bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geochemical and Petrological Significance of the Archaean-Proterozoic Boundary
Authors: Taylor S. R. 
Published: April 2008

Summary

A significant change in the nature of igneous activity responsible for continental growth apparently occurred at the Archaean-Proterozoic boundary. The sedimentary record is consistent with an Archaean upper crust dominated by the bimodal basic-felsic suite, with both units derived by melting at mantle depths. In contrast, the Proterozoic (and younger) upper continental crust is dominated by K-rich granites, derived by intracrustal melting. This major episodic event produced an upper crust enriched in incompatible elements (e.g. Rb, U) as attested inter alia by the increase in
87
Sr/
86
Sr in marine carbonates in the early Proterozoic, and the abundance of early Proterozoic uranium deposits. This event seems to have been connected with the widespread initiation of subduction related calcalkaline volcanism, which, since that time, has been the principal contributor to continental growth. Although the change at the Archaean-Proterozoic boundary was the major episodic event in continental growth, minor episodes of cratonization occurred in the early Archaean, and some greenstone belt development lingered into the early Proterozoic. More recent episodes of continental growth (e.g. 1800 Ma event) appear to have been on a smaller scale. The sedimentary record is transparent to them, and they do not represent any fundamental change in the igneous processes responsible for continental growth.
Early Proterozoic Subaerial Volcanism and Its Relationship to Broken Hill-type Mineralization in Central Sweden
Authors: Parr Joanna , Rickard David 
Published: April 2008

Summary
Broken Hill-type mineralization is characterized by abundant exhalites in a sulphur-poor, felsic volcanic environment. It is typically Proterozoic. The Ljusnarsberg area in central Sweden is a microcosm of this mineralization type. One part of the amphibolite-grade, supracrustal succession is characterized by a thick sequence of subaerial volcaniclastics which grade into diverse chemical sediments interpreted as exhalities containing sulphide, iron oxide and manganese mineralization. The environment is interpreted as terrestrial with frequent lakes which are fed by volcanic exhalations. Evaporites may also have been present. The non-marine environment may not only have helped determine the nature of the mineralization in the area but also affected the chemistry of the volcanic host rocks. Thus, the occurrence of potassic and sodic metavolcanics may be related to the effects on hydrothermal solution chemistry and water-rock ratios of non-marine surface conditions, as well as alteration temperature and primary volcanic chemistry.
U-Pb Geochronology of Accreted Terranes in the Trans-Hudson Orogen, Northern Saskatchewan, Canada
Authors: Lewry J. F. , MacDonald R. , Livesey C. , Meyer M. , Van Schmus R. , Bickford M. E. 
Published: April 2008

Summary
U-Pb zircon ages from magmatic rocks in predominantly juvenile accreted terranes of the Trans-Hudson Orogen in northern Saskatchewan constrain timing of orogenic events, and enhance understanding of local domain relations and the relation of the Trans-Hudson to other early Proterozoic orogens in North America. Most units yield zircon ages of 1890 to 1835 Ma. Six metarhyolites, from the La Ronge and Glennie Domains and Hanson Lake Block, give ages of 1888 to 1876 Ma. Most plutons, ranging from ‘early synkinematic’ tonalites and granodiorites to less deformed ‘late’ intrusions such as the Wathaman Batholith and other smaller bodies, yield ages between 1870 and 1835 Ma. Some of the youngest ages were obtained from highly deformed plutons, suggesting that regional thermotectonism postdated 1835 Ma, that variation in deformation of the plutons is a function of extreme heterogeneity of regional strain and that degree of deformation is not a reliable field indicator of relative age. Similarity of ages of volcanics and plutons in different domains suggests that domainal distinctions are mainly lithotectonic, rather than temporal.

Zircons from the Sahli ‘granite’, Hanson Lake Block, yield equivocal data. Discordia upper and lower intercepts for this body suggest that
c.
2500 Ma old granitic rocks were subjected to high grade metamorphism
c.
1900 Ma ago, with substantial resetting of zircons: this supports published Rb-Sr isochron data and indicates that the Sahli granite represents reworked Archaean basement.

