The tuff of Elevenmile Canyon (TEC) is a 25.1 Ma trachydacite to rhyolite intracaldera tuff produced by the largest of 6 Oligocene overlapping calderas that, along with related plutons, constitute the Stillwater Caldera Complex, one of the largest eruptions of the Western Nevada Volcanic Field during the mid-Tertiary ignimbrite flare-up. Typically crystal-rich with a mineral assemblage of plagioclase > quartz  sanidine > biotite ± hornblende and clinopyroxene, there are two discernable pumice types throughout the tuff: a lighter crystal-rich pumice and a darker, commonly aphyric pumice type. Rb-Sr and Sm-Nd isotopic compositions of pumice fragments and whole rock samples indicate an enriched mantle component (87Sr/86Srin = 0.70495 – 0.70535, Nd[t=25.1Ma] = -1.13 to -0.39) similar to that of coeval Cenozoic mafic lavas. Pb isotopes (206Pb/204Pbin = 19.042 – 19.168, 207Pb/204Pbin = 15.557 – 15.664) fall along a tight trend between the Northern Hemisphere Reference Line (Hart 1984) and an endmember similar to local granitic units. Major and trace element modelling support a source for the TEC derived from the mixing of anatectic melts of crustal rocks with intruded mantle-derived magmas similar to a local basaltic-andesite.

The Wah Wah Springs Tuff and the Wah Wah Springs Intrusive Granodiorite Porphyry(Wah Wah Springs Intrusion) both originated from the Indian Peak caldera complex, which wasa major focus of explosive silicic activity in the middle Cenozoic Great Basin ignimbrite flareup. This caldera formed 30.0 Ma when an estimated 5,900 km3 of crystal-rich dacitic magma erupted to create the Wah Wah Springs Tuff. The Wah Wah Springs Intrusion later intruded the tuff, causing resurgence of the caldera. Field, modal, and geochemical evidence suggest the tuff and intrusion are cogenetic. The mineral assemblages of the two rocks are similar: both include similar proportions of plagioclase, quartz, hornblende, biotite, clinopyroxene, and Fe-Ti oxides, with trace amounts of titanite, apatite, and zircon. Whole rock geochemistry also matches, and both rocks have distinctively high Cr concentrations. Plagioclase, hornblende, and clinopyroxene have similar compositions but biotite and Fe-Ti oxides have been hydrothermally altered in the intrusion. Both hornblende and quartz provide clues to the magmatic evolution of the Wah Wah Springs Intrusion. Hornblende grains are either euhedral, have reaction rims, or are completely replaced by anhydrous minerals. Deterioration of hornblende was caused by decompression as the magma ascended and then stalled and solidified at shallow depths. Two stages of quartz growth are shown in cathodoluminescence (CL) imagery. Quartz first grew then was resorbed during eruption, then grew again at lower pressures indicated by CL-bright quartz rims and groundmass grains. The geochemical and mineralogical similarities, together with the distinctive hornblende and quartz characteristics suggest that after the Wah Wah Springs Tuff erupted, the unerupted mush rose to a shallow level where it crystallized at low pressure to form the Wah Wah Springs Intrusion. This indicates that the both rocks formed in the same chamber, and that tuffs and associated intrusions can be intimately related.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: To date, the only volcanic rocks described from the Cape Granite Suite are ignimbrites that crop out along the western margin of Langebaan lagoon, to the south of Saldahna. These ignimbrites, with an age of 515 ± 3 Ma, represent the youngest rocks within the Suite. This study aims to investigate the petrogenesis of fine grained granitic rocks exposed to the north of Langebaan lagoon, as well as to reassess the classification of these rocks as a sub-volcanic quartz porphyritic intrusive. These rocks exhibit a dark grey to brown micro- to crypto-crystalline matrix containing prominent feldspar and quartz phenocrysts that are often embayed and broken. Phenocrysts of biotite and orthopyroxene (Fs50-70) can be identified microscopically, as can replacement of both phases by chlorite. Ilmenite commonly occurs in close association with the orthopyroxene phenocrysts. A second generation of