bluuebunny/crossref_metadata_2025_split huggingface dataset:
Grenvillian and Caledonian tectono-magmatic activity in northeasternmost Svalbard
Authors: Johansson Åke , Larionov Alexander N. , Gee David G. , Ohta Yoshihide , Tebenkov Alexander M. , Sandelin Stefan 
Published: April 2008

Abstract
The Nordaustlandet Terrane of NE Svalbard forms an exposed part of the Barentsia microcontinent. Augen gneisses, migmatites, granites and gabbros dominate the scattered outcrops along the northeastern coast of Nordaustlandet, and on the smaller islands to the north and east, as far as Kvitøya. These outcrops probably represent the deepest exposed crustal levels within the folded Caledonian basement of the Nordaustlandet Terrane. In the present study, a variety of rock types have been analysed by different U-Pb dating techniques (conventional, Pb-evaporation and ion microprobe) on zircon, titanite and monazite The major and trace element compositions and Sm-Nd isotope geochemistry of these rocks have also been investigated.

The augen gneisses yield U-Pb ages of
c.
950 Ma, indicating that they are deformed late Grenvillian granites, similar to the Grenville-age granites and augen gneisses of northwestern and central Nordaustlandet. Migmatites, grey granites, aplitic dykes and a syenite (boulder) yield U-Pb ages mainly falling in the 430–450 Ma range, slightly older than the 410–420 Ma late-tectonic Caledonian granites further west. Both the Grenvillian and Caledonian granites are of crustal anatectic origin, and the Caledonian granites and migmatites may have formed largely by remelting of Grenvillian crust. The ages of the mafic rocks are uncertain, but Sm-Nd data indicate a possible emplacement age of
c.
700 Ma for two of the gabbros, suggesting that they may be the result of rift-related magmatism in connection with the opening of the Iapetus Ocean. A few enigmatic inherited zircons of similar late Neoproterozoic age found in younger granites may possibly be related to this event. No evidence for late Neoproterozoic orogenic activity, similar to that in the Timanides of northern Russia, is seen in eastern Svalbard. At this time, eastern Svalbard (Barentsia) was probably part of the Laurentian margin, and probably located far away from northern Baltica.
Correlation of the Hellenide nappes in the south-east Aegean and their tectonic reconstruction
Authors: Bonneau Michel 
Published: April 2008

Summary
The central Aegean nappe pile can be readily related to that of the mainland Hellenides and has the advantage that the deeper levels are well displayed, particularly in the Cyclades.

The following units can be distinguished, from base to top:

(1)

The para-autochtonous
Ida
or
Talea Ori Sequence
, recognized in Crete, Kassos, Rhodes (Lindos sequence) and Amorgos is, in part, a neritic carbonate platform sequence. It can be correlated with the Ionian-Preapulian autochthon of the mainland and most probably with the Menderes sequence of western Anatolia, there exposed in a tectonic window.

(2)

The major
Tripolitza Nappe
, a carbonate platform sequence, with the
Phyllite Nappe
at its base, is well represented in the outer arc as well as in Astypaleia and Santorini.

(3)

The
Pindos
and
Arvi Nappes
of Crete, Rhodes and Tilos are the remnants of an ocean basin active from Upper Triassic to Late Cretaceous times.

(4)

The Cycladic Blueschist Unit
exposed on Syros, Siphnos, Naxos and other islands, occupies a tectonic position similar to the Pindos Nappe. It is interpreted as the subducted margin of the European plate, while the Pindos Nappe, the abyssal plain of the Apulian plate, was obducted just before continental collision in the Late Eocene-Oligocene.

