Thesis advisor: J. Christopher Hepburn / The Nashoba terrane of SE New England is one of three peri-Gondwanan tectonic blocks caught between Laurentia and Gondwana during the closure of the Iapetus Ocean in the early to mid- Paleozoic. U-Pb analyses (LA-ICP-MS) were carried out on zircon suites from the meta-sedimentary rocks of the Nashoba terrane. The youngest detrital zircons in the meta-sedimentary rocks of the Nashoba terrane are Ordovician in age. There is no significant difference in age between meta-sedimentary units of the Nashoba terrane across the Assabet River Fault Zone, a major fault zone that bisects the NT in a SE and a NW par. Zircon in meta-sedimentary rocks in the Marlboro Fm., the oldest unit of the Nashoba terrane, is rare, which may reflect the basaltic nature of the source material, and is commonly metamict. The Marlboro Fm. contained the oldest detrital grain of all the analyzed samples, with a core of ~3.3 Ga and rim of ~2.6 Ga indicating that it was sourced from Archaen crustal material. Detrital zircons from the Nashoba terrane show a complete age record between the Paleoproterozoic and Paleozoic that strongly supports a provenance from the Oaxiqua margin of Amazonia. The detrital zircon suite of the Nashoba terrane is distinct from both Avalonia and the Merrimack belt; however, they resemble zircon suites from Ganderia. This study proposes that the Nashoba terrane of Massachusetts correlates with the passive trailing edge of Ganderia. Finally, metamorphic zircon analyses of the terrane show that the Nashoba terrane experienced a peak in hydrothermal fluid infiltration during the Neoacadian orogeny. / Thesis (MS) — Boston College, 2011. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Thesis advisor: John C. Hepburn / The bedrock geology of the Maynard quadrangle of east-central Massachusetts was examined through field and petrographic studies and mapped at a scale of 1:24,000. The quadrangle spans much of the Nashoba terrane and a small area of the Avalon terrane. Two stratigraphic units were defined in the Nashoba terrane: the Cambrian to Ordovician Marlboro Formation and the Ordovician Nashoba Formation. In addition, four igneous units were defined in the Nashoba terrane: the Silurian to Ordovician phases of the Andover Granite, the Silurian to Devonian Assabet Quartz Diorite, the Silurian to Devonian White Pond Diorites (new name), and the Mississippian Indian Head Hill Igneous Complex. In the Avalon terrane, one stratigraphic unit was defined as the Proterozoic Z Westboro Formation Mylonites, and one igneous unit was defined as the Proterozoic Z to Devonian Sudbury Valley Igneous Complex. Two major faults were identified: the intra-terrane Assabet River fault zone in the central part of the quadrangle, and the south-east Nashoba terrane bounding Bloody Bluff fault zone. Petrofabric studies on fault rocks in two areas indicated final motion in those areas: the sheared Marlboro Formation amphibolites indicated dextral transpressive NW over SE motion, and the Westboro Formation Mylonites indicated sinistral strike-slip motion. Fracture characterization of entire quadrangle where attributes (orientation, trace length, spacing, and termination) of fractures and joints were used to identify dominant sets of fractures that affect the transmissivity and storage of groundwater. Orientations of SW - NE are dominant throughout the quadrangle and consistent with regional trend. / Thesis (MS) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

Thesis advisor: Yvette Kuiper / 40Ar/39Ar single-grain total-fusion ages of muscovite and biotite and one 40Ar/39Ar furnace step-heating age of hornblende from the Tadmuck Brook Schist, Nashoba Formation, and Ball Hill mylonite zone are used to reconstruct the late tectonic and metamorphic history of the Nashoba terrane in eastern Massachusetts. The data fall into three age populations. Age population I (~376-330 Ma) is interpreted as cooling after a migmatization event in the Nashoba terrane, population II (~300 Ma) may be associated with normal movement on the Clinton-Newbury fault, and population III (~267 Ma) is possibly related to cooling of the Rocky Pond Granite. No younger Alleghanian overprint was observed. / Thesis (MS) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

