A petrographic study has been made of the contact relations between metagabbro and nepheline gneiss underlain by marble, in Monmouth township, Haliburton County, Ontario. A bad of hornblende nepheline-garnet gneiss about 80 feetwide trending north-south is underlain at a shear contact by marble. Round inclusion up to 18 inches across of red pyroxene with some spinel and rimmed by olivine occur in the marble a few feet below the contact. For a few inches above the contact the nepheline gneiss sometimes is biotite-bearing. To the east the nepheline gneiss grades into a band of hybrid nepheline metagabbro (containing pink augite) about 50 feet wide. This in turn is followed by a zone of garnetiferous clinozoisite metagabbro about 220 feet wide. Clinozoisite persists in the metagabbro for 100 feet beyond this zone and is followed by hornblende-(pyroxene)-plagioclase metagabbro. Pyroxene-garnet-(nepheline) skarn is interlayered with nepheline gneiss at one outcrop ear the fault contact with marble. It appears that gabbroic magma has intruded limestone and developed a skarn at the contact. Assimilation of lime by the magma has developed pink augite (titanaugite ?) , clinozoisite and grossularite in the gabbro. Subsequent injection of a highly fluid nepheline magma, or of solutions containing soda, alumina and iron and not saturated with silica, formed nepheline-bearing rock between marble and gabbro. Soda metasomatism produced a hybrid nepheline gabbro adjacent to the nepheline-bearirg rock. Regional metamorphism later imparted a foliation to the marble and nepheline rock, and produced a metamorphic texture the gabbro. Faulting of a unknown age brought nepheline gneiss and marble into sharp contact and probably trapped the skarn as horses only one of which is now exposed. / Thesis / Doctor of Philosophy (PhD)

