scholarly journals Resolving multiple geological events using in situ Rb-Sr geochronology: implications for metallogenesis at Tropicana, Western Australia

2020 ◽  
Author(s):  
Hugo K. H. Olierook ◽  
Kai Rankenburg ◽  
Stanislav Ulrich ◽  
Christopher L. Kirkland ◽  
Noreen Evans ◽  
...  
Keyword(s):  
Western Australia ◽  
Coarse Grained ◽  
Thin Sections ◽  
Fine Grained ◽  
Regional Deformation ◽  
Mineral Assemblages ◽  
Two Generations ◽  
Minimum Age ◽  
First Time

Abstract. Dating multiple geological events in single samples using thermochronology and geochronology is relatively common but it is only with the recent advent of triple quadrupole LA-ICP-MS that in situ Rb-Sr dating has become a more commonly applied and powerful tool to date K- and Rb-bearing minerals. Here, we date, for the first time, two generations of mineral assemblages in individual thin sections using the in situ Rb-Sr method. Two distinct mineral assemblages, both probably associated with Au mineralization, are identified in samples from the Tropicana gold mine in the Albany–Fraser Orogen, Western Australia. For Rb-Sr purposes, the key dateable minerals are two generations of biotite, and additional phengite associated with the second assemblage. Our results reveal that the first, coarse-grained generation of biotite grains records a minimum age of 2535 ± 18 Ma, coeval with previous 40Ar/39Ar biotite, Re-Os pyrite and U-Pb rutile results. The second, fine-grained and recrystallized generation of biotite grains record an age of 1207 ± 12 Ma across all samples. Phengite and muscovite yielded broadly similar results at ca. 1.2 Ga but data is overdispersed for a single coeval population of phengite and shows elevated age uncertainties for muscovite. We propose that the ca. 2530 Ma age recorded by various geochronometers represents cooling and exhumation, and that the age of ca. 1210 Ma is related to major shearing associated with the regional deformation associated with Stage II of the Albany–Fraser Orogeny. This is the first time that an age of ca. 1210 Ma has been identified in the Tropicana Zone, which may have ramifications for constraining the timing of mineralization in the region. The in situ Rb-Sr technique is currently the only tool capable of resolving both geological events in these rocks.

scholarly journals Resolving multiple geological events using in situ Rb–Sr geochronology: implications for metallogenesis at Tropicana, Western Australia

Geochronology ◽  
2020 ◽  
Vol 2 (2) ◽  
pp. 283-303
Author(s):  
Hugo K. H. Olierook ◽  
Kai Rankenburg ◽  
Stanislav Ulrich ◽  
Christopher L. Kirkland ◽  
Noreen J. Evans ◽  
...  
Keyword(s):  
Western Australia ◽  
Inductively Coupled Plasma ◽  
Coarse Grained ◽  
Thin Sections ◽  
Inductively Coupled ◽  
Fine Grained ◽  
Mineral Assemblages ◽  
Two Generations ◽  
Minimum Age

Abstract. Dating multiple geological events in single samples using thermochronology and geochronology is relatively common, but it is only with the recent advent of triple quadrupole laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) that in situ rubidium–strontium (Rb–Sr) dating has become a more commonly applied and powerful tool to date K-rich or Rb-bearing minerals. Here, we date two generations of mineral assemblages in individual thin sections using the in situ Rb–Sr method. Two distinct mineral assemblages, both probably associated with Au mineralization, are identified in samples from the Tropicana gold mine in the Albany–Fraser Orogen, Western Australia. For Rb–Sr purposes, the key dateable minerals are two generations of biotite as well as additional phengite associated with the younger assemblage. Our results reveal that the first, coarse-grained generation of biotite grains records a minimum age of 2535±18 Ma, coeval with previous 40Ar∕39Ar biotite, rhenium–osmium (Re–Os) pyrite and uranium–lead (U–Pb) rutile results. The second, fine-grained and recrystallized generation of biotite grains record an age of 1207±12 Ma across all samples. Phengite and muscovite yielded broadly similar results at ca. 1.2 Ga, but data are overdispersed for a single coeval population of phengite and show elevated age uncertainties for muscovite. We propose that the ca. 2530 Ma age recorded by various geochronometers represents cooling and exhumation and that the age of ca. 1210 Ma is related to major shearing associated with the regional deformation as part of Stage II of the Albany–Fraser Orogeny. This is the first time that an age of ca. 1210 Ma has been identified in the Tropicana Zone, which may have ramifications for constraining the timing of mineralization in the region. The in situ Rb–Sr technique is currently the only tool capable of resolving both geological events in these rocks.

