South-dipping Thrust Research Articles

Constraints on surface deformation in the Seattle, WA, urban corridor from satellite radar interferometry time-series analysis

SUMMARY We apply differential InSAR (DInSAR) time-series techniques to the urban corridor between Tacoma, Seattle and Everett, WA, using 93 interferograms from three satellites (ERS 1, ERS 2 and RADARSAT-1) between 1992 and 2007. Our goal is to study local tectonic, geomorphic and groundwater processes. Consequently, we remove long-wavelength (>50–100 km) deformation signals from unwrapped interferograms. By comparing surface velocities generated via the time-series technique at more than two million points within the overlapping region between two independent ERS tracks, we estimate the uncertainty of relative surface velocity measurements to be ∼0.5 mm yr−1 in the vertical. We estimate the uncertainty of relative displacement measurements to be ∼5.4 mm, given our comparisons of DInSAR-derived time-series to GPS data, a result that is consistent both with previous DInSAR time-series analysis and with the uncertainty expected from GPS displacements projected onto the radar line-of-sight. Active tectonic deformation at shallow depths on the region's numerous east–west structures is absent over the ∼11.5 yr of SAR data examined. Assuming that the south-dipping thrust beneath Seattle and Tacoma takes up 3 mm yr−1 of north–south shortening, our data indicate that the fault must be currently locked to a depth of greater than 10 km. We also document extensive groundwater-related deformation throughout much of the study region. Most notably, we identify sharp, linear deformation gradients near Federal Way, WA, and running between Sumner, WA, and Steilacoom, WA. These features may mark the locations of previously unmapped fault splays that locally control groundwater movement. We find no slow landslide deformation on any of the numerous mapped slide complexes within Seattle, although regions of known active landsliding, such as along Perkins Lane in Seattle, exhibit radar phase de-correlation. These observations are consistent with relatively infrequent and rapid landslide deformation within Seattle.

The 2004 May 28 Baladeh earthquake (Mw6.2) in the Alborz, Iran: overthrusting the South Caspian Basin margin, partitioning of oblique convergence and the seismic hazard of Tehran

We use teleseismic waveform analysis and locally recorded aftershock data to investigate the source processes of the 2004 Baladeh earthquake, which is the only substantial earthquake to have occurred in the central Alborz mountains of Iran in the modern instrumental era. The earthquake involved slip at 10–30 km depth, with a south-dipping aftershock zone also restricted to the range 10–30 km, which is unusually deep for Iran. These observations are consistent with co-seismic slip on a south-dipping thrust that projects to the surface at the sharp topographic front on the north side of the Alborz. This line is often called the Khazar Fault, and is assumed to be a south-dipping thrust which bounds the north side of the Alborz range and the south side of the South Caspian Basin, though its actual structure and significance are not well understood. The lack of shallower aftershocks may be due to the thick pile of saturated, overpressured sediments in the South Caspian basin that are being overthrust by the Alborz. A well-determined earthquake slip vector, in a direction different from the overall shortening direction across the range determined by GPS, confirms a spatial separation ('partitioning') of left-lateral strike-slip and thrust faulting in the Alborz. These strike-slip and thrust fault systems do not intersect within the seismogenic layer on the north side, though they may do so on the south. The earthquake affected the capital, Tehran, and reveals a seismic threat posed by earthquakes north of the Alborz, located on south-dipping thrusts, as well as by earthquakes on the south side of the range, closer to the city.

Shallow high-resolution seismics and reprocessing of industry profiles in southern Bavaria: The Molasse and the northern Alpine front