(5)

The
Asteroussia Nappe
, composed of high-grade metamorphic rocks yielding cooling ages around 75 Ma, is present in Crete and in the Cycladic islands of Syros, Nikouria, Denoussa and Keros. It is interpreted as the remnants of a Pelagonian basement nappe, eroded in Miocene times. In the external or outer belt it has been thrust on to the unmetamorphosed Pindos Nappe but in the Cyclades it rests on the Cycladic Blueschist unit.
The three metamorphic belts of the Hellenides: a review and a kinematic interpretation
Authors: Papanikolaou Dimitrios J. 
Published: April 2008

Summary
New results obtained in the three metamorphic belts of the Hellenides suggest that each belt has a different structure, geotectonic setting and evolution. The external metamorphic belt of Peloponnesus-Crete has probably resulted from nappe movement in the vicinity of an evolving island arc system. The blueschists occurring within this external belt are allochthonous and have been transported with other nappes over the external carbonate platform of the Pre-Apulian-Plattenkalk-Ionian-Tripolitza-Almyropotamos Units. This implies that there was only one true blueschist domain, initiated in the Cycladic area during ?Early Eocene. The kinematic interpretation is based on the distinction of a- and b-structures and on the nature of the shear zones between the different domains, especially that between the metamorphic Hellenides below and the non-metamorphic Hellenides above. The existence of the probably Lower Palaeozoic meta-sedimentary sequence of Kastoria in the northern Pelagonian zone indicates that the overlying, ophiolite-bearing Almopias unit has been derived from within the Hercynian domain. The Kastoria sedimentary sequence, the ophiolites of Vertiskos and the carbonate platform of Pangeon are considered to be most likely elements of a probable Hercynian orogeny.
Tertiary to Quaternary evolution of volcanism in the Aegean region
Authors: Fytikas M. , Innocenti F. , Manetti P. , Peccerillo A. , Mazzuoli R. , Villari L. 
Published: April 2008

SummaryWidespread orogenic volcanic activity has continued in the Aegean area from the Oligocene to present. Two main phases of activity are recognized. One developed in the North Aegean area from Oligocene to Middle Miocene times and a second started in the Pliocene, building the active South Aegean volcanic arc. Between these two phases, Upper Miocene to Quaternary volcanism of variable petrogenetic affinity occurred to a limited extent, essentially on the margins of the Aegean microplate.The products erupted during the Oligo-Miocene phase consist mainly of calc-alkaline and shoshonitic intermediate lavas and pyroclastics with minor acidic and basic rock types. The volcanic activity started in the northernmost part of the North Aegean area with mostly calc-alkaline intermediate and acidic volcanics. The volcanism shifted successively southwards becoming progressively enriched in potassium. This evolution is interpreted as being related to an increase in the dip of the Benioff zone under the Eurasian plate, resulting from a reduction in the plate convergence rate after continental collision.The volcanic products of the active south Aegean arc are mainly andesites with minor basalts and rhyolites which display the chemical character typical of calc-alkaline series erupted on thin continental margins. The South Aegean arc is believed to be the surface expression of active subduction of the African plate.Scattered Upper Miocene to Quaternary activity is interpreted as occurring in zones of tensional strain along the borders of the Aegean microplate.
Graben formation and associated seismicity in the Gulf of Korinth (Central Greece)
Authors: Myrianthis M. L. 
Published: April 2008

Summary
Extensional stresses in the central Aegean region reflect isostatic subsidence and uplift of brittle crustal blocks in response to crustal thinning. Block re-arrangements along active normal faults are probably the general cause for the generation of earthquakes. Reflection seismic data for the Gulf of Korinth graben is given here. It is concluded that the main factor controlling earthquakes is continuing uplift of the Peloponnesos block relative to the Gulf of Korinth graben.
The Western Arabia rift system
Authors: Quennell A. M. 
Published: April 2008

