Comparative geodynamics and geothermy of the Alpine and Pacific belts. Mechanical-mathematical modeling

Формирование и эволюция геологических структур отражают взаимодействие коры и мантии. Актуальность работы определяется предметом исследования – решением задачи механико-математического моделирования формирования и эволюции геологических структур над поднимающимся мантийным диапиром. Для моделирования геологических процессов и эволюции геологических структур в связи с движениями глубинных слоев мантии были собраны и проанализированы все возможные геолого-геофизические данные и использованы механико-математические модели различной реологии. Геолого-геофизические данные для Альборанского, Балеарского, Тирренского, Эгейского, Ионического, Черного, Каспийского морей, Левантийской, Прикаспийской, Паннонской, Алеутской впадин, Охотского, Японского, Филиппинского морей собраны и проанализированы. Взаимодействие литосферы и астеносферы находит свое отражение в формировании и эволюции геологических структур. Зоны столкновения литосферных плит характеризуются высокими P-T условиями, высокой сейсмичностью, землетрясениями, вулканизмом, магматизмом и активными проявлениями геотермальной энергии: вулканами, минеральными водами, дегазацией, горячими источниками. Целью исследования является разработка адекватной модели формирования и эволюции геологических структур на поверхности Земли в связи с глубинными геодинамическими процессами. Методы работы. Для изучения динамики литосферы в процессе эволюции на больших временах использовались механико-математические модели геологической среды на основе модели многослойной высоковязкой несжимаемой жидкости. Для приближенного решения уравнений Навье-Стокса и уравнения неразрывности использовались метод разложения по малому параметру, метод последовательных приближений и метод сращиваемых асимптотических разложений. Моделирование дает возможность рассчитывать распределение P-T параметров в слоях осадочного чехла, коры и верхней мантии в процессе эволюции структур. Существование зон растяжения в задуговых бассейнах можно объяснить подъемом мантийных диапиров в результате геотермального эффекта и подъемом астеносферы в процессе столкновения глубинных мантийных потоков. Результаты работы. Результаты механико-математического моделирования показывают, что в процессе развития осадочных бассейнов над поднимающимся мантийным диапиром структура поверхностного свода сменяется структурой глубокой депрессии. В аналитическом решении найдены критические параметры задачи, связывающие форму диапира, его глубину и скорость подъема со структурой земной поверхности. Результаты моделирования исследованы на примерах геологического строения Альпийского и Тихоокеанского поясов и хорошо согласуются с геолого-геофизическими данными. The origin and evolution of geological structures reflect crust-mantle interaction. The relevance of the work is determined by the subject of the study - the solution of the problem of mechanical and mathematical modeling of the formation and evolution of geological structures above the rising mantle diapir. For simulation of geological processes and geological structures evolution in connection with deep mantle movements all possible geological-geophysical data were combined and analyzed and the mechanical-mathematical models of different rheology were used. Geological-geophysical data for Alboran sea, Balearic sea, Tyrrhenian sea, Aegean sea, Ionian sea, Levant sea, Black sea, Caspian sea, Pre-Caspian depression, Pannonian depression, Aleutian depression, Okhotsk sea, Sea of Japan, Philippines sea are combined and analyzed. Lithosphere-asthenosphere interaction is reflected in geological structures formation and evolution. The zones of the lithosphere plates collision are characterized by high P-T conditions, high seismicity, earthquakes, volcanism, magmatism and active geothermal energy manifestations: volcanoes, mineral waters, degazation, hot springs. The aim of the study is to develop an adequate model of the formation and evolution of geological structures on the Earth's surface in connection with deep geodynamic processes. Methods. To study the dynamics of the lithosphere in the process of evolution at long times, we used mechanical and mathematical models of the geological medium based on the model of a multilayer high-viscosity fluid. For the approximate solution of the Navier-Stokes equations and the continuity equation, the method of decomposition in a small parameter, the method of successive approximations and the method of splicing asymptotic decomposition were used. Modeling gives possibility to calculate P-T parameters distribution in the layers of sedimentary cover, crust and upper mantle in the process of the structures evolution. The existing of stretching zones in back-arc basins can be explained by upwelling of mantle diapirs as a result of geothermal effect and raising of asthenosphere in the process of collision of deep mantle flows. Results. The results of mechanical and mathematical modeling show that during the development of sedimentary basins above the rising mantle diapir, the structure of the surface vault is replaced by the structure of a deep depression. In the analytical solution, the critical parameters of the problem are found that relate the shape of the diapir, its depth, and the ascent rate with the structure of the Earth's surface. The results of modeling are investigated on the examples of the Alpine and Pacific belts geological structures and give good agreement with geological-geophysical data

