Iron-rich Melt Research Articles

Textural Entrapment of Core-Forming Melts

Small volume fractions of metal-rich, iron-nickel-sulfur-oxygen melt do not form an interconnected network in polycrystalline olivine at pressures up to 11 gigapascals. These results suggest that iron-rich melts could not have migrated downward along olivine grain edges to form Earth's core. Core separation at pressures below 11 gigapascals within planetary bodies must have been facilitated by large degrees of partial melting, resulting in either separation of immiscible silicate and metal-sulfide melts or extraction of the silicate melt to concentrate the metallic remainder.

Discordant Iron-Rich Ultramafic Pegmatites in the Bushveld Complex and their Relationship to Iron-Rich Intercumulus and Residual Liquids

The iron-rich ultramafic pegmatites comprise a suite of coarse-grained rocks that form discordant bodies within the layered sequence of the Bushveld Complex. These pegmatites, which are considerably more abundant than is generally realized, provide evidence for the differentiation of iron-rich residual melts. The pegmatites are composed largely of iron-rich olivine and clinopyroxene, together with Ti-magnetite and ilmenite. Feldspar is characteristically absent, but paradoxically the pegmatites preferentially replace anorthositic cumulates. Two subgroups are recognized, olivine-clinopyroxene pegmatite and Fe-Ti oxides pegmatite. With increased stratigraphic height the pegmatites become richer in Fe-Ti oxides. Thus, olivine-clinopyroxene pegmatite is prevalent in the Upper Critical and Lower Main Zones, whereas Fe-Ti oxide pegmatite is restricted to the Upper Main and Upper Zones. Zoned pegmatite, with a core of Fe-Ti oxide pegmatite, is transitional between the two subgroups. New whole-rock and electron microprobe analyses of olivine-clinopyroxene pegmatite from the Upper Critical and Lower Main Zones provide convincing evidence that their composition is directly related to height. Cryptic compositional variations are analogous to those displayed by the layered cumulates, but for a given height the pegmatites are always more evolved. Compositions of clinopyroxene in the pegmatites reflect a near-linear relationship with height, whereas cumulus pyroxenes display upward iron-enrichment trends complicated by replenishment and reaction with trapped intercumulus liquid. The olivine-clinopyroxene pegmatite formed by magmatic replacement of earlier-formed cumulates in response to infiltration of iron-rich melts. Suitably differentiated melts comprised intercumulus and residual liquids derived from thick anorthosite layers. The absence of feldspar, although not fully understood, is attributed to an immiscible relationship between dense, iron-rich melts and light, silica-alkali-rich liquids. The latter infiltrated upward to be reincorporated into the resident magma. The iron-rich melts, however, drained down into the crystallizing cumulate pile. Channelling along early-formed fractures and joints was significant, locally resulting in huge pipe-like bodies of pegmatite. The iron-rich melts became increasingly differentiated with height, partly in response to the fractional crystallization of more evolved cumulates. The olivine-clinopyroxene pegmatites are related to infiltration of Fe-Ti oxide-rich silicate melt, whereas Fe-Ti oxide pegmatite is ascribed to Fe-Ti oxide liquid, as originally argued by Bateman (1951). The Bushveld Complex followed the Fenner trend of almost uninterrupted iron enrichment. Evidence of pronounced iron enrichment is, however, manifested in the discordant iron-rich ultramafic pegmatites several thousands of metres below the height at which iron-rich cumulates are observed.

Effect of melt composition on tricalcium silicate: Its formation and composition

This study describes the effect of several clinker melt phases on the kinetics of tricalcium silicate (C 3S) formation. At a given burning temperature, a maximum amount of C 3S was apparently formed for a given melt. The iron-rich melt phases promoted the consumption of lime and the rate of formation of C 3S in the order C 2F > C 4AF > C 6A 2F > C 3A. Results of the microprobe analyses of C 3S and melt phases suggest that iron and alumina entered the C 3S lattice during clinkering. Silica also apparently entered the melt phase, although conclusive evidence could not be obtained.

The growth of single crystals of magnetic garnets

Crystals of magnetic garnets, Y 3Fe 5O 12, Sm 3Fe 5O 12, Er 3Fe 5O 12, and Gd 3Fe 5O 12, suitable for many research purposes have been grown from iron-rich melts of lead oxide. A satisfactory composition is PbO 52·5, Fe 2O 3 44, and M 2O 3 3·5 mole per cent, where M is Y, Sm, Er, or Gd. Portions of the phase equilibrium diagrams for the systems Fe 2O 3-YFeO 3 and PbO-Y 2O 3-Fe 2O 3 have been approximately determined. All the data obtained concerning the growth of magnetic garnets are consistent with these diagrams.