Geochemical evidence for subduction in the early Archaean from quartz-carbonate-fuchsite mineralization, Isua Supracrustal Belt, West Greenland: AGU2011 U13A-0036

Emily Catherine Pope; Minik Thorleif Rosing; Dennis K. Bird

Abstract

Quartz, carbonate and fuchsite (chromian muscovite) is a common metasomatic assemblage observed in orogenic gold systems, both in Phanerozoic convergent margin settings, and within supracrustal and greenstone belts of Precambrian rocks. Geologic and geochemical observations in younger orogenic systems suggest that ore-forming metasomatic fluids are derived from subduction-related devolitilization reactions, implying that orogenic Au-deposits in Archaean and Proterozoic supracrustal rock suites are related to subduction-style plate tectonics beginning early in Earth history. Justification of this metasomatic-tectonic relationship requires that 1) Phanerozoic orogenic Au-deposits form in subduction-zone environments, and 2) the geochemical similarity of Precambrian orogenic deposits to their younger counterparts is the result of having the same petrogenetic origin. Hydrogen and oxygen isotope compositions of fuchsite and quartz from auriferous mineralization in the ca. 3.8 Ga Isua Supracrustal Belt (ISB) in West Greenland, in conjunction with elevated concentrations of CO2, Cr, Al, K and silica relative to protolith assemblages, suggest that this mineralization shares a common petro-tectonic origin with Phanerozoic orogenic deposits and that this type of metasomatism is a unique result of subduction-related processes. Fuchsite from the ISB has a δ¹⁸O and δD of 7.7 to 17.9‰ and -115 to -61‰, respectively. δ¹⁸O of quartz from the same rocks is between 10.3 and 18.6‰. Muscovite-quartz oxygen isotope thermometry indicates that the mineralization occurred at 560 ± 90oC, from fluids with a δD of -73 to -49‰ and δ¹⁸O of 8.8 to 17.2‰. Calculation of isotopic fractionation during fluid-rock reactions along hypothetical fluid pathways demonstrates that these values, as well as those in younger orogenic deposits, are the result of seawater-derived fluids liberated from subducting lithosphere interacting with ultramafic rocks in the mantle wedge and lower crust, before migrating up crustal-scale vertical fracture zones. Thus, the presence of quartz-carbonate-fuchsite mineralization in the Isua supracrustal belt and other Archaean-age deposits provides strong evidence for the existence of modern-style subduction as early as 3.8 Ga.

Original language	English
Publication date	2011
Number of pages	1
Publication status	Published - 2011
Event	American Geophysical Union Fall Meeting - San Francisco, United States Duration: 5 Dec 2011 → 9 Dec 2011

Conference

Conference	American Geophysical Union Fall Meeting
Country/Territory	United States
City	San Francisco
Period	05/12/2011 → 09/12/2011

Keywords

Faculty of Science
subduction zone processes
stable isotope geochemistry
evolution of the Earth
Archean

Access to Document

http://abstractsearch.agu.org/meetings/2011/FM/sections/U/sessions/U13A/abstracts/U13A-0036.html

Cite this

Pope, E. C., Rosing, M. T., & Bird, D. K. (2011). Geochemical evidence for subduction in the early Archaean from quartz-carbonate-fuchsite mineralization, Isua Supracrustal Belt, West Greenland: AGU2011 U13A-0036. Abstract from American Geophysical Union Fall Meeting, San Francisco, United States. http://abstractsearch.agu.org/meetings/2011/FM/sections/U/sessions/U13A/abstracts/U13A-0036.html

Geochemical evidence for subduction in the early Archaean from quartz-carbonate-fuchsite mineralization, Isua Supracrustal Belt, West Greenland : AGU2011 U13A-0036. / Pope, Emily Catherine; Rosing, Minik Thorleif; Bird, Dennis K.