Most zircon ages are older than reported Rb-Sr isochron ages on the same or similar units, suggesting open-system Rb-Sr behaviour. Zircon ages from this part of Trans-Hudson Orogen are similar to those from igneous units of the Penokean, Wopmay and Svecofennian Orogens, suggesting near-synchroneity of igneous and tectonic events during early Proterozoic continental assembly.
Geochemistry, Tectonic Setting, and Mineralization of High-Potassium Middle Proterozoic Rocks in Central Labrador, Canada
Authors: Ryan A. B. , Baragar W. R. A. , Kontak D. J. 
Published: April 2008

Summary
The Sylvia Lake Formation of the Bruce River Group is one of several middle Proterozoic volcanic sequences along the northern margin of the Grenville structural province. It comprises a variety of basaltic to rhyolitic lava flows and pyroclastic rocks, of which the majority are felsic welded ash-flow tuff. The Sylvia Lake Formation is a bimodal sequence, in which low silica (basaltic) and esite and rhyolite are the predominant compositions. The rocks are enriched in potassium, and exhibit other characteristics of the high-K calcalkaline and shoshonite association. The volume of rhyolitic ash-flows in relation to the amount of mafic material, the presence of trachyandesites, and the overall chemistry are indicative of substantial influence of continental crust on the development of the volcanic pile. The volcanics are host to numerous base metal and uranium showings, and have potential for precious metal concentrations. The volcanism of the Sylvia Lake Formation represents the last expression of a long-lived middle Proterozoic plutonic episode in this area, but the tectonic framework at the time of generation of these magmas is poorly constrained.
Proterozoic Volcanic Rocks of the Northern Guiana Shield, South America
Authors: Gibbs A. K. 
Published: April 2008

Summary

Early Proterozoic greenstone belts exposed over approximately 100 000 km
2
in the northern Guiana Shield resemble many late Archaean greenstone belts in lithostratigraphy, styles of deformation and metamorphism, and probably also in mineral resource potential. Basalts dominate the lower sections, overlain by more diverse and porphyritic mafic, intermediate, and felsic volcanics. Tholeiitic and calcalkaline suites are both common. Few rocks have 63–68 wt% silica, making the population bimodal. Tholeiitic basalts have Ni, Cr, and Co contents as high as many Late Archaean basalts. Magnesian basalts and concordant ultramafic schists suggest the presence of komatiites. Minor high-K calcalkaline andesites occur high in the volcanic sections in Guyana, and might belong to a younger sequence. Hundreds of placer and shallow gold deposits have been developed; exploration for deeper gold deposits is warranted. Common evidence of synvolcanic hydrothermal activity suggests that volcanogenic sulphide ore deposits may be found when appropriate exploration methods are applied.

Felsic volcanics were erupted over much of the Amazonian craton following its consolidation in the 2.1–2.0 Ga Trans-Amazonian orogenic cycle. These were accompanied by epizonal granitoid intrusives and mafic dykes and sills. Alkaline mafic volcanics, alkaline complexes, carbonatites, and possibly also kimberlites were erupted in the late Proterozoic.
Fundamental Uniformity in the Trace Element Patterns of the Volcanics of the Kaapvaal Craton from 3000 to 2100 Ma: Evidence for the Lithospheric Origin of These Continental Tholeiites
Authors: Myers R. E. , Cawthorn R. G. , McCarthy T. S. , Anhaeusser C. R. 
Published: April 2008

Summary
In order to examine the nature of the mantle beneath the Kaapvaal Craton in southern Africa, data from thirteen volcanic sequences ranging in age from 3000 to 2100 Ma have been examined in this study. Variations in Nb, La, Ce, P, Zr, Ti, and Y have been evaluated using a niobium-normalized spidergram which minimizes variations due to fractional crystallization and clearly illustrates mantle source variations. Using this diagram a pattern, showing strong LREE enrichment of source relatively depleted in niobium and titanium, has been identified which remains quantitatively the same throughout this time period, indicating that it is the result of a reproducible equilibrium process. Melting of an incompatible element enriched (modally metasomatized) subcontinental lithosphere in which renewable metasomatic phases, such as diopside, are residual during melting can explain the quantitative uniformity and the time independence of this pattern.
Geochemistry of Proterozoic Volcanics, Mount Isa Inlier, Australia
Authors: Wilson I. H. 
Published: April 2008

