Silurian subduction-related assembly of fault-defined tracts at the Laurieston Fault, Southern Uplands accretionary terrane, Scotland, U.K.

2000 ◽  
Vol 91 (3-4) ◽  
pp. 435-446 ◽  
Author(s):  
M. C. Akhurst ◽  
A. A. McMillan ◽  
G. S. Kimbell ◽  
P. Stone ◽  
R. J. Merriman
Keyword(s):  
Depositional Environment ◽  
Surface Expression ◽  
Strike Slip ◽  
Basement Structure ◽  
Geochemical Composition ◽  
Provenance Studies ◽  
Iapetus Ocean ◽  
Vertical Step ◽  
Regional Gravity ◽  
Basement Surface

ABSTRACTSubduction-related accretion of fault-defined tracts built up the Southern Uplands terrane during the final stages of closure of the Iapetus Ocean (Llandovery to Wenlock). Contrasts in depositional environment and pronounced differences in geochemical composition, provenance studies and metamorphic grade across the Laurieston Fault between the Gala and Hawick groups, suggests that it has a greater regional significance than most other tract-bounding structures. Initiated by underthrusting, and acting as a locus for subsequent sinistral strike-slip, the fault overlies a regional gravity anomaly gradient that is interpreted to be due, in part, to a concealed NW-ward dipping shallow basement surface. This is modelled as an open ramp in the NE that steepens to a near-vertical step along-strike to the SW. A change in structural geometry noted at the Laurieston Fault, with excision of accretionary tracts, is related to a period of oblique closure of the Iapetus Ocean. The youngest Gala Group tracts were accreted during a period of intense transpression to form a regional strike-slip duplex over the shallow basement ramp with termination of the tracts at the Laurieston Fault, its surface expression. The ramp acted as an obstacle to forward-breaking thrust progress, forcing the out-of-sequence thrusting and repetitive thrust imbrication noted in the eastern Southern Uplands. Upper Palaeozoic reactivation of this basement structure may have transferred strain between extensional Permian basins.

scholarly journals Amazonian Mesoproterozoic basement in the core of the Ibero-Armorican Arc: 40Ar/39Ar detrital mica ages complement the zircon's tale

Geology ◽  
2005 ◽  
Vol 33 (8) ◽  
pp. 637-640 ◽  
Author(s):  
G. Gutiérrez-Alonso ◽  
J. Fernández-Suárez ◽  
Alan S. Collins ◽  
I. Abad ◽  
F. Nieto
Keyword(s):  
Detrital Zircon ◽  
Sedimentary Rocks ◽  
Age Groups ◽  
Strike Slip ◽  
Zircon Age ◽  
Provenance Studies ◽  
The Core ◽  
Pan African ◽  
Rio Negro ◽  
Northwest Iberia

Abstract The 40Ar/39Ar age data on single detrital muscovite grains complement U-Pb zircon ages in provenance studies, as micas are mostly derived from proximal sources and record low-temperature processes. Ediacaran and Cambrian sedimentary rocks from northwest Iberia contain unmetamorphosed detrital micas whose 40Ar/39Ar age spectra suggest an Amazonian–Middle American provenance. The Ediacaran sample contained only Neoproterozoic micas (590–783 Ma), whereas the Cambrian sample contained three age groups: Neoproterozoic (550–640 Ma, Avalonian–Cadomian–Pan African), Mesoproterozoic- Neoproterozoic boundary (ca. 920–1060 Ma, Grenvillian-Sunsas), and late Paleoproterozoic (ca. 1580–1780 Ma, Rio Negro). Comparison of 40Ar/39Ar muscovite ages with published detrital zircon age data from the same formations supports the hypothesis that the Neoproterozoic basins of northwest Iberia were located in a peri-Amazonian realm, where the sedimentary input was dominated by local periarc sources. Tectonic slivering and strike-slip transport along the northern Gondwanan margin affected both the basins and fragments of basement that were transferred from Amazonian to northern African realms during the latest Neoproterozoic–earliest Cambrian. Exhumation and erosion of these basement sources caused shedding of detritus to the Cambrian basins, in addition to detritus sourced in the continental mainland. The apparent dominance of Rio Negro–aged micas in the Cambrian sandstone suggests the presence of unexposed basement of that age beneath the core of the Ibero-Armorican Arc.

