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Full-Text Articles in Physical Sciences and Mathematics
Constraining Prograde Metamorphic Paths In Archean High-Grade Garnet-Bearing Lithologies From The Eastern Beartooth Mountains, Montana, Usa, Larry Fisher Cliff-Tuttle Jr
Constraining Prograde Metamorphic Paths In Archean High-Grade Garnet-Bearing Lithologies From The Eastern Beartooth Mountains, Montana, Usa, Larry Fisher Cliff-Tuttle Jr
LSU Master's Theses
Prograde metamorphic pressures and temperatures of Archean high-grade garnet-bearing lithologies from the eastern Beartooth Mountains of Montana provide an important constraint on the tectonometamorphic history of this terrane and the early Earth in general. A particularly useful means to approximate prograde metamorphic conditions is examining entrapment conditions of garnet mineral inclusions during garnet growth. Lithologies of the eastern Beartooth Mountains are well-suited to this approach because of the presence of abundant mineral inclusions within garnet porphyroblasts. Consequently, prograde metamorphic pressures and temperatures in the Beartooth Mountains, conditions that have only been broadly constrained previously, can be more accurately determined and …
Archean Geodynamic Conditions Using P-T Constraints Of The East Pilbara Craton Ttgs, Andrew Kody Webb
Archean Geodynamic Conditions Using P-T Constraints Of The East Pilbara Craton Ttgs, Andrew Kody Webb
LSU Master's Theses
We know very little about the tectonic setting present during the Hadean, but based on studies of surviving Hadean zircons, we know that a Hadean protocrust must have been established by at least 4.4 Ga (Kemp et al. 2010), and it must have also been able to accommodate minimum melt conditions (Harrison 2005). Tectonic models for Earth during the Hadean and Archean follow two trends: uniformitarianism and non-uniformitarianism. Uniformitarian models (following the famed geological concept that the present is the key to the past) argue that Hadean zircons and Archean rocks formed via processes akin to modern-style oceanic crust production …
Augite In Komatiitic Basalts: A Study Of The Mobility Of Trace Elements During Rock Alteration, Alesha C. Morabito
Augite In Komatiitic Basalts: A Study Of The Mobility Of Trace Elements During Rock Alteration, Alesha C. Morabito
LSU Master's Theses
Komatiitic basalts are ultramafic rocks formed from volcanic liquids containing less than 18 wt.% magnesium oxide that can be linked, spatially, geochemically and texturally to komatiites. Archean komatiites and komatiitic basalts are critical to models of early Earth’s mantle evolution. Major and trace elements in these rocks are poorly preserved due to early sub-seafloor alteration with superimposed regional metamorphism: in particular the alkali, alkaline earths, and other elements with low valence numbers. Current analytical methods focus on analyzing whole rock, fresh olivines and melt inclusions to evaluate elemental concentrations and for petrogenetic studies. Although these methods establish elemental concentrations, REE, …
Evaluation Of Stromatolites From The 3.4 Ga Kromberg Formation, Barberton Greenstone Belt, South Africa, Corey E. Shircliff
Evaluation Of Stromatolites From The 3.4 Ga Kromberg Formation, Barberton Greenstone Belt, South Africa, Corey E. Shircliff
LSU Master's Theses
Silicified sedimentary rocks from the 3.4 Ga Kromberg Formation of the Barberton Greenstone Belt in South Africa contain laminated structures that have been identified as possible stromatolites in the field. Morphological evaluation and a variety of chemical analyses are presented here, in an effort to describe the samples in a sedimentary context and consider biogenicity of these laminated forms. Two major types of laminated structures were identified in the field – domical laminates and flat-laminated samples with little to no synoptic relief. The domical sample presents the best morphological evidence for biogenicity. There are several characteristics that suggest the deposition …
Temperature And Pressure Conditions Of Archean Amphibolite-Granulite Facies Metamorphic Xenoliths From The Eastern Beartooth Mountains, Montana And Wyoming, Usa, Celina N. Will
LSU Master's Theses
Compositionally-diverse Archean metamorphic rocks occur as xenoliths within the well-dated 2.8 Ga granitic gneisses that volumetrically-dominate the eastern Beartooth Mountains of the northern Wyoming Province. Common mafic lithologies in the Quad Creek-High Line Trails-Christmas Lake-Wyoming Creek-Line Creek Plateau area include granitic gneiss, amphibolites, mafic granulites and biotite and garnet-bearing peraluminous gneisses. The region also has sillimanite-biotite ± cordierite ± garnet gneisses and migmatites, as well as a single occurrence of a noteworthy orthopyroxene-cordierite gneiss with late-stage anthophyllite. A combination of detailed petrographic analysis and thermobarometric modeling were used to constrain the metamorphic conditions of the xenoliths prior to inclusion in …
