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The Paleoproterozoic Waterberg Group, South Africa: Provenance and its relation to the timing of the Limpopo orogeny

01 Jun 2013-Precambrian Research (Elsevier)-Vol. 230, pp 45-60

AbstractFour Paleoproterozoic formations of the Waterberg Group in South Africa are composed of coarse clastic detritus derived from erosion of the Limpopo Belt. Timing of the Limpopo orogeny, an event involving the collision of the Kaapvaal and Zimbabwe cratons, has long been a contentious issue. The results of point counting, major and trace element geochemistry, and U–Pb detrital zircon geochronology indicate that the Waterberg sedimentary formations in the study area were primarily sourced by siliceous (rifted margin) sedimentary and minor mafic volcanic rocks of the Archean Beit Bridge Complex, Limpopo Central Zone. The volumetrically predominant beige/brown sandstones in the four studied formations are quartz-rich with average QFR ratios of 80:7:13 (Blouberg), 70:19:11 (Setlaole), 88:5:7 (Makgabeng), and 89:3:8 (Mogalakwena). Chert and arenite account for >90% of lithic fragments in all formations, with minor siliceous gneiss fragments. Although all formations are silica enriched, the Makgabeng dune samples produce extremely high SiO2 abundances (92–99 wt%), which are attributed to the presence of silica cement and quartz within rock fragments. Geochemically, the stratigraphically highest Mogalakwena Formation is unique with elevated Ti and Zr values, and intra-formational differences in REE patterns; the latter feature is consistent with a mixed provenance. Volumetrically minor green and purple sandstones in the Waterberg formations contain the greatest Cr, Ni, Ti, and V abundances, which supports localized derivation from a mafic or ultramafic source. Chemical index of alteration (CIA) values range from 57 to 89, which could indicate significant chemical weathering of the source rocks, but a plot of Th/Sc versus Zr/Sc illustrates that the sandstones have undergone recycling, which was probably responsible for enrichments in Al2O3 relative to Na2O3, CaO and K2O. Combinations of well rounded and subangular quartz grains support a recycled origin. Detrital zircons in the lowermost Blouberg Formation produced a wide array of ages ranging from ca. 3379 to 2043 Ma. The youngest peak at 2046 Ma is also the largest, and represents the maximum age of deposition for the formation. Additional peaks at 3281 Ma, 3330 Ma, and 3379 Ma are consistent with ages previously determined from the Beit Bridge Complex, whereas peaks at 2578 Ma and 2649 Ma coincide with ages determined from gneisses of the Limpopo Central Zone. Derivation of detritus from the Beit Bridge Complex is directly indicated by sedimentary and siliceous gneiss fragments in the sandstones, subrounded quartz grains suggestive of relatively short transport distances, green and purple sandstone drapes derived from mafic volcanic units, and paleocurrent patterns consistent with south to southwest flow directions. Therefore the timing of deposition of the Blouberg Formation (2046 Ma) equates to the end stages of the Limpopo orogeny. This negates previous suggestions that the Limpopo orogeny occurred only during the Neoarchean.

Topics: Limpopo Belt (59%), Lithic fragment (57%), Detritus (geology) (57%), Clastic rock (55%), Gneiss (54%)

