Hornblende Gabbro Research Articles

Coexisting Intermediate and Basic Magmas, Ingonish, Cape Breton Island

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 injected through pipelike bodies into a chamber of actively fractionating dioritic magma. There, the basic magma flowed out onto diorite cumulate-liquid interfaces and solidified as "flows" and "pillows" of hornblende gabbro. These flows can be termed "intramagmatic." Deposition of major cumulus minerals from the dioritic magma continued on top of the gabbroic bodies. Beneath the solidifying gabbro, the diorite cumulates contained a large amount of interstitial liquid. Because of higher solidus temperatures, the gabbroic layers solidified well before the underlying diorite cumulates. Some gabbroic layers have been fractured, allowing upward injection by these cumulates. Mixing and reaction between diorite and gabbro are quite restricted. Gabbro inclusions above the thickest layers show the greatest effects of assimilation by diorite. Extensive crystallization of intercumulus liquid in the diorites led to the formation of a separate vapor phase which concentrated, rose into, and reacted with overlying gabbro layers forming "flame" structures.

ON THE TABITO COMPOSITE MASS IN THE ABUKUMA PLATEAU

The Tabito composite mass in the southern Abukuma plateau, consisting of a granitic body and small gabbroic masses, is studied petrographically and petrochemically by the present author. The granitic body is mainly composed of granodiorite and quartz diorite and is divided into three rock types, namely Myojin-ishi, Komuro and Iritabyuto. The Myojin-ishi type has prismatic hornblendes characteristically and often contains a small amount of cummingtonite and pyroxenes. The Komuro type does not contain cummingtonite and pyroxenes, and is intruded by many leucocratic veins derived from the Iritabyuto type. The Iritabyuto type is the most leucocratic of the three and contains dark inclusions ubiquitously. Four gabbroic masses consist mainly of hornblende gabbro with a small amount of cortlandtite and gabbro pegmatite. Modal analyses on 53 rocks and new chemical analyses on 41 rocks are given. As to modal compositions and variation trends on the SiO2-Al2O3, SiO2-MgO diagrams, there is a discontinuity between the Iritabyuto type rocks and other rocks. Dark inclusions are always more mafic than the host rocks.

Electrical conductivity of serpentinized rocks to 6 kilobars

Electrical conductivity of serpentinized rocks from the Indian Ocean ridge is 3–4 orders of magnitude higher than that of serpentine-free peridotite, hornblende gabbro, and basalt from the same area and from the Tonga trench. The enhanced conduction is apparently characteristic of many but not all serpentine-rich rocks and may be due in part to high porosity and in part to mineral conduction associated with the magnetite formed during serpentinization. Observations of high oceanic crustal conductivity could be explained by the presence of serpentine in these rocks, although this might be ruled out on the basis of temperature, velocity, or local petrology.

ON THE GABBROIC IN THE NORTHERN ABUKUMA MOUNTAINS

There are many gabbroic masses intruded prior to the emplacement of the older group granite in the Abukuma plateau. These intrusives are mainly hornblende gabbros with a small amount of cortlandite. Two representative intrusions, that is, Hayama and Utsushigatake‾bodies occupying about 3×2km. respectively, were described petrographically in some detail. Chemical and modal analyses were done on fifteen rocks including a hornblende gabbro pegmatite and two cortlandites. They are characterized by high Al2O3 and CaO, and relatively low SiO2 contents. Measured age of K-Ar dating on biotite from a gabbro is 86×106 years. This obtained age is apparently corresponding to that of the younger group granite.

Petrology of mafic inclusions from Itinome-gata, Japan

Various types of mafic inclusions up to 30 cm in size occur in lapilli tuff of alkali basalt at Itinome-gata crater, northeastern Japan. They are divided into the following four groups: amphibolite, hornblendite—hornblende gabbro, leucogabbro, and pyroxene gabbro. Also occurring with the mafic inclusions are lherzolite and websterite inclusions and megacrysts of Mg-rich olivine and chromian diopside. New analyses are presented for twenty five representative mafic inclusions, eight clinopyroxenes, six orthopyroxenes, and fifteen brown hornblendes.

