Heat flow and age of the Gulf of Oman

We present the results of twenty heat flow stations in the Gulf of Oman which are used to infer the first reliable age estimates for the basin. A mean surface heat flux of 42.6±3.6 mW m^?2 exhibits no significant regional variation. After correction for thick and rapidly deposited sediments this yields an age of 70 to 100 Ma according to oceanic thermal models. This age is also consistent with the sediment corrected basement depths of 5.5–6.0 km and with formation during the Cretaceous quiet zone. The latter can explain the absence of magnetic sea-floor spreading lineations. Heat flow measurements are also used to confirm the presence of gas hyrdate layers. The measured thermal gradient yields a depth for the solid to free gas phase transition which is the same as that deduced from “bright spots” seen on seismic reflection profiles.     

Heat flow measured in five holes in eastern and central Slovakia

Five new heat flow values obtained in deep boreholes in the Western Carpathians are presented. Three holes were located in pre-Neogene folded units, the other two holes in Tertiary volcanites. The heat flow values range from 50.7 to 73.3 mW m^?2 with an average value of 65.9 mW m^?2 and they represent very needed information on the geothermal field in an area where heat flow values are still scarce.     

Thermal conditions of the central Sinai Microplate inferred from new surface heat-flow values and continuous borehole temperature logging in central and southern Israel

This paper reports ten new surface heat-flow density (qs) values for central and southern Israel (central Sinai Microplate), whose crystalline crust and lithosphere formed as part of the Neoproterozoic Arabian-Nubian Shield. Heat flow was calculated in Mesozoic sediments using the classical approach of heat-flow determination by implementing in the analysis high-precision continuous temperature logs obtained in air- and/or water-filled boreholes. Thermal conductivity (TC) measured for a large suite of rock samples of lithotypes making up the sequence was assigned to temperature gradients in intervals for which the lithology was known. The heat-flow values obtained for different depth intervals in a borehole as well as the average values for the individual borehole locations cover a narrow range, attesting heat-conduction conditions. A steady-state thermal model along an E–W crustal cross section through the area shows that the observed systematic spatial distribution of the qs values, which range between 50 and 62 mW m⁻², can primarily be explained by variations in the thickness of the upper crust and in the ratio between sedimentary and crystalline rocks therein. Given the time lapse of thermal heat transfer through the lithosphere, the qs data monitor the crustal thermal conditions prior to rift- and plume-related lithospheric thermal perturbations that have started in the larger area ca. 30 Ma ago. Observed and modeled qs display the best fit for a pre-Oligocene lithosphere–asthenosphere boundary (LAB) at ∼150 km, which would be at the upper end of LAB depths determined from stable areas of the Arabian Shield (150–120 km) not affected by the young, deep-seated thermal processes that have caused a further uprise of the LAB. Our data imply or predict that the surface heat flow of the Sinai Microplate generally tends to increase along N–S and W–E traverses, from ∼45–50 mW m⁻² to ∼55–60 mW m⁻². Surface heat flows on the order of 55–60 mW m⁻² may be common in the northern Arabian Shield, where it exhibits typical lithosphere structure and composition and is unaffected by young heating processes, compared to values of ≤45 mW m⁻² recently determined in the southern Arabian Plate for the Arabian Platform.     

Role of bedrock groundwater in the rainfall–runoff process in a small headwater catchment underlain by volcanic rock

The role of bedrock groundwater in rainfall–runoff processes is poorly understood. Hydrometric, tracer and subsurface water potential observations were conducted to study the role of bedrock groundwater and subsurface flow in the rainfall–runoff process in a small headwater catchment in Shiranui, Kumamoto prefecture, south‐west Japan. The catchment bedrock consists of a strongly weathered, fractured andesite layer and a relatively fresh continuous layer. Major chemical constituents and stable isotopic ratios of δ¹⁸O and δD were analysed for spring water, rainwater, soil water and bedrock groundwater. Temporal and spatial variation in SiO₂ showed that stream flow under the base flow condition was maintained by bedrock groundwater. Time series of three components of the rainstorm hydrograph (rainwater, soil water and bedrock groundwater) separated by end member mixing analysis showed that each component fluctuated during rainstorm, and their patterns and magnitudes differed between events. During a typical mid‐magnitude storm event, a delayed secondary runoff peak with 1·0 l s⁻¹ was caused by increase in the bedrock groundwater component, whereas during a large rainstorm event the bedrock groundwater component increased to ≈ 2·5 l s⁻¹. This research shows that the contribution of bedrock groundwater and soil water depends strongly on the location of the groundwater table, i.e. whether or not it rises above the soil–bedrock interface. Copyright © 2010 John Wiley & Sons, Ltd.     

