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Showing papers in "The Journal of Geology in 1974"


Journal ArticleDOI
TL;DR: Bar formation and sediment distribution patterns were examined in a 4-mile braided reach of the upper Kicking Horse River at Field, British Columbia, which was mainly supplied by meltwater from icefields straddling the continental divide at the British Columbia-Alberta boundary in the southeastern Canadian Cordillera as mentioned in this paper.
Abstract: Bar formation and sediment distribution patterns were examined in a 4-mile braided reach of the upper Kicking Horse River at Field, British Columbia, which is mainly supplied by meltwater from icefields straddling the continental divide at the British Columbia-Alberta boundary in the southeastern Canadian Cordillera. Marked diurnal variations in discharge, suspended sediment concentration, and water temperature occur during peak summer melting periods when rates of sediment transport and bar formation are greatest. Bed material is mostly limestone and dolomite gravel which undergoes rapid fining in the downstream direction. Gravel bars occurring in a wide variety of shapes and sizes comprise the dominant bed forms. Most exposed braid bars have undergone complex depositional and erosional histories and rarely show simple or consistent patterns of grain size or structures, either internal or superficial. Active bars with simple histories and predominantly depositional morphologies are termed "unit bars." Fo...

370 citations


Journal ArticleDOI
TL;DR: In this article, the effect of oxygen fugacity on the equilibrium crystallization of two basaltic melts has been determined at 1 atm total pressure, where the authors focused on the relationship between chromite and titaniferous magnetite and the ferrous-ferric ratio.
Abstract: The effect of changing oxygen fugacity on the equilibrium crystallization of two basaltic melts has been determined at 1 atm total pressure. Liquidus curves for spinel (chromite-titaniferous magnetite), hexagonal oxide, olivine, pyroxene, and plagioclase are represented on temperature versus $$log f_{O_{2}}$$ diagrams covering the $$log f_{O_{2}}$$ range -0.68 (air) to -14.0 atm and a temperature range of l,100°C-1,325°C. Particular emphasis has been placed on the role of oxygen fugacity as applied to the relationship between chromite and titaniferous magnetite and the ferrous-ferric ratio. Complete solid solution between chromite and titaniferous magnetite is demonstrated at basaltic liquidus temperatures, however at oxygen fugacities below about $$10^{-8} atm$$ the crystallization of early chromite is interrupted by the crystallization of clinopyroxene. At lower temperatures, a spinel again crystallizes as titaniferous magnetite together with pyroxene and other silicates. This supports the suggestion of...

288 citations


Journal ArticleDOI
TL;DR: In this paper, the relative contributions of outflow inertia, turbulence, bottom friction, buoyancy, and marine forces to river mouth outflow dynamics and consequent sediment deposition vary spatially and temporally.
Abstract: Repeated observations from the mouths of the Mississippi River from 1968 to 1973 indicate that the relative contributions of outflow inertia, turbulence, bottom friction, buoyancy, and marine forces to river mouth outflow dynamics and consequent sediment deposition vary spatially and temporally. Effluent behavior varies significantly with river stage and between four discrete dynamic regions. During low and normal river stages, when a distinct salt wedge intrudes into the distributary channel, Region I, which extends from the mouth to about four channel widths seaward, is characterized by buoyancy-dominated lateral effluent expansion and vertical thinning and by vertical saltwater entrainment. In Region II, which is situated over the distributary-mouth bar crest, the density interface approaches closest to the surface, densimetric Froude numbers attain maxima, internal waves break, and intense mixing occurs. Region III lies approximately between six and ten channel widths seaward of the mouth and is chara...

181 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied carbonaceous coal, black slate, graphite schist, and mica schist in regionally metamorphosed coal, showing continuous changes with increasing metamorphic grade: increase in particle size; loss of hydrogen, nitrogen, and oxygen ; increase in the carbon content; a decrease in the peak width of the (002) reflection; and a shift of the reflection to a higher position.
Abstract: Carbonaceous material in regionally metamorphosed coal, black slate, graphite schist, and mica schist shows the following continuous changes with increasing metamorphic grade: increase in particle size; loss of hydrogen, nitrogen, and oxygen ; increase in the carbon content; a decrease in the peak width of the (002) reflection; and a shift of the (002) reflection to a higher $$2\theta$$ position. These changes are greatest in the chlorite zone, where distinct (111) lines replace an unmodulated (111) band. In this study, only carbonaceous material from the staurolite and sillimanite zones is pure carbon. A large extent of layer ordering is acquired in the chlorite and biotite zones, but well-ordered graphite, comparable with Ceylon graphite, is limited to the sillimanite zone. There is little growth in the carbonaceous particles until the staurolite zone; in lower-grade zones, they rarely exceed 0.02 mm. The temperature at which layer ordering first appears in regionally metamorphosed rock is roughly 300°-...

