Alkaline Olivine Basalts Research Articles

Thermal diffusivity of lunar rocks under atmospheric and vacuum conditions

Thermal diffusivity, k, of three lunar rocks (10049 and 10069; Type A, Apollo 11 and 14311; Apollo 14) and a terrestrial basalt (alkaline olivine basalt, Oki-doˆgo, Japan) was measured under one atmosphere and in vacuum conditions (10 −3 ∼ 10 −5 mmHg) in the temperature range from 85 to 850°K. The semi-empirical curve of k =A + B/T +CT 3 is fitted to the data in each condition. The porosity of rocks strongly affects the thermal diffusivity at low temperature ( T ≲ 500°K) in vacuum condition. At 150°K, thermal diffusivity of lunar rocks with porosity of 5.5% (10049) and 11% (10069) at one atmosphere is about 1.7 and 3.2 times of that in vacuum, respectively. The difference between the values at one atmosphere and those in vacuum decreases as the temperature increases. Measurements of k should be made at gas pressures at least lower than 10 −3 mmHg to estimate the value under lunar surface conditions.

K/Ar Age Determinations on Alkaline Olivine Basalts from Skåne, Southern Sweden

Abstract K/Ar dating of alkaline olivine basalts from Skåne has produced Cretaceous ages between 79 million years (m. y.) and 131 m. y. These basalts were previously believed to be of Tertiary age.

Contributions to the volcanic succession and petrology of the Auckland Islands, New Zealand

Twelve new analyses confirm that the bulk of exposed lavas fonning the upper twothirds of the Ross volcano are largely undifferentiated mildly alkaline olivine basalts. Twelve analyses (11 new) from minor intrusive bodies, ranging from picritic to trachytic in composition, show that the last phase of activity in the Ross volcano was characterised by more alkaline and undersaturated magmas than those preceding it. Three conveniently distinguishable magma batches contributed to the growth of this volcano, as at present known: the first, forming about the lower third of the exposed succession, was a strongly fractionated series, from alkaline olivine basalt to soda-rhyolite, with intennediate types well represented; the second batch erupted alkaline olivine basalts to build a virtually undifferentiated lava pile fonning the main bulk of the volcano; and the third, represented only by minor intrusives, was again a differentiated series (olivine basalt to trachyte), but more undersaturated and without intenned...

Herradura: A New Lava Flow Feature

Lava ridges which are horseshoe-shaped in plan occur on the flanks of several volcanic cones in the La Mesa Basalts, Quaternary alkaline olivine basalts in south-central New Mexico. I propose to call these newly described features herradura (Spanish: horseshoe). They formed by extrusion of lava through an already existing sloping crust of lava.

The Peralkaline Volcanic Suite of Aden and Little Aden, South Arabia

The volcanic rocks of Aden, Little Aden, and Ras Imran, here designated as belonging to the Aden Volcanic Series, were erupted through central-vent, strato-volcanoes about 5 m.y. ago. In its major element chemistry the Aden Volcanic Series is intermediate between the alkaline and tholeiitic associations, and this is demonstrated by comparing it with the alkaline suite of Hawaii and the tholeiitic series of Thingmuli, Iceland. It is proposed that the most acceptable ‘parental’ magma is a mildly alkaline olivine basalt which, on fractionation, produced a series ranging from trachybasalts through trachyandesites and trachytes to rhyolites. These rhyolites are peralkaline as the molecular proportion of alumina is less than that of the combined alkalis, and are comenditic as the series is poor in normative femic constituents. Trace element data suggest that the peralkaline silicic eruptives are chemically comparable with those of Mayor Island, New Zealand, where a mildly alkaline olivine basalt parent has also been postulated. Although the age of eruption of c. 5 m.y., given by K-Ar measurements, is entirely consistent with an age deduced from geomorphological criteria, an 87Sr/86Sr versus 87Rb/86Sr isochron plot suggests that the series is related to a thermal event some 20-30 m.y. older than the age of eruption. As this earlier age corresponds directly to the age of the previous magmatic episode, the eruption of the Yemen Trap Series, the upper part of which is petrologically similar to the Aden Volcanic Series, and as the initial 87Sr/86Sr ratios suggest that the magma originated in the mantle, it is proposed that the most acceptable petrogenetic scheme, which would also explain the anomalously old Rb-Sr age, is: (a) Partial fusion in the upper mantle giving rise to the alkaline Yemen Trap Series, (b) After the cessation of surface activity, a large body of magma existed in the upper mantle and this magma, on crystallizing, fractionated to produce a layered sequence, (c) About 5 m.y. ago some event, either pressure relief or further thermal activity, resulted in the partial remelting of this fractionated plutonic sequence and the liquids so formed reached the surface without significant mixing or chemical fractionation.

