George E. Gehrels - US grants

The rocks of the Alexander-Stikine suture zone in southeastern Alaska include the boundary between locally derived geological terranes formed on the west coast of the North American plate and the exotic terranes which have, over geological time, migrated long distances due to the movement of the Pacific plate. Field studies in this zone by the principal investigator of this project will be focused on the global tectonic processes through which these distant terranes were displaced and finally joined on the western margin of North America. This proposal requests 50% of the funds required to purchase a small research boat for field transportation in this otherwise inaccessible region. The NSF-sponsored research in the geological history of the rocks of the Alexander-Stikine suture zone of southeastern Alaska will provide new and specific interpretations of the growth of continents during plate tectonic changes.

The western margin of North America has experienced several episodes of tectonic activity, culminating in large-scale accretion of allochthonous terranes in the Mesozoic. The Kootenay Arc is an arcuate belt of Proterozoic to Jurassic rocks extending from east-central Washington to SE British Columbia. This study will examine and attempt to date the emplacement of early Paleozoic eugeoclinal sedimentary and volcanic rocks over Cambrian and older miogeoclinal rocks. Emplacement of the allochthonous rocks could have occurred either during the mid-Paleozoic Antler orogeny, or during Jura-Cretaceous accretion of outboard tectonic fragments. Results will have considerable impact on models of the tectonic evolution of the western continental margin of North America including indication of how close some of the allochthonous terranes were to the margin during the Jurassic and perhaps Paleozoic time.

The northern part of the North American Cordillera comprises a mosaic of tectonic fragments, some of which formed in intra- oceanic environments far from North America. Other fragments appear to have accumulated in a continental margin environment. Present information about terranes in northern British Columbia and adjacent Yukon indicates that the Nisling terrane was originally formed in proximity to a continent, and is now surrounded by fragments of oceanic affinity. Prior work has out- lined relations that permit several different tectonic scenarios. This renewal will attempt, by mapping, structure and strati- graphic studies and isotopic analysis, to resolve between these possible scenarios. Results are expected to place significantly tighter constraints on the rate and processes of continental assembly in the northern cordillera.

Discordant Cretaceous paleomagnetic directions observed in plutons of the North Cascades and the Coast Mountains Batholith indicate major tectonic disturbance subsequent to magnetization. Several lines of geological evidence suggest that consistent and large-scale tilting has affected intrusive rocks of this Mesozoic plutonic welt along the western margin of North America from the North Cascades to southeast Alaska. This may be a fundamental tectonic process the scope of which has not been previously appreciated. The Bell Island pluton is a 90 Ma pluton on the western flank of the Coast Mountain Batholith north of Ketchikan in southeast Alaska. Extensive structural, petrologic, and isotopic data indicate that the Bell Island pluton experienced 25o of northeast-side-up tilting in the 90 Ma to 50 Ma interval. This pluton provides an excellent opportunity to study the paleomagnetic and geologic record resulting from tilting of a large panel of crust and the tectonic processes involved in regional-scale tilting. This study is a combined geologic and paleomagnetic investigation along a southwest to northeast transect across the Bell Island pluton. The research could provide crucial information towards: (1) resolution of the northwards transport - versus - crustal tilting debate regarding discordant Cretaceous paleomagnetic directions (and therefore determination of a Cretaceous paleogeography for North America); and (2) determination of the importance of tilting of crustal panels in the tectonic evolution of North America.

This study will establish the first detrital zircon reference dataset for Paleozoic and Mesozoic western margin of North America, from eastern Alaska to northern Sonora. The work will use and further define a new technique for detrital zircon geochronology. Zircon populations from the Paleozoic-Mesozoic Cordilleran miogeocline will be compared with those from outboard allochthonous terranes to determine the displacement and accretionary history of the latter. The results will provide an important tectonic framework for the analysis of the tectonic evolution of the western margin of North America.

The Alexander Terrane, an accreted crustal fragment in southeast Alaska, affords a unique opportunity to determine its paleolatitudinal motion history through paleomagnetic and detrital zircon analysis. Alternative paleopositions for the terrane during the Paleozoic are: (1) the Sierra-klamath province of California; (2) the paleo-Pacific margin of Gondwana; or (3) an intra-oceanic setting. This study will resolve the controversy surrounding the origins and movement history of the Alexander Terrane, and will have major implications for the accretionary history of the North American Cordillera. The results will have bearing on orogenic processes in other tectonic settings.

9303824 Gehrels The Coast Mts. Orogen of the North American Cordillera, comprises several important tectonic features, including one of the largest batholiths in the world, a major suture zone, regionally extensive upper amphibolite granulite facies rocks and a major thrust belt. This research will determine the detailed geochronology of the major structures and integrate the findings with interpreted plate motions. The results will provide tight constraints on timing and style of plate-margin processes, especially at the cessation of subduction and onset of orogen-parallel transform motion.

9416933 Gehrels One of the fundamental questions in Cordilleran tectonics is the degree of orogen-parallel transport of outboard terranes before final docking and amalgmations to North America. Paleomagnetic data has commonly been used to determine latitude shifts of allochthouous terranes, but the method has many possible sources of error. As a result, geologic data is frequently at adds with paleomagnetic interpretations. This project intends to employ an entirety different technique to detect and quantify orogen-parallel terrane translation. Prior work has assembled a database of the distribution of zircons in source rocks along the western north american craton. This project will examine suites of detrital zircons from outboard terranes and match their age distributions to the North American craton database to estimate the degree of allochthoniety. Successful results will provide an independent test for possible northward translation of several exotic terranes in western Nevada and northern California, thereby helping to resolve the discrepancy between paleomagnetic results and geology analysis. ***

9404843 Butler An important problem in the tectonics of the Pacific Northwest concern the displacement and accretionary history of the Alexander- Wrangellia terrane of southeast Alaska and Coastal British Columbia. There is presently no consensus on the positions of the terrane during Jurassic through Paleocene time and tectonic processes by which the terrane was accreted to North America are controversial. This project, a collaborative effort between working at the University of Arizona and the University of Mississippi., will test various tectonic models of the area by paleomagnetic and detrital zircon age dating methods. Results should help place new constraints on the displacement and accretionary history of the Alexander-Wrangellia terrane.

9315625 Patchett This project will measure Nd isotopes, REE and other trace elements in sandstone from the miogeocline of the Canadian Rocky Mountains in order to quantify the amount of continental material supplied during the lifetime of the Canadian Cordillera. Detrital zircon data will also be used to determine the relative amounts of far-traveled versus near-travelled detritus. The results will give a useful baseline for future provenance studies in the region. Results will also have implications for the existence of a large, 340 Ma terrane in the region and the movement of individual terranes within the orogen. These findings will have broad application to the study of tectonic terranes in other orogenic belts.

