bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two Stage Felsic Volcanism in the Lower Proterozoic Upper Aillik Group, Labrador, Canada: Its Relationship to Syn- and Post-Kinematic Plutonism
Authors: Gower Charles F. , Ryan Bruce 
Published: April 2008

Summary
The Aillik Group, situated in the Lower Proterozoic Makkovik Province, Labrador, Canada, is a bimodal volcanic suite consisting of a lower mafic volcanicsedimentary sequence and an upper felsic volcanic-volcaniclastic association. These rocks have been intruded by syn-and postkinematic granitoid rocks.
Previous mapping and stratigraphic interpretations suggest that the upper Aillik Group is itself divisible into ‘early’ and ‘late’ parts separated by a mafic volcanic/tuffaceous unit. Both involve dacitic to rhyolitic volcanism, but the earlier one has a much higher proportion of metasedimentary material and the later one is dominated by rhyolitic volcanic rocks. Major and trace element data suggest that these two sequences are compositionally distinct. The late sequence is compositionally similar to the postkinematic granites, but data are inadequate to establish a link between the early sequence and synkinematic granites, yet do not preclude it.

Although geochronological data suggest
c.
1800 Ma and 1660 Ma events in both the upper Aillik Group and granitoid plutons, a straightforward model linking early upper Aillik Group with synkinematic granites and late upper Aillik Group with postkinematic granites is complicated by
c.
1800 Ma ages from some felsic volcanic rocks assigned as late upper Aillik Group. Inadequate stratigraphic control, insufficient petrochemical data and (or) inherited ages could account for the contradictions; or the model may be invalid. Detailed stratigraphic analysis and careful geochemical studies are required to resolve the conflicts.
The Orange River Group: a Major Proterozoic Calcalkaline Volcanic Belt in the Western Namaqua Province, Southern Africa
Authors: Reid D. L. , Erlank A. J. , Welke H. J. , Moyes A. 
Published: April 2008

Summary

The Orange River Group (ORG) consists of a thick volcano-sedimentary pile (> 8 km) preserved as a subprovince within the Namaqua Province of southern Africa. Volcanic activity during deposition of the ORG was predominantly subaerial, and involved the eruption of an andesite dominated calcalkaline suite ranging from basalt through to rhyolite. Agreement between Rb-Sr, Th-Pb, Pb-Pb and Sm-Nd isochron ages indicate extrusion of the ORG around 2000 Ma ago. Compared with modern arc suites, the ORG is characterized by high K and Mg, together with related trace elements (Rb, Sr, Ba, U, Th, LREE; Ni, Cr). Basic lavas differ from many modern calcalkaline types in having lower A1 contents reminiscent of tholeiites. When normalized to N-type MORB, the ORG basic lavas show enrichments in K, Rb, Ba, Th, and the LREE, and depletions in Nb, Ta, Zr, Hf, Ti, Y and the HREE). Metamorphic overprinting associated with the ∼ 1000 Ma Namaqua tectonothermal event are evident to varying degrees throughout the subprovince, and precludes precise monitoring of initial isotope ratios at time of eruption. Evidence from the rocks least affected by metamorphic overprinting suggests common initial Sr, Pb and Nd isotopic compositions for the entire basalt to rhyolite suite in this particular area, which would support a fractional crystallization model and rule out major involvement of old Archaean crust to produce the voluminous andesites. Initial isotopic data translate to ɛ
sr
(T) + 10), ɛNd(T)∼0, and an apparent high μ value, which, when taken together with the geochemical features described previously, indicate that the source region to the mafic parental magmas of the ORG shows patterns similar to those in the mantle wedge overlying subduction zones. The calcalkaline ORG volcanic suite may therefore represent the remnants of a 2000 Ma old Proterozoic arc complex. The high K character, the intimate association of comagmatic granitoids, the development of copper porphyries, and the lack of any direct or indirect evidence for underlying Archaean crust all point to a mature island arc environment. Active continental margins such as the Andes show similar geochemical and isotopic features, but it is argued that the high elevation of such margins will cause them to be preferentially eroded and lack representation in ancient terrains.
Geochemical Patterns of Metabasites in the Southern Part of the Damara Orogen, SWA/Namibia: Applicability to the Recognition of Tectonic Environment
Authors: Breitkopf J. H. , Maiden K. J. 
Published: April 2008

