Basalt Thickness Research Articles

New insights into the geological evolution history of Mare Fecunditatis

The Luna 16 probe returned 101 g of lunar regolith from the northeast of the Mare Fecunditatis in 1970. Studies on these samples were primarily conducted in the 1970s and 1980s, and limited scientific achievements were obtained due to available technology at that time. China received 1.5 g Luna 16 samples in 2023 and it is expected to conduct in-depth research in the near future. We conducted a thorough investigation on several fundamental issues in this region to provide a refined geological background in the paper. Firstly, a detailed division of the basaltic units within the Mare Fecunditatis was conducted based on the TiO2 content, and impact craters in each geological unit were mapped with the high-resolution Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) images. With the method of lunar surface dating from the crater size-frequency distribution, we found that the model ages of these basalt units range from 3.71 Ga to 3.31 Ga. Next, the thickness of the basalt within the Mare Fecunditatis is estimated with different types of craters, and local basalt thickness ranges from 3 m to 304 m from seven rim-completely-exposed craters in the mare. The rim-completely-exposed craters on the mare-highland boundary, the rim-partially-exposed craters in the mare, and rim-completely-buried craters in the maria also provide information on the thickness of local basalt. Finally, numerical simulations of the formation process of the largest young impact crater in this region, Langrenus crater, was conducted. The simulations show that the Langrenus crater could be formed by a 11.2-km-diameter asteroid hitting the lunar surface with a speed of ∼10 km/s. The average thickness of the ejecta from the Langrenus crater is ∼4.9 m near Luna 16 landing site, indicating that a significant fraction of Luna 16 samples might be the ejecta from the Langrenus crater. The simulations also reveal that the maximum shock pressure on the materials ejected to Luna 16 landing site can reach 92 GPa, and their maximum source depth is approximately 7.1 km. These interpretations can provide valuable information for further study of the Luna 16 samples and inferring the geological history of the Mare Fecunditatis.

The Ancient Lithospheric Parameters of Impact Basins on the Far Side of the Moon Based on the Mantle and Mare Basalt Load Model

AbstractResearch on the lithospheric elastic thickness (Te) of lunar mascon basins can provide a deeper understanding of heterogeneous thermal activity. In this study, we focused on four basins (Moscoviense, Freundlich‐Sharonov, Hertzsprung, and Apollo) located on the far side of the Moon. These basins exhibit a significant variation in admittance and correlation spectra, making it challenging to develop precise fitted models. Based on the global lunar crustal thickness model and mare basalt thickness, we developed a mantle and mare basalt load model to estimate the Te. This small Te (10.1 km) suggests a double impact process or extreme thermal activity caused by volcanism during the formation of the Moscoviense. For the typical highland basins, that is, Freundlich‐Sharonov and Hertzsprung, the Te (∼20 km) corresponds to a minimum heat flux of 34 mW m−2. Considering the additional energy introduced by the impact, this heat flux can be considered as the upper limit for the heat flux of the highland itself during the formation of a mascon basin. For the Apollo basin within the South Pole‐Aitken (SPA) terrane, the Te is 30.7 km. The crust beneath the SPA region is thinned, allowing a greater contribution of stiffer mantle material to the lithosphere, perhaps explaining the higher effective Te. Furthermore, the disparity between the highland and SPA terranes can give rise to their distinct basin formation processes. Impact basins formed within the SPA terrane may have experienced a faster cooling process compared to those formed on the highland terrane following the impact event, leading to a higher Te.

New insights into the regional and local geological context of the Luna 16 landing site

