Geodynamic Research Articles

On the reduction of geodetic and gravimetric measurements on technogenic and geodynamic polygons

On the reduction of geodetic and gravimetric measurements on technogenic and geodynamic polygons

НЕКОТОРЫЕ ЭПИЗОДЫ ЖИЗНИ АКАДЕМИКА Л. И. ЛОБКОВСКОГО (К 75-ЛЕТИЮ ЮБИЛЯРА)

This essay is dedicated to the 75th anniversary of the outstanding Russian scientist Leopold Isaevich Lobkovsky. The article describes the path of formation and professional transformation of a graduate of the Faculty of Mechanics and Mathematics of Lomonosov Moscow State University, who in the course of his work made a significant contribution to World science in the field of geodynamics. In particular, he created the prerequisites for a significant revision of the physical foundations of the theory of lithospheric plate tectonics and its transformation into the theory of tectonics of deformable lithospheric plates. The second important achievement of L. I. Lobkovsky is the creation of a keyboard model of island-arc systems and the trigger effect of energy unloading in subduction zones. The most important geopolitical achievement of the hero of the day is the creation of a model for the development of the Canadian Basin and the Arctic Ocean in the Mesozoic and Cenozoic. This made it possible to substantiate the continental nature of the vast areas of the Arctic for the declaration of Russian priority over them in the relevant UN commission.

Design, Regulation, and Fast Measurement Method of Weak Magnetic Force Gradient Based on Superconducting Gravimeter

In this article, based on the magnetic levitation structure of superconducting gravity measurement, the design, adjustment, and fast measurement method of the weak magnetic force gradient are introduced. Based on the numerical simulation method of H-formulation, the weak magnetic force gradient of minimum −0.001 N·m is designed. The proposed “semiopen-loop magnetic force gradient adjustment method” can achieve the magnetic force gradient adjustment of less than −0.01 N·m. Aiming at the defect that the conventional solid earth tide observation method requires several or even tens of hours of long-term observation when measuring the magnetic force gradient, the proposed “closed-loop electromagnetic excitation method” can realize fast and accurate measurement in the process of force gradient adjustment, and evaluate the measurement accuracy of the gravity instrument at any time. The prototype is placed in the field observation station of the National Institute of Metrology where the environment is more stable to observe the solid earth tide signals. The force gradient of −0.00264 N·m was obtained using the method proposed in this article, and its correctness was verified by comparison with experimental results. This article is of great significance for improving the convenience of users, promoting the localization and commercialization of superconducting gravimeters, and promoting the in-depth research in the field of geodynamics.

InSight seismic waveform data reveal more marsquakes

Analyzing seismic waveforms recorded by the InSight mission seismometer, we discovered and documented 47 marsquakes in the Cerberus Fossae region of Mars. Their repetitive nature at all times of the Martian day tells a story of their likely volcanic origin and of a mobile Martian mantle. Mars harbours a liquid core, and it remains to be understood why the Martian geodynamic field ceased to exist.

Site survey and assessment for the planned seismogeodynamic monitoring network in the Republic of Armenia

We present results of a detailed analysis of data obtained from seismic geodynamic field studies conducted at proposed sites for the development of advanced seismic monitoring stations in the Republic of Armenia. These studies aim to determine the background seismic and geodynamic noise level around such sites. Finally, based on the received data and international standards, nine survey points were classified into respective classes according to their noise level. We also calculated minimum significant earthquake magnitude detectable by the proposed seismic network in different regions of Armenia and mapped it based on recorded regional earthquakes. The resulting map indicates that the proposed seismic monitoring network will provide homogenous initial data for the various seismically active regions of the territory of the Republic of Armenia.

