MARGINS Post Doctoral Fellows
2008, Heather Savage, University of California, Santa Cruz
Title: “The effect of frictional properties in subduction zones on earthquake triggerability”
NSF Award Number: 0742242
Advisor: Emily Brodsky
Biography:
I recently began work on my NSF-MARGINS postdoc at the University of California, Santa Cruz with
Emily Brodsky comparing the triggering potential of subduction zones and relating differences in
triggerability to fault zone architecture. To date, my research has generally focused on the complex
behavior of faults using experiments, fieldwork, and theory. During my Master’s with Michele
Cooke at the University of Massachusetts, Amherst, I was very interested in questions of fault
interactions over long time periods and how these interactions could affect structures such as
overlying folds. I became interested in shorter time scale interactions and fault friction behavior
during my Ph.D. with Chris Marone at Penn State. Using the biaxial deformation apparatus in the
Penn State Rock and Sediment Mechanics lab, I conducted stick-slip friction experiments on bare
rock and granular material to assess how oscillating stresses such as seismic waves and tides trigger
seismicity. To do this, I applied a small oscillating shear velocity on a constant shear loading rate to
mimic seismic stresses superimposed on tectonic rates. These experiments indicated that the
presence or absence of a fault gouge layer (or any granular material in a shear zone) changed the
sensitivity of a fault to earthquake triggering. In bare rock surface experiments the roughness of the
surfaces determined sensitivity to triggering, whereas in the granular layer experiments, layer
thickness determines triggerability. The bare rock experiments can be interpreted as immature
faults where asperity contact determines fault strength, while the granular layers model mature
faults with well-devel- oped gouge zones. If the analogy holds, I predict that fault maturity should
influence triggerability. For my MARGINS postdoc, I will test this hypothesis on the largest scale
possible: subduction zones.
Beneath Cost Rica, the seafloor being subducted is dotted with seamounts and ridges that act as
asperity contacts with the overriding plate. Presumably, we should see a difference in triggering
potential between this subduction zone and others. By looking at triggering events of similar sizes in
different subduction zones, I aim to assess which areas are more sensitive to changes in stress. To do
this, we will search for locally triggered events during the passage of seismic waves from large,
remote events, as well as counting the number of aftershocks from local events. I am excited to have
this opportunity to learn some observational seismology and apply my ideas to real world
observations.
Current Position Held: Post-Doctoral Research Associate at UCSC
MARGINS Post Doctoral Fellows
2007, Ben Holzman, Columbia University
Title: “Deciphering the Role of Melt Segregation and Strain Partitioning in Rifting Continents”
NSF Award Number: 0646696
Advisor: Ben Holzman
Biography:
My current research, including that funded by the MARGINS postdoctoral fellowship, lies somewhere
between rock mechanics, seismology and geo-dynamics. I want to understand how to interpret
seismic anisotropy measured at plate boundaries in terms of both rock fabrics and melt distribution,
creeping towards a more detailed image of the structure of rheological properties of plate
boundaries. While still involved with experimental rock deformation studies, I am also working with
models of anisotropic elastic and viscous properties of partially molten rocks developed by Yasuko
Takei at the University of Tokyo. At Lamont, I am collaborating
with Jim Gaherty’s group on the
measurement, inversion and interpretation of surface wave anisotropy from the East African Rift in
Ethiopia and the
Gulf of California (the MARGINS site). But more generally, or in more detail (I’m
not sure which), my research focuses on the interactions of melt migration and deformation, or how
melt influences rheological properties of rocks
at high temperature. As research often proceeds
as a series of accidents, I have migrated from field geology to geophysics. My education in Earth
Science began at Brown University. I did a field-based structural geology project on the nearest
ophiolite (in Maine), mapping the structure and constraining emplacement with U/Pb dating of
