Thesis (M. Sc.), Memorial University of Newfoundland, 1998. / Restricted until June 1999. Bibliography: leaves 195-106. Also available online.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Six maps and diagrams on folded leaves in pocket. Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 380-389).

The Madurai Block is the largest granulite block in Southern Granulite Terrain which lies between Palghat-Cauvary shear zone in the North and Achankovil shear zone in the South. This terrain underwent extreme crustal metamorphism under ultrahigh-temperature metamorphic conditions which provides vital information about the tectonic process of the lower crust. Ultrahigh temperature metamorphism was defined by Harley (1998b) as a subclass of granulite facies metamorphism of crustal rocks in which peak temperature exceeds 900°C at moderate pressures (7-13 kbar) in the deep crust. However, considering the lacunae about the present understanding of ultrahigh temperature metamorphism, the study attempts to identify the heat source and role of lower crustal fluids in high temperature metamorphism. To understand the role of lower crustal fluids, a case study on migmatised metapelites from the Kodaikanal region was done where the metapelites have undergone UHT metamorphism. In-situ electron microprobe Th-U-Pb isochron (CHIME) dating of monazites in a leucosome and surrounding silica saturated and silica under saturated restite from the same outcrop indicate three principal ages which can be linked in with the evolutionary history of these rocks. The monazite grains in leucosome sample show alteration along the rims. These altered rims are experimentally replicated in a monazite-leucosome experiment at 800°C and 200MPa. This experiment, coupled with earlier published monazite-fluid experiments involving high pH alkali-bearing fluids at high P-T, helps to confirm the idea that alkali-bearing fluids, in the melt and along grain boundaries during crystallization, were responsible for the formation of the altered monazite grain rims via the process of coupled dissolution-reprecipitation. Lower crustal fluids during migmatization and high temperature metamorphism from leucosome monazites signify the need for a more precise texturally-controlled geochronological determination. Considering the possible heat source of high temperature metamorphism, the role of associated rocks of charnockites/granites and ultramafics was studied from Kodaikanal and Ganguvarrpatti. The results indicate that both charnockites and granites are not the heat source of high temperature metamorphism. However, to recognize the ultramafic as the potential heat source the sapphirine-bearing high Mg-Opx bearing rock was studied from Kambam town. The sapphirine–cordierite intergrowth pods are characterized by unique texture and peraluminous sapphirine composition suggesting that these domains could represent cryptic pathways through which aluminous melts migrated. The mineral phase equilibria considerations suggest that such peraluminous melts interacted with Mg-rich orthopyroxene in the host granulite at 1025°C and 8 kbar, with subsequent isobaric cooling. The underplated mafic magma (T>1000°C) is suggested as a possible mechanism that provided the heat source for partial melting of lower crust and the UHT metamorphism. Moreover, field evidence of metapelite in direct contact with an ultramafic body was observed resulting into granulite grade metamorphism. The other evidence of ultramafic magma as heat source is though the mineral chemistry and geochemical modeling of the studied ultramafic rocks.

The Archean North Caribou greenstone belt (NCGB) possesses abundant transpressive deformation zones on its northern margins, which appear to have formed under amphibolite facies conditions. Protracted deformation and regional metamorphism are coeval with widespread magmatism and accretion events in the Superior Province, yet the importance of these shear zones in the tectonic evolution of the NCGB is equivocal. Structural analyses support a transpressive system that strongly implicates horizontal tectonism. This is partly in contrast with some currently proposed models for Archean greenstone belts suggesting synchronous vertical and horizontal movements. Geochemical and microstructural analyses from shear zones indicate heterogeneous deformation/fluids conditions on a km-scale. Monazite and mica geochronological ages indicate metamorphism and deformation occurring during the amalgamation of the Superior craton from ca. 2.75 to 2.4 Ga. The high metamorphic grade background may obscure tectonic signatures, yet some structural and geochemical characteristics remain consistent with other greenstone belts where vertical and horizontal displacement are recorded.

The northerly trending Hozameen, Yale and Hope faults transect the northwesterly trending Custer Gneiss and Hozameen, Ladner and Jackass Mountain Groups. Yale Fault separates gneisses of the Hozameen Group to the east from Custer Gneiss to the west. The Custer Gneiss, as herein restricted, is compositionally distinct from the Hozameen Group and shows a period of early deformation not present in the Hozameen Group. During the Cretaceous, regional deformation and greenschist facies metamorphism of the biotite zone affected rocks between the Yale and Hozameen faults. These rocks grade into gneisses of the hornblende hornfels facies within a few hundred yards of the Spuzzum Quartz Diorite and Yale Intrusions. This restricted contact metamorphism contrasts with the widespread, high temperature and pressure metamorphism found in this and other areas around the Spuzzum Quartz Diorite on the west side of the Hope fault. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Pelitic metasediments immediately southwest of Yale, British Columbia contain mineral assemblages characteristic of staurolite through sillimanite zones of the Barrovian facies series. Isograds are steeply dipping. Two phases of deformation are recognized with metamorphism being syn- to post-tectonic. Pseudomorphs after andalusite indicate that contact metamorphism preceded regional upgrading of the pelites. Microprobe analyses of major silicate phases in the pelites are combined with linear regression techniques in discussing possible kyanite- and sillimanite-forming reactions. A zone some 3 kilometers wide contains the assemblage staurolite-kyanite-garnet-biotite-muscovite-quartz which is univariant in AFM projection. Regression analysis of the staurolite-kyanite assemblage reveals the sensitivity of regression methods to error limits associated with the different minerals present. Precision of the analyses was not high enough for regression analysis to differentiate between stable, divariant equilibrium and a buffered, univariant reaction relation for this assemblage. Pelitic and calc-silicate assemblages from the metasediments restrict pressure-temperature conditions during regional metamorphism to 5½-8 kilobars and 550-700°C. It is suggested that deformation, emplacement of granitic intrusions, and regional metamorphism are all part of the Cretaceous orogeny which formed structures of the Cascades Mountains. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

