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Monazite in metasediments from Stensjöstrand : a pilot study

Olsson, Andreas LU (2013) In Dissertations in Geology at Lund University GEOL01 20131
Department of Geology
Abstract (Swedish)
Monazit är ett Ree– och Th-bärande fosfatmineral som förekommer i vissa magmatiska och metamorfa bergarter. Mineralet är användbart för datering av den metamorfa utvecklingen och kan bidra till att yt-terligare karaktärisera metamorfosen i en bergart, detta genom att man undersöker zoneringar i kristallerna. Mo-nazit har upptäckts i metasediment i Stensjöstrand och tunnslip har gjorts ifrån prover för att undersöka mineralet. Tunnslip 3c och 3b kommer ifrån en migmatitgnejs som har två skilda faser, mesosom och leukosom. Tunnslipen har studerats med polarisationsmikroskopi och två olika typer av monaziter har upptäckts. Den första typen är små och ovala eller runda, ofta med distinkt zonering, och de förekommer i leukosomen. Den andra... (More)
Monazit är ett Ree– och Th-bärande fosfatmineral som förekommer i vissa magmatiska och metamorfa bergarter. Mineralet är användbart för datering av den metamorfa utvecklingen och kan bidra till att yt-terligare karaktärisera metamorfosen i en bergart, detta genom att man undersöker zoneringar i kristallerna. Mo-nazit har upptäckts i metasediment i Stensjöstrand och tunnslip har gjorts ifrån prover för att undersöka mineralet. Tunnslip 3c och 3b kommer ifrån en migmatitgnejs som har två skilda faser, mesosom och leukosom. Tunnslipen har studerats med polarisationsmikroskopi och två olika typer av monaziter har upptäckts. Den första typen är små och ovala eller runda, ofta med distinkt zonering, och de förekommer i leukosomen. Den andra typen har stora, påtagligt oregelbundet formade kristaller med otydlig zonering och de förekommer i mesosomen. Kemisk samman-sättning och zonering i olika monazitkristaller och resterande mineralsällskap har analyserats med SEM-EDX. Re-sultaten visar en tydlig skillnad i mineralsammansättningen och texturer mellan leukosomen och mesosomen. Mi-neral som förekommer i leukosomen är kvarts, plagioklas, K-fältspat, zirkon och små biotit-, ilmenit- och mo-nazitkristaller. Mineral som förekommer i mesosomen är sillimanit, kvarts, plagioklas, K-fältspat, granat, zirkon och stora biotit- (vissa har symplektit-inneslutningar), ilmenit-, hematit– och monazitkristaller. Back-scatterbilder visar avblandningar i både K-fältspat och ilmenit. Erhållna analysresultat från olika domäner i olika monazitkristal-ler är inkonsekventa och inte fullständigt korrekta och kunde endast användas för att jämföra relativa skillnader i de kemiska sammansättningarna mellan olika kristaller. Den faktiska orsaken till skillnaderna mellan de två olika ty-perna av moanzitkristallerna är inte säker. En hypotes är att orsaken till skillnaden är en skillnad i ålder mellan de två typerna och resorbtion av de de stora monazitkristallerna i mesosomen. (Less)
Abstract
Monazite is a Th-bearing REE phosphate mineral which is present in some igneous and metamorphic rocks. It is a useful mineral for determination of the metamorphic history and age of its host rock because clues to past mineral reactions can be seen in trace element zoning. Monazite has been found in metasediments in Sten-sjöstrand and thin sections have been made from rock samples to study the mineral. Thin sections 3c and 3b repre-sent a migmatite gneiss with two different phases, mesosome and leucosome. The thin sections have been observed using polarization microscopy and two different types of monazite were discovered. The first type appears as small and oval or round crystals, often with distinct compositional domains and is found the... (More)
