Michael Perfit - US grants

This proposal is a continuation of studies of rock samples from the Galapagos and Axial Seamount hydrothermal areas. They wish to integrate petrologic and geochemical studies of fresh glasses, hydrothermally altered lavas and mineralized samples recovered by dredge, ALVIN and Pisces IV with fine scale field studies including Sea Beam, deep-tow photography, magnetic and resistivity measurements. The PI will act as project coordinator, will collaborate on all phases of the work, and will perform many of the geochemical analyses on the samples. Isotopic studies will be carried out by co-investigators. The PI will also participate on an ALVIN dive to the Southern Juan de Fuca if it is funded by NOAA. It is hoped that the data from a dead hydrothermal system (Galapagos) and a very young one (Axial Seamount) will further constrain the models developed by the PI that the ore deposits are associated with hydrothermal systems that are driven by heat from small, highly fractionated magma bodies at depths of < 2 km beneath the seafloor.

Funds are provided to continue geochemical and tectonic investigations of the eastern Galapagos Rift and southern Juande Fuca Ridge including: Axial volcano, the Cleft and Vance segments of the Juan de Fuca Ridge (JDF) and the Vance seamount chain. Studies on samples from the Galapagos recovered during a 1988 AII/ALVIN cruise will be completed. PI will also participate in a 1990 field program along the southern JDF Ridge. The results of these investigations, integrated with available geophysical and geological data, will provide the basis for comprehensive models of the tectonomagmatic and hydrothermal processes that occur along these ridge segment sand their associated seamounts. These studies include the lava types and their marphology; chemical variability of Mid Ocean Ride Basalts and the role of magma mixing, crystal fractionation and crustal assimitation; chemical characteristic of axial volcano and seamount lavas and magna chamber processes.

This program will focus on a petrological and geochemical characterization of the intra-transform spreading centers in the Siqueiros transform fault, on determining the structural histroy along the transform domain through ALVIN field mapping, structural studies of deformed rocks recovered from the walls of each fault scarp, and on understanding the tectonci processess that have influenced the development of the Siqueiros tranform for the past 4 Ma. There will be eighteen ALVIN dives in the transfrom and a night-time program of rock coring and dredging that will provide additional samples from along the spreading axis and at various sites along the strike- slip faults. SeaBeam will be used at night to produce detailed 10 m contour maps of each spreading axis. Questions to be addressed include: What processes are responsible for initiating intra-transform spreading? What is the evolutionary sequence of lava types erupted when a new spreading center start? What is the nature of major transform-affiliated compositional discontinuities in the mantle? What is the scale of chemical heterogeneity in the mantle? Are unique magma types generated along transform faults?

9402360 Perfit The PIs collected samples by rock coring and Alvin dives (Adventure I & II Cruises) on the ridge crest and flanks from EPR 9N area. In this project, they will obtain U-Th dates and geochemical analyses of these samples, and combine them with their photo interpretation to check their 3-D model of the magmatic system beneath fast- spreading ridge. Their goal is to determine magma residence times and magma residence times and magma generation and fractionation processes.

OCE-9403773 Perfit In this project the PIs will participate in the EDISON cruise (Germany, Canada, US, and Australian participants; Crusie ship- Sonne (German) to investigate structure, petrology, tectonics of the young alkaline volcanic centers (TLTF) in the southwestern Pacific. An intriguing aspect of this study is the presence of mantle wedge xenoliths in some of the alkaline basalts. These xenoliths are sulfate and carbonate-rich (metasomatized). Another intriguing aspect is the 1982 discovery of a gold deposit in Lihir island. The authors argue that "this is probably the best known locality in the world" in which to investigate the interrelation- ship between extensional tectonics in a convergent margin, arc magmatism, mantle metasomatism, and gold-copper mineralization. This is what the team will do. Ship time and other expenses at sea will be borne by the Germans; the PIs are only requesting funds for pre-cruise expenses and post-cruise research.

9530299 Perfit The Juan de Fuca Ridge has been the site of an extensive study of volcanology and hydrothermal activity. The segment that appears to be most volcanically active (known as the Coaxial segment) has had two eruptions since 1981. The PI has been involved in the collection of basalts from this ridge for several years and wishes to analyze these rocks to investigate the compositions of the lavas and how they change with time. This work would be synthesized into a map that contained the data from the rocks, the hydrothermal vents, and photos.

