide a window into the inner workings of magmatic systems. Both mineral chemistry and volatile distributions within melt inclusions can provide valuable information about the processes modulating magma ascent and preceding volcanic eruptions. Many melt inclusions host vapour bubbles which can be rich in CO<sub>2</sub> and H<sub>2</sub>O and must be taken into consideration when assessing the volatile budget of magmatic reservoirs. These vapour bubbles can be the product of differential volumetric contraction between the melt inclusion and host phase during an eruption or indicate an excess fluid phase in the magma reservoir. Thus, determining the distribution of volatiles between melt and vapour bubbles is integral to our fundamental understanding of melt inclusions, and by extension the evolution of volatiles within magmatic systems.</p><p>A large dataset of 79 high-resolution tomographic scans of clinopyroxene and leucite phenocrysts from the Colli Albani Caldera Complex (Italy) was recently acquired at the German Electron Synchrotron (DESY). These tomograms allow us to quantify the volume of melt inclusions and associated vapour bubble both glassy and microcrystalline melt inclusions. Notably, in the glassy melt inclusions the vapour bubbles exist either as a single large vapour bubble in the middle of the melt inclusion or as several smaller vapour bubbles distributed around the edge of the melt inclusion. These two types of melt inclusions can coexist within a single crystal. We suggest that the occurrence of these rim- bubbles is caused by one of two exsolution pathways, either pre-entrapment and bubble migration or post entrapment with preferential exsolution at the rims. By combining the analysis of hundreds of melt inclusions with the chemistry of the host phase we aim to unveil magma ascent rates and distribution of excess fluids within the magmatic system of Colli Albani, which produced several mafic-alkaline large volume ignimbrites.</p>

scholarly journals Petrogenesis of Ultramafic Lamprophyres from the Terina Complex (Chadobets Upland, Russia): Mineralogy and Melt Inclusion Composition

Minerals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 419 ◽  
Author(s):  
Ilya Prokopyev ◽  
Anastasiya Starikova ◽  
Anna Doroshkevich ◽  
Yazgul Nugumanova ◽  
Vladislav Potapov
Keyword(s):  
Mineral Composition ◽  
Fractional Crystallization ◽  
Fluid Inclusions ◽  
Siberian Craton ◽  
Melt Inclusions ◽  
Melt Inclusion ◽  
Inclusion Composition ◽  
Accessory Minerals ◽  
Secondary Minerals ◽  
Peridotite Mantle

The mineral composition and melt inclusions of ultramafic lamprophyres of the Terina complex were investigated. The rocks identified were aillikites, mela-aillikites, and damtjernites, and they were originally composed of olivine macrocrysts and phenocrysts, as well as phlogopite phenocrysts in carbonate groundmass, containing phlogopite, clinopyroxene and feldspars. Minor and accessory minerals were fluorapatite, ilmenite, rutile, titanite, and sulphides. Secondary minerals identified were quartz, calcite, dolomite, serpentine, chlorite, rutile, barite, synchysite-(Ce), and monazite-(Ce). Phlogopite, calcite, clinopyroxene, Ca-amphibole, fluorapatite, magnetite, and ilmenite occurred as daughter-phases in melt inclusions. The melt inclusions also contained Fe–Ni sulphides, synchysite-(Ce) and, probably, anhydrite. The olivine macrocrysts included orthopyroxene and ilmenite, and the olivine phenocrysts included Cr-spinel and Ti-magnetite inclusions. Crystal-fluid inclusions in fluorapatite from damtjernites contain calcite, clinopyroxene, dolomite, and barite. The data that were obtained confirm that the ultramafic lamprophyres of the Terina complex crystallized from peridotite mantle-derived carbonated melts and they have not undergone significant fractional crystallization. The investigated rocks are considered to be representative of melts that are derived from carbonate-rich mantle beneath the Siberian craton.

The chlorine-isotopic composition of lunar KREEP from magnesian-suite troctolite 76535

2020 ◽  
Vol 105 (8) ◽  
pp. 1270-1274
Author(s):  
Francis M. McCubbin ◽  
Jessica J. Barnes
Keyword(s):  
Isotopic Composition ◽  
Melt Inclusions ◽  
Melt Inclusion ◽  
Isotopic Fractionation ◽  
Magma Ocean ◽  
Geochemical Composition ◽  
Isotopic Compositions ◽  
Stable Isotopic ◽  
Lunar Samples

Abstract We conducted in situ Cl isotopic measurements of apatite within intercumulus regions and within a holocrystalline olivine-hosted melt inclusion in magnesian-suite troctolite 76535 from Apollo 17. These data were collected to place constraints on the Cl-isotopic composition of the last liquid to crystallize from the lunar magma ocean (i.e., urKREEP, named after its enrichments in incompatible lithophile trace elements like potassium, rare earth elements, and phosphorus). The apatite in the olivine-hosted melt inclusion and within the intercumulus regions of the sample yielded Cl-isotopic compositions of 28.3 ± 0.9‰ (2σ) and 30.3 ± 1.1‰ (2σ), respectively. The concordance of these values from both textural regimes we analyzed indicates that the Cl-isotopic composition of apatites in 76535 likely represents the Cl-isotopic composition of the KREEP-rich magnesian-suite magmas. Based on the age of 76535, these results imply that the KREEP reservoir attained a Cl-isotopic composition of 28–30‰ by at least 4.31 Ga, consistent with the onset of Cl-isotopic fractionation at the time of lunar magma ocean crystallization or shortly thereafter. Moreover, lunar samples that yield Cl-isotopic compositions higher than the value for KREEP are likely affected by secondary processes such as impacts and/or magmatic degassing. The presence of KREEP-rich olivine-hosted melt inclusions within one of the most pristine and ancient KREEP-rich rocks from the Moon provides a new opportunity to characterize the geochemistry of KREEP. In particular, a broader analysis of stable isotopic compositions of highly and moderately volatile elements could provide an unprecedented advancement in our characterization of the geochemical composition of the KREEP reservoir and of volatile-depletion processes during magma ocean crystallization, more broadly.

Volatiles in basaltic magmas of ocean islands and their mantle sources: I. Melt compositions deduced from melt inclusions and glasses in the rocks

2007 ◽  
Vol 45 (2) ◽  
pp. 105-122 ◽  
Author(s):  
V. I. Kovalenko ◽  
V. B. Naumov ◽  
A. V. Girnis ◽  
V. A. Dorofeeva ◽  
V. V. Yarmolyuk
Keyword(s):  
Melt Inclusions ◽  
Mantle Sources ◽  
Basaltic Magmas ◽  
Ocean Islands
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