scholarly journals 40Ar–39Ar isotope constraints on the age of deformation in Charnwood Forest, UK

2008 ◽  
Vol 145 (5) ◽  
pp. 702-713 ◽  
Author(s):  
J. N. CARNEY ◽  
P. ALEXANDRE ◽  
M. S. PRINGLE ◽  
T. C. PHARAOH ◽  
R. J. MERRIMAN ◽  
...  
Keyword(s):  
Shear Zone ◽  
Lake District ◽  
The West ◽  
Eastern Margin ◽  
Step Heating ◽  
Caledonian Orogeny ◽  
Spot Analysis

Abstract40Ar–39Ar dating by a combination of spot analysis and step-heating has been carried out on mica fabrics from slaty cleavage and a shear zone in the Neoproterozoic to Cambrian rocks of Charnwood Forest, Leicestershire. The results indicate that crust adjacent to the eastern margin of the Midlands Microcraton was affected by localized epizonal metamorphism and penetrative deformation between 425 and 416 Ma (Silurian to earliest Devonian), somewhat earlier than the Acadian Phase of the Caledonian orogeny recorded elsewhere in southern Britain. The Charnwood cleavage geometry suggests that the deformation arose within a dextral transpressional regime along the eastern margin of the Midlands Microcraton. This tectonism may have overlapped with pre-Acadian sinistral transtensional movements documented for the Welsh Basin and Lake District areas, to the west and north of the Midlands Microcraton.

Unravelling the enigmatic Grampian Shear Zone: In-situ monazite and titanite U-Pb analysis of the juxtaposed Badenoch and Grampian Groups

2021 ◽  
Author(s):  
Lewis Evason ◽  
Anna Bird ◽  
Eddie Dempsey ◽  
Kit Hardman ◽  
Martin Smith ◽  
...  
Keyword(s):  
Shear Zone ◽  
Major Elements ◽  
Metamorphic Rocks ◽  
High Grade ◽  
Icp Ms ◽  
Wide Range ◽  
Caledonian Orogeny ◽  
Detailed Picture ◽  
Spot Analysis

<p>The Grampian Shear Zone (GSZ) represents a highly deformed tectonostratigraphic contact between the Proterozoic metamorphic rocks of the Dalradian Group from the underlying high grade metamorphic Neoproterozoic rocks of the Badenoch Group within the Grampian Highlands. The nature (tectonic suture or palaeo-unconformity), age and structure of the GSZ and indeed the underling Badenoch Group are poorly constrained. Previous studies of the GSZ and synkinematic (intruded during shearing) pegmatites found therein, yielded metamorphic/deformation (and magmatic) ages ranging from c.a. 808 to 440 M. This study reinvestigates this shearzone using in-situ (within section) petrochonological analysis on a range of U-Pb and Rb-Sr chronometers – Monazite, zircon, titanite, rutile and mica. Carrying out this analysis in-situ and using a variety of minerals allows us to directly date deformation fabrics over a wide range of deformation temperatures, giving us a far more detailed picture of the events recorded within these rocks. Large monazite grains (≥100μm) were mapped using in-situ LA-ICP-MS to show within grain variation of major elements and REEs. Monazite U-Pb spot analysis from the GSZ has yielded ages ranging from 784.11 ± 1.2Ma to 442.58 ± 0.58Ma. The same analysis was performed on a sample from the Grampian group which yielded an age of 441.34 ± 037Ma. In addition to this monazite data, in-situ U-Pb Titanite analysis from the Badenoch Group gave ages of 526.96 ± 1.33 Ma from a metabasite sample, with a metasedimentary sample giving a range of titanite U Pb ages from 540 to 460Ma. These age ranges show that the Badnoch Group and the GSZ have recorded a complex polyorogenic history relative to the “simple” overlying Dalradian metasediments. We propose that the Grampian Shear Zone represents a deep-seated Knoydartian (808 to 784Ma) age shear zone within the meso-Neoproterozoic Badenoch Group. This shear zone was then reactivated during the Grampian phase of the Caledonian Orogeny resulting in the tectonic emplacement of the Dalradian metasediments above the Badenoch group.</p>

40Ar–39Ar dating of alkali basaltic dykes along the southwest coast of Greenland: Cretaceous and Tertiary igneous activity along the eastern margin of the Labrador Sea

