The ilmenite/titano-magnetite assemblage: kinetics of re-equilibration

Hammond, Patrick A.; Taylor, L. A.

doi:10.1016/0012-821x(82)90047-4

Cited by 54 publications

(24 citation statements)

References 8 publications

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“…Fe-Ti oxides re-equilibrate rapidly and so cannot preserve evidence of any longer-term history (Buddington and Lindsley 1964;Hammond and Taylor 1982;Ghiorso and Sack 1991)]. By utilising two-feldspar thermometry we avoid entering into ongoing debates over the use of Fe-Ti oxide and Ti in quartz thermometry (cf.…”

Section: Discussionmentioning

confidence: 99%

Timescales of mixing and mobilisation in the Bishop Tuff magma body: perspectives from diffusion chronometry

Chamberlain

Morgan

Wilson

2014

Contrib Mineral Petrol

135

173

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Abstract:We present two-feldspar thermometry and diffusion chronometry from sanidine, orthopyroxene and quartz from multiple samples of the Bishop Tuff, California, to constrain the temperature stratification within the pre-eruptive magma body and the timescales of magma mixing prior to its eruption. Two-feldspar thermometry yields estimates that agrees well with previous Fe-Ti oxide thermometry and gives a ~80 °C temperature difference between the earlier-and later-erupted regions of the magma chamber. Using this thermometry, we model diffusion of Ti in quartz, and Ba and Sr in sanidine as well as Fe-Mg interdiffusion in orthopyroxene to yield timescales for the formation of overgrowth rims on these phenocryst phases. Diffusion profiles of Ti in quartz and Fe-Mg in orthopyroxene diffusion both yield timescales of <150 years for the formation of overgrowth rims. In contrast, both Ba and Sr diffusion in sanidine yield nominal timescales 1-2 orders of magnitude longer than these two methods. The main cause for this discrepancy is inferred to be an incorrect assumption for the initial profile shape for Ba and Sr diffusion modelling (i.e., growth zoning). Utilising the divergent diffusion behaviour of Ba and Sr, we place constraints on the initial width of the interface and can refine our initial conditions considerably, bringing Ba and Sr data into alignment, and yielding timescales closer to 500 years, the majority of which are then within uncertainty of timescales modelled from Ti diffusion in quartz. Care must be thus taken when using Ba-in-sanidine geospeedometry in evolved magmatic systems where no other phases or elements are available for comparative diffusion profiling. Our diffusion modelling reveals piecemeal rejuvenation of the lower parts of the Bishop Tuff magma chamber at least 500 years prior to eruption. Timescales from our mineral profiling imply either that diffusion coefficients currently used are uncertain by 1-2 orders of magnitude, or that the minerals concerned did not experience a common history, despite being extracted from the same single pumice clasts. Introduction of the magma initiating crystallization of the contrasting rims on sanidine, quartz, orthopyroxene and zircon was prolonged, and may be a marker of other processes that initiated the Bishop Tuff eruption rather than the trigger itself. 2 AbstractWe present two-feldspar thermometry and diffusion chronometry from sanidine, orthopyroxene and quartz from multiple samples of the Bishop Tuff, California, to constrain the temperature stratification within the pre-eruptive magma body and the timescales of magma mixing prior to its eruption. Twofeldspar thermometry yields estimates that agree well with previous Fe-Ti oxide thermometry and gives a ~80 °C temperature difference between the earlier-and later-erupted regions of the magma chamber. Using this thermometry, we model diffusion of Ti in quartz, and Ba and Sr in sanidine as well as Fe-Mg interdiffusion in orthopyroxene to yield timescales for the formation of overgrowth rims on th...

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Section: Discussionmentioning

confidence: 99%

Timescales of mixing and mobilisation in the Bishop Tuff magma body: perspectives from diffusion chronometry

Chamberlain

Morgan

Wilson

2014

Contrib Mineral Petrol

135

173

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“…In fact, the reaction mechanism which dominates here can be either a function of nucleation or supply of reactant gas at and removal of product gas in the direction of fluid flow. This includes diffusion of the reactant gas (Hammond and Taylor 1982).…”

Section: Fe 3 +-Bearing Phasesmentioning

confidence: 99%

Formation of ferriolivine and magnesioferrite from Mg ? Fe-olivine: Reactions and kinetics of oxidation

et al. 1995

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Abstract. Olivine samples (Fa 11) have been oxidized in air 0Co2=0.2 atm) at temperatures ranging from 350-700 ~ and examined by M6ssbauer spectroscopy, transmission electron microscopy, X-ray powder diffraction and thermomagnetic analysis. Oxidation of olivine was found to result in ferriolivine, magnesioferrite (major oxide phase) and magnetite (minor oxide phase) formation. Ferriolivine forms planar (001) precipitates, 0.6 nm in thickness, in the olivine host; the composition is likely to be Mgo.sVo.5(Fe3+)l.0SiO 4. Magnesioferrite MgFe20 4 exsolves as fine-grained precipitates (5-6 nm in size) filling interstices between the ferriolivine planar precipitates. Oxidation kinetic data at 700 ~ show two stages of oxidation corresponding to formation of ferriolivine in the first stage and magnesioferrite in the second stage. The linear rate law with a rate constant kvol = 1.23-10 -3 S-1 was found for the first stage whereas a parabolic rate-law with a constant of koxi=3.28 9 10 -3 s -1 was determined for the second stage of oxidation. It was found that ferriolivine is not an intermediate metastable phase in the oxidation process, terminated by magnesioferrite formation. The ferriolivine and magnesioferrite are considered to have formed by independent reactions which do not necessarily proceed simultaneously.

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“…The method is best suited to extrusive and hypabyssal igneous rocks that were subjected to rapid cooling and are unmetamorphosed (Hammond & Taylor 1982). The method is best suited to extrusive and hypabyssal igneous rocks that were subjected to rapid cooling and are unmetamorphosed (Hammond & Taylor 1982).…”

Section: {J Phasementioning

confidence: 99%

Understanding Mineral Deposits

Misra¹

2000

100

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The ilmenite/titano-magnetite assemblage: kinetics of re-equilibration

Cited by 54 publications

References 8 publications

Timescales of mixing and mobilisation in the Bishop Tuff magma body: perspectives from diffusion chronometry

Timescales of mixing and mobilisation in the Bishop Tuff magma body: perspectives from diffusion chronometry

Formation of ferriolivine and magnesioferrite from Mg ? Fe-olivine: Reactions and kinetics of oxidation

Understanding Mineral Deposits

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