Marc M. Hirschmann

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Hydrous melting driven by changes in H2O storage capacity may occur in a variety of settings in the mantle, including in oceanic basalt sources and in deeper regions above and below the transition zone. The 50–200 ppm H2O in the upper mantle likely derives from a blend of sources that may include residues of hydrous partial melting, either in the deep(More)
melting. This too can be demonstrated both by MELTS calculations We present a rigorous calculation of the isobaric entropy (S) change and by calculations in simple model systems. Productivities for of the melting reaction for peridotite (∂S/∂F ) P , where F is the systems enriched in incompatible components are systematically melt fraction. Calculations at(More)
[1] We present new experimentally determined trace element partition coefficients for nine garnet/melt and two clinopyroxene/melt pairs at 2.9–3.1 GPa and 1325 –1390 C, applicable to anhydrous partial melting of MORB-like eclogite in the upper mantle. Phase compositions are similar to those documented in partial melting experiments of eclogite at these(More)
The abrupt warming that took place in the late Paleocene Epoch (55 Ma) is one of the most pronounced, transient (<105 yr) climatic events in the geologic record (e.g., Zachos et al., 1993). Known as the late Paleocene thermal maximum (LPTM), this event was associated with dramatic changes in the Earth’s oceans, climate, and biosphere. High-latitude(More)
Composition, mean pressure, mean melt fraction, and crustal thickINTRODUCTION ness of model mid-ocean ridge basalts (MORBs) are calculated Comparison of observed basalt compositions with the using MELTS. Polybaric, isentropic batch and fractional melts predictions of polybaric mantle melting models places from ranges in source composition, potential(More)
Thermodynamic calculation of partial melting of peridotite using of the results of calculations of peridotite melting using MELTS, there are a number of shortcomings to application of this thermothe MELTS algorithm has the potential to aid understanding of a wide range of problems related to mantle melting. We review the dynamic model to calculations of(More)
The onset of partial melting beneath mid-ocean ridges governs the cycling of highly incompatible elements from the mantle to the crust, the flux of key volatiles (such as CO2, He and Ar) and the rheological properties of the upper mantle. Geophysical observations indicate that melting beneath ridges begins at depths approaching 300 km, but the cause of this(More)
Many oceanic-island basalts (OIBs) with isotopic signatures of recycled crustal components are silica poor and strongly nepheline (ne) normative and therefore unlike the silicic liquids generated from partial melting of recycled mid-oceanic-ridge basalt (MORB). High-pressure partial-melting experiments on a garnet pyroxenite (MIX1G) at 2.0 and 2.5 GPa(More)
The upper mantle is widely considered to be heterogeneous, possibly comprising a “marble-cake” mixture of heterogeneous domains in a relatively well-mixed matrix. The extent to which such domains are capable of producing and expelling melts with characteristic geochemical signatures upon partial melting, rather than equilibrating diffusively with(More)
A fundamental question regarding the dynamics of mantle convection is whether some intraplate volcanic centers, known as “hotspots,” are the surface manifestations of hot, narrow, thermally driven upwellings, or plumes, rising from the lower mantle. Shown here is a global negative correlation between the thickness of the mantle transition zone (near 410–660(More)