Reading list:

Brantley, S., and 26 others, 2011, 12 testable hypotheses on the geobiology of weathering, Geobiology, 9, 140-165.

Hamblin, W.K. and Dr. Eric H. Christiansen, E.H., 2004, Chapter 10 - Weathering, Earth's Dynamic Systems, Tenth Edition, Prentice Hall.

Kump, L., Brantley, S., and Arthur, M., 2000, Chemical weathering, atmospheric CO2 and climate, Annual Reviews of Earth and Planetary Science, v. 28, pp. 611-667.

Liu, Z., Dreybrodt, W., and Liu, H., 2011, Atmospheric CO2 sink: silicate weathering or carbonate weathering? Applied Geochemistry, v. 26, pp. S292-S294.

Riebe, C., Kirchner, J.W., and Finkel, R.C., 2004, Erosional and climatic effects on long-term chemical weathering rates in granitic landscapes spanning diverse climate regimes, Earth and Planetary Science Letters, v. 224, pp. 547-562.

Weathering

L. HinnovFebruary 17, 2012

Physical weathering is the mechanical fragmentation of rocks from stress acting on them from Earth surface processes.

Chemical weathering involves chemical reactions between Earth surface chemistry (water) and minerals that progressively decompose solid rock.

Major products of weathering:

(1) fractured rock (2) regolith (3) ions in solution

PHYSICAL CHEMICALfeedbacks

Famous experiment:Griggs, 1936 heated and cooled cubes of granite 140ºC to 30ºC for the equivalent of 240 years of daily fluctuations, but nothing happened.That was dry, but with wetting, in ~2.5 years they fell apart.

Brantley et al. (2011) Hamblin & Christiansen (2004)

CONDITIONS ASSOCIATED WITH CHEMICAL V. PHYSICAL WEATHERING

Crustal abundance of minerals

Ronov & Yaroshevsky, 1969

COMMON MINERALS IN ROCKS

Common rock-forming minerals

COMMON MINERALS IN ROCKS

The higher the Si:O ratio, the more resistant a mineral is to chemical weathering:

Goldich Stability Series

“Reverse Bowen Reaction Series”

High temp. minerals weather first….

QuickTime™ and a decompressor

are needed to see this picture.

CARBONATION (DISSOLUTION):

Calcite:

Plagioclase (albite):

COMMON WEATHERING REACTIONS:carbonation (breakdown by weakly acidic rainwater)hydrolysis (breakdown by water)hydration (breakdown by the absorption of water)oxidation (breakdown by the oxygen in air and water)

CHEMICAL WEATHERING OF ROCKS AND CO2 DRAWDOWN:1) Congruent-minerals totally dissolve2) Incongruent-mineral is transformed into another mineral

HYDROLYSIS:

Crustal abundance of minerals

2KAlSi3O8 + 9H2O + 2CO2 Al⇌ 2Si2O5(OH)4 (kaolinite) + 2HCO3- + 4H4SiO4 + 2K+

3KAlSi3O8 + 14H2O + 2CO2 KAl⇌ 3Si3O10(OH)2(illite) + 2HCO3- + 6H4SiO4 + 2K+

Depending on K+ content of the solution.

Potassium Feldspar:

CHEMICAL WEATHERING OF ROCKS AND CO2 DRAWDOWN:

Olivine:

Wollastonite:

(a pyroxene)

Note: BET analysis = Brunauer-Emmett-Teller (BET) Surface Area Analysis

Laboratory rates are order of magnitude faster than natural rates

DISSOLUTION RATE OF PLAGIOCLASE

Brantley et al. (2011)