Ultramafic rocks – that are usually located deep below the Earth's surface – are occasionally exhumed by the motion of tectonic plates. The massive chemical disequilibrium that exists between these exposed rocks and the surface waters and atmosphere leads to geologically rapid reactions that consume water and CO₂, binding them to form secondary hydrated/carbonated solid minerals that are found extensively in continental exposures (ophiolites) and at the seafloor near mid-ocean ridges. Pervasive fracturing and faulting in oceanic lithosphere generates pathways for fluids to access and react with rocks that are in some cases located down to depths of tens of kilometers. Over time, the large volumes of fluids and volatiles that are bound up in crustal and upper mantle rocks via such reactions are eventually subducted to extreme depths where subsequent fluid release can trigger melting, arc volcanism and seismic activity. In addition to their geophysical importance, these reactions are also considered to be critical for the survival of organisms in deep sea hydrothermal systems, and a potential source in the origin of life hypothesis. The natural transfer of atmospheric CO₂ to stable, solid carbonate minerals has, in recent years, motivated a large research effort towards investigating its potential as a large-scale carbon sequestration alternative. Understanding the geophysical impact and environmental potential of these reactions and their related processes requires knowledge of their basic physical and chemical behavior. Because of the difficulties of observing these processes in real-time, either experimentally or in the field, there has been a heavy reliance on hypothetical arguments that have been driven by observations in natural rocks. The observations paint a very complex picture – involving an interplay between reaction, fluid flow and fracturing – that is not easily explained by simple model descriptions. Although there has been increasing interest in modeling this class of problems in recent years, to date there remains a considerable gap between the theory and computational framework that is required for a consistent model description. A major theme in said models is their omission of poro-mechanical effects and complications arising from clogging of pore space with precipitating minerals. Both of these are necessary ingredients for a consistent model; however, they require a more complex description that is based on coupled multiphase continuum mechanics, reactive transport, and potentially brittle failure. Each of these components is a technical challenge in its own right, requiring development of novel theory and computation that integrates them in a suitable manner. The overall goals and themes of this thesis are aimed at closing this gap. To this end, I develop a modeling framework and computational tools that are capable of describing reactive flow in brittle media, with a specific focus on fluid-mineral reactions in near-surface ultramafic rock environments. The exposition of this framework is split into 3 separate chapters that build on one other in increments of complexity. Specifically, Chapter 1 presents a poromechanics-based description of coupled fluid flow, mass transfer and solid deformation for a simplified hydration reaction. This model is extended in Chapter 2 to incorporate cracking by adopting modern developments in computational fracture mechanics. Finally, in Chapter 3 I extend the set of reactions to support mixed H₂O-CO₂ fluids by leveraging recently developed tools in computational thermodynamics. Along the way I present a number of numerical model simulations that develop intuition and draw comparisons with natural observations, whilst remaining mindful of its limitations and areas for improvement. Overall, this work represents progress towards better understanding of physical and chemical feedbacks of reactive-brittle processes in the Earth's near-surface and the potential for large-scale carbon sequestration.

This paper reports a phylogeny of the African killifishes (Genus Nothobranchius, Order Cyprinodontiformes) informed by five genetic markers (three nuclear, two mitochondrial) of 80 taxa (seven undescribed and 73 of the 92 recognized species). These short-lived annual fishes occupy seasonally wet habitats in central and eastern Africa, and their distribution coincides largely with the East African Rift System (EARS). The fossil dates of sister clades used to constrain a chronometric tree of all sampled Nothobranchius recovered the origin of the genus at ~13.27 Mya. It was followed by the radiations of six principal clades through the Neogene. An ancestral area estimation tested competing biogeographical hypotheses to constrain the ancestral origin of the genus to the Nilo-Sudan Ecoregion, which seeded a mid-Miocene dispersal event into the Coastal ecoregion, followed closely (~10 Mya) by dispersals southward across the Mozambique coastal plain into the Limpopo Ecoregion. Extending westwards across the Tanzanian plateau, a pulse of radiations through the Pliocene were associated with dispersals and fragmentation of wetlands across the Kalahari and Uganda Ecoregions. We interpret this congruence of drainage rearrangements with dispersals and cladogenic events of Nothobranchius to reflect congruent responses to recurrent uplift and rifting. The coevolution of these freshwater fishes and wetlands is attributed to ultimate control by tectonics, as the EARS extended southwards during the Neogene. Geobiological consilience of the combined evidence supports a tectonic hypothesis for the evolution of Nothobranchius.

