Middle-Late Ordovician Mt. Wilson Quartzite, southern British Columbia, Canada, is a supermature quartz arenite deposited in shallow marine-marginal marine environments on the Early Paleozoic western Laurentian passive margin. Facies-stacking patterns indicate the Mt. Wilson Quartzite is an unconformity bounded, 2nd-order depositional sequence, containing two 3rd-order sequences, and numerous parasequences. Detrital zircon age spectra of six samples of the Mt. Wilson Quartzite have numerous peaks that are unique to Middle to Late Ordovician quartz arenites of western Laurentia. The main peaks, 1800-2000 Ma, 2000-2200 Ma, and 2300-2400 Ma are interpreted to have been derived from basement rocks that were exposed east of the study area: Trans-Hudson Orogeny (1800-2000 Ma), Taltson Orogen (1800-2000 Ma), Buffalo Head Terrane (2000-2400 Ma), Paleoproterozoic crust (2000-2400 Ma), and the Wopmay Terrane (2000-2400 Ma). It is likely that these areas were sourced by local rivers and tributaries draining the Transcontinental Arch and delivered sediment to the deposition location of the Mt. Wilson Quartzite. While longshore transport was a viable distribution method for sediment along the passive margin, it is unlikely that the Peace River Arch (located northwest of the Mt. Wilson Quartzite) was its sole point source; rather it is more likely that there were multiple sediment sources for these western Laurentian quartz arenites. Temporal changes in provenance indicate different areas of basement rock were exposed throughout the deposition of the Mt. Wilson Quartzite, most likely reflecting long-term flooding of North America. The potential for spatial changes in provenance remains unsolved.

Thesis (Ph.D.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Mar. 8, 2010). Includes bibliographical references.

South America provides an outstanding laboratory for studies of magmatism and crustal evolution because it contains older Archean-Paleoproterozoic cratons that amalgamated during Mesoproterozoic and Neoproterozoic supercontinent assembly, as well as a long history of Andean magmatism that records crustal growth and reworking in an accretionary orogen. We have attempted to reconstruct the growth and evolution of South America through U-Pb geochronology and Hf isotope analyses of detrital zircons from 59 samples of sand from modern rivers and shorelines. Results from 5,524 new U-Pb ages and 1,199 new Hf isotope determinations are reported. We have also integrated our data into a compilation of all previously published zircon geochronologic and Hf isotopic information, yielding a record that includes>42,000 ages and>1,600 Hf isotope analyses. These data yield five main conclusions: (1) South America has an age distribution that is similar to most other continents, presumably reflecting the supercontinent cycle, with maxima at 2.2-1.8 Ga, 1.6-0.9 Ga, 700-400 Ma, and 360-200 Ma; (2)<200 Ma magmatism along the western margin of South America has age maxima at 183 Ma (191-175 Ma), 151 Ma (159-143 Ma), 126 Ma (131-121 Ma), 109 Ma (114-105 Ma), 87 Ma (95-79 Ma), 62 Ma (71-53 Ma), 39 Ma (43-35 Ma), 19 Ma (23-15 Ma), and 6 Ma (10-2 Ma); (3) for the past 200 Ma, there appears to be a positive correlation between magmatism and the velocity of convergence between central South America and Pacific oceanic plates; (4) Hf isotopes record reworking of older crustal materials during most time periods, with incorporation of juvenile crustal materials at ~1.6-1.0 Ga, 500-400 Ma and ~200-100 Ma; and (5) the Hf isotopic signature of<200 Ma magmatism is apparently controlled by the generation of juvenile magmas during extensional tectonism and reworking of juvenile versus evolved crustal materials during crustal thickening and arc migration.

