KECK GEOLOGY CONSORTIUM PROCEEDINGS OF THE TWENTY-FIFTH ANNUAL KECK RESEARCH SYMPOSIUM IN GEOLOGY

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1 KECK GEOLOGY CONSORTIUM PROCEEDINGS OF THE TWENTY-FIFTH ANNUAL KECK RESEARCH SYMPOSIUM IN GEOLOGY April 2012 Amherst College, Amherst, MA Dr. Robert J. Varga, Editor Director, Keck Geology Consortium Pomona College Dr. Tekla Harms Symposium Convenor Amherst College Carol Morgan Keck Geology Consortium Administrative Assistant Diane Kadyk Symposium Proceedings Layout & Design Department of Earth & Environment Franklin & Marshall College Keck Geology Consortium Geology Department, Pomona College 185 E. 6 th St., Claremont, CA (909) , keckgeology@pomona.edu, keckgeology.org ISSN# The Consortium Colleges The National Science Foundation ExxonMobil Corporation

2 KECK GEOLOGY CONSORTIUM PROCEEDINGS OF THE TWENTY-FIFTH ANNUAL KECK RESEARCH SYMPOSIUM IN GEOLOGY ISSN# April 2012 Robert J. Varga Editor and Keck Director Pomona College Keck Geology Consortium Pomona College 185 E 6 th St., Claremont, CA Diane Kadyk Proceedings Layout & Design Franklin & Marshall College Keck Geology Consortium Member Institutions: Amherst College, Beloit College, Carleton College, Colgate University, The College of Wooster, The Colorado College, Franklin & Marshall College, Macalester College, Mt Holyoke College, Oberlin College, Pomona College, Smith College, Trinity University, Union College, Washington & Lee University, Wesleyan University, Whitman College, Williams College PROJECTS TECTONIC EVOLUTION OF THE CHUGACH-PRINCE WILLIAM TERRANE, SOUTH-CENTRAL ALASKA Faculty: JOHN GARVER, Union College, Cameron Davidson, Carleton College Students: EMILY JOHNSON, Whitman College, BENJAMIN CARLSON, Union College, LUCY MINER, Macalester College, STEVEN ESPINOSA, University of Texas-El Paso, HANNAH HILBERT-WOLF, Carleton College, SARAH OLIVAS, University of Texas-El Paso. ORIGINS OF SINUOUS AND BRAIDED CHANNELS ON ASCRAEUS MONS, MARS Faculty: ANDREW DE WET, Franklin & Marshall College, JAKE BLEACHER, NASA-GSFC, BRENT GARRY, Smithsonian Students: JULIA SIGNORELLA, Franklin & Marshall College, ANDREW COLLINS, The College of Wooster, ZACHARY SCHIERL, Whitman College. TROPICAL HOLOCENE CLIMATIC INSIGHTS FROM RECORDS OF VARIABILITY IN ANDEAN PALEOGLACIERS Faculty: DONALD RODBELL, Union College, NATHAN STANSELL, Byrd Polar Research Center Students: CHRISTOPHER SEDLAK, Ohio State University, SASHA ROTHENBERG, Union College, EMMA CORONADO, St. Lawrence University, JESSICA TREANTON, Colorado College. EOCENE TECTONIC EVOLUTION OF THE TETON-ABSAROKA RANGES, WYOMING Faculty: JOHN CRADDOCK. Macalester College, DAVE MALONE. Illinois State University Students: ANDREW KELLY, Amherst College, KATHRYN SCHROEDER, Illinois State University, MAREN MATHISEN, Augustana College, ALISON MACNAMEE, Colgate University, STUART KENDERES, Western Kentucky University, BEN KRASUSHAAR INTERDISCIPLINARY STUDIES IN THE CRITICAL ZONE, BOULDER CREEK CATCHMENT, FRONT RANGE, COLORADO Faculty: DAVID DETHIER, Williams College Students: JAMES WINKLER, University of Connecticut, SARAH BEGANSKAS, Amherst College, ALEXANDRA HORNE, Mt. Holyoke College

3 DEPTH-RELATED PATTERNS OF BIOEROSION: ST. JOHN, U.S. VIRGIN ISLANDS Faculty: DENNY HUBBARD and KARLA PARSONS-HUBBARD, Oberlin College Students: ELIZABETH WHITCHER, Oberlin College, JOHNATHAN ROGERS, University of Wisconsin-Oshkosh, WILLIAM BENSON, Washington & Lee University, CONOR NEAL, Franklin & Marshall College, CORNELIA CLARK, Pomona College, CLAIRE McELROY, Otterbein College. THE HRAFNFJORDUR CENTRAL VOLCANO, NORTHWESTERN ICELAND Faculty: BRENNAN JORDAN, University of South Dakota, MEAGEN POLLOCK, The College of Wooster Students: KATHRYN KUMAMOTO, Williams College, EMILY CARBONE, Smith College, ERICA WINELAND- THOMSON, Colorado College, THAD STODDARD, University of South Dakota, NINA WHITNEY, Carleton College, KATHARINE, SCHLEICH, The