Petrology of fine-grained rock fragments and petrologic implications of single crystals from the Luna 20 soil     

K.L Cameron  J.J Papike  A.E Bence  S Sueno 《Geochimica et cosmochimica acta》1973,37(4):775-793

Only fine-grained rocks are present in the Luna 20 samples, and coarser grained rocks are represented by fragments of single crystals. A petrologic study has been made of 47 fine-grained crystalline rocks, microbreccias, and glassy aggregates. In addition, a total of 33 single crystals of pyroxene, plagioclase, olivine and spinel, in the size range 125 to 500 μ, have been examined using electron microprobe and single crystal X-ray diffraction techniques.The most abundant fine-grained crystalline rocks in the samples we have examined are recrystallized anorthositic norite and anorthositic troctolite. Gabbroic rocks, anorthosite, and KREEP basalt are present but not common. Most of the single crystals of pyroxene and plagioclase could have been derived from coarser grained noritic, troctolitic and anorthositic rocks. However, three of the 14 pyroxene crystals, and 2 of the 5 olivine crystals have $\text{Fe}\text{(Fe + Mg)}$ contents greater than 0.45 and are believed to have been derived from mare basalts or related rocks. Two relatively sodic crystals of plagioclase were found. One is a crystal zoned at least over the range An₈₅ to An₆₃, and the second is a homogeneous crystal of albite (~An₃).  相似文献   

Oxide minerals in lithic fragments from Luna 20 fines     

Robin Brett  R.C Gooley  Eric Dowty  Martin Prinz  Klaus Keil 《Geochimica et cosmochimica acta》1973,37(4):761-773

One hundred and seventy-six oxide mineral grains in the Luna 20 samples were analyzed by electron microprobe. Spinel is the most abundant oxide, occurring in troctolite fragments. Next most abundant is ilmenite, which occurs in all rock types except those containing spinel. Chromite also occurs in all rock types except those containing spinel. Minor amounts of ulvöspinel, armalcolite, zirkelite, baddeleyite and an unidentified TiO₂-rich phase were also found.Spinel grains are predominantly spinel-hercynite solid solutions, commonly with very minor chromite. The $\text{Fe}\text{(Fe + Mg)}$ ratio is generally lower than in spinel from Apollo 14 rocks. Chromites in non-mare rocks are similar to those from mare rocks. Ilmenite of mare origin is Mg-poor and Zr-rich compared to non-mare ilmenite; these elements may therefore be useful in determining the origin of ilmenite grains.Phase equilibria considerations suggest that spinel troctolite crystallized from a melt high in alumina; a likely candidate is the high-alumina basalt of Prinzet al. (1973a).Sub-micron wide rods of metallic Fe occur in plagioclase grains and may have formed by sub-solidus reduction processes.  相似文献   

The mineralogy and petrology of the Luna 20 soil sample     

Stephen J. Kridelbaugh  Daniel F. Weill 《Geochimica et cosmochimica acta》1973,37(4):915-926

Fragments of igneous rocks, glasses and minerals comprise 25 per cent of the studied sample of the Luna 20 soil. Basalt fragments in the Luna 20 soil are similar to basalts from the mare regions of the Moon—in that they are characterized by the presence of iron-rich olivines and pyroxenes. On the basis of the FeO contents of plagioclases, it appears possible to distinguish between the plagioclase of the mare and highland regions of the Moon. Other igneous rock fragments are anorthosite, gabbroic anorthosite and anorthositic gabbro. The most abundant rock type (75 per cent of the sample) is microbreceia. One third of the fragments of microbreccia have undergone thermal metamorphism resulting in the homogenization of phases and the development of poikioblastic and hornfelsic textures. Excluding the basalt fragments, the dominant minerals in the Luna 20 soil are anorthite (An_93–98), magnesium-rich orthopyroxenes, intermediate clinopyroxenes and olivine (< Fa₅₀). Chemically, the Luna 20 and Apollo 16 soil samples are similar, but the Luna 20 soil is slightly depleted in aluminum and calcium and enriched in iron and magnesium relative to the Apollo 16 soils. The slight difference in bulk chemistry of the two soils may be a result of the presence of a minor amount of mare material in the Luna 20 soil and its apparent absence in the Apollo 16 soils.  相似文献   

Petrology of some lithic fragments from Luna 20     

Edwin Roedder  Paul W. Weiblen 《Geochimica et cosmochimica acta》1973,37(4):1031-1052

