Adjacent Granite Research Articles

Metasomatic crystallization of muscovite in granite and tourmaline in schist related to pegmatite emplacement near Yellowknife, Canada

Numerous pegmatite dikes occur in the Sparrow pluton (muscovite-biotite granite) and in the adjacent cordierite-zone schist-hornfels of the Yellowknife Supergroup. Where pegmatite dikes cut granite, the adjacent granite is enriched in muscovite and apatite, and depleted in K-feldspar. Mass transfer calculations, based on rock, mineral, and modal analyses, indicate that H, P, and locally B, Ti, Fe, and Ca were added, and K, Sr, Ba, and locally Na were removed (hydrogen metasomatism). In one alteration zone (8 cm wide) the calculated change (in terms of μ mols/gram of unaltered granite) is, 600 K-feldspar+24 biotite+190 plagioclase +[770 H+36 P+3 Ti+13 Fe+13 Ca] → 400 muscovite+1100 quartz +11 apatite+[240 Na+260 K]. Where pegmatite dikes cut schist-hornfels (biotite-plagioclase-quartz), the adjacent rock is, in places, enriched in tourmaline, apatite, and quartz, and depleted in biotite and plagioclase. These alteration zones are variable in width; most are less than 20 cm wide. Mass transfer calculations, based on rock, mineral, and modal analyses, indicate that B, P, Zn, and locally Ca, Fe, and Al were added, and that Na, K, Fe, Rb, Sr, Ba, and locally Mg and Si were removed (boron metasomatism). In one zone, 2 cm wide, the calculated reaction (in units of μ mols/gram of unaltered schist) is, 730 biotite+1530 plagioclase +[1080 B+600 H+430 P+360 Ca] → 480 tourmaline+480 quartz+115 apatite +[3630 Si+870 Na+590 K+110 Fe]. Changes in the volume fraction of muscovite, K-feldspar, tourmaline, and biotite, relative to distance from pegmatite, are progressive, and in most alteration zones may be expressed by use of an error-function equation. Some tourmaline zones are more complex. Zone formation is considered in terms of a steady-state reaction model in which grainboundary diffusion is the transport mechanism.

南部阿武くま山地花こう岩類の角せん石Ｋ‐Ａｒ年代

K-Ar age determinations were carried out on 19 homblendes and 4 biotites from 9 granitic masses and two metamorphic rocks in the southern Abukuma Plateau, Northeast Japan. Hornblende ages for granitic rocks range from 96.4 to 119 Ma and are apparently not correlated with area or mass. Biotites show a limited age range of 96.1-97.8 Ma. The variation in hornblende age is attributed to the difference in cooling rate of granitic rocks. Hornblende ages for the Gosaisho and Tamadare metamorphic rocks are 115 and 103 Ma, respectively, and nearly equal to those for the adjacent granites. No old ages were found on hornblendes from the Ishikawa, Miyamoto and Samegawa masses, which constitute the older type granites and gave Rb-Sr whole-rock ages of about 400 Ma. This may impose a severe constraint on the thermal history of the older type granites.

Dalbildning i den arktiska klimatzonen

Rudberg, Sten: Dalbildning i den arktiska klimatzonen. Geografisk Tidsskrift, Bd. 82, 30–36, november 9. 1982. The Arctic permafrost zone is thought to be favourable for erosion of fluvial valleys, and three, once glaciated Arctic areas give good examples. All have sedimentary rocks. In adjacent granite and gneiss areas such valleys are rare, and glacial sculpture dominates. It is also found that all sites with young valleys are sides of trough valleys, fiords and sounds—a parallel to V-shaped valleys of once glaciated mountains. The reason is lowering of the local base level. All Arctic areas with young fluvial valleys also had a strong postglacial uplift.

