Showing papers on "Petrography published in 1969"
TL;DR: In this article, the isotopic composition of lead and the uranium, thorium and lead concentrations in potassium feldspars are determined for more than 30 1.0-b.y. old North American igneous rocks.
75 citations
TL;DR: The Sherman erosion surface is developed principally on the Precambrian Trail Creek granite facies of the Sherman Granite as mentioned in this paper, and it is characterized by extensive, high-temperature oxidation of Preambrian age.
Abstract: The Sherman erosion surface is developed principally on the Precambrian Trail Creek granite facies of the Sherman Granite. A distinctive petrographic characteristic of the Trail Creek granite is extensive, high-temperature oxidation of Precambrian age. Minerals so affected were principally the opaques and biotite. Later weathering processes exploited the oxidized biotites to produce vermiculite, montmorillonite, kaolinite, and gibbsite, all contributing to additional biotite expansion which has shattered the near-surface rock. Disintegration to gruss is so rapid and complete that outcrops are scarce, and a smooth, gently rolling topography results. Other crystalline rocks, lacking the early alteration, weather more slowly and selectively, providing the parkland-tor topography.
70 citations
TL;DR: Early Precambrian Onverwacht microstructures studied in petrographic thin sections and powdered preparations for possibility of oldest terrestrial fossils were used in this article for finding the earliest terrestrial fossils.
Abstract: Early Precambrian Onverwacht microstructures studied in petrographic thin sections and powdered preparations for possibility of oldest terrestrial fossils
58 citations
TL;DR: In this article, the main hypotheses for the alkali-carbonate rock reaction were reviewed and evidence supporting the mechanism advanced by this laboratory was presented, including no volume change of pure dolomite crystals immersed in 2M NaOH for 4 months, decreasing expansion of solid plus liquid of rock powders in 2m NaOH with increasing particle size of pure Dolomites, using a dilatometer technique.
Abstract: Summary This paper reviews the main hypotheses proposed for the alkali-carbonate rock reaction, and presents evidence supporting the mechanism advanced by this laboratory. The latter postulates that the alkali-expansivity of certain carbonate rocks containing dolomite is due to a wetting of previously unwetted clay minerals; the wetting is made possible by the de-dolomitization reaction which produces access channels for moisture. The new evidence consists of (a) no volume change of pure dolomite crystals immersed in 2M NaOH for 4 months; (b) the decreasing expansion of solid plus liquid of rock powders in 2M NaOH with increasing particle size of pure dolomite, using a dilatometer technique; (c) the observation from scanning electron micrographs of alkali-reactive and non-reactive rocks that much of the clay constituent appears to be distributed close to the dolomite rhombs, thus accounting more readily for the idea that dedolomitization opens up channels for moisture to gain access to the clay; and (d) a detailed study of some 50 carbonate rocks from the highly calcitic to the highly dolomitic with special emphasis on petrographic examinations and their correlations with results of laboratory performance.
47 citations
TL;DR: Sedimentary regimen, effects of Nevadan orogenesis, development of elastic-wedge configuration, sediment composition and textures, source areas, paleotectonic synthesis, time-stratigraphic cross-section.
Abstract: Sedimentary regimen, effects of Nevadan orogenesis, development of elastic-wedge configuration, sediment composition and textures, source areas, paleotectonic synthesis, time-stratigraphic cross-section
38 citations
TL;DR: The cordierite-gedrite rocks and associated gneisses on the north side of Fishtail Lake, Harcourt Township, Ontario, occur within the Grenville Gneiss complex of the Haliburton Highlands as mentioned in this paper.
Abstract: The cordierite–gedrite rocks and associated gneisses on the north side of Fishtail Lake, Harcourt Township, Ontario, occur within the Grenville gneiss complex of the Haliburton Highlands The investigation comprises a petrographic study, based on geologic mapping, and supplemented by new chemical analyses of gedrites, cordierites, garnets, biotites, and typical rocks Comparison with compositional data from other metamorphic environments shows that the compositions of associated cordierite, garnet, and anthophyllite (gedrite) and garnet–cordierite–biotite have lower FeO/(MgO + FeO) ratios in high-grade regional metamorphic environments such as exemplified at Fishtail Lake than in contact metamorphic associations The chemical composition of the rocks is characterized by high MgO and FeO and low lime and alkalies, compared with argillaceous rocks and metamorphic rocks derived from them It is suggested that this unusual composition results from the removal of an anatectic granite fluid from the parent rock
38 citations
TL;DR: In this article, the authors classified ultramafic rocks in terms of their field associations and tectonic environment and distinguished eleven associations, some with subdivisions, and emphasized that the variety of field and petrographic associations indicates that a variety of processes are involved in the origin and emplacement of these rocks.
