Caledonian Granites Research Articles

Lead isotope studies on mineral showings and ore deposits in East Greenland

Lead isotope studies indicate an age of 680 ± 65 Ma for syn-diagenetic stratiform copper mineralisation in the Upper Proterozoic Eleonore Bay Supergroup (EBS) sediments. Metals in EBS-hosted veins were remobilised from local host rocks, or derived from underlying Middle Proterozoic gneisses. Tungsten-arsenic skarns associated with Caledonian granites intruded into the EBS incorporated lead mobilised from the basement gneisses mixed with Caledonian granite lead. Isotopic compositions of trace lead in sparse sulphide occurrences in North-East Greenland point to Late Archaean – Early Proterozoic sources, comparable to the local basement gneisses. Base metal mineralisation in Upper Palaeozoic – Mesozoic rocks in central East Greenland shows a limited range. in lead isotope compositions, suggesting that a large, homogeneous crustal reservoir supplied the metals, or that metals from different sources were effectively mixed. Mineralisation in Tertiary igneous rocks in the Kangerdlugssuaq area of southern East Greenland shows lead isotope evidence for contamination by material from lower crustal Archaean sources.

A stable isotope study of retrograde alteration in SW Connemara, Ireland

Dalradian metamorphic rocks, Lower Ordovician meta-igneous rocks (MGS) and Caledonian granites of the Connemara complex in SW Connemara all show intense retrograde alteration. Alteration primarily involves sericitization and saussuritization of plagioclase, the alteration of biotite and hornblende to chlorite and the formation of secondary epidote. The alteration is associated with sealed microcracks in all rocks and planes of secondary fluid inclusions in quartz where it occurs, and was the result of a phase of fluid influx into these rocks. In hand specimen K-feldspar becomes progressively reddened with increasing alteration. Mineralogical alteration in the MGS and Caledonian granites took place at temperatures ∼275±15°C and in the MGS Pfluid is estimated to be ≤1.5 kbar during alteration. The °D values of alteration phases are:-18 to-29‰ (fluid inclusions),-47 to-61‰ (chlorites) and-11 to-31‰ (epidotes). Chlorite δ18O values are +0.2 to +4.3‰, while δ18O values for quartz-K-feldspar pairs show both positively sloped (MGS) and highly unusual negatively sloped (Caledonian granites) arrays, diverging from the normal magmatic field on a δ-δ plot. The stable isotope data show that the fluid that caused retrogression continued to be present in most rocks until temperatures fell to 200–140°C. The retrograde fluid had δD ∼-20 to-30‰ in all lithologies, but the fluid δ18O varied both spatially and temporally within the range-4 to +7‰. The fO2 of the fluid that deposited the epidotes in the MGS varied with its δ18O value, with the most 18O-depleted fluid being the most oxidizing. The δD values, together with low (<0‰) δ18O values for the retrograde fluid in some lithologies indicate that this fluid was of meteoric origin. This meteoric fluid was probably responsible for the alteration in all lithologies during a single phase of fluid infiltration. The variation in retrograde fluid δ18O values is attributed to the effects of variable oxygen isotope shifting of this meteoric fluid by fluid-rock interaction. Infiltration of meteoric fluid into this area was most likely accomplished by convection of pore fluids around the heat anomaly of the Galway granite soon after intrusion at ∼400 Ma. However convective circulation of meteoric water and mineralogical alteration could possible have occurred considerably later.

