bluuebunny/crossref_metadata_2025 huggingface dataset:
Sr-Nd isotope and chemical evidence that the Ballantrae ‘ophiolite’, SW Scotland, is polygenetic
Authors: Thirlwall M. J. , Bluck B. J.
Published: April 2008

Sr-Nd isotope and major- and trace-element analyses, including REE, are presented for a suite of basaltic lavas from the Ballantrae complex, SW Scotland. The chemistry of the lavas is discussed with reference to ‘spider’ diagrams, using normalization of incompatible element abundances to those estimated in the primordial earth, rather than conventional element-element plots. These diagrams facilitate assessment of element mobility during alteration, and some samples are shown to have close to original igneous concentrations of the mobile elements Rb, K, Sr etc. Clinopyroxene-phyric basalts from Games Loup and Mains Hill have chemical affinities with modern intra-oceanic arc volcanics, and their acid-leached augite phenocrysts have more radiogenic Sr than the mantle array, defined using clinopyroxene separates from Ordovician oceanic basalts from the Southern Uplands. Basalts from Pinbain, Bennane Head and Downan Point are in contrast typical ocean-island tholeiites in both chemistry and Nd-Sr isotopes. At least four independent volcanic sequences can be recognized from the chemical data: these do not form a continuous 5 km thick sequence but rather represent tectonically juxtaposed units generated in very different environments. The ‘ophiolite’ can not therefore be regarded as a single entity, produced in a single tectonic environment. Sm-Nd mineral ages have been determined for samples from Games Loup, Mains Hill and Downan Point in an attempt to provide a chronology for the development of the different units, but ages obtained are indistinguishable from the zircon age reported by Bluck
et al.
(1980) for a Ballantrae trondhjemite. Evaluation of the significance of the complex to Caledonian plate models will only be possible with more precise age determinations on the different members of the complex.
Petrology and mineralization of the Sakhakot-Qila ophiolite, Pakistan
Authors: Ahmed Zulfiqar , Hall A.
Published: April 2008

The Sakhakot-Qila complex is an incomplete, dominantly ultramafic ophiolite. The geology, rock and mineral compositions, and occurrences of chromite ore deposits are described. The predominant ultramafic rock types are harzburgite, wehrlite and dunite, and dykes of pyroxenite. The mafic components of the complex are a metamorphosed gabbro and dykes of metadolerite. Postmagmatic alteration is common, and several kinds of rodingite are abundant. They formed by addition of Ca, Al, Cl and Cu and removal of Si, Mg, Fe and Ni from pre-existing rocks, and contain corundum, clintonite and Al-depleted ferritchromite in addition to the more usual minerals such as grossular and vesuvianite. The rodingites appear to have developed independently of serpentinization, probably with the participation of seawater. There are numerous small chromite deposits, varying widely in texture and composition. There is a strong reciprocal Cr-Al variation and lesser Mg-Fe
2+
variation, partly related to the stratigraphic position of the chromite. Nickeliferous opaque mineral assemblages are well developed.
An ophiolite suite in Fiji?
Authors: Colley H.
Published: April 2008

In SW Viti Levu, Fiji rocks formerly described as part of an island-arc succession are regarded as possibly representing the upper part of an ophiolite suite. Foraminiferal oozes, cherts, red clays, Fe-Mn metalliferous sediments, fine-grained volcanic turbidites, and reworked polymict lapillistones can be equated with Layer 1 of the oceanic lithosphere. Underlying these sediments are pillow basalt sequences and deeper structural levels in the suite may be represented by a tonalite body intruded by a dyke swarm. The chemistry of the igneous rock is ambiguous showing affinities with both arc tholeiites and oceanic tholeiites.

Emplacement of the ophiolite suite against arc rocks has occurred along arcuate thrusts with the ophiolitic rocks, principally Layer-1 sediments, being folded along the leading edge of the thrusted block.

The Oligocene-Lower Miocene age of the ophiolite suite suggests it is an obducted portion of the South Fiji Basin, however, emplacement from this direction requires a complex tectonic model involving up to 180° anticlockwise rotation of Viti Levu. This is supported to some degree by palaeomagnetic data.
Emplacement of ophiolite in Papua New Guinea
Authors: Davies H. L. , Jaques A. L.
Published: April 2008

The major ophiolite complexes of Papua New Guinea lie on the northeastern margin of the Australian craton and are flanked, externally, by Palaeogene volcanic arcs. The ophiolites are segments of oceanic lithosphere which occupied the forearc zone prior to arc-continent collision. In the case of the easternmost ophiolite, the Papuan ultramafic belt, there is evidence that emplacement was preceded by development of a secondary rupture in the down-going plate, at some distance from the subduction zone, and was followed by extension, buoyant emergence, and reversed movement of the ophiolite. The westernmost ophiolite (April ultramafics) has more complex structure and probably developed as a series of thrust sheets in a subduction system; the thrust sheets were subjected to renewed deformation and thrusting by continued convergence after arc-continent collision.
The role of Landsat Multispectral Scanner (MSS) imagery in mapping the Oman ophiolite
Authors: Rothery D. A.
Published: April 2008

