Field and microanalytical isotopic investigation of ultradepleted in 18O Paleoproterozoic "Slushball Earth" rocks from Karelia, Russia
I.N. Bindeman et al., Department of Geological Sciences, 1272 University of Oregon, Eugene, Oregon 97403, USA. Published online 21 Feb. 2014, http://dx.doi.org/10.1130/GES00952.1.
Geologic records on the composition of Earth's ancient atmosphere, hydrosphere, and meteoric precipitation are rare and are typically derived from isotopic and chemical materials that resided near the surface. There is still enigmatic connection between the first appearance of oxygen in the air 2.2-2.4 billion years ago and three to four pan-global glaciation events that preceded it, each lasting millions of years. Here I.N. Bindeman and colleagues describe rocks with the lowest known values of oxygen isotopes (delta-18O down to -27.3 per mil), mapped individually and regionally, and now extending 450 km along the Paleoproterozoic Belomorian complex in Karelia, Russia. The protolith of these rocks, now represented by nearly-gem quality rubies, carries isotopic signatures of glacial ice and is interpreted to have formed by subglacial hydrothermal alteration inside of intracontinental rift zones, which affected tens of cubic kilometers of rocks. As Karelia was located near equatorial latitudes during Pale
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