Fissure Metasomatism in Volcanic Rocks Adjacent to the Shap Granite, Westmorland

Firman, R. J.

doi:10.1144/gsl.jgs.1957.113.01-04.09

Cited by 26 publications

(9 citation statements)

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“…Aspects of its petrology have been described by Nicholson (1868), Aveline et al (1888), Harker and Mart (1891), Grantham (1928) and Caunt (1986). Contact metamorphism and fissure-related metasomatic alteration of the country rocks have been investigated by Harker and Marr (1893) and Firman (1957), respectively.…”

Section: Geological Backgroundmentioning

confidence: 99%

Exsolution and alteration microtextures in alkali feldspar phenocrysts from the Shap granite

1995

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Alkali feldspar phenocrysts (bulk composition Or75.oAb24.6Ano.4) in the subsolvus Shap granite comprise a fine-scale mixture of subregular pristine crypto-and micro-perthites with altered, micropore-rich feldspar with irregular microstructures. The regular perthites are strain-controlled intergrowths of Albite and/or Periclinetwinned albite exsolution lamellae within tweed orthoclase. The microperthites formed at ~< 590~ by heterogeneous nucleation of thin albite films which coarsened to > 1 ~tm length. Cryptoperthites developed at < 400~ by homogeneous nucleation of sub-~tm long platelets between films. Platelets are coherent, but the coarser microperthite lameUae are semi-coherent, with pairs of misfit dislocations sub-regularly spaced along the albite--orthoclase interface. As much as 30% of any one feldspar crystal is turbid, a result of the formation of numerous Ixm to sub-~tm sized micropores during deuteric alteration. In some areas, deuteric fluids gained access to the interior of feldspar crystals by exploiting semi-coherent film lameUae. Albite was selectively dissolved and micropore-rich irregular microcline was reprecipitated in its place. In other parts of the feldspars deuteric recrystaUization completely cross-cuts the pristine microtextures and patch perthites have formed. These are coarse, incoherent to semi-coherent intergrowths of irregular microcline (replacing tweed orthoclase) and Albite-twinned albite. The deuteric reactions occurred at < 400~ the main driving force for dissolution and reprecipitation was decrease in the elastic strain energy at the coherent interfaces of cryptoand micro-perthite lamellae, and the recrystallization of tweed orthoclase to irregular microcline.

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Section: Geological Backgroundmentioning

confidence: 99%

Exsolution and alteration microtextures in alkali feldspar phenocrysts from the Shap granite

1995

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“…The Shap Granite does have its characteristic attendant mineralization, but apart from fissure metasomatism in the metamorphic aureole (see Firman, 1957) no discrete vein deposits are discernable. The only igneous masses which are traversed by mineral veins are those of Skiddaw and the Carrock Fell complex.…”

Section: A Age Of Mineralization -Geological Evidencementioning

confidence: 99%

K—Ar isotopic age determinations from some Lake District mineral localities

Ineson

Mitchell

1974

Geol. Mag.

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Forty-seven new K-Ar analyses are reported from 15 mines in the Lake District. Analyses of clay mineral concentrates from vein gouges and altered wallrock support a hypothesis of at least 3 distinct isotopic events. Caledonian ages (388 Ma) are reported from the Coniston Copper deposits, while the extensive mineralization in and around the Vale of Newlands indicates a metasomatic event occurring at around 360 Ma. The ages of the sporadic mineral localities to the E of the area (i.e. Greenside, Threlkeld, etc.) are grouped around 325 Ma while those of the Caldbeck Fell deposits are close to 230 Ma. An epidosic model may be advanced for the Carrock Fell Tungsten deposits with a range from 197 to 282 Ma. The geochronological significance of these and other previously published results is considered.

