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Deformation in the striped rock pluton, southwest VirginiaKalaghan, Theresa A. January 1987 (has links)
The Striped Rock pluton of the late-Proterozoic Crossnore Plutonic-Volcanic suite is located beneath the Fries Thrust zone in the Blue Ridge province of southwest Virginia. The multiphase granite pluton has been affected by episodes of brittle and crystal plastic deformation at both the microscopic and mesoscopic scales. Brittle deformation preceded and postdated crystal plastic deformation.
The pluton is cut by pervasive centimeter-scale cataclasite zones and ductile shear zones that vary in width from a few millimeters to several hundred meters. The majority of mylonite zones in the pluton strike east and northeast and are inclined moderately southeast. Cataclasite zones strike northeast and northwest. Deformation is most intense along the southern contact with the Cranberry gneiss where both pluton and country rock are deformed into a northeast-striking zone of mylonitic augen gneiss. The intensity of deformation decreases northwestward. Southeastdirected normal fault displacement is common to east and northeast-trending shear zones. A minor group of northwest-oriented shear zones dip moderately southwest and northeast and show sinistral, strike-slip displacement. Quartz-, chlorite- and stilpnomelane-filled cracks and veins with northeast and northwest trend uniformly overprint mylonite and cataclasite zones of all scales.
Microstructure changes progressively with increasing strain. Feldspar grains are cut by at least two generations of mineralized, dilatant microcracks. Minerals precipitated in the early set of microcracks have undergone extensive crystal plastic deformation. Late-stage microcracks are filled with completely undeformed minerals.
The spatial distribution of normal fault mylonite zones is geometrically consistent with generation during 1) late-Proterozoic extension, 2) Mesozoic extension, 3) rigid-body rotation during Paleozoic thrusting, or 4) "gravitational collapse" during Paleozoic thrusting. Field and microstructural evidence favor (4). The exact timing of deformation is not, however, well-constrained. / Master of Science
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The emplacement and crystallization of the cornelia pluton, Ajo, Arizona: an analysis based on the compositional zoning of plagioclase and field relationsHarris, Jonathan O. January 1984 (has links)
The Cornelia Pluton was previously found to have been faulted in two (Gilluly, 1946). The downthrown apex is host to a copper ore-body, and the upthrown block represents a vertical cross-section of the igneous system. Field work confirmed the character of the relationship between three texturally-distinct quartz monzonites described by Wadsworth (1968). Plagioclase crystals were chosen from all the phases, including previously undescribed hydrothermal rocks, and analyzed with a microprobe. Graphs of anorthite content versus radial distance revealed systematic patterns of compositional variation, analysis of which yielded a consistent, time-dependent model for the emplacement and crystallization of the system. The granodiorite resulted from an earlier intrusive event. The quartz monzonites crystallized initially downward from the system's roof, and, subsequently, upward from the floor. Saturation of the remaining pocket(s) of magma led to the development of an inner fine-grained phase, and possibly, the evolution of hydrothermal fluids. The genetic connection between these fluids and eventual mineralization of the cupola is suggested.
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The Darling granite batholithSchoch, A. E.(Aylva Ernest) 09 1900 (has links)
Thesis (PhD) -- Stellenbosch Univesrsity, 1972. / The Darling batholith is characterised by large scale hybridisation,
but mainly consists of the coarsely porphyritic
Darling granite. This granite changes gradationally into a
biotite-rich variety which occupies a roughly elliptical area
with a major, northwesterly trending axis of 30 km. The biotite
granite envelops a large irregular body of hybrid granodiorite. Small intrusions of younger granite occur within
the batholith namely the Klipberg and Contreberg granites and
possibly the biotite-rich Dassenberg granite. Dassen Island
is underlain by fine-grained granite which could be related to
either the younger or coarsely porphyritic granites. A prominent
northwesterly trending mylonite zone can be traced through
Darling to Swartberg, and ultimately to Trekoskraal in the Saldanha
batholith, but is not continuous since it occasionally
changes into gneissic granite and is also interrupted by the
younger intrusives. Quantitative mapping included measurement of matrix grain size, average maximum phenocryst length, xenolith distribution density, quartz nodule distribution density and average size, lineation, dark mineral index and gneissosity. On Dassen Island the distribution of tourmaline nodules was , determined.
