bluuebunny/crossref_metadata_2025 huggingface dataset:
Metamorphic history of the Hemlo gold deposit from Al2SiO5 mineral assemblages, with implications for the timing of mineralization
Authors: Powell Wayne G , Pattison David RM , Johnston Paul
Published: April 2011

Textural relations between Al2SiO5 phases, and deformation fabrics, provide constraints on the metamorphic history of the Hemlo gold deposit. Kyanite in the deposit is most common within and on the margins of boudinaged quartz ± realgar veins, and less commonly as rotated porphyroblasts within the matrix of schistose rocks. Kyanite predates the main (D2) schistosity. Sillimanite postdates kyanite, occurring irregularly as discrete knots and foliae that run parallel to, but sometimes cut across, the principal (D2) foliation, indicating that sillimanite postdates the D2 foliation. We regard kyanite to be part of the peak metamorphic assemblage, with sillimanite representing a partial later overprint most likely related to fluid infiltration. Rare andalusite occurs in two associations: as late-stage, clean, idioblastic crystals; and as large, fractured grains, locally overprinted by sillimanite, in boudinaged quartz-realgar veins. We suggest two possible origins for this second form of andalusite, one involving generally late growth, the second involving early growth prior to the development of peak metamorphic kyanite. Although not unambiguous, we prefer the second scenario. P-T conditions from petrogenetic grid constraints, and new geothermobarometric estimates, indicate 6-7 GPa, 600-650°C for the peak kyanite grade metamorphism (ca. 2677 Ma?), and 4-5 GPa, 600°C for the later sillimanite overprint (ca. 2672 Ma?). We see these two events as part of an evolving P-T path in a single metamorphic event. In our early andalusite scenario, the andalusite may have formed from pyrophyllite breakdown at 2-4 GPa, 450°C, possibly associated with emplacement of the regional suite of granodiorite plutons (ca. 2686 Ma). Late andalusite formed sporadically on the retrograde path. The occurrence of deformed andalusite and aligned kyanite in and on the margins of boudinaged auriferous realgar-stibnite-quartz veins provides evidence in support of a premetamorphic mineralization event.
Contrasting arc and MORB-like assemblages in the Paleoproterozoic Flin Flon Belt, Manitoba, and the role of intra-arc extension in localizing volcanic-hosted massive sulphide deposits
Authors: Syme E C , Lucas S B , Bailes A H , Stern R A
Published: April 2011

The Flin Flon Belt (Trans-Hudson Orogen, Manitoba and Saskatchewan) is the largest Paleoproterozoic volcanic-hosted massive sulphide (VMS) district in the world, with 118.7 million tonnes (Mt) of Zn-Cu-(Au-Ag) sulphide ore in 25 past or presently producing mines and 64.3 Mt in subeconomic deposits. The orebodies are restricted to isotopically juvenile volcanic-arc sequences, dated at 1.903-1.881 Ga at Flin Flon. Sequences of ca. 1.904-1.901 Ga back-arc and ocean-plateau basalts and related plutonic rocks, structurally juxtaposed with the arc assemblages at 1.880-1.870 Ga, are not known to contain economic base metal deposits. The juvenile arc tectono-stratigraphic assemblages are generally marked by older and stratigraphically lower tholeiitic submarine volcanic packages (ca. 1.903-1.886 Ga) that are observed or interpreted to be overlain by extensive and lithologically varied sequences of calc-alkaline and alkaline (shoshonitic) arc rocks and arc rift deposits (ca. 1.888-1.881 Ga). VMS deposits occur in both the tholeiitic and calc-alkaline arc sequences, but the 62 Mt Flin Flon deposit occurs in a 1.903 Ga tholeiitic primitive arc package. It can be demonstrated that for the Flin Flon - Callinan - Triple 7, Cuprus, and White Lake VMS deposits, whose stratigraphic context is preserved, deposition of the massive sulphides was temporally associated with inferred arc rifting processes. Critical observations for arc rifting include evidence for extensional faulting, erosion, and development of unconformities; extrusion of MORB-like basalts and associated rhyolites; and development of depositional basins with thick sequences of shoshonitic turbidites. As has been proposed for other major VMS camps (e.g., Kuroko, Kidd Creek, Bathurst), arc rifting can generate the loci of sustained high heat flow and fluid pathways required for the development of long-lived hydrothermal convection systems.
Surficial materials and related ground ice conditions, Slave Province, N.W.T., Canada
Authors: Dredge Lynda A , Kerr Daniel E , Wolfe Stephen A
Published: April 2011

Surficial mapping and geologic information on the nature and evolution of surficial materials in the Slave geologic province indicate that the geotechnical properties and potential ground ice contents associated with these materials depend largely upon their provenance, depositional conditions, and the postglacial climatic history. This information may be used to provide a regional-scale view of the distribution of ground ice conditions and terrain sensitivities associated with various surficial materials. In till veneers and blankets, ground ice content is generally low, as suggested by lack of thermokarst and other permafrost features. However, distinctive surface relief in hummocky till including kettle depressions, rim-ridges, and shallow thaw flowslides may be attributed to massive ice, resulting in sensitive till terrain. Although many outwash sediments have low ice contents near the surface, massive ice ranging from 5 to 10 m thick is present in some eskers and ice-contact outwash sediments. These are associated with thermokarst, slope movement, and collapse features, indicative of meltout or creep of large bodies of massive ice. The terrain sensitivity associated with these deposits is typically low to moderate, due to the coarse-grained nature of the sediments. In contrast, terrain sensitivity is high, and active-layer detachment slides are common along the Coronation Gulf coast where frozen silty clay marine sediments contain a wide range of ice contents. Results from this study may be applied to a much more extensive area of the glaciated western Arctic mainland and adjacent Arctic coastal plain in which materials with a similar glacial history are found.
Borden dykes of Baffin Island, Northwest Territories: a Franklin U-Pb baddeleyite age and a paleomagnetic reinterpretation
Authors: Pehrsson Sally J , Buchan Kenneth L
Published: April 2011

