bluuebunny/crossref_metadata_2025 huggingface dataset:
Glacial advances and stratigraphy in Otto Fiord and adjacent areas, Ellesmere Island, Northwest Territories
Authors: Bednarski Jan
Published: April 2011

Hvitland and Svartfjeld peninsulas have been glaciated at least two or three times since the Late Pliocene. The earliest recognized glaciation is constrained by amino acid ratios on in situ pelecypods from marine sediments stratigraphically overlying till in Otto Fiord. High amino acid ratios suggest that the shells may be Pliocene and related to recently discovered Late Pliocene Hvitland beds at White Point. The same samples yielded finite radiocarbon ages in the 30.2–34.8 ka BP range, which cautions against their acceptance. A second, mid Quaternary glaciation is suggested by intermediate amino acid ratios from in situ pelecypods and shell-bearing till covering coastal uplands along Nansen Sound. During the last glaciation the peninsula was covered by coalesced ice caps, with glacial tongues descending tributary valleys and extending into the fiords. Deglaciation of a tributary valley in outer Otto Fiord proceeded before 11.6 ka BP and before 9.1 ka BP in mid Otto Fiord, but major ice margins remained at the coast until 8–8.5 ka BP. Lateral meltwater channels record systematic ice retreat up tributary valleys into the interior of the peninsulas. The highest recognized marine limits are marked by prominent deltas at least 164 m asl on western Hvitland Peninsula. The marine limit declines eastward inside Otto, Jugeborg, and Hare fiords. The highest strandlines could not be dated; however, by ~8.3 ka BP relative sea level stood at 103 m asl.
U–Pb geochronology of the Opatica tonalite-gneiss belt and its relationship to the Abitibi greenstone belt, Superior Province, Quebec
Authors: Davis W.J. , Machado N. , Gariépy C. , Sawyer E. W. , Benn K.
Published: April 2011

U–Pb ages for zircon, monazite, and titanite from samples collected from two transects across the Opatica tonalite-gneiss belt in the Superior Province of Quebec indicate that the belt contains rocks that are significantly older than those in the adjacent low-grade northern Abitibi belt. Tonalite and tonalite gneiss, which make up most of the belt, formed over an interval of 100 Ma, from pre-2800 to 2702 Ma. Five samples have ages of ca. 2807 ± 13, 2773 ± 23, [Formula: see text], [Formula: see text], and 2702 ± 3 Ma. Zircon growth at 2718–2721 Ma in the two oldest samples may record an early period of high-grade metamorphism in the belt. Hornblende diorite, monzodiorite, and tonalite plutons were intruded at 2693–2696 Ma, particularly along the southern boundary with the Abitibi belt. These include the Canet pluton at [Formula: see text][Formula: see text] Ma, the Lac Ouescapis pluton at 2693 ± 2 Ma, and the Barlow pluton at 2696 ± 3 Ma. Pink granite plutons and dykes are the youngest intrusive rocks in the belt; three samples have yielded zircon ages of 2690 ± 2 and 2686 ± 4 Ma and a monazite age of 2678 ± 2 Ma. The timing of D1 deformation is bracketed by the age of the youngest gneiss sample containing the D1 structures, at 2702 ± 3 Ma, and the 2690 ± 2 Ma age of a granite dyke that cuts D1 structures. The south-vergent D2 event is recorded in the 2693–2696 Ma plutons and must have occurred synchronously with or after this plutonism. D3 dextral strike-slip movement on the Nottoway River shear zone occurred after 2686 ± 4 Ma, and may be associated with post-regional metamorphic titanite growth at 2672 and 2657 Ma. Titanite ages cluster at 2678–2681 Ma along the Matagami transect and at 2665 Ma north of Chibougamau, and record the time of cooling of the belt below the titanite closure temperature.
Magnetism and age of the Porteau Pluton, southern Coast Belt, British Columbia: evidence for tilt and translation
Authors: Irving E. , Baker J. , Wright N. , Yorath C. J. , Enkin R. J. , York D.
Published: April 2011

The Porteau Pluton is a variably foliated quartz diorite to granodiorite intrusion in the southern Coast Belt of the Canadian Cordillera (49.6°N, 123.2°W). 40Ar/39Ar ages are 95 ± 5 Ma from biotite and 101.5 ± 0.7 Ma from hornblende, which, together with an earlier U–Pb zircon age of 100 ± 2 Ma, indicate that the body was emplaced, uplifted, and cooled rapidly in mid-Cretaceous time. The rocks contain high coercive force (hard) remanent magnetizations with unblocking temperatures between 500 and 600 °C, close to those of Ar in hornblende, indicating that remanence was acquired at or close to the hornblende plateau age. The hard remanence directions have an elongate distribution, in agreement with the predictions of M.E. Beck regarding magnetization acquired during tilting, uplift, and cooling of plutons. No part of the distribution agrees with the direction expected from observations from rocks of mid-Cretaceous age from cratonic North America. The elongate distribution defines the axis of tilt (347° east of north) but not its direction; tilt could have been down toward the east or down toward the west. The former yields an inclination that is 29.0 ± 4.9° shallower than expected from cratonic observations, corresponding to a displacement from the south of 3200 ± 500 km. The latter reconstruction yields an inclination that is anomalously shallow by 14.8 ± 3.9°, corresponding to a displacement from the south of 1600 ± 400 km, which is a minimum estimate. It is argued, therefore, that the Porteau Pluton has undergone both tilt and displacement from the south by distances substantially in excess of 1000 km.
Geochemistry of Cenozoic basaltic and silicic magmas in the central portion of the Loei–Phetchabun volcanic belt, Lop Buri, Thailand
Authors: Intasopa Suporn , Dunn Todd , Lambert Richard StJ.
Published: April 2011

