bluuebunny/crossref_metadata_2025 huggingface dataset:
Crustal architecture and tectonic assembly of the Central Gneiss Belt, southwestern Grenville Province, Canada: a new interpretation
Authors: Ketchum J WF , Davidson A
Published: April 2011

The Central Gneiss Belt, southwestern Grenville Province, is characterized by parautochthonous crust in the north and allochthonous lithotectonic domains in the south. Despite nearly two decades of study, the basal décollement to allochthonous domains transported from the southeast, known as the allochthon boundary thrust, has not been precisely located throughout much of the belt. Between Lake Nipissing and Georgian Bay where its surface trace is known, it separates 1.24 Ga Sudbury metadiabase in the footwall from eclogite remnants and 1.17-1.15 Ga coronitic olivine metagabbro confined to its hanging wall. On the premise that this relationship can be used to trace the allochthon boundary thrust elsewhere in the Central Gneiss Belt, we have sought to extend the known distribution of these mafic rock types, making use of field, petrographic, and geochemical criteria to identify them. New occurrences of all three mafic types are identified in a region extending from south of Lake Nipissing to western Quebec, and the mutually exclusive pattern of occurrence is maintained within this region. Structural trends and reconnaissance mapping of high-strain zones that appear to represent a structural barrier to the mafic suites suggest that the allochthon boundary thrust lies well to the north of its previously suggested location. Our preferred surface trace for it passes around the southern end of the Powassan batholith and through the town of North Bay before turning east to join up with the Lac Watson shear zone in western Quebec. This suggests that a large segment of "parautochthonous" crust lying north of, and including, the Algonquin domain is in fact allochthonous. The mutually exclusive distribution of the mafic suites points to significant separation of allochthonous and parautochthonous components prior to the Grenvillian orogeny, in accord with models of pre-Grenvillian continental rifting proposed by others. Despite a relative abundance of geological and geochronological data for the Central Gneiss Belt and a mafic rock distribution that appears to successfully locate a major tectonic boundary, we emphasize the need for additional field and laboratory work aimed at testing our structural model.
U-Pb ages of syndeformational dykes associated with the Mesoproterozoic Nain Plutonic Suite, Labrador
Authors: Cadman Andrew C , Noble Steve R , Tarney John , Park R Graham , Ryan A Bruce , Royse Kate R
Published: April 2011

Field and U-Pb zircon geochronological studies in a suite of crosscutting, deformed, and metamorphosed basic dykes show that they were emplaced in a syndeformational environment between 1328 ± 2 and 1316.5 ± 1.6 Ma. Earlier dykes in the suite are granulitic, commonly folded along north-south axes or strongly rotated into north-south-trending shear zones. Later dykes are metamorphosed to amphibolite grade. These sometimes retain igneous porphyritic textures and occasionally crosscut the granulite dykes. The amphibolite dykes were emplaced in a less ductile crustal environment and a structural environment less dominated by shear deformation. Both granulitic and to a lesser extent amphibolite dykes show evidence of synshear emplacement. The episode of emplacement is broadly coeval with the injection of the mid-Proterozoic Nain Plutonic Suite (NPS) and suggests that the dykes were injected as a series of leaks from NPS feeder chambers. If so, the granulite dykes may represent leaks intruded near the culmination of NPS activity, whereas the amphibolite dykes were probably injected during the waning phase of tectono-thermal conditions.
The Caldwell Group lavas of southern Quebec: MORB-like tholeiites associated with the opening of Iapetus Ocean
Authors: Bédard Jean H , Stevenson Ross
Published: April 2011

The Caldwell Group belongs to the Internal Nappe Domain of the Humber Zone and consists of basaltic lavas, quartzo-feldspathic sandstones, and mudslates. The lavas are clinopyroxene ± plagioclase ± olivine-phyric tholeiites, and are typically altered to epidote-, chlorite-, carbonate-, and (or) hematite-rich secondary assemblages. In most cases, the high field strength elements do not appear to have been perturbed by the alteration, and preserve magmatic signatures. Most Caldwell basalts exhibit coupled major and trace element variations compatible with low- to medium-pressure ([Formula: see text] 10 kbar, where 1 kbar = 100 MPa) fractional crystallization. Paleotectonic discriminants imply an ocean-floor or normal mid-ocean ridge basalt (N-MORB) affinity. Most basalts have flat N-MORB-normalized profiles, except for the highly incompatible elements (Ba, Th, Nb), which show slight relative enrichment. Melting models suggest that most of these lavas formed by about 20% melting from a mantle slightly less depleted than fertile MORB mantle (FMM). Subpopulations of Caldwell lavas (types 1b and 1a) are characterized by slightly higher incompatible element abundances, with similarly shaped N-MORB-normalized profiles, and can be modeled by slightly smaller degrees of melting (6-15%) of a similar source mantle. The Caldwell basalts erupted in the final stages of Iapetus rifting, when the predominant mantle source involved in melting was the depleted asthenosphere. Isotopic data preclude significant crustal contamination, yet the basalts are associated with sandstones, implying that a mature continental crust was present nearby. Nd isotopic data on the sandstones suggest erosion of an ancient Archean-Proterozoic composite terrane.
Correlation among lower to upper crustal components in an island arc: the Jurassic Bonanza arc, Vancouver Island, Canada
Authors: DeBari Susan M , Anderson Robert G , Mortensen James K
Published: April 2011