U-Pb baddeleyite geochronology for two Borden diabase dykes of northern Baffin Island gives an intrusion age of ca. 720 Ma, coeval with the age established elsewhere for the Franklin igneous event. Thus, the Borden dykes belong to the Franklin dyke swarm, rather than forming a separate swarm that intruded at ca. 950-900 Ma, as has been suggested previously on the basis of paleomagnetism and K-Ar ages. As a result, the paleopole from the Borden dykes can no longer be utilized to help constrain the ca. 1050-850 Ma Grenville Loop of the North American polar wander path. Reevaluation of paleomagnetic data for the dykes of northern Baffin Island suggests that Borden dyke magnetizations resulted from superposition of a steeply directed component of chemical remanent magnetization on normal and reversed primary Franklin components. The overprint direction is consistent with a Cretaceous-Tertiary age and is likely related to normal faulting and graben development during the opening of Baffin Bay.
Glacitectonized lake sediments, Barrier Lake, Kananaskis Country, Canadian Rocky Mountains
Authors: Evans David JA , Salt Keith E , Allen Claire S
Published: April 2011

Stratigraphic and sedimentological analyses of exposures through a glacilacustrine sedimentary sequence along the south shore of Barrier Lake, Kananaskis Country, reveal evidence of glacitectonic disturbance, relating to a readvance of the Bow Valley glacier at the end of the last glaciation. Prior to disturbance, palaeocurrent measurements in gravel and sand foreset beds record the deposition of subaqueous fans-deltas from a glacier lobe retreating eastwards along the Barrier Lake depression. The fan-delta sediments fine upwards into ripple- and cross-bedded sands and laminated muds with dropstones, documenting progressively distal sedimentation. Palaeostress directions measured from large-scale folds, shear zones and glacitectonites, and deformation tills indicate that glacier ice readvanced southwards from a glacier lobe located over the Barrier Lake depression. These stress directions are used to reconstruct the flow lines within the southern margin of a low-profile glacier lobe that terminated halfway up lower Barrier Lake, a more extensive readvance than previously envisaged in the area for this period. Comparisons of diamicton and glacitectonite fabric shapes with similar sediments elsewhere indicate that the subglacially deformed material that caps some of the sections is immature and has undergone short travel distances. Although the exact age of the readvance is unknown, it probably represents the Canmore Readvance of the Late Wisconsinan glaciation.
Age verification of the Lake Gribben forest bed and the Younger Dryas Advance of the Laurentide Ice Sheet
Authors: Lowell Thomas V , Larson Graham J , Hughes John D , Denton George H
Published: April 2011

Analysis of nine wood samples from the Lake Gribben forest bed near Lake Gribben, Michigan, yielded a combined age of 10 025 ± 100 14C years BP, which confirms and refines prior age estimates for the bed. The stratigraphic position of these samples below a prograding ice-contact fan indicates the time that a glacial margin reached the southern edge of the Lake Superior basin. Geomorphic tracing and correlation of associated deposits indicate that a contemporaneous margin extended almost 1000 km from Duluth, Minnesota, across the Lake Superior basin to North Bay, Ontario. Along the southern shore of Lake Superior ice-margin expansion began during and ended at the close of the Younger Dryas. A surging glacier system would not produce a nearly linear moraine system across both a major basin (Lake Superior) and a major upland (Abitibi Upland). Therefore, we attribute this advance of the Laurentide Ice Sheet to climatic forcing of the Younger Dryas event.
Kilometre-scale folding in the Teslin zone, northern Canadian Cordillera, and its tectonic implications for the accretion of the Yukon-Tanana terrane to North America
Authors: de Keijzer Martin , Williams Paul F , Brown Richard L
Published: April 2011

The Teslin zone in south-central Yukon has previously been described as a discrete zone with a steep foliation unique to the zone. It includes the Anvil assemblage and the narrowest portion of the Yukon-Tanana terrane (the Nisutlin assemblage), and is defined by post-accretionary faults: the Big Salmon fault to the west and the d'Abbadie fault system to the east. The zone was interpreted as a lithospheric suture or a crustal-scale transpression zone, and as the root zone of klippen lying on the North American craton to the east. We demonstrate that deformation and metamorphism are the same inside and outside the zone. The steep transposition foliation in the zone, in contrast to adjacent rocks to the east, coincides with the steep limb of a regional F3 structure. This fold has a shallow limb in the easternmost part of the zone and immediately east of the zone. Thus we reject earlier interpretations. If a suture exists between the obducted Anvil and Yukon-Tanana Nisutlin assemblages and North America, it is a shear zone that occurs at the base of the obducted rocks, which has been folded by the F3 fold. However, evidence that this thrust boundary is a lithospheric suture is lacking. A consequence of our interpretation is that North American rocks pass under the eastern Teslin zone and outcrop to the west of the Nisutlin and Anvil assemblages. This geometry precludes the possibility of the Teslin zone being the root zone of the klippen.
The Central Slave Basement Complex, Part I: its structural topology and autochthonous cover
Authors: Bleeker Wouter , Ketchum John WF , Jackson Valerie A , Villeneuve Michael E
Published: April 2011

