Sergey Smirnov

Formation and properties of hydrosilicate liquids in the systems Na 2 O-Al 2 O 3 -SiO 2 -H 2 O and granite-Na 2 O-SiO 2 -H 2 O at 600°C and 1.5 kbar

In order to determine the mechanisms of formation and properties of natural hydrosilicate liquids (HSLs), which are formed during the transition from magmatic to hydrothermal mineral formation in granitic pegmatites and rare-metal granites, the formation of HSLs was experimentally studied in the Na2O-SiO2-H2O, Na2O-Al2O3-SiO2-H2O, and Na2O-K2O-Li2O-Al2O3-SiO2-H2O systems at 600°C and 1.5 kbar. It was shown that the sequential extension of composition does not suppress HSL formation in the systems and expands the stability field of this phase. However, HSLs formed in extended chemical systems have different structure and properties: the addition of alumina induces some compression of the structure of the silicate framework of HSLs, which results in a decrease in water content in this phase and probably hinders the reversibility of its dehydration. It was demonstrated that HSL can be formed by the coagulation of silica present in a silica-oversaturated alkaline aqueous fluid. It was supposed that the HSL formed during this process has a finely dispersed structure. It was argued that anomalous enrichment in some elements in natural HSLs can be due to their sorption by the extensively developed surface of HSL at the moment of its formation.

Identification of the deep-seated component in paleo fluidscirculated through a potential nuclear waste disposal site: Yucca Mountain, Nevada, USA

Using a combination of mineralogical, fluid inclusion and stable isotope techniques, chemical data have been obtained thathelp characterize the hydrogeochemistry of paleogroundwaters that circulated through the vadose zone of Yucca Mountain, Nevada, USA—a prospective site for geological disposal of high-level nuclear waste. The results depict unidirectional evolution of groundwaters from reducing to oxidizing states concomitantly with an overall cooling from ∼ 85 °C to < 35–50 °C. Early calcite has strongly positive δ13C values (up to +9 %o PDB), which are interpreted as an indication of the partitioning between reduced and oxidized dissolved carbon species in anoxic (reducing) environment. Reducing character of fluids is further supported by the chemistry of gases trapped in inclusions (dominant CH4, CO2, very little O2). The maximum homogenization temperatures of fluid inclusions and reconstructed paleoheat flows form a non-uniform field with prominent maximum near the block-bounding Paintbrush fault. The data support the model of invasion(s) of the deep-seated thermal fluids, into the vadose zone, along the permeable fault zone. Chemical properties of early portions of the fluid were acquired during its long residence in the deep-seated part of the Earths crust. At advanced stages, the fluid evolved in response to the overall cooling and mixing with oxidized waters from shallow aquifers.

The feeder system of the Toba supervolcano from the slab to the shallow reservoir

The Toba Caldera has been the site of several large explosive eruptions in the recent geological past, including the worlds largest Pleistocene eruption 74,000 years ago. The major cause of this particular behaviour may be the subduction of the fluid-rich Investigator Fracture Zone directly beneath the continental crust of Sumatra and possible tear of the slab. Here we show a new seismic tomography model, which clearly reveals a complex multilevel plumbing system beneath Toba. Large amounts of volatiles originate in the subducting slab at a depth of ∼150 km, migrate upward and cause active melting in the mantle wedge. The volatile-rich basic magmas accumulate at the base of the crust in a ∼50,000 km3 reservoir. The overheated volatiles continue ascending through the crust and cause melting of the upper crust rocks. This leads to the formation of a shallow crustal reservoir that is directly responsible for the supereruptions.

Geochemistry and age of rare-metal dyke belts in eastern Kazakhstan

The results of studies of the Chechek and Akhmirovo dyke belts (the Kalba-Narym zone of Eastern Kazakhstan) constituted by rare-metal Li-F-granitoids (ongonites) are presented. The results of geochemical mapping of dyke belts are given, as are the first-obtained data on the rare-metal composition of rock-forming minerals and melt inclusions. The data on precision dating of rocks by means of the 40Ar/39Ar-isotope technique are presented. It is shown that the dyke belts were formed from the melts of three different geochemical types. The existence of these types might be caused by differentiation within the deep-seated magma chambers. The data of geochronology permit us to conclude that the centers of rare-metal Li-F-magmatism characteristic of the large magma provinces that appeared under the impact of mantle plumes on the arisen continental crust might have been formed at the final stages of the formation of the Kalba-Narym batholith. This allows one to assume the rare-metal Li-F-granitoids (ongonites) of the dyke belts in Eastern Kazakhstan belong to the large Late-Paleozoic magma province that appeared in the region of Central Asia as a result of the activity of the Tarim plume.