College of Wooster. SEDIMENT DYNAMICS OF THE LOWER CONNECTICUT RIVER Faculty: SUZANNE O CONNELL and PETER PATTON, Wesleyan University Students: MICHAEL CUTTLER, Boston College, ELIZABETH GEORGE, Washington & Lee University, JONATHON SCHNEYER, University of Massaschusetts-Amherst, TIRZAH ABBOTT, Beloit College, DANIELLE MARTIN, Wesleyan University, HANNAH BLATCHFORD, Beloit College. ANATOMY OF A MID-CRUSTAL SUTURE: PETROLOGY OF THE CENTRAL METASEDIMENTARY BELT BOUNDARY THRUST ZONE, GRENVILLE PROVINCE, ONTARIO Faculty: WILLIAM PECK, Colgate University, STEVE DUNN, Mount Holyoke College, MICHELLE MARKLEY, Mount Holyoke College Students: KENJO AGUSTSSON, California Polytechnic State University, BO MONTANYE, Colgate University, NAOMI BARSHI, Smith College, CALLIE SENDEK, Pomona College, CALVIN MAKO, University of Maine, Orono, ABIGAIL MONREAL, University of Texas-El Paso, EDWARD MARSHALL, Earlham College, NEVA FOWLER-GERACE, Oberlin College, JACQUELYNE NESBIT, Princeton University. Funding Provided by: Keck Geology Consortium Member Institutions The National Science Foundation Grant NSF-REU ExxonMobil Corporation

4 Keck Geology Consortium: Projects Short Contributions Northwestern Iceland Project CRUSTAL MAGMATIC PROCESSES IN ICELAND S OLDEST CENTRAL VOLCANO Project Faculty: BRENNAN JORDAN, University of South Dakota, MEAGEN POLLOCK, The College of Wooster, JEANNE FROMM, University of South Dakota THE HRAFNFJORDUR CENTRAL VOLCANO: PETROGENESIS OF LAVAS IN THE EARLY STAGES OF AN ICELANDIC RIFT ZONE EMILY CARBONE, Smith College Research Advisor: Mark Brandriss MAGMATIC PROCESSES OF THE HRAFNFJÖRÐUR CENTRAL VOLCANO, NORTHWEST ICELAND KATHRYN KUMAMOTO, Williams College Research Advisor: Reinhard Wobus A GEOCHEMICHAL AND PETROLOGIC ANALYSIS OF THE HRAFNFJORDUR CENTRAL VOLCANO, WESTFJORDS, ICELAND KATHARINE SCHLEICH, The College of Wooster Research Advisor: Meagen Pollock ORIGIN OF SILICIC VOLCANISM AT SAURATINDUR, NORTHWEST ICELAND THAD STODDARD, University of South Dakota Research Advisor: Brennan Jordan GEOCHEMICAL ANALYSIS OF TERTIARY DIKES HRAFNFJORDUR CENTRAL VOLCANO, NORTHWEST ICELAND: IMPLICATIONS FOR DIKE ORIGIN NINA WHITNEY, Carleton College Research Advisor: Cameron Davidson PETROLOGIC AND GEOCHEMICAL CHARACTERIZATION OF BASALTIC AND INTERMEDIATE MAGMAS IN AN ABANDONED TERTIARY RIFT, NORTHWEST ICELAND ERICA WINELAND-THOMSON, Colorado College Research Advisor: Jeff Noblett Keck Geology Consortium Pomona College 185 E. 6 th St., Claremont, CA Keckgeology.org

5 25th Annual Keck Symposium: 2012 Amherst College, Amherst, MA CRUSTAL MAGMATIC PROCESSES AT HRAFNFJÖRĐUR: ICELAND S OLDEST CENTRAL VOLCANO BRENNAN JORDAN, University of South Dakota MEAGEN POLLOCK, The College of Wooster JEANNE FROMM, University of South Dakota INTRODUCTION Iceland is a 103,000 km 2 island in the middle of the North Atlantic Ocean. It lies on the Mid-Atlantic Ridge, which rises above sea level at Iceland because of excess magmatism due to the intersection of the ridge with the Iceland hotspot. The hotspot is generally interpreted as a mantle plume (e.g., Hardarson et al, 1997), but alternative explanations have been proposed (e.g., Foulger and Anderson, 2005). The Mid-Atlantic Ridge drifts west in the hotspot reference frame, and when an active rift has drifted far enough off of the hotspot it is abandoned in favor of a new rift which develops over the hotspot. These rift relocation events have occurred at least twice in the geologic history of Iceland (e.g., Hardarson et al., 1997), and a third event appears to be ongoing with propagation of the eastern rift zone at the expense of the western rift zone. The last abandoned rift system in Iceland is the Skagi-Snaefellsnes rift zone which was active between 15 and 7 Ma (Fig. 1). Figure 1. Map of Iceland showing the 2003, 2004, 2007, and 2011 Keck project areas, the position of the hypothesized mantle plume, neovolcanic zones, and the last