The structural evolution of the Ox Mountains Granodiorite (478±12Ma) during and after its emplacement is described. This pluton has been emplaced within and synchronously with, a major transpressional shear zone which is expressed as a 11km wide belt of strongly deformed NE-SW striking, steeply dipping metasediments. The steep shear zone cleavage is intensified to a mylonitic fabric in a braided system of high strain zones formed through out the Ox Mountains Inlier. Pervasive ductile, sinistral deformation in the shear zone is interupted by the emplacement of the pluton and by the synchronous development in the country rocks of series of brittle thrust structures, which produced a displacement upwards and towards the centre of the shear zone. These thrusts are intimately associated with the emplacement of moderately inclined granodiorite sheets belonging to the main intrusive phase indicating a component of vertical extension in the country rocks at this time. The CMC is a heterogeneous, four component pluton internally composed of a series of large sheets or dykes. Minor muscovite granite sheets emplaced along the northern contacts, preceeded the main intrusive sheets of Group 1 and Group 2 granodiorite with associated diorites. Sheets of tonalites and minor components completed the emplacement history. A prolonged history of sinistral transpressional shearing has deformed the pluton. Discrete sinistral shears indicate an early localization event is overprinted by a main ductile penetrative fabric which cross-cuts ail internal contacts. This fouation is deformed by extensive sinistral S-C fabrics. Later deformation becomes increasingly partitioned into late sinistral and dextral shear zones which are locally mylonitic. Microstructural evidence suggests that the main foliation was formed under lower amphibolite facies and deformed by a steady state flow process. The S-C fabric and late shear zone formation, best developed in the granodiorites and granites, may have been initiated by a switch in the predominant alkalifeldspar deformation mechanism from crystal plastic to a diifusive mass transfer process. This may be a retrogessive effect, and the product is a grain size reduction which may lead to ultramylonite production. The emplacement model for the Ox Mountains Granodiorite is constrained by the original geometry of the dykes or sheets. These data rule out emplacement of the OMG in a releasing bend or pull-apart structure. Strain data does not allow a forceful mechanism and a permissive emplacement model is preferred, in which vertical extension during the intrusive episode created an area of dilation in which dyking occurred. This was caused by oblique movements on two upwardly converging high strain zones outside the pluton. Two satellite plutons, the Lough Talt Adamelhte and the Easkey Lough Adamellite were emplaced in extensional cavities created by reactivated sinistral movements on one of the high strain zones at a much later date. (c400Ma).Transpressional shear zones may initiate or enhance melting in the lower crust and mantle lithosphere where thermal perturbation has occurred. The shear zones may provide conduits for the melts and emplacement sites, especially where high transpressional strains are accommodated by vertical uplift.

No description available.

Thesis (M.S.)--Brigham Young University. Dept. of Geological Sciences, 2006. / Includes bibliographical references (p. 34-39).

<p> The thesis pluton is part of the Saanich granodiorite batholithic complex on south-east Vancouver Island. The pluton is 11 Km by 2 Km, elliptical and trends NW-SE. </p> <p> Petrographically its mineral composition is that of a granodiorite. Alteration is fairly intense as shown by plagioclase and potassium feldspar altering to sericite, as well as biotite and hornblende altering to chlorite. Deformation textures were observed in the form of strained quartz and bent cleavage in biotite. </p> <p> From chemical analyses it was found that the granodiorite represents part of a fractionation process along a calc-alkaline trend. The magma was derived from partial melting of the lower crust. </p> / Thesis / Bachelor of Science (BSc)

Orbicular and comb layer textures in igneous environments are evidence of an unusual heating and cooling regime in small pockets at the edges of crystallizing magmas. Changes in the composition of a magma spark rapid changes in temperature, which cause the temporary suppression of normal crystal nucleation. As the superheated or supercooled magma returns to equilibrium temperature, crystallization occurs exclusively on pre-existing nucleation surfaces (floating xenoliths or wall rocks), creating orbicular and comb layering textures. Orbs and comb layers collected from two localities in the central Sierra Nevada Batholith were analyzed to determine 1) how they formed and 2) what their formation history reveals about the emplacement histories of their respective host plutons. Geochemical analysis including XRF, U-Pb dating and Sr-Nd and O isotope analysis was used to constrain the characteristics of the orbicular magma. Cathodoluminescence as well as macro and microscale petrography was used to determine the specific growth history of the orbs and comb layers. This study shows that orbs and comb layers from both localities formed due to superheating caused by the influx of water into the orbicular melt. Subsequent cooling was caused by mixing–induced depolymerization and fluid enrichment (Big Meadows Creek) or emplacement into a cooler host rock (Deer Creek). Both locations studied are 2–3 Ma younger than their host plutons, indicating that the processes which form orb and comb layers may cause late melting and magma remobilization in larger plutons.

