Department Abstracts submitted to the 2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

GSA 2014

 

MIDDLE MIOCENE HIGH-MAGNESIUM ANDESITE AND HIGH-SILICA ADAKITE IN THE JACUMBA VOLCANICS AND ALVERSON FORMATION OF SAN DIEGO AND IMPERIAL COUNTIES, CALIFORNIA

 

KIMBROUGH, David L., Geological Sciences, San Diego State University, San Diego, CA 92182-1020, dkimbrough@mail.sdsu.edu and CAMP, Victor E., Geological Sciences, San Diego State Univ, 5500 Campanile Dr, San Diego, CA 92182-1020
The central part of the Baja California Peninsula is a classic locality where distinctive post-subduction volcanic geochemistry was recognized nearly 30 years ago in the form of Late Miocene to Quaternary high magnesium andesite (bajaite) volcanic fields, thought to derive from partial melting of subducted oceanic crust. The distribution of central Baja California high-magnesium andesite correlates tightly with the lateral extent of fossil Farallon plate slab, as imaged by seismic tomography, along a segment of the margin where subduction ceased before the Pacific-Farallon spreading center reached the trench. Here we report discovery of Middle Miocene high-magnesium andesite and high-silica adakite within the Jacumba Volcanics and Alverson Formation of southern California, 350 km to the north of the nearest Baja California examples, within a presumed slab-free segment of the margin. The Jacumba Volcanics and Alverson Formation volcanic fields both record an evolution from initial primitive high-magnesium andesite eruptions to subsequent high-silica adakite. Recognition of these volcanic rock types in southern California adds important new insight into interpretation of post-subduction magmatism and mantle dynamics along the margin. 

LINKING UNDERGRADUATE RESEARCH WITH COMMUNITY OUTREACH IN ARGENTINA: THE INTERNATIONAL FELLOWS PROGRAM AT THE UNIVERSITY OF WISCONSIN-EAU CLAIRE

BUELOW, Ellen K.1, MAHONEY, J. Brian2, KIMBROUGH, David L.3, TAYLOR, Samantha S.4, NEHRING, Brian5, HUTTER, Alex6, and LEIDEL, Alyssa6, (1) Department of Geology, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, buelowek@uwec.edu, (2) Dept. of Geology, Univ. of Wisconsin-Eau Claire, 105 Garfield Ave, Eau Claire, WI 54701, (3) Geological Sciences, San Diego State University, 5500 Campanile Dr, San Diego, CA 92182, (4) Department of Geology, University of Wisconsin-Eau Claire, Eau Claire, WI 54701, (5) Department of Geology, University of Wisconsin-Eau Claire, Eau Claire, WI 53702, (6) Department of Geology, University of Wisconsin-Eau Claire, 105 Garfield Avenue, Eau Claire, WI 54702
International immersion experiences and collaborative student/faculty research are hallmarks of the undergraduate curriculum at UW-Eau Claire. In 2010, students voted in favor of a tuition surcharge called the Blugold Commitment, which supports high-impact practices including collaborative research and global/multicultural immersion experiences. The International Fellows Program (IFP), initiated in 2012, is dedicated to supporting international student-faculty collaborative research/creative activity and service-learning opportunities.

In 2013, IFP supported a project entitled Establishing Societal Linkages: Introducing the Relevance of the Geology of the Andes to Argentinian Secondary-School Students. This program expanded on the relationship between faculty and Argentinian professionals established during a semester-long multidisciplinary immersion experience (2011 TIES Argentina) and by a subsequent 2012 NSF Tectonics grant. The IFP had two principal components: 1) educational outreach, involving development of a short course for secondary school students that describes the close linkage between geology and society in Mendoza, Argentina. UWEC students designed a series of ‘hands-on’ laboratory exercises that introduced the students to earthquakes, volcanoes, and plate tectonics, utilizing the Andes as a natural laboratory. UWEC students interacted with approximately 150 students and 9 faculty to present a short course to students grades 9-12 at Colegio ICEI. The educational program was extremely successful, and the Colegio has requested that the presentation become a semi-annual event; 2) student/faculty collaborative research, with the students collaborated in international research, including regional planning sessions, analysis of stratigraphic sections, geologic mapping, and geochronologic and geochemical sampling transects. They participated in analysis of the Las Penas and Uspallata basins, and are currently conducting geochronologic and isotopic geochemistry analyses. The lead author will expand her research interests in Argentina into a M.Sc. project at San Diego State University, starting in 2014. The groundwork set during the IFP has led to three (3) additional UWEC students conducting ongoing collaborative research in Argentina. 