The purpose of this seismic investigation in the Upper Bavarian Miesbach area, as part of the international TRANSALP project, was to study the tectonic contact between the autochthonous Foreland Molasse and the allochthonous Folded Molasse marking the tectonic front of the Alpine orogen. Another specific target was the dip of the frontal emerging main thrust of the tectonic units Helveticum/Ultrahelveticum and Rhenodanubian Flysch overriding the Folded Molasse. Twelve seismic profiles obtained from the hydrocarbon industry were reprocessed. From the Foreland Molasse southward to the Autochthonous Molasse in the subsurface of the overthrust Folded Molasse conspicuous features such as steep normal faults at the Molasse base, S-directed thickening of Molasse sediments or sedimentary discordant base of Upper Marine Molasse can be recognized. Shallow high-resolution seismic measurements were conducted along two profiles across the tectonic contact between Foreland Molasse and Folded Molasse, as well as along a profile across the frontal emerging main thrust of the Helveticum/Ultrahelveticum and the Rhenodanubian Flysch. Geological structures could be identified in the top 300–500 ms two-way traveltime interval, which is hardly possible with the usual deep-seismic method. The method thus provides a bridge between deep-reflection seismics and surface geology. In contrast to the western Bavarian Molasse zone, the tectonic boundary between the Foreland Molasse and the Folded Molasse in the investigated area is not characterized by a large blind-thrust triangle zone but by a simple south-dipping thrust plane. Adjacent to the S follow several steeply south-dipping inverse Molasse thrust slices and the Miesbach syncline. The inverse thrust slices are interpreted as the overturned and sheared northern limb of a fault propagation fold, which linked the Folded Molasse to the Foreland Molasse during a final orogenic phase. The main thrust of the Helveticum/Ultrahelveticum and the Rhenodanubian Flysch are well imaged in the near-surface interval of the high-resolution reflection seismic data. In contrast to previously published results, these thrust planes show a gentle dip to the S from the surface down to at least 500–1000 m depth.

Tectonic and Seismologic Setting of the 22 September 2003, Puerto Plata, Dominican Republic Earthquake: Implications for Earthquake Hazard in Northern Hispaniola

On 22 September 2003 a Mw 6.4 earthquake occurred beneath the northern coast of Hispaniola near the resort city of Puerto Plata, Dominican Republic. The earthquake caused extensive damage in Puerto Plata, as well as in the regional capitol of Santiago, located 30 km south of the coast (Figures 1 and 2). A large ( Mw 5.6) aftershock occurred about one hour after the mainshock, and felt aftershocks continued for more than a month. The large north-south extent of the aftershock zone, the mainshock focal mechanism, and geologic evidence for an active fold-thrust belt offshore of Hispaniola indicate that the 2003 earthquake occurred on the south-dipping thrust fault mapped offshore of and beneath Puerto Plata (Dolan et al. , 1998) (Figure 3). The Puerto Plata earthquake (as we refer to it) was thus the latest in a westward-propagating series of moderately large to great (M 6.4-8.1) earthquakes that have occurred along the Caribbean-North America plate boundary in Hispaniola since 1943 (Dolan and Wald, 1998). The occurrence of these earthquakes highlights the seismic risks affecting the rapidly developing and densely populated island of Hispaniola (which is shared by the Dominican Republic and Haiti). In particular, the occurrence of the 22 September 2003 earthquake focused attention on the nearby Septentrional Fault, a major left-lateral strike-slip fault that extends by various names for more than 1,000 km along the Caribbean-North America plate boundary (Mann et al. , 1984; Mann and Burke,1984; Calais et al. , 1992; Grindlay et al. , 1997; Dolan et al. , 1998; Mann et al. , 1998). Because of its proximity to major population centers in Hispaniola ( e.g. , Santiago, Dominican Republic and Cap Haitien, Haiti), the Septentrional Fault constitutes perhaps the most dangerous seismic source in the region. In this study, we …

The Yavapai-Mazatzal boundary: A long-lived tectonic element in the lithosphere of southwestern North America

A seismic reflection profile crossing the Jemez lineament in north-central New Mexico images oppositely dipping zones of reflections that converge in the deep crust. We interpret these data as a Paleoproterozoic bivergent orogen, centered on the Jemez lineament, that formed during original Proterozoic crustal assembly by collision of Mazatzal island arcs with Yavapai proto–North American continent at ca. 1.68–1.65 Ga. The two major sets of reflections within the Yavapai-Mazatzal transition boundary dip at 15°–20°, and we interpret them as part of a south-dipping thrust system and as a north-dipping crustal-scale duplex that formed synchronously with the thrust system. The upper crust shows structures recording a succession of tectonic and magmatic events from the Paleoproterozoic to the Holocene. Notable among these structures is a system of nappes that formed during development of the bivergent orogen. Elements of the nappe system are exposed in Rocky Mountain uplifts and have been dated as having formed at 1.68 Ga, at depths of 10 km and at temperatures of >500 °C. We also see continuous bright reflections in the upper part of the middle crust that we associate with basaltic sills that postdate accretion. The data show that the Yavapai-Mazatzal suture is low angle (∼20°), an observation that explains why the boundary between the provinces has previously been so hard to define in the surface geology. The Jemez lineament overlies the root of this bivergent orogen that we also suggest is a Paleoproterozoic zone of weakness that has subsequently acted as a conduit for magmas and a locus of tectonism.

