Part of the Slave Structural Province, the Hope Bay Greenstone Belt is a 82 km long north-striking sequence of supracrustal rocks dominated by mafic volcanic rocks with lesser felsic volcanic and sedimentary rocks. Mapping of two transects in the southern section and two transects in the northern section have contributed to a robust stratigraphic framework the belt. Three recently discovered Archean lode gold deposits in the Hope Bay Greenstone belt have associations with major structures and specific lithologies (Fe-Ti enriched basalts). The Flake Lake and the Clover Transects are in the southern part of the belt and the Wolverine and Doris-Discovery Transects are in the northern part of the belt. This work subdivides the volcanic rocks into distinct suites based upon field, petrologic, geochemical, and geochronologic criteria. Some of the suites are stratigraphically continuous and can be correlated tens of kilometres along strike thereby linking the two parts of the Hope Bay Greenstone Belt. U-Pb geochronology supports work by Hebel (1999) concluded that virtually all the supracrustal rocks in the Hope Bay Greenstone Belt were deposited over at least 53 m.y. (2716-2663 Ma), with the majority of the volcanism occurring after 2700 Ma. A number of basalt groups are identified and include the normal basalt, the LREE-enriched basalt, the Ti-enriched basalt and the Ti-enriched Al-depleted basalt groups. They have chemical signatures that vary in trace elements particularly HFSE and REE’s, and can be easily be distinguished by geochemical screening. The felsic volcanic suites are also divided into three main groups, tholeiitic rhyolite, calc-alkaline dacite and calc-alkaline rhyolite groups. Nd and Hf isotope signatures are consistent with trace element signatures in identifying mafic and felsic volcanic groups, with the tholeiitic rhyolite showing highly variable signature. The Hope Bay Greenstone Belt has been show to have a number of felsic and volcanic cycles. An early construction phase of the belt is made up of primarily mafic volcanics which is followed by felsic volcanism equalled mafic volcanism which lacks basalts enriched in Ti. The geodynamic environment that created the Hope Bay Greenstone Belt can be explained by plume influenced subduction zone. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

This study utilised U-Pb geochronology, and 40Ar/39Ar and (U-Th)/He thermochro-nology to delineate arc magmatism, metamorphism, and exhumation of the pericratonic Yukon-Tanana terrane in the McQuesten map area of west-central Yukon, Canada. SHRIMP U-Pb ages delineate Mid to Late Paleozoic arc magmatism and fit key units into the regional lithotectonic framework of the terrane. The juxtaposition of unmetamorphosed and predomi-nantly undeformed Devono-Mississippian rocks in the northwest of the study area with polydeformed and up to amphibolite facies metamorphosed rocks in the southwest suggests a crustal-scale discontinuity, the Willow Lake fault, bounds the two domains. The asymmetric distribution of 40Ar/39Ar ages across the fault suggest it is extensional, and was active in the Early Jurassic. Zircon (U-Th)/He ages delineate erosion of rocks in the northwest through the upper crust during the Late Triassic and Late Jurassic to Early Cretaceous followed by Mid-dle Cretaceous erosion of the southwestern domain and possibly fault reactivation.

New geochronological and field data were examined from Triassic-Jurassic strata in the Sverdrup Basin, Arctic Canada. Detailed analysis of detrital-zircon data identified a pronounced near-syndepositional age-fraction in Triassic strata, which significantly is absent in Jurassic strata of the Sverdrup Basin suggesting a protracted history of magmatism and sediment dispersal from areas north of the basin during the Triassic. However, as a result of rifting, during the Early Jurassic, the northern source region became disconnected from the Sverdrup Basin, and opened the precursor basin (Amerasia Basin) to the Arctic Ocean. Jurassic rifting of the Amerasia Basin would have had associated rift-flank uplift. Time-temperature models produced from zircon (U-Th)/He thermochronological data elucidate the unknown thermal history between the regional Devonian-Cretaceous unconformity in the southwestern Canadian Arctic suggesting ~4 km of addition deposition on Banks Island and ≤1 km of deposition towards the craton interior.