two abandoned rifts. Volcanism in Iceland is bimodal, predominantly basaltic, with subordinate silicic volcanic rocks, and minor andesites. One of the fundamental petrologic debates about Iceland regards the origin of silicic magmas in this oceanic setting. The two end-member models are: (1) silicic magmas are the product of high degrees of fractional crystallization from a basaltic magma (e.g., Furman et al., 1992); and (2) silcic magmas are produced by partial melting of the mafic crust (e.g., Gunnarson et al., 1998; Jonasson, 2007). Martin and Sigmarsson (2007) argue that crustal melting is responsible for silicic magmas in the main rift zones, while they are the products of fractional crystallization in the off-rift flank zones. Previous Iceland Keck projects in 2003, 2004, and 2007 focused on rocks erupted in the Skagi-Snaefellsnes rift zone at different times in the history of the rift (Figs. 1 and 2). The 2003 project and half of the 2004 project focused on the southern Skagi Peninsula, where central volcanoes were erupted right up to the abandonment of the rift at about 7 Ma. The second half of the 2004 project focused on the western edge of the Hrafnfjörður (anglicized Hrafnfjordur) central volcano in the Westfjords which erupted at about 14 Ma, when the rift was young, and presumably near the hotspot. The 2007 Keck project studied the Árnes central volcano, representing an intermediate stage of the evolution of the rift. The goal of these projects has been to consider the crustal magmatic processes of different central volcanoes through the history of rift, from its inception to its abandonment. The projects have focused on intermediate and siliic volcanic rocks, considering the relative importance of fractional crystallization, crustal melting, and magma mixing in the origin of these rocks. The projects have always also studied associated basaltic rocks, and some student projects 226

6 25th Annual Keck Symposium: 2012 Amherst College, Amherst, MA Figure 2. Geologic map of the northern Westfjords region and Skagi Peninsula showing 2003, 2004, 2007, 2011 Keck project areas (after Jóhannesson and Saemundsson, 1998). Emily Carbone, Smith College, conducted a study on the south side of Hrafnfjörður, in an area on both sides of Baejardalur. This field area featured one unit not present in the other areas, a dacite lava with a very high Zr concentration, 1012 ppm. This lava may well have erupted from a vent in the field area, represented by the domal mass on the west side of Baejardalur. The lava is an end-member of a trend through a series of dacites exposed in other student field areas that likely reflects fractional crystallization of a zirconbearing assemblage. Emily also conducted SEM- 227 have even focused on the origin and evolution of basaltic magmas. The 2004 Iceland Keck project involved work only on the margin of the Hrafnfjörður central volcano, but tantalizingly the study area included andesites and dacites, but no rhyolites. So in 2011 we set out to study the core of the Hrafnfjörður central volcano, the oldest central volcano exposed on land in Iceland. STUDENT PROJECTS Upon arrival in Iceland we took a three-day field trip through the neovolcanic zones to observe modern analogues of the Tertiary volcanic rocks we would study in the Westfjords. We then flew to Isafjörður, and were taken by boat to the head of Hrafnfjörður where we set up a primitive base camp (Fig. 3). We conducted twelve days of fieldwork in the remote study area, beginning with a brief reconnaissance. Fieldwork consisted of characterizing volcanic lithologies and field relations, geologic mapping, and collecting samples for laboratory analysis. Students worked their own field areas (Fig. 4), but also assisted in each other s. After returning to Isafjörður, but before traveling back to Reykjavik, we conducted a one-day reconnaissance, in three teams, of the silicic unit