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46 P.L.
Corcoran
et
al.
/
Precambrian
Research
230 (2013) 45–
60
ZC
LMB
KC
Indian
Ocean
Quartzo-
feldspathic
gneisses
Greenstone
belts
Post-
Limpopo
cover
Strike-slip
shear zone
Thrust
Fault
LEGEND
ZIMBABWE CRATON
KAAPVAAL CRATON
Palala-Zoetfontein Shear Zone
Melinda Fault Zone
Beit Bridge Complex
Magogaphate Shear Zone
Northern Marginal Zone
Northern Marginal
Shear Zone
Triangle Shear Zone
Central Zone
Mahalapye
Complex
Phikwe
Complex
Southern Marginal
Zone
Hout River
Shear Zone
Soutpansberg Group
Study
area
23 S
21 S
0
100
Kilometres
28 E
30 E 32 E
Fig.
1.
Simplified
geological
map
showing
features
of
the
Limpopo
Belt
in
relation
to
the
study
area.
KC,
Kaapvaal
Craton;
LMB,
Limpopo
Mobile
Belt;
ZC,
Zimbabwe
Craton.
Modified
from
Kröner
et
al.
(1999),
Roering
et
al.
(1992),
and
Barton
et
al.
(2006).
active
throughout
an
extended
period
of
time
(ca.
2.7–2.04
Ga)
with
many
separate
orogenic
events,
which
could
explain
the
different
P–T–t
paths
extrapolated
from
various
areas.
Bumby
et
al.
(2004)
interpreted
the
long
history
of
post-Limpopo
sedimentation
and
the
development
of
numerous
unconformities
within
these
strata,
to
favor
a
Neoarchean
age
for
the
high-grade
metamorphism
in
the
southern
parts
of
the
Limpopo
Belt.
This
would
have
allowed
ca.
600
million
years
for
the
exhumation
of
high-grade
Limpopo
rocks
prior
to
the
nonconformable
deposition
of
the
lowermost
Waterberg
unit,
the
Blouberg
Formation.
The
authors
considered
Paleopro-
terozoic
ages
in
the
central
and
southern
part
of
the
Limpopo
Belt
to
reflect
metamorphism
during
localized
reactivation.
This
is
in
contrast
to
the
recent
publication
by
Kramers
and
Mouri
(2011)
who,
based
on
a
geochronological
review,
suggest
the
occurrence
of
two
distinct
tectono-metamorphic
events
during
the
late
Archean
and
Paleoproterozoic.
In
addition,
Barton
et
al.
(2006)
envisage
the
Palaeoproterozoic
event
as
the
last
stage
in
juxtaposition
of
the
Zimbabwe
and
Kaapvaal
cratons
along
the
Palala-Zoetfontein
Shear
Zone
(PZSZ).
The
study
area
contains
four
formations
of
the
Waterberg
Group
that
are
separated
by
unconformities
(Figs.
2
and
3).
The
durations
of
missing
time
represented
by
these
hiatuses
are
unknown,
although
based
on
structural
interpretations,
Bumby
et
al.
(2001a)
suggested
that
the
strata
were
deposited
during
two
distinct
phases,
represented
by
the
(1)
Blouberg
Formation,
and
(2)
Makgabeng
and
Mogalakwena
formations.
The
Setlaole
Formation,
which
underlies
the
Makgabeng
strata,
may
be
cor-
relative
with
the
Blouberg
Formation,
but
poor
outcrop
exposure
of
the
Setlaole
deposits
has
made
stratigraphic
characterization
challenging.
Fluvial
paleocurrent
patterns
determined
from
the
Setlaole,
Makgabeng
and
Mogalakwena
formations
indicate
flow
to
the
south–southwest,
which
suggests
a
similar
northern
source
terrane
for
the
upper
Waterberg
strata
(Bumby
et
al.,
2001a).
The
basal
Blouberg
Formation
displays
a
polymodal
paleocurrent
pattern,
which
is
associated
with
its
deposition
in
a
pull-apart
basin
along
the
Melinda
Fault
zone,
a
reactivation
structure
of
the
PZSZ.
Dorland
et
al.
(2006)
determined
U–Pb
zircon
dates
of
2054
±
4
Ma
and
2051
±
8
Ma
from
lavas
near
the
base
of
the
Waterberg
Group
south
of
the
study
area
(Lower
Swaershoek
and
Rust
de
Winter
Formations).
Hanson
et
al.
(2004)
obtained
U–Pb
dates
of
ca.
1.92–1.87
Ga
for
baddeleyite
in
dolerite
dykes
that
cut
the
Mogalakwena
Formation,
suggesting
that
the
lower
and
medial
strata
of
the
Waterberg
Group
were
deposited
prior
to
1.9
Ga.
Such
an
early
onset
of
deposition
seems
unlikely
in
the
most
northerly
part
of
the
basin,
where
ductile
deformation
along
the
PZSZ
seems
to
have
continued
until
1.97
Ga
(Schaller
et
al.,
1999).
However,
it
is
also
possible
that
the
syn-tectonic
Blouberg
strata
preserved
along
the
PZSZ
(and
unconformably
overlain
by
the
>1.9
Ga
Mogalakwena
Formation)
represent
deposition
during,
or
immediately
after
the
final
stages
of
Limpopo
accretion
at
2.04
Ga.
One
of
the
major
objectives
of
this
paper
is
to
present
new
petro-
graphic
and
geochemical
data
that
when
combined
with
previous
facies
analyses
and
paleocurrent
determinations,
indicate
that
the
Blouberg
Formation
was
deposited
during
the
Limpopo
orogenic
event.
Establishing
that
deposition
of
the
Waterberg
strata
was
synchronous
with
uplift
and
erosion
caused
during
collision
of
the
Kaapvaal
and
Zimbabwe
cratons
is
a
significant
step
toward
determining
the
timing
of
the
Limpopo
orogeny.
Our
second
major
objective
is
to
use
U–Pb
detrital
zircon
and
monazite
ages
from
the
Blouberg
Formation
in
order
to
constrain
the
age
of
termination
of
the
Limpopo
event.
2.
General
geology
The
Waterberg
Group
of
southern
Africa
is
a
clastic
sedimentary
succession
preserved
across
the
northern
part
of
the
Kaapvaal
Cra-
ton,
and
is
generally
thought
to
have
been
deposited
during
the
late
Palaeoproterozoic.
The
strata
that
characterize
the
northern-most