Summary
The origin of the Dead Sea rift has generally been linked with that of the Red Sea, the widening of the latter involving left-lateral strike-slip on the rift. Its extension through the Lebanese fold belt has been denied by some because of the absence of linear and displacement continuity. Others, however, have been unable to see any other choice in spite of these difficulties, but a satisfying structural model has not yet been offered. The present author claims that the rift system is a transform plate boundary between the Arabian plate and the Sinai-Levant plate, but without uniformity along its length.
It is here suggested that during the Lower Miocene the Arabian planation surface, which before the opening of the Red Sea was the probable extension of the African mid-Tertiary surface, was ruptured by the first phase of movement on the west Arabian transform fault system, which probably reflected a geosuture zone in the continental plate and was originally a simple arc. The Arabian plate moved northward with the opening of the Red Sea and the closing of the Bitlis ocean, leaving behind the Sinai-Levantine part of the African Plate. Oblique compression on the northern Syria unstable platform across the East Anatolian transform fault caused dextral distortion on the Lebanon-Palmyra zone to create mountain ranges of two styles and a translation in the alignment of the rift segment. This inhibited further uniform strike-slip movement on the rift and displacement on the Yammouné fault was subsequently predominantly vertical. The movements on the rifts to the south and the north thus became independent. There was Arabian plate lithosphere consumption north-east of the Houlé depression to accommodate the second phase of rift movement. On the basis of this explanation, the vexed question of transmission of left lateral strike-slip across the Lebanon segment does not arise.
Clastic diagenesis
Authors: Burley S. D. , Kantorowicz J. D. , Waugh B. 
Published: April 2008

Summary
Diagenesis is the sum of those processes by which originally sedimentary clastic assemblages attempt to reach equilibrium with their environments. The subject has rapidly evolved, over the last 20 years, after several decades of routine petrographical analysis, to become a discipline of sophisticated analytical geochemistry. This progression may be traced through the evolution of depositional facies models, the growth of theoretical geochemistry, and the development and application of quantitative analytical techniques. Consequently, the study of diagenesis today involves the integration of data gathered from a range of interrelated disciplines.
The publication in recent years of such integrated studies, particularly from the Texas Gulf Coast of the U.S.A., has led to a number of wide ranging models being established. These models allow an interpretation of the sequence of authigenic minerals in terms of their relationship to the depositional environment or surface chemistry (eogenesis), burial or subsurface conditions (mesogenesis) and weathering or reexposure to surface conditions (telogenesis).
More specifically, once the pre-depositional controls on diagenesis have been established, it is possible to relate the inferred eogenetic mineral assemblages to exact geochemical sedimentary environments. Sedimentary mineral assemblages chemically are characterized by relative instability and so tend to interact with interstitial pore waters. Thus, in non-marine environments, mineral authigenesis may reflect arid-oxidizing, or wet-reducing pore-water conditions, and in the marine environment, either oxidizing or reducing pore waters.
During mesogenesis different processes become important. Elevated temperatures add energy to the reacting system, lowering reaction barriers and increasing reaction rates. Furthermore, widespread pore fluid migration at depth, transporting large quantities of solute, is likely to impart major, regional diagenetic changes to sediments. That there is a remarkable degree of consistency in deep burial settings suggests that depth-related processes conform to a predictable pattern.
Additional geochemical instability is introduced into the diagenetic system during uplift and exposure to the telogenetic realm. Minerals formed during burial, at elevated temperatures and pressures, and from concentrated formation waters, may become unstable in oxidizing, meteoric waters.
Diagenetic research requires the complete dissection of sedimentary rocks and, subsequently, the quantitative chemical and mineralogical analysis of their individual components. Such an approach to diagenetic studies, when related to an assessment of their paragenesis, may eventually lead to a predictive, integrated model for the evolution of sedimentary clastic rocks.
Role of clastic sedimentology in the exploration and production of oil and gas in the North Sea
Authors: Johnson H. D. , Stewart D. J. 
Published: April 2008

Summary
The nature and quality of clastic reservoir rocks is the result of a complex interplay of tectonic setting, provenance, depositional environment and diagenesis. In particular, it is now well established that the reconstruction of depositional environments in clastic successions provides the optimum framework for describing and predicting reservoir development and reservoir quality distribution on both regional (exploration) and field (production) scales.
This review, in the context of the 21st anniversary of the British Sedimentological Research Group (BSRG), expands the above-mentioned theme in relation to the development of depositional models of each of the major oil- and/or gas-bearing clastic reservoirs in the U.K. sector of the North Sea, which has been the subject of a surge in geological interest following the first gas discoveries approximately 21 years ago.
Each major reservoir interval is used to illustrate specific themes, with emphasis placed on how the application of depositional models has contributed to a better understanding of the exploration for, and the production from, the following reservoirs: (i) Permian aeolian and fluvial sands (Rotliegendes Sandstones, southern North Sea), (ii) Jurassic fluvial, deltaic and marginal marine sands (Lower Jurassic Statfjord Formation and Middle Jurassic Brent Group, northern North Sea), (iii) Jurassic shallow marine and deeper marine (mass flow) sands and conglomerates (Upper Jurassic Fulmar/Piper-type sands and Brae/Magnus-type deposits; central and northern North Sea), and (iv) Tertiary deep marine, turbidite fan deposits (Palaeocene and Eocene sands, central and northern North Sea).
Metamorphism and magmatism during the Himalayan collision
Authors: Le Fort Patrick 
Published: April 2008

