DOCSLIB.ORG

Magmatic History of Lavas from Kīlauea Volcano, Hawai'i and South Pagan Volcano, Northern Mariana Islands

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Magmatic History of Lavas from Kīlauea Volcano, Hawai'i and South Pagan Volcano, Northern Mariana Islands MAGMATIC HISTORY OF LAVAS FROM KĪLAUEA VOLCANO, HAWAI'I AND SOUTH PAGAN VOLCANO, NORTHERN MARIANA ISLANDS A DISSERTATION SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAWAI'I IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN GEOLOGY AND GEOPHYSICS MAY 2010 By Jared P. Marske Thesis Committee: Michael Garcia, Chairperson Eric Hellebrand Aaron Pietruszka Scott Rowland David Muenow “May all your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view…where something strange and more beautiful and more full of wonder than your deepest dreams waits for you.” -Edward Abbey “Civilization exists by geological consent, subject to change without notice.” -Will Durant “I choose to live, not just exist” -James Hetfield iii ACKNOWLEDGEMENTS I want to extend my sincerest thanks to my graduate advisors Michael Garcia and Aaron Pietruszka for their guidance, support, and dedication over the past 7 years. I want to thank my Mom, Dad, and Brother Gearz for their love and support over these many years. Many thanks to my dissertation committee members Eric Hellebrand, David Muenow, and Scott Rowland for their support, enthusiasm, and constructive reviews. Much appreciation goes out to my collaborators Marc Norman, Michael Rhodes, and Frank Trusdell for their helpful contributions to my dissertation. I want to extend a big mahalo to Dale Burns, Barry Hanan, Brian Jicha, Chad Shishido, Kyle Taniguchi, Michael Vollinger, and Joan Willis for their assistance in sample preparation and analyses. Thank you to Julie Herring, Game McGimsey, Maurice Sako, Daisy Wheeler, and the CNMI hazards personnel for their assistance during the Pagan Island fieldwork. I want to acknowledge a number of institutes (Hawaiian Volcano Observatory, National Science Foundation, and the Smithsonian Institute) for their helpful assistance. I am grateful for my officemates and husband, Wendy Stovall, Rebecca Carey, Carrie Brugger, Heidi Hansen, Anette von der Handt, Lisa Petrochilos, and Owen Neill for helping me stay sane over the years. I want to extend a special thank you to Angelo Bernardino, Adam Johnson, Francois Paquay, and Thomas Shea (a.k.a. The Horsemen) with whom, I have shared some of the best moments of my life. Finally, my warmest aloha goes out to all of my fellow graduate students who have made a positive impact on me both personally and professionally. You guys rock! iv ABSTRACT Petrologic and geochemical time-series studies of active volcanoes yield valuable insight into the crustal processes (e.g., crystal fractionation and accumulation, and crustal assimilation) and mantle source and melting variations (e.g., mantle source heterogeneity, and melt production, extraction, and transportation). This dissertation is composed of three main projects related to the magmatic history of lavas from Kīlauea Volcano, Hawai'i and South Pagan Volcano, Northern Mariana Islands. These volcanoes are highly active providing an excellent opportunity to investigate the magmatic processes that operate in both intra-plate (Kīlauea) and island-arc (South Pagan) settings over timescales of hours to thousands of years. Here, I present a comprehensive petrologic evaluation of: (1) 1998-2005 Pu‘u ‘Ō‘ō lavas from Kīlauea’s east rift zone (Chapter 1); (2) Quaternary to Holocene lavas from two volcanoes in South Pagan (Chapter 2); and (3) Historical (1790-1980 A.D.) Kīlauea rift lavas (Chapter 3) using Pb, Sr, and Nd isotope ratios, major and trace element abundances, olivine compositions, and petrographic data. Chapter 1 discusses the compositional evolution of 1998-2005 Pu‘u ‘Ō‘ō lavas and the implications for the nature and scale of mantle source heterogeneity within the Hawaiian plume. Chapter 2 examines the chemistry of stratigraphically-controlled southern Pagan lavas to assess and identify the slab contributions (fluid and sediment components) involved in arc magma genesis, determine the nature and extent of mantle partial melting, and evaluate crustal magmatic processes beneath Mariana volcanoes. Chapter 3 investigates the temporal geochemical variations of historical Kīlauea rift lavas to examine the petrogenetic relationship between summit and rift parental magmas, evaluate the magmatic link between the summit and rift zones, and determine the timescales of magma transport, mixing, and differentiation processes within the shallow plumbing system. v TABLE OF CONTENTS ACKNOWLEDGEMENTS................................................................................................. i ABSTRACT.........................................................................................................................v LIST OF TABLES........................................................................................................... viii LIST OF FIGURES ........................................................................................................... ix Chapter 1: Geochemical Variations during Kīlauea 's Pu‘u ‘Ō‘ō Eruption reveal a fine-scale mixture of mantle heterogeneities within the Hawaiian Plume 1.1 Abstract..........................................................................................................................1 1.2 Introduction....................................................................................................................2 1.3 Results............................................................................................................................6 1.3.1 Overview of the Pu‘u ‘Ō‘ō eruption .......................................................................6 1.3.2 Petrography.............................................................................................................7 