Review: Samples from the mantleReview: Samples from the mantle Ophiolites Dredge samples from oceanic crustNdldli hiblNodules and xenolithsin some basaltsKimberlite xenolithsKimberlite xenolithsMelting of the mantleMelting of the mantleIncreasing temperature:Intraplate igneousIncreasing temperature: Intraplate igneous activity (OIB, continental basalts etc.)DiDlDecreasing 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 Ridges5. Back-Arc Basinsg2. Intracontinental Rifts3. Island Arcs6. Ocean Island Basalts7. Miscellaneous Intra-4. Active Continental Margins 7. sce a eous t aContinental Activitykimberlites, carbonatites, th itganorthosites...Primary magmasyg Formed at depth and not subsequently modified by FX or AssimilationCriteriaCe Highest Mg# (100Mg/(Mg+Fe))E i t l lt f lh lit ltExperimental results of lherzolite melts Mg# = 66-75 Cr > 1000 ppm Ni > 400-500 ppmMagmatic diversification Partial meltingMagmatic diversificationg Fractional crystallization Magma mixing Assimilation AFC Soret effectDegree of partial meltingFigure 10.9 After Green and Ringwood (1967). Earth Planet. Sci. Lett. 2, 151-160.Fractional crystallization: gravity settling First Æ olivine layer at base of pluton if first olivine sinksolivine sinks Next Æ ol+cpx layer finally Æ ol+cpx+plagCumulate texture:Mutually touching ygphenocrysts with interstitial crystallized id l lresidual meltKilauea Iki lava lake, Hawaii: A b k l f diff i iThe Hawaiian IslandsA textbook example of magma differentiationKilauea Iki lava lakeKilauea Iki lava lake, Hawaii, USABefore eruptionAfter eruptionTeng et al. 08 ScienceCrystallization sequence of Kilaueasequence of Kilauea Iki lavasMgO = 11%: primitive magma11% > MgO > 7.5%: olivineHelz (1987)7.5% > MgO > 5%: augite+ plag5%> MgO: oxides MO 11%MgO > 11%: Olivine + primitive magmaTeng et al. 08 ScienceMagma MixingMagma MixingEnd member mixingfor a suite of rocksEnd member mixingfor a suite of rocks Mixing line: variation on Harker-type diagrams should lie on a straight linebetween the two most extreme compositionsComingled basalt-Rhyolite MtRhyolite Mt. McLoughlin, OregonFigure 11.8 From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice HallBasalt pillows accumulating at theaccumulating at the bottom of a granitic magma chamber, Vinalhaven Island, MaineAssimilation Incorporation of wall rocks: e.g., crustal rocks in pg,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 CrystallizationThe Soret Effect and hiiliffiThermogravitational Diffusion Thermal diffusion, or the Soret effect Heavy elements/molecules migrate toward the colder end and lighter ones to the hotter end of gthe gradient Heavy isotopes migrate toward the colder end and ypglighter ones to the hotter end of the gradientWalker and DeLong (1982) subjected two basalts to h l di f l 50C/ (!)thermal gradients of nearly 50oC/mm (!) Found that: Samples reached a steady state in a few days y Heavier 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 iifi tlf ti tit hilf ti lsignificantly fractionate isotopes while fractional crystallization generally does
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