P.L.
Corcoran
et
al.
/
Precambrian
Research
230 (2013) 45–
60 47
Fig.
2.
Map
of
the
study
area
illustrating
the
Waterberg
formations
and
main
sampling
locations
(stars).
(1)
SA-1,
2,
4,
5,
6,
8,
10-13,
SA-38
to
SA-41,
44,
45.
(2)
SA-14,
15.
(3)
SA-16.
(4)
SA-17,
18.
(5)
SA-19-29.
(6)
SA-30
to
SA-35,
37.
Modified
from
Eriksson
et
al.
(2006).
part
of
the
Waterberg
basin
unconformably
overlie
high-grade
rocks
of
the
Limpopo
Belt.
There
remains
little
consensus
regarding
the
style
of
deformation
in
the
Limpopo
Belt,
although
it
has
been
considered
at
least
partly
analogous
to
a
Himalayan-
(e.g.
Treloar
et
al.,
1992)
transpressional-
(e.g.
Holzer
et
al.,
1998)
or
Turkic-type
(Barton
et
al.,
2006)
orogeny.
The
Limpopo
Belt
is
characterized
by
a
number
of
shear
zone-bound
terranes,
which
lie
between
the
cra-
tons
(Fig.
1).
The
Southern
Marginal
and
Northern
Marginal
zones
(SMZ
and
NMZ)
are
on
the
edges
of
the
Kaapvaal
and
Zimbabwe
cratons
respectively,
and
are
interpreted
as
rocks
of
the
neighbor-
ing
craton,
but
at
a
much
higher
grade,
that
were
thrust
onto
their
host
craton
during
orogenic
events.
Between
the
SMZ
and
NMZ
are
a
number
of
other
terranes,
such
as
the
Beit
Bridge,
Phikwe
and
Mahalapye
Complexes,
which
together
have
become
termed
the
Central
Zone
(CZ;
Fig.
1;
Barton
et
al.,
2006).
There
is
some
consensus
that
the
SMZ,
which
largely
forms
the
basement
to
the
Waterberg
Group,
was
thrust
southwards
along
the
Hout
River
Shear
Zone
during
a
Neoarchean
event
(e.g.
Barton
et
al.,
2006).
The
Palala-Zoetfontein
Shear
Zone
(PZSZ;
Fig.
1)
marks
the
boundary
between
the
SMZ
(northernmost
Kaapvaal
Craton)
and
the
CZ,
and
underlies
the
present
study
area.
Barton
et
al.
(2006)
and
Schaller
et
al.
(1999)
proposed
that
the
final
juxtaposition
of
the
Zimbabwe
Craton
(together
with
the
previously
assembled
NMZ
and
CZ
ter-
ranes)
with
the
northern
edge
of
the
SMZ
took
place
along
the
PZSZ
during
the
ca.
2.04
event.
Schaller
et
al.
(1999)
suggested
that
ductile
dextral
strike-slip,
post-orogenic
shearing
along
the
PZSZ
continued
between
ca.
2.0
and
1.9
Ga,
and
this
movement
may
account
for
the
development
of
some
of
the
sedimentary
for-
mations
described
below.
In
a
similar
vein
Bumby
et
al.
(2001a)
suggested
that
strike-slip
and
southwards-vergent
tectonics
along
the
Melinda
Fault
Zone
(a
brittle
reactivation
of
the
PZSZ)
at
ca.
2.0
Ga
were
responsible
for
the
development
of
the
Waterberg
basins
along
the
northern
edge
of
the
Kaapvaal
Craton.
The
Waterberg
strata
that
are
preserved
along
the
Melinda
Fault
Zone
suggest
at
least
two
phases
of
basin
development.
The
first
phase
of
basin
development
is
associated
with
deposi-
tion
of
the
Blouberg
Formation
(Fig.
4a),
which
is
only
preserved
in
localized
areas,
directly
along
the
trace
of
the
Melinda
Fault
Zone.
The
Blouberg
strata
are
locally
up
to
1400
m
thick,
despite
their
limited
areal
extent,
and
contain
an
upward-coarsening

