DOCSLIB.ORG

Middle Jurassic Within-Plate Granites in West Antarctica and Their Bearing on the Break-Up of Gondwanaland

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Middle Jurassic Within-Plate Granites in West Antarctica and Their Bearing on the Break-Up of Gondwanaland Journal of the Geological Society, London, Vol. 145, 1988, pp. 999-1007, Printed in Northern Ireland Middle Jurassic within-plate granites in West Antarctica and their bearing on the break-up of Gondwanaland B. C. STOREY,'M. J. HOLE,' R. J. PANKHURST,'I. L. MILLAR' & W. VENNUM2 British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 OET, UK 2Department of Geology, Sonoma State University, Rohnert Park, California 94928, USA Abstract: Five post-tectonic granitic plutons isolated within the central Ellsworth-Whitmore moun- tains crustal block in West Antarctica form a distinctive geochemical suite. All have some characteris- tics of S-type granites and are atypical of active continental margins. They rangein composition from a within-plate granite (WPG) end member, with the lowest "Sr/'"Sr initial ratio (0.707), to granites with a much more marked crustal signature and high initial ratios (0.722). The granitic suite was emplaced over a restricted Middle Jurassic time interval at the same time as the extensive Ferrar- Karoo-Tasman mafic suite and just prior to the disintegration of the supercontinent Gondwanaland. Petrogeneticmodelling suggests that the WPG end member couldhave been derived entirely by differentiation of the enriched mantle-derived Ferrar magma, and the end member with the highest initial ratio by partialmelting of a crustal source. Low initial '43Nd/144Nd ratiosand Proterozoic model ages are compatible with a Precambrian crustal component but may alternatively, as in the case of Ferrar Supergroup magmas, reflect partial inheritance from enriched lithospheric mantle geochemi- callycoupled to the lower crust since Precambrian differentiation. Data from these granites are consistent with large-scale underplating of mafic magma and crustal melting in response to a thermal disturbance in the Gondwanaland lithosphere related in some way to break-up of the supercontinent. Although granitic rocks from a large and important part of thesuite was emplacedjust prior to the disintegration of thebedrock geology of WestAntarctica, they pre- Gondwanaland itis tectonically importantand mayhave dominantly crop out as a linearbelt along the Pacific margin some bearing on the causes of supercontinent break-up. We and are related toMesozoic subduction processes. However, consider thesource and evolution of thegranite magmas a suite of geographicallyisolated Middle Jurassic granites andapossible petrogenetic relationship tothe contem- (175 f 8 Ma) occurs within the centre of West Antarctica, poraneousFerrar mafic suite. The tectonicsetting of the up to 1500 km from the Pacific margin. These granites have granites is explored by use of adiscrimination diagram previouslybeen interpretedas allochthonous subduction- combined with Sr and Nd isotope data. related granites that moved to their present-day position as a result of the reorganization of the crustal blocks of West Antarctica during Gondwanaland break-up (Dalziel & Elliot Geological setting 1982).Recent palaeomagnetic data reveallimited a Thegranitic suite occurswithin theEllsworth-Whitmore movement of the crustal blocksof West Antarctica (Grunow mountains crustal block (EWM),which is the central one of et al. 1987) andsuggest thegranites may have been five crustal blocks making up the mosaic of West Antarctica emplaced well awayfrom an active margin. Moreover (Fig. 1). The blocks are separated by deep crustal rift zones geochemical and isotopic data from the combined 'British (Storey et al. 1988),and are regarded as having moved AntarcticSurvey-United States Antarctic Research Pro- during thebreak-up of Gondwanalandalthough