bluuebunny/crossref_metadata_2025 huggingface dataset:
The distribution of gold in sub-seafloor stockwork mineralization from DSDP hole 504B and the Agrokipia B deposit, Cyprus
Authors: Hannington Mark D. , Herzig Peter M. , Alt Jeffrey C.
Published: April 2011

The distribution of gold has been examined in sub-seafloor stockworks from two sections of hydrothermally altered oceanic crust beneath the axial zones of fossil spreading centers. Deep Sea Drilling Project hole 504B (Leg 83) contains a narrow zone of stockwork-like sulfides in 6 Ma old basalt from the transition zone between sheeted dikes and overlying pillow lavas (910–928 m). Mineralization occurred as a result of local mixing between ascending hydrothermal fluids (350 °C) and seawater that penetrated the top of the dike section. Previous studies indicate that a significant amount of gold was leached from the sheeted dikes during high-temperature greenschist-facies alteration, but mineralized wall rock in the transition zone is not substantially enriched in gold. Sulfide concentrates from the narrow stockwork average 26 ppb Au, and one sample of As-rich pyrite from a quartz-epidote breccia contains 100 ppb Au. Cyprus Custal Study Project hole CY-2a contains an equivalent section of altered Cretaceous pillow lavas from the Troodos Ophiolite but includes a near-surface stockwork from the ore zone of the Agrokipia B deposit. The combined effects of hydrothermal metasomatism and regional metamorphism are represented by zeolite facies mineralogy above the ore zone (0–154 m), intense silicification and argillic alteration within the stockwork (154–300 m), and propylitic alteration at depth (300–400 m). The sheeted dikes below 400 m are altered uniformly to greenschist-facies mineralogy. Extensive sulfide mineralization in the pillow lavas occurred within a few hundred metres of the seafloor in response to a steep thermal gradient caused by mixing of high-temperature fluids with cold seawater. Pyrite from the stockwork ore contains up to 480 ppb Au and averages 160 ppb Au. A narrow zone of quartz-sulfide veinlets also occurs at the pillow–dike transition. Two samples of As-rich pyrite (up to 0.75 wt.% As) from this zone contain 980 ppb Au, but gold contents in fracture-filling and disseminated pyrite throughout most of the transition zone and sheeted dikes are < 20 ppb Au.Despite local enrichment within specific sulfide phases, deep sub-seafloor mineralization does not appear to have been an important sink for gold in either CY-2a or 504B. At higher levels in the crust, as in Agrokipia B, the locus and extent of mixing may be important controls on the intensity of mineralization and the deposition of gold within near-surface stockworks. Without an effective means of interrupting the flow of high-temperature fluids to vents on the seafloor, gold may be carried through the upflow zone at the time when high-temperature stockworks are forming.
Late Quaternary paleoceanography of the western Baffin Bay region: evidence from fossil diatoms
Authors: Williams Kerstin M.
Published: April 2011

Seven marine cores from the east coast of Baffin Island were examined for variations in diatom content. The cores have good age control and were used for Holocene paleoceanographic reconstruction. A diatom barren zone or a zone of much reduced diatom productivity is evident some time during the early to middle Holocene. This zone ends earlier in the southern area than farther north. The changes in diatom productivity may be caused by changing oceanographic variables such as sea ice extent and the presence of a meltwater cap during deglaciation. Light isotope 18O events ("meltwater spikes") generally coincide with barren or reduced productivity zones in the cores from the middle and southern part of the shelf and from Jones Sound, suggesting a general surficial cooling of the fjord and ocean water. If diatom productivity was depressed because of a meltwater cap over the core sites with increasing sea ice extent, the theory of a general "marine optimum" in all of Baffin Bay and Davis Strait from 8000 to 6000 BP may have to be modified.
Radioelement distribution in U, Th, Mo, and rare-earth-element pegmatites, skarns, and veins in a portion of the Grenville Province, Ontario and Quebec
Authors: Lentz David
Published: April 2011

Gamma-ray spectrometer measurements were obtained at and in the vicinity of 104 of the 124 U, Th, Mo, and rare-earth-element (REE) occurrences examined in the Central Metasedimentary Belt of the Grenville Province. Spatial, temporal, mineralogical, and geochemical relationships among granitic pegmatites, phlogopite – scapolite – Ca pyroxene skarns, and fluorite – apatite – calcite veins hosting U, Th, Mo, and REE minerals indicate a common magmatic–hydrothermal origin. Quartz–feldspar gneisses in the Central Metasedimentary Belt (n = 54) have low abundances of uranium (1–7 ppm) and thorium (4–27 ppm) suggesting that partial melting, fractional crystallization, and volatile phase separation were responsible for the enrichment of uranium (2–37 ppm) and thorium (5–102 ppm) in uncontaminated granitic pegmatites (n = 163) derived during ultrametamorphism. The U/Th ratio is probably inherited from the source quartz–feldspar gneiss protolith and enhanced during fractionation.Average U and Th concentrations and U/Th ratios at numerous localities show significant positive correlations among pegmatites, skarns, and veins, providing further evidence for a related origin. The interaction of the pegmatite-derived hydrothermal fluids with host rocks produced a spectrum of types and styles of alteration, which include (i) hybridization and (or) endoskarnification along pegmatite margins; (ii) marble- and clinopyroxenite-hosted exoskarn; and (iii) fluorite–apatite–calcite veins. The deposition of U, Th, Mo, and REE from the evolving hydrothermal fluid is responsible for the heterogeneous distribution of U, Th, and REE minerals and molybdenite within pegmatites, skarns, and veins at each locality. Secondary enrichment of uranium in association with hematitized sheared pegmatites and veins may be responsible for the observed large variation in U/Th ratios at some sites.
Reorientation of structures near granitic plutons and orthogonal lineaments, Russell Lake supracrustal domain, southwestern Slave Province
Authors: Fyson W. K. , Jackson V. A.
Published: April 2011