This study utilised U-Pb geochronology, and 40Ar/39Ar and (U-Th)/He thermochro-nology to delineate arc magmatism, metamorphism, and exhumation of the pericratonic Yukon-Tanana terrane in the McQuesten map area of west-central Yukon, Canada. SHRIMP U-Pb ages delineate Mid to Late Paleozoic arc magmatism and fit key units into the regional lithotectonic framework of the terrane. The juxtaposition of unmetamorphosed and predomi-nantly undeformed Devono-Mississippian rocks in the northwest of the study area with polydeformed and up to amphibolite facies metamorphosed rocks in the southwest suggests a crustal-scale discontinuity, the Willow Lake fault, bounds the two domains. The asymmetric distribution of 40Ar/39Ar ages across the fault suggest it is extensional, and was active in the Early Jurassic. Zircon (U-Th)/He ages delineate erosion of rocks in the northwest through the upper crust during the Late Triassic and Late Jurassic to Early Cretaceous followed by Mid-dle Cretaceous erosion of the southwestern domain and possibly fault reactivation.

The Alexander terrane is an allochthonous terrane within the North American Cordillera. New structural mapping and geochronology within the southern Alexander terrane in the vicinity of Porcher Island provides evidence for two major tectonic events. The oldest is Late Silurian to Early Devonian magmatism and deformation assigned to the Klakas orogeny. The area has subsequently been affected by mid-Cretaceous conjugate shear zones potentially associated with tectonic escape. Northwest-striking sinistral shear zones characterize mid-Cretaceous deformation in the western Coast Belt south of Prince Rupert in north coastal British Columbia. Structurally focused mapping and geochronology has revealed a component of lateral extension to this deformation. General flow characteristics of the shear zones are identified by comparison of fabric patterns to published models for fabric development in shear zones. U-Pb ages from synkinematic dykes constrain motion on northwest-striking sinistral transpressional shear zones, including the Useless, Barrett and Salt Lagoon shear zones, to ca. 104 – 96 Ma, and dextral transpression on the north-striking Telegraph Passage shear zone to ca. 97.6 ± 0.2 Ma. The geometry, kinematics, and coeval nature of these shear zones suggests that they formed in part as a ductile conjugate set. The presence of similarly-oriented conjugate shear bands in the apex zone between sinistral and dextral shear zones further reinforces this interpretation. The orientation of these conjugate sets indicates a component of north-northwest east-southeast extension. The conjugate shear zones merge together into the Grenville Channel shear zone, a sinistral transpressional shear zone with high strike-parallel stretch. A U-Pb age of 103 ± 32 Ma from a synkinematic dyke in the Grenville Channel shear zone coincides with a previously published Lu-Hf age of 102.6 ± 3.7 Ma on synkinematic garnet. Overall, structural and geochronological data from Porcher Island and surrounding area in north coastal British Columbia indicate that mid-Cretaceous deformation was characterized by ENE-WSW (orogen normal) shortening and NNW-SSE (orogen parallel) extension. This local strain regime is consistent with large-scale mid-Cretaceous tectonic escape as proposed for the northern Cordillera at that time, expressed in coeval sinistral faulting in the Coast Belt and dextral faulting in the northern Omineca belt. The Late Silurian to Early Devonian Ogden Channel complex is a mafic to intermediate metaplutonic-metamorphic complex within the southern Alexander terrane on southern Porcher Island and adjacent Pitt Island in north coastal British Columbia. Lithological characteristics of the complex suggest that it represents the mid-crustal roots of a volcanic arc. An age of 413.3 ± 2.5 Ma from a comparatively weakly deformed quartz diorite dyke indicates that the synkinematic Ogden Channel complex is at least in part Early Devonian in age, corresponding to the Klakas orogeny that affected the Alexander terrane in southeast Alaska. Crosscutting relationships indicate that individual intrusions within the Ogden Channel complex were emplaced syn- to post-kinematically with respect to southwest-vergent sinistral reverse deformation (present coordinates). The structural and lithological characteristics of the Ogden Channel complex are consistent with the interpretation that this part of the Alexander terrane was located in the upper plate of a northeast-dipping subduction zone, which culminated in the Klakas orogeny.

