bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rb-Sr geochronology of the Bitlis Massif, Avnik (Bingöl) area, S.E. Turkey
Authors: Helvaci Cahit , Griffin William L. 
Published: April 2008

Summary
In the Avnik area, felsic metavolcanics are interbedded with banded and massive apatite-rich iron ores, and are intruded by the Avnik and Yayla granitoids. These rocks are unconformably overlain with depositional contact by micaschists and (?) Permian marbles, which were folded and metamorphosed during the Alpine orogeny. The metavolcanics and the granitoids are extensively feldspathized and silicified.
The Yala granite gives a poorly defined Rb-Sr age of 347 ± 52 Ma (IR = 0.7217 ± 80) but the albitized Avnik body gives only a scatter of data suggesting an age of 250–425 Ma. Feldspathized metavolcanics from a 100-metre section define an age of 91 ± 9 Ma. One sample of the Avnik granitoid gives an amphibole-rock-feldspar age of 71 ± 28 Ma and another gives a biotite-rock age of 41 ± 1 Ma; a micaschist gives a chlorite-muscovite age of 38 ± 2 Ma.

An isochron age of 454 ± 13 Ma (IR = 0.7105) for metavolcanics in the Cacas area can be extracted from the data of Yilmaz
et al.
(1981). We interpret this as the age of eruption, and suggest a similar age for the Avnik metavolcanics. Our 90 Ma (Eoalpine) data on these metavolcanics requires metamorphic resetting of whole-rock Rb-Sr systems over tens of metres, and probably records the time of pervasive feldspathization and silicification. The data for the Yala granite are interpreted as the age of intrusion; the high IR indicates an origin by anatexis of older crust. The late-Alpine mineral ages probably reflect recrystallization during folding and thrusting.
Basic and ultrabasic rocks from the Ankara Melange, Turkey
Authors: Tankut Ayla 
Published: April 2008

Summary
The Ankara Melange consists from west to east of three major parallel belts: (i) metamorphic melange, (ii) limestone melange and (iii) ophiolitic melange. A Triassic age for the metamoprhic and limestone belts and a Cretaceous age for the ophiolitic belt have been suggested by several authors (Norman 1973, Çapan 1981, Yilmazer 1981).
The ophiolitic belt includes lenses of serpentinite, occasionally unserpentinized peridotite, gabbro, pillow lava, agglomerate and basic dykes. The ultrabasic rocks show tectonic fabrics and the gabbros cumulate textures. The metamorphic and limestone melange belts contain basic volcanic rocks only as blocks, clasts and dykes, and are devoid of ultrabasic rocks.
Petrochemical studies reveal that the volcanic rocks of the ophiolitic and metamorphic belts are very similar in mineralogical and chemical composition, including representatives of both the tholeiitic and calc-alkaline series.
The presence of almost all the members of an ophiolite suite may indicate an ocean floor origin for the ultrabasic and basic rocks of the ophiolitic melange belt, and the occurrence of calc-alkaline rocks in both belts may suggest at least one phase of island arc volcanism. These rocks may represent several phases of rifting and island arc generation during the evolution of the Mediterranean Tethyan domain.
High pressure metamorphism in Ghiaros Island, Cyclades, Greece
Authors: Katagas Christos G. 
Published: April 2008

Summary
The various rock types encountered in Ghiaros island have suffered an episode of progressive regional metamorphism which produced high pressure low temperature assemblages with Na-pyroxene and glaucophane. Later in their metamorphic history the rocks were affected by retrograde metamorphism. Glaucophane crystals became continuously zoned and sodic pyroxene crystals developed a patchy composition. Zoning in amphiboles extends from glaucophanitic cores through intermediate Na-Ca winchite compositions to actinolite rims. The compositional differences observed between the various patches in individual pyroxene crystals are interpreted to reflect contrasting P-T conditions which drive the continuous reaction jadeitic pyroxene + quartz ⇋ albite + acmitic pyroxene + quartz, to progressively less jadeite-rich pyroxene.
Tectonic setting of the Mesozoic Pindos basin of the Peloponnese, Greece
Authors: Pe-Piper Georgia , Piper David J. W. 
Published: April 2008

