The East Greenland Rifted Volcanic Margin
Total Page:16
File Type:pdf, Size:1020Kb
GEOLOGICAL SURVEY OF DENMARK AND GREENLAND BULLETIN 24 • 2011 The East Greenland rifted volcanic margin C. Kent Brooks GEOLOGICAL SURVEY OF DENMARK AND GREENLAND DANISH MINISTRY OF CLIMATE, ENERGY AND BUILDING 1 Geological Survey of Denmark and Greenland Bulletin 24 Keywords East Greenland, North Atlantic, rifted volcanic margin, large igneous province, LIP, Palaeogene, basalt, syenite, nephelinite, carbona- tite, uplift. Cover Sundown over the nunataks in the Main Basalts (Skrænterne Fm) to the south of Scoresby Sund. Camped on the glacier, the 1965 Ox- ford University East Greenland Expedition travelled and collected from this area on foot, manhauling equipment on the sledge to the left. The expedition results were published in Fawcett et al. (1973). Frontispiece: facing page Mountains of horizontally layered basalt flows rising to about 2000 m on the south side of Scoresby Sund. Typical trap topography as found throughout most of the Kangerlussuaq–Scoresby Sund inland area. Chief editor of this series: Adam A. Garde Editorial board of this series: John A. Korstgård, Department of Geoscience, Aarhus University; Minik Rosing, Geological Museum, University of Copenhagen; Finn Surlyk, Department of Geography and Geology, University of Copenhagen Scientific editor of this volume: Adam A. Garde Editorial secretaries: Jane Holst and Esben W. Glendal Referees: Dennis K. Bird (USA) and Christian Tegner (DK) Illustrations: Eva Melskens with contributions from Adam A. Garde Digital photographic work: Benny Schark Graphic production: Kristian A. Rasmussen Printers: Rosendahls · Schultz Grafisk A/S, Albertslund, Denmark Manuscript received: 1 March 2011 Final version approved: 20 September 2011 Printed: 22 December 2011 ISSN 1604-8156 ISBN 978-87-7871-322-3 Citation of the name of this series It is recommended that the name of this series is cited in full, viz. Geological Survey of Denmark and Greenland Bulletin. If abbreviation of this volume is necessary, the following form is suggested: Geol. Surv. Den. Green. Bull. 24, 96 pp. Available from Geological Survey of Denmark and Greenland (GEUS) Øster Voldgade 10, DK-1350 Copenhagen K, Denmark Phone: +45 38 14 20 00, fax: +45 38 14 20 50, e-mail: [email protected] or at www.geus.dk/publications/bull © De Nationale Geologiske Undersøgelser for Danmark og Grønland (GEUS), 2011 For the full text of the GEUS copyright clause, please refer to www.geus.dk/publications/bull 2 3 Contents Abstract ..................................................................................................... 5 Introduction ...............................................................................................7 Historical background ...................................................................................7 Note on stratigraphic nomenclature and radiometric dating ................................11 Components of the rifted volcanic margin ...........................................................13 Th e Precambrian and Caledonian crystalline basement .......................................13 Th e pre-basaltic sedimentary rocks (the Kangerdlugssuaq Group) ...........................14 Th e Lower Basalts ..................................................................................16 Th e Main Basalts ...................................................................................19 Introduction .................................................................................19 Extent .........................................................................................20 Structure .....................................................................................21 Stratigraphy ..................................................................................21 Composition and genesis ...................................................................24 Radiometric ages and timing of volcanism ...............................................25 Zeolite zones .................................................................................27 Comments on the plume hypothesis ....................................................27 Late basalts and sedimentary rocks (the Prinsen af Wales Bjerge Formation etc.) ...........27 Miocene basalts ....................................................................................28 Off shore basalts ....................................................................................29 Basalts of northern East Greenland ..............................................................29 Long-distance tephra falls .........................................................................31 Gabbroic intrusions ...............................................................................32 Th e Skaergaard intrusion .................................................................32 Other gabbroic intrusions .................................................................34 Ultramafi c plugs etc. ..............................................................................36 Felsic intrusions and volcanic rocks .............................................................39 Th e Kangerlussuaq – Blosseville Kyst area ..............................................41 Th e Mesters Vig area .......................................................................45 Th e Kialeeq (Kialineq) – Kap Gustav Holm area ......................................47 Syenite genesis ..............................................................................49 Nephelinites, carbonatites etc. ....................................................................50 Nephelinite genesis ........................................................................53 Dykes and sills .....................................................................................54 Hydrothermal activity .............................................................................60 Geomorphology ....................................................................................61 Structure of the East Greenland margin and its setting within the North Atlantic region .....64 Th e coastal fl exure and its dykes .........................................................64 Segmentation of the margin ..............................................................65 Vertical and horizontal distribution of igneous material in the crust ................66 Plate-tectonic patterns .....................................................................67 Vertical movements and erosion .........................................................67 Time frame for magmatism and margin deformation .................................69 Mechanisms of North Atlantic rifting ...................................................70 Summary and perspectives ..............................................................................72 Concluding remarks ...............................................................................74 Acknowledgements .......................................................................................75 References ..................................................................................................76 Appendix ...................................................................................................93 4 Abstract Brooks, C.K. 2011: The East Greenland rifted volcanic margin. Geological Survey of Denmark and Greenland Bulletin 24, 96 pp. The Palaeogene North Atlantic Igneous Province is among the largest igneous provinces in the world and this review of the East Greenland sector includes large amounts of information amassed since previous reviews around 1990. The main area of igneous rocks extends from Kangerlussuaq (c. 67°N) to Scoresby Sund (c. 70°N), where basalts extend over c. 65 000 km2, with a second area from Hold with Hope (c. 73°N) to Shannon (c. 75°N). In addition, the Ocean Drilling Project penetrated basalt at five sites off South-East Greenland. Up to 7 km thickness of basaltic lavas have been stratigraphically and chemically described and their ages determined. A wide spectrum of intrusions are clustered around Kangerlussuaq, Kialeeq (c. 66°N) and Mesters Vig (c. 72°N). Layered gabbros are nu- merous (e.g. the Skaergaard and Kap Edvard Holm intrusions), as are under- and oversaturated syenites, besides small amounts of nephelinite-derived products, such as the Gardiner complex (c. 69°N) with carbonatites and silicate rocks rich in melilite, perovskite etc. Felsic extrusive rocks are sparse. A single, sanidine-bearing tuff found over an extensive area of the North Atlantic is thought to be sourced from the Gardiner complex. The province is famous for its coast-parallel dyke swarm, analogous to the sheeted dyke swarm of ophiolites, its associated coastal flexure, and many other dyke swarms, commonly related to central intrusive complexes as in Iceland. The dyke swarms provide time markers, tracers of magmatic evolution and evidence of extensional events. A set of dykes with harzburgite nodules gives unique insight into the Archaean subcontinental lithosphere. Radiometric dating indicates extrusion of huge volumes of basalt over a short time interval, but the overall life of the province was prolonged, beginning with basaltic magmas at c. 60 Ma and continuing to the quartz porphyry stock at Malmbjerg (c. 72°N) at c. 26 Ma. Indeed, activity was renewed in the Miocene with the emplacement of small volumes of basalts of the Vindtoppen Formation to the south of Scoresby Sund. Although the basalts were extruded close to sea level, this part of East Greenland is