Showing papers on "Petrography published in 1974"

Laboratory handbook of petrographic techniques

Abstract: Contents include: Thin-section preparation. Aids in thin-section study. Grain size, modal analysis, and photomicrography. Rotation methods for the polarizing microscope. Mineral separation, Powder methods of x-ray diffraction. Application of x-ray powder data to specific mineral groups. Specific gravity determination, Refractive index determination. X-ray fluorescence spectrometry. Atomic absorption spectrophotometry. Determination of chemical components not attainable by the foregoing methods. Display of data. Thermal analysis techniques. References. Appendix. Index. This handbook stresses the practical aspects of commonly-used petrographic techniques that are generally applicable to igneous and metamorphic rocks, Author is with the University of Malaya, Kuala Lumpur, Malaysia. -- AATA

Deposition and Diagenetic Alteration of Sandstone in Northeast Pacific Arc-Related Basins: Implications for Graywacke Genesis

Abstract: Sedimentary basins characterized by continental to marine shelf depositional regimes are common adjuncts to active lithospheric plate junctions of the northeast Pacific area. Most of these basins are elongate troughs and may form in both fore-arc and back-arc positions. Andesitic composition of volcanic and plutonic rocks that form the major source lithologies in active or recently active arcs produces petrologically distinctive sands that are dominated compositionally by volcanic rock fragments, plagioclase feldspar, and mafic heavy minerals. Quartz content of the sands is low and rarely exceeds 50 percent. Such sands are mineralogically unstable and react upon shallow to moderate burial and consequent increase in temperature and pressure to produce a recurrent sequence of authigenic cements. Three progressive stages of diagenesis are differentiated in sample suites from the Bristol, Queen Charlotte, Grays Harbor, and Chehalis basins: stage 1, early diagenetic calcite pore-filling cement; stage 2, authigenic clay rims and coats around detrital grains; stage 3, authigenic phyllosilicate and (or) laumontite pore-filling cement. Development of silicate overgrowths with chlorite and calcite replacement of rock fragments and plagioclase becomes more pronounced as burial is further increased. As the depth of burial increases, higher temperature, overburden pressure, and fluid pressure result. Of these three factors, geologic evidence favors temperature as the primary control of burial diagenetic reactions. Petrographic data support the concept of a diagenetic origin for graywacke matrix. The second and third diagenetic stages recognized here result in the authigenesis of clay minerals and micas and can reasonably be considered precursors of a graywacke lithology.

Alteration and Fluid Inclusion Studies of the Porphyry Copper Ore Body at Bingham, Utah

Abstract: Distribution patterns for biotitic alteration, sericitic alteration, and distinctive fluid-inclusion types in igneous host rocks of the porphyry copper ore body at Bingham, Utah, have been determined by petrographic examination of about 300 samples. These patterns are related to differences in original rock composition, variations in physical-chemical conditions during periods of intrusion and mineralization, and spatial position within the ore body.The distribution of biotitic (potassium-silicate) alteration assemblages and high-salinity fluid inclusions generally follows the crudely triangular form of the disseminated copper ore zone. Variations in abundance of hydrothermal biotite are attributed to differences in original mafic mineral content of the igneous host rocks. Biotitic alteration and initial copper mineralization were accomplished by high-salinity fluids concentrated during final crystallization of the monzonitic parent magma; genetic continuity between magmatic and hydrothermal stages is indicated.Pervasive sericitic alteration of plagioclase is confined to rocks in the northern one-third of the Bingham stock; a subzone of argillic alteration in the north-central part of the ore body occurs within the broader area of sericitic alteration. Fluids responsible for sericitic and argillic alteration were channeled by a broad zone of northeast-trending fractures.Hydrothermal minerals and high-salinity fluid inclusions occur within a large volume of shattered rock. Boiling of fluids during crystallization of the aplitic porphyry may account for the shattering. Sericitic (and argillic) alteration were apparently super-imposed on the earlier biotitic assemblage as the hydrothermal system cooled. Cooling and hydrolytic alteration were promoted by progressive introduction of meteoric waters. The many generations of inclusions trapped from boiling fluids in the temperature range 400 degrees to 600 degrees C suggest that the system was recharged repeatedly during the period of mineralization. Estimated fluid pressures of about 800 bars in the early stages of mineralization correspond to a lithostatic load of about 3 km; pressures were even lower (less than 200 bars) in the later stages and were probably controlled by hydrostatic conditions.