Structural and stratigraphic problems of the Argylla Formation near Mary Kathleen, Queensland

Abstract Rocks formerly mapped as Lower Proterozoic Argylla Formation near Mary Kathleen in northwest Queensland consist of parallel lenses of very deformed schist, quartzite and various types of metaporphyry. Completely intermingled with these are bands of amphibolite and lenses of the adjacent Wonga Granite. Finite ductile strains of 65–80% maximum shortening have been measured; these have produced transposition on both a mesoscopic and macroscopic scale. It is shown that the major stratigraphic boundaries are much shallower than the steeply dipping, constantly oriented unit boundaries. Intrusive relationships and structural criteria indicate that all the lithologies found within the mapped boundaries of the Argylla Formation are chronologically separate. This is confirmed by mapping in the much less deformed area near Winston Churchill Mine to the north. It is concluded that an original sedimentary pile was intruded first by dolerite dyke swarms and then by acid porphyry sills followed by granitic sill...

Tuffisite with topaz from the Nigerian Younger Granite province — the Balfour Hill ‘sediments’

SummaryNear one of the Younger Granite intrusives of the Jos Plateau is a series of steeply dipping dark and predominantly fine grained rocks. Originally interpreted as argillaceous sediments thermally metamorphosed by the adjacent granite, with development of andalusite, later work established their volcanic origin but did not account for the andalusite. Field relationships and petrography of the rocks suggest they are tuffisites, emplaced by volcanic fluidization processes into part of the fracture system associated with the Younger Granite magmatism. The ‘andalusite’ is topaz, widespread in this province, mainly in the Younger Granite tin veins and greisens, sometimes as an accessory in the granites themselves, but not known from the volcanics — yet abundant in some of these tuffisites. It occurs in well formed crystals, displaying a ‘chiastolite-cross’ arrangement of inclusions, characteristic of andalusite but appearing not to have been previously recorded in topaz. The origin of the topaz must lie either in late-volcanic emanations or in hydrothermal fluids from the mineralizing stage of Younger Granite emplacement.

Petrology of the tabashine granitic body, Kitakami mountains, northeastern Japan.

To reveal the chemical characters of the Tabashine granitic body, southern Kitakami mountains, thirteen rocks, ten biotites and seven hornblendes were analysed chemically. As a result, the analyses indicate high K2O in rocks, high TiO2 in biotites, and low Al2O3 in both biotites and hornblendes. These chemical features of the Tabashine body are common to the Orikabe and Hirota, while the other adjacent granites called Senmaya, Hitokabe and Kesengawa are different. Judging from the fact that all rock types of the Tabashine body, i. e. gabbroic, granodioritic and adamellitic rocks, show similar features of mineral chemistry, it is considered that they are comagmatic dervatives. On the other hand, the reason why the rocks of the three bodies, Tabashine, Orikabe and Hirota, show similar features and are different from the other adjacent granites of Senmaya, Hitokabe and Kesengawa, is probably that their magmas had the same origin and had been passed under similar physicochemical conditions.

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.

The role of hydration in the spatial distribution of metasomatic cations in the Land's End aureole, Cornwall

An account is given of the distribution of selected major and trace cations in the Land's End granite aureole, Cornwall. Two metasomatic processes were operative during contact metamorphism: (1) “internal” metasomatism involved the local migration and redistribution of Fe, Mg and Ca within the basic hornblendic hornfelses and (2) “external” or allochemical metasomatism involved the addition of F and the alkalis to basic and pelitic hornfelses from the adjacent granite. As element migration took place in a dominantly aqueous environment it is suggested that the metasomatic cations were in the hydrated state and not in the “bare” ionic state. If this were the case their spatial distribution relative to the granite contact could be explained in terms of the relative sizes of the hydrated species. That is, large highly hydrated ions would be less mobile than smaller hydrated ions and thus be restricted in their movement and distribution.

The deformation of a basement granite and the development of major silicified shear zones in Uganda

"The Kateti shear zone is of exceptional interest because almost continuous exposures show a complete gradation over several hundred feet, from foliate granite through granulated and partly silicified rocks into banded quartz tectonites. The structures of the rocks occurring at Kateti suggest that this shear zone represents an intermediate stage in the development of more massive and continuous bodies of quartz rocks which are completely detached from the adjacent granite."

The Deformation of a Basement Granite and the Development of Major Silicified Shear Zones in Uganda

The Kateti shear zone is of exceptional interest because almost continuous exposures show a complete gradation over several hundred feet, from foliate granite through granulated and partly silicified rocks into banded quartz tectonites. The structures of the rocks occurring at Kateti suggest that this shear zone represents an intermediate stage in the development of more massive and continuous bodies of quartz rocks which are completely detached from the adjacent granite.

