bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seismic anisotropy of the crystalline crust: what does it tell us?
Authors: Rabbel Wolfgang , Mooney Walter D. 
Published: July 2007

ABSTRACTThe study of the directional dependence of seismic velocities (seismic anisotropy) promises more refined insight into mineral composition and physical properties of the crystalline crust than conventional deep seismic refraction or reflection profiles providing average values of P‐and S‐wave velocities. The alignment of specific minerals by ductile rock deformation, for instance, causes specific types of seismic anisotropy which can be identified by appropriate field measurements. Vice versa, the determination of anisotropy can help to discriminate between different rock candidates in the deep crust. Seismic field measurements at the Continental Deep Drilling Site (KTB, S Germany) are shown as an example that anisotropy has to be considered in crustal studies. At the KTB, the dependence of seismic velocity on the direction of wave propagation in situ was found to be compatible with the texture, composition and fracture density of drilled crustal rocks.
Local site effects in the northern North Sea based on single‐station spectral ratios of OBS recordings
Authors: Atakan Kuwet , Havskov Lens 
Published: July 2007

ABSTRACTIn recent years, there has been a growing awareness of the importance of local site effects in earthquake damage. A number of studies of recent destructive earthquakes have illustrated the relative contribution of enhanced ground shaking due to unconsolidated sediment layers.Among the different methods used to estimate local site response, the spectral ratio of shaking at a sedimentary site with respect to a bedrock reference site, has been successfuly applied in different geological environments. In this study, a technique recently proposed by Nakamura (1989) is used to evaluate site response using spectral ratios of horizontal vs. vertical components of earthquake recordings from a temporary ocean bottom seismograph (OBS) network in the northern North Sea and a permanent OBS at Oseberg oil field. Comparison with results obtained from the standard spectral ratios, indicate that the method is applicable also to subsea conditions, and the estimates obtained in this study indicate similar amplification factors to those obtained previously from analytical techniques. The ambient noise data on the other hand, gave unstable results, probably due to different noise characteristics in the marine environment. The results obtained on the earthquake data, however, provide an encouraging alternative to previously used analytical techniques for estimating local site response.
The Amirante ridge/trough complex: response to rotational transform rift/drift between Seychelles and Madagascar
Authors: Plummer Ph. S. 
Published: July 2007

ABSTRACTThe Amirante ridge/trough complex developed along the Late Cretaceous transform boundary that separated the Seychelles/India and Madagascar/Somali Basin plates. Motion between these plates was complex, comprising sinistral N‐S strike‐slip movement coupled and coeval with counter‐clockwise rotation induced when seafloor spreading developed in only the southern portion of the transform. The overall morphology of the complex comprises a series of arcuate ridge and trough segments. These segments were successively produced by tectonic and volcanic activity within the zone of migrating plate contact adjacent to the rotational pivot where compression was replaced by extension along the transform boundary. In the extensional regime to the south of this contact zone the Mascarene oceanic basin developed, whilst in the compressional zone further north island arcs developed and the ophiolites of Baluchistan were obducted from the Somali Basin onto the leading edge of the Seychelles/India plate.
Field, petrophysical and carbon isotope studies on the Lapland Granulite Belt: implications for deep continental crust
Authors: Korja T. , Tuisku P. , Pernu T. , Karhu J. 
Published: July 2007

ABSTRACTThe Palaeoproterozoic Lapland Granulite Belt is a seismically reflective and electrically conductive sequence of deep crustal (6–9 kbar) rocks in the northern Fennoscandian Shield. It is composed of garnet‐sillimanite gneisses (khondalites) and pyroxene granulites (enderbites) which in certain thrust sheets form about 500 m thick interlayers. The structure was formed by the intrusion of intermediate to basic magmas into turbiditic sedimentary rocks under granulite facies metamorphism accompanied by shearing of the deep crust about 1.93–1.90 Gyr ago (Gal. Granulites were upthrust 1.90–1.87 Ga and the belt was divided by crustal scale duplexing into four structural units whose layered structure was preserved. The thrust structures are recognized by the repetition of lithological ensembles and by discordant structural patterns well distinguishable in airborne magnetic and electromagnetic data. Thrusting gave rise to clockwise pressure‐temperature evolution of the belt. However, some basic rocks possibly record an isobaric cooling path. The low bulk resistivity of the belt (200–1000 Ωm) is caused by interconnected graphite and subordinate sulphides in shear zones. On the basis of carbon isotope ratios this graphite is derived mostly from sedimentary organic carbon. The seismic reflectivity of the belt may be caused by velocity and density differences between pyroxene granulites and khondalites, as well as by shear zones.
The significance of Messinian occurrences of Globorotalia margaritae and Globorotalia puncticulata in Sicily
Authors: Butler R.W.H. , Pedle H.M. , Maniscalco R. , Grasso M. , McClelland E. , Finegan B. 
Published: July 2007

