This study aims to constrain how the composition of pyrite changes through metamorphism prior to its transition to pyrrhotite. For this, we used metasedimentary rock samples with different metamorphic grades from the Yukon- Tanana terrane, Yukon. Sulfide composition was analyzed by LA-ICP-MS, and metamorphic grades were constrained by Raman spectroscopy analyses of carbonaceous matter. Peak metamorphic temperatures in the sample suite range from 347 +/- 9 degrees C to 598 +/- 34 degrees C, consistent with a variation from greenschist to amphibolite metamorphic facies. Compositional changes in pyrite were observed as a function of increasing metamorphic grades. Manganese, Cu, Mo, Ag, As, Sb and Tl show consistent decreasing trends, while Co and Ni concentrations increase with prograde metamorphism. The magnitude of these changes is smaller than the element release associated with the transformation of pyrite into pyrrhotite.

The tectonic assembly of the Northern Cordillera is currently disputed and directly impacts Paleozoic‐to‐recent paleogeographic and plate tectonic reconstructions of North America. In this study, we present new U‐Pb zircon geochronology from the allochthonous Yukon‐Tanana terrane and the parautochthonous Cassiar terrane of the Northern Cordillera from south‐central Yukon, Canada. Our data provide new constraints for the assembly of the Northern Cordillera in this region. Metasedimentary samples from the Ingenika Group (Cassiar terrane) and the Snowcap and Finlayson assemblages (Yukon‐Tanana terrane) yielded detrital zircon age spectra that are comparable to known northwest Laurentia age spectra. One of our samples from the Snowcap assemblage yields a detrital zircon age spectrum that is anomalous for northwest Laurentia, but comparable to Early Paleozoic strata deposited in the Nevada‐Idaho‐Utah region. Zircon rim growth and Pb‐loss recorded by detrital zircon in the Snowcap assemblage and Ingenika Group samples record metamorphism at 370 ± 4 Ma and between 171 ± 5 and 135 ± 3 Ma. Late Devonian metamorphism and magmatism possibly corresponds to rifting of the Snowcap assemblage from the Laurentian margin. Middle Jurassic‐Early Cretaceous metamorphic zircon rim ages from the Cassiar terrane record metamorphism during collisions between the Intermontane superterrane (including the Yukon‐Tanana terrane) and Laurentia (Early to Middle Jurassic), and between the Insular superterrane and Laurentia (Middle to Late Jurassic). Our study suggests that collision between the Yukon‐Tanana terrane and the Laurentian margin began no earlier than ∼205 Ma.

The Yukon Tanana (YTT) and Slide Mountain terranes (SMT) of the Cordillera in Canada and Alaska were interpreted in terms of opening and closing of a Late Devonian-Permian Japan Sea-style backarc basin behind a continental arc built upon YTT, which rifted from Laurentia during the Famennian-early Mississippian. Formation of Famennian transitional oceanic lithosphere supports rifting, but a combination of existing and new data on the setting and age of SMT ophiolites do not support the Japan Sea model. The studied Clinton Creek and Midnight Dome complexes represent suprasubduction zone ophiolites formed at ca. 265 Ma, consistent with analyses of other SMT ophiolites. Ultramafic rocks dominate most ophiolites. They lack sheeted dikes and contain relatively minor volumes of mafic plutonic and volcanic rocks, suggesting they formed in oceanic core complexes characterised by slow spreading and low magma productivity. The Permian ophiolites formed during or immediately after eclogite formation in YTT, coeval with or immediately preceding emplacement of orogenic peridotites into YTT due to hyperextension. Several tectonic scenarios are discussed. We propose that YTT is a composite terrane comprising a continental block and an oceanic arc-backarc complex with the latter obducted onto the former during the middle Permian-early Triassic Klondike orogeny. Obduction may have come from the west or east, but east-directed obduction is most consistent with geological constraints. Obduction was followed by initiation of west-dipping subduction east of the composite YTT; slab roll back causing extension in the composite upper plate, leading to exhumation of orogenic peridotites. Tectonic relationships show many analogies to the collision between Australia and the New Britain arc, in which collision in the Huon Peninsula of New Guinea is contemporaneous with extension in Australian crust in the adjacent Woodlark basin. Syn-orogenic Permian Klondike calc-alkaline magmatism is attributed to extension in a Woodlark basin-like setting rather than a representing a continental arc.

