Anorthositic Breccia Research Articles

산청 철-티탄 광화대의 발달양상과 연성변형

하동-산청 회장암체의 북부에 해당하는 산청회장암체 서쪽부인 경남 산청군 금서면 방곡리 일대에는 철-티탄 광체가 발달하고 있다. 광체에는 엽리가 잘 발달하고 있으며, 대체로 남-북 방향에 서쪽으로 중각 내지 저각의 경사를 보인다. 이들 엽리는 2차 엽리로 회장암 내에 발달하는 북동 방향의 1차 엽리를 자르고 있다. 엽리면에는 신장선구조가 잘 관찰되며, 동북동-서남서의 일반적인 방향을 보인다. 광체의 엽리를 자르는 단면에서는 수 cm의 크기의 회장암편들이 심하게 변형되어져 있으며, 철-티탄 광물을 함유하는 암색의 염기성 물질에 둘러싸여 백색의 안구상의 형태를 이루고 있다. 이는 회장암질암을 함철-티탄 마그마가 파쇄하며 주입할 당시에 각력화 되었던 회장암편들이 이후에 발생한 연성의 전단운동에 의해 변형을 받은 결과로 해석된다. 엽리면에 수직하며 신장선구조에 평행한 단면에서의 전단증거에 의하면, 엽리면을 전단면으로 하며 신장선구조를 따라 상부가 동북동 쪽으로 이동한 강력한 전단작용이 존재함이 특징적이다. 이러한 전단운동에 의해 변형된 특징적인 기하학적인 양상의 이해는 이 지역에 발달하는 광체의 위치와 분포, 그리고 불규칙한 폭 등 기하학적인 양상을 파악하는데 기초적인 것으로 판단된다. Fe-Ti ore bodies occur in the western part of the Sancheong anorthosites around Banggok-ri, Sancheong, Korea. Within ore bodies, a several centimetric size of anorthositic breccia are enclaved by ore-bearing mafic part and deformed strongly as a sigmoidal form by ductile shearing. The ore bodies have a general N-S trending foliations with westward dipping directions. The foliation developed in the ore bodies cut the foliation in anorthosites. The stretching lineations are well developed in the foliated plane of the ore bodies, showing ENE-trending with gentle plunging angle to the ESE direction. The sigmoidal patterns of anorthositic breccia in the ore bodies indicates the top-to-the-eastnortheastward shearing. Thus, in this study area the relationship between the geometric pattern and the ductile deformation is an important fact to understand the Sancheong Fe-Ti mineralized zone, Korea.

Geochemistry, petrology and ages of the lunar meteorites Kalahari 008 and 009: New constraints on early lunar evolution

Kalahari 008 and 009 are two lunar meteorites that were found close to each other in Botswana. Kalahari 008 is a typical lunar anorthositic breccia; Kalahari 009 a monomict breccia with basaltic composition and mineralogy. Based on minor and trace elements Kalahari 009 is classified as VLT (very-low-Ti) mare basalt with extremely low contents of incompatible elements, including the REE. The Lu–Hf data define an age of 4286 ± 95 Ma indicating that Kalahari 009 is one of the oldest known basalt samples from the Moon. It provides evidence for lunar basalt volcanism prior to 4.1 Ga (pre-Nectarian) and may represent the first sample from a cryptomare. The very radiogenic initial 176Hf/ 177Hf (εHf = +12.9 ± 4.6), the low REE, Th and Ti concentrations indicate that Kalahari 009 formed from re-melting of mantle material that had undergone strong incompatible trace element depletion early in lunar history. This unusually depleted composition points toward a hitherto unsampled basalt source region for the lunar interior that may represent a new depleted endmember source for low-Ti mare basalt volcanism. Apparently, the Moon became chemically very heterogeneous at an early stage in its history and different cumulate sources are responsible for the diverse mare basalt types. Evidence that Kalahari 008 and 009 may be paired includes the similar fayalite content of their olivine, the identical initial Hf isotope composition, the exceptionally low exposure ages of both rocks and the fact that they were found close to each other. Since cryptomaria are covered by highland ejecta, it is possible that these rocks are from the boundary area, where basalt deposits are covered by highland ejecta. The concentrations of cosmogenic radionuclides and trapped noble gases are unusually low in both rocks, although Kalahari 008 contains slightly higher concentrations. A likely reason for this difference is that Kalahari 008 is a polymict breccia containing a briefly exposed regolith, while Kalahari 009 is a monomict brecciated rock that may never have been at the surface of the Moon. Altogether, the compositions of Kalahari 008 and 009 permit new insight into early lunar evolution, as both meteorites sample lunar reservoirs hitherto unsampled by spacecraft missions. The very low Th and REE content of Kalahari 009 as well as the depletion in Sm and the lack of a KREEP-like signature in Kalahari 008 point to a possible source far from the influence of the Procellarum-KREEP Terrane, possibly the lunar farside.

