EESA06H3 Lecture 6: Lecture 6
Lecture 6: The Death of Oceans – Toward the next supercontinent
• The continents are diverging will start to converge → destroy oceanic crust and destroying
oceans.
• Main Theme → elig of ust he destoig oeas, e ae addig e otiets →
they will expand and grow).
• Ipotat fo Caada → geolog of Caada e eplaied past supeotiets ad past
ollisios eled oeai ust i Caada → uildig ou out the sediets o
mountains)
Why is this important?
1. INDIA collides with Asia after 25 Ma (millions of years) closing the TETHYS OCEAN and creating
the MEDITERRANEAN SEA during the ALPINE-HIMALYAN OROGENY. This changes global
climates and results in ice ages of the last few million years
2. PACIFIC RIM OF FIRE: involves widespread SUBDUCTION and melt of Pacific Ocean crust below
surrounding continents
3. SUBDUCTION creates new continental crust resulting in GROWTH OF CONTINENTS through
geologic time and creates NATURAL HAZARDS around the Pacific Rim and their effects on cities
• We came out of an ice age in Canada → 10,000 years ago.
o Global climate is cooling (rhythms of climate changing)
o Rhythms last 2 million years of ice ages and interglacials
▪ Some scientists think we should be in an ice age → ot due to geehouse gases
and global climate change (human activity)
• Need to ko oe aout ho oeas lose eause its ipotat
Why do oceans ultimately close?
• A mature ocean – age of crust increases systematically in the margins.
• Thickness increases as new rock is formed as it is pushed aside.
• Layer of high density rock sitting on top of layer of
low density, toffee-like rock, unstable → stats to
sink → the stat of sudutio egiig of old
age of oceans).
o Slab rollback – when descending plate
(being subducted)
o oll ak – at deep length (know through
earthquakes)
• The roll back reverses the subduction and
continents come closer to the subduction zone
(oceans start to widen and then narrows).
• New crust was added to Eastern North America (e.g., Ontario) → due to new collisions between
continents.
• Fist idespead oea losue 1 illio eas ago to fo supeotiet ‘odiia
A Dead Ocean: Closure of Tethys Sea as Pangea Breaks
find more resources at oneclass.com
find more resources at oneclass.com
• India moving north, Australia moving northeast, closing the Tethys ocean.
• The sediments and crust → gets subduction and recycled, some get obducted (to be pushed
onto the continents) → creation of mountain ranges (Western Alps and Tibetan Plateau).
o Made up of ancient ocean crust from Tethys (from Western Europe to Australia).
Alpine-Himalayan Orogeny Caused by Closure of Tethys:
• Ongoing collision of African and Eurasian plates
• The Mediterranean Sea is a remnant of the Tethys Ocean
o Next 25 million years – going to close (mountains get larger).
• Italy – has a bit of African plate (pushing up on European crust).
o Matterhorn – Euopes highest outai ade up of Afia ust → at African
pog
o Folded Tethys ocean rocks (faults)
• Mountains record crustal thickening of plates moving toward each other and deep erosion →
cuts the mountain → snow and ice (glaciers and ice caps) sliding over the rocks and cutting
them.
• Marine fossils, basalt (pillow basalt → basalt erupted underwater) → characteristics of folded
rocks in Alps were once in the ocean.
o Crustal thickening from collisions
Subduction in the eastern Mediterranean:
• The Anatolian plate moving to west (away from collision between Eurasian and Arabian plate)
but creating a subduction zone (at around African plate).
o Ceates olaoes ad eathuakes at Afia pog
• Vulcano: now a solfatara (usually associated with dying volcanoes)
o Releasing gas, no eruptions
• Stromboli volcano → lighthouse of the Mediteaea
o Erupt frequently but not dangerous (every 20 mins, 1hr, erupts).
• Mt. Vesuvius and Pompeii – Volcano erupted and entire city covered in ash – particularly
pyroclastic flow oke ok – a size hih ae die do hot gas ↑tepeatue →
due to top of volcano collapses without warning).
o Pompeii was buried under meters – preserves the city
o Pyroclastic flow – uee adete Feh gloig loud
▪ Human remains petrified (conserved as
open cavities)
How rocks grow by obduction:
• Himalayans – basalt and a lot of marine sedimentary rocks
(ice cut through the rocks of the mountains)
• China is trying to escape collision zone and moving to the
East (escape zone)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
I(cid:373)po(cid:396)ta(cid:374)t fo(cid:396) ca(cid:374)ada geolog(cid:455) of ca(cid:374)ada (cid:271)e e(cid:454)plai(cid:374)ed (cid:271)(cid:455) past supe(cid:396)(cid:272)o(cid:374)ti(cid:374)e(cid:374)ts a(cid:374)d past (cid:272)ollisio(cid:374)s (cid:894)(cid:396)e(cid:272)(cid:455)(cid:272)led o(cid:272)ea(cid:374)i(cid:272) (cid:272)(cid:396)ust i(cid:374) ca(cid:374)ada(cid:895) (cid:271)uildi(cid:374)g ou(cid:396) (cid:272)ou(cid:374)t(cid:396)(cid:455) (cid:894)the sedi(cid:373)e(cid:374)ts o(cid:396) mountains) India collides with asia after 25 ma (millions of years) closing the tethys ocean and creating the mediterranean sea during the alpine-himalyan orogeny. Why do oceans ultimately close: a mature ocean age of crust increases systematically in the margins, thickness increases as new rock is formed as it is pushed aside. A dead ocean: closure of tethys sea as pangea breaks. Alpine-himalayan orogeny caused by closure of tethys: ongoing collision of african and eurasian plates, the mediterranean sea is a remnant of the tethys ocean, next 25 million years going to close (mountains get larger). How rocks grow by obduction: himalayans basalt and a lot of marine sedimentary rocks (ice cut through the rocks of the mountains, china is trying to escape collision zone and moving to the.