The geology of two small layered hornblende peridotite (picrite) plutons in South Greenland

Two ultramafic dykes, which pinch and swell both vertically and horizontally and have a form similar to some kimberlite bodies, were intruded 1700 to 1335 m.y. ago during the 2nd episode of Ketilidian plutonism. Contact metamorphism of the adjacent granite was slight -albite-epidote hornfels facies. Petrological, mineralogical and chemical evidence indicates that the parent magma was picritic in composition, that it underwent flowage differentiation as a result of rapid intrusion, and then magmatic differentiation with gravity settling. The internal picritic (chemical classification) layered group crystallised first and includes hornblende peridotites, hornblende-hypersthene peridotites and rare harzburgite. The border group which crystallised later is formed of hypersthene-olivine hornblendites that chemically are picrites, and mica hornblendites that chemically are monzonites with affinities to kentallenite. Hornblende gabbro is a minor late differentiate. Steeply dipping banding cuts the earlier rhythmic layering and is thought to have formed by diffusion of material into cooling cracks developed prior to complete solidification. There are local concentrations of sulphides and platinoids. Three complete silicate analyses and a number of analyses for the platinoids, Au, Cr, Co, Cu, Ni, Ag, Pb and Zn are presented.

Composition and evolution of the oceanic crust

Laboratory measurements of compressional wave velocities in rocks are consistent with an oceanic crust composed of an assemblage of hornblende and plagioclase (layer 3) overlain by tholeiitic basalt (layer 2). Partial melting of mantle peridotite under mid-oceanic ridges marks the initial stages in the development of the oceanic crust. Tholeiitic magma, which escapes to the ocean floor, forms layer 2. Layer 3, composed of amphibolite and hornblende gabbro, originates beneath the ocean floor by crystallization of tholeiitic magma under hydrous conditions and subsequent metamorphism in the vicinity of ridge crests. Once formed, the oceanic crust is transported laterally by horizontally spreading upper mantle. Disposal of the oceanic crust is accomplished by downward movement in the vicinity of descending limbs of convection cells. Partial melting of the oceanic crust in regions of downward convection results in the formation of the calc-alkaline suite of rocks and eclogite.

Relations of Granitic and Gabbroic Rocks, Northern Santa Lucia Range, California

The plutonic rocks of the northern Santa Lucia Range arc calc-alkaline and consist of hornblende gabbro, tonalite-granodiorite, and quartz monzonite of probable Cretaceous age. They were emplaced as concordant plutons during regional folding and metamorphism at temperatures above 650° C and at depths of 15 to 20 km. The country rocks consist predominantly of quartzofeldspathic meta-sedimentary rocks (Sur series) of probable Paleozoic age. The earliest major intrusions were of hornblende gabbro and leucocratic quartz monzonite. These formed homogeneous, mappable plutons and heterogeneous mixtures of gabbro and quartz monzonite with locally abundant hybrid rock. Tonahte-granodionte plutons were emplaced next and locally intruded the heterogeneous gabbro-quartz monzonite terrane. The last major intrusions were of quartz monzonite. Contacts between quartz monzonite and hornblende gabbro vary Irom sharp to gradational, and hybrid rocks are locally developed. Most contact relations indicate that gabbro was solid when quartz monzonite magma intruded it. Structural evidence of the broad contemporaneity of quartz monzonitic and gabbroic magmas allows the possibility that some mixing of magmas furthered the development of hybrid rocks and gradational contacts. Tonalite-granodiorite plutons emplaced somewhat later may have formed by hybridization of gabbro and quartz monzonite.

The Palestina Fault, Colombia

The Palestina fault is an inactive right-lateral wrench fault more than 350 km long in the largely metamorphic and igneous terrain of the northern Central Cordillera of the Colombian Andes. It strikes north to north-northeast, nearly parallel to the regional Andean structures. Much of the fault is followed by straight canyons 50 to 600 m deep. A zone of breccia and mylonite less than 50 m thick marks the fault. Rock is intensely fractured within 50 m of this breccia zone. Deformational effects of the Palestina include large fault-block slivers of megabreccia and drag “tails” that contain some allochthonous material. A gravity profile across the Palestina shows no associated anomaly. Horizontal displacement on the Palestina of 27.7 km is well documented because the fault has offset ten unique lithologic, metamorphic, and structural features that have been mapped on both blocks. These offset features are: marble, quartzite, feldspathic and aluminous gneiss, diorite, zones of diorite mixed with Precambrian gneiss, hornblende gabbro, Cretaceous shale, metamorphic isograds, a major wrench fault, and several minor faults. The Palestina fault is only one of several recently recognized wrench faults in the northern Central Cordillera, and its documentation should call attention to the possible importance of these features in the tectonics of the area. Published analyses of wrench-fault tectonics in northern Colombia and Venezuela assume a genetic relationship between all the wrench faults: they originated in response to a single unchanging regional stress system. A more meaningful analysis might result from the individual study of smaller geographic areas and consideration of the relative ages of the wrench faults.

