The Neoproterozoic is one of the most enigmatic periods in Earth history. In the juxtaposition of glacial and tropical deposits the sedimentary record provides evidence for extreme climate change. Various models have tried to explain these apparent contradictions. One of the most popular models is the Snowball Earth Hypothesis which envisages periods of global glaciations. All climatic models are dependent on palaeogeography which as yet remains poorly constrained for the Neoproterozoic. This thesis presents a multidisciplinary study of two Neoproterozoic sedimentary basins on the Congo and West Africa cratons including radiometric dating of glacial deposits themselves. In the West Congo Belt, western Congo Craton, a new U-Pb baddeleyite age for the Lower Diamictite provides the first high quality direct age for the older of two glacial intervals. This age is significantly different from previously dated glaciogenic deposits on the Congo Craton. This result strongly suggests that the mid-Cryogenian was a period during which several local glaciations occurred, none of which were global. While the palaeomagnetic results from carbonates around the younger glacial interval are probably remagnetised, detrital zircon and chemostratigraphic results allow correlation with numerous late-Cryogenian glaciogenic deposits worldwide and a Snowball Earth scenario is favoured here. In the Adrar Sub-Basin of the vast Taoudéni Basin, West Africa, the terrigenous Jbeliat glacial horizon has been studied in great detail. Detrital zircon geochronology reveals large changes in provenance through this glacial unit with implications for sedimentological approaches and techniques for provenance characterisations based on one sample alone. Together with recently published U-Pb data these results constrain the age of the Jbeliat Group to a narrow window providing vital geochronological information for this younger glacial event. Combining provenance geochemistry, chemostratigraphy and U-Pb dating has greatly improved our understanding of two of the largest Neoproterozoic sedimentary basins. The dominance of Mesoproterozoic detrital material, for which no source has been reported near either of the field areas, has consequences for the proximity of other cratons at the time of deposition, prior to the final amalgamation of Gondwana.

No description available.

The oxidation state, reflected in the oxygen fugacity (fO2), of the lithospheric mantle is both laterally and vertically heterogeneous. Depth-fO2 profiles from kimberlite-borne peridotitic mantle xenoliths from the Bultfontein kimberlite, Kimberley, South Africa and the A154-N and A154-S kimberlites of the Diavik Mine, NWT, Canada were constructed by measuring ferric iron concentrations in garnets using the flank method. These data demonstrate that mantle metasomatic re-enrichment processes had a significant effect on fO2. In the garnet stability field, the Kaapvaal lithospheric mantle becomes progressively more reducing with increasing depth from Δlog fO2 (FMQ) of -2 at 110 km to -4 at 210 km. The lithospheric mantle beneath Diavik is vertically layered with respect to its bulk and trace-element composition. The shallow ‘ultradepleted’ layer is oxidized, to the point that carbonate rather than graphite is the anticipated carbon host. The deeper layer is more fertile and has fO2 conditions extending down to Δlog fO2 (FMQ) -3.8. Deviations from predicted depth-fO2 trends in both xenolith localities result from metasomatic re-enrichment caused by transient fluids and melts. Diamond formation in the Kaapvaal lithospheric mantle may have occurred through the infiltration of reduced fluids into relatively more oxidized mantle. Trace-element concentrations in garnets preserve evidence of two distinct melt metasomatic enrichment events. One was a craton-wide event that is commonly observed in garnet peridotite xenoliths and xenocrysts worldwide; the other was melt infiltration event, preserved as MARID xenoliths, related to the eruption of the Group 2 kimberlites in the western portion of the Kaapvaal craton. The effect of the former melt metasomatism on fO2 is unclear ambiguous whereas the MARID event was clearly oxidizing. Diavik xenoliths preserve evidence for events similar to the fluid and ‘common’ melt metasomatism seen in the Bultfontein samples. Fluid metasomatism affected the entire depth range of xenoliths sampled from Diavik and was oxidizing. A stage of melt metasomatism affected only the deeper (>140 km) portion of the lithospheric mantle and had an overall reducing effect. The observation of sharp-edged octahedral diamonds in microxenoliths affected by the fluid metasomatic event may indicate that this was a major diamond-forming event in the mantle beneath Diavik.

