Geology of Mozambique

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The geology of Mozambique is primarily extremely old Precambrian metamorphic and igneous crystalline basement rock, formed in the Archean and Proterozoic, in some cases more than two billion years ago. Mozambique contains greenstone belts and spans the Zimbabwe Craton, a section of ancient stable crust. The region was impacted by major tectonic events, such as the mountain building Irumide orogeny, Pan-African orogeny and the Snowball Earth glaciation. Large basins that formed in the last half-billion years have filled with extensive continental and marine sedimentary rocks, including rocks of the extensive Karoo Supergroup which exist across Southern Africa. In some cases these units are capped by volcanic rocks. As a result of its complex and ancient geology, Mozambique has deposits of iron, coal, gold, mineral sands, bauxite, copper and other natural resources. [1]

Contents

Stratigraphy, Tectonics & Geologic History

The oldest rocks in Mozambique are part of the Irumide Belt, outcropping near the border with Zimbabwe. Over two billion years old, these rocks date to the Archean and Paleoproterozoic and are an extension of greenstone belts and granite-gneisses, within the Zimbabwe Craton.

The schist of the greenstone belt is divided between the Manica Group, Gairezi Group and Umkondo Group, which together are the oldest individual rock units in the country. The formation of these schists and the Irumide Belt is tied to the Irumide orogeny about 1.35 billion years ago. [2]

Proterozoic (2.5 billion-539 million years ago)

During the Neoproterozoic, the Pan-African orogeny emplaced granites and pegmatites throughout what is now Mozambique. This 250 million year tectonic event (which continued into the Phanerozoic Eon) overprinted many of the Precambrian rocks in Mozambique. The Snowball Earth global glaciation event 600 million years ago, at the same time as the orogeny began, left glacial sedimentary rocks in the Katangula Group in northwestern Mozambique, which is the same unit as the Katanga Supergroup in the Democratic Republic of the Congo and Zambia. [2]

Phanerozoic (539 million-present)

As the Pan-African orogeny continued, in parallel with the proliferation of multi-cellular life, a large rift formed across the south of the supercontinent Gondwana across what is now South Africa and southern South America. The Karoo Supergroup, the most widely dispersed stratigraphic unit in southern Africa formed from the Carboniferous through the Early Jurassic in the Mesozoic. The Alto Zambezi Basin, Rio Lunho Basin and Rio Lugenda Basin, large intracratonal basins in Mozambique filled with sedimentary rocks. For the most part, the basins contain sequences of fluvial and glacial sediments, with layers of red mudstone with fossils and some coal layers. The Alto Zambezi Basin is capped by volcanic basalt and rhyolite in the south. Sedimentary rock formation continued in Mozambique along the coasts in the Jurassic, Cretaceous and into the Paleogene and Neogene periods of the Cenozoic, with some sedimentary units formed in the past 2.5 million years of the Quaternary. Sedimentation shifted to different basins, including the Mozambique Basin, Limpopo Basin, Baixa Zambezi Basin and Rovuma Basin. [3]

Hydrogeology

South of the Save River, unconsolidated sediments are an important source of groundwater, overlying the Mozambique Basin. A 30 kilometer wide belt of dune sands occupies the southern coast of the country, atop Cretaceous and Paleogene rocks and form a moderately productive unconfined aquifer. Thick alluvium in the Limpopo River and Incomati River valleys forms a major aquifer in high porosity sands north of Maputo.

Marine and continental sandstones dominate deeper Cretaceous-Paleogene sedimentary aquifers and some also contain layers of limestone. These underlying rocks in the Mozambique Basin form the largest aquifer, beneath 21% of the country. Cut by large river valleys, arkosic sandstones give way to limestone closer to the coast. North of the Save River, the basin is moderately productive, but to the south it has high salinity nearly unusable groundwater for much of its extent. The Rovuma Basin is poorly studied, but impermeable marl and high incidences of brackish groundwater suggest it would not be a major potential source. As much as 57% of Mozambique is directly underlain by Precambrian basement rock, which forms some small and locally productive aquifers in weathered rock near the surface. Mountain areas tend to have thicker weathered mantle, with most productive locations near fault zones. In northern Mozambique, average weathered rock cover is less than 20 meters thick, rising to as much as 50 meters in valleys. Fractured volcanic rocks form locally productive aquifers, producing high quality water, often in 10 to 20 meter thick weathered rock near the surface. However, weathered basalt often ends up with high clay concentrations, limiting productivity. [4]

