The Middle Ordovician Ancell Group, including the St. Peter Sandstone, Glenwood Shale and Starved Rock Formation, records intracontinental basin development during eustatic sea level changes in Iowa and Illinois. The St. Peter Sandstone overlies the Prairie du Chien Group across an erosional unconformity that marks a major sequence boundary, whereas upper contact of the St. Peter Sandstone with the Glenwood Shale also is a second sequence boundary. Data from 80 wells, selected well logs, and 20 cores were integrated to refine the high-resolution sequence stratigraphy of the Ancell Group. Two main sequences bounded by three sequence boundaries are interpreted to represent 3rd order sequences. Distinctive shallowing-upward parasequences bounded by flooding surfaces in many cores record higher frequency relative sea level fluctuations in the Ancell Group, but these cannot presently be correlated regionally. Facies variations define an aggradational transgressive systems tract TST), a prograding highstand systems tract (HST) and down stepping falling stage system tract (FSST) in both the St. Peter Sandstone and the Glenwood Shale-Starved Rock Formation units. The St. Peter Sandstone thickens towards the northeast and thins to the northwest and southwest in Iowa. In contrast, the St. Peter Sandstone in Illinois thickens to the south likely recording a prolonged FSST incised valley or channel fill. Detrital zircon geochronology of 13 samples from the St. Peter Sandstone and Starved Rock Formation define common peaks at 1100-1500 Ma and 2500-2700 Ma with minor components at 1670-1750 Ma and 3000-3600 Ma. The detrital zircon signature is dominated by Archean, and Grenville (1000-1300 Ma) ages. The detrital zircon geochronology indicates that the Ancell Group was sourced directly from the Archean Superior Province to the north and Grenville Province to the northeast, although recycling of Archean grains from the Paleoproterozoic Huron Basin cannot be ruled out. The near complete lack of 1800-1900 Ma ages argues against derivation of detritus from the Trans-Hudson or Penokean Orogens. The Transcontinental Arch northwest of the Iowa Basin acted as a barrier to sediment transport from the Trans-Hudson Orogen. Basement rocks of the Penokean Orogen are inferred to have been covered by water or younger sediments southeast of the Iowa Basin. CIA analyses of Ordovician shale samples from around the Transcontinental Arch indicate that the climate condition during Middle Ordovician time was warm and humid. This is consistent with a paleoclimate interpretation where mechanical erosion and chemical weathering yielded first cycle mature quartz arenites (Witzke, 1980).

The Cartoogechaye terrane (CT) is an enigmatic migmatite terrane within the Central Blue Ridge province of the southern Appalachians. Previous work identified exotic Pb isotope compositions within the CT (Quinn, 2012). More recent studies that mapped the extent of potentially exotic metaigneous lithologies yield U-Pb zircon ages consistent with a native Laurentian margin metasedimentary origin (Larkin, 2016). This study focused on the possible extent of similar lithologies in the Clyde quadrangle and provides further constraints on the crustal affinity of the CT. The Clyde quadrangle consists of four distinct lithologic packages: the CT, Ashe metamorphic suite, Great Smoky Group, and Grenville basement. Five samples within the Clyde quadrangle and one sample from Wayah Bald quadrangle were collected for detrital zircon (DZ) U-Pb geochronology and whole rock geochemistry for comparison similar anlayses from other bedrock units in the region. Dominant DZ age modes consist of the Grenville doublet (1050 Ma and 1150 Ma) or a modified version of it. Minor age modes exist at ~450 Ma, 600-750 Ma, and 1300-1550 Ma. Zircons for all but one sample display heterogeneous external and internal cathodoluminescence morphologies, consistent with a sedimentary protolith for the paragneisses. Whole rock compositions are consistent with weathering of and derivation from a local basement source. U-Pb age data are most consistent with an eastern Laurentian sedimentary provenance for five samples. The presence of 450-460 Ma grains is most consistent with high-grade Taconian regional metamorphism. The lack of a major Shawinigan age mode and zircon morphology for ca. 980-1050 Ma metamorphic zircons indicate that sample CLY16-1 is a syn-orogenic metasediment within the Grenville basement underlying the CT.

