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The chemical, mechanical, and hydrological evolution of weathering granitoid

Goodfellow, Bradley W. LU ; Hilley, George E.; Webb, Samuel M.; Sklar, Leonard S.; Moon, Seulgi and Olson, Christopher A. (2016) In Journal of Geophysical Research - Earth Surface 121(8). p.1410-1435
Abstract

Surprisingly few studies connect the chemical, mechanical, and hydrological evolution of rock as it weathers to saprolite and soil. We assess this coevolution in granodiorite from Monterey Peninsula, California, by measuring changes in bulk chemistry, mineralogy, volumetric strain, the oxidation state of Fe in biotite crystals, tensile strength, abrasion rate, connected porosity, and hydraulic conductivity in samples covering a range of weathering grades. We identify the oxidative dissolution of biotite as the key chemical reaction because of the volumetric expansion that accompanies formation of altered biotite and precipitation of ferrihydrite. We show how the associated accumulation of elastic strain produces an energy density that... (More)

Surprisingly few studies connect the chemical, mechanical, and hydrological evolution of rock as it weathers to saprolite and soil. We assess this coevolution in granodiorite from Monterey Peninsula, California, by measuring changes in bulk chemistry, mineralogy, volumetric strain, the oxidation state of Fe in biotite crystals, tensile strength, abrasion rate, connected porosity, and hydraulic conductivity in samples covering a range of weathering grades. We identify the oxidative dissolution of biotite as the key chemical reaction because of the volumetric expansion that accompanies formation of altered biotite and precipitation of ferrihydrite. We show how the associated accumulation of elastic strain produces an energy density that is sufficient to support rock fracturing over length scales equivalent to constituent crystals. The resulting intragranular and intergranular cracking profoundly reduces tensile strength and increases the abrasion rate, connected porosity, and hydraulic conductivity of the rock matrix. These changes increase the rate of plagioclase weathering, and ultimately the rock disintegrates into grus and clay. Major changes in rock properties can occur with only minor element leaching, and the threshold behavior of weathering that arises from the coevolution of chemical, hydrological, and mechanical properties may be difficult to capture using simplified weathering models that fail to incorporate these properties. Our results, which combine the mechanical and hydrological evolution of weathering rock with more common measurements of chemical changes, should help to more accurately model the effects of, and mechanical and hydrological feedbacks upon, chemical weathering of rock.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
biotite, granite, hydrology, iron oxidation, rock fracture, weathering
in
Journal of Geophysical Research - Earth Surface
volume
121
issue
8
pages
26 pages
publisher
American Geophysical Union
external identifiers
  • scopus:84982975736
  • wos:000384442100001
ISSN
2169-9003
DOI
10.1002/2016JF003822
language
English
LU publication?
yes
id
61a9c4f5-63c0-4cd6-bc8f-5d4955952f20
date added to LUP
2016-12-15 13:08:03
date last changed
2017-09-18 11:31:28
@article{61a9c4f5-63c0-4cd6-bc8f-5d4955952f20,
  abstract     = {<p>Surprisingly few studies connect the chemical, mechanical, and hydrological evolution of rock as it weathers to saprolite and soil. We assess this coevolution in granodiorite from Monterey Peninsula, California, by measuring changes in bulk chemistry, mineralogy, volumetric strain, the oxidation state of Fe in biotite crystals, tensile strength, abrasion rate, connected porosity, and hydraulic conductivity in samples covering a range of weathering grades. We identify the oxidative dissolution of biotite as the key chemical reaction because of the volumetric expansion that accompanies formation of altered biotite and precipitation of ferrihydrite. We show how the associated accumulation of elastic strain produces an energy density that is sufficient to support rock fracturing over length scales equivalent to constituent crystals. The resulting intragranular and intergranular cracking profoundly reduces tensile strength and increases the abrasion rate, connected porosity, and hydraulic conductivity of the rock matrix. These changes increase the rate of plagioclase weathering, and ultimately the rock disintegrates into grus and clay. Major changes in rock properties can occur with only minor element leaching, and the threshold behavior of weathering that arises from the coevolution of chemical, hydrological, and mechanical properties may be difficult to capture using simplified weathering models that fail to incorporate these properties. Our results, which combine the mechanical and hydrological evolution of weathering rock with more common measurements of chemical changes, should help to more accurately model the effects of, and mechanical and hydrological feedbacks upon, chemical weathering of rock.</p>},
  author       = {Goodfellow, Bradley W. and Hilley, George E. and Webb, Samuel M. and Sklar, Leonard S. and Moon, Seulgi and Olson, Christopher A.},
  issn         = {2169-9003},
  keyword      = {biotite,granite,hydrology,iron oxidation,rock fracture,weathering},
  language     = {eng},
  month        = {08},
  number       = {8},
  pages        = {1410--1435},
  publisher    = {American Geophysical Union},
  series       = {Journal of Geophysical Research - Earth Surface},
  title        = {The chemical, mechanical, and hydrological evolution of weathering granitoid},
  url          = {http://dx.doi.org/10.1002/2016JF003822},
  volume       = {121},
  year         = {2016},
}