Olivine Nodules in Trachyte from the Jos Plateau, Nigeria

THE Cenozoic volcanics on the Jos Plateau consist almost entirely of small flows of alkaline olivine basalt, erupted from widely scattered small cinder cones now in various stages of erosion. The trachytic Bokkos plug1 is a rare exception. The trachyte forming the plug is composed chiefly of tabular anorthoclase and pale green clinopyroxene, and it contains olivine nodules ranging in size from small angular fragments to ovoids up to 15 cm long. They are typically lherzolitic in their mineralogy (and practically identical with nodules from a New Zealand phonolite2). Magnesian olivine is optically neutral with γ = 1.681 ± 0.002; enstatite has γ = 1.676 ± 0.002; chrome diopside is bright green in hand specimen and has β = 1.685 ± 0.002; spinel is red-brown in section, with n = l.78 ± 0.01.

Observations on the Deborah Volcanic Formation Near Kakanui, New Zealand

Abstract The Deborah Volcanic Formation near Kakanui, South Island, New Zealand, consists of lapilli tuffs from two eruptions of alkaline olivine basalt or atlantite (Tuffs I and II) and a final eruption of melanephelinite (Mineral Breccia Member). The field relations and the topography of the lavas are described.

Eclogite nodules associated with alkaline olivine basalts, Kenya

Alkaline olivine basalts and associated eclogite nodules from southern Kenya are described and attention drawn to the chemical and mineralogical similarities between these rocks and other continental, inclusion-bearing olivine basalts. The possibility of deriving the basalts from spinel pyroxenite and eclogite at high temperatures and pressures is discussed.

Late Caenozoic Shoshonitic Lavas in North-western Viti Levu, Fiji

MOST petrologists recognize two fundamental types of basaltic magma—tholeiite and alkaline olivine basalt1. The ratio of alkalis to silica is consistently higher in alkaline olivine basalts than in tholeiitic (sub-alkaline2) basalts3,4. Kuno5 recognized a third type of magma, high-alumina basalt characterized by high contents of alumina and intermediate alkali, and Hamilton6 noted its apparent genetic relationship to the calc–alkaline intermediate magmas of island arcs. Joplin7 recognized a fourth type of basaltic magma characterized by high potash content, and proposed the name shoshonite8 for the magma series derived from a high-potash parent magma. The potash-rich shoshonites are as alkalic as the soda-rich alkaline olivine basalts, but the ratio of potash to soda in shoshonites is near or in excess of 1.0, whereas the same ratio is 0–5 or less in typical alkaline olivine basalts and their derivatives. Joplin noted that shoshonitic lavas seem to be especially characteristic of newly stabilized or just consolidated orogenic regions. The possibility that shoshonitic lavas might be characteristic of the late Caenozoic volcanic sequence of Fiji was called to our attention by G. A. Joplin and A. J. R. White on the basis of an analysis obtained by V. lyengar and quoted by Rickard9. The estimated volume of late Caenozoic shoshonite in Fiji is about 104 km3; therefore the origin of the magma presents a significant challenge to petrologic theory.