at the top of the mountain Sauratindur, east of Isafjörður. In contrast to previous Iceland Keck projects, this project included lab time to prepare samples within the four-week project framework. The final week of the project was spent at The College of Wooster doing sample preparation work. There, students cut thin section billets, and prepared fused beads and pressed pellets for X-ray fluorescence (XRF) analysis. The XRF analyses were then conducted by Pollock using the Rigaku ZSX Primus II at The College of Wooster. Brief descriptions of the student projects are presented below, highlighting unique contributions of each.

7 25th Annual Keck Symposium: 2012 Amherst College, Amherst, MA Figure 3. Two views of camp: (A) looking west down Hrafnfjörður, the cliff forming units on both shores are dacite lavas; and (B) from camp looking east to the basalt cliffs of Bláfell above less well exposed intermediate and silicic units in Katharine Schleich s study area. EDS studies of several samples, acquiring mineral composition data which contributed to her interpretations of the origin of rocks in her field area. Kathryn Kumamoto, Williams College, studied the sequence exposed above base camp and extending for 2 km west along the south shore of Hrafnfjörður. Her study area included the cliff Sólheimafjall which is a thick dacite lava flow that extends into field areas to the north and east. Katie recognized in her area a sequence of compositionally distinct basaltic andesites produced by magma mixing. She also ascribed another distinctive unit, with an unusually well developed ophitic texture, to magma mixing (unit occurs in Carbone s field area as well). Katharine Schleich, The College of Wooster, worked in a large field area at the head of the Hrafnfjörður. She shared the fieldwork in the area with Thad Stoddard. With steep paleotopographic relationships in her area, likely near the center of the volcanic system, working out stratigraphic relationships was difficult. This study area featured the broadest spectrum of volcanic compositions, including the most evolved rocks (on the dacite/rhyolite boundary) which likely erupted from the area around the peak Hvítserkur, which is composed of this unit. The diverse dacites in this study area are critical in expressing a trend of decreasing Zr with increasing SiO 2, likely indicative of zircon fractionation, though Katharine also considered mixing of two silicic magmas as a possibility to generate this trend. Erica Wineland-Thomson, Colorado College, had the only field area on the north shore of the fjord, and thus started each day with a crossing of the river Skorará and a 3 km hike to get to the near edge of her field area. Her study area encompassed a wide spectrum of compositions, including the most primitive basalts analyzed in this year s project, or any other Iceland Keck project to date, with 13.1 wt.% MgO. Erica considered also trace element patterns, recognizing an E-MORB character in the basaltic compositions. Nina Whitney, Carleton College, broke the mold of projects defined by a specific field area, studying dikes in the three study areas at the head of Hrafnfjörður. All of the dikes were basaltic in composition. The character of dike occurrence varied greatly from wide individual dikes, to complexes of several major dikes, to packages of many (up to 52) small dikes. She considered the compositional variation within individual dikes, along the length of a dike, and between dikes in dike complexes. Nina assessed the question of whether dikes originated in the central volcano system or propagated intro the central volcano from adjacent fissure systems. Thad Stoddard, University of South Dakota, hav- 228

