Review: Samples from the mantleReview: Samples from the mantle
Ophiolites
Dredge samples from oceanic crust
N d l d li h i b lNodules and xenoliths in some basalts
Kimberlite xenolithsKimberlite xenoliths
Melting of the mantleMelting of the mantleIncreasing temperature: Intraplate igneousIncreasing temperature: Intraplate igneous activity (OIB, continental basalts etc.)D i D lDecreasing pressure: Divergent plate boundaries (MORBs, rifts, back-arc basins
)etc.)Adding volatiles: Convergent plate boundaries (arc lavas, continental margins, etc.)
Plate Tectonic - Igneous Genesis g1. Mid-Ocean Ridges 5. Back-Arc Basinsg2. Intracontinental Rifts3. Island Arcs
6. Ocean Island Basalts7. Miscellaneous Intra-
4. Active Continental Margins
7. sce a eous t aContinental Activity
kimberlites, carbonatites, th it
ganorthosites...
Primary magmasy gFormed at depth and not subsequently modified by FX or AssimilationCriteriaC e
Highest Mg# (100Mg/(Mg+Fe))
E i t l lt f lh lit ltExperimental results of lherzolite meltsMg# = 66-75Cr > 1000 ppmNi > 400-500 ppm
Magmatic diversification
Partial melting
Magmatic diversification
g
Fractional crystallization
Magma mixing
Assimilation
AFC
Soret effect
Degree of partial melting
Figure 10.9 After Green and Ringwood (1967). Earth Planet. Sci. Lett. 2, 151-160.
Fractional crystallization: gravity settling
First olivine layer at base of pluton if first olivine sinksolivine sinks
Next ol+cpx layer
finally ol+cpx+plag
Cumulate texture:Mutually touching y gphenocrysts with interstitial crystallized
id l lresidual melt
Kilauea Iki lava lake, Hawaii: A b k l f diff i i
The Hawaiian IslandsA textbook example of magma differentiation
Kilauea Iki lava lake
Kilauea Iki lava lake, Hawaii, USA
Before eruption
After eruption
Teng et al. 08 Science
Crystallization sequence of Kilaueasequence of Kilauea Iki lavas
MgO = 11%: primitive magma
11% > MgO > 7.5%: olivine
Helz (1987)7.5% > MgO > 5%: augite+ plag
5%> MgO: oxides
M O 11%MgO > 11%: Olivine + primitive magma
Teng et al. 08 Science
Magma MixingMagma Mixing
End member mixing for a suite of rocksEnd member mixing for a suite of rocksMixing line: variation on Harker-type diagrams should lie on a straight linebetween the two most extreme compositions
Comingled basalt-Rhyolite MtRhyolite Mt.
McLoughlin, Oregon
Figure 11.8 From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall
Basalt pillows accumulating at theaccumulating at the bottom of a granitic
magma chamber, Vinalhaven Island,
Maine
Assimilation
Incorporation of wall rocks: e.g., crustal rocks in p g ,a basaltic magmaAssimilation by melting is limited by the heatAssimilation by melting is limited by the heat available in the magmaAFC: Assimilation and Fractional CrystallizationAFC: Assimilation and Fractional Crystallization
The Soret Effect and h i i l iff iThermogravitational Diffusion
Thermal diffusion, or the Soret effectHeavy elements/molecules migrate toward the colder end and lighter ones to the hotter end of gthe gradientHeavy isotopes migrate toward the colder end and y p glighter ones to the hotter end of the gradient
Walker and DeLong (1982) subjected two basalts to h l di f l 50 C/ (!)thermal gradients of nearly 50oC/mm (!)
Found that:Samples reached a steady state in a few days yHeavier elements → cooler end and the lighter → hotend and the lighter → hot endThe chemical concentrationThe chemical concentration is similar to that expected from fractionalfrom fractional crystallization
Figure 7.4. After Walker, D. C. and S. E. DeLong (1982). Contrib. Mineral. Petrol., 79, 231-240.
Richter et al (2008, 2009) show that Soret effect can i ifi tl f ti t i t hil f ti lsignificantly fractionate isotopes while fractional
crystallization generally does not