Kimberlite magmatism and origin of K-rich metasomatic melt-fluid

<p>The experimental study indicates that high-K magmas and kimberlites are in equilibrium with metasomatic minerals, such as phlogopite, richterite, and apatite during their formation in the mantle; i.e., metasomatic processes played a decisive role in their genesis.</p><p>In the uppermost part of the mantle, K is entirely concentrated in plagioclase. With increasing depth the K budget is determined mainly by clinopyroxene and, to a lesser extent, garnet A further increase in pressure causes pyroxene and garnet to react to form majorite, which has K and Na partition coefficients equal to 0.015 and 0.39, respectively [1]. In the depth interval of 410–660 km, majorite is associated with wadsleyite (410–500 km) and ringwoodite (500–660 km), neither of which incorporate K or Na into their structures. At deeper levels, below 660 km, the majorite–ringwoodite assemblage is replaced by the ferropericlase–bridgmanite–Ca-perovskite paragenesis. Here, the modal content of Ca-perovskite  is ~8%. The K partition coefficient for Ca-perovskite is relatively high (0.39), and that of Na is even higher (2.0) [2].The.hexagonal NAL phase content up to 1.1 and  6.2wt% K2O and Na2O respectively Thus, practically all K and Na will be concentrated in Ca-perovskite and  the NALphase in the upper parts of the lower mantle. When a mantle diapir ascends from a depth  more then of ~660 km, Ca-perovskite and NAL becomes unstable and reacts with bridgmanite and ferripericlase to produce majorite and ringwoodite, and, with a further decrease in pressure wadsleyite becomes stable. The K partition coefficient in Ca-perovskite is 26 times higher compared with that of majorite The K partition coefficient of NAL is unknown. The remaining K likely remains excluded from the lattices of minerals in this mantle zone .Majorite may be an important concentrator of Na in the uppermost part of the lower mantle and transition zone. Experimental data indicate that 12 molar % sodium can be incorporated in majorite solid solutions. The chemical composition of the natural majorite contains 0.27-1.12 wt % Na<sub>2</sub>O Taking into consideration values of the K partition coefficient for Ca-perovskite and majorite, it can be confidently stated that the thermodynamic activity of K<sub>2</sub>O in the system increases by more than an order of magnitude with the transition of the bridgmanite–Ca-perovskite–ferripericlase – NAL association to the majorite–ringwoodite paragenesis. This is evidence that majorite will markedly fractionate K and Na, resulting in conditions favorable for the transfer of K into a melt or fluid phase at the boundary between the lower mantle and the transition zone.</p><p>1 Corgne A. and Wood B.J., Trace element partitioning between majoritic garnet and silicate melt at 25 GPa. Physics of the Earth and Planetary Interiors, 2004, 143–144, 407-419.</p><p>2 Liebske C., Wood B.J., Rubie D.C., Frost D.J., Silicate perovskite-melt partitioning of trace elements and geochemical signature of a deep perovskitic reservoir. Geochimica et Cosmochimica Acta, 2005, 69(2), 485-496. </p>

H3e/H4e Ratio in Olivines from Linosa, Ustica, and Pantelleria Islands (Southern Italy)

We report helium isotope data for 0.03–1 Ma olivine-bearing basaltic hawaiites from three volcanoes of the southern Italy magmatic province (Ustica, Pantelleria, and Linosa Islands). Homogenous H3e/H4e ratios (range: 7.3–7.6 Ra) for the three islands, and their similarity with the ratio of modern volcanic gases on Pantelleria, indicate a common magmatic end-member. In particular, Ustica (7.6±0.2 Ra) clearly differs from the nearby Aeolian Islands Arc volcanism, despite its location on the Tyrrhenian side of the plate boundary. Although limited in size, our data set complements the large existing database for helium isotope in southern Italy and adds further constraints upon the spatial extent of intraplate alkaline volcanism in southern Mediterranea. As already discussed by others, the He-Pb isotopic signature of this magmatic province indicates a derivation from a mantle diapir of a OIB-type that is partially diluted by the depleted upper mantle (MORB mantle) at its periphery.