Imagerie sismique de la zone de collision hercynienne dans le Sud-Est du Massif armoricain (projet Armor 2/programme Géofrance 3D)

The structure of the Hercynian collision zone in the southeast of the Armorican Massif is illustrated by a 70-km long deep seismic profile acquired in September 2000. The profile images a previously unknown south-dipping thrust that brought the Champtoceaux Domain on top of the Central Armorican Domain during Carboniferous times. Dextral strike-slip motions along the South Armorican Shear Zone, which is downward cut by the thrust zone, are partly coeval with northward thrusting. A major discontinuity, hidden by the thrust front, is also imaged in the lower crust between the Champtoceaux area and the Central Armorican Domain. These new data lead to a structural and kinematic re-interpretation of this part of the Hercynian collision zone. To cite this article: A. Bitri et al., C. R. Geoscience 335 (2003).

Differential structural and geomorphic mountain-front evolution in an active continental collision zone: The northwest Pamir, southern Kyrgyzstan

Research Article| February 01, 2003 Differential structural and geomorphic mountain-front evolution in an active continental collision zone: The northwest Pamir, southern Kyrgyzstan Manfred R. Strecker; Manfred R. Strecker 1Institut für Geowissenschaften, Universität Potsdam, Postfach 601553, 14415 Potsdam, Germany Search for other works by this author on: GSW Google Scholar George E. Hilley; George E. Hilley 1Institut für Geowissenschaften, Universität Potsdam, Postfach 601553, 14415 Potsdam, Germany Search for other works by this author on: GSW Google Scholar J Ramón Arrowsmith; J Ramón Arrowsmith 2Department of Geological Sciences, Arizona State University, Tempe, Arizona 85287, USA Search for other works by this author on: GSW Google Scholar Isabelle Coutand Isabelle Coutand 3Institut für Geowissenschaften, Universität Potsdam, Postfach 601553, 14415 Potsdam, Germany Search for other works by this author on: GSW Google Scholar GSA Bulletin (2003) 115 (2): 166–181. https://doi.org/10.1130/0016-7606(2003)115<0166:DSAGMF>2.0.CO;2 Article history received: 15 Sep 2001 rev-recd: 15 Apr 2002 accepted: 30 Apr 2002 first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Manfred R. Strecker, George E. Hilley, J Ramón Arrowsmith, Isabelle Coutand; Differential structural and geomorphic mountain-front evolution in an active continental collision zone: The northwest Pamir, southern Kyrgyzstan. GSA Bulletin 2003;; 115 (2): 166–181. doi: https://doi.org/10.1130/0016-7606(2003)115<0166:DSAGMF>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Western, central, and eastern segments of the Trans Alai mountain front in the northern Pamir of Kyrgyzstan have accommodated varying degrees of approachment of the Pamir orogen with respect to the Tien Shan (Shan = Mountains) to the north. Ongoing collision between the northwestern corner of the Indian indenter and Eurasia has resulted in closure of the intramontane Alai Valley, which separates the Tien Shan and Trans Alai (Pamir) ranges. The different segments highlight the processes of shaping tectonically active mountain fronts in a semiarid environment. In this study, we have characterized this variation in processes with compilations of regional tectonic information, detailed geologic and geomorphic maps, topographic analyses, and interpretation of seismic reflection data. Along the sinuous western segment of the mountain front, dextrally oblique thrusting has created a wide (>500 m) zone of highly erodible fault gouge. This fault zone impinges on the southern Tien Shan, but complete basin closure is prevented by erosion due to the westward-flowing Kyzilsu River; the Kyzilsu valley forms the only outlet and is the vestige of a formerly contiguous sedimentary basin linking the Tarim Basin of China with the Tadjik Depression in the west. Numerous large landslides rooted in the fault zone have covered the active fault, which is partially undercut by the Kyzilsu River. Older, large landslides in this setting are associated with different levels of fluvial terraces of the former or present course of the Kyzilsu River, suggesting a causative relationship between lateral fluvial scouring, failure of mechanically weak mountain fronts, ongoing faulting, and mass transfer. Along the linear central segment, deformation is confined to a narrow single south-dipping thrust fault that juxtaposes Pliocene–Pleistocene and Holocene conglomerates. In this sector, the mountain front has numerous Holocene offsets. This prevailing structural style and the long-term deformation are underscored by multiple flights of gently sloping pediments and glaciogenic terrace surfaces that abruptly terminate at the steep mountain front, which also forms the boundary with the wide regraded piedmont. In contrast, closure between the Pamir and Tien Shan is complete along the eastern segment. The eroded and sinuous mountain front has been tectonically inactive during late Quaternary time. Small drainage-basin areas and low stream power apparently were not conducive to maintaining an eastern outlet to the Tarim Basin. Active deformation has stepped back into the orogen and now is concentrated along the Markansu Fault and within the Tien Shan to the north. The large drainage-basin area of the Kyzilsu River and the constant, glacially fed runoff guarantee that an effective interplay between tectonic uplift and erosion is maintained. Therefore, the geomorphically different mountain-front segments highlight the relationships between tectonic uplift and geomorphic processes, which in turn are controlled by lithology, topography, and the history of sediment routing throughout the landscape. You do not currently have access to this article.