ABSTRACT Globorotalia puncticulata and Globorotalia margaritae are critical species that define internationally recognized planktonic foraminiferal biozones in the Pliocene. These biozones are defined from stratotype sections on Sicily and their fauna are commonly considered to have been introduced to the Mediterranean after an influx of Atlantic water that terminated the late Miocene desiccation of the basin. Herein new discoveries of these species in rocks that predate the late Miocene desiccation are described. These data are supported by magneto‐ and lithostratigraphy that have been integrated at a single continuous section. Not only do these discoveries question the existing foraminiferal biozone stratigraphy, they also suggest new models for the dispersal of planktonic species. It is proposed that Globorotalia puncticulata and perhaps even Globorotalia margaritae evolved in the Mediterranean during earliest Messinian times (during or before chron C3Bn1n) and dispersed into the Atlantic. This suggests that a marine connection remained between the two sea areas until at least chron C3An.1n. Using the existing geomagnetic polarity time scale, these occurrences are some 2 Myr earlier than previously recorded in the Mediterranean. The distribution of G. margaritae and G. puncticulata in Mediterranean sections is likely to reflect palaeoenvironment or the preservation of deposits rather than the absolute age of the sediments.
Revision of the earthquake catalogue and seismicity of Croatia, 1908–1992
Authors: Herak Marijan , Herak Davorka , Markušić Snježana 
Published: July 2007

ABSTRACTThe paper presents the results of Croatian earthquake catalogue revision for the period 1908–1992. The revised catalogue lists a total of 4853 events (4486 after 1908), of which 3700 are mainshocks. All primary data sources available to us (seismograms, phase onset time readings, macroseismic questionnaires…) were consulted in order to improve the quality and reliability of magnitude, intensity and location. Along with the most important earthquake parameters the catalogue contains entries that enable assessment of the reliability of location and bibliographic references. Using the temporal analysis of the maximum‐likelihood estimate of the b‐value in the frequency‐magnitude relation, the catalogue is estimated to be complete for events with M ≥ 4.0 throughout the investigated period. The magnitude completeness threshold decreases to 3.8 after the middle of the century, and to about 3.6 in the last three decades. It is noted that the b‐value variation with time is closely tied to the seismic activity, as well as that at present there seems to be a lack of seismic energy release corresponding to the M = 6.0–6.5 earthquake.
Electronic Publishing: The issues and ways forward
Authors: Whaler Kathy 
Published: July 2007

ABSTRACTOn 10 April 1995, during the EUG 8 meeting in Strasbourg, about 100 people gathered to participate in a Forum on Electronic Publishing, organized by Dominic Vaughan (Elsevier Science) and Kathy Whaler (University of Edinburgh and Royal Astronomical Society). In what follows, I have tried to convey a flavour of the style of the various presentations, as well as their content. Many points were reiterated by more than one speaker; in general, I have not repeated them.
Tectono‐magmatic control on vertical dip slip basement faulting: An example from the Fennoscandian Shield
Authors: Heeremans M. , Stel H. , van der Beek P. , Lankreijer A. 
Published: July 2007