Microscopic and electron microprobe studies were made of polished thin sections of part of a 30-mg sample of 250–500 μm lunar soil returned by Luna 20 from a point between Mare Fecunditatis and Mare Crisium. Very fine-grained lithic (crystalline) rock fragments, composing about one fifth of the total sample, have mineralogical compositions equivalent to various types of gabbro, anorthositic gabbro, gabbroic anorthosite and troctolite, with minor basalt. The textures now observed in these fragments are in large part metamorphic. Twentyseven electron microprobe analyses of minerals from these fragments are presented, including olivine, plagioclase, pyroxene, spinel, nickel-iron and a Zr-Ti-REE mineral possibly similar to ‘phase B’ of Lovering and Wark (1971). Analyses of seven melt inclusions and twenty-eight defocused beam analyses of lithic fragments are also given. Some of the fragments contain ‘gas’ inclusions which, along with the fine grain size, are believed to indicate final crystallization under low pressure near surface conditions. The almost complete absence of granophyric material in this sample raises the question of whether or not there are at least two distinct magmas for the plagioclase-rich terrae rocks from which this soil sample was derived in part.  相似文献   

Luna 20 soil: abundance and composition of phases in the 45–125 micron fraction     

Arch M. Reid  J.L. Warner  W.I. Ridley  R.W. Brown 《Geochimica et cosmochimica acta》1973,37(4):1011-1030

Glass compositions in the Luna 20 soil indicate a minor contribution of mare rocks and a major contribution of highly feldspathic highland material. Glasses with the composition of Highland basalt (anorthositic gabbro or norite) predominate in a range of highly aluminous glasses.The analyses of minerals in the soil show that the highland rocks have a unique assemblage of minerals that can readily be distinguished from the mineral assemblages of either mare or KREEP basalts. The soils are characterized by abundant anorthitic (An_92–99), low-Fe plagioclase. Highly magnesian orthopyroxenes, pigeonites and augites are the most prominent pyroxenes. Unlike mare basalt pyroxenes, clinopyroxenes with intermediate Ca values are not abundant, but extreme iron enrichment towards pyroxferroite does occur. Olivines are more abundant than at other sites and are Mg-rich, low in Ca and Cr. Spinels with compositions approaching MgAl₂O₄ predominate over pleonastes and chromites. Ilmenite and metal are present but not abundant.These data establish the unique nature of the minerals in the highland soils. The mineral compositions are consistent with derivation from a suite of highly feldspathic rocks in which Highland basalt compositions predominate. Some of the mineral data, particularly from the pyroxenes, are suggestive of surface or near-surface processes, rather than plutonic crystallization.  相似文献   

The Luna 20 lithic fragments,and the composition and origin of the lunar highlands     

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 $\text{Fe}\text{(Fe + Mg)}$ 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   

Chemical composition of Luna 20 rocks and soil and Apollo 16 soils     

J.C Laul  E.A Schmitt 《Geochimica et cosmochimica acta》1973,37(4):927-942

The abundances of 24 major, minor and trace elements have been measured by INAA in Luna 20 metaigneous rocks 22006,1 and 22007,1, breccia 22004 and soil 22001,9 and in Apollo 16 soils 62281, 66041 and 66081. An additional 12 trace meteoritic and non-meteoritic elements have also been determined in 22001 and 62281 soils by RNAA. The bulk compositions of L 20 and Ap 16 rocks and soils show close similarity between the two highland sites. There are appreciable differences in bulk compositions between the L 20 highland and the L 16 mare site (120 km apart), suggesting little intermixing of rocks and soils from either site. Luna 20 rocks 22006 and 22007 are nearly identical in chemical composition to Ap 16 metaigneous rocks 61156 and 66095. Luna 20 rocks are feldspathic and are similar to low K-type Fra Mauro basalts. Such rocks and anorthositic gabbros appear to be the major components in highland soils. Luna 20 soil can be distinguished from Ap 16 soils by lower abundances of Al₂O₃, CaO and large ion lithophilic elements. Luna 20 breccia 22004 probably is compacted soil. All L 20 samples show negative Eu anomalies with $\text{Sm}\text{Eu}$ ratios of 5.8, 7.2, 3.9 and 3.3 for rocks 22006, 22007, breccia 22004 and soil 22001, respectively. Norite-KREEP is insignificant, ≤1 per cent, at the L 20 highland site. The derivation of the L 20 soil may be explained by ≈33 per cent of L 20 metaigneous rocks and ≈ 65 per cent anorthositic gabbroic breccia rocks like 15418 (with a positive Eu anomaly) and ≈ 2 per cent meteoritic contributions. Interelement correlations observed previously for maria are also found in highland samples. Luna 20 and Ap 16 soils are low in alkalis. Both soils show an apparent Cd-Zn rich component similar to that observed at the mare sites and high 11 abundances relative to mare sites. The Ap 16 (62281) soil contains a fractionated meteoritic component (probably ancient) of ≈ 1.5 per cent in addition to ≈ 1.9 per cent Cl like material. Luna 20 soil may simply contain 1.9 per cent Cl equivalent.  相似文献   