A SHRIMP ion microprobe study of inherited and magmatic zircons from four Scottish Caledonian granites

ABSTRACTUsing the ion microprobe SHRIMP we have analysed zircons from the Ben Vuirich, Glen Kyllachy, Inchbae and Vagastie Bridge granites from the Scottish Caledonides, in an attempt to resolve the ages of inherited zircons shown to be present in these granites by previous conventional multigrain analyses. Middle Proterozoic age components were found in inherited zircons from all four granites. Late Proterozoic (900–1,100 Ma) components have been identified in zircons from the Glen Kyllachy and Ben Vuirich granites in the Grampian Highlands. A Late Archaean age has only been detected in one zircon from the Glen Kyllachy granite. The distribution of inherited components in the granite zircon populations could reflect fundamental divisions in the age composition of granite source rocks; however, detailed assessment of this possibility must await further ion microprobe analyses on zircons from many more granites.SHRIMP isotopic and U, Th and Pb analyses were made on successive shells of zoned zircon surrounding inherited cores from the Glen Kyllachy granite to monitor chemical changes during magmatic zircon growth. Results show that zircon shells have characteristic but significantly different Th, U and Pb concentrations. Magmatic zircon from the Vagastie Bridge granite also forms as clearly defined oscillatory zoned shells around unzoned nuclei of inherited zircon. However, the distinction between magmatic and inherited zircon in zircons from the Inchbae granite is less clear. Zircons from the Ben Vuirich granite occur as euhedral, magmatic zircons, or as rounded, subhedral, inherited zircon grains. A SHRIMP age of 597 ± 11 (2σ) Ma for euhedral magmatic zircon from this granite is identical, within the uncertainty, to the conventional multigrain zircon age of 590 ± 2 (2σ) Ma reported by Rogers et al. (1989) and confirms the conclusions of those authors that sedimentation of the Dalradian sequence took place in the Precambrian.

Isotopic evidence for the extent of early Proterozoic basement in Scotland and northwest Ireland

AbstractTightly clustered Sm–Nd model ages, with an average of 1.96±0.02Ga, for the gneiss complex of Inishtrahull indicate coeval development with the earlyProterozoic gneiss terrane of Islay. The extent of this terrane, largely beneath the Dalradian Supergroup, is argued to be 100×600 km, from northeast Scotland to western Ireland. This is based on the distribution of dated basement in conjunction with Pb, Sr and Nd isotope systematics and inherited zircons in Caledonian granites of the region.

Significance of a late Caledonian igneous complex revealed by clasts in Lower Old Red Sandstone conglomerates, central Scotland

Boulder-bearing conglomerates from the Lower Old Red Sandstone (ORS) Crawton Group in east-central Scotland contain large granite clasts (0.4-1.0 m in diameter) which were derived from an area of the Midland Valley now concealed by younger rocks. These clasts provide new information concerning early Paleozoic magmatism along the margin of Laurentia. Rb/Sr mineral-whole-rock age dating for a series of calcalkaline tonalite, granodiorite, and granite boulders produces a cluster of late Wenlock-early Ludlow ages (ca. 420 Ma) which are interpreted as recording the original emplacement of hinterland plutons. The clast ages extend back to the late Ashgill (443 Ma), and the magmatism identified thus bridges a gap between an older Ordovician detrital record of coeval magmatism in the Midland Valley, and in situ ORS (Late Silurian/Early Devonian) volcanic rocks in this zone. Evidence from hornfels clasts and xenoliths within igneous boulders suggests that some of the granitoid intrusions were emplaced into an unseen, Lower Ordovician flysch sequence from which graywacke and limestone clasts were also derived. Textural and other evidence indicates that the source plutons rose to a high structural level in the crust. Both foliated and unfoliated granites have been distinguished, but these have no straight-forward relationship with Rb/Sr age. The foliated tonalite clasts are unlikely to have been derived from an autodeformed marginal facies, and the association of synchronous deformed and undeformed granitoids resembles the pattern of emplacement in areas undergoing transcurrent shear; this is consistent with evidence suggesting that juxtaposition of the northern Midland Valley and Grampian terranes was largely achieved during this interval. The cryptic igneous rocks share some features with in situ late Caledonian granites with which they overlap in age (for example, high Na, initial low 87 Sr/ 86 Sr), but differ in that tonalitic compositions and uniform positive ϵ Nd values were developed. The isotopic distinction between Silurian Midland Valley and Grampian Highlands magmas probably reflects the disparate lithospheric structure of the terranes now separated by the Highland Boundary fault and is a robust feature of subsequent magmatism, persisting for at least 70 m.y. Temporal changes in magmatism associated with the Midland Valley during the Ordovician to mid-Silurian may have been influenced by thinning of previously thickened arc crust.

