Xenolith-bearing orthogneiss of Amazonian affinity discovered in the Dellwood quadrangle in the Blue Ridge basement complex represents the oldest crustal component of the southern Appalachians (1.33 – 1.37 Ga: Quinn, 2012). New U-Pb zircon ages for migmatitic paragneiss of the Cartoogechaye terrane exposed in the Dellwood quadrangle reveal two unique detrital zircon age signatures that indicate either a local eastern Laurentian margin source or an exotic source. Detailed mapping, whole rock geochemistry, and U-Pb zircon geochronology were conducted to determine whether this exotic crustal component extends farther south into the Hazelwood 7.5” quadrangle. Lithological similarities exist between paragneisses in the Dellwood quadrangle and those in the Hazelwood quadrangle. However, the increase in proportion of leucosome and polyphase folding prevent direct correlation of lithologies between the areas. Whole rock major element compositions overlap the composition of basement orthogneisses. Zircon ages of six paragneiss samples reveal multiple detrital zircon age modes that are dominated by two Grenville modes at ~1050 and 1150 Ma. Minor zircon populations exist at ~450 – 480, 700 – 900, and 1300 – 1500 Ma. Age distributions and compositional trends are evidence that the protolith of the paragneiss in the Hazelwood quadrangle was Neoproterozoic rift sediments with a dominant Laurentian margin source.

The Andes Mountains provide an ideal natural laboratory to analyze the relationship between the tectonic evolution of a subduction margin, retroarc shortening, basin morphology, and volcanic activity. Timing of initial shortening and foreland basin development in Argentina is diachronous along strike, with ages varying by 20-30 million years. The Neuquén Basin (32°S-40°S) of southern-central Argentina sits in a retroarc position and provides a geological record of sedimentation in variable tectonic settings from the Late Triassic to the early Cenozoic including: 1.) active extension and deposition in isolated rift basins in the Late Triassic-Early Jurassic; 2.) post-rift back-arc basin from Late Jurassic-Late Cretaceous; 3.) foreland basin from Late Cretaceous to Oligocene; and 4.) variable extension and contraction along-strike from Oligocene to present. The goal of this study is to determine the timing of the transition from post-rift thermal subsidence to foreland basin deposition in the northern Neuquén Basin and then assess volcanic activity and composition during various tectonic regimes. The Aconcagua and Malargüe areas (32°S and 35°S) are located in the northern segment of the Neuquén Basin and preserve Upper Jurassic to Miocene sedimentary rocks, which record the earliest phase of shortening at this latitude. This study presents new sedimentological and detrital zircon U-Pb data from the Jurassic to latest Cretaceous sedimentary strata to determine depositional environments, stratigraphic relations, provenance, and maximum depositional ages of these units and ultimately evaluate the role of tectonics on sedimentation in this segment of the Andes. The combination of provenance, basin, and subsidence analysis shows that the initiation of foreland basin deposition occurred at ~100 Ma with the deposition of the Huitrín Formation, which recorded an episode of erosion marking the passage of the flexural forebulge. This was followed by an increase in tectonic subsidence, along with the appearance of recycled sedimentary detritus, recorded in petrographic and detrital zircons analyses, as well development of an axial drainage pattern, consistent with deposition in the flexural forebulge between 95 and 80 Ma. By ca. 70 Ma the volcanic arc migrated eastward and was a primary local source for detritus. Growth structures recorded in latest Cretaceous units very near both the Aconcagua and Malargüe study areas imply 35-40 km and 80-125 km of foreland migration between 95 and 60 Ma in the Aconcagua and Malargüe areas, respectively. Strata ranging in age from Middle Jurassic to Neogene were analyzed to determine their detrital zircon U-Pb age spectra and Hf isotopic composition to determine the relationship between magmatic output rate, tectonic regime, and crustal evolution. When all detrital zircon data are combined, significant pulses in magmatic activity occur from 190-145 Ma, and at 128 Ma, 110 Ma, 69 Ma, 16 Ma, and 7 Ma. The duration of magmatic lulls increased markedly from 10-30 million years during back-arc deposition (190-100 Ma) to ~40-50 million years during foreland basin deposition (100-~30 Ma). The long duration of magmatic lulls during foreland basin deposition could be caused by flat-slab subduction events during the Late Cretaceous and Cenozoic or by long magmatic recharge events. There are three major shifts towards positive Hf isotopic values and all are associated with regional extension events whereas compression seems to lead to more evolved isotopic values.

