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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Using Detrital-Zircon Geochronology and (U-Th)/He Thermochronology to Re-evaluate the Triassic-Jurassic Tectonic Setting of Northern Laurentia, Canadian Arctic

Midwinter, Derrick January 2016 (has links)
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.
2

Tectonic evolution of northern Ellesmere Island: insights from the Pearya Terrane, Ellesmerian Clastic Wedge And Sverdrup Basin

Malone, Shawn Joseph 01 December 2012 (has links)
The tectonic evolution of northern Ellesmere Island is dominated by the accretion of the Pearya Terrane and the progressive reworking of materials from the Pearya Terrane and the northern Caledonides. Geochronology from a suite of seven Succession I orthogneiss samples defines a range of earliest Neoproterozoic ages from 962 ± 6 Ma to 974 ± 8 Ma. Geochemistry of both zircon and whole rock samples reveal a complex magmatic history tapping multiple sources. The rocks include both I and S type granitoids, with silica contents ranging from 62% to 73%. Trace element geochemistry reveals LILE enrichment decoupled from low to depleted HFSE values, suggestive of an origin above a subduction zone. Isotope geochemistry supports input from juvenile and evolved materials, with εNd(i) values between -1 and -4.6, and a similar range for εHf from zircon. The northern elements of the Caledonian Orogen preserve a record of magmatism in the c. 985 Ma to 920 Ma range. These ages are also observed in orthogneiss units of the south central Brooks Range and Farewell terrane, Alaska. The Pearya Terrane orthogneiss units and those currently dispersed in Alaska are interpreted to have originated near or on the eastern margin of Greenland and record post-Rodinia assembly subduction outboard of the supercontinent. Succession II (Trettin, 1987) of the Pearya Terrane represents variably metamorphosed metasedimentary rocks of Proterozoic to early Paleozoic age. These units are structurally juxtaposed with Succession I orthogneiss and Paleozoic sedimentary units of the Pearya Terrane. Detrital zircon age spectra from seven samples of Neoproterozoic meta-sedimentary rocks reveal three groups defined by observed dominant age peaks and youngest observed age populations. Group I includes three quartzite samples and contains numerous c. 1100 Ma to 1800 Ma peaks, with the youngest population at c. 1050 Ma. Two samples of immature meta-sandstone form Group II, defined by a dominant c. 970 Ma age peak. Two samples from the diamictite unit below the Deutchers Glacier thrusts form Group III, with a similar pattern of c. 1000 Ma to 1800 Ma age peaks to Group I; however, this group includes a small population of c. 600 Ma to 700 Ma grains as well. The ubiquitous Mesoproterozoic ages reflect a Grenvillian-Sveconorwegian provenance. These data are consistent with detrital zircon datasets from other North Atlantic-Arctic Caledonide terranes, reinforcing stratigraphic links between the Pearya Terrane and the northern Caledonides. The utility of the Pearya Terrane dataset is multiplied by probable links to Circum-Arctic and Cordilleran terranes, many of which contain similar populations of Mesoproterozic-aged detrital zircon. U/Pb ages and Hf isotopic data from detrital zircon suites sampled from Ordovician to Carboniferous sedimentary rock of the Pearya Terrane and northern Ellesmere Island record define the background for terranes translating along the northeastern Laurentian margin in the Paleozoic. Ordovician to Silurian clastic sediments deposited on the Pearya Terrane record pre terrane accretion provenance dominated by recycling of the metaigneous and metasedimentary Proterozoic basement as well as an Ordovician arc source. The provenance of Late Devonian sediments deposited during the Ellesmerian Orogen is dominated by similar recycled materials, with new sources derived from Paleoproterozoic domains of the Canadian-Greenland shield and documented late Devonian granitoids emplaced the Canadian Arctic Islands and Arctic Alaska. The basal Sverdrup Basin records increasing proportions of Paleoprtoerozoic and Archean aged grains relative to Mesoproterozoic ages, suggestive of increased contributions from the Laurentian craton and no little detritus exotic to Laurentia. Detrital zircon age spectra from Devonian to Carboniferous sediments in the northern Cordilleran clastic wedge and western Canadian Arctic Islands contain abundant exotic zircon likely derived from the Caledonian and Timanian Orogens. This variance of sediment provenance indicates that the eastern Canadian Arctic Island were isolated from non-Laurentian or Caledonian detritus, and that sources of the exotic Timanian zircon reconstruct farther west along the margin.

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