The Sibiel Shear Zone is a 1-3km wide, ductile shear zone located in the South Carpathian Mountains, Romania. In the Rsinari area, the ductile shear zone juxtaposes amphibolite facies rocks of the Lotru Metamorphic Suite against greenschist facies rocks of the Rauorul Cisndioarei Formation. The first represents the eroded remnants of Peri-Gondwanan arcs formed between the Neoproterozoic-Silurian (650-430Ma), regionally metamorphosed to amphibolite facies during the Variscan orogeny (350-320Ma). The second is composed of metasedimentary and metavolcanic Neoproterozoic-Ordovician (700-497Ma) assemblages of mafic to intermediate bulk composition also resembling an island arc metamorphosed during the Ordovician (prior to similar to 463Ma). Between these lie the epidote amphibolite facies mylonitic and ultramylonitic rocks of the Sibisel Formation, a tectonic melange dominated by mafic actinolite schists attenuated into a high strain ductile shear zone. Mineral Rb-Sr isochrons document the time of juxtaposition of the three domains during the Permian to Early Triassic (similar to 290-240Ma). Ductile shear sense indicators suggest a right lateral transpressive mechanism of juxtaposition; the Sibiel shear zone is a remnant Permo-Triassic suture between two Early Paleozoic Gondwanan terranes. A zircon and apatite U-Th/He age transect across the shear zone yields Alpine ages (54-90Ma apatite and 98-122Ma zircon); these data demonstrate that the exposed rocks were not subjected to Alpine ductile deformation. Our results have significant implications for the assembly of Gondwanan terranes and their docking to Baltica during Pangea's formation. Arc terranes free of Variscan metamorphism existed until the Early Triassic, emphasizing the complex tectonics of terrane amalgamation during the closure of Paleotethys.

The Saglek-Hebron Complex (SHC) in Northern Labrador represents one of the oldest terrains on Earth and it is closely related to the Archean Itsaq Gneiss Complex (IGC) in Greenland. The SHC is a typical granite-greenstone terrain that recorded over one billion years of magmatic history between ~3900 Ma and ~2700 Ma. Our geochronological and geochemical study shows that the SHC includes five generations of trondhjemite-tonalite-granodiorite suites (TTG): the ~3870 Ma Iqaluk gneiss, the ~3750 Ma Uivak I gneiss, the ~3600 Ma Uivak II gneiss, the newly described ~3300 Ma Iluilik gneiss, and the ~3220 Ma Lister gneiss. These granitoid units are mostly consist of trondhjemite and tonalite with only rare granodiorites that appear to define a distinct unit formed at ~3330 Ma and newly defined as the Iluilik gneiss. The Iluilik granodiorite appears to be derived from a Hadean mafic crust as supported by its combined whole-rock geochemical composition, its positive µ142Nd value of +6, and its low εHf= -6 and εNd= -3, at 3300 Ma. SHC granites were emplaced throughout the Archean, from 3800 to 2700 Ma, but are predominant in the Neoarchean. They appear to have been mainly formed from the reworking of the SHC TTG, as supported by their low εHf and εNd initial values of respectively -16 and -11 at 2700 Ma. The granitoids include numerous enclaves of supracrustal rocks from various size, up to a few kilometers in scale, consisting of metavolcanic metasedimentary rocks. Previous work has suggested that they were formed at two different ages, with the younger Upernavik supracrustal unit deposited around 3400 Ma and the older Nulliak supracrustal assemblage deposited at around 3750 Ma. We show that both units are comparatively geochemically homogeneous with no distinction between the mafic and ultramafic rocks from both supracrustal assemblages. They mainly consist of mafic metavolcanic amphibolites with tholeiitic affinities, consistent with more depleted mafic and more enriched compositions produced by magmatic differentiation. Their complementary Eu anomaly and whole-rock geochemistry suggest that they formed from fractional crystallization of gabbroic assemblage that derived from similar if not the same parental magma. The mafic metavolcanic rocks are also often associated with ultramafic rocks that we divided into two distinct units, respectively referred as the high-Fe and the low-Fe ultramafic rocks, characterized by different FeO contents and Al/Ti ratio. They both represent olivine-rich cumulative rocks derived from distinct parental komatiitic basalt magmas. Our interpretation contrasts with previous work suggesting that the SHC ultramafic rocks were komatiites and slivers of residual lithospheric mantle. Most SHC TTG exhibit a positive 142Nd anomaly, as high as µ142Nd = +15, suggesting a source formed by differentiation in the Hadean. This 142Nd isotopic composition is similar to the Nulliak supracrustal rocks that exhibit on average a µ142Nd of +10. TTG is generally considered to derive from a mafic precursor. This study therefore shows that mafic crustal source of the SHC Eoarchean TTG, potentially the Nulliak metabasalts, derives from an ancient highly depleted mantle, described as the Saglek mantle, sharing a similar early history as the mantle reservoir involved in the formation of the ancient Itsaq terrane of southwest Greenland. The Saglek depleted mantle is interpreted to have formed at ~4400 Ma, exhibit highly depleted signature with a 147Sm/144Nd ratio of 0.221-0.240.