The Oman ophiolite is well exposed, and all the major structural and lithological features are visible on suitably processed Landsat images. Visual interpretation of such images provides a synoptic view of the Oman mountains which is in many aspects as useful as inspection of published maps at scales of 1:500,000 to 1:100,000. This study is an investigation of image processing for semi-automated lithological mapping. The differences between the visible and near-infrared multispectral signatures of ophiolite rock types in the Oman mountains have been shown by
in-situ
measurements to be considerably less than for fresh, particulate samples of similar rocks, in the Landsat MSS spectral bands. The muting of their reflectance spectra is due to a combination of alteration and weathering, and this hinders discrimination between rock types on MSS images. The problem is further compounded by topographically induced variations in brightness (BV), and the presence of shadows containing no valid data. The first-order topographic effects can be partly overcome by the generation of intensity-normalized bands. By using training sets of less than 2 km
2
from within an area of less than 2000 km
2
; a thematic map can be produced which shows the approximate distribution of major rock types over virtually an entire MSS scene (30,000 km
2
). The problem of misclassification due to topography and other effects can be largely side-stepped by the use of a suitable post-classification filter.
Erosion, transport and deposition of fine-grained marine sediments
Authors: McCave I. N.
Published: April 2008

Fine-grained marine sediments are cohesive but their degree of cohesion is not simply determined by grain size. Cohesion controls erodibility, and water content, mineralogy, cation exchange capacity, salinity of interstitial and eroding fluid, organic mucus content and Bingham yield strength are all parameters relating to cohesion that have been proposed. No unique relation to erodibility has emerged and for erosion of slowly deposited sediment, modified by biota, it seems that measures of surface properties such as aggregate strength should be more relevant than bulk properties such as yield strength. The latter may be more appropriate for rapidly deposited estuarine muds. Once eroded, suspended sediment is subject to flocculation and biological aggregation, which alters size and settling velocity distributions, thereby controlling distribution in the flow and rate of deposition. Disaggregation may also occur through turbulent straining of particles, but in most marine situations this will permit stable particles over 1 mm in diameter, though under higher shear close to the bed the upper limit may be 100–200 μm. For deposition where
τ
0
< 0.1 Pa the maximum stable aggregate size is probably ≥ 100 μm. Deposition of fine sediment on smooth beds probably occurs by entrapment in, and settling through, the viscous sublayer. On rough beds particles are trapped in the interstices between roughness elements. We have only a rough idea of critical deposition conditions but can give a fairly good estimate of deposition rate in given conditions. The longer term net deposition rate as measured by radiometric methods over weeks to months probably owes as much to frequency of erosion as to frequency and rate of deposition and is not yet well predicted from fluid and sediment parameters.
Methods and observations in the study of deep-sea suspended particulate matter
Authors: Eittreim S. L.
Published: April 2008

Forward light scattering and light transmission are the two best techniques, coupled with direct sampling, to measure the spatial and temporal variations in suspended sediments of the ocean. It has been difficult to calibrate these methods with satisfactory precision in terms of suspended particulate matter (SPM) concentration; the best precision is approximately ± 10 μgL
−1
. The poor resolution is due to the many unknown factors in the relationship between optical effects and concentration of SPM, in addition to errors in direct sampling of SPM concentration. Because typical deep-sea concentrations are in the range of 5 to 50 μgL
−1
, extreme care must be taken to avoid contamination by airborne dust and salt filter residues. As a short-lived tracer of water motions, SPM is useful because its settling rates range from about 10
−1
to 10
2
m day
−1
, rates giving half-life time-scales roughly comparable to time-scales of deep-water eddy motions and boundary layer events. More needs to be learned, however, to define these settling rates with some confidence. Much progress has recently been made in studies with sediment traps which directly measure the downward vertical flux of particles. The work with sediment traps is prompted by the realization that large fast-settling aggregates and faecal pellets are important in the delivery of material to the bottom, and due to their short residence time and hence low concentrations in the water column, they are not sampled adequately by water bottles.
Grain-size characteristics of turbidites
Authors: Kranck Kate
Published: April 2008

