Continental crustal fragments, partly
synonym
A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...
ous with microcontinents, are pieces of
continent
A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven ...
s that have broken off from main continental masses to form distinct islands that are often several hundred kilometers from their place of origin.
Causes
Continental fragments and microcontinent crustal compositions are very similar to those of regular
continental crust
Continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called ''sial'' be ...
. The rifting process that caused the continental fragments to form most likely impacts their layers and overall thickness along with the addition of
mafic
A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...
intrusions to the crust. Studies have determined that the average crustal thickness of continental fragments is approximately . The
sedimentary layer of continental fragments can be up to thick and can overlay two to three crustal layers. Continental fragments have an average crustal density of which is very similar to that of typical continental crust.
Strike-slip
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
fault zones cause the fragmentation of microcontinents. The zones link the extensional zones where continental pieces are already isolated through the remaining continental bridges. Additionally, they facilitate quick
crustal thinning
Extensional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the stretching of a planetary body's crust or lithosphere.
Deformation styles
The types of structure and the geometries formed depend on ...
across narrow zones and near-vertical strike-slip-dominated
faults. They develop
fault-block
Fault blocks are very large blocks of rock, sometimes hundreds of kilometres in extent, created by tectonic and localized stresses in Earth's crust. Large areas of bedrock are broken up into blocks by faults. Blocks are characterized by relat ...
patterns that slice the portion of continent into detachable slivers. The continental fragments are located at various angles from their
transform fault
A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subductio ...
s.
History
Some microcontinents are fragments of
Gondwana
Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...
or other ancient
craton
A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and ...
ic continents; some examples include
Madagascar
Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...
; the northern
Mascarene Plateau
The Mascarene Plateau is a submarine plateau in the Indian Ocean, north and east of Madagascar. The plateau extends approximately , from Seychelles in the north to Réunion in the south. The plateau covers an area of over of shallow water, wi ...
, which includes the
Seychelles Microcontinent
The Seychelles Microcontinent is a microcontinent underlying Seychelles in the western Indian Ocean made of Late Precambrian rock.
The granite outcrops of the Seychelles Islands in the central Indian Ocean were amongst the earliest examples cit ...
; and the island of
Timor
Timor is an island at the southern end of Maritime Southeast Asia, in the north of the Timor Sea. The island is East Timor–Indonesia border, divided between the sovereign states of East Timor on the eastern part and Indonesia on the western p ...
. Other islands, such as several in the
Caribbean Sea
The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...
, are composed largely of granitic rock as well, but all continents contain both granitic and basaltic crust, and there is no clear dividing line between islands and microcontinents under such a definition. The
Kerguelen Plateau
The Kerguelen Plateau (, ), also known as the Kerguelen–Heard Plateau, is an oceanic plateau and a large igneous province (LIP) located on the Antarctic Plate, in the southern Indian Ocean. It is about to the southwest of Australia and is ...
is a
large igneous province
A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation ...
formed by a volcanic
hotspot; however, it was associated with the breakup of
Gondwana
Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...
and was for a time above water, so it is considered a microcontinent, though not a continental fragment.
[UT Austin scientist plays major rule in study of underwater "micro-continent".](_blank)
Retrieved on 2007-07-03 Other hotspot islands such as the
Hawaiian Islands
The Hawaiian Islands ( haw, Nā Mokupuni o Hawai‘i) are an archipelago of eight major islands, several atolls, and numerous smaller islets in the North Pacific Ocean, extending some from the island of Hawaii in the south to northernmost Kur ...
and
Iceland
Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...
are considered neither microcontinents nor continental fragments. Not all islands can be considered microcontinents:
Borneo
Borneo (; id, Kalimantan) is the third-largest island in the world and the largest in Asia. At the geographic centre of Maritime Southeast Asia, in relation to major Indonesian islands, it is located north of Java, west of Sulawesi, and eas ...
, the
British Isles
The British Isles are a group of islands in the North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner and Outer Hebrides, the Northern Isles, ...
,
Newfoundland
Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...
, and
Sri Lanka
Sri Lanka (, ; si, ශ්රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
, for example, are each within the continental shelf of an adjacent continent, separated from the mainland by
inland seas
An inland sea (also known as an epeiric sea or an epicontinental sea) is a continental body of water which is very large and is either completely surrounded by dry land or connected to an ocean by a river, strait, or "arm of the sea". An inland se ...
flooding its margins.
Several islands in the eastern
Indonesian Archipelago
The islands of Indonesia, also known as the Indonesian Archipelago ( id, Kepulauan Indonesia) or Nusantara, may refer either to the islands comprising the country of Indonesia or to the geographical groups which include its islands.
History ...
are considered continental fragments, although this designation is controversial. The
archipelago
An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster, or collection of islands, or sometimes a sea containing a small number of scattered islands.