poikiloblastic biotite overgrows the matrix and is clearly formed through sub-solidus reaction. The feldspar phenocrysts are commonly microcline microperthite. Contact exposures can be observed in the study area which indicates that the finer grained rock intruded older coarser grained granites. The predominance of broken phenocrysts as well as the presence of fiamme present in outcrop in rocks with a microcrystalline matrix is indicative of a volcanic origin, suggesting that these rocks be classified as ignimbrite as opposed to quartz porphyry. The foregoing observations and features could be interpreted to represent a welded ignimbrite deposit which is underlain by coarse grained granite. The finer grained ignimbrite would then represent a subsequent intrusion by a later pulse of similar magma along the contact with the coarser grained granite. The ignimbrites are silicic with SiO2 ranging between 69 and 76 wt. %; they are mildly peraluminous with values for ASI (ASI = mol. Al2O3/ (CaO+Na2O+K2O)) ranging from 1.02 to 1.09; and ASI is negatively correlated with Mg + Fe (hereafter maficity). Tight to very tight inter-element correlations exist for several major elements as well as trace elements when plotted against maficity. The following R² values apply: Al =0.94; Ca = 0.98; Si = 0.97; Ti = 1.00; Na =0.90; Zr =0.95; La = 0.87. These elements are all positively correlated with maficity, except for Si which is negatively correlated. Orthopyroxene and ilmenite represent early formed, high temperature minerals in the magma. In the biotite-poor rocks, ilmenite represents the main reservoir of titanium whilst orthopyroxene represents the main MgO and FeO reservoir. The exceptionally tight Ti: maficity correlation requires that both these minerals always be present at the same molecular ratio in the magma, despite the significant range in maficity portrayed by the rocks and despite the fact that these minerals have different size-density relationships. This exceptionally tight correlation can be readily interpreted to reflect entrainment of a peritectic assemblage consisting of ilmenite and orthopyroxene. The Al, Ca and Na correlations require the entrainment of peritectic plagioclase. The decreasing trend for ASI requires the entrainment of peritectic clionopyroxene. A near perfect match with the concentrations of these elements in the ignimbrites is produced by modelling entrainment of a peritectic assemblage consisting of plagioclase, ilmenite, orthopyroxene and clionopyroxene in stoichiometric proportions dictated by the melting reaction. A peritectic assemblage formed by these phases’ points to the partial melting of a source undergoing coupled biotite and hornblende fluid-absent melting, with hornblende being subordinate. The opx- and ilmenite-rich micro-domains in the rocks represent zones in the magma rich in original peritectic orthopyroxene and ilmenite. In contrast, the peritectic plagioclase demanded by the chemistry of the rocks has melted during ascent due to overheating and decreasing water solubility in the melt. The phenocrystic potassium feldspar observed in the rocks crystallised after significant cooling and the physical behaviour of these crystals does not shape the chemistry of the magma. K contents of the ignimbrites are however not well replicated by this modelling, which predicts a significant K decrease due to dilution. K in the rocks is not correlated with maficity. This may reflect the fact that the K behaviour represents two slightly different source protoliths with differing K contents. / AFRIKAANSE OPSOMMING: Tot op hede is die enigste vulkaniese rots van die Kaapse Granietgroep wat al beskryf is ignimbriete wat teen die westelike grens van die Langebaan-lagune, na die suide van Saldanha, aan die oppervlak kom. Hierdie ignimbriete, met ’n ouderdom van 515 ± 3 Ma, verteenwoordig die jongste gesteentes in die Groep. Die doel van hierdie studie was om die petrogenese van fynkorrelrige granietrots wat na die noorde van die Langebaan-lagune blootgestel is, te ondersoek, en ook die klassifikasie van hierdie rotse as ’n subvulkaniese kwartsporfier- intrusiewe gesteentes te assesseer. Hierdie gesteentes toon ’n donker grys tot