9526269 Patchett This grant provide partial support of the costs of acquiring a new thermal ionization mass spectrometer (TIMS) with multiple collectors and ion counting capabilities which will used for isotopic research at the University of Arizona's Department of Geosciences. Specifically, the new TIMS will complement an existing VG-354 TIMS purchased entirely with University of Arizona funds in 1983 that is presently oversubscribed and is beginning to show degradation, particularly with regard to measurements of Strontium isotope ratios. Thus the older TIMS will be used primarily for analyses of U-Pb, Lu-Hf and Sm-Nd isotopes in studies of tectonics and crustal genesis while the new TIMS would be largely used for research utilizing Sr isotopes in studies of Himalayan tectonics and the use of 87Sr/86Sr in lacustrine carbonates as a proxy for paleolake levels. ***

9526263 Gehrels The ACCRETE program is a collaborative endeavor to determine how continents grow by magmatic and terrane accretion, and to investigate the relative roles of these processes. This award is part of a project which involves a three year coordinated geophysical and geological study of mid-Mesozoic to mid-Cenozoic continental growth by accretion. The goal is to develop a four dimensional (X,Y,Z,and time) understanding of accretionary processes along the portion of the northwestern margin of North America underlain by the Coast Mountains orogen, British Columbia and southeastern Alaska. Specifically, the project involves a transect of the orogen close to the British Columbia-Alaska border. A geophysical pilot project along this transect in the summer of 1994 resulted in over 1700 km of new marine MCS (Multi-Channel Seismic), gravity and magnetic data, and common receiver gathers from 60 REFTEK seismometers. Building on the high quality of this geophysical data base, the Principal Investigators propose a group of studies designed to construct a 400 km cross section of the orogen through the entire crust and into the upper mantle. To accomplish this, they must resolve fundamental questions regarding how continental crust is formed during terrane accretion. ***

9725663 Butler The Altyn Tagh fault in northern Tibet has unique characteristics that make establishing its kinematic history pivotal to understanding the evolution of the Indo-Asian collision. This feature, arguably the largest active intracontinental strike-slip fault system on Earth, is a focal point in both end-member models that have been proposed to describe the mechanical behavior of continental deformation: distributed shortening and lateral extrusion. This project involves a four year, integrated geological, geochronological and geophysical investigation that will focus on the determination of the magnitude, rate, and distribution of slip on the Altyn Tagh fault at time scales between 10,000,000 years to 4 years. The principal investigators will utilize geologic mapping and geochronology to establish piercing points, use paleomagnetic analysis to investigate several possible oroclinal folds along the fault, undertake a GPS survey to establish the slip rate, slip distribution and locking depth along the fault zone, and use mapping and cosmogenic dating of geomorphological features to establish Quaternary slip rates. ***

9976676
Ruiz

This award provides partial funding for the acquisition of a multicollector inductively-coupled plasma mass spectrometer (MC-ICP-MS) to be installed and operated by the Department of Geological Sciences at the University of Arizona. The University of Arizona is committed to providing the remaining funds necessary for the acquisition. Research applications at the University of Arizona requiring the capabilities of the MC-ICP-MS include (1) Origin of metal deposits at convergent plate margins from Os and Pb isotope analysis, (2) Life in extreme environments from Fe, Cu, and Zn isotopes, (3) Origin of silicic magma chambers from in situ Sr analysis of feldspars, (4) History of crust and mantle evolution using Hf isotopes, (5) Geochronology of convergent plate margins using in-situ U-Pb in zircons, and (6) U-Th dating of carbonate soils and calibration of the C-14 time scale by U-Th dating of speleothems and corals.

***

0105339
Gehrels

The Himalaya has received intensive study as if is an active continent - continent collision, and many parameters such as amount of shortening, rates and subducted material measured in the Himalaya have been used in developing general models for continent - continent collisions. Recent results indicate that some of the shortening in the Himalaya may be due to an older event. This project aims to investigate this pre-Himalayan deformation and separate it from the tertiary collision of India with Asia, generally considered to be the Himalayan orogen. Results are expected to refine or correct important aspects of the deformation history of this important system that will have widespread application.

One of the most interesting data sets to emerge from recent studies of the Himalayan orogenic belt consists of U-Th-Pb ages reported by Harrison et al. (1997) and Catlos et al. (2001a, 2001b) from monazite inclusions within garnet crystals in the metamorphic rocks associated with the Main Central thrust (MCT) in central and eastern Nepal. Some of the monazite inclusions crystallized and were incorporated into the gamets during late Miocenc-Pliocene time. Geothen-nometry and geobarometry data indicate that metamorphic temperatures ranged from 500'-SOO'C and pressures ranged from 8-12 kbar. Because detn'tal monazite in pelitic sediments is destroyed during burial to the depths recorded by the mineral assemblages, the monazite ages most likely record the timing of garnet growth during Himalayan orogenesis (Harrison et al., 1998). Thus, the monazite ages contain infon-nation that is vital for kinematic reconstructions of Himalayan thrust systems, particularly the MCT and its proximal footwall rocks.
The interpretation of the monazite ages offered in these previous studies suggests that the MCT was reactivated during late Miocene time, and that rocks in the footwall of the MCT were progressively incorporated into the hanging wall and raised to the surface. A number of independent lines of evidence suggest that this hypothesis may be correct, including 'o Ar/ " Ar cooling ages (Copeland et al., 1991; Macfarlane et al., 1992; Copeland et al., 2001); (2) levelling and GPS studies (Jackson and Bilham, 1994; Bilham et al., 1997; Larsen et al., 1998); and (3) neotectonic and geomorphic studies of the MCT zone in central Nepal (e.g., Bilham et al., 1997). Although reasonable, the MCT reactivation hypothesis incorporates some surprising kinematic processes. Paramount among these is the requirement that approximately 40 km of slip on the MCT occurred during late Miocene-Pliocene time in order to convey the garnets and their monazite inclusions to the surface. If the MCT was indeed reactivated, it would be (by far) the largest out-of-sequence event on a thrust fault ever documented. Whereas out-of-sequence thrusting is now widely accepted in thrust belt models, it generally is restricted to relatively minor displacements (a few km). A reactivation event of the hypothesized magnitude would significantly alter current concepts of how the Himalayan fold-thrust belt operates, and how foldthrust belts in general operate. It is conceivable that the extreme rate of erosion along the MCT in Nepal has shifted the fold-thrust belt into a near terminal state of subcriticality, stalling its forward propagation and completely reorganizing the locus of major thrusting. Thus, the out-ofsequence MCT hypothesis is worthy of careful and critical examination. The key to understanding the young monazite ages lies in the structure of the rocks below the MCT from which the youngest monazite ages were obtained. Unfortunately, the stratigraphy and structure of the rocks below the MCT in central Nepal (where the monazite studies have been executed) are not well documented. Exact placement of the MCT in the field is still hotly debated, such that the tectonostratigraphic context of the samples remains in doubt. Alternatives to out-of-sequence reactivation of the MCT can explain equally well the young monazite ages. In this work, the PI's will implement a critical test of the out-of-sequence hypothesis in western Nepal. They will collect samples for U-Th-Pb monazite dating of gamet-bearing rocks and " Ar/ " Ar dating of micaceous lithologies along north-south transacts from the Main Boundary thrust in the south to the South Tibetan detachment in the north. They have already established the regional stratigraphy, structure, geochronology, and Nd isotope geochemistry of the Lesser Himalayan zone south of the MCT in western Nepal during the past six years (DeCelles et al., 1998a, 1998b, 2000, 2001; Robinson et al., 2001, 2002). They propose to obtain U-Th-Pb ages from monazite inclusions in garnets collected from rocks that span the MCT zone. They will also map the zone in detail and collect samples for U-Pb zircon and Nd-isotopic analysis in order to locate the MCT exactly in the field. The " Ar/ " Ar cooling ages should help to document the regional history of thrust sheet emplacement, which will be needed to support any interpretation of what occurred along the MCT. The proposed work should help to resolve whether the MCT experienced major (several tens of km) slip during late Miocene-Pliocene time. The result of the MCT question will have an impact on general models for orogenic wedges, in particular whether rapid erosion can relocate the locus of major thrusting on a scale required by large-scale reactivation of the MCT. In addition, the proposed " Ar/ " Ar dating should provide an unprecedented level of detail and precision for the timing of thrust sheet emplacement in the Himalaya. Because the Himalaya is intimately related to the growth of the Tibetan Plateau and changes in global ocean chemistry, the PI's results should have applications beyond Himalayan tectonics.

