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21.
Prepared by the MSR Campaign Science Group A. D. Czaja M.-P. Zorzano the rest of the MCSG team with Chairs G. Kminek M. A. Meyer Members D. W. Beaty E. Sefton-Nash B. L. Carrier F. Thiessen T. Haltigin A. Bouvier N. Dauphas K. L. French L. J. Hallis R. L. Harris E. Hauber L. E. Rodriguez S. P. Schwenzer A. Steele K. T. Tait M. T. Thorpe T. Usui J. Vanhomwegen M. A. Velbel S. Edwin K. A. Farley D. P. Glavin A. D. Harrington L. E. Hays A. Hutzler M. Wadhwa 《Meteoritics & planetary science》2023,58(6):885-896
The Mars 2020/Mars Sample Return (MSR) Sample Depot Science Community Workshop was held on September 28 and 30, 2022, to assess the Scientifically-Return Worthy (SRW) value of the full collection of samples acquired by the rover Perseverance at Jezero Crater, and of a proposed subset of samples to be left as a First Depot at a location within Jezero Crater called Three Forks. The primary outcome of the workshop was that the community is in consensus on the following statement: The proposed set of ten sample tubes that includes seven rock samples, one regolith sample, one atmospheric sample, and one witness tube constitutes a SRW collection that: (1) represents the diversity of the explored region around the landing site, (2) covers partially or fully, in a balanced way, all of the International MSR Objectives and Samples Team scientific objectives that are applicable to Jezero Crater, and (3) the analyses of samples in this First Depot on Earth would be of fundamental importance, providing a substantial improvement in our understanding of Mars. At the conclusion of the meeting, there was overall community support for forming the First Depot as described at the workshop and placing it at the Three Forks site. The community also recognized that the diversity of the Rover Cache (the sample collection that remains on the rover after placing the First Depot) will significantly improve with the samples that are planned to be obtained in the future by the Perseverance rover and that the Rover Cache is the primary target for MSR to return to Earth. 相似文献
22.
Contrasts between cloud condensation nuclei (CCN) spectral volatility (thermal fractionation) measurements in two aircraft
field projects provide insight into the relative contribution of sea salt. During the much more cloudy Rain in Cumulus over
the Ocean (RICO) project there was a high correlation coefficient (R) between refractory (non-volatile) CCN concentrations
(NCCN) and horizontal wind speed (U), especially for low supersaturation (S) NCCN, whereas this R was significantly lower in the nearly cloud free Pacific Aerosol Sulfur Experiment (PASE) project. Volatile
NCCN at all S were uncorrelated with U. Ambient particle concentrations over a broad range of large sizes displayed consistently
high R with U in both projects that was similar to the R of refractory NCCN with U in RICO. The size range of this high R extended down to 0.2 μm in RICO but only down to 9 μm in PASE. In both projects
particle concentrations smaller than these respective sizes were highly correlated with NCCN, at all S in PASE, but mainly with NCCN at high S in RICO. In each project NCCN at all S was uncorrelated with all ambient particle concentrations larger than these same respective sizes. NCCN at all S was also uncorrelated with U in both projects. The contrast in cloudiness between the two projects was responsible
for many of the differences noted between the two projects. The results indicate that the effects of clouds on NCCN play a major role in the relative influence of sea salt on NCCN and ultimately on climate. Sea salt is a minor component of maritime CCN except at high wind speeds especially at low S. 相似文献
23.
Meenakshi Wadhwa 《Meteoritics & planetary science》2013,48(9):1705-1706
24.
J. Brian Balta Matthew Sanborn Harry Y. McSween Jr. Meenakshi Wadhwa 《Meteoritics & planetary science》2013,48(8):1359-1382
Several olivine‐phyric shergottites contain enough olivine that they could conceivably represent the products of closed‐system crystallization of primary melts derived from partial melting of the Martian mantle. Larkman Nunatak (LAR) 06319 has been suggested to represent a close approach to a Martian primary liquid composition based on approximate equilibrium between its olivine and groundmass. To better understand the olivine–melt relationship and the evolution of this meteorite, we report the results of new petrographic and chemical analyses. We find that olivine megacryst cores are generally not in equilibrium with the groundmass, but rather have been homogenized by diffusion to Mg# 72. We have identified two unique grain types: an olivine glomerocryst and an olivine grain preserving a primary magmatic boundary that constrains the time scale of eruption to be on the order of hours. We also report the presence of trace oxide phases and phosphate compositions that suggest that the melt contained approximately 1.1% H2O and lost volatiles during cooling, also associated with an increase in oxygen fugacity upon degassing. We additionally report in situ rare earth element measurements of the various mineral phases in LAR 06319. Based on these reported trace element abundances, we estimate the oxygen fugacity in the LAR 06319 parent melt early in its crystallization sequence (i.e., at the time of crystallization of the low‐Ca and high‐Ca pyroxenes), the rare earth element composition of the parent melt, and those of melts in equilibrium with later formed phases. We suggest that LAR 06319 represents the product of closed‐system crystallization within a shallow magma chamber, with additional olivine accumulated from a cumulate pile. We infer that the olivine megacrysts are antecrysts, derived from a single magma chamber, but not directly related to the host magma, and suggest that mixing of antecrysts within magma chambers may be a common process in Martian magmatic systems. 相似文献
25.