bruin mikro- tot kriptokristalvormige matriks wat prominente veldspaat en kwartsfenokriste bevat wat dikwels bogtig en gebreek is. Fenokriste van biotiet en ortopirokseen (Fs50-70) asook vervanging van albei fases deur chloriet kan mikroskopies geïdentifiseer word. Ilmeniet kom dikwels naby ortopirokseenfenokriste voor. ’n Tweede generasie poikiloblastiese biotiet groei die matriks toe en is duidelik deur subsolidusreaksie gevorm. Die veldspaatfenokriste is gewoonlik mikroklien-mikropertiet. Kontakblootstelling kan in die studiegebied waargeneem word, wat aantoon dat die fynkorrelrige rots ander grofkorrelrige granietgesteentes intrudeer het. Die oorheersing van gebroke fenokriste asook die teenwoordigheid van ‘fiamme’ strukture in die rotsdagsoom met ’n mikrokristalvormige matriks dui op vulkaniese oorsprong, wat aan die hand doen dat hierdie gesteentes as ignimbriete eerder as kwartsporfier geklassifiseer kan word. Hierdie waarnemings en eienskappe kan geïnterpreteer word as verteenwoordigend van ’n gelaste ignimbriet-afsetting wat deur grofkorrelrige graniet onderlê word. Die fynkorrelrige ignimbriet stel dan ’n daaropvolgende intrusie voor deur ’n latere puls van soortgelyke magma teen die kontak met die grofkorrelrige graniet af. Die ignimbriete is silisies met SiO2 wat wissel tussen 69 en 76 wt. %; hulle is matig peralumineus met waardes vir ASI (ASI = mol. Al2O3/ (CaO+Na2O+K2O)) wat wissel van 1.02 tot 1.09; en ASI is negatief gekorreleer met Mg + Fe (hierná mafiese komponent). Nou tot baie nou inter-elementkorrelasies bestaan vir verskeie groot elemente asook spoorelemente wanneer dit teen die mafiese komponent gestip word. Die volgende R²-waardes is van toepassing: Al =0.94; Ca = 0.98; Si = 0.97; Ti = 1.00; Na =0.90; Zr =0.95; La = 0.87. Hierdie elemente is almal positief met die mafiese komponent gekorreleer, buiten Si, wat negatief gekorreleer is. Ortopirokseen en ilmeniet verteenwoordig vroeg gevormde, hoëtemperatuur-minerale in die magma. In die biotiet-arme rotse stel ilmeniet die hoofreservoir van titaan voor, terwyl ortopirokseen die vernaamste MgO- en FeO-reservoir voorstel. Die buitengewoon nou Ti: mafiese-korrelasie vereis dat albei hierdie minerale altyd in dieselfde molekulêre verhouding in die magma teenwoordig moet wees, ondanks die beduidende omvang van die mafiese komponent wat deur die gesteentes getoon word en ondanks die feit dat hierdie minerale verskillende grootte–digtheidsverhoudings het. Hierdie buitengewoon nou korrelasie kan geredelik geïnterpreteer word om meesleping van ’n peritektiese groep te weerspieël wat uit ilmeniet en ortopirokseen bestaan. Die Al-, Ca- en Na-korrelasies vereis die meesleping van peritektiese plagioklaas. Die verminderende neiging tot ASI vereis die meesleping van peritektiese klionopirokseen. ’n Byna perfekte passing met die konsentrasies van hierdie elemente in die ignimbriete word voortgebring deur die modellering van meesleping van ’n peritektiese groep bestaande uit plagioklaas, ilmeniet, ortopirokseen en klionopirokseen in stoïgiometriese verhoudings wat deur die smeltreaksie bepaal word. ’n Peritektiese groep wat deur hierdie fases gevorm word, dui op die gedeeltelike smelting van ’n bron wat gekoppelde biotiet- en horingblende- vloeistofafwesige smelting ondergaan, met horingblende wat ondergeskik is. Die ortopirokseen- en ilmeniet-ryke mikrodomeins in die gesteentes verteenwoordig sones in die magma wat ryk is aan oorspronklike peritektiese ortopirokseen en ilmeniet. Hierteenoor het die peritektiese plagioklaas wat deur die chemie van die gesteentes vereis word tydens styging gesmelt weens oorverhitting en dalende wateroplosbaarheid in die smeltsel. Die fenokristiese kaliumveldspaat wat in die rotse waargeneem is wat ná aanmerklike afkoeling gekristalliseer het en die fisiese gedrag van hierdie kristalle vorm nie die chemie van die magma nie. Die K-inhoud van die ignimbriete word egter nie goed deur hierdie modellering gerepliseer nie, wat ’n aanmerklike K-afname weens verdunning voorspel. K in die rotse is nie met mafiese komponente gekorreleer nie. Dit kan die feit weerspieël dat die K-gedrag twee effens verskillende bronprotoliete met verskillende K-inhoud voorstel.

