Download THEME 8: The Mokolian Era Namaqualand Metamorphic Complex

THEME 8:
The Mokolian Era
Namaqualand Metamorphic
Complex.
This is a granite-gneiss
complex. Includes folded and
metamorphosed volcanosedimentary bodies
Volcano-sedimentary rocks:
Marydale and Kaaien groups,
Korannaland succession,
Bushmanland Group, Okiep
Group and Orange River
Group
This runs from 2050 Ma (end of
Bushveld Complex) to 1080 Ma (start
of Pan African)
Includes: Namaqualand metamorphic
Complex, Natal metamorphic
Complex, sedimenatery sequences
of the Waterberg and Soutpansberg
groups, the Wilgenhoutsdrif and
Koras groups and Mokolian intrusive
rocks
Namaqualand
Metamorphic
Complex
Intrusive granites include:
Vioolsdrif, Klein Namaqua,
Hoogoor, Keimoes, Spektakel
and Koperberg Suites
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The volcano-sedimentary
successions and granitic
intrusions are reminiscent of
greenstone belts……addition
of new curst to the southern
edge of the Kalahari Craton.
Rocks have been re-worked
by subsequent (Pan African)
tectonic events
Namaqualand Metamorphic
Complex contains many
important base metal deposits
(Cu-Pb-Zn), Fe, Mn, Ba
e.g. Aggenys and Gamsberg
Folded rocks in the Aggenys area:
Rodinia assembly
Natal Metamorphic Complex
Very similar to Namaqualand
Metamorphic Complex.
Gneiss, Granite, Schist,
metasediment, metavolcanics
Four stratigraphic units are:
Ntingwe, Mfongozi, Tugela,
Mapumulo groups.
Also strongly reworked later in
the Pan-African
Natal
Metamorphic
Complex
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Because of the similarities
between the Namaqualand
and Natal Complexes, we can
consider them to be a single
mobile belt….the NamaquaNatal Mobile Belt
Microterranes and small
plates (some of which have an
older history >3.0Ga), island
arcs and ophiolites that were
accreted onto the southern
edge of the Kalahari and
Namibian Craton
What else was going on at this
time? Fresh sedimentation
close to the Limpopo
Belt….the Blouberg
Formation, Waterberg Group
and Soutpansberg Group
Soutpansberg Group
Waterberg Group
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Blouberg Formation
All of these rocks were
deposited between 2.0 and
1.8 Ga, and relate to
reactivation in the adjacent
Limpopo Belt. They are
continental sediments and
lesser volcanics….and are red
in colour
Aeolian deposits in the Waterberg Group
Waterberg Group
Soutpansberg Group
The red colour suggests that
the Earth now has an
oxygenated atmosphere….no
more Fe in the oceans to form
BIF, so O2 enters the
atmosphere
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Waterberg sedimentation
began in the Wilgerivier area
(‘Middelburg basin’) just East
of Pretoria: coarse alluvial
sandstones and
conglomerates of the
Wilgerivier Formation
Coarse clastic
granulestone and
conglomerate
(Blouberg Fm)
At a similar time, in the
Blouberg area (on the Limpopo
Belt) and in the Warmbaths
area (Nylstroom protobasin
and Alma trough) by deposition
immediately adjacent to fault
scarps….reactivation of the
Limpopo Belt and the TML
All of these are coarsegrained immature sediments
deposited close to their
source, at the northern and
southern extremes of the main
basin. Movement along faults
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N
S
N
S
Alma trough
Nylstroom
Protobasin
Blouberg
Pull-apart basin
Palala
Shear
Zone
TML
Sedimentation was then
spread across a much larger
area of the ‘Main basin’ with
the onset of rifting. Lesser
conglomerates,
granulestones, sandstones,
shales, lavas and pyroclastics
Palala
Shear
Zone
TML
Because of tectonism
(reactivation of the Limpopo
Belt) at this time, a
spectacular angular
unconformity is developed
between the Blouberg Fm and
the Upper Waterberg Group
Blouberg
Formation
(1250m)
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In addition to fluvial deposits, the
Waterberg also contains the world’s
oldest and best preserved palaeodeserts
The Makgabeng Formation
The Makgabeng Formation contains the
earliest evidence for life in a terrestrial
environment
The NE corner of the
Waterberg Group is
unconformably overlain by the
Soutpansberg Group. These
form a long mountain chain
from Punda Maria to
Blouberg, and represent
renewed rifting
Sibasa Formation
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Wyllie’s Poort Formation
Other rocks of Mokolian age:
Wilgenhoutsdrif Gp: metalavas and
metasediments north of
Groblershoop in Northern Cape.
1350-1150 Ma, 2000m thick.
Koras Gp: alluvial sedimentary rocks,
lavas, pyroclastics, deposited in
grabens. 1180-1080 Ma
So the Blouberg, Waterberg and
Soutpansberg all represent
reactivation of faults, especially the
Limpopo Belt, between 2.0 and 1.8
Ga. Might be related to the Eburnean
Orogeny, when other cratons were
been added to the northern edge of
the Zimbabwe Craton. This same
timing for orogenic activity is also
recorded in other parts of Africa
Mokolian intrusive rocks:
a range of compositions and and
ages. Granite, mafic/ultra-mafic
layered intrusions, alkaline
complexes. Most important are
Pilanesberg Complex: 1850 Ma
(alkaline volcanic pipe) and
Phalaborwa Complex: 2049 Ma (Cu,
vermiculite and Fluorite)
Phalaborwa
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