Geological Survey ofFinland, Special Paper 55A.B. Phil Westerhof, Paavo Hörmä, Edward Isabirye, Edwards Katto, Tapio Koistinen, Eira Kuismanen, Tapio Lehto, Mitti I. Lehtonen,

Hannu Mäkitie, Tuomo Manninen, Irmeli Mänttöri, Yrjö Pekkala, Jussi Pokki, Kerstin Saalmann and Petri Virransalo

CONTENTS

FOREWORDSUMMARY

1 AFRTCAS MAIOR CHRONO-TECTONO-THERMAL DOMATNS_ THE'BUILDING BLOCKS' 15

1.2 Archaean Cratons and Mobile Belts .......... ..........1g1.3 Palaeoproterozoic Fold Belts of the Eburnian Orogenic Cycle .......... ...........;........ ......201.4 Palaeoproterozoic post-Eburnian Platform Deposits ...........231.5 Mesoproterozoic Grenvillean/ Kibaran Fold Belts ................251.6 Post-Rodinia Neoproterozoic Platform Rocks of the Malagarasi Supergroup ..........281.7 Neoproterozoic-Cambrian Pan-African Fold Belts ........... ........................321.8 Phanerozoic post-Pan-African Extensional Basins ...............3g

2 LAKE VICTORIA TERRANE OF THE ARCHAEAN TANZANIA CRATON .....................,.........,,.44

2.2 Major Lithostratigraphic Units of the Lake Victoria Terrane ..................472.2.1 Pre-Nyanzian Basement ............. ...............472.2.2 Nyanzian Supergroup .......... ......................492.2.3 Syn- to post-Nyanzian granitoids .......... ...................... 482.2.4 Kavirondian Supergroup .......482.2.5 Youneer granitoids ............... ......................49

2.3 Lithostratigraphy of the Lake Victoria Terrane in SE Uganda ................. ....................492.3.1 Nyanzian Supergroup .......... ......................502.3.2 Kavirondian Supergroup ........512.3.3 Synkinematic granitoids of the Lake Victoria Terrane ..................522.3.4 Postkinematic intrusives of the Lake Victoria Terrane ................. 532.3.5 lganga Suite .........552.3.6 Nabukalu gabbro intrusions .....................592.3.7 Geochemistry ......63

2.5 Geodynamic Development ...............64

3 WEST TANZANIA TERRANE OF THE ARCHAEAN TANZANIA CRATON ................................693.1 Introduction - Archaean'Building Blocks'of Uganda .........693.2 Airborne Geophysical Data .........;....693.3 Litho-Stratigraphy of the West Tanzania Terrane .................74

3.3.1 TTG Gneisses ......753.3.2 Tororo Suite .........773.3.3 Kampala Suite .....803.3.4 Kiboga Suite ........813.3.5 Bubulo Formation ................ ......................82

3.5 Geodynamic Development of the West Tanzania Terrane .......................84

4 WEST NrLE BLOCK OF THE BOMU-KTBALTAN SHTELD (CONGO CRATON) ...... 86

4.2 Bomt-Kibalian Shield (Congo Craton) ..............864.3 Tectono-Thermal Domains of the West Nile Block ...............88

4.3.1 Introduction ........88

Geological Survey of Finland, Special Paper 55

Geology and Geodynamic Development of Uganda with Explanation of the l:1,000,000 -Scale Geological Map

