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GSRJ
VOLUME 1
ISSUE 5
(MARCH –APRIL 2015)
ISSN : 2349-9397
A PEER REVIEWED INTERNATIONAL
JOURNAL OF GLOBAL SCHOLASTIC
RESEARCH JOURNAL
GSRJ
GLOBAL SCHOLASTIC RESEARCH
JOURNAL OF MULTIDISCIPLINARY
PETROGRAPHY, QUANTIFICATION OF THE FINISHED DEFORMATION: CASE
OF NAGARWA – WALUNGU / SOUTH KIVU/ DRCONGO
ONGEZO MUZALIWA SÉVERIN1, NKERE BULIBA1, KWINJA FRANÇOISE1, WAZI
NANDEFO1, MAKABU KAYEMBE2, KAPAJIKA BADIBANGA2.
1
Université Officielle de Bukavu (UOB) / RD Congo
Université de Lubumbashi (UNILU) / RD Congo
2
Abstract
From the petrographic point of view, we have 6 types of the rocks level in the sector of Nagarwa:
siltites, conglomerates, sandstones, quartzites, shales and schists. The objects of this work were
to determine the petrography and to quantify the finished deformation in structural domain.
Microscopic observation of thin plates crafted from samples in PNAL and APL, highlights the
transmitted light hétérogranulaire structure and equigranular; there is abundance of quartz grains
mixed with opaque minerals and, incidentally, muscovite and clay phyllites. They occupy 80% of
the total size of the rock. Their diameters range from 300 to 900 microns. Phyllites occupy less
than 5% of the rock. Quartz crystals are recognizable by their low relief and a rolling extinction.
In other cases it is observed muscovite and opaque reddish brown products due to oxidation.
These are probably iron oxides and hydroxides. Sometimes they occupy more than 15% of the
rock and have a size of 100 to 200 microns. The muscovite flakes show a bright color. Quartz
grains essentially have sub rounded shapes, irregular and contiguous. Some phyllites are
concentrated in the vacuolar areas.
The microscopic description of schists in NPAL and APL shows that Phyllites are often
preferentially oriented and occupy 55% of the rock. Their diameter is about 50 microns. The
phyllites length goes beyond 500 microns. A part from the phyllites, quartz grains are observed,
although embedded in these abundant mass phyllites and occupy less than 10% of the rock. Their
sizes range from 70 to 150 microns. The opaque minerals occupy 35% of the rock. In most cases
the rock is mica schist. The shale are yellowish and reddish iron oxides in transmitted light
appear in clusters in the rock. These clusters have a diameter of 850 microns and occupy about
15%. Biotite abounds. The flakes are elongated along the stratification plane and are long of
about 450 microns and diameters of less than 50 microns. Quartz ghosts are detectable in the
mass. They have a fine grain size and they occupy less than 15% of the rock. Sometimes
observed blackish material, isotropic, organic aspect, aligned in parallel bands when it comes
graphitic shales and they occupy 40% of the rock and are spaced approximately 200 microns. We
observed four types of sandstone. The nature of the cement, the size of elements, the dominant
mineralization and metamorphic grade allowed us to discriminate these sandstones.
The quantification of finished deformation helped us to describe the preferred direction of the
layers which is N156° E / 60° NE. Schistosity is subparallel to the bedding and has a preferential
orientation of N135° E / 51° NE. Joints have a preferred direction of N67°E/42°NW. They are
Global Scholastic Research Journal Of Multidisciplinary
www.globalscholasticresearch.org
GSRJ
VOLUME 1
ISSUE 5
(MARCH –APRIL 2015)
ISSN : 2349-9397
not abundant in the Nagarwa sector. We highlighted one family of joints. The maximum
concentration of poles is 53.81%. Statistical of veins in Stereonet shows two families of veins
with the front N10°E / 40°E and N50°/80°SE. However veins are rare in Nagarwa sector. The
maximum pole of concentration is 41.03%. Flinn diagram gave us the state of the deformation
using Flinn parameter. Ramsay diagram demonstrates the nature of spread values and shows a
slight concentration values at Rs. The preferred orientation of the pebbles is N108°E / 50°WNW
and deformation rate is less than 1 then, medium intensity.
Key words: petrography, finished deformation, transmitted light, metamorphic grade,
phyllites, shales, quartzites, schists, sandstones, Flinn diagram, Ramsay diagram, and
Stereonet.
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