Abstract
Olivine crystals in basaltic andesites which crop out in the Abert Rim, south-central Oregon have been studied by high-resolution and analytical transmission electron microscopy. The observations reveal three distinct assemblages of alteration products that seem to correspond to three episodes of olivine oxidation. The olivine crystals contain rare, dense arrays of coherently intergrown Ti-free magnetite and inclusions of a phase inferred to be amorphous silica. We interpret this first assemblage to be the product of an early subsolidus oxidation event in the lava. The second olivine alteration assemblage contains complex ordered intergrowths on (001) of forsterite-rich olivine and laihunite (distorted olivine structure with Fe3+ charge balanced by vacancies). Based on experimental results for laihunite synthesis (Kondoh et al. 1985), these intergrowths probably formed by olivine oxidation between 400 and 800°C. The third episode of alteration involves the destruction of olivine by low-temperature hydrothermal alteration and weathering. Elongate etch-pits and channels in the margins of fresh olivine crystals contain semi-oriented bands of smectite. Olivine weathers to smectite and hematite, and subsequently to arrays of oriented hematite crystals. The textures resemble those reported by Eggleton (1984) and Smith et al. (1987). We find no evidence for a metastable phase intermediate between olivine and smectite (“M” — Eggleton 1984). The presence of laihunite exerts a strong control on the geometry of olivine weathering. Single laihunite layers and laihunite-forsteritic olivine intergrowths increase the resistance of crystals to weathering. Preferential development of channels between laihunite layers occurs where growth of laihunite produced compositional variations in olivine, rather than where coherency-strain is associated with laihunite-olivine interfaces.
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References
Baker I, Haggerty SE (1967) The alteration of olivine in basaltic and associated lavas Part II: Intermediate and low temperature alteration. Contrib Mineral Petrol 16:258–273
Bartels KS, Burns RG (1986) Structural Fe3+ induced in heated Mg−Fe and Mn−Fe olivines (abstract). EOS, Trans Am Geophys Union 44:1270
Bartels KS, Burns RG (1989) Heat oxidized olivines: Characterization of reaction products by 4.2K Mössbauer spectroscopy (abstract). Int Geol Congr 28:92–93
Buening DK, Buseck PR (1973) Fe−Mg lattice diffusion in olivine. J Geophys Res 78:6852–6862
Champness PE (1970) Nucleation and growth of iron oxides in olivines, (Mg,Fe)2SiO4. Mineral Mag 37:790–800
Colman SM (1982) Chemical weathering of basalts and andesites; evidence from weathering rinds. US Geol Surv Prof Pap 1246
Eggleton RA (1984) Formation of iddingsite rims on olivine: a transmission electron microscope study. Clays Clay Miner 32:1–11
Eggleton RA (1986) The relation between crystal structure and silicate weathering rates. In: Colman SM, Dethier DP (eds) Rates of chemical weathering of rocks and minerals. Academic Press Inc, Orlando, Florida, pp 21–40
Evans BW, Guggenheim S (1988) Talc, pyrophyllite and related minerals. In: Bailey SW (ed) Reviews in Mineralogy. Mineral Soc Am 19: 225–294
Haggerty SE, Baker I (1967) The alteration of olivine in basaltic and associated lavas Part 1: High temperature alteration. Contrib Mineral and Petrol 16:233–257
Hazen RM (1976) Effects of temperature and pressure on the crystal structure of forsterite. Am Mineral 61:1280–1293
Kan X, Coey JMD (1985) Mössbauer spectra, magnetic and eletrical properties of laihunite, a mixed valence iron olivine mineral. Am Mineral 70,576–580
Kitamura M, Shen B, Banno S, Morimoto N (1984) Fine textures of laihunite, a nonstoichiometric distorted olivine-type mineral. Am Mineral 69:154–160
Kohlstedt DL, Vander Sande JB (1975) An electron microscopy study of naturally occurring oxidation produced precipitates in iron-bearing olivines. Contrib Mineral Petrol 53:13–24
Kondoh S, Kitamura M, Morimoto N (1985) Synthetic laihunite [()xFe 2+2-3x Fe 3+2x ] an oxidation product of olivine. Am Mineral 70:737–746
Livi KJT, Veblen DR (1987) “Eastonite” from Easton, Pennsylvania: A mixture of phlogopite and a new form of serpentine. Am Mineral 72:113–125
Longhnan FC (1969) Chemical Weathering of the Silicate Minerals. American Elsevier, New York
Misener DJ (1974) Cationic diffusion in olivine to 1400°C and 35 kbar. In: Hoffman AW, Gilletti BJ, Yoder HS Jr, Yund RA (eds) Geochemical transport and Kinetics. Carnegie Inst Washington Publ 634, pp 117–129
Moseley D (1984) Symplectic exsolution in olivine. Am Mineral 69:139–153
Nahon D, Colin F, Tardy Y (1982) Formation and distribution of Mg, Fe, Mn-smectite in the first stage of laterite weathering of forsterite and tephroite. Clay Miner 17:339–348
Putnis A (1979) Electron petrography of high-temperature oxidation in olivine from Rhum layered intrusion. Mineral Mag 43:293–296
Shen B, Tamada O, Kitamura M, Morimota N (1986) Superstructure of laihunite-3M [()0.4Fe 2+0.8 Fe 3+0.8 SiO4]. Am Mineral 71:1455–1460
Smith KL, Milnes AR, Eggleton RA (1987) Weathering of basalt: formation of iddingsite. Clays Clay Miner 35:418–428
Tamada O, Shen B, Morimoto N (1983) The crystal structure of laihunite [()0.4Fe 2+0.8 Fe 3+0.8 SiO4]-nonstoichiometric olivine-type mineral. Mineral J 11:382–391
Walker GW (1963) Reconnaissance geologic map of the eastern half of the Klamath Falls (AMS) Quadrangle, Lake and Klamath Counties, Oregon. US Geol Surv Mineral Invest Field Studies Map MF-260
Wu T, Kohlstedt DL (1988) Rutherford backscattering spectroscopy study of the kinetics of oxidation of (Mg,Fe)2SiO4. J Am Ceram Soc 71:540–545
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Banfield, J.F., Veblen, D.R. & Jones, B.F. Transmission electron microscopy of subsolidus oxidation and weathering of olivine. Contr. Mineral. and Petrol. 106, 110–123 (1990). https://doi.org/10.1007/BF00306412
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DOI: https://doi.org/10.1007/BF00306412