Experimental petrology of ancient lunar mare basalt Asuka-881757: Spinel crystallization as a petrologic indicator

The paucity of titanian chromites in lunar-meteorite basalt Asuka (A)-881757 is unusual compared to the general occurrence of co-existing chromites and ulvospinels in the Apollo and Luna mare basalts. The unique spinel crystallization of A-881757 is expected to hold a key to elucidate the crystallization and cooling episodes of the basalt. In this study, we investigated the possible reason for the missing chromite by conducting isothermal and cooling experiments on the bulk-rock composition of A-881757 and discuss the petrogenesis of the ancient low-Ti mare basalt in light of spinel crystallization. A series of isothermal experiments showed the A-881757 basalt magma is not saturated with chromite under the expected lunar oxygen fugacity condition (IW～IW-1). A peritectic reaction among chromite, melt, and pyroxene is present for A-881757 basalt magma under the more oxidized condition which is one or two log unit higher than the lunar condition. The cooling experiment successfully reproduced the chromian ulvospinels with similar compositions to those in A-881757. The result of the cooling experiments further implies that ulvospinels solely crystallized from highly-fractionated interstitial melts in the late crystallization stage. The disparity in the crystallization of the liquidus chromite between the low-Ti and very low-Ti basalts might reflect the difference of bulk Cr_2O_3 concentration. The low liquidus temperature and the paucity of the liquidus olivine in A-881757 infer that the A-881757 basalt represents a liquid derived from near-surface fractionation processes. Chromites might possibly have been present during that near-surface fractionation episode prior to the eruption of the magma

Comparison of Fe-Mg interdiffusion coefficients in olivine

We have compared Fe-Mg interdiffusion coefficients in olivine reported in several literatures by analyzing experimentally produced diffusion profiles. The chemical zoning profiles of olivine measured with an electron microprobe were compared with those calculated by numerically solving the diffusion equation by using different diffusion coefficients. For our experimental results, the Fe-Mg interdiffusion coefficient in olivine reported by D. J. Misener (Carnegie Inst. Washington Publ., 634,117,1974) with oxygen fugacity dependence gives the best fit to the observed profile. The Fe-concentration dependence of the Fe-Mg interdiffusion coefficient in olivine is important when the Fe content varies widely

Mineralogical studies of lunar meteorite Yamato-793169, a mare basalt

A preliminary mineralogical study of the lunar meteorites Yamato (Y)-793169 and Asuka (A)-881757,which were apparently derived from a mare region of the Moon, has been performed to identify crystallization trends of their pyroxenes. Y-793169 is a crystalline basalt with similar basaltic components to lunar breccias EET87521 and Y-793274,containing strongly zoned Fe-Ca-rich pyroxenes. Their zoning trends in the pyroxene quadrilateral are closest to those found in the basaltic clast in an Apollo 16 breccia. Differentiation trends expressed by Ti/(Ti+Cr) versus Fe/(Fe+Mg) of Y-793169 and A-881757 pyroxenes are similar but they differ from those of EET87521. The Y-793169 trend starts at a more Mg-rich composition point than the A-881757 trend. Based on differences in textures and ranges of zoning trends, the pyroxene of A-881757 could represent growth deeper in the lava unit under conditions more closely approaching equilibrium, than Y-793169,which appears to have formed from a lava flow of similar bulk composition. Although Y-793169 has been described as the VLT basalt, some mesostases contain significant amounts of ilmenite and ulvospinel, together with fayalite, troilite, chromite and a silica mineral. Mg-rich pyroxenes as found in Y-793274 and EET87521 are not present in Y-793169 and A-881757 basalts

Impact of Social Networks on Diffusion of Products

In light of the rapid growth of social networks around the world, this study analyses the impact of social networks on the diffusion of products and demonstrates the effective way to diffuse products in the society where social networks play an important role. We construct a consumer behaviour model by multi-agent simulation taking the movie market as an example. After validating it by using data from 13 US movies, we conduct simulations. Our simulation results show that the impact of social networks on the diffusion differs according to the customers’ expectations and evaluation for a movie. We also demonstrate the effective weekly advertising budget allocations corresponding to the types of movies. We find that the difference of weekly advertising budget allocations gives greater impact on the diffusion with the growth of social networks. This paper provides firm’s managers with important suggestions for diffusion strategy considering the impact of social networks

Mineralogy of the Asuka 87 and 88 eucrites and crustal evolution of the HED parent body

