bluuebunny/crossref_metadata_2025 huggingface dataset:
Geology of the Zamboanga Peninsula, Mindanao, Philippines: an enigmatic South China continental fragment?
Authors: Yumul Graciano P. , Dimalanta Carla B. , Tamayo Rodolfo A. , Maury Rene C. , Bellon Herve , Polvé Mireille , Maglambayan Victor B. , Querubin Cliff L. , Cotten Joseph
Published: April 2008

Mindanao Island in the southern Philippines is made up of two blocks: the island-arc-related eastern-central Mindanao block and the continental Zamboanga Peninsula, which contains several ophiolitic bodies and mélanges. The Middle Miocene Siayan-Sindangan Suture Zone represents the tectonic boundary between the island-arc and continental blocks. A Middle Miocene age of collision is interpreted from the unconformity between the Late Miocene Motibot Formation and the underlying Middle Miocene Gunyan Mélange, which serves as basement to the suture zone. The Middle Miocene Siayan-Sindangan Suture Zone was formerly a subduction zone complex that was reactivated as a sinistral strikeslip fault following the collision of eastern-central Mindanao with the Zamboanga Peninsula. New
40
K-
40
Ar whole-rock dating of lava flows from the Zamboanga Peninsula has revealed Middle to Late Miocene ages, which is consistent with the possible existence of an Early Miocene Sulu Trench. The possibility that the Zamboanga Peninsula could be part of the Palawan microcontinental block has been forwarded by previous workers, due to their similarity in stratigraphy, geological structure and metamorphic rock suites. The Palawan microcontinental block separated from southern China during the opening of the South China Sea in Oligo-Miocene times. If indeed the Zamboanga Peninsula was once part of Palawan, it represents the southernmost part of the rifted southeastern China continental margin.
Strain gradients in transpressional to transtensional attachment zones
Authors: Teyssier C. , Cruz L.
Published: April 2008

Attachment zones couple the rheological layers of lithosphere. In wrench settings, attachment zones accommodate the transition from relatively continuous wrenching at depth to discrete strike-slip faulting of rigid blocks in the upper crust. Strain is controlled by a component of wrench shearing as well as a component of horizontal shearing associated with the differential displacement of finite-width rigid blocks. Strain modelling of wrench attachments predicts high lateral and vertical strain gradients and specific foliation patterns showing antiforms and funnel-shaped synforms. Lineations are shallowly plunging and oriented close to the direction of wrenching. Shear sense reverses across the vertical axial surfaces of synforms and antiforms. In transpression and transtension attachments developed during low-angle oblique convergence or divergence, the pattern of foliation and lineation is similar to that produced in wrench attachments. Transpression attachments display gradients in the shape of the finite strain ellipsoid, from flattening at the base to strongly constrictional beneath the rigid blocks, owing to the increased effect of the horizontal shear component. Conversely, transtension attachments show constriction at the base changing to flattening beneath the rigid blocks. The location of this fabric change within attachment zones is insensitive to finite displacement and angle of convergence or divergence, and therefore should be one of the most robust criteria to identify transpression and transtension attachments. In general, the component of coaxial flow that characterizes transpressional and transtensional systems decreases upward through attachment zones, due to the increased role of the horizontal simple shear in the finite vorticity. These strain and kinematic gradients are a robust result of attachment modelling and can be used as indicators of attachments developed in wrench, transpression, or transtension.
The evolution of an exposed mid-lower crustal attachment zone in Fiordland, New Zealand
Authors: Klepeis Keith A. , Clarke Geoffrey L.
Published: April 2008

Studies of convergent margins suggest that large subhorizontal shear zones in the lower crust help regulate how displacements are transferred horizontally and vertically through the lithosphere. We present structural data from the Fiordland belt of SW New Zealand that illustrate the progressive evolution of a 25 km thick section of exhumed, Early Cretaceous middle and lower crust. The data show that the mechanisms by which displacements were relayed through the crust during a 25 Ma cycle of arc-related magmatism, high-grade metamorphism and contraction changed repeatedly. During the period 126–120 Ma, a ≥10 km thick batholith composed of gabbroic-dioritic magma was emplaced into the lower crust. Melt-enhanced shear zones evolved at the upper and lower contacts of the batholith where magma and steep temperature gradients created strength contrasts. By ∼ 120 Ma, partial melting of mafic-intermediate lower crust resulted in the formation of high-pressure (14–16 kbar) migmatite and steep, regionally extensive vein networks up to 10 km below the batholith. Melt segregation and transfer through and out of the lower crust were aided by melt-induced fracture arrays and ductile deformation in shear zones. During the period 116–105 Ma, differential shortening of the crust produced a network of subhorizontal and subvertical shear zones at different crustal depths. Near-vertical shear zones up to 15 km wide formed at the deepest part of the section. These shear zones cut upwards across the entire lower crust to merge with a gently dipping upper amphibolite facies fold-and-thrust zone that formed in the middle crust. A 1 km thick, subhorizontal shear zone underlies this mid-crustal fold-and-thrust zone and physically connected shear zones that formed at different crustal depths. Our data suggest that deformation above and below this mid-lower crustal attachment zone was coupled kinematically and accommodated subhorizontal arc-normal displacements in the middle crust and oblique sinistral displacements on steep shear zones in the lower crust. The steep lower crustal shear zones also record components of subhorizontal arc-normal shortening and vertical thickening. These results strongly suggest that large, kinematically coupled networks of flat and steep shear zones separated the Fiordland crust into distinctive structural domains and relayed displacements vertically and horizontally through the lithosphere during Early Cretaceous oblique convergence.
Attachment formation during partitioning of oblique convergence in the Ketilidian orogen, south Greenland
Authors: McCaffrey K. J. W. , Grocott J. , Garde A. A. , Hamilton M. A.
Published: April 2008

