Active volcanic fumaroles are one of the most spectacular natural objects in terms of mineral diversity. The Great Tolbachik Fissure Eruption (GTFE) (Kamchatka) fumaroles are renowned for its exceptional number of mineral species. The total number of mineral species that have been reliably identified from this particular locality exceeds 600, which is approximately 10 % of all known minerals to date. In this study, we employ a comprehensive approach (bulk chemistry, microprobe analysis, powder X-ray diffraction, HR X-ray computed tomography, and 34S, 18O, and 65Cu isotope measurements) to study the distribution of primary exhalation and secondary mineral assemblages and to reveal the driving factors responsible for the unique mineral diversity in the Yadovitaya fumarole. High oxygen fugacity, interaction of minerals with atmospheric oxygen and water from seasonal precipitation (leading to abundant hydrated mineral associations), temperature conditions controlling the spatial distribution of mineral-forming components, gas-rock interactions, and basaltic scoria morphology perfect for the crystallization of various minerals are some of the factors revealed. The Yadovitaya fumarole cross-section consists of 12 zones, each of which has characteristic mineral assemblages. The temperature ranges from 400 °C at the bottom to 30 °C at the surface. The zonal cross-section and sequential formation of exhalative fumarolic minerals are associated with the gradual distribution of a number of key mineral-forming elements, primarily S, Cu, Pb, Zn, and As. Furthermore, characteristic patterns for Rb and Cs are observed. The significance of atmospheric oxygen (δ18O = 23 ‰) and the impact of δ18O fractionation versus δ65Cu fractionation on the formation of exotic fumarolic minerals is discussed.
Abstract Samples 73001 and 73002, which make up the lower and upper portions, respectively, of the double drive tube containing regolith (“soil”) collected on the “light mantle” at Station 3 during Apollo 17. Using a quadrupole inductively coupled plasma‐mass spectrometer (ICP‐MS) and fused‐bead electron‐probe microanalysis (FB‐EPMA), we determined the chemical composition of every 0.5 cm dissection interval of the entire 56.9 cm length of the double drive tube, which penetrated to a depth of 70.6 cm below the regolith surface. We used the chemical compositions to model the proportions of different lithologic components found at the Apollo 17 site. Elemental variations with depth were linked to different proportions of these components. Higher amounts of high‐Ti mare basalt near the 73002 surface (uniformly dark‐toned regolith from 0 to 1.5 cm) indicate mixing of local mare materials by small impact cratering. Decreasing proportions of high‐Ti mare basalt below 1.5 cm result from the mixing of dark and light regolith components during the dissection process on Earth. Below about 7.5 cm, compositions indicate consistent amounts of primarily highlands material (<5% high‐Ti mare basalt), which can be described as a mixture of noritic impact‐melt and anorthositic‐norite components. In detail, the modeled anorthositic‐norite component, which may represent the pre‐basin upper crust in this part of the Moon, ranges from 50 to 60 wt.%. The modeled noritic impact‐melt breccia component remains relatively uniform at 35–40 wt.% throughout the length of 73002 and increases to 45 wt.% at the bottom of 73001.
Tektite and microtektite formation have important implications on our understanding of impacts both on Earth, the Moon and on other bodies within our solar system. Here, we investigate the formation mechanisms of microtektites by analysing the K isotope systematics and elemental compositions of forty-four Australasian microtektites from various distances from the proposed impact location. Based on the K isotope and concentration data, the microtektites analyzed here are split into two groups, the "ODP group" and the "MB group". The ODP group were recovered from the Ocean Drilling Project (ODP) sediment cores and consist of microtektites which landed closer to the proposed impact site (∼1220–1240 km) and show limited δ41K variation (–1.06 ‰ to −0.21 ‰) and higher K concentrations (2.48 wt% to 3.66 wt% K2O). In contrast, the MB group were mostly collected from the surface of Miller Butte (MB) in Antarctica and represent microtektites which landed significantly further from the proposed impact site (∼4100–10800 km) and contain large δ41K variations (−4.04 ‰ to 0.57 ‰) and low K concentrations (0.49 wt% to 1.45 wt% K2O). For the microtektites studied here, the overall correlation observed is consistent with condensation whereby a greater extent of K depletion correlates with lighter K isotope compositions. This simple condensation model is in contrast to previous studies which find evidence for complex evolution involving evaporation, condensation, and mixing. For the ODP group microtektites, the isotopic and elemental data suggest condensation from an upper continental crust (UCC) starting composition. Conversely, for the MB group a UCC starting composition is not compatible, as even the most K-rich MB group microtektites are significantly depleted in K and display δ41K values much higher than the UCC. These observations can be explained by a vapor plume with a progressively evolving K isotope composition, with the earliest K condensates depleting and fractionating K within the plume, thus altering the starting K compositions for the later K condensates. From this data we calculate a cooling rate of up to 2,600 K/hour for the ODP group and up to 20,000 K/hour for the MB group, which are comparable to the cooling rates measured for tektites and considerably faster than those theoretically calculated or experimentally determined for chondrules. Overall, when assessed within the context of previous studies, microtektite formation appears very complex with evidence for different volatilization processes to different degrees observed within different microtektites. As such, while condensation appears dominant for K within the Australasian microtektites studied here, more work is needed to fully untangle the processes involved in microtektite formation.
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