Sandstone‐hosted thorium‐bitumen mineralization in the Northwest Irish Basin

ABSTRACTLow‐grade sandstone‐hosted thorium mineralization is recorded in the Carboniferous Northwest Irish Basin in the Republic of Ireland and Northern Ireland. The thorium is concentrated within bitumen nodules which are replacive within the sandstones. A source of thorium was available in a Caledonian granite in the basin watershed, and the bitumen was a product of hydrocarbons generated within the basin. The thorium occurs as thorite inclusions in the bitumen, and the development of the nodules was enhanced by the polymerization of fluid hydrocarbons by irradiation from the thorium. Thorium mobility may have been enhanced by the formation of organometallic complexes. Mineralization probably therefore occurred during hydrocarbon migration, dated as Late Carboniferous to Permian.

Granite magmas: their sources, initiation and consequences of emplacement

Geochemical and other evidence shows that granite magmas are generally derived from a mixture of melted crust and mantle material and the existence of a spectrum of types varying from largely mantle-derived to mainly crustal-derived is emphasized. Each pluton possesses a unique mix or range of mixtures which preserves an adumbrate history of the deeper levels of the crust and mantle at the particular location. Four illustrative granite-forming provinces are considered: (1) Archaean cratons with their voluminous tonalites, (2) magmatic arcs as exemplified by the western Americas, (3) the British Tertiary Province as an example of the results of extensional faulting and (4) the British and Irish Caledonide granites, the main phase (440–390 Ma) of which was produced during major Acadian strike-slip faulting. All these granites provide evidence of mixing of source materials. Geochemistry, especially of the Rare Earth Elements, U-Pb ages and isotopic studies of Sr, Nd, Pb, O, H and in some volcanic rocks Be, is beginning to enable quantification of the source components. The importance of major fracturing of the crust and mantle in providing magma triggers, magma focusses and magma consolidation sites is stressed; major batholiths probably occupy holes created by pulling apart the crust. Geophysical evidence does not suggest that granite plutons are distributed throughout the thickness of the crust, but rather that they are concentrated relatively near the surface. The extant elevation of the whole of the north British crust, its altitude over the last 400 Ma and even in places the present shape of the coastline, are significantly influenced by Caledonian granites, the tops of which are generally within about 3 km of the present landsurface. Thus relatively little erosion of most of these bodies has taken place and the dominant sources of post-Silurian clastic sediments in the area were stripped off volcanic cover rocks and recycled sediments and metasediments. By inference, other continental areas with numerous exposed granite pluton roofs had a similar history. The process of granite formation is an important means of density-stabilization of the crust with high-level emplacement of light sialic granite refined out of the mantle and lower, middle and even upper crust. The refractory mafic residues generally become denser and sink or stay down in the density-stratified crust but the division into residue and magma is not sharp with some granite magmas including significant quantites of restite.

A sulphur isotope study on selected Caledonian granites of Britain and Ireland

AbstractA sulphur isotope study was carried out to assess the value of such isotopic data in constraining the contributions of igneous and sedimentary protoliths for British and Irish Caledonian granites. Conventional separation techniques yielded sulphides from only 19 of the 50 selected granites, including both Newer and Older intrusions. These sulphides are dominated by pyrite, with lesser pyrrhotite, and rare chalcopyrite.Two groups emerge from consideration of δ34S in conjunction with δ18O, initial 87Sr/86Sr (ISr) and age; Group I have δ18O generally &lt; + 10·5‰, ISr in the range 0·703 to 0·708, and are younger than 435 Ma. δ34S of this group ranges from −4·5‰ to +4·4‰ x̄ = +0·7 ± 2·6‰ (n=40:1σ). Group II have δ18O generally &gt; + 10·5‰, are generally older, ISr between 0·710 and 0·7208, with δ34S in the range +6·2‰ to +16‰: x̄ = +9·5 ± 3·3% (n = 13:1σ). The source region for group II granites contained a significant sedimentary component.Since sulphides in Lower and Middle Dalradian metasediments are characterized by unusually high δ34S values, between +11‰ and +17‰. we suggest that group II granites contain a significant proportion of sulphur derived from these rocks.