The Westcoast Crystalline Complex (WCC), Island Intrusions, and Bonanza Group of Vancouver Island, Canada, form three different crustal levels of the Early to Middle Jurassic Bonanza island arc. Differential uplift has exposed the plutonic roots and the volcanic carapace of the arc for a strike length of ~500 km, and for another 250 km on the Queen Charlotte Islands. At deeper crustal levels within the arc, influx of mantle-derived magmas was accompanied by metamorphism and melting of Wrangellian basement rocks, yielding the heterogeneous WCC. Upward mobilization and hybridization of magmas to shallower levels in the crust resulted in the batholiths of the Island Intrusions and the lavas and pyroclastic rocks of the Bonanza Group. New U-Pb crystallization ages for plutonic rocks of the arc span an age range of 190.3 ± 1.0 to 168.6 ± 5.3 Ma. Ages of the WCC and western Island Intrusions are indistinguishable and overlap with published fossil and isotopic ages for the Bonanza Group. Younger Middle Jurassic ages for the eastern Island Intrusions overlap with those for plutonic rocks in the southern Coast Belt and Queen Charlotte Islands. All plutonic and volcanic rocks within the arc have overlapping geochemical signatures, supporting their comagmatic origin. All are light rare earth element-enriched with abundances 10-50× chondrites. The most mafic noncumulate gabbroic rocks have compositions typical of island arc basalts, with intermediate values of Al2O3 (16-17 wt.%) and high MgO (7-9 wt.%). More differentiated rocks follow a calc-alkaline trend with concomitant increase in Al2O3 (18-20 wt.%). Their geochemistry indicates varying degrees of mixing with melts of mafic Wrangellian basement.
Late glacial stratigraphy and history of the Gulf of St. Lawrence, Canada
Authors: Josenhans Heiner , Lehman Scott
Published: April 2011

The three-dimensional configuration of the Quaternary sediments in the Gulf of St. Lawrence is described based on analysis of 8000 km of high-resolution seismic reflection data complemented by analysis of seven piston cores. Till and or ice-contact deposits, glaciomarine sediments, postglacial basinal muds, and bank-top lagoonal sediments grading to sands and gravels make up the stratigraphic succession. Numerous thick accumulations of ice-contact - morainal deposits and "till tongues" indicate the position of former ice margins. The sequence of breakup of the last glacial ice in the gulf has been interpreted on the basis of these data and associated accelerator mass spectroscopy 14C dates. Grounded ice extended beyond Cabot Strait before 14.3 ka and retreated rapidly to north of Anticosti Island by 13.7 ka. Local residual piedmont lobes of glacial ice within the Cape Breton Channel and Baie des Chaleurs persisted longer, until about 12.2 ka. Ancestral hanging valleys formed the Cape Breton Channel and Baie des Chaleurs and served as conduits for ice lobes that flowed into the deeper Laurentian Channel. As many as four superimposed (Late Wisconsinan) glaciogenic sequences, up to 190 m in composite thickness, occur at the mouths of these (hanging) valleys. The thickest glacial sections were deposited on the southwestward slope of the Laurentian Channel. The surface of the till - ice-contact sediments between 440 and 100 m below present sea level has been extensively modified by iceberg scouring. The deeper limit (440 m) marks the maximum draft of icebergs, which was in large part determined by the thickness of the calving ice front. The disappearance of iceberg scour marks at 100 m is interpreted to have resulted from erosion of the glacial deposits by a Late Wisconsinan transgression whose low stand is suggested by a well-developed terrace on parts of the Magdalen Plateau at a present water depth of 110 m. A piston core that penetrated sediments overlying the uppermost (Late Wisconsinan) till in the Cape Breton Channel is interpreted to represent a deposit of lagoonal or shallow-marine sediments with localized deposits in excess of 65 m thickness. The depositional style of the postglacial deposits suggests sufficient bottom currents to erode sediments on the Magdalen Plateau.
Late Pleistocene glacial geomorphology and environment of the Hand Hills region and southern Alberta, related to Middle Wisconsin fossil prairie dog sites
Authors: Young R R , Burns J A , Rains R B , Schowalter D B
Published: April 2011

Ichnofossils (burrow casts) and fossils from an extinct form of prairie dog, Cynomys niobrarius churcherii, in the Hand Hills of south-central Alberta, have provided an important Late Pleistocene stratigraphic marker. The marker fossils provide relative and chronostratigraphic (radiocarbon) ages for nonglacial, periglacial, glacial, and glaciotectonic events and environments in the region. The high-elevation, hilltop position of the fossil sites (~200 m above the surrounding plains) permits reliable extrapolations of glacial environments to the surrounding region. The burrow casts were preserved by infilling from surrounding and overlying sediments through processes of inwashing and animal activity. Three thousand bones, primarily of the extinct prairie dog Cynomys niobrarius churcherii, were recovered from one site, and several hundred more from other locations. Accelerator radiocarbon dates (AMS) on bone collagen show that the prairie dogs lived in the area from at least

33 000 BP to around 22 000 BP. Prairie dog burrow casts crosscut well-developed periglacial structures and stratigraphically underlie all glacial sediments, indicating that harsh periglacial environments preceded their colonization and that the region was later submerged by Laurentide ice. Deformed sediments, 0.5 to 1.5 m thick, were found throughout the upland. The products of deformation overlie, truncate, and (or) incorporate burrow casts, indicating that only limited erosion and glacial deformation occurred during glaciation. Reconstructed ice sheet profiles show a northwest-southeast flow that could only have been achieved by coalescent Laurentide and Cordilleran ice sheets. This demonstrates that a theoretical "ice-free corridor" that some think persisted between the ice sheets during the Late Wisconsin "maximum," did not exist.
The 1991-1996 NATMAP Slave Province Project: Introduction
Authors: Bleeker Wouter , Davis W J
Published: April 2011