Subhorizontal attachment zones provide coupling between lithospheric layers in orogenic belts. A mid-crustal attachment zone is exposed in the Palaeoproterozoic Ketilidian orogen, south Greenland, which formed as a result of north-directed oblique convergence at a cordilleran-type margin. Rifting (
c.
2.1 Ga) and compressional deformation and magmatism (> 1850 Ma) on the continental margin was followed by an extended sinistral transpression from 1850 to 1730 Ma now separated into three episodes or peaks of activity. The first episode was focused on the back-arc region and was followed by the main arc construction phase during which transpression was partitioned into strike-slip and contraction components. Despite the longevity of this active margin system, individual tectonic events took place rapidly, e.g. development of fore-arc D
1
-D
3
and accompanying high-temperature, low-pressure metamorphism took place over
c.
12 Ma. We explain the fore-arc and batholith evolution by the upward migration of an underlying attachment structure through the upper crustal partitioned blocks. This migration may be attributed to an increase in the geothermal gradient accompanied by, or followed by, exhumation of the mid-crust. The partially molten, hence weak, attachment zone solidified and strengthened during cooling before emplacement of the post-orogenic rapakivi suite during the third distinct phase of mild sinistral transpression.
Lower Miocene deformation in the hanging wall of the Internal-External Zone boundary of the Betic Cordillera: deformation at the edges of vertical-axis rotation domains in oblique convergent margins
Authors: Fernández-Fernández E. , Jabaloy A. , González-Lodeiro F.
Published: April 2008

In the eastern Betic Cordillera, non-cylindrical doubly plunging folds deform the Subbetic Zone (the hanging wall of the Internal-External Zone boundary). Their hinges define an arc from north-south trends in the east to ENE-WSW in the west. These folds began to form during the Early Burdigalian with a NNE-SSW trend. Middle Burdigalian rocks define progressive unconformities in the cores of the synforms, recording the tightening of the folds and an increase in the plunge of the fold hinges. All these folds experienced verticalaxis rotations during the Early Miocene, acquiring the present-day arcuate pattern. During the Middle Burdigalian, the thrusting of the External Zones over the Internal Zones occurred with a top-to-the-SE sense of movement. Upper Burdigalian deposits seal the tectonic windows eroded in these thrust surfaces. This deformational history records a constrictional deformation with area reduction in the Subbetic Zone during the Early Miocene, which can be correlated with the dextral oblique convergence between the Internal and the External Zones.
Flow patterns during exhumation of the Sambagawa metamorphic rocks, SW Japan, caused by brittle-ductile, arc-parallel extension
Authors: Takeshita Toru , Yagi Koshi
Published: April 2008

Mesoscopic and microscopic structural analyses of the high-pressure/temperature Sambagawa metamorphic rocks (accretion complexes), SW Japan, have been carried out. Deformation characterized by extreme layer-normal thinning and nearly arc-parallel stretching occurred during exhumation in the Late Cretaceous. Asymmetric quartz
c
-axis fabrics and orientation of shear band cleavages reveal a pervasive top-to-the-west sense of shear in the Sambagawa metamorphic rocks during the exhumation stage. The 3D strain geometries, inferred from quartz
c
-axis fabric patterns, vary from plane strain to flattening across the metamorphic belt. We hypothesize that the data are most reasonably explained by a model of counter-flow in the subduction channel. The counter-flow was induced by a left-lateral oblique subduction of the oceanic (Izanagi) plate, which was strongly coupled with the subducting sediments. The 3D strain geometries suggest that the counter-flow (i.e. simple shear in the model) must have been accompanied by some arc-normal ‘press’ component. The mode of deformation changed from ductile to brittle arc-parallel extension, when the rocks were elevated and cooled below the temperature condition for the brittle-ductile transition of quartz (
c.
/it 300 °C). The normal faulting (i.e. brittle extension) at subgreenschist conditions was often accompanied by the precipitation of actinolite. This change in deformation mechanism with decreasing temperature is recorded by a conjugate set of normal faults found in the oligoclase-biotite zone in the study area, for which the palaeostress directions conform to the ductile strain geometries.
Transtensional deformation at the junction between the Okinawa trough back-arc basin and the SW Japan island arc
Authors: Fabbri Olivier , Monié Patrick , Fournier Marc
Published: April 2008

The Okinawa trough is a back-arc basin currently forming above the subducting Philippine Sea plate by crustal stretching of the Eurasia lithosphere. Existing geophysical investigations have revealed that the northern part of the Okinawa trough consists of a series of en echelon left-stepping grabens or half-grabens, some of which were formed in Miocene times and are presently inactive. In the Kyushu island, three major zones of extensional deformation are recognized. They are characterized by 20–40 km long sediment-filled basins lying on the hanging-wall side of N60°- to N80°-trending, north- or NW-dipping normal faults. These basins display an en echelon left-stepping arrangement. The ages of faulted rocks, the ages of graben-filling sediments and radiometric ages newly obtained on pseudotachylites associated with normal faulting indicate that extension started at 13 Ma at the southern end of Kyushu and migrated northwards in the middle part of Kyushu (Beppu Bay), where it is still active today.

