Igwisi Hills

Coordinates: 4°53′13.18″S 31°56′4.46″E / 4.8869944°S 31.9345722°E / -4.8869944; 31.9345722
Source: Wikipedia, the free encyclopedia.
Igwisi Hills
Highest point
Elevation1,146 m (3,760 ft)[1]
Coordinates4°53′13.18″S 31°56′4.46″E / 4.8869944°S 31.9345722°E / -4.8869944; 31.9345722[2]
Geography
LocationTanzania
Geology
Age of rockPleistocene?
Mountain typePyroclastic Cone
Last eruption10450 BC

The Igwisi Hills are a volcanic field in

lava flow. They are one of the few locations of possibly kimberlitic
lava flows on Earth.

The volcanoes are located in the middle of the Tanzania craton, away from other Tanzanian volcanoes. There have been prior episodes of kimberlitic volcanism in the craton, however.

The age of the Igwisi Hills is poorly known but may be early Holocene-late Pleistocene in age. Some rainfall-induced chemical modification is found, and the hills have a unique vegetation profile.

Geology

The Igwisi hills are formed by three tuff cones formed in the middle of the Tanzania craton. They are 70 metres (230 ft) above the landscape with a karst morphology and craters covered with grass, on a low ridge that may be the product of early eruptive stages. The northeastern hill has two craters, one with a breach from which a 500 metres (1,600 ft) long lava flow originates, probably formed when a lava lake in the crater escaped through a breach. The central volcano has a lava coulee and a tephra cone in its crater.[3][4][5]: 72, 73 [6] Craters have diameters of 200–400 metres (660–1,310 ft).[7] The total volume of these cones is less than 0.001 cubic kilometres (0.00024 cu mi).[6] Weak pyroclastic activity probably accompanied the eruptive activity.[3] Presumably, low intensity explosive activity built the cones, starting from the northeast cone and ending with the southwest cone. Afterwards, lava flows were generated.[8]

The Igwisi Hills are the only places in the world where possible

Democratic Republic of Congo.[8]

These kimberlites are also the youngest kimberlites in the world by over thirty million years, cosmogenic

East African Rift System may have played a role in their genesis.[16]: 3  Prior kimberlite activity in the Tanzania craton is recorded 1,150, 189 and 53 million years ago.[8]

The tuffs are highly calcitic, vesicular and contain numerous microxenoliths. The petrologically similar lavas show evidence of a differentiation by flow and gravity and have trachytic textures.

orthopyroxene is associated with the diopside.[18] Olivines are surrounded by chromite.[7] Olivines characterize the texture of the Igwisi rocks, where they form spherical inclusions. The olivines are primarily forsteritic in composition.[19] Inclusions in the kimberlite include skeletal apatite, stellate aragonite and calcite.[20] High concentrations of CO2 are found in the rock,[12] which may have resulted in the depolymerization of the melt, increasing its fluidity and resulting in effusive activity.[21] Peridotite xenoliths originate from 180 kilometres (110 mi) of depth.[5]: 15  Spinels in the groundmass suggest that crustal contamination was extensive,[21] with dunite nodules originating from the middle lithosphere,[16]: 2  but isotope data instead indicate a low contamination.[16]: 3  The geochemistry suggests an origin at high pressures (depths of 150–200 kilometres (93–124 mi)) and equilibrium temperatures of 1,000 °C (1,830 °F).[19] Rainfall has subsequently modified the pyroclastics and formed secondary calcite, while the less permeable lava flows were less modified.[8]

The hills have a unique vegetation, with aquatic plants found in the middle of the craters and distinct vegetation on inner crater slopes from the extra-crateric territory.[22] The hills have a rare occurrence of Asclepias pseudoamabilis.[23]

References

  1. ^ a b "Igwisi Hills". Global Volcanism Program. Smithsonian Institution.
  2. ^ Brown, R.J.; Sparks, R.S.J. "Mapping the Igwisi Hills kimberlite volcanoes, Tanzania: understanding how deep-sourced mantle magmas behave at the Earth's surface" (PDF). GEF Scientific Reports. Natural Environment Research Council. Retrieved 20 March 2016.
  3. ^
    S2CID 55963140
    .
  4. ^
    ISBN 978-3-642-67742-7
    .
  5. ^
    ISBN 9781862392670
    . Retrieved 28 February 2016.
  6. ^
    doi:10.1130/B30749.1
    .
  7. ^
    ISBN 9781489905680
    . Retrieved 28 February 2016.
  8. ^
    doi:10.1016/j.chemgeo.2015.04.012
    .
  9. ISBN 978-1-4613-5822-0
    . Retrieved 28 February 2016.
  10. doi:10.1016/j.jvolgeores.2006.02.010
    .
  11. S2CID 128822277
    .
  12. ^
    S2CID 131412395
    .
  13. doi:10.1016/j.jvolgeores.2011.01.010
    .
  14. doi:10.1016/j.epsl.2007.12.013
    .
  15. ISBN 978-81-322-1173-0
    .
  16. ^
    S2CID 236523877
    .
  17. ISBN 978-3-642-67742-7
    .
  18. S2CID 126520733
    .
  19. ^
    doi:10.1016/0079-1946(75)90017-8
    .
  20. ISBN 978-3-642-67742-7
    .
  21. ^
    S2CID 58896592
    .
  22. doi:10.1016/j.revpalbo.2013.04.002
    .
  23. S2CID 37633722
    .

External links
Retrieved from "https://en.wikipedia.org/w/index.php?title=Igwisi_Hills&oldid=1189837748"