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När började plattektoniken? : bevis för plattektoniska processer i geologisk tid

Gustafsson, Jon LU (2015) In Examensarbeten i geologi vid Lunds universitet GEOL01 20151
Department of Geology
Abstract
Plate tectonic processes shapes our earth due to volcanism, related to divergent and convergent plate motions. When did plate tectonics begin and how can we trace plate tectonic processes throughout time? This Bachelor thesis address and discuss different plate tectonic indicators and their reliability. Modern analogues are indicators that can be linked to modern plate tectonic processes, and does not exist anywhere else. High-pressure metamorphic rocks and ophiolites are examples of modern analogues. Ophiolitic occurences helps us trace plate tectonic processes back to 2 Ga. Further back in time, modern analogues are absent. Therefore, incidental proxys such as paleomagnetism and geochemistry has to be used. With paleomagnetism we are... (More)
Plate tectonic processes shapes our earth due to volcanism, related to divergent and convergent plate motions. When did plate tectonics begin and how can we trace plate tectonic processes throughout time? This Bachelor thesis address and discuss different plate tectonic indicators and their reliability. Modern analogues are indicators that can be linked to modern plate tectonic processes, and does not exist anywhere else. High-pressure metamorphic rocks and ophiolites are examples of modern analogues. Ophiolitic occurences helps us trace plate tectonic processes back to 2 Ga. Further back in time, modern analogues are absent. Therefore, incidental proxys such as paleomagnetism and geochemistry has to be used. With paleomagnetism we are able to trace cratonic lateral movements back to ca 2,6 Ga. Geochemistry is based on the assumption that a specific geochemical signature can be associated with certain plate tectonic processes, which can be used for a more or less probable interpretation of processes further back in time. Calc-alcaline rocks as old as 3,5 Ga, and granitoids dated back to 3,8 Ga are abundant. Furthermore, the oldest zircons has been dated to ca 4,2 Ga. It is important to distinguish between direct evidence, such as modern analogues, and incidental proxys, that’s not necessarily correct, as geochemistry is much-debated. Finally, I conclude that plate tectonics likely began at 3,5 Ga, based on calc-alcaline rock findings. Additionally, further research and field work in regions with older crust, continued modelling and development of new analytical methods, are necessary to better trace and help understand plate tectonic processes. (Less)
Abstract (Swedish)
Plattektoniska processer formar idag vår jord genom vulkanism, relaterad till divergenta och konvergenta plattrörelser. Hur länge har plattektoniken existerat och hur kan vi spåra plattektoniska processer bakåt i tiden? Detta kandidatarbete behandlar och diskuterar olika typer av plattektoniska indikatorer, hur de går att koppla till moderna processer och hur tillförlitliga de anses vara. Moderna analogier är indikatorer som går att koppla till moderna plattektoniska processer och påträffas inte någon annanstans. Högtrycksmetamorfa bergarter och ofio-liter är exempel på moderna analogier. Ofiolitfynd lyckas spåra plattektoniska processer till ca 2 Ga. Längre tillbaks i tiden finns inga moderna analogier och indirekta metoder såsom... (More)
Plattektoniska processer formar idag vår jord genom vulkanism, relaterad till divergenta och konvergenta plattrörelser. Hur länge har plattektoniken existerat och hur kan vi spåra plattektoniska processer bakåt i tiden? Detta kandidatarbete behandlar och diskuterar olika typer av plattektoniska indikatorer, hur de går att koppla till moderna processer och hur tillförlitliga de anses vara. Moderna analogier är indikatorer som går att koppla till moderna plattektoniska processer och påträffas inte någon annanstans. Högtrycksmetamorfa bergarter och ofio-liter är exempel på moderna analogier. Ofiolitfynd lyckas spåra plattektoniska processer till ca 2 Ga. Längre tillbaks i tiden finns inga moderna analogier och indirekta metoder såsom paleomagnetism och geokemi krävs. Paleomagnetism kan spåra kratonska rörelsemönster till ca 2,6 Ga. Geokemi bygger på att man kan koppla en specifik geokemisk signatur till plattektoniska processer, vilket kan användas för en mer eller mindre sannolik tolkning längre tillbaks i tiden. Kalkalkalina bergarter återfinns till ca 3,5 Ga och granitoider till 3,8 Ga. Vidare återfinns zirkoner daterade till ca 4,2 Ga. Det är viktigt att skilja på direkta bevis, så som moderna analogier gentemot indirekta spår som nödvändigtvis inte är korrekta då geokemi är högst omdebatterat. Slutligen drar jag slutsatsen att plattektoniken troligtvis inleddes vid 3,5 Ga baserat på kalkalina fynd. Vidare krävs mer forskning och mer fältarbete i regioner med äldre skorpa, fler modelleringar och utveckling av nya analysmetoder för att bättre spåra och förstå geokemiska och plattektoniska processer. (Less)
Please use this url to cite or link to this publication:
author
Gustafsson, Jon LU
supervisor
organization
alternative title
When did plate tectonics begin? : evidence for plate tectonic processes throughout geological time
course
GEOL01 20151
year
type
M2 - Bachelor Degree
subject
keywords
tektoniska indikatorer, ofiolit, prekambrium, plattektonik
publication/series
Examensarbeten i geologi vid Lunds universitet
report number
455
language
Swedish
id
7761887
date added to LUP
2015-08-17 09:50:13
date last changed
2015-08-17 09:50:13
@misc{7761887,
  abstract     = {Plate tectonic processes shapes our earth due to volcanism, related to divergent and convergent plate motions. When did plate tectonics begin and how can we trace plate tectonic processes throughout time? This Bachelor thesis address and discuss different plate tectonic indicators and their reliability. Modern analogues are indicators that can be linked to modern plate tectonic processes, and does not exist anywhere else. High-pressure metamorphic rocks and ophiolites are examples of modern analogues. Ophiolitic occurences helps us trace plate tectonic processes back to 2 Ga. Further back in time, modern analogues are absent. Therefore, incidental proxys such as paleomagnetism and geochemistry has to be used. With paleomagnetism we are able to trace cratonic lateral movements back to ca 2,6 Ga. Geochemistry is based on the assumption that a specific geochemical signature can be associated with certain plate tectonic processes, which can be used for a more or less probable interpretation of processes further back in time. Calc-alcaline rocks as old as 3,5 Ga, and granitoids dated back to 3,8 Ga are abundant. Furthermore, the oldest zircons has been dated to ca 4,2 Ga. It is important to distinguish between direct evidence, such as modern analogues, and incidental proxys, that’s not necessarily correct, as geochemistry is much-debated. Finally, I conclude that plate tectonics likely began at 3,5 Ga, based on calc-alcaline rock findings. Additionally, further research and field work in regions with older crust, continued modelling and development of new analytical methods, are necessary to better trace and help understand plate tectonic processes.},
  author       = {Gustafsson, Jon},
  keyword      = {tektoniska indikatorer,ofiolit,prekambrium,plattektonik},
  language     = {swe},
  note         = {Student Paper},
  series       = {Examensarbeten i geologi vid Lunds universitet},
  title        = {När började plattektoniken? : bevis för plattektoniska processer i geologisk tid},
  year         = {2015},
}