Cenozoic volcanic rocks outcrop in the central portion of the Loei–Phetchabun volcanic belt in central Thailand in the Lop Buri area. The volcanic rocks range in composition from basalt to high-silica rhyolite. In general, the volcanic rocks decrease in age from south to north. The oldest rocks studied are 55–57 Ma rhyolites that are isotopically and geochemically distinct from younger (13–24 Ma) rhyolites that occur farther north. Intermediate rocks (andesite and dacite) are less voluminous than rhyolite. Basalt occurs in the central and northern parts of the area and ranges in composition from olivine tholeiites to nepheline normative alkali basalts. The isotopic, major, and trace element compositions of the andesites, dacites, and younger rhyolites are consistent with an origin for these rocks by variable degrees of partial melting of metabasaltic crustal rocks, themselves derived from a depleted mantle source at approximately 530 ± 100 Ma. The apparent extent of partial melting of metabasalt increases from rhyolite to andesite. The isotopic and trace element systematics of the basalts are consistent with a refertilized depleted mantle source with characteristics of a mixture of normal mid-ocean ridge basalt source mantle and enriched mantle II type mantle.
Epizonal I- and A-type granites and associated ash-flow tuffs, Fogo Island, northeast Newfoundland
Authors: Sandeman Hamish A. , Malpas John
Published: April 2011

Magmatic activity of Silurian–Devonian age is widespread in the Appalachian–Caledonian Orogen. A marked characteristic of this magmatism is the composite nature of the igneous suites, which range from peridotite to granodiorite in single plutonic bodies. The origin of these suites is still enigmatic, and the assumption that all are the same not proven. Such a suite of intrusive rocks, ranging in composition from minor peridotite to granodiorite, intrudes an openly folded sequence of Silurian volcanogenic sandstones and ash-flow tuffs on Fogo Island, northeast Newfoundland. Two units, the Rogers Cove and Hare Bay microgranites, consist of fine-grained hastingsite granites with spherulitic and flow-banded textures, and exhibit drusy cavities and microfractures that contain the mineral assemblage hastingsitic hornblende + plagioclase + magnetite + zircon. These rocks are characterized by elevated high field strength element contents (e.g., Zr = 74–672 and Y = 21–103 ppm), very high FeO*/MgO ratios (FeO*/MgO = 2.4–93.5), and 10 000 Ga/Al ratios of 1.67–10.52, indicating an A-type granitoid affinity. A third and the most voluminous granitic unit, the Shoal Bay granite, is an alkali-feldspar-phyric, medium-grained, equigranular biotite–hastingsite granite with hastingsite and annitic biotite interstitial to euhedral plagioclase, anhedral quartz, and perthite crystals. The Shoal Bay granite exhibits mineral parageneses similar to the microgranites, but chemical characteristics more typical of calc-alkaline, I-type granitoids. Volcanic–sedimentary sequences spatially associated with the granitic rocks include dense, welded, high-silica, hastingsite-bearing ash-flow tuffs with compositions that suggest they represent erupted equivalents of fractionated end members of the Shoal Bay granite. The rocks making up the Fogo Island batholith have been directly equated with the bimodal, calc-alkaline Mount Peyton batholith of northeast Newfoundland, but the specialized A-type nature of the Fogo granites suggests differing source conditions for the two suites.
La zone tectonique du front de Grenville à l'est de Louvicourt, Québec : exhumation de la croûte archéenne pendant l'orogénie grenvillienne
Authors: Berclaz Alain , Hébert Réjean , Rocheleau Michel
Published: April 2011

The Grenville Front tectonic zone, East of Louvicourt in Quebec, defines a tectonometamorphic domain marked by the Grenville Front oriented North 50°, that is locally crosscut by a North 30° reverse fault, the Matchi-Manitou Fault. These tectonic accidents separate the central parts of the Superior Province to the northwest from the Grenville Province to the southeast. The Archean age, high-grade polymetamorphic sequences of the Grenville Province consist of paragneisses and migmatitic quartzofeldspathic gneisses associated to coarse-grained, anatectic pegmatitic veins, the whole containing shreds of two pyroxenes-bearing mafic gneisses. The metamorphic disequilibrium textures, the chemical analyses of the mineral phases, and the whole-rock chemistry of these sequences indicate that a strong crustal thickening, marked by the incorporation of shreds of volcanic rocks in the metasedimentary sequences, led to the granulitization of the lithologies and the quartzofeldspathic pegmatitic vein formation by fluid-absent partial melting of the surrounding migmatitic quartzofeldspathic gneisses under 750–825 MPa and 675–745 °C conditions. Subsequently, a higher pressure and slightly lower temperature episode (920–990 MPa and 625–750 °C) is at the origin of a development of secondary coronitic garnet around primary garnet. A late fluid is responsible for final retrograde reequilibrations in all the lithologies. All these successive events probably occurred during the Archean ages. During the Grenvillian orogeny (1.0 Ga), the thrusting movement with a strong sinistral component of the Grenvillian Province onto the Superior Province is characterized: (i) to the east of the Grenville Front, by the exhumation and the rotation of 9–12 km thick sequences of the Grenville Province; (ii) to the west of the Grenville Front, by the development of a 705–845 MPa and 570–605 °C medium-grade metamorphism that overprints the 400–565 MPa and 600–660 °C regional metamorphism of Kenorean age. Both metamorphic episodes define a 1–6 km width band made of biotite and garnet-bearing paragneisses.
Constraints on temperature–pressure conditions and fluid composition during metamorphism of the Sullivan orebody, Kimberley, British Columbia, from silicate–carbonate equilibria
Authors: De Paoli Glen R. , Pattison David R.M.
Published: April 2011