Natural resource geology

Mozambique has extensive natural resources, although most remain undeveloped. The Manica Belt is a continuation of the Mutare-Manica Gold Belt from Zimbabwe and contains iron, copper, asbestos, gold, lead and nickel hosted in an Archean and Paleoproterozoic greenstone belt. Small mines in the region have targeted placer gold in sediments in the area and there is also a small, high-grade bauxite deposit. The metasediments of Gairezi Group and Umkondo Group both host limestone, copper and iron near the border with Zimbabwe. Mozambique has four asbestos deposits. One has chrysotile asbestos crystals, separated by serpentinite in the Zimbabwe Craton, near Manica. Others are in the Mozambique Belt, or associated with serpentinization south of Manica. Seven out of the nation's 10 provinces have graphite in Proterozoic rock associated with schist and gneiss. Semi-precious stones, feldspar, beryl (including aquamarine and morganite), mica and radioactive minerals are found with pegmatites in the Proterozoic rocks in Zambezia Province and Nampula Province. Elsewhere, in the northeast, pegmatite hosts lithium, bismuth, quartz, beryl, columbium, antimony and tantalum.

The Eocene Cheringoma Formation and the Miocene Jofane Formation contain limestone, halite and gypsum. Mozambique is also notable for beach sands between Quelimane and Angoche, laden with zircon, rutile, monazite and ilmenite. The country has 120 to 380 million tons of coal reserves in the bottom units of the Karoo Supergroup in the Rio Lunho Basin. The Cretaceous Grudja Formation in shows the most promise for potential hydrocarbons and Mesozoic sedimentary sequences in the north and south both have the possibility of future discoveries. [5]

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Geology of Zimbabwe

The geology of Zimbabwe in southern Africa is centered on the Zimbabwe Craton, a core of Archean basement composed in the main of granitoids, schist and gneisses. It also incorporates greenstone belts comprising mafic, ultramafic and felsic volcanics which are associated with epiclastic sediments and iron formations. The craton is overlain in the north, northwest and east by Proterozoic and Phanerozoic sedimentary basins whilst to the northwest are the rocks of the Magondi Supergroup. Northwards is the Zambezi Belt and to the east the Mozambique Belt. South of the Zimbabwe Craton is the Kaapvaal Craton separated from it by the Limpopo Mobile Belt, a zone of deformation and metamorphism reflecting geological events from Archean to Mesoproterozoic times. The Zimbabwe Craton is intruded by an elongate ultramafic/mafic igneous complex known as the Great Dyke which runs for more than 500 km along a SSW/NNE oriented graben. It consists of peridotites, pyroxenites, norites and bands of chromitite.

The geology of Central African Republic (CAR) is part of the broader geology of Africa. CAR occupies a swath of ancient rocks, dating back billions of years that record significant aspects of Earth history and yield minerals vital to the country's small economy.

Gabon is situated at the northwestern margin of the Congo Craton—a region of stable, ancient crust—and preserves very ancient rock units across 75% of the country, with overlying sedimentary units from the Cretaceous and other more recent periods.

Geology of the Republic of the Congo

The geology of the Republic of the Congo, also known as Congo-Brazzaville, to differentiate from the Democratic Republic of the Congo, formerly Zaire, includes extensive igneous and metamorphic basement rock, some up to two billion years old and sedimentary rocks formed within the past 250 million years. Much of the country's geology is hidden by sediments formed in the past 2.5 million years of the Quaternary.

Geology of Ghana

The geology of Ghana is primarily very ancient crystalline basement rock, volcanic belts and sedimentary basins, affected by periods of igneous activity and two major orogeny mountain building events. Aside from modern sediments and some rocks formed within the past 541 million years of the Phanerozoic Eon, along the coast, many of the rocks in Ghana formed close to one billion years ago or older leading to five different types of gold deposit formation, which gave the region its former name Gold Coast.

