Haruj

Coordinates: 27°15′N 17°30′E / 27.25°N 17.5°E / 27.25; 17.5
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Haruj
Haroudj
Arabic)
Geography
Country
Tholeiitic-alkali basalt
Last eruption2,310 ± 810 years ago

Haruj (

Arabic: هروج, also known as Haroudj[1]) is a large volcanic field spread across 42,000–45,000 km2 (16,000–17,000 sq mi) in central Libya. It is one of several volcanic fields in Libya along with Tibesti, and its origin has been attributed to the effects of geologic lineaments in the crust
.

It contains about 150 volcanoes, including numerous

Lake Megafezzan
.

Volcanic activity in Haruj commenced about 6 million years ago and continued into the late

solfataric
activity.

Geography and geomorphology

Haruj lies in central

oil fields can be found north of the field.[5]

The field is a low-relief expanse of volcanic rocks occasionally interrupted by volcanic cones

lava flows,[8] the total volume of volcanic rocks has been estimated to be about 5,000 cubic kilometres (1,200 cu mi).[9] The Al Haruj al Aswad ("Black mountain") field in the northern part of Haruj and Al Haruj al Abyad ("White mountain") south are considered to be subdivisions of the main Haruj volcanic field[10] with Aswad covering a much larger surface than Abyad,[11] or even two separate volcanoes[12] that started overlapping each other during the Pliocene.[13]

Older lava flows have been completely flattened by erosion, while more recent ones still display fresh surface structures

pahoehoe lava traits,[16] and there are lava channels,[17] skylights and tumuli.[18] The volcanic rocks are usually not very thick, their thickness decreasing from 145 metres (476 ft) in the central sector to only a few metres at the margins,[12] and thus the underlying sedimentary rocks often crop out between lava flows.[19]

Vents

Most of the

Phreatomagmatic processes triggered by groundwater interacting with rising magma have generated some of these large craters, while others formed when lava lakes[23] drained through gaps in their rims.[16] Like the fissure vents, the position of individual cones and massifs is controlled by ground fractures and often reflect the activity of dykes,[24] and some cones appear to have been active more than once.[25]

There are about 30

subplinian eruptions that deposited tephra over large areas.[29]

Hydrology

Small depressions in the lava fields contain

Lake Megafezzan, although it is possible that the lake at times overflowed across the volcanic field.[33]

Geology

Haruj is not located close to a

Tibesti[38] some of which belong to a long line known as the Tibesti lineament.[9] Volcanism in general has shifted southward over time,[39] although more recent radiometric dating efforts indicate that volcanic activity in the fields was more contemporaneous than thought.[40]

The volcanic field overlies a 250-to-530-metre-high (820 to 1,740 ft)

embayment during the Miocene reached into the Haruj mountains.[41] A number of swells and tectonic lineaments, some of which are located at the margins between geologic blocks, characterize the basement beneath Haruj and have influenced the location of volcanic vents.[42] The basement is of Eocene to Oligocene age and consists of conglomerate, dolomite, limestone, marl and sandstone,[2] known as the Bishimah Formation;[4] where the lavas of Haruj are thinner, it often forms white outcrops.[2]

Composition

Eruptions at Haruj have produced relatively uniform volcanic rocks consisting of

clinopyroxene, olivine, plagioclase and titanomagnetite, with secondary calcite, iddingsite, serpentine and zeolite.[43] Based on compositional differences, the volcanic rocks have been subdivided into an older and a younger family.[44]

In some places in the northern Haruj a modified basalt has been found, which is dense and whose olivine has been transformed into iddingsite.[15] The lavas contain inclusions of lithic material as well as pyroxene and peridotite lherzolite.[27] Phonolite and trachyte are absent.[35] The magmas ultimately originated at depths of 70 to 74 kilometres (43 to 46 mi).[40]

Eruption history

The oldest volcanic rocks in Haruj appear to be not older than Pliocene, although the presence of buried Miocene age flows in the northern sector of the field has been suggested.[41] The oldest eruptions have been dated to be either 6.4 million years old[8] or of Late Pliocene age[15] and activity was originally thought to have continued to the Late Pleistocene;[45] Wau an Namus may be 200,000 years old.[36] Most of the field is younger than 2.2 million years ago[46] and output appears to have decreased over time.[12] Some eruptions may have been large enough to impact the regional environment.[47]

Volcanic activity in Haruj has been subdivided into a variable number of phases, including one six generation scheme and a four class scheme based on composition and age.

paleomagnetic analysis are coherent with those established on the basis of the degree of erosion of flows.[48] The oldest generation of lava flows makes up the bulk of the field and has been completely flattened by erosion, save some exceptions.[49] Pre-existent valleys have influenced the emplacement of the oldest generation lava flows, and also that of the second oldest albeit to a lesser degree.[50]

An intermediary lava flow generation has most likely been emplaced during the Pleistocene.[15] Lava flows of intermediate age crop out mainly in the central part of the Haruj mountains and have recognizable flow forms. Their surfaces have lost the original microstructures and are often covered with large blocks.[51]

