bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phreatomagmatic eruptions on the Ontong Java Plateau: an Aptian
40
Ar/
39
Ar age for volcaniclastic rocks at ODP Site 1184
Authors: Chambers Lynne M. , Pringle Malcolm S. , Fitton J. Godfrey 
Published: April 2008

Abstract

The discovery of a thick (337.7 m drilled) succession of volcaniclastic sediments at Ocean Drilling Program (ODP) Site 1184, on the eastern salient of the Ontong Java Plateau (OJP), shows that at least part of the plateau formed at or near sea level. All the other parts of the OJP that have been drilled or are exposed on land are composed of basaltic lava flows erupted in a deep-marine environment. The composition of the volcaniclastic rocks at Site 1184 is essentially indistinguishable from that of basaltic lava flows recovered from the other drill sites on the OJP, suggesting that the eastern salient formed during the same magmatic event (at approximately 120 Ma) that formed the main part of the plateau. A steep (−54°) magnetic inclination preserved in the volcaniclastic succession is consistent with an Early Cretaceous age, but rare nannofossils recovered from the volcaniclastic rocks suggest a much younger Eocene age. In order to resolve this paradox, we attempted to date the succession by the
40
Ar/
39
Ar technique, even though the rocks are highly altered. Two samples of feldspathic material separated from basaltic clasts give
minimum
age estimates of
c.
74 Ma. The basaltic clasts have compositions similar to that of their host rocks and are therefore probably cognate. A weighted average of the results of total fusion experiments on four or five small euhedral plagioclase crystals separated from the matrix of the volcaniclastic rocks at each of four levels in the lower part of the succession gave a value of 123.5 ± 1.8 Ma, and this probably represents a reasonable estimate of the age of eruption. Although not very precise, the
40
Ar/
39
Ar results are the best that presently can be obtained from such altered rocks. They rule out an Eocene age for the volcaniclastic succession at Site 1184, and we suggest that the Eocene nannofossils were introduced through contamination, probably along fractures.
Compositional variability in lavas from the Ontong Java Plateau: results from basalt clasts within the volcaniclastic succession at Ocean Drilling Program Site 1184
Authors: Shafer John T. , Neal Clive R. , Castillo Paterno R. 
Published: April 2008

Abstract
Tholeiitic basalts have been recovered from drill sites in different locations on the Ontong Java Plateau (OJP) and are remarkably homogeneous across this large igneous province. The most abundant basalt type is represented by the Kwaimbaita Formation on Malaita in the Solomon Islands, where it is capped by the isotopically distinct and slightly more incompatible-element-enriched basalt of the Singgalo Formation. Ocean Drilling Program (ODP) Leg 192 drilled five sites on the OJP, four of which penetrated basement lava successions. All basalt recovered during Leg 192 is chemically and isotopically indistinguishable from Kwaimbaita-type lavas.

Site 1184 of ODP Leg 192 is situated on the eastern salient of the OJP, and is unique because the recovered volcaniclastic succession contains the first conclusive evidence for emergence of part of the OJP above sea level. Within this succession are clasts of basaltic material. We report the major element-, trace-element and isotopic compositions of 14 moderately to highly altered basalt clasts. On the basis of incompatible-element concentrations, specifically high field strength elements (HFSE) and rare earth elements (REE), four groups of clasts are defined. Group 1 clasts are similar to basalt from the Kwaimbaita Formation. Group 2 clasts show variable composition, but the heavy rare earth element (HREE) concentrations are similar to those of basalts from the Kwaimbaita Formation. Group 3 clasts have compositions similar to the high-MgO Kroenke-type basalt recovered during ODP Leg 192. Group 4 clasts are more evolved than the Kwaimbaita or Singgalo lavas, and contain deep negative Eu and Sr anomalies on primitive-mantle (PM)-normalized diagrams, as well as high concentrations of Nb, Ta and Th. Group 4 clasts also show a large fractionation of Nb from La and have (Nb/La)
PM
ratios of approximately 2. Sr-, Nd- and Pb-isotope ratios were measured on five clasts covering all four groups. Although the Sr- and Pb-isotope ratios exhibit some variability, which we attribute to alteration, the Nd-isotope ratios are within the field defined for Kwaimbaita-type lavas.

