Peter Reiners - US grants

0001484
Wolff

This award provides partial (50%) funding support for the acquisition of a laser ablation inductively coupled plasma source multicollector mass spectrometer (LA-ICP-MCMS) system to be installed and operated in the GeoAnalytical Laboratory at Washington State University. Washington State University is committed to provide the remaining funding required for the acquisition. The new instrument will be used in research and training of graduate students requiring precise microanalysis of elemental and isotopic compositions.
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Reiners
EAR-0073576

Recent resurgence of interest in (U-Th)/He dating has been made possible by interpretational advances combined with careful diffusion studies and apparently successful tectonic applications and calibrations against other thermochronometers. Nevertheless, many exciting aspects of He dating remain unexplored. This work comprises a series of experimental studies to develop, extend, and calibrate new (U-Th)/He thermochronologic methods. One objective is to extend He dating to new phases, including zircon, fluorite, and garnet. This is motivated by the potential benefits of low-T thermal constraints in rocks that lack these phases in abundance such as many sedimentary and hydrothermally mineralized rocks, as well as the unique diffusion properties and closure temperatures (Tc) of other phases. A second objective is to exploit the property that the diffusion domain for He is equivalent to the crystal or grain itself. We will attempt to use this to constrain not only cooling ages, but thermal histories of crystals, by examining the potential uses of 1) core-to-rim He concentration and age zonation within individual crystals using abrasion techniques, and 2) age-grain size correlations that reflect specific thermal histories of partially reset crystals. A final objective is to rigorously compare (U-Th)/He thermochronometry with other methods, primarily multi-domain K-feldspar 40Ar/39Ar dating to provide intermethod
calibrations and unprecedentedly dense time-temperature sampling and thermal constraints. The (U-Th)/He lab at W.S.U. is set to begin measuring ages and performing diffusion experiments in May of 2000, and this funding will provide support for graduate students working on experimental development of these methods, in collaboration with with regional fission-track and 40Ar/39Ar thermochronologic labs, the economic geology programs at W.S.U. and the nearby U.I.

9909996
Reiners

This grant provides partial support for the costs of establishing a (U-Th)/He dating facility at Washington State University. The PI, Peter Reiners, is a recent addition to the Department of Geology, having just completed a postdoctoral program in helium thermochronometry at Caltech. The primary functions of this facility will be to: 1) measure contents of radiogenic helium in minerals for applied thermochronologic studies of tectonic and geomorphologic processes, and 2) develop and establish new techniques and approaches of (U-Th)/He dating in order to expand the method to suit a wider variety of phases, closure temperatures, and geologic applications. The lab will consist of mineral preparation equipment, apparatus for diffusion experiments, a He extraction, purification, quadrupole mass-spectrometry vacuum line, and lab facilities for measurement of U and Th contents on the department's ICP-MS. The lab will provide thermochronologic capabilities to researchers throughout the Pacific northwest, including WSU, Central Washington University, the University of Washington, the University of Idaho, and a nearby commercial fission-track dating lab (Donelick Analytical). In addition to providing thermochronologic constraints to applied studies, this lab will also be focused on the experimental development of (U-Th)/He dating in a variety of minerals and systems, including economic ore systems.

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0111875
Reiners

This grant provides partial support for acquisition of a laser extraction system for (U-Th)/He chronometry. Laser heating and gas extraction from crystals for (U-Th)/He thermochronometry and geochronometry provides significantly lower He blanks, allows very small aliquots (single crystals) and very young samples to be dated, dramatically increases sample throughput, and allows dating of refractory minerals such as titanite, zircon, and garnet. The laser extraction system will be incorporated into a He mass spectrometry line and (U-Th)/He dating lab at Yale University, which is supported by a new geochemistry lab manager position in the Department of Geology and Geophysics, and a new HR-ICP-MS for U-Th determinations. The lab will focus on both experimental development of new (U-Th)/He approaches and applications, as well as routinely providing low-temperature cooling ages for establishing the timing and rates of tectonic and geomorphologic processes and dating of volcanic rocks. The laser extraction system will be a critical component of this lab, both because of its ability to provide relatively rapid, low-blank, He extraction from a wide variety of minerals for experimental and methodological studies, as well as its ability to process large numbers of routine samples for collaborative research projects (primarily apatite, titanite, and zircon He ages for tectonic studies).
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0208652
Brandon

The paradox of how horizontal contraction and extension can occur simultaneously in convergent mountain belts remains a fundamental and largely unresolved problem in continental dynamics. The Apennines represent one of the most accessible "type locality" areas of syn-convergent extension. Rollback - which describes the tendency of a subducting plate to retreat from the orogenic front - is commonly invoked as an explanation for syn-convergent extension, but this idea does not address how the retrograde motion of the subducting plate, which is a mantle-based process, causes horizontal extension in the overlying zone of crustal convergence, especially in light of the large accretionary fluxes typically associated with continental subduction.