CUENCA USPALLATA:  AN INTERMONTANE BASIN RECORDS EPISODIC UPLIFT OF THE CORDILLERA FRONTAL AND PRECORDILLERA IN THE LATE MIOCENE

 

MAHONEY, J. Brian1, KIMBROUGH, David L.2, HOKE, Gregory D.3, MESCUA, Jose F.4, GIAMBIAGI, Laura B.5, BUELOW, Ellen K.6, HUTTER, Alex7, and LEIDEL, Alyssa7, (1) Dept. of Geology, Univ. of Wisconsin-Eau Claire, 105 Garfield Ave, Eau Claire, WI 54701, mahonej@uwec.edu, (2) Department of Geological Sciences, San Diego State University, San Diego, CA 92182, (3) Department of Earth Sciences, Syracuse University, 204 Heroy Geology Laboratory, Syracuse, NY 13244, (4) Instituto Argentino de Nivologia, Glaciologia y Ciencias Ambientales, CCT Mendoza, CONICET, Av. Ruiz Leal s/n, Parque General San Martin, Mendoza, 5500, Argentina, (5) Instituto Argentino de Niviología Glaciología y Ciencias Ambientales, CCT, Parque San Martin s/n, Mendoza, 5500, Argentina, (6) Department of Geological Sciences, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, (7) Department of Geology, University of Wisconsin-Eau Claire, 105 Garfield Avenue, Eau Claire, WI 54702
The timing, rate of subsidence and stratigraphic architecture within retroarc and foreland basin successions is strongly controlled by the kinematics of the thrust system and subsequent magnitude and migration of the tectonic load. The record of west-to-east crustal shortening is well-established in the south-central Andes, with a significant decrease in the magnitude of shortening from the flat slab segment to the north (>150 km) to the normal slab segment to the south (<90 km). Synorogenic Neogene foreland basins at the latitude of 33°S (Mendoza), including the Alto Tunuyan, Uspallata and Cacheuta basins, provide a sensitive record of the spatial and temporal patterns of tectonics, magmatism and orogenic exhumation. An important question relevant to the evolution of the Andean system is whether these basins constitute the remnants of an initially contiguous foreland basin that has be subsequently cannibalized, or if they evolved independently during thrust migration.

Cuenca Uspallata (Uspallata Basin) straddles the boundary between the Frontal Cordillera and Precordillera, and contains a complex succession of conglomerate, sandstone and mudstone deposited in an arid fluvial system. Basin strata unconformably overlie Permian-Triassic volcanic rocks of the Cordillera Frontal, and basal units contain coarse conglomerates and megaclasts of volcanic debris representing a basin margin facies. Sedimentary provenance, constrained by conglomerate clast composition and detrital zircon data, records an initial influx of detritus from the Cordillera Principal and Cordillera Frontal that interfingers upsection with distinct detritus from the Precordillera. Available U-Pb age constraints from a resedimented tuff and detrital sandstone ages suggest sedimentation was active from at least 9-12 Ma, which is significantly younger (>5 Ma) than synorogenic deposits in the Cacheuta basin to the east. Sedimentologic and geochronological constraints suggest Cuenca Uspallata developed as an intermontane basin trapped between the uplifting Cordillera Frontal and the Precordillera, and was not part of the main foreland succession. 

STRATIGRAPHIC ANALYSIS OF THE NEOGENE CACHEUTA BASIN: A RECORD OF OROGENIC EXHUMATION AND BASIN INVERSION IN THE SOUTH CENTRAL ANDES

 

BUELOW, Ellen K., Department of Geology, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, buelowek@uwec.edu, SURIANO, Julieta, Igeba (UBA-CONICET), Instituto de Geociencias Básicas Ambientales y Aplicadas, Ciudad Universitaria Pabellón II, Intendente Güiraldes 2160, Ciudad Autónoma de Buenos Aires, CP:C1428EHA, Argentina, MAHONEY, J. Brian, Dept. of Geology, Univ. of Wisconsin-Eau Claire, 105 Garfield Ave, Eau Claire, WI 54701, MESCUA, José F., Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, CCT Mendoza, CONICET, Av. Ruiz Leal s/n, Parque General San Martín, Mendoza, 5500, Argentina, GIAMBIAGI, Laura B., Instituto Argentino de Niviología Glaciología y Ciencias Ambientales, CCT, Parque San Martin s/n, Mendoza, 5500, Argentina, and KIMBROUGH, David L., Department of Geological Sciences, San Diego State University, San Diego, CA 92182
Neogene synorogenic strata in the south-central Andes (28-35S) provide a sensitive record of the structural evolution of the Andean orogenic system and may be utilized to constrain the chronology of deformation and pattern of orogenic exhumation. The precise succession of thrust belt propagation and foreland basin development is a matter of debate. Analysis of the Cacheuta basin at the latitude of Mendoza, Argentina (33S) provides critical constraints on basin evolution and orogenic exhumation.

