bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ocean-ridge segmentation and vent tubeworms (Vestimentifera) in the NE Pacific
Authors: Southward Eve C. , Tunnicliffe Verena , Black Michael B. , Dixon David R. , Dixon Linda R.J. 
Published: April 2008

Abstract

Vestimentiferan tube worms are important components of the hydrothermal vent and cold seep communities of the Pacific Ocean. The distribution and geographic intraspecies variation of
Ridgeia piscesae
and
Lamellibrachia barhami
were examined in the region of the Explorer (1 site), Juan de Fuca (33 sites) and Gorda (2 sites) Ridges and the nearby Cascadia Subduction zone. Isozyme electrophoresis, DNA restriction fragment length polymorphism (RFLP) and DNA sequencing techniques have been used.
Ridgeia piscesae
is widespread at hot vent sites along the ridges. The transform offset between Explorer and Juan de Fuca does not appear to impede gene flow (isozyme and RFLP data). Hydrographic conditions close to the Juan de Fuca Ridge favour bidirectional along-axis transport of planktonic larvae and some cross-axis transport. Rapid colonization by
R. piscesae
has been observed at a new vent site on CoAxial Segment of the Juan de Fuca Ridge, supporting the idea of a pool of larvae in the water overlying the ridge. The 360 km offset between southern Juan de Fuca and Gorda Ridges is associated with a significant level of genetic differentiation (shown by RFLP) which indicates some interruption to larval dispersal at this scale. The occurrence of the cold-seep species
Lamellibrachia barhami
is confirmed at one hydrothermal site, the sedimented Middle Valley on Juan de Fuca Ridge. Vestimentiferans appear to have a tremendous dispersal, location and adaptation capability. It is only at the thousand kilometre scale, that complete barriers to dispersal occur.
Plate tectonic history and hot vent biogeography
Authors: Tunnicliffe Verena , Fowler C. Mary R. , Mcarthur Andrew G. 
Published: April 2008

AbstractSince the 1977 discovery of hydrothermal vents and their extraordinary fauna, vents have been discovered along mid-ocean ridges in the eastern Pacific, on the Mid-Atlantic Ridge and on the spreading centres behind western Pacific subduction zones. The dependence of these habitats on plate activity suggests that plate history may play a strong role in their evolution. As few of the species known from vents are found in other marine habitats, an examination of biogeographic patterns with respect to plate history is feasible. An examination of taxon overlap with other sulphide-rich habitats (seeps and whale carcasses) suggests that a minority of faunal elements have common ancestors. Proximity of vent sites to each other does reflect regional similarities but it is the distance along ridge pathways and vicariant events that appear most important. An understanding of the tectonic history of our oceans provides a framework for predicting the composition of vent communities in unexplored areas.
Australian Proterozoic high-temperature, low-pressure metamorphism in the conductive limit
Authors: Sandiford Mike , Hand Martin 
Published: April 2008

Abstract

High-temperature, low-pressure (HTLP) metamorphism often reflects transient advection of heat due to magma ascent. However, the origin of HTLP metamorphism in a number of Australian Proterozoic terranes remains contentious either because of the deficiency of magmatic bodies in the terranes, or because the long time delay (>100 Ma) between magmatism and metamorphism precludes heating by existing magmatic bodies. Furthermore, a number of Australian Proterozoic HTLP terranes (such as the Reynolds Range in central Australia) show evidence of an extended history (
c.
30 Ma) of HTLP mineral growth suggesting metamorphism during a thermal regime dominated by conduction at lithospheric length scales. Australian Proterozoic metamorphic terranes are characterized by both elevated modern-day heat flows (averaging
c.
85 mW m
−2
) and granitic gneisses with anomalously high heat production rates (commonly >5–10 μW m
−3
). We show that the conditions required for HTLP metamorphism may result from conduction if the crustal heat production responsible for modern-day heat flows is concentrated at mid-crustal levels (15–20 km). Importantly, for low-intermediate mantle heat fluxes (10–20 mW m
−2
) and moderate synmetamorphic crustal thicknesses (
c.
45 km), the conductive geotherms attendant with such HTLP metamorphism do not necessarily lead to significant melting of a refractory lower crust. Importantly, the thermal regimes are very sensitive to the depths at which crustal heat production is localized. The strong dependence of the resulting geotherms on the depth of the heat-producing layer has the important consequence that only minor burial may be required to induce HTLP metamorphism, while only minor erosion (
c.
5 km) is necessary to terminate the event.
The implications of Sr-isotope disequilibrium for rates of prograde metamorphism and melt extraction in anatectic terrains
Authors: Harris Nigel , Ayres Michael 
Published: April 2008

