D.Sc. (Geology) / Please refer to full text to view abstract

M.Sc. (Geology) / Please refer to full text to view abstract

Investigations in the northwestern part of the Willyama Complex centred on the Mt Franks - Mundi Mundi area have established a 4 km thick stratigraphic section of conformable metasediments containing thin horizons of basic volcanics in the lower two - thirds of the sequence. Establishment of this sequence was only possible once it was shown that the dominant lithological layering in metasediments is bedding, and that there has been no mesoscopic transposition during deformation. The metasediments represent a sequence of clay sands deposited in a distal shelf-slope or basin type of environment. A sequence of deformational and metamorphic events established in these rocks is regarded as an expression of the Middle Proterozoic Olarian Orogeny ( c.1695 - 1520 Ma. ) and except for some reactivation of shear zones, predate deposition and deformation of the unconformably overlying Adelaidean sediments. The important D₁ deformation is a complex, progressive event with pre-S₁ static mineral growth (biotite, andalusite, sillimanite, white mica) and early minor micro-folding recognized before syn-S₁ growth and F₁ folding. An even earlier period of pre-S₁ fabric formation mainly defined by white mica, biotite and ilmenite, is not related to any visible folding and may either represent an earlier discrete event or an early phase of the D₁ event, However, as now defined, minerals outlining this pre-S₁ fabric are related to the D₁ event. The low, medium and high grade metamorphic zones defined in the field by biotite, andalusite and sillimanite respectively are pre-S₁ in age and predate F₁ folding. The intensity of metamorphism increases with depth so that there is a broad depth control on metamorphism. Relations at the andalusite/sillimanite isograd conform to a Carmichael (1969) type model and reactions took place via an intermediate sericite phase. The main effect of F₁ folding is the formation of the variably plunging variably oriented Kantappa - Lakes Nob Syncline of regional extent. Only the western limb of this fold is now visible over much of its length. This fold deforms existing metamorphic zones and thus controls the relationship of low, medium and high grade rocks in this part of the Willyama Complex. The orientation of this syncline changes from vertical in the low grade rock to inclined at depth. The western limb becomes overturned at depth so that subsequent folds are downward facing. There is also a change in fold tightness with depth - from open-tight in the low grades to tight-isoclinal in the high grades, and this is accompanied by a change in S₀/S₁ relations (from core to limb area) from non parallel to parallel. These changes are coupled with a rotation of extension direction (mass transfer direction) from subvertical to inclined and may be explained by original formation and subsequent modification of upright F₁ folds. Later modifications are recorded by open folding and overturning of S₁ - this is ascribed to a final phase of the D₁ event. Mineral growth in D₁ time resulted in the formation of S₁ varying in grade from muscovite + quartz to sillimanite. S₁ varies from homogeneous to layered, and in the latter case, consists of M + QM layers,the spacing of which is controlled by F₁ microfolding. S₁ formation involved rotation, mass transfer, and volume decrease in M layers and (re) crystallisation. The D₂ event in this area was of only minor significance. The D₃ event developed in response to NW-SE shortening and resulted in the formation of variably plunging, vertical northeast trending folds. Where SW plunging, these folds lie subparallel to L₁. The nature of the D₃ event is controlled to a large extent by S₀ / S₁ relations and folding of S₁ across unfolded S₀ occurs where S₀ lies parallel to the XY plane of the D₃ event. S₃ formed as a muscovite + quartz schistosity by rotation, re crystallisation, mass transferand mimetic growth. During the final stages of the D₃ event, north-east trending retrograde schist zones were formed. These were later reactivated during the folding of the Adelaidean. The final phase of the Olarian Orogeny consists of minor D₄ folding and crenulation. / Thesis (Ph.D.) -- University of Adelaide, Department of Geology and Mineralogy, 1978.