Mountain building is the result of large compressional forces in the Earth’s crust where two tectonic plates collide. This is why mountains only form at plate boundaries, of which the Al Hajar Mountains in Oman and the United Arab Emirates is thought to be an example of. These mountains have formed near the Arabian–Eurasian convergent plate boundary where continental collision began by 30 Ma at the earliest. However, the time at which the Al Hajar Mountains developed is less well constrained. Therefore, the timing of both the growth of the mountains, and the Arabian–Eurasian collision, needs to be understood first to be able to identify a correlation. Following this a causal link can be determined. Here we show, using apatite fission track and apatite and zircon (U-Th)/He dating, as well as stratigraphic constraints, that the Al Hajar Mountains were uplifted from 45 Ma to 15 Ma. We found that the mountains developed 33 Myr to 10 Myr earlier than the Arabian–Eurasian plate collision. Furthermore, the plate collision is ongoing, but the Al Hajar Mountains are tectonically quiescent. Our results indicate that the uplift of the Al Hajar Mountains cannot be correlated in time to the Arabian–Eurasian collision. Therefore the Al Hajar Mountains are not the result of this converging plate boundary.

Relative plate motion history since 30 Ma between the Pacific and the southern portion of the Nazca (Farallon) plates is examined. The history is constrained by available seafloor magnetic anomaly data and a two-minute grid of predicted bathymetry derived from satellite altimetry and shipboard sensors. These data are used to create a new plate motion reconstruction based on new magnetic anomaly identifications and finite poles of motion. The new identified magnetic isochrons and tectonic reconstruction provides greater resolution to the tectonic history between chrons 7y (24.73 Ma) and 3 (4.18 Ma) than previous interpretations. Shipboard magnetics and aeromagnetic data from over 250 expeditions were plotted and used to extrapolate magnetic anomalies picked from 2D magnetic modeling from selected cruises. Magnetic anomalies were further constrained by tectonic features evident in the predicted bathymetry. Previously published magnetic anomaly locations consistent with this work were used where interpretation could not be constrained by 2D modeling and map extrapolation. Point locations for anomalies were used as input for calculation of finite poles of motion for chrons 10y, 7y, 6c, 5d, 5b, 5aa, 5o, 4a and 3a. An iterative process of anomaly mapping, pole calculation and anomaly point rotations was used to refine the finite poles of motion. Eleven stage poles were calculated from the nine finite poles from this study and two published instantaneous Euler vectors. Tectonic reconstructions indicate a history dominated by two major southward ridge propagation events, the first starting by 28 Ma and completed by 18 Ma. The second event initiated in association with breakup of the Farallon plate around 24 Ma and ceased by about 11 Ma. Lithosphere was transferred from Nazca to Pacific during the first event and in the opposite sense during the second. Development of the Mendoza microplate east of the later propagator occurred at about 20 Ma and this dual spreading process appears to have lasted until about 15 Ma.

This study synthesizes the deposition and tectonic evolution of the Tertiary deposits in southern Cache Valley, a narrow, north-trending valley in the northeastern Basin-and- Range Province. The surrounding mountains consist of Proterozoic and Paleozoic sedimentary rocks. Southern Cache Valley is an east-tilted half-graben. The oldest Tertiary sediments are on the west side of the basin, and the overall dip is to the east. The Late Miocene to Early Pliocene Salt Lake Formation (Tsl) accumulated above the thin (to absent) Early to Middle Eocene Wasatch Formation (Tw) and the newly identified Fowkes and Norwood Tuff equivalents (Tfn; late Middle Eocene to Middle Oligocene). The two post-Wasatch units consist of felsic tuff, tuffaceous sandstone, pebble to boulder conglomerate, limestone, and sandstone. Pebble counts, generalized measured sections, and detailed mapping permitted subdivision of the Tertiary deposits into mappable subunits. Numerous faults and N-trending folds are present in Tertiary deposits in the SW part of the area. The Cenozoic-Paleozoic contact is offset by normal faults. The faults with ENE trends offset both the Paleozoic and Tertiary rocks, and thus are younger than 5 .1 Ma. Thick gravels, rich in Paleozoic carbonates, dominate exposures in the east, near the East Cache fault zone. Few cobbles are present within the Tfn except near the base, whereas conglomerates rich in clasts of Paleozoic carbonates are intertongued with tuffaceous sediments throughout the Tsl, especially eastward. Up to 8,000 feet (3439 m) of the Tsl accumulated as the narrow Cache Valley basin formed during the Neogene by rapid eastward downfaulting.

