Las universidades objeto de esta investigación

Geochronological studies of Precambrian basement and supracrustal rocks provide a framework for interpreting detrital age spectra by identifying possible original source areas and secondary sources of reworked zircon. Comparing the age populations of detrital zircon in the Kamoa sub- basin to the ages of possible Congolese cratonic and supracrustal rocks identifies their origin and illuminates the geological events that affected the Katangan basin and more specifically the Kamoa sub-basin (Fig. 6, 7).

Previous detrital zircon geochronology studies of the Katangan succession are few and focus predominantly on the Roan Group (Armstrong et al., 2005; Master et al., 2005; Halpin and Selley, 2010; Liu et al., 2019); only one previous study included detrital zircon work on the ‘grand conglomérat’ (Master et al., 2005). Collectively, the studies of Roan Group zircon

provenance span much of the basin. Given that the nature and age of nearby source terranes would have differed according to location, it should be expected that a given stratigraphic unit might contain a different suite of detrital zircon populations in different locations. The presence of a zone of Paleoproterozoic-cored basement highs (‘domes’) that spans the centre of the basin is of particular concern, because several of the previous studies collected at least some of their samples from the flanks of these structures (Fig. 1; Armstrong et al., 2005; Master et al., 2005; Halpin and Selley, 2010; Liu et al., 2019). Detrital zircon geochronological results for the Katanga Supergroup and other relevant geological units are summarised in Figs. 8 and 9.

Armstrong et al. (2005) analysed detrital zircon from the lower Roan Group from drill-core on the northern flank of the Kafue anticline, where Katanga Supergroup strata directly overlie the Nchanga granite. The combined results for both samples of the lower Roan Group show that it is dominated by a mid-Paleoproterozoic population ~1900 Ma that corresponds to locally exposed LMC of the Kafue anticline with minor Neoproterozoic grains ~900 Ma sourced from the underlying Nchanga granite, which intrudes the LMC (Armstrong et al., 2005).

Master et al. (2005) analysed the detrital zircon geochronology of the lower Roan Group and the ‘grand conglomérat’ in the southeasternmost part of the basin (Fig. 1). Detrital zircon from the three lower Roan Group samples are dominated by mid-Paleoproterozoic populations ~2000- 1800 Ma, but contain two ~900 Ma grains. The Mwashya Subgroup sample has most grains ~2000 Ma and ~900 Ma. The sample from the ‘grand conglomérat’ has grains ~1945-1845 Ma, ~1000 Ma, and a discordant mid-Neoproterozoic grain with an age of 729±50 Ma. The dominant source areas are interpreted to be the Ubendian belt (mid-Paleoproterozoic population), the Kibaran belt (Mesoproterozoic population), and early Neoproterozoic granitoid intrusions (~900 Ma grains). Samples analysed in Master et al. (2005) are from the eastern part of the basin, near

both the Paleoproterozoic Bangweulu block and the Paleoproterozoic-cored Kafue anticline; the number of zircon analysed was low in all samples, and, especially when placed under a 5% discordance filter rather than the 10% discordance filter used in the paper, is statistically insufficient to make meaningful comparisons for provenance studies.

Halpin and Selley (2010) collected samples for detrital zircon geochronology from throughout the Katangan basin in the central and northwestern parts of the basin but focussed predominantly on the Roan Group. The dominant age populations in all samples of RAT, RGS, Mines, lower Roan Group, and upper Roan Group strata are mid-Paleoproterozoic, ranging from ~2000-1800 Ma, with secondary populations of Mesoproterozoic grains ~1400-1200 Ma and minor amounts of Archean grains. Rare early Neoproterozoic grains are present (~900 Ma) in some of the samples. The only sample in the study that does not have a dominant mid-Paleoproterozoic population is a sample of the ‘poudingue’ conglomerate from Kolwezi, which has a dominant Mesoproterozoic population. There were 91 grains analysed of the ‘poudingue’ conglomerate, which is an adequate number of grains.