The PI's propose a multidisciplinary study of Cretaceous and Tertiary rocks along an east-west transect in the Wrangell - Petersburg - Prince of Wales Island area of SE Alaska (= Wrangell transect). Previous research demonstrates that integration of paleomagnetic studies with geochronologic, therinochronologic, barometric, and structural geologic observations can produce important insights into the tectonic evolution of the Insular superterrane and Coast Mountains orogen in western BC and SE Alaska. The PI's recent results from near Prince Rupert show that paleomagnetism is a key component of multidisciplinary efforts investigating exhumed shallow and mid-crustal sections. When accompanied by geologic observations resulting from a carefully coordinated multidisciplinary research program, paleomagnetic data on intrusive igneous rocks 'eld critical information on the tectonic development of deformed yi
regions that cannot otherwise be obtained. For example, the PI's have documented that panels of crust containing the Paleocene Quottoon igneous complex east of the Coast shear zone have experienced east-side-up tilts ranging to 40' during Eocene extension. In addition, their geochronologic, palcomagnetic, barometric, and structural geologic data suggest that the midCretaceous Ecstall pluton was folded during west-directed thrusting. These discoveries are fundamental to understanding the crustal architecture and tectonic development of the continental margin in the northern Cordillera.

Because igneous rocks were emplaced into this part of the magmatic arc during the Cretaceous, throughout the Paleogene, and into the Miocene, the Wrangell transect provides the opportunity to track deformation of an evolving convergent to strike-slip plate margin in space and time. Methods will include U/Pb geochronology of zircon and spheric, Al-in-homblende barometry, 40 Ar/39 Ar thennochronology, (U-Th)/He dating of zircon, metamorphic petrology, and structural geologic investigations in addition to paleomagnetic analysis. Preliminary investigations on the eastern portion of the transect indicate that this area experienced - 1 7' ESEside-up tilt about an axis with azimuth 22' since 20 Ma. Observations from across the transect indicate that paleomagnetic directions from Cretaceous plutons are variable, with both concordant and discordant inclinations. Paleomagnetic study of the Cretaceous and Tertiary igneous rocks of the Wrangell transect, coupled with the geochronologic, thennochronologic, and barometric analyses, can determine: (1) when and where Cenozoic defontiation occurred; and (2) whether regionally consistent tilting/folding and/or large-scale transport can account for discordant paleomagnetic directions from Cretaceous plutons. Combined with results from the Prince Rupert area, successful completion of the proposed research can provide a comprehensive model for the tectonic and paleogeographic evolution of the Coast Mountains and Insular superterrane for the past I 00 m.y.

0309885
Ducea

The goal of this project is to establish the existence or absence of mafic-ultramafic roots to batholiths and whether such roots can reconcile the fundamentally basaltic nature of mantle magmatism with the intermediate average composition of the crust. Two hypotheses are considered: 1) that the dense ultramafic residue founders into the mantle leaving the intermediate crustal compositions above, or 2) the residue exists below the Moho and is seismologically indistinct from mantle peridotite. The PIs will use a combination of petrology, geochemistry and geochronology on the plutons of the Central Coast Range Batholith to track changes in source, depth of origin through time and seismic and gravity data to image the present state of the lithosphere. The Central Coast Range Batholith (CCRB) in British Columbia is a very good location for this study. It is a very large batholith which is relatively young and has not had a protracted tectonic history. It's rugged topography gives access to depth profiles of 20 to 25 km.

Barton
EAR-0230091

This work will study arc magmatism and hydrothermal activity in a 75x30x10 km block of the upper crust in central Arizona. The area has exceptional 3-D exposure due to the topographic relief, arid climate, and extensional fault rotation. This area presents an exceptional opportunity to study shallow (<10 km) magmatic systems, and address near versus far-field controls on mineralization, hydrothermal systems, and styles of magmatic evolution. We hope to develop a picture of the evolution of large magmatic centers in arc settings. The work will focus on geologic mapping, structural reconstruction, geochronology, and petrology of contrasting Laramide centers in the Tortilla and Dripping Spring Mountains. This area encompasses the Ray, Globe-Miami, and Superior mining districts. Mapping will resolve the distribution, timing, and character of igneous, metamorphic, and hydrothermal features. Using these results, pre-extension geometries will be reconstructed and linked to industry and USGS studies. Magmatic and hydrothermal events will be constrained with U-Pb, Ar-Ar, and Re-Os dating and whole rock, mineral, isotope and fluid inclusion studies. Broader impacts include education of post-doctoral, graduate and undergraduate students, collaborations with the USGS and the mining industry, and improved exploration models for porphyry copper and related ore deposits.

Detrital Zircon Geochronology of Colorado Plateau Mesozoic Strata:
Implications for Continental Paleogeography and Paleotectonics

W.R. Dickinson, G.E. Gehrels, P.G. Decelles (University of Arizona)
EAR-0341987

ABSTRACT

The ability to obtain radiometric ages for individual sand grains of the mineral zircon by determining isotopic ratios of uranium and lead contained within the zircon now makes it possible to establish the ages of the eroded bedrock sources that contributed sand grains to sedimentary strata. By applying this technique systematically for the first time to strata of the Colorado Plateau, which exposes the most complete Mesozoic succession in North America, we expect to advance our understanding of the Mesozoic paleogeography of the continent to a level not previously attainable. By coupling knowledge of the ages of potential bedrock sources in different parts of North America with the new information on the ages of zircon grains in strata of the Colorado Plateau, we can infer the patterns of Mesozoic paleorivers that transported sand across the ancient continental surface, and of paleowind systems responsible for deposition of vast paleodune fields that are among the largest in the global geologic record. Knowing the directions of transcontinental sediment transport through Mesozoic time will shed light in turn on evolution of the Appalachian (eastern) and Cordilleran (western) mountain chains of the continental margins because paleodrainages head in highlands, and change configuration as highlands are uplifted by tectonic activity or subdued by erosion. The design of the project involves participation by undergraduate students in all phases of the research as junior colleagues of the faculty investigators.

Within the middle of the Qiangtang terrane of central Tibet is an enormous (greater than 500-km-long and up to 100-km-wide) east-west trending belt of blueschist-bearing melange. This belt occurs structurally beneath continental margin strata, in the footwall of early Mesozoic domal low-angle normal faults, requiring the melange to have underplated continental margin strata prior to exhumation. The tectonic significance of the melange is highly uncertain, with two leading hypotheses proposed to date: (1) the melange marks the location of a suture zone separating formerly unrelated crustal fragments to the north and south. (2) the melange consists of Songpan-Ganzi sedimentary and subduction-accretion rocks which have been underthrust approximately 200 km from the Jinsha suture to the north. In an effort to test these hypotheses, this three-year investigation is conducting (1) regional and detailed geologic mapping and structural analysis along two N-S traverses across the Qiangtang terrane, (2) detailed structural analyses and thermochronologic and thermobarometric studies within the Qiangtang melange, (3) comparative studies of detrital zircon ages from the melange, Songpan-Ganzi strata, and northern and southern Qiangtang region strata, and (4) biostratigraphic studies, led by colleagues from the collaborating Institute of Tibetan Plateau Research in Beijing. Project findings will have a major impact on understanding the tectonic assembly and crustal structure of central Tibet and the general tectonic processes by which melange is incorporated into continental crust. If project results indicate that Qiangtang melange has been underthrust from the Jinsha suture to the north, then much of the deeper central Tibetan crust should include underplated melange. This relationship would also provide an unparalleled opportunity to directly examine processes of low-angle subduction which are rarely observed in the geologic record. Conversely, the conclusion of a major oceanic suture in the central Qiangtang region would require significant revisions to conventional thought regarding the tectonic framework and development of central Tibet. The project involves one Ph.D. student and is engaging a group of undergraduate students to assist in the collection and interpretation of detrital zircon data. In addition, a Tibetan Tectonics" seminar is being organized that will bring together University of Arizona faculty, graduate and undergraduate students, and researchers from Chinese and other U.S. institutions.