Desilication of Caledonian granites in the Barnesmore complex, Co. Donegal: The origin and significance of metasomatic syenite bodies

AbstractThe ca. 400 Ma Caledonian Barnesmore complex, Donegal, includes a 1·5 km2 area in the Main Granite (G2) in which pristine biotite monzogranite has undergone in situ alteration to brick‐red, two feldspar, chloritic syenite which is virtually quartz‐free. The principal chemical changes involve major elements (Si, Al, Ca, Na, K) rather than trace elements. Stable isotope mineral data (O, H) show essentially magmatic values. It is proposed that a silica‐under‐saturated, volatile (halogen?) — and alkali (+Al)‐enriched, late‐stage, aqueous magmatic fluid was channelled into vertical conduits, dissolving quartz, precipitating feldspar(s) and disrupting the fabric of the host granite. The resulting syenitic bodies and vents exposed elsewhere in the complex are believed to represent different levels in such pipes. The mineralogical and chemical modification recorded here has important implications for the study of granitic rocks elsewhere in the world in that more subtle degrees of alteration may have escaped recognition and other equally drastic examples may have associated mineralization potential.

中国，福建省のジュラ・白亜紀花こう岩類について

1. On the basis of tectonic lines, geological features and crustal movements, Fujian Province is divided into the three geological districts : north-west uplift, south-west depression and east volcanic depression districts. There are 6 deep and large fault zones, four of which run north-east (Sinian direction) and two of which run north-west.2. Caledonian granites are mainly found in the north-west uplift district and Variscan-Indosinian granites in the south-west district, but Jurasso-Cretaceous (Yanshanian) granites distribute in all of the three districts. Thus, Jurrasso-Cretaceous granites are most prominent in Fujian Province throughout the whole of the geological age.3. It is remarkable that the Jurasso-Cretaceous granites are closely related to the four fault zones running north-east. The intrusive and volcanic rocks, derived from the same magma source, took place in the similar tectonic environment and formed polygenetic intrusions. The magmatism was most active in the late Jurassic period with four intrusions.4. Cretaceous granites, emplaced mainly in the east volcanic depression district, compose of many kind of rocks such as granite, granodiorite, quartz diorite, monzogranite and so on. The intrusion in the Cretaceous period took place four times with miarolite granite comming into being in the third intrusion, but their granites show the same absolute age of 100-80 Ma by radioactive isotopes.5. Miarolite granite runs north-east from Shantou in Guangdong Province through east Fujian Province to Zhoushan in east Zhejiang Provice, and then across the East China Sea to Masan in South Korea. This is one of the most remarkable features of the geological structure of East Asia.6. Details of the petrological characteristics of Fujian Province are described in the paper.

Caledonian and pre-Caledonian geology of the region between Grandjean Fjord and Bessel Fjord (75°–76°N), North-East Greenland

The area between Grandjean Fjord and Bessel Fjord was the focus in 1988 of regional geological investigations and 1:500000 mapping during the North-East Greenland project (Henriksen, 1989). The greater part of the area forms part of the East Greenland Caledonides and can be divided into three distinct rock groups: infracrustal gneisses and granites of possibie Archaean or early Proterozoic origin; a metasedimentary sequence which has probably suffered both mid-Proterozoic and Caledonian migmatisation and metamorphism; and the late Proterozoic Eleonore Bay Group, a thick sedimentary sequence which has undergone amphibolite facies Caledonian metamorphism in its lower parts and is intruded by Caledonian granites. Aspects of the stratigraphy and sedimentology of the Eleonore Bay Group are described by Sønderholm et al. (1989); only the structures affecting the sequence are described here.

