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1.
Abstract: Several native sulfur specimens, collected from Shiretoko-Iwozan volcano, eastern Hokkaido, Japan, exhibit spinifex texture, which appears to resemble that often observed in komatiite. The spinifex texture is exhibited by yellow-colored elongated skeletal native sulfur crystals up to 5 cm long settled in medium gray-colored fine–grained clayey matrix. One surface of a specimen is coated by layers of micro pillow lava of native sulfur. Such specimens were rarely found as clasts or fragments around the 1936 No. 1 crater that erupted native sulfur flows, together with the most common monomineralic native sulfur fragments of native sulfur flows having pahoehoe surface and of native sulfur dikes. The elongated spinifex native sulfur crystals presently consist of aggregated polygrains of orthorhombic sulfur crystals formed through crystallo-graphic transition from the single crystal of monoclinic sulfur initially crystallized. The spinifex texture exhibited by elongated skeletal native sulfur crystals is a product of rapid cooling of sulfur melt. Many lithic fragments of altered country rocks are present in the specimens exhibiting native sulfur spinifex texture. This suggests that segregation of the sulfur melt from the mixture of lithic fragments and sulfur melt was incomplete because the mixture was chilled before the melt segregation. Elongated skeletal native sulfur crystals may have nucleated and crystallized directly from the molten sulfur liquid. Lithic fragments mixed in the melt are supposed to have acted as nuclei for the nucleation of the native sulfur crystals. On the other hand, the most of native sulfur flows consist of monomineralic massive native sulfur with very scarce lithic fragments. Such massive monomineralic native sulfur crystallized from the supercooled, solidified amorphous sulfur. Such supercooled amorphous state may have been attained due to the lack of nuclei because of the scarcity of lithic fragments. The unique structures exhibited by native sulfur lava flow, including pahoehoe surface and spinifex texture, are due to the characteristic physical property of molten sulfur liquid, that is, low viscosity. 相似文献
2.
Sand samples from piston cores taken in the Peru-Chile Trench and adjacent areas were examined petrographically in an attempt to characterize sands from the oceanward side of a continent-margin volcanic arc. Framework composition averaged Q18F44L38, close to the average reported for this type of setting, but showed wide variation in the ratio of feldspar to lithic fragments; quartz was uniformly low, less than 30%. Samples rich in lithic grains were from sites that lie off areas of recent volcanism on the adjacent continent. Samples from off southern Central America had compositions more like those found in island-arc settings, averaging Q3F21L76, whereas those from the Straits of Magellan increased in quartz and decreased in lithic fragments toward the Atlantic. Plagioclase was greatly predominant over K-feldspar in all samples, and averaged An28. A considerable portion of the plagioclase was close to end-member albite, suggesting recycling from pre-existing sedimentary rocks. Climate had no obvious effect on the framework proportions or the feldspar composition, but the volume of sediment in the trench increases with increasing rainfall on the continent. 相似文献
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Obianwu I. Victor Chimezie C. Innocent Akpan E. Anthony George N. Jimmy 《Central European Journal of Geosciences》2011,3(4):368-374
Twenty seven vertical electrical sounding (VES) profiles surrounding four known traverses were obtained in Ngor-Okpala local government area of Imo state to examine the subsurface geomaterials and the associated groundwater potential. The VES data, constrained by borehole data, provided useful information about the subsurface hydrogeologic and lithologic conditions. From the validated interpretation, the area assessed has loamy soil, medium grained sands, well-sorted medium-grained/gravelly sands and river sand as the lithologic succession from top to the bottom of the depth penetrated. The aquifers in the area were found in the medium-grained sands and well-sorted medium-coarse-grained sands. The aquifer depth for all-season groundwater that would be devoid of draw-down can be found at a depth range of 42–50 m. The resistivity maps of selected depths exhibit sharp resistivity changes at depth due mainly to undulating subsurface topography. A map of the distribution of the kσ-values shows that good quality groundwater can be found in most parts of the area. 相似文献
5.
