bluuebunny/crossref_metadata_2025_split huggingface dataset:
River management and conservation issues on formerly braided river systems; the case of the River Tay, Scotland
Authors: Gilvear David J. 
Published: April 2008

Abstract
Although the present-day River Tay, Scotland is generally confined to a single course and exhibits limited lateral mobility, historical maps (1747–53) reveal that during the eighteenth and nineteenth centuries a braided river channel pattern was more characteristic of a number of reaches on the piedmont valley floor. Possible explanations of the change in channel pattern include flood embankment construction, flow regulation by impoundment and possibly a change in flood magnitude and frequency, and alterations in sediment supply.
Areas of former braiding isolated from the main channel by embankments or incorporated into the floodplain sediments, exhibit a greater susceptibility to erosion and are prone to flood embankment breaches. In contrast, river channel reaches still exhibiting unconfined braiding tendencies have been designated areas of high conservational value due to large expanses of gravel at different stages of vegetation colonization and high plant species diversity.
It is suggested that the identification of areas of former braiding and reaches prone to braiding is useful for land use management both for improved flood protection and floodplain habitat conservation.
Sedimentary structures exposed in bar tops in the Brahmaputra River, Bangladesh
Authors: Bristow C. S. 
Published: April 2008

Abstract
The Brahmaputra River is one of the world’s largest sand-bed braided rivers with a channel belt up to 15 km wide, a mean channel depth of 5 m and maximum scour depths of up to 40 m. The recorded discharge varies by around 60 000 cumecs every year following the annual monsoon, producing dramatic stage fluctuations with the water level falling between 7 and 8 m from bankfull to low flow stage. In the dry season large areas of bar top and channel bed are exposed and low flow channels cut natural sections through bar tops exposing the internal stratification. Elements of upstream, downstream and lateral accretion are identified, although the high width/depth ratio of channels (up to 500:1) results in extremely low depositional dips on bed bounding surfaces. Within the accretionary elements vertical and lateral changes in sedimentary structures are ubiquitous and varied but some patterns can be discerned. Channel deposits are dominated by sinuous-crested dunes and trough cross-stratification. Upper stage plane bed lamination, often with a very low angle depositional dip, has been observed in beds up to 4 m thick and is generally found at the base of the exposed bar top sections. Trough cross-stratification in bar tops occurs in sets from 0.1 m to 3 m thick with rapid vertical and lateral changes in set thickness. Very large sets of trough cross-stratification, >3 m thick, do not occur in the bar top sections. Current ripple lamination is most abundant on the tops of bars with very high rates of climb associated with high rates of sediment deposition. From these observations a generalised vertical sequence of bar top origin might include trough cross-stratification overlain by upper stage plane bed lamination, isolated sets of trough cross-stratification truncated and capped by current ripple lamination. This sequence, which is considered to represent the deposits of a single flood, may occur within the upstream, downstream or lateral accretion elements. However, it should be noted that vertical and lateral changes in facies are extremely abundant with many changes in sedimentary structures and reactivation surfaces within each depositional episode.
Differentiated rocks of the Galapagos hotspot
Authors: McBirney Alexander R. 
Published: April 2008