Abstract

The preservation of chemical disequilibrium during anatexis can provide constrains on the rates of high-temperature processes provided that, firstly, the appropriate diffusion coefficients are known, and secondly, isotopes in the protolith have not been reset by dynamic recrystallization. In one example of an anatectic migmatite from the western Himalaya, isotopic homogenization has been approached between the leucosome, mesosome and melanosome at
c.
20 Ma, although apatite, with a low Sr diffusivity, remained in strong disequilibrium at that time. Intrusive granites are more likely to preserve evidence of isotopic disequilibrium provided a rapid rate of prograde metamorphism culminates in a rapid rate of melt extraction. Evaluation of the available Sr-isotope database from the Miocene Himalayan granites and their metasedimentary protoliths suggests that any increase of
87
Sr/
86
Sr in the melt relative to its source is less than 0.002. Mass-balance calculations indicate that isotopic exchange between plagioclase and mica in the protolith, and plagioclase and melt prior to extraction, must have occurred over a period in excess of 100–200 ka. Since rapid melt extraction (within <50 ka) is indicated by accessory phase dissolution rates, a comparatively slow rate of prograde metamorphism is indicated by the lack of Sr-isotope disequilibrium. This supports heating from internal heat production in thickened crust rather than from thermal advection or dissipative heating.
Chemical and volume changes during deformation and prograde metamorphism of sediments
Authors: Vernon R. H. 
Published: April 2008

Abstract
A long-standing problem is the extent of selective removal of chemical components and the amount of volume loss during the formation of slaty and crenulation cleavages during prograde metamorphism of sediments. Heterogeneous deformation leads to the formation of strongly deformed phyllosilicate-rich (P) domains and less deformed quartz-rich (Q) domains. The rocks generally show evidence of solution of quartz in P domains and addition of quartz in Q domains. The problem is whether the subtractions and additions balance or whether silica is lost from the system on the metre or broader scales. Structural studies tend to favour volume loss, whereas chemical studies tend to favour no volume loss. This review indicates that it is not yet possible to determine which of these views is correct. Deformation heterogeneity and fluid activity on a range of scales may play an important part in the development of slaty cleavage, suggesting the need for a detailed coordinated study, in which structural geologists and geochemists study identical material from the same sedimentary beds, in different parts of folds.
Local compositional changes may develop adjacent to quartz veins, and some aluminous (‘pseudopelitic’) mineral assemblages may develop in igneous rocks by base-cation leaching before or during metamorphism. However, broad chemical changes with metamorphic grade are difficult to determine, owing to protolith variation on all scales, although much more detailed chemical work with good geological control remains to be done. Marked local protolith variability may also hamper attempts to determine the chemical effects of cleavage formation.
As the density of metamorphic rocks increases generally with increasing grade, inferred conservation of mass on a regional scale implies loss of volume, which conceivably could be accommodated by collapse during deformation. Inferred volume loss implies a mass loss appropriate to the density increase. Inferred volume conservation implies regional mass gain, which is intuitively less probable. Marked chemical and volume changes occur when partial melts are removed at highest metamorphic grades.
The role of microcracking and grain-boundary dilation during retrograde reactions
Authors: Barker Andrew J. , Zhang Xing 
Published: April 2008