M. Wadhwa Y. Amelin O. Bogdanovski A. Shukolyukov P. Janney 《Geochimica et cosmochimica acta》2009,73(17):5189-5323
Asuka 881394 is a unique basaltic meteorite that originated in the crust of a differentiated planetesimal in the early Solar System. We present high precision Pb, Mg, and Cr isotopic compositions of bulk samples and mineral separates from this achondrite. A 207Pb-206Pb internal isochron obtained from the radiogenic pyroxene and whole-rock fractions of Asuka 881394 yields an absolute age of 4566.5 ± 0.2 Ma, which we consider to be the best estimate for the crystallization age of this basaltic achondrite. The 26Al-26Mg systematics show some evidence of disturbance, but 5 of the 6 analyzed whole-rock and mineral fractions define an isochron corresponding to a 27Al/26Al ratio of (1.28 ± 0.07) × 10−6. Comparison with the 26Al-26Mg and Pb-Pb systematics in the D’Orbigny achondrite translates to a 26Al-26Mg age of 4565.4 ± 0.2 Ma for Asuka 881394. The 53Mn-53Cr systematics in whole-rock, silicate and chromite fractions correspond to a 53Mn/55Mn ratio of (3.85 ± 0.23) × 10−6. Compared to the most precise 53Mn-53Cr and Pb-Pb systematics available for the D’Orbigny angrite, this translates to a 53Mn-53Cr age of 4565.3 ± 0.4 Ma; similarly, a comparison with the NWA 4801 angrite yields a 53Mn-53Cr age of 4565.5 ± 0.4 Ma, in agreement with the age obtained relative to D’Orbigny. While the 26Al-26Mg and 53Mn-53Cr ages appear to be concordant in Asuka 881394, these ages are ∼1 Ma younger than its 207Pb-206Pb age. This discordance might have been caused by one or more of several reasons, including differences in the closure temperatures for Pb versus Cr and Mg diffusion in their host minerals combined with slow cooling of the parent body as well as differential resetting of isotopic systems by a process other than volume diffusion, e.g., shock metamorphism. The ancient age of Asuka 881394 suggests that basaltic volcanism on its parent planetesimal occurred within ∼3 Ma of the formation of earliest solids in the Solar System, essentially contemporaneously with chondrule formation. This requires that the Asuka 881394 parent body was fully accreted within ∼500,000 yrs of Solar System formation. 相似文献
26.
Summary The problem of a transition layer lying between two homogeneous liquid media is discussed. After obtaining the formal solution for a periodic point source lying in the upper layer, the integrand in the expression for the displacement potential of the upper layer is expanded into series of negative powers of exponentials. Some of the terms in the Bromwich expansion are then evaluated along the Sommerfeld loops which give various reflected and refracted waves. The results for the refracted waves are discussed for the two extreme cases, when frequency is extremely low and extremely high. In both the cases it is found that the frequency dependence for refraction arrivals is the same as expected from a sharp boundary, viz., –1. And that for high frequency the travel-time of refraction arrivals is the same as expected from geometric ray theory. Both first- order and second-order discontinuities in density and bulk modulus are considered at the boundaries of the transition layer. 相似文献
27.
Miss Santosh Kumari Wadhwa 《Pure and Applied Geophysics》1971,89(1):67-83
Summary The problem of a periodic point source in a homogeneous liquid layer overlying a heterogeneous liquid half-space is discussed. After obtaining the formal solution, the path of integration for the displacement potential of the layer is transformed from the positive real axis to the positive imaginary axis and the Sommerfeld contour and the latter is further distorted to the modified Sommerfeld contour. The residues of the integrand at the poles contained within the Sommerfeld loop constitute the normal mode solution to the problem. The integrands in the expressions for the integrals along the imaginary axis are expanded in a series of negative powers of exponentials and then some of the terms in these expansions are evaluated approximately. This gives various waves reflected from the interface and the integral along the Sommerfeld loop
vanishes. The frequency equation is obtained, also by the principle of constructive interference. An expression for the reflection coefficient at an interface of two liquid media, the upper medium being homogeneous and the lower one inhomogeneous, is obtained. 相似文献
28.
