Chilled and Baked Margins
-
Upload
maisarah-idrus -
Category
Documents
-
view
217 -
download
0
Transcript of Chilled and Baked Margins
7/22/2019 Chilled and Baked Margins
http://slidepdf.com/reader/full/chilled-and-baked-margins 1/7
Chilled and Baked Margins• The specification states that
you need to be able to:
• explain the origin and nature
of chilled and baked margins
and metamorphic aureoles. • distinguish between intrusive
and extrusive igneous rocks.
• Explain the differences
between rocks formed by
these methods
– Sill
– Lava flow
7/22/2019 Chilled and Baked Margins
http://slidepdf.com/reader/full/chilled-and-baked-margins 2/7
Chilled and Baked Margins• When an intrusion of hot magma occurs the
surrounding rocks will be heated up and baked.• This is a kind of metamorphism and it is called a
baked margin.
• The magma at the edge of the intrusion will cooldown quickly and so will form smaller crystals
than in the middle.• This is called a chilled margin.
7/22/2019 Chilled and Baked Margins
http://slidepdf.com/reader/full/chilled-and-baked-margins 3/7
Metamorphic Aureole
• Batholiths heat a much
larger zone of country
rock so that a
metamorphic aureole is
100's of metres toseveral kilometres.
• The rocks are altered by
contact metamorphism to produce a
metamorphic aureole.
7/22/2019 Chilled and Baked Margins
http://slidepdf.com/reader/full/chilled-and-baked-margins 4/7
Distinguishing between intrusive
and extrusive igneous rocks.•
Write down as many differences asyou can think of.
• Grain size.
– Extrusive will be fine grained or glassy.
–
Intrusive from fine grained to coarsegrained.
• Relationship to the country rock.
– Extrusive parallel to beds.
– Intrusive concordant if a sill but often
discordant (dykes and batholiths).
• Extrusive may have vesicles.
• Extrusive may have weathered
surfaces.
7/22/2019 Chilled and Baked Margins
http://slidepdf.com/reader/full/chilled-and-baked-margins 5/7
Distinguishing between a sill and
a lava flow
• Look at the diagram above which shows a sill and a lavaflow.
• Look carefully at the diagram and note down as manydifferences as you can.
7/22/2019 Chilled and Baked Margins
http://slidepdf.com/reader/full/chilled-and-baked-margins 6/7
Distinguishing between a
sill and a lava flow•
Baked margins: – Sill will have 2.
– Lava flow will have 1
• Both will have 2 chilled
margins.• Grain size:
– The lava flow will be fine orglassy.
– The sill will be fine or medium.• The sill may occasionally cut
across the beds.
• Lava flow should remain
concordant.
7/22/2019 Chilled and Baked Margins
http://slidepdf.com/reader/full/chilled-and-baked-margins 7/7
Distinguishing between a
sill and a lava flow• The lava flow may have
vesicles towards the top.
• The lava flow may have aweathered (reddened?) topsurface.
• The sill may have xenolithsfrom the country rock(included fragments)
• A xenolith is a bit of thecountry rock that has fallen
into the intruding magmabecause of the forcefulnature of the intrusion.
• There may be clasts of thelava flow in the next
(younger bed).