DataSheet1_Ba, Sr, and Rb feldspar/melt partitioning in recent eruptions from Teide-Pico Viejo volcanic complex, Tenerife: New insights into pre-eruptive processes.xlsx

The behaviour of Group I and II elements during the petrogenesis of felsic igneous rocks is largely controlled by feldspar-liquid relationships. Numerous experimental studies have addressed plagioclase/melt element partitioning, with fewer studies devoted to potassium feldspar, and very few to albite-rich ternary-composition feldspar (An ∼ Or < Ab). However, the partition coefficient for Ba is known to increase by at least an order of magnitude through the crystallisation sequence sodic plagioclase–anorthoclase–potassium feldspar that is typical of sodic alkaline suites. Feldspars, glasses, and whole rocks in such suites may exhibit strong enrichments and depletions that can be used to track processes of crystal fractionation, cumulate formation, and cumulate recycling. Here, we review experimental feldspar/melt partitioning data for Ba, Sr, and Rb for all feldspars. Regression of available data provides expressions that appear to adequately model the compositional and temperature dependence of partition coefficients for albite-rich compositions. We have applied this model to feldspar and melt compositions of the products of several Holocene eruptions (Pico Viejo C, Pico Viejo H, Teide J2, Lavas Negras, Arenas Blancas, Montaña Rajada and Montaña Reventada) of the basanitic-phonolitic suite of the Teide-Pico Viejo volcanic system (Tenerife, Spain), using EPMA and LA-ICP-MS analyses. Comparing analysed feldspar/groundmass pairs with predicted partition coefficients obtained with the models provides a way of distinguishing between feldspars that are in or out of equilibrium with their host melt, and of reconstructing feldspar histories. The results demonstrate the existence of a distinct population of feldspars that had undergone accumulation, fusion and recrystallisation events, in Lavas Negras and Arenas Blancas flows. In addition, the anomalous trachytic composition of Montaña Reventada is due to melting of a feldspar-dominated cumulate. Application of these techniques to active magmatic systems will allow us a better understanding of different pre-eruptive processes, and ultimately improve volcanic hazard assessment.</p

Open-system processes in the differentiation of mafic magma in the Teide–Pico Viejo succession, Tenerife

<p>Oceanic island basalts are commonly thought to differentiate by fractional crystallization, yet closed-system fractionation models have so far failed to reproduce major and trace element variations observed in mafic lavas from the Teide–Pico Viejo stratovolcano complex on Tenerife. Here, new high-precision plagioclase trace element data are fed into such a fractionation model. The results confirm that fractionation of phenocrysts found in the lavas does not reproduce trace element variations, in particular enrichment of Sr and Zr observed in the Teide–Pico Viejo mafic suite. This enrichment of Sr and Zr is tested by an energy-constrained recharge, assimilation and fractional crystallization (EC-RAFC) model at high <em>T</em> and low Δ<em>T</em> intervals, consistent with previously determined magma storage beneath Tenerife at sub-Moho depths. Published mineral–melt equilibrium relations using the plagioclase anorthite content (0.4 < <em>X</em>_An < 0.8) constrain the temperature during differentiation. Gabbroic xenoliths found in Tenerife lavas are assumed as contaminant. Enrichment of Sr and Zr in the Teide mafic suite is reproduced by this combined assimilation and fractional crystallization model, as assimilation causes higher degrees of enrichment in incompatible trace elements than is possible by crystal fractionation alone. Recycling of plutonic roots may thus have significantly enriched trace elements in the primitive lavas of the Teide–Pico Viejo succession. </p

New Dates for Megalithic Stele Monuments of Gedeo, South Ethiopia

This paper reports the results of an archaeological survey and test excavation conducted in one of the ancient megalithic stele sites in south Ethiopia, Sakaro Sodo. The Sakaro Sodo stele site is situated in Gedeo zone, which is known to have the largest number and highest concentration of megalithic stele monuments in Africa, with an estimate of more than 10,000 stelae in sixty or more sites. Prior to our work, only one absolute date was available (850±40 BP) (Joussaume 2012) from a stele site in the Gedeo zone, suggesting stele sites began to be constructed in the region approximately a millennium ago. We report here new AMS dates suggesting that stelae were being emplaced about 2000 BP, pushing the creation of these monuments back at least a millennium. Additionally, we report preliminary findings from characterizing the geochemical properties of obsidian artifacts recovered from stele sites, and stone used to make stelae. While compositional analysis of obsidian suggests long-distance movement of material from sources located in northern Kenya, petrographic microscopy and electron microprobe analyses show a strong connection of stelae to local geological tuff exposures/sources.</p

Supplemental material: Constraints on fluids in subduction zones from electromagnetic data

Geosphere, August 2017, v. 13, p. 1066-1112, doi:10.1130/GES01473.1, Supplemental Table 2 - Comprehensive 40Ar/39Ar data

Supplemental material: Constraints on fluids in subduction zones from electromagnetic data

Geosphere, August 2017, v. 13, p. 1066-1112, doi:10.1130/GES01473.1, Plate 1 - Geologic map of the McDermitt caldera by Henry et al. (2016)

Supplemental material: Constraints on fluids in subduction zones from electromagnetic data

Geosphere, August 2017, v. 13, p. 1066-1112, doi:10.1130/GES01473.1, Supplemental Table 1 - Chemical analyse