Strata in the Cook Inlet forearc basin in south-central Alaska record the effects of tectonic events related to normal subduction and two flat-slab subduction events. Through detrital zircon geochronology we track provenance changes of strata deposited in a forearc basin in conjunction with these different subduction processes. Our data from strata deposited concurrent with normal subduction help to confirm previous provenance models of forearc basins that suggest provenance is sourced primarily from a proximal, coeval arc. However, compared to these models, our data from strata deposited coincident to flat-slab events show markedly different provenance signatures dependent upon: (1) geographic position relative to the flat-slab event; (2) pre-established, or lack thereof, topography; and (3) type of flat-slab event. Detrital zircon signatures of strata deposited in the Cook Inlet after flat-slab subduction of a mid-ocean ridge diversify to include older detritus found in the distal inboard region. This distal signature is then incrementally cut-off in younger strata due to deformation of the upper-plate from progressive insertion of a shallowly subducted oceanic plateau. Detrital zircon signatures for strata associated with each flat-slab event are largely older than depositional age due to the lack of coeval arc activity. Our data may help to improve the ability to recognize other flat-slab events through detrital zircon geochronology. In particular, changes in detrital zircon signatures found in strata deposited during flat-slab subduction of an oceanic plateau correlate well with the exhumation of rocks associated with the propagation of deformation in the over-riding plate due to plate coupling.

Detrital zircon U-Pb geochronology is a useful tool for analyzing provenance in the sedimentary record. Differentiating recycled and first cycle populations in the detrital record, however, is not a straightforward process. A second potential problem in using detrital signatures to determine provenance of sediment lies in the assumption that detrital signatures of modern rivers reflect input from each exposed unit in the catchment boundaries. To investigate each of these problems, I present U-Pb analysis of detrital zircon (DZ) from modern river sand collected from 20 watersheds, 6 detrital apatite (DA) signatures from modern river sand, and 6 DA signatures from exposed strata, all within the Talkeetna Mountains (south-central Alaska). DA rarely survives past the first cycle of erosion and deposition due to its inability to survive chemical weathering, and thus dominantly represent igneous input in detrital signatures, whereas zircon can be of igneous origin or can survive multiple cycles of erosion and deposition. By comparing the DA signatures with the DZ signatures, I present a method to better differentiate first cycle, igneous sediment contributions from recycled populations within a detrital signature. The results of these comparisons show that DA signatures provide ages of igneous input into the detrital record; these ages are also reflected in the DZ signature, thus signaling these DZ populations as igneous in origin. This study also investigates the potential for DA recycling and DA input from recycled strata. To address the second problem, I present a method using GIS software and the most recent map of Alaska to create simulated signatures that records input on a scale proportionate to the exposed surface area of each bedrock unit. In ~35% of the watersheds tested, the simulated signatures predict trends similar to the DZ signatures from the modern river sands, in 55% of the watersheds tested the simulated signatures missed one or more populations present in the DZ signature, and in 10% of watersheds tested, the simulated signature predicted trends very different from the DZ signatures. In cases where the DZ and simulated signatures do not match, I believe this represents influences of climate and relief and zircon fertility.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24175号 / 理博第4866号 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 成瀬 元, 准教授 河上 哲生, 教授 田上 高広 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Middle Ordovician (Whiterockian) sandstone units within the Oil Creek, McLish, and Tulip Creek formations of the Simpson Group of Oklahoma, and the Everton (Calico Rock Member) and St. Peter formations of Arkansas were deposited on the southern margin of Laurentia. They represent the first major siliciclastic input to the southern U.S. Midcontinent above the post-Sauk unconformity. Samples were collected from outcrops of the major sandstone units to determine their U-Pb detrital zircon age distributions for provenance. Samples were prepared and analyzed using laser ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS). Probability-density plots were created to determine likely source areas for sediment, based on comparing detrital zircon ages to known ages of basement terranes. Detrital zircon grains from the Early Whiterockian Calico Rock sandstone indicate a majority of its zircon population was ultimately derived from the 900-1300 Ma Grenville orogenic province, with secondary input ultimately derived from the 1300-1550 Ma Granite-Rhyolite/Anorogenic Province and the Archean Superior province along the Transcontinental Arch. It is likely, at this time, that zircons were also sourced from reworked sediments from more proximal secondary sources. With sea level rise and transgression, the depositional shoreline and the sediment source areas moved to the north and west. The basal Oil Creek Sandstone of the Simpson Group was deposited unconformably above the Arbuckle Group in southern Oklahoma, and its zircon population is dominated by grains from Archean source terranes along the Transcontinental Arch. The basal sandstone unit of the McLish Formation indicates renewed sediment input containing zircons from 1300-1550 Ma Granite-Rhyolite/Anorogenic and 1600-1700 Ma Yavapai-Mazatzal terranes along the Transcontinental Arch. The Nemaha Ridge in northeastern Kansas likely acted as a source of first-cycle sediment in the southern midcontinent during this time. Small populations of detrital zircon grains between 1800 Ma and 2000 Ma occur in the majority of the samples. Their probability density peaks are generally centered at roughly 1850 Ma, suggesting an ultimate source in the Penokean orogenic province along the Transcontinental Arch.