ABSTRACTVertical dip‐slip basement faults play an important role in the evolution and structuring of the Earth's crust. The Proterozoic anorogenic rapakivi‐anorthosite setting of the Fennoscandian Shield in southern Finland exhibits a widespread pattern of vertical dip‐slip basement faults that are deeply eroded. The Porkkala‐Mantsala (PM)‐fault, located c. 30 km W of Helsinki is part of a system of crustal lineaments that closely follows the outcrop pattern of Mid‐Late Proterozoic anorogenic crustal elements, such as basic dyke swarms, the outline of rapakivi granites and remnants of sediment‐filled grabens. These lineaments are formed by low‐grade dip‐slip faults that overprint Svecofennian shear zones. Structural analysis of the PM‐fault supports an interpretation in terms of reactivation of a high‐grade ductile wrench zone. Successive stages of brittle deformation visible in as well the PM‐fault and the Obbnäs granite demonstrate that brittle deformation in the PM‐fault is coeval with the intrusion of the anorogenic Obbnäs rapakivi granite. Based on the spatial and temporal relationship of anorogenic magmatism and block faulting, a genetic relationship is proposed.
A consistent map of the postglacial uplift of Fennoscandia
Authors: Ekman Martin 
Published: July 2007

ABSTRACTA consistent map of the recent postglacial rebound of Fennoscandia is constructed on the basis of sea‐level records, lake‐level records and repeated high‐precision levellings.The uplift rates calculated from the sea‐level series form a consistent framework of the map. The sea‐level stations used are 56 reliable stations in the Baltic Sea and adjacent waters with series spanning 60 years or more, many of them about 100 years. Using a reference station in the Baltic Sea and another one outside the Baltic, all results are reduced to a common time span, the 100‐year‐period 1892–1991, in order to eliminate oceanographic changes. Inland, uplift differences are obtained from the repeated national levellings and, in four of the large lakes, from long water level series in pairs. The levellings, however, yield less accurate land uplift values than the sea‐level and lake‐level data.The resultant map shows a fairly smooth phenomenon, with a maximum apparent uplift in the Gulf of Bothnia of 9.0 mm yr‐1. The standard error is typically 0.2 mm yr‐I close to the sea level stations, larger inland.Finally the pattern of the present uplift as determined here is observed to be very similar to that of the past uplift as determined from ancient shore‐lines of the Litorina Sea. However, the ratio between the past uplift and the present uplift rate tends to increase somewhat towards the uplift centre. This might reflect a non‐uniform mantle viscosity. Also, the uplift maximum seems to have migrated towards NNE.
The Bälinge conglomerate in northern Sweden reinterpreted as a magmatic, hydraulic breccia
Authors: Wikström Anders , Mellqvist Claes , Barbarid Bernard 
Published: July 2007

ABSTRACTThe Bälinge conglomerate has played a key role in the lithostratigraphy of northern Sweden. The conglomerate, with pebbles dominated by granodiorites and tonalites in a generally biotite‐rich matrix, borders volcanic rocks with unclear relative age relationships. In nearby areas these volcanites have been intruded by plutonic rocks (c. 1.9 Ga) which are similar to the pebble material. On these grounds, the conglomerate has been regarded as younger than the volcanic rocks and an important marker in the geological evolution of the region. In this preliminary study, it is suggested that the features displayed by the Balinge conglomerate are not compatible with an epiclastic origin. On the contrary, they indicate that this rock represents a hydraulic breccia where the roundness of the granitoid ‘pebbles’ has resulted from erosion in a fluidised, heterogeneous and magmatic environment. In the actual area the ‘conglomerate’ must thus be dismissed as a stratigraphic marker horizon. It belongs to the early Svecofennian evolution.
Contiguous Laurentia and Baltica before the Grenvillian‐Sveconorwegian orogeny?
Authors: Romer Rolf L. 
Published: July 2007

ABSTRACTClose geochronological correspondence of Mesoproterozoic extension‐related magmatism and comparable tectonic and geochronological evolution of the Grenville and Svecononvegian orogens suggests that the Laurentian and Baltic Shields could have been joined during the Mesoproterozoic and did not separate until after the Grenvillian‐Sveconorwegian orogeny. The combined Grenville‐Svecononvegian orogen is here interpreted to have formed during the collision of coherent Laurentia‐Baltica with an unknown craton, which is in contrast to earlier explanations that favour a late‐Mesoproterozoic rotation between Laurentia and Baltica followed by collision of these two cratons with each other.
Pre‐Tertiary blueschist terrains in the Hellenides: evidence from detrital minerals of flysch successions
Authors: Faupl P. , Pavlopoulos A. , Wagreich M. , Migiros G. 
Published: July 2007