1999 ◽  
pp. 19-29 ◽  
Author(s):  
Lotte Melchior Larsen ◽  
David C. Rex ◽  
W. Stuart Watt ◽  
Philip G. Guise
Keyword(s):  
Alkali Basalt ◽  
Dyke Swarm ◽  
Labrador Sea ◽  
Precambrian Basement ◽  
Stress Regime ◽  
Southwest Coast ◽  
Eastern Margin ◽  
Step Heating ◽  
Igneous Activity ◽  
Break Up

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Melchior Larsen, L., Rex, D. C., Watt, W. S., & Guise, P. G. (1999). 40Ar–39Ar dating of alkali basaltic dykes along the southwest coast of Greenland: Cretaceous and Tertiary igneous activity along the eastern margin of the Labrador Sea. Geology of Greenland Survey Bulletin, 184, 19-29. https://doi.org/10.34194/ggub.v184.5227 _______________ A 380 km long coast-parallel alkali basalt dyke swarm cutting the Precambrian basement in south-western Greenland has generally been regarded as one of the earliest manifestations of rifting during continental stretching prior to break-up in the Labrador Sea. Therefore, the age of this swarm has been used in models for the evolution of the Labrador Sea, although it has been uncertain due to earlier discrepant K–Ar dates. Two dykes from this swarm situated 200 km apart have now been dated by the 40Ar–39Ar step-heating method. Separated biotites yield plateau ages of 133.3 ± 0.7 Ma and 138.6 ± 0.7 Ma, respectively. One of the dykes has excess argon. Plagioclase separates confirm the biotite ages but yield less precise results. The age 133– 138 Ma is earliest Cretaceous, Berriasian to Valanginian, and the dyke swarm is near-coeval with the oldest igneous rocks (the Alexis Formation) on the Labrador shelf. A small swarm of alkali basalt dykes in the Sukkertoppen (Maniitsoq) region of southern West Greenland was also dated. Two separated kaersutites from one sample yield an average plateau age of 55.2 ± 1.2 Ma. This is the Paleocene–Eocene boundary. The swarm represents the only known rocks of that age within several hundred kilometres and may be related to changes in the stress regime during reorganisation of plate movements at 55 Ma when break-up between Greenland and Europe took place.

scholarly journals IV.—On the Drifts of the West and South Borders of the Lake District, and on the Three Great Granitic Dispersions

1871 ◽  
Vol 8 (85) ◽  
pp. 303-312 ◽  
Author(s):  
D. Mackintosh
Keyword(s):  
Small Area ◽  
Irish Sea ◽  
Lake District ◽  
The West ◽  
Boulder Clay ◽  
The Irish Sea ◽  
Sea Cliff

Boulder-scars.—From Maryport to Parkgate, the E. coast of the Irish Sea at intervals exhibits accumulations or concentrations of large boulders, which are locally called scars. They may be seen in all stages of formation, from the denudational area, where they are in course of being left by the washing away of the clayey matrix, to the depositional area, where they have become half-covered with recent sand and shingle. In many places (as between Seascale and near Silecroft) there are so many boulders within a small area as to show that a considerable thickness of the clay must have been removed. With the exception of having tumbled down as the cliffs were undermined and worn back by the sea, many of the boulders may still rest nearly in the positions they occupied in the clay, but (as is evidenced on the coast at Parkgate) others, up to a great diameter, may have been shifted horizontally. Some of the scars exist where the Boulder-clay would appear to have risen up into ridges or mounds, as no clay is now found opposite to them at the base of the sea-cliff. Others are clay and boulder plateaux, visibly connected with the cliff-line. Most of the scars, I believe, are remnants of the great Lower Brown Boulder-clay. The most conspicuous boulder in the scars S.W. of Bootle, is Eskdale-fell granite, accompanied by a little Criffell granite, and a great number of the usual felspathic erratics.

Submarine landslides in the west continental slope of the South China Sea and their tsunamigenic potential

2021 ◽  
Author(s):  
Xiaoyi Pan ◽  
Linlin Li ◽  
Hong Phuong Nguyen ◽  
Dawei Wang
Keyword(s):  
South China Sea ◽  
Shear Zone ◽  
Continental Slope ◽  
South China ◽  
Water Depth ◽  
Red River ◽  
Submarine Landslides ◽  
The West ◽  
Tsunami Waves ◽  
Central Vietnam