Summary
The Mount Isa Inlier contains four early to middle Proterozoic depositional cycles comprising terrestrial and shallow marine metasediments and intercalated metavolcanics. Several phases of granite and swarms of dolerite dykes (both partly comagmatic with the volcanics) intrude the sequence which is regionally metamorphosed in the greenschist and amphibolite facies. Structure is locally complex.
The oldest cycle (Leichhardt Metamorphics: 1865 Ma) comprises metamorphosed rhyodacite and rhyolite. The second cycle (Magna Lynn Metabasalt and Argylla Formation: 1777 Ma) contains metamorphosed basalt, andesite, dacite, rhyolite, and clastic sediments. The Eastern Creek Volcanics (about 1700 Ma) is the most extensive example of the third cycle which is dominantly metabasalt and metamorphosed clastic sediments. The final cycle (1680–1610 Ma) is characterized by highly potassic (alkaline or altered) volcanics ranging from mafic lavas to felsic tuffs, interbedded with clastic and dolomitic sediments (e.g. at Mount Isa) which show little evidence of metamorphism.

Almost five hundred specimens from twenty volcanic formations have been analysed since 1969, in conjunction with 1:100 000 regional mapping of the Inlier (60 000 km
2
) by the Bureau of Mineral Resources and Geological Survey of Queensland. For most specimens eleven major elements, four volatiles, and fifteen trace elements were determined, but up to thirty eight trace elements (including REE and F) were determined for representative pecimens of each major rock type. The analyses and isotopic dating have been used in characterizing the different volcanic units, petrological studies, tectonic modelling, and studies of alteration and ore genesis. Most of the mafic volcanics have tholeiitic affinities. The older felsic volcanics have calcalkaline affinities consistent with partial melting of a pelitic source. The later volcanics have bimodal characteristics.
Post-Palaeocene evolution of regional groundwater flow systems and their relation to petroleum accumulations, Taber Area, southern Alberta, Canada
Authors: Tóth J. , Corbet T. 
Published: April 2008

Summary

Three regionally extensive fluid dynamic systems have been mapped in a 23 500 km
2
portion of the Western Canada Sedimentary Basin in south-eastern Alberta. The Modern Land Surface System reaches depths of 300 m and is well adjusted to the modern relief. The subjacent Erosional Rebound System occupies most of the 600 m thick predominantly shale Colorado Aquitard including its often gas-bearing sand members. It is characterized by extensive regions of sub-hydrostatic pressures. Below the Colorado Aquitard is the Cypress Plain System which has strong upward-directed forces and mild but definite lateral components. The lateral components oppose the modern relief and are oriented from the centre of the study area toward its western and eastern boundaries where most of the known oil fields are also located. The three dynamic systems are interpreted to be transient stages of sequentially superimposed gravitational and dilatational force fields. The gravitational fields depend on topography and the dilatational field results from elastic rebound of the Colorado Aquitard in response to erosional removal of 700 m of overburden during Pliocene and Pleistocene times.

The flow pattern that existed during the time of the Cypress Plain was generated after Palaeocene (58 Ma) or Eocene (36 Ma) times by a palaeo-relief dominated by the NE-SW-trending Bow Island Topographic High. It was composed of and maintained as cross-formational gravity-flow systems throughout at least the Miocene (i.e. for more than 30 m.y.). Oil migrated to and was entrapped in the discharge regions of these systems. Subsequently, dilation of the Colorado Aquitard created the hydraulic sink in the Erosional Rebound System and induced gas to exsolve and accumulate in the sands.
Based on a one-dimensional solution of the diffusion equation, periods of 10 m.y. and 0.1 m.y. respectively were calculated to be required for pore pressures below and above the Colorado Aquitard to adjust to changes in the land surface. Compared with inferred ages and durations of palaeo-topographies, these times agree with the hypothesized evolutionary history of flow systems. There was sufficient time for flow in the Cypress Plain System to adjust to the post-Eocene relief but not enough time has yet elapsed for it to re-adjust to the Modern Land Surface which was initiated during middle Pleistocene (1 Ma) times. In contrast, the Modern Land Surface System has had 10 times the 0.1 m.y. required for it to adjust to the modern relief, and thus its apparent steady state is expected.
Fluid flow and diagenesis in the East Midlands Triassic sandstone aquifer
Authors: Bath A. H. , Milodowski A. E. , Strong G. E. 
Published: April 2008