The Sullivan mine, in southeastern British Columbia, is one of the world's largest sediment-hosted, massive sulphide deposits. It has undergone at least one period of metamorphism since it was deposited in mid-Proterozoic times. Mineral textures within the deposit are predominantly of metamorphic origin. A well-constrained estimate of metamorphic conditions is required to understand how the original, depositional character of the orebody has been modified by metamorphism. Metamorphic conditions were estimated using multiequilibrium thermobarometric techniques involving silicate–carbonate–fluid equilibria. Peak metamorphic temperature constrained by calibration of the garnet–biotite Fe–Mg exchange equilibrium is 450 ± 50 °C. Lower temperature estimates from some samples are interpreted to record the temperature of cessation of garnet growth prior to the attainment of peak metamorphic temperature. Peak metamorphic pressure as determined from equilibria applicable to the assemblage garnet–biotite–muscovite–chlorite–calcite–quartz–fluid is 380 ± 100 MPa. The fluid composition accompanying this pressure estimate is [Formula: see text], [Formula: see text]. This estimate is particular to one sample and may not be representative for the deposit as a whole. Metamorphic fluids at the estimated P–T conditions would not have contained significant concentrations of C–O–H–S species other than H2O and CO2. Textural evidence and temperature–pressure results from a titanite-bearing metamorphosed mafic intrusion in the deposit suggest published titanite ages near 1330 Ma in the area of the mine represent the age of the peak metamorphic event. The results of this study carry tectonic implications for the Sullivan area, and may have application to other metamorphosed ore deposits and low-grade metamorphic settings.
Boninitic and tholeiitic dykes in the Lewis Hills mantle section of the Bay of Islands ophiolite: implications for magmatism adjacent to a fracture zone in a back-arc spreading environment
Authors: Edwards Stephen J.
Published: April 2011

A detailed, integrated field, petrographic, and geochemical study of the Springers Hill area of the Bay of Islands ophiolite exposed in the Lewis Hills was undertaken to explain the anomalously high abundance of veins and dykes of chromitite, orthopyroxenite, and clinopyroxenite, and their associated dunites, hosted by a refractory harzburgite–dunite mixture. A geodynamic situation is presented, which is constrained by previous studies requiring formation of the Springers Hill mantle section at a ridge–fracture zone intersection, and the whole of the Bay of Islands ophiolite within a back-arc spreading environment. The veins and dykes formed during magmatism at the ridge–fracture zone intersection and along the fracture zone, as progressively hotter, more fertile (richer in clinopyroxene) asthenosphere ascended and was channelled up and along the fracture zone wall. Shallow melting of refractory harzburgite in the presence of subduction-derived hydrous fluids produced light rare earth element (LREE)-enriched boninitic magma from which crystallized chromitites, some of their associated dunites, and orthopyroxenites. This melting event dehydrated much of the mantle in and around the zone of partial melting. Continued rise and shallow partial melting of hotter, more fertile mantle under conditions of variable hydration generated LREE-depleted, low-Ti tholeiitic magma. This magma crystallized olivine clinopyroxenite, some associated dunite, and clinopyroxenite. The final magmatic event may have involved partial melting of mid-ocean-ridge basalt-bearing mantle at depth, ascent of the magma, and formation of massive wehrlite–lherzolite bodies at the ridge–fracture zone intersection and along the fracture zone. Ridge–fracture zone intersections in suprasubduction-zone environments are sites of boninitic and tholeiitic magmatism because refractory asthenospheric mantle may melt as it is channelled with subduction-derived fluids to shallow depths by the old, cold lithospheric wall of the fracture zone. Heat for melting is provided by the ascent of hotter, more fertile mantle. Extremely refractory magmas do not occur along "normal" oceanic fracture zones because volumes of highly refractory mantle are much less, subduction-derived hydrous fluids are not present, and fracture zone walls extend to shallower depths.
Petrology and age of the Mechanic Settlement Pluton, Avalon terrane, southern New Brunswick
Authors: Grammatikopoulos A. L. , Barr Sandra M. , Reynolds P. H. , Doig R.
Published: April 2011

The Mechanic Settlement Pluton, located at the northern margin of the Caledonian Highlands in southern New Brunswick, is composed of rocks ranging from ultramafic (lherzolite, plagioclase-bearing lherzolite) through mafic (mainly olivine gabbronorite and gabbro) to intermediate (quartz diorite and monzodiorite). Spatial distribution of these lithologies, textural features, and geochemistry are consistent with evolution of a tholeiitic mafic parent magma by crystal fractionation processes, with some evidence for magma mingling between evolved gabbroic and quartz dioritic magmas. The dioritic rocks form most of the southwestern (upper?) part of the pluton, whereas the varied gabbroic rocks with ultramafic layers form the northeastern part. U–Pb (zircon) dating of a quartz diorite sample from the southwestern part of the pluton indicates crystallization at 557 ± 3 Ma. Amphibole and phlogopite in two lherzolite samples from the northeastern part of the pluton gave 40Ar/39Ar dates of 550 ± 5 and 539 ± 5 Ma, respectively, indicating that the pluton cooled rapidly through the closure temperature for amphibole, with subsequent slower cooling to the time of phlogopite closure. The pluton is interpreted to be the intrusive equivalent of basaltic units in the host Coldbrook Group, analogous to granitic plutons elsewhere in the Caledonian Highlands which appear to be the intrusive equivalents of felsic volcanic rocks in the group. These plutonic and volcanic rocks represent a major, short-lived (ca. 560–550 Ma), dominantly bimodal igneous event, apparently related to late Precambrian extension within the Avalon terrane of southern New Brunswick.
Influence of thermophilic bacteria on calcite and silica precipitation in hot springs with water temperatures above 90 °C: evidence from Kenya and New Zealand
Authors: Jones Brian , Renaut Robin W.
Published: April 2011

