t032 D. Submarine Geology and Geophysics OLR (1985) 32 (12)

85:7171 Kawakami, Shin-ichi and Hitoshi Mizutani, 1984.

Geolo~ and ~ of A~haean cr~t and i ~ s for the early history of the Earth. J. Earth Sci. Nagoya Univ., 32:49-94. Dept. of Earth Sci., Nagoya Univ., Nagoya 464, Japan.

85:7172 Nagumo, Shozaburo, Junzo Kasahara and Sadayuki

Koresawa, 1984. Hypoeenter ~ in the Japan Trench region, off Samiku, northeast Japan, determined by an ocean--bottom seis- mometer array observation. Bull, Earthq. Res. Inst., Univ. Tokyo, 59(4):441-465.

Three distinct groups of earthquakes were detected during a one-month deployment of 7 ocean bottom seismometers in the Japan Trench. The first group, aligned along the 6 km bathymetric contour on the outer slope, is shallow and represents the bending motion of the oceanic crust. The second clusters near the trench axis and extends from the crust into the upper mantle. These earthquakes appear 'to be associated with the subsidence and sharp bending deformation of the subducting crust.' The third group, in the inner-slope region, 'represents either a slip or a thrust faulting motion along the interface' between the overlying rock mass and the underlying oceanic crust. A new earthquake location algorithm which can deal with a 3-D heterogeneous velocity structure is also discussed. Earthquake Res. Inst., Univ. of Tokyo, Japan. (amt)

85:7173 Richter, F.M., 1985. Models for the ~ thermal

regime. Earth planet. Sci. Letts, 73(2-4):350-360. Dept. of the Geophys. Sci., Univ. of Chicago, IL 60637, USA.

85:7174 Rouland, D., S.H. Xu and F. Schindele, 19851 Upper

nmatle structure in the southeast ~ Ocean: a surface wave investigation. Tectonophysics, 114(1-4):281-292.

An 8% decrease of group velocity is observed when passing from paths coming from the north of Dumont D'UrviUe to those coming from the east. Variations in both the lithospheric thickness and the upper mantle shear velocity are needed to explain this group velocity decrease by means of isotropic models. The corresponding change in upper mantle structure does not appear to be correlated with seafloor age. It suggests the existence of a low velocity region, several hundred kilometers in extent, in which transform faulting is active. A strong azimuthal anisotropy of Rayleigh wave velocity in the investigated area could partially account for the

observed velocity variations. Inst. de Phys. du Globe, 5 rue R. Descartes, 67084 Strasbourg Cedex, France.

85:7175 Wetzel, K. and H. Schtltze, 1985. On the dynamics

and ~ mechanism of the evointion of the continental crust. 4. Communication: New arguments in favour of the model. Chemie Erde, 44(1):89-96. (In German, English abstract.)

Further evidence of the authors' earlier derived constraint that subducted oceanic crust is the source of continental growth is presented. Processes in the downgoing slab/mantle system indicate that mantle wedges can provide source material for continental growth only if the wedge underlies an area of rapid exchange with the mantle. Initial 143Nd/~d and STSr/a6Sr ratios of island arc volcanics and ocean rift basalts indicate both rock types originate from the same region of the mantle and that island arc magmas are formed by partial melting of subducted oceanic crust. The chemical composition of the downgoing slab assimilated by the mantle corre- sponds with that of ophiolites and common eclogites. Zentralinst. fur Isotopen- und Strahlenforschung der Akad. der Wissensch. der DDR, Leipzig, DRG.

D320. Economic geology (see also D330- Oil and gas, D340-Manganese nodules)

85:7176 Batiza, Rodey, 1985. Qualitative assessment of

poly~ta i lk sulfide mineral deposits on sea- mounts. Mar. Min., 5(2): 181-190.

It is estimated that seamount sulfide deposits, characteristically associated with summit craters and calderas, may represent ~10% of the sulfide gen- erated at mid-ocean ridges. The shallower depths typical of seamount sulfide deposits Should enhance their resource potential. Dept. of Earth and Planet. Sci., Washington Univ., St. Louis, MO 63130, USA. (hbf)

85:7177 Koski, R,A., W.R. Normark and J.L. Morton, 1985.

~ve ~ ~ on the uthern ~ de Fnca ~ : ~ of iavestigadm~ in the USGS study area, 1 ~ . Mar. Min~ 5(2):147-164.

Multidisciplinary survey data 'establish the geologic framework for metallogenesis on the southern Juan de Fuca Ridge' within the l-kin wide valley where a series of active hydrothermal vents, sulfide deposits, and communities of benthic organisms have been located around a collapse structure along the valley