48 P.L.
Corcoran
et
al.
/
Precambrian
Research
230 (2013) 45–
60
Fig.
3.
Schematic
block
diagrams
illustrating
the
development
of
the
northern
part
of
the
Waterberg
basin.
Modified
from
Bumby
et
al.
(2001a).
succession
of
trough
cross-bedded
granular
sandstones,
and
an
upper
sedimentary
breccia
containing
angular
boulders
of
foliated
feldspathic
gneiss.
Bumby
et
al.
(2001a)
interpreted
these
strata
as
a
syntectonic
succession
that
was
deposited
in
rapidly
subsiding
pull-apart
basin
that
developed
as
a
result
of
strike-slip
move-
ment
along
the
Melinda
Fault.
The
radial,
generally
west-directed
patterns
of
paleocurrents
recorded
in
the
Blouberg
Formation
sup-
port
such
a
tectonic
setting.
Although
the
Blouberg
Formation
has
been
affected
by
very
low-grade
metamorphism,
it
is
nevertheless
strongly
deformed.
Bedding
planes
dip
sub-vertically,
or
are
over-
turned
and
dip
northwards.
Folded
Blouberg
strata
have
an
E–W
trending
fold
axis,
and
are
locally
affected
by
southward-vergent
thrusts
(Fig.
4b).
The
second
phase
of
basin
development
at
the
northern
edge
of
the
Waterberg
basin
is
associated
with
deposition
of
the
Setlaole,
Makgabeng
and
Mogalakwena
formations.
The
lowermost
Setlaole