M.Sc. (Geology) / The south-easternmost Kaapvaal Craton is composed of scattered inliers of Archaean basement granitoid-greenstone terrane exposed through Phanerozoic cover successions. In addition, erosional remnants of the supracrustal Mesoarchaean Pongola Supergroup unconformably overlay this granitoid-greenstone terrane in the same inliers. Into this crust a variety of Precambrian intrusions occur. These are comprised of SE-, ENE- and NE-trending dolerite dykes. Also, the Hlagothi Complex intrudes into Pongola strata in the Nkandla region, particularly the quartzites of the basal Mantonga Formation. The whole area, including Phanerozoic strata, has in turn been intruded by Jurassic sills and dykes related to the Karoo Large Igneous Province. All the rocks of the Archaean inliers, with the exception of the Jurassic sills and dykes have been subjected to greenschist facies metamorphism and deformation, with petrographic, Ar-Ar geochronologic and palaeomagnetic studies attesting to this. This metamorphism and deformation is associated with the Mesoproterozoic orogeny from the nearby Namaqua-Natal Mobile Belt located to the south. This orogeny has a decreasing influence with distance from the cratonic margin, and is highly variable from locality to locality. However, it is generally upper greenschist facies up to a metamorphic isograd 50 km from the craton margin. Overprints directions seen within the palaeomagnetic data confirm directions associated with the post-Pongola granitoids across the region and the Namaqua-Natal Mobile Belt. The dolerite dykes consist of several trends and generations. Up to five different generations within the three Precambrian trends have potentially been recognised. SEtrending dykes represent the oldest dyke swarm in the area, being cross-cut by all the other dyke trends. These dykes consist of two possible generations with similar basaltic to basaltic andesite geochemistry. They provide evidence of a geochemically enriched or contaminated magma having been emplaced into the craton. This is similar to SE-trending dolerite dyke swarms across the Barberton-Badplaas region to the north from literature. In northern KwaZulu-Natal the SE-trending dolerite dyke swarms have been geochronologically, geochemically and paleomagnetically linked to either ca. 2.95 or ca. 2.87 Ga magmatic events across the Kaapvaal Craton. The 2866 ± 2 Ma Hlagothi Complex is composed of a series of layered sills intruding into Nkandla sub-basin quartzites of the Pongola Supergroup. The sills consist of meta-peridotite, pyroxenite and gabbro. At least two distinct pulses of magmatism have been recognised in the sills from their geochemistry. The distinct high-MgO units are compositionally different from the older Dominion Group and Nsuze Group volcanic rocks, as well as younger Ventersdorp volcanic rocks. This resurgence of high-MgO magmatism is similar to komatiitic lithologies seen in the Barberton Greenstone Belt. It is indicative of a more primitive magma source, such as one derived from a mantle plume. A mantle plume would also account for the Hlagothi Complex and the widespread distribution of magmatic events of possible temporal and spatial similarity across the craton. Examples include the layered Thole Complex, gabbroic phases of the ca. 2990 to 2870 Ma Usushwana Complex, and the 2874 ± 2 Ma SE-trending dykes of northern KwaZulu-Natal already described above and dated herein. A generation of NE-trending dolerite dykes in northern KwaZulu-Natal can also be palaeomagnetically linked to this event with either a primary or overprint direction. Flood basalts seen within the upper Witwatersrand and Pongola Supergroups (i.e., Crown, Bird, Tobolsk and Gabela lavas) may also be related. This large, voluminous extent of magmatism allows us to provide evidence for a new Large Igneous Province on the Kaapvaal Craton during the Mesoarchaean. This new Large Igneous Province would encompass all of the above mentioned geological units. It is possible that it could be generated by a shortlived transient mantle plume(s), in several distinct pulses. This plume would also explain the development of unconformities within the Mozaan Group. This is reasoned through thermal uplift from the plume leading to erosion of the underlying strata, culminating in the eruption of flood basalts coeval to the Hlagothi Complex. Marine incursion and sediment deposition would occur during thermal subsidence from the plume into the Witwatersrand-Mozaan basin. This magmatic event also assists in resolving the apparent polar wander path for the Kaapvaal Craton during the Meso- to Neoarchaean. Between existing poles established for the older ca. 2.95 Ga Nsuze event, to poles established for the younger ca. 2.65 Ga Ventersdorp event, a new magnetic component for this ca. 2.87 Ga magmatic event can be shown. This new component has a virtual geographic pole of 23.4° N, 53.4° E and a dp and dm of 8.2° and 11.8° for the Hlagothi Complex, with a similar magnetic direction seen in one generation of NE-trending dolerite dykes in the region. This new ca. 2870 Ma addition to the magmatic barcode of the Kaapvaal Craton allows for comparisons to be made to other coeval magmatic units on cratons from around the world. Specific examples include the Millindinna Complex and the Zebra Hills dykes on the Pilbara Craton. Precise age dating and palaeomagnetism on these magmatic units is needed to confirm a temporal and spatial link between all the events. If substantiated, this link would assist in further validating the existence of the Vaalbara supercraton during the Mesoarchaean. After the Hlagothi Complex event, different pulses of magma can be seen associated with the Neoarchaean Ventersdorp event. A generation of NE-trending dolerite dykes in the region was dated herein at 2652 ± 11 Ma. In addition, a primary Ventersdorp virtual geographic pole established in Lubnina et al. (2010) from ENE-trending dolerite dykes was confirmed in this study. This ENE-trending dolerite dyke has a virtual geographic pole of 31.7° S, 13.6° E and a dp and dm of 7.0° and 7.2°. This date and virtual geographic poles from NE- and ENE-trending dolerite dyke swarms in northern KwaZulu-Natal match up with NE- and E-trending palaeostress fields seen in the Neoarchaean Ventersdorp and proto- Transvaal volcanics by Olsson et al. (2010). Both generations of dolerite dykes also demonstrate variable geochemistry. The NE-trending dolerite dyke swarm is tholeiitic, and the ENE dolerite dyke swarm is calc-alkaline. In addition, some of the tholeiitic NE-trending dolerite dykes have a similar magnetic component to NE-trending dolerite dykes much further to the north in the Black Hills area according to Lubnina et al. (2010). This magnetic component is also similar to the Mazowe dolerite dyke swarm on the Zimbabwe Craton. The NE-trending dolerite dykes in the Black Hills area differ geochemically from those in northern KwaZulu-Natal though, but are also of ca. 1.90 Ga age. The Mazowe dolerite dyke swarm was linked to the dyke swarm of the Black Hills dyke swarm through palaeomagnetic studies. The Mazowe dolerite dyke swarm however is geochemically similar to the NE-trending dolerite dykes of northern KwaZulu-Natal, creating greater complexity in the relationship between the three dyke swarms. It is clear from the complex array of dolerite dyke swarms and other intrusions into these Archaean inliers of northern KwaZulu-Natal, that much more work on the dykes within the south-easternmost Kaapvaal Craton needs to be done. This will resolve these complex patterns and outstanding issues with regard to their palaeo-tectonic framework.

