Peralkaline Silicic Extrusive Rocks: Magma Genesis, Evolution, Plumbing Systems, and Eruption.

Peralkaline silicic extrusive rocks are an important component of the volcanological record. Here we review several aspects of their formation and evolution, including the tectonic settings in which they occur, their main petrological and geochemical features, the magmatic lineages along which they evolve, and the parameters (T, P, fO2, melt water contents) that control the lineages. Particular attention is paid to the composition of the extraordinary melts formed at the lowest temperatures. Various lines of evidence are presented to explain the silica-gaps in some lineages. The partial melting of continental crust and the role of crustal contamination are considered to be of relatively minor importance in their genesis. High P-T experiments aimed at quantifying the lineages are assessed. Geophysical and petrological evidence for the depth and nature of the plumbing systems is presented. Differentiation mechanisms within reservoirs and the ubiquity of the formation of compositional zonation are discussed, as are the timescales involved. Volcanic hazards and the environmental impact of eruptions are described and a brief assessment of the ore potential of the extrusives is given

Bulk rock composition and geochemistry of olivine-hosted melt inclusions in the Grey Porri Tuff and selected lavas of the Monte dei Porri volcano, Salina, Aeolian Islands, southern Italy.

The Aeolian Islands are an arcuate chain of submarine seamounts and volcanic islands, lying just north of Sicily in southern Italy. The second largest of the islands, Salina, exhibits a wide range of compositional variation in its erupted products, from basaltic lavas to rhyolitic pumice. The Monte dei Porri eruptions occurred between 60 ka and 30 ka, following a period of approximately 60,000 years of repose. The bulk rock composition of the Monte dei Porri products range from basaltic-andesite scoria to andesitic pumice in the Grey Porri Tuff (GPT), with the Monte dei Porri lavas having basaltic-andesite compositions. The typical mineral assemblage of the GPT is calcic plagioclase, clinopyroxene (augite), olivine (Fo72−84) and orthopyroxene (enstatite) ± amphibole and Ti-Fe oxides. The lava units show a similar mineral assemblage, but contain lower Fo olivines (Fo57−78). The lava units also contain numerous glomerocrysts, including an unusual variety that contains quartz, K-feldspar and mica. Melt inclusions (MI) are ubiquitous in all mineral phases from all units of the Monte dei Porri eruptions; however, only data from olivine-hosted MI in the GPT are reported here. Compositions of MI in the GPT are typically basaltic (average SiO2 of 49.8 wt %) in the pumices and basaltic-andesite (average SiO2 of 55.6 wt %) in the scoriae and show a bimodal distribution in most compositional discrimination plots. The compositions of most of the MI in the scoriae overlap with bulk rock compositions of the lavas. Petrological and geochemical evidence suggest that mixing of one or more magmas and/or crustal assimilation played a role in the evolution of the Monte dei Porri magmatic system, especially the GPT. Analyses of the more evolved mineral phases are required to better constrain the evolution of the magma

Magma mixing and exsolution phenomena in peralkaline rhyolites: insights from the Gold Flat Tuff, Nevada

The distribution and compositions of chevkinite-group minerals (CGMs) in the pantelleritic Gold Flat Tuff, Nevada, USA, are used to examine three aspects of the evolution of the tuff, which we feel are of general significance in peralkaline magmatism. First, both chevkinite-(Ce) and perrierite-(Ce) occur in certain facies, although normally these phases almost invariably occur in different igneous lithologies. Their co-occurrence in the tuff is due to the mixing of pantelleritic and intermediate magmas. Second, the tuff is the first recorded occurrence of a CGM in a pantellerite eruptive, with possible implications for the crystallization conditions. In particular, low values of ${{a}}\mathrm{SiO}_{2}$ may have stabilized ilmenite + chevkinite rather than aenigmatite, although the unusually high LREE contents ($\sum$La–Sm ${\le }$ 1517 ppm) in the pantellerite may have played a role. Third, an unusual lamellar texture in the CGM is revealed by Atomic Force Microscopy to be formed by a rutile-like phase. The lamellae may have formed by exsolution from a rutile-like layer in the crystal structure. An electron back-scattered diffraction study of a single crystal showed a structural dislocation not apparent optically or by electron back-scattered imaging. This may have wider implications in mineralogical studies

Magma mixing and exsolution phenomena in peralkaline rhyolites: insights from the Gold Flat Tuff, Nevada