177 citations


Journal ArticleDOI
Abstract: An analysis of the Permo-Triassic fauna and paleogeography on a stage-by-stage basis supports previous more general summaries by concluding that the number of families of marine invertebrates was significantly reduced (essentially halved) during the last three Permian stages (32 m.y.), and that the extinctions were not markedly selective. Shallow marine seas were reduced from a coverage of 40% of their possible distribution in the early Permian to less than 15% coverage in latest Permian, and then were expanded to 34% coverage in the lower Triassic. If this apparent reduction in shallow marine seas is due to selective erosion of late Permian sediments, there seems no way to account for it unless there was significant reduction in sea level. Alternatively, late Permian marine seas may never have been widespread, again due to lowering of sea level. The apparent late Permian marine regression is attributed to water withdrawing into a deepening ocean basin. The basaltic ocean bottom continued to sink during a...

162 citations


Journal ArticleDOI
TL;DR: The eight bivalve life habit groups (e.g., epifaunal suspension feeders, borers, deep-burrowing siphonate suspension feeder, infaunal nonsiphonate suspendor feeders (INFSA), infaunally mucus tube feeders), shallow-burrowed siphonately suspension feedsers, labial palp deposit feeders as mentioned in this paper, and infaunality siphonates deposit feeder) are distinct with regard to escape potentials.
Abstract: The eight bivalve life habit groups-(1) epifaunal suspension feeders, (2) borers, (3) deep-burrowing siphonate suspension feeders, (4) infaunal nonsiphonate suspension feeders, (5) infaunal mucus tube feeders, (6) shallow-burrowing siphonate suspension feeders, (7) labial palp deposit feeders, and (8) infaunal siphonate deposit feeders-are distinct with regard to escape potentials. Escape potentials (i.e., the maximum depth of burial from which the members of an animal group or taxon are able to dig out and successfully reestablish themselves in normal feeding position) have been determined through laboratory experiments for 25 species of bivalves. Escape potentials range from 50 cm. Major factors controlling escape potentials are bivalve life habits, degree of mantle fusion and siphon formation, and sediment type. Examination of sedimentary structures formed by escaping bivalves has revealed that, while all species produce what appears in vertical section to be a nested series of inverted con...

158 citations


Journal ArticleDOI
TL;DR: In this article, an estimate of the solidus of peridotite with 0.2% water bound in hydrous minerals was presented and compared with other studies and the results are consistent with a published conclusion that St. Paul's Rocks is a diapiric, solid-state mantle intrusion initially mobilized at a depth between 45 km and 70 km near 1,000 - 1,050°C.
Abstract: Crystalline pargasite-rich spinel peridotite mylonite from St. Paul's Rocks containing 5.7% water bound in hydrous minerals was reacted in sealed platinum capsules in a piston-cylinder apparatus from 10 - 30 kb. At 10 kb the subsolidus assemblage is amphibole, olivine, orthopyroxene, clinopyroxene and spinel, an amphibole lherzolite; with increasing pressure garnet appears at 18 kb, spinel and amphibole disappear at about 25 kb; the resulting high pressure assemblage is that of a garnet lherzolite. The solidus was located in the presence of water-rich vapor, but vapor dissolves completely in the liquid at higher temperatures, and the liquid becomes water-undersaturated. Stability limits in the melting interval were determined for amphibole, garnet, spinel, clinopyroxene, orthopyroxene, and olivine (the liquidus mineral). The results are consistent with a published conclusion that St. Paul's Rocks is a diapiric, solid-state mantle intrusion initially mobilized at a depth between 45 km and 70 km near 1,000 - 1,050°C. An estimate of the solidus of peridotite with 0.2% water is presented and compared with other studies. At intermediate pressures this solidus is determined by the breakdown of amphibole. Discrepancies among results of the various studies probably arise at least in part from experimental problems involved in the complex systems.