Geology of the Democratic Republic of the Congo

The geology of the Democratic Republic of the Congo is extremely old, on the order of several billion years for many rocks. The country spans the Congo Craton: a stable section of ancient continental crust, deformed and influenced by several different mountain building orogeny events, sedimentation, volcanism and the geologically recent effects of the East Africa Rift System in the east. The country's complicated tectonic past have yielded large deposits of gold, diamonds, coltan and other valuable minerals.

Geology of Ivory Coast

The geology of Ivory Coast is almost entirely extremely ancient metamorphic and igneous crystalline basement rock between 2.1 and more than 3.5 billion years old, comprising part of the stable continental crust of the West African Craton. Near the surface, these ancient rocks have weathered into sediments and soils 20 to 45 meters thick on average, which holds much of Ivory Coast's groundwater. More recent sedimentary rocks are found along the coast. The country has extensive mineral resources such as gold, diamonds, nickel and bauxite as well as offshore oil and gas.

The geology of Malawi formed on extremely ancient crystalline basement rock, which was metamorphosed and intruded by igneous rocks during several orogeny mountain building events in the past one billion years. The rocks of the Karoo Supergroup and newer sedimentary units deposited across much of Malawi in the last 251 million years, in connection with a large rift basin on the supercontinent Gondwana and the more recent rifting that has created the East African Rift, which holds Lake Malawi. The country has extensive mineral reserves, many of them poorly understand or not exploited, including coal, vermiculite, rare earth elements and bauxite.

The geology of Mauritania is built on more than two billion year old Archean crystalline basement rock in the Reguibat Shield of the West African Craton, a section of ancient and stable continental crust. Mobile belts and the large Taoudeni Basin formed and filled with sediments in the connection with the Pan-African orogeny mountain building event 600 million years ago and a subsequent orogeny created the Mauritanide Belt. In the last 251 million years, Mauritania has accumulated additional sedimentary rocks during periods of marine transgression and sea level retreat. The arid country is 50% covered in sand dunes and has extensive mineral resources, although iron plays the most important role in the economy.

The geology of Niger comprises very ancient igneous and metamorphic crystalline basement rocks in the west, more than 2.2 billion years old formed in the late Archean and Proterozoic eons of the Precambrian. The Volta Basin, Air Massif and the Iullemeden Basin began to form in the Neoproterozoic and Paleozoic, along with numerous ring complexes, as the region experienced events such as glaciation and the Pan-African orogeny. Today, Niger has extensive mineral resources due to complex mineralization and laterite weathering including uranium, molybdenum, iron, coal, silver, nickel, cobalt and other resources.

Geology of Sierra Leone

The geology of Sierra Leone is primarily very ancient Precambrian Archean and Proterozoic crystalline igneous and metamorphic basement rock, in many cases more than 2.5 billion years old. Throughout Earth history, Sierra Leone was impacted by major tectonic and climatic events, such as the Leonean, Liberian and Pan-African orogeny mountain building events, the Neoproterozoic Snowball Earth and millions of years of weathering, which has produced thick layers of regolith across much of the country's surface.

Geology of Tanzania

The geology of Tanzania began to form in the Precambrian, in the Archean and Proterozoic eons, in some cases more than 2.5 billion years ago. Igneous and metamorphic crystalline basement rock forms the Archean Tanzania Craton, which is surrounded by the Proterozoic Ubendian belt, Mozambique Belt and Karagwe-Ankole Belt. The region experienced downwarping of the crust during the Paleozoic and Mesozoic, as the massive Karoo Supergroup deposited. Within the past 100 million years, Tanzania has experienced marine sedimentary rock deposition along the coast and rift formation inland, which has produced large rift lakes. Tanzania has extensive, but poorly explored and exploited natural resources, including coal, gold, diamonds, graphite and clays.

The geology of Uganda extends back to the Archean and Proterozoic eons of the Precambrian, and much of the country is underlain by gneiss, argillite and other metamorphic rocks that are sometimes over 2.5 billion years old. Sedimentary rocks and new igneous and metamorphic units formed throughout the Proterozoic and the region was partially affected by the Pan-African orogeny and Snowball Earth events. Through the Mesozoic and Cenozoic, ancient basement rock has weathered into water-bearing saprolite and the region has experienced periods of volcanism and rift valley formation. The East Africa Rift gives rise to thick, more geologically recent sediment sequences and the country's numerous lakes. Uganda has extensive natural resources, particularly gold.

