Variscan shear-zone deformation of late Precambrian basement in SW Iberia: implications for circum-Atlantic pre-Mesozoic tectonics

1992 ◽  
Vol 14 (7) ◽  
pp. 807-823 ◽  
Author(s):  
Benito Abalos
Keyword(s):  
Shear Zone ◽  
Precambrian Basement ◽  
Late Precambrian ◽  
Zone Deformation

scholarly journals The Nordre Strømfjord shear zone and the Arfersiorfik quartz diorite in Arfersiorfik, the Nagssugtoqidian orogen, West Greenland

2006 ◽  
Vol 11 ◽  
pp. 145-162 ◽  
Author(s):  
Kai Sørensen ◽  
John A. Korstgård ◽  
William E. Glassley ◽  
Bo Møller Stensgaard
Keyword(s):  
Shear Zone ◽  
Volcanic Rocks ◽  
Quartz Diorite ◽  
Ductile Deformation ◽  
Chemical Compositions ◽  
West Greenland ◽  
South West ◽  
Wide Range ◽  
Inland Ice ◽  
Zone Deformation

The Nordre Strømfjord shear zone in the fjord Arfersiorfik, central West Greenland, consists of alternating panels of supracrustal rocks and orthogneisses which together form a vertical zone up to 7 km wide with sinistral transcurrent, ductile deformation, which occurred under middle amphibolite facies conditions. The pelitic and metavolcanic schists and paragneisses are all highly deformed, while the orthogneisses appear more variably deformed, with increasing deformation evident towards the supracrustal units. The c. 1.92 Ga Arfersiorfik quartz diorite is traceable for a distance of at least 35 km from the Inland Ice towards the west-south-west. Towards its northern contact with an intensely deformed schist unit it shows a similar pattern of increasing strain, which is accompanied by chemical and mineralogical changes. The metasomatic changes associated with the shear zone deformation are superimposed on a wide range of original chemical compositions, which reflect magmatic olivine and/ or pyroxene as well as hornblende fractionation trends. The chemistry of the Arfersiorfik quartz diorite suite as a whole is comparable to that of Phanerozoic plutonic and volcanic rocks of calc-alkaline affinity.

Kinematics of Shear Zone Deformation in Soft Sensitive Clays

2007 ◽  
pp. 341-357 ◽  
Author(s):  
V. Thakur ◽  
S. Nordal ◽  
H. P. Jostad ◽  
L. Andresen
Keyword(s):  
Shear Zone ◽  
Zone Deformation

On the position of the Variscan front in southern New Brunswick and its relation to Precambrian basement

1976 ◽  
Vol 13 (1) ◽  
pp. 194-196 ◽  
Author(s):  
N. Rast ◽  
K. L. Currie
Keyword(s):  
New Brunswick ◽  
Precambrian Basement ◽  
Precambrian Rocks ◽  
Late Precambrian ◽  
Mylonite Zone

The Variscan front is marked by a zone of cataclasis that generally follows an older and larger mylonite zone, but locally cuts across relatively undeformed Precambrian rocks. The older mylonite zone probably developed in Late Precambrian (Avalonian) time. Correlative Precambrian rocks extend across both the Variscan front, and the Bellisle fault to the northwest.

Understanding 21Ne inventories in Precambrian basement below the Great Unconformity in Estonia

2021 ◽  
Author(s):  
Adrian M. Hall ◽  
Fin Stuart ◽  
Kalle Kirsimae ◽  
Peeter Somelar
Keyword(s):  
Isotope Composition ◽  
Precambrian Basement ◽  
Weathering Profile ◽  
Deep Time ◽  
Late Precambrian ◽  
Cosmogenic Nuclide ◽  
The Earth ◽  
Land Surfaces ◽  
Natural Decay ◽  
Geochemical Mass Balance

