Evolution of the Appalachian Laurentian margin: Lithoprobe results in western Newfoundland

1998 ◽  
Vol 35 (11) ◽  
pp. 1271-1287 ◽  
Author(s):  
John WF Waldron ◽  
Scott D Anderson ◽  
Peter A Cawood ◽  
Laurel B Goodwin ◽  
Jeremy Hall ◽  
...  
Keyword(s):  
Foreland Basin ◽  
Shear Zones ◽  
Passive Margin ◽  
Thrust Sheets ◽  
External Part ◽  
Laurentian Margin ◽  
Seismic Reflection Profiles ◽  
Seismic Reflections ◽  
Seismic Lines ◽  
Thermal Subsidence

The Humber Zone of the western Newfoundland Appalachians represents the early Paleozoic Laurentian margin established by Neoproterozoic rifting. After a period of passive margin thermal subsidence, Taconian deformation began in the Early Ordovician with westward thrusting. Subsequently, an extensive foreland basin developed beneath the Gulf of St. Lawrence. It records rapid Late Ordovician to Early Silurian subsidence; mid-Silurian erosion; and renewed Late Silurian to Devonian subsidence. The Humber Zone was traversed by Lithoprobe seismic reflection profiles. Within the external part of the orogen, seismic reflections in the upper crustal section appear more coherent where seismic lines are parallel to fold hinges. Some subhorizontal reflectors are interpreted as thrust sheets of shelf limestone, but others probably represent intrabasement structures. A group of moderately northwest-dipping reflections probably represents late extensional shear zones. On the Baie Verte Peninsula, low-angle reflections passing beneath the Baie Verte Line are probably also late extensional shears, possibly reactivating earlier thrusts. Tectonism in the Humber Zone probably began with attempted eastward subduction of the Laurentian margin. Deep burial of the margin, accompanied by eclogite-facies metamorphism, probably coincided with rapid subsidence in the foreland basin. Later Barrovian metamorphism was associated with cleavage development and east-directed shear, and with dextral oblique slip, in Baie Verte Peninsula. Later Silurian sinistral transpression with thrusting east of the Baie Verte Line was followed by dextral transpression to transtension. "Acadian" thrusting dominated the western margin of the orogen in the Devonian and possibly earliest Carboniferous.

A Cretaceous Neo-Tethyan carbonate margin in Argolis, southern Greece

1990 ◽  
Vol 127 (4) ◽  
pp. 299-308 ◽  
Author(s):  
Peter D. Clift ◽  
Alastair H. F. Robertson
Keyword(s):  
Late Cretaceous ◽  
Foreland Basin ◽  
Ocean Basin ◽  
Passive Margin ◽  
Accretionary Complex ◽  
Early Tertiary ◽  
Thrust Sheets ◽  
Pelagonian Zone ◽  
Structural Levels ◽  
Southern Greece

AbstractThe Argolis Peninsula, southern Greece, is believed to form part of a Pelagonian microcontinent located between two oceanic basins, the Pindos to the west and theVardar to the east, in Triassic to Tertiary time. In eastern Argolis, two important units are exposed: (i) the Ermioni Limestones cropping out in the southwest; (ii) the Poros Formation, observed on an offshore island in the northeast, and on the adjacent mainland. Both these units comprise late Cretaceous (Aptian-Maastrichtian) pelagic limestones, calciturbidites, lenticular matrix- and clast-supported limestone conglomerates and slump sheets. However, the Poros Formation is distinguished from the Ermioni Limestones by the presence of bituminous micritic limestones and an increasing proportion of shale up sequence. These successions are deep-water slope carbonates that once formed the southeast-facing passive margin of the Pelagonian platform (Akros Limestone). Beyond this lay a late Cretaceous ocean basin in the Vardar Zone. This ocean was consumed in an easterly-dipping subduction zone in latest Cretaceous (?) to early Tertiary time, giving rise to an accretionary complex (Ermioni Complex). During early Tertiary (Palaeocene-Eocene) time the passive continental margin (Pelagonian Zone) collided with the trench and accretionary complex to the east. As the suture tightened, former lower-slope carbonates (Ermioni Limestones) were accreted to the base of the over-riding thrust sheets and emplaced onto the platform. Farther west, bituminous upper slope carbonates (Poros Formation) flexurally subsided and passed transitionally upwards into calcareous flysch and olistostromes in a foreland basin. These sediments were then overridden by the emplacing thrust stack and themselves underplated. Late-stage high-angle faulting then disrupted the tectonostratigraphy, in places juxtaposing relatively high and low structural levels of the complex.

