The geochemistry and petrology of tertiary basalt lavas from east Greenland

The 2,660m-thick basalt pile described in this thesis represents one of the upper parts, which were extruded predominantly under subaerial conditions, of the Tertiary basalt sequence in East Greenland. The pile rests on Lower Cretaceous sediments and is overlain by the sediments of Kap Dalton Formation Chemically (XRF analysis), the basalts can be classified as ocean-island tholeiites and are broadly comparable to the Tertiary tholeiites from mid-west Iceland and the tholeiites of the Neovolcanic zone of Iceland. Although they have rather limited compositional ranges, they show evidence of two episodes of fractionation. The magma compositions were controlled largely by olivine fractionation in the initial stage and subsequently by plagioclase fractionation. Comparisons between bivariate and multivariate analyses have been made and it is found that in the case of rather narrow compositional ranges, the multi variate analysis (R-mode factor analysis) is the best method for illustrating geochemical patterns. Petrographically, the basalt suite consists chiefly of plagioclase (average labradorite), augite and Fe-Ti oxides with small amounts of olivine, pigeonite and interstitial glass, except for pillow lavas where the groundmass is entirely glass. The textures are variable from glassy to coarse-grained types. Thus they can be divided, in terms of textures and field observations, into four main groups and then subdivided into a number of rock types. The majority appear to be aphyric types. The principal microphenocryst and/or phenocryst assemblages are plagioclase, plagioclase + olivine, plagioclase + olivine + augite, Fe-Ti oxides, or Fe-Ti oxides + plagioclase. The plagioclase compositions (electron probe analysis) vary from An(_83.4)Ab(_16.3)Or(_0.3) to An(_27.3)Ab(_68.7)Or(_4.0). The great majority of analysed clinopyroxenes are augite and they follow the equilibrium fractionation trend typified in the Skaergaard tholeiitic intrusion. Olivine microphenocrysts and groundmass olivines were analysed and have chrysolitic and hyalosideritic compositions, respectively. Temperatures and oxygen fugacities, which have been estimated from the coexisting phases of titaniferous magnetite and ilmenite, are comparable to those of the Icelandic Thingmuli tholeiitic suite. The origin of these East Greenland tholeiites is attributed to low-degree partial melting of undepleted mantle beneath the region on the present seaward side of the Blosseville coast and, subsequently, low-pressure crystal fractionation

The evolution and storage of primitive melts in the Eastern Volcanic Zone of Iceland: the 10 ka Grímsvötn tephra series (i.e. the Saksunarvatn ash)