Plant Taphonomy and Paleoecology of Late Pennsylvanian Intramontane Wetlands in the Graissessac-Lodève Basin (Languedoc, France)

Palaios ◽  
2005 ◽  
Vol 20 (3) ◽  
pp. 249-265 ◽  
Author(s):  
CARLES MARTÍN-CLOSAS ◽  
JEAN GALTIER
Keyword(s):  
Detailed Comparison ◽  
Alluvial Fans ◽  
Fluvial Sediments ◽  
Tree Fern ◽  
Massif Central ◽  
Fine Grained ◽  
Tree Ferns ◽  
First Time ◽  
Diverse Plant

Abstract The Late Pennsylvanian Graissessac-Lodève basin is a small, fluvio-palustrine depocenter located in the southern part of the Massif Central (France). A taphonomic and sedimentologic study carried out in this area allows a reconstruction of Late Carboniferous vegetation in an intramontane context. The paleoecology of such limnic settings is poorly known, and this study permits detailed comparison with paralic basins for the first time. The Graissessac peat mires developed in abandoned fluvial channels, in floodplains, and above distal alluvial fans. The vegetation was dominated by monospecific stands of the arborescent lycopsid Sigillaria brardii, whereas the tree fern Psaronius occurred during the later stages of mire accretion. This is in contrast to coeval North American peat mires, which generally were dominated by tree ferns and pteridosperms throughout the mire profile. Stephanian floodplains and distal alluvial fans of the Graissessac-Lodève Basin were devoid of vegetation, with the exception of isolated thickets of sphenopsids that were composed of Calamites and Sphenophyllum. These plants were found growing in situ in the floodplain mudstones as well as in fine-grained sands of secondary channels. Parautochthonous foliage assemblages of ferns and pteridosperms found in floodplain mudstones represent the most diverse plant community. The plants supplying these remains were growing in exposed areas close to floodplains. Large logs attributed to cordaitaleans and monotypic assemblages of large Cordaites leaves were found in fluvial sediments, and suggest that the plants were riparian elements in the basin.

Formation of the hour-glass structure in augite

1969 ◽  
Vol 37 (288) ◽  
pp. 472-479 ◽  
Author(s):  
D. F. Strong
Keyword(s):  
Glass Structure ◽  
Coarse Grained ◽  
Crystal Face ◽  
Thin Sections ◽  
Rapid Crystallization ◽  
Fine Grained ◽  
Rock Types ◽  
The Common

SummaryA study of augite in over three hundred thin sections of mainly alkalic rocks permits the distinction of two main types of hour-glass structure. The common ‘swallow-tailed’, sometimes skeletal augite crystals are found in the fine-grained groundmass of many rock types, and it is suggested that rapid crystallization alone accounts for their formation. Hence, this type of hour-glass structure has been called ‘quench hour-glass’. The hour-glass structures of larger augite crystals of porphyritic and coarse-grained rocks are commonly described as hour-glass ‘zoning’, as they result primarily from compositional differences between the different sectors. These were formed under conditions of relatively slower cooling than the ‘quench hour-glass’, and thus cannot be explained in the same way. They are thought to have formed by a process involving adsorption of impurities on a particular crystal face so as to impede growth of these faces, producing an initial skeleton of hour-glass form, which is completed by later crystallization of augite richer in FeO, Na2O, TiO2, and Al2O3. This hypothesis also explains the patchy zoning of other augite crystals, casting doubt on some petrogenetic interpretations of such zones as core zones.

scholarly journals Visual interference can help and hinder memory: Capturing representational detail using the Validated Circular Shape Space

2019 ◽  
Author(s):  
Aedan Y. Li ◽  
Keisuke Fukuda ◽  
Andy C. H. Lee ◽  
Morgan D. Barense
Keyword(s):  
Shape Space ◽  
Angular Distance ◽  
Visual Similarity ◽  
Coarse Grained ◽  
Retrieval Task ◽  
Circular Shape ◽  
Fine Grained ◽  
Visual Interference ◽  
Color Memory ◽  
First Time

