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Field and microanalytical isotopic investigation of ultradepleted in ^(18)O Paleoproterozoic “Slushball Earth” rocks from Karelia, Russia

Bindeman, I. N. and Serebryakov, N. S. and Schmitt, A. K. and Vazquez, J. A. and Guan, Y. and Azimov, P. Ya. and Astafiev, B. Yu. and Palandri, J. and Dobrzhinetskaya, L. (2014) Field and microanalytical isotopic investigation of ultradepleted in ^(18)O Paleoproterozoic “Slushball Earth” rocks from Karelia, Russia. Geosphere, 10 (2). pp. 308-339. ISSN 1553-040X. doi:10.1130/GES00952.1.

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The 1.85 Ga Belomorian Belt, Karelia, Russia, hosts ultralow δ^(18)O and δD (as low as −27.3‰ and −235‰ standard mean ocean water [SMOW], respectively), high-Al gneisses and amphibolites that we attribute to the Paleoproterozoic “Slushball Earth” glaciation. They now occur in at least 11 localities spanning 450 km. To constrain distribution of ^(18)O-depleted rocks, we performed detailed field mapping in Khitostrov, where δ^(18)O values are the lowest. Using 430 new and previously published laser fluorination isotope analyses, we show that the elongated, concentrically zoned area of δ^(18)O depletion is greater than 6 × 2 km in areal extent, ∼10 times larger than previously thought. Relationships between δ^(17)O versus δ^(18)O strictly adhere to the equilibrium terrestrial mass-dependent fractionation with a slope of 0.527. We also report the results of ion microprobe U-Pb geochronology of zircons coupled with co-registered oxygen isotope spot analyses for mafic intrusions and host gneisses in six localities. The 2.9–2.7 Ga gneiss zircon cores are normal in δ^(18)O (5‰–7‰). They show truncated oscillatory cathodoluminescence (CL) patterns and rounded shape indicative of original igneous crystallization with subsequent detrital overprinting. A younger 2.6–2.55 Ga metamorphic zircon domain with normal δ^(18)O, low Th/U, dark cathodoluminescence, and also with rounded crystal morphology is commonly preserved. Cores are surrounded by ubiquitous rims highly depleted in δ^(18)O (re-)crystallized with Svecofennian (1.85–1.89 Ga) ages. Rims are interpreted as metamorphic due to bright and uniform CL and Th/U <0.05. Mafic intrusions preserve few igneous zircon crystals between ca. 2.23 and 2.4 Ga in age, but neoblastic zircon in these intrusions originated mostly during 1.85 Ga Svecofennian metamorphism. The δ^(18)O-age relationship for metamorphic rims in zircon and corundum grains suggests that δ^(18)O values of fluids were subtly increasing with time during metamorphism. Large metamorphic corundum grains have ∼3‰ intracrystalline δ^(18)O isotope zonation from –24 to –21‰, which likely developed during interaction with metamorphic fluids. The Zr-in-rutile geothermometer temperatures are in the range of 760 to 720 °C, in accordance with mineral assemblages and amphibolite metamorphic grade. High and irregular rare-earth element (REE) abundance in cores and rims of many zircons correlates with high phosphorus content and is explained by nanometer-scale xenotime and monazite inclusions, likely in metamict zones during 1.85 Ga Svecofennian metamorphism. A survey of oxygen isotopes in ultrahigh-pressure diamond and coesite-bearing metamorphic terrains around the world reveals normal to high-δ^(18)O values, suggesting that the low δ^(18)O in metamorphic rocks of Dabie Shan, Kokchetav, and in Karelia, are genetically unrelated to metamorphism. We discuss alternative ways to achieve extreme δ^(18)O depletion by kinetic, Rayleigh, and thermal diffusion processes, and by metamorphism. We prefer an interpretation where the low-δ^(18)O and high-Al signature of the rocks predates metamorphism, and is caused by shallow hydrothermal alteration and partial dissolution of the protolith surrounding shallow mafic intrusions by glacial meltwaters during pan-global Paleoproterozoic “Slushball Earth” glaciations between ca. 2.4 and ca. 2.23 Ga.

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Guan, Y.0000-0002-7636-3735
Alternate Title:Field and microanalytical isotopic investigation of ultradepleted in 18O Paleoproterozoic “Slushball Earth” rocks from Karelia, Russia
Additional Information:© 2014 Geological Society of America. Received 28 May 2013. Revision received 4 January 2014. Accepted 29 January 2014. We thank the National Science Foundation for funding of grants EAR-1049351 and EAR-CAREER 0805972; IF-EAR funding of the CAMECA 1270 ion microprobe facility; the University of California, Los Angeles; and the Russian Foundation for Basic Research for grant 12-05-00706a. We also thank Pavel Medvedev, Sergei Svetov, and Denis Korpechkov for help during fi eldwork of 2011 and 2012, and Markus Walle for help with LA-ICP MS. V. Kulikov kindly supplied samples from Vetreny Belt, and Kurt Panter is thanked for collaboration on Antarctic secondary quartz. J. Eiler and Caltech Ion microprobe facility are thanked for hosting I. Bindeman during sabbatical, and Cliff Dax is thanked for electronics support. Associate Editor Aaron Cavosie and two anonymous reviewers are thanked for their careful reviews.
Funding AgencyGrant Number
Russian Foundation for Basic Research12-05-00706a
Issue or Number:2
Record Number:CaltechAUTHORS:20140807-150733584
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Official Citation:I.N. Bindeman, N.S. Serebryakov, A.K. Schmitt, J.A. Vazquez, Y. Guan, P. Ya. Azimov, B. Yu. Astafiev, J. Palandri, and L. Dobrzhinetskaya Field and microanalytical isotopic investigation of ultradepleted in 18O Paleoproterozoic “Slushball Earth” rocks from Karelia, Russia Geosphere, April 2014, v. 10, p. 308-339, first published on February 21, 2014, doi:10.1130/GES00952.1
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48203
Deposited By: Ruth Sustaita
Deposited On:07 Aug 2014 22:33
Last Modified:10 Nov 2021 18:30

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