129 citations


Journal ArticleDOI
TL;DR: Schopf as discussed by the authors suggests that the decrease in number of families of marine invertebrates during the Permian and subsequent increase in the Lower Triassic are due to changes in the area of the shallow marine seas.
Abstract: Schopf (1974) suggests that the decrease in number of families of marine invertebrates during the Permian and subsequent increase in the Lower Triassic are due to changes in the area of the shallow marine seas. Shallow marine sea coverage fell by two-thirds, then more than doubled, and the number of families appears roughly to have tracked areal change. Since a change in area cannot be followed immediately by extinction or origination of families, the Permo-Triassic situation may have been a short-term nonequilibrium one, with number of families constantly changing but lagging behind the instantaneous equilibrium number. In the Recent, the widely studied and experimentally observed increase in species number with area, even in the absence of increased habitat diversity, implies a monotonic relationship between area and equilibrium number of families. Increase in number of species with area appears usually to be linear in a log-log plot, and this leads inductively to a nearly linear relationship between lo...

116 citations


Journal ArticleDOI
TL;DR: The stability field of sapphirine has been located in the PT range 1 bar-7 kb, 600°-1500° C by experimental study of compatibility relations between the phases chlorite, cordierite, enstatite, spinel, sappHirine, corundum and mullite in the presence of excess water.
Abstract: The stability field of sapphirine has been located in the PT range 1 bar-7 kb, 600°-1500° C by experimental study of compatibility relations between the phases chlorite, cordierite, enstatite, spinel, sapphirine, corundum and mullite in the presence of excess water. In the pressure range from about 300 to at least 7,000 bars $PH_{2}O$ sapphirine forms from chlorite + spinel + corundum at temperatures between 600° and 760° C, depending on pressure. The assemblage chlorite + sapphirine is only stable over a narrow temperature range of at most 50° C. By the appearance of a stable tie line, enstatite + sapphirine at pressures above about 3.5 kb and temperatures in excess of 765° C sapphirine can also occur in relatively $Al_{2}O_{3}$-poor bulk compositions at these elevated PT conditions. The petrogenetic grid of the system $MgO-Al_{2}O_{3}-SiO_{2}- H_{2}O$ derived for the phases involved as well as data on the compatibility relations of sapphirine outside the PT range discussed explains most of the natural t...

108 citations


Journal ArticleDOI
TL;DR: The Waitemata Group formed following major mid-to Upper Oligocene block faulting in northern New Zealand as discussed by the authors, which consisted of a central flysch basin 130 km by 60 km, bounded to the north and south by basement horst on which shelf facies accumulated.
Abstract: The Waitemata Group formed following major Mid-to Upper Oligocene block faulting in northern New Zealand. It consisted of a central flysch basin 130 km by 60 km, bounded to the north and south by basement horst on which shelf facies accumulated, to the west by an active andesitic/basaltic ridge, and to the east by a high basement ridge/active andesitic arc. Lithic sediment from the north mingled with contemporaneous volcanic debris to give poor-volcanic, rich-volcanic, and mixed flysch facies. Turbidity currents entered the basin from a western shelf, traveled an average distance of 30 km, and built a south-easterly palaeoslope oblique to the basin axis. The flysch is relatively proximal, overstepping eastwards across a steep and uneven basement surface with a thin basal shallow-water facies. Conglomerate moved south along the western shelf, entering the basin via submarine valleys to form thick lenses within a 4 km radius. Turbidity currents carried pebbles a further 20 km. Pebbly mudstones occur. Lahars...

85 citations


Journal ArticleDOI
TL;DR: The Nama Group in South West Africa is subdivided slightly differently and in greater detail than before as mentioned in this paper, showing that the lower shelf deposits were supplied mainly from the easterly Kalahari shield and the more feldspathic and more detrital reddish upper sediments from uplifted regions of the inferred adjacent Damara geosyncline.
Abstract: The Nama Group in South West Africa is subdivided slightly differently and in greater detail than before. The lower shelf deposits were supplied mainly from the easterly Kalahari shield and the more feldspathic and more detrital reddish upper sediments from uplifted regions of the inferred adjacent Damara geosyncline, which probably formed part of the extensive Pan-African Geosyncline to the west and north. There is much evidence of severe climatic conditions and volcanism having existed. This group and the underlying Gariep Group appear to represent a single geotectonic cycle, towards the end of which the Nama Group was deposited. The fauna found in the Nama Group seems to indicate a Vendian (Ediacarian) age for the lower Nama Group but the age for the upper Nama Group is uncertain. The Ediacara fauna in Australia and the related Nama fauna have only one identical fossil thus far. The Nama Group is a good test for the model of Valentine and Moores (1972) and in general confirms it. The Nama Group is cons...

