Km In Size Research Articles

Bulk and Atmospheric Metallicities as Direct Probes of Sequentially Varying Accretion Mechanisms of Gas and Solids Onto Planets

Core accretion is the standard scenario of planet formation, wherein planets are formed by sequential accretion of gas and solids, and is widely used to interpret exoplanet observations. However, no direct probes of the scenario have been discussed yet. Here, we introduce an onion-like model as one idealization of sequential accretion and propose that bulk and atmospheric metallicities of exoplanets can be used as direct probes of the process. Our analytical calculations, coupled with observational data, demonstrate that the trend of observed exoplanets supports the sequential accretion hypothesis. In particular, accretion of planetesimals that are ≳100 km in size is most favored to consistently explain the observed trends. The importance of opening gaps in both planetesimal and gas disks following planetary growth is also identified. A new classification is proposed, wherein most observed planets are classified into two interior statuses: globally mixed and locally (well) mixed. Explicit identification of the locally (well) mixed status enables reliable verification of sequential accretion. During the JWST era, the quality and volume of observational data will increase drastically and improve exoplanet characterization. This work provides one key reference of how both the bulk and atmospheric metallicities can be used to constrain gas and solid accretion mechanisms of planets.

Origin of the Ca-phosphate inclusions in Ivory Coast and Australasian Muong-Nong-type tektites

Tektites are reduced (Fe2+) glasses formed by the quenching of molten material ejected from Earth’s surface as a result of a hypervelocity impact. The vast majority of tektites are usually homogeneous glasses, but rare samples containing mineral inclusions can provide insights about the source material, sample thermal history, and tektite formation process. Tektites from two distinct strewn fields presenting Ca-phosphate inclusions detected from anomalous magnetic susceptibility were studied: one sample from the Ivory Coast tektite (ICT) field ejected at 1.07 Ma from the Bosumtwi crater (10.5 km in size) in Ghana and two Muong Nong type samples from the Australasian tektite field (MN-AAT) ejected at 0.79 Ma from a crater possibly situated in southeast Asia. In ICT, Ca-phosphate inclusions are systematically embedded in lechatelierite (SiO2 glass). In MN-AAT Ca-phosphate are either embedded in lechatelierite or in Fe-rich glass forming schlieren. Multiscale petrographic characterization using correlative microscopy associating scanning electron microscopy, microprobe and, transmission electron microscopy reveals that rounded inclusions in ivoirite are composed of acicular Ca-phosphates (merrillite) embedded in an amorphous P-rich glass. In MN-AAT, inclusions consist mostly of single droplets of Fe-Mg rich Ca-phosphate (structurally related to apatite), but few droplets often forming an emulsion texture show a complex assemblage of apatite, magnetite, pyroxene, and spinel growing from a Pt-rich nucleus. Diffusion profile around lechatelierite domains reveals maximum temperatures greater than 2200–2400 °C in the impact plume of the Australasian tektite and the Ivory coast tektite. Heating time is of the order of seconds-tens of seconds rather than minutes as previously suggested (20 s for MN-AAT and 5 s for ICT). The number, the density, and the fact that inclusions are entirely crystallized in MN-AAT support relatively slow cooling rates (<200 °C/h), in comparison with the faster cooling rates (>2000 °C/h) indicated by the precipitation of amorphous P-rich glass in ICT. In both impact events, ejecta that had been heated to high temperatures did not remain in the vapor plume for an extended period of time and landed rapidly (within tens of seconds) at a relatively high temperature (>1000 °C) on the Earth’s surface.Phosphate inclusions systematically embedded in lechatelierite in ICT provide clues about the source material. It suggests that the parent material for these silica-rich inclusions is not conventional detrital quartz. Rather, parts of lechatelierite domains may be inherited from a biogenic source that could be consistent with tropical soil (source of the phosphor) and its biomass (silica of plant origin). The reduction process that tektites record during their formation may be explained by superficial material since forests can contain a sizable mass of carbon that can reduce iron in tektites and produce platinoid-rich metallic nuclei and the Fe3+/ΣFe gradient recorded by the dendritic spinels.