The Central Asian Orogenic Belt (CAOB), the largest accretionary collage on the Earth, has a complicated and prolonged accretionary history which remains being highly debated. High-grade terranes were previously interpreted as Precambrian micro-continents which played a very important role during the evolution of the CAOB. However, some of their presumed old ages are challenged by recent high-resolution dating results which raise questions on their Precambrian origins. The Chinese Altai and Tseel Terrane in the SW CAOB, two typical high-grade terranes occupy vital structural positions, feature various lithological elements and exhibit complicated deformation-metamorphism patterns, making them key areas in the reconstructing of the evolution of central Asia. However, their origins are not firmly constrained. Paragneisses were considered as Precambrian basements, but yielded detrital zircon ages predominantly between 440 and 580 Ma. The associated granitic gneisses and amphibolite gave crystallization ages at 420-463 Ma. Geochemical and zircon Hf isotopic data of paragneisses support that their protoliths may represent significant erosion products of arc rocks that were developed in a subduction environment. This feature is similar with that of the associated low-grade volcanogenic schists which probably represent immature sediments in an active margin. Detrital zircons from the paragneisses and schists show similar age patterns, supporting derivation from similar provenance. Accordingly, our data reveal that these high-grade terranes do not represent Precambrian microcontinents. Moreover, the U-Pb age pattern for the detrital zircons, and some xenocrystic zircons from the associated granitoids, is comparable with the age patterns of the micro-continents and arc terranes in western Mongolia. The predominant zircon population of 440-580 Ma matches the widely distributed granitoids within the Neoproterozoic-early Paleozoic terranes in western Mongolia, while the minor Precambrian ages (>540 Ma) resemble those old rocks preserved in the Tuva-Mongolian (TM) block and its adjacent Neoproterozoic arc terranes. These features suggest that detrital and xenocrystic zircons more likely represent the detritus recycled from western Mongolia. Accordingly, the crustal growth of the SW CAOB in the early Paleozoic could be outlined by secular amalgamation of magmatic arcs around a Precambrian micro-continent. In addition, the TM-derived Precambrian zircons are further used to trace the origin of the TM block, which favors that the TM block was possibly rifted from the Indian block in the Neoproterozoic. Further efforts have been made to decipher the controversial tectono-metamorphic history. In the Chinese Altai, U-Pb dating on the metamorphic zircon portions yielded consistent ages of ~390 Ma. Temperature estimations using mineral-pair as well as Ti-in-zircon thermometers revealed high-temperature conditions up to ~720℃. Detailed investigations on the metamorphic rocks in the Tseel area revealed that middle-pressure metamorphic fabrics developed under progressive NNE-SSW convergent setting, possibly at 385-374 Ma. A later low-pressure/high-temperature metamorphic sequence developed during decompression, associated with high-level anatexis at 374-363 Ma. Collectively, our data support that the final amalgamation of North Mongolian Domain on its southern margin occurred at Middle-Late Devonian, and might be immediately followed by the subduction of an active oceanic ridge. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

