THE GEOTECTONIC EVOLUTION OF THE KAZAURE SCHIST BELT IN THE PRECAMBRIAN BASEMENT OF NW NIGERIA
THE GEOTECTONIC EVOLUTION OF THE KAZAURE SCHIST BELT IN THE PRECAMBRIAN BASEMENT OF NW NIGERIA
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Date
1999-10
Authors
DANBATTA, UMAR ADAMU
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Abstract
In this study, a systematic geological investigation of the
Kazaure Schist Belt (KZSB) and its adjacent areas in the
basement of northwestern Niqeria have led to the
interpretation of its qeotectonic evolution, and the
production of a geological map on a scale of 1:100,000. The
KZSB consists predominantly of quartettes, politic rocks, and
metaconqlomerates. Minor rocks include metavolcanics,
meta-sandstones and ferruqinous quartzite s.
The Belt as a whole is enclosed by miqmatite-qneiss basement
and I-type Older Granites. The mitigate-qneiss basement
comprises of mitigate, biotech gneiss and Older Meta-sediments
and underlies the Younger Meta-sediments. However the granites
are considered to be intrusive into the meta sediments. The
Kalanqai Fault System (Truswell and Cope, 1963) of Birnin
Gwari-Malumfashi Schist Belts is shown to extend into the KZSB
and even beyond. It has produced fault breccias and granitic
rocks which have now been studied in detail.
The rocks in the area have been subjected to at least two
intense phases of ductile deformation (Dj and D2), which
conform to a pattern of recumbent N-S trending Fl folds
locally refolded to NNE-SSW trending upright F2 folds and
affected by granite intrusion and heterogeneous strain related
to faulting. The deformation events were accompanied by two
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phases of progressive regional metamorphism followed bv a
static metamorphic phase. The first phase of reqional
metamorphism attained amphitheater fancies (Mj), whilst the
second phase was of revanchist fancies (M2).
The granitic rocks in the KZSB have limited range in SiO2
(69.76-72.03%), have hiqh alkali contents, low CaO and MqO
values and a Sand index of < 2. In the meta-sediments the
values of potash are higher than those of soda, contents of
alumina are hiqh, MqO is in excess of CaO, while there is
relative liqht R.E.E. enrichment relative to heavy R.E.E
depletion in the schists. Geochemical characterisation
indicates the Kazaure qranitoids to be I-type qenerated in a
syn-collisional settinq and the metasediments oriqinated from
post-Archaen qreywacke-type sediments.
Five samples of a syntectonic coarse-qrained porphvritic
qranite define a 4-point, whole-rock Rb-Sr. errorchron
correspondinq to an aqe of 592 +14 Ma with an initial ratio
of 0.7097 + 0.0004. This is distinctly a Pan-African aqe and
is taken as the crystallization aqe of the qranite. The aqe of
D1 and D2 deformations and metamorphisms in the Kazaure Belt
is therefore shown to be Pan-African. However the Younqer
Granite rocks of the Daura Iqneous Complex rocks were emplaced
much later durinq the Mesozoic era (Jacobson et al.. 1964).
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These with other supportive qeological data from adiacent
schist belts have allowed the erection of a model of evolution
for the KZSB. The KZSB evolved throuqh ensialic processes on
the miqmatite-gneiss basement with the protoliths forminq the
metasediments deposited in a predominantly shelf or deltaic
environment to allow deposition of coarse clastic sediments.
This model has specifically been linked to basinal marqin
development related to the compressional reqimes of the Pan-
African subduction at the West African craton marqin. The
Kazaure basin developed as a result of dominq, extension and
continental riftinq due to back-arc spreadinq related to the
Pan-African subduction.
Description
A DISSERTATION SUBMITTED TO THE
POSTGRADUATE SCHOOL, AHMADU
BELLO UNIVERSITY, IN PARTIAL
FULFILLMENOF THE REQUIREMENTS
FOR THE AWARD OF THE DEGREE OF
DOCTOR OF PHILOSOPHY ( P h . D .)
DEPARTMENT OF GEOLOGY,
FACULTY OF SCIENCE,
AHMADU BELLO UNIVERSITY ZARIA.
OCTOBER, 1999
Keywords
GEOTECTONIC,, EVOLUTION,, SCHIST,, BELT,, PRECAMBRIAN,, BASEMENT,, NIGERIA