The results of our regional and local studies of the Fecunditatis basin and Mare Fecunditatis, and areas adjacent to the Luna 16 landing site suggest the following. If the Fecunditatis basin is an impact structure, which is consistent with the crustal thickness models and gravity data, it predates the Nectaris basins (∼4.17 Ga). The unusually flat topographic profile of the Fecunditatis basin can be explained by viscous relaxation of the original topography of the basin and the subsequent filling of the basin by ejecta from the Nectaris and Crisium basins. The results of our crater size-frequency measurements within the mare domain of the Fecunditatis basin yield an absolute model age (AMA) of ∼3.81 Ga. Thus, the population of all recognizable craters within Mare Fecunditatis denotes the existence of an extensive episode/episodes of resurfacing that has erased the ancient crater population accumulated after the Fecunditatis impact event but before the mare emplacement. Our determinations of AMAs of the surface of Mare Fecunditatis (∼3.45 Ga) are consistent with most radiometric age determinations from the Luna 16 samples that are clustered at ages of ∼3.5–3.4 Ga. The current Mare Fecunditatis surface is likely to represent the latter episodes of volcanism, the main phase of which was active during this time interval. Although older radiometric ages have not yet been reported, the presence of older basalts in the Luna 16 sample should not be ruled out, taking into account the likely multiple sources of its materials and the complex nature of the emplacement of lavas in Mare Fecunditatis. The thickness of mare basalts in Mare Fecunditatis are highly variable. At the regional scale, thicknesses are most likely at least ∼1.5 km, in order to be able to hide a significant number of ancient larger craters. In the areas of partly or completely flooded craters, the mare thickness increases up to ∼2–2.7 km. In the vicinity of the Luna 16 landing site, however, the thickness of the most than a few hundred meters.

Burial history and thermal maturity of the atypical petroleum system of the Paraná Basin (Irati and Ponta Grossa formations), Brazil

The main characteristic of the intracratonic sedimentary Paraná Basin, southern Brazil, is the atypical hydrocarbon generation through the heat from basic intrusive rocks. Potential hydrocarbon source shales from the Irati and Ponta Grossa formations were identified and characterised via stratigraphic data, total organic carbon (TOC - LECO) analyses and pyrolysis (Rock-Eval 6) of well samples. Geochemical analyses showed that in wells under study, the Irati Formation has organically rich shales, and the Ponta Grossa Formation has low potential for hydrocarbon generation. 1D generation modelling using 16-well 1D and PetroMod® software was developed aiming to establish the thermal and subsidence history in the area and to determine hydrocarbon generation and expulsion. Geochemical data from the wells was used, and information on sedimentology and stratigraphy was obtained from the literature. Thermal history was calibrated using values of vitrinite reflectance, Tmax and downhole temperature, and the geothermal gradient used in the models was 28–42 °C/km. The relative erosive thicknesses of the stratigraphic units were estimated. The results showed that in regions without igneous intrusions, the Irati shales are immature for hydrocarbon generation and do not have an organic matter transformation rate, which is consistent with the results of Rock-Eval pyrolysis and %Ro. However, in wells containing igneous intrusive rocks in the Irati shales, the transformation rates varied according to the thickness and number of intrusions, reaching 100% organic matter transformation; due to its quality (Type I kerogen), this rate is favourable for oil and gas generation. The Ponta Grossa source rock showed thermal maturation by subsidence corresponding to the oil generation window, with higher maturation anomalies near igneous intrusions. The organic matter transformation rate reached 70% in the absence of igneous intrusions and nearly 100% in the presence of igneous intrusions. Despite having good maturity, the characteristics regarding the quantity and quality of organic matter suggest a moderate potential for gas generation in the Ponta Grossa Formation in the study area. The depositional history model showed that the highest subsidence rate occurred during the Early Cretaceous and was related to the burial associated with the basalt thickness of the Serra Geral Formation.

Thicknesses of Mare Basalts in the Chang’E‐5 Landing Region: Implications for the Late‐Stage Volcanism on the Moon

AbstractChina's Chang’E‐5 mission has collected lunar samples from a young mare plain with elevated thorium contents in the northeastern Oceanus Procellarum of the Moon. In this study, we first established a local stratigraphic column of the landing region based on the radial variation of the titanium content in the ejecta of large penetrating craters, and we found that the landing region was flooded by at least four layers of mare basalts. By using the latest imagery, spectral, topographic, and gravity data, we then estimated the basalt thickness of each layer based on the excavation depth of penetrating craters, the morphology of partially buried craters, and the effective density spectrum technique, which can help to better understand the late‐stage volcanism on the Moon. Our results show that the four layers of basaltic lava flows in the landing region have accumulated thicknesses of 9–175, 11–167, 19–478, and 0–800 m. Combined with surface areas and ages of the basaltic units, we then calculated the eruption rate of mare basalts in the landing region, which shows an uptick at about 2 Ga. This result indicates a rejuvenated volcanic activity on the Moon, most likely due to the presence of heat‐producing elements in the KREEP layer. Alternatively, the long‐standing volcanism in this region could be also sustained by extra heating induced by the tidal force and/or a thin crust layer that favors the magma ascent.