The 11 papers contributed to this issue on the geology of the Slave Province are summarized, and where appropriate, links between data from the various contributions are emphasized. In the discussion, we provide a synthesis of the present knowledge base on pre-Yellowknife Supergroup basement rocks throughout the Slave Province. All available age data on Mesoarchean and Paleoarchean basement rocks are compiled and, in a first attempt to seek regional correlations, 10 "events" of crustal growth and (or) reworking are recognized, spanning well over 1 billion years of Earth's history. The spatial distributions of these events across the craton are discussed. Finally, we pose a series of important questions that remain and that may help guide future research.
Calcite lilypads and ledges at Lorusio Hot Springs, Kenya Rift Valley: travertine precipitation at the air-water interface
Authors: Renaut Robin W , Jones Brian , Le Turdu Caroline
Published: April 2011

Travertine forming at Lorusio Hot Springs in the northern Kenya Rift is constructed mainly by lilypads and ledges. The lilypads are flat, accretionary structures rooted to the substrate that are composed mostly of platy calcite crystals. They grow outward from a nucleus, subparallel to the water surface, at or just below the air-water interface. Precipitation results from rapid degassing of CO2. Ledges, which have a similar morphology and internal structure, are attached to the margin of a spring pool or outflow channel. As they grow laterally, lilypads and ledges may coalesce with their neighbours to produce thin (1-3 cm) beds of travertine, examples of which are exposed in subfossil deposits at the site. Once established, lilypads and ledges modify the outflow and can act as substrates for precipitation of other minerals and colonization by microbes on their cooler subaerial surfaces. Pore fluids are drawn upward through the lilypads by capillary evaporation. Amorphous silica then precipitates as surficial crusts upon microbial mats or forms spicular microstromatolites, some of which also contain calcite laminae. Efflorescent Na-CO3 salts commonly encrust the drier central platforms of the exposed lilypad. The unusual abundance of lilypads and ledges at Lorusio reflects (i) the low-relief setting and the hydrostatic head, which limit terrace development, and (ii) the high temperature (>75°C) of the waters, which inhibits colonization by microbial mats at crystal growth sites. Similar structures form in cave pools, evaporating brines, and freezing water at sites where precipitation is induced by several processes active at the air-water interface.
Convergent margin on southeastern Laurentia during the Mesoproterozoic: tectonic implications
Authors: Rivers Toby , Corrigan David
Published: April 2011

A continental-margin magmatic arc is inferred to have existed on the southeastern (present coordinates) margin of Laurentia from Labrador to Texas from ~1500-1230 Ma, with part of the arc subsequently being incorporated into the 1190-990 Ma collisional Grenville Orogen. Outside the Grenville Province, where the arc is known as the Granite-Rhyolite Belt, it is undeformed, whereas within the Grenville Province it is deformed and metamorphosed. The arc comprises two igneous suites, an inboard, principally quartz monzonitic to granodioritic suite, and an outboard tonalitic to granodioritic suite. The quartz monzonite-granodiorite suite was largely derived from continental crust, whereas the tonalitic-granodiorite suite is calc-alkaline and has a juvenile isotopic signature. Available evidence from the Grenville Province suggests that the arc oscillated between extensional and compressional settings several times during the Mesoproterozoic. Back-arc deposits of several ages, that formed during relatively brief periods of extension, include (1) mafic dyke swarms subparallel to the arc; (2) continental sediments, bimodal volcanics and plateau basalts; (3) marine sediments and volcanics formed on stretched continental crust; and (4) ocean crust in a marginal basin. Closure of the back-arc basins occurred during the accretionary Pinwarian (~1495-1445 Ma) and Elzevirian (~1250-1190 Ma) orogenies, as well as during three pulses of crustal shortening associated with the 1190-990 Ma collisional Grenvillian Orogeny. During the Elzevirian Orogeny, closure of the Central Metasedimentary Belt marginal basin in the southeastern Grenville Province was marked by subduction-related magmatism as well as by imbrication of back-arc deposits. The presence of a continental-margin magmatic arc on southeastern Laurentia during the Mesoproterozoic implies that other coeval magmatism inboard from the arc took place in a back-arc setting. Such magmatism was widespread and chemically diverse and included large volume "anorogenic" anorthosite-mangerite-charnockite-granite (AMCG) complexes as well as small volume alkaline, quartz-saturated and -undersaturated "within-plate" granitoids. Recognition of the ~300 million year duration of the Mesoproterozoic convergent margin of southeastern Laurentia suggests that there may be useful parallels with the evolution of the Andes, which has been a convergent margin since the early Paleozoic.
Lithoprobe line 55: integration of out-of-plane seismic results with surface structure, metamorphism, and geochronology, and the tectonic evolution of the eastern Grenville Province
Authors: Hynes Andrew , Indares Aphrodite , Rivers Toby , Gobeil André
Published: April 2011

