Continental crustal fragments, partlysynonymous withmicrocontinents,[1] are pieces ofcontinents that have broken off from main continental masses to form distinct islands that are often several hundred kilometers from their place of origin.[2]
Continental fragments and microcontinent crustal compositions are very similar to those of regularcontinental crust. The rifting process that caused the continental fragments to form most likely impacts their layers and overall thickness along with the addition ofmafic 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] Thesedimentary 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-slipfault 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 quickcrustal thinning across narrow zones and near-vertical strike-slip-dominatedfaults. They developfault-block patterns that slice the portion of continent into detachable slivers. The continental fragments are located at various angles from theirtransform faults.[4]
Some microcontinents are fragments ofGondwana or other ancientcratonic continents; examples includeMadagascar; the northernMascarene Plateau, which includes theSeychelles Microcontinent; and the island ofTimor.[5] Other islands, such as several in theCaribbean 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. TheKerguelen Plateau is alarge igneous province formed by a volcanichotspot; however, it was associated with the breakup ofGondwana 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 theHawaiian Islands andIceland are considered neither microcontinents nor continental fragments. Not all islands can be considered microcontinents:Borneo, theBritish Isles,Newfoundland, andSri Lanka, for example, are each within the continental shelf of an adjacent continent, separated from the mainland byinland seas flooding its margins.[8]
^"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. 177–189In Drake, Charles L. (1976) (editor)Geodynamics: Progress and Prospects American Geophysical Union, Washington, D.C.,ISBN978-0-87590-203-6. But, using Scrutton's definition, "microcontinent" is a narrower term, excluding aseismic ridges of continental material, such as theLomonosov Ridge and theJan 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.ISBN978-962-593-076-3.
^Monk, K.A.; Fretes, Y.; Reksodiharjo-Lilley, G. (1996).The Ecology of Nusa Tenggara and Maluku. Hong Kong: Periplus Editions Ltd. pp. 27–29.ISBN978-962-593-076-3.
^Monk, K.A.; Fretes, Y.; Reksodiharjo-Lilley, G. (1996).The Ecology of Nusa Tenggara and Maluku. Hong Kong: Periplus Editions Ltd. p. 41.ISBN978-962-593-076-3.
.jpg)
