Daniel F. Stockli - US grants

This project will support the investigation of the dynamics of a system of intraplate faults in the southern part of the central Walker Lane belt, known as the Mina deflection, using an integrated approach of field mapping, tectonic geomorphology, paleoseismology, thermochronology, and geochronology. Faults within the Mina deflection define a regional-scale releasing bend that transfers slip from the Eastern California Shear Zone to the Walker Lane Belt. The Eastern California Shear Zone and Walker Lane Belt straddle the boundary between dominantly east-west extension in the Basin and Range province to the east and dominantly NW-shear along the Pacific-North American plate boundary to the west. The interaction between extension and transcurrent shear has resulted in the development of a complex array of faults that accommodate intraplate strain.

The research is motivated in large part by ongoing geodetic investigations on the magnitude of present-day strain accumulation and pattern of strain distribution across the Eastern California Shear Zone and Walker Lane Belt. In light of these geodetic constraints on strain accumulation, it is timely to improve our understanding of the spatial and temporal patterns of strain release during late Cenozoic to Recent times. The two data sets will provide important constraints on geodynamic hypotheses proposed for the evolution of the Eastern California Shear Zone and Walker Lane Belt. An accurate characterization of the temporal and spatial strain distribution within the Eastern California Shear Zone and Walker Lane Belt is crucial for understanding tectonic processes over a much broader area of intraplate deformation associated with the interaction between the Pacific and North American plates.

0309976
Stockli

Cenozoic extension within the Tibetan Plateau is expressed as a series of prominent
N-S trending rift valleys. Recent GPS studies show that these graben systems and associated conjugate strike-slip systems accommodate a significant portion of internal N-S shortening and E-W expansion of the Tibetan Plateau. The development of these structures represents a significant shift in deformational style and marks the transition to a constrictional strain field within the Tibetan crust. Determining the timing of the formation of these structures is a critical step in understanding the evolution of the plateau. In order to test existing hypotheses proposed to explain these N-S trending rifts and to understand the geodynamic significance of Cenozoic E-W extension in Tibet, the PI needs to answer two fundamental questions. (1) What is the timing of initiation and spatial distribution of E-W extension in Tibet? (2) What is the temporal and kinematic interplay between conjugate strike-slip deformation and E-W extension within central Tibet? A regionally synchronous versus diachronous onset of rifting or progressive migration versus discrete episodes of fault initiation have very different implications for the evolution of the intraplate strain field and the driving forces responsible for rift formation. Currently, the different geodynamic models for the Cenozoic evolution of Tibet are difficult to evaluate due to the lack of sufficient temporal constraints on the onset of rifting. The PI proposes to use an integrated approach, combining structural mapping with apatite (U-Th)/He and fission track dating, to elucidate the timing and magnitude of faulting associated with the Cenozoic strain pattern across central Tibet. Thermochronological methods directly dating the cooling of rocks in exhumed fault blocks will complement field-based kinematic analysis of the rift systems and should help resolve outstanding questions regarding the timing and geodynamic significance of the Tibetan rifts. This proposed study will have far-reaching implications for our understanding of how the lithosphere behaves during continent-continent collision. New data will yield insights into the fundamental problem of how and when Tibet extended after thickening, information that is critical for evaluating the many different tectonic models for this entire region. Furthermore, results will shed light on the hotly debated question of whether there is a temporal link between E-W extension and surface uplift of the Tibetan plateau. Given the implications of the uplift of the Tibetan plateau for regional and global climate, the PI expects his results to be of interest to a wide spectrum of geoscientists. This project also has substantial educational and societal merit. The proposed international collaboration with scientists from the Chinese Academy of Science will permit an exchange of scientific ideas and knowledge. This exchange will greatly benefit KU students, exposing them to the classic Himalayan-Tibetan orogenic system. Two KU graduate students will be deeply involved in several mapping expeditions and will work closely with scientists from UCLA and the Chinese Academy of Science.

The PIs will undertake a structural and thermo-chronological study of the Saudi Arabian Red Sea margin as a part of the MARGINS "Rupture of the Continental Lithosphere" initiative. This margin offers an exceptional opportunity to study the processes associated with continental rifting and how extensional strain is distributed in space and time. The PIs will employ apatite fission-track and (U-Th)/He thermo-chronology and structural mapping in the study area to achieve their objectives. The study will contribute to a more comprehensive understanding of the Red Sea rift and will form a part of the overall geological/geophysical work planned in this area under the MARGINS program. A close collaboration with the Saudi Geological Survey is envisaged.

