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Article: Earth's Earliest Phaneritic Ultramafic Rocks: Mantle Slices or Crustal Cumulates?

TitleEarth's Earliest Phaneritic Ultramafic Rocks: Mantle Slices or Crustal Cumulates?
Authors
Keywordsgeochemistry
Isua
petrogenesis
Pilbara
tectonics
ultramafic rocks
Issue Date1-Dec-2022
PublisherWiley Open Access
Citation
Geochemistry, Geophysics, Geosystems, 2022, v. 23, n. 12 How to Cite?
Abstract

When plate tectonics initiated remains uncertain, partly because many signals interpreted as diagnostic of plate tectonics can be alternatively explained via hot stagnant-lid tectonics. One such signal involves the petrogenesis of early Archean phaneritic ultramafic rocks. In the Eoarchean Isua supracrustal belt (Greenland), some phaneritic ultramafic rocks have been dominantly interpreted as subduction-related, tectonically-exhumed mantle slices or cumulates. Here, we compared Eoarchean phaneritic ultramafic rocks from the Isua supracrustal belt with mantle peridotites, cumulates, and phaneritic ultramafic samples from the Paleoarchean East Pilbara Terrane (Australia), which is widely interpreted to have formed in non-plate tectonic settings. Our findings show that Pilbara samples have cumulate and polygonal textures, melt-enriched trace element patterns, relative enrichment of Os, Ir, and Ru versus Pt and Pd, and chromite-spinel with variable TiO2 and Mg#, and relatively consistent Cr#. Both, new and existing data show that cumulates and mantle rocks potentially have similar whole-rock geochemical characteristics, deformation fabrics, and alteration features. Geochemical modeling results indicate that Isua and Pilbara ultramafic rocks have interacted with low-Pt and Pd melts generated by sequestration of Pd and Pt into sulphide and/or alloy during magmatism. Such melts cannot have interacted with a mantle wedge. Correspondingly, geochemical compositions and rock textures suggest that Isua and Pilbara ultramafic rocks are not tectonically-exhumed mantle peridotites, but are cumulates that experienced metasomatism by fluids and co-genetic melts. Because such rocks could have formed in either plate or non-plate tectonic settings, they cannot be used to differentiate early Earth tectonic settings.


Persistent Identifierhttp://hdl.handle.net/10722/331144
ISSN
2023 Impact Factor: 2.9
2023 SCImago Journal Rankings: 1.457
ISI Accession Number ID

 

DC FieldValueLanguage
dc.contributor.authorZuo, JW-
dc.contributor.authorWebb, AAG-
dc.contributor.authorChin, EJ-
dc.contributor.authorAckerman, L-
dc.contributor.authorHarvey, J-
dc.contributor.authorHaproff, PJ-
dc.contributor.authorMuller, T-
dc.contributor.authorWang, Q-
dc.contributor.authorHickman, AH-
dc.contributor.authorSorger, D-
dc.contributor.authorRamirez-Salazar, A-
dc.date.accessioned2023-09-21T06:53:07Z-
dc.date.available2023-09-21T06:53:07Z-
dc.date.issued2022-12-01-
dc.identifier.citationGeochemistry, Geophysics, Geosystems, 2022, v. 23, n. 12-
dc.identifier.issn1525-2027-
dc.identifier.urihttp://hdl.handle.net/10722/331144-
dc.description.abstract<p>When plate tectonics initiated remains uncertain, partly because many signals interpreted as diagnostic of plate tectonics can be alternatively explained via hot stagnant-lid tectonics. One such signal involves the petrogenesis of early Archean phaneritic ultramafic rocks. In the Eoarchean Isua supracrustal belt (Greenland), some phaneritic ultramafic rocks have been dominantly interpreted as subduction-related, tectonically-exhumed mantle slices or cumulates. Here, we compared Eoarchean phaneritic ultramafic rocks from the Isua supracrustal belt with mantle peridotites, cumulates, and phaneritic ultramafic samples from the Paleoarchean East Pilbara Terrane (Australia), which is widely interpreted to have formed in non-plate tectonic settings. Our findings show that Pilbara samples have cumulate and polygonal textures, melt-enriched trace element patterns, relative enrichment of Os, Ir, and Ru versus Pt and Pd, and chromite-spinel with variable TiO<sub>2</sub> and Mg#, and relatively consistent Cr#. Both, new and existing data show that cumulates and mantle rocks potentially have similar whole-rock geochemical characteristics, deformation fabrics, and alteration features. Geochemical modeling results indicate that Isua and Pilbara ultramafic rocks have interacted with low-Pt and Pd melts generated by sequestration of Pd and Pt into sulphide and/or alloy during magmatism. Such melts cannot have interacted with a mantle wedge. Correspondingly, geochemical compositions and rock textures suggest that Isua and Pilbara ultramafic rocks are not tectonically-exhumed mantle peridotites, but are cumulates that experienced metasomatism by fluids and co-genetic melts. Because such rocks could have formed in either plate or non-plate tectonic settings, they cannot be used to differentiate early Earth tectonic settings.<br></p>-
dc.languageeng-
dc.publisherWiley Open Access-
dc.relation.ispartofGeochemistry, Geophysics, Geosystems-
dc.rightsThis work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.-
dc.subjectgeochemistry-
dc.subjectIsua-
dc.subjectpetrogenesis-
dc.subjectPilbara-
dc.subjecttectonics-
dc.subjectultramafic rocks-
dc.titleEarth's Earliest Phaneritic Ultramafic Rocks: Mantle Slices or Crustal Cumulates?-
dc.typeArticle-
dc.description.naturepublished_or_final_version-
dc.identifier.doi10.1029/2022GC010519-
dc.identifier.scopuseid_2-s2.0-85145020677-
dc.identifier.volume23-
dc.identifier.issue12-
dc.identifier.eissn1525-2027-
dc.identifier.isiWOS:000924664300001-
dc.identifier.issnl1525-2027-

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