| 1. |
- Aftabi, Pedram, et al.
(författare)
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InSAR mapping and modelling of an active Iranian salt extrusion
- 2010
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 167:1, s. 155-170
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Tidskriftsartikel (refereegranskat)abstract
- Interferometric synthetic aperture radar (InSAR) imaging is a powerful technique that is increasingly used to extract detailed 3D information on Earth surface structures, including exposed diapiric surfaces. We have used InSAR to map, for the first time, the cumulative surface deformation in a 6 km × 3 6 km region surrounding an active salt diapir (Syahoo) and its associated surface salt flow (or namakier) exposed in the Zagros Mountains of southern Iran. Images provided by the European Space Agency were acquired in 12 increments (ranging in length between 35 and 1248 days) over a 14 year interval between July 1992 and May 2006. The deformation of the salt surface is non-steady, with (extrapolated) rates of displacement varying between surficial uplifts of +1.4 mm day-1 (+511 mm a-1) and subsidence of -2.2 mm day-1 (-803 mm a-1). Growth of a central topographic dome occurs following short wet intervals to create a salt fountain morphology, which then slowly decays during the intervening long dry periods. Salt associated with dynamic 'bulging' of the central dome during wet intervals may flow laterally via gravity spreading into the surrounding salt sheet, resulting in deflation and subsidence of the dome, which is counteracted by growth and inflation of the adjacent namakiers. Salt 'bulges' that migrate down the namakier, resulting in local inflationary and deflationary cycles of the surface, may be regarded as episodic pulses of gravity spreading. Areas of inflation and deflation are also observed to commonly reverse during dry to wet periods, as the overall salt system effectively self regulates as it continually strives for dynamic equilibrium. As long as the source of salt remains undepleted, gravity spreading of the dome ultimately results in more buoyancy-driven salt flowing up the diapiric neck to replenish and feed the extrusion and maintain the gross fountain morphology.
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| 2. |
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| 3. |
- Augustsson, Carita, et al.
(författare)
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0.3 byr of drainage stability along the Palaeozoic palaeo-Pacific Gondwana margin; a detrital zircon study
- 2015
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Ingår i: Journal of the Geological Society. - : The Geological Society of London. - 0016-7649 .- 2041-479X. ; 172, s. 186-200
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Tidskriftsartikel (refereegranskat)abstract
- The palaeo-Pacific margin of Gondwana in the present-day south–central Andes is marked by tectonic activity related to subduction and terrane accretion. We present detrital zircon U–Pb data encompassing the Palaeozoic era in northern Chile and northwestern Argentina. Cathodoluminescence images reveal dominantly magmatic zircon barely affected by abrasion and displaying only one growth phase. The main age clusters for these zircon grains are Ediacaran to Palaeozoic with an additional peak at 1.3–0.9 Ga and they can be correlated with ‘Grenvillian’ age, and the Brasiliano, Pampean, and Famatinian orogenies. The zircon data reveal main transport from the nearby Ordovician Famatinian arc and related rocks. The Silurian sandstone units are more comparable with Cambrian units, with Brasiliano and Transamazonian ages (2.2–1.9 Ga) being more common, because the Silurian deposits were situated within or east of the (extinct) Famatinian arc. Hence, the arc acted as a transport barrier throughout Palaeozoic time. The complete suite of zircon ages does not record the accretions of exotic terranes or the Palaeozoic glacial periods. We conclude that the transport system along the palaeo-Pacific margin of Gondwana remained stable for c. 0.3 byr and that provenance data do not necessarily reflect the interior of a continent. Hence, inherited geomorphological features must be taken into account when detrital mineral ages are interpreted.
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| 4. |
- Ayarza, P, et al.
(författare)
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Contrasting tectonic history of the are-continent suture in the Southern and Middle Urals: implications for the evolution of the orogen
- 2000
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 157, s. 1065-1076
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Tidskriftsartikel (refereegranskat)abstract
- The Main Uralian Fault has been considered the original arc–continent suture for 2000 km along the Uralide orogen. The symmetry of the tectonic units across it suggested a consistent east-dipping polarity for the palaeosubduction zone, which, together with its topographic and aeromagnetic signature, supported the idea of a single suture. However, several characteristics vary at different latitudes. In the Middle Urals, it is a strike-slip fault zone with moderately deformed and metamorphosed volcanic arc fragments in its hanging wall, and low-grade metamorphic rocks of the East European Craton in its footwall. Here, it has a prominent NNW-trending magnetic signature which cross-cuts north-trending anomalies in its hanging wall, and a pronounced reflection seismic signature that can be traced to the top of the middle crust at c. 5 s. TWT. In the Southern Urals, it is a serpentinite mélange zone of ambiguous kinematics, with a weakly deformed and metamorphosed volcanic arc in its hanging wall, and moderately metamorphosed to high pressure rocks of the East European Craton in its footwall. In this part of the orogen, it has a weak reflection seismic character, and a magnetic signature that parallels that of its hanging wall. On the basis of an integrated analysis of these different data sets, we suggest that the Main Uralian Fault, as it is currently defined, is not a single entity, but rather the original arc–continent suture in the south, and the western strand of a strike-slip fault system that reworked the original suture in the Middle Urals.
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| 5. |
- Bahroudi, Abbas, et al.
(författare)
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Effect of spatial distribution of Hormuz salt on deformation style in the Zagros fold and thrust belt: an analogue modelling approach
- 2003
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Ingår i: Journal of the Geological Society of London. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 160, s. 719-733
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Tidskriftsartikel (refereegranskat)abstract
- Scaled analogue models of thin-skinned simultaneous shortening above adjacent viscous and frictional décollements simulate the effect of Hormuz salt on the shortening in the Zagros fold and thrust belt. The models consisted of sand layers that partly overlay a viscous layer of silicone and were shortened from one end. Spatial distribution of the viscous décollement varied along strike and dip, as occurs in part of the Zagros fold and thrust belt. In this belt, Phanerozoic sedimentary cover was shortened partly above the Hormuz salt lying on the Precambrian crystalline basement, behaving as a basal viscous décollement. Model results display how the nature of the décollement affects the evolution of an orogenic belt. Using model results, we explain the development of deflection zones, and discuss strain partitioning, formation of different topographic wedges and differential sedimentation along the Zagros fold and thrust belt. Model results suggest the formation of a gentle taper, consisting of both foreward and backward thrusts above a viscous décollement and a relatively steeper taper consisting only of forward-vergent imbricates above a frictional décollement. However, in our models, the steepest wedge with the highest topography formed where the viscous substrate had a limited extent with a transitional boundary (pinch-out) perpendicular to the shortening direction. Shortening of this boundary led to development of frontal ramps associated with significant uplift of the area behind the deformation front.
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| 6. |
- Barnes, C. J., et al.
(författare)
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Ordovician-Silurian deformation of the Neoproterozoic upper gneiss unit in the northern Seve Nappe Complex : implications for subduction of the Baltican margin
- 2023
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 180:4
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Tidskriftsartikel (refereegranskat)abstract
- The upper gneiss unit is exposed in the northernmost Seve Nappe Complex (SNC) in the Scandinavian Caledonides. To investigate the Caledonian tectonic history of the unit, in situ white mica and biotite Ar-40/Ar-39 geochronology was applied to a leucogranite and two paragneisses. The leucogranite exhibits low-strain traits. Biotite porphyroblasts yielded a cooling age of 459 +/- 2 Ma. White mica that replace biotite and plagioclase provided a crystallization age of 436 +/- 5 Ma. White mica in both paragneisses exhibit high-strain characteristics associated with top-to-the-east sense of shear. One paragneiss provided dispersed late Cambrian to Late Ordovician dates with the youngest approximating deformation at 459 +/- 2 Ma. The older dates are interpreted to reflect Ar-40 inherited from a previous metamorphic event. The second paragneiss yielded a deformation age of 434 +/- 2 Ma. The collective dataset is interpreted to record exhumation of the upper gneiss unit at c. 459 Ma and deformation and fluid infiltration at c. 434 Ma during continental collision. The events closely resemble the deformation histories of other northern SNC terranes. Synthesizing these results with those for other northern SNC terranes suggests that the Baltican margin underwent oblique, south-to-north subduction during late Cambrian time.
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| 7. |
- Beranek, Luke, et al.
