2019

Permanent URI for this collectionhttps://hdl.handle.net/1807/92950

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Observations: What for
(Canadian Science Publishing, 2019-06-21) Şengör, Celâl
Observations are to test hypotheses and without hypotheses there can be no usable observations. Geology students should be taught to be independent, bold, imaginative thinkers before they become assiduous observers.
Geochronology, geochemistry, Sr–Nd–Hf isotopic composition of the late Permian adakite in West Ujimqin, Inner Mongolia: petrogenesis and tectonic implications
(Canadian Science Publishing, 2019-09-30) Fan, Yuxu; Xiao, Qinghui; Li, Tingdong; Cheng, Yang; Li, Yan; Guo, Lingjun; Luo, Pengyue
We report new zircon U–Pb ages, whole-rock major and trace elements, and the Sr–Nd–Hf isotope composition for adakitic intrusives collected from the West Ujimqin district in the Southeast region of the Central Asian Orogenic Belt (CAOB). These data provide important constraints on the petrogenetic evolution and geodynamic setting of late Permian magmatism in the Southeast CAOB. The U–Pb dating of zircon shows that the ages of Seerbeng pluton and Nuhetingshala pluton in West Ujimqin are 255.3 0.71 Ma and 254.4 1.2 Ma, respectively, which signifies that these are products of magmatic activity in the late Permian. The adakitic intrusives are characterized by high Sr (Sr ≥ 741 ppm), low Y, low Yb, as well as high Sr/Y ratios, and strongly fractionated rare earth elements (10.3
Hyperpycnal flow depositional characteristics and model in an ancient continental basin: a record from the Oligocene Lower Huagang Formation in the Xihu Sag, East China Sea Shelf Basin
(Canadian Science Publishing, 2019-01-20) Liu, Jiangyan; Zhu, Rui; Zhang, Changmin; Hou, Guowei; He, Miao; Huang, Lingyu
Modern observations have determined the presence of hyperpycnal flows; however, their presence in ancient rocks is scarcely reported in the literature, particularly with respect to continental strata. The present study is the first to use core and thin-section analyses and examination of physical reservoir properties to identify hyperpycnal flow sediment from the lower section of the Oligocene Huagang Formation in the central Xihu Sag, East China Sea Shelf Basin. The multiple fine sandy layers are characterized by lower reverse-graded and upper normal-graded bedding with horizontal bedding, climbing-ripple lamination, wavy bedding, and small foreset laminae. Microerosion surfaces are occasionally present between the reverse-graded and normal-graded bedding, and plant fragments are sometimes visible in the deposits. The same grain size sequence changes are observed in the thin sections. This lithologic combination is considered to be related to hyperpycnal flow sedimentation caused by flood events. The lower reverse-graded and upper normal-graded bedding sequences indicate that the flood energy first increased then decreased and the microerosion surfaces were formed through erosion of lower sediments by the flood. Hyperpycnal flows can directly transport deposits from an estuary to a deep-water basin, which distinguishes them from typical turbidity currents. This study also establishes a sedimentary model of the hyperpycnal flow in lacustrine basin, which can be used as a reference for future hyperpycnal deposit studies.