zircons. Then I went to the University of Minnesota to work with Christian Teyssier to study
ophiolites as tectonic markers in the Himalayas, but I broke my knee playing soccer, so he concocted
a modeling project (in Montpellier,
France, where he was on sabbatical at the time) to study the
phenomenon of fracturing pebbles in soft sediment (asking whether it was caused by seismic waves
or by slow deformation of the matrix). My two month visit grew to seven months. The lab next door,
headed by Adolphe Nicolas, focused on the Oman Ophiolite. He saw an analogy in my pebble problem
to chromite grains that fracture while olivine creeps around them, as observed in Oman. So I had the
great fortune of working with their group for three field seasons. I wrote my master’s thesis on these
analogical problems. In studying the “chromite pods,” it seemed that the chromite was reducing the
permeability of the rock, and modifying the flow of melt as they deformed. After a cheap sabbatical in
Boston, I went back to Minnesota and joined David Kohlstedt’s lab, to do experiments on the
deformation of partially molten olivine rocks. I added a little chromite to reduce the permeability and
the melt segregated dramatically into networks of melt-rich shear zones. This phenomenon became
the subject of my PhD thesis. In applying to Lamont, I proposed to study the seismic expression and
rheological consequences of these melt rich networks, to explore their geodynamical role in the
Earth. After several years, these ideas are taking a practical form. I am very grateful to the
MARGINS program for granting me this support to pursue them further.
Publications Produced as a Result of this Research:
B. K. Holtzman and Y. Takei. "Viscous and elastic anisotropy in partially molten rocks I:
Experimental, field, and seismic observations,? (INVITED)," Trans. AGU, Fall Meet. Suppl.,, v.88(52),
2007, p. Abstract.
Y. Takei and B. K. Holtzman. "Viscous and elastic anisotropy in partially molten rocks II: Significant
role of viscous anisotropy in melt migration dynamics," EOS Trans. AGU, v.88(52), 2007, p.
Abstract.
Current Position Held: Associate Research Scientist at Lamont Doherty Earth Observatory of
Columbia University
MARGINS Post Doctoral Fellows
2006, Jeremy Boyce, Arizona State University
Title: “Exploring the Record of Magmatic Volatiles in a Volcanic Arc via H, C, F, S, and CI in
Apatite, Arizona State University”
NSF Award Number: 0549082
Advisor: Richard Hervig
Biography:
When I approached Rick Hervig with the idea for our MARGINS proposal I had never met him, I had
zero secondary ion mass spectrometer (SIMS) experience, and I had not worked on igneous
processes in more than 5 years. Yet here I am, a MARGINS Postdoctoral Fellow in the School of Earth
and Space Exploration at Arizona State University, using the SIMS to study volatiles in magmatic
systems.
As an undergraduate at UCLA, I was fortunate to be surrounded by energetic faculty and graduate
students who challenged me, broadened my horizons, and introduced me to geology in the field at
exotic locations all over the world. I stayed at UCLA for an M.S. degree with Mary Reid and Marty
Grove, evaluating the hypothesis that 40Ar/39Ar ages from melt-inclusion bearing quartz crystals
represent magma residence time. For my Ph.D, I knew I wanted to work on the (U-Th)/He system,
and Mary suggested that I apply to her alma mater (MIT) to work with Kip Hodges. My visit with the
faculty and graduate students there quickly convinced me that MIT was the place I wanted to
continue my education. After we built the (U-Th)/He lab at MIT, we tackled a variety of problems
related to (U-Th)/He, including a critical evaluation of the Durango apatite (U-Th)/He standard,
determination of He diffusion rates in monazite, and most importantly, the development and
application of laser microprobe (U-Th)/He geochronology.
I stumbled upon the idea of using apatite to constrain H2O and CO2 in magmas during my first year
at MIT. At the time, one of my committee members suggested (as it did not fit into my thesis plan)
that I keep the idea to myself until I had a chance to write a proposal. Years later, as I wrapped up my
Ph.D, I recognized the need to diversify my research portfolio beyond noble gas geochronology. The
long-dormant apatite project seemed like a perfect change of pace, and I decided to try to make it
happen. I wrote to Rick, introducing myself and the idea I wanted to pursue, and the rest (as they
say) is history.