(författare)
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Silurian flysch successions of Ellesmere Island, Arctic Canada, and their significance to northern Caledonian palaeogeography and tectonics
- 2015
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 172:2, s. 201-212
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Tidskriftsartikel (refereegranskat)abstract
- Detrital zircon provenance studies of Silurian flysch units that underlie the Hazen and Clements Markham fold belts of Ellesmere Island, Arctic Canada, were conducted to evaluate models for northern Caledonian palaeogeography and tectonics. Llandovery flysch was deposited along an active plate margin and yields detrital zircons that require northern derivation from the adjacent Pearya terrane. If Pearya originated near Svalbard and NE Greenland, it was transported by strike-slip faults to Ellesmere Island by the Early Silurian. Wenlock to Ludlow turbidites yield Palaeozoic-Archaean detrital zircons with dominant age-groupings c. 650, 970, 1150, 1450 and 1650 Ma. These turbidite systems did not fill a flexural foreland basin in front of the East Greenland Caledonides, but rather an east-west-trending trough that was probably related to sinistral strike-slip faulting along the northern Laurentian margin. The data support provenance connections with the Svalbard Caledonides, especially Baltican-affinity rocks of SW Spitsbergen that were proximal to NE Greenland during the Baltica-Laurentia collision. Pridoli flysch has sources that include Pearya, the East Greenland Caledonides and the Canadian Shield. Devonian-Carboniferous molasse in Arctic Canada has analogous detrital zircon signatures, which implies recycling of Silurian flysch during mid-Palaeozoic (Ellesmerian) collisional tectonism or that some collisional blocks were of similar Baltican-Laurentian crustal affinities.
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| 8. |
- Bomfleur, Benjamin, et al.
(författare)
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Uncharted Permian to Jurassic continental deposits in the far north of Victoria Land, East Antarctica
- 2020
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Ingår i: Journal of the Geological Society. - London : Geological Society of London. - 0016-7649 .- 2041-479X. ; 178
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Tidskriftsartikel (refereegranskat)abstract
- The remote lower reaches of the Rennick Glacier in the far north of Victoria Land hold some of the least-explored outcrop areas of the Transantarctic basin system. Following recent international field-work efforts in the Helliwell Hills, we here provide a comprehensive emendation to the regional stratigraphy. Results of geological and palaeontological reconnaissance and of petrographic, geochemical and palynostratigraphic analyses reveal a stack of three previously unknown sedimentary units in the study area: the Lower Triassic Van der Hoeven Formation (new unit, 115+ m thick) consists mainly of quartzose sandstone and non-carbonaceous mudstone rich in continental trace fossils. The Middle to Upper Triassic Helliwell Formation (new unit, 235 m thick) consists of coal-bearing overbank deposits and volcaniclastic sandstone and yielded typical plant fossils of the Gondwanan Dicroidium flora together with plant-bearing silicified peat. The succession is capped by c. 14 m of the sandstone-dominated Section Peak Formation (uppermost Triassic–Lower Jurassic). Our results enable more detailed correlation of the Palaeozoic–Mesozoic successions throughout East Antarctica and into Tasmania. Of particular interest is one section that spans the end-Permian mass extinction interval, which promises to allow detailed reconstructions of high-latitude vegetation dynamics across this critical interval in Earth history.
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| 9. |
- Burns, K.L, et al.
(författare)
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The Flinders Ranges breccias of South Australia diapirs or décollement?
- 1977
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 134:3, s. 363-384
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Tidskriftsartikel (refereegranskat)abstract
- Breccia-cored domes in the Northern Flinders Ranges, South Australia, have been regarded as diapirs analogous to diapiric salt structures in northwestern Germany and the Gulf Coast. It is shown that the core of the Blinman Dome is not intrusive and is not composed of less dense rocks; hence a diapiric process cannot apply. It is suggested that much of the breccia of the core is formed by deformation of a stratigraphic unit composed of interbedded competent and incompetent beds at a Flinders Ranges dgcollernent and results from folding. If this model is correct, the Flinders Ranges structures should occur at ddcollements in other parts of the world.
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| 10. |
- Callegari, Riccardo, et al.
(författare)
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Early Neoproterozoic magmatism and Caledonian metamorphism recorded by the Mårma terrane, Seve Nappe Complex, northern Swedish Caledonides
- 2023
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 180:5
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Tidskriftsartikel (refereegranskat)abstract
- Petrology, geochronology and bulk-rock chemistry are combined to investigate the early Neoproterozoic magmatismand Cambrian–Ordovician metamorphism in the northern Swedish Caledonides. This work includes several lithologies of theMårma terrane in the Seve Nappe Complex exposed in the Kebnekaise region. U–Pb zircon geochronology yielded crystallizationages of 835 ± 8 Ma for a mylonitic orthogneiss, 864 ± 3 Ma for the Vistas Granite and 840 ± 7 Ma for an intruded granitic dyke,whereas a gabbro and a granodiorite intrusion gave U–Pb zircon crystallization ages of 856 ± 3 Ma and 850 ± 1 Ma, respectively.U–Pb monazite dating of the mylonitic orthogneiss gave an upper intercept age of 841 ± 7 Ma and a lower intercept age of443 ± 20 Ma. Pressure–temperature estimates derived for the mylonitic orthogneiss reveal metamorphic peak-pressure and peaktemperatureof 10.5–11.75 kbar and 550–610°C and 7.4–8.1 kbar at 615–675°C, respectively.Metamorphic pressure–temperatureestimates for the Vistas Granite yield 6.5–7.5 kbar at 600–625°C. Whole-rock chemistry coupled with U–Pb geochronologyindicates that bimodal magmatism was related to attempted rifting of Rodinia between 870 and 840 Ma.
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| 11. |
- Caron, Jean-Bernard, et al.
(författare)
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The lower Cambrian Cranbrook Lagerstätte of British Columbia
- 2024
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 181:1
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Forskningsöversikt (refereegranskat)abstract
- Discovered over a century ago, the lower Cambrian (Series 2, Stage 4) Cranbrook Lagerstatte of southeastern British Columbia's Eager Formation is one of the oldest Burgess Shale-type deposits in North America. This Konservat-Lagerstatte is rich in olenelloid trilobites, but also yields a very low-diversity soft-bodied fossil assemblage including Tuzoia and Anomalocaris, and a low-diversity ichnofauna. Its scientific study, however, remains limited. A 2015 field-based investigation by the Royal Ontario Museum has revealed new information about the site's biota, depositional environment and taphonomic conditions. Not only is the Cranbrook Lagerstatte significant for early Cambrian biostratigraphy and comparisons with other Burgess Shale-type deposits, it also reveals some of the little-known diversity of life in a distal outer shelf environment during the Cambrian period.
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| 12. |
- Carter, Isabel S. M., et al.
(författare)
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Cambrian ages for metavolcanic rocks in the Lower Köli Nappes, Swedish Caledonides: implications for the status of the Virisen arc terrane
- 2023
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 180:6
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Tidskriftsartikel (refereegranskat)abstract
- The Köli Nappe Complex (KNC) of the Scandinavian Caledonide orogen originated as oceanic terranes within the Iapetus Ocean. These terranes have characteristics of magmatic arcs and associated forearc or back-arc basins and underwent several periods of rifting and magmatism prior to their accretion to the Baltican margin. We present new U–Pb zircon ages from the Lower Köli Ankarede Volcanite Formation in Västerbotten, Sweden. U–Pb ages of magmatic zircon grains from metamorphosed dacitic to andesitic rocks show ages of 512 ± 3.5, 497 ± 2, 491 ± 1 and 488 ± 4 Ma. The three younger ages fit with previous ages for Lower Köli volcanic rocks, but the 512 Ma age is older than any previous age for this unit. These dates constrain the age of magmatism in an ensimatic arc system within Iapetus. We compare this evolution with published information from the other Köli nappes. Magmatic ages within the KNC overlap with ages for an early episode of ultrahigh-pressure (UHP) metamorphism within the underlying Seve Nappe Complex (SNC), supporting the hypothesis that attributes UHP metamorphism within the SNC to subduction beneath the island arc now preserved within the Lower Köli Nappes.
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| 13. |
- Cawood, P. A., et al.