The investigators in multidisciplinary collaborative project are examining the Tertiary exhumation history of the Colorado Plateau and adjacent southern Rocky Mountains. The goals of this work are to understand the thermal history of rocks of the Colorado Plateau region, and how these rocks came to be at near-surface levels. Together with simple calculations of how the Colorado Plateau landscape has been eroded, the thermal history of the rocks is being used to constrain the surface uplift history of the Colorado Plateau. This project relies on rock exhumation recorded in the thermal and geologic history of the Colorado Plateau region. The thermal history is reconstructed from two techniques that record the low-temperature (less than 110 deg C) cooling of rocks, fission-track annealing and the relative abundance of uranium, thorium, and helium inside minerals such as apatite. The project involves creating a Geographic Information Systems database (to be shared with the scientific community) of the rock exhumation and erosion data. These data are used in a preliminary modeling effort to study the implications of our data for the uplift history of the Colorado Plateau and southern Rocky Mountains. This research is providing new products that may be used in educational displays at National Parks across the Colorado Plateau.

0414817
Stockli

In recent years, (U-Th)/He dating of U- and Th-bearing accessory minerals has attracted tremendous interest as a means of constraining the timing and rates of a wide spectrum of upper-crustal to near-surface geological processes. The rapidly increasing demand for high-quality low-temperature thermochronological data exceeds the current analytical capacity of the few operating laboratories. This is clearly expressed by the large number of researchers interested in utilizing the KU facilities and the number of ongoing collaborative projects. The biggest obstacle toward meeting the demand for (U-Th)/He data is the availability of personnel to carry out the analytical work and assist visiting scientists. The addition of a full-time technician dedicated to the KU (U-Th)/He laboratory will ensure the smooth and efficient operation of the laboratory, dramatically accelerate research productivity and sample throughput, and allow the laboratory to engage in additional collaborations and to host visiting scientists and students that want to use the laboratory. The addition of a full-time technician to the KU (U-Th)/He laboratory represents an important investment into the national and international thermochronology research infrastructure with the prospect of a high payoff for the geosciences community in terms of scientific merit and educational impact. KU and visiting graduate and undergraduate students will work one-on-one with the technician in the KU (U-Th)/He laboratory, gaining invaluable hands-on experience important to their intellectual growth.
***

(U-Th)/He dating of phosphate and silicate minerals such as apatite, zircon, monazite, and titanite has attracted considerable interest; however, U- and Th-bearing Fe- or Ti-oxides have not been systematically investigated and developed as low-T thermochronometers. A common oxide mineral is rutile (TiO2), which is present as an accessory mineral in many magmatic rocks and also occurs widely in high-grade metamorphic rocks, especially in blueschists, eclogites, and granulites. We propose to develop and calibrate rutile (U-Th)/He geo- and thermochronometry by investigating its He diffusion characteristics; we will include such factors as grain size and chemical composition. Furthermore, we will test rutile (U-Th)/He dating on fast-cooled volcanic rocks as well as more slowly-cooled sample arrays from the KTB ultra-deep borehole and an exhumed extensional fault block in the Wassuk Range, western Basin and Range province. We will also apply rutile (U-Th)/He thermochronometry to date the cooling of high-pressure metamorphic rocks from Oman. The (U-Th)/He calibration of rutile will provide a new geo- and thermochronometer that will be widely applicable, but should be especially useful for studies of high-P to ultrahigh-P samples that are notoriously difficult or impossible to date at the present. The scientific results and methodologies developed during our study will be disseminated to the geosciences community through publication of research papers and presentations at international meetings. The study will significantly impact the education of two students that will work with the PIs in the KU (U-Th)/He and TIMS laboratories, providing them the opportunity for active learning and exposing them to state-of-the-art analytical facilities and new research directions. This background will be important to the intellectual growth of the students and give them experience in working in collaborative and group/team situations.

