Geochemistry and petrogenesis of tertiary granitic rocks from the Island of Mull, Northwest Scotland

Walsh, J. N.; Beckinsale, R. D.; Skelhorn, R. R.; Thorpe, R. S.

doi:10.1007/bf00375426

Cited by 67 publications

(47 citation statements)

References 23 publications

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“…The conclusion reached above that the Hebridean Tertiary 'primitive' granites cannot be products of simple crustal fusion is consistent with published geochemical studies which model them as mixtures of mantle-derived magmas and sialic melts or selective contaminants (Moorbath and Welke, 1969;Thorpe et al, 1977;Carter et al, 1978;Meighan, 1979;Walsh et al, 1979;Dickin, 1981;Thompson, 1982a;Walsh and Clarke, 1982). Nevertheless, several interesting problems remain, such as: did sialic contamination occur before, during, or after fractional crystallization of the mantle-derived magma component; was the contaminant a silicate melt or some other fluid (Thompson et al, 1982); what are the identities of the crustal rock types providing the sialic fractions (Brown, 1963;Bell, 1976)? In fig.…”

Section: Evolution Of Hebridean Tertiary Granitessupporting

confidence: 86%

“…The Ardnamurchan cone sheets (Holland and Brown, 1972) appear to have evolved in a similar way (Thompson, 1982a). The normalized incompatible element pattern for a basic sample (M 13) from Centre 2, Mull (Walsh and Clarke, 1982), is shown in fig. 4, together with data for sample SK 271 (Table III) from the Marsco Summit Gabbro, Skye, which was emplaced very shortly before the Glamaig Granite (Thompson, 1969).…”

Section: Evolution Of Hebridean Tertiary Granitesmentioning

confidence: 99%

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Thermal aspects of the origin of Hebridean Tertiary acid magmas. II. Experimental melting behaviour of the granites at 1 kbar P_H₂0

Thompson

1983

Mineral. mag.

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ABSTRACT. Experimental melting equilibria at 1 kbar PH2O are reported for three early Tertiary granites from Skye and one from Rhum, together with a quartz rnonzonite from Ardnamurchan. The Hebridean Province leucogranites show cotectic melting behaviour, whilst associated 'primitive' (mostly adamellitic) acid plutons have silicate liquidi N 925 ~ and plagiodase liquidi ~ 875 ~ At such high temperatures the morefusible crustal rock types of the region would be almost completely molten. If the Tertiary 'primitive' acid magmas were simple crustal melts, they would inherit the incompatible element ratios of their sialic progenitors. This is demonstrably not so. Minor element ratios in these plutons are consistent with extensive fractional crystallization during the evolution of their magmas. But it is, in most individual instances, extremely difficult to specify, either by thermal or geochemical arguments, whether (1) fractional crystallization followed sialic contamination of basic magmas or (2) mixing occurred between fractionation residua and sialic melts. Both the minor element ratios and cotectic melting behaviour of the Hebridean Province leucogranites are consistent with the view that they are products of extreme fractional crystallization of (sial contaminated) more-basic magmas. Nevertheless, it is clear--when the sequence and timing of emplacement of acid magmas within individual intrusive centres is considered--that very complex polycyclic combinations of fusion, fractionation, and re-fusion were involved in the evolution of these granites.The solidi of the samples studied experimentally, together with published data, show a progressive rise in temperature as the compositions of the rocks diverge from the minimum melting composition in NaA1Si30 sKA1Si3Os SiO2 at 1 kbarH2 o. This relationship is important when considering the likely nature of sialic contamination of basic to intermediate continental magmatic suites fed through reservoir systems which are swarms of dykes and, or, sills. Because salic low-solidus crustal rock types also show near-cotectic melting behaviour, (~ Copyright the Mineralogical Society

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Section: Evolution Of Hebridean Tertiary Granitessupporting

confidence: 86%

Section: Evolution Of Hebridean Tertiary Granitesmentioning

confidence: 99%

Thermal aspects of the origin of Hebridean Tertiary acid magmas. II. Experimental melting behaviour of the granites at 1 kbar P_H₂0

Thompson

1983

Mineral. mag.