The continentward-dipping, listric geometry inferred in depth for the fault systems is consistent with that of faults imaged by existing seismic profiles obtained off-shore in the Okinawa trough and across the Beppu Bay. The spatial association between Miocene or younger normal faults and pre-Miocene regional low-angle thrust faults suggests the possibility of a reactivation of some of the thrust faults as low-angle detachment faults merging in depth into a mid-crustal partial attachment zone.
Strain-rate-dependent rheology of partially molten rocks
Authors: Vigneresse J. L. , Burg J. P.
Published: April 2008

Coupling or decoupling in the lithosphere is often related to the absence or the presence of a layer of partially molten rocks, although the rheology of such rocks remains unsolved. Theoretical arguments correlated with structural observations provide new insights into the rheology of partially molten rocks, namely migmatites and magma. These rocks are simplified to two-phase pseudo-fluids constituted of a quasi-solid matrix and a variable amount of melt. Previous experiments indicate that the matrix deforms plastically according to a power law. The melt is Newtonian and weakens at high shear strain rates. Because of the heterogeneous distribution of matrix and melt phases, their rheologies cannot be averaged to obtain the rock rheology. Four behaviours are identified. (i) At high stress and strain rates, the viscosity contrast between melt and matrix is lowest. Both phases can accommodate strain at a comparable rate, allowing migmatite and magma bodies to deform as quasi-solid units. (ii) At low strain rates, the viscosity contrast between melt and matrix is highest. Melt deforms and relaxes much faster than the matrix. The simultaneous coexistence of a weak and a strong phase is expressed in a 3D viscosity-strain rate-melt fraction diagram, in which a cusp-shaped surface represents viscosity. The cusp graphically shows that the viscosity of partially molten rocks may jump several orders of magnitude. These jumps, leading to sudden melt segregation, are temporally erratic. (iii) At low strain rates, strain partitioning may lead to internal instabilities and segregation between melt and restitic phases, as observed in the leucosome/melanosome separation. (iv) Cyclic processes follow hysteresis loops and trigger strain localization.
Stratigraphic applications of substrate-specific ichnofacies: delineating discontinuities in the rock record
Authors: Pemberton S. George , MacEachern James A. , Saunders Tom
Published: April 2008

Trace fossils represent both sedimentological and palaeontological entities, providing a unique blending of potential environmental indicators in the rock record. Trace fossils and trace fossil suites can be employed effectively to aid in the recognition of various discontinuity types and to assist in their genetic interpretation. Ichnology may be employed to resolve surfaces of stratigraphic significance in two main ways: (1) through the identification of discontinuities using substrate-controlled ichnofacies (the firmground Glossifungites ichnofacies, the hardground Trypanites ichnofacies and the woodground Teredolites ichnofacies); and (2) through careful analysis of trace fossils in vertical (soft-ground) successions (analogous to facies successions). Integrating the data derived from substrate-controlled ichnofacies (so-called omission suites) with palaeoecological data from vertically and laterally juxtaposed softground ichnological successions greatly enhances the recognition and interpretation of a wide variety of stratigraphically significant surfaces. When this is coupled with conventional sedimentary facies analysis and sequence stratigraphy, a powerful approach to the interpretation of the rock record is generated.
Ichnofabrics and sedimentary facies of a tide-dominated delta: Jurassic Ile Formation of Kristin Field, Haltenbanken, Offshore Mid-Norway
Authors: McIlroy Duncan
Published: April 2008

Tide-dominated deltas are poorly known from the stratigraphic record and are notoriously complex, owing to the wide spectrum of facies encountered and their spatial/temporal variability. The tide-dominated deltaic palaeoenvironment combines the ecological harshness of brackish-water settings with complex tidal channel/tidal-flat type facies architecture on the delta top, in association with more classic deltaic facies-stacking patterns. The Ile Formation is interpreted herein as a tide-dominated delta deposited in a microtidal setting. Its palaeoenvironments are interpreted based on a combination of ichnology, ichnofabric analysis and sedimentology. Ichnofabric stacking patterns are used to elucidate the internal architecture of the notoriously problematic aggradational multi-storey tidal channel units. The tide-dominated deltas of the Ile Formation have a distinctive ichnological signature that may be used to characterize tide-dominated deltas. In comparison to typical river-dominated deltas the Skolithos ichnofacies is less well developed and ichnodiversity is lower than expected in wave-dominated deltas. The ichnofabric model presented has potential to be used, with modification, in other tide-dominated deltaic settings.
Animal-substrate interactions in freshwater environments: applications of ichnology in facies and sequence stratigraphic analysis of fluvio-lacustrine successions
Authors: Buatois Luis A. , Mángano M. Gabriela
Published: April 2008