Detailed sampling using a very small sample size and grain-size analysis with a Coulter Counter of three fine-grained turbidites enabled a distinction to be made between the well-sorted single-grain Stokes’-deposited and unsorted ‘whole suspension’ floc-deposited grain-size populations. The results indicate that each turbidite is a continuous sequence deposited from the same source suspension. Particles settle to the bottom as flocculated masses. Initially flocs are broken up by near-bottom shear forces and only the coarsest silt and sand remains on the bed. The remaining mud forms a temporary mud suspension near the bottom which reflocculates and intermittently deposits at some critical concentration producing mud interlayers between silt laminae. Decrease in current velocity eventually allows simultaneous deposition of single grains and flocs with the latter becoming progressively more abundant resulting in formation of graded beds. Eventually, all deposition occurs in the form of mud flocs and a massive sediment results. The study essentially confirms the basic mechanism of the fine-grained turbidite deposition model proposed by Stow & Bowen (1978).
Sedimentary sequences on the north-west Mediterranean margin during the Late Quaternary: a dynamic interpretation
Authors: Monaco A. , Mear Y.
Published: April 2008

The methods we have used in this study of pelitic sediments are based on the concept of fine-grained particle populations, and include: the counting of grains in the >40 μm fraction (lithoclastic, biogenic, authigenic and aggregates); grain-size analysis of the pelitic fraction expressed as a bi-logarithmic frequency curve giving the ‘evolution index’ of three granulometric classes—silt, clayey-silt and clay; mineralogical indices based on the ratios between particles with different hydrodynamic behaviour—quartz, mica-illite and smectite; and geochemistry of Mn, Cu and Fe to characterize the biogenic nature of the sediment.

A succession of turbiditic (heterogeneous population), hemipelagic and pelagic (homogeneous population) sediments were examined from the NW Mediterranean margin. We identify three main sequences in the Pleistocene to Recent succession, each of which may be interrupted by episodic events: (1) a palaeoclimatic sequence (∼ 5 m thick) of Pleistocene to Holocene age, marking the end of deep channelized lobe construction on the Rhone deep-sea fan; (2) a dynamic sequence (repeated intervals of 20–50 cm thick) of Würmian and Holocene age respectively, in the lower fan and in the central basin; and (3) a uniform sequence (without granulometric, mineralogical or geochemical grading) corresponding to a ponded unit filled with reworked sediments (contourites) and slumps.
Sedimentary processes on the west Hellenic Arc margin
Authors: Got H.
Published: April 2008

High-resolution seismic surveys across the western Hellenic Arc show that the Plio-Quaternary cover is highly discontinuous along most of the margin. The slope displays a series of basins separated by ridges generally devoid of sediment. Sedimentological analyses of the recent sediment permit the origin and processes of sedimentation to be defined. The sediments provided by a specific area on land are successively trapped, released by the slope basins and transferred via channels and canyons towards the deeper trench basins. Several main provinces can be distinguished. Each of them includes one or more slope basins and trenches without either lateral connection or the mixing of sediment inputs. The diversity and complexity of sedimentary structures, the granulometric characters, and the variability in rates of sedimentation argue for the prevalence of mass gravity processes. The transfer of sediment from the upper slope basins to the outer trench is effected by an alternation of short periods of giant mudflows and regular but slight reworking between slope basins. This cascade-feeding process, characteristic of the Hellenic subduction margin, does not appear to prevent terrigenous material from reaching the deep trenches. We compare this briefly with sedimentation on passive margins in the western Mediterranean Basin.
Open-ocean, off-bank transport of fine-grained carbonate sediment in the Northern Bahamas
Authors: Heath K. C. , Mullins H. T.
Published: April 2008

The contribution of fine-grained, bank-derived versus pelagic-derived carbonate sediment in periplatform oozes has been evaluated by means of a detailed, quantitative carbonate mineralogy study of 35 surface sediment samples from north of Little Bahama Bank. Our data indicate that large volumes of aragonite and magnesian calcite are being exported along the open-ocean margin of Little Bahama Bank during the present high-stand of sea-level. Percentages of mud-size aragonite + magnesian calcite display a strong negative correlation (r = −0.912) with distance from the edge of the bank, whereas percentages of calcite show a strong positive correlation (+0.914). Immediately adjacent to the northern, windward margin of Little Bahama Bank, 86% of the fine-grained carbonates are bank-derived. This value decreases in a linear fashion to 50% bank-derived muds at a distance of 50 km from Little Bahama Bank. Direct seaward projection of our data suggests that fine-grained, metastable, shallow-water carbonate sediments are transported laterally at least 120 km from open-ocean bank margins. This has important implications for the global budget of CO
2
, the diagenetic potential of periplatform oozes, and the growth potential of carbonate slopes.
Depositional model for calcilutites: Scaglia Rossa limestones, Umbro-Marchean Apennines
Authors: Stow D. A. V. , Rainey S. C. R. , Angell G. , Wezel F. C. , Savelli D.
Published: April 2008