Earth’s gradients as the engine of plate tectonics and earthquakes

The processes occurring on the Earth are controlled by several gradients. The surface of the Planet is featured by complex geological patterns produced by both endogenous and exogenous phenomena. The lack of direct investigations still makes Earth interior poorly understood and prevents complete clarification of the mechanisms ruling geodynamics and tectonics. Nowadays, slab-pull is considered the force with the greatest impact on plate motions, but also ridge-push, trench suction and physico-chemical heterogeneities are thought to play an important role. However, several counterarguments suggest that these mechanisms are insufficient to explain plate tectonics. While large part of the scientific community agreed that either bottom-up or top-down driven mantle convection is the cause of lithospheric displacements, geodetic observations and geodynamic models also support an astronomical contribution to plate motions. Moreover, several evidences indicate that tectonic plates follow a mainstream and how the lithosphere has a roughly westerly drift with respect to the asthenospheric mantle. An even more wide-open debate rises for the occurrence of earthquakes, which should be framed within the different tectonic setting, which affects the spatial and temporal properties of seismicity. In extensional regions, the dominant source of energy is given by gravitational potential, whereas in strike-slip faults and thrusts, earthquakes mainly dissipate elastic potential energy indeed. In the present article, a review is given of the most significant results of the last years in the field of geodynamics and earthquake geology following the common thread of gradients, which ultimately shape our planet.

ГЕОДИНАМІКА

The purpose of the presented work was to model the electrical conductivity distribution in the northwestern part of the Ukrainian shield and to study the relationship of geoelectric anomalies with natural mineral deposits and with signs of possible tectonic activation of long-lived fault systems on the Shield. The methodology was based on long-period magnetotelluric and magnetovariational measurements in the period range of 3-16 to 2500-3600 s. The dense network of measurement sites made it possible to explore the geoelectric structure of the Ukrainian Shield segment limited by the coordinates 26°-30°E and 48°-51,7°N. 2D and quasi-3D inversion of the obtained magnetotelluric and geomagnetic responses resulted in the creation of overview models of electrical resistivity/conductivity for the territory of investigation. As a result, geoelectrically anomalous structures were identified at different depths. The local character of the conductors and their position indicate their connection with recently activated fault zones, their junctions and with metallogeny. The Precambrian age of crystalline rocks of the investigated area refers mainly to the electronic-type graphite-sulphite origin of increased conductivity, however the depth of conductive features, their vertical extent and their link to rejuvenated fault systems may indicate the genetic connection of various minerals and their subsequent precipitation with deep fluid migration. Originality. The obtained results aimed at clarifying the deep structure and correlating the geoelectric features of the earth’s crust and upper mantle with fault systems and deposits of various natural mineral sources. In addition, they alone can serve as further evidence of possible tectonic activation processes in the studied area. Practical significance. The presented results can bring social benefits by identifying areas of mineral endowment, and in the field of geodynamics they can contribute to the assessment of natural hazard in mapping the course of tectonically active fault systems.

Особенности связи между пространственно-временным распределением сейсмичности, уровнем геодинами­ческого потенциала блоков земной коры и разломно-блоковой тектоникой Восточного Кавказа

