A detailed gravity profile across the English River Subprovince, northwestern Ontario

1984 ◽  
Vol 21 (2) ◽  
pp. 145-151 ◽  
Author(s):  
V. K. Gupta ◽  
R. B. Barlow
Keyword(s):  
Seismic Data ◽  
Bouguer Anomaly ◽  
Density Data ◽  
Density Measurements ◽  
Anomaly Field ◽  
Red Lake ◽  
Northwestern Ontario ◽  
Crustal Model ◽  
Regional Gravity ◽  
Gravity Profile

This paper presents the results of a detailed gravity profile measured across the two lithotectonic domains of the English River Subprovince from Vermilion Bay to Red Lake, a distance of 190 km, in northwestern Ontario. Along the profile 283 fresh rock samples were collected for density measurements. The density data clearly suggest that there is a measurable and significant density difference between the migmatized metasediments and plutonic rocks.A crustal model based on the seismic data, along the profile, has been used for computing a regional gravity field, which in turn has been used in isolating the residual anomalies from the Bouguer anomaly field. A strong correlation has been found to exist between the residual anomalies, the rock densities, and the surface lithologies. The Northern Supracrustal Domain, which is at its widest (60 km) along the profile, is dominated by a pronounced 15 mGal (150 μm s−2) positive residual anomaly believed to be caused by outcropping, anomalously dense metasediments extending to a modelled depth of approximately 10 km. In the Southern Plutonic Domain the residual anomalies along the profile are small (less than 5 mGal (50 μm s−2)) and limited in depth. The Mystery Lake dome extends to a modelled depth of approximately 2.5 km.

Preliminary determination of crustal structure in the Katmai National Monument, Alaska

1967 ◽  
Vol 57 (6) ◽  
pp. 1367-1392
Author(s):  
Eduard Berg ◽  
Susumu Kubota ◽  
Jurgen Kienle
Keyword(s):  
Crustal Structure ◽  
Seismic Data ◽  
Bouguer Anomaly ◽  
Volcanic Area ◽  
Average Depth ◽  
S Wave ◽  
Contour Map ◽  
Alaska Peninsula ◽  
National Monument

Abstract Seismic and gravity observations were carried out in the active volcanic area of Katmai in the summer of 1965. A determination of hypocenters has been aftempted using S and P arrivals at a station located at Kodiak and two stations located in the Monument. However, in most cases, deviations of travel times from the Jeffreys-Bullen tables were rather large. Therefore hypocenters are not well located. A method based on P- and S-wave arrivals yields a Poisson's ratio of 0.3 for the upper part of the mantle under Katmai. This higher value is probably due to the magma formation. The average depth to the Moho from seismic data in the same area is 38 km and 32 km under Kodiak. Using Woollard's relation between Bouguer anomaly and depth to the Moho, a small mountain root under the volcanoes with a depth of 34 km was found dipping gently up to 31 km on the NW side. The active volcanic cones are located along an uplift block. This block is associated with a 35 mgal Bouguer anomaly. The Bouguer anomaly contour map for the Alaska Peninsula is given and an interpretation attempted.

scholarly journals Ionospheric variations before some large earthquakes over Sumatra

2011 ◽  
Vol 11 (2) ◽  
pp. 597-611 ◽  
Author(s):  
A. M. Hasbi ◽  
M. A. Mohd Ali ◽  
N. Misran
Keyword(s):  
Electron Density ◽  
Earthquake Epicenter ◽  
Equatorial Anomaly ◽  
Density Data ◽  
Density Measurements ◽  
Champ Satellite ◽  
Density Analysis ◽  
Large Earthquakes ◽  
Electron Density Analysis ◽  
Champ Data

Abstract. The paper investigates the ionospheric variations before some large earthquakes that occurred during 2004–2007 in Sumatra using GPS and CHAMP data. The TEC shows the occurrence of positive and negative anomalies detected within a few hours to 6 days before the earthquakes. These anomalies mostly occur during the daytime hours between 4 and 17 LT. The TEC anomalies are mostly consistent with the CHAMP satellite electron density data. The electron density analysis over the 28 March 2005 earthquake epicenter shows that an equatorial anomaly modification took place a few days before the event. The modification took shape in the form of crest amplification during the daytime. The comparison between the TEC and electron density measurements during very quiet geomagnetic conditions is shown to be a useful indicator of a forthcoming earthquake.