Summary
The Pindos isopic zone of western Greece comprises a 1 km thick sequence of Mesozoic and early Tertiary deep water sediments now preserved in a series of imbricate thrust slices in the Central Hellenic Nappe. This paper examines the question as to whether the basement to the Pindos Zone was oceanic or continental crust.
Mid-Triassic volcanic rocks around the margins of the Pindos basin suggest initial development as a back-arc basin by subduction of Mesogea beneath Apulia. There is then no volcanic record through the Late Triassic, but tuffs are widespread in the Jurassic. Rare lavas and pyroclastics of Late Jurassic or earliest Cretaceous age are shown by new chemical analyses to be mid-ocean ridge type basalts associated with calc-alkaline andesites and dacites characteristic of subduction. This close juxtaposition of such rock types suggests a back-arc basin setting. Thus at least part of the Pindos Zone appears to have been underlain by oceanic crust. This Late Jurassic oceanic basin is probably tectonically unrelated to the earlier mid-Triassic basin.
A half-ridge transform model for the Hellenic-Dinaric ophiolites
Authors: Smith A. G. , Spray J. G. 
Published: April 2008

Summary
We speculate that the similarity of the E and W ophiolite belts in Greece, Albania and Yugoslavia can be plausibly explained by the disruption of a once continuous subduction-linked marginal basin and adjacent continent by a Middle to Late Jurassic sinistral transcurrent fault along the E edge of the Pelagonian Drina-Ivanjica Zones. The fault may itself have been linked to the Jurassic opening of the central Atlantic. This model is supported by the age relations between igneous crystallization of the ophiolites and the timing of metamorphic sole formation. Present isotopic dating, together with simple thermal calculations, suggests that the ages of these events differed by at most 10 Ma. Together with lateral variations in the ophiolites themselves and their soles, this apparent similarity of ages is most readily accounted for by the overthrusting at the ridge crest of one half of a narrow marginal basin by the other half.
Palaeomagnetic evidence of Miocene and Pliocene rotational deformations of the Aegean Area
Authors: Kissel Catherine , Laj Carlo , Jamet Marc 
Published: April 2008

Summary
Palaeomagnetic measurements have been made on the Mio-Pliocene sedimentary series along the external Hellenic Arc as well as in the Oligocene to Middle Miocene Ionian flysch of northwestern Greece.
The results show that the central and eastern parts of the arc (Crete and Rhodes) have not undergone significant rotation since the Tortonian-Messinian stage. On the other hand, the northwestern part has undergone a clockwise rotation which, in the Ionian islands, has begun 5 Ma ago and has proceeded since then at roughly 5 degrees/Ma. We suggest that the beginning of this rotation is related to the Lower Pliocene compressive phase which most probably initiated the tectonic activity of the present day Aegean Arc.
No rotational deformation occurred between 5 and 12 Ma, but the results from 16 sites in Epirus and Akarnania sampled in Ionian flysch sections indicate that another clockwise rotation, of the order of 30 degrees, occurred between 30 and 12 Ma ago.
These Oligo-Miocene and Plio-Quaternary episodes of rotational deformation may be related to the Oligo-Miocene and Plio-Quaternary arc-related volcanic activity in the Aegean Sea.
Subsidence history of the North Aegean Trough
Authors: Pichon Xavier Le , Lybéris Nicolas , Alvarez Francis 
Published: April 2008

Summary
The subsidence of the North-Aegean trough is examined quantitatively using available geophysical data, the emphasis being on thermal and gravity computations. The two dimensional thermal calculations incorporate conduction as well as convection with lateral variations, the effect of the sedimentary cover being treated as a perturbation. The data can be explained within the framework of the homogeneous stretching model with a maximum stretching factor of about 3.5. The stretched lithosphere has a very small flexural parameter so that local compensation prevails. The effect of conduction is sufficiently important to prevent large-scale melting of the mantle, thus making the transition to oceanic accretion rather improbable. The narrowness of the zone of extreme stretching, compared to the widths now observed on most continental margins where comparable stretching values have been observed, may be due to the presence of an earlier deep lithospheric fault which enabled the strain to concentrate along its path.
Deep-sea clastics: where are we and where are we going?
Authors: Stow D. A. V. 
Published: April 2008