ABSTRACTDetrital blue amphiboles detected in flysch sandstones of the Hellenides of mainland Greece give important information on uplift and exhumation history of blueschist terrains. The occurrence of these HP/LT minerals in the terminal flysch of the Pindos zone as well as in the Othrys flysch of the Subpelagonian zone from late Maastrichtian/ Palaeocene time onwards proves a Pre‐Tertiary (Eohellenic) stage of blueschist formation. Detrital blue amphiboles from flysch sequences of the Ionian zone indicate a further pulse of uplift of high‐pressure rocks during the Palaeocene/Eocene. Blueschist rocks of this latter time range are radiometrically well documented in the Hellenides.
Petrology of pumices of April 1993 eruption of Lascar (Atacama, Chile)
Authors: Bernard Déruelle , Oscar Figueroa A. , Eduardo Medina T. , Jose Viramonte G. , Mario Maragaño C. 
Published: July 2007

ABSTRACTLascar Volcano (Atacama, Chile) erupted on 18–20 April 1993. Several sub‐Plinian explosions occurred, and some were mushroom‐shaped. The highest column rose up to 23 km. Ash clouds crossed South America eastwards. Dacite pumice falls made of blocks and ashes were deposited on the flanks of the volcano as a result of collapsed columns. The pumice contains phenocrysts of plagioclase, enstatite, augite, biotite, magnetite and ilmenite and small crystals of apatite. The 1992 previous andesite dome inside the crater was destroyed. Banded blocks resulting from mingling of the dacitic pumice and andesite from the dome are found in the pumice flow. Both the lava dome and the pumice are representative of the Lascar high‐K magma unit. Dacitic pumice is a product of crystal fractionation of the andesitic magma.
Permeability and stress in crystalline rocks
Authors: Banks David , Odling Noelle E. , Skarphagen Helge , Rohr‐Torp Erik 
Published: July 2007

ABSTRACTGroundwater from crystalline rocks is a significant resource in many areas of the world. It is also an important medium for contaminant transport from, for example, deep nuclear waste repositories. Stress distributions in fractured rocks are important in controlling groundwater flow in several ways: (i) palaeostress fields are responsible for the evolution of fracture systems which transmit groundwater; (ii) current in situ stress fields will influence the shape and aperture of fractures; (iii) humans can influence the natural stress field in a rock mass to enhance fracture flows. The significance of stresses for groundwater flow can be investigated by field techniques (hydraulic fracturing), laboratory techniques (stress cells) or by numerical modelling.
Strain localization and large‐scale block rotation in the lower continental crust, Kataragama area, Sri Lanka
Authors: Kleinschrodt Reiner 
Published: July 2007

ABSTRACTIn Sri Lanka a suite of rocks is regionally exposed which once formed a part of the middle to lower crust of a collisional orogen with about doubled crustal thickness. A subhorizontal to gently west‐dipping major thrust zone (Highland Basal Thrust) crosses Sri Lanka from NNE to SSW. It separates a granulite facies upper unit, the Highland Complex from an amphibolite facies lower unit, the Vijayan Complex with a displacement of more than 300 km. The basal Highland Complex was migmatized during thrusting. Rheological contrasts between dry granulites and migmatites were high in the presence of partial melts. Granulite facies fragments within the migmatites vary from the decimetre to kilometre scale. Granulites in the area of Kataragama, formerly interpreted as the Kataragama Klippe, are now identified as a large‐scale raft within the migmatites, which is completely separated from the overriding Highland Complex. During thrusting strain was concentrated in the migmatized basal parts of the Highland Complex. After crystallization of the migmatites thrusting continued, and strain was still localized within the migmatites. Therefore, granulite facies parageneses, structures and textures are preserved in the granulite rafts. The deviation of the granulite facies structures in the Kataragama raft from the general trend in the Highland Complex is interpreted to indicate counterclockwise rotation of the whole raft by about 90° around a subvertical rotation axis.
Seasonally ice free glacial nordic seas without deep water ventilation
Authors: Seidov Dan , Mastin Mark 
Published: July 2007

