Geology Reference
In-Depth Information
Fig. 8.15
Microphotographs (
left
: reflected light;
right
: polarized
light) of selected detrital zircons of core-sample D600 from the Dekese
Formation (Fig.
8.8a
for location). Zircons from this aeolian formation
(Unit D4) are small to medium in size (200-400
m), elongated, well
μ
rounded and generally transparent
8.6.1 U-Pb Results
8.6.2 Maximum Age and Source Provenance
Analysis
In total, 201 zircons were analyzed from the Lower Kwango
Group outcropping in the southwestern CB (in the Kwango
Valley), and from the Dekese cores (Unit D4) in the center of
the basin. Detrital zircons from these samples are relatively
small
U-Pb detrital zircon dates from the aeolian, Kwango Group
and the Dekese Formation shows five age-populations
(Fig.
8.16
): (1) Archean, (2) Paleoproterozoic (Eburnian),
(3) early Neoproterozoic to Mesoproterozoic (Kibaran), (4)
Cambrian to late Neoproterozoic (Pan African), and (5) mid-
Phanerozoic.
m), elongated, sub-rounded to well-
rounded, and generally transparent (e.g. Fig.
8.15
).
The U-Pb results (Tables
8.2
and
8.3
; details of which
are given in Linol
2013
; Linol et al.
2014
) are plotted on
Concordia-diagrams and compared on frequency age-
diagrams in Fig.
8.16
. The youngest grains (
(100-300
μ
8.6.2.1 Archean (2.5-3.1 Ga)
In total, 30 zircons date between 2.5 Ga and 3.1 Ga in the
samples, indicating some contributions from Archean aged
sources to the CB, such as for example the Kasai and NE
Angola Cratons along the southern margin of the basin
also have been derived from recycling older sediments, as
suggested by the small and rounded shape of the grains (e.g.
Fig.
8.15
).
500 Ma),
which commonly have low uranium and lead concen-
trations, were analyzed repeatedly to improve the lower
intercept dates and determine the maximum age of sedimen-
tation (Fig.
8.17
).
<
8.6.1.1 Sample WP19 (the Lower Kwango Group)
63 zircons (65 analyses) were dated from sample WP19
(the Lower Kwango Group), collected in outcrop near
Swamasangu (Fig.
8.6
for sample location). Results are
summarized in Table
8.2
.
8.6.2.2 Paleoproterozoic (1.8-2.2 Ga)
28 zircons date between 1.8 Ga and 2.2 Ga, overlapping in
age with the conventional Eburnian period of west and
central Africa (Cahen et al.
1984
). Such dates are relatively
common within basement rocks of the West Congo, Lufilian
and Ubendian Belts along the western, southern and eastern
margins of the CB, respectively (Lenoir et al.
1995
; Tack
et al.
2001
; Rainaud et al.
2005
), as well as from their
overlying Neoproterozoic sequences (Master et al.
2005
;
Frimmel et al.
2006
).
8.6.1.2 Samples D470 and D600 (The Dekese
Formation)
Two core-samples: D470 and D600 were taken from the
Dekese Formation at depths of -470 m and -600 m (Unit
D4), respectively, in the middle part of the Dekese section
(Fig.
8.8a
for samples location). 76 analyses were performed
on 70 grains in sample D470, and 72 analyses on 68 grains in
sample D600. Results are summarized in Table
8.3
.
Search WWH ::
Custom Search