Keck Geology Consortium Proceedings of the Twenty-Fifth Annual Keck Research Symposium in Geology Issn# 1528-7491

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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. 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-FIFTH ANNUAL KECK RESEARCH SYMPOSIUM IN GEOLOGY ISSN# 1528-7491

April 2012

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

2011-2012 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

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 1005122 ExxonMobil Corporation Keck Geology Consortium: Projects 2011-2012 Short Contributions— Grenville Province, Ontario Project

PETROLOGY AND STRUCTURE OF THE CENTRAL METASEDIMENTARY BELT BOUNDARY THRUST ZONE ITS HANGING WALL, GRENVILLE PROVINCE, ONTARIO Project Faculty: WILIAM H. PECK, Colgate University, STEVEN R. DUNN, Mount Holyoke College MICHELLE J. MARKLEY, Mount Holyoke College

GEOCHEMISTRY AND GEOCHRONOLOGY OF CENTRAL METASEDIMENTARY BELT BOUNDARY THRUST ZONE THRUST SHEETS IN SOUTHERN ONTARIO, GRENVILLE PROVINCE KENJO S. AGUSTSSON, California Polytechnic State University, San Luis Obispo Research Advisor: Scott Johnston

CONFLICTING KINEMATICS OF THE SALERNO CREEK DEFORMATION ZONE, GRENVILLE PROVINCE, ONTARIO NAOMI BARSHI, Smith College Research Advisor: Jack Loveless

THERMOBAROMETRIC EVIDENCE FOR A COMMON CENTRAL METASEDIMENTARY BELT AFFINITY OF THE BANCROFT AND ELZEVIR TERRANES, ONTARIO, CANADA NEVA FOWLER-GERACE, Oberlin College Research Advisor: F. Zeb Page

HETEROGENEOUS DEFORMATION OF GABBROIC ROCKS CALVIN MAKO, University of Maine Research Advisor: Christopher Gerbi

PETROLOGY AND GEOCHEMISTRY OF THE ALLSAW ANORTHOSITE: A SCAPOLITIZED META- ANORTHOSITE IN GRENVILLE PROVINCE, ONTARIO EDWARD W. MARSHALL, Earlham College Research Advisor: Meg Streepey Smith

GARNET-BIOTITE GEOTHERMOBAROMETRY OF THE CENTRAL METASEDIMENTARY BELT BOUDARY THRUST ZONE OFTHE GRENVILLE PROVINCE, ONTARIO, CANADA ABIGAIL MONREAL, University of Texas at El Paso Research Advisor: Jasper G. Konter

CARBON ISOTOPE THERMOMETRY IN THE CENTRAL METASEDIMENTARY BELT BOUNDARY THRUST ZONE GRENVILLE PROVINCE, ONTARIO BO MONTANYE, Colgate University Research Advisor: William H. Peck

CALCITE-GRAPHITE THERMOMETRY IN THE SOUTHWESTERNMOST CENTRAL METASEDIMENTARY BELT, GRENVILLE PROVINCE, SOUTHERN ONTARIO JACQUELYNE NESBIT, Princeton University Research Advisor: Blair Schoene

USING STRUCTURAL ANALYSES TO ASSESS POSSIBLE FORMATION MECHANISMS OF THE CHEDDAR GNEISS DOME CALIE SENDEK, Scripps College Research Advisor: Linda Reinen Keck Geology Consortium Pomona College 185 E. 6th St., Claremont, CA 91711 Keckgeology.org

25th Annual Keck Symposium: 2012 Amherst College, Amherst, MA PETROLOGY AND STRUCTURE OF THE CENTRAL METASEDIMENTARY BELT BOUNDARY THRUST ZONE AND ITS HANGING WALL, GRENVILLE PROVINCE, ONTARIO

William H. Peck, Colgate University Steven R. Dunn, Mount Holyoke College Michelle J. Markley, Mount Holyoke College

INTRODUCTION provenance of these thrust sheets and dismembered blocks (i.e. if they originate from the CGB, CMB, or The southern Grenville Province in Ontario (Fig. 1) elsewhere) is generally unclear. exposes metasedimentary, metavolcanic, and metaplutonic rocks of the 1.3–1.2 Ga Central Metasedi- Structurally above the CMBbtz are the Bancroft Ter- mentary Belt (CMB) sitting on top of orthogneiss- rane and the Harvey-Cardiff Domain (Fig. 2). The dominated 1.7–1.4 Ga rocks of the Central Gneiss Bancroft Terrane may be a deformed extension of Belt (CGB, Easton 1992). The boundary between the CMB, which it resembles lithologically, or it may these tectonic belts is the Central Metasedimentary be a supracrustal package deposited on the margin Belt boundary thrust zone (CMBbtz; Fig. 2 and 3): of Laurentia, now the CGB (Carr et al., 2000). The a region of annealed, heterogeneously deformed position of the CMB during its formation is unclear. mylonitic tectonites and marble mélange tectonites The Harvey Cardiff Domain of the CMB includes a surrounding dismembered metaplutonic thrust sheets lithologically distinctive suite of four granitic gneiss (Hanmer, 1988; Hanmer and McEachern, 1992). The domes with strongly deformed mantles of amphibolite and marble. The CMBbtz, Bancroft Terrane, and Harvey-Cardiff Domain all share similar structural geometries: east-dipping lithologic boundaries associated with a strong foliation in the same orientation and a sporadic but consistently oriented stretching lineation that is down-dip and associated with a top- to-the-west sense of shear.

