MAGMA-WALLROCK INTERACTIONS in the SEQUOIA REGION Faculty: JADE STAR LACKEY, Pomona College, STACI L

KECK GEOLOGY CONSORTIUM

PROCEEDINGS OF THE TWENTY-FOURTH ANNUAL KECK RESEARCH SYMPOSIUM IN GEOLOGY

April 2011 Union College, Schenectady, NY

Dr. Robert J. Varga, Editor Director, Keck Geology Consortium Pomona College

Dr. Holli Frey Symposium Convenor Union 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. 6th St., Claremont, CA 91711 (909) 607-0651, [email protected], keckgeology.org

ISSN# 1528-7491

The Consortium Colleges The National Science Foundation ExxonMobil Corporation

KECK GEOLOGY CONSORTIUM PROCEEDINGS OF THE TWENTY-FOURTH ANNUAL KECK RESEARCH SYMPOSIUM IN GEOLOGY ISSN# 1528-7491

April 2011

Robert J. Varga Keck Geology Consortium Diane Kadyk Editor and Keck Director Pomona College Proceedings Layout & Design Pomona College 185 E 6th St., Claremont, CA Franklin & Marshall College 91711

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

2010-2011 PROJECTS

FORMATION OF BASEMENT-INVOLVED FORELAND ARCHES: INTEGRATED STRUCTURAL AND SEISMOLOGICAL RESEARCH IN THE BIGHORN MOUNTAINS, WYOMING Faculty: CHRISTINE SIDDOWAY, MEGAN ANDERSON, Colorado College, ERIC ERSLEV, University of Wyoming Students: MOLLY CHAMBERLIN, Texas A&M University, ELIZABETH DALLEY, Oberlin College, JOHN SPENCE HORNBUCKLE III, Washington and Lee University, BRYAN MCATEE, Lafayette College, DAVID OAKLEY, Williams College, DREW C. THAYER, Colorado College, CHAD TREXLER, Whitman College, TRIANA N. UFRET, University of Puerto Rico, BRENNAN YOUNG, Utah State University.

EXPLORING THE PROTEROZOIC BIG SKY OROGENY IN SOUTHWEST MONTANA Faculty: TEKLA A. HARMS, JOHN T. CHENEY, Amherst College, JOHN BRADY, Smith College Students: JESSE DAVENPORT, College of Wooster, KRISTINA DOYLE, Amherst College, B. PARKER HAYNES, University of North Carolina - Chapel Hill, DANIELLE LERNER, Mount Holyoke College, CALEB O. LUCY, Williams College, ALIANORA WALKER, Smith College.

INTERDISCIPLINARY STUDIES IN THE CRITICAL ZONE, BOULDER CREEK CATCHMENT, FRONT RANGE, COLORADO Faculty: DAVID P. DETHIER, Williams College, WILL OUIMET. University of Connecticut Students: ERIN CAMP, Amherst College, EVAN N. DETHIER, Williams College, HAYLEY CORSON-RIKERT, Wesleyan University, KEITH M. KANTACK, Williams College, ELLEN M. MALEY, Smith College, JAMES A. MCCARTHY, Williams College, COREY SHIRCLIFF, Beloit College, KATHLEEN WARRELL, Georgia Tech University, CIANNA E. WYSHNYSZKY, Amherst College.

SEDIMENT DYNAMICS & ENVIRONMENTS IN THE LOWER CONNECTICUT RIVER Faculty: SUZANNE O’CONNELL, Wesleyan University Students: LYNN M. GEIGER, Wellesley College, KARA JACOBACCI, University of Massachusetts (Amherst), GABRIEL ROMERO, Pomona College.

