878 D. Submarine Geology and Geophysics OLR (1984) 31 (12)

84:6141 Wolf, Detlef, 1984. On the relation between two-

dimensional and axisymmetric loads in plate flexure problems. J. Geophys. (Z. Geophys.), 54(3):232-235. Dept. of Physics, Univ. of To- ronto, Ont., M5S 1A7 Canada.

84:6142 Zytko, Kazimierz, 1982. The Atlantic, the Indian

Ocean and main linear fracture zones of the post-Variscan Europe. Annls Soc. Geol. Poloniae, 52(1/4):3-38.

Two linear rifting belts, one running NW-SE from the North Sea to the Aegean Sea and the other SW-NE in western Europe and Africa, are related to early rifting events during the opening of the Indian and Atlantic oceans, respectively. Both systems interfere with a supposed W-E geosynclinal Tethys system. A transform fault line running from North Anatolia through the Alps to the Gibbs Fracture Zone separates the Alpine-Mediterranean micro- plate belt from the rest of Europe. Geol. Inst. Carpathian Branch, ul. Skrzatow 1, 31-560 Krakow, Poland. (amt)

D280. Volcanism, magmatism 84:6143

Baker, P.E., 1984. Geochemical evolution of St. Kitts and Montserrat, Lesser Antilles. J. geol. Sac., Land., 141(3):401-411. Dept. of Geol., Univ. of Nottingham, University Park, Nottingham NG7 2RD, UK.

84:6144 Briqueu, Louis, H. Bougault and J.L. Joron, 1984.

Quantification of Nb, Ta, Ti and V anomalies in magmas associated with subduction zones: pet- rogenetic implications. Earth planet. Sci. Letts, 68(2):297-308.

This study shows that hygromagmaphile elements (elements which exhibit an affinity for the liquid phase of magma: Th, Ta, Nb, Zr, Hf, Ti, Y, V) can be plotted on an extended rare earth diagram. The position of these elements among rare earths is determined and normalization values calculated from data on ocean tholeiites and alkali basalts. Representation in an extended rare earth diagram permits detection of behavioral anomalies which can be quantified and used for petrogenic interpreta- tions. Ti and V anomalies observed in magmas associated with subduction zones are interpreted as the result of opaque fractionation between the fractional crystallization of magmas; Nb and Ta

anomalies are more primitive and are associated with the presence in the mantle of a phase which is stable under the P, T and H20 conditions generated by the geodynamic context. Lab. de Geochim. isotope CGG et UER des Sci. de la Terre, USTL Place E. Bataillon, 34060 Montpellier Cedex, France.

84:6145 Brothers, R.N., 1984. Subduction regression and

oceanward migration of volcanism, North Island, New Zealand. Nature, Land., 309(5970):698-700.

New data from K-Ar ages and K20-SiO 2 indices for magma source depths indicate an oceanward migra- tion pattern for North Island's volcanism, from NW to SE toward the Hikurangi Trench. Movement of this volcanic front throughout the Neogene and Quaternary was controlled by subduction zone regression which followed rapid, shallow, non- volcanic Oligocene underplating of the island. In areas of accelerated subduction retreat, tensional tectonism caused widespread foundering of the Mesozoic greywacke basement. Dept. of Geol., Univ. of Auckland, Private Bag, Auckland, New Zealand.

84:6146 Campsie, John, G.L. Johnson, M.H. Rasmussen and

Jens Laursen, 1984. Dredged basaits from the western Nazca Plate and the evolution of the East Pacific Rise. Earth planet. Sci. Letts, 68(2):271- 285.

Ocean-floor basalts and glasses recovered from a sublinear topographic feature believed to represent the proto-EPR include abyssal tholeiites, FeTi- basalts and glasses, and transitional and little fractionated compositions. They exhibit the com- positional diversity expected for propagating rifts and probably represent more than one volcanic episode. Geochemical and geophysical interpreta- tions support the inference that the EPR grew from Miocene times by the progressive growth and propagation of mantle perturbations, leaving a remnant sublinear zone of rough topography char- acteristic of slower accretion as the proto-EPR trace. Continuing translations and rotations of axial segments are occurring along the EPR, probably in response to self-reorganizations of mantle flow patterns arising from rapid melting and depletion of the source regions. Ocean Study Group, Borgergade 34, 2th, DK 1300 Copenhagen K, Denmark.

84:6147 Hole, M.J., A.D. Saunders, G.F. Marriner and J.

Tarney, 1984, Snbduction of pelagic sediments: implications for the origin of Ce-anomalous