The results are displayed as small scale contour maps which
show strong correlation between the various parameters. The
average values of matrix grain size, average phenocryst length
and xenolith distribution density are respectively 2-5mm,
20-60mm and 0-1,5 per m² for the Darling granite, and 1-2 mm,
5-20 mm and 1-9 per m² for the hybrid granodiorite. It was
found that the matrix grain size decreases with increase in
hybridisation. The spotty distribution pattern of tourmaline
nodules on Dassen Island indicates addition of boron by assimilation of metamorphites and a late stage liquid immiscibility process. The granites :.have normal mineralogy and the K-feldspar of the phenocrysts is maximum microcline (Δ = 0,9 - 1,0). The hybrid granodiorite contains much pinitised cordierite and locally garnet. The deeply pleochroic bioti te is probably of the 2M1 polytype and has a higher Fe:Mg ratio in the hybrid granodiorite than in the granite (2,8 - 3,0 vs. 2,2 - 2,3). The intimately associated chlorite seems to be of the Ia polytype. The cordierite is of the normal and low temperature type with average intensity index of 2,7 , distortion index of 0,3 and 2 a of 63°. The xenoliths are predominantly quartzitic metagraywackes, but lime-rich types holding sphene and diopside were occasionally encountered.
Thirteen new chemical analyses and thirty-one previously
published analyses are used to calculate average composite
analyses of the various rock types. The results of calculations
employing Barth standard cell values indicate that the
hybrid granodiorite could have originated by reaction between
granite magma and Malmesbury quartzitic metagraywacke and pe-lite with a little limestone. A "granite differentiation index" based on weight percentages of (Ti02 + MgO + FeO + Fe2O3) and (Si02 + Na2O + K2O) shows a linear relationship between the granites in probable order of age. The magmatic differentiation trend is separated from the hybridisation trend on a 6alk - 2(al - alk) - (100 - 2al) diagram. Mesonorms and their cordierite variants are used to effect comparison with the experimental granitic system of von Platen (1965). The Darling and Contreberg granites plot near the relevant cotectic surfaces. A pilot experimental study of
melting behaviour indicates that the Contreberg granite is
closer to a minimum melt composition than the Darling granite. Comparison of alkali values with a M Na2O - M K2O Schreinemakers diagram of Korzhinskii (1959), shows that the alkali ratio of the older analyses may be incorrect, and indicates that the dark minerals have a greater effect on plagioclase composition than the amount of K-feldspar. The classification of granites by means of Harpum diagrams is shown to have little relevance to the reconstruction of the ancient thermodynamical variants. The Darling granite is correlated with the Hoedjies Point granite of the Saldanha batholith and on geochronological evidence probably corresponds in age (500- 600 m.y.) with the Cape Peninsula granite. The younger granites of Darling are tentatively correlated with the Cape Columbine granite of the
Saldanha batholith. The northeastern boundary of the Darling
batholith is a major fault, the Colenso fault, which is considered to extend as far as Northwest Bay, Saldanha. It is
proposed that the Darling batholith occupies a down-faulted
block within a graben and that the hybrid granodiorite represents a remnant synform of the roof rocks intruded by the granite. The younger granites constitute only four percent by volume of the batholith and may represent anatectic melts from a nearby subjacent source.
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The history of deformation and fluid phenomena in the top of the wilderness suite, Santa Catalina Mountains, Pima County, ArizonaYoung, David Paul January 1988 (has links)
No description available.