(författare)
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Provenance of the Highland Border Complex : constraints on Laurentian margin accretion in the Scottish Caledonides
- 2012
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 169:5
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Tidskriftsartikel (refereegranskat)abstract
- Contrasting tectonic models for the Highland Border Complex in the Scottish Caledonides view it either as part of the rifted Laurentian margin of the Iapetus Ocean or as an oceanic terrane. Detrital zircon data from sandstones of the complex yield age peaks at 2.8–2.6, 1.3 and 1.1–1.0 Ga and minor peaks at c. 1.7–1.9 Ga. These characteristics compare closely with those of the upper Dalradian Supergroup of the adjacent Grampian terrane, and with the record of eastern Laurentia. The data are also consistent with the Laurentian provenance indicated by palaeontological evidence from the complex, and field evidence for continuity with the Dalradian Supergroup. Detrital ages for the Cambrian Salterella Grit of the Caledonian foreland compare with those for approximately age-equivalent sandstones from the Highland Border Complex. Both were contemporaneous with the regressive Hawke Bay event, accounting for similarities in provenance, and further linking the Highland Border Complex to Laurentia. The Grampian terrane was being uplifted and shedding detritus throughout the Ordovician and Silurian. The absence of this event from the detrital zircon records of either the Midland Valley or Southern Upland terranes suggests that these blocks cannot have been in their current location relative to the Grampian terrane before the end of the Silurian.Supplementary material: The complete analytical dataset and cathodoluminescence images are available at http://www.geolsoc.org.uk/SUP18531.
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| 14. |
- Chew, D M, et al.
(författare)
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The tectonothermal evolution and provenance of the Tyrone Central Inlier, Ireland: Grampian imbrication of an outboard Laurentian microcontinent?
- 2008
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 2041-479X .- 0016-7649. ; 165:3, s. 675-685
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Tidskriftsartikel (refereegranskat)abstract
- The Tyrone Central Inlier is a metamorphic terrane of uncertain affinity situated outboard of the main Dalradian outcrop (south of the Fair Head-Clew Bay Line) and could represent sub-arc basement to part of the enigmatic Midland Valley Terrane. Using a combination of isotopic, structural and petrographic evidence, the tectonothermal evolution of the Tyrone Central Inlier was investigated. Sillimanite-bearing 14 metamorphic assemblages (c. 670 degrees C, 6.8 kbar) and leucosomes in paragneisses are cut by granite pegmatites, which post-date two deformation fabrics. The leucosomes yield a weighted average Pb-207/Ph-206 zircon age of 467 +/- 12 Ma whereas the main fabric yields a Ar-40-Ar-39 biotite cooling age of 468 +/- 1.4 Ma. The pegmatites yield 457 +/- 7 Ma and 458 +/- 7 Ma Rb-Sr muscovite-feldspar ages and Ar-40-Ar-39 step-heating plateaux of 466 +/- 1 Ma and 468 +/- 1 Ma, respectively. The metasedimentary rocks yield Palaeoproterozoic Sm-Nd model ages and laser ablation inductively coupled plasma mass spectrometry detrital zircon U-Pb analyses from a psammitic gneiss yield age populations at 1.05-1.2, 1.5, 1.8, 2.7 and 3.1 Ga. Combined, these data permit correlation of the Tyrone Central Inlier with either the Argyll or the Southern Highland Group of the Dalradian Supergroup. The inlier was thus part of Laurentia onto which the Tyrone ophiolite was obducted.
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| 15. |
- Coxall, Helen K., et al.
(författare)
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The Eocene-Oligocene transition in Nanggulan, Java : lithostratigraphy, biostratigraphy and foraminiferal stable isotopes
- 2021
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 178:6
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Tidskriftsartikel (refereegranskat)abstract
- The Nanggulan section in south central Java comprises open marine sediments and volcanic deposits of Eocene-Oligocene age that accumulated in a marginal basin within the young Sunda Arc complex. A new borehole captures the stratigraphy and showcases the exceptional preservation of calcareous microfossils across an apparently complete Eocene-Oligocene Transition (EOT), a time interval significant for the initiation of continental-scale glaciation on Antarctica. Low-resolution benthic and planktonic foraminifera oxygen and carbon stable isotopes (delta O-18 and delta C-13) record increasing delta O-18 and delta C-13 in the basal Oligocene, allowing correlation to global records. Isotopic values imply warm temperatures and relatively high nutrients along the SE Java margin. The Nanggulan EOT is a valuable archive for reconstructing ocean-climate behaviour and plankton evolution and extinction in the Indo-Pacific Warm Pool. The borehole also adds to understanding of the early stages of Sunda Arc volcanism.
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| 16. |
- Cunningham, John A., et al.
(författare)
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The Weng’an Biota (Doushantuo Formation): an Ediacaran window on soft bodied and multicellular microorganisms.
- 2017
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Ingår i: journal of the geological society. - London : Geological Society. - 2041-479X .- 0016-7649. ; 174:5, s. 793-802
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Tidskriftsartikel (refereegranskat)abstract
- The Weng’an Biota is a fossil Konservat-Lagerstätte in South China that is approximately 570-600 million years old and provides an unparalleled snapshot of marine life during the interval in which molecular clocks estimate that animal clades were diversifying. It yields specimens that are three-dimensionally preserved in calcium phosphate with cellular and sometimes subcellular fidelity. The biota includes candidates for the oldest animals in the fossil record, including embryonic, larval and adult forms. We argue that, while the Weng’an Biota includes forms that could be animals, none can currently be assigned to this group with confidence. Nonetheless, the biota offers a rare and valuable window on the evolution of multicellular and soft-bodied organisms in the prelude to the Cambrian radiation.
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| 17. |
- Davies, Neil, et al.
(författare)
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Discussion on ‘Tectonic and environmental controls on Palaeozoic fluvial environments: reassessing the impacts of early land plants on sedimentation’
- 2017
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 174, s. 947-950
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Tidskriftsartikel (refereegranskat)abstract
- The first-order importance of tectonic and environmental controlsfor terrigenous sediment supply has rarely been questioned, but the role of vegetation in the modification of ancient alluvial signatures has been observed since the mid-20th century (Vogt 1941). Studies of sparsely vegetated rivers (Schumm 1968) and alluvial stratigraphic variation (Cotter 1978; Davies & Gibling 2010) led to observations of (1) plant modulation of alluvial signatures and (2) Palaeozoic facies shifts (PFS): unidirectional changes to facies diversity and frequency, in stratigraphic alliance with the plant fossil record. One PFS is the Siluro-Devonian appearance of mud rich, architecturally complex alluvium, traditionally ascribed to meandering rivers, and sedimentologically distinct from pre vegetation strata (Davies & Gibling 2010; Long 2011). Using selected secondary data, Santos et al. (2017) dispute the correlation of these observations using three key points, as follows. (1) The mid-Palaeozoic was typified by orogenic assembly of low-gradient equatorial continents and elevated sea level, which led to tropical weathering (abundant fine sediment) and extensive alluvial plains. This drove the PFS by promoting river meandering independently of vegetation. (2) Meandering does not require vegetation; this is shown by examples in Precambrian deposits, on other planets, and in ‘non-vegetated’ deserts. Meandering rivers were more abundant than the pre vegetation rock record suggests, owing to selective bypass and deflation of fine material. (3) Early Siluro-Devonian (meaning Ludlow–Early Devonian) land plants were too small, their biomass and cover too limited, and their wetland habitat too narrow to have stabilized meandering channels, influencing landscape little more than earlier microbial communities. We contest the conclusions and method of the paper, and deal with each point in turn.
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| 18. |
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| 19. |
- Dunkley, Daniel J., et al.
(författare)
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Two Neoarchean tectonothermal events on the western edge of the North Atlantic Craton, as revealed by SIMS dating of the Saglek Block, Nain Province, Labrador
- 2020
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 177:1
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Tidskriftsartikel (refereegranskat)abstract
- The Saglek Block forms the northern part of the Nain Province and underwent widespread metamorphism at c. 2.7 Ga, producing the dominant gneissosity and intercalation of supracrustal sequences. Zircon dating of gneiss samples collected along 80 km of the Labrador coast from Ramah Bay in the north to Hebron Fjord in the south confirms the widespread extent of high-grade metamorphism between 2750 and 2700 Ma. In addition, a distinct event between 2550 and 2510 Ma produced felsic melt with peritectic garnet in metavolcanic gneiss and granoblastic recrystallization in mafic granulite. Ductile deformation of granite emplaced at c. 2550 Ma indicates that this later event involved a degree of tectonism during high-T metamorphism. Such tectonism may be related to a hypothesized post-2.7 Ga juxtaposition of the predominantly Eoarchean Saglek Block against the Mesoarchean Hopedale Block, along a north–south boundary that extends from the coast near Nain to offshore of Saglek Bay. Evidence of reworking of c. 2.7 Ga gneisses by c. 2.5 Ga tectonothermal activity has been found elsewhere on the margins of the North Atlantic Craton, of which the Nain Province represents the western margin. In particular, a recent suggestion that c. 2.5 Ga metamorphic ages along the northern margin of the North Atlantic Craton in SW Greenland may record the final assembly of the craton could also apply to the western margin as represented by the rocks of the Nain Province.Supplementary material: Plots and geochemical data are available at https://doi.org/10.6084/m9.figshare.c.4567934
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| 20. |
- Elming, Sten-åke, et al.