Summary
The transition from our belief in a deep calm ocean to a recognition that deep-sea clastics other than pelagic clays exist in the oceans, spanned nearly a century. In the last three decades enormous strides have been made in understanding these sediments and their deposition. There is a continuum of processes that transfer material from shallow to deep water and rework sediments within the deep sea. These include: (1) resedimentation processes, ranging from giant rockfalls and slumps to low-density turbidity currents; (2) normal bottom currents; and (3) pelagic settling through the water column. More than fifty distinct facies have been described from the deep sea and these can be interpreted in terms of depositional process via ten standard facies models for resedimented, normal bottom current and pelagic sediments. Environmental models can be constructed for: (1) normal, faulted, carbonate and ridge-flank slope-aprons; (2) radial, elongate and fan-delta submarine fans; and (3) under- and oversupplied basin-plains. These show the generalized horizontal and vertical distribution of facies and the chief morphological elements in each of the three major deep-sea settings. Sedimentary, tectonic and sea-level changes are the main groups of factors that control deep-sea sedimentation within these separate environments. Part of the interest in deep-sea clastics stems from their demonstrable economic importance for the generation and entrapment of hydrocarbons. Many areas of deep-sea sedimentology remain to be investigated and earlier models to be refined; these advances will depend significantly on improvements in our methodology.
Diagenesis of shallow-marine carbonates
Authors: Dickson J. A. D. 
Published: April 2008

Summary

The utility of carbonate petrography in solving diagenetic problems is often underrated. Staining and cathodoluminescence are complementary to petrographic studies; their application is compared. Interpretation of carbonate trace element concentration through the distribution coefficient, as illustrated by Sr
2+
, was oversimplified in the 1970s and often tied to repeated recrystallization episodes in meteoric waters. Kinetic factors complicate the use of the distribution coefficient in calcite. δ
13
C values from carbonates help in identifying the source of carbon but δ
18
O values are difficult to interpret due to control by temperature as well as the isotopic composition of the precipitation fluids. Data on the composition of sedimentary waters, geothermometry and geobarometry of buried sedimentary rocks can be provided by fluid inclusion studies but interpretation has often been over-optimistic, because insufficient account has been taken of the difficulties which exist with fluid inclusion work.

Near-surface, carbonate diagenesis is well understood through field studies of Recent and Pleistocene sediments. Research effort in the future, it is predicted, will concentrate on burial diagenesis because it is the least understood diagenetic realm. The large variations in temperature, pressure and time which distinguish burial from near-surface environments are exemplified by the burial history of the Carboniferous Limestone of South Wales.
Carbonate facies analysis in the exploration for hydrocarbons: a case-study from the Cretaceous of the Middle East
Authors: Burchette T. P. , Britton S. R. 
Published: April 2008

Summary

This paper presents a case-study of an investigation into a Middle Eastern carbonate reservoir, the Mishrif Formation of eastern offshore Abu Dhabi, and its lateral equivalent, the Shilaif Member of the Salabikh Formation. The work represents a major part of a sedimentological/seismic stratigraphic study, the aims of which were to model reservoir facies and geometry, and to predict areas of best reservoir potential. The study is based on interpretation of cores, cuttings and wireline logs from 30 wells distributed over some 200 km
2
.

The Mishrif of the study area forms part of an extensive Cenomanian carbonate platform. It represents deposition on a local leeward (i.e. shelfward) margin which prograded westwards into an intrashelf (the Shilaif) basin. Six lithofacies associations were recognized in the Shilaif and Mishrif, representing lateral and vertical transitions from silt-grade basinal pelagic-foraminiferal wackestones (I), through a platform margin sequence (II) which coarsens upwards to coarse rudist/ostreiid shoal (III) and biostromal (IV) packstones and grainstones. Shoal and biostromal facies are overlain in the east by bedded back-shoal packstones (V) and nodular micritic platform-lagoonal (VI) sequences. A significant unconformity exists at the top of the Mishrif.
Three stages of diagenesis have been recognized in Mishrif limestones: early (micritization, submarine cementation); unconformity-related (extensive leaching, freshwater cementation); and burial diagenesis (stylolitization, fracturing, burial cementation, neomorphism). Leaching and burial cementation were the most important diagenetic events and significantly overprint the generally simple variations in reservoir character due to original depositional facies distribution. Most favourable porosity and permeability values occur in coarse-grained shoal, upper-slope, and biostromal sediments (upper II, III, IV) where exposed and leached at the final platform margin, whereas to the east, in the platform interior, these facies have suffered severe burial cementation. The slight regional eastwards dip of the Mishrif reservoir, its westwards pinch-out into basinal facies, and the presence of a proved top-seal fulfil the requirements for stratigraphic trapping of hydrocarbons, with the best reservoir facies advantageously situated. A well drilled to test this play encountered the predicted sequence but found only residual oil. This may be due to imperfect lateral or bottom reservoir sealing.
Intracontinental subduction, crust-mantle décollement and crustal-stacking wedge in the Himalayas and other collision belts
Authors: Mattauer M. 
Published: April 2008