We conclude that most of the compositional variability displayed by these clasts is a result of alteration and that Ta appears to be the most immobile incompatible trace element. All of the clasts were derived from the mantle source that produced the Kwaimbaita-type and Kroenke-type basalts. Our data emphasize the widespread nature of Kwaimbaita-type basalt and show that the source region was active under both the eastern salient and the high plateau of the OJP.
Age and depth evidence for pre-exhumation joints in granite plutons: fracturing during the early cooling stage of felsic rock
Authors: Bankwitz P. , Bankwitz E. , Thomas R. , Wemmer K. , Kämpf H. 
Published: April 2008

Abstract
This chapter documents the fracture process associated with the early cooling stage of felsic magma. Characteristics of pre-exhumation joints include their spatial distribution in granite bodies, their fracture surface morphology, and geological and petrological evidence for the depth of fracture initiation. These characteristics allow inferences about the depth and the time of joint origin in the South Bohemian Pluton. The intrusion levels of currently exposed granites of the pluton were 7.4 km in the northern part and 14.3 km in the southern part.

Within the northern Mrákotín Granite (Boršov) early NNE joints propagated while the granite was at a temperature near the solidus, and, in part, magma was still being injected, post-dated by thin granite dykes along NNE joints. Evidence for the pre-exhumation initiation of these joints comes from the geochronological dating of these late-granite dykes (1–2 cm thick) at 324.9 Ma in age, which were creating their own rupture in the rock. The timing of the pluton emplacement at 330–324 Ma and the cooling ages of 328–320 Ma have been given by previous studies. From fluid inclusions within the late-granite dykes that occupy joint surfaces, the trapping depth of the analysed inclusions was calculated to be 7.4 km. Near the solidus H
2
O separates during the crystallization of anhydrous phases. The associated increasing H
2
O pressure can initiate the first cracks and can generate a small portion of new granitic melt, which forces the cyclic fracture propagation together with mobile, low-viscosity ‘residual melt’ input into the fracture.

The determination of the intrusion level and time at which the dykes began cooling provide evidence for the joint initiation at a depth of 7.4 km, which was connected with the level and process of final emplacement and early cooling of the Mrákotín Granite long before the main exhumation. At the earliest, the erosion of the upper rock pile, 7.4 km in thickness, started significantly after generation of the early joint sets. The NNE-trending joints are persistent in orientation throughout the South Bohemian Pluton, but the joint-surface morphology varies in all subplutons and occupies all sections of the stress intensity v. crack-propagation velocity curve (Wiederhorn-Bahat curve).
Using differential geometry to characterize and analyse the morphology of joints
Authors: Pollard D. D. , Bergbauer S. , Mynatt I. 
Published: April 2008

Abstract
Concepts of differential geometry are reviewed, and it is demonstrated through examples that the main joint surface, rib marks and hackle of a joint may be described using parametric representations such that the first and second fundamental forms fully characterize these surfaces. Other useful quantities are the unit normal vector, the principal normal curvatures, and the Gaussian and the mean curvature. Sufficiently close to any point on a surface the shape is planar, parabolic, elliptical or hyperbolic. The surface of a joint in chert and another in siltstone were scanned and the resulting data analysed. Although the main joint surface of the chert sample is approximately planar, it is composed of low-amplitude undulations with elliptical and hyperbolic forms. The unit normal vector does not vary by more than about 3.4° over this surface, which is consistent with the threshold angle for the initiation of hackle based on laboratory experiments. An individual hackle is found to be approximately helicoidal in shape, but only in the breakdown zone. Rib marks on the siltstone sample have distinct and similar morphologies, with a concave base and convex peak. Field and laboratory campaigns designed to test hypothese about the geometry of joints should use the principles and tools of differential geometry.
Palaeostress orientation inferred from surface morphology of joints on the southern margin of the Bristol Channel Basin, UK
Authors: Belayneh Mandefro 
Published: April 2008

Abstract
A field study of the orientation of surface features on joint planes has been carried out on the north Somerset coast along the southern margin of the Bristol Channel Basin (BCB), with the aim of inferring the palaeostress orientations. Surface features are very delicate structures on joint surfaces and when preserved give important clues regarding the direction of propagation of a joint and the interaction between the remote and local stresses.
In this chapter surface features (i.e. plumose structures and twist-hackle fringes) observed on joints in Liassic limestone beds interbedded with shales from the BCB are described and their implications regarding the evolution of the stress field operating during their formation considered. The results are then compared with the generally accepted model for the region of an anticlockwise rotation of the stress field. The incompatibility between N-S-directed remote compression and continually changing local stress caused by the local structures (folds and faults), inhomogeneities and the anisotropy created by rapidly alternating limestone and shale beds resulted in the master joints breaking down into en echelon cracks (twist-hackle fringes). Joints in thicker limestone beds show well-developed plumose structures and twist-hackle fringes, whereas in thinner beds the fringe zones extend from the top to the bottom of the bed. It is found that regardless of the orientation of the parent joint in which the twist-hackle fringes are contained, they generally strike E-W and show both right- and left-stepping arrangements.
The orientation distribution of single joint sets
Authors: Engelder Terry , Delteil Jean 
Published: April 2008