(författare)
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Palaeomagnetism and AR-40/AR-39 age determinations of the Ediacaran traps from the southwestern margin of the East European Craton, Ukraine : relevance to the Rodinia break-up
- 2007
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 164:5, s. 969-982
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Tidskriftsartikel (refereegranskat)abstract
- A palaeomagnetic study and age determinations have been performed on Ediacaran basalts from the northwestern Ukraine. Whole-rock ^sup 40^Ar/^sup 39^Ar age determination revealed plateau ages at 590-560 Ma and 393 Ma, the latter probably reflecting a resetting of the radiometric system. Palaeomagnetic poles have been calculated from five basalt flows, two of which (A poles) are considered reliable with ages that range from 580 to 560 Ma. Tentative poles (B poles), calculated from most probably primary magnetizations, have ages estimated at 580-545 Ma. Secondary magnetizations, possibly of late Ediacaran or Devonian age, have also been isolated (C poles). Based on the new poles, Baltica drifted together with Laurentia from an equatorial position at c. 750 Ma to occupy high southern latitude positions at c. 580 Ma. Baltica during that time period was joined to Laurentia in a similar relative position to that at 750 Ma. The two shields then split up from each other and from c. 550 Ma Baltica drifted at moderately high latitudes and rotated some 180° during the final opening of the Iapetus ocean. This reconstruction suggests that during the Ediacaran glaciation Baltica occupied high-latitude positions, which contradicts the high-obliquity model to explain low-latitude Neoproterozoic glaciations
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| 21. |
- Emeleus, C. Henry, et al.
(författare)
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Lateral versus vertical emplacement in shallow-level intrusions? : The Slieve Gullion Ring-complex revisited
- 2012
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 169:2, s. 157-171
-
Tidskriftsartikel (refereegranskat)abstract
- Recent studies on shallow-level arcuate intrusions have identified numerous examples of horizontal mineral fabrics. These are commonly interpreted as reflecting considerable lateral flow during magma emplacement, thus querying established 'semi-vertical' ring-dyke models. We question the recent lateral emplacement model proposed for the Palaeocene Slieve Gullion Ring-complex, NE Ireland, where the absence of steep fabrics in parts of the ring-complex has been used to support a shallow, semi-horizontal sheet intrusion mechanism. We argue that such simple flow models cannot be applied to explosive ring-fissure eruptions and that fabric data alone do not warrant rejection of the ring-dyke model. Moreover, the apparent 'absence of steep intrusive contacts' along the intrusion's perimeter is readdressed and we present numerous examples of outcrops (27) with steep-sided geometries. The Camlough Breccias are reinterpreted as the product of gas-driven tuffisites injected along the active ring-fault (rather than of purely tectonic origin). Crucially, the porphyritic microgranite and porphyritic rhyolite ring-dyke rocks exhibit geochemical and petrographic signatures of contamination by the geographically restricted Palaeozoic Newry granodiorite and are best explained through crustal interaction vertically beneath the ring-complex. Subsequently, these silicic magmas rose into ignimbrite feeders along a caldera ring-fault system that was emplaced into near-surface vent-filling breccias.
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| 22. |
- Farzipour-Saein, A., et al.
(författare)
-
Mechanical stratigraphy and folding style of the Lurestan region in the Zagros Fold–Thrust Belt, Iran
- 2009
-
Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 166:Part 6, s. 1101-1115
-
Tidskriftsartikel (refereegranskat)abstract
- The structural style of the folds from the central part of the Lurestan salient located in the NW portion of the Zagros Fold-Thrust Belt has been studied by constructing a regional balanced cross-section from field data, existing geological maps, seismic profiles, stratigraphic surface sections and well data. The regional balanced structural cross-section that is constructed front the High Zagros Fault to the Mountain Front Fault highlights the difference in the folding style across the area. The vertical and lateral changes in the style of the folding indicate the influence of mechano-stratigraphic contrast between the sedimentary units. Three main decollement levels (the basal Lower Palaeozoic, the intermediate Triassie, and the upper Upper Cretaceous-Lower Palaeocene) have been interpreted. Folds developed during the Zagros Fold-Thrust Belt evolution above and below these decollement horizons are decoupled from each other and are different in both geometry and size. Similarly, thickness and facies changes of some formations across the region cause lateral variation in folding pattern from the north to the south. Polyharmonic folds exist in the South, where the different structural levels are relatively strongly coupled. To the north, however, strongly disharmonic folding occurs where a combination of increased decollement thickness and decreased mechanical competence has led to decoupling at different structural levels. This change in folding style has a direct impact on hydrocarbon exploration in the area. To reduce structural risk in exploration, the incorporation of high-resolution deep seismic data with the surface geology is recommended for future hydrocarbon exploration activities within the Lurestan region.
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| 23. |
- Gasser, Deta, et al.
(författare)
-
A review of the Caledonian Wilson cycle from a North Atlantic perspective
- 2024
-
Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 181:3
-
Tidskriftsartikel (refereegranskat)abstract
- The opening and closure of the Paleozoic Iapetus Ocean, leading to the collision of Laurentia and Baltica forming the Caledonian orogen, is one of the prime examples of a Wilson cycle. In this perspective article, we summarize and discuss the content of 10 new research articles within a 5-stage framework of the Caledonian Wilson cycle from a North Atlantic perspective. Stage 1 covers Neoproterozoic rifting of both the Laurentian and Baltican margins, where the plate tectonic configurations and the timing for the onset of rifting are far from resolved; Stage 2 covers the onset of sea-floor spreading within Iapetus, with several different oceanic basins opening at different times, and with variable geometries of the rifted margins; Stage 3 covers the narrowing of the Iapetus basins along several subduction zones, the number, location and orientation of which are debated; Stage 4 covers the main continent-continent collision, documenting advances in our understanding of (U)HP metamorphism within the Western Gneiss Region; Stage 5 covers post-orogenic extension, transitioning into stage 1 of the subsequent Atlantic Wilson cycle. We review the evolution of the Caledonian Wilson cycle in the light of the recent literature from the past decade and highlight open questions and unresolved issues.
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| 24. |
- George, Hady, et al.
(författare)
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The famous fish beds of Lebanon : the Upper Cretaceous LagerstÀtten of Haqel, Hjoula, Nammoura and Sahel Aalma
- 2024
-
Ingår i: Journal of the Geological Society. - : GEOLOGICAL SOC PUBL HOUSE. - 0016-7649 .- 2041-479X. ; 181:5
-
Forskningsöversikt (refereegranskat)abstract
- The fossils of the Lebanese Upper Cretaceous Lagerst & auml;tten, especially the articulated fish, are world renowned. Famous for their soft tissue preservation and highly sought after by fossil collectors, Lebanese fossils provide key information concerning the evolution of several major extant and extinct groups of Mesozoic organisms including cephalopods, crustaceans, hagfish, sharks, marine reptiles and pterosaurs. In fact, fossils from Lebanon are so exceptional that historical documentation describing them extends back to the Roman Empire. However, despite over 1600 years of knowledge of these fossils, a thorough understanding of the depositional environments, taphonomy and palaeoecology of the four main sites, Haqel, Hjoula, Nammoura (each Cenomanian in age) and Sahel Aalma (Santonian), is lacking. Here we compile a review of the palaeoenvironments, fauna and flora of these four Lebanese Lagerst & auml;tten. Our synthesis outlines the history of fossil discovery, and describes the current understanding of the geology, ages, mode of preservation and organisms found at these four sites. We also undertake a bibliometric and holotype analysis to investigate the impact that scientific colonialism has had on Lebanon. Our data confirm that local Lebanese researchers are typically not included in publications pertaining to Lebanese fossils and that the majority of Lebanese type material is stored in large historical collections outside Lebanon, predominantly in institutions within the northern hemisphere. Here, we recommend some basic practices for researchers utilizing historical collections that can help develop local Lebanese fossil collections and establish more research opportunities for local palaeontologists.
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| 25. |
- Harper, David A.T., et al.
