TheConrad discontinuitycorresponds to the sub-horizontal boundary in thecontinental crustat which theseismic wavevelocity increases in a discontinuous way. This boundary is observed in various continental regions at a depth of 15 to 20 km, but it is not found inoceanicregions.
The Conrad discontinuity (named after theseismologistVictor Conrad) is considered to be the border between the upper continental (sial,for silica-aluminium)crust and the lower one (sima,for silica-magnesium). It is not as pronounced as theMohorovičić discontinuityand absent in some continental regions.[1]Up to the middle 20th century, the upper crust in continental regions was seen to consist offelsic rockssuch asgranite(sial), and the lower one to consist of more magnesium-richmafic rockslikebasalt(sima). Therefore, the seismologists of that time considered that the Conrad discontinuity should correspond to a sharply defined contact between the chemically distinct two layers, sial and sima.[2]Despite the fact that sial and sima are two solid layers, the lighter sial is thought to "float" on top of the denser sima layer. This forms the basis ofAlfred Wegener's'Continental Drift Theory.'The area of contact during the movement of the Continental plates is on the Conrad discontinuity.[3]
However, from the 1960s onward, this theory was strongly contested amonggeologists.The exact geological significance of the Conrad discontinuity is still not clarified. The possibility that it represents the transition fromamphibolitefaciestogranulitefaciesmetamorphismhas been given some support from observations of the uplifted central part of theVredefort impact structureand the surroundingKaapvaal Craton.[4]
References
edit- ^Lowrie, W. (1997).Fundamentals of Geophysics.Cambridge University Press.p. 149.ISBN9780521467285.Retrieved30 June2012.
- ^Kearey, P.; Klepeis K.A.; Vine F.J. (2009).Global Tectonics(3 ed.).John Wiley & Sons.pp. 19–21.ISBN9781405107778.Retrieved30 June2012.
- ^Elena Shenoy, Theresa Maria (2012).Mordern Certificate Geography(9th ed.). 21, Patullos Road, Chennai 600 002, India: FRANK BROS. &CO. pp. 31–32.ISBN9789356662636.
{{cite book}}:CS1 maint: location (link) - ^Muundjua, M.; Hart R.J.; Golder S.A.; Carporzen L.; Galdeano A. (2007). "Magnetic imaging of the Vredefort impact crater, South Africa".Earth and Planetary Science Letters.261(3–4): 456–468.Bibcode:2007E&PSL.261..456M.doi:10.1016/j.epsl.2007.07.044.
 | Thisplate tectonicsarticle is astub.You can help Wikipedia byexpanding it. |
 | Thisgeophysics-related article is astub.You can help Wikipedia byexpanding it. |