A complex array of folds and cleavages in metasedimentary and metavolcanic rocks in the Russell Lake domain could reflect regional compression recurrently reoriented across crustal lineaments. Several generations of steeply inclined folds trending northward across the domain curve into or interfere with folds parallel to margins of bordering granite batholiths aligned orthogonally northwest (LNW) and northeast (LNE). Sets of later subvertical cleavages strike northward, northwest parallel and oblique to LNW, and northeastward subparallel to LNE. The cleavages extend beyond the aligned margins, indicating that the association with the granites is indirect.The arrangements of folds and cleavages are consistent with intermittent redirection of subhorizontal compression of cover rocks perpendicular to orthogonal, steep crustal fractures that were intruded by syndeformational granitic plutons. Additionally, overturning of folds near plutons suggests local reorientation of compression near shallow-dipping margins. Following folding, further reorientations resulted in reversals in strike-slip bedding shear and cleavage sets locally symmetric about fold limbs.
Gold distribution in the Val-d'Or Formation and a model for the formation of the Lamaque–Sigma mines, Val-d'Or, Quebec
Authors: Taner Mehmet F. , Trudel Pierre
Published: April 2011

Recent lithogeochemical studies by accurate analytical techniques (e.g., instrumental and radiochemical neutron-activation analyses) have been used to explore the possibility of using gold distribution in the research for new gold deposits; these show that anomalous gold distribution occurs in some parts of the Val-d'Or Formation in the Val-d'Or mining district of Quebec. Gold lithogeochemistry in the Val-d'Or Formation has shown that it is possible to distinguish: (i) background values (1.4–3.5 ppb Au); (ii) zones of primarily anomalous gold values around the Lamaque–Sigma mines (median: 15 ppb Au); (iii) enrichment halos around gold orebodies (median: 70 ppb Au); and (iv) secondary gold enrichment in shear zones. We conclude that the Val-d'Or Formation is auriferous, i.e., anomalously rich in gold at least in some of its parts and contains the Lamaque – Sigma gold mines, representing 68% of the total gold production in the district. The Val-d'Or Formation is part of a central volcanic complex within an island-arc system. The centre of this complex is located in the main Lamaque plug, and this environment may be compared to high-temperature active geothermal systems that are commonly responsible for the formation of epithermal gold deposits. Gold mineralization at Sigma and Lamaque is considered to be related to a late hydrothermal phase or a retrograde phase of regional metamorphism. For the formation of the gold deposits, two distinct and successive events are postulated: (i) a gold-rich synvolcanic geothermal activity and (ii) a late remobilisation from the host rocks followed by deposition of gold ore within favourable structures.
A northern Cordilleran ocean–continent transect: Sitka Sound, Alaska, to Atlin Lake, British Columbia
Authors: Brew David A. , Karl Susan M. , Barnes David F. , Jachens Robert C. , Ford Arthur B. , Horner Robert
Published: April 2011

The 155 km wide, 310 km long Sitka Sound – Atlin Lake continent–ocean transect includes almost all the geologic, geophysical, and geotectonic elements of the Canadian Cordillera. It crosses the Chugach, Wrangellia, Alexander, Stikine, and Cache Creek terranes, the Gravina and Laberge overlap assemblages, intrusive and metamorphic belts, and neotectonic faults that bound major blocks. Linear belts of magnetic highs are associated with Jurassic and Cretaceous granitic belts in Wrangellia and the western and central parts of the Alexander terrane and with the granitic rocks of the Coast plutonic–metamorphic complex (CPMC). The Border Ranges fault may be expressed at depth on either side of the Peril Strait fault. An enigmatic northeast-trending gradient in the CPMC and adjacent rocks separates a regional magnetic low to the northwest from a 300 nT high field to the southeast. The Bouguer gravity field decreases in broad steps from Pacific crust high values to lows at the international boundary, with pronounced gradients at the east edge of Chugach terrane and west edge of of CPMC. It indicates that the crust thickens from about 20 to 40 km from southwest to northeast. Ultramafic bodies in the Chugach, Alexander, and Wrangellia terranes and Gravina assemblage underlie local highs. Most of the accumulated seismic strain is released by large earthquakes on the Fairweather – Queen Charlotte Islands plate-margin fault, but the northern part of the Glacier Bay region, the Denali fault zone, and the Coast Mountains also have significant seismicity. Part of the Glacier Bay region is being uplifted at a high rate. Most of these features are related to the joining of (i) Wrangellia to Alexander terrane (Carboniferous), (ii) Stikine to Cache Creek terrane (Early Jurassic), (iii) Alexander terrane and Gravina assemblage to Stikine (Late Cretaceous), and (iv) Chugach to Wrangellia and Alexander terrane (Late Cretaceous or Paleogene).
U-Pb geochronology of two pre-Tertiary plutons in the Coast Mountains batholith near Ketchikan, southeastern Alaska
Authors: Gehrels George E. , Mcclelland William C. , Samson Scott D. , Jackson Jay L. , Patchett P. Jonathan
Published: April 2011