4.3.2 Redefinition of tectono-thermal units in the West Nile Block ..... 90

4.4 Lithostratigraphy of the Uleppi Complex ...........91

4.4.1 Uleppi Group...... .....................92

4.4.2 Pltttonic Units of the Uleppi Complex ........................96

4.5 Lithostratigraphy of the War Group (Arua-Kibale Supergroup) ............... ..................98

4.6 Lithostratigraphy of the Lobule Group and Abiba Formation (Arua-Kibale Supergroup) .......101

4.6.1 Lobule Group..... .................... 102

4.6.2 Abiba Formation ..................106

4.6.3 Plutonic Rocks... .................... 106

4.7 Lithostratigraphy of the Yumbe Complex ........110

4.7.1 Introduction...... ..................... 110

4.7.2 Supracrustal rocks of the Yumbe Complex.... ............ 111

4.7.3 Phttonic rocks of the Yumbe Complex.... ................... 112

Mafic metavolcanic rocks ....113

4.10 Tectono-Thermal Evolution of the West Nile Block.......... ......................118

ROCKS OF THE NORTH UGANDA TERRANE. ..................... 121

5.2 Tectono-Thermal Domains of the North Uganda Terrane .....................121

5.3 Geology of the Mesoarchaean Karuma Group of the North Uganda Terrane ........121

5.4 Geology of the Neoarchaean Amuru Group of the North Uganda Terrane ............125

5.5 Geology of Neoarchaean Granitoids and Gneisses of the North Uganda Terrane .....................131

5.6 Nakasongola-Bukungu Suite... ........147

5.8 Tectono-Thermal Evolution of the North Uganda Terrane ...................148

5.8.1 Archaean development of the NUT.......... ................. 148

5.8.2 Late Mesoproterozoic development of the NUT.......... ................ 150

5.8.3 Neoproterozoic development of the NUT during the Pan-African ............... 151

6 PALAEOPROTEROZOIC ROCKS OF THE RWENZORI FOLD 8ELT.......... .,,,,..........152

6.2 Lithostratigraphy of the Palaeoproterozoic Rwenzori Basement ...........155

Rukungiri Suite .......... ...........155

6.3 Lithostratigraphy of the Palaeoproterozoic Buganda Group .................157

6.3.1 Introduction ......157

6.3.2 Yictoria Formation............... ....................157

6.3.3 Nile Formation (incl. Bujagali Member) .................. ..................... 159

6.4SyrrkinematicGranitoidsoftheRwenzoriBelt,''..'......Sembabule Suite........... ......... 165

6.5 Postkinematic Granitoids of the Rwenzori Be1t............. .......167

Mubende-Singo Suite ...........167

6.6 Lithostratigraphy and Structure of the Rwenzori Block .....L70

6.8 Tectono-Thermal Evolution of the Rwenzori Belt ............ .......................175

7 PALAEOPROTEROZOIC POST-RWENZORI PLATFORM SEDIMENTS...................................... 180

7.2 Geology of the Namuwasa Group ......................182

7.2.2 Lithostratigraphic units........ ................".. 182

6

Geological Survey ofFinland, Special Paper 55A.B. Phil Westerhof, Paavo Hörmä, Edward Isabirye, Edwards Katto, Tapio Koistinen, Eira Kuosmanen, Tapio Lehto, Matti I. Lehtonen,

Hannu Mökitie, Tuomo Manninen, Irmeli Mönttäri, Yrjö Pekkala, Iussi Pokki, Kerstin Saalmann and Petri Virransalo

7.3 Geology of the Bwezigoro Group .......................1857.3.1 Introduction .......... ................185

T.4Geology of the Kagera-Buhjewu supergroup ........... ..............t877.4.1 Introduction ...............;.... ......1877.4.2 Llthostratigraphic units .......188

Muyaga Group......... .............. 188Ruvubu Group ...................... 191

7.6 Geodynamic Development .............L94

8 ROCKS OF THE MESOPROTEROZOIC NORTH KIBARAN BELT.......... ................... 199

8.1.1 Kibaran Belt .......1998.1.2 Short Outline of the South Kibaran Belt ............ .......2008.1.3 Structural Zones of the North Kibaran Belt ............ .....................201

8.2 Lithostratigraphy of the pre-Kibaran Basement ....................2028.3 Lithostratigraphy of the Akanyaru-Ankole Supergroup .......204

8.3.1 Introduction ......2048.3.2 Gikoro Group ....2088.3.3 Pindura Group ......................2118.3.4 Cyohoha Group ....................2t38.3.5 Rugezi Group ....216