Summary

The Himalayas exhibit the large-scale geometric characteristics of deformation in a classic collision belt. After the continental collision, which occurred 40 Ma ago, the continuous northward motion of India resulted in an important northward subduction of continental lithosphere. The two main consequences of this subduction were (i) building of a
crustal-stacking wedge
with an average thickness of 70 km; the continental crust was thickened mainly by extensive low-angle (20–30°) overthrusting (crustal duplex) with the width of the wedge increasing with time by southward migration; and (ii)
crust-mantle décollement
along which the relatively rigid lithospheric mantle slid below the more deformable continental crust during crustal thickening. At the same time, farther N, large-scale strike-slip faulting gave way to lateral E-W crustal extension. Such a model may be applied to other collision belts such as the Alps, the Canadian Cordillera and the Variscan Belt of Europe.
Some thermal and tectonic models for crustal melting in continental collision zones
Authors: England Philip C. , Thompson Alan 
Published: April 2008

Summary

Calculated geotherms and the pressure-temperature-time (
PTt
) paths followed by rocks during continental thickening episodes are interpreted with respect to the volumes of crustal melt that may be formed during orogenesis in the absence of heat transfer by mantle-derived melts. Particular attention is paid to a tectonic history that may characterize wider orogenic belts, such as are represented most obviously at present by Tibet. This comprises a period of crustal thickening, followed by an interval during which the crust is thinned by extensional strain, rather than by erosion. The amount of crustal melt produced depends strongly on the amount of water (free, and in hydrated minerals) contained in the lower crust. However, we may expect several (1–5) km
3
of crustal melt per km
2
of orogen if a crust of around average continental surface heat flux (60–70 mW m
−2
) is thickened by a factor of two. For the lower surface heat flux, partial melting of a sedimentary source would produce predominantly S-type granites and, with slightly higher geotherms, doubling of crustal thickness can lead to partial melting of amphibolites to give I-type granitic activity and calc-alkaline volcanism.
On the mechanics of the collision between India and Asia
Authors: Tapponnier P. , Peltzer G. , Armijo R. 
Published: April 2008

SummaryField studies of active faulting in S Tibet indicate that Quaternary extension has been taking place at a rate of ≃1 cm yr−1in a direction of ≃ 100°. This implies that underthrusting in the Himalayas now absorbs less than half of the total convergence between rigid India and Asia, the rest being taken up primarily by strike-slip faulting N of the collision belt.En échelonright-lateral, strike-slip faults in S Tibet now allow this corresponding eastward displacement of the plateau with respect to India. The reproducible pattern of faulting obtained from plane-strain indentation experiments on unilaterally confined blocks of plasticine suggests that this extrusion process has occurred during most of the collision history. The Tertiary geological record in SE Asia corroborates a polyphase extrusion model, with displacements in excess of 1000–1500 km, in which India has successively pushed Sundaland, then Tibet and S China towards the ESE. Most of the Middle Tertiary movements may have occurred along the then left-lateral Red River-Ailao Shan Fault Zone, together with the opening of most of the eastern S China Sea. Regional geology, stratigraphy and deformation observed in Yunnan are consistent with this inference, as well as the timing, geometry and rates of sea-floor spreading in the S China Sea. Fast spreading (5 cm yr−1) in that sea implies that the Tibetan highlands formed mostly after 17 Ma BP. Sideways movements can also account for the existence of large, conjugate but asymmetric, Tertiary strike-slip faults within Sundaland and the formation of Middle Tertiary pull-apart and rift basins on the Sunda Shelf. Changing directions of opening are predicted in the Mergui and Andaman Basins and the lowlands of Burma, as well as large right-lateral displacements along the Shan Scarp. Most of Sundaland probably lay initially in a frontal position with respect to impinging India and the Shan Plateau may have been a Middle Tertiary analogue of the present Tibetan Plateau. In contrast with dominant overthrusting in the Himalayas, Tertiary strike-slip faulting, with more subordinate folding and thrusting, appears to have been important along and N of the Zangbo Suture. This difference must be accounted for in all models of formation of the Tibet Plateau. The surface of the indentation mark, left by the impaction of India onto the presumably simpler Early Tertiary margin of Asia (> 6 million km2), implies that mountain building and strike-slip faulting have absorbed, perhaps alternately, roughly equal amounts of collisional shortening. Since analogous interplays of extrusion and thickening probably govern the evolution of most collision zones, the Tertiary tectonics of Asia may be the best guide to unravel the interactions between Palaeozoic and Precambrian plates, for which sea-floor spreading constraints are unattainable.
Some aspects of collision tectonics in the Indus Suture Zone, Ladakh
Authors: Colchen M. , Mascle G. , Van Haver T. 
Published: April 2008

