Velbel,M.A.(2009): Dissolution of olivine during natural weathering. Geochimica et Cosmochimica Acta, 73, 6098-6113.

『天然風化におけるカンラン石の溶解』


Abstract
 Naturally weathered olivine occurring as phenocrysts in Hawai'ian volcanic rocks from several volcanic centers and regolith/outcrop settings, and as tectonized olivines from several metadunite bodies in the southern Appalachian Blue Ridge, are all similarly corroded by natural weathering. Conical (funnel-shaped) etch pits occur as individual pits, base-to-base pairs of cone-shaped pits, or en echelon arrays. Etch-pit shapes and orientations in the smallest etch-pit arrays visible in conventional scanning electron microscopy resemble even smaller features previously reported from transmission electron microscope investigations of olivine weathering. Etch pits occur in samples with chemical and/or mineralogical evidence of weathering, and/or are associated with, or proximal or directly connected to, fractures or exposed outcrop surface, and therefore are formed by weathering and not inherited from pre-weathering aqueous alteration (e.g., serpentinization, iddingsitization) of these parent rocks. Many etch pits are devoid of weathering products. Natural weathering of olivine is surface-reaction-limited. similarity of corrosion forms from naturally weathered olivine from multiple igneous and metamorphic parent-rock bodies suggests that olivine weathers in the same manner regardless of its specific crystallization/recrystallization history, eruption/weathering/exposure ages of the olivine's host rock, and the local regolith history.』

1. Introduction
 1.1. Background and previous work
2. Materials and methods
 2.1. Samples
  2.1.1. Basalt
  2.1.2. Dunite
 2.2. Sample preparation and analysis
3. Results
 3.1. Overall and comparative results
 3.2. Specific variations between samples at individual localities
  3.2.1. Oahu
  3.2.2. Hawai'i
  3.2.3. Metadunites from southern Appalachian Blue Ridge
4. Discussion
 4.1. Various geometric expressions of olivine etch-pit geometry
 4.2. Formation of olivine etch pits exclusively by low-temperature weathering
 4.3. Uniformity of olivine etching during natural weathering
 4.4. Implications for reaction mechanism and rate-determining process
 4.5. Comparison with putative biogenic features in naturally exposed olivine
 4.6. Comparison with experimental etching
  4.6.1. Comparison with textures formed in abiotic/inorganic laboratory dissolution-kinetics experiments
  4.6.2. Similarities and variations of corrosion features with olivine composition
  4.6.3. Comparison with textures formed in biotically mediated laboratory experiments
  4.6.4. Comparison with textures formed by extreme etchants
5. Conclusions
Acknowledgments
References



戻る