<p>The 109 meridian fault is located in the west of the South China Sea (SCS) connecting to the offshore Red River Shear Zone. The evolution processes of the 109 meridian fault: striking-uplifting-subsidence of adjacent basin led to a nearly 1000m sharp bathymetric difference in the offshore region of central Vietnam. Combined with the high sediment input from numerous montane rivers in the rising hinterland, the continental slope near central Vietnam possesses the ideal condition for developing submarine landslides. Seismic data indicates many submarine landslides were developed along the steep continental slope. In this study, we analyze the possible trigger mechanisms of these landslides based on the local geological background and sedimentary environment, and assess their tsunamigenic potential along the coast of the Southern Central Vietnam (SCV). We point out that the landslide failures in this region could be triggered by several mechanisms, including seismic activities in the offshore SCV, volcanic activities, gas seep on the slope and the relative sea-level changes. The seismic and volcanic activities are related directly to the late middle Miocene volcanism generated by the change from left- to right-lateral motion on the Red River Shear Zone, showing that tectonism play a significant role in the generation of submarine landslide in the western continental slope of the SCS. To estimate the impact of tsunami waves on SCV coastline, we use two numerical models—NHWAVE and FUNWAVE-TVD to model 4 representative landslides with volume ranging between 1-4km<sup>3</sup> and water depth of 300-1000m. The submarine landslides were treated as rigid slump and deformable slide corresponding to two different sedimentary environments. Our results show that the tsunami waves generated by rigid slump can reach up to 20m height in the landslide source area and arrive earlier to the coast of SCV than waves generated by deformable slide. Among these simulated scenarios, tsunami waves generated by the worst-case scenario arrive at the populated cities including Quy Nhơn (109.3°E,13.77°N), Tuy Hòa (109.37°E ,13.08°N) and Vung Ro Bay (109.43°E，12.86°N) in less than 25mins with maximum height of 5m. It is worth mentioning that the Vung Ro Bay will be affected by tsunami waves in all simulated scenarios. We quantify the influence of landslide characteristics (volume, water depth and material) and highlight the local effect of coastal bathymetry on the tsunami generation and propagation which lead to different hazard level of SCV coast.</p>

scholarly journals Eburnean deformation pattern of Burkina Faso and the tectonic significance of shear zones in the West African craton

2020 ◽  
Vol 191 ◽  
pp. 2 ◽  
Author(s):  
Dominique Chardon ◽  
Ousmane Bamba ◽  
Kalidou Traoré
Keyword(s):  
Burkina Faso ◽  
Shear Zone ◽  
Regional Scale ◽  
Kinematic Model ◽  
Shear Zones ◽  
West African ◽  
Deformation Pattern ◽  
The West ◽  
West African Craton ◽  
Regional Flow

Shear zones of the Paleoproterozoic Eburnean accretionary Orogen (West African craton) are investigated by means of large-scale structural mapping. Regional scale (10-100 km) mapping was based on the aeromagnetic survey of Burkina Faso and craton-scale (1000 km) mapping on a compilation of fabric data. At both scales, shear zones are arranged as an anastomosed transpressional network that accommodated distributed shortening and lateral flow of the orogenic lithosphere between the converging Kénéma-Man and Congo Archean provinces. Structural interference patterns at both scales were due to three-dimensional partitioning of progressive transpressional deformation and interactions among shear zones that absorbed heterogeneities in the regional flow patterns while maintaining the connectivity of the shear zone network. Such orogen-scale kinematic patterns call for caution in using the deformation phase approach without considering the “bigger structural picture” and interpreting displacement history of individual shear zones in terms of plate kinematics. The West African shear zone pattern is linked to that of the Guiana shield through a new transatlantic correlation to produce an integrated kinematic model of the Eburnean-Transamazonian orogen.

On a Quartz-porphyry from the Lake District

1924 ◽  
Vol 61 (11) ◽  
pp. 513-515 ◽  
Author(s):  
Sidney Melmore
Keyword(s):  
Igneous Rock ◽  
The Body ◽  
Lake District ◽  
The South ◽  
The West ◽  
Quartz Porphyry ◽  
West Side ◽  
South Side ◽  
The Road

A Small quarry was opened about three years ago at Thwaite Head, which lies between the southern ends of Coniston Lake and Windermere. It is on the west side of the road between that hamlet and Hawkshead, and exposes a nearly vertical sill, 40 feet wide, running E.N.E.-W.S.W. in the Bannisdale slates. On the south side a series of joint-planes running parallel to the bedding of the slates and curving inwards at the top have split the igneous rock into flags, while in the body of the rock the jointing is much coarser, so that it is quarried in large blocks. Both the igneous rock and the slates are much decomposed and friable along the southern junction, and it is here a little galena is said to have been found when the quarry was first opened. This is not improbable, as the old Thwaite Head lead mine is situated not far off on the banks of Dale Park Beck.

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