North Dakota Geological Survey Deep Geothermal Resources ...
North American Geological History
description
Transcript of North American Geological History
North American Geological History
So what did we figure out about the East Coast so far?
• Proterozoic: suture zone, rifting• Cambrian: passive margin• Ordovician: subduction complex (Japan-like)
hits North America
OK, on to the rest of the Paleozoic
• Silurian: passive margin• Devonian: collision of continental fragment
with North America – Avalonia: Acadian Orogeny
• Miss/Penn: Acadian mountains shed sediment into the interior of the continent
• Permian:collision with Africa and Europe makes Pangaea
Pangaea• The Permian collision was only a piece of the
formation of a supercontinent called Pangaea
http://3dparks.wr.usgs.gov/nyc/images/fig83.jpg
How do we know Pangaea existed and finished forming in the Permian?
• Age patterns on ocean floor (reflected in magnetic stripes
http://sos.noaa.gov/ge/land/sea_floor_age/topo/4096.png
How do we know Pangaea existed and finished forming in the Permian?
• Age patterns on ocean floor (reflected in magnetic stripes
• Mountain belts /terranes that run from one continent to another
• Climate belts that run from one continent to another
• Fossils
http://www.mrsciguy.com/sciimages/fossil_record.gif
How do we know Pangaea existed and finished forming in the Permian?
• Age patterns on ocean floor (reflected in magnetic stripes
• Mountain belts /terranes that run from one continent to another
• Climate belts that run from one continent to another
• Fossils• Glaciation
Meanwhile, back on the craton…
• Cambrian: lots of sandstones, limestone – some land to erode to make sand
• Ordovician: lots of limestone, whole continent is covered in water – no land eroding to make sediment
• Silurian - Devonian: evaporites in Michigan Basin because reefs around the edge restrict circulation
Middle Paleozoic Michigan Basin
Reefs around the edge, salty water in the middle
Late Paleozoic craton
• Remember what happened in the Appalachians?
• As the big mountains started to go up, the sea drained off the continent
• More terrestrial deposits, including widespread coal swamps
http://www.museum.state.il.us/exhibits/changes/htmls/tropical/upland_emerges.html
Cyclothems
• Repeating sequences of sedimentary rocks that go from non-marine to marine
• Repeat tens to hundreds of times.
http://www.isgs.uiuc.edu/maps-data-pub/publications/geonotes/geonote2.shtml
Cyclothems
• Repeating sequences of sedimentary rocks that go from non-marine to marine
• Repeat tens to hundreds of times.• What caused the many repetitions?– Deltas growing off the rising Appalachian
mountains– Small changes in sea level across a low-lying area
can cause changes
So what happened to Pangaea?
• Triassic Rocks of East Coast:– Red sandstones and shales, red conglomerates
and breccias– Basalts– Normal faults– What happened?
• Age of the Atlantic Ocean floor
Then what happened to Pangaea?
• Breaks up in Triassic: normal faults, basalt, redbeds
• Atlantic Ocean forms• Atlantic grows wider throughout the Mesozoic
and Cenozoic• So what tectonic facies has the East Coast
been throughout this time?
And on the craton…
• Let’s watch the movie all the way from Cambrian on…
• http://www.youtube.com/watch?v=2y43-yJu3DA
Mesozoic-Cenozoic Craton
• Triassic: craton dry – very little rock• Jurassic: mostly dry, little deposition in Gulf
Coast• Cretaceous: Great Cretaceous seaway cuts NA
in half – marine rocks on west edge of craton.
Paleozoic Cordillera
• Paleozoic – subduction zone with many collisions of small things – island arcs, continental fragments – builds the NA continent wider
• Orogenies: Antler, Sevier• Accreted terranes have ophiolites in between
them
Jurassic-Cretaceous• Foothills: now-metamorphosed volcaniclastic
sedimentary rocks.– Andesitic bits– Graded greywackes– Cherts
• Coast Range:– Great Valley Sequence:
• Graded greywackes, laminated shales
– Franciscan Formation:• Greenschist with blueschist, basalt and marble inclusions
So what is it?
Cretaceous change
• Great Valley sediments contain granite bits by mid-late Cretaceous – what does it mean?
• Pause of 10 million years – no volcanoes in Western US
• Volcanoes pop up in Colorado – what happened?
Cretaceous time
• Western volcanoes shut down, and the subduction mountains erode away-
• Great Valley deep water rocks contain bits of granite from the magma chamber
• 10 million years later – volcanoes start erupting in Colorado
• Low angle subduction moves the volcanoes of the subduction zone far inland from the trench
Cenozoic complications• Subduction of a diverging boundary• San Andreas Fault forms• Tensional tectonics across the Basin and Range –
stretches to twice its width and creates fault block mountains
• Colorado Plateau rises intact• Santa Barbara block spins around opening pull-
apart basins that produce oil• North America arches up, water drains off the
Atlantic and Gulf Coast