Workshop Support: GeoFrame Walker Lane
Principal Investigator:
Daniel Stockli, University of Kansas, Lawrence
GeoFrame is an integrative geologic initiative that takes a multi-dimensional view of the
building and modification of the North American continent through time and space. The
initiative's goals can be achieved by systematic integration of geologic and geochronometric
investigations and the results from unprecedented geophysical imaging as part of the EarthScope
Program. The overarching EarthScope geophysical experiment has the potential to be a
transformative program for the Earth Sciences, building a foundation for a more complete
geodynamic understanding of the evolution of the North American continent. GeoFrame has
outlined seven focus regions across the conterminous U.S., specifically to address fundamental
aspects of the growth and modification (e.g., rifting) of the North American continent through
time. The GeoFrame effort envisions these focus site investigations to entail map-scale arrays of
passive source seismic receivers and associated active source seismic studies and complementary
geophysics in conjunction with geologic-based synthesis and targeted studies. Study of these
regions should proceed in an intensified fashion, in concert with planned USArray steps.
One of these focus sites is the Walker Lane region in eastern California and western
Nevada. We propose to organize a two-day workshop that will bring together a wide spectrum of
geologists and geophysicists who are working in the Walker Lane. This GeoFrame focus site
workshop is particularly timely given the deployment schedule of the USArray "BigFoot" array.
This workshop is intended to facilitate the organization of an integrated geophysical and
geological approach to understanding the geodynamic evolution of the Walker Lane.

Implicit in the design and implementation of EarthScope is the recognition that progress on
issues such as these requires the collaborative efforts of researchers working in complementary
disciplines. This workshop is designed to build a broad-based community of researchers focused
on integrative geophysical and geological investigation of the Walker Lane. As such, it will open
new avenues of collaboration between working groups and identify new research needs and
opportunities. We anticipate the integration of results and efforts with the NSF Margins
Rupturing of Continental Lithosphere (RCL) initiative in the Gulf of California by continuing the
work onshore from the Gulf of California to the north into Nevada.

Intellectual merit. Continental and oceanic basaltic extrusive rocks are the most common volcanic rock types on the earth's surface and their temporal and spatial evolution are critical for the understanding of plate tectonics, mantle melting processes, paleomagnetism, continental flood basalt provinces, etc. At the same time, basaltic rocks, especially when aphanitic and altered, are often difficult to date. Magnetite (Fe3O4) is found in nearly all types of extrusive rocks and common in basaltic to intermediate volcanic rock types. It is proposed to develop and calibrate magnetite (U-Th-[Sm])/He dating as a novel technique for reliably determining ages of basaltic rocks. We anticipate that this approach and results from the proposed case studies should be of significant interest to a large and diverse portion of the geosciences community interested in the continental and oceanic realm. In a feasibility study, analytical procedures were developed for magnetite (U-Th-[Sm])/He dating and its potential demonstrated in reliably dating basaltic lavas where other techniques might not provide meaningful results. This project will rigorously develop and calibrate the dating of magnetite and explore its geological application to both continental and oceanic basaltic rocks. Specific objectives of this study are to (1) investigate 4He and 3He diffusion kinetics in magnetite, (2) refine analytical techniques to improve precision and accuracy of magnetite (U-Th-[Sm])/He geochronology, (3) conduct a magnetite (U-Th-[Sm])/He dating case study on the Steens-Columbia River basalts, and (4) apply magnetite (U-Th-[Sm])/He date to oceanic basalts from the N Emperor Seamount chain (IODP Leg 197) and Ninetyeast Ridge (IODP Leg 183).

Broader impacts. The proposed project evaluate a new geochronometer for use with samples that are notoriously difficult or impossible to date at present, especially when dealing with aphanitic and/or altered basalt. This will represent a considerable methodological advance and will offer a new technique for other scientists to utilize. The study will support a female graduate research assistant and involve an undergraduate student in some aspects of the research. The project will involve collaboration between the Kansas U. group and with scientists from MIT and Berkeley Geochronology Center. The PI strives to involve minority students in isotope geochemistry through participation in a KU Geology collaborative diversity initiative with the University of Puerto Rico Mayaguez (UPRM). This diversity initiative encourages minority students to pursue undergraduate summer research and graduate work.