Thermal history of thrust sheets in an orogenic wedge: 40Ar/39Ar data from the polymetamorphic Seve Nappe Complex, northern Swedish Caledonides

2000 ◽  
Vol 137 (4) ◽  
pp. 437-446 ◽  
Author(s):  
OLAF M. SVENNINGSEN
Keyword(s):  
Shear Zones ◽  
Passive Margin ◽  
Fault System ◽  
Dyke Swarm ◽  
Slow Cooling ◽  
Nappe Complex ◽  
Thrust Sheets ◽  
Seve Nappe Complex ◽  
The Baltic ◽  
The Individual

The Seve Nappe Complex in the Scandinavian Caledonides contains the fragmented late Precambrian continent–ocean transition between Baltica and the Iapetus Ocean. This passive margin was fragmented and thrust eastwards over the Baltic Shield during Caledonian orogenesis. The individual thrust sheets in the Seve Nappe Complex went through different P–T–t evolutions, resulting in dramatic metamorphic contrasts: eclogite-bearing nappes are juxtaposed with nappes showing no evidence of Caledonian deformation or metamorphism in their interiors. Strain localization to the marginal parts of the thrust sheets left records of both pre-orogenic (rift) and early orogenic (subduction and subsequent uplift) processes in the thrust sheets of the Seve Nappe Complex. Even though it has been transported several hundred kilometres, only the margins of the eastern part of the Sarektjåkkå Nappe are affected by penetrative Caledonian deformation. This part of the Sarektjåkkå Nappe is dominated by pristine tholeiitic dykes and cross-bedded sandstones. The dykes are 608±1 Ma old and make up 70–80% of the nappe. Widely spaced thin shear zones of the Ruopsok fault system represent the only Caledonian penetrative deformation in the interior of the nappe. Previously published Ar–Ar dates indicate cooling below the closure temperature of hornblende at c. 470 Ma, but numerous ages have been recorded. Ar dating of biotite and muscovite from a cross-laminated metapsammite in the Sarektjåkkå Nappe gave well-defined ages of 428.5±3.6 and 432.4±3.8 Ma, respectively. Muscovite from a shear zone in the Ruopsok Fault System gave 428.2±4.0 Ma, whereas hornblende from the same locality did not yield interpretable data. The results indicate that these rocks were completely degassed at some unknown time, presumably at the emplacement of the dyke swarm. No subsequent excess argon contamination can be detected. A likely candidate for the degassing event is the emplacement of the dykes at 608 Ma. The interior of the nappe, and thus the entire nappe complex, cooled below ∼ 350 °C at around 430 Ma. Cooling from more than 500 °C at c. 470 Ma to 350 °C at c. 430 Ma suggests an average cooling rate of [les ] 4 °C/Ma. A prolonged period of slow cooling (≈exhumation?) following the initial, rapid uplift of the eclogite-bearing nappes and Early Ordovician construction of the Seve Nappe Complex is suggested.

Development of a folded thrust stack: Humber Arm Allochthon, Bay of Islands, Newfoundland Appalachians

2003 ◽  
Vol 40 (2) ◽  
pp. 237-253 ◽  
Author(s):  
John WF Waldron ◽  
Amber D Henry ◽  
James C Bradley ◽  
Sarah E Palmer
Keyword(s):  
Continental Slope ◽  
Continental Margin ◽  
Sedimentary Rocks ◽  
Foreland Basin ◽  
Shear Zones ◽  
The West ◽  
Kinematic Indicators ◽  
Thrust Sheets ◽  
Shelf Margin ◽  
Normal Sense

In the Humber Arm area of the western Newfoundland Appalachians, four distinct stratigraphic successions derived from the Laurentian continental margin are exposed. Each succession is believed to be characteristic of a separate thrust sheet. The platform sheet represents the ancient Laurentian shelf and its foreland basin cover; the Watsons Brook sheet is characterized by a succession including shelf-margin carbonates overlying foreland basin clastics; the Corner Brook sheet comprises continental slope and rise clastic and carbonate sedimentary rocks of the Humber Arm Supergroup; and the Woods Island sheet includes clastics of the Blow Me Down Brook formation that overlie mafic volcanics. Sheets are subdivided by thrusts into tectonic slices. Disrupted units and mélange, with scaly S1 foliation, are found along the boundaries of some slices. Thrust sheets and related structures have been deformed by F2 folds with axial planar S2 cleavage. S1 scaly foliations are transposed into parallelism with S2. There is a transition in the style of F2 folds across the area, from upright and subhorizontal in the west to overturned folds with west-dipping axial planes and steeply raking or reclined fold hinges in the east. Strongly curved fold hinges may reflect later shearing along the S2 surfaces, producing sheath-like fold geometries. Shear zones close to the east edge of the outcrop of the Watsons Brook sheet display kinematic indicators indicating both D2 reverse-sense and D3 normal-sense dip-slip shears. Subsequent events produced L4 and L5 crenulation lineations on the S2 surfaces. At minimum, several tens of kilometres of shortening affected the part of the margin preserved in the Humber Arm area; true shortening and transport amounts may have been much larger.