Summary
Collision of India and Eurasia occurred sometime during the Eocene following the Tethyan oceanic subduction. Post-collision metamorphic and magmatic events in Tibet and in the Himalaya are reviewed. Metamorphism is limited to the Himalaya where at least four zones may be recognized which from S to N are, (i) high-pressure metamorphism produced before, but emplaced, during obduction, (ii) a belt of low-grade metamorphism produced during the first nappe emplacement, (iii) the pre-granitic Barrovian metamorphism of the High Himalaya, and (iv) the inverted metamorphism induced during shearing along the Main Central Thrust. Magmatism in the Himalayan domain resulted in two parallel belts of granitoids that were generated in the same way but differ in their mode of emplacement. In Tibet, magmatism spread over most of the domain following collision and magma is probably present now at shallow depths. The relationship between crustal thickening, uplift and magma generation is not clear. The difference in metamorphic and magmatic characteristics in the two domains may help to trace palaeocollision zones.
Collision tectonics in the Western Alps
Authors: Ricou L. E. , Siddans A. W. B. 
Published: April 2008

Summary
This paper gives a brief review of some different models that have been proposed to account for the tectonic development of the Western Alps, emphasizing the field evidence which indicates the major role played by strike-slip tectonics. Sketch maps of the tectonic evolution since Cretaceous times are presented which interpret the Alps as a strike-slip collision belt followed by ‘hypercollision’ on the western edge of the northward-moving Adriatic Promontary. There was early local collision along N-S strike-slip faults, while intervening E-W trending basins remained open. General collision is considered to have been completed by Eocene times when the pre-existing basins disappeared and the previously stretched lithosphere was restored to normal thickness. The following hypercollision first continued along the same N-S strike-slip displacements, with thickening of the lithosphere and migration of flysch basins. Later Oligocene hypercollision evolved into mainly westward displacement, limited by E-W strike-slip zones, dextral in the N and sinistral in the S. Strike-slip collision and hypercollision are considered as sufficient to explain the particuliarities of the tectonic development of the Western Alps, with associated metamorphisms and basinal evolution, since 80 Ma.
The Distribution of Porosity in Zechstein Carbonates
Authors: Clark D. N. 
Published: April 2008

Summary
Zechstein carbonates form important gas reservoirs in Germany and the Netherlands and in at least one commercial field in the U.K. southern North Sea but elsewhere they are largely unexploited. The carbonates occur in four separate units and all are known to contain potential reservoir rocks. Distribution of porosity is controlled either by a combination of depositional facies and diagenesis or by the occurrence of collapse breccias. Intragranular porosity resulting from early leaching predominates in shallow-marine grainstones and intercrystalline porosity caused by late leaching occurs in deepermarine carbonate mudstones. Using a knowledge of facies distribution, it is possible to predict where these potential reservoirs might occur and as facies distribution can be related to the overall thickness of each carbonate unit, it is also possible to make tentative predictions of porosity distribution from isopach maps. Collapse breccias, however, are not related to any particular facies and potential reservoirs resulting from this process are most likely to be found around structural highs that became exposed at various times since, the Zechstein.
Metamorphism and crustal rheology—implications for the structural development of the continental crust during prograde metamorphism
Authors: Weber K. 
Published: April 2008

