DOCSLIB.ORG

Research Article U-Pb and Hf Analyses of Detrital Zircons from Paleozoic and Cretaceous Strata on Vancouver Island, British Colu

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Research Article U-Pb and Hf Analyses of Detrital Zircons from Paleozoic and Cretaceous Strata on Vancouver Island, British Colu GeoScienceWorld Lithosphere Volume 2021, Article ID 7866944, 20 pages https://doi.org/10.2113/2021/7866944 Research Article U-Pb and Hf Analyses of Detrital Zircons from Paleozoic and Cretaceous Strata on Vancouver Island, British Columbia: Constraints on the Paleozoic Tectonic Evolution of Southern Wrangellia Daniel Alberts ,1 George E. Gehrels ,1 and Joanne Nelson 2 1Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA 2British Columbia Geological Survey, Victoria, British Columbia V8W 9N3, Canada Correspondence should be addressed to Daniel Alberts; [email protected] Received 23 February 2020; Accepted 25 January 2021; Published 26 February 2021 Academic Editor: Sarah Roeske Copyright © 2021 Daniel Alberts et al. Exclusive Licensee GeoScienceWorld. Distributed under a Creative Commons Attribution License (CC BY 4.0). Wrangellia is a late Paleozoic arc terrane that occupies two distinct coastal regions of western Canada and Alaska. The Skolai arc of northern Wrangellia in south-central Alaska and Yukon has been linked to the older, adjacent Alexander terrane by shared Late Devonian rift-related gabbros and also by Late Pennsylvanian postcollisional plutons. Late Devonian to Early Permian Sicker arc rocks of southern Wrangellia are exposed in uplifts on Vancouver Island, southwestern British Columbia, surrounded by younger strata and lacking physical connections to other terranes. Utilizing the detrital zircon record of Paleozoic and Cretaceous sedimentary rocks, we provide insight into the magmatic and depositional evolution of southern Wrangellia and its relationships to both northern Wrangellia and the Alexander terrane. 1422 U-Pb LA-ICPMS analyses from the Fourth Lake Formation (Mississippian–Permian) reveal syndepositional Carboniferous age peaks (344, 339, 336, 331, and 317 Ma), sourced from the Sicker arc of southern Wrangellia. These populations overlap in part known ages of volcanism, but the Middle Mississippian cumulative peak (337 Ma) documents a previously unrecognized magmatic episode. Paleozoic detrital zircons exhibit intermediate to juvenile ƐHf ðtÞ values between +15 and +5, indicating that southern Wrangellia was not strictly built on primitive oceanic crust, but instead on transitional crust with a small evolved component. The Fourth Lake samples yielded 49 grains (3.4% of the total grains analyzed) with ages between 2802 Ma and 442 Ma, and with corresponding ƐHf ðtÞ values ranging from +13 to -20. In age—ƐHf ðtÞ space, these grains fall within the Alexander terrane array. They were probably derived from sedimentary rocks in the basement of the Sicker arc. By analogy with northern Wrangellia, this basement incorporated rifted fragments of the Alexander terrane margin as the combined Sicker-Skolai arc system advanced ocean-ward due to slab rollback in Late Devonian to Early Mississippian time. Ultimately, data from detrital zircons preserved in the Fourth Lake Formation provides significant information allowing for an updated tectonic model of Paleozoic Wrangellia. 