Heat flow and depth versus age for the Mesozoic northwest Atlantic Ocean: results from the Sohm abyssal plain and implications for the Bermuda Rise

Heat flow in the Sohm abyssal plain is measured to be 53 mW/m² at an age of 163 Ma. This is 25% higher than predicted by conductive cooling models, even though the sediment-corrected basement depth of 6.5 km at this location is normal for its age. An analysis of existing heat flow, depth and geoid anomalies in the northwest Atlantic shows that there is little correlation between heat flow and depth throughout the entire region. Depth and geoid are clearly related to the Bermuda swell while the associated heat flow anomaly, once adjusted for variations with age, is limited to 5 mW/m² and only decays to the south. This means that the Bermuda swell is probably not caused by extensive thermal reheating within the lithosphere, but instead by dynamic uplift at its lower boundary due to the convective upwelling of a mantle plume. The regionally high heat flow in the northwest Atlantic may be a thermal remanent of previous plumes which passed beneath this region early in its history. Therefore, depth and heat flow anomalies from this region cannot be used to provide constraints on steady-state parameters of the lithosphere, such as the presence or absence of a long-term boundary layer at its base.     

Heat flow and ground water flow in the Great Plains of the United States

Regional groundwater flow in deep aquifers adds advective components to the surface heat flow over extensive areas within the Great Plains province. The regional groundwater flow is driven by topographically controlled piezometric surfaces for confined aquifers that recharge either at high elevations on the western edge of the province or from subcrop contacts. The aquifers discharge at lower elevations to the east. The assymetrical geometry for the Denver and Kennedy Basins is such that the surface areas of aquifer recharge are small compared to the areas of discharge. Consequently, positive advective heat flow occurs over most of the province. The advective component of heat flow in the Denver Basin is on the order of 15 mW m⁻² along a zone about 50 km wide that parallels the structure contours of the Dakota aquifer on the eastern margin of the Basin. The advective component of heat flow in the Kennedy Basin is on the order of 20 mW m⁻² and occurs over an extensive area that coincides with the discharge areas of the Madison (Mississippian) and Dakota (Cretaceous) aquifers. Groundwater flow in Paleozoic and Mesozoic aquifers in the Williston Basin causes thermal anomalies that are seen in geothermal gradient data and in oil well temperature data. The pervasive nature of advective heat flow components in the Great Plains tends to mask the heat flow structure of the crust, and only heat flow data from holes drilled into the crystalline basement can be used for tectonic heat flow studies.     

Heat flow in the Ozark Plateau, Arkansas and Missouri: relationship to groundwater flow

Heat flow values were calculated from direct measurements of temperature and thermal conductivity at thirteen sites in the Arkansas-Missouri Ozark Plateau region. These thirteen values are augmented by 101 estimates of heat flow, based on thermal conductivity measurements and temperature gradients extrapolated from bottom-hole temperatures. The regional heat flow profile ranges from 9 mW m⁻² to over 80 mW m⁻², but at least two distinct thermal regimes have been identified. Seven new heat flow determinations are combined with three previously published values for the St. Francois Mountains (SFM), a Precambrian exposure of granitic and rhyolitic basement rocks, average 47 mW m⁻². Radioactive heat production of 76 samples of the exposed rocks in the SFM averages 2.4 μW m⁻² and a typical continental basement contribution of 14 mW m⁻² is implied. Conversely, the sedimentary rock sequence of the plateau is characterized by an anomalously low heat flow, averaging approximately 27 mW m⁻². Groundwater transmissivity values that are based on data from 153 wells in deep regional aquifers demonstrate an inverse relationship to the observed heat flow patterns. The areas of high transmissivity that correspond to areas of low total heat flux suggest that the non-conservative vertical heat flow within the Ozark sedimentary sequence can be attributed to the effects of groundwater flow.     