Возросший интерес к сейсмоактивному региону Восточного Кавказа включая самую сейсмоактивную в европейской части России область диктуется тем, что в сферу повышенных сейсмических воздействий попадают крупные энергетические объекты Сулакского каскада ГЭС, а также строящееся множество малых ГЭС, основные транспортные коммуникации, высоковольтные линии электропередач, нефте-газопроводы федерального и республиканского значений, аэро- и морской порты и крупные, разросшиеся города и поселки региона. Отсутствие исследований по проблеме оценки геодинамической и геотектонической ситуации с привлечением материала по истории геологического развития системы может привести к нежелательным экологическим последствиям. По своим разрушительным действиям, количеству жертв, материальному ущербу и деструктивному воздействию на среду обитания человека, землетрясения занимают одно из первых мест среди других видов природных катастроф. Эти грозные явления природы опасны, прежде всего, потому, что происходят там, где человек живет и работает. Исторически так сложилось, что людям было удобно и экономически выгодно селиться именно там, где время от времени возникают землетрясения. Восточный Кавказ в этом плане не является исключением. Современные геодинамически активные зоны региона в условиях позднеальпийского тектогенеза характеризуется иными геодинамическими условиями по сравнению с герцинской и киммерийской. Альпийский этап тектогенеза характеризуется значительным максимумом своей активизации, с которым связаны современные геодинамические процессы и повышенная современная сейсмическая активность региона. Цель исследования. Установление особенностей связи между пространственно-временным распределением сейсмичности, уровнем геодинами­ческого потенциала блоков земной коры и разломно-блоковой тектоникой региона. Методы исследования. Основными методами исследования являются палеосейсмогеологический, структурно-тектонический с учетом геодинамического потенциала блоков региона и анализ пространственно-временного распределения сейсмичности за инструментальный период наблюдений. Результаты исследования. Установлены особенности связи между пространственно-временным распределением сейсмичности, уровнем геодинами­ческого потенциала блоков земной коры и разломно-блоковой тектоникой региона заключающиеся в том, что области с повышенной современной сейсмической активностью хорошо коррелируются с геодинамическими зонами, имеющими критический геодинамический потенциал и историческую активность. Составлены соответствующие сейсмотектонические схемы. Выявлены три субширотные зоны повышенной тектонической активности в Предгорной и Горной частях региона, контролируемые известными субкавказскими разломами. Составлена предварительная схема зон ВОЗ региона The increased interest in seismically active region of the Eastern Caucasus, including the most seismically active in the European part of Russia, the region is dictated by the fact that elevated seismic effects get a large energy facilities Sulak cascade, and also built many small hydroelectric power station, the main transport lines, high voltage power lines, oil pipelines Federal and Republican values, aerial and sea ports, and a large, sprawling cities and towns of the region. The lack of research on the problem of assessing the geodynamic and geotectonic situation with the involvement of material on the history of the geological development of the system can lead to undesirable environmental consequences. The purpose of the study. To establish the relationship between the spatial-temporal distribution of seismicity, the level of geodynamic potential of the crustal blocks and the fault-block tectonics of the region. Research methods. The main research methods are paleoseismogeological, structural-tectonic, taking into account the geodynamic potential of the blocks of the region, and the analysis of the spatial-temporal distribution of seismicity over the instrumental period of observations. The results of the study. The features of the relationship between the spatial-temporal distribution of seismicity, the level of geodynamic potential of crustal blocks and the fault-block tectonics of the region are established, which consist in the fact that areas with increased modern seismic activity are well correlated with geodynamic zones with critical geodynamic potential and historical activity. The corresponding seismotectonic schemes are drawn up. Three sublatitudinal zones of increased tectonic activity in the Foothill and Mountainous parts of the region, controlled by known Subcaucasian faults, have been identified. A preliminary map of the WHO zones in the region has been drawn up

Зонирование высокогорных территорий по геоэкологическим нагрузкам, обусловленным геодинамическими и климатическими воздействиями

Геотектонические, литологические и ландшафтно-морфологические особенности территорий, функционирующих туристско-рекреационных комплексов Центрального Кавказа, определяют платформенный характер развития Скифской плиты, южной окраиной вовлеченной совместно с причлененными микроплитами-террейнами (Предкавказская, Бечасынская, Восточно-Кавказская) в горообразовательный процесс Большого Кавказа. Иной характер геологического развития претерпели территории южного склона Большого Кавказа, вовлеченные в горообразовательный процесс как океанические плиты – террейны (Закавказская плита, Южная микроплита – сложенные толщей чередующегося флиша глинистых сланцев с прослоями песчаников, мергелей, известняков). Прижатая к жесткой Скифской плите с юга Закавказской плитой, подпираемой Аравийской платформой, Южная микроплита подверглась интенсивной деформации, глубинным тектоническим проявлениям субширотной ориентировки, являющимся каналами активного проявления эндогенных геодинамических процессов. Создание туристско-рекреационного комплекса на Южном склоне Центрального Кавказа предполагает прогноз темпов геоэкологической эволюции в условиях активной геодинамики и интенсивного проявления опасных геологических процессов. Цель исследований – зонирование интенсивностей уровней геоэкологических нагрузок геодинамических и климатических воздействий для дифференцированного целевого использования соответствующих площадей. В процессе исследований выявлены геодинамические и климатические факторы, характерные для территории и реализовано ранжирование интегральных воздействий на исследуемой территории. Методика заключалась в разбиении территории на элементы площади размерами 4×4 кв. км, учете значимых факторов воздействия на элемент площади и суммировании интенсивностей, определяемых экспертными оценками ранжирования, обусловленных каждым из природных воздействий. В процессе решения задач были определены геодинамические и климатические факторы, характерные для территории; дифференцированы геотектонические и геоморфологические условия их проявления; проведена экспертная оценка интенсивности воздействия каждого фактора по пятибалльной системе и установлен суммарный максимально возможный потенциал воздействия. Результаты исследований стали основой составления соответствующей карты – схемы зонирования исследуемой территории на зоны с интенсивностями, характеризующими различные уровни геоэкологической нагрузки. The geotectonic, lithological and landscape-morphological features of the territories where tourist and recreational complexes are functioning in the Central Caucasus determine the platform nature of the development of the Scythian plate. The southern margin of this plate is involved, together with the attached microplate-terranes (Ciscaucasia, Bechasynskaya, East Caucasian), in the mountain-forming process of the Greater Caucasus. The territories of the southern slope of the Greater Caucasus, involved in the mountain-forming process as oceanic plates - terranes (Transcaucasian plate, South microplate - folded by a layer of alternating flysch of clay shales with interlayers of sandstones, marls, limestones) have undergone a different character of geological development. The Southern microplate is pressed against the rigid Scythian plate from the south by the Transcaucasian plate, supported by the Arabian platform. It has undergone intense deformation, deep tectonic manifestations of sublatitudinal orientation, which are channels for the active manifestation of endogenous geodynamic processes. The creation of a tourist and recreational complex on the southern slope of the Central Caucasus presupposes a forecast of the geoecological evolution rate in conditions of active geodynamics and intensive manifestation of dangerous geological processes. The Aim of the study is the zoning of the intensity levels of the geoecological loads of geodynamic and climatic influences for the differentiated target use of the corresponding areas. In the course of research, geodynamic and climatic factors characteristic for the territory were identified and the ranking of integral impacts on the studied territory was implemented. The methodsconsisted in dividing the territory into area elements of 4 × 4 square km., taking into account the significant factors of influence on the element of the area and summing up the intensities determined by expert estimates of the ranking caused by each of the natural impacts. In the process of solving the problems, the geodynamic and climatic factors characteristic for the territory were determined; differentiated geotectonic and geomorphological conditions of their manifestation; an expert assessment of the intensity of the impact of each factor was carried out according to a five-point system and the total maximum possible impact potential was established. Results of the study became the basis for the compilation of the corresponding map - the zoning scheme of the study area into zones with intensities characterizing different levels of geoecological load

