bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pliocene to Recent mud diapirism and related mud volcanoes in the Alboran Sea (Western Mediterranean)
Authors: Talukder A.R. , Comas M.C. , Soto J.I. 
Published: April 2008

Abstract
High resolution and multichannel seismic profiles depict the Pliocene to Recent evolution of the mud diapirism in the West Alboran Basin (WAB) and its relationship with the Miocene diapir province that occupies the WAB depocentre. During the early to middle Miocene period of basin extension (16 to 9 Ma), normal faulting triggered the diapirism from mobile overpressured shale containing olistostromes. Plio-Quaternary diapirism evolved as a second main stage of diapiric activity and developed throughout the subsequent contractive tectonic evolution of the basin (9 Ma to Holocene). Mud volcanoes, discovered to the south of the WAB, developed on the flank of Recent diapirs as a consequence of the rise of fluidized sediments through diapiric bodies and/or through fractures connecting with deeper diapirs. During the Pliocene to Recent, some diapirs stopped ascending, leading to the production of collapse structures on their tops due to lateral subsurface mud migration and/or fluid escape. Other cylindrical shaped diapirs continued rising and produced mud volcanoes on the sea floor. All the studied volcanoes seem to be currently inactive. Two major pulses of diapiric rise have been distinguished during the Pliocene to Recent contractive evolution of the basin.
The origin and processes of mud volcanism: new insights from Trinidad
Authors: Deville E. , Battani A. , Griboulard R. , Guerlais S. , Herbin J.P. , Houzay J.P. , Muller C. , Prinzhofer A. 
Published: April 2008

Abstract
The mobilized sediments expelled by the mud volcanoes in Trinidad correspond to liquefied argillaceous and sandy material in which the solid fraction is systematically polygenic and originating from several formations (Cretaceous to Pliocene). The mud is notably rich in thingrained quartz that is angular and frequently mechanically damaged related to shearing at great depth, during the sedimentary burial, and/or hydraulic fracturing processes. The exotic clasts are mostly fractured fragments from various formations of the tectonic wedge (mostly Palaeocene to Miocene). The origin of the solid particles of the mud is polygenic, including deep Cretaceous-Palaeogene horizons close to the décollement, and various materials from the stratigraphic pile pierced by the mud conduits. Moreover, the fluids expelled by the mud volcanoes have a deep origin and notably the gas phase is thermogenic methane generated probably below a depth of 5000 m. The effusions occur either during cycles of moderate effusion of mud and fluids (quiescence regime), or during catastrophic events responsible for the expulsion of huge volumes of mud, clasts and fluids (transient regime). Available subsurface data suggest that the deep structure of the mud volcanoes includes: (1) a focused deep conduit at depth in the zone of overpressure; (2) a mud chamber intruding the surrounding formations around and above the top of the abnormal pressure zone; and (3) a superficial outlet leading to the surface vents.
A new scaphognathine pterosaur from the Upper Jurassic Morrison Formation of Wyoming, USA
Authors: Carpenter Kenneth , Unwin David , Cloward Karen , Miles Clifford , Miles Clark 
Published: April 2008

Abstract

A partial rostrum of a new species of scaphognathine pterosaur, distinguished by a thin median crest along its dorsal margin and a deep embayment of the dental margin, is the first identifiable cranial fragment of a pterosaur from the Upper Jurassic Morrison Formation of western North America. By contrast with pterodactyloids, cranial crests are rare in “rhamphorhynchoids” and this is the first record of such a structure. The new material provides fresh insights into the taxonomic diversity of Late Jurassic North American pterosaurs. Based on the ratio of the skull and skeleton of
Scpahognathus
, the fragment represents an individual with an estimated wing span of 2.5 m. Consequently, this is one of the largest “rhamphorhynchoids” found so far. A mandible fragment from the same quarry has closely spaced alveoli, therefore cannot be referred to the rostrum. Its large size indicates another large “rhamphorhynchoid” in the Morrison Formation.
A new species of tapejarid pterosaur with soft-tissue head crest
Authors: Frey Eberhard , Martill David M. , Buchy Marie-Céline 
Published: April 2008

