DOCSLIB.ORG

U^Pb Zircon Chronostratigraphy of Early-Pliocene Ignimbrites from La Pacana, North Chile: Implications for the Formation of Strati¢Ed Magma Chambers

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
U^Pb Zircon Chronostratigraphy of Early-Pliocene Ignimbrites from La Pacana, North Chile: Implications for the Formation of Strati¢Ed Magma Chambers Journal of Volcanology and Geothermal Research 120 (2002) 43^53 www.elsevier.com/locate/jvolgeores U^Pb zircon chronostratigraphy of early-Pliocene ignimbrites from La Pacana, north Chile: implications for the formation of strati¢ed magma chambers Axel K.Schmitt a;Ã, Jan M.Lindsay b, Shan de Silva c, Robert B.Trumbull d a Department of Earth and Space Sciences, UCLA, Los Angeles, CA 90095-1567, USA b Seismic Research Unit, University of the West Indies, St. Augustine, Trinidad and Tobago c Department of Space Studies, University of North Dakota, Grand Forks, ND USA d GeoForschungsZentrum, Potsdam, Germany Received 15 October 2001; accepted 30 January 2002 Abstract High spatial resolution U^Pb dates of zircons from two consanguineous ignimbrites of contrasting composition, the high-silica rhyolitic Toconao and the overlying dacitic Atana ignimbrites, erupted from La Pacana caldera, north Chile, are presented in this study.Zircons from Atana and Toconao pumice clasts yield apparent 238U/206Pb ages of 4.11 þ 0.20 Ma and 4.65 þ 0.13 Ma (2c), respectively.These data combined with previously published geochemical and stratigraphic data, reveal that the two ignimbrites were erupted from a stratified magma chamber.The Atana zircon U^Pb ages closely agree with the eruption age of Atana previously determined by K^Ar dating (V4.0 þ 0.1 Ma) and do not support long ( s 1 Ma) residence times.Xenocrystic zircons were found only in the Toconao bulk ignimbrite, which were probably entrained during eruption and transport.Apparent 238U/206Pb zircon ages of V13 Ma in these xenocrysts provide the first evidence that the onset of felsic magmatism within the Altiplano^Puna ignimbrite province occurred approximately 3 Myr earlier than previously documented. ß 2002 Elsevier Science B.V. All rights reserved. Keywords: La Pacana caldera; strati¢ed magma chamber; ignimbrite; rhyolite; U/Pb; zircon 1. Introduction de Silva, 2001).Evidence for crystal^liquid sepa- ration is nearly ubiquitous (e.g. Smith, 1979; Hil- It is widely accepted that a spectrum of process- dreth, 1981).Recharge, where transiently distinct es operate to produce compositional diversity in magma batches are juxtaposed immediately prior silicic magma systems, but their relative impor- to eruption, may be important in some systems tance is debated (Eichelberger et al., 2000, 2001; (e.g. Eichelberger and Izbekov, 2000; Schmitt et al., 2001).Since both models are based on studies of heterogeneous pyroclastic deposits, elucidating * Corresponding author.Tel.: +1-310-794-5047; the roles of these mechanisms depends critically Fax: +1-310-825-2779. on detailed and precise volcanic chronostratigra- E-mail address: [email protected] (A.K. Schmitt). phy. 0377-0273 / 02 / $ ^ see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII: S0377-0273(02)00359-1 VOLGEO 2519 1-11-02 44 A.K. Schmitt et al. / Journal of Volcanology and Geothermal Research 120 (2002) 43^53 Stratigraphic and geochemical evidence sug- magma body of cordilleran batholith proportions gested that two huge compositionally contrasting (e.g. Chmielowski et al., 1999; Haberland and ignimbrites, the Atana and Toconao ignimbrites Rietbrock, 2001).Previous studies suggested that (combined volume V2700 km3), erupted from La ignimbrite activity in the APVC started at V10 Pacana caldera in the Central Andes and that Ma and reached its peak between approximately they are consanguineous and represent separate 7 and 3 Myr ago with the caldera-forming erup- layers of a strati¢ed magma (Lindsay et al., tions of La Pacana in north Chile (Gardeweg and 2001a,b).However, the