Changes

[[File:Updated lwandle4.jpg|thumbnail|400px|right|Lwandle and its neighboring plates are shown. This figure is simplified, modified from Stamps et al 2008.]]

[[File:Updated lwandle4.jpg|thumbnail|400px|right|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 micro-plates that previously made up the African Plate, along with the [[Somali Plate]] and the [[African Plate|Nubian Plate]]. Its discovery is very recent, so the velocity of the plate isn't well known or understood.<ref>Saria, E (April 2014). "Present-day kinematics of the East African Rift". Journal of Geophysical Research: Solid Earth 119 (4).</ref> Many experiments are ongoing to quantify this. The Lwandle Plate lies between 30°E and 50°E, sharing a boundary with the Nubia, Somali and [[Antarctic plate|Antarctic Plates]].<ref name=Textbook>{{cite journal|last1=DeMets|first1=Charles|last2=Gordon|first2=Richard|last3=Argus|first3=Donald|title=Geologically current plate motions|journal=Geophys. J. Int|date=2010|volume=1-80|page=39|doi=10.1111/j.1365-246X.2009.04491.x|accessdate=25 October 2014}}</ref>

The '''Lwandle Plate''' is one of three tectonic micro-plates that previously made up the African Plate, along with the [[Somali Plate]] and the [[African Plate|Nubian Plate]]. Its discovery is very recent, so the velocity of the plate isn't well known or understood.<ref>Saria, E (April 2014). "Present-day kinematics of the East African Rift". Journal of Geophysical Research: Solid Earth 119 (4). doi:10.1002/2013JB010901</ref> Many experiments are ongoing to quantify this. The Lwandle Plate lies between 30°E and 50°E, sharing a boundary with the Nubia, Somali and [[Antarctic plate|Antarctic Plates]].<ref>DeMets, Charles; Gordon, Richard; Argus, Donald (2010). "Geologically current plate motions". Geophys. J. Int 1–80: 39. doi:10.1111/j.1365-246X.2009.04491.x</ref>

The Lwandle Plate is largely oceanic, resting off the southeast coast of Africa. It is currently believed that the bottom half of [[Madagascar]] is part of the Lwandlean Plate, with one of the plate boundaries cutting through the island.<ref name=Textbook /><ref name=primary /><ref name=Stamps />

The Lwandle Plate is largely oceanic, resting off the southeast coast of Africa. It is currently believed that the bottom half of [[Madagascar]] is part of the Lwandlean Plate, with one of the plate boundaries cutting through the island.<ref>DeMets, Charles; Gordon, Richard; Argus, Donald (2010). "Geologically current plate motions". Geophys. J. Int 1–80: 39. doi:10.1111/j.1365-246X.2009.04491.x</ref><ref>Horner-Johnson, Benjamin; Gordon, Richard; Argus, Donald (May 2007). "Plate kinematic evidence for the existence of a distinct plate between the Nubian and Somalian plates along the Southwest Indian Ridge". Journal of Geophysical Research 112 (B5). doi:10.1029/2006JB004519</ref><ref>Stamps et al, Sarah (2008). "A kinematic model for the East African Rift". Geophysical Research Letters 35 (5). doi:10.1029/2007GL032781</ref>

== Origin ==

== Origin ==

[[File:EAfricaRift updated.jpg|thumbnail|400px|right|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 micro-plates. The Afar Triangle, shaded at the center, is a [[triple junction]] that separates the three plates.<ref name=website>{{cite web|url=http://pubs.usgs.gov/gip/dynamic/East_Africa.html|title=U.S. Geological Survey|accessdate=25 October 2014}}</ref>]]

[[File:EAfricaRift updated.jpg|thumbnail|400px|right|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 micro-plates. The Afar Triangle, shaded at the center, is a [[triple junction]] that separates the three plates.<ref>"U.S. Geological Survey". Retrieved 25 October 2014.</ref>]]

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.<ref name="astro geophys">{{cite journal|last1=Ebinger|first1=C.J.|title=Continental break-up: the East African perspective|journal=Astro. Geophys.|date=2005|volume=46|issue=2}}</ref>  However, most recently, through the application of GPS technology and integration of earthquake data, it was discovered that the rift created three additional “micro-plates” plates - the Lwandle Plate, [[Victoria Plate]], and [[Romuva Plate]].<ref name=Saria_2014 />