there is gram West Antarctic tectonics project' (Dalziel & Pankhurst some doubt as to their precise pre-drift positions (Grunowet 1985) indicate that the granites are adistinctive geochemical al. 1987). TheEWM blockhas a deformed Cambrian to suite with some of thecharacteristics of S-typegranites Permian stratigraphy, comparable with the Cape fold belt of (Vennum & Storey1987a) and are atypical of active South Africa and partsof the Transantarctic Mountains. It is continentalmargins. These granites were emplaced at the geologically distinct fromthe adjoining Haag Nunataks sametime as the extensive Ferrar Supergroup mafic suite block, which consists of Precambrian crystalline basement, (179 f 7 Ma) within the Transantarctic Mountains (Kyle et andfrom theAntarctic Peninsula, Thurston Island and al. 1981) and just prior tothe disintegration of the Marie Byrd Land blocks, which for the most part represent supercontinent.The Ferrar tholeiites are noted for their the Mesozoic-Cenozoic proto-Pacific margin of Gondwana- anomalous enriched continental trace element and isotopic land. characteristics and are part of a larger magmatic province The granites are post-tectonic, intruded into the deformed that includes the Karoo and Tasman dolerites. These have sedimentary rocks (Storey & Dalziel 1987), and now form been related to a lithospheric melting event associated with the main exposure within the central partof the EWM block the break-up of Gondwanaland (Dalziel et al. 1987). (Fig. 1). In the Nash and Pirrit hills, large granite plutons Thispaper summarizes both new and published are surrounded by thermally altered metasedimentary roof geochemical and isotopic datafrom the unusual suite of pendants,and in theMartin Hills smallleucocratic granites isolated within the centre of West Antarctica. As rhyodacitestocks intrude shallowmarine calcareous 999 Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/145/6/999/4889636/gsjgs.145.6.0999.pdf by guest on 29 September 2021 loo0 STOREY B. C. ET AL. ... .. Fig. 1 (a). The crustal blocks of West Antarctica. AP, Antarctic Peninsula; TI, Thurston Island; MBL, Marie Byrd Land;HN, Haag Nunataks; EWM, Ellsworth-Whitmore mountains; TAM, Trans- antarctic Mountains, WSE, Weddell Sea embayment. The solid black areas are the main mountains. (b) The Middle Jurassic granites of the Ellsworth-Whitmore mountains crustal block. J, Jurassic; C, Cambrian; P, Permian. Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/145/6/999/4889636/gsjgs.145.6.0999.pdf by guest on 29 September 2021 JURASSIC GRANITES IN WEST ANTARCTICA 1001 sedimentaryrocks of possibleCambrian age (Storey & Geochronology and isotope geology Macdonald 1987). The largest outcrop area, the Whitmore Previousradiometric dating of thesegranites has been Mountains,exhibits two principal granite types; the summarized by Millar & Pankhurst (1987), who presented coarse-grainedMount Seelig granite, which commonly Rb-Srwhole-rock isochron ages of 173 f 3, 175 f 8 and possesses an aligned mica fabric, is cut by the fine-grained 175 f 8 Ma, respectively, for the Pirrit Hills, Nash Hills and leucocratic Linck Nunatak granite. The remaining exposure PaganoNunatak plutons. They proposed that the EWM at Pagano Nunatak is entirely formed of a granitic pluton granites form a coherent and contemporaneous suite. Thisis with no preserved sedimentary envelope. extended by new data which give an age of 176 f 5 Ma for Although thegranitoids are not associated with mafic the LinckNunatak granite of theWhitmore Mountains intrusionsat thepresent erosion level, they are clearly (Pankhurst et al. 1989). Thesefour intrusions are relatedto distinctive low-amplitude,moderate wavelength collectively termed the EWM granitic suite. This does not E-W orientated magnetic anomalies (Garrett et al. 1988). include theMount Seelig granite phase of theWhitmore The only mafic igneous rocks exposed in this area