A seismic-based cross-section of the Grenville Orogen in southern Ontario and western Quebec

2000 ◽  
Vol 37 (2-3) ◽  
pp. 183-192 ◽  
Author(s):  
D J White ◽  
D A Forsyth ◽  
I Asudeh ◽  
S D Carr ◽  
H Wu ◽  
...  
Keyword(s):  
Cross Section ◽  
Seismic Refraction ◽  
Shear Zones ◽  
Tectonic Zone ◽  
Grenville Province ◽  
Crustal Layer ◽  
Seismic Reflection Data ◽  
Velocity Models ◽  
Laurentian Margin ◽  
Structural Boundary

A schematic crustal cross-section is presented for the southwestern Grenville Province based on reprocessed Lithoprobe near-vertical incidence seismic reflection data and compiled seismic refraction - wide-angle velocity models interpreted with geological constraints. The schematic crustal architecture of the southwest Grenville Province from southeast to northwest comprises allochthonous crustal elements (Frontenac-Adirondack Belt and Composite Arc Belt) that were assembled prior to ca. 1160 Ma, and then deformed and transported northwest over reworked rocks of pre-Grenvillian Laurentia and the Laurentian margin primarily between 1120 and 980 Ma. Reworked pre-Grenvillian Laurentia and Laurentian margin rocks are interpreted to extend at least 350 km southeast of the Grenville Front beneath all of the Composite Arc Belt. Three major structural boundary zones (the Grenville Front and adjacent Grenville Front Tectonic Zone, the Central Metasedimentary Belt boundary thrust zone, and the Elzevir-Frontenac boundary zone) have been identified across the region of the cross-section based on their prominent geophysical signatures comprising broad zones of southeast-dipping reflections and shallowing of mid-crustal velocity contours by 12-15 km. The structural boundary zones accommodated southeast over northwest crustal stacking at successively earlier times during orogeny (ca. 1010-980 Ma, 1080-1060 Ma, and 1170-1160 Ma, respectively). These shear zones root within an interpreted gently southeast-dipping regional décollement at a depth of 25-30 km corresponding to the top of a high-velocity lower crustal layer.

Westward propagation of thrusts in the external Western Alps (France) reappraised from an updated chronostratigraphy of the Miocene Molasses

2021 ◽  
Author(s):  
Amir Kalifi ◽  
Philippe-Hervé Leloup ◽  
Philippe Sorrel ◽  
Albert Galy ◽  
François Demory ◽  
...  
Keyword(s):  
Multidisciplinary Approach ◽  
Foreland Basin ◽  
Western Alps ◽  
Seismic Profiles ◽  
Stratigraphic Framework ◽  
Basin Scale ◽  
Deformation Kinematics ◽  
Westward Migration ◽  
External Part ◽  
Tectonics And Sedimentation

<p>The fact that the western Alps Miocene foreland basin succession is poorly dated impacts directly our understanding of the deformation kinematics of that part of the external part of the Alpine belt (France). Here we propose a multidisciplinary approach aiming at building a robust tectono-stratigraphic framework of the Miocene deposits at the basin scale (northern subalpine massifs, southern Jura, Royans, Bas-Dauphiné and La Bresse basins). Sr isotopes stratigraphy combined with magnetostratigraphy and biostratigraphy enable sequence stratigraphy subdivisions S1 to S8 between the Upper Aquitanian (-21 Ma) and the Tortonian (-9 Ma) dated with a precision <0.5 Ma. These results highlight four different palaeogeographical domains during the Miocene: (i) the oriental domain with depositional sequences S1a to S3 (~21.3 to 15Ma), (ii) the median domain, in which sequences S2, S3, S4 and S5 occurred (~17.8 to 14Ma), (iii) the occidental domain with sequences S2 to S8 (~17.8 to ~9.5Ma); and (iv) the Bressan domain, in which sequences S6 to S8 are found (~ 11.5 to ~9.5Ma).</p><p>This revised chronostratigraphy was complemented with a structural and tectono-sedimentary study based on new fieldwork data and a reappraisal of regional seismic profiles, allowing to highlight five major faults zones (FZ). It appears that the oriental, median and occidental paleogeographical domains are delineated by FZ1, FZ2 and FZ3, therefore suggesting a strong interplay between tectonics and sedimentation. Evidences of syntectonic deposits and a westward migration of the depocenters impart the following deformation chronology : a Oligocene compressive phase (P1) corresponding to thrusting above FZ1 rooted east (above) Belledonne, which generated reliefs that limited the early Miocene transgression to the east; an Early- to Middle Miocene W-WNW/E-ESE-directed compressive phase (P2) involving the Belledonne massif basal thrust, which between 18.05 +/- 0.15 Ma and 12Ma successively activated the Salève thrust fault, and the FZ2 to FZ5 from east to west. P2 deeply impacted the Miocene palaeogeographical evolution by a rapid westward migration of depocenters in response to the exhumation of piggy-back basins above the growing fault zones; a last Tortonian phase (P3), less well constrained, apparently implied a significant uplift in the subalpine massifs, combined with the activation of the frontal Jura thrust.</p>