Petrology of some lithic fragments of alkalic high-alumina basalt composition from Apollo 12 coarse fines     

Dr. G. Kurat  Prof. K. Keil  Dr. M. Prinz 《Mineralogy and Petrology》1974,21(3-4):179-195

Summary The mineralogy and petrology of three lithic fragments of alkalic highalumina basalt (Kreep) composition from the Apollo 12 coarse fines was studied in detail, using an electron microprobe, in order to gain insight into their crystallization histories. Most rocks of this composition are brecciated and our study indicates that a variety of environments of crystallization can be distinguished for mineral fragments and matrices. Mineral fragments are derived from members of the ANT suite (probably troctolites) in fragments 2 and 5, and the alkalic high-alumina basalt suite in fragment 3. The rocks from which they were derived were coarse-grained, recrystallized and equilibrated, as indicated by major, and especially, minor elements. Minor elements in plagioclase, olivine, pyroxene, and zircon are consistently lower in mineral fragments as compared with matrix minerals. The origin of large zircon fragments is problematic but they are probably from the alkalic high-alumina basalt suite. Mineral fragments may have been derived from plutonic rocks (none have yet been recognized from the alkalic high-alumina basalt suite), but possibly also from breccia fragments which were recrystallized in hot, thick ejecta blankets. The matrix of the lithic fragments is of alkalic high-alumina basalt composition and is either igneous or metamorphic, or both. Hence, lithic fragments 2 and 5 are polymict breccias whereas fragment 3 is a monomict breccia. Matrix glasses in fragments 2 and 3 represent melts fractionated along the orthopyroxeneplagioclase cotectic in the olivine-anorthite-silica pseudoternary system. If these liquids could be separated from the residuum and crystallized they would be, as yet, unrecognized members of the alkalic high-alumina basalt suite. The alkalic high-alumina basalt mixing component of fragment 5 (a polymict breccia) has such a composition and may be derived from such a fractionated rock. A mineral fragment of pyroxene intergrown with ilmenite, approximately parallel to (001), is interpreted as decorated shock lamellae rather than as a deep-seated intergrowth, as found in kimberlites. A glass coating on one side of fragment 3 has SiO₂-rich and feldspathic schlieren and appears to be derived, by impact melting, from a rock of granite composition.

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Petrologie einiger Gesteinsfragmente mit alkalic high-alumina basalt Chemismus aus dem Grobanteil von Apollo 12 Bodenproben