1.3.3 Olivine composition................................................................................................9 1.3.4 Whole-rock analytical methods ............................................................................12 1.3.5 Geochemistry of 1998-2005 Pu‘u ‘Ō‘ō lavas ......................................................26 1.4 Discussion....................................................................................................................29 1.4.1 Crustal magmatic processes during the eruption ..................................................29 1.4.2 Temporal compositional variations.......................................................................30 1.4.3 Pu‘u ‘Ō‘ō source characteristics ...........................................................................33 1.4.3.1 A lithospheric source component for Pu‘u ‘Ō‘ō lavas?.................................33 1.4.3.2 A third mantle source for the Pu‘u ‘Ō‘ō eruption..........................................35 1.4.3.3 A pyroxenite source for Pu‘u ‘Ō‘ō lavas? .....................................................39 1.4.4 Small-scale mantle heterogeneity .........................................................................40 1.4.5 Chemical structure of the Hawaiian plume...........................................................42 1.5 Conclusions..................................................................................................................45 Chapter 2: Geochemistry of southern Pagan Island lavas, Mariana Arc: The role of subduction zone processes 2.1 Abstract........................................................................................................................47 2.2 Introduction..................................................................................................................48 2.3 Results..........................................................................................................................51 2.3.1 Pagan geology and sampling ................................................................................51 2.3.2 Analytical methods ...............................................................................................54 2.3.3 Major element chemistry ......................................................................................64 2.3.4 Trace element chemistry.......................................................................................64 2.3.5 Pb, Sr, and Nd isotope ratio variations .................................................................67 2.4 Discussion....................................................................................................................68 2.4.1 Magmatic differentiation ......................................................................................68 2.4.2 The role of slab contributions ...............................................................................71 2.4.2.1 Aqueous fluid component..............................................................................71 2.4.2.2 Sediment component......................................................................................75 2.4.3 Mantle source and melting model for Mariana lavas............................................80 2.4.4 Dynamics of the partial melting processes beneath Pagan ...................................89 2.5 Conclusions..................................................................................................................91 vi Chapter 3: Evolution of Kīlauea Volcano's shallow magmatic plumbing system: a geochemical perspective from historical rift lavas (1790-1980 A.D.) 3.1 Abstract........................................................................................................................93 3.2 Introduction..................................................................................................................94
Load more

Recommended publications
  • Uplift, Rupture, and Rollback of the Farallon Slab Reflected in Volcanic
    PUBLICATIONS Journal of Geophysical Research: Solid Earth RESEARCH ARTICLE Uplift, rupture, and rollback of the Farallon slab reflected 10.1002/2017JB014517 in volcanic perturbations along the Yellowstone Key Points: adakite hot spot track • Volcanic perturbations in the Cascadia back-arc region are derived from uplift Victor E. Camp1 , Martin E. Ross2, Robert A. Duncan3, and David L. Kimbrough1 and dismemberment of the Farallon slab from ~30 to 20 Ma 1Department of Geological Sciences, San Diego State University, San Diego, California, USA, 2Department of Earth and • Slab uplift and concurrent melting 3 above the Yellowstone plume Environmental Sciences, Northeastern University, Boston, Massachusetts, USA, College of Earth, Ocean, and Atmospheric promoted high-K calc-alkaline Sciences, Oregon State University, Corvallis, Oregon, USA volcanism and adakite generation • Creation of a seismic hole beneath eastern Oregon resulted from thermal Abstract Field, geochemical, and geochronological data show that the southern segment of the ancestral erosion and slab rupture, followed by Cascades arc advanced into the Oregon back-arc region from 30 to 20 Ma. We attribute this event to thermal a period of slab rollback uplift of the Farallon slab by the Yellowstone mantle plume, with heat diffusion, decompression, and the release of volatiles promoting high-K calc-alkaline volcanism throughout the back-arc region. The greatest Supporting Information: • Supporting Information S1 degree of heating is expressed at the surface by a broad ENE-trending zone of adakites and related rocks • Data Set S1 generated by melting of oceanic crust from the Farallon slab. A hiatus in eruptive activity began at ca. • Data Set S2 22–20 Ma but ended abruptly at 16.7 Ma with renewed volcanism from slab rupture occurring in two separate • Data Set S3 regions.