Trace element partition between two pyroxenes and the host lava

Partition coefficients for +1, +2, +3 and +4 valent trace ions between alkaline olivine basalt lava and the coexisting ortho- and clinopyroxene phenocrysts from Takashima, North Kyushu, Japan, have been determined by neutron activation analysis. Substitution of trace elements in crystal lattice sites is proposed for the mechanism of trace element partition by examining the relation between measured partition coefficients and ionic radius and ionic charge.

Magmatic evolution on the mid-atlantic ridge

Recent field and experimental evidence is used to produce a model which explains the generation and characteristics of the basalts found on the Mid-Atlantic Ridge. Multiple cycles of partial melting of the upper mantle, related to tectonic patterns beneath the axis of the Ridge, are thought to generate the different magma types. The sudden stress releases due to faulting on the Median Rift Valley result in considerable partial melting of a pyrolite mantle, which initiates a volcanic cycle with the subsequent extrusion of tholeiitic lava. As the original energy is consumed, the extent of partial melting possible is gradually reduced, so that smaller quantities of magma, progressively enriched in alkalis, are generated. The last extrusions of a volcanic cycle consist of small quantities of alkaline olivine basalt. Since the magmas extrude onto an actively spreading ocean floor, there results a distribution of the different basalt types which can be correlated to the topographic features of the Median Rift Valley.

Ultramafic inclusions in basaltic rocks from Hawaii

Ultramafic inclusions and the enclosing basaltic rocks were collected from a number of localities in the Hawaiian Islands; these and other specimens were studied by standard petrographic techniques and with an electron microprobe. Emphasis was on determination of mineral assemblages, mineral compositions, and variations in composition. Sixty-eight inclusions and thirteen basaltic rocks are described, with partial chemical analyses (Ti, Al, Cr, Fe, Mn, Ni, Mg, Ca, Na, K) of olivines, orthopyroxenes, clinopyroxenes, and some feldspars and other minerals. Inclusions range from dunite to anorthosite, and basaltic hosts range from olivine nephelinite to olivine tholeiite. The inclusions are separable into three categories, which correlate with three groups basaltic hosts: Lherzolite inclusions are relatively poor in Fe, and the component minerals have limited ranges of composition. In Hawaii, lherzolite inclusions occur preferentially in extremely undersaturated hosts (olivine nephelinite, nepheline basanite, and ankaratrite). Other varieties of inclusions (dunite, wehrlite, feldspathic peridotite, pyroxenite) are relatively rich in Fe, and the component minerals have wider ranges of composition. These inclusions, together with gabbro, occur preferentially in hosts which are but moderately undersaturated (alkaline olivine basalt, hawaiite, and ankaramite). The sparse inclusions in nearly-saturated basalt (olivine tholeiite) are petrographically distinct from those in the other two categories. These correlations suggest that the inclusions and the enclosing basaltic rocks are genetically related. As the three suites of inclusions differ chemically, mineralogically, physically, and texturally, more than one origin is probable.

Observations on the geology of an area near lakes Thomson and Hankinson, Fiordland

Abstract The physiography of the area is dominated by glaciated landforms carved in gneiss of the Fiordland Complex.The gneiss is generally dioritic, with gradations to quartzo-feldspathic and amphibolitic varieties, and is cut by mainly barren pegmatite veins; epidote is abundant.The rocks commonly show signs of post-consolidational shearing and crushing. There is a well defined zone of strongly crushed rocks, trending approximately north, which cuts obliquely across the northern end of Lake Han-kinson.In general the rocks are petrographically similar to those near Lake Manapouri.Chemical analyses of a microcline-bearing gneiss, a hornblende-biotite gneiss, and an amphibolite are compatible with derivation of these from acid and intermediate volcanic or tuffaceous sedimentary rocks and mildly alkaline olivine basalts respectively.Geometric analysis of foliation attitudes, lineations, and minor fold axes, shows that there is a statistical fold axis plunging gently to the south-west.

