Geological Observations Research Articles

Long-Term Spatial–Temporal Evolution of Seismicity of the 2010 Ms 7.1 Yushu, Qinghai, China Earthquake

On 14 April 2010, a destructive earthquake (Ms 7.1) occurred along the Ganzi–Yushu fault (GYF), which is the boundary between the Songpan–Ganzi and Qiangtang Blocks of the eastern Tibetan Plateau. In this study, we present an effective workflow for microearthquake detection and location that assembles three main methods including a graphics processing unit-based match and locate technology (GPU M&L), a deep-neural-network-based noise-reduction technique (DeepDenoiser), and a U-net-based phase picking method (PhaseNet). Following this workflow, a high-resolution catalog has been constructed based on continuous seismic data from 2008 to 2018 recorded by 13 seismic stations deployed by Qinghai seismic network in Yushu, Qinghai. The GPU M&L is first applied to detect earthquakes which are usually hard to pick by routine methods due to their low signal-to-noise ratios. Then the DeepDenoiser is applied to remove noises from events we detected by GPU M&L, providing a better picking of seismic phases. The PhaseNet and hypoDD are conducted to pick seismic phases and relocate detected events, respectively. The spatial–temporal evolution of the foreshock sequence of the Yushu earthquake suggests that a triggered cascade model is responsible for the nucleation of the mainshock. The mainshock and aftershocks southeast of the mainshock mainly rupture on the primary northwest (NW)-trending GYF while the foreshocks and aftershocks on the NW segment rupture along the northeast (NE)-trending fault normal to the strike of the GYF. The average cumulative slip rate of the GYF estimated from six repeating earthquakes is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7.4~\pm ~1.7$ </tex-math></inline-formula> mm/year, which is consistent with the geodetic and geological observations.

Prospective pyroxenite–peridotite mixed mantle source for the northern Carlsberg Ridge

The geochemical heterogeneity of the mantle source beneath the mid-ocean ridge has been well studied, while the lithologic variability within the source has yet been rarely mentioned. We report new major, trace elements, and Sr-Nd-Pb isotopic data of fresh mid-ocean ridge basalts from the northern part of Carlsberg Ridge (i.e., CR Seg-1). The geological and geophysical observations, such as the lesser spreading rate, greater axial depth, and higher mantle Bouguer anomaly of the Seg-1, all indicate magma deficiency and lower melting degree, whereas the segment's lower average Na8 and higher Ca8/Al8 indicate a higher apparent melting degree. These contradictions cannot be reconciled by melting the lithologically homogeneous peridotite mantle. We proposed that fusible pyroxenite components in the Seg-1 source melt preferentially and generate lower Na8 magma. Moreover, it cools the ascending mantle and decreases the supply of melt derived from peridotite, leading to a magma shortage in the segment. The garnet signature revealed by the rare earth elements, higher Zn/Fe and Fe/Mn ratios, and source enrichment evidenced by Sr-Nd-Pb isotopes, support the presence of a trace quantity of garnet-pyroxenite in the mantle source. The mixing model of trace elements supports the origin of Seg-1 MORBs by mixing the depleted peridotite-derived melt and the enriched pyroxenite-derived melt. Based on the significant negative correlation between Fe/Mn and 206Pb/204Pb, the delaminated lower continental crust, which might not be completely homogenized in the convective mantle, may have been transformed into the pyroxene-rich rock. The retained material would then result in lithological heterogeneity, probably in the form of pyroxenite, and cause geochemical anomalies within the source mantle for mid-ocean ridge basalts.

