Review: The thermal regime along the southern Canadian Cordillera Lithoprobe corridor

1995 ◽  
Vol 32 (10) ◽  
pp. 1611-1617 ◽  
Author(s):  
R. D. Hyndman ◽  
T. J. Lewis
Keyword(s):  
Heat Flow ◽  
Heat Generation ◽  
Thermal Regime ◽  
Volcanic Belt ◽  
Normal Fault ◽  
High Heat ◽  
General Level ◽  
Canadian Cordillera ◽  
Seismic Structure ◽  
Brittle Ductile Transition

This summary article describes the surface heat flow and heat generation data available for the Southern Canadian Cordillera Lithoprobe Transect, and the inferred crustal temperatures. At the western end of the transect, the continental margin has the characteristic heat flow pattern of a subduction zone; there are high heat flows over the young oceanic crust of the deep-sea Cascadia Basin (~120 mW·m−2), decreasing values landward on the continental slope and shelf (90–50 mW·m−2), and very low heat flow and low crustal temperatures in the forearc region of Vancouver Island and the adjacent mainland (30–40 mW·m−2). Very high and irregular heat flow occurs in the Garibaldi Volcanic Belt at the northern end of the Cascade volcanic arc. To the east, across the Intermontane and Omineca belts to the Rocky Mountain Trench, the heat flow and inferred crustal temperatures are high. The highest values are in the east in the Omineca Belt, where the radioactive heat generation is especially great. The crustal thermal regime has important implications for the interpretation of the deep seismic structure: (1) The brittle–ductile transition (~450 °C), which occurs in the mid-crust for most of the transect, is expected to represent a general level of thrust and normal fault detachment. The deeper crust may be mechanically decoupled from that above. (2) Crustal thickness may be related to temperature. If the lithosphere temperature is high and its density decreased by thermal expansion, there can be isostatic equilibrium with a thin crust and high topography. (3) The thermal regime appears to control the depth to the widespread crustal reflectivity and high electrical conductivity in the deep crust.

Crustal temperatures near the Lithoprobe Southern Canadian Cordillera Transect

1992 ◽  
Vol 29 (6) ◽  
pp. 1197-1214 ◽  
Author(s):  
T. J. Lewis ◽  
W. H. Bentkowski ◽  
R. D. Hyndman
Keyword(s):  
British Columbia ◽  
Heat Flow ◽  
Heat Generation ◽  
Lower Crust ◽  
Volcanic Belt ◽  
The United States ◽  
Canadian Cordillera ◽  
Upper Crust ◽  
Thermal Data ◽  
Seismic Reflectors

Heat flow and radioactive heat generation have been measured and the data compiled across southern British Columbia in the region of the Lithoprobe Southern Canadian Cordillera Transect. Heat flow in the trench-arc zone between the continental margin and the Garibaldi volcanic belt is very low, but in the volcanic belt it is high and very irregular. Farther inland, to the east, the heat flow is moderately high, with the highest values in southeastern British Columbia, associated with high surface radioactive heat production. The thermal data from the central and eastern interior of southern British Columbia define a single heat-flow province with a reduced heat flow of 63 mW/m2 flowing into the upper crust. This indicates a warm, thin lithosphere similar to that of the Basin and Range of the United States to the south. Occurrences of seismic reflective bands in the lower crust of the Cordillera were compared with temperatures calculated from surface heat flow and heat generation using a simple one-dimensional conductive model. The 450 °C isotherm corresponds approximately to the brittle– ductile transition, and deeper crust may be rheologically detached from the upper crust. Where the thermal data approximately coincide with the transect seismic reflection lines, the 450 °C isotherm often corresponds to the top of characteristic sub-horizontal reflector bands, as found in Phanerozoic areas elsewhere around the world. The lower limit of the reflective band in a number of Cordilleran reflection sections is near the 730 °C isotherm, which corresponds to the transition from present "wet" amphibolite- to "dry" granulite-facies conditions. This control of the depth to the deep crustal reflective bands by present temperature provides support for the model of the reflectors being produced by fluids trapped at lithostatic pressure (layered porosity), a model that can also explain the high electrical conductivity in the deep crust of the area. The probable rheological detachment of the lower crust and a possible nonstructural origin of the deep reflectors require that interpreted lower crustal structural boundaries such as the top of the basement of the North American craton under the Lithoprobe Southern Canadian Cordillera Transect be treated with caution. However, there is no doubt that many seismic reflectors are related to crustal structures, and the model is presented as an explanation for bands of seismic reflectors in the lower Phanerozoic crust, not as a model for all seismic reflectors.