EAR-0443387
Gehrels

This award supports the development and operation of a U-Th-Pb geochronology lab (the Arizona LaserChron Center) that utilizes a multicollector ICP mass spectrometer (from GV Instruments) coupled with a 193 nm excimer laser (from New Wave Research). These instruments are capable of generating U-Th-Pb ages rapidly (40 per hour), with a precision of 2-3% (2-sigma), utilizing a beam size of 10 to 50 microns. This rapid throughput is optimal for applications that require generation of large data sets (e.g., detrital zircon provenance studies). The spatial resolution provided by laser ablation also provides a powerful tool for unraveling complex growth/disturbance histories commonly encountered in igneous and metamorphic terranes. The laboratory is presently able to routinely conduct U-Th-Pb age determinations on zircon, sphene, monazite, and monazite inclusions in garnet grains, and efforts to develop analytical methods for analysis of apatite, rutile, and xenotime are ongoing. We anticipate generating ~50,000 U-Th-Pb ages per year in support of ~50 different projects. Students are encouraged to use the facility, and funds are available to support student involvement. We also encourage use of the instrument in a classroom setting as it can be operated remotely with simultaneous displays of laser excavation and age calculation.

0732436
Gehrels

Innovations in experimental methods and instrumentation are revolutionizing the acquisition and application of geochronologic information in Earth Science research. Some of the most exciting advances are being driven by Laser-Ablation Multicollector ICP Mass Spectrometry (LA-MC-ICPMS), which allows for rapid determination of U-Th-Pb ages with micron-scale spatial resolution. This technique is fundamentally changing the way that geochronologic information is utilized, with impacts that cover the span of structural geology, tectonics, stratigraphy, paleontology, petrology, economic geology, and geochemistry.

The Arizona LaserChron Center (ALC) is a multi-user facility that utilizes LA-MC-ICPMS to provide the NSF-supported Earth Science community with U-Th-Pb geochronologic information and training. Primary goals of the ALC are to (1) generate high quality/low cost U-Th-Pb geochronologic information for NSF-supported researchers, (2) use every aspect of facility operation as an opportunity to train student and faculty researchers in geochronologic theory and methodology, and (3) drive the development of new techniques and applications that take advantage of the strengths of LA-MC-ICPMS.

The funding will provide support for ALC staff members to assist NSF-supported researchers in acquiring geochronologic information and to drive the development of new analytical techniques, for maintenance and modernization of instrumentation, and for students to be able to conduct research in the laboratory. This support will enable the ALC to provide geochronologic information for ~50 researchers per year in support of ~30 different NSF-EAR awards. This collaborative research will drive important new developments in studies of the growth of continents, processes of mountain building, generation and dispersal of sediment through space and time, formation of mineral and hydrocarbon resources, history of evolutionary changes, chronology of early hominids, and genetic linkages between climate and tectonics.

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 will provide funds for a workshop that will bring together an international group of approximately 40 geochemists and software engineers to identify and develop solutions for problems in processing and archiving LA-ICP-MS U-Th-Pb data. The first day of the workshop will focus on progress made since the first community discussion of this topic (Vancouver, July 2008), and the second day will focus on using expertise acquired from the EARTHTIME and EarthChem initiatives to enhance existing data-handling systems and to develop new tools that are more robust, powerful, transparent, and user-friendly. Workshop results will be reported through EOS-Transactions of the American Geophysical Union and GSA Today.

This workshop is a crucial next step in the community development of standards for acquiring, processing, reporting, and archiving U-Pb geochronologic data by LA-ICPMS. Developing these standards, and building them into the next generation of datahandling tools, will result in U-Pb ages that are more robust and more easily integrated with other types of data. This will enable researchers, students, teachers, and the general public to use geochronologic in studies of far-ranging fields such as understanding the growth of continents, processes of mountain building, generation and distribution of sediment through space and time, formation of mineral and hydrocarbon resources that are essential to our society, chronology of evolutionary changes, timing of early hominid evolution, and linkages between climate and tectonics.

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

The Department of Geosciences at the University of Arizona will receive funds to build a new electron imaging facility to support the geochronological research of the Arizona LaserChron Center (ALC), and also to serve a broad range of research activities in the Departments of Geosciences and Planetary Sciences. The instrument to be purchased is a variable-pressure, tungsten filament scanning electron microscope equipped with secondary electron (SE), back-scattered electron (BSE), energy-dispersive spectrum (EDS), color cathodoluminescence (CCL) and electron back-scattered diffraction (EBSD) imaging and detection systems.

The primary use for the scanning electron microscope will be to obtain BSE, color CL imaging, and trace element characterization of U-bearing accessory phases required for in situ geochronology at the ALC (an NSF Multi-User Facility). The images that will be obtained with the scanning electron microscope are critical to unravel the dates obtained from single U-bearing minerals, such as zircon by our laser ablation ICPMS National Facility. However, we also expect to support the research of others at The University of Arizona, where the SEM will yield images and elemental analytical data for: (1) Petrologic and geochemical studies of meteorites, (2) Identification of fossils and minerals for paleoclimate studies, (3) Identification of minerals, fluid inclusions, and textures and orientations for investigating petrogenesis, diffusion rates, and ore-forming processes, (4) Augmenting mineral composition and diffraction databases using coupled EBSD and EDS.

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.

U-Pb laser ablation geochronology has become the most commonly applied tool for dating zircons. Despite the widespread application of this tool to a host of geological problems, there is little consensus with regard to analytical strategies and data reduction protocols. The result is inter-laboratory bias and both under- and over-estimation of errors on calculated dates. This limits our ability to compare results from different labs and limits rigorous compilations from databases such as EarthChem. This project will remedy this situation by developing cyber infrastructure tools in support of Laser-Ablation ICP-Mass Spectrometry (LA-ICP-MS). The project will develop open-source, free, software in consultation with the international community to treat with statistical rigor all aspects of data reduction, from calculation of ratios to correction for interferences and drift. Our approach will follow that used in developing similar software as part of the EARTHTIME project and requires the integration of the fields of software engineering and geochemistry. The resulting software will eliminate large sources of interlaboratory bias and serve as a teaching tool showing clearly how raw ratios are converted into dates and uncertainties.

Creating the software for connecting the LA-ICP-MS community with the developing EarthChem database for geochronology and thermochronology will provide the integration of data from this important technique into the larger data structure of geochemistry and geology. These data will play an important role in far-ranging fields such as understanding the growth of continents, chronology of evolutionary changes, timing of early hominid evolution, and linkages between climate and tectonics. During all phases of the planned work, we will involve a broad cross section of the community from undergraduates to post-doctoral scientists to help develop the next generation of analysts and software engineers. In particular, the systematic evolution of the collaboration between software engineers and earth scientists will be advanced as it produces robust and reliable workflow tools.

This project will test the hypothesis that much of southern Alaska formed along the Arctic margin of Canada, with transport to its present position only in the relatively recent geologic past. Such a displacement history is counter to the more traditional view that these rocks, and most other portions of western North America (e.g., Baja California), have moved northward along the continental margin. It also differs from previous suggestions that these rocks formed along the western margin of the paleo-Pacific and are truly exotic to North America. Fortunately, recent technological developments have provided a technique that will provide a robust evaluation of these possible displacement scenarios. The technique involves the determination of ages of zircon crystals in the displaced rocks and in potential correlatives in the western US, along the western margin of the paleo-Pacific, and in the Canadian Arctic. The occurrence of similar ages would suggest potential linkages, whereas the occurrence of different ages of zircon crystals in rocks of the same age would be inconsistent with geographic proximity. This project will provide opportunities for undergraduate and graduate students at two universities to participate in a research project that involves both field studies in frontier regions and laboratory analyses utilizing sophisticated instrumentation.