comprise Mountains, which is distinct in terms of its petrography and small gabbro stocksand sills geochemicallysimilar to the geochemistry,and for which preliminaryRb-Sr and U-Pb Ferrardolerites (Vennum & Storey19876). These occur zircon data suggest an age perhaps as old as Triassic. within deformed metasedimentary rocks at Hart Hills (Fig. The uniformity of initial R7Sr/mSrratios within each 1) and within the same magnetic anomaly as the granite at pluton is strongevidence that anyinternal differentiation Pagano Nunatak, suggesting thatthe granites may be wasby crystal-liquidprocesses such as fractional crystal- underlain by and related to a magnetite-rich mafic batholith. lization and did not involve variable crustal contamination effects. But between the plutons, initial *'Sr/% ratios are extremelyvariable (Table l), rangingfrom 0.707 forthe Petrography Pirrit Hills to 0.722 for the Linck Nunatak granite. These Thegranite outcrops are fairly uniformin appearance, ratios are all higher thanexpected for mantle-derived consistingpredominantly of medium- to coarse-grained magmas, and mostly higher than in subduction-related arc white or palepink leucocratic biotite-(muscovite) granite granites, which suggests a considerableamount of crustal (for details seeVennum & Storey1987a). Plagioclase contribution in theirpetrogenesis. The MiddleJurassic feldspar is An,,,. Some granites are porphyritic, with up to (179 f 7 Ma) basic magmasof the Ferrar Supergroupof East 40% of K-feldsparphenocrysts, which areoften strongly Antarcticashow acomparable range of elevated initial perthitic. Othersare fine-grainedaplogranites, and veins s7Sr/X6Srratios (0.7085-0.7153), in this case ascribed only in andsmall bodies of apliteare common. Alteration and part to crustalcontamination and thought to primarily xenoliths are rare although pegmatitic segregations contain- reflect anomalousmantle (e.g. Kyle 1980). These com- ing tourmaline, beryl and muscovite
Load more

Recommended publications
  • Mapping Blue-Ice Areas and Crevasses in West Antarctica Using ASTER Images, GPS, and Radar Measurements
    CHAPTER 31 Mapping blue-ice areas and crevasses in West Antarctica using ASTER images, GPS, and radar measurements Andre´s Rivera, Fiona Cawkwell, Anja Wendt, and Rodrigo Zamora ABSTRACT from ASTER imagery, with the aim of identifying other landing sites for aircraft, as well as providing Before the satellite era, relatively little was known a detailed map for meteorite seekers. ASTER com- about the interior of the West Antarctic Ice Sheet posite images have also been used to map safe (WAIS). Of special interest are the rock outcrops routes for terrestrial traverses through crevasse associated with blue-ice areas (BIAs), which have zones. High-pass filters enhanced crevasse features, been exploited for logistical purposes as well as but visual analysis proved to be the most reliable being the subject of scientific research. The blue method of identifying all crevasses. ASTER images ice consists of relatively snow-free glacier ice that were superior to microwave imagery for crevasse is undergoing ablation. detection, as the latter can lack sufficient contrast; One of these BIAs is Patriot Hills (80180S, however, only Radarsat imagery provided coverage 81220W) where aircraft with conventional landing of higher latitude regions. Information gleaned gear have been landing for more than 20 years. This from visible imagery can be combined with that is now the main hub supporting large terrestrial of field-based radio-echo sounding and ground- expeditions conducted by Chilean scientists within penetrating radar profiles through the ice to map Antarctica. Kinematic GPS has been used to map internal layers and bedrock topography with the BIAs since 1996, with areas delineated on ASTER objective of enhancing our knowledge of this images since 2001 using both manual and auto- remote region.