D.Phil. / Please refer to full text to view abstract

Combining petrological and geochronological data we were able to show that rocks in south Naxos completed a full blueschist-/greenschist-facies metamorphic loop in about 10 Myr, distinctly faster than hitherto believed. We show that the high-pressure rocks reached peak pressure (16.3±0.9 kbar - 619 ±32°C) between 40.5±1.0 and 38.3±0.5 Ma and were re-equilibrated in the middle crust (3.8±1.1 kbar - 384±30 °C) under greenschist-facies metamorphism during in the Oligocene ~32 Ma. Our data indicate that this exhumation occurred at rates of 7.4±4.6 km Ma-1. Therefore, the Oligocene greenschist-facies overprint of the blueschist-facies rocks from south Naxos is unrelated to the Miocene amphibolite-/greenschist-facies metamorphism observed in Naxos. / Genom att kombinera petrologiska och geokronologiska data kan vi visa att bergarter på södra Naxos fullföljt en fullständig blåskiffer-/grönskiffer-facies metamorfisk loop på 10 Ma. Detta är mycket snabbare änn vad man tidigare trott. Vi visar att högtrycks bergarter nådde maximalt tryck (16.3±0.9 kbar - 619 ±32°C) mellan 40.5±1.0 och 38.3±0.5 Ma och var åter i jämnvikt i mitten av jordskorpan (3.8±1.1 kbar - 384±30 °C) under grönskiffer-facies metamorfism under Oligocen vid ~32 Ma.Våra data visar att exhumeringen skedde med hastigheter av 7.4±4.6 km Ma-1. Därför är den Oligocena grönskiffer-facies ersättningen av blåskiffer-facies på södra Naxos ej relaterad till den Miocena amfibolit-/grönskiffer-facies som observerats på Naxos. / En combinant les données pétrologiques et géochronologiques, nous avons été en mesure de montrer que les roches du Sud Naxos ont effectué un trajet complet en métamorphisme schiste bleue/schiste vert en 10 Ma, distinctement plus rapide que ce qui était admis jusqu’alors. Nous montrons que les roches de haute pression ont atteint un pic de pression (16.3±0.9 kbar - 619 ±32°C) entre 40.5±1.0 et 38.3±0.5 Ma et ont été rééquilibrées en croûte moyenne (3.8±1.1 kbar - 384±30 °C) en métamorphisme de facies schiste vert pendant l’Oligocène ~32 Ma. Nos données indiquent que cette exhumation a une vitesse de 7.4±4.6 km Ma-1. Par conséquent, la surimpression des roches de haute pression en métamorphisme de facies schiste vert dans le sud de Naxos n’est pas à relier au métamorphisme de facies amphibolite/schiste vert du Miocène observé à Naxos.

To constrain the thermal histories of two complex L chondrite melt breccia samples (NWA 5964 and NWA 6580) we compare textures and chemical compositions of metal and sulfide to L melt rock (NWA 6454 and NWA 6579) and strongly shocked (shock stage S6) (NWA 4860) samples. The inferred thermal histories can be used to evaluate formation settings on the L chondrite parent body. The L melt samples probably formed as different melt units within warm but largely unmelted material relatively close to the surface of the parent body, and the same is true for the S6 sample, except it experienced less melting. The breccia samples likely formed deeper, below different impact craters, by the injection of shock melt into a cooler chondritic basement. Carbide grains in the melt breccias could have formed by a contact metamorphic process caused by heating of the chondritic basement in proximity to the melt. Within the melt regions of the various samples, inferred cooling rates are on the order of 1-10 °C/sec, whereas in the chondritic portions of the melt breccias, the inferred cooling rates are many orders of magnitude slower, ~1-100 °C/My. The complex intergrowths of metal and FeS (hereafter referred to as dendritic grains) within the melt are recording cooling rates above the metal-sulfide eutectic, while the metal grains outside of the melt regions are recording cooling rates at much lower temperatures. It is likely the melt regions in the breccias cooled substantially prior to coming to rest against the chondritic basement, and thereafter the melt-chondrite rocks cooled more slowly.

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