DOCSLIB.ORG

Volatile Mobility of Trace Metals in Volcanic Systems

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

AN ABSTRACT OF THE DISSERTATION OF Matthew W. Loewen for the degree of Doctor of Philosophy in Geology presented on December 16, 2013. Title: Volatile Mobility of Trace Metals in Volcanic Systems. Abstract approved: _____________________________________________________________________ Adam J.R. Kent Semi-volatile trace metals like Li, Cu, Mo, Sn, In, and Pb have the potential to track mobility of a volatile phase in volcanic systems. In this dissertation four studies are presented that either directly investigate or are motivated by observations of trace metal behavior in volcanic systems. A common tool for trace element determination in solid materials is laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Although this technique has the potential to measure concentrations of many elements to << 1 ppm, it also has the potential to fractionate elements of different volatility resulting in increased analytical uncertainty. Potential sources of fractionation in two different laser ablation systems are characterized, including a previously unrecognized source of fractionation related to differential carrier gas flow at the site of ablation. Glass and melt inclusions from the 1959 eruption of Kilauea Iki record little evidence for volatile behavior of metals, but do record variations related to mixing of distinct batches of magma. Variations in concentrations of metals like Cu, Zn, and Mo can be explained with olivine fractionation. Only Sn variations appear to be compatible with volatile mobility. Lithophile element variations in both glass and melt inclusions require that the Kilauea Iki magma was a mixture of melts generated from different mantle sources by variable degrees of melting. Amphibole phenocrysts from Mt. Pinatubo, Mt. Hood, Mt. St. Helens, and Shiveluch Volcano record a variety of trace element signatures related to the sources and fractionation processes acting in each of these systems. Variations in Li and Cu in amphiboles are decoupled from any other trace element but positively correlate with each other. Their behavior appears to be consistent with mobility in volatile-rich fluids followed by rapid equilibration with amphibole phenocrysts. New 40Ar-39Ar incremental heating age determinations and whole rock major and trace element analyses from the Curaçao Lava Formation and the Dumisseau Formation have provided a revision of the timing and geochemical character of the Caribbean Large Igneous Province. These data provide evidence for almost 30 million years of volcanic history beginning around 94-60 Ma with mantle plume-like geochemical character. To reconcile the duration of volcanism and the observed geochemical signature with models of mantle plume impingement, a new model for development of the Caribbean Large Igneous Province is proposed that calls on nearby subduction zones to induce asthenospheric flow in the mantle that allows for continuous tapping of plume-influenced mantle for a 30 million year period. ©Copyright by Matthew W. Loewen December 16, 2013 All Rights Reserved Volatile Mobility of Trace Metals in Volcanic Systems by Matthew W. Loewen A DISSERTATION submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Presented December 16, 2013 Commencement June 2014 Doctor of Philosophy dissertation of Matthew W. Loewen presented on December 16, 2013. APPROVED: Major Professor, representing Geology Dean of the College of Earth, Ocean, and Atmospheric Sciences Dean of the Graduate School I understand that my dissertation will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my dissertation to any reader upon request. Matthew W. Loewen, Author ACKNOWLEDGEMENTS A small acknowledgements section at the beginning of this dissertation cannot properly thank or even recognize all of the many people who made completing this work possible and more importantly enjoyable. In each chapter separate acknowledgement sections address important logistical support, funding, and reviews that went into each chapter. Here I want to recognize people who were most important to my completion of this overall degree. First I want to note my appreciation for Adam Kent, my advisor, and the members of my thesis committee: Bob Duncan, John Dilles, Frank Tepley, and Anthony Koppers as well as late substitutes for my defense Anita Grunder and Dave Graham who stepped in after a beautiful December snowstorm cancelled my original defense date and required me to reschedule for a time when Bob and John could not attend. I could not ask for a better advisor than Adam. He trusted me with the freedom to work out my own problems and work on my own schedule, but also readily answered questions and gave exceptional guidance on how to write. The data we collected often was unexpected and quite frankly disappointing, but he kept me positive and helped to point