    [Show full text]
  • Mem170-Bm.Pdf by Guest on 30 September 2021 452 Index
    Index [Italic page numbers indicate major references] acacamite, 437 anticlines, 21, 385 Bathyholcus sp., 135, 136, 137, 150 Acanthagnostus, 108 anticlinorium, 33, 377, 385, 396 Bathyuriscus, 113 accretion, 371 Antispira, 201 manchuriensis, 110 Acmarhachis sp., 133 apatite, 74, 298 Battus sp., 105, 107 Acrotretidae, 252 Aphelaspidinae, 140, 142 Bavaria, 72 actinolite, 13, 298, 299, 335, 336, 339, aphelaspidinids, 130 Beacon Supergroup, 33 346 Aphelaspis sp., 128, 130, 131, 132, Beardmore Glacier, 429 Actinopteris bengalensis, 288 140, 141, 142, 144, 145, 155, 168 beaverite, 440 Africa, southern, 52, 63, 72, 77, 402 Apoptopegma, 206, 207 bedrock, 4, 58, 296, 412, 416, 422, aggregates, 12, 342 craddocki sp., 185, 186, 206, 207, 429, 434, 440 Agnostidae, 104, 105, 109, 116, 122, 208, 210, 244 Bellingsella, 255 131, 132, 133 Appalachian Basin, 71 Bergeronites sp., 112 Angostinae, 130 Appalachian Province, 276 Bicyathus, 281 Agnostoidea, 105 Appalachian metamorphic belt, 343 Billingsella sp., 255, 256, 264 Agnostus, 131 aragonite, 438 Billingsia saratogensis, 201 cyclopyge, 133 Arberiella, 288 Bingham Peak, 86, 129, 185, 190, 194, e genus, 105 Archaeocyathidae, 5, 14, 86, 89, 104, 195, 204, 205, 244 nudus marginata, 105 128, 249, 257, 281 biogeography, 275 parvifrons, 106 Archaeocyathinae, 258 biomicrite, 13, 18 pisiformis, 131, 141 Archaeocyathus, 279, 280, 281, 283 biosparite, 18, 86 pisiformis obesus, 131 Archaeogastropoda, 199 biostratigraphy, 130, 275 punctuosus, 107 Archaeopharetra sp., 281 biotite, 14, 74, 300, 347 repandus, 108 Archaeophialia,
    [Show full text]
  • 5 Yr Drilling Tec Plan
    Ice Drilling Program LONG RANGE DRILLING TECHNOLOGY PLAN June 30, 2020 Sponsor: National Science Foundation Ice Drilling Program - LONG RANGE DRILLING TECHNOLOGY PLAN - June 30, 2020 Contents 1.0 INTRODUCTION ................................................................................................................................. 4 2.0 ICE AND ROCK DRILLING SYSTEMS AND TECHNOLOGIES ................................................................. 7 Chipmunk Drill ........................................................................................................................................... 8 Hand Augers .............................................................................................................................................. 9 Sidewinder .............................................................................................................................................. 10 Prairie Dog ............................................................................................................................................... 11 Stampfli Drill ............................................................................................................................................ 12 Blue Ice Drill (BID) ................................................................................................................................... 13 Badger-Eclipse Drill ................................................................................................................................. 14 4-Inch
    [Show full text]
  • ICE SHELF MELT RATES and 3D IMAGING by Cameron Scott Lewis Submitted to the Graduate Degree Program in Electrical Engineering An
    ICE SHELF MELT RATES AND 3D IMAGING By ©2015 Cameron Scott Lewis Submitted to the graduate degree program in Electrical Engineering and Computer Science and the Graduate Faculty of the University of Kansas in partial fulfillment of the requirements for the degree of Doctor of Philosophy. _____________________________________ Chairperson: Prasad Gogineni _____________________________________ Chris Allen _____________________________________ Carl Leuschen _____________________________________ Fernando Rodriguez-Morales _____________________________________ Rick Hale Date Defended: May 8, 2015 This Dissertation Committee for Cameron Lewis certifies that this is the approved version of the following dissertation: Ice Shelf Melt Rates and 3D Imaging _____________________________________ Chairperson: Prasad Gogineni Date Approved: ii Abstract Ice shelves are sensitive indicators of climate change and play a critical role in the stability of ice sheets and oceanic currents. Basal melting of ice shelves plays an important role in both the mass balance of the ice sheet and the global climate system. Airborne- and satellite-based remote sensing systems can perform thickness measurements of ice shelves. Time-separated repeat flight tracks over ice shelves of interest generate data sets that can be used to derive basal melt rates using traditional glaciological techniques. Many previous melt rate studies have relied on surface elevation data gathered by airborne- and satellite-based altimeters. These systems infer melt rates by assuming hydrostatic equilibrium, an assumption that may not be accurate, especially near an ice-shelf’s grounding line. Moderate bandwidth, VHF, ice-penetrating radar has been used to measure ice-shelf profiles with relatively coarse resolution. This study presents the application of an ultra-wide bandwidth (UWB), UHF, ice-penetrating radar to obtain finer resolution data on the ice shelves.