Analysis on distribution and main controlling factors of OM carbonization in marine shale in the Sichuan Basin of China and its periphery

The distribution and main controlling factors of the organic matter carbonization points/zones of over-mature marine shale are important issues for shale gas exploration. This paper focuses on the Lower Cambrian and Lower Silurian shales in the Sichuan Basin and its periphery. Based on the detailed anatomy of key carbonization zones, predictions of shale organic matter carbonization zones and regional mapping of thermal maturity are carried out to explore and reveal the distribution and main controlling factors of the carbonization zones of organic matter in the two sets of shales. Four preliminary conclusions were obtained: (1) There are four organic matter carbonization zones in the Lower Silurian shale distribution area, namely eastern Sichuan-western Hubei, northwestern Hubei, west of southern Sichuan, and Renhuai-southwestern Chongqing, covering an area of nearly 40 × 103 km2. The main part of the western carbonization zone in the southern Sichuan is located in the Emei basalt distribution area. (2) The organic matter carbonization zone accounts for more than 80% of the Lower Cambrian shale distribution area, The non-carbonization zone is only distributed in Weiyuan-Ziyang, Moxi-Gaoshiti, Changyang, and Weng'an-Zhenyuan with an area of about 62.6 × 103 km2. (3) The Lower Silurian and Lower Cambrian shales in the west of southern Sichuan experienced an increase in thermal maturity RO values of 0.2%–0.4% and 0.2%–1.0%, respectively, as a result of the Emei large igneous province, an extreme heat event in the Late Permian. The Lower Cambrian and Lower Silurian shales have the highest degree of carbonization of organic matter in Mabian-Ebian, which is also in the high-value area of the Emei basalt thickness. (4) The main controlling factors of organic matter carbonization of the Lower Cambrian and Lower Silurian shales have similarities and differences. The main controlling factor of the former is the long-term deep burial background, and the extreme thermal event in the Late Permian only exacerbated the degree of carbonization in some areas more seriously. The latter's main controlling factors are relatively complex and are controlled by deep burial background in the three regions of Renhuai-southwestern Chongqing, eastern Sichuan-western Hubei, and northwestern Hubei. It was governed by a deep burial background and a high geotemperature in the Late Permian.

Magmatism at oceanic core complexes on the ultraslow Southwest Indian Ridge: Insights from near-seafloor magnetics

Abstract Oceanic core complexes (OCCs) and detachment faults play a key role in crustal accretion at slow and ultraslow spreading centers. We investigated the effect of different magma supply at three OCCs of the Southwest Indian Ridge using high-resolution deep-sea bathymetric and magnetic data. The average equivalent thickness of extrusive basalt deduced from the magnetic anomalies, a proxy for magma supply, decreases from west to east, from the Yuhuang (49.25°E) to Longqi (49.65°E) to Junhui (51.75°E) OCCs. Conversely, serpentinite outcrops become more abundant, the domal OCC morphology flattens as the footwall rotation (measured by the magnetization vector inclination) increases, and hydrothermal evidence becomes sparse. Combined with results from the amagmatic easternmost Southwest Indian Ridge, our study shows that the magma supply controls the character and evolution of the OCCs and detachment faults on the Southwest Indian Ridge.