temporal relations be- Ram|¤rez, 1987; de Silva, 1989b) and of Pastos tween the two units were ambiguous since pre- Grandes, Cerro Guacha and Cerro Panizos in vious K^Ar dating yielded inconclusive and, in south Bolivia (Francis and Baker, 1978; Ort, part, geologically unreasonable ages (see review 1993). in Lindsay et al., 2001a).The abundance of xen- The Toconao and Atana ignimbrites are both olithic material and scarcity of datable materials distributed around and thicken towards La Paca- in the crystal-poor Toconao ignimbrite rendered na caldera (Lindsay et al., 2001a; Fig.1 ).The conventional dating methods ine¡ective.Recent Toconao ignimbrite (180 km3) comprises a thin success in ion microprobe dating of Pliocene^ ( 6 10 cm) lower fall unit with glassy crystal- Pleistocene zircons (e.g. Baldwin and Ireland, poor ( 6 3%) tubular pumice and a thick (V30 1995; Brown and Fletcher, 1999; Dalrymple et m) upper £ow unit and locally displays two facies al., 1999; Reid and Coath, 2000) established ion that are caused by varying degrees of vapor-phase microprobe 238U/206Pb dating as a promising tool alteration.The overlying 2500 km 3 dacitic Atana for unraveling the history of young pyroclastic ignimbrite is homogeneous, crystal-rich (40^50%), systems.Here we demonstrate that 238U/206Pb relatively pumice-poor, and constitutes a single dating of zircons yields insights into the crystalli- cooling unit.The Atana intracaldera facies is zation history of the two La Pacana ignimbrites. densely welded, whereas degree of welding varies U^Pb zircon geochronology indicates a close tem- in extracaldera outcrops.There is no ¢eld evi- poral relationship between the Toconao and Ata- dence for a hiatus between deposition of the To- na magmas and, in combination with petrological conao and the overlying Atana ignimbrite but data from La Pacana, challenges the view that previous geochronology is inconclusive as to the compositional gaps in pyroclastic deposits are in timing of the two eruptions.Two stratigraphically general best explained by incomplete mixing be- consistent whole-rock and biotite K^Ar ages were tween magmas of di¡erent origin (e.g. Eichelberg- previously determined for Toconao pumice, these er et al., 2000).We suggest instead that strati¢ca- are 4.0 þ 0.9 and 5.27 þ 1.12 Ma (all errors 2c, see tion in the La Pacana system developed due to Lindsay et al., 2001a).Recent K^Ar biotite ages e¡ective crystal-melt separation within an upper- from Atana pumice have generally smaller uncer- crustal magma reservoir and that the layers con- tainties and range between 3.77 þ 0.09 Ma and tinued to evolve independently after separation. 4.23 þ 0.12 Ma (Lindsay et al., 2001a). 2. Geologic background of La Pacana caldera 3. Methods One of Earth’s most extensive silicic volcanic Zircons were recovered by heavy liquid separa- provinces is the Altiplano^Puna Volcanic Com- tion from the 6 350-Wm fraction from three sam- plex (APVC), located between 21 and 24‡S in ples used for K^Ar dating by Lindsay et al. the Central Andes (de Silva, 1989a).Here, at least (2001a): Atana single pumice (Lari-96h-6), Toco- 30 000 km3 of late-Miocene to Pleistocene ignim- nao bulk ignimbrite (Quis-96-3), and a Toconao brites and silicic lavas are preserved above a zone single pumice clast (Toc-97h-2) collected at the of extremely low S-wave velocities at mid-crustal same location (Fig.1 ) as the composite pumice depths that probably represents a partially molten sample (Toc-97h-3) dated by Lindsay et al. VOLGEO 2519 1-11-02 A.K. Schmitt et al. / Journal of Volcanology and Geothermal Research 120 (2002) 43^53 45 Fig.1.Map of La Pacana Caldera in the APVC showing the distribution of Atana ignimbrite and the estimated extent of the underlying Toconao ignimbrite (modi¢ed after Lindsay et al., 2001b).Sample locations for K^Ar and U^Pb zircon dating are in- dicated (T = Toc-97h-2; Q = Quis-96-3; L = Lari-96h-6). (2001a).Lithic clasts are abundant in the