8 25th Annual Keck Symposium: 2012 Amherst College, Amherst, MA be the product of crustal melting rather than fractional crystallization or magma mixing. PROJECT RESULTS Mapping Figure 4. Map of Hrafnfjörður study area, showing the student study areas by last name. ing served primarily as a field assistant in the Hrafnfjörður field areas, took the lead on the mountain Sauratindur, east of Isafjörður. The area was sampled by two teams working the basaltic stratigraphy below the silicic unit at Sauratindur, and one team, led by Thad, which characterized and sampled the silicic unit at the top of the mountain. The silicic unit of Sauratindur was found to be a single dacite lava flow. Its composition is distinct from other Westfjords silicic rocks sampled at Hrafnfjörður, or in the 2004 and 2007 Keck projects. Thad interpreted the dacites to As a group we mapped approximately 30 km2 of the Hrafnfjörður central volcano, including the apparent core of the system. Recognizing lithologies in the field was challenging, as had been the experience of previous Keck projects; rocks could be readily identified as basaltic or intermediate to silicic, but knowing exact compositional categories required chemical analysis. XRF analyses revealed a spectrum of lava compositions from primitive basalt to dacite, with one sample on the dacite/rhyolite border (Fig. 5). Most distinct andesite and dacite lavas were traced across multiple field areas, and some may correlate with units found to the west in the 2004 Leirufjörður study area. Dikes were near vertical, and strongly aligned on a north-south trend. This pattern aligns with the likely geometry of the Skagi-Snaefellsnes rift at this latitude. Only a few dikes were found to have significantly different geometries, likely owing to local perturbation of the stress field in association with a volcanic edifice or magma chamber. No major faults were observed, though some remain plausible in areas where they might be difficult to detect because of Hrafnfjörður Na2O + K2O (Wt.%) 8 Wineland-Thomson Schleich 6 Rhyolite Grunnavik & Leirufjörður Andesite Basalt Other Westffjords Basaltic Andesite 55 Carbone Whitney - Dikes Dacite 2 Kumamoto Stoddard - Sauratindur 2007 Kaldalon 60 SiO2 (Wt.%) Figure 5. Classification of rocks analyzed in this study and previous Keck projects in this portion of the Westfjords using the total alkalis vs. silica scheme of LeBas et al. (1986). Colors of Hrafnfjörður field area symbols link to Figure

9 25th Annual Keck Symposium: 2012 Amherst College, Amherst, MA Zr (ppm) SiO2 (Wt.%) Figure 6. Zr vs. SiO 2 plot of rocks analyzed in this study and previous Keck projects in this portion of the Westfjords. Symbols are as defined in Figure 5. Note different trends that emerge on this plot, particularly in the intermediate- and high-silicic dacites at Hrafnfjörður, which appears to be a suite connected by zircon fractionation (decreasing Zr with increasing SiO 2 ). complicated paleotopographic relationships. Petrology Students examined thin sections of 126 samples, and 110 of these were successfully analyzed by XRF for major and trace elements. Entering a new area, with no published previous research, we are always uncertain as to home much compositional diversity we will find, so it was pleasing to see find the diversity of volcanic rocks that we found, including basalts, basaltic andesites, andesites, and dacites (Fig. 5). The bulk of the basalts and basaltic andesites can be related by fractional crystallization, but several basaltic units lie off of the main fractionation trends and reflect magma mixing. At Hrafnfjörður several distinct intermediate units, andesite and low-silica dacite, lie on different geochemical trends, suggesting a range of processes, either fractional crystallization under different conditions (perhaps reflecting varying depth of magma chambers) or some involvement of magma mixing in one or more trends. A suite of interrelated intermediate- to high-silica dacites appears to be the result of zircon-involved fractional crystallization from the highest Zr, lowest SiO 2, end-member of the suite (Fig. 