Abstract
Virtually all the MORB-like tholeiites and differentiated rocks of the Galapagos Islands are concentrated along the central axis of the archipelago within 100 km of its leading island. Both have a remarkable symmetry. Those close to the centre are strongly tholeiitic, but towards the north and south they become increasingly alkaline.
Most of the differentiated suites are readily explained by crystal fractionation at shallow depths, but voluminous, aphyric rhyolites erupted from a large active volcano immediately downstream from the hotspot are more difficult to explain. Although the geochemical criteria are consistent with crystal fractionation, these extreme differentiates are not accompanied by expected amounts of intermediate compositions, such as those found on older islands; instead, they have been erupted concurrently with basalts that have undergone only minor amounts of differentiation.
The central region in which tholeiitic rocks and their differentiates have been erupted lies west of a transform fault that separates 10 million-year-old lithosphere on the west from thinner 5 million-year-old lithosphere on the east. It is also the region of thickest crust: the MOHO reaches a maximum depth of about 18 km below sea-level directly underneath the same region.
Three possible mechanisms of differentiation have been considered for the voluminous rhyolites: (a) inward crystallization of a large reservoir; (b) side-wall crystallization with convective segregation of a light felsic liquid; and (c) melting of the base of the crust. Although the first two are consistent with the geochemical nature of the rhyolites, they are not compatible with the geological relations. Moreover, they do not explain why such rocks are found only in very restricted settings. In the case of the Galapagos, these extreme differentiates are found only in the region where the crust reaches a maximum thickness near the centre of the Galapagos Platform and directly downstream from the hotspot. On a global scale, oceanic rhyolites are found close to spreading ridges and nowhere else.
These relations indicate that oceanic rhyolites are generated only where the lithospheric mantle is thin enough to permit the thermal effect of hotspots to reach the base of unusually thick crust. Remelting of pockets of felsic differentiates produced by earlier differentiation when the gabbroic layer was close to the ridge would result in trace element compositions consistent with crystal fractionation.
Palaeozoic and Cenozoic lithoprobes and the loss of >120 km of Archaean lithosphere, Sino-Korean craton, China
Authors: Menzies Martin A. , Fan Weiming , Zhang Ming 
Published: April 2008

Abstract
In eastern China Palaeozoic kimberlites and Cenozoic basalts have been erupted through the same Archaean crust, thus providing deep probes of the cratonic lower lithosphere over a period of 400 Ma. While Palaeozoic diamondiferous kimberlites point to the existence of thick, refractory lower lithosphere in the east, Cenozoic basalt-borne xenoliths reveal the presence of hot, thin, less refractory lower lithosphere. Remnants of the Archaean lithosphere may have survived as harzburgites which are chemically similar to those from the Kaapvaal craton but very different from recently accreted lherzolites. In the absence of convincing evidence for supra-subduction or intraplate processes it is believed that the dramatic change of lithosphere architecture in the Phanerozoic was caused by indentor tectonics resulting from the collision of India and Eurasia. Passive reactivation and remobilization of the Archaean lower lithosphere, in particular metasome horizons, contributed to Cenozoic magmatism aligned along major lithospheric faults.
Spreading-induced faulting and fracturing of oceanic crust: examples from the Sheeted Dyke Complex of the Troodos ophiolite, Cyprus
Authors: Dietrich Dorothee , Spencer Sara 
Published: April 2008

AbstractDetailed mapping and structural analysis of the Sheeted Dyke Complex of the Troodos ophiolite, Cyprus, has provided valuable insight into the extensional processes active during the formation of oceanic crust. Oceanic extension is essentially accommodated by: (1) a dense network of small-scale normal faults (metric to several metres spacing of the fault planes) which migrate upwards in time and space through the Sheeted Dyke Complex; and (2) larger-scale normal faults (decametric spacing of the fault planes) which detach into sub-horizontal shear zones and which cause rotation of overlying dyke packets. Geometric models are derived from these structures which differ markedly from the known models of continental extension. In particular, a new ramp/flat model of normal faulting is proposed for the most frequently occurring type of small-scale faults.
Troodos revisited: the Mount Olympus gravity anomaly
Authors: Shelton A. W. 
Published: April 2008

Abstract
Eighty new gravity stations have been established to define the intense gravity low reported by Gass & Masson-Smith in 1963. The anomaly is confirmed as circular; the implications of this, against a background 200 mGal positive with an E-W trend, are explored.
The residual anomaly has been isolated and an anomalous mass determined. From this, permissible volumes have been calculated assuming serpentinization of mantle material to be solely responsible for the anomaly. Within these constraints, modelling of the residual reveals a solution with a northerly dip consistent with the underlying subduction polarity. The modelling excludes causative bodies other than those near-surface, equidimensional in plan and having a high density contrast.
The anomalous mass allows an estimate of the uplift forces acting beneath the summit of Mt Olympus. These are shown to be three times the mass of the topography above the level of 1000 m. Implications for the rate of uplift are discussed.
MORB peridotite-sea water interaction: experimental constraints on the behaviour of trace elements,
87
Sr/
86
Sr and
143
Nd/
144
Nd ratios
Authors: Menzies Martin A. , Long Andrew , Ingram Gerry , Tatnell Matthew , Janecky David 
Published: April 2008

