Included blocks (and blocks within blocks) in the Skaergaard intrusion: Geologic relations and the origins of

rhythmic modally graded layers

By T. Neil Irvine, Jens Christian Andersen and C. Kent Brooks

Autolith blocks and rhythmic modally graded layers in the

Skaergaard intrusion

Presented by: Angelique Laurie

The Skaergaard intrusion: Introduction and emplacement

Fig 1: Skaergaard emplacement (Geological Society of America, November, pg 1401)

Skaergaard : Series’

• Layered Series

• Marginal Series

• Upper Border Series

The Skaergaard intrusion: Series’

Fig 2: Skaergaard shape and series’ (Origin of Igneous Layering edited by Ian Parsons, pg 205)

Fig 3: Skaergaard Series’ (www.union.edu/PUBLIC/GEODEPT/hollocher/skaergaard/

Skaergaard layering

1) Modally graded layers

2) Uniform/isomodal layers

3) Macro-rhythmic layers

4) Micro-rhythmic layers

Fig 4: Modally graded and uniform layers

(www.union.edu/PUBLIC/GEODEPT/hollocher/skaergaard/ )

Fig 5: Macro-rythmic layers (www.union.edu/PUBLIC/GEODEPT/hollocher/skaergaard/ ) Fig 6: Micro-rhythmic layers

(www.union.edu/PUBLIC/GEODEPT/hollocher/skaergaard/ )

Blocks and Block Structures1) Streamlining 2) Block impact structures

3) Fragmental layers

4) Trough layering structures

Fig 9: Fragmental layers (www.union.edu/PUBLIC/GEODEPT/hollocher/skaergaard/ )

Fig 7: Steamlining (Geological Society of America Bulletin, November, pg 1420)

Fig 10: Fragmental layers (Geological Society of America Bulletin, November, pg 1420)

Fig 8: Block impact structures (Origins of igneous layering, Ian Parsons, pg 218)

Deposition of modally sorted layers

1) Boundary flow seperation and reattachment

Fig 11: S-R cell (Geological Society of America Bulletin, November, pg 1438)

Deposition of modally sorted layers

2) Density surge currents

Fig 12:Density surge currents (Geological Society of America Bulletin, November, pg 1438)

Conclusion

Fig 13: Processes occuring in the western hal fof the Skaergaard magma chamber (Geological Society of America Bulletin, November 1998 pg 1442)

Comparison with Bushveld Igneous complex

Bushveld SkaergaardLocation South Africa Greenland

Age Precambrian Eocene

Size 66 000 km2 100 km2

Shape Flat funnel Oval

Magma injection Repeated Single

System and magma movement

Open feeder, non convecting

Closed feeder, convecting

Layering horizontal,rhythmic modally graded

concentric,rhythmic modally

graded

Blocks uncommon common

Value economic- platinum (chrome) scientific - “type locality”

Thank –you!