GEOMORPHIC AND PALEOENVIRONMENTAL CHANGE IN GLACIER NATIONAL PARK, MONTANA, U.S.A. Faculty: KELLY MACGREGOR, Macalester College, CATHERINE RIIHIMAKI, Drew University, AMY MYRBO, LacCore Lab, University of Minnesota, KRISTINA BRADY, LacCore Lab, University of Minnesota Students: HANNAH BOURNE, Wesleyan University, JONATHAN GRIFFITH, Union College, JACQUELINE KUTVIRT, Macalester College, EMMA LOCATELLI, Macalester College, SARAH MATTESON, Bryn Mawr College, PERRY ODDO, Franklin and Marshall College, CLARK BRUNSON SIMCOE, Washington and Lee University.

GEOLOGIC, GEOMORPHIC, AND ENVIRONMENTAL CHANGE AT THE NORTHERN TERMINATION OF THE LAKE HÖVSGÖL RIFT, MONGOLIA Faculty: KARL W. WEGMANN, North Carolina State University, TSALMAN AMGAA, Mongolian University of Science and Technology, KURT L. FRANKEL, Georgia Institute of Technology, ANDREW P. deWET, Franklin & Marshall College, AMGALAN BAYASAGALN, Mongolian University of Science and Technology. Students: BRIANA BERKOWITZ, Beloit College, DAENA CHARLES, Union College, MELLISSA CROSS, Colgate University, JOHN MICHAELS, North Carolina State University, ERDENEBAYAR TSAGAANNARAN, Mongolian University of Science and Technology, BATTOGTOH DAMDINSUREN, Mongolian University of Science and Technology, DANIEL ROTHBERG, Colorado College, ESUGEI GANBOLD, ARANZAL ERDENE, Mongolian University of Science and Technology, AFSHAN SHAIKH, Georgia Institute of Technology, KRISTIN TADDEI, Franklin and Marshall College, GABRIELLE VANCE, Whitman College, ANDREW ZUZA, Cornell University.

LATE PLEISTOCENE EDIFICE FAILURE AND SECTOR COLLAPSE OF VOLCÁN BARÚ, PANAMA Faculty: THOMAS GARDNER, Trinity University, KRISTIN MORELL, Penn State University Students: SHANNON BRADY, Union College. LOGAN SCHUMACHER, Pomona College, HANNAH ZELLNER, Trinity University.

KECK SIERRA: MAGMA-WALLROCK INTERACTIONS IN THE SEQUOIA REGION Faculty: JADE STAR LACKEY, Pomona College, STACI L. LOEWY, California State University-Bakersfield Students: MARY BADAME, Oberlin College, MEGAN D’ERRICO, Trinity University, STANLEY HENSLEY, California State University, Bakersfield, JULIA HOLLAND, Trinity University, JESSLYN STARNES, Denison University, JULIANNE M. WALLAN, Colgate University.

EOCENE TECTONIC EVOLUTION OF THE TETONS-ABSAROKA RANGES, WYOMING Faculty: JOHN CRADDOCK, Macalester College, DAVE MALONE, Illinois State University Students: JESSE GEARY, Macalester College, KATHERINE KRAVITZ, Smith College, RAY MCGAUGHEY, Carleton College.

Funding Provided by: Keck Geology Consortium Member Institutions The National Science Foundation Grant NSF-REU 1005122 ExxonMobil Corporation

Keck Geology Consortium: Projects 2010-2011 Short Contributions— Sierra Nevada Mountains

KECK SIERRA: MAGMA-WALLROCK INTERACTIONS IN THE SEQUOIA REGION Project Faculty: JADE STAR LACKEY, Pomona College, STACI L. LOEWY, California State University—Bakersfield

ORIGIN OF MIGMATITIC ROCKS IN THE SEQUOIA PENDANT, SIERRA NEVADA, CALIFORNIA MARY BADAME, Oberlin College Research Advisor: Steve Wojtal

PLUTON-WALLROCK INTERACTION OF THE EMPIRE QUARTZ DIORITE, SOUTHERN SIERRA NEVADA: IMPLICATIONS FOR SKARN FORMATION IN THE MINERAL KING PENDANT MEGAN D’ERRICO, Trinity University Research Advisor: Dr. Benjamin Surpless