Journal ArticleDOI
TL;DR: In this article, nine pairs of Lambert equal-area maps of the world are presented and the probable distributions of major continents and oceans at the present day and during the "Tertiary" (Eocene), "Cretaceous," "Jurassic," "Triassic," and "Permian" periods.
Abstract: Nine pairs of Lambert equal-area maps of the world are presented. Six pairs show the probable distributions of major continents and oceans at the present day and during the "Tertiary" (Eocene), "Cretaceous," "Jurassic," "Triassic," and "Permian" periods. The remaining three pairs of maps show the probable latitudinal distributions of major continental and oceanic regions during the "Lower Carboniferous (Mississippian)," "Lower Devonian," and "Cambrian/Lower Ordovician" periods. All maps are centered on the equator or inferred paleoequator. Each pair shows two views of the world from diametrically opposite equatorial points. The maps are essentially the same reassemblies as those drawn as Mercator and polar stereographic projections.

Journal ArticleDOI
TL;DR: In this paper, the authors examined the composition of the liquids formed by partial melting of an eclogite nodule from the Roberts Victor kimberlite pipe and showed that at high pressures and low degrees of partial melting, a nepheline normative liquid is formed.
Abstract: We have examined the composition of the liquids formed by partial melting of an eclogite nodule from the Roberts Victor kimberlite pipe. We show that at high pressures and low degrees of partial melting, a nepheline normative liquid is formed. Hypersthene normative melts are formed with greater degrees of partial melting or partial melting at lower pressures. Nonetheless, the demonstration of the possibility of the formation of nepheline normative magmas by partial melting of an eclogite does not mean that this is the only possible origin. Although alkaline rock may be formed by partial melting at great depths, abundant field data suggest that many alkaline rocks are formed at shallow depths in a volcanic edifice. Volatiles also apparently play an important role in the genesis of the melts. It seems quite possible to one of us (GCK) that a large number of alkaline magmas are formed by access of sea water to basaltic magma chambers at shallow depths.

Journal ArticleDOI
TL;DR: In this paper, an examination of more than 200 cornstone profiles of New Red Sandstone age, in western Scotland, confirms that these carbonate accumulations are analogues to the caliche of semi-arid areas.
Abstract: An examination of more than 200 cornstone (concretionary carbonate) profiles of New Red Sandstone age, in western Scotland, confirms that these carbonate accumulations are analogues to the caliche of semi-arid areas. New evidence of laminated, pisolitic and brecciated textures from the cornstone "caprock" strongly suggests that downward percolating water and non-tectonic fracturing were important during subaerial diagenesis. The cornstones occur preferentially in floodplain deposits, and particularly within the upper parts of alluvial, fining-upwards cyclothems. The occurrence of cornstones in this part of the cyclothems and their persistence through such cyclothemic sequences suggest, contrary to a commonly accepted hypothesis, that climatic controls are important in the formation of such alluvial sequences. The cornstones are stratigraphically more significant than the associated rock types in the monotonous New Red continental sequences. In particular, thick, mature cornstones indicate condensed sequen...

Journal ArticleDOI
TL;DR: In this paper, it was shown that combustion of organic matter in a Cretaceous bituminous sedimentary sequence supplied the heat for the high-temperature, low-pressure metamorphism of the Mottled Zone in Israel.
Abstract: New evidence is presented in support of the previously suggested hypothesis that combustion of organic matter in a Cretaceous bituminous sedimentary sequence supplied the heat for the high-temperature, low-pressure metamorphism of the Mottled Zone in Israel. Such a model is compatible with stable isotope data on carbonates from the Mottled Zone which are strongly enriched in $C^{12}$ and $O^{16}$.