0080086
Foster

This grant provides partial support for the acquisition of a noble gas mass spectrometer, a UV/IR dual laser system, high precision furnace, and associated vacuum equipment and electronics to construct a facility for 40Ar/39Ar geochronology and rare gas geochemical investigations at the University of Florida. The lead PI, David Foster recently (1998) joined the faculty at the University of Florida after spending several years as a senior researcher at La Trobe University in Australia. He joins Paul Mueller, Michael Perfit and Ann Heatherington in the geochemistry and petrology group. Establishment of a thermochronology facility at Florida will complement existing and successfully operated geochemical instrumentation in the Geology Department including a TIMS, ICP-MS and SIRMS and will add capacity to a limited U.S. geoscience analytical infrastructure for Ar/Ar geochronology. The noble gas mass spectrometer will facilitate research in tectonics, economic geology, basin studies, geomorphology and anthropology by providing for constraints on the timing and rates of geologic processes.

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Under this award, the PI will continue participating in a collaborative study of the Cleft segment of the Juan de Fuca ridge. The field work has been and will continue to be done with MBARI vessels and ROVs, in active collaboration with D. Stakes, M. Tivey, and others. The PI's main responsibility is in sampling of volcanic rocks, interpreting volcanic land forms, and undertaking laboratory analyses of the rock samples. One field program occurred in 2000, and another will take place in 2002. The PI has additional rock samples from the area collected in 1990 and 1994. The PI proposes flow mapping of the axial and off-axis region with a variety of goals and objectives, one of which is to test the "split-ridge" model of Kappel and Ryan for tectonic and magmatic cycles forming the symmetrical land forms on either side of the present ridge axis. Axial and off-axis sampling out to ~6km (150 ka) will be used to test this idea, and elucidate the processes of crust creation and evolution in the near-axis region. A full laboratory program of major and trace element studies and isotopic studies are planned for ROV-collected and wax cored samples.

This proposal outlines a two-year course of study to fully analyze and synthesize petrologic and geochemical data together with geologic and geophysical constraints to come up with fully integrated models of melting, melt ascent, plumbing and eruptive systems at the fast-spreading EPR 8 degrees -10 degrees N. The PI will collaborate with geologists and geophysicists at IPGP in Paris and WHOI. Distinct goals include using existing and new analyses to understand the mantle sources, melting, and fractionation of the axial and off-axis basalts, using gabbroic xenoliths, U-series dating, and geologic information to paint a picture of layer 2a thickening and the role of off-axis eruptions, and to evaluate the correlations between U-series ages, magnetic paleointensity values, and volcanic and geomorphic features. This ABR will bring together a decade of sampling and analytical work to produce a fully integrated interpretive model of crustal growth and evolution at fast spreading rates.

Abstract

Under this award the PIs will study ice-rafted detritus (IRD) in high-sedimentation-rate cores from the high-latitude South Atlantic (SA). Previos studies have identified six to seven discrete episodes of IRD deposition between 12 and 60 kyr during the last glaciation that have been suggested to be regionally correlative. If these events can be shown to be widely distributed and synchronous, they may indicate instability in Antarctic ice sheets. The PIs will examine the origin of these South Atlantic IRD (SA-IRD) events, their significance for Antarctic ice-sheet dynamics, and their exact relationship to millennial-scale climate events recorded in polar ice cores. This project will 1.) map the aerial distribution of IRD events in the South Atlantic basin; 2.) date SA-IRD events using AMS-14C and estimating particle flux and sediment redistribution using the Th-normalization method; 3.) trace the origin of IRD events to their Antarctic source area(s) using mineralogy and geochemistry; and 4.) correlate South Atlantic IRD events to Antarctic and Greenland ice cores, other marine sediment cores (e.g., North Atlantic), and global sea level records.