Zusammenfassung Drei Gesteinsfragmente mit alkalic high-alumina basalt (Kreep) Chemismus aus der Grobraktion von Apollo 12 Bodenproben wurden mittels einer Elektronenstrahl-Mikrosonde einer detaillierten Studie unterzogen, um Einblick in ihre Genese zu gewinnen. Der überwiegende Teil von Gesteinen dieser Zusammensetzung ist brekziös und unsere Studie zeigt, daß unterschiedliche Kristallisationsbedingungen für die Mineralfragmente und Matrizes herrschten. Die Mineralfragmente in den Fragmenten 2 und 5 stammen von Gesteinen der ANT- (Anorthositisch-Noritisch-Troctolitischen) Reihe (wahrscheinlich von Troctoliten) und in Fragment 3 von Gesteinen der alkalic high-alumina basalt-Reihe.Die Verteilung der Haupt- und Nebenelemente in den Mineralfragmenten zeigt, daß diese von rekristallisierten und equilibrierten, grobkörnigen Gesteinen stammen. Die Konzentrationen der Nebenelemente sind in allen Mineralfragmenten (Plagioklas, Olivin und Zirkon) deutlich geringer als in den Mineralen der Matrix. Die Herkunft der großen Zirkon-Fragmente ist nicht genau zu klären. Sie stammen jedoch wahrscheinlich von Gesteinen der alkalic high-alumina basalt-Reihe. Alle Mineralfragmente könnten von plutonischen Gesteinen stammen (solche sind von der alkalic highalumina basalt-Reihe zur Zeit noch nicht bekannt), sie könnten ihren Ursprung jedoch auch in prä-existenten Brekzien haben, welche in dichten, heißen Auswurfdecken rekristallisierten. Die Matrix der Gesteinsfragmente hat durchwegs eine alkalic high-alumina basalt Zusammensetzung und ist entweder magmatisch oder metamorph, oder beides. Die Fragmente 2 und 5 sind daher als polymikte und das Fragment 3 als monomikte Brekzie zu bezeichnen.Die Matrixgläser in den fragmenten 2 und 3 repräsentieren Rest-schmelzen, welche entlang der Orthopyroxen-Plagioklas-Kotektik im Olivin-Anorthit-SiO₂-System fraktionierten. Diese Schmelzen würden-könnten sie vom System getrennt werden-bisher noch nicht bekannte Glieder der alkalic high-alumina basalt-Reihe darstellen. Eine derartige Zusammensetzung hat jedoch die Mischkomponente im Fragment 5 (eine polymikte Brekzie), welche von einem auf diesem Wege fraktioniertem Gestein stammen könnte.Ilmenit-Lamellen [subparallel zu (001)] in einem Pyroxenfragment stellen eher dekorierte Schocklamellen als Verwachsungen, wie sie aus Kimberliten bekannt sind, dar. Fragment 3 ist einseitig mit einem schlierigen Glas bedeckt, dessen Schlieren angenähert die Zusammensetzung von Alkalifeldspat und reinem SiO₂ haben. Dieses Glas ist offensichtlich eine Impakt-Schmelze eines Gesteines von granitischer Zusammensetzung.

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With 5 Figures  相似文献   

P-bearing Olivines from the “Luna-20” Soil Samples,Their Sources and Possible Phosphorus Substitution Mechanisms in Lunar Olivine     

S. I. Demidova  T. Ntaflos  F. Brandstätter 《Petrology》2018,26(3):314-327

Rocks with P-bearing olivine were found in soil samples delivered by the “Luna-20” automated station. They are ascribed to the highland anorthosite–norite (more rarely, gabbro-norite)–troctolite rock series enriched in phosphorus and other incompatible elements, but are not related to typical KREEP rocks enriched in incompatible elements. Their source is presumably of hybrid origin and related to primary high- Mg suite (HMS) rocks. The occurrence of high- and low-Cr populations of P-bearing olivine in different structural rock types can be attributed to the annealing-related more rapid chromium diffusion (relative to that of phosphorus) in olivine from metamorphosed rocks. This assumption is supported by stoichiometric formula calculations of these olivines. An alternative explanation for these olivine populations is their derivation from at least two different sources. Disequilibrium crystallization of the P-bearing olivines, which is confirmed by an intricate phosphorus zoning, excludes the existence of P-rich melts, which is consistent with previous observations. At the same time, olivine fractionation can be responsible for the phosphorus content in lunar melts. The incorporation of phosphorus in olivine of the “Luna-20” anorthosite troctolites is presumably controlled by a coupled substitution mechanism of divalent cations and silicon for phosphorus and chromium in the tetrahedral and octahedral sites (Milman-Barris et al., 2008). Another possible mechanism is the substitution of divalent cations in octahedral sites by phosphorus and chromium, which provides the possible presence of P³⁺.  相似文献   

Rock 14318: A polymict lunar breccia with chondritic texture     

Gero Kurat  Klaus Keil  Martin Prinz 《Geochimica et cosmochimica acta》1974,38(7):1133-1146

