The formation of garnet in olivine-bearing metagabbros from the Adirondacks

A regional study of olivine-bearing metagabbros in the Adirondacks has permitted testing of the P(pressure)-T(temperature)-X(composition) dependence of garnet-forming reactions as well as providing additional regional metamorphic pressure data. Six phases, olivine, orthopyroxene, clinopyroxene, garnet, plagioclase and spinel, which can be related by the reactions: orthopyroxene+clinopyroxene+spinel +anorthite=garnet, and forsterite+anorthite=garnet occur together both in coronal and in equant textures indicative of equilibrium. Compositions of the respective minerals are typically Fo 25–72 , En 44–75 , En 30–44 Fs 9–23 Wo 47–49 , Pp 13–42 Alm 39–63 Gr 16–20 , An 29–49 and Sp 16–58 . When they occur in the same rock, equant and coronal garnets are homogeneous and compositionally identical suggesting that chemical equilibrium may have been attained despite coronal textures. Extrapolating reactions in the simple CMAS system to granulite temperatures and making thermodynamic corrections for solid solutions gives equilibration pressures (using the thermometry of Bohlen et al. 1980b) ranging from about 6.5 kb in the Lowlands and southern Adirondacks to 7.0–8.0 kb in the Highlands for the assemblage olivine-plagioclase-garnet. These results are consistent with inferred peak metamorphic conditions in the Adirondacks (Valley and Bohlen 1979; Bohlen and Boettcher 1981). Thus the isobaric retrograde path suggested by Whitney and McLelland (1973) and Whitney (1978) for the formation of coronal garnet in olivine metagabbros may not be required. Application of the same equilibria gives >8.7 kb for South Harris, Scotland and 0.9 kb for the Nain Complex. Disagreement of the latter value with orthopyroxeneolivine-quartz barometry (Bohlen and Boettcher 1981) suggests that the use of iron-rich rocks (olivines ≧Fa 50 ) results in errors in calculated pressures.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47335/1/410_2004_Article_BF00371301.pd

Microtextures and microintergrowths of irontitanium-aluminium oxide minerals in a magmatic tinaniferous iron ore from Attu island, southwestern Finland

Microtextures of coexisting magnetite, ilmenite and aluminous spinel and their chemical composition have been studied in a magmatic titaniferous iron ore from Attu Island in south-western Finland. Primary ilmenite contains exsolution lamellae of magnetite and aluminous spinel, oriented along the basal plane (0001). The microtextures of magnetite have been formed by exsolution of aluminous spinel and by oxidation-exsolution of ilmenite along {100} and {111} — planes respectively. To some extent the exsolutions have been formed preferentially along planar structures like grain interfaces and intragranular high angle boundaries. Primary magnetite forms intergrowths with secondary ilmenite and aluminous spinel in border zones adjacent to primary ilmenite. These intergrowths partly show a similarity with exsolution textures of primary magnetite. The available data suggest that they have been formed by privileged growth of exsolved ilmenite and aluminous spinel in the magnetite border zones adjacent to ilmenite. Corrosion of magnetite by the adjacent ilmenite is considered to be less probable for the genesis of these intergrowths

A New One bath Method for Continuous or Pad—Roll Vat Dyeing

A description is given of a new one-bath method for continuous vat dyeing, which can be used in both pad—steam installations and Pad—Roll machines. Although at present the full details concerning the best procedure are not available, it is expected that the method developed for the continuous vat dyeing of relatively short lengths of cloth will prove most suitable for Pad—Roll machines

Electronic reconstruction at n -type SrTiO 3_{3} / LaAlO 3_{3} interfaces

Electron-energy-loss spectroscopy (EELS) is used to investigate single layers of LaAlO3 grown on SrTiO3 having an n-type interface as well as multilayers of LaAlO3 and SrTiO3 in which both n- and p-type interfaces occur. Only minor changes in Ti valence at the n-type interface are observed. This finding seems to contradict earlier experiments for other SrTiO3/LaAlO3 systems where large deviations in Ti valency were assumed to be responsible for the conductivity of these interfaces. Ab initio calculations have been carried out in order to interpret our EELS results. Using the concept of Bader charges, it is demonstrated that the so-called polar discontinuity is mainly resolved by lattice distortions and to a far lesser extent by changes in valency for both single layer and multilayer geometries

Electronic structure and band gap of zinc spinel oxides beyond LDA: ZnAl2O4, ZnGa2O4 and ZnIn2O4

We examine the electronic structure of the family of ternary zinc spinel oxides ZnX2O4 (X = Al, Ga and In). The band gap of ZnAl2O4 calculated using density functional theory (DFT) is 4.25 eV and is overestimated compared with the experimental value of 3.8-3.9 eV. The DFT band gap of ZnGa2O4 is 2.82 eV and is underestimated compared with the experimental value of 4.4-5.0 eV. Since DFT typically underestimates the band gap in the oxide system, the experimental measurements for ZnAl2O4 probably require a correction. We use two first-principles techniques capable of describing accurately the excited states of semiconductors, namely the GW approximation and the modified Becke-Johnson (MBJ) potential approximation, to calculate the band gap of ZnX2O4. The GW and MBJ band gaps are in good agreement with each other. In the case of ZnAl2O4, the predicted band gap values are >6 eV, i.e. similar to 2 eV larger than the only reported experimental value. We expect future experimental work to confirm our results. Our calculations of the electron effective masses and the second band gap indicate that these compounds are very good candidates to act as transparent conducting host materials