The distribution and compositions of chevkinite-group minerals (CGMs) in the pantelleritic Gold Flat Tuff, Nevada, USA, are used to examine three aspects of the evolution of the tuff, which we feel are of general significance in peralkaline magmatism. First, both chevkinite-(Ce) and perrierite-(Ce) occur in certain facies, although normally these phases almost invariably occur in different igneous lithologies. Their co-occurrence in the tuff is due to the mixing of pantelleritic and intermediate magmas. Second, the tuff is the first recorded occurrence of a CGM in a pantellerite eruptive, with possible implications for the crystallization conditions. In particular, low values of ${{a}}\mathrm{SiO}_{2}$ may have stabilized ilmenite + chevkinite rather than aenigmatite, although the unusually high LREE contents ($\sum$La–Sm ${\le }$ 1517 ppm) in the pantellerite may have played a role. Third, an unusual lamellar texture in the CGM is revealed by Atomic Force Microscopy to be formed by a rutile-like phase. The lamellae may have formed by exsolution from a rutile-like layer in the crystal structure. An electron back-scattered diffraction study of a single crystal showed a structural dislocation not apparent optically or by electron back-scattered imaging. This may have wider implications in mineralogical studies

First Record of Fungal Diversity in the Tropical and Warm-Temperate Middle Miocene Climate Optimum Forests of Eurasia

The middle Miocene Climate Optimum (MMCO) was the warmest interval of the last 23 million years and is one of the best analogs for proposed future climate change scenarios. Fungi play a key role in the terrestrial carbon cycle as dominant decomposers of plant debris, and through their interactions with plants and other organisms as symbionts, parasites, and endobionts. Thus, their study in the fossil record, especially during the MMCO, is essential to better understand biodiversity changes and terrestrial carbon cycle dynamics in past analogous environments, as well as to model future ecological and climatic scenarios. The fossil record also offers a unique long-term, large-scale dataset to evaluate fungal assemblage dynamics across long temporal and spatial scales, providing a better understanding of how ecological factors influenced assemblage development through time. In this study, we assessed the fungal diversity and community composition recorded in two geological sections from the middle Miocene from the coal mines of Thailand and Slovakia. We used presence-absence data to quantify the fungal diversity of each locality. Spores and other fungal remains were identified to modern taxa whenever possible; laboratory codes and fossil names were used when this correlation was not possible. This study represents the first of its kind for Thailand, and it expands existing work from Slovakia. Our results indicate a total of 281 morphotaxa. This work will allow us to use modern ecological data to make inferences about ecosystem characteristics and community dynamics for the studied regions. It opens new horizons for the study of past fungal diversity based on modern fungal ecological analyses. It also sheds light on how global variations in fungal species richness and community composition were affected by different climatic conditions and under rapid increases of temperature in the past to make inferences for the near climatic future

Clam feeding plasticity reduces herbivore vulnerability to ocean warming and acidification

Ocean warming and acidification affect species populations, but how interactions within communities are affected and how this translates into ecosystem functioning and resilience remain poorly understood. Here we demonstrate that experimental ocean warming and acidification significantly alters the interaction network among porewater nutrients, primary producers, herbivores and burrowing invertebrates in a seafloor sediment community, and is linked to behavioural plasticity in the clam Scrobicularia plana. Warming and acidification induced a shift in the clam's feeding mode from predominantly suspension feeding under ambient conditions to deposit feeding with cascading effects on nutrient supply to primary producers. Surface-dwelling invertebrates were more tolerant to warming and acidification in the presence of S. plana, most probably due to the stimulatory effect of the clam on their microalgal food resources. This study demonstrates that predictions of population resilience to climate change require consideration of non-lethal effects such as behavioural changes of key species. Changes in ocean temperature and pH will impact on species, as well as impacting on community interactions. Here warming and acidification cause a clam species to change their feeding mode, with cascading effects for the marine sedimentary food web

Investigation of Association between PFO Complicated by Cryptogenic Stroke and a Common Variant of the Cardiac Transcription Factor GATA4

Patent foramen ovale (PFO) is associated with clinical conditions including cryptogenic stroke, migraine and varicose veins. Data from studies in humans and mouse suggest that PFO and the secundum form of atrial septal defect (ASDII) exist in an anatomical continuum of septal dysmorphogenesis with a common genetic basis. Mutations in multiple members of the evolutionarily conserved cardiac transcription factor network, including GATA4, cause or predispose to ASDII and PFO. Here, we assessed whether the most prevalent variant of the GATA4 gene, S377G, was significantly associated with PFO or ASD. Our analysis of world indigenous populations showed that GATA4 S377G was largely Caucasian-specific, and so subjects were restricted to those of Caucasian descent. To select for patients with larger PFO, we limited our analysis to those with cryptogenic stroke in which PFO was a subsequent finding. In an initial study of Australian subjects, we observed a weak association between GATA4 S377G and PFO/Stroke relative to Caucasian controls in whom ASD and PFO had been excluded (OR = 2.16; p = 0.02). However, in a follow up study of German Caucasians no association was found with either PFO or ASD. Analysis of combined Australian and German data confirmed the lack of a significant association. Thus, the common GATA4 variant S377G is likely to be relatively benign in terms of its participation in CHD and PFO/Stroke

Mineralogy, geochemistry, and petrography of upper permian bituminous and carboniferous anthracite coals from Xuanwei County, Eastern Yunnan Province, China

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