Lithoprobe line 55, in the Grenville Province of eastern Quebec, provides unusually good control on the three-dimensional (3-D) geometry and structural relationships among the major lithological units there. Archean basement underlies the exposed Proterozoic rocks, along the entire seismic line, and there is a lateral ramp in this basement immediately behind a lobate stack of thrust slices of high-pressure metamorphic rocks comprising the Manicouagan Imbricate Zone (MIZ). Integration of the 3-D geometry with P-T and geochronological data allows derivation of a tectonic model for the region. The MIZ was buried to depths >60 km at 1050 Ma. Preservation of its high-pressure assemblages, and the absence of metamorphism at 990 Ma, which is characteristic of lower pressure metamorphic rocks that tectonically overlie them, indicates the MIZ rocks were rapidly unroofed, early in the tectonic history. There were two discrete pulses of crustal thickening during the Grenvillian Orogeny in this region. The first, involving imbrication of Labradorian and Pinwarian rocks that comprised part of southeast Laurentia, culminated in the Ottawan pulse at ca. 1050 Ma, and produced the high-pressure metamorphism of the MIZ. Its effects were rapidly reversed, with extrusion of the MIZ rocks to shallow crustal levels at ca. 1020 Ma. The crust was again thickened, with the Moho subsiding to depths >60 km, in the Rigolet pulse at ca. 990 Ma. The site of extrusion of the MIZ was probably controlled by the subsurface lateral ramp. High geothermal gradients indicate that extrusion may have been aided by lithospheric delamination in the crustal-thickening zone.
Quaternary ice transport in the Canadian Arctic and extent of Late Wisconsinan Glaciation in the Queen Elizabeth Islands
Authors: Bischof Jens F , Darby Dennis A
Published: April 2011

Most of the ice-rafted debris in channels off the Queen Elizabeth Islands, Nunavut, is of local origin, particularly in the inner part of the archipelago, but samples from the Arctic shelf contain as much as 40% grains from sources as far away as 2000 km, including the Siberian shelves. Particle transport by drifting sea ice from distant shelves is an important process on the Arctic continental shelf of the Queen Elizabeth Islands. In the interior of the Queen Elizabeth Islands and in the Viscount Melville and Lancaster sounds, particle transport is limited to distances of approximately 200 km. Mixing is more common among grains of coarse silt to fine sand than in the >250 µm fraction, but even the latter contains debris from sources far apart. During the Late Wisconsinan, the northern, southern, and eastern Queen Elizabeth Islands were covered by glaciers flowing radially from ice centers on the islands into the inter-island channels. Queens Channel was completely filled by ice, and a glacier lobe moved north from an ice divide northwest of Devon Island to Peary Channel. This lobe redistributed crystalline and carbonate erratics that are derived in part from a strongly weathered and degraded till that was deposited by a pre-Late Wisconsinan glaciation, and in part from glacial erratics that were deposited below the marine limit by icebergs during the Late Wisconsin deglaciation. Tills from eastern Bathurst Island are locally derived and devoid of erratics, but submarine tills west of Bathurst Island contain crystalline erratics that could be from either the Canadian Shield or Victoria Island.
Mineral aerosols: a comparison of the last glacial maximum and preindustrial Holocene
Authors: Reader M C , Fung I , McFarlane N
Published: April 2011

A passive mineral dust aerosol model based on source strengths deduced from polar ice core dust concentrations is introduced into the Canadian Centre for Climate Modelling and Analysis (CCCma) second-generation atmospheric general circulation model (GCMII) and used to compare features of the fine particle mineral dust aerosol in a last glacial maximum (LGM) simulation to those of a preindustrial Holocene (MOD) dust simulation. The resulting dust optical thickness is 8-16 times greater over most of the globe during the LGM. The model displays several seasonal characteristics observed in present-day satellite observations of dust, such as the summer maximum over the Arabian Sea and the seasonal north-south shift of the Sahara-Sahel plume. Both of these features are also present in the LGM simulation, though there are some noticeable differences in seasonal variation of dust between the last glacial maximum and the preindustrial Holocene. Since the simulated dust lifetimes are very similar for the MOD and LGM climates, it seems that increased LGM dust lifetime is not the major reason for the observed increase in dust concentration in polar ice cores during the LGM relative to the present.
The Midway sequence: a Timiskaming-type, pull-apart basin deposit in the western Wawa subprovince, Minnesota
Authors: Jirsa Mark A
Published: April 2011

The Midway sequence is an assemblage of subaerially deposited clastic and volcanic rocks that forms a narrow wedge within Neoarchean greenstone of the western Wawa subprovince of the Superior Province. Volcanic conglomerate in the Midway sequence contains clasts of stratigraphically older greenstone, together with clasts of a distinctive hornblende-phyric trachyandesite that is not represented among the older greenstone flows. The trachyandesite forms flows and pyroclastic units that are interbedded with lenticular deposits of volcanic conglomerate in a manner interpreted to indicate approximately coeval volcanism and alluvial fan - fluvial sedimentation within a linear, restricted, and tectonically active depocentre. The Midway sequence unconformably overlies greenstone on one side and is bounded by a regional-scale, strike-slip fault on the other. Structural analyses show that the Midway sequence was deposited after an early, precleavage folding event (D1) in greenstone, but before the regional metamorphic cleavage-forming D2 deformation. Lithologic and structural attributes are consistent with deposition in a strike-slip "pull-apart" basin. The stratigraphic and structural characteristics of the Midway sequence are generally similar to those of the Timiskaming Group and Timiskaming-type rocks in Canada, and more specifically to those of the Shebandowan Group in the Thunder Bay district. This similarity implies that the latest Archean tectonic and magmatic history of the western Wawa subprovince may have been nearly synchronous over great distances.
Hurricanes Pauline and Nora rainwater chemical composition
Authors: Padilla H G , Belmont R , Torres M B , Báez A P
Published: April 2011