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Geochemistry of mafic dykes from the Discovery Bay granitic pluton, Hong KongWong, Lai-man, Kennis., 王麗敏. January 2004 (has links)
published_or_final_version / Applied Geosciences / Master / Master of Science
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Magmatic Evolution and Eruptive History of the Granitic Bumping Lake Pluton, Washington: Source of the Bumping River and Cash Prairie TuffsKing, John Frederick 24 May 1994 (has links)
The 25 Ma Bumping Lake pluton ranges in composition from quartz diorite to granite with the granitic facies comprising approximately 90% of the pluton's surface area. The granite may be classified as calcalkaline, peraluminous and I-type with some Stype characteristics. A late-stage, mafic-poor facies fills cooling related extensional fractures. The pluton was passively emplaced into the Ohanapecosh Formation at a shallow level in the crust. Contact relationships vary from sharp where the contact is vertical to gradational at the roof of the pluton. Where gradational, stoped xenoliths from the roof of the pluton increase in size, angularity and retain more of their primary textures as the contact is approached. Spacial trends in major and trace elements support the interpretation that xenoliths were stoped and assimilated into the melt The predicted Rayleigh number for the pluton when molten is 107 and the predicted Reynolds number is approximately 10-9. Based on these values, the magma of the pluton probably did not convect, and if it did, convection was weak and not a significant process. Based on variations in Eu/Eu* and Sr values, plagioclase fractionation was an important process in the petrogenesis of the pluton. Additionally, fractionation of accessory minerals rich in light rare-earth elements (LREE) resulted in successive depletion of LREE with progressive differentiation. Two separate regions of the pluton are highly differentiated as indicated by high Si02 values, high Rb/Zr ratios, and low Zr and Ti02 values. Mapping by the author indicates that the pluton projects beneath the Mount Aix caldera. Dates of three tuffs derived from the caldera are equivalent to the pluton, and two of these tuffs are chemically indistinguishable from the granite facies of the pluton. This implies that the Bumping Lake pluton represents the chilled remains of the magma chamber that fed the Mount Aix caldera.
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Paleomagnetism of Jurassic plutons in the central Klamath Mountains, southern Oregon and northern CaliforniaSchultz, Karin L. 11 February 1983 (has links)
An understanding of the tectonic history of the Klamath Mountains
is crucial for a valid paleogeographic reconstruction of the Pacific
Northwest. However, prior to this study there were very few
paleomagnetic (PM) data from the Klamath Mountains (KN), which resulted
in conflicting interpretations about the role of the KM province in
the tectonic evolution of western North America. Twenty-eight sites
from five unmetamorphosed Middle Jurassic KM plutons with K-Ar ages
ranging from 161 to 139 m.y.B.P. yielded stable PM results showing
(1) a direction for the 160 in.y.B.P. Ashland pluton (D=324°, I=163°,
α₉₅=8°, n=6) nearly concordant with the coeval expected direction
(D=337°, 1=54°) and (2) clockwise rotated directions for the plutons
of Grants Pass (D=045°, I=67°, α₉₅=12°, n=4), Greyback (D=083°,I=63°,
α₉₅=9, n=9), and the Wooley Creek batholith and Slinkard pluton
combined (D=037°, 160°, α₉₅=ll°, n=9).
Tectonic interpretations of these PM data are difficult; two
interpretations are offered to explain the observed directions. In
the first, the mean PM direction of the four plutons with discordant
directions (D=057°, 1=65°, α₉₅=7°, n=22) is restored to the expected
150 m.y.B.P. (the average K-Ar age for these four plutons) direction
by rotation of a rigid block ~87° in a counterclockwise sense about a
vertical axis (the possibility of tilt of these four plutons is disregarded
in this interpretation). The Ashland pluton which shows no
rotation is problematic. Either there was (is) a tectonic boundary
west of the Ashland pluton, separating it from the rotation of the
others, or the Ashland pluton was influenced both by clockwise rotation
and tilt, the combined effect producing an essentially concordant
PM direction. In the second interpretation we distinguish
between the northern KN, intruded by the Grants Pas and Greyback
Mountain plutons, and the southern region intruded by the Wooley
Creek batholith and the Ashland and Slinkard plutons. The bases for
this distinction are recent geologic and gravity studies which
suggest that post-Middle Jurassic uplift of the domal Condrey
Mountain Schist may have caused radially outward tilt of its
adjacent terranes and plutons intruded therein, causing some of the
observed discordances in their PM directions. Thus, in the second
interpretation it is envisioned that (a) the northerly portion of
the KM, intruded by the Grants Pass and Greyback plutons, was
affected primarily by clockwise rotation about a vertical axis, and
(b) discordant directions for the remaining plutons intruded farther
south are due primarily to tilt in response to Condrey Mountain
uplift. Based on the observed inclinations, there is no evidence
of transport of the Klamath Mountain province along lines of longitude
since Middle Jurassic time.