Liu et al. (2019) collected samples from the Kitwe and Mindola formations on the western flank of the Kafue anticline (lower Roan Group in Zambia; Liu et al., 2019), stratigraphic equivalents of the Mines and RAT subgroups in the DRC), exclusively from the Chambishi ‘basin’ on the flank of the Kafue inlier (“anticline”) in the southeastern part of the basin. The material is dominated by mid-Paleoproterozoic grains (i.e., >90% of the total detrital zircon) that are ~2098- 1744 Ma. The interpretation based on the dominance of the mid-Paleoproterozoic age population is that the strata of the lower Roan Group were derived from the LMC and Bangweulu block. There are some ~1850-1744 Ma grains in both samples that are ~100 m.y. younger than the LMC and Bangweulu block, but that do not have a known source area. The presence of this

population suggests that the lower Roan Group had other source areas apart from the LMC and Bangweulu block. Minor Archean grains are suggested to be derived from the Muva Supergroup, a Paleoproterozoic (> 1800 Ma) succession overlying Paleoproterozoic basement in the

Bangweulu block, which inherited zircon originally from Archean terranes such as the Tanzania craton (De Waele and Fitzsimons, 2007). Minor Mesoproterozoic grains ~1500 Ma and ~1000 Ma are suggested to be derived from two separate granitoid suites in the Irumide belt.

The only detrital zircon samples of the Kibaran Supergroup are the four samples of the Nzilo Group from the Mitwaba area, DRC ~200 km north of Kamoa (Kokonyangi et al., 2007). All four samples were collected a few 100 metres from one another above the interpreted

disconformity separating the Nzilo Group from the older Kiaora Group. A basal conglomerate, a metapelite, and two quartzite samples were collected from the Nzilo Group for the detrital zircon study; there are no significant differences in the detrital zircon age distributions between samples (Kokonyangi et al., 2007). The combined number of grains analysed with a 5% discordance filter is 105 grains, which is an adequate number of grains for the detrital zircon age spectra to be meaningful.

The main issue concerning the validity of the detrital zircon data from Kokonyangi et al. (2007) when comparing them to the results of the preset study is that the samples of Nzilo Group were from far enough away that there may be significant differences in the surrounding basement rocks of the Mitwaba area compared to the Kamoa area. Another possible issue is that the metasedimentary rocks of the Kibaran Supergroup in the Nzilo promontory in the Kamoa area are undifferentiated on maps and have no stratigraphic constraints, which means that the Kibaran metasedimentary rocks locally exposed near Kamoa could be from any one of the four

study to those of Kokonyangi et al. (2007) as a proxy for the Kibaran metasedimentary rocks located on the Nzilo promontory should be taken approached cautiously. Future work should include samples of basement rocks underlying the Katangan sedimentary rocks at Kamoa, which would be analysed to determine what its detrital zircon spectrum is. Kibaran basement samples analysed in the present study yielded too few zircon to be useful for detrital zircon

geochronology.

Kibaran-aged intrusives (i.e., ~1380-1370 Ma) should be common in strata in the NW part of the basin adjacent to the Kibaran belt where Kibaran intrusives outcrop and are relatively abundant (~30-40% of map distribution; Kokonyangi et al., 2007).Detrital zircon samples from the NW part of the basin (Halpin and Selley, 2010; this study) have a more significant contribution of Mesoproterozoic grains in their detrital zircon age distributions than strata from elsewhere in the Katangan basin (Fig. 8).

Conversely, the Irumide belt contains relatively abundant ~1000 Ma intrusives (~30-50% of map area; De Waele and Fitzsimons, 2007),but detrital zircon samples in the SE part of the basin only have minor contributions of Mesoproterozoic grains ~1000 Ma (Fig. 8). The lack of a detrital zircon population ~1000 Ma is probably due to the fact that many of the detrital zircon samples analysed in previous studies in the area were based on too few grains to account for minor populations such as the Mesoproterozoic population ~1000 Ma. However, Liu et al. (2019) sampled a large number of grains and still the number of Mesoproterozoic grains in their detrital zircon age distributions are relatively small (Fig. 8). The lack of the ~1000 Ma

population is probably because the Irumide-aged intrusions are relatively far away from where the samples were taken, and demonstrates that the Roan Group was predominantly sourcing locally exposed basement material rather than distal source areas.