Magmatic Processes • Some useful definitions: – Primary magma Primary magma: magma originating in (mantle) source directly from melting – Primitive magma Primitive magma: magma that underwent minimal differentiation – Parental magma Parental magma: least differentiated magma in a series leading to evolved rocks • Liquid line of descent Liquid line of descent: relates series of liquids derived from single parent magma Magmatic Processes From: Wilson (1989) Igneous Petrogenesis Stagnation Stagnation • wallrock wallrock- magma density contrast magma density contrast • pooling coalescence in chamber pooling coalescence in chamber • solidification into solidification into pluton pluton? Partial melting Magma Ascent Eruption ?
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Magmatic Processes - Richard Allenrallen.berkeley.edu/teaching/F04_GEO302_PhysChemEarth/Lectures/lec...3 Magmatic Processes From: Wilson (1989) Igneous Petrogenesis Fractional crystallization
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Magmatic Processes
• Some useful definitions:–– Primary magmaPrimary magma: magma originating in (mantle) source
directly from melting
–– Primitive magmaPrimitive magma: magma that underwent minimal differentiation
–– Parental magmaParental magma: least differentiated magma in a series leading to evolved rocks
•• Liquid line of descentLiquid line of descent: relates series of liquids derived from single parent magma
Magmatic Processes
From: Wilson (1989) Igneous Petrogenesis
StagnationStagnation•• wallrockwallrock--magma density contrastmagma density contrast•• pooling coalescence in chamberpooling coalescence in chamber•• solidification into solidification into plutonpluton??
Partial melting
Magma Ascent
Eruption ?
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Magma DifferentiationMagma Differentiationhow do we get from here to there?how do we get from here to there?
–– crystallization releases latent heat needed to melt rocks crystallization releases latent heat needed to melt rocks surrounding the magmasurrounding the magma
•• Fractional CrystallizationFractional Crystallization– Separation of crystals from liquid – Gravitative settling or flotation play a significant role
Magma DifferentiationMagma Differentiation
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Magmatic Processes
From: Wilson (1989) Igneous Petrogenesis
Fractional crystallization of basaltFractional crystallization of basalt•• liquid line of descent: illustrated major element variationliquid line of descent: illustrated major element variation
Fractional crystallization of basaltFractional crystallization of basalt•• liquid line of descent: illustration of trace element variationliquid line of descent: illustration of trace element variation
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•• Assimilation Assimilation "" Fractional CrystallizationFractional Crystallization– Reaction/dissolution of wallrock– Crystallization provides heat for reaction– Can strongly modify trace element concentrations in magma
– If isotopic contrastIs large between wallrock and magma,isotopic ratios of the magma change
? Where might this beMost significant ?
Magma DifferentiationMagma Differentiation
• Quantifying crustal contamination (AFC) – Amount of assimilation limited by thermal energy of
magma— latent heat of xtlln —maximum is 10-20% – For crustal magma chamber undergoing fractional
crystallization, trace element behavior is described by:
where: CoL is conc. of TE in original magma, C* is conc. of TE in
contaminant, r is ratio of rate of assimilation to rate of fractional xtlln, D is the bulk distribution coefficient for the fractionating assemblage, and f is F –[(r-1+D)/(r-1)] and F is fraction of magma remaining.
– For any radiogenic isotope, ratio in the magma will be:
where εoL is isotope ratio in original magma, ε* is ratio of contaminant
)1(1 * fC
DrrfCC o
LL −•+−
+=
)1)((0
* fCC
LL
oLL
L−−+= εεεε
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From: Wilson (1989) Igneous Petrogenesis
AssimilationAssimilation--Fractional crystallization of basaltFractional crystallization of basalt•• liquid line of descent: illustration of trace element variationliquid line of descent: illustration of trace element variation
incompatible vs. compincompatible vs. compatible elementsatible elements
• Trace element modeling of magma series– Assimilation-Fractional Crystallization of basalt in the crust