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Climate or Tectonics; what determines mountain topography? 
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Joined: Mon Feb 21, 2011 4:38 am
Posts: 4
Post Climate or Tectonics; what determines mountain topography?
Hi all,

Many basins show some sort of continuous sediment supply over millions of years, with a orbital climate signal affecting sediment input. Baselevel will affect accomodation space in the basin itself... The source of this sediment is usually from nearby mountain belts. I understand isostacy will basically uplift mountains as more and more sediment is removed from them. This allows more sediment to be eroded and deposited over time than the volume of the mountain peaks above sea-level would suggest. Climate can cause more erosion and therefore higher isiostacic uplift rates and different topography. Now my question is, are there any records of climate doing this or is climate cyclicity only recorded in the transportation/depostion rate and not so much in mountain uplift? Or does tectonics generally overrule this signal?

hope this is clear!

thanks!


Wed Mar 23, 2011 8:37 am

Joined: Wed Jun 09, 2010 9:25 pm
Posts: 47
Post Re: Climate or Tectonics; what determines mountain topograph
Very good question and this is actually currently under debate...

Basically one must first understand that mountain ranges can affect climate themselves via three mechanisms; alteration of atmospheric circulation, increased albedo effect by more glaciers and, probably the most important, increased erosion rates, causing more CO2 uptake. Also climate can have great affect on the morphology and height of mountain ranges. Increased height causes more erosion, through more precipitation and in more glacier erosion (in colder climates). Basically, the higher the mountain, the faster erosion takes place, causing deeper valleys. These deep valleys lower the overall weight of the mountain and through isostatics the entire mountain range is uplifted. This causes high peaks to be uplifted even higher, whilst the average height will stay the same, given enough time (Masek et Al. 1994).

A good example of this are the Himalaya and he Andes, as the results of this climate-tectonic system can bee seen, where the area’s experiencing more precipitation have been uplifted more than dryer regions. But what has triggered the uplift? Was it a tectonic influx causing higher mountain ranges, thereby altering the climate, causing more erosion and deeper valleys. Or was it a global climate shift, causing more erosion and thereby increasing isostatic uplift. Molnar & England, 1990, suggest a climate triggered system in which a system of positive feedback increases isostatic rebound?

Basically, several sources could not find proof for mayor isostatic uplift in the outer margins of the Andes, but do not rule out an increased uplift due to the removal of material in humid climates. Molnar defends his ideas by finding proof for increased uplift due to erosion.
Most sources support the idea that mountain ranges are initialized by tectonic forces razing their peaks so they enter a different climate regime. The outer edges of mountain ranges thereby receive more rain as humid air is forces up. This caused increased erosion and leads to a rugged terrain with deep valleys and high peaks, were isostatic equilibrium causes uplift. I therefore believe both systems are coupled and as Whipple KX, Meade BJ, 2006 state, the cause of uplift can change over time.

Here are the articles I refer to and they are very interesting too read.

    Gillis RJ (Gillis, Robert J.), Horton BK (Horton, Brian K.), Grove M (Grove, Marty), 2006, Thermochronology, geochronology, and upper crustal structure of the Cordillera Real: Implications for Cenozoic exhumation of the central Andean plateau TECTONICS 25 (6): Art. No. TC6007 DEC 21

    Barnes JB (Barnes, J. B.), Ehlers TA (Ehlers, T. A.), McQuarrie N (McQuarrie, N.), O'Sullivan PB (O'Sullivan, P. B.), Pelletier JD (Pelletier, J. D.), 2006, Eocene to recent variations in erosion across the central Andean fold-thrust belt, northern Bolivia: Implications for plateau evolution EARTH AND PLANETARY SCIENCE LETTERS 248 (1-2): 118-133 AUG 15
    Through research in fision tracks and structural mapping of the Andes these researchers suggest tectonic driven uplift in middle Eocene to late Oligocene, but can not reconstruct late Miocene causes for uplift.

    Whipple KX, Meade BJ, 2006, Orogen response to changes in climatic and tectonic forcing EARTH AND PLANETARY SCIENCE LETTERS 243 (1-2): 218-228 MAR 15
    Have discovered both tectonic as climate driven uplift in certain mountain ranges and state: “Moreover, it is important to consider the possibility that the relations among climate, topography, erosion rate, and tectonics may differ markedly during transient evolution of a mountain belt.”

    Molnar P, 2005, Mio-Pliocene growth of the Tibetan Plateau and evolution of East Asian climate PALAEONTOLOGIA ELECTRONICA 8 (1): Art. No. 2A
    Proves that erosion rates increased long after the initial uplift of the Himalaya and only shows erosion on the outer edges, therefore implying a climate driven uplift as he stated 15 years before.


Wed Mar 23, 2011 2:36 pm

Joined: Mon Feb 21, 2011 4:38 am
Posts: 4
Post Re: Climate or Tectonics; what determines mountain topograph
Thank you so much O_Stevens for that explanation and the resources!

This basically means that tectonics can actually cause climate to change in the mountain range and therefore can affect the type and volumes of sediment supplied to the basin. Am I right?


Wed Mar 23, 2011 2:57 pm

Joined: Wed Jun 09, 2010 9:25 pm
Posts: 47
Post Re: Climate or Tectonics; what determines mountain topograph
Indeed, that's the theory here...

If you're interested in this stuff than the following essay may also be of interest to you. I still had it on my pc:

Tectonic forcing of late Cenozoic Climate

Through O18 records it becomes clear that the late Cenozoic experienced a temperature drop. Also glacial detritus supports this progressive cooling. The drop in CO2 levels could have been the result of tectonics. There are two tectonic forces that control CO2 levels in the atmosphere. Volcanic degassing increase atmospheric CO2 and tectonic uplift decrease atmospheric CO2 as chemical weathering increases.