Structural evolution and sequence of thrusting in the Tethyan fold-thrust belt and Indus-Yalu suture zone, southwest Tibet

Regional mapping of a north-south traverse from the India-Nepal-China border junction to Mount Kailas in southwest Tibet—combined with previously published geochronologic and stratigraphic data—is the basis for an incremental restoration of the Tethyan fold-thrust belt and deformation along the Indus-Yalu suture zone. From north to south, the major structural features are (1) the Indus-Yalu suture zone, composed of five south-dipping thrust faults involving rocks interpreted to represent parts of the former Indian passive margin and Asian active margin, (2) the Tethyan fold-thrust belt, composed of a dominantly north-dipping system of imbricate thrust faults involving Precambrian through Upper Cretaceous strata, and (3) the Kiogar-Jungbwa thrust sheet. A linelength cross-section reconstruction indicates a minimum of 176 km of north-south horizontal shortening partitioned by the Tethyan fold-thrust belt (112 km) and IndusYalu suture zone (64 km). Sequential restoration of the cross section shows that the locus of shortening prior to the late Oligocene occurred significantly south (possibly .60 km) of the Indus-Yalu suture zone within the Tethyan fold-thrust belt and that a significant amount of unsubducted oceanic lithosphere was present south of the suture in southwest Tibet until that time. An implication of this result is that postcollision (Oligocene/Miocene) high-K, calcalkaline magmatism may be explained by melting due to active subduction of oceanic crust beneath the Kailas magmatic complex until the late Oligocene. A regional profile across the Tibetan-Himalayan orogen from

Structural Evolution of the Tuzgölü Basin in Central Anatolia, Turkey

The Central Anatolian segment of the Alpine-Himalayan orogen contains "interior" basins, the largest of which is the Tuzgölü (Salt Lake) basin (>20,000 km2). It is bounded on the east by the Tuzgölü (Salt Lake) fault zone and on the west by the Yeniceoba and Cihanbeyli fault zones. Structural, stratigraphic, and sedimentologic evidence suggests that the Tuzgölü basin started as a fault-controlled basin during late Maastrichtian tectonism when the present-day northwest-trending faults that bound the basin were initiated. These faults may have been formed as normal faults suggesting extension or strike-slip faults with a normal component of movement indicating a large transtension at the time of their initiation. The late Maastrichtian faults were reactivated as strike-slip faults in response to late Eocene compression in the region that produced the Central Anatolian thrust belt to the north and the late Eocene south-dipping thrust faults of the Ulukisla basin to the south. This reactivation is suggested by structurally repeated and missing Paleocene-Eocene deposits in some of the basin's wildcat wells. The late Eocene regression in the Tuzgölü basin was caused by the combined effects of Eocene shortening and a large environmental change. Late Eocene evaporites suggest that the basin was dry before the start of the Neotectonic period, while during the Neotectonic itself the Tuzgölü fault zone was reactivated again, predominantly as a normal fault with a right-lateral strike-slip component. This is evidenced by (1) a major unconformity between the post-Eocene Koçhisar Formation of the Tuzgölü basin and the underlying Eocene rock units; (2) a well-developed rollover anticline observed on seismic reflection profiles; and (3) a right-step along the Tuzgölü fault zone seen in the field.

