The purpose of this study is to understand the geological, petrographical, mineralogical and geochemical characteristics of analcime-bearing tuffs in the Biga Peninsula and to determine formation process of these tuffs. The study area lies between Ayvacik and K&uuml / &ccedil / &uuml / kkuyu. The rock units are pre-Eocene basement rocks, Miocene Behram Volcanics (Arikli Tuff, andesite, andesitic agglomerate), Pliocene volcanics, Miocene lacustrine sediments (K&uuml / &ccedil / &uuml / kkuyu Formation) and Quaternary alluvium. Analcimes which are found in Arikli Tuff are the main objective of this study. Detailed petrographical, mineralogical and geochemical studies were caried out on the Arikli Tuff samples by using petrographical microscope, X-ray diffractometry, scanning electron microscopy, diffrential thermal analyses inductively coupled plasma &amp / #8211 / mass spectrometry and optical emission spectrometry. Fine-grained and coarse-grained analcime crystals in Arikli Tuff were determined by their colorless, isotropic, trapezohedral and low relief. In addition to petrographic study, SEM and XRD methods also confirmed the presence of analcime. Two modes of occurrences were determined by the petrographical and mineralogical studies / coarse-grained euhedral or anhedral crystals in cavities and pumice fragments and single crystals or clusters of fine-grained analcimes embedded in the matrix. It was stated that there are two types of formation of analcime / alteration of volcanic glass and precipitation from alkaline solution based on petrographical and SEM studies. Geochemical methods, moreover, support the formation types.

Fluid-mobile elements (FMEs) such as B, Cs, As, Li and Tl can mobilize readily under low P-T conditions (0.2-0.5 GPa). This makes them effective geochemical tracers that can be used as a way of tracking fluid-rock exchanges at the shallow depths encountered in the earliest stages of subduction. The Izu-Bonin-Mariana (IBM) subduction system is unique in that it preserves a record of the sequences produced from the onset of subduction through the development of arc magmatism. International Ocean Discovery Program (IODP) Expedition 352 recovered >800m of boninite core material from the earliest IBM magmatic events. Select boninitic glasses from these IODP 352 cores, found mostly as selvages on the rinds of pillow lavas and as clasts within hyaloclastites, were examined via EPMA and laser ablation ICP-MS techniques. The boninite glasses analyzed were separated into two categories – low-silica boninite (LSB) and high-silica boninites (HSB), based on the bulk chemistry and mineralogy of the lithostratigraphic locations from which the glass samples occur in the drill core. LSB are the earlier erupted boninite series, which show both greater variation in extent of differentiation and reflect less depleted mantle sources than HSB. Boron concentrations in the Expedition 352 boninite glasses analyzed range from 0.08 to 12.91 ppm, arsenic contents vary from 0.15 to 3.26 ppm, and cesium varies from 0.01 to 0.91 ppm. Lithium concentrations in the boninites range from 1 to 18.35 ppm while Tl concentrations vary from 10 to 155 ppb. FME concentrations trend toward higher values in HSB than in LSB. Low-Si boninites appear to form via simple mixing of depleted mantle source and an FME enriched fluid endmember, which mobilizes B, As, Cs, (Tl) and Li very early in the subduction process. Coupled with inputs from upwelling mantle, this FME-rich fluid triggers fluid-fluxed boninite melting. The high-Si boninites reflect the addition of a subduction component with a higher Ba/La ratio than that of the depleted mantle; this higher ratio more closely resembles that of Mariana cherts from altered Pacific crust. Thus, the high-Si boninites are consistent with the fluid-fluxed melting of a highly depleted, harzburgitic mantle source and reflect inputs of two distinguishable slab-derived components, one that is sedimentary in nature and another that is FME-enriched. This model for melting that is more similar to the melting regime of modern arcs and reflects the transition from early extension-related melting into that of a “normal” subduction system.

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Yes / In the present paper, the author offers new absolute and contextual dating evidence for Scottish archaeological pitchstone. Much archaeological pitchstone from the Scottish mainland is recovered from unsealed contexts of multi-period or palimpsest sites, and pitchstone artefacts from radiocarbon-dated pits therefore provide important dating evidence for this material group and its associated exchange network. In Scotland, all archaeological pitchstone derives from outcrops on the Isle of Arran, in the Firth of Clyde, and on the source island pitchstone-bearing assemblages include diagnostic types from the Mesolithic, Neolithic and Early Bronze Age period. Off Arran, pitchstone-bearing assemblages never include Mesolithic types, such as microliths, suggesting a post Mesolithic date. This suggestion is supported by worked pitchstone from radiocarbon-dated pits, where all presently available dates indicate that, on the Scottish mainland, Arran pitchstone was traded and used after the Mesolithic period, and in particular during the Early Neolithic period.

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