Sahendra Singh Karun Kumar Chandan Vandana Jha 《Journal of the Geological Society of India》2018,92(2):166-172
The Mesoproterozoic metasedimentary units of Chandil Formation belong to the northern part of Singhbhum crustal province, eastern India. The Formation lies north of Dalma volcano-sedimentary belt and is separated from the Meso- Neoproterozoic Chhotanagpur granite gneissic complex (CGGC) by Tamar-Porapahar shear zone (TPSZ), i.e. South Purulia shear zone, (SPSZ) at its northern boundary. The metasedimentary unit comprises of quartz-mica-sericite-schist, quartzite, amphibolites and carbonaceous phyllites, which have not been studied well, so far in terms of their geochemistry, source rock and provenance characterization. In this work, the existing gaps in all those aspects are studied to infer the provenance of these metasedimentary sequences. The high silica contents of the Chandil Formation (~95% for the quartzites and ~70% for the metapelites) and low trace element concentrations indicate silica-rich source. The REE patterns of the quartzites and the metapelites exhibit LREE enrichment and HREE depletion with moderate negative Eu-anomalies which strongly favor felsic nature of the provenance. The significant enrichment of LREE, flat HREE patterns and negative Eu-anomalies of the metapelites suggest their derivation from an old upper continental crust, which is composed of felsic components and the negative Eu-anomalies indicate intra-crustal differentiation. The higher concentrations of the HFSE i.e. Zr, Hf and Ta, within the Chandil metasediments relative to those of EPC (Early Proterozoic Continental Crust), also suggests a felsic provenance. The geochemical signatures of the Chandil metasediments indicate that the sediments were derived during a prolonged period of weathering due to the slow upliftment and unroofing of the southern evolving Singhbhum granitic complex (SGC). 相似文献
29.
30.
C.K. Shearer P.V. Burger Z. Sharp L. Borg J.J. Papike M. Wadhwa J. Shafer N.-V. Atudorei B.P. Weiss S.A. Crowther 《Geochimica et cosmochimica acta》2010,74(3):1172-1199
The recently recovered paired Antarctic achondrites Graves Nunatak 06128 and 06129 (GRA) are meteorites that represent unique high-temperature asteroidal processes that are identified in only a few other meteorites. The GRA meteorites contain high abundances of sodic plagioclase, relatively Fe-rich pyroxenes and olivine, abundant phosphates, and low temperature alteration. They represent products of very early planetesimal melting (4565.9 ± 0.3 Ma) of an unsampled geochemical reservoir from an asteroid that has characteristics similar to the brachinite parent body. The magmatism represented by these meteorites is contrary to the commonly held belief that the earliest stages of melting on all planetary bodies during the first 2-30 Ma of solar system history were fundamentally basaltic in nature. These sodic plagioclase-rich rocks represent a series of early asteroidal high-temperature processes: (stage 1) melting and partial extraction of a low-temperature Fe-Ni-S melt, (stage 2) small degrees of disequilibrium partial melting of a sodium- or alkali-rich chondritic parent body with additional incorporation of Fe-Ni-S melt that was not fully extracted during stage 1, (stage 3) volatile-enhanced rapid extraction and emplacement of the Na-rich, high-normative plagioclase melt, (stage 4) final emplacement and accumulation of plagioclase and phosphates, (stage 5) subsolidus reequilibration of lithology between 962 and 600 °C at an fO2 of IW to IW + 1.1, and (stage 6) replacement of merrillite and pyroxene by Cl-apatite resulting from the interaction between magmatic minerals and a Cl-rich fluid/residuum melt. The subsolidus events started as early as 4561.1 Ma and may have continued for upwards of 144 million years.The existence of assemblages similar to GRA on several other planetary bodies with different geochemical characteristics (ureilite, winonaites, IAB irons) implies that this type of early asteroidal melting was not rare. Whereas, eucrites and angrites represent extensive melting of a parent body with low concentrations of moderately-volatile elements, GRA represents low-degrees of melting of a parent body with chondritic abundances of moderately volatile elements. The interpretation of the low-temperature mineral assemblage is somewhat ambiguous. Textural features suggest multiple episodes of alteration. The earliest stage follows the interaction of magmatic assemblages with a Cl-rich fluid. The last episode of alteration appears to cross-cut the fusion crust and earlier stages of alteration. Stable isotopic measurements of the alteration can be interpreted as indicating that an extraterrestrial volatile component was preserved in GRA. 相似文献