The goal of the project (project RETREAT) is to develop a self-consistent dynamic model of syn-convergent extension, using the Northern Apennines as a natural laboratory. This part of the Apennine orogen has been the site of relatively steady orthogonal convergence and 2D (plane strain) orogenic deformation since ~30 Ma. GPS measurements indicate that convergence is presently active, and tomography indicates that the full length of subducted slab is still intact to depths of 250 km. Syn-convergent extension has been active since at least 15 Ma. The Northern Apennines are well studied, and all important features of the orogen are onland and thus directly accessible for detailed geological and geophysical research.

The specific objectives of project RETREAT are 1) to determine in detail the velocity field across the orogen, including deformation in the orogenic wedge, the motion of lithospheric plates, and the flow fields in the surrounding asthenospheric mantle, and 2) to use this kinematic information to develop and test specific dynamic models for deformation in the orogenic wedge and underlying mantle. The research techniques to be used include; geodesy, tectonic geomorphology, low-temperature thermochronometry, structural geology and tectonic syntheses, seismic studies, and geodynamic modeling.

The RETREAT project links together a broad multidisciplinary group with eleven PIs from six institutions, plus some 27 foreign collaborators in Italy, Switzerland, Canada, and France.
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Reiners
EAR-0236965

Recent developments in methods and interpretational bases of (U-Th)/He chronometry have demonstrated that this technique poses significant potential for advancing understanding of a wide variety of processes, many of which have been difficult to address with other geochronometric approaches. This project will integrate (U-Th)/He chronometric research in technique development, innovative applications, and undergraduate student research. Work will focus in particular on development of single-crystal He-Pb dating, geomorphologic investigations using ancient coal-fires, tectonic applications that constrain timing, rate, and styles of exhumation and landscape development, and analytical and methodological improvements. To facilitate integration of (U-Th)/He chronometry in undergraduate research, a series of summer workshops for students outside of Yale will be conducted. Students will perform a suite of (U-Th)/He chronometric measurements with modeling and interpretation, over three weeks at Yale, to complement their individual senior theses or other types of projects; faculty mentors will also participate in the latter stages of the workshops. The topical and regional diversity of projects will serve as an introduction to a wide range of research (and the general importance of chronometric constraints) for the students, as well as to test and broaden the range of geologic problems that can be addressed by He dating. This work will facilitate broader impacts in research, learning, and infrastructure by: 1) providing access to, and training and experience in (U-Th)/He chronometry for a wide range of investigators both at Yale and beyond, 2) emphasizing integration of innovative (U-Th)/He chronometric approaches into a wide range of studies besides typical tectonogeomorphic applications, 3) integrating He dating into student research and teaching efforts at Yale, 4) establishing structured annual summer workshops for research by undergraduates and faculty mentors, and helping faculty at primarily undergraduate institutions get plugged-in to analytical facilities for future projects, and 5) creating an opportunity to involve students (including members of underrepresented groups) in a positive research-oriented experience at critical junctures in their educations.

EAR-0233767
Reiners

The use of (U-Th)/He chronometry has expanded significantly in the last several years, primarily in applications involving constraints on the timing and rate of shallow-crustal exhumation as applied to tectonic and geomorphic problems. The Yale He dating lab supports many of these projects, both within and outside the department, involving students and other researchers. In addition, the lab also conducts both experimental development and innovative applications of He dating, performing experiments necessary for use of the technique on new phases, improved analytical methods, and applying He dating to a wide range of problems such as the dynamics of magmatic heating in the shallow crust, detrital studies, and natural coal fires. All of these projects (as well as use of the sector ICP-MS) require support from the lab manager/technician for sample processing and user training. This funding will provide partial support for a full-time lab manager/technician (Dr. Stefan Nicolescu) for the Yale (U-Th)/He chronometry and sector ICP-MS facilities. Nicolescu's responsibilities include user training, sample processing, equipment maintenance, and planning/design in the lab, as well as maintenance of and user-training on the high-resolution ICP-MS associated with the lab. This support will facilitate broader impacts in research, learning, and infrastructure by providing support for: a) access to, and user training and experience in, He chronometry and ICP-MS analysis for students and other researchers both at Yale and other institutions; b)
undergraduate/faculty advisor summer workshops on He chronometry, modeling, and interpretations in a variety of applications; c) continued professional development and training for Nicolescu.
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EAR-0345789
Reiners