At present, three continental archetypal ichnofacies are widely accepted: the Scoyenia, Mermia and Coprinisphaera ichnofacies. The last is present in palaeosols, and the first two occur in fluvio-lacustrine environments. Additionally, the Skolithos ichnofacies may be present in relatively high-energy fluvio-lacustrine deposits. The ichnofauna from active fluvial channels is characterised by low-diversity assemblages of simple vertical burrows and escape traces, referred to the Skolithos ichnofacies. Abandoned or inactive channel deposits characteristically contain low-diversity assemblages dominated by meniscate traces. Floodplain water bodies that experienced progressive drying (desiccated overbank deposits) may contain abundant arthropod and vertebrate trackways, backfilled meniscate traces, ornamented burrows and bilobate traces with scratch marks, which allow recognition of the Scoyenia ichnofacies. Floodplain water bodies that are filled by overbank vertical accretion without experiencing desiccation (overfilled overbank deposits) include simple grazing trails, locomotion trails and horizontal dwelling burrows, representing impoverished occurrences of the Mermia ichnofacies. Hydrologically closed lakes are very stressful environments in which subaqueous ichnofaunas are rare. The richest ichnofaunas in closed lakes are present at the lake margins, and record the activity of terrestrial rather than aquatic faunas (Scoyenia ichnofacies). Hydrologically open lakes host relatively diverse and abundant ichnofaunas, comprising the Scoyenia ichnofacies in low-energy, lake-margin areas, and the Mermia ichnofacies in permanent subaqueous lacustrine zones. Sediments deposited in relatively high-energy lacustrine environments, such as wave-dominated shorelines and delta mouth-bars, commonly are represented by the Skolithos ichnofacies. Although continental trace fossils have not been extensively used in sequence stratigraphy, they have potential for future integrated study. Softground trace fossils are commonly well developed in overfilled lake basins and are useful to delineate parasequences and parasequence sets. In balanced-fill and underfilled lake basins, softground ichnofaunas are poorly developed because of stressful conditions. In contrast, firmground suites are rare in overfilled lake basins, but widespread in lowstand deposits of balanced-fill and underfilled lake basins. Early lowstand amalgamated incised fluvial channels are usually unbioturbated, but palaeosol ichnofaunas (e.g. the Coprinisphaera ichnofacies) may delineate sequence boundaries in interfluve areas. Increasingly isolated fluvial channels encased in overbank deposits develop during late lowstand, and lacustrine deposits accumulate during transgressions, favouring preservation of biogenic structures.
Trace fossil distribution in lacustrine deltas: examples from the Triassic rift lakes of the Ischigualasto-Villa Unión basin, Argentina
Authors: Melchor Richardo N.
Published: April 2008

This paper reports six trace fossil assemblages from lacustrine deltas of the Triassic Ischigualasto-Villa Unión rift basin, northwest Argentina. They were recognized in three correlated stratigraphic sections separated by about 100 km, and come from river- and wave-influenced deltas developed in low- and high-accommodation lacustrine basins. Trace fossil assemblages correspond to delta front (six), delta plain (two) and marginal lacustrine (one) facies associations. Each trace fossil assemblage is described, together with a detailed lithofacies characterization of the trace fossil-bearing interval. They are analysed in conjunction with previously described ichnological assemblages from partially correlative sections of the same basin. Delta front facies contains a high-diversity assemblage (22 ichnotaxa), including
Cochlichnus
(a ubiquitous form),
Gordia, Helminthoidichnites, Helminthopsis, Didymaulichnus, Diplichnites, Stiaria, Cruziana, Bifurculapes, Protichnites, Diplopodichnus, Archaeonassa, Palaeophycus, Treptichnus, Rusophycus, Avolatichnium
, ‘rhomboidal traces’, ‘fusiform structures’ and ‘millimetre burrows’. Trace fossil assemblages from delta plain facies are much less diverse (seven ichnotaxa), but display representatives of a greater variety of ethological categories, including
Rhynchosauroides, Skolithos, Palaeophycus
, ‘horseshoeshaped structures’, escape trace and drab-haloed root traces. Marginal lacustrine deposits of a river-dominated delta yielded a monospecific assemblage consisting of
Cochlichnus anguineus
. Comparison of trace fossil assemblages in wave- and river-dominated lacustrine deltas from the basin (mainly those of the delta front facies) revealed important differences in ichnodiversity that can be useful in the discrimination between these lacustrine delta types. Lacustrine delta deposits contain trace fossils that can be ascribed to three different ichnofacies: a high-diversity occurrence of the Mermia ichnofacies in subaqueous delta front sediments, a low-diversity occurrence of Mermia ichnofacies in subaqueous marginal lacustrine facies, the Skolithos ichnofacies in high-energy upper delta front/lower delta plain facies, and the Scoyenia ichnofacies in intermittently exposed upper delta plain facies. The analysed trace fossil assemblages from delta front and marginal lacustrine settings suggest environmental gradients within the Mermia ichnofacies.
Modelled palaeolatitudes for the Louisville hot spot and the Ontong Java Plateau
Authors: Antretter Maria , Riisager Peter , Hall Stuart , Zhao Xixi , Steinberger Bernhard
Published: April 2008