    [Show full text]
  • We Thank the Reviewers for Their Helpful Feedback, Which Has Improved Our Manuscript. in the Interactive Discussion, We Have Replied to Each Reviewer Directly
    Dear Dr. Stroeven (editor), We thank the reviewers for their helpful feedback, which has improved our manuscript. In the Interactive Discussion, we have replied to each Reviewer directly. Below are copies of the Reviewers' comments and our responses as well as the revised manuscript with changes tracked. We would also like to bring to your attention the fact that we have made some changes to the manuscript regarding issues that were not raised by the Review- ers. These changes are described below. In the last paragraph of Section 5.3, we have changed the sentence which read \Circulation of drilling fluid in the RB-1 borehole hydrofractured the basal ice...". The new sentence reads \An unexplained hydrofracture of the basal ice of the RB-1 borehole...". After our initial manuscript submission, we realized that the present-day ground- ing line in our ice-sheet simulation was located upstream of Robin Subglacial Basin in the Weddell Sea sector of the WAIS (compare to Fig. 1). This misfit affects the plots in Fig. 2e-s because, at sites upstream of this area, thinning during interglacial periods is underestimated and thickening during glacial pe- riods is overestimated. To address this, we have taken the following actions. (i) We have added a figure (Fig. 3 in the revised manuscript) showing the misfit between the modeled and the observed present-day ice sheet. This figure shows that the model does reasonably well in most areas, but very poorly in the region of Robin Subglacial Basin. (ii) We added a paragraph to the end of Section 3 explaining this misfit and its consequences.
    [Show full text]
  • REE Tetrad Effect and Sr-Nd Isotope Systematics of A-Type Pirrit Hills Granite from West Antarctica
    minerals Article REE Tetrad Effect and Sr-Nd Isotope Systematics of A-Type Pirrit Hills Granite from West Antarctica Hyo Min Lee 1, Seung-Gu Lee 2,* , Hyeoncheol Kim 2, Jong Ik Lee 3 and Mi Jung Lee 3 1 Geoscience Platform Division, Korea Institute of Geoscience and Mineral Resources, 124 Gwahak-ro, Yuseong-gu, Daejeon 34132, Korea; [email protected] 2 Geology Division, Korea Institute of Geoscience and Mineral Resources, 124 Gwahak-ro, Yuseong-gu, Daejeon 34132, Korea; [email protected] 3 Division of Polar Earth-System Sciences, Korea Polar Research Institute, 26 Songdomirae-ro, Yeonsu-gu, Incheon 21990, Korea; [email protected] (J.I.L.); [email protected] (M.J.L.) * Correspondence: [email protected]; Tel.: +82-42-868-3376 Abstract: The Pirrit Hills are located in the Ellsworth–Whitmore Mountains of West Antarctica. The Pirrit Hills granite exhibits significant negative Eu anomalies (Eu/Eu* = 0.01~0.25) and a REE tetrad effect indicating intensive magmatic differentiation. Whole-rock Rb-Sr and Sm-Nd geochronologic analysis of the Pirrit Hills granite gave respective ages of 172.8 ± 2.4 Ma with initial 87Sr/86Sr = 0.7065 ± 0.0087 Ma and 169 ± 12 Ma with initial 144Nd/143Nd = 0.512207 ± 0.000017. The isotopic ratio data indicate that the Pirrit Hills granite formed by the remelting of Mesoproterozoic mantle- derived crustal materials. Both chondrite-normalized REE patterns and Sr-Nd isotopic data indicate that the Pirrit Hills granite has geochemical features of chondrite-normalized REE patterns indicating that REE tetrad effects and negative Eu anomalies in the highly fractionated granites were produced Citation: Lee, H.M.; Lee, S.-G.; Kim, from magmatic differentiation under the magmatic-hydrothermal transition system.