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.<ref>Ebinger, C.J. (2005). "Continental break-up: the East African perspective". Astro. Geophys. 46 (2).</ref>  However, most recently, through the application of GPS technology and integration of earthquake data, it was discovered that the rift created three additional “micro-plates” plates - the Lwandle Plate, [[Victoria Plate]], and [[Romuva Plate]].<ref>Saria, E (April 2014). "Present-day kinematics of the East African Rift". Journal of Geophysical Research: Solid Earth 119 (4). doi:10.1002/2013JB010901</ref>

[[Earthquakes]] occur most often at plate boundaries and have been used as a guide to predict the locations of multiple plate boundaries.<ref name=Calais>{{citebook|last1=Calais|first1=E.|last2=Ebinger|first2=C.J.|last3=Hartnady|first3=C.|last4=Nocquet|first4=J.M.|editor1-last=Yirgu|editor1-first=G.|editor2-last=Ebinger|editor2-first=C.J.|editor3-last=Maguire|editor3-first=P.K.H.|title=Kinematics of the East African Rift from GPS and earthquake slip vector data, in The Afar Volcanic Province Within the East African Rift System|publisher=Geol. Soc. Spec. Publ.|location=London, U.K.|pages=pp. 9-22|edition=vol 259|accessdate=23 October 2014}}</ref><ref name=Kelleher>{{cite journal|last1=Kelleher|first1=John|last2=Sykes|first2=Lynn|last3=Oliver|first3=Jack|title=Possible criteria for predicting earthquake locations and their application to major plate boundaries of the Pacific and the Caribbean|journal=Journal of Geophysical Research|date=1973|volume=78|issue=14|pages=2547-2585|doi=10.1029/JB078i014p02547|accessdate=24 October 2014}}</ref> “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.<ref name=Hartnady>{{cite journal|last1=Hartnady|first1=C.J.H.|title=Earthquake hazard in Africa : perspectives on the Nubia-Somalia boundary : news and view|journal=South African Journal of Science|date=2002|volume=98|issue=9 & 10|pages=425-428|accessdate=5 October 2014}}</ref>  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.  

[[Earthquakes]] occur most often at plate boundaries and have been used as a guide to predict the locations of multiple plate boundaries.<ref>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. pp. 9–22.</ref><ref>Kelleher, John; Sykes, Lynn; Oliver, Jack (1973). "Possible criteria for predicting earthquake locations and their application to major plate boundaries of the Pacific and the Caribbean". Journal of Geophysical Research 78 (14): 2547–2585. doi:10.1029/JB078i014p02547</ref> “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.<ref>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.</ref>  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.<ref name=Nocquet>{{cite journal|last1=Nocquet|first1=J.-M.|last2=Calais|first2=E.|title=Crustal velocity field of western Europe from permanent GPS array solutions, 1996-2001|journal=Geophysical Journal International|date=June 2003|volume=154|issue=1|pages=72-88|doi=10.1046/j.1365-246X.2003.01935.x|accessdate=24 October 2014}}</ref><ref name=Altamimi>{{cite journal|last1=Altamimi|first1=Z.|last2=Métivier|first2=L.|last3=Collilieux|first3=X.|title=ITRF2008 plate motion model|journal=Journal of Geophysical Research|date=July 2012|volume=117|issue=B7|doi=10.1029/2011JB008930|accessdate=24 October 2014}}</ref><ref name="Calais et al">{{cite journal|last1=Calais|first1=E.|last2=Dong|first2=L.|last3=Wang|first3=M.|last4=Shen|first4=Z.|last5=Vergnolle|first5=M.|title=Continental deformation in Asia from a combined GPS solution|journal=Geophysical Research Letters|date=October 2006|volume=33|doi=10.1029/2006GL028433|accessdate=24 October 2014}}</ref>