Magnesian anorthosites and a deep crustal rock from the farside crust of the moon

Among over thirty lunar meteorites recovered from the hot deserts and Antarctica, Dhofar 489 is the most depleted in thorium (0.05 ppm), FeO, and rare earth elements (REE). Dhofar 489 is a crystalline matrix anorthositic breccia and includes clasts of magnesian anorthosites and a spinel troctolite. The Mg / (Mg + Fe) mol% (Mg numbers = 75–85) of olivine and pyroxene grains in this meteorite are higher than those of the Apollo ferroan anorthosites. Such materials were not recovered by the Apollo and Luna missions. However, remote sensing data suggest that the estimated concentrations of Th and FeO are consistent with the presence of such samples on the farside of the Moon. The differentiation trend deduced from the mineralogy of the anorthositic clasts define a magnesian extension of the ferroan anorthosite (FAN) trend constructed from the Apollo samples. The presence of magnesian anorthositic clasts in Dhofar 489 still offers a possibility that the farside trend with magnesian compositions is more primitive than the FAN trend, and may require a revision of this classical differentiation trend. The Ar–Ar age of Dhofar 489 is 4.23 ± 0.034 Gyr, which is older than most Ar ages reported for highland rocks returned by Apollo. The old Ar–Ar age of impact formation of this breccia and the presence of a fragment of spinel troctolite of deep crustal origin suggest that a basin forming event on the farside excavated the deep crust and magnesian anorthosites before formation of Imbrium.

Lunar nitrogen: indigenous signature and cosmic-ray production rate

Abstract Indigenous lunar nitrogen composition and abundances have been determined in old ferroan anorthosite 60025 and in anorthositic breccia 67915 from North Ray Crater, as well as in 55 cm deep volcanic glasses of 74001 double-drive core from Shorty Crater. Also included in the set is the well-documented lunar basalt 75075, collected near the Camelot Crater. Indigenous lunar N abundances are low (at ppm level), but there is some variation between glass-rich cores, mare basalts and anorthosites. The uniform indigenous N isotopic signature of δ 15 N=+13.0±1.2‰, is consistent with data reported previously for Shorty Crater samples. The indigenous δ 15 N cannot account for the light nitrogen component, observed in the lunar regolith samples. We have determined cosmic-ray production rates P ( 15 N) for the above rocks and the drill core samples. The average production rate estimate (for low shielding) of P ( 15 N)=5.8±0.6 pg 15 N/g/Ma is ∼60% higher than published lunar 15 N production rates, but consistent with the meteoritic production rate derived from silicates in the Enon meteorite, when normalized to 2π-irradiation geometry. From the observed cosmogenic 15 N excesses and the reported cosmogenic 21 Ne abundances in core 74001 we derive a ( 15 N C / 21 Ne C ) production rate ratio of 4.0±0.3 for silicates.