Geology of the Bozdag area, central Menderes massif, SW Turkey: Pan-African basement and Alpine deformation

The Menderes massif consists of a Precambrian Core Series that preserves evidence for a polymetamorphic history and a Paleozoic/Mesozoic Cover Series that experienced only the Alpine tectonometamorphic evolution. Structural, petrographic, and geochronologic investigations in the central Menderes massif demonstrate that (a) part of the metamorphic and structural evolution of the Precambrian basement is older than the undeformed 551±1.4-Ma-old Birgi metagranite, and (b) inferred Alpine fabrics overprinting the Cover Series largely have the same attitudes as the old structures in the much older Core Series. The inferred Alpine fabrics include both contractional and extensional structures. Contraction under greenschist to amphibolite facies conditions resulted in the imbrication of the Core and Cover Series and generated an inverted metamorphic sequence by north-directed thrusting. During Alpine extension, most of the south-dipping thrust faults were reactivated as extensional shear zones under decreasing greenschist facies conditions.

Crustal thickening in Gansu-Qinghai, lithospheric mantle subduction, and oblique, strike-slip controlled growth of the Tibet plateau

Crustal thickening in Gansu-Qinghai, lithospheric mantle subduction, and oblique, strike-slip controlled growth of the Tibet plateau

Embaluh Group turbidites in Kalimantan: evolution of a remnant oceanic basin in Borneo during the Late Cretaceous to Palaeogene

Turbidites crop out in large parts of NW Borneo, including Kalimantan and Sarawak. The strata predominantly comprise the Embaluh Group in Kalimantan and lateral equivalents the Rajang Group in Sarawak (collectively known as the Rajang–Embaluh Group). Previous interpretation of these rocks as the product of deep marine deposition and deformation as part of an accretionary prism during Late Cretaceous to Palaeogene subduction implies south-dipping thrusts, northward stratigraphic younging, the existence of a complete arc to trench system, and significant deformation and metamorphism of the turbidites. However new fieldwork described here established consistent southward stratigraphic younging in Kalimantan, no evidence for southward-dipping thrusts and a lack of metamorphism and associated accretionary complex-related deformation features. Furthermore all available palaeontological and radiometric age data indicate that deposition of the bulk of the Rajang–Embaluh Group postdates in-board subduction-related magmatism and thus a complete arc-trench system cannot be demonstrated. Consequently the Rajang–Embaluh Group turbidites are re-interpreted as having formed in either a post-collisional foreland basin or a remnant ocean basin. The lack of a identifiable mountain belt and linked thrust system, and probable oceanic aYnity of crust beneath the Rajang–Embaluh Group basin favour the latter interpretation. Borneo occupies a pivotal position within southeast Asia. This new model of a remnant oceanic basin setting for extensive turbidite units of Borneo therefore has far-reaching implications for the tectonic evolution of Borneo, the South China Sea and SE Asia. The new model is compared with older, Palaeozoic orogenic belts which also contain thick turbidites sequences.

Rotation and exhumation of a thrust plane: Apatite fission-track data from the Glarus thrust, Switzerland

Research Article| July 01, 1997 Rotation and exhumation of a thrust plane: Apatite fission-track data from the Glarus thrust, Switzerland M. K. Rahn; M. K. Rahn 1Institut für Mineralogie, Petrologie und Geochemie, University of Freiburg, Albertstrasse 23b, 79104 Freiburg, Germany Search for other works by this author on: GSW Google Scholar A. J. Hurford; A. J. Hurford 2London Fission Track Research Group, University and Birkbeck Colleges, Gower Street, London WC1E 6BT, United Kingdom Search for other works by this author on: GSW Google Scholar M. Frey M. Frey 3Mineralogisch-Petrographisches Institut, University of Basel, Bernoullistrasse 30, 4056 Basel, Switzerland Search for other works by this author on: GSW Google Scholar Author and Article Information M. K. Rahn 1Institut für Mineralogie, Petrologie und Geochemie, University of Freiburg, Albertstrasse 23b, 79104 Freiburg, Germany A. J. Hurford 2London Fission Track Research Group, University and Birkbeck Colleges, Gower Street, London WC1E 6BT, United Kingdom M. Frey 3Mineralogisch-Petrographisches Institut, University of Basel, Bernoullistrasse 30, 4056 Basel, Switzerland Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1997) 25 (7): 599–602. https://doi.org/10.1130/0091-7613(1997)025<0599:RAEOAT>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M. K. Rahn, A. J. Hurford, M. Frey; Rotation and exhumation of a thrust plane: Apatite fission-track data from the Glarus thrust, Switzerland. Geology 1997;; 25 (7): 599–602. doi: https://doi.org/10.1130/0091-7613(1997)025<0599:RAEOAT>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Apatite fission-track ages and track-length measurements are presented from 22 samples from the Glarus Alps, eastern Switzerland, where maximum temperatures of 100 to 350 °C along an Alpine thrust plane were reached during late Tertiary metamorphism. With the exception of the northernmost sample, apatite ages are fully reset and range between 5 and 12 Ma. Apatite fission track data along a vertical profile and a horizontal profile indicate that isothermal planes were oriented parallel to the Glarus thrust plane and that the thrust plane cooled below a mean apatite fission track closure temperature of 110 °C at 9 Ma.The metamorphic pattern and fission-track data indicate a south-dipping thrust plane during the times of peak metamorphic conditions, postmetamorphic thrusting over a distance of ∼ 10 km, and gradational exhumation of the plane to a horizontal position at ca. 9 Ma. Ongoing rotation of the plane is reflected by the present dip of about 7°NNW. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geology and geochemistry of the Barneys Canyon gold deposit, Utah

