Fluid Dynamic Processes in Basaltic Magma Chambers

1996 ◽  
pp. 45-76 ◽  
Author(s):  
I.H. Campbell
Keyword(s):  
Fluid Dynamic ◽  
Basaltic Magma ◽  
Dynamic Processes ◽  
Magma Chambers

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 for ascent of differentiated liquids in a silicic magma chamber found in a granitic pluton

1992 ◽  
Vol 83 (1-2) ◽  
pp. 63-69 ◽  
Author(s):  
Gail A. Mahood ◽  
Paula C. Cornejo
Keyword(s):  
Fluid Dynamic ◽  
Volcanic Rocks ◽  
Dynamic Modelling ◽  
Wall Rock ◽  
Main Body ◽  
Passive Mode ◽  
Magma Chambers ◽  
Fractionation Model ◽  
Physical Features ◽  
Melt Segregation

ABSTRACTFluid dynamic modelling of crystallising calc-alkalic magma bodies has predicted that differentiated liquids will ascend as boundary layers and that accumulation of these buoyant liquids near chamber roofs will result in compositionally stratified magma chambers. This paper reports physical features in La Gloria Pluton that can be interpreted as trapped ascending differentiated liquids. Leucogranitic layers decimetres thick, which are locally stratified, are trapped beneath overhanging wall contacts. The same felsic magmas were also preserved where they were injected into the wall rocks as dykes and as large sill complexes. These rocks do not represent differentiated magmas produced by crystallisation along the exposed walls because the felsic layers occur at the wall rock contact, not inboard of it. Rather, we speculate that evolved felsic liquids are generated by crystallisation all across the deep levels of chambers and that initial melt segregation occurs by flowage of melt into tension fractures. Melt bodies so formed may be large enough to have significant ascent velocities as diapirs and/or dykes. The other way in which the leucogranite occurrence is at variance with the convective fractionation model is that the ascending liquids did not feed a highly differentiated cap to the chamber, as the composition at the roof, although the most felsic in this vertically and concentrically zoned pluton, is considerably more mafic than the trapped leucogranitic liquids. This suggests that these evolved liquids were usually mixed back into the main body of the chamber. Backmixing may be general in continental-margin calc-alkalic magmatic systems, which, in contrast to those in intracontinental settings, rarely produce volcanic rocks more silicic than rhyodacite. That the highly differentiated liquids are preserved at all at La Gloria is a result of the unusual stepped nature of the contact and the entirely passive mode of emplacement of the pluton, which, in contrast to ballooning in place, does not result in wall zones being “scoured”.

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.

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