    [Show full text]
  • Full-Text PDF (Final Published Version)
    Pritchard, M. E., de Silva, S. L., Michelfelder, G., Zandt, G., McNutt, S. R., Gottsmann, J., West, M. E., Blundy, J., Christensen, D. H., Finnegan, N. J., Minaya, E., Sparks, R. S. J., Sunagua, M., Unsworth, M. J., Alvizuri, C., Comeau, M. J., del Potro, R., Díaz, D., Diez, M., ... Ward, K. M. (2018). Synthesis: PLUTONS: Investigating the relationship between pluton growth and volcanism in the Central Andes. Geosphere, 14(3), 954-982. https://doi.org/10.1130/GES01578.1 Publisher's PDF, also known as Version of record License (if available): CC BY-NC Link to published version (if available): 10.1130/GES01578.1 Link to publication record in Explore Bristol Research PDF-document This is the final published version of the article (version of record). It first appeared online via Geo Science World at https://doi.org/10.1130/GES01578.1 . Please refer to any applicable terms of use of the publisher. University of Bristol - Explore Bristol Research General rights This document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/red/research-policy/pure/user-guides/ebr-terms/ Research Paper THEMED ISSUE: PLUTONS: Investigating the Relationship between Pluton Growth and Volcanism in the Central Andes GEOSPHERE Synthesis: PLUTONS: Investigating the relationship between pluton growth and volcanism in the Central Andes GEOSPHERE; v. 14, no. 3 M.E. Pritchard1,2, S.L. de Silva3, G. Michelfelder4, G. Zandt5, S.R. McNutt6, J. Gottsmann2, M.E. West7, J. Blundy2, D.H.
    [Show full text]
  • Hawaiian Volcanoes: from Source to Surface Site Waikolao, Hawaii 20 - 24 August 2012
    AGU Chapman Conference on Hawaiian Volcanoes: From Source to Surface Site Waikolao, Hawaii 20 - 24 August 2012 Conveners Michael Poland, USGS – Hawaiian Volcano Observatory, USA Paul Okubo, USGS – Hawaiian Volcano Observatory, USA Ken Hon, University of Hawai'i at Hilo, USA Program Committee Rebecca Carey, University of California, Berkeley, USA Simon Carn, Michigan Technological University, USA Valerie Cayol, Obs. de Physique du Globe de Clermont-Ferrand Helge Gonnermann, Rice University, USA Scott Rowland, SOEST, University of Hawai'i at M noa, USA Financial Support 2 AGU Chapman Conference on Hawaiian Volcanoes: From Source to Surface Site Meeting At A Glance Sunday, 19 August 2012 1600h – 1700h Welcome Reception 1700h – 1800h Introduction and Highlights of Kilauea’s Recent Eruption Activity Monday, 20 August 2012 0830h – 0900h Welcome and Logistics 0900h – 0945h Introduction – Hawaiian Volcano Observatory: Its First 100 Years of Advancing Volcanism 0945h – 1215h Magma Origin and Ascent I 1030h – 1045h Coffee Break 1215h – 1330h Lunch on Your Own 1330h – 1430h Magma Origin and Ascent II 1430h – 1445h Coffee Break 1445h – 1600h Magma Origin and Ascent Breakout Sessions I, II, III, IV, and V 1600h – 1645h Magma Origin and Ascent III 1645h – 1900h Poster Session Tuesday, 21 August 2012 0900h – 1215h Magma Storage and Island Evolution I 1215h – 1330h Lunch on Your Own 1330h – 1445h Magma Storage and Island Evolution II 1445h – 1600h Magma Storage and Island Evolution Breakout Sessions I, II, III, IV, and V 1600h – 1645h Magma Storage
    [Show full text]
  • Experimental Constraints on Adakitic Metasomatism of Mantle Wedge Peridotites Below Patagonia
