Igneous Layering in Basaltic Magma Chambers

2015 ◽  
pp. 75-152 ◽  
Author(s):  
O. Namur ◽  
Bénédicte Abily ◽  
Alan E. Boudreau ◽  
Francois Blanchette ◽  
John W. M. Bush ◽  
...  
Keyword(s):  
Basaltic Magma ◽  
Magma Chambers ◽  
Igneous Layering

Origin of non-cotectic cumulates: A novel approach

Geology ◽  
2020 ◽  
Vol 48 (6) ◽  
pp. 604-608 ◽  
Author(s):  
R.M. Latypov ◽  
S.Yu. Chistyakova
Keyword(s):  
Phase Equilibria ◽  
Basaltic Magma ◽  
Parental Magma ◽  
Magma Chambers ◽  
Mechanical Mixing ◽  
Novel Approach ◽  
In Situ Crystallization ◽  
Mechanical Separation ◽  
Novel Concept

Abstract Plutonic mafic complexes are composed of cumulates in which minerals mostly occur in cotectic proportions. This is consistent with a concept that basaltic magma chambers predominantly crystallize in situ from margins inward. However, cumulates with two (or more) minerals in proportions that are at odds with those expected from liquidus phase equilibria also locally occur in these complexes. Such non-cotectic cumulates are commonly attributed to either mechanical separation of minerals crystallizing from the same parental magma or mechanical mixing of minerals originating from different parental magmas. Here we introduce a novel concept that does not require any of these processes to produce non-cotectic cumulates. The model involves melts that start crystallizing upon their cooling, while ascending along feeder conduits from deep staging reservoirs toward the Earth’s surface. Depending on the degree of cooling, the melts become successively saturated in one, two, and more liquidus phases. Given that most crystals are kept in suspension, the resulting magmas would contain a cargo of equilibrium phenocrysts in notably non-cotectic proportions. The replenishment of basaltic chambers developing through in situ crystallization by such magmas is likely responsible for the occasional formation of non-cotectic cumulates in plutonic mafic complexes.

Flow mechanism and viscosity in basaltic magma chambers

1996 ◽  
Vol 23 (16) ◽  
pp. 2013-2016 ◽  
Author(s):  
A. Nicolas ◽  
B. Ildefonse
Keyword(s):  
Basaltic Magma ◽  
Flow Mechanism ◽  
Magma Chambers

Evidence in Variscan Corsica of a brief and voluminous Late Carboniferous to Early Permian volcanic-plutonic event contemporaneous with a high-temperature/low-pressure metamorphic peak in the lower crust

2015 ◽  
Vol 186 (2-3) ◽  
pp. 171-192 ◽  
Author(s):  
Philippe Rossi ◽  
Alain Cocherie ◽  
C. Mark Fanning
Keyword(s):  
High Temperature ◽  
Basaltic Magma ◽  
Low Pressure ◽  
Calc Alkaline ◽  
Magma Chambers ◽  
Zircon Dating ◽  
North West ◽  
Deep Crust ◽  
Field Evidence ◽  
Exposed Part

Abstract The U2 group of plutonic rocks constituting the main exposed part of the Corsica-Sardinia batholith (CSB) was emplaced from 308 to 275 Ma (the early Visean U1 group of Mg-K intrusions is not considered here). Field evidence earlier established volcanic-plutonic relationships in the U2 group of calc-alkaline intrusions of the CSB, though detailed chronological data were still lacking. Large outcrops of U2 volcanic formations are restricted to the less eroded zone north-west of the Porto-Ponte Leccia line in Corsica, but volcanic and volcano-sedimentary formations were widely eroded elsewhere since Permian times. They probably covered most of the batholith before the Miocene, as testified by the volcanic nature of the pebbles that form much of the Early Miocene conglomerates of eastern Corsica. U-Pb zircon dating (SHRIMP) was used for deciphering the chronology and duration of different volcanic pulses and for better estimating the time overlap between plutonic and volcanic rock emplacement in the CSB. The obtained ages fit well with field data, showing that most of the U2 and U3 volcanic formations were emplaced within a brief time span of roughly 15 m.y., from 293 to 278 Ma, coeval with most U2 monzogranodiorites and leucomonzogranites (295–280 Ma), alkaline U3 complexes (about 288 Ma), and mafic-ultramafic tholeiitic complexes (295–275 Ma). The same chronological link between deep-seated magma chambers and eruptions was identified in the Pyrenees. These results correlate with U-Pb zircon dating of HT-LP granulites from the Variscan deep crust exhumed along the “European” margin of the thinned Tethys margin in Corsica and Calabria. Here, the peak of the low-pressure/high-temperature metamorphism was dated at about 285–280 Ma. Our results throw light on the condition of magma production during the orogenic collapse in the southern Variscan realm. While juvenile tholeiitic basaltic magma was produced by the melting of spinel mantle lithosphere, all fertile protoliths melted in a brief period during the HT-LP peak in lower continental crust, leading to massive emplacement of large felsic U2 calc-alkaline and minor U3 A-type volcano-plutonic formations over about 15 Ma.