A Scale‐Dependent Analysis of the Barotropic Vorticity Budget in a Global Ocean Simulation

AbstractThe climatological mean barotropic vorticity budget is analyzed to investigate the relative importance of surface wind stress, topography, planetary vorticity advection, and nonlinear advection in dynamical balances in a global ocean simulation. In addition to a pronounced regional variability in vorticity balances, the relative magnitudes of vorticity budget terms strongly depend on the length‐scale of interest. To carry out a length‐scale dependent vorticity analysis in different ocean basins, vorticity budget terms are spatially coarse‐grained. At length‐scales greater than 1,000 km, the dynamics closely follow the Topographic‐Sverdrup balance in which bottom pressure torque, surface wind stress curl and planetary vorticity advection terms are in balance. In contrast, when including all length‐scales resolved by the model, bottom pressure torque and nonlinear advection terms dominate the vorticity budget (Topographic‐Nonlinear balance), which suggests a prominent role of oceanic eddies, which are of km in size, and the associated bottom pressure anomalies in local vorticity balances at length‐scales smaller than 1,000 km. Overall, there is a transition from the Topographic‐Nonlinear regime at scales smaller than 1,000 km to the Topographic‐Sverdrup regime at length‐scales greater than 1,000 km. These dynamical balances hold across all ocean basins; however, interpretations of the dominant vorticity balances depend on the level of spatial filtering or the effective model resolution. On the other hand, the contribution of bottom and lateral friction terms in the barotropic vorticity budget remains small and is significant only near sea‐land boundaries, where bottom stress and horizontal viscous friction generally peak.

Epithermal Gold Discoveries in the Emerging Khundii Metallogenic Province, Southwest Mongolia

Abstract Mineral exploration since 2005 in a previously underexplored region of southwestern Mongolia resulted in the definition of the Zuun Mod porphyry Mo-Cu deposit, followed by discovery of the Altan Nar and Bayan Khundii epithermal gold deposits along with several prospects and advanced exploration projects. These discoveries form the core of the emerging Khundii (“Valley”) metallogenic province, ~50 × 100 km in size, located within a single island-arc terrane of Middle Carboniferous to early Permian age and predominantly within an individual mapped subterrane. The province is situated ~700 km west-northwest of the late Devonian Oyu Tolgoi porphyry Cu-Au deposit in a belt of mid-Paleozoic island arcs that are part of the Central Asian orogenic belt, host to world-class porphyry Cu-Au and epithermal gold deposits that stretch from southern Mongolia to the west, into China, Kazakhstan, and beyond. The Zuun Mod porphyry Mo-Cu deposit (297 ± 4.8 Ma) is hosted by a granodiorite intrusion cut by B-type quartz-molybdenite-chalcopyrite veins with K-feldspar alteration selvages plus disseminated biotite and magnetite. After definition of this deposit, a regional exploration program was initiated in 2009 over 110,000 km2, based on the underexplored nature of the region. Exploration included compilation of existing geologic, geochemical, and geophysical data and interpretation of satellite imagery followed by ground exploration that included stream, soil, and rock-chip sampling and geologic and alteration mapping. The Nomin Tal Cu-Au prospect was discovered in early 2011, and based on the indications from initial soil sampling, a 400- × 400-m soil survey was conducted over the southern part of the exploration license, which identified a Pb-, Zn-, and Au-in-soil anomaly over an area of ~1.5 × ~5.5 km. The first drill hole within the soil anomaly in late 2011 resulted in the discovery of the Altan Nar Au-polymetallic epithermal deposit with veins of coarsely crystalline quartz-adularia (309.7 ± 0.5 Ma) and Ca-, Mg-, Mn-, and Fe-carbonate gangue that host the base metal sulfides. The Bayan Khundii gold deposit was discovered in 2015 as the result of prospecting, ~16 km southeast of Altan Nar. Subsequent discovery of the Khar Mori gold project was announced in early 2021, ~3 km north of Bayan Khundii along a structural trend, and later in 2021 drilling discovered wide zones of disseminated gold at Ulaan Southeast, ~800 m west of Bayan Khundii. The epithermal quartz-adularia-gold veins (336.8 ± 0.5 Ma) at Bayan Khundii have colloform bands with minor pyrite and are enveloped by proximal illite alteration. The epithermal veins and alteration overprint an earlier, unrelated alteration style of residual quartz and pyrophyllite ± dickite ± diaspore-kaolinite. Similarly, residual quartz and pyrophyllite-dickite at Khar Mori are overprinted by epithermal mineralization, including arsenopyrite. At the central Ulaan project, ~3 km northwest of Bayan Khundii, intense quartz-white mica-pyrite alteration is widespread at surface, including tourmaline bodies and local copper anomalies, associated with nearby residual quartz and related aluminosilicate alteration. These alteration styles indicate erosion of a lithocap to its base, exposing K-feldspar and magnetite plus quartz-white mica-pyrite related to the top of a porphyry deposit, as yet only tested by a few scout drill holes. The undated porphyry-related alteration was subsequently overprinted by the gold-bearing epithermal veins after significant erosion.

