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Intracrustal partial melting of garnet amphibolite from southwestern Sweden - a possible analogue for TTG formation

Magnell, Ylva LU (2026) In Dissertations in Geology at Lund University GEOL02 20261
Department of Earth and Environmental Sciences (MGeo)
Abstract (Swedish)
Den arkeiska jordskorpan är den äldsta bevarade kontinentala jordskorpan på jorden och den består till stor del av bergartssviten tonalit-trondhjemit-granodiorit (TTG). Kvarts och plagioklas är de dominerande mineralen i TTG bergarter, som karakteriseras av hög SiO2, Na2O och låg K2O. TTG bildas sällan idag vilket har lett till en osäkerhet runt deras ursprung, men de tros vara bildade genom partiell uppsmältning av meta-basalter. En granatamfibolit innehållande kvarts och plagioklas rika områden som förmodas vara resultatet av partiell uppsmältning, analyserades i denna studie för att få en bättre förståelse av TTG bildning. Granatamfibolit hällen är belägen i Östra Segmentet som påverkades av den Svekonorvegiska orogensen genom... (More)
Den arkeiska jordskorpan är den äldsta bevarade kontinentala jordskorpan på jorden och den består till stor del av bergartssviten tonalit-trondhjemit-granodiorit (TTG). Kvarts och plagioklas är de dominerande mineralen i TTG bergarter, som karakteriseras av hög SiO2, Na2O och låg K2O. TTG bildas sällan idag vilket har lett till en osäkerhet runt deras ursprung, men de tros vara bildade genom partiell uppsmältning av meta-basalter. En granatamfibolit innehållande kvarts och plagioklas rika områden som förmodas vara resultatet av partiell uppsmältning, analyserades i denna studie för att få en bättre förståelse av TTG bildning. Granatamfibolit hällen är belägen i Östra Segmentet som påverkades av den Svekonorvegiska orogensen genom underskjutning. Analyser av kvarts-plagioklas områden visar hög SiO2 (>70 wt. %), hög Na2O (2.0-6.0 wt. %), och låg K2O (<1.0 wt. %), vilka är jämförbara med TTG sammansättning. Amfibolit matrix är dominerad av hornblände och plagioklas, men finkorniga klinopyroxen bärande områden observeras även. Utbredningen av kvarts-plagioklas områdena och variationer i matrix stärker antagandet att bergarten har genomgått partiell uppsmältning. Förekomsten av granat, frånvaron av epidot och klinopyroxen bärande områden i matrix, indikerar temperaturer över 850 °C och tryck över 10 kbar. Baserat på förhållanden som området utsattes för under den Svekonorvegiska orogenesen, föreslår resultatet att TTG-smältor kan bildas genom infrakrustal partiell uppsmältning av granatamfibolit utan att det behövs en omfattande subduktionszon. (Less)
Abstract
The Archean crust is the oldest preserved continental crust on Earth, and it is largely made up of the rock suite tonalite-trondhjemite-granodiorite (TTG). Quartz and plagioclase are the dominating minerals of TTG rocks, that are characterized by a high SiO2, Na2O, and a low K2O. TTG rarely form today which have led to an uncertainty around their origin, but they are believed to be generated through partial melting of meta-basalts. A garnet amphibolite containing quartz and plagioclase rich areas that are thought to be the result of partial melting, were analyzed in this study to get a better understanding of TTG formation. The garnet amphibolite outcrop is located in the Eastern Segment, which were affected by the Sveconorwegian orogeny... (More)
The Archean crust is the oldest preserved continental crust on Earth, and it is largely made up of the rock suite tonalite-trondhjemite-granodiorite (TTG). Quartz and plagioclase are the dominating minerals of TTG rocks, that are characterized by a high SiO2, Na2O, and a low K2O. TTG rarely form today which have led to an uncertainty around their origin, but they are believed to be generated through partial melting of meta-basalts. A garnet amphibolite containing quartz and plagioclase rich areas that are thought to be the result of partial melting, were analyzed in this study to get a better understanding of TTG formation. The garnet amphibolite outcrop is located in the Eastern Segment, which were affected by the Sveconorwegian orogeny through underthrusting. Analyses of the quartz-plagioclase areas show a high SiO2 (>70 wt. %), high Na2O (2.0-6.0 wt. %), and low K2O (< 1.0 wt. %), which are comparable with TTG composition. The amphibolite matrix is largely dominated by hornblende and plagioclase, but finer grained clinopyroxene bearing areas are also observed. The distribution of the quartz-plagioclase areas and variations in the matrix corroborates the assumption that the rock has been through partial melting. The presence of garnet, absence of epidote and the clinopyroxene bearing areas in the matrix, indicates temperatures above 850 °C and pressures over 10 kbar. Based on conditions that affected the area during the Sveconorwegian orogeny, the results suggests that TTG-melts could be generated through intracrustal partial melting of garnet amphibolite and without the need of an extensive subduction zone. (Less)
Please use this url to cite or link to this publication:
author
Magnell, Ylva LU
supervisor
organization
course
GEOL02 20261
year
type
M2 - Bachelor Degree
subject
keywords
TTG, tonalite-trondhjemite-granodiorite, garnet amphibolite, partial melt, geochemistry, Sveconorwegian orogeny, Eastern Segment
publication/series
Dissertations in Geology at Lund University
report number
736
language
English
id
9240135
date added to LUP
2026-06-25 12:38:33
date last changed
2026-06-25 12:38:33
@misc{9240135,
  abstract     = {{The Archean crust is the oldest preserved continental crust on Earth, and it is largely made up of the rock suite tonalite-trondhjemite-granodiorite (TTG). Quartz and plagioclase are the dominating minerals of TTG rocks, that are characterized by a high SiO2, Na2O, and a low K2O. TTG rarely form today which have led to an uncertainty around their origin, but they are believed to be generated through partial melting of meta-basalts. A garnet amphibolite containing quartz and plagioclase rich areas that are thought to be the result of partial melting, were analyzed in this study to get a better understanding of TTG formation. The garnet amphibolite outcrop is located in the Eastern Segment, which were affected by the Sveconorwegian orogeny through underthrusting. Analyses of the quartz-plagioclase areas show a high SiO2 (>70 wt. %), high Na2O (2.0-6.0 wt. %), and low K2O (< 1.0 wt. %), which are comparable with TTG composition. The amphibolite matrix is largely dominated by hornblende and plagioclase, but finer grained clinopyroxene bearing areas are also observed. The distribution of the quartz-plagioclase areas and variations in the matrix corroborates the assumption that the rock has been through partial melting. The presence of garnet, absence of epidote and the clinopyroxene bearing areas in the matrix, indicates temperatures above 850 °C and pressures over 10 kbar. Based on conditions that affected the area during the Sveconorwegian orogeny, the results suggests that TTG-melts could be generated through intracrustal partial melting of garnet amphibolite and without the need of an extensive subduction zone.}},
  author       = {{Magnell, Ylva}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{Dissertations in Geology at Lund University}},
  title        = {{Intracrustal partial melting of garnet amphibolite from southwestern Sweden - a possible analogue for TTG formation}},
  year         = {{2026}},
}