Megan

CONTACT

University of Oklahoma
School of Geology and Geophysics 
100 East Boyd St. Rm 952
melwood@ou.edu
(405) 325-1563 phone

(405) 325-3140 fax

goethite on jarosite

 

 

 

 

 

 

 

Links

Examples of research accomplishments

Publications

Teaching

Physical and Environmental Geochemistry Laboratory

Geochemistry at OU

School of Geology and Geophysics

 

 

 

 

 

 

 

 

 

 

 

Stubbeman-Drace Presidential Professor
School of Geology and Geophysics, University of Oklahoma

Wigner Fellow, 2005-2007, Oak Ridge National Laboratory
Ph.D. (geochemistry), 2005, Virginia Tech
B.S. (geology), 2000, University of Illinois

PHYSICAL AND PLANETARY GEOCHEMISTRY

Planetary Geochemistry is a rapidly growing sub-discipline of Geology and Planetary Science, applying what geochemists have learned about minerals, fluids, isotopes, and rocks on Earth to fluid-rock interactions, mineral assemblages, and suites of rocks on other planets. My research program focuses on the thermodynamics and kinetics of geochemical processes at low temperature and low to moderate pressure conditions analogous to near‐surface conditions on Mars, Earth, Titan, Europa, Enceladus, and other icy bodies. My students and I use laboratory experiments to measure the rate of mineral dissolution, gas hydrate formation/decomposition, and volatile diffusion under a range of planetary analog conditions. Combining kinetic data from these experiments with thermodynamic models of mineral assemblages, aqueous fluids, and/or gas hydrate systems, we constrain the duration and magnitude of volatile fluxes and aqueous systems in cold, water‐rich environments. Current projects apply these techniques to constrain near‐surface carbon dioxide and methane hydrate reservoirs on Mars, Earth, and other icy planetary bodies; determine jarosite dissolution rates, and hence particle lifetimes, under a wide‐range of Mars‐analog aqueous conditions; as well as collaborative projects to determine chemical weathering fluxes and processes within streams in the Antarctic Dry Valleys and investigate hematite nanoparticle aggregation during freezing and/or drying to better understand nanophase iron oxides and their potential role in forming “crystalline” hematite deposits on Mars.

I co-direct the Physical and Environmental Geochemistry Laboratory with Dr. Andrew Elwood Madden. For examples of research facilites, please visit the websites for the laboratory.

CURRENT AND RECENT STUDENTS

Seth Gainey (MS 2011) Kinetics of methane hydrate formation and dissociation under Mars relevant conditions

Margaret Root (MS 2011) Effects of obliquity change on gas hydrate stability zones on Mars

Allison Stumpf (MS 2011) Chemical weathering in glacial meltwater streams, Wright and Taylor Valleys, Antarctica    

Brittany Pritchett (MS 2012) Effects of activity of water on the dissolution of                              jarosite

Dan Ambuehl (MS 2013)

Current advisees: Emily Dixon (MS expected 2014), Debajyoti Basu Sarkar (MS expected 2014)

Co-advised: Kristen Marra (expected  PhD 2015). 

Undergraduates: Shayda Zahrai (2008-2012), John Leeman (2008-2011), John Guest (2007-2008), Brandon Guttery (2009), Carey Legett (2013-2014), Tiffany Legg (2009-2011), Emma Baker (2011), Jamie Miller (2012-2014), Rebecca Funderburg (2013-).

TEACHING  

GEOL 1114 Physical Geology for Scientists and Engineers
GEOL 3333 GeoWriting
GEOL 4223/ 5223 Principles of Geochemistry
GEOL 4970/ 6970 Planetary Geology
HONS 3993 Deep Time - Deep Space