ГЕОДИНАМИКА И ИСТОРИЯ ФОРМИРОВАНИЯ ОКРАИННЫХ МОРЕЙ ЗАПАДНОЙ ЧАСТИ ТИХОГО ОКЕАНА КАК ВИХРЕВЫХ СТРУКТУР

In the tectonic structure of the Earth, formed by rotational processes, a stable regmatic network (tectonic framework) and structures of the central type (ring, vortex, etc.) are of the main importance. Lithosphere plates are global vortex systems arisen as a result of the tectonic flow of masses in the state of a viscous fluid. Eddy structures are tectonic complexes in which the results of vertical and horizontal tectonic movements combination are captured and can be recorded by direct geological observations. In the Western Pacific Ocean, it is noteworthy a series of structures in the form of a system of marginal seas representing the Western Pacific continent-ocean transition zone. The tectonic evolution of the West Pacific region is the formation of lithosphere eddies series in the continent-ocean junction zone. It is associated with the Earth mantle and upper shells (tectonospheres) energy interaction, due to the unstable regime of the planet’s rotational dynamics. Of particular interest are the global shear zones and eddies of the lithosphere formed as a result of horizontal and vertical tectonic movements combination. It is shown that: 1) all tectonic dislocations contain both horizontal and vertical components of the movement velocity, the former dominating in the structure formation of the region; 2) their interaction outcome is vortex and other nonlinear deformations of the lithosphere, which constitute the main type of structural elements of the region; 3) they are often accompanied by the tectonosphere magmatic activation in the form of convective movements and / or plumes “floating”; 4) the Western Pacific marginal-sea depressions are the funnels of convective cells, which formed lithosphere eddies under the conditions of a shift in the interacting lithosphere plates velocities.

Total Shortening Estimates Across the Western Greater Caucasus Mountains from Balanced Cross Sections and Area Balancing

The Greater Caucasus orogen forms the northern edge of the Arabia-Eurasia collision zone. Although the orogen has long been assumed to exhibit dominantly thick-skinned style deformation via reactivation of high-angle extensional faults, recent work suggests the range may have accommodated several hundred kilometers or more of shortening since its ~30 Ma initiation, and this shortening may be accommodated via thin-skinned, imbricate fan-style deformation associated with underthrusting and/or subduction. However, robust shortening estimates based upon surface geologic observations are lacking. Here we present line-length and area balanced cross sections along two transects across the western Greater Caucasus that provide minimum shortening estimates of 130-200 km. These cross sections demonstrate that a thin-skinned structural style provides a viable explanation for the structure of the Greater Caucasus, and highlight major structures that may accommodate additional, but unconstrained, shortening.

Constraints on Moon's Orbit 3.2 Billion Years Ago From Tidal Bundle Data

AbstractThe angular momentum of the Earth‐Moon system was initially dominated by Earth's rotation with a short solar day of around 5 hr duration. Since then, Earth gradually transferred angular momentum through tidal friction to the orbit of the Moon, resulting in an increasing orbital radius and a deceleration of Earth's rotation. Geologic observations of tidal deposits can be used to verify and constrain models of lunar orbital evolution. In this work we reexamine the oldest tidal record suitable for analysis from the Moodies Group, South Africa, with an age of 3.22 billion years. Time frequency analysis of the series of thicknesses of the sandstone‐shale layers yields a periodicity of 15.0 layers, taking into account the possibility of missing laminae. Assuming a mixed tidal system, the duration of two neap‐spring‐neap cycles was 30.0 lunar days for dominant semidiurnal or 30.0 sidereal days for dominant diurnal tides. We derive the relationship between this observation and the past Earth‐Moon distance and re‐visit related published work. We find that the Earth‐Moon distance 3.2 billion years ago was about 70% of today's value. The Archean solar day was around 13 hr long. The ratio of solar to lunar tide‐raising torque controls the leakage of angular momentum from the Earth‐Moon system, but deviation from the assumed ratio of 0.211 results in only moderate changes. A duration of a postulated 21‐hr atmospheric resonance shorter than 200 million years would be consistent with our observation; it would significantly alter the Earth‐Moon distance.

Charles Darwin’s final transect aboard HMS Beagle: Cape Town to Shrewsbury May-October 1836

There is some evidence that Charles Darwin was somewhat tired and homesick on the last leg of the Beagle’s voyage, from Cape Town to Falmouth, May to October 1836. However, his geological observations remained at a high level, and numerous rock specimens were collected in Cape Province, at Bahia and Pernambuco in Brazil, and on the volcanic islands of St. Helena, Ascension, St. Jago (Cape Verde Islands), and Terceira in the Azores. Throughout the voyage, he frequently adopted a comparative approach. Thus, he noted similarities amongst the granite landscapes of South Africa, Australia (seen earlier in the voyage), and South America both from his fieldwork and his reading of Humboldt’s Personal Narrative. He also saw similarities (and differences) among the volcanic islands in topography, petrology, and mineralogy. By this stage, steeped in the doctrine of uniformitarianism from his reading of Lyell’s Principles of Geology, he understood that processes of both land formation and denudation had been at work throughout long periods of geological time. Frequently Principles and Narrative must have been open alongside his notes as HMS Beagle sailed homewards. Thus did Charles Darwin embrace the conceptual framework of gradualism, later of such importance.

