Fluid processes in the early Earth and the growth of continents

Hartnady, Michael I.H.; Johnson, Tim; Schorn, Simon; Smithies, R. Hugh; Kirkland, Christopher L.; Richardson, Stephen H.

doi:10.1016/j.epsl.2022.117695

Cited by 13 publications

(11 citation statements)

References 46 publications

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“…Above the wet basalt solidus, tremolite and chlorite breakdown release a further 5 wt.% H 2 O across a temperature range of 670 to 800 • C (Figs. 5, 9), comparable with estimates of water release from metamorphosed komatiites from Hartnady et al (2022) of approximately 20 vol.%. The experimental constraints of Mg-chlorite breakdown are also shown, to represent the maximum thermal stability of chlorite (Staudigel and Schreyer, 1977;Jenkins, 1981;Lakey and Hermann, 2022).…”

Section: Komatiites Can Transport and Release Water Into The Crust To...supporting

confidence: 74%

“…However, one could envisage that hydrated komatiite-basalt associations (i.e., greenstone belts) were thickened in an oceanic plateau style setting, or underthrust in a hot subduction style setting, to reach temperatures of 670-800 • C for komatiite dehydration and wet basalt melting (e.g. Hartnady et al, 2022). The subsequent magmas have TTG-compositions, and most likely formed the Archean continental crust.…”

Section: Komatiites Can Transport and Release Water Into The Crust To...mentioning

confidence: 99%

“…As amphibolite-facies metabasalt itself cannot provide the amount of free water needed at these conditions, various tectonic mechanisms for transport of fluid to the deep crust have been suggested to trigger wet basalt melting, including modern-style subduction (e.g., Laurie and Stevens, 2012). Nevertheless, the source of free fluid at lower crustal conditions in the Archean has remained elusive, with the suggestion that hydrated ultramafic rocks like komatiites may hold the key (Hartnady et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

“…Recently, it has been suggested from mineral equilibria modelling that high-MgO mafic rocks, including komatiites, from greenstone belts may have played a critical role in the capture and release of water during prograde metamorphism in the Archean, leading to the formation of TTGs (Hartnady et al, 2022). In this study we combine data from the petrology and phase equilibria modelling of a representative komatiite from the Barberton Greenstone belt, the mineral chemistry of metamorphosed komatiite samples from key greenstone belts worldwide, and a global compilation of geochemical data from 5589 komatiites and komatiitic basalts (Fig.…”

Section: Introductionmentioning

confidence: 99%

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Hydrated komatiites as a source of water for TTG formation in the Archean

Hermann¹,

Tamblyn²,

Hasterok

et al. 2023

Preprint

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Water plays a crucial role in the formation of new crust on modern Earth. Today, new continental crust is created through arc magmatism by fluid-fluxed mantle melting above subduction zones. The aqueous fluid is derived from the breakdown of hydrous phases in subducted oceanic crust as a result of a delicate interplay between phase stability and the cold thermal conditions in the slab. Hydrated and subducted ultramafic (mantle) rocks play a key role in supplying the water needed for wet mantle melting and provide an important link between the Earth&#8217;s deep water cycle and formation of crust with an average andesitic composition. Archean felsic crust consists of the typical Tonalite-Trondhjemite-Granite (TTG) Series, which were likely produced from melting of altered basaltic precursors. Previous studies suggest that the water-present partial melting of metamorphosed basalt at temperatures of 750&#8211;950 &#176;C is required to produce large volumes of partial melt with TTG compositions. However, the source of such water is unknown and exposed serpentinised mantle rocks likely played a negligible role in the early Earth&#8217;s water cycle. We propose that hydrated komatiites played a vital role in TTG genesis. Using petrology, mineral chemistry and phase equilibria modelling of representative komatiite samples, combined with analysis of a global geochemical dataset of komatiites and basaltic komatiites, we show that during metamorphism hydrated komatiites can release at least 6 wt. % mineral-bound water. The great majority of this water is released by breakdown of chlorite and tremolite at temperatures between 680 and 800 &#176;C. As the temperatures of komatiite dehydration are above the wet basalt solidus, the released water can trigger voluminous partial melting of basalt to ultimately create TTG batholiths. This considerable hydration potential of komatiites is due to their high XMg, which stabilises hydrous minerals during oceanic alteration on the seafloor, but also extends the stability of Mg-rich chlorite to high temperatures. During prograde metamorphism, the XMg, CaO and Al2O3 content of the reactive rock composition determines the proportion of chlorite vs amphibole, and therefore the volume of water which can be transported to temperatures of > 750 &#176;C. Therefore, we suggest that water released from dehydrating komatiites - regardless of the prograde P&#8211;T path (i.e., tectonic scenario) they experienced - provided the free water necessary to partially melt large volumes of basalts to form the prominent and expansive TTG suits in the Archean. Even though komatiites make up moderate portions of greenstone belts, they thus likely played a key role in early crustal formation and the Earths&#8217; early water cycle.

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Section: Komatiites Can Transport and Release Water Into The Crust To...supporting

confidence: 74%

Section: Komatiites Can Transport and Release Water Into The Crust To...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Hydrated komatiites as a source of water for TTG formation in the Archean

Hermann¹,

Tamblyn²,

Hasterok

et al. 2023

Preprint

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“…Basaltic komatiite and komatiite have a strong ability to preserve water (Hartnady et al., 2022; Tamblyn et al., 2023). Most komatiitic rocks are erupted underwater and thus undergo interaction with seawater, as evidenced by the pillow structures of komatiitic rocks (e.g., Arndt et al., 2008).…”

Section: Discussionmentioning

confidence: 99%

Decoupled Zircon Si–O Isotopes Tracing the Supracrustal Silicification and Komatiitic‐Derived Fluids in the Source of TTGs

Lei,

Wang,

Wang

et al. 2023

Geophysical Research Letters

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The tonalite–trondhjemite–granodiorite suites (TTGs) are key components of the Archean continental crust and therefore crucial to the understanding of the evolution of the early Earth. Here, we present in situ zircon Si–O isotope data of TTGs from Barberton. Results show that the 3.45–3.42 Ga (Group 1) and 3.24–3.23 Ga TTGs (Group 2) have elevated δ30Simelt values but mantle‐like δ18Ozrc values, whereas the 3.23–3.22 Ga TTGs (Group 3) have coupled elevated δ30Simelt and δ18Ozrc values relative to mantle‐derived rocks. We suggest that the Group 1 and 2 TTGs had a silicified source that was affected by low‐δ18O fluid released from the komatiitic rocks. The low‐δ18O fluid decreased the δ18Ozrc values of Group 1 and 2 TTGs but had negligible influence on their δ30Simelt values. The Group 3 TTGs were generated solely from the silicified source, as the low‐δ18O fluid had become exhausted at that time.

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