The extremely reduced silicate-bearing iron meteorite Northwest Africa 6583: Implications on the variety of the impact melt rocks of the IAB-complex parent body

AbstractSeveral low-Ni iron meteorites previously assigned to group IAB are reclassified IIICD on the basis of lower Ge, Ga, W and Ir concentrations and higher As concentrations; the low-Ni extreme of IIICD is now 62 mg/g, that of IAB is 64 mg/g. The resulting fractionation patterns in the two groups are quite similar. It has long been established that, in contrast to the magmatic iron meteorite groups, IAB and IIICD did not form by fractional crystallization of a metallic magma. Other models have been proposed, but all have serious flaws. A new model is proposed involving the formation of each iron in small pools of impact melt on a parent body consisting of material similar to the chondritic inclusions found in some IAB and IIICD irons, but initially unequilibrated. These impact melts ranged in temperatures from ~ 1190 K to ~ 1350 K. The degree of equilibration between melt and unmelted solids ranged from minimal at the lowest temperature to moderate at the highest temperature. The lowest temperature melts were near the cotectic in the Fe-Ni-S system with Ni contents of ~ 12 atom %. Upon cooling, these precipitated metal having ~ 600 mg/g Ni by equilibrium crystallization. The Ni-rich melt resulted from the melting of Ni-rich sulfides and metal in the unequilibrated chondritic parent. Low-Ni irons formed in high temperature melts near the composition of the FeS-Fe eutectic or somewhat more metal rich. We suggest that the decreasing Ge, Ga and refractory abundances with increasing Ni concentration reflect the trapping of these elements in oxide phases in the unequilibrated chondritic material, and that very little entered the Ni-rich melt parental to the Oktibbeha County iron. The remaining elements tended to have element/Ni ratios in the melts that were more or less independent of temperature. The remarkable correlation between I-Xe age of the chondritic inclusions and Ni content of the host metal is explained by a detailed evolution of (mega)regolith in which these groups originated. The most Ni-rich melts could only be generated from an unequilibrated chondrite parent; as the continuing deposition of impact energy produced increasingly higher grades of metamorphism, the maximum Ni content of the impact melts (and their subsequently precipitated metal) gradually decreased.

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Petrology and geochemistry of the unbrecciated achondrite Northwest Africa 1240 (NWA 1240): an HED parent body impact melt

Geochimica et Cosmochimica Acta ◽

10.1016/s0016-7037(03)00092-9 ◽

2003 ◽

Vol 67 (20) ◽

pp. 3959-3970 ◽

Cited By ~ 60

Author(s):

J.A. Barrat ◽

A. Jambon ◽

M. Bohn ◽

J. Blichert-Toft ◽

V. Sautter ◽

...

Keyword(s):

Parent Body ◽

Impact Melt ◽

Northwest Africa ◽

Petrology And Geochemistry

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Evidences for Bimodal volcanism on 4-Vesta Asteroid from impact-melt clast

10.5194/epsc2020-548 ◽

2020 ◽

Author(s):

Dwijesh Ray ◽

Sambhunath Ghosh

Keyword(s):