Formation of the Ontong Java Plateau (OJP), a large igneous province in the western Pacific, has been attributed to a rising plume head in the initial stage of the Louisville hot spot, approximately 120–125 Ma ago. However, the Neal
et al.
plate reconstruction suggests that the plateau formed approximately 9° north of the current location of this hot spot at 51°S. The magnetization of the plateau’s basement records a palaeolatitude of approximately 25°S which further increases the discrepancy with the plume-head model. Modelling the motion of the Louisville hot spot for the last 120 Ma yields a possible southward motion of up to about 6°. True polar wander (TPW) models also shift the predicted palaeolatitudes of the plateau farther north. Taking into account both hot-spot motion and TPW, formation of the OJP by the Louisville not spot remains a possibility.
Early Cretaceous Pacific palaeomagnetic pole from Ontong Java Plateau basement rocks
Authors: Riisager Peter , Hall Stuart , Antretter Maria , Zhao Xixi
Published: April 2008

We present new palaeomagnetic data from Ocean Drilling Program Site 1184 on the eastern salient of the Ontong Java Plateau (OJP) where 337.7 m of Early Cretaceous (
c.
120 Ma) volcaniclastic rocks were drilled. Alternating field and thermal demagnetizations were equally effective in removing secondary components, allowing the characteristic remanent magnetization directions from a total of 173 samples (out of 183) to be defined. All samples have negative inclinations (normal polarity), and by treating each sample as an independent reading of the palaeomagnetic field a site-mean inclination of −53.9° (
N
= 173; α
95
= 1.0°,
k
= 109) was obtained. The corresponding palaeo-colatitude is in excellent accordance with previously published time-averaged palaeo-colatitudes from contemporaneous basalts drilled at OJP and the Nauru Basin. Based on the intersection of the seven palaeo-colatitudes a new Early Cretaceous (
c.
120 Ma) Pacific palaeomagnetic pole was obtained with co-ordinates 63.0°N, 10.1°E (95% confidence ellipse with a minor semi-axis of 2.9° with an azimuth of 32° and a major semi-axis of 47.7° with an azimuth of 122°). This pole is far more easterly than previously published Early Cretaceous Pacific palaeomagnetic poles. Based on published Pacific palaeogeographic reconstructions in the fixed hot-spot reference frame we were able to calculate different Pacific true polar wander (TPW) poles. All Pacific TPW poles are found to be statistically different from contemporaneous TPW poles obtained in the Indo-Atlantic realm, illustrating motion between the two groups of hot spots.
Rock magnetic results from Ocean Drilling Program Leg 192: implications for Ontong Java Plateau emplacement and tectonics of the Pacific
Authors: Zhao Xixi , Antretter Maria , Riisager Peter , Hall Stuart
Published: April 2008

A rock magnetic study has been performed on rock samples recovered at Ocean Drilling Program Leg 192 sites on the Ontong Java Plateau in the western Pacific. Igneous rocks from the five Leg 192 sites displayed variable rock magnetic properties. The differences in the rock magnetic properties are a function of mineralogy and alteration. Titanomagnetite and titanomaghemite are present in the Ontong Java rocks. Samples with titanomagnetite exhibit Verwey transitions in the vicinity of 120K. Low-temperature curves for samples with multiple magnetic phases do not clearly show the Verwey transition. The inversion of titanomaghemite to a strongly magnetized magnetite is shown by the irreversible thermomagnetic-cooling curve. Despite the geographically widespread locations of the drill sites, variations in rock magnetic properties closely resemble each other, consistent with the fundamental results of the leg that the basement rocks were derived from homogeneous Kwaimbaita-type magma with a single age of approximately 120 Ma. The rock magnetic investigation provides constraints to evaluate the fidelity of the natural magnetic memory in the basalt rocks and corroborates the palaeomagnetic palaeolatitudes determinations for the Ontong Java Plateau. The generally good quality of rock magnetic data exhibited by Leg 192 rocks supports the inference that the characteristic directions of magnetization isolated from the Cretaceous Ontong Java Plateau sites were acquired near the onset of the Cretaceous Long Normal Superchron about 120 Ma. The portion of the Pacific plate containing the Leg 192 sites was in the southern hemisphere during the mid-Cretaceous volcanism.
Experimental petrology of basement lavas from Ocean Drilling Program Leg 192: implications for differentiation processes in Ontong Java Plateau magmas
Authors: Sano Takashi , Yamashita Shigeru
Published: April 2008

Melting relations of the basement lavas drilled from the Ontong Java Plateau during ODP Leg 192 were experimentally determined at 1150–1250°C and 0.1–190 MPa under the oxygen fugacity along the fayalite-magnetite-quartz (FMQ) and cobalt-cobalt oxide (CCO) buffers. The basement lavas were classified into two types according to phenocryst assemblage and whole-rock composition: one type is low in MgO (<8 wt%) and olivine + plagioclase + augite-phyric (Kwaimbaita type); and the other is rich in MgO (>8 wt%) and olivine-phyric (Kroenke type). One sample was chosen from each type as a starting material of the melting experiments. The experimental results demonstrate that the variations in phenocryst assemblage and whole-rock composition in the basement lavas can be modelled adequately by fractional crystallization processes in a shallow magma chamber (<6 km in depth). The experimentally determined mineral-melt equilibria, in combination with detailed petrographical investigation, revealed that the vast majority of phenocrysts are in equilibrium with their host magma composition, but some are not. The latter include unusually An-rich parts of plagioclase phenocrysts in the Kwaimbaita-type lavas. These An-rich parts probably crystallized in a mushy boundary layer along the wall of the magma chamber where the melt was relatively rich in H
2
O. Some olivine phenocrysts in the Kroenke-type lavas show reverse zoning, with core compositions that can be in equilibrium with the Kwaimbaita-type magmas. The cores of these olivine phenocrysts were most probably assimilated from a solidified pile of the Kwaimbaita-type lavas when the Kroenke-type magmas ascended through it.
Geochemistry of Cretaceous volcaniclastic sediments in the Nauru and East Mariana basins provides insights into the mantle sources of giant oceanic plateaus
Authors: Castillo Paterno R.
Published: April 2008