New field and geochronological data are used to define the distribution of Mesoarchean basement rocks in the south-central Slave Province. This distribution reflects a single contiguous basement terrane that we propose to call the Central Slave Basement Complex. It shows a structural topology that is internally consistent and compatible with known regional folding and faulting events. A sample of a proposed basement gneiss below the Courageous Lake greenstone belt, central Slave Province, has been dated by U-Pb methods and yields an age of 3325 ± 8 Ma, consistent with the new basement distribution. This sample also contains 2723 ± 3 Ma metamorphic zircon and ca. 2680 Ma titanite. The Central Slave Basement Complex is overlain by a thin, discontinuous, but distinctive cover sequence that includes minor volcanic rocks, clastic sedimentary rocks, and banded iron formation. All previously known and some new occurrences of this distinctive cover sequence occur in the immediate stratigraphic hanging wall of the Central Slave Basement Complex, locally overlying a preserved in situ unconformity. We propose to call this post-2.93 Ga cover sequence the Central Slave Cover Group. It is perhaps best typified by detrital chromite-bearing, fuchsitic quartzites. Formal formation names are proposed for the spatially separate occurrences of the Central Slave Cover Group. Detrital zircon ages are presented for one of the formations of the Central Slave Cover Group, the Patterson Lake Formation, which occurs on the western flank of a local basement culmination known as the Sleepy Dragon Complex. The detrital zircon data provide evidence for two discrete basement sources dated at ca. 2943 Ma and ca. 3147-3160 Ma. These detrital ages reinforce the depositional link between the Central Slave Cover Group and underlying crystalline rocks of the Central Slave Basement Complex.
Heat flow and deep thermal structure near the southeastern edge of the Canadian Shield
Authors: Mareschal J C , Jaupart C , Gariépy C , Cheng L Z , Guillou-Frottier L , Bienfait G , Lapointe R
Published: April 2011

Five new heat-flow and heat-production measurements in the Archean Superior Province are presented. These measurements include the first heat-flow values to be reported for the Opatica subprovince and the Otish basin. These new data complete the data set acquired in the eastern Canadian Shield during the Abitibi-Grenville Lithoprobe transect. The data set now available in eastern Canada, covering geological provinces ranging in age from 2700 to 400 Ma, achieves sufficient sampling to define the deep thermal structure of a continent near the edge of the craton. It shows that, for the Canadian Shield, there is no simple relation between heat flow and the age of tectonic provinces. The map of heat flow in eastern Canada demonstrates that there is no significant difference in heat flow between the Abitibi subprovince and the Grenville Province (including the Adirondacks) where the area-weighted average heat flow is the same (39 vs. 38 mW·m-2, respectively). Outside the Abitibi, the Superior Province is characterized by a higher heat flow (45 mW·m-2). Heat-flow and gravity data are used together to determine changes in crustal composition and thickness. The analysis of these data and constraints from seismology support the view that the variations in surface heat flow can be entirely accounted for by changes in crustal composition. Heat-flow variations across the Abitibi subprovince indicate that there are significant differences in crustal composition that reflect the complex assemblages that make up the Archean crust. The heat-flow map shows a sharp transition between the Grenville Province and the Appalachians, where the average heat flow is significantly higher (57 mW·m-2). This difference is due to higher heat production in the Appalachian upper crust with the same mantle heat flow as in the shield (~12 mW·m-2 throughout eastern Canada). Lower crustal and upper mantle temperatures are typically low, which might explain the preservation of irregular crustal thickness over several billion years.
High-resolution seismic stratigraphy of late Quaternary deposits in Manitounouk Sound, northern Quebec: effects of rapid postglacial emergence
Authors: Hill Philip R , Simard Annie , Héquette Arnaud
Published: April 2011

Manitounouk Sound contains a succession of postglacial deposits consisting of three acoustic units separated by disconformities. From base to top, these are (1) a stratified draped unit interpreted as of glaciolacustrine and glaciomarine origin, (2) an onlapping basin-fill unit of thick transparent beds interpreted as gravity-flow deposits, and (3) a divergent fill unit of stratified and transparent modern marine deposits. The gravity-flow deposits of unit 2 pass laterally into slide scars that truncate unit 1. Pollen and dinoflagellate analysis of cores correlated with the acoustic sections indicate that unit 1 is of early Holocene age and confirms a glaciomarine environment. Unit 3 contains modern assemblages of pollen and dinoflagellates. The slide scar and gravity-flow deposits of unit 2 correspond to the period of transition from glaciomarine to modern conditions and are interpreted to result from a period of relatively intense earthquake activity due to stress release along faults during or shortly after the deglaciation of Hudson Bay.
Structural development of the Snow Lake Allochthon and its role in the evolution of the southeastern Trans-Hudson Orogen in Manitoba, central Canada
Authors: Kraus Jürgen , Williams Paul F
Published: April 2011