34 citations
TL;DR: The phase relationships of four specimens from the Farrington Complex ranging in composition from granite to tonalite, and of four examples from the Star Mountain Rhyolite, have been determined in the presence of 15-20 weight per cent H 2 O in the pressure range from 1 to 3 kb.
Abstract: The phase relationships of four specimens from the Farrington Complex ranging in composition from granite to tonalite, and of four specimens from the Star Mountain Rhyolite, have been determined in the presence of 15-20 weight per cent H_2O in the pressure range from 1 to 3 kb. PT curves have been located for the beginning of melting and for the complete melting of quartz, alkali feldspar, and plagioclase. Glass percentages have been determined for representative samples by point counting in polished thin sections. The melting relationships for these two widely different series of rocks aid in defining the primary phase volumes in the "Granodiorite Tetrahedron." It has not been possible experimentally to reproduce the unusual natural phenocryst-groundmass relationships of the Star Mountain Rhyolite; this failure is attributed at least partly to the experimental condition of excess water, and confirms the conclusion, drawn from petrographic evidence, that these magmas were erupted with very low water contents.
30 citations
01 Jan 1969
TL;DR: Many of the pebbles in the late Precambrian Torridonian arkose (Applecross Formation) of northwest Scotland cannot be traced to the underlying Lewisian basement complex as mentioned in this paper.
Abstract: Many of the pebbles in the late Precambrian Torridonian arkose (Applecross Formation) of northwest Scotland cannot be traced to the underlying Lewisian basement complex. Pebbles regarded as exotic include quartz-tourmaline rock, tourmaline-aplite, quartz-fuchsite schist, pure and iron-rich metaquartzite, fine-grained igneous rocks comparable with porphyritic rhyolite and acid tuffs, and a large variety of orthoquartzite and chert. The Applecross Formation was deposited as large alluvial fans which spread out from the west. These arkosic sediments, with the exception of the exotic pebbles, probably were derived from a basement complex similar to that of northwest Scotland. The approximate maximum area of the drainage basin of the Torridonian alluvial fans has been estimated by comparison with those of modern alluvial fans. The Torridonian drainage basin, as plotted on Bullard et al.'s (1965, Fig. 7) reconstruction of the North Atlantic region prior to continental drift, is within the continental margins between Scotland and southeast Greenland. A study of the literature concerning the Precambrian rocks of southeast Greenland indicates that several of the Torridonian exotic pebble types can be matched with Precambrian rocks exposed in that region.
28 citations
TL;DR: The Atokan Series in east-central and southern Nevada and western Utah consists mostly of a repetitive sequence of carbonate rocks belonging to the Ely Group (Ely Limestone of several workers), and the many vertical changes in local stratigraphic sections and general lack of persistent thin lithostratigraphic markers attest to deposition conducive to numerous and complex lateral variations as discussed by the authors.
