<p> Five pyroclastic breccia rock samples from a felsic volcanic sequence at Kakagi Lake, Northwestern Ontario, have been analysed for eight major elements using X-Ray Fluorescence to study the fragment-matrix relationships. The salic fragments represent a rhyodacitic composition and the matrices are of andesitic composition showing Fe and Mg enrichment and Si deficiency compared to the fragment. </p> <p> Four matrix and four fragment samples were obtained from one rock,and a triplicate analysis of one of these matrices,compared to the average of the four matrices, showed that the variability of the composition throughout the rock was not due to the analytical procedure. </p> <p> These results agree reasonably well with the trends found in previous work by Goodwin (1968) and Baragar and Goodwin (1969) considering the matrices only. The fragment-matrix study for this area is unique and has been carried out in conjunction with Smith (1971). </p> / Thesis / Bachelor of Science (BSc)

The Neoarchaean Agnew-Wiluna greenstone belt (AWB) of the Kalgoorlie Terrane, within the Eastern Goldfields Superterrane (EGS) of the Yilgarn Craton, Western Australia, contains several world-class, komatiite-hosted, nickel-sulphide ore bodies. These are commonly associated with felsic volcanic successions, many of which are considered to have a tonalite-trondhjemite-dacite (TTD) affinity. The Cosmos greenstone sequence lies on the western edge of the AWB and this previously unstudied mineralised volcanic succession contrasts markedly in age, geochemistry, emplacement mechanisms and probable tectonic setting to that of the majority of the AWB and wider EGS. Detailed subsurface mapping has shown that the footwall to the Cosmos mineralised ultramafic sequence consists of an intricate succession of both fragmental and coherent extrusive lithologies, ranging from basaltic andesites through to rhyolites, plus later-formed felsic and basaltic intrusions. The occurrence of thick sequences of amygdaloidal intermediate lavas intercalated with extensive sequences of dacite lapilli tuff, coupled with the absence of marine sediments or hydrovolcanic products, indicates the succession was formed in a subaerial environment. Chemical composition of the non-ultramafic lithologies is typified by a high-K calc-alkaline to shoshonite signature, indicative of formation in a volcanic arc setting. Assimilation-fractional crystallisation modelling has shown that at least two compositionally distinct sources must be invoked to explain the observed basaltic andesite to rhyolite magma suite. High resolution U-Pb dating of several units within the succession underpins stratigraphic relationships established in the field and indicates that the emplacement of the Cosmos succession took place between ~2736 Ma and ~2653 Ma, making it significantly older and longer-lived than most other greenstone successions within the Kalgoorlie Terrane. Extrusive periodic volcanism spanned ~50 Myrs with three cycles of bimodal intermediate/felsic and ultramafic volcanism occurring between ~2736 Ma and ~2685 Ma. Periodic intrusive activity, related to the local granite plutonism, lasted for a further ~32 Myrs or until ~2653 Ma. The Cosmos succession either represents a separate, older terrane in its own right or it has an autochthonous relationship with the AWB but volcanism initiated much earlier in this region than currently considered. Dating of the Cosmos succession has demonstrated that high-resolution geochronology within individual greenstone successions can be achieved and provides more robust platforms for interpreting the evolution of ancient mineralised volcanic successions. The geochemical affinity of the Cosmos succession indicates a subduction zone was operating in the Kalgoorlie Terrane by ~2736 Ma, much earlier than considered in current regional geodynamic models. The Cosmos volcanic succession provides further evidence that plate tectonics was in operation during the Neoarchaean, contrary to some recently proposed tectonic models.

[Truncated abstract] Many researchers have proposed the use of silicate rock fertilizers (SRFs) as alternatives to chemical fertilizers. However, the application of SRFs in modern agricultural practices is limited due mainly to the slow release of plant-nutrient elements from SRFs and consequently many tonnes/ha of SRFs may need to be applied. Simple and inexpensive methods of modifying the physicochemical properties of SRFs are needed to improve the agronomic effectiveness of SRFs. This thesis is focused on the evaluation of high-energy milling to produce superfine particles to improve the effectiveness of mafic (basalt and dolerite) and felsic (gneiss and K-feldspar) rocks for use as fertilizers. The ground mafic rocks are for use as Ca and Mg fertilizers and the ground felsic rocks as K fertilizers. Laboratory and glasshouse experiments were conducted with several potential SRFs. In laboratory experiments, initially milled rocks (Ø< 250 μm for basalt, dolerite, and gneiss; Ø < 150 μm for K-feldspar) were further milled with a ball mill (Spex-8000) for 10, 30, 60, 90, and 120 min under dry and wet (rock/water ratio = 1/3) conditions. To investigate possible reaction between constituents, other subsamples of initially milled basalt, dolerite, and gneiss were added to reagent grade NaCl or KCl (4.5 g rock + 0.5 g NaCl or KCl) and milled for 120 min under dry and wet conditions. Basalt and dolerite were also mixed with K-feldspar at a ratio of 1 : 1 and milled for 120 min under dry and wet conditions. For use in the glasshouse experiment, the initially milled rocks were further milled with a vertical stirred ball mill for 1 h in a dry condition. The elemental and mineralogical compositions of the SRFs were determined using XRF and XRD. Effects of milling on major physicochemical properties of milled rocks were determined, including particle size (Malvern Mastersizer), surface area (BET-N2), quantities of amorphous constituents (XRD, oxalic acid-oxalate extraction, TEM), extractable cations (1M CH3COONH4 pH 7), pHH2O, and electric conductivity. Dissolution kinetics in 0.01M acetic-citric acids (for 56 days) and soil (for 10 months) were determined. Based on the results of these laboratory experiments, a glasshouse experiment was carried out for 12 months to evaluate the effects of SRF application on growth and nutrient uptake of ryegrass grown on several soils. Milling reduced particle size, enhanced amorphism, and increased the release of structural cations from the rocks, with the effects due to dry milling being greater than for wet milling. The optimum milling times which produced maximum amounts of exchangeable cations (Na, K, Ca, and Mg) were 30 - 90 min, depending on rock type. The use of NaCl and KCl as milling additives did not enhance the properties of the SRF