The Snow Lake Allochthon is a zone of tectonic interleaving of sedimentary rocks of an inverted marginal basin (Kisseynew Domain) with island-arc and oceanic rocks. It is located in the southeastern part of the exposed internal zone of the Paleoproterozoic Trans-Hudson Orogen in Manitoba, Canada, near the external zone (Superior collision zone or Thompson Belt), which constitutes the local boundary between the Trans-Hudson Orogen and the Archean Superior Craton. The Snow Lake Allochthon formed, was deformed, and was metamorphosed up to high grade at low to medium pressure during the Hudsonian orogeny as a result of the collision of Archean cratons ~1.84-1.77 Ga. Four generations of folds (F1-F4) that formed in at least three successive kinematic frames over a period of more than 30 Ma are described. Isoclinal to transposed southerly verging F1-2 structures are refolded by large, open to tight F3 folds and, locally, by open to tight F4 folds. The axes of the F1-2 folds are parallel or near parallel to the axes of F3 folds, owing to progressive reorientation of the F1-2 axes during south- to southwest-directed tectonic transport, followed by F3 refolding around the previous linear anisotropy. A tectonic model is presented that reconciles the distinct tectono-metamorphic developments in the Snow Lake Allochthon and the adjacent part of the Kisseynew Domain on the one hand, and in the Thompson Belt on the other, during final collision of the Trans-Hudson Orogen with the Superior Craton.
Deposition and imbrication of a 2670-2629 Ma supracrustal sequence in the Indin Lake area, southwestern Slave Province, Canada
Authors: Pehrsson S J , Villeneuve M E
Published: April 2011

New U-Pb age data from the southwestern Slave Province demonstrate that units of the Indin Lake supracrustal belt form an imbricated structural stack. The oldest rocks of the belt are undated mafic volcanic flows of the Hewitt Lake group that are crosscut by a 2670 Ma felsic sill, itself coeval with mafic through felsic volcanic rocks of the 2668-2671 Ma Leta Arm group. The youngest rocks of the belt are 2647-2629 Ma turbidites and felsic volcanic rocks of the unconformably overlying Chalco Lake group. Tonalite orthogneiss of the adjacent Cotterill gneiss complex is 2680 Ma, suggesting that it does not represent in situ basement to the supracrustal belt. Intercalation of the older Hewitt Lake and Leta Arm groups with the younger Chalco Lake group is interpreted to result from D1 imbrication and folding between 2629 and 2609 Ma, the age of a crosscutting tonalite intrusion. Subsequent D2 folding and regional low-pressure metamorphism occurred between 2609 Ma and ca. 2590 Ma. D3 normal faulting between the belt and Cotterill gneisses, ca. 2590 Ma, is interpreted to overlap with retrograde amphibolite-facies metamorphism and decompression of the gneiss complex. Comparisons between the tectonic history of the Indin Lake area and the central Slave Province show that turbidite deposition was regionally diachronous and overlapped with regional deformation elsewhere, supporting existing models favouring some form of accretionary orogenesis. The imbricated and intercalated 2670-2629 Ma supracrustal sequence may characterize a distinct crustal block in the southwestern Slave Province.
A new study of Solenodonsaurus janenschi, and a reconsideration of amniote origins and stegocephalian evolution
Authors: Laurin Michel , Reisz Robert R
Published: April 2011

A restudy of the holotype and other known specimens of Solenodonsaurus, a Late Carboniferous relative of amniotes, suggests that this taxon did not have a tympanum. Its teeth lack labyrinthine infolding, and the frontal did not reach the orbit. A new phylogenetic analysis of stegocephalians suggests that Solenodonsaurus is an anthracosaur, and that it is the sister group of Cotylosauria. It also shows that the problematic taxon Westlothiana may not be an anthracosaur (not a stem-amniote). A recent suggestion that diadectomorph cotylosaurs laid amniotic eggs is shown to be based on tenuous evidence, although this remains a possibility. The evolution of the otic region is studied using parsimony to determine whether the emargination present in Solenodonsaurus and in some diadectomorphs is a primitive or a secondary character, but this procedure yields equivocal results.
New perspectives on the Flin Flon Belt, Trans-Hudson Orogen, Manitoba and Saskatchewan: an introduction to the special issue on the NATMAP Shield Margin Project, Part 1
Authors: Lucas S B , Syme E C , Ashton K E
Published: April 2011

A new tectonic framework for the Flin Flon Belt in southeastern Reindeer Zone of the Trans-Hudson Orogen has emerged in recent years through four-dimensional studies (bedrock and subsurface mapping, seismic reflection profiling, U-Pb geochronology) associated with the NATMAP Shield Margin Project and Lithoprobe Trans-Hudson Orogen Transect. This special issue contains 10 papers covering a wide variety of topics related to the NATMAP Shield Margin Project.
Hesperornis (Aves) from Ellesmere Island and palynological correlation of known Canadian localities
Authors: Hills L V , Nicholls E L , Núñez-Betelu L (Koldo) M. , McIntyre D J
Published: April 2011

A tarsometatarsus of Hesperornis from the Kanguk Formation on Ellesmere Island is described and illustrated and constitutes the northernmost occurrence of the genus. Palynological evidence and stratigraphic position indicate that Canadian occurrences of Hesperornis are Campanian in age except the specimen from the Mason River Formation which might be as young as early Maastrichtian. Paleogeographic reconstructions indicate that all specimens are from a seaway extending along the western interior of North America.
Geoscience impact: a synthesis of studies of the Sudbury Structure
Authors: Boerner D E , Milkereit B , Davidson A
Published: April 2011