The Scandinavian Caledonides form a mountain range comprising nappe stacks of numerous far-travelled thrust sheets. The thrust sheets consist of diverse lithologies representing pre- and synorogenic sedimentary and igneous rocks subsequently metamorphosed to various degrees, from the Late Neoproterozoic to Middle Devonian. In particular, (ultra)-high-grade metamorphic rocks have been recorded in the Seve Nappe Complex (SNC), extending >1000 km along strike of the Scandinavian Caledonides. Included in the SNC of northern Sweden is the Vássačorru Igneous Complex (VIC), consisting of bimodal magmatic suites, that formed c. 845 Ma. Fieldwork was conducted in the Kebnekaise mountains of northern Sweden, focusing on the high-grade Aurek metagabbro within the VIC of the SNC. Aurek is a key locality representing both initial stages of Iapetus Ocean formation in the Ediacaran and later stage Caledonian subduction affinities, from the collision between Laurentia and Baltica. In this study, petrological description, zircon U-Pb geochronology, mineral chemistry analysis, whole rock composition, and thermodynamic modeling was performed. Zircon U-Pb geochronology yielded protolith ages of 609±2.5 Ma, and 614±2.3 Ma, suggesting the Aurek metagabbro to not be part of the VIC, as has previously been described. The age of Aurek can instead be correlated to the Kebnekaise Dyke Swarms at c. 607 Ma, in the Kebnekaise mountains. Whole rock major and trace element data of e.g., Al2O3 (15.0 – 25.0 ppm) versus SiO2 (46.0 – 53.0 ppm), Rb (2.0 – 18.0 ppm), Zr (8.0 – 58.0 ppm) versus Y (2.7 – 18.0 ppm), Th/Yb ratio 0.25 – 2.0 and Nb/Yb ratio 1.30 – 5.14, indicate assimilation of continental crust. These major and trace element signatures show that the protolith of the Aurek metagabbro probably was emplaced in a continental rift setting in the Ediacaran. Semi-quantitative thermodynamic modeling from this study present blueschist to amphibolite facies conditions for the Aurek metagabbro at 11.8 – 12.6 kbar and 480 – 565 oC, confirming the unit experienced subduction, possibly in the Late Cambrian to Early Ordovician. The metamorphic grade and protolith age show similar features to correlative rock sequences in the Tsäkkok Lens, south of Aurek, in Norrbotten. Consequently, this study concludes that subduction, exhumation and subsequent deformation for Aurek, probably was equivalent to those of the Tsäkkok Lens, extending the HP affinities of the SNC further north in the Swedish Caledonides. / Skandinaviska Kaledoniderna utgör en bergskedja bestående av olika skollor som transporterats hundratals kilometer från sin ursprungskälla. Skollorna består av varierande bergarter som representerar olika utvecklingsskeden i formationen av Kaledoniderna under senare Neoproterozoikum och mellan Devon. Utmärkande har höggradiga metamorfiska bergarter återfunnits i Seveskollan som sträcker sig >1000 km längs med strykningsriktningen av de Skandinaviska Kaledoniderna. I norra Sverige inkluderar Seveskollan det magmatiska Vássačorru-komplexet, bestående av bimodal magmatism som bildats ca 845 Ma. Fältarbete utfördes kring Kebnekaisebergen i norra Sverige, med fokus på höggradig metagabbro från Aurek, ett område inom det magmatiska Vássačorru-komplexet. Aurek är ett viktigt område som representerar både initiala stadier av Iapetushavets bildande och efterföljande formationer från kollisionen mellan Laurentia och Baltica plattorna. I denna studie utfördes petrologisk beskrivning av mineral, U-Pb geokronologi av zirkon, kemisk analys av mineral och bulkkomposition av bergarter, samt termodynamisk modellering. U-Pb dateringen av zirkon resulterade i en ursprungsålder på 609±2,5 Ma och 614±2,3 Ma för metagabbro från Aurek. Detta indikerar att metagabbro i Aurek inte är en del av det magmatiska Vássačorru-komplexet, något som tidigare antagits. Åldern kan istället korreleras till Kebnekaise-gångkomplexet med en ålder på ca 607 Ma. Huvud- och spårelement i Aureks metagabbro tyder på assimilering av kontinentalskorpa, vilket föreslår att ursprungsbergarten till metagabbro i Aurek bildades i en kontinental spridningszon. Den termodynamiska modelleringen resulterade i metamorfiska förhållanden på mellan 11,8 – 12,6 kbar och 480 – 565 oC för bergarterna, vilket påvisar att den tektoniska miljön som senare präglat bergarterna förmodligen var associerad med en subduktionszon.

Meta-mafic intrusions with an intrusion age of 1.6-0.9 Ga are found along a north-south trend in theTransitional section of the Eastern Segment in Sweden. These intrusions are garnet-bearing and thus anexception to other meta-mafic intrusions found in Sweden. Meta-mafic intrusions that are garnet-bearingare usually found in the Caledonides to the northeast and in the south west of Sweden where the pressureshave been naturally high due to orogenic events or subduction.The study was conducted on these intrusions around the community of Ölme, to understand themetamorphic and metasomatic history of the area. The focus lies on the transition from magmaticgabbroic intrusions to metamorphosed metagabbros and highly foliated garnet-amphibolites. AveragePT estimates was calculated using THERMOCALC and classical geothermobarometry, so that acomparison between the qualitative and quantitative data could be made.The study indicates metamorphism at amphibolite to upper amphibolite facies conditionsfor the metagabbros and the garnet-amphibolites.Average PT-estimates for the garnet-amphibolites gives metamorphic peak temperatures of 680°-730° Cwith pressures of 9.0-11.0 kbar at the Träfors locality, and metamorphic peak temperatures of 660°-770° Cwith pressures of 9.5-11.0 kbar at the Skråkvik locality. These results are comparable to research donefurther to the south on similar intrusions, with temperatures of 700° C and pressures of 10 kbar.It is concluded that the meta-mafic intrusions at the Skråkvik locality have been metamorphosed in adry system, in contrast to the Träfors locality which seems to have been affected by more pervasiveretrograde metamorphism and fluid-rock interaction. It is also concluded that mafic intrusionscan preserve their magmatic textures even under high pressure conditions.

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.