U-Pb geochronologic studies indicate that the central part of the Coast Mountains batholith in the Ketchikan area contains plutons of Triassic and possibly mid-Paleozoic age in addition to the previously recognized early Tertiary plutons. Zircons from a foliated granodiorite in Burroughs Bay yield an upper concordia intercept of 336 ± 34 Ma, which is tentatively interpreted as the crystallization age, and a lower intercept of 79 ± 7 Ma, which may record extreme Pb loss and growth of metamorphic zircon during amphibolite- to granulite-facies metamorphism. Zircons from a tonalite in Boca de Quadra yield an upper intercept (crystallization age) of 215 ± 15 Ma and a lower intercept (Pb-loss age) of 50 ± 20 Ma. The presence of these Triassic and possibly mid-Paleozoic plutons supports previous interpretations that pre-Tertiary rocks in this part of the batholith may belong to the Yukon-Tanana terrane.
U–Pb geochronology of Late Cretaceous and early Tertiary plutons in the northern Coast Mountains batholith
Authors: Gehrels George E. , McClelland William C. , Samson Scott D. , Patchett P. Jonathan , Brew David A.
Published: April 2011

U–Pb geochronologic studies demonstrate that steeply dipping, sheetlike tonalitic plutons along the western margin of the northern Coast Mountains batholith were emplaced between ~83 and ~57 (perhaps ~55) Ma. Less elongate tonalitic–granodioritic bodies in central portions of the batholith yield ages of 59–58 Ma, coeval with younger phases of the tonalitic sheets. Large granite–granodiorite bodies in central and eastern portions of the batholith were emplaced at 51–48 Ma. Trends in ages suggest that the tonalitic bodies generally become younger southeastward and that, at the latitude of Juneau, plutonism migrated northeastward across the batholith at ~0.9 km/Ma. Variations in the age, shape, location, and degree of fabric development among the various plutons indicate that Late Cretaceous – Paleocene tonalitic bodies were emplaced into a steeply dipping, dip-slip shear zone that was active along the western margin of the batholith. Postkinematic Eocene plutons were emplaced at shallow crustal levels. Inherited zircon components in these plutons range in age from mid-Paleozoic to Early Proterozoic and are coeval with detrital zircons in adjacent metasedimentary rocks. These old zircons, combined with evolved Nd isotopic signatures for most plutons, record assimilation of continental crustal or supracrustal rocks during the generation and (or) ascent of the plutons.
Nd and Sr isotopic constraints on the petrogenesis of the west side of the northern Coast Mountains batholith, Alaskan and Canadian Cordillera
Authors: Samson Scott D. , Patchett P. Jonathan , McClelland William C. , Gehrels George E.
Published: April 2011

Nd and Sr isotopic ratios are reported from 15 samples of plutons of the northern Coast Mountains batholith (CMB), between. the Alexander–Wrangellia terrane and the Stikine terrane of southeastern Alaska. Samples of plutons that are part of the Late Cretaceous – Eocene CMB suite have a range in initial εNd of −3.0 to −0.2 and 87Sr/86Sr of 0.70494–0.70607. There is no correlation of isotopic ratio with age, lithology, or geographic location of these plutons. Two plutons that are probably older than the bulk of the CMB plutons have present-day εNd values of −6.8 and −2.6.The Late Cretaceous – Eocene plutons have Nd depleted-mantle model ages (tDM) of 620–1070 Ma. These data indicate that the northern CMB must contain a significant component of old, evolved continental crust. The presence of an old crustal component is further demonstrated by inherited zircons of average Early Proterozoic age contained in some plutons. The mid to Late Proterozoic tDM ages of the CMB plutons are therefore a result of a mixture of Early Proterozoic crustal material with. younger, juvenile crust. The most likely source of this old crustal component is the Yukon–Tanana terrane, a fragment composed of ancient crustal material that occurs within and directly to the west of the northern CMB. The juvenile component is probably a combination of material derived from the mantle and from anatexis of the surrounding juvenile terranes. Crustal anatexis may have occurred as a result of the intrusion of mafic melts related to subduction along the outboard margin of the Alexander–Wrangellia terrane, by crustal thickening due to the underthrusting of the Alexander–Wrangellia terrane beneath the Yukon–Tanana and Stikine terranes, or by a combination of both processes.
Late Paleozoic and Mesozoic terrane interactions in north-central British Columbia
Authors: Gabrielse Hubert
Published: April 2011

Five clearly defined terranes, comprising from northeast to southwest, Ancestral North America, Slide Mountain, Quesnellia, Cache Creek, and Stikinia, are the dominant tectonic elements of north-central British Columbia. Stratigraphic, sedimentological, plutonic, metamorphic, and structural data show that the Slide Mountain Terrane evolved as a subduction, accretion, and island-arc complex during Permian time. Sedimentological data hint at the demise of the Slide Mountain and Cache Creek oceanic environments in the Permian or Early Triassic and Late Triassic, respectively. Subduction led to the development of volcanic–plutonic island arcs on Stikinia, Quesnellia, and locally on the Cache Creek Terrane in Late Triassic to Middle Jurassic time. Marked inter- and intra-terrane contraction in the Middle Jurassic resulted in the south westward thrusting of the Cache Creek Terrane onto Stikinia, the subsequent development of the Bowser Basin on Stikinia, and possible coeval culmination of the emplacement of Quesnellia and the Slide Mountain Terrane onto Ancestral North America. Deformation, metamorphism, and plutonism along the western margin of Ancestral North America closely followed these events. Contraction was succeeded by a dextral strike-slip regime during the mid-Cretaceous accompanied by the intrusion of voluminous potassic, silica-rich granitic rocks in Ancestral North America. The emplacement of Early to mid-Cretaceous plutons postdated the development of broad, open, regional anticlinoria and synclinoria, perhaps during Early Cretaceous time. The plutonic episode coincided approximately with initiation of the Sustut Basin. Dextral strike-slip faulting further disrupted Ancestral North America until post-Eocene time.
Effects of strong seismic shaking in lake sediments, and earthquake recurrence interval, Témiscaming, Quebec
Authors: Doig Ronald
Published: April 2011