Barneys Canyon is a sediment-hosted, disseminated gold deposit located 7 km from the large, gold-rich, Bingham porphyry copper deposit. Host rocks for gold mineralization are the Permian Park City dolomite and siltstone and the Kirkman-Diamond Creek sandstone. The gold deposit is approximately 430 m long, 370 m wide, up to 90 m thick and contains 8.5 million metric tons (t) of reserves averaging 1.6 g/t gold. Intrusive igneous rocks are conspicuously absent. The gold deposit is located on the northern flank of the northeast-trending Copperton anticline, an overturned box fold. A small east-striking, south-dipping thrust fault, the Barneys Canyon thrust fault, with 200 m displacement, repeats the Park City Formation, and north-south-striking steep normal faults form a graben in which the gold deposit is located. The Barneys Canyon thrust fault predates mineralization and the Phosphate normal fault postdates mineralization.Alteration of the host rocks is similar to other sediment-hosted, disseminated gold deposits but at lower alteration mineral abundances. Kaolinite and illite comprise less than 10 percent of the altered rock. Silicification is minor, barite is rare, and pyrite and marcasite are common, but not abundant. Trace As, Sb, Hg, Tl, and Ba show pronounced increase.K/Ar age determinations on vein illite from ore grade (1.5 ppm gold) bedding-plane gougelike material yield Jurassic ages.Fluid inclusion measurements from barite and jasperoid show a mean salinity of 1.7 wt percent NaCl equiv and homogenization temperatures of 130 degrees to 393 degrees C with weak modes at 350 and 230 degrees C, suggesting that two fluids have interacted with rocks at Barneys Canyon. Kaolinite-bearing assemblages formed below 280 degrees C. Pressure correction at hydrostatic pressure is 12 degrees C.Fluid inclusion measurements, geochronology, structure, trace elements, and distance from Bingham are inconsistent with genesis of the Barneys Canyon deposit as part of the Bingham porphyry copper system. It is unlikely that genesis of the Barneys Canyon gold deposit involved igneous activity.

Age and mode of emplacement of the collector anomalY, (Canada): Is it the northwestern boundary of Gondwana?

A direct study of the Collector Anomaly, a prominent positive gravity and magnetic anomaly, located between Boston (U.S.A.) and southern Spain, suggests that this Paleozoic feature, which follows or corresponds with a suture, may be modelled magnetically, in the Grand Banks area, by a northward dipping dyke-like body. This body could have originated when Gondwanaland and Avalon collided. The magnetic and seismic data available in the eastern part of the Grand Banks do not permit us to understand the geometric relationship where this body intersects with two post-Givetian south deepening thrusts, the roots of which are located in the Ghomarids of northern Morocco. Since, in plan view, the body causing the Collector Anomaly cuts Meguma sediments—which are Emsian in their upper part—this mafic body could be younger than Emsian. But recent geochronological data have been interpreted to indicate a 400–415 Ma metamorphic age as the collision age between Avalon and Meguma. The study of the previous seismic lines cutting across the Avalon-Meguma boundary, in the Gulf of Maine, in the Bay of Fundy and east of Nova-Scotia, show a western extension of the Morroccan-Grand Banks south dipping thrust system. This system is cut by the suture which separates Meguma from Avalon. The geometrical relationship suggests that the seismic and mafic suture between the two zones cannot be older than the Frasnian, which therefore gives a maximum age for the last docking of Meguma. This is the first study where the magnetic modelling of the Collector Anomaly is associated with the seismic reflection data along its entire length. The Collector magnetic trend is not as clear in southern Spain as in Canada, because of Hercynian southward thrusting involving the mafic and ultramafic rocks which developed in Spain during the pre-Variscan northward subduction. These data show that the magnetic rocks responsible for the Collector Anomaly are sometimes affected by tectonic transport which locally may differ in age and direction. As a consequence, the northwestern plate boundary of Gondwanaland imaged on the deep seismic data does not everywhere correspond with the shallow expression of the Collector Anomaly.