Abstract

Poles from line samples of systematic joint sets scatter about a mean pole because joints are neither perfectly planar nor parallel, and because measurement instruments are imprecise. Definition of a single joint set can be based solely on its orientation distribution and this distribution is assessed using two statistical parameters: square root of the circular variance (approximately equal to the standard deviation σ for two-dimensional (2D) data) and cone of confidence (α
95
for 3D data). The distribution for joints generated in the absence of tectonic deformation is well clustered with σ = 1.7° and α
95
= 0.48° based on a bootstrap sample of 50. Jointing associated with various fold styles show less clustering: the kink of a fault-bend fold (σ = 6.1° and α
95
= 1.7°), basement-cored anticline (σ = 3.5° and α
95
= 1.5°), regional joint set transected by a basement-cored anticline (σ = 5.2° and α
95
= 1.8°) and a buttress anticline (σ = 4.3° and α
95
= 1.7°). Jointing associated with local faulting tends to show even less clustering: a Cretaceous marl (σ = 8.3° and α
95
= 2.4°) and a glauconitic sandstone (σ = 8.6° and α
95
= 2.2°). The latter sample was drawn from two overlapping joint sets, indicating that distribution data greater than α
95
= 2.2° may signal overlapping joint sets.
Stress-controlled localization of deformation and fluid flow in fractured rocks
Authors: Sanderson David J. , Zhang Xing 
Published: April 2008

Abstract
The discrete-element method (UDEC — Universal Distinct Element Code) was used to numerically model the deformation and fluid flow in fracture networks under a range of loading conditions. A series of simulated fracture networks were generated to evaluate the effects of a range of geometrical parameters, such as fracture density, fracture length and anisotropy.

Deformation and fluid flow do not change progressively with increasing stress. Instability occurs at a critical stress and is charzacterized by the localization of deformation and fluid flow usually within intensively deformed zones that develop by shearing and opening along some of the fractures. The critical stress state may be described in terms of a driving stress ratio,
R
= (fluid pressure — mean stress)/1/2 (differential stress). Instability occurs where the
R
ratio exceeds some critical value,
R
C
, in the range – 1 to −2.

At the critical stress state, the vertical flow rates are characterized by a large increase in both their overal magnitude and degree of localization. This localization of deformation and fluid flow develops just prior to the critical stress state and may be characterized by means of multifractals. The stress-induced criticality and localization displayed by the models is an important phenomenon, which may help in the understanding of deformation-enhanced fluid flow in fractured rock masses.
Forensic applications of Raman spectroscopy to the non-destructive analysis of biomaterials and their degradation
Authors: Edwards Howell G. M. 
Published: April 2008

Abstract
An initial survey of the advantages and disadvantages of Raman spectroscopic techniques for application to forensic crime scene analysis in a geoscience context is followed by some illustrative examples that demonstrate the potential information which can be forthcoming from Raman spectral data and molecular characterization. A range of specimens is reported, including Egyptian human mummies, ice-mummified bodies, resins and ivories; all of these can be related through a geoscience context and the potential for forensic application is indicated.
Forensic geology of bone mineral: geochemical tracers for post-mortem movement of bone remains
Authors: Trueman Clive N. 
Published: April 2008

Abstract
The trace element chemistry of bone is rapidly altered post-mortem, and the post-mortem chemistry of bone mineral has been used successfully to discriminate between fossil bones removed from stratigraphically and spatially separate excavations. These techniques can be used to identify and protect scientifically or culturally sensitive artefacts. Measurable changes in the trace element composition of bone may occur within a few years of death. These changes show considerable potential for use in forensic investigations, particularly where post-mortem movement or scattering of bone remains has occurred. Early post-mortem alteration is complex, governed by a number of environmental variables, and measuring subtle changes in bone chemistry presents considerable analytical challenges. More work is needed in this area.
The use of plant hydrocarbon signatures in characterizing soil organic matter
Authors: Dawson Lorna A. , Towers Willie , Mayes Robert W. , Craig Julie , Väisänen R. Katariina , Waterhouse E. Clare 
Published: April 2008