A geochemical investigation of pressure solution and the formation of veins in a deformed greywacke

Abstract: Pressure solution and vein formation often occur simultaneously in shear zones during the deformation of sedimentary rocks. The mineralogical and chemical variations around a typical example of an en echelon zone of quartz veins from north Cornwall are discussed in detail. Solution of quartz is confined to the shear zone and occurs along discrete surfaces. Accumulation of insoluble minerals along these surfaces gives rise to spaced pressure solution cleavage. Petrographic data show that during pressure solution the breakdown of felspar and epidote results in the crystallisation of clay mineral, quartz and siderite. Redistribution of silica within the shear zone by pressure solution does not account for all the quartz in the veins, or for the observed increased concentration of iron and calcium. It is concluded that material was introduced from an external source into the shear zone.

Stratigraphy, lithology, structure, and metamorphism of Permian, Triassic, and Tertiary rocks between the Mararoa River and Mount Snowdon, western Southland, New Zealand

Abstract: An area in western Southland underlain by Permian, Triassic, and Tertiary rocks is mapped and described geologically. New stratigraphic, lithologic, and petrographic data are presented, and several new mapping units are proposed. These latter include Upukerora Formation, a predominantly coarse-grained, volcanogenic sedimentary unit which occurs at the base of the Bryneira Group; Key Summit Volcanic Sandstone a characteristically massive green rock which underlies large portions of Bryneira Group outcrop north of the present area ; Snowdon Formation, a resistant conglomeratic and tuffaceous unit belonging to the Murihiku Supergroup; and the Annick and Waiau groups, Tertiary sediments of the Te Anau Basin. Several previously defined units are also mapped, described and in some cases, revised: Red Mountain, Livingstone, Howden, Anneal, Tapara, Winton, and Countess. Bryneira and Murihiku rocks comprise sparsely fossiliferous, richly volcanogenic geosynclinal strata which accumulated adjacent to an is...

Les glaucophanites et roches associées de l'île de Groix (Morbihan, France): étude minéralogique et pétrogénétique

Abstract: The petrographic and mineralogic study of the different rock facies on ile de Groix shows that two metamorphic episodes have affected the alkaline basic rocks and associated pelitic schists. The first is represented by a zonation (west-east): II-III-II-I-II where I= eclogite facies glaucophanites (8,5 bars, 530°C), II=glaucophane-epidote-garnet facies (8 kbars, 500°C), III=greenschist facies containing blue-green amphibole (7,5 kbars, 470°C). The second metamorphic episode has partially transformed these rocks to the albite-chlorite-epidote-blue green amphibole facies (6,5 kbars, 470°C). The variations of $$P_{O_2 } $$ and $$P_{{\text{H}}_{\text{2}} {\text{O}}}$$ as they affect local assemblages is detailed.

Petrology of carbonate rocks of the Green River Formation (Eocene)

Abstract: Lacustrine carbonate rocks of the Green River Formation contain a diversity of lithologic components and sedimentary features that are comparable to carbonate formations of marine origin. Fossils (algal plates, ostracodes, molluscs), coated grains (ooliths, pisoliths, circumcrusts), and polygenetic microcrystalline carbonate aggregates (intraclasts, peloids) are the main rock-forming carbonate grains. No genetic difference between ooliths and pisoliths was found. Both grain types display probable algal cell molds and are believed to be algal precipitates. Microcrystalline carbonate is more abundant than sparry carbonate in most rocks, although well-washed, grain-supported sparites are not uncommon. Dolomicrite is ubiquitous in the formation and petrographic evidence indicates that it ormed as a selective replacement product of calcium carbonate mud during early diagenesis prior to lithification. Admixed terrigenous constituents are an important component in most of the carbonate rocks; siltstone and sandstone are transitional with silty and sandy carbonate rocks. The similarity of lacustrine and marine carbonate rocks indicates that the two types can not be differentiated solely on the basis of petrographic relations. Sedimentary structures and stratification types are especially well developed in many of the carbonate rocks and greatly aid in the interpretation of subenvironments of deposition. The use of structures and stratification types in conjunction with lithologic variations and associations permits the recognition of several lacustrine subenvironments: mudflat, beachbar, lagoonal, shoal, transitional and offshore. Algal stromatolite bioherms locally are present in rocks of the shoal facies.