This grant provides partial funding for a 193 nm laser ablation system for use in laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) and (U-Th)/He chronometry at Yale. The laser will increase the versatility of the existing sector ICP-MS and the inorganic geochemistry program at Yale, allowing in situ, spatially-resolved trace element and isotopic analyses of a wide variety of geological materials. Besides benefits to trace element and isotopic studies in ongoing petrologic and environmental studies, the laser will particularly benefit two new geochronologic applications: 1) characterization of intracrystalline U-Th zonation in zircon, to improve precision and accuracy of (U-Th)/He ages and thermochronologies derived from them, and 2) routine measurement of U/Pb ages in single zircon crystals also dated by (U-Th)/He (He-Pb double dating), which is a new and powerful technique for detrital provenance studies of sedimentary rocks. The laser will provide analytical experience and state-of-the-art analyses for graduate and undergraduate students, postdocs, technical staff, and faculty at Yale, as well as for visiting researchers performing (U-Th)/He and ICP-MS analyses including undergraduate participating in summer He dating workshops at Yale.

Clinker, rock metamorphosed by natural coal burning, has formed in the Powder River Basin (and other areas of the Rocky Mountains) since at least Pliocene. Clinker dominates the topographic form of many of the basins in which it is found, because it is more resistant to weathering than surrounding unaltered bedrock. It also preserves a record of the spatial-temporal patterns of fluvial incision, lateral backwasting, and plateau formation in these landscapes, because coal only burns when close to the surface, above the water table and ventilated with surface oxygen. Using (U-Th)/He ages of detrital zircons that are reset during clinker formation, we will map the patterns of coal burning and shallow exhumation in detail in several regions of the PRB in Wyoming and Montana, as well as characterize clinker ages over a broader scale throughout the basin. Model predictions of clinker age-patterns in individual drainages and across the landscape suggest that our results will be able to discriminate between at least some of these possible climatological or tectonic mechanisms driving landscape evolution. This work will form the basis of collaborative research between Reiners and Riihimaki, as well as individuals in the BLM and the Northern Cheyenne Tribe, and undergraduate students from Yale and Bryn Mawr.

The remarkable match between the glacial equilibrium line altitude (ELA) and summit elevations in many active mountain ranges of the world has led to the supposition that glaciers act as an erosional buzzsaw. Since most observed rates of glacial erosion are very high they are thought to be able to effectively remove most topography tectonically uplifted through the ELA. However, the glacial buzzsaw idea is based largely on circumstantial evidence. Only preliminary attempts have been made to theoretically simulate quantitative predictions of this process. This proposed research aims to test the glacial buzzsaw hypothesis using modern technical and computational methods. Understanding the importance of glacial erosion is complicated by the fact that elevated topographies are often the result of plate convergence, and so an appreciation of the feedbacks involved between orogenic wedge mechanics and surface processes is required. Development of a coupled geodynamic and surface process model that incorporates glacial erosion in an active critical orogenic wedge is proposed to examine these feedbacks. Preliminary model predictions indicate that the temporal and spatial patterns of uplift and erosion for both a weak and strong glacial buzzsaw in an active orogen contrast significantly with erosion patterns of an orogen that responds to the buzzsaw by passive isostasy. Testing the model predictions to judge whether glacial erosion acts as a 'strong' or 'weak' buzzsaw will be achieved by applying combined apatite (U-Th)/He and fission-track low temperature thermochronology to evaluate changes in erosion rates and spatial erosion patterns following the onset of late Cenozoic glaciation in the Patagonian Andes - the orogen where the match between the height of the ELA and summit elevation was first recognized. The Patagonian Andes are an exceptional natural laboratory. As well as having a suitable and well-documented tectonic and climatic history, their north-south range provides an opportunity to study a spatially varying glacial history. Two different transects will be targeted: one at 39S to 41S (Valdivia, Pucn, Bariloche), and another between 46S and 51S (Canal Baker, Lago General Carrera, South Patagonian Icefield). This will include the collection of both near-vertical and trans-orogen sample profiles. The proposed work will address the following research questions: 1) Does the glacial buzzsaw hypothesis explain the behavior of surface erosion in the Patagonian Andes? 2) Was the buzzsaw diachronous or synchronous along the length of the Patagonian Andes? 3) Is the orogen close to steady state, or still responding to the drop in ELA? and 4) How accurate are current models of glacial erosion over regional scales and long time periods?
Broader Impact
The long-term behavior of the earth system is dependent on dynamic interactions between climate, albedo, tectonics, orogenic topography, weathering, and greenhouse gases, such as CO2. In particular, there has been much speculation about the role that erosional fluxes from orogenic landscapes might play in moderating the greenhouse effect, given the important role of silicate weathering in moderating CO2 concentrations in the atmosphere. Orogenic topography as influences the distribution of precipitation, and can also change global atmospheric circulation, if the topography gets high enough, as is presently the case in the Himalaya and central Andes. Thus, there remains broad interest in the factors that might influence the evolution of orogenic topography, or limit the maximum size of the topography. This research will make a significant contribution towards understanding the role that alpine glaciation plays in controlling the maximum height of mountain ranges. The multidisciplinary approach of this proposal will foster a number of national and international educational and research links. Students and researchers from Louisiana State, Yale, GFZ Potsdam, the Universidad de Chile will be involved in this project. Students from two US institutions will have an opportunity to combine field research and theory. The proposed study has the potential to provide research support for an alumnus of the NSF funded Geoscience Alliance to Enhance Minority Participation in the Earth Sciences (GAEMP) project, through co-PI Jonathan
Tomkin's participation in the program at LSU. The results of the research will be integrated into a GAEMP summer school program, which emphasizes the value of ongoing earth science research to minority undergraduates.
This award is being supported with funds from the Geomorphology and Land Use Dynamics Program, the Tectonics Program, and the Americas Program in the Office of International Science and Engineering.