    O EOL GIC G A D D A E D C E I H C I L E O S F u n 2 d 6 la serena octubre 2015 ada en 19 Experimental constraints on adakitic metasomatism of mantle wedge peridotites below Patagonia Alexandre Corgne * and Manuel Schilling D. Instituto de Ciencias de la Tierra, Universidad Austral de Chile, Campus Isla Teja, Valdivia, Chile *Contact email: [email protected] Abstract. We performed a series of high-pressure (1.5 and Quaternary alkali lavas in the back-arc region (e.g. GPa) and high-temperature (1000-1300 ºC) experiments to Stern and Kilian, 1996; Gorring et al., 1997). The back-arc investigate the geochemical imprints of adakitic lavas are hosts of frequent mantle xenoliths, the study of metasomatism on mantle wedge peridotite. Reaction which has contributed to a better understanding of the couples were prepared using a powdered adakite from petrological and geochemical variability of the sub- Cerro Pampa (Argentina) placed next to a fragment of continental lithospheric mantle (e.g. Stern et al., 1990, spinel lherzolite from Pali Aike (Chile). Preliminary results 1999; Gorring and Kay, 2000; Laurora et al., 2001; show that the main changes in phase relations are Bertotto, 2002; Kilian and Stern, 2002; Bjerg et al., 2005, incongruent dissolution of olivine and associated 2009; Schilling et al., 2005; Rivalenti et al., 2004; Ntaflos precipitacion of secondary orthopyroxene, incongruent dissolution of primary spinel and formation of secondary et al., 2007; Wang et al., 2008; Dantas et al. 2009). spinel, as well as precipitation of secondary clinopyroxene and in some instances zoned plagioclase.
    [Show full text]
  • Potassic “Adakite” Magmas and Where They Come From: a Mystery Solved? John Clemens Kingston University (London) Long Xiao China University of Geosciences (Wuhan)
    1 Potassic “adakite” magmas and where they come from: a mystery solved? John Clemens Kingston University (London) Long Xiao China University of Geosciences (Wuhan) 2 3 4 . Adakites are volcanic and intrusive igneous rocks with 55 to 65 wt% SiO2, Al2O3 > 15 wt%, K2O/Na2O typically < 0.6, high La/Yb and Sr/Y ratios and strong depletion in Yb, Y, and HFSE. The name is from Adak island in the Alaskan Aleutians (Aleut “adak” = father). They are typically found in island and continental arc settings. Some believe then to be equivalents of Archæan TTG rocks – hence their importance. Their geochemical and isotopic characteristics suggest an origin by partial melting of mafic crust at pressures high enough to stabilise garnet and eliminate plagioclase. 5 . Adakites that occur in arcs have been interpreted as melts of the down-going slab. Thermal models suggest that slab melting should be restricted to young, hot subduction zones. Atherton and Petford (1993) suggested melting of young lower crustal rocks, in the upper plate, as an alternative to slab melting. There is some direct geological evidence for this alternative in some areas. 6 . Late Mesozoic granitoids in eastern China occur over wide areas, and lack either temporal or spatial association with subduction. Apart from their SiO2 contents, some have all the other geochemical attributes of typical subduction-related adakites, including a lack of Eu anomalies in their REE spectra, except that their K2O/Na2O > 0.95. This is possibly an erroneous attribution as “adakitic”. However this occurrence casts doubt on the assumption of a subduction-related origin for all adakitic magmas.