out the value of whatever results we found. All of my committee members have provided support beyond their required rolls. Bob has acted more like a co-advisor, especially with the Caribbean project, and made huge contributions to publishing that chapter before my defense. I have only been able to apply a fraction of John’s wealth of knowledge to the discussion of metal behavior in volcanic systems, and all of his suggestions including those not included here will help improve the eventual publications of those projects. In addition, I am grateful to have had the opportunity to learn from him by working as his teaching assistant in Mineralogy and taking several of his courses. Frank was always a friendly face with his office down the hall from mine. I probably dropped in on him and asked him for as much advise as I asked Adam for. Most importantly, he was always willing to help and take the time to listen. Anthony played the role of a GCR, but actually taught me how to prepare samples for Ar-Ar dating and gave me my first examination on the literature of the Caribbean LIP during his isotope geochemistry class. ACKNOWLEDGEMENTS (Continued) Beyond my committee, I want to acknowledge the entire VIPER community of fellow students and faculty. While working at OSU, I had the fortune to work with a group of genuinely good people who made work fun. The students who were here when I arrived established a culture of friendliness and excitement. I especially want to acknowledge the conversation and friendships with Alison Koleszar, Mark Ford, Allison Weinsteiger, Morgan Salisbury, BJ Walker, and Erin Lieuallen. My cohort of incoming VIPERs in 2008-09, Ashley Bromley, Amy Lange, and Fede Cernuschi, still blow me away with their intelligence, but they are also the best people I could ever hope to work with and are among my best friends. Ashley especially has become a lifelong friend in all adventures geologic and union. New students have come (and gone) since I got here and I don’t know half of them as well as I’d like, but I want to point out some who have been especially helpful as sounding boards and friends including Dale Burns, Jason Kaiser, Stephanie Grocke, Kyle Krawl, Richard Bradshaw, Luc Farmer, Christine Chan, Daniel Eungard, Andrew Burleigh, Casey Tierney, Darrick Boschmann. The good nature of most people who have chosen to join the VIPER group at OSU is this research programs’ strongest asset. Outside of the VIPER group, I have been lucky to be involved in the Coalition of Graduate Employees (CGE 6069). This is the best organization I have ever been a part of and have been proud to be a member and volunteer. The people I have met in this organization are some of the most generous people I know and have made meaningful improvements in both Oregon State University and the university/research communities around the country. I think the best work I’ve done while working on a PhD are not in this dissertation but with this organization. I hope as long as CGE represents graduate employees at OSU people do not hesitate to join this great union and continue to volunteer to make it better. ACKNOWLEDGEMENTS (Continued) Before coming to OSU many important people inspired me to not only study first in the sciences but then geology. Dr. Kaser was an especially inspiration high school physics/astronomy teacher. My undergraduate advisor, Jeff Tepper, is a geologic role model and taught me my core skills in this wonderful subject. Two of my closest friends as an undergraduate, Eric and Marissa, helped drive my passion and excitement in all things scientific and academic. My immediate and extended family has been a big part of my life and gave me the encouragement and support to get through all my schooling. I have ben fortunate to have them close the last few years even if school has kept me too busy to see everyone as much as I would like. I want to especially note my Dad from whom I inherited a love for debate, thinking, and standing up for what is right, and my Mom who taught me to love the mountains and the world around me. Studying geology for almost 10 years now started with exploring the spectacular volcanoes of the central Cascades in Oregon. My most important acknowledgement is reserved for my best friend and wife, Caitlin. When I started at OSU she lived in McMinnville and then Portland. Without the fun of visiting her almost every weekend my first two years in grad school I would have burned out and never continued past a masters degree. After marrying me and living with me she has been my most important companion sharing my excitement and comforting my dismay through all of my experiences the last few years. My best memories in graduate school have been adventures with her and those experiences are what fueled my ability to work hard on my degree.
Recommended publications
  • Experimental Partitioning of Rb, Cs, Sr, and Ba Between Alkali Feldspar and Peraluminous Melt

