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Three very low-Ti (VLT) basalt fragments (two with granular texture and one with granular to subophitic texture) were found during a study of light-colored lithic fragments hand-picked from the Apollo-17 deep drill core. In the present paper, some unique features of these fragments are revealed.
Possible components of the ancient solar wind, particularly the N-15/N-14 ratio, are investigated on the basis of lunar microbreccia studies. Nitrogen contents and isotope ratios were determined for Apollo 11 and 15 microbreccia samples by means of vacuum pyrolysis techniques. The Apollo 11 soil breccias, which had been closed to the addition of recent solar wind due to their compaction, are found to contain the lowest N-15/N-14 ratios yet reported for the solar wind, extending the range of variation of the ratio to between a delta N-15 of -190% in the past to +120% at present. Nitrogen isotope analysis of the Apollo 15 drill core, which had undergone two episodes of solar wind exposure, also support the secular variation in the N-15 content of the solar wind, which is attributed to spallation reactions in the sun. The formation of the breccias at the Apollo 11 and 15 sites is discussed on the basis of the observed nitrogen systematics, and differences between N-15 and Ne-21 cosmic ray exposure ages implied are attributed to the diffusive loss of neon from lunar soils.
Proposed machine would sample rock or soil automatically. Mounted on a wheeled or tracked vehicle, machine positions drill for cut at any angle from horizontal to vertical, moves power head to drive drill into cut, and stores drilled core in a container. New concept may also be useful in terrestrial agricultural and geologic surveys.
The lunar soil is an efficient trap for nitrogen in the solar wind. The concentration of nitrogen in lunar soils implies a flux of solar wind at least three times greater than that which is observed today. The implication is that the present-day flux is anomalously low. Soil samples from drill cores, and soil breccias excavated from buried levels of the regolith provide samples of ancient solar wind. From these samples it is apparent that the N-15/N-14 ratio in the solar wind has undergone a monotonic secular increase over the last 2.5 billion years, at a rate of about 15% per billion years. Nuclear reactions in the sun appear to be the most likely cause of the variation.
Topics discussed include studies of chondrites, mesosiderites, and achondrites; isotope modeling; Antarctic weathering; irradiation effects; lunar regolith studies; the Apollo 17 drill core; soils and agglutinates; and volatiles. Particular attention is given to the proportional retention of I and Xe-129 in preheated Allende, olivine clasts from mesosiderites and howardites as clues to the nature of achondritic parent bodies, a record of solar corpuscular radiation in minerals from lunar soils, the experimental shock metamorphism of lunar soil, and the clouding of pyroxene and plagioclase in eucrites.
The two current models to explain the nearly 40% variation of the lunar nitrogen isotopic composition are: (1) secular variation of solar wind nitrogen; and (2) a two component mixing model having a constant, heavy solar wind admixed with varying amounts of indigenous light lunar N (LLN). Both models are needed to explain the step pyrolysis extraction profile. The secular variation model proposes that the low temperature release is modern day solar wind implanted into grain surfaces, the 900 C to 1100 C release is from grain surfaces which were once exposed to the ancient solar wind but which are now trapped inside agglutinates, and the >1100 C release as spallogenic N produced by cosmic rays. The mixing model ascribes the components to solar wind, indigenous lunar N and spallogenic N respectively. An extension of either interpretation is that the light N seen in lunar breccias or deep drill cores represent conditions when more N-14 was available to the lunar surface.
A hydrogen-oxygen fuel cell system is identified as a viable power source for a long range inhabited surface transportation system for the exploration of Mars. Power system weights and power requirements are determined as a function of vehicle weight. For vehicles weighing from 2700 to 7300 kg in LEO, the total power system weight ranges from 1140 to 1860 kg, with the reactants and energy conversion hardware (fuel cells, reactant storage, and radiator) weighing 430 to 555 kg and 610 to 1110 kg, respectively. Vehicle power requirements range from 45 kW for a 2700 kg vehicle to 110 kW for a 7300 kg vehicle. Power system specific weights and power profiles for housekeeping and the operation of scientific equipment such as coring drills and power tools are also specified.
It is shown that the distribution of refractory metals in a comet-nucleus drill core carries a chemical memory quite distinct from that of volatiles. Using aluminum as an example, it is demonstrated that very refractory structures, either grain cores or refractory aggregates of cores, must be much older than the volatile component. It is argued that isotopic anomalies are specifically associated with aluminum. An evolutionary model capable of rationalizing the interstellar gas depletions of Al and Mg is advocated. The distribution of Al in comets is shown to be crucial to understanding the origin of comets and of the solar system.