Tsiolkovsky crater: A window into crustal processes on the lunar farside

Mineralogy and distribution of rock types in the Tsiolkovsky region of the lunar farside are evaluated in terms of crustal stratigraphy and evolution. Calibrated multispectral images from five orbits of Clementine data provide compositional information at a scale that allows diverse geologic features to be analyzed and compared. The entire region is seen to be highly anorthositic, with outcrops of relatively pure anorthosite quite common. The crater itself has excavated blocks of anorthosite and noritic anorthosite from the near‐surface highland crust, often in a mixed jumble. The central peaks of Tsiolkovsky, which have exhumed much deeper material, however, are composed of relatively pure anorthosite with olivine‐rich zones concentrated near the ridge crests. Boundaries between the anorthosite and olivine‐rich zones are sharp, but spatial relations suggest the coherent olivine‐rich zone is relatively thin (<1 km). The composition of the mare material filling Tsiolkovsky is shown to be low‐titanium basalt. Smaller exposures of mare basalt occur about one crater radius from the rim. The crustal structure to ∼25 km in this region prior to the Tsiolkovsky impact appears to be (top to bottom) a few kilometers of anorthositic breccias comprising the megaregolith, a zone of crystalline anorthosite with pockets of noritic anorthosite, a zone of anorthosite devoid of iron‐bearing minerals, and a zone of relatively pure anorthosite containing olivine‐rich material, possibly emplaced as intrusions.

Mineralogy of meteorite groups

Abstract— Approximately 275 mineral species have been identified in meteorites, reflecting diverse redox environments, and, in some cases, unusual nebular formation conditions. Anhydrous ordinary, carbonaceous and R chondrites contain major olivine, pyroxene and plagioclase; major opaque phases include metallic Fe‐Ni, troilite and chromite. Primitive achondrites are mineralogically similar. The highly reduced enstatite chondrites and achondrites contain major enstatite, plagioclase, free silica and kamacite as well as nitrides, a silicide and Ca‐, Mg‐, Mn‐, Na‐, Cr‐, K‐ and Ti‐rich sulfides. Aqueously altered carbonaceous chondrites contain major amounts of hydrous phyllosilicates, complex organic compounds, magnetite, various sulfates and sulfides, and carbonates.In addition to kamacite and taenite, iron meteorites contain carbides, elemental C, nitrides, phosphates, phosphides, chromite and sulfides. Silicate inclusions in IAB/IIICD and IIE iron meteorites consist of mafic silicates, plagioclase and various sulfides, oxides and phosphates. Eucrites, howardites and diogenites have basaltic to orthopyroxenitic compositions and consist of major pyroxene and calcic plagioclase and several accessory oxides. Ureilites are made up mainly of calcic, chromian olivine and low‐Ca clinopyroxene embedded in a carbonaceous matrix; accessory phases include the C polymorphs graphite, diamond, lonsdaleite and chaoite as well as metallic Fe‐Ni, troilite and halides. Angrites are achondrites rich in fassaitic pyroxene (i.e., Al‐Ti diopside); minor olivine with included magnesian kirschsteinite is also present. Martian meteorites comprise basalts, lherzolites, a dunite and an orthopyroxenite. Major phases include various pyroxenes and olivine; minor to accessory phases include various sulfides, magnetite, chromite and Ca‐phosphates. Lunar meteorites comprise mare basalts with major augite and calcic plagioclase and anorthositic breccias with major calcic plagioclase.Several meteoritic phases were formed by shock metamorphism. Martensite (α2‐Fe,Ni) has a distorted body‐centered‐cubic structure and formed by a shear transformation from taenite during shock reheating and rapid cooling. The C polymorphs diamond, lonsdaleite and chaoite formed by shock from graphite. Suessite formed in the North Haig ureilite by reduction of Fe and Si (possibly from olivine) via reaction with carbonaceous matrix material. Ringwoodite, the spinel form of (Mg,Fe)2SiO4, and majorite, a polymorph of (Mg,Fe)SiO3 with the garnet structure, formed inside shock veins in highly shocked ordinary chondrites.Secondary minerals in meteorite finds that formed during terrestrial weathering include oxides and hydroxides formed directly from metallic Fe‐Ni by oxidation, phosphates formed by the alteration of schreibersite, and sulfates formed by alteration of troilite.