scholarly journals Geophysical perspective on the structural interference zone along the Neoproterozoic Brasília and Ribeira fold belts in West Gondwana

2017 ◽  
Vol 47 (1) ◽  
pp. 3-19
Author(s):  
João Gabriel Motta ◽  
Norberto Morales ◽  
Walter Malagutti Filho
Keyword(s):  
Bouguer Anomaly ◽  
Shear Zones ◽  
Magnetic Data ◽  
Gravity Modeling ◽  
West Gondwana ◽  
Fold And Thrust Belt ◽  
Fold Belts ◽  
Thrust Sheets ◽  
Anomaly Map ◽  
Bouguer Anomaly Map

ABSTRACT: The Brasília and Ribeira fold belts have been established in south-southwestern São Francisco Craton during the Brasiliano-Pan African orogeny (0.9-0.5 Ga - Tonian to Cambrian), and played an important role in West Gondwana continent assembly. The region is given by a complex regional fold and thrust belt superposed by shearing during the orogeny late times, with superposing stress fields forming a structural interference zone. These thrust sheets encompasses assemblies from lower- to upper-crust from different major tectonic blocks (Paranapanema, São Francisco), and newly created metamorphic rocks. Re-evaluation of ground gravity datasets in a geologically constrained approach including seismology (CRUST1 model) and magnetic data (EMAG2 model) unveiled details on the deep- crust settings, and the overall geometry of the structural interference zone. The Simple Bouguer Anomaly map shows heterogeneous density distribution in the area, highlighting the presence of high-density, high metamorphic grade rocks along the Alterosa suture zone in the Socorro-Guaxupé Nappe, lying amid a series of metasedimentary thrust scales in a regional nappe system with important verticalization along regional shear zones. Forward gravity modeling favors interpretations of structural interference up North into Guaxupé Nappe. Comparison to geotectonic models shows similarities with modern accretionary belts, renewing the discussion.

scholarly journals Structural controls on earthquake rupture revealed by the 2020 Mw 6.0 Jiashi earthquake (Kepingtag belt, SW Tian Shan, China)

2021 ◽  
Author(s):  
Siyu Wang ◽  
Edwin Nissen ◽  
Timothy Craig ◽  
Eric Bergman ◽  
Léa Pousse-Beltran
Keyword(s):  
Cross Sections ◽  
Surface Deformation ◽  
Coseismic Deformation ◽  
Southern Chinese ◽  
Pattern Length ◽  
Waveform Modelling ◽  
Thrust Sheets ◽  
Dip Angle ◽  
Seismic Reflection Profiles ◽  
Tian Shan

The Kepingtag (Kalpin) fold-and-thrust belt of the southern Chinese Tian Shan is characterized by active shortening and intense seismic activity. Geological cross-sections and seismic reflection profiles suggest thin-skinned, northward-dipping thrust sheets detached in an Upper Cambrian décollement. The January 19 2020 Mw 6.0 Jiashi earthquake provides an opportunity to investigate how coseismic deformation is accommodated in this structural setting. Coseismic surface deformation resolved with Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) is centered on the back limb of the frontal Kepingtag anticline. Elastic dislocation modelling suggests that the causative fault is located at ~7 km depth and dips ~7° northward, consistent with the inferred position of the décollement. The narrow slip pattern (length ~37 km but width only ~9 km) implies that there is a strong structural or lithological control on the rupture extent, with up-dip slip propagation possibly halted by an abrupt change in dip angle where the Kepingtag thrust is inferred to branch off the décollement. A depth discrepancy between mainshock slip constrained by InSAR and teleseismic waveform modelling (~7 km) and well-relocated aftershocks (~10-20 km) may imply that sediments above the décollement are velocity strengthening. We also relocate 148 regional events from 1977 to 2020 to characterize the broader distribution of seismicity across the Kepingtag belt. The calibrated hypocenters combined with previous teleseismic waveform models show that thrust and reverse faulting earthquakes cluster at relatively shallow depths of ~7-15 km but include abundant out-of-sequence events both north and south of the frontal Kepingtag fault.

