Advanced

Using Fe-Ti oxides and trace element analysis to determine crystallization sequence of an anorthosite-norite intrusion, Älgön SW Sweden.

Kullberg, Sara LU (2015) In Dissertations in Geology at Lund University GEOR02 20151
Department of Geology
Abstract (Swedish)
På Älgön, SV Sverige, finns en anortosit-norit intrusion tillhörande Hakefjordenkomplexet. Det finns dessutom två tillhörande enheter; en marginell monzonorit och en centralt belägen ilmenitberikad norit (IRL). I den ilmenitberikade noriten finns även olika sorters aggregat av Fe-Ti oxider. Genom att undersöka Mn-innehållet i ilmenit i alla litologiska enheter var det möjligt att få fram en kronologisk kristallisationsordning; oxidaggregat i IRL → IRL → anortosit → anortosit/norit → monzonorit, där monzonoriten är mest rik på Mn och därmed yngst. En analys av inkompatibla spårämnen visar även på att monzonoriten är den mest berikade enheten och därmed den mest utvecklade och yngsta enheten i Hakefjordenkomplexet. Tvärtom är det för... (More)
På Älgön, SV Sverige, finns en anortosit-norit intrusion tillhörande Hakefjordenkomplexet. Det finns dessutom två tillhörande enheter; en marginell monzonorit och en centralt belägen ilmenitberikad norit (IRL). I den ilmenitberikade noriten finns även olika sorters aggregat av Fe-Ti oxider. Genom att undersöka Mn-innehållet i ilmenit i alla litologiska enheter var det möjligt att få fram en kronologisk kristallisationsordning; oxidaggregat i IRL → IRL → anortosit → anortosit/norit → monzonorit, där monzonoriten är mest rik på Mn och därmed yngst. En analys av inkompatibla spårämnen visar även på att monzonoriten är den mest berikade enheten och därmed den mest utvecklade och yngsta enheten i Hakefjordenkomplexet. Tvärtom är det för oxidaggregaten i den ilmentiberikade noriten. Dock beror berikningen i monzonoriten även delvis på kontamination av omkringliggande bergart; toppar av Pb, K och Th indikerar detta. En geokemisk modellering (AFC) visar på att förhållandet mellan kontaminering och kristallisation är 0.05, det vill säga låg. Fortsättningsvis visar förhållanden mellan inkompatibla spårelement att källan för magman är homogen. Eftersom spårelementkurvan i ett spindeldiagram ej innehar en U-form, vilket är indikativt för en mantelkälla som har blivit berikad av metasomatiska fluider, eller har negativa anomalier för både Nb och Ta är det inte troligt att magman har sitt ursprung i manteln. Slutligen, eftersom Th koncentrationen är låg är det inte troligt att källan är en övre skorpa utan snarare en undre, mafisk skorpa. (Less)
Abstract
The Hakefjorden Complex is an anorthosite-norite intrusion at Älgön, SW Sweden. There are two lithological units associated with it; a marginal monzonorite and a central Ilmenite-Rich Leuconorite (IRL). In the IRL there is a variety of aggregates of Fe-Ti oxides. By investigating Mn-content of ilmenite from all lithological units a chronological order of crystallization could be assessed; oxide aggregates within the IRL → IRL-matrix → anorthosite → anorthosite/norite → monzonorite with monzonorite being the most enriched in Mn and hence the youngest unit. Analysis of incompatible trace elements show that the monzonorite is the most enriched unit and hence also the most evolved and youngest unit of the Hakefjorden Complex. The opposite is... (More)
The Hakefjorden Complex is an anorthosite-norite intrusion at Älgön, SW Sweden. There are two lithological units associated with it; a marginal monzonorite and a central Ilmenite-Rich Leuconorite (IRL). In the IRL there is a variety of aggregates of Fe-Ti oxides. By investigating Mn-content of ilmenite from all lithological units a chronological order of crystallization could be assessed; oxide aggregates within the IRL → IRL-matrix → anorthosite → anorthosite/norite → monzonorite with monzonorite being the most enriched in Mn and hence the youngest unit. Analysis of incompatible trace elements show that the monzonorite is the most enriched unit and hence also the most evolved and youngest unit of the Hakefjorden Complex. The opposite is true for the oxide aggregates within the IRL. The enrichment in the monzonorite can partly be explained by contamination by the country rock, visible as peaks in Pb, K and Th. Although the contamination is low, r=0.5 (assimilation:fractional crystallization) as deduced by an AFC-model. Furthermore, incompatible trace element ratios show that the magma source is homogenous. As the trace element diagrams lack a U-shape which is indicative of a metasomatically enriched mantle, as well as the double-dip in Nb-Ta, it is not believed that the magma originates from an enriched mantle. Finally, as the Th concentration is low, as opposed to levels in the upper crust, it is theorized that the Hakefjorden Complex originates from a lower mafic crust. (Less)
Please use this url to cite or link to this publication:
author
Kullberg, Sara LU
supervisor
organization
course
GEOR02 20151
year
type
H2 - Master's Degree (Two Years)
subject
keywords
magma origin, AFC-model, ilmenite, ilmenite-rich leuconorite, anorthosite-norite
publication/series
Dissertations in Geology at Lund University
report number
454
language
English
id
7440628
date added to LUP
2015-06-23 14:30:34
date last changed
2017-06-23 04:10:40
@misc{7440628,
  abstract     = {The Hakefjorden Complex is an anorthosite-norite intrusion at Älgön, SW Sweden. There are two lithological units associated with it; a marginal monzonorite and a central Ilmenite-Rich Leuconorite (IRL). In the IRL there is a variety of aggregates of Fe-Ti oxides. By investigating Mn-content of ilmenite from all lithological units a chronological order of crystallization could be assessed; oxide aggregates within the IRL → IRL-matrix → anorthosite → anorthosite/norite → monzonorite with monzonorite being the most enriched in Mn and hence the youngest unit. Analysis of incompatible trace elements show that the monzonorite is the most enriched unit and hence also the most evolved and youngest unit of the Hakefjorden Complex. The opposite is true for the oxide aggregates within the IRL. The enrichment in the monzonorite can partly be explained by contamination by the country rock, visible as peaks in Pb, K and Th. Although the contamination is low, r=0.5 (assimilation:fractional crystallization) as deduced by an AFC-model. Furthermore, incompatible trace element ratios show that the magma source is homogenous. As the trace element diagrams lack a U-shape which is indicative of a metasomatically enriched mantle, as well as the double-dip in Nb-Ta, it is not believed that the magma originates from an enriched mantle. Finally, as the Th concentration is low, as opposed to levels in the upper crust, it is theorized that the Hakefjorden Complex originates from a lower mafic crust.},
  author       = {Kullberg, Sara},
  keyword      = {magma origin,AFC-model,ilmenite,ilmenite-rich leuconorite,anorthosite-norite},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Using Fe-Ti oxides and trace element analysis to determine crystallization sequence of an anorthosite-norite intrusion, Älgön SW Sweden.},
  year         = {2015},
}