bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polyphase deformation and metamorphism at the Kalahari Craton — Mozambique Belt boundary
Authors: Manhica A. D. S. T. , Grantham G. H. , Armstrong R. A. , Guise P. G. , Kruger F. J. 
Published: April 2008

Abstract

The rocks of the Kalahari Craton in central western Mozambique have crystallization ages of between
c.
2300 and 3400 Ma and comprise dominantly granite-greenstones, peraluminous two-mica granites, subordinate younger mafic and granitic intrusions of uncertain age and cover sedimentary rocks. The rocks of the Mozambique Belt comprise
c.
1100 Ma intrusive granitoids as well as mafic intrusives and supracrustal migmatite gneisses of uncertain age. The boundary zone between and including these two crustal provinces is characterized by a strong N-S penetrative planar and migmatitic fabric. Sparse kinematic indicators suggest a sinistral sense of displacement along this shear zone. The metamorphic gradient increases from west to east from low grade on the Kalahari Craton to high-grade in the east, characterized by two generations of anatectic migmatization.
40
Ar/
39
Ar thermochronology on mica suggests that the Kalahari Craton lithologies have experienced heating above at least
c.
300°C during the
c.
1100 Ma Grenville age orogeny and again at
c.
530 Ma during the Pan-African Orogeny, possibly related to the collisional amalgamation of East and West Gondwana. The Mozambique Belt lithologies record a
c.
550 Ma thermal overprint with the lithologies in the vicinity of the N-S shear zone recording thermal reactivation at
c.
470 Ma. Comparisons of the new data with that from western Dronning Maud Land, which was adjacent to the study area prior to Gondwana fragmentation, yield many similarities.
Polymetamorphism of mafic granulites in the North China Craton: textural and thermobarometric evidence and tectonic implications
Authors: Zhao Guochun , Cawood Peter A. , Wilde Simon A. , Sun Min 
Published: April 2008

Abstract

The basement of the North China Craton can be divided into the Archaean Eastern and Western Blocks, separated by major Palaeoproterozoic terrane boundaries that roughly correspond with the limits of a 100–300 km wide zone, named the Trans-North China Orogen. Some mafic granulites from the orogen and adjoining areas in the Eastern and Western Blocks preserve textural evidence for two granulite facies events involving contrasting P-T paths. The first event is characterized by three distinct mineral assemblages, M
1a
to M
1c
. M
1a
is represented by fine-grained orthopyroxene + clinopyroxene + plagioclase ± quartz, which is surrounded by the M
1b
garnet + quartz symplectite, which itself is mantled by the M
1c
plagioclase + biotite symplectite. These assemblages and their P-T estimates define an anticlockwise P-T path, with peak metamorphism of 7.0–8.0 kbar and 800–850°C (M
1a
) followed by isobaric cooling to 700–750°C (M
1b
) and pressure-decreasing cooling to 630–700°C (M
1c
). The second event also includes three mineral assemblages, M
2a
to M
2c
. M
2a
represents growths of garnet porphyroblasts and matrix orthopyroxene + plagioclase + clinopyroxene + quartz; M
2b
consists of orthopyroxene + plagioclase ± clinopyroxene symplectites or coronas; and M
2c
is represented by plagioclase + hornblende symplectites. These assemblages and their P-T estimates define a clockwise P-T path, with peak metamorphism of 9.2–9.8 kbar and 820–850°C (M
2a
), followed by near-isothermal decompression (M
2b
) of 7.0–7.6 kbar and 760–810°C and cooling (M
2c
) to 690–760°C. The isobaric cooling, anticlockwise, P-T path of the first granulite facies event is similar to the P-T paths inferred for the
c.
2.5 Ga metamorphosed mafic granulites from the Eastern and Western Blocks, whereas the near-isothermal decompression, clockwise, P-T path of the second granulite facies event is similar to the P-T paths inferred for the
c.
1.8 Ga metamorphosed khondalite series in the Western Block and some mafic granulites in the Trans-North China Orogen. These relations suggest that the polymetamorphic granulites were derived from the reworking of the 2.5 Ga metamorphosed granulites during the 1.8 Ga collision between the Eastern and Western Blocks that resulted in the final amalgamation of the North China Craton.
A Quaternary geological perpective on geochemical exploration in glaciated terrain
Authors: Klassen Rodney A. 
Published: April 2008