Abstract

The geochemical changes associated with the experimental serpentinization of peridotite are due to reaction with sea water and to the growth of new mineral phases. Since the rare earth elements (REE) and Sr are primarily ensconced in clinopyroxene, it is the unreactive nature of this phase in the presence of sea water that determines the REE content, the
87
Sr/
86
Sr and
143
Nd/
144
Nd ratio of the experimentally produced serpentinites. Serpentinites (after lherzolite and dunite) have chondrite-normalized REE abundance patterns similar to the initial peridotite indicating that the light REE (LREE) are not selectively mobilized by peridotite-sea water interaction at 300°C. However, the serpentinites produced as a result of harzburgite-sea water experiments show an increase in LREE content. Despite the sporadic behaviour of the LREE, the
143
Nd/
144
Nd ratios in experimentally produced serpentinites (after lherzolite and harzburgite) are identical to primary clinopyroxene in the unaltered peridotite. In contrast, a marked change in the strontium isotopic composition of the peridotites occurs during experimental serpentinization due to the growth of hydrous and Ca-rich phases which facilitates the uptake of sea water Sr. Whereas harzburgite and dunite alter to produce serpentinites with high Sr contents and
87
Sr/
86
Sr > 0.709, lherzolites tend to alter to serpentinites with
87
Sr/
86
Sr < 0.709. This behaviour invalidates the use of Rb-Sr data in understanding the origin of oceanic and ophiolitic peridotites, but the relative immobility of the light REE (in clinopyroxene-bearing peridotites) and the low REE content of sea water encourages the careful use of the REE and neodymium isotopes as a petrogenetic indicator for elucidating the origin of serpentinized abyssal peridotites.
The growth of continental crust during the Late Proterozoic: geochemical evidence from the Arabian Shield
Authors: Harris N. B. W. , Hawkesworth C. J. , Tindle A. G. 
Published: April 2008

Abstract
Proterozoic magmatic provinces that result from active subduction provide a critical link between contrasting styles of crustal growth during the Archæan and Phanerozoic. The Arabian Shield is an excellent example of Late Proterozoic (860–560 Ma ago) felsic magmatism that is largely calc-alkaline in composition and displays the selective enrichment of LIL elements indicative of subduction. Juvenile Nd and Sr isotope ratios confirm that the Arabian Shield represents a collage of island arcs that were responsible for a significant proportion of global crustal growth (as measured by volume of magma extracted from the mantle per unit time) during the Pan-African tectonothermal event.
The high Rb/Sr ratios and low Sr concentrations of the majority of granitoids from the Arabian Shield suggest that they may be modelled as the products of intra-crustal feldspar fractionation from a basaltic source. However, about 250f Arabian granitoids, mostly formed between 860 and 820 Ma ago, are characterized by high Sr and depleted Y abundances, indicative of melts which have not undergone fractional crystallization of feldspar, derived from a garnet-rich source. In the absence of tectonic thickening this suggests that these magmas were generated by melting the subducted slab, a process observed in contemporary arcs where unusually young, hot crust has been subducted.

The average composition of the Arabian crust at its present level of exposure is highly silica rich (SiO
2
= 66%), and mass balance constraints on the composition of the continental crust of the Arabian Shield together with seismic evidence for a lower crust of gabbroic composition, require that either delamination of a mafic lower crust has occurred or the average composition of the mantle-to-crust flux was intermediate rather than basic in composition. The latter explanation is preferred since crustal delamination implies unrealistically high crustal growth rates during the Pan-African event. A flux of intermediate composition is indicative of slab melting during subduction.