bulk the outermost zones, rim analyses were performed ignimbrite sample, but were separated by hand- on one unpolished Toconao zircon grain using the picking prior to crushing and sieving.Prior to depth-pro¢ling mode, which improves the spatial ion probe analyses, a total of V50 polished zir- resolution by a factor of V100 (c.f. Grove and cons was examined for internal zonation by cath- Harrison, 1999). Fig.3 and Table 1 show increas- odoluminescence (CL) imaging (Fig.2 ). ing radiogenic 206Pb coupled with decreasing Ion microprobe spot analyses were performed 207Pb/206Pb ratios for four successive analyses on using the UCLA CAMECA ims 1270 ion micro- an unpolished crystal face.This implies that com- probe on all zircons recovered from the two To- mon Pb is largely surface derived and therefore a conao samples (V10 each) and on 11 selected 5-min pre-sputtering was applied during analyses grains from the Atana sample.A 5^10-nA O 3 on polished surfaces. primary beam was focused to a spot size of V30 Wm in diameter (see Fig.2 ) and secondary ions extracted at 10 kV with an energy band pass 4. Results of 35 eV.O 2 pressure in the sample chamber was adjusted to V0.002 Pa to increase Pb sensitivity. A 204Pb-based common Pb correction can in- The reproducibility on the reference zircon AS3 troduce large uncertainties for young unradiogen- (Paces and Miller, 1993) during the three analyt- ic samples and therefore the uncorrected data (an- ical sessions between March and August 2001 var- alytical results shown in Table 1) were regressed ied between 1 and 3%.To determine the age of in the 238U/206Pb vs. 207Pb/206Pb diagram to ob- VOLGEO 2519 1-11-02 46 A.K. Schmitt et al. / Journal of Volcanology and Geothermal Research 120 (2002) 43^53 Fig.2.CL images of zircons from La Pacana.Ion microprobe spots are indicated by dashed line together with 204Pb-corrected ages (1c errors).Arrows indicate truncation of oscillatory zonation.(A) Toconao bulk ignimbrite Quis-96-3 grain 11.(B) Grain 2 from same sample.(C) Toconao pumice Toc-97h-2 grain 7.(D) Atana pumice Lari-96h-6 grain 5.
Load more

Recommended publications
  • Appendix A. Supplementary Material to the Manuscript
    Appendix A. Supplementary material to the manuscript: The role of crustal and eruptive processes versus source variations in controlling the oxidation state of iron in Central Andean magmas 1. Continental crust beneath the CVZ Country Rock The basement beneath the sampled portion of the CVZ belongs to the Paleozoic Arequipa- Antofalla terrain – a high temperature metamorphic terrain with abundant granitoid intrusions that formed in response to Paleozoic subduction (Lucassen et al., 2000; Ramos et al., 1986). In Northern Chile and Northwestern Argentina this Paleozoic metamorphic-magmatic basement is largely homogeneous and felsic in composition, consistent with the thick, weak, and felsic properties of the crust beneath the CVZ (Beck et al., 1996; Fig. A.1). Neodymium model ages of exposed Paleozoic metamorphic-magmatic basement and sediments suggest a uniform Proterozoic protolith, itself derived from intrusions and sedimentary rock (Lucassen et al., 2001). AFC Model Parameters Pervasive assimilation of continental crust in the Central Andean ignimbrite magmas is well established (Hildreth and Moorbath, 1988; Klerkx et al., 1977; Fig. A.1) and has been verified by detailed analysis of radiogenic isotopes (e.g. 87Sr/86Sr and 143Nd/144Nd) on specific systems within the CVZ (Kay et al., 2011; Lindsay et al., 2001; Schmitt et al., 2001; Soler et al., 2007). Isotopic results indicate that the CVZ magmas are the result of mixing between a crustal endmember, mainly gneisses and plutonics that have a characteristic crustal signature of high 87Sr/86Sr and low 145Nd/144Nd, and the asthenospheric mantle (low 87Sr/86Sr and high 145Nd/144Nd; Fig. 2). In Figure 2, we model the amount of crustal assimilation required to produce the CVZ magmas that are targeted in this study.