Rainwater from hurricanes Pauline and Nora was sampled for chemical analysis at the Pacific Coast of Mexico. Rainwater sampling under extreme conditions presents a unique opportunity to study oceanic rain chemical composition. An excess sulphate ((SO24)xs) as low as 0% was measured near the centre of hurricane Pauline in Huatulco Bays. Another remarkable result was obtained in another rainwater sample of Pauline rain bands with a total SO24 concentration below the detection limit. Also, Na+ and Cl concentrations were extremely low (0.02 and 0.025 mg L1, respectively). The explanation of these results is also presented. Some light rains were also collected in Tapachula while Pauline was severely affecting Huatulco Bays. Only rainwater samples from hurricane Nora outer rain bands were sampled in Manzanillo, where it was interesting to evaluate the profound impact that a single power plant had on the chemical composition of hurricane Nora rains. Excess sulphate did not correlate with Mg2+ in Huatulco Bays and Manzanillo. However, it correlated with Mg2+ in Tapachula, even though this town is located 27 km from the coast. A further oxidation of organic sulphur containing compounds combined with a simultaneous transport of sea spray inland is proposed to explain this correlation.
New UPb zircon ages integrated with ammonite biochronology from the Jurassic of the Canadian Cordillera
Authors: Pálfy J , Mortensen J K , Smith P L , Friedman R M , McNicoll V , Villeneuve M
Published: April 2011

The accuracy of published Jurassic time scales is compromised by a paucity of sufficiently accurate and stratigraphically well-constrained isotopic dates. UPb dating of volcaniclastic rocks within fossiliferous marine successions is a method suitable of providing additional useful calibration points. Stikinia and Wrangellia, two of the major accreted terranes of the Canadian Cordillera, comprise volcanosedimentary assemblages of magmatic arc origin. Within them we selected sections from which we report 14 new UPb zircon ages that are integrated with ammonite biochronology at the zonal level. Poor zircon recovery and complex UPb systematics made it difficult to obtain precise ages for many of the samples. The following ages were determined (with 2σ errors): 194.0+9.11.8 Ma from the Plesechioceras? harbledownense Assemblage (upper Sinemurian), 191.5 ± 0.8 Ma from the Plesechioceras? harbledownense Assemblage (upper Sinemurian) to the Whiteavesi Zone (lower Pliensbachian), 185.6+6.10.6 Ma from the Freboldi Zone (lower Pliensbachian), 184.7 ± 0.9 Ma from the Kunae Zone (upper Pliensbachian), 180.4+8.00.4 Ma from the Kanense to Planulata zones (lower to middle Toarcian), 179.8 ± 6.3 Ma from the Yakounensis Zone (upper Toarcian) to the lower Bajocian, 167.2+10.50.4 Ma from the Rotundum Zone (upper Bajocian), 158.2+1.90.4 Ma from the upper Bathonian, and 162.6+2.97.0 from the upper Bathonian to lower Callovian. Five other dates are inferior in precision, but still provide some constraints for time-scale calibration. The UPb dates reported here together with a wealth of other recently obtained Cordilleran isotopic dates will be used for a significant revision of the Jurassic time scale.
Granite petrogenesis in the Gander Zone, NE Newfoundland: mixing of melts from multiple sources and the role of lithospheric delamination
Authors: Schofield David I , D'Lemos Richard S
Published: April 2011

Silurian to Devonian granites within the Gander Zone of the Appalachian Central Mobile Belt in northeastern Newfoundland formed adjacent to the former Gondwanan continental margin following terminal closure of the Iapetus Ocean. Comparison of geochemical and isotopic characteristics of the granites with their host migmatites and metasediments, amphibolite, and orthogneiss constrain their potential source. Nd and Sr isotopic compositions indicate that no single source or binary mixing product could have produced the granites. Instead, we show that they result from multicomponent mixing involving a contribution from unexposed crystalline basement, mantle or underplate, and variable contamination by supracrustal host rocks. The timing and composition of granite magmatism do not exhibit collisional orogenic, subduction-related, or continental rifting characteristics. Hence, we relate magmatism to lithospheric melting following delamination of an orogenic keel. This process provides the influx of mantle-derived magma into fertile crust and hence promotes lower crustal melting and primary magma mixing.
Dawson tephra: a prominent stratigraphic marker of Late Wisconsinan age in west-central Yukon, Canada
Authors: Westgate John A , Preece Shari J , Kotler Erica , Hall Sheila
Published: April 2011

Dawson tephra is the most prominent tephra bed in the Quaternary deposits of the Klondike and Sixtymile areas of the Yukon. It occurs in organic-rich, reworked, Late Wisconsinan loess deposits that occupy valley-bottom sites and has a maximum thickness of 30 cm, although most values are in the range of 1530 cm. The tephra consists of thin, bubble-wall shards that have a distinctive, rhyolitic composition. Orthopyroxene, plagioclase, magnetite, and ilmenite are relatively abundant in the small crystal component, which also contains minor amounts of clinopyroxene, apatite, and zircon. Overall, the composition of Dawson tephra bears a close resemblance to that of the well-known Old Crow tephra, and, like that tephra, demonstrates a source in the Aleutian  Alaska Peninsula region. Given that the nearest vent in the Alaska Peninsula is 700 km distant from the Klondike, it follows that this explosive eruption must have been of great magnitude, distributing tephra over southern and central Alaska and the Yukon. The age of this eruption is not precisely known, but it did occur during the interval 2212 ka.
Karyotype polymorphism in Drosophila albomicans
Authors: Hatsumi Machiko
Published: April 2011

Supernumerary (B) chromosomes are present in Thai, Malay, and Burmese populations of Drosophila albomicans (2n = 6) in a polymorphic state. Although usually stable at mitosis, their numbers differed between individuals and their frequency was also different between isofemale lines and between populations. Arm 3 of the X3 chromosome was polymorphic for the presence and the size of a procentric heterochromatic segment. Chromosome 4 is polytypic for variation in length governed by differences in the amount of heterochromatin and the long variant is polymorphic for the location of its secondary constriction.