The Alexander terrane is an allochthonous terrane within the North American Cordillera. New structural mapping and geochronology within the southern Alexander terrane in the vicinity of Porcher Island provides evidence for two major tectonic events. The oldest is Late Silurian to Early Devonian magmatism and deformation assigned to the Klakas orogeny. The area has subsequently been affected by mid-Cretaceous conjugate shear zones potentially associated with tectonic escape. Northwest-striking sinistral shear zones characterize mid-Cretaceous deformation in the western Coast Belt south of Prince Rupert in north coastal British Columbia. Structurally focused mapping and geochronology has revealed a component of lateral extension to this deformation. General flow characteristics of the shear zones are identified by comparison of fabric patterns to published models for fabric development in shear zones. U-Pb ages from synkinematic dykes constrain motion on northwest-striking sinistral transpressional shear zones, including the Useless, Barrett and Salt Lagoon shear zones, to ca. 104 – 96 Ma, and dextral transpression on the north-striking Telegraph Passage shear zone to ca. 97.6 ± 0.2 Ma. The geometry, kinematics, and coeval nature of these shear zones suggests that they formed in part as a ductile conjugate set. The presence of similarly-oriented conjugate shear bands in the apex zone between sinistral and dextral shear zones further reinforces this interpretation. The orientation of these conjugate sets indicates a component of north-northwest east-southeast extension. The conjugate shear zones merge together into the Grenville Channel shear zone, a sinistral transpressional shear zone with high strike-parallel stretch. A U-Pb age of 103 ± 32 Ma from a synkinematic dyke in the Grenville Channel shear zone coincides with a previously published Lu-Hf age of 102.6 ± 3.7 Ma on synkinematic garnet. Overall, structural and geochronological data from Porcher Island and surrounding area in north coastal British Columbia indicate that mid-Cretaceous deformation was characterized by ENE-WSW (orogen normal) shortening and NNW-SSE (orogen parallel) extension. This local strain regime is consistent with large-scale mid-Cretaceous tectonic escape as proposed for the northern Cordillera at that time, expressed in coeval sinistral faulting in the Coast Belt and dextral faulting in the northern Omineca belt. The Late Silurian to Early Devonian Ogden Channel complex is a mafic to intermediate metaplutonic-metamorphic complex within the southern Alexander terrane on southern Porcher Island and adjacent Pitt Island in north coastal British Columbia. Lithological characteristics of the complex suggest that it represents the mid-crustal roots of a volcanic arc. An age of 413.3 ± 2.5 Ma from a comparatively weakly deformed quartz diorite dyke indicates that the synkinematic Ogden Channel complex is at least in part Early Devonian in age, corresponding to the Klakas orogeny that affected the Alexander terrane in southeast Alaska. Crosscutting relationships indicate that individual intrusions within the Ogden Channel complex were emplaced syn- to post-kinematically with respect to southwest-vergent sinistral reverse deformation (present coordinates). The structural and lithological characteristics of the Ogden Channel complex are consistent with the interpretation that this part of the Alexander terrane was located in the upper plate of a northeast-dipping subduction zone, which culminated in the Klakas orogeny.