The impact of Tintina Fault displacement on the development of the Yukon River and drainage basins of central Yukon is investigated through geophysical and hydrological modeling of digital terrain model data. Regional geological evidence suggests that the age of the planation of the Klondike Plateau is at least Late Cretaceous, rather than Neogene as previously assumed, and that surprisingly there has been little net incision in the region since the late Mesozoic. The Tintina Fault has been previously interpreted to have experienced ∼430 km of dextral displacement, primarily during the Eocene. However, the alignment of river channels across the fault at specific displacements, coupled with recent seismic events and related fault activity, suggests that the fault may have moved in stages over a longer time span. Topographic restoration and hydrological models show that the drainage of the Yukon River northwestward into Alaska via the ancestral Kwikhpak River was only possible at restored displacements of up to ∼50–55 km on the Tintina Fault. We interpret the published drainage reversals convincingly attributed to the effects of Pliocene glaciation as an overprint on earlier Yukon River reversals attributed to tectonic displacements along the Tintina Fault. At restored displacements between 230 and 430 km, our models illustrate that paleo-Yukon River drainage may have flowed eastward into the continental interior via an ancestral Liard River. The revised drainage evolution has wide-reaching implications for surficial geology deposits, the flow direction and channel geometries of the region’s ancient rivers, and importantly, for exploration of placer gold deposits.

Back-arc extension during Devonian-Mississippian eastward subduction beneath the western fl ank of ancestral North America led to separation of Yukon-Tanana terrane from Laurentia, and opening of the Slide Mountain marginal ocean basin. Rocks exposed in imbricated thrust sheets of the Sylvester allochthon record the opening and closing of this marginal basin. At the highest structural level in the allochthon, the Rapid River tectonite is interpreted as a remnant of Yukon-Tanana basement. Pre-Late Devonian deformation in the Rapid River tectonite may represent collision of an exotic arc terrane with the outer peri-Laurentian margin that was the precursor to east-dipping subduction. Preliminary observations indicate that at least part of the Rapid River tectonite has a protolith of mafi c mylonite and marble, possibly representing parts of a primitive arc. At two localities the tectonite is intruded by late synkinematic diorite/gabbro-tonalite-trondjemite plutons, one of which has been previously dated (ca. 362 Ma). Limited shear-sense indicators in the mylonite show top-to-the-northwest displacement.Thrust panels in the lower part of the Sylvester allochthon expose ultramafi c-gabbro-supracrustal complexes that represent the youngest pre-accretionary phase in the YTT-Slide Mountain system. Near Zus Mountain northeast of the Cassiar townsite, and near Blue Dome 20 kilometres to the north, partly serpentinized harzburgite tectonites form the lower parts of thrust panels within the Slide Mountain terrane. These tectonites are overlain by interlayered peridotite tectonite, lherzolite, dunite, and gabbro; all are cut by trondhjemite dikes. The trondhjemite dikes cut previously serpentinized hosts, suggesting their emplacement during or after exhumation. At Zus Mountain, a large gabbro body overlies the ultramafi tes. At the Blue Dome section, seafl oor deposits of locally pillowed basalt and radiolarian chert directly overlie the ultramafi c rocks. This section also contains polymictic conglomerates with mainly 1 to 5 cm-sized angular clasts derived from subjacent units. Mafi c clasts contain an internal ductile deformation fabric. The conglomerates indicate exhumation and erosional unroofi ng of previously deformed rocks, possibly along penecontemporaneous faults. Notably lacking are the sheeted dike complexes that intervene between ultramafi c and supracrustal sections found in classical ophiolites. The Sylvester rocks may not have formed through ‘normal’ sea-fl oor spreading. Instead, they more closely resemble sections formed at slow-spreading ridges or hyperextending margins where the subcontinental mantle is exhumed by low-angle detachment faults. A previously dated (ca. 268 Ma) trondhjemite dike from the Zus Mountain area is coeval with similar dikes in Slide Mountain ophiolites in the Yukon, but signifi cantly younger than supracrustal successions elsewhere in the Slide Mountain terrane. The late ocean opening documented in the Sylvester allochthon and the Yukon was broadly coeval with ocean closing elsewhere, as ocean crust was consumed by westerly subduction beneath the Yukon-Tanana terrane.