The disequilibrium partial melting and assimilation of Caledonian granite by Tertiary basalt at Barnesmore, Co. Donegal

AbstractA regional Tertiary basaltic dyke swarm intensifies within a Caledonian granite at Barnesmore, Co. Donegal. Rapid heating along the contact of one (possible feeder) dyke resulted in disequilibrium partial melting of granite wall-rock and the generation of a range in melt composition by the in situ melting of feldspar. The compositional variability of the melt is preserved in a glass containing feldspar spherulites and other quench phases which suggest rapid cooling. During partial melting the trace elements, Rb, Sr, and Ba were mobile and have been concentrated in glassy melted granite close to the contact of one dyke. The textures, mineralogy and geochemistry of dolerite in two dykes indicate localized bulk contamination and mixing with melted granite. This had a particularly marked effect on the crystallization of pyroxene and resulted in a wide range in mineral composition reflecting the degree of contamination. The intensification of a regional dyke swarm in well-jointed granite might control the siting of some major intrusive centres. Granite melted and mixed with basaltic magma may contribute to the evolution of granites in such centres.

The crustal evolution of Central Scotland and the nature of the lower crust: Pb, Nd and Sr isotope evidence from Caledonian granites

The identification of the wide range of isotope characteristics and chemical heterogeneities within the sub-continental mantle has demanded a re-appraisal of the crustal evolution of many terrains. A recent publication has suggested that such heterogeneities may also exist beneath Scotland [1]. This, together with inadequate knowledge of the age and geochemical nature of the lower crust has fuelled the controversy of the relative involvement of mantle and crust in the formation of the Caledonian granites [2–8]. This paper reports 31 Pb isotope analyses, on feldspars from six granite complexes, and four new Nd and four new Sr whole-rock analyses. These data demonstrate that a major source of the granites is the lower crust which is characterised by relatively unradiogenic Sr, Pb and Nd. It is, by inference, old, depleted in U and Th, and has a low |Th/U ratio. Isotopic constraints suggest the sub-Grampian (Central Scottish) lower crust is dominated by Grenville (ca. 1200-1000 Ma) age rocks in addition to an older Scourian (ca. 2700 Ma) component. The major episodes of crustal growth in Central Scotland occurred during the Scourian and Grenville orogenies. The Caledonian orogeny produced only limited crustal addition.

Gold-Silver vein mineralization at Tyndrum, Scotland

Electrum, hessite, petzite and sylvanite have been recorded from veins at Tyndrum, Scotland. Electron probe micro-analyses have also revealed two un-named Ag-Te-S phases. Fluid inclusion studies suggest that the mineralising fluids responsible for the precious metal mineralization contained ∼ 7.0 mol % CO2 and 7 wt % NaCl. TH (temperature of homogenisation) determinations were in the range 295°C to 325°C and a depth of vein formation ∼ 4 km is indicated. Mineral precipitation was probably caused by cooling and adsorption of gold onto pyrite. Δ34S values of + 1.8%o for galena from the Au + Ag + Te veins suggest a different (possibly igneous) sulphur source to that producing the Pb +Zn vein mineralization in the Tyndrum area. Although an age of ∼ 380 Ma was obtained using K-feldspar in the veins the data are not conclusive. It is argued that the Au + Ag mineralization at Tyndrum is due to hydrothermal activity related to Cu +Mo mineralization associated with the Late Caledonian granites.