Habitability, Geodynamics, and the Case for Venus

Primary author: Suzanne Smrekar Jet Propulsion Laboratory/California Institute of Technology, Pasadena CA ; Co-authors: Jeff Andrews-Hanna (U.AZ), Doris Breuer (DLR Berlin), Paul Byrne (NCSU), Debra Buczkowski (JHU/APL), Bruce Campbell (Nat. Air Space Museum), A. Davaille (CNRS/U. Paris-Saclay), Darby Dyar (Mt. Holyoke/PSI), G. Di Achille (INAF/Astro Obs. Teramo), Caleb Fassett (Marshall), Martha Gilmore (Wesleyan), Robert Grimm (SWRI), Jorn Helbert (DLR Berlin), Scott Hensley (JPL), Robert Herrick (U. Alaska), Luciano Iess (U.Roma), Lauren Jozwiak (JHU/APL), Tiffany Katiaria (JPL), Marco Mastrogiuseppe (U. Roma), Erwan Mazarico (Goddard), Nils Mueller (DLR Berlin), Daniel Nunes (JPL), Joseph O'Rourke (ASU); Patrick McGovern (LPI), Maria Raguso (Caltech), Joann Stock (Caltech), Constantine Tsang (SwRI), Thomas Widemann (Obs. Paris), Jennifer Whitten (Tulane), Thomas Widemann (LESIA), Howard Zebker (Stanford)

Результаты исследования геодинамики осетинской части Центрального Кавказа на основе данных спутниковой геодезии и региональной сейсмичности

В результате проведённой работы была получена информация о геодинамическом поведении ос- новных тектонических блоков Земной коры (ЗК) в границах Горной Осетии. Принимая полученную информацию как первичную, в рамках данной работы продемонстрировано несколько методических приёмов по её матема- тической обработке. В частности, приёмы интерполяции дискретно представленных данных позволили вы- полнить построение поля скоростей GPS-пунктов в условной системе координат, проведено сопоставление его с полем распределения сейсмической энергии по территории. Выявленные локальные деформационные аномалии ЗК логично вписываются в тектоническую схему региона, установленную независимыми геологиче- скими и геофизическими методами. As a result of the work carried out, information was obtained on the geodynamic behavior of the main tectonic blocks of the Earth’s crust (GC) within the boundaries of Mountainous Ossetia. Taking the information received as primary, within the framework of this work, several methodological techniques for its mathematical processing are demonstrated. In particular, the methods of interpolation of discretely presented data made it possible to construct the velocity fi eld of GPS points in a conventional coordinate system, and compare it with the fi eld of seismic energy distribution over the territory. The identifi ed local deformation anomalies of the ZK logically fi t into the tectonic scheme of the region, established by independent geological and geophysical methods.