Noble gases in lunar anorthositic rocks 60018 and 65315: Acquisition of terrestrial krypton and xenon indicating an irreversible adsorption process

Lunar anorthositic breccias 60018 and 65315 contain a trapped Xe component with isotope ratios similar to those in terrestrial atmospheric Xe. We analyzed all five noble gases in eight grain size fractions of 60018 and in several bulk samples of 65315 in order to characterize the nature of the trapped components. Trapped gas abundances in 60018 are 100 to 1000 times lower than in a typical regolith breccia; they are grain size anticorrelated for grain sizes < 30 μm. In 65315, trapped He, Ne, and Ar concentrations are among the lowest ever observed for lunar material. Except for Xe, the isotopic abundances of the trapped components in both rocks are consistent with solar wind composition. Because of the uncertain results as to the origin of the terrestrial-like Xe component, we crushed samples of 60018 and 65315 in atmospheres spiked with 86Kr and 129Xe. These experiments showed unequivocally that anorthositic samples can be contaminated by Kr and Xe, and maybe also by Ar, from the ambient atmosphere. At least 75% of the acquired terrestrial and spike gases are released only at temperatures above 600°C. Krypton and xenon concentrations are grain-size anticorrelated, indicating surface adherence of the gas atoms. Furthermore, the amount of gas in a sample is approximately proportional to the partial pressure of the gas to which the sample was exposed, as described by Henry's law. Xenon uptake is about one order of magnitude more effective than Kr uptake, and activation energies, measured at room temperature, are in the range of 10–20 kJ/mol. Both characteristics are typical for ordinary physical adsorption. However, the high extraction temperatures show that somehow the gas atoms get fixed, either by strong chemisorptive bonding with activation energies around 200 kJ/mol, or by getting trapped beneath the surface. Therefore, we use the term “irreversible adsorption” for the phenomenon. Fixation is likely to take place during crushing, when mechanical, thermal, and maybe electromagnetic energy is supplied, although the air contamination of an uncrushed 65315 sample cannot be explained in this way. Irreversible adsorption of terrestrial Kr and Xe has been observed for several lunar anorthosites with low solar wind content, but also for some meteoritic samples, in particular diogenites, which are composed mainly of pyroxene. A similar process may have been responsible for the incorporation of nonterrestrial noble gas components into extraterrestrial material, e.g., the planetary trapped gases in meteorites or the surface-correlated components of 129Xe and fission-type Xe in some lunar breccias. Furthermore, other volatile elements might be affected by irreversible adsorption.

MacAlpine Hills 88104 and 88105 lunar highland meteorites: General description and consortium overview

MacAlpine Hills 88104 and 88105 are new lunar meteorites returned from Antarctica by the 1988–1989 US meteorite collection team. The two specimens were found in nearby locations and, based on field and laboratory evidence, are thought to be pieces of the same meteorite. MAC88105 is the largest lunar meteorite yet found (662g). MAC88104/5 is an anorthositic breccia consisting of numerous small clasts in a glassy matrix. An origin on the Moon is supported by the mineral, bulk, and oxygen isotope compositions. A consortium of twenty research groups has studied these meteorites. Samples were prepared at the NASA Johnson Space Center meteorite processing laboratory. Details of consortium plans and allocations are documented herein. A summary list of lunar meteorites and an overview of consortium research is presented. Discussions in this and the following consortium papers involve the issue of paired meteorites and paired ejecta, and what new information about the nature and evolution of the lunar crust is provided by the lunar meteorites.

Petrology and chemistry of Apollo 12 regolith breccias

Petrographic, mineral chemical, and bulk chemical data are reported for the three large Apollo 12 regolith breccias of the regolith breccia suite and for eight breccias handpicked from Apollo 12 coarse fines. Two samples formed from non‐KREEPy anorthositic regolith not presently found at the sampling site. Eight of the samples can be considered mixtures of local basalt and KREEP components, with minor anorthositic components. Mare:KREEP ratios indicated by chemical mixing models range from 86:7 to essentially endmember KREEP. One sample is unlike the others (FeO 23.7; MgO 21.7) and may be a new lithology or alternatively a nonrepresentative sample. Of the 11 samples studied, 5 appear to be of local origin, 3 are most likely exotic to the site, and results for 3 others are inconclusive. The anorthositic breccias formed from Apollo 16‐like regolith and may have been transported over several hundred kilometers from the non‐KREEPy highlands to the east. Alternatively, they may be of local origin, formed from the material beneath the Apollo 12 basalt flows.

