Mountain Building

Question 1

Effect of climate on morphology of Andes
Reference
Orogenic zones result of what two processes?
Why Andes appropriate?
Three main climate zones?
hypsometry shows?
Shape of three zones?

Answer 1

Montgomery et al, 2001
Climate and tectonics
Andes covers whole of southern hemisphere so different climates
Three main climate zones are upper - tropical high precipitation and erosion, small percentage of mountains at maximum height
Central region is desert, low erosion, high percentage at max height
Lower is glacial, limits height of mountains, mountains get smaller towards south, low hyposymmetry

Question 2

Mantle subduction creating Tibetan plateau
Reference
Deformation where? Process called? What’s deformed? Suggests?
In Himalaya it is thought that? Why? Alternative solution? Evidence?
Evidence from altai? How does it explain Tibetan plateau?

Answer 2

Willet and Beaumont, 1994
Deformation away from continental margin by mantle subduction, crust is deformed not mantle suggesting very like normal subduction
In Himalaya underthrusting of India cannot be main source of crystal shortening as not consistent with palaeomagnetics and lack of Indian shield type lithosphere
Subduction of lithosphere in mantle provides alternative solution, supported by formation of Altai mountains and basic volcanism nearby
Altai mountains formation evidenced baby crystal suture marks, indicate initiation of subduction which migrates continuously in direction of subduction plate creating progeny
Tibetan plateau explained by this as rollback creates space between the two mantle lithospheric plates which allow emplacement of hot mantle underneath plateau

Question 3

Using palaeoaltimetry to work out how Tibetan Plateau has developed with time
Reference
Used for? Age of Tibetan plateau at present elevation? How did they work it out? What does Age of plateau elevation suggest?

Answer 3

Currie et al, 2005
Used for reconstructing past elevations, can help reconstruct formation of Tibetan plateau, worked out using oxygen isotopes from early diagenetic carbonates and composition of modern streams ad hydrothermal vents
Results show Tibetan plateau is same elevation last 15Ma, suggests mantle lithosphere thickening not a major part

Question 4

Crustal thickening not to account for changes in elevation - Colorado plateau
Reference
What raised the Colorado plateau? How does this happen? Why did this happen? What was the driving force?

Answer 4

McQuarrie and Chase, 2000
Raised by crustal thickening
Pressure gradient from overthickened crust and overheated hinterland crust from nearby progeny led to intracrustal flow and isostatically rose the Colorado plateau. Occurred as crystal roots very large, excessive roots became source of hot, weak midcrustal material that flowed to low elevation Colorado plateau and raised it. Driving force was pressure exerted from topographic gradient between elevated progeny and low-lying plateau

Question 5

Crustal flow building Tibetan plateau
Reference
Two end members in topography
Why morphology in eastern side? 
How does crystal material flow? What does this imply about Asian crust before plateau formed?

Answer 5

Clark and Royden, 2000
Steep abrupt edge and long wave low gradient
Steep abrupt on east result of fluid flow underneath.
Crystal material flows around strong crust creating gentle margins and piles up behind basins which creates narrow steep margins. Implies Asian crust heterogeneous but largely weak before tibet

Question 6

Evolution of Tibetan plateau
Reference
Three things created Tibetan plateau? What data does data indicate About extrusion of lithospheric fragments? What did the ending of this process do?

Answer 6

Royden et al, 2008
Initial subduction of Indian lithosphere, thickening of continental margin and eastward extrusion of Tibetan plateau. Lithospheric fragments correlates with trench rollback, of the western pacific around Indonesia. Halting of process resulted in vertical uplift of Tibetan plateau as weak crust injected underneath instead of in trench in western pacific.

Question 7

Low viscosity crystal flow coupled with surface denudation explains Himalayan tectonics
Reference
Growth of Tibet explained by channel flow where? What can ductile extrusion of metamorphic rocks explain? What is channel flow linked to?
Without surface deduction what happens to surface flow? What does this explain? What does denudation focussed on the flanks lead to? What happens when denudation falls? What does this process require?

Answer 7

Beaumont et al, 2001
Crystal flow in middle to lower crust
Exhumation of Himalayan sequence
Channel flow linked to surface denudation
Without surface denudation channel flow tunnel through converging crust explaining its eastward propagation
Denudation on flanks leads to symmetrical exhumation when upper crust does not detach above the channel creating asymmetrical thrust extrusion
Fall in denudation and will return to crystal channels. Process requires low viscosity material in middle to lower crust, variation in crystal thickness and surface denudation on flank of plateau