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Cited by 1,042Geological and Geochemical AnalysisGeochemistry and Elemental AnalysisAstro and Planetary Science

The origins of granulites: A metamorphic perspective

Harley, S. L.·1989·Geological Magazine
DOI 10.1017/s0016756800022330
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Abstract

Abstract Although many recent reviews emphasize a uniformity in granulite pressure–temperature ( P – T ) conditions and paths, granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation. A thorough survey of over 90 granulite terranes or occurrences reveals that over 50% of them record P – T conditions outside the 7.5 ± 1 kbar and 800 ± 50 °C average granulite regime preferred by many authors. In particular, an increasing number of very high temperature (900−1000 °C) terranes are being recognized, both on the basis of distinctive mineral assemblages and geothermobarometry. Petrogenetic grid and geothermobarometric approaches to the determination and interpretation of P – T histories are both evaluated within the context of reaction textures to demonstrate that the large range in P – T conditions is indeed real, and that both near-isothermal decompression (ITD) and near-isobaric cooling (IBC) P – T paths are important. Amphibolite–granulite transitions promoted by the passage of CO 2 -rich fluids, as observed in southern India and Sri Lanka, are exceptional and not representative of fluid-related processes in the majority of terranes. It is considered, on the contrary, that fluid-absent conditions are typical of most granulites at or near the time of their recorded thermal maxima. ITD granulites are interpreted to have formed in crust thickened by collision, with magmatic additions being an important extra heat source. Erosion alone is not, however, considered to be the dominant post-collisional thinning process. Instead, the ITD paths are generated during more rapid thinning (1−2 mm/yr exposure) related to tectonic exhumation during moderate-rate or waning extension. IBC granulites may have formed in a variety of settings. Those which show anticlockwise P – T histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion, with or without additional crustal extension. IBC granulites at shallow levels (< 5 kbar) may also be formed during extension of normal thickness crust, but deeper-level IBC requires more complex models. Many granulites exhibiting IBC at deep crustal levels may have formed in thickened crust which underwent very rapid (5 mm/yr) extensional thinning subsequent to collision. It is suggested that the preservation of IBC paths rather than ITD paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust, and that hybrid ITD to IBC paths should also be observed. Most IBC granulites, and probably many ITD granulites, have not been exposed at the Earth's surface as a result of the tectonic episodes which produced them, but have resided in the middle and lower crust for long periods of time (100−2000 Ma) following these events. The eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation.

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  • Granulite-facies metamorphism is ubiquitous throughout the rock record and occurs prominently in Archean terranes.

    “Granulite-facies metamorphism is ubiquitous throughout the rock record (Fig. 8a) and occurs prominently in Archean terranes”

    From Secular change and the onset of plate tectonics on Earth (2020) · cites this paper as Harley, 1989

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Authors
Harley, S. L.
Affiliations
University of Oxford (GB)
Corresponding author
Harley, S. L.
ORCID
Harley, S. L.
Venue
Geological Magazine
Publisher
Cambridge University Press (CUP)
Published
1989-05
Volume
126
Issue
3
Pages
215-247
ISSN
  • 0016-7568 (ISSN-L)
  • 1469-5081
DOI
10.1017/s0016756800022330
OpenAlex
W2008691821
Cited by
1,042
References
124
Citations by year
2026: 27 · 2025: 25 · 2024: 39 · 2023: 42 · 2022: 45 · 2021: 40 · 2020: 47 · 2019: 36 · 2018: 32 · 2017: 50 · 2016: 35 · 2015: 19 · 2014: 33 · 2013: 21 · 2012: 25
FWCI
13.82
Type
journal article
Language
en
Open access
closed
Licence
www.cambridge.org/core/terms (unspecified, 7305 d)
Locations
Geological Magazine (publishedVersion)
Topics
  • Physical Sciences › Earth and Planetary Sciences › Geophysics › Geological and Geochemical Analysis
  • Physical Sciences › Earth and Planetary Sciences › Geochemistry and Petrology › Geochemistry and Elemental Analysis
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astro and Planetary Science
Keywords
granulite, pressure-temperature conditions, CO2-rich fluids, crustal thickening, magmatic accretion, tectonic exhumation

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