34 research outputs found
Data for: Cataclastic deformation and metasomatism in the subduction zone of mafic blocks in shale-matrix mélange near San Simeon, California
No full textAppendix Method
Data for: Outcrops as Guides to Subsurface Natural Fractures: Example from the Nikanassin Formation tight-gas sandstone, Grande Cache, Alberta Foothills, Canada
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Fracture abundance and strain in folded cardium formation, Alberta fold-and-thrust belt, Canada
No full texttextThe folded and thrusted Mesozoic clastic sequence of the Canadian Rocky Mountain foothills forms important hydrocarbon reservoirs. Understanding the distribution of natural fractures, their evolution, and timing of formation relative to the evolution of the fold-and-thrust system could potentially improve exploration and development outcomes in these otherwise tight unconventional reservoirs. However, the formation of fractures and their timing relative to folding and thrusting have remained unclear. I investigated the relation between folding and fracture formation in the Upper Cretaceous Cardium Sandstone by combining field structural observations and kinematic modeling of the fold-and-thrust belt evolution. I explored the relationship between fracture intensity and fracture strain with structural position by analyzing fracture spacing or frequency and aperture data collected along outcrop and micro-scanlines in the backlimb, in the forelimb close to the crest, and in the steeper dipping forelimb away from the crest of the Red Deer River anticline. Fracture frequency and aperture data collected both at the outcrop and micro scales indicate that variation in fracture strain is small across these three structural domains of the fold, with somewhat lower fracture intensity in the forelimb close to the crest. These fracture strain measurements are qualitatively consistent with calculated horizontal strain in the tectonic transport direction obtained through kinematic numerical models that simulate fold development associated with slip along the underlying Burnt Timber thrust. The models predict roughly similar amount of horizontal extension in both the back and forelimbs, and somewhat lower extension in the upper forelimb during early development of the Red Deer River anticline. Fracture formation early during fold development is consistent with the field structural observations of shear reactivation during later stages of folding. This combined kinematic modeling and field structural study demonstrates that deforming fold and thrust belts can undergo a complex evolution of bed-parallel extension in both space and time, resulting in spatially variable fracture formation in such structurally complex subsurface reservoirs.Earth and Planetary Science
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Fold-related brittle structures and associated strain in a limestone bed of the Carmel Formation, San Rafael Swell, Utah
No full textThe San Rafael Swell (SRS) is a basement-cored Laramide uplift located in central-eastern Utah. The SRS is bounded on the east by a 70 km long monocline, a fault-propagation fold, with excellent exposure of sedimentary strata including the Carmel Formation. This monocline is an ideal natural laboratory for studying brittle deformation associated with folding. Qualitative and quantitative observations for brittle structures in a limestone bed near the base of the Carmel Fm. were made in a wide range of bedding dip, curvature, and fold domains. Kinematic data was collected for 2942 structures (1865 veins, 746 stylolites, 314 faults) in 30 locations in order to calculate principal directions of strain. Additionally, data was collected along 71 scanlines at 19 of those locations in order to estimate structure intensities and strain magnitudes.
Dekameter-displacement thrust faults, acting as ramps between inferred layer-parallel faults, accommodate orders of magnitude more strain than all other observed brittle structures. These faults are only found in segments of the monocline where bedding dip is high, but curvature is low, which provides strong evidence that limb rotation more strongly controls strain magnitudes than layer bending in the SRS.
The trishear model effectively predicts SRS monocline geometry, specifically observed limb thickening, broad, curved hinges, and progressively rotating limb. This is likely due to the dominance of thick, homogeneous rock packages, such as the Navajo Sandstone, in the SRS monocline. In contrast, strain localization within the Carmel Fm. is poorly predicted by trishear: there is strong evidence of flexural slip, and folding induced structure orientations and calculated principal strain directions remain consistent relative to bedding. These strain directions are inconsistent with trishear forward models produced by workers such as Zuluaga et al. (2014) that do not stay consistent relative to bedding. These divergences are likely due to the fact that trishear is a kinematic model that assumes rock homogeneity, while the Carmel Fm. is stratigraphically and mechanically heterogeneous. Because this heterogeneity appears to have a strong effect on strain localization, kink band models likely better estimate strain localization in the Carmel limestone bed as well as other layers in folded heterogeneous strata.