Hydrothermal Friction Experiments on Simulated Basaltic Fault Gouge and Implications for Megathrust Earthquakes

AbstractNucleation of earthquake slip at the plate boundary fault (décollement) in subduction zones has been widely linked to the frictional properties of subducting sedimentary facies. However, recent seismological and geological observations suggest that the décollement develops in the subducting oceanic crust in the depth range of the seismogenic zone, at least in some cases. To understand the frictional properties of oceanic crustal material and their influence on seismogenesis, we performed hydrothermal friction experiments on simulated fault gouges of altered basalt, at temperatures of 100–550°C. The friction coefficient (μ) lies around 0.6 at most temperature conditions but a low μ down to 0.3 was observed at the highest temperature and lowest velocity condition. The velocity dependence of μ, (a−b), changes with increasing temperature from positive to negative at ∼100°C and from negative to positive at ∼450°C. Compared to gouges derived from sedimentary facies, the altered basalt gouge showed potentially unstable velocity weakening over a wider temperature range. Microstructural observations and microphysical interpretation infer that competition between dilatant granular flow and viscous compaction through pressure‐solution creep of albite contributed to the observed transition in (a−b). Alteration of oceanic crust during subduction produces fine grains of albite and chlorite through interactions with interstitial water, leading to reduction in its frictional strength and an increase in its seismogenic potential. Therefore, shear deformation possibly localizes within the altered oceanic crust leading to a larger potential for the nucleation of a megathrust earthquake in the depth range of the seismogenic zone.

Experience and prospects of mobile GIS use for practical training of geography students

Problem statement. In recent decades, approaches to conducting field research have been significantly modernized. The use of smartphones, tablets and other portable devices with mobile GIS for field data collection has increased significantly. The rapid change in geospatial research technologies makes it necessary to introduce them into the educational process, in particular, in practical training of geography students. Research methodology. Paper forms of field data collection, materials and reports from practical trainings of the previous years, stored at the Department of Physical Geography and Cartography of V. N. Karazin Kharkiv National University, served us as the source materials for the research. To implement the practical part of the research, ESRI software products such as Collector for ArcGIS, ArcGIS Online, ArcGIS Desktop were used. The purpose of the research is to substantiate the content and to create electronic forms of field data collection with mobile GIS for the physiographic part of the educational natural science training of first-year students of specialty 106 Geography of V. N. Karazin Kharkiv National University. Results. The use of mobile GIS for practical training of future geographers is widespread in Ukrainian and foreign universities. In particular, in recent years, teachers of the Department of Physical Geography and Cartography have been introducing mobile GIS into field data collection. We have developed 4 electronic forms of field data collection for the physiographic part of the educational natural science training of first-year students. They are soil profile description, forest phytocenosis description, geological and geomorphological observations, and hydrological station. Due to the wide functionality of Collector for ArcGIS, in particular, the ability to work offline, this mobile application and ArcGIS Online were used to develop forms. To optimize the work with individual text fields in electronic forms, we created domain values that allow students to select a certain option from the drop-down list. Practical significance and research perspectives. The implementation of mobile GIS into practical training of future geographers contributes to the formation of cartographic and geoinformation competencies and helps students master modern approaches to the organization of various types of field studies. Testing developed electronic forms during summer practical training of students or through independent research in the study area remains a relevant task. In the future, it is advisable to create electronic forms for all sections of the physiographic part of the first-year students' practical training and to adapt data collection forms for independent use.

GEOMORPHOLOGY AND CHARACTERISTICS OF NICKEL LATERITE IN BAINGKETE VILLAGE, MAKBON DISTRICT, SORONG REGENCY WEST PAPUA PROVINCE