0732380
Reiners

This grant provides partial support for a full time lab manager/technician for the (U-Th)/He dating and sector ICP-MS labs in Geosciences at the University of Arizona. The lab manager supports user training, sample processing, equipment maintenance, and planning and design in both labs. (U-Th)/He chronometry (He dating) has expanded dramatically in the last decade and is now a staple of many regional tectonic and geomorphologic studies requiring constraints on the timing and rate of shallow-crustal exhumation. The He dating lab at the UofA supports training and analyses for diverse projects and workshops involving both external and internal PIs, undergraduate and graduate students, postdocs, and faculty. The lab conducts research in tectonic and geomorphic applications and experimental development and innovative applications of He dating. It performs experiments necessary for dating and interpreting He ages of unexplored phases, improved analytical methods, and applying He dating to a range of novel problems such as surface wildfire, detrital studies, and meteorite thermal histories. All of these projects require support from the lab manager/technician for user training, sample processing, and instrument maintenance. In addition to supporting He dating operations for both internal and external users, the technician support proposed here will provide for routine high-resolution (sector) ICP-MS analyses and training to a broad spectrum of users internal and external to the University of Arizona.

This Small Grant for Exploratory Research investigates the origin and evolution of the Gamburtsev subglacial mountains (GSM). These mountains are considered the nucleation point for Antarctica's largest ice sheets; however, being of indeterminate age, they may postdate ice sheet formation. As well, their formation could reflect tectonic events during the breakup of Gondwana. The project studies GSM-derived detrital zircon and apatite crystals from Prydz Bay obtained by the Ocean Drilling Program. Analytical work includes triple-dating thermochronometry by U/Pb, fission track, and (U/Th)/He methods. The combined technique offers insight into both high and low temperature processes, and is potentially sensitive to both the orogenic events and the subsequent cooling and exhumation due to erosion. In terms of broader impacts, this project supports research for a postdoctoral fellow and an

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Much of the inventory of East Antarctic bedrock geochronology, as well as a record of its erosional history, is preserved in Cenozoic sediments around its margin. This project is to use these sediments to understand their sub-ice provenance and the erosional history of the shield by measuring ages of multiple geo- and thermochronometers on single detrital crystals and on multiple crystals in detrital clasts (U/Pb, fission-track, and (U-Th)/He dating of zircon and apatite, and 40Ar/39Ar dating of hornblende, mica, and feldspar). The combination of multi-chronometer ages in single grains and clasts provides a powerful fingerprint of bedrock sources, allowing us to trace provenance in Eocene fluvial sandstones through Quaternary diamicts around the margin. Multiple thermochronometric (cooling) ages in the same grains and clasts also allows us to interpret the timing and rates of erosion from these bedrock sources. Delineating a distribution of bedrock age units, their sediment transport connections, and their erosional histories over the Cenozoic, will in turn allow us to test tectonic models bearing on: (1) the origin of the Gamburtsev Subglacial Mountains, (2) fluvial and topographic evolution, and (3) the history of glacial growth and erosion.