The petrography and origin of dedolomitized, veined or brecciated carbonate rocks, the ‘cornieules’, in the Fréjus region, French Alps

Abstract: Cornieules (or rauhwackes) are essentially dedolomitized, veined or brecciated carbonate rocks or marls with a characteristic porous to cellular appearance. In hand specimen, they can be divided into two types, those with a veined structure, and those showing a brecciated structure. In the Frejus region and in most other areas both inside and outside the Alps, cornieules are restricted in occurrence to evaporitic sequences. They are frequently associated with gypsum or anhydrite, which suggests a genetic link between cornieule and evaporites. This was confirmed when a full petrographic investigation was carried out, first on a Triassic evaporite sequence and then on cornieules. Field and petrographic evidence has revealed that cornieules are formed from a starting material of gypsum and dolomite that had been fractured, veined and brecciated many times. The causes of fracturing were probably tectonic in the initial phases, and non-tectonic later. Due to the major post F 4 metamorphism, the gypsum was replaced by calcite and the calcite was subsequently dolomitized. Dolomitization was accompanied by a 12–13% increase in porosity. When the rocks were brought near to the earth’s surface, chemically active sulphate-rich percolating solutions invaded the rocks, brought about dedolomitization and formed the cavernous structure of cornieule.

Red Sea Evaporites: A Petrographic and Geochemical Study

Abstract: The top of the evaporite sequence correlates with a strong reflector (Reflector S) which has been mapped over much of the Red Sea (Ross et al., 1969, Phillips and Ross, 1970). This indicates that the Red Sea appears to be underlain by late Miocene evaporites throughout most of its extent. Miocene sediments, including evaporites, are known from a few outcrops along the coastal plains of the Gulf of Suez to lat 14°N (Sadek, 1959, cited in Friedman, 1972; Heybroek, 1965; Friedman, 1972). Along the length of the Red Sea, the presence of Miocene salt is indicated by seismic reflection studies (Lowell and Genik, 1972) and confirmed by drilling. The recently published data from deep exploratory wells (Ahmed, 1972) demonstrate the great thickness of elastics and evaporites which were deposited in the Red Sea depression during Miocene time. The Red Sea evaporites are of the same age as the evaporites found by deep sea drilling (DSDP Leg 13) in the Mediterranean Sea. Therefore, Reflector S in the Red Sea is comparable to Reflector M in the Mediterranean. It is assumed that during Miocene time a connection between these two basins was established (Coleman, this volume) resulting in a similar origin for the evaporites deposited in the Red Sea and in the Mediterranean Sea. The origin of the Mediterranean evaporites has been discussed in great detail (Hsü et al., 1973; Nesteroff, 1973; Friedman, 1973). The formation of evaporites may be interpreted by three different hypotheses. 1) Evaporation of a shallow restricted shelf sea or lagoon which receives inflows from the open ocean. 2) Evaporation of a deep-water basin which is separated from the open ocean by a shallow sill (Schmalz, 1969). 3) Evaporation of playas or salt lakes which are situated in desiccated deep basins isolated from the open ocean (Hsü et al., 1973). The purpose of this study is to show whether one of these models might apply to the formation and deposition of the Red Sea evaporites. Therefore, a detailed petrographic and geochemical investigation was carried out.

Evidence for a ∼ 4.5 aeon age of plagioclase clasts in a lunar highland breccia

Abstract: Argon from neutron-irradiated mineral separates and whole rock samples of a metamorphosed breccia (65015) from Apollo 16 has been analysed with a large number of gas extraction steps in order to obtain a high resolution in the apparent ages and to identify the gas released from different sources. The results on plagioclase show a 40Ar–39Ar plateau age of 3.98 × 109 yr, which we attribute to the time of metamorphism, and an age of ∼ 4.5 × 109 yr in the high temperature fraction. Correlation of the release pattern with 37Ar instead of 39Ar permits the association of the ∼4.5 × 109 yr age with relict plagioclasts which were demonstrated in previous petrographic and Rb-Sr studies as being unequilibrated. This result suggests that it is possible to identify lithic components which represent the early lunar crust.

Meteoritic and volatile elements in Apollo 16 rocks and in separated phases from 14306

Abstract: Recent evidence from two sources provides a basis for a reexamination of the relationship between the stratigraphy at the Apollo 16 site and the trace element distribution. Information concerning the surface exposure ages makes it possible to relate many samples to specific local impact events. At least five ancient meteoritic components have been tentatively assigned to individual basin-forming impacts on the basis of trace element analyses of Apollo 17 rocks. Attention is given to a petrographic examination of separates from two soils from Station 11 (North Ray Crater).

Petrography and mineralogy of the peralkaline silicic rocks

Abstract: The mineralogy and textures of quartz-normative peralkaline trachytes and the comendites and pantellerites are described in detail, using published examples and new information on rocks from the Naivasha area, central Kenya. Mineral assemblages are tabulated for each rock type, and attention is drawn to the mineralogical differences between glassy and crystalline varieties. The petrography of peralkaline ignimbrites is briefly discussed.

