Overview

East Africa’s Geology was First Mapped in 1900 by Gregory Rift.

East Africa Rift System subsequently taking its Name after the Geologist, Gregory Rift.  The Earliest Gold Discovery in East Africa was made in 1890 by German Prospectors around Lake Victoria Area.  Since then Broad Spectrum of Geology Studies have been undertaken to Study East Africa’s Geology’s Evolution and Mineralization. Geophysical and Geochemical Surveys to Collect Data and Map East Africa’s Natural Resources have been undertaken by Independent Geologist, Geological Survey Departments of Various, Countries Including Canada, Britain and Australia. Others include Non- Governmental Organization such as United Nations Development Programs, Multinational Mining Companies such as Brocken Hill Propriety, De Beers, and Anglo America.

Individual Governments also over the last Decade have also Proactively Undertaken Mineral Exploration Surveys to Identify and Map Natural resources as Part of Initiative to Promote Investment into the Extractive Sectors. Mostly Engaging the Modern Exploration Technology to carry out Air bone Survey and Document the Data on Mineralization on Geo – Portal Cadastral.

The Development of New Advance Exploration Technology has had a Profound Positive Impact on Mineral Exploration and Deposit Discoveries. In the last decade significant advances have been made on Proven Geophysical methods and Techniques to interpret and Visualize Geophysical Data.  One of the most significant recent advances in Geophysics is the routine 3D Inversions of Potential Field Data.

Progress in Computing power and Software Innovation has enhanced Data integration and inversions to be applied to a variety of Problems from Modeling to desecrate targets of Region Geology.  A review of Discovery methods by Experts Indicate that Understating the Geological feature is the Key Element in both Greenfield and Brownfield Exploration. Therefore ultimately application of proven and emerging detection techniques in close integration with Geology is remain important in underpinning the Future Mineral Exploration Programs.

The Pan-Africa Orogeny Mobile Belts

Pan-African can now be used to describe tectonic, magmatic and metamorphic activities of Neoproterozoic to Earliest Paleozoic age. The Pan – African is a Protracted Orogenic cycle reflecting the opening and closing of Large Oceanic realms as well as   accretion and collision of Buoyant crustal rock Blocks.
The Pan- African Domain Consist of two types of Broad Mobile Orogenic Belts.
a.    Neoproterozoic Collision & Accretion Belts
One type consists predominantly of Neoproterozoic Supercrustal and magmatic assembles many of Juvenile origin with Structural and Metamorphic histories similar to those in Phanerozoic collision and accretion belts.  These Belts expose upper middle crustal Levels and contain diagnostic features such as Ophiolites, Subduction- or Collision- Related Granatoids. Island- arc or Passive Continental margins as well as Exotic terrains that permit the reconstruction of their Evolution in Phanerozoic –style plate scenarios.

– Arabia- Nubia Shield of Arabia and North Africa.

– Darama Kaoko- Gariep Belt of Lufilian Arc and central and western Africa.

– West Congo Belt of Angola and Democratic Republic of Congo.

-Trans- Saharan Belt of West Africa.

– Rokelide and Mauretian Belts along Western part of Western African Cratons.

b.    Mesoproterozoic to Archaean Belts.

The other type of Mobile Belt generally contains Polydeformed high grade of metamorphic assemblages. Exposing middle to lower levels whose origin Environment of formation and structural Evolution are more difficult to reconstruct. The Protoliths of these assemblages consists Polydeformed high grade metamorphic assemblages consists predominantly of much older Mesoproterozoic to Archaean Continental crust that was strongly  reworked during the Neoproterozoic. Well Studied Example of this Belt is the Mozambique belt of East Africa.
Others Include;

– Mozambique Belt of East Africa Including Madagascar with Extension into West Africa.
– Zambezi Belt of Northern Zimbabwe and Zambia.
– Little Known Migmatitic Terrains of Chad
– The Central African Republic
– Tibesti Massif in Libya and the Western parts of Egypt and Sudan.

It has been proposed that the latter type of belt represents the deeply eroded part of collisional Orogen and that the two types of Pan- Africa Belts are not fundamentally different but they Constitute different Crustal Levels of Collisional and / or accretional systems.

For this reason the East African Orogen has been proposed for combined upper Crustal Arabian – Nubian – Shield and Lower crustal Mozambique Belt.

The Mozambique Belt

This broad belt defines the Southern Part of East African Orogen and essentially consist of medium to high – Grade Gneisses and Voluminous Granatoids.

The Mozambique Belt Extends south from the Nubian –Arabian Shields into southern Ethiopia, Kenya and Somalia via Tanzania, Malawi and Mozambique and also includes Madagascar.. The southward continuation of the belt into droning Maud Land of East Antarctica has been proposed on the basis of Geophysical patterns, Structural features of Geochronology. Most parts of the Belts are not covered by detailed Mapping making regional correlations difficult. There is no Overall model for Evolution of the Mozambique Belt although most workers agree that it resulted from Collision between East and West Gondwana.