scholarly journals Terrestrial Heat Flow in New Zealand

2021 ◽  
Author(s):  
◽  
Om Prakash Pandey
Keyword(s):  
New Zealand ◽  
Heat Flow ◽  
Heat Generation ◽  
Plate Tectonics ◽  
High Heat ◽  
The North ◽  
Rock Types ◽  
Flow Heat ◽  
Geophysical Anomalies ◽  
First Time

<p>In this regional heat flow study of New Zealand temperatures have been measured in available boreholes using a specially constructed thermistor probe, and existing temperature information has been incorporated from various sources including oil prospecting boreholes. Thermal conductivity has been measured in the laboratory on 581 samples. Newly determined values of heat flow are given for 105 locations; values for the South Island are here presented for the first time. Most of the heat flow values have been grouped in eight regions based on the level of heat flow. This classification can be related to the occurrence of certain surface manifestations and geophysical anomalies, and to regional plate tectonics. High heat flow in three regions is consistent with melting conditions being reached at depths between 35km and 45km. These are the Taranaki Region, the West Coast Region and the Great South Basin. The average regional heat flow for these regions varies from 86.4 mW/m2 to 110.7 mW/m2. Much lower heat flow is obtained in the Hikurangi and Marlborough-Canterbury Regions; these may possibly be interconnected. Elsewhere the heat flow is low to normal with isolated highs. The broad distribution of heat flow in the North Island is typical for an active subduction region. Radioactive heat generation has been measured on rock types from various localities, and large variations have been found. The heat flow - heat generation relationship has been studied for 42 sites. A linear relationship is found only in the Taranaki and Hikurangi Regions. Temperature calculations show large differences in the deep-seated temperature distribution beneath New Zealand, and this has also been reflected in the distribution of "reduced heat flow". Temperature and heat flow can be correlated with upper mantle inhomogeneity. The inferred variation of radioactive heat generation with depth has been studied for areas beneath the Western Canterbury Region. A mean heat generation of 1.56 plus-minus .07 muW/m3 has been found in a sequence which has been inferred to occur between 17km and 30km in depth under the region; this is very much higher than the usually adopted values for the lower crust. Normal heat flow observed in the Western Cook Strait Region, and the existence of good seismic wave transmission beneath the same region, can be attributed to crustal and lithospheric thickening. The relevance of present study to petroleum occurrences has been examined and it is found that in areas of proven hydrocarbon potential the heat flow is high.</p>

scholarly journals Terrestrial Heat Flow in New Zealand

2021 ◽  
Author(s):  
◽  
Om Prakash Pandey
Keyword(s):  
New Zealand ◽  
Heat Flow ◽  
Heat Generation ◽  
Plate Tectonics ◽  
High Heat ◽  
The North ◽  
Rock Types ◽  
Flow Heat ◽  
Geophysical Anomalies ◽  
First Time