A reevaluation of the position of the Baie Verte – Brompton Line in the Quebec Appalachians: the influence of Middle Devonian strike-slip faulting in Gaspé Peninsula

1992 ◽  
Vol 29 (6) ◽  
pp. 1265-1273 ◽  
Author(s):  
Michel Malo ◽  
Donna Kirkwood ◽  
Gilles De Broucker ◽  
Pierre St-Julien
Keyword(s):  
Middle Devonian ◽  
Surface Expression ◽  
Strike Slip ◽  
Aeromagnetic Data ◽  
Geological Data ◽  
Appalachian Orogen ◽  
Eastern Townships ◽  
Gaspe Peninsula ◽  
Gaspé Peninsula

The Baie Verte – Brompton Line (BBL), the surface expression of the Taconian suture in the Canadian Appalachian Orogen, extends from southern Quebec to the northeast end of Newfoundland. In the Quebec Appalachians, the BBL was previously located under the post-Taconian cover rocks between the Eastern Townships and Gaspé Peninsula. New geological data and reinterpretation of gravimetric and aeromagnetic data suggest that the BBL follows the southern edge of the Cambrian–Ordovician rocks of northern Gaspé Peninsula and is displaced by Middle Devonian strike-slip faults on the southern part of the peninsula. On a pre-Middle Devonian palinspastic map, the BBL is parallel to the Quebec Reentrant – St. Lawrence Promontory and the Appalachian structural front.

MICROEARTHQUAKE INVESTIGATION OF THE MESA GEOTHERMAL ANOMALY, IMPERIAL VALLEY, CALIFORNIA

Geophysics ◽  
1977 ◽  
Vol 42 (1) ◽  
pp. 17-33 ◽  
Author(s):  
Jim Combs ◽  
David Hadley
Keyword(s):  
Vertical Component ◽  
Surface Expression ◽  
High Gain ◽  
Strike Slip ◽  
Imperial Valley ◽  
Natural Period ◽  
Near Surface ◽  
Geothermal Fluids ◽  
First Motion ◽  
Motion Studies

Microearthquakes associated with the Mesa geothermal anomaly were recorded for five weeks during the summer of 1973 using an array of six portable, high‐gain seismographs equipped with vertical‐component 1-sec natural period seismometers. Background seismicity of the area is thus determined prior to development for geothermal power and water. The local seismicity changed considerably over the recording period. Most daily activity was characterized by only one or two potentially locatable events, while two microearthquake swarms of two‐ and three‐day duration included as many as 100 or more distinct local events per day. Hundreds of small events (nanoearthquakes), some clustered in swarms, were recorded by each seismograph; however, most were not detected on four or more seismograms so that hypocentral locations usually could not be determined. Locations were determined for 36 microearthquakes having epicenters situated in the [Formula: see text] areal extent of the geothermal anomaly. Focal depths ranged from near‐surface to about 8 km. More than half of the located events have hypocenters greater than the 4.0 km which is approximately the depth to crystalline basement. Stress associated with the Mesa geothermal anomaly is relieved by a combination of continuous microseismic activity and intermittent microearthquake swarms. Based on the results of the present study, a new right‐lateral strike‐slip fault, the Mesa fault, was defined. First motion studies indicate strike‐slip faulting although there is no surface expression of the fault. The northwest‐southeast trending Mesa fault is an active fault functioning as a conduit for rising geothermal fluids of the Mesa geothermal anomaly. This investigation is another demonstration that geothermal areas are characterized by enhanced microearthquake activity.

Gravity and magnetic anomalies of the Sutton Mountains region, Quebec and Vermont: expressions of rift volcanics related to the opening of Iapetus

1981 ◽  
Vol 18 (4) ◽  
pp. 680-692 ◽  
Author(s):  
P. S. Kumarapeli ◽  
A. K. Goodacre ◽  
M. D. Thomas
Keyword(s):  
Gravity Anomaly ◽  
Magnetic Anomaly ◽  
Triple Junction ◽  
Three Dimensional ◽  
Surface Expression ◽  
Magnetic Anomalies ◽  
Iapetus Ocean ◽  
Metavolcanic Rocks ◽  
Gravity And Magnetic ◽  
Narrow Belt

Prominent, nearly coincident, positive gravity and magnetic anomalies occur in the Sutton Mountains region, centered about 100 km east of Montreal, Quebec. Several lines of evidence indicate that the gravity anomaly stems from two principal sources: a deep (mid and lower crustal) source of speculative origin and a shallow source identifiable with a narrow belt of late Precambrian – early Cambrian metavolcanic rocks, the Tibbit Hill volcanics. The magnetic anomaly seems to be produced mainly by the metavolcanic rocks. Three-dimensional modelling of a residual gravity anomaly, supplemented by two-dimensional modelling of the magnetic anomaly, shows that the seemingly minor belt of metavolcanic rocks constitutes the surface expression of a thick (maximum thickness ~8 km) pile of dominantly mafic volcanics, which are only slightly exposed at the present level of erosion.The Tibbit Hill volcanics are regarded as products of rift-related volcanism that occurred at an rrr triple junction developed during the early stages of the opening of the Iapetus Ocean. The Ottawa graben is probably the failed arm of this triple junction. The emplacement of the Grenville dike swarm whose trend is nearly coincident with that of the Ottawa graben was probably coeval with the volcanism in the Sutton Mountains region. The present work shows that the volcanism in the region was on a much larger scale than hitherto recognized.