(författare)
-
The Sirius Passet Lagerstätte of North Greenland: a remote window on the Cambrian Explosion
- 2019
-
Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 176, s. 1023-1037
-
Tidskriftsartikel (refereegranskat)abstract
- The lower Cambrian Lagerstätte of Sirius Passet, Peary Land, North Greenland, is one of the oldest of the Phanerozoic exceptionally preserved biotas. The Lagerstätte evidences the escalation of numbers of new body plans and life modes that formed the basis for a modern, functionally tiered ecosystem. The fauna is dominated by predators, infaunal, benthic and pelagic, and the presence of abundant nekton, including large sweep-net feeders, suggests an ecosystem rich in nutrients. Recent discoveries have helped reconstruct digestive systems and their contents, muscle fibres, and visual and nervous systems for a number of taxa. New collections have confirmed the complex combination of taphonomic pathways associated with the biota and its potentially substantial biodiversity. These complex animal-based communities within the Buen Formation were associated with microbial matgrounds, now preserved in black mudstones deposited below storm wave base that provide insight into the shift from late Neoproterozoic (Ediacaran) to Cambrian substrates and communities. Moreover, the encasing sediment holds important data on the palaeoenvironment and the water-column chemistry, suggesting that these animal-based communities developed in conditions with very low oxygen concentrations.
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| 26. |
- Heinonen, A., et al.
(författare)
-
The source of Proterozoic anorthosite and rapakivi granite magmatism: evidence from combined in situ Hf–O isotopes of zircon in the Ahvenisto complex, southeastern Finland.
- 2015
-
Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 172, s. 103-112
-
Tidskriftsartikel (refereegranskat)abstract
- The isotope compositions of massif-type anorthosites in Proterozoic anorthosite–mangerite–charnockite–granite (AMCG) complexes are commonly dominated by crustal values. Olivine-bearing anorthositic rocks in several AMCG suites have, however, been shown to display juvenile character, suggesting that variably depleted mantle reservoirs were involved in their genesis. A coupled in situ zircon Hf–O isotope dataset from the 1.64 Ga Ahvenisto AMCG complex in the 1.54–1.65 Ga Fennoscandian rapakivi granite–massif-type anorthosite province reveals correlated juvenile isotope signals (δ18Ozrn = 5.4–6.6‰; initial ϵHf = −1.1 to +3.4) in the most primitive gabbroic rock type of the suite suggesting a depleted mantle origin for the anorthositic rocks. This signal is not as prominent in the more evolved co-magmatic anorthositic rocks (δ18Ozrn = 6.3–7.8‰; initial ϵHf = −0.8 to +2.0), most probably owing to contamination of the mantle-derived primary magma by crustal material. A rapakivi granite associated with the anorthositic rocks has different isotope composition (δ18Ozrn = 7.4–8.6‰; initial ϵHf = −2.1 to +0.5) that points to a crustal source.
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| 27. |
- Hessami, Khaled, et al.
(författare)
-
Active deformation within the Zagros Mountains deduced from GPS measurements
- 2006
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 163:1, s. 143-148
-
Tidskriftsartikel (refereegranskat)abstract
- We present and interpret the results of Global Positioning System (GPS) measurements at 35 stations in and beside the Zagros Mountain belt, SW Iran, for three campaigns ending March 1998, December 1999 and June 2001. Preliminary motion estimates show clearly the change in character along the strike of the belt. Stations to the SE move at 13–22 ± 3 mm a–1 towards N 7 ± 5°E with respect to Eurasia. Most of the shortening indicated by the GPS velocities seems to occur in the SE Zagros along two major seismic zones and along the Zagros front. To the NW, stations move oblique to the trend of the belt towards N 12 ± 8°W, at 14–19 ± 3 mm a–1. Most of the shortening in the NW Zagros seems to occur along the Mountain Front Fault with its major earthquakes as well as along the Zagros front. The change in direction and magnitude of the velocity vectors across the north–south-trending Kazerun and Karebas faults involves extension of up to 4 mm a–1 along the strike of the Zagros belt.
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| 28. |
- Hessami, Khaled, et al.
(författare)
-
Progressive unconformities within an evolving foreland fold-thrust belt, Zagros Mountains.
- 2001
-
Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 158:6, s. 969-981
-
Tidskriftsartikel (refereegranskat)abstract
- A major angular unconformity between the Bakhtyari conglomerates and the underlying Agha Jari Formation has long been interpreted as indicating that orogeny in the Zagros Simply Folded Zone took place in Plio-Pleistocene times. This study uses field evidence of unconformities between older units in conjunction with geological maps and cross sections to argue that the front of the Zagros Simply Folded Zone has propagated in time and space. These unconformities indicate that deformation started as early as end Eocene in the northeast of the Simply Folded Zone and propagated progressively to the southwest, where unconformable contacts are only seen between younger units. As shortening continued, the southwest migration of the deformation front drove the foreland basin in front of it to its present position along the Persian Gulf and Mesopotamia. The climax of orogeny took place at end Pliocene time when the most extensive unconformity in the Zagros Simply Folded Zone developed between the (upper) Bakhtyari Formation and older units. Active seismicity and documented present uplift imply that the Simply Folded Zone is still propagating southwestward.
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| 29. |
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| 30. |
- Japsen, Peter, et al.
(författare)
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Mountains of southernmost Norway : uplifted Miocene peneplains and re-exposed Mesozoic surfaces
- 2018
-
Ingår i: Journal of the Geological Society. - : GEOLOGICAL SOC PUBL HOUSE. - 0016-7649 .- 2041-479X. ; 175:5, s. 721-741
-
Tidskriftsartikel (refereegranskat)abstract
- The origin of the Norwegian mountains (the Scandes) is a key controversy in modern geoscience. Are they remnants from the Caledonian Orogeny, modified shoulders of late Mesozoic rifts, or are they evidence of Neogene uplifts? Our synthesis of geological data, landscape analysis and new thermochronological data from Norway south of c. 60 degrees N, combined with previously published data from southern Sweden, reveals a four-stage history: (1) Middle Triassic and Middle Jurassic exhumation produced a weathered basement surface with a hilly relief; (2) after late Mesozoic rifting, Upper Jurassic-Oligocene sediments accumulated across most of the area; (3) early Miocene uplift and erosion to the base level of the adjacent ocean led to formation of a peneplain that extended across sedimentary basins and Caledonian rocks; the subhorizontal Hardangervidda plateau represents this peneplain; (4) early Pliocene uplift raised Hardangervidda to its present elevation of c. 1200 m above sea-level and led to re-exposure of the tilted, Mesozoic surface at lower elevations. The Southern Scandes are thus, like other elevated passive continental margins around the world, the product of post-breakup uplift. Identification of the mechanisms driving these uplifts awaits geodynamic modelling constrained by observations such as those presented in this study.
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| 31. |
- Jess, Scott, et al.
(författare)
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Sediment supply on the West Greenland passive margin : redirection of a large pre-glacial drainage system
- 2020
-
Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 177:6, s. 1149-1160
-
Tidskriftsartikel (refereegranskat)abstract
- The Mesozoic–Cenozoic separation of Greenland and North America produced the small oceanic basins of theLabrador Sea and Baffin Bay, connected via a complex transform system through the Davis Strait. During rifting and partialbreakup sedimentary basins formed that record the changing regional sediment supply. The onshore and offshore stratigraphyof Central West Greenland outlines the presence of a major fluvial system that existed during the Cretaceous and was laterredirected in the Early Cenozoic by the formation of the West Greenland Igneous Province. Hydrological analysis ofGreenland’s isostatically balanced basement topography outlines two major drainage systems that likely flowed acrossGreenland prior to the onset of glaciation and emptied into the Sisimiut Basin within the Davis Strait, offshoreWest Greenland.The course of the northern drainage system suggests that it initially flowed NW into the Cretaceous/Palaeocene NuussuaqBasin, before being redirected SW around the West Greenland Igneous Province in the Mid-Palaeocene. Moreover,characteristics of these two drainage systems suggest they acted as a single larger fluvial system, prior to the onset of glaciation,that was likely the primary source of sediment across CentralWest Greenland throughout the Cretaceous and Palaeogene. Thisscenario provides a greater understanding of theWest Greenland margin’s late Cenozoic evolution, which differs from previousinterpretations that hypothesize a period of considerable post-rift tectonism and uplift. This work highlights the importance oflarge pre-glacial drainage systems across North Atlantic passive margins and their relevance when studying post-riftstratigraphy in rifted margin settings.
