GRAVITY ANOMALY

CONFIRMED IMPACT CRATERS

BRENT

Bouguer gravity anomaly over Gilmour and Tecumseh lakes region. The crater lies at the center (Modified from Millman et al, 1960.

A gravity anomaly at the Brent Crater produced by the sediments and fragmented rocks in the crater reinforces the meteoritic origin of this crater similar to other structures (seeWest Hawk and Wanapitei) that have been identified as impact events by similar gravity anomalies. It is interesting to note that in this gravity map that was published in 1960 the magnetic north had an indicated west declination (variation) of 10° 05’ W. Today in 2012 it is 12° 00’ W. The change is due to the drift of the magnetic north pole over the past 52 years (Chavez 1986).

BEAVERHEAD

Bouguer gravity map of region surrounding the proposed thrust detached root to the Beaverhead structure, East Idaho.

CARSWELL

CHICXULUB

Chicxulub crater image of its gravitational field (NASA)

CLEARWATER

GLOVER BLUFF

 

Bouguer gravity map showing the location of the Glover Bluff disturbed area (gravity data from Koenen, 1956). Contours in milligals. B, Ground magnetic map showing the location of the Glover Bluff disturbed area (magnetic data from Koenen, 1956). Contours in gammas.

HOLLEFORD

The Bouguer gravity anomaly map produced by the Gravity Division, indicate that the gravity magnitude contours were circular and follow in a general way the outline of the impact structure depression. The central gravity low indicates an anomaly of approximately two milligals. This suggests a circular depression filled to an estimated depth of ~250 metres with material which is on the average of a lower density than the surrounding Precambrian rocks.

MANICOUAGAN CRATER / CAN-AM STRUCTURE

There is a strong similarity between the profiles of the Can-Am structure and the Manicouagan Impact Crater. The coincidence between magnetic and gravity signatures strongly suggests a common source for both fields. This data documents that the Precambrian basement rocks are interrupted by anomalies that clearly outline the circular nature of the structure and provides evidence that the remnants of a complex meteorite crater is situated in the south end of Lake Huron.

MAPLE CREEK

MONTAGNAIS

Bouguer gravity analysis of the Montagnais impact crater.

PINGUALUIT

WANAPETEI

(Dence and Popelar 1972).
Geophysical evidence is in the form of a circular gravity low of ~15 mgal, documented in this Bouguer gravity anomaly map. The low is observed over the north-central, island free area of the lake. This gravity anomaly reinforces the meteoritic origin of this structure similar to other structures (see West Hawk and Brent) that have been identified as impact events by similar gravity anomalies. The data was corrected using water depth measurements from the Ontario Department of Lands and Forests.

WEST HAWK

 

A gravity survey of the West Hawk Lake and surrounding region (Halliday and Griffin 1963) indicated a peak negative gravity anomaly of over 6 milligals, illustrated in the Bouguer anomaly map (right) of the West Hawk Lake Impact Crater. The anomaly is produced by the sediments and fragmented rocks under the crater. This gravity anomaly reinforces the meteoritic origin of this crater similar to other craters (see Brent and Wanapitei) that have been identified as impact events by similar gravity anomalies.

SUSPECTED IMPACT CRATERS

CAN-AM (PROBABLE) IMPACT STRUCTURE

Can-Am bouguer anomaly field. G.F. = Grenville front.

Odale-canam-Gravity profiles.jpg