P. E. Potter 《International Journal of Earth Sciences》1994,83(1):212-232
Standard petrographic methods were used to study 604 modern sands from South America, of which 351 came from rivers and 253 from beaches. In spite of the wide geomorphic contrasts, these sands belong to only three great families: (1) an immature Andean family of lithic arenites rich in volcanic and metamorphic grains that covers about 30% of South America; (2) a cratonic association rich in quartz that covers about 62% of the continent; and (3) a transitional, molasse association, which occurs between these two and covers only about 8% of the continent. The grand arithmetic average Q:F: Rf ratio for the entire continent is 60:11:29 and the area-weighted, carbonate-free average Qa:Fa:Rfa is 68:10:22, a superior continental estimate, and the first ever for an entire continent.Rock fragments are the most informative of all the provenance indicators and in South America they range from tropical alterites of the cratonic family through the dominant volcanic and metamorphic grains of the Andean family to biogenic carbonate in beach sands. Carbonate grains are almost totally absent in modern South American rivers because of present day tropical weathering and a long geological evolution that has favored sand production. They are present in many of the beach sands, however, and are most abundant along the tropical Brazilian and Caribbean coasts. Metamorphic grains rival volcanics as earmarks of the Andean family and survive tropical weathering far better than volcanic grains.There is a strong association between continental soil types and the composition of river sand, but the ultimate controls are tectonic history — the ancient landscapes preserved on the Gondwana shields of South America versus the tectonically young landscapes of the Andes — and climate. Climate can either cause leaks to a far distant ocean where weathering is retarded by aridity or it can serve as a barrier to continental sand dispersion, where tropical weathering eliminates unstable grains in transit to the sea.When provenance studies are conducted across an entire, unglaciated continent, events in the far distant past need to be considered when seeking fundamental explanations of its contemporary, surficial sands. 相似文献
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Siliciclastic sediments on the insular shelf of Puerto Rico are derived from a volcanic arc. The sands are feldspatholithic and subquartzose. They confirm predictions about sandstones of arc derivation in the following ways. The quartz content is low, usually less than 25 %. Feldspar is more abundant than quartz, but less so than lithic fragments. If mud rip-up clasts are excluded from the lithic suite, the ratio V/L (volcanic lithic grains to total unstable lithic grains) assumes values near 0.75. Most of the volcanic lithic grains have textures suggesting intermediate volcanics as source rocks. Ratios of plagioclase to total feldspar are high. Values of the parameter C/Q (stable lithic fragments to total lithic grains) are higher than expected for sandstones of volcanic provenance. Four compositionally and areally distinct assemblages of clay minerals are recognized. Clay suites characterized by major concentrations of both halloysite and smectite are found off the north-west coast. Sediments off the north-central and north-east coasts contain major concentrations of halloysite and lesser amounts of smectite, illite and chlorite. Major concentrations of kaolinite are present off the south-east coast. An assemblage of poorly crystallized smectite with lesser amounts of illite and chlorite occurs off the south-west and south-central coasts. Variation in the mineralogic composition of clays around the perimeter of the island reflects changes in the intensity of chemical weathering and the type of rock exposed in the immediate source area and, in instances, either early diagenetic alteration or, more likely, sorting within the clay fraction by currents on the shelf. 相似文献
7.
Detrital modes of recent deep-sea sands and their relation to tectonic setting: a first approximation 总被引：5，自引：0，他引：5
Complete petrographic analyses of modern deep-sea sands are surprisingly rare, but are needed if problems such as the influence of tectonics on petrology, or changes in petrology due to diagenesis, are to be understood in ancient sandstones. This paper is a first attempt, using data from our own study of 80 sands plus data from the literature, to establish a baseline for modern deep-sea sands with which ancient sandstones can be compared. We assigned sands to five plate-tectonic categories, each of which has a distinct average petrologic composition: (1) basins associated with trailing-edge continental margins, Q62F26L12; (2) with leading-edge continental margins, either subduction, Q16F53L31, or (3) strike-slip, Q34F39L27; (4) back-arc basins, Q20F29L51; (5) fore-arc basins, Q8F17L75. The amount and type of lithic fragments and the type of feldspar are particularly important discriminators, the amount of quartz less so. Trailing-edge and fore-arc basins have quite distinctive compositions, but back-arc basins and basins near the two types of leading-edge margins show some overlap, and thus may be hard to differentiate in ancient sandstones. 相似文献
8.