Mineralogical study of three apparently crystalline eucrites, Asuka (A)-87272,A-881388 and A-881394 revealed that their textures are not primary crystallization products from a magma. A-87272 is a monomict breccia, but the finegrained matrix is recrystallized to a granulitic texture with fine, rounded pyroxene crystals set in a plagioclase matrix. Large fragments of pyroxene are inverted to orthopyroxene with coarse exsolution lamellae on (001) and fine ones on (100). A-881388 contains a large, rounded opaque grain with a tail, and with an ilmenite-chromite-troilite-metal assemblage in fine-grained granulitic silicates, suggesting recrystallization. A-881394 is coarser grained than A-881388 and contains more magnesian pyroxene as in cumulate eucrites, but the plagioclase composition is extremely calcic (An 98) and the grains are composed with a few rounded grains. The A-881394 chromite, showing a pokilitic texture with rounded plagioclase and minor pyroxene, suggests a metamorphic texture. Our present interpretation for a common formation process among these eucrites is that despite their crystalline texture, they might have experienced extensive metamorphism after the initial crystallization in the early history of the crustal evolution

An attempt to reproduce petrographic features of mesosiderites

The Tenth Symposium on Polar Science/Poster presentations: [OA] Antarctic meteorites, Wed. 4 Dec. / Entrance Hall (1st floor), National Institute of Polar Researc

Metamorphic transformations of opaque minerals in some eucrites

Eucrites have undergone varying degrees of metamorphism on their parent body. We investigated mineralogical constraint on the eucrite metamorphism, especially from opaque mineralogy. Three eucrites with distinct degrees of metamorphism were studied : Y-75011,84 is the least equilibrated basaltic clast, Juvinas shows complex histories of shock and thermal metamorphism, and A-881388 is an extensively annealed and unbrecciated. Three eucrites with different metamorphic histories show distinct opaque mineralogy. In Y-75011,84,ilmenite and troilite are found crystallized in the mesostasis and opaque precipitates within pyroxenes are barely recognized. Juvinas has complicated texture, consisting of a variety of lithologies : Minute precipitates within pyroxene area and recrystallized mesostases. In A-881388,during extensive prolonged annealing episode, opaque phases, such as ilmenite, troilite, and chromite are almost completely separated from silicate phases and segregated, resulting in a formation of opaque nodules. Several geothermometers, experimental results and the textural appearance of A-881388 suggest that it might have slowly cooled from near 1000-1050℃ to ∿800℃ during a prolonged annealing episode. While chromite is not observed in Y-75011,84,Juvinas and A-881388 contain chromite in recrystallized mesostases and in an nodule respectively. This implies that chromite could be a metamorphic product

Mineralogy of Yamato 983885 lunar polymict breccia with a KREEP basalt,a high-Al basalt, a very low-Ti basalt and Mg-rich rocks

Y983885 is a polymict regolith breccia with a KREEP basalt, Mg-rich troctolite/norite, a high-Al basalt, a very low-Ti basalt, a granulite originated from ferroan anorthosite, and Si, Na-rich impact spherules. An igneous KREEP basalt is first reported among lunar meteorites to date. The KREEP basalt is mineralogically distinct from Apollo KREEP basalts due to the lack of the typical Ca zoning from orthopyroxene to pigeonite, instead, the presence of the co-existing pigeonite/augite with chemical zonings and micron-scale exsolution. With these mineral characteristics, the KREEP basalt is probably cooled slightly slower than the Apollo KREEP basalts under the subsurface condition such as hypabyssal setting or lava pond. Further study of the additional samples is necessary to fully understand the petrogenesis of this new KREEP basalt. The troctolite and norite are also distinct in lower mg# of mafic minerals and higher modal abundance of olivine in norite, comparing to Apollo troctolites and norites, implying the existence of a rock type with intermediate modal abundance between norite and troctolite, and the compositional diversity of Mg-rich lithologies. Simultaneous occurrence of a KREEP basalt and a genetically KREEP-related, high-Al basalt, a Mg-rich troctolite/norite and the Si, Na-rich impact glasses can constrain the source region of Y983885 to the KREEP-rich Procellarum terrane in the northwestern hemisphere of the lunar nearside

Near-infrared observations of active asteroid (3200) Phaethon reveal no evidence for hydration

Asteroid (3200) Phaethon is an active near-Earth asteroid and the parent body of the Geminid Meteor Shower. Because of its small perihelion distance, Phaethon's surface reaches temperatures sufficient to destabilize hydrated materials. We conducted rotationally resolved spectroscopic observations of this asteroid, mostly covering the northern hemisphere and the equatorial region, beyond 2.5-micron to search for evidence of hydration on its surface. Here we show that the observed part of Phaethon does not exhibit the 3-micron hydrated mineral absorption (within 2-sigma). These observations suggest that Phaethon's modern activity is not due to volatile sublimation or devolatilization of phyllosilicates on its surface. It is possible that the observed part of Phaethon was originally hydrated and has since lost volatiles from its surface via dehydration, supporting its connection to the Pallas family, or it was formed from anhydrous material