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."


Intellectual Merit: Expanded use of (U-Th)/He and 4He/3He thermochronology in tectonic and geomorphic studies over the last decade have elucidated several first-order challenges facing their practical application and interpretation. Quantitative understanding of the phenomena behind these challenges is required to confidently integrate He dating with other approaches, develop realistic diffusion models, and robustly interpret thermal histories in general. This proposal focuses on addressing two primary challenges in zircon and apatite He dating. The first challenge is development of a robust kinetic model for He diffusion in zircon that incorporates anisotropy and the effects of radiation damage. Zircon He ages show two distinct types of correlations between age and parent nuclide concentrations, depending on the specific thermal histories of individual samples. This leads to a hypothesis whereby initially high and anisotropic diffusivity becomes progressively lower and more isotropic with increasing damage, followed by a rapid decrease in diffusivity after damage exceeds a critical threshold. Evaluation of this behavior may provide constraints on distinct parts of sample thermal histories. Kinetic calibration will be done through a series of crystallographically controlled He diffusion experiments and age analyses on zircons with varying degrees of radiation damage and thermal histories. The second challenge is to understand the origin of anomalous and highly dispersed apatite He ages in some samples. Detailed examination of detrital and bedrock samples documents formation of secondary phases in grain boundaries around at least some fraction of apatite crystals; in many cases these phases have U-Th concentrations comparable to or higher than the apatite. Such samples are likely to be affected by extracrystalline U-Th-bearing secondary phases in distinct ways, depending on the timing of secondary phase growth and whether some proportion of the phases are analyzed with the apatite. The secondary-phase hypothesis will be tested through a series of analyses to characterize in situ U-Th distributions in and around apatite in detrital and Laramide basement bedrock samples through SEM, ion-imaging, and induced-track imaging of thin sections. Methods to ameliorate or avoid the problem will be tested using grain abrasion and measurement of elements associated with the secondary phases on problematic samples. A final component of this study involves funding for continued support of two-week summer student workshops to be held each year for undergraduate and graduate students, allowing them to learn analytical and interpretational aspects of low-temperature thermochronology as applied to samples from their own research projects.

Broader Impacts: This work will fund the research of two promising students who are members of underrepresented groups: PhD student Kendra Murray, and undergraduate Guleed Ali, and will provide partial funding for establishing FT analytical facilities for Research Scientist Dr. Stuart Thomson. The student workshops will provide direct training and research experience to a broad spectrum of students in the tectonics and geomorphology communities.

Thermochronometer Kinetics in a Contact Aureole

Driven by the demand for constraints on thermal histories of rocks in the upper few kilometers of the Earth's crust, intermediate- and low-temperature thermochronology has proliferated in tectonic and geomorphic applications in the last two decades. Despite this growth, every thermochronologic application is limited by uncertainties in fundamental kinetic calibrations and intra-sample variation that to one degree or another raise questions about geologic interpretations derived from them. These uncertainties arise from many sources, but perhaps most importantly from the interpretation and extrapolation of empirical laboratory step-heating diffusion and annealing experiments that are usually performed at rates and temperatures many orders of magnitude different from relevant natural conditions. Several lines of evidence, including ab initio kinetic models, deviations of natural samples from idealized configurations, and simply observations of "intriguing complexities" in many cooling-age, -spectra, -profile and track-length data sets, suggest the existence of significant gaps in our understanding of routinely used fundamental thermochronologic kinetic calibrations. A careful and deliberate benchmarking and intercalibration study of multiple thermochronometers from a well-controlled natural laboratory is needed to illuminate these issues and to ultimately establish more confidence in kinetic models and geologic interpretations derived from them. It is proposed to resample and analyze the detailed behavior of 13 different noble-gas and fissiontrack thermochronometers in profiles adjacent to Little Devils Postpile, a classic natural laboratory studied by Calk and Naeser in 1973, where a ~100 m basalt plug intruded ~80-Ma granitoid rock at ~8 Ma. Although possibly complicated by hydrothermal circulation and other effects, the relatively simple configuration of this natural experiment will allow construction of realistic models of the thermal histories associated with the intrusion, hence prediction of profiles of age and other thermochronometric properties as a function of distance from the contacts. The abundance of many different minerals dateable by both noble gas and fission-track methods in the country rock will then allow comparison between and predicted the observed thermochronologic patterns based on many parameters (incl. bulk ages, profiles, spectra, and track lengths, etc.). Inter-combinations of well-calibrated dating systems will serve as benchmarks to identify interpretive problems and to infer potential refinements needed to improve calibrations of other dating systems.

