HEAT FLOW AND EARTHQUAKE SYNERGY IN CALIFORNIA
Jessie L. Bonner

Comparison of the heat flow and earthquake databases for California provides detailed geologic and geophysical information about the earthquake process. Using the high-quality databases for California seismicity (SCEC and NCEC) and the extensive compilation of thermal measurements in California (SMU Geothermal Lab), the temperature range for the maximum depth of seismicity has been established within workable error limits. Two different methods were employed to obtain this range. The first considered the entire heat flow and earthquake database for California, and the inverse relationship between heat flow and the cutout depth for seismicity is obvious. Temperatures for this depth were calculated using the steady-state, one-dimensional, heat conduction equation, assuming average values for heat generation and thermal conductivity. Temperatures range between 400 degrees C and 700 degrees C, higher than accepted rheologic models predict for continental crust. An alternative method considered temperature calculations for regions where the geologic, seismic, and thermal regimes are well constrained. By considering such profiles of collocated heat flow measurements and seismicity, we reduce the error in the temperature calculation to start at 0 degrees C at the surface and increase linearly +/-4.5 degrees C/km, as determined by the inner 900 of 1000 Monte Carlo simulations. Temperatures for the cutout depth range between 300 degrees C to 500 degrees C and 600 degrees C for profiles in Southern and Northern California, respectively. Differences in the temperatures may be the results of misassociation of the available heat flow and earthquake databases, contrasting rheologies, or other explanations including localized strain accumulations that need by investigated. Along profiles with significant seismic activity, the envelope for the maximum energy released by earthqukes follows the 300+/-100 degrees C isotherm. Detailing the heat flow and earthquake synergy in this manner allows estimating the depth of initial rupture for great earthquakes, thus reducing uncertainties in hazard calculations.

STRUCTURAL ANALYSIS OF CENTRAL AND EASTERN OVDA REGIO, VENUS
Rebecca R. Ghent

Introduction. Ovda Regio is the largest of the Venusian crustal plateaus and lies in Western Aphrodite Terra, Venus. Understanding the strain history of this region will provide a key to understanding the formation of Ovda Regio and will have implications for the formation of other crustal plateaus.
Observations. We mapped tectonic features of Ovda Regio using Magellan SAR images. The three major structures in Ovda Regio are folds, "ribbons" and graben. Folds are present everywhere in Ovda and have different characters in different regions. Graben are lens-shaped depressions bounded by paired normal faults, and they occur dominantly at the crests of folds. "Ribbons" are steep-sided, flat-floored troughs, 1-3 km wide and spaced 1-5 km apart. They extend for hundreds of km over vast areas of Ovda Regio. The folds are interpreted to be contractional, and graben and ribbons extensional. Ribbons are structurally quite different from the graben and therefore their origins should be considered separately.
Implications. Some workers have proposed that Ovda Regio records early contractional strain (fold formation) and later extension (graben and "steep trough" formation) [1]. We propose that ribbon formation predates, rather than postdates, fold formation. Formation of ribbons before folds indicates that the earliest recorded strain in Ovda Regio is broad radial membrane extension, rather than contraction. This pattern of extension is consistent with the idea that Ovda formed above a mantle plume [2,3]. Many of the same tectonic features present in Ovda have also been observed in Alpha Regio [4], and it is therefore possible that Alpha also records early extension. This would have important implications for the formation of other crustal plateaus.
References. [1] Binschadler et al., (1992a) JGR 97, 13495; [2] R.J. Phillips and V.L. Hansen (1994) Ann. Rev. Earth Planet. Sci. 22, 597, 651; [4] Binschadler et al., (1992b) JGR 97, 13563.

A PRIMITIVE HADROSAUR (DINOSAURIA: ORNITHISCHIA) FROM THE CENOMANIAN OF TEXAS AND ITS IMPLICATIONS FOR HADROSAURIAN PHYLOGENETIC AND BIOGEOGRAPHIC HISTORIES
Jason J. Head

The nearly complete skull of a hadrosaur from the Cenomanian Woodbine Formation (95 Ma) of northeast Texas is a mixture of derived hadrosaurian and generalized iguanodontid characters. The premaxillae form an expanded rostral bill, a wide diastema occurs between the predentary and dentary tooth battery, and the maxillary teeth are small. The jugal-ectopterygoid articulation and surangular foramen are retained, and the quadrate is massive with poorly differentiated mandibular condyles. The most striking features of the specimen are the massive, expanded dentary and ventrally deflected muzzle.
Phylogenetic analysis places the specimen at the basal position within Hadrosauridae. The age and location of the Texas hadrosaur along the eastern coast of the Western Interior Seaway makes it the oldest definitive hadrosaur from eastern North America, and indicates that the suggested Turonian radiation of hadrosaurs from western Asia may have occurred earlier elsewhere.

ARCHOSAURS FROM THE KITADANI FORMATION (APTIAN-ALBIAN), JAPAN
Yoshitsugu Kobayashi

Early Cretaceous (Aptian-Albian) archosaurs have been found from the Kitadani Formation in Fukui, Japan. The formation yields iguanodontian and crocodylomorph fossil remains. In this study, one nearly complete skeleton of a crocodylomorph and cranial elements of iguanodontians have been analyzed. The crocodylomorph is the most complete fossil archosaur found in Japan, and shares a dental characteristic with Bernissartia restricted to western Europe and possibly North America. Iguanodontian materials are similar to those described from European taxa: however, several characters indicate this is a new taxon.
These remains from the Kitadani Formation indicate that the continuation of western European fauna to eastern Asia. The similarity of the archosaur faunas supports a previous hypothesis of a global-circular distribution of European taxa and indicates a biogeographic connection between Japan and mainland Laurasia during the Aptian-Albian. Further study will be focused on the comparison with Chinese dinosaurian fauna during the same age.