Carapace Length-weight, Carapace Width-weight Relationships, Condition Factor and Sex Ratio of Freshwater Crab Sartoriana spinigera (Wood-Mason, 1971) from the River Burhi Gandak, North Bihar, India

Background: The Burhi Gandak river origins in the Chautarwa Chaur region near Bisambharpur in the West Champaran district of Bihar and flows through the East Champaran, Muzafarpur, Samastipur and Begusarai districts. It falls into the river Ganga near Khagaria district. Its coordinates are 25°51'40''N latitudes and 85°48'36''E longitudes. The total area of catchment is 12500 sq. km in size overall, of which 9601 sq. km are in Bihar and the rest in Nepal. The study will be helpful for stock estimation, developing conservation and choosing appropriate species for aquaculture. The present data can be used to develop conservation plans while providing biological data needed for an effective management of this fishery. Methods: The carapace length-weight, carapace width-weight relationship, condition factor and sex ratio of freshwater crab Sartoriana spinigera (n=663) collected from River Burhi Gandak, North Bihar, between July 2020 to June 2021. In the present investigation, freshwater crabs were collected from different types of techniques, including hand-picking, digging, setting traps and taking them from their nest. Result: Total of 663 specimens of Sartoriana spinigera (Wood-Mason, 1971) of both sexes (male and female) were collected in which 363 female and 300 male. The carapace length-weight of Sartoriana spinigera females were calculated as W = 0.9122.521 with R2 = 0.875, male W = 0.43102.505 with R2 = 0.853 and length-weight of combined sex (male and female) were calculated as W = 0.6612.701 with R2 = 0.954. The carapace width-weight of female were calculated as W = 0.5542.331 with R2 = 0.831, male W = 0.7912.421 with R2 = 0.802 and carapace length-weight of combined sex (male and female) were calculated as W = 0.18122.601 with R2 = 0.900. From this study showed it could be stated that crabs have allometric growth pattern. The Fulton’s condition factor (Kn) value were calculated as 1.10 and sex ratio calculated was 1:1.49. This paper provides information.

Formation-flying interferometry in geocentric orbits

Context. Spacecraft formation flying serves as a method of astronomical instrumentation that enables the construction of large virtual structures in space. The formation-flying interferometry generally requires very high control accuracy, and extraterrestrial orbits are typically selected. To pave the way for comprehensive missions, proposals have been made for preliminary space missions, involving nano- or small satellites, to demonstrate formation-flying interferometry technologies, especially in low Earth orbits. From a theoretical perspective, however, it is unknown where and to what extent feasible regions for formation-flying interferometry should exist in geocentric orbits. Aims. This study aims to demonstrate the feasibility of formation-flying interferometry in geocentric orbits in which various perturbation sources exist. Geocentric orbits offer the advantage of economic accessibility and the availability of proven formation-flying technologies tailored for Earth orbits. Its feasibility depends on the existence of specific orbits that satisfy a small-disturbance environment with good observation conditions. Methods. Spacecraft motions in Earth orbits subjected to perturbations are analytically modeled based on celestial mechanics. The magnitudes of the accelerations required to counteract these perturbations are characterized by parameters such as the semimajor axis and the size of the formation. Results. Small-perturbation regions tend to appear in higher-altitude and shorter-separation regions in geocentric orbits. Candidate orbits are identified in high Earth orbits for the triangular laser-interferometric gravitational-wave telescope, which is 100 km in size, and in medium Earth orbits for the linear astronomical interferometer, which is 0.5 km in size. A low Earth orbit with a separation of approximately 0.1 km may be suitable for experimental purposes. Conclusions. Geocentric orbits are potentially applicable for various types of formation-flying interferometry.