Investigations in the northwestern part of the Willyama Complex centred on the Mt Franks - Mundi Mundi area have established a 4 km thick stratigraphic section of conformable metasediments containing thin horizons of basic volcanics in the lower two - thirds of the sequence. Establishment of this sequence was only possible once it was shown that the dominant lithological layering in metasediments is bedding, and that there has been no mesoscopic transposition during deformation. The metasediments represent a sequence of clay sands deposited in a distal shelf-slope or basin type of environment. A sequence of deformational and metamorphic events established in these rocks is regarded as an expression of the Middle Proterozoic Olarian Orogeny ( c.1695 - 1520 Ma. ) and except for some reactivation of shear zones, predate deposition and deformation of the unconformably overlying Adelaidean sediments. The important D₁ deformation is a complex, progressive event with pre-S₁ static mineral growth (biotite, andalusite, sillimanite, white mica) and early minor micro-folding recognized before syn-S₁ growth and F₁ folding. An even earlier period of pre-S₁ fabric formation mainly defined by white mica, biotite and ilmenite, is not related to any visible folding and may either represent an earlier discrete event or an early phase of the D₁ event, However, as now defined, minerals outlining this pre-S₁ fabric are related to the D₁ event. The low, medium and high grade metamorphic zones defined in the field by biotite, andalusite and sillimanite respectively are pre-S₁ in age and predate F₁ folding. The intensity of metamorphism increases with depth so that there is a broad depth control on metamorphism. Relations at the andalusite/sillimanite isograd conform to a Carmichael (1969) type model and reactions took place via an intermediate sericite phase. The main effect of F₁ folding is the formation of the variably plunging variably oriented Kantappa - Lakes Nob Syncline of regional extent. Only the western limb of this fold is now visible over much of its length. This fold deforms existing metamorphic zones and thus controls the relationship of low, medium and high grade rocks in this part of the Willyama Complex. The orientation of this syncline changes from vertical in the low grade rock to inclined at depth. The western limb becomes overturned at depth so that subsequent folds are downward facing. There is also a change in fold tightness with depth - from open-tight in the low grades to tight-isoclinal in the high grades, and this is accompanied by a change in S₀/S₁ relations (from core to limb area) from non parallel to parallel. These changes are coupled with a rotation of extension direction (mass transfer direction) from subvertical to inclined and may be explained by original formation and subsequent modification of upright F₁ folds. Later modifications are recorded by open folding and overturning of S₁ - this is ascribed to a final phase of the D₁ event. Mineral growth in D₁ time resulted in the formation of S₁ varying in grade from muscovite + quartz to sillimanite. S₁ varies from homogeneous to layered, and in the latter case, consists of M + QM layers,the spacing of which is controlled by F₁ microfolding. S₁ formation involved rotation, mass transfer, and volume decrease in M layers and (re) crystallisation. The D₂ event in this area was of only minor significance. The D₃ event developed in response to NW-SE shortening and resulted in the formation of variably plunging, vertical northeast trending folds. Where SW plunging, these folds lie subparallel to L₁. The nature of the D₃ event is controlled to a large extent by S₀ / S₁ relations and folding of S₁ across unfolded S₀ occurs where S₀ lies parallel to the XY plane of the D₃ event. S₃ formed as a muscovite + quartz schistosity by rotation, re crystallisation, mass transferand mimetic growth. During the final stages of the D₃ event, north-east trending retrograde schist zones were formed. These were later reactivated during the folding of the Adelaidean. The final phase of the Olarian Orogeny consists of minor D₄ folding and crenulation. / Thesis (Ph.D.) -- University of Adelaide, Department of Geology and Mineralogy, 1978.

Investigations in the northwestern part of the Willyama Complex centred on the Mt Franks - Mundi Mundi area have established a 4 km thick stratigraphic section of conformable metasediments containing thin horizons of basic volcanics in the lower two - thirds of the sequence. Establishment of this sequence was only possible once it was shown that the dominant lithological layering in metasediments is bedding, and that there has been no mesoscopic transposition during deformation. The metasediments represent a sequence of clay sands deposited in a distal shelf-slope or basin type of environment. A sequence of deformational and metamorphic events established in these rocks is regarded as an expression of the Middle Proterozoic Olarian Orogeny ( c.1695 - 1520 Ma. ) and except for some reactivation of shear zones, predate deposition and deformation of the unconformably overlying Adelaidean sediments. The important D₁ deformation is a complex, progressive event with pre-S₁ static mineral growth (biotite, andalusite, sillimanite, white mica) and early minor micro-folding recognized before syn-S₁ growth and F₁ folding. An even earlier period of pre-S₁ fabric formation mainly defined by white mica, biotite and ilmenite, is not related to any visible folding and may either represent an earlier discrete event or an early phase of the D₁ event, However, as now defined, minerals outlining this pre-S₁ fabric are related to the D₁ event. The low, medium and high grade metamorphic zones defined in the field by biotite, andalusite and sillimanite respectively are pre-S₁ in age and predate F₁ folding. The intensity of metamorphism increases with depth so that there is a broad depth control on metamorphism. Relations at the andalusite/sillimanite isograd conform to a Carmichael (1969) type model and reactions took place via an intermediate sericite phase. The main effect of F₁ folding is the formation of the variably plunging variably oriented Kantappa - Lakes Nob Syncline of regional extent. Only the western limb of this fold is now visible over much of its length. This fold deforms existing metamorphic zones and thus controls the relationship of low, medium and high grade rocks in this part of the Willyama Complex. The orientation of this syncline changes from vertical in the low grade rock to inclined at depth. The western limb becomes overturned at depth so that subsequent folds are downward facing. There is also a change in fold tightness with depth - from open-tight in the low grades to tight-isoclinal in the high grades, and this is accompanied by a change in S₀/S₁ relations (from core to limb area) from non parallel to parallel. These changes are coupled with a rotation of extension direction (mass transfer direction) from subvertical to inclined and may be explained by original formation and subsequent modification of upright F₁ folds. Later modifications are recorded by open folding and overturning of S₁ - this is ascribed to a final phase of the D₁ event. Mineral growth in D₁ time resulted in the formation of S₁ varying in grade from muscovite + quartz to sillimanite. S₁ varies from homogeneous to layered, and in the latter case, consists of M + QM layers,the spacing of which is controlled by F₁ microfolding. S₁ formation involved rotation, mass transfer, and volume decrease in M layers and (re) crystallisation. The D₂ event in this area was of only minor significance. The D₃ event developed in response to NW-SE shortening and resulted in the formation of variably plunging, vertical northeast trending folds. Where SW plunging, these folds lie subparallel to L₁. The nature of the D₃ event is controlled to a large extent by S₀ / S₁ relations and folding of S₁ across unfolded S₀ occurs where S₀ lies parallel to the XY plane of the D₃ event. S₃ formed as a muscovite + quartz schistosity by rotation, re crystallisation, mass transferand mimetic growth. During the final stages of the D₃ event, north-east trending retrograde schist zones were formed. These were later reactivated during the folding of the Adelaidean. The final phase of the Olarian Orogeny consists of minor D₄ folding and crenulation. / Thesis (Ph.D.) -- University of Adelaide, Department of Geology and Mineralogy, 1978.