Three modes for obtaining samples of cometary material: remote sampling, hover mode sampling, and landed (anchored) sampling are discussed. For each mode, trade-offs involving complexity, risk factors, and cost must be analyzed for the spacecraft and the sampling system. Flyby results for comet Halley indicate heterogeneity in the cometary nucleus that could dictate sampling at several different locations. Coring drills, drive tubes, and specialized mantle sampling devices must operate at cold temperatures (100 to 180 K) without heating the sample. Sample selections must be accomodated by the sample return canister, which must also be protected from thermal excursions.
Planar microdeformations in quartz from basement or collar rocks of the Vredefort Dome have been cited for years as the main microtextural evidence for shock metamorphism in this structure. In addition, Schreyer describes feldspar recrystallization in rocks from the center of the Dome as the result of transformation of diaplectic glass, and Lilly reported the sighting of mosaicism in quartz. These textural observations are widely believed to indicate either an impact or an internally produced shock origin for the Vredefort Dome. Two types of (mostly sub) planar microdeformations are displayed in quartz grains from Vredefort rocks: (1) fluid inclusion trails, and (2) straight optical discontinuities that sometimes resemble lamellae. Both types occur as single features or as single or multiple sets in quartz grains. Besides qualitative descriptions of cleavage and recrystallization in feldspar and kinkbands in mica, no further microtextural evidence for shock metamorphism at Vredefort has been reported to date. Some 150 thin sections of Vredefort basement rocks were re-examined for potential shock and other deformation effects in all rock-forming minerals. This included petrographic study of two drill cores from the immediate vicinity of the center of the Dome. Observations recorded throughout the granitic core are given along with conclusions.
Two rover concepts were considered: an unpressurized skeleton vehicle having available 4.5 kW of electrical power and limited to a range of about 10 km from a temporary Martian base and a much larger surface exploration vehicle (SEV) operating on a maximum 75-kW power level and essentially unrestricted in range or mission. The only baseline reference system was a battery-operated skeleton vehicle with very limited mission capability and range and which would repeatedly return to its temporary base for battery recharging. It was quickly concluded that laser powering would be an uneconomical overkill for this concept. The SEV, on the other hand, is a new rover concept that is especially suited for powering by orbiting solar or electrically pumped lasers. Such vehicles are visualized as mobile habitats with full life-support systems onboard, having unlimited range over the Martian surface, and having extensive mission capability (e.g., core drilling and sampling, construction of shelters for protection from solar flares and dust storms, etc.). Laser power beaming to SEV's was shown to have the following advantages: (1) continuous energy supply by three orbiting lasers at 2000 km (no storage requirements as during Martian night with direct solar powering); (2) long-term supply without replacement; (3) very high power available (MW level possible); and (4) greatly enhanced mission enabling capability beyond anything currently conceived.
The prediction of future greenhouse-gas-warming depends critically on the sensitivity of earth's climate to increasing atmospheric concentrations of these gases. Data from cores drilled in polar ice sheets show a remarkable correlation between past glacial-interglacial temperature changes and the inferred atmospheric concentration of gases such as carbon dioxide and methane. These and other palaeoclimate data are used to assess the role of greenhouse gases in explaining past global climate change, and the validity of models predicting the effect of increasing concentrations of such gases in the atmosphere.
Ar-40/Ar-39 dating of drill-core samples of a glassy melt rock recovered from beneath a massive impact breccia contained with the 180-kilometer subsurface Chicxulub crater yields well-behaved incremental heating spectra with a mean plateau age of 64.98 +/- 0.05 million years ago (Ma). The glassy melt rock of andesitic composition was obtained from core 9 (1390 to 1393 meters) in the Chicxulub 1 well. The age of the melt rock is virtually indistinguishable from Ar-40/Ar-39 ages obtained on tektite glass from Beloc, Haiti, and Arroyo el Mimbral, northeastern Mexico, of 65.01 +/- 0.08 Ma (mean plateau age for Beloc) and 65.07 +/- 0.10 Ma (mean total fusion age for both sites). The Ar-40/Ar-39 ages, in conjunction with geochemical and petrological similarities, strengthen the suggestion that the Chicxulub structure is the source for the Haitian and Mexican tektites and is a viable candidate for the Cretaceous-Tertiary boundary impact site.