SummaryIn the Indus Suture Zone, five tectonic zones can be recognized, which are from N to S: (i) the Ladakh or Trans-Himalayan Batholith (103−25 Ma) and the Dras Volcanoplutonic Group; (ii) the Indus Detrital Group with marine formations of Aptian to Ilerdian age (103−45 Ma) and continental formations of Oligocene- ?Miocene age; (iii) the Nindam (Cretaceous) and Lamayuru (Ladinian-Dogger) Flysch Nappes; (iv) the Zanskar Structural Nappe Complex (Upper Palaeozoic-Ilerdian) resting on a metamorphic ‘basement’; and (v) the Spongtang-Photaksar Ophiolitic Nappe. Several folding phases affect these tectonic units; analyses of mesoscopic and microscopic structures show a polyphase tectonic history with a syn-metamorphic cleavage (S1or S1–2, striking 090–120°) which is axial planar to recumbent folds associated with a N-S mineral lineation, a fracture cleavage (striking 120°) which varies in dip and this is cut by a still later steeply dipping fracture cleavage striking 030–040°. The tectonic contacts, the kinematics, relative chronology and structural evolution are discussed. We propose that the structural sequence results from continuous N-S compression occurring during collision.
Collision tectonics in the NW Himalayas
Authors: Coward Michael P. , Rex David C. , Asif Khan M. , Windley Brian F. , Broughton Roger D. , Luff Ian W. , Petterson Michael G. , Pudsey Carol J. 
Published: April 2008

Summary
West Himalayan tectonics involve the collision of microplates between the Indian and Asian Plates. The Kohistan Complex consists largely of tightly folded basic volcanics and sediments generated as Late Jurassic to Late Cretaceous island arcs. These were intruded by post-folding Mid-Cretaceous — Eocene plutonics produced from continued subduction of the Indian Plate after closure of a suture between Kohistan and the Karakorum. The Himalayan structures show major thrust sheets and the Kohistan Arc is essentially a crustal ‘pop-up’ with southward-upright and northward-verging structures developed above a thick ductile decoupling zone (the Indus Suture), which can be traced for >100 km beneath Kohistan on large reentrants. This pop-up formed by a two stage process, closure of the Northern Suture followed by closure of the southern Indus Suture. Granitic rocks of the Kohistan-Ladakh Batholith (dated at ≅ 100-40 Ma) post-date most of the structures related to the Northern Suture but were deformed and carried southwards on shear structures related to the Indus Suture. Post-collisional deformation carried this Kohistan Complex on deep decoupling zones over the Indian Plate on a series of imbricated gneiss sheets, the thrusts climbing up section in the movement direction so that in the far S some override their own molasse debris. Folds above these deep decoupling zones deformed their overlying thrust sheets into large antiforms—i.e. the Nanga Parbat and Hazara Syntaxes. The Nanga Parbat Syntaxis probably formed due to a shear couple near a branch line where one of the main Himalayan thrusts joined the Indus Suture beneath Kohistan. Crustal delamination, to produce the imbricated gneiss sheets, could not account for all the displacement of India into Asia, suggested by palaeomagnetic data. There must also have been lateral displacement as demonstrated by the large oblique-slip shear zone in the Hunza Valley, N of Kohistan.