Cretaceous volcaniclastic sediments sampled at the Nauru and East Mariana basins were chemically and isotopically analysed in order to learn more about the formation and mantle source of the Ontong Java Plateau, an oceanic large igneous province. Despite their variably altered state, the volcanogenic sedimentary components still contain petrogenetic tracers (e.g. high field strength elements, and Nd- and Pb-isotopes) that can be used to constrain the composition of their respective mantle sources. The Nauru volcaniclastics have incompatible trace-element and Nd- and Pb-isotope compositions typical of the Kwaimbaita-type tholeiitic lavas of the Ontong Java Plateau. Combined with the results of recent investigations, the presence of Kwaimbaita-type volcaniclastics in the Nauru Basin reinforces the proposal that the Kwaimbaita-type lavas comprise the bulk of the giant plateau. On the other hand, the East Mariana volcaniclastics have high incompatible trace-element concentrations and Nd- and Pb-isotope ratios typical of alkalic ocean island basalts. Their source is either the Limalok Guyot in the Ratak seamount chain of the Marshall-Gilbert Islands or the ancestral Manihiki-Hikurangi Plateau. Other geological data argue for the Manihiki-Hikurangi Plateau as the source. This implies that the mid-Cretaceous Pacific upper mantle was dominated by the sources of lavas that formed giant oceanic plateaus.
Growth of ductile opening-mode fractures in geomaterials
Authors: Eichhubl Peter
Published: April 2008

Opening-mode fractures in clinker and opal-CT chert spheroids form by growth and coalescence of pores, and are associated with extensive textural and compositional changes in the host material. Extensive inelastic deformation outside the immediate vicinity of fracture tips characterizes these fracture processes as ductile. Fracture formation in clinker is concurrent with high-temperature combustion alteration of diatomaceous mudstone. Fracture formation in chert spheroids is associated with the opal-CT to quartz transition in the same host material during early marine diagenesis. In both cases, growth of elongate pores is attributed to the combined effects of diffusive-fracture growth and flow by solution-precipitation creep. Pore growth and coalescence occur preferentially ahead of fracture tips along two directions oblique to the mean macroscopic fracture direction. This growth process, referred to as side-lobe damage, is interpreted to reflect the shear-stress dependence of pore growth by solution-precipitation creep. The tendency for oblique fracture growth is suppressed by global stress and strain-boundary conditions forcing the fracture along a characteristic zig-zag propagation path that is macroscopically perpendicular to the loading direction. These examples of ductile fracture demonstrate that macroscopic fracture formation is not uniquely associated with damage processes by microfracture at low-temperature ‘brittle’ subsurface conditions. Instead, fracture is a deformation process that can occur due to various inelastic-deformation mechanisms under diverse crustal environments, which include high-temperature conditions.
The index of hackle raggedness on joint fringes
Authors: Bahat Dov , Bankwitz Peter , Bankwitz Elfriede
Published: April 2008

In a previous laborious study we showed that considerably more new area is formed in hackle sections than in en echelon section per given nominal area of fringe. In the present study we resort to an alternative quantitative method that would enable a relatively rapid correlation between the fracture mode of secondary fractures on joint fringes and their change in fracture morphology. We introduce a set of seven criteria that enable a geologist to place every fringe on the ‘index of hackle raggedness’ (IHR) along a scale between 1 and 10. This method is applied to the ‘Mrákotin joint set’ from a granite quarry in the Bohemian Massif of the Czech Republic. The results show an IHR range between 1.4 ± 0.7 and 6.8 ± 0.7. The gap between the top value of the scale, 10, and the value 6.8 probably suggests that the joints in this study did not form under the most dynamic conditions. Experimental results carried out on polymers show that dynamic fracture is better correlated with the dynamic stress intensity and additional fracture mechanics parameters than with fracture velocity. The demonstration that en echelon segmentation may be obtained at maximum fracture velocity, if mechanical constraints are imposed on the system by crystal anisotropy, possibly suggests that similar results may be obtained under other constraints that need to be elucidated.
Preferential jointing of Upper Devonian black shale, Appalachian Plateau, USA: evidence supporting hydrocarbon generation as a joint-driving mechanism
Authors: Lash Gary , Loewy Staci , Engelder Terry
Published: April 2008