The magnitude 6.3 Timiskaming earthquake of 1935 resulted in discoloration in small lakes in the epicentral region. Sonar profiles for Lac Tee have shown that organic-rich gyttja has been removed from the sides and redeposited in the deep parts of the lake. Lake sediment cores from deep basins contain a 2–3 cm uppermost layer, which is interpreted as the normal accumulation of sediment since 1935. This is followed by a 20 cm chaotic zone of black gyttja mixed with partly tabular fragments of a previously formed silt layer, underlain by a dense 1–2 cm thick silt horizon. The latter is interpreted as having formed by rapid settling of the denser silicate portion of the resuspended sediment. This 20 cm zone is insufficient to account for the abnormal thickness of gyttja in the basins, so events of this kind would have had to have occurred repeatedly since deglaciation. The only major prehistoric event revealed by these ~100 cm cores is at a depth equivalent to about 1500 years ago, based on the amount of sediment deposited since 1935. A minor silting event occurred about 400 years ago. On this basis, the recurrence interval of magnitude 6 or greater earthquakes is longer at Témiscaming than at Charlevoix, Quebec (75 years historically), consistent with the present relative frequency of small earthquakes in these two regions.
Prehistoric debris avalanches from Mount Cayley volcano, British Columbia
Authors: Evans S. G. , Brooks G. R.
Published: April 2011

An investigation of diamicton units exposed in an extensive accumulation of volcanic debris in the Squamish valley, west of Mount Cayley volcano, has yielded evidence for at least three major debris avalanches, initiated by the collapse of the western flank of Mount Cayley in the mid-Holocene. Radiocarbon ages obtained from tree fragments contained in the deposits indicate that the events took place at 4800, 1100, and 500 BP. All three debris avalanches dammed the Squamish River and formed temporary lakes upstream of the debris. Failure of the cone took place after considerable dissection of the original edifice had exposed weak pyroclastic materials at the base of the steep upper slope of the volcano. No evidence of older debris avalanches from Mount Cayley has been discovered. Smaller scale debris avalanches probably have been common, and at least two have occurred in historic time (1963 and 1984). Debris avalanches from Mount Cayley and the effects of a possible damming of the Squamish River are major geomorphic hazards to public safety and economic development in the Squamish valley.
New acritarch taxa from the Middle and Upper Devonian (Givetian–Frasnian) of western Canada
Authors: Turner Robert E.
Published: April 2011

Eight new acritarch species, four of which are assigned to new genera, are described from Givetian and Frasnian strata of Alberta and the Northwest Territories. The new taxa are Apectosphaeridium apoplanium n.gen. et sp., Asyncosmium isum n.gen. et sp., Cerastum pelorum n.gen. et sp., Variolidium omnium n.gen. et sp., Goniosphaeridium rallum n.sp., Leiosphaeridia gigantea n.sp., Polyedryxium leptum n.sp., and Saharidia perplexa n.sp.
Tectonic setting and regional correlation of Ordovician–Silurian rocks of the Aspy terrane, Cape Breton Island, Nova Scotia
Authors: Barr Sandra M. , Jamieson Rebecca A.
Published: April 2011

Interlayered mafic and felsic metavolcanic rocks and metasedimentary rocks of Ordovician to Silurian age are characteristic of the Aspy terrane of northwestern Cape Breton Island. These rocks were affected by medium- to high-grade metamorphism and were intruded by synkinematic granitoid orthogneisses during Late Silurian to Early Devonian times. They were intruded by posttectonic Devonian granitic plutons and experienced rapid Devonian decompression and cooling. The chemical characteristics of the mafic metavolcanic rocks indicate that they are tholeiites formed in a volcanic-arc setting. The volcanic rocks of the Aspy terrane differ from many other Silurian and Silurian–Devonian successions in Atlantic Canada, which have chemical and stratigraphic characteristics of volcanic rocks formed in extensional within-plate settings, and are somewhat younger than the Aspy terrane sequences. Aspy terrane units are most similar to Ordovician–Silurian volcanic and metamorphic units in southwestern Newfoundland, including the La Poile Group and the Port aux Basques gneiss. Together with other occurrences of Late Ordovician to Early Silurian volcanic-arc units, they indicate that subduction-related compressional tectonics continued into the Silurian in parts of the northern Appalachian Orogen. The complex Late Silurian – Devonian tectonic history of the Aspy terrane may reflect collision with the southeastern edge of a Grenvillian crustal promentory.
The magnetization of oceanic crust: contribution to knowledge from the Troodos, Cyprus, ophiolite
Authors: Hall James M. , Walls Charles C. , Yang Jing-Sui , Hall S. Lata , Bakor Abdul Razzak
Published: April 2011