The Magnitude 6.7 Northridge, California, Earthquake of 17 January 1994

The most costly American earthquake since 1906 struck Los Angeles on 17 January 1994. The magnitude 6.7 Northridge earthquake resulted from more than 3 meters of reverse slip on a 15-kilometer-long south-dipping thrust fault that raised the Santa Susana mountains by as much as 70 centimeters. The fault appears to be truncated by the fault that broke in the 1971 San Fernando earthquake at a depth of 8 kilometers. Of these two events, the Northridge earthquake caused many times more damage, primarily because its causative fault is directly under the city. Many types of structures were damaged, but the fracture of welds in steel-frame buildings was the greatest surprise. The Northridge earthquake emphasizes the hazard posed to Los Angeles by concealed thrust faults and the potential for strong ground shaking in moderate earthquakes.

Tectonic Evolution of the Northern Caribbean/Bahamas/Florida Region: Implications for Exploration

ABSTRACT The northern Caribbean/Florida/Bahamas region consists of (1) a major thrust belt striking from western Cuba to Puerto Rico and (2) a broad carbonate foreland to the north in Florida and the Bahamas. A major exploration problem in Florida and the Bahamas has been the interpretation of many anomalous vertical seismic features in the carbonate platform. Are they vertical faults or the effect of statics and paleokarst problems? If these features are true faults, uncertainties remain concerning fault geometry, timing, and trap potential. In order to clarify these uncertainties the following tectonic scenario was developed by (1) analyzing regional structure and stratigraphy and (2) testing palinspastic interpretations on an interactive 3D computer graphics system. Triassic/Jurassic. The study area serves as a transform zone in continental crust between the opening Central Atlantic and Gulf of Mexico basins. Continental crust is variably stretched between NW striking wrench faults and subsidiary NNE striking normal faults. By the latest Jurassic, the Gulf of Mexico stops opening and transform motion in the study area ceases. Early Cretaceous. Seafloor spreading begins east of Yucatan in the proto-Caribbean ocean and the proto-Cuba, Bahamas, and Florida area develops into a young continental margin sequence characterized by rapid subsidence and deposition of pelagic limestone (good source rocks). Mid Cretaceous. Changes in regional stresses surrounding the enlarging Atlantic Ocean disrupt the continental margin. Older rift and wrench-related structures in the basement reactivate and propagate into the overlying Neocomian section creating highs and lows at the surface. Late Cretaceous-Tertiary. The Cuban arc collides with the continental margin and forms a south-dipping thrust stack. Traps form in thrust-related anticlines that are charged as continental margin source rocks are overthrust and matured. Convergent stresses reactivate rift- and wrench-related structures in the foreland causing a jostling of crustal blocks. New faults propagate upward into overlying carbonates creating low-amplitude anticlinal closures. For explorationists, the tectonic scenario developed by this study suggests that in Florida/Bahamas, the anomalous seismic features in the carbonate platform are true vertical faults making this area more structurally complicated (but also more prospective) than previously recognized. End_of_Record - Last_Page 321-------

Structural analysis of a ductile-brittle Precambrian shear zone in the Sierra Madre, Wyoming: western extension of the Cheyenne belt?