How Continuous Are the “Relict” Landscapes of Southeastern Tibet?

Pervasive low-relief, high-elevation surfaces separated by incised canyons are common across the Southeastern margin of the Tibetan Plateau and have been used to define the nature of crustal deformation that drove plateau growth. A common assumption is that these surfaces were once part of a continuous low-relief paleotopography that has undergone surface uplift and dissection. Recent research, however, has questioned this assumption and the derived geodynamic models, which suggests that these surfaces formed in situ through drainage network reorganization and the piracy of upstream drainage area. Here, we test the continuity of the low-relief surfaces across SE Tibet using a new inversion scheme that also illuminates the nature of conflicting hypotheses. Our analysis is based on combining the local information contained in maps of normalized channel steepness with the more distributed and integrated information contained in maps of normalized landscape response time. This allows us to model the formation of a hypothetical landscape prior to rock uplift and dissection. We find that large variations in channel steepness are required along the trunk channels within the inferred paleotopography. This is inconsistent with a low-relief surface prior to surface uplift and indicates that a surface interpolated between remnants cannot be used to robustly measure geodynamic processes in space and time. Furthermore, our inverse framework highlights many different solutions to this ill-posed problem and thus provides an explanation as to why the topography alone cannot be used to provide a unique solution to the debate.

SYN-EXHUMATION COUPLING OF OCEANIC AND CONTINENTAL UNITS ALONG THE WESTERN EDGE OF THE ALPINE CORSICA: A REVIEW

The Alpine Corsica represents a segment of the Alpine collisional belt. In its western edge, it is characterized by the close association of continental unitsdeformed under high-pressure metamorphic conditions (Lower Units) and oceanic units showing a metamorphism ranging from high-pressure (Schistes LustresComplex) to very low-grade conditions (Upper Units). This paper provides a complete review of the relationships between the continental and oceanicunits in selected five areas where the stratigraphic features, deformation history, metamorphic P-T path and tectonic setting are available for each unit. Thecollected data indicate that the oceanic units occur not only at the top of the continental ones, as generally proposed in the literature, but also intercalated withinthem. Such relationships were achieved at shallow structural level during the late stage of exhumation, when the continental units were tectonically coupledwith the oceanic units which were dragged as slices from the orogenic wedge. The coupling probably occurred immediately before the transition from syn- topost-orogenic geodynamic regime that affected the whole Alpine-Apennine collisional system in the early Oligocene. After the coupling, the stack of oceanicand continental units experienced a further exhumation-related deformation before their final exposure at the surface.

Underworld2: Python Geodynamics Modelling for Desktop, HPC and Cloud

Underworld2: Python Geodynamics Modelling for Desktop, HPC and Cloud

Plagioclase-facies thermobarometric evolution of the External Liguride pyroxenite-bearing mantle (Suvero, Italy)

Plagioclase peridotites are an important marker of the shallow geodynamic evolution of the lithospheric mantle at extensional settings. Based on lowpressure experiments, a recent study by Fumagalli et al. (2017) defined and calibrated a geobarometer for peridotitic bulk compositions, based on the Forsterite-Anorthite-Ca-Tschermak-Enstatite (FACE) pressure-sensitive equilibrium. The Suvero plagioclase-bearing peridotites, on which the FACE geobarometer was calibrated, are primarily associated to plagioclase pyroxenites. Assuming that the pyroxenites record the same Pressure-Temperature evolution than the plagioclase peridotites, they represent ideal candidates to test the applicability of the FACE geobarometer on pyroxenitic compositions. As documented in the plagioclase peridotites, the pyroxenites are characterized by the development of fine-grained neoblastic assemblages, indicative of partial recrystallization under plagioclase-facies conditions. Chemical zonations in these neoblastic mineral aggregates suggest equilibration stages at variable pressure and temperature and allowed to document two re-equilibration stages corresponding to the onset of plagioclase-facies recrystallization (830-850°C, 6.9-8.1±0.5 kbar) and a shallower colder re-equilibration (770-790°C, 5.8-5.9±0.5 kbar), respectively. The decompressional evolution reported for pyroxenitic bulk compositions is consistent with the exhumation history documented in the associated Suvero peridotite, although at slightly higher equilibrium pressures (~ 1 kbar). Remarkably, the much lower XCr in pyroxenites reflects in lower Cr incorporation in pyroxenes and, consequently, in significantly higher Ca-Tschermak activity in clinopyroxene that might introduce the systematic pressure overestimation by FACE geobarometer.