This study utilised U-Pb geochronology, and 40Ar/39Ar and (U-Th)/He thermochro-nology to delineate arc magmatism, metamorphism, and exhumation of the pericratonic Yukon-Tanana terrane in the McQuesten map area of west-central Yukon, Canada. SHRIMP U-Pb ages delineate Mid to Late Paleozoic arc magmatism and fit key units into the regional lithotectonic framework of the terrane. The juxtaposition of unmetamorphosed and predomi-nantly undeformed Devono-Mississippian rocks in the northwest of the study area with polydeformed and up to amphibolite facies metamorphosed rocks in the southwest suggests a crustal-scale discontinuity, the Willow Lake fault, bounds the two domains. The asymmetric distribution of 40Ar/39Ar ages across the fault suggest it is extensional, and was active in the Early Jurassic. Zircon (U-Th)/He ages delineate erosion of rocks in the northwest through the upper crust during the Late Triassic and Late Jurassic to Early Cretaceous followed by Mid-dle Cretaceous erosion of the southwestern domain and possibly fault reactivation.

The analysis and interpretation of Vendobionta morphology is critical to elucidating a range of issues about their ontogeny and evolution, as well as life habits. These analyses, however, are complicated because these organisms are often morphologically enigmatic and defy ready categorization within modern taxonomic schemes. This study delves into the morphology of one of these problematic groups: Pteridinium. Specimens were investigated from two localities, Namibia and North Carolina, using geometric morphometrics. The landmark data, which was analyzed to compare specimens based on locality, taphonomy, and preservation, were subjected to three statistical tests: Principle Components Analysis, Procrustes shape analyses, and Foote's disparity test. All tests revealed no distinct clustering within or by either group due to any of the variables. All variables plotted within the same 95% confidence ellipses, displaying a lack of statistical support for the distinctness of these groups. Therefore, the most parsimonious reason for the lack of differences observed by these two groups stem from them being part of the same morphological group, a conclusion that places into question the validity of the inclusion of two separate species in the genus Pteridinium.

>Magister Scientiae - MSc / The Proterozoic Namaqua-Natal Province comprises highly deformed rocks of medium to high grade metamorphism and is bordering the Archean Kaapvaal Craton to the west, south and east in South Africa. The sector to the west of the Craton, namely the Namaqua Sector, is structurally complex and subdivided from west to east into the Bushmanland Subprovince, the Kakamas and Areachap terranes of the Gordonia Subprovince and the Kheis Subprovince. The prominent Neusberg Mountain Range, with exposures to the north and south of the Orange River in the Kakamas Terrane constitutes evidence of crustal shortening as a result of continental collision of the Namaqua Sector block with the Kaapvaal Craton during the Namaquan Orogeny. The Mesoproterozoic Korannaland Group in the Kakamas Terrane is affected by faulting, folding and shearing.

The Tibetan plateau is a vast, elevated region located in central Asia, which is underlain by the thickest crust known on Earth (up to 90 km). An outstanding question of importance to many fields within geology is how and why did the Tibetan plateau form? Models attribute the growth of the plateau to a consequence of the ongoing India-Asia continental collision, but differ in the details of how the crustal thickening was accommodated: was it by underplating of Indian lower crust or by homogeneous shortening? High-grade metamorphic rocks sampled from the region potentially hold the key to answering this question, as they contain a record of past tectonic events that can discriminate between the various proposed models. This record can be decoded by integrating field, thermobarometric and geochronological techniques, to elucidate a detailed thermotectonic understanding of a region. This methodology was applied to three case studies, each of which targeted rare tectonic windows into the mid-crust of the plateau. These regions comprise Danba in eastern Tibet, Basong Tso in south-eastern Tibet and the Western Nyainqentanglha in southern Tibet. Each case study documents previously unreported metamorphic events that have allowed original interpretations to be made regarding tectonic evolution: in Danba, all metamorphism is shown to be early Jurassic; in Basong Tso, two metamorphic belts are documented that reveal a late Triassic--early Jurassic orogenic event; and in the Western Nyainqengtanglha, Cretaceous--Neogene magmatism is shown to overprint late Triassic metamorphism. Integration of the results has enabled commentary on the large scale evolution of the Tibetan plateau from the Permian until the present day, and even hinted at its future. The results indicate that the closure of the Paleotethys played an important role in the construction of the Tibetan plateau, and suggest that homogeneous crustal thickening is not a viable model for the documented exposure levels.