ГЕОДИНАМІКА

Purpose. The main purpose of this paper is to investigate the peculiarities of the spatial distribution of thickness and paleorelief of continental flood basalts of Luchychi stratum of Ratne suite of the Ediacaran of the Ratne–Kamin-Kashyrskyi Area in Western Volyn using maps of the thickness and relief of the paleosurface. The study also focuses on correlation between the specified parameters of the stratum and the spatial change of concentrations of native mineralization and its localization relative to the roof (sole) of the stratum. Method. The research applies a number of methods, including field geological surveys; petrography of basalts, structural features (degree of crystallization of mesostasis, structural position of minerals and, in particular, copper, ratio of globular formations and minerals that surround them, relationship between globules), macro- and microtextural features of rocks; geochemical research: determination of the content of the main chemical components of the rocks by the method of gross chemical analysis and copper content; geological and morphostructural studies: construction of a map of paleorelief and thickness of continental flood basalt of the Luchichiv stratum (according to the section of wells). Results. The constructed maps of the thickness and paleo surface of the Luchychi stratum show the spatial variability of the basalt thickness and the reflection of the effective tectonic situation on its paleo surface, which can be "read" by relief elements. It is established that high copper content in basalts is spatially confined to areas of maximum thickness and shifted vertically to the near-roof and, partially, plantar parts of the basalt thickness, and the degree of their crystallization increases in the direction of the inner parts of bodies. This situation with the spatial arrangement of native mineralization indicates the existence within these areas of local isolated thermostated systems. They evolved in their internal parts in conditions close to the intrusive ones (relatively slow decrease in melt temperature, crystallization of rock differences almost devoid of volcanic glass – dolerite-basalts with the transition to dolerites in the central part). Such physicochemical conditions caused long-term migration of gaseous, gaseous-liquid and liquid fluids, providing concomitant extraction, concentration, transfer and deposition not only of native copper, but also a number of petrogenic oxides (alkalis, iron, partially calcium, silicium). The latter subsequently formed a number of low-temperature minerals, the most common of which are zeolites, calcite, and iron compounds. In areas with small and minimum thickness of basalts, the above facts are observed in a reduced form, and in some places are virtually absent. The research has established the complete absence of signs of hydrothermal copper ore mineralization. The latter indicates the lack of evidence about the formation of native mineralization of the hydrothermal type. We provide the geological and petrogeochemical facts that give grounds to consider the scenario of the process of formation of native copper mineralization in relation to the fluid-liquidation hypothesis, earlier developed and proposed by the authors. Scientific novelty. For the first time, the study made it possible to construct maps of the thickness and relief of the paleo surface of the basalts of the Luchychi strata of the Ratne–Kamin-Kashyrskyi area of Western Volyn. Based on the actual material it is shown that the vertical distribution and localization of native mineralization within basaltic bodies are naturally related to their thickness. The value of native copper is directly related to body thickness, reaching a maximum in areas with maximum thickness and background values at the minimum thickness. Practical significance. For the first time, geological, petrographic, geological and morphostructural data were compared with the copper content in basalts of the Luchichi stratum. The proposed approach can be used by geological production organizations in conducting exploration work to prepare promising areas for exploration of the North-Hirnyky and Rafalivka ore fields (ore nodes) within the Ratne Horst anticline. The obtained original material can be distributed as a new method of native mineralization search in other areas of the continental flood basalts distribution.

Thickness of Lunar Mare Basalts: New Results Based on Modeling the Degradation of Partially Buried Craters

AbstractPartially buried craters on the Moon are those craters whose distal ejecta are covered by lava flows and where the crater rim crest still protrudes above the mare plain. Based on the difference in rim heights between a partially buried crater and an unburied crater, previous studies estimated the thicknesses of the lunar mare basalts. However, these studies did not consider the erosion of the crater rim height, which can result in an overestimate in the derived thickness. By using recent high‐resolution topographic data, we report a basalt thickness estimation method based on numerically modeling the topographic degradation of partially buried craters. We identified 661 buried craters over the lunar surface, and their spatial distribution suggests a preferential occurrence along the mare‐highland boundaries. An elevation model of fresh lunar craters was derived, and the topographic diffusion equation was used to model crater degradation. By modeling the formation, degradation, and flooding of partially buried craters, basalt thicknesses were estimated for 41 mare craters whose rims are completely exposed. The resulting mare basalt thicknesses vary from 33 to 455 m, with a median value of 105 m that is 95 m smaller than that derived when not considering crater degradation. The estimated eruption rate of lunar mare basalts is found to have peaked at 3.4 Ga and then decreased with time, indicating a progressive cooling of the lunar interior. As a by‐product from the crater degradation model, our results suggest that the topographic diffusivity of lunar craters increases with diameter.