Intellectual Merit: This focused and collaborative study will provide a relatively rare and needed opportunity to test, refine, and in some cases establish kinetic calibrations used by many Earth and planetary scientists for hundreds of applications each year. This will be accomplished using a natural experiment performed under conditions not achievable in the laboratory, through a relatively simple contact relationship that allows for straightforward modeling, but with reasonable opportunity for revealing complexities (such as intrasample variations) that are likely to be commonly encountered in many geologic applications.

Broader Impacts: Besides contributing to thermochronologic calibrations widely used in the geologic community, and potentially establishing a thermochronologic "type locality" useful for testing other systems, this work will provide training and support for several undergraduate and graduate students, establish new fission-track dating capabilities (in zircon, titanite, and epidote) at UT, and will provide for outreach opportunities to visitors at Yosemite National Park, through our collaboration with Park Geologist Dr. Gregory Stock.

Bedrock-hosted secondary Fe-oxide minerals are practically ubiquitous in faults, fractures, and localized high porosity zones in shallow crustal rocks. Unlike primary minerals, their formation is usually the result of reactions associated with fluid migration long after formation of the host rock. Radioisotopic dates and compositional information preserved in secondary Fe-oxides have the potential to reveal much about the timing and dynamics of regional fluid flow histories, as well as processes that create high permeability zones, like brittle deformation, in bedrock. Despite their potential, bedrock-hosted secondary oxides have proven difficult to date by radioisotopic means. However, new results show that, in many cases, (U-Th)/He dating provides apparently reliable and geologically consistent dates suggesting significant potential for this approach. This project will develop methods for radioisotopic dating and geochemical characterization of bedrock-hosted secondary iron-oxide minerals and focuses primarily on (U-Th)/He geo- and thermochronology of hematite and associated iron-oxide minerals in these environments, combined with characterization of trace element and oxygen isotopic compositions of the minerals. The goal is to use dates and compositions of these secondary phases to constrain the timing and conditions of brittle deformation that created the voids in which the minerals formed, and understand the timing and conditions of fluid flow that resulted in their precipitation. This project develops these approaches in a range of geologic settings, primarily in the western U.S., where results can be compared with other geologic and geochronologic constraints.

Dates and compositions of secondary iron-oxides have the potential to improve the understanding of the timing and conditions of a wide range of important processes ranging from brittle fault movement, to groundwater migration, to atmospheric conditions, to ancient episodes of bedrock exposure. This project will also provide support for continued community use of the Arizona Radiogenic Helium Dating Lab, and support for a summer student workshop on low-temperature thermochronology, allowing visiting students to perform analyses and learn how to use and interpret thermochronology in geologic research.

Dating brittle fault slip is a research frontier essential for characterizing numerous upper crustal processes. Direct, robust, and efficiently obtained timing constraints are necessary to reconstruct structural-tectonic histories, mountain building processes, and landscape evolution, as well as to document ancient seismicity histories to assess modern seismic hazards, earthquake forecasting, and fault mechanics. However, direct dating of fault activity in the upper crust is challenging due to limited applicable radioisotopic techniques, and few robust geologic indicators of past seismic slip exist in the rock record. This project tests a new potentially transformative method to directly date fault slip by using the (U-Th)/He on iron oxide coatings on fault surfaces collected from active and ancient faults as well as explores the chemistry and physics underpinning the method. The project advances desired societal outcomes through: (1) increased public scientific literacy and public engagement with science and technology through contributions to traveling displays for K-12 students, development and presentation of elementary school educational modules, participation in university outreach activities, and development of projects and lessons for northern Utah home-schooled students; (2) development of a globally competitive STEM workforce through training of graduate and undergraduate students; (3) increased partnerships with other academic institutions and the U.S. Geological Survey.