Nickel deposits geologically came from weathering of abducted ultrabasic igneous rock. The rock is exposed during removal, followed by a geomorphological process that develops laterazation. Geologically the Makbon area is on the path of the Sorong horizontal fault field which has been active since the beginning of the Miocene. The dominant Sorong fault movement to the west exposed ocean floor rocks including blocks of ultrabasic rock. To determine the mineralization of nickel laterite in the Makbon area, this study combines mapping and surface geological observation methods with XRF analysis in the laboratory. The results of the study are known that the research area is composed of six land formations, namely the Makbon Fault Block Ridge, Baingkete Fault Block Ridge, Bancuh Baingkete Hills, Baingkete Bald Mountain Bancuh Hills, Makbon Fault Structure Denudation Plain, and Dore Bay Hills. Geomorphological control of the distribution of laterite nickel on steep slopes produces a thin, thickened laterite layer on the topography of the ramps. The characteristics of laterite nickel deposits in Baingkete Village are Type A deposits (Mg-Ni Silicate), on serpentinite bedrock, which consist of laterite profiles of limonite zone, saprolite zone, and bedrock zone

Emplacement of the Franklin large igneous province and initiation of the Sturtian Snowball Earth.

During the Cryogenian (720 to 635 Ma ago) Snowball Earth glaciations, ice extended to sea level near the equator. The cause of this catastrophic failure of Earth's thermostat has been unclear, but previous geochronology has suggested a rough coincidence of glacial onset with one of the largest magmatic episodes in the geological record, the Franklin large igneous province. U-Pb geochronology on zircon and baddeleyite from sills associated with the paleo-equatorial Franklin large igneous province in Arctic Canada record rapid emplacement between 719.86±0.21 and 718.61±0.30 Ma ago, 0.9 to 1.6 Ma before the onset of widespread glaciation. Geologic observations and (U-Th)/He dates on Franklin sills are compatible with major post-Franklin exhumation, possibly due to development of mafic volcanic highlands on windward equatorial Laurentia and increased global weatherability. After a transient magmatic CO2 flux, long-term carbon sequestration associated with increased weatherability could have nudged Earth over the threshold for runaway ice-albedo feedback.

Geology, Mineralogy, and Age of Li-Bearing Pegmatites: Case Study of Tochka Deposit (East Kazakhstan)

New geological, mineralogical, geochemical, and geochronological data have been obtained for Li-bearing pegmatites from the Tochka deposit located within the Karagoin–Saryozek zone in East Kazakhstan. Earlier, the exploration works in this zone were carried out to detect only Ta and Sn mineralization, but other ores (including Li) were not considered. The estimation of lithium resources in pegmatites from the area was methodologically imperfect. Previously, it was believed that the formation of rare-metal pegmatite veins was associated with Late Carboniferous Na-granites. The obtained geological observation confirms that the ore-bearing rare-metal pegmatites at the Tochka deposits cut the Late Carboniferous Na-granites and do not cut the Early Permian Kalba granites. The associations of the accessory minerals in host hornfels, Na-granites, and rare-metal pegmatites are different and the accessory minerals in pegmatites are similar to the accessory minerals in the Kalba granites. Geochemical data show that the behavior of rare elements (Ba, Th, HFSE, and REE) and the levels of accumulation of rare metals prove that pegmatites are similar to the product of the differentiation of the granitic magmas of the Kalba complex. The 40Ar/39Ar muscovite age of the Tochka pegmatites (~292 Ma) fits the age range of the Kalba granite complex. Based on the main principles of the generation of rare-metal pegmatites, the Tochka pegmatites formed during the fluid–magmatic fractionation of magma in large granitic reservoirs of the Kalba complex. The Karagoin–Saryozek zone—located between several large granite massifs of the Kalba complex where host rocks play a role as a roof—may be very promising for rare-metal pegmatite mineralization.

Strain partitioning in the Kahdan shear zone: Microstructural and kinematic evidence from the SE Sanandaj-Sirjan zone, Zagros orogeny

Microstructural, vorticity and strain analyses, combined with geological field observations are fundamental tools for retrieving information about kinematics of deformation in crustal-scale shear zones. The Kahdan shear zone is located in the SE part of the Sanandaj-Sirjan metamorphic zone within the Zagros orogen, SW Iran. The Zagros Orogen that formed due to the oblique convergence between the Afro-Arabian plate and the central Iranian plateau. Three-dimension strain analyses show that finite strain ellipsoids shape is oblate (K = 0.38–0.89). Vorticity analysis on mylonites yielded arithmetic mean maximum (Wm max) and mean minimum values (Wm min) of 0.83 and 0.72, respectively (63–47% simple shear). Higher values of Wm and Rxz estimated adjacent to the shear zone boundaries and gradually decrease toward the central part of the zone. Our yielded results show a non-unified spatial variations of vorticity and strain values in the deformed metasandstone (Late Jurassic to Early Cretaceous) of the Kahdan shear zone. Vorticity analyses and noncoaxial indicators indicate that this zone experienced general shear deformation. The horizontal shortening of ∼13–27% measured perpendicular to the shear zone boundaries. Based on yielded results, this area provides a good example of strain partitioning in a ductile shear zone.