The Cacheuta basin is subdivided into five distinct formations [Divisadero Largo, Mariño, La Pilona, Tobas Angostura and Río de los Pozos] that reflect episodic sediment flux produced during eastward thrust belt propagation. Stratigraphic analysis, U/Pb geochronology, conglomerate clast counts, and (U-Th)/He analyses constrain basin evolution and subsequent inversion. A ca. 17.9 Ma U/Pb age from a volcanic tuff near the base of the succession constrains initial basin subsidence to >18 Ma, and suggests that previous magnetostratigraphic age constraints require revision. Provenance analysis identifies episodic sediment flux from the Cordillera Costal (JuraCretaceous zircon), Cordillera Principal (distinctive Jurassic conglomerate, Cretaceous fossiliferous limestone, and Tertiary hornblende andesite clasts) and the Cordillera Frontal (PermoTriassic clasts and detrital zircon). Results from the overlapping U-Pb crystallization ages and (U-Th)/He ages on detrital zircon confirm that the Permo-Triassic Choiyoi Group of the Cordillera Frontal has remained at upper crustal levels (<6 km) since emplacement. Evidence of sediment input to the Cacheuta basin from the Precordillera is equivocal at this time.

Preliminary detrital apatite (U-Th)/He analyses suggest an estimated cooling age of approximately 6 Ma, which is interpreted to reflect basin uplift and inversion in the late Miocene. 

CHARACTERIZING THE EFFECTS OF ILLUVIATION ON THE PETROLOGY AND CHEMISTRY OF TONALITIC SAPROCK: IMPLICATIONS FOR INTERPRETING COMPOSITIONAL LINEAR TRENDS

 

HEATH, Ashley R., Geological Sciences, San Diego State University, 5500 Campanile Drive, San Diego, CA 92128, ashleyrheath@gmail.com, GIRTY, Gary H., Geological Sciences, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, and REPLOGLE, Crystal, 5500 Campanile Drive, San Diego, CA 92128
In order to characterize the petrological and chemical effects of illuviation, we collected 17 samples of saprock adjacent to, and 14 samples of corestone from, an ~6.7 m high tonalitic corestone (tor). Based on thin section observations, all saprock samples are characterized by a network of transgranular and intergranular cracks filled or lined with illuviated clay. In contrast, the silicate framework has been weakly to mildly weathered, and as result, biotite has been partially transformed into mixed-layer biotite/vermiculite, plagioclase has been weakly weathered to a dusting of smectite, and hornblende has been weakly weathered to Fe- and/or Mn-oxyhydroxide. The weathering of biotite translates into an ~5-6% loss of K mass while the weathering of plagioclase resulted in no statistically significant loss of Ca or Na mass.

The above effects of eluviation contrast markedly with the statistically significant additions of Si, Al, Fe, Mn, Ti, Sc, Cr, Cu, Rb, Y, and Yb mass produced by illuviation. Such additions translate into an overall statistically significant 12-15% increase in bulk mass. The above increases in elemental and bulk mass are a reflection of eluvial processes operating in the now eroded overlying ≥6.7 m section of regolith. Within that overlying section, kaolinite; minute particles of biotite, hornblende, and ilmenite; and ions derived from leaching of these mineral were suspended into downward percolating fluids. The dominance of kaolinite, along with the apparent severity of leaching implied by the downward transfer of significant elemental mass, suggest a climatic regime that is unlike that currently existing in the Peninsular Ranges, or during the Quaternary, ~35,000 years ago, the exhumation age of a nearby corestone. Though poorly constrained, after removal of ~300 km of displacement along the San Andreas fault, the section of regolith studied during this investigation, may reflect Paleocene weathering within a subtropical setting.

On centered p(A)-p(CN)-p(K) ternary diagrams, illuviation resulted in a compositional linear trend anchored by the geometric mean of the corestone samples and the projected composition of kaolinite at the p(A) apex. Notably, this trend is unlike that documented for biotite-controlled and plagioclase-controlled weathering. 