TEMPORAL VARIATION IN PLUTON-WALLROCK INTERACTION IN THE SIERRAN ARC STANLEY HENSLEY, California State University, Bakersfield Research Advisor: Dr. Staci Loewy

THE PETROGENESIS OF THE ASH MOUNTAIN INTRUSIVE COMPLEX: IMPLICATIONS FOR SIERRAN MAGMATISM JULIA HOLLAND, Trinity University Research Advisor: Ben Surpless

EARLY SIERRA NEVADA MAGMATISM EXAMINED USING SHRIMP-RG U-PB AGES AND TRACE ELEMENT COMPOSITIONS OF ZIRCONS FROM THE MINERAL KING ROOF PENDANT RHYOLITE UNITS JESSLYN STARNES, Denison University Research Advisor: Dr. Erik Klemetti

STABLE ISOTOPE GEOCHEMISTRY OF MARBLES IN THE KINGS SEQUENCE, SIERRA NEVADA, CA JULIANNE M. WALLAN, Colgate University Research Advisor: William H. Peck

Keck Geology Consortium Pomona College 185 E. 6th St., Claremont, CA 91711 Keckgeology.org

24th Annual Keck Symposium: 2011 Union College, Schenectady, NY KECK SIERRA: MAGMA-WALLROCK INTERACTIONS IN THE SEQUOIA REGION

JADE STAR LACKEY, Pomona College STACI L. LOEWY, California State University - Bakersfield

INTRODUCTION

The Sierra Nevada has been the center for geologic discovery and fomented geologic thinking for well over 100 years. Pioneering explorations and studies by the likes of Clarence King, Joseph LeConte, and John Muir shaped how geologists understood granitoid rocks, glaciers, weathering, and the interplay of Biology and Geology. The discoveries that followed, especially after the discovery of plate tectonics, re-stoke discussions of how magmas form and crystallize to form plutons, how much crust is recycled at subduction zones, and the role of magmatism in Figure 1. Bedrock geology of the Sequoia region of the Si- climate change. This Keck project, the first in the Si- erra Nevada batholith. The project focused several plutons erra, embraced many of the discoveries of the past— ranging from gabbro to high-silica granite in composi- standing on the shoulders of giants—in its concep- tion, and their associated mafic intrusions, and migmatite tion, while striving to use the Sierra to push the limits complexes in the King Sequence. Initial 87Sr/86Sr = 0.706 of our knowledge. boundary is thought to represent the former boundary between accreted oceanic arc terrains and North America The Sequoia region (Fig. 1) was a natural choice for a crust. Note locations of the CSUB, Pomona, and Stanford Campuses relative to the field area. Abbreviations: EM = project because of the geologic diversity, exceptional Empire Mountain; FP = Fry’s Point Pluton; GF = Giant variety of igneous and metamorphic rocks in vari- Forest Pluton; GG = Grant Grove Pluton; MK = Mineral ous associations telling the story of the interplay of King; SP = Sequoia Pendant. magmas and the rocks they intrude. This area affords a cross section through rocks of many different ages, and the actions of tectonic uplift, water, and ice have conspired to expose many different structural levels a Cordilleran-type convergent margin batholith. in the batholith. Our fieldwork in the region was Subduction of the Farallon plate beneath western conducted in a wide range of environments. Some North America in the Cretaceous produced at least field sites in the Foothills, at just over 1100 feet saw 1,000,000 km3 of granitic magmas in the Sierran daytime temperatures routinely exceeded 100°F (Fig. arc. Most magmatism occurred between 120 and 2A). Chaparral and oak savannah landscapes graded 85 million years ago and involved melting, mixing, into Sequoia groves in our mid-altitude sites (Fig. and recycling of various amounts of mantle, arc and 2B), and at Mineral King, we worked in glacially crustal rocks (Ague and Brimhall, 1988; Bateman, “remodeled,” quoting Muir, alpine terrains at over 1992; Ducea, 2001; Saleeby et al., 2003; Coleman et 11,000 feet (Fig. 2C). al., 2004; Wenner and Coleman, 2004; Lackey et al., 2006; 2008). The resulting batholith is a collage of SIERRAN GEOLOGY plutons interspersed with steeply dipping pendants and septa of pre-batholith metamorphic wallrocks The Sierra Nevada batholith is the classic example of (Fig. 1). The granitoid rocks range from gabbro to 303 24th Annual Keck Symposium: 2011 Union College, Schenectady, NY high-silica, peraluminous rocks, with mafic and felsic plutons commonly displaying a range of textures in- dicative of mingling and mixing (Fig. 2D), as well as entrainment of xenolithic material (Fig. 2E). Several of the high-silica granites are peraluminous and have evidence of contamination at their margins (Ague and Brimhall, 1988; Lackey et al., 2006; 2008). Oxygen and strontium isotope data for Grant Grove and other Sequoia region plutons suggest contamination in ar- eas close to contacts with wallrocks (Chen and Tilton, 1991; Lackey et al., 2006). Additionally, previous bulk zircon U-Pb analyses (Chen and Moore, 1982) for many of these plutons, indicate considerable com- plexity and inheritance of diverse age populations of zircon crystals, a result consistent with assimilation of metasedimentary rocks.