1. Introduction Wrangellia and Karmutsen Formation of southern Wrangel- lia, that overlie Paleozoic arc-related sequences [1, 2]. Paleo- Wrangellia is one of the most outboard of the major northern zoic sequences of southern Wrangellia comprise the Upper Cordilleran terranes. It occupies two separate regions: south- Devonian to Lower Permian Sicker and Buttle Lake Groups central Alaska and southwestern Yukon (northern Wrangel- [3–7]. Those in northern Wrangellia comprise the Carbonif- lia) and Haida Gwaii and Vancouver Island (southern erous to Lower Permian Skolai Group, including the Station Wrangellia) (Figure 1 inset). It was originally defined as a Creek and Hasen Creek formations [8–13]. coherent terrane based on characteristic thick piles of Until recently, the records of Paleozoic arc activity in Triassic flood basalts, the Nikolai Greenstone of northern southern versus northern Wrangellia were considered to be Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/doi/10.2113/2021/7866944/5292498/7866944.pdf by guest on 23 September 2021 2 Lithosphere Knight inlet Bute inlet 129°W, 50°N Coast Plutonic Complex Tertiary Rocks Nanaimo Eocene Crescent terrane Dragon Property = Eocene Pacifc Rim terrane Bedingfeld Uplif = Buttle Lake Uplif = Cretaceous Nanaimo Group Cowichan Uplif = Wrangellia Terrane Comox Samples Tis Study Jurassic Island Intrusions/ Fourth Lake Samples West Coast Crystalline Complex North Samples Saltspring Jurassic Bonanza Group Island South Samples Ruks, 2015 Triassic Karmutsen Formation Detrital Samples Victoria Devonian Sicker/ Samples CO1 and CO2 Matthews et al., [2017] Trust Fault Carboniferous Buttle Lake Groups 100 km 125°W, 48°N Figure 1: Generalized geologic map of Vancouver Island (modified from Massey et al. [82, 83]). Inset map indicates relevant terranes of the northern Cordillera, location of study area, and general locations for three subdivisions of the Alexander terrane: SEM: Saint Elias Mountain region [17, 18]; SE: Alaska [65, 66, 71]; and BIM: Banks Island assemblage [65]. Abbreviations for displayed tectonic components on inset map: YA: Yakutat; CH: Chugach; CPC: Coast Plutonic Complex; PE: Peninsular; WR: Wrangellia; sWR: southern Wrangellia; nWR: northern Wrangellia; AX: Alexander. Sample locations for this study are denoted with squares. Colored circles are used to represent samples from Ruks [14]. Yellow hexagon represents sample location for samples from Matthews et al. [42]. Dashed ellipses mark the area of uplifts. divergent, with Sicker volcanism confined to the Late Devo- to E-MORB basalts [7]. As such, the Sicker arc has been nian [7] and Station Creek volcanism poorly constrained as modeled as developing in an intraoceanic setting as a possible Carboniferous [11], with Pennsylvanian plutonism [12]. An extension of the Skolai arc, but with no direct connection to Early Mississippian U-Pb age from the base of the Station older terranes [15]. Creek Formation [13] and an extensive database of Devonian This study presents U-Pb ages and Hf isotope composi- to Permian U-Pb and microfossil ages from the Sicker Group tions of detrital zircons from upper Paleozoic strata of south- [14] now support consideration of the Sicker and Station ern Vancouver Island. These data are then used to refine Creek as parts of a single, evolving arc system, such as pro- interpretations on the tectonic evolution of southern Wran- posed by Beranek et al. [15], mainly based on data from gellia. First, the main grain populations will provide addi- northern Wrangellia. tional information on the nature and duration of Paleozoic The tectonic settings of northern and southern Wrangel- arc-related igneous activity. Second, minor grain populations lia are also distinct. Northern Wrangellia lies adjacent to the can be used to test for the possible presence of pre-Late Devo- older Alexander terrane and has been linked to it by Late nian basement to this part of Wrangellia. We analyzed nine Devonian gabbro complexes [13] and Pennsylvanian plu- samples from southern Vancouver Island, including five tonic suites that crosscut the terrane boundary [12, 15]. samples from the Fourth Lake Formation of the Buttle Lake Southern Wrangellia is isolated from other terranes by faults, Group and four samples from the Comox Formation at the by the Late Jurassic Coast Plutonic Complex, and by seaways, base of the Upper Cretaceous Nanaimo Group where it which render its Paleozoic tectonic context highly enigmatic. directly overlies Paleozoic strata (Figure 1). Nanaimo Group Moreover, the Sicker Group of Vancouver Island has been samples were analyzed primarily to gather additional infor- modeled as a Late Devonian nascent arc succession that mation about the Paleozoic history of Vancouver Island via developed on oceanic crust [4–7]. The lowest exposed rock primary and second-cycle zircons potentially preserved in unit, the lower Duck Lake Formation, is a pile of N-MORB these rocks. Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/doi/10.2113/2021/7866944/5292498/7866944.pdf by guest on 23 September 2021 Lithosphere 3 2. Geological Background Near the Duke River fault, the Station Creek Formation is absent, and the Hasen Creek nonconformably overlies the 2.1. Alexander Terrane. The late Paleozoic arc complex at the Late Devonian Steele Creek gabbro complex [13]. The Hasen base of northern Wrangellia has been linked to the adjacent Creek Formation represents postsubduction clastic sedimen- Alexander terrane in terms of probable basement and tec- tation following the Alexander-Wrangellia collision. tonic coevolution [13, 15]. This section begins with a descrip- tion of that older crustal fragment. The Alexander terrane 2.3. Paleozoic Stratigraphy and History of Southern extends over thousand kilometers from the St. Elias Moun- Wrangellia. The oldest rocks on Vancouver Island record tains on the Yukon-Alaska border, through southeast Alaska the early evolution of the southern Wrangellia arc. Included and along the north and central coast of British Columbia are Late Devonian–Carboniferous rocks of the Sicker Group ff (Figure 1 inset). It is a composite of two terranes with di er- and Mississippian–Permian strata of the Buttle Lake Group ent pre-Permian histories, the main Craig subterrane and the (Figures 1 and 3), which are exposed in the Buttle Lake and much smaller Admiralty subterrane of Admiralty Island, Cowichan uplifts of central and southern Vancouver Island southeast Alaska
Load more

Recommended publications
  • Subduction Polarity in Ancient Arcs: a Call to Integrate Geology And
    COMMENT & REPLY Subduction Polarity in Ancient Arcs: A Call to Integrate Geology and Geophysics to Decipher the Mesozoic Tectonic History of the Northern Cordillera of North America: REPLY Terry L. Pavlis, Dept. of Geological Sciences, University of Texas, El Paso, Texas 79968, USA; Jeffrey M. Amato, Dept. of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA; Jeffrey M. Trop, Dept. of Geology and Environmental Geosciences, Bucknell University, Lewisburg, Pennsylvania 17837, USA; Kenneth D. Ridgway, Dept. of Earth, Atmospheric and Planetary Sciences, Purdue University, West Lafayette, Indiana 47907, USA; Sarah M. Roeske, Earth and Planetary Sciences Dept., University of California, Davis, California 95616, USA; and George E. Gehrels, Dept. of Geosciences, University of Arizona, Tucson, Arizona, 85721, USA INTRODUCTION drafts of the paper. However, when we problem is not solved, which underscores We welcome the opportunity to discuss the realized that experts in this field were our conclusion that resolving ancient sub- views expressed by Sigloch and Mihalynuk in actively debating the topic, we reduced our duction polarity problems requires a con- their Comment (Sigloch and Mihalynuk, discussion to a short paragraph. In their certed collaborative effort between the geo- 2020; referred to here as SM) on Pavlis et al. Comment, SM reiterate parts of their model logic and geophysical communities. (2019) because it provides an opportunity to but emphasize a consensus in the geophysi- A foundation of Sigloch and Mihalynuk’s elaborate on the criteria for determining sub- cal community that deep mantle tomo- (2013, 2017) interpretations is that plate duction polarity, an important problem in the graphic anomalies are subduction zone rem- reconstructions restore North America to a North American Cordillera and for tectonic nants.