Summary
In the southern part of the late Precambrian Damara Orogen, mafic schist and amphibolite represent metamorphic equivalents of tholeiitic basalt and gabbro. The metabasites are extensively developed in several stratigraphic units and extend laterally along strike over more than 300 km. In the Southern Margin Zone, they are interbedded with pelitic schist, quartzite, diamictite and minor marble, whereas in the Southern Zone (Trough Zone) the Matchless Amphibolite Belt occurs within a sequence of predominantly quartz-mica schist.
The Geochemistry of the Lower Proterozoic Willyama Complex Volcanics, Broken Hill Block, New South Wales
Authors: James S. D. , Pearce J. A. , Oliver R. A. 
Published: April 2008

Summary

The major and trace element geochemistry of the early to middle Proterozoic meta-igneous rocks of the Willyama Complex in the Broken Hill Block indicates that the basic rocks originated by partial melting of a depleted mantle source, followed by fractional crystallization along a trend of strong iron enrichment coupled with some crustal assimilation. At least some of the intermediate-acid rocks were derived from fractionation of these basic parents, but major crustal involvement may be necessary to explain the large quantities of felsic volcanics in the lower part of the Complex. The volcanic rocks in the Broken Hill mine area show an unusually high degree of primary iron enrichment (up to 25 wt % total iron as Fe
2
O
3
) and a lesser degree of bimodality than elsewhere. By analogy with Recent ferrobasalt provinces, this extreme iron enrichment may indicate an origin in a propagating rift where small, high-level magma chambers separated from the magma source. If so, the consequent high geothermal gradient and high fracture permeability may have provided the necessary conditions for genesis of the Broken Hill ore deposit.
The Petrology and Geochemistry of Alteration Assemblages in the Eastern Creek Volcanics, as a Guide to Copper and Uranium Mobility Associated with Regional Metamorphism and Deformation, Mount Isa, Queensland
Authors: Wyborn L. A. I. 
Published: April 2008

Summary

At least four alteration types are identified in the basaltic Eastern Creek Volcanics of the Mount Isa Inlier. The earliest alteration type, found in predominantly massive rocks, contains albite + actinolite with lesser chlorite + epidote + sulphides + magnetite. These basalts are enriched in K
2
O and S, and Cu has been locally redistributed within the lava flows. The remaining three alteration types are only found in deformed rocks. Two are closely related and are dominated by either epidote + sphene, or calcite + magnetite, with the mineralogy of the alteration type controlled by the concentration of CO
2
in the fluid phase. Both assemblages are depleted in S, K
2
O, Cu, Rb, Ba, and Sr, whilst Zr, V, Y and Cr are enriched, and these samples also have the highest ratio of Fe
2
O
3
/FeO. These two alteration types are associated with major regional metamorphism, and some uranium deposits in the western Mount Isa Inlier and possibly some small Cu deposits are related to them. The final alteration was the most profound, producing rocks dominated by albite + chlorite + rutile, and strongly depleted in CaO, MnO, Fe
2
O
3
, Cu, Sr, Ba, and Ni, and enriched in MgO and SiO
2
. This last alteration is believed to be linked to the formation of the Mount Isa copper ore body.
The Trace Element Geochemistry of Metavolcanics and Dykes From the Central Metasedimentary Belt of the Grenville Province, Southeastern Ontario, Canada
Authors: Smith T. E. , Holm P. E. 
Published: April 2008

Summary
The trace element chemistry, including the rare earth elements, of two Proterozoic metavolcanic sequences in the Central Metasedimentary Belt of the Grenville Province is presented. The older Tudor suite is a bimodal mafic-silicic sequence comprising dominant tholeiitic basalts with minor rhyodacites. The younger Turriff metavolcanic sequence, is also a bimodal mafic-silicic series made up predominantly of tholeiitic basalts with some calcalkaline andesites and minor rhyolites. In each suite the tholeiitic basalts and the felsic rocks were formed by fractional crystallization of mafic magmas formed by partial melting of enriched (spinel) lherzolite source materials. The Turriff andesites are considered to have formed by fractional crystallization of a parental basaltic andesite produced by partial melting of an eclogite source.
Both suites are enriched in light rare earth elements (LREE), heavy rare earth elements (HREE), and high field strength elements (HFSE). This enrichment is interpreted as resulting largely from metasomatism of the sub-continental lithosphere sources. The two sequences are interpreted as having erupted in a marginal basin formed by rifting of the continental crust. Comparisons are made with similar Proterozoic volcanic sequences from the southwestern USA and with Mesozoic and Quaternary suites formed in marginal basins in central and southern Chile.
Dynamic basin analysis: an integrated approach with large data bases
Authors: Hitchon Brian , Bachu S. , Sauveplane C. M. , Lytviak A. T. 
Published: April 2008