The discovery and initial characterization of Allan Hills 81005: The first lunar meteorite

Antarctic meteorite ALHA81005, discovered in the Allan Hills region of Victoria Land, is a polymict anorthositic breccia which differs from other meteorites in mineralogical and chemical composition but is strikingly similar to lunar highlands soil breccias. The petrologic character and several independent lines of evidence identify ALHA81005 as a meteorite from the Moon. Two small clasts of probable mare basalt occur among the highlands lithologies in Thin Section 81005,22. This lunar specimen, which shows relatively minor shock effects, has generated new ideas on the types of planetary samples we may find on the Earth, and has added fresh excitement to the Antarctic meteorite program.

Rock 67015: A feldspathic fragmental breccia with KREEP‐rich melt clasts

Breccia 67015, one of the feldspathic fragmental breccias (FFBs) from the rim of North Ray Crater, contains a wider range of clast lithologies than has been described previously in FFB's. Our petrologic and INAA studies have revealed two components of major petrologic and geologic significance. One of these is a dark, vesicular, KREEP‐rich melt rock of VHA (very high alumina) basalt composition, which occurs in clasts up to 6 cm long. Melt rocks of this type are common at the Apollo 16 site, but in previous years had not been discovered as prominent constituents of the feldspathic fragmental breccias. Their apparent absence led to hypotheses, no longer valid, that the KREEPy melt rocks were younger than the anorthositic breccia matrices and that the two lithologies might represent Imbrian and Nectaris ejecta, respectively. The second lithology we discovered is a large clast of medium‐grained ferroan anorthositic norite with a composition that falls among the most magnesian members of the ferroan anorthosite suite of pristine cumulate rocks. This material constitutes a previously ‘missing’ member of certain mixing models designed to account for the North Ray Crater melt rocks and bulk breccias.

Allan Hills A81005: A rare bird

A sole, crystalline metal grain about 1 mm in diameter is lodged in a small sample (3×2.5×3 cm) of anorthositic breccia that was collected with other pristine meteorites in the ice floe at Allan Hills, Antarctica. The fascination of sample ALHA81005 is that it is a very unusual anorthositic breccia, the only such meteorite ever found. This breccia sample is composed mostly of Ca‐rich plagioclase, averaging An 97 (range An 95–98), with striking similarity to anorthositic samples collected during the Apollo missions from the lunar highlands. Only time and the results of chemical analyses of major and trace elements will tell whether this is the first meteoritic sample identified from the moon. Meanwhile, in the Antarctic Meteorite Newsletter (Nov. 1982), Brian Mason describes this sample as ‘a very rare bird’ indeed.

Meteoritic material in a Boulder from the Apollo 17 Site: Implications for its origin

Sixteen samples of Boulder 1 from Station 2 at the Apollo 17 site were analyzed by radiochemical neutron activation analysis for Ag, Au, Bi, Br, Cd, Cs, Ge, Ir, Ni, Rb, Re, Sb, Te, Tl, U, and Zn. Two clast samples contam no meteoritic material and appear to consist of relatively pristine igneous rocks: an unusual, KREEP-rich pigeonite basalt of very high Ge content, and an alkali-poor coarse norite. Nine grey or black breccia samples contain a unique, Group 3 meteoritic component of Ir/Au ratio 0.65–0.82, which appears to separate into subgroups 3H and 3L on the basis of Ni, Ge, and Re content. It is quite distinct from the Group 2 component (Ir/Au - 0.46–0.54) that dominates at the Apollo 17 site. The unique black-rimmed clasts from this boulder show striking compositional zoning. The cores of anorthositic breccia are very low in Rb, Cs, and U, and have a distinctive 5L meteoritic component (Ir/Au≈1.1). The black rinds are 5- to 10-fold richer in Rb, Cs, and U and have a Group 3 meteoritic component. The cores may represent breccias formed in an earlier impact that became coated with alkali-rich ejecta during the event that produced the boulder. Because of the rarity of the Group 3 meteoritic component at the Apollo 17 site, this boulder cannot represent ordinary Serenitatis ejecta, with their characteristic admixture of the Group 2 Serenitatis projectile. It may represent pre-Serenitatis material excavated from the fringes of the crater during late stages of the Serenitatis impact, but only lightly shocked and hence uncontaminated by the Serenitatis projectile.