    [Show full text]
  • New Late Carboniferous Heritschioidinae (Rugosa) from the Kuiu Island Area and Brooks Range, Alaska
    Geologica Acta, Vol.12, Nº 1, March 2014, 29-52 DOI: 10.1344/105.000002074 New Late Carboniferous Heritschioidinae (Rugosa) from the Kuiu Island area and Brooks Range, Alaska J. FEDOROWSKI1 C.H. STEVENS2 E. KATVALA3 1Institute of Geology, Adam Mickiewicz University Makow Polnych 16, PL-61-606, Poznan, Poland. E-mail: [email protected] 2Department of Geology, San Jose Unversity San Jose, California 95192, USA. E-mail: [email protected] 3Department of Geology, University of Calgary Calgary, Canada. E-mail: [email protected] ABS TRACT Three new species of the genus Heritschioides, i.e., H. alaskensis sp. nov., H. kuiuensis sp. nov., and H. splendidus sp. nov., and Kekuphyllum sandoense gen. et sp. nov. from the northeastern Kuiu Island area and nearby islets, part of Alexander terrane in southeastern Alaska, and Heritschioides separatus sp. nov. from the Brooks Range, Alaska, are described and illustrated. The three new fasciculate colonial coral species from the Kuiu Island area, collected from the Moscovian Saginaw Bay Formation, are phylogenetically related to those of probable Bashkirian age in the Brooks Range in northern Alaska as shown by the presence of morphologically similar species of Heritschioides. These corals from both areas also are related to one species in the Quesnel terrane in western Canada. Kekuphyllum sandoense from the Saginaw Bay Formation of the Kuiu Island area is the only cerioid-aphroid species within the Subfamily Heritschioidinae described so far. The complete early ontogeny of a protocorallite is for the first time described here on a basis of H. kuiuensis sp. nov. and compared to the hystero-ontogeny in order to show similarities and differences in those processes.
    [Show full text]
  • Wrangellia Flood Basalts in Alaska, Yukon, and British Columbia: Exploring the Growth and Magmatic History of a Late Triassic Oceanic Plateau
    WRANGELLIA FLOOD BASALTS IN ALASKA, YUKON, AND BRITISH COLUMBIA: EXPLORING THE GROWTH AND MAGMATIC HISTORY OF A LATE TRIASSIC OCEANIC PLATEAU By ANDREW R. GREENE A THESIS SUBMITTED iN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Geological Sciences) UNIVERSITY OF BRITISH COLUMBIA (Vancouver) August 2008 ©Andrew R. Greene, 2008 ABSTRACT The Wrangellia flood basalts are parts of an oceanic plateau that formed in the eastern Panthalassic Ocean (ca. 230-225 Ma). The volcanic stratigraphy presently extends >2300 km in British Columbia, Yukon, and Alaska. The field relationships, age, and geochemistry have been examined to provide constraints on the construction of oceanic plateaus, duration of volcanism, source of magmas, and the conditions of melting and magmatic evolution for the volcanic stratigraphy. Wrangellia basalts on Vancouver Island (Karmutsen Formation) form an emergent sequence consisting of basal sills, submarine flows (>3 km), pillow breccia and hyaloclastite (<1 1cm), and subaerial flows (>1.5 km). Karmutsen stratigraphy overlies Devonian to Permian volcanic arc (—‘380-355 Ma) and sedimentary sequences and is overlain by Late Triassic limestone. The Karmutsen basalts are predominantly homogeneous tholeiitic basalt (6-8 wt% MgO); however, the submarine part of the stratigraphy, on northern Vancouver Island, contains picritic pillow basalts (9-20 wt% MgO). Both lava groups have overlapping initial and ENd, indicating a common, ocean island basalt (OIB)-type Pacific mantle source similar to the source of basalts from the Ontong Java and Caribbean Plateaus. The major-element chemistry of picrites indicates extensive melting (23 -27%) of anomalously hot mantle (‘—1500°C), which is consistent with an origin from a mantle plume head.