abstract: In this thesis, I investigate possible formation processes in the northern Claritas Fossae and the large Thaumasia graben on Mars. In particular, I assess three proposed formation hypotheses for the region: a mega-landslide across the Thaumasia plateau, originating in Tharsis and moving to the south-west; a rift system pulling apart Claritas Fossae and opening the large Thaumasia graben generally propagating in a north-south direction: and extension caused by uplifting from underlying dike swarms. Using digital terrain models (DTMs) from the High Resolution Stereo Camera (HRSC) aboard Mars Express and visual images from the Context Camera (CTX) aboard the Mars Reconnaissance Orbiter (MRO), I analyzed the geomorphic and structural context of the region. Specifically, I produced geomorphologic and structural feature maps, conducted sector diagram analyses of fault propagation direction, calculated and compared extension and strain in local and regional samples, analyzed along strike throw-profiles of faults, and conducted surface age estimates through crater counting. I found that no single formation mechanism fully explains the surface features seen in Northern Claritas Fossae today. Instead I, propose the following sequence of events led to the surface characteristics we now observe. The region most likely underwent two episodes of uplift and extension due to sub-surface magmatic intrusions, then experienced an extensional event which produced the large Thaumasia graben. This was followed by the emplacement of a layer of lava burying the bottom of the Thaumasia graben and the eastern edge of the region. Additional extension followed across the eastern portion of the study area, and finally of a young lava flow was emplaced abutting and overprinting the southwestern edge. / Dissertation/Thesis / Masters Thesis Geological Sciences 2019

The Reno-Sparks community is in a seismically hazardous area. Recent research indicates that a Richter 7.0 or greater magnitude earthquake could affect the area. Many of the emergency and essential facilities are situated in dangerous geological locations and are housed in outdated structures which could be severely damaged in the event of a major earthquake. Detailed site evaluations need to be made with respect to location of new structures and of existing building safety. The 1979 Unified Building Code seismic provisions should be adopted without exception; Nevada Revised Statute 278 .160 needs to be revised to require a seismic safety plan; Alquist-Priolo legislation should be implemented, and creation of a comprehensive civil defense plan for seismic hazards is essential.

A fault-like linearity along the lower Clackamas River is evaluated by analysis of physiographic and structural alignments, geological relationships, and by gravity and magnetic data. The study has resulted in the verification of a structural feature extending along the Clackamas River and the eastern front of the Portland Hills. Physiographic alignments were examined in twelve 15 minute and two 7-1/2 minute quadrangle maps. A significant northeasterly morphologic trend, N. 20⁰ W. and N. 40° W., and other secondary trends, namely, the N-S, E-W, and N. 50-60° E., has developed in the Portland area. The consistent northwest trend is observed throughout the entire area studied which strongly suggests that the alignments are very good indicators of underlying structural features. Structural alignments show that approximately 60% of the known mapped faults and fold axes concur with the dominant northwest physiographic trend. Seismic first motion analysis supports the established morphologic trend. A series of regionally co-aligned morphologic and structural features striking S. 40 -50⁰ E. across the state of Oregon suggest the presence of a major structural fault system aligned with the Portland Hills-Clackamas River structural alignment. The geologic cross sections developed from map and well data generally lack any tangible evidence as to the nature of the physiographic alignment. An apparent offset of the lower Pliocene Sandy River mudstone suggests movement as recent as middle Pliocene. Geophysical information was obtained from six gravity traverses and three magnetic traverses. The consistency of the size and shape of the gravity anomaly, 2.18 milligals/O. 2 mile, downdropped to the east, across the physiographic alignment defines the zone of a fault or a steep fold developed in the Columbia River basalt. The magnetic anomalies show a consistent change in the magnetic gradient corresponding to the structural zone.

No description available.

The exposed Tertiary carbonates of the Dammam Dome present an opportunity to study fractures in outcrops within the oil-producing region of Eastern Saudi Arabia. The study focuses on: 1) the characterization of fractures, 2) interpretation of their fracturing mechanism, and 3) the implications for the deep carbonate reservoirs of the Dammam Dome. The characterization of the outcrop fractures is integrated with structural analysis of the near-surface horizons mapped from reflection seismic and well data. Fractures are observed within all exposed carbonate units, but predominantly within the widely exposed Middle Rus unit. The fractures are opening-mode, bed-bound joints that form orthogonal sets (NW-SE and NE-SW trending joints). The trends of through-going, primary NW-SE trending joints do not correlate with the trends of remote regional stress associated with compression of Zagros uplift, suggesting they did not develop due to that orogenic event. The primary joints also seem to have developed independently of the observed karst features and interpreted near-surface faults. The analysis of joint pattern and their spacings generally seem to reflect the fold growth of the strata, position on fold and mechanical stratigraphy. The study results provide a first-order conceptual fracture model for the subsurface reservoirs to guide future development.