EAR-0418905
Mueller

This proposal seeks support for the appointment of a Ph.D. scientist to act as laboratory manager for a new ICP-based analytical facility at the University of Florida for an initial 3-year period. The University of Florida will assume 100% financial responsibility for this position on a permanent basis subsequent to this initial period. The construction of the ICP laboratory and the acquisition of two new ICP mass spectrometers (Finnegan-MAT Element-2 and Nu Plasma multicollector) are part of the recent relocation into >10,000 sq. ft. of new geochemical laboratories as part of an overall relocation of our Department into greatly expanded and renovated facilities (Williamson Hall). These instruments have been interfaced with newly acquired Excimer (193 nm) and Nd-YAG (213 nm) lasers, as well as a desolvating nebulizer and autosamplers. Financial support for both laboratory renovation and instrument acquisition involved cost sharing between the University of Florida and the NSF. The primary responsibilities of this person will include: 1) contribute to method development and participate in collaborative and independent research, 2) maintain quality control of the facility, which will be a challenge in light of the large number of users; 3) oversee and administer day-to-day activities such as maintenance and scheduling, in order for the facility to efficiently produce the highest quality data; and 4) make the instruments capabilities known to and accessible to a wide range of users inside and outside of the department, including students. In addition, the laboratory manager will be the primary instructor for students exposed to elemental and isotopic methods both in courses and via individual research projects at the graduate and undergraduate levels. Without an experienced laboratory manager, access to this facility for these students and other users will be very limited.
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Collaborative Research: From Local to Extreme Environments: Deepening Earth Systems Science Understanding with GLOBE

This project is working to bring current ocean science research on marine environments and ecosystems into the GLOBE program and provide opportunities for GLOBE students to make comparisons between their local environments and extreme environments of the deep sea. Scientists and educators from the Ridge 2000 (R2K), InterRidge, and ChEss (Biogeography of Deep-Water Chemosynthetic Ecosystems) programs engaged in interdisciplinary studies of deep-sea systems are working in collaboration with the Center for Science and the Schools (CSATS) to support collaborations between marine scientists and elementary and secondary students. The foundation of this project is the "From Local to Extreme Environments" (FLEXE) program, in which students collect data in their local environment and compare it with equivalent data from partner schools and from an extreme environment, namely the deep sea. Hydrothermal vents and cold seeps are among the extreme environments being compared. Students, working either as a Tier 1 (stand-alone) or Tier 2 (paired with another school) effort, participate in three main activities: (1) protocol-driven fieldwork and analysis, and analysis of data from an extreme environment; (2) web-based interactions with scientists and students from partner schools; and (3) culminating activities that include reporting and peer review. New protocols to collect key environmental parameters (e.g., temperature, salinity), some of which can be adapted from existing GLOBE protocols, will be implemented each year. The FLEXE Forum provides an online data system for exploring Learning Activities developed for the project and for facilitating interactions between students and between students and scientists. Through this Forum, collaborating scientists submit scientific questions to the students for them to answer as they carry out their investigations, and provide feedback on the answers in a timely manner. As a culminating Wrap Up experience, students write template-based scientific reports that are peer-reviewed by other participating students. Teacher professional development resources, including Teacher's Guides, online training, and other web-based learning and assessment tools, are also being developed through this project. These combined activities are helping students to develop inquiry skills, learn about life in the marine environment and their local ecosystems, and gain new understanding of the fundamental integrated Earth system processes that control habitability in diverse settings.

PI/Institution: Klein, Emily (Duke)
Title: Collaborative Proposal: Anatomy of an overlapping spreading center; geochemical and geological study of the EPR 9 03'N OSC

Abstract: 0526120 (Klein/White/Von Damm/Sims/Perfit)

Intellectual Merit. The objective of this project is to test the hypothesis that lava composition, hydrothermal vent field location, and eruption sites on the East Pacific Rise are linked to the behavior and location of melt in the upper mantle. The project builds upon recently acquired seismic data that details existing melt sills and estimates of melt volume beneath the crust in the area. The intent is to determine whether a relationship exists between exposed geological features and composition, and sill and melt volume and distribution. The PIs will perform more detailed mapping and sampling using magnetics, sonar, and Jason II. That data would then be compared to and integrated with existing seismic data at the SIO Visualization Center. Students would be involved in the cruise and data analyses.

