Clastic matrix in EH3 chondrites     

Alan E. RUBIN  Christian D. GRISET  Byeon‐Gak CHOI  John T. WASSON 《Meteoritics & planetary science》2009,44(4):589-601

Abstract— Patches of clastic matrix (15 to 730 μm in size) constitute 4.9 vol% of EH3 Yamato (Y‐) 691 and 11.7 vol% of EH3 Allan Hills (ALH) 81189. Individual patches in Y‐691 consist of 1) ?25 vol% relatively coarse opaque grain fragments and polycrystalline assemblages of kamacite, schreibersite, perryite, troilite (some grains with daubréelite exsolution lamellae), niningerite, oldhamite, and caswellsilverite; 2) ?30 vol% relatively coarse silicate grains including enstatite, albitic plagioclase, silica and diopside; and 3) an inferred fine nebular component (?45 vol%) comprised of submicrometer‐size grains. Clastic matrix patches in ALH 81189 contain relatively coarse grains of opaques (?20 vol%; kamacite, schreibersite, perryite and troilite) and silicates (?30 vol%; enstatite, silica and forsterite) as well as an inferred fine nebular component (?50 vol%). The O‐isotopic composition of clastic matrix in Y‐691 is indistinguishable from that of olivine and pyroxene grains in adjacent chondrules; both sets of objects lie on the terrestrial mass‐fractionation line on the standard three‐isotope graph. Some patches of fine‐grained matrix in Y‐691 have distinguishable bulk concentrations of Na and K, inferred to be inherited from the solar nebula. Some patches in ALH 81189 differ in their bulk concentrations of Ca, Cr, Mn, and Ni. The average compositions of matrix material in Y‐691 and ALH 81189 are similar but not identical‐matrix in ALH 81189 is much richer in Mn (0.23 ± 0.05 versus 0.07 ± 0.02 wt%) and appreciably richer in Ni (0.36 ± 0.10 versus 0.18 ± 0.05 wt%) than matrix in Y‐691. Each of the two whole‐rocks exhibits a petrofabric, probably produced by shock processes on their parent asteroid.  相似文献   

Oxygen isotopes in magnetite and fayalite in CV chondrites Kaba and Mokoia     

Byeon‐Gak CHOI  Alexander N. KROT  John T. WASSON 《Meteoritics & planetary science》2000,35(6):1239-1248

Abstract— We report in situ measurements of O‐isotopic compositions of magnetite and primary and secondary olivine in the highly unequilibrated oxidized CV chondrites Kaba and Mokoia. In both meteorites, the magnetite and the secondary olivine (fayalite, Fa_90–100) have O‐isotopic compositions near the terrestrial fractionation (TF) line; the mean Δ¹⁷O (= δ¹⁷O‐0.52 × δ¹⁸O) value is about ?1%‰. In contrast, the compositions of nearby primary (chondrule), low‐FeO olivines (Fa_1–2) are well below the TF line; Δ¹⁷O values range from ?3 to ?9%‰. Krot et al. (1998) summarized evidence indicating that the secondary phases in these chondrites formed by aqueous alteration in an asteroidal setting. The compositions of magnetite and fayalite in Kaba and Mokoia imply that the O‐isotopic composition of the oxidant was near or somewhat above the TF line. In Mokoia the fayalite and magnetite differ in δ¹⁸O by ～20%‰, whereas these same materials in Kaba have virtually identical compositions. The difference between Mokoia magnetite and fayalite may indicate formation in isotopic equilibrium in a water‐rich environment at low temperatures, ～300 K. In contrast, the similar compositions of these phases in Kaba may indicate formation of the fayalite by replacement of preexisting magnetite in dry environment, with the O coming entirely from the precursor magnetite and silica. The Δ¹⁷O of the oxidant incorporated into the CV parent body (as phyllosilicates or H₂O) appears to have been much (7–8%‰) lower than that in that incorporated into the LL parent body (Choi et al, 1998), which suggests that the O‐isotopic composition of the nebular gas was spatially or temporally variable.  相似文献   

Multivariate water quality assessment from the Tamiraparani river basin,Southern India     

P. Kumarasamy  R. Arthur James  Hans-Uwe Dahms  Chan-Woo Byeon  R. Ramesh 《Environmental Earth Sciences》2014,71(5):2441-2451

The hydrochemistry of a perennial river has been investigated with multivariate cluster analysis (CA) and principal component analysis/factor analysis (PCA/FA). The aim was to investigate parameters responsible for spatial and temporal variations of river water quality. Water quality was monitored along the river basin at 20 different sites over a period of 1 year from July, 2008 to June, 2009. Multivariate statistics revealed that Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃ ^?, Cl^?, H₄SiO₄, SO₄ ^2?, NO₂ ^?, and PO₄ ^3? were influenced by seasonal and spatial variations and that water quality was in the first place determined more by natural weathering processes than by anthropogenic activities. We could prove by (a) Box and Whisker plot, (b) matrix scatter score mean plot, (c) ternary plot, and (d) Gibbs plot that the chemistry of river water is controlled by lithogenic weathering processes. The higher concentration of dissolved silica during summer and the pre-monsoon season is explained by natural and tropical climatic conditions of the environment.  相似文献   

Application of a Conceptual Ecological Model to Predict the Effects of Sand Mining around Chilsan Island Group in the West Coast of Korea     

Jae-Won Yoo  Chan-Woo Lee  Yong-Woo Lee  Chang-Soo Kim  Chang-Gun Lee  Keun-Hyung Choi  Seung Won Jung  Sung-Joo Jin  Kyu-Hee Son 《Ocean Science Journal》2018,53(3):521-534

Chilsan Island Group, located on the west coast of South Korea, has been recognized as a critical breeding and nursery ground for endangered seabirds because food is abundant and human activity is low. Chilsan Island Group has been under protection as a Natural Monument (Article no. 389) since 1997, but attempts were made in 2004 to exploit the coastal sands around the islands. A conceptual ecological model (CEM) was employed with energy flow diagram (EFD) to predict the effects of sand mining on the islands’ ecosystem. The results showed that sand mining activities caused long-term damage to benthic ecosystems and threatened seabird communities by reducing fish populations throughout the food web. The changes in energy flow in the ecosystem due to sand mining operations predict that reduction in secondary production of benthic animal communities might reduce energy transfer to humans and seabirds by 30%. Different ranges of uncertainty provided by the Monte Carlo simulation lead to the conclusion that sand mining could bring about undesirable consequences. One concern is that such negative consequences would have a much more severe impact on seabirds than humans because seabirds cannot compete effectively against humans for the limited food sources. In this study, the complex interrelationships between ecosystem members were simplified and a CEM was established to clearly identify which elements would be affected. The CEM with EFD was found to be helpful in promoting communication between stakeholders, and it is expected to be widely used as a decisionmaking tool by public officials.  相似文献