This project focuses on quantifying peak pressure and temperature conditions during thrusting of the CMB over the CGB. We also explore possible protoliths for metaplutonic rocks in the CMBbtz thrust sheets. Finally, we report preliminary results from analysis of foliation and kinematic evolution of a gneiss dome from the Harvey-Cardiff Domain and a newly identi- fied shear zone at the boundary of the Bancroft Ter- Figure. 1. A. Location map of the Grenville Province, rane and the Harvey-Cardiff Domain. showing the Ontario Grenville in black. AM= Adirondack Mountains, GM= Green Mountains. B. The southern CONTROVERSIAL TECTONICS Grenville Province of Ontario, after Hanmer and McEach- ern (1992). CMBbtz, Central Metasedimentary Belt Although the term “terrane” pervades the literature on boundary thrust zone; the Composite Arc Belt (Elzevir ter- this region, the nature and origin of these distinctive rane) is sub-divided into the Harvey-Cardiff (H), Belmont and strongly deformed suites of rock is controversial. (B), Grimsthorpe (G), Mazinaw (M), and Sharbot Lake (S) The western CMB is dominated by greenschist- and domains after Easton (1992). 310 25th Annual Keck Symposium: 2012 Amherst College, Amherst, MA

Figure 2. Cross section of the southern-central Grenville province based on seismic interpretations (modified from White et al., 2000). Historically, the Bancroft and Elzevir terranes have been considered closely related, but recently this has been questioned (Carr et al., 2000; Easton and Carr, 2009). The extensional Bancroft shear zone is not shown.

amphibolite facies metasedimentary and 1.29–1.24 Timmermann et al. (1997) as representing docking Ga metavolcanic and volcanoclastic rocks that are of the Composite Arc Belt. The tectonic significance intruded by suites of gabbroic, tonalitic, and granitic of the 1.19 Ga event and new 1.12 Ga metamorphic plutons (Easton, 1992). The volcanic rocks have arc ages (Peck and Kylander-Clark, unpub. data) from geochemical signatures and are dominated by mafic the CMBbtz is unknown. The work presented below tholeiitic suites, but include intermediate and felsic informs but does not resolve some of these long- rocks, some with calc-alkaline signatures. Carr et standing debates about regional tectonics. al. (2000) term this region the Composite Arc Belt, and interpret this package of rocks to be a collage STRUCTURAL GEOLOGY OF THE HANGING of volcanic arc environments, some of which were WALL OF THE CMBbtz formed on oceanic crust away from Laurentia. This tectonic interpretation is controversial, as others have The top of the CMBbtz has historically not been well assigned these rocks to rifting and back-arc environ- defined in the field. Carlson et al. (1990) propose ments underlain by continental crust and developed that it is an extensional shear zone called the Bancroft on the Laurentian margin (e.g. Hanmer et al., 2000). shear zone (BSZ). The BSZ is controversial in this The youngest cross-cutting plutonic rocks appear to context because it clearly records late extension after constrain terrane amalgamation of the Composite Arc peak Grenville orogenesis, and it does not offset any Belt to 1.24–1.22 Ga (Carr et al., 2000). metamorphic isograds, implying it does not accom- modate regionally significant displacement. More to The timing of accretion of the Composite Arc Belt to the point, if the BSZ is the top of the CMBbtz, then the Central Gneiss Belt is also controversial, as there the fundamental relationship between the CMBbtz is evidence for two deformation events in the CMBbtz and the adjacent Harvey-Cardiff domain is one of at ca. 1.19 and 1.08–1.06 Ga (McEachern and van tectonic collapse. This interpretation is starkly at Breemen, 1993). The 1.08–1.06 Ga event is interpret- odds with the equally controversial terrane accretion ed to date the most pervasive deformation, and CGB model for the different suites of rock in the CMB. rocks structurally below the CMBbtz only record Recently, Easton and Carr (2009) proposed the newly- the 1.08 Ga metamorphism, which is interpreted by mapped Salerno Creek deformation zone (SCDZ) as 311 25th Annual Keck Symposium: 2012 Amherst College, Amherst, MA