Monazite is a Th-bearing REE phosphate mineral which is present in some igneous and metamorphic rocks. It is a useful mineral for determination of the metamorphic history and age of its host rock because clues to past mineral reactions can be seen in trace element zoning. Monazite has been found in metasediments in Sten-sjöstrand and thin sections have been made from rock samples to study the mineral. Thin sections 3c and 3b repre-sent a migmatite gneiss with two different phases, mesosome and leucosome. The thin sections have been observed using polarization microscopy and two different types of monazite were discovered. The first type appears as small and oval or round crystals, often with distinct compositional domains and is found the leucosome. The second type appears as large, markedly irregular shaped crystals with indistinct compositional domains and is found the meso-some. The chemical compositions as well as the compositional domains of different monazite crystals and the main mineral assemblage have been analyzed using SEM-EDX. The results show a clear difference in mineral composit-ion and texture between the leucosome and the mesosome. Minerals found in the leucosome are quartz, plagioclase, K-feldspar, zircon and small biotite, ilmenite and monazite crystals. Minerals found in the mesosome are sillima-nite, quartz, plagioclase, K-feldspar, garnet, zircon, and large biotite (some of them containing symplectites), ilme-nite, hematite and monazite crystals. BSE-images reveal exsolution textures in K-feldspar and ilmenite. Analytical results from different compositional domains of different monazite crystals were inconsistent and not completely accurate and could only be used to compare relative differences in chemical composition between crystals. The acual reason for the difference between the two types of monazite crystals is not certain. It is hypothesized that the difference is due to a difference in age between the two types and resorption of the large monazite crystals in the mesosome. (Less)
Please use this url to cite or link to this publication:
author
Olsson, Andreas LU
supervisor
organization
alternative title
Monazit i metasediment från Stensjöstrand : en pilotstudie
course
GEOL01 20131
year
type
M2 - Bachelor Degree
subject
keywords
pilot study monazit, Stensjöstrand, Sveconorwegian orogen, monazite, metasediments, metasediment, Sveconorvegiska orogenesen, pilotstudie
publication/series
Dissertations in Geology at Lund University
report number
358
language
English
id
3911804
date added to LUP
2013-06-28 15:51:28
date last changed
2015-06-28 04:21:18
@misc{3911804,
  abstract     = {Monazite is a Th-bearing REE phosphate mineral which is present in some igneous and metamorphic rocks. It is a useful mineral for determination of the metamorphic history and age of its host rock because clues to past mineral reactions can be seen in trace element zoning. Monazite has been found in metasediments in Sten-sjöstrand and thin sections have been made from rock samples to study the mineral. Thin sections 3c and 3b repre-sent a migmatite gneiss with two different phases, mesosome and leucosome. The thin sections have been observed using polarization microscopy and two different types of monazite were discovered. The first type appears as small and oval or round crystals, often with distinct compositional domains and is found the leucosome. The second type appears as large, markedly irregular shaped crystals with indistinct compositional domains and is found the meso-some. The chemical compositions as well as the compositional domains of different monazite crystals and the main mineral assemblage have been analyzed using SEM-EDX. The results show a clear difference in mineral composit-ion and texture between the leucosome and the mesosome. Minerals found in the leucosome are quartz, plagioclase, K-feldspar, zircon and small biotite, ilmenite and monazite crystals. Minerals found in the mesosome are sillima-nite, quartz, plagioclase, K-feldspar, garnet, zircon, and large biotite (some of them containing symplectites), ilme-nite, hematite and monazite crystals. BSE-images reveal exsolution textures in K-feldspar and ilmenite. Analytical results from different compositional domains of different monazite crystals were inconsistent and not completely accurate and could only be used to compare relative differences in chemical composition between crystals. The acual reason for the difference between the two types of monazite crystals is not certain. It is hypothesized that the difference is due to a difference in age between the two types and resorption of the large monazite crystals in the mesosome.},
  author       = {Olsson, Andreas},
  keyword      = {pilot study monazit,Stensjöstrand,Sveconorwegian orogen,monazite,metasediments,metasediment,Sveconorvegiska orogenesen,pilotstudie},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Monazite in metasediments from Stensjöstrand : a pilot study},
  year         = {2013},
}