scholarly journals The Wurawina Supergroup, Late Cambrian to Early Devonian, Tasmania

1986 ◽  
Vol 120 ◽  
pp. 95-96
Author(s):  
MR Banks ◽  
E Williams
Keyword(s):  
Early Devonian ◽  
Late Cambrian

Precambrian and Palaeozoic rocks of the Inner Hebrides

1983 ◽  
Vol 83 ◽  
pp. 31-45
Author(s):  
R. Anderton ◽  
D. R. Bowes
Keyword(s):  
Small Area ◽  
Early Devonian ◽  
Red Sandstone ◽  
North West ◽  
Late Cambrian ◽  
Thrust Zone ◽  
Lower Palaeozoic ◽  
Caledonian Orogeny ◽  
Peripheral Areas ◽  
Mountain Chain

SynopsisThe Lewisian complex, which forms the continental basement to north-west Scotland, crops out on the Inner Hebridean islands of Rona, Raasay, Skye, Coll, Tiree, Iona and Islay. Upon this basement, four major rock successions were deposited before the Caledonian orogeny. The upper Precambrian Moine assemblage forms only a small area of metamorphosed rocks on Mull but the c. 790 m.y. (million year) old Torridonian sediments are found on Raasay, Scalpay. the Sleat of Skye, Soay and Rhum. The upper Precambrian to Cambrian Dal radian Supergroup dominates Islay, Jura, Gigha and the islands of the Firth of Lome whilst also forming a partial rim around the Tertiary Northern granite in Arran. Other Precambrian rocks of uncertain affinity are found on Islay, Oronsay, Colonsay and Iona. Cambro-Ordovician sediments are found on Skye where they have been partially metamorphosed by Tertiary intrusions.South-east of the Moine thrust zone, the Precambrian and lower Palaeozoic rocks were deformed and metamorphosed during the late Cambrian to early Devonian Caledonian orogeny which resulted in the development of the Caledonian mountain chain. Subsequently, Scotland north-west of the Highland Boundary fault has tended to persist as a land area undergoing erosion with sedimentation restricted to peripheral areas now preserved around the present coast. Upper Palaeozoic rocks are therefore only well represented on Arran although Old Red Sandstone (Devonian) sediments are found in the Firth of Lome and a very small area of possible Permian rocks occurs on Islay.

scholarly journals Tracking low-temperature tectonism of the St. Lawrence Platform and Humber Zone, southern Quebec Appalachians, through apatite and zircon (U–Th)/He thermochronology

2017 ◽  
Vol 54 (8) ◽  
pp. 827-849 ◽  
Author(s):  
J.M. Emberley ◽  
D.A. Schneider
Keyword(s):  
Low Temperature ◽  
Late Jurassic ◽  
Late Ordovician ◽  
Petroleum Exploration ◽  
Accelerated Cooling ◽  
Early Devonian ◽  
Late Cambrian ◽  
Thermal Maximum ◽  
Order Of Magnitude ◽  
The Subject

The St. Lawrence Platform (SLP) and Humber Zone (HZ) of the southern Quebec Appalachians have been the subject of extensive studies to resolve the degree of thermal maturation, yet the timing of the thermal maximum is not well understood. We have employed apatite (AHe) and zircon (ZHe) (U–Th)/He thermochronometry across a network of Late Cambrian to Late Ordovician siliciclastic and Grenvillian basement outcrops to resolve the thermal history below 200 °C. Single crystal dates from individual samples exhibit age dispersion by as much as 300 million years, with a strong positive to negative correlation with increasing effective uranium (eU) concentration. The data in the southwestern portion of the basin allow for thermal maxima of up to 200 °C during the Late Ordovician or Early Devonian. Regional burial trends combined with local estimates of paleogeothermal gradients indicate that, if sedimentation continued after the Late Ordovician, there was no significant increase in burial in southwestern portions of the SLP as previously suggested. Heating was followed by protracted cooling through 180–100 °C during the Late Jurassic and Early Cretaceous, and the cooling rate increased by an order of magnitude through the uppermost crust (80–60 °C) until ca. 100 Ma. Both the external and internal HZ sections experienced rapid cooling through the Silurian after a Taconic thermal maximum. The HZ witnessed protracted cooling through the Late Jurassic, followed by accelerated cooling until the present. Increased recognition of these low-temperature events can augment our understanding of the evolution of accretionary orogens, consequently increasing the efficiency of petroleum exploration.