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| 32. |
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| 33. |
- Kenny, Gavin, et al.
(författare)
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Age of the Sääksjärvi impact structure, Finland: reconciling the timing of small impacts in crystalline basement with regional basin development
- 2020
-
Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 177, s. 1231-1243
-
Tidskriftsartikel (refereegranskat)abstract
- We report a new age for the Sääksjärvi impact structure, Finland, a 6 km diameter feature that formed in crystalline rocks of the Precambrian Baltic Shield. Two previous studies reported 40Ar/39Ar data for Sääksjärvi and suggested conflicting formation ages of ≤330 Ma or c. 560 Ma. The former age represents a possible complication for models which indicate that the region was covered by sediments of the Caledonian foreland basin throughout much of the Phanerozoic. We conducted a study combining imaging, microstructural analysis and U–Pb dating of shocked zircon from Sääksjärvi. The U–Pb dataset indicates a c. 600 Ma impact into predominantly c. 1850 Ma target rocks. A concordia age of 608 ± 8 Ma (2σ) confirms Sääksjärvi as the first known Ediacaran impact structure in the Baltic Shield and only the second worldwide. Our data indicate that the Sääksjärvi impact structure formed in exposed crystalline basement rocks of the Baltic Shield prior to the development of the Caledonian foreland basin. Given that most impact structures on Earth are relatively small features, radiometric dating of small impact structures in crystalline basement may place boundaries on the timing and spatial extent of palaeobasins that might otherwise be difficult to constrain.
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| 34. |
- Koyi, Hemin A., et al.
(författare)
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The mechanical relationship between strike-slip faults and salt diapirs in the Zagros fold-thrust belt
- 2008
-
Ingår i: Journal of the Geological Society. - 0016-7649 .- 2041-479X. ; 165, s. 1031-1044
-
Tidskriftsartikel (refereegranskat)abstract
- Analogue models are used to study the mechanical relationship between basement strike-slip faults and salt diapirs. Displacement along a strike-slip fault in 1 g models resulted in extension along pre-existing jogs and the formation of oblique extensional faults, where reactive diapirs were triggered in some models. In the centrifuge models prescribed cuts, simulating pre-existing structures, were reactivated during simple shear deformation of the models, resulting in formation of pull-apart basins, which were intruded by diapirs. The models show that because of the low ratio of salt to overburden thickness in the Zagros (0.15-0.35). It is unlikely that diapirs have formed solely, if at all as a result of movement along basement strike-slip faults. Two mechanisms are suggested. First, pre-kinematic thin overburden and continuous movement along a releasing bend in the cover units may have triggered some of the diapirs in the Zagros, which were later downbuilt to their current geometry by additional sedimentation. Second, movement along the strike-slip faults (e.g. the Kazerun and Mangarak faults) induced oblique movement along NW-SE Zagros structures (folds or thrusts) resulting in the formation of pull-part basins where diapirs were eventually intruded. Fault plane solution of shallow earthquakes supports the second scenario, which is also in agreement with previous interpretations that some of the salt diapirs associated with basement faults are younger than Zagros shortening and young southwestwards.
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| 35. |
- Kroger, Bjorn, et al.
(författare)
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Subaerial speleothems and deep karst in central Sweden linked to Hirnantian glaciations
- 2015
-
Ingår i: Journal of the Geological Society. - : Geological Society of London. - 2041-479X .- 0016-7649. ; 172:3, s. 349-356
-
Tidskriftsartikel (refereegranskat)abstract
- The limestones of the upper Katian Boda mud mounds (Ordovician) of the Siljan district in central Sweden are deeply fractured. The fissures were partly synsedimentary and are often lined with stromatolite-like crusts. These crusts thus far are the only known subaerial Ordovician speleothems. They reach depths of up to 30 m below the former mound top. Macroscopically the crusts form decimetre-sized, cone-shaped domal aggregates, stalactites and stalagmites. Microfabric and morphology identify them as microbially mediated speleothems in a dark environment. Combined Sr and C isotope values indicate a formation of the speleothems from meteoric waters without influence of a significant soil horizon. For the first time the age of the speleothems can be precisely constrained by delta C-13 whole-rock and brachiopod shell isotope data to the mid-Hirnantian. Repeated and/or prolonged subaerial exposure of the Boda mud mounds during the Hirnantian is evident from karst surfaces and early cements in the mound capping carbonates. The speleothems and the karst surfaces record an estimated sea-level fall in the range of 80-130 m within the time window of the Hirnantian Isotopic Carbon Excursion. This massive regression coincides with maximum ice sheet extent inferred from sections in West Gondwana.
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| 36. |
- Lisica, Karlo, et al.
(författare)
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High precision U-Pb geochronology of the Lundy igneous complex : implications for North Atlantic volcanism and the far field Paleocene-Eocene ash record
- 2024
-
Ingår i: Journal of the Geological Society. - London : Geological Society of London. - 0016-7649 .- 2041-479X.
-
Tidskriftsartikel (refereegranskat)abstract
- The Lundy Island granite (Bristol Channel, UK) is a felsic expression of the southernmost igneous centre of the North Atlantic Igneous Province (NAIP) that emplaced millions of km3 of magma in the Paleogene. The distinctive S-type, peraluminous, two mica ± garnet ± tourmaline composition has led to the hypothesis that eruptions from the Lundy volcanic centre may be the source of thick felsic ash layers within the early Eocene Fur Formation (Denmark) that act as key marker horizons for the onset and duration of the Paleocene–Eocene Thermal Maximum (PETM). This study presents high-precision zircon U-Pb emplacement ages of 57.24 ± 0.11/0.12/0.13 Ma for the granite and 55.970 ± 0.021/0.030/0.070 Ma for a felsic ‘lundyite’ dyke. Trace and REE element patterns indicate close similarities between late-stage Lundy activity and ash layer ‘-33’ in Denmark that was deposited during the PETM carbon isotope excursion, suggesting that this centre is likely to be the source of this key ash horizon and that magmatism at Lundy likely continued into the early Eocene.
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| 37. |
- Mazur, S., et al.
(författare)
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A strike-slip terrane boundary in Wedel Jarlsberg Land, Svalbard, and its bearing on correlations of SW Spitsbergen with the Pearya terrane and Timanide belt
- 2009
-
Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 166:Part 3, s. 529-544
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Tidskriftsartikel (refereegranskat)abstract
- Southwest Spitsbergen, Wedel Jarlsberg Land consists of two Proterozoic terranes with differing structural and metamorphic histories. The northern terrane experienced two Early Palaeozoic deformation events both accompanied by greenschist-facies metamorphism of similar grade. The southern terrane records a Neoproterozoic pervasive amphibolite-facies metamorphism and strong deformational fabric only locally retrogressed during a Caledonian greenschist-grade event. The terranes are seperated by an important sinistral ductile shear zone defined as the Vimsodden Kosibapasset zone, which comprises wrench- and contraction-dominated domains characteristic of strain partitioning in transpression zones; in this case apparently controlled by contrasting rheologies of the juxtaposed crustal domains. The northern terrane of Wedel Jarlsberg Land shares affinities with Pearya in northern Ellesmere Island of Arctic Canada whereas the southern one resembles the Timanide belt of NE Europe. A quantitative approach facilitated by a numerical plate model demonstrates that correlation with Pearya is feasible if sinistral displacement of c. 600 km occurred during the Caledonian orogeny. The correlation with the Timanides is valid if the southern terrane represents an outlier of the Timanide belt seperated from Baltica by the opening of the lapetus Ocean.
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| 38. |
- Merle, Renaud E., 1976-, et al.