Summary

Basin analysis must include an appreciation of both the rocks and the processes affecting their contained fluids. Therefore the objective of dynamic basin analysis is to synthesize and evaluate the present geological, hydrogeological, thermal and geochemical situation of sedimentary basins as well as their past history. For sedimentary basins such as that in western Canada, where petroleum exploration has resulted in a vast amount of information, synthesis and evaluation can only be achieved through an integrated multidisciplinary computer-oriented approach. This requires the development of a data-base management system and specialized data-processing techniques. These have been developed by the Basin Analysis Group of the Alberta Geological Survey for geological, hydrogeological, thermal and hydrochemical parameters. The synthesized information can then be integrated into a descriptive steady-state model which forms the basis of the numerical simulation of various processes and phenomena related to present fluid, heat and mass flows in the subsurface. These techniques have been applied to studies of the baseline hydrogeology of the Cold Lake oil sands deposit area and the deep waste disposal site at Swan Hills, Alberta, Canada. They are also applicable to petroleum exploration,
in situ
oil recovery, gas storage, geothermal resource evaluation and mineral exploration. Future research directions are to focus on the inclusion of models for mass transport and on the determination of the palaeohydrogeological regimes in sedimentary basins.
Ancient fluid flow within foreland terrains
Authors: Bradbury Harry J. , Woodwell Grant R. 
Published: April 2008

Summary
Dewatering of the front Ranges of the Canadian Cordillera in the Campanian and Maastrichtian was achieved by expulsion of connate fluids from thrust sheets during active translation. Each major thrust sheet behaved as a separate hydrodynamic unit. Flow was consistently from hinterland to foreland sections of basal-sheet aquifers. The rate of fluid expulsion exceeded that of rock translation during hydrofracturing. Two flow systems, separated in time, utilized basal-sheet aquifers. Fluid flow at the margin of foreland basins in the Southern Pyrenees in the Oligocene was focused within both the crystalline infrastructure and the sedimentary suprastructure. Ascending metamorphic fluids passed from shear zone conduits in the basement into and through the basin margin, creating ghost vertical and lateral fluid fronts within the sedimentary pile. Connate fluids escaped via cleavage network channelways. Ponding of metamorphic and connate volumes of the fluid budget occurred at high levels close to the leading edge of natural strain within the basin margin, where excess fluid pressures were achieved.
Wind-blown materials and W African soils: an explanation of the ‘ferrallitic soil over loose sandy sediments’ profile
Authors: Vine H. 
Published: April 2008

Summary

It is suggested that incorporation of dust from the hinterland during episodes in the Pleistocene when the Sahara encroached far S of its present limits accounts for much of the clay and Fe
2
O
3
content of soils of southern Nigeria. The amount of pelagic deposition of clay reported for DSDP Site 366 on the Sierra Leone Rise in the last 1–3 million years is shown to correspond to the anomalous accumulation of clay in deep uniform subsoils of the ‘red ferrallitic soils over loose sandy sediments’. Particle-size analyses of soils at seven sites (showing 10% to 50% clay in the subsoil) are given, with determinations of Fe
2
O
3
in the clay fraction (5% to 9%). Silt-size quartz in the dust is thought to have been lost through solution, and feldspars and clay minerals have weathered to kaolin. Wind systems displaced 600–800 km to the S compared with the situation today would have deposited dust similar to present-day Harmattan fall-out in the N of Nigeria, in the latitude of southern Nigeria and of the Sierra Leone Rise. Creep, mass-movement, faunal activity and eluviation of clay and Fe
2
O
3
have affected the incorporation of dust, in addition to mixing coarser and finer layers of sediments together.
Continental sabkha pans and associated nebkhas in southern Kuwait, Arabian Gulf
Authors: Gunatilaka A. , Mwango S. 
Published: April 2008