The Catskill Delta Complex of western New York State contains fractured Upper Devonian black shales throughout a 300 km-transect from the more distal, somewhat shallower, deposits of the western region of the state eastward to more proximal and more deeply buried deposits. Each black shale unit grades upward into organically lean grey shale and abruptly overlies another grey shale unit. Within each black shale-grey shale sequence, ENE-trending vertical joints, interpreted to be hydraulic fractures, are best developed (i.e. more closely and uniformly spaced) in the organic-rich shale. Moreover, the density of ENE joints diminishes up-section through each black shale unit, as does the total organic carbon (TOC) content. While ENE joints are less well developed outside the black shale intervals, joints that formed during the Alleghanian orogeny (NW-trending) are found throughout the Upper Devonian shale sequence. Both sets are best developed in black shales in the distal delta sequence, whereas in more proximal deposits the Alleghanian joint sets are best developed in grey shales. Moreover, the density of ENE joints within each stratigraphic level of the black shale exceeds that of Alleghanian joints at the same level, except in the deepest black shale where Alleghanian joints are locally best developed at the top of the black shale interval. The preferential jointing of black shale units in the Appalachian Plateau reflects an extended hydrocarbon generation history. In the distal delta, hydrocarbon generation began when black shale was close to or at maximum burial depth (
c.
2.3 km) during the Alleghanian orogeny with the propagation of a NW joint set and continued through post-Alleghanian uplift of the Appalachian Plateau when the ENE joints propagated. In the proximal delta deposits ENE joints propagated before the onset of Alleghanian deformation suggesting that the base of the Upper Devonian section was buried to thermal maturity by progradation of the Catskill Delta Complex before the advent of Alleghanian sedimentation.
Eight distinct fault-joint geometric/genetic relationships in the Beer Sheva syncline, Israel
Authors: Bahat Dov
Published: April 2008

Extended research over two decades reveals more than 20 distinct fracture episodes in the Beer Sheva syncline. This paper focuses on eight fault-joint systems that differ from each other in their genetic affiliation and/or their geometric relationship and fracture properties. Two systems are linked to burial, whereas six others relate to various syntectonic-uplift associations. Joint sets within these systems are categorized into three, pre-, syn- and post-fault groups. Correspondingly, synfault early uplift and post-fault early uplift events can be distinguished from prefault and synfault late uplift events. Water drainage may be considerably improved along certain fault-joint systems. Accordingly, in formulating fracture-network models the particular distribution of fault-joint systems and their properties need to be taken into consideration.
Environmental influences on resistivity mapping for the location of clandestine graves
Authors: Scott J. , Hunter J. R.
Published: April 2008

Geophysical surveys are being increasingly applied for the detection of clandestine burials. Ground-penetrating radar has been used successfully but is not appropriate for many sites. For this reason, other techniques such as resistivity mapping are being tested. Resistivity is sensitive to many different changes in the ground that can be caused by a grave; however, the small physical extent of the target makes location extremely difficult. Other environmentally caused variations in resistivity may be of the same magnitude as those caused by a grave, and it is important to consider whether the resistivity anomaly caused by a grave can be detected over this background variation. This paper provides a summary of the method and discusses two case studies in which resistivity mapping was employed to locate a clandestine grave. The resistivity results of a survey over moorland were dominated by the thickness of the peat coverage while the resistivity of a survey in a river valley was dominated by various environmental variations, including a medieval furrow system. Both sites were eliminated from enquiries after extensive cadaver dog searches and some excavation, although it was considered that the environmentally caused resistivity variations at both sites would have made location of a grave by resistivity alone extremely difficult. However, the success of resistivity for landfill locations suggests that resistivity may be more appropriate for the location and delineation of larger features such as mass graves.
Colour theory and the evaluation of an instrumental method of measurement using geological samples for forensic applications
Authors: Croft Debra J. , Pye Kenneth
Published: April 2008

Colour is a fundamental characteristic of many materials, including soils and sediments, and has been much used in geological, pedological and Quaternary science research. Traditionally, colour has been described qualitatively by visual comparison with standard charts, such as the
Munsell Soil Color Charts
or the Geological Society of America
Rock Color Chart
. Instrumental colour determination has been developed and used in industry for a variety of applications, including quality testing of paints, dyes and foodstuffs. In this paper, colour theory is outlined, and the Minolta® CM-2002® hand-held spectrophotometer is tested on geological samples to investigate reproducibility, discriminatory power, and accuracy in analysis. Standard methods for calibration, presentation and testing of a variety of (often small) samples have been developed. Examples are provided for the use of the method in forensic geoscience casework.
Mineralogy and microanalysis in the determination of cause of impact damage to spacecraft surfaces
Authors: Graham G. A. , Kearsley A. T. , Drolshagen G. , McDonnell J. A. M. , Wright I. P. , Grady M. M.
Published: April 2008

Cosmic dust grains are the abundant, fine-grained end-member of a range of extraterrestrial materials travelling through space. These particles can impact orbiting space vehicles (e.g. satellites and the International Space Station) at velocities ranging from 10 to 72 km s
−1
. Impact damage resulting from such a collision could potentially disable or limit the operational use of a spacecraft. There is great commercial interest from the satellite companies and space agencies to understand the nature and proportion of impacts that are caused by cosmic dust particles to assist in risk management studies and for protective shielding optimization. The successful recovery of any surface that has been exposed to the near-Earth environment offers an excellent opportunity to search for micrometre-scaled impact features and the associated projectile residues using scanning electron microscopy and X-ray microanalysis.
Assessing element variability in small soil samples taken during forensic investigation
Authors: Jarvis Kym E. , Wilson H. Elizabeth , James Sarah L.
Published: April 2008