Melt Inclusions ◽

Bulk Composition ◽

Parent Body ◽

Total Iron ◽

Volcanic Complex ◽

Element Geochemistry ◽

Silicic Volcanism ◽

Impact Melt ◽

Acid Volcanism ◽

The Impact

Silicic / acid volcanism has not been widely described either on Moon, Mars or in Asteroid 4 Vesta. The occurrence of sialic crustal rocks on the lunar surface is extremely limited. Reports on silicic (non-mare) volcanic rocks on Moon is found to be associated in Compton-Belkovich volcanic complex, Hansteen Alpha volcanic crater, Lassell massif, Gruithuisen domes and ejecta of Aristarchus crater (Clegg-Watkins et al., 2017). The occurrence of several volcanic constructs (e.g. collapse features, domes) and volatile-rich pyroclastics in association with silicic rocks further emphasize existence of viscous magmas on Moon. A localized occurrence of silicic volcanism on Mars is also envisaged by the presence of tridymite in mudstone of Gale crater (Morris et al., 2016). However, the exact formation mechanism of silicic volcanism on Moon, Mars or even in 4-Vesta has been largely hindered due to lack of silicic meteorite samples or mission-returned samples. The HED (Howardite, Eucrite, Diogenite) meteorites is considered to have originated from a common parent body Asteroid 4-Vesta. Recent Dawn mission also attempts to validate its geologic context and formulate a possible HED-Vesta connection (McSween et al., 2013). Based on Dawn findings, Vesta&#8217;s surface appears to be similar to a mixture of basaltic eucrite and diogenite resembling a more complex breccia howardite (De Sanctis et al., 2012; Prettyman et al., 2012). A variety of clasts are apparently common in howardite. Here, we report the petrography and major element geochemistry of a new impact-melt clast from Lohawat howardite. Our results show that the clast composition is unique and unlikely to be explained by typical impact melting of HED mafic lithologies. One of the impact melts (~20&#181; across) hosted in ferroaugite (Wo42En2.7Fs55.3) clast substantially differ in composition from the other impact-melt (~50&#181; across) hosted in ilmenite clast, specially in terms of SiO2 wt%, CaO wt%, K2O wt% and K2O / (K2O + Na2O) ratio. Moreover, one appears nearly homogeneous in contrast to evolved nature with limited heterogeneity as compared to other. Both the melts are oblong-shaped, smooth textured with sharp outline and embedded in the host monomict mineral clast of different composition belonging to possible parent of cumulate eucrite. The average bulk composition of Lohawat is consistent with basaltic crusts (SiO2 ~50.3-51.8 wt%, Al2O3 ~3.5-8.2 wt%, total iron-magnesia ~31.2-38.0 wt%, CaO ~2.2-7.6 wt%) (Chattopadhyay et al. 1998; Sisodia et al. 2001; Ghosh, 2011). Supplement to basaltic volcanism, we report for the first time the incipient acid volcanism in a HED meteorite based on two impact melt inclusions of nearly rhyolitic composition (SiO2 ~76-79.5 wt%, Al2O3 ~11.4 - 12.8 wt%, total alkali ~3 - 8 wt% with K2O/ (Na2O + K2O) ~0.21-0.95, CaO ~ 0.8 - 4.67wt% and low total iron-magnesia ~1-2 wt%). Our study thus reinforces to conceive the idea that some rhyolitic crusts formed due to differentiation of mafic magma were exposed on Vesta and heterogeneity of Vestan surface is definitely different from one as previously thought. References: Clegg-Watkins, R.N. et al. 2016, Icarus 285:169-184. Morris, R.V. et al. 2016, 113:7071-7076. McSween, H.Y. et al. 2013, MAPS 48:2090-2104. De Sanctis, M.C. et al. 2012, Science 336:697-700. Prettyman, T.H. et al. 2012, Science 338:242-246. Chattopadhyay, B. et al. 1998. JGSI 51:171-174. Sisodia, M.S. et al. 2001 MAPS 36:1457-1466. Ghosh, S. IJG 65:251-264.

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The Impact of Initial Conditions in N-Body Simulations of Debris Discs

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2015.41 ◽

2015 ◽

Vol 32 ◽

Cited By ~ 4

Author(s):

E. Thilliez ◽

S. T. Maddison

Keyword(s):