Summary
Small evaporitic pans within a sand-sheet/gravel-plain terrain characterize the coastal margins of southern Kuwait. Sedimentological studies indicate that the pans commenced as ephemeral lakes during a Pleistocene pluvial phase, and later evolved into sabkhas during the Holocene with the changing climatic and hydrological regimes. The lacustrine episode is represented by laminated calcite micrite in the lower parts of the section, grading upward into a diagenetic gypsum facies of the sabkhas, with diagnostic evaporite textures. Dunes are represented only by nebkhas, which occur within the sabkha pans. Their initial build-up is controlled by a halophyte which colonizes the sabkha surface, trapping any moving sand. The nebkhas pass through phases of growth, stabilization and decay that are controlled by fluctuations in the water table. A rise of the water table can waterlog the roots and kill the plants—in which case the trapped sand starts drifting. A continued fall in the water table can lead to deflation of the entire complex. The nebkhas have a poor preservation potential. In this area the aeolian system is highly starved of sand in relation to the available wind energy. Stable isotope data indicate that the groundwaters are derived from old formation waters, with only minor meteoric recharge.
The statistical analysis of ‘mixed’ grain size distributions from aeolian sands in the Libyan Pre-Desert using log skew Laplace models
Authors: Flenley E. C. , Fieller N. R. J. , Gilbertson D. D. 
Published: April 2008

Summary
This paper describes the statistical analysis and modelling of simple and ‘mixed’ particle mass-size distributions. The particular sediments discussed derive from modern climbing, seif and barchan dunes. The statistical methods considered include calculation of sample moments (mean, sorting, skewness and kurtosis), in particular by semigraphical techniques. Additionally, attention is given to the construction of log normal probability plots and their supposed interpretation in terms of distinct segments representing different components of a ‘mixed’ distribution. Whilst these techniques have been used with some effect in the case of analysing simple or pure sand samples, it is shown that their application to mixed size distributions can be misleading. The approach advocated as an alternative is to model the size distribution directly by one of a family of parametric statistical distributions and use the estimated parameters to characterize the individual samples. The particular family preferred is the three-parameter log skew Laplace, which can be extended readily to a seven-parameter family incorporating mixture densities. This family provides computational advantages over the log hyperbolic family, whilst retaining its geological interpretability and theoretical derivation.
Spring mounds in southern Tunisia
Authors: Roberts C. R. , Mitchell C. W. 
Published: April 2008

Summary
Chotts Djerid and Fedjadj lie in the arid zone of southern Tunisia, and are chemically active, artesian environments which give rise not only to extensive emergent groundwater gypsum and salt deposits, but also to landforms of more complex architecture. In some geological situations belts of spring mounds up to 25 or 30 m high straddle former high-level late Pleistocene lake shorelines. Spring mounds are circular, gypsiferous or calcareous, volcano-like structures fed by point sources of artesian water rising from aquifers in the Continental Intercalaire and Complexe Terminal aquifer series. Similar mounds have been identified around playas in the USA, Australia, Egypt, Iraq and elsewhere. In some mounds a central well is occupied by a small pond with water conduits in the base, whilst others are dry and degraded. In these latter, water is only present at depth and wind erosion and redeposition are moulding the landforms. The morphology of spring mounds is determined by the balance between aquifer pressure head, output, chemical content, net evaporation, aeolian activity, and plant colonization. Their stratigraphy comprises alternations of crystalline materials, wind-blown gypsiferous sand, wash and splash deposits, and organic layers arranged in overlapping sequences which dip outwards from the water source. Such deposits offer a potentially sensitive index of environmental changes in the late Quaternary and Holocene.
Silicification fabrics from the Cenomanian and basal Turonian of Devon, England: isotopic results
Authors: Carson Greg A. 
Published: April 2008