Abstract
The application of Quaternary geology and glacial sedimentology is given as a broad guide for geochemical exploration in glaciated terrain. Predictive models of glacial dispersal provide an important basis for tailoring drift prospecting methods to suit regional variations in ice flow history and dynamics. The models relate compositional variations in glacial dispersal trains to ice flow direction, glacial history and subglacial processes. They are continually refined with reference to the geological and physical properties of the ice bed; new empirical field evidence constraining particle trajectories; and knowledge of subglacial processes affecting glacial erosion, transport and deposition. Transport at the ice bed leads to an exponential decrease in indicator concentrations with increasing distance of glacial transport, whereas linear decrease is associated with englacial transport, and may be characteristic of ice streams. The partitioning of rock and mineral fragments through subglacial comminution leads to compositional differences among size fractions that can reflect intensity of subglacial process, distance of transport, and provenance; hence, the choice of size fraction is important to drift prospecting by geochemical methods.
Till geochemistry and sampling techniques in glaciated shield terrain: a review
Authors: McMartin Isabelle , McClenaghan M. Beth 
Published: April 2008

Abstract
Till is a favoured sample medium for locating mineral deposits in glaciated shield terrains of Canada and Fennoscandia because it best reflects the primary composition of the bedrock source area. In the sampling phase, an important and costly component of till surveys, sample density, sample depth and sample method must be chosen according to the needs of the exploration program. Surface till sampling methods in forested areas differ from those used in permafrost terrain. However, in both areas, concentrations of labile ore minerals and their products of decomposition can be detected in the fine fraction (< 2 mm) of weakly oxidized till. In thin drift-covered areas, till samples are collected by hand excavation or trenching at < 5 m depth. In areas of thicker drift, more expensive methods such as reverse circulation rotary drills, rotasonic drills and portable drills are used to collect till samples at depth and to determine lateral and vertical variations in till geochemistry. Laboratory methods are an essential part of till geochemical surveys. The choices of the size fraction and analytical methods are determined by the nature and composition of the expected bedrock target, and by costs.
Indicator mineral and geochemical methods for diamond exploration in glaciated terrain in Canada
Authors: McClenaghan M. B. , Kjarsgaard B. A. 
Published: April 2008

Abstract
This paper provides a summary of selected diamond exploration techniques used in the glaciated terrain of Canada, focusing on indicator mineral methods and till geochemistry but also including geochemistry of lake sediments and vegetation. Diamond exploration in Canada focuses on kimberlite, the primary host rock for diamonds in this country. Kimberlite is a mineralogically and chemically distinct point source which may yield discrete dispersal trains in glacial sediments. Understanding the ice flow history and depositional history of glacial sediments and identifying multiple till sheets in areas covered by thick glacial sediments are essential for successful sampling, interpretation and follow-up of indicator mineral and geochemical anomalies related to these rocks. Orientation studies over known kimberlites provide important information on the mineralogical and geochemical signatures of kimberlite, and the size fractions of glacial sediments that are best suited to indicator mineral and geochemical analysis. Kimberlite indicator minerals survive glacial transport over long distances and the relative abundance of each mineral in till is a function of the primary mineralogy of individual kimberlites. Indicator mineral distributions observed at a regional scale define the net effect of glacial dispersal, often along different ice flow directions. Local scale distributions define individual dispersal trains. The finer (0.25 to 0.5 mm) fraction of heavy mineral concentrates prepared from till samples is best suited for indicator mineral surveys. Till geochemistry is gaining popularity in diamond exploration because it is significantly cheaper than indicator mineral analysis and it can be performed quickly. Important kimberlite pathfinder elements that provide good contrast in till geochemical surveys include Ni, Cr, Ba, Co, Sr, Rb, Nb, Mg, Ta, Ca, Fe, K, Ti and REE, the relative importance of which will depend on kimberlite composition as well as that of the surrounding bedrock. Biogeochemical studies over kimberlites in Canada reveal geochemical signatures in vegetation despite the glacially transported substrate.
Biogeochemical exploration methods in the Canadian Shield and Cordillera
Authors: Dunn Colin E. 
Published: April 2008

