Flowerdew, M.J.

Haselwimmer, C.E.

Riley, T.R.

NERC Open Research Archive

2217222478221824207346702785756070834588713057608457562545127045558880416080484035 2347254188236828 252814408363434042182527221402037553851010103530551105 180504030388938897545103037540211512287615099176217255296102216301581302011157201312394 2331433101020158122116 5121155010341010110 10520560301010111165201015555544°20'W44°20'W44°30'44°30'44°40'44°40'44°50'44°50'45°45°W45°10'45°10'45°20'45°20'45°30'W45°30'45°40'45°40'45°50'W45°50'46°W46°46°10'W46°10'W60°30'S60°30'S60°35'60°35'60°40'S60°40'60°45'S60°45'60°50'S60°50'S5046°40'W46°40'W60°35'S60°35'S46°46°10'W60°45'60°50'SPOWELL ISLANDSIGNYISLANDMoe IslandMatthews IslandFredricksen IslandSaddle IslandWeddell IslandsLarsen IslandsMonroe IslandC O R O N A T I ON I S L ANDL A U R I E  I SLANDGibbon BayRayner PointJohns PeaksINACCESSIBLE ISLANDS3323333333332222222222555544221111111155222Scale: 1:150 0000 2.5 50 2.5 5 7.5 10kilometresmilesA1A(3) TriassicRWR 243KWR 98 91 86KWR 239A100020000-1000-2000-3000-4000metresA1GEOLOGICAL CROSS SECTION FROM CLEFT POINT TO CAPE WHITSON (Line A-A1 drawn on the map)Horizontal scale 1:150 000   Vertical exaggeration x 214522222222222 33333322 211 1P O W E L L  I S L A N DCape Robertson Cape WhitsonEcho MountainCleft PointDevils PeakBeaufoy Ridge Roald Glacier Spence Harbour W a s h i n g t o n  S t r a i tL A U R I E    I S L A N DC O R O N A T I O N     I S L A N D333344°40'44°40'W45°45°45°20'45°20'45°40'45°40'46°W46°W60°40'S60°40'Sthermal aureoleMAP OF METAMORPHIC FACIES  AND GEOCHRONOLOGYScale 1:300 000Extreme retrogression into greenschist-faciesModerate retrogression into greenschist-faciesPristineEpidote-amphiboliteAndalusite localityEpidote-amphibolite with dominant ﬂsGarnet-biotite greenschistGarnet greenschistAnchi-low greenschistUnmetamorphosedRMu 187KMu 187RBt 179KBt 195 199KBt 176KBt 177KBt 183KBt 184KBt 189KBt 193KHb 188 192KHb 190 190 193KHb 191 185 184 183RMu193RBt 175KMu 176KBt 195KMu 189KMu 186KBt 178RMu 188RBt 176RMu190AHb190/174AMu184AAAPERIOD EPOCH/AGEGEOLOGICAL LEGENDGeological units are coloured as dark and light tints representing exposed (nunataks) or inferred geology (under ice or snow)Scotia Metamorphic ComplexProtoliths equivalent to Greywacke Shale Formation (1) but Late Triassic / early Jurassic metamorphism reached epidote amphibolite-facies grade.Scotia Metamorphic Complex (mixed unit)Scotia Metamorphic Complex (2) with abundant interleaved units of ocean ﬂoor derived sequences of uncertain (probable Permian - early Jurassic) age.  The oceanic elements include marble, amphibolite and epidote amphibolites, metapelite and metachert which were juxtaposed with the Scotia Metamorphic Complex (2) during Late Triassic / early Jurassic deformation at epidote amphibolite facies metamorphic grade.  The mixed unit is exposed on Signy Island, Coronation Island and the Inaccessible Islands.Greywacke Shale FormationPermian - Triassic sandstone (feldspathic arenite and feldspathic wacke) with minor siltstone, mudstone and diamictite deposited as turbidity currents in submarine fans and widely exposed east of Coronation Island.  Variably deformed and foliated, metamorphosed to between anchizone to upper greenschist-facies during the Late Triassic / early Jurassic.Powell Island ConglomerateConglomerate and sandstone exposed on southern Powell Island, deposited as debris ﬂows and braided stream deposits in alluvial fans within terrestrial to marine fault-bounded basins.  