AMNH EPS: MOR mantle melts
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Experimental Constraints on Melting of the Earth's Upper Mantle to Produce Oceanic Crust
Oceanic crust covers roughly 80% of the Earth's surface and is created through volcanic and tectonic processes at mid-ocean ridge spreading centers at the rate of approximately 20 cubic km per year. Thus volcanism at mid-ocean ridge spreading centers is volumetrically the most significant volcanism that occurs on earth. The magma which forms the oceanic crust through eruption and intrusion is likely the result of a dynamic, near-fractional melting process during which pressure, temperature and source composition change as melting proceeds.
In this research experiments have been carried out at pressures up to 3.0 GPa to investigate the effects of
pressure, temperature and variable bulk chemistry on the composition of melts produced by melting upper
mantle peridotite. The approach taken recognizes that these melts must be multiply saturated with the
minerals present in the upper oceanic mantle at the temperature and pressure at which they were
produced. Thus any experiment containing silicate melt in near equilibrium with the mantle minerals
olivine (ol), orthopyroxene (opx), clinopyroxene (cpx), and one or more of the aluminous phases
plagioclase, spinel (sp) or garnet places constraints on the mantle melting equilibrium. Two such
experiments reported in Kinzler (1997) carried out at 1.9 GPa and 1401 and 1416 degrees C on the same bulk
composition are pictured here, labeled a and b, respectively. While both experiments contain silicate
liquid coexisting with the minerals ol, opx, cpx, and sp, the lower temperature experiment (a) contains
less melt (~11% by weight) than the higher temperature experiment (b) (~58% by weight). Thus the two
experiments combined provide a direct estimate of the mantle melting reaction: 1.16 cpx + 0.09 sp + 0.14
ol = 1 liq + 0.38 opx. In addition, the compositions of the phases present in each experiment provide
information about the compositions of minerals and melts within the upper mantle.
References
- Kinzler, R.J., and T.L. Grove (1992) Primary magmas of mid-ocean ridge basalts, 1, Experiments and
Methods, J. Geophys. Res., 97, 6885-6906.
- Kinzler, R.J., and T.L. Grove (1992) Primary magmas of mid-ocean ridge basalts, 2, Applications, J.
Geophys. Res., 97, 6907-6926.
- Kinzler, R.J., (1995) Magmatism at ocean ridges, Reviews of Geophysics, Supplement, pages 63-69,
IUGG.
- Putirka, K., M. Johnson, R. Kinzler, J. Longhi, and D. Walker (1996) Thermobarometry of mafic igneous
rocks based on clinopyroxene-liquid equilibria, 0 - 30 kbar, Contrib. Mineral. Petrol., 123, 92-108.
- Yang, H-J., R.J. Kinzler, and T.L. Grove (1996) Experiments and models of anhydrous, basaltic olivine-
plagioclase-augite saturated melts from 0.001 to 10 kbar, Contrib. Mineral. Petrol., 124, 1-8.
- Kinzler, R.J., (1997) Melting of mantle peridotite at pressures approaching the spinel to garnet transition: Application to mid-ocean ridge basalt petrogenesis, J. Geophys. Res., 102, 853-874.
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