The Alleghanian orogeny was a collision between the Gondwanan and Laurentian continents that produced the Pangean supercontinent. Mechanical and kinematic models of collisional orogens are believed to follow a critical taper geometry, where the tectonic imbrication of continental crust begins nearest to the edge of continental plate and advances toward the craton in a break- forward sequence. Studies of shear zones within the Alleghanian collisional orogen, however, suggest that most of the early deformation was translational. Propagation of craton-directed thrusts into the foreland did not occur until the latest Pennsylvanian in the southern Appalachians, and the middle-late Permian in the central Appalachians. Radiometric sedimentary provenance proxies have been applied to the late Mississippian-early Permian strata within the Appalachian foreland basin to determine the crustal composition and structural evolution of the orogen during the continental collision. U-Pb ages of detrital zircons from the early to middle Pennsylvanian sandstones suggest that most of the detritus within the Appalachian basin was recycled from Mesoproterozoic basement and Paleozoic strata of the Laurentian margin. The presence of Archean and late Paleoproterozoic age detrital zircons is cited as evidence of recycling of the Laurentian syn-rift and passive-margin sandstones. Detrital zircon ages from early-middle Permian-age sandstones of the Dunkard Group do not contain any Archean or Paleoproterozoic detrital-zircon ages, implying a source of sediment with a much more restricted age population, possibly the igneous and metamorphic internides or middle Paleozoic sandstones from the Appalachian basin. The persistance of 360-400 Ma K/Ar ages of detrital white mica suggest that the sediment was supplied from a source that was exhumed during the Devonian Acadian orogeny. Detrital-zircon and detrital-white-mica ages from Pennsylvanian-age sandstones indicate that the late Paleozoic orogen did not incorporate any significant synorogenic juvenile crust. The 87Sr/86Sr ratios of middle Pennsylvanian-early Permian lacustrine limestones within the Appalachian basin show a slight enrichment through time, suggesting that labile 87Sr-rich minerals in the Alleghanian hinterland are being exposed. Stable isotopic data from the lacustrine limestones also corroborates that the Appalachian basin became much more arid through time.

The Tibetan plateau is arguably the most important geological feature on Earth, yet its formation and evolution are poorly understood. This investigation utilizes Cretaceous sedimentary strata exposed in the Lhasa terrane of southern Tibet in order to constrain the paleogeography and tectonic setting of the region prior to the Indo-Asian collision. Lower Cretaceous strata consist of clastic sedimentary units that were deposited in shallow marine and fluvial environments. In northern Lhasa these sediments were deposited in a peripheral foreland basin that formed in response to the Lhasa-Qiangtang collision. The lower Cretaceous sediments in southern Lhasa are quartzose and were derived from cover strata exposed by local uplifts. A marine limestone of Aptian-Albian age overlies the lower Cretaceous clastic strata and was deposited in a shallow continental seaway. The paleogeography of the Lhasa terrane during deposition of the carbonate units was dominated by the effects of the Lhasa-Qiangtang collision, although other conditions, such as a high eustatic sea-level, influenced sedimentation as well. The Upper Cretaceous Takena Formation is composed of a basal member of marine limestone and an overlying member of fluvial red beds. The arkosic strata of the Takena Formation were deposited in a retro-arc foreland basin that formed to the north of the Gangdese magmatic arc. Collectively, the Cretaceous sedimentary strata indicate significant tectonic activity occurred in southern Tibet prior to the Indo-Asian collision. Moreover, the data suggest the crust of southern Tibet was thickened and possibly at high elevations before the Cenozoic.

No description available.

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.

The Middle-Late Ordovician Eureka Quartzite in south-central Nevada and eastern California is a supermature quartz arenite that was deposited along the Lower Paleozoic western passive margin of Laurentia. Measured section descriptions and facies stacking patterns indicate that the Eureka Quartzite represents a 3rd-order sequence and contains three ~2-4 m.y. sequences and many small parasequences. Detrital zircon analysis of eight samples from the base and top of four locations contains three main populations of ~1.8-2.0 Ga, ~2.6-2.8 Ga, and ~2.0-2.3 Ga, and a smaller infrequent population of ~1.6-1.8 Ga grains. These peaks are interpreted to represent sediment sourced from exposed proximal basement to the east, likely from the Yavapai and Mazatzal Provinces (~1.6-1.7 Ga), the Trans-Hudson Orogen (~1.8-1.9 Ga), Paleoproterozoic crusts (~2.0-2.3 Ga), and underlying or proximal Archean (~2.6-2.8 Ga) sources. Sediment likely was transported to the shoreline and across Archean basement by rivers draining the Transcontinental Arch. Long-shore currents played an important role in deposition and likely account for the similarity of Middle-Late Ordovician, supermature, quartz arenite deposits on western Laurentia. Although the Peace River Arch likely provided some sediment for the Eureka Quartzite, it is apparent its provenance was mostly Trans-Hudson Orogen and Archean basement. Temporal and spatial provenance changes are inferred from probability-density plots of the detrital zircon analyses to indicate sea-level changes covered or exposed possible sediment sources during deposition.