Summary

The flow system, hydrochemistry and isotope hydrology of the freshwater aquifer in the E Midlands Triassic sandstone are reviewed. Isotopic data suggest a mean flow velocity of around 0.6 m.y. over the last 30 k.y., in contrast with the present-day velocity of around 0.2 m.y. The difference is attributed to changes in hydraulic gradients over this period; fluctuations in recharge and gradients would have influenced meteoric water influx and diagenesis over the last 10
7
years or more. The diagenetic modifications to the arkosic sandstone are described and are divided into those taking place before and during compaction, probably with saline pore water, and those occurring as a result of meteoric water influx following uplift and denudation.

The relation between the kinetics of diagenetic reactions and the groundwater flow velocity is discussed. Relevant experimental data for reaction kinetics are summarized. The hydrochemistry and flow velocity of the present regime are used to deduce mass transfers within and outside the aquifer. These are equivalent to uniform porosity increases of only about 0.17fb3e69cer million years for each of the dolomite and K-feldspar dissolution reactions. Both these dissolution reactions are incongruent, and precipitate calcite and kaolinite respectively. The spatial arrangement of reactant and product minerals in incongruent reactions is expected to reflect interplay between dissolution/precipitation kinetics and water flow rate. Scanning electron micrographs show the proximity of K-feldspar and kaolinite. Constraints can be placed on the flow rates responsible by considering chemical balances for aluminium and silicon and their maximum production rates by feldspar dissolution.
This approach involves many simplifications and assumptions, but with further experimental kinetic data it offers the possibility of deducing information on past flow systems from detailed measurements of diagenetic mineralogy and geochemistry in clastic sediments.
Quaternary landforms, sediments, depositional environments and gastropod isotope ratios at Adrar Bous, Tenere Desert of Niger, south-central Sahara
Authors: Williams M. A. J. , Abell P. I. , Sparks B. W. 
Published: April 2008

Summary

Sediments deposited in a variety of environments including fluviatile sands and gravels, aeolian sands, lacustrine clays and diatomites, and swamp clays crop out in and around Adrar Bous, an isolated ring-complex in the northern Tenere Desert of Niger. These sediments range from Recent to at least Middle Pleistocene in age, and contain both reworked and primary-context stone artefact assemblages testifying to recurrent prehistoric occupation of the plains around the massif from at least Upper Acheulian times onwards. During the early Holocene a small lake, stable at 710 m a.s.l. supported a community of Epi-Palaeolithic hunter-gatherers who also ate aquatic foods until the lake dried out at around 7500–7000
bp
. Occupation of the piedmont plains resumed during 6000–4000
bp
when Neolithic pastoralists grazed their cattle around a smaller lake stable at 700 m a.s.l. The Holocene mollusc assemblage and the stable isotope ratios obtained for different species of Holocene gastropods are entirely consistent with, and help to refine, the palaeoenvironmental reconstruction based upon stratigraphic and sedimentary analyses supplemented by the use of prehistoric stone tool assemblages as ‘zonal fossils’.
Aeolian abrasion of quartz particles and the production of silt-size fragments: preliminary results
Authors: Whalley W. B. , Smith B. J. , McAlister J. J. , Edwards A. J. 
Published: April 2008