[[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.<ref>Nocquet, J.-M.; Calais, E. (June 2003). "Crustal velocity field of western Europe from permanent GPS array solutions, 1996-2001". Geophysical Journal International 154 (1): 72–88. doi:10.1046/j.1365-246X.2003.01935.x</ref><ref>Altamimi, Z.; Métivier, L.; Collilieux, X. (July 2012). "ITRF2008 plate motion model". Journal of Geophysical Research 117 (B7). doi:10.1029/2011JB008930</ref><ref>Calais, E.; Dong, L.; Wang, M.; Shen, Z.; Vergnolle, M. (October 2006). "Continental deformation in Asia from a combined GPS solution". Geophysical Research Letters 33. doi:10.1029/2006GL028433</ref>

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.<ref name=primary>{{cite journal|last1=Horner-Johnson|first1=Benjamin|last2=Gordon|first2=Richard|last3=Argus|first3=Donald|title=Plate kinematic evidence for the existence of a distinct plate between the Nubian and Somalian plates along the Southwest Indian Ridge|journal=Journal of Geophysical Research|date=May 2007|volume=112|issue=B5|doi=10.1029/2006JB004519|accessdate=14 September 2014}}</ref><ref name="Geophys textbook">{{cite book|last1=Fowler|first1=C.M.R.|title=The solid earth : an introduction to global geophysics|date=2006|publisher=Cambridge University Press|location=Cambridge, UK|isbn=9780521893077|edition=2nd ed., repr. with corrections.|accessdate=27 October 2014}}</ref>

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.<ref>Horner-Johnson, Benjamin; Gordon, Richard; Argus, Donald (May 2007). "Plate kinematic evidence for the existence of a distinct plate between the Nubian and Somalian plates along the Southwest Indian Ridge". Journal of Geophysical Research 112 (B5). doi:10.1029/2006JB004519</ref><ref>Fowler, C.M.R. (2006). The solid earth : an introduction to global geophysics (2nd ed., repr. with corrections. ed.). Cambridge, UK: Cambridge University Press. ISBN 9780521893077.</ref>

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.<ref name=Stamps>{{cite journal|last1=Stamps et al|first1=Sarah|title=A kinematic model for the East African Rift|journal=Geophysical Research Letters|date=2008|volume=35|issue=5|doi=10.1029/2007GL032781|accessdate=5 October 2014}}</ref>

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.<ref>Stamps et al, Sarah (2008). "A kinematic model for the East African Rift". Geophysical Research Letters 35 (5). doi:10.1029/2007GL032781</ref>

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.<ref name=Saria_2014 /><ref name=Stamps /> For this reason, the presumed evolution and formation of the micro-plates are not well known.  

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.<ref>Saria, E (April 2014). "Present-day kinematics of the East African Rift". Journal of Geophysical Research: Solid Earth 119 (4).</ref><ref> Stamps et al, Sarah (2008). "A kinematic model for the East African Rift". Geophysical Research Letters 35 (5). doi:10.1029/2007GL032781</ref> For this reason, the presumed evolution and formation of the micro-plates are not well known.  

The discovery of this plate is revolutionary. Its discovery clarifies that the term “African plate” no longer applies to present-day plate tectonics.<ref name="Horner-Johnson 2005">{{cite journal|last1=Horner-Johnson|first1=Benjamin|last2=Gordon|first2=Richard|last3=Cowles|first3=Sara|last4=Argus|first4=Donald|title=The angular velocity of Nubia relative to Somalia and the location of the Nubia—Somalia–Antarctica triple junction|journal=Geophysical Journal International|date=2005|volume=199|issue=3|pages=221-238|doi=10.1111/j.1365-246X.2005.02608.x|accessdate=5 October 2014}}</ref>

The discovery of this plate is revolutionary. Its discovery clarifies that the term “African plate” no longer applies to present-day plate tectonics.<ref>Horner-Johnson, Benjamin; Gordon, Richard; Cowles, Sara; Argus, Donald (2005). "The angular velocity of Nubia relative to Somalia and the location of the Nubia—Somalia–Antarctica triple junction". Geophysical Journal International 199 (3): 221–238. doi:10.1111/j.1365-246X.2005.02608.x</ref>