High Resolution Tephra And U/Pb Chronology Of The 3.33 – 3.26 Ga Mendon Formation, Barberton, Greenstone Belt, South Africa, Nicholas Burns Decker
High Resolution Tephra And U/Pb Chronology Of The 3.33 – 3.26 Ga Mendon Formation, Barberton, Greenstone Belt, South Africa, Nicholas Burns Decker
LSU Master's Theses
The Mendon Formation in the Barberton Greenstone Belt of South Africa marks the boundary between the Onverwacht and Fig Tree Groups. These groups are characterized by mafic to ultramafic volcanism and felsic volcanism with related epiclastic sedimentation, respectively. This transition marks the end of komatiitic volcanism in the Barberton Greenstone Belt and is accompanied by numerous impact-related spherule layers. This study characterizes the upper Mendon Formation texturally and geochemically over a wide areal extent and across structure and facies change in an attempt to better understand the evolution of tectonic processes at this boundary. A suite of whole rock and …
Volcanological And Petrogenetic Characteristics Of Komatiites Of The 3.3 Ga Saw Mill Complex, Weltevreden Formation, Barberton Greenstone Belt, South Africa, Matthew Stephen Huber
Volcanological And Petrogenetic Characteristics Of Komatiites Of The 3.3 Ga Saw Mill Complex, Weltevreden Formation, Barberton Greenstone Belt, South Africa, Matthew Stephen Huber
LSU Master's Theses
The Saw Mill Complex (SMC) is a 1275 m thick layered komatiitic sequence in the 3.3 Ga Weltevreden Formation, uppermost stratigraphic unit of the Onverwacht Group in the northern part of the Barberton Greenstone Belt, South Africa. A series of ultramafic complexes in the Weltevreden Formation have been interpreted as layered ultramafic intrusions, consisting of thick, layered ultramafic units of peridotite, pyroxenite, dunite, and gabbro. However, recent work on the Pioneer complex of the Weltevreden Formation has demonstrated an extrusive origin of komatiites and tuffs. The Weltevreden Formation has been less studied than other Onverwacht Group units. It is likely …
Komatiitic Flows Of The Pioneer Ultramafic Complex Of The 3.3ga Weltevreden Formation, Barberton Greenstone Belt, South Africa: Stratigraphy, Petrology, And Geochemistry, Marc Romain Cooper
Komatiitic Flows Of The Pioneer Ultramafic Complex Of The 3.3ga Weltevreden Formation, Barberton Greenstone Belt, South Africa: Stratigraphy, Petrology, And Geochemistry, Marc Romain Cooper
LSU Master's Theses
The 3.29 Ga Pioneer Ultramafic Complex (WPC) is a 1 km thick east-northeast trending tilted (90° dip) section of layered ultramafic rock in the Weltevreden Formation in the west-northwest region of the Barberton Greenstone Belt (BGB). It was originally interpreted as an intrusive complex with slaty zones that have a linear horizontal fabric produced by shear. However, a recent study identifies these slaty zones as komatiitic tuffs and attributes their horizontal fabric to plane and cross bedding. The present study suggests the non-slaty zones are extrusive komatiitic flows with abundant pyroxene spinifex tops, normal volcanic textures and crystal sizes, and …
Carbonated Sections From Komatiite Flow- Top Alteration Zones In The Barberton Greenstone Belt: Implications For Near-Surface Archean Environments, Judith E. F. Stoute
Carbonated Sections From Komatiite Flow- Top Alteration Zones In The Barberton Greenstone Belt: Implications For Near-Surface Archean Environments, Judith E. F. Stoute
LSU Master's Theses
Over a dozen komatiitic flows in the 3.2-3.5 Ga Barberton Greenstone Belt are topped with unique green silica- and carbonate-rich rocks, which likely formed from interaction of the cooling lava flow with seawater shortly after deposition. This study focuses on an alteration zone in the Mendon Formation. Two styles of alteration are observed in this alteration zone: silicification and carbonation. The goal of this study is to characterize the carbonates in the alteration zone, constrain the timing of alteration, test whether the alteration zones are due to interaction with seawater after deposition, and estimate the elemental fluxes between the rock …
Komatiites Of The Weltevreden Formation, Barberton Greenstone Belt, South Africa: Implications For The Chemistry And Temperature Of The Archean Mantle, Keena Kareem
LSU Doctoral Dissertations
The komatiites of the 3.29 Ga Weltevreden Formation, Barberton Greenstone Belt, South Africa represent extremely magnesian lavas derived from the Archean mantle. Three related papers are presented on aspects of the temperature and composition of the Archean mantle, and surface alteration processes. Petrographical and geochemical analyses confirm that olivines from the komatiites retain much of their original igneous character, containing fresh olivines, pyroxenes, and chromites. The olivines from the Weltevreden Formation are extremely magnesian, with Fo contents up to 95.6. Primitive mantle normalized Gd/Yb values near 1, and Al2O3/TiO3 values of 26-33 for these rocks …