bluuebunny/crossref_metadata_2025_split huggingface dataset:
Basement-cover relations in Shetland
Authors: Flinn Derek , Frank P. L. , Brook Maureen , Pringle I. R. 
Published: May 2008

Summary
The relationship between basement and cover can be studied in two places in Shetland. In NW Shetland, orthogneisses with a minimum age of 2900 Ma are followed to the east and southeast by Caledonian metasediments and greenschists and these in turn by schists and gneisses with a minimum age of 860 Ma. The metasediments contain bands of mylonite and blastomylonite. Wide belts of superposed schistosity occur in the schist and gneiss unit and also at the junction of the orthogneisses with the metasediments. This area is interpreted as including the Caledonian front. In NE Shetland, two nappes of ultramafic and basic rocks, one above the other, have been thrust over the surface of the earth onto Caledonian (lower Dalradian?) schists and gneisses. During transport the nappes have suffered erosion, and sediments, including nappe detritus, have been deposited on and in front of them and subsequently been over-ridden and metamorphosed by the nappes. The occurrence forms a typical obducted ophiolite complex.
Regional geochemistry of the Northern Highlands of Scotland
Authors: Johnstone G. S. , Plant Jane , Watson Janet V. 
Published: May 2008

Summary
The distribution of trace-elements between the Lewisian basement and the Caledonian cover-formations can be assessed from regional geochemical maps based on stream-sediment sampling. The Lewisian basement is characterised by depletion in heat-producing elements, U, K, Rb, and in Pb, Be and by high values of Sr, Mg and first row transition elements. The range of Zr, Ba, B and Y levels are comparable with those over the Moine. Regional variations relate to crustal level and to the presence of zones of high deformation. Anomalies for Mo, Zr and U are associated with granite and pegmatites in some of these zones. Within the Moine nappe the zone of tectonically emplaced Lewisian slices divides an area where the bulk geochemistry is consistent with that of continental arkoses—the Morar Division—from the Glenfinnan and Loch Eil divisions which have geochemical characteristics closer to those of greywacke facies. No other geochemical discontinuity has been recognised in the Moine but the boundary with the Dalradian is marked by an increase in boron. Clear misfits of element distribution across the Great Glen fault are apparent but the data so far available could be interpreted in terms of either sinistral or dextral displacement.
New evidence for a Central Highland Root Zone
Authors: Thomas Peter R. 
Published: May 2008

Summary
The major nappe structures of the west Central Highlands of Scotland have been found to diverge from the upward facing Ossian-Geal Charn steep belt, trending NE-SW through the Ben Alder Forest. As the deep equivalent of the Loch Awe synclinal complex to the southwest, it more probably represents a root zone than the Tummel steep belt which is largely controlled by later deformational events. A structural synthesis of the west Central Highlands describes how the large elongated Drumochter-Dochard dome influences at least three subsequent phases of deformation.
The tectonic evolution of the lower Palaeozoic rocks of extreme SE Ireland
Authors: Shannon Patrick M. 
Published: May 2008

Summary

Five deformation phases (D
0
–D
4
) and four metamorphic events (M
0
–M
3
) are recognised in the lower Palaeozoic rocks of an extensive area lying to the south of the Leinster granite. D
0
and M
0
features are interpreted as being the result of post diagenetic burial metamorphism. The main regional deformation (D
1
) preceded the intrusion of the Leinster granite and produced tight folds and an axial-planar slaty cleavage. D
2
and D
3
deformations produced more brittle linear and planar structures. They show a localised development which is interpreted as being due to late stage movements of unexposed granite bodies at relatively shallow depths.
A metamorphic map of the British and Irish Caledonides
Authors: Fettes D. J. 
Published: May 2008

Summary
The metamorphic rocks of the British and Irish Caledonides fall into two groups. The first group constitutes the northern belt. These rocks have been subjected to a lower Ordovician metamorphism (Grampian event of Lambert & McKerrow 1976) which was probably, in part at least, diachronous. The metamorphic pattern ranges from the low- to the intermediate-pressure facies series and from the low greenschist- to the upper amphibolite-facies groups. The distribution of facies within the belt is complex and may relate to a depth-controlled metamorphism with locally induced thermal highs. The second group constitutes the southern belt. Here the rocks have been subjected to a late-Silurian event which, in general, causes slight crystallisation but very locally rises to upper greenschist facies.
The pattern of three-dimensional metamorphism in the Killin area, Inverness-shire: a direct method of determining the thickness of metamorphic zones in the Caledonides
Authors: Winchester J. A. , Whittles K. H. 
Published: May 2008