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“…These xenoliths have been converted into diopside-rich assemblages, indicating that the lime-bearing solutions were available at the late stage of the crystallization of the granitic rocks. Though granitic rocks are normally poor in lime, several examples are known where they have formed lime-rich minerals in the late stages of crystallization; the formation of epidote-rich rocks like unakite (Jonas, 1935) and helsinkite (Laitakari, 1918), and lime-metasomatism of the wall rocks (Firman, 1957) by some granites are noteworthy in this respect.…”

Section: An Increase In Cao In These Contact Zones Between the Dikes mentioning

confidence: 99%

Petrology of Dikes Emplaced in the Ultramafic Rocks of Southeastern Quebec and Origin of the Rodingite

De¹

1972

Geological Society of America Memoirs

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The ultramafic rocks of the Appalachian region in the Eastern Townships of Quebec consist mainly of serpentinized harzburgite and dunite. They are intruded by dikes of dioritic rocks, quartz monzonites (adamellites), pegmatite, and albitite. Near contacts with the dikes the serpentinite with 7-A serpentines has been transformed to a zone with 14-A chlorites with higher Al/Si ratio; serpentinite may also be converted into diopside, talc, anthophyllite, and so forth, indicating dehydration and loss of water into the intruding dike. The granitic and dioritic rocks are modified especially at the borders to assemblages consisting of grossularite, diopside, vesuvianite, prehnite, zoisite, and calcite, forming a rodingite.In general, the water-rich and silica-deficient environment of serpentinized ultramafic rock is responsible for affecting the normal sequence of crystallization of the dikes. This leads to the conversion of pyroxene to hornblende and finally to chlorite and (or) biotite; at the same time the crystallizing plagioclase becomes albitic. The lime and alumina that would normally form clinopyroxene or hornblende and plagioclase remain in the residual hydrous melt to form abundant lime-rich hydrothermal minerals. The lime in these rodingites is, therefore, not derived by serpentinization of the ultramafic wall rocks. PETROLOGY OF DIKES AND ORIGIN OF RODINGITE, QUEBEC 491Thetford Mines on a large peridotite-dunite body is the Jeffrey mine, located in the mining town called Asbestos. DIKE ROCKS Granitic RocksThe granitic rocks are the commonest dike rocks of the area. Granitic pegmatite dikes are also common. There are two main types of granitic rocks: (a) biotitemuscovite quartz monzonite, the most abundant granitic rock, particularly common in the Black Lake area; and (b) a leuco-quartz monzonite found in the Normandie mine, Black Lake, and hence termed the Normandie quartz monzonite. Several rock types have been produced by the desilication and subsequent albitization of the granitic rocks, out of which syenodiorite and albitite are noteworthy.These dikes were emplaced in the epizone (Buddington, 1959, p. 677-690) by wedging along the shear zone, fractures, and joints in the serpentinized ultramafic rocks.Both the above types of quartz monzonite consist of plagioclase An24_12, potash feldspar Or77 Ab(+An)23, and quartz. The micas are the important constituents, and a biotite of red-brown variety (Ny = 1.643 ± .001; d (060) = 1.543 A) is widely developed. A second generation of plagioclase, An0_10, is commonly present.The chemical, normative, and modal compositions of the granitic rocks show that the specimens of biotite-muscovite quartz monzonite and of the leuco-quartz monzonite are all typical quartz monzonites (adamellites); chemical analyses of two specimens (nos. 194 and 548) are given in Table 1. The normative quartz, orthoclase, and albite content of these two specimens (194 and 548), recalculated to 100, are 41.6, 33.0, 25.4; and 39.0, 26.8, 34.2, respectively. They fall close to

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Fissure Metasomatism in Volcanic Rocks Adjacent to the Shap Granite, Westmorland

Cited by 26 publications

References 10 publications

Exsolution and alteration microtextures in alkali feldspar phenocrysts from the Shap granite

Exsolution and alteration microtextures in alkali feldspar phenocrysts from the Shap granite

K—Ar isotopic age determinations from some Lake District mineral localities

Petrology of Dikes Emplaced in the Ultramafic Rocks of Southeastern Quebec and Origin of the Rodingite

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