| 词条 | Bayuda volcanic field |
| 释义 |
|name=Bayuda volcanic field |photo=Bayuda Vulkanfeld.jpg|photo_caption=The volcanic field from space|map=Sudan |coordinates={{coord|18.33|N|32.75|E|display=inline,intitle}} |coordinates_ref=[1] |last_eruption=1,102 +- 48 years ago|elevation_m=670 |elevation_ref=[1] }} Bayuda volcanic field (also spelled Bayiuda[1]) is a volcanic field in Sudan, within the Bayuda Desert. It covers a surface of about {{convert|11|x|48|km}} and consists of a number of cinder cones as well as some maars and explosion craters. These vents have erupted aa lava flows. The field rises above a Precambrian-Paleozoic basement that may be a domal uplift. There is little known about the occurrence of volcanic eruptions, but the last eruption has been dated to 1,102 ± 48 years before present. Geography and geomorphologyThe volcanic field is located in the Bayuda Desert within the great bend of the Nile,[1] {{convert|300|km}} north of Khartoum.{{sfn|Lenhardt|Borah|Lenhardt|Bumby|2018|p=2}} It lies {{convert|80|km}} away from Merowe; there are wells at Abu Khorit and Sani{{sfn|Almond|Ahmed|Khalil|1969|p=550}} north of the volcanic field.{{sfn|Almond|1974|p=346}} The field was discovered by aerial photography in 1920.{{sfn|Almond|Ahmed|Khalil|1969|p=550}} Bayuda is an elongated volcanic field[1] with fresh volcanic features{{sfn|Almond|Ahmed|Khalil|1969|p=550}} extending over an area of {{convert|11|x|48|km}} in northwesterly direction. Within this area, a number of volcanic vents within a narrow space have formed a continuous volcanic surface.{{sfn|Almond|Ahmed|Khalil|1969|p=557}} Some individual lava fields cover over {{convert|20|km2}} of surface,{{sfn|Almond|Ahmed|Khalil|1969|p=561}} but surfaces of about {{convert|10|km2}} are more typical.{{sfn|Almond|Kheir|Poole|1984|p=235}} There are usually only a few flows per vent, although they often have lobate structures. The surface of the lava flows has varying textures and often contains hills or ridges,{{sfn|Almond|Ahmed|Khalil|1969|p=558}} generally corresponding to aa lava.{{sfn|Almond|Ahmed|Khalil|1969|p=559}} Some flows reach lengths of {{convert|10|km}}.{{sfn|Klitzsch|Thorweihe|1999|p=129}} Cinder cones make up the bulk of the field,[1] of which there are about one hundred.{{sfn|Almond|Ahmed|Khalil|1969|p=556}} Usually the cones reach heights of over {{convert|400|m}}{{sfn|Almond|Kheir|Poole|1984|p=235}} and are formed by volcanic ash, lapilli, lava bombs and scoria.{{sfn|Lenhardt|Borah|Lenhardt|Bumby|2018|p=4}} Many of these aside from pyroclastics also erupted lava flows{{sfn|Almond|Ahmed|Khalil|1969|p=557}} which then broke the crater rims.[1] Explosion craters[1] and sporadic maars are also found,{{sfn|Lenhardt|Borah|Lenhardt|Bumby|2018|p=2}} they are surrounded by tephra deposits which form low rims of pyroclastic material{{sfn|Lenhardt|Borah|Lenhardt|Bumby|2018|p=7}} and which also cover neighbouring volcanoes.{{sfn|Almond|1974|p=346}} Individual vents form two separate alignments.{{sfn|Klitzsch|Thorweihe|1999|p=129}} Hosh ed Salam ("dark enclosure"{{sfn|Grabham|1920|p=134}}) crater is {{convert|500|m}} deep and {{convert|1300|m}} wide,[1] other craters are Jebel Hebeish and El Muweilih which have formed shallow rises above the surrounding terrain and have cut into the basement rocks.{{sfn|Almond|Ahmed|Khalil|1969|p=559}} El Muweilih contains a salt lake after which it is named and which was used as a source of salt,{{sfn|Almond|Ahmed|Khalil|1969|p=561}} while Jebel El Abour contains a secondary cone. The Sergein hills and Jebel Azrub are composite volcanoes.{{sfn|Almond|Ahmed|Khalil|1969|p=557}} Angalafib, Goan and Jebel El Abour are also quite high.{{sfn|Almond|Ahmed|Khalil|1969|p=561}} Pumice blocks from the field were found in Wadi Abu Dom,{{sfn|Almond|Ahmed|Khalil|1969|p=550}} and scoria downstream in the Nile.{{sfn|Grabham|1920|p=134}} Tephra identified in deposits on Mograt Island in the Nile most likely comes from this volcanic field.