== Changing the world map ==

== Changing the world map ==

== Boundary types ==

== Boundary types ==

The majority of Lwandle's plate boundaries are not well understood.<ref name=Stamps /> What is known is:

The majority of Lwandle's plate boundaries are not well understood.<ref>Stamps et al, Sarah (2008). "A kinematic model for the East African Rift". Geophysical Research Letters 35 (5). doi:10.1029/2007GL032781</ref> What is known is:

* '''Southern Boundary''' - The Southwest Indian Ridge, an ultra-slow [[spreading ridge]] with a slow spreading rate of about 12-18 mm/yr, acts as the southern boundary.<ref name=Saria_2014 /><ref name="Horner-Johnson 2005" /> This spreading ridge separates Lwandle from the Antarctic plate.<ref name="Dezhi SWIR">{{cite journal|last1=Chu|first1=Dezhi|last2=Gordon|first2=Richard|title=Evidence for motion between Nubia and Somalia along the Southwest Indian ridge|journal=Nature|date=1999|volume=398|doi=10.1038/18014|accessdate=26 October 2014}}</ref>

* '''Southern Boundary''' - The Southwest Indian Ridge, an ultra-slow [[spreading ridge]] with a slow spreading rate of about 12-18 mm/yr, acts as the southern boundary.<ref>Saria, E (April 2014). "Present-day kinematics of the East African Rift". Journal of Geophysical Research: Solid Earth 119 (4). doi:10.1002/2013JB010901</ref><ref>Horner-Johnson, Benjamin; Gordon, Richard; Cowles, Sara; Argus, Donald (2005). "The angular velocity of Nubia relative to Somalia and the location of the Nubia—Somalia–Antarctica triple junction". Geophysical Journal International 199 (3): 221–238. doi:10.1111/j.1365-246X.2005.02608.x</ref> This spreading ridge separates Lwandle from the Antarctic plate.<ref>Chu, Dezhi; Gordon, Richard (1999). "Evidence for motion between Nubia and Somalia along the Southwest Indian ridge". Nature 398. doi:10.1038/18014</ref>

* '''Eastern Boundary''' - To the east, the boundary may be more of a diffuse boundary. There are current studies trying to pinpoint the exact location of this boundary; it is believed to cut across Madagascar, making it Lwandle's only boundary that is not purely oceanic. Earthquake slip vectors are the primary constraint that predict the actual plate boundaries. Velocity predicted at this boundary is 1.3-1.4 mm/yr.<ref name=Textbook /> This boundary separates Lwandle from the Somali Plate.<ref name=Textbook />

* '''Eastern Boundary''' - To the east, the boundary may be more of a diffuse boundary. There are current studies trying to pinpoint the exact location of this boundary; it is believed to cut across Madagascar, making it Lwandle's only boundary that is not purely oceanic. Earthquake slip vectors are the primary constraint that predict the actual plate boundaries. Velocity predicted at this boundary is 1.3-1.4 mm/yr.<ref>DeMets, Charles; Gordon, Richard; Argus, Donald (2010). "Geologically current plate motions". Geophys. J. Int 1–80: 39. doi:10.1111/j.1365-246X.2009.04491.x</ref> This boundary separates Lwandle from the Somali Plate.<ref>DeMets, Charles; Gordon, Richard; Argus, Donald (2010). "Geologically current plate motions". Geophys. J. Int 1–80: 39. doi:10.1111/j.1365-246X.2009.04491.x</ref>

* '''Western Boundary''' - The western boundary is especially poorly understood; there is very little [[seismic activity]] along this boundary.<ref name=Hartnady /> Despite that, a misfit to a seafloor [[magnetic anomaly]] strongly suggests that motion exists.<ref name=Textbook /><ref name=Lemaux>{{cite journal|last1=Lemaux|first1=James|last2=Gordon|first2=Richard|last3=Royer|first3=Jean-Yves|title=Location of the Nubia-Somalia boundary along the Southwest Indian Ridge|journal=Geology|date=2002|volume=42|issue=10|accessdate=25 October 2014}}</ref> Some models suggest it is a right-lateral strike slip boundary with a rate of about 1 mm/yr, with some extension.<ref name=Stamps /> Still, others even suggest that motion ceased at this boundary approximately 11 million years ago.<ref name=Patriat>{{cite journal|last1=Patriat|first1=Philippe|last2=Sloan|first2=Heather|last3=Sauter|first3=Daniel|title=From slow to ultraslow: A previously undetected event at the Southwest Indian Ridge at ca. 24 Ma|journal=Geology|date=October 2014|volume=42|issue=10|doi=10.1130/G24270A.1|accessdate=25 October 2014}}</ref><ref name=Textbook /> This boundary separates Lawndale from the Nubian Plate.<ref name=Textbook />