    Experimental Partitioning of Rb, Cs, Sr, and Ba Between Alkali Feldspar and Peraluminous Melt

    American Mineralogist, Volume 81, pages 719-734,1996 Experimental partitioning of Rb, Cs, Sr, and Ba between alkali feldspar and peraluminous melt JONATHAN IcENHOWER AND DAVID LoNDON School of Geology and Geophysics, University of Oklahoma, 100 East Boyd Street, SEC 810, Norman, Oklahoma 73019, U.S.A. ABSTRACT Hydrous partial melting experiments performed between 650 and 750 °C at 200 MPa (H20) on synthetic metapelite compositions (quartz + albite + muscovite + biotite min- eral mixtures) doped with Ba, Sr, Rb, and Cs yielded alkali feldspar crystals with a wide range of compositions in equilibrium at their rims with peraluminous melt. Measured partition coefficients for normally trace lithophile elements between feldspar and melt [D(M)FSP/gl,M = Ba, Sr, Rb, Cs] do not depend on either temperature or bulk composition of melt for the compositions studied. Values of D(Sr)FSP/glare between 10 and 14 and appear to be independent of the albite and orthoclase contents of the feldspar crystals. In contrast, values of D(Ba)FSP/gland D(Rb)FsP/glare strongly dependent on the orthoclase content of feldspar, relationships that can be expressed by the following linear equations: D(Ba)FSP/gl= 0.07 + 0.25(orthoclase) and D(Rb)FsP/gl= 0.03 + 0.0 1(orthoclase), where orthoclase is in mole percent. These equations reproduce the range of previously reported values for D(Ba) and D(Rb) determined on natural and synthetic samples. A single par- tition coefficient for Cs was also determined at D(CS)Fsp/gl= 0.13. These data can be used in conjunction with recently published partition coefficients for muscovite, biotite, and plagioclase feldspars (Blundy and Wood 1991; Icenhower and London 1995) to model quantitatively the trace element signatures of peraluminous mag- mas during anatexis and crystallization.
  • Using Rare Earth Elements to Model Silicate Melting and Crystallization

    Using Rare Earth Elements to Model Silicate Melting and Crystallization

    Using Rare Earth Elements to Model Silicate Melting and Crystallization The Rare Earth Elements (REE) The lanthanide series is formed by filling of 4f orbitals, and its constituents are commonly termed the rare earth elements (REE). The common valence state is +3 for all REE over a wide range of oxygen fugacity; Ce+4 can occur in highly oxidized environments at the earth's surface, and Eu+2 in reducing environments in the crust and mantle. The rare earth elements are lithophile elements (low electronegativities lead to the formation of highly ionic bonds), which substitute into many silicates and phosphates. Ionic radii of the lanthanides decreases with increasing atomic number from La to Lu, the lanthanide contraction… Because of their high charge and large radii, the rare earth elements are usually relatively incompatible in silicate minerals. However, due to the lanthanide contraction, the heavier rare earths are smaller and thus can "fit" within some lattice sites (although there must be charge compensation for the 3+ valence), so incompatibility decreases with increasing Z. Class Discussion #1: What mineral lattice sites could host the heavy rare earth elements? What about Eu2+? REE diagrams If we plot the concentrations of the rare earth elements as a group on a diagram of abundance versus atomic number, we observe two cosmochemical phenomena: 1) the decrease in absolute abundance with increasing atomic number; 2) the “even-odd effect” in relative abundances (higher abundances of even atomic number elements). Because these cosmochemical effects are common to all terrestrial rocks, we would rather ignore them in order to accentuate more subtle variations in absolute and relative concentrations of REE between samples.
  • Trace Elements in Igneous Petrology