Petrography and Geochemistry of Red Sea Dolomite

Abstract: Examination of piston cores and, particularly, sediments collected by the Deep Sea Drilling Project has shown that authigenic dolomite occurs in a wide range of sedimentary associations. While the trace to a small percentage of dolomite often encountered in pelagic carbonate sequences may be a result of authigenesis under "normal" deep-sea conditions, the few studies to date seem to indicate that dolomite is abundant only in sediments presumably formed under conditions other than normal open marine. For example, certain dolomite sequences have been ascribed to magnesium enrichment associated with igneous activity (Bonatti, 1966; Riedel et al., 1961). In other cases dolomites are thought to have formed in association with hypersaline brines. A DSDP core (Site 12) from the African continental margin contained abundant dolomite and palygorskite. Peterson, Edgar, et al. (1970) feel that hypersaline brines, formed in near-shore lagoons, moved down through the deep-water sediment sequence by a process of refluxion. In other cases, hypersalinity is associated with desiccation. Miocene sediment sequences drilled in the Mediterranean contain abundant dolomite associated with halite and anhydrite. Ryan, Hsü, et al. (1973) postulate that these sediments formed during a "salinity crisis." Another compelling association is that of dolomite and inferred reducing conditions noted in cores recovered by DSDP from the African continental margin and the Cariaco Trench of the Caribbean Sea (Hayes, Pimm, et al., 1973; Edgar, Saunders, et al., 1973). Whether organic matter itself is a big factor, or whether hypersalinity associated with environmental extremes in these inferred barred basins is controlling, is still a problem.

Petrology of the highlands massifs at Taurus-Littrow - An analysis of the 2-4 mm soil fraction

Abstract: The petrography, phase chemistry, and Ar-40/Ar-39 ages of 2-4 mm fragments from the soils of both mare and highlands stations sampled by Apollo 17 are studied. It is found that the massifs consist of a complex stratigraphy of interlayered noritic breccias of varying metamorphic grades, melt rocks, and anorthositic rocks. A stratigraphic correlation of the lithologies within the North Massif and the South Massif is carried out. The petrogenesis of rock types with respect to thermal and impact history is discussed. The observed spinel cataclasites may represent relatively deep material sampled by the Serenitatis event.

Source rocks of the Lower Old Red Sandstone: Exotic Pebbles from the Brownstones, Ross-on-Wye, Hereford and Worcester

Abstract: The pebble suite, preserved in sandstones and conglomerates, comprises various igneous, sedimentary, and metamorphic rocks. The igneous rocks are acid lavas and tuffs, some of the latter with Ordovician graptolites. The sediments include gray-wackes and a variety of well sorted sandstones, some preserving Silurian shelf-facies faunas, and others Old Red Sandstone faunas together with an Old Red petrography. There are also cataclasites, a metamorphic quartzite, and jaspers that invite comparisons with Precambrian rocks of the type now known in Anglesey. It is concluded on the grounds of fauna, petrographic comparisons, and the facies and cross-bedding orientation of the preserving deposit, that the assemblage originated in the Welsh region from Ordovician, Silurian, early Lower Old Red Sandstone and, perhaps, Precambrian rocks. Its character amplifies the earlier view that by late Lower Devonian times denudation in the Welsh region had already led to the partial removal of early Devonian and Silurian rocks.

Opaque mineralogy - Apollo 17, rock 75035

Abstract: Rock 75035 is a medium-grained, holocrystalline, subophitic ilmenite basalt collected from the rim of Camelot Crater, and is believed to represent the subfloor basalts of the Taurus-Littrow valley. The rock consists of the major minerals pyroxene (45%), plagioclase (31%), and ilmenite (17%). Minor minerals include cristobalite (about 5%), troilite, native Fe, tranquillityite, baddeleyite, zirconolite, and rare ulvospinel. No olivine or armalcolite was observed in the specimen 75035,76. Mineralogically and chemically, as well as in age, this rock is similar to others collected from Camelot and other stations during the Apollo 17 mission. These rocks are almost identical to the Type B ilmenite basalts of Mare Tranquillitatis.

