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Abstract: Exploration methods for diamonds often employ the geochemistry of single minerals to identify deposits. Due to the scarcity of diamonds, exploration practices use minerals known as “kimberlite indicator minerals” as these minerals are typically more abundant than diamond and may have equilibrated under conditions where diamond may have been stable. One of these minerals is clinopyroxene from garnet lherzolites, because garnet lherzolites are stable in the diamond stability field. There are multiple published discrimination methods to identify clinopyroxenes from garnet lherzolites such as Ramsay (1992), Nimis (1998), Morris et al. (2002) and Grütter (2009). After applying these discrimination methods to identify garnet lherzolite clinopyroxene, the chemistry of clinopyroxenes can be used with geothermobarometers to calculate pressure and temperature estimates for mantle xenoliths or xenocrysts and thereby identify potentially diamond-bearing kimberlite deposits. Using published major-element compositions of 678 clinopyroxenes from garnet lherzolites, these clinopyroxene discrimination methods were found to accurately identify clinopyroxenes from garnet lherzolites. Trends between cations were also observed in clinopyroxene. Specifically, with the cations Na and Al+Cr having an approximate 1:1 ratio, suggesting that Na, Al and Cr are substituting dominantly as jadeite (NaAlSi2O6) and kosmochlor (NaCrSi2O6) in garnet lherzolite clinopyroxene. Elemental cations are also compared with the calculated pressure and temperature from multiple geothermobarometers with specific focus on the clinopyroxene geothermobarometers. Na, Al and Cr cations were all found to decrease with increasing pressure. Mg and Fe were found to increase with increasing temperature while Ca decreased with increasing temperature. These natural clinopyroxene samples were compared with clinopyroxenes from high P-T experiments on garnet lherzolites. The experimental clinopyroxenes were noticeably richer in Al and poorer in Na and Cr than natural clinopyroxenes. The differences between natural and experimental clinopyroxenes, specifically with Al, Cr and Na shows a disconnect between the experimental and natural garnet lherzolite clinopyroxenes. The richer Al in experimental samples suggests a higher tschermak component than in the natural clinopyroxenes. Using the program THERMOCALC, garnet lherzolites were modelled at specific bulk compositions to compare modelled clinopyroxenes to natural clinopyroxenes. The modelled clinopyroxenes, in the garnet lherzolite stability field, did not match well with natural garnet lherzolites as the modelled clinopyroxenes failed garnet lherzolite clinopyroxene discrimination plots. However, the cation trends against pressure and temperature appeared to follow the trends seen in natural samples. Using compositions calculated along geotherms, clinopyroxene appeared more like natural samples based on garnet lherzolite clinopyroxene discrimination methods and followed the cation trends seen in natural samples except for Al cations. Finally, an updated single-grain clinopyroxene geobarometer was calibrated from natural garnet lherzolites by modifying the Nimis and Taylor (2000) barometer. This barometer was calibrated using the calculated temperature of Taylor’s (1998) two pyroxene thermometer and the calculated pressure of the Nickel and Green (1985) barometer, with Al calculated after Carswell and Gibb (1987) (the recommend thermometer and barometer of Nimis and Grütter 2010). Through multiple linear regression an expression was developed to calculate P (kbar) as a function of T(K), Cr/(Cr+AlM1), Cr/Al, Cr+Al-0.86(Na+K) and Ca/(Ca+Mg+Fe) in clinopyroxene. The expression is: P(kbar) = 1239.28 – 0.0076 ⋅ T(K) ⋅ ln(Cr/(Cr+AlM1)) + 9.2988 ⋅ ln(Cr/Al) + 0.2056 ⋅ T(K) – 0.0051 ⋅ T(K) ⋅ ln(Cr+Al–0.86(Na+K)) – 201.2262 ⋅ ln(T(K)) + 56.8249 ⋅ ln(Ca/(Ca+Mg+Fe)) With AlM1 calculated as: AlM1 = Al – 0.5(Al + Cr + 2Ti – Na – K) Application of this updated barometer was applied to xenoliths from four localities. These localities are Chidliak kimberlite field, Diavik-Ekati kimberlites, Finsch diamond mine and Jagersfontein diamond mine. The updated barometer performs well as pressures calculated from xenoliths from the four localities using the updated barometer are in good agreement with the Nickel and Green (1985) barometer, with Al calculated after Carswell and Gibb (1987).

Volcanic rocks record the complex nature of magmatic systems. The mineralogical, petrological, and geochemical heterogeneity that exists within an eruptive unit at a single volcano is challenging to reconcile with a static magma chamber model. Current understanding, therefore, supports the presence of complex, dynamic trans crustal magmatic systems (TCMSs) that consist of interconnected regions of magma storage where liquid-poor, crystal-rich mushes exist and variably interact. This dissertation presents an investigation into the magmatic and crustal components of TCMSs through a study of andesitic-dacitic lavas, hornblendite cumulates, and crustal xenoliths from the Plio- Pleistocene Pampa Aullagas (PA) and Quillacas (QL) monogenetic centers on the Bolivian Altiplano, Central Andes. In Chapter 1, amphibole’s role in continental arc petrogenesis is investigated through a textural and geochemical study of hornblendite cumulates entrained within QL lavas. Granular, idiomorphic textures, the absence of relict clinopyroxene, and mesocumulate textures defined by intercumulus feldspar, apatite, and Fe-Ti oxides all support the formation of the hornblendites as cumulates in the lower arc crust. Reaction rims associated with cumulus amphiboles record cumulate mobilization, ascent, and eruption through TCMSs over relatively short timescales (