Hot and boiling springs in Kenya and New Zealand that are emitting water with temperatures more than 90 °C are commonly characterized by a complex array of CaCO3and SiO2precipitates that have been formed through abiogenic and biogenic processes. Thermophilic bacteria are the only microbes that can survive in the boiling water that is discharged into pools around the spring orifice. Analysis of modern substrates from various springs in the Kenya Rift Valley and the Taupo Volcanic Zone in New Zealand shows that they are inhabited by a diverse array of coccoid and filamentous bacteria. In some areas these bacteria produce copious amounts of mucus that coat the substrates. Although the coccoid and filamentous bacteria provide substrates for CaCO3and SiO2precipitation, the microbes do not seem to have any direct influence on the morphology of the precipitates that are produced. Conversely, the mucus found in these hot spring pools selectively takes up elements such as Si, Mg, Al, and Fe, but is not calcified. In many cases the elements that are selectively fixed by the mucus are only present in very low concentrations in the spring water. In one of the Waikite springs in New Zealand, the mucus plays an active role in the formation of the calcite deposits by providing a template for crystal nucleation and binding the small calcite crystals to the substrate. The latter process is especially important because the flowing waters of the spring could easily transport the grains if they were not bound to the substrate.
Oblique extension in the Jurassic trough of the central and eastern High Atlas (Morocco)
Authors: El Kochri Abdesselam , Chorowicz Jean
Published: April 2011

A field structural analysis has been carried out in the High Atlas Mountains of Morocco. Paleostress solutions provide information on the successive orientations of major stress patterns during Mesozoic and Cenozoic time. An initial rift stage in the Early Jurassic is characterized by normal–oblique faults bounding tilted blocks, which are associated with tensional paleostress patterns whose minimum component trends west-northwest–east-southeast. Faults parallel to this direction are interpreted as paleotransfer faults. We assume that the divergent motion responsible for the opening of the rift system in the Early Jurassic was oriented west-northwest–east-southeast, subparallel to the paleotransfer faults and the trend of the minimum component (σ3) of the paleostress field. The east–west-trending Jurassic central–eastern High Atlas rift opened obliquely, and not in a pure strike-slip stress regime along east–west-striking faults as previously proposed. A later stage of rifting (Middle Jurassic) is characterized by large normal faults and is supposed to accompany local movements, probably due to gravity. The uplift of the High Atlas belt occurred mainly during the Cenozoic period as a consequence of a north–south- to northwest–southeast-directed compression related to collision between Europe and Africa.
Mississippian assembly of the Nisutlin assemblage: evidence from primary contact relationships and Mississippian magmatism in the Teslin tectonic zone, part of the Yukon–Tanana terrane of south-central Yukon
Authors: Stevens R. A. , Erdmer P. , Creaser R. A. , Grant S. L.
Published: April 2011

Metamorphosed and ductilely deformed sedimentary, plutonic, and volcanic rocks of the Nisutlin and Anvil assemblages make up the Yukon–Tanana terrane in the Teslin tectonic zone study area. The Nisutlin assemblage consists of siliceous schist–quartzite and graphitic phyllite that share a primary depositional contact, and Early Mississippian tonalite to quartz diorite that intrudes the siliceous schist–quartzite and possibly the graphitic phyllite. The Anvil assemblage includes metagabbro and mafic schist–greenstone that share an intrusive contact relationship. Tonalite to quartz diorite of the Nisutlin assemblage is characterized by minor zircon inheritance with an average Proterozoic age, εNd(350 Ma) values of −2.5 to −6.2, and Nd model ages of 1.50–1.79 Ga. These data suggest that the magmatic bodies have inherited a component of continentally derived material. Primary contact relationships and age data indicate that the Nisutlin assemblage had formed by Mississippian time, and regional correlations show that this assemblage makes up a large part of the Yukon–Tanana terrane of southern Yukon. Assembly of the Nisutlin assemblage by Mississippian time indicates that it did not form as a late Paleozoic and early Mesozoic subduction melange, and it suggests that its tectonic fabrics did not result from the progressive growth of a Permo-Triassic subduction complex. We suggest that the Nisutlin assemblage was part of a crustal block that lay outboard of North America in Mississippian time, and that it lay in the hanging-wall plate of a Permo-Triassic subduction zone as a relatively coherent assemblage, rather than forming within the zone as a subduction complex.
The position and nature of the Gander–Avalon boundary, southern New Brunswick, based on geochemical and isotopic data from granitoid rocks
Authors: Whalen Joseph B. , Fyffe Leslie R. , Longstaffe Frederick J. , Jenner George A.
Published: April 2011

In southern New Brunswick, the Gander–Avalon boundary is obscured by boundary-parallel faults and various cover sequences. Siluro-Devonian granites, which intrude unequivocal Gander or Avalon rocks, display exclusively negative (−1.9 ± 1.0) and positive (+1.9 ± 0.7) εNd(T) signatures, respectively. Such contrasting Nd isotopic signatures, combined with other geochemical differences between plutons, are potentially valuable tools for terrane analysis. Nine small Devonian plutons intruding the boundary zone fall into contrasting geochemical groups with (La/Lu)N <4 and >4. The former are topaz-bearing granites, while the latter are volcanic-arc-type granites. Except for one pluton, with an εNd(T) signature of –2.0, εNd(T) values range from –0.4 to +0.7, spanning the gap between "type" Avalon and "type" Gander plutons. These results suggest the plutons sampled either (i) stratigraphically overlapping or tectonically interleaved Gander and Avalon basement rocks, or (ii) a distinct basement source beneath the boundary zone. Our results demonstrate that the Gander–Avalon boundary in southern New Brunswick is not a simple throughgoing crustal fault, and that the Gander and Avalon zones are underlain by different continental basement blocks. Comparison with results from Newfoundland and Nova Scotia suggests that these basement blocks are continuous throughout the Canadian Appalachians.
Nature and evolution of the eastern margin of lapetus: geochemical and isotopic constraints from Siluro-Devonian granitoid plutons in the New Brunswick Appalachians
Authors: Whalen Joseph B. , Jenner George A. , Longstaffe Frederick J. , Hegner Ernst
Published: April 2011