An extensive study of a segment of the Troodos, Cyprus, ophiolite using both outcrop and drill-core samples, and extending from the sediment–extrusive interface through sheeted dikes to cumulate ultramafics, has allowed a number of key questions regarding the magnetization of oceanic crust to be addressed. These include the number of strongly magnetized intervals with depth, their lateral variability and controls on their occurrence. Comparison has also been made with the section in Ocean Drilling Program (ODP) hole 504B, and a reinterpretation of its constructional setting is offered.Two strongly magnetized intervals occur in the area studied. The upper is in the extrusive sequence, extends on average from 0.2 to 0.6 km depth, and has a thickness of ~0.4 km. Here magnetization is dominated by remanence. The lower interval extends from the lowest level at which flows occur with dikes (average depth = 0.9 km) into the Sheeted Complex (average depth = 1.2 km) and has a thickness of 0.3 km. Here magnetization is dominantly induced. No other strongly magnetized intervals occur in the section. The extent of dike intrusion is closely related to the position of the lower limit of the high-remanence layer and to the occurrence of the high induced magnetization layer. In both cases the replacement of primary magnetite, which can carry a strong remanence, by magnetically soft secondary magnetite appears to be the controlling process.Comparison of the Troodos and hole 504B magnetization profiles shows close similarity in the upper, remanence-dominated magnetic interval. The absence of the deeper interval of high induced magnetization in the hole 504B profile is interpreted as meaning that sheeted dikes have not been penetrated by the drill hole.
The Ordovician–Silurian boundary on Cornwallis and Truro islands, Arctic Canada: preliminary data
Authors: Melchin Michael J. , McCracken Alexander D. , Oliff Fred J.
Published: April 2011

Four sections of the lower part of the Cape Phillips Formation, two outcrops on northeastern Cornwallis Island and one outcrop and one drill core from Truro Island, Northwest Territories, Canada, provide significant new data on the Ordovician–Silurian boundary. They show evidence of continuous sedimentation through the boundary interval and a continuous sequence of graptolite zones, including the bohemicus and persculptus zones, which have not been previously found in Arctic Canada. Strata yield graptolites, including uncompressed specimens, and conodonts through most of the sections. The ordovicicus conodont Zone occurs within the pacificus to lower persculptus graptolite zones. The nathani conodont Zone contains a "transitional fauna," a mixing of species typical of the preceeding ordovicicus Zone and those generally regarded as Silurian indicators. This conodont zone ranges from the middle of the persculptus graptolite Zone into the lower acuminatus graptolite Zone and, thus, spans the Ordovician–Silurian boundary. The Ordovician–Silurian faunal turnover of the conodonts, therefore, also spans the Ordovician–Silurian boundary and is not coincident with the interval of major graptolite extinction, which occurs earlier, at the end of the pacificus Zone. The base of the kentuckyensis conodont Zone occurs in the acuminatus graptolite Zone. Sedimentologic evidence of the maximum eustatic sea-level drop can be seen within the bohemicus Zone (early Hirnantian) and possibly one or several smaller scale sea-level fluctuations through the underlying zones.
Age and timing of igneous activity in the Temagami greenstone belt, Ontario: a preliminary report
Authors: Bowins R. J. , Heaman L. M.
Published: April 2011

The southernmost remnants of Archean supracrustal and intrusive rocks in eastern Ontario are exposed through a window in the Early Proterozoic Huronian Supergroup near the town of Temagami. U–Pb zircon ages from this area indicate the presence of some of the oldest felsic magmatism so far discovered in this portion of the Superior Province. The Iceland Lake pluton (2736 ± 2 Ma) and a nearby rhyolite flow ([Formula: see text]) are contemporaneous, which establishes that at least some of the intrusive rocks in the region are synvolcanic and coeval with the oldest volcanic cycle. The youngest plutonic activity is the emplacement of a late rhyolite porphyry dike at 2687 ± 2 Ma, an age that is bracketed by the 2675–2700 Ma emplacement ages of late internal plutons found throughout the Abitibi Subprovince. The 2736 Ma dates, however, are older than the nearest portion of the exposed Abitibi, some 120 km to the north near Kirkland Lake.
U–Pb zircon and titanite ages of three Mesozoic igneous rocks south of the Thor–Odin – Pinnacles area, southern Omineca Belt, British Columbia
Authors: Carr Sharon D.
Published: April 2011

U–Pb zircon and titanite ages were obtained from three intrusive rocks near the Monashee Highway between the Valhalla complex and the Okanagan Valley in the southern Omineca Belt. Granitoid phases that have been previously grouped together and referred to as the Whatshan batholith have been subdivided on the basis of lithology and U–Pb geochronology into the Middle Jurassic Spruce Grove batholith and the Late Cretaceous Whatshan batholith. A 77 ± 0.5 Ma phase of the Whatshan places a maximum age limit on regional F3 folding in the Pinnacles area.
Note on a second occurrence of thalattosaur remains (Reptilia: Neodiapsida) in British Columbia
Authors: Storrs Glenn W.
Published: April 2011

A fragmentary thalattosaur specimen from the Late Triassic Pardonet Formation of northeastern British Columbia is the second reported occurrence of such animals in Canada. The group was previously known with certainty only from the Hosselkus Limestone of California, the Monte San Giorgio region shales of Italy and Switzerland, the Natchez Pass Formation of Nevada, and most recently, the Sulphur Mountain Formation of British Columbia. As such, the described material, which is indeterminate to genus, represents a slight geographic range extension of the Thalattosauria. The Norian age of this material represents a significant temporal range extension for the Thalattosauria, and it is the geologically youngest material known of this taxon.
Volcanism in an arc-transform transition zone: the stratigraphy of the St. Clare Creek volcanic field, Wrangell volcanic belt, Yukon, Canada
Authors: Skulski Thomas , Francis Don , Ludden John
Published: April 2011

