The geology of Seychelles is an example of a felsic granite microcontinent that broke off from the supercontinent Gondwana within the past 145 million years and become isolated in the Indian Ocean. The islands are primarily granite rock, with some sequences of sedimentary rocks formed during rift basin periods or times when the islands were submerged in shallow water.
Charles Darwin first published an account of the geology of the archipelago, while Alfred Wegener cited the area as evidence of continental drift. [1] [2]
Seychelles began to form in the Neoproterozoic as a granite microcontinent. Granite is the bedrock of Mahe, Praslin, La Digue and Fregate, with the rock dated as 748-755 Ma. Much of the rock is gray granite, while in southwest it is a pink porphyry form of granite. [3] [1]
The granites were cut by doleritic dykes, trending WNW-ESE, in the Precambrian and early Tertiary. [1] [2]
The rifting apart of the supercontinent Gondwana in the Late Paleozoic created failed rift grabens. The rifting process stalled and then continued in the Triassic until the Middle Jurassic as between two and six kilometers of [1] clastic sediments accumulated on the western margin of the Seychelles microcontinent. Along the passive northwest margin with Gondwana, the coastline was submerged and one kilometer of fine sediments deposited there as the Somali oceanic basin formed.
East Gondwana fragmented 120 million years ago, splitting up Antarctica-Australia and Madagascar-Seychelles-India, which ultimately separated 85 million years ago as the Mascarene basin formed. The Deccan Traps hotspot, which poured out immense basalt flows in India 65 million years ago and ultimately formed islands such as Mauritius and Réunion, isolated Seychelles. [4]
The microcontinent was confined between northern Madagascar and western India until the Late Cretaceous and evolved during the Cenozoic through a process of rift and drift tectonics. The microcontinent was uplifted, eroded and impacted by volcanic eruptions. [5]
In the early Cenozoic, around 61-67 Ma, alkaline igneous rocks emplaced to become the Silhouette and Île du Nord islands. [1]
Seychelles sources most of its water from rainfall and desalination and receives 2300 millimeters of precipitation every year. Surface water is stored by the La Gogue dam and the Rochon dam. However, the government has had to institute water rationing during the dry season from May to October. Beginning in 2009, the Seychelles government took interest in groundwater as a backup supply in fractured granite bedrock, looking to the example of granite aquifers in Sweden and commercial water companies such as Gondwana Water Drilling Company, which drilled eight test wells in the 1990s. [6]
Seychelles had a small scale guano mining industry until the 1980s and has ongoing exploration for offshore oil and gas. Currently, there is no mining in Seychelles except quarrying for clay, coral and sand to use as building material. [5]
The Mascarene Plateau is a submarine plateau in the Indian Ocean, north and east of Madagascar. The plateau extends approximately 2,000 km (1,200 mi), from Seychelles in the north to Réunion in the south. The plateau covers an area of over 115,000 km2 (44,000 sq mi) of shallow water, with depths ranging from 8–150 m (30–490 ft), plunging to 4,000 m (13,000 ft) to the abyssal plain at its edges. It is the second-largest oceanic plateau in the Indian Ocean after the Kerguelen Plateau.
The geology of England is mainly sedimentary. The youngest rocks are in the south east around London, progressing in age in a north westerly direction. The Tees-Exe line marks the division between younger, softer and low-lying rocks in the south east and the generally older and harder rocks of the north and west which give rise to higher relief in those regions. The geology of England is recognisable in the landscape of its counties, the building materials of its towns and its regional extractive industries.
The geological history of Earth follows the major geological events in Earth's past based on the geological time scale, a system of chronological measurement based on the study of the planet's rock layers (stratigraphy). Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun, which also created the rest of the Solar System.
Continental crustal fragments, partly synonymous with microcontinents, are pieces of continents that have broken off from main continental masses to form distinct islands that are often several hundred kilometers from their place of origin.
This is a list of articles related to plate tectonics and tectonic plates.
The Seychelles Microcontinent is a microcontinent underlying Seychelles in the western Indian Ocean made of Late Precambrian rock.
The Madagascar Plate or Madagascar block was once attached to the Gondwana supercontinent and later the Indo-Australian Plate.