Journal ArticleDOI
TL;DR: In this article, a geological and geophysical study of the Samoan Passage in the west equatorial Pacific (168-170°W; 7-10°S) was carried out in 1971, utilizing underway seismic reflection profiles (3.5 kHz and sparker), bottom photographs, bottom current measurements, bottom water temperature profiles, and sediment cores.
Abstract: A geological and geophysical study of the Samoan Passage in the west equatorial Pacific (168-170°W; 7-10°S) was carried out in 1971, utilizing underway seismic reflection profiles (3.5 kHz and sparker), bottom photographs, bottom current measurements, bottom water temperature profiles, and sediment cores. These data and those of previous expeditions were synthesized in this study of dynamic sedimentation processes. Specific sedimentation processes were found to be associated with surface (12 kHz) and subsurface (3.5 kHz) morphology and composition of the sea floor. (1) Parabolic echo returns, rugged topography, some local conformable subbottom penetration (< 10 m); process- pelagic draping of sediment, infrequent slumping (Passage walls). (2) Highly reflective, smooth topography, no subbottom penetration, manganese nodules on semi-indurated sediment; process- continued fast (20-50 cm/sec) bottom current flow causing erosion or non-deposition (Passage axis). (3) Moderately reflective bottom with up to 20 m...

Journal ArticleDOI
TL;DR: A small layered and differentiated diorite pluton in Cape Breton Island contains abundant layers and pillow-like inclusions of hornblende gabbro as mentioned in this paper, which is characterized by cryptic layering, lamination, and sporadic mineral layering.
Abstract: A small layered and differentiated diorite pluton in Cape Breton Island contains abundant layers and pillow-like inclusions of hornblende gabbro. The diorite is characterized by cryptic layering, lamination, and sporadic mineral layering. Compositional variation (diorite to adamellite) was controlled largely by gravitative settling and accumulation of plagioclase, hornblende, magnetite, biotite, and quartz at appropriate levels of the intrusion. Hornblende gabbro layers and inclusions have sharp, generally chilled margins and are conformable with layering and lamination in the diorite. Many of the layers have forms resembling pahoehoe lava flows. Hornblende gabbro also occurs as a large homogeneous pipe and as pillow-like inclusions within several small pipes of re-mobilized diorite cumulates. These small composite pipes have fed inclusion-rich layers in the diorite. Bodies of hornblende gabbro often carry rounded, apparently stretched inclusions of diorite. Field relations indicate that basic magma was i...

Journal ArticleDOI
TL;DR: Paleolatitude distributions of oceanic cherts support those dynamic models of the atmosphere that require the later Mesozoic and Tertiary high-pressure subtropical belts to have been more or less stable features of atmospheric circulation as mentioned in this paper.
Abstract: On five Lambert equal-area maps and three Lambert equal-area "composites" of the world in Phanerozoic time are plotted distributions of evaporites, tillites, coal, eolian sands, and radiolarian cherts. The paleolatitude distributions of tillites and evaporites confirm the plausibility of the view that the Earth's magnetic field has approximated to a geocentric dipole whose axis paralleled the Earth's spin axis throughout Phanerozoic time. Coal formed in a wide range of latitudes. Paleolatitude distributions of oceanic cherts support those dynamic models of the atmosphere that require the later Mesozoic and Tertiary high-pressure subtropical belts to have been more or less stable features of atmospheric circulation. Paleolatitude distributions of eolian sands provide inconclusive evidence for the extent of these belts. Though rainfall and temperature have varied at a particular paleolatitude, marked equatorward shrinkage of the subtropical high-pressure belts during ice-sheet glaciations and marked polewar...


Journal ArticleDOI
TL;DR: Kaihikuan (upper Middle Triassic) clastics of the Hokonui belt fine from west to east, and hence were derived from the west. as discussed by the authors showed that the Alpine belt sequences do not fit lateral extrapolations of sedimentologic or petrologie trends, and thus cannot be explained as distal facies of the same sedimentary basin.
Abstract: Kaihikuan (upper Middle Triassic) clastics of the Hokonui belt fine from west to east, and hence were derived from the west. Deep erosion of a volcanic terrane and associated shallow intrusives contributed most of the sediment, but reworking of contemporaneous pyroclastic debris was also an important process. In the Alpine belt, the source of Kaihikuan sediments was a deep-seated acidic plutonio terrane. At least some of the deposits formed in nearshore, shallow-marine environments. The Alpine belt sequences do not fit lateral extrapolations of sedimentologic or petrologie trends of the Hokonui belt, and thus cannot be explained as distal facies of the same sedimentary basin. The two belts probably were juxtaposed by faulting.