An attempt to calculate the curie point in the Eastern part of Egypt

A curie point depth (CPD) map of the selected area in Egypt (Safaga–Hurghada area along the Red Sea coast), was constructed from the spectral analysis of aeromagnetic data. It was chosen there because the Red Sea and the Gulf of Suez coasts are considered as two of the highest temperature geothermal potential in Egypt. The CPD values were estimated from 10 overlapping blocks, 90 × 90 km in size, using band-pass filtered of aeromagnetic data. The Curie point depth was calculated. The CPD for the region ranges between 26.69 km and 42.69 km.A corresponding heat flow map was also generated from CPD and thermal gradient estimation. The boundaries between the zones of the shallow and deep CPD's coincide well with faults trending NW direction (more or less parallel to the Red Sea) and NE direction. Deepening of CPD's (low heat flows) was detected in two parts, the first one at the northern part of the study area (NW part of Ras Gemsa region). The second, at the southern part (east of Qena).

Global cascade of kinetic energy in the ocean and the atmospheric imprint.

Here, we present an estimate for the ocean's global scale transfer of kinetic energy (KE), across scales from 10 to 40,000 km. Oceanic KE transfer between gyre scales and mesoscales is induced by the atmosphere's Hadley, Ferrel, and polar cells, and the intertropical convergence zone induces an intense downscale KE transfer. Upscale transfer peaks at 300 gigawatts across mesoscales of 120 km in size, roughly one-third the energy input by winds into the oceanic general circulation. Nearly three quarters of this "cascade" occurs south of 15°S and penetrates almost the entire water column. The mesoscale cascade has a self-similar seasonal cycle with characteristic lag time of ≈27 days per octave of length scales; transfer across 50 km peaks in spring, while transfer across 500 km peaks in summer. KE of those mesoscales follows the same cycle but peaks ≈40 days after the peak cascade, suggesting that energy transferred across a scale is primarily deposited at a scale four times larger.

Convection and segregation in heterogeneous orogenic crust with a VOF method – II: how to form migmatite domes

SUMMARY Migmatites and granitic-gneisses exhumed in Archean to Phanerozoic segments are former partially molten crustal roots, display typical domes structures ranging in size from kilometres to decakilometres, and are often interpreted as resulting from the development of diapiric or convective gravitational instabilities. In previous work (part I), we determined various regimes of gravity-driven segregation, by considering a thick continental crust heated from below and containing melt related heterogeneities. These heterogeneities, represented by inclusions of distinct densities and viscosities with respect to the ambient partially molten material, can be entrained into convection cells (in the ‘suspension’ and ‘layering’ regimes) and/or accumulate as clusters (in the ‘layering’ and ‘diapirism’ regimes). Here we further investigate the specific conditions that allow for the formation and preservation of domes resulting from diapirism at the top of convective cells. We show that both the cessation of basal heating and the freezing of the buoyant inclusions density favour their stacking and preservation at ca. 15 km depth, within about 10 Myr. The buoyant inclusions form domes, 5–20 km in size, that also record several convective cycles at velocities ranging from 0.5–4 cm yr−1. 3-D models demonstrate their radial geometrical nature. The influence of the size and concentration of the inclusions is also assessed, complementing the characteristics of crustal heterogeneity in driving its differentiation and the formation of migmatite domes.

Key Factors for Improving the Resolution of Mapped Sea Surface Height from Multi-Satellite Altimeters in the South China Sea

A satellite altimeter measures sea surface height (SSH) along the nadir track. Multiple satellite altimeters have been in orbit, and the measurements been merged for mapping mesoscale eddies of ~100 km in size in the oceans. The capability of the mapped SSH for resolving mesoscale eddies depends on mapping algorithms. A two-dimensional variational (2DVAR) algorithm was implemented to generate mapped SSH at a grid size of 1/12° in the South China Sea. A range of comparisons were performed between the mapped SSH and the commonly used AVISO (Archiving, Validation, and Interpretation of Satellite Oceanographic satellite data) mapped SSH data product at a grid size of 1/8° and 1/4°. The effective resolution, which represents the spatial scale that the data can resolve, was examined. The effective resolution of the mapped SSH using the 2DVAR algorithm is approximately 100 km, while it is 250 km with the 1/8° and 1/4° AVISO data products. The difference in the effective resolution results from the difference in the background state and thus the background error. The result suggests that the effective resolution of the mapped data could be increased by choosing a background state so that the associated errors could have a smaller decorrelation length scale.