This thesis employs crystal-specific techniques, combined with field observations, petrology, geochemistry and numerical modelling to reconstruct the magmatic system associated with the ~ 340 ka Whakamaru supereruption, New Zealand. Comparisons are drawn with the ~ 74 ka Youngest Toba Tuff (YTT) supereruption. Whakamaru Group Ignimbrites contain five pumice types, characterised by different mineralogies and crystal contents. Pumice petrography and geochemistry indicate that basaltic magma mixing occurred, possibly triggering eruption. Geothermobarometers suggest an eruption temperature of ~ 770°C and magma storage at ~ 5 km depth. High-resolution thermal records from Ti-in-quartz analysis indicate a thermal pulse of ~ 100°C prior to eruption. Diffusion timescales show multiple recharge events with the most significant event occurring ~ 35 y prior to eruption. Zircon U-Pb data show that most crystallisation occurred at ~ 400 ka, with antecrysts and xenocrysts incorporated. Zircon trace-element data suggest multiple recharge events and complex mixing over ~ 100 ky, consistent with an incrementally growing reservoir. Oxygen-isotope data illustrate that zircon, quartz and feldspar crystallised together in equilibrium, with isotopically homogenous magma sources feeding the reservoir over time. Whakamaru and YTT tephra thickness and grain-size data were used in ash dispersal modelling. Results indicate the YTT eruption had a ~ 35 km column height and erupted volumes of 1500 – 1900 km³, with deposition from a co-ignimbrite phase; whereas Whakamaru had a Plinian column ~ 45 km high with SE dispersal and a minimum volume of ~ 400 km³. The widespread dispersal of large volumes of fine ash from both eruptions would have had global environmental consequences. The data are integrated to reconstruct a new Whakamaru magma reservoir model. The complex crystal records indicate the system was characterised by long periods of incremental assembly, mixing, recycling of material, and reactivation during multiple recharge episodes which perturbed the system and primed the magma for eruption.

This thesis attempts to detect the ignimbrite units in which the underground cities were carved and the relationship between the joints in these ignimbrites and the walls of underground cities. Orientation of rooms, directions of walls and joints are input data used in the study. Two sites in Cappadocia (Derinkuyu and Kaymakli) are selected to investigate the relationship. Measurements taken from 46 rooms of Derinkuyu and 64 rooms of Kaymakli are analyzed for the room and joint directions, joint locations in the room and joint densities. The density analyses are also performed in the field for Kizilkaya and G&ouml / rdeles ignimbrites. Conclusions derived from the analysis are: 1) Derinkuyu is carved within Kizilkaya and Kaymakli is carved within G&ouml / rdeles ignimbrite, 2) The thickness of Kizilkaya and G&ouml / rdeles ignimbrites observed 13.5 and 34 m, respectively, in the field. The probable thickness of Derinkuyu and Kaymakli underground cities are 40 and 25 m, respectively, 3) The rooms and the joints are oriented arbitrarily, 4) Forming the room walls that are perpendicular to joints were not preferred, 5) The joint densities in Derinkuyu show ascending tendency, while the joint densities in Kaymakli have descending tendency from top to ground floors, 6) The joint density of Kizilkaya in the field is higher than the joint density in Derinkuyu underground city. Similarly, the joint density of G&ouml / rdeles in the field is higher than the density of Kaymakli underground city, 7) The joint density of Kizilkaya ignimbrite is higher than G&ouml / rdeles ignimbrite in both field and underground measurements.

The south-west portion of the main caldera was mapped and a stratigraphy for the caldera-fill was constructed. The exact timing of formation of the main caldera is unclear; However, caldera collapse either predates or was synchronous with the eruption of the Campagnola Tuff. The proximal facies of the Campagnola Tuff exists as a complex relation of ignimbrite, lithic breccia and pyroclastic surge deposits. Overlying this the Galluccio Tuff a compound ignimbrite, ~6 km3 D.R.E, forms the base of the exposed caldera fill. Caldera lakes then became well established and following activity was predominantly phreatomagmatic. Pyroclastic surge deposits possess sand wave structures of several types and their migration direction was apparently controlled by the velocity/flow regime of the surge rather than the moisutre content. The morphology of juvenile clasts from phreatomagmatic deposits indicates that the eruptions were driven by a combination of vesiculation and magma/water interaction. The uppermost pyroclastic deposits are thought to represent the early phase of dome building where water still had access to the vent. The construction of the lava domes brought activity to a close within the main caldera. The Galluccio Tuff on the flanks of the volcano may be divided into three compositionally distinct eruptive units. The Lower Galluccio Tuff, correlated with the bulk of the Galluccio Tuff filling the main caldera. The Middle Galluccio Tuff commenced with the eruption of pumice-rich pyroclastic flows followed by flows enriched in both the size and amount of lithic fragments forming lithic-rich ignimbrite and co-ignimbrite lithic breccias of which several types exist. The Upper Galluccio Tuff is composed of lithic-rich ignimbrite which possess dense pumice fragments and are thought to be the product of a combination of both vesiculation and magma water interaction. Field relations indicate that pyroclastic flows were sometimes generated in quick succession and may have overrun earlier slower moving flows. Occasionally internal shear may have caused the overriding of portions of the same flow, these often coincide with lithic breccias and represent the climax of the eruptive phases. The grading of lithic fragments indicates that the expansion and fluidization decreased and yield strength increased with time in a pyroclastic flow.