Abstract
This review article focuses on field methods in biogeochemical exploration and is based largely on the author’s experience. Consideration is given to reasons for applying biogeochemical methods as alternatives or supplements to other surficial sampling media that can be used in the exploration for mineral deposits in glaciated terrain. Extensive root systems can absorb metals from the substrate and integrate the geochemical signature of large volumes of sediment, groundwater and sometimes bedrock, thereby providing a more representative reflection of the chemical environment than that obtained from some other media. Sampling methods and precautions that should be taken are outlined. Variables that govern plant chemistry include the heterogeneity of composition among plant species and plant tissues, and the modifying effects of the seasons and contamination from external sources. Studies indicate that biogeochemical methods can provide a more proximal indication of concealed mineralization than the distal indications typical of till geochemistry programmes. Consequently, comparisons of till and biogeochemical data can help to define vectors toward mineralized sources such that the two methods are complementary.
Analysis of geochemical data for mineral exploration using a GIS — A case study from the Swayze greenstone belt, northern Ontario, Canada
Authors: Harris J. R. , Wilkinson L. , Bernier M. 
Published: April 2008

Abstract
Geographic Information Systems (GIS) provide the geologist with a powerful tool, when used in concert with statistical and geostatistical analysis, for archiving, manipulating, analysing and visualizing geochemical data. This paper uses geochemical (Zn, Cu) data obtained from various media (rock, lake sediments, till, soil and humus) over the Swayze greenstone belt in northern Ontario, to explore methods for analysing and visualizing geochemical data with a focus to mineral exploration applications.
The behaviour of Zn and Cu in both bedrock and the surficial environment is studied using statistical and geostatistical techniques. Interpretation and uses of traditional statistics and dot plots are contrasted with interpolated geochemical maps as well as red-green-blue (RGB) ternary maps. Techniques for multimedia comparison and geochemical anomaly detection and screening are presented. The processing methods presented in this paper can be utilized and adapted by other geologists for exploring their own geochemical data. Many of the algorithms presented here are available within standard GIS software packages, or can be written easily using a GIS macro language.
Application of composite glacial boulder geochemistry to exploration for unconformity-type uranium deposits in the Athabasca Basin, Saskatchewan, Canada
Authors: Earle Steven 
Published: April 2008

Abstract
Sampling glacially transported boulders is effective for mapping subcrop clay alteration patterns associated with deeply-buried unconformity-type uranium deposits in the Athabasca Basin of northern Saskatchewan, Canada. The technique works well because the subcrop alteration haloes show significant geochemical contrast with background, because the glacial deposits are consistently distributed and rich in boulders, and the altered boulders are typically well-represented in the boulder population. Boulder sampling is preferred over some other techniques because it is rapid and inexpensive, and the use of a lithological sampling medium provides a direct measure of subcrop clay-mineralogy, in an area where outcrop exposure is very restricted.

A large composite boulder sample data set, comprising
c.
20 000 samples from within the eastern part of the Athabasca Basin, has been compiled. Sampling and analytical techniques are descirbed, and results are presented at both regional and semi-regional scales. The distributions show clear correlations with both basin-scale features, such as stratigraphical variation and regional alteration patterns, and with deposit-related features, such as hydrothermal illite, dravite and chlorite alteration. Composite boulder lithogeochemistry may be equally effective for mineral exploration in other glaciated regions with restricted bedrock exposure.
Contrasting styles of glacial dispersal in Newfoundland and Labrador: methods and case studies
Authors: Batterson Martin J. , Liverman David G. E. 
Published: April 2008