    [Show full text]
  • Upper-Crustal Cooling of the Wrangellia Composite Terrane in the Northern St. Elias Mountains, Western Canada
    RESEARCH Upper-crustal cooling of the Wrangellia composite terrane in the northern St. Elias Mountains, western Canada Sarah Falkowski1 and Eva Enkelmann2 1UNIVERSITY OF TÜBINGEN, DEPARTMENT OF GEOSCIENCES, 72074 TÜBINGEN, GERMANY 2UNIVERSITY OF CINCINNATI, DEPARTMENT OF GEOLOGY, CINCINNATI, OHIO 45221-0037, USA ABSTRACT This study presents the long-term exhumation history of the Wrangellia composite terrane of the remote and ice-covered northern St. Elias Mountains in southwest Yukon, northwest British Columbia, and adjacent Alaska. Detrital zircon and apatite fission-track age distributions are presented from 21 glacial catchments. The detrital sampling approach allows for a large spatial coverage (~30,000 km2) and access to material eroded beneath the ice. An additional five bedrock samples were dated by zircon fission-track analysis for a comparison with detrital results. Our new thermochronology data record the Late Jurassic–mid-Cretaceous accretion of the Wrangellia composite terrane to the former North American margin and magmatism, which reset the older thermal record. The good preservation of the Jurassic–Cretaceous record suggests that Cenozoic erosion must have been limited overall. Nonetheless, Eocene spreading-ridge subduction and Oligocene–Neogene cooling in response to the ongoing Yakutat flat-slab subduction are evident in the study area despite its inboard position from the active plate boundary. The results further indicate an area of rapid exhumation at the northern end of the Fairweather fault ca. 10–5 Ma; this area is bounded by discrete, unmapped structures. The area of rapid exhumation shifted southwest toward the plate boundary and the center of the St. Elias syntaxis after 5 Ma. Integrating the new data with published detrital thermochronology from the southern St.
    [Show full text]
  • Flood Basalts of the Wrangellia Terrane II
    Downloaded from geosphere.gsapubs.org on April 19, 2011 Geosphere The architecture of oceanic plateaus revealed by the volcanic stratigraphy of the accreted Wrangellia oceanic plateau Andrew R. Greene, James S. Scoates, Dominique Weis, Erik C. Katvala, Steve Israel and Graham T. Nixon Geosphere 2010;6;47-73 doi: 10.1130/GES00212.1 Email alerting services click www.gsapubs.org/cgi/alerts to receive free e-mail alerts when new articles cite this article Subscribe click www.gsapubs.org/subscriptions/ to subscribe to Geosphere Permission request click http://www.geosociety.org/pubs/copyrt.htm#gsa to contact GSA Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. Individual scientists are hereby granted permission, without fees or further requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequent works and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms to further education and science. This file may not be posted to any Web site, but authors may post the abstracts only of their articles on their own or their organization's Web site providing the posting includes a reference to the article's full citation. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. Notes © 2010 Geological Society of America Downloaded from geosphere.gsapubs.org on April 19, 2011 The architecture of oceanic plateaus revealed by the volcanic stratigraphy of the accreted Wrangellia oceanic plateau Andrew R.