Abstract

Resistant compounds associated with vegetation have potential for understanding and uniquely describing soil. Although much of the forensic identification of soils has focused on the mineral component, this study illustrates how the origin of the organic component can be a useful tool in soil identification. The epicuticular wax of most plants containts mixtures of hydrocarbons (mainly
n
-alkanes) and plant species differences are persistent. Evidence from three separate studies is compiled to show the validity of this approach. In the first example, on upland grassland vegetation, the
n
-alkane pattern of the soil at one site reflected that of the overlying grass, whereas at another site, it reflected that of the previous vegetation, heather. In the second study,
n
-alkane analysis data indicated the presence of heather in a buried horizon, matching independent evidence from pollen identification. The third study was one covering the whole of Scotland, using an unbiased grid-sampling strategy. Results show that the patterns in the soil
n
-alkane profiles reflected the overlying vegetation. Where this was not the case, the profiles matched previously grown vegetation. Such biomarker information, derived from plant wax signatures, coupled with soil spatial information, has potential in the unique identification of soils.
The use of diatom analysis in forensic geoscience
Authors: Cameron N. G. 
Published: April 2008

Abstract
Diatoms are unicellular, siliceous algae that are common in most aquatic environments. Their species composition is strongly related to water quality and aquatic habitats and, because of their silica skeletons, diatom valves can be well preserved and provide a record of past and present environmental conditions. Diatom remains are often diverse and can be identified with high taxonomic precision. These factors allow diatoms to be used in a range of applications in forensic geoscience. These include: the matching of environmental samples with items that have been in contact with water, the investigation of cases of drowning, and the identification of traces of diatomaceous materials used in the manufacture of materials or liquids. Recent developments include an assessment of the potential to use the succession of colonizing, attached diatom species in the determination of time of death. Advances in analytical quality control and the use of multivariate statistical techniques will improve the analysis, presentation and interpretation of diatom data in forensic investigations.
Geological storage of carbon dioxide
Authors: Baines Shelagh J. , Worden Richard H. 
Published: April 2008

Abstract

Carbon dioxide is the main compound identified as affecting the stability of the Earth’s climate. A significant reduction in the volume of greenhouse gas emissions to the atmosphere is a key mechanism for mitigating against climate change. Geological storage of CO
2
, or the injection and stabilization of large volumes of CO
2
in the subsurface in saline aquifers, existing hydrocarbon reservoirs or unmineable coal-seams, is one of the more technologically advanced options available. A number of studies have been carried out aimed at understanding the behaviour and long term fate of CO
2
when stored in geological formations.
Carbon dioxide sequestration in the Campine Basin and the adjacent Roer Valley Graben (North Belgium): an inventory
Authors: Laenen B. , Van Tongeren P. , Dreesen R. , Dusar M. 
Published: April 2008

Abstract

The Campine Basin offers a variety of potential CO
2
storage sites. Within the Roer Valley Graben area Triassic Buntsandstein rocks have an estimated CO
2
storage capacity of several hundred million tons. Mesozoic shales and younger sediments provide adequate sealing. Westphalian D sandstones may possess storage opportunities in the southern graben area, and the karstified/dolomitized parts of the Dinantian carbonates in the western sub-basin have an estimated CO
2
storage capacity of 130 × 10
6
tons. In places, the Dinantian reservoirs may be combined with carbonate reservoirs in the underlying Devonian strata. Sealing is provided by Namurian shales and Westphalian coals and shales. Along the western and southern edge of the basin the Dinantian reservoir is sealed by Cretaceous chalks and marls.

Besides aquifers, the available coal qualifies for CO
2
storage. Six Six methane target areas contain a producible enhanced coalbed methane (ECBM), volume of 53–79 × 10
9
m
3
. This provides a minimum CO
2
sequestration potential of 400 × 10
6
tons. ECBM development factors include the sedimentological setting of the coal sequence as well as changes in porosity, permeability and stress conditions induced by former mining activities. The CO
2
storage capacity in abandoned coalmines is limited. Nevertheless, CO
2
storage in the abandoned mines may be an option when it is combined with coalmine methane extraction or ECBM production in neighbouring areas.
Sedimentation, volcanism and subvolcanic intrusions in a late Palaeozoic intramontane trough (the Intra-Sudetic Basin, SW Poland)
Authors: Awdankiewicz Marek 
Published: April 2008

Abstract
The Intra-Sudetic Basin is a Late Palaeozoic intramontane trough, situated in the eastern part of the European Permo-Carboniferous Basin and Range Province. Within the basin, tectonics, sedimentation and volcanic/subvolcanic activity were intimately related. Tectonics controlled the location of the depositional and volcanic centres. Many volcanic centres with subvolcanic intrusions of rhyodacitic, rhyolitic and trachyandesitic composition were located close to the intra-basinal depositional troughs, where thick accumulations of sedimentary rocks partly obstructed the movement of magma to the surface. Differences in the structure and geometry of intrusions at separate subvolcanic complexes reflect the influence of different discontinuities, faults, margins of collapse structures, boundaries of contrasting lithologies in the country rocks and the volcanic structures.