In light of the recent increase of mineral exploration in the northern Cordillera, private, educational, and governmental agencies have been compelled to revisit and research areas of the Cordillera whose geologic evolution still remains enigmatic. The current study is concerned with better understanding how a region of the boundary zone separating the peri-Laurentian realm from the exotic, Insular realm evolved following deposition of the meta-sedimentary Kluane schist in the Late Cretaceous. The schist is a northwest striking 30 km wide and 160 km long belt of highly deformed greenschist to amphibolite facies meta-sedimentary rocks located east of Kluane Lake, southwestern Yukon Territory. These deformed sediments as well as numerous other deformed Jurassic-Cretaceous meta-sedimentary units present along the same boundary zone (north and south of the schist) represent important rocks that can help constrain how this part of the Cordillera has evolved since the mid-Mesozoic. To better understand how the Kluane schist evolved, detailed field mapping, petrography, and U-Pb geochronological studies were undertaken in the area encompassing the schist. This data is integrated with pre-existing and recently collected geologic databases from the region to propose a model for the tectonic and structural evolution of the Kluane schist. Conclusions drawn from this study indicate the Kluane sediments were likely deposited into a closing Late Cretaceous seaway from sources derived from Yukon-Tanana terrane (YTT) to the east. The basin into which the sediments were deposited represents a remnant ocean basin that was present between Insular terrane and YTT prior their amalgamation in the Jurassic. Thrusting of YTT over the Kluane schist basin resulted in burial, metamorphism, and ductile deformation of the schist. Contemporaneously, the early stages of the Ruby Range batholith (RRB) were intruding the schist as well as the schist/YTT contact. This batholith intruded syn- to post-tectonically from approximately ca. 77 Ma to 65 Ma and it is responsible for imparting a kilometer scale inverted contact metamophic aureole onto the Kluane schist wherein metamorphic grade decreases to the southwest. Subsequently, a gneissic sub-unit of the Kluane ‘schist’ was formed by partial melting of the RRB/Kluane schist contact. During this composite deformation event, the schist was transported to mid-crustal depths by an oblique sinistral shear zone. Shortly thereafter, the schist was exhumed and deformed by consistent northeast-over-southwest shearing. Regional scale, broad open folding of the schist ensued and likely occurred by flexural slip along foliation planes with low cohesion. Two syn- to post- tectonic igneous phases associated with Hayden Lake intrusive suite have been dated to ca. 55 Ma. This timing likely correlates with broad, open folding and a ‘late’ syn- to post-kinematic thermal overprint of the schist. The combined results of this study indicate that deformation and metamorphism of the Kluane schist was a long-lived event, extending from ca. 82 Ma to ca. 55 Ma.

Middle-Late Ordovician Mt. Wilson Quartzite, southern British Columbia, Canada, is a supermature quartz arenite deposited in shallow marine-marginal marine environments on the Early Paleozoic western Laurentian passive margin. Facies-stacking patterns indicate the Mt. Wilson Quartzite is an unconformity bounded, 2nd-order depositional sequence, containing two 3rd-order sequences, and numerous parasequences. Detrital zircon age spectra of six samples of the Mt. Wilson Quartzite have numerous peaks that are unique to Middle to Late Ordovician quartz arenites of western Laurentia. The main peaks, 1800-2000 Ma, 2000-2200 Ma, and 2300-2400 Ma are interpreted to have been derived from basement rocks that were exposed east of the study area: Trans-Hudson Orogeny (1800-2000 Ma), Taltson Orogen (1800-2000 Ma), Buffalo Head Terrane (2000-2400 Ma), Paleoproterozoic crust (2000-2400 Ma), and the Wopmay Terrane (2000-2400 Ma). It is likely that these areas were sourced by local rivers and tributaries draining the Transcontinental Arch and delivered sediment to the deposition location of the Mt. Wilson Quartzite. While longshore transport was a viable distribution method for sediment along the passive margin, it is unlikely that the Peace River Arch (located northwest of the Mt. Wilson Quartzite) was its sole point source; rather it is more likely that there were multiple sediment sources for these western Laurentian quartz arenites. Temporal changes in provenance indicate different areas of basement rock were exposed throughout the deposition of the Mt. Wilson Quartzite, most likely reflecting long-term flooding of North America. The potential for spatial changes in provenance remains unsolved.