Mafic bedrock being beneficial to vegetation is a relationship that is being mentioned in different kinds of nature related litterature. This relationship is however not always explained and other factors may be as important as, or even more influential than, the bedrock content. In this study the relationship between mafic rock and protected areas of nature is being examined, based on the following questions. -          How does geology, with respect to bedrock content and weathering, create benign conditions for vegetation? -          To what extent is the environment on mafic bedrock, or in its proximity, often judged as worth protecting? The theoretical basis for the study is soil formation regarding parent material, based on Jenny´s formula, and weathering according to the Goldich dissolution series. The method used is a comparison between maps showing bedrock and maps showing areas with protected nature. The protected areas are considered as connected to the mafic bedrock if they are within the mafic area, or up to 2 km from the mafic area in the direction of the ice movement during the last ice age (Weichsel) in Sweden. The mainland of the municipality of Oskarshamn, on the southeast coast of Sweden, is used for a case study. The bedrock in this area is mainly felsic, with some minor areas being mafic. The result shows a higher degree of protected nature, for the types “naturreservat” and ”Natura 2000”, on mafic bedrock, or in the vicinity of the mafic area, than for felsic bedrock. The result for Oskarshamn is compared to mafic bedrock areas around Åseda and Fagerhult and to the limestone area around Vintrosa. For all of these three cases there are areas of protected environment, within or in the vicinity of the studied bedrock areas. Although there seems to be a relationship between mafic bedrock and protected nature, other factors need to be considered as well. The influence of topography, access to water, local climate and e.g. the particle size of the soil, may contribute considerably to the content and distribution of the vegetation at a specific place.

Master of Science / Department of Geology / Mary Hubbard / The southern Sawatch Range of the Southern Rocky Mountains of south-central Colorado is composed of Precambrian crystalline igneous and metamorphic rocks that have undergone at least three major mountain building events during the Phanerozoic, the Ancestral Rockies Orogeny, the Laramide Orogeny, and Rio Grande rifting. In order to determine how the ancient basement structures might have influenced later episodes of deformation, a small area of basement terrain was mapped along the western margin of the Poncha Pass transfer zone between the San Luis and Upper Arkansas basins in the northern Rio Grande rift. The two dominant rock types in the map area, (hornblendic) amphibolite gneiss and (felsic) quartzofeldspathic gneiss, may represent interlayered metabasalt/metadiorite and metarhyolite/metagranite, with lenses of exotic lithologies throughout. Metamorphic foliations were found to be oriented predominantly N35ºW 47ºNE and to have had an influence on younger brittle structures related to the rifting episode. Lineations and fractures in the gneissic fabric also are parallel to brittle deformation structures. Apatite Fission-Track (AFT) analysis provided a means of determining when this crust was exhumed and cooled by the removal of overburden in response to erosion and/or tectonics. The resultant AFT age distribution revealed that exhumation occurred at the higher elevations during the Laramide orogeny (~299-46 Ma), and at lower elevations during Rio Grande rifting (~29-19 Ma). Although it is commonly thought that these mountains were exhumed during the rifting episode, the results of this study indicate that older events played a significant role in the exhumation.

The Bohemian Massif was consolidated during the Variscan orogeny (~400-300 Ma), which involved several oceanic subductions and collisions of continental micro-plates. The central part of the Bohemian Massif, the Moldanubian domain, shows a large accumulation of felsic high-pressure metamorphs. We present a numerical model of exhumation of these rocks due to continental collision and underthrusting. The key feature of the model is a felsic (light, rheologically weak and rich in radioactive elements) material in the lower crust of one of the colliding blocks. We examine the influence of the rate of convergence of the two blocks, radiogenic heating in the felsic lower crust and efficiency of erosion, on the model evolution and pressure-temperature conditions in the lower-crustal material. The models where the material is sufficiently weakened due to radiogenic heating show formation of an orogenic plateau, sedimentation in a foreland basin, and crustal thickening accompanied by gravity-driven exhumation of the lower crust and subsequent sub-horizontal flow in the middle crust. In colder and/or faster models, the thickening is dominated by folding. We correlate the tectonic style of these two types of models with differences between the high-grade rocks in the southern (Moldanubian) and northern (Sudetic) parts...

