Roger Hewins

Roger Hewins
Rutgers, The State University of New Jersey | Rutgers · Department of Earth and Planetary Sciences

About

313
Publications
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5,200
Citations
Citations since 2017
24 Research Items
1798 Citations
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20172018201920202021202220230100200300
20172018201920202021202220230100200300
20172018201920202021202220230100200300

Publications

Publications (313)
Article
The mechanisms responsible for the formation of Fe-rich, metasomatic features in eucrites and their debris in howardites are yet controversial. In this study, secondary phases found in polymict eucrite NWA (Northwest Africa) 11911, howardite NWA 1664, monomict eucrite NWA 8675 and unbrecciated basaltic eucrite NWA 13269 were investigated to elucida...
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The formation and differentiation of the crust of Mars in the first tens of millions of years after its accretion can only be deciphered from incredibly limited records. The martian breccia NWA 7034 and its paired stones is one of them. This meteorite contains the oldest martian igneous material ever dated: ~4.5 Ga old. However, its source and geol...
Article
The formation of chondrules involved major processes in the protoplanetary disk and therefore needs to be understood. Identifying possible precursors and the conditions of their transformation into chondrules is an essential step. Here we investigate whether refractory inclusions (RI) can be converted into Type IA chondrule analogs by isothermal he...
Article
In order to understand the nature of the dust that accreted onto chondrules in the nebula and to unravel the conditions of formation of fine grained rims (FGRs), we studied three of the least altered chondrites from different chondrite groups (LL3.00 Semarkona, CO3.0 DOM 08006, CR2.8 QUE 99177) and compared the results with our previous work on the...
Conference Paper
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Northwest Africa 7533 (and Northwest Africa 7034 pairing group) is an exceptional martian meteorite as it is a regolith breccia giving unique access to the martian crust [1]. Together with in situ observations by MSL Curiosity [2] and reconstruction models of the primitive crust [3], this meteorite has completely changed our view of the martian cru...
Article
Many asteroids in the main belt have spectra like those of Mighei-type CM chondrites, but some Near Earth Objects (NEO) resemble less well known types of C2 chondrite. Northwest Africa (NWA) 12563, a new find with affinities to C2 chondrites, could help us understand the differences between observations of CM2 chondrites and bodies that are current...
Article
Mars was habitable in its early history, but the consensus is that it is quite inhospitable today, in particular because its modern climate cannot support stable liquid water at the surface. Here, we report the presence of magmatic Fe/Mg clay minerals within the mesostasis of the martian meteorite NWA 5790, an unaltered 1.3 Ga nakhlite archetypal o...
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The Martian breccias NWA 7034, NWA 7533, and paired meteorites record events ranging in age from 4.47 Ga to <200 Ma. Published ages indicate a period of major disturbance at ~1.4 Ga, examined in detail here through 40Ar/39Ar dating of handpicked grains and two small chips. Argon diffusion parameters were obtained for six samples. Also presented are...
Article
Fine-grained rims (FGRs) are ubiquitous in chondrites. They consist of unequilibrated mineral assemblages that surround chondrules and refractory inclusions. As such, they carry information about the material that was accreted onto chondrules. To decipher the nature and the formation mechanism of FGRs and compare them to adjacent matrix material, w...
Article
The sulfur isotope budget of Martian regolith breccia (NWA 7533) has been addressed from conventional fluorination bulk rock analyses and ion microprobe in situ analyses. The bulk rock analyses yield 865 ± 50 ppm S in agreement with LA‐ICP‐MS analyses. These new data support previous estimates of 80% S loss resulting from terrestrial weathering of...
Article
The origin(s) of the chassignites and nakhlites, closely related martian olivine and augite cumulates, respectively, are much debated. Northwest Africa (NWA) 8694 is the third chassignite to be discovered and the most ferroan, containing 85% olivine (Fo54). Its O-isotope compositions (δ¹⁸O ∼ 4.4‰, Δ¹⁷O ∼ 0.30‰) are typical of other martian meteorit...
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Full-text available
The global-scale crustal structure of Mars is shaped by impact basins, volcanic provinces, and a hemispheric dichotomy with a thin crust beneath the northern lowlands and a thick crust beneath the southern highlands. The southern highlands are commonly treated as a coherent terrain of ancient crust with a common origin and shared geologic history,...