An ensemble of Antarctic deglacial simulations constrained by geological observations

The Antarctic ice sheet has the potential to make a significant contribution to future sea-level rise. Understanding this potential and making projections of future ice sheet mass change requires use of numerical models. Confidence in model projections can be improved by hindcasting: testing the model against past ice sheet changes. Robust deglacial model reconstructions are also used to correct satellite gravimetric measurements of current change for glacial isostatic adjustment processes. Here we present a new model ensemble of post-Last Glacial Maximum Antarctic deglaciation reconstructions. The ensemble is generated using the Parallel Ice Sheet Model (PISM) in which we vary a range of parameters including key glaciological controls, basal sediment strength, mantle viscosity, and climate forcing. We test the ensemble results against a database of geological constraints, and develop a new scoring scheme that allows us to determine metrics of model performance against past ice sheet grounding line extent, ice sheet thickness, and thinning rates, as well as present-day ice sheet configuration. We discuss the parameter combinations that lead to the highest-scoring simulations and we also compare our ensemble performance with existing published deglacial models, using the same scoring scheme. Exploring the characteristics of the highest-scoring ensemble members highlights some key features of deglacial behaviour including a relatively narrow range of past excess ice volumes at the LGM, Holocene retreat behind present-day grounding lines with commensurate volume minima, and readvance behaviours. The comparison also allows us to identify areas where more geological data would have high constraining power for ice sheet models.

Mixture distribution model for three-dimensional geometric attributes of multiple discontinuity sets based on trace data of rock mass

The geometric attributes of discontinuities are critical to an accurate discrete fracture network (DFN) model of rock mass. It is difficult to estimate three-dimensional (3D) geometric parameters of multiple groups of discontinuities by observation data. The study proposes a mixture distribution model for the 3D geometric attributes of multiple discontinuity sets. The method of estimating the mixture distributions of 3D geometric attributes of all discontinuity sets from the two-dimensional (2D) trace data in a sampling window is established and modified, including discontinuity diameter distribution estimation, volume density estimation, orientation distribution estimation, and distribution mixing. Discontinuities are assumed to be thin disks uniformly distributed in space, and their roughness and aperture are ignored. Discontinuity diameter and orientation follow lognormal distribution and bivariate normal distribution, respectively. Orientation distributions defined on the definitional domain of the geological coordinate system are derived to represent the real frequency distributions of orientation measurements in 3D rock mass space. The mixture distribution model is verified by using Monte Carlo method to generate DFNs with different volume densities, and distribution parameters of orientation and diameter. The maximum error of volume density is <0.5 m−3. The estimated distributions of diameter and orientation are in good agreement with the true distributions, while there are limited symmetry estimation errors of the discontinuity sets with orientation samples covering both sides of the 0° or 180° polar axis. The model is applied to Sejilashan tunnel, and the result indicates that the surrounding rock of two excavation faces have a high probability to be rated as the V classification according to the engineering classification of rock mass in China, which is in good agreement with the reality according to the geological survey and field observation.

GPS and InSAR derived evidences of intra‐basin stress and strike‐slip tectonics in the vicinity of 2001 (M7.7) earthquake, Kachchh, western India