The Thickness and Scale of Late-stage Basalts in Oceanus Procellarumtwo

Oceanus Procellarum, the largest lunar mare, is distributed with a large area of the late-stage (Eratosthenian) basalts. Research on the thickness, volume, and eruption flux of the late-stage basalts is essential for understanding the late thermal evolution of Oceanus Procellarum, even the Moon. The Eratosthenian basalts are rich in olivine and ilmenite, while the underlying Imbrian basalts are rich in pyroxene. Their significant spectral differences are easy to be distinguished using the hyperspectral data. We determine whether a crater has penetrated the overlying basalt layer by the data of Moon Mineralogy Mapper (M3), and estimate the thickness of Eratosthenian basalts in the Oceanus Procellarum region by using a crater excavation technique. A high-resolution thickness distribution map of the last-stage basalts within the Oceanus Procellarum has been acquired. The results show that the averaged thickness of Eratosthenian basalts in the Oceanus Procellarum region varies from (24±2) m to (88±2) m. Among them, the thickness of Eratosthenian basalts in the western Aristarchus is the greatest (>60m), whereas the southernmost area of the study has a minimum thickness of about 28–31m. The basalt thickness at the Chang’e-5 potential landing site Mons Rümker is about 31–38m. The thickness of Eratosthenian basalts in the east of Marius is about 35–45m, which is much smaller than the value of 100∼300m estimated by Weider et al. The total volume of Eratosthenian basalts is estimated to be ∼1.39×104km3, which is only about 1.6% of total basalts in Oceanus Procellarum. This indicates that the magmatism in the Eratosthenian period has been greatly weakened compared to the Imbrian period.

Extent, thickness and erosion of the Jurassic continental flood basalts of Dronning Maud Land, East Antarctica: A low-T thermochronological approach

The Dronning Maud Land Mountains form a c. 1500 km long, coast-parallel escarpment that possibly formed by flexural uplift during Jurassic rifting between East and West Gondwana. Contemporaneous to the rifting, considerable amounts of continental flood basalts, associated with the Karoo mantle plume, were emplaced at c. 183 Ma. The basalts are still widespread in South Africa, making up elevated topography, but are only preserved as smaller remnants in western Dronning Maud Land. By investigating the paleo-thermal effect of the basalts, we aim to constrain the extent and original thickness, as well as the subsequent erosion history of the Jurassic continental flood basalts. Thus, we have applied low-temperature thermochronological methods to 40 samples from western Dronning Maud Land. This has resulted in 34 new apatite fission track ages, ranging from c. 310 to 90 Ma, 31 apatite (U–Th)/He ages spanning from c. 400 to 50 Ma and, and 9 zircon (U–Th)/He ages between c. 650 and 200 Ma.Thermal modelling of 26 samples indicates variable thickness of the Jurassic basaltic cover. The greatest basaltic thicknesses are recorded in Heimefrontfjella and H.U. Sverdrupfjella, where up to c. 2 km are estimated. Thicknesses at Kirwanveggen, Hochlinfjellet, Midbresrabben and Ahlmannryggen range from c. 100 m to 600 m. Thickness variations are attributed to the proximity to the emplacement zone, possible pre-existing topography and syn-volcanic rift flank uplift.Since the continental flood basalt emplacement, two phases of enhanced cooling have been documented: 1) A Jurassic-Cretaceous cooling phase is attributed to reactivation of the Jutulstraumen–Penckgraben rift, the initial rifting and opening of the South Atlantic and enhanced chemical weathering and deep erosion due to a Jurassic temperate–subtropical climate. 2) Late Paleogene cooling is attributed to the transition from green house to ice-house conditions and ice-sheet initiation at the Eocene-Oligocene boundary. Post-Jurassic denudation of at least 2 km in some places is suggested.