[10] The volcanic field is a potential site for geothermal power development, with temperatures underground of about {{convert|200|C}}.GeologyVolcanic activity has been taking place in Sudan since the Cretaceous, with most recent manifestations documented in the Bayuda volcanic field, Marra Mountains and Meidob volcanic field{{sfn|Almond|Ahmed|Khalil|1969|p=550}} both in Darfur,{{sfn|Grabham|1920|p=135}} and elsewhere in the form of small basaltic outcrops.{{sfn|Almond|Kheir|Poole|1984|p=233}} Bayuda is a small volcanic field in comparison to other African volcanic fields.{{sfn|Almond|1974|p=346}} Volcanism at Bayuda may be associated with the Central African Shear Zone{{sfn|Pachur|Altmann|2006|p=266}} and of Precambrian faults,{{sfn|Pachur|Altmann|2006|p=97}} perhaps together with a mantle plume.{{sfn|Klitzsch|Thorweihe|1999|p=109}} The basement consists of granites of Precambrian and Paleozoic age[1] that belong to the Bayuda terrane,{{sfn|Lenhardt|Borah|Lenhardt|Bumby|2018|p=2}} which together with gneisses form a gentle pedeplain away from rougher landscape along the Nile.{{sfn|Almond|Ahmed|Khalil|1969|p=551}} Later on during the Cretaceous the Nubian Formation was laid down and there are hints of a domal uplift in the Bayuda area,{{sfn|Almond|Ahmed|Khalil|1969|p=550}} which probably predates the onset of volcanism and may have influenced the course of the Nile.{{sfn|Almond|Ahmed|Khalil|1969|p=551}} The existence of such a dome has been questioned, however.{{sfn|Almond|Kheir|Poole|1984|p=242}} CompositionBayuda has erupted basaltic rocks,{{sfn|Almond|Ahmed|Khalil|1969|p=557}} with most collected rocks belonging to an alkali basalt suite{{sfn|Almond|Ahmed|Khalil|1969|p=564}} although basanite, melabasanite, hawaiite and trachybasalt have been identified as well.{{sfn|Lenhardt|Borah|Lenhardt|Bumby|2018|p=2}}{{sfn|Almond|1974|p=350}} Phenocrysts include clinopyroxene and olivine.{{sfn|Almond|Ahmed|Khalil|1969|p=564}} Various xenoliths have been found, including garnet-containing clinopyroxenite, harzburgite, garnet hornblendite, amphibole-containing peridotite, olivine and spinel pyroxenite and websterite.{{sfn|Klitzsch|Thorweihe|1999|p=132}} In general the composition resembles that of other Sudanese-Egyptian volcanoes,{{sfn|Lenhardt|Borah|Lenhardt|Bumby|2018|p=2}} about two different magma families have been identified which originate from disparate mantle domains.{{sfn|Klitzsch|Thorweihe|1999|p=129}} The total volume of the volcanic rocks is about {{convert|18|km3}},{{sfn|Almond|Ahmed|Khalil|1969|p=563}} the rocks reach thicknesses of about {{convert|200|m}} maximally.{{sfn|Almond|1974|p=346}} Eruptive historyVolcanic activity has been dated to 1.7 - 0.9 million years ago,{{sfn|Almond|Kheir|Poole|1984|p=234}} but it continued after the end of the latest wet period 5,000 years ago[1] as indicated by the uneroded state of some of the volcanoes{{sfn|Almond|1974|p=346}} such as Hosh ed Salam.{{sfn|Pachur|Altmann|2006|p=398}} The presence of maars and volcanoes with signs of phreatomagmatic activity may indicate activity during pluvials.{{sfn|Lenhardt|Borah|Lenhardt|Bumby|2018|p=12}} Volcanism at Bayuda commenced with isolated volcanoes. After a while, new edifices were constructed atop the older ones, influencing the morphology of the new volcanoes.{{sfn|Almond|Ahmed|Khalil|1969|p=563}} The most recent lava flow was dated to less than 1,100 years before present,[1] with radiocarbon dating producing an age of 1,102 ± 48 years before present.{{sfn|Almond|Kheir|Poole|1984|p=235}} Aside from this date, however, there is little information on the timing of recent volcanic activity in the Bayuda volcanic field.{{sfn|Lenhardt|Borah|Lenhardt|Bumby|2018|p=12}} References1. ^1 {{cite journal|last1=Dittrich|first1=Annett|last2=Neogi|first2=Sayantani|title=Holocene Lake and Shallow Water Sediments at Mograt Island, Sudan|journal=Studia Quaternaria|date=27 January 2017|volume=34|issue=1|page=17|doi=10.1515/squa-2017-0001}} [1][2]2. ^1 2 3 4 5 6 7 8 9 10 11 12 {{Cite GVP|vn=225060|name=Bayuda Volcanic Field}} }} Sources{{refbegin}}
3 : Mountains of Sudan|Volcanoes of Sudan|Volcanic fields |
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