A revised correlation of Silurian rocks in the Girvan district, SW Scotland

2002 ◽  
Vol 93 (4) ◽  
pp. 383-392 ◽  
Author(s):  
James D. Floyd ◽  
Mark Williams
Keyword(s):  
Depositional Environment ◽  
Late Ordovician ◽  
Important Research ◽  
British Geological Survey ◽  
Marine Fauna ◽  
Comprehensive Review ◽  
Iapetus Ocean ◽  
Northern Side ◽  
Lower Palaeozoic ◽  
Early Palaeozoic

ABSTRACTIn late Ordovician and early Silurian times, the Girvan district lay in a shelf marinesetting on the margin of Laurentia, on the northern side of the Iapetus Ocean. The Lower Palaeozoic rocks of the Girvan district, and their shelly and graptolitic fossil fauna, were systematically described by Lapworth in 1882 and have formed an important research resource ever since. They provide valuable evidence for the depositional environment and geological setting of Girvan during the early Palaeozoic, in both regional and wider contexts, and demonstrate the long-recognised close affinity with contemporaneous Laurentian faunas. However, by late Ordovician and into Silurian times, the earlier Iapetus oceanic barrier to faunal migration had largely gone and there is good correlation between contemporaneous marine fauna throughout the British Isles and Scandinavia. Despite much recent research in the area, including resurvey work by the British Geological Survey, no comprehensive review of Silurian lithostratigraphy at Girvan has been published since the revision by Cocks and Toghill in 1973. The present review of the Silurian rocks addresses this need and complements the recently published (Fortey et al. 2000) revision of the underlying Ordovician rocks, thus bringing the entire Girvan Lower Palaeozoic succession up to modern standards of nomenclature.

Geomagnetic induction anomaly near Kootenay Lake—a strike–slip feature in the lower crust?

1970 ◽  
Vol 7 (6) ◽  
pp. 1568-1579 ◽  
Author(s):  
J. J. Lajoie ◽  
B. Caner
Keyword(s):  
Surface Expression ◽  
Strike Slip ◽  
Conductive Layer ◽  
Geomagnetic Induction ◽  
Western Cordillera ◽  
Early Mesozoic ◽  
Conductivity Structure ◽  
Kootenay Lake ◽  
Lower Crustal ◽  
East West

A geomagnetic induction anomaly in southeastern British Columbia has been investigated in detail with a 20-station network. The results indicate a sharp (near vertical) discontinuity in deep electrical conductivity structure, trending roughly east–west and located at the south end of Kootenay Lake. It is interpreted as evidence for sinistral strike–slip which intersected the edge of the main conductive layer which underlies most of the western Cordillera.Geological evidence indicates that such a feature (which has no known surface expression) must predate the late Paleozoic or early Mesozoic (200–250 m.y.). The persistence of sharp discontinuities over such long periods would confirm the compositional, rather than thermal, nature of the lower crustal conductive layer under the western Cordillera.

Recycled acritarchs as provenance indicators: implications for Caledonian terrane reconstruction

1992 ◽  
Vol 129 (4) ◽  
pp. 457-464 ◽  
Author(s):  
W. D. Mccaffrey ◽  
H. F. Barron ◽  
S. G. Molyneux ◽  
B. C. Kneller
Keyword(s):  
Source Area ◽  
Lake District ◽  
Provenance Studies ◽  
Iapetus Ocean ◽  
English Lake District

AbstractSilurian successions deposited on the margins of the Iapetus Ocean in the English Lake District, Southern Uplands of Scotland and Ireland contain recycled Ordovician acritarchs. These include taxa known only from Avalonia and Gondwana, with other recycled acritarchs possibly derived from Baltica. There is no palynological evidence to indicate that Laurentiaconstituted a source area. The data presented herein suggest that provinciality in derived microfossils may be profitably exploited in provenance studies.

