The Central Asian Orogenic Belt formed by accretion subsequent to the contraction of the Palaeo-Asian Ocean that ultimately disappeared along the Solonker Suture Zone in East Asia. Since typical regional collisional features are absent, the tectonic evolution of the suture remains speculative. Integrated sedimentary provenance analyses across the accretionary collision zone between the Mongolian Arcs and the North China Craton place new constraints on the events that led to final suturing. An investigation on the geochronological and geochemical variability in Permian strata along a southeast-northwest transect revealed distinct differences across the Solonker Suture Zone: northern basins carry a broad Mesoproterozoic to latest Precambrian age signature, and their provenance terranes are of mixed juvenile to crustal magmatic origin. In contrast, southern basins contain detritus from the North China Craton, and their sources are of dominantly crustal contaminated magmatic origin. Provenance analysis suggests, that in the Early Palaeozoic (ca. 429 Ma) the Palaeo-Asian Ocean was consumed along the Uliastai Arc and the North China Craton, initiating the formation of the Northern and Southern Accretionary Orogens, respectively. By the end of the Middle Carboniferous the Mongolian Arcs consolidated after accretion of the Uliastai Arc. In the Late Carboniferous (ca. 314 Ma) the Hegenshan back-arc basin opened, detaching the Northern Accretionary Orogen. While subduction continued there, it may have temporarily ceased along the Southern Accretionary Orogen after accretion of a microcontinent (ca. 300 Ma). During the Middle Permian back-arc basin closure led to the formation and obduction of the Hegenshan supra-subduction zone ophiolite. Eventually, the Palaeo-Asian Ocean closed after wedge-wedge collision, which would not involve continental deep subduction, thus, leading to cryptic suturing from the Late Permian to Early Triassic. Statistical analyses on the heterogeneity and similarity of the age probability density functions require a complex Permian palaeo-geographic setting, involving a variety of arc basins, which received sediments dependent on the contemporary arc geometry. Early stages of the sequence likely resembled a Pacific-type scenario, including Japan-type back-arc basin opening, whereas the late stages were similar to the archipelago-type setting of present-day Southeast Asia. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

Thesis (Ph.D.)--University of Wyoming, 2007. / Title from PDF title page (viewed on June 17, 2009). Includes bibliographical references.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 199-230) Also available in print.

Thesis (M. Phil.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

Thesis (M.S.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Mar. 26, 2010). Includes bibliographical references (p. 113-120).

Thesis (Ph. D.)--University of Wisconsin--Madison, 2003. / Includes bibliographical references. Also available on the Internet.

Thesis (M.S.)--Brigham Young University. Dept. of Geological Sciences, 2008. / Includes bibliographical references (p. 39-44).

published_or_final_version / abstract / toc / Earth Sciences / Master / Master of Philosophy

The Southeastern US is an ideal location to explore the interactions between mountain-building, rifting, magmatism and intraplate deformation. It experienced the formation of the Southern Appalachians over multiple episodes of orogenesis, continental rifting that formed the South Georgia Rift Basin, and widespread magmatism associated with the Central Atlantic Magmatic Province (CAMP). CAMP was followed by the breakup of Pangea, but the suture between Laurentia and Gondwana from the Appalachian orogeny is preserved in the crust of the Southeastern US. Intraplate seismicity indicates ongoing deformation in the Southeastern US today, but the mechanisms controlling this seismicity are poorly understood. This thesis uses seismic constraints to examine the tectonic history of the Southeastern United States (US). We use new wide-angle refraction seismic data to model crustal and upper mantle velocities in order to investigate the structures formed by mountain-building, rifting, and magmatism. Broadband seismic data are then used to detect and characterize earthquakes in the central Georgia-South Carolina region. Wide-angle seismic data were collected on three profiles crossing major geological features in Georgia to investigate the tectonic history of the Southeastern United States as a part of the SUwanee Suture and GA Rift basin experiment (SUGAR) project. We model VP and VS of the crust and upper mantle on SUGAR Line 2, which extends from the Inner Piedmont to the Georgia coast. We identify a north to south decrease in upper crustal VP/VS at the Higgins-Zietz magnetic boundary, which other recent studies have identified as the location of the suture between Laurentia and Gondwana. This boundary also lies near the northwestern edge of the South Georgia Rift Basin, the southeastern termination of the low velocity zone interpreted as the Appalachian detachment, and localized crustal thinning. Together, these results provide new evidence in support of the Alleghanian suture being located at the Higgins-Zietz magnetic boundary, and suggest that this orogenic boundary influenced the location of subsequent rifting. We compare the VP structures of two SUGAR wide-angle transects that cross western and eastern segments of the South Georgia Rift, respectively. Elevated (>7.0 km/s) lower crustal velocities are observed where the rift basin sedimentary fill is thickest and the crust is most thinned. The quantities of mafic magmatic intrusions are consistent with decompression melting at modestly elevated mantle potential temperatures, such as those estimated for CAMP intrusions. These results suggest that, in contrast with the widespread CAMP-aged magmatism at the Earth’s surface, lower crustal magmatic intrusions in the Southeastern US are limited and localized in areas that experienced extension. These new constraints on the velocity structure and tectonic history of the Southeastern United States are then applied to understand earthquakes in the region today. Using broadband seismic data, we find that earthquakes southeast of the Eastern Tennessee Seismic Zone are concentrated within the Carolina Terrane, a particularly heterogeneous accreted terrane of the Southern Appalachians. Within this terrane, seismicity concentrates near rivers and reservoirs, including a sequence of earthquakes in 2013 associated with an increase in water levels at Thurmond Lake on the Georgia-South Carolina border. Focal mechanisms suggest that the earthquakes are occurring on structures that are oblique to the trend of the Appalachians that are more optimally oriented in the modern stress regime.

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy