How Minerals Control Hydrothermal Organic Reactivity

Project: Research project

Description

PROJECT SUMMARY Overview: Page A Recent experimental results show that mineral surfaces determine the rates and products of organic compound transformations in high temperature-pressure fluids. Experiments will be conducted at temperatures from 200 to 350 C and pressures from 700 to 1000 bars, using model organic compounds to identify the reaction mechanisms that are enhanced by mineral surfaces. This work builds on results of prior support that supply a foundation of hydrothermal organic reaction mechanisms in the absence of minerals. Experiments will be conducted in gold capsules and a collapsible gold bag apparatus to minimize catalysis by the surface of the reaction vessels. Gas chromatography (GC) and GC-mass spectrometry procedures for analyzing organic solutes and dissolved gases are in place based on previous work. Mechanisms will be explored in short-duration experiments that follow details of product distributions over time using isotopic labels, chiral compounds, and variable pH, ionic strength and redox states. Experiments will be designed to explore the effects of mineral surface area, charge distributions, and semi-conductor properties using a suite of common oxides, sulfides and silicates. Procedures for bulk and surface mineral analysis will be developed using X-ray diffraction, scanning electron microscopy, and scanning transmission electron microscopy - electron energy loss spectroscopy. Results will be combined in theoretical models of geocatalysis yielding predictions about the fate of organic compounds in fluids circulating throughout the oceanic crust in diverse submarine settings including accretionary margins, seamounts, detachment faults and ridges. Intellectual Merit : Fluids moving through the seafloor at seamounts, accretionary margins, continental shelves, mid-ocean ridges and elsewhere deliver dissolved organic compounds to high temperature-pressure environments where they are transformed. Organic reaction paths and products depend on the minerals present. Products may remain associated with mineral surfaces, or stay in solution and be transported away from the reaction zone to lower temperature environments including vast volumes of the subsurface biosphere. Developments in theoretical geochemistry have advanced to the point that thermodynamic models of many of these processes are now routine. What is now needed are experimental tests of thermodynamic predictions, and the development of a deeper kinetic understanding of the mineral controls on organic reactivity. Abundant experimental and theoretical evidence now exists for reversibility of reactions among structurally similar groups of organic compounds in hydrothermal fluids. The major unknowns are the irreversible processes associated with carbon-carbon bond breaking that determine the overall rates of organic transformations. Mechanisms of several of these reactions in hydrothermal fluids are now established through short-duration experiments, making it profitable to move to experiments that include the minerals that expedite irreversible bond-breaking reactions. How this happens is poorly understood and the major focus of the proposed research. Broader Impacts : Despite the fact that most organic reactions in the Earth occur in the presence of minerals and aqueous fluids, geologists are not trained to study the effects of minerals on organic reactions, and organic chemists are seldom introduced to the prevailing conditions in nature that differ so dramatically from the conventions of the organic chemistry lab. As a consequence, mineralogy is unknown to most organic chemists and organic chemistry is unknown to most petrologists, even though the interaction of organic compounds and minerals feeds the subsurface biosphere, controls the long-term global deep carbon cycle, and is responsible for the fossil fuels on which society is built. Since 2008 the Hydrothermal Organic Geochemistry research group at Arizona State University has trained graduate researchers to bridge the gap between organic chemistry and petrology by focusing on hydrothermal experiments involving organic transformations. These efforts are transforming how undergraduate geochemistry and organic chemistry are taught in the Environmental Chemistry major in the Department of Chemistry and Biochemistry, as well as the Astrobiology and Biogeoscience major in the School of Earth& Space Exploration at ASU. Pod casts on themes relating to submarine hydrothermal systems and hydrothermal organic geochemistry will be developed as part of course offerings, improved through student feedback, and then released to the world through ASU on iTunes U.
StatusFinished
Effective start/end date1/1/1412/31/16

Funding

  • National Science Foundation (NSF): $448,932.00

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mineral
organic compound
experiment
organic geochemistry
seamount
hydrothermal fluid
biosphere
fluid
gas chromatography
gold
thermodynamics
geochemistry
scanning electron microscopy
detachment fault
dissolved gas
biochemistry
carbon
mid-ocean ridge
catalysis
fluid pressure