Primary activities involved in this project will include:

1. Conducting geologic field studies and collecting samples from Paleozoic strata of the Alexander terrane in southeast Alaska and the Pearya terrane in the Canadian Arctic. These studies will be based from zodiacs and a live-aboard boat (presently operated by the University of Arizona) in SE Alaska and with helicopter support in the Canadian Arctic.

2. Determining U-Pb ages and Hf isotope ratios of detrital zircons utilizing a new Laser Ablation-ICPMS system (Nu HR ICPMS) and SEM system (Hitachi 3400N and Gatan Chroma CL) at the University of Arizona.

3. Comparison of our new data with U-Pb ages and Hf isotope information from other assemblages in the circum-Pacific and circum-Arctic realms in an effort to test various possible displacement models for the Alexander terrane.

Much of the field and lab research will be conducted by graduate students at the University of Arizona and the University of Iowa. Undergraduate students will be involved as field assistants, with possible senior-thesis-type projects available as appropriate.

The suturing of continental fragments following the subduction of intervening oceanic lithosphere is a fundamental process in lithospheric dynamics and the shaping and growth of Earth?s continents. However, our understanding of this fundamental process remains limited. Ancient sutures manifest themselves in regional structural, sedimentary, and petrologic patterns across thousands of kilometers, and record evidence of past plate dynamics. The suturing process itself results in drastic changes in plate dynamics, creates Earth?s largest mountain belts, and changes global climate dynamics by closing ocean basins and raising high topography. In terms of a fundamental and global tectonic process, suturing is on par with oceanic subduction and mid-ocean ridge formation, yet little more can be found in Earth-science textbooks than its definition and passing reference to the India?Asia collision. The primary aims of this project are to understand the geodynamic processes before, during, and after suturing, and how these processes impact continental physiography and are expressed in the geological record. To achieve this goal, the PIs propose to study the India?Asia collision zone (IACZ) in southern Tibet and the northern Himalaya. Techniques to be employed include structural geology, stratigraphy, geochronology, thermochronology, stable and radiogenic isotope geochemistry, igneous and metamorphic petrology, paleomagnetism, and numerical geodynamical modeling of the associated processes.

Innovations in experimental methods and instrumentation are revolutionizing the acquisition and application of geochronologic information in Earth Science research. Some of the most exciting advances are being driven by Laser-Ablation Multicollector ICP Mass Spectrometry (LA-MC-ICPMS), allowing one to determine U-Th-Pb ages with micron-scale spatial resolution. This technique is fundamentally changing the way that geochronologic information is utilized, with impacts that cover the span of structural geology, tectonics, stratigraphy, paleontology, petrology, economic geology, and geochemistry.

The Arizona LaserChron Center (ALC) is a multi-user facility that utilizes LA-MC-ICPMS to provide the NSF-supported Earth Science community with U-Th-Pb geochronologic information and training. Primary goals of the ALC are to (1) generate high quality/low cost U-Th-Pb geochronologic information for NSF-supported researchers, (2) use every aspect of facility operation as an opportunity to train student and faculty researchers in geochronologic theory and methodology, and (3) drive the development of new techniques and applications that take advantage of the strengths of LA-MC-ICPMS.

The funding will provide support for ALC staff members to assist NSF-supported researchers in acquiring geochronologic information and to drive the development of new analytical techniques, for maintenance and modernization of instrumentation, and for students to be able to conduct research in the laboratory. This support will enable the ALC to provide geochronologic information NSF-EAR awardees. This collaborative research will drive important new developments in studies of the growth of continents, processes of mountain building, generation and dispersal of sediment through space and time, formation of mineral and hydrocarbon resources, history of evolutionary changes, chronology of early hominids, and genetic linkages between climate and tectonics.

The Himalayan Mountains in Nepal were formed over the last 55 million years by forces associated with the collision of the Indian and Asian continents. Since the onset of the collision, layered rocks draping the upper crust of India have been crumpled and shortened by at least 650 kilometers as the Asian landmass has overridden northern India. This process has produced the highest mountains on Earth. These mountains are important in many respects: they control the climate system of southern Asia, including the all-important Asian monsoon which provides rain in a region that would otherwise be much drier; they store water in the form of glaciers and snow, thus mitigating the effects of drought and providing hydroelectric power to much of southern Asia; they generate the sediments that form the agricultural breadbasket of the region, feeding approximately one quarter of the world?s population; and they embody a dramatic high mountain landscape upon which humans have been inspired to feats of adventure, exploration, and religious devotion. As the mountains have grown, continuous erosion has generated vast quantities of sediment that accumulates along the southern flank of the Himalaya in the Indo-Gangetic foreland basin and in deep sea fans that flank India on the floors of the Arabian Sea and the Bay of Bengal. This sediment provides a record of the history of growth of the Himalaya. Our project aims to reconstruct the history of deformation of the Himalaya in Nepal. The analysis is forensic, as we attempt to retrodeform the rocks that have been folded and thrust faulted in the Himalaya, according to constraints imposed by thermochronology, structural geology, geochronology, and the erosional sedimentary record. Thermochronology measures the time at which a mineral passes through its "blocking temperature" with respect to a particular radiogenic isotopic system en route to the topographic surface as the mountains are growing and erosion is exhuming the rocks. Thermochronological ages can be inverted to assess erosion rates and in some cases the timing of slip on major faults. We will also use Uranium-Lead geochronology to determine the ages of mineral grains in both the eroded sediments and the bedrock source areas of the mountain range. Together these data will allow use to (a) determine the timing of major thrust faulting events within the southern half of the Himalaya; (b) calculate the rate of exhumation of the mountains; and (c) determine precisely the specific sources of the sediments and when they were deposited. Our fieldwork will involve sample collection, and detailed documentation of sections of the sedimentary erosional products where they are uplifted and exposed in the frontal Himalaya. This work promises to elucidate the tectonic and erosional history of the Himalaya at an unprecedented level of detail, and has far-reaching implications for our understanding of changing seawater chemistry, the origin and timing of the South Asian monsoon, and the dynamic interplay between tectonics and climate in orographic systems. Within the context of ongoing research on Himalayan tectonics by numerous international groups, this work fills a gap in understanding of the critical last ~20 million years of deformation of the Himalaya, a timespan during which it is postulated that more than one half of the total Himalayan shortening took place, and during which many of the iconic features of the system developed, including the Main Central thrust, the South Tibetan detachment, the Greater Himalayan leucogranites, and the Lesser Himalayan duplex. Densely populated Nepal and northern India remain seismically active, with potential for a >M8 earthquake in a major seismic gap in the western part of Nepal. Because estimates of earthquake probability are in part based on understanding of the long-term history of shortening in the frontal Himalaya, a small change in the long-term shortening rate would have significant implications for predictions of co-seismic fault slip.

This is a project to reconstruct the position of the winds, the patterns of the circulation and the source regions for the dust in central and eastern Asia during the Quaternary, the last 2.5 million years. The researchers will employ a novel technique of "fingerprinting" the chemical composition of the dust found in wind-derived sediments as well as in a variety of potential upstream source regions. The chemical characterization will be made using laser ablation mass spectrometry and the measurements will include U/Pb dating, trace metal measurements, and Hf (hafnium) isotope variability to determine source regions for the dust. The approach - using laser ablation mass spectrometry on individual zircon grains - is likely to provide unprecedented chemical information about the minerals and the rapid rate of sample analysis will produce strong a strong statistical basis for evaluating changes in grain chemistry and source region.

