Mapping of volcanic facies variations onshore West Greenland Asger Ken Pedersen Geological Museum...
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Transcript of Mapping of volcanic facies variations onshore West Greenland Asger Ken Pedersen Geological Museum...
Mapping of volcanic facies variations onshore West
GreenlandAsger Ken Pedersen
Geological Museum
University of Copenhagen
The Nuussuaq Basin in central West Greenland
Sediments: Mid Cretaceous
to Palaeogene
Volcanic Formations:
Main stage in Paleocene
Late stage in Eocene
Volcanism starts in marine basin. Volcanic island stage: Lavas, hyaloclastites, mass flows
Lava plateau expands, narrowing of marine basin, large scale infilling by hyaloclastites
Lava plateau expands. Formation of largeLake complexes, infilling by hyaloclastites,Abundant eruption sites on land and in theLakes.
Plateau basalt lava stage. Lavas progress far beyond basin margin into graiss hinterlandLava-infilling of lakes, subaqueatic lava flows and invasive lavas (sills)
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Five sections through the Nuussuaq Basinconstructed 1993 and 2001 to 2006
Nuussuaq south coast 1993
Central Disko 2005
Disko south coast 2003
Central Nuussuaq 2002
Nuussuaq north coast 2006
Multi-model photogrammetry: Photos takes with stereo-overlapusing calibrated small-frame cameras.
Photos taken from helicopter,boat and fixed-wing plane.
Construct multi-stereo panelsCombine with aerial photographs
Product: Geological mapsLarge sectionsDetailed sectionsStructural measurements
The sections compileInformation fromField work PetrologyGeochemistryPalaeomagnetismPalaeontologySedimentology
Section 1: South coast of Nuussuaq, 1.20 000, 80 km profile length.
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Section 2: Aaffarsuaq valley in central Nuussuaq, 1:20 000, 110 km profile length
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Section 3: The south and south-west coast of Disko, 1:20 000, 130 km profile length
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Section 4: Across central Disko, 1:20 000, ca. 110 km profile length
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Topics to be presented
• Subaerial lava flows• Infilling of marine basins• Basin subsidence and early volcanic aggradation• Large plateau lavas and their interaction with sediments• The early volcanic island stage, mass flows and
conglomerates• Significance of the volcanic feeder systems
Picrite lavas on gneiss in central Nuussuaq
The transition between the Vaigat Formation (picritic pahoehoe flows) and the Maligât Formation (thick plateau basalts) on Nuussuaq
Vaigat Formation: Lavas and hyaloclastites
cover Cretaceous and Palaeogene sediments
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Hawaii,USGS
Pahoehoe lava flows enter the sea at the south coast of Hawaii
Facies transition at Nuuk Killeq, Nuussuaq
Lava
Hyaloclastite
Nuussap Qaqqarsua
Nuussap Qaqqarsua
Magnetic transition zone ca 5000 y
Chron 26R
Large plateau basalts from the Maligât Formation at Giesecke Monument, Nuussuaq
Skarvefjeld east of Qeqertarsuaq, Godhavn. 1.Subaqueous lavas 2: hyaloclastites 3: Subaerial lavas
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Subaqueous lava flow who has started to burrow into Paleocene mudstone, Maligât Formation, Disko
On top subaerial lava flows, below lava flows who have continued eastwards as ”sills” (invasive lavas), eastern part of the sediment basin
Drill cores and profiles in Anaanaa Member
Heavy colours: lava series, light colours: hyaloclastitesMax duration of A Mb ca 300 000 y, chron 27n
Lipman et al. 2006
Early picritic eruption site on the sea floor. It is a pillow cone
Anaanaa Member in the Vaigat Formation on Nuussuaq
Clast supported conglomerate formed by erosion of lava flows at the coast of small lava island. The conglomerate is now oil-saturated. Early Vaigat Formation at Sikillingi on Nuussuaq
Mass flow
Large fragment with several subaerial lava flows
A more than 20 m sized fragment with several lava flows, who has slided to a palaeodepth of more than 200 m from the old shore zone.
Large mass flow at Nuusaq, Early Vaigat Formation
Eruption sites
• Subaerial on the lava plain
• On the sea or lake floor
• Eruptions channeled into older fault structures
• Phreatic craters
Feeder dyke
Picrite crater
Eruption site in central Nuussuaq
Two picrite crater sites within the upper part of the
Vaigat Formation on Nuussuaq
Thin subaerial picritic lava flows
Hyaloclastite with numerous thin picritic
feeder dykes
Subaqueous eruption site within a large lake
Subaqueous eruption site
Thin picritic lava flows
Thin feeder dykes
SubaqueousEruptionsite
Several hundred metres deep lake being filled by hyaloclastites derived from lava flows and by subqueous eruption sites
Picritic lava flows
Hy
Gneiss
Large fault at basin margin in central Nuussuaq
Foreset-bedded picritic hyaloclastites from the Vaigat Formation covered by lava flows
Central Nuussuaq just west of a large marginal fault zone.
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Pi LavaPi Hy
Submarine graphite andesite tuff
Subaerial graphite andesite tuff
Southern cone
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L Erosion on top of cone
Pi Hy
Southern part of the Ilugissoq graphite andesite volcano
What can you learn by studying the Nuussuaq Basin in West Greenland
• A wide range of subaerial basalt lava features• Volcanic infilling patterns in passive and dynamically
active marine and lacustrine basins.• The morphology and distribution of basaltic eruption
sites.• Well exposed examples of interaction between basalts
and unconsolidated sediments. Invasive lavas.• Large and coherent exposures of a sedimentary and
volcanic basin and its margin.