* '''Western Boundary''' - The western boundary is especially poorly understood; there is very little [[seismic activity]] along this boundary.<ref> 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.</ref> Despite that, a misfit to a seafloor [[magnetic anomaly]] strongly suggests that motion exists.<ref>DeMets, Charles; Gordon, Richard; Argus, Donald (2010). "Geologically current plate motions". Geophys. J. Int 1–80: 39. doi:10.1111/j.1365-246X.2009.04491.x</ref><ref> Lemaux, James; Gordon, Richard; Royer, Jean-Yves (2002). "Location of the Nubia-Somalia boundary along the Southwest Indian Ridge". Geology 42 (10).</ref> Some models suggest it is a right-lateral strike slip boundary with a rate of about 1 mm/yr, with some extension.<ref>Stamps et al, Sarah (2008). "A kinematic model for the East African Rift". Geophysical Research Letters 35 (5). doi:10.1029/2007GL032781</ref> Still, others even suggest that motion ceased at this boundary approximately 11 million years ago.<ref>Patriat, Philippe; Sloan, Heather; Sauter, Daniel (October 2014). "From slow to ultraslow: A previously undetected event at the Southwest Indian Ridge at ca. 24 Ma". Geology 42 (10). doi:10.1130/G24270A.1</ref><ref>DeMets, Charles; Gordon, Richard; Argus, Donald (2010). "Geologically current plate motions". Geophys. J. Int 1–80: 39. doi:10.1111/j.1365-246X.2009.04491.x</ref> This boundary separates Lawndale from the Nubian Plate.<ref>DeMets, Charles; Gordon, Richard; Argus, Donald (2010). "Geologically current plate motions". Geophys. J. Int 1–80: 39. doi:10.1111/j.1365-246X.2009.04491.x</ref>

* '''Northern Boundary''' - Bordering the Lwandle plate to the north is the Romuva plate.<ref name=Stamps />

* '''Northern Boundary''' - Bordering the Lwandle plate to the north is the Romuva plate.<ref>Stamps et al, Sarah (2008). "A kinematic model for the East African Rift". Geophysical Research Letters 35 (5). doi:10.1029/2007GL032781</ref>

== Modern movements ==

== 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 shows exactly that.<ref name=Saria_2014 /> 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.<ref name=NOAA>{{cite web|last1=Cheadle|first1=Mike|last2=John|first2=Barbara|title=Ultra Slow Spreading Ridges and Oceanic Core Complexes: Big Mountains and Bigger Faults|url=http://oceanexplorer.noaa.gov/okeanos/explorations/ex1104/background/tectonic/tectonic.html|website=National Oceanic and Atmospheric Administration|accessdate=29 October 2014}}</ref> It appears that, for now, Lwandle will be in its current position for quite some time.<ref name=Textbook />

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 shows exactly that.<ref>Saria, E (April 2014). "Present-day kinematics of the East African Rift". Journal of Geophysical Research: Solid Earth 119 (4). doi:10.1002/2013JB010901</ref> 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.<ref>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.</ref> It appears that, for now, Lwandle will be in its current position for quite some time.<ref>DeMets, Charles; Gordon, Richard; Argus, Donald (2010). "Geologically current plate motions". Geophys. J. Int 1–80: 39.</ref>

[[File:Stamps2008animatedX.jpg|center|300px|Red arrows show the relative plate velocity at that boundary.]]

[[File:Stamps2008animatedX.jpg|center|300px|Red arrows show the relative plate velocity at that boundary.]]