The monocline’s interpreted transition from layer-parallel shortening to extension at the steepest locations in the monocline, and thus at most advanced stage of folding, enabled estimation of the dip of the basement fault beneath the SRS as ~30°. This shallow dip contrasts with the steep dip (~60°) assumed for the SRS by Zuluaga et al. (2014) and observed in the Kaibab uplift (Huntoon and Sears, 1975; Tindall, 2000), but is consistent with a recent estimation of 20-40° for the SRS by Davis and Bump (2009) using trishear modeling.Earth and Planetary Science
Filtered EBSD data set of listvenites from Oman Drilling Project Hole BT1B
No full textThe dataset contains electron backscattered diffraction (EBSD) filtered data acquired on samples collected on cores from Oman Drilling Project Hole BT1B (International Continental Drilling Project Expedition 5057‐4B). A suite of 7 samples in foliated listvenites was analyzed through 11 EBSD maps of variable area width at specific sites of interest. The scanning resolution varies from 0.5 µm to 3 µm. Raw pixel data was filtered with the Channel 5 analysis suite from HKL Technology (Oxford Instruments) and consists in noise reduction followed by a wild spikes extrapolation (level 6; in few cases level 5). Datafiles are provided as channel text files (CTF), which can be processed and viewed with Channel 5 or MTEX
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P-T-t paths and deformation of blueschist and associated graphite-schist blocks from the Franciscan mélange, San Simeon, California
No full texttextThe Franciscan Complex forms the structurally complicated, locally
chaotic basement of the Northern and Central California and southwestern
Oregon Coast Ranges. It is an accretionary wedge formed during the Late-
Jurassic-Tertiary subduction along the west coast of North America.
In northern California, the Franciscan is subdivided into three belts, the
Western, Central, and Coastal belts, which show a zonation in age,
metamorphic “grade”, and structural style. Franciscan mélanges are present
in the Central belt, as well as the Diablo Range --a tectonic window within the
structurally overlying Great Valley Group--, and the Nacimiento Block, where
the study area is located.
One of the best exposures of Franciscan mélange, where contact
relationships between blocks and matrix can be observed, crops out along 6
km of seacliffs near San Simeon. Boudinaged blocks of graywacke,
greenstone, chert, and much rarer blueschist and graphite-schist are
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dispersed in the shale matrix. Block sizes range from 10 cm to 15 m. The
discovery of interlayered blueschist and graphite-schists, and the presence of
lawsonite in some graphite-schists demonstrates that these two lithologies
were metamorphosed together. Graphite-schist blocks in the Franciscan have
not been reported prior to this study.
Two main mineral assemblages were recognized among the studied
34 mafic blueschist blocks: 1) Lws + Na-amp + Pmp + Phe + Ttn + Chl
recrystallized at ~5 kbar and 200-250°C, and 2) Lws + Na-amp + Pmp + Phe
+ Ttn + Ep + Chl, which recrystallized under slightly higher temperatures but
similar pressures (300-350°C, at 5 kbar). A pre-blueschist facies metamorphic
event under greenschist facies conditions is recorded by calcic cores
overprinted by Na-amp rims in about half of the blocks. Sodic amphibole rims
with a higher Fe3+ content probably developed due to the breakdown of
epidote during a decrease in T. These mafic blueschists followed a
counterclockwise P-T path.
Remnants of “actinolitic rinds”, which are reaction zones formed when
the blocks were in contact with serpentine, were found associated with nine of
the studied mafic blueschist blocks. Such rinds were thought to be unique to
better-studied Franciscan high-T blocks.
Graphite-schist blocks (30 studied) contain Qtz + Phen + Ab + Gr, and
are of two types. One type has relict sedimentary textures with a weak
foliation defined by graphite and pressure solution seams. The other type has
a compositional layering with layers containing well recrystallized quartz. Nine
of these blocks also contain lawsonite within the more graphitic layers.
The geochemistry of the blueschist blocks indicates that they were
derived from the MORB-like oceanic crust, and seamounts underplated during the initiation of subduction. The mainly mafic protolith contained a
small volume of interlayered sediment, as indicated by the presence of
associated metasedimentary graphite-schists. Blueschist facies conditions
were attained at the bottom of the overriding plate during the initial states of
Franciscan subduction (150-155 Ma). Mafic material continued to be
underplated, and low-T dynamic blueschist-facies metamorphism continued
to form until at least ~137 Ma.
A model is proposed in which exhumation was facilitated by normal
faulting near the surface driven by gravitational collapse driven by decrease in
subduction plate dip around 80 Ma that is known to have caused the
Laramide orogeny. During this time, blueschist and graphite-schist blocks
were plucked from the bottom of the hanging wall, incorporated into the shaleand
water-rich shear zone at the plate interface, and exhumed during the
upward flow of mélange driven by the movement of the downgoing plate.