Geophysical probing results are synthesized into a three-dimensional framework necessary for understanding the genesis of the Sudbury Structure, based primarily on seismic reflection results centred on the Sudbury Igneous Complex. Remnants of crustal melting from a catastrophic meteorite impact are superimposed on the juxtaposition of mid-crustal rocks exhumed during the Archean against deformed Paleoproterozoic sedimentary rocks. Sedimentation, metamorphism, deformation, and metasomatic overprints are all part of the post-impact history of Sudbury and tend to dominate the geophysical response of the structure. Pre-impact deformation, although certainly preserved in some aspects of Sudbury geology, is not clearly expressed in the geophysical data, nor are any elements of impact-induced deformation. Geophysical views of the Sudbury Igneous Complex are thus somewhat biased in representing mostly the post-impact, but pre-Grenvillian history of the region, with the exception of igneous events. Establishing the proper context for integrating these geophysical results in the genetic interpretation of the Sudbury Structure depends crucially upon timing constraints.
Contrasting Si-saturation in troctolite-anorthosite intrusions along the Manicouagan corridor of the Abitibi-Grenville transect
Authors: Francis Don , Scowen Pamela , Panneton Gerald , Doig Ronald
Published: April 2011

A survey of troctolite-anorthosite complexes along the Manicouagan corridor of the Abitibi-Grenville Lithoprobe transect reveals the existence of two distinct crystallization sequences in their cumulate rocks. In two intrusions (Brien and Raudot), olivine crystallized first, followed by plagioclase, Fe-oxides, and then clinopyroxene; and magmatic orthopyroxene is absent. In five other intrusions (Lucie, Tétépisca, Blache, Baie-Comeau, and Pentecôte), plagioclase and olivine are followed by orthopyroxene, and then clinopyroxene. These two distinct crystallization sequences correlate with compositional differences in gabbroic marginal rocks and dykes associated with the intrusions. The Raudot intrusion exhibits a fine-grained gabbroic margin that is Fe- and Al-rich, but Si-poor and nepheline normative. In contrast, the marginal rocks of the Blache, Baie-Comeau, and Pentecôte intrusions are typically gabbronorites that are poorer in Fe and richer in Si. Dyke rocks cutting this latter group of intrusions share these compositional characteristics and are typically orthopyroxene normative. The differences between the two types of intrusions appear to reflect the degree of Si-saturation of their parental magmas with respect to the troctolite divide. Together, the array of estimated parental magma compositions of the troctolite-anorthosite intrusions mimics that of Tertiary picritic magmas. The low forsterite (Fo) contents in olivine and the late appearance of clinopyroxene in the cumulates of the intrusions may reflect the interaction of mantle-derived parental magmas with relatively juvenile feldspathic crust.
Data-model comparison of the Younger Dryas event
Authors: Rutter Nathaniel W , Weaver Andrew J , Rokosh Dean , Fanning Augustus F , Wright Daniel G
Published: April 2011

The Younger Dryas cooling event is well established in the North Atlantic region through numerous climate proxy records. Although the climatological controls vary from site to site, it is considered to have taken place between about 10 000 and 11 000 BP (radiocarbon years) (~11 500-13 000 calendar years ago). Outside the North Atlantic region, climate proxy records and chronology commonly become problematic because of weaker signals and less dating control. In addition to this evidence, oceanic records reveal conflicting evidence for Younger Dryas forcing mechanisms and the timing of events. We compare proxy evidence with the results from an ocean general circulation model coupled to the energy-moisture balance atmospheric model. The model results reveal a global pattern and regional magnitude which generally agree with temperature changes interpreted from paleoclimate reconstructions. The model also supports the general duration of global cooling of the Younger Dryas. Although proxy data can be controversial outside of the North Atlantic region, the authors believe that there is enough evidence to support the Younger Dryas event on a global scale. They also recognize, however, that more concrete evidence is needed before the question can be unequivocally answered.
Structural setting, textures, and timing of hydrothermal vein systems in the Val d'Or camp, Abitibi, Canada: implications for the evolution of transcrustal, second- and third-order fault zones and gold mineralization
Authors: Neumayr P , Hagemann S G , Couture J -F
Published: April 2011

In the Val d'Or camp, Archean Abitibi greenstone belt, Canada, numerous gold-mineralized second- and third-order fault zones are spatially associated with the transcrustal Cadillac Tectonic Zone (CTZ). This situation is used to test whether fluid systems in the CTZ have a similar structural timing to those in the gold-hosting structures, and hence the CTZ could represent the main fluid conduit in the camp. The transcrustal CTZ at Orenada No. 2 contains structurally complex vein systems, with mineralized quartz-tourmaline veins related to both D2 oblique-reverse faulting and F3 dextral asymmetric folding, both of which have been overprinted by unmineralized subhorizontal and subvertical quartz veins. Quartz ± tourmaline veins within second- and third-order shear zones at Paramaque and Rivière Héva also formed during D2 deformation and have been, at least at Rivière Héva, deformed by F3 asymmetric folding. In contrast, mineralized quartz vein systems at Cartier Malartic are controlled by F3 folding and overprinted by late-stage D3 faults which host late quartz-tourmaline veins. Quartz vein textures are consistent with these timing relations, because D2-controlled veins contain deformed quartz grains, whereas quartz in D3-controlled veins is unstrained. The D2 and D3 timing of mineralized quartz veins in the transcrustal CTZ and in second- and third-order structures is consistent with the notion that the CTZ represents the main fluid conduit and that mineralization occurred in linked second- and third-order structures. The different timing of quartz-tourmaline veins in different shear zones indicates that the veins were probably hydraulically linked to the CTZ during at least two different episodes. The location of Cartier Malartic structurally below the CTZ indicates that fluids travelled either downward from the main conduit or that the shear zone was part of the CTZ.
Late Holocene diatom biostratigraphy and sea-level changes in the southeastern Beaufort Sea
Authors: Campeau Stéphane , Héquette Arnaud , Pienitz Reinhard
Published: April 2011