Some geomorphological perspectives on the structure associated with the Petrinja M6.2 earthquake in Croatia

2021 ◽  
Author(s):  
Petra Jamšek Rupnik ◽  
Marko Budić ◽  
Matija Vukovski ◽  
Branko Kordić ◽  
Marko Špelić ◽  
...  
Keyword(s):  
Active Fault ◽  
Surface Expression ◽  
Vertical Movement ◽  
Strike Slip ◽  
Strike Slip Fault ◽  
Mountain Range ◽  
Active Structure ◽  
Dextral Strike Slip Fault ◽  
Main Fault ◽  
Channel Patterns

<p>After the earthquake of 29/12/2020 in Petrinja (ML6.2, ImaxVIII-IX EMS), an attempt was made to characterize the active structure associated with the earthquake. As a first step towards this goal, we performed a geomorphological analysis in order to contribute to the identification and characterization of the surface expression of the active Pokupsko dextral strike-slip fault. We focused on the area between the southernmost parts of Vukomeričke Gorice and the southernmost parts of Hrastovica Mountain, where the NW-SE striking Pokupsko fault has slipped during and after the recent earthquake (Ganas et al., 2021). Using available 1 : 5 000 scale topographic maps and various 10 m resolution digital elevation model visualizations, we mapped lineaments that could represent relatively recently active fault segments. We used a quantitative approach to perform stream sinuosity analysis (e.g., Leopold et al., 1964; Zamolyi et al., 2010) on major streams crossing the structure to identify distinct changes in channel patterns that may be associated with vertical movement along the predominantly strike-slip fault. We observed changes in the shape of the valleys, especially the changes in width, height, and direction. By summarizing various geomorphological indicators of active fault segmentation at the surface with available geological data (Pikija, 1987) and so far limited field observations, we provide insights into the structure of the Pokupsko fault.<br>Preliminary results show good agreement between lineament mapping, changes in valley shape, changes in the stream sinuosity index, and (to some extent) previously mapped faults. In addition, some of the changes in stream sinuosity correspond to locations where coseismic surface ruptures occurred during the December 29 earthquake (Budić et al., this session; Pollak et al., 2021). Results suggest that the several-kilometer-wide zone of uplifted Neogene deposits results from the dextral-transpressive structure, which at the surface consists of a series of subparallel fault strands branching off the main fault that runs along the SE slopes of the Hrastovica Mountain. The SW-most fault strands are associated with significant changes in the shape of the valleys: the wide valleys of Petrinjčica, Utinja and Šanja change to narrow and deeply incised as they cross the uplifted structure. Paleocene and Eocene rocks, which otherwise underlie the Neogene, outcrop in the NE parts of the fluvial breakthrough valleys, indicating the uplift of the Hrastovica Mountain. Topographic data show a decrease of the mountain range elevation towards the SW. This evidence suggests that the main fault runs on the NE side of the mountain, strikes NW-SE and dips steeply towards the SW. The fault strike deviates between Župić and Farkašić. The fault plane solution for the December 29 earthquake suggests a nearly pure strike-slip fault, while geomorphic evidence strongly indicates areas of active uplift along the fault, further supported by the general antiformal structure. We interpret this as an indication of either a general current transpressional character of the fault or as local kinematic variations due to segmentation and changes in the strike of the fault; further analyses are pending.</p>

The Iapetus suture in the British Isles

1989 ◽  
Vol 126 (1) ◽  
pp. 1-8 ◽  
Author(s):  
W. S. McKerrow ◽  
N. J. Soper
Keyword(s):  
Continental Crust ◽  
North American ◽  
Seismic Reflection ◽  
Plate Boundary ◽  
Surface Expression ◽  
Lake District ◽  
North West ◽  
The North ◽  
Iapetus Ocean ◽  
Seismic Reflection Profiling

AbstractThe position of the Iapetus Ocean suture can be traced between Ordovician fossil localities in the Southern Uplands and the Lake District which contain, respectively, distinct North American and European faunas. The Southern Uplands contains North American Caradoc faunas in the Northern Belt, and is considered to have been accreted onto the Laurentian (North American) margin between the Llandeilo and the end of the Wenlock. Deep seismic reflection profiling shows that a surface, probably parallel to the suture zone, dips down to the northwest from the Solway Line. In eastern Ireland, the surface trace of the suture coincides with the Navan Fault, which separates the Longford-Down massif from Ordovician sediments containing European faunas. The Navan–Silvermines Fault may represent the surface expression of the suture, but it is masked by Wenlock turbidites, which appear to have crossed over the plate boundary. Northward subduction of continental crust below the margin of Laurentia during the late Silurian may explain the influx of turbidite fans from the north or north west onto depressed crust to the south of the suture. Termination of subduction coincides with the widespread Acadian Orogeny in the Emsian (at 395±5 Ma).

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