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A detrital record of the Nile River and its catchment

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1 A detrital record of the Nile River and its catchment
by Laura Fielding, Yani Najman, Ian Millar, Peter Butterworth, Sergio Ando, Marta Padoan, Dan Barfod, and Ben Kneller Journal of the Geological Society Volume 174(2): March 3, 2017 © 2017 The Author(s)‏

2 Modern river samples and hinterland geology of Nile River source areas.
Modern river samples and hinterland geology of Nile River source areas. Inset shows location of map as boxed area. Map modified from Kazmin (1972), al-Miṣrīyah (1981), Ministry of Energy and Mines (1981) and Johnson (2014). Laura Fielding et al. Journal of the Geological Society 2017;174: © 2017 The Author(s)‏

3 Petrographic variability of detrital modes in modern river sands, bedrock and aeolian sands from the Nile trunk and hinterland, illustrating the proportion of quartz (Q), K-feldspar (Kfs) and plagioclase feldspar (Pl). Petrographic variability of detrital modes in modern river sands, bedrock and aeolian sands from the Nile trunk and hinterland, illustrating the proportion of quartz (Q), K-feldspar (Kfs) and plagioclase feldspar (Pl). Samples are modern river sands unless otherwise stated. *Data from Garzanti et al. (2006); **data from Garzanti et al. (2015). Laura Fielding et al. Journal of the Geological Society 2017;174: © 2017 The Author(s)‏

4 Selected trace element concentrations from each of the Nile source areas and the main Nile trunk, normalized to trace element concentrations of Post-Archaean Australian Shale (PAAS: McLennan & Taylor 1985). Selected trace element concentrations from each of the Nile source areas and the main Nile trunk, normalized to trace element concentrations of Post-Archaean Australian Shale (PAAS: McLennan & Taylor 1985). All samples are modern muds or mudstones, except for samples from the Nile trunk in Egypt collected prior to construction of the Aswan Dam (Shukri 1949), which are modern sands. *Data from Garzanti et al. (2013). The field for Red Sea Hills samples encompasses 11 samples. Other distributions represent single analyses, or averages of small groups of samples. Laura Fielding et al. Journal of the Geological Society 2017;174: © 2017 The Author(s)‏

5 U/Pb age and hafnium isotope composition of complex zircons in Archaean gneiss within the Saharan Metacraton (WD16A), and detrital zircons in White Nile sand draining Archaean craton (N7-17S). U/Pb age and hafnium isotope composition of complex zircons in Archaean gneiss within the Saharan Metacraton (WD16A), and detrital zircons in White Nile sand draining Archaean craton (N7-17S). Two-sigma uncertainties are smaller than the symbol size, typically c. 20 Ma on the age determinations, and 1 – 2 εHf units. Laura Fielding et al. Journal of the Geological Society 2017;174: © 2017 The Author(s)‏

6 Detrital zircon U–Pb age frequency and relative probability plots for samples from the Nile catchment and surrounds. Detrital zircon U–Pb age frequency and relative probability plots for samples from the Nile catchment and surrounds. Laura Fielding et al. Journal of the Geological Society 2017;174: © 2017 The Author(s)‏

7 Detrital zircon U–Pb age frequency and relative probability plots with ɛHf v.
Detrital zircon U–Pb age frequency and relative probability plots with ɛHf v. U–Pb age. The vertical line at 600 Ma marks the approximate time of the Pan-African Orogeny and the collision of the Arabian–Nubian Shield with the Saharan Metacraton and Congo Craton. The vertical line at 1000 Ma highlights the dual juvenile and cratonic populations of the enigmatic 1000 Ma population. The reference line for 3500 Ma crust is calculated using 176Lu/177Hf ratio of 0.017, which is derived from the apparent crustal evolution trend displayed in Figure 4. Laura Fielding et al. Journal of the Geological Society 2017;174: © 2017 The Author(s)‏

8 Tera–Wasserburg plot illustrating the effect of Pb loss on an apparently ‘young’ Hammamat Formation zircon grain. Tera–Wasserburg plot illustrating the effect of Pb loss on an apparently ‘young’ Hammamat Formation zircon grain. Replicate analyses of the same grain indicate a true age c. 40 myr older. Laura Fielding et al. Journal of the Geological Society 2017;174: © 2017 The Author(s)‏

9 Cenozoic zircon data from the modern Nile catchment.
Cenozoic zircon data from the modern Nile catchment. (a) Histograms for Cenozoic detrital zircons from the Nile and its tributaries, together with zircons from Lake Tana rhyolites from the Ethiopian Highlands (ages from Prave et al. 2016). Probability density plot is shown for combined data. (b) Plot of initial εHf values against age for detrital zircons from the modern Nile and its tributaries, together with zircons from the Lake Tana rhyolites. Numbers in parentheses in the key indicate the number of Cenozoic grains detected in each sample relative to the total number of grains analysed. It should be noted that zero Cenozoic grains were recorded in the modern White Nile and Red Sea Hills modern wadi sediments. Laura Fielding et al. Journal of the Geological Society 2017;174: © 2017 The Author(s)‏

10 87Sr/86Sr v. ɛNd isotope data for Nile river muds; Egyptian Nile trunk sands taken prior to the construction of the Aswan Dam (samples from Shukri 1949); Nile hinterland mudstones, wadi muds and aeolian sands; and Sudanese Holocene Nile trunk samples (Woodward et al. 2015). 87Sr/86Sr v. ɛNd isotope data for Nile river muds; Egyptian Nile trunk sands taken prior to the construction of the Aswan Dam (samples from Shukri 1949); Nile hinterland mudstones, wadi muds and aeolian sands; and Sudanese Holocene Nile trunk samples (Woodward et al. 2015). Also shown for comparison are average data from the Ethiopian Continental Flood Basalts (Pik et al. 1999). Laura Fielding et al. Journal of the Geological Society 2017;174: © 2017 The Author(s)‏

11 ɛHf plotted against ɛNd for the same samples as shown in Figure 8
ɛHf plotted against ɛNd for the same samples as shown in Figure 8. *Ethiopian basalt data from Meshesha & Shinjo (2010). ɛHf plotted against ɛNd for the same samples as shown in Figure 8. *Ethiopian basalt data from Meshesha & Shinjo (2010). Symbols as in Figure 9, except as noted. Laura Fielding et al. Journal of the Geological Society 2017;174: © 2017 The Author(s)‏

12 Probability density plot illustrating the Hf isotope–time evolution of the Nile source regions supplying detrital zircons discussed in this study. Probability density plot illustrating the Hf isotope–time evolution of the Nile source regions supplying detrital zircons discussed in this study. The density of the data distribution is calculated using a modified version of the MATLAB implementation of the Kernel Density Estimation procedure supplied by Botev et al. (2010) using bandwidths equivalent to the typical analytical uncertainty of the U/Pb ages (±20 Ma) and ɛHf values (±1 epsilon units). Contours are generated by the MATLAB contour3 function and plotted using the plot3d function. Also shown are the compilation of African detrital data from Condie & Aster (2010), and the modern African river data of Iizuka et al. (2013) filtered using the discordance criteria applied in this paper. Laura Fielding et al. Journal of the Geological Society 2017;174: © 2017 The Author(s)‏

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