Implementation and Use of Coarse-grained Parallel Branch-and-bound in Everest Distributed Environment

Abstract This paper examines the coarse-grained approach to parallelization of the branch-and-bound (B&B) algorithm in a distributed computing environment. This approach is based on preliminary decomposition of a feasible domain of mixed-integer programming problem into a set of subproblems. The produced subproblems are solved in parallel by a distributed pool of standalone B&B solvers. The incumbent values found by individual solvers are intercepted and propagated to other solvers to speed up the traversal of B&B search tree. Presented implementation of the approach is based on SCIP, a non-commercial MINLP solver, and Everest, a web-based distributed computing platform. The implementation was tested on several mixed-integer programming problems and a noticeable speedup has been achieved. In the paper, results of a number of experiments with the Traveling Salesman Problem are presented.

Focused magmatism beneath Uturuncu volcano, Bolivia: Insights from seismic tomography and deformation modeling

We have carried out a tomographic inversion for seismic velocity in the vicinity of Uturuncu volcano (Bolivia) based on a 33-station temporary seismic network deployment. We combine travel times from earthquakes in the shallow crust with those from earthquakes on the subducting Nazca plate to broadly constrain velocities throughout the crust using the LOTOS tomography algorithm. The reliability and resolution of the tomography is verified using a series of tests on real and synthetic data. The resulting three-dimensional distributions of Vp, Vs, and Vp/Vs reveal a large tooth-shaped anomaly rooted in the deep crust and stopping abruptly 6 km below the surface. This feature exhibits very high values of Vp/Vs (up to 2.0) extending to ~80 km depth. To explain the relationship of this anomaly with the surface uplift observed in interferometric synthetic aperture radar (InSAR) data, we propose two scenarios. In the first, the feature is a pathway for liquid volatiles that convert to gas, due to decompression, at ~6 km depth, causing a volume increase. This expansion drives seismicity in the overlying crust. In the second model, this anomaly is a buoyant pulse of magma within the batholith, ascending due to gravitational instability. We propose a simplified numerical simulation to demonstrate how this second model generally supports many of the observations. We conclude that both of these scenarios might be valid and complement each other for the Uturuncu case. Based on joint analysis of the tomography results and available geochemical and petrological information, we have constructed a model of the Uturuncu magma system that illustrates the main stages of phase transitions and melting.

Conditions of crystallization, composition, and sources of rare-metal magmas forming ongonites in the Kalba—Narym zone, Eastern Kazakhstan

This paper presents a study of ongonites from the Chechek and Akhmirovo dike belts located within the Kalba—Narym batholith in Eastern Kazakhstan. The obtained conclusions are based on the investigations of melt and fluid inclusion in quartz phenocrysts, supplemented by mineralogical and geochemical data. It was established that the dike rocks were formed by crystallization of volatile-rich rare-metal melts in the presence of an aqueous fluid phase with subordinate amounts of carbon dioxide and methane. The ongonites crystallized from three geochemically different melts. Porphyritic phenocrysts in the ongonites of the Chechek and Akhmirovo dike belts crystallized at close temperatures 560–605°C and pressure of 3.6–5.3 kbar. Ongonite magmas that formed the Chechek and Akhmirovo dike belts had a high ore potential. However, degassing dynamics was not favorable for the development of metasomatism and formation of hydrothermal mineralization at the level of dike emplacement. The area of the rare-metal magmatism represented by ongonite dikes and rare-metal granite pegmatites has been distinguished in the northern part of the Kalba—Narym zone. The formation of rare-metal magmas was related to the differentiation in large granitoid chambers under the effect of juvenile fluids derived from the Tarim mantle plume.

Geology and mineralogy of the Alakha spodumene granite porphyry deposit, Gorny Altai, Russia

The Alakha lithium–tantalum deposit in the southern Altai, Russia, is represented by a stock of spodumene-bearing granite porphyry localized in the Kalba–Narym–Koktogai lithium–tantalum rare-metal granitic belt, unique in extent (more than 1000 km). This belt is a part of the Altai accretionary–collisional system. Judging from forecasting, the Alakha deposit can be regarded as an uneroded proxy of a pegmatite body both in dimensions and mean Li2O and Ta2O5 contents (0.98 wt % and 114 ppm, respectively); however, the oregenerating potential of this deposit remains insufficiently studied and had not yet been claimed. In this paper, we attempt to fill this gap with a detailed mineralogical study, which allows us to provide insights into the crystallization of Li-bearing high-silicic magma and redistribution of components during magmatic and postmagmatic processes. Accessory mineral assemblages in muscovite–spodumene–K-feldspar granite porphyry and muscovite albitite—the main petrographic rock varieties of the Alakha stock—turned out to be almost identical. A significant similarity in the chemistry of major rock-forming minerals is established for spodumene granite porphyry of the Alakha stock and spodumene pegmatites from large deposits, which makes it possible to suggest that they are close in the petrogenetic mechanism of their formation. The mineral assemblages of muscovite albitite in the apical portion of the Alakha stock are connected by gradual transition with those of spodumene granite porphyry. Such a transition is caused by postmagmatic metasomatic alteration of the latter.