In the Sequoia region, metamorphic wallrocks of the Kings Sequence are typically biotite schist, marble, Figure 2. Geography and geology of the Sequoia region. quartzite, and felsic to mafic metavolcanic rocks (A) Foohills view east toward step-wise increasing ranges. (Saleeby and Busby, 1993; Fig. 1). Kings Sequence (B) Kaweah River valley with chaparral landscape (in- metavolcanic rocks show pronounced evidence for cluding blooming yucca); (C) View from Empire Mountain a spectrum of metamorphic processes in the region. toward Mount Whitney; (D) Magma mingling in the Fry’s For example, biotite schist show migmatitic textures Point pluton; (E) Xenolith in the Grant Grove pluton; close to contacts with plutons (Fig. 2F); marbles are (F) Migmatite in the Marble Fork canyon; (G) Coarse- coarsely recrystallized (Fig 2G), and in places alumi- grained graphitic marble; (H) Calc-silicate with alter- nating garnet and wollastonite layers; (I) Late epidote nous, marl protoliths yield spectacular garnet + wol- veining in garnetite of the Empire Mountain skarn. lastonite ± diopside calc-silicate assemblages (Fig. 2H). At Empire Mountain, fluid infiltration during contact metamorphism allowed development of mas- sive garnetite skarns (Fig. 2I). felsic and mafic, ascended from source regions, and locally became contaminated by partial melting or THE MAGMA-WALLROCK INTERFACE wholesale assimilation of metamorphic wallrocks. In this scenario, mafic magmas associated with the The balance of evidence indicates that high-silica high-silica plutons are largely coeval and potentially plutons in the Sequoia region, especially those with supplied heat to drive partial melting of the metamor- peraluminous compositions, are locally contaminated phic rocks. Migmatite complexes in the region may in response to partial melting of the Kings Sequence contain quenched former partial melts and therefore (Lackey et al., 2008), and thus have veneers of super- can be evaluated for melting reactions and potentially imposed contamination. Contamination and melting the “budget” of melt that they could produce. While of metamorphic wallrocks is widely recognized in the granites exposed at the current crustal levels are deeper exposures of the batholith (25–30 km) in the complex integrations of different source and con- Southern Sierra (Saleeby et al., 1987; Pickett and tamination histories, crystal cargoes of inherited Saleeby, 1994; Zeng et al., 2005), but mid-crustal xenocrysts (zircon, garnet, aluminosilicate minerals, (10–20 km; Ague and Brimhall, 1988) contamination spinel, monazite) can be employed to begin to decon- was largely unrecognized until recently and has not volute this history. been studied in detail. Thus our governing research theme was to test the hypothesis that magmas, both The significance of testing this hypothesis is that it 304 24th Annual Keck Symposium: 2011 Union College, Schenectady, NY directly informs our understanding of the tempo and granites, granodiorites, and gabbros in the Ash Peaks mode by which convergent margin batholiths recycle region (Holland et al., 2010, this volume). An impor- pre-existing crust (Kay et al., 1991; Ducea, 2001, tant finding of Julia’s work is that much of the felsic 2002; Saleeby et al., 2003). Such constraints allow and mafic magmatism at the Ash Mountain complex, estimation of mass and thermal transport in such including the Fry’s Point granite, occurred in a narrow settings, which lends to understanding of the crustal span of time at ca. 105 Ma. This is a period when growth and evolution. The findings can also shed few plutonic units are recognized and a point in the light on ongoing discoveries regarding the mecha- batholith evolution when