Summary
The mineral assemblages in calc-silicates from the Killin area suggest an eastward increase in metamorphic grade. By comparing the chemistry and mineral assemblages of the calc-silicates, the isograd surfaces were defined. They were found to dip 13° west, to the east of Glen Brein, and approximately 4° east in the western part of the area. Thus a metamorphic synform is defined. The interval measured between the isograd surfaces shows that the combined thickness of the hornblende and bytownite zones is less than 1400 m, and therefore, by correlation, the kyanite zone in the Killin area cannot exceed this thickness.
Lower Palaeozoic soft-sediment deformation structures in the western end of the Longford-Down inlier, Ireland
Authors: Morris J. H. 
Published: May 2008

Summary

Two types of interrelated soft-sediment deformation (D
0
) structures are described, disturbed bedding and folds. Disturbed bedding varies from pinch-and-swell bed(s) to lenticular boudins. Folds are variable in style and scale; one fold is associated with a welded contact, two with décollement zones. All structures are stratabound. The structures are considered to be the product of dewatering of channel infill deposits combined with slope instabilities caused by channeling and/or penecontemporaneous volcanism. Packages of beds of alternating, opposed younging direction are also present and predate tectonic folds and cleavage. These structures may correlate with either D
0
or represent an intermediate stage between D
0
and post-lithification D
1
tectonic structures.
Tremadoc to Llanvirn volcanism on the southeast side of the Harlech dome (Rhobell Fawr), N Wales
Authors: Kokelaar B. P. 
Published: May 2008

Summary
A volcanic episode, initiated in the late Tremadoc and persisting into the lower Llanvirn, is represented around Rhobell Fawr (SH 7825) by basaltic lavas and their breccias (the Rhobell Volcanic Group), by dolerite, microdiorite and microtonalite intrusions, by a rhyolite tuff and by the basic and intermediate constituents of certain sedimentary rocks. Initially basalts were erupted, at a variable rate, subaerially from fissures. This effusive phase was followed by eruptions of andesite and dacite, which, in turn, were followed by explosive eruption of rhyolite. A dyke regime in the west of the area represents the sub- and intravolcanic parts of a major site of eruption and was the source of the volcanic group. The rocks of the Rhobell episode are genetically related by amphibole-dominated fractional crystallisation of mantle-derived basaltic magma and are similar to those of modern destructive plate margin environments. The Rhobell fractionation series, from silica-undersaturated to quartz-normative, is closely paralleled by that at Grenada, at the southern end of the Lesser Antilles island arc. The tectonovolcanic evolution of the area is consistent with the development of a N-S basement fracture situated beneath the eastern margin of the Harlech Dome.
Ignimbrite volcanism in the Ordovician Borrowdale volcanics of the English Lake District
Authors: Millward David 
Published: May 2008

Summary
Ignimbrites within the Borrowdale Volcanic Group predominantly occur in two situations; thick dacitic sheets associated with lavas of similar composition, and thin dacitic-to-andesitic units interbedded with basic-to-andesitic pyroclastic fall deposits. Mapping and examination of samples from the units has revealed petrological and chemical variations which can be attributed to the variations in components (crystals, fiamme and lithic fragments) and to post emplacement processes including crystallisation, ion-exchange with vapour phases and leaching by groundwater.
Geochemistry of the appinite suite
Authors: Wright A. E. , Bowes D. R. 
Published: May 2008

Summary
The suite is highly enriched in many of the trace elements, both those typical of basaltic rocks (Co, Ni, Cr) and those more frequently richer in calc alkaline suites (Ba, Sr). The suite is rich in these elements and in K in all the members of the suite and the geochemical characters are indicative of normal igneous differentiation of a volatile, K and trace element-rich basaltic magma. The suite is not similar to any of the more widespread basaltic or andesitic suites although the rocks mostly vary in composition from a rather ultramafic basalt to a silica-poor andesite. There are also abundant acidic and alkaline differentiates but these do not show any more extreme enrichment in major or trace elements than the more basic rocks.
The strain profile above a major thrust fault, Finnmark, N Norway
Authors: Milton N. J. , Williams G. D. 
Published: May 2008

