Fluid processes in the early Earth and the growth of continents
Water is an essential ingredient in transforming primitive mantle-derived (mafic) rocks into buoyant (felsic) continental crust, thereby driving the irreversible differentiation of Earth's lithosphere. The occurrence in Archaean cratons of sodic granites of the tonalite–trondhjemite–granodiorit...
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| Format: | Journal Article |
| Language: | English |
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ELSEVIER
2022
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| Online Access: | http://purl.org/au-research/grants/arc/DP200101104 http://hdl.handle.net/20.500.11937/90818 |
| _version_ | 1848765437109600256 |
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| author | Hartnady, Michael Johnson, Tim Schorn, S. Hugh Smithies, R. Kirkland, Christopher Richardson, S.H. |
| author_facet | Hartnady, Michael Johnson, Tim Schorn, S. Hugh Smithies, R. Kirkland, Christopher Richardson, S.H. |
| author_sort | Hartnady, Michael |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | Water is an essential ingredient in transforming primitive mantle-derived (mafic) rocks into buoyant (felsic) continental crust, thereby driving the irreversible differentiation of Earth's lithosphere. The occurrence in Archaean cratons of sodic granites of the tonalite–trondhjemite–granodiorite (TTG) series, high-MgO variolitic basalts, high-Mg diorites (sanukitoids) and diamonds with harzburgitic inclusion assemblages, all require the presence of hydrous fluids in Earth's deep crust and upper (lithospheric) mantle since at least the Paleoarchaean (3.6–3.2 billion years ago). However, despite its importance, where and how water was stored in Archaean crust, and how some water was transported into the upper mantle, are poorly understood. Here, we investigate Archaean crustal fluid budgets through calculated phase equilibria for three protolith compositions — a low-MgO mafic (basaltic) composition, a high-MgO (picritic) composition and an ultrahigh-MgO ultramafic (komatiitic) composition — that are representative of mafic to ultramafic magmatic rocks in Archaean greenstone belts. We show that the mode and stability of hydrous minerals, in particular chlorite, is positively correlated with protolith MgO content, such that high-MgO basalts can store up to twice the amount of crystal-bound H2O than low-MgO basalts. Importantly, ultrahigh-MgO rocks such as komatiite can store four times as much H2O, most of which is retained until temperatures exceeding 700 °C. Warmer geotherms in the early Archaean favoured dehydration of hydrated high-MgO and ultramafic rocks in the deep crust, leading to hydration and/or fluid-fluxed melting of overlying basaltic rocks to produce ‘high-pressure’ TTG magmas. Burial of Archaean mafic–ultramafic crust along cooler geotherms resulted in dehydration of ultramafic material within the lithospheric mantle, providing the source of enriched Archaean basalt that was parental to large volumes of ancient TTG-dominated continental crust. |
| first_indexed | 2025-11-14T11:35:14Z |
| format | Journal Article |
| id | curtin-20.500.11937-90818 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| language | English |
| last_indexed | 2025-11-14T11:35:14Z |
| publishDate | 2022 |
| publisher | ELSEVIER |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-908182023-04-24T04:53:00Z Fluid processes in the early Earth and the growth of continents Hartnady, Michael Johnson, Tim Schorn, S. Hugh Smithies, R. Kirkland, Christopher Richardson, S.H. Science & Technology Physical Sciences Geochemistry & Geophysics fluid processes komatiite tonalite-trondhjemite-granodiorite (TTG) Archaean crustal evolution ISUA SUPRACRUSTAL BELT OXYGEN ISOTOPES ARCHEAN CRUST ORIGIN SUBDUCTION ROCKS PETROGENESIS METAMORPHISM AMPHIBOLITE GENERATION Water is an essential ingredient in transforming primitive mantle-derived (mafic) rocks into buoyant (felsic) continental crust, thereby driving the irreversible differentiation of Earth's lithosphere. The occurrence in Archaean cratons of sodic granites of the tonalite–trondhjemite–granodiorite (TTG) series, high-MgO variolitic basalts, high-Mg diorites (sanukitoids) and diamonds with harzburgitic inclusion assemblages, all require the presence of hydrous fluids in Earth's deep crust and upper (lithospheric) mantle since at least the Paleoarchaean (3.6–3.2 billion years ago). However, despite its importance, where and how water was stored in Archaean crust, and how some water was transported into the upper mantle, are poorly understood. Here, we investigate Archaean crustal fluid budgets through calculated phase equilibria for three protolith compositions — a low-MgO mafic (basaltic) composition, a high-MgO (picritic) composition and an ultrahigh-MgO ultramafic (komatiitic) composition — that are representative of mafic to ultramafic magmatic rocks in Archaean greenstone belts. We show that the mode and stability of hydrous minerals, in particular chlorite, is positively correlated with protolith MgO content, such that high-MgO basalts can store up to twice the amount of crystal-bound H2O than low-MgO basalts. Importantly, ultrahigh-MgO rocks such as komatiite can store four times as much H2O, most of which is retained until temperatures exceeding 700 °C. Warmer geotherms in the early Archaean favoured dehydration of hydrated high-MgO and ultramafic rocks in the deep crust, leading to hydration and/or fluid-fluxed melting of overlying basaltic rocks to produce ‘high-pressure’ TTG magmas. Burial of Archaean mafic–ultramafic crust along cooler geotherms resulted in dehydration of ultramafic material within the lithospheric mantle, providing the source of enriched Archaean basalt that was parental to large volumes of ancient TTG-dominated continental crust. 2022 Journal Article http://hdl.handle.net/20.500.11937/90818 10.1016/j.epsl.2022.117695 English http://purl.org/au-research/grants/arc/DP200101104 http://purl.org/au-research/grants/arc/LP180100199 http://creativecommons.org/licenses/by-nc/4.0/ ELSEVIER fulltext |
| spellingShingle | Science & Technology Physical Sciences Geochemistry & Geophysics fluid processes komatiite tonalite-trondhjemite-granodiorite (TTG) Archaean crustal evolution ISUA SUPRACRUSTAL BELT OXYGEN ISOTOPES ARCHEAN CRUST ORIGIN SUBDUCTION ROCKS PETROGENESIS METAMORPHISM AMPHIBOLITE GENERATION Hartnady, Michael Johnson, Tim Schorn, S. Hugh Smithies, R. Kirkland, Christopher Richardson, S.H. Fluid processes in the early Earth and the growth of continents |
| title | Fluid processes in the early Earth and the growth of continents |
| title_full | Fluid processes in the early Earth and the growth of continents |
| title_fullStr | Fluid processes in the early Earth and the growth of continents |
| title_full_unstemmed | Fluid processes in the early Earth and the growth of continents |
| title_short | Fluid processes in the early Earth and the growth of continents |
| title_sort | fluid processes in the early earth and the growth of continents |
| topic | Science & Technology Physical Sciences Geochemistry & Geophysics fluid processes komatiite tonalite-trondhjemite-granodiorite (TTG) Archaean crustal evolution ISUA SUPRACRUSTAL BELT OXYGEN ISOTOPES ARCHEAN CRUST ORIGIN SUBDUCTION ROCKS PETROGENESIS METAMORPHISM AMPHIBOLITE GENERATION |
| url | http://purl.org/au-research/grants/arc/DP200101104 http://purl.org/au-research/grants/arc/DP200101104 http://hdl.handle.net/20.500.11937/90818 |