This thesis attempts to seek a relationship between the joints developed in the ignimbrites and the rock settlements carved in the same units. Orientation of rooms, directions of walls and joints (both in the rooms and in the field) are input data used in the study. Two sites in Cappadocia (Eskig&uuml / m&uuml / Sler and &Ccedil / anlikilise) are selected to investigate the relationship. Both sites are carved within the same ignimbrite (Kizilkaya) and are located on the south-southeastern slopes of the ignimbrite scarp. Measurements taken from 61 rooms of the former and 27 rooms of the latter are analyzed for the room and joint directions, joint locations in the room and joint densities both in the rooms and in the field. Conclusions derived from the analyses are: 1) The rooms are oriented oblique to joint strike to get the maximum sunlight, 2) Joint directions in the rooms strike in one single direction and greatly differ from the field joint directions, 3) Density of the room joints is less than the field joints indicating that joint spacing is an important factor in the selection of sites, 4) Joints in the Eskig&uuml / m&uuml / Sler sites are concentrated towards the margins of the room while an opposite observation is made for the &Ccedil / anlikilise site, 5) Total length of joints in the largest rooms are relatively shorter.

>Magister Scientiae - MSc / The Saldania Belt in southern Africa, a product of the Pan-African Saldanian Orogeny, forms part of a system of Neoproterozoic mobile belts that border and weld older cratons on the African continent. It is a low-grade orogenic belt situated along the southwestern margin of the Kalahari Craton and is composed of several inliers of greenschist facies metasedimentary and metavolcanic rocks (Malmesbury Group), unroofed in megaanticlinal hinges of the Permo-Triassic Cape Fold Belt. The Malmesbury Group rocks were syn- and post-tectonically intruded in a pervasive transpressive regime between 555 Ma and 515 Ma by Neoproterozoic to early Cambrian S-, I- and A-type granites, monzodiorites, gabbros and quartz syenites, which collectively constitute the rocks of the Cape Granite Suite (CGS). Along the south-western coastline of South Africa, the Saldanha Bay Volcanic Complex (which forms part of the CGS) is divided into two eruption centres both of which have been identified as “intra-caldera pyroclastic ignimbrites”. The Postberg eruption centre is situated to the south of the Saldanha Bay entrance and the Saldanha eruption centre is situated to the north of the entrance. Both eruption centres display distinct geochemical signatures, the most apparent being the greater TiO2 concentrations (> 0.25 wt. %) of the Saldanha centre ignimbrites when compared to its Postberg centre counterparts. The Postberg eruption centre consists of S-type rhyolitic ignimbrites which are subdivided into the two geochemically distinct Plankiesbaai and Tsaarsbank Ignimbrites. Small amounts of the Jacobs Bay and Saldanha Ignimbrites (less felsic tephra from the Saldanha eruption centre) are also present in the Postberg eruption centre. A robust geochemical analysis of both the Plankiesbaai and Tsaarsbank magma groups display high SiO2 content (>76 wt. %), a lack of variation in TiO2 and Zr, high Al2O3 and ASI (aluminium saturation index) values (> 1.0 and generally >1.1 which, on average, is higher than the Saldanha eruption centre ignimbrites), low CaO and Na2O, and a highly ferroan character. The Plankiesbaai ignimbrite also display lower #Mg concentration compared to the Tsaarsbank ignimbrite. Typical geochemical trends in the Postberg eruption centre include the lack of variation in Zr content, higher Rb content and lower Sr, Ba, V and Zn concentrations when compared to the tephra of the Saldanha eruption centre found in the Postberg area. The study’s main aim is not only to assess the geochemistry of the ignimbrites relative to the previous phases of magmatism originally proposed by Scheepers (1995) for the magmatism of the Cape Granite Suite, but also their age distribution. Previously defined phases of magmatism include Phase I (S-type granites subdivided into Sb, Sa1 and Sa2 all of which are dated to 555 - 540 Ma), Phase II (I-type granites subdivided into Ia and Ib both dated to 540 – 520 Ma), Phase III (A-type granites subdivided into Aa and Ab dated to ~ 520 Ma) and Phase IV (S-type volcanic and subvolcanic rocks dated to 515 Ma). Re-examination of the geochronology displays a U-Pb age for Postberg Centre Jacobs Bay Ignimbrite (tephra from the Saldanha eruption centre) of 538 ± 2.2 Ma: and for the Postberg Centre Tsaarsbank Ignimbrite between 536 ± 2 Ma – 540 ± 3.4 Ma. These new dates, in combination with the geochronological work done in the Saldanha Centre (particularly in light of the Clemens and Stevens (2016) and Clemens et al. (2017) studies that reclassify these rocks differing from the original and previous studies), place all the ignimbrites of the Saldanha Bay Volcanic Complex securely within the age bracket for the initial S-type magmatism of the CGS. This thesis presents a revised order for the phases of magmatism of the Saldania Belt, and by extension, of the Cape Granite Suite. All S-type magmatism, including that of the Saldanha Bay Volcanic Complex (Sv), forms part of the Phase I magmatism of the Saldania Belt (Sa1, Sa2, and Sb) emplaced between 555 – 540 Ma.