H. M. Zakir Hossain Quazi Hasna Hossain Atsushi Kamei Daisuke Araoka 《Arabian Journal of Geosciences》2018,11(23):749
The modal and chemical composition of sands from Cox’s Bazar beach (CBB) and Kuakata beach (KB) areas of Bangladesh has been investigated to infer their maturity, chemical weathering, and provenance signatures. The CBB and KB sands are typically high quartz, low feldspar, and lithic fragments, representing a recycled orogen source. Major element compositions of CBB sands are characterized by high SiO2 (83.52–89.84 wt%) and low Al2O3 (4.39–6.39 wt%), whereas KB sands contained relatively low SiO2 (63.28–79.14 wt%) and high Al2O3 (9.00–11.33 wt%) contents. The major, trace and rare earth element (REE) compositions of beach sands display comparable distribution patterns with enriched Th and SiO2 for both sands relative to upper continental crust (UCC). Pb, Rb, Y, and Fe for KB sands are little higher than UCC and the rest of the elements are marked depleted for both suites reflecting destruction of plagioclase and K-feldspar during fluvial transportation. The CBB and KB sands are compositionally low mature to immature in nature subsequently classified as subarkose and litharenite, respectively. Chondrite-normalized REE patterns for CBB and KB sands show LREE enrichment and nearly flat HREE (LaN/YbN, 7.64–9.38 and 5.48–8.82, respectively) coupled with prominent Eu anomalies (Eu/Eu*, 0.51–0.72 and 0.52–0.76, respectively), suggesting felsic source provenance. The provenance discrimination diagrams, immobile trace element ratios (Th/Sc, Zr/Sc, Ce/Sc, and Ti/Zr), and REE (∑LREE/HREE, Eu/Eu* and GdN/YbN) parameters indicate that CBB and KB sands were largely derived from felsic source rocks, with compositions close to average rhyolite, granodiorite, granite, and UCC. 相似文献
9.
Md. Aminul Islam 《Journal of the Geological Society of India》2010,76(5):493-504
This study deals with petrography and provenance of the Neogene reservoir sandstones encountered in the Kailas Tila, Titas, Bakhrabad and Shahbazpur Gas Fields of Bengal Basin. Framework grains are sand-sized to silt-sized particles of mainly detrital origin. The most common detrital grains are quartz, feldspars, and rock fragments. Mica occurred as minor and non-opaque heavy minerals found as minor accessories. Among the main detrital framework grains, quartz constitutes 51–60%, feldspar 3–15%, lithic fragments 8–22%. Sandstones encountered in the studied wells have been classified as sublithic arenite, feldspathic arenite and lithic arenite in order of abundance. Different triangular plots reveal that the Neogene sandstones of the studied wells exhibit a quartzolithic composition, low feldspar, very low volcanic grains and abundant sedimentary and low grade metamorphic lithic clasts indicating that the sands were derived from quartzose recycled orogen province, such as a fold thrust province or a collision suture zone. This study suggests that either the eastern Himalayas or Indo-Burman Ranges might act as the source of the sandstones of the studied wells of the Bengal Basin. 相似文献
10.
Diagenesis has a significant impact on reservoir quality in deeply buried formations. Sandstone units of the Shahejie Formation (Es1 Member) of Nanpu Sag, Bohai Bay Basin, East China is a typical deeply buried sandstone with large hydrocarbon accumulations. The methodology includes core observations and thin section studies, using fluorescence, scanning electron microscope (SEM), cathodoluminescence (CL), fluid inclusion and isotope and electron probing analysis as well as the numerical determination of reservoir characteristics. The sandstones consist of medium to coarse-grained, slight to moderate sorted lithic arkose and feldspathic litharenite. Porosity and permeability values range from 0.5 to 30% and 0.006 to 7000 mD, respectively. The diagenetic history reveals mixed episodes of diagenesis and deep burial followed by uplift. The main diagenetic events include compaction, cementation alteration, dissolution of unstable minerals and grain fracturing. Compaction resulted in densification and significantly reduced the primary porosity. Quartz, calcite and clay are the dominant pore-occluding cement and occur as euhedral to subhedral crystals. Alteration and dissolution of volcanic lithic fragments and pressure solution of feldspar grains were the key sources of quartz cement whereas carbonate cement is derived from an external source. Clay minerals resulted from the alteration of feldspar and volcanic lithic fragments. Porosity and permeability data predict a good inverse relationship with cementation whereas leaching of metastable grains, dissolution of cement and in some places formation of pore-lining chlorite enhanced the reservoir quality. The best reservoir is thicker sandstone bodies that are medium to coarse-grained, well-sorted sandstone with low primary ductile grains with a minor amount of calcite cement. The present study shows several diagenetic stages in the Es1 Member, but the overall reservoir quality is preserved. 相似文献
11.
