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Metamorphic microtextures and mineral assemblages in orthogneisses in NW Skåne – how do they correlate with technical properties?

Taxopoulou, Maria Eleni LU (2020) In Dissertations in Geology at Lund University GEOR02 20201
Department of Geology
Abstract (Swedish)
Glacifluviala avlagringar har varit de vanligaste källorna för byggmaterial i Sverige under de senaste decennierna. De är dock ändliga resurser som måste bevaras eftersom de också fungerar som akvifärer. Krossat bergmaterial har i stor utsträckning ersatt naturgrus, men standarderna för deras tekniska egenskaper beror på många faktorer av vilka en del kan försämra deras kvalitet.
Denna studie behandlar granitiska bergarter i området i och runt Söderåsen i nordvästra Skåne, vilket geologiskt sett är en del av det Östra segmentet i den Svekonorvegiska provinsen. Nitton prover av granitisk ortognejs har undersökts. Det primära målet var att undersöka om det finns ett samband mellan deras tekniska kvalitet och deras petrografiska egenskaper.... (More)
Glacifluviala avlagringar har varit de vanligaste källorna för byggmaterial i Sverige under de senaste decennierna. De är dock ändliga resurser som måste bevaras eftersom de också fungerar som akvifärer. Krossat bergmaterial har i stor utsträckning ersatt naturgrus, men standarderna för deras tekniska egenskaper beror på många faktorer av vilka en del kan försämra deras kvalitet.
Denna studie behandlar granitiska bergarter i området i och runt Söderåsen i nordvästra Skåne, vilket geologiskt sett är en del av det Östra segmentet i den Svekonorvegiska provinsen. Nitton prover av granitisk ortognejs har undersökts. Det primära målet var att undersöka om det finns ett samband mellan deras tekniska kvalitet och deras petrografiska egenskaper. Lämpligheten för dessa bergarter som aggregat, uppskattat från tekniska standardtestvärden (Los Angeles-, MicroDeval-, Studded Tyre-tester utförda av Sveriges geologiska undersökning),
jämfördes med mineralinnehåll, metamorfa förhållanden, struktur och mikrotexturer.
Studieområdet har geonmgått metamorfos i övre amfibolitfacies till högtrycks-granulitfacies. De flesta bergarter av högre kvalitet (klass 1 och 2) är belägna i den nordvästra delen av studieområdet. Detta område tillhör metamorfa zon 6 (Möller & Andersson, 2018) som har högst metamorf grad, vilket också indikeras av närvaron av ortopyroxen i det prov av metagabbro som studerades. Den sydöstra delen av studieområdet, som innehåller prover av lägre kvalitet (mestadels klass 3), har klassats som zon 5 (Möller & Andersson, 2018) och har genomgått metamorfa förhållanden av något lägre grad än zon 6. Låg genomsnittlig kornstorlek och höga deformationsgrad korrelerar med låga Los Angeles-värden, dvs. god kvalitet. En annan viktig faktor är mängden mycket finkornigt material såväl som korngränsernas komplexitet. Den senare påverkar sammanväxningen mellan kornen, där komplexa former resulterar i bättre tekniska egenskaper. I den här studien visar prover av högre kvalitet större mängder mycket fina korn och medelhög till hög korngränskomplexitet.
Proverna i den nordvästra delen av studieområdet har större andel kvarts och pertitisk avblandning i K-fältspat; granat förekommer som mycket små, rundade kristaller. I dessa prover saknas titanit och gallertvillingar i kalifältspat är sällsynt, medan apatit är vanligare.
Denna undersökning poängterar att proverna i den norra och nordvästra delen av studieområdet tillhör metamorf zon 6 i Östra segmentet och att dessa är bäst lämpade för väg- och järnvägsbyggande. Områdets geologiska förhållanden, såsom metamorf grad och deformationsgrad har en direkt inverkan på tekniska kvaliteter hos granitiska bergarter. (Less)
Abstract
Glaciofluvial deposits used to be the most common source for construction aggregates in Sweden during the past decades; however, their source is limited and they must be preserved, as they also act as aquifers. Gravel has largely been replaced by crushed rock materials, but the technical properties of crushed rock depend on many factors, some of which can reduce the quality.
This study deals with granitic rocks in the Söderåsen area in northwest Skåne, south Sweden. Nineteen orthogneiss samples from the Eastern Segment of the Sveconorwegian Province have been analyzed. The primary goal was to investigate whether there is a correlation between their technical quality and their petrographic characteristics. The suitability of these rocks as... (More)
Glaciofluvial deposits used to be the most common source for construction aggregates in Sweden during the past decades; however, their source is limited and they must be preserved, as they also act as aquifers. Gravel has largely been replaced by crushed rock materials, but the technical properties of crushed rock depend on many factors, some of which can reduce the quality.