Abstract: The Atokan Series in east-central and southern Nevada and western Utah consists mostly of a repetitive sequence of carbonate rocks belonging to the Ely Group (Ely Limestone of several workers). The many vertical changes in local stratigraphic sections and general lack of persistent thin lithostratigraphic markers attest to deposition conducive to numerous and complex lateral variations. Moreover, the probability that species of fusulinids used for time-stratigraphic determinations are facies-restricted and the widespread deformation preclude precise correlation of narrowly defined time-stratigraphic units within the more broadly defined Atokan Series. Petrographic analysis, however, permitted recognition of nine limestone types that have been linked in a conceptual model elating environmental energy, relative depth, and biologic distribution: type 1, spiculiferous fine-grained limestone; type 2, fine-grained limestone and skeletal calcarenitic limestone; type 3, mud-supported calcarenitic limestone with pelletoid grains absent or not abundant; type 4, grain-supported calcarenitic limestone with pelletoid grains absent or subordinate; type 5, fine-grained and medium-grained calcarenite; type 6, coarse calcarenite and calcirudite; type 7, mud-supported and grain-supported pelletoid calcarenitic limestone; type 8, Komia limestone; type 9, Donezella limestone. Rock type 1 and most varieties of type 2 probably represent deepest water deposition and, with type 9, they are interpreted as having originated under the lowest energy conditions. Rock type 6 formed under the highest energy conditions of deposition. Chaetetes-bearing units are common, and Chaetetes is believed to have flourished primarily in areas of deposition of fine-grained limestone and calcarenitic limestone, the rocks which constitute most of the "matrices" in Chaetetes-bearing units. Most of the foregoing characteristics apply to Atokan carbonate sequences in other parts of the eastern Great Basin.
27 citations
TL;DR: In this paper, a summary of chemical and mineralogical data on intrusive igneous rocks in a segment of the Southern Appalachian orogenic be]~ The exposed crystalline part of the southern Appalachians reaches a maximum width of about 300 km in North Carolina and South Carolina and narrows along strike to the northeast and southwest.
Abstract: This paper presents a summary of chemical and mineralogical data on intrusive igneous rocks in a segment of the Southern Appalachian orogenic be]~ The exposed crystalline part of the Southern Appalachians reaches a maximum width of about 300 km in North Carolina and South Carolina and narrows along strike to the northeast and southwest (Fig I) We have attempted to delineate the major groups of intrusions in this segment Few detailed studies or discussions of differentiation trends shown by intrusive rocks in this region have been published previously The purpose of this paper is: (1) To give the general characteristics and distribution of major groups of p]utons (2) To define the chemical trends in major elements that are exhibited by the groups and (3) to discuss the origin of the intrusive rocks and their role in the evolution of the Southern Appalachians Major element analyses by rapid methods were made of 198 selected samples Chemical methods, and precision and accuracy of analyses are the same as described by RAGLA~D et al (1968) The chemical analyses were performed by a combination of atomic absorption and x-ray spectrometry All chemically analyzed samples, except for 27 that are very fine-grained, were also modally analyzed The point-count method of CHAu (1956) was used for fine- or medium-grained rocks About 1500 points were counted over an area large enough to maintain an analytical error for major minerals of 2 % or less (CHAYES, 1956, p 82) Where average grain size is greater than about 5 ram, the required number of thin sections becomes prohibitively large; therefore, slabs stained with sodium cobaltinitrite were also used A slab area at least 100 times greater than the area of the largest mineral grain was used, and 1000 to 1500 points were counted A point count of two to four thin sections was used to determine the approximate percentage of biotite, sphene, opaque minerals and other minerals in the "dark minerals" category obtained from the slab count Rock names are used as defined in the descriptive modal classification of PETEI~SON (1961) Modern, large-scale geological maps are available for only a small percentage of total area in the c;ysta]line Southern Appalachians It will take considerably more mapping, petrographic and chemical studies, and determination of radiometrie ages to decipher the complex intrusive history of the region We present here a first approximation, which will undoubtedly be modified by later studies
01 Jan 1969
TL;DR: Granitic rock types have been studied extensively in the literature, see as mentioned in this paper for a survey of the main types of granitic rocks and their application in the field of petroglastic metamorphism.
Abstract: __________________________________________ Introduction_______________________________________ Methods of study.__________________________________ Granitic rock types___._____________________________ Tinemaha Granodiorite..________________________ Santa Rita Flat pluton._____________________ Hunter Mountain Quartz Monzonite. _____________ Pat Keyes pluton___________________________ Type 1, seriate quartz monzonite ___-__-__ Type 2, quartz monzonite-granodiorite_ __ Type 3, dark-colored contaminated rocks. _ _ Willow Creek mass__________________________ Page 1 1 2 3 3 3 11 11 11 20 22 24 Granitic rock types Continued Paiute Monument Quartz Morizonite. Structural features.____________________ Chemical trends.______________________ Petrogenesis__ _ _ _____________________ Contact metamorphism.________________ Methods of emplacement-_____--____-__ Age.---_____-___-__-_-_-_---_-____--_ Distribution of minor elements._________ References cited.______________________ Index ________________________________ Page
TL;DR: In this article, the reliability of K-Ar ages on fresh basaltic rocks, various fractions and whole rocks were dated and the dates provided no evidence of argon leakage.
