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

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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

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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.