Geology, geochronology, and fluid inclusion studies of the Xiaorequanzi volcanogenic massive sulphide Cu–Zn deposit in the East Tianshan Terrane, China
(Canadian Science Publishing, 2019-10-11) He, Xi-Heng; Deng, Xiao-Hua; Bagas, Leon; Zhang, Jing; Li, Chao; Zhang, Wen-Dong
The Xiaorequanzi Cu–Zn deposit is in the westernmost part of East Tianshan Terrane in northwestern China. The deposit is unique in the region being a volcanogenic massive sulphide (VMS) deposit located near a zone (or belt) containing giant late Paleozoic porphyry Cu deposits. Aiming to better understand the genesis of the mineral deposits in the terrane and their tectonic setting, we report our findings of detailed studies on fluid inclusion microthermometry, Re–Os dating of chalcopyrite from the massive ore, and U–Pb dating of zircons from the host volcanic rocks. There are two sulphide stages with early pyrite succeeded by chalcopyrite–sphalerite, which are hydrothermally overprinted and supergene enriched. The hydrothermal overprinting is characterised by quartz–sulphide veins crossed by carbonate-rich quartz veins. Quartz from the chalcopyrite–sphalerite stage is characterised by primary fluid inclusions containing H2O–NaCl(–CO2) and homogenise at 228–392 °C with a salinity of 2.2–13.3 wt.% NaCl equiv. Secondary fluid inclusions related to the hydrothermal overprinting homogenise at 170–205 °C with a salinity of 2.7–12.1 wt.% NaCl equiv. Fluid inclusions in the quartz–sulphide stage of the hydrothermal overprinting contain H2O–NaCl with homogenisation temperatures of 164–281 °C and salinities in ranging from 2.9 to 12.4 wt.% NaCl equiv. Fluid inclusion in the quartz–calcite stage contain H2O–NaCl with homogenisation temperatures of 122–204 °C with salinities of 1.4–12.4 wt.% NaCl equiv. These characteristics are like those of the secondary fluid inclusions in the VMS mineralisation. Combining these findings with H–O isotopic data from previous studies, we propose that the primary mineralising fluid is magmatic in origin. Tuff hosting the mineralisation yields a SHRIMP U–Pb zircon age of 352 ± 5 Ma, which is interpreted as the age of the tuff, and a porphyritic felsite dyke intruding the tuff yields a SHRIMP U–Pb zircon date of 345 ± 6 Ma, interpreted as the emplacement age of the dyke. Chalcopyrite from the main orebody at Xiaorequanzi yields a Re–Os isochron age of 336 ± 13 Ma with an initial 187Os/188Os ratio of 0.25 ± 0.55 (MSWD = 12). Given that the VMS deposit is a syngenetic deposit, we regard the upper ca. 349 Ma limit of the Re–Os date as the approximate age of the chalcopyrite. The three dates are the same within error, and the upper limit of the Re–Os date of ca. 349 is taken as the age of the volcanic, dyke, and mineralisation. The volcanic rocks around the Xiaorequanzi deposit have been previously classified as calc–alkaline to high-K calc–alkaline enriched in large-ion lithophile elements and depleted in high-field-strength elements, which are characteristics indicative of a forearc setting. It is suggested that VMS mineralisation formed in a forearc setting related to the north-directed subduction of the Palaeo-Kangguer or North Tianshan oceanic plates.
Origin and formation of Metabreccia in the Parkin Offset Dike, Sudbury impact structure, Canada
(Canadian Science Publishing, 2019-12-15) Anders, Denise; Osinski, Gordon R.; Grieve, Richard; Pilles, Eric; Pentek, Attila; Smith, David
The 1.85 Ga Sudbury impact structure is considered a remnant of a peak-ring or multi-ring basin with an estimated original diameter of 150 to 200 km. The Offset Dikes are radial and concentric dikes around the Sudbury Igneous Complex (SIC) and are composed of the so-called inclusion-rich Quartz Diorite (IQD) and inclusion-poor Quartz Diorite (QD), and in some Offset Dikes, Metabreccia (MTBX). We carried out a detailed field and analytical investigation of MTBX from the Parkin Offset Dike in the North Range of the Sudbury structure. Our observations suggest that MTBX represents impact breccia that originally formed underneath the Main Mass of the SIC and that was subsequently contact-metamorphosed and entrained during the emplacement of the Parkin Offset Dike. The MTBX bears no resemblance to the QD and IQD in which it is hosted, but it does share many similarities with Footwall Breccia (FWBX), suggesting that the two shared a similar initial origin. A genetic relationship between MTBX and FWBX is also supported by whole rock geochemical analyses.