    Trace Elements in Igneous Petrology

    Trace Elements in igneous petrology •Abundances of trace elements are used to test petrogenetic hypotheses •No universal definition of TE: Concentration usually less than 100 ppm, often < 10 ppm •Useful trace elements: a)First transition series: Sc Ti V Cr Mn Fe Co Ni Cu Zn Ti and Fe are usually major elements, Cr, Mn, and Ni are minor elements Progressive filling of 3d orbitals Variable crystal field stabilization Commonly multivalent (Sc3, Ti4,3, V2,3,4,5, Cr2,3,6, Mn2,3, Fe2,3, Co2, Ni2 b) Lanthanides (REE): La Ce Pr Nd (Pm) Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Light REE and heavy REE (Y behaves like a HREE) normalization factors (chondrites) 1 Eu2+ REE Chondritic abundances Lanthanide Contraction odd vs. even abundances 1.2 .8 .6 1.1 .4 Eu3+ Ionic radius (Å) Ionic radius Abundance (ppm) .2 Based on 8-fold 1.0 coordination 0 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu (c) Large Ion Lithophile Elements (LILE): may also be partitioned into fluid phase Alkalis: K Rb Cs (monovalent) Alkaline earths: Ba Sr (divalent) Actinides: U, Th, Ra, Pa (multiple valency) (d) High field strength elements (HFSE): small, highly-charged ions Zr, Hf (4 valent) Nb, Ta (4 and 5 valent) (e) Chalcophile elements: Cu, Zn, Pb, Ag, Hg, PGE, (Fe, Co, Ni) (f) Siderophile elements: Fe, Ni, Co, Ge, P, Ga, Au (PGE)… • Decoupled from major elements: lack of stoichiometric constraints (not strictly true) • Goldschmidt’s Rules • Generalities: Incompatible elements are elements that tend to be excluded from common minerals (olivines, pyroxenes, garnets, feldspars, oxides…) in equilibrium with a melt, i.e., they have low D values.
  • Implications of Subduction Rehydration for Earth's Deep Water

    Implications of Subduction Rehydration for Earth's Deep Water

    Implications of Subduction Rehydration for Earth’s Deep Water Cycle Lars Rüpke Physics of Geological Processes, University of Oslo, Oslo, Norway, and SFB 574 Volatiles and Fluids in Subduction Zones, Kiel, Germany Jason Phipps Morgan Cornell University, Ithaca, New York, USA and SFB 574 Volatiles and Fluids in Subduction Zones, Kiel, Germany Jacqueline Eaby Dixon RSMAS/MGG, University of Miami, Miami, Florida, USA The “standard model” for the genesis of the oceans is that they are exhalations from Earth’s deep interior continually rinsed through surface rocks by the global hydrologic cycle. No general consensus exists, however, on the water distribution within the deeper mantle of the Earth. Recently Dixon et al. [2002] estimated water concentrations for some of the major mantle components and concluded that the most primitive (FOZO) are significantly wetter than the recycling associated EM or HIMU mantle components and the even drier depleted mantle source that melts to form MORB. These findings are in striking agreement with the results of numerical modeling of the global water cycle that are presented here. We find that the Dixon et al. [2002] results are consistent with a global water cycle model in which the oceans have formed by efficient outgassing of the mantle. Present-day depleted mantle will contain a small volume fraction of more primitive wet mantle in addition to drier recycling related enriched components. This scenario is consis- tent with the observation that hotspots with a FOZO-component in their source will make wetter basalts than hotspots whose mantle sources contain a larger fraction of EM and HIMU components.
  • The Transition-Zone Water Filter Model for Global Material Circulation: Where Do We Stand?

    The Transition-Zone Water Filter Model for Global Material Circulation: Where Do We Stand?

    The Transition-Zone Water Filter Model for Global Material Circulation: Where Do We Stand? Shun-ichiro Karato, David Bercovici, Garrett Leahy, Guillaume Richard and Zhicheng Jing Yale University, Department of Geology and Geophysics, New Haven, CT 06520 Materials circulation in Earth’s mantle will be modified if partial melting occurs in the transition zone. Melting in the transition zone is plausible if a significant amount of incompatible components is present in Earth’s mantle. We review the experimental data on melting and melt density and conclude that melting is likely under a broad range of conditions, although conditions for dense melt are more limited. Current geochemical models of Earth suggest the presence of relatively dense incompatible components such as K2O and we conclude that a dense melt is likely formed when the fraction of water is small. Models have been developed to understand the structure of a melt layer and the circulation of melt and vola- tiles. The model suggests a relatively thin melt-rich layer that can be entrained by downwelling current to maintain “steady-state” structure. If deep mantle melting occurs with a small melt fraction, highly incompatible elements including hydro- gen, helium and argon are sequestered without much effect on more compatible elements. This provides a natural explanation for many paradoxes including (i) the apparent discrepancy between whole mantle convection suggested from geophysical observations and the presence of long-lived large reservoirs suggested by geochemical observations, (ii) the helium/heat flow paradox and (iii) the argon paradox. Geophysical observations are reviewed including electrical conductivity and anomalies in seismic wave velocities to test the model and some future direc- tions to refine the model are discussed.
  • Incompatible Element Ratios in Plate Tectonic and Stagnant Lid Planets Kent C. Condie1 and Charles K. Shearer 2. 1Department Of