Summary

Silicification fabrics within the Cenomanian and basal Turonian of Devon may be classified by their morphology and petrological relationships. The replacement of bioclasts by silica was often a two stage process; the early stage has δ
18
O values ranging from 30.0 to 32.4‰ SMOW. The palaeotemperatures calculated from these are close to values for Cenomanian sea water and thus the early silicification took place in marine porewaters and before significant burial. The consistently lighter values for the later replacement (ranging from 27.2 to 29.4‰) cannot be explained by an increase in burial depth. Partial recrystallization in meteoric waters is believed to be the mechanism responsible. Isotopic data suggest that the formation of siliceous nodules (chalcedony cemented sands) within the arenaceous lower members of the Cenomanian was an early process, although petrographic evidence points to possible (later?) recrystallization. The formation of late-stage drusy quartz occurred entirely in meteoric porewaters.
Mixed-water dolomitization in a transgressive beach-ridge system, Eocene Catalan Basin, NE Spain
Authors: Taberner C. , Santisteban C. 
Published: April 2008

Summary
Dolomitization occurs at the top of alluvial fan deposits in the SE margin of the Eocene Catalan Basin, NE Spain. The dolomitized rocks occur just below erosion terraces which show a step-like disposition on the continental sediments and on which shallow marine facies (beach-ridge systems and reefs) are developed. Petrography shows that diagenesis in the continental sediments mainly originated under meteoric water influence, while in beach-ridge systems and reef carbonates there is evidence of early diagenesis in a marine environment. All the nearshore sediments (from alluvial fan to reefs) record a distinct geochemical pattern where a progressively more marine influence parallels the regional trend in facies across the ancient shoreline. Petrographic and geochemical data suggest that mixing of meteoric and marine waters in the sediments representing the continental-to-marine transition caused dolomitization at the top of the alluvial fan deposits. Unlike most mixing-zone dolomites, in this case mixing took place when shallow marine sedimentation took place on erosional surfaces causing the inflow of marine waters that mixed with meteoric porewaters.
Wilcox sandstone diagenesis, Texas Gulf Coast: a regional isotopic comparison with the Frio Formation
Authors: Land Lynton S. , Fisher R. Stephen 
Published: April 2008

Summary
The burial diagenesis of Eocene Wilcox sandstones differs significantly from the burial diagenesis of other Gulf Coast terrigenous clastic formations. Differences between the onshore Wilcox and Oligocene-Miocene Frio Formations are larger than regional variations within either formation. Younger, offshore units have undergone less diagenetic alteration than either of the older, onshore units, whereas Mesozoic sandstones are generally more extensively altered.

Cementation by quartz and calcite was the first diagenetic modification of volumetric significance to affect either the Wilcox or Frio Formations. The average δ
18
O of Wilcox quartz cement is approximately +25‰ SMOW, in contrast to + 31‰ for the Frio. In both formations, quartz cement is more abundant in the overpressured zone. Calcite has an average δ
18
O of −10.8‰ PDB in the Wilcox Formation (compared to −7.2‰ for the Frio).
87
Sr/
86
Sr values suggest that calcite was derived from coeval nannofossils, carbonate rock fragments of Mesozoic age, or by local input of fluids from underlying Mesozoic carbonates. Most calcite cement (and therefore quartz which pre-dates calcite cement) was apparently emplaced prior to extensive alteration of detrital silicates which would have released strontium with a high
87
Sr/
86
Sr ratio.

The most common carbonate cement in the Wilcox Formation is ankerite which replaces calcite with increasing depth. The δ
13
C of ankerite is essentially identical to that of calcite at the same depth, and is also similar to Frio and younger carbonate cements. In contrast, δ
18
O values of Wilcox ankerite (average −9.8‰) indicate emplacement at higher temperature or from more depleted water than was true of Wilcox calcite.
87
Sr/
86
Sr values for Wilcox ankerite are very radiogenic (>0.7100), indicating that ankerite emplacement occurred during or after active silicate diagenesis. Both ankerite and dolomite are very uncommon phases in Frio and younger sandstones despite massive smectite stabilization, suggesting that the conversion of smectite to illite was not the source of iron and magnesium for the late cements.

The volume of secondary porosity is similar in both Wilcox and Frio sandstones. Albitization and K-feldspar removal from both formations are essentially complete below 3000 m and essentially no unaltered detrital feldspar occurs below that depth.
Differences between the Gulf Coast formations are attributed to different geothermal gradients, differences in the basinal sediments over which the units prograded, and to the changing nature of connate fluids in the units themselves. Diagenesis of the Wilcox Formation, like other Gulf Coast terrigenous wedges, is understandable only in terms of interaction with underlying units during the large-scale evolution, in both time and in space, of the Gulf Coast diagenetic system.