The calcilutites of the mid-Cretaceous to uppermost Eocene Scaglia Rossa Formation in Italy have previously been interpreted as a continuous sequence of slowly deposited pelagic limestones. However, regional considerations of thickness, sedimentation rates and facies distribution, together with detailed analysis of composition, texture and sedimentary structures suggest that turbidity currents have played an important part in the deposition of, at least, the middle (Maastrichtian) member. Turbiditic calcilutites are very fine-grained and massive, whereas the pelagites are coarser-grained, mottled and bioturbated. There is, however, a continuous gradation of facies and processes between these two end-members, that we believe is applicable to many other modern and ancient deep-water carbonate systems. The common overlap of turbiditic and pelagic processes in fine-grained ‘pure’ carbonates arises partly from their relative lack of flocculation compared with muddier sediments.
Basin model for hemipelagic sedimentation in a tectonically active continental margin: Santa Barbara Basin, California Continental Borderland
Authors: Thornton S. E.
Published: April 2008

A variety of Holocene sedimentary processes and depositional environments in Santa Barbara Basin may serve as a model for terrigenously-dominated hemipelagic basins devoid of submarine canyons: (1) suspensate transport; (2) turbidity current transport; (3) mass movement on the lower slope; (4) the imprint of current patterns on both fine-grained suspended load and bedload transport; and (5) preservation of resulting stratigraphy on the deep basin floor by anoxic water conditions which result in annual varves plus turbidites and flood suspensate layers. Silt patterns define a river-derived suspensate pathway driven by surface currents, which coincides with the distribution of 1969 flood layer sediments. A ‘hemipelagic core’ is present on the western portion of the basin floor, where terrigenous and biogenous input are most balanced. Mass-movement covers 13% of the basin-slopes and is typified by mud-flows interpreted from seismic profiles and characteristic sedimentary structures in cores. A generalized vertical sequence of sedimentary structures derived from radiograph analysis may serve as a model for mud-flow deposits. Turbidites and flood suspensate layers have been traced from the middle slope to the basin floor on a canyonless slope and their distribution is controlled by surface current delivery of suspensates. Vertical sequences of turbidite sedimentary structures in grey-layer turbidites provide support for Piper’s (1978) model for fine-grained turbidites. Varve counting in the central basin yields a sedimentation rate of 173 cm/1000 years and frequencies of 59 years for all grey-layers (flood + turbidite), and 120 years for grey-layer turbidites, which probably reflect roughly 50 and 100 year frequency floods. Fine-grained sedimentary processes in hemipelagic settings with high sedimentation rates and low slope gradients may be typified by: (1) mud-flows on the lower slope; (2) unchannelized turbidity currents and flood layer deposition controlled by surface currents and proximity to source; (3) laminated sediments in the deep basin if oxygen levels are sufficiently low, or preservation of only flood suspensate layers and turbidites if bottom waters are not anoxic; (4) sediment pathways definable from texture and coarse fraction analysis.
Hemipelagic deposits in a Miocene basin, California: toward a model of lithologic variation and sequence
Authors: Isaacs C. M.
Published: April 2008

Deep marine basins began to form along the continental margin of central California in late Oligocene time as a result of the initiation of a translational plate boundary. Deposition of transgressive shallow-marine sand (Vaqueros Formation) was followed by deposition of a thick (> 500 m) massive clay unit (Rincon Shale). Rapid subsidence (> 2000 m) coincident with rising sea-level created sediment-starved basins by late early Miocene time (
c.
18 Ma).

Typical of many of these borderland basins was the Santa Barbara basin, located at least 50 km from the Miocene strandline. In this basin, between late early and latest Miocene time (18–5.5 Ma), was deposited a heterogeneous sequence of highly biogenous sediment (Monterey Formation) consisting of mixed diatomaceous, foraminiferal-coccolithic, and terrigenous debris generally rich in organic matter (mean 8%). Overlying latest Miocene and Pliocene sediments (Sisquoc Formation) contain increasingly abundant clay debris.

The Miocene biogenous sequence reflects hemipelagic sedimentation from highly productive coastal waters during an extended period of generally low terrigenous influx. Accumulation of terrigenous debris decreased markedly in the early Miocene (from 11 to 1 g/cm
2
·10
3
yr) and was low throughout the middle Miocene, increasing somewhat at about 8 Ma and markedly after 5.5 Ma; this pattern is partly related to global sea-level changes but also resulted from high rates of subsidence and tectonic events. Biogenous silica accumulation peaked (mean 2.5 g/cm
2
·10
3
yr) in the late early Miocene (18–15 Ma) and again in the late Miocene and early Pliocene (8–3.5 Ma) and was 5 to 25 times slower in the interval 15–11 Ma; these variations are thought to reflect primarily variations in the intensity of upwelling and associated production of diatoms. Accumulation rates of biogenous calcite gradually declined from a late early Miocene peak through the early late Miocene and virtually ceased in latest Miocene (8–5.5 Ma), probably due to dissolution.