    [Show full text]
  • Petrogenesis of Cretaceous Adakite-Like Intrusions of the Gangdese Plutonic Belt, Southern Tibet: Implications for Mid-Ocean Ridge Subduction and Crustal Growth
    Lithos 190–191 (2014) 240–263 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos Petrogenesis of Cretaceous adakite-like intrusions of the Gangdese Plutonic Belt, southern Tibet: Implications for mid-ocean ridge subduction and crustal growth Yuan-chuan Zheng a,b,⁎, Zeng-qian Hou b, Ying-li Gong c, Wei Liang a,Qing-ZhongSunb,SongZhanga, Qiang Fu a, Ke-Xian Huang a, Qiu-Yun Li a,WeiLia a School of Earth Sciences and Resources, China University of Geosciences, Beijing 100082, PR China b Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China c Laboratory of Department of Thermal Engineering, Tsinghua University, Beijing 100084, PR China article info abstract Article history: We have conducted a whole-rock geochemical, U–Pb zircon geochronological, and in situ zircon Hf–Oisotopic Received 15 August 2013 compositional study of rocks in southern Tibet from the Langxian igneous suite (including a lamprophyre Accepted 16 December 2013 dyke, mafic enclaves, a granodiorite, and a two-mica granite) and the Nuri igneous suite (a quartz–diorite). U– Available online 24 December 2013 Pb zircon dating indicates that the timing of crystallization of the mafic enclaves and host granodiorite of the Langxian suite are ca. 105 Ma and 102 Ma, respectively, that the Langxian lamprophyre dyke and the two- Keywords: – – Geochemistry mica granite were emplaced at ca. 96 Ma and 80 76 Ma, respectively, and that the Nuri quartz diorite was fi U–Pb zircon ages emplaced at ca. 95 Ma. With the exception of the lamprophyre dyke and ma c enclaves in the Langxian area, Zircon Hf–Oisotopes felsic rocks from the Langxian and Nuri igneous suites all show signs of a geochemical affinity with adakite- 18 Adakite-like rocks like rocks.
    [Show full text]
  • Can Slab Melting Be Caused by Flat Subduction? Geology
    See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/234073692 Can slab melting be caused by flat subduction? Geology Article in Geology · June 2000 DOI: 10.1130/0091-7613(2000)28<535:CSMBCB>2.0.CO;2 CITATIONS READS 428 1,167 4 authors, including: M.-A. Gutscher René C Maury Université de Bretagne Occidentale Université de Bretagne Occidentale 164 PUBLICATIONS 5,573 CITATIONS 356 PUBLICATIONS 11,783 CITATIONS SEE PROFILE SEE PROFILE Erwan Bourdon CFG Services 38 PUBLICATIONS 1,092 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: ACTIVEMARGINS View project Eastern Indonesian Geodynamic Evolution View project All content following this page was uploaded by M.-A. Gutscher on 20 May 2014. The user has requested enhancement of the downloaded file. Can slab melting be caused by flat subduction? Marc-André Gutscher* Laboratoire GTS, UMR 5573, Université Montpellier II, F-34095 Montpellier, France René Maury IUEM/Université Bretagne Occidentale, Place Nicolas Copernic, F-29280 Plouzané, France Jean-Philippe Eissen IRD Centre de Bretagne, B.P. 70, F-29280 Plouzané, France Erwan Bourdon ABSTRACT tion of adakitic magmas for these cases, related to Slab melting has been suggested as a likely source of adakitic arc magmas (i.e., andesitic an unusual subduction geometry known as flat and dacitic magmas strongly depleted in Y and heavy rare earth elements). Existing numerical subduction (Fig. 3) (Sacks, 1983; Pennington, and petrologic models, however, restrict partial melting to very young (<5 Ma) oceanic crust 1984; Cahill and Isacks, 1992; Abbott et al., (typically at 60–80 km depth).