Journal ArticleDOI
TL;DR: In this article, a world-wide correlation of Middle Cambrian biostratigraphic units was found and the epoch was divided into three periods of time that may be approximately equal and perhaps be of 10 m.y. duration.
Abstract: After a world-wide correlation of Middle Cambrian biostratigraphic units the epoch is divided into three periods of time that may be approximately equal and perhaps be of 10 m.y. duration. Trilobite occurrences for each of these periods for different parts of the world have been recorded. The smallest faunally homogeneous areas with a sufficiently large list of generic occurrences are compared both at the family and generic levels. This comparison, based on Simpson's coefficient, employs cluster, principal component and discriminative analyses. The groups so produced are interpreted as indicating provinciality. Three provinces-Columban (Americas), Viking (Europe, northwestern Africa, and maritime North America), and Tollchuticook (Asia, Australia, and Antarctica)-are denned as being distinct through the Middle Cambrian. It is stressed that although the data analysis provides fairly concrete evidence for faunal similarity the planetary reconstructions are an attempt to express these results within the cont...

Journal ArticleDOI
TL;DR: In this article, the Manning equation and a well-known empirical law of sediment transport were used to derive a downstream hydraulic geometry for steady-state channels, where the sediment mass is conserved during transport and the channel has a form just sufficient to transport its total water discharge.
Abstract: Representing a stream channel of finite width as a surface z = z(x, y, t) subject to the three conditions: (1) that sediment mass is conserved during transport; (2) that the channel has a form just sufficient to transport its total water discharge; (3) that the channel has a form just sufficient to transport its total sediment load; and then applying the Manning equation and a well-known empirical law of sediment transport, it is possible to derive a downstream hydraulic geometry for steady-state channels. In the present case, the following geometry is derived: channel width $\propto Q^{0.6}$; channel depth $\propto Q^{0.3}$; stream velocity $\propto Q^{0.1}$; water slope $\propto Q^{-0.2}$; where Q is the total stream discharge. The model has considerable flexibility and, in modified form, should prove of use in future channel studies.

Journal ArticleDOI
TL;DR: Melting relations of a finely ground, crystalline tonalite with excess water have been studied at pressures between 10 kbar and 30 kbar, to a maximum temperature of 850° C, and these data have been combined with previously published results at lower pressures and higher temperatures as mentioned in this paper.
Abstract: Melting relations of a finely ground, crystalline tonalite with excess water have been studied at pressures between 10 kbar and 30 kbar, to a maximum temperature of 850° C, and these data have been combined with previously published results at lower pressures and higher temperatures. The rock mineralogy of plagioclase, quartz, orthoclase, biotite, and amphibole begins to change just below 10 kbar, and by 30 kbar it is coesite, clinopyroxene, garnet, and kyanite. Runs were planned to determine the curve for the beginning of melting, but combining these with published results for andesites and andesite compositions between 1 kbar and 20 kbar permits delineation of the major features of the phase diagram through the melting interval. The solidus temperatures are: 1 kbar, 765° C; 3 kbar, 690° C; 10 kbar, 635° C; 15 kbar, 628° C; 20 kbar, 670° C; 30 kbar, 735° Orthoclase dissolves in the aqueous vapor phase between 3 kbar and 10 kbar. The quartz out-(coesite-out) phase boundary varies from about 30° to 65° above the solidus. The plagioclase-out phase boundary extends from about 2 kbar, 1,000° to the solidus near 15.5 kbar, 630° C. The liquidus phase is pyroxene up to about 10 kbar, 950° C, and amphibole from there to about 18 kbar, 950° C. Garnet is the liquidus phase at higher pressures. Biotite, stable to 800°-850° C, reacts out between 15 kbar and 17.5 kbar, with the formation of garnet and kyanite. Garnet is reluctant to nucleate, but it appears at 15 kbar and is probably stable at considerably lower pressures. The amphibole reaction boundary extends from 18.5 kbar, 950° to 21.5 kbar, 700° C, but the equilibrium phase boundary could be lower by a few kilobars at 700° according to some published work. No orthopyroxene was found in any runs. The experimental results have applications to high-grade metamorphism and the nature of the lower crust, the generation of batholiths, and the crystallization of andesite magmas rising from subduction zones.

