ALBERT

Description: Rocks from the 23 Ma Lake City caldera show diverse chemical affinities attesting to a complex magmatic system beneath the caldera. Field and geochemical data from ignimbrites and intrusions constrain magma storage and magma interactions during the formation of the caldera. Two geochemically distinct magma batches erupted during caldera formation: batch A, consisting of rhyolites and trachytes, and batch B, consisting of dacites and trachyandesites. The ignimbrites of the Lower, Middle, and Upper Sunshine Peak Tuff represent the bulk of erupted batch A magma, with an increasing proportion of trachyte to rhyolite as the eruption progressed. Overall, the observed trends of major and trace elements are consistent with the sequential eruption of a magmatic system with a rhyolitic upper portion and trachytic lower portion. The Middle Sunshine Peak Tuff contains two distinct types of pumice clast, while the Upper Sunshine Peak Tuff contains four distinct pumice clast types, with one type chemically related to batch B magma. The link between the rhyolite and trachyte of batch A is supported by major- and trace-element geochemical modeling of an initially trachytic magma that fractionated and was subjected to crystal/melt segregation following 50%–60% crystallization. Compositional gaps and chemical heterogeneity in the bulk ignimbrite composition show that the proportions of these different magma types varied significantly during eruption. We propose that the fractionating batch A and B magmas formed distinct magma pods, some containing residual magma mush, that were tapped during different phases of caldera formation. After collapse, dacite lavas of batch B were erupted concurrent with resurgent uplift from shallow intrusion of both residual mingled batch A and batch B magma. In summary, our observations suggest (1) a complex magma chamber geometry from two fractionating magma batches, and (2) magma replenishment and accelerated periods of magma reorganization in the shallow magma plumbing system during a single caldera cycle at Lake City.

Description: Materials, Vol. 11, Pages 666: Effect of Inoculant Alloy Selection and Particle Size on Efficiency of Isomorphic Inoculation of Ti-Al Materials doi: 10.3390/ma11050666 Authors: J. R. Kennedy B. Rouat D. Daloz E. Bouzy J. Zollinger The process of isomorphic inoculation relies on precise selection of inoculant alloys for a given system. Three alloys, Ti-10Al-25Nb, Ti-25Al-10Ta, and Ti-47Ta (at %) were selected as potential isomorphic inoculants for a Ti-46Al alloy. The binary Ti-Ta alloy selected was found to be ineffective as an inoculant due to its large density difference with the melt, causing the particles to settle. Both ternary alloys were successfully implemented as isomorphic inoculants that decreased the equiaxed grain size and increased the equiaxed fraction in their ingots. The degree of grain refinement obtained was found to be dependent on the number of particles introduced to the melt. Also, more new grains were formed than particles added to the melt. The grains/particle efficiency varied from greater than one to nearly twenty as the size of the particle increased. This is attributed to the breaking up of particles into smaller particles by dissolution in the melt. For a given particle size, Ti-Al-Ta and Ti-Al-Nb particles were found to have a roughly similar grain/particle efficiency.

Description: A series of Cu-substituted goethites, single and co-substituted with Cr, Zn, Cd and/or Pb was prepared, having molar ratios equal to 2.00, 3.33 and 5.00 mol%. All the samples contained only goethite, except Cu-, (Cu,Zn)- and (Cu,Pb)-samples synthesized at 5.00 mol% where hematite was also formed. The presence of Cr/Cd suppressed the hematite-forming effects of Cu. The general sequence of metal entry into the single-metal-substituted goethites was Zn = Cr 〉 Cd 〉 Cu 〉 Pb and in di- (5.00 mol%) and tri- (3.33 mol%) metal-substituted goethites was Cu 〉 Zn 〉 Cd 〉 Cr 〉〉 Pb. Cu incorporation increased all the unit-cell parameters in single-metal-substituted goethite, and these parameters increased in combination with other metals as follows: Cd 〉 Zn 〉 Cr 〉 Pb in the multimetal-substituted goethites. The Cu-substituted goethite dissolved faster than pure goethite. Co substitutions of Cr/Pb reduced the dissolution rate (kFe), while substitutions of Cd/Zn increased kFe.