Key words: Drosophila albomicans, karyotype polymorphism, B chromosome.
Relative stability among barley plants regenerated from cultured immature embryos
Authors: Karp A. , Steele S. H. , Parmar S. , Jones M. G. K. , Shewry P. R. , Breiman A.
Published: April 2011

Relative genetic stability was observed among barley plants regenerated from cultured immature embryos. Regenerated plants were studied cytologically and their seed progenies assayed for (i) the isoenzymes esterase and glutamate-oxaloacetate transaminase, (ii) ribosomal DNA spacer length polymorphism, and (iii) hordein patterns on SDS–PAGE. Of 42 regenerated plants, 1 regenerant had abnormal meiosis and the same plant produced one seed with a variant hordein pattern. These findings are discussed in relation to the factors affecting somaclonal variation in cereals and to methods of assaying the variation.

Key words: barley, isozymes, somaclonal variation, tissue culture.
Possible role of heterochromatin in chromosome breakage induced by tissue culture in oats (Avena sativa L.)
Authors: Johnson S. S. , Phillips R. L. , Rines H. W.
Published: April 2011

Perturbations in the replication of heterochromatic regions during tissue culture may be the cause of chromosome alterations observed in regenerated hexaploid oat plants (Avena sativa L.). An idiogram based on pachytene chromosome analysis was developed depicting the heterochromatin distribution on 17 of the 21 chromosomes. Heterochromatic regions were present pericentromerically on each chromosome, at telomeres in five of the chromosomes, and in the NORs of the three satellited chromosomes. Centromeric heterochromatin covered most of the short arm in several chromosomes. Tritiated-thymidine autoradiography was used to determine the nuclear cycle duration (G1 + S + G2 + mitosis = 0.8 + 5.2 + 0.3 + 3.8h = 10.1 h) in root-tip cells and revealed regions of late replication around the primary and secondary constrictions and at chromosome ends. Replication of heterochromatic regions late in the DNA synthetic period makes it plausible that these regions are more sensitive to nuclear cycle alterations caused by the culture process. Pachytene analysis of a heteromorphic chromosome pair that originated during culture showed the break in the deficient chromosome to be in centromeric heterochromatin. The presence of proximal and telomeric heterochromatin means that bridges resulting from replication problems in these regions could result in various alterations including deficiencies, duplications, and translocations and can account for heterochromatin amplification, all of which have been observed in plants that have been regenerated from tissue culture.

Key words: heterochromatin, meiosis, telocentric chromosomes, oats, tissue culture, variation.
Breeding foxtail millet (Setaria italica) for quantitative traits after interspecific hybridization and polyploidization
Authors: Darmency H. , Ouin C. , Pernes J.
Published: April 2011

An interspecific cross was carried out between the cultivated foxtail millet, Setaria italica, and its wild relative the green foxtail, S. viridis. Quantitative characters (19 descriptors of morphology and reproduction) were studied using the F1 F2, and F3 generations. Moreover, this F2 was compared with the tetraploid F2 obtained from a colchicine-induced F1. The multivariate analysis of the diploid F2 showed two complex associations of characters: one concerning developmental traits (organs dimensions and flowering) and the other dealing with taxonomical characteristics (tillering, seed shedding, and seed weight). The tetraploidization resulted in a shift in characteristics towards the crop species, especially a twofold increase in seed weight. Nonadditive effects were found for most characters, except for the seed shedding, which was found to be encoded by at least four loci. However, cultivated type plants were easily recovered in both the diploid and the tetraploid F2. This demonstrates the potential of interspecific hybridization and polyploidization to improve the crop properties of the foxtail millet.

Key words: foxtail millet, polyploid, quantitative inheritance, hybridization (interspecific).
Polyploid complexes of Glycine tabacina (Labill.) Benth. and G. tomentella Hayata revealed by cytogenetic analysis
Authors: Singh R. J. , Kollipara K. P. , Hymowitz T.
Published: April 2011

Observations on geographical distribution, cytotypes, crossability, and meiotic chromosome behavior in intra- and interspecific F1 hybrids revealed that the complexes of Glycine tabacina (2n = 40, 80) and G. tomentella (2n = 38, 40, 78, 80) evolved through allopolyploidization. It is apparent from this study that 80-chromosome tabacinas are composed of two distinct morphological complexes having one common genome: with and without adventitious roots. In contrast, the tomentellas are inseparable morphologically. They are composed of accessions with at least three genomic complexes: (i) 2n = 80, accessions from Australia and Taiwan; (ii) 2n = 80, an accession from Papua New Guinea; and (iii) 2n = 78, accessions from Australia and Papua New Guinea. Hybrids within each group showed complete synapsis and set normal seeds; however, hybrids between the groups apparently differed by one genome and were completely sterile. Chromosome pairing in triploid interspecific F1 hybrids (2n = 59, 60) indicated that G. canescens (2n = 40) was probably the donor of the common genome for 80-chromosome tabacinas and tomentellas. Glycine latifolia (2n = 40) appears to have contributed its genome to G. tabacina (2n = 80) but could not have participated in the speciation of 80-chromosome tomentellas. Likewise, the 38-chromosome G. tomentella has no genomic affinity with 80-chromosome tabacinas but has complete affinity with 80-chromosome tomentellas. On the basis of present findings and the results published earlier, the evolution of the genus Glycine will be discussed.

