Compositional gaps in igneous rock suites controlled by magma system heat and water content

Melekhova, Elena; Annen, Catherine; Blundy, Jon

doi:10.1038/ngeo1781

Cited by 82 publications

(69 citation statements)

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“…As crustal melting is widely believed to occur at the crustmantle boundary [34][35][36] , mixing possibilities were also tested at high pressures (0.7-1 GPa), exploring two situations: mixing between basalt and a discrete felsic layer (Fig. 5e,f), as would arise from a compaction-segregation process of a partially melted crustal layer 35 , and mixing between basalt and a partially melted, but unsegregated, metamorphic rock (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…For more felsic reservoirs, dacitic or rhyolitic, the onset of mixing requires a larger mass fraction, , , Figure 4 | Evolution of magma viscosity with temperature. The melt fraction trends and compositions needed for viscosity calculations are derived from the phase equilibrium works 36,[44][45][46][47][48][49][50] . Melt viscosities (that is, the straight lines in the high temperature part of each curve) differ by o2 orders of magnitude of each other.…”

Section: Resultsmentioning

confidence: 99%

“…Systems characterized by relatively low magma fluxes will, in contrast, produce bimodal magmatic provinces, if mixing is the main driver of magma compositional diversity. Recent modelling studies have concluded that magmatic bimodality is favoured by volatiles-poor magmas and low-heat input 36 . The present work reinforces and adds a rheological dimension to such a paradigm, showing that low-heat input and bubble-free regime inhibit efficient small-scale homogenization, thus preserving magma diversity.…”

Section: Discussionmentioning

confidence: 99%

“…These results are then combined with recent phase equilibria of magmas to evaluate the optimum conditions, leading to efficient mixing, that is, hybrids, when mafic and felsic magmas come into contact during single-intrusive events. We consider both lower and upper crust conditions, as mixing may occur at virtually all stages of magma evolution, either during emplacement in upper crust [28][29][30] , including before eruptions [31][32][33] , or in the deep crust [34][35][36] . In our modelling, we explore specifically the roles of mafic/felsic mass ratio, shear rate at the felsic-mafic interface and amount of gas, showing that mixing is promoted by higher values of any of these parameters.…”

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confidence: 99%

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On the conditions of magma mixing and its bearing on andesite production in the crust

et al. 2014

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Mixing between magmas is thought to affect a variety of processes, from the growth of continental crust to the triggering of volcanic eruptions, but its thermophysical viability remains unclear. Here, by using high-pressure mixing experiments and thermal calculations, we show that hybridization during single-intrusive events requires injection of high proportions of the replenishing magma during short periods, producing magmas with 55-58 wt% SiO 2 when the mafic end-member is basaltic. High strain rates and gas-rich conditions may produce more felsic hybrids. The incremental growth of crustal reservoirs limits the production of hybrids to the waning stage of pluton assembly and to small portions of it. Large-scale mixing appears to be more efficient at lower crustal conditions, but requires higher proportions of mafic melt, producing more mafic hybrids than in shallow reservoirs. Altogether, our results show that hybrid arc magmas correspond to periods of enhanced magma production at depth.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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On the conditions of magma mixing and its bearing on andesite production in the crust

et al. 2014

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“…Relatively early silica enrichment during fractional crystallization is driven by the crystallization of silica-poor minerals such as hornblende, garnet, An-rich plagioclase, and oxides for the calc-alkaline series Müntener et al, 2001;Sisson and Grove, 1993;Sisson et al, 2005) or biotite, apatite, and oxides from high-K hydrous melts (Esperança and Holloway, 1987;Righter and Carmichael, 1996). Often silica enrichment occurs rather rapidly upon multiple saturation of these low-Si minerals with other crystallized phases (e.g., plagioclase or pyroxenes) Melekhova et al, 2013;. The effect of an early increase in silica content is observed in the increase of modeled δ 18 O of hydrous basalts at higher F (Fig.…”

Section: Modeling Results Compared To Datamentioning

confidence: 84%

Chemical, isotopic, and temporal variations during crustal differentiation : insights from the Dariv Igneous Complex, Western Mongolia