Abstract Existing plate tectonic models for the Cheyenne belt, a Proterozoic suture at the southern margin of the Archean Wyoming craton, are based largely on data from the Medicine Bow Mountains, southern Wyoming. This paper tests the hypothesis that a major structural and geochronological discontinuity in the Sierra Madre of southern Wyoming is the western extension of the Cheyenne belt. The Sierra Madre shear zone consists of a cataclastic western segment and a mylonitic eastern segment that comprises several mylonite zones. The eastern segment records early ductile thrusting (ca. 1750 Ma) and later dextral strike-slip faulting as revealed by macrostructural, microstructural, and quartz fabric analysis. Structures associated with these events are kinematically compatible and coeval with structures within the suture zone in the Medicine Bow Mountains. The correlation of shear zones in the two ranges is supported further by lithologic similarity of distinctive rocks north of and within the shear zones and the presence of unusual quartz fabrics documenting 〈 c 〉 slip in synkinematic granites in both ranges. Isolated exposures of mylonite along the dominantly cataclastic western segment suggest that the mylonitic shear zone was formerly more extensive. The western segment of the Sierra Madre shear zone is a single zone of intense cataclasis that truncated and dismembered the earlier ductile shear zone. Kinematic analysis within the cataclastic zone suggests that it formed during north-directed thrusting. East-striking, south-dipping thrust faults and associated overturned-to-the-north recumbent folds are developed in supracrustal rocks directly north of the cataclastic fault zone. This spatial association of north-vergent structures and their apparent kinematic compatibility suggests that they are genetically related. Two major northwest-striking, cataclastic, dextral strike-slip in the eastern Sierra Madre appear to merge with the cataclastic thrust fault. These cataclastic faults are interpreted as parts of a north-vergent, thrust-tear system that cut across the original suture zone as rocks in the upper plate of the thrust were transported to the north. It is not known whether this deformational event occurred in response to continued, post-suture convergence to the south or if it represents a separate and distinct Precambrian event. The prominent bend in the Sierra Madre shear zone may be an oroclinal flexure produced as a consequence of northward translation along the cataclastic thrust system.

Ouachita Mountain Thrust Front: An Integrated Approach to Prospect Analysis in Thrust Belts: ABSTRACT

The thrust front of the Ouachita Mountains in western Arkansas is defined by the prominent asymmetric Washburn anticline. Previously interpreted as a complexly thrust-faulted anticline, the feature has been reinterpreted as a delta or triangle structure based on integration of surface mapping from thematic mapper (TM) data with subsurface interpretation of seismic and well-log cross sections. The northern limb of the Washburn anticline consists of a relatively unfaulted steeply north-dipping sheet above a major north-dipping backthrust. The southern limb consists of several steeply south-dipping thrust sheets that form a duplex zone in the center of the delta structure. Seismic and well-log interpretations suggested the presence of the imbrication in the core of the structure, but poor seismic resolution within the structure made interpretation of the backthrust and duplex geometry difficult. Surface mapping from TM imagery indicates the presence of the backthrust and the extent and geometry of the delta structure. Thrust sheets and horses also crop out, and their geometry is a guide to interpretation of subsurface data sets. The new model of the Ouachita thrust front as a delta structure has aided in subsurface data analysis and has resulted in a better understanding of trap geometry and distribution. Thismore » study also demonstrates the application of detailed surface mapping from satellite remote-sensing data to prospect-scale analysis.« less

Washburne Anticline Delta Structure: Model Based on Integration of Thematic Mapper, Seismic, and Well-Log Data: ABSTRACT

The Washburne anticline located in western Arkansas is a prominent, thrust-related structure at the leading edge of the Ouachita orogenic belt. Previously interpreted as a complexly thrust-faulted anticline, the feature has been reinterpreted as a delta or triangle structure based on integration of surface mapping from thematic mapper (TM) data with subsurface interpretation of seismic and well-log cross sections. The northern limb of the Washburne anticline consists of a relatively unfaulted, steeply north-dipping sheet above a major north-dipping backthrust. The southern limb consists of several steeply south-dipping imbricate thrust sheets that form a duplex zone in the center of the delta structure. Seismic and well-log interpretations indicate the presence of the imbrication in the duplex zone, but poor seismic resolution within the structure made interpretation of the back thrust difficult. Surface mapping from TM imagery indicates the presence of the back thrust and the extent and geometry of the delta structure. Imbricate thrust sheets and horses also crop out, and their geometry is a guide to interpretation of subsurface data sets. The new model of the Washburne anticline as a delta structure has aided in subsurface-data analysis and has resulted in a better understanding of trap geometry and distribution. Thismore » study also demonstrates the application of detailed surface mapping from satellite remote-sensing data to prospect-scale analysis.« less