Summary
The base of the Laksefjord Nappe, Finnmark, N Norway consists of a strained conglomerate. Field studies of the deformation suggest a simple strain profile, with strain depending on height above the basal thrust within the Nappe. A combination of simple shear deformation, related to movement on, or initiation of, the basal thrust, with a relatively constant flattening component is proposed. A mathematical model based on down surface slope stress and the steady state flow law is suggested for the simple shear component of the strain.
The 3D propagation of décollement in the Jura
Authors: Laubscher H. P. 
Published: May 2008

Summary
The sequence of instabilizations leading to the formation of shallow nappes may be illustrated by the kinematics of the embryonic Jura Nappe. On the first order arc, due to regional boundary conditions, are superposed second and third order arcs that developed around more local irregularities in the distribution of strength. Successive instabilization of the Rheintal part of the Jura Décollement Nappe generally proceeds from S to N. Location of ramps where décollement climbs to the surface is largely influenced by pre-existing Rhinegraben structures. These also convey a certain anisotropy to the sedimentary cover which seems to be responsible, at least partly, for a different aspect of sinistral and dextral shear zones. Whereas sinistral shears are usually along discrete faults, mostly reactivated Rhinegraben faults, the dextral shears commonly are diffuse zones. Arcuate elements, convex to the N, connect the sinistral and dextral shear zones frontally. Regionally, the shear zones accommodate the divergence of movement, with lateral elongation, within the overall Jura Arc. More locally, they bound arcuate segments of ever smaller dimensions, and also seem to ease diverging movements in these smaller arcs.
Wrench related thrusting along a Mesozoic-Cenozoic continental margin: Antalya Complex, SW Turkey
Authors: Woodcock N. H. , Robertson A. H. F. 
Published: May 2008

Summary
An imbricate thrust belt and a geometrically related wrench-fault terrain are reported from the Antalya Complex, SW Turkey. The deformation occurred between late Cretaceous and Miocene time along a former Mesozoic rifted continental margin. The thrusting appears to have been temporally and mechanically related to at least the early stages of wrench tectonics.
An overview of thrusts and nappes of western Himalaya
Authors: Thakur V. C. 
Published: May 2008

SummaryThe Shali-Deoban Parautochthon, Krol Berinag Nappes and Outer Crystallines Nappes are the main lithostructural units of the Lesser Himalaya of Kumaun, Garhwal and eastern Himachal. Two thrust sheets, the Chail Nappe and the Jutogh Nappe are recognized in the Outer Crystallines Nappes. The Chail Nappe forms a separate thrust sheet, and the Jutogh Nappe overlying it represents a southward extension of the Central Crystallines Nappe of the Higher Himalaya. The Chail Nappe rocks constitute the base of the Palaeozoic-Mesozoic sequence of the Kashmir-Chamba Parautochthon, whereas the Central Crystallines Nappe forms the basement for the late Precambrian-Cretaceous sequence of the Tethyan Zone in the Kumaun, Spiti and Zaskar regions. The Central Crystallines Nappe shows a progressive regional metamorphism, chlorite to sillimanite grade, whereas the metamorphism of the Chail Nappe is mainly confined to the greenschist facies. Metamorphic inversion is a characteristic feature of the Jutogh Nappe which occurs as crystalline klippen in the Lesser Himalaya Zone. The ophiolite suite of rocks of the Indus-Tsangpo suture occurs also as klippen above the sediments of the Tethys Himalaya and metamorphics of the Tso Morari Dome. They appear to have resulted from squeezing out from the root zone and subsequent gravity gliding. The Indus Suture Zone is unique with regard to its thrust tectonics, in that, whereas all the principal thrusts elsewhere in the Himalaya are directed towards the S, within this zone they are directed only toward the N.
Thrust nappes in the Rocky Mountain Foothills near Mountain Park, Alberta
Authors: Charlesworth H. A. K. , Kilby W. E. 
Published: May 2008