The current geodetic investigation is based on nearly a decade of continuous Global Positioning System (GPS) data towards the western part of the Indian Plate (2009–2019). This research focused on the Kachchh Rift Basin (KRB), the seismically most active intra‐plate region of the Indian Plate, which has seen three ≥ M 7.0 earthquakes in the last two centuries. The GPS stations on the northern and southern margins show SSW and NNE directed motion, indicating that the KRB is currently under the influence of regional compressive stress on both flanks and the same is reflected in the form of earthquake activity in the center portion. Furthermore, the existence of intra‐basin stress, in addition to regional stress, increases strain accumulation and results in the creation of a Principal Deformation Zone (PDZ) in the central part of the KRB. The average annual deformation in the middle of KRB remains 1.0 ± 0.5 mm/year, while sites near the South Wagad Fault (SWF) experience 1.2 mm/year of fault parallel motion. The dominant fault normal motion along the flanks with a maximum fault parallel motion in the middle intimates the existence of strike‐slip tectonics in the central Kachchh. The geometric relationship of strike‐slip faults in a compressive margin and strain accumulation in pre‐existing faults (PDZ) is responsible for current strike‐slip and thrust motion in the Kachchh, including the 2001 Bhuj earthquake (M 7.7). Our geodetic model is well‐corroborated with the geological observations of the wrench fault model of strike‐slip faults. PS‐InSAR results in the northern part of the region between Khadir and Bela Islands show ≤6.0 mm of annual LOS displacement. GPS results indicate ≈ 1.3 to 1.4 ± 0.5 mm/year of fault parallel motion along the transverse Ekal Amrapar Fault (EAF). The non‐significant variation in GRACE‐derived TWS values (from 2009 to 2018) rules out non‐tectonic deformation in the vicinity of EAF and thus points to tectonic activity as the cause of the derived deformation in the region.

India-Antarctica collisional ridge structure below Nellore Schist and Eastern Ghats Belts as revealed by seismic studies

In Columbia, Rodinia and Gondwana supercontinental assembly periods, eastern margin of India lay quite close to the east Antarctica. During these periods, this region underwent prolonged sedimentation, magmatism, oceanic subduction, multiple accretion and continent-continent collision which have left their imprints in the geological and geophysical observations. In the present study, we have analyzed crustal seismic velocity structure along the DSS profiles located in the eastern part of the Indian shield that cuts across the Proterozoic Cuddapah Basin, Godavari and Mahanadi Gondwana grabens. The study revealed presence of a prominent high velocity (6.2-6.5 km/s) hidden ridge structure, which is 30 to 50 km wide and located at a shallow subsurface depth beneath the Nellore Schist Belt and Eastern Ghats Belt. It underlies below Kaligiri-Duttaluru along the Kavali-Parnapalle profile, Darsi-Addanki along the Alampur-Koniki-Ganapeswaram profile and Sattupalli-Ashwaraopet in Kallur-Polavaram profile. This ridge structure is conspicuously characterized by high gravity anomaly gradients from -90 to -15 mGal. Gravity patterns over these regions further indicate that this ridge which appears to continue from the north of Chennai to Bhavanipatna region in Bastar Craton, may have been formed due to the collision of East Antarctic terrain with eastern Indian Shield after the cessation of supra-subduction at the end of Mesoproterozoic. Further, this ridge structure is flanked by Proterozoic sediments on either side; in Cuddapah Basin on its western side and East Coast Sedimentary Basin on its eastern side, which together with the possible occurrence of Proterozoic sediments in other basins, would indicate that the extent of Proterozoic sedimentation was much larger than hitherto known. We suggest that this region was rifting during Paleo-Mesoproterozoic period and possibly a shallow marine basin existed, when it was an integral part of the Columbia supercontinent assembly. It underwent another rifting phase and denudation during the Gondwana period as indicated by thin patches of Gondwana sediments which are lined up all along the east coast. Quite likely, the rifting between India and Antarctica during the Gondwana super assembly period initiated in the Permo-Triassic Gondwana period itself, with final separation taking place much later during early Cretaceous period.

Tibetan Plateau insights into &amp;gt;1100 °C crustal melting in the Quaternary

AbstractPartial melting during high-temperature to ultrahigh-temperature (UHT) metamorphism facilitates crustal differentiation, element transfer, and the evolution of topography in orogens, however the mechanisms that drive heating of Earth’s crust remain controversial. We provide new evidence from ca. 2.3 Ma dacites in the Tibetan Plateau, representing the youngest known UHT metamorphic event. Our results show that these dacites were mainly generated by fluid-absent melting of metasedimentary rocks and minor mafic rocks at peak temperatures of 1100–1150 °C and pressures of 0.8–0.9 GPa. The dacites represent mixtures of UHT melts and granulite residues and are geochemically similar to A-type granites with extremely high heat-production values (5.33–5.99 μW m–3). Compared with the geological and geophysical observations, numerical modeling indicates that the key factor determining the thermal evolution of Tibet is the thickness of the radioactive layer. Orogens dominated by rocks of felsic composition, like Tibet, could easily reach UHT conditions within a short period of time (20–40 m.y.) after crustal thickening by radioactive heating, without the need for an additional tectonic mechanism.

