Michael A. Hobart

Geothermal convection through oceanic crust and sediments in the Indian ocean.

Closely spaced heat flow surveys at four sites on the flanks of the Central Indian Ridge and the Southeast Indian Ridge delineate a pattern of oscillatory heat flow which can only result from cellular convection of oceanic bottom water through the oceanic crust and overlying sediment. These cells have a wavelength of 5 to 10 kilometers and are presently active in sea floor 18 x 106, 25 x 106, and 45 x 106 years old of the Crozet Basin and in sea floor 55 x 106 years old of the Madagascar Basin. The precise measurement of nonlinear temperature profiles makes it possible to calculate the conductive and convective heat transfer components through the sea floor. Even in the oldest sites, geothermal convection is still a major component of heat transfer through both the crust and sedimentary layers. These observations coupled with the results of earlier oceanwide geothermal studies indicate that more than one-third of the entire surface area of the worlds ocean floor contains presently active geothermal convection that is cellular in plan form.

Conrad deep: a new northern Red Sea deep: Origin and implications for continental rifting

A previously unknown deep, here called Conrad Deep, was discovered during an extensive geophysical survey of the northern Red Sea in June, 1984. Conrad Deep is located at 27°03′N, 34°43 ′E,only 90 km south of the Gulf of Suez and is the most northern deep yet discovered in the Red Sea. It is located within a well developed axial depression which also contains Charcot Deep, 100 km to the south. The axial depression is associated with abundant recent deformation and is situated at the peak of a regional heat flow high extending across the rift. Conrad Deep is typical of the small northern type Red Sea Deep. It is 10 km long, 2 km wide and has a maximum depth of 1460 m. It is associated with high and variable heat flow values and large magnetic anomalies. There is no evidence of a dense brine layer. Detailed analysis of the geophysical data implies that the deep probably results from a very recent (

Heat flow in the oceanic crust bounding Western Africa

Abstract Over four hundred widely distributed heat-flow measurements have been made in the eastern Atlantic Ocean between the Azores—Gibraltar Ridge and the Walvis Ridge, permitting a study of the correlation of heat flow with crustal age and tectonic province. The mean heat flow over crust less than 80 m.y. old is less than that predicted by cooling-lithosphere models. Near the ridge axis the standard deviation of the heat-flow values is as large as the mean, but it decreases rapidly near the 20 m.y. isochron to about half of the mean and then again near 70–80 m.y. to about one third of the mean. The heat-flow values observed over crust older than 80 m.y. are the same as predicted by a cooling-lithosphere model and show little scatter. In the younger ocean crust, water circulation between the crust and ocean bottom water is the dominant mechanism of heat transfer from the crust, but after 80 m.y., heat is transferred primarily by conduction. The age dependence of the mean heat flow and standard deviation north and south of the equator were examined independently and were found to be nearly identical. This implies that heat-transfer processes in the oceanic crust evolve in a similar manner in the two portions of the ocean. Over the older oceanic crust, regions delineated by their mean heat flow and the scatter in the heat-flow values correspond roughly with tectonic province. Volcanic regions have a higher and more variable heat flow than a normal oceanic basin. The scatter in the heat-flow values may be caused by water circulation between the crust and the bottom water. In the equatorial region, the Guinea and Sierra Leone basins have a uniform and relatively high heat flow, averaging 1.4 HFU (10−6 cal cm−2 sec−1). This may mean that the equatorial eastern Atlantic Ocean is underlain by an anomalously thin lithosphere, possibly caused by upwelling asthenosphere and higher shear-stress heating at the base of the lithosphere.

Active fluid flow in the Eugene Island area, offshore Louisiana

A sedimentary basin is a thermochemical reactor; i.e., a complex, dynamically interrelated system that is deformed and faulted by tectonic forces, modified by sedimentation and erosion, influenced by geopressuring and chemical reaction, and subjected to constantly changing temperature, pressure, and fluid composition and movement. We understand little about the coupling among these processes that comprise basin thermochemical reactors despite many recent advances in basin science and technology. However, we are certain that these processes are coupled so strongly that changes in one can completely alter the operation of all the others in a basin.

Heat flow and mass wasting in the Wilmington Canyon Region: U.S. Continental Margin

The average corrected heat flow in the Wilmington Canyon region, an area of inferred slope instability, is 35 ± 10 mW/m2. This average heat flow is marginally consistent with the 46 ± 9 mW/m2 measured at other North Atlantic sites over 160 m.y. old. High topographic relief causes most of the variability in surface heat flow and may lower the mean surface heat flow. There is no significant difference between the average corrected heat flow of 35 ± 10 mW/m2 in sediment slide areas and the average corrected heat flow of 34 ± 10 mW/m2 in undisturbed sediments.

Correlation of shear strength, hydraulic conductivity, and thermal gradients with sediment disturbance: South Pass region, Mississippi Delta

The degree of sediment disturbance in the South Pass area is correlated to the average hydraulic conductivity, shear strength, and thermal gradient. Hydraulic conductivity averages 18, 6, and 4 × 10−7 cm/s in the undisturbed, moderately disturbed, and most disturbed sediments, respectively. Shear strength also decreases with increasing disturbance, from 7.6 to 4.4 to 3.5 kPa. Excluding the four stations dominated by annual temperature variations, the remaining 19 thermal gradients correlate well with sediment disturbance. The average gradient is positive in all of the disturbed sediments (0.12 ± 0.07° C/m) and 0 in the undisturbed sediments (0.02 ± 0.05° C/m).