Geological and petrological studies on the Tanzawa mountainland (4)

In the Tanzawa mountainland, there are various types of plutonic rocks such as norite, tonalite and schistose gabbro in the plutonic mass which have been known as the Tanzawa Quartz diorite mass. The present paper described on the petrography and discussed on the petrogeny of the plutonic rocks based on the field and microscopic observations. They are summarized as follows. 1. The Tanzawa plutonic mass consists of gabbroic rocks and dioritic rocks which were formed in successive order. 2. Gabbroic rocks are composed of mylonitic hornblende gabbro, plagioclase porphyritic hornblende gabbro, schistose hornblende gabbro, metasomatic gabbro, dioritic gabbro, tonalitic gabbro, and diabasic gabbro, which are grouped into two series. Gabbro amphibolite series and hornblende gabbro series. Both of the series are originated from diabasic gabbro, but one metamorphosed to the amphibolite by mylonitization and recrystallization and other to the hornblende gabbro by the acidification, though the two courses were displayed simultaneously. 3. The dioritic rocks are composed of gabbroic diorite, normal hornblende diorite, gneissose biotite diorite, plagioclase porphyritic diorite, quartz porphyritic diorite, and tonalitic diorite, which were formed in successive order. The first two are related to the initial stage, the middle one to the upheaval stage, and the last three to the intrusion stage of the complex. These dioritics are derived from gabbroics resulting from the strong enrichment of SiO2 and Na2O. 4. Gabbro amphibolite series often gradually changes into or intercalate with amphibolites while the dioritic rocks of the intrusion stage has hornfelses around them. The other series or types of gabbroic and dioritic rocks has least relation with metamorphic rocks. They are in close strict relation to each other as main constituents of the dioritization process of gabbro in the plutonic mass.

HORNBLENDE GABBROIC INCLUSIONS IN THE CALC-ALKALINE ANDESITES FROM THE NORTHERN DISTRICT OF NAGANO PREFECTURE, JAPAN (I)

There are many hornblende gabbroic inclusions found in the later Miocene to the early Pleistocene lavas developed in the northern Fossa Magna district, central Japan. These lavas are all hypersthenic rock series rich in groundmass orthopyroxene. It is noticed that a few augite-olivine-basalt lavas are often intercalated in the enormous effusives (1000m in the maximum thickness) of the calc-alkaline andesites. For this study 18 new chemical analyses have been made by one of the writers (Oji). In addition to these, 3 analyses already published by Yagi and Yagi (1958) and one analysis reproted by S. Yamada (1934) are cited; of these six are ultramafic hornblende gabbros and three are pyroxene-(±hornblende)-diorites, both as inclusions, five are andesites and the rest are augite-olivine-basalts both occurring in intimate association. They include 12 analyses of the later Miocene or early Pliocene rocks from the Shigarami Formation and 10 analyses of the later Pliocene to Pleistocene rocks. In MgO-total iron-alkalis diagram the plots of the rocks including hornblende gabboric and dioritic inclusions and their host andesites are arranged along a calc-alkaline trend. The points of the gabbros are closer to MgO-total iron side, while the points of the andesites are plotted on the extension of the gabbro-diorite line twoard the alkali apex. From intimate association of the gabbro-andesite-basalt and their petrochemistry, the writers are led to the conclusion that a calc-alkaline andesite magma rich in mafic components (SiO2 range 52-56%) has been derived from basaltic magma by subtracting hornblende gabboric crystalline aggregates, without contamination by any granitic or sedimentary materials. It is estimated that a considerable amount of ultramafic hornblende gabboric mass should be remained by this means within the depths, for instance at the geosynclinial bottoms of the Fossa Magna, and that the volume of the gabbro should exceed that of the effusive andesite composing the volcanics. Any geological evidences for such an enormous mass of hornblende gabbro of Pliocene, or even of Miocene age, have not been found in the regions composed mainly of volcanic rocks. On the contrary hornblende gabbros are much more commonly found in granite regions of Japan and they are intimately associated with diorite intrusives which had been under condition of granitization, and hence they have somewhat different characters from the segregated gabbros here cited.