Key words: Glycine spp., genome, hybridization (intraspecific), hybridization (interspecific), speciation.
Unusual germ line limited chromosomes in Acricotopus lucidus (Diptera, Chironomidae)
Authors: Staiber W.
Published: April 2011

A small supernumerary polytene chromosome was found during the last 8 years in some rare cases in larval salivary gland cells of Acricotopus lucidus (Diptera, Chironomidae). The chromosome may be derived from the germ line restricted parts of the genome. It consists of a short heterochromatic segment and of euchromatic sections with banding patterns homologous to sections of the short arm of soma chromosome I. When examining male meiosis, an exceptional small germ line limited chromosome was found. It is believed that this chromosome was not always recognized during soma elimination as a germ line limited chromosome, probably because of its partial homology to one of the soma chromosomes, and was then polytenized in salivary gland cells. Another germ line limited chromosome with a characteristic morphology and with a special behavior in differential gonial mitosis was found to have existed for more than 12 years in a laboratory stock. In differential gonial mitosis this special germ line limited chromosome partly pairs with the long arm of soma chromosome I. The present results strongly support the idea that the germ line limited chromosomes of A. lucidus are derived from the soma chromosomes, and show that chromosomes of the germ line restricted part of the genome can persist for many generations in a laboratory stock in spite of complex chromosome elimination mechanisms in the primary germ cells.

Key words: germ line limited chromosomes, supernumerary polytene chromosome, salivary gland, Acricotopus lucidus.
Detection of the time of occurrence of nondisjunction induced by the r-X1 deficiency in Zea mays L.
Authors: Simcox Kevin D. , Shadley Jeffery D. , Weber David F.
Published: April 2011

The r-X1 deficiency in maize produces high frequencies of aneuploid progeny by inducing nondisjunction during embryo sac development. The purpose of this investigation was to determine the embryo sac division at which the nondisjunctive event takes place. Monosomic-6 individuals were generated by crossing r-X1 containing plants by those carrying the y-pastel-8549 allele of the Y locus on chromosome 6. A strict dosage relationship exists between the number of dominant alleles of the Y locus and the level of β-carotene in the endosperm. We found that the level of β-carotene in the endosperm of kernels containing monosomic-6 embryos was comparable with that found in endosperms with one Y allele. This indicated that they contained only one maternally contributed chromosome 6. Only nondisjunction at the second postmeiotic division could have produced such an endosperm; thus, the nondisjunctive event occurs at this division. Another endosperm type expected from nondisjunction at this same division, with three dominant Y alleles, was not found. The absence of this endosperm type suggests that the egg nucleus and the polar nucleus originating at the micropylar pole are sister nuclei that arose from the same cell at the third embryo sac mitotic division.

Key words: aneuploidy, embryo sac, nondisjunction, r-X1 deficiency, Zea.
A revised map of chromosome 16 in Gossypium hirsutum
Authors: Menzel Margaret Y. , Richmond Kenneth L. , Dougherty Brian J.
Published: April 2011

Four translocations involving chromosome 16 (H16) in cotton (T1R;16R 2770, T1R;16R 4672, T15L;16R 8-5Ga, and T15R;16R 2767) were tested against telosomes for chromosome 16 and the H16 marker gene red plant (R1). The telosome tests confirmed that bp-2770 and bp-4672 are in the long (=right) arm of chromosome 16 and showed that bp-8-5Ga and bp-2767 are also in the long arm of H16, rather than in the short (=left) arm as previously reported. The locations of the chromosome 15 (H15) bp's for 8-5Ga and 2767 are also revised. A telosome test showed that H15 bp-8-5Ga is in the long (=left) arm. Consequently, H15 bp-2767 is placed in the short (=right) arm of chromosome 15. Duplication deficiencies mono- or tri-segmental for H16 (verified cytologically) showed that R1 is in the right (R) arm 24 cM distal to bp-2767 and 10 cM distal to bp-8-5Ga. Recombination frequencies showed that R1 is 13 cM from bp-4672 and 15 cM from bp-2770 (not significantly different). However, both of the T1R;16R translocations yield negligible frequencies of duplication deficiencies and therefore offered no direct evidence as to whether their breakpoints are proximal or distal to R1. Previous estimates have placed both bp-2770 and bp-4672 43 cM from the centromere. Therefore the order must be as follows: (left)–centromere–bp-2767-bp-8-5Ga–R1–bp-4672/bp-2770 (right).