Geophysical measurements for site effects characterisation in the urban area of Girona, Spain

ABSTRACTAmplitude level, duration, and spectral content of earthquake ground motions are strongly influenced by local soil conditions. Reliable estimation of site effects is, therefore, crucial in order to avoid damage to infrastructures and mitigate other losses. Traditional geophysical exploration techniques are restricted in urban environments due to the presence of anthropogenic noises causing low seismic signal‐to‐noise ratio and other logistical issues. These problems are even more critical when the maximum investigation depth extends to hundreds of metres.The city of Girona, located in northeastern Spain, has seismic hazard represented by a peak ground acceleration value of 0.08 g for a return period of 500 years. The city was built at the confluence of four rivers, generating a complex surface geology with bedrock outcrops and the presence of stiff soils, soft soils, and also a volcanic basalt layer. This paper presents the results of the geophysical work, which was carried out in order to characterise the soil layers present in the urban area of Girona. All information obtained in this research will be useful in computing the amplification of ground motion and to perform microzonation studies. We have obtained the shear‐wave velocity profile in the study area using a combination of seismic noise array and multichannel analysis of surface waves techniques. Using the horizontal‐to‐vertical spectral ratio method, we have obtained the soil fundamental frequency. The combination of shear‐wave velocity and values of soil fundamental frequency provides a complete map of the bedrock topography. The expected velocity inversion due to the presence of shallow basalt flow has been targeted. Electrical resistivity tomography is found to be suitable to define the volcanic basalt thickness. This thickness value is used to constrain the inversion of surface wave dispersion curves and reduce shear‐wave velocity uncertainty. The new methodology overcomes the limitations that are typical to urban conditions and other geological complexities.

Thickness of extrusive basalts dominating the magnetic structure along the ultraslow-spreading Mohns Ridge axis (71.8°–73.7°N)

The equivalent magnetization (EM) and mantle Bouguer anomaly (MBA) were calculated along the ultraslow-spreading Mohns Ridge axis in the Norwegian-Greenland Sea. The magnetic anomaly and the associated EM were compared with the bathymetry, MBA, seismically determined crustal structure and geochemical data at both the inter-segment scale (>60 km) and the intra-segment scale (20–60 km). At the inter-segment scale, the magnetic highs at the segment centers are independent of the MBA. Of the 13 segments, 9 with magnetic anomalies >700 nT coincide with axial volcanic ridges identified from multibeam bathymetry maps, which suggests that the magnetic highs at the segment centers may be more associated with the extrusive lavas rather than the amount of magma supply. With few exceptions, the magnetic anomaly lows associated with MBA highs at the segment ends increase from south to north. This trend might be explained by thickened extrusive basalts and/or more serpentinized peridotites at the segment ends in the north. At the intra-segment scale, the most prominent features are the decreases in the magnetic anomalies and associated EMs from the segment centers to the ends. The intra-segment magnetic anomalies have positive and negative correlations with the bathymetry and MBA, respectively. The magnetic signal modeled by the seismically determined layer 2A with an assumed constant magnetization is remarkably consistent with the observed magnetic anomaly, which strongly suggests that the thickness of the extrusive basalts dominates the magnetic structure in each segment along the Mohns Ridge. In general, the thickness of the extrusive basalts dominates the magnetic structure along the Mohns Ridge, whereas the contributions from serpentinized peridotites may be significant at the segment ends and may produce long-wavelength magnetic variations. The magnetic data can be used as an indicator of the thickness of the extrusive basalts within segments along the ultraslow-spreading Mohns Ridge.

Spatial and temporal variation of tectonic uplift in the southeastern Ethiopian Plateau from morphotectonic analysis

We use morphotectonic analysis to study the tectonic uplift history of the southeastern Ethiopian Plateau (SEEP). Based on studies conducted on the Northwestern Ethiopian Plateau, steady-state and pulsed tectonic uplift models were proposed to explain the growth of the plateau since ~30 Ma. We test these two models for the largely unknown SEEP. We present the first quantitative morphotectonic study of the SEEP. First, in order to infer the spatial distribution of the tectonic uplift rates, we extract geomorphic proxies including normalized steepness index ksn, hypsometric integral HI, and chi integral χ from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) digital elevation model (DEM). Second, we compare these rates with the thickness of flood basalt that we estimated from geological maps. Third, to constrain the timing of regional tectonic uplift, we develop a knickpoint celerity model. Fourth, we compare our results to those from the Northwestern Ethiopian Plateau to suggest a possible mechanism to explain regional tectonic uplift of the entire Ethiopian Plateau. We find an increase in tectonic uplift rates from the southeastern escarpments of the Afar Depression in the northeast to that of the Main Ethiopian Rift to the southwest. We identify three regional tectonic uplift events at ~11.7, ~6.5, and ~4.5 Ma recorded by the development of regionally distributed knickpoints. This is in good agreement with ages of tectonic uplift events reported from the Northwestern Ethiopian Plateau.