Numerical Simulations ◽

Initial Conditions ◽

Parent Body ◽

Dust Trapping ◽

Physical Context ◽

Disc Width ◽

Wide Range ◽

Belt Width ◽

New Generation ◽

The Impact

AbstractNumerical simulations are a crucial tool to understand the relationship between debris discs and planetary companions. As debris disc observations are now reaching unprecedented levels of precision over a wide range of wavelengths, an appropriate level of accuracy and consistency is required in numerical simulations to confidently interpret this new generation of observations. However, simulations throughout the literature have been conducted with various initial conditions often with little or no justification. In this paper, we aim to study the dependence on the initial conditions of N-body simulations modelling the interaction between a massive and eccentric planet on an exterior debris disc. To achieve this, we first classify three broad approaches used in the literature and provide some physical context for when each category should be used. We then run a series of N-body simulations, that include radiation forces acting on small grains, with varying initial conditions across the three categories. We test the influence of the initial parent body belt width, eccentricity, and alignment with the planet on the resulting debris disc structure and compare the final peak emission location, disc width and offset of synthetic disc images produced with a radiative transfer code. We also track the evolution of the forced eccentricity of the dust grains induced by the planet, as well as resonance dust trapping. We find that an initially broad parent body belt always results in a broader debris disc than an initially narrow parent body belt. While simulations with a parent body belt with low initial eccentricity (e ~ 0) and high initial eccentricity (0 < e < 0.3) resulted in similar broad discs, we find that purely secular forced initial conditions, where the initial disc eccentricity is set to the forced value and the disc is aligned with the planet, always result in a narrower disc. We conclude that broad debris discs can be modelled by using either a dynamically cold or dynamically warm parent belt, while in contrast eccentric narrow debris rings are reproduced using a secularly forced parent body belt.

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Pb isotopes in the impact melt breccia 66095: Association with the Imbrium basin and the isotopic composition of lithologies at the Apollo 16 landing site

Chemical Geology ◽

10.1016/j.chemgeo.2017.07.012 ◽

2017 ◽

Vol 466 ◽

pp. 608-616 ◽

Cited By ~ 6

Author(s):

Joshua F. Snape ◽

Alexander A. Nemchin ◽

Jeremy J. Bellucci ◽

Martin J. Whitehouse

Keyword(s):

Isotopic Composition ◽

Landing Site ◽

Pb Isotopes ◽

Impact Melt ◽

The Impact

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Ocean resurge-induced impact melt dynamics on the peak-ring of the Chicxulub impact structure, Mexico

International Journal of Earth Sciences ◽

10.1007/s00531-021-02008-w ◽

2021 ◽

Author(s):

Felix M. Schulte ◽

◽

Axel Wittmann ◽

Stefan Jung ◽

Joanna V. Morgan ◽

...

Keyword(s):

Impact Structure ◽

Physical Processes ◽

Hydrothermal Conditions ◽

Chemical Examination ◽

Impact Melt ◽

Target Rock ◽

Single Process ◽

Chicxulub Impact ◽

The Impact

AbstractCore from Hole M0077 from IODP/ICDP Expedition 364 provides unprecedented evidence for the physical processes in effect during the interaction of impact melt with rock-debris-laden seawater, following a large meteorite impact into waters of the Yucatán shelf. Evidence for this interaction is based on petrographic, microstructural and chemical examination of the 46.37-m-thick impact melt rock sequence, which overlies shocked granitoid target rock of the peak ring of the Chicxulub impact structure. The melt rock sequence consists of two visually distinct phases, one is black and the other is green in colour. The black phase is aphanitic and trachyandesitic in composition and similar to melt rock from other sites within the impact structure. The green phase consists chiefly of clay minerals and sparitic calcite, which likely formed from a solidified water–rock debris mixture under hydrothermal conditions. We suggest that the layering and internal structure of the melt rock sequence resulted from a single process, i.e., violent contact of initially superheated silicate impact melt with the ocean resurge-induced water–rock mixture overriding the impact melt. Differences in density, temperature, viscosity, and velocity of this mixture and impact melt triggered Kelvin–Helmholtz and Rayleigh–Taylor instabilities at their phase boundary. As a consequence, shearing at the boundary perturbed and, thus, mingled both immiscible phases, and was accompanied by phreatomagmatic processes. These processes led to the brecciation at the top of the impact melt rock sequence. Quenching of this breccia by the seawater prevented reworking of the solidified breccia layers upon subsequent deposition of suevite. Solid-state deformation, notably in the uppermost brecciated impact melt rock layers, attests to long-term gravitational settling of the peak ring.