Broader Impacts. Graduate students and undergraduates will be involved in the project, both directly at sea, and through project work that develops as a consequence of the field program. The PIs' track record in involvement of students, and academic outputs from those efforts, indicates that this will be a very successful means of involving graduate and undergraduate students in marine geological research. Involvement in the SEAS program also provides an opportunity for middle school students to gain an understanding of marine geology. The impact on the scientific community, particularly if the underlying goals of co-registering surficial geology/geochemistry with geophysical evidence for source magma sills, will be most significant, and is well in line with R2K goals. This will be amplified by making use of the SIO Visualization facility's seismic tomography database.

Intellectual Merit: This research addresses a first-order problem in ocean crustal construction: i.e., how magmas rising through the shallow mantle affect mantle melting processes. This work identifies and characterizes hypothesized diffusion-reaction processes that occur around melt conduits that feed seamount volcanoes near mid-ocean ridge spreading centers. Samples come from the Lamont and Vance Seamount chains located just off the northern East Pacific Rise and adjacent to the southern Juan de Fuca ridge, respectively. These two different settings allow comparison between two well-studied areas of high present interest in the ocean science community. This work tests whether seamount chains, aligned along absolute plate motion directions, reflect the effects of olivine-rich (i.e. dunite) magma conduits in the upwelling mantle that focus melts to near-ridge locations. If true, then seamount chains aligned along absolute plate motion directions will have different petrogenetic origins and eruption histories from those aligned along relative plate motion directions. The research will also examine whether diffusive flux-melting of the mantle surrounding a conduit occurs once a dunite melt channel is established. Tests of the models will be carried out by measuring U-Th-Ra-Pa disequilibria, Sr-Nd-Pb isotopes, Si and Ca isotopes and selected trace elements in seamount lava samples. 231Pa excesses and light isotopic compositions of Si and Ca will be examined to determine if temperature gradients play a significant role in magma composition. These data will also help ascertain the role of different mantle sources in magma genesis and test whether temperature gradients play a role in mineralogical and compositional traits that currently are not well explained.

Broader Impacts: Broader impacts of the work include training of two graduate students and collaboration between institutions. Undergraduates will be integrated into the research and engaged in the whole laboratory experience. Outreach to high school earth science classes at University Laboratory High School in Urbana Illinois will provide opportunities for students to learn about ocean floor geology and work with bathymetric maps and geochemical data. The study will greatly expand the current global database for a number of geochemical traits for seamount chain samples.

ABSTRACT

OCE-0819469


Intellectual Merit: Since its designation as a RIDGE 2000 Integrated Study Site (ISS) in 2001, the 8°-11° N segment of the East Pacific Rise (EPR) has become one of the best characterized regions of the global mid-ocean ridge (MOR) system. However, even here our understanding of ocean-ridge volcanism has been significantly limited by the lack of geologic, chemical and petrologic data on individual on- and off-axis Fundamental questions remain regarding the spatial and, in particular, the temporal chemical evolution of fast spreading centers. In 2005-06, a submarine eruption occurred within the EPR ISS (9º 47?-54? N) at exactly the same location as the well-documented 1991-1992 EPR. This cyclic eruption provides a unique opportunity for the proposed multidisciplinary study in that it is the first time ridge geologists will be able to evaluate variations in MOR lava geochemistry at one place over a controlled time period (~15 years). Moreover, pre-eruption seismic data, high-resolution mapping and high-precision 210Po-Pb dating of the lavas from the 2005-06 eruption have resulted in its emergence as the best spatially and temporally-constrained MOR eruption in the world. Together with the dense lava sampling completed since 2006, these data provide an unprecedented opportunity to examine the petrologic and geochemical aspects of the eruption as well as the temporal and spatial changes that accompanied this magmatic event.

The investigators will search for systematic variations in lava chemistry over space and time, as well as differences in fractional crystallization and mixing between lavas erupted in 2005-06 and those erupted in 1991-92. Melt-hosted xenoliths will be studied to reveal details of the magmatic conditions in the source melt lens, as well as for possible signatures of contamination, degassing and water-magma interactions within the sub-seafloor. The project involves laboratory analysis of existing samples, including isotopic, petrologic and studies of volatiles, halogens and high-precision Pb isotopes.