<p>Stable cosmogenic Ne isotopes are widely used to determine the erosion rate of slowly-eroding land surfaces through the Cenozoic. Constraining erosion and surface exposure back in Earth history remains a challenge largely due to the presence of Ne isotopes generated by natural decay processes over the lifetime of rocks.  Prospects are best when cosmogenic nuclide production has been significant and nucleogenic Ne production is low and can be quantified.  We have explored the limits of palaeo-cosmogenic Ne in one of the Earth’s most extensive erosion surfaces, the late Precambrian Great Unconformity in Estonia. Here deep kaolinitic saprolites formed on Baltica prior to the deposition of Late Ediacaran quartz sandstones. On the basis of geochemical mass balance the duration of saprolite development is estimated to be of the order of a few Myr.</p><p>Borehole F163 samples a section through still-buried weathered unconformity that includes a saprolite surface consistent with negligible erosion during the marine transgression. Samples from the unconformity have <sup>21</sup>Ne concentrations (>10<sup>8</sup> atoms/g) that are significantly higher than shielded samples from >20 m below the unconformity. This difference is borne out by Ne isotope composition, and leads to the tanatalising prospect that Precambrian cosmogenic Ne is present in the saprolite. Using modern <sup>21</sup>Ne production rates the palaeosols appear to record a few million years irradiation. This is broadly consistent with geochemical estimates of saprolite development.  Samples from the uppermost preserved part of the weathering profile in borehole F231 have low <sup>21</sup>Ne concentrations that are indistinguishable from deeper in the rock profile. This would require profile truncation or the redeposition of weathered material.  The borehole is located on the western flank of an uplifted basement block rising ca 130 m above the typical Precambrian basement level in the area and likely that the thick regolith contains material eroded from the uplifted basement units. Clearly these are early days and quantifying surface exposure in deep time will require effort in field as well as the lab.</p>

Sm–Nd isotopic geochemistry of Precambrian to Paleozoic granitoid suites and the deep-crustal structure of the southeast margin of the Newfoundland Appalachians

1995 ◽  
Vol 32 (2) ◽  
pp. 224-245 ◽  
Author(s):  
Andrew Kerr ◽  
George A. Jenner ◽  
Brian J. Fryer
Keyword(s):  
Fault System ◽  
Mobile Belt ◽  
Simple Extension ◽  
Precambrian Basement ◽  
Zone Boundary ◽  
First Order ◽  
Metasedimentary Rocks ◽  
Late Precambrian ◽  
Deep Crustal Structure ◽  
Appalachian Orogen

In the Eastern Central Mobile Belt of the Newfoundland Appalachians, late Precambrian basement inliers have εNd from −3 to +2, but Cambro-Ordovician metasedimentary rocks have initial εNd below −7. This region is inferred to have an "inverted" crustal residence structure, which influenced subsequent Appalachian-cycle magmatism. Ordovician and Silurian granitoid suites have εNd of −8 to −2, bracketing both basement and cover, but peraluminous, "S-type" granites have the lowest εNd. Devonian granites have initial εNd values from −5 to +1, and low εNd is associated with peraluminous character. These Paleozoic granites show geographic trends, with lowest εNd values in areas where metasedimentary rocks are abundant. They are suggested to contain anatectic material from both Precambrian basement and metasedimentary cover, but some "I-type" suites probably also include a mantle-derived component. In the adjacent Avalon Zone, Precambrian plutonic suites mostly have εNd from +1 to +6, but there are negative εNd values (−8 to −4) in the westernmost Avalon Zone. Devonian plutonic suites mostly have εNd from +2 to +5. Thus, the Precambrian crust of the Avalon Zone is largely "juvenile," except at its westernmost edge. Contrasts across the Eastern Central Mobile Belt–Avalon Zone boundary, defined by the Dover–Hermitage Bay fault system, indicate a major, crustal-scale structure, and suggest an isotopically distinct "central block" beneath the central Appalachian Orogen, rather than a simple extension of "Avalonian" crust. Similar geographic–isotopic patterns have been reported in Nova Scotia and New Brunswick, suggesting that this pattern represents a first-order deep-crustal subdivision of the northern Appalachian Orogen.

