Dr. Megan Elwood Madden

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. Some of this work is theoretical- “If water, CO2 and sulfuric acid are present in a subsurface ocean on Europa, what aqueous species and minerals will form?” Other questions are analytical- “What is the isotopic composition of water trapped 4 Ga in halite grains in the Zag and Monahans meteorites?” Now, with two long term (over 3 years!) robotic missions on Mars and numerous orbiters sending back data and images, the science is also focused on interpreting field data- “What does this outcrop tell us about past environments at Meridiani Planum; where should we go next to test this hypothesis?”

Using observations of mineral assemblages in meteorites and within outcrops on the surface of terrestrial planets to better understand the geochemical history of near-surface fluids and the atmospheres throughout the solar system. Many minerals form only under a narrow range of pressure, temperature, and chemical conditions. Therefore, careful interpretation of mineral assemblages can lead to constraints on the composition of geologic fluids as well as the physical conditions under which the minerals formed. Using thermodynamic modeling of mineral- fluid systems and laboratory experiments, we can test hypotheses of how mineral assemblages may have formed on other planets and what they can tell us about past environments

Jarosite dissolution on Mars- How long was it wet? Jarosite is a key phase observed in all of the outcrops at Meridiani Planum. On Earth, jarosite forms in wet, acidic, oxidizing environments near mine tailings in Acid Mine Drainage (AMD) systems, in acidic soils, and around volcanic vents. However, it is a metastable phase and doesn’t last very long in the presence of liquid water. Therefore, in order to preserve the jarosite at Meridiani, the water must have dried up after a relatively short period of time, but how short? By measuring jarosite dissolution rates in the laboratory, we can constrain the duration of liquid water at Meridiani and have a clearer picture of the history and nature of water in the region.

Analyzing fluid inclusions in Meteorites: what was the source of water in the inner Solar System? Fluid inclusions provide direct samples of geologically active fluids trapped within the minerals they precipitate. Combined with careful interpretations of mineral assemblages, fluid inclusions can be used to build a complete picture of ancient mineral-fluid systems and the P-T conditions in which they were active. Fluid inclusions have historically played an important role in interpreting ore petrogenesis, conditions during diagenesis that lead to petroleum migration, metamorphic P-T-X conditions, and studies of magmatic systems. However, fluid inclusions also have the potential to provide critical data in many other terrestrial and planetary systems where fluids play an active role, including evaporite systems, low-temperature aqueous alteration of near-surface rocks, pore fluids associated with fault zones, etc.

In order to expand the boundaries of the data available from fluid inclusions beyond what is currently achievable in the laboratory, I am involved in a collaborative effort to develop a novel analytical technique which will allow us to directly measure the D/H isotopic composition of individual fluid inclusions using Raman spectroscopy. This ability to measure the isotopic composition of individual fluid inclusions will allow for nondestructive analyses of samples of the original fluid trapped during a geological process of interest, eliminating the need for pressure and temperature dependent fractionation calculations to determine the isotopic composition of the original fluid from analysis of alteration products. This technique will not only allow us to directly analyze early Solar System water trapped in halite in the Monahans and Zag H-5 chondrites, it will also provide an important new tool for investigating a wide range of terrestrial research questions including the source of fluids involved in ore genesis and the isotopic composition of ancient seawater.

Gas hydrates on Earth and throughout the Solar System. Gas hydrates represent a potentially enormo us reservoir for natural gas on earth. However, the geologic controls on hydrate accumulation in terrestrial sediments as well as the time-scale and environmental effects of hydrate dissociation under changing P-T-X conditions remain largely unknown. In addition to natural resource driven studies of methane hydrate deposits in heterogeneous sediment systems, I’m also measuring gas hydrate stability and dissociation rates in high-salinity planetary-analog systems. Gas hydrates are likely important reservoirs for greenhouse gases on Earth as well as Mars, Europa, Titan, and other planetary bodies and may significantly impact planetary atmospheres and climates if they become destabilized. Adding salt is one way to trigger this destabilization. I’m currently designing an experimental system to synthesize gas hydrates and measure their dissociation rates under a wide range of geologic and planetary conditions

The effects of impact processes on low-temperature alteration phases. Past research projects have demonstrated through laboratory shock experiments as well as field studies in terrestrial impact craters that shock metamorphism effectively destroys fluid inclusions in quartz at moderate to high shock pressures. Future studies include the effect of shock metamorphism on the hydration state of various salts and clays, the structural stability of rocks which have experienced significant alteration during impact (and therefore their likelihood to survive impact and interplanetary transport as meteorites), and the global effect of impact-related volatile release on planetary bodies.

	Planetary Geochemistry
	Megan E. Elwood Madden Assistant Professor 405-325-1563 melwood@ou.edu	Office: 952 Sarkeys Energy Center Mailing Address: 100 E Boyd, Suite 810 Norman, OK 73019
		PHYSICAL GEOCHEMISTRY LABORATORY
	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. Some of this work is theoretical- “If water, CO2 and sulfuric acid are present in a subsurface ocean on Europa, what aqueous species and minerals will form?” Other questions are analytical- “What is the isotopic composition of water trapped 4 Ga in halite grains in the Zag and Monahans meteorites?” Now, with two long term (over 3 years!) robotic missions on Mars and numerous orbiters sending back data and images, the science is also focused on interpreting field data- “What does this outcrop tell us about past environments at Meridiani Planum; where should we go next to test this hypothesis?”