Quartile-deviation (QDa) and median-diameter (Md) values have been calculated from the grain-size distributions of a variety of Pleistocene and modern glacial and para-glacial sediments. The QDa—Md pairs are plotted on double-log graph paper to determine whether their graphic distributions are distinctive, and to examine their sedimentological implications. Three distributions emerge. The first has a shallow gradient and represents coarse bi-modal tills consisting largely of rock fragments — distribution (a). The second, with an intermediate gradient, represents fine uni- or non-modal tills consisting mainly of monomineralic grains — distribution (b). The third (c) has a steep gradient and consists of bi-modal tills with a dominant proportion of monomineralic grains. Each of these distributions is explained by using the grain-size characteristics of physically weathered rock debris as a starting point for discussion. By a process dominated by the continual addition of weathered-grain populations (population addition), tills with (a) characteristics are formed. By a process dominated by comminution and the selective removal of grains by ablation (population subtraction), tills with (b) characteristics are formed. Any of these tills, when subjected to flowing water, rapidly lose their glacial characteristics and assume QDa—Md characteristics of fluvial deposits (although they are fluvioglacial). 相似文献
12.
DANIELA FONTANA 《Sedimentology》1991,38(6):1085-1095
The Upper Cretaceous Pietraforte Formation, an allochthonous unit of the Ligurian domain in the northern Apennines, provides a case study of the importance of detrital carbonate grains for provenance determination in sandstones. The Pietraforte Formation is composed of turbidite sandstones with subordinate conglomerate, deposited in an external sector of the Ligurian ocean, close to the Adriatic margin. The sandstones have a lithic composition, characterized by abundant sedimentary and metasedimentary rock fragments (35–56% of the terrigenous framework), little feldspar (<7%) that is almost exclusively plagioclase, and a high ratio of fine- to coarse-grained polycrystalline quartzose grains to total quartzose grains (average Qp/Qt=0.37). Carbonate rock fragments dominate the lithic association of both sandstones and conglomerates and provide the most detailed information for provenance determination. They are composed primarily of dolostones and a wide variety of limestones containing identifiable age-diagnostic microfossils. Fossils and rock textures of carbonate clasts document the erosion of Upper Triassic to Lower Cretaceous shelf and pelagic carbonate units which can be matched with Mesozoic rock types present in the Tuscan domain of the northern Apennines. Compositional results constrain the source of the Pietraforte Formation sandstones to the western margin of the Adriatic plate, from uplifted sedimentary and metasedimentary rocks of the Tuscan domain and its low-grade metamorphic basement. Coeval intrabasinal sources provided additional supplies to the depositional basin of the Pietraforte Formation; this intrabasinal supply consists of shelf carbonate allochems, planktonic foraminifera and argillaceous rip-up clasts. The presence of carbonate grains from shallow-water environments may indicate the existence during deposition of marginal shelf areas favourable for carbonate allochem production. 相似文献
13.
F Wlotzka H Palme B Spettel H Wänke K Fredriksson A.F Noonan 《Geochimica et cosmochimica acta》1983,47(4):743-757
The LL-group chondrites Krähenberg (Krbg) and Bhola are heterogeneous agglomerates containing a variety of lithic fragments and chondrules as well as crystal fragments. The + Mg content of most olivine grains is uniform (Fa28), although a few with distinctly lower Fe contents were found (Fa19). Both meteorites contain large, cm-sized, fragments with high enrichments of K (~12×), Rb (~45×) and Cs (~70×) relative to LL-chondrites, while the REE concentrations are normal (except for a negative Eu anomaly); Na and Sr are depleted (~0.5×) and the weight ratio is 0.33 compared to 11 in the host. However, there is no difference in the sum of Na + K atoms. Also, the major elements, Si, Al, Mg, Ca and Fe, are nearly the same in fragments as in the host material. The K-rich igneous lithic fragments have a microporphyritic texture of euhedral to skeletal olivines in a partly devitrified glass with ~4% K2O. The main pans of both Krbg and Bhola contain mesostasis glasses in porphyritic chondrules and lithic fragments with varying K content (0.1–8.6% K2O) and ratios (0.2–100). Crystalline plagioclase is depleted in K with an average ratio of 22, i.e. higher than that for ordinary chondritic plagioclase, 8.4. Olivines in the large, K-rich fragments and in the host meteorites have the same iron content (Fa28), indicating that both formed under the same oxygen fugacity and probably on the same parent body.Conceivable mechanisms for the formation of the K-rich rocks from normal LL-chondrite parent material are: 1, magmatic differentiation: 2. Na-K exchange via a vapor phase; 3. silicate liquid immiscibility; 4. volatilization and condensation in impact events. Process 2 appears most feasible for forming a rock enriched only in K and heavier alkalies and depleted in Na without noticeably changing other elements including the REE. 相似文献