Mafic-silicic layered intrusions: the role of basaltic injections on magmatic processes and the evolution of silicic magma chambers

1996 ◽  
Vol 87 (1-2) ◽  
pp. 233-242 ◽  
Author(s):  
R. A. Wiebe
Keyword(s):  
Basaltic Magma ◽  
Mafic Magma ◽  
Silicic Magma ◽  
Granitic Magma ◽  
Magma Chambers ◽  
Mechanical Mixing ◽  
Diffusive Convection ◽  
Type Granite ◽  
Mafic Magmas ◽  
Silicic Magmas

ABSTRACT:Plutonic complexes with interlayered mafic and silicic rocks commonly contain layers (1–50 m thick) with a chilled gabbroic base that grades upwards to dioritic or silicic cumulates. Each chilled base records the infusion of new basaltic magma into the chamber. Some layers preserve a record of double-diffusive convection with hotter, denser mafic magma beneath silicic magma. Processes of hybridisation include mechanical mixing of crystals and selective exchange of H2O, alkalis and isotopes. These effects are convected away from the boundary into the interiors of both magmas. Fractional crystallisation aad replenishment of the mafic magma can also generate intermediate magma layers highly enriched in incompatible elements.Basaltic infusions into silicic magma chambers can significantly affect the thermal and chemical character of resident granitic magmas in shallow level chambers. In one Maine pluton, they converted resident I-type granitic magma into A-type granite and, in another, they produced a low-K (trondhjemitic) magma layer beneath normal granitic magma. If comparable interactions occur at deeper crustal levels, selective thermal, chemical and isotopic exchange should probably be even more effective. Because the mafic magmas crystallise first and relatively rapidly, silicic magmas that rise away from deep composite chambers may show little direct evidence (e.g. enclaves) of their prior involvement with mafic magma.

The fluid dynamics of crustal melting by injection of basaltic sills

1988 ◽  
Vol 79 (2-3) ◽  
pp. 237-243 ◽  
Author(s):  
Herbert E. Huppert ◽  
R. Stephen ◽  
J. Sparks
Keyword(s):  
Continental Crust ◽  
Basaltic Magma ◽  
Source Region ◽  
Thermal Relaxation ◽  
Silicic Magma ◽  
Granitic Magma ◽  
Low Density ◽  
Magma Chambers ◽  
Theoretical Investigations ◽  
High Level

ABSTRACTWhen basaltic magma is emplaced into continental crust, melting and generation of granitic magma can occur. We present experimental and theoretical investigations of the fluid dynamical and heat transfer processes at the roof and floor of a basaltic sill in which the wall rocks melt. At the floor, relatively low density crustal melt rises and mixes into the overlying magma, which would form hybrid andesitic magma. Below the roof the low-density melt forms a stable layer with negligible mixing between it and the underlying hotter, denser magma. Our calculations applied to basaltic sills in hot crust predict that sills from 10-1500 m thick require only 2-200 years to solidify, during which time large volumes of overlying layers of convecting silicic magma are formed. These time scales are very short compared with the lifetimes of large silicic magma systems of around 106 years, and also with the time scale of 107 years for thermal relaxation of the continental crust. An important feature of the process is that crystallisation and melting occur simultaneously, though in different spots of the source region. The granitic magmas formed are thus a mixture of igneous phenocrysts and lesser amounts of restite crystals. Several features of either plutonic or volcanic silicic systems can be explained without requiring large, high-level, long-lived magma chambers.

Dissolving driven by vigorous compositional convection

1994 ◽  
Vol 280 ◽  
pp. 287-302 ◽  
Author(s):  
Ross C. Kerr
Keyword(s):  
Boundary Layer ◽  
Basaltic Magma ◽  
Critical Rayleigh Number ◽  
Scaling Analysis ◽  
Magma Chambers ◽  
Boundary Layer Instability ◽  
Fluid Concentration ◽  
The One ◽  
Rayleigh Benard ◽  
Compositional Convection

The one-dimensional dissolution that occurs when a binary melt is placed above or below a solid of a different composition is examined both theoretically and experimentally. In the case considered, the dissolution is driven by vigorous compositional convection that results from a Rayleigh-Bénard instability of the compositional boundary layer in the vicinity of the dissolving solid. A scaling analysis is used to derive theoretical expressions for both the dissolving velocity and the interfacial fluid concentration. Laboratory experiments are also described in which ice is dissolved when it is overlain or underlain by aqueous solutions. The measured dissolving velocities are consistent with the theoretical expressions, and yield estimates of the critical Rayleigh number for boundary-layer instability. The results of this study are then applied to predict the rate at which dissolution will occur when undersaturated mixed magmas are generated during the periodic replenishment of large basaltic magma chambers in the Earth's crust.