Abstract
Two specimens of a tapejarid pterosaur (Pterodactyloidea, Tapejaridae) are described as representing a new species. Both specimens show evidence for soft tissues preserved in association with a sagittal bony cranial crest. Both specimens are from the Nova Olinda Member Konservat Lagerstätte of the Crato Formation of the Araripe Basin, northeastern Brazil. They represent the second tapejarid species from this formation. Comparisons are made with other crested pterosaurs and comments on the utility and aerodynamics of pterosaurian head crests are made.
Ichnological evidence for quadrupedal locomotion in pterodactyloid pterosaurs: trackways from the Late Jurassic of Crayssac (southwestern France)
Authors: Mazin Jean-Michel , Billon-Bruyat Jean-Paul , Hantzpergue Pierre , Lafaurie Gérard 
Published: April 2008

Abstract

More than 30 well-preserved pterosaurian trackways have been excavated from the site of Crayssac (Lower Tithonian, southwestern France), along with hundreds of isolated imprints. The general pattern of pterosaurian trackways is described and corresponds to the morphology of the ichnogenus
Pteraichnus
Stokes 1957. A crocodilian origin for
Pteraichnus
is rejected. The morphology of the pes and manus prints is described and discussed, and exhibits a great dynamic variability. The three manus digit prints are confirmed as the marks of digits I–III, but the high angle of divarication may reflect strong digit abduction as well as a backward folding of the digit III. The manus gait-width is as much as 3 × the pes gait-width. The narrowest manus trackways corresponds to low-velocity walking in a semi-erect stance, whereas the widest manus trackways corresponds to higher velocity walking (perhaps even running), with a subhorizontal body.
The systematic problem of tetrapod ichnotaxa: the case study of
Pteraichnus
Stokes, 1957 (Pterosauria, Pterodactyloidea)
Authors: Billon-Bruyat Jean-Paul , Mazin Jean-Michel 
Published: April 2008

Abstract

This paper deals with the systematics of tetrapod ichnotaxa based on footprints. Beyond the consideration of the nomenclatural rules for ichnotaxa in the ICZN, this paper tries to determine how to establish an ichnotaxonomy that reflects the identity of the track-maker (the organism that has made the track) and how to include this ichnotaxonomy in the skeleton-based taxonomy. This leads to the establishment of several criteria, e.g. ichnospecies should be defined on the print morphology and the relative position of the prints (including the variability due to the track-maker’s dynamics), two ichnospecies should represent different species, the ichnospecies and ichnogenus levels are sufficient to discriminate the ichnotaxa and link them to the skeleton-based taxonomy. These ichnotaxonomical criteria are applied to a revision of the ichnogenus
Pteraichnus
Stokes 1957 (Pterosauria, Pterodactyloidea). Only the type species
Pteraichnus saltwashensis
is considered as valid, the pterosaurian origin of
Purbeckopus
is questioned and
Agadirichnus
is highlighted because it could be a senior synonym of
Pteraichnus
. The result of this drastic revision underlines the importance of the proposed ichnotaxonomical principles to avoid the unfounded proliferation of tetrapod ichnotaxa.
Petrology and evolution of the Brezovica ultramafic massif, Serbia
Authors: Bazylev B. A. , Karamata S. , Zakariadze G. S. 
Published: April 2008

Abstract
The tectonomagmatic history of ultramafic rocks in the Brezovica massif (Serbia) involved two separate magmatic stages, as inferred from the mineral and bulk-rock chemistry data and thermal history of the peridotites. In the first stage, a suite of spinel harzburgites was formed during partial melting of the mantle and segregation of tholeiitic melts. During the second stage, these spinel harzburgites were repeatedly heated and affected by percolating melt. This process formed dunites and refractory spinel harzburgies during melt-harzburgite interaction. The melt that segregated from these rocks during the second magmatic stage was of high-Ca boninite affinity. Both magmatic stages occurred in a suprasubduction geodynamic setting at a relatively deep level (25–28 km). In its present position the Brezovica massif has been interpreted as a relic of a suprasubduction-type oceanic lithosphere derived from the Central Dinaridic-Mirdita ocean basin. During eastward emplacement of the Brezovica massif over the underlying olistostrome, the ultramafic rocks were cooled to temperatures around 735 ± 20°C.
Structural and microstructural analysis of a palaeo-transform fault zone in the Neyriz ophiolite, Iran
Authors: Sarkarinejad Khalil 
Published: April 2008