In the Gander Zone, Ordovician to Devonian, metaluminous to slightly peraluminous plutons, with within-plate affinities, intrude a lower Paleozoic metasedimentary package. During the Siluro-Devonian, εNd(T) and δ18O values of the metasedimentary rocks would have been about −7 to −8 and +10 to +14[Formula: see text], respectively. Granitoid εNd(T) values range from −0.3 to −4.2, δ18O values lie between +6.6 and +10.4[Formula: see text], and published Pb isotopic compositions are radiogenic (207Pb/204Pb > 15.65). εNd(T) values of associated Silurian gabbros are somewhat positive (+1.2 to +2.3); some plutons exhibit evidence for comingling with this mafic component. Potential source materials include enriched-mantle, supracrustal, and infracrustal sources. Although some constraints can be put on the first two sources, the nature of infracrustal material is difficult to evaluate. Heterogeneous data obtained from Silurian plutons can be explained by crust–mantle mixing. If some plutons contain a significant mantle component, then Mesoproterozoic or older crust is required. However, mixing is potentially complex and significant Neoproterozoic contributions cannot be excluded. The more compositionally homogeneous Devonian plutons probably represent partial melts of hybridized lower crust. The crustal component is interpreted as reflecting the seismically defined Central Crustal Block. The Gander Zone was probably deposited on Avalonian Brookville belt basement when it formed part of the Amazonian craton. Gander Zone clastic sediments, which are characterized by pre-Neoproterozoic isotopic signatures, were derived from this composite Gondwanan craton. We attribute Siluro-Devonian plutonism to collision and lithospheric delamination which accompanied, and followed, accretion of Avalonian belts to Laurentia during its collision with Gondwana.
Paleoproterozoic lithotectonic divisions of the southeastern Churchill Province, western Labrador
Authors: James D. T. , Connelly J. N. , Wasteneys H. A. , Kilfoil G. J.
Published: April 2011

The southeastern Churchill Province (SECP) is a Paleoproterozoic system of orogens that formed during collision of the Nain and Superior cratons with a composite lithotectonic terrane that now forms the medial, metamorphic–plutonic core zone of the SECP. In western Labrador, the core zone consists of reworked Archean gneisses, Paleoproterozoic supracrustal rocks, and variably deformed 1.83–1.81 Ga granitic plutons. It is subdivided into three Paleoproterozoic lithotectonic domains (McKenzie River, Crossroads, and Orma), which are separated from each other by dextral transpressive high-strain zones. Crossroads and Orma domains are thought to be derived from Archean high-grade granite–greenstone terrane crust, whereas McKenzie River domain is inferred to have been part of an Archean orthogneiss terrane dominated by the ca. 2776 Ma Flat Point gneiss. U–Pb geochronological data indicate that the igneous precursor of the Flat Point gneiss is >80 Ma older than the oldest tonalité–granite intrusions in Crossroads and Orma domains. The three domains were variably reworked during dextral oblique convergence of the Superior and Rae cratons. Field and geochronological data demonstrate that in McKenzie River and Crossroads domains, 1.83–1.80 Ga tectono-thermal reworking included medium- to high-grade metamorphism and the formation of north-trending structures and regionally persistent high-strain zones. Crossroads domain also contains a significant amount of 1.83–1.81 Ga granitic intrusions, including the southern part of the 500 km long De Pas batholith. Orma domain appears to have escaped Paleoproterozoic metamorphism and deformation, suggesting that a "Hudsonian" tectono-thermal front separates it from Crossroads and McKenzie River domains.
Alleged vertebrate eggs from Upper Cretaceous redbeds, Gobi Desert, are fossil insect (Coleoptera) pupal chambers: Fictovichnus new ichnogenus
Authors: Johnston Paul A. , Eberth D. A. , Anderson Paul K.
Published: April 2011

Small egg-like structures from the Upper Cretaceous (Campanian) Djadokhta Formation of Mongolia were previously interpreted as casts of crocodile, lizard, and turtle eggs, or as inorganic nodules. Identical structures from coeval redbeds at Bayan Mandahu in northern China indicate the structures are not vertebrate eggs, nor of vertebrate origin. Comparisons with Recent and Quaternary beetle (Coleoptera) pupal chambers show close similarities in size, shape, and the presence of a round to irregular exit hole for the adult beetle. Most importantly, the Cretaceous structures are enveloped by a thin clay-rich zone, which is expected if constructed by beetle larvae but inexplicable in any egg or inorganic nodule model. Additional evidence contradicting a vertebrate egg origin for the structures includes (i) the structures are too small to have been laid by turtle or crocodile species occurring in the Bayan Mandahu redbeds; (ii) the structures are isolated, not in clutches or pairs; and (iii) unlike newly hatched soft-shelled lizard eggs, the Cretaceous structures are not collapsed and show a round to irregular exit hole rather than a slit. It is concluded that the egg-like structures are sand casts (steinkerns) of beetle pupal chambers, probably of Scarabaeidae, Tenebrionidae, or Curculionidae. The Cretaceous pupal chambers are assigned to a new ichnogenus, Fictovichnus, and new ichnospecies, Fictovichnus gobiensis and Fictovichnus parvus.
Systematics and taxonomic diversity of squamates from the Upper Cretaceous Djadochta Formation, Bayan Mandahu, Gobi Desert, People's Republic of China
Authors: Gao Keqin , Hou Lianhai
Published: April 2011