XVI.—Metamorphism of Tertiary Lavas in Strathaird, Skye

SynopsisIn Strathaird, Tertiary lavas occupy an area of about 7 square miles and are up to 1000 ft. thick. Most of the sequence consists of alkaline olivine basalts but there is also a flow of trachybasalt and a thin group of picritic lavas. Pyroclastic rocks are rare.The area lies along the south-eastern margin of the Cuillin gabbro and thermal metamorphism is evident to a varying degree over the whole of the lava outcrop. In the immediate vicinity of the gabbro the lavas have been recrystallized to pyroxene-bearing hornfelses, and these rocks are followed outwards by a broader zone characterized by the presence of actinolite, chlorite, albite and epidote. In the outermost of the three zones, which extends for at least 3 miles from the gabbro, thermal effects are limited to the local growth of chlorite, albite and epidote. When compared with Turner's (1958) scheme of metamorphic facies the inner zone is equivalent to the pyroxene hornfels and sanidinite facies whereas the two outer zones form subdivisions of the albite-epidote hornfels facies. The hornblende hornfels facies appears to be only poorly represented by a few hornfelses found on the outer boundary of the inner zone.The metamorphism was not progressive since the mineral assemblages of each zone developed independently from unmodified lavas. There is evidence that a small amount of silica was added to some of the inner zone lavas during metamorphism.Eight new chemical analyses of metamorphosed basalts are presented, together with one new analysis of a metamorphosed bole.

Stratigraphical Study on the Nishiyatsushiro Group (Miocene) in the Area of the Upper Stream of the Fuji, Japan

The geosynclinal sediments (Late Cenozoic) which comprise much Volcanic products, are developed in the South Fossa Magna, Central Japan, and are intensively deformed by later crustal movements., In this paper, the Nishiyatsushiro group, one of the representatives of these sediments, is described and some problems are discussed., 1 The group consists mainly of pyroclastics and mudstone-rich alternations, and is divided into the following four formations: (Shizukawa group)., ., ., ., ., ., ., ., ., unconformity (?)., ., ., ., ., ., ., ., ., Nishiyatsushiro group Shimobe formation., ., ., ., ., ., ., ., ., mostly of an alternation of sandstone and mudstone with fine conglomerate beds., The upper part is cut off by a fault., Daigoyama formation., ., ., ., ., ., ., ., ., basic (lower) and acidic (upper) pyroclastics, sandstone and mudstone., The lower part consists of basalt and basic tuffaceous sandstone, and the upper of pumiceous tuff, sandstone and mudstone., Ichinose formation., ., ., ., ., ., ., ., ., mostly of mudstone and alternated acidic tuff., Alkaline olivine basalt occurs in the lowest part as thin lavas and sheets., Furusekigawa formation., ., ., ., ., ., ., ., ., mostly of basic lavas and pyroclastics with thin tuffaceous sandstone and mudstone., The base is unknowxn., (in descending order) Besides the above, two mudstone members are intercalated between the Daigoyama formation and the Shizukawa group, but their stratigraphical position remains unsettled., 2 In the area where the group is exposed, igneous activities are represented in the following sequence in ascending order., 1) A large amount of tholeiitic (pigeonitic according to H., KUNO) basalt acompanied with a small quantity of alkaline olivine basalt (in the upper horizons)., 2) Subordinate amount of acidic tuff alternating with mudstone and other sediments., 3) Acidic intrusives 4) Calc-alkalic (hypersthenic according to H., KUN0) andesite eruptives (in the shizukawa group)., It is remarkable that similar sequences of igneous activities and associated sediments are found in the other areas within the South Fossa Magna regions., 3 The group is probably Miocene in age., There are few fossils except Sagarites and small foraminifers., 4 Alteration of the igneous rocks is comparatively slight., The texture of the rocks and most of the rock-forming minerals are fairly well preserved., However, all of olivine and some of hypersthene and plagioclase are altered., Iron saponite is most conmon as a secondary mineral., Chlorite, prehnite and epidote appear in the tuff only in the southeastern part contiguous to the area of many intrusive bodies which are not shown in the map.,

