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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Chemical petrology of metamorphosed basic rocks of the Dalradian Series, with particular reference to the Knapdale area of Argyll

Graham, C. M. January 1973 (has links)
No description available.
2

Tectono-stratigraphy and evolution of the Mesozoic Pindos Ophiolite and associated units, northwest Greece

Jones, Gregory January 1990 (has links)
The northwest Pindos Mountains of Greece expose a sequence of Mesozoic and Tertiary thrust sheets, which include the Jurassic Pindos ophiolite, composed of ultramafic and mafic oceanic crust and mantle. Regional mapping has established the tectonic order of these units from top to base as follows: i) a mainly ultramafic ophiolitic thrust sheet (Dramala Complex of the Pindos Ophiolite Group) and basal metamorphic sole (Loumnitsa Unit of the Pindos Ophiolite Group); ii) Late Cretaceous platformal limestones (Orliakas Group); iii) dismembered intrusive and extrusive ophiolitic rocks (Aspropotamos Complex of the Pindos Ophilite Group); iv) tectonic melange and olistromes, dominated by Triassic-Jurassic volcanic and sedimentary rocks (Avdella Melange); v) coherent thrust sheets of Late Jurassic-Late Cretaceous deep-water sediments (Dio Dendra Group); vi) Early Tertiary flysch (Pindos Flysch). Immobile trace-element studies indicate that the Triassic and Jurassic extrusives of the volcanic-sedimentary melange, formed mainly at within-plate through to mid ocean ridge settings. By contrast, the structurally overlying ophiolitic extrusives include boninite series volcanic rocks and depleted island arc tholeiites, indicative of a supra-subduction zone origin. Initial displacement of the ophilite (ca 165 Ma) is recorded in the formation of a metamorphic sole, passing structurally downwards from a basal peridotite mylonite zone into amphibolite and greenschist facies rocks. The sole rocks in general have MORB and WPB trace-element chemical affinities, although a limited number of samples are more depleted in high field strength elements, and can be correlated with rocks of island arc origin, including boninites. Petrological and structural comparisons suggest the Pindos ophiolite is regionally continuous beneath the Meso-Hellenic trough with the Vourinos ophiolite to the east. This ophiolite, similarly has a supra-subduction zone chemical signature, and is also underlain by fragmentary metamorphic sole and melange units. In the favoured tectonic model, the Pindos ophiolite formed above a Early to Mid Jurassic westerly-dipping intra-oceanic subduction zone. Continuing subduction produced a thick accretionary complex, now represented by the Avdella melange that underlies the Pindos ophiolitic units. During the Late Jurassic, the supra-subduction zone ophiolite was emplaced as a relatively undeformed sheet, northeastwards onto the Pelagonian Zone, an assumed microcontinent. The 'fore-arc' crust situated immediately above the subduction zone was detached and overthrust by the remainder of the ophiolite sheet. Following this, the Pindos ocean remained partly open to the west as a remnant basin, undergoing deep-water and marginal carbonate deposition from the Late Jurassic to late Cretaceous. In Early Tertiary time (?Palaeocene-Eocene), this basin began to close; the Pindos ophiolite was sliced, and together with the Jurassic melange and younger deep-water sediments, was thrust westwards over a flexural foreland basin (Pindos Flysch), and then onto the Apulian continental margin as an inboard-propagating thrust stack. Inferred footwall structures (old palaeogeographic features?) or late stage folding were mainly responsible for the formation of large orthogonal (e.g. Armata-Milea corridor) and transverse (e.g. Perivoli corridor) culminations. Final thrusting was accompanied by extension behind the deformation front, leading to the formation and infilling of the Meso-Hellenic molasse basin.
3

Potassium-Argon age studies in Peru with particular reference to the chronology of emplacement of the coastal batholith

Wilson, Paul Anthony January 1975 (has links)
This research was initiated in order to study the chronology of emplacement of the Coastal batholith of Central Peru particularly to find out if the batholith had evolved by a continuous or an episodic process of intrusive activity. Some 135 new K.Ar age determinations on mineral separates from igneous rocks of the western Cordillera of Central Peru are presented and produce a broad spectrum of ages between 98 and 3 m.y.
4

The structural evolution of the coastal batholith in the provinces of Ancash and Lima, Central Peru

Bussell, Michael Andrew January 1975 (has links)
The current research was undertaken in order to clarify the regional structural setting of the batholith, the mechanism of emplacement o~ successive plutons and the extent of the control exerted by the envelope fracture pattern on the contact form of individual plutons. Regional mapping in Ancash shows that , in the Albian, a rapidly subsiding trough filled with a great thickness of volcanic caterial while, to the east, thinner and more condensed volcanic strata interdigitated with sediments on the western margin of the Peruvian miogeosyncline.The line of facies divide between the two troughs is concurrent with the axis of a large monoclinal structure which is thought to have been generated by a reversal of movement, with uplift along the fault - bound margins of the earlier basins. Gabbro injection accompanied the deformation which may reflect the generation and accumulation of batholithic magmas at greater depth.
5