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Environmental Change Threatens Freshwater Insect Communities in Northwest Africa: A Meta-Analysis

Frontiers in Environmental Science ◽

10.3389/fenvs.2021.671715 ◽

2021 ◽

Vol 9 ◽

Author(s):

Nils Kaczmarek ◽

Ralf B. Schäfer ◽

Elisabeth Berger

Keyword(s):

Climate Change ◽

Water Temperature ◽

Negative Binomial ◽

Small Body ◽

Future Research ◽

Insect Communities ◽

Data Set ◽

Temperature Conductivity ◽

Northwest Africa ◽

The Impact

A climatic shift from temperate to arid conditions is predicted for Northwest Africa. Water temperature, salinity, and river intermittency are likely to increase, which may impact freshwater communities, ecosystem functioning, and related ecosystem services. Quantitative data and information on the impact of climate change on insect communities (e.g., richness, taxonomic and trait composition) are still scarce for Northwest Africa. In this study, we extracted information on freshwater insect occurrence and environmental variables in Northwest Africa from the results of a literature search to study potential consequences of changing climatic conditions for these communities. Our data set covered 96 families in 165 sites in Morocco and Algeria. We quantified the impact of several explanatoryvariables (climate, altitude, water temperature, conductivity, intermittency, flow, aridity, dams, and land cover) on richness, taxonomic and functional trait composition using negative binomial regression models and constrained ordination. Family richness in arid sites was on average 37 % lower than in temperate sites in association with flow, river regulation, cropland extent, conductivity, altitude, and water temperature. With 36 % of the studied temperate sites predicted to turn arid by the end of the century, a loss of insect families can be predicted for Northwest Africa, mainly affecting species adapted to temperate environments. Resistance and resilience traits such as small body size, aerial dispersal, and air breathing promote survival in arid climates. Future research should report insect occurrences on species level to allow for better predictions on climate change effects.

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Unique igneous textures and shock metamorphism of the Northwest Africa 7203 angrite: Implications for crystallization processes and the evolutionary history of the angrite parent body

Meteoritics and Planetary Science ◽

10.1111/maps.13776 ◽

2021 ◽

Author(s):

Hideyuki Hayashi ◽

Takashi Mikouchi ◽

Nak Kyu Kim ◽

Changkun Park ◽

Yuji Sano ◽

...

Keyword(s):

Evolutionary History ◽

Parent Body ◽

Shock Metamorphism ◽

Northwest Africa ◽

History Of

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The Kara astrobleme size, age and potential paleo-ecological effects of the impact event (European Arctic Zone, Russia)

10.5194/egusphere-egu21-8523 ◽

2021 ◽

Author(s):

Tatyana Shumilova

Keyword(s):

Mass Extinction ◽

Black Shales ◽

Ecological Effects ◽

Impact Event ◽

Arctic Zone ◽

Russian Science ◽

Future Possibility ◽

Impact Melt ◽

European Arctic ◽

The Impact

The Kara astrobleme is one of the biggest meteoritic craters which is set at the Baydarata Bay of the Kara sea (European Arctic Zone, Russia). It is a result of the catastrophic impact event occurred close to the K/&#1058; extinction. The Kara astrobleme is the largest European crater at the modern erosion level.&#160; At present it is estimated with the diameter from rim to rim about 65 km. While, some scientists have proposed its larger initial size &#8211; up to 120 km diameter, but no any well presented proof has been provided for the hypothesis. In 2015-2019 we have provided wide geological observations at the Kara crater and the near-set Ust`-Kara area (UKA) impactites. We have found for the first time that the UKA impactites, described in earlier Russian scientists publications as a synchronic independent crater of the same bolide, can be presented with bottom-flow impactites from the Kara crater (Shumilova et al., 2020). The found bottom-flow impactites abundant with belt-like impact melt bodies enriched in coesite and liquation structures similar to the Kara UHPHT vein and vein-like melt bodies with UHPHT impact glasses. Thus, they belong to UHPHT impactites. According to our air-bird view observations and impactites outcrops description at the UKA we support the hypothesis of the larger Kara crater getting 100-120 km in diameter of the initially originated size. Such giant meteorite event should be followed by catastrophic effects at the planet level, such as mass extinction. The present accepted Kara impact event age followed by the most recent measurements by 40Ar-39Ar method is equal to 70.3 &#177; 2.2 Ma (Trieloff et al., 1998), that is a bit earlier than the Cretaceous/Tertiary boundary (K/&#1058;) mass extinction at 66 Ma. But, previously, Kara age has been proposed by 65.7 Ma as a probable K/T impact (Kolesnikov et al., 1988; Nazarov et al., 1992). According to different data, the Kara event age lies within the range from 60 to 81 Ma (Masaitis & Mashchak, 1982; Nazarov et al., 1989; Kolesniov et al., 1990; Koeberl et al., 1990). It is clear that the accuracy of the age measurements depend on the quality of the studied samples, including their crystallinity, velocity of impact melt cooling and alteration, and from the used type of a method. By the moment, we have found out &#8220;in situ&#8221; crystallized zircons within the just discovered real UHPHT impact melt glasses (Shumilova et al., 2018, 2020). The UHPHT glasses do not have any alteration, thus, they can be used for accurate age measurements. Taking a future possibility for more accurate age analysis in the nearest future we can propose a correct vision of the possibility of the giant Kara influence to K-T mass extinction or other ecological effects. In any case following to the giant size of the Kara event touched the sedimentary rocks abundant with black shales and carbonates, which should be a result of essential atmospheric changes. The study has been supported by the Russian Science Foundation project #17-17-01080.