    [Show full text]
  • Chulitnacula, a New Paleobiogeographically Distinctive Gastropod Genus from Upper Triassic Strata in Accreted Terranes of Southern Alaska
    Journal of the Czech Geological Society 46/1ñ2(2001) 213 Chulitnacula, a new paleobiogeographically distinctive gastropod genus from Upper Triassic strata in accreted terranes of southern Alaska (3 figs) JIÿÕ FR›DA 1 ñ ROBERT B. BLODGETT 2 1 Czech Geological Survey, Kl·rov 3, 118 21 Praha 1, Czech Republic; e-mail: [email protected] 2 Department of Zoology, Oregon State University, Corvallis, Oregon, 97331 USA; e-mail: [email protected] A new protorculid gastropod genus, Chulitnacula, is based on Protorcula alaskana Smith, 1927, from the Chulitna terrane of south- central Alaska. The type species also occurs in two other accreted terranes of southern Alaska: 1.) in the Farewell terrane (Nixon Fork subterrane) of southwestern Alaska; and 2.) in the Alexander terrane of southeastern Alaska. This taxon is a common to dominant element in shallow-water, near-shore late Norian age strata of all of these terranes. It appears to be biogeographically significant in that while it so abundant in these southern Alaskan accreted terranes, it is completely unknown elsewhere in Upper Triassic para-autochthonous rocks of western North America (i.e. Nevada, Sonora). The occurrence of Chulitnacula alaskana (Smith, 1927) in the Chulitna, Farewell (Nixon Fork subterrane) and Alexander terranes suggests that they were in close reproductive communication in the Late Triassic. The absence of this taxon in either the Wrangellia terrane of southern Alaska and British Columbia, as well as in the related Wallowa terrane of northeast- ern Oregon and adjacent western Idaho is worthy of note. This absence plus many other major differences in their respective Late Triassic gastropod faunas indicate that the Chulitna-Farewell-Alexander terrane association was far removed from the Wrangellia-Wallowa terrane couplet.
    [Show full text]
  • The Architecture of Oceanic Plateaus Revealed by the Volcanic Stratigraphy of the Accreted Wrangellia Oceanic Plateau
    The architecture of oceanic plateaus revealed by the volcanic stratigraphy of the accreted Wrangellia oceanic plateau Andrew R. Greene* James S. Scoates Dominique Weis Pacifi c Centre for Isotopic and Geochemical Research, Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia V6T1Z4, Canada Erik C. Katvala Department of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N1N4, Canada Steve Israel Yukon Geological Survey, 2099-2nd Ave, Whitehorse, Yukon Y1A2C6, Canada Graham T. Nixon British Columbia Geological Survey, P.O. Box 9320, Station Provincial Government, Victoria, British Columbia V8W9N3, Canada ABSTRACT gellia fl ood basalts were emplaced during a from low-viscosity, high-temperature tholei- single phase of tholeiitic volcanism ca. 230– itic basalts, sill-dominated feeder systems, The accreted Wrangellia fl ood basalts and 225 Ma, and possibly within as few as 2 Myr, limited repose time between fl ows (absence associated sedimentary rocks that compose onto preexisting submerged arc crust. There of weathering, erosion, sedimentation), sub- the prevolcanic and postvolcanic stratigraphy are distinct differences in volcanic stratig- marine versus subaerial emplacement, and provide an unparalleled view of the architec- raphy and basement composition between relative water depth (e.g., pillow basalt– ture, eruptive environment, and accumula- Northern and Southern Wrangellia. On volcaniclastic transition). tion and subsidence history of an oceanic Vancouver Island, ~6 km of high-Ti basalts, plateau. This Triassic large igneous province with minor amounts of picrites, record an INTRODUCTION extends for ~2300 km in the Pacifi c North- emergent sequence of pillow basalt, pil- west of North America, from central Alaska low breccia and hyaloclastite, and subaerial Approximately 3% of the ocean fl oor is and western Yukon (Nikolai Formation) to fl ows that overlie Devonian– Mississippian covered with oceanic plateaus or fl ood basalts, Vancouver Island (Karmutsen Formation), (ca.
