8898 Seminar Colloquium in the Earth Sciences
Speakers: Christopher Conwell and Kenneth Peterman
Seminar Titles:
Links between tectonic uplift, continental weathering, and the Ordovician climate transition
and
Redox Conditions of the Iceland Plume
Abstracts:
Earth's multimillion-year climate fluctuates between warm and cold states, but the factors that modulate fluxes of carbon between the solid Earth and atmosphere are poorly understood. This research examines the role of the continental silicate weathering CO2 sink in creating global cooling observed during the Ordovician Period (484–443 Ma), leading to a widespread glaciation and the first mass extinction event of the Phanerozoic. I will show paired isotope proxy records of continental weathering (Sr, Nd) and paleotemperature (O) from Ordovician limestone strata of central Nevada. These proxy signals demonstrate covariation through the Middle–Late Ordovician which supports that increased silicate weathering during the Taconic orogeny was a primary driver of Ordovician cooling. These data inform a coupled Sr-C mass balance model to further test scenarios of the Ordovician carbon cycle.
A major goal for igneous petrologists is to assess whether magmas are relatively reduced or oxidized (the redox state of the magma), and how this impacts natural phenomena, such as the origin and evolution of magmas and the control of oxygen in the atmosphere. Knowledge of the magma redox state is essential to fully understand these processes, and plays an important role in controlling which minerals can coexist and crystallize from magma. Therefore, in principle it is possible to estimate the magma redox state from analyses of equilibrium pairs of the mineral olivine and volcanic glass (representing quenched melt). This research describes a novel procedure based on this principle called the Olivine-Melt Equilibrium Method. Samples have been obtained from locations along the Reykjanes Ridge, on the Reykjanes Peninsula, and on the Western and Northern Volcanic Zones of Iceland. The purpose of this is to test the application of the Olivine-Melt Equilibrium Method using natural olivine-melt pairs, to precisely constrain the redox state of Icelandic magmas, and to evaluate factors that may influence this property from source to surface. These samples have also been analyzed using Fe K-edge µ-X-ray Absorption Near Edge Structure (XANES) spectroscopy. This powerful analytical technique is capable of measuring the proportion of ferric and ferrous iron in basaltic glasses and provides a comparison with the Olivine-Melt Equilibrium Method.
Host: TDB
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