Rock 14318 is a complex microbreccia consisting of lithic fragments, chondrules, glass spherules, and glass and mineral fragments that are embedded into a fine-grained, partly glassy matrix. Rock fragmenta, chondrules, and glasses are tightly welded to the matrix and partly recrystallized, indicating a relatively high-temperature agglomeration history. Few lithic fragments have igneous textures; most are miorobreccias that have suffered various degrees of recrystallization before they were embedded into rock 14318. Compositions of lithic fragments, glasses and chondrules, in terms of compositional rock and rock suite equivalents, represent members of the ANT (anorthositic-noritic-troctolite) suite; the alkalic high-alumina basalt (KREEP) group; high-alkali quartz basalt; basalt; and dunite. The polymict nature of many lithic fragments suggests that rook 14318 require at least two, and probably more, impact episodes for its formation. Final agglomeration took place while part of the material was hot, as is indicated by the welded texture, suggesting that the final impact event was a large one, producing a fiery cloud similar to a nuée ardente. The close similarity in texture of lunar rock 14318 to certain polymict-brecciated meteorites such as Siena suggests that meteorites of this type were also formed by complex and successive impact events on the surface of the meteorite parent body, rather than during agglomeration of the parent body.  相似文献   

Paleoproterozoic emplacement and Cambrian ultrahigh-temperature metamorphism of a layered magmatic intrusion from the Central Madurai Block,southern India: From Columbia to Gondwana     

Bing Yu  M.Santosh  Ming-Xian Wang  Cheng-Xue Yang 《地学前缘(英文版)》2022,13(1):101260

The Madurai Block in the Southern Granulite Terrane(SGT)of Peninsular India is one of the largest crustal blocks within the Neoproterozoic Gondwana assembly.This block is composed of three sub-blocks:the Neoarchean Northern Madurai block,Paleoproterozoic Central Madurai block and the dominantly Neoproterozoic Southern Madurai Block.The margins of these blocks are well-known for the occurrence of ultrahigh-temperature(UHT)granulite facies rocks mostly represented by Mg-Al metasediments.Here we report a dismembered layered mafic–ultramafic intrusion occurring in association with Mg-Al granulites from the classic locality of Ganguvarpatti in the Central Madurai Block.The major rock types of the layered intrusion include spinel orthopyroxenite,garnet-bearing gabbro,gabbro and gabbroic anorthosite showing rhythmic stratification and cumulate texture.The orthopyroxene-cordierite granulite from the associated Mg-Al layer is composed of spinel,cordierite and orthopyroxene.The pyroxene in both rock units is high-Al orthopyroxene formed under UHT metamorphic conditions.Conventional thermobarometry yields near-peak metamorphic conditions of 9.5–10 kbar pressure and a minimum temperature of 980℃.We computed P–T pseudosections and contoured for the compositional as well as modal isopleths of the major mineral phases,which yield temperature above 1000℃.FMAS petrogenetic grid,Al-in-orthopyroxene isopleth,conventional thermobarometry and calculated pseudosection reveal a clockwise pressure–temperature(P–T)path and near isothermal decompression.The U–Pb data on zircon grains from the layered magmatic suite indicate emplacement of the protolith at ca.2.0 Ga and the metamorphic overgrowths yield weighted ²⁰⁶Pb/²³⁸U mean ages ca.520 Ma.Monazite from the garnet-bearing gabbro and Opx-Crd granulite yielded ²⁰⁶Pb/²³⁸U weighted mean ages of ca.532 Ma and 523 Ma marking the timing of metamorphism.We correlate the layered intrusion to a Paleoproterozoic suprasubduction zone setting,defining the Ganguvarpatti area as part of a collisional suture assembling the Northern and Central Madurai Blocks.The Paleoproterozoic magmatism and late Neoproterozoic-Cambrian UHT metamorphism can be linked to the tectonics of the Columbia and Gondwana supercontinents.  相似文献   

Petrology,geochemistry and geochronology of the Chilka Lake igneous complex,Orissa state,India     