Late Holocene sediments from the Atkinson Point area were analysed to provide quantitative reconstructions of recent sea-level changes in the southeastern Beaufort Sea. The succession of diatom assemblages in five cores revealed paleoenvironmental changes induced by the transgression of the Beaufort Sea during successive periods of lacustrine conditions, breaching and flooding of thermokarst lakes by the sea, and the landward migration of sandy spits. Based on radiocarbon dates and quantitative paleodepth determinations, a relative sea-level curve for the late Holocene has been developed. Despite a loss of temporal precision due to old carbon contamination, an envelope of sea-level change has been defined for the last 2 ka BP, suggesting a sea-level rise in the order of 1.1 mm a-1 for the last millennium. This paper presents the first sea-level reconstruction inferred from a diatom-based transfer function. It represents an improvement over traditional methods which were limited to qualitative estimates of past sea levels.
Instabilities in the Labrador Sea water mass structure during the last climatic cycle
Authors: Hillaire-Marcel Claude , Bilodeau Guy
Published: April 2011

In the modern Labrador Sea, the North Atlantic deep water components are found below the ~2 km deep, intermediate Labrador Sea water (LSW) mass, which is renewed locally through winter convective mixing. This water mass structure remained relatively stable since ~9.5 14C ka BP, as indicated by isotopic studies of foraminifer assemblages from deep-sea cores. Almost constant differences in δ18O values are observed between major species. These average -0.5 between the epipelagic species Globigerina bulloides and the mesopelagic species Neogloboquadrina pachyderma, left coiled, and -1 between Neogloboquadrina pachyderma and the benthic species Cibicides wuellerstorfi, after correction for Cibicides wuellerstorfi specific fractionation. These isotopic compositions represent thermohaline conditions in surface waters, in the pycnocline with the LSW, and in the deep component of the North Atlantic deep water, respectively. A drastically different structure characterized the glacial Labrador Sea. Differences in δ18O values of ~ -2 to -2.5 are then observed between Globigerina bulloides and benthic species, indicative of a strong halocline between the corresponding water masses, thus for reduced production of intermediate waters. During the same interval, Neogloboquadrina pachyderma shows 13C and 18O fluctuations of 1 to 1.5 amplitude, in phase with Heinrich-Bond events and higher frequency climate oscillations. The δ18O values in Neogloboquadrina pachyderma vary between those of Globigerina bulloides and of benthic foraminifers, suggesting large amplitude bathymetric fluctuations of the halo-thermocline above and below the bathymetric range occupied by Neogloboquadrina pachyderma. Minimum δ18O values in Neogloboquadrina pachyderma match intervals of maximum ice rafting deposition, such as the late Heinrich events, thus intervals with a deeper, more dilute buoyant surface water layer.
Heterosis and genetic distance in rapeseed (Brassica napus L.): crosses between European and Asiatic selfed lines
Authors: Lefort-Buson M. , Guillot-Lemoine B. , Dattee Y.
Published: April 2011

Different types of F1 hybrids from the same and different geographic origins were studied. European and Asiatic inbred lines were hand crossed in three ways: a diallel design among European lines (European group), a diallel design among Asiatic lines (Asiatic group), and a factorial design between European and Asiatic lines (mixed group). Selfed lines and F1 hybrids of each group have been tested in the field at a normal seeding rate (4 kg/ha) in replicated trials. The experiment has been conducted over 2 years in two localities. Mixed group F1 hybrids were taller and more productive in seed yield than both European and Asiatic ones. For flowering, they were intermediate between both parents and close to the check Bienvenu. Variability was not organized the same way among the three groups. It was mainly additive for hybrids from lines of the same geographic origin (either European or Asiatic). However, specific effects, as great as the parental ones, occurred for hybrids from lines of different origins. Moreover, variability revealed for parental effects was greater within both European and Asiatic groups than in the mixed one.

Key words: heterosis, genetic distance, geographic origin, genetic parameters, Brassica napus L.
Genetic variability in Muscari comosum L. (Liliaceae). II. Characterization and effects of the polymorphic variants of chromosome 2 on chiasmata formation
Authors: Rejon C. Ruiz , Lozano R. , Rejon M. Ruiz
Published: April 2011

Muscari comosum L. (Liliaceae) displays a striking chromosomal polymorphism in the second largest chromosome. This polymorphism involves four cosmopolitan types. Two of these are shorter than the other two homologues. One of these is submetacentric (SSM) and the other is subtelocentric (SST). The two longer types also include a submetacentric (LSM) and a subtelocentric (LST) morph. Each of the two submetacentric chromosomes has one interstitial C-band in the short arm and each of the two subtelocentric morphs has an interstitial C-band in the long arm. The change of position of this interstitial C-band is most easily explained by a pericentric inversion. Furthermore, all four types of chromosome 2 have a centromeric C-band, while the two subtelocentrics have an additional terminal C-band in the long arm. The variability in the size of the second chromosome is most likely the consequence of an unequal interchange or an insertional translocation. The meiotic behaviour of the chromosome 2 bivalents in individuals heterozygous for the pericentric inversion is characterized by normal pairing between homologues with no inversion loops, though asynapsis was present in some meiocytes. Chiasmata are absent in two regions of chromosome 2 bivalents in these heterozygotes in which they regularly form in both classes of homozygotes. In individuals heterozygous for the long morphs of chromosome 2 the bivalents again showed normal pairing at pachytene, with chiasmata again absent in some regions in which they normally form. The net result is that homozygotes have significantly higher chiasmata frequencies than hterozygotes.