Some zoned skarns from granite-marble contacts near Puyvalador, in the Quérigut area, eastern Pyrenees, and their petrogenesis (With Plate XIX.)

SummaryDescriptions, with chemicaland mineralogical data, are given of zoned wollastonite-grossular-clinozoisite skarns found at the contact of limestone and granite at Puyvalador, near Quérigut, France. It is shown that the silica and alumina necessary for the formation of the skarn were supplied by the adjacent granite, which in return received lime from the marble replaced by the skarn zones. The modified facies of the granite in contact with the skarn is also described; it shows evidence of migration of silica towards the contact and of accumulation of lime derived from the neighbouring marble.Similar, but not identical, changes are found at other localities along the Quérigut granite contact with limestone. The features of the Puyvalador granite-limestone contacts are compared and contrasted with those described from some other regions. The contact rocks dealt with here are characterized by the presence of abundant clinozoisite, indicative of relatively low temperatures and abundance of water at the contact in the later stages of evolution of the granite.

The Jersey lead-zinc deposit, Salmo, B. C

The orebody lies in a dolomitized zone at the base of a limestone bed in a series of lower Cambrian sediments. The sediments are isoclinally folded and the ore is in the upper limb of the fold. The ore minerals are pale-colored iron-free sphalerite, and galena. Silver is virtually absent but cadmium is associated with the sphalerite. Pyrite and some pyrrhotite are present.The major control of ore deposition has been open and overturned folding. In places the folding is accompanied by brecciation and minor pre-mineral faulting. The ore occurs in the troughs and on the limbs of the folds. The sediments have been intruded by granite, which has formed a tactite or skarn zone beneath the ore. This zone is in places overfolded and high-grade ore occurs around the nose and within the overfold.The deposit is typical of a type of world-wide distribution normally far removed from any igneous masses. The adjacent granite is not necessarily the source of the ore solutions.Trace element analyses show considerable zinc in the overlying argillite and this is considered to be a possible source of the mineralization that has been concentrated in a favorable zone in the limestone by meteoric water.

XXIII.— Contact Phenomena associated with a Dolerite Dyke at Creag Strollamus, Skye

In the account of the structure and igneous activity of the Creag Strollamus area a number of dolerite dykes of post-granite age were recorded (King, 1953, p. 395). One of these dykes possesses interesting contact features. It has been traced intermittently for about 200 yards trending NNW-SSE on the north-eastern slopes of the hill ( op. cit., Pl. I; grid reference on map—L 20). The dyke is, however, only well exposed over a distance of some 40 yards, where it is marked by a conspicuous ledge on the steep granite hill slope. Here the dyke has a width of about 9 feet and exposures are continuous between granite on either side. The dolerite from the central part of the dyke is moderately coarse-grained and sparsely porphyritic with phenocrysts of plagioclase (zoned from An65 to An70) about 3 or 4 mm. in length (Pl. I, B). The matrix consists of abundant laths of similar plagioclase together with anhedral pale-coloured augite, sometimes in sub-ophitic relations with the felspar. Numerous patches and and pseudomorphs of yellowish-green flaky aggregates of a secondary chloritic mineral occur. There are also occasional small interstitial turbid patches having a radiating habit, which appear to consist of alkali felspar. Within six inches or so of the margins of the dyke the texture becomes rapidly finer and small, almost perfectly spherical amygdales, largely occupied with a weakly birefringent green chlorite, make their appearance (Pl. I, F). The adjacent granite, where completely unaltered, is of the usual granophyric variety found in the This 250-word extract was created in the absence of an abstract

BRUCITE DEPOSITS IN THE RUTHERGLEN DISTRICT, ONTARIO

Some deposits of brucitic limestone with a ratio of MgO: CaO higher than that of dolomite are described. Evidence is given to show that the excess magnesia derived from dissociation of dolomite by the heat of the adjacent granite. Selective transfer of the products of dissociation into the carbonate rocks is attributed to igneous emanations. The bulk of the brucite is believed to have been deposited by direct replacement of carbonates, rather than by hydration of previously formed periclase, as has been suggested for similar occurrences elsewhere.

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