    Incompatible Element Ratios in Plate Tectonic and Stagnant Lid Planets Kent C. Condie1 and Charles K. Shearer 2. 1Department Of

    47th Lunar! and Planetary Science Conference (2016) 1058.pdf Incompatible Element Ratios in Plate Tectonic and Stagnant Lid Planets Kent C. Condie1 and Charles K. Shearer2. 1Department of Earth and Environmental Science, New Mexico Tech, Socorro, New Mexico 87801, 2 Institute of Meteoritics, Department of Earth and Planetary Science, University of New Mexico, Albuquerque, New Mexico 87131, 2 NASA Johnson Space Center, Houston, TX 77058. Introduction: Because ratios of elements with group centered near Earth’s primitive mantle (PM) similar incompatibilities do not change much with composition (Fig. 2). This distribution is similar to degree of melting or fractional crystallization in the the distribution of most mare basalts from the Moon mantles of silicate planets, they are useful in sampled by the Apollo missions, except for the high- characterizing compositions of mantle sources of Ti basalts from Apollo 11 and 17 both of which are basalts that have not interacted with continental crust enriched in Nb. The primitive mantle grouping is [1,2]. Using Nb/Th and Zr/Nb ratios in young especially evident for Apollo 11, 12 and 15 basalts in oceanic basalts, three mantle domains can be which samples cluster tightly around primitive identified [3]: enriched (EM), depleted (DM), and mantle (PM) composition on Zr/Nb-Nb/Th, Th/Yb- hydrated mantle (HM) (Fig. 1). DM is characterized Nb/Yb and La/Sm-Nb/Th diagrams (Fig. 3). Very by high values of both ratios (Nb/Th > 8; Zr/Nb > 20) low-Ti green volcanic glasses (and some due to Th depletion relative to Nb, and to Nb intermediate-Ti yellow volcanic glasses) plot in a depletion relative to Zr.
  • Durham Research Online

    Durham Research Online

    Durham Research Online Deposited in DRO: 14 March 2018 Version of attached le: Accepted Version Peer-review status of attached le: Peer-reviewed Citation for published item: Namur, Olivier and Humphreys, Madeleine C.S. (2018) 'Trace element constraints on the dierentiation and crystal mush solidication in the Skaergaard intrusion, Greenland.', Journal of petrology., 59 (3). pp. 387-418. Further information on publisher's website: https://doi.org/10.1093/petrology/egy032 Publisher's copyright statement: This is a pre-copyedited, author-produced version of an article accepted for publication in Journal Of Petrology following peer review. The version of record Namur, Olivier Humphreys, Madeleine C.S. (2018). Trace element constraints on the dierentiation and crystal mush solidication in the Skaergaard intrusion, Greenland. Journal of Petrology is available online at: https://doi.org/10.1093/petrology/egy032. Additional information: Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full DRO policy for further details. Durham University Library, Stockton Road, Durham DH1 3LY, United Kingdom Tel : +44 (0)191 334 3042 | Fax : +44 (0)191 334 2971 https://dro.dur.ac.uk Trace element constraints on the differentiation and crystal mush solidification in the Skaergaard intrusion, Greenland Olivier Namur1*, Madeleine C.S.
  • WM White Geochemistry Chapter 7: Trace Elements

