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New constraints on paleoreconstructions through geochronology of mafic dyke swarms in North Atlantic Craton

Nilsson, Mimmi LU (2016)
Abstract (Swedish)
Ett antal superkontinenter har existerat under jordens 4.6 Ga ( miljarder år gamla ) historia. Utav dessa är superkontinenten Pangea, som betyder ”allt land”, den senaste och mest väldefinierade. Bildning och uppsprickning av superkontinenter drivs av plattektoniska processer som i sin tur beror på strömningar ( konvektion ) i jordens mantel. Förutom dessa processer så anses numera mantelplymer ha haft betydelse för uppsprickning av superkontinenter. Dessa kan ses som uppvälvning av varmt material från jordens inre som rör sig uppåt tills de kommer i kontakt med jordens yttre hårda skal – litosfären. Då detta sker kommer sprickor bildas i litosfären längs vilka magmor kan röra sig mot ytan och där orsaka omfattande vulkanism. Det är idag... (More)
Ett antal superkontinenter har existerat under jordens 4.6 Ga ( miljarder år gamla ) historia. Utav dessa är superkontinenten Pangea, som betyder ”allt land”, den senaste och mest väldefinierade. Bildning och uppsprickning av superkontinenter drivs av plattektoniska processer som i sin tur beror på strömningar ( konvektion ) i jordens mantel. Förutom dessa processer så anses numera mantelplymer ha haft betydelse för uppsprickning av superkontinenter. Dessa kan ses som uppvälvning av varmt material från jordens inre som rör sig uppåt tills de kommer i kontakt med jordens yttre hårda skal – litosfären. Då detta sker kommer sprickor bildas i litosfären längs vilka magmor kan röra sig mot ytan och där orsaka omfattande vulkanism. Det är idag allmänt accepterat att ett antal mantelplymer var involverade i Pangeas uppsprickning. Magma från jordens inre kan tränga upp genom berggrunden och kristallisera som diabasgångar med olika geometrier, såsom parallella eller radierande svärmar. Större magmatiska händelser som leder till uppsprickning av kontinenter är ofta relaterade till s.k. mantelplymer och ger upphov till radierande gånggeometrier. Det finns ett antal superkontinenter före Pangea som idag är mer eller mindre vedertagna: 0.6–1.1 Ga Rodinia och 1.3–1.8 Ga Columbia. Mycket tyder på att det också funnits en äldre superkontinent. Fragment från denna äldsta kontinentala landmassa återfinns idag som ca. 35 lithosfärfragment utspridda över jordens yta. Ett av dessa fragment utgörs av södra Grönlands berggrund tillsammans med en del av nordöstra Kanada ( Nain province ) samt Lewisian Complex i nuvarande Skottland. Förekomsten av diabas gångar utgör spår av yngre episoder av magmatiska händelser. Diabas innehåller ofta små mängder av mineralet baddeleyit, som går att åldersbestämma med U–Pb metoden, genom att uran sönderfaller till bly med känd hastighet. Genom att mäta halterna av olika uran- och blyisotoper kan man beräkna åldern för dessa episoder av magmatism. Varje kontinentalt fragment har således en egen ”magmatisk historia”, som går att visualisera i ett så kallat streckkodsdiagram. Streckkodsdiagrammet tillåter oss att jämföra tidpunkterna för dessa magmatiska händelser och utifrån dessa jämförelser kunna utvärdera vilka kontinentala fragment som en gång satt ihop i en större landmassa. I mitt doktorandarbete har jag åldersbestämt diabasgångar från sydvästra och sydöstra Grönland ( arkeiska provinsen North Atlantic Craton ). Ett stort antal generationer av diabasgångar har identifierats tack vare dessa nya åldersbestämningar och deras åldrar är ca. 2.5 Ga, 2.37 Ga, 2.21 Ga, 2.17 Ga, 2.13 Ga och 2.04 Ga. Streckkodsdiagram för Grönland visar att flera likåldriga diabasgenerationer också finns i Dharwar craton i nutida södra Indien samt i Superior Craton i Kanada. I denna avhandling presenterar jag en rekonstruktion över dessa kontinenters möjliga lägen relativt varandra. Min hypotes utifrån dessa resultat är att dessa tre landmassor kan ha suttit i en större landmassa kallad Superia. (Less)
Abstract