Massive stratification indicates that bottom waters were oxygenated until latest early Miocene time (
c.
16 Ma), when expansion of the oxygen-minimum zone or tectonic formation of a sill within the oxygen-minimum zone produced marked lowering of oxygen levels resulting in the dominance of laminated stratification between 16 and 5.5 Ma. Abundance of organic matter is closely associated with the abundance of clay and of calcite but is inversely correlated with silica content. Organic matter is also about twice as abundant in massive or discontinuously laminated beds (indicating good to moderate oxygenation) than in associated beds with varve-like lamination (indicating minimal oxygenation). These relations indicate that grain-size outweighed the influence of low-oxygen bottom waters in preserving organic matter.
Fabric of muds and shales: an overview
Authors: Moon C. F. , Hurst C. W.
Published: April 2008

This contribution essentially constitutes an attempt to update a previous review of clay sediment microstructure written over a decade ago. Recent developments in this field are considered and a scheme has been developed in which the fabric of argillaceous sediments is traced from its inception during sedimentation and its subsequent modification at and below the depositional interface. It is held throughout that the primary control in the determination of clay fabric is the chemical environment that prevails during and after the deposition of the sediment. Consideration of the evidence from a variety of sources suggests that fissility in mudrocks is the result of an anisotropic microfabric in which clay aggregates are preferentially aligned. This microstructure is thought to result from the dispersing action of organic compounds common in certain sedimentary environments; a brief discussion of these compounds is included. Other factors are also taken into account which have been offered as the cause of differing mudrock fabrics.
Marginal basins of the SW Pacific and the preservation and recognition of their ancient analogues: a review
Authors: Leitch E. C.
Published: April 2008

Marginal basins of the SW Pacific floored by oceanic lithosphere comprise those formed by sea-floor spreading immediately behind active magmatic arcs (back-arc basins) and those created by the rifting of continental crust without obvious connection to an arc system (small ocean basins). The basins opened rapidly, range greatly in shape and size, and show diverse relations to sediment sources. Thick sediment piles mainly accumulated adjacent to emergent continental margins or active arcs, with thin sequences of pelagic sediments, ash, and fine grained turbidites on basin floors. Facies are commonly asymmetrically distributed. Basaltic magmatic activity, mild deformation and submarine erosion affect both types of basins. Ancient back-arc basins should be identifiable on the basis of their temporal relations to magmatic arcs and the volcanic influence in their sedimentary sequence, but distinguishing between small and major ocean basins is often difficult. Narrow marginal basins may collapse following accumulation of a thick sediment pile, but most basins close by subduction. Similarities are recognized between the present-day SW Pacific and the formative stage of the North American Cordillera. The Late Mesozoic palaeogeography of the Western Alps resembles the complex of small ocean basins and continental fragments west of the Norfolk Ridge, and the Ordovician palaeogeography of central Newfoundland bears close resemblance to the assemblage of back-arc basins, remnant arcs and active arc east from the Norfolk Basin.
Hydrothermal and volcaniclastic sedimentation on the Tonga-Kermadec Ridge and in its adjacent marginal basins
Authors: Cronan D. S. , Hodkinson R. , Moorby S. A. , Glasby G. P. , Knedler K. , Thomson J.
Published: April 2008

Analyses of over 180 sediment samples from the Tonga-Kermadec Ridge and adjacent marginal basins demonstrate volcaniclastic, biogenic, lithogenous and hydrothermal influences on them. The volcaniclastic component decreases westwards from the Tonga-Kermadec Ridge where volcanism is presently active. Biogenic components are predominant in sediment throughout most of the region, but a significant lithogenous component becomes apparent in the S, in the vicinity of New Zealand. Hydrothermal influences have been detected in two areas: (i) on the Tonga-Kermadec Ridge where Mn oxide crusts represent the end member of a hydrothermal fractionation sequence, earlier members of which may occur beneath the sea-floor; and (ii) in the Lau Basin where Fe and Mn are widely dispersed in the sediments and where sulphide deposits may occur in the immediate vicinity of hydrothermal vents.
Volcano-tectonic evolution of Fiji and adjoining marginal basins
Authors: Colley H. , Hindle W. H.
Published: April 2008