Originally mapped as Precambrian and uppermost Ocoee Supergroup (OS), recent discoveries of Paleozoic microfossils have placed the Walden Creek Group (WCG), eastern Tennessee, into a younger depositional framework (Silurian or younger). In this study, monazite geochronology using SIMs, detrital zircon U-Pb geochronology determined by LA-ICP-MS, feldspar compositions determined by microprobe, zircon-tourmaline-rutile (ZTR) indices, and framework mineral modes were used to characterize provenance of sandstones of the WCG. Monazite ages cluster at 450 and 1050 Ma. All Ordovician ages are from grains that, in BSE images, have inclusion-rich microtextures interpreted as diagenetic and/or metamorphic, thus requiring that the WCG was deposited prior to Taconic metamorphism. The WCG heavy mineral suite is similar to the OS in its low modal abundance of monazite, but contains a slightly higher ZTR index. WCG Feldspar compositions are sodium poor-Kfs and sodic plagioclase, like the OS. Detrital zircon U-Pb ages for three formations of the WCG (seven samples total, n = 620) match the Ocoee signature. The dominant age modes are at ca. 1000 and 1150 Ma, with smaller modes at 1450 and 650 Ma. The monazite ages and supporting observations prove the WCG is not Paleozoic and its source rock signature matches the underlying OS.

In light of the recent increase of mineral exploration in the northern Cordillera, private, educational, and governmental agencies have been compelled to revisit and research areas of the Cordillera whose geologic evolution still remains enigmatic. The current study is concerned with better understanding how a region of the boundary zone separating the peri-Laurentian realm from the exotic, Insular realm evolved following deposition of the meta-sedimentary Kluane schist in the Late Cretaceous. The schist is a northwest striking 30 km wide and 160 km long belt of highly deformed greenschist to amphibolite facies meta-sedimentary rocks located east of Kluane Lake, southwestern Yukon Territory. These deformed sediments as well as numerous other deformed Jurassic-Cretaceous meta-sedimentary units present along the same boundary zone (north and south of the schist) represent important rocks that can help constrain how this part of the Cordillera has evolved since the mid-Mesozoic. To better understand how the Kluane schist evolved, detailed field mapping, petrography, and U-Pb geochronological studies were undertaken in the area encompassing the schist. This data is integrated with pre-existing and recently collected geologic databases from the region to propose a model for the tectonic and structural evolution of the Kluane schist. Conclusions drawn from this study indicate the Kluane sediments were likely deposited into a closing Late Cretaceous seaway from sources derived from Yukon-Tanana terrane (YTT) to the east. The basin into which the sediments were deposited represents a remnant ocean basin that was present between Insular terrane and YTT prior their amalgamation in the Jurassic. Thrusting of YTT over the Kluane schist basin resulted in burial, metamorphism, and ductile deformation of the schist. Contemporaneously, the early stages of the Ruby Range batholith (RRB) were intruding the schist as well as the schist/YTT contact. This batholith intruded syn- to post-tectonically from approximately ca. 77 Ma to 65 Ma and it is responsible for imparting a kilometer scale inverted contact metamophic aureole onto the Kluane schist wherein metamorphic grade decreases to the southwest. Subsequently, a gneissic sub-unit of the Kluane ‘schist’ was formed by partial melting of the RRB/Kluane schist contact. During this composite deformation event, the schist was transported to mid-crustal depths by an oblique sinistral shear zone. Shortly thereafter, the schist was exhumed and deformed by consistent northeast-over-southwest shearing. Regional scale, broad open folding of the schist ensued and likely occurred by flexural slip along foliation planes with low cohesion. Two syn- to post- tectonic igneous phases associated with Hayden Lake intrusive suite have been dated to ca. 55 Ma. This timing likely correlates with broad, open folding and a ‘late’ syn- to post-kinematic thermal overprint of the schist. The combined results of this study indicate that deformation and metamorphism of the Kluane schist was a long-lived event, extending from ca. 82 Ma to ca. 55 Ma.