A COMINED ISOTOPE (C, O, H and Sr) AND CHEMICAL STUDY OF CRUDE OILS AND FORMATION WATERS FROM THE UPPER CRETACEOUS WOODBINE AND LOW CRETACEOUS TRAVIS PEAK FORMATIONS, EAST TEXAS BASIN.
Vladimir V. Liakhovitch

The project is designed to characterize the regional variations in the isotopic and chemical composition of the crude oils and formation waters from the Upper Cretaceous Woodbine and Low Cretaceous Travis Peak formations, East Texas basin. The overall goals of the study are: 1) to reconstruct the diagenetic history of the waters, 2) to discuss a possible bearing of local geological structures (salt domes, fault zones, etc.) on the compositional variations, 3) to detect any correlation between the composition of coexisting crude oil and formation water, and 4) to determine if the oil and aqueous phase migrated together from their source (source formation) to the trap (producing formation).
The Upper Cretaceous Woodbine and Low Cretaceous Travis Peak formations are the main oil-producing formations of the East Texas basin separated by the regionally defined aquitard, the Ferry Lake Massive Anhydrite. Our data confirm that the Upper Cretaceous and Low Cretaceous waters differ in their chemical, radiogenic (Sr) and stable isotope (O, H and C) composition and follow different evolutionary paths representing two major hydrologic subsystems in the basin. The East Texas crude oils are of Upper Cretaceous, Low Cretaceous and Jurassic origin. A combined geochemical and isotope study of the crude oils and formation waters from the two formations not only allows one to reconstruct the evolution and circulation of the aqueous and oil phases in one of the world's largest continental basins but also provides a unique opportunity to address a most intriguing problem of petroluem geology: "Do formation waters reflect reservoired oil?"

THERMAL CONSTRAINTS ON POTENTIAL CASCADIA SUBDUCTION ZONE EARTHQUAKES NEAR 45 DEGREES N
Jason R. McKenna

Geologic and geophysical evidence points to past and future great earthquakes in the Pacific Northwest. The absence of seismicity along the Cascadia margin makes characterization of rupture processes and maximum moment magnitudes of great subduction zone earthquakes very difficult. An alternative methodology for risk evaluation must be employed. A series of one-dimensional temperature profiles parallel to convergence were used to create a thermal cross section of the subduection zone, determining the thermal state of the accretionary wedge near 45 degrees N, 125 degrees W. Different rheologis are then used to determine the down-dip brittle-ductile transition of the main decollement. Limits on the width of the seismogeneic (brittle) segment of these various rheologies are used to assess the regional seismic hazard.

THE GEMSTONE BEARING PEGMATITES OF KERALA, SOUTH INDIA
Ajith-Kumar S. Nair

Gemstones, the most precious of all minerals, are found associated with pegmatite (primary gemstones), stream gravels and placer deposits (secondary gemstones). Southern Kerala preserves a wide variety of gemstones associated with pegmatites or stream gravels in various localities. The gemstone pegmatite field of Southern Kerala defines an area of 70 x 35 square km, hosting precious and semiprecious stones such as chrysoberyl, ruby, sapphire, topaz, emerald, zircon and korneurupine. In the geological history this part of the world was associated with the Gondwana supercontinent and defines three distinct zones trending NW-SE. Petrologic, fluid inclusion, thermal decriptation and isotopic studies shows that the gemstones crystallized from a felsic melt at temperatures around 550 degrees C and pressures of around 2 - 4 kbar. The volatiles were enriched with CO2 (70 - 140 ppm) and their carbon isotopic composition value of -8 per mil suggest a juvenile magmatic nature. The gemstone bearing pegmatites may therefore represent cryptic pathways through which large volumes of felsic melts migrated. The timing of these pegmatites is correlated with a prominent tectono-thermal event (Pan-African) at around 500 Ma.

ARRAY MEASUREMENTS OF TELESEISMIC P AND PcP SLOWNESS AND AZIMUTH RESIDUALS WITH IMPLICATIONS FOR LATERAL HETEROGENEITY IN THE LOWER MANTLE
Ileana M. Tibuleac

Anomalous slowness residuals as large as 2-3 s/deg, for P waves turning in the lower-most mantle as well as for PcP waves, were observed for all the seismic arrays in North America. Actual data recorded at TXAR (Lajitas, Texas) present definite patterns with abrupt changes of sign between different regions. Seismic reflections from the Earth's core (PcP) show angles of incidence up to 75 percent greater than predicted by the standard Earth model currently used in seismology. The variations are reflected also by the azimuth residuals but not by the travel time residuals.
These observations indicate that the velocity gradient in the lower 1500 km of the mantle in the vicinity of the reflection points is not radial as assumed in the standard model, but is significantly inclined. A non-radial gradient is to be expected in the transition zone between high velocity and low velocity regions in the lower mantle.
Maps of slowness anomalies in the lower mantle, from array data available at this time are presented.
The method uses short period (about 1 second) P and PcP waves, therefore has a resolution of several tens of kilmoeters, unattained by other previously used methods and should prove to be a powerful tool for the investigation of mantle velocity structure when used in conjunction with travel time tomography.

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