    [Show full text]
  • Ancient Pre-Glacial Erosion Surfaces Preserved Beneath the West
    Edinburgh Research Explorer Ancient pre-glacial erosion surfaces preserved beneath the West Antarctic Ice Sheet Citation for published version: Rose, KC, Ross, N, Jordan, TA, Bingham, RG, Corr, HFJ, Ferraccioli, F, Le Brocq, AM, Rippin, DM & Siegert, MJ 2015, 'Ancient pre-glacial erosion surfaces preserved beneath the West Antarctic Ice Sheet', Earth Surface Dynamcs, vol. 3, pp. 139-152. https://doi.org/10.5194/esurf-3-139-2015 Digital Object Identifier (DOI): 10.5194/esurf-3-139-2015 Link: Link to publication record in Edinburgh Research Explorer Document Version: Publisher's PDF, also known as Version of record Published In: Earth Surface Dynamcs Publisher Rights Statement: The copyright of any article is retained by the author(s). he article as well as associated published material is distributed under the Creative Commons Attribution 3.0 License General rights Copyright for the publications made accessible via the Edinburgh Research Explorer is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. Take down policy The University of Edinburgh has made every reasonable effort to ensure that Edinburgh Research Explorer content complies with UK legislation. If you believe that the public display of this file breaches copyright please contact [email protected] providing details, and we will remove access to the work immediately and investigate your claim. Download date: 04. Oct. 2021 Earth Surf. Dynam., 3, 139–152, 2015 www.earth-surf-dynam.net/3/139/2015/ doi:10.5194/esurf-3-139-2015 © Author(s) 2015.
    [Show full text]
  • AUTARKIC a NEWS BULLETIN Published Quarterly by the NEW ZEALAND ANTARCTIC SOCIETY (INC)
    AUTARKIC A NEWS BULLETIN published quarterly by the NEW ZEALAND ANTARCTIC SOCIETY (INC) One of Argentina's oldest Antarctic stations. Almirante Brown, which was destroyed by fire on April 12. Situated in picturesque Paradise Bay on the west coast of the Antarctic Peninsula, it was manned first in 1951 by an Argentine Navy detachment, and became a scientific Station in 1955. Pnoto by Colin Monteath w_i -f n M#i R Registered at Post Office Headquarters, VOI. IU, IMO. D Wellington. New Zealand, as a magazine June, 1984 • . SOUTH SANDWICH It SOUTH GEORGIA / SOU1H ORKNEY Is ' \ ^^^----. 6 S i g n y l u K , / ' o O r c a d a s a r g SOUTH AMERICA ,/ Boroa jSyowa%JAPAN \ «rf 7 s a 'Molodezhnaya v/' A S O U T H « 4 i \ T \ U S S R s \ ' E N D E R B Y \ ) > * \ f(f SHETLANO | JV, W/DD Hallev Bay^ DRONNING MAUD LAND / S E A u k v ? C O A T S I d | / LAND T)/ \ Druzhnaya ^General Belgrano arg \-[ • \ z'f/ "i Mawson AlVTARCTIC-\ MAC ROBERTSON LANd\ \ *usi /PENINSUtA'^ [set mjp below) Sobral arg " < X ^ . D a v i s A u s t _ Siple — USA ;. Amundsen-Scon QUEEN MARY LAND ELLSWORTH " q U S A ') LAND ° Vostok ussr / / R o , s \ \ MARIE BYRD fee She/ r*V\ L LAND WILKES LAND Scon A * ROSSI"2*? Vanda n 7 SEA IJ^r 'victoria TERRE . LAND \^„ ADELIE ,> GEORGE V LJ ■Oumout d'Urville iran< 1 L*ningradsfcaya Ar ■ SI USSR,-'' \ ---'•BALIENYU ANTARCTIC PENINSULA 1 Teniente Matienzo arg 2 Esperanza arg 3 Almirante Brown arg 4 Petrel arg 5 Decepcion arg 6 Vicecomodoro Marambio arg * ANTARCTICA 7 Arturo Prat cm.le 8 Bernardo O'Higgms chile 9 Presidents Frei cmile 500 tOOOKiloflinnn 10 Stonington I.