2011. Abstract from American Geophysical Union Fall Meeting, San Francisco, United States.

Research output: Contribution to conference › Conference abstract for conference › Research

Pope, EC, Rosing, MT & Bird, DK 2011, 'Geochemical evidence for subduction in the early Archaean from quartz-carbonate-fuchsite mineralization, Isua Supracrustal Belt, West Greenland: AGU2011 U13A-0036', American Geophysical Union Fall Meeting, San Francisco, United States, 05/12/2011 - 09/12/2011. <http://abstractsearch.agu.org/meetings/2011/FM/sections/U/sessions/U13A/abstracts/U13A-0036.html>

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title = "Geochemical evidence for subduction in the early Archaean from quartz-carbonate-fuchsite mineralization, Isua Supracrustal Belt, West Greenland: AGU2011 U13A-0036",

abstract = "Quartz, carbonate and fuchsite (chromian muscovite) is a common metasomatic assemblage observed in orogenic gold systems, both in Phanerozoic convergent margin settings, and within supracrustal and greenstone belts of Precambrian rocks. Geologic and geochemical observations in younger orogenic systems suggest that ore-forming metasomatic fluids are derived from subduction-related devolitilization reactions, implying that orogenic Au-deposits in Archaean and Proterozoic supracrustal rock suites are related to subduction-style plate tectonics beginning early in Earth history. Justification of this metasomatic-tectonic relationship requires that 1) Phanerozoic orogenic Au-deposits form in subduction-zone environments, and 2) the geochemical similarity of Precambrian orogenic deposits to their younger counterparts is the result of having the same petrogenetic origin. Hydrogen and oxygen isotope compositions of fuchsite and quartz from auriferous mineralization in the ca. 3.8 Ga Isua Supracrustal Belt (ISB) in West Greenland, in conjunction with elevated concentrations of CO2, Cr, Al, K and silica relative to protolith assemblages, suggest that this mineralization shares a common petro-tectonic origin with Phanerozoic orogenic deposits and that this type of metasomatism is a unique result of subduction-related processes. Fuchsite from the ISB has a δ18O and δD of 7.7 to 17.9‰ and -115 to -61‰, respectively. δ18O of quartz from the same rocks is between 10.3 and 18.6‰. Muscovite-quartz oxygen isotope thermometry indicates that the mineralization occurred at 560 ± 90oC, from fluids with a δD of -73 to -49‰ and δ18O of 8.8 to 17.2‰. Calculation of isotopic fractionation during fluid-rock reactions along hypothetical fluid pathways demonstrates that these values, as well as those in younger orogenic deposits, are the result of seawater-derived fluids liberated from subducting lithosphere interacting with ultramafic rocks in the mantle wedge and lower crust, before migrating up crustal-scale vertical fracture zones. Thus, the presence of quartz-carbonate-fuchsite mineralization in the Isua supracrustal belt and other Archaean-age deposits provides strong evidence for the existence of modern-style subduction as early as 3.8 Ga.",

keywords = "Faculty of Science, subduction zone processes, stable isotope geochemistry, evolution of the Earth, Archean",

author = "Pope, {Emily Catherine} and Rosing, {Minik Thorleif} and Bird, {Dennis K.}",

year = "2011",

language = "English",

note = "American Geophysical Union Fall Meeting, AGU2011 ; Conference date: 05-12-2011 Through 09-12-2011",

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T1 - Geochemical evidence for subduction in the early Archaean from quartz-carbonate-fuchsite mineralization, Isua Supracrustal Belt, West Greenland

T2 - American Geophysical Union Fall Meeting

AU - Pope, Emily Catherine

AU - Rosing, Minik Thorleif

AU - Bird, Dennis K.