Key words: genetic variability, chiasma formation, Muscari.
Inheritance of aconitase isozymes in soybean
Authors: Doong Joe-Yuan H. , Kiang Yun-Tzu
Published: April 2011

A six-band electrophoretic zymogram for aconitase was observed in mature soybean seeds. Among 750 Glycine max (L.) Merr. strains and cultivars examined, 10 zymogram types were identified. Genetic studies showed that the second band (Rf's of 0.35 or 0.42) and the fourth band (Rf's of 0.61, 0.63, or 0.69) in the zymograms were the products of two unlinked loci, Aco2 and Aco4, with two and three codominant alleles, respectively. Heterozygotes displayed both parental band sets without any intermediate band, indicating a monomeric structure for aconitase. The most common alleles at the two loci were Aco2-b (0.793) and Aco4-c (0.818). Linkage analyses revealed that both Aco2 and Aco4 loci are inherited independently of four other biochemical loci (Adh1, Am3, Ap, Dial).

Key words: aconitase, isozymes, electrophoresis, gene locus, soybean, Glycine max.
Hypervariation associated with a 12-nucleotide direct repeat and inferences on intergenomic homogenization of ribosomal RNA gene spacers based on the DNA sequence of a clone from the wheat Nor-D3 locus
Authors: Lassner Michael , Anderson Olin , Dvořák Jan
Published: April 2011

A ribosomal RNA gene (rDNA) unit from the Nor-D3 locus (D genome) of Triticum aestivum L. was cloned and the "nontranscribed spacer" (NTS) was sequenced. The DNA sequence was compared with previously reported Nor-B2 locus (B genome) NTS sequences to study the molecular basis of evolution of these repeated genes and to look for evidence of homogenization between B- and D-genome rDNA. The NTS has seven subrepeats with a modal repeat length of 120 nucleotides; the subrepeats are shorter than Nor-B2 subrepeats owing to loss of one element of a 12-bp duplication present in Nor-B2 subrepeats. This 12 nucleotide sequence or its permutation, whose consensus sequence is CACGTACACGGA, is found at all sites where the B- and D-genome rDNA spacers differ by insertions or deletions longer than two nucleotides. The DNA sequence information was used to identify restriction sites unique to each locus that could be used in search of conversions between the B- and D-genome rDNA loci. Despite the coexistence of rDNA of the B- and D-genomes in the same nucleus for a minimum of 8000 years, no evidence for frequent interchromosomal conversion events between chromosomes 1B or 6B and 5D was found.

Key words: Triticum, rDNA, concerted evolution, spacer.
An eye color mutant (tan) in the tsetse fly, Glossina palpalis palpalis (Diptera: Glossinidae)
Authors: D'Haeseleer F. , Abbeele J. van den , Gooding R. H. , Rolseth B. M. , Vloedt A. Van der
Published: April 2011

A nondeleterious eye color mutant, tan, is described as the first visible mutant in Glossina palpalis palpalis (Robineau-Desvoidy). The locus for tan is on the X chromosome approximately 24 recombination units from the locus for testicular esterase (Est-t). Homozygous (tan/tan) females and hemizygous (tan/Y) males have compound eyes and ocelli that are pink (instead of dark brown) while the flies are alive but these fade to a tan color after death. No other differences in physical appearance of flies were found. General bionomic features of tan flies are not significantly different from those of wild-type flies. The mutant flies have a lower propensity for mating than do wild-type flies in the laboratory and there is assortative mating. Approximately half the offspring produced by tan females, which had mated twice, are sired by the second mate. Wild-type and tan adults excrete kynurenine and both types have tryptophan oxygenase and kynurenine formamidase. The lesion causing the abnormal eye color in the tan mutant appears to occur late in the metabolism of tryptophan to xanthommatin, possibly at the level of retention of xanthommatin in the eyes.

Key words: eye color mutant, Glossina.
Segregation in the pollen of F2 rye (Secale cereale) plants for induction of homoeologous chromosome pairing in hybrids with wheat (Triticum aestivum)
Authors: Gupta P. K. , Fedak G.
Published: April 2011

