A GRAVITY INVESTIGATION OF THE YOUNGER GRANITES IN LERE/SAMINAKA AREA, KADUNA STATE, NIGERIA
A GRAVITY INVESTIGATION OF THE YOUNGER GRANITES IN LERE/SAMINAKA AREA, KADUNA STATE, NIGERIA
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Date
1994-04
Authors
EKWUE, ELEAZER UCIIECIIUKWU
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Abstract
A g r a v i t y survey of the Younger Grinite s u i t e s around
Lere-Saminaka was c a r r i e d out to obtain more s u b s u r f a ce
i n f o r m a t i o n on the Geology of the area following a general
s t u d y e a r l i e r c a r r i e d out on the Younger G r a n i t e s e r i e s of
N i g e r i a in the e a r l y s e v e n t i e s . A number of g r a v i t y and
h e i g h t m e a s u r e m e n t s were c a r r i e d out on 190 field s t a t i o n s in
Saminaka a r e a . Also, a t o t a l of 154 f r e s h rock samples were
c o l l e c t e d from the field to aid i n t e r p r e t a t i o n of the field
r e s u l t s . The r e s u l t showed that the a r e a is c h a r a c t e r i s e d by
n e g a t i v e Bouguer Anomaly ranging from -26 mgal in the
n o r t h e a s t part, to -80 mgal in the c e n t r e of the s o u t h e rn
p o r t i o n of the s u r v e y e d a r e a . The mean value for all the
s t a t i o n s is -55 mgal.
A two dimensional i n t e r p r e t a t i o n of the r e s i d u a ls
c a r r i e d out along t h r e e d i f f e r e n t p r o f i l e s i n d i c a t e t h a t the
Younger Granite s u i t e s in the area extend to d e p t h s of 7.5
to 11.5 km with a d e n s i t y of 2.62 kg.m-3 in c o n t r a s t to an
a v e r a g e d e n s i t y of 2.65 kg-m- 3 for the basement complex which
t h e y i n t r u d e . S t r u c t u r a l l y , the c o n t a c t s between the Younger
G r a n i t e s and the basement complex is v e r t i c a l in some p l a c es
and inclined in some other, with outward dips and spread
l a t e r a l l y at depth beyond the exposed c o n t a c t.
The models also suggest the e x i s t e n c e of some
unexposed i n t r u s i o n s in the area. These i n t r u s i o n s are
s u s p e c t e d to be b a s a l t in J a n g r e a r e a and in Mariri a r e as
r e s p e c t i v e l y ; dolerite towards the e a s t of Saminaka and the
g r a n i t e around Saminaka.
The l a r g e n e g a t i v e Bouguer anomalies and the r e l a t i v e ly
low d e n s i t y values of the g r a n i t e s as compared to t h o s e of
t h e surrounding host rocks strongly indicate the acidic
n a t u r e of the Younger G r a n i t e , and hence the p o s s i b i l i t y of a
p a r e n t magma as the s o u r c e.
Description
A thesis submitted to the Postgraduate School
Ahmadu Bello University, Zaria,
in p a r t i a l fulfilment of the requirements for the award of
the degree of
Master of Science in Applied Geophysics.
Keywords
GRAVITY, INVESTIGATION, YOUNGER, GRANITES, LERE/SAMINAKA, AREA, KADUNA STATE, NIGERIA