Inductively coupled plasma analytical techniques are widely used in forensic geochemistry because they can provide concentration data for a wide range of major and trace elements relatively rapidly and at reasonable cost. A pilot study was undertaken to identify the relative importance of uncertainty resulting from instrumental measurement sources and that due to the procedures used to prepare the samples initially. Three soils with a range of major and trace element concentrations were collected to permit an evaluation of uncertainty. A reference sample of demonstrated homogeneity was also prepared and analysed. Samples were prepared in replicate (five preparations) of each, and assessment made of uncertainty in the instrumental measurement alone and for replicated preparations of the same material. Small sample sizes (0.05g) were used to mimic the situation common in forensic investigation. Results show that, while instrumental variability may be an important factor during measurement, between-sample variation has a dominant effect on uncertainty in the final result. It is clear that, without replicated measurement and preparation, the uncertainty of the measured data is unknown. Thus, critical samples, on which a case might depend, must be analysed in a way that defines clearly that uncertainty.
Isotope and trace element analysis of human teeth and bones for forensic purposes
Authors: Pye Kenneth
Published: April 2008

Isotopic and elemental concentration data can be extremely useful in the identification of human remains. Archaeological, ecological and forensic investigations to date have primarily made use of
87
Sr/
86
Sr,
143
Nd/
144
Nd,
18
O/
16
O and trace element data obtained from analysis of carbonate-hydroxyapatite in bones and teeth, and/or
12
C/
13
C,
14
N/
15
N,
18
O/
16
O and
35
S/
37
S ratios in bone collagen. However, a wide range of other chemical parameters are potentially useful for intersample comparison and environmental characterization, and increasing attention is being given to hair, nail and skin tissues, which provide dietary and environmental information over shorter time periods than bones and teeth. This paper reviews some of the principles which underlie such work and the current position with regard to modern forensic applications.
Soil as significant evidence in a sexual assault/attempted homicide case
Authors: Stam Marianne
Published: April 2008

In October 1999, a woman and her two small children were assaulted by a male acquaintance on the banks of the New River in the Imperial Valley desert region of California, USA, approximately 160 km east of San Diego. The area includes a number of agricultural fields, old lake deposits, sand dunes and the Salton Sea, a large saline inland sea. The victims escaped from the suspect and hid for 30 h in the New River, thus diminishing the possibility of obtaining physiological fluids as evidence for DNA testing. Wet and soiled clothing and shoes were collected from a suspect’s residence within hours of the assault being reported. The suspect denied any contact with the victims or with the crime scene. Analyses of the soil on the suspect’s clothing and shoes, and of crime scene soil using microscopical methods and X-ray diffraction, indicated that the soil from the crime scene and soil on the suspect’s clothing and shoes were similar. Predominant wind directions and observations of the soil distribution at the crime scene added significance to the observed similarities between the soil samples at the crime scene and the soil on the suspect’s clothing and shoes.
The case for underground CO
2
sequestration in northern Europe
Authors: Chadwick R. A. , Holloway S. , Brook M. S. , Kirby G. A.
Published: April 2008

In northern Europe numerous industrial point sources of CO
2
surround the North Sea Basin, which contains a number of viable underground sequestration opportunities. These include injection into depleted oil and gas fields and into major regional aquifers; the latter probably offering the greatest ultimate storage potential. At the Sleipner gas field, CO
2
is being injected into the Utsira Sand, a large saline aquifer. More than 6 Mt of CO
2
have currently been injected, with a projected final target of about 20 Mt. Time-lapse seismic reflection data are being used to monitor the operation and have provided clear images of the CO
2
plume and its development with time. Moreover, CO
2
volumetrics derived from the seismic data are consistent with the well injection figures. In conjunction with reservoir simulation studies, time-lapse seismic monitoring seems, therefore, to offer an effective means of predicting the future growth, migration and dispersion of the CO
2
plume. Another important aquifer, the Bunter Sandstone, stretches from Britain to Poland. In the UK sector alone, the pore volume in structural closures is equivalent to about 350 years’ worth of current CO
2
emissions from UK power generation. Industrial CO
2
sources in northern Europe are well placed to exploit these major subsurface reservoirs and European countries are technically very well equipped to use and develop this emerging technology.
Reservoir geology of the Utsira Formation at the first industrial-scale underground CO
2
storage site (Sleipner area, North Sea)
Authors: Zweigel Peter , Arts Rob , Lothe Ane E. , Lindeberg Erik B. G.
Published: April 2008

At the Sleipner fields in the North Sea, CO
2
is being injected into sands of the Miocene-Pliocene Utsira Formation, which is overlain by thick Pliocene shales. The highly porous (35%–40%) and extremely permeable (approximately 2 D) Utsira sands are organized into approximately 30 m thick packages. These packages are separated by thin (predominantly 1 m thick), low-permeability shale layers, which are assumed to contain potential fluid pathways of erosive or deformational origin. A 6.5 m thick shale layer close to the top of the sands separates an eastward thickening sand wedge from the main sand package below. Migration simulations indicate that the migration pattern of CO
2
below the shale layer would differ strongly from that within the sand wedge above. Time-lapse seismic data acquired prior to the start, and after three years, of injection confirmed a reservoir model based on these findings and showed that the thin shale layers act as temporary barriers and that the 6.5 m thick shale layer does not fully inhibit upward migration of CO
2
.