Abstract: In this study we present data from three lower crustal xenoliths suites collected in a northeast to southwest transect across the Slave craton. The samples are from the Artemisia kimberlite, located near the Coronation diamond district of the northwestern Slave (Nunavut), the Ekati kimberlite from the central Slave (NWT) and the Munn Lake kimberlite of the southeastern Slave (NWT). Samples from the Artemisia Suite have a range of bulk composition but the majority are granitic to semi-pelitic in composition and comprise Garnet + Plagioclase + Quartz + Rutile ± K-feldspar ± Biotite and significant amounts of retrograde hydrous minerals that likely pseudomorph orthopyroxene. As well, there are accessory grains of zircon and monazite. The garnet in these samples is characterized by relatively low grossular contents. In contrast to the Artemisia xenoliths, the Ekati and Munn Lake samples are garnet-bearing mafic granulites with a primary mineralogy of Garnet + Clinopyroxene + Plagioclase ±Quartz ± Orthopyroxene ± Amphibole ± Rutile ± Ilmenite. Metamorphic conditions of the lower crust as indicated by mineral equilibria are in the 9-12 kbar range of pressures with temperatures of at least 750-800°C. In the northern Slave, Neoarchean metamorphic events are recorded at 2624±11 Ma and 2520 Ma and Paleoproterozoic metamorphic events are recorded at 2415 Ma, 2150 Ma, and 2050 Ma and weakly at 2010 Ma. The ages observed in the Artemisia suite may be showing events not seen on the surface and there is a possible correlation with rocks of the Hottah terrane or mafic dike swarms that affected the Slave craton between 2200 and 2000 Ma. Still younger Paleoproterozoic ages of 1826-1868 Ma may be related to the Wopmay orogen. The Artemisia, Ekati and Munn Lake xenolith suites investigated in this study illustrates the complexity of unravelling the history of the lower crust.

The geology of the Precambrian East Antarctic shield remains enigmatic due to extensive ice-cover in continental East Antarctica. Understanding the nature of this large Precambrian shield is essential for understanding its assembly, which has bearing on past supercontinent cycles as well as modern ice sheet growth. Optical petrography and mineral chemical analysis of metamorphic glacial clasts collected from the Lonewolf Nunataks, Antarctica, reveal a complex metamorphic history representative of bedrock in the East Antarctic shield beneath the Byrd Glacier drainage. Three lithologic groups were identified: (a) felsic gneisses, (b) mafic gneisses and amphibolites, and (c) schists. Both felsic gneisses and mafic gneisses and amphibolites include garnet-bearing and garnet-free varieties. Typical mineral assemblages consist of quartz + plagioclase ± microcline + biotite ± muscovite ± garnet ± scapolite in felsic gneisses, and quartz + plagioclase ± microcline + biotite ± muscovite ± garnet ± tschermakite ± hypersthene ± scapolite in mafic gneisses and amphibolites. Petrologic evidence, including the presence of garnet, tschermakitic Ca-amphibole, hypersthene and scapolite in relatively anhydrous mineral assemblages, indicate amphibolite- to granulitefacies metamorphism. Of 16 suitable garnet-bearing samples, eight show compositional zoning in garnet indicative of prograde metamorphism, 12 show evidence of retrograde metamorphism, and two display no discernable compositional zoning. P-T calculations give prograde to peak temperatures ranging from ~500 to ~800 °C, with all samples reaching peak metamorphic conditions of at least 600 °C. Metamorphic pressures are less well constrained due to a lack of pelitic mineralogy. In one pelitic gneiss sample, GASP (garnet-aluminosilicate-silica-plagioclase) barometry indicates pressures of ~8-9 kbar. In five other samples of mafic gneiss and amphibolite, pressures determined from the Al content in calcic amphiboles give pressures of ~10-20 kbar. Clasts from Lonewolf Nunataks exhibit petrographic and P-T similarities with Archean to Proterozoic metamorphic rocks in the Terre Adélie craton in East Antarctica, the Gawler craton in southern Australia, and the Nimrod Group in the Transantarctic Mountains (TAM). These correlations are consistent with continuation of the Proterozoic Mawson Continent into the vast area of East Antarctica underlying the Byrd Glacier drainage. Specifically, it is possible that a geographically widespread metamorphic/magmatic tectonic event produced metamorphism in all of these areas, but that P-T variations between them is the result of differing local tectonic environments. Previous studies indicate that metamorphism documented in the Terre Adélie craton, Gawler craton, and Nimrod Group resulted from the ~1.7 Ga Nimrod-Kimban orogenies. Although geochronologic data are lacking to confirm a correlation, this study indicates that similar high-grade metamorphic rocks extend well into the East Antarctic shield beneath the Byrd Glacier drainage. Combined with recent age-dating of igneous glacial clasts that confirm the presence of heterogeneous Proterozoic basement underlying the Byrd Glacier drainage, this study also provides further evidence consistent with an interpretation of a connection between East Antarctica and Laurentia during the time of Rodinia.