EXAMPLES OF CURRENT RESEARCH PROEJCTS

Jarosite Dissolution and Hematite Aggregation  

Jarosite ((K,Na,H)Fe3(SO4)2(OH)6) is commonly found as an ephemeral phase in acidic, oxidizing, sulfate and iron‐rich environments on Earth. The discovery of jarosite within deposits on Mars provides evidence for oxidizing, acidic fluids in these regions during the time of jarosite deposition. In addition, the preservation of jarosite over billions of years on Mars places constraints on the post‐jarosite geochemical environment, including the duration of aqueous diagenesis. Observations of hematite spherules within the same outcrops may further constrain the chemistry of these diagenetic fluids. Our recent experiments demonstrate that K and Na‐jarosite dissolution rates vary considerably with pH, as well as ionic strength. Nanophase iron (hydr)oxide reaction products (observed using TEM and electron diffraction) which form during incongruent jarosite dissolution at pH >3.5 also vary with pH and time, suggesting kinetic as well as thermodynamic controls affect the weathering assemblage. Based on these reaction products and dissolution rates, abundant iron oxides observed at Meridiani Planum may have formed as secondary reaction products of jarosite dissolution at pH> 3.5 over timescales less than tens to thousands of years. In addition, collaboration with A. Madden has led to a follow‐on study investigating the role of hematite nanoparticle aggregation during freezingand/or drying in forming “crystalline” hematite phases under low temperature conditions at Meridiani Planum The results of these studies not only constrain the duration of aqueous diagenesis at Meridiani Planum, but also provide fundamental data on jarosite dissolution mechanisms and processes affecting the mineralogy of incongruent iron (hydr)oxide reaction products on Earth and Mars. Therefore, these results can also be integrated into hydrologic models to predict the fate of heavy metals and acidity in acid mine drainage systems and may inform studies of red‐bed and banded iron deposits as well.

figBElwood Madden, M.E., R.J Bodnar, and J.D. Rimstidt (2004) Jarosite as geochemical indicator of water-limited chemical weathering on Mars. Nature, 431, 821-823.    

Elwood Madden ME, Madden AS, Rimstidt JD (2009) How long was Meridiani Planum wet? Applying a jarosite stopwatch to constrain the duration of diagenesis, Geology 37(7) 635-638.

high pH jarosite dissolution

 

Gas hydrates on Earth and throughout the Solar System.

Gas hydrate clathrates are compounds in which cages of water ice encapsulate a guest molecule.
(typically CO2, CH4, CO, H2S, N2, O2, Xe, Kr, Ar, H2, and higher mass hydrocarbons). Stable at low
temperatures and moderate to high pressures, these solid phases may serve as reservoirs for
volatile phases in many low temperature, water‐rich planetary environments. While the
thermodynamic stability fields of many clathrate phases are well established, these stability fields
provide only a snapshot of a system at one moment in time under equilibrium pressure,
temperature, and composition conditions. However, recent observations have demonstrated that
Mars, Titan, Enceladus, Earth and other planetary bodies are dynamic systems, producing gas fluxes and changing surface features over time. Therefore, rates of gas hydrate formation and dissociation processes are needed to fully understand the potential role of gas clathrates in dynamic planetary systems and test hypotheses of clathrate‐driven atmospheric, tectonic, and geomorphic changes.

planetaryhydrateMy students and I have investigated the initial rate of methane hydrate and carbon dioxide hydrate formation and decomposition at low temperatures and low-moderate pressures to constrain the lifetime of potential near-surface, metastable gas hydrate reservoirs on Mars and determine the magnitude and duration of gas fluxes from near-surface gas hydrates on Mars, Titan, Europa, Enceladus, and other icy planetary bodies. Coupling the results of gas hydrate formation and dissociation experiments with geologic and thermodynamic models of gas hydrate stability in the near-subsurface, we have demonstrated that near-surface methane hydrate reservoirs are a feasible source for recent methane plumes on Mars, especially if they contain mixed gas hydrate phases which include H2S.

 

 

 

PUBLICATIONS

submitted

Dixon E, Elwood Madden AS, Hausrath E, Elwood Madden ME (submitted) Groundwater flow or stagnant pond? Assessing hydrodynamic effects on jarosite dissolution rates, reaction products, and particle lifetimes, JGR-Planets.

Marra, KR, Elwood Madden, ME, Soreghan, GS, Hall, BL (in revision) BET surface area distributions in polar stream sediments: implications for silicate weathering in a cold-arid environment, Applied Geochemistry.

in press / published

Ambuehl D, Elwood Madden ME (2014) CO2 Hydrate formation and dissociation rates: Application to Mars.  Icarus, v. 234, 45-52.

Marra KR, Soreghan GS, Elwood Madden ME, Keiser LJ, Hall BL (2014) Trends in Grain Size and Surface Area in Cold-Arid vs Warm Semi-Arid Fluvial Systems. Geomorphology, v. 206, 483-491.

Kendall MR, Madden AS, Elwood Madden ME, Hu Q (2013) Rates and products of arsenojarosite dissolution¸ Geochimica et Cosmochimica Acta, 112, 192-207.

Lin B, Cerato AB, Madden AS, and Elwood Madden ME (2013) Microscopic Analysis of the Effect of Fly Ash on the Hydromechanical Alterations of Two Expansive Soils from Oklahoma. Environmental & Engineering Geoscience19, 85-94.