Implications of Early Devonian poles from the Canadian Arctic Archipelago for the North American apparent polar wander path

1982 ◽  
Vol 19 (9) ◽  
pp. 1802-1809 ◽  
Author(s):  
Peter Dankers
Keyword(s):  
North American ◽  
Canadian Arctic ◽  
Canadian Arctic Archipelago ◽  
Early Devonian ◽  
Polar Wander ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Late Cambrian ◽  
Normal Polarity ◽  
North American Craton

Lower Devonian red beds from the upper member of the Peel Sound Formation at Prince of Wales Island (Canadian arctic) yield two different paleopoles at 25N 099E and at 01N 091E, the first one being older than the second one. The magnetic directions from which the poles are calculated are derived from vector analysis of thermal, chemical, and alternating magnetic field demagnetization results. Normal and reversed polarities are recorded for the northerly pole, whereas the pole at the equator reveals mainly a normal polarity. The position of the pole close to the equator has significant implications for the early Paleozoic apparent polar wander path of the North American craton. It appears that from the Late Cambrian to Early Devonian the craton moved continuously in a counter-clockwise direction that ended abruptly in the Early Devonian when the direction of the motion of the continent was reversed in a very similar manner to what occurred in Late Cambrian times.

Devonian–Carboniferous paleogeography and orogenesis, northern Yukon and adjacent Arctic Alaska

2007 ◽  
Vol 44 (5) ◽  
pp. 679-694 ◽  
Author(s):  
Larry S Lane
Keyword(s):  
Early Carboniferous ◽  
Sensu Stricto ◽  
Thrust Faults ◽  
Mackenzie Delta ◽  
Early Devonian ◽  
The North ◽  
Late Cambrian ◽  
Arctic Alaska ◽  
Tectonic Transport ◽  
Regional Tectonic

Surface and subsurface data from northern Yukon document a northward facies transition from shelf carbonates to basinal graptolitic shales and cherts from Late Cambrian to Early Devonian time. Parts of this north-facing continental margin were deformed during separate orogenic events of Early Devonian and Early Carboniferous ages. The first event, the Romanzof Orogeny, is identified in exposures across northwestern Yukon, in adjacent northeastern Alaska, and locally in the subsurface of the Alaska North Slope. It resulted in tight folds, north-directed thrust faults, and intrusion by Late Devonian posttectonic granitic plutons. Notwithstanding the thrust-fault orientations, southward diminution of deformation intensity combined with facies variations suggest that tectonic transport was generally southward. Evidence for an Early Carboniferous event is preserved in the northern Richardson Mountains and locally in the subsurface of the Mackenzie Delta region. It consists of detached open folds and minor thrust faults. Geological and geophysical data from northern Yukon document the location and orientation of the Early Carboniferous deformation front, and define a regional tectonic transport direction toward the south or southeast. This event is a distal foreland element of the Ellesmerian Orogeny (sensu stricto) of the Canadian Arctic Islands and is distinct from the Romanzof event in age, intensity, and extent. Endicott and Lisburne group strata, deposited on a southwest-facing subsiding shelf, overstep rocks deformed by the Romanzof event even as Ellesmerian deformation encroached from the north.