P.L.
Corcoran
et
al.
/
Precambrian
Research
230 (2013) 45–
60 49
Fig.
4.
Schematic
stratigraphic
sections
of
the
Waterberg
formations
in
the
study
area.
(A)
Blouberg
unconformably
overlies
gneissic
basement
and
is
unconformably
overlain
by
the
Mogalakwena
Formation
in
the
northwest
part
of
the
study
area
(see
Fig.
2).
(B)
Blouberg
is
absent
in
the
southeast
part
of
the
study
area
where
the
Mogalakwena
strata
is
underlain
unconformably
by
the
Makgabeng
Formation.
Formation
is
only
locally
exposed,
but
it
may
correlate
with
the
Blouberg
Formation,
as
both
strata
seem
to
have
been
deposited
nonconformably
on
gneiss
of
the
SMZ.
However
the
Setlaole
For-
mation
is
not
affected
by
any
of
the
deformation
typical
of
the
Blouberg
Formation,
and
thus
may
be
younger.
The
extensive
out-
crops
of
the
generally
aeolian
Makgabeng
Formation
appear
to
thin
toward
the
north,
and
are
nowhere
developed
close
to
the
Blou-
berg
Formation.
Bumby
et
al.
(2001a)
proposed
that
Makgabeng
strata
onlapped
northward
over
Limpopo
mountains
that
had
been
created
during
southward-vergent
tectonics
that
deformed
the
Blouberg
strata
(Fig.
4c).
Although
the
Makgabeng
Formation
is
generally
composed
of
aeolian
foresets,
localized
fluvial
facies
indicate
southward-flowing
palaeocurrent
directions,
similarly
implying
uplifted
areas
in
the
north.
The
Mogalakwena
Forma-
tion
is
composed
of
granular
sandstone,
interbedded
siltstone
and
quartz-conglomerate
sheets
that
were
deposited
discon-
formably
on
the
Makgabeng
Formation.
Toward
the
north,
where
the
Makgabeng
Formation
does
not
crop
out,
the
Mogalakwena
Formation
was
deposited
directly
on
steeply-dipping
Blouberg
strata,
and
a
sharp
angular
unconformity
is
preserved
(Fig.
4c).
The
Mogalakwena
Formation
thins
northward
across
the
width
of
the
PZSZ,
which
suggests
that
the
northward
onlapping
rela-
tionship
across
the
craton
edge
was
preserved
throughout
at
least
medial
Waterberg
times.
Palaeocurrent
directions
recorded
in
the
Mogalakwena
Formation
are
unimodal
toward
the
SW
(Fig.
4c).
Additional
sedimentary
deposits
in
the
area
are
those
of
the
younger
Soutpansberg
Group,
where
basalt
of
the
Sibasa
Formation
and
quartzite
of
the
Wyllie’s
Poort
Formation
overlie
the
Mogalak-
wena
Formation
on
a
slight
angular
unconformity
(Bumby
et
al.,
2001b;
Fig.
2).
These
Soutpansberg
strata
are
similarly
preserved
only
along
and
parallel
to
the
northern
edge
of
the
Kaapvaal
Craton,
approximately
along
the
trace
of
the
PZSZ,
and
have
been
inter-
preted
to
have
been
deposited
in
a
post-Waterberg
half-graben
developed
along
the
cratonic
margin
(Bumby
et
al.,
2002).
3.
Waterberg
Paleoenvironments
Detailed
descriptions
and
interpretations
of
the
lithofacies
composing
the
Blouberg,
Setlaole,
Makgabeng
and
Mogalakwena
formations
are
provided
in
Bumby
(2001)
and
Bumby
et
al.
(2001a).
This
section
briefly
reviews
the
major
sedimentary
structures
and
bedforms
characterizing
each
unit,
and
the
interpretations
of
depo-
sitional
processes
and
environments.
The
Blouberg
Formation
unconformably
overlies
gneissic
base-
ment,
and
is
unconformably
overlain
by
the
Mogalakwena
Formation
(Fig.
3).
Blouberg
Formation
sandstones
are
very
coarse
grained
to
granular,
and
on
the
weathered
surface
are
beige
and
purple
in
color,
with
thin,
green
siltstone
drapes
developed
locally
on
foresets
and
between
bedforms.
The
lower,
sandstone-
dominated
portion
of
the
Blouberg
Formation
mainly
contains
medium-
to
large-scale
sets
of
trough
and
planar
cross-beds,
and
local
granule-
to
pebble-filled
channel
forms
(Fig.
5a).
The
trough
cross-bedded
sandstone
developed
as
sinuous
crested
dunes
on
longitudinal
bars,
whereas
the
planar
cross-beds
are
considered
to
have
formed
as
linguoid
bars
(Miall,
1978)
or
bar-top
sands
(Best
and
Bridge,
1992).
The
generally
west-flowing
paleocurrent
direc-
tions
determined
from
cross-bed
measurements,
combined
with
a
predominance
of
bedload
material
over
suspended
detritus
sup-
port
a
low-sinuosity
braided
sheetflood
system
(Miall,
1992).
The
upper
portion
of
the
Blouberg
Formation
is
composed
of
crudely
to
well
stratified,
matrix-
to
clast-supported
conglomerate
with
sub-
angular
to
rounded
clasts
(Fig.
5b).
Planar
and
trough
cross-bedded
sandstone
interbeds
are
in
places
well
developed.
Matrix-
supported
units
are
interpreted
as
debris
flow
deposits
(Mack
and
Rasmussen,
1984),
whereas
clast-supported
conglomerates
repre-
sent
longitudinal
gravel
bars
in
a
stream-dominated
alluvial
fan
(Collinson,
1996)
or
proximal
braided
stream
setting.
Interstrat-
ified
trough
cross-bedded
and
planar
sandstone
beds
represent
in-channel
dunes
and
bar
top
sands,
respectively
(Eriksson,
1978).
The
abrupt
transition
from
sandstone-
to
conglomerate-dominated
strata
is
considered
a
response
to
tectonic
activity
in
the
source
area.
Eriksson
et
al.
(2006)
determined,
based
on
paleohydraulic
calculations,
a
general
increase
in
stream
discharge,
drainage
area,
and
length
toward
the
center
of
the
preserved
Blouberg
basin,
and
combined
with
the
preservation
of
the
Blouberg
Formation
along
the
PZSZ,
points
toward
deposition
in
a
pull-apart
basin.
The
relatively
poorly
exposed
Setlaole
Formation
is
overlain
by
the
Makgabeng
Formation,
and
mainly
contains
trough
cross-
bedded
and
planar
bedded
sandstone
(Figs.
4
and
5c).
The
former
structure
is
consistent
with
in-channel
migration
of
sinuous-
crested
dunes
(Mueller
et
al.,
1994),
whereas
planar
beds
represent
bar-top
sands
(Eriksson,
1978).
A
relatively
unimodal
southerly
palaeocurrent
pattern
supports
a
fluvial
interpretation
(Bumby
et
al.,
2001a).
The
lack
of
mudstone
in
both
the
Setlaole
and
Blouberg
formations
points
toward
a
braided
fluvial
environment,
which
is
consistent
with
the
absence
of
land
plants
during
the
Pre-
cambrian
(Long,
2011).
The
Makgabeng
Formation
overlies
the
Setlaole
Formation
and
is
unconformably
overlain
by
the
Mogalakwena
Formation
(Figs.
3
and
5d).
It
is
considered
to
represent
mainly
aeolian
sedi-
mentation
based
on
inverse-grading
of
sand
grains
in
laminations
(c.f.
Hunter,
1977,
1981;
Kocurek
and
Dott,
1981),
ripple
indices
indicating
wind
transport
(Bumby,
2001),
and
planar
cross-bedded
strata
with
steep
angles
of
inclination
(Fig.
5e)
consistent
with
sinuous-crested
or
barchanoid
sand
dunes
(c.f.
McKee,
1979).
The
well-exposed
formation
is
composed
of
five
lithofacies,
which
include:
(1)
large-scale
trough
and
planar
cross-bedded
sandstone,
(2)
horizontally
bedded
and
rippled
mudstone
and
sandstone,
(3)
rippled
and
cross-bedded
sandstone,
(4)
massive
sandstone,
and
(5)
pebbly
sandstone
(Bumby,
2001).
Of
these,
the
strongest
evi-
dence
for
arid
conditions
appears
in
the
horizontally
bedded
and