The Boothia mainland region of the north-central Rae domain is underlain by remnants of a Neoarchean volcano sedimentary sequence dismembered by two regionally extensive Neoarchean high-potassium granitoid suites with rare occurrences of a structurally interleaved, Paleoproterozoic sedimentary cover sequence. The granitoids and their gneissic equivalents are dominated by variably deformed and metamorphosed I-type, metaluminous, polyphase, commonly porphyritic to augen, biotite ± hornblende monzogranite, and subordinate granodiorite, with rare tonalite. New geochronological results, the first for this area, demonstrate that the widespread Neoarchean granitoid plutonism is dominantly 2.61–2.59 Ga, with a less prominent 2.66 Ga plutonic event. The age of zircon recrystallization suggests that ca. 2.60 Ga Archean metamorphism and fabric development (S1) affected the 2.66 Ga plutons prior to or contemporaneously with intrusion of the voluminous ca. 2.6 Ga suite. εNd(t) for the ca. 2.61–2.59 Ga suite range from 1.4 to –1.9, overlapping with the ca. 2.66 Ga suite that range from 1.4 to 1.5. The Nd isotopic data, coupled with the presence of inherited ca. 2.65, 2.70, and 2.85–2.90 Ga zircon, suggests recycling of older, Neoarchean to Mesoarchean crust in the formation of these suites. Metaplutonic rocks preserve Paleoproterozoic deformation (F4 and F5) and amphibolite-facies metamorphism, sporadically recorded in zircon rims that formed at 1.81 Ga. This event strongly reoriented the Neoarchean fabrics in metaplutonic rocks, generally without the development of a new coaxial Paleoproterozoic fabric, and we attribute this strain and metamorphism to the Hudsonian orogeny.

An iterative remote predictive mapping approach was applied in regional-scale bedrock mapping of the Boothia mainland area, Nunavut, Canada. A geological interpretation of high-resolution airborne magnetic, Landsat Enhanced Thematic Mapper (ETM), and legacy field data resulted in a provisional remote predictive map (RPM) that was used to guide regional bedrock mapping in the summer of 2005. After the newly acquired field data were incorporated in the geoscience database, the provisional RPM was upgraded to 1 : 250 000 scale geological maps in a second iteration of geological interpretation. In general, the RPM was much better at predicting where major changes in lithology occurred than at predicting specific rock types. A comparative assessment of the generalized units of the RPM and geological maps at field stations yields an overall agreement of 82.3%. The number and dimensions of supracrustal belts on the RPM, however, were exaggerated and showed a relatively low agreement of 31% with geological map units at the field stations. This is explained by the confusion between supracrustal belts and metaplutonic units being both associated with high-spatial frequency linear and low-relief magnetic anomaly patterns. Field observations confirm that linear high-spatial frequency magnetic anomaly patterns in metaplutonic units are induced by metamorphic new growth of magnetite. These magnetic anomaly patterns parallel curvilinear features extracted from Landsat imagery and foliation strike measurements to the extent that regional fold structures can be reliably traced throughout the survey area. Spectral absorption features of carbonate in Landsat ETM band 7 and the overall high albedo of quartzite and marble allow differentiating Paleoproterozoic supracrustal units from their carbonate-and quartzite-barren Archean counterparts.