Thus trace element and mass balance considerations support the hypothesis that a significant proportion of Arabian granitoids formed during the early stages of the Pan-African event were derived from partial melting of the subducted slab, indicating that subduction of young, hot oceanic lithosphere was widespread at that time.
Evaluating Late Quaternary uplift in Greece and Cyprus
Authors: Vita-Finzi Claudio 
Published: April 2008

Abstract

Uplift data based on radiometric and archaeological dating are being used to trace the tectonic history of the eastern Mediterranean. In the Gulf of Corinth new U-series and
14
C ages suggest that there is an upper limit to coseismic uplift on both main and antithetic normal faults and that distributed extension develops serially. U-series and
14
C dates from southwestern Cyprus support geomorphological and archaeological evidence for Late Quaternary southward tilting of the island.
Basic and intermediate volcanism of the Mogollon-Datil volcanic field: implications for mid-Tertiary tectonic transitions in southwestern New Mexico, USA
Authors: Davis Jon M. , Elston Wolfgang E. , Hawkesworth Chris J. 
Published: April 2008

Abstract

Basic to intermediate volcanism of the Tertiary Mogollon-Datil volcanic field can be divided petrologically and geochemically into three temporal groups; Pre-30 Ma, 30–20, Ma and Post-20 Ma. The Pre-30 Ma and 30–20 Ma groups are dominated by high-K calc-alkaline andesites and mildly alkaline basaltic andesites respectively. These both have major and trace element characteristics typical of an orogenic origin. In contrast, the late Tertiary, Post-20 Ma lavas are typically alkaline basalts and have geochemical characteristics more consistent with a within-plate setting. The 30–20 Ma basic lavas have high Ba and Sr, and low Nb contents, resulting in high LIL/HFS element ratios (Ba/Nb
c.
80).
87
Sr/
86
Sr ratios are > 0.7065. These features are inferred to have been derived from continental mantle lithosphere modified by subduction-related processes in the Proterozoic. The Pre-30 Ma lavas have many similar characteristics but with Rb and Th enriched relative to Ba and Sr, lower
87
Sr/
86
Sr, and more subalkalic parental magmas. In contrast, the Post-20 Ma lavas show a tendency to higher Nb contents (low LIL/HFS ratios), and lower
87
Sr/
86
Sr ratios similar to OIB-like magmas derived from partial melting of the convecting asthenospheric mantle. The overall shift from predominantly lithosphere to asthenosphere-derived magmas with time in the evolution of the Mogollon-Datil volcanic field is consistent with models in which magmatism was triggered by lithosphere extension. It is concluded that calc-alkaline magmas with minor and trace element features similar to those from destructive plate margins were generated in an extensional tectonic setting. In detail, the marked change to within-plate style magmatism took place
c.
10 Ma after the period of maximum extension.
Terrestrially sourced oils: where do they exist and what are our limits of knowledge? — a geochemical perspective
Authors: Powell T. G. , Boreham C. J. 
Published: April 2008

Abstract
There are relatively few well-documented cases where significant amounts of oil (> 500 million barrels) have their origin from coals or their associated carbonaceous shales. The best-documented cases are from Australia and Indonesia and possibly the North Sea. The extensive debate as to whether coals as such or their associated carbonaceous shales are the source for oil has been essentially sterile: it has failed to take into account the heterogeneous nature of coals, the variety of their floral origins and the continuity of mineral dilution from pure coal to carbonaceous shale. Each case must be considered on its merits.
The overall petrographic composition of coal is a poor guide to its petroleum potential. Sub-microscopic lipids of bacterial and also plant origin occur in vitrinite and inertinite and contribute significantly to petroleum potential. Suberinite and cutinite are the major source of waxy hydrocarbons.
Hydrogen Indices measured on the immature versions of documented terrigenous source rocks are surprisingly low falling in the range 200–350 and occasionally lower. There is not a simple relationship between the elemental composition of terrigenous kerogen, the gross pyrolysis yield by Rock-Eval and the yield of normal hydrocarbons in pyrolysis gaschromatography. Our assessment of liquid potential in marginal source rocks, wherein most terrigenous sediments lie, is far from perfect.
A combination of the mass balance approach in conjunction with pyrolysis studies has been shown to be the most effective way of demonstrating source potential and hydrocarbon products (gas vs. oil) expected from these marginal source rocks. There is clear evidence that significant amounts of gas are generated in the conventional oil window, and that high gas to oil ratios facilitate migration from the leaner source rocks. Comparative maturation studies on oils and gas-condensates show that they can be generated at similar maturation levels.