Deep and shallow crustal structure control on the late-stage volcanism in Syria Planum (Mars)

Long-lasting widespread volcanism in Mars is testified by the Tharsis volcanic province, one of the largest volcanic provinces with the largest shield volcanoes of the Solar System. However, volcanism on Mars is characterized also by the occurrence of broad volcanic fields, either in the form of small lava shields or monogenic volcanic cones. The region of Syria Planum (SP) is located east of the Tharsis province and between Noctis Labyrinthus to the North and Claritas Fossae to the southwest. It is an example of diffuse volcanism, presenting hundreds of small edifices (namely Syria Colles) which occur on top of a large bulge roughly 300 km × 200 km in size. SP exhibits a complex magmatic and volcano-tectonic evolution spanning from the early-Noachian to the more recent Amazonian. In this work, we investigate the geometry of the plumbing system of the SP volcanic field as well as the geometries of the volcanic constructs (i.e., vent elongation and vent alignment) that may be linked to the structures that fed the magma presenting a possible tectonic and volcanic evolution of the distributed volcanism phase in this area. The spatial distribution of vents and the overall map view shape of the volcanic field were studied in terms of vent clustering and spatial distribution. We show that the widespread and diffuse volcanism in SP presents clear vent clusters that are related to a deep source magma reservoir located at ∼100 km depth. We also show that Syria Colles vent elongations and azimuth distributions suggest that the magma exploited the inherited regional structural framework, coherent with the Syria Colles late-stage Amazonian magmatic event, and highlighting the role of a shallow crustal tectonic framework in shaping the Martian volcanism.

The Sensitivity of Convective Cloud Ensemble Statistics to Horizontal Grid Spacing in Idealized RCE Simulations

Abstract In this work, cloud ensemble statistics are extracted from idealized radiative–convective equilibrium simulations performed at horizontal grid spacings Δ ranging from 2 km to 125 m. At the coarsest resolution, convection remains randomly distributed in space such that the equilibrium statistical mechanics theory proposed by Craig and Cohen in 2006 (CC06; assumes Poisson distributed clouds and exponential mass flux distributions) remains valid. Using classical organization metrics, clustering is already observed at Δ = 1 km, but substantial deviations between the simulated cloud ensemble statistics and CC06 are only observed for grid spacings Δ &lt; 500 m. At these resolutions, the cloud mass flux distributions exhibit heavy tails and cloud counts become overdispersed (higher variance than a Poisson distribution). These changes in ensemble statistics are accompanied by a shift in subcloud organization patterns as well as with the fact that individual cloudy updrafts start to be resolved. Consequently, a horizontal grid spacing no larger than 250 m is recommended, not only to properly resolve the dynamics of individual convective clouds, but also to capture the mesoscale organization of the cloud ensemble. Finally, it is shown that the CC06 theory and our high-resolution results including mesoscale organization may be reconciled if one considers 1) areas smaller than approximately 2 km in size, corresponding roughly to the narrow bands along which clouds develop almost randomly; and 2) individual cloud cores instead of cloud objects, core mass fluxes being shown to generally follow exponential distributions.

The introduction of African cheetahs to India was planned without considering their spatial ecology

The introduction of African cheetahs to India was planned without considering their spatial ecology

Sources and spatial variations of heavy metals in offshore sediments of the western Pearl River Estuary

The concentrations of six heavy metals (Cd, Cr, Cu, Pb, Zn, and As) in offshore surface sediments of western Pearl River Estuary were analyzed to investigate their sources and spatial variations using factorial kriging analysis. Three-scale spatial variations in heavy metal concentrations were identified and separated: nugget, local, and regional scale, which indicated sample errors, anthropogenic pollution and natural variation, respectively. Anthropogenic heavy metals varied sharply and heterogeneous at range of 60 km. Maoming Port, Hailing Bay and coastal area northeastern Hainan Island were potential polluted areas of Cd, Cr, Cu, Pb, Zn and As, also the Nandu River, Baoling River and Wanquan River estuaries were potential polluted areas of As. These polluted areas ranged up to 60 km in size and tended to extend with currents. The natural heavy metals varied continuously and relatively homogeneous at range of 180 km, which was dominated by riverine input and paleo-sea-level changes.