>Magister Scientiae - MSc / The Saldania Belt in southern Africa, a product of the Pan-African Saldanian Orogeny, forms part of a system of Neoproterozoic mobile belts that border and weld older cratons on the African continent. It is a low-grade orogenic belt situated along the southwestern margin of the Kalahari Craton and is composed of several inliers of greenschist facies metasedimentary and metavolcanic rocks (Malmesbury Group), unroofed in megaanticlinal hinges of the Permo-Triassic Cape Fold Belt. The Malmesbury Group rocks were syn- and post-tectonically intruded in a pervasive transpressive regime between 555 Ma and 515 Ma by Neoproterozoic to early Cambrian S-, I- and A-type granites, monzodiorites, gabbros and quartz syenites, which collectively constitute the rocks of the Cape Granite Suite (CGS). Along the south-western coastline of South Africa, the Saldanha Bay Volcanic Complex (which forms part of the CGS) is divided into two eruption centres both of which have been identified as “intra-caldera pyroclastic ignimbrites”. The Postberg eruption centre is situated to the south of the Saldanha Bay entrance and the Saldanha eruption centre is situated to the north of the entrance. Both eruption centres display distinct geochemical signatures, the most apparent being the greater TiO2 concentrations (> 0.25 wt. %) of the Saldanha centre ignimbrites when compared to its Postberg centre counterparts. The Postberg eruption centre consists of S-type rhyolitic ignimbrites which are subdivided into the two geochemically distinct Plankiesbaai and Tsaarsbank Ignimbrites. Small amounts of the Jacobs Bay and Saldanha Ignimbrites (less felsic tephra from the Saldanha eruption centre) are also present in the Postberg eruption centre. A robust geochemical analysis of both the Plankiesbaai and Tsaarsbank magma groups display high SiO2 content (>76 wt. %), a lack of variation in TiO2 and Zr, high Al2O3 and ASI (aluminium saturation index) values (> 1.0 and generally >1.1 which, on average, is higher than the Saldanha eruption centre ignimbrites), low CaO and Na2O, and a highly ferroan character. The Plankiesbaai ignimbrite also display lower #Mg concentration compared to the Tsaarsbank ignimbrite. Typical geochemical trends in the Postberg eruption centre include the lack of variation in Zr content, higher Rb content and lower Sr, Ba, V and Zn concentrations when compared to the tephra of the Saldanha eruption centre found in the Postberg area.

This study includes a systematic investigation of the bond strength of cementitious borehole plugs in welded tuff. Analytical and numerical analysis of borehole plug-rock stress transfer mechanics is performed. The interface strength and deformation are studied as a function of Young's modulus ratio of plug and rock, plug length and rock cylinder outside-to-inside radius ratio. The tensile stresses in and near an axially loaded plug are analyzed. The frictional interface strength of an axially loaded borehole plug, the effect of axial stress and lateral external stress, and thermal effects are also analyzed. Implications for plug design are discussed. Push-out tests are used to determine the bond strength by applying an axial load to the cement plugs. A total of 130 push-out tests are performed as a function of borehole size, plug length, temperature, and degree of saturation of the tuff cylinder. The use of four different borehole radii enables evaluation of size effects. A well-defined exponential strength decrease with increasing plug diameter results.