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Nilpena (173 g), a new ureilite find from the Parachilna area of South Australia, is an unusual polymict breccia containing polymineralic aggregates, mineral fragments and achondritic and chondritic lithic enclaves in a dark, C-rich matrix. The polymineralic aggregates consist of equigranular-textured olivine Fa20 and pigeonite En75Wo9FS16, and exhibit evidence of shock in the form of undulose extinction and kink-banding. Monomineralic fragments consist of olivine Fa19–24 (with highly forsteritic rims up to Fa3) and pigeonite, and appear to be derived by brecciation of the polymineralic aggregates. The enclave material consists of lithic granular olivine fragments, porphyritic enstatite fragments (either enstatite chondrite or aubrite), olivine-clinobronzite fragments resembling an H3 chondrite, and eucritelike lithic fragments composed of plagioclase An98, salitic clinopyroxene Wo48.5En31.4Fs20.1 and olivine Fa49–53. The matrix contains kamacite (generally rich in P), schreibersite and troilite. The texture of Nilpena suggests formation by disruption of a olivine-pigeonite granular aggregate while the presence of the diverse chondritic and achondritic enclave material suggests an origin as a surface or near-surface breccia.Like other ureilites Nilpena is strongly differentiated with respect to cosmic abundances but is significantly enriched in Ba and LREE. A lack of correlation of lithophile elements with ratio among ureilites suggests that the differentiation was not caused by varying degrees of partial melting of a homogeneous source. A cumulate origin therefore seems more plausible. 相似文献
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《Chemie der Erde / Geochemistry》2019,79(2):369-383
We present a modified model for the paleogeographic evolution of Mexico during Early and Late Jurassic time that is constrained by the tectonic setting and the weathering conditions of the Early Jurassic Huayacocotla Formation and Late Jurassic Alamitos Sandstone basins in state San Luis Potosí in central Mexico. Framework petrography constrains feldspato-quartzose sandstone (mean of Q68F22L10) and litho-quartzose (mean of Q75F6L19) sandstone compositions for the two units, respectively. The abundant lithic fragments are totally dominated by volcanic fragments. Quartz cathodoluminescence colours and textures from the Alamitos Sandstone supports a large input of volcanic material, but also indicates the presence of metamorphic quartz. Similarly, the geochemical composition is more mafic for the Huayacocotla Formation (Th/Sc: ˜0.6 and Cr/Th: ˜10) than for the Alamitos Sandstone (Th/Sc: ˜1.1 and Cr/Th: ˜48). Also the weathering conditions were less intense during the Early (CIA: ˜60, PIA: ˜61) than the Late Jurassic (CIA ˜85, PIA ˜97). Well preserved lithic fragments and feldspar grains, particularly in the Huayacocotla Formation, indicate that weathering indeed was minor for this unit. We interpret the difference between the two units as a combined result of climate change and tectonic setting. During the Early Jurassic, transport of volcanic detritus probably dominated from the active Nazas arc in the west. Later, additional sources from the metamorphic basement of Mexico were included. During Late Jurassic time strike-slip faulting related to the opening of the Gulf of Mexico may have re-directed the sediment-transport systems. Finally, the degree of weathering was affected by drastic climatic change from arid to humid tropical conditions during the Middle to Upper Jurassic, possibly related to the first incursions of Gulf of Mexico marine environments linked to the rotation of the Yucatan block. 相似文献
17.
辽南金伯利岩岩区是我国最大的原生金刚石矿产区,该区金刚石主要寄主岩石类型为斑状金伯利岩。橄榄石是金伯利岩中最重要的造岩矿物,根据其结构特征可以分为橄榄石粗晶、橄榄石斑晶以及基质中微细粒三个世代。本文将岩相学特征和前人研究成果相结合,构建辽南斑状金伯利岩岩浆起源、上升、喷发和成岩模型,探讨各世代矿物的形成过程。具体包括：深部交代地幔部分熔融,形成初始碳酸盐岩浆;初始岩浆上升过程中捕获的岩石圈地幔橄榄岩不断溶解(形成橄榄石粗晶),岩浆成分发生改变,成为金伯利岩岩浆;金伯利岩岩浆迅速上升侵位,至地表处爆破喷发,最后冷却固结形成包含粗晶及其他两个世代橄榄石的斑状金伯利岩。 相似文献
18.
