Hadal aragonite records venting of stagnant paleoseawater in the hydrated forearc mantle

The hadal zone at trenches is a unique region where forearc mantle rocks are directly exposed at the ocean floor owing to tectonic erosion. Circulation of seawater in the mantle rock induces carbonate precipitation within the deep-sea forearc mantle, but the timescale and rates of the circulation are unclear. Here we investigated a peculiar occurrence of calcium carbonate (aragonite) in forearc mantle rocks recovered from ~6400 m water depth in the Izu–Ogasawara Trench. On the basis of microtextures, strontium–carbon–oxygen isotope geochemistry, and radiocarbon analysis, we found that the aragonite is sourced from seawater that accumulated for more than 42,000 years. Aragonite precipitation is triggered by episodic rupture events that expel the accumulated fluids at 10−2–10−1 m s−1 and which continue for a few decades at most. We suggest that the recycling of subducted seawater from the shallowest forearc mantle influences carbon transport from the surface to Earth’s interior.

Mathematical modeling of the process of magma formation in the Earth’s crust

<p>One of the mechanisms of magma generation in the Earth's crust is the reaction of dehydration during subduction process. Water is released from subducting lithosphere which leads to the lowering of the melting temperature of mantle rock by hundreds of degrees.</p><p>In this work, we present a numerical study of the formation and rise of magma to the Earth's surface, considering partial melting and crystallization of rocks and chemical differentiation of magma. We develop a coupled model of the filtration flow of melt and magmatic fluid through deformable permeable rocks and a thermodynamic model of plagioclase melting based on Gibbs energy minimization approach. The formation of regions with a high melt concentration due to spontaneous focusing of filtration flow being the result of viscoplastic (de)compaction of the pore space is shown. The influence of mechanical properties of rocks and chemical composition of the system on the dynamics of the process is investigated.</p>

Petrological features of picrobasaltic melts on Lanzarote, Canary Islands

The paper discusses issues related to the petrology of picrobasaltic melts forming lava flows on Lanzarote, Canary Islands. During ascientific and educational expedition on the aforementioned island, lava flows of picro basalt of the third phase of the 1731–1732 eruption were studied and tested. Preference was given to the well-preserved streams in the west and south of the island thatare accessible for direct study. Volcanogenic-sedimentary associations were identified in the studied outcropsand described, the structural and textural features of the flows were characterized, and samples with mantle rock xenoliths were taken for petrological reconstructions. New geochemical data onrocks and minerals are presented. It was established that the temperature of the initial melt was 1100–1180°C. Large harzburgitephenocrysts in picro basalt are xenocrysts formed as a result of melting and disintegration of mantle xenoliths.

Hydrogen Isotopic Variations in the Shergottites

Hydrogen isotopes in the shergottite Martian meteorites are among the most varied in Mars laboratory samples. By collating results of previous studies on major hydroxyl, deuterium, and H2O bearing phases, we provide a compendium of recent measurements in order to elucidate crustal-rock versus mantle-rock processes on Mars. We summarize recent works on volatile and δD measurements in a range of shergottite phases: from melt inclusions, apatite, merrillite, maskelynite, impact melt glass, groundmass glass, and nominal anhydrous minerals. We interpret these observations using an evidence-based approach, considering two particular scenarios: (1) water-rock crustal interactions versus (2) magmatic-based processes. We consider the implications of these measurements and the scope they have for future studies, paying particular attention to future works on H, S, and Cl isotopes in situ, shedding light on the nature of volatiles in the hydrosphere and lithosphere of Mars.