The St. Clare Creek volcanic field in the southwestern Yukon overlies a tectonic transition in the Wrangell volcanic belt between subduction to the northwest in Alaska and transform faulting along the Duke River fault in the southeast. Two large polygenetic volcanic centres dominated the Miocene landscape of the St. Clare Creek field: the 18–16 Ma Wolverine centre and the 16–10 Ma Klutlan centre. The Wolverine centre evolved from a small alkaline shield volcano at 18 Ma, from which alkaline basalts, hawaiites and mugearites erupted, to a larger composite volcano between 18 and 16 Ma composed of transitional basalt, basaltic trachyandesite, trachyte and rhyolite lavas, and pyroclastic rocks. The youngest Wolverine lavas are calc-alkaline basaltic andesites, andesites, and hybrid lavas (transitional–calc-alkaline). This temporal progression from alkaline through transitional to calc-alkaline volcanism is accompanied by a systematic increase in the degree of silica saturation and decrease in Fe/Si, Nb/Y, and P/Y ratios. Klutlan lavas have lower Nb/Y and P/Y ratios and are characterized by an opposite eruption sequence. The earliest Klutlan lavas (16–13 Ma) erupted from a composite volcano and include calc-alkaline andesite, rhyolite, and hybrid trachyandesite lavas, followed by transitional basaltic trachyandesites, trachyandesites, trachytes, and rhyolites. Klutlan vulcanism between 13 and 11 Ma was dominated by basaltic fissure eruptions on the southern flanks of the earlier centre and include early mildly alkaline basalts followed by more voluminous transitional basalts. Volcanism reverted to a more central type of activity between 11 and 10 Ma and includes calc-alkaline dacite lava followed by transitional basaltic trachyandesite, trachyandesite, and trachyte lavas.The volcanic stratigraphy of the St. Clare Creek field and 40Ar/39Ar geochronological data provide the basis for understanding the origin of St. Clare magmas in a regional tectonic context. Early Wolverine alkaline volcanism largely reflects leaky transform faulting, whereas subsequent transitional and calc-alkaline lavas record the onset of subduction-related volcanism at the margins of the then active Wrangell arc. The opposite eruption sequence at the Klutlan centre records the demise of subduction-related volcanism between 16 and 13 Ma, due to northwestward migration of the subducted plate. Upwelling of asthenospheric mantle in place of the subducted slab led to the generation of transitional basalts between 13 and 11 Ma, which resulted in more evolved lavas between 11 and 10 Ma.
The seismic velocity structure of northern Appalachian crust around western Newfoundland
Authors: Michel H. Karin , Louden K. E. , Marillier F. , Reid I.
Published: April 2011

The crustal velocity structure beneath western Newfoundland is constrained by a reanalysis of older, regional refraction profiles together with an analysis of one new profile. Initial interpretation of the older data gave inconsistent and discontinuous structures that are difficult to reconcile with more recent deep reflection profiles. We also show that traveltimes predicted by the earlier models often do not yield acceptable fits to the original observations. Our reinterpretation reveals a simpler pattern, in which the crust is characterized by a persistent, high-velocity, lower crustal (HVLC) layer. This layer has velocities of 7.0–7.9 kmls and thicknesses of 5–23 km. It is thickest beneath the Grenville crustal block, east of the Appalachian structural front, and thins or is possibly absent within the Central block. Analysis of the new, much higher resolution profile off western Newfoundland confirms the existence of the HVLC layer with a velocity of 7.2 kmls and thicknesses of 11–19 km, increasing to the northeast. The upper crust has well-defined velocities of 6.2–6.4 kmls and is overlain by a complex sandwich of sediment layers with principal velocities of 3.9, 4.95, and 5.58 kmls and maximum total thicknesses of 8.5 km in the south to 5.5 km in the north. Total crustal thickness varies from 39 to 43 km from south to north. Comparison of the velocity–depth models with the pattern of deep crustal reflectivity revealed by deep multichannel profiles shows that the HVLC layer is coincident with a zone of flat-lying reflectors that terminate to the west at the base of the crust beneath the Appalachian structural front. The HVLC may continue eastward to cover a broad region of central Newfoundland as suggested by the older data, but its association with the reflectivity is not clear.
Age and tectonic setting of the Duke Island ultramafic intrusion, southeast Alaska
Authors: Saleeby Jason B.
Published: April 2011

Concordant U–Pb zircon ages on hornblende–plagioclase pegmatites and a related granophyre from marginal and roof zones of the Duke Island ultramafic intrusion, and from leucoquartz diorite internal to hornblende–clinopyroxenite of nearby Mary Island cluster between 108 and 111 Ma. Sm–Nd mineral and bulk-rock data from pegmatite and granophyre zircon samples and from wehrlites and clinopyroxenites of the main Duke Island cumulate sequence are consistent with the consanguinity of the ultramafic cumulates and the zircon-bearing feldspathic rocks, and with an Early Cretaceous igneous age for the intrusion. Wall rocks for the intrusion consist of Ordovician–Silurian amphibolite- and greenschist-grade metamorphosed plutonic, volcanic, and minor sedimentary rocks and crosscutting Late Triassic gabbro–diorite of the Alexander terrane.The Duke Island ultramafic intrusion formed as a northwest-trending elongate funnel-shaped stratiform body commensurate with extensional brittle–ductile faulting in its roof and adjacent wall rocks. Intrusion occurred in a basinal setting within the Gravina volcanic arc along the Cordilleran continental margin. During the latter phases of intrusive activity the Gravina basin began to close by regional thrust faulting, which in the Duke Island region was west-northwest directed. The intrusion may have still had local intercumulate liquid upon initiation of thrust faulting. It responded first by open folding with incipient crystal plasticity. Once completely solidified, the intrusion behaved like a large "augen" with ductile deformation concentrated along its margins and within quartzo-feldspathic and micaceous members of its wall-rock complex. Much of the intrusion's northern margin behaved as a ductile shear zone serving as a tear fault between thrust plates to the northeast and an oblique thrust complex that roots beneath the southwest margin of the intrusion. The intrusion may thus be tectonically transported relative to its original underpinnings. North-trending high-angle faults and parallel fracture cleavage also cut the intrusion in response to axial loading as a result of its initial elongate shape and orientation relative to the thrust kinematics.
A depositional model for Rogen moraine, with examples from the Avalon Peninsula, Newfoundland
Authors: Fisher Timothy G. , Shaw John
Published: April 2011