Summary

In 200 km
2
of W central Alberta, the thrusts associated with seven nappes cut up section to the NE at about 5° through 1000 m of Upper Jurassic and Lower Cretaceous strata whose overall dip is gentle and to the SW. The thrusts, whose horizontal spacing ranges from 0 to 4 km, have a combined displacement of about 12 km. Most folds affecting the nappe assemblage originated through bending over steps in the thrusts against which they end downwards. Up plunge to the NW the upper nappes, most of which involve older strata, are apparently truncated by the McConnell Nappe, whereas three of the thrusts underlying the lower nappes appear to run into the Miette thrust which to the NW replaces the McConnell as the SW boundary of the Foothills. Down plunge to the SE the thrusts merge in an Upper Cretaceous décollement zone whose 15 km of movement are dissipated in the Foothills to the NE by low-angle thrusts splaying into the overlying strata. The décollement and associated thrusts are cut by a younger generation of faults that include the McConnell, Nikanassin and Folding Mountain.
Deformational styles in two Mesozoic fault zones, western Washington, USA
Authors: Cowan D. S. , Miller R. B. 
Published: May 2008

Summary
The Navaho Divide and Lopez fault zones record sub-greenschist facies, brittle fragmentation and tectonic mixing at an active Mesozoic continental margin. Displacement directions across these zones are interpreted as partly or wholly dip-slip, although unambiguous criteria in these and many other Cordilleran fault zones are lacking. The moderate to high-angle Navaho Divide zone, which is part of the ophiolitic Ingalls Complex, contains variously sized elongate fragments of serpentinized ultramafic rocks, gabbro, and related rock types set in a voluminous matrix of foliated, scaly serpentinite. The moderately dipping Lopez zone comprises larger slices of turbidites, pebbly mudstone, and minor mafic metavolcanic rocks separated by faults and narrow fault zones locally filled with mudstone that apparently flowed during thrusting. In both complexes, the elongate slices and subparallel faults define an imbricate or schuppen structure geometrically similar to the macroscopic fabric of intracratonic, Rocky Mountain-type imbricate zones. However, the Navaho Divide and Lopez zones are fundamentally different in that they both juxtapose and contain rock units that are difficult, or impossible, to restore palinspastically to a pre-faulting configuration.
Mechanisms for basement shortening in the Andean foreland fold belt of southern South America
Authors: Winslow Margaret A. 
Published: May 2008

Summary
A mechanism for basement shortening underneath allochthonous foreland fold and thrust belts is reverse faulting along inherited normal faults. Normal faulting of basement rocks beneath much of southernmost South America indicates that up to 30–40% extension occurred before sedimentation in a subsiding foredeep. The basement is divided into blocks of similar dimensions to those in the Basin and range of Nevada, U.S.A. Post-depositional reverse motion along some of these high-angle block boundaries under the foreland can account for the 20–40 km of shortening observed in the cover rocks, without showing upthrust wedges of basement rocks.
The folds in the cover rocks of the foreland fold-belt are asymmetric, open to closed with over-steepened to overturned limbs which are frequently truncated by high-angle reverse faults. These faults attain a shallower dip with depth toward a décollement plane above a basal volcanic section. Basement involvement in thrusts (0.5–1.5 km vertical displacement) is suggested where basal volcanics are involved in thrust wedges, as revealed by drilling and seismic reflection data. Block faults have been observed beneath many forelands and have always been assumed to be pre-orogenic and passive with respect to deformation of the cover. The block dimensions, fault angles, vertical displacements and other parameters from the southern Andes are inserted to calculate pre-depositional extension and syn-orogenic shortening that can occur without producing obvious basement upthrusting. The results are compared with data from the Appalachians and Canadian Rockies.
Sedimentation across the Japan Trench off northern Honshu Island
Authors: von Huene Roland , Arthur Michael A. 
Published: May 2008