LATE CRETACEOUS BASIN EVOLUTION ALONG THE WESTERN MARGIN OF THE INSULAR SUPERTERRANE:  THE NANAIMO GROUP, BRITISH COLUMBIA

 

MAHONEY, J. Brian, Dept. of Geology, Univ. of Wisconsin-Eau Claire, 105 Garfield Ave, Eau Claire, WI 54701, mahonej@uwec.edu, HAGGART, James W., Geol Survey Canada, 101-605 Robson St, Vancouver, BC V6B 5J3, Canada, LINK, Paul K., Department of Geosciences, Idaho State University, Pocatello, ID 83209, FANNING, C. Mark, Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia, and KIMBROUGH, David L., Department of Geological Sciences, San Diego State University, San Diego, CA 92182
The Turonian to Maastrichtian Nanaimo Group provides an excellent record of orogenic exhumation and basin evolution, and constrains the tectonic evolution of the combined Insular and Intermontane superterranes. The Group was deposited on the western edge of the superterranes, flanked on the west by Wrangellian basement and on the east by the Coast Plutonic Complex. Basin subsidence began in Turonian time in response to contractional crustal thickening in the Coast Belt and Cascade Range to the east/southeast. Initial basin sedimentation occurred on a complex paleotopography, resulting in accumulation of locally derived sediment in non-marine, marginal marine, and shallow marine environments. However, the presence of syndepositional Late Cretaceous (ca. 87 Ma) zircon indicates the initiation of rapid unroofing of the arc system to the east. Subsidence dramatically increased in late Santonian time, resulting in progradation of submarine fan systems to the west/northwest across the basin, resulting in a thick succession (>4 km) of complexly intertonguing fan lobes that reflect episodic sediment flux corresponding to contractional tectonism in the Coast Range Thust Belt to the east. Paleocurrent data, abundant volcanoplutonic debris and the presence of syndepositional detrital zircon demonstrate a strong linkage between rapid orogenic exhumation of the CPC and basin subsidence.

The tight linkage between orogenic exhumation and basin subsidence was interrupted in early Campanian time, as the arc system was breached by at least one major fluvial system that delivered extraregional sediment from the back arc region into the basin. Significant (locally >50%) quantities of Precambrian detrital zircon (ca. 1300-1800 Ma), apparently derived from the Belt and Windemere Supergroups to the east, mixed with JuraCretaceous grains derived from the CPC. The timing of this older zircon flux corresponds to uplift of Mesoproteroic and Neoproterozoic successions along the Sevier orogenic system to the east. Extraregional sedimentation peaked in late Campanian time, with a distinct increase in quartzite pebbles and cobbles in conglomeratic facies. The extraregional component was substantially diluted by Maastrichtian time by a major pulse of plutonic detritus derived from final unroofing of the Cretaceous arc system. 

DEVELOPMENT OF A GEOLOGIC GUIDE FOR FLORISSANT FOSSIL BEDS NATIONAL MONUMENT

 

BORCE, Bridget, Department of Geological Sciences, San Diego State University, 5500 Campanile Dr, San Diego, CA 92182, bborce87@yahoo.com, MEYER, Herbert W., Florissant Fossil Beds National Monument, National Park Service, P.O. Box 185, Florissant, CO 80816, CONNORS, Timothy B., Geologic Resource Division, National Park Service, 12795 West Alameda Parkway, Denver, CO 80225, and EVANOFF, Emmett, Earth Sciences, University of Northern Colorado, Campus Box 100, Greeley, CO 80639
The Florissant Fossil Beds National Monument Geologic Guide is designed to acquaint visitors with the geologic history of the monument with a self-guided tour. The geology includes the Proterozoic granitic pluton of the Pikes Peak Granite as well as Eocene volcanic, fluvial, and lacustrine units of the Wall Mountain Tuff and Florissant Formation. This guide communicates the geologic significance of Florissant Fossil Beds National Monument by relating these stratigraphic and igneous rock units to geologic events, then indicating specific locations to view tangible examples of the area’s geologic history. The guide begins with a small scale 1:117,000 map of the monument as well as areas to the north and south. The late Eocene Florissant Formation, the primary fossil-bearing formation in the area, is initially shown on this map as a homogeneous unit, showing its broader relation to the surrounding units. This view illustrates an outline of the ancient lake. The next geologic map is a 1:20,000 perspective showing the rock units and topography only within the monument’s boundaries. This map differentiates the Florissant Formation into its six separate lithologies previously defined. The third map shows an enlarged 1:10,000 perspective of the principle hiking trails within the monument, indicating specific points of geologic interest along those trails. Those points are explained below the map with photos and texts describing geologic significance. A table of waypoints is provided for GPS navigation.

The rock units portrayed on the geologic maps are then put into context with an illustration of a stratigraphic column. Each rock layer is further described with photos in outcrop and as a hand sample. Fossils are illustrated for the fossiliferous layers. In depth descriptions of each rock layer include lithology, deposition, paleontology (if applicable), and locations where outcrops can be viewed. The guide ends with a brief text describing the geologic history of the area and a customized time scale, placing the deposition of the Florissant Formation and other surrounding units into context with the entirety of geologic time.