8.4 Plutonic Rocks of the North Kibaran Belt ............ ..................2188.4.1 Introduction ......2L88.4.2 'Older'Kibaran granitoids (1.57-1.45 Ga) ............. .......................2198.4.3 Plutonic Rocks of the bimodal North Kibaran Igneous Province (1.38-1.33 Ga) ..........22I8.4.4 A-We granites of the Transition Zone (1.25 Ga) ............ ............2268.4.5 'Tin granites' and other'younger granites' (1.10-1.00 Ga) and related pegmatite

bodies (0.97 Ga) and quartz veins (0.95 Ga) ............. ....................226

8.6 Geodynamic Evolution of the North Kibaran Belt ............ ......................230

9 ROCKS OF THE LATE MESOPROTEROZOIC MADI-IGISIBELT........ .....,.,.....,,,,...,.236

9.3 Lithostratigraphy of the Igisi Group ..................244

9.5 Geodynamic Evolution of the Madi-Igisi 8e1t............. .........254

10 POST-RODINIAN NEOPROTEROZOIC PLATFORM ROCKS OF THE MALAGARASISUPERGROUP............. ...26310.1 Malagarasi Supergroup........... .........26310.2 Geology of the M§ana Group ......264

10.2.1lntroduction...... ....................26410.2.2 Lithostratigraphy of the Mityana Group ...................265

10.3 Geology the Bunyoro Group ..........267

10.3.1 Introduction...... ....................26710.3.2 Lithostratigraphy of the Bunyoro Group ..................268

10.5 Geodynamic Evolution of the Bunyoro Group ....................275

Geological Survey ofFinland, Special Paper 55Geology and Geodynamic Development of Uganda with Explanation of the 1:1,000,000 -Scale Geological Map

11 ROCKS OF THE KARAMOIA BELT AND OTHER ROCKS OF THE NEOPROTEROZOTCPAN-AFRICAN CYCLE ..,.,,..,,......,,..279

11.2 Karamoja Belt (East Africa Orogen)..... .............27911.3 Lithostratigraphy of the Karasuk Supergroup ......................282

11.3.1 Ophiolites from the Neoproterozoic Mozambique Ocean ........28411.3.2 Metasediments from the post-Rodinia passive margin .............28411.3.3 Rocks of the syn-collisional magmatic arc .......... .....286L1.3.4 Rocks of uncertain derivation ................286

11.4 Geology of the West Karamoja Group ..............288

1 1.4. 1 Introduction ..... 28811.4.2 Structural subdivision of the West Karamoja CompIex.................. ................28811.4.3 Lithostratigraphy of the West Karamoja Group ......289ll.4.4lntrusive rocks of the West Karamoja Complex .......297

11.5 In-situ Intrusive Rocks in the Karamoja Belt ........... ...........30211.6 Other Pan-African Granitoids in North Uganda ................305

11.8.1 Introduction ..... 31011.8.2 Textures and Structures within the ASZ ...................310

11.10 Geodynamic Development during the Pan-African Orogenic Cycle .....................31511.10.1 Introduction ................ .......31511.10.2 Karamoja 8e1t............ .........31611.10.3 Geodynamic development of the Aswa Shear Zone .......... .......320

12 POST-PAN-AFRICAN PHANEROZOIC DEPOSITS: KAROO, EAST AFRICAN RIFTSYSTEM AND QUATERNARY DEPOSTTS ........323

L2.2Palaeozoic-Mesozoic Karoo Supergroup .........323l2.Z.Ilntroduction .....32312.2.2 Lithology of Karoo Supergroup in Uganda ..............32412.2.3 Geodynamic development ............. ........325

12.3 Cenozoic Lithologies of the East African Rift System ........32612.3.1 Introduction .....326L2.3.2 Neogene Elgon Complex (Eastern branch of EARS) ..................32712.3.3 Albertine Supergroup (Western branch of EARS) ......................33712.3.4 Geodynamic setting of the EARS volcanics in Uganda ..............357

12.4 Quaternary deposits outside the EARS ............360

l2.4Jlntroduction .....36012.4.2 Stratigraphy of Pleistocene and Holocene Deposits ...................361

Appendices

App. 1: Tectono-Thermal Units of Uganda 1:2 500 000App. 2: Representative chemical whole-rock analyses

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Geological Map of Uganda 1:1 000 000