P R

D B H Ca Ba

A CChh

Central Gneiss Belt Early Granitic and Tonalitic Rocks Mafic Rocks Late Granitic and Tonalitic Rocks M Marble and Tectonites Marble Breccia Kilometers 0 10 20 Clastic Metasediments Metavolcanic Rocks Figure 3. Geology of the southern CMBbtz and adjacent Central Gneiss Belt and Central Metasedimentary Belt, from Ontario Geological Survey 1:100,000 Bedrock Coverage (2000). R= Redstone, D= Dysart, G= Glamorgan thrust sheets; A= Alsaw, P= Percy Lake anorthosites; An= Ansruther, Ch= Chedar, Ca= Cardiff domes; Ba= Bancroft Shear Zone; Sa= Salerno Creek Deformation Zone; H= Haliburton, B= Bancroft, M= Madoc. the boundary between the CMBbtz and the Harvey- by later extension associated with tectonic collapse). Cardiff domain. Barshi’s quest for dateable monazite associated with deformation fabrics in the SCDZ was tragi- Two student projects focus on the structural geology cally unsuccessful. Calvin Mako completed a more of SCDZ. Naomi Barshi’s work shows that the steep process-oriented project in the SCDZ. He looked at lineation in the SCDZ is associated with both exten- meter-scale strain localization and fabric develop- sional (E side down) and contractional (E side up) ment in a gabbro caught up and variably deformed in sense of shear. Barshi documents both senses of shear the SCDZ. His work shows that deformation (and the using clast tiling and sigma and delta porphyroclasts, development of gneissic fabric) involved grain size mostly in a meta-granite that crops out sporadically reduction of both hornblende and plagioclase. As- along the SCDZ. She suggests that the SCDZ may sociated with this deformation are changes in am- have accommodated both types of events (early ter- phibole composition and crystallographic preferred rane accretion or thrusting in the CMBbtz, followed orientation, without similar changes in the feldspar