The Archaean craton of southern India has four main components. The multi-phase Peninsular gneiss, with ages from 3360-2900 Ma, is spatially dominant and grades from granulite facies in the south to greenschist facies in the north. Ages for the Peninsular gneiss range from 3360-2900 Ma. Within the craton are two suites of Greenstone Belts and supracrustal rocks. The older, high-grade Sargur type occur as enclaves in the Peninsular gneiss and are in places older than 3360 Ma. The younger, lower-grade type occur occasionally have unconformable bases with the Peninsular gneiss and have been dated from 3100-2605 Ma. Granitoids form the last major component with the Closepet granite being the largest, ages for the emplacement of the Closepet granite and many of the other granitoids cluster around 2500 Ma. The Closepet granite outcrops from Kabbal Durge in the south to the Deccan Plateau in the north, a distance of some 450 km. A 320 km section from Kabbal Durga to Hospet in the north exposes a linear trending granite. The granite outcrop varies from one of essentially partial melting and melt extraction in the south to a zone of melt accumulation in the central zone to a zone of high level intrusion of large granite bodies. Related to these changes in primary processes are changes in the granite phases, size, shape and intrusive style. The petrography of the granite phases is described. These studies help to constrain phase relationships. The petrography also provides evidence to suggest that the K-feldspar megacrysts are in fact phenocrysts. Analyses of major and trace elements utilised standard X.R.F. methods. However, the analyses of REE on selected samples involved the setting up of the department's "ICP for routine operation. This procedure is outlined. The geochemistry of the granite's is described melting and crystallization models being used to explain their petrogenesis. Harker diagrams indicate that plagioclase, sphene and apatite have strong controls on major element composition and that biotite was a residual or fractionating phase. The removal of restite biotite as granite magmas intrude is thought to be a significant process.Evidence from the petrography agrees with the equilibrium phase diagram at PH2 0 ~ 5 kbar. Plots of Peninsular gneiss in the granite phase diagram have a range of compositions which could provide minimum and non-minimum melts capable of producing the Closepet granite trend. Predicted fractional crystallization would produce a sequence of magma compositions comparable to those of the Closepet granite with an order of phase crystallization that agrees with petrographic evidence. The phase relationships further constrain subsequent melting and crystallization models utilising trace elements and REE.