<p>In this regional heat flow study of New Zealand temperatures have been measured in available boreholes using a specially constructed thermistor probe, and existing temperature information has been incorporated from various sources including oil prospecting boreholes. Thermal conductivity has been measured in the laboratory on 581 samples. Newly determined values of heat flow are given for 105 locations; values for the South Island are here presented for the first time. Most of the heat flow values have been grouped in eight regions based on the level of heat flow. This classification can be related to the occurrence of certain surface manifestations and geophysical anomalies, and to regional plate tectonics. High heat flow in three regions is consistent with melting conditions being reached at depths between 35km and 45km. These are the Taranaki Region, the West Coast Region and the Great South Basin. The average regional heat flow for these regions varies from 86.4 mW/m2 to 110.7 mW/m2. Much lower heat flow is obtained in the Hikurangi and Marlborough-Canterbury Regions; these may possibly be interconnected. Elsewhere the heat flow is low to normal with isolated highs. The broad distribution of heat flow in the North Island is typical for an active subduction region. Radioactive heat generation has been measured on rock types from various localities, and large variations have been found. The heat flow - heat generation relationship has been studied for 42 sites. A linear relationship is found only in the Taranaki and Hikurangi Regions. Temperature calculations show large differences in the deep-seated temperature distribution beneath New Zealand, and this has also been reflected in the distribution of "reduced heat flow". Temperature and heat flow can be correlated with upper mantle inhomogeneity. The inferred variation of radioactive heat generation with depth has been studied for areas beneath the Western Canterbury Region. A mean heat generation of 1.56 plus-minus .07 muW/m3 has been found in a sequence which has been inferred to occur between 17km and 30km in depth under the region; this is very much higher than the usually adopted values for the lower crust. Normal heat flow observed in the Western Cook Strait Region, and the existence of good seismic wave transmission beneath the same region, can be attributed to crustal and lithospheric thickening. The relevance of present study to petroleum occurrences has been examined and it is found that in areas of proven hydrocarbon potential the heat flow is high.</p>

Geothermal measurements in northern British Columbia and southern Yukon Territory

1984 ◽  
Vol 21 (5) ◽  
pp. 599-608 ◽  
Author(s):  
Alan M. Jessop ◽  
J. G. Souther ◽  
Trevor J. Lewis ◽  
A. S. Judge
Keyword(s):  
British Columbia ◽  
Heat Flow ◽  
Heat Generation ◽  
Water Movement ◽  
Volcanic Belt ◽  
Yukon Territory ◽  
Eastern United States ◽  
Basin And Range Province ◽  
Probable Effect ◽  
Few Data

Measurements at seven sites in the Intermontane region of northern British Columbia and southern Yukon show heat flow of 63–100 mW/m2 and heat generation, obtained from intrusive rocks at three of these sites, of 1.8–6.5 μW/m1. These few data cannot define a linear relation between heat flow and heat generation for this region, but the plotted points lie between the lines of the stable crust of the eastern United States and of the Basin and Range Province. Conductive thermal models of the crust, assuming a basalt composition for the lower crust, predict at 35 km depth a heat flow of 30 mW/m2 and temperatures between 645 and 775 °C at most sites.At two sites conductive models based on reasonable properties do not yield reasonable temperatures. The site on the axis of the Stikine Volcanic Belt shows a probable component of convectively enhanced heat flow or the presence of a young intrusion at depth. The site in the Bowser Basin shows the probable effect of water movement in the sediments.

Heat flux measurements in southwestern British Columbia: the thermal consequences of plate tectonics

1985 ◽  
Vol 22 (9) ◽  
pp. 1262-1273 ◽  
Author(s):  
T. J. Lewis ◽  
A. M. Jessop ◽  
A. S. Judge
Keyword(s):  
Heat Flux ◽  
British Columbia ◽  
Heat Flow ◽  
Heat Generation ◽  
High Heat ◽  
Heat Fluxes ◽  
Eastern Coast ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Reduced Heat Flow

