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