Abstract
Under conditions of sub-greenschist and low greenschist facies retrogression, both intragranular microcracking and grain-boundary dilatancy are important processes for facilitating fluid access into domains between fractures in metamorphic rocks. Both processes play a crucial role in promoting retrogression of high-temperature minerals. In a quartz-rich schist from Norway, garnet retrogression is clearly linked to microcracking in the vicinity of a minor fracture. Intense microcracking of quartz extends up to 12 mm from the fracture, and permits fluid infiltration. This causes extensive (70–100%) garnet retrogression to chlorite. At distances >16 mm from the fracture there is no sign of fluid infiltration and garnets are entirely unaltered.
The spatial distribution of grain-boundary reaction products in a scapolite-dominated rock from Scotland provides evidence for the significant role played by transient grain-boundary dilatancy in promoting grain-scale fluid access and resultant retrogression. By applying distinct element modelling (UDEC code) the geometrical differences in distribution of grain-boundary reaction products are directly related to subtle differences in the magnitude and orientation of applied stresses and patterns of transient grain-boundary dilatancy.
Recent experimental progress in the physical description of silicic magma relevant to explosive volcanism
Authors: Dingwell Donald B. 
Published: April 2008

Abstract
Explosive eruptions of silicic magmas are the result of a complex interplay of physico-chemical processes (e.g. decompression, volatile saturation, bubble nucleation and growth, crystallization, foaming, fragmentation and annealing). These processes occur over a relatively wide range of temperature, pressure, stresses and time scales. Furthermore, substantial changes in the chemical and physical properties of the eruptive magmas are induced by decompression and degassing. Numerical modelling of eruptive processes presents us with a picture of a magma column where enormous vertical gradients in the physical state and properties of the continuous magma body in the conduit result from decompression and degassing. Adequate representation of the physico-chemical evolution of eruptive systems therefore requires a relatively detailed description of melt properties in order to be robust and generalizable. The source of property data for silicate melts is experimental investigation. In recent years much effort has been concentrated on rhyolitic melts under conditions relevant to explosive volcanism. Here several aspects of this work are highlighted. (1) The description of hydrous rhyolitic melt properties (density, surface tension, viscosity and thermal conductivity) has been greatly improved. (2) The solubility of water as well as its diffusivity in silicic melts has been investigated in detail at relatively low pressures. (3) Rheological and transport complexities of melts and magmas such as non-Newtonian melt rheology, viscoelasticity, crystal and bubble suspension rheology, and foam deformation, permeability and stability have been explored. (4) Studies of the mechanical strength of magma have been initiated. Some of the insights into the nature of explosive volcanism provided by these studies are also of a qualitative nature (e.g. the degree of equilibrium during degassing, the longevity of textural magmatic states and the mechanism of fragmentation). It is hoped that this description of experimental progress in melt properties will encourage the reader to conpare the assumptions, descriptions and predictions of the modelling of eruptive processes presented in this volume with the physical nature of the magmas involved that is described herein.
Gas loss from magmas through conduit walls during eruption
Authors: Jaupart C. 
Published: April 2008

Abstract
There is ample evidence that the transition from an explosive eruption regime to an effusive regime can be due to magma losing gas to fractured country rock during ascent towards the surface. This is shown by the deuterium: hydrogen isotopic ratios and dissolved water contents of erupted samples, and by various petrological observations. Field studies demonstrate that the walls of an eruption conduit are fractured and penetrated by veins infilled with vesicular pyroclasts and ash. At Mule Creek, New Mexico, USA, a fossil eruption conduit filled with lava can be studied over a height of 300 m. The gas volume fraction exhibits complex variations with height and with horizontal distance from the walls, which is not compatible with closed system degassing. Lava close to the conduit walls is almost devoid of vesicles, showing that gas escape has been efficient. Gas flow through liquid magma may be achieved through fractures or through connected bubbles. Theoretical flow models which account for gas loss through conduit walls show that eruptive behaviour is very sensitive to the eruption rate and to the chamber pressure. A gradual decrease of chamber pressure, due to withdrawal of magma, leads to a transition from explosive to effusive conditions. Conversely, a gradual increase of chamber pressure, due to reinjection from a deeper source of magma, leads to a transition from effusive to explosive conditions. The initiation and propagation of gas-filled fractures during an ongoing eruption may be detected seismically. This chapter puts together several independent pieces of evidence in a coherent framework and includes a discussion of unresolved questions.
Analysis of digital elevation data for the Scottish Highlands and recognition of pre-Quaternary elevated surfaces
Authors: Ringrose Philip S. , Migoń Piotr 
Published: April 2008