Geophysical surveys for identifying saline groundwater in the semi‐arid region of the central Altiplano,Bolivia

In the central part of the Bolivian Altiplano, the shallow groundwater presents electrical conductivities ranging from 0·1 to 20 mS/cm. In order to study the origin of this salinity pattern, a good knowledge is required of the geometry of the aquifer at depth. In this study, geophysics has been used to complement the sparse data available from drill holes. One hundred time‐domain electromagnetic (TDEM) soundings were carried out over an area of 1750 km². About 20 geological logs were available close to some of the TDEM soundings. Three intermediate results were obtained from the combined data: (i) the relationship between the electrical conductivity of the groundwater and the formation resistivity, (ii) geoelectrical cross‐sections and (iii) geoelectrical maps at various depths. The limited data set shows a relationship between resistivity and the nature of the rock. From the cross‐sections, a conductive substratum with a resistivity of less than 1 Ω·m was identified at most of the sites at depths ranging from 50 to 350 m. This substratum could be a clay‐rich formation containing brines. Using derived relationships, maps of the nature of the formation (sandy, intermediate and clayey sediments) were established at depths of 10 and 50 m. Discrimination between sand and clays was impossible where groundwater conductivity is high (>3 mS/cm). In the central part of the area, where the groundwater conductivity is low, sandy sediments are likely to be present from the surface to a depth of more than 200 m. Clayey sediments are more likely to be present in the south‐east and probably constitute a hydraulic barrier to groundwater flow. In conclusion, the study demonstrates the efficiency of the TDEM sounding method to map conductive zones. Copyright © 2001 John Wiley & Sons, Ltd.     

Heat flow in Italy

More than fifty heat flow measurements in Italy are examined. The values, corrected only for local influences (when present), are related to the main geological features with the following results: foreland areas, 55±19 mW m^–2, foredeep areas, 45±21 mW m^–2; folded regions and intermountain depressions, 76±29 mW m^–2. In volcanic areas the heat flow rises to in excess of 600 mW m^–2. From a tectonic point of view, these values are consistent with the hypothesis that the Apennine chain is intersected by two arcuate structures: the first from Liguria to Latium is very probably a continental arc, that is an are which occurs within a continent, and the second from Campania to Calabria is very similar from geophysical evidence to the classic island arcs.     

Novel Well Completions in Small Diameter Coreholes Created Using Portable Rock Drills

Difficult access conditions have limited techniques for groundwater system characterization and monitoring in bedrock exposed landscapes. This condition is common in the mining industry and resulted in the development of lightweight portable drills. This paper describes how these drills were used at a contaminated site to understand the groundwater flow system by adapting piezometer designs, ensuring effective seals to obtain reliable hydraulic head, hydrochemistry, and contaminant concentrations. Two drilling machines were evaluated: the Shaw Portable Core Drill? fits in a backpack and can advance continuously cored rock holes, nominal 51 millimeters (mm) diameter, to depths up to approximately 15 meters (m); and the larger Winkie Drill? requires a two or more people to mobilize and can advance continuously cored holes, nominal 48 mm diameter, to depths of approximately 45 m. The resulting small diameter coreholes were accommodated in the design of each well using a seal created by injecting grout into a semipermeable fabric sleeve. This “fabric sleeve” serves as a means to contain the grout and ensures that the entire annulus above the screen is sealed without loss of grout into the formation, allowing the well to perform as a piezometer. To develop and demonstrate this methodology for groundwater monitoring in bedrock, the two drills were used in drainages located along the slopes of an elevated sandstone outcrop near Los Angeles, California. Unique insights into the groundwater flow system of this bedrock environment, which would otherwise be unattainable, were achieved. This methodology overcomes the accessibility limitations of conventional drilling methods that prevent installation of wells in remote and rugged mountainous terrains.     

A detailed study of the distribution of heat flow and radioactivity in New Hampshire (U.S.A.)