Citations
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Journal ArticleDOI
Abstract: The early history of the Yangtze Block is not well constrained owing to scarce outcrops of the Archean to Paleoproterozoic rocks. In this paper, we report an integrated study of major and trace element data, SHRIMP and LA–ICP–MS zircon U–Pb age data, and Hf isotopic data for the granites from the Lengshui Complex in the northern Yangtze Block. Zircon U–Pb dating yields a 207Pb/206Pb age of 1960 ± 19 Ma for gneissic granites, and 1936 ± 32 Ma for K-granites, which indicates that these granites were almost contemporaneously emplaced. The gneissic granites have SiO2 contents ranging from 71.11% to 75.10%, K2O contents from 4.61% to 5.95%, with relatively high differentiation indexes of 90.91–95.28, and they have alkalinity ratios of 3.31–4.48 and A/CNK values of 1.14–1.29. Also, low Sr, Ta, and Nb contents but relatively high Y, Rb, Nd, and Yb contents are found. The K-feldspar granites have higher contents of trace and rare earth elements. All the samples display typical I-type evolutionary trends in chemical variation diagrams, which are plotted into the syn-collision granite fields in the tectonic discrimination diagrams. The zircon ɛHf (t) value of −15.77 and the TDM2 age dated at ca. 3.6 Ga for the Lengshui Complex suggest that the Complex could be derived from the old crustal partial melting of the old crustal material such as ca. 2.9 Ga TTGs in the Kongling terrain. Taking nearby rapakivi and A-type granites into consideration, the Lengshui Complex may represent part of the rock records of the progression from plate convergence to continental extension and rifting in the Yangtze Block, implying that the Yangtze Block could be an important part of the Paleoproterozoic Columbia supercontinent.

60 citations


Journal ArticleDOI
Abstract: U-Pb ages on detrital zircons are often utilised for stratigraphic and paleogeographic interpretations and correlation. Sampling is carried out in such a way that the samples are representative for a formation, and then used for provenance identification and/or defining a maximum time limit for deposition. Is it possible that sedimentological factors and sampling would influence the results? This is perhaps an obvious consideration for sedimentologists, but is in many studies treated as a secondary concern or even not mentioned. U-Pb LA-ICP-MS analysis on detrital zircons from two samples of Cambrian age (Herreria Formation, Cantabrian Mountains, Spain) revealed very different provenance signatures at the base and top of the formation. Both successions have been deposited in a shallow marine environment, are lithologically comparable (arenites, feldspathic arenites, siltstone, shales intercalated with marls and dolomite) and differ only slightly in age. Nearly 80% of all detrital zircons (n = 152; discordance ≤ 10) at the base of the formation are younger than 650 Ma. Detrital zircons older than 1.0 Ga amount to only 10% (n = 16) of the entire population. In contrast, only around 32% of all detrital zircons from the top of the formation (n = 123; discordance ≤ 10) are younger than 650 Ma while more than 16% are Archean and nearly 50% Paleoproterozoic. This implies a fundamental change in provenance, with a shift from Neoproterozoic to Paleoproterozoic (1.9–2.2 Ga) aged sediment sources. Consequently, changes of sediment transport systems have had an extremely profound impact on the provenance of the formation. Therefore, when correlating sedimentary rocks, interpreting source rocks and modelling paleogeography from U-Pb ages of detrital zircons, sedimentological parameters are possibly paramount and these need to be at least discussed before any interpretation is made.