Key words: cotton, Gossypium hirsutum, chromosome 16, translocations, linkage map, duplication-deficiences, red plant, linkage group III.
Genetic variation in survival of chinook salmon (Oncorhynchus tshawytscha) alevins exposed to an unidentified agent of mortality
Authors: Withler R. E.
Published: April 2011

Mortality of an unknown etiology occurs after hatching and before emergence among Harrison River chinook salmon (Oncorhynchus tshawytscha) alevins incubated in the Chehalis River Hatchery, British Columbia. Inter- and intra-stock genetic variation for alevin survival and time to death was investigated at Chehalis Hatchery in factorial crosses among chinook salmon from the Harrison and Capilano rivers. Alevin survival by family ranged from 0 to 100%, with a mean value of 35.2%. The mean family survival of pure Harrison alevins (13.0%) was significantly lower than that of Capilano alevins (64.1%). For the Harrison stock, estimates of the heritability of survival were 1.05 ± 0.62 (sire component) and 0.03 ± 0.07 (dam component). For the Capilano stock, the corresponding estimates were 0.79 ± 0.53 and 0.80 ± 0.54. Family means of time to death ranged from 7.5 to 48 days after exposure to mortality-inducing agents. The mean times to death for pure Harrison (15.3 days) and Capilano (21.8 days) families were not significantly different. Sire and dam component heritability estimates for time to death were high for the Harrison stock (1.39 ± 0.87 and 0.71 ± 0.46) but low for the Capilano stock (0.06 ± 0.11 and 0.17 ± 0.18). Values of survival and time to death for the reciprocal interstock hybrid alevins generally fell between those of the parental stocks. Neither survival nor time to death differed significantly between the reciprocal hybrids, but both traits were more strongly influenced by sire than by dam. The possibility of asynchronous paternal and maternal allele activation during embryonic development was proposed as an explanation for the strong paternal effects observed in this study.

Key words: Oncorhynchus, salmon, heritability, mortality.
Cytogenetic analysis of interspecific hybrids between alfalfa (Medicago sativa L.) and M. rhodopea Velen.
Authors: Denton C. R. , McCoy T. J.
Published: April 2011

Interspecific hybrids between diploid (2n = 2x = 16) Medicago sativa L. and diploid (2n = 2x = 16) M. rhodopea Velen., were recovered using an ovule–embryo culture methodology. Most hybrids were vigorous, and morphological comparisons demonstrated that F1 hybrids were generally intermediate between that of the parents. Peroxidase isozyme phenotypes of the F1 hybrids confirmed hybridity. The chromosome number of most of the hybrids was diploid (2n = 2x = 16), with the exceptions of two triploids (2n = 3x = 24) and two tetraploid (2n = 4x = 32) plants. Chromosome pairing configurations in diploids were almost exclusively eight bivalents or seven bivalents and two univalents, indicating a high level of homology between the M. sativa and M. rhodopea genomes. However, the one triploid hybrid analyzed had only 0.4 trivalents per microspore mother cell indicating preferential pairing of parental genomes. Pollen stainability, pollen germination, and fertility of the diploid F1 hybrid plants were very low; however, it was possible to obtain backcross progeny (BC1) from seed. Pollen stainability, pollen germination, and fertility of the BC1 plants were also very low; however, most BC1 plants had workable levels of male and female fertility. The utilization of M. rhodopea in studies of the evolution of hexaploid Medicago species is discussed.

Key words: interspecific hybrids, ovule–embryo culture, isozymes, Medicago.
Arm homoeology of wheat and rye chromosomes
Authors: Naranjo T. , Roca A. , Goicoechea P. G. , Giraldez R.
Published: April 2011

Meiotic pairing was studied at metaphase I in three different cv. Chinese Spring × rye hybrid combinations (5B deficient, 3D deficient, and normal ABDR) to establish the arm homoeology of wheat and rye chromosomes. The majority of individual wheat chromosomes and their arms, as well as the arms of chromosomes 1R and 5R, were identified by means of C-banding. The results on pairing relationships support the genome reallocation of chromosomes 4A and 4B. The short arms of wheat chromosomes belonging to homoeologous groups 1, 3, 5, and 6 and of chromosome pairs 4A–4D and 7A–7D showed full pairing homoeology as well as the long arms of wheat chromosomes of groups 1, 3, 6, and 7 and of chromosome pairs 4A–4D and 5B–5D. Chromosomes 2A, 2B, and 2D were homoeologous, but the homoeologies of their arms were not identified. Reduced homoeologies of the 4BL arm to 7AS and 7DS, of the 5AL arm to 4AL and 4DL, and of the 7BS arm to 5BL and 5DL were identified. Arms 4BL, 5AL, and 7BS are involved in a double translocation that arose during the evolution of common wheat. The homoeology relationships of chromosome arm 4BS were not identified since this arm seldom paired. The homoeologous pairing pattern between wheat chromosomes was characterized by a remarkable predominance of A–D associations, altered only by structural changes in groups 4 and 5. Chromosome arm 1RL showed full pairing homoeology to 1AL, 1BL, and 1DL, while 5RL was homoeologous to 5AL and partially homoeologous to 4AL and 4DL. It is concluded that 5RL carries a translocated segment from 4RL.

Key words: homoeologous pairing, translocations, wheat evolution, C-banding.
Differences in meiotic pairing induction between the A genomes of Triticum boeoticum Boiss. and T. urartu Tum. using diploid species of the subtribe Triticineae as analysers
Authors: Lucas H. , Jahier J.
Published: April 2011

The number of associations between chromosome arms in the pollen mother cells of the hybrid Triticum boeoticum × T. urartu is similar to that in the pollen mother cells of the parental accessions. The latter two species were crossed with the following diploid species: T. tauschii, T. comosum, T. umbellulatum, and Haynaldia villosa. The meiotic behaviour of the hybrids showed that the chromosomes of T. urartu share more homology with the diploid Triticum species than do those of T. boeoticum. On the other hand, there is more pairing in the hybrid T. boeoticum × H. villosa than in T. urartu × H. villosa. These results confirm that T. boeoticum and T. urartu are distinct species.

Key words: Triticineae, interspecific hybrids, meiotic behaviour, speciation.