Victor Vacquier

CALCULATION OF THE MAGNETIZATION OF UPLIFTS FROM COMBINING TOPOGRAPHIC AND MAGNETIC SURVEYS

The direction and magnitude of the magnetization of a uniformly magnetized structure can be computed by combining topographic and magnetic surveys. The previously reported method has been extended to include more than one structure, each possessing its particular magnetization. Also, the bottom of the structure need not be a horizontal plane but can be an arbitrary surface. The method was applied to 21 seamounts, one laccolith and two Aleutian volcanoes. Four of the seamounts were found to be reversely magnetized. The virtual paleomagnetic pole positions for 16 Pacific Ocean seamounts, representing three widely separated locations, are significantly different from the present geomagnetic pole position but near Mesozoic virtual pole positions from Australia. For two locations, radiometric age determinations give an average date for their formation in the Cretaceous. The apparent 30 degree shift in geomagnetic latitude of the seamounts is interpreted as the result of large scale movements of the Pacific Oce...

The measurement of thermal conductivity of solids with a transient linear heat source on the plane surface of a poorly conducting body

Abstract During the last ten years the transient hot-wire method for measuring thermal conductivity of ocean bottom muds and other soft materials has been adapted for measuring the conductivity of solid rocks because it is cheaper and quicker than the steady state methods such as the divided bar. This is done by embedding the hot wire in the form of a hypodermic needle or a ribbon flush into the surface of a block of a poorly conducting material. When a flat surface of a specimen is placed on the surface of such a sensor, the line source can be said to diffuse heat into an infinite half-space if one neglects the heat absorbed by the poorly conducting block into which the needle is embedded. The rate of the temperature rise of the line source with respect to the logarithm of time elapsed since turning on the heater is inversely proportional to the conductivity. In practice the rates of temperature rise are compared for the unknown and for a standard specimen, a fused silica plate in our case. The percentage of the total heat flowing into the sensor block is in general different for the standard and for the unknown, thus possibly creating an error when the conductivity of the sensor block is neglected. It was determined experimentally that the temperature rise for a silica plate is decreased only by 1.3% by the heat absorbed by the material of the sensor block. An empirical equation is proposed to correct errors arising from this source. This correction needs to be used only for materials of conductivity less than 2 mcal/cm °C s. The equation gives somewhat larger but still acceptable conductivity values for substances in the range of 0.208–3.25 mcal/cm°C s as shown in Table 1 and Fig. 2. For measurements on common rocks corrections for the heat diffused into the material of the sensor block can be neglected.

A comparison of terrestrial heat flow and transient geomagnetic fluctuations in the southwestern United States

Magnetic time‐variations between Tucson, Arizona and Sweetwater, Texas indicate that a zone of high electrical conductivity underlies the southwestern United States. The interpretation of this zone by Schmucker as a rise of the isotherms in the upper mantle is supported by six heat flow observations along the line of the geomagnetic profile. These and other observations indicate a high but variable heat flow in the Basin and Range Province which contrasts strongly with the uniform values of 1.1μcal/cm2sec reported for the Texas Foreland. The width of this high heat flow anomaly, which may extend across the entire Basin and Range Province, suggests anomalously high temperatures in the upper mantle. This interpretation is further supported by magnetotelluric data between Phoenix, Arizona and Roswell, New Mexico and by the low seismic Pn velocity and negative gravity anomaly. It is suggested that the “anomalous mantle” may be related to the tectonic evolution of the western United States and the late Cenozoi...