published_or_final_version / abstract / Earth Sciences / Doctoral / Doctor of Philosophy

The Fish Creek-Vallecito Basin exposes an archive of sediment related to early rifting of the Gulf of California beginning at 8.0 Ma followed by Colorado River delta progradation from 5.3-3.0 Ma. Mio-Pliocene deposits from the Fish Creek-Vallecito Basin of southern California and a sample from the modern Colorado River delta were analyzed through detrital zircon U-Pb (n=1996) and (U-Th)/He (n=280) double-dating in order to better constrain sediment provenance, hinterland exhumation, and Colorado River evolution. Coupling this dataset with outcrop study of the first Colorado River-sourced turbidites into the basin at 5.3 Ma, allows for evolution of the Colorado River system to be viewed from a source-to-sink perspective. Detrital zircon U-Pb and (U-Th)/He (ZHe) ages obtained in this study suggest earliest derivation of sediment was from the Peninsular Ranges followed by more distant sediment sourcing from the Colorado River. Initial Colorado River-sourced deposits show Yavapai-Mazatzal U-Pb ages with Laramide ZHe ages suggesting that the river was sourcing from Laramide basement cored uplifts at the onset of deposition into the Gulf of California, supporting a top-down model of river evolution. An increased percentage of Grenville U-Pb age grains as well as a wider range of ZHe ages associated with western US basement-derived zircon from a modern Colorado River delta sample indicate erosion into older stratigraphic units through time which is consistent with deep erosion on the Colorado Plateau since ~6 Ma. Vertically measured sedimentology logs through the Wind Caves Member, the first Colorado River-sourced unit deposited, were used to determine slope and basin floor architecture as the Colorado River and delta dispersed subaqueous sediment gravity flows into the marine Gulf. Measured sections arrayed along depositional strike show a 4.5 km wide pod of sand-rich turbidites that were delivered through a broad Fish Creek exit point from the paleo-Colorado shelf. The vertical sedimentation trend is one showing thick bedded, amalgamated channelized and sheet-like sandstones initially, shifting to thinnerbedded sheets and more isolated channels higher in the increasingly muddy section. The facies variability up section is interpreted as a change from a submarine basin floor fan to a lower slope environment as the Colorado River prograded its delta into the Gulf. / text

The Laramide Rocky Mountains in western U.S.A is an important topographic feature in the continental interior, yet its formation and evolution are poorly constrained. This study uses the oxygen and strontium isotope geochemistry of freshwater bivalve fossils from six Laramide basins in order to reconstruct the spatial evolution of the paleotopography and Precambrian basement erosion in late Cretaceous-early Eocene. In addition it uses the sedimentology, detrital zircon U-Pb geochronology, and isotope paleoaltimetry of early Eocene sedimentary strata to constrain the tectonic setting, paleogeography and paleoclimate of the Wind River basin. Annual and seasonal variation in ancient riverwater δ¹⁸O reconstructed from shell fossils shows that the Canadian Rocky Mountains was 4.5±1.0 km high in late Cretaceous-early Paleocene, and the Laramide ranges in eastern Wyoming reached 4.5±1.3 km high, while the ranges in western Wyoming were 1-2 km high in late Paleocene. The ⁸⁷Sr/⁸⁶Sr ratios of riverwaters reconstructed from the same fossils show that Proterozoic metamorphic carbonates in the Belt-Purcell Supergroup were not exposed in the Canadian Rocky Mountains during Late Cretaceous-early Paleocene, but that Precambrian silicate basement rock was exposed and eroded in the Laramide ranges during late Paleocene-early Eocene. The sedimentary environment of the early Eocene Wind River basin changed from gravelly fluvial and/or stream-dominated alluvial fan to low-sinuosity fluvial systems. Tectonic uplift of the Washakie and Wind River Range in early Eocene formed the modern paleodrainage system, although the elevation of the basin floor was only ~500 m high at that time, and early Eocene paleoclimate is more humid than modern climate.