    WM White Geochemistry Chapter 7: Trace Elements

    W. M. White Geochemistry Chapter 7: Trace Elements Chapter 7: Trace Elements in Igneous Processes 7.1 INTRODUCTION n this chapter we will consider the behavior of trace elements, particularly in magmas, and in- troduce methods to model this behavior. Though trace elements, by definition, constitute only a I small fraction of a system of interest, they provide geochemical and geological information out of proportion to their abundance. There are several reasons for this. First, variations in the concentrations of many trace elements are much larger than variations in the concentrations of major components, of- ten by many orders of magnitude. Second, in any system there are far more trace elements than major elements. In most geochemical systems, there are 10 or fewer major components that together account for 99% or more of the system. This leaves 80 trace elements. Each element has chemical properties that are to some degree unique, hence there is unique geochemical information contained in the varia- tion of concentration for each element. Thus the 80 trace elements always contain information not available from the variations in the concentrations of major elements. Third, the range in behavior of trace elements is large and collectively they are sensitive to processes to which major elements are in- sensitive. One example is the depth at which partial melting occurs in the mantle. When the mantle melts, it produces melts whose composition is only weakly dependent on pressure, i.e., it always pro- duces basalt. Certain trace elements, however, are highly sensitive to the depth of melting (because the phase assemblages are functions of pressure).
  • Significant Zr Isotope Variations in Single Zircon Grains Recording Magma Evolution History

    Significant Zr Isotope Variations in Single Zircon Grains Recording Magma Evolution History

    Significant Zr isotope variations in single zircon grains recording magma evolution history Jing-Liang Guoa,b,1, Zaicong Wanga,1, Wen Zhanga, Frédéric Moyniera,c, Dandan Cuia, Zhaochu Hua, and Mihai N. Duceab,d aState Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China; bDepartment of Geosciences, University of Arizona, Tucson, AZ 85718; cInstitut de Physique du Globe de Paris, Université de Paris, CNRS, 75238 Paris Cedex 05, France; and dFaculty of Geology and Geophysics, University of Bucharest, 010041 Bucharest, Romania Edited by Bruce Watson, Rensselaer Polytechnic Institute, Troy, NY, and approved July 20, 2020 (received for review February 27, 2020) Zircons widely occur in magmatic rocks and often display internal differentiation processes of the silicate Earth (17, 18), the Zr zonation finely recording the magmatic history. Here, we presented isotopes of zircon might also record related messages. in situ high-precision (2SD <0.15‰ for δ94Zr) and high–spatial-resolution Recent developments of bulk and in situ analytical methods (20 μm) stable Zr isotope compositions of magmatic zircons in a have permitted studies on mass-dependent Zr isotope fraction- suite of calc-alkaline plutonic rocks from the juvenile part of the ation in terrestrial samples, including zircons (15, 19–24). They Gangdese arc, southern Tibet. These zircon grains are internally show the great potential of Zr isotope in tracing magmatic zoned with Zr isotopically light cores and increasingly heavier processes. However, available data have been rather limited and rims. Our data suggest the preferential incorporation of lighter resulted in very controversial interpretation (21, 22), such as for Zr isotopes in zircon from the melt, which would drive the residual fractionation factor α (whether greater or smaller than 1).
  • Mineral Potential for Incompatible Element Deposits Hosted In

    Mineral Potential for Incompatible Element Deposits Hosted In

    Prepared in cooperation with the Ministry of Petroleum, Energy and Mines, Islamic Republic of Mauritania Second Projet de Renforcement Institutionnel du Secteur Minier de la République Islamique de Mauritanie (PRISM-II) Mineral Potential for Incompatible Element Deposits Hosted in Pegmatites, Alkaline Rocks, and Carbonatites in the Islamic Republic of Mauritania: Phase V, Deliverable 87 By Cliff D. Taylor and Stuart A. Giles Open-File Report 2013–1280 Chapter Q U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior SALLY JEWELL, Secretary U.S. Geological Survey Suzette M. Kimball, Acting Director U.S. Geological Survey, Reston, Virginia: 2015 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod To order this and other USGS information products, visit http://store.usgs.gov Suggested citation: Taylor, C.D., and Giles, S.A., 2015, Mineral potential for incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites in the Islamic Republic of Mauritania (phase V, deliverable 87), chap. Q of Taylor, C.D., ed., Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II): U.S. Geological Survey Open-File Report 2013‒1280-Q, 41 p., http://dx.doi.org/10.3133/ofr20131280. [In English and French.] Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S.
  • Melting Depths and Mantle Heterogeneity Beneath Hawaii and the East Pacific Rise

