Incipient fluid fluid-induced metamorphism in the mid mid- to deep crust: a petrological case study of seemingly pristine igneous gabbro, southern Scandinavia.
(2025) In Examensarbeten i geologi vid Lunds universitet GEOR02 20251Department of Geology
- Abstract
- In the easternmost Sveconorwegian Province, field studies have shown that some intrusions remained largely unaffected by the Sveconorwegian orogeny. However, seemingly pristine gabbros locally display the incipient development of amphibolite amphibolite-facies mineral assemblages in microscale corona textures. The primary objective of this study is to document in detail the microtextures that occur in these apparently unaltered igneous gabbros.
Petrographic analysis was carried out using standard polarized polarized-light microscopy and scanning electron microscopy (SEM) coupled with energy energy-dispersive X X-ray spectroscopy (EDS). The protoliths classify as olivine gabbros with a primary igneous assemblage of plagioclase,... (More) - In the easternmost Sveconorwegian Province, field studies have shown that some intrusions remained largely unaffected by the Sveconorwegian orogeny. However, seemingly pristine gabbros locally display the incipient development of amphibolite amphibolite-facies mineral assemblages in microscale corona textures. The primary objective of this study is to document in detail the microtextures that occur in these apparently unaltered igneous gabbros.
Petrographic analysis was carried out using standard polarized polarized-light microscopy and scanning electron microscopy (SEM) coupled with energy energy-dispersive X X-ray spectroscopy (EDS). The protoliths classify as olivine gabbros with a primary igneous assemblage of plagioclase, clinopyroxene, olivine ± orthopyroxene, and biotite, with minor apatite and opaque phases. Metamorphic phases include orthopyroxene, biotite, calcic amphibole, garnet, and epidote.
Diffusion-controlled reactions produced multilayered coronas: around olivine, typically a double corona of orthopyroxene and hornblende; and around Fe Fe–Ti oxides, a double corona of biotite and hornblende. Volume changes associated with these reactions induced microfractures, which in turn provided fluid pathways, as indicated by metamorphic minerals occurring along fractures and grain boundaries. Collectively, these features record metamorphism under amphibolite amphibolite-facies conditions. (Less) - Popular Abstract
- The crust in southern Scandinavia has been reworked by the Sveconorwegian Orogeny, a major mountain-building event that occurred approximately one billion years ago. The now exposed rocks, used to lie deep in the crust and are visible now through extensive erosion.
While most of the rocks have been reworked through intense pressure and temperature changes during mountain formation, some dark rock intrusions appear to be unaffected by these processes when observed in the field. A closer look under the microscope reveals tiny signs of metamorphosis, though.
The study used optical and electron microscopes. The examination revealed that the rock is made of common magmatic minerals, like plagioclase, pyroxene and olivine, classifying it as a... (More) - The crust in southern Scandinavia has been reworked by the Sveconorwegian Orogeny, a major mountain-building event that occurred approximately one billion years ago. The now exposed rocks, used to lie deep in the crust and are visible now through extensive erosion.
While most of the rocks have been reworked through intense pressure and temperature changes during mountain formation, some dark rock intrusions appear to be unaffected by these processes when observed in the field. A closer look under the microscope reveals tiny signs of metamorphosis, though.
The study used optical and electron microscopes. The examination revealed that the rock is made of common magmatic minerals, like plagioclase, pyroxene and olivine, classifying it as a gabbro – however, new minerals – such as amphibole, garnet, and epidote formed during later metamorphism.
One of the most significant features are coronas: thin, layered rims of new minerals surrounding the old ones. For example, double coronas have formed around olivine made of orthopyroxene and amphibole. These textures grew through slow, diffusion-controlled reactions.
These new minerals caused a volume change and created fractures. Small crystallisations of new minerals in these fractures give a hint that these new fractures have been used as pathways for hydrous fluids. Similar features are found along grain boundaries. Together, these microstructures and new minerals show that even rocks that seem untouched have metamorphic features representing amphibolite-facies conditions, around 600°C. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9216063
- author
- Damm, Germaine LU
- supervisor
- organization
- course
- GEOR02 20251
- year
- 2025
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- fluid-induced metamorphism, multilayered corona, Eastern Segment, amphibolite amphibolite-facies metamorphism
- publication/series
- Examensarbeten i geologi vid Lunds universitet
- report number
- 722
- language
- English
- id
- 9216063
- date added to LUP
- 2025-12-10 09:18:59
- date last changed
- 2025-12-10 09:18:59
@misc{9216063,
abstract = {{In the easternmost Sveconorwegian Province, field studies have shown that some intrusions remained largely unaffected by the Sveconorwegian orogeny. However, seemingly pristine gabbros locally display the incipient development of amphibolite amphibolite-facies mineral assemblages in microscale corona textures. The primary objective of this study is to document in detail the microtextures that occur in these apparently unaltered igneous gabbros.
Petrographic analysis was carried out using standard polarized polarized-light microscopy and scanning electron microscopy (SEM) coupled with energy energy-dispersive X X-ray spectroscopy (EDS). The protoliths classify as olivine gabbros with a primary igneous assemblage of plagioclase, clinopyroxene, olivine ± orthopyroxene, and biotite, with minor apatite and opaque phases. Metamorphic phases include orthopyroxene, biotite, calcic amphibole, garnet, and epidote.
Diffusion-controlled reactions produced multilayered coronas: around olivine, typically a double corona of orthopyroxene and hornblende; and around Fe Fe–Ti oxides, a double corona of biotite and hornblende. Volume changes associated with these reactions induced microfractures, which in turn provided fluid pathways, as indicated by metamorphic minerals occurring along fractures and grain boundaries. Collectively, these features record metamorphism under amphibolite amphibolite-facies conditions.}},
author = {{Damm, Germaine}},
language = {{eng}},
note = {{Student Paper}},
series = {{Examensarbeten i geologi vid Lunds universitet}},
title = {{Incipient fluid fluid-induced metamorphism in the mid mid- to deep crust: a petrological case study of seemingly pristine igneous gabbro, southern Scandinavia.}},
year = {{2025}},
}