Abstract: To evaluate the reliability of K-Ar ages on fresh basaltic rocks, various fractions and whole rocks were dated. The samples were chosen to obtain a variety of petrographic types representing several petrologic kindred and cooling environments. The dates provided no evidence of argon leakage. One sample of an unusual rock type (a troctolite) gave an anomalously high age, suggesting excess radiogenic argon. Nepheline separates from two rocks yielded ages equivalent to the ages of biotite and pyroxene.
TL;DR: In this paper, field, petrographic and chemical studies on the Silurian volcanic rocks of the Mendip Hills show that there are probably 15 or more rock units in the series including andesite and rhyodacite lavas, rhyodicite tuffs, agglomerates, and a dolerite dyke.
Abstract: Field, petrographic and chemical studies on the Silurian volcanic rocks of the Mendip Hills show that there are probably 15 or more rock units in the series including andesite and rhyodacite lavas, rhyodacite tuffs, agglomerates, and a dolerite dyke. The predominant rock type is rhyodacite which may be as much as 80 percent of the volcanics. Volcanics of Silurian age from the Tortworth area, Gloucestershire, are of latite-andesite composition.The Mendip rocks have been deuterically altered. Calcite-quartz-laumontite veins are common in fractures in these rocks. The agglomerates are particularly susceptible to weathering and some bombs are extensively altered to clays. Twelve rocks were chemically analysed for 36 elements each. No anomalous base metal concentrations were found in the volcanics although Pb, Zn, and Cu mineralisation is known in the area. K/Rb varies from 202 to 909 in these calc-alkaline rocks.
TL;DR: The Troodos volcanic series as mentioned in this paper is a series of olivine crystals layering in lava flows and pillows and is composed of two types of petrography: Picritic-peridotitic and peridotite.
Abstract: Picritic-peridotitic composition, olivine crystals layering in lava flows and pillows, field relations, petrography, mineralogy and chemistry, Troodos volcanic series
01 Jan 1969
TL;DR: The ophiolitic suite studied in the northern Pindus range (Greece) includes, from bottom to top, the following petrographic types as discussed by the authors : various peridotites (dunites, harzburgites, lherzolites), olivine-rich gabbros (allivalites), and Gabbros without olivines passing progressively to dolerites and albitophyres the Upper levels of which are pillow lavas.
Abstract: The ophiolitic suite studied in the northern Pindus range (Greece) includes, from bottom to top, the following petrographic types : various peridotites (dunites, harzburgites, lherzolites), olivine-rich gabbros (allivalites), and gabbros without olivine passing progressively to dolerites and albitophyres the Upper levels of which are pillow lavas. The petrographic observations from a sample series taken systematically along the tut, at regular close intervals, as well as from the corresponding chemical analyses, show the presence of two important breaks in the suite - these breaks separate three principle rock groups : at the base the peridotites, in the middle the gabbros and dolerites, and at the top the albitophyres. However the close association of these three groups at the site seems to support the hypothesis of an original common magma, the composition of which would be close to that of a melanocratic olivine tholeiite. The two breaks referred to above imply nevertheless important and consecutive ensemble which could have occurred just before effusion, even during the rise of the original common magma. The ophiolitic suite would thus be the result of simultaneous settling of three preformed rock groups.
01 Jan 1969
TL;DR: In this article, an attempt is made to report on the quantitative petrography of the Payande stock and associated metamorphic rocks, which is a composite body of Late Jurassic or Early Cretaceous age, which thermally metamorphosed de surrounding rocks.
Abstract: An attempt is made to report on the quantitative petrography of the Payande stock and associated metamorphic rocks.
The Jura-Triassic sediments and the regionally metamorphosed Precambrian rocks were intruded by the Payande Stock, a composite body of Late Jurassic or Early Cretaceous age, which thermally metamorphosed de surrounding rocks.