The broader impacts include: 1) application of a novel, new approach for characterizing the chemistry of the dust grains; 2) support for graduate students and undergraduates at two universities to participate in the research; 3) support for a new researcher embarking on an academic career; and 4) a strong element of international collaboration between the Institute of Tibetan Research in China and two universities in the United States.

This project aims to resolve a long-standing controversy regarding the earliest evolution and deep structure of the Precambrian lithosphere of southwestern North America. This area is a globally important field laboratory for studies of the processes that form continents. Current debate has focused on the need to resolve the relative importance of accretion of juvenile arcs versus recycling of older crustal materials, and/or rift-related addition of mafic crust. The objectives of this project are to: 1) resolve the nature of the cryptic Archean and other pre-1.8 Ga lithospheric components in the Mojave Province and elucidate the timing and processes of their incorporation into an assembling 1.8-1.6 Ga orogenic system; 2) discover more definitive piercing points (relative to Australia, Antarctica, etc.) that can be used for supercontinent reconstructions of Nuna (1.8 Ga) and Rodina (1.0 Ga); and 3) provide a comprehensive basement provenance age template in support of the wide array of detrital zircon studies of sedimentary basins of all ages in the Southwest. The approach is to use U/Pb radiometric dating and Hf isotopic characterization of zircons from the oldest rocks in the Southwest. Pilot studies show that these rocks contain still older grains, whose history will be decipherable using these approaches. The research team will analyze inherited zircons from the oldest plutons, which act as probes what was being melted in the lower crust, and detrital zircons from the oldest metasedimentary rocks, which are an indication of eroding source regions and resulting sedimentary basin and depositional systems.

The project involves collaboration between PIs in U.S. academia, the USGS, and Australian collaborators from academia and the mineral industry. The combined datasets will be integrated with several decades of previous work by the PIs and with emerging new geophysical images from the NSF EarthScope experiment. The importance of the work will be a new integrated synthesis of the structure and evolution of the basement architecture of this part of the North American continent that will be useful for many subfields in the geosciences, including tectonics, deep time geologic history of our continent, ground-truth of geophysical interpretations of the subsurface, and applications for minerals exploration. The project also has a strong outreach component that integrates research and education via training of student geoscientists, including minority students, and working with the Parks for informal geoscience education of the public.

Collaborative Research: Filling the Triassic Geochronologic Gap: A Continuous Cored Record of Continental Environmental Change in Western North America.

Paul Olsen, Lamont-Dougherty, EAR-0958976
George Gehrels, University of Arizona, EAR-0959107
Randall Irmis, University of Utah, Ear-0958915
Dennis Kent, Rutgers University, EAR-0958859
Roland Mundil, Berkeley Geochronology Laboratory, EAR-0958723

ABSTRACT
The Triassic Period was punctuated by two of the largest mass-extinctions of all time and witnessed the evolution of most elements of the modern biota, as well as the advent of the age of the dinosaurs. One of the richest archives of the biotic and environmental changes on land for this period is on the Colorado Plateau, which despite over 100 years of study still remains poorly calibrated in time and poorly registered to the rest of the global record. To provide this desiderata, we will drill a continuous a ~500 m core through nearly the entire Triassic age section (Chinle and Moenkopi formations) at Petrified Forest National Park (PFNP), Arizona, USA, one of the most famous and best studied successions of the continental Triassic on Earth. A continuous sampling (core) is needed to place this spectacular record in a reliable quantitative and exportable time scale, which has proved impractical in outcrop. The Petrified Forest core will provide a quantitatively sound reference section in which magnetostratigraphic, geochronologic, environmental, and paleontologic data are registered to a common thickness scale with unambiguous superposition and will provide pristine unweathered samples. With such a reference section in hand the entire voluminous assemblage of outcrop data from the PFNP and the surrounding region can be integrated into the global framework. The hole will be deviated 30° from vertical to provide core-bedding orientation intersections for an azimuthal guide; additionally, the orientation of the core will be registered to the hole wall using whole-core-scans and compass-oriented acoustic and optical televiewer images and dipmeter surveys. Core orientation will facilitate the recovery of a high-resolution magnetic polarity stratigraphy for correlation to the fossil-rich outcrop sections. The polarity sequence will be calibrated by a series of high-precision U-Pb zircon dates obtained from discrete levels in the core, and will provide critical data to fill the geochronologic gap in global terrestrial and marine time scales for the Late Triassic. The age-calibrated chronostratigraphy of the PFNP core will be used to address major issues of early Mesozoic biotic and environmental change. These include whether marine and continental biotic turnover events in the Late Triassic were coupled; was the largest magnitude faunal turnover event on land during the Late Triassic synchronous with the giant Manicouagan impact; Is the NSF-funded Newark basin astronomically-calibrated time scale consistent with high precision U-Pb zircon age data from the Chinle Formation; and was the cyclical climate change recorded in the Newark basin lacustrine record paced by Milankovitch climate change?
In addition to the science generated by the core and its integration into the local and global environmental and biotic framework, the project will have a major education and outreach component. The Petrified Forest National Park is a major tourist destination, averaging 600,000 visitors a year. We plan to leverage this huge resource by developing a permanent exhibit on the coring project and its important scientific results for the park. We will involve numerous student groups during the actual coring activities, including Native American geoscience concentrators at The University of New Mexico/Gallup and K-12 students from throughout the Gallup area. In addition, we will sponsor several workshops at the Park and will reach out to the general public for their participation. The project involves six co-PIs from different institutions and will last 24 months and is intended to provide an initial synopsis of basic stratigraphic, logging, magnetic polarity, and geochronologic data for utilization by the international scientific community for further research and integration with other studies, as well as a major platform for outreach, and a better understanding of how the modern world came to be.

EAGER: TESTING THE HYPOTHESIZED GRAND CANYON-APPALACHIAN CONNECTION

George Gehrels and William Thomas
University of Arizona

This project has a specific goal of testing the hypothesis that some of the sand that make up the sandstones of the Grand Canyon were supplied primarily from the Appalachian mountains, and a more general goal of reconstructing dispersal pathways for sediment across the US during late Paleozoic (350-245 million years ago) time. Conducting source area studies for this time period is challenging because of the complex interplay of mountian building processes and climate. During this time the Ouachita-Appalachian-Caledonian mountain range formed as result of collisional interactions during assembly of the supercontinent Pangea, the Cordilleran mountain range experienced arc-type magmatism and several phases of convergent tectonism, and the Ancestral Rocky Mountains were uplifted. There were also dramatic changes in regional and global paleoclimate as North America moved northward across the paleo-equator and as southern hemisphere glaciation created large changes in sea level. North America accordingly serves as a fabulous laboratory in which to examine the interplay between these disparate processes, potentially serving as an ancient analogue of our modern world. The hypothesized Grand Canyon-Appalachian connection is based on detrital zircon grains of ~720-280 Ma that appear in increasing abundance in Mississippian through Permian strata of the Grand Canyon, as reported in the June 2011 issue of Lithosphere by Gehrels and colleagues. These young grains were interpreted to have been shed from the Appalachian orogen primarily on the basis of similarities with crystallization ages of Appalachian plutons and detrital zircon ages reported from upper Paleozoic strata of the Appalachian foreland basin. This interpretation was challenged in the August 2011 issue of Lithosphere by Thomas because there is little evidence that clastic detritus was transported westward out of the Appalachian foreland basins, and because the young sediment could have been shed from other orogens (e.g. the Fanklinian system to the north) and in part from local igneous rocks. Thomas (2011) also proposed that testing these hypotheses by combining additional DZ provenance data with facies relations, thickness patterns, and petrographic characteristics of upper Paleozoic strata would enable reconstruction of the dispersal pathways of sediment transport across North America during late Paleozoic time. We propose to combine U-Pb age and Hf isotope determinations of ~60 samples with traditional stratigraphic information to specifically test the Grand Canyon-Appalachian hypothesis and more generally reconstruct late Paleozoic dispersal pathways of southern North America.