Abstract
A review of practical approaches to drift exploration intended for use by exploration geologists working in drift covered areas is presented. The contrasting styles of glacial dispersal between Labrador, dominated by the effects of the Laurentide ice sheet, and the Island of Newfoundland, affected by small, coalescing ice caps at the glacial maximum and smaller topographically-controlled ice centres during deglaciation, are described. The effect has been to produce longer, ribbon-shaped dispersal trains in Labrador, except in the Labrador Trough near the centre of the Labrador sector of the Laurentide Ice Sheet, and shorter more diffuse dispersal patterns in Newfoundland.
Geochemical signatures around massive sulphide deposits in southern British Columbia, Canada
Authors: Lett Ray E. 
Published: April 2008

Abstract
This paper demonstrates the application of geochemical exploration for sulphide mineralization in glaciated areas by a case history illustrating the discovery of Cu-Pb-Zn-Ag-Au massive sulphide deposits in southern British Columbia, Canada. These deposits, hosted by Palaeozoic metasedimentary and metavolcanic rocks of the Kootenay Terrane, were first detected by weakly anomalous Cu and Au values in regional stream sediment samples and subsequently confirmed by more detailed stream and soil geochemical surveys, prospecting and diamond drilling.
Till geochemistry is a very effective exploration method because there is a well developed dispersal plume of mineralized bedrock down-ice from the massive sulphide deposits. Elevated Au, Pb, Cu and As levels in till samples collected up to 8 km down-ice from the deposits are direct indicators for sulphide mineralization. Barium, Cr and Ni are pathfinders for distinguishing different types of sulphide mineralization. The relationship between the bedrock, stream sediment, stream water and till geochemistry is shown more clearly in a conceptual model. This model has a practical application to future exploration for massive sulphides in southern British Columbia by establishing criteria such as geochemical anomaly size and contrast for different sample media.
Glacial transport and secondary hydromorphic metal mobilization: examples from the southern interior of British Columbia, Canada
Authors: Paulen Roger C. 
Published: April 2008

Abstract
Glacial transport of trace elements was studied at seven mineral occurrences in the southern interior of British Columbia; a region where mineral exploration is hampered by the scarcity of bedrock outcrop and by a variable sediment thickness associated with the Cordilleran Ice Sheet. The till deposited in the region was, for the most part, a product of the last glacial period. A review of previous geochemical studies conducted by the mineral exploration industry provides an indication to the variable configuration of the local dispersal patterns in the area. Dispersal trains in till are short, generally < 1–2 km, rarely exceeding 10 km in length and are usually proximal to bedrock source. They are commonly ribbon-shaped and rarely exceed 1 km in width. Observed dispersal patterns suggest that drastic changes in topography might have affected basal ice velocity which increased the distance of glacial transport. In addition, the distance that separates bedrock mineralization from its surficial geochemical expression in till varies with drift thickness and topography. Several glacial dispersal trains have been modified in shape by secondary hydromorphic dispersion.
Experimental constraints on the mechanical and hydraulic properties of deformation bands in porous sandstones: a review
Authors: Main Ian , Mair Karen , Kwon Ohmyoung , Elphick Stephen , Ngwenya Bryne 
Published: April 2008

Abstract

Deformation bands form in porous, clay-poor, sandstones in the top few kilometres of the Earth’s surface, involving the sequential growth of a set of discrete fault strands with minimal individual offset, ultimately culminating in the development of a slip surface with a large offset. We review some of our recent experimental results designed to reproduce the early stages of this sequence, obtained at room temperature and low confining pressure (
P
< 70 MPa) in a large-capacity (10 cm core diameter) deformation rig. We examine the physical weakening and strengthening mechanisms at work in the experiments, and discuss the implications for fault sealing. We describe laboratory experiments where deformation occurs by the progressive formation of new bands with a finite small offset and a relatively constant fault gouge grain-size distribution, at a relatively constant stress measured at the sample boundaries. The friction coefficient is 0.6, i.e. within the standard range. No large-offset slip surfaces were observed. Cross-fault permeability is transiently increased during dynamic stress drop, associated with the ‘suction pump’ provided by rapid near-fault dilatancy under conditions of constant flow rate. As the deformation band develops quasi-statically, permeability is then reduced further by up to two orders of magnitude as a result of shear-enhanced compaction and porosity loss of the poorly sorted gouge fragments. A simple microstructural model successfully predicts the physical sealing rates in the post-failure stage. Finally, we estimate the chemical sealing rates from mass balance calculations based on direct measurement of the pore fluid chemistry during constant flow experiments at temperatures up to 120°C. When extrapolated to longer timescales, these account quantitatively for the differences between permeability reductions measured in the laboratory and in the field.
Microfracturing associated with reactivated fault zones and shear zones: what can it tell us about deformation history?
Authors: Mitra Gautam , Ismat Zeshan 
Published: April 2008