Bucholz¹

2016

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Fractional crystallization of mantle-derived basaltic melts is a critical process in producing a compositionally stratified continental crust characterized by a silicic upper crust and a mafic lower crust. This thesis explores outstanding questions associated with fractional crystallization through detailed field, petrological, and geochemical studies of the Dariv Igneous Complex in Western Mongolia. The Dariv Igneous Complex records the crystallization of a high-K primitive arc melt at shallow crustal levels, preserving both biotite-bearing ultramafic and mafic cumulates, as well as liquid-like evolved plutonics, such as (quartz-)monzonites. Chapter 2 presents comprehensive field and petrographic descriptions of the complex and establishes the petrogenetic groundwork to understand the conditions under which it formed. Results of this study indicate that the observed lithologies formed through the fractional crystallization of a high-K hydrous basalt, typical of alkali-rich basalts found in subduction zone settings, at 0.2-0.5 GPa and elevated oxygen fugacities. Chapter 3 presents a quantitatively modeled liquid line of descent (LLD) for the complex based on whole rock geochemical analyses, which is able to explain the trends observed in the monzonitic plutonic series observed in continental arcs. The oxygen isotope trajectory of fractionally crystallizing melts is rigorously constrained through modeling and mineral analyses in Chapter 4. This study indicates that large (1 to 1.8‰) increases in δ 18 O as a melt evolves from basaltic to granitic in composition due to the fractionation of low δ 18 O minerals. As such, the majority of δ 18 O values of upper crustal silicic plutonics can be explained through fractional crystallization of primitive arc basalts alone without needing to invoke assimilation of high δ 18 O crustal material. Finally, Chapter 5 explores the timescales associated with fractional crystallization through high precision U-Pb geochronology of zircon from the Dariv Igneous Complex. Evolution from a basaltic melt to a silica-rich monzonitic melt in the Dariv Igneous Complex occurred in <300 ka. If rates of fractional crystallization are primarily a function of cooling, this study provides an end-member constraint for fractional crystallization of a basaltic melt at relatively cool, shallow crustal levels. Together, these studies advance our understanding of the compositional, isotopic, and temporal variations associated with the formation of the continental crust.

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The competing effects of sulfide saturation versus degassing on the behavior of the chalcophile elements during the differentiation of hydrous melts

Jenner

Hauri

Bullock

et al. 2015

Geochem Geophys Geosyst

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There is a lack of consensus regarding the roles of sulfide saturation versus volatile degassing on the partitioning of Cu and Ag during differentiation and eruption of convergent margin magmas. Because of their oxidized character, volatile-rich magmas from the Eastern Manus Back-arc Basin (EMBB) only reach sulfide saturation following magnetite-driven reduction of the melt: the so-called ''magnetite crisis.'' If sulfide saturation typically precedes volatile saturation, the magnetite crisis will limit the proportion of Cu and Ag that can partition from the melt into an exsolving volatile-rich phase, which may contribute to the sporadic occurrence of magmatic-hydrothermal ore deposits at convergent margins. However, it is unclear whether the magnetite crisis is a common or rare event during differentiation of volatile-rich magmas. We report major and trace element data for submarine volcanic glasses from the Tonga arc-proximal Valu Fa Ridge (VFR; SW Pacific). Cu-Se-Ag systematics of samples erupting at the southern VFR suggest magnetite fractionation-triggered sulfide saturation. The similarity in chalcophile element systematics of the southern VFR and EMBB samples is unlikely to be coincidental, and may indicate that the magnetite crisis is a common event during differentiation of hydrous melts. However, unlike many convergent margin magmas, it is unlikely that the evolving VFR and EMBB were saturated in a S-bearing volatile phase prior to magnetite fractionation. Hence, the metal-depleting magnetite crisis may be restricted to back-arc basin magmas that do not degas volatiles prior to magnetite fractionation and potentially convergent margin magmas fractionating at high pressures in the continental crust.

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Compositional gaps in igneous rock suites controlled by magma system heat and water content

Cited by 82 publications

References 28 publications

On the conditions of magma mixing and its bearing on andesite production in the crust

On the conditions of magma mixing and its bearing on andesite production in the crust

Chemical, isotopic, and temporal variations during crustal differentiation : insights from the Dariv Igneous Complex, Western Mongolia

The competing effects of sulfide saturation versus degassing on the behavior of the chalcophile elements during the differentiation of hydrous melts

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