87:6358 Recent advances in Hawaiian petrology and geochemistry

87:6358 Recent advances in Hawaiian petrology and geochemistry

OLR fl'9g'~)34 (1 l) D. Submarine Geology and Geophysics decoupled from Sm-Nd, U-Pb, and Th-Pb fractionation. Small isotopic variations occurring on...

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OLR fl'9g'~)34 (1 l)

D. Submarine Geology and Geophysics

decoupled from Sm-Nd, U-Pb, and Th-Pb fractionation. Small isotopic variations occurring on regional scales of 1-100 km are of lesser amplitude than those observed on large scales. On regional scales Pb isotope ratios are more highly correlated than in Pacific MORB overall and may record the age of events that created t h e regional mantle heterogeneities. Available data do not support the relationship of isotopic diversity and mean isotopic composition to spreading rate. Dept. of Geol. Sci., Cornell Univ., Ithaca, NY 17853-1504, USA. 87:6358 Wright, T.L. and R.T. Helz, 1987. Recent advances in Hawaiian petrology and geochemistry. Prof. Pap. U.S. geol. Surv., 1350:625-640.

Active volcanism at Kilauea Volcano has provided natural laboratories to study the cooling, crystallization, and differentiation of basaltic magma which has resulted in the recognition of new petrologic processes, including storage of mantle-derived magma batches and mixing of these batches with magma stored and fractionated in rift zones. Detailed study of the recently discovered Loihi Seamount has revealed a preshield alkalic stage similar to postshield alkalic stages. Stratigraphic studies of individual volcanoes show the diversity of chemical evolution of volcanoes in the chain, and combined isotopic and chemical data reveal significant complexity in the source mantle. The origin of Hawaiian magma, as defined by depth and degree of partial melting, enriched vs depleted sources, and mineralogy of source mantle, is unresolved. Includes ca. 100 references.

D290. Crust, mantle, core 87:6359 Abe, Katsuyuki, 1987. Seismieity of Japan: earthquakes and tsunamis. [Overview.] Impact Sci. Soc., 145:63-74.

Japan and its environs are a typical island arc system in which the oceanic plates subduct on their way back into the mantle. Both shallow and deep earthquakes occur there, and many set off tsunamis. Japan has one of the longest histories of recorded earthquake activity in the world. A close examination of the characteristics of its seismicity reveals some interesting features. Earthquake Res. Inst., Univ. of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan.

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87:6360 Behrendt, J.C. and Annette Yuan, 1987. The Helena Banks strike--slip (?) fault zone in the Charleston, South Carolina, earthquake area. Results from a marine, high-resolution, multichannel, seismicreflection survey. Geol. Soc. Am. Bull., 98(5): 591-601. The results of a high-resolution, multi-channel seismic reflection survey offshore of Charleston, South Carolina, indicate the Helena Banks fault zone (HBFZ) trends N66°E for ~ 1 1 0 km and consists of several left-stepping en echelon 10-40 km long segments suggestive of left-lateral strike-slip movement. Survey lines across the HBFZ indicate a displacement of 68 _+13 m on the J reflector (Jurassic basalt layer surface) and a 51_ 12 m/km increase with depth. Deep-penetration profiles identify the HBFZ as a reactivated boundary fault of the underlying narrow Kiawah Triassic (?) basin. USGS, Denver, CO 80225, USA. (hbf) 87:6361 Campbell, W.H. (ed.), 1987. Electrical properties of the Earth's mantle. Special issue. Pure appl. Geophys., 125(2-3):193-497; 15 papers. This collection of papers 'representative of recent international efforts to understand the electrical properties of the Earth's mantle,' is introduced by an article presenting an overview of current knowledge on the mantle--its characteristics, seismic investigations, observed electrical properties, and methods of investigation. A table and eight figures showing fifty model profiles summarize some published conductivity results on a common scale display. The profiles indicate agreement within an order of magnitude on the general level of conductivity for the mantle and provide evidence of heterogeneous electrical structure within the uppermost mantle. Other presentations review relevant seismic properties, interrelations between mantle conductivity and other basic properties, conductivity modelling methods, and various research programs. (hbf) 87:6362 Clowes, Ron, 1987. LITHOPROBE: exploring the snbdnction zone of western Canada. Leading Edge, 6(6): 12-19.

Southern Vancouver Island was selected as the focus for the 1984 phase I of this Canadian program planned to investigate the rigid outer 100 km of the Earth. The area was selected because it is a region of complex accreted terranes being underthrust by the subducting oceanic Juan de Fuca Plate where reconnaissance information, maps, and profiles are already available. CDP reflection profiles, supple-