    [Show full text]
  • Exposure History of West Antarctic Nunataks
    Exposure history of West Antarctic nunataks Perry Spector, John Stone, Howard Conway, Dale Winebrenner Department of Earth and Space Science University of Washington Cameron Lewis, John Paden, Prasad Gogineni Center for Remote Sensing of Ice Sheets University of Kansas There is strong evidence that the West Antarctic Ice Sheet has been thinner during the Pleistocene, however the timing, duration, and magnitude of past deglaciations are poorly known. Ice-sheet elevation changes over glacial and interglacial periods can be revealed by cosmogenic-nuclide measurements of bedrock surfaces. Whether ice was thinner during past warm climates can be tested by measuring cosmogenic nuclides in currently subglacial bedrock surfaces, provided that cold-based ice has protected the surfaces from erosion. During 2012-13, we visited three groups of small nunataks in West Antarctica with the intention of locating favorable drilling sites for the recovery of subglacial bedrock to look for evidence of thinner ice in the past. We traveled to the Whitmore Mountains, located near the ice-sheet divide, and the Pirrit and Nash Hills, nunatak groups located in the Weddell sector of West Antarctica at ~1300 and ~1500 m, respectively. At the Pirrit Hills, fresh glacial erratics are evidence of thicker ice during the last ice age and indicate that ice levels were at least ~350 m, but less than ~510 m, above the present level. Despite thicker ice, bedrock at all three sites, extending down to the present ice level, is weathered and exhibits delicate cavernous forms, evidence of prolonged subaerial weathering prior to the last ice age. The preservation of these features, along with the lack of evidence for wet-based glacial erosion, indicates that former ice cover was cold-based and protected the underlying bedrock.
    [Show full text]
  • Ancient Pre-Glacial Erosion Surfaces Preserved Beneath the West Antarctic Ice Sheet
    Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Earth Surf. Dynam. Discuss., 2, 681–713, 2014 www.earth-surf-dynam-discuss.net/2/681/2014/ doi:10.5194/esurfd-2-681-2014 ESURFD © Author(s) 2014. CC Attribution 3.0 License. 2, 681–713, 2014 This discussion paper is/has been under review for the journal Earth Surface Dynamics (ESurfD). Ancient pre-glacial Please refer to the corresponding final paper in ESurf if available. erosion surfaces preserved beneath Ancient pre-glacial erosion surfaces the West Antarctic Ice Sheet preserved beneath the West Antarctic Ice K. C. Rose et al. Sheet K. C. Rose1, N. Ross2, R. G. Bingham3, H. F. J. Corr4, F. Ferraccioli4, Title Page 4 5 6 7 T. A. Jordan , A. M. Le Brocq , D. M. Rippin , and M. J. Siegert Abstract Introduction 1 Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, Conclusions References Bristol, BS8 1SS, UK 2School of Geography, Politics & Sociology, Newcastle University, Tables Figures Newcastle upon Tyne, NE1 7RU, UK 3 School of GeoSciences, University of Edinburgh, Edinburgh, EH8 9XP, UK J I 4British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK 5School of Geography, University of Exeter, Exeter, EX4 4RJ, UK J I 6 Environment Department, University of York, York, YO10 5DD, UK Back Close 7Grantham Institute and Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ, UK Full Screen / Esc Printer-friendly Version Interactive Discussion 681 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Received: 16 June 2014 – Accepted: 29 June 2014 – Published: 15 July 2014 Correspondence to: K.