An attempt was made to determine the inheritance of the rye genes which induce high chiasma frequency in hybrids with wheat and to study if the ability of rye to induce partial amphiploidy in hybrids with wheat was heritable. Five to eight F2 pollen plants were derived from seeds taken from each of three F1 plants that had given high chiasma frequency in hybrids with 'Chinese Spring' wheat in earlier studies. Similarly, six to seven F2 pollen plants were derived from each of three F1 plants that had given partial amphiploids in hybrids with 'Chinese Spring' wheat in earlier studies. Chiasma frequency was studied in 127 hybrids with 'Chinese Spring' wheat. In the present study, significant differences in chiasma frequency were observed (i) among the 38 families represented by 127 plants, and (ii) between two groups of three sets each, one known for inducing high pairing and the other known for inducing partial amphiploidy associated with low pairing in wheat × F1 rye plants. Significant variation was also observed between families within sets (each originated from one F1 rye plant) suggesting that F2 rye plants derived from the same F1 plants also differed genetically for inducing heterogenetic (homoeologous) pairing in wheat × rye hybrids. One of the six sets particularly showed significantly higher pairing with a mean of 2.13 per cell (individual hybrids gave a chiasma frequency as high as a mean of 6.07 per cell) as against a range of 0.96 to 1.18 in the remaining five sets, suggesting accumulation of genes in F2 rye plants for inducing pairing in wheat × rye hybrids. It is expected that by intermating the segregating rye plants, it should be possible to accumulate genes and eventually to isolate homozygous lines inducing high pairing in hybrids with wheat. Contrary to expectation, no partial amphiploids were obtained in a study of 127 wheat × F2 rye hybrids, although three of the six F1 rye plants had earlier given partial amphiploids in wheat × F1 rye hybrids.

Key words: intergeneric hybrids, wheat, rye, genetic control, chromosome pairing.
Maximum likelihood estimates of fitness in iteroparous species population replacement experiments using compound chromosomes
Authors: Barclay Hugh J. , Fitz-Earle Malcolm
Published: April 2011

We have developed a method of estimating fitness in competing populations of compound autosome or similar rearranged strains and wild insects. The technique is based in part on the method of maximum likelihood as developed by DuMouchel and Anderson. Simulations of maximum likelihood estimates of overall fitness (MLEOF) revealed that the method is robust. For Drosophila melanogaster the MLEOF for compound autosome strains were in the order of 0.02–0.09, and for compound;free-arm combinations they ranged from 0.10–0.14. These values are comparable to those obtained from a previously-developed successive intervals method. However, the maximum likelihood technique is much simpler to apply and should prove to be useful in estimating fitness of competing lines in insect control programs.Key words: fitness estimation, maximum likelihood, population replacement, compound chromosomes.
Karyotypic characterization of some Liolaemus lizards in Chile (Iguanidae)
Authors: Lamborot Madeleine , Alvarez-Sarret E.
Published: April 2011

A comparative cytological study of 10 taxa of Liolaemus from different localities in Chile shows that several of them display a conservative karyotype, with six pairs of macrochromosomes similar in size and shape to other species within Liolaemus that are believed to be primitive in the family. These karyotypes may exhibit interspecific variation in the number and shape of the microchromosome pairs 7, 8, and 9 and in the chiasmata characteristics, thus permitting chromosomal characterization at the species level. Other taxa show an increased diploid number of chromosomes, mainly explained by Robertsonian derivation, pericentric inversion, translocation, and triploidy. One species presents intraspecific chromosomal variation. Thus, chromosomes can serve as genetic markers and improve our understanding of the evolution, systematics, and population genetics of these iguanids.Key words: Liolaemus (Iguanidae), karyotypic variation, chiasmata, triploidy.
Cytomorphological studies of a spontaneous triploid in Pennisetum hohenackeri Hochst. ex Steud.
Authors: Rao Y. Saideswara , Mengesha Melak H. , Rao S. Appa
Published: April 2011

During studies on the genomic relationships of the wild species of the genus Pennisetum, one spontaneous triploid (3x = 27) plant was identified among the diploid cytotypes (2n = 18) of Pennisetum hohenackeri Hochst. ex Steud. The triploid plant resembled the diploid in most morphological characters, except for the reduced number of spikelets. Chromosome associations of 9 II + 9 I were observed at diakinesis and metaphase I. The bivalents divided normally, while the univalents lagged and formed a separate nucleus, which was included in one of the daughter cells. On the basis of these studies, this plant was considered to be an allotriploid and might have originated as a spontaneous hybrid between diploid P. hohenackeri and an unknown tetraploid (amphidiploid) taxon with one of its genomes homologous to that of diploid P. hohenackeri. The possible donor of this genome could be P. orientale, which is a tetraploid with a basic chromosome number of x = 9.Key words: allotriploid, meiosis, diakinesis, univalents, micronuclei, laggards.
Long-term deflection prediction of concrete members reinforced with glass fibre reinforced polymer bars
Authors: Hall Tara , Ghali Amin
Published: April 2011

This paper presents the results of an experimental investigation of the long-term deflection behaviour of concrete shallow beams reinforced with glass fibre reinforced polymer (GFRP) bars. The long-term deflections of the GFRP-reinforced beams are compared to deflections of identical beams reinforced with steel bars. All beams were under sustained loading for approximately 8 months. The variables were the level of sustained loading and the reinforcement materials: steel or GFRP. The experimental immediate and long-term deflections of both the steel- and the GFRP-reinforced beams were compared to calculated deflections using the CEB-FIP Model Code 1990, and the ACI 318-95 code using the recommendations of ACI Committee 209; these references are for steel reinforced concrete members. The test results indicate that under similar loading conditions and the same reinforcement ratio, the GFRP-reinforced beams had long-term deflections, due to creep and shrinkage, 1.7 times greater than those of the steel-reinforced beams. A comparison of the theoretical and experimental immediate and long-term deflections indicates that the CEB-FIP Model Code 1990 gives reasonable predictions for all beams, and that the ACI 318-95 code, using the ACI Committee 209 recommendations, overestimates the deflections due to the combined effects of creep and shrinkage.Key words: glass fibre reinforced polymer (GFRP), steel, reinforced concrete, long-term, deflections, flexure, elastic modulus.