Crystal fractionation and partial melting in the petrogenesis of a Proterozoic high-MgO volcanic suite, Ungava, Qu�bec

1981 ◽  
Vol 78 (1) ◽  
pp. 27-36 ◽  
Author(s):  
D. M. Francis ◽  
A. J. Hynes ◽  
J. N. Ludden ◽  
J. B�dard
Keyword(s):  
Partial Melting ◽  
Crystal Fractionation ◽  
Volcanic Suite

The petrologic evolution and pre-eruptive conditions of the rhyolitic Kos Plateau Tuff (Aegean arc)

2010 ◽  
Vol 2 (3) ◽  
Author(s):  
Olivier Bachmann
Keyword(s):  
Partial Melting ◽  
Magma Chamber ◽  
Mafic Magma ◽  
Shallow Depth ◽  
Volcanic Center ◽  
Crystal Fractionation ◽  
Calc Alkaline ◽  
Aegean Arc ◽  
Event Triggered

AbstractThe Kos Plateau Tuff is a large (>60 km3) and young (160 k.y.) calc-alkaline, high-SiO2 rhyolitic ignimbrite from the active Kos-Nisyros volcanic center in the Aegean arc (Greece). Combined textural, petrological and geochemical information suggest that (1) the system evolved dominantly by crystal fractionation from (mostly unerupted) more mafic parents, (2) the magma chamber grew over ≥ 250 000 years at shallow depth (∼1.5-2.5 kb) and was stored as a H2O-rich crystalline mush close to its solidus (∼670-750°C), (3) the eruption occurred after a reheating event triggered by the intrusion of hydrous mafic magma at the base of the rhyolitic mush. Rare banded pumices indicate that the mafic magma only mingled with a trivial portion of resident crystal-rich rhyolite; most of the mush was remobilized following partial melting of quartz and feldspars induced by advection of heat and volatiles from the underplated, hotter mafic influx.

scholarly journals Competing effects of spreading rate, crystal fractionation and source variability on Fe isotope systematics in mid-ocean ridge lavas

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Marianne Richter ◽  
Oliver Nebel ◽  
Martin Schwindinger ◽  
Yona Nebel-Jacobsen ◽  
Henry J. B. Dick
Keyword(s):  
Partial Melting ◽  
Upper Mantle ◽  
Crystal Fractionation ◽  
The Arctic ◽  
Iron Isotope ◽  
Mid Ocean Ridge ◽  
Fast Spreading ◽  
Ocean Ridge ◽  
Isotope Systematics ◽  
Source Heterogeneity

AbstractTwo-thirds of the Earth is covered by mid-ocean ridge basalts, which form along a network of divergent plate margins. Basalts along these margins display a chemical diversity, which is consequent to a complex interplay of partial mantle melting in the upper mantle and magmatic differentiation processes in lower crustal levels. Igneous differentiation (crystal fractionation, partial melting) and source heterogeneity, in general, are key drivers creating variable chemistry in mid-ocean ridge basalts. This variability is reflected in iron isotope systematics (expressed as δ57Fe), showing a total range of 0.2 ‰ from δ57Fe =  + 0.05 to + 0.25 ‰. Respective contributions of source heterogeneity and magma differentiation leading to this diversity, however, remain elusive. This study investigates the iron isotope systematics in basalts from the ultraslow spreading Gakkel Ridge in the Arctic Ocean and compares them to existing data from the fast spreading East Pacific Rise ridge. Results indicate that Gakkel lavas are driven to heavier iron isotope compositions through partial melting processes, whereas effects of igneous differentiation are minor. This is in stark contrast to fast spreading ridges showing reversed effects of near negligible partial melting effects followed by large isotope fractionation along the liquid line of descent. Gakkel lavas further reveal mantle heterogeneity that is superimposed on the igneous differentiation effects, showing that upper mantle Fe isotope heterogeneity can be transmitted into erupting basalts in the absence of homogenisation processes in sub-oceanic magma chambers.

The geochemistry of komatiites and basalts from the Deadman Hill area, Munro Township, Ontario, Canada

1987 ◽  
Vol 24 (5) ◽  
pp. 998-1008 ◽  
Author(s):  
Dante Canil
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Lower Degree ◽  
Crystal Fractionation ◽  
Trace Element Data ◽  
Garnet Lherzolite ◽  
Element Data ◽  
Hill Area ◽  
Partial Melts ◽  
Element Variation

A sequence of Archean komatiites (> 18 wt.% MgO), komatiitic basalts (10–18 wt.% MgO), high-Mg tholeiites (6–10 wt.% MgO), and high-Fe tholeiites (< 8 wt.% MgO) is exposed in the Deadman Hill area of Munro Township, Ontario, Canada. Major- and trace-element analyses of 28 samples are used to assess their petrogenetic significance. The use of molecular proportion ratio plots shows the samples have maintained their primary SiO2, FeO*, MgO, TiO2, Al2O3, Ni, Cr, Zr, Y, and V contents. Secondary redistribution of Na2O, K2O, Rb, Sr, Ba, and, in some samples, CaO has occurred.Covariation in both major- and trace-element data suggests the komatiites are primary melts that equilibrated with a harzburgite residua at pressures of 3–6 GPa. Garnet did not have a major role in their petrogenesis or in the petrogenesis of spatially related komatiitic basalts and high-Mg tholeiites. Major- and trace-element variation in komatiitic basalts with 17–12 wt.% MgO requires that they be partial melts in equilibrium with clinopyroxene at pressures of < 3 GPa. They are unrelated to the komatiites. Both lower degree partial melting of the same source as lavas with 17–12 wt.% MgO and crystal fractionation of clinopyroxene from liquids with ~12 wt.% MgO can model the evolution of less magnesian komatiitic basalts and high-Mg tholeiites. The Zr/Y and Zr/Ti ratios of the high-Fe tholeiites indicate that they are unrelated to the komatiites, komatiitic basalts, and high-Mg tholeiites and were derived by partial melting of a garnet lherzolite source.

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