Tectonic interpretations of the PM results of this study are
consistent with significant post-Middle Jurassic clockwise rotation
of the Klamath Mountains. The first interpretation above yields
~87° of clockwise rotation of the terrane examined. According to the
second interpretation, a clockwise rotation of ~l00° is inferred
from the average of the PM results of the northern Grants Pass and
Greyback plutons. Therefore, 10° to 25° of clockwise rotation of the
KM may have occurred prior to the formation of the Oregon Coast
Range (~55 m.y.B.P.) and the two provinces may have rotated together
since post-Lower Eocene time. / Graduation date: 1983
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A petrochemical study of the Mount Fubilan Intrusion and associated ore bodies, Papua New GuineaDoucette, John 02 March 2000 (has links)
The Mount Fubilan Intrusion is part of a geologically young hypabyssal stock in the Star Mountains of Papua New Guinea. This stock was mapped as the Ok Tedi Intrusive Complex and divided into four separate bodies: the Mount Fubilan, Sydney Intrusion, Kalgoorlie, and Ningi Intrusions. Hydrothermal fluids caused alteration of the Mount Fubilan, and parts of the other intrusions, to potassic and propylitic mineral assemblages and deposited gold and copper.
This investigation documents similarities and differences between the least-altered intrusive rocks of the complex and those that have undergone potassic metasomatism. The study involved detailed petrographic examination of more than two hundred thin-sections, major-oxide and trace element chemistry, and microprobe analyses of individual minerals. The magmas that crystallized to form the stock are shown to be intermediate in composition between andesite and latite. They were quartz-saturated, metaluminous, weakly iron-rich, and crystallized under oxidizing conditions. The principal mineral phases in the least-altered intrusive rocks are andesine, pyroxene, orthoclase, and quartz. The accessory mineral suite in least-altered rocks includes biotite, sphene, apatite, magnetite, and zircon.
Hornblende is present in a few samples Magmatic pyroxene is diopsidic in composition; hornblendes is cdenitic; and biotite is annitic. Potassic alteration has converted andesine to orthoclase, or mixtures of albite and orthoclase, ferro magnesian minerals to hydrothermal biotite, sphene to rutile, and magnetite to pyrite and chalcopyrite. Hydrothermal biotite is phlogopitic in composition. Gold and copper were concentrated in the zone of potassic alteration.
The mineralogical transformation of the intrusive rocks of the Mount Fubilan and associated intrusions was caused by the infiltration of hydrothermal fluids that deposited potassium, gold, and copper and that leached and removed virtually all other rock constituents. Leached components were transported away from the zone of potassic alteration and deposited in peripheral parts of the intrusive complex to form propylites, endoskarn, and massive replacement bodies or removed from the system entirely.
The Mount Fubilan intrusion was closely similar in chemistry and mineralogy to the other intrusions of the complex prior to alteration. Petrochemical differences between the Mount Fubilan Intrusion and the other intrusions were produced entirely by hydrothermal alteration. / Graduation date: 2000
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Igneous intrusions and thermal evolution in the Raton Basin, CO-NM contact metamorphism and coal-bed methane generation /Cooper, Jennifer Rebecca. January 2006 (has links)
Thesis (M.S.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 6, 2007) Includes bibliographical references.
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Geology, geochemistry, and mineral potential of cretaceous and tertiary plutons in the eastern part of the Soldier Mountains, IdahoLewis, Reed S. (Reed Stone) 21 May 1990 (has links)
Graduation date: 1991
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