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“…The Myggbukta rocks display an essentially continuous composition range from 46-76 wt. ?/o SiO2, a slightly greater range than the otherwise closely comparable suite from the Beinn Chaisgidle Centre, Mull (Walsh and Clarke, 1982). This sequence, with Fe, Ti, V, P, and Cu attaining maxima in the intermediate stages between basaltic and rhyolitic extremes, cannot be attributed to magma mixing or primary melt batches and has all the hall-marks of extreme fractionation.…”

Section: Discussionmentioning

confidence: 74%

“…The concentration of Zr in the residual liquids suggests an affinity with peralkaline rhyolites (Carmichael, 1962) and the Myggbukta acid rocks may be compared to the peralkaline granophyres of the British Tertiary Province (Meighan, 1979;Thompson, 1982). In the British Province an origin for the acid rocks involving strong fractionation from basaltic parents with variable degrees of crustal contamination, has now become a consensus view (Bell, 1976;Thorpe et al, 1977;Meighan, 1979;Walsh et al, 1979;Walsh and Clarke, t982). Similarly, crystal fractionation has been regarded as the key petrogenetic process for generation of salic rocks in the Tertiary complexes of the Blosseville Coast by Wager and Brown, 1968, Brown et al, 1977, and Myers, 1980, as also in Iceland (Carmichael, 1964).…”

Section: Discussionmentioning

confidence: 99%

Myggbukta and Kap Broer Ruys: the most northerly of the East Greenland Tertiary igneous centres(?)

et al. 1984

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ABSTRACT. The Myggbukta Complex is a shallowly dissected central volcano superimposed on the early Tertiary Plateau Basalts of NE Greenland. This, and the Kap Broer Ruys centre, 30 km to the east, appear to be the most northerly central complexes of the North Atlantic Tertiary Province. The Myggbukta Complex comprises a suite of extrusions and minor intrusions ranging from picritic basalt to potassic rhyolite: most of the suite appears related by relatively low pressure (< 10 kbar) crystal fractionation. A small rise in initial 87Sr/86Sr (0.70593) with silica content is attributed to minor contamination through crustal anatexis. A basic dyke-swarm associated with the complex, precedes it and shows more limited differentiation. The basalts of the dyke-swarm and the Myggbukta Complex are genetically intimately related to the lavas forming the upper part of the earlier plateau basalt succession (UPLS). It is proposed that a large shield volcano developed some 100 km west of the developing spreading centre (Mohns/Aegir ridge), of which the UPLS, the dyke-swarm and the Myggbukta Complex represent three successive evolutionary stages. A generalized increase in differentiation through time can be recognized from one stage to the next. The acid intrusions of the Kap Broer Ruys area are probably also largely residues of basalt fractionation like their Myggbukta counterparts. However, higher initial STSr/86Sr ratios (0.70625 0.71034) imply a greater degree of crustal contamination.

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“…A few years ago there was a widespread consensus that melting of older crustal material was the predominant mechanism for the formation of the acid magmas in the province. This concept is by no means rejected but the role of magmatic fractionation as an associated and complimentary process is now widely accepted (Moorbath and Welke, 1969, Walsh et al, 1979, and Thompson, 1983.…”

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Recent Advances in Ideas on the Origin of the Igneous Rocks of the Tertiary Igneous Province—Introduction

Walsh

1984

Mineral. mag.

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The first five papers of this issue of the Mineralogical Magazine have as a common theme Tertiary Igneous Geology. In May 1983 the Society held a thematic meeting on the igneous rocks of the Tertiary Province and from this has followed a collection of papers, grouped here together for convenience. The range of topics covered is broadly based and the papers demonstrate the extent of current research activity in the area. All readers of the Magazine will be aware of the extent of the contribution made to igneous petrology and geochemistry by work done on the Tertiary Igneous Province. The Tertiary age of the igneous rocks had been recognized from work during the last century by Sir Archibald Geike and Professor J. W. Judd.

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Geochemistry and petrogenesis of tertiary granitic rocks from the Island of Mull, Northwest Scotland

Cited by 67 publications

References 23 publications

Thermal aspects of the origin of Hebridean Tertiary acid magmas. II. Experimental melting behaviour of the granites at 1 kbar P_H₂0

Thermal aspects of the origin of Hebridean Tertiary acid magmas. II. Experimental melting behaviour of the granites at 1 kbar P_H₂0

Myggbukta and Kap Broer Ruys: the most northerly of the East Greenland Tertiary igneous centres(?)

Recent Advances in Ideas on the Origin of the Igneous Rocks of the Tertiary Igneous Province—Introduction

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Geochemistry and petrogenesis of tertiary granitic rocks from the Island of Mull, Northwest Scotland

Cited by 67 publications

References 23 publications

Thermal aspects of the origin of Hebridean Tertiary acid magmas. II. Experimental melting behaviour of the granites at 1 kbar PH20

Thermal aspects of the origin of Hebridean Tertiary acid magmas. II. Experimental melting behaviour of the granites at 1 kbar PH20

Myggbukta and Kap Broer Ruys: the most northerly of the East Greenland Tertiary igneous centres(?)

Recent Advances in Ideas on the Origin of the Igneous Rocks of the Tertiary Igneous Province—Introduction

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Thermal aspects of the origin of Hebridean Tertiary acid magmas. II. Experimental melting behaviour of the granites at 1 kbar P_H₂0

Thermal aspects of the origin of Hebridean Tertiary acid magmas. II. Experimental melting behaviour of the granites at 1 kbar P_H₂0