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Anisotropy of magnetic susceptibility (AMS) of impact melt breccia and target rocks from the Dhala impact structure, India

Large Meteorite Impacts and Planetary Evolution VI ◽

10.1130/2021.2550(14) ◽

2021 ◽

Author(s):

Anuj Kumar Singh ◽

Jayanta Kumar Pati ◽

Shiva Kumar Patil ◽

Wolf Uwe Reimold ◽

Arun Kumar Rao ◽

...

Keyword(s):

Magnetic Susceptibility ◽

Anisotropy Of Magnetic Susceptibility ◽

Impact Structure ◽

Magnetic Phases ◽

Impact Melt ◽

Rock Samples ◽

Average Value ◽

Magnetic Fabrics ◽

Target Rock ◽

The Impact

ABSTRACT The ~11-km-wide, Paleoproterozoic Dhala impact structure in north-central India comprises voluminous exposures of impact melt breccia. These outcrops are discontinuously spread over a length of ~6 km in a semicircular pattern along the northern, inner limit of the monomict breccia ring around the central elevated area. This study of the magnetic fabrics of impact breccias and target rocks from the Dhala impact structure identified a weak preferred magnetic orientation for pre-impact crystalline target rocks. The pre- and synimpact rocks from Dhala have magnetite and ilmenite as common magnetic phases. The distributions of magnetic vectors are random for most impact melt breccia samples, but some do indicate a preferred orientation. Our anisotropy of magnetic susceptibility (AMS) data demonstrate that the shape of susceptibility ellipsoids for the target rocks varies from prolate to oblate, and most impact melt breccia samples display both shapes, with a slight bias toward the oblate geometry. The average value for the corrected degree of anisotropy of impact melt rock (P′ = 1.009) is lower than that for the target rocks (P′ = 1.091). The present study also shows that both impact melt breccia and target rock samples of the Dhala structure have undergone minor postimpact alteration, and have similar compositions in terms of magnetic phases and high viscosity. Fine-grained iron oxide or hydroxide is the main alteration phase in impact melt rocks. Impact melt rocks gave a narrow range of mean magnetic susceptibility (Km) and P′ values, in contrast to the target rock samples, which gave Km = 0.05–12.9 × 10−3 standard international units (SI) and P′ = 1.036–1.283. This suggests similar viscosity of the source magma, and limited difference in the degrees of recorded deformation. Between Pagra and Maniar villages, the Km value of impact melt breccias gradually decreases in a clockwise direction, with a maximum value observed near Pagra (Km = 1.67 × 10−3 SI). The poor grouping of magnetic fabrics for most impact melt rock samples implies local turbulence in rapidly cooled impact melt at the front of the melt flow immediately after the impact. The mean K1 for most impact melt samples suggests subhorizontal (<5°) flow in various directions. The average value of Km for the target rocks (4.41 × 10−3 SI) is much higher compared to the value for melt breccias (1.09 × 10−3 SI). The results of this study suggest that the melt breccias were likely part of a sheet-like body of sizeable extent. Our magnetic fabric data are also supported by earlier core drilling information from ~70 locations, with coring depths reaching to −500 m. Our extensive field observations combined with available widespread subsurface data imply that the impact melt sheet could have covered as much as 12 km2 in the Dhala structure, with an estimated minimum melt volume of ~2.4 km3.

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