SummaryBased on its metamorphic development it can be argued that the orogenic continental crust during prograde metamorphism consists of three layers of contrasting bulk rheology: a lower layer of granulite-facies rocks able to carry relatively high flow stresses; a middle layer of migmatites and amphibolite-facies rocks of very low mechanical strength and an upper layer of low-grade and very low-grade metamorphic rocks, the so-called ‘brittle’ crust in the geophysical sense with higher yield strength possibly increasing upward. There are presumably main décollement horizons between the lithospheric mantle and lower crust, in the roof of a granulite-facies lower crust and along the boundary between the middle and upper crust, giving rise to large-scale displacements and the formation of nappe structures of different metamorphic rocks. Granulite-facies rocks of the lower crust will tend to form large-scale folds which pierce the overlying crust during increasing amplification. Further crustal shortening may produce granulite-facies nappes from strongly amplified large-scale fold structures leading to inverse metamorphism which is generally accompanied by granulite-facies nappe complexes.
The South India-Sri Lanka high-grade terrain as a possible deep-crust section
Authors: Newton R. C. , Hansen E.C. 
Published: April 2008

SummaryPrecambrian granulite-facies terrains are regarded as possible models for the deep crust. In the South India-Sri Lanka late Archaean-early Proterozoic terrain, there is a regional gradation from greenschist and amphibolite facies south through an orthopyroxene isograd to the Granulite Massifs of S. India and of Sri Lanka. The metamorphic gradation is unusually complete and continuous and may represent a partial Archaean crustal profile. Large areas of low-grade grey gneiss may have been formed after charnockite in a retrogression event or may have somehow escaped late Archaean granulite facies metamorphism.Palaeopressures indicate an increase from 5 kbar to more than 7 kbar in the Transition Zone, though various fault-bounded blocks in the high-grade massif area show different pressure ranges, indicative of different amounts of uplift. The highest pressures of above 9 kbar are for Rb- and U-depleted intermediate charnockites. Undepleted acid charnockites show pressures of 6.5–7.5 kbar, and supracrustal sequences show still lower pressures. The supracrustal-rich Central Highlands of Sri Lanka show pressures of 6 to 7.5 kbar, and most or all rocks are undepleted in Rb. Associated temperatures of all the Massif rocks are in the range 700°–800°C.This grossly-stratified Archaean crustal section is only the upper half of a thickened crust: there is no indication of what lies below the deepest exposed section, and no compelling reason that depleted intermediate charnockite continues down to the Mohorovicic Discontinuity. Another possibility is deep thrust-bounded repetitions of the section which is exposed at the surface.
Early rift sedimentation in the Turkana basin, northern Kenya
Authors: Williamson P. G. , Savage R. J. G. 
Published: April 2008

SummaryThe ‘Turkana Grit’ deposits of northern Kenya are a thick sequence of immature arkosic sediments of pre-Plio-Pleistocene age. Originally described by Murray-Hughes in the 1930s, these sediments have been variously considered as of either Mesozoic or Miocene age by subsequent authors. These extremely immature, tectonically controlled sediments clearly reflect intense local deformation; their age is of considerable interest, as they clearly signal the onset of significant tectonic activity in the central sector of the East African rift. A regional survey of the Turkana Grits as currently known, coupled with recently available information from the hitherto unmapped Kajong area in the SE Turkana basin, clearly indicates that these sediments represent two distinct episodes of local tectonism and deposition. On the basis of available radiometric and biostratigraphic evidence, the earlier of these episodes appears to be of Cenomanian-basal Palaeocene age, while the later episode dates from the mid-Miocene. These observations suggest that significant tectonic activity in East Africa commenced in the late Mesozoic rather than—as generally assumed—in the mid-Cenozoic. The earliest (late Mesozoic) episode of clastic deposition in the Kajong area was initially controlled by a set of major E-W trending transform faults; these deposits are primarily preserved in associated fault-wedge basins. The documentation of a major transform element in the Kajong area has important implications for the early development of the African Rift as a whole. We suggest here the possibility that the enigmatic distribution of the late Mesozoic rift sediments—which are restricted to the southern sector of the Western Rift and the northern sector of the Eastern Rift—reflects the fact that the original late Mesozoic rift consisted of a single graben. The southern and northern portions of this graben have been subsequently displaced by a major E-W trending dextral transform system, extending some 500 km from the SE Turkana basin to the present northern termination of the Western Rift on the Uganda-Sudan border.