Since my arrival in Tempe last Spring, my collaboration with Rick and interaction with other ASU
researchers and visitors has opened up to me many new frontiers in the geosciences, stimulating a
tremendous number of ideas for future projects. Our MARGINS study, along with the work of
colleagues, collaborators, and competitors worldwide, is helping to develop apatite as a powerful
indicator of volatile processes. Perhaps even more exciting is our recent discovery that apatite
crystals may not only yield information about pre-eruptive magmatic water content, but also about
the timescales of volatile processes in magmas.
Every year Ph.D programs produce far more graduates who want faculty positions than can be placed
in them. For those who want or need more time to develop their skills before starting the tenure
clock, postdoctoral research experience is essential. Yet few NSF programs set aside money for postdocs. I know how lucky I am that the MARGINS program has the vision to promote postdoctoral
research, and I hope other NSF programs follow this example.
Publications Produced as a Result of this Research:
Jeremy W Boyce and Richard L Hervig. "Magmatic degassing histories from apatite volatile
stratigraphy," Geology, v.36, 2008, p. 63.
Current Position Held: Post-Doctoral Research Associate at Arizona State University
MARGINS Post Doctoral Fellows
2004, Jennifer Garrison, University of Iowa
Title: “Time-scales and mechanisms of differentiation of mafic parents to rhyodacite in Central
America”
NSF Award Number:
0405262
Advisor: Mark Reagan
Biography:
In August of 2004, I packed my belongings and headed out to the Midwest to begin two years of
research for my MARGINS post-doc at the University of Iowa with Mark Reagan. This was the
beginning of a series of challenging opportunities that will benefit me the rest of my career.
My Ph.D. research at UCLA with Jon Davidson had taken me to Ecuador, where I studied the
geochemistry of lava flows and pyroclastic deposits related to Cotopaxi volcano in the Northern
volcanic zone (NVZ) of South America. Cotopaxi is one of the few composite volcanoes in Ecuador
that has erupted a bimodal suite of rhyolite and andesite lavas, and we used trace element and
isotopic compositions of whole rocks and mineral separates to study the timescales and processes of
magma differentiation operating in the NVZ. In addition to valuable research and travel
opportunities, my Ph.D. project provided me with a solid background in the analytical techniques
that I would soon put to use during my postdoc.
I initially met with Mark Reagan at the 2003 AGU/EGS meeting in Nice, France where we discussed
possibilities and funding options for a project in Central America. In spring 2004, I was excited to
receive notification that our MARGINS project had been funded, and we started working in El
Salvador in February of 2005. Our MARGINS project focused on voluminous dacites erupted from
three calderas in El Salvador and Nicaragua (Ilopango, Apoyo and Apoyeque) over the last 20 ka. The
youngest of these was the climactic eruption from Ilopango caldera in El Salvador about 1605 years
ago. We used trace element and isotope geochemistry to assess differences among these calderas.
While conducting our field research in El Salvador we were fortunate to be accompanied by Dolors
Ferres from the local government office that monitors volcanic activity in El Salvador (Servicio
Nacional de Estudios Territoriales, or SNET). After completing field work in El Salvador, I had the
opportunity to participate in a field excursion to Santa Maria volcano in Guatelama, led by Dr. Bill
Rose from MTU. The hike and three day stay in this very active crater was an experience I’ll never
forget. After returning to Iowa City, I began the process of separating minerals and preparing rocks
for analysis. Most of the sample preparation was done in the University of Iowa clean lab facility.
The analysis of the U-series isotopes (U, Th, Ra), and the long-lived radiogenic isotopes (Pb, Sr, Nd)
were accomplished at Woods Hole Oceanographic Institute.