The northeast African continental margin of the Western Desert of Egypt is host to a complexly deformed series of Phanerozoic basins. Substantial sedimentary deposition (~5 km) and basin formation resulted from regional deformation due to continental collision and repeated rifting and inversion cycles. Limited sedimentary exposure and exploration has prevented elucidation of Phanerozoic basin evolution, particularly in the Paleozoic. Previous studies of the region have largely relied upon sedimentary analysis, gravity, and 2D/3D seismic data. This study, in contrast, has employed extensive use of detrital zircon (U-Th)/He thermochronology (n=1004) from 17 wells in conjunction with 3D seismic, well log correlation, and heat flow data to elucidate a spatiotemporally comprehensive tectonic and stratigraphic model. The detrital zircon thermochronometric data provides new evidence that the lower Paleozoic, Carboniferous, and Mesozoic stratigraphic sequences of the Western Desert represent thermally distinct, tectonically controlled sequences with independent thermal evolutions. The lower Paleozoic sequence has been partially thermally reset, reaching temperatures of ~140-170 ̊C. Partial resetting is noted throughout the region and reached its thermal maximum in the Permo-Triassic, synchronous with onset of Neotethyan rifting. The Carboniferous sequence has not been thermally reset, with exposure to temperatures no greater than ~140 ̊C and reaching thermal maximum presently. Carboniferous (U-Th)/He ages have dominant input from short-lag-time zircons (exhumation to deposition) and indicate the stratigraphic sequence was proximally sourced. The proximal sourcing is likely from transmitted stress and fault reactivation in Egypt during the Hercynian Orogeny that caused fault block exhumation and erosional unroofing. Sediment was shed from uplifted fault blocks that formed the eastern boundary of the Carboniferous sequence. The Mesozoic sequence has not been thermally reset, reaching temperatures no greater than ~120 ̊C and presently reaching thermal maximum. Localized areas with stacking of lower Paleozoic, Carboniferous, and Mesozoic sequences likely bury the lower Paleozoic to abnormally deep depths (~7 km) and elevated temperatures of ~200 ̊C. Evidence from faulting relationships, basin controlling structures, and heat flow data indicate that N-S trending basement structures may define a region of crustal transition between the Archean-Paleoproterozoic Saharan Metacraton and the juvenile Arabian-Nubian Shield. / text

The Taimyr Peninsula is a key element in the circum-Arctic region and represents thenorthern margin of the Siberian Craton. The Taimyr Peninsula is a late Paleozoic fold andthrust belt and preserves late Paleozoic through Mesozoic siliciclastic sedimentarysuccessions and providing an ideal location to investigate the Paleozoic to Mesozoictectonic evolution associated with the Uralian orogeny, the Siberian Trap magmatism andopening of Amerasia Basin within a circum-Arctic framework. Multiple methods areadopted, including petrography, heavy mineral analysis and detrital zircon U-Pbgeochronology for provenance investigation, apatite fission track dating for revealingthermal history and balanced cross section for understanding the deformation style ofTaimyr.The results of this thesis indicate that the Late Carboniferous to Permian sediments ofsouthern Taimyr were deposited in a pro-foreland basin of the Uralian orogen during theUralian orogeny. In the Triassic, the siliciclastic deposits still show a strong Uraliansignature but the initiation of Siberian Trap-related input begins to be significant. Erosionof the Uralian orogen has reached a deep metamorphic level. By Late Jurassic andCretaceous time, the deposition setting of southern Taimyr is an intracratonic basin.Erosion and input from Uralian sources waned while greater input from SiberianTrap-related rocks of the Taimyr region dominated. The Taimyr Peninsula underwent atleast three cooling and uplifting episodes: 280 Ma, 250 Ma and 220 Ma, corresponding tothe Uralian orogeny, the Siberian Traps and the late Triassic transpression. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: In press. Paper 3: Manuscript. Paper 4: Manuscript.</p>

