Baffin Island - Idiots guide please!
Andrew Huddart
Why is Baffin Island there, from a tectonic point of view?
Question number two; whilest a lot of the rocks in greenland are
sedimentary, why is Baffin's geology dominated by granite?
Many thanks,
Andrew
--------------------------------------------------------------------------------
geopolitics hudd...@lancs.ac.uk
Daryl Krupa
> I'm a new-comer to geomorphology, so be gentle!
> Why is Baffin Island there, from a tectonic point of view?
>
> Question number two; whilest a lot of the rocks in greenland are
> sedimentary, why is Baffin's geology dominated by granite?
Andrew:
If you're asking why it's an island, it's because of rifting
associated with the opening of the Atlantic Ocean.
Baffin Island is part of the Canadian Shield; there are matching
igneous/metamorphic rocks on the Greenland coast opposite (not
surprising, as they were only relatively recently rifted apart).
Your first question is a tad vague; if the answer above is
insufficient for your purposes, perhaps you might expand upon it.
Be well,
Daryl Krupa
Andrew Huddart
batholith?), which due to faulting has become mountainous in some
areas? I'm not a complete beginner, but from what I've read, there's
nothing that explains it someone without a geology PhD!
thanks,
Andrew
Robin J. Wyllie, P.Geol.
While Baffin Island is part of the Canadian Shield, it is not all
composed of granites. There are a lot of metamorphosed sedimentary and
volcanic rock belts on the island, which can be traced to the east, into
Greenland, and to the west, into the mainland Arctic via the Melville
Peninsula.
Part of the reason for it being an island is that the body of water
between Baffin Island and Greenland is a failed arm of the Atlantic
Ocean, occupied by the Ran Ridge. Activitiy on the Ran Ridge probably
ceased about 40 Ma ago, when the Reykjanes Ridge took over. The reason
for the water being there is the retreat of continental ice about 7000 to
9000 years ago and subsequent rise of sea level.
Now the reason for the mountainous topography is quite simple. It is due
to isostatic rebound. When the last glacial advance (Wisconsinan) was at
its maximum, the mass of ice in the Arctic region actually caused
lithospheric plates to sink into the Earth's mantle. Once the ice melted,
these rafts of continental rock are now bobbing back up.
Drainage systems developing on this rebounding landscape (both liquid
water and ice) are cutting into the landscape as it is still rising
vertically. This is producing the mountainous topography. If you look
along the shorelines of Hudson Bay and James Bay, you will see numerous,
parallel strand lines indicating the positions of former shorelines as
the Canadian Arctic has risen.
Hope this helps!
Robin
Andrew Huddart wrote:
--
Robin J. Wyllie, P.Geol.
Research Exploration Geologist
Lands and Resources Department
Nunavut Tunngavik Inc.
#17 Mitik St., P.O. Box 1269
Cambridge Bay, Nunavut
X0B 0C0
Ph: (867) 983-2517
Fx: (867) 983-2723
E-Mail: rwy...@polarnet.ca
Christof Kuhn
>
> While Baffin Island is part of the Canadian Shield, it is not all
> composed of granites. There are a lot of metamorphosed sedimentary and
> volcanic rock belts on the island, which can be traced to the east, into
> Greenland, and to the west, into the mainland Arctic via the Melville
> Peninsula.
>
Island.
> Now the reason for the mountainous topography is quite simple. It is due
> to isostatic rebound. When the last glacial advance (Wisconsinan) was at
> its maximum, the mass of ice in the Arctic region actually caused
> lithospheric plates to sink into the Earth's mantle. Once the ice melted,
> these rafts of continental rock are now bobbing back up.
>
> Drainage systems developing on this rebounding landscape (both liquid
> water and ice) are cutting into the landscape as it is still rising
> vertically. This is producing the mountainous topography. If you look
> along the shorelines of Hudson Bay and James Bay, you will see numerous,
> parallel strand lines indicating the positions of former shorelines as
> the Canadian Arctic has risen.
>
AFAIK, the isostatic rebound is negative on the edges of a continent. As
the ice on the continent pushes the crust into the mantle, mantle
material moves to the edges of the continent so that the regions at the
edge of the inland ice move up. When the ice melts, the center of the
continent rises whereas the edges sink again.
Compare this to a sheet of paper: if you put it on a bed, for example,
and push into the middle of the sheet - the center of the sheet is
pushed downwards whereas the edges move up.