35 citations


Journal ArticleDOI
Abstract: The precise age of the volcano-sedimentary Soutpansberg Group, which was deposited upon the Palala shear belt separating the Kaapvaal Craton from the Central Zone of the Limpopo Belt, has long been debated. The Soutpansberg Group is subdivided into a lower and upper succession, which are separated from each other by a prominent regional unconformity. Zircon grains from silicic pyroclastic rocks of both successions were investigated in order to constrain the timing of deposition of the Soutpansberg Group rocks. The zircon grains of the investigated samples from both successions yield a wide range of ages, spanning from 1831 to 3937 Ma. Most of the zircon grains have rounded shapes, however it is not clear whether they are mainly xenocrystic or detrital, or have been rounded by resorption in a silicic magma chamber. The youngest zircon grain ages obtained come from the lower succession and are 1832 ± 9 and 1831 ± 15 Ma. We interpret these youngest zircon grains as magmatic grains that have been rounded by resorption. This view is corroborated by the fact that no magmatic rocks of this particular age have been observed in the Kaapvaal Craton or the Central Zone of the Limpopo Belt, and that no apparent sedimentary admixtures are present in the well exposed pyroclastic rocks. We therefore conclude that deposition of the Soutpansberg volcano-sedimentary succession commenced around 1830 Ma. The Soutpansberg rocks were deposited apparently over a lengthy period of time (ca. 230 Ma), as provided by the published age of 1604 Ma for pyroclastic rocks of the upper succession in Botswana. Zircon grain age spectra of our Soutpansberg samples show prominent peaks at 2.0, 2.6 and 3.2 Ga, indicating the Central Zone of the Limpopo Belt as the source area, but excludes the adjacent northern part of the Kaapvaal Craton. The oldest zircon grain identified in the Soutpansberg samples has an age of 3937 ± 4 Ma, one of the oldest zircon grain ages yet reported from the African continent.

25 citations


Journal ArticleDOI
11 Jan 2016-Gff
Abstract: The volcanic Hartley Formation (part of the Olifantshoek Supergroup, which is dominated by red bed successions) in South Africa recorded depositional and tectonic conditions along the western Kaapvaal Craton during the late Palaeoproterozoic. It formed in association with red bed deposition elsewhere in the cratonic hinterland and along the craton’s northern margin. However, the exact correlation of the Olifantshoek Supergroup with these other red-bed successions is hindered by poor geochronological constraints. Herein, we refine the age and palaeopole of the Hartley Formation, and provide geochronological constraints for large-scale 1.93–1.91 Ga bimodal magmatism on the Kaapvaal Craton (herein named the Hartley large igneous province). We present new age constraints for the mafic and felsic phases of this event at 1923 ± 6 Ma and 1920 ± 4 Ma, respectively, which includes the first reported age dating of the Tsineng Dyke Swarm that has been linked to Hartley volcanism. A mean 1.93–1.91 Ga palaeoma...

23 citations


Cites background from "The Paleoproterozoic Waterberg Grou..."

  • ...…Group commenced some 200 million years after the initiation of deposition in the Waterberg Group and Blouberg Formation at 2.04 Ga (Dorland et al. 2006; Corcoran et al. 2013; Geng et al. 2014), while deposition continued possibly as late as 1604 Ma within the Palapye Group (Mapeo et al. 2004)....

    [...]


Journal ArticleDOI
Abstract: The Palaeoproterozoic Hartley Formation in the Olifantshoek Group was deposited in one of the rift-related Waterberg (sensu lato) red bed basins which formed on the Kaapvaal Craton after the 2.05 Ga Bushveld intrusions and coeval thermal event. The age of these basins is not well constrained due to the shortage of directly dateable rock types. The Hartley Formation contains rare quartz-porphyry lavas interbedded with the dominant basalts and these provide the means to date the formation by analyses of zircon. In this work zircon from one sample has been dated by six Th-U-Pb methods, namely Laser Ablation ICP Quadrupole Mass Spectrometry, Laser Ablation ICP High-resolution Mass Spectrometry, Laser Ablation ICP Multicollector Mass Spectrometry U-Pb (also Lu-Hf), Nordsim Ion probe U-Pb and Th-Pb; and Krogh method ID-TIMS. Our precise ages give a combined age of 1915.2 ± 1.1 Ma. Including one published ion probe date from the only other known occurrence of quartz porphyry, the results only agree if the quoted analytical errors are increased by 20%, which gives a combined result of 1915.6 ± 1.4 Ma. This is considered a reliable, precise and accurate age for the Hartley Formation and supersedes the published Kober method 207Pb/206Pb age of 1928 ± 4 Ma. The new Lu-Hf zircon data, supported by published whole rock Sm-Nd and Rb-Sr data, suggests that both the dominant basalts and the rare quartz porphyries of the Hartley Formation were derived from mafic source rocks which had been in the crustal domain from Archaean times. By contrast with the intracratonic rifts of the other Waterberg Basins, the Olifantshoek Supergroup reflects the development of a western passive margin as the Archaean Kaapvaal Craton rifted and drifted. This was followed by accretion of the Rehoboth Province along the Kalahari Line, accompanied by the development of the east-vergent Kheis Province thrust complex. This created a larger cratonic block against which the 1.2 Ga collisions of Namaqua-Natal terranes impacted. The Kheis Province now yields ~1.17 Ma cooling ages, reflecting the Namaqua collisions, but the true age of the Kheis event is still enigmatic.

