Physical Sciences and Mathematics Commons^™

Hierarchical Segmentation Of The Malawi Rift: The Influence Of Inherited Lithospheric Heterogeneity And Kinematics In The Evolution Of Continental Rifts, Daniel A. Lao-Davila, Haifa S. Al-Salmi, Mohamed G. Abdel Salam, Estella A. Atekwana

Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works

We used detailed analysis of Shuttle Radar Topography Mission-digital elevation model and observations from aeromagnetic data to examine the influence of inherited lithospheric heterogeneity and kinematics in the segmentation of largely amagmatic continental rifts. We focused on the Cenozoic Malawi Rift, which represents the southern extension of the Western Branch of the East African Rift System. This north trending rift traverses Precambrian and Paleozoic-Mesozoic structures of different orientations. We found that the rift can be hierarchically divided into first-order and second-order segments. In the first-order segmentation, we divided the rift into Northern, Central, and Southern sections. In its Northern Section, …

The Unusual 3d Interplay Of Basement Fault Reactivation And Fault-Propagation-Fold Development: A Case Study Of The Laramide-Age Stillwell Anticline, West Texas (Usa), Benjamin E. Surpless, Nicola Hill, Cara Beasley

Geosciences Faculty Research

Subsurface fault geometries have a systematic influence on folds formed above those faults. We use the extraordinarily well-exposed fold geometries of the Laramide-age Stillwell anticline in west Texas (USA) to develop a strain-predictive model of fault-propagation fold formation. The anticline is a 10-km long, NW-trending, NE-vergent, asymmetric fold system with an axis that displays a map-view left-stepping, en echelon pattern. We integrated field observations, geologic and structural data, cross-sections, and 2D kinematic modeling to establish an unusual 3D two-stage model of contractional fold formation, including: 1) reverse reactivation of a pre-existing, NW-striking, SW-dipping, left-stepping, en echelon normal fault system in …

The Unusual 3d Interplay Of Basement Fault Reactivation And Fault-Propagation-Fold Development: A Case Study Of The Laramide-Age Stillwell Anticline, West Texas (Usa), Benjamin Surpless, Nicola Hill, Cara Beasley

Benjamin E Surpless

Subsurface fault geometries have a systematic influence on folds formed above those faults. We use the extraordinarily well-exposed fold geometries of the Laramide-age Stillwell anticline in west Texas (USA) to develop a strain-predictive model of fault-propagation fold formation. The anticline is a 10-km long, NW-trending, NE-vergent, asymmetric fold system with an axis that displays a map-view left-stepping, en echelon pattern. We integrated field observations, geologic and structural data, cross-sections, and 2D kinematic modeling to establish an unusual 3D two-stage model of contractional fold formation, including: 1) reverse reactivation of a pre-existing, NW-striking, SW-dipping, left-stepping, en echelon normal fault system in …

No Thermal Anomalies In The Mantle Transition Zone Beneath An Incipient Continental Rift: Evidence From The First Receiver Function Study Across The Okavango Rift Zone, Botswana, Youqiang Yu, Kelly H. Liu, M. Moidaki, Cory A. Reed, Stephen S. Gao

Geosciences and Geological and Petroleum Engineering Faculty Research & Creative Works

Mechanisms leading to the initiation and early-stage development of continental rifts remain enigmatic, in spite of numerous studies. Among the various rifting models, which were developed mostly based on studies of mature rifts, far-field stresses originating from plate interactions (passive rifting) and nearby active mantle upwelling (active rifting) are commonly used to explain rift dynamics. Situated atop of the hypothesized African Superplume, the incipient Okavango Rift Zone (ORZ) of northern Botswana is ideal to investigate the role of mantle plumes in rift initiation and development, as well as the interaction between the upper and lower mantle. The ORZ developed within …

The Lithotectonic Setting And Paragenetic History Of Deposit No.1, Mary River District, North Baffin Island, Sean A. Fulcher

Electronic Thesis and Dissertation Repository

Baffinland Iron Mines Corporation is currently extracting the highest grade BIF-hosted direct shipping iron ore in the world from their flagship Deposit No.1 on north Baffin Island. This deposit and several other prospects are hosted within the isoclinally folded Mary River Group, a Neoarchean greenstone belt terrane hosting Algoma-type BIF, ultramafics volcaniclastics and sediment. Mary River Group supracrustals are juxtaposed against Mesoarchean basement gneisses due to a regional Transhudson Orogen overprint, forming a regional dome-keel tectonic framework.

