Mafic Archean continental crust prohibited exhumation of orogenic UHP eclogite
The absence of ultrahigh pressure (UHP) orogenic eclogite in the geological record older than c. 0.6 Ga is problematic for evidence of subduction having begun on Earth during the Archean (4.0–2.5 Ga). Many eclogites in Phanerozoic and Proterozoic terranes occur as mafic boudins encased within low-de...
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sg-ntu-dr.10356-1535342021-12-11T20:11:11Z Mafic Archean continental crust prohibited exhumation of orogenic UHP eclogite Palin, Richard.M. Moore, James Daniel Paul Zhang, Zeming Huang, Guangyu Wade, Jon Dyck, Brendan Earth Observatory of Singapore Science::Geology Archean Eclogite The absence of ultrahigh pressure (UHP) orogenic eclogite in the geological record older than c. 0.6 Ga is problematic for evidence of subduction having begun on Earth during the Archean (4.0–2.5 Ga). Many eclogites in Phanerozoic and Proterozoic terranes occur as mafic boudins encased within low-density felsic crust, which provides positive buoyancy during subduction; however, recent geochemical proxy analysis shows that Archean continental crust was more mafic than previously thought, having greater proportions of basalt and komatiite than modern-day continents. Here, we show via petrological modelling that secular change in the petrology and bulk composition of upper continental crust would make Archean continental terranes negatively buoyant in the mantle before reaching UHP conditions. Subducted or delaminated Archean continental crust passes a point of no return during metamorphism in the mantle prior to the stabilization of coesite, while Proterozoic and Phanerozoic terranes remain positively buoyant at these depths. UHP orogenic eclogite may thus readily have formed on the Archean Earth, but could not have been exhumed, weakening arguments for a Neoproterozoic onset of subduction and plate tectonics. Further, isostatic balance calculations for more mafic Archean continents indicate that the early Earth was covered by a global ocean over 1 km deep, corroborating independent isotopic evidence for large-scale emergence of the continents no earlier than c. 3 Ga. Our findings thus weaken arguments that early life on Earth likely emerged in shallow subaerial ponds, and instead support hypotheses involving development at hydrothermal vents in the deep ocean. Published version The authors are grateful for comments on earlier version of thiswork by Clare Warren, Alan Hastie, and Daniel Wiemer, and formalcomments on this most recent version by two anonymous review-ers. JDPM acknowledges support from Marsden grant 14-VUW-085, Royal Society of New Zealand. Codes for reproducing the iso-static balance calculation and yield strength envelopes may befound at www.jamesdpmoore.com 2021-12-07T07:29:25Z 2021-12-07T07:29:25Z 2021 Journal Article Palin, R., Moore, J. D. P., Zhang, Z., Huang, G., Wade, J. & Dyck, B. (2021). Mafic Archean continental crust prohibited exhumation of orogenic UHP eclogite. Geoscience Frontiers, 12(5), 101225-. https://dx.doi.org/10.1016/j.gsf.2021.101225 1674-9871 https://hdl.handle.net/10356/153534 10.1016/j.gsf.2021.101225 2-s2.0-85107692227 5 12 101225 en Geoscience Frontiers ©2021 China University of Geosciences (Beijing) and Peking University. Production and hosting byElsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) application/pdf |
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Science::Geology Archean Eclogite Palin, Richard.M. Moore, James Daniel Paul Zhang, Zeming Huang, Guangyu Wade, Jon Dyck, Brendan Mafic Archean continental crust prohibited exhumation of orogenic UHP eclogite |
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The absence of ultrahigh pressure (UHP) orogenic eclogite in the geological record older than c. 0.6 Ga is problematic for evidence of subduction having begun on Earth during the Archean (4.0–2.5 Ga). Many eclogites in Phanerozoic and Proterozoic terranes occur as mafic boudins encased within low-density felsic crust, which provides positive buoyancy during subduction; however, recent geochemical proxy analysis shows that Archean continental crust was more mafic than previously thought, having greater proportions of basalt and komatiite than modern-day continents. Here, we show via petrological modelling that secular change in the petrology and bulk composition of upper continental crust would make Archean continental terranes negatively buoyant in the mantle before reaching UHP conditions. Subducted or delaminated Archean continental crust passes a point of no return during metamorphism in the mantle prior to the stabilization of coesite, while Proterozoic and Phanerozoic terranes remain positively buoyant at these depths. UHP orogenic eclogite may thus readily have formed on the Archean Earth, but could not have been exhumed, weakening arguments for a Neoproterozoic onset of subduction and plate tectonics. Further, isostatic balance calculations for more mafic Archean continents indicate that the early Earth was covered by a global ocean over 1 km deep, corroborating independent isotopic evidence for large-scale emergence of the continents no earlier than c. 3 Ga. Our findings thus weaken arguments that early life on Earth likely emerged in shallow subaerial ponds, and instead support hypotheses involving development at hydrothermal vents in the deep ocean. |
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Earth Observatory of Singapore |
author_facet |
Earth Observatory of Singapore Palin, Richard.M. Moore, James Daniel Paul Zhang, Zeming Huang, Guangyu Wade, Jon Dyck, Brendan |
format |
Article |
author |
Palin, Richard.M. Moore, James Daniel Paul Zhang, Zeming Huang, Guangyu Wade, Jon Dyck, Brendan |
author_sort |
Palin, Richard.M. |
title |
Mafic Archean continental crust prohibited exhumation of orogenic UHP eclogite |
title_short |
Mafic Archean continental crust prohibited exhumation of orogenic UHP eclogite |
title_full |
Mafic Archean continental crust prohibited exhumation of orogenic UHP eclogite |
title_fullStr |
Mafic Archean continental crust prohibited exhumation of orogenic UHP eclogite |
title_full_unstemmed |
Mafic Archean continental crust prohibited exhumation of orogenic UHP eclogite |
title_sort |
mafic archean continental crust prohibited exhumation of orogenic uhp eclogite |
publishDate |
2021 |
url |
https://hdl.handle.net/10356/153534 |
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1718928691631751168 |