DETAILED GRAVITY STUDY OF THE DANGE ANOMALY IN SOKOTO STATE, NIGERIA
DETAILED GRAVITY STUDY OF THE DANGE ANOMALY IN SOKOTO STATE, NIGERIA
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Date
2000-09
Authors
Egwuonwu, Gabriel Ndubuisi
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Abstract
A detailed gravity survey of the Dange area within the Sokoto Basin, Northwestern
Nigeria has been carried out to determine the structure and probable mode of
emplacement of the causative body of Dange aeromagnetic anomaly. One hundred and
ninety five gravity stations were occupied at one kilometer interval using a LaCoste and
Romberg Model G gravimeter for the relative gravity measurements and two Wallace and
Tiernan Aneroid Altimeters for the elevation determination. Density measurements on one
hundred and ninety six rock samples were carried out to aid the interpretation of the gravity
data.
The Bouguer gravity in the area is characterized by negative anomaly with relative
values ranging in amplitude from -58mGal to -32mGal. The regional field is a plane dipping
at about 10° northeastwards with a gradient of 0.38mGal per km. The residual anomaly
map of the area is characterized by a prominent positive anomaly of +10mGal amplitude
located at the southeastern portion of the survey area. This positive residual anomaly
corresponds well in it's location with the prominent Dange aeromagnetic anomaly which
earlier workers have attributed to an intra basement intrusion underlying the sediment in the
region.
A two and half-dimensional modeling of the residual anomaly suggests a body
which is probably schistotic with depth extent of about 10.0km. It is located at a depth of
about 2.0km with inward dipping contrasts ranging from 20° to 48° in the underlying
basement. This body has probably resulted from a metamorphic process which is believed
to have taken place during the middle Eocene uplift which gave rise to some synclinal
structures and general irregularities of the basement surface in the area.
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Description
A Thesis submitted to the Postgraduate School, Ahmadu Bello University, Zaria in
partial fulfillment of the requirements for the degree of Master of Science, Applied
Geophysics
Keywords
DETAILED, GRAVITY STUDY, DANGE, ANOMALY, SOKOTO STATE, NIGERIA