Article
Northwest Africa (NWA) 10414 is an unusual shergottite with a cumulate texture. It contains 73% coarse prismatic pigeonite, plus 18% interstitial maskelynite, 2% Si‐rich mesostasis, 2% merrillite, and minor chromite‐ulvöspinel. It contains no olivine, and only ~3% augite. Phase compositions are pigeonite (En68‐43Fs27‐48Wo5‐15) and maskelynite An~54...
Article
Numerous geosciences samples display a multi-scale mineralogical heterogeneity for which it is challenging to obtain spatially resolved quantitative chemical data. It is the case for chondritic meteorites, which can contain up to 10 different phases with grain size ranging from the nanometer to the millimeter. We developed a method providing multip...
Article
Unlike other martian meteorites studied so far, Martian regolith breccia NWA 7533 and paired meteorites that have sampled 4.4 Ga-old impact lithologies show only sulfides of hydrothermal origin (mostly pyrite (<1 vol.%) and scarce pyrrhotite). NWA 7533 pyrite has been analyzed for 25 chalcophile-siderophile trace elements with laser ablation-induct...
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The Chassigny meteorite, a martian dunite, contains trace amounts (0.005 vol%) of Fe-Ni sulfides, which were studied from two polished mounts in reflected light microscopy, scanning electron microscope (SEM), and electron microprobe (EMP). The sulfide phases are, by decreasing order of abundance, nickeliferous (0-3 wt% Ni) pyrrhotite with an averag...
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It has been proposed that some meteorites, CB and CH chondrites, contain material formed as a result of a protoplanetary collision during accretion. Their melt droplets (chondrules) and FeNi metal are proposed to have formed by evaporation and condensation in the resulting impact plume. We observe that the SO (skeletal olivine) chondrules in CBb ch...
Article
Cooling rates are one of the few fundamental constraints on models of chondrule formation. In this study, we used Cu and Ga diffusion profiles in metal grains to determine the cooling rates of type I chondrules in the Renazzo CR2 chondrite. To improve previous estimations of cooling rates obtained using this method, we used CT scanning and serial p...
Article
We conducted a transmission electron microscope study of the exsolution microstructures of Ca-rich pyroxenes in type I chondrules from the Paris CM and Renazzo CR carbonaceous chondrites in order to provide better constraints on the cooling history of type I chondrules. Our study shows a high variability of composition in the augite grains at a sub...
Article
Northwest Africa 7533, a polymict Martian breccia, consists of fine-grained clast-laden melt particles and microcrystalline matrix. While both melt and matrix contain medium-grained noritic-monzonitic material and crystal clasts, the matrix also contains lithic clasts with zoned pigeonite and augite plus two feldspars, microbasaltic clasts, vitroph...
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Northwest Africa (NWA) 7533 is a Martian regolith breccia. This meteorite (and its pairings) offers a good opportunity to study (near-) surface processes that occurred on early Mars. Here, we have conducted a transmission electron microscope study of medium- and coarse-grained (a few tens to hundreds of micrometers) Ca-rich pyroxene clasts in order...
Article
Until recently, Mars was considered a basalt-covered world, but this vision is evolving thanks to new orbital, in situ and meteorite observations, in particular of rocks of the ancient Noachian period. In this contribution we summarize newly recognized compositional and mineralogical differences between older and more recent rocks, and explore the...
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Martian regolith breccia NWA 7533 (and the seven paired samples) is unique among Martian meteorites in showing accessory pyrite (up to 1% by weight). Pyrite is a late mineral, crystallized after the final assembly of the breccia. It is present in all of the lithologies, i.e., the fine-grained matrix (ICM), clast-laden impact melt rocks (CLIMR), mel...
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The Martian surface is covered by a fine-layer of oxidized dust responsible for its red color in the visible spectral range (Bibring et al., 2006; Morris et al., 2006). In the near infrared, the strongest spectral feature is located between 2.6 and 3.6 μm and is ubiquitously observed on the planet (Jouglet et al., 2007; Milliken et al., 2007). Alth...
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The Paris meteorite is a weakly altered CM chondrite that has been discovered recently (Hewins et al., 2014). Its matrix offers the opportunity to search for well-preserved pristine pre-accretional material, as well as to study the earliest stages of aqueous alteration in the CM parent body. The study of the matrix of Paris has been conducted by an...
Conference Paper
Full-text available
Introduction: Chondrules are ubiquitous components of carbonaceous chondrites (CCs) [e.g., 1]. Since the recognition of the igneous texture of chondrules by [2], numerous heating mechanisms have been proposed for chondrule formation, which were extensively commented and reviewed [e.g., 3]. The most evolved models involve either the Sun to explain t...