This thesis investigates the morphological, chemical and growth characteristics of zircon mineral in relation with the granitoid petrology. Physical and chemical variations recorded within zircon crystals during evolution of the Central Anatolian Granitoids are discussed. The thesis focuses on twelve granitoid samples from the Ekecikdag, Aga&ccedil / &ouml / ren and Terlemez regions from western part of central Anatolia. These granitoids are differentiated into S- and H-type granitoids on the basis of field, petrographical and whole-rock geochemical aspects. In granitoids concerned, zircon is associated with biotite, allanite and plagioclase, and zircon populations mainly comprise P- and S-type zircon crystals, with rare G-, L- and J-types. Typology method combined with cathodoluminescence imaging revealed that S- and H-type granitoids show intrusive aluminous autochthonous and hybrid character, respectively. Zircons generally have euhedral to subhedral cores exhibiting zoning, although sometimes faint, but inherent and embayed cores also exist. Large scale, first order, and/or small-scale second order oscillatory zoning and effects of late stage recrystallization are observed within zircon crystals. Multi-corrosion zones within zircons are characterized by sharp changes in crystal forms with decreased Zr and Si, and increased U, Th and REE+Y contents, beside infrequent increase in Hf, Sc, Ta, Ti, Ca, Al and Fe elements. These zones are interpreted to be formed by transient heating of the resident felsic magma due to mafic melt contribution, at the time of mixing/mingling processes of the H-type granitoids, and then zircons re-grow in magma source reflecting a mafic character. Corrosion stages within zircons of S-type granitoids, on the other hand, were probably formed by mantle-derived melts producing heat for resorption of zircons without direct contribution.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

There are two industrial sources of zirconia: zircon and baddeleyite [1-5]. The baddeleyite reserves in Phalaborwa (the world’s major baddeleyite source) are expected to be depleted by the year 2005 [1-3]. This leaves the Russian Baddleyite (Kola Peninsula) and zircon as the only industrial sources of zirconia. The major drawback to zircon use is the large amounts of impurities it is found concentrated with, especially radioactive impurities (Uranium and Thorium) [2-3]. Acid leaching of zircon does not remove these impurities [4-5]. The impurities are usually included in the zircon lattice. The tetragonal structure of zircon with the high coordinated bisdisphenoids ZrO8 and low coordinated tetrahedra SiO4 create a safe (inaccessible and stable) habitat for these impurities [7]. Processes for the recovery of zirconia and zirconium chemicals rely heavily on precipitation or cyrstallisation techniques for purification [8-16]. Precipitation techniques need to be repeated to obtain the required purity. The purity of products from such methods is still suspect, as there still remains a high radioactivity content after purification [2]. The long process time is another disadvantage of these precipitation processes. These factors together are the reason for the high cost of zirconia and zirconium chemicals. Zirconium and its compounds are regarded to be of low toxicity [1-6]. This implies that they have a great potential of replacing numerous high toxic chemicals. Prominent examples are seen in leather tanning and paints. In leather tanning chromium chemicals can be replaced. In paints lead driers and chromium chemicals for corrosion resistance can be replaced. The objective of this study was to characterise and optimise the De Wet’s zirconium extraction processes for the beneficiation of zircon sand into high purity zirconia and zirconium chemicals. However, at each process step some factors were varied e.g. fusion temperature, reactant mole ratios and composition of leach solutions. Attention was also paid to reducing the total number of process steps. The products produced at each step were analysed. Particular attention was given to the fate of the radioactive impurities. Characterisation of the decomposition step, showed that within the zircon tetragonal structure, the SiO4 bisdisphenoids linkages. This was shown by the preference of sodium for the SiO4 tetrahedra. Fusion for 336 hours with periodic intermediate milling proved the preference of sodium for attacking the SiO4 tetrahedra linkages. This selectivity was clearly demonstrated when decomposing zircon in sodium poor(<4 moles NaOH per mol of zircon) and low temperature (e.g. 650°C) reaction conditions. The advantage of fusing at 650°C with a mole (or even two moles) of sodium hydroxide is that it leads to minimal (<5% m/m Na2O) sodium in the insoluble solids after the removal of soluble silicates. This is a solution to alkali fusion processes, as high amounts of water are usually required to wash out the neutralised sodium salt e.g. 50g of NAC1 usually requires a litre of distilled water to reach levels below 600 ppm NA2O. This reaction condition can be employed when synthesising products where low amounts of sodium are required in the final products e.g. when synthesising zirconia for the ceramic industry. When fusing for two hours without the intermediate milling step the following results were observed. The reaction at 850°C when fusing a mole of zircon with two moles of sodium hydroxide, was the most efficient in consuming sodium hydroxide. Near complete zircon decomposition was at 850°C when fusing a mole of zircon with six moles of sodium hydroxide. Characterisation with XRD, Raman and IR spectroscopy was misleading as complex spectra were measured, indicating many different phases present. The inconsistency was partly attributed to non-homogeneity in the samples due to NaOH migration. When fusing for 336 hours with the intermediate milling step the following results were observed. The reaction at 850°C when fusing a mole of zircon with a mole of sodium hydroxide was the most efficient in consuming sodium hydroxide. This reaction condition was able to liberate 0.58 moles of zirconia per mole of sodium hydroxide. The highly improved efficiency was attributed to the formation of phases Na2ZrSiO5, Na4Zr2Si3O12 and SrO2. The process is pseudo-catalytic as it liberates zirconium while showing minimal sodium consumption. Decomposition at 650°C also showed improved efficiency but not as efficient as the 850°C sub-stoichiometric fusion. The improved decomposition was attributed to the polymerisation of the orthosilicate monomers Na4SiO4 to the metasilicate chains Na2SiO3. / Dissertation (MSc (Chemical Technology))--University of Pretoria, 2007. / Chemical Engineering / unrestricted