From the Eocene to the Middle Miocene, Fiji was part of a N-facing Outer Melanesia arc system, stretching from Papua New Guinea to Tonga, and was dominated by tholeiitic arc volcanism. Oligocene back-arc spreading to the S of Fiji led to the formation of the Minerva Plain (South Fiji Basin). Reorganization of the plate boundaries in Outer Melanesia during the Middle Miocene fractured the simple arc system and caused polarity reversal in arc segments W of Fiji. Fiji, the major yield point in the break-up, experienced a compressive event followed by progressive isolation from a subduction regime as arc segments were rotated away from the region. This led to asthenospheric melting with a decreasing subduction component, and a consequent change in Fiji volcanism from arc andesites and tholeiites to alkalic ocean island basalts. During the Upper Miocene to Lower Pliocene, rotation of the Vanuatu arc segment caused opening of the Fiji Plateau marginal basin. This was accompanied by widespread, chemically diverse volcanism in Fiji, in which contamination of rising magma by pre-existing crust may have been an important process. The most recent phase of arc rotation resulted in opening of the Lau Basin between Fiji and Tonga, and effected the final divorce of Fiji from a subduction influence with commencement of ocean island basalt volcanism in the Middle Pliocene.
Spreading-subsidence and generation of ensialic marginal basins: an example from the early Cretaceous of central Chile
Authors: Åberg G. , Aguirre L. , Levi B. , Nyström J. O. , Aguirre L.
Published: April 2008

During the early Cretaceous, intracontinental rifting, spreading and subsidence led to the formation of an ensialic trough in central Chile. This trough is interpreted as an aborted marginal basin since no oceanic crust was generated. However, mantle-derived material, represented by flood basalts with low initial
87
Sr/
86
Sr ratio and evolved geochemical characteristics, was deposited in the basin. Rb-Sr dating shows that the lavas suffered burial metamorphism shortly after their extrusion. The flood basalts were extruded during an episode of slow oceanic spreading in the Pacific, and subsequent folding, granitoid intrusion and uplift are correlated with an episode of fast oceanic spreading and plate subduction. The intracontinental events related to these two episodes constitute a cycle, repetition of which might account for the geological evolution of central Chile during the Mesozoic and the Palaeogene.

The western margin of South America, during the Cretaceous, was characterized by basin formation with eruption of mantle-derived basalts. Some basins developed into marginal basins proper, with generation of oceanic crust, others were aborted. The type of basin was determined by the rate and volume of upwelling mantle material, and continental crust thickness. Rapid upwelling gave rise to back-arc spreading and marginal basins with primitive basalts and ocean-floor metamorphism or burial metamorphism reflecting steep thermal gradients. Slow upwelling produced ensialic basins with evolved basalts affected by burial metamorphism with less steep thermal gradients, as in central Chile during the early Cretaceous.
Proximal volcaniclastic sedimentation in a Cretaceous back-arc basin, northern Antarctic Peninsula
Authors: Farquharson G. W. , Hamer R. D. , Ineson J. R.
Published: April 2008

During Cretaceous times, the northern Antarctic Peninsula was the site of an active ensialic magmatic arc. Volcanism was dominated by pyroclastic eruptions with rare lava flows. Marine conglomerates and sandstones formed a volcaniclastic apron along the eastern margin of the arc and represent the proximal deposits of an extensive back-arc basin. Volcanogenic material, redeposited by turbidity currents and other sediment gravity flows, forms an important part of the proximal basin fill. Air-fall tuffs and eruption-induced sediment flows form a small but significant part of the succession and large exotic slideblocks of Jurassic sediment are a distinctive feature of the Lower Cretaceous strata on James Ross Island. Aeromagnetic data and regional geology indicate that the arc-back-arc basin boundarv was fault-controlled. Sedimentation within the basin was strongly influenced by both the steep, unstable nature of the faulted arc flanks and the coeval volcanism.
Mud-magma interactions in the Dunnage Mélange, Newfoundland
Authors: Lorenz B. E.
Published: April 2008

The Dunnage Mélange, part of back-arc basinal assemblages in north central Newfoundland, is host to a suite of dacitic to rhyolitic intrusions. Intrusion occurred during the late stages of mélange formation. Lobate, pillowed, corrugated and pahoehoe-like igneous contact surfaces, complex interlayering of host mudstone and dacite, and the occurrence of peperite, indicate that the magma intruded unconsolidated mud and the adjacent sediment was fluidized. This evidence for shallow emplacement of the magma is inconsistent with the existence of a tectonic overburden during mélange formation, and supports an olistostromal origin for the Dunnage Mélange.
Introduction: aspects of the geological evolution of the Eastern Mediterranean
Authors: Robertson A. H. F. , Dixon J. E.
Published: April 2008

We review extensively the evidence and arguments bearing on the nature of Palaeotethys in relation to the age of formation, location and multiplicity of Neotethyan strands and their fate. We conclude that Palaeotethys did not die early but was only finally subducted northwards in the Tertiary along the Vardar-Intra Pontide-East Anatolian suture. Neotethyan strands must have opened into it at all times. The Adriatic promontory remained attached to Africa but rotated anti-clockwise in the mid-Tertiary. The Pontides are considered to be Eurasian and the Cimmerides are viewed as a ‘collage terrain’ formed along an oblique-convergence margin. The south Aegean, Greek and Turkish microcontinental blocks were rifted-off Gondwana in the Triassic but formation of braided Neotethyan oceanic crustal strands was essentially confined to mid-Jurassic in the Hellenides and to the Cretaceous in Turkey.