Geology of Zambia

The geological history of Zambia begins in the Proterozoic eon of the Precambrian. The igneous and metamorphic basement rocks tend to be highly metamorphosed and may have formed earlier in the Archean, but heat and pressure has destroyed evidence of earlier conditions. Major sedimentary and metamorphic groups formed in the mid-Proterozoic, followed by a series of glaciations in the Neoproterozoic and much of the Paleozoic which deposited glacial conglomerate as well as other sediments to form the Katanga Supergroup and rift-related Karoo Supergroup. Basalt eruptions blanketed the Karoo Supergroup in the Mesozoic and Zambia shifted to coal and sandstone formation. Geologically recent windblown sands from the Kalahari Desert and alluvial deposits near rivers play an important role in the modern surficial geology of Zambia. The country has extensive natural resources, particularly copper, but also cobalt, emeralds, other gemstones, uranium and coal.

The geology of Eswatini formed beginning 3.6 billion years ago, in the Archean Eon of the Precambrian. Eswatini is the only country entirely underlain by the Kaapvaal Craton, one of the oldest pieces of stable continental crust and the only craton regarded as "pristine" by geologists, other than the Yilgarn Craton in Australia. As such, the country has very ancient granite, gneiss and in some cases sedimentary rocks from the Archean into the Proterozoic, overlain by sedimentary rocks and igneous rocks formed during the last 539 million years of the Phanerozoic as part of the Karoo Supergroup. Intensive weathering has created thick zones of saprolite and heavily weathered soils.

Geology of Senegal

The geology of Senegal formed beginning more than two billion years ago. The Archean greenschist Birimian rocks common throughout West Africa are the oldest in the country, intruded by Proterozoic granites. Basins formed in the interior during the Paleozoic and filled with sedimentary rocks, including tillite from a glaciation. With the rifting apart of the supercontinent Pangaea in the Mesozoic, the large Senegal Basin filled with thick sequences of marine and terrestrial sediments. Sea levels declined in the Eocene forming large phosphate deposits. Senegal is blanketed in thick layers of terrestrial sediments formed in the Quaternary. The country has extensive natural resources, including gold, diamonds, and iron.

Geology of Sudan

The geology of Sudan formed primarily in the Precambrian, as igneous and metamorphic crystalline basement rock. Ancient terranes and inliers were intruded with granites, granitoids as well as volcanic rocks. Units of all types were deformed, reactivated, intruded and metamorphosed during the Proterozoic Pan-African orogeny. Dramatic sheet flow erosion prevented almost any sedimentary rocks from forming during the Paleozoic and Mesozoic. From the Mesozoic into the Cenozoic the formation of the Red Sea depression and complex faulting led to massive sediment deposition in some locations and regional volcanism. Sudan has petroleum, chromite, salt, gold, limestone and other natural resources.

The geology of Nigeria formed beginning in the Archean and Proterozoic eons of the Precambrian. The country forms the Nigerian Province and more than half of its surface is igneous and metamorphic crystalline basement rock from the Precambrian. Between 2.9 billion and 500 million years ago, Nigeria was affected by three major orogeny mountain-building events and related igneous intrusions. Following the Pan-African orogeny, in the Cambrian at the time that multi-cellular life proliferated, Nigeria began to experience regional sedimentation and witnessed new igneous intrusions. By the Cretaceous period of the late Mesozoic, massive sedimentation was underway in different basins, due to a large marine transgression. By the Eocene, in the Cenozoic, the region returned to terrestrial conditions.

The geology of Nunavut began to form nearly three billion years ago in the Archean and the territory preserves some of the world's oldest rock units.

References

  1. Schlüter, Thomas (2008). Geological Atlas of Africa. Springer. pp. 180–183.
  2. 1 2 Schlüter 2008, p. 180.
  3. Schlüter 2008, pp. 180–182.
  4. "Hydrogeology of Mozambique". British Geological Survey.
  5. Schlüter 2008, pp. 182–183.