Major, trace and volatile elements were measured in a suite of primitive macrocrysts and melt inclusions from the thickest layer of the 10 ka Grímsvötn tephra series (i.e. Saksunarvatn ash) at Lake Hvítárvatn in central Iceland. In the absence of primitive tholeiitic eruptions (MgO > 7 wt.%) within the Eastern Volcanic Zone (EVZ) of Iceland, these crystal and inclusion compositions provide an important insight into magmatic processes in this volcanically productive region. Matrix glass compositions show strong similarities with glass compositions from the AD 1783–84 Laki eruption, confirming the affinity of the tephra series with the Grímsvötn volcanic system. Macrocrysts can be divided into a primitive assemblage of zoned macrocryst cores (An_78–An_92, Mg#_cpx = 82–87, Fo_79.5–Fo_87) and an evolved assemblage consisting of unzoned macrocrysts and the rims of zoned macrocrysts (An_60–An_68, Mg#_cpx = 71–78, Fo_70–Fo_76). Although the evolved assemblage is close to being in equilibrium with the matrix glass, trace element disequilibrium between primitive and evolved assemblages indicates that they were derived from different distributions of mantle melt compositions. Juxtaposition of disequilibrium assemblages probably occurred during disaggregation of incompatible trace element-depleted mushes (mean La/Yb_melt = 2.1) into aphyric and incompatible trace element-enriched liquids (La/Yb_melt = 3.6) shortly before the growth of the evolved macrocryst assemblage. Post-entrapment modification of plagioclase-hosted melt inclusions has been minimal and high-Mg# inclusions record differentiation and mixing of compositionally variable mantle melts that are amongst the most primitive liquids known from the EVZ. Coupled high field strength element (HFSE) depletion and incompatible trace element enrichment in a subset of primitive plagioclase-hosted melt inclusions can be accounted for by inclusion formation following plagioclase dissolution driven by interaction with plagioclase-undersaturated melts. Thermobarometric calculations indicate that final crystal-melt equilibration within the evolved assemblage occurred at ~1140°C and 0.0–1.5 kbar. Considering the large volume of the erupted tephra and textural evidence for rapid crystallisation of the evolved assemblage, 0.0–1.5 kbar is considered unlikely to represent a pressure of long-term magma accumulation and storage. Multiple thermometers indicate that the primitive assemblage crystallised at high temperatures of 1240–1300°C. Different barometers, however, return markedly different crystallisation depth estimates. Raw clinopyroxene-melt pressures of 5.5–7.5 kbar conflict with apparent melt inclusion entrapment pressures of 1.4 kbar. After applying a correction derived from published experimental data, clinopyroxene-melt equilibria return mid-crustal pressures of 4±1.5 kbar, which are consistent with pressures estimated from the major element content of primitive melt inclusions. Long-term storage of primitive magmas in the mid-crust implies that low CO_2 concentrations measured in primitive plagioclase-hosted inclusions (262–800 ppm) result from post-entrapment CO_2 loss during transport through the shallow crust. In order to reconstruct basaltic plumbing system geometries from petrological data with greater confidence, mineral-melt equilibrium models require refinement at pressures of magma storage in Iceland. Further basalt phase equilibria experiments are thus needed within the crucial 1–7 kbar range.D.A.N. was supported by a Natural Environment Research Council studentship (NE/1528277/1) at the start of this project. SIMS analyses were supported by Natural Environment Research Council Ion Microprobe Facility award (IMF508/1013).This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s00410-015-1170-

Processing of hornblende syenite for ceramics

The purpose of this research is to preliminarily study the hornblende syenite processing. The study includes characterization,separation and evaluation. Characterization has been carried out using thin section, X-ray diffraction, X-ray fluorescenceand electrokinetic measurement. A variety of techniques such as magnetic separation, froth flotation and combinationof these techniques were used to separate feldspar from syenite. Evaluation of the separations has been done using data fromyield of feldspar, X-ray fluorescence and cone firing test. The feldspar yield was used to evaluate the process efficiency.Besides chemical analysis, cone shrinkage, fired color and degree of vitrification were used to monitor the quality of therecovered feldspars. The feldspars were furthermore compared to the standard feldspar samples obtained from a ceramicmanufacturer. Finally, the processed feldspars were graded for using in various kinds of ceramics

Petrochemistry and origin of basalt breccia from Ban Sap Sawat area, Wichian Buri, Phetchabun, central Thailand

Thailand is usually considered to be controlled by escape tectonics associated with India-Asia collision during theLate Cenozoic, and basaltic volcanism took place in this extensional period. This volcanism generated both subaqueous andsubaerial lava flows with tholeiitic to alkalic basaltic magma. The subaqueous eruptions represented by the studied WichianBuri basalts, Ban Sap Sawat in particular, are constituted by two main types of volcanic lithofacies, including lava flows andbasalt breccias. The lava flows are commonly porphyritic with olivine and plagioclase phenocrysts and microphenocrysts,and are uncommonly seriate textured. The basalt breccias are strongly vitrophyric texture with olivine and plagioclasephenocrysts and microphenocrysts. Chemical analyses indicate that both lava flows and basalt breccias have similar geochemical compositions, signifying that they were solidified from the same magma. Their chondrite normalized REE patternsand N-MORB normalized patterns are closely analogous to the Early to Middle Miocene tholeiites from central Sinkhote-Alinand Sakhalin, northeastern margin of the Eurasian continent which were erupted in a continental rift environment. The originfor the Wichian Buri basalts show similarity of lava flows and basalt breccias, in terms of petrography and chemical compositions, signifying that they have been formed from the same continental within-plate, transitional tholeiitic magma