High-precision U-Pb CA-ID-TIMS dating and chronostratigraphy of the dinosaur-rich Horseshoe Canyon Formation (Upper Cretaceous, Campanian–Maastrichtian), Red Deer River valley, Alberta, Canada
(Canadian Science Publishing, 2019-08-09) Eberth, David A.; Kamo, Sandra L.
The non-marine Horseshoe Canyon Formation (HCFm, southern Alberta) yields taxonomically diverse, late Campanian to middle Maastrichtian dinosaur assemblages that play a central role in documenting dinosaur evolution, paleoecology, and paleobiogeography leading up to the end-Cretaceous extinction. Here, we present high-precision U–Pb CA–ID–TIMS ages and the first calibrated chronostratigraphy for the HCFm using zircon grains from (1) four HCFm bentonites distributed through 129 m of section, (2) one bentonite from the underlying Bearpaw Formation, and (3) a bentonite from the overlying Battle Formation that we dated previously. In its type area, the HCFm ranges in age from 73.1–68.0 Ma. Significant paleoenvironmental and climatic changes are recorded in the formation, including (1) a transition from a warm-and-wet deltaic setting to a cooler, seasonally wet-dry coastal plain at 71.5 Ma, (2) maximum transgression of the Drumheller Marine Tongue at 70.896 ± 0.048 Ma, and (3) transition to a warm-wet alluvial plain at 69.6 Ma. The HCFm’s three mega-herbivore dinosaur assemblage zones track these changes and are calibrated as follows: Edmontosaurus regalis – Pachyrhinosaurus canadensis zone, 73.1–71.5 Ma; Hypacrosaurus altispinus – Saurolophus osborni zone, 71.5–69.6 Ma; and Eotriceratops xerinsularis zone, 69.6–68.2 Ma. The Albertosaurus Bonebed — a monodominant assemblage of tyrannosaurids in the Tolman Member — is assessed an age of 70.1 Ma. The unusual triceratopsin, Eotriceratops xerinsularis, from the Carbon Member, is assessed an age of 68.8 Ma. This chronostratigraphy is useful for refining correlations with dinosaur-bearing upper Campanian–middle Maastrichtian units in Alberta and elsewhere in North America.
Using geographic information systems to make transparent and weighted decisions on pit development: incorporation of interactive economic, environmental, and social factors
(Canadian Science Publishing, 2019-11-16) Risk, C.; Zamaria, S.A.; Chen, J.; Ke, J.J.; Morgan, G.; Taylor, J.; Larsen, K.; Cowling, S.A.
A geographic information systems platform with an analytical hierarchy process was employed to rank the importance of different economic, environmental, and social factors involved in choosing the location of an open-pit operation within a small county in the province of Ontario, Canada. Weighted environmental (hydraulic conductivity, soil types, slope, and elevation) and social (distance from population zones) overlays were combined and then compared against a map of potential sources of sand and gravel deposits (economic factor) to locate the most ideal location for a pit. This resulted in the delineation of four ideal locations for the operation in the north of the county. Here, permeability values are low and there are no major population centres. The decision-making tool developed here has the ability to adapt to changing social and (or) environmental criteria and could greatly improve transparency in natural resource management decisions. The largest limitation to this decision-making tool is that it treats all water sources as equal. As research continues to identify different ecosystem services (i.e., acid neutralization, low contamination source waters, and high biological diversity) for different types of waterways, a ranking scheme could be added along the lines of high versus low conservation priorities for nonrenewable freshwater lake and river resources.
The nature and origin of furrows in lake-bed sediments: Okanagan Lake, British Columbia, Canada
(Canadian Science Publishing, 2019-10-24) Nowak, Raphael; Bauer, Bernard O.; Siddiqua, Sumi
Recent sonar surveys of Okanagan Lake, in the central interior of British Columbia, revealed the presence of linear, contour-parallel furrows at depths of 50–130 m. Underwater video imagery shows these furrows to be approximately 0.5–1 m wide by 0.5–1 m deep with variable lengths extending 1–100 m. Their cross-sectional topology varies from semi-rectangular features with steep-walled sides that expose weak laminations in the sediments to shallow U-shaped troughs that appear to be infilled by lacustrine mud. The most likely origin of the furrows is extension deformation (i.e., tension fracturing) caused by periodic failure along the steeply inclined marginal slopes of this deep, glaciated lake basin. A positive feedback mechanism leading to arrested downslope movement, based on the recent findings reported in Carey et al. (2019), is suggested to apply. Less likely alternative explanations are considered and dismissed. The furrows highlight the nature of long-term geomorphic processes in lacustrine environments that contribute to sediment transport and deposition on the lake bed but are not directly linked to the action of surface waves and currents.