312 25th Annual Keck Symposium: 2012 Amherst College, Amherst, MA grains. Mako uses these observations to argue that plagioclase was the weaker phase during deformation, A common problem with conventional geother- possibly undergoing a fluid-assisted transition from mobarometry is that results using different min- dislocation creep to diffusion creep as deformation eral assemblages or calibrations can be difficult to progressed. compare. Two student projects focused on using a carbon isotope thermometer in marbles as a way of Callie Sendek’s project focuses on the Cheddar assessing metamorphic temperatures in a series of Dome, one of the northernmost gneiss domes of the transects across the Elzevir and Bancroft terranes. Harvey Cardiff Domain (structurally, this Domain is Jacquelyne Nesbit documented an east to west gradi- directly above both the CMBbtz and the SCDZ). The ent of increasing metamorphic temperatures from Cheddar dome (like the other three) shows a distinc- ~600°C south of the Anstruther dome to ~700°C in tive map pattern of steep foliation striking subparallel the western Bancroft terrane, broadly agreeing with to the dome margins (distinct from the generally E- but refining published thermometry. Bo Montayne‘s and ENE- dipping foliation elsewhere in the region). northwest/southeast transect from north of the Ched- Sendek teases out fabrics that appear to be associated dar Dome to northwest of the Redstone thrust sheet with dome formation and argues that the Cheddar yielded different results: no temperature gradient was Dome is likely the product of solid-state diapirism. detected and temperatures are consistently higher The timing of both dome formation and shearing in (averaging ~750°C). Higher temperatures in Mon- the SCDZ remains poorly constrained. tayne’s northern transect may have been predicted by extrapolation of thermometry in the Harvey-Cardiff METAMORPHIC PETROLOGY OF THE Domain and further east, but the magnitude of the dif- CMBBTZ ference between the northern and southern transects is surprising. Because these data were collected in two A major objective of student projects was to obtain different laboratories, a direct lab-lab comparison of constraints on the conditions of the metamorphism of selected samples will be carried out. Several meta- the CMBBtz. Previous thermobarometry and phase morphic events are recognized in the CMB, as well equilibria studies had focused on the CGB footwall as differences in cooling ages across some terrane and the CMB hanging wall, inexplicably leaving the boundaries, but titanite U-Pb ages from marble in the CMBBtz’s amphibolite-facies metamorphism poorly study area are quite consistent at ca. 1.05-1.03 Ga characterized (see Streepey et al., 1997 and references (Mezger et al., 1993; Cosca et al., 1992). We interpret therein). Four students undertook projects to better this to be the age of the metamorphism characterized understand the metamorphic history of the area. Two in these studies. of those projects were petrologic studies of a variety of metamorphic rocks in the CMBbtz (+Bancroft) and Elzevir terrane. Neva Fowler-Gerace examined IGNEOUS PETROLOGY OF CMBBTZ THRUST garnet-bearing schists and gneisses, mainly metaba- SHEETS sites, from the Elzevir and Bancroft terranes. Garnet- biotite temperatures from these rocks range from be- Fault-bounded orthogneiss blocks within the CMBbtz tween 620 and 780°C and cluster around 650–700°C. range in size from outcrop-sized to 10s of square Assemblages that constrain pressure are more limited kilometers and contain a variety of lithologies (Fig. in these rocks, with most giving pressures in the range 3; Hanmer, 1988; Hanmer and McEachern, 1992). 6-8 kbar with a few in the 9-10 kbar range. Abigail Hanmer (1988) proposed that the tonalitic Redstone, Monreal focused on pelitic schists and gneisses from Dysart, and Glamorgan sheets could have once been around the Dysart and Redstone thrust sheets in the a coherent plutonic body that has been dismembered. westernmost CMBBtz. The petrology of these units This question has been debated in the literature, as has is consistent with ~650–800°C and a range of pres- the tectonic significance of these rocks. Unpublished sures up to 11 kbar, which will be further constrained geochronology and reconnaissance geochemistry of using mineral composition data. the Redstone and Dysart thrust sheets (Lumbers et al., 313 25th Annual Keck Symposium: 2012 Amherst College, Amherst, MA 1990) has linked them to similar rocks in the Adiron- project during visits to analytical laboratories. Mike dacks and Vermont (Fig. 1). Kenjo Agustsson studied Easton and Nick Culshaw are also thanked for helping the geochemistry and geochronology of the Redstone identify possible student projects and their generous and Dysart bodies. He found that both bodies have advice throughout. J. Nesbit was partially supported igneous ages of 1.33-1.30 Ga, and contain a similar by NSF-EAR 0635816. suite of calc-alkaline tonalites and amphibolites with associated tholeiitic amphibolites having MORB-like REFERENCES rare earth element compositions. 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CO2-rich fluids from the surrounding marble units. constraints from Ar-40 Ar-39 thermochronology. Easton (1990) linked the Allsaw anorthosite with the Contributions to Mineralogy and Petrology, adjacent Glamorgan thrust sheet, but new rare earth 10:211-225. element data point to an affinity with other Gren- ville anorthosites, and not the Glamorgan complex. Easton, RM, 1990, Meta-anorthosites in the Grenville Marshall documents both channelized and pervasive Province of Ontario, In Gower, C.F., T. Rivers, infiltration of this body, producing scapolite ±zoisite and B. Ryan (eds.), Mid-Proterozoic Laurentia- assemblages consistent with metasomatism under up- Baltica: Geological Association of Canada Spe- per amphibolite facies conditions. cial Paper 38, p. 387-397.

ACKNOWLEDGEMENTS Easton, RM, 1992, The Grenville Province and the Proterozoic history of central and southern This project was made possible by funding from the Ontario, In Geology of Ontario, Edited by PC Keck Geology Consortium and logistical support Thurston, HR Williams, RH Sutcliffe and GM from Colgate University and Mount Holyoke Col- Stott. Ontario Geological Survey Special Paper lege. Jodi McNamara, David Linsley, Di Keller, and 4, p. 715–904. Sarah Lemon at Colgate are especially thanked for their support of this project in the office and in the Easton, RM and Carr, SD, 2009, Field trip guidebook, laboratory. Also, Alianora Walker at Mount Holyoke Precambrian geology of Cavendish Township and David Finkelstein at the University of Massachu- and environs, Grenville Province. Friends of the setts assisted with some of the stable isotope work. Grenville 38th Annual Meeting and Field Trip, Chris Gerbi, Scott Johnston, Jasper Konter, Jack Ontario Geological Survey Open File Report Loveless, Zeb Page, Linda Reinen, Blair Schoene, 6230, 59p. and Meg Streepey-Smith are all thanked for advis- ing these projects during the academic year. Andrew Hanmer, S, and McEachern, S, 1992, Kinematical and Kylander-Clark (UC-Santa Barbara) and Yang Chen rheological evolution of a crustal scale duc- (U Michigan) hosted and assisted members of this tile thrust zone, Central metasedimentary belt, 314 25th Annual Keck Symposium: 2012 Amherst College, Amherst, MA Grenville orogen: Canadian Journal of Earth Sci- based cross-section of the Grenville Orogen in ences, 29:1779–1790. southern Ontario and western Quebec. Canadian Journal of Earth Sciences, 37:183-192. Hanmer, S, Corrigan, D, Pehrsson, S, and Nadeau, L, 2000, SW Grenville Province, Canada: The case against post–1.4 Ga accretionary tectonics: Tectonophysics, 319:33–51.

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