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 St. Lawrence Platform (SLP) and Humber Zone (HZ) of the southern Quebec Appalachians has historically been explored as a potential hydrocarbon reservoir. Extensive vitrinite reflectance studies on the basin resolved the degree of thermal maturation yet the timing of the thermal maximum is not well undertood. Determining the timing of such low temperature events can allow for a better understanding of the shallow crustal processes that may have allowed for the generation and entrapment of oil and gas. We have employed apatite (AHe) and zircon (ZHe) (U-Th)/He thermochronmetry across a network of late Cambrian to late Ordovician siliciclastic and Grenvillian basement samples in order to resolve the history within the ~210-35°C window. Single crustal dates from individual samples show age dispersion by as much as 300 m.y. with a strong positive to negative correlation with increasing eU concentration. A similar positive correlation can be observed when significant intra-sample grain size variation is present. AHe and ZHe data in the southwestern portion of the basin, near Montreal, allow for thermal maxima of up to 200°C to occur either during the late Ordovician, as a result of the Taconic orogeny, or from the continued sedimentation into the Devonian as a result of the Acadian orogeny. Regional burial trends deduced from these thermal maxima along with local paleo-geothermal gradients indicate that if sedimentation continued after the late Ordovician there was no significant increase in burial in southwestern portion of the SLP as previously suggested. Maximum heating is followed by a protracted cooling through the ZHe partial retention zone (PRZ) into the late Jurassic and early Cretaceous where the cooling rate increases by an order of magnitude through the AHe PRZ until ca. 100 Ma. The timing of this accelerated cooling is coeval with the passage of the Great Meteor Hot Spot across the area; the cooling may be a result of increased erosion from thermal uplift. Within the HZ, both the external and internal sections experienced rapid cooling through the Silurian after the Taconic thermal maximum. The timing of relatively rapid cooling coincides with documented normal faulting and back-thrusting in the orogen, which is the likely cause of exhumation. The HZ witnessed protracted cooling through the late Jurassic, when there is a one order of magnitude increase in cooling rate until surface conditions are attained. Increased recognition of these low temperature events has augmented our understanding of the evolution of accretionary orogens and consequently reduces the risks associated with oil and gas exploration.