The petrographic study of the stock shows it to be composed of two different intrusions: a small intrusion of quartz-diorite that was followed by a larger one of granodiorita, closely related in time. These were followed by intrusions of pegmatite-aplite, andesite---dacite, and lampro phyric dikes.
The thermal metamorphism of the host rocks was studied using a combination of petrographic, chemical and X-ray diffraction methods. Two metamorphic facies, the hornblende-hornfels and albite-epidote-hornfels, are present and are asymmetrically distributed about the stock.
The characteristic mineral assemblages as well as the isograds are shown on the geologic map. An effort is made to give some idea of the pressure-temperature conditions that prevailed during the metamorphism on the basis of critical mineral assemblages and individual minerals.
On the basis of the distribution of the isograds it is concluded that the Payande Stock is a rather thin irregular sheet with a westerly dip.
TL;DR: X-ray diffraction analysis can be used as a routine, rapid, and supplementary method for analyzing large numbers of heavy mineral samples as mentioned in this paper, which can be classified according to their gross diffraction patterns or diffraction "finger prints".
Abstract: Techniques have been developed which yield reproducible results for X-ray diffraction analysis of heavy mineral samples. Uniformity of grinding, orientation of mounted mineral particles, mass absorption fluorescence, and textural character of heavy mineral grains are the important, influential variables whose effects on X-ray diffraction analysis of heavy minerals have been determined and minimized. Heavy mineral samples can be grouped according to their gross diffraction patterns or diffraction "finger prints," which correspond to petrographic groups. X-ray diffraction analysis can be used as a routine, rapid, and supplementary method for analyzing large numbers of heavy mineral samples.
01 Jan 1969
TL;DR: In this paper, the mineral compositions of sediments of the Caribbean Sea have been ascertained on the basis of X-ray diffraction analyses, and it is possible to divide the Caribbean basin into at least two general petrographic provinces, a western province bordering the Central American coast and a southern province extending out from the coast of South America.
Abstract: The mineral compositions of sediments of the Caribbean Sea have been ascertained on the basis of X-ray diffraction analyses. As a result of the studies of the clay-size fraction (smaller than 2 µ) and the silt-size fraction (2-37 µ) it is possible to divide the Caribbean basin into at least two general petrographic provinces, a western province bordering the Central American coast and a southern province extending out from the coast of South America. There is probably another province adjacent to the Greater and Lesser Antilles, but the data from these regions were insufficient to outline the province clearly.
TL;DR: Hercynian biotite and two-mica granites were used for petrography in central France as mentioned in this paper, where the relation to crystalline basement was investigated.
Abstract: Hercynian biotite and two-mica granites, petrography, relation to crystalline basement, tabulated chemical data, central France
TL;DR: Petrographic and mineralogic characters can be used to define four major units in the Black River Group of southwestern Ontario as mentioned in this paper, which are considered to be ancient analogues of the present day supratidal carbonate environments.
Abstract: Petrographic and mineralogic characters can be used to define four major units in the Black River Group of southwestern Ontario. The presence of large scale sedimentary structures, extremely high dolomite content, abundance of anhydrite, celestite in insoluble residues, and certain textural features suggest a shallow water environment with high salinity and subaerial exposure of wide areal extent during the deposition of the two lower units. These basal carbonates of the Black River Group are considered to be ancient analogues of the present day supratidal carbonate environments.
TL;DR: Feldspathoidal rocks are generally considered to be postorogenic and concentrated in the stable portions of continents as mentioned in this paper, however, these erroneous ideas have biased petrogenetic hypotheses.
Abstract: Feldspathoidal rocks are generally considered to be postorogenic and concentrated in the stable portions of continents. These erroneous ideas have biased petrogenetic hypotheses. Of the more than 120 feldspathoidal rock occurrences in North America, only one-third are in the shield and stable craton; the remainder are within Phanerozoic orogenic belts. Approximately 20 percent of all occurrences are pretectonic or syntectonic. In several regions (usually considered petrographic provinces) superficially identical feldspathoidal rocks were emplaced over spans of several hundred million years. Time correlation based upon petrologic similarity and geographic proximity is as risky for these igneous rocks as it is for sedimentary rocks. Hypotheses stating that feldspathoidal rocks are generated during “crustal tension” and rift faulting seem inapplicable to North America.