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The matrix of NWA 7533 is a submicrometer granoblastic assemblage, partly sintered. The grain boundaries show evidence for a late-stage destabilization.
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Martian meteorite NWA 7533 is a regolith breccia that compositionally resembles the Martian surface measured by orbiters and landers. NWA 7533 contains monzonitic clasts that have zircon with U–Pb ages of 4.428 Ga. The Pb isotopic compositions of plagioclase and alkali feldspars, as well as U–Pb isotopic compositions of chlorapatite in the monzonit...
Conference Paper
Introduction: Isheyevo, classified as a CH/CB-like chondrite, consists of a mixture, in various proportions, of nebular and impact-produced materials [e.g. 1–4]. Although the Isheyevo, CH, and CB chondrites appear to be genetically linked, the origin of these metal-rich chondrites remains debated [e.g. 5– 10]. The study of the peculiar texture of I...
Conference Paper
Introduction: The origin of the metal-rich CH and CB chondrites is still debated. Both nebular [e.g. 1–4] and planetary processes [e.g. 5–9] have been proposed to explain the mineralogy and chemistry of their components. The Isheyevo meteorite displays numerous similarities with CB and CH chondrites [e.g. 10], as well as prominent metal-silicate la...
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Mars exhibits ample evidence for an ancient surface hydrosphere. The oxygen isotope compositions of carbonate minerals and alteration products in martian meteorites suggest that this ancient hydrosphere was not in isotopic equilibrium with the martian lithosphere(1-4). Martian meteorite NWA 7533 is composed of regolith breccia from the heavily crat...
Article
Although petrologic, chemical and isotopic studies of ordinary chondrites and meteorites in general have largely helped establish a chronology of the earliest events of planetesimal formation and their evolution, there are several questions that cannot be resolved via laboratory measurements and/or experiments only. Here we propose rationale for se...
Article
Mercury is notorious as the most reduced planet with the highest metal/silicate ratio, yet paradoxically data from the MESSENGER spacecraft show that its iron-poor crust is high in sulfur (up to ∼6 wt%, ∼80× Earth crust abundance) present mainly as Ca-rich sulfides on its surface. These particularities are simply impossible on the other terrestrial...
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We determined the cooling rate of a Type I chondrule in Renazzo to provide additional constraints on the heating mechanisms proposed for chondrule formation.
Conference Paper
Type I chondrules cooling rates were determined by a TEM study of exsolution in Ca-rich pyroxenes revealing different cooling rates, as for type II chondrules.
Article
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Despite solid-state secondary processes, a metal grain in Renazzo displays igneous features formed by the fractional crystallization of a CR-type liquid metal.
Article
Weathering of an olivine-bearing regolith to form Fe-oxides, followed by impact melting, creates an opx and magnetite mineralogy in the early martian crust.
Conference Paper
Composition properties of matrices at a submicrometer scale are established for two primitive chondrites (Acfer 94 and Paris) and compared with that of GEMS in IDPs.
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This martian breccia contains feldspathic clasts with Ni-rich pyroxene and some Ni-poor orthopyroxene clasts, respectively interpreted as impact-related and pristine material.
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Oxygen-isotope compositions of zircon from martian meteorite NWA 7533 suggest existence of different oxygen reservoirs during zircon formation and alteration.
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The nature of hydration products in the martian meteorite NWA 7533 enables us to unravel the hydration of surface dust and the 3-µm band of Mars.
Article
The Paris chondrite provides an excellent opportunity to study CM chondrules and refractory inclusions in a more pristine state than currently possible from other CMs, and to investigate the earliest stages of aqueous alteration captured within a single CM bulk composition. It was found in the effects of a former colonial mining engineer and may ha...
Article
77th Annual Meeting of the Meteoritical-Society, Casablanca, MOROCCO, SEP 08-13, 2014
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The ancient cratered terrain of the southern highlands of Mars is thought to hold clues to the planet's early differentiation, but until now no meteoritic regolith breccias have been recovered from Mars. Here we show that the meteorite Northwest Africa (NWA) 7533 (paired with meteorite NWA 7034) is a polymict breccia consisting of a fine-grained in...
Article
We present a description of opaque minerals, opaque mineral compositions, magnetic properties, and paleomagnetic record of the Tissint heavily shocked olivine-phyric shergottite that fell to Earth in 2011. The magnetic mineralogy of Tissint consists of about 0.6 wt% of pyrrhotite and 0.1 wt% of low-Ti titanomagnetite (in the range ulvöspinel 3-15 m...