Converging ice streams: an unreasonable hypothesis for deposition of the Oak Ridges Moraine, southern Ontario
(Canadian Science Publishing, 2019-12-06) Sharpe, David R.; Russell, Hazen A.J.
The hypothesis that Oak Ridges Moraine (ORM) formed between converging ice streams requires critical testing. Available data (e.g., digital elevation models, maps, seismic profiles, continuous cores, and pit exposures) are inconsistent with the converging ice stream hypothesis. Combined analysis of landform and subsurface data permits testing the ORM area stratigraphic sequence and sedimentary origin. Stratigraphic data indicate that drumlinized Newmarket Till, incised by north–south-oriented (tunnel) valleys, extends beneath ORM. Thus, streamlining on Newmarket Till is older than ORM and has no direct bearing on its formation. The north–south-trending valleys truncate streamlined Newmarket Till, extend to bedrock, have inset eskers, and occur beneath ORM. Hence, these valleys are older than ORM and have a subglacial rather than a proglacial origin. Overlying the mega-scale lineations and incised channels are topographically elevated (>300 m a.s.l.), ORM glaciofluvial–glaciolacustrine sequences. Its east to west paleoflow trend indicates an east–west-oriented hydraulic gradient, orthogonal to expected gradients of proposed north-south converging ice streams. The exclusive presence of ORM meltwater sediments, with rare deformation, is incompatible with a converging ice stream, deforming-bed hypothesis. Halton sediment grades upward from stratified sand (ORM) to interbedded diamicton and glaciolacustrine sediment, rather than deformation till. Halton sediment overlies ORM and consequently the proposed Halton ice streaming is younger than the moraine. Halton Till is present in few of the predicted ice stream areas, and where Halton Till is present, it has no mega-scale lineations. In sum, the weight of evidence unequivocally argues against a converging ice-stream process model for the ORM.
Biological mats in siliciclastic sediments of the Paleoproterozoic Gunflint Formation, northwestern Ontario, Canada
(Canadian Science Publishing, 2019-11-16) Fischer, Sadie; Fralick, Philip
The Gunflint Formation of southern Superior Province, Canada, contains an extensive array of stromatolite morphologies and associated fossilized bacteria. It, and correlative units in the United States, provided some of the most persuasive early interpretations of stromatolites and evidence of Precambrian bacterial life. This study examined the siliciclastic rocks in the Gunflint Formation and discovered a multitude of features formed by the development of cohesive biogenic mats on bedding surfaces. In former shallow subtidal depositional settings evidence of mat erosion was most common, with the presence of various types of wrinkle structures. Microscopically carbonaceous layers and rip-up fragments representing mats and their eroded remnants are well preserved. This emphasizes the abundance of bacterial life in the shallow nearshore of the Gunflint Formation about 1.88 billion years ago and further indicates an increased flux of reductants was necessary during this time period to establish low oxygen levels in the ocean.