Originally mapped as Precambrian and uppermost Ocoee Supergroup (OS), recent discoveries of Paleozoic microfossils have placed the Walden Creek Group (WCG), eastern Tennessee, into a younger depositional framework (Silurian or younger). In this study, monazite geochronology using SIMs, detrital zircon U-Pb geochronology determined by LA-ICP-MS, feldspar compositions determined by microprobe, zircon-tourmaline-rutile (ZTR) indices, and framework mineral modes were used to characterize provenance of sandstones of the WCG. Monazite ages cluster at 450 and 1050 Ma. All Ordovician ages are from grains that, in BSE images, have inclusion-rich microtextures interpreted as diagenetic and/or metamorphic, thus requiring that the WCG was deposited prior to Taconic metamorphism. The WCG heavy mineral suite is similar to the OS in its low modal abundance of monazite, but contains a slightly higher ZTR index. WCG Feldspar compositions are sodium poor-Kfs and sodic plagioclase, like the OS. Detrital zircon U-Pb ages for three formations of the WCG (seven samples total, n = 620) match the Ocoee signature. The dominant age modes are at ca. 1000 and 1150 Ma, with smaller modes at 1450 and 650 Ma. The monazite ages and supporting observations prove the WCG is not Paleozoic and its source rock signature matches the underlying OS.

In light of the recent increase of mineral exploration in the northern Cordillera, private, educational, and governmental agencies have been compelled to revisit and research areas of the Cordillera whose geologic evolution still remains enigmatic. The current study is concerned with better understanding how a region of the boundary zone separating the peri-Laurentian realm from the exotic, Insular realm evolved following deposition of the meta-sedimentary Kluane schist in the Late Cretaceous. The schist is a northwest striking 30 km wide and 160 km long belt of highly deformed greenschist to amphibolite facies meta-sedimentary rocks located east of Kluane Lake, southwestern Yukon Territory. These deformed sediments as well as numerous other deformed Jurassic-Cretaceous meta-sedimentary units present along the same boundary zone (north and south of the schist) represent important rocks that can help constrain how this part of the Cordillera has evolved since the mid-Mesozoic. To better understand how the Kluane schist evolved, detailed field mapping, petrography, and U-Pb geochronological studies were undertaken in the area encompassing the schist. This data is integrated with pre-existing and recently collected geologic databases from the region to propose a model for the tectonic and structural evolution of the Kluane schist. Conclusions drawn from this study indicate the Kluane sediments were likely deposited into a closing Late Cretaceous seaway from sources derived from Yukon-Tanana terrane (YTT) to the east. The basin into which the sediments were deposited represents a remnant ocean basin that was present between Insular terrane and YTT prior their amalgamation in the Jurassic. Thrusting of YTT over the Kluane schist basin resulted in burial, metamorphism, and ductile deformation of the schist. Contemporaneously, the early stages of the Ruby Range batholith (RRB) were intruding the schist as well as the schist/YTT contact. This batholith intruded syn- to post-tectonically from approximately ca. 77 Ma to 65 Ma and it is responsible for imparting a kilometer scale inverted contact metamophic aureole onto the Kluane schist wherein metamorphic grade decreases to the southwest. Subsequently, a gneissic sub-unit of the Kluane ‘schist’ was formed by partial melting of the RRB/Kluane schist contact. During this composite deformation event, the schist was transported to mid-crustal depths by an oblique sinistral shear zone. Shortly thereafter, the schist was exhumed and deformed by consistent northeast-over-southwest shearing. Regional scale, broad open folding of the schist ensued and likely occurred by flexural slip along foliation planes with low cohesion. Two syn- to post- tectonic igneous phases associated with Hayden Lake intrusive suite have been dated to ca. 55 Ma. This timing likely correlates with broad, open folding and a ‘late’ syn- to post-kinematic thermal overprint of the schist. The combined results of this study indicate that deformation and metamorphism of the Kluane schist was a long-lived event, extending from ca. 82 Ma to ca. 55 Ma.

New geochronological and field data were examined from Triassic-Jurassic strata in the Sverdrup Basin, Arctic Canada. Detailed analysis of detrital-zircon data identified a pronounced near-syndepositional age-fraction in Triassic strata, which significantly is absent in Jurassic strata of the Sverdrup Basin suggesting a protracted history of magmatism and sediment dispersal from areas north of the basin during the Triassic. However, as a result of rifting, during the Early Jurassic, the northern source region became disconnected from the Sverdrup Basin, and opened the precursor basin (Amerasia Basin) to the Arctic Ocean. Jurassic rifting of the Amerasia Basin would have had associated rift-flank uplift. Time-temperature models produced from zircon (U-Th)/He thermochronological data elucidate the unknown thermal history between the regional Devonian-Cretaceous unconformity in the southwestern Canadian Arctic suggesting ~4 km of addition deposition on Banks Island and ≤1 km of deposition towards the craton interior.