Squamate fossils collected for the Sino-Canadian dinosaur expeditions (1986–1990) include some 70 specimens from the Upper Cretaceous (Campanian) Djadochta Formation, exposed at the vicinity of Bayan Mandahu, Inner Mongolia, China. Well-preserved skulls, jaws, postcranial skeletons, and even osteodermal armor document a fossil assemblage composed of at least 18 genera in 8 families. Besides showing considerable taxonomic diversity, several families recorded in the assemblage are of importance in understanding the geologic and biogeographic distribution of the relevant groups, and the paleoenvironment in which these lizards lived. Comparison of the Gobi lizard assemblage with North American and Central Asian assemblages is briefly discussed. Taxonomic differences in the assemblage from that of the Upper Cretaceous in the North American Western Interior reflect endemism and suggest a low frequency of interchange of small terrestrial vertebrates between the two regions during Campanian time. The taphonomic setting of the squamate fossils indicates quick burial in arid to semiarid environments in the Gobi Desert, differing importantly from the Western Interior of North America, where the accumulation of disarticulated jaw fragments reflects postmortem decomposition and fluvial transportation under subtropical to warm temperate conditions.
An atoposaurid neosuchian (Archosauria: Crocodyliformes) from the Lower Cretaceous of Inner Mongolia (People's Republic of China)
Authors: Wu X.-C. , Sues H.-D. , Brinkman D. B.
Published: April 2011

Cranial and postcranial remains from the Laolonghuoze locality in the Ordos Basin, Inner Mongolia (China), represent a previously unrecorded taxon of crocodyliform archosaurs from the Lower Cretaceous Luohandong Formation (Zhidan Group). Several cranial features indicate that this form is referable to the Atoposauridae, which were previously definitely known only from the Upper Jurassic and Lower Cretaceous of Europe. Certain derived characters further indicate that the Ordos material is closely related to, if not actually referable to, Theriosuchus. The Ordos atoposaurid differs from the species of Theriosuchus in only a few features. In view of its fragmentary nature, the new material is identified as cf. Theriosuchus sp. at present.
Unraveling the boundary between turbidites of the Kisseynew belt and volcano-plutonic rocks of the Flin Flon belt, Trans-Hudson Orogen, Canada
Authors: Connors Karen A.
Published: April 2011

The Flin Flon – Kisseynew boundary in the eastern Trans-Hudson Orogen is interpreted here as an early thrust fault that places 1.86–1.84 Ga Kisseynew belt turbidites over previously deformed 1.91–1.88 Ga arc and ocean-floor assemblages of the Flin Flon belt. The basin in which sedimentary rocks of the Kisseynew belt were deposited has been interpreted to have formed partly within the Flin Flon belt. The fault that juxtaposes the two belts is interpreted to have been localized near the ancestral basin margin, resulting in development of a major ramp zone during basin closure. This interpreted ramp zone provides an explanation for the steep to shallow structural transition that corresponds to increasing metamorphic grade. Collapse of the Kisseynew sedimentary basin and juxtaposition of the two belts are attributed to southwest-verging folding and thrusting that initiated prior to emplacement of 1.83 Ga plutons. This magmatism was followed by regional greenschist- to upper-amphibolite-grade metamorphism (1.82–1.805 Ga) and renewed southwest-directed folding and thrusting. Late backfolds developed at the leading edge of the fold-thrust belt. Postpeak metamorphic deformation resulted in large-scale, upright folding of the fold–thrust stack (including the Flin Flon – Kisseynew boundary). This stage of deformation is interpreted to record a transition from southwest-directed transport to northwest-southeast-directed shortening at ~1.8 Ga.
Stratigraphic signature of a terminal Early Cambrian regressive event in the Iberian Peninsula
Authors: Álvaro J Javier , Vennin Emmanuelle
Published: April 2011

In the Iberian Peninsula, the uppermost Lower Cambrian (early Bilbilian age) is represented by the deposition of conglomerates and sandstones, except in a northwestern region (the Cantabrian Mountains), where carbonate deposition took place. These coarse siliciclastic deposits indicate a regressive trend, called the Daroca regression. In its type area (the Iberian Chains, northeast Spain), this regressive episode represents a progradational highstand systems tract, which did not result in widespread subaerial exposure of the shelf. In addition, the absence of important stratigraphical gaps and the good biostratigraphical control based on trilobites and acritarchs in the Iberian Chains permit a correlation of this regressive trend with other neighboring areas, where the top of this trend is represented by a regional unconformity and a hiatus that began in the latest Early Cambrian and extended through early Middle Cambrian times.
Magnetostratigraphy of Quaternary and late Tertiary sediments on Banks Island, Canadian Arctic Archipelago
Authors: Barendregt R W , Vincent J -S , Irving E , Baker J
Published: April 2011