The geochemistry and mineralogy of Cañas and Puscao plutons, Lima Province, Peru

Taylor, William Proctor January 1973 (has links)
The aim of the investigation was to study variations within two of the many plutons which make up the composite Coastal Batholith of Central Peru. The variations were believed to be the result of differentiation and the author wished to establish whether the process was solely operational prior to emplacement or took place 'in situ' during the period preceding the total consolidation of the magma. Response surface techniques were used on partial whole-rock chemical analyses from the Canas and Puscao plutons to establish the three dimensional nature of the chemical variations. The Canas pluton was selected because of its apparent homogeneity and lack of contamination by assimilation of country rock, which suggest that the magma solidified without differentiation once it had been emplaced. By contrast the Puscao pluton was chosen because it showed signs of large scale layering in the field and was believed to have been contaminated by xenolithic roof material. As a result of careful statistical assessment of the resulting analyses it was possible to isolate the various scales of variation within each pluton.
6

The geology and petrology of the Engaruka-Oldowyo L'Engai-Lake Natron area of northern Tanganyika territory

Guest, Norman James January 1953 (has links)
This region· lies .in the northern part of the Tanganyika Gregory Rift Valley. Amongst certain aspects which are con-' sidered in less detail are the questions of tectonics and age, the rocks of the basement complex, and the geology of Lake Natron. The main work consists of the systematic petrography of a group of Older Extrusives, andesitic. and basaltic rocks, and of a series of Younger Extrusives, soda-rich alkaline rocks, including· the carbonat1tes of the volcano, Kerimasi. The former occurred after a period of rift faUlting;- they are associated with larger volcanoes, and cover greater areas than the probable Upper Pleistocene Younger Extrusives. Utiliz1ng 12 ne~l chemical analyses of rocks, 2 partial analyses, and incorporating all additional known rock analyses, a regional magmatic trend is 'outlined, with a parent magma of ... basic-andes1t1c composition, be11eved to have been derived from / an o11vine-basalt magma. This parent magma eXh1b1ts different1ation by fr~ctiona1 crystall1sat10n together with alteration through contamination w1th the basement rocks. To the east, .on the. volcanoes of Ketumbaine and Gelai, the magmatic trend is essentially, basic-andesite, andes1te, Mawenzi-, trachyandesite, phonolite, phonolitic-trachyte, trachyte. NepheI1ne-Irlelabasalt, nepheline-andesite, i\\ugear1 te, and nephe1initic-phono1ites were also noted. Similar rocks were mapped' on the rift wall to the west. After further rift-faulting, the nephelinitic-phonolite magma was further contaminated with the basement rocks, as shown -by the fenites and tveitlsites noted on the active volcano of Oldonyp L'Engai. Moreover, the nephelinitic-phono1ite magma was desil~cated by the assimilation of basement dolomitic limestone, and carbonatite was formed. Subsequently the source of the 1imesto~e having becon~ exhausted, the parent magma returned to near its pre-deailication composition. A detailed geological map has been constructed, and photomicrographs have been made or slides or most or the rook types.
7

Petrography, porosity, permeability and geochemistry of the Upper Magnesian Limestone of N.E. England

Al-Rekabi, Yasser S. January 1982 (has links)
Petrographic observations of the sediments of the Upper Magnesian Limestone reveal that the main lithologies are the "dolomitized" carbonate mud and ooliths, bioclasts are not generally common. Stromatolites and depositional laminations together with massive beds are common in the formation. Apart from psuedo-pellets (of diagenetic origin), no depositional pellets have been recognized. The variations in the lithologies of the formation, the absence of pelletoidal sediments and the general lack of preserved fauna together with the presence of sulphates suggests that the environment of deposition was characterized by saline waters. The energy of depositional currents ranged from low to vigorous. Therefore, the sediments are believed to have accumulated in a shelf area of shallow depth with only temporary restriction of circulation.
8

