Continental fragment

Continental crustal fragments, partly synonymous with microcontinents,[1] 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.[2]

Causes

Continental 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 ± 5.7 kilometres (15.4 ± 3.5 mi).[3] The sedimentary layer of continental fragments can be up to 5 kilometres (3.1 mi) thick and can overlay two to three crustal layers. Continental fragments have an average crustal density of 2.81 g/cm3 (0.102 lb/cu in) 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

Some microcontinents are fragments of Gondwana or other ancient cratonic continents; 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 the Hawaiian Islands and Iceland are considered neither microcontinents nor continental fragments. Not all islands can be considered microcontinents: Borneo, the British Isles, Newfoundland, and Sri Lanka, 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 landmasses and determine causation for the formation of the landmass.[9] These include southern Bacan, Banggai-Sulu Islands (Sulawesi), the Buru-Seram-Ambon complex (Maluku), Obi, Sumba, and Timor (Nusa Tenggara)[10]

List of continental fragments and microcontinents

Continental fragments (pieces of Pangaea smaller than Australia)
Azores Plateau, a continental fragment located in the North Atlantic Ocean

Other microcontinents (formed post-Pangaea)

Future microcontinents
  • Ajan, a continent that will form in 3 to 20 million years time because of its breakoff with mainland Africa. [13]

References
  1. "Microcontinent" was initially the broader term, because it was defined morphologically rather than genetically (in terms of 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".
  2. 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.
  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. Bibcode:2014SolE....5.1243T. doi:10.5194/se-5-1243-2014. ISSN 1869-9529.
  4. 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. Bibcode:2016GSLSP.431..323N. doi:10.1144/SP431.14. ISSN 0305-8719. S2CID 131615662.
  5. 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.
  6. UT Austin scientist plays major rule in study of underwater "micro-continent". Retrieved on 2007-07-03
  7. Sci/Tech 'Lost continent' discovered Retrieved on 2007-07-03
  8. 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. Bibcode:2010PetGe..16..189P. doi:10.1144/1354-079309-903. ISSN 1354-0793. S2CID 131142997.
  9. 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.
  10. 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.
  11. "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.
  12. 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. S2CID 53705372.
  13. https://www.iflscience.com/africa-is-splitting-into-two-continents-and-may-open-a-vast-new-ocean-67848
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