Earth history is punctuated by a series of events of supercontinent amalgamation and break-up. Fragments of old continents display rifted margins and orogenic sutures that testify their involvement in supercontinent cycles. Periods of break-up are associated with widespread magmatism due to extensional thinning and rifting of the lithosphere and in some instances the arrival of mantle plumes. Mantle plumes are thought to, at least in part, be responsible for Large Igneous Provinces (LIPs for short), voluminous short-lived outburst of mafic magmatism, whose products are continental flood basalts and oceanic plateaus, layered intrusions, sills and dykes. While continental flood basalts and oceanic plateaus are sensitive to subsequent erosion... (More)
Earth history is punctuated by a series of events of supercontinent amalgamation and break-up. Fragments of old continents display rifted margins and orogenic sutures that testify their involvement in supercontinent cycles. Periods of break-up are associated with widespread magmatism due to extensional thinning and rifting of the lithosphere and in some instances the arrival of mantle plumes. Mantle plumes are thought to, at least in part, be responsible for Large Igneous Provinces (LIPs for short), voluminous short-lived outburst of mafic magmatism, whose products are continental flood basalts and oceanic plateaus, layered intrusions, sills and dykes. While continental flood basalts and oceanic plateaus are sensitive to subsequent erosion and subduction, the plumbing system of LIPs comprising deep-seated intrusions, sills and dykes have a high preservation potential. Thus, these events should be possible to trace back in time through multiple supercontinent cycles. LIPs typically have temporal scales of a few million years, but spatial scales of several hundred to thousand kilometers. After break-up and subsequent ocean basin opening, the products of LIPs may end up on different continents. Ancient crustal fragments, or cratons, have experienced a number of magmatic events, and thus have their individual record. Cratons that were once adjacent in a single landmass should share a part of their magmatic record during the interval of time they were connected. Because mafic rocks contains trace amounts of baddeleyite (ZrO2), and because baddeleyite incorporate abundant uranium but only neglible amounts of lead in its crystal structure, we can age determine mafic intrusions using U-Pb geochronology. H Date: 2016-05-16 ence, we can elucidate these events, craton by craton, and compare them to each other. Multiple individual age matches between different cratons suggest a common ancestry in a supercontinent or supercraton. In addition, dyke swarms provide geometric information as they often display radiating or parallel patterns. Fragments of ancient supercontinents or larger landmasses can thus theoretically be reconstructed by comparing geometry of dyke swarm matches in the magmatic record. My PhD-project has been focused on Paleoproterozoic mafic dykes from the present-day southern Greenland part of the Archean North Atlantic Craton (NAC). Precise U-Pb baddeleyite age determinations of multiple events of dyke emplacement are presented in this thesis at ca. 2500, 2375−2365, 2215−2210, 2165−2160, 2125 and 2050−2020 Ma. This magmatic record show temporal correlations with a number of Archaean cratons worldwide, and notably share multiple matches with Superior and Dharwar cratons in present day Canada and India, respectively. A tentative paleoreconstruction of possible cratonic configurations of North Atlantic, Superior and Dharwar cratons during the time interval 2.37−2.17 Ga is presented in the context of supercraton Superia. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor Heaman, Larry, Department of Earth and Atmospheric Sciences, University of Alberta, Canada
organization
publishing date
type
Thesis
publication status
published
subject
keywords
baddeleyit, U-Pb, geokronologi, large igneous province, mantelplym, superkontinent, paleorekonstruktion, North Atlantic craton, baddeleyite, Large Igneous Province, Mantle plume, supercontinent, paleoreconstruction, U-Pb, geochronology, North Atlantic craton
pages
104 pages
publisher
Lund University, Faculty of Science, Department of Geology, Lithosphere and Biosphere Science
defense location
Geocentre II, lecture hall "Pangea", Sölvegatan 12, Lund
defense date
2016-06-17 13:00
ISBN
978-91-87847-21-9
language
English
LU publication?