    [Show full text]
  • Miocene to Late Quaternary Patagonian Basalts (46–478S): Geochronometric and Geochemical Evidence for Slab Tearing Due to Active Spreading Ridge Subduction
    Journal of Volcanology and Geothermal Research 149 (2006) 346–370 www.elsevier.com/locate/jvolgeores Miocene to Late Quaternary Patagonian basalts (46–478S): Geochronometric and geochemical evidence for slab tearing due to active spreading ridge subduction Christe`le Guivel a,*, Diego Morata b, Ewan Pelleter c,d, Felipe Espinoza b, Rene´ C. Maury c, Yves Lagabrielle e, Mireille Polve´ f,g, Herve´ Bellon c, Joseph Cotten c, Mathieu Benoit c, Manuel Sua´rez h, Rita de la Cruz h a UMR 6112 bPlane´tologie et Ge´odynamiqueQ, Universite´ de Nantes, 2 rue de la Houssinie`re, 44322 Nantes, France b Departamento de Geologı´a. Fac. Cs. Fı´sicas y Matema´ticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile c UMR 6538 bDomaines oce´aniquesQ, UBO-IUEM, place Nicolas-Copernic, 29280 Plouzane´, France d CRPG-CNRS UPR A2300, BP 20, 54501 Vandoeuvre-les-Nancy, France e UMR 5573, Dynamique de la Lithosphe`re, Place E. Bataillon, case 60, 34095, Montpellier Cedex 5, France f LMTG-OMP, 14 Avenue E. Belin, 31400 Toulouse, France g IRD-Departamento de Geologia de la Universidad de Chile, Chile h Servicio Nacional de Geologı´a y Minerı´a, Avda. Santa Marı´a 0104, Santiago, Chile Received 18 May 2005; received in revised form 29 August 2005; accepted 14 September 2005 Abstract Miocene to Quaternary large basaltic plateaus occur in the back-arc domain of the Andean chain in Patagonia. They are thought to result from the ascent of subslab asthenospheric magmas through slab windows generated from subducted segments of the South Chile Ridge (SCR). We have investigated three volcanic centres from the Lago General Carrera–Buenos Aires area (46–478S) located above the inferred position of the slab window corresponding to a segment subducted 6 Ma ago.
    [Show full text]
  • Geologic Map of the State of Hawai 'I
    Geologic Map of the State of Hawai‘i By David R. Sherrod, John M. Sinton, Sarah E. Watkins, and Kelly M. Brunt Open-File Report 2007–1089 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DIRK KEMPTHORNE, Secretary U.S. Geological Survey Mark D. Myers, Director U.S. Geological Survey, Reston, Virginia 2007 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Suggested citation: Sherrod, D.R., Sinton, J.M., Watkins, S.E., and Brunt, K.M., 2007, Geologic Map of the State of Hawai`i: U.S. Geological Survey Open-File Report 2007-1089, 83 p., 8 plates, scales 1:100,000 and 1:250,000, with GIS database Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted material contained within this report. ii Geologic Map of the State of Hawai‘i By David R. Sherrod, John M. Sinton, Sarah E. Watkins, and Kelly M. Brunt About this map Sources of mapping, methods of This geologic map and its digital databases present compilation, origin of stratigraphic the geology of the eight major islands of the State of names, and divisions of the geologic Hawai‘i.
    [Show full text]
  • The Boring Volcanic Field of the Portland-Vancouver Area, Oregon and Washington: Tectonically Anomalous Forearc Volcanism in an Urban Setting
    Downloaded from fieldguides.gsapubs.org on April 29, 2010 The Geological Society of America Field Guide 15 2009 The Boring Volcanic Field of the Portland-Vancouver area, Oregon and Washington: Tectonically anomalous forearc volcanism in an urban setting Russell C. Evarts U.S. Geological Survey, 345 Middlefi eld Road, Menlo Park, California 94025, USA Richard M. Conrey GeoAnalytical Laboratory, School of Earth and Environmental Sciences, Washington State University, Pullman, Washington 99164, USA Robert J. Fleck Jonathan T. Hagstrum U.S. Geological Survey, 345 Middlefi eld Road, Menlo Park, California 94025, USA ABSTRACT More than 80 small volcanoes are scattered throughout the Portland-Vancouver metropolitan area of northwestern Oregon and southwestern Washington. These vol- canoes constitute the Boring Volcanic Field, which is centered in the Neogene Port- land Basin and merges to the east with coeval volcanic centers of the High Cascade volcanic arc. Although the character of volcanic activity is typical of many mono- genetic volcanic fi elds, its tectonic setting is not, being located in the forearc of the Cascadia subduction system well trenchward of the volcanic-arc axis. The history and petrology of this anomalous volcanic fi eld have been elucidated by a comprehensive program of geologic mapping, geochemistry, 40Ar/39Ar geochronology, and paleomag- netic studies. Volcanism began at 2.6 Ma with eruption of low-K tholeiite and related lavas in the southern part of the Portland Basin. At 1.6 Ma, following a hiatus of ~0.8 m.y., similar lavas erupted a few kilometers to the north, after which volcanism became widely dispersed, compositionally variable, and more or less continuous, with an average recurrence interval of 15,000 yr.