A series of crustal-scale shear zones demarcates the northern and eastern margins of the North Caribou greenstone belt (NCGB), proximal to a Mesoarchean terrane boundary in the core of the western Superior Province of Canada. The dominant deformation produced a pervasive steeply dipping fabric that trends broadly parallel to the doubly arcuate shape of the belt and was responsible for tight folding the banded iron formation host to Goldcorp’s prolific gold deposit at Musselwhite mine. The shear zones in the North Caribou greenstone belt are of particular interest because of their ability to channel hydrothermal fluids with the potential to bear ore and cause alteration of the middle to shallow crust. Shear zones are commonly reactivated during subsequent tectonism, but exhibit a consistent and dominant dextral shear sense across the belt; fabric-forming micas and chlorite are generally Mg-rich. Although garnets samples from within the shear zones are dominantly almandine, they possess variable geochemical trends (HREEs of >2 orders of magnitude) and can be syn-, intra-, or post-tectonic in origin. In situ geochronological analysis of zircon (U-Pb) and monazite (total-Pb) in high strain rocks in and around the NCGB, interpreted in light of in situ geochemical analysis of garnet and fabric-forming micas and chlorite, reveals four relatively discrete events that span 400 million years. Metamorphism of the mid-crust was coeval with magmatism during docking of the Island Lake domain at c. 2.86 Ga and subsequent terrane accretion at the north and south margins of the North Caribou Superterrane from c. 2.75 to 2.71 Ga. Transpressive shear at c. 2.60 to 2.56 Ga and late re-activation of shear zones at c. 2.44 Ga produced a steeply-dipping pervasive fabric, and channeled fluids for late crystallization of garnet and monazite recorded in the Markop Lake deformation zone. These observations implicate a horizontal tectonic model similar to the modern eastern Pacific plate margin. Further, this study highlights the caution that should be exercised when using traditional rock forming metamorphic minerals (mica, chlorite, garnet) when attempting to vector into zones of hydrothermal alteration within midcrustal rocks.

The Middle-Upper Jurassic sedimentary rocks (i.e., the Entrada Sandstone, Wanakah Formation, and Morrison Formation) in western Colorado were mostly deposited in the Paradox Basin and form part of the modern-day Colorado Plateau in the Cordilleran foreland region. These rocks were deposited in the Mesozoic during periods of active tectonic processes in western and eastern Laurentia due to the Cordilleran magmatism and continued rifting of Pangaea, respectively. The Middle-Late Jurassic sedimentary record in the Paradox Basin shows rapid transition in depositional environments, pulses in sedimentation, post-depositional alteration, and changes in provenance. This dissertation project utilizes three main scientific tools to address pertinent geologic questions regarding the stratigraphic evolution of these units in the Paradox Basin. U-Pb detrital zircon geochronology of sandstones from these units show local and distal provenance sources. The anisotropy of magnetic susceptibility (AMS) of sediments and rock magnetism attribute the post-depositional alteration to percolation of ferruginous fluids driven by an adjacent regional uplift. Multi-geochemical proxies in paleosols suggest variable redox conditions, and a sub-humid to humid paleoclimate with seasonal precipitation during sedimentary hiatus in the Paradox Basin.

The long-term (>1 Ga) thermal histories of cratons are enigmatic, with geologic data providing only limited snapshots of their evolution. We use zircon (U-Th)/He (zircon He) thermochronology and age composition correlations to understand the Proterozoic-Phanerozoic thermal history of Archean Wyoming province rocks exposed in the northern Laramide ranges of western North America. Zircon He ages from the Wind River Range (54 dates) and Bighorn Mountains (32 dates) show negative correlations with effective uranium (eU), a proxy for radiation damage. Zircon dates from the Bighorns are between 960 Ma (low-eU) and 20 Ma (high-eU) whereas samples from the Wind Rivers are between 582 Ma (low-eU) and 33 Ma (high-eU). We applied forward modeling using the zircon radiation damage and annealing model ZrDAAM to understand this highly variable dataset. A long-term t-T path that is consistent with the available geologic constraints successfully reproduced age-eU correlations. The best fit to the Wind Rivers data involves two phases of rapid cooling at 1800-1600 Ma and 900-700 Ma followed by slower cooling until 525 Ma. During the Phanerozoic, these samples were heated to maximum temperatures between 160 and 125 degrees C prior to Laramide cooling to 50 degrees C between 60 and 40 Ma. Data from the Bighorn Mountains were successfully reproduced with a similar thermal history involving cooler Phanerozoic temperatures of similar to 115 degrees C and earlier Laramide cooling between 85 and 60 Ma. Our results indicate that age-eU correlations in zircon He datasets can be applied to extract long-term thermal histories that extend beyond the most recent cooling event. In addition, our results constrain the timing, magnitude and rates of cooling experienced by Archean Wyoming Province rocks between recognized deformation events, including the >1 Ga period represented by the regionally-extensive Great Unconformity.