Geology, geochemistry and petrology of basalts from Paraná Continental Magmatic Province in the Araguari, Uberlândia, Uberaba and Sacramento regions, Minas Gerais state, Brazil

This study covers the region between the cities of Sacramento and Araguari/Uberlândia (Minas Gerais State, Brazil), where basalt flows from the Parana Continental Magmatic Province outcrop. The investigated rocks present tholeiitic signature, with high titanium content, and are classified as Pitanga magma-type. The preserved basalt thickness is between 10 and 200 meters and individual flows do not exceed 15 meters thick. Flows were identified as sheet lobes, smaller and thinner flows units — stacked laterally and vertically forming compound lavas —, or frontal, centimetric lobes. The basalt flows show decimetric to metric intercalations of clastic sedimentary rock, with depositional characteristics that can vary from aeolian to lacustrine, and are important markers on prevailing environmental conditions. The plagioclases are dominantly labradorite and pyroxene is augite, whereas olivine can be hyalosiderite or hortonolite/ferrohortonolite. The behavior of the major, minor and trace elements is compatible with the presence of at least two parental magmas, which were subjected to fractional crystallization mainly of plagioclase, clinopyroxene, ilmenite and magnetite. There is a chemistry distinction between basalts from Sacramento to those from Araguari/Uberlândia region, the former one showing more evolved than the last one. The high (La/Lu)N values are indicative of partial melting of a garnet peridotite, while the Rare Earth Elements (REE) values are indicative of fractional crystallization.

The Thickness and Volume of Young Basalts Within Mare Imbrium

AbstractBasaltic volcanism is one of the most important geologic processes of the Moon. Research on the thickness and volume of late‐stage basalts of Mare Imbrium helps better understand the source of lunar volcanism and eruption styles. Based on whether apparent flow fronts exist or not, the late‐stage basalts within Mare Imbrium were divided into two groups, namely, Upper Eratosthenian basalts (UEm) and Lower Eratosthenian basalts (LEm). Employing the topographic profile analysis method for UEm and the crater excavation technique for LEm, we studied the thickness and distribution of Eratosthenian basalts in Mare Imbrium. For the UEm units, their thicknesses were estimated to be ~16–34 (±2) m with several layers of individual lava (~8–13 m) inside. The estimated thickness of LEm units was ~14–45(±1) m, with a trend of reducing thickness from north to south. The measured thickness of late‐stage basalts around the Chang'E‐3 landing site (~37 ± 1 m) was quite close to the results acquired by the lunar penetrating radar carried on board the Yutu Rover (~35 m). The total volume of the late‐stage basalts in Mare Imbrium was calculated to be ~8,671 (±320) km3, which is 4 times lower than that of Schaber's estimation (~4 × 104 km3). Our results indicate that the actual volume is much lower than previous estimates of the final stage of the late basaltic eruption of Mare Imbrium. Together, the area flux and transport distance of the lava flows gradually decreased with time. These results suggest that late‐stage volcanic evolution of the Moon might be revised.