The youngest generations of lava flows are little eroded, although they can still be subdivided into an older generation that has lost most of its surface features and a younger generation with fresh surfaces. This younger generation has been inferred to post-date a wet period that commenced 4000

BCE[15] and the Neolithic; the youngest dates obtained on lava flows are 2,310 ± 810 years BP.[45] Prior to the discovery of these youngest dates, volcanic activity was believed to have ended 100,000 years ago.[52]

Haruj may still be

solfataric activity has been reported in the field.[26]

Climate, animal life and vegetation

Temperatures in Haruj fluctuate between 12 and 32 °C (54 and 90 °F) in January and July respectively. The volcanic field lies within an

arid climate with annual precipitation of 5 to 25 millimetres (0.20 to 0.98 in),[2] but the higher parts of the mountains are wetter than the surroundings.[1] 6,000 years ago, the region was much wetter and the extent of the Sahara was approximately half the size of today.[21]

Vegetation occurs in

Tibbus.[1] 4,000 year old petroglyphs in the field show antelopes and cattle.[26] Neolithic stone weapons made out of Haruj rocks have been found[45] and several millstones discovered in the Roman cities of Leptis Magna and Cyrene did originate in the volcanic field.[54]

See also

References

  1. ^ a b c d e f g Klitzsch 1968, p. 587.
  2. ^ a b c d e f Németh 2004, p. 421.
  3. .
  4. ^ a b Farahat et al. 2006, p. 200.
  5. ^ "Volcanism, Tectonism, and Hydrocarbon Potential of Parts of Al Haruj Area, SW Sirt Basin, Libya". Conference: The Geology of Sirt Basin, At Tripoli, Libya, Volume: II. January 1996. p. 319. Retrieved 10 May 2018.
  6. ^ Ade-Hall et al. 1974, p. 999.
  7. ^ a b c Elshaafi & Gudmundsson 2019, p. 286.
  8. ^ a b c Martin & Németh 2006, p. 106.
  9. ^ a b Bardintzeff et al. 2012, p. 1048.
  10. ^ a b Elshaafi & Gudmundsson 2016, p. 189.
  11. ^ Elshaafi & Gudmundsson 2017, p. 50.
  12. ^ a b c Elshaafi & Gudmundsson 2017, p. 47.
  13. ^ Drake et al. 2008, p. 136.
  14. ^ a b c Klitzsch 1968, p. 588.
  15. ^ a b c d e f Klitzsch 1968, p. 594.
  16. ^ a b Németh et al. 2008, p. 3.
  17. ^ Németh et al. 2008, p. 11.
  18. ^ Németh et al. 2008, p. 9.
  19. ^ a b Abdel-Karim, Ramadan & Embashi 2013, p. 2.
  20. ^ a b Klitzsch 1968, p. 596.
  21. ^ a b Németh 2004, p. 422.
  22. ^ Németh 2004, p. 424.
  23. ^ Németh 2004, p. 433.
  24. ^ Elshaafi & Gudmundsson 2016, p. 201.
  25. ^ Elshaafi & Gudmundsson 2017, p. 60.
  26. ^ a b c d Klitzsch 1968, p. 597.
  27. ^ a b Martin & Németh 2006, p. 109.
  28. ^ Németh 2004, p. 429.
  29. ^ Martin & Németh 2006, p. 115.
  30. ^ Klitzsch 1968, pp. 591–592.
  31. ^ Martin & Németh 2006, p. 110.
  32. ^ Drake et al. 2008, p. 134.
  33. ^ Drake et al. 2008, p. 137.
  34. ^ Elshaafi & Gudmundsson 2016, p. 190.
  35. ^ a b c Farahat et al. 2006, p. 199.
  36. ^ a b Bardintzeff et al. 2012, p. 1060.
  37. ^ Elshaafi & Gudmundsson 2019, p. 284.
  38. ^ Farahat et al. 2006, p. 198.
  39. ^ Drake et al. 2008, p. 132.
  40. ^ a b Elshaafi & Gudmundsson 2018, p. 553.
  41. ^ a b Klitzsch 1968, p. 589.
  42. ^ Klitzsch 1968, pp. 598–600.
  43. ^ Abdel-Karim, Ramadan & Embashi 2013, p. 3.
  44. ^ Farahat et al. 2006, p. 201.
  45. ^ a b c Elshaafi & Gudmundsson 2017, p. 46.
  46. .
  47. ^ Elshaafi & Gudmundsson 2019, p. 299.
  48. ^ Ade-Hall et al. 1974, p. 1005.
  49. ^ Klitzsch 1968, pp. 589–590.
  50. ^ Klitzsch 1968, p. 591.
  51. ^ Klitzsch 1968, p. 592.
  52. ^ a b Elshaafi & Gudmundsson 2019, p. 285.
  53. ^ Elshaafi & Gudmundsson 2018, p. 549.
  54. ISSN 1296-2074
    .

Sources

External links

  • Media related to Haruj at Wikimedia Commons
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