Transcript Mapping of volcanic facies variations onshore West Greenland

Mapping of volcanic facies
variations onshore West
Greenland
Asger 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
Plateau basalt lava stage. Lavas progress far
beyond basin margin into graiss hinterland
Lava-infilling of lakes, subaqueatic lava flows
and invasive lavas (sills)
Lava plateau expands. Formation of large
Lake complexes, infilling by hyaloclastites,
Abundant eruption sites on land and in the
Lakes.
Lava plateau expands, narrowing of marine
basin, large scale infilling by hyaloclastites
Volcanism starts in marine basin. Volcanic
island stage: Lavas, hyaloclastites,
mass flows
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Nuussuaq north coast 2006
Five sections
through the
Nuussuaq
Basin
constructed
1993 and 2001
to 2006
Central Nuussuaq 2002
Nuussuaq south coast 1993
Central Disko 2005
Disko south coast 2003
Photos taken from helicopter,
boat and fixed-wing plane.
Construct multi-stereo panels
Combine with aerial
photographs
Product: Geological maps
Large sections
Detailed sections
Structural measurements
The sections compile
Information from
Field work
Petrology
Geochemistry
Palaeomagnetism
Palaeontology
Sedimentology
Multi-model photogrammetry: Photos takes with stereo-overlap
using calibrated small-frame cameras.
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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
Topics to be presented
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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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Pahoehoe lava flows enter the sea at the south
coast of Hawaii
Hawaii,USGS
Lava
Hyaloclastite
Facies transition at Nuuk Killeq, Nuussuaq
Nuussap Qaqqarsua
Chron 26R
Magnetic transition
zone ca 5000 y
Nuussap Qaqqarsua
Large plateau basalts from the Maligât Formation at Giesecke Monument, Nuussuaq
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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: hyaloclastites
Max 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
Large fragment with several subaerial lava flows
Mass flow
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
Picrite crater
Feeder dyke
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
Thin picritic lava flows
Thin feeder dykes
Subaqueous eruption site
Picritic lava flows
Hy
Subaqueous
Eruption
site
Several hundred metres deep lake being filled by hyaloclastites
derived from lava flows and by subqueous eruption sites
Large fault at basin margin in central Nuussuaq
Gneiss
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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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Southern cone
Subaerial graphite
andesite tuff
Pi Lava
Pi Hy
Submarine graphite
andesite tuff
Pi Hy
Southern part of the Ilugissoq graphite andesite volcano
Erosion
on top of
cone
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.