The majority of terrigenous oils and condensates are paraffinic and the oils may have a high wax content. Exceptions occur when resin is a significant source in which case there is an increased proportion of naphthenic and aromatic hydrocarbons. Oils derived from coal-bearing sequences have high pristane to phytane ratios (>4.0); they have a high proportion of iso- and anteiso-alkanes derived from bacterial sources; hopanes predominate over steranes which are dominated by the C
29
member. A variety of diterpenoid hydrocarbons may be found which relate to the nature of the parent flora and increasingly can be used for oil-source correlation in non-marine sequences.
The oil-generating potential of plants from coal and coal-bearing strata through time: a review with new evidence from Carboniferous plants
Authors: Collinson Margaret E. , Van Bergen Pim F. , Scott Andrew C. , De Leeuw Jan W. 
Published: April 2008

Abstract

A combination of microscopy and chemistry is used to characterize high molecular weight components of plant material which contributed to Carboniferous coals and coal-bearing strata. Material was selected from coals, paper coals, coal balls, oil-shales and shales and included cuticles from stems and leaves, periderm from stems and rooting systems, spore walls, algal cell walls and ‘resin’ rodlets. Chemical analyses were undertaken using Curie-point pyrolysis-gas chromatography (-mass spectrometry) (Py-GC-(MS)) and
13
C solid state Nuclear Magnetic Resonance (NMR). Light microscopy and scanning electron microscopy were used to ensure a detailed understanding of the plant material which was analysed chemically. This study has emphasized those plants, plant tissues and organs which are known to have been dominant or major contributors to Carboniferous coals and coal-bearing sequences: arborescent lycophyte periderm (
Diaphorodendron
stems and
Stigmaria
rhizomorphs); pteridosperm cuticles (medullosan (e.g.
Alethopteris
) and
Karinopteris
), lycophyte stem cuticle (
Eskdalia
) and arborescent lycophyte spores (megaspores and microspores). Several algal cell walls (
Tetraedron, Tasmanites
and
Gloeocapsomorpha
) and the ‘resin’ rodlets derived from medullosan pteridosperm petioles have also been analysed. Results show that all of these elements (except resins) contain (or are dominated by) highly resistant, highly aliphatic macromolecules which have the potential to yield, upon catagenesis,
n
-alkanes which are found in crude oils. Resins potentially contribute cyclic hydrocarbons to crude oils. Combining all this evidence it is concluded that Carboniferous coals are oil prone and that explanations for the absence of oil-pools derived from such coals must be sought in geological or exploration factors and not in the nature of the coals themselves. A review of coal-forming floras through time, and of suggested terrestrially sourced oils and their parent coals, leads us to conclude that high molecular weight components of higher plant materials have potentially made a major contribution to oils sourced from coals and coal-bearing strata over a long period of geological time (Devonian onwards). Cell walls of freshwater algae have made a comparable contribution since the Ordovician. The oil-generating potential of each coal or organic-rich sediment will depend upon a combination of depositional environment and the floristic and chemical composition of the source vegetation and its component plants and plant parts.
Microstructural and microchemical consequences of fluid flow in deforming rocks
Authors: Knipe R.J. , McCaig A.M. 
Published: April 2008

Abstract
The different deformation mechanisms possible in rocks impact differently on fluid flow processes because of the range of induced volume changes associated with different deformation histories. Microstructural analysis of deformed rocks can provide crucial information for the identification of fluid flow pathways, determination of the physico-chemical properties of the fluid, quantification of the amount of fluid involved and an assessment of the variation in the open/closed nature of the fluid flow system. A critical factor in the efficiency of fluid flow in deformed rocks is the competition between the processes which maintain the connectivity of the high permeability pathways and those which close such pathways. The range of deformation processes which are involved in this competition will be different depending on the tectonic settings, the deformation conditions and the rock types involved. A brief review of the processes which interact to control fluid flow during deformation in sedimentary basins, crystalline basement under low to moderate grade metamorphism and during prograde metamorphism at moderate to high grades is given.