We present a set of 39 new determinations of heat flow and radiogenic heat production for several different geological environments in the State of New Hampshire (U.S.A.). With the extensive data set now available for the state, the linear relation of heat flow and heat production appears as a very useful generalization for the study of the heat flow field of a geological province. Our measurements indicate that the vertical distribution of radiogenic heat production is similar in plutonic and metasedimentary rocks. Our data are compatible with the linear relationship established earlier by F. Birch and his co-workers in 1968. Young granites are markedly enriched in radioactive elements and those which do not outcrop are revealed by anomalies in the general relation of heat flow versus radioactivity.Heat flow is high for plutons by low elsewhere. The mean heat flow through metasedimentary formations is 1.15 μcal/cm² s (48 mW/m²), a value near the mean heat flow for old cratons. The lowest heat flow measured is 0.76 μcal/cm² s (32 mW/m²) for a unit poor in radioactivity. The heat flow field grades smoothly into the low heat flow regions of the Canadian Shield.The New Hampshire region is in thermal equilibrium: its heat flow is in secular equilibrium with the heat generated by crustal sources and that supplied from the mantle. In this area, the thermal perturbations due to orogenic events decrease below the detection level in less than 200–275 Ma. The thickness of the layer which is thermally affected during continent-continent collision-type orogenies cannot be greater than about 190 km.     

Porosity determinations and the thermal conductivity of rock fragments with application to heat flow on Cyprus

A standard core analysis technique has been modified to estimate porosities from measurements on rock fragments. For the range of rocks tested, chip-determined fractional porosities were within ±0.025 of the values measured on solid-core samples. This has enabled thermal conductivity measurements on rock fragments to be corrected for the effect of porosity, yielding agreement with conductivity determinations on solid core generally to better than ± 10%. The application of this is illustrated by the determination of heat flow in a 300-m borehole in western Cyprus (latitude 34°54′N, longitude 32°34′E, elevation 82 m). A decrease in temperature gradient with depth is almost completely compensated for by increasing thermal conductivity, and the best value for heat flow at this site is 23 ± 4 mW m^?2.     

Heat flow map of the European part of the U.S.S.R.

A heat flow isoline map is presented. Low and relatively constant heat flow has been observed in the old shield areas of the East European Platform (25–40 mW/m²). Increased heat flow (>50 mW/m²) has been found in the Dniepr-Donetz depression. The area south of the East European Platform is characterized by highly variable heat flow (55–100 mW/m²). Some geophysical implications are discussed.     

MTS studies on the upper mantle conductivity in China

Based on the data from more than 200 MTS sites distributed within different areas of the Chinese continent, general characteristics of upper mantle conductivity have been described. At least two conductive layers have been found in the upper mantle of some areas. The first is thin with a resistivity of a modicum to few tens m; the second one is thicker with a resistivity of one to m. Nearly 300 heat-flow values indicate that there exists an exponential correspondent relationship between a depth of the upper mantle conductive layer with a thickness and an average value of heat flow. Based on the above results, the top depth map of this upper mantle conductive layer has been outlined for parts of the Chinese continent. This conductive layer is basically consistent with the low velocity zone in the upper mantle, and Cenozoic tectonism and current seismicity are significantly related to the variation of depth of the conductive layer in the upper mantle. The possible origins of the conductive layers in the upper mantle have been discussed here.     

Long-term temperature monitoring in a borehole drilled into the Nojima Fault, southwest Japan

Abstract Long-term monitoring of temperature distribution in an active fault zone was carried out using the optical fiber temperature-sensing technique. An optical fiber cable was installed in a borehole drilled into the Nojima Fault in Awaji Island, south-west Japan, and the temperature profile to a depth of 1460 m had been measured for 2.5 years (July 1997–January 2000). Although the obtained temperature records showed small temporal variations due to drifts of the measurement system all along the cable, local temperature anomalies were detected at two depths. One at around 80 m seems to correspond to a fracture zone and may be attributed to groundwater flow in the fracture zone. This anomaly had been stable throughout the monitoring period, whereas the other anomaly at around 500 m was a transient one. The water level in the borehole could be estimated from the diurnal temperature variations in the uppermost part of the borehole and may provide information on the hydrological characteristics of the fault zone, which is connected to the borehole through perforations on the casing pipe. Except for these minor variations, the temperature profile had been very stable for 2.5 years. The conductive heat flow calculated from this profile and the thermal conductivity measured on core samples increases with depth, probably resulting from errors in thermal conductivity due to sampling problems and/or from advective heat transfer by regional groundwater flow. Assuming that the middle part of the borehole (less fractured granite layer) is least affected by these factors, heat flow at this site is estimated to be approximately 70 mW/m².     