The Oligocene-Miocene Maikop Series in the South Caspian and Kura Basins is the key petroleum source rock for both offshore and onshore petroleum development in Azerbaijan. The Maikop is a thick (up to 3 km) succession of silty mudstones containing up to 15% total organic carbon (TOC), but is greatly lacking diagnostic microfaunal assemblages useful for dating and stratigraphically constraining the deposition of the mudstone. Current stratigraphic constraints relying on microfaunal assemblages, radiostratigraphy, and chemostratigraphy are robust, but key information is still missing. This study adds numerical age data to Maikop stratigraphy through Re-Os geochronology. Of five sample suites analyzed from the Kura Basin of eastern Azerbaijan, one Re-Os data set produced significant range in 187Re/188Os vs 187Os/188Os space to yield an isochron of 17.2± 3.2 Ma. Other sample suites yield imprecise Re-Os age constraints as a result of variable initial 187Os/188Os values and limited range in 187Re/188Os vs 187Os/188Os space. The initial 187Os/188Os values of these data sets were compared with the known 187Os/188Os of seawater values for the past 70 million years to provide the best qualitative age constraints. Pre-Maikopian strata studied at Perikeshkul was found to coincide in 187Os/188Os values with the Eocene-Oligocene Transition (EOT) Os excursion, indicating deposition initiation of Maikopian strata following the EOT. Preservation of organic matter in intervals with initial 187Os/188Os values that deviate significantly from global 187Os/188Os values indicate basin restriction and the development of anoxia. High Os abundances, enrichment in detrital elements Al, Ti, Ga, Sc, and La, and changing basin circulation during the deposition of Maikop strata at 17.2 Ma may indicate the initial episodic uplift of the Greater Caucasus Mountains, changes in sediment provenance, or changing proximity to sediment source.

The transition from the end of the Ordovician to the beginning of the Silurian Period is characterized by the glaciation of the Gondwana paleocontinent, eustatic sea level change, a perturbation to the global carbon cycle and one of the ve major mass extinctions of the Phanerozoic Eon. Due to signi cant sea level fall, the Ordovician-Silurian (O-S) boundary is often marked by hiatus and exposure in the shallow marine geologic record (e.g., Copper et al. [2013]). Two locations that host stratigraphic succession close to the boudary are Anticosti Basin of Quebec (Canada, e.g., Desrochers et al. [2010]), and the carbonate mounds of the Siljan ring district (Dalarna County, Sweden, e.g., Ebbestad et al. [2015]). The exact timing and dynamics of the glaciation and mass extinction are yet to be understood. Similarly, the interplay between those events and the carbon cycle perturbation are still unclear. As a result, there is a serious need for radiometric age constraints in this crucial part of the Paleozoic Era. The acquisition of more radiometric dates, achieved in this study, aims to address the present dearth of absolute dates close to the boundary. The dates produced in this study represent the first modern geochronologic constraints on the O-S boundary, leveraging the development of the EARTHTIME initiative and the latest U-Pb dating techniques that have improved accuracy and allowed for dating of single zircon crystals at <=0.1% precision level. Here I present two new U-Pb zircon ages obtained via bentonite dating. The first bentonite, 443.61+-0.52 Ma (2, including analytical, tracer calibration and decay constant uncertainties) was collected from the base of the Lousy Cove Member, Ellis Bay Formation (Anticosti Island, Quebec, Canada). The second one, 443.28+-0.50 Ma (including analytical, tracer calibration and decay constant uncertainties) comes from a karstic void within the Boda Core Facies of the Boda Formation (Dalarna County, Sweden). U-Pb geochronology (chemical abrasion, isotope dilution, thermal ionization mass spectrometry: CA-ID-TIMS) on single zircons was used to obtain these ages. These results are the closest radiometric ages to the current O-S boundary (compared to any time constraints in the 2012 Geologic Time Scale) and allow to signifcantly reduce the uncertainty of the current age boundary (443.8+-1.5, Cohen et al. [2018]). Furthermore these absolute ages have been used to make models that explore drivers of Earth system change, such as an end-Ordovician global carbon cycle perturbation. / Graduate / 2022-07-07

The Golo River in Corsica, France, is a short, steep river (~95 km, 2706 m relief) in the Western Mediterranean with formerly glaciated headwaters. The small size and location of the Golo River make this system ideal for observing the influence of climate and sea-level change on river dynamics over the 100,000 years. A rapidly advancing dating technique, optically stimulated luminescence, was utilized to determine the timing of these river deposits on the coastal plain in order to frame them in the context of previous glacial and interglacial episodes. Climate fluctuations in the headwaters supplied the vast majority of sediment into the system during glacial time periods, which was then transported and deposited near the mouth of the Golo River on the coastal Marana Plain. Sea- level also played a vital role in defining a geometric configuration that ultimately governed whether large amounts of sediment stored onshore or offshore. Analysis of the Golo River longitudinal profile and watershed reveals changes in steepness and gradient that are related to changes in rock type, fault movement and tectonically-driven base-level fall.