Significant differences in Rock type structural style, age metamorphic Evolution suggest that the Belt as a whole constitutes a Pan – African Collage of terrains accreted to East Margin of Combined Congo and Tanzania Cratons and Significant Volumes of Older Crust of these Cratons were reconstituted during this event.

Mapping and Geochronology in Kenya have recognized that undated Neoproterozoic Supercrustal Sequences that are sandwiched between Basement Gneisses of Archaean and younger age. A 700 Ma Dismember Ophiolites complex at the Kenya Ethiopia Border Testifies to the Consumption and Obduction of Marginal Basin Oceanic Crust. Major deformation and high grade Metamorphism is ascribed to two major events between 830 Ma and 620 Ma based on Rb- Sr dating but the Older of these appear Questionable.

A similar situation prevails in Tanzania where Metamorphic Grade is Generally Highly and many granulite – facies Rocks of Neo- Proterozoic Supercrustal sequence are rare, whereas late Archaean to Paleoproterozoic Granatoids Gneisses Volumetrically greatly dominate over Juvenile- Pan – African Intrusives. These older rocks strongly reworked during the Pan – African Orogenic Cycle and Locally Migmatized and /or Mylonitized wither represent Eastward Extension of Tanzania Cratons that were structurally reworked during the Pan – African events or the separate Crustal entities ( Exotic Blocks) of Unknown origin

The significance of rare Granatoids Gneisses with Proliths ages of rare Granitoid Gneisses with Proliths ages of 1000 – 1100 Ma in Southern Tanzania and Malawi is unknown. From these some workers have Postulated a major Kabaran (Grenvillian) even in the Mozambique Belt, but there is no Geological Evidence to relate these Rocks to an Orogeny. A Layered Gabbros Anthorsite Complex was emplaced at 695 Ma in Tanzania. The Peak of Granulite- facies Metamorphism was dated at 620 Ma – 640 Ma over wide Areas of Mozambique Belt in Tanzania suggesting that this was the major collision and Crustural Thickening event in this part of the Belt.

In Northern Mozambique the High-grade Gneisses, granulites and Migmatitic of the Mozambique belt were interpreted to have been reformed and metamorphosed during two distinct events Namely, The Mozambican Cycle at 1100 – 850 Ma. Also Known as “Lurian Orogeny”   and the Pan – African Cycle at 800-550 Ma recent high precision Zircon Geochronology has confirmed the older represent a major phase of Granitoid Plutonism, including emplacement of Large Gabbro Anorthosite Massif near Tete at 1025 Ma, but there is yet no Conclusive Evidence for deformation and granulite – Facies Metamorphism in this Rocks during this time. The Evidence points to only one severe events of Ductile deformation and high grade metamorphism with a peak some 615 -540 Ma ago.

A similar situation prevails in Southern Malawi where High grade Granitoid Gneissis with Protolith ages of 1040 – 555 Ma, ductilely deformed together with Supercrustal rocks and the peak of Granulite – facies Metamorphism was reached 550-570 Ma.

Tanzania Cratons

There are seven Cratonic Nuclei from the Foundation of Africa. The Kaapval Cratons, Zimbabwe Cratons, the Tanzania Cratons, the Congo Cratons, the Man Shield, the Reguibat shield, and Elusive East or Nile Sahara.

During the Neoarchean and Paleoproterozoic, these Archaean emerged into three major Cratons which will be referred to as West Africa Cratons, Central Africa ( Congo and Tanzania) and Southern Africa.

[Source: Geological Evolution of Africa; Paul H.G.M Dirks, Tom G. Blenkinsop and Dr. Heilke A. Jelsma ]

Central Africa (Congo & Tanzania) Cratons

The Congo – Tanzania Cratons is a region of pre – 2.5 G.a Continental crust, located in central Africa includes Tanzania and Congo Cratons, linked by Uganda Basement Gneisses and west Nile Complex 2.8 G.a Kilo – Moto Terrain.

The Tanzania Cratons Stretches 0.5 Million Square Kilometers in Tanzania across into South west Kenya and South East Uganda. The Tanzania Cratons is consists of 2.9 G.a Dodoma Terrane in South and younger Lake Victoria Terrane in the North. The Lake Victoria Terrane Comprises High grade TTG –Type Orthogenesis, Mafic, Ultramafic rocks, Quartzite and Phyllite.

Lake Victoria Terrane consist of Tectonized Greenstone Belt Intruded by Large amounts if Granite. The Greenstone consist of 28.81 -2.70Ga.Bimodal Volcanics and Clastic sediments (Nzega and Kakamega Group). Basalt Andesite, Shoshonitic Rhyolite and Conglomerate,(Rongo group), unconformably, overlie the older sequences.

Granite was emplaced during several stages of Early Syntectonic, late Syntectonic and post tectonic western Granite complex. The Platform sequence was deposited on the North East and North Parts of the Cratons (Kisii, Buganda Groups).

The Archaean Outcrops of Congo cartons include Chailu – Gabon Block, South west Cameroon, Equitorial Guinea, Gabon, Congo, Zaire Block, North East DR Congo, West Uganda, The Angola Block and Kasai Block.