One-Dimensional Thermal Modeling of the Eastern Pontides Orogenic Belt (NE Turkey)

The eastern Pontides orogenic belt is one of the most complex geodynamic settings in the Alpine–Himalayan belt due to the lack of systematical geological and geophysical data. In this study, 1D crustal structure and P-wave velocity distribution obtained from gravity modeling and seismological data in the area has been used for the development of the thermal model of the eastern Pontides orogenic belt. The computed temperature-depth profiles suggest a temperature of 590?±?60°C at a Moho depth of 35?km indicates the presence of a brittle-ductile transition zone. This temperature value might be related to water in the subducted crust of the Tethys oceanic lithosphere. The Curie temperature depth value of 29?km, which may correspond to the crustal magma chambers, is found 5–7?km below the Moho depth. Surface heat flow density values vary from 66.5 and 104.7?mW?m^?2. High mantle heat flow density value of 48?mW?m^?2 is obtained for the area should be related to melting of the lithospheric mantle caused by upwelling of asthenosphere.     

On the evolution of the geothermal regime of the North China Basin

Recent heat flow and regional geothermal studies indicate that the North China Basin is characterized by relatively high heat flow compared with most stable areas in other parts of the world, but lower heat flow than most active tectonic areas. Measured heat flow values range from 61 to 74 mW m⁻². The temperature at a depth of 2000 m is generally in the range 75 to 85°C, but sometimes is 90°C or higher. The geothermal gradient in Cenozoic sediments is in the range 30 to 40°C/km for most of the area. The calculated temperature at the Moho is 560 and 640°C for surface heat flow values of 63 and 71 mW m⁻², respectively. These thermal data are consistent with other geophysical observations for the North China Basin. Relatively high heat flow in this area is related to Late Cretaceous-Paleogene rifting as described in this paper.     

Review of heat flow data from the eastern Mediterranean region

Heat flow data from the eastern Mediterranean region indicates an extensive area of low heat flow, spreading over the whole basin of the Mediterranean east of Crete (Levantine Sea), Cyprus, and northern Egypt. The average of the marine heat flow measurements in the Levantine Sea is 25.7±8.4 mW/m², and the heat flow on Cyprus is 28.0±8.0 mW/m². The estimated values of heat flow in northern Egypt range from 38.3±7.0 to 49.9±9.3 mW/m², apparently with no consistent trend. To the east, on the coast of Israel, the heat flow values increase, ranging from 36.6±22.4 to 56.7±14.2 mW/m² along a SSE trend. The trend apparently correlates with an increase in crustal thickness, which is about 23 km at the north-west base of the Nile-Delta-cone, and close to 40 km beneath Israel.Contribution No. 157, Department of Geology, Kent State University, Kent, Ohio, USA.     

Geothermal observations in east Liaoning and haicheng seismic area

We have obtained altogether heat flux data of 23 drill holes including 2 observational holes of thermal flow in the Haicheng seismic area. These data show roughly thermal structure of the crust in eastern Liaoning and in the Haicheng seismic area. The results indicate that there is higher value of heat flow in the belt north by east from Liaoyang to Xiongyue, the average thermal flux being 8.29× 10⁻²J/m²·s (2.0 hfu). The average thermal fulx in the Haicheng seismic area is 9.22×10²J/m²·s (2.2 hfu). Comparing with other known geophysical data of the Haicheng seismic area, we give a geophysical section of comprehensive interpretation. We suppose the low-velocity layer in the lower crust of the Haicheng seismic area is a result from intrusion of large-scale uper mantle substance. High temperature and low velocity mean that the layer has the nature of plastic mechanics. The focal region of the Haicheng earthquake is situated right in the upper part of that plastic layer. Obviously, this result is significant for studying the seismogenic process of the Haicheng earthquake and other intra-plate earthquakes. We attempt to emphasize that observation of heat flow is necessary for earthquake study. Gu Haoding did the actual writing.