Contact-style magmatic sulphide mineralisation in the Labrador Trough, northern Quebec, Canada: implications for regional prospectivity
(Canadian Science Publishing, 2019-11-23) Smith, William Daniel; Maier, Wolfgang D.; Bliss, Ian
The Labrador Trough in northern Qubec is currently the focus of ongoing exploration for magmatic Ni-Cu-PGE sulphide ores. This geological belt hosts voluminous basaltic sills and lavas of the Montagnais Sill Complex, which are locally emplaced amongst sulphidic metasedimentary country rocks. The recently discovered Idefix PGE-Cu prospect represents a stack of gabbroic sills that host stratiform patchy net-textured sulphides (0.2 to 0.4 g/t PGE + Au) over a thickness of ~ 20 m, for up to 7 km. In addition, globular sulphides occur at the base of the sill, adjacent to the metasedimentary floor rocks. Whole-rock and PGE geochemistry indicates that the sills share a common source and that the extracted magma underwent significant fractionation before emplacement in the upper crust. To develop the PGE-enriched ores, sulphide melt saturation was attained before final emplacement, peaking at R factors of ~ 10,000. Globular sulphides entrained along the base of the sill ingested crustally-derived arsenic and were ultimately preserved in the advancing chilled margin.
Timing of magmatic crystallization and Sn-W-Mo greisen vein formation within the Mount Douglas Granite, NB, Canada
(Canadian Science Publishing, 2019-11-23) Mohammadi, Nadia; McFarlane, Christopher R.M.; Lentz, David D.R.; Thorne, Kathleen G
U-Pb geochronology was applied to a combination of magmatic and hydrothermal minerals to help constrain the timing of emplacement of three units in the Mount Douglas Granite (MDG) and reveal their association with a complex mineralized hydrothermal system containing endogranitic Sn-W-Mo-Zn-Bi-U-bearing greisen/sheeted veins within the pluton. Magmatic monazite and zircon U-Pb ages obtained by LA ICP-MS overlap at 368 Ma, recording a Late Devonian crystallization age for the MDG. Although discrimination, outside analytical error, of sequential pulses of magmatism is beyond the resolution of LA ICP-MS U-Pb geochronology, geochemical variations of monazite accompanied by previous whole-rock geochemical analyses support a progressive fractional crystallization process starting from a parental magma (Dmd1), leading to the generation of Dmd2, and finally Dmd3 as the most fractionated unit. Hydrothermal uraninite, cassiterite, and monazite, collected from endogranitic greisen/sheeted veins, reveal evidence for syn-magmatic-related mineralization and a longer-lived post-magmatic hydrothermal system. The first stage is recorded by concordant uraninite dates at 367 3 Ma and by an inverse isochron lower intercept of 362 8 Ma for cassiterite. In contrast, hydrothermal monazite crystallized over a wider range of ages from 368 to 344 Ma, demonstrating post-magmatic hydrothermal activity within the MDG. These magmatic and hydrothermal ages combined with the geochemical signature of the MDG are similar to those documented for the nearby Mount Pleasant Sn-W-Mo-Bi-In granite-related deposit, which suggests that the two mineralizing systems occur at different levels of the same magmatic system.
New insights into the geologic evolution of the Grenvillian Trenton Prong inlier, Central Appalachian Piedmont, USA
(Canadian Science Publishing, 2019-11-16) Volkert, Richard
New geochemical and 40Ar/39Ar hornblende and biotite data from the Grenvillian Trenton Prong inlier provide the first constraints for the identification of lithotectonic units, their tectonic setting, and their metamorphic to post-metamorphic history. Gneissic tonalite, diorite, and gabbro compose the Colonial Lake Suite magmatic arc that developed along eastern Laurentia prior to 1.2 Ga. Spatially associated low- and high-TiO2 amphibolites were formed from island-arc basalt proximal to the arc front and mid-ocean ridge basalt-like basalt in a back-arc setting, respectively. Supracrustal paragneisses include meta-arkose derived from a continental sediment source of Laurentian affinity and metagraywacke and metapelite from an arc-like sediment source deposited in a back-arc basin, inboard of the Colonial Lake arc. The Assunpink Creek Granite was emplaced post-tectonically as small bodies of peraluminous syenogranite produced through partial melting of a subduction-modified felsic crustal source. Prograde mineral assemblages reached granulite- to amphibolite-facies metamorphic conditions during the Ottawan phase of the Grenvillian Orogeny. Hornblende 40Ar/39Ar ages of 935–923 Ma and a biotite age of 868 Ma record slow cooling in the northern part of the inlier following the metamorphic peak. Elsewhere in the inlier, biotite 40Ar/39Ar ages of 440 Ma and 377–341 Ma record partial to complete thermal resetting or new growth during the Taconian and Acadian orogens. The results of this study are consistent with the Trenton Prong being the down-dropped continuation of the Grenvillian New Jersey Highlands on the hanging wall of a major detachment fault. The Trenton Prong therefore correlates to other central and northern Appalachian Grenvillian inliers and to parts of the Grenville Province proper.