(författare)
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Occurrence of inherited supra-subduction zone mantle in the oceanic lithosphere as inferred from mantle xenoliths from Dragon Seamount (southern Tore–Madeira Rise)
- 2012
-
Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 169:3
-
Tidskriftsartikel (refereegranskat)abstract
- Spinel-bearing peridotite and pyroxenite xenoliths dredged from the Dragon Seamount (southern Tore–Madeira Rise, West Iberia and Morocco margin) give an insight into the composition of the underlying lithosphere. These xenoliths are devoid of evidence of strong host lava–peridotite interaction and re-equilibration or late impregnation in the plagioclase facies. The spinels and pyroxenes from the Dragon peridotites have compositions distinct from those of both lherzolites and harzburgites from the Iberia margin and the Mid-Atlantic Ridge. They display a highly depleted composition, in particular, high Cr-number, up to 0.63 in the spinels, consistent with a melting degree between 12 and 19%. Because of the strong chemical similarities between the Tore–Madeira Rise, Newfoundland peridotites, and peridotites from supra-subduction zones, we propose that the Dragon peridotites formed in a similar context. The pyroxenites display a cumulate texture and are probably a high-temperature–high-pressure cumulate formed by fractional crystallization from a melt. The Tore–Madeira Rise peridotites may represent a former mantle wedge in an oceanic arc, later included into the continental lithosphere and finally tectonically disseminated within the lithosphere during the rifting of the Newfoundland–Iberia continental lithosphere. As a consequence, rifting processes may produce heterogeneities in the oceanic lithosphere and influence isotopic compositions of ocean island basalt-type lavas during plume–lithosphere interactions, as inferred for the southern Tore–Madeira Rise.Supplementary material: Further information on the analytical results is available at http://www.geolsoc.org.uk/SUP18512.
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| 39. |
- Merle, Renaud, et al.
(författare)
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Evidence of multi-phase Cretaceous to Quaternary alkaline magmatism on Tore–Madeira Rise and neighbouring seamounts from 40Ar/39Ar ages
- 2009
-
Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 166:5, s. 879-894
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Tidskriftsartikel (refereegranskat)abstract
- The Tore-Madeira Rise is a seamount chain located 300 kin off the Portugal and Morocco coasts attributed to hotspot activity. U-Pb ages of lavas from the northern and central Tore-Madeira Rise range between 103 and 80.5 Ma whereas Ar-40/Ar-39 ages from the central and southern Tore-Madeira Rise yield ages ranging from 94.5 to 0.5 Ma. We performed new Ar-40/Ar-39 measurements to better understand the geodynamic history of the Tore-Madeira Rise. Plagioclase ages from the Bikini Bottom and Torillon seamounts suggest ages of >90 Ma and >= 60 Ma, respectively. Amphiboles from the Seine seamount yield an age of 24.0 +/- 0.8 Ma. Biotites from lavas of the Ashton seamount give ages of 97.4 +/- 1.1 Ma and 97.8 +/- 1.1 Ma. The geochronological database available on the Tore-Madeira Rise has been filtered on statistical criteria to eliminate unreliable ages. The resulting database reveals three pulses of alkaline magmatism on the Tore-Madeira Rise at 103-80.5 Ma, at c. 68 Ma and between 30 Ma and the present. The magmatism was continuous from 103 Ma until c. 68 Ma and from c. 30 Ma until the present on the Tore-Madeira Rise, the surrounding seamounts and the Portugal coast. We suggest that the space-time distribution of this magmatism results from the interaction between a wide thermal anomaly emitting magmatic pulses and the complex motion of the Iberian plate.
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| 40. |
- Morris, GA, et al.
(författare)
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New dates (415 Ma) for the Etive Dyke Swarm and the end of the Caledonian Orogeny in the SW Grampian highlands of Scotland
- 2005
-
Ingår i: Journal of the Geological Society. - : Geological Society of London. - 2041-479X .- 0016-7649. ; 162:5, s. 741-744
-
Tidskriftsartikel (refereegranskat)abstract
- New laser stepwise heating Ar-40-Ar-39 dates (415 +/- 1.8 and 414 +/- 2 Ma) from the Etive Dyke Swarm in the SW Grampian Highlands of Scotland indicate that the dykes are 10-20 Ma older than previously assumed. The dykes constitute the final phase of the Late Caledonian Granites in the region, which themselves define the end of the Caledonian Orogeny, therefore these dates can be taken as the end of the orogeny in this area. The dates show a temporal link between the Etive magmatism and early precious metal mineralization at Tyndrum as well as emphasizing the NW to SE diachronous nature of the end of Caledonian magmatism across Scotland.
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| 41. |
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| 42. |
- Pease, Victoria L., et al.
(författare)
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The New Siberian Islands and evidence for the continuation of the Uralides, Arctic Russia
- 2015
-
Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 172:1, s. 1-4
-
Tidskriftsartikel (refereegranskat)abstract
- U–Pb detrital zircon results from New Siberian Islands sandstones illuminate the long-lived controversy regarding the continuation of the Uralian orogen into the Arctic region. A dominant age peak of c. 285 Ma from Permian sandstone requires proximal derivation from Taimyr’s Carboniferous–Permian granites, thought to reflect syn- to post-tectonic Uralian magmatism. The provenance of Devonian sandstone has Baltica affinities. The data record a dramatic change in provenance between Devonian and Permian time, from Baltica to a mixed Baltica + Uralian source. Our results confirm that the Uralian foreland basin extended from Taimyr to the New Siberian Islands.
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| 43. |
- Peillod, Alexandre, et al.
(författare)
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Quo vadis Zeus : is there a Zas shear zone on Naxos Island, Aegean Sea, Greece? A review of metamorphic history and new kinematic data
- 2021
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 178:5
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Forskningsöversikt (refereegranskat)abstract
- Detecting zones of considerable early-orogenic displacement in rather monotonous rock sequences which have undergone a late and pervasive tectonometamorphic overprint is challenging. It has been proposed that the alleged Zas shear zone in the passive margin sequence of the Cycladic Blueschist Unit on Naxos Island, Greece, separates amphibolite facies, non-high-pressure rocks (Koronos Unit) below the shear zone from Eocene high-pressure rocks (Zas Unit) above the shear zone. We review existing pressure-temperature data from the Koronos Unit and present new kinematic data from the anticipated Zas shear zone to evaluate the tectonic significance of this recently proposed structure. This has implications for unravelling the subduction history of rock units from tectonometamorphic datasets. Common to all pressure-temperature data from the Koronos Unit is a well-defined amphibolite facies equilibration stage at 8-11 kbar and 600-700 degrees C, followed by initial near-isothermal to slightly prograde decompression and subsequent pronounced cooling. This segment of the high-temperature pressure-temperature loop is associated with top-to-the-NNE extensional deformation in the footwall of the Miocene Naxos-Paros detachment. Little is known about the metamorphism preceding the amphibolite facies overprint in the Koronos Unit. Our review shows that it is likely that the rocks experienced a prior high-pressure metamorphic overprint that is typical of rocks of the Cycladic Blueschist Unit. Our kinematic data show that the Zas shear zone contains variably deformed rocks with dominantly top-to-the-NNE shear sense indicators that developed under greenschist facies metamorphism in the footwall of the Naxos-Paros detachment. No significant offset can be detected across the Zas shear zone and the geology on either side of it does not support large-scale movement across the shear zone. We discuss a model in which the Zas shear zone is considered to be a minor zone of deformed schist near the biotite-in isograd of Miocene high-temperature metamorphism. We conclude that there is no need to tectonically subdivide the passive margin sequence of the Cycladic Blueschist Unit on Naxos.
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| 44. |
- Pettersson, Carl Henrik, et al.
(författare)
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Detrital zircon U-Pb ages of Silurian-Devonian sediments from NW Svalbard: A fragment of Avalonia and Laurentia?
- 2010
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Ingår i: Journal of the Geological Society (London). - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 167:5, s. 1019-1032
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Tidskriftsartikel (refereegranskat)abstract
- Detrital zircon populations from Silurian-Devonian clastic rocks of NW Svalbard were analysed by U-Pb laser ablation inductively coupled plasma mass spectrometry to investigate the pre-Caledonian provenance of Svalbard's Northwestern Terrane. Changes in the resulting age spectra suggest a major shift in sources from the Laurentian-Avalonian suture in the latest Silurian to the local metasedimentary basement of the Northwestern Terrane in the Late Silurian-Early Devonian, and in the Lochkovian to Grenvillian-Sveconorwegian sources. These data, together with structural, additional geochronological and metamorphic data from Svalbard, East Greenland and Avalonia, support the amalgamation of Svalbard as the result of long-distance transport along sinistral strike-slip faults. A unifying model for the final amalgamation of Svalbard, consistent with the stratigraphical and tectonothermal history of Svalbard, involves fragments from the Grampian orogen and Avalonian crust originally accreted to the Laurentian margin being subsequently transported northward along sinistral strike-slip faults during Scandian deformation.
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| 45. |
- Pettersson, Carl Henrik, et al.