Abstract

The Neyriz ophiolite in SW Iran includes a NNW-SSE-trending, steeply dipping oceanic palaeo-transform fault zone that consists mainly of deformed and sheared gabbros and peridotites. Mylonitic rocks within the fossil palaeo-transform fault display C-, C′- and S-band shear cleavages containing green hornblende- and feldspar-rich bands. Deformed hornblendemantled porphyroclasts have symmetrical tails or σ-type porphyroclast systems, which show clockwise stair-stepping rotation and oblique foliation with asymmetrical complex stripes and wings. These microstructures indicate dextral shearing on the palaeo-transform fault. The
c
-axes of hornblende in high-grade S-C mylonitic rocks exhibit strong lattice-preferred orientation (LPO) patterns with M- and G-type origin. These LPO patterns are asymmetrical with respect to the shear zone foliation and also indicate dextral shearing. The NNW-SSE trend of the palaeo-transform fault is perpendicular to the general NE strike of sheeted dykes and is parallel to the average harzburgite foliation. These observations suggest a noncoaxial shear orientation of mantle flow, which progressively rotated toward parallelism with the fossil fracture zone. This dextral transform fault is inferred to have connected ENE-trending oceanic spreading centre segments in a Neo-Tethyan ocean basin.
The nature of faulting and deformation in the Mineoka ophiolite, NW Pacific Rim
Authors: Takahashi Akiko , Ogawa Yujiro , Ohta Yasufumi , Hirano Naoto 
Published: April 2008

Abstract
A belt of disrupted ophiolitic rocks occurs on the Boso Peninsula (Japan), currently located north of the oblique subduction boundary between the Philippine Sea and North American Plates, under which the Pacific Plate has been subducting westwards. This ophiolitic belt (Mineoka Belt) is composed of mafic-ultramafic rocks together with Tertiary chert and limestone and island-arc volcaniclastic rocks. Our detailed structural studies in and around the basaltic rock bodies within the ophiolite reveal three phases of deformation. The first phase is further divided into three stages, all related to oblique normal faulting associated with extensional tectonics at or near a spreading axis. Fluid pressures appear to have fluctuated in association with faulting and veining during this phase. The second phase of deformation is characterized by thrust-related shear zones with a significant strike-slip component and is probably related to the final emplacement of the ophiolite by oblique subduction-obduction processes. The third and final phase of deformation affected not only the ophiolite but also later terrigenous and island-arc pyroclastic rocks. This deformation involved large-scale transpressional dextral slip on forearc sliver faults, which are still active today.
Oxygen isotope and chemical studies on the origin of large plagiogranite bodies in northern Oman, and their relationship to the overlying massive sulphide deposits
Authors: Stakes Debra S. , Taylor Hugh P. 
Published: April 2008

Abstract
The extraordinarily well-preserved and well-exposed Semail ophiolite of northern Oman hosts several large plagiogranite intrusions in proximity to economic copper sulphide deposits of the Lasail mining district. A progression of isotopic, chemical and mineralogical transformations observed within the plagiogranites and high-level gabbros (HLG), and a comparison of these effects with those in the lowermost dykes of the immediately overlying sheeted dyke complex (SDC) tracks the evolution of hydrothermal fluids and the alteration of overlying dykes and pillow lavas during discharge of these fluids on the sea floor. The largest hydrothermal alteration aureoles, and the greatest extent of metamorphic veins and metasomatic replacement features, are found adjacent to the largest high-level plagiogranite bodies, beneath and adjacent to the major ore bodies in northern Oman. The ubiquitous presence of metamorphic actinolitic hornblende, sodic plagioclase, epidote and titanite in metabasalts within the high-temperature alteration zones points to the most likely mineralogical and structural controls on the development and evolution of the hydrothermal fluids. Depleted Cu contents of the adjacent crustal rocks and Cu enrichments above the plagiogranite intrusions demonstrate the redistribution of heavy metals adjacent to the complexes. Field relationships implicate the formation of both the epidosites and plagiogranites in the genesis of the ore deposits. An important process inferred from the field and geochemical data is the assimilation of previously hydrothermally altered basaltic and gabbroic country rocks by stoping into the magma chambers developed near the SDC-gabbro horizon in the ophiolite. We suggest that this process of combined assimilation-fractional crystallization, together with replenishment and recharge by injection and quenching of basaltic magma ‘pillows’ into these plagiogranite magma chambers (i.e. RAFC), plays a major role in the development of these composite intrusions.
Bioalteration recorded in ophiolitic pillow lavas
Authors: Furnes H. , Muehlenbachs K. 
Published: April 2008