Broader Impacts: This project will provide new quantitative information on the petrologic, geochemical, and thermal evolution of the EPR magma plumbing system, of immediate and significant consequence to achieving Ridge2000 Program goals to integrate and synthesize results across data sets at the East Pacific Rise Integrated Study Site. The project will bring two young scientists into the marine geologic and geochemical field. The principal investigator has been extensively involved in outreach activities over the past decade, and will continue with to co-Principal Investigator to support and develop University of Florida and RIDGE 2000 education and outreach programs both locally and nationally.

This research is designed to answer basic questions about how magmatic systems operate and how magmas change composition. The work is societally relevant in terms of advancing our understanding of geologic hazards associated explosive volcanic eruptions. It involves making a comprehensive set of laboratory experiments and geochemical analyses on previously collected ocean bottom volcanic rocks to understand the mechanism by which these magmas evolve in the magma chamber from low to high silica in content. Newly developed isotopic techniques will be used to test the novel hypothesis that high silica magmas form through magma based diffusional transport processes related to sustained temperature gradients across the magma lens at the top of the magma chamber. This hypothesis runs counter to the more traditionally invoked mechanism of assimilation fractional crystallization as the primary process causing the compositional differentiation of magmas. Broader impacts of the work include integration of training and research which involves a graduate student, a postdoctoral researcher, undergraduates, and middle school students. Results of the work will be incorporated into university courses in petrology, geochemistry and numerical modeling.

Understanding how ocean crust is created and its how melts of different chemistry are created is an essential but presently poorly constrained aspect of global geochemical cycling between the mantle and crust. This research investigates the geochemical relationship between on- and off-axis volcanism at a variety of mid-ocean ridge spreading center settings to try and develop an integrated dynamic geochemical and geophysical modeling approach to better understand the interaction of mantle heterogeneities with the mid-ocean ridge system. A key component of this work will be to examine the geochemistry of four well-studied mid-ocean ridges (East Pacific Rise, Iceland, Galapagos, and the Juan de Fuca Ridge) to predict the degree and depth of melting required to produce off-axis melts and relate these predictions to physically realistic origins in the mantle. To create a more complete geochemical record of off-axis geochemical variation, samples from 20 seamounts near the East Pacific Rise will be analyzed for the radiogenis isotoes of Sr, Nd, and Pb, which are indicators of magmatic and magma differentiation processes. A major reserach goal is to develop robust one and two dimensional models to determine whether or not there are globally consistent off-axis processes that underpin mantle melting beneath mid-ocean ridges. The broader impacts of the work include developing the career of a postdoc from a group under-represented in the sciences and public outreach through a local Florida museum. Broader impacts also include international collaboration with a UK scientist, with the postdoc spending time in the collaborator's laboratory and being cross-trained in state-of the art geochemical analytical techniques and geodynamical modeling.

Non-Technical: This research contract centers on the acquisition of a new high-resolution electron probe microanalysis system with an integrated electron backscatter diffraction detector. This instrument will be the only one in the US and only one of three in the world with the capability of performing simultaneous crystallographic and chemical mapping at the sub-micron scale, and will permit trace elemental analysis with superb accuracy in a user-friendly environment. The instrument will have regional and international accessibility making it a multi-use, multi-institutional piece of state-of the-art equipment. This research program brings together a unique set of 15 researchers from 7 Florida state universities (University of Florida, University of North Florida, Florida State University, Florida A&M University, University of Central Florida, Florida International University and University of South Florida) that have one commonality: the need to understand the connection between chemistry and structure at the sub-micron scale. The central theme of this instrumentation program with regards to teaching, education and outreach is lowering institutional barriers. A multi-pronged approach has been developed to execute this objective: 1) a remote access system, 2) K-12 education modules developed for teachers to help them integrate microscopy into their classroom curricula, 3) partnerships with the on-campus NSF REU program to expose talented undergraduates to advanced microscopy techniques, where selection will be based on talent and focused on increasing diversity of women and underrepresented groups, 4) continuing education programs, and 5) strategic partnerships with 2 minority serving institutions and 5 emerging Hispanic serving institutions provide fertile ground and access to underrepresented groups to increase the impact of the proposed education and outreach initiatives.