This study deals with granitic rocks in the Söderåsen area in northwest Skåne, south Sweden. Nineteen orthogneiss samples from the Eastern Segment of the Sveconorwegian Province have been analyzed. The primary goal was to investigate whether there is a correlation between their technical quality and their petrographic characteristics. The suitability of these rocks as aggregates, estimated from technical standard test values performed by the Geological Survey of Sweden (Los Angeles, MicroDeval, Studded Tyre), was compared with mineral content, metamorphic conditions, fabric, and micro-textures.
The study area was exposed to metamorphic conditions of upper amphibolite- up to granulite-facies. Most of the samples of higher quality (classes 1 and 2) are located in the northwest part of the study area. This area belongs to zone 6 (Möller & Andersson, 2018) that has higher metamorphic grade, as also indicated by the presence of orthopyroxene in the one metagabbro that was studied. On the other hand, the southeast part of the study area that includes the lower quality samples (mostly class 3), is located in zone 5 and has undergone slightly lower metamorphic conditions. A low average grain size and higher degree of strain also show good correlation with low Los Angeles values. Another important factor is the amount of very fine-grained material, as well as the grain boundary complexity. The latter factor contributes to a higher degree of interlocking between the grains, resulting in better technical properties. In this study, higher quality samples show higher amounts of very fine grains and medium- to high grain boundary complexity.
The samples located in the northwest part of the study area have higher proportion of quartz and perthitic exsolution in K-feldspar; garnet is present in very small, rounded crystals. In these samples, titanite is absent and tartan twinning in feldspars is rare, whereas apatite is more abundant.
The present investigation reveals that the samples located in the north and northwest part of the study area belong to the metamorphic zone 6 of the Eastern Segment and they are the most suitable for road and railway construction. The geological conditions are of high importance, as the metamorphic grade and the degree of deformation have a direct effect on the mineralogy and the fabrics, and therefore affect the technical quality in various ways. (Less)
Please use this url to cite or link to this publication:
author
Taxopoulou, Maria Eleni LU
supervisor
organization
course
GEOR02 20201
year
type
H2 - Master's Degree (Two Years)
subject
keywords
granitic gneiss, Eastern Segment, Söderåsen, rock quality, quantitative analyses, grain size, aspect ratio, circularity, mineralogy
publication/series
Dissertations in Geology at Lund University
report number
607
language
English
id
9032230
date added to LUP
2020-11-23 12:49:22
date last changed
2022-12-31 03:40:57
@misc{9032230,
  abstract     = {{Glaciofluvial deposits used to be the most common source for construction aggregates in Sweden during the past decades; however, their source is limited and they must be preserved, as they also act as aquifers. Gravel has largely been replaced by crushed rock materials, but the technical properties of crushed rock depend on many factors, some of which can reduce the quality.
This study deals with granitic rocks in the Söderåsen area in northwest Skåne, south Sweden. Nineteen orthogneiss samples from the Eastern Segment of the Sveconorwegian Province have been analyzed. The primary goal was to investigate whether there is a correlation between their technical quality and their petrographic characteristics. The suitability of these rocks as aggregates, estimated from technical standard test values performed by the Geological Survey of Sweden (Los Angeles, MicroDeval, Studded Tyre), was compared with mineral content, metamorphic conditions, fabric, and micro-textures.
The study area was exposed to metamorphic conditions of upper amphibolite- up to granulite-facies. Most of the samples of higher quality (classes 1 and 2) are located in the northwest part of the study area. This area belongs to zone 6 (Möller & Andersson, 2018) that has higher metamorphic grade, as also indicated by the presence of orthopyroxene in the one metagabbro that was studied. On the other hand, the southeast part of the study area that includes the lower quality samples (mostly class 3), is located in zone 5 and has undergone slightly lower metamorphic conditions. A low average grain size and higher degree of strain also show good correlation with low Los Angeles values. Another important factor is the amount of very fine-grained material, as well as the grain boundary complexity. The latter factor contributes to a higher degree of interlocking between the grains, resulting in better technical properties. In this study, higher quality samples show higher amounts of very fine grains and medium- to high grain boundary complexity.
The samples located in the northwest part of the study area have higher proportion of quartz and perthitic exsolution in K-feldspar; garnet is present in very small, rounded crystals. In these samples, titanite is absent and tartan twinning in feldspars is rare, whereas apatite is more abundant.
The present investigation reveals that the samples located in the north and northwest part of the study area belong to the metamorphic zone 6 of the Eastern Segment and they are the most suitable for road and railway construction. The geological conditions are of high importance, as the metamorphic grade and the degree of deformation have a direct effect on the mineralogy and the fabrics, and therefore affect the technical quality in various ways.}},
  author       = {{Taxopoulou, Maria Eleni}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{Dissertations in Geology at Lund University}},
  title        = {{Metamorphic microtextures and mineral assemblages in orthogneisses in NW Skåne – how do they correlate with technical properties?}},
  year         = {{2020}},
}