    [Show full text]
  • Baja British Columbia Hypothesis
    A Moderate Translation Alternative to the Baja British Columbia Hypothesis Rob e r t F.Butler and George E. Ge h re l s , km. The resulting paleogeography has Luyendyk, 1979; Beck et al., 1986). This De p a r tment of Geosciences, the appealing feature of an Andean-like, history suggests that apparent conflicts Un i ve r s i t y of Ar i zo n a , Tuc s o n , AZ 85721, continuous subduction-related magmatic between paleomagnetism and geology USA ,b u t l e r @ g e o . a r i zo n a . e d u ar c along the Cordilleran margin during can lead to significant insights that Cr etaceous time. neither discipline alone could have de l i v e re d . Kenneth P.Kod a m a , De p a r tment of IN T R O D U C T I O N The Baja B.C. controversy is focused Ea r th and Envi ro n m e n t al Sciences, One may quibble over the details, but on the magnitude of post–mid- Lehigh Univer s i t y, Be t h l e h e m , PA 18015- the general picture on paleomagnetism Cr etaceous northward transport of 3 1 8 8 ,U SA is sufficiently compelling that it is much segments of the North American m o re reasonable to accept it than to Cordillera. Did southeast Alaska, d i s re g a rd it. we s t e r n British Columbia, and the North AB S T R AC T —H.H.
    [Show full text]
  • Wrangellia Terrane on Vancouver Island, British Columbia
    Wrangellia Terrane on Vancouver Island, British Columbia: Distribution of Flood Basalts with Implications for Potential Ni-Cu-PGE Mineralization in Southwestern British Columbia By A.R. Greene1, J.S. Scoates1 and D. Weis1 KEYWORDS: Wrangellia, large igneous province, basalt, appear to be present. In this respect, Wrangellia is a much contamination, Ni-Cu-PGE mineralization more reasonable exploration target than many other oceanic and continental plateaus where the underlying crust consists mainly of granitic or ultramafic rocks. INTRODUCTION The ongoing study seeks to provide insight into the potential for Ni-Cu-PGE mineralization for the portion of Wrangellia consists largely of an oceanic plateau, a the Wrangellia Terrane on Vancouver Island. This vast outpouring of basalt and more Mg-rich magma that overview is a preliminary report of fieldwork and a erupted onto the ocean floor and was subsequently summary of previous research. This study represents one accreted to the western margin of the North American important aspect of a larger study on the significance of plate. Flood basalts form extensive sequences on the Wrangellia Terrane as a giant accreted oceanic Vancouver Island and are believed to have formed by plateau. Oceanic plateaus are enigmatic phenomena that melting in a mantle plume (an upwelling zone of hot represent the largest known magmatic events on Earth. mantle rock). They form the oceanic variety of a Large Such enormous volumes of magma erupt over Igneous Province (LIP). A peculiarity of the Wrangellia geologically short time intervals (several million years) plateau is that it erupted into an extinct island arc. and, in addition to potentially generating world-class ore The continental equivalents of oceanic plateaus are deposits, their formation may have catastrophic effects on the hosts of world-class ore deposits.
    [Show full text]
  • Terrane Processes at the Margins of Gondwana: Introduction
    Terrane Processes at the Margins of Gondwana: introduction Alan P.M. Vaughan1, Philip T. Leat1 & Robert J. Pankhurst2 1British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, U.K. (e-mail: [email protected]) 2British Geological Survey, Keyworth, Nottingham NG12 5GG, U.K. NB. The introduction should be aimed at the non-specialist geologist and about the 2nd to 3rd year undergraduate. No of words in text: 6878 No of references: 260 No of tables: 0 No of Figures: 2 Running Title: Terrane Processes 1 Abstract: The process of terrane accretion is vital to the understanding of the formation of continental crust. Accretionary orogens affect over half of the globe and have a distinctively different evolution to Wilson type orogens. It is increasingly evident that accretionary orogenesis has played a significant role in the formation of the continents. The Pacific-margin of Gondwana preserves a major orogenic belt, termed here the “Australides”, that was an active site of terrane accretion from Neoproterozoic to Late Mesozoic times, and comparable in scale to the Rockies from Mexico to Alaska, or the Variscan–Appalachian orogeny. The New Zealand sector of this orogenic belt was one of the birthplaces of terrane theory and the Australide orogeny overall continues to be an important testing ground for terrane studies. This volume summarizes the history and principles of terrane theory and presents sixteen new works that review and synthesize the current state of knowledge for the Gondwana margin, from Australia through New Zealand and Antarctica to South America, and examine the evolution of the whole Gondwana margin through time.
