Zircon populations in Lewisian quartzite, gneiss and granite north of Loch Laxford, Sutherland

Chowdhary, Pankaj

doi:10.1017/s0016756800051608

Cited by 3 publications

(2 citation statements)

References 10 publications

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“…While additional information from other zircon-bearing quartzites from the Lewisian complex (e.g. Chowdhary, 1971) may permit more precise interpretation of aspects of crustal history, two important conclusions have resulted from the present investigation, namely (1) there was crustal material in existence in the Scottish region before the development of the Lewisian complex and (2) some of this material was at the surface and subject to erosion at the time of the development of at least some of the crust-building pile that immediately preceded the Scourian episode.…”

Section: Discussionmentioning

confidence: 99%

Source ages of zircons in an Archaean quartzite, Rona, Inner Hebrides, Scotland

Bowes¹,

Hopgood²,

Pidgeon³

1976

Geol. Mag.

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SummaryThe internal variations in the discordance of an inhomogenous zircon population from a bedded quartzite within a c. 2700 Ma old gneiss have been studied. Varying degrees of response to events in a common multi-episodic, post-depositional history are reflected in the uranium and lead isotopic systems of size and magnetic fractions.A minimum 207Pb/206Pb age for non-magnetic zircons is 2840 Ma with 206Pb/238U and 207Pb/235U data for the three size fractions raising the possibility of an age of at least 3250 Ma. This is interpreted as a minimum age for crustal material that was in existence in the region before the formation of the Lewisian complex. Some of the slightly magnetic zircons also have a pre-2700 Ma radiogenic lead component.

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Section: Discussionmentioning

confidence: 99%

Source ages of zircons in an Archaean quartzite, Rona, Inner Hebrides, Scotland

Bowes¹,

Hopgood²,

Pidgeon³

1976

Geol. Mag.

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“…2) which is thought to be the parent material of the mesosome. Roundness of a zircon may be caused by either chemical corrosion during metamorphic processes or by sedimentary transportation (Poldervaart, 1955;Verspyck, 1961;Kalsbeek & Zwart, 1967;Pande & Mohabey, 1969;Chowdhary, 1971). If roundness is caused by chemical corrosion, the zircon crystals will appear corroded and clouded because of the chemical attack, especially by alkaline solutions.…”

Section: Crystal Habitmentioning

confidence: 99%

Effect of metamorphism and partial melting of host rocks on zircons

Gupta

Johannes

1985

Journal Metamorphic Geology

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Abstract. Zircons have been studied from different layers of migmatites (from Arvika, western Sweden and Nelaug, southern Norway) and from a paragneiss (from Arvika) associated with one of the migmatites. The main purpose of the investigation is to establish whether or not information about zircons can help in the elucidation of the parentage and rock-forming processes of migmatites.The elongation ratio of zircons from all layers is small and characteristic of sedimentary zircons. Further, the absence ofcharacteristic colours and the growth trends of the zircons (indicated by the reduced major axes) observed in the various samples both support a sedimentary parentage for these rocks. The zircons of all layers exhibit secondary growth (overgrowth, outgrowth and multiple growth) due to metamorphism. Compared with the zircons from the paragneiss, those of the migmatite layers are more clouded and less rounded, some of them becoming opaque or even skeletal; this is especially true of the zircons from the leucosomes. These observations indicate an alteration of the original sedimentary zircons in the migmatite, especially in the leucosomes, in response to the migmatization process, previously interpreted as partial melting.

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Lewisian Complex of Strath Dionard–Rhiconich and its significance in the early history of the NW Highlands of Scotland

Dash

Bowes

2014

SJG

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Synopsis Remapping of a quartzofeldspathic gneiss-dominated part of the Lewisian Complex in the NW Highlands of Scotland, originally mapped by the Geological Survey in the latter part of the nineteenth century, has added new information about the lithologies and their distribution, and established a tectonothermal–igneous history. Linking new data for the gneisses of Strath Dionard–Rhiconich to the results of isotopic studies points to the development of their protolith in late Archaean times as the result of arc magmatism similar to that at a modern ocean–continent margin. Compositionally, most of the gneisses, and those southwards towards Laxford, correspond to granodiorite with adakitic affinities. Using a comparison with a well-substantiated model for coeval late Archaean crust formation of part of the Wyoming Craton, they are interpreted as representing a stage in a tectonomagmatic cycle when the products of metasomatism and melting in the mantle were emplaced as sheet-like banded plutons at middle crustal levels. Less common granitic gneisses represent products of further melting in the thickened middle crust. Xenolithic blocks of subducted older sedimentary rocks, carried upwards by the magmas, are now seen as elongate lensoid masses of calc-silicate rock and quartzite that are grossly concordant with the banding in the gneisses. Also generally concordant with this banding are elongate lensoid masses of amphibolite, the protolith of which is considered to have been the product of mafic magmatism during the convergent margin arc activity. In early Proterozoic times the late Archaean assemblage was extensively reworked. The development of penetrative foliation in both gneisses and amphibolites was associated with isotopic homogenization that, in the southerly continuation of the domain towards the type locality of the Laxfordian orogenic belt at Laxford, has been dated at c . 1860 Ma. This preceded the imposition of the current major structural pattern that included the formation of the Strath Dionard antiform and the parasitic Gharbh Mhòr folds. Abundant granites and pegmatites, subsequently emplaced in an injection complex at Strath Dionard, are linked with the c . 1855 Ma suite of acidic intrusions that are prominent at Laxford. The rock assemblage and sequence of development are like those of other early Proterozoic mobile belts formed as the result of extensive reworking of late Archaean cratons. Limited mineralogical and structural modification of the ≥1850 Ma gneiss–amphibolite–granite assemblage, and pegmatite emplacement associated with (micro)-plate collision, took place during the development of the c . 1750 Ma Calvian orogenic belt. Further limited modification and pegmatite emplacement was at c. 1670 Ma. The structural–metamorphic–igneous histories described, integrated with isotopic data, do not support interpretations proposing a transition between the Strath Dionard–Rhiconich (–Laxford) gneiss–amphibolite domain and the adjacent granulite–dolerite dyke domain; or that the quartzofeldspathic gneiss–amphibolite domains in some other parts of the NW Highlands can be correlated with the type area of the Laxfordian orogenic belt.

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Zircon populations in Lewisian quartzite, gneiss and granite north of Loch Laxford, Sutherland

Abstract: SummaryZircon populations in quartzo-feldspathic gneisses of the Rhiconich group of the Lewisian are indicative of a sedimentary derivation of the rocks. They are similar to the zircon population of an interbanded quartzite but differ markedly from that of an intrusive granite vein.

Cited by 3 publications

References 10 publications

Source ages of zircons in an Archaean quartzite, Rona, Inner Hebrides, Scotland

Source ages of zircons in an Archaean quartzite, Rona, Inner Hebrides, Scotland

Effect of metamorphism and partial melting of host rocks on zircons

Lewisian Complex of Strath Dionard–Rhiconich and its significance in the early history of the NW Highlands of Scotland

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