The activity of chromite in multicomponent spinels
- 出版日期：2002.
- 页数：205 p. :
- 第一责任说明：Ronit Kessel.
- 分类号：a333.1
- ISBN：0493610766(ebk.) :
MARC全文
02h0025403 20110920152655.0 cr un||||||||| 110920s2002 xx ||||f|||d||||||||eng | AAI3046708 0493610766(ebk.) : CNY371.35 NGL NGL NGL a333.1 Kessel, Ronit. The activity of chromite in multicomponent spinels [electronic resource] : an experimental study with implications for the metamorphic history of equilibrated ordinary chondrites / Ronit Kessel. 2002. 205 p. : digital, PDF file. Source: Dissertation Abstracts International, Volume: 63-03, Section: B, page: 1222. ; Adviser: Ed Stolper. Thesis (Ph.D.) -- California Institute of Technology, 2002. An experimental technique for evaluating the activity of chromite in multicomponent spinels was developed by equilibrating the spinel of interest with a Pt-alloy under a controlled temperature and oxygen fugacity. The thermodynamic properties of the ternary Pt-Fe-Cr system was evaluated, such that activities of Cr and Fe in an equilibrated Pt-alloy can be used to calculate the activity of chromite in the spinel of interest.;The ternary activity model formulation used is based on the characterization of each bounding binary system, Pt-Fe, Pt-Cr, Fe-Cr, with the addition of ternary interaction terms. The Pt-Fe and Pt-Cr systems are described as asymmetric regular solutions with interaction parameters of WPtFe = -138.0 ± 3.3, WFePt = -90.8 ± 24.0, and WPtCr = -129.1 ± 1.2, WCrPt = -80.9 ± 4.4, and DPtCr = +94.4 ± 2.5 kJ/mol (1σ), respectively. Combined with literature thermodynamic properties for the Fe-Cr system, the ternary interaction parameters in the Pt-Fe-Cr system were found to be C Cr = 0, CPt = +115.7, and C Fe = -68.6 kJ/mol.;Using this technique, the metamorphic history of equilibrated ordinary chondrites was evaluated by examining the compositions and textures of olivines, pyroxenes, spinels, and alloys. Equilibrium temperatures based on Fe-Mg exchange between olivine and spinel exhibit a range of 680–796°C in H, L, and LL ordinary chondrites spanning petrographic type 4 to 6. Type 4 chondrites in all groups record variable temperatures that are lower than or equal to those of types 5 and 6 chondrites, implying decoupling of metamorphic temperature from petrographic type. Cooling rates near 800°C were found to be 1–3 K/Ma, slow enough to allow continuous re-equilibration of spinel grains from peak metamorphic temperatures to the olivine-spinel equilibration temperature.;The temperature-oxygen fugacity relationships in equilibrated H chondrites were constrained from spinel-alloy and olivine-pyroxene-alloy phase assemblages based on the mineral compositions and activity-composition models. Log10fO2 values based on the assemblage olivine-pyroxene-alloy are -1.75 ± 0.02 log units below Iron-Wüstite (IW) buffer, regardless of petrographic type. The log10fO 2 values calculated based on the spinel-alloy coexistence are at least -1.5 log units more oxidizing than those based on the olivine-pyroxene-alloy if olivine-spinel equilibration temperatures (728–820°C) are assumed. This probably indicates that closure for spinel-alloy equilibria occurred under retrograde conditions at temperatures below 700°C. Chromite. Electronic books. aeBook. aCN bNGL http://proquest.calis.edu.cn/umi/detail_usmark.jsp?searchword=pub_number%3DAAI3046708&singlesearch=no&channelid=%CF%B8%C0%C0&record=1 NGL Bs935 rCNY371.35 ; h1 bs1107