major episodes of rhyolitic nisms by which plutons are assembled and crystallize volcanism occurred. The range of composition and (Coleman et al., 2004; Glazner et al., 2004). AFC trend indicates that a diverse suite of magmas were generated and synchronously emplaced in the With this in mind, we designed student projects to Ash Mountain complex. look at the records of the timing of intrusion of different plutons, both mafic and felsic, as well as to look at Stanley Hensley (CSU-Bakersfield) completed a the crystal cargoes in these rocks. From the perspec- companion study of the large Grant Grove and Giant tive of metamorphic rocks, projects were designed to Forest plutons (Hensley et al., 2010, this volume). appraise peak metamorphic temperatures, the record Stanley’s work refined the age of emplacement of the of partial melting, and how fluids moved between Grant Grove and Giant Forest plutons, and showed magmas and their metamorphic wallrocks. that ca. 113 Ma Grant Grove has considerably more crustal contamination from wallrocks than the ca. 100 PROJECTS AND FINDINGS Ma Giant Forest pluton, but that both plutons have locally assimilated material from their metamorphic Our team worked an aggressive schedule, allowing us wallrocks. Zircons in both plutons provide evidence to gather field observations and samples for the first of both inheritance and Pb loss, factors that compli- half of the project, and date and analyze geochemis- cated the interpretation of early bulk U-Pb zircon try on many of the rocks in the following half of the ages. project. Despite the usual host of hiccups in the field and challenges with weather, we literally went from Mary Badame (Oberlin College) investigated migma- standing on outcrops, discussing the cross-cutting tites in the Marble Fork of the Kaweah River, a site relations, to knowing the exact age of the same rocks where the Sequoia pendant is in direct contact with in less than two weeks. The effort produced several the Fry’s Point Granite. A lone magmatic zircon from data sets, including U-Pb and trace element data for a leucosome provided a critical link between the tim- single zircons, and major, minor, and trace element, ing of the formation of the migmatites and intrusion data from whole rock. These data were shared among of the Ash Mountain Complex (Badame et al., 2010, all students. A flurry of abstract writing before the this volume). Her petrologic and geochemical results National GSA deadline produced four abstracts before further elucidate the origin and condition by which the end of the project. These and a later abstract to these migmatites formed, including the potential melt- AGU served to consolidate the major findings of ing conditions. projects in order to send students home with a first pass sense their findings, priming them to use the fall Julianne Wallan (Colgate University) addressed the and spring to reconcile petrographic and geochemical metamorphic history of marbles in the Ash Mountain data, and frame their data against the literature. The and Sequoia Pendant area, using carbon and oxygen findings detailed in the following student contribu- isotopes, including an evaluation of carbon isotope tions show a range of discoveries in their individual thermometry. Working in outcrops of marble, in the projects that address aspects of the overall theme of Sequoia pendant and in plutons, Julie shows that the project. They are briefly summarized below. 