    [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]
  • Three-Dimensional Resistivity Image of the Magmatic System Beneath
    PUBLICATIONS Geophysical Research Letters RESEARCH LETTER Three-dimensional resistivity image of the magmatic system 10.1002/2015GL064426 beneath Lastarria volcano and evidence for magmatic Key Points: intrusion in the back arc (northern Chile) • Electrical resistivity images of the Lastrarria volcano Daniel Díaz1,2, Wiebke Heise3, and Fernando Zamudio1 • The magmatic source is located to the south of Lastarria volcano 1Departamento de Geofísica, Universidad de Chile, Santiago, Chile, 2Centro de Excelencia en Geotermia de Los Andes, • Deep conductor in the back arc 3 suggests magmatic intrusion Santiago, Chile, GNS Science, Lower Hutt, New Zealand Supporting Information: Abstract Lazufre volcanic center, located in the central Andes, is recently undergoing an episode of uplift, • Readme conforming one of the most extensive deforming volcanic systems worldwide, but its magmatic system and • Text S1 • Figure S1 its connection with the observed uplift are still poorly studied. Here we image the electrical resistivity structure • Figure S2 using the magnetotelluric method in the surroundings of the Lastarria volcano, one of the most important • Figure S3 features in the Lazufre area, to understand the nature of the magmatic plumbing, the associated fumarolic • Figure S4 activity, and the large-scale surface deformation. Results from 3-D modeling show a conductive zone at 6 km Correspondence to: depth south of the Lastarria volcano interpreted as the magmatic heat source which is connected to a shallower D. Díaz, conductor beneath the volcano, showing the pathways of volcanic gasses and heated fluid. A large-scale [email protected] conductive area coinciding with the area of uplift points at a magma intrusion at midcrustal depth.
    [Show full text]
  • Persistent Uplift of the Lazufre Volcanic Complex (Central 10.1002/2014GC005370 Andes): New Insights from PCAIM Inversion of Insar Time
    PUBLICATIONS Geochemistry, Geophysics, Geosystems RESEARCH ARTICLE Persistent uplift of the Lazufre volcanic complex (Central 10.1002/2014GC005370 Andes): New insights from PCAIM inversion of InSAR time Key Points: series and GPS data InSAR and GPS analysis using PCAIM D. Remy1, J. L. Froger2, H. Perfettini3, S. Bonvalot1, G. Gabalda1, F. Albino2,4, V. Cayol2, 5,6 1 Correspondence to: D. Legrand , and M. De Saint Blanquat D. Remy, 1 2 [email protected] GET/UMR 5563 (UPS, CNRS, IRD, CNES), Observatoire Midi-Pyren ees, Universite P. Sabatier, Toulouse, France, LMV/UMR 6524 (UBP-CNRS-IRD), Observatoire de Physique du Globe de Clermont-Ferrand, Universite B. Pascal, Clermont-Ferrand, France, 3ISTERRE/UMR 5275 (UJF, CNRS, IRD), Observatoire des Sciences de l’Univers de Grenoble, Universite Joseph Fou- Citation: 4 Remy, D., J. L. Froger, H. Perfettini, rier, Grenoble, France, Now at Department of Earth Sciences, Cartography & Remote Sensing Unit, Royal Museum for S. Bonvalot, G. Gabalda, F. Albino, Central Africa, Tervuren, Belgium, 5Departamento de Geofısica, Universidad de Chile, Santiago, Chile, 6Now at Instituto de V. Cayol, D. Legrand, and M. Saint Geofisica, Universidad Nacional Autonoma de Mexico, Coyoacan, Mexico Blanquat (2014), Persistent uplift of the Lazufre volcanic complex (Central Andes): New insights from PCAIM inversion of InSAR time series and GPS Abstract We reanalyzed the surface displacements observed at the Lazufre volcanic complex in the data, Geochem. Geophys. Geosyst., 15, Southern Andean Central Volcanic Zone using GPS measurements made between 2006 and 2008 and a doi:10.1002/2014GC005370. large InSAR data set. We performed a detailed spatiotemporal analysis of the displacements using a princi- pal component analysis inversion method (PCAIM).