    [Show full text]
  • Andean Flat-Slab Subduction Through Time
    Andean flat-slab subduction through time VICTOR A. RAMOS & ANDRE´ S FOLGUERA* Laboratorio de Tecto´nica Andina, Universidad de Buenos Aires – CONICET *Corresponding author (e-mail: [email protected]) Abstract: The analysis of magmatic distribution, basin formation, tectonic evolution and structural styles of different segments of the Andes shows that most of the Andes have experienced a stage of flat subduction. Evidence is presented here for a wide range of regions throughout the Andes, including the three present flat-slab segments (Pampean, Peruvian, Bucaramanga), three incipient flat-slab segments (‘Carnegie’, Guan˜acos, ‘Tehuantepec’), three older and no longer active Cenozoic flat-slab segments (Altiplano, Puna, Payenia), and an inferred Palaeozoic flat- slab segment (Early Permian ‘San Rafael’). Based on the present characteristics of the Pampean flat slab, combined with the Peruvian and Bucaramanga segments, a pattern of geological processes can be attributed to slab shallowing and steepening. This pattern permits recognition of other older Cenozoic subhorizontal subduction zones throughout the Andes. Based on crustal thickness, two different settings of slab steepening are proposed. Slab steepening under thick crust leads to dela- mination, basaltic underplating, lower crustal melting, extension and widespread rhyolitic volcan- ism, as seen in the caldera formation and huge ignimbritic fields of the Altiplano and Puna segments. On the other hand, when steepening affects thin crust, extension and extensive within-plate basaltic flows reach the surface, forming large volcanic provinces, such as Payenia in the southern Andes. This last case has very limited crustal melt along the axial part of the Andean roots, which shows incipient delamination.
    [Show full text]
  • Phreatomagmatic and Phreatic Fall and Surge Deposits from Explosions at Kilauea Volcano, Hawaii, 1790 A.D.: Keanakakoi Ash Member
    Bull Volcanol (1990) 52:334-354 Vol 61ogy 9 Springer-Verlag1990 Phreatomagmatic and phreatic fall and surge deposits from explosions at Kilauea volcano, Hawaii, 1790 A.D.: Keanakakoi Ash Member Jocelyn McPhie 1., George PL Walker I , and Robert L Christiansen 2 1 Hawaii Institute of Geophysics, 2525 Correa Road, Honolulu, HI96822, USA 2 US Geological Survey, 345 Middlefield Road, Menlo Park, CA94025, USA Received July 28, 1989/Accepted November 9, 1989 Abstract. In or around 1790 A.D. an explosive eruption phreatic phases may reflect the progressive degassing took place in the summit caldera of Kilauea shield vol- and cooling of the magma during deep withdrawal: cano. A group of Hawaiian warriors close to the cal- throughout the phreatomagmatic phases magma vesicu- dera at the time were killed by the effects of the explo- lation contributed to the explosive interaction with wa- sions. The stratigraphy of pyroclastic deposits sur- ter by initiating the fragmentation process; thereafter, rounding Kilauea (i.e., the Keanakakoi Ash Member) the principal role of the subsiding magma column was suggests that the explosions referred to in the historic to supply heat for steam production that drove the record were the culmination of a prolonged hydrovol- phreatic explosions of the final phase. canic eruption consisting of three main phases. The first phase was phreatomagmatic and generated well- bedded, fine fallout ash rich in glassy, variably vesicu- lated, juvenile magmatic and dense, lithic pyroclasts. The ash was mainly dispersed to the southwest of the Introduction caldera by the northeasterly trade winds. The second phase produced a Strombolian-style scoria fall deposit Kilauea caldera is surrounded by well-bedded ash and followed by phreatomagmatic ash similar to that of the lapilli deposits of the Keanakakoi Ash Member (Easton first phase, though richer in accretionary lapilli and li- 1987).
    [Show full text]