Triple Oxygen Isotope in High-Temperature Hydrothermally Altered Rocks: A Record of Paleoclimate and Ancient Hydrosphere-Rock Interactions
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Date
2020-02-27
Authors
Zakharov, David
Journal Title
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Publisher
University of Oregon
Abstract
In this dissertation, I use isotopes of H, O and Sr to trace interaction between meteoric waters, seawater and rocks in modern and extinct areas of high-temperature hydrothermal alteration. The ancient hydrothermal systems are used here as a tool to investigating paleoclimate, paleogeography, and the long-term evolution of global isotope budget of hydrosphere. The dissertation begins with exploring triple oxygen isotopes to trace local fluids in modern geothermal systems of Iceland (Krafla, Reykjanes), where seawater and meteoric waters participate in reaction with mid-ocean ridge basalts at high temperatures (> 250 °C). Next, I present results of the triple oxygen and hydrogen isotope study of the 2.43-2.41 Ga altered basalts from the Vetreny belt, Russia to constrain the isotope composition of contemporaneous seawater. I find that the δD, δ18O and Δ17O values of the early Paleoproterozoic seawater were similar to that of Cenozoic seawater values. This study is supported by demonstrating the combined strontium and oxygen isotope exchange between Precambrian seawater and basalt with implications for the effects of low marine sulfate levels. Further, I explore the low δ18O signature of the Belomorian belt, Russia that was likely generated during subglacial rifting and magmatism at low latitudes in the early Paleoproterozoic. Using Δ17O approach, I reconstruct the δ18O values of the low latitude precipitation to ca. -40 ± 5 ‰. This value is evident of an active hydrologic cycle facilitated through evaporation of seawater and precipitation at extremely low temperatures (between -45 and -40 °C) during the Paleoproterozoic snowball Earth glaciations. Using high-precision U-Pb zircon dating, I constrain the timing of subglacial magmatism to 2.44-2.41 Ga and 2.29 Ga. The triple oxygen isotope approach is also applied to the low δ18O 2.42-2.38 Ga Scourie dikes of the Lewisian complex, Scotland to test for assimilation or/and recycling of very low δ18O component, similar to the rocks from the Belomorian belt.
This dissertation includes previously published and unpublished co-authored material. This dissertation is accompanied by electronic supplemental file that contains U-Pb geochronology data.
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Keywords
Isotope geochemistry, Precambrian, Triple oxygen isotopes, Water-rock interaction