Displacement-length ratios and contractional strains of lunar wrinkle ridges in Mare Serenitatis and Mare Tranquillitatis

Wrinkle ridges are complex thrust faults commonly found in lunar mare basalts and caused by compressional stresses from both local basin and global Moon. In this paper, we select 59 single wrinkle ridges in Mare Serenitatis and 39 single wrinkle ridges in Mare Tranquillitatis according to WAC mosaic image. For each wrinkle ridge, several topographic profiles near its midpoint are generated to measure its height and maximum displacement (Dmax) through LOLA DEM data. Then we make 2D plots of displacement-length (L) for ridge population in the two maria. The Dmax-L ratios (γ) are derived by a linear fit method according to the D-L data. The γ value (2.13 × 10−2) of ridges in Mare Tranquillitatis is higher than the γ value (1.73 × 10−2) of ridges in Mare Serenitatis. In the last, the contractional strains (ε) in Mare Serenitatis and Mare Tranquillitatis are estimated to be ∼0.36% and 0.14% (assuming the fault plane dip θ is 25°). The values of the free-air gravity anomalies in Mare Serenitatis range from 78 to 358 mGal higher than those of the gravity anomalies in Mare Tranquillitatis which range from −70 to 120 mGal. The average thickness of basalts in Mare Tranquillitatis is 400 m, while that of basalts in Mare Serenitatis is 798 m. Moreover, the average age for ridge group in Mare Serenitatis is bigger than the wrinkle ridge's age in Mare Tranquillitatis. The formation of ridge group in Mare Serenitatis takes longer time than that in Mare Serenitatis. Therefore, we think the higher value of gravity anomalies, thicker basaltic units and longer formation time for wrinkle ridge in Mare Serenitatis maybe result in the higher value of contractional strain, although the formation of Tranquillitatis basin is earlier than that of Serenitatis basin.

Review of velocity models in the Faroe–Shetland Channel

Abstract Over the last few decades, a number of wide-angle seismic experiments have been conducted in the Faroe–Shetland Channel area with the objective of mapping the crustal structure. However, the volcanic rocks covering most of the area present a challenge for the imaging of sub-basalt structures. The results of the seismic studies are consistent in describing the Faroe–Shetland Channel as thinned continental crust and in establishing the presence of sub-basalt sediments. However, the various datasets often show differences in depth to crystalline basement and to the Moho. This paper presents a review of the velocity models in the Faroe–Shetland Channel and analyses the differences at line intersections. Down to top basalt the models are fairly consistent, while there are deviations of up to 1 km s −1 in basalt velocities and sub-basalt sediment velocities, 2 km in basalt thickness, 3.2 km in depth to crystalline basement, and 11.7 km in depth to the Moho.

Thicknesses of mare basalts on the Moon from gravity and topography

AbstractA new method of determining the thickness of mare basalts on the Moon is introduced that is made possible by high‐resolution gravity data acquired from NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission. Using a localized multitaper spherical‐harmonic analysis, an effective density spectrum is calculated that provides an estimate of the average crustal density as a function of spherical harmonic degree. By comparing the observed effective density spectrum with one generated from a theoretical model, the thickness of mare basalts can be constrained. We assume that the grain density of the basalts is known from remote sensing data and petrologic considerations, we assign a constant porosity to the basalts, and we let both the thickness of the basalts and the density of the underlying crust vary. Using this method, the total thickness of basalts was estimated on the nearside hemisphere, yielding an average of 0.74 km with 1σ upper and lower bounds of 1.62 km and 100 m, respectively. The region of Marius Hills, which is a long‐lived volcanic complex, is found to have the thickest basalts, with an average of 2.86 km and 1σ limits of 3.65 and 1.02 km, respectively. The crust beneath the Mare Imbrium basalts is found to have an atypically high density of about 3000 kg m−3 that we interpret as representing a mafic, unfractured, impact melt sheet.

The Oldest Pillow Lavas, 3.8-3.7Ga from the Isua Supracrustal Belt, SW Greenland: Plate Tectonics Had Already Begun by 3.8Ga

The presence of pillow basalts in the 3.8-3.7 Ga Isua supracrustal belt, Southern West Greenland indicates the presence of liquid water on early Earth around 3.8-3.7 Ga. The total thickness of pillow basalts is up to 1.0 km for the thickest unit, suggesting an ocean depth of at least 1.0 km. The rigidity of the Early Archean oceanic lithosphere can be calculated from the petrologically estimated mantle potential temperature of 1450°C and ocean surface temperature below 100°C. The results show that the oceanic lithosphere was sufficiently rigid to operate modern-style plate tectonics only 0.7-0.8 Ga after the formation of the Earth.