Technical: This electron probe microanalysis system produces a small spot size with high spatial resolution on the nanometer scale. The uniqueness of the instrument can be highlighted in its use in transforming research in 4 critical areas. These areas include: 1) revealing the fundamental connections between microstructure, chemistry and microtexture in light element structural alloys, 2) understanding chemical diffusion in metallic and oxide systems to develop a unified theory for thermal diffusion while gaining deeper insight into the relationship between chemistry and structure in functional oxides, and 3) mapping phase boundaries in nanoprecipitation dispersion strengthened systems, and 4) robust and accurate measurement of minor and trace element with high spectral resolution needed for geological materials. The key features of this instrument that create maximal impact are the ability to perform: 1) trace elemental analysis with superb accuracy in a user-friendly environment, 2) quantitative mapping of light elements to show their true concentration distribution and advanced spectral resolution to avoid peak overlaps that are common with light elements, 3) fine-scale microstructural, chemical and crystallographic analysis, and 4) research and teaching by logging in online to remotely view and control the instrument.

Understanding how melts are generated and focused across hundreds of kilometers through the upper mantle to the narrow mid-ocean ridge (MOR) axis is fundamental to understanding how Earth's ocean crust is formed and how elements and heat are exchanged between the interior of our planet and its surface. Significant advancements have been made in the use of computer models to investigate mantle melting and melt transport. However, the lack of complementary geophysical and geochemical data from the same area is a critical information gap that needs to be filled before progress can be made in refining present models. This research entails a multidisciplinary geophysical and geochemical program to map, sample, and analyze samples from the 8°20'N Seamount Chain that extends 200 km westward from the East Pacific Rise Siqueiros ridge-transform intersection in the Pacific Ocean. Seamounts provide a unique opportunity to test hypotheses of melt distribution and source variation that occur away from spreading centers. Melts that build these seamounts provide geochemical windows into the upper mantle.

The research includes an oceanographic cruise to map and sample the targeted region. This will be followed by geophysical data processing and petrographic, petrologic, and geochemical analyses of samples collected by both using ALVIN, a manned deep submersible, and dredging. Goals of the research are to develop new, integrated models for upper lithosphere structure, deformation, and melt distribution at a fast-spreading center and investigate the dynamics of off-axis melting. The approach is interdisciplinary and includes analysis of geophysical and geochemical data and geodynamic modeling. Rock samples will be analyzed for all major and trace elements and radiogenic isotopes of Nd, Sr, and Pb will also be analyzed. Broader impacts of the project include creation of a marine geology curricular unit targeted at the middle school level and compliant with Next Generation Sciences Standards that have currently been adopted by 45 states. The project involves working closely with teachers and administrators of Pipkin Middle School, a nationally ranked Title I school that serves 580 students in the low-income center-city of Springfield, MO (poverty index of 78%). The teachers will work closely with the reserachers and both parties will jointly create the educational materials. Emphasis will be placed on inquiry learning and connecting fundamental science processes with current research. The pilot implementation will coincide with the proposed field program. The developed unit will be made broadly available via the web on curricular resource sites.

This project is enabling the acquisition of a state-of-the-art multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) to support a team of researchers within the Department of Geological Sciences at the University of Florida to make significant advances for research applications in the Earth and Ocean Sciences. This instrumentation facilitates the research program of the lead investigator, who is an early career female with a research focus on Uranium-series geochemistry, a technique used widely to determine the age of materials in studies of past climate and sea level change on time scales from a human life to thousands of years. This MC-ICP-MS instrument allows the development of sea level reconstructions with high temporal accuracy and precision, to define the rates and tempo of ice sheet retreat and sea level rise during past warm climates. These reconstructions can be paired with climate data to inform future projections of sea level rise over the coming decades to millennia. Additional capabilities afforded by this instrument will significantly improve other existing research programs as well as enabling new lines of research in a wide range of Earth science applications.