AbstractDeformation in fault zones is commonly characterized by grain-scale microfracturing, with microcrack density typically increasing toward the middle of the zone. The cracks can form under a wide variety of conditions and need to be used with great caution in making tectonic interpretations, particularly in areas with a complex history of fault reactivation. Microcracks may be intragranular (contained within single grains) or intergranular (with a length of several grain diameters). Intragranular cracks formed under dominantly plastic deformation conditions are crystallographically controlled and may not be directly related to regional stresses. Intragranular cracks formed during initial fracturing under cataclastic conditions develop only in grains that are optimally oriented to the deforming stresses. Intergranular cracks form during progressive cataclasis as intragranular cracks grow to join one another: they may develop as transgranular cracks that cut across several grains or as grain-boundary cracks. Once formed, microcracks may be preserved in a variety of ways (e.g. sintering, healing, cementation) depending on post-deformation conditions, and may be distinguished from one another on the basis of microstructural characteristics. Distinguishing between successive generations of microcracks in areas of fault reactivation is particularly important in determining the deformation history and obtaining deformation conditions. For example, Proterozoic quartzites collected from the central Utah Sevier belt have undergone multiple episodes of contractional deformation followed by Basin-and-Range extension. The use of polarized and dark-field optical microscopy and scanning electron microscopy allows microcracks related to the separate episodes of deformation to be distinguished on the basis of morphology, mode of preservation and consistent cross-cutting relationships. Variations in microcrack density and volume of cataclasized rock for the different generations of microcracks are used to establish the patterns of overprinting during fault reactivation. Anastomosing zones of intense deformation formed during successive episodes of faulting may not coincide with one another, as grain-size reduction and cementing during each episode hardens the zones, causing deformation to shift to adjoining weaker rock. However, the fault zone as a whole is a sufficiently large inhomogeneity that it is reactivated during successive faulting events.
Episodic weakening and strengthening during synmetamorphic deformation in a deep-crustal shear zone in the Alps
Authors: Steffen Kurt , Selverstone Jane , Brearley Adrian 
Published: April 2008

Abstract

The Greiner shear zone (western Tauern Window) deformed a variety of metasedimentary, metavolcanic, and plutonic lithologies at conditions of
c.
525–575 °C and 30–40 km depth. Microstructural relationships point to a succession of weakening and strengthening episodes. Stage I involved softening via a change in deformation mechanism. Grain-size reduction in plagioclase-rich horizons locally produced rocks with an average grain size of <30 μm microstructural features consistent with deformation via grain boundary diffusion creep (GBDC; a fluid-assisted deformation mechanism similar to pressure solution, which may result in superplastic behaviour). At constant stress, GBDC will result in a significant increase in strain rate relative to neighbouring layers. Stage II involved reaction-induced strengthening. Rapid bulk diffusion rates associated with GBDC allowed rapid growth of large (up to 20 cm) hornblende cystals. This growth of large cross-cutting crystals shut down grain-size-sensitive flow mechanisms in the plagioclase matrix and locally ‘locked’ the shear zone, shifting ductile deformation to weaker horizons. Stage III involved reaction-induced softening. Local variations in bulk composition and/or fluid availability caused large hornblende grains in some horizons to be partially replaced by biotite. These biotite-rich layers localized subsequent deformation, whereas adjacent layers with intact hornblende record minimal strain. Deformation and metamorphism together exert control on fluid availability, diffusion rates, and reaction kinetics, and these factors collectively control fabric development and rheology. The effects of interaction between small-scale deformational and metamorphic processes are difficult to predict, but can have an important influence on shear zone behaviour at depth. The resulting complexities need to be accounted for in models of crustal strength-depth relationships and shear zone rheologies.