Rogen moraine is explained by subglacial meltwater processes through a form analogy between moraine ridges and ripples produced on the underside of river ice. This mechanism for Rogen moraine formation is compatible with the meltwater hypothesis for drumlins. A unified explanation for Rogen moraines and drumlins is attractive and necessary because they are part of a continuum. The meltwater hypothesis is tested on Rogen moraine of the Avalon Peninsula, Newfoundland. Mapping shows that ice and meltwater flowed northeastwards from St. Mary's Bay and fanned out across the peninsula. The sedimentology of four moraine ridges and one moraine hummock favours deposition in subglacial cavities. Sediment in the ridges travelled only short distances, and there is abundant evidence of water sorting and deposition from debris flows. Bedding within ridges conforms with surface slopes, and clast fabrics relate to local morphology rather than to the regional ice-flow direction. Additional sedimentary observations from Quebec and Sweden support the meltwater hypothesis. The prevalence of local debris in Rogen moraines may reflect the importance of subglacial entrainment by freeze-on under permafrost conditions. This may explain the geographical distribution of Rogen moraine around former ice-sheet centres.
The Scotian Basin offshore Nova Scotia: thermal history and provenance of sandstones from apatite fission track and 40Ar/39Ar data
Authors: Grist A. M. , Reynolds P. H. , Zentilli M. , Beaumont C.
Published: April 2011

Apatite fission track and 40Ar/39Ar age spectrum data from sandstone drill-core minerals taken from depths of 2–5 km in nine wells from the Scotian Basin are presented and interpreted in terms of the thermal history of the basin and the provenance of its sediments. The focus of the study is a comparison of the data from these thermochronometers with each other and with previously published vitrinite reflectance and aromatization–isomerization (A–I) reactions in biomarker compounds from the same or nearby wells.Apatite fission track ages are generally in agreement with expectations in that they trend to zero at a depth of ~4 km (corrected bottom-hole temperature ~120 °C). Shallower (lower present temperature) samples are partially annealed; the degree of partial annealing correlates closely with the degree of A–I reactions. Both thermal indicators are activated over the temperature range 60–120 °C.Samples from two wells, Mic Mac J-77 and Erie D-26, are anomalous. They are more annealed than present formation temperatures would predict, an anomaly that is also indicated by the A–I data. These samples are interpreted as having experienced higher than present temperatures subsequent to deposition, possibly resulting from the passage of hot fluids related to localized volcanism or the sudden venting of an overpressured reservoir.K-feldspars record minor (< 20%) argon loss as a result of burial heating in the basin only at the greatest depths of the sampled range (> 4.3 km). This result is in agreement with the thermal models of the Scotian Basin and extrapolation of the A–I and fission track data to greater depths. The inferred argon loss implies an activation energy of 40 ± 4 kcal/mol for the smallest diffusion domains.The argon age spectra for samples that have not lost argon during residence in the basin provide evidence on the provenance of the sediments. K-feldspars from the Early Cretaceous Missisauga Formation have spectra that are similar to those obtained from K-feldspars from the Grenville Province of the Canadian Shield, whereas muscovites from the same formation give Cambrian to Carboniferous argon ages (mean 387 Ma), an indication of contributions from other source rocks. Corresponding data from the Jurassic Mohican Formation are similar to those reported for plutons from the southern Nova Scotia mainland (ca. 250–350 Ma argon ages). By implication, the Mohican Formation, which is the earliest postrift deposit, was derived from local sources inferred to be adjacent flank uplifts, whereas the Missisauga Formation was derived in part either directly or indirectly from the Grenvillian-aged interior of eastern Canada.
Relocation of earthquakes west of Vancouver Island, British Columbia, 1965–1983
Authors: Wahlström Rutger , Rogers Garry C.
Published: April 2011

In the tectonically complex region of young plate interaction west of Vancouver Island, 360 earthquakes have been relocated. The earthquakes occurred in the years 1965 – 1983, when the Canadian seismograph network in the region did not significantly change configuration, and are in the magnitude range 3–5. A traveltime model was derived and applied to arrival times for a selected, limited set of station–phase combinations. Time corrections for these combinations were derived from joint-hypocentre locations of earthquakes in specific regions using independently located reference events. An algorithm for routine location of offshore earthquakes in this region is suggested.The correlation between seismicity and mapped bathymetrical features is strong along the Revere–Dellwood transform fault and the northern segments of the Explorer ridge – transform fault system. Considerable seismicity occurs inside the Explorer Plate, indicating internal deformation. The Sovanco and Nootka shear zones, the southern borders of the Explorer Plate, are characterized by broad belts of seismicity and evidently are not simple transform margins. The Explorer and northern Juan de Fuca ridges are aseismic in the investigated magnitude range.
Peritidal origin of the Lower Ordovician Upton Group, southern Quebec Appalachians
Authors: Lavoie Denis
Published: April 2011