The new MC-ICP-MS acquired through this project will enable the incorporation of new investigators and new research directions within our department, as will improve our analytical capabilities. Specifically, the primary new capabilities will allow for several ion-counting channels, including multiple high abundance sensitivity filters to facilitate the analysis of U-series measurements. The instrumentation will also allow for simultaneous measurement capability of U-Th-Pb-Hg during laser ablation analyses for U-Pb geochronology applications. These advances, among others, will impact research in a wide range of disciplines beyond earth and ocean sciences, including existing collaborations within anthropology, chemistry, agriculture, paleontology, biology, medicine, engineering, and forensic science. The instrumentation will be used to train students and post-doctoral scholars supported by a wide range of NSF programs.

Eruptions of lava form submarine volcanoes, known as seamounts, near mid-ocean ridge spreading centers. These lavas can provide important information about what Earth?s uppermost (~ 120 miles) mantle is composed of and how it melts to form the majority of Earth?s crust. At present no studies have examined long chains of seamounts adjacent to mid-ocean ridges to address these fundamental questions. In this study, we plan to analyze over 400 well located lava samples from the 8°20'N seamount chain. The chain was previously sampled and mapped in 2016 and 2018 using the submersible Alvin and autonomous vehicle Sentry. The geochemical, mineralogical, and age data to be obtained under this project will allow us to determine the origin of the magmas that feed the seamounts and nearby ridge. The data will also tell us how those magmas evolve to form oceanic lavas, and how the volcanism is related to regional tectonic processes. The study will promote advances in the field of geochemistry, marine geology, and geodynamics. This project will provide significant mentorship and training for students at a variety of levels. It will fully or partially support three graduate students at Florida and Boise State and will provide training for several undergraduates in geochemical techniques and interpretation, and support senior research projects. The project will also support education and diversity by funding two female scientists, one a first-generation college graduate, toward obtaining their PhDs in geochemistry. Both principal investigators are heavily involved in outreach and education at the K-12 levels in Florida and Idaho.

Sparse sampling and geochemical analyses of seamounts scattered throughout the northeastern Pacific suggest the sub-ridge mantle associated with the East Pacific Rise (EPR) has far greater compositional variability then is preserved in lavas erupted on-axis. While the relative homogeneity of axial lavas has resulted in intriguing generalizations about magma differentiation and mixing processes at mid-ocean ridges (MOR), seamount studies have had a significant impact on our understanding of the source compositions for oceanic basalts, the scales of mantle heterogeneity, and mantle melting systematics at MOR. However, many of these studies have focused on dredged lavas from individual seamounts with very few combining in situ sampling and high-resolution mapping from a single chain oriented perpendicular to the ridge axis. To fill this gap in knowledge about the sub-ridge mantle, two research cruises in 2016 and 2018 investigated the 8°20?N seamount chain that extends ~200km west of the EPR. The 8°20?N seamount chain was unexplored and virtually unsampled before our highly successful OASIS cruises. Geophysical, observational, and preliminary geochemical data from this nearly continuous chain of volcanoes led us to unexpected discoveries about their construction and revealed extreme compositional variability in the near MOR mantle that was previously only surmised from regional seamount studies in the northeast Pacific. The location, orientation, and preliminary data from the 8°20'N seamount chain make it an ideal a natural laboratory to investigate source heterogeneity and melting systematics in the near-ridge mantle. We propose to study the petrologic processes and mantle sources feeding MOR and near-axis volcanoes though comprehensive geochemical analyses of lavas and melt inclusions from the 8°20?N seamounts. Site-specific sampling using HOV Alvin and extensive, fine-scale mapping with AUV Sentry along the seamount chain, coupled with our previous comprehensive investigations of the 8°- 10°N EPR provide an exceptional opportunity to constrain geodynamic and geochemical models of mantle melting near MOR and determine the extent and length scales of mantle heterogeneity. We propose to collect a wide spectrum of petrologic and geochemical data including Sr, Nd, Pb, and Os isotopes, melt inclusion compositions, volatile contents, and 40Ar/39Ar age dates of lavas from the extensive collection of samples we have from the 8°20?N seamount chain. These results will be combined with numerical models to produce a petrologic model of mantle melting and magmatic processes in the near-ridge mantle. This extensive off-axis seamount chain provides a rare opportunity to probe the compositions of the mantle near MOR and to understand how magmas are spatially and temporally distributed in the shallow mantle and crust. Results from this research have implications for the generation of the majority of Earth?s crust.

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.