Assimilation and crystallization in basic magma chambers: trace-element and Nd-isotopic variations in the Kerns sill, Nipissing diabase province, Ontario

1989 ◽  
Vol 26 (4) ◽  
pp. 737-754 ◽  
Author(s):  
Peter C. Lightfoot ◽  
Anthony J. Naldrett
Keyword(s):  
Trace Element ◽  
Incompatible Element ◽  
Basaltic Magma ◽  
Basic Magma ◽  
Magma Chambers ◽  
Degree Of Contamination ◽  
Incompatible Elements ◽  
Laboratory Investigations ◽  
Isotopic Variations ◽  
Isotopic Effects

An investigation has been made of the trace-element and Nd-isotopic effects of assimilation at the roof of the Proterozoic Kerns sill in the 2.2 Ga Nipissing diabase province in Ontario. The ratios Th/Zr, La/Zr, and U/Zr and the concentrations of incompatible elements all tend to increase with decreasing Mg#, Ni, and Cr. These variations have been simulated by computer models in which assimilation and fractionation are coupled (AFC) and the most fractionated magmas (identified by low Mg#, Ni, and Cr and by high incompatible-element concentrations) are also the most contaminated (indicated by higher Th/Zr, La/Zr, and U/Zr and lower 143Nd/144Ndo). The results suggest that the ratio (r) of the change of magma mass due to assimilation relative to the change due to fractionation gradually increased. The latent heat of crystallization may have contributed sufficient heat to melt the roof of the intrusion where ponded crustal melts were separated from the underlying basic magma by a double-diffusive interface. Field relations suggest that this interface was progressively destroyed by convective erosion; thus the degree of contamination increased as the magma became more fractionated. These results are consistent with laboratory investigations designed to simulate assimilation at the roof of basaltic magma chambers.

Igneous layering in a dacite: on the origin and significance of Layer Cake Mountain, Kelowna, B.C., Canada

1998 ◽  
Vol 62 (6) ◽  
pp. 731-742 ◽  
Author(s):  
J. D. Greenough ◽  
J. V. Owen
Keyword(s):  
Major Elements ◽  
Fault Scarp ◽  
Thin Layers ◽  
Magma Chambers ◽  
Mafic Lava ◽  
Land Form ◽  
Layer Cake ◽  
Small Primary ◽  
Thick Layers ◽  
Igneous Layering

AbstractA Tertiary, dacitic volcanic land-form in Kelowna, British Columbia, shows layering that has not been recognized elsewhere. Layering is expressed as thin (0.5 m) layers separated by thick (4.5 m) layers exposed along a weathered fault scarp. The major elements show that both thick and thin layers are dacitic and geochemically very similar. Trace element modelling indicates that thin layers formed from thick layers via crystal fractionation involving removal of plagioclase, biotite and magnetite in the proportions 75:20:5, and with only 12% fractionation. The thin layers represent segregation veins generated during crystallization of the dacite. They formed when the crystal mush at the bottom of the upper crust successively, thermally contracted, fractured and foundered, siphoning evolved interstitial liquid from the mush into the horizontal crack. Cooling of the segregation veins led to further fracturing. Later, fluids following these fractures altered the thin layers and precipitated secondary carbonate minerals. The altered thin layers weather preferentially, thus visually accentuating the small primary chemical differences between thick and thin layers. The scale of layering, mode of formation and differentiation mechanisms appear different from those in felsic magma chambers and it is unclear how common this phenomenon is. However, similar layering is more easily identified and commonly developed in mafic lava flows.

All at Sea

2018 ◽  
Author(s):  
Roy Livermore
Keyword(s):  
Plate Tectonics ◽  
First Generation ◽  
Basaltic Magma ◽  
Ocean Floor ◽  
Tennis Ball ◽  
Magma Chambers ◽  
Transform Faults ◽  
Ocean Ridges ◽  
Sea Floor Spreading ◽  
Ocean Ridge

According to first-generation plate tectonics, sea-floor spreading was nice and simple. Plates were pulled apart at mid-ocean ridges, and weak mantle rocks rose to fill the gap and began to melt. The resulting basaltic magma ascended into the crust, where it ponded to form linear ‘infinite onion’ magma chambers beneath the mid-ocean tennis-ball seam. At frequent intervals, vertical sheets of magma rose from these chambers to the surface, where they erupted to form new ocean floor or solidified to form dykes, in the process acquiring a magnetization corresponding to the geomagnetic field at the time. Mid-ocean ridge axes were defined by rifted valleys and divided into segments by transform faults with offsets of tens to hundreds of kilometres, resulting in the staircase pattern seen on maps of the ocean floor. All mid-ocean ridges were thus essentially identical. Such a neat and elegant theory was bound to be undermined as new data were acquired in the oceans.

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