We propose a new model of ophiolite genesis by asymmetrical spreading-ridge collapse in an attempt to explain both arc-like ophiolite chemistry prior to major volcanic arc edifice construction, and the synchroneity of sub-ophiolite metamorphic sole formation with Atlantic opening phases.

Jurassic dispersal of Hellenide blocks had little effect in the unexpanded Turkish mosaic, but northwards Cretaceous opening of Tauride Neotethyan strands caused oblique collision deformation in the Pelagonian zone and unresolvable complexity in the Aegean. Late Cretaceous and Tertiary arc-volcanism was related in part to continuing Palaeotethyan subduction, and in part to Neotethyan destruction initiated after ridge-collapse. Diachronous collisions ensued from the Late Cretaceous onwards but significant oceanic tracts must have persisted at least to Mid-Tertiary to satisfy Africa-Eurasia separation constraints determined from Atlantic anomaly fitting. Our favoured plate evolutionary model is presented in 7 sketch-maps.
Facies and tectonic setting of the Upper Carboniferous rocks of Northwestern Turkey
Authors: Kerey I. E.
Published: April 2008

In various outcrops along the Black Sea coast, a thick Dinantian shallow water carbonate succession is overlain by four formations of highest Visean to highest Westphalian age. The succession changes upwards from generally shallow marine, to non-marine giving way in the upper levels of flood-plain, lacustrine and fluviatile deposits. All the present outcrops are believed to have belonged to a single large basin in which material was derived from a former Black Sea continent to the north. In contrast to some recent suggestions, the basin was located near the southern edge of the Laurasian plate.

A model is discussed in which uplift of the area north of the modern North Anatolian Fault is attributed to dextral strike-slip faulting in approximately E-W and NNE-SSW directions. Although evidence of strike-slip faulting has been obscured by later tectonic events, in general the North Turkish Upper Carboniferous sedimentary rocks were deformed during a late Hercynian phase of large-scale wrench-faulting caused by oblique collision of the Gondwana and Laurasian plates after Carboniferous time, which may have also displayed the former Black Sea continent eastwards.
Stratigraphic evidence of Variscan and early Alpine tectonics in Southern Turkey
Authors: Demirtaşh E.
Published: April 2008

The area between Silifke and Anamur forms the central Taurus belt, in which four geotectonic zones are recognized: the Southern, Intermediate and Northern zones and the Hadim nappe. Stratigraphic successions in each zone show considerable differences from the early Palaeozoic onwards. For example, a Late Triassic non-marine clastic basin dominated the Intermediate and Northern zones, while a marine carbonate basin existed to the south.

The contrasting stratigraphic development of each of the three main tectonic zones studied, particularly reflects Early Permian (Variscan) and Late Triassic (‘Eocimmerian’) orogenic events. Overthrusting of the Northern zones over the Intermediate zone took place before a Late Permian transgression. Later overthrusting of the Intermediate zone over the Southern zone occurred during Middle to Upper Triassic times producing large-scale nappes. The Variscan and early Alpine structures were then unconformably overlain by platform carbonates of Early Jurassic to Late Cretaceous age. Middle and late Alpine movements are also observed in the Intermediate and Northern zones. Ophiolitic melange was thrust over Late Cretaceous-Palaeocene flysch and olistostrome while platformal carbonate deposition continued in the Southern zone, confirming that an ocean basin existed to the north. Orogenic movements ended before the Early Miocene, followed by block-faulting to produce graben (e.g. Çavuşlar basin). Formations of Middle and Late Miocene age unconformably overlying all other units are post-tectonic.
Tectonic and sedimentary history of the NE African margin (Egypt—Libya)
Authors: Sestini G.
Published: April 2008

The present structure and thickness variations of the Mesozoic-Cenozoic sediments of the Mediterranean coastal belt of Egypt (west of Sinai) and of North Cyrenaica, indicate that the African Plate at this latitude was part of an unstable zone characterized by a number of fault-controlled marginal depocentres. Triassic to Middle Cretaceous facies are almost everywhere shallow marine, nearshore, deltaic and continental, with no indication of a paleobasin margin. Deeper-water sedimentation occurred in parts, from Senonian onwards. During the Campanian-Eocene phase of plate collision, overthrusting and folding, the African margin was raised in the north and depressed southwards, and mild folding was superimposed on the block structures. Widespread Oligo-Miocene faulting and differential vertical movements shifted the focus of deposition to the Nile Delta region and the Gulf of Suez, while transcurrent movements to NNE (Aqaba-Dead Sea faults) created local compression that magnified and skewed Eocene folds. It is concluded that the onshore coastal belt of NE Egypt-Cyrenaica belongs to a relatively southerly part of the African plate margin.
Emergence of Wadi Mujib (Central Jordan) during Lower Cenomanian time and its regional tectonic implications
Authors: Abed Abdulkader M.
Published: April 2008