I spent a total of four months at WHOI working with Ken Sims to prepare and analyze samples. On
the basis of Th, Sr, Nd, and Pb isotopes, our preliminary data show that the rhyodacites in this system
are produced by fractionation of local, more mafic magmas. Samples from all three systems have
230Th excesses, which is significant because most of the more mafic rocks from this area have 238U
excesses that result from fluid addition from the slab. Positive correlations between (230Th/232Th),
Ba/Th, and Ce/Pb, as well as large differences in Th isotope ratios from north to south suggest that
these differences correspond to changes in the amount of subducted sediment involved in magma
genesis. This is important because relating geochemical variation to petrogenetic processes and
subsequently relating these processes to timescales is critical to our understanding of magma genesis
and volcanic evolution. I am currently preparing these results for publication, and we will also
present our research at the upcoming June MARGINS workshop in Costa Rica (Workshop to Integrate
Subduction Factory and Seismogenic Zone Studies in Central America, June 18-22, 2007).
As a result of my time spent at WHOI, I have initiated important contacts and have planned future
collaborations, including research in Ecuador on El Reventador volcano. I am very thankful to have
been afforded the opportunity for this research project.
Publications Produced as a Result of this Research:
Garrison, J., Reagan, M. Sims, K. and Patino, L.. "Timscales of rhyodacite formation in Central
America: U-series disequilibrium and implications for petrogenetic processes in El Salvador and
Nicaragua," EOS, v.87, 2006, p. V41B-1734.
Current Position Held: Assistant Professor at California State University, Los Angeles
MARGINS Post Doctoral Fellows
2003, James Conder, Washington University, St. Louis
Title: “A Numerical Investigation of the Relative Importance of Different Melting Mechanisms
at Volcanic Arcs”
NSF Award Number:
0305292
Advisor: Douglas Wiens
Biography:
Working as a post-doc at Washington University has been a great opportunity to study geologic
processes at volcanic arcs and back-arc basins and also to become involved with the MARGINS
program. Previous and ongoing WashU seismic experiments at the Tonga and Mariana subduction
zones have helped stimulate my interest in magma production and migration at these geologically
important regions.
Growing up in Salt Lake City helped give me an appreciation for the outdoors and the many diverse,
but interlinked, aspects of the natural and physical sciences. I discovered Geology as an
undergraduate at the University of Utah, and worked for a year at a mining exploration company
before heading to the East Coast for graduate school. Although my snowboarding skills severely
atrophied after leaving the Wasatch Mountains, it has been an immensely rewarding experience,
particularly because of the interaction with the many great people and discussions of interesting
research I have encountered within the geophysical community.
While a graduate student at Brown University, I learned the value of combining different seismic
observations with other methods, particularly numerical modeling, to understand mantle flow and
melt processes. My research at Brown primarily focused on the South- east Indian Ridge and the East
Pacific Rise. One thesis chapter demonstrated with numerical models of mantle flow incorporating
pressure- and temperature-dependent viscosity that asthenospheric flow driven from one side of the
spreading axis to the other can account for the unexpected degree of asymmetry observed across the
East Pacific Rise from the MELT experiment. Applying these same modeling techniques to
understand the observed asymmetric seismic structure of the Lau back-arc spreading cen- ter led to
the find that decompression melting should be expected beneath some volcanic arcs as the
subducting slab viscously erodes the base of the overlying lithosphere. Models using temperaturedependent viscosity also predict slab temperatures >100 deg C warmer than isoviscous models.
These observations put volcanic arcs in the interesting position of potentially having three possible
melting mechanisms for magma generation: wedge hydration, wedge decompression, and slab
heating. As a MARGINS post-doc, I plan to use numerical models along with seismic observations to
map out how the importance of each melting mechanism varies from arc-to-arc as the thermal
structure and other governing parameters at subduction zones change.