PY - 2011

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N2 - Quartz, carbonate and fuchsite (chromian muscovite) is a common metasomatic assemblage observed in orogenic gold systems, both in Phanerozoic convergent margin settings, and within supracrustal and greenstone belts of Precambrian rocks. Geologic and geochemical observations in younger orogenic systems suggest that ore-forming metasomatic fluids are derived from subduction-related devolitilization reactions, implying that orogenic Au-deposits in Archaean and Proterozoic supracrustal rock suites are related to subduction-style plate tectonics beginning early in Earth history. Justification of this metasomatic-tectonic relationship requires that 1) Phanerozoic orogenic Au-deposits form in subduction-zone environments, and 2) the geochemical similarity of Precambrian orogenic deposits to their younger counterparts is the result of having the same petrogenetic origin. Hydrogen and oxygen isotope compositions of fuchsite and quartz from auriferous mineralization in the ca. 3.8 Ga Isua Supracrustal Belt (ISB) in West Greenland, in conjunction with elevated concentrations of CO2, Cr, Al, K and silica relative to protolith assemblages, suggest that this mineralization shares a common petro-tectonic origin with Phanerozoic orogenic deposits and that this type of metasomatism is a unique result of subduction-related processes. Fuchsite from the ISB has a δ18O and δD of 7.7 to 17.9‰ and -115 to -61‰, respectively. δ18O of quartz from the same rocks is between 10.3 and 18.6‰. Muscovite-quartz oxygen isotope thermometry indicates that the mineralization occurred at 560 ± 90oC, from fluids with a δD of -73 to -49‰ and δ18O of 8.8 to 17.2‰. Calculation of isotopic fractionation during fluid-rock reactions along hypothetical fluid pathways demonstrates that these values, as well as those in younger orogenic deposits, are the result of seawater-derived fluids liberated from subducting lithosphere interacting with ultramafic rocks in the mantle wedge and lower crust, before migrating up crustal-scale vertical fracture zones. Thus, the presence of quartz-carbonate-fuchsite mineralization in the Isua supracrustal belt and other Archaean-age deposits provides strong evidence for the existence of modern-style subduction as early as 3.8 Ga.

AB - Quartz, carbonate and fuchsite (chromian muscovite) is a common metasomatic assemblage observed in orogenic gold systems, both in Phanerozoic convergent margin settings, and within supracrustal and greenstone belts of Precambrian rocks. Geologic and geochemical observations in younger orogenic systems suggest that ore-forming metasomatic fluids are derived from subduction-related devolitilization reactions, implying that orogenic Au-deposits in Archaean and Proterozoic supracrustal rock suites are related to subduction-style plate tectonics beginning early in Earth history. Justification of this metasomatic-tectonic relationship requires that 1) Phanerozoic orogenic Au-deposits form in subduction-zone environments, and 2) the geochemical similarity of Precambrian orogenic deposits to their younger counterparts is the result of having the same petrogenetic origin. Hydrogen and oxygen isotope compositions of fuchsite and quartz from auriferous mineralization in the ca. 3.8 Ga Isua Supracrustal Belt (ISB) in West Greenland, in conjunction with elevated concentrations of CO2, Cr, Al, K and silica relative to protolith assemblages, suggest that this mineralization shares a common petro-tectonic origin with Phanerozoic orogenic deposits and that this type of metasomatism is a unique result of subduction-related processes. Fuchsite from the ISB has a δ18O and δD of 7.7 to 17.9‰ and -115 to -61‰, respectively. δ18O of quartz from the same rocks is between 10.3 and 18.6‰. Muscovite-quartz oxygen isotope thermometry indicates that the mineralization occurred at 560 ± 90oC, from fluids with a δD of -73 to -49‰ and δ18O of 8.8 to 17.2‰. Calculation of isotopic fractionation during fluid-rock reactions along hypothetical fluid pathways demonstrates that these values, as well as those in younger orogenic deposits, are the result of seawater-derived fluids liberated from subducting lithosphere interacting with ultramafic rocks in the mantle wedge and lower crust, before migrating up crustal-scale vertical fracture zones. Thus, the presence of quartz-carbonate-fuchsite mineralization in the Isua supracrustal belt and other Archaean-age deposits provides strong evidence for the existence of modern-style subduction as early as 3.8 Ga.

KW - Faculty of Science

KW - subduction zone processes

KW - stable isotope geochemistry

KW - evolution of the Earth

KW - Archean

M3 - Conference abstract for conference

Y2 - 5 December 2011 through 9 December 2011

ER -