Analysis of a Pull-Apart Basin and Its Associated Fractures in the Woodford Shale, Central Oklahoma

Pull-apart basins are faulting and folding zones with high intensity of fractures that strongly affect the production in unconventional shale gas. While most observations of pull-apart basins were from surface mapping or laboratory experiments, we investigated a nascent pull-apart basin in the subsurface. We characterized a nascent pull-apart basin along the strike-slip fault within the Woodford Shale by using seismic attributes analyses, including coherence, dip-azimuth, and curvature. The results indicate a 32 km long, N-S striking strike-slip fault that displays a distinct but young pull-apart basin, which is ~1.6 km by 3.2 km in size and is bounded by two quasi-circular faults. The curvature attribute map reveals two quasi-circular folds, which depart from the main strike-slip fault at ~25°, resulting in an elliptical basin. Inside the basin, a series of echelon quasi-circular normal faults step into the bottom of the basin with ~80 m of total subsidence. We propose that the controls of the shape of pull-apart basin are the brittleness of the shale, and we suggest proper seismic attributes as a useful tool for investigating high fracture intensity in the subsurface for hydrofracturing and horizontal drilling within the shale.

Global energy spectrum of the general oceanic circulation

Advent of satellite altimetry brought into focus the pervasiveness of mesoscale eddies {{{{{{{bf{{{{{{{{mathcal{O}}}}}}}}}}}}}}}}({100}) km in size, which are the ocean’s analogue of weather systems and are often regarded as the spectral peak of kinetic energy (KE). Yet, understanding of the ocean’s spatial scales has been derived mostly from Fourier analysis in small "representative” regions that cannot capture the vast dynamic range at planetary scales. Here, we use a coarse-graining method to analyze scales much larger than what had been possible before. Spectra spanning over three decades of length-scales reveal the Antarctic Circumpolar Current as the spectral peak of the global extra-tropical circulation, at ≈ 104 km, and a previously unobserved power-law scaling over scales larger than 103 km. A smaller spectral peak exists at ≈ 300 km associated with mesoscales, which, due to their wider spread in wavenumber space, account for more than 50% of resolved surface KE globally. Seasonal cycles of length-scales exhibit a characteristic lag-time of ≈ 40 days per octave of length-scales such that in both hemispheres, KE at 102 km peaks in spring while KE at 103 km peaks in late summer. These results provide a new window for understanding the multiscale oceanic circulation within Earth’s climate system, including the largest planetary scales.

Stirring of interior potential vorticity gradients as a formation mechanism for large subsurface-intensified eddies in the Beaufort Gyre

Abstract The Beaufort Gyre (BG) is hypothesized to be partially equilibrated by those mesoscale eddies that form via baroclinic instabilities of its currents. However, our understanding of the eddy field’s dependence on the mean BG currents and the role of sea ice remains incomplete. This theoretical study explores the scales and vertical structures of eddies forming specifically due to baroclinic instabilities of interior BG flows. An idealized quasi-geostrophic model is used to show that flows driven only by the Ekman pumping contain no interior potential vorticity (PV) gradients and generate weak and large eddies, ℴ(200km) in size, with predominantly barotropic and first baroclinic mode energy. However, flows containing realistic interior PV gradients in the Pacific halocline layer generate significantly smaller eddies of about 50 km in size, with a distinct second baroclinic mode structure and a subsurface kinetic energy maximum. The dramatic change in eddy characteristics is shown to be caused by the stirring of interior PV gradients by large-scale barotropic eddies. The sea ice-ocean drag is identified as the dominant eddy dissipation mechanism, leading to realistic sub-surface maxima of eddy kinetic energy for drag coefficients higher than about 2×10−3. A scaling law is developed for the eddy potential enstrophy, demonstrating that it is directly proportional to the interior PV gradient and the square root of the barotropic eddy kinetic energy. This study proposes a possible formation mechanism of large BG eddies and points to the importance of accurate representation of the interior PV gradients and eddy dissipation by ice-ocean drag in BG simulations and theory.