G.Jeffrey Taylor Michael J Drake John A Wood Ursula B Marvin 《Geochimica et cosmochimica acta》1973,37(4):1087-1106
Luna 20 soil 22003,1 (250–500 μ) is similar to Apollo 16 soil 61501,47 (250–500 μ) in terms of the percentage of different types of particles. However, among the lithic fragments, the Apollo 16 sample contains a greater percentage of fragments with more than 70 wt. % modal plagioclase and a significantly greater proportion of KREEP-rich particles. Modal analyses of non-mare lithic fragments in Luna 20 and Apollo 11, 14, 15 and 16 indicate that the KREEP-poor highland regions (the bulk of the lunar terrae), though relatively feldspathic, are compositionally inhomogeneous, ranging in plagioclase content from approximately 35 to 100 wt. %. The average plagioclase content lies in the range 45–70 wt.%. Luna 20 pyroxene analyses cluster in two groups, one more magnesian than the other. The groups persist when pyroxene analyses from KREEP-poor noritic, troctolitic and anorthositic lithic fragments from Apollo 11, 14, 15 and 16 and Luna 20 are included. Olivine compositions mimic these pyroxene groups.Within each pyroxene group Cr2O3 and TiO2 decrease as increases, suggesting a relationship by fractional crystallization. The two groups suggest that at least two magma compositions were involved. To account for these observations we envisage a Moon-wide magma system in which initial accretionary heterogeneities were imperfectly erased by diffusion and convection. During the cooling of this magma system fractional crystallization was effected by the flotation of plagioclase and sinking of pyroxene, olivine and perhaps ilmenite. The endproduct was an upper layer enriched in plagioclase and a lower layer enriched in mafic silicates. KREEP-rich rocks, which are predominantly noritic in major element composition, may be mechanical mixtures of KREEP-poor norite and material residual after fractional crystallization of the surface magma system. 相似文献
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华池油田华152区长3油层组储层以粉细粒长石砂岩、岩屑长石砂岩为主,发育多种孔隙类型,主要有粒间溶孔、粒内溶孔、剩余粒间孔、晶间微孔隙和构造缝,其中粒间溶孔是长3油层组储层的主要孔隙类型。主要成岩矿物为伊利石、绿泥石、伊／蒙混层、高岭石、方解石、白云石、石英等。根据成岩作用的矿物岩石学标志,将研究区成岩阶段界定为中成岩A期。压实和胶结作用破坏了砂岩的原生孔隙结构,而溶蚀作用形成次生孔隙,有效地改善了砂岩的孔隙结构。 相似文献
20.
The Plainview. Texas, meteorite is a polymict-brecciated H-group chondrite composed of recrystallized light-colored portions embedded in a well-compacted, dense, somewhat recrystallized, dark-colored matrix. Both portions consist of equilibrated silicates (H5 classification), but a small number of silicate grains and unequilibrated lithic fragments not compatible with equilibrated ordinary H-group material are present in the dark-colored matrix. Lithic fragments include: (i) dark-colored, more or less altered, type II carbonaceous chondrites. (ii) unequilibrated ordinary chondrites and (iii) light-colored, unequilibrated and equilibrated fragments, some of which are compositionally similar to the host. Also present are fragment-like dark areas that are highly-shocked host material and not true lithic fragments (pseudo-fragments). Conclusions: Plainview represents a complex regolith breccia formed by repeated impact episodes. Recrystallized, light-colored portions represent surface or near-surface material of a small (asteroidal-sized) parent body. Impacts broke up this material to form fine-grained, dark material which enclosed light-colored protolith. Lithic fragments (i-iii) and some unequilibrated silicate grains and chondrules (apparently derived from unequilibrated chondrites) were embedded in the dark matrix during these repeated impacts. Xenolitlils of carbonaceous and unequilibrated ordinary chondrites are either residues of projectiles that impacted the Plainview parent body, or material from coexisting regoliths impact-splashed into Plainview regolith. Chondrules and silicate grains in the dark matrix which differ from H-group material are likely related to these xenoliths and their regoliths. Light-colored lithic fragments may represent shock-melted chondritic material, sometimes compositionally-modified, or new, achondritic meteoritic types. Unequilibrated and carbonaceous lithic fragments in the dark-colored host matrix indicate that equilibration of the host occurred before incorporation of the fragments and that compaction and lithification of the Plainview regolith to form a coherent meteorite must have occurred at temperatures below 300°C and/or on a short time scale. 相似文献