Abstract

Remnants of elevated palaeosurfaces in the Scottish Highlands, proposed in numerous earlier studies, have been re-evaluated using digital elevation data from the Ordnance Survey. Histograms of elevation frequency, for areas 5, 10 and 20 km
2
, display multi-modal distributions which can be interpreted in terms of plateau and base-level components. The effects of glaciation, lithology and faulting can be inferred from patterns in the elevation distribution. The histogram modes reveal a series of elevated surfaces which broadly confirm previous, qualitative models of inclined Tertiary palaeosurfaces, but indicate a much more complex pattern. Many of the elevated surfaces are seen to be inclined towards two major faults, the Great Glen Fault and the Ericht-Laidon Fault. However, the highest surfaces may have crossed these fault zones uninterrupted. A model in which an episode of tectonic reactivation imposes a major change on pre-Quaternary geomorphological evolution in this area is proposed.
A pre-Pliocene or Pliocene land surface in County Galway, Ireland
Authors: Coxon Peter , Coxon Catherine 
Published: April 2008

Abstract
This paper describes a site on the Carboniferous limestone of County Galway, Ireland, where a complex of gorges, cave passages and shallow surface depressions is filled with organic silt and clay overlain by white quartz sand. The dating of the biogenic deposits to the Late Pliocene by biostratigraphical means provides a record of this largely undocumented period of Irish geological history. However, the particular importance of this site is that unlike other Irish karst infills, it represents not just the localized preservation of material in a closed depression but evidence of a more widespread cover of sediments suggesting the preservation of a Pliocene or pre-Pliocene land surface. This implies that glacial action throughout the Pleistocene has resulted in relatively little bedrock erosion in this region and raises the possibility that the present day landscape of the western Irish limestone lowlands may retain influences of preglacial karstification.
Palaeosurface palynofloras of the Skye lava field and the age of the British Tertiary volcanic province
Authors: Jolley David W. 
Published: April 2008

Abstract

Collection and palynological analysis of intratrappean boles, mudstones, sands, conglomerates and coals from the Skye lava field has allowed the reconstruction of geomorphological features and vegetation distribution on five palaeosurfaces. These palaeosurfaces show a changing pattern of streamside, swamp and upland vegetation which fall into three forest types: mixed mesophytic, upland Taxodiaceae and montane conifer forest. Comparisons of the Skye palynofloras with others analysed from the intra and intertrappean beds of the Antrim, Mull and Small Isles lavas, gives evidence of three (possibly four) main phases of British Tertiary volcanic province extrusive activity. In comparison to complete palynological records from the Faeroe-Shetland Basin, Skye and Antrim palynofloras can be dated as ranging from 58.23 Ma to 57.99 Ma, while those of the Mull Lavas, and coals below the Faeroe Islands Middle/Upper Basalts indicate initiation and resumption of extrusion after 55.00 Ma. Evidence of the age of palynofloras from the intratrappean beds of Eigg and Muck is limited, and does not dispute the Chron 27r age suggested by isotopic analysis (
c.
62 Ma). Finally palynological evidence is presented showing two major subsidence phases, and one uplift phase during the 0.24 Ma existence of the Skye Lava field. It is suggested that altitudes in excess of 1200 m were experienced during thermal doming related to the emplacement of the Cuillin centre. The relative timing of this and other volcanic events is compared to subsidence patterns in the marine sedimentary record.
Tertiary palaeosurfaces of the SW Deccan, Western India: implications for passive margin uplift
Authors: Widdowson M. 
Published: April 2008