Detail mapping and core logging of Deposit No.1 combined with geochemistry and geochronology reveal the footwall rocks, previously interpreted as gneisses, volcanics and …

(U-Th)/He Chronologic Constraints On Secondary Fe-Oxide Mineralization In Southwestern New Mexico, Mike Channer, Alexis Ault

Mike Channer

Temporal constraints on fluid flow, mineralization, and brittle deformation are important for understanding a variety of upper-crustal processes. However, limited radioisotopic methods exist to directly date these processes. Hematite commonly co-precipitates with economically valuable mineral phases in hydrothermal ore deposits, such as copper, uranium, gold, and other rare-earth elements, and occurs in fracture systems and faults. Hematite is amenable to (U-Th)/He dating, and we will apply this method to two case studies in the Rio Grande rift, New Mexico. First, a suite of millimeter-thick hematite- and turgite-coated fracture surfaces cross-cut an ~54-60 Ma porphyritic rhyolite near Lordsburg in southwest New …

Tectono-Metamorphic History Of The Eastern Taureau Shear Zone, Mauricie Area, Québec: Implications For The Exhumation Of The Mid-Crust In The Grenville Province, Renaud Soucy La Roche, Félix Gervais, Alain Tremblay, James L. Crowley, Gilles Ruffet

Geosciences Faculty Publications and Presentations

This study investigates the tectono-metamorphic history and exhumation mechanisms of the mid-crustal Mékinac-Taureau domain of the Mauricie area, central Grenville Province. Macro- and micro-structural analyses reveal the top-down-to-the-ESE sense of shear on the eastern Taureau shear zone, a major extensional structure that exhumed the mid-crustal Mékinac-Taureau domain and juxtaposed it against the lower grade rocks of the Shawinigan domain. Peak metamorphism in the Mékinac-Taureau domain, inferred to be the result of northwestward thrusting and regional crustal thickening, took place under P–T conditions of 1000–1100 MPa and 820–880 °C prior to 1082 ± 20 Ma. Retrograde conditions varying from …

Understanding The Contractional History Of Surprise Canyon, California Through Digital Field Mapping, 3d Modeling, And U-Pb Zircon Geochronology, Joshua A. Cobb

Open Access Theses & Dissertations

Detailed digital mapping of lower-middle Surprise Canyon has revealed a more complex structure than previously interpreted. Rock units derived from the metamorphosed equivalents of the Pahrump Group exposed in Surprise Canyon display juxtapositions inconsistent with stratigraphic variations suggested in previous studies. This study proposes a contractional history of the central Panamint Mountains defined by two kinematically distinct and geochronologically constrained deformation events. D1 is characterized by a shallow dipping, NNW striking L and LS tectonite fabric ubiquitously observed in all metasedimentary and basement units. F1 folds are mesoscopic in scale and isoclinal with an axial planar S1 foliation. A prominent …

New La-Icp-Ms U-Pb Zircon Dating For Strandja Granitoids (Se Bulgaria): Evidence For Two-Stage Late Variscan Magmatism In The Internal Balkanides, Philip Machev, Valentin Ganev, Laslo Klain

Turkish Journal of Earth Sciences

The Strandja Massif (Sakar-Strandja Zone) forms an important link between the Balkan Zone (external Balkanides) of Bulgaria, which is commonly correlated with the Variscan orogen in Central Europe, and the Western Pontides of Turkey. The Bulgarian part of the massif is composed of a metamorphic basement (various granite gneisses, paragneisses, and schists) traditionally interpreted as having Precambrian age, Triassic-Jurassic metasedimentary cover, and Upper Cretaceous volcanosedimentary sequences. The basement is intruded by large granitic plutons of Variscan age that are widespread mostly across Turkish territory. New LA-ICP-MS data support the suggestion of Variscan granitoid magmatism in the studied area but do …

Sub-Marine Sediment Instability Near Southwest Pass Of The Mississippi River: Evidence Of Mass Movements From Raciochemistry And Other Proxies, Gregory Paul Keller

LSU Master's Theses

Mass wasting events are an important geomorphic control on the Mississippi River Delta Front. Short multicores (<50cm) and longer gravity cores (<3m) were collected seaward of the Southwest Pass of the Mississippi River Delta and were analyzed to assess the frequency, extent, and potential causes of submarine mass wasting events. Cores were analyzed for radionuclide activity, grain size, and density at 2cm resolution. Short-term sedimentation rates calculated from 7-Be are 2-16cm/y, while longer-term accumulation from 210-Pb are only 1.3-7.3 cm/y. In most cores, 210-Pb activity steadily decreases downcore without displaying a “stairstep” nature. However, seven cores have layers of low 210-Pb activity stratigraphically above layers with higher activity. In a gravity core from a mudflow gully, 210-Pb steadily decreases for the upper 70 cm before stabilizing for the remaining 150 cm. Clay content generally ranges between 25-40% and sand ranges between 5-15% with silt making up the rest of each sample. Sediment accumulation rates derived from 210-Pb in the short cores indicate that proximity to the river mouth has stronger influence than depositional environment (mudflow gully, depositional lobe, prodelta). This finding may be explained by rapid sedimentation rates coupled with a reduced tropical cyclone activity over the delta in the last seven years (2006-2013) which is a known cause of mass wasting events. The regions of decreased 210-Pb activity may be evidence of scavenging effects of plume sedimentation because they do not correspond with decreases in clay fraction. The layer of homogenized activity below 70cm in the gully core corresponds with a layer of decreased density. This layer occurs at a depth equivalent to 9-18 years, indicating mixing on a decadal scale from mudflows. These results may be explained by a lack of recent mass failures corresponding with lulls in tropical cyclone activity over the delta, preceded by a period of more active hurricane-driven mudflow activity.