13C/12C partitioning between of calcite and graphite Julia Holland’s (Trinity University) study added are consistent with peak metamorphic temperatures of several new U-Pb age determinations in high silica 560–610°C in the marbles (Wallan et al., this vol- 305 24th Annual Keck Symposium: 2011 Union College, Schenectady, NY ume). Such temperatures agree well with phase equi- ACKNOWLEDGEMENTS libria; d18O and d13C trends in calcite reveal modest infiltration of igneous fluids into most marbles, with This project could not have gone forward without higher fluid fluxes in other marbles. the assistance of many individuals. First, we thank the administrative staff, rangers, and camp hosts of In the Mineral King roof pendant, Jessylyn Starnes Sequoia-Kings Canyon national park invaluable assis- (Denison University) undertook a geochemical and tance with permitting, gate access, camping reserva- geochronologic study of felsic metavolcanic rocks tions, safety advice, and general assistance throughout from a Triassic caldera complex. In the first modern the project. Among these are David Graber, Harold geochronologic and geochemical study of the Mineral Werner, Mary Andrade, Len Dickey, and Margaret King volcanic rocks, Jessie reports that the pendant Johnson. Tom Sisson (USGS), Cathy Busby (UCSB), has both Triassic and Cretaceous sections, thus requir- Diane Clemens-Knott (CSU-Fullerton) shared valu- ing tectonic assembly of disparate volcanic packages able advice on field sites. We thank all of the proj- in the pendant in the Cretaceous (Starnes et al., 2010, ect advisors for their time and skillful input on the this volume) she also demonstrates increasing crustal project, including: William Peck, Steven Wojtal, Ben involvement in the younger rhyolite. Surpless, and Erik Klemetti. We were delighted that three of them were able to join us in the field. Lee Megan D’Errico (Trinity University) investigated of Finley-Blasi helped with analyses at Pomona and the fluid driven skarn mineralization in the contact kept the XRF lab humming. We also thank Geology metamorphic aureole of the Empire Mountain quartz faculty and staff at Pomona and CSUB for assistance diorite. A refined intrusion age of ca. 109 Ma estab- during the project. Jaime Barnes (UT-Austin) and lishes the age of metamorphism in the pendant, with a Ilya Bindeman (U. of Oregon) aided us with stable Ti-in-zircon temperature of 890 ± 23°C for the pluton isotope analyses. We thank Joe Wooden for his expert being the hottest yet obtained from a Sierran granit- assistance on the Stanford SHRIMP that enabled us to oid pluton (D’Errico et al., 2010, this volume). The obtain the highest quality measurements. Lastly, we discovery that the Empire Mountain skarns have low thank our families for their patience and support as d18O values also shows that the Mineral King pendant we undertook the project. was near enough to Earth’s surface for meteoric water to form a considerable component of the fluid budget of the hydrothermal system. REFERENCES CITED

CONCLUSIONS Ague, J.J., and Brimhall, G.H., 1988, Magmatic arc asymmetry and distribution of anomalous plu- As a whole, the findings from this project contribute tonic belts in the batholiths of California: effects new perspective on timing, sequence, and character of of assimilation, crustal thickness, and depth of magmatism and metamorphism in the western Sierra. crystallization: Geological Society of America In particular, our team demonstrates that varying Bulletin, v. 100, p. 912-927. styles of magmatism and involve considerable interaction of magmas with metamorphic wallrocks. 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Starnes, J.K., Klemetti, E.K., Lackey, J.S., Loewy, S.L., and Wooden, J.L., 2010, New U-Pb Shrimp-RG Zircon Ages of Mineral King Roof Pendant Rhyolite Units Revise the Volcanic History of the Sierra Nevada, California: GSA Abstracts W/ Programs, v. 42, n. 5, p. 626.

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