abstract: Establishing the timing of impact crater formation is essential to exploring the relationship between bolide impact and biological evolution, and constraining the tempo of planetary surface evolution. Unfortunately, precise and accurate impact geochronology can be challenging. Many of the rock products of impact (impactites) contain relict, pre-impact phases that may have had their isotopic systematics completely reset during the impact event, only partially reset, or not reset at all. Of the many isotopic chronometers that have been used to date impactites, the U/Pb zircon chronometer (ZrnPb) seems least susceptible to post-impact disturbances, and ZrnPb dates are typically much more precise than those obtained using other chronometers. However, the ZrnPb system is so resistant to resetting that relict zircons in impactites often yield dates that reflect the igneous or metamorphic ages of the target rocks rather than the age of the impact itself. The present study was designed to answer a simple question: is there a straightforward sample collection and analysis strategy for high-accuracy ZrnPb dating of an impact structure if the impactites collected from it may contain inherited zircons? To study this, ZrnPb dates were determined for impactites from a single crater with a well-constrained impact age: the West Clearwater Lake impact structure, located at Lake Wiyâshâkimî, Québec, Canada. The amount of ZrnPb resetting and the mechanisms responsible for resetting varied amongst the samples. Each sample characteristically contained either: newly crystallized zircons from the impact melt ("neocrystalline"), relict zircons ~50-100% reset, or, relict zircons ~0-50% reset. The variably reset relict zircons define a discordia line from ~2700 Ma to ~286 Ma – consistent with the ages of the target rock and the impact, respectively (Schmieder et al., 2015a; Simard, 2004). ZrnPb measurements from the neocrystalline zircons provided a new preferred impact age of 286.64 ± 0.35 Ma (2σ), a ~10x improvement in precision. The characteristics of the West Clearwater ZrnPb data vary between samples yet become easily interpretable as a whole, showing that efforts to measure robust, precise impact ages benefit from strategies that prioritize applying multiple analytical techniques to multiple types of impactite from the same crater. / Dissertation/Thesis / Masters Thesis Geological Sciences 2019

Indiana University-Purdue University Indianapolis (IUPUI) / A broad range of samples were collected from the Huron-Erie Lobe, Lake Michigan Lobe, Saginaw Lobe, and Tipton Till Plain of northern Indiana to determine the provenance of Laurentide Ice Sheet till in the Midwest U.S. during the Illinoian and Wisconsinan glaciations. U-Pb age distributions from approximately 300 detrital zircons (DZ) were used as provenance indicators for each till sample. Till from the Lake Michigan Lobe and was found to be largely homogenized. The distinct lobe DZ age distributions are the Lake Michigan Lobe till with a dominant ~1465 Ma peak, the northern Huron-Erie Lobe till with a dominant ~1060 Ma and a secondary peak at ~1450 Ma, the southern Huron-Erie Lobe till with nearly equal peaks at ~1435 Ma, ~1175 Ma, and ~1065 Ma, and the southern Saginaw Lobe till with a dominant peak at ~1095 Ma. Those four DZ age distributions were treated as endmembers in a nonlinear least-squares mixing model to calculate the contribution of each lobe to till in the Tipton Till Plain. Huron-Erie and Saginaw lobe tills were found to be the primary components of the Tipton Till Plain, and Lake Michigan Lobe till was only found in the western Tipton Till Plain. Zircons from the Saginaw Lobe till increased 39 % in the eastern Tipton Till Plain between the Illinoisan and Wisconsinan glaciations. The mixing model was also applied to relate the DZ age distributions of the lobes to bedrock within and near their flow paths. When comparing nearby bedrock to each lobe’s till, mixing model results, yield an approximate maximum transport distance between 500 and 630 kilometers for the matrix vii fraction of till in the Lake Michigan, Huron-Erie, and Saginaw lobes. Samples for the southern Huron-Erie Lobe indicate that the most of the zircon ages within the southern Huron-Erie Lobe till in Indiana were specifically entrained between Niagara County, New York and east-central Indiana. Within the model’s error, 93 – 100 % of the detrital zircons in each of the three lobes are relatable to nearby Paleozoic and Precambrian sedimentary and metamorphic bedrock formations.