22 citations


References
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01 Jan 1985
Abstract: This book describes the composition of the present upper crust, and deals with possible compositions for the total crust and the inferred composition of the lower crust. The question of the uniformity of crustal composition throughout geological time is discussed. It describes the Archean crust and models for crustal evolution in Archean and Post-Archean time. The rate of growth of the crust through time is assessed, and the effects of the extraction of the crust on mantle compositions. The question of early pre-geological crusts on the Earth is discussed and comparisons are given with crusts on the Moon, Mercury, Mars, Venus and the Galilean Satellites.

11,940 citations


Journal ArticleDOI
18 Jun 1982-Nature
Abstract: The early Proterozoic Huronian Supergroup of the north shore of Lake Huron (Fig. 1) is a thick (up to 12,000 m) succession of sedimentary and volcanic rocks deposited between about 2,500 and 2,100 Myr ago1. Here we present a palaeoclimatic interpretation of the Huronian based on approximately 200 major elements analyses of lutites. Most of these are new analyses from the Gowganda and Serpent Formations (Fig. 2). The remainder are from published sources cited in Fig. 4. The composition of lutites from the Huronian Supergroup records an early period of intense, probably tropical, weathering followed by climatic deterioration that culminated in widespread deposition of glaciogenic sediments of the Gowganda Formation. Climatic amelioration followed during deposition of the succeeding Huronian formations. The Huronian succession can be interpreted using a uniformitarian approach in that present day seafloor spreading rates and latitude-related climatic variations are compatible with available geochronological and palaeomagnetic data.

3,884 citations



Journal ArticleDOI
Abstract: The graywackes of Paleozoic turbidite sequences of eastern Australia show a large variation in their trace element characteristics, which reflect distinct provenance types and tectonic settings for various suites. The tectonic settings recognised are oceanic island arc, continental island arc, active continental margin, and passive margins. Immobile trace elements, e.g. La, Ce, Nd, Th, Zr, Nb, Y, Sc and Co are very useful in tectonic setting discrimination. In general, there is a systematic increase in light rare earth elements (La, Ce, Nd), Th, Nb and the Ba/Sr, Rb/Sr, La/Y and Ni/Co ratios and a decrease in V, Sc and the Ba/Rb, K/Th and K/U ratios in graywackes from oceanic island arc to continental island arc to active continental margin to passive margin settings. On the basis of graywacke geochemistry, the optimum discrimination of the tectonic settings of sedimentary basins is achieved by La-Th, La-Th-Sc, Ti/Zr-La/Sc, La/Y-Sc/Cr, Th-Sc-Zr/10 and Th-Co-Zr/10 plots. The analysed oceanic island arc graywackes are characterised by extremely low abundances of La, Th, U, Zr, Nb; low Th/U and high La/Sc, La/Th, Ti/Zr, Zr/Th ratios. The studied graywackes of the continental island arc type setting are characterised by increased abundances of La, Th, U, Zr and Nb, and can be identified by the La-Th-Sc and La/Sc versus Ti/Zr plots. Active continental margin and passive margin graywackes are discriminated by the Th-Sc-Zr/10 and Th-Co-Zr/10 plots and associated parameters (e.g. Th/Zr, Th/Sc). The most important characteristic of the analysed passive margin type graywackes is the increased abundance of Zr, high Zr/Th and lower Ba, Rb, Sr and Ti/Zr ratio compared to the active continental margin graywackes.

1,806 citations


Journal ArticleDOI
Abstract: Detrital framework modes of sandstone suites from different kinds of basins are a function of provenance types governed by plate tectonics. Quartzose sands from continental cratons are widespread within interior basins, platform successions, miogeoclinal wedges, and opening ocean basins. Arkosic sands from uplifted basement blocks are present locally in rift troughs and in wrench basins related to transform ruptures. Volcaniclastic lithic sands and more complex volcano-plutonic sands derived from magmatic arcs are present in trenches, forearc basins, and marginal seas. Recycled orogenic sands, rich in quartz or chert plus other lithic fragments and derived from subduction complexes, collision orogens, and foreland uplifts, are present in closing ocean basins, diverse succ ssor basins, and foreland basins. Triangular diagrams showing framework proportions of quartz, the two feldspars, polycrystalline quartzose lithics, and unstable lithics of volcanic and sedimentary parentage successfully distinguish the key provenance types. Relations between provenance and basin are important for hydrocarbon exploration because sand frameworks of contrasting detrital compositions respond differently to diagenesis, and thus display different trends of porosity reduction with depth of burial.

1,541 citations