The geology of Massachusetts includes numerous units of volcanic, intrusive igneous, metamorphic and sedimentary rocks formed within the last 1.2 billion years. The oldest formations are gneiss rocks in the Berkshires, which were metamorphosed from older rocks during the Proterozoic Grenville orogeny as the proto-North American continent Laurentia collided against proto-South America. Throughout the Paleozoic, overlapping the rapid diversification of multi-cellular life, a series of six island arcs collided with the Laurentian continental margin. Also termed continental terranes, these sections of continental rock typically formed offshore or onshore of the proto-African continent Gondwana and in many cases had experienced volcanic events and faulting before joining the Laurentian continent. These sequential collisions metamorphosed new rocks from sediments, created uplands and faults and resulted in widespread volcanic activity. Simultaneously, the collisions raised the Appalachian Mountains to the height of the current day Himalayas.
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.
The geology of Somalia is built on more than 700 million year old igneous and metamorphic crystalline basement rock, which outcrops at some places in northern Somalia. These ancient units are covered in thick layers of sedimentary rock formed in the last 200 million years and influenced by the rifting apart of the Somali Plate and the Arabian Plate. The geology of Somaliland, the de facto independent country recognized as part of Somalia, is to some degree better studied than that of Somalia as a whole. Instability related to the Somali Civil War and previous political upheaval has limited geologic research in places while heightening the importance of groundwater resources for vulnerable populations.
The geology of Cameroon is almost universally Precambrian metamorphic and igneous basement rock, formed in the Archean as part of the Congo Craton and the Central African Mobile Zone and covered in laterite, recent sediments and soils. Some parts of the country have sequences of sedimentary rocks from the Paleozoic, Mesozoic and Cenozoic as well as volcanic rock produced by the 1600 kilometer Cameroon Volcanic Line, which includes the still-active Mount Cameroon. The country is notable for gold, diamonds and some onshore and 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 Rhode Island is based on nearly one billion year old igneous crystalline basement rocks formed as part of the microcontinent Avalonia that collided with the supercontinent Gondwana. The region experienced substantial folding associated with its landlocked position during the Alleghanian orogeny mountain building event. The region accumulated sedimentary rocks, including small deposits of coal. The region was covered with thick Atlantic Coastal Plain sediments, with the erosion of the Appalachians and the creation of the Atlantic Ocean throughout the past 200 million years. These surficial sediments and soils were substantially reworked by the Pleistocene glaciations. The state's geology is part of the broader geology of New England.
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 Somaliland is very closely related to the geology of Somalia. Somaliland is a de facto independent country within the boundaries that the international community recognizes as Somalia. Because it encompasses the former territory of British Somaliland, the region is historically better researched than former Italian Somaliland. Somaliland is built on more than 700 million year old igneous and metamorphic crystalline basement rock.. These ancient units are covered in thick layers of sedimentary rock formed in the last 200 million years and influenced by the rifting apart of the Somali Plate and the Arabian Plate.
The geology of Morocco formed beginning up to two billion years ago, in the Paleoproterozoic and potentially even earlier. It was affected by the Pan-African orogeny, although the later Hercynian orogeny produced fewer changes and left the Maseta Domain, a large area of remnant Paleozoic massifs. During the Paleozoic, extensive sedimentary deposits preserved marine fossils. Throughout the Mesozoic, the rifting apart of Pangaea to form the Atlantic Ocean created basins and fault blocks, which were blanketed in terrestrial and marine sediments—particularly as a major marine transgression flooded much of the region. In the Cenozoic, a microcontinent covered in sedimentary rocks from the Triassic and Cretaceous collided with northern Morocco, forming the Rif region. Morocco has extensive phosphate and salt reserves, as well as resources such as lead, zinc, copper and silver.
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.
The bedrock of Colorado was assembled from island arcs accreted onto the edge of the ancient Wyoming Craton. The Sonoma orogeny uplifted the ancestral Rocky Mountains in parallel with the diversification of multicellular life. Shallow seas covered the regions, followed by the uplift current Rocky Mountains and intense volcanic activity. Colorado has thick sedimentary sequences with oil, gas and coal deposits, as well as base metals and other minerals.
The geology of Newfoundland and Labrador includes basement rocks formed as part of the Grenville Province in the west and Labrador and the Avalonian microcontinent in the east. Extensive tectonic changes, metamorphism and volcanic activity have formed the region throughout Earth history.
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