The principal research objective of this project is to develop hematite (U-Th)/He geochronology as a method to directly date fault slip. (U-Th)/He dates from hematite-coated fault surfaces record brittle deformation events by constraining the timing of either synkinematic hematite formation or the rapid cooling from frictional heating during faulting. In some cases, these dates may track regional cooling, yielding a new tool to quantify tectonic exhumation or erosion linked to broader fault zone evolution. This method is tested on three active or ancient fault systems in the North American Cordillera: the northern Wasatch fault zone in Utah; faults in the central Colorado Front Range; and the eastern Denali fault zone in the Yukon. The project involves: (1) macroscopic characterization and structural analysis of hematite-coated faults and microscopic determination of hematite occurrence, texture, and grain size; (2) characterization of He diffusivity from 4He/3He diffusion experiments; (3) targeted (U-Th)/He dating of hematite-coated faults at each locale including multiple samples from the same fault surface; (4) development of independent constraints on fault surface thermal histories using transition metal paleothermometry from X-ray photoelectron spectroscopy and 4He/3He thermochronometry; and (5) establishment of independent constraints on fault activity timing using U-Pb dating and existing 40Ar/39Ar illite age data of related synkinematic calcite and clay-rich fault gouge, respectively, and regional cooling patterns from host-rock apatite (U-Th)/He and fission track data.

The noble gases (helium, neon, argon, krypton, xenon, and radon) play a central role in understanding a wide variety of Earth and planetary processes, from tracing the origins of meteorites, to the differentiation of Earth's mantle, to dating the timing and rates of geologic processes. However, while we can now measure noble gases in minerals very precisely, our understanding of how they are incorporated into, migrate through, and are lost from minerals is simplistic and likely wrong in important ways. This work will use a series of novel experiments to understand the behavior of one noble gas, helium, in one mineral, zircon, to build a general understanding of noble gas behavior in other systems.

The ability to measure distinct isotopes of helium in zircon specimens with differing amounts and types of crystal defects and crystallographic orientations (as well as the widespread utility of the radiogenic He radioisotopic dating system) make this an ideal model system for this work. The project will focus on radiogenic 4He, as well as 3He and 4He implanted or generated in situ in zircons with varying amounts of radiation damage from both heavy nuclide recoil and light ion or neutron damage, and will also examine the effects of damage defect annealing on He behavior. These experiments will distinguish between the effects of damage defects as traps, tortuosity enhancers, and fast-paths at various levels of pro- and retrograde accumulation.

Antarctica is almost entirely covered by ice, in places over two miles thick. This ice hides a landscape that is less well known than the surface of Mars and represents one of Earth's last unexplored frontiers. Ice-penetrating radar images provide a remote glimpse of this landscape including ice-buried mountains larger than the European Alps and huge fjords twice as deep as the Grand Canyon. The goal of this project is to collect sediment samples derived from these landscapes to determine when and under what conditions these features formed. Specifically, the project seeks to understand the landscape in the context of the history and dynamics of the overlying ice sheet and past mountain-building episodes. This project accomplishes this goal by analyzing sand collected during previous sea-floor drilling expeditions off the coast of Antarctica. This sand was supplied from the continent interior by ancient rivers when it was ice-free over 34 million year ago, and later by glaciers. The project will also study bedrock samples from rare ice-free parts of the Transantarctic Mountains. The primary activity is to apply multiple advanced dating techniques to single mineral grains contained within this sand and rock. Different methods and minerals yield different dates that provide insight into how Antarctica?s landscape has eroded over the many tens of millions of years during which sand was deposited offshore. The dating techniques that are being developed and enhanced for this study have broad application in many branches of geoscience research and industry. The project makes cost-effective use of pre-existing sample collections housed at NSF facilities including the US Polar Rock Repository, the Gulf Coast Core Repository, and the Antarctic Marine Geology Research Facility. The project will contribute to the STEM training of two graduate and two undergraduate students, and includes collaboration among four US universities as well as international collaboration between the US and France. The project also supports outreach in the form of a two-week open workshop giving ten students the opportunity to visit the University of Arizona to conduct STEM-based analytical work and training on Antarctic-based projects. Results from both the project and workshop will be disseminated through presentations at professional meetings, peer-reviewed publications, and through public outreach and media.


