552 D. Submarine Geology and Geophysics OLR (1988) 35 (6)

Beaufort Sea. Temperature~lepth profiles exhibit curvatures that may be explained by seasonal changes in bottom-water temperature; some may arise from other causes. It is unlikely that thermal effects of the underlying, degradational permafrost can be detected from such shallow temperatures due to the magnitude of, and lack of independent knowledge of, these transient and local influences. Thermal conductivities measured on sediment cores and corrected to -1 °C range from 0.9 to 2.4 W m K t. These values are higher than typical conduc- tivities of deep-ocean sediments. The wide range of thermal conductivities observed may be explained by a varying fraction of quartz sand that represents a component of high conductivity. Geol. Survey of Canada, Energy, Mines and Resour. Canada, 1 Observ. Cres., Ottawa, ON K1A 0Y3, Canada.

D240. Local or regional tectonics

88:3459 Anderson-Fontana, Sandra, J.F. Engeln, Paul

Lundgren, R.L. Larson and Seth Stein, 1987. Tectonics of the Nazca-Antarctic plate boundary. Earth planet. Sci. Letts, 86(1):46-56.

A new bathymetric chart of the Chile transform system from 100°W to its intersection with the East Ridge of the Juan Fernandez microplate has been constructed. A generally continuous lineated trend can be followed through the region, the transform valley being narrow and well-defined from 109°W to ~104°30"W. The fracture zone then widens to the east, with at least two probable en echelon offsets to the south at 104 ° and 102°W. Six new strike-slip mechanisms along the Chile Transform and one normal fault mechanism near the northern end of the Chile Rise, inverted together with other plate motion data from the eastern portion of the boundary, produce a new best fit Euler pole for the Nazca-Antarctic plate pair, providing tighter con- straints on relative plate motions. Grad. School of Oceanogr., Univ. of Rhode Island, Narragansett, RI 02882, USA.

88:3460 Hempton, M.R., 1987. Constraints on Arabian Plate

motion and extensional history of the Red Sea. Tectonics, 6(6):687-705.

New geological and geophysical data from the Dead Sea fault and geological data on Arabian Plate boundaries support a two-stage extensional history in the Red Sea and Gulf of Aden. The data indicate that extension first began in the Mid- to Late-Eocene due to NW propagation of the Central Indian Ridge

spreading center and halted in the Mid-Miocene when the Arabian Plate was sutured to Eurasia. By Early Pliocene, due to the slow northward movement of the African/Arabian plates and the formation of large continental wedges north of the Bitlis/Zagros sutures, the Arabian Plate was again able to move northward faster than Africa, reopening the Red Sea and initiating seafloor spreading. Bellaire Res. Center, Shell Develop. Co., P.O. Box 481, Houston, TX 77001, USA. (hbf)

88:3461 Izzeldin, A.Y., 1987. Seismic, gravity and magnetic

surveys in the central part of the Red Sea: their interpretation and implications for the structure and evolution of the Red Sea. Tectonophysics, 143(4):269-306.

New, high-precision paleomagnetic, seismic, gravity, magnetic, and bathymetric measurements from the central and northern Red Sea area are used to construct a model for the evolution of the area. At 19°N the data reveal the presence of oceanic crust for ~ 8 0 km on either side of the spreading axis. Additional data on the symmetrical distribution of the various seafloor spreading anomalies are inter- preted to indicate that spreading which started between 10 and 12 mya and has continued since that time to produce a separation of 70 to 160 km, was preceded by an extension of 40-55 km in the continental lithosphere. Geophys. Dept., Ministry of Energy and Mining, P.O. Box 410, Khartoum, Sudan. (hbf)

88:3462 Jo6, I. (guest editor), 1987. Recent crustal movements

in the Carpatho-Balkan region. Symposium proceedings, Budapest, Hungary, October 1985. Special issue. J. Geodynam., 8(2-4):95-376; 26 papers. Natl. Office of Lands and Mapping, Budapest, Hungary.

88:3463 Karasik, A.M., S.A. Merkur'yev, L.I. Mitin, N.A.

Sochevanova and V.N. Yanovskiy, 1986. Main features in the history of opening of the Arabian Sea, according to data of a systematic magnetic survey. Dokl. Earth Sci. Sect. (a translation of Dokl. Akad. Nauk SSSR), 286(1-6):81-84.

A systematic magnetic survey on the northeast flank of the Carlsberg Ridge was undertaken to better define the history of the opening of the Arabian Sea, and a new magnetic map is presented which reveals both marked linearities of magnetic anomalies and the presence of two discordant systems of anomalies. The data support a continuous, two-stage process of opening, not the discontinuous three-stage process