Discovery of a significant cave entrance in stripe karst, Horsethief Creek Group, Wells Gray Provincial Park, British Columbia, Canada
(Canadian Science Publishing, 2019-12-07) Hickson, Catherine; Pollack, John; Struik, Lambertus; Hollis, Lee; Yonge, Chas
In April 2018, a significant cave entrance was recognized during an aerial survey in Wells Gray Provincial Park, British Columbia. A September 2018 assessment of the site confirmed one of the largest known, and previously undocumented, cave entrances in Canada. The feature is a large vertically walled sink swallowing a small river, likely leading to a spring 2.16 km horizontally from, and 460 m below, the sink. The entrance shaft was partially descended, surveyed, and found to have a volume of over 450 000 m3. Formed in a carbonate unit of the upper Proterozoic Horsethief Creek Group, the cave entrance occurs in stripe karst extending well beyond the known cave drainage. The disappearing river drains an area of 6.3 km2 in a valley containing two small glaciers. The river has a low flow (September) rate estimated at 0.3–0.5 m3/s, comparable with some of the largest sinks in Canada. Historic aerial photographs of the area show the entrance was hidden by perennial snowfields until regional climatic warming caused the snow plug to collapse sometime within the past decade.
Cranial variation in Gryposaurus and biostratigraphy of hadrosaurines (Ornithischia: Hadrosauridae) from the Dinosaur Park Formation of Alberta, Canada
(Canadian Science Publishing, 2019-09-10) Lowi-Merri, Talia M.; Evans, David C.
The Dinosaur Park Formation (Campanian) of Alberta documents one of the most diverse assemblages of hadrosaurine dinosaurs. Historically, two species of the genus Gryposaurus Lambe, 1914 have been recognized in the Dinosaur Park Formation, Gryposaurus notabilis Lambe, 1914 and Gryposaurus incurvimanus Parks, 1919, which are differentiated primarily on their nasal arch morphology. These two species have recently been suggested to represent either variable morphs within G. notabilis (e.g., ontogeny) or two distinct taxa within an evolving Gryposaurus lineage (e.g., anagenesis). These alternative hypotheses have never been adequately tested via detailed morphological comparisons, morphometrics, or biostratigraphy. A geometric morphometric analysis of hadrosaurine skulls from the Dinosaur Park Formation was performed to assess the influence of ontogeny on skull morphology. Gryposaurus incurvimanus skulls were found to be distinctly smaller, and morphologically divergent from those of G. notabilis, with larger G. notabilis skulls having higher nasal arches set farther back on the skull, a size-correlated pattern consistent with ontogenetic nasal retraction documented in other hadrosaurids. Stratigraphic data were used to map this morphology through time, to evaluate the anagenesis hypothesis. The stratigraphic distributions of the two species showed considerable overlap, rejecting anagensis and indicating that the sampled individuals lived over a short period of time (<0.5 Myr). Overall, our results suggest that the hypothesis that G. incurvimanus and G. notabilis represent different ontogenetic stages within a single species cannot be rejected. This study improves our understanding of the extent of potential individual variation within a single Gryposaurus species, which will be useful in assessing the validity of other hadrosaurines.
Ancient DNA reveals northwest range extension of Richardson’s ground squirrel (Urocitellus richardsonii) into northeastern British Columbia, Canada, during the Late Pleistocene
(Canadian Science Publishing, 2019-02-07) Royle, Thomas C.A.; Yang, Dongya Y.; Driver, Jonathan C.