REGIONAL GRAVITY SURVEY IN NORTHEASTERN OKLAHOMA AND SOUTHEASTERN KANSAS

Geophysics ◽  
1956 ◽  
Vol 21 (1) ◽  
pp. 88-106 ◽  
Author(s):  
Kenneth L. Cook
Keyword(s):  
Structural Geology ◽  
Bouguer Anomaly ◽  
Gravity Anomalies ◽  
Close Correlation ◽  
Geodetic Survey ◽  
Gravity Survey ◽  
Complex Nature ◽  
Gravity Gradients ◽  
Anomaly Map ◽  
Regional Gravity

In 1948 the U. S. Geological Survey, in cooperation with the U. S. Coast and Geodetic Survey, made a regional gravity survey in northeastern Oklahoma and southeastern Kansas in connection with the studies of the deflection of the vertical. About 550 gravity stations were occupied with spacings of 5 to 10 miles in parts of 54 counties, and a Bouguer anomaly map, contoured at intervals of 5 milligals, was drawn. In southeastern Kansas there is a lack of correlation of regional gravity with known regional structural geology. The observed gravity anomalies are apparently caused principally by variations of density in the Precambrian basement and indicate a basement of complex nature, made up of rocks of contrasting properties, with a regional grain striking predominantly west or west‐northwest. In northeastern Oklahoma the several observed regional gravity anomalies indicate different degrees of correlation of regional gravity with regional structural geology. In the Precambrian highland area in Osage, Pawnee, and Creek Counties, there is a lack of correlation, as the gravity anomaly is probably caused chiefly by density contrasts within the basement complex. The anomaly associated with the Hunton arch is probably caused partly by structural relief of the rocks of pre‐Pennsylvanian age and partly by density contrasts within the basement, and thus indicates some correlation. The steep gravity gradients along the outer flanks of the Ozark uplift indicate good correlation with the subsurface geology. The great anomaly over the Arkansas basin, which indicates a close correlation, is probably caused largely—but perhaps not entirely—by downwarping of the basement and pre‐Pennsylvanian rocks.

Regional gravity anomaly map and crustal model of the Central–Southern Apennines (Italy)

2005 ◽  
Vol 40 (1) ◽  
pp. 73-91 ◽  
Author(s):  
M.M. Tiberti ◽  
L. Orlando ◽  
D. Di Bucci ◽  
M. Bernabini ◽  
M. Parotto
Keyword(s):  
Gravity Anomaly ◽  
Southern Apennines ◽  
Crustal Model ◽  
Anomaly Map ◽  
Regional Gravity

Alteration, mineralization, and metamorphism in the area of the East South "C" ore zone, 24th level of the Dickenson mine, Red Lake, northwestern Ontario

1984 ◽  
Vol 21 (1) ◽  
pp. 35-52 ◽  
Author(s):  
Neil A. Mathieson ◽  
C. Jay Hodgson
Keyword(s):  
Volcanic Rocks ◽  
Fluid Pressure ◽  
Chemical Effect ◽  
Iron Formation ◽  
Mesoscopic Scale ◽  
Red Lake ◽  
Northwestern Ontario ◽  
Mineral Associations ◽  
Mineral Assemblages ◽  
Volcaniclastic Rocks

The area of the East South "C" (ESC) orebody of the Dickenson mine, Red Lake, consists of variably altered and mineralized basalt, basaltic volcaniclastic rocks, minor sulphidic iron formation, and a series of mainly postdeformation dykes. Except for the dykes, the rocks are in general well foliated. The macroscopic structural geometry of the stratiform rocks has been determined to a large extent by movement on schistosity-parallel faults.Three broad types of mineralization or alteration are recognized: an Na–Ca–Mg depletion with associated Fe–Mn enrichment controlled by primary permeable structures in basalt; a series of carbonate and quartz or "chert" veins emplaced into fissures; and auriferous silicified and sulphidized zones controlled by vein-filled fractures. The last is the main mineralization type in the ESC orebody on the 24th level of the mine, which was the focus of this study. Although all mineralization types occur within the mine, they are not directly associated either temporally or spatially on a mesoscopic scale. All, however, appear to have been overprinted by or formed synchronously with the amphibolite-facies metamorphism.A rich variety of metamorphic mineral assemblages occurs in the volcanic rocks because of the chemical effect of pre- or synmetamorphic hydrothermal alteration. These assemblages and the composition and mineral associations of arsenopyrite in the ESC orebody closely constrain the conditions of metamorphism to 520–540 °C and 3.8–4.2 kbar (380–420 MPa) fluid pressure.

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