Article
Ordinary chondrite meteorites (OCs) are by far the most abundant meteorites (80% of all falls). Their study along with that of other chondrite classes has provided numerous constraints on the formation and early evolution of the solar system, including a) the migration processes that occurred in the protoplanetary disk prior to primary accretion (i...
Article
NWA 7533 is a pre-Noachian regolith breccia, containing siderophiles consistent with 5% chondritic impactor, 4.44 Ga zircons, and LILE enrichments implying a crustal thickness of 50 km established in the first 100 Ma of martian history.
Conference Paper
NWA 7533 contains FeNi grains (~1μm), up to 4.5% Ni in pyrite, and 500 nm Os-Ir-rich particles. Lithic clasts are pyroxenite, norite and zircon-bearing monzonite. The impact melt can be modeled as a mixture of crystal clasts and is poor in monzonite.
Article
Implications of the matrix chemistry of the new martian impact breccia, NWA 7533, for the origin of martian soils and crustal thickness will be presented.
Conference Paper
We present a TEM study on the weakly altered Paris CM chondrite to specify the first stages of evolution of the fine-grained components in a CM parent body.
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Tissint (Morocco) is the fifth martian meteorite collected after it was witnessed falling to Earth. Our integrated mineralogical, petrological, and geochemical study shows that it is a depleted picritic shergottite similar to EETA79001A. Highly magnesian olivine and abundant glass containing martian atmosphere are present in Tissint. Refractory tra...
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We present the magnetic mineralogy and paleomagnetic signal of Tissint.
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We recognize five populations of olivine with FeO/MnO ratios. OC Type II chondrules formed in a more reduced reservoir than most CC Type II chondrules, consistent with metal fractionation in OC.
Article
Despite its 3.0 petrographic type, alteration features are observed in NWA 5958 by SEM observations. Magnetometry suggests the presence of Fe-phyllosilicates, as in the Paris CM. These two CCs allow us to study early stages of hydrothermal alteration.
Article
The large number of pallasite parent bodies suggests that their formation was a common event in asteroid evolution. New microprobe data has been generated for pallasite olivines and chromites that indicate subsolidus redox processes, while literature data has been collated and correlated to form new results and interpretations. The new data include...
Article
Chondrule compositions suggest either ferroan precursors and evaporation, or magnesian precursors and condensation. Type I chondrule precursors include granoblastic olivine aggregates (planetary or nebular) and fine-grained (dustball) precursors. In carbonaceous chondrites, type I chondrule precursors were S-free, while type II chondrules have high...
Article
LA-ICP-MS analyses of unaltered matrix, chondrules, and bulk CM and CR chondrites show that the preaccretionary matrix had a CI composition. Chondrules could have formed in the inner disk and been transported to be embedded in matrix further out.
Article
We have investigated the Na distributions in Semarkona Type II chondrules by electron microprobe, analyzing olivine and melt inclusions in it, mesostasis and bulk chondrule, to see whether they indicate interactions with an ambient gas during chondrule formation. Sodium concentrations of bulk chondrule liquids, melt inclusions and mesostases can be...
Article
In Paris (CM) Type II chondrules, olivine cores are Fa7-76 with Fa1-19 relics. Fe-Mn correlations show that CM and LL chondrules come from different reservoirs and formed by condensation of Fe and Mn onto Type I material in a late oxidizing environment.
Article
Paris has a CM bulk chemistry (volat. depleted/refract. enriched), but ~40vol% of it was preserved from PB-alteration. Matrix is CI in unaltered zones and closer to the bulk elsewhere. These data are consistent with the two-component model of Anders.
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Part I. Introduction: 1. Chondrules and the protoplanetary disk: An overview R. H. Hewins; Part. II. Chonrules, Ca-Al-Rich Inclusions and Protoplanetary Disks: 2. Astronomical observations of phenomena in protostellar disks L. Hartmann; 3. Overview of models of the solar nebula: potential chondrule-forming environments P. Cassen; 4. Large scale pro...
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The formation of phosphoran olivine by crystallization from a melt was investigated experimentally using a one atmosphere furnace, using San Carlos olivine [(Mg,Fe)2SiO4] mixed with either iron phosphide (FeP) or magnesium pyrophosphate (Mg2P2O7). Both dynamic crystallization and isothermal experiments produced phosphoran olivine as zoned single cr...