Textural, geochemical, and isotopic data from silicified rocks and associated chemical sedimentary rocks in the ~ 2.7 Ga Abitibi greenstone belt, Canada: Insight into the role of silicification

Latisha A. Brengman, Christopher M. Fedo, Martin J. Whitehouse, Iffat Jabeen, Neil R. Banerjee

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1 Scopus citations

Abstract

Silica-rich Precambrian rocks often preserve geochemical information and microfossil remnants from the early biosphere and could play a critical role in the formation of early crust. Because these rocks are important geochemical and paleontological archives, we need to better constrain their geochemical and isotopic attributes and generate a refined picture of the evolving Archean silica cycle. Here, we investigate a series of sub- to greenschist facies Si-rich Archean rocks from the ~ 2.7 Ga Abitibi greenstone belt, Canada, that represent chemical sedimentary rocks and rocks formed via silica-addition through the process of silicification. We report data for major and trace element geochemistry, multi-crystal silicon and oxygen isotopes of quartz using isotope ratio mass spectrometry, and texture-specific silicon isotope values measured using secondary ion mass spectrometry on Neoarchean chemical sedimentary rocks, their silicified equivalents, and associated silicified volcanic rocks. We find that in such a well-preserved terrane we can utilize petrographic textures and geochemical attributes to establish rock origin, distinguishing siliceous rocks that form via chemical sedimentation from those that form via silicification. Chemical sedimentary rocks display a wide range of 30Si-depleted silicon isotopes values that vary with stratigraphy similar to other Archean iron formation. Silicified volcanic rocks possess 30Si-enriched values, similar to Archean silicified basalts. We conclude that because silicon isotope values of iron formation shift toward 30Si-enriched values up stratigraphy, basinal changes in the composition of the silicon isotope reservoir may be preserved. Silicon isotope values of silicified volcanic rocks by contrast, likely represent precipitation from an isotopically heavy silicon reservoir, influenced by downward percolating seawater and upward moving convecting fluids interacting with host volcanic rock (basalt or andesite). Overall, we confirm that Neoarchean silicified rocks are 30Si-enriched like their Paleoarchean counterparts.

Original languageEnglish (US)
Article number105946
JournalPrecambrian Research
Volume351
DOIs
StatePublished - Dec 2020

Bibliographical note

Funding Information:
This work was funded by NASA grant EXOB08-0063 awarded to C.M. Fedo, and student research grants awarded to L.A. Brengman from ExxonMobil, the Geological Society of America, the Sedimentary Division of GSA, and the Department of Earth and Planetary Sciences at the University of Tennessee. The University of Minnesota – Duluth provided additional funding for travel to analytical facilities and additional fieldwork for L.A. Brengman. The NordSIMS facility is a joint Swedish-Icelandic infrastructure operated under Swedish Research Council grant 2014-06375, contribution 661. Over the duration of the project, several people helped locate outcrops and aided in the field. We would like to thank Wulf Mueller for inspiration to study the rocks of the Abitibi greenstone belt, and Brian Atkinson, Pierre Doucet, Dave Guindon, Pierre Bousquet, Erica Cayer, Lyndsay Abbott for their help in the field. We also thank the Editor, N. Wodicka, Reviewer 1 - B. Gourcerol, and Reviewer 2 (anonymous) for their helpful, constructive comments and suggestions that greatly improved the manuscript. We thank the Editor V. Pease for editorial handling. L.A. Brengman and C.M. Fedo planned the research. L.A. Brengman collected samples and completed the main field work. L.A. Brengman, C.M. Fedo, and M.J. Whitehouse performed silicon isotope analyses using SIMS. I. Jabeen and L.A. Brengman completed IRMS analyses in the lab directed by N.R. Banerjee at Western University. L.A. Brengman and C.M. Fedo interpreted the data with input by M.J. Whitehouse, N. Banerjee, and I. Jabeen. L.A. Brengman and C.M. Fedo wrote the paper with input from M.J. Whitehouse, N.R. Banerjee, and I. Jabeen.

Funding Information:
This work was funded by NASA grant EXOB08-0063 awarded to C.M. Fedo, and student research grants awarded to L.A. Brengman from ExxonMobil, the Geological Society of America, the Sedimentary Division of GSA, and the Department of Earth and Planetary Sciences at the University of Tennessee. The University of Minnesota – Duluth provided additional funding for travel to analytical facilities and additional fieldwork for L.A. Brengman. The NordSIMS facility is a joint Swedish-Icelandic infrastructure operated under Swedish Research Council grant 2014-06375, contribution 661. Over the duration of the project, several people helped locate outcrops and aided in the field. We would like to thank Wulf Mueller for inspiration to study the rocks of the Abitibi greenstone belt, and Brian Atkinson, Pierre Doucet, Dave Guindon, Pierre Bousquet, Erica Cayer, Lyndsay Abbott for their help in the field. We also thank the Editor, N. Wodicka, Reviewer 1 - B. Gourcerol, and Reviewer 2 (anonymous) for their helpful, constructive comments and suggestions that greatly improved the manuscript. We thank the Editor V. Pease for editorial handling.

Publisher Copyright:
© 2020 Elsevier B.V.

Keywords

  • Geochemistry
  • Iron formation
  • Oxygen isotopes
  • Silica cycle
  • Silicification
  • Silicon isotopes

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