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TitleGravity surveys in the Alexandria area, eastern Ontario
AuthorSobczak, L W
SourcePublications of the Dominion Observatory vol. 39, no. 6, 1970, 19 pages, (Open Access)
MapsPublication contains 1 map
Map Info.geophysical, gravity, ground
Mediapaper; on-line; digital
File formatpdf
Subjectsgeophysics; regional geology; densities; densities; gravity interpretations; mohorovicic rise; gravity surveys, ground; Alexandria High; Billings Formation; Chatham-grenville Stock; Eastview Formation; Grenville Series; March Formation; Morin Series; Nepean Formation; Ottawa Formation; Oxford Formation; Rigaud Stock; Rockcliffe Formation; St Martin Formation; Trembling Mountain Series; Precambrian; Ordovician
Illustrationsgravity profiles
Released1970 01 01; 2018 11 19
AbstractThe results of 1700 gravity observations completed by the Dominion Observatory from 1945 to 1964 are presented in the form of a Bouguer anomaly map. Seven profiles are analyzed. The Bouguer anomalies are correlated with magnetic and geological information and the interpretation of the gravity datais based on rock density measurements. Two maps showing the compu ted first and second vertical derivatives of gravity are also presented. Negative Bouguer anomalies are correlated with the Chatham-Grenville syenite stock and a similar intrusion at Mount Rigaud on the southern border of the Grenville-A subprovince. lt is postulated that the negative anomaly near Plaisance indicates the presence of a sirtlilar intrusion below the Paleozoic cover. The Alexandria High, a positive residual Bouguer anomaly which extends Crom Lunenburg to Pointe-au-Chêne, may be explained by the presence of a basic lenticular body of thickness varying Crom 6000 to 9000 feet and width of 50,000 feet at a depth varying from 3000 to 5000 feet. The approximate thickness of the Grenville Series is 11,000 to 12,000 feet along the crest of the Alexandria High. The regional gravity gradient which increases from -30 mgal in the northwest to +10 mgal in the southeast of the area is correlated with arise of over 3 kilometres (10,000 feet) of the Mohorovicic discontinuity.