Sediments approximately 50 m thick from Banks Island (Canadian Arctic Archipelago) contain one of the longest terrestrial records of Pleistocene climate changes in North America. Samples have been obtained from 126 horizons distributed among four localitites, of which 116 horizons yielded acceptable paleomagnetic data. In sediments of the Matuyama Reversed Zone, there are recorded at least two and possibly as many as five full continental glaciations, two interglacial intervals, and a nonglacial interval at the beginning which is considered preglacial. Subzones attributable to the Olduvai and Jaramillo are present within the Matuyama Reversed Zone. The Brunhes Normal Zone records three full continental glaciations and three interglaciations. The Brunhes-Matuyama boundary occurs within interglacial deposits. The preglacial Worth Point Formation records a climate milder than today, and cooler than that of the late Tertiary. Based on floral, faunal, stratigraphic, and paleomagnetic constraints, a normal polarity sequence in the Worth Point Formation is assigned to the Olduvai normal polarity subzone (1.95-1.77 Ma). The earliest direct evidence of glaciation on Banks Island occurs in sediments that postdate the Worth Point Formation ( <<1.77 Ma). Consequently, in the western Canadian Arctic, the first continental glaciation postdated the first glaciation in the Canadian Cordillera (2.6 Ma) by at least a million years. The overall mean direction of the Quaternary geomagnetic field in Banks Island does not differ significantly from the geocentric axial dipole field, and these sediments contain no inclination error.
Duration of the Early Cambrian: U-Pb ages of volcanic ashes from Avalon and Gondwana
Authors: Landing Ed , Bowring Samuel A , Davidek Kathleen L , Westrop Stephen R , Geyer Gerd , Heldmaier Wolfram
Published: April 2011

Volcanic zircons from three ashes give a U-Pb date of 511 ± 1 Ma on trilobite-bearing, upper Lower Cambrian (upper Branchian Series) strata of southern New Brunswick that correlate into the Siberian middle Botomian - Toyonian Stage interval. This very young age on the late, but not latest, Early Cambrian of Avalon is consistent both with a 519 ± 1 Ma age on the older Caerfai Bay Shales of south Wales that are tentatively correlated into strata with the oldest Avalonian trilobites (lower Branchian) and with a 517 ± 1.5 Ma age on the Antatlasia gutta-pluviae Zone (trilobites) of Morocco. Determination of a 522 ± 2 Ma zircon age on the Moroccan subtrilobitic Lower Cambrian Lie de vin Formation is consistent with an earlier reported 521 ± 7 Ma age from the Lie de vin but suggests that a 526 ± 4 Ma age on Australian trilobite-bearing Lower Cambrian rocks may be too old. A 33+ Ma duration of the Avalonian Early Cambrian and an 8+ Ma length of the Avalonian trilobite-bearing Lower Cambrian support proposals that most Cambrian time was Early Cambrian and the majority of the Early Cambrian was pretrilobitic.
Detrital zircon constraints on the tectonic evolution of the Gravina belt, southeastern Alaska
Authors: Kapp Paul A , Gehrels George E
Published: April 2011

Upper Jurassic - Lower Cretaceous marine clastic strata and mafic to intermediate volcanic rocks of the Gravina belt are part of a complex suture zone separating the Alexander and Wrangellia terranes on the west from the Yukon-Tanana and Stikine terranes to the east. U-Pb ages have been determined on 118 single detrital zircon grains from Gravina strata in an effort to determine the tectonic setting of the Gravina belt and the paleoposition of outboard terranes prior to their Late Cretaceous juxtaposition against inboard terranes. Samples from five stratigraphic units yield ages of 105-120 (n = 5), 140-165 (n = 56), 310-380 (n = 17), 400-450 (n = 19), 520-560 (n = 5), 920-1310 (n = 5), and 1755-1955 Ma (n = 5). The 105-120 and 140-165 Ma grains were shed primarily from arc-related plutons that lie outboard of the Gravina belt. The lack of 120-140 Ma ages coincides with a lull in magmatism in the outboard arc and in the western United States, which suggests that Gravina strata accumulated during major changes in plate motion along the Cordilleran margin. The 400-560 Ma zircons were derived from rocks of the Alexander terrane which also lie to the west. In contrast, the 310-380 and >900 Ma grains were apparently shed from inboard regions. Likely sources include the Yukon-Tanana and Stikine terranes in the northern Cordillera and assemblages in the northern California region which contain igneous rocks and detrital zircons of the appropriate ages. Our data accordingly support models in which the Gravina basin formed in narrow rift or transtensional basins, whereas the outboard Alexander and Wrangellia terranes were located along the California - Oregon - Washington - British Columbia - Alaska margin. Our data are less supportive of models in which the Gravina strata and underlying Alexander and Wrangellia terranes were separated from western North America by a large ocean basin, or were located along the coast of Mexico.
Braided stream aggradation on an alluvial fan margin: Emerald Lake fan, British Columbia
Authors: Goedhart Marc L , Smith Norman D
Published: April 2011

Evolving bar and channel patterns were observed at the distal margin of an active alluvial fan at Emerald Lake, British Columbia, during peak midsummer flows. At the fan margin, bed slope is 0.024, sediment is predominantly coarse gravel, flow is shallow and fluctuating, and sediment transport and deposition are dominated by chutes and lobes. Flow unconfinement at the exit of rapidly formed shallow scour channels typically results in deposition of sediment lobes 0.2 m thick and 10-250 m2 in area. Closely spaced deposition of a number of these sediment lobes results in aggradation of composite sediment sheets. One such sheet, monitored daily over a 15 day period, deposited 129 m3 of gravel over 710 m2 of adjacent marsh sediment, locally extending the distal fan margin by 39 m. Thickness of the aggraded bed varied up to 0.37 m, depending on surface topography. During active deposition, individual lobe deposits formed simple unit bars that partly projected above the water surface. These bars caused local flow division that, together with avulsion of the dominant channel, initiated a braided stream pattern. Complex braid bars composed of several annealed lobe remnants are gradually exposed as waning discharge becomes confined to adjacent chutes. The newly aggraded fan margin is mainly composed of massive to crudely stratified imbricated gravel with interstratified, discontinuous, centimetre-thick finer grained layers. High-angle cross-stratification was not observed. Since chutes and lobes dominate sediment transport and deposition in streams at the distal margin of this rapidly aggrading fan, it is likely that similar deposits should be present in many ancient alluvial fan sequences, but as yet have gone largely unrecognized.
The big flush: paleomagnetic signature of a 70 Ma regional hydrothermal event in displaced rocks of the northern Canadian Cordillera
Authors: Wynne P Jane , Enkin Randolph J , Baker Judith , Johnston Stephen T , Hart Craig JR
Published: April 2011