6). The dacite postulated to have been parental to the suite was likely the product of crustal melting (based 230 on a higher Zr/Nb ratio than basalts in the study area). The Sauratindur dacite is compositionally distinct from Hrafnfjörður dacites. Variability within the unit suggests that it did not reach the zircon saturation. This unit also appears to be the product of crustal melting (again based on Zr/Nb). The four Keck projects conducted in the northwest of Iceland have produced 397 analyses of volcanic and shallow intrusive rocks at three major central volcanic systems as well as several smaller, sometimes monogenetic, systems. Diverse magmatic processes have been documented in these systems. Of the systems studied, only at Árnes (2007) were silicic rocks pretty clearly dominated by the products of high degrees of fractional crystallization from a basaltic parent. Applying the model of Martin and Sigmarsson (2007) this suggests that Árnes may have formed in an offrift setting. Hrafnfjörður is distinct from the others in that it lacks rhyolites, while the others all had diverse rhyolites, including high-silica rhyolites. This raises the question, does the dominance of andesites and dacites and Hrafnfjörður relate to its being erupted early in the history of the Skagi-Snaefellsnes rift? Hrafnfjörður is the oldest central volcano in Iceland, so was there something fundamentally different about crustal magmatic processes in Iceland early in its his-

10 25th Annual Keck Symposium: 2012 Amherst College, Amherst, MA tory? Research on this subject will continue, leveraging the work of four generations of Keck students, by further plumbing of the data set, and hopefully with additional study of the remainder of Hrafnfjörður central volcano, and perhaps application of additional techniques to the study of these rocks. ACKNOWLEDGMENTS We thank the Keck Geology Consortium for supporting a fourth project in this cycle of Iceland Keck projects which has now served 28 students. We thank Umhverfisstofnun (the Environment Agency of Iceland), responsible for the management of the Hornstrandir Nature Reserve for permission to conduct this study in the reserve, with special thanks to Jón Björnsson for his discussion of access issues in the reserve. We are particularly grateful to the volunteer crew who boated in to upgrade the outhouse during our time in Hrafnfjörður. And lastly, Jordan thanks Russell Robertson, Jack, and Tyson for hosting him during the week of work in Wooster. REFERENCES Foulger, G.R., and Anderson, D.L., 2005, A cool model for the Iceland hot spot: Journal of Volcanology and Geothermal Research, v. 141, p Furman, T., Frey, F.A., Meyer, P.S., 1992, Petrogenesis of evolved basalts and rhyolites at Austurhorn, southeastern Iceland: The role of fractional crystallization: Journal of Petrology, v. 33, p Gunnarsson, B., Marsh, B.D., Taylor, H.P., 1998, Generation of Icelandic rhyolites: Silicic lavas from Törfajökull central volcano: Journal of Volcanology and Geothermal Research, v. 83, p Hardarson, B. S., Fitton, J.G., Ellam, R.M., and Pringle, M.S., 1997, Rift relocation a geochemical and geochronological investigation of a paleorift in northwest Iceland: Earth and Planetary Science Letters, v. 153, p Jóhannesson, H., and Saemundsson, K., 1998, Geological map of Iceland: Iceland Institute of Natural History, scale 1:500,000. Jónasson, K., Silicic volcanism in Iceland: composition and distribution within the active volcanic zones: Journal of Geodynamics, v. 43, p LeBas, M.J., LeMaitre, R.W., Streckeisen, A., and Zanettin, B., A chemical classification of volcanic rocks based on the total alkali silica diagram: Journal of Petrology, v. 27, p Martin, E., and Sigmarsson, O., 2007, Crustal thermal state and origin of silicic magma in Iceland: the case of Torfajokull, Ljosufjoll and Snaefellsjokull volcanoes: Contributions to Mineralogy and Petrology, v. 153, p