Examples of archipelagos include: the Indonesian Archi ...
is home to numerous microcontinents with complex geology and tectonics. This makes it complicated to classify landmasses and determine causation for the formation of the landmass. These include southern
Bacan
The Bacan Islands, formerly also known as the Bachans, Bachians, and Batchians, are a group of islands in the Moluccas in Indonesia. They are mountainous and forested, lying south of Ternate and southwest of Halmahera. The islands are administe ...
,
Banggai-
Sulu Islands (
Sulawesi
Sulawesi (), also known as Celebes (), is an island in Indonesia. One of the four Greater Sunda Islands, and the world's eleventh-largest island, it is situated east of Borneo, west of the Maluku Islands, and south of Mindanao and the Sulu Ar ...
), the
Buru
Buru (formerly spelled Boeroe, Boro, or Bouru) is the third largest island within the Maluku Islands of Indonesia. It lies between the Banda Sea to the south and Seram Sea to the north, west of Ambon and Seram islands. The island belongs to Ma ...
-
Seram
Seram (formerly spelled Ceram; also Seran or Serang) is the largest and main island of Maluku province of Indonesia, despite Ambon Island's historical importance. It is located just north of the smaller Ambon Island and a few other adjacent is ...
-
Ambon
Ambon may refer to:
Places
* Ambon Island, an island in Indonesia
** Ambon, Maluku, a city on Ambon Island, the capital of Maluku province
** Governorate of Ambon, a colony of the Dutch East India Company from 1605 to 1796
* Ambon, Morbihan, a c ...
complex (
Maluku),
Obi #REDIRECT Obi {{redirect category shell, {{R from other capitalisation{{R from ambiguous title ...
,
Sumba
Sumba ( id, Pulau Sumba) is an island in eastern Indonesia. It is one of the Lesser Sunda Islands and is in the province of East Nusa Tenggara. Sumba has an area of , and the population was 779,049 at the 2020 Census; the official estimate as a ...
, and
Timor
Timor is an island at the southern end of Maritime Southeast Asia, in the north of the Timor Sea. The island is East Timor–Indonesia border, divided between the sovereign states of East Timor on the eastern part and Indonesia on the western p ...
(
Nusa Tenggara
The Lesser Sunda Islands or nowadays known as Nusa Tenggara Islands ( id, Kepulauan Nusa Tenggara, formerly ) are an archipelago in Maritime Southeast Asia, north of Australia. Together with the Greater Sunda Islands to the west they make up t ...
)
List of continental fragments and microcontinents
Continental fragments (pieces of Pangaea smaller than Australia)
![Ilha_do_Pico_P6030580_(34526717664)](https://upload.wikimedia.org/wikipedia/commons/0/06/Ilha_do_Pico_P6030580_%2834526717664%29.jpg)
*
*
*
*
*
*
*
**
*
* Parts of
* Possibly
Sumba
Sumba ( id, Pulau Sumba) is an island in eastern Indonesia. It is one of the Lesser Sunda Islands and is in the province of East Nusa Tenggara. Sumba has an area of , and the population was 779,049 at the 2020 Census; the official estimate as a ...
,
Timor
Timor is an island at the southern end of Maritime Southeast Asia, in the north of the Timor Sea. The island is East Timor–Indonesia border, divided between the sovereign states of East Timor on the eastern part and Indonesia on the western p ...
, and other islands of eastern Indonesia;
Sulawesi
Sulawesi (), also known as Celebes (), is an island in Indonesia. One of the four Greater Sunda Islands, and the world's eleventh-largest island, it is situated east of Borneo, west of the Maluku Islands, and south of Mindanao and the Sulu Ar ...
formed via the subduction of a microcontinent
*
*
* South Orkney Microcontinent
*
Other microcontinents (formed post-Pangaea)
*
*
Cuba
Cuba ( , ), officially the Republic of Cuba ( es, República de Cuba, links=no ), is an island country comprising the island of Cuba, as well as Isla de la Juventud and several minor archipelagos. Cuba is located where the northern Caribbea ...
,
Hispaniola
Hispaniola (, also ; es, La Española; Latin and french: Hispaniola; ht, Ispayola; tnq, Ayiti or Quisqueya) is an island in the Caribbean that is part of the Greater Antilles. Hispaniola is the most populous island in the West Indies, and th ...
,
Jamaica
Jamaica (; ) is an island country situated in the Caribbean Sea. Spanning in area, it is the third-largest island of the Greater Antilles and the Caribbean (after Cuba and Hispaniola). Jamaica lies about south of Cuba, and west of His ...
, and other granitic
Caribbean islands
Almost all of the Caribbean islands are in the Caribbean Sea, with only a few in inland lakes. The largest island is Cuba. Other sizable islands include Hispaniola, Jamaica, Puerto Rico and Trinidad and Tobago. Some of the smaller islands are re ...
*
References
{{Continents of Earth
Plate tectonics
Fragments