Diploma thesis - Kateřina Schlöglová - 2011 1/2 English abstract Granulites of the Rychleby Mts. represent relics of high-pressure eclogite-facies metamorphic rocks that are scattered in various crustal and mantle segments of the Variscan orogen in central Europe. These rocks may provide important insights into early stages of Variscan plate convergence and burial as well as exhumation mechanisms. We use mineral assemblages and chemistry to reconstruct the pressure-temperature paths, mechanisms of melting, and conditions of mineral preservation of high-pressure granulites, as well as whole- rock geochemistry to aid in interpretation of granulite precursors and their geodynamic setting. The mafic granulites consist of garnet, omphacite, two feldspars, and quartz with accessory rutile and zircon. The peak assemblage was partly replaced by pargasitic amphibole and biotite. Garnet grains are zoned from Grs36Py10Alm54 (core) to Grs20Py38Alm42 (rim), and host inclusions of phengite, omphacite, unmixed feldspars, kyanite, and rutile. Omphacite composition varies from Di44Hd14Jd42 (inclusions in garnet) through Di63Hd20Jd17 (porphyroblasts) and Di63Hd24Jd13 (symplectitic intergrowths with plagioclase). Reintegrated composition of the feldspar porphyroblasts is Or43Ab53An04. The felsic granulite variety is composed...

No description available.

The oldest dated rocks from the Acasta gneisses of the western Slave Province, Canada present an igneous age of ~4030 Ma. Following this the detrital zircons from the Jack Hills, Narryer Gneiss Terrane, Yilgarn Craton, Western Australia are identified as 4404 ±8 Ma. These discoveries suggest that crustal formation started as early as the Priscian Eon. Hitherto the Earth has gone through a series of interactions involving the atmosphere, hydrosphere, crust, mantle and core. However, only limited remnants of these early processes remain on the accessible crust due to extensive crustal reworking. The Southern Granulite Terrane (SGT) in the southern part of India represents the most extensive exposure of lower crustal granulite terranes in the world. This study mainly focuses on the characteristics of Archean (~2500 Ma) tectonics and nature of subsequent crustal growth, which led to the formation of Archean Nilgiri Block. Detailed fieldwork in this terrane and subsequent petrographic analysis revealed charnockites, hornblende-biotite gneiss, metagabbro/mafic granulite, websterite, amphibolite, Grt-Ky metasediment, metatuff and banded iron formation as the main rock types in this terrane. Field and petrographic results show a regional trend with garnet-orthopyroxene-biotite-quartz-plagioclase-K- feldspar bearing charnockites in the southern part which gets subsequently enriched in clinopyroxene that forms garnet-absent two pyroxene granulites consisting of orthopyroxene-clinopyroxene-quartz-plagioclase-K-feldspar towards the central part. Further north, metagabbro/mafic granulite is enriched in garnet-clinopyroxene-plagioclase assemblage. Websterite, amphibolite, metasediment, metatuff and banded iron formation are stacked and closely associated within this mafic belt in the north. The metagabbro represents peak P-T conditions of ~850°C and ~14kbar compared to the charnockites, which recorded a peak P-T of ~850°C and 9-10kbar. Petrographic results of oxide minerals show that the southern charnockitic part is abundant in rutile-ilmenite association represent reduced conditions compared to the oxidized magnetite-hematite-ilmenite associations in the mafic rocks. This oxidation trend is followed by pyrrhotite-chalcopyrite enriched southern charnockitic region that transforms to pyrite rich northern mafic belt. Ilmenite¬titanite association with no sulphides characterizes the hornblende-biotite gneiss in the entire Nilgiri Block. The geochemical variations of major, trace and rare earth elements show that the granulite-amphibolite grade felsic rocks evolved in an arc magmatic process leaving behind mafic magma, which later intruded into these rocks, in a subduction related arc magmatic process. The U-Pb LA-ICPMS and SHRIMP dating of charnockite, hornblende-biotite gneiss and met gabbros shows ca. 2550 Ma formation age and ca. 2450 Ma metamorphism in this terrane.

<p> A petrological and geochemical study has been carried out on some Archean mafic and felsic volcans of Dome Township, Central Red Lake area, Ontario. Included are a discussion on petrographic descriptions along with chemical investigations of the rocks and a discussion concerning the general problem of petrogenesis. Analytical methods used are explained, and di scussions of the results are included. </p> / Thesis / Bachelor of Arts (BA)