Planet Earth-Lecture 9.docx

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18 Apr 2012
School
Course
Professor
Lecture 9
Final exam: focus on plate tectonics and last two lectures (10 and
11). Chapters 1-4, 11, 19, 20.
Future planet Earth
Supercontinent cycle: can use to predict future
Pangea 2
Alpine-Himalayan Orogeny: Indian Sub-continent collides with Asia
after 25 Ma destroying the Tethys ocean.
Uplift of the Himalayas and climate change after 2 Ma.
Orogeny: mountain building
Alps, Himalayas have long kms belt which record closure of an
ocean called the teths (teths ocean). Mediterranean is a reminant, a
dying ocean createdqueezing of teths ocean between India and
Africa as they move North
Climate (100, 000 year cycles) in Canada? Interglacial (short
compared to ice age). Around 10,000 years ago. Before that, ice was
here. Ice thirty thousand years ago and Ice age 100,000 years ago.
Long ice ages (100,000) and short interglacials.
Present interglacial should’ve stopped a long time ago but is
extended by our activities.
Ice ages and interglacials result of uplift of Himalayas. Uplift
changed global climate. Resulted in global cooling.
Changes in climate in Africa near the rift are controlled by the
uplift of Himalayas and global climatic change that it made (species
origination).
Peak of Pangea: Teths Sea (around it with a big continent)
As Pangea breaks up, the teths ocean gets squeezed (northern
movement of Africa and India). Thrusts, subduction, obduction- cause
long Himalayan belt-mountains made up of reminant of teths ocean
Mediterranean sea (reminant of teths ocean): will be part of the
alpine block and will be a continuous range from alps to Himalayas
down to Indonesian arc (Building of next supercontinent).
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India embedded in Eurasia.
How to view the future? View the process backwards. 250 million
years in the future.
Closure of the Tethys ocean as pangea breaks up: 200 mill
East Gondwana (Australia): Proximity to Tokyo in 70 million years.
Moving up. Collide with Southeast Asia
Pangea 2: obduction o Indian crust and asia grows in size
Obduction not have that subduction has? No under thrusting.
Subduction recycles oceanic crust. Volcanoes with subduction. Slabs
pulled down (max: 700 km). Obduction: no melting, some thrusting,
no volcanoes, two plates colliding.
Volcanoes absent in area undergoing subduction.
North America: by obduction: not just destroying but also creating
crust
Subduction zone (ocean): colliding oceanic plate against oceanic crust.
Indonesian island arc, Japan island arc created by subduction of
oceanic crust. Production of volcanoes
Volcanism produces island arcs that are regarded as continenetal
crust.
Island arcs: rocks dominated by andesites (have silica) and are less
dense than continental crust. Buoyant, less dense but cannot be
subducted themselves. Over millions of years, island arcs will collide
with other platelets and aggregate bigger continents.
First continent of the world probably looked like an island arc that
exists today.
Grabon: area of extending crust where blocks are growing down
forming valleys. Valleys with step sides. Grave in Italian. Valleys are
grounded by faults. Which ones? Normal faults. Allowing central
blocks of grabbon to subside. Horsts (bounding blocks on either side
of grabbon): rift shoulders, high standing, can look into the grabbon
basin.
Compression plus extension
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Asian plate stretched
Indenter: India: pushing away China, Southern Asia. As they are
escaping from collision zone, there is extension
Asthenosphere: base floor. Soft rocks in which plates are moving.
Continenetal crust dominate by gneiss. Across the two plates: there
is a suture.
Ophiolites: ancient oceanic crust dominated by basalt but what is
distinct about the basalt? Pillow basalt (round masses that tell us
that basalt was erupted underwater of the floor of the ancient
water-typically occur along sutures). Fold and thrust belts on either
sides of suture (good examples are Appalachians and Rocky
mountains). Thrusts shoved over gneiss (important for oil and gas).
Antecline: rocks are closed-important in terms of oil and gas
because it creates a trap, hydrocarbons migrating from depth
become trapped in folded rocks.
Some melting going on in granite plutons (aka batholiths).
(NO UNDERTHRUSTING, NO VOLCANOES)
Professor Augusto Gansser: wander through Himalayas. In 1920-30s.
Dress up as a Buddhist monk. Made a profound discovery:
ophiolites in the Himalayas, ancient marine rocks and fossils, pioneer
in understanding origin of Himalayas. Existence of teths ocean before
India collided, recognization. Swiss geologist. Book: geology of
Himalayas
Arabian plate into Europe (like India). Turkey trying to move away.
China: massive earthquakes due to India’s push.
China is cursed by Himalayas
Tangshan earthquake in 1976
China: country driven by major faults.
Obduction: there is some subduction.
India is pushing underneath Asian continental crust. Tibetan plateau
(uplifted crust). Mount Everest
Thrust fault. Locked. What do they produce? Seismic gaps. No
activity. But gaps get filled. Gap filling earthquakes
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