Amitabha Sarkar  L. Bhanumathi  M.N. Balasubrahmanyan 《Lithos》1981,14(2):93-111

The Chilka Lake igneous complex of Orissa, the largest known anortosite massif of the Indian Shield, occurs in a catazonal environment of high-grade metamorphics of the Eastern Ghats Precambrian Orogenic Province. The syntectonic massif consists of the anorthositic Balugaon dome, leuconoritic Rambha lobe and quartz-mangeritic Kallikota cover. A completely gradational suite comprising anorthosite-leuconorite-norite-minor jotunite (the anorthositic suite) constitutes most of the complex. The subordinate of suite of acid rocks spatially associated with this is of a broad quartz-mangeritic lithology with minor granitic rocks (the acidic suite). Geochemical evolution of the complex in the sequence anorthosite-leuconorite-norite-jotunite-acidic rocks shows moderate iron enrichment in the noritic-jotunitic stage and is marked by an overall decrease in Al₂O₃, CaO, MgO, Ni/Co, Sr/Ba, K/Rb and increase in SiO₂, K₂O, V/Ni, K/Ba and Rb/Sr. Such progressive variation in geochemical parameters appears (i) essentially gradual and frequently overlapping in rock members of the intergradational anorthositic suite and (ii) rather abrupt across transition zones between the anorthositic suite and the acidic suite due to near absence of intervening intermediate lithologies. RbSr whole rock isochron studies indicate that the complex was emplaced ca. 1400 Ma ago. The initial ⁸⁷Sr/⁶⁸Sr (0.70661) implies limited hybridisation of the parent magma prior to emplacement. A critical appraisal of all the available evidence suggests that (i) the anorthositic suite of rocks form a perfectly consanguinous and comagmatic assemblage and (ii) the spatially associated acidic suite emerged through a convergence of magmatic and metasomatic processes (the latter brought about by contact anatexis of the host rocks). The complex as well as the host metamorphics are intruded by an atectonic suite of noritic dykes emplaced ca 850 Ma ago.  相似文献   

Petrology and petrogenesis of the Mount Stuart batholith — Plutonic equivalent of the high-alumina basalt association?     

Erik H. Erikson Jr. 《Contributions to Mineralogy and Petrology》1977,60(2):183-207

The Mount Stuart batholith is a Late Cretaceous calc-alkaline pluton composed of rocks ranging in composition from two-pyroxene gabbro to granite. Quartz diorite is most abundant. This batholith may represent the plutonic counterpart of the high-alumina basalt association. A petrogenetic model is developed in which this intrusive series evolved from one batch of magnesian high-alumina basalt, represented by the oldest intrusive phase, by successive crystal fractionation of ascending residual magma. However, the possibility that this intrusive suite originated from an andésite (quartz diorite) parent by fractionation cannot be excluded.Computer modeling of this intrusive sequence provides a quantitative evaluation of the sequential change of magma composition. These calculations clearly indicate that the igneous suite is consanguineous, and that subtraction of early-formed crystals from the oldest rock is capable of reproducing the entire magma series with a remainder of 2–3% granitic liquid. This model requires that large amounts of gabbroic cumulate remain hidden at depth- an amount equal to approximately 8–10X the volume of the exposed batholith. Mass balances between the amounts of cumulate and residual liquid calculated compare favorably with the observed amounts of intermediate rocks exposed in the batholith, but not with the mafic rocks.Mafic magmas probably fractionated at depth by crystal settling, whereas younger quartz diorite and more granitic magmas underwent inward crystallization producing gradationally zoned plutons exposed at present erosional levels.  相似文献   

The Talazhin plagiodunite–troctolite–anorthosite–gabbro massif (East Sayan): petrogeochemistry and ore potential     

A.N. Yurichev  A.I. Chernyshov  A.E. Konnikov 《Russian Geology and Geophysics》2013,54(2):166-180

The petrology and ore potential of the Talazhin massif located in northwestern East Sayan are studied. The internal structure of the intrusion, the petrographic composition of its rocks, and their metallogenic, petrostructural, and petrogeochemical features are considered. The probable temperature and chemical composition of the parental magma of the pluton were computed using the KOMAGMAT-3.52 program on the modeling of equilibrium crystallization. The obtained data indicate that the Talazhin massif is a rhythmically layered plagiodunite–troctolite– anorthosite–gabbro intrusion formed from low-Ti high-alumina olivine–basalt melt. It is promising for Cu–Ni–PGE mineralization.  相似文献   

Petrogenesis of monzonoritic dykes in the Egersund-Ogna anorthosite (Rogaland,S.W. Norway): trace elements and isotopic (Sr,Pb) constraints     