No description available.

Thesis (Ph. D.)--University of Adelaide, Dept. of Geology, 1998? / Two folded coloured maps and 2 coloured overlays in back cover pocket. Includes bibliographical references (p. 183-142).

The 2.68 Ga Zn-Pb-Cu-Ag Hackett River Main Zone (HRMZ) volcanogenic massive sulfide (VMS) deposit, within the Hackett River Greenstone Belt of the Archean Slave Craton is highly enriched in Ag (and Pb) compared to other VMS deposits of a similar age and type. The mineralization has been sub-divided into five categories based on mineralogy, textures and stratigraphic location: 1) disseminated footwall sulfides, 2) copper-rich stringer sulfides, 3) pyrite-poor sphalerite-pyrrhotite-chalcopyrite mineralization located at the top of the stringer zone, 4) mineralization in calc-silicate altered units and 5) sphalerite-pyrite massive sulfide mineralization. Using a mass-balance for Ag calculated from electron microprobe analyses, pyrrhotite and chalcopyrite in type 1 mineralization contain negligible Ag and in type 2, Bi-Ag-(Pb) sulfides, Ag-Bi-Se enriched galena and chalcopyrite are the dominant Ag hosts. Within type 3, freibergite and galena are the main silver hosts. In type 4, Ag is hosted in disseminated electrum and freibergite while freibergite in type 5 hosts 99% of the Ag. Overall, Ag-rich freibergite contains 79.4% of the total Ag, chalcopyrite hosts 6.3% and galena contains 1.8% of the Ag. Trace minerals such as electrum, stephanite, acanthite and Bi-bearing sulfides host the remainder of the Ag (12.5%) and have a restricted spatial distribution. Mineral assemblages have undergone pervasive recrystallization and annealing during amphibolite grade metamorphism with localized redistribution of base and precious metals from metamorphism at a grain scale only. Within freibergite and chalcopyrite, Ag directly substitutes for Cu within the mineral lattice and replaces Pb in galena by coupled substitution with Bi and to a lesser extent, Sb. The principal controls on Ag residence in the HRMZ are temperature and redox conditions (which varies with distance to the hydrothermal vent) and the ratio of Bi and Sb available for coupled substitution with silver within galena. Subsequent deposit-scale zone refining is the principal factor influencing the distribution of Ag. Lower temperatures and more oxidizing conditions favour partitioning of Ag into freibergite and less oxidizing conditions favour galena. At higher temperatures, the most reducing conditions favour incorporation of Ag in Ag-Bi rich galena (plus Se) and Bi-bearing sulfides or Ag-rich chalcopyrite under lesser reducing conditions. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2009-03-12 10:46:49.993

No description available.