Boulders resembling Greywacke Shale Formation (1) suggest a local derivation from the north and east.  Youngest braided stream deposits at Johns Peaks contain Middle Jurassic ﬂora.Spence Harbour ConglomeratePredominantly conglomerate with thin persistent sandstone interbeds, exposed on eastern Coronation Island and Matthews Island, deposited as debris ﬂows and braided stream deposits in alluvial fans within terrestrial to marine fault-bounded basins.  Boulders lithologically resembling the Scotia Metamorphic Complex (2) are dominant and suggest a local derivation from the west.  Age constraints come from calcareous sandstone boulders at Rayner Point which contain a Late Jurassic - Early Cretaceous fauna and also from a poorly preserved Late Jurassic marine fauna on Matthews Island.  Basal units in the vicinity of Gibbon Bay, eastern Coronation Island, consist of sparsely fossiliferous (Late Jurassic - Early Cretaceous) dark marine shale, the Gibbon Bay Shale.  It rests unconformably on the Scotia Metamorphic Complex (1).JURASSICMiddleLateEarlyEarlyCRETACEOUSGEOLOGICAL SYMBOLSOTHER SYMBOLSCleavage or metamorphic foliation55Bedding70Overturned bedding42Geological boundaryFaultUnconformityDolerite Dykes: tholeiitic augite and rarely olivine-bearing dolerite dykes recognised intermittently along the southern Coast of Coronation Island and on Matthews Island.  K-Ar whole rock geochronology suggests a Late Cretaceous intrusion age for the dolerites.Fold hinge line7Rodding within L-tectonites5Fault brecciaDuctile shear zoneTRIASSIC / PERMIANSEDIMENTARY ROCKS PLUTONIC AND METAMORPHIC ROCKS1 2345AMu Ar-Ar muscovite radiometric age RBt Rb-Sr biotite radiometric age KMu K-Ar muscovite radiometric age RWR Rb-Sr whole rock radiometric age KBt K-Ar biotite radiometric age Unreliable ageAge reliability (main and metamorphic maps) Inferred protolith ages (main map) Metamorphic ages (metamorphic map)KHb K-Ar hornblende radiometric age KWR K-Ar whole rock radiometric age Possibly reliable ageAHb Ar-Ar hornblende radiometric age RMu Rb-Sr muscovite radiometric age Reliable ageRadiometric agesColoured circles (key below) on the 'Map of Metamorphic Facies and Geochronology' indicate method and ages (Ma) of metamorphism and on the main map indicate method and ages of sedimentary and igneous protoliths. Geological Map of the South Orkney Islands1:150 000 ScaleFossil leavesRadiolarian fossilInvertebrate fossilCoastlineGeological interpretation and map compilation by M.J. Flowerdew, T.R. Riley and C.E. Haselwimmer. Geological cross sections compiled by M.J. Flowerdew and C.E. Haselwimmer. Data preparation, digital cartography, design, and layout by C.E. Haselwimmer. Geological mapping and digital map production was undertaken as part of the BAS Environmental Change and Evolution (ECE) programme.Base map data for coastlines, rock outcrops, and ice shelves from the Antarctic Digital Database. The Antarctic Digital Database is copyright © 1993-2006 Scientiﬁc Committee on Antarctic Research.Preferred reference for map:FLOWERDEW, M.J., RILEY, T.R. and HASELWIMMER, C.E. 2011. Geological Map of the South Orkney Islands (1:150 000 scale). BAS GEOMAP 2 Series, Sheet 3, British Antarctic Survey, Cambridge, UK.Projection: WGS 1984 Antarctic Polar Stereographic, Central Meridian: 60°W, Spheroid: WGS84. Latitude of true scale: 71°S.Published by BRITISH ANTARCTIC SURVEY, High Cross, Madingley Road, Cambridge, CB3 0ET, United Kingdom. This geological map is copyright © British Antarctic Survey, Natural