AbstractAlthough we can all agree that interference induces forgetting, there is surprisingly little consensus regarding what type of interference most likely disrupts memory. We previously proposed that the similarity of interference differentially impacts the representational detail of color memory. Here, we extend this work by applying the Validated Circular Shape Space (Li et al., 2020) for the first time to a continuous retrieval task, in which we quantified both the visual similarity of distracting information as well as the representational detail of shape memory. We found that the representational detail of memory was systematically and differentially altered by the similarity of distracting information. Dissimilar distractors disrupted both fine- and coarse-grained information about the target, akin to memory erasure. In contrast, similar distractors disrupted fine-grained target information but increased reliance on coarse-grained information about the target, akin to memory blurring. Notably, these effects were consistent across two mixture models that each implemented a different scaling metric (either angular distance or perceived target similarity), as well as a parameter-free analysis that did not fit the mixture model. These findings suggest that similar distractors will help memory in cases where coarse-grained information is sufficient to identify the target. In other cases where precise fine-grained information is needed to identify the target, similar distractors will impair memory. As these effects have now been observed across both stimulus domains of shape and color, and were robust across multiple scaling metrics and methods of analyses, we suggest that these results provide a general set of principles governing how the nature of interference impacts forgetting.

scholarly journals Membrane asymmetry and enhanced ultrastructural detail of sarcoplasmic reticulum revealed with use of tannic acid.

1978 ◽  
Vol 79 (3) ◽  
pp. 601-616 ◽  
Author(s):  
A Saito ◽  
C T Wang ◽  
S Fleischer
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Tannic Acid ◽  
Freeze Fracture ◽  
Membrane Vesicles ◽  
Thin Sections ◽  
Membrane Asymmetry ◽  
The Asymmetry ◽  
First Time ◽  
Negative Staining Electron Microscopy

Fixation of purified sarcoplasmic reticulum (SR) membrane vesicles, using glutaraldehyde supplemented with 1% tannic acid, reveals newly visualized ultrastructure in thin sections. The trilaminar appearance of the membrane is highly asymmetric; the outer electron-opaque layer is appreciably wider (70 A) than the inner layer (20 A). The asymmetry is not referable to lack of penetration of the tannic acid since: (a) SR vesicles made permeable with 1 mM EDTA, pH 8.5, show similar asymmetry; (b) treatment of SR with trypsin results in progressive loss in protein content and decrease in the thickness of the outer layer, until in the limit the trilayer has a symmetric appearance; (c) within the same muscle section, the SR membrane appears highly asymmetric whereas the sarcolemma has a more symmetric appearance; (d) reconstituted SR vesicles have a symmetric appearance with equally broad inner and outer layers (approximately 70 A); the symmetric structure is confirmed by freeze-fracture and negative staining electron microscopy. Heavy and light SR vesicles obtained by isopycnic density sedimentation of purified SR have the same asymmetric appearance of the membrane and seem to differ mainly in that the heavy vesicles contain internal contents consisting largely of Ca++-binding protein. The asymmetry of the SR membrane is referable mainly to the unidirectional alignment of the Ca++ pump protein, the major component (90% of the protein) of the membrane. The asymmetry of the SR membrane can be visualized now for the first time in situ in thin sections of muscle.

Combined In Situ Neutron Diffraction and Acoustic Emission of Twin Nucleation & Twin Growth in Extruded ZM20 Mg Alloy

2010 ◽  
Vol 652 ◽  
pp. 149-154 ◽  
Author(s):  
Ondrej Muránsky ◽  
Matthew R. Barnett ◽  
David G. Carr ◽  
Sven C. Vogel ◽  
E.C. Oliver
Keyword(s):  
Acoustic Emission ◽  
Neutron Diffraction ◽  
Room Temperature ◽  
Coarse Grained ◽  
Fine Grained ◽  
Grain Sizes ◽  
Twin Nucleation ◽  
Twin Growth ◽  
In Situ Neutron Diffraction

In the present work in situ neutron diffraction and acoustic emission were used concurrently to study deformation twinning in two ZM20 Mg alloys with significantly different grain sizes at room temperature. The combination of these techniques allows differentionation between the twin nucleation and the twin growth mechanisms. It is shown, that yielding and immediate post-yielding plasticity in compression is governed primarily by twin nucleation, whereas the plasticity at higher strains is governed by twin growth. The current results further suggest that yielding by twinning happens in a slightly different manner in the fine-grained as compared to the coarse-grained alloy.

