Lwandle Plate

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Lwandle and its neighboring plates are shown. This figure is simplified, modified from Stamps et al. 2008.

The Lwandle Plate is one of three tectonic microplates, along with the

Antarctic Plates.[3]

The Lwandle Plate is largely oceanic, lying off the southeast coast of Africa. It is currently believed that the southern part of Madagascar forms part of the Lwandlean Plate, with one of the plate boundaries cutting through the island.[3][4][5]

Discovery of the Lwandle Plate

The East African Rift, where three plates are pulling away from one another: the Arabian Plate and two parts of the African Plate—the Nubian and Somali—which eventually led to the formation of the Lwandle plate as well as other microplates. The Afar Triangle, shaded at the center, is a triple junction that separates the three plates.[6]

For many years it was widely accepted that rifting in the East African Rift system, 22–25 million years ago, resulted in the splitting of the African Plate into 2 smaller plates – the Somali Plate and the Nubian Plate.[7] However, most recently, through the application of GPS technology and integration of earthquake data, it was discovered that the rift created three additional “microplates” – the Lwandle Plate, Victoria Plate, and Rovuma Plate.[1]

Earthquakes occur most often at plate boundaries and have been used as a guide to predict the locations of multiple plate boundaries.[8][9] “Lwandle’s” existence was postulated after studying earthquake data in areas that were once assumed to be the interiors of the Nubian and Somali plates.[10]
By including the Lwandlean Plate in their calculation, researchers were able to more accurately solve for the intersection between the East African Rift and the Southwest Indian Ridge.

GPS technology and data was also introduced in an effort to show with certainty the difference between the Somali Plate and the Nubian Plate. Using the GPS data, researchers could measure the velocity of tectonic plates from their interiors.[11][12][13]

The existence of the Lwandle Plate was first quantified using the Lwandle-Antarctica-Nubia plate circuit closure constrained by spreading rates and transform azimuths along the Southwest Indian Ridge. Mathematical plate circuit closure is attained while including the existence of Lwandle; using plate circuit closure, plate velocities can be calculated from the velocities of other plates.[4][14]

In 2008, the entire East African Rift System was successfully "quantified" through the integration of the GPS and earthquake data with the spreading rate and transform azimuth constraints.[5]

There have been very few studies that directly study the Lwandlean Plate. Previous studies about Lwandle have primarily been focused on attempting to quantify the mechanics of the African Rift System.[1][5] For this reason, the presumed evolution and formation of the microplates are not well known.

Evolution

Lwandle was assumed to be part of the Somali plate, at first. Here are two models that show how thinking about Lwandle has evolved.

Tectonic Model Excluding Lwandle Plate Tectonic Model Including Lwandle Plate
In this model, Lwandle is considered to be part of the Somali Plate.
In this model, Lwandle is its own, separate plate.

Boundary types

The majority of Lwandle's plate boundaries are not well understood.[5] What is known is:

Modern movements

GPS data paired with earthquake slip data is used to estimate the velocity of the Lwandle Plate and its neighbors. The velocity of the Lwandlean Plate, relative to the Nubian and Somali plates, is estimated to be a very slow rate (1–2 mm/yr). With these low rates of motion, it is expected that this area wouldn't have much seismic activity. The data supports this expectation.[1] Though Lwandle is moving faster relative to the Antarctic plate than to Nubian and Somali, this spreading ridge is one of the slowest on planet Earth, spreading at less than half the rate of human fingernail growth.[19] It appears that Lwandle will be in its current position for quite some time.[3]

Red arrows show the relative plate velocity at that boundary

See also

References

  1. ^
    doi:10.1002/2013JB010901
    .
  2. ^ Stamps, Sarah; Rambolamanana, Gerard; Calais, Eric; Rajaonarison, Tahiry. "Geodetic Constraints of Rift Initiation Across the Somalia-Lwandle Plate Boundary in Madagascar". {{cite journal}}: Cite journal requires |journal= (help)
  3. ^
    doi:10.1111/j.1365-246X.2009.04491.x
    .
  4. ^
    doi:10.1029/2006JB004519
    .
  5. ^
    doi:10.1029/2007GL032781
    .
  6. ^ "U.S. Geological Survey". Retrieved 25 October 2014.
  7. doi:10.1111/j.1468-4004.2005.46216.x
    .
  8. ^ Calais, E.; Ebinger, C.J.; Hartnady, C.; Nocquet, J.M. Yirgu, G.; Ebinger, C.J.; Maguire, P.K.H. (eds.). Kinematics of the East African Rift from GPS and earthquake slip vector data, in The Afar Volcanic Province Within the East African Rift System (vol 259 ed.). London, U.K.: Geol. Soc. Spec. Publ. pp. 9–22.
  9. doi:10.1029/JB078i014p02547
    .
  10. ^ a b Hartnady, C.J.H. (2002). "Earthquake hazard in Africa : perspectives on the Nubia-Somalia boundary : news and view". South African Journal of Science. 98 (9 & 10): 425–428.
  11. S2CID 128437306
    .
  12. doi:10.1029/2011JB008930
    .
  13. S2CID 55349527
    .
  14. ISBN 9780521893077
    .
  15. doi:10.1111/j.1365-246X.2005.02608.x
    .
  16. S2CID 4403043
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  17. doi:10.1130/0091-7613(2002)030<0339:lotnsb>2.0.co;2
    .
  18. doi:10.1130/G24270A.1
    .
  19. ^ Cheadle, Mike; John, Barbara. "Ultra Slow Spreading Ridges and Oceanic Core Complexes: Big Mountains and Bigger Faults". National Oceanic and Atmospheric Administration. Retrieved 29 October 2014.
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