Panther Mountain, located near Phoenicia, New York, is part of the Catskill Mountains, which form the eastern end of the Allegheny Plateau in New York. It is a circular mass defined physiographically by an anomalous circular drainage pattern produced by Esopus Creek and its tributary Woodland Creek. The circular valley that rings the mountain is fracture-controlled; where bedrock is exposed, it shows a joint density 5 to 10 times greater than that on either side of the valley. Where obscured by alluvial valley fill, the bedrock's low seismic velocity suggests that this anomalous fracturing is continuous in the bedrock underlying the rim valley. North-south and east-west gravity and magnetic profiles were made across the structure. Terrane-corrected, residual gravity profiles show an 18-mgal negative anomaly, and very steep gradients indicate a near-surface source. Several possible explanations of the gravity data were modeled. We conclude that the Panther Mountain circular structure is probably a buried meteorite crater that formed contemporaneously with marine or fluvial sedimentation during Silurian or Devonian time. An examination of drill core and cuttings in the region is underway to search for ejecta deposits and possible seismic and tsunami effects in the sedimentary section. Success would result in both dating the impact and furnishing a chronostratigraphic marker horizon.
The Barberton Greenstone belt is a 3.5- to 3.2-Ga-old formation situated in the Swaziland Supergroup near Barberton, northeast Transvaal, South Africa. The belt includes a lower, predominantly volcanic sequence, and an upper sedimentary sequence (e.g., the Fig Tree Group). Within this upper sedimentary sequence, Lowe and Byerly identified a series of different beds of spherules with diameters of around 0.5-2 mm. Lowe and Byerly and Lowe et al. have interpreted these spherules to be condensates of rock vapor produced by large meteorite impacts in the early Archean. We have collected a series of samples from drill cores from the Mt. Morgan and Princeton sections near Barberton, as well as samples taken from underground exposures in the Sheba and Agnes mines. These samples seem much better preserved than the surface samples described by Lowe and Byerly and Lowe et al. Over a scale of just under 30 cm, several well-defined spherule beds are visible, interspaced with shales and/or layers of banded iron formation. Some spherules have clearly been deposited on top of a sedimentary unit because the shale layer shows indentions from the overlying spherules. Although fresher than the surface samples (e.g., spherule bed S-2), there is abundant evidence for extensive alteration, presumably by hydrothermal processes. In some sections of the cores sulfide mineralization is common. For our mineralogical and petrographical studies we have prepared detailed thin sections of all core and underground samples (as well as some surface samples from the S-2 layer for comparison). For geochemical work, layers with thicknesses in the order of 1-5 mm were separated from selected core and underground samples. The chemical analyses are being performed using neutron activation analysis in order to obtain data for about 35 trace elements in each sample. Major elements are being determined by XRF and plasma spectrometry. To clarify the history of the sulfide mineralization, sulfur isotopic compositions are being determined.
The Pretoria Saltpan Crater is located in the southern portion of the Bushveld Igneous Complex, some 40 km NNW of Pretoria, South Africa, at 25 deg 24 min 30 sec S/28 deg 4 min 59 sec E. An origin by impact for this crater structure was recently confirmed. The results of the only gravity reconnaissance carried out over the crater to date failed to support an impact origin. With the aid of recent results obtained from a central drill-core, it was necessary to carry out more geophysical work which would include a gravity profile of higher resolution. A second, smaller, circular depression (about 400 m in diameter) to the SW of the crater is suggestive of a twin crater. This site had never been investigated, and thus various geophysical surveys were conducted.
Reimold et al. suggested that the 640 m diameter Kalkkop crater, at 32 deg 43 min S/24 deg 34 min E in the Eastern Cape Province (South Africa), could possibly be of impact origin. This idea was based on the circularity of this structure, its regional uniqueness, lack of recent igneous activity in the region, and descriptions of drillcore indicating that the crater is not underlain by a salt dome and is partially filled with a breccia layer of a thickness which would agree with the dimensions expected for an impact structure of this size. Unfortunately the old drillcore was no longer available for detailed study, and in the absence of sufficient surface exposure only drilling could provide the evidence needed to solve the problem of the origin of Kalkkop. For this reason and to study the crater fill from a paleoenvironmental point of view, the S. African Geological Survey decided to sponsor a new research drilling project at the Kalkkop site. First petrographic and isotopic results from Kalkkop drill core studies confirming, without doubt, that this crater is of impact origin are presented.
The Pretoria Saltpan impact crater, situated about 40 km NNW of Pretoria, South Africa, has a diameter of about 1.13 km. The structure was formed in 2.05 Ga Nebo granite of the Bushveld Complex. The impact origin of the crater was recently established by the discovery of characteristic shock-metamorphic features in breccias found in drill cores at depths greater than 90 m. Impact glass fragments were recovered by standard magnetic separation techniques and handpicking from the melt breccias. As no reliable crater age was known so far, several hundred sub-millimeter-sized glass fragments were studied for fission tracks. The results show that the Saltpan impact crater has an age of 220 +/- 52 ka. This is in agreement with field geological observations.