The Middle Ordovician Ancell Group, including the St. Peter Sandstone, Glenwood Shale and Starved Rock Formation, records intracontinental basin development during eustatic sea level changes in Iowa and Illinois. The St. Peter Sandstone overlies the Prairie du Chien Group across an erosional unconformity that marks a major sequence boundary, whereas upper contact of the St. Peter Sandstone with the Glenwood Shale also is a second sequence boundary. Data from 80 wells, selected well logs, and 20 cores were integrated to refine the high-resolution sequence stratigraphy of the Ancell Group. Two main sequences bounded by three sequence boundaries are interpreted to represent 3rd order sequences. Distinctive shallowing-upward parasequences bounded by flooding surfaces in many cores record higher frequency relative sea level fluctuations in the Ancell Group, but these cannot presently be correlated regionally. Facies variations define an aggradational transgressive systems tract TST), a prograding highstand systems tract (HST) and down stepping falling stage system tract (FSST) in both the St. Peter Sandstone and the Glenwood Shale-Starved Rock Formation units. The St. Peter Sandstone thickens towards the northeast and thins to the northwest and southwest in Iowa. In contrast, the St. Peter Sandstone in Illinois thickens to the south likely recording a prolonged FSST incised valley or channel fill. Detrital zircon geochronology of 13 samples from the St. Peter Sandstone and Starved Rock Formation define common peaks at 1100-1500 Ma and 2500-2700 Ma with minor components at 1670-1750 Ma and 3000-3600 Ma. The detrital zircon signature is dominated by Archean, and Grenville (1000-1300 Ma) ages. The detrital zircon geochronology indicates that the Ancell Group was sourced directly from the Archean Superior Province to the north and Grenville Province to the northeast, although recycling of Archean grains from the Paleoproterozoic Huron Basin cannot be ruled out. The near complete lack of 1800-1900 Ma ages argues against derivation of detritus from the Trans-Hudson or Penokean Orogens. The Transcontinental Arch northwest of the Iowa Basin acted as a barrier to sediment transport from the Trans-Hudson Orogen. Basement rocks of the Penokean Orogen are inferred to have been covered by water or younger sediments southeast of the Iowa Basin. CIA analyses of Ordovician shale samples from around the Transcontinental Arch indicate that the climate condition during Middle Ordovician time was warm and humid. This is consistent with a paleoclimate interpretation where mechanical erosion and chemical weathering yielded first cycle mature quartz arenites (Witzke, 1980).

The Cartoogechaye terrane (CT) is an enigmatic migmatite terrane within the Central Blue Ridge province of the southern Appalachians. Previous work identified exotic Pb isotope compositions within the CT (Quinn, 2012). More recent studies that mapped the extent of potentially exotic metaigneous lithologies yield U-Pb zircon ages consistent with a native Laurentian margin metasedimentary origin (Larkin, 2016). This study focused on the possible extent of similar lithologies in the Clyde quadrangle and provides further constraints on the crustal affinity of the CT. The Clyde quadrangle consists of four distinct lithologic packages: the CT, Ashe metamorphic suite, Great Smoky Group, and Grenville basement. Five samples within the Clyde quadrangle and one sample from Wayah Bald quadrangle were collected for detrital zircon (DZ) U-Pb geochronology and whole rock geochemistry for comparison similar anlayses from other bedrock units in the region. Dominant DZ age modes consist of the Grenville doublet (1050 Ma and 1150 Ma) or a modified version of it. Minor age modes exist at ~450 Ma, 600-750 Ma, and 1300-1550 Ma. Zircons for all but one sample display heterogeneous external and internal cathodoluminescence morphologies, consistent with a sedimentary protolith for the paragneisses. Whole rock compositions are consistent with weathering of and derivation from a local basement source. U-Pb age data are most consistent with an eastern Laurentian sedimentary provenance for five samples. The presence of 450-460 Ma grains is most consistent with high-grade Taconian regional metamorphism. The lack of a major Shawinigan age mode and zircon morphology for ca. 980-1050 Ma metamorphic zircons indicate that sample CLY16-1 is a syn-orogenic metasediment within the Grenville basement underlying the CT.