		Research	Teaching


Research:
Using observations of mineral assemblages in meteorites and within outcrops on the surface of terrestrial planets to better understand the geochemical history of near-surface fluids and the atmospheres throughout the solar system. Many minerals form only under a narrow range of pressure, temperature, and chemical conditions. Therefore, careful interpretation of mineral assemblages can lead to constraints on the composition of geologic fluids as well as the physical conditions under which the minerals formed. Using thermodynamic modeling of mineral- fluid systems and laboratory experiments, we can test hypotheses of how mineral assemblages may have formed on other planets and what they can tell us about past environments
Jarosite dissolution on Mars- How long was it wet? Jarosite is a key phase observed in all of the outcrops at Meridiani Planum. On Earth, jarosite forms in wet, acidic, oxidizing environments near mine tailings in Acid Mine Drainage (AMD) systems, in acidic soils, and around volcanic vents. However, it is a metastable phase and doesn’t last very long in the presence of liquid water. Therefore, in order to preserve the jarosite at Meridiani, the water must have dried up after a relatively short period of time, but how short? By measuring jarosite dissolution rates in the laboratory, we can constrain the duration of liquid water at Meridiani and have a clearer picture of the history and nature of water in the region.
	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. and J.D. Rimstidt (2006) Lifetime of jarosite on Mars: preliminary estimates. Workshop on Martian Sulfates as Recorders of Atmospheric-Fluid-Rock Interactions, October 22–24, 2006, Houston, Texas.

Analyzing fluid inclusions in Meteorites: what was the source of water in the inner Solar System? Fluid inclusions provide direct samples of geologically active fluids trapped within the minerals they precipitate. Combined with careful interpretations of mineral assemblages, fluid inclusions can be used to build a complete picture of ancient mineral-fluid systems and the P-T conditions in which they were active. Fluid inclusions have historically played an important role in interpreting ore petrogenesis, conditions during diagenesis that lead to petroleum migration, metamorphic P-T-X conditions, and studies of magmatic systems. However, fluid inclusions also have the potential to provide critical data in many other terrestrial and planetary systems where fluids play an active role, including evaporite systems, low-temperature aqueous alteration of near-surface rocks, pore fluids associated with fault zones, etc.
In order to expand the boundaries of the data available from fluid inclusions beyond what is currently achievable in the laboratory, I am involved in a collaborative effort to develop a novel analytical technique which will allow us to directly measure the D/H isotopic composition of individual fluid inclusions using Raman spectroscopy. This ability to measure the isotopic composition of individual fluid inclusions will allow for nondestructive analyses of samples of the original fluid trapped during a geological process of interest, eliminating the need for pressure and temperature dependent fractionation calculations to determine the isotopic composition of the original fluid from analysis of alteration products. This technique will not only allow us to directly analyze early Solar System water trapped in halite in the Monahans and Zag H-5 chondrites, it will also provide an important new tool for investigating a wide range of terrestrial research questions including the source of fluids involved in ore genesis and the isotopic composition of ancient seawater.
	Elwood Madden, M.E., R.J. Bodnar, K. Cheung, and M. Zolensky (2005) Development of a Nondestructive Technique Using Raman Spectroscopy to Measure the D/H Ratio of Extraterrestrial Water. 68th Annual Meteoritcial Society Meeting, Sept. 12-16, Gatlinburg, TN.

Gas hydrates on Earth and throughout the Solar System. Gas hydrates represent a potentially enormo us reservoir for natural gas on earth. However, the geologic controls on hydrate accumulation in terrestrial sediments as well as the time-scale and environmental effects of hydrate dissociation under changing P-T-X conditions remain largely unknown. In addition to natural resource driven studies of methane hydrate deposits in heterogeneous sediment systems, I’m also measuring gas hydrate stability and dissociation rates in high-salinity planetary-analog systems. Gas hydrates are likely important reservoirs for greenhouse gases on Earth as well as Mars, Europa, Titan, and other planetary bodies and may significantly impact planetary atmospheres and climates if they become destabilized. Adding salt is one way to trigger this destabilization. I’m currently designing an experimental system to synthesize gas hydrates and measure their dissociation rates under a wide range of geologic and planetary conditions
	Elwood Madden, M.E., P. Szymcek, S.M. Ulrich, S. McCallum, and T.J. Phelps (Submitted) Experimental formation of massive hydrate deposits from accumulation of CH4 gas bubbles within synthetic and natural sediments. Marine and Petroleum Geology. 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.

The effects of impact processes on low-temperature alteration phases. Past research projects have demonstrated through laboratory shock experiments as well as field studies in terrestrial impact craters that shock metamorphism effectively destroys fluid inclusions in quartz at moderate to high shock pressures. Future studies include the effect of shock metamorphism on the hydration state of various salts and clays, the structural stability of rocks which have experienced significant alteration during impact (and therefore their likelihood to survive impact and interplanetary transport as meteorites), and the global effect of impact-related volatile release on planetary bodies.
	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., F. Horz, and R. J. Bodnar (2004) Experimental simulation of shock reequilibration of fluid inclusions during meteorite impact. Canadian Mineralogist, 42, 1357-1368.


Teaching:
GEOL1114	Physical Geology for Science and Engineering Majors- This course gives a basic introduction to the geosciences, focusing on processes, systems, and Earth materials	Fall 2007 Fall 2008
GEOL4970	Introductory Geochemistry- How can we use chemistry to answer geologic questions? This course is designed to provide an overview of geochemical principles to upper level undergraduates and graduate students.	Spring 2008 Spring 2009
GEOL4970/5970	Current Topics in Planetary Geology- The realm of geoscience is expanding rapidly as rovers and spacecraft send back data on rocks and minerals from throughout the Solar System. Students will learn about the geology of Solar System bodies while discussing current discoveries and long-lived controversies.	Spring 2009