Feldspar microtextures and the cooling histories of high-grade terrains

Cayzer, Nicola January 2002 (has links)
Perthitic, antiperthitic and mesoperthitic microtextures were observed in this study representing the wide range of bulk compositions exhibited by ternary feldspars. The mesoperthites were often coarse, but semicoherent, regular intergrowths and often showed fine secondary exsolution. They are likely to have formed by spinodal decomposition below the coherent spinodal. Unusual mesoperthites with two orientations of lamellae may have been the result of deformation of existing mesoperthitic textures. Perthitic textures were characterised be blebs of oligoclase-andesine plagioclase and fine, albitic, secondary lamellae. The blebs are likely to have formed by homogenous nucleation with coarser blebs nucleating earlier by heterogeneous nucleation. The host to the blebs was compositionally homogeneous before the exsolution of the fine secondary lamellae. The orientation of the blebs was sometimes oblique to the lamellae due to the influence of deformation on the blebs as they were forming. Antiperthitic textures were characterised by K-feldspar blebs that had nucleated on the twin boundaries of the host plagioclase. Some samples had compositions with excess K-feldspar for the metamorphic conditions of the terrain and appear to have been altered by replacement involving addition of K-feldspar. Both the perthitic and antiperthitic textures were seen in all of the terrains and similar textures have been reported from other granulite terrains worldwide. The mesoperthitic textures in this study were restricted to the Napier Complex, but are also reported from other granulite terrains with different cooling histories. The feldspar do not show any evidence that the cooling history played a significant part in the development of the texture, but show that bulk composition was the major influence. The bulk composition of the feldspar determined where the coherent ternary solvus and spinodal were intersected and thus the nature of the exsolution. The effects of deformation and later fluid infiltration during the cooling history are, however, recorded by the microtextures.
9

The metamorphic histories of some proterozoic granulites from East Antarctica

Fitzsimons, Ian Christopher William January 1991 (has links)
The Proterozoic Complex of East Antarctica is an extensive metamorphic terrain, which comprises various outcrop areas preserving granulite-facies mineral assemblages ascribed to a 1000 Ma metamorphic event. This study has focused on two areas of this terrain: the Brattstrand Bluffs coastline of Prydz Bay, Princess Elizabeth Land, and the Nemesis Glacier region in the northern Prince Charles Mountains of Mac. Robertson Land. Both areas are composed of granulite-facies gneisses and migmatites of igneous and sedimentary origin, with a complex history of deformation, anatexis and intrusion at high grade. The structure of both areas is dominated by a flat-laying, layer-parallel, foliation. This foliation is locally overprinted by folds and shear zones which are flat lying in the Brattstrand Bluffs coastline, but upright in the Nemesis Glacier region. Pressure-temperature (<i>P-T</i>) estimates were derived through application of suitable barometers and thermometers to selected specimens of garnet-orthopyroxene-plagioclase-quartz gneiss from both areas. A spread of temperature data from garnet-orthopyroxene thermometers, and pressure data from a barometer based on the solubility of alumina in coexisting garnet and orthopyroxene, are attributed to a variable extent of retrograde Fe-Mg exchange. <i>P-T</i> estimates were corrected for this exchange by using the Fe-Mg distributon coefficient required to bring the pressures derived from the exchange-sensitive barometer into agreement with pressures derived from garnet-orthopyroxene-plagioclase-quartz barometers, which are relatively insensitive to Fe-Mg exchange. Correct peak <i>P-T</i> estimates are <i>c</i>. 6.0 kbar and 860<SUP>o</SUP>C for the Brattstrand Bluffs coastline and <i>c</i>. 6.5 kbar and 800<SUP>o</SUP>C for the Nemesis Glacier region. Zonation trends in garnet, orthopyroxene and plagioclase from the two areas are consistent with a retrograde <i>P-T</i> path gradient of <i>c</i>. 17 bar/<SUP>o</SUP>C in the Brattstrand Bluffs coastline, and <i>c</i>. 6 bar/<SUP>o</SUP>C in the Nemesis Glacier region. Well-layered and migmatitic metapelites in the Brattstrand Bluffs coastline exhibit abundant field evidence for the generation and extraction of leucocratic melts at the metamorphic peak, and metapelite mineral assemblages imply low values of αHSO (less than 0.2). Textural studies indicate that H<SUB>2</SUB>O was partitioned in the silicate melt phase as melting progressed, and that the final stages of melting proceeded through incongruent reactions such as biotite + sillimanite + quartz = garnet + cordierite + K-feldspar + melt, which require fluid absence. Mineral assemblage development subsequent to the melting, for example spinel-cordierite symplectites after garnet and sillimanite, indicates decompression from pressures over 5 kbar to <i>c</i>. 3 kbar. Integration of microtextures with the structural history indicates that some of this decompression was synchronous with localized development of flat-lying folds and shear fabrics. This combination of decompression and sub-horizontal shearing is attributed to progressive extension after the metamorphic peak. Hydrous fluids were released by the melts as they crystallized, and were transported along the shear zones, thus preserving anhydrous assemblages in most of the rocks.
10

A petrological study of the western part of the Kilpatrick Hills

Hamilton, J. January 1955 (has links)
No description available.

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