Terrestrial Heat Flow in the Tertiary Basin of Central Sumatra

Abstract Heat flow at 170 locations in the Central Tertiary basin of Sumatra was determined from thermal gradients obtained from the extrapolated oil well bottom hole formation temperature and the assumed temperature of 80°F at the surface. The effective thermal conductivity of the whole rock column, by which the gradient is multiplied to get the heat flow was calculated from measurements on 273 specimens of the geologic section and inspection of 92 well logs. For the whole basin the gradient averaged 3.71 ± 1.04°F/ 100 ft (67.6°C/km) the conductivity 4.83 ± 0.31 mcal °C−1 cm−1 sec−1, giving an average heat flow of 3.27 ± 0.93 10 −6 cal cm−2 sec−1 which is about twice the world average. The gradient and the heat flow vary inversely with the depth of the wells most of which bottom in the pre-Tertiary basement. This may result from the basement rocks being several times more conductive than the sediments. Mocel calculations on a narrow heat-flow anomaly which rises from a base level of 3.2 HFU to 8.8 HFU suggest that it can be caused by the intrusion less than 55,000 years ago of an igneous plug or laccolith no deeper than 3 km and 2.2 to 4.6 km wide. Using the gradients from the SEAPEX Geothermal Gradient Map and assuming a conductivity of 5 mcal cm−1 °C−1 sec−1, the heat flow in the North Sumatra basin, the South Sumatra Basin, Sunda Strait and West Java is 2.5 HFU, while in Java east of 110°E longitude it drops to 1.9 HFU. Since subduction off Sumatra dates back at least to the Cretaceous, compression of the Asian plate against the Benioff zone is preventing the opening of a back-arc basin. This does not preclude the possibility of occasional periods of crustal tension corresponding perhaps to episodes of transgression which allow magma to rise into the rocks underlying the basin.

Terrestrial heat flow measurements on Lake Titicaca, Peru

Between 29 May and 16 June, 1969, 19 succesful observations of terrestrial heat flow were made with Bullard-type probes on Lake Titicaca within the 250-m depth curve. The 19 heat-flow measurements have a mean of 1.32 μcal cm−2 sec−1 (u.f.u.) which is slightly below the continental average Thirteen of these observations were made with a 2.5-in-long probe and for the other six a probe 4.5 m long was used. The differences of temperature gradient found at four depths in the lake sediments can be accounted for by an annual variation of the bottom water of approximately 0.02°C by comparing them to the computed penetration into the lake bottom of an annual sinusoidal oscillation of the bottom water temperature. At each of five stations the water column was nearly isothermal from a depth of 50 m to the bottom. Above 50 m the temperature rises, reaching about 14°C at the surface. Newell has suggested that normal running faults along the axis of the lake separate an eastern Devonian-Cretaceous province from a western Tertiary province. This boundary lies just west of Isla Soto. The mean heat flow in the Tertiary province appears to be significantly higher than in the Devonian-Cretaceous province. This difference might reflect a greater content of radioactive elements in and under the Tertiary terrain.

Method for determining terrestrial heat flow in oil fields

A method of determining terrestrial heat flow in oil fields from bottom‐hole temperatures, electric logs, and thermal conductivity of core samples has been tried in six Reco⁁ncavo Basin oil fields in Brazil. The average heat‐flow value so determined for the Reco⁁ncavo Basin is 1.10±0.15microcalories/cm2sec. The technique can be used for calculating heat flow in continental areas elsewhere. A more significant outcome of our experiment is that it demonstrates an inexpensive method of obtaining terrestrial heat‐flow values in the sedimentary basins of the world.

Experiment on estimating thermal conductivity of sedimentary rocks from oil well logging

Oil well are an important source of geothermal data for studying regional tectonics, reconstructing the evolution of sedimentary basins, and theorizing petroleum generation, migration, and accumulation. A more satisfactory, less laborious method of estimating the thermal conductivity of sedimentary rocks is badly needed. The thermal conductivity of cores from two gas wells in France was measured and correlated with neutron porosity index, sonic interval travel time, bulk density, and gamma-ray logs. To obtain reasonable predictions of conductivity, data were segregated into lithologic groups such as sand-shale, carbonate-shale, and carbonate-sand. A set of regression coefficients in the equation that predicts the conductivity from the logs was calculated for each group. T e correlation coefficients between the measured and predicted conductivities of the core samples were 0.81, 0.75, and 0.61, respectively, for the three lithologic groups. The average percent difference between the measured and the calculated conductivities for the lithologies likely to be encountered in practice is 13.4%. We expect this figure can be reduced to 10% by enlarging the data base for calculating the regression coefficients. In the same basin or oil field, the relative errors from well to well probably will be 6% or smaller because the lithology will be nearly homogeneous.