Blocks were extended and boudinaged, and metasomatically altered in the
cataclastic zones that developed along necks and margins of the blocks
during upwelling and the dewatering that led to final compaction near the
surface.Earth and Planetary Science
Syn- and postkinematic cement textures in fractured carbonate rocks: Insights from advanced cathodoluminescence imaging
No full textActs of re-membering: representations of the past in Irish and Basque literature
No full text"The aim of this study is to unravel the complex narratives animating the remembrance of Ireland’s and the Basque Country’s tumultuous past as represented in contemporary literature. Scholarly interest in Irish and Basque literature has been largely limited to nation-centered approaches, emphasizing the particularity of the Irish and Basque histories of nationalist conflict in an otherwise harmonious European landscape. My project, however, argues that the narratives that emerged from the 1930s to the present around the Irish and Basque tumultuous past did so in dialogue with and shaped by transnational processes as well as each country’s relationships with Europe. Thus, the purpose of this dissertation is twofold. On the one hand, it adopts a comparative and transnational approach, situating the Irish and Basque histories of violence in a broader context, with the aim to showcase the multiple social, political, and economic factors as well as other histories of violence that have shaped the understanding and representation of the Irish and Basque conflicts. On the other hand, it focuses on literature as an artifact that can function as both an archive and testimony of past atrocities in the absence of recognition and legal justice by recuperating forgotten, complex, and intersecting histories of violence that involve different kinds of perpetration and victimhood. In the process of re-membering, that is, recuperating and articulating what has been forgotten, the fiction that I analyze (Edna O’Brien’s ""House of Splendid Isolation,"" Jamie O’Neill’s ""At Swim Two Boys,"" Iban Zaldua’s “Gerra zibilak,” Ramon Saizarbitoria’s ""Gudari zaharraren gerra galdua,"" and Harkaitz Cano’s Twist) showcases moments of possibility within the past that not only may alter its interpretation but could also lead to a different envisioning of the present and the future."Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2021-08-01The student, Estibalitz Ezkerra Vegas, accepted the attached license on 2019-07-12 at 15:55.The student, Estibalitz Ezkerra Vegas, submitted this Dissertation for approval on 2019-07-12 at 16:08.This Dissertation was approved for publication on 2019-07-12 at 16:14.DSpace SAF Submission Ingestion Package generated from Vireo submission #14310 on 2019-11-26 at 14:04:14Made available in DSpace on 2019-11-26T20:59:48Z (GMT). No. of bitstreams: 2
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Previous issue date: 2019-07-12Embargo set by: Seth Robbins for item 113094
Lift date: 2021-11-26T20:59:54Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 113094 on 2021-11-27T10:15:20Z.U of I Only Restriction set for Item 113094 on 2021-12-20T18:26:48Z with date 2023-12-20 by [email protected] received from Thesis Office 12/20/2021.U of I Onl
TECTONIC FLOW MÉLANGE AND OLISTOSTROMES IN THE FRANCISCAN COMPLEX: WHICH IS MORE ABUNDANT?
No full textFirst Ar-40-Ar-39 ages from low-T mafic blueschist blocks in a Franciscan Melange near San Simeon: implications for initiation of subduction
No full textThe Franciscan Complex of California is a type example of an accretionary prism with widespread high-P/T subduction- zone metamorphism. Low-T, fine-grained, lawsonite-bearing mafic blueschists encased in a shale-matrix mélange near San Simeon have been dated for the first time. Ar- Ar ages were obtained for phengite separated from four blocks and from an actinolitic rind on the margin of one of the blocks. The three blocks with lawsonite + epidote yield ages of between 154 and 151 ±2 Ma, while the actinolitic rind yields an age of 150.9±1.6 Ma. These ages are from the part of the Franciscan Complex west of the San Andreas Fault that moved northward at least 300 km with respect to the extensive Franciscan exposures east of the fault. The ages obtained in this study show that some finegrained, low-T (lawsonite + epidote) Franciscan blueschist blocks formed at the same time as coarse-grained, high- T (garnet ± epidote) Franciscan blueschist blocks. These dated rocks indicate that both high- and low-T mafic blueschists are coeval and probably formed along 1000+ km of the North American Plate margin at ~160-155 Ma. The episode of dynamic blueschist metamorphism was soon followed by high-Mg rind formation and a long period of nearly static high-P/T conditions