Geodynamics and its implications to environmental protection: A case study of Aule area, Akure, Ondo State, Southwestern Nigeria

This research work evaluates the effects of geodynamics processes on the emerging local geology of an area, especially against the background of global tectonic activities, the gradual but continuous earth movement and the depletion of the ozone layer, as it were and its implications on the local geology of a place, especially as it affects the rate of weathering, fracturing and other geologic processes which may pose environmental challenges. A ten year template was adopted for this study, while geophysical and metrological approach was engaged in the study with the use of electrical resistivity method and rainfall data. Two techniques involving lateral resistivity profiling of near E-W orientation with a profile length of 150 m with electrode separation at a = 10 and 20 meters while electrode movement was at 5 meters. Nine vertical electrical soundings (VES) with maximum spread AB/2 = 100 m was carried out at same locations and period (July to August) as was obtained ten years ago for the purpose of effective correlation from the point of data acquisition, data analysis, interpretation, results and findings. Rain data within study area was also collected covering a period of ten (10) years was analysed and presented as bar chart. The result obtained revealed the nature of changes that has taken place within the study area in terms of weathering, and the rate of weathering in the last ten years. Vertical variation/changes occurred at a weathering rate of 1.573, 1.489 and 1.711 cm along the three traverses with average rate of 1.591 cm per year. Horizontal variations also indicated some changes in position of strata, implying an average yearly weathering of about 1.591 cm when compared with the principle of plate tectonics and gradual but continuous earth movement which is at the rate of about 2 cm per year. Therefore, the local geodynamic constant was determined from product of lateral movement and vertical earth weathering trend/gradient which is 3.182 cm2. The rainfall analysis reflects the global weathered changes which is a major contributory factor to geological processes/weathering.

地殻流体の起源・分布と変動現象

地殻流体の起源・分布と変動現象

High-Temperature Evolution of Point Defect Equilibria in Hydrous Forsterite Synthesized at 1100 °C and up to 4 GPa

Water distribution in the deep Earth represents one of the most important topics in the field of geodynamics due to its large impact on the physical and chemical properties of the Earth’s mantle, such as electrical conductivity, seismic anisotropy, diffusion, and rheology. In this study, we synthesized hydrous forsterite at 1100 °C and up to 4 GPa with either a piston-cylinder or multianvil apparatus. As a starting material, we used synthetic forsterite, unbuffered by SiO2, obtained by thermo-mechanical activation of talc and magnesium carbonate hydroxide. Hydration was carried out using liquid H2O as hydrogen source. Samples were polycrystalline in an effort to distribute H2O throughout the sample both rapidly and homogeneously. Using the Paterson calibration, we observed total water content concentrations ranging between 100 and 500 ppm wt H2O. Multiple absorption bands are found in the frequency range between 3400 and 3650 cm−1, identifying at least seven peaks in all samples. Vibrational bands were centered at 3476, 3535, 3550, 3566, 3578, 3605, and 3612 cm−1, in good agreement with experimental studies conducted on both hydrous forsterite and single crystals of olivine. The stronger OH stretching peaks can be attributed to vibrational modes associated with the hydrogarnet defect 4 H Si x in which four protons occupy a vacant tetrahedral site. None of the OH bands observed are found at frequencies associated with hydrogen occupying vacant octahedral sites. High-temperature FTIR spectroscopy was used to evaluate the evolution of IR spectra as a function of temperature, up to 500 °C. The complete reversibility of peak absorption vs. temperature in the OH stretching region confirms that no water loss occurred during heating. We observe an overall a decrease in total absorption with increasing temperature, and a prominent decrease in the relative intensities of the higher frequency bands (>3600 cm−1) with respect to lower frequency bands. We have assigned a series of equilibrium expressions based on the variation of relative peak areas with temperature and find that enthalpies of these processes range between 0.047–0.068 eV (4.5–6.5 kJ/mol), very low in comparison to activation energies observed for electrical conduction in hydrous olivine. Major changes in the vibrational spectrum are expected to be related to configurational changes of the same fully protonated hydrogarnet defect species. However, the complexity of the FTIR spectra may also be related to partially protonated defects, such as the associate defect 3 H Si ′ + H i • generated by a dissociation reaction of the hydrogarnet species.