Geological and petrological studies on the tanzawa mountainland

In the Tanzawa mountainland, there are various types of plutonic rocks such as norite, tonalite and schistose gabbro in the plutonic mass which have been known as the Tanzawa Quartz diorite mass. The present paper described on the petrography and discussed on the petrogeny of the plutonic rocks based on the field and microscopic observations. They are summarized as follows. 1. The Tanzawa plutonic mass consists of gabbroic rocks and dioritic rocks which were formed in successive order. 2. Gabbroic rocks are composed of mylonitic hornblende gabbro, plagioclase porphyritic hornblende gabbro, schistose hornblende gabbro, metasomatic gabbro, dioritic gabbro, tonalitic gabbro, and diabasic gabbro, which are grouped into two series. Gabbro amphibolite series and hornblende gabbro series. Both of the series are originated from diabasic gabbro, but one metamorphosed to the amphibolite by mylonitization and recrystallization and other to the hornblende gabbro by the acidification, though the two courses were displayed simultaneously. 3. The dioritic rocks are composed of gabbroic diorite, normal hornblende diorite, gneissose biotite diorite, plagioclase porphyritic diorite, quartz porphyritic diorite, and tonalitic diorite, which were formed in successive order. The first two are related to the initial stage, the middle one to the upheaval stage, and the last three to the intrusion stage of the complex. These dioritics are derived from gabbroics resulting from the strong enrichment of SiO2 and Na2O. 4. Gabbro amphibolite series often gradually changes into or intercalate with amphibolites while the dioritic rocks of the intrusion stage has hornfelses around them. The other series or types of gabbroic and dioritic rocks has least relation with metamorphic rocks. They are in close strict relation to each other as main constituents of the dioritization process of gabbro in the plutonic mass.

A preliminary note on the syenitic rocks form the Osawa-gawa area near Matsumae-mati, Oshima Province, southwestern Hokkaido

The Matsumae district is situated in the southern parts of the Oshima Peninsula in Hokkaido. Acidic and basic igneous rocks occur in the present area as a small mass at some places, that is, Osawa-gawa, Araya-gawa and Matsukura-gawa. The rocks consist mainly of pyroxene-biotite-hornblende diorite, hornblende-biotite granite, hornblende gabbro and pyroxene peridotite. The related minor rocks such as pegmatite, aplite and fine-grained granite are found in the dioritic complex. The writer describes the petrographical characters of the syenodiorite and melanocratic hornblende syenite found in the dioritic mass of the Osawa-gawa, and gives some considerations on their genesis.

The bedrock Geology of Vatnahverfi, Julianehåb district, South Greenland

The petrology, structure and chronology of the Vatnahverfi area comprising ca. 300 sq. km SE of Igaliko fjord, Julianehåb district, S Greenland, is described. All the rocks are of Precambrian age and belong to the Ketilidian, Kuanitic, Sanerutian and Gardar periods. The Ketilidian period is represented by a migmatite complex comprising various biotite and hornblende gneisses showing relict supracrustal structures and intermingled with foliated granites. The complex belongs to the lower amphibolite facies. Mapping combined with stereographic structural analysis shows that the complex was initially folded about NE-trending B1 axes and subsequently on vertical to NW-trending B2 axes. The Kuanitic period was a hiatus in the plutonism and is represented by the intrusion of discordant dolerite and microdiorite dykes and hornblende gabbro (appinitic) plutons. Renewed plutonism during the Sanerutian period caused local reactivation of the Julianehåb granite as is indicated by fragmentation and, granitisation of the older basic bodies. Discordant amphibolite dykes and sheets, including a net-veined meladiorite - leucogranodiorite suite, were subsequently intruded under synplutonic conditions. A discordant batholith and satellitic sheets of biotite adamellite were emplaced towards the close of the Sanerutian period. The subsequent Gardar period is represented by faulting, mineralisation and the intrusion of various generations of dolerite, trachyte and alkali trachyte dykes.

K-A dating on the igneous rocks in Japan (III)

K-A dating on seventeen samples of granitic rocks, one pegmatitic vein in hornblende gabbro and one epidote-amphibolite from the Abukuma massif were carried out. As a result, maximum and minimum values of granitic rocks show 107×106 years and 87×106 years respectively, and these ages of emplacement of granitic rocks are broadly divided into two periods 90×106 and 100×106 years. On the other hand, formerly the ages of intrusion of granitic rocks in the Abukuma massif have been geologically divided into two main periods younger and older. But the results of K-A dating of this time do not accord well with the former geological observations, and even the reverse cases are recognized indicating the minor time difference of these emplacements. It is clarified that the granitic rocks of the Abukuma massif are emplaced in later Cretaceous and younger than that of Kitakami massif about 20×106 years on the average. K-A dating on metamorphic rock from the northern Abukuma by muscovite minerals shows 300×106 years; this indicates that the metamor-phism would have occurred older than Carboniferous age at least.