Geochemistry and origin of listwaenites within the Northern Branch of Neo-Tethyan ophiolites, Turkey

The study presents geological field observations, petrographic characteristics and bulk rock geochemical data of listwaenitic occurrences related to Jurassic–Cretaceous IAESZ ophiolites of the northern part of Turkey. Listwaenites of the Jurassic–Cretaceous Eldivan ophiolite and the Cretaceous Dağküplü ophiolite occur as mineralised or non-mineralised blocks and/or veins associated with serpentinised peridotites and ophiolitic mélanges along major thrust zones within the Izmir–Ankara–Erzincan Suture Zone (IAESZ) of the Northern Branch of the Neo-Tethys, Turkey. The silica–carbonate listwaenites (Type I) consist mainly of dolomite and minor calcite with quartz and minor phyllosilicates (chlorite, mica), serpentine and hematite. They are formed by circulation of meteoric hydrothermal fluids, along major décollement faults and thrust faults during the emplacement of serpentinised peridotites. The Kaymaz listwaenites (Type II) are composed mainly of fine-grained microcrystalline quartz with negligible dolomite, calcite, magnesite, serpentine and Fe-hydroxides. They display hard resistant masses, and are adjacent to the Eocene granitic bodies. Listwaenites are gentically related to the serpentinised peridotites, while the mineralisation appears to be related to the granite-related hydrothermal fluids.

Active seismic exploration along a human lunar mission traverse analogue in the San Francisco volcanic field

Lunar surface activities during Apollo and terrestrial analogue lunar mission simulations have commonly focused on traverses that prioritize surface observations and sample collection activities. Along the way, geophysical measurements are often made. However, they are not necessarily made in a way that optimizes information about the physical subsurface properties, which is something that geophysics can provide. In 2010, NASA simulated a high-quality multiweek human lunar rover traverse analogue mission in the San Francisco volcanic field in Arizona. The traverse route and associated science station locations were selected based on addressing surface observation and sampling tasks. Geophysical studies were not included in the simulation. We returned to the same field area and obtained data on 19 active seismic refraction geophone lines from the science station locations accessed during the simulation. We analyzed the data to calculate 1D seismic velocity profiles for each of the lines. Results revealed up to seven distinct seismically defined material types, including a nearly ubiquitous veneer of regolith of variable thickness at the surface. Results also provided depth and thickness of the seven material types in the first 60 m of the subsurface at each of the science station locations. These cannot be obtained by geologic observations of the outcrops. Systematic interpretation of the area's overall subsurface stratigraphy was not feasible due to the geophysically nonsystematic nature of the original traverse's prioritization of the science station locations. The added geophysical understanding of a region could drive additional geologic investigations to locate samples of otherwise unknown material through the location of surface exposures or coring. This emphasizes the importance of synchronizing geologic and geophysical research requirements during lunar traverse planning and execution to optimize addressing scientific and utilization questions.

Lithostructural Mapping Using Landsat OLI images and Field Investigations in the Oumjrane–Boukerzia Mining District, Eastern Anti-Atlas, Morocco

The application of remote sensing is considered to be highly efficient in the field of geology, particularly for mapping and discrimination between lithological units, as well as the identification of different surface minerals which enable the acquisition of all the optical and radar data needed to obtain more reliable and particular information, especially in inaccessible areas. Landsat 8 (Operational Land Imager) image bands, which include color compositions 7, 4, and 1, band ratios 7/5, 4/2, 3/1, and 6/3, 6/1, 5/2, Principal Component Analyses PC1, PC4, and PC3, and directional filtering at 0° (NS), 45° (NE–SW), and 90° (EW), were used to analyze the spectral characteristics of the lithological units of the study area and delineate the alteration zones which may contain significant concentrations of base metals. Combined with geological field observations, these data were integrated and analyzed in a geographic information system to establish a multi-criteria characterization of mineralized zones. Hence, the use of remote sensing contributed to the improvement and updating of available geological maps of the Oumjrane–Boukerzia area. Lineament extraction allowed for performed analyses of the structural elements that play a crucial role in the mineral distribution in the study area. Several of the targeted areas were examined in the field by selective sampling. Consequently, the results helped identify new mineralized zones with important mining potential which could be evaluated in the future through detailed geophysical and geochemical work.