Relationship between the Aspy and Bras d'Or "terranes" in the northeastern Cape Breton Highlands, Nova Scotia

1993 ◽  
Vol 30 (9) ◽  
pp. 1773-1781 ◽  
Author(s):  
Shoufa Lin
Keyword(s):  
Shear Zone ◽  
Sedimentary Rocks ◽  
The West ◽  
Precambrian Rocks ◽  
Late Precambrian ◽  
Cape Breton ◽  
Basal Conglomerate ◽  
Back Arc ◽  
Eastern Highlands ◽  
Basin System

According to previous interpretations, the Eastern Highlands shear zone separates Ordovician–Silurian volcano-sedimentary rocks to the west (Cheticamp Lake Gneiss of the Aspy "terrane") from late Precambrian sedimentary rocks and dioritic – tonalitic plutons and Early Ordovician granite to the east (Bras d'Or "terrane"). New mapping discovered a basal conglomerate of the Cheticamp Lake Gneiss that rests on deformed diorite of the Bras d'Or "terrane" and contains clasts similar or identical to rocks of the Bras d'Or "terrane." The late Precambrian rocks of the Bras d'Or "terrane" are also overlain by a volcano-sedimentary sequence of Silurian age (Clyburn Brook formation). These observations suggest that rocks of the Aspy "terrane" lie unconformably on those of the Bras d'Or "terrane." The Eastern Highlands shear zone is therefore not a terrane boundary. The Ordovician–Silurian rocks of the Aspy "terrane" are interpreted to have formed in an arc–back-arc basin system. The back-arc basin is interpreted to have formed by rifting in the Bras d'Or "terrane" and the Eastern Highlands shear zone to have been related to the closure of the basin.

Shear-zone deformation in the Yackandandah Granite, northeast Victoria

1988 ◽  
Vol 35 (2) ◽  
pp. 223-230 ◽  
Author(s):  
Michael Sandiford ◽  
Stuart F. Martin ◽  
Eric M. Lohe
Keyword(s):  
Shear Zone ◽  
Zone Deformation

scholarly journals Deformation Characteristics of the Shear Zone and Movement of Block Stones in Soil–Rock Mixtures Based on Large-Sized Shear Test

2020 ◽  
Vol 10 (18) ◽  
pp. 6475
Author(s):  
Zhiqing Li ◽  
Feng Hu ◽  
Shengwen Qi ◽  
Ruilin Hu ◽  
Yingxin Zhou ◽  
...  
Keyword(s):  
Shear Deformation ◽  
Shear Zone ◽  
Failure Mode ◽  
Deformation Pattern ◽  
Deformation Characteristics ◽  
Shear Surface ◽  
Field Samples ◽  
Deformation Properties ◽  
Shear Process ◽  
Zone Deformation

Soil–rock mixtures (SRM) have the characteristics of distinct heterogeneity and an obvious structural effect, which make their physical and mechanical properties very complex. This study aimed to investigate the deformation properties and failure mode of the shear zone as well as the movement of block stones in SRM experimentally, not only considering SRM shear strength. The particle composition and proportion of specimens were based on field samples from an SRM slope along national highway 318 in Xigaze, Tibet. Shear zone deformation tests were carried out using an SRM-1000 large-sized geotechnical apparatus controlled by a motor servo, considering the effects of different stone contents by mass (0, 30%, 50%, 70%), vertical pressures (50, 100, 200, 300, and 400 kPa), and block stone sizes (9.5–19.0, 19.0–31.5, and 31.5–53.0 mm). The characteristics of the shear zone deformation and block stone interactions were monitored by placing aluminum wires and dry ash in holes in the specimens. The results showed that the stone content 30% and 70% were two critical thresholds to determine the deformation characteristics of SRM. Under the conditions of high stone content and large particle size, the stones throughout the shear surface tended to extrude and roll during the shear process. The block stones around the shear surface were mainly affected by dilatancy and exhibited extrusion, particle breakage, and redistribution. The deformation pattern could be considered as be analogous to push-type shear deformation from the back to front or composite shear deformation from the front and back to the middle of the slope. It is of great importance to study the shear characteristics and deformation evolution of SRM to understand the progressive shear process of the sliding zone and the failure mode of landslides.

Sign in / Sign up

Export Citation Format

Share Document