The available experimental data and steady-state calculations make it difficult to explain the M discontinuity beneath both oceans and continents on the basis of the same phase change. The oceanic M discontinuity may be a chemical discontinuity between basalt and peridotite , and a similar chemical discontinuity ma,y thus be expected b�neath the conti­ nents. Since ayailable experimental data p...

The kinetics of the reaction of majorite plus ferropericlase to ringwoodite: Implications for mantle upwellings crossing the 660 km discontinuity a r t i c l e i n f o a b s t r a c t Keywords: 660 km discontinuity reaction kinetics perovskite ringwoodite majorite We have measured the kinetics of reaction between MgO and majoritic garnet at 20 GPa and 1773–2123 K as a proxy for the reaction bet...

Zoned, silica-deficient, calcic garnets containing up to 5 mol% F substitution for 0 formed during contact metamorphism of basalts by the Skaergaard intrusion in East Greenland. Fluorian calcic garnets occur as a retrograde alteration of prograde wollastonite and clinopyroxene that fills vesicles and vugs in lavas 30-70 m from the intrusion. Paragenetically equivalent phases include fluorite, w...

We present thermodynamic estimates of pressures, temperatures, and volatile activities in vailably deformed, gabbroic to granitic, Cretaceous (115-100 Ma) batholithic and framework rocks of the Tehachapi Mountains, southernmost Sierra Nevada, California. A1 contents of hornblende in granitoids imply igneous emplacement at --8 kbar in the southernmost Tehachapi Mountains, with lower pressures (3...

The Bossòst dome is an E–W-trending elongated structural and metamorphic dome developed in Cambro-Ordovician metasedimentary rocks in the Variscan Axial Zone of the central Pyrenees. A steep fault separates a northern half-dome, cored by massif granite, from an E–W-trending doubly plunging antiform with granitic sills and dykes in the core to the south. The main foliation is a flat-lying S1/2 s...

S U M M A R Y This study applies high-resolution Radon transform to a large set of SS precursors and explores the mantle reflectivity structure beneath 17 potentially ‘deep-rooted’ hotspots. The combined reduced time (τ ) and ray parameter (p) information effectively constrains the depth, spatial distribution and sharpness of upper-/mid-mantle reflectors. The olivine to wadsleyite phase boundar...

Concentrations of OH, and major and trace elements were determined in a suite of mantle-derived megacrysts that represent the crystallization products of a kimberlite-like magma at 5 GPa and 1400---1100 C. OH concentrations, determined by singlecrystal Fourier transform infrared spectroscopy, display the following ranges (ppmw H2O): olivine 54---262, orthopyroxene 215---263, garnet 15---74, cli...

The trace element compositions of igneous augite preserved in metamorphosed komatiite samples from the lower Komati Formation, Barberton Mountainland, South Africa (3.49 Ga), were analyzed in order to estimate the pre-metamorphic bulk composition of the samples. The chemical effects of metamorphism are evaluated by calculating the trace element (TE) composition of a hypothetical augite in equil...

New mapping, geochronology, and geochemistry of the supracrustal enclave and associated orthogneisses at Akilia, West Greenland, support a >3825 6 Ma age for the sequence and a chemical sedimentary origin for the controversial Fe-rich quartz-pyroxene gneisses. Lithologies of the enclave comprise laterally continuous, mappable units of mafic amphibolite, ultramafic rocks, and two Fe-rich quartzp...

Experimental and geochemical studies were performed to understand the formation of certain terrestrial and lunar igneous rocks. Chapter one is a study of convergent margin magmatism at Medicine Lake Volcano, California. The petrogenesis of a suite of variably porphyritic, high-alumina lavas was inferred from field relations, hydrous melting experiments and geochemical modeling. I conclude that ...