The North Caribou Greenstone Belt (NCGB) lies at the core the granitoid-dominant North Caribou Terrane (NCT). Two sedimentary assemblages; the Eyapamikama (ELS) and Zeemal-Heaton Lake (ZHA) form the core of the NCGB. Geochemistry of garnets from the orogenic Au deposit at Musselwhite suggest that the auriferous fluids have a contribution of metamorphic fluids and mineralization consisted of prolonged, multi-stage periods. Chemical zoning suggests changes in the influx of chalcophile and lithophile elements and that Au/sulphide ratios during nucleation were lower relative to later growth events. Zircons from the ELS and ZHA suggest a c. 100 My hiatus in the onset of sedimentation, with the ZHA showing younger, “Timiskaming-type” ages. Age distributions from each assemblage reflect proximal, igneous sources. Nd isotopic compositions of the ZHA suggest a mixture of ancient and contemporaneous sources which are similar to external TTG rocks. Deplete mantle model ages of the ZHA rocks indicate a Mesoarchean inheritance.

The Western European Variscan orogenic belt is thought to represent the final in a series of Paleozoic continental collisions that culminated with the amalgamation of the supercontinent Pangea. The Iberian segment of the Variscan belt is characterized by Cantabrian orocline, which is 180º and convex toward the west. Several lines of evidence are at odds with classical interpretation of the Cantabrian orocline as the core of the much larger ‘Ibero-Armorican’ arc, suggesting instead that it is structurally continuous with a second more southerly and complimentary orocline. Paleocurrent data collected from the Lower Ordovician Armorican Quartzite of the deformed Iberian Paleozoic passive margin sequence confirm the existence of the so-called Central Iberian orocline. Structural continuity between the Cantabrian and Central Iberian oroclines suggests that they formed contemporaneously and in the same fashion. Mesoscale vertical-axis folds deforming slaty cleavage and shear fabric within the Ediacaran Narcea Slates have a dominant vergence toward the hinge of the Cantabrian orocline, suggesting that its formation was in part accommodated by a mechanism of flexural shear during buckling of a linear belt in response to an orogen parallel principle compressive stress. The Cantabrian-Central Iberian coupled oroclines therefore palinspastically restore to an originally linear belt 2300 km in length. Provenance analysis of detrital zircons sampled from the Armorican Quartzite along a 1500-km-long segment of the palinplastically restored Iberian passive margin indicate that it originated in a paleogeographic position stretching east-west along the northern limits of north African Gondwana, from the Arabian-Nubian Shield to the Saharan hinterland. Paleomagnetic data and the distribution of Variscan ophiolites support a model of mid-Paleozoic separation of the Variscan autochthon (Armorican continental ribbon) from north Gondwana preceding or in conjunction with a 90º rotation required to reorient the ribbon to a Late Carboniferous north-south trend. Formation of the Iberian coupled oroclines accommodated 1100 km of orogen parallel shortening. The Western European Variscan belt, North American Cordillera, and Eastern European Alpine system are orogens similarly characterized by both coupled oroclines and paleomagnetic inclinations that are significantly shallower than cratonic reference values. Palinspastic restoration of the Alaskan and Carpathian–Balkan coupled oroclines fully resolves inclination anomalies within the Cordillera and Eastern Alpine system, respectively. Inclination anomalies within the Iberian Variscan belt are only partially resolved through palinspastic restoration of the Iberian coupled oroclines, but the sinuous geometry of the belt is not yet fully deciphered. Oroclines within the Western European Variscan belt, not the orogen itself, provide the true record of Pangean amalgamation. / Graduate