The 70 Ma Carmacks Group, a subaerial volcanic succession which once covered much of central southwest Yukon, has a paleomagnetic remanent direction which passes the fold test and the reversal test. A new collection of 13 sites, combined with 13 sites from a previous study, renders a pole (088.6°E, 78.4°N, A95 = 7.8°) which is far-sided with respect to the pole for cratonic North America and implies a displacement from the south of 1900 ± 700 km. Late Triassic Mandanna Member red beds and Early Jurassic Nordenskiöld Formation tuffs, deformed in the Late Jurassic, fail the fold test and conglomerate test but pass a contact test with Eocene dykes. The postdeformational remanent direction is identical to that isolated from the Carmacks Group. The magnetic signature contained in these older formations is probably an overprint produced by an extensive hydrothermal system active during Carmacks extrusion. Geological work indicates that the Carmacks Group is plume related. Given its paleomagnetic latitude and geological nature, we hypothesize that the Carmacks Group is a displaced segment of the Yellowstone hot-spot track, and the hydrothermal system which remagnetized the older rocks was established by mantle upwelling below the region.
40Ar/39Ar dating of detrital micas from Oligocene-Pleistocene sandstones of the Olympic Peninsula, Klamath Mountains, and northern California Coast Ranges: provenance and paleodrainage patterns
Authors: Aalto K R , Sharp W D , Renne P R
Published: April 2011

Sandstones of the Eocene-Miocene Hoh assemblage of the Olympic Peninsula and Late Oligocene - Miocene Weaverville Formation (Klamath Mountains) were studied to determine if the Hoh sandstones could be tectonically transported equivalents of the Weaverville Formation. Distinct Hoh sandstone types exposed between La Push and the Hoh River include (1) highly brecciated and veined, quartz-poor, mica-poor volcaniclastic sandstone preserved in mélange blocks; and (2) relatively unveined and unbrecciated, quartzose micaceous sandstone preserved in mélange blocks and bounding turbidites. 40Ar/39Ar laser heating analyses of single crystals of detrital muscovite grains from quartzose Hoh sandstones yield Late Cretaceous - early Tertiary ages, consistent with contributions to Hoh detritus from the Idaho batholith. Volcaniclastic mélange block sandstones could be derived from older Tertiary volcanic terranes of the northeast Olympic Peninsula, or from Mesozoic accretionary terranes. Analyses of muscovites from the fluviatile Weaverville Formation of the Klamath Mountains, California, yield Pennsylvanian ages with a possible source within the Klamath Central Metamorphic terrane. No provenance link was detected between the Hoh assemblage and Weaverville Formation. Analyses of muscovites from Pliocene and Pleistocene sandstones of the Wildcat Group of the northern California Coast Ranges yield both Cretaceous - early Tertiary and Pennsylvanian ages, suggesting derivation from both local and distant sources. Although an ancestral "Snake River" paleodrainage system to the Klamath Mountains region was shutoff during Weaverville sedimentation, it may have been reestablished in the Late Miocene when Idaho-derived sediments were again transported to northwestern California.
Geochemical and Nd isotopic evolution of Paleoproterozoic arc-type granitoid magmatism in the Flin Flon Belt, Trans-Hudson orogen, Canada
Authors: Whalen Joseph B , Syme Eric C , Stern Richard A
Published: April 2011

Granitoid magmatism spans three Flin Flon Belt evolutionary stages: (i) "evolved" arc (~1920 Ma) plus early juvenile arc (1904-1880 Ma) plutonism during intraoceanic arc-back-arc formation; (ii) early (1878-1860 Ma) and middle (1860-1844 Ma) successor arc plutonism following accretion and successor arc(s) development and; (iii) late (1843-1826 Ma) successor arc plutonism accompanying successor basin formation and waning arc magmatism. Amphibole-bearing mineralogy, metaluminous compositions, and igneous microgranitoid enclaves indicate derivation from infracrustal sources. Predominance of intermediate calc-alkaline compositions and negative Nb anomalies on normalized patterns over a 46-77 wt.% silica range indicate an arc setting. Basaltic end members indicate important contributions directly from the mantle. εNd(T) values are predominately in the range 0 to +4.3, reflecting mixing between depleted mantle melts and an Archean crustal component preserved in evolved arc plutons (-3.9 to -6). Temporal variations include the following: (i) early juvenile arc plutons are low K, high field strength element (HFSE) depleted, with relatively flat rare earth element (REE) patterns and negative Eu anomalies, indicative of low-pressure partial melting - fractionation in the mantle wedge, with residual pyroxene and plagioclase; (ii) early and middle successor arc plutonism is medium K, with steep REE patterns and no Eu anomalies, indicative of input from melting of basaltic sources (likely subducted back-arc oceanic crust) under high-pressure conditions with residual garnet and (or) amphibole and no plagioclase; (iii) late successor arc plutons are high K, more HFSE enriched, with both variable REE pattern slopes and Eu anomalies, indicative of a significant petrogenetic role of recycling of preexisting juvenile arc - accretionary complex crust.