Ancient DNA was extracted from 12 500 to 10 500 year old ground squirrel bones from Tse’K’wa, an archaeological site in the Peace River region of northeastern British Columbia, Canada. Analysis of mitochondrial DNA from seven individuals demonstrates that all are Urocitellus richardsonii (Richardson’s ground squirrel), a species not found in the region today. Phylogenetic and sequence analyses indicate these individuals share a previously undocumented mitochondrial control region haplotype that is most closely related to haplotypes observed in modern specimens from Saskatchewan and Montana. At the end of the Pleistocene these ground squirrels extended their range north and west into open vegetation communities that developed when ice sheets melted and glacial lakes drained. They were subsequently extirpated from the Peace River region when forests replaced earlier pioneering vegetation communities.
Petrogenesis of early Permian granitic dykes in the Wulanhuduge area, central Inner Mongolia, North China: constraints from geochronology, geochemistry, and Sr–Nd–Pb isotopes
(Canadian Science Publishing, 2019-10-25) Zhang, Xiang-xin; Gao, Yong-feng; Lei, Shi-he
Early Permian granitic dykes are well developed in the Wulanhuduge area, central Inner Mongolia, North China. In this study, we investigated the petrography, geochronology, and whole-rock geochemistry of the granite porphyry dykes in the Wulanhuduge area. Laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating yielded 206Pb/238U ages of 289–288 Ma for these granite porphyry dykes, indicating they were emplaced in the early Permian. These granitic dykes are high in silica and alkali contents, and low in total Fe2O3, MgO, CaO, and P2O5 contents. They show enrichment in large-ion lithophile elements such as Rb, Ba, Th, U and K, and depletion in high field strength elements such as Nb, Ta, and Ti, typical of arc-like magma. Their Sr–Nd–Pb isotopic compositions indicate low initial 87Sr/86Sr ratios (0.70306–0.70564), positive εNd(t) values (+3.3 to +3.9), and radiogenic Pb isotopes with (206Pb/204Pb)i of 18.080–18.616, (207Pb/204Pb)i of 15.497–15.555, and (208Pb/204Pb)i of 37.713–38.175. These geochemical data, along with petrological characteristics, suggest that they belong to high K calc-alkaline I-type granites and were generated by the partial melting of the mafic rocks from the pre-existing juvenile arc crust in a post-subduction extensional setting caused by slab breakoff. Therefore, the emplacement of these granite porphyry dykes in the Wulanhuduge area may represent the end stage of the subduction–accretion process in central Inner Mongolia.
Cretaceous flora and fauna of the Sustut Group near the Sustut River, northern British Columbia, Canada
(Canadian Science Publishing, 2019-08-09) Arbour, Victoria; Evans, David C.; Simon, D. Jade; Cullen, Thomas; Braman, Dennis R.
A partial ornithischian dinosaur skeleton discovered near the Sustut River in 1971 has, to date, represented the only vertebrate fossil remains recovered from the Sustut Basin in northern British Columbia, Canada, but the geological provenance and age of this specimen has remained unclear. We provide new data on the age of this dinosaur specimen based on reconnaissance palaeontological prospecting along the Sustut River, and also report new vertebrate and plant fossils from this region. A skeletal fragment of a species of the turtle Basilemys Hay, 1902 was discovered at a site closely matching field notes describing the initial collection of the ornithischian dinosaur, suggesting that the new turtle fossil derives from the same locality as the dinosaur. Palynomorphs collected from this site include the marker taxon Pseudoaquilapollenites bertillonites (Sriv.), found in the lower Hell Creek Formation, and suggesting an age range of between 68.2 and 67.2 Ma for the locality. To the west of this locality we discovered multiple new fossil plant sites preserving wood and the leaves of Metasequoia Miki and several angiosperms, and one site preserved fronds resembling a species of the tree fern Coniopteris Brong., suggesting a Cenomanian or older age for sites in the area. The complex translational history of the Intermontane Terrane means that the newly discovered turtle may not represent a northern range extension for Basilemys, but it does represent one of the westernmost occurrences of this genus. The discovery of new vertebrate fossil remains in a region with relatively little accessible outcrop at present indicates the potential for future discoveries in the higher elevation outcrops of the Sustut Basin in this mountainous region of British Columbia.