Measured heat fluxes from previously published data and 34 additional boreholes outline the terrestrial heat flow field in southern British Columbia. Combined with heat generation representative of the crust at 10 sites in the Intermontane and Omineca belts, the data define a heat flow province with a reduced heat flow of 63 mW m−2 and a depth scale of 10 km. Such a linear relationship is not found or expected in the Insular Belt and the western half of the Coast Plutonic Complex where low heat fluxes are interpreted to be the result of recent subduction. The apparent boundary between low and high heat flux is a transition over a distance of 20 km, located in Jervis Inlet 20–40 km seaward of the Pleistocene Garibaldi Volcanic Belt.The warm, thin crust of the Intermontane and Omenica Crystalline belts is similar to that of areas of the Basin and Range Province where the youngest volcanics are more than 17 Ma in age. Processes 50 Ma ago that completely heated the crust and upper mantle could theoretically produce such high heat fluxes by conductive cooling of the lithosphere. But it is more likely that the asthenosphere flows towards the subduction zone, bringing heat to the base of the lithosphere. Since the reduced heat flow is high but constant, large differences in upper crustal temperatures within this heat flow province at present are caused by large variations in both crustal heat generation and near-surface thermal conductivity. The sharp transition in heat flux near the coast is the result of the combined effects of convective heating of the eastern Coast Plutonic Complex, pronounced differential uplift and erosion across a boundary within the Coast Plutonic Complex, and the subducting oceanic plate.

Thermal regime and hydrodynamics in Tunisia and Algeria

Geophysics ◽  
1991 ◽  
Vol 56 (7) ◽  
pp. 1093-1102 ◽  
Author(s):  
Hamed Ben Dhia
Keyword(s):  
Heat Flow ◽  
Transition Zone ◽  
Thermal Regime ◽  
High Heat ◽  
Hydrodynamic Regime ◽  
High Heat Flow ◽  
Normal Heat ◽  
Tectonically Active ◽  
Potential Recharge ◽  
Hydrodynamic Perturbation

The thermal regime of Algeria and Tunisia and its relation to hydrodynamics is studied by means of available geological and geothermal, and petroleum data. Heat flow densities in the area range from [Formula: see text] to [Formula: see text]. Several Paleozoic to Tertiary aquifers have been identified, together with potential recharge and discharge areas. The area is a transition zone between the African and European plates. The more tectonically active northern Alpine domain does not exhibit an obvious geothermal trend, and high heat flow anomalies that occur there may be related to structure rather than hydrodynamics. The more stable southern Saharan tectonic domain, with background heat flow of approximately [Formula: see text], exhibits anomalous zones correlated to the hydrodynamic regime with low values in recharge areas (Algerian Tinrhert and High Plateaux) and values in discharge areas (Tunisian Jeffara and Algerian Tademait). The hydrodynamic perturbation to the normal heat flow is estimated to be as great as [Formula: see text] in recharge and discharge zones.

Estimates of terrestrial heat flow in offshore eastern Canada

1985 ◽  
Vol 22 (10) ◽  
pp. 1503-1517 ◽  
Author(s):  
Marshall Reiter ◽  
Alan M. Jessop
Keyword(s):  
Heat Flow ◽  
Heat Generation ◽  
Newfoundland And Labrador ◽  
High Heat ◽  
Magmatic Activity ◽  
Shelf Edge ◽  
Eastern Canada ◽  
Heat Flows ◽  
Bottom Hole ◽  
Outer Half

From available bottom-hole temperatures and conductivities estimated from lithologic descriptions, heat-flow estimates are calculated for 72 sites on the Canadian Atlantic Shelf. The resulting data suggest a pattern of low heat flow (~055 mW/m2) within the Paleozoic basins in proximity to land areas and generally intermediate heat flow (~60–80 mW/m2) along the outer half of the continental shelf. Higher heat flows (~90 mW/m2) are estimated along the shelf edge in some areas, e.g., the southwestern Scotian Shelf and the eastern Newfoundland and Labrador shelves. Radioactive heat generation in sediments that thicken seawards probably does not account for the observed increase in heat flow. The possibility that higher heat flows in some areas may arise because of fluid movement from depth is suggested. Various other causes for the high heat flows, e.g., tectonic or magmatic activity, are considered less likely.

Sign in / Sign up

Export Citation Format

Share Document