Current Position Held: Senior Research Associate at Washington University, St. Louis
MARGINS Post Doctoral Fellows
2003, Alison Shaw, Carnegie Institution of Washington
Title: “Constraining the Volatile and Sub Flux in the Izu-Bonin-Mariana MARGIN Using
Geothermal Fluids, Phenocrysts and Melt Inclusions”
NSF Award Number:
0305052
Advisor: Erik Hauri
Biography:
After completing my undergraduate degree in geosciences at McGill University, I left the Great White
North to pursue graduate studies in sunny Southern California at Scripps Institution of
Oceanography. During the course of my Ph.D. research at Scripps with Dr. David Hilton, I had the
opportunity to work on a MARGINS related project investigating the CO2 flux though the Central
American Arc. Using He-C relationships in geothermal fluids (fumaroles, hot springs and geothermal
well gases) collected from various volcanic centers along the arc, I was able to assess the provenance
of the volcanic C output, allowing for an estimate of how much of the C input at the trench (as pelagic
carbonates, organic C and altered oceanic crust carbonate) was recycled through the arc system. As a
complement to my geothermal fluid arc studies, my postdoctoral research at the Carnegie Institution
of Washington with Dr. Erik Hauri will focus on melt inclusions in recently erupted tephras from the
Izu-Bonin-Marianas arc system. Melt inclusions are thought to represent preeruptive melts, and thus
offer the exciting possibility to look at the composition of sub-arc partial melts. Since it is assumed
that inclusions remain isolated after entrapment, they are thought to preserve the characteristics of
primitive melts and are less influenced by magma chamber processes than erupted lavas. This study
will be part of a collaborative volatile study of the arc using geothermal fluid data and remote sensing
techniques, along with melt inclusions in mafic phenocrysts, to gain a better understanding of how
volatiles are cycled through arc systems.
Current Position Held: Assistant Scientist, Woods Hole Oceanographic Institution
MARGINS Post Doctoral Fellows
2003, Glenn Spinelli, University of Missouri-Columbia
Title: “The role of sediment diagenesis and dewatering on fluid and heat flow, Costa Rica
margin”
NSF Award Number:
0304946
Advisor: Michael Underwood
Biography:
I am excited to be starting a MARGINS post-doctoral fellowship this year. After spending most of my
life near the edges of this continent (including growing up in New Jersey and attending grad school at
the University of California, Santa Cruz), it seems natural to head to the heartland (Missouri) to study
continental margins. After getting a B.S. at Penn State, I went to UC Santa Cruz where my research
encompassed hydrogeology and sedimentology — ranging from groundwater seepage into San
Francisco Bay and fluid seepage through sediments on the Juan de Fuca Ridge flank, to sedimentation
patterns on northern California’s Eel River margin. As a MARGINS post-doctoral fellow, I will further
develop my interests in both hydrogeology and sediments by studying sediment dewatering within
the Costa Rica margin subduction zone.
Sediments subducted off Costa Rica have high opal and smectite contents (both contain a large
amount of water that is expelled at moderate temperatures and pressures within the shallow
subduction zone). Smectite dewatering has been shown to significantly affect pore fluid pressure and
chemistry in the subduction zones of Barbados and Nankai. On the Costa Rica margin, opal
dewatering provides another source of water during sediment diagenesis. Additionally, in Costa Rica,
large along-strike variations in heat flow may lead to differences in the depth within the subduction
zone at which the dewatering reactions occur. This has the potential to generate along-strike fluid
pressure gradients and therefore margin parallel fluid flow within the subduction zone. Fluid
pressure and fluid flow patterns in response to sediment dewatering in the subduction zone, in turn
have implications for fault strength and potentially the location of the updip limit of seismicity.
This study will consist of two phases: a characterization of the sediments offshore Costa Rica (in
cooperation with Mike Underwood at the University of Missouri), and modeling of sediment
dewatering and fluid flow within the Costa Rica margin subduction zone (in cooperation with
Demian Saffer at the University of Wyoming).
Current Position Held: Assistant Professor, New Mexico Tech