My knowledge on Canadian geology is poor, but I would believe that
Baffin Island is in fact sinking. The only ancient shorelines I know of
are those of Hudson Bay and James Bay (as you mention) - that's exactly
the center of the inland ice.
The situation is the same in Greenland, Norway and Antarctica -
depressions in the centre and mountains at the shore. This is also quite
effective in preventing the glaciers from flowing into the sea.
Interesting case of feedback.
Cheers, Christof
--
Christof Kuhn
Inst. f. Angewandte Geologie,
Univ. f. BoKu Wien, Austria
ku...@edv1.boku.ac.at
http://homepage.boku.ac.at/h9440283/index.htm
Daryl Krupa
<snip>
> Part of the reason for it being an island is that the body of water
> between Baffin Island and Greenland is a failed arm of the Atlantic
> Ocean, occupied by the Ran Ridge. Activitiy on the Ran Ridge probably
> ceased about 40 Ma ago, when the Reykjanes Ridge took over. The reason
> for the water being there is the retreat of continental ice about 7000 to
> 9000 years ago and subsequent rise of sea level.
Robin:
This is misleading.
The reason for the water being there is that the floor of Baffin Bay
is hundreds of metres below sea level, and has been for dozens of
millions
of years.
Melting of the continental ice sheets only increased the depth.
Also, the retreat of continental ice started about 18000 years ago,
and
the melting, and the global sea level rise that resulted, was
essentially finished by 6000 years ago. I can only imagine that your
limited period
between 9000 and 7000 years ago refers either to deglaciation of
Nunavut
in general or to Baffin Island in particular; both areas were
deglaciated
after most of the temperate-latitude ice sheets had disappeared, and
after
the greater part of post-glacial global sea level rise.
> Now the reason for the mountainous topography is quite simple.
> It is due to isostatic rebound. When the last glacial advance
> (Wisconsinan) was at its maximum, the mass of ice in the Arctic
> region actually caused lithospheric plates to sink into the
> Earth's mantle. Once the ice melted, these rafts of continental
> rock are now bobbing back up.
True enough, as far as it goes . . .
> Drainage systems developing on this rebounding landscape (both liquid
> water and ice) are cutting into the landscape as it is still rising
> vertically. This is producing the mountainous topography.
Actually, it is only accentuating the pre-existing mountainous
topography. Post-glacial isostatic rebound responsible for only
a small fraction of the height of the western Baffin highlands.
They were mountains long before large-scale continental
glaciation started about 3 million years ago.
The highlands are the result of plate-tectonic activity, not
isostatic rebound after deglaciation.
Given that the difference in height between the highlands and
the sea is less now than at glacial maximum, and that the size of
the modern glaciers on Baffin is quite limited, I'd say that
'drainage systems' are much less effective at carving valleys now
than they were at glacial maximum, when the western valleys were
acting as outlet glaciers for a full-size ice sheet inland. I.e.,
the mountainous topography of coastal western Baffin was mostly
formed _before_ post-glacial isostatic rebound uplifted it slightly.
> If you look along the shorelines of Hudson Bay and James Bay,
> you will see numerous, parallel strand lines indicating the
> positions of former shorelines as the Canadian Arctic has risen.
Um, no, they don't.
Hudson Bay, and James Bay even more so, are not in the Canadian
Arctic. Though the islands in these two water bodies are considered
part of the (primarily) Arctic territory of Nunavut, this is only
a historical accident; the northern end of James Bay is more than
a thousand kilometres south of the Arctic Circle.
In any case, the raised beaches of the Hudson Bay lowland are a
poor example, as they are not associated with mountainous topography
(even though they have risen much more than the coast of Baffin),
any more than the raised gravel beaches of Cambridge Bay are.
Perhaps you could get ahold of one of the volumes in the
centennial project of the Geological Survey of Canada (and later,
also a centennial project of the U. S. Geological Survey),
The Geology of North America
Specifically,
The Quaternary Geology of Canada and Greenland
This should be a standard reference for a Canadian Geologist.
Contact the GSC to see if they are still selling them.
If not, I'm sure that you could browse through the copies in
the University and Public Libraries next time you're in Edmonton.
And of course, the GSC has an excellent web site.
Good luck learning about the Cenozoic geological history of
the Canadian Arctic, because it's required knowledge for
effective exploration geology there,
Daryl Krupa