This project will investigate how modern continental extensional systems and associated basins are developing in regions of hot, thick crust. Tibet is underlain by the thickest crust on Earth that is arguably flowing at mid-crustal levels, and is actively extending East-West at greater that one-third the total North-South convergence rate between India and Asia. Recent studies show that North-trending Tibetan normal faults and adjacent basins vary systematically in their characteristics as a function of extension magnitude, and may provide sequential snapshots of rift basin evolution during progressive extension. Nascent rifts are characterized by half-graben basins bounded by high-angle normal faults. In contrast, more evolved rifts are bounded by low-angle detachment faults characterized by basins undergoing incision with intrabasin drainage divides in areas of inferred maximum extension. The goal of this research is to test the hypothesis that Tibetan rifts initiate as high-angle normal faults and associated half-grabens that evolve into detachment faults active at uppermost crustal levels and above which rift basin fill is uplifted and eroded, in response to progressive tectonic unloading and isostatic rebound. This hypothesis, along with several alternatives, will be tested in this project along a well exposed in central Tibet by using geological and structural mapping, cosmogenic dating, basin analysis, and low-temperature thermochronology. The project is a multi-disciplinary and collaborative research effort between faculty and students at the University of Kansas, University of Arizona, University of Texas, Dalhousie University in Canada, and the Institute of Tibetan Plateau Research in China.


Project findings will have a major scientific impact by documenting in detail how modern extensional systems develop in regions of active orogenesis that are underlain by hot, thick crust. The results will allow testing of contrasting models for the development of metamorphic core-complexes and low-angle normal faults, and may shed new light on the role of mid-crustal flow in enhancing isostatic rebound during continental extension.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). The funds will be used acquire a diode laser heating system for the (U-Th)/He thermochronology laboratory in the Department of Geology of the University of Kansas. The acquisition of a new diode laser heating system will allow (1) continuation of our NSF-sponsored research at KU currently involving many graduate and undergraduate students, (2) countless national and international collaborative efforts, providing a multitude of faculty, researchers, and students access to a state-of-the-art facility, and (3) development of new thermochronometric techniques and exploration of new research avenues. There is a tremendous demand for low-temperature thermochronometry data to address crucial questions about the timing and rates of a wide spectrum of geological processes ranging from tectonics and landscape evolution to energy related research. In addition to our enormous collaborative and service work load, new research avenues in our laboratory as a result of this acquisition will focus among other things on: (1) laser (U-Th)/He dating of carbonate and hydrous phases; (2) diffusion experiments at higher temperatures (900-600ºC), (3) heating and degassing of larger samples (e.g., magnetite), and (4) U-Pb and (U-Th)/He double-dating of zircon and rutile from sedimentary basins. The proposed acquisition will help maintain the current productivity levels, enhance the existing facilities, and impact the national/international user community of our laboratory. The PI and his colleagues also have a long record of integrating research and education, involving graduate and undergraduates in research and attracting minority and underrepresented students to geology and geochemistry.

Northwesterly displacement of the Sierra Nevada with respect to the Great Basin in the western US Cordillera has been ongoing for the last 12 to 15 Ma. This motion is accommodated by a complicated and incompletely understood belt of deformation along the western margin of the Great Basin that links major, misaligned strike-slip faults in eastern California and western Nevada. Based on previous research and our preliminary work, we have identified that the deformed belt underlies a region of nearly 15,000 km2 and contains large tectonic blocks that both translate toward the northwest as the crust is pulled apart and also undergo vertical-axis rotations of 20° to 90°. In this project, we will provide a better understanding of the dimensions of the tectonic blocks, how far they have moved laterally, to what degree they experienced vertical-axis rotation, and the spatial-temporal pattern of deformation. Much of the western borderland of North America and many parts of other continents around the world reside in similar tectonic settings and record comparable histories of deformation. This study will provide the opportunity to better understand how and to what degree the translation and rotation of large crustal blocks is accommodated as the continental crust is fragmented in response to the relative movement of lithospheric plates.


Crustal response to displacement transfer in structural stepovers linking misaligned segments of large-magnitude transcurrent faults is accommodated by components of translational and rotational displacement and strain and results in complex three-dimensional arrays of structures. The mechanisms by which rotational and translational strain are accommodated either by rigid-blocks and/or by distributed strain and to what degree the translational and rotational processes are coupled in space-time are poorly understood. In this study, we integrate detailed and regional geologic mapping with thermochronologic, structural, and paleomagnetic analysis to unravel the history of transcurrent structures separating the Sierra Nevada and central Great Basin. The objective of the work is to characterize transcurrent and high-angle normal fault displacement, estimate slip on low-angle detachment faults, and assess the relation between translational deformation and differential rotation. Our research results will provide the needed detailed understanding of the spatial and temporal pattern of deformation and supply the constraints to differentiate between coeval and serial translational and rotational deformation histories within the stepover system and provide the means to assess whether or to what degree rotation is accommodated by rigid-body motion or distributed strain processes.