Summary
The convergent margin along the International Program of Ocean Drilling (IPOD) Japan Trench transect was sampled by dredging, piston coring, and drilling by the Deep Sea Drilling Project (DSDP). This sampling was within an extensive network of single-and multichannel seismic reflection records. The Quaternary uplift of northern Honshu Island, climatic change, and lowered sea-levels, provided coarser grained sediment during the Quaternary than during the late Miocene and Pliocene. Within the Quaternary sediments, those in the forearc basin, in a slope basin, and on the trench floor are coarser grained and accumulated more rapidly than the clayey sediment from the trench slope. But overall, the sediment sampled from all environments is mainly clay and silt. Rates of accumulation varied greatly and prior to 3 Ma ago they were higher in trench slope basins than in the forearc basin. Tectonism along the Japan Trench transect must have changed the Miocene-Pliocene morphology by tilting some of the former trench slope basins; this may have actually triggered slumping and erosion rather than allowing sediment deposition.
The lower slope has a relatively large number of channels and a greater amount of slumped material then is found elsewhere; thus it may contain vertical and lateral changes of facies in sediments deposited over relatively short periods of time. Morphological features and sedimentation patterns on the lower slope are greatly affected by local tectonic structure which has changed significantly in the past 2–3 Ma. Slope basin and trench-floor deposits are distinguished from those of the main forearc basin by the relative abundance of material deposited by mass movement. Channels commonly cross the forearc basin and trench slope and provide the transport paths for coarse sediment to any part of the margin. No specific characteristics appear exclusively in a given environment, but the relative abundance of features can help identify broad environments of deposition.
Structural evolution of coherent terranes in the Ghost Rocks Formation, Kodiak Island, Alaska
Authors: Byrne Tim 
Published: May 2008

Summary

The Late Cretaceous to Palaeocene Ghost Rocks Formation, Kodiak Island, Alaska, comprises two structural styles: multiply deformed mélange and relatively coherent terranes of turbidite deposits which together constitute a probable ancient accretionary complex. The mélange consists almost exclusively of orientated, elongate sandstone boudins which lie in a foliated pelitic matrix. In the coherent terranes, structural histories, rock types and hornfels metamorphism delineate two NE trending units: Unit A, and a probably younger Unit B. Unit A can be subdivided into two gradational structural belts, a seaward conjugate fold belt and a landward spaced cleavage belt. The conjugate fold belt contains ‘S’ and ‘Z’ type kink folds that often intersect to form conjugate fold sets. The folds of this fold belt are hornfelsed by a sill which intruded partially lithified sediments; the fold belt therefore also formed when the sediments were partially lithified. Analyses of the fold axial surfaces indicate a shortening direction of 319°, when later folding is removed. Sill emplacement and hornfels metamorphism interrupted the conjugate fold deformation and resulted in a change in style of deformation in Unit B to broad, open to tight folds associated with a spaced cleavage. The cleavage strikes 046° and dips approximately vertically, fanning divergently about fold axial surfaces. The approximately coaxial conjugate folding and folding with cleavage in unit A constitute D
1
. Unit B generally contains sub-horizontal beds except for a large-scale, overturned, thrusted fold, which emplaced mélange to the NW and above Unit B. Slickenlines, fold axes and poles to bedding indicate this unit was shortened along a trend of 334°. This deformation is termed D
2
and is correlated elsewhere in the Ghost Rocks Formation to thrust faults which place mélange to the NW and under the coherent terranes.

The structural histories of the coherent terranes in the Ghost Rocks Formations show that accretionary prism deformation can involve coaxial deformations and the tectonic deformation of partially lithified sediments. The structural histories also show that the Palaeocene deformation axes in the Ghost Rocks Formation have not rotated out of their original sub-horizontal orientations.
Sedimentation in the Sunda Trench and forearc region
Authors: Moore Gregory F. , Curray Joseph R. , Emmel Frans J. 
Published: May 2008

SummarySedimentation in the Sunda Trench and forearc region is dominated by the transport of terrigenous detritus from orogenic and volcanic terranes around the margins of the north-eastern Indian Ocean. Quartzose Himalayan detritus is transported into the Bay of Bengal and down the trench axis as far south as the Sunda Strait. Prior to development of the outer-arc ridge, the majority of arc-derived sediment bypassed the forearc basin and was deposited in the trench. Nearly all sediment derived from the arc terranes of Java and Sumatra during the Neogene has been trapped in the forearc basin and has not reached the trench.Hemipelagic sedimentation dominates on the lower part of the inner trench slope. Calcareous microfossils and volcanic ash are the dominant constituents of these hemipelagic deposits. Higher on the slope, terrigenous and hemipelagic sediments accumulate in large trench-slope basins.The Sunda forearc basin is a series of smaller individual basins separated from each other by transverse highs, isolating the respective sedimentary sequences. Off north Sumatra, quartzose detritus accumulates, whereas off Java, volcaniclastic sediments predominate.Long-distance transport of sediment down the trench axis, damming of sediments behind the outer-arc ridge, and the segmented nature of the forearc basin leads to the juxtaposition of sediment bodies with different provenances.