    [Show full text]
  • The Ellsworth Subglacial Mountains and the Early Glacial History of West
    1 The Ellsworth Subglacial Highlands: inception and retreat of the West Antarctic Ice 2 Sheet 3 4 Neil Ross1, Tom A. Jordan2, Robert G. Bingham3, Hugh F.J. Corr2, Fausto Ferraccioli2, 5 Anne Le Brocq4, David M. Rippin5, Andrew P. Wright4, and Martin J. Siegert6 6 7 1. School of Geography, Politics and Sociology, Newcastle University, Newcastle upon 8 Tyne, NE1 7RU, UK 9 2. British Antarctic Survey, Cambridge CB3 0ET, UK 10 3. School of Geosciences, University of Aberdeen, Aberdeen AB24 3UF, UK 11 4. School of Geography, University of Exeter, Exeter EX4 4RJ, UK 12 5. Environment Department, University of York, York YO10 5DD, UK 13 6. Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, 14 Bristol BS8 1SS 15 16 ABSTRACT 17 Antarctic subglacial highlands are where the Antarctic ice sheets first developed 18 and the ‘pinning points’ where retreat phases of the marine-based sectors of the 19 ice sheet are impeded. Due to low ice velocities and limited present-day change in 20 the ice sheet interior, West Antarctic subglacial highlands have been overlooked 21 for detailed study. These regions have considerable potential, however, for 22 establishing from where the West Antarctic Ice Sheet (WAIS) originated and grew, 23 and its likely response to warming climates. Here, we characterize the subglacial 24 morphology of the Ellsworth Subglacial Highlands (ESH), West Antarctica, from 25 ground-based and aerogeophysical radio-echo sounding (RES) surveys and the 26 MODIS Mosaic of Antarctica. We document well-preserved classic landforms 27 associated with restricted, dynamic, marine-proximal alpine glaciation, with 28 hanging tributary valleys feeding a significant overdeepened trough (the Ellsworth 29 Trough) cut by valley (tidewater) glaciers.
    [Show full text]
  • Terrestrial Geology and Geophysics
    Terrestrial geology and geophysics This research is supported by National Science Founda- Geology of the Ellsworth tion grant DPP 76-11867. Mountains to Thiel Mountains ridge Reference CAMPBELL CRADDOCK and GERALD F. WEBERS Thiel, E.C. 1961. Antarctica, one continent or two? Polar Record, Department of Geology and Geophysics 10(67): 335-348. University of Wisconsin Madison, Wisconsin 53706 An area of scattered nunataks and small mountain ranges between the Ellsworth Mountains (79 0S. 85 0W.) and the Thiel Mountains (85°S. 88°W.) comprises the only presently Geology of Queen Maud exposed geologic tie between West Antarctica and East Ant- arctica. Within this area bedrock exposures occur, in Mountains and Marie Byrd Land roughly southward order, in the Pirrit Hills, the Martin Hills, the Nash Hills, the Whitmore Mountains, Pagano Nunatak, the Hart Hills, and the Stewart Hills. In place be- F. ALTON WADE tween these outcrops the bedrock commonly lies near or below sea level (Thiel, 1961). Antarctic Research Center The Ellsworth Mountains consist of a strongly deformed, The Museum, Texas Tech University slightly metamorphosed sequence of Upper Precambrian Lubbock, Texas 79409 (?) - Paleozoic sedimentary and minor volcanic rocks. The section is at least 13,000 meters thick, and fossils range from Middle Cambrian to Permian in age. The structural grain During 1976-1977, activities at the Antarctic Research in this 350-kilometers mountain chain trends northwest at Center were primarily restricted to data reduction, map its southern end but changes gradually to a northerly trend compilations, and report preparation. Investigations con- at its northern end. cerned the geology of two widely separated areas where field Although outcrops are limited, geologic similarities exist studies had been carried out in previous years: (1) Queen among the Pirrit Hills, Martin Hills, Nash Hills, Whitmore Maud Mountains in the vicinity of the Shackleton and Mountains, and Pagano Nunatak.
    [Show full text]