The Gawler Craton, South Australia, consists of late Archaean to early Mesoproterozoic igneous and supracrustal lithologies which preserve a deformation history lasting the duration of the Palaeoproterozoic. Understanding the evolution of the Gawler Craton is of significance in global supercontient reconstructions as it preserves evidence for earliest Palaeoproterozoic collisional orogenesis (c. 2460-2430 Ma) and, in conjunction with the North Australian Craton and Antarctica, has often been correlated to the western margin of Laurentia. In addition, the Gawler Craton is also host to the world-class Olympic Dam Fe-oxide-Cu-Au-U type-deposit (world's fourth largest Cu and largest U deposit) and related Fe-oxide-Cu-Au-U and Cu-Au mineralising systems. Despite the various geologically and economically important characteristics of the Gawler Craton there has traditionally been a poor understanding of the tectonothermal evolution of the Gawler Craton, in particular for the Palaeoproterozoic. This study addresses and refines the Palaeo-to Mesoproterozoic tectonothermal evolution of the Gawler Craton. This is done using geochemical, geochronological and isotopic analytical techniques to better understand selected supracrustal and igneous lithologies in the Gawler Craton and the orogenic events which have affected them. Largely unexposed metasedimentary lithologies of the northern Gawler Craton record multiple deformation events but have previously been virtually unconstrained with respect to their timing of protolith deposition and the age of deformation/metamorphism. New geochronological data demonstrate these metasedimentary lithologies were deposited during the time period -1750-1730 Ma before being metamorphosed and deformed during the Kimban (1730-1690 Ma) and Kararan (1570-1545 Ma) Orogenies. Detrital zircon geochronology and isotopic and geochemical characteristics of the sampled metasedimentary lithologies suggest a relatively similar protolith sedimentary succession was deposited across a large extent of the northern Gawler Craton. Detritus for the sedimentary protolith does not appear to have been sourced from the Gawler Craton. Instead the protolith it is more consistent with a North Australian Craton provenance suggesting a proximity between the northern Gawler Craton and North Australian Craton at the time of protolith deposition. The newly defined presence of the Palaeoproterozoic Kimban Orogeny in the northern Gawler Craton demonstrates the Kimban Orogeny to be a major, high-grade, craton-wide orogenic event. This finding contradicts previous suggestions that the northern Gawler Craton was accreted to the proto-Gawler Craton during the later Mesoproterozoic Kararan Orogeny. In addition, previous reconstruction models for the Palaeo-to early Mesoproterozoic often cite the felsic Tunkillia Suite (1690-1670 Ma), western and central Gawler Craton, as representing arc magmatism prior to the subsequent amalgamation of the Gawler Craton during the Kararan Orogeny. New geochemical and isotopic data for the Tunkillia Suite have allowed for re-examination of the tectonic setting for the petrogenesis of the Tunkillia Suite. Contrary to previous suggestions (based upon discrimination diagrams), the mineralogy, geochemistry and isotopic characteristics of the Tunkillia Suite are not consistent with arc-magmatism. Instead the Tunkillia Suite is interpreted to represent a late-to post-tectonic magmatic suite generated during the waning stages of the Kimban Orogeny. This petrogenesis further highlights the importance of the Kimban Orogeny as a fundamental tectonothermal event in the evolution of the Gawler Craton. Subsequent to the Kimban Orogeny, the Gawler Craton was thought to undergo a period of subduction-related magmatism (St Peter Suite) prior to the anorogenic magmatism of the voluminous felsic Gawler Range Volcanic (GRV) and Hiltaba Suite magmatism (1595-1575 Ma). New geochronological data for the ms-bi-gt-bearing peraluminous Munjeela Suite (1590-1580 Ma) have demonstrated the Hiltaba/GRV event was accompanied by significant crustal anatexis not associated with the Hiltaba/GRV magmatism. The Munjeela Suite and metasedimentary enclaves within it demonstrate that the Gawler Craton was likely to be undergoing compressive deformation and crustal thickening sometime during the petrogenesis of the Hiltaba/GRV magmatism. This suggests the Hiltaba/GRV magmatism did not occur in an anorogenic setting as previously proposed. The findings of this study are incorporated into a revised tectonothermal evolution of the Gawler Craton. This is used to discuss previous reconstruction models for Proterozoic Australia and provide a new reconstruction model of Australia and Antarctica during the Palaeoproterozoic. Important facets of the proposed model are links to the Archaean-Early Palaeoproterozoic Sask Craton in the Trans-Hudson Orogen, Laurentia, and the joint evolution of the North Australian and Gawler Cratons throughout the entire Palaeoproterozoic. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1330862 / Thesis (Ph.D.) - University of Adelaide, School of Earth and Environmental Sciences, 2008