The age of the Oughterard Granite, Connemara, Ireland

AbstractDespite a wide latitude for interpretation of previous Rb–Sr isotopic data on the Oughterard Granite the age of this intrusion has been regarded as a critical time‐marker in resolving the Caledonian evolution of Connemara. New isotopic data suggest that the age of the intrusion be revised from c. 460 Ma to c. 400 Ma, thus making the Oughterard Granite one among the many Newer Caledonian Granites in Ireland. The preferred age is 407 ± 23 Ma, and the initial 87 Sr/86Sr ratio is 0·7076 ± 1. Heterogeneity within the granite is demonstrated, which explains the difficulty in obtaining reliable isotopic ages from this intrusion.

The ammonium content of Caledonian granites

The Caledonian granites of the British Isles have NH + 4 contents in the range of 0–167 parts per million. High contents (&gt;60 ppm) are confined to muscovite-rich granites, occurring principally in a restricted area, namely SE Ireland and the Isle of Man. Their magmas are inferred to have formed by the partial melting of a sedimentary protolith rich in organic matter. There is no apparent correlation between NH + 4 content and initial 87 Sr/ 86 Sr ratios.

The progressive illitization of interstratified illite-smectite from Carboniferous sediments of Northern England and its relationship to organic maturity indicators

AbstractInterstratified illite-smectites from Carboniferous sediments from the Alston and Askrigg blocks and the intervening Stainmore trough of the northern Pennines, UK, were examined by XRD. Both blocks are underlain by Caledonian granites. During late Carboniferous times sediments overlying the Alston block were intruded by the Whin Sill. The percentage smectite in illite-smectite (%S in I/S) varies from ∼35% to &lt;5% only homogeneous mudstones give consistent results. In the case of the Askrigg block and Stainmore trough, a good inverse correlation was found between %S in I/S and vitrinite reflectance. Both illitization of illite-smectite and vitrinite reflectance increase towards the centre of the block. This is thought to be related to high heat-flow centred about the granite basement. In the case of the Alston block, there is no direct relationship between clay and vitrinite data, vitrinite reflectance being controlled by the position and thickness of the Whin Sill. Except where close to the contact, the Whin Sill had no apparent effect on %S in I/S. As observed for the Askrigg block, %S in I/S is directly related to the position of the underlying granite. The progressive illitization of illite-smectites of low expandability is very slow when compared to vitrinite alteration in response to rapidly increasing temperature. Consequently, %S in I/S is a potential indicator of thermal maturation in situations where vitrinites, by virtue of their rapid response to increasing temperatures, fail to provide a regional view of heat-flow patterns.

The geochemistry, metasomatism and petrogenesis of the granites of the English Lake District

New geochemical data for the Carrock, Threlkeld, Ennerdale, Shap, Skiddaw and Eskdale granites of the Lake District are presented and discussed with particular reference to the metasomatism and petrogenesis of the intrusions. The Caledonian granites of the Lake District have more associated hydrothermal activity and mineralization than their equivalents north of the Iapetus suture in Scotland. Pervasive high-temperature metasomatism which affects the Shap, Skiddaw and Eskdale intrusions is accompanied by remobilization of the large ionic lithophile elements (K, Rb, Sr, U) and Li and B, although high field strength elements, including the rare earth elements, remain unaffected except near greisen and mineral veins. The Threlkeld intrusion appears to have suffered loss of a Ba and Sr during a low-temperature event. However, there is no consistent relationship between granite composition, hydrothermal activity and mineralization which could be used to support the granite cupola model for mineralization in the province. Rather, the episodic mineralization which affects the Lake District may be related more to the broad geothermal field consequent upon the emplacement of the deeper Lake District batholith, identified from geophysical data. Despite the variable metasomatic perturbations of their primary chemistry, three distinct groups of intrusions can be recognized on geochemical grounds. The Carrock granophyre is a product of tholeiitic fractionation and the Threlkeld and Ennerdale bodies are more typical calc-alkaline intrusions, whereas the Eskdale, Shap and Skiddaw plutons show a progressive evolution towards more complex geochemical patterns, suggesting decreasing hornblende but increasing plagioclase control of fractionating processes. The culmination of this trend may have been the emplacement of a large, high heat production granite beneath the Lake District at the end of the Caledonian orogeny. The suggestion made on geophysical grounds that the Eskdale intrusion is a cupola of the Lake District batholith cannot be simply reconciled with geochemical modelling. None of the Lake District granites has geochemical or isotopic characteristics which are convincingly S-type (i.e. formed by partial melting of a sedimentary protolith), and a model of subcrustal magmagenesis beneath an evolving arc or continental margin appears to be more appropriate.