Dissertation•
01 Jan 1969
TL;DR: The Lahanos pyritic sulphide deposit is one of the important copper deposits occurring within the submarine volcanic environment of the Eastern Pontus Ore province as mentioned in this paper, it is situated 10 miles to the south of Espiye, Giresun Vilayeti.
Abstract: The Lahanos pyritic sulphide deposit is one of the important copper deposits occurring within the submarine volcanic environment of the Eastern Pontus Ore province. It is situated 10 miles to the south of Espiye, Giresun Vilayeti. Petrographic study of the Lahanos rocks, despite their heavy alteration, shows that they belong mainly to the calc alkaline and tholeiitic basalt suites, and in addition, there are some high-alumina basalts. The intense igneous activity took place during the Mesozoic and the early and middle Tertiary periods. This phase of igneous activity culminated in the intrusion of syntectonic granites, tonolites and adamellites, and was followed by aplitic and hydrothermal phases, in the Pontid Geosyncline. The ore mineralisation, associated with dacites, is characterised by large quantities of pyrite associated with other base metal sulphides such as chalcopyrite, sphalerite, galena and other sulphides and sulphosalts. Field, underground and borehole evidence shows that the Lahanos ore body displays a zonal arrangement, which is similar to the well documented "Kuroko" type ore deposits in Japan. The results of detailed chemical and mineralogical study of the ore and country rock are given and the temperature of formation is estimated. Comparative details are given for the Murgul and Karadere deposits. The evidence supports an epigenetic hydrothermal origin for this "strata bound" deposit, but the volcanicity alone is inadequate to explain the source of the base metals, which are probably derived from the granites. The role of pyroclastic horizons of restricted permeability as a control of precipitation is discussed.
TL;DR: New petrographic and chemical data for pseudoleucite from Spotted Fawn Creek and two new nearby localities in central Yukon Territory are presented and discussed in the light of recent experimental results.
Abstract: New petrographic and chemical data for pseudoleucite from Spotted Fawn Creek and two new nearby localities in central Yukon Territory are presented and discussed in the light of recent experimental...
01 Jan 1969
TL;DR: The main factors that lead to variation in detrital sediments are conceptually labelled as source material, which may consist of fresh rock and its weathered products, erosion, transportation, deposition and diagenesis; interpretive petrology depends upon the specification of petrographic properties which reflect the variation which arises from these six sources of variation as mentioned in this paper.
Abstract: The main factors that lead to variation in detrital sediments are conceptually labelled as source material, which may consist of fresh rock and its weathered products, erosion, transportation, deposition and diagenesis; interpretive petrology depends upon the specification of petrographic properties which reflect the variation which arises from these six sources of variation.
TL;DR: In this paper, carbonatitic fragments from the West Eifel were described in terms of their petrography and trace-element content, and the trace element content was analyzed.
Abstract: Newly-discovered carbonatitic fragments from the West Eifel are described in terms of their petrography and trace-element content.
TL;DR: In this article, a detailed study of stained Pleistocene-Recent biolithites from Erromango reveals an advanced state of diagenesis in carbonate sediments.
Abstract: Petrographic study of stained Pleistocene-Recent biolithites from Erromango reveals an advanced state of diagenesis. Micrite is produced by grain diminuton of algal colonies, and probably by fragmental abrasion. Other fabrics developed include granular mosaics and simple syntaxial rims. In samples collected from carbonates sandwiched between volcanic ash bands, two phases of cementation are apparent. The first phase cement is composed of ferroan calcite, which is followed by a second phase of non-ferroan calcite cement. Ferroan calcite is previously unrecorded as a cement in Recent carbonates, and in addition it is very rare as a first stage cement in ancient carbonates. Diagenesis of these carbonate sediments has produced in a very short time a hard, compact, partially recrystallized rock. Reasons for this advanced state of diagenesis are unknown, but in all probability they are connected with the high heat values in the rocks resulting from contemporaneous volcanicity.