Abstract

In this paper we summarize the present knowledge on bioalteration of basaltic glass from pillow lava rims of former oceanic crust, based on the study of four ophiolite complexes. These complexes range in age from Late Cretaceous to Mid-Proterozoic, and their metamorphic grades vary from non-metamorphosed to low greenschist- to low amphibolite-facies metamorphism. In the non-metamorphosed volcanic part of ophiolite complexes, in which undevitrified glass is still present in pillow lava rims and/or hyaloclastites, biogenerated textures are common. These textures (termed granular and tubular) are similar to those found in volcanic glass of recent to old (170 Ma)
in situ
ocean floor, and mimic microbes in terms of size and shape. In the metamorphic and completely recrystallized examples, the textural evidence of bioalteration is generally obliterated, although it may still be visible in little-deformed volcanic domains of low-grade greenschist-facies metamorphism. Where biogenerated textures are present, element mapping invariably reveals the presence of organic carbon, and sometimes nitrogen, sulphur and phosphorus. Carbon-isotope signatures (δ
13
C) in the pillow lava rims from all four investigated ophiolites show lower values than those of the adjacent crystalline parts. This phenomenon may be attributed to bio-induced fractionation of carbon isotopes during preferential bioalteration of the pillow lava glass, and may further represent a feature that seems to survive metamorphism and deformation.
Ophiolite obduction and the Samail Ophiolite: the behaviour of the underlying margin
Authors: Gray D. R. , Gregory R. T. 
Published: April 2008

Abstract

Samail ophiolite emplacement has become a type-example for ophiolite obduction. Despite this, problems and controversy remain with respect to the age of high-
P
metamorphism, the vergence of structures in deformed rocks beneath the ophiolite, the suprasubduction character of the ophiolite and the
P-T
conditions of the metamorphic sole. The presence of major, regional-scale NE-facing isoclinal folds and SW- and west-dipping shear zones with top-to-the-NE shear sense in Arabian margin rocks beneath the Samail Ophiolite nappe requires that the margin was not simply passively overridden during obduction of the ophiolite. The development of these folds at 72–76 Ma is at the time the ophiolite is emplaced finally onto the margin (80–70 Ma), accompanied by development of a major shear zone in Saih Hatat (the upper plate-lower plate discontinuity described by earlier workers) at
c.
82–80 Ma. Structural scenarios that incorporate these folds and shear zones include lateral escape from a rising buoyant crustal slice along the former subduction interface, back-folding (‘retrocharriage’) associated with major oceanwards-directed underthrusting, or simple underthrusting of the margin by the oceanic realm. Previous models involving craton-directed overthrusting with domal culminations related to deep-seated footwall and lateral ramps are more applicable to the Tertiary structure and Tertiary evolution of the mountain range. Oman ophiolite obduction clearly involves ocean-vergent thrusting within the continental margin platform to slope facies sequences.
Geochemical evolution of magmatism in an arc-arc collision: the Halmahera and Sangihe arcs, eastern Indonesia
Authors: Macpherson Colin G. , Forrde Emily J. , Hall Robert , Thirlwall Matthew F. 
Published: April 2008

Abstract
The Molucca Sea Collision Zone in eastern Indonesia is the site of an orthogonal collision between two active subduction systems. Both the Halmahera subduction zone, to the east, and the Sangihe subduction zone, to the west, have subducted oceanic lithosphere of the Molucca Sea Plate, which has now been completely consumed. Both volcanic arcs were active since the Neogene and provide a means of probing the element fluxes through the two systems. The geochemistry of Neogene and Quaternary lavas from each volcanic arc is compared to constrain changes in the mass fluxes through the systems and the processes controlling these fluxes at different times during their history. Both arcs show increased evidence for sediment recycling as the collision progressed, but for contrasting reasons. In Halmahera this may represent an increased sediment flux through the arc front, while in Sangihe it may simply reflect a greater opportunity for melting of sediment-fluxed portions of the mantle wedge. In both cases the change in arc geochemistry can be related to the evolving architecture of the particular subduction zone. The Halmahera lavas also record a temporal change in the chemistry of the mantle component that resulted from induced convection above the falling Molucca Sea Plate drawing compositionally distinct peridotite into the mantle wege.
Geochronology: linking the isotopic record with petrology and textures — an introduction
Authors: Vance Derek , Müller Wolfgang , Villa Igor M. 
Published: April 2008

