- Email: [email protected]
Outgassing of ocean-floor magma as a reflection of volatile conditions in the magma generation region
OLR (1984)31 (12)
D. SubmarineGeologyand Geophysics
basalts from the Marlana Islands. J. geol. Soc., Lond., 141(3):453-472. The authors attempt to answer questions about 'the destiny of sediments at convergent plate margins and the ultimate consequences of their recycling into the mantle' by analyzing REE and other trace elements in a series of pelagic clays and nannofossil oozes from the Nazca Plate. They then model the contribution of this material to the magmas of the intraoceanic Mariana Island Arc. They conclude that 'a ternary mixing between 0.4% sediment, 1.0% fluid derived from dehydrating ocean crust and 98.6% mantle host' is required and that 'significant volumes of sediment may be carried into the deeper mantle.' (amt) 84:6148 Marriner, G.F. and D. Millward, 1984. The petrology and geochemistry of Cretaceous to Recent volcanism in Colombia: the magmatic history of an accretiounry plate mar~n. J. geol. Soc., Lond., 141(3):473-486. Dept. of Geol., Bedford Coll., Univ. London, NW1 4NS, UK. 84:6149 McBimey, A.R. and Tsutomu Murase, 1984. Rheological properties of magmas. A. Rev. Earth planet. Sci., 12:337-357. Dept. of Geol., Univ. of Oregon, Eugene, Oreg. 97403, USA. 84:6150 Shilobreyeva, S.N., A.A. Kadik and O.A. Lukanin, 1983. Outgassing of ocean-floor magma as a reflection of volatile conditions in the magma generation region. Geochem. int. (a translation of Geokhimiya), 20(5):27-43.
The H20 and CO 2 contained in volcanic glasses are compared with the paths of these volatiles in magma outgassing associated with pressure reduction. It is shown that upper mantle rocks beneath the ocean are low in H20 and other volatiles if there is no interaction of magma and graphite at depth, and that mid-ocean ridge basalts have lower H20 and higher CO 2 concentrations than island arc magmas, suggesting a heterogeneous distribution of volatiles in the upper mantle under the ocean. Vernadskiy Inst. of Geochem. and Analy. Chem., Acad. of Sci. of the USSR. 0abf) 84:6151 Thirlwall, M.F. and A.M. Graham, 1984. Evolution of high--Ca, high-Sr C-series basalts from Grenada, Lesser Antilles: the effects of intracrustal contamination. J. geol. Soc., Lond., 141(3):427-445. Dept. of Earth Sci., Univ. of Leeds, Leeds 2, UK.
879
D290. Crust, mantle, core 84:6152 Banerjee, S.K., 1984. The magnetic layer of the ocean crust----how thick is it? Tectonophysics, 105(1/4): 15-27.
Special features of linear marine magnetic anomalies and the magnetic measurements made on samples of ocean crust require the thickness of the marine magnetic source layer to be thicker than the 0.5 km thick pillow lava layer (seismic layer 2A) alone. It is proposed that the magnetic properties of the samples studied to date indicate a two-layered source as the most likely: an upper 0.5 km thick pillow lava layer with NRM of 5 A / m and a lower 3.5 km thick dike and upper gabbro layer with a magnetization of 0.5 A/m. Dept. of Geol. and Geophys., Univ. of Minnesota, Minneapolis, Minn. 55455, USA. 84:6153 Beloussov, V.V., 1984. Certain problems of the structure and evolution of transition zones hetween continents and oceans. Tectonophysics, 105(1/4):79-102.
A type of continental-oceanic transition zone, the Columbian, is distinguished from two other common types of transition zones. Subsidence of the Earth's crust, typical of all transition zones, is shown to be connected (by geophysical properties) to the transformation of continental crust into intermediate crust and later into oceanic. The most likely mechanisms of such changes are the basification of continental crust; its foundering, block by block, into the heated upper mantle; and its substitution by new oceanic crust. Acad. of Sci., Soviet Geophys. Comm., Moscow B-296, USSR. 84:6154 Christensen, U.R. and D.A. Yuen, 1984. The interaction of a subducting lithospheric slab with a chemical or phase boundary. J. geophys. Res., 89(B6):4389-4402.