Detailed sedimentological investigations of Wadi Mujib (Central Jordan), east of the Dead Sea, show that the regional contact of Lower Cretaceous fluviatile deposits on Upper Cretaceous carbonates ushered in a shallow marine environment all over Jordan. Later, an emergent area, in Wadi Mujib only, passes upwards and laterally eastwards into a supratidal environment, followed again by shallow marine conditions. The emergence is marked by a major eroisional unconformity with wadi deposits, caliche and karstification. Wadi Mujib is believed to have been an island during Lower Cenomanian time and is thought to be an example of vertical tectonics in the area prior to Tertiary rifting of the Dead Sea to the west.
Ophiolites and volcanic activity near the western edge of the Arabian plate
Authors: Delaloye Michel , Wagner Jean-Jacques
Published: April 2008

The geology of the Eastern Mediterranean is governed partly by the collision of the Arabian plate with the Anatolian block and partly by the Dead Sea Rift.

The oceanic elements which have been formed between these two blocks are still visible as obducted fragments represented amongst others by the two ophiolitic massifs of Hatay and Baër-Bassit.

The opening of the Atlantic ocean give rise, in the Eastern Mediterranean, to complex relative movements which can partly be resolved into a west to east shear and a south to north compression. The shear pre-dates the compression and took place between the Triassic and middle Cretaceous. It is responsible for the rifting and the volcanism in Syria, as well as the formation of a basin capable of producing ophiolites such as Hatay and Baër-Bassit.

The compressive phase began in the middle Cretaceous and resulted in the detachment and the emplacement of the ophiolites on the Arabian continental margin. The timing of this phase can be determined from the age of the Baër-Bassit amphibolitic sole. Traces of this compressive episode are seen as late as the Neogene.
The extension of the Ionian trough into southwestern Turkey
Authors: Poisson A.
Published: April 2008

During Mesozoic time the Ionian trough in Greece shows a relatively complex and distinctive geodynamic evolution compared to the adjacent platforms. A similar evolution is found in several series of the Western Taurides in Turkey. The existence of a Mesozoic intra-Tauric trough (previously named ‘Kizilca-Çorak göl trough’), is established and interpreted as an homologue of the Ionian trough.

This situation, external with respect to the Helleno-Tauric belt, is used as a basis for a reconstruction of the general evolution of the eastern part of the Aegean ‘curvature’ that seems to have been initiated during the mid-Miocene (after Langhian but prior to Tortonian). The recent (neotectonic) evolution of the arc started after the Tortonian, possibly as late as the Lower Pliocene.
Miocene clastic sedimentation related to the emplacement of the Lycian Nappes and the Antalya Complex, S.W. Turkey
Authors: Hayward A. B.
Published: April 2008

The western Tauride Mountains of S.W. Turkey comprise a central relatively autochthonous carbonate platform unit, the Tauride autochthon bordered by two allochthonous units, the Lycian Nappes to the west and the Antalya Complex to the east. Sequences of Miocene clastic sediments up to 1000 m thick that were derived from both the allochthons document the timing and direction of their emplacement onto the carbonate platform.

Along the western margin of the Miocene basin intial emplacement of the Lycian Nappes, from the northwest, in the Lower Miocene, was coupled with rapid subsidence of the previously stable carbonate platform. The resulting basin was ca 170 km across. Fan-deltas were derived from the leading edge of the nappes and passed basinwards into a series of small submarine fans. At the same time rapid uplift of the central parts of the carbonate-platform, along the margin of the basin opposite the nappe pile, led to a thick wedge of carbonate-derived clastics being shed northwestwards into the basin. Varying sedimentation rates and migrating facies belts in the overlying Middle and Upper Miocene basin-fill document the progressive emplacement of the Lycian Nappes ca 100 km from the northwest over the basin margin.

Along the eastern margin of the basin, palaeocurrent analysis and downslope facies-transitions in the Miocene sediments show that the Antalya Complex was emplaced from the east but only advanced a short distance beyond the eastern margin of the basin.

The Lycian Nappes and the Antalya Complex approached the basin from opposite directions and so their respective ophiolite units must have originated in separate ocean basins on either side of the Bey Daḡlari and the Susuz Daḡ carbonate platform.
Rb-Sr geochronology of the Bitlis Massif, Avnik (Bingöl) area, S.E. Turkey
Authors: Helvaci Cahit , Griffin William L.
Published: April 2008

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

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

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

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.