yes
id
c0e93a10-c07c-4ecc-ac26-72cc82b5983c
date added to LUP
2016-05-23 12:23:52
date last changed
2016-09-19 08:45:20
@phdthesis{c0e93a10-c07c-4ecc-ac26-72cc82b5983c,
  abstract     = {Earth history is punctuated by a series of events of supercontinent amalgamation and break-up. Fragments of old continents display rifted margins and orogenic sutures that testify their involvement in supercontinent cycles. Periods of break-up are associated with widespread magmatism due to extensional thinning and rifting of the lithosphere and in some instances the arrival of mantle plumes. Mantle plumes are thought to, at least in part, be responsible for Large Igneous Provinces (LIPs for short), voluminous short-lived outburst of mafic magmatism, whose products are continental flood basalts and oceanic plateaus, layered intrusions, sills and dykes. While continental flood basalts and oceanic plateaus are sensitive to subsequent erosion and subduction, the plumbing system of LIPs comprising deep-seated intrusions, sills and dykes have a high preservation potential. Thus, these events should be possible to trace back in time through multiple supercontinent cycles. LIPs typically have temporal scales of a few million years, but spatial scales of several hundred to thousand kilometers. After break-up and subsequent ocean basin opening, the products of LIPs may end up on different continents. Ancient crustal fragments, or cratons, have experienced a number of magmatic events, and thus have their individual record. Cratons that were once adjacent in a single landmass should share a part of their magmatic record during the interval of time they were connected. Because mafic rocks contains trace amounts of baddeleyite (ZrO2), and because baddeleyite incorporate abundant uranium but only neglible amounts of lead in its crystal structure, we can age determine mafic intrusions using U-Pb geochronology. H Date: 2016-05-16 ence, we can elucidate these events, craton by craton, and compare them to each other. Multiple individual age matches between different cratons suggest a common ancestry in a supercontinent or supercraton. In addition, dyke swarms provide geometric information as they often display radiating or parallel patterns. Fragments of ancient supercontinents or larger landmasses can thus theoretically be reconstructed by comparing geometry of dyke swarm matches in the magmatic record. My PhD-project has been focused on Paleoproterozoic mafic dykes from the present-day southern Greenland part of the Archean North Atlantic Craton (NAC). Precise U-Pb baddeleyite age determinations of multiple events of dyke emplacement are presented in this thesis at ca. 2500, 2375−2365, 2215−2210, 2165−2160, 2125 and 2050−2020 Ma. This magmatic record show temporal correlations with a number of Archaean cratons worldwide, and notably share multiple matches with Superior and Dharwar cratons in present day Canada and India, respectively. A tentative paleoreconstruction of possible cratonic configurations of North Atlantic, Superior and Dharwar cratons during the time interval 2.37−2.17 Ga is presented in the context of supercraton Superia.},
  author       = {Nilsson, Mimmi},
  isbn         = {978-91-87847-21-9},
  keyword      = {baddeleyit,U-Pb,geokronologi,large igneous province,mantelplym,superkontinent,paleorekonstruktion,North Atlantic craton,baddeleyite,Large Igneous Province,Mantle plume,supercontinent,paleoreconstruction,U-Pb,geochronology,North Atlantic craton},
  language     = {eng},
  pages        = {104},
  publisher    = {Lund University, Faculty of Science, Department of Geology, Lithosphere and Biosphere Science},
  school       = {Lund University},
  title        = {New constraints on paleoreconstructions through geochronology of mafic dyke swarms in North Atlantic Craton},
  year         = {2016},
}