Uncommon preservation of dinosaur footprints in a tidal breccia: Eubrontes giganteus from the Early Jurassic Mongisty tracksite of Aveyron, southern France

2021 ◽  
pp. 1-18
Author(s):  
Jean-David Moreau ◽  
Jacques Sciau ◽  
Georges Gand ◽  
Emmanuel Fara
Keyword(s):  
Scale Up ◽  
Lower Jurassic ◽  
Depositional Environments ◽  
Early Jurassic ◽  
Coarse Grained ◽  
Southern France ◽  
Fine Grained ◽  
The North ◽  
Dinosaur Tracks ◽  
First Time

Abstract A recent excavation yielded 118 large tridactyl footprints in the Lower Jurassic Dolomitic Formation of the Causses Basin, at Mongisty in southern France. Most of the tracks are ascribed to Eubrontes giganteus Hitchcock, 1845. They are preserved on a surface of 53 m2 and form parallel rows with a preferential orientation towards the north. Such an abundance and density of E. giganteus is observed for the first time in the Early Jurassic from the Causses Basin. Sedimentological and ichnotaphonomical analyses show that the footprints were made at different time intervals, thus excluding the passage of a large group. In contrast to all other tracksites from the Dolomitic Formation, where tracks are preserved in fine-grained sediments corresponding to low-energy depositional palaeoenvironments, the tracks from Mongisty are preserved in coarse-grained sediment which is a matrix- to clast-supported breccia. Clasts consist of angular to sub-rounded, millimetric to centimetric-scale (up to 2 cm), poorly sorted, randomly oriented, homogeneous dolostone intraclasts floating in a dolomudstone matrix. Sedimentological analysis shows that the depositional environments of Mongisty varied from subtidal to intertidal/supratidal settings in a large and protected flat marsh. The lithology of the track-bearing surfaces indicates that the mudflat of the Causses Basin was sporadically affected by large mud flows that reworked and redeposited mudstone intraclasts coming from the erosion of upstream, dry and partially lithified mud beds. Throughout the world, this type of preservation of dinosaur tracks in tidal matrix- to clast-supported breccias remains rare.

scholarly journals Petrology and geochemistry of granitoids and their mafic micogranular enclaves (MME) in marginal part of the Małopolska Block (S Poland)

Mineralogia ◽  
2012 ◽  
Vol 43 (1-2) ◽  
pp. 3-127 ◽  
Author(s):  
Anna Wolska
Keyword(s):  
Trace Elements ◽  
Continental Crust ◽  
Coarse Grained ◽  
Granitic Rocks ◽  
Mixing Process ◽  
Na2o Content ◽  
Fine Grained ◽  
Małopolska Block ◽  
First Time ◽  
Different Sources