ABSTRACTAt present the Nordic Seas are a key region of North Atlantic Deep Water (NADW) formation. Two alternative scenarios have been suggested by some authors for the Last Glacial Maximum: (i) the Nordic Seas were permanently covered by sea ice, preventing the formation of NADW, or (ii) that they were seasonally free of ice and that deep water formation did occur. A modified scenario is presented here based on parallel ocean circulation modelling results from the GFDL primitive equation model and a planetary geostrophic model. It is suggested that the glacial Nordic Seas were at least seasonally ice free, but it is observed that there was never deep water formation from the surface; rather it occurred only in the North Atlantic south of 40°–50°N. North of 40°N, the weaker LGM northward flowing thermohaline conveyor is subducted below a reverse conveyor which occurred to a depth of over 1000 m. Various modelling experiments presented here indicate that the reversed conveyor was primarily caused by the colder conditions of the glacial North Atlantic that led to far stronger zonality of glacial analogue of the North Atlantic Current.
Near‐K/T age of clastic deposits from Texas to Brazil: impact, volcanism and/or sea‐level lowstand?
Authors: Keller Gerta , Stinnesbeck Wolfgang 
Published: July 2007

ABSTRACTNear‐K/T boundary clastic deposits from Texas, Mexico, Haiti, Guatemala and Brazil, often described as impact‐generated tsunami deposits, are stratigraphically below well‐defined K/T boundary horizons and appear not to be causally related to the K/T boundary event. Stratigraphic evidence indicates that their deposition began during the last 170–200 kyr of the Maastrichtian, coincident with a major eustatic sea‐level lowstand that lowered sea level by as much as 70–100 m. Clastic deposition ended a few tens of thousands of years before the K/T boundary during a rapidly rising sea level. The presence of glass in clastic deposits in Haiti, northeastern Mexico and Yucatan suggests that the sea‐level lowstand coincided with a time of major volcanism or pre‐K/T boundary bolide impact.
A review of studies of the earliest glaciation of Iceland
Authors: Geirsdóttir Áslaug , Eiriksson Jón 
Published: July 2007

ABSTRACTGlaciers and volcanoes have been the trademark of Iceland for centuries. The glaciers now cover ≅10% of the country and the volcanic regions are covered by lava flows every 5–10 kyr on average. Naturalists have concentrated on these two aspects, making notes on volcanic eruptions and traveling along the glacier margins ever since the first settlement of Iceland in the ninth century in some of the earliest episodes of geological research. Systematic studies of the glaciers began in the latter half of the 18th century. Even earlier, features such as striations and moraines were discovered and described in locations remote from the contemporary glacier margins. These features were interpreted as the effect of a much more extensive ice sheet on the island. At the beginning of the 20th century the discussion of the origin of sediments was unseparable from the age problem. From 1910 to 1950 very few new data were presented on the glaciation history of Iceland. A few sporadic publications either accepted or rejected previous conclusions. Systematic geological mapping of the country started in the wake of World War II encouraged by the acceptance of the plate tectonic theory in the late sixties. One of the most important results of this revived mapping effort was the identification of interbedded sediments interpreted as glacial deposits. Around 1975 Iceland was known in the geological literature for preserving more numerous glacial deposits than found elsewhere on land in the northern hemisphere. Over the last few years, systematic lithofacies analysis of sediments interbedded within lava flows has been conducted with the aim of delineating the earliest glaciation of Iceland and the periodicity of glaciation through the Tertiary and Quaternary. The results show a gradual growth of ice from south‐east towards the north and west during the Pliocene‐Pleistocene transition interrupted by periods of recessions and intermittent ice‐free conditions.
How detrital mica affects compactional porosity loss?
Authors: Mátyás János 
Published: July 2007

ABSTRACTDetrital micas are moderately abundant components in lithic sandstones. Examples from the Törtel and Szolnok Formations (Pannonian basin) and from the Lower Freshwater Molasse and Upper Marine Molasse (Swiss Molasse basin) show that the response of micas to increasing effective stress due to burial is substantially different from that of true ductile particles: the mica plates bend, but their thickness remains essentially constant. Based on this observation, a new model is proposed to describe the relationship between porosity loss and the ratio of mica‐thickness and grain size. The results of calculations emphasize the importance of this latter parameter, as opposed to porosity loss from deformation of true ductile grains which is independent of the relationship between the grain sizes of deforming and rigid components.