    [Show full text]
  • Cenozoic Subduction Complex Imaged by Deep Seismic Reflections•
    31 LITHOPROBE-southern Vancouver Island: Cenozoic subduction complex imaged by deep seismic reflections• R. M. CLOWES Department of Geophysics and Astronomy, 22I9 Main Mall, The University of British Columbia, Vancouver, B.C., Canada V6T I W5 M. T. BRANDON2 Pacific Geoscience Centre, Geological Survey of Canada, P. Box , Sidney, B. C., Canada VBL 4B2 0. 6000 A. G. GREEN Lithosphere and Canadian Shield Division, Geological Survey of Canada, I Observatory Crescent, Ottawa, Ont., Canada KIA OY3 C. J. YORATH AND A. SUTHERLAND BROWN Pacific Geoscience Centre, Geological Surv y of Canada, P. Box , Sidney, B. Canada VBL 4B2 _e 0. 6000 C., E. R. KANASEWICH Institute of Earth and Planetary Physics, University of Alberta, Edmonton, Alta., Canada T6G 2JJ AND C. SPENCER Lithosphere and Canadian Shield Division, Geological Survey of Canada, I Observatory Crescent, Ottawa, Ont., Canada KIA OY3 Received December 9, 1985 Revision accepted June 23, 1986 The LITHOPROBE seismic reflection project on Vancouver Island was designed to study the large-scale structureof several accreted terranes exposed on the island and to determine the geometry and structural characteristics of the subducting Juan de Fuca plate. In this paper, we interpret two LITHOPROBE profiles from southernmost Vancouver Island that were shot across three important terrane-bounding faults-Leech River, San Juan, and Survey Mountain-to determine their subsurface geometry and relationship to deeper structures associated with modem subduction. The structure beneath the island can be divided into an upper crustal region, consisting of several accreted terranes, and a deeper region that represents a landward extension of the modem offshore subduction complex.
    [Show full text]
  • DGGS Geological Investigations in Western Wrangellia Evan Twelker1
    DGGS Geological Investigations in Western Wrangellia Evan Twelker1 and Lauren L. Lande1,2 1Alaska Division of Geological & Geophysical Surveys (DGGS) 2Department of Geoscience, University of Alaska Fairbanks Base and precious metal deposits geologically associated with Late Triassic mafic to ultramafic magmatism constitute a significant metallogenic province of the northern North American Cordillera. Deposits of signficance include the Wellgreen magmatic Ni-Cu-Co-PGE sulfide deposit in the Yukon Territory and bonanza-grade sediment-hosted Cu-Ag systems at Kennecott. In central Alaska, this magmatic event comprises the Nikolai Greenstone and cogenetic mafic and ultramafic intrusions of the Wrangellia terrane. Notable mineralization includes magmatic Ni-Cu-PGE mineralization at the Eureka Zone and Butte Creek prospects, and sediment-hosted Cu-Ag mineralization at the Caribou Dome deposit. Through the State’s Strategic and Critical Minerals Assessment Project and the United States Geological Survey’s STATEMAP Program, the DGGS has pursued a multi-year effort to improve the geological knowledge base with an emphasis on the geologic setting of Ni-Cu-PGE mineralization. Newly released data include geophysical surveys (GPR 2014-1), geochemistry (RDF 2014-3; RDF 2014-5, RDF 2014-22), geochronology (RDF 2014-18, RDF 2015-10), and geologic mapping (PIR 2015-6). All reports are available free of charge from the DGGS website (dggs.alaska.gov). Building on recent advances in the geochemical understanding of the Wrangellia volcanic stratigraphy, we have used geochemical classification and targeted fieldwork to refine the geologic maps of the area. Additionally, geochemical data and field relationships have enabled us to better establish the relationship of mineralized ultramafic intrusions to the broader Late Triassic magmatic episode.
    [Show full text]