New terrestrial heat flow measurements on the Nazca Plate

Abstract Sixty-seven new heat flow measurements on the Nazca Plate are reported, and the thermal regimes of three specific areas on the plate are examined. The Nazca Ridge is an aseismic ridge which may have been generated as an “island trail” from the Easter Island “hot spot” and/or may be a fossil transform fault. The Nazca Ridge has lower heat flow than the surrounding sea floor implying that the ridge might have low “effective” thermal conductivity causing heat to preferentially flow or refract to surrounding ocean crust which has higher conductivity, or, the low heat flow values may be caused by hydrothermal circulation on the ridge. The Carnegie Plateau is an elevated region south of the Carnegie Ridge on the northeastern Nazca Plate with high heat flow and shallow topography consistent with an age of less than 20 m.y. B.P. The central Nazca Plate is an area of highly variable heat flow which is possibly related to thin sediment and to rough regional topography.

Heat Flow and Magnetic Profiles on the Mid-Indian Ocean Ridge

Sixty heat flow values were measured along nine profiles across the Mid-Indian Ocean Ridge. The results were roughly of the same character as the ones previously reported for the South Atlantic Ridge. The correlation of high heat flow with the centre of the ridge was less pronounced. The scatter of heat flow values when plotted as a function of distance from the ridge was even greater. The average of all values is 1.35 /tcal cm-2 s-1, indicating that over the surveyed area the heat flow is normal. The cause for the low values on the flanks of the ridge remains unknown. A right lateral displacement of about 200 km across the Vema Trench was measured from the offset of the magnetic anomaly on the ridge crest.

Oil fields—A source of heat flow data

Abstract A method of calculating terrestrial heat flow from oil fields is evaluated by reviewing its application to twelve petroliferous basins, three of them in Brazil and nine in Indonesia. In each well, terrestrial heat flow was calculated by multiplying the temperature gradient (obtained by commonly used procedures) by the effective thermal conductivity. The latter was calculated from quick thermal conductivity measurements on core samples by a transient hot-wire method and from the lithologic log. Typically, in each basin the conductivity of about 300 core specimens was measured and logs of 50–150 wells were examined. In each formation penetrated by a well, the total thickness of each rock type such as shale, sandstone, etc., was determined from the composite lithologic log. The harmonic mean of the thermal conductivity of a formation in the well was computed from these thicknesses and the average values of the conductivities of the rock types measured on cores collected from that formation. The conductivity of the well is the harmonic mean of the conductivities of the formations. The average precision of the determination of formation conductivity can be expressed as the α95 limits divided by the average value. For twelve basins this measure of precision for formation conductivities averages 3.6% and the average precision of the conductivity of a basin is 2.0%. On the same basis, the precision of the determination of the temperature gradient in a basin averages 4.7% and that of the heat flow 5.8%. Expressing the variability of the geothermal quantities in a basin determined at discrete locations as the standard deviation divided by the average value, we get for the mean variability in the twelve basins: 6.7% for conductivity, 15.0% for the gradient and 16.4% for the heat flow. The variability must come in part from natural causes. In general, at the present level of accuracy no correlation between anomalous heat flow and the occurrence of oil in a basin was found. Values of thermal conductivity of sedimentary rocks and their variation with depth are useful in calculating paleotemperatures. The magnitude of the mean heat flows of the basins is normal (63 mW/m2) for the Jurassic basins of the stable continental margin of Brazil and somewhat elevated in the Tertiary basins of Indonesia, north of the Sunda trench subduction zone, the values decreasing from 130 mW/m2 in Central Sumatra to 70 mW/m2 in eastern Kalimantan. Future improvements in the procedures for determining conductivity might possibly bring out local anomalies in heat flow that might be caused by vertical seepage of water. This would support the hydraulic theory of accumulation of oil and gas.