The Spi Group is a package of plagioclase porphyritic, amygdaloidal basalt flows and sandstone (Spi Lake Formation) conformably overlain by coarse conglomerate and sandstone (Old Boot Formation). These unconformably overlie the Kaminak Lake segment of the Central Hearne supracrustal belt, western Churchill Province. The Spi Group developed in a small, isolated basin (8 km2) and is older than the Paleoproterozoic Hurwitz Group. Our data demonstrate that the basalts of the Spi Lake Formation are genetically related to the ca. 2450 Ma Kaminak dyke swarm, a speculation previously promoted by some workers based on field characteristics alone. They are continental tholeiites with large ion lithophile and light rare-earth element enriched multielement profiles with prominent high field-strength element troughs. The 143Nd/144Nd compositions overlap the contemporaneous chondritic bulk-earth data. All of these are features we infer to have resulted from mixing of melts from dominantly depleted mid-ocean ridge basalt (MORB) mantle with low-degree partial melts of metasomatically enriched sub-continental lithospheric mantle. These composite magmas then underwent clinopyroxene + plagioclase ± olivine fractionation with minor assimilation of local tonalitic middle crust. The Spi Lake basin is <1 km wide, trends 020° parallel to Kaminak dykes but is discordant to the more common 045° to 070° trends of fold keels of the Hurwitz Group. The basin is a graben filled first with basalt and then molassoid sediments, representing the expression of crustal extension associated with Kaminak dyke emplacement. This indicates that the present erosional surface in the region is broadly at the same level as at the time of both Hurwitz and Spi Group deposition.

Potassic feldspar-bearing augen granitoids are a fundamental component of the architecture of the Yukon-Tanana terrane and the ancient Pacific margin of the northern Cordillera. These augen granitoids form a belt that extends from Alaska to southeast Yukon Territory, vary in age, and provide probes of the crustal evolution and tectonic history of the Yukon-Tanana terrane and ancient Pacific margin of North America in the Paleozoic. We present results of an integrated field mapping, geochemical, Sm-Nd tracer isotopic, and U-Pb zircon geochronologic study of the augen granitoids in the Stewart River area in an attempt to understand their role in the crustal evolution and tectonic history of the Yukon-Tanana terrane and ancient Pacific margin of North America.Augen granitoids of the Stewart River area are of three distinct ages: Late Devonian, early Mississippian, and Permian. U-Pb zircon geochronology of these augen granitoids has yielded ages of 362.1 +/- 2.7 Ma (Stewart River augen granite), 347.5 +/- 0.7 Ma (Mount Burnham augen granite), and 264.8 +/- 3.7 Ma (Wounded Moose augen granite). All of the augen granitoids, regardless of age, have negative epsilon(Ndt) values (-2.0 to -15.3) and Proterozoic-Archean depleted-mantle model ages (T-DM = 1.37-2.56 Ga). These geochemical and isotopic attributes, coupled with the presence of inherited zircon with Precambrian ages, suggest that these granitoids are the product of crustal melting and crust-mantle mixing during three different cycles of arc magmatism in the Paleozoic. Furthermore, these granitoids represent net crustal recycling along the ancient Pacific margin of North America in the Paleozoic. Importantly, however, there are minor secular variations in crustal recycling, and the younger Permian augen granitoids exhibit higher epsilon(Ndt), Nb/Ta, V/Yb, and Sc/Yb, consistent with a greater juvenile component in their genesis. This juvenile component is probably due to assimilation of underplated mafic material derived from older early Mississippian Yukon-Tanana terrane arc magmatism and/or a greater mantle component due to enhanced infiltration of underplated mafic material into augen granitoid magma chambers through rheologically weak crust associated with Permian subduction.The older Late Devonian and early Mississippian augen granitoid suites represent two pulses of Yukon-Tanana terrane arc magmatic activity that developed in response to east-dipping subduction along the western edge of the North America craton in the mid-Paleozoic. This east-dipping Yukon-Tanana terrane arc system continued to evolve throughout the Mississippian to Early Permian and was coincident with the development of the Slide Mountain backarc basin that formed between the Yukon-Tanana terrane arc system and the North American craton; this east-dipping arc-backarc system continued until ca. 275 Ma. After ca. 275 Ma, the east-dipping arc and backarc magmatism ceased and was replaced by ca. 270-269 Ma high-pressure metamorphism and the establishment of a new subduction zone that formed in response to the closure of the Slide Mountain backarc basin. The Permian augen granitoids from the Stewart River are the magmatic record of this new west-dipping subduction zone.Although there are subtle variations, the petrogenetic and tectonic histories of the three suites of augen granitoids in the Stewart River area are remarkably similar and attest to the constancy of magmatic and tectonic processes that occurred along the ancient Pacific margin of North America in the Paleozoic.