Sanogawa gabbroic mass

The gabbroic mass described in the present paper, is situated along the Sano Valley, southern Kanto, and its geologic age is probablly Miocene. The petrographic features of this mass are described here, with special reference to the anorthite contents (An%) of plagioclase in some rocks of the mass. The study of plagioclase is summarized in the An composition frequency diagram proposed by C. Kim (1962). In this diagram, it seems likely that the maximum peaks of the frequency curve show stable environments in the lithological evolution of a rock series. The conclusions derived from the above studies are as follows. 1. The mass consists of three groups; i) gabbroic rocks (norite, pyroxene gabbro, pyroxene porphyrite, uralite porphyrite, hornblende gabbro), ii) dioritic rocks (diorite, quartz diorite) and iii) albite porphyrite. 2. Various parts of gabbroic rocks and of dioritic rocks grade gradually to each other, while albite porphyrite forms another by sheared zones. 3. From the frequency curves of An% of plagioclases, it is noted that frequency curves of plaigoclase of norites and of quartz diorites are the most stable, while those of hornblende gabbros are the most unstable. The gabbros and diorites were subjected to different tectonic movements and the formation of hornblendes in pyroxene gabbro occurred at the stage between the above two tectonic movements. Coarse-medium grained plagioclases in norite, and fine grained plagioclase in quartz diorite show the most stable frequency curves. 4. The evolutional succession of the mass is as follows: i) intrusion of pyroxene porphyrite, ii) emplacement of norite, iii) transformation of the two rocks facies into uralite porphyrite and hornblende gabbro, iv) shearing movement, followed by formation of diorites, and v) formation of albite porphyrite along the sheared zones around the diorites.

Metablastic hornblende gabbro and diorite from the middle of Horoman river, Hidaka, Hokkaido

Hornblende gabbro, diorite and gabbro-diorite occur in the sheared zone of biotite gneiss and basic hornblende plagioclase rocks. Careful observations on the occurrence of these rocks and the comparison of the component minerals between the coarse igneous textured rocks and the country metamorphic rocks have revealed that the basification and the acidification of plagioclase occur more intensively in igneous textured rocks than in metamorphic rocks, and moreover quality of the country metamorphic rocks provide for that of gabbro and diorite and the regulation is not vice versa. Consequentry, these igneous textured rocks in these districts are the metablastic rock originated from the country rocks, from which it is produced by metamorphic differentiation.

Petrochemical study of the Kagura ultramafic body, Kitakami mountainland

Abstract: A small ultramafic body which is a member of the Hayachine ultramafic complex crops out at Kagura, Kawai district, central Kitakami mountainland. This Kagura body consists of serpentinite, serpentinized pyroxene peridotite, pyroxenite, hornblende hornblende pyroxenite or pyroxene hornblendite, hornblendite, pyroxene hornblende gabbro, hornblende gabbro and hornblende gabbro pegmatite. And a little rodingitic rocks occur as wein like form within gabbroic rocks. The petrochemical features of the Kagura body and discussed by means of the chemical analyses of thirteen representative rocks. It is seemed that all the rock types are derived from and ultramafic magma in the order listed above and are formed by the succession of noted below: peridotite dunite pyroxene peridotite hornblendite (largely liquid) hornblende gabbro pyroxene hornblendite (liq.+cryst.) pyroxene hornblende gabbro hornblende gabbro pyroxenite. (largely crystalline) hornblende gabbro pegmatite Some opinion on the chemical character of the rodingitic rocks which are formed by hydrothermal reaction is give.

Some analysed rocks from Westland, New Zealand

Abstract Chemical and mineralogical compositions are given for biotite hornfels from the Paringa River, greywacke from near Waiho, and hornblende gabbro, tinguaite, and camptonite from the Haast Valley.

Minor elements in a metasomatic zone related to a copper-bearing pyrite deposit

Metasomatic alteration of sheared hornblende gabbro and quartz diorite which accompanied mineralization in the Hitachi mine district, northeast Japan, resulted in development of anthophyllite-cordierite and biotite-cordierite rocks in the ore zone. Both types of metasomatic rocks exhibit considerable enrichment in Mg and Fe and a decrease in Ca. Among changes in the minor element composition, an increase in Ba, a decrease in Sr and V, and little variation in Ni, Cr, Co, and Ga are noted.