الصفيحة الأفريقية
| الصفيحة الأفريقية | |
|---|---|
| النمط | رئيسية |
| المساحة التقريبية | 61,300,000 كم² |
| السمات | أفريقيا، المحيط الأطلسي، البحر المتوسط |
الصفيحة الأفريقية ، هي صفيحة تكتونية رئيسية، ترْكب خط الإستواء وخط الزوال. وتضم معظم قارة أفريقيا، وكذلك القشرة المحيطية التي تقع بين القارة ومختلف النتوءات المحيطية. وبين و، بدأت الصفيحة الصومالية في الانفلاق من الصفيحة الأفريقية بطول فالق شرق أفريقيا. ولما كانت قارة أفريقيا تتكون من قشرة من كلٍ من الصفيحتين الأفريقية والصومالية، فإن بعض الكتابات تشير إلى الصفيحة الأفريقية بإسم الصفيحة النوبية لتمييزها عن القارة ككل.
الحدود
The westerly side is a divergent boundary with the North American Plate to the north and the South American Plate to the south forming the central and southern part of the Mid-Atlantic Ridge. The African plate is bounded on the northeast by the Arabian Plate, the southeast by the Indo-Australian Plate, the north by the Eurasian Plate and the Anatolian Plate, and on the south by the Antarctic Plate. All of these are divergent or spreading boundaries with the exception of the northern boundary with the Eurasian Plate (except for a short segment near the Azores, the Terceira Rift).
المكونات
The African Plate comprises several continental blocks or cratons, stable continental blocks of old rocks, which came together to form the African continent during the assembly of the supercontinent Gondwana around 550 million years ago. These cratons are, from south to north, the Kalahari, Congo, Sahara and West African craton. Each of these cratons can further be subdivided into even smaller blocks or terranes, sutured along pre-Gondwanan orogenic belts.
التحركات الحديثة
The African Plate is rifting in the eastern interior along the East African Rift. This rift zone separates the Nubian subplate to the west from the Somalian subplate to the east. One hypothesis proposes the existence of a mantle plume beneath the Afar region, while an opposing hypothesis asserts that the rifting is merely a zone of maximum weakness where the African Plate is deforming as plates to its east are moving rapidly northward.
تصل سرعة الصفيحة الأفريقية إلى حوالي 2.15 سنتيمتر في العام. وهي تتحرك منذ 100 مليون عام مضى أوفي إتجاه الشمال الشرقي بصفة عامة.This is drawing it closer to the Eurasian Plate, causing subduction where oceanic crust is converging with continental crust (e.g. portions of the central and eastern Mediterranean). In the western Mediterranean, the relative motions of the Eurasian and African plates produce a combination of lateral and compressive forces, concentrated in a zone known as the Azores-Gibraltar Fault Zone. Along its northeast margin, the African Plate is bounded by the Red Sea Rift where the Arabian Plate is moving away from the African Plate.
The New England hotspot in the Atlantic Ocean has probably created a short line of mid to late-Tertiary age seamounts on the African Plate but appears to be currently inactive.
المصادر
- ^ "Sizes of Tectonic or Lithospheric Plates". About.com. Retrieved 30 June 2015.
- ^ "Somali Plate". Ashten Sawitsky. Retrieved 30 June 2015.
- ^ Chu, D.; Gordon, R. G. (1999). "Evidence for motion between Nubia and Somalia along the Southwest Indian ridge". Nature. 398 (6722): 64–67. Bibcode:1999Natur.398...64C. doi:10.1038/18014. Retrieved 20 June 2015.
- ^ Age Progressive Volcanism in the New England Seamounts and the opening of the Central Atlantic Ocean Retrieved on 2007-10-05
وصلات خارجية
- USGS - Understanding plate motions
- Cenozoic dynamics of the African plate with emphasis on the Africa-Eurasia collision
- Huang, Zhen Shao (1997). "Speed of the Continental Plates". The Physics Factbook.