The initiation of the early Paleozoic Cordilleran miogeocline: evidence from the uppermost Proterozoic – Lower Cambrian Hamill Group of southeastern British Columbia

1988 ◽  
Vol 25 (1) ◽  
pp. 1-19 ◽  
Author(s):  
William J. Devlin ◽  
Gerard C. Bond
Keyword(s):  
British Columbia ◽  
Lower Cambrian ◽  
Direct Evidence ◽  
Thermal Anomaly ◽  
Passive Margin ◽  
Early Paleozoic ◽  
Upper Proterozoic ◽  
Windermere Supergroup ◽  
Depositional Setting ◽  
Thermal Subsidence

The uppermost Proterozoic–Lower Cambrian Hamill Group of southeastern British Columbia contains geologic evidence for a phase of extensional tectonism that led directly to the onset of thermally controlled subsidence in the Cordilleran miogeocline. Moreover, the Hamill Group contains the sedimentological record of the passage of the ancient passive margin from unstable tectonic conditions associated with rifting and (or) the earliest phases of thermal subsidence to post-rift conditions characterized by stabilization of the margin and dissipation of the thermal anomaly generated during the rift phase (the rift to post-rift transition). Widespread uplift that occurred prior to and during the deposition of the lower Hamill Group is indicated by an unconformable relation with the underlying Windermere Supergroup and by stratigraphic relations between Middle and Upper Proterozoic strata and unconformably overlying upper Lower Cambrian quartz arenites (upper Hamill Group) in the southern borderlands of the Hamill basin. In addition, the coarse grain size, the feldspar content, the depositional setting, and the inferred provenance of the lower Hamill Group are all indicative of the activation of basement sources along the margins of the Hamill basin. Geologic relations within the Hamill Group that provide direct evidence for extensional tectonism include the occurrence of thick sequences of mafic metavolcanics and rapid vertical facies changes that are suggestive of syndepositional tectonism.Evidence of extensional tectonism in the Hamill Group directly supports inferences derived from tectonic subsidence analyses that indicate the rift phase that immediately preceded early Paleozoic post-rift cooling could not have occurred more than 10–20 Ma prior to 575 ± 25 Ma. These data, together with recently reported isotopic data that suggest deposition of the Windermere Supergroup began ~730–770 Ma, indicate that the rift-like deposits of the Windermere Supergroup are too old to represent the rifting that led directly to the deposition of the Cambro-Ordovician post-rift strata. Instead, Windermere sedimentation was apparently initiated by an earlier rift event, probably of regional extent, that was part of a protracted, episodic rift history that culminated with continental breakup in the latest Proterozoic – Early Cambrian.

Velocity Models for the Crust Hosting the Main Aftershock Cluster of the 2011 Mineral, Virginia, Earthquake

2021 ◽  
Author(s):  
S. M. Ariful Islam ◽  
Christine A. Powell ◽  
Martin C. Chapman
Keyword(s):  
Three Dimensional ◽  
Passive Margin ◽  
Depth Range ◽  
Good Resolution ◽  
S Wave ◽  
Velocity Models ◽  
Taconic Orogeny ◽  
Thrust Sheets ◽  
Local Earthquake ◽  
Virginia Earthquake

Abstract Three-dimensional P- and S-wave velocity (VP and VS) models are determined for the crust containing the main aftershock cluster of the 2011 Mineral, Virginia, earthquake using local earthquake tomography. The inversion uses a total of 5125 arrivals (2465 P- and 2660 S-wave arrivals) for 324 aftershocks recorded by 12 stations. The inversion volume (22 × 20 × 16 km) is completely contained within the Piedmont Chopawamsic metavolcanic terrane. The models are well resolved in the central portion of the inversion volume in the depth range 1–5 km; good resolution does not extend to the hypocenter depth of the mainshock. Most aftershocks are located within a northeast-trending, southeast-dipping region containing negative VP anomalies, positive VS anomalies, and VP/VS ratios as low as 1.53. These velocity results strongly argue for the presence of quartz-rich rocks, which we attribute to either the presence of a giant quartz vein system or metamorphosed orthoquarzite sandstones originally deposited on the Laurentian passive margin and subsequently incorporated into the Chopawamsic thrust sheets during island arc collision in the Taconic orogeny.

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