Previous work on the Strontian complex has been substantiated by the present investigation, and the knowledge of the structures in the rocks of the complex, and in the adjoining Moine schists end gneisses has been considerably augmented. It has been shown that a planar structure occurs throughout two of the three main unite of the complex - the tonalite and the porphyritic granodiorite. A linear structure also occurs in these rocks in a restricted area it the north. These structures largely conform to a simple pattern common to both tonalite and granodiorite. In the northern part of the complex, the granitic veins end the joints both appear to possess distinctive patterns of orientation, which prevail throughout this northern region. These patterns show little similarity to each other, and appear to be largely unrelated to the orientation of the foliation and lineation in the tonalite and granodiorite in this area. The formation of the complex appears to have been attended by considerable shearing and folding in the Moine country rocks which lie within half a mile of the complex. The overall pattern of the structures within the complex and the adjoining areas of country rock, appears to be distinctive, and does not closely resemble the structural pattern within and around other granitic complexes. It is suggested that the two main units of the complex with a common internal structural pattern have been formed by the more or less simultaneous intrusion of two magmas, and that these magmas were probably emplaced by a process which involved forcible intrusion, and may have under the control of forces associated with the Caledonian orogeny.

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Στην πρώτη ενότητα της έρευνας, σκοπός μας είναι ο προσδιορισμός των λιθοτύπων και του πετροτεκτονικού περιβάλλοντος εναπόθεσης του πλουτωνίτη. Για το λόγο αυτό χρησιμοποιούνται πετρογραφικές, πετροχημικές καθώς και ορυκτοχημικές μέθοδοι ταξινόμησης. Μελετώνται οι συνθήκες πίεσης και θερμοκρασίας κάτω από τις οποίες εναποτέθηκε ο πλουτωνίτης με τη χρήση γεωβαρομέτρου και γεωθερμομέτρου. Διερευνάται, επίσης η γεωχημεία των περιβαλλόντων πετρωμάτων του πλουτωνίτη καθώς και οι πιθανοί τους πρωτόλιθοι. Η δεύτερη ενότητα της έρευνας περιλαμβάνει τη μελέτη της, συνδεδεμένης με τον πλουτωνίτη, μεταλλοφορίας οξειδίων του σιδήρου (αιματίτη, μαγνητίτη) και σουλφιδίων. Μελετάται η θερμοκρασία κάτω από την οποία έγινε η κοιτασματογένεση, καθώς και η πιθανή πηγή προέλευσής της. Για το σκοπό αυτό χρησιμοποιούνται στοιχειομετρικές, γεωχημικές και ιστολογικές μέθοδοι για τις μεταλλικές παραγενέσεις. Γίνεται, επίσης, προσδιορισμός της θερμοκρασίας εναπόθεσης των σουλφιδίων καθώς και της πηγής προέλευσης του υδροθερμικού ρευστού από το οποίο αποτέθηκαν. Για το σκοπό αυτό χρησιμοποιείται η μέθοδος των σταθερών ισοτόπων 34S. Απαντάμε επίσης στο ερώτημα αν η μεταλλοφορία των σουλφιδίων και οξειδίων προϋπάρχει της διείσδυσης του πλουτωνίτη ή δημιουργήθηκε εξαιτίας αυτής. Τέλος, ως τρίτη, εξίσου σημαντική ενότητα της έρευνας θεωρείται η αναφορά στις αρνητικές επιδράσεις της μεταλλοφορίας οξειδίων του σιδήρου και σουλφιδίων στο περιβάλλον. Στην ενότητα αυτή περιλαμβάνεται και η πρόταση πιθανών τρόπων αντιμετώπισής τους. / The aim of the first part of this study is the determination of the lithotypes of the studied area and also the definition of the petro-tectonic environment of the emplacement of the pluton. Petrographic, petrochemical and mineralogical methoda of classification have been used to accomplish this aim. The conditions of pressure and temperature of the pluton emplacement have been determined with the use of geobarometric and geothermometric methods. In this part of the study, the geochemistry of the country rocks of the pluton and their possible protoliths are also presented. The second part of the study refers to the mineralization of iron oxides (hematite, magnetite) and sulfides related to the pluton emplacement. Stoichiometric, geochemical and textural methods have been used to identify the paragenesis of the mineralization in order to determine the temperature of the mineralization and assume the possible heat origin. the sulfides emplacement temperature, as well as the origin of their hydrothermal fluid is determined, using the method of the stable isotope 34S. We also adress to the question if the sulfides and oxides ores prexisted the pluton inavsion or were created because of it. Finally, as athird equally important aspect of this study is considered the reference to the negative effects of the sulfides and oxides ores in the environment. This unit includes recomendations of possible solutions.