Low-grade burial metamorphism in the Midland Valley of Scotland, has been investigated with reference to the Silurian sediments and to the Carboniferous volcanics. In the Silurian sediments, facies definitive phyllosilicates are absent. Thin-section examination indicates that cementation was early and despite strong deformation, the lack of cleavage is related to the isotropic dispersal of domains during burial. Scanning electron microscopy and X-ray diffraction define clay mineral assemblages which characterize the transformation of montmorillonite to illite during burial. Illite crystallinity, bo and conodont alteration, show values consistent with this transformation and are indicative of diagenetic/anchizone conditions. Metamorphism is related to Siluro-Devonian syn-sedimentary burial. Despite tentative links between the Midland Valley and the Southern Uplands during the Llandovery, the relative simplicity of the burial metamorphic sequence in the former region suggests that the Silurian trough became palaeo-geographically distinct. The Carboniferous volcanics have undergone burial metamorphism in the zeolite facies, which occurred once the bulk of the lavas had been extruded, and following burial beneath the Central and Ayrshire Basins. Alteration was dominated by hydrothermal processes and has resulted in the production of early greenstones, later burial metamorphic zones and palaeo-geothermal plumes. Seven zones have been defined upon the distribution of amygdale minerals. Thin-section examination however divides the zeolite facies in the Midland Valley into an upper analcime and a lower laumontite zone. Mineralogical assemblages are conducive with metamorphism at a) Pfluid = 2-4 kb at 200 °C and b) Pfluid = 2 kb at 350-420 °C, for the zeolite zones and the palaeo-geothermal plumes respectively. These values are compatible with burial depth estimates, with homogenization temperatures in fluid inclusions and with calcite-water fractionation temperatures. Water/rock ratios indicate that metamorphism was related to the flow of seawater and meteoric water through the volcanic sequences. Evidence for episodic boiling in fluid inclusions indicates fluid convection occurred, and was related to fracturing associated with a change from a lithostatic to a hydrostatic pressure regime. Seismic pumping was related to fracturing and to renewed magmatic activity in shallow chambers beneath the Midland Valley.

No description available.

Thesis (M.S.)--University of Montana, 2008. / Title from title screen. Description based on contents viewed Aug. 28, 2008. Includes bibliographical references (p. 95-100).

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1900. / The entire thesis text is included in file. Typescript. Illustrated by author. Title from title screen of thesis/dissertation PDF file (viewed December 22, 2008)