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( 英 文 ). Johnson S P; De Waele B; Evans
D; Banda W; Tembo F; Milton J A;
Tani K. Journal of Geology, 2007,
115(3): 355-374
The Zambezi supracrustal sequence
(ZSC) of southern Zambia comprises a
metasedimentary package of clastics and
carbonates, with a thick sequence of
basal volcanics and lavas. The sequence
has traditionally been interpreted as a
Neoproterozoic continental rift succession,
but the lack of reliable age constraints
hinders any tectonic interpretation.
In this article, we date magmatic
and detrital zircons using the U-Pb
SHRIMP method in order to better constrain
the timing of rifting, volcanism,
and basin deposition. The basal volcanoclastic
Kafue Rhyolite and
Nazingwe formations were erupted at ca.
880 Ma, and the sequence was intruded
by the Lusaka Granite at ca. 820 Ma,
providing lower and upper limits on the
age of sedimentation. Whole-rock Nd
isotopic signatures of these volcanics
indicate that they formed as a result of
assimilation and recycling of basement
gneisses, probably during crustal thinning
and extension. We uphold the correlation
between the ZSC and the Roan
Group in the Zambian Copperbelt and
suggest that both successions formed in
discrete rift basins along the southern
margin of the Congo-Tanzania-
Bangweulu (CTB) Craton; however, extension
at this time probably did not result
in complete continental separation.
If the CTB Craton were an integral part
of Rodinia, then rifting at ca. 880 Ma
would represent one of the first known
records of attempted breakup of the supercontinent.
2010010520
Nzilo 群 (Kibaran 带 ) 碎 屑 锆 石 的
U-Pb SHRIMP 定 年 : 对 非 洲 中 部 沉
积 物 来 源 及 中 元 古 代 演 化 的 启 示 = U-
PbSHRIMP dating of detrital zircons
from the Nzilo Group (Kibaran belt):
Implications for the source of sediments
and Mesoproterozoic evolution of central
Africa. ( 英 文 ). Kokonyangi J W;
Kampunzu A B; Armstrong R; Arima M;
Yoshida M; Okudaira T. Journal of Geology,
2007, 115(1): 99-113
The Kibaran Supergroup, a >= 13000-
km-long belt of metasedimentary and
igneous rocks in the southeastern Congo,
is in a critical location between the
Congo Craton (sensu stricto) and the
Tanzania-Bangweulu Block. Understanding
its tectonic evolution will shed
much-needed light on the amalgamation
history of sub-Saharan Africa. This
study presents U-Pb SHRIMP age data
for 150 detrital zircons from four metasedimentary
formations of the Nzilo
Group, the middle lithostratigraphic unit
within the Kibaran Supergroup in Katanga
Province. These samples yielded
dates between 3214 +/- 7 and 1329 +/-
32 Ma. Prismatic Mesoproterozoic detrital
zircons (dated at 1499 +/- 49 to 1329
+/- 32 Ma, with a peak at 1380 Ma) occur
in all samples and are inferred to be
derived from the Mitwaba orthogneisses,
which intrude the Kiaora Group, the
oldest lithostratigraphic unit of the Kibaran
Supergroup. More than threequarters
of the zircon population is
composed of recycled grains, yielding
dates between and Ma, with 2434 +/- 5
1696 +/- 18 peaks at 2050 and 1850 Ma.
These peaks overlap with the timing of
geological events in the adjacent Paleoproterozoic
Bangweulu Block, including
the Ubendian-Usagaran belts. Archean
zircons were not found in the oldest
Nzilo units and are restricted to the
youngest Nzilo rocks, where they form
only a minor component (