Geodynamic evolution of the San Vitero basin, a foreland-type basin developed in the hinterland of the Variscan Orogen (Zamora, NW Spain)

espanolLa region de Alcanices se situa en las zonas internas del Orogeno Varisco de la Peninsula Iberica y esta constituida por la sucesion Paleozoica autoctona de la Zona Centroiberica (CIZ), la sucesion aloctona del Dominio Esquistoso de la Zona de Galicia-Tras-Os-Montes (GTOMZ) y depositos sinorogenicos discordantes de tipo fysch (Formacion San Vitero). La realizacion de una cartografia geologica detallada y el analisis estructural a todas las escalas han permitido establecer las relaciones entre estas sucesiones y especialmente con los sedimentos sinorogenicos, que dada su localizacion en las partes internas del orogeno proporcionan una importante informacion acerca de la evolucion tectonica. La restauracion parcial de las estructuras variscas permite establecer la existencia de un sistema imbricado de cabalgamientos asociado con una cuenca de antepais. La reconstruccion de esta cuenca permite estimar su anchura en unos 100 km, con una profundidad aproximada de 1500 m en su depocentro. La cuenca sinorogenica comienza a desarrollarse durante el Carbonifero temprano en relacion con el emplazamiento de grandes unidades aloctonas adscritas a la fase de deformacion varisca D2. La evolucion de la cuenca termina durante la tercera fase de deormacion varisca (D3) con la formacion de cabalgamientos fuera de secuencia (que involucran al basamento) y pliegues asociados. EnglishThe Alcanices region, located in the internal zones of the Variscan Orogen of the Iberian Peninsula, is composed of the autochthonous Paleozoic succession of the Central Iberian Zone (CIZ), the allocthonous Schistose Domain of the Galicia-Tras-OsMontes Zone (GTOMZ) and the unconformable synorogenic fysch-type deposits. A new detailed geological map and the analysis of the structure at all scales contribute to establishing the geological relationships between the diferent paleo-geographic units, and in particular of the synorogenic sediments, that given their location in the hinterlands provide further insights into the tectonic evolution of the orogen. The partial restoration of the Variscan structures suggests a model of imbricate thrust-system and an associated foreland-type basin. A reconstruction of the basin allows estimating its width in c.100 km, with a depth of c. 1500 m in its depocenter. During the Early Carboniferous the basin developed ahead in relation with the emplacement of the large allochthonous units linked to the D2 deformation event. The evolution of the basin ends with the formation of out-of-sequence thrusts involving their basement and associated folds during the third Variscan deformation event (D3).

Mapping the progressive geologic history at the junction of the Alpine Mountain Belt and the Western Mediterranean Ocean

This contribution illustrates a new type of map, the “geological event map” (1:250,000 scale), which highlights the progressive steps of the geologic history recorded in the polycyclic orogenic belt of the European Alps, at their southwestern termination facing the western Mediterranean Sea. The formula of historical progression simplifies comprehension of significant phenomenal visions and reorients public curiosity towards geologic processes. This part of the Alpine belt records a geologic history starting with the Variscan convergence during Devonian, throughout the opening of the Tethys Ocean, Alpine convergence, followed by Apennine subduction driving the opening of the Ligurian-Provencal Ocean. Finally, from late Miocene to Present a progressive tectonic inversion characterizes the Ligurian-Provencal continental margin. This geologic history, over a time period of 400 million years, which includes three successive Wilson Cycles, is displayed in 8 plates composed of maps and illustrations. Each map explains the effects of successive tectonic events by adding geologic changes that modify the petrogenetic and structural configurations. The last plate shows the finite state of the geologic history at present-time. The map legend is based on ten major geodynamic events of which rock associations, and their genetic environment, are described in simple divulgation terms, to stimulate interest of neophytes. Illustration of the evolution of rocks and structures side of each map aims at conveying to non specialists in tectonics and petrology the impact of mechanisms associated with the Earth’s deep engine upon surface changes.