    Melting Depths and Mantle Heterogeneity Beneath Hawaii and the East Pacific Rise

    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 104, NO. B2, PAGES 2817–2829, FEBRUARY 10, 1999 Melting depths and mantle heterogeneity beneath Hawaii and the East Pacific Rise: Constraints from Na/Ti and rare earth element ratios Keith Putirka Lawrence Livermore National Laboratory, Livermore, California. Abstract. Mantle melting calculations are presented that place constraints on the mineralogy of the basalt source region and partial melting depths for oceanic basalts. Melting depths are obtained from pressure-sensitive mineral-melt partition coefficients for Na, Ti, Hf, and the rare earth elements (REE). Melting depths are estimated by comparing model aggregate melt compositions to natural basalts from Hawaii and the East Pacific Rise (EPR). Variations in melting depths in a peridotite mantle are sufficient to yield observed differences in Na/Ti, Lu/Hf, and Sm/Yb between Hawaii and the EPR. Initial melting depths of 95–120 km are calculated for EPR basalts, while melting depths of 200–400 km are calculated for Hawaii, indicating a mantle that is 3008C hotter at Hawaii. Some isotope ratios at Hawaii are correlated with Na/Ti, indicating vertical stratification to isotopic heterogeneity in the mantle; similar comparisons involving EPR lavas support a layered mantle model. Abundances of Na, Ti, and REE indicate that garnet pyroxenite and eclogite are unlikely source components at Hawaii and may be unnecessary at the EPR. The result that some geochemical features of oceanic lavas appear to require only minor variations in mantle mineral proportions (2% or less) may have important implications regarding the efficiency of mantle mixing. Heterogeneity required by isotopic studies might be accompanied by only subtle differences in bulk composition, and material that is recycled at subduction zones might not persist as mineralogically distinct mantle components.
  • Nevado De Longaví Volcano (Chilean Andes, 36.2 ˚S): Adakitic Magmas Formed by Crystal Fractionation from Hydrous Basalts

    Nevado De Longaví Volcano (Chilean Andes, 36.2 ˚S): Adakitic Magmas Formed by Crystal Fractionation from Hydrous Basalts

    Geophysical Research Abstracts, Vol. 7, 01205, 2005 SRef-ID: 1607-7962/gra/EGU05-A-01205 © European Geosciences Union 2005 Nevado de Longaví Volcano (Chilean Andes, 36.2 ˚S): adakitic magmas formed by crystal fractionation from hydrous basalts C. Rodríguez, D. Sellés, M.A. Dungan Université de Genève, Département de Minéralogie. 13 Rue des Maraîchers, 1205 Geneva, Switzerland. The formation of adakites by partial melting of oceanic lithosphere is limited to re- gions where young, hot slabs are subducted. Adakitic melts also occur in continental arcs related to subduction of cold oceanic lithosphere, where they have been explained in terms of remelting of basaltic material underplated at the base of thickened orogenic crust (e.g., Petford et al., 1996; Kay and Mpodozis, 2002) or as the result of modifi- cation of the sub-arc mantle related to tectonic erosion of the forearc crust (e.g. Kay et al., 2004 in press). The only occurrence of Quaternary magmas in the accessible Andean Southern Volcanic Zone (SVZ 33-41˚ S) with an unequivocal adakitic signa- ture is at Nevado de Longaví (NLV; 36˚12’S – 71˚10’ W; Sellés et al. 2004), which is located to the south of the region that has been strongly affected by Tertiary crustal shortening and thickening, and associated eastward arc migration. We propose that the generation of adakitic melts at NLV has occurred via fractional crystallization of water-rich basalts. The unusual chemistry and unusually high modal abundance of hornblende in dacitic magmas at NLV appears to be ultimately related to an excep- tionally high fluid-flux from the subducted Mocha Fracture Zone (Eocene-age Nazca plate), which projects beneath NLV, and which is inferred to have generated water-rich but incompatible element-poor basalts through flux-melting.