Petrographic and electron microprobe investigation of some deep- and shallow-water manganese nodules

Abstract: Manganese-rich nodules from the flanks of the Carlsberg Ridge in the Indian Ocean, the Jervis Inlet on the Pacific Coast of Canada, and Loch Fyne, western Scotland have been examined by petrographic, X-ray diffraction, bulk chemical, and electron micro-probe methods. The deep-water nodule from the Carlsberg Ridge is typical of oceanic nodules and is characterised by well developed concentric structures, a high content of Cu, Ni, Co, and Pb and a low Mn/Fe ratio (1.3). The trace elements show associations found in previous studies, although they are less regular. The shallow-water nodules (Jervis Inlet and Loch Fyne) do not show the concentric structures to the same extent, are much poorer in trace elements, and have much higher Mn/Fe ratios (8.8 and 14.9, respectively) than the Carlsberg Ridge nodule. δ-MnO2 is the principal mineral in the deep-sea nodule but 10A manganite (todorokite) is the principal phase in the shallow-water nodules. Angular detrital quartz and feldspar are common in the shal...

Chemical Trends across Cretaceous Batholithic Rocks of Southern California

Abstract: Nine major and minor chemical elements and specific gravity have been determined for composite samples from 542 localities in Cretaceous batholithic rocks of southern California. The rocks range from gabbro to quartz monzonite. Chemical variations reflect the strong petrographic zonation of the region from abundant low-silica rocks near the continental margin to abundant high-silica rocks inland 100 to 150 km. The rocks are mostly quartz plutonites, and within each quartz plutonite group, most chemical variations are opposite those of the batholith as a whole; potassium, however, increases consistently inland. The variation of K cannot be correlated with the variation of any other major or minor element of the batholithic rocks in any of the rock types except gabbro. Though field relations and radiometric ages prove that the gabbroic rocks belong to the batholith, their magmatic origins appear to be separate from those of the intermediate- and high-silica rocks.

Notes on the petrology of some ophiolites, othris mountains, Greece

Abstract: Igneous rocks typical of ophiolite complexes are preserved in a stack of thrust sheets in the Othris Mountains of eastern Greece. Mineralogical studies of mafic rocks indicate that the majority have tholeiitic affinities, but there is evidence of a subordinate, mildly alkaline trend. Petrographic and chemical evidence suggest that the present mineral assemblage in the mafic rocks may be the result primarily of the activity of deuteric or secondary hydrothermal fluids. The “amphibolites” so common in dredge-hauls from the oceans may have originated in the same way. These metamorphic rocks, with perfectly preserved igneous textures, must be distinguished from schistose amphibolites, which also occur on the ocean floors and in ophiolite complexes.

Petrology and Chemistry of the Rock Creek Flow, Columbia River Basalt, Idaho

Abstract: A detailed re-examination of the Rock Creek flow, one of the thickest known pre-Yakima basalt flows of the Columbia Plateau, includes 5 wet-chemical and 55 rapid x-ray fluorescent analyses for major elements. The samples were collected at regular intervals from five sections through the flow over a distance of ~ 20 mi. A revised description of the flow9s field characteristics and petrography is included. The Rock Creek flow is typical of the pre-Yakima basalt in most of its field, petrographic, and chemical properties and is quite distinct in all these properties from the Yakima basalt. It differs from the Picture Gorge basalt type in its higher olivine, TiO 2 ; and K 2 O content, and is regarded as a member of a discrete Rock Creek basalt type which will form a valuable marker horizon in the southeast part of the plateau. In the Whitebird Creek section, the lower part of the Rock Creek flow cooling unit is formed from a different chemical type with a different mineralogy, similar to the Roza and Frenchman Springs chemical types as defined by Wright and others (1973). The mineralogy of the main part of the flow is typical of alkali basalt. Plagioclase and olivine were stable before eruption and were joined by a high-calcium pyroxene soon after eruption. Olivine continued to crystallize with the plagioclase and pyroxene, which were later joined by ilmenite and then apatite. Late chabazite and secondary analcite occur in the scoria. Lack of crystal settling and the high potassium content of the unusually thick scoriaceous top, which is locally replaced by a pyroclastic capping, may be associated with exceptionally vigorous degassing of the magma. Chemically, the Rock Creek flow is an olivine tholeiite, but its alkali basalt mineralogy makes either of these terms misleading. Together with many other basalts possessing a similar combination of mineralogy and chemistry, it is classified as a transitional basalt. The mineralogy of the residual material suggests a peralkaline composition.

Paleocurrents and composition of lower Bryneira strata (Permian) at Barrington Peak, north-west Otago

Abstract: Cross-stratification in the Annear Formation (lower Bryneira Group) in northwestern Otago indicates sediment transport from west (c. 250°) towards east (c. 70°). Petrographic and chemical data indicate that these rocks are of mixed quartzo-feldspathic-volcanic provenance and are decidedly more silicic than overlying and underlying Bryneira volcanogenic terrigenous sediments. Compositional and stratigraphic similarities with Permian sediments of the Torlesse terrane are noted, and a common source area is tentatively suggested.