J. C. Duchesne  I. Roelandts  D. Demaiffe  D. Weis 《Contributions to Mineralogy and Petrology》1985,90(2-3):214-225

Two major monzonoritic dykes occur in the Egersund-Ogna anorthositic massif (S.W. Norway): the Lomland dyke, which varies from norite to monzonite, and the Vettaland ferronoritic dyke. They are characterized by high Fe, Ti and P contents, low SiO₂, variable K₂O (0.5%–4.5%) and high Fe/Mg ratios. Small variations in REE distribution are observed inside the Lomland dyke [La/Yb=12; LREE ca. 150–180 (chondrite-normalized values), neutral to slightly positive Eu anomaly]. Part of the Vettaland dyke is severely depleted in Zr, Rb and REE and shows a positive Eu anomaly. All rocks are depleted in U and Th, and show very low Cr and Ni contents, as well as high Sr contents (400–600 ppm). Variation within the Lomland dyke is satisfactorily ex-plained through subtraction of an apatite-bearing noritic cumulate. The role of apatite is predominant in controlling the REE behaviour. Eutectic partial melting of a Fe-rich noritic cumulate (containing apatite) under low pH₂O conditions is suggested for the Vettaland dyke by REE modelling. Sr isotopic initial ratios are different in Lomland (ca. 0.708) and Vettaland (ca. 0.706) dykes. These values preclude direct derivation from the mantle as well as comagmatic relationship with anorthosite. Contamination of a mantle derived magma by deep crustal material or anatexis of the LIL depleted lower crust is compatible with the low U and Th contents, and with the Pb isotopic ratios. The Vettaland partial melting process is extended to all monzonoritic types, the necessary heat being provided by the high temperature anorthositic crystal mush. Chargé de Recherches du F.N.R.S (Belgium)  相似文献   

Geochemical relationships between anorthosite and associated iron-rich rocks,Laramie Range,Wyoming     

S. A. Goldberg 《Contributions to Mineralogy and Petrology》1984,87(4):376-387

Rocks enriched in iron oxide and mafic silicates are commonly present as minor volumes of Proterozoic anorthosite complexes. In the Laramie Range, Wyoming, anorthositic rocks, gabbros, and iron oxide ore have been chemically analyzed to determine if the spatial association is a result of genetic relationships between the rock types.Variations in abundances of REE, Th, Sc, and Sr in whole-rock and in mineral separates from anorthositic rocks provide evidence for the presence of trapped intercumulus liquid. Initial ⁸⁷Sr/⁸⁶Sr ratios in apatites separated from iron oxide ore (0.70535±0.00004) are analogous to initial ⁸⁷Sr/⁸⁶Sr ratios in Laramie Range anorthosite (0.70531 and 0.70537). In addition, REE abundances in calculated parental liquids for both anorthositic rocks and iron ore are similar, providing further evidence for a comagmatic relationship.Trace element and textural characteristics of spatially associated Laramie Range gabbros indicate that they are not mixtures of the trapped liquid and cumulus components which formed anorthositic rocks. It is suggested that gabbros are early differentiation products of a high-Al gabbroic magma which subsequently crystallized large volumes of plagioclase to produce the anorthosite massif.  相似文献   

Trace elements and Sr-isotopes in some mantle-derived hydrous minerals and their significance     

Asish R. Basu 《Geochimica et cosmochimica acta》1978,42(6):659-668

New analyses of K, Rb, Sr and Ba contents and the ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios of eight amphiboles, one phlogopite, two diopsides and one host alkalic basalt for an amphibole are reported: The samples are mostly inclusions in alkalic basalts and occur in association with peridotite inclusions. Two of the samples are from alpine-type peridotite bodies — one from the Etang de Lhers massif in the French Pyrenees and the other from the Finero massif in the Ivrea zone in northern Italy. The kaersutites come from the following localities: Hoover Dam, Arizona; Deadman Lake, California; Massif Central, France; Queensland; Spring Mountain, New South Wales.The data indicate that kaersutitic amphiboles are genetically unrelated to their host basalts. The isotopic and trace element data of these amphiboles further strengthens the suggestion of BASU and MURTHY (1977) that kaersutites play a significant role in ocean ridge basalt genesis. In addition, pargasitic amphibole with higher ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios, if present, may be important in the source regions of alkalic basalts.The bulk amphibole lherzolite from Lherz has the $\text{K}\text{Rb}$ratio and ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio appropriate for source material of ridge tholeiites. If the diopside and the amphibole in this rock had isotopically equilibrated under upper mantle conditions, the data show the time of last equilibration to be approximately 735 m.y., in contrast to the young emplacement age of the ultramafic massif.The coexisting phlogopite and diopside in the spinel lherzolite inclusion from Kilbourne Hole, New Mexico, show, surprisingly, isotopic equilibration under upper mantle conditions despite their drastically different $\text{Rb}\text{Sr}$ ratios. The data show that the phlogopite must have formed very recently in the upper mantle. This phlogopite also has a high $\text{K}\text{Rb}$ ratio (1133), contrary to the commonly held view that mantle phlogopites have low $\text{K}\text{Rb}$ ratios. The coexisting diopside shows high K content (778 ppm) and a lower $\text{K}\text{Rb}$ ratio than the phlogopite. This phlogopite lherzolite has trace elemental and isotopic characteristics that may be adequate for the origin of alkalic basalts upon partial melting.  相似文献   