Early–Middle Permian postcollisional granitoids in the northern Beishan orogen, NW China: Evidence from U–Pb ages and Sr–Nd–Hf isotopes
(Canadian Science Publishing, 2019-10-12) Min, Li; Houtian, Xin; Bangfang, Ren; Yunwei, Ren; Wengang, Liu
The geochemistry and Sr–Nd isotope, zircon U–Pb, and zircon Hf isotope compositions are reported for monzogranites and granodiorites from the Hazhu area in the northern Beishan orogen, NW China. Zircon U–Pb dating yields two ages of 270.1 1.1 and 277.4 1.2 Ma for the monzogranites and 263.6 1.2 and 262.2 1.1 Ma for the granodiorites. These granitoids are metaluminous to weakly peraluminous I-type and belong to mid-K calc-alkaline and high-K calc-alkaline series. They exhibit high Mg# values and middle degrees of differentiation (D.I. = 70.7–88.1). They are enriched in large-ion lithophile elements and light rare-earth elements and depleted in high field strength elements. They display high (87Sr/86Sr)i ratios of 0.6995 to 0.7070 and high εNd(t) values of 4.37–5.70 with Nd model ages (TDM) of 522–789 Ma. Furthermore, their εHf(t) values are all positive, and Hf isotopic crustal model ages (TC DM = 394–1097 Ma) also indicate a juvenile crustal origin. The Hazhu granitoids were derived from common sources of melting from the juvenile crusts. The younger intrusions are more basic, probably as a result of more juvenile lower crust being melted along with asthenospheric upwelling, which led to the addition of more basic components. The tectonic regime transformed from an arc-related compressional setting to postcollisional extension, probably as a result of lithospheric extension and thinning in response to oceanic lithospheric delamination. These granitoids in the northern Beishan orogen were probably emplaced in a postcollisional extensional setting and suggest vertical continental crustal growth in the southern CAOB.
Rock and age relationships within the Talkeetna forearc accretionary complex in the Nelchina area, southern Alaska
(Canadian Science Publishing, 2019-07-03) Barefoot, John; Nadin, Elisabeth S; Newberry, Rainer; Camacho, Alfredo
Subduction-zone processes are challenging to study because of the rarity of good exposures and the complexity of rock relationships within accretionary prisms. We report results of field mapping and petrographic, geochemical, and geochronological analyses of McHugh Complex accretionary prism mlange in south-central Alaska that was recently exposed due to retreat of the Nelchina Glacier. Our new mapping and analyses of the mlange, as well as adjacent Talkeetna arc intrusives, suggests that the previously mapped trace of the Border Ranges fault should shift northward in this location. Detailed petrographic analysis places this mlange exposure with the Potter Creek assemblage of the McHugh Complex. Blocks of pillow lavas within the mlange have both MORB and intra-plate geochemical affinity, attesting to the complex relations of subduction-zone inputs in an alternating erosive–accretionary margin. A new zircon U-Pb age and geochemical analyses of a set of felsic dikes that crosscut the accretionary sequence provide constraints on the regional tectonic evolution, including near-trench plutonism associated with the migration of a subducting spreading ridge along the southern Alaska margin in Paleocene–Eocene time. The McHugh section and crosscutting dikes in this location are pervasively hydrothermally altered, which we attribute to elevated temperatures related to ridge subduction. Late-stage motion along the Border Ranges fault system, which is also recorded in the area, may also have contributed to the widespread alteration. Our data indicate that the Talkeetna volcanic arc and associated accretionary prism sediments were in their current configuration by 55 Ma.

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