In the Cenozoic, an increased seafloor spreading rate was present that could have led to the input of CO2, but this input was counteracted by the uplift of the Tibetan plateau, causing high erosion rates. The Tibetan plateau caused by the collision of the Indian plate and the Eurasian plate covers a massive area and lies at low latitudes near a warm ocean (causing a humid, monsoonal climate).

Research in 87SR/86SR rates also support the increase in erosion rates in the late Cenozoic.
It is therefore believed that the uplift of the Tibetan plateau, and the increase in chemical weathering caused by this, partially removed CO2 from the atmosphere causing a drop in global temperatures over the past 40 Myr.

Although tectonic forces do influence atmospheric CO2, this only influences long CO2 cycles. Raymo & Ruddiman correctly state that the uplift of the Tibetan plateau could have caused a drop in Temperature, but climate over the past 14 Myr is primarily influenced by astronomical cyles. Their sediment records may have not been detailed enough to support their conclusions and their idea about erosion rate linked to hill slope rather than precipitation has also been criticized. Their conclusion is probably right, but several of their assumptions seem to have been proved wrong.

I believe the massive size of the Tibetan plateau and the erosion caused by this uplift could have had a substantial influence on our planets climate, but an equilibrium has probably been reached 14 Ma giving astronomical cycles more influence on global temperatures.

References

    Kuz'min MI, Yarmolyuk VV, 2006, Mountain growth and climatic variations in the earth's history RUSSIAN GEOLOGY AND GEOPHYSICS 47 (1): 4-20

    Abels HA, Hilgen FJ, Krijgsman W, Kruk RW, Raffi I, Turco E, Zachariasse WJ, 2005,
    Long-period orbital control on middle Miocene global cooling: Integrated PALEOCEANOGRAPHY 20 (4): Art. No. PA4012 NOV 10

    The tectonic uplift could have caused a temperature drop in the Cenozoic, but the Milankovitch cycles have primarily influenced climate (glacials and interglacials) over the past 3 Myr.

    Holbourn A, Kuhnt W, Schulz M, Erlenkeuser H, 2005, Impacts of orbital forcing and atmospheric carbon dioxide on Miocene ice-sheet expansion NATURE 438 (7067): 483-487 NOV 24
    The cause of glaciations in Antarctica was caused by climatic isolation and coincides with the change from obliquity to eccentricity. Sedimentary records studied in the past did not have enough detail to support the ‘uplift-driven’ climate change.

    Chumakov NM, 2005, Factors of global climatic changes inferred from geological data STRATIGRAPHY AND GEOLOGICAL CORRELATION 13 (3): 221-241 MAY-JUN
    Climate fluctuations over long periods (100-10 Myrs) are primarily caused by endogenic changes, whereas shorter fluctuations find there cause in astronomical cycles. The timescale wherein the Tibetan plateau was formed could therefore have caused a long period of global cooling.

    Oehm B, Hallet B, 2005, Rates of soil creep, worldwide: weak climatic controls and potential feedback ZEITSCHRIFT FUR GEOMORPHOLOGIE 49 (3): 353-372 SEP
    Erosion is primarily influenced by precipitation and can cause a negative feedback to the CO2 cycle, where more CO2 caused higher temperatures and more rain. This rain will cause more erosion and this will consume CO2. This article suggest an equilibrium and states that erosion rates depend more on precipitation than on hill slope (as stated by Raymo & Ruddiman).


Wed Mar 23, 2011 4:36 pm

Joined: Thu Jul 26, 2012 7:57 am
Posts: 2
Post Re: Climate or Tectonics; what determines mountain topograph
Just adding to this question, anybody have any idea on what data can be used to constrain the paleo-elevations of mountains?


Thu Jul 26, 2012 8:11 am

Joined: Wed Jun 09, 2010 9:25 pm
Posts: 47
Post Re: Climate or Tectonics; what determines mountain topograph
Lyeo,

Good question and please allow me to give my opinion. I believe there are several techniques.

A) One could look at mineralogy of basement rock to assess burial history through Pressure-Temperature analysis. Different minerals forum under different P/T conditions and from this one could asses how deep certain mineral where buried prior to erosion removing the top layer, resulting in uplift due to isostacy.

B) A second option would be to look at sediment volumes and from that deduct the eroded volumes. This is tricky due to compaction and because it is usually very difficult to figure out which depocenter correspond to what areas of the hinterland. Through biostratigraphy one can, however, get a good idea of deposition speed and from that erosion speed.

C) Another option would be to look at the same biomarkers (primarilly pollen) and from that deduct vegetation of the hinterland. This can point towards the climate and elevation that was present at the time of deposition of the pollen. Often when pollen travel far they are oxidized making it more difficult to identify them. Furthermore, reworking can complicate things a lot.

I am probably missing a lot of other options, but this is what I could dream up at this moment. Additions and comments are very welcome!


Wed Aug 01, 2012 9:01 pm

Joined: Tue Jan 27, 2015 8:23 am
Posts: 1
Post Re: Climate or Tectonics; what determines mountain topograph
A good example of this are the Himalaya and he Andes, as the results of this climate-tectonic system can bee seen, where the area’s experiencing more precipitation have been uplifted more than dryer regions. But what has triggered the uplift? Was it a tectonic influx causing higher mountain ranges, thereby altering the climate, causing more erosion and deeper valleys. Or was it a global climate shift, causing more erosion and thereby increasing isostatic uplift. Molnar & England, 1990, suggest a climate triggered system in which a system of positive feedback increases isostatic rebound?

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Tue Jan 27, 2015 8:28 am
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