wAbstract
@The Neoproterozoic Ikorongo Group, which lies unconformably on
the late Archean Nyanzian Supergroup of the Tanzania Craton, is
comprised of conglomerates, quartzites, shales, siltstones, red
sandstones with rare flagstones and gritstones and is regionally
subdivided into four litho-stratigraphic units namely the Makobo,
Kinenge, Sumuji and Masati Formations.
@we report geochemical data for the mudrocks (i.e., shales and
siltstones) from the Ikorongo basin in an attempt to constrain
their provenance and source rock weathering. These mudrocks are
compositionally similar to PAAS and PS indicating derivation from
mixed mafic-felsic sources. However, the siltstones show depletion
in the transition elements (Cr, Ni, Cu, Sc and V) and attest to
a more felsic protolith than those for PAAS and PS. The Chemical
Index of Alteration (CIA: 52-82) reveal a moderately weathered
protolith for the mudrocks. The consistent REE patterns with LREE-enriched
and HREE-depleted patterns ((La/Yb)CN = 7.3-38.3)
coupled with negative Eu anomalies (Eu/Eu* = 0.71 on
average), which characteristics are similar to the average PAAS
and PS, illustrate cratonic sources that formed by intra-crustal
differentiation.
@Geochemical considerations and palaocurrent indications suggest
that the provenance of the Ikorongo Group include high-Mg basaltic-andesites,
dacites, rhyolites and granitoids from the Neoarchaean Musoma-Mara
Greenstone Belt to the north of the Ikorongo basin. Mass balance
calculations suggest relative contributions of 47, 42 and 11
from granitoids, high-magnesium basaltic-andesites and dacites,
respectively to the detritus that formed the shales. Corresponding
contributions to the siltstones detritus are 53, 43 and 4.
Keywords: Ikorongo Group; Mudrocks; Geochemistry; Weathering;
Provenancex
1. Introduction
2. Geological setting
3. Sampling and analytical methodology
4. Geochemistry
5. Discussion
@5.1. Source area weathering and diagenesis
@5.2. Mineral sorting
@5.3. Provenance
6. Conclusions
Acknowledgements
References