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.

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.

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.

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 of the lithosphere in the Canadian ShieldThis article is one of a series of papers published in this Special Issue on the theme Lithoprobe — parameters, processes, and the evolution of a continent.

2010 ◽  
Vol 47 (4) ◽  
pp. 389-408 ◽  
Author(s):  
Claire Perry ◽  
Carmen Rosieanu ◽  
Jean-Claude Mareschal ◽  
Claude Jaupart
Keyword(s):  
Heat Flow ◽  
Heat Generation ◽  
Seismic Refraction ◽  
Surface Heat ◽  
Canadian Shield ◽  
P Wave ◽  
Seismic Velocities ◽  
Flow Measurements ◽  
Surface Heat Flow ◽  
Mantle Heat Flow

Geothermal studies were conducted within the framework of Lithoprobe to systematically document variations of heat flow and surface heat production in the major geological provinces of the Canadian Shield. One of the main conclusions is that in the Shield the variations in surface heat flow are dominated by the crustal heat generation. Horizontal variations in mantle heat flow are too small to be resolved by heat flow measurements. Different methods constrain the mantle heat flow to be in the range of 12–18 mW·m–2. Most of the heat flow anomalies (high and low) are due to variations in crustal composition and structure. The vertical distribution of radioelements is characterized by a differentiation index (DI) that measures the ratio of the surface to the average crustal heat generation in a province. Determination of mantle temperatures requires the knowledge of both the surface heat flow and DI. Mantle temperatures increase with an increase in surface heat flow but decrease with an increase in DI. Stabilization of the crust is achieved by crustal differentiation that results in decreasing temperatures in the lower crust. Present mantle temperatures inferred from xenolith studies and variations in mantle seismic P-wave velocity (Pn) from seismic refraction surveys are consistent with geotherms calculated from heat flow. These results emphasize that deep lithospheric temperatures do not always increase with an increase in the surface heat flow. The dense data coverage that has been achieved in the Canadian Shield allows some discrimination between temperature and composition effects on seismic velocities in the lithospheric mantle.

scholarly journals The 31 March 2020 Mw 6.5 Stanley, Idaho, Earthquake: Seismotectonics and Preliminary Aftershock Analysis

2020 ◽  
Author(s):  
Lee M. Liberty ◽  
Zachery M. Lifton ◽  
T. Dylan Mikesell
Keyword(s):  
Surface Displacement ◽  
Volcanic Belt ◽  
Normal Fault ◽  
Fault System ◽  
Basin And Range Province ◽  
Ground Shaking ◽  
The North ◽  
Show Evidence ◽  
Tectonic Framework ◽  
Tectonic Belt

Abstract We report on the tectonic framework, seismicity, and aftershock monitoring efforts related to the 31 March 2020 Mw 6.5 Stanley, Idaho, earthquake. The earthquake sequence has produced both strike-slip and dip-slip motion, with minimal surface displacement or damage. The earthquake occurred at the northern limits of the Sawtooth normal fault. This fault separates the Centennial tectonic belt, a zone of active seismicity within the Basin and Range Province, from the Idaho batholith to the west and Challis volcanic belt to the north and east. We show evidence for a potential kinematic link between the northeast-dipping Sawtooth fault and the southwest-dipping Lost River fault. These opposing faults have recorded four of the five M≥6 Idaho earthquakes from the past 76 yr, including 1983 Mw 6.9 Borah Peak and the 1944 M 6.1 and 1945 M 6.0 Seafoam earthquakes. Geological and geophysical data point to possible fault boundary segments driven by pre-existing geologic structures. We suggest that the limits of both the Sawtooth and Lost River faults extend north beyond their mapped extent, are influenced by the relic trans-Challis fault system, and that seismicity within this region will likely continue for the coming years. Ongoing seismic monitoring efforts will lead to an improved understanding of ground shaking potential and active fault characteristics.

A new locality for primary xenolith-bearing nephelinites in northwestern British Columbia

1985 ◽  
Vol 22 (10) ◽  
pp. 1556-1559 ◽  
Author(s):  
Michael D. Higgins ◽  
John M. Allen
Keyword(s):  
British Columbia ◽  
Trace Element ◽  
Volcanic Belt ◽  
Primary Magma ◽  
Similar Composition ◽  
Element Abundances ◽  
Late Tertiary

High Ni abundances (420–500 ppm) and Mg* values (100 × Mg/(Mg + Fe2+) = 69–71) and the presence of mantle-derived xenoliths indicate that a subvolcanic nephelinite intrusion in northwestern British Columbia represents an unmodified primary magma. A separate, closely associated nephelinite intrusion shows evidence of minor olivine fractionation from a similar composition. Only three other occurrences of primary nephelinite have been described. This new occurrence suggests that these magmas may not be so rare as previously supposed. The trace-element abundances closely resemble those of primary nephelinites of similar La content from Freemans Cove, Canada. Such compositions are usually taken as evidence of intraplate rifting and doming. Therefore, these rocks are further evidence of late Tertiary or Quaternary rifting in the Stikine volcanic belt.

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