Three impacts beyond the geologic contributions noted above include:
(1) Providing opportunities for faculty members and undergraduate students at academic institutions near study areas to become involved in sample collection, analysis, and interpretation.
(2) Advancing the field of provenance analysis by integrating U-Pb geochronology, Hf isotope analysis, and traditional stratigraphic/sedimentologic analysis of sandstones in an effort to reconstruct dispersal pathways and to examine linkages between tectonics and climate.
(3) Sharing information with the public by providing operators of State and National Parks near our study areas with the results of our work, following the model of the 'Trail of Time' exhibits at the Grand Canyon.

Growth of the ancient North American continent (Laurentia) along its western margin in Paleozoic times occurred by addition of materials of both local and exotic origins: a sedimentary apron derived from erosion of the western flank of the continent (the miogeocline), and also a complex of accreted terranes displaced by plate tectonics from other parts of the globe and faulted into the continent. Research of this study will examine the history of the accreted Chilliwack terrane in northwest Washington about which preliminary studies suggest that at least parts came from northwestern Europe. A primary tool in our work is acquisition of U-Th-Pb ages of zircon grains in igneous and sedimentary rocks. Preliminary data from igneous rocks in the Chilliwack terrane yield ages not known in western North America, but common in ancient Scandinavia (Baltica). In sedimentary rocks, age distributions of zircons are in some rocks similar to North America and in other rocks point to an exotic (European or other) homeland. Additional zircon ages will clarify these possible correlations. Further Hf isotopic data from zircons will be used to test possible derivation of parts of the Chilliwack terrane from a primitive oceanic island arc, specifically the early Paleozoic Alexander arc terrane accreted in southeast Alaska, as opposed to evolved continental crust (Laurentian or other). Field mapping of rock units will evaluate the genetic and structural relationship among parts of the Chilliwack terrane that have North American vs. exotic affinities. The fundamental goal of the project is basic knowledge of mechanisms of plate tectonics and processes of formation of an active continental margin.

The research plan is designed to address the scientific issue described above, and also to enhance the education and training of students and elevate interest and understanding of earth history of the Pacific Northwest in the general public. Project funds will support undergraduate students as assistants in the field and laboratory, and pay for students to attend a professional meeting. Student research on the project will likely form the basis of senior theses. Knowledge gained from this study will be incorporated into course work in the classroom, on field trips, and off-campus Pacific Northwest field courses taught at Western Washington University. With respect to the broader community, and aside from technical publications and lectures, results of the proposed study will be integrated into and will enhance frequently occurring field trips for professional groups, such as the Geological Society of America, National Association of Geology Teachers, and Northwest Geological Society. The public lands of the San Juan Islands and Cascades are global tourist destinations, presenting opportunity for reaching a broad audience through geologic displays in parks and in popular geologic literature. The scale of continental margin tectonics on display in western Washington is fascinating at any level of knowledge.

This project will evaluate processes responsible for the non-steady-state growth of continental crust in Cordilleran-type magmatic arcs. These batholiths develop as a result of subduction of oceanic lithosphere at convergent margins, but the processes that control the tempo of magma production are unclear; even in arcs where subduction is continuous, magmatism is strongly episodic (e.g. Sierra Nevada batholith, Peninsular Ranges batholith, Central Andes). Short periods (10-15 million years) of intense magmatism or 'flare-ups' may generate as much as 90% of total batholithic volumes, with little magmatism occurring during intervening lulls. Geochemical and isotopic signatures indicate that magmas produced during flare-ups incorporate more upper plate material than magmas formed during lulls. This pattern raises the question of whether continental growth by magmatic addition is controlled primarily by the behavior of the subducting oceanic plate or by the tectonics of the continental lithosphere at the plate margin. We are investigating this question through an integrated geologic, geochronological and geochemical study of the southern Coast Mountains Batholith in British Columbia. This project directly addresses a basic question in earth science: how do continents grow? In addition to the research goals of this project, this endeavor is enhancing the scientific education and training of students at four academic institutions recognized for the diversity of their student populations. Engagement of students in fieldwork, laboratory analysis, data interpretation and presentation of results are providing them with insights into all aspects of the science process and career options, and increase retention in STEM fields. Samples and datasets generated as a result of this project are being used to design problem sets and interpretive exercises for classes taught by the investigators. Data generated during this the course of this project is being added to NSF-funded databases, such as NAVDAT, for access by the larger community.

Recent developments in geochronologic methods and instrumentation are revolutionizing many different aspects of Earth Science research. Some of the most exciting advances are being driven by Laser-Ablation ICP Mass Spectrometry (LA-ICPMS), which generates U-Th-Pb ages and complementary geochemical information rapidly and with micron-scale spatial resolution.

The Arizona LaserChron Center (ALC) is a multi-user facility that utilizes LA-ICPMS to determine U-Th-Pb ages, Hf isotope ratios, and trace element abundances from a variety of minerals that occur in sedimentary, igneous, and metamorphic rocks. We also utilize a dedicated Scanning Electron Microscope that generates the high-resolution and high-magnification images necessary for state-of-the-art micro-analysis. Primary goals of the ALC are to (1) generate robust geochronologic and geochemical data in support of many different NSF-funded projects, (2) use every aspect of facility operation as an opportunity to train faculty and student researchers in geochronologic theory and methodology, and (3) drive the development of new techniques and applications that take advantage of the high efficiency and fine spatial resolution of LA-ICPMS. Research at the ALC is conducted in a highly collaborative mode, with ALC scientists providing assistance with all aspects of a project (from initial design of the study to final publication of results) and faculty members and students from other institutions visiting the lab to generate their own data and learn the theory and methodology of U-Th-Pb geochronology.

Funding from this award will enable the ALC to facilitate the acquisition of geochronologic information in support of a large number of NSF-funded projects, drive the development of numerous new analytical techniques and applications, and provide a broad array of educational opportunities such as teaching short courses at annual meetings, developing materials that can be used in Earth Science courses, creating new tools for displaying and interpreting geochronologic data, and driving the development of a global database "Geochron" that hosts U-Th-Pb geochronologic information. Research conducted at the ALC will continue to generate important new knowledge about the growth of continents, processes of mountain building, generation and dispersal of sediment, formation of mineral and hydrocarbon resources, history of evolutionary changes, and genetic linkages between climate and tectonics.

Multiple recent lines of evidence suggest that the onset of modern-like plate tectonic processes started rather abruptly in the Archean (about 3 billion years ago) and that tectonically, the Earth has evolved through several distinctive dynamic stages. The overarching question here is to test the hypothesis of several step-like changes in the tectono-magmatic evolution of the Earth. Such change should be reflected in the geochemical composition of intermediate and felsic igneous rocks - the basic building blocks of continental masses. If this did happen, can we better constrain the age of that change, was it sudden or gradual? Unraveling tectonics stages and transitions between them on our dynamic planet has important implications for our overall understanding of resource distribution as well as feedbacks with other evolutionary processes in the mineral and biologic realms.