Problems of Carboniferous-Permian volcanicity in Scotland

In this paper a first attenpt is made to account for the eruptive sequence of Scottish Carboniferoius-Permian igneous rocks by means of a synthesis involving the mechanism of eruption as well as the broader aspects of differentiation. The time-sequence of extrusion and intrusion is considered in detail and summarized graphically in tabular form. The rocks concerned are regarded as including camptonite-monchiquite and quartz-dolerite dyke suites widely distributed in the Highlands and Islands. The main facts to be accounted for are : (1) the wide distribution of felsic differentiates of alkaline basaltic magma, in the form of lavas and intrusions, in early Calciferous Sandstone times (Clyde and Forth areas), as contrasted with the absence of felsic lavas and intrusions from the products of late Calciferous Sandstone, Carboniferous Limestone, Millstone Grit and Permian volcanicity; (2) the availability, for extrusion, of alkaline basaltic magma long before (Calciferous Sandstone to Millstone Grit times) and shortly after (Permian times) the period of intrusion of calc-alkaline quartz-dolerite; (3) the common occurrence of alkaline basaltic magma as lava flows in Carboniferous and in Permian times, as contrated with the absence of extrusive equivalents of the Permo-Carboniferous quartz-dolerite dykes and sills; (4) the occurrence of teschenite almost exclusively as sills, and or kylitic rocks mainly as sills (but in a few instances as isolated dykes or elongated plugs), as contrasted with the prevalence of quartz-dolerite in the form of long wide dykes, some of which represent the feeding channels of adjacent sills; (5) the frequent occurrence in monchiquitic intrusions (dykes, etc.) and in Permian neck-agglomerates, of xenoliths or large xenocrysts of peridotite, pyroxenite, alkali-felspar, biotite, hornblende and augite, and of local country rocks; (6) the availability, for dyke-formation, of alkaline basaltic magma (in the form of basanite, camptonite, monchiquite etc.) over the greater part of Scotland in late Carboniferous or early Permian times, very shortly after the intrusion of calc-alkaline basaltic magma (in the form of quartz-dolerite and tholeiite dykes) throughout much of the same area. In the attempt to account for these facts, crustal layering of one of the types suggested by W. Q. Kennedy and E. M. Anderson is assumed to exist. Primary magma is envisaged as rising, along vertical crustal fissures, from horizontal sheet-like magma reservoirs of wide extent, situated at depths between 29 and 35 kilometres. The crustal fusion that formed these reservoirs is assumed to have taken place at different levels at different periods, but never simultaneously at different levels. Differentiation is assigned to a high level in the crust, at the relatively cool tops of magma-filled fissures; it is assumed to have taken place during pauses in the rise of primary basaltic magmas derived from parts of a graded Lower Intermediate (Alkaline olivine-basalt) Layer and from the base of the Upper Intermediate (Tholeiitic) Layer. Differentiation of the calc-alkaline tholeiitic magma was negligible. Violently explosive eruptions of near-surface origin are regarded as controlled by the extent of felsic-mafic layering due to advanced crystallization-differentiation. Evidence is given indicating that Permian volcanic vents originated on monchiquite dykes, owing to a release of explosive energy that may have occurred at great depths. Local evidence is cited against R. A. Daly's suggestion that Scottish Permian necks originated from satellitic sill-intrusions. S. I. Tomkeieff, in his petro-chemical synthesis of the Carboniferous and Permian igneous rocks of the Midland Valley of Scotland, appears to postulate one or more layered (differentiated) magma reservoirs with teschenitic magma at the top and quartz-doleritic magma at the bottom. It appears very difficult to imagine an eruptive mechanism that will reconcile such a conception with the temporal and (extended) geographical distribution of magmas and rocks summarized above.