Summary
Experimental abrasion of quartz sand in an air stream shows that particles with initially high angularity are progressively rounded by the chipping of edges and corners. Grains closely resemble dune sand grains from deserts with respect to rounding and microscopic surface textures after 48 hours of abrasion. Results show an initially high weight loss from the original grains (primarily by edge chipping), compared with subsequent abrasion. High percentages of coarse and medium silt are produced but there is a gradual increase in the percentage of fine silt as rounding increases and the quantity of fines generated declines. Silica extraction from the fines using water shows concentrations of several hundred ppm. Implications for loess production and silcrete formation are suggested.
The mechanics and geological implications of dust transport and deposition in deserts with particular reference to loess formation and dune sand diagenesis in the northern Negev, Israel
Authors: Pye K. , Tsoar H. 
Published: April 2008

Summary
Entrainment, transport and deposition of dust in and around deserts has major geological implications. A consideration of the mechanics of dust transport and deposition shows that ‘desert loess’ can only accumulate in vegetated desert fringe areas which are relatively close to a major source of dust. Dust deposition can also contribute to the stabilization of active sand dunes, and infiltrated dust plays an important role in the early diagenesis of a wide range of desert sediments.
Dune networks
Authors: Warren A. , Kay S. 
Published: April 2008

Summary
Dune networks are one of the commonest of dune types, and yet the least understood. A nomenclature is developed for describing the components of these systems. It uses the idea of dune memory: dune systems with little sand have little memory, those with more sand ‘remember’ the effect of the most dominant wind throughout the year; some dunes may have ‘mega-memories’, remembering events from the Pleistocene. The nomenclature defines the components of dune networks according to both relative dominance and whether the components are transverse, seif-like or nodal elements. Using this nomenclature, the dynamics of two dune networks in the Wahiba Sands of Oman are described. In one low-memory dune system, where individual dunes are 1 to 2 m high, a plot of 150 by 50 m was surveyed. In a second, higher memory dune system, where individual dunes are 5 to 6 m high, a 200 by 200 m plot was surveyed and an intensive study of sand movement was conducted. Both areas were surveyed in January and March 1986. A further survey was conducted in mid-July. Dune movement is related to topographic parameters such as altitude, slope angle and slope azimuth, slope curvature and proximity to other slopes. An analysis of sand loss or gain at one site is also presented. The dunes were found to be highly mobile. Some crests moved up to 80 cm in 9 hr. Movement was restricted to the upper flanks of ridges. However, adjustment to new wind conditions is very quick.
Late Palaeozoic cold-climate aeolianites, southern Cooper Basin, South Australia
Authors: Williams B. P. J. , Wild E. K. , Suttill R. J. 
Published: April 2008

Summary
Core facies analysis of the Permo-Carboniferous Gidgealpa Group of the southern Cooper Basin, South Australia has revealed sandstones of aeolian origin within the glacigenic Merrimelia Formation. The aeolianites comprise exclusively porous, poorly cemented, medium- and fine-grained sandstones dominated by parallel lamination. Sharp, planar truncation surfaces divide the suite into units composed mainly of translatent windripple lamination and minor amounts of sandflow bedding with primary depositional dip (post-compaction) varying between 0° and 25°. Distinctive compressional, tensional and dissipation structures are preserved in deformed lee-slope deposits and the inclusion of low-angle cross-strata and wedge-bedded units locally indicate deposition on the basal aprons of dunes or in contiguous sand sheets. Wet interdune sediments with adhesion ripples are also exhibited in the cores. The aeolianites, up to 232 m thick, have been traced subsurface by integrating core facies, wireline logs and seismic reflection analysis. A low-interval transit time on sonic logs is characteristic of the porous aeolianite sand and has facilitated mapping of the dune field using seismic data. The sandstone body trends SE-NW, is 6 to 8 km wide and passes laterally into outwash fan and fluvioglacial, braidplain deposits. Potential hydrocarbon traps may occur at the top of the aeolianites, or within them beneath intraformational seals formed by possible muddy interdune facies. The overall high-latitude, cold-climate nature of the Merrimelia Formation, deposited during the extensive Gondwanaland glaciation, is well known but this discovery not only records the first Gondwanan aeolianite suite but may also detail the first pre-Quaternary example of paraglacial aeolianites.