Mousis O, Chassefiere E, Chevrier V, Elwood Madden ME, Lakhlifi A, Lunine JI, Montmessin F, Picaud S, Schmidt F, and Swindle TD (2013) Volatile trapping in Martian clathrates. Space Science Reviews, 173, 213-250.

Zahrai SK, Elwood Madden ME, Madden AS, Rimstidt JD, Miller MA (2013) Na-jarosite dissolution rates: The effect of mineral composition on jarosite lifetimes. Icarus, v. 223 438-443.

Elwood Madden ME, Madden AS, Rimstidt JD, Zahrai S, Kendall MR, and Miller MA (2012) Jarosite dissolution rates and nanoscale mineralogy, Geochimica et Cosmochimica Acta, 91, 306-321.

Gainey, S.R. and Elwood Madden, M.E. (2012) Kinetics of Methane Clathrate Formation and Dissociation Under Mars Relevant Conditions.  Icarus, 218, 513-524.

Leeman, J.  Rawn, C.J., Alford, J., Phelps, T.J., Elwood Madden, ME Interpreting Temperature Strain Data from Meso-Scale Clathrate Experiments (2012) Computers and Geosciences, 38, 62-67.

Miller M.A., Madden AS, Elwood Madden ME, Elmore RD (2012) Laboratory-simulated diagenesis of nontronite, Clays and Clay Minerals 60(6), 616-632.

Pritchett, B.N., Elwood Madden ME, Madden AS (2012) Effects of water and chloride activity on jarosite dissolution rates and maximum lifetimes in high salinity brines: Implications for Earth and Mars, Earth and Planetary Science Letters, 357-358: 327-336.

Root, M.J. and Elwood Madden, M.E. (2012) Potential Effects of Obliquity Change on Gas
Hydrate Stability Zones on Mars. Icarus, 218, 534-544.

Stumpf AR, Elwood Madden ME, Soreghan GS, Hall BL (2012)  Chemical weathering within glacial melt water streams, Wright and Taylor Valley, Antarctica. Chemical Geology, 322-323, 79-90.

Zahrai SK, Elwood Madden ME, Madden AS, Rimstidt JD (2013) Dissolution rates and particle lifetimes of Na-jarosite under Mars-relevant conditions. Icarus 223, 438-443.

Elwood Madden ME, Leeman JR, Root MJ, Gainey S (2011) Reduced sulfur-carbon- water systems on Mars may yield shallow methane hydrate reservoirs. Planetary and Space Science, doi:10.1016/j.pss.2010.05.016.

Rawn CJ,  Leeman JR, Alford JE, Phelps TJ, Elwood Madden ME, Ulrich SM (2011) Fiber Optic Sensing Technology for Detecting Gas Hydrate Formation and Decomposition. Review of Scientific Instruments, 59, 203-206.

Madden AS, Hamilton VE, Elwood Madden ME, Larson PR, Miller MA (2010) Low-temperature mechanism for formation of coarse crystalline hematite through nanoparticle aggregation, Earth and Planetary Science Letters 298, 377-384.

Elwood Madden ME, Madden AS, Rimstidt JD (2009) How long was Meridiani Planum wet? Applying a jarosite stopwatch to constrain the duration of diagenesis, Geology 37(7) 635-638. Link

Elwood Madden, M.E., P. Szymcek, S.M. Ulrich, S. McCallum, and T.J. Phelps (2009) Experimental formation of massive hydrate deposits from accumulation of CH4 gas bubbles within synthetic and natural sediments. Marine and Petroleum Geology 26(3) 369-378. Link

Elwood Madden, M.E., S.M. Ulrich, T.C. Onstott, and T.J. Phelps (2007) Salinity-induced hydrate dissociation: a mechanism for recent CH4 release on Mars. Geophysical Research Letters 34, Issue 11, CiteID L11202.

Elwood  Madden, M. E., D. A. Kring, and R. J. Bodnar (2006) Shock re-equilibration of fluid inclusions in crystalline basement rocks from the Ries Crater, Germany. Meteoritics and Planetary Sciences 41, n. 2, 247-262.

Elwood Madden, M.E., D. Kring, and R.J. Bodnar, (2006) Shock reequilibration of fluid inclusions in Coconino Sandstone from Meteor Crater, Arizona. Earth and Planetary Science Letters 241, 32-46.

Elwood Madden, M.E., R.J Bodnar, and J.D. Rimstidt (2004) Jarosite as geochemical indicator of water-limited chemical weathering on Mars. Nature, 431, 821-823.

Elwood Madden, M.E., F. Horz, and R. J. Bodnar (2004) Experimental simulation of shock reequilibration of fluid inclusions during meteorite impact. Canadian Mineralogist, 42, 1357-1368.