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Continental crustal fragments, partially synonymous with microcontinents,[1] are pieces of continents that have broken off from main continental masses to form distinct islands and often several hundred kilometers from their place of origin.[2]
Causes
editContinental fragments and microcontinent crustal compositions are very similar to those of regular continental crust. The rifting process that caused the continental fragments to form most likely impacts their layers and overall thickness along with the addition of mafic intrusions to the crust. Studies have determined that the average crustal thickness of continental fragments is approximately 24.8±5.7km[3]. The sedimentary layer of continental fragments can be up to 5km thick and can overlay two to three crustal layers. Continental fragments have an average crustal density of 2.81 g cm-3 which is very similar to that of typical continental crust.
Strike-slip 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 across narrow zones and near-vertical strike-slip-dominated faults. They develop fault-block patterns that slice the portion of continent into detachable slivers. The continental fragments are located at various angles from their transform faults[4].
History
editSome microcontinents are fragments of Gondwana or other ancient cratonic continents; some examples include Madagascar; the northern Mascarene Plateau, which includes the Seychelles microcontinent; and the island of Timor.[5]Other islands, such as several in the Caribbean Sea, 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 is a large igneous province formed by a volcanic hotspot; however, it was associated with the breakup of Gondwana and was for a time above water, so it is considered a microcontinent, though not a continental fragment.[6][7] Other hotspot islands such as Iceland and Hawaii are considered neither microcontinents nor continental fragments. Not all islands can be considered microcontinents: the British Isles, Sri Lanka, Borneo, and Newfoundland, for example, are each within the continental shelf of an adjacent continent, separated from the mainland by inland seas flooding its margins.[8]
Several islands in the eastern Indonesian Archipelago are considered continental fragments, although this designation is controversial. The archipelago is home to numerous microcontinents with complex geology and tectonics. This makes it complicated to classify land masses and determine causation for the formation of the land mass.[9] These include Sumba, Timor (Nusa Tenggara), Banggai-Sulu Islands (Sulawesi), Obi, southern Bacan, and the Buru-Seram-Ambon complex (Maluku).[10]
List of continental fragments and microcontinents
edit- Continental fragments (pieces of Pangaea smaller than Australia)
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- Bollons Seamount – Continental fragment seamount southeast of New Zealand
- East Tasman Plateau – Submerged microcontinent south east of Tasmania
- Gilbert Seamount – Continental fragment seamount west of New Zealand
- Jan Mayen Microcontinent – Atlantic fragment of continental crust
- Madagascar – Island country in the Indian Ocean
- Mascarene Plateau – Submarine plateau in the western Indian Ocean
- Seychelles microcontinent – A microcontinent underlying the Seychelles Islands in the western Indian Ocean
- Mauritia – A Precambrian microcontinent that broke away as India and Madagascar separated
- Parts of Wallaby Plateau – Undersea bathymetric high west of Australia
- Possibly Sumba, Timor, and other islands of eastern Indonesia; Sulawesi formed via the subduction of a microcontinent
- Rockall Plateau – Bathymetric feature northwest of Scotland and Ireland
- Socotra – Largest of four islands of the Socotra Archipelago, Yemen[11]
- South Orkney Microcontinent[12]
- Zealandia – Mostly submerged continental crust area in Oceania
- Other microcontinents (formed post-Pangaea)
- Barbados – Island nation in the Caribbean
- Cuba, Hispaniola, Jamaica, and other granitic Caribbean islands
- Kerguelen Plateau – Oceanic plateau in the southern Indian Ocean
References
edit- ^ "Microcontinent" was initially the broader term, because it was defined morphologically rather than genetically (in term or genesis or origin). Scrutton, Roger A. (1976) "Microcontinents and Their Significance" pp. 177–189 In Drake, Charles L. (1976) (editor) Geodynamics: Progress and Prospects American Geophysical Union, Washington, D.C., ISBN 978-0-87590-203-6. But, using Scrutton's definition, "microcontinent" is a narrower term, excluding aseismic ridges of continental material, such as the Lomonosov Ridge and the Jan Mayen Ridge, which could still be considered "continental fragments".
- ^ Monk, K.A.; Fretes, Y.; Reksodiharjo-Lilley, G. (1996). The Ecology of Nusa Tenggara and Maluku. Hong Kong: Periplus Editions Ltd. pp. 41–43. ISBN 978-962-593-076-3.
- ^ Tetreault, J. L.; Buiter, S. J. H. (2014). "Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments". Solid Earth. 5 (2): 1243–1275. ISSN 1869-9529.
- ^ Nemčok, M.; Sinha, S. T.; Doré, A. G.; Lundin, E. R.; Mascle, J.; Rybár, S. (2016). "Mechanisms of microcontinent release associated with wrenching-involved continental break-up; a review". Geological Society, London, Special Publications. 431 (1): 323–359. ISSN 0305-8719.
- ^ Monk, K.A.; Fretes, Y.; Reksodiharjo-Lilley, G. (1996). The Ecology of Nusa Tenggara and Maluku. Hong Kong: Periplus Editions Ltd. pp. 27–29. ISBN 978-962-593-076-3.
- ^ UT Austin scientist plays major rule in study of underwater "micro-continent". Retrieved on 2007-07-03
- ^ Sci/Tech 'Lost continent' discovered Retrieved on 2007-07-03
- ^ Péron-Pinvidic, Gwenn; Manatschal, Gianreto (2010). "From microcontinents to extensional allochthons: witnesses of how continents rift and break apart?". Petroleum Geoscience. 16 (3): 189–197. ISSN 1354-0793.
- ^ T. O. Simanjuntak (1994). "Tectonic Development of the Indonesian Archipelago and its Bearing on the Occurrence of Hydrocarbons: ABSTRACT". AAPG Bulletin. 78. doi:10.1306/a25fe8fb-171b-11d7-8645000102c1865d. ISSN 0149-1423.
- ^ Monk, K.A.; Fretes, Y.; Reksodiharjo-Lilley, G. (1996). The Ecology of Nusa Tenggara and Maluku. Hong Kong: Periplus Editions Ltd. p. 41. ISBN 978-962-593-076-3.
- ^ "Socotra Archipelago – a lifeboat in the sea of changes: advancement in Socotran insect biodiversity survey" (PDF). Acta Entomologica Musei Nationalis Pragae. 52 (supplementum 2): 1–26. Archived from the original (PDF) on 2013-11-11.
- ^ R. A. J. Trouw; C. W. Passchier; L. S. A. Simőes; R. R. Andreis; C. M. Valeriano (1997). "Mesozoic tectonic evolution of the South Orkney Microcontinent, Scotia arc, Antarctica". Geological Magazine. 134 (3): 383–401. Bibcode:1997GeoM..134..383T. doi:10.1017/S0016756897007036. hdl:11449/36781.