(författare)
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Timing of migmatization and granite genesis of the Northwestern Terrane, Svalbard
- 2009
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 166, s. 147-158
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Tidskriftsartikel (refereegranskat)abstract
- U–Pb ion microprobe investigations of zircons from gneisses, granites and migmatites of the pre-Devonian Smerenburgfjorden and Richarddalen Complexes constrain the tectonic evolution and origin of Svalbard's Northwestern Terrane. Field relationships combined with U–Pb age data indicate that a late Meso- to Neoproterozoic metapelitic protolith was intruded by Tonian (c. 960 Ma) granitoids and suggest that the entire Northwestern Terrane is underlain by early Neoproterozoic granitoids intruding older metasediments. Both rock types were later involved in Caledonian deformation, with subsequent migmatization and granite genesis at c. 435–420 Ma. Ages of inherited zircons in granites and migmatites reflect anatexis of this late Meso- to Neoproterozoic protolith, with zircon xenocrysts ranging in age from c. 1030 to 1820 Ma. Pronounced lithological, geochronological and tectonothermal similarities to NE Svalbard (Nordaustlandet) and the Krummedal supracrustal sequence of East Greenland suggest a strong correlation between Svalbard and East Greenland prior to Caledonian orogenesis.
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| 46. |
- Pitcairn, Iain K., et al.
(författare)
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Structurally focused fluid flow during orogenesis : the Islay Anticline, SW Highlands, Scotland
- 2010
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 167:4, s. 659-674
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Tidskriftsartikel (refereegranskat)abstract
- Displacement of isotopic compositions at boundary layers across strata of contrasting composition is commonly used to investigate hydrothermal fluid flow during orogeny. This study investigates whether hydrothermal fluid flow was focused along the Islay Anticline, Islay, SW Highlands of Scotland, as shown in the axial zone of the neighbouring Ardrishaig Anticline. Four localities from the limb to the axial plane of the Islay Anticline were investigated for isotopic homogenization of metacarbonate units to silicate values. At Mull of Oa on the limb of the anticline, metacarbonate samples show limited isotopic resetting and the fluid flux is estimated to be <1 m(3) m(-2). Within the axial zone of the Islay Anticline, metacarbonate units from Port a' Chotain and Bagh an Da Dhoruis show complete isotopic homogenization to silicate values indicating higher fluid fluxes. Fluid flow was enhanced along localized parasitic folds such as at Port an t-Sruthain, where metacarbonates have been isotopically reset, and there are abundant quartz-carbonate veins that precipitated during D-1-D-2 deformation. Metamorphic fluid flow was higher in the axial zone of the Islay Anticline and in localized antiformal structures. Fluid fluxes are estimated to be considerably lower than at the neighbouring Ardrishaig Anticline.
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| 47. |
- Riley, T.R., et al.
(författare)
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Early Jurassic magmatism on the Antarctic Peninsula and potential correlation with the Subcordilleran plutonic belt of Patagonia.
- 2017
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 174, s. 365-376
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Tidskriftsartikel (refereegranskat)abstract
- Early Jurassic silicic volcanic rocks of the Chon Aike Province (V1: 187 – 182 Ma) are 30 recognised from many localities in the southern Antarctic Peninsula and northeast Patagonia and are 31 essentially coeval with the extensive Karoo (182 Ma) and Ferrar (183 Ma) large igneous provinces of 32 pre-breakup Gondwana. Until recently, plutonic rocks of this age were considered either rare or 33 absent from the Antarctic Peninsula batholith, which was thought to have been mainly constructed 34 during the Middle Jurassic and the mid-Cretaceous. New U-Pb zircon geochronology from the 35 Antarctic Peninsula and recently published U-Pb ages from elsewhere on the Peninsula and 36 Patagonia are used to demonstrate the more widespread nature of Early Jurassic plutonism. Eight 37 samples are dated here from the central and southern Antarctic Peninsula. They are all moderately 38 to strongly foliated granitoids (tonalite, granite, granodiorite) and locally represent the crystalline 39 basement. They yield ages in the range 188 – 181 Ma, and overlap with published ages of 185 – 180 40 Ma from granitoids from elsewhere on the Antarctic Peninsula and from the Subcordilleran plutonic 41 belt of Patagonia (185 – 181 Ma). Whilst Early Jurassic plutons of the Subcordilleran plutonic belt of 42 Patagonia are directly related to subduction processes along the proto-Pacific margin of Gondwana, 43 coeval volcanic rocks of the Chon Aike Province are interpreted to be directly associated with 44 extension and plume activity during the initial stages of Gondwana break-up. This indicates that 45 subduction was ongoing when Chon Aike Province volcanism started. The Early Jurassic plutonism on 46 the Antarctic Peninsula is transitional between subduction-related and break-up related 47 magamatism.
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| 48. |
- Ring, Uwe, et al.
(författare)
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Faulting in Banks Peninsula : tectonic setting and structural controls for late Miocene intraplate volcanism, New Zealand
- 2012
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 169:6, s. 773-785
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Tidskriftsartikel (refereegranskat)abstract
- An analysis of faulting in the late Miocene volcanic rocks of Banks Peninsula, South Island, New Zealand, shows that the formation of the volcanic edifice was largely controlled by NE-SW-striking dextral-oblique strike-slip faults. The data show a variable component of west-east-or NW-SE-oriented shortening and north-south or NE-SW extension. Synvolcanic faults reactivated Cretaceous normal faults and are interpreted to have formed a local pull-apart basin that controlled volcanism. Further east, the geometry of Akaroa Harbour is controlled by a north-south-striking oblique reverse fault. Limited fault-slip data collected from sub-recent loess deposits are not significantly different from the data collected in the volcanic rocks and appear to show that the kinematic field did not change significantly over the last c. 10 Ma. The overall kinematic field causing the recent series of earthquakes in the greater Christchurch region is also not fundamentally different from the one that controlled the eruption of the volcanic rocks. We conclude that the inherited Cretaceous faults controlled the development of the late Miocene volcanism on Banks Peninsula and largely provided a major anisotropy along which the recent faults ruptured.
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| 49. |
- Schmitz, Birger, et al.
(författare)
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The middle Darriwilian (Ordovician) delta C-13 excursion (MDICE) discovered in the Yangtze Platform succession in China: implications of its first recorded occurrences outside Baltoscandia
- 2010
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 2041-479X .- 0016-7649. ; 167:2, s. 249-259
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Tidskriftsartikel (refereegranskat)abstract
- The middle Darriwilian delta C-13 excursion (MDICE), one of the least known of the Ordovician delta C-13 excursions, has previously been recorded only from the Middle Ordovician of Baltoscandia. Analysis of many recently collected limestone samples from the Guniutan Formation at two Yangtze Platform localities show elevated delta C-13 values in the same biostratigraphic interval (Microzarkodina ozarkodella Conodont Subzone) as the MDICE in Baltoscandia, which justifies identification of the Chinese delta C-13 excursion as the MDICE. These occurrences, which are in strata that show striking lithological and conodont faunal similarity to the Swedish Holen Limestone and some coeval units in Estonia, indicate that the MDICE, the stratigraphically oldest of the named Ordovician delta C-13 excursions, is likely to have a world-wide distribution and to have great potential for local and long-range chemostratigraphic correlations.
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| 50. |
- Skelton, Alasdair, et al.
(författare)
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Regional mapping of pre-metamorphic spilitization and associated chemical mobility in greenschist-facies metabasalts of the SW Scottish Highlands
- 2010
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 167:5, s. 1049-1061
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Tidskriftsartikel (refereegranskat)abstract
- Both spilitic and non-spilitic metabasaltic sills are hosted by greenschist-facies metasediments in the SW Scottish Highlands. Spilitization is mainly characterized by enrichment in Na2O, elevated modal plagioclase and epidote segregations. Mapping of the spatial distribution of spilitic metabasalts reveals an ancient sub-sea-floor fluid cell centred on the extrusive Tayvallich Volcanics. Fluid circulation was most extensive at shallow levels where most sills were spilitized. We attribute this to pervasive flow of saline fluid, which was thermally driven by the cooling suite of lava flows and sills. Spilitization below this lithostratigraphic depth was restricted to only a few sills. Their spilitization is largely unrelated to specific properties of these sills (e. g. width, chemistry or host lithology). We conclude that fluid channelling was an intrinsic property of sub-sea-floor fluid flow either at deeper levels or earlier during fluid circulation. By profiling of the size distributions of relic phenocrysts in a partly spilitized sill, we conclude that spilitization proceeds with the symmetric propagation of a spilitization front from the sill margins towards the sill interior. Based on chemical profiling across the margin of an epidote segregation, we conclude that spilitization is associated with chemical transport on scales ranging from 0.1 to 10 m.
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