Molecular beam epitaxy of metamorphic buffer for InGaAs/InP photodetectors with high photosensitivity in the range of 2.2–2.6 um

The present work is concerned with finding optimal technological conditions for the synthesis of heterostructures with a metamorphic buffer for InGaAs/InP photodetectors in the wavelength range of 2.2–2.6 um using molecular beam epitaxy. Three choices of buffer structure differing in design and growth parameters were proposed. The internal structure of the grown samples was investigated by X-ray diffraction and transmission electron microscopy. Experimental data analysis has shown that the greatest degree of elastic strain relaxation in the InGaAs active layer was achieved in the sample where the metamorphic buffer formation ended with a consecutive increase and decrease in temperature. The said buffer also had InAs/InAlAs superlattice inserts. The dislocation density in this sample turned out to be minimal out of three, which allowed us to conclude that the described heterostructure configuration appears to be the most appropriate for manufacturing of short wavelength infrared range pin-photodetectors with high photosensitivity

Evidence for Archean hydrous deep-mantle reservoir provided by Abitibi komatiites

Archean komatiites result from melting under extreme conditions of the Earth’s mantle. Their chemical compositions evoke very high eruption temperatures, up to 1600°C, providing clues to still higher temperatures in their mantle source [1]. This message is clouded, however, by uncertainty about the water content in komatiite magmas. One school holds that komatiites were essentially dry and originated in mantle plumes [2] while the other argues that these magmas contained several percent of water, which drastically reduced their eruption temperature and links them to subduction processes [3]

Belingwe komatiites (2.7 Ga) originate from a plume with moderate water content, as inferred from inclusions in olivine

Major and trace elements, and volatile components have been measured in melt inclusions in olivine from fresh 2.7 Ga old komatiites from the Reliance Formation of the Belingwe Greenstone Belt, Zimbabwe. Reconstructed compositions of melt inclusions contain 20–23.5 wt% MgO and up to 0.3 wt% H2O; these compositions probably represent those of the erupted lava. In inclusions in relatively evolved (low Fo) olivines, an excess of Na2O, CaO, Li, La, Cu, Rb, Y, Sc as well as volatile components (H2O, F, Cl and S) relative to other highly incompatible elements is attributed to assimilation of seawater altered mafic material. No assimilation signature is observed for the most primitive melt inclusions hosted in the magnesium rich olivines. The primary melt composition, estimated using melt inclusions in the most magnesian olivine (Fo 93.5), contains up to 27.5 wt% MgO and ca. 0.2 wt% H2O. The presence of H2O slightly depressed the liquidus temperature to ca. 1513 °C. Our results suggest formation of the Belingwe komatiite magma at ca. 7 GPa pressure and ca. 1790 °C temperature in a mantle plume. The plume picked up water and probably chlorine through interaction with a hydrous transition mantle zone in the way similar to that previously proposed by Sobolev et al. (2016) for komatiites in Canada

Paleoarchean mantle hydrous reservoir beneath South Africa?

Recent study of melt inclusions in high magnesian olivines (Fo 92.4-Fo 94.2) from the 2.7 Ga komatiites of the Abitibi Greenstone Belt, Canada [Sobolev et al, Nature, 2016] demonstrates an early contamination of melts by seawater brines indicated by elevated concentrations of Cl. Yet the melt inclusions in the most magnesian olivines (Fo 94-94.5) that have not been affected by the seawater contain up to 0.8 wt.% H2O suggesting presence of hydrous reservoir in the deep mantle at Neoarchean time. The present contribution may extend the age of this reservoir by 800 million years..

Composition, crystallization conditions and genesis of sulfide-saturated parental melts of olivine-phyric rocks from Kamchatsky Mys (Kamchatka, Russia)

Highlights • Parental melts of sulfide-bearing KM rocks have near primary MORB-like composition. • Crystallization of these S-saturated melts occurred in near-surface conditions. • Extensive fractionation and crustal assimilation are not the causes of S-saturation. • S content in melts can be restored by accounting for daughter sulfide globules. Abstract Sulfide liquids that immiscibly separate from silicate melts in different magmatic processes accumulate chalcophile metals and may represent important sources of the metals in Earth's crust for the formation of ore deposits. Sulfide phases commonly found in some primitive mid-ocean ridge basalts (MORB) may support the occurrence of sulfide immiscibility in the crust without requiring magma contamination and/or extensive fractionation. However, the records of incipient sulfide melts in equilibrium with primitive high-Mg olivine and Cr-spinel are scarce. Sulfide globules in olivine phenocrysts in picritic rocks of MORB-affinity at Kamchatsky Mys (Eastern Kamchatka, Russia) represent a well-documented example of natural immiscibility in primitive oceanic magmas. Our study examines the conditions of silicate-sulfide immiscibility in these magmas by reporting high precision data on the compositions of Cr-spinel and silicate melt inclusions, hosted in Mg-rich olivine (86.9–90 mol% Fo), which also contain globules of magmatic sulfide melt. Major and trace element contents of reconstructed parental silicate melts, redox conditions (ΔQFM = +0.1 ± 0.16 (1σ) log. units) and crystallization temperature (1200–1285 °C), as well as mantle potential temperatures (~1350 °C), correspond to typical MORB values. We show that nearly 50% of sulfur could be captured in daughter sulfide globules even in reheated melt inclusions, which could lead to a significant underestimation of sulfur content in reconstructed silicate melts. The saturation of these melts in sulfur appears to be unrelated to the effects of melt crystallization and crustal assimilation, so we discuss the reasons for the S variations in reconstructed melts and the influence of pressure and other parameters on the SCSS (Sulfur Content at Sulfide Saturation)

Fluorine in primitive magmas of the Troodos Ophiolite Complex, Cyprus: Analytical methods and main results

Modern models for the development and evolution of the geochemical heterogeneity in the Earth's mantle and the genesis of mantle magmas attach much importance to the processes of interaction between deepseated rocks and metasomatic fluids, which are able, when occurring under mantle conditions, to dissolve significant amounts of major and trace elements (see, for example, [1]). Fluorine is one of the major anions of natural fluids and also one of the principal complex-forming ligands of several metals. To evaluate the possible role of fluorine in the processes of mantle magma genesis and to identify the source of this element in natural magmas in various geodynamic environments, it is necessary to know the fluorine concentration in primitive mantle melts. These data are still relatively scarce, particularly for low alkaline magmas [2-4]. The fluorine concentrations in magmas from suprasubduction zones, whose genesis is largely controlled by the interaction between mantle rocks and fluids, remain poorly known and need further refinement. Data presented in this paper are among the first to characterize the concentrations of fluorine in primitive magmas of suprasubduction zones. These data were obtained by secondary ion mass spectrometry of chill glasses from the lava complex of the Troodos ophiolites in Cyprus. Along with information on the concentrations of major and trace elements, H2O, and Cl in the glasses, our results make it possible to utilize the example of the Troodos ophiolites to characterize the main regularities in the geochemistry of fluorine during the origin of magmas above subduction zones and to assay the contributions of various components that participated in the processes of mantle melting. These data are among the first to demonstrate that subduction-related melts became enriched in F relative to LREE