A finite element model of time-dependent convection employs temperature-dependent and non-Newtonian rheology to achieve platelike behavior of the upper and sinking thermal boundary layer of convection. The 650-km discontinuity is taken as a chemical and/or phase boundary. When the compositional density contrast >5%, the descending slab is deflected sideward at the boundary and two-layer convection prevails. Below 5% density difference the slab plunges several hundred kilometers into the lower mantle, and below 2% it will probably not stop
D. SubmarineGeologyand Geophysics
basalts from the Marlana Islands. J. geol. Soc., Lond., 141(3):453-472. The authors attempt to answer questions about 'the destiny of sediments at convergent plate margins and the ultimate consequences of their recycling into the mantle' by analyzing REE and other trace elements in a series of pelagic clays and nannofossil oozes from the Nazca Plate. They then model the contribution of this material to the magmas of the intraoceanic Mariana Island Arc. They conclude that 'a ternary mixing between 0.4% sediment, 1.0% fluid derived from dehydrating ocean crust and 98.6% mantle host' is required and that 'significant volumes of sediment may be carried into the deeper mantle.' (amt) 84:6148 Marriner, G.F. and D. Millward, 1984. The petrology and geochemistry of Cretaceous to Recent volcanism in Colombia: the magmatic history of an accretiounry plate mar~n. J. geol. Soc., Lond., 141(3):473-486. Dept. of Geol., Bedford Coll., Univ. London, NW1 4NS, UK. 84:6149 McBimey, A.R. and Tsutomu Murase, 1984. Rheological properties of magmas. A. Rev. Earth planet. Sci., 12:337-357. Dept. of Geol., Univ. of Oregon, Eugene, Oreg. 97403, USA. 84:6150 Shilobreyeva, S.N., A.A. Kadik and O.A. Lukanin, 1983. Outgassing of ocean-floor magma as a reflection of volatile conditions in the magma generation region. Geochem. int. (a translation of Geokhimiya), 20(5):27-43.
The H20 and CO 2 contained in volcanic glasses are compared with the paths of these volatiles in magma outgassing associated with pressure reduction. It is shown that upper mantle rocks beneath the ocean are low in H20 and other volatiles if there is no interaction of magma and graphite at depth, and that mid-ocean ridge basalts have lower H20 and higher CO 2 concentrations than island arc magmas, suggesting a heterogeneous distribution of volatiles in the upper mantle under the ocean. Vernadskiy Inst. of Geochem. and Analy. Chem., Acad. of Sci. of the USSR. 0abf) 84:6151 Thirlwall, M.F. and A.M. Graham, 1984. Evolution of high--Ca, high-Sr C-series basalts from Grenada, Lesser Antilles: the effects of intracrustal contamination. J. geol. Soc., Lond., 141(3):427-445. Dept. of Earth Sci., Univ. of Leeds, Leeds 2, UK.
879
D290. Crust, mantle, core 84:6152 Banerjee, S.K., 1984. The magnetic layer of the ocean crust----how thick is it? Tectonophysics, 105(1/4): 15-27.
Special features of linear marine magnetic anomalies and the magnetic measurements made on samples of ocean crust require the thickness of the marine magnetic source layer to be thicker than the 0.5 km thick pillow lava layer (seismic layer 2A) alone. It is proposed that the magnetic properties of the samples studied to date indicate a two-layered source as the most likely: an upper 0.5 km thick pillow lava layer with NRM of 5 A / m and a lower 3.5 km thick dike and upper gabbro layer with a magnetization of 0.5 A/m. Dept. of Geol. and Geophys., Univ. of Minnesota, Minneapolis, Minn. 55455, USA. 84:6153 Beloussov, V.V., 1984. Certain problems of the structure and evolution of transition zones hetween continents and oceans. Tectonophysics, 105(1/4):79-102.
A type of continental-oceanic transition zone, the Columbian, is distinguished from two other common types of transition zones. Subsidence of the Earth's crust, typical of all transition zones, is shown to be connected (by geophysical properties) to the transformation of continental crust into intermediate crust and later into oceanic. The most likely mechanisms of such changes are the basification of continental crust; its foundering, block by block, into the heated upper mantle; and its substitution by new oceanic crust. Acad. of Sci., Soviet Geophys. Comm., Moscow B-296, USSR. 84:6154 Christensen, U.R. and D.A. Yuen, 1984. The interaction of a subducting lithospheric slab with a chemical or phase boundary. J. geophys. Res., 89(B6):4389-4402.
A finite element model of time-dependent convection employs temperature-dependent and non-Newtonian rheology to achieve platelike behavior of the upper and sinking thermal boundary layer of convection. The 650-km discontinuity is taken as a chemical and/or phase boundary. When the compositional density contrast >5%, the descending slab is deflected sideward at the boundary and two-layer convection prevails. Below 5% density difference the slab plunges several hundred kilometers into the lower mantle, and below 2% it will probably not stop