AbstractGranitic plutons (the Dolina Będkowska valley and Pilica area) were found in a few boreholes in the Małopolska Block (MB). These granitic rocks may represent apical parts (apophyses) of a great magmatic bodies (batholiths) located in deeper level of the Ediacaran/Paleozoic basement. They are described as ‘stitching intrusions’, generated during/after collision in Carboniferous/Permian period (~300 Ma) between the Upper Silesian Block (USB) and the Małopolska Block (MB).These rocks are fresh, unaltered granodiorites that are pale grey in colour. They have holocrystalline, medium- to coarse-grained structure and massive texture. For the first time, several mafic microgranular enclaves (MME), varying in size and colour, were found in the granodioritic host (HG). The occurrence of MME in the host granodioritic rocks is evidence of a mingling process between mafic and felsic magmas.The MME are pale/dark grey in colour, fine-grained rocks with ‘porphyritic’ textures. They consist of large megacrysts/xenocrysts of plagioclase, quartz, alkali feldspars and the fine-grained groundmass of pseudo-doleritic textures (lath-shaped plagioclases, blade-shaped amphiboles/biotites). According to their modal/mineral composition, they represent Q-diorites and tonalites.The MME, similar to the host granodiorites (HG), are I-type rocks, exhibit high Na2O content >3.2 wt%; normative diopside or normative corundum occurs (mainly <1%). They are metaluminous to slightly peraluminous (ASI <1.1) and have calc-alkaline, medium-K to high-K character. They generally belong to magnesian series (#Mg=0.20-0.40) and have low agpaitic index (<0.87). They are low evolved magmatic rocks. The rocks studied are enriched in LREEs (La, Ce, Sm) compared to HREEs. The Eu* negative anomaly and high Sr contents point to varying degrees of plagioclase fractionation connected to the mixing process rather than simple fractional crystallization. Both rocks studied (HG and MME) are characterized by a high content of LILEs (K, Ba, Rb) in normalized patterns and a low HFS/LIL elements ratio (Ta, Nb)/(K, Rb, La). The projection points of the rocks studied plot in different fields of various petrochemical diagrams: mainly in the arc granites that are rare in the pre-collisional granites as well as the syn-subductional to post-collisional granites fields.For the first time, inner textures in rock-forming minerals related to mixing processes are described both in the granodioritic host (HG) and in the MME. Mantled boxy cellular plagioclase megacrysts with ‘old cores’ of labradorite composition, and amphibole aggregates with titanite and opaque minerals, represent peritectic rather than primary residual minerals. The plagioclase, quartz and alkali feldspar megacrysts/xenocrysts were mechanically transferred from the granodioritic host (HG) to MME. The presence of lath-shaped plagioclases, blade-shaped amphiboles/biotites and acicular-shaped apatites in the groundmass of the MME is evidence of undercooling of hot mafic blobs in a relatively cold granodioritic magma chamber. The MME were hybridized by leucocratic melt squeezed from the granodioritic magma in a later stage of the mixing process (quartz and alkali crystals in the interstices in the MME groundmass). In the granodiorites (HG), the spike and spongy cellular zones as well as biotite/amphibole zones in plagioclase megacrysts are connected to the mixing process.Both of the rocks studied are characterized by different amounts of major elements (SiO2, Na2O and K2O), trace elements (Ni, Cr, V, Ti and P), #Mg and modified alkali-lime index (MALI) that is related to their origins from different sources. On the other hand, they have similar chondrite-normalized patterns (for trace elements and REE), LILEs contents (Sr, Ba, Rb), aluminum saturation index (ASI) and isotopic signatures (high 86Sr/87Sr (0.079-0.713) and low 143Nd/144Nd (0.512) values but lower than in continental crust), which are evidence of the strong hybridisation of mafic enclaves by the granodioritic host magma. The parental rocks of both rocks studied have a similar mafic signature but were generated in different sources: the host granodiorites (HG) magma in lower continental crust rocks, and the MME magma in enriched upper mantle. The MME crystallized from strongly hybridized magma of intermediate compositions (Q-diorite, tonalite) rather than from primary mafic magma. The host granodiorites (HG) originated from completely homogenized crustal granodioritic magma which inherited its geochemical signature from ancient arc-rocks in a subduction-related setting

scholarly journals Ground-Penetrating Radar Evaluation of Moisture and Frost across Typical Saskatchewan Road Soils

2010 ◽  
Vol 2010 ◽  
pp. 1-9 ◽  
Author(s):  
Curtis Berthelot ◽  
Diana Podborochynski ◽  
Timo Saarenketo ◽  
Brent Marjerison ◽  
Colin Prang
Keyword(s):  
Dielectric Constant ◽  
Moisture Content ◽  
Ground Penetrating Radar ◽  
Soil Type ◽  
Structural Condition ◽  
Coarse Grained ◽  
Fine Grained ◽  
Survey Results ◽  
Ground Penetrating

This study was undertaken to evaluate the effect of soil type, moisture content, and the presence of frost on road substructure permittivity. Permittivity sensitivity of typical road soils was characterized in the laboratory to provide baseline dielectric constant values which were compared to field ground penetrating radar (GPR) survey results. Both laboratory devices, the complex dielectric network analyzer and the Adek Percometer, as well as the field GPR system were used in this study to measure the dielectric constant of soils. All three systems differentiated between coarse-grained and fine grained soils. In addition, at temperatures below freezing, all three systems identified an increase in water content in soils; however, when frozen, the sensitivity of dielectric constant across soil type and moisture content was significantly reduced. Based on the findings of this study, GPR technology has the ability to characterize in situ substructure soil type and moisture content of typical Saskatchewan road substructure soils. Given the influence of road soil type and moisture content on in-service road performance, this ability could provide road engineers with accurate estimates of in situ structural condition of road structures for preservation and rehabilitation planning and optimization purposes.

Sign in / Sign up

Export Citation Format

Share Document