Abstract
One of the key aims of geochronology, and the subject of the papers in this Special Publication, is the linkage of isotopic ages to petrological and textural information. A close link between the two types of information greatly improves the constraints available from geochronology on the nature and rates of lithospheric processes such as metamorphism and deformation. There have been several key advances in this area over the past 10–20 years, relating to increased precision and accuracy of isotopic ages but also, and crucially, to the spatial resolution available to geochronologists. This resolution now approaches that on which petrological, chemical and textural information is obtained. We also, in this introduction, identify the barriers that have impeded further progress, which relate both to technical issues as well as to problems of understanding. Finally we set the papers in this volume in the context of the preceding discussion and outline the key ways in which these papers point towards further progress in the future.
Effect of metamorphic reaction history on the U-Pb dating of titanite
Authors: Romer Rolf L. , Rötzler Jochen 
Published: April 2008

Abstract

Drill core samples of garnet-clinopyroxene granulite at Tirschheim and a reference sample at Waldheim (Saxon Granulite Massif, Germany) endured the same P-T conditions, but developed variable mineral assemblages due to differences in bulk chemistry, reaction progress, deformation and retrogression. Titanite formed during peak-metamorphic conditions of 22–24 kbar and 1020–1050 °C. Dating titanite from the various samples should yield the same age for all. The observed age variation, which exceeds the duration of the entire metamorphic cycle, originates from the contrasting preservation of isotopic inheritance during peak metamorphism and from post-peak re-equilibration. (1) Pb inheritance observed in some peak-metamorphic titanite demonstrates that geochronologically relevant elements are redistributed among remaining reactants and reaction products during prograde metamorphism and that the sequence of metamorphic reactions does not result in isotopic homogenization. Instead, metamorphic minerals inherit the radiogenic signatures of the precursor minerals and may in extreme cases approach the age of the precursor mineral. (2) Titanite that formed at peak-metamorphic conditions is characterized by high A1 contents and X
F
≈ 0.8−1. Texturally comparable titanite that re-equilibrated during cooling (reduced Al contents and X
F
) yields too young U-Pb ages. The age of such re-equilibrated titanite does not correspond to the age of the event indicated by the texture.
Evidence from Rb-Sr microsampling geochronology for the timing of Alpine deformation in the Sonnblick Dome, SE Tauern Window, Austria
Authors: Cliff R. A. , Meffan-Main S. 
Published: April 2008

Abstract

The Sonnblick Dome forms a large antiformal structure within the Pennine of the SE Tauern Window. The structural and metamorphic evolution of this area is relatively well constrained. However, mineral age determinations of the Alpine event within the Zentralgneis granitoid basement remain ambiguous due to a lack of isotopic equilibration during the Alpine event. In this paper we use a newly developed technique, namely Rb-Sr microsampling, in an attempt to place more reliable age constraints upon Alpine deformation. The new age determinations range between
c.
22 Ma and 28 Ma. The oldest ages are interpreted to result from shearing related to the earliest stages of dome formation while the youngest ages probably represent late fabric development during uplift of the Zentralgneis complex. A clustering of six fabric ages around 25.5 ± 0.3 Ma is thought to represent the peak of deformation activity associated with formation of the dome. These new data can be fitted into a model for the metamorphic and structural evolution of the SE Tauern Window.

In most of the rocks studied isotopic disequilibrium is apparent between and within minerals. It is clear that large feldspar augen did not attain isotopic equilibrium despite amphibolite facies metamorphism. In fact, even where chemical equilibrium was achieved isotopic homogenization did not always occur. The Rb-Sr data from white mica suggest that isotopic equilibration may occur during isochemical rotation of grains suggesting differing mechanisms for chemical and isotopic movement within grains. The data presented herein suggest that small-scale,
in-situ
sampling methods may provide the most reliable method for deformation chronology in basement gneisses.