High-alumina basalts of Taupo Volcanic Zone,New Zealand     

J.W. Cole 《Lithos》1973,6(1):53-64

High-alumina basalt occurs at eight localities in the Taupo Volcanic Zone associated with the Okataina, Maroa and Taupo calderas. At Tarawera the basalt is associated with a series of craters aligned NNE, and at K Trig. a series of scoria cones of similar alignment. On a broader scale the eruptive centres lie on three lines probably corresponding to major faults within the graben.Petrographically the rocks are plagioclase-olivine-augite basalts with varying percentages of each mafic phenocryst. Most are fine-medium grained, but the Ongaroto basalt is coarser-grained, and has a higher modal percentage of olivine. Chemically all are high-alumina basalts. The Ongaroto basalts has lower Al₂O₃ and higher MgO, Ni and Cr, and this, together with petrographic evidence, suggests that the rock is a cumulate.All the basalts are likely to be derived from the mantle, with intrusion into the crust controlled largely by faulting.  相似文献   

Luna 20: mineral chemistry of spinel,pleonaste, chromite,ulvöspinel,ilmenite and rutile     

Stephen E Haggerty 《Geochimica et cosmochimica acta》1973,37(4):857-867

Electron microprobe analyses of the spinel mineral group, ilmenite and rutile have been carried out on part of the Luna 20 soil sample. The spinel group shows an almost continuous trend from MgAl₈O₄ to FeCr₂O₄ and a discontinuous trend from FeCr₂O₄ to Fe₂TiO₄. Well defined non-linear relationships exist within the spinel group for Fe-Mg substitution, for divalent ($\text{FeO}\text{FeO + MgO}$) versus trivalent ($\text{Cr}{}_2\text{O}{}_3\text{Cr}{}_2\text{O}{}_3\text{+ A1}{}_2\text{O}{}_3$), and for divalent versus $\text{TiO}{}_2\text{TiO}{}_2\text{+ A1}{}_2\text{O}{}_3\text{+ Cr}{}_2\text{O}{}_3$. For Cr-Al substitution the relationship is linear and is negative for Mg-rich spinel and positive for Fe-Ti rich spinel. In general a combination of aluminous-rich chromite and ulvöspinel in the Luna 16 samples, combined with the chromian-pleonaste in Apollo 14 define comparable major compositional trends to those observed in Luna 20. Ilmenite is present in trace amounts. It is exsolved from pleonaste and pyroxene, is present in subsolidusreduced ulvöspinel and has undergone reequilibration to produce oriented intergrowths of chromite + rutile. Primary ilmenite is among the most magnesian-rieh (6 wt.% MgO) yet found in the lunar samples. The high MgO, inferred high Cr₂O₃ concentrations and the iron content of rutile (2.5 wt.% FeO) suggest crystallization at high temperatures and pressures for some components of the Luna 20 soil.  相似文献   

⁸⁷Rb-⁸⁷Sr age of fragments and soils from the lunar sea of fertility     

Jean Louis Birck  Claude J Allegre 《Geochimica et cosmochimica acta》1973,37(9):2025-2031

The Luna 16 materials were dated by the Rb-Sr method.An internal isochron age of 3.4 ± 0.2 has been determined for a 6 mg fragment.The Luna 16 total soil is poorer in radiogenic Sr than any other analyzed soil from the Moon. Apollo 14 and 15 soils have also been studied; all of them fall nearly on a 4.65 b.y. isochron with the ADOR initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio.A comparison of the integrated $\text{Rb}\text{Sr}$ of the basalt source region and the $\text{Rb}\text{Sr}$ of the rocks suggests that these basaltic fragments have been generated with only minor $\text{Rb}\text{Sr}$ fractionation.The existence of an old Rb-rich subcrust which contaminated the basalts is also in agreement with the present results.  相似文献