Deformation recorded in the Amisk collage in the central part of the Paleoproterozoic Flin Flon Belt (southeastern Trans-Hudson Orogen) is divided into pre-, early, late, and post-Hudsonian orogeny, distinguished by significant changes in metamorphic conditions and the orientation of structures. Detailed structural analysis, petrography, and high-precision geochronology, combined with previous mapping and geochemical studies, indicate a structural history spanning 180 Ma in the Amisk collage, and the database provides an excellent opportunity to study the structural evolution of Precambrian greenstone belts. Accretion of the 1.92-1.88 Ga tectono-stratigraphic assemblages in the Amisk collage began prior to 1.868 Ga. The deformational history records six generations of ductile structures (F 1 -F 6 ), followed by development of brittle-ductile and brittle structures (F 7 ), which may have continued as late as 1.690 Ga, during exhumation of the collage. The steep, generally north-northeast macroscopic structural grain is dominated by two regional foliations (S 2 and S 5 ), and contrasts strongly with the less steeply inclined, east-west grain in the adjacent Kisseynew Domain. Maximum displacements between tectono-stratigraphic assemblages occurred along early rather than late shear zones. Vertical extension was important in post-D 1 deformations, even in the later stages. Postorogenic, low-angle extensional features that are common to many mountain belts appear to be absent, possibly indicating that erosion was the dominant unroofing mechanism.

Results are presented of a survey of faculty members concerning their observations and opinions about the effects of student evaluation of instruction in a university where this practice had been a mandatory requirement for personnel evaluation purposes for several years. The respondents reported a definite reduction in morale and job satisfaction, changes in various instructional practices—mainly reduced course work demands on students and the occurrence of counterproductive actions as a result of this policy. Only limited expectations of improved ratings were indicated. There was also a clear division of opinion about the use of SEI ratings for personnel decisions that corresponded mainly with judgments about the validity of the ratings students provide.

Nearly all experimental data available implicate the role of anticoagulation in the mechanism of metastases. Using 3 separate experimental tumor-host systems in mice, the growth rate of an implanted, primary tumor can be significantly reduced with sodium warfarin induced anticoagulation. In all experimental test conditions a surgically safe prothrombin time prolongation of 2 to 3 times normal increased the long-term survival, cure rate and evidence of metastatic tumor dissemination in all experimental models. While complications from bleeding were occasionally encountered, surgery could be performed safely and anticoagulation levels satisfactorily monitored and stabilized. There is good experimental documentation to warrant a proposed clinical adjuvant anticoagulation study to determine if coumadin may effect a reduction in metastatic spread and subsequent cure-rate in patients who are to undergo surgery "for cure" of localized malignant disease, particularly the sarcomas which have such tremendous propensity for hematogeneous metastasis.

A simple method of detecting circulating tumor cells in the blood of mice is described. This method allows some assessment of the metastatic potential of contained pulmonary embolized tumor cells. The sensitivity in detecting the presence of circulating tumor cells and the ability to quantitate the numbers of cells remain to be established.

Warfarin anticoagulation throughout the pre-, intra-, and early postoperative periods significantly improved the long-term survival and the cure rate following amputation of a well-established primary tumor. In the case of the tumor system with the more virulent metastatic spread, the T241 sarcoma in C57BL/6N mice, the increase in the cure rate was seven-fold or 8% to 55%. In the C3H/HeN mice with mammary adenocarcinoma, the increase in the cure rate was from 29% to 53%. The weight of the primary tumor-bearing limb was also significantly reduced in the Warfarin-treated mice. The level of anticoagulation producing this improvement was not excessive, with the prothrombin time prolonged between 2.8 and 3.5 times the normal, average value. Deaths from complications were increased in the Warfarin-treated mice, but not nearly to the extent that deaths with metastatic disease were reduced.

Long-term oral administration of sodium warfarin significantly reduced the incidence of spontaneous metastases in the lungs from 83 percent in controls to 8 percent in treated C57/BL/6N mice. The size and weight of primary tumors in mice treated with warfarin were less than in control mice. Length of survival was unaffected.