    [Show full text]
  • The Causes and Effect of Temporal Changes in Magma Generation Processes in Space and Time Along the Central Andes (13°S – 25°S)
    The causes and effect of temporal changes in magma generation processes in space and time along the Central Andes (13°S – 25°S) Dissertation zur Erlangung des mathematisch-naturwissenschaftlichen Doktorgrades "Doctor rerum naturalium" der Georg-August-Universität Göttingen im Promotionsprogramm Geowissenschaften / Geographie der Georg-August University School of Science (GAUSS) vorgelegt von Rosanne Marjoleine Heistek aus Nederland/Niederlande Göttingen 2015 Betreuungsausschuss: Prof. Dr. Gerhard Wörner, Abteilung Geochemie, GZG Prof. Dr. Andreas Pack, Abteilung Isotopengeologie, GZG Referent: Prof. Dr. Gerhard Wörner Prof. Dr. Andreas Pack Weitere Mitglieder der Prüfungskommission: Prof. Dr. Sharon Webb Prof. Dr. Hilmar von Eynatten Prof. Dr. Jonas Kley Dr. John Hora Tag der mündlichen Prüfung: 25.06.2015 TABLE OF CONTENTS Acknowledgements .................................................................................................................................1 Abstracts .................................................................................................................................................2 Chapter 1: Introduction .........................................................................................................................7 1.1.The Andean volcanic belt .............................................................................................................................. 7 1.2. The Central volcanic zone ...........................................................................................................................
    [Show full text]
  • Convergent Margin Magmatism in the Central Andes and Its Near Antipodes in Western Indonesia: Spatiotemporal and Geochemical Considerations
    AN ABSTRACT OF THE DISSERTATION OF Morgan J. Salisbury for the degree of Doctor of Philosophy in Geology presented on June 3, 2011. Title: Convergent Margin Magmatism in the Central Andes and its Near Antipodes in Western Indonesia: Spatiotemporal and Geochemical Considerations Abstract approved: ________________________________________________________________________ Adam J.R. Kent This dissertation combines volcanological research of three convergent continental margins. Chapters 1 and 5 are general introductions and conclusions, respectively. Chapter 2 examines the spatiotemporal development of the Altiplano-Puna volcanic complex in the Lípez region of southwest Bolivia, a locus of a major Neogene ignimbrite flare- up, yet the least studied portion of the Altiplano-Puna volcanic complex of the Central Andes. New mapping and laser-fusion 40Ar/39Ar dating of sanidine and biotite from 56 locations, coupled with paleomagnetic data, refine the timing and volumes of ignimbrite emplacement in Bolivia and northern Chile to reveal that monotonous intermediate volcanism was prodigious and episodic throughout the complex. 40Ar/39Ar age determinations of 13 ignimbrites from northern Chile previously dated by the K-Ar method improve the overall temporal resolution of Altiplano-Puna volcanic complex development. Together with new and updated volume estimates, the new age determinations demonstrate a distinct onset of Altiplano-Puna volcanic complex ignimbrite volcanism with modest output rates beginning ~11 Ma, an episodic middle phase with the highest eruption rates between 8 and 3 Ma, followed by a general decline in volcanic output. The cyclic nature of individual caldera complexes and the spatiotemporal pattern of the volcanic field as a whole are consistent with both incremental construction of plutons as well as a composite Cordilleran batholith.
    [Show full text]
  • Erosion, Transport and Segregation of Pumice and Lithic Clasts in Pyroclastic ¯Ows Inferred from Ignimbrite at Lascar Volcano, Chile
    Journal of Volcanology and Geothermal Research 104 (2000) 201±235 www.elsevier.nl/locate/jvolgeores Erosion, transport and segregation of pumice and lithic clasts in pyroclastic ¯ows inferred from ignimbrite at Lascar Volcano, Chile E.S. Caldera,*, R.S.J. Sparksa, M.C. Gardewegb aDepartment of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK bServicio Nacional de Geologia y Mineria, Avenida Santa Maria 0104, Casilla 10465, Santiago, Chile Received 4 November 1998; revised and accepted 4 May 2000 Abstract Investigations have been made on the distribution of pumice and lithic clasts in the lithic rich Soncor ignimbrite (26.5 ka) and the 1993 pumice ¯ow deposits of Lascar Volcano, Chile. The Soncor ignimbrite shows three main lithofacies which grade into one another. Coarse lithic breccias range from matrix poor strati®ed varieties, irregular shaped sheets and elongate hummocks in proximal environments, to breccia lenses with pumiceous ignimbrite matrix. Massive, lithic rich facies comprise the bulk of the ignimbrite. Pumice rich facies are bimodal with abundant large pumice clasts (often with reverse grading), rare lithic clasts and occur distally and on high ground adjacent to deep proximal valleys. In the 1993 pyroclastic ¯ow deposits lithic rich facies are deposited on slopes up to 148 whereas pumice rich facies are deposited only on slopes ,48. Lithic rich parts show a thin pumice rich corrugated surface which can be traced into the pumice rich facies. The high lithic content in the Soncor ignimbrite is attributed to the destruction of a pre-existing dome complex, deep explosive cratering into the interior of the volcano and erosion during pyroclastic ¯ow emplacement.