The origin of the Variscan upper allochthons in the Ortegal Complex, northwestern Iberia: Sm–Nd isotopic constraints on the closure of the Rheic Ocean

2008 ◽  
Vol 45 (6) ◽  
pp. 651-668 ◽  
Author(s):  
J. Brendan Murphy ◽  
Gabriel Gutiérrez-Alonso
Keyword(s):  
Suture Zone ◽  
Variscan Orogeny ◽  
Common Source ◽  
Massif Central ◽  
Early Devonian ◽  
Composite Body ◽  
Mafic Rocks ◽  
Rheic Ocean ◽  
Late Cambrian ◽  
Nw Iberia

Northwestern Iberia preserves a stack of allochthons in which the vestiges of a suture zone generated during the Variscan orogeny by the late Paleozoic collision between Laurussia and Gondwana are exposed. Lower allochthons contain Ordovician ophiolite (known as the Lower Ophiolite), and are structurally overlain by Devonian ophiolite (Upper Ophiolite), which are in turn structurally overlain by allochthons containing high-grade metamorphic rocks with continental affinities and Late Cambrian – Early Ordovician protolith ages (known as the Upper Units). Geochemical and Sm–Nd isotopic data from the Upper Ophiolite and the structurally overlying Upper Units exposed in the Ortegal Complex of Galicia show that these allochthons are derived from a variety of mantle and crustal sources and indicate that the suture zone juxtaposes a variety of oceanic assemblages. The general isotopic characteristics of each assemblage are similar to allochthons in other Variscan complexes in NW Iberia suggesting that the allochthons are each derived from a common source and may be regionally extensive. One of the bodies mapped within the Upper Ophiolite (Purrido amphibolite) is a composite body that, in addition to recently identified Mesoproterozoic mafic rocks, is characterized by a juvenile signature at ca. 395 Ma that was chemically modified from coeval intra-oceanic subduction. The very high ϵNd of this Late Devonian ophiolite is typical of several penecontemporaneous ophiolites within the Variscan orogen including the Lizard Complex (Britain) and the Massif Central (France), suggesting derivation from a regionally extensive anomalous mantle characterized by time-integrated depletion in Nd relative to Sm. Paleozoic mafic rocks in the Upper Units have ϵNd values typical of Paleozoic mafic rocks in Avalonia, which are thought to have been derived from subcontinental lithospheric mantle (SCLM) that was enriched at ca. 1.0 Ga. They exhibit elevated Th/Yb and Ce/Yb relative to Ta/Yb suggesting that their composition has been contaminated by subduction zone components, although the age of this contamination is unclear. Felsic rocks in the Upper Units were derived by melting of Mesoproterozoic or older (West African?) crust. These data, when combined with other geologic constraints, including the outboard position of the Upper Units relative to the ophiolite, support the hypothesis that the Upper Units collectively represent a crustal fragment that drifted from Gondwana during the formation of the Rheic Ocean, was transferred to Laurussia in Silurian or early Devonian times, and was subsequently thrust over the Gondwanan margin during the closure of the Rheic Ocean and the Variscan orogenesis.

Early Ordovician alkali-ultramafic Zhilandy complex (Central Kazakhstan): structure and age of formation

2019 ◽  
Vol 484 (1) ◽  
pp. 61-65
Author(s):  
R. M. Antonuk ◽  
A. A. Tretyakov ◽  
K. E. Degtyarev ◽  
A. B. Kotov
Keyword(s):  
Complex Formation ◽  
Central Asian Orogenic Belt ◽  
Early Cambrian ◽  
Early Ordovician ◽  
Late Cambrian ◽  
Central Asian ◽  
Geochronological Study ◽  
Three Stages ◽  
Late Neoproterozoic ◽  
Quartz Monzodiorites

U–Pb geochronological study of amphibole-bearing quartz monzodiorites of the alkali-ultramafic Zhilandy complex in Central Kazakhstan, whose formation is deduced at the Early Ordovician era (479 ± 3 Ma). The obtained data indicate three stages of intra-plate magmatism in the western part of the Central Asian Orogenic Belt: Late Neoproterozoic stage of alkali syenites of the Karsakpay complex intrusion, Early Cambrian stage of ultramafic-gabbroid plutons of the Ulutau complex formation, and Late Cambrian–Early Ordovician stage of formation of the Zhilandy complex and Krasnomay complex intrusions.

Sign in / Sign up

Export Citation Format

Share Document