Journal ArticleDOI
TL;DR: In this article, a suite of lavas from the Great Ararat is described, and two distinct series can be recognized, each consisting of andesite, dacite, and rhyodacite (designated Low-Y and high-Y series), they are distinguished by significantly different K.
Abstract: A suite of lavas from Great Ararat is described. Analyses are reported for Si, Al, Fe, Mg, Ca, Na, K, Ti, Mn, S, P, Ba, Nb, Zr, Y, Sr, Rb, Zn, Cu, and Ni. Two distinct series can be recognized, each consisting of andesite, dacite, and rhyodacite (designated Low-Y and high-Y series), they are distinguished by significantly different K. Mn, P, Nb, Zr, Y, Rb, Cu, and normative feldspar contents-The high-Y series corresponds closely to a normal calc-alkali series, but the low-Y series is relatively deficient in K, Mn, P, Nb, Zr, Y, and Rb. $$^{87}Sr/^{86}Sr$$ from both series is $$0.7050 \pm 0.0005$$. Petrographi-cally, both series are characterized by three generations of feldspar, all rock types containing labradorite together with more sodic phenocrysts and groundmass plagioclase: orthopyroxene, clinopyroxene, magnetite and ilmenite are present. Quartz and K-feldspar phenocrysts are absent. Suggestions of the former presence of garnet and brown hornblende, together with relevant experimental and geo-chemic...



Journal ArticleDOI
TL;DR: The Cambrian Chickies Quartzite was produced by a migrating mosaic of subtidal channels, intertidal flats and tidal flat ponds, each of which has unique hydrodynamic implications as mentioned in this paper.
Abstract: The Cambrian Chickies Quartzite was produced by a migrating mosaic of subtidal channels, intertidal flats and tidal flat ponds. These tidal zone subenvironments are interpreted from assemblages of physical and biogenic structures, each of which has unique hydrodynamic implications. The highest flow regimes and most persistent currents occur in channels represented by non-burrowed tangentially cross-stratified dune deposits. The range of flow conditions on the intertidal sand flat is represented by burrowed sandstones containing a sequence of physical structures from tangential to avalanche cross-stratification to lower flat bed. The high-energy low flat deposits contain closely spaced Scolithus burrow forms. Lower-energy high flat deposits contain Monocraterion burrow tops in conjunction with widely spaced Scolithus dwelling tubes. Quiet water ponds in abandoned channels on the intertidal flat are represented by lenses of non-burrowed gray clay immediately overlying channel deposits.

Journal ArticleDOI
TL;DR: Sediments of the Panama Basin contain >90% nonbiogenous components adjacent to Central and South America, but <5% in the area west of the Galapagos Islands.
Abstract: Sediments of the Panama Basin contain >90% nonbiogenous components adjacent to Central and South America, but <5% in the area west of the Galapagos Islands. The nearshore deposits are quartz rich, with clay fractions consisting of roughly equal amounts of chlorite, illite, and kaolinite. These sediments are dispersed over distances of several hundred kilometers by currents in waters of intermediate depth (below the photic zone, but not deep enough to be affected by bottom topography), and to a lesser extent by bottom currents that flow through the deepest parts of the Basin. In the outer parts of the basin, the nonbiogenous deposits are quartz poor, with clay fractions dominated by authigenic montmorillonite. Winnowing and lateral reworking at the sea floor, which strongly affect the distribution of biogenous components, have little effect on the patterns of occurrence of the clay minerals.


Journal ArticleDOI
TL;DR: In this article, the authors have shown that the simplest models of Highland Basalt as the mean lunar composition and Highland basalt as comprising the outer 250-270 km (formed as a partial melt from a Ca, Al-rich lunar interior) fail to meet the lunar density constraint but could do so if the hypotheses were modified towards more Fe-rich compositions.
Abstract: Lunar Highland Basalt (gabbroic anorthosite) composition transforms with increasing pressure through assemblages of spinel + clinopyroxene + anorthite, and garnet + clinopyroxene + anorthite ± quartz to eclogitic assemblages of garnet + clinopyroxene + kyanite + quartz (p = 3.51 - 3.52). Estimates of the lunar thermal gradient allow evaluation of the mineralogical variation with depth in the moon and thus allow calculation of mean lunar density and coefficient of moment of inertia for several models for the moon. These calculations show that the simplest models of Highland Basalt as the mean lunar composition and Highland Basalt as comprising the outer 250-270 km (formed as a partial melt from a Ca, Al-rich lunar interior) fail to meet the lunar density constraint but could do so if the hypotheses were modified towards more Fe-rich compositions. The geochemical constraints are much stronger and show that it is not possible for Highland Basalt to act as a source rock for mare basalt magmas under any condit...