Environment Research Council, 2011. All rights reserved.BAS GEOMAP 2 Series, Sheet 3, Edition 1SeaREFERENCES1-457-95-61011121213 15-17141. Matthews, D.H. & Malling, D.H. 1967. The Geology of the South Orkney Islands I. Signy Island. Falkland Islands Dependencies Survey scientiﬁc reports, 25, 32pp.2. Thomson, J.W. 1968. The Geology of the South Orkney Islands II. The Petrology of Signy Island. Falkland Islands Dependencies Survey scientiﬁc reports, 62, 30pp.3. Meneilly, A.W. & Storey, B.C. 1986. Ductile thrusting within subduction complex rocks on Signy Island, South Orkney Islands. Journal of Structural Geology, 8, 457-472.4. Storey, B.C. & Meneilly, A.W. 1985. Petrogenesis of metamorphic rocks within a subduction-accretion terrane, Signy Island, South Orkney Islands. Journal of Metamorphic Geology, 3, 21-42.5. Elliot, D.H. & Wells, N.A. 1982. Mesozoic alluvial fans of the South Orkney Islands. In: Antarctic Geoscience, ed. C. Craddock, University of Wisconsin Press, Madison, 235-244.6. Cantrill, D.J. 2000. A new macroﬂora from the South Orkney Islands, Antarctica: evidence of an Early to Middle Jurassic age for the Powell Island Conglomerate. Antarctic Science, 12, 185-195.7. Trouw, R.A.J., Pankhurst, R.J. & Ribeiro, A. 1997. On the relation between the Scotia Metamorphic Complex and the Trinity Peninsula Group, Antarctic Peninsula, In: The Antarctic Region: Geological Evolution and Processes, ed. C.A. Ricci. Terra Antarctica Publication, Siena, 383-389.8. Trouw, R.A.J., Passchier, C.W., Simões, L.S.A., Andreis, R.R. & Valeriano, C.M. 1997. Mesozoic tectonic evolution of the South Orkney microcontinent, Scotia arc, Antarctica. Geological Magazine, 134, 383-401.9. Thomson, J.W. 1973. The geology of Powell, Christoffersen and Michelsen islands, South Orkney Islands. British Antarctic Survey Bulletin, 33-34, 137-167.10. Andreis, R.R., Ribeiro, A., Trouw, R.A.J. 1997. Remarks on the petrofacies of Permo-Triassic turbidites from the Antarctic Peninsula, South Shetland and South Orkney islands, In: The Antarctic Region: Geological Evolution and Processes, ed. C.A. Ricci, 401-407.11. Dalziel, I.W.D., Elliot, D.H., Jones, D.L., Thonson, J.W., Thomson, M.R.A., Wells, N.A. & Zinsmeister, W.J. 1981. The geological signiﬁcance of some Triassic microfossils from the South Orkney Islands, Scotia Ridge. Geological Magazine, 118, 15-25.12. Thomson, M.R.A. 1981. Late Mesozoic stratigraphy of the South Orkney Islands, British Antarctic Survey Bulletin, 54, 65-83.13. Thomson, J.W. 1974. The geology of the South Orkney Islands III. Coronation Island. British Antarctic Survey Scientiﬁc Reports,  86, 39pp.14. Storey, B.C. & Meneilly, A.W. 1983. Melange within subduction-accretion complex rocks of Fredriksen Island, South Orkney Islands. Geological Magazine, 120, 555-566.15. Dalziel, I.W.D. 1984. Tectonic evolution of a forearc terrane, southern Scotia ridge, Antarctica. Geological Society of America Special Paper 220, 32pp.16.  Thomson, J.W. & Harris, J.S. 1984. BAS British Antarctic Territory Geological map 1:500,000, Sheet 1.17.  Unpublished British Antarctic Survey records: ﬁeld notes, maps, rock and thin section collections.MAP COMPILATION DIAGRAMNumbers of the bounding boxes refer to the references listed abovePrinted by Butler, Tanner and Dennis, Frome, Somerset

Geological Map of the South Orkney Islands

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Geological Map of the South Orkney Islands

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