The Lower Ordovician Upton Group is part of the Cambrian–Ordovician external domain of the Appalachian Orogen of southern Quebec. It is a mixed carbonate–siliciclastic–volcanic succession occurring within flyschoid sediment of the Lower Cambrian Granby Nappe. The bulk of the Upton Group is a grey, massive, recrystallized limestone of probable peritidal and shallow subtidal origin. Associated siliciclastic lithofacies are typical of peritidal and outer-shelf settings. The proposed peritidal paleoenvironmental model differs from previous interpretations and indicates that it is unlikely that the Upton Group is a slab derived from the Ordovician continental margin which has slid into the Granby Nappe.
Manganese precipitates in the karst terrain of Grand Cayman, British West Indies
Authors: Jones Brian
Published: April 2011

Ten morphologically distinct forms of Mn precipitates (probably birnessite) occur in a wide variety of paleokarst features that characterize dolostones of the Bluff Formation on Grand Cayman. These Mn-rich precipitates, which commonly contain variable amounts and selections of Al, Si, Fe, K, Ti, Ni, Na. Mg, and Ca, are not evenly distributed throughout the Bluff Formation of Grand Cayman. Thus, some areas have abundant Mn precipitates, whereas other areas are devoid of such precipitates. Mn precipitates, of variable morphology, have teen found in stalactites, karst breccia, caymanite, terrestrial oncoids, and root calcretes and along fractures and cavities in the dolostone. There does not appear to be any correlation between the morphology and composition of the Mn precipitate and its host substrate.The Mn and its associated elements may have been derived from the terra rossa and (or) swamps that formed on the surface of the Bluff Formation at various times. The scattered distribution of the soils and swamps, with respect to time and space, accounts for the patchy occurrence of the Mn precipitates presently found in the Bluff Formation. Although some of the Mn precipitates are abiogenic in origin, others appear to have formed through the direct or indirect intervention of various microbes.Paragenetic analysis of the Mn precipitates and their associated cements shows that Mn precipitation has not been a constant, ongoing process. Indeed, Mn precipitation does not appear to be occurring at the present day. Available evidence suggests that Mn precipitation occurred at various times when climatic conditions were suitable for Mn mobilization.
Porphyry intrusions and albitites in the Bardoc–Kalgoorlie area, Western Australia, and their role in Archean epigenetic gold mineralization
Authors: Witt W. K.
Published: April 2011

Minor intrusions in the Menzies – Kambalda greenstone belt of the Archean Eastern Goldfields Province, Western Australia, range from quartz–feldspar porphyry to plagioclase–hornblende porphyry. The porphyries display enrichment of mobile and incompatible elements (K to Zr) and depletion of relatively compatible elements, with negative Nb, P, and Ti anomalies, on mid-ocean-ridge basalt-normalized spidergrams. The composition and timing of emplacement of the porphyries are consistent with a genetic relationship with spatially related granitoids. Porphyries occur in 30% of gold mines in the Menzies–Kambalda belt. The association appears to be largely structural, since both the intrusions and the mineralizing fluids exploit zones of weaknesses, such as lithological contacts and shear zones. Porphyries have been modified to varying degrees by hydrothermal alteration, especially pervasive albitization. Textural evidence indicates that secondary albite and associated sodic amphibole formed late in the deformation history of the greenstones and were broadly contemporaneous with secondary phyllosilicate, carbonate and sulphide minerals related to gold mineralization. Recent studies in the Alleghany district of California suggest the initial rock composition may critically influence the nature of alteration associated with gold mineralization. Therefore, albitization of porphyries may be caused by the same hydrothermal fluids that deposit gold and produce potassic alteration in mafic rocks.
U–Pb age constraints for deposition of clastic metasedimentary rocks and late-tectonic plutonism, Michipicoten Belt, Superior Province
Authors: Corfu F. , Sage R. P.
Published: April 2011

The study investigates the ages of clastic metasedimentary rocks and of late-tectonic alkalic to calc-alkalic intrusions and puts constraints on the timing of major deformation in the Michipicoten greenstone belt of the Wawa Subprovince. A trondhjemitic boulder in the Doré conglomerate of the southern metasedimentary belt is dated at 2698 ± 2 Ma. This is a maximum age of sedimentation that is also supported by ages of detrital zircons in the matrix and may directly reflect the time of synvolcanic deposition. Detrital zircons in metapsammites of the central and northern sedimentary belts yield younger ages of 2682 ± 3 and 2680 ± 3 Ma, respectively, suggesting that sedimentation occurred significantly later in the northern than in the southern parts of the greenstone belt. The ≤2682 Ma sedimentary rocks were affected by multiphase deformation that is related to the development of a large-scale recumbent fold and superimposed folds and faults. This tectonism was followed by the emplacement of the granodioritic Troupe Lake and Maskinonge Lake stocks that yield identical zircon and titanite ages of 2671 ± 2 Ma. The structurally older and deformed Herman Lake nepheline syenite has an imprecise titanite age of [Formula: see text]. The isotopic composition of Pb in feldspar of these intrusions is relatively evolved and, in light of geochemical considerations, may reflect provenance of the melts from enriched mantle reservoirs.