AbstractTwo genetically distinct lateritized palaeosurfaces of different ages are recognized in the southwest Deccan Traps region of Western India using a combination of geochemical, topographical, and satellite image data. The Deccan Traps were erupted at the Cretaceous-Tertiary boundary (c.65 Ma), and comprise a huge area of originally near-horizontal basalt lavas covering much of northwest Peninsular India, and topographically forming the coast-parallel Western Ghats escarpment and elevated Maharashtra plateau to the east.Remnants of the older, palaeosurface currently exist as a series of isolated, laterite-capped plateaux forming the highest elevations along the Western Ghats (15°30′–18°15′ N). This surface is of late Cretaceous-early Tertiary age, and originally developed upon flows which lay at, or near to, the top of the lava sequence. This lateritization phase was terminated by a period of uplift and extensive erosion in lower- to mid-Tertiary times during which the low-lying, low-relief coastal (Konkan) plain developed through the eastward recession of the Ghats scarpline. A second phase of lateritisation occurred upon this coastal pediplain during mid- to late Tertiary times. Since the earlier uplift had gently deformed the lava pile prior to the development of the pedimented surface, the low-level Konkian laterite lies with marked angular unconformity upon the lava stratigraphy. Both surfaces have been subject to further large-scale distortion resulting from continuing uplift effects.Development and evolution of these Deccan palaeosurfaces is important since together they provide a record of uplift effects in western India. Moreover, they offer a datum against which the uplift erosional history may be further constrained and demonstrate that uplift effects have acted upon the Indian margin throughout the Tertiary. Since such longevity of uplift is difficult to reconcile with the commonly cited thermal and dynamic post-rift mechanisms known to act upon passive margins, the morphological and structural evolution of the rifted Deccan margin is better described in terms of denudational isostasy.
Topography, palaeosurfaces and denudation over the Karnataka Uplands, southern India
Authors: Gunnell Yanni 
Published: April 2008

AbstractA synthesis of new information from extensive field reconnaissance and systematic map analysis from southern India is presented. A new interpretation for landscape development in the Karnataka upland region is given. Three phases of geomorphological evolution are identified.A fundamental, pre-Deccan Trap palaeosurface is recognized. While becoming largely fossilized at 65 Ma by the eruption of the Deccan lavas, its southern continuation, studied here, remained exposed throughout the Tertiary and evolved in response to uplift and crustal flexuring of the Indian margin. Remnants of this surface now occur as the highest summits of the region (c.1900 m above sea level).A younger, intermediate or post-Deccan Trap palaeosurface may be recognized by a combination of superimposed drainage and morphological mapping techniques. It evolved in response to the loading of the Indian shield by the 1–2 km thick Deccan lava pile.The third and final phase of landform development is complex since it has not resulted in a single surface of regional extent but rather a series of contemporaneous, but locally restricted, levels at varying altitudes. These are not interpreted as the result of cyclical erosion but as controlled in acyclical fashion by individual river catchments and lithological heterogeneity. The possible causes for this complexity are discussed and confronted with existing schemes of landscape development on other continents.
Archaean crustal growth and tectonic processes: a comparison of the Superior Province, Canada and the Dharwar Craton, India
Authors: Choukroune P. , Ludden J. N. , Chardon D. , Calvert A. J. , Bouhallier H. 
Published: April 2008

AbstractWe present a comparison of the processes involved in the tectonic evolution of two Archaean cratons, the Superior Province of Canada and the Dharwar Craton of India. These two cratons exhibit distinct map patterns, the Superior Province being dominated by elongate belts, while the Dharwar Craton is characterized by dome and basin features.We suggest that certain tectonic processes operating in the Phanerozoic, such as enhanced mantle plume activity, subduction of young (warm) oceanic crust, and faster than usual accretion of crust, may have been the norm during the Archaean. In the Superior Province rapid crustal growth occurred, largely due to horizontal tectonic forces. Models analagous to modern plate tectonics are applicable, but the rates of convergence and accretion exceeded those normal for the present day. Accreted crust was warm and subject to more ductile deformation than in modern accretionary zones. These accreted arc, ocean-floor and ocean-plateau fragments would have been underlain by a thick refractory, buoyant, warm lithospheric root that was rapidly underplated (or imbricated) below the recently accreted terranes. In the Dharwar craton a major thermal event appears to characterize its evolution at 2.5 Ga. Reheating of the lower and middle crust in response to magmatism and metamorphism, resulted in diapirism and growth of crust in a vertical sense.The southern Superior Province’s evolution reflects accretion at the margins of a protocraton, while the Dharwar craton’s tectonic environment may reflect plume impact and incipient rifting in the centre of an Archaean craton.