The main objective of this project is to reconstruct a chronology of East Antarctic subglacial landscape evolution to understand the tectonic and climatic forcing behind landscape modification, and how it has influenced past ice sheet inception and dynamics. Our approach focuses on acquiring a record of the cooling and erosion history contained in East Antarctic-derived detrital mineral grains and clasts in offshore sediments deposited both before and after the onset of Antarctic glaciation. Samples will be taken from existing drill core and marine sediment core material from offshore Wilkes Land (100°E-160°E) and the Ross Sea. Multiple geo- and thermo-chronometers will be employed to reconstruct source region cooling history including U-Pb, fission-track, and (U-Th)/He dating of zircon and apatite, and 40Ar/39Ar dating of hornblende, mica, and feldspar. This offshore record will be augmented and tested by applying the same methods to onshore bedrock samples in the Transantarctic Mountains obtained from the US Polar Rock Repository and through fieldwork. The onshore work will additionally address the debated incision history of the large glacial troughs that cut the range, now occupied by glaciers draining the East Antarctic Ice Sheet. This includes collection of samples from several age-elevation transects, apatite 4He/3He thermochronometry, and Pecube thermo-kinematic modeling. Acquiring an extensive geo- and thermo-chronologic database will also provide valuable new information on the poorly known ice-hidden geology and tectonics of subglacial East Antarctica that has implications for improving supercontinent reconstructions and understanding continental break-up.

This project will establish a laboratory with state-of-the-art instruments for measuring noble gases in rock, mineral, and water samples, for geochronologic and geochemical studies in Earth, planetary, and environmental science. The facility will enable a wide variety of scientific studies by researchers and students at the University of Arizona and collaborating institutions. Some of the primary goals of these studies will be: 1) to investigate the timing and rates of geologic events and processes using radioisotopic dating, including faulting, magmatism, and erosion, 2) to characterize the behavior of noble gases in minerals to understand the material properties of natural crystals, and 3) to trace the movement and evolution of groundwater and other fluids in the Earth's subsurface. This project will also enable hands-on research training for students who will use the instruments and laboratory, helping them develop the quantitative and technical skills and experience for Earth, planetary, and environmental science.

The centerpiece of the laboratory will be a new multi-collector gas-source sector mass spectrometer and sample introduction equipment including devices for extracting gases using resistance (furnace) and laser heating, crushing of fluid-inclusions, and exsolution from fluids. State of the art high-resolution, high-sensitivity, and multi-collection capabilities of the mass spectrometer will enable simultaneous measurement of all isotopes of argon and neon, and helium will be measured by peak-hopping. Important research foci for the instrument will include 1) geo- and thermochronology using the 40Ar/39Ar system for applications in tectonic, detrital, volcanic, and fault-systems; 2) low-temperature 4He/3He thermochronology and understanding helium mobility in minerals; 3) cosmogenic and nucleogenic 21Ne dating for geomorphic applications and for dating secondary minerals like iron oxides; and 4) isotopic compositions and concentrations of noble gases for tracing the fluxes and evolution of subsurface fluid-rock systems. In addition to serving researchers and students at the University of Arizona, Utah State University, and University of Texas El Paso, the facility will also provide analytical services and research experience opportunities for collaborators at a variety of institutions, including universities and liberal arts colleges, through analyses and workshops for diverse cohorts of students.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

This project investigates how changes to the Earth’s surface over geologic time have affected the deep biosphere, the geologic and climatic factors that favor or limit the potential for subsurface microbial life, and the history of microbial life and its relationship to fluids and fluid-rock reactions. Knowledge of how water and other fluids flow at great depths beneath the Earth’s surface, and how this supports and affects life deep within the Earth’s crust, is very limited. Yet, understanding the ways that these subsurface fluids, rocks, and microbes interact and evolve over geologic time is essential for sustainable use of water, mineral, and energy resources and disposal of their unwanted by-products. Results will identify specific time periods in the geologic past and locations within the Earth’s crust where subsurface conditions promoted microbial activity and provide insights into the long-term history of microbial habitability in the planet’s deep biosphere. This project will train several graduate students, help to recruit and retain first-generation, low-income, community college, and under-represented minority undergraduate students, engage K-12 students through development of Earth Science curriculum, and share research results more broadly with the general public through educational videos.

This project will develop an interdisciplinary framework and approaches necessary to track the evolution of subsurface microbe-rock-fluid systems in the upper few kilometers of the Earth’s crust. The research will explore the interconnections between fluid circulation, fluid-rock reactions, and subsurface microbial habitability, and make predictions regarding the evolution of these conditions over geologic time. The project will identify the drivers and permeability changes promoting convergence of compositionally disparate fluids and rocks that alter subsurface redox gradients, thermodynamic conditions, and metabolic potentials for microbial activity.The Paradox and Rio Grande Rift basins in the southwestern US will be the field sites used to develop and test models that can be applied to other subsurface microbe-rock-fluid systems. Research outcomes will generate critical information on the lower boundaries of the active hydrologic cycle and deep microbial ecosystems required for effective management of subsurface water, mineral, and energy resources and storage of alternative energy and waste-products.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.