Isotopic and chemical constraints on the building of the deep Scottish lithosphere

Synopsis The Scottish late Caledonian granites define a chemical province characterised by high Na, Ba and Sr abundances, particularly towards the north and west where they also have higher Zn, REEs and La/Y and lower Rb and Th. A comparison with data for inclusions found in younger volcanics and hypabyssal intrusions and thought to have been excavated from the mantle and lower crust indicates that the source of at least some of the chemical variation in the granitic magmas lies in the lithospheric mantle. The asthenosphere or postulated subducted slab material from the Iapetus ocean floor cannot have directly contributed significant amounts of these elements to most of the granitoids. Further, isotopic data clearly indicate that lower crust-derived materials are essential components of the more evolved granites, implying that considerable melting took place near the Moho. The age of the lower crust parallels the changes in chemistry in the lithospheric mantle which suggests that the Moho is not a major tectonic discontinuity. The Mid-Grampian line probably represents the rifted continental edge during Dalradian deposition. There is no isotopic evidence for primary crust of Grenville age under Scotland; rather the lower crust appears to be a complicated mixture including some components which are very young (probably Lower Palaeozoic) under the Midland Valley. The only location where clearly enriched mantle has been identified is under the Lewisian of the Outer Hebrides. The lower crust in this region is also Lewisian, apparently metasomatised. We tentatively suggest that the chemical enrichments and depletions in the lithosphere north of the Mid Grampian line are most simply explained by a volatile flushing mechanism.

Caledonian Magma Genesis and Crustal Recycling

The isotopic compositions of Sr, Nd, Pb and O together with abundance data for Rb, Sr, Sm, Nd, U and Pb are reported for samples from the component parts of the c. 400 Ma old Etive Complex, temporally and spatially related Lorne and Glencoe lavas, and the Dalradian country rocks into which the Complex has been emplaced. These and published data available for other Caledonian granites are used to evaluate the petrogenesis of the Etive Complex in particular, and the role of crustal recycling in the generation and evolution of the Caledonian granites in general. Nd-isotope compositions of Etive samples at 400 Ma εNd400 range from – 9.9 to – 4.7 compared with –8.4 εNd400 < – 3.2 for the associated volcanics investigated here, and an estimated value for depleted mantle 400 Ma ago at approximately ³ 7. Dalradian country rocks have – 23.4 εNd400 < – 7.5 and two partially digested metasedimentary xenoliths within the granite have εNd400 values of –9. 3 and -4.0. Initial 87Sr/ 86Sr ratios for the Etive Complex range from 0–7043 to 0–7079, whereas Dalradian metasediment in the immediate vicinity of the granite has an initial ratio of 0–726. Oxygen isotopes in the Complex have 7. 6 per mil <δ18O < 10.0 per mil, all in excess of typical values of mantle oxygen and reflect a crustal component. An upper limit of 25 per cent Dalradian assimilation is set by the Nd-Sr isotopic variations with the granites and xenoliths. The Etive complex parent magma prior to Dalradian xenolith assimilation is estimated to have εNd400 values between – 10 and – 5. In order to satisfy the Sr and Pb isotope composition, additional components from a deeper source within the lithosphere (lower crust or continental lithospheric mantle) with relatively unradiogenic Sr, Nd and Pb are required. The crustal residence ages of the Etive Complex average about 1.5 Ga, similar to those of many other late and post-tectonic Caledonian granites. The generation of the Etive Complex and Caledonian granites in general has been dominated by recycling of the continental lithosphere, rather than the addition of new material from asthenospheric sources.