    [Show full text]
  • Compositional Characteristics of Middle to Upper Tertiary Volcanic Rocks of the Bolivian Altiplano
    AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the current-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications re­ leased prior to the current year are listed in the most recent annual "Price and Availability List." Publications that may be listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" may no longer be available. Reports released through the NTIS may be obtained by writing to the National Technical Information Service, U.S. Department of Commerce, Springfield, VA 22161; please include NTIS report number with inquiry. Order U.S. Geological Survey publications by mail or over the counter from the offices listed below. BY MAIL OVER THE COUNTER Books Books and Maps Professional Papers, Bulletins, Water-Supply Papers, Tech­ Books and maps of the U.S. Geological Survey are available niques of Water-Resources Investigations, Circulars, publications over the counter at the following U.S. Geological Survey offices, all of general interest (such as leaflets, pamphlets, booklets), single of which are authorized agents of the Superintendent of Docu­ copies of Earthquakes & Volcanoes, Preliminary Determination of ments. Epicenters, and some miscellaneous reports, including some of the foregoing series that have gone out> of print at the Superintendent of Documents, are obtainable by mail from • ANCHORAGE, Alaska-Rm. 101,4230 University Dr.
    [Show full text]
  • PLUTONS: Investigating the Relationship Between Pluton Growth and Volcanism in the Central Andes
    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. Christensen7, N.J. Finnegan8, 9 2 10 11 7 12 2 13 2 6 doi:10.1130/GES01578.1 E. Minaya , R.S.J. Sparks , M. Sunagua , M.J. Unsworth , C. Alvizuri , M.J. Comeau , R. del Potro , D. Díaz , M. Diez , A. Farrell , S.T. Henderson1,14, J.A. Jay15, T. Lopez7, D. Legrand16, J.A. Naranjo17, H. McFarlin6, D. Muir18, J.P. Perkins19, Z. Spica20, A. Wilder21, and K.M. Ward22 1 10 figures; 3 tables Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York 14853, USA 2School of Earth Sciences, University of Bristol, BS8 1RJ, United Kingdom 3College of Earth, Ocean, and Atmospheric Science, Oregon State University, Corvallis, Oregon 97331, USA CORRESPONDENCE: pritchard@ cornell .edu 4Department of Geography, Geology and Planning, Missouri State University, 901 S. National Ave, Springfield, Missouri 65897, USA 5Department of Geosciences, The University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721-0001, USA CITATION: Pritchard, M.E., de Silva, S.L., Michel‑ 6School of Geosciences, University of South Florida, 4202 E. Fowler Avenue, Tampa, Florida 33620, USA felder, G., Zandt, G., McNutt, S.R., Gottsmann, 7Geophysical Institute, University
    [Show full text]
  • Magma Evolution in the Purico Ignimbrite Complex, Northern Chile: Evidence for Zoning of a Dacitic Magma by Injection of Rhyolitic Melts Following Ma®C Recharge
    Contrib Mineral Petrol 12001) 140: 680±700 DOI 10.1007/s004100000214 A. K. Schmitt á S. L. de Silva á R. B. Trumbull R. Emmermann Magma evolution in the Purico ignimbrite complex, northern Chile: evidence for zoning of a dacitic magma by injection of rhyolitic melts following ma®c recharge Received: 4 May 2000 / Accepted: 18 October 2000 / Published online: 16 January 2001 Ó Springer-Verlag 2001 Abstract The 1.3 Ma Purico complex is part of crystal-rich dacitic pumice 164±66 wt% SiO2). Rare an extensive Neogene±Pleistocene ignimbrite province andesitic and banded pumice 160±61 wt% SiO2) are in the central Andes. Like most other silicic complexes also present in the uppermost part of the ¯ow unit. The in the province, Purico is dominated by monotonous dierent compositional groups of pumice in LPI II ¯ow intermediate ash-¯ow sheets and has volumetrically unit 1rhyolite, andesite, dacite) have initial Nd and Sr minor lava domes. The Purico ignimbrites 1total vol- isotopic compositions that are indistinguishable from ume 80±100 km3) are divided into a Lower Purico Ig- each other and from the dominant dacitic pumice nimbrite 1LPI) with two extensive ¯ow units, LPI I and 1Nd=)6.7 to )7.2 and 87Sr/86Sr=0.7085±0.7090). LPI II; and a smaller Upper Purico Ignimbrite 1UPI) However, two lines of evidence show that the andesite, unit. Crystal-rich dacite is the dominant lithology in all dacite and rhyolite pumices do not represent a simple the Purico ignimbrites and in the lava domes. It is es- fractionation series.