In the project, the researchers will use detrital zircon U-Pb ages and trace elemental concentrations (with a focus on the rare earth elements) on grains from sediments and sedimentary rocks that satisfy the following conditions: (1) are draining sizable segments of the continental mass, and (2) contain zircons encompassing large geologic time intervals, especially from the Precambrian. The age range target will especially focus on the Hadean, Archean and Proterozoic area. Recent work shows that whole rock geochemical parameters measured on young igneous rocks correlate positively with crustal thickness globally and regionally. La/Yb and other trace elemental ratios are calibrated against crustal thickness on intermediate igneous rocks from modern subduction systems and have been used to show variations in crustal thickness over time in a few Phanerozoic orogenic regions. The implied variation in crustal thickness is consistent with the tens of million years cyclicity of crustal thickness in continental areas being affected by modern plate tectonics and is also indicative of the fact that the deepest parts of the continental crust (regardless of its thickness) are the factories of differentiation leading to the diversity of intermediate igneous rocks found in subduction and collision systems.

One of the most controversial aspects of North American geology concerns the degree to which rocks extending from California to Alaska have been transported south and then north along the continental margin due to convergence and translation between the North American and ancestral Pacific tectonic plates during Late Cretaceous-Paleogene time. Some relationships suggest limited mobility - geologic features remain close to where they formed. In contrast, other data sets suggest thousands of kilometers of transport - rocks in much of Alaska, British Columbia, Washington, and Oregon first moved south to the latitude of Mexico, and then moved back north to their present positions. The uncertainty in coast-wide transport hinders our ability to reconstruct the geologic evolution of western North America and to understand the origin (and future discovery) of important energy and mineral resources located in these regions. This project focuses on determining the amount of southward motion accommodated on fault systems that extend from northwestern Washington to southern Alaska. In addition to the scientific goals of the project, the award is supporting important societal outcomes by training students in an important discipline that is contributing to the development of a diverse, globally competitive STEM workforce. The research project also involves collaboration with researchers from the British Columbia Geological Survey.

This project involves field and laboratory analysis of fault systems that may have accommodated up to 1600 km of southward motion of rock assemblages. The investigators will conduct detailed structural analyses to determine the amounts of displacement on recognized faults, map areas between recognized faults to evaluate continuity, and collect samples that will constrain when motion occurred. Field studies will focus on faults in coastal British Columbia given that these are the best-known segments of the faults - their extensions into Alaska and Washington are not well constrained. The scientific objectives of the project include: 1) testing the hypotheses that each of these two fault record approximately 800 kilometers of Late Jurassic-Early Cretaceous sinistral motion, (2) evaluating the alternative interpretation that the Insular and Intermontane tectonostratigraphic terranes are separated by an Early Cretaceous suture zone, (3) using this new information to evaluate current models for Cordilleran paleogeography, and (4) establishing the sinistral faults as world-class examples of shear zones operating within an active magmatic arc during oblique subduction. Field and laboratory analyses will be conducted in large part by undergraduate students at the University of Arizona in an effort to provide opportunities to learn techniques of geologic mapping in a frontier area, and to perform geochronologic and geochemical analyses using state-of-the-art instruments at the Arizona LaserChron Center (University of Arizona). Each student will be sufficiently engaged in the field and laboratory studies that they will be able to prepare a manuscript for publication that includes detailed and regional geologic maps, descriptions of critical structural/intrusive relations, large geochronologic and geochemical data sets, and interpretations of broad significance.

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 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.

Much of our understanding of the geologic history of the Earth comes from radiometric dating of Earth processes. Currently, Earth scientists have a difficult time placing narrow constraints on the precise time that a fault occurs deep within the crust of the Earth. This project combines two state-of-the-science techniques to directly date the time of faulting along a key fault zone in southeast Alaska, and thereby date when ancient earthquakes occurred. Development of this new analytical technique will enable considerable future research and understanding of how Earth materials deform. In addition, this research project will provide training and research opportunities for a female graduate student and several undergraduate students. Visits to local elementary schools will enable potential future scientists to experience the methods and results of Earth science research, with direct implications for earthquake hazards.

This collaborative project consists of two principal objectives: 1) develop the mineral titanite as a tool for dating high-temperature deformation by a combined microstructural and microgeochronology approach, and 2) apply this tool to the evolution of the spectacular Coast Shear Zone and Great Tonalite Sill in the Coast Mountains orogen of southeast Alaska. Research methods will incorporate a field study to understand qualitatively the evolution of a mid- to deep crustal intra-arc shear zone and synkinematic sheeted-sill complex exposed in the Coast shear zone of Alaska and Canada. Titanite analyses will include electron-backscatter diffraction maps of titanite microstructure, and laser-ablation split-stream inductively coupled plasma maps of titanite composition that incorporate U-Pb dates. These data will allow assessment of the physical and chemical processes that affected the crystal, and the identification of crystals whose U-Pb distribution reflects high-temperature deformation. Because titanite is a widespread crustal mineral, this technique should have broad application globally and enhance our understanding of how crust deforms and orogens assemble and change through time.

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 MRI award provides funding to acquire a next-generation Multicollector – Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS) equipped with a collision/reaction cell and MS/MS mass filter. The instrument will be housed within the Arizona LaserChron Center (ALC), an NSF-supported Community Facility at the University of Arizona (UA) that supports research in Earth Sciences. It will be co-managed between ALC and the Arizona Heavy Isotopes Laboratory (AHIL). Science questions pursued by ALC and AHIL researchers include reconstructing the igneous evolution of Earth, Moon, Mars, and other planetary materials; the timing of volcanic eruptions; tectonic evolution and uplift of mountain ranges; transport and accumulation of sediments; formation of base metal deposits and other strategic and energy resources; reconstructing the history of Earth’s climate, including patterns of ice sheets and tracing of aeolian (loess) deposits. The new instrument will directly support the research efforts of ~350 faculty members, professional geologists, and students that visit the ALC each year, by making state-of-the-art analytical methods accessible to the broader Earth Science community. Furthermore, the instrument will provide new opportunities for students and researchers to learn the theory and methods of mass spectrometry; data acquisition and processing; and offer educational and outreach activities for a broad user base including participants from under-represented minority groups in STEM.<br/><br/>The new MC-ICPMS will complement other ICPMS and laser-ablation systems available at ALC by enabling improved accuracy/precision using existing analytical methods, development of new techniques only achievable with the proposed instrumentation, as well as increasing analytical capacity. In particular, research in ALC will emphasize: i) developing new techniques in laser-based MC-ICPMS geochronology that take full advantage of the novel collision/reaction cell and MS/MS capabilities (e.g., Rb-Sr); and ii) providing greater capacity to meet the growing community demands for U-Th/Pb geochronology and complementary Lu-Hf isotope analysis. We anticipate that in-situ Rb-Sr methods applied to feldspar and mica will transform petrochronology and detrital mineral studies in much the same way that zircon U-Pb has impacted many different areas of Earth science research. AHIL research will emphasize the development and application of emerging techniques in non-traditional stable isotopes of Ti, Zr, and Hf in bulk-rocks and minerals to study high-temperature petrologic processes influencing magmatism, fluid flow, crust-mantle differentiation, and the distribution of critical elements. Through connections with researchers in the UA Lunar and Planetary Laboratory, we will leverage these novel capabilities to study aspects of planetary geochemistry/geochronology that bear on Earth’s origin and evolution. Through community outreach and research training for underrepresented students and postdoctoral researchers, the PI/Co-PIs will ensure that the new MC-ICPMS takes advantage of UA’s position as an R1 Hispanic Serving Institution and American Indian and Alaska Native-Serving Institution for enhancing diversity in geosciences, while addressing exciting new questions in petrology, geochemistry, tectonics, and planetary sciences.<br/><br/>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.