Compressional and extensional tectonics in low-medium pressure granulites from the Larsemann Hills, East Antarctica
Abstract Meta-sediments in the Larsemann Hills that preserve a coherent stratigraphy, form a cover sequence deposited upon basement of mafic–felsic granulite. Their outcrop pattern defines a 10 kilometre wide east–west trending synclinal trough structure in which basement–cover contacts differ in th...
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1995
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crcambridgeupr:10.1017/s0016756800011729 2024-09-15T17:45:08+00:00 Compressional and extensional tectonics in low-medium pressure granulites from the Larsemann Hills, East Antarctica Carson, C. J. Dirks, P. G. H. M. Hand, M. Sims, J. P. Wilson, C. J. L. 1995 http://dx.doi.org/10.1017/s0016756800011729 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800011729 en eng Cambridge University Press (CUP) https://www.cambridge.org/core/terms Geological Magazine volume 132, issue 2, page 151-170 ISSN 0016-7568 1469-5081 journal-article 1995 crcambridgeupr https://doi.org/10.1017/s0016756800011729 2024-07-31T04:04:04Z Abstract Meta-sediments in the Larsemann Hills that preserve a coherent stratigraphy, form a cover sequence deposited upon basement of mafic–felsic granulite. Their outcrop pattern defines a 10 kilometre wide east–west trending synclinal trough structure in which basement–cover contacts differ in the north and the south, suggesting tectonic interleaving during a prograde, D 1 thickening event. Subsequent conditions reached low-medium pressure granulite grade, and structures can be divided into two groups, D 2 and D 3 , each defined by a unique lineation direction and shear sense. D 2 structures which are associated with the dominant gneissic foliation in much of the Larsemann Hills, contain a moderately east-plunging lineation indicative of west-directed thrusting. D 2 comprises a colinear fold sequence that evolved from early intrafolial folds to late upright folds. D 3 structures are associated with a high-strain zone, to the south of the Larsemann Hills, where S 3 is the dominant gneissic layering and folds sequences resemble D 2 folding. Outside the D 3 high-strain zone occurs a low-strain D 3 window, preserving low-strain D 3 structures (minor shear bands and upright folds) that partly re-orient D 2 structures. All structures are truncated by a series of planar pegmatites and parallel D 4 mylonite zones, recording extensional dextral displacements. D 2 assemblages include coexisting garnet–orthopyroxene pairs recording peak conditions of ∼ 7 kbar and ∼ 780°C. Subsequent retrograde decompression textures partly evolved during both D 2 and D 3 when conditions of ∼ 4–5 kbar and ∼ 750°C were attained. This is followed by D 4 shear zones which formed around 3 kbar and ∼ 550°C. It is tempting to combine D 2–4 structures in one tectonic cycle involving prograde thrusting and thickening followed by retrograde extension and uplift. The available geochronological data, however, present a number of interpretations. For example, D 2 was possibly associated with a clockwise P–T path at medium pressures around ∼ 1000 Ma, ... Article in Journal/Newspaper Antarc* Antarctica East Antarctica Cambridge University Press Geological Magazine 132 2 151 170 |
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Open Polar |
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Cambridge University Press |
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crcambridgeupr |
language |
English |
description |
Abstract Meta-sediments in the Larsemann Hills that preserve a coherent stratigraphy, form a cover sequence deposited upon basement of mafic–felsic granulite. Their outcrop pattern defines a 10 kilometre wide east–west trending synclinal trough structure in which basement–cover contacts differ in the north and the south, suggesting tectonic interleaving during a prograde, D 1 thickening event. Subsequent conditions reached low-medium pressure granulite grade, and structures can be divided into two groups, D 2 and D 3 , each defined by a unique lineation direction and shear sense. D 2 structures which are associated with the dominant gneissic foliation in much of the Larsemann Hills, contain a moderately east-plunging lineation indicative of west-directed thrusting. D 2 comprises a colinear fold sequence that evolved from early intrafolial folds to late upright folds. D 3 structures are associated with a high-strain zone, to the south of the Larsemann Hills, where S 3 is the dominant gneissic layering and folds sequences resemble D 2 folding. Outside the D 3 high-strain zone occurs a low-strain D 3 window, preserving low-strain D 3 structures (minor shear bands and upright folds) that partly re-orient D 2 structures. All structures are truncated by a series of planar pegmatites and parallel D 4 mylonite zones, recording extensional dextral displacements. D 2 assemblages include coexisting garnet–orthopyroxene pairs recording peak conditions of ∼ 7 kbar and ∼ 780°C. Subsequent retrograde decompression textures partly evolved during both D 2 and D 3 when conditions of ∼ 4–5 kbar and ∼ 750°C were attained. This is followed by D 4 shear zones which formed around 3 kbar and ∼ 550°C. It is tempting to combine D 2–4 structures in one tectonic cycle involving prograde thrusting and thickening followed by retrograde extension and uplift. The available geochronological data, however, present a number of interpretations. For example, D 2 was possibly associated with a clockwise P–T path at medium pressures around ∼ 1000 Ma, ... |
format |
Article in Journal/Newspaper |
author |
Carson, C. J. Dirks, P. G. H. M. Hand, M. Sims, J. P. Wilson, C. J. L. |
spellingShingle |
Carson, C. J. Dirks, P. G. H. M. Hand, M. Sims, J. P. Wilson, C. J. L. Compressional and extensional tectonics in low-medium pressure granulites from the Larsemann Hills, East Antarctica |
author_facet |
Carson, C. J. Dirks, P. G. H. M. Hand, M. Sims, J. P. Wilson, C. J. L. |
author_sort |
Carson, C. J. |
title |
Compressional and extensional tectonics in low-medium pressure granulites from the Larsemann Hills, East Antarctica |
title_short |
Compressional and extensional tectonics in low-medium pressure granulites from the Larsemann Hills, East Antarctica |
title_full |
Compressional and extensional tectonics in low-medium pressure granulites from the Larsemann Hills, East Antarctica |
title_fullStr |
Compressional and extensional tectonics in low-medium pressure granulites from the Larsemann Hills, East Antarctica |
title_full_unstemmed |
Compressional and extensional tectonics in low-medium pressure granulites from the Larsemann Hills, East Antarctica |
title_sort |
compressional and extensional tectonics in low-medium pressure granulites from the larsemann hills, east antarctica |
publisher |
Cambridge University Press (CUP) |
publishDate |
1995 |
url |
http://dx.doi.org/10.1017/s0016756800011729 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800011729 |
genre |
Antarc* Antarctica East Antarctica |
genre_facet |
Antarc* Antarctica East Antarctica |
op_source |
Geological Magazine volume 132, issue 2, page 151-170 ISSN 0016-7568 1469-5081 |
op_rights |
https://www.cambridge.org/core/terms |
op_doi |
https://doi.org/10.1017/s0016756800011729 |
container_title |
Geological Magazine |
container_volume |
132 |
container_issue |
2 |
container_start_page |
151 |
op_container_end_page |
170 |
_version_ |
1810492847810412544 |