Imaging magmatic intrusions using derivatives of high-resolution aeromagnetic data over the Nigerian sector of the chad Basin

Magmatic activities can either positively or negatively affect hydrocarbon generation in sedimentary basins. The effect of these activities can be positive when they prevent further migration and escape or negative when extreme pressure and high temperature force the hydrocarbon to evaporate at the time of emplacement. The aim of the study is to confirm the presence of intrusive structures in the Nigerian sector of the Chad Basin using derivatives of aeromagnetic data. The enhanced body and edges suggest a dyke-like structure intruding the Chad Basin. The edges are identified as areas that are skewed on the first vertical derivative and maxima over the analytic signal generated by the dyke-like intrusion. Three profiles with lengths ranging from 68.4 km to 263.9 km were generated on the derivatives of aeromagnetic data, and the analytical results indicate dyke-like structures of 0.3 km to 0.4 km in size.

A Numerical Approach Using a Finite Element Model to Constrain the Possible Interior Layout of (16) Psyche

Asteroid (16) Psyche (278 × 238 × 171 km in size) is notable for the largest M-type asteroid and has the high radar albedo (0.34 ± 0.08) among the main-belt asteroids. The object is likely a mixture of metal and silicates because of its lower bulk density (∼4.0 g cm−3) than metallic materials (∼7.5 g cm−3) and observations inferring the existence of silicate materials on the surface. Here, we numerically investigate the interior layout when the structure of Psyche consists of a spherical iron core and two types of the silicate-rich layers (compressed and uncompressed ones) resulting from the compaction process (later known as a three-layer model). We develop an inverse problem algorithm to determine the layout distribution by combining a finite element model approach that accounts for density variations and constrains pressure-based crushing conditions. The results show that, given the crushing limit of 10 MPa, the smallest core size likely reaches 72 km in radius, and the silicate-rich layer, consisting of both compressed and uncompressed regions, has a thickness ranging up to 68 km. To support the localized metal concentration at the crater-like region detected in the recent radar observation, we give more constraints on the minimum core size, which takes up to 34%–40% of the entire size of Psyche. Our study also addresses that the ferrovolcanic surface eruptions could still be a source of metal-rich materials. Finally, while the differentiated structure having a spherical core condition is just part of potential scenarios, the present study infers that the core and compressed layer conditions likely control the surface condition. Further investigations will provide key information for observable properties on NASA’s Psyche mission to provide insight into its evolution history.

Geology and Geochronology of the Miocene Rio Blanco Porphyry Cu-Mo Deposit, Northern Peru

Abstract The Rio Blanco porphyry Cu-Mo deposit occurs at the north end of the Miocene metallogenic belt of northern Peru. It has a thick supergene enrichment blanket; while normal for hyperarid Chile, this is unusual in mountainous, cloud forest terrain. Rio Blanco is hosted by the Portachuela batholith. Zircon U-Pb dating shows that the youngest part of the batholith was emplaced at 12.43 ± 0.13 Ma. The deposit formed during three magmatic-hydrothermal cycles. Cycle 1, by far the most important, occurred at 11.50 ± 0.17 to 10.92 ± 0.14 Ma (zircon U-Pb). Two intermineralization intrusions caused early potassic and propylitic alteration. This was then overprinted by a blanket of quartz-sericite, grading down into sericite-chlorite alteration. Cycle 1 was finally cut by a quartz-sericite–cemented breccia, which contains the highest-grade hypogene Cu-Mo grades. A cycle 1 molybdenite-bearing vein has a molybdenite Re-Os model age of 11.43 ± 0.16 Ma. Molybdenite Re-Os dating of the quartz-sericite–cemented breccias shows brecciation occurred at 11.28 ± 0.24 to 11.11 ± 0.18 Ma. Cycle 2 was restricted to the east side, where narrow porphyritic dacite 1 dikes (dated by zircon U-Pb at 10.62 ± 0.16 Ma) show biotite alteration and economic copper. Cycle 3, at 10.02 ± 0.12 to 9.06 ± 0.09 Ma (zircon U-Pb), was triggered by a swarm of NE-striking quartz-plagioclase porphyry and porphyritic dacite 2 dikes. Alteration was milder, and this cycle did not introduce economic copper. Nonmineralized pebble dikes cut the system, emanating from a major diatreme, about 3 × 1.3 km in size, on the north side of the deposit. The magmatic-hydrothermal history spanned about 2.5 m.y., with economic mineralization over about 1.48 m.y. However, metals were mostly introduced during cycle 1, which lasted approximately 0.58 m.y. Our work shows that while multiple magmatic-hydrothermal cycles produced Rio Blanco, sufficient metals were introduced to form a giant porphyry deposit within a single magmatic-hydrothermal cycle.