    [Show full text]
  • Tectonic and Climate History Influence the Geochemistry of Large-Volume
    Journal of Volcanology and Geothermal Research 262 (2013) 90–103 Contents lists available at ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores Tectonic and climate history influence the geochemistry of large-volume silicic magmas: New δ18O data from the Central Andes with comparison to N America and Kamchatka Chris B. Folkes a,⁎, Shanaka L. de Silva b, Ilya N. Bindeman c, Raymond A.F. Cas a a School of Geosciences, Building 28, Monash University, Victoria 3800, Australia b College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA c Department of Geological Sciences, University of Oregon, Eugene, OR 97403, USA article info abstract Article history: New δ18O data from magmatic quartz, plagioclase and zircon crystals in Neogene large-volume, rhyodacitic Received 27 November 2012 18 18 ignimbrites from the Central Andean Ignimbrite Province reveal uniformly high-δ O values (δ O(Qtz) from Accepted 30 May 2013 18 +8.1 to +9.6‰—43 analyses from 15 ignimbrites; δ O(Plag) from +7.4 to +8.3‰—10 analyses from 6 Available online 18 June 2013 18 ignimbrites; δ O(Zrc) from +6.7 to +7.8‰—5 analyses from 4 ignimbrites). These data, combined with crustal radiogenic isotopic signatures of Sr, Nd and Pb, imply progressive contamination of basaltic magmas Keywords: with up to 50 vol.% upper crust in these large volume silicic systems. The narrow range of δ18O values also Central Andes Crustal assimilation demonstrate that surprising homogeneity was achieved through space (100's km) and time (~10 Ma to Hydrothermal alteration recent) in these large-volume magmas, via residence in their parental middle to upper crustal bodies.
    [Show full text]
  • MMA Memo 251
    MMA Memo 251 MMA Site East of San Pedro De Atacama North Chile Volcanic Hazards Assessment and Geologic Setting Moyra C. Gardeweg P. Consultant Geologist August 1996 Fig. 1 - Location of map of the MMA site. Access roads, villages, and well known volcanic centers are shown. The stippled zone shows the area comprised by the simplified geologic map of Fig. 2. Fig 2. - Simplified geological map of the site area over a 1:500.000 scale satellite image. Based on Marinovic and Lahsen (1984) and Ramfrez and Gardeweg (1982). Fig. 3. - Satellite image of the MMA site (white arrow). Shown are the Chascón dome (ch), Chajnantor dome (cj) and Purico complex (p). The Cajón ignimbrite (ci) extends radially from the Purico complex and is covered by the lavas of the volcanoes Licancabur (l), Guayaques (g), and Santa Bárbara (sb). The north end of the La Pacana caldera resurgent dome (prd), source of the Atana Ignimbrite, is also observed as are the salty lakes of Laguna Verde (lv) in Bolivia. Fig. 4. - Chascón dome and the Agua Amarga creek, immediately east of the MMA site. View northward; in rear the Chajnantor dome, Juriques and Licancabur volcanoes and a NS linear group of volcanoes in the border with Bolivia. 9 Fig 5. - Distribution of volcanic vents (active, potentially active and extint) and calderas in the study and surrounding areas. Contours to depth of the scenter of the Wadati-Benioff zone and the Peéu-Chile trench are shown Currently Putana is in a solfataric stage, with extensive fumarolic activity observed from the end of the 19th century that persists to the present day.
    [Show full text]