Emeleus, C.H. & Gyopari, M.C. 1992. British Tertiary Volcanic Province, Geological Conservation Review Series No. 4. JNCC, Peterborough, ISBN 0 412 47980 X.
The original source material for these web pages has been made available by the JNCC under the Open Government Licence 3.0. Full details in the JNCC Open Data Policy
| Late dykes (dolerite, felsite and peridotite) |
| Eastern Red Hills Centre |
| Composite acid/basic sheets |
| Five granite intrusions |
| Kilchrist hybrids (possibly post-date some of the granites) |
| Broadford and Beinn nan Cro gabbros |
| Acid lavas, ignimbrites, tuffs and agglomerates of Kilchrist vent (may pre-date this Centre by a considerable amount) |
| Dykes (dolerite, pitchstone) |
| Western Red Hills Centre |
| Marsco and Meall Buidhe granites |
| Marscoite suite of hybrids, etc. |
| Nine granite and major felsite intrusions |
| Marsco Summit Gabbro |
| Belig vent |
| Dykes (dolerite) |
| Strath na Crèitheach Centre Three granite intrusions Loch na Crèitheach vent |
| Dykes (dolerite) |
| Cuillin Centre |
| Cone-sheets (dolerite) |
| Coire Uaigneich Granophyre (but see text) |
| Intrusive tholeiites |
| Druim na Ramh Eucrite |
| Explosive vents (of several ages) |
| Inner Layered Series: allivalite, eucrite, gabbro |
| Outer Layered Series: allivalite, eucrite, gabbro |
| Layered Peridotite Series |
| Border Group: gabbro, allivalite |
| Cone-sheets and dykes (overlap with many of the above) |
| Palaeocene lavas |
| Preshal More tholeiitic flows |
| Skye Main Lava Series (SMLS) flows (with sparse clastic |
| sedimentary horizons, and basal sediments and tuffs) |
| N.B. Additional details through text. |
| NORTHERN SKYE | WEST-CENTRAL SKYE | Based mainly on NORTHERN SKYE |
| (1) Anderson and Dunham (1966) | (2) Williamson (1979) | (3) Thompson et al. (1972) |
| 7. Talisker Group | Preshal Mhor tholeiitic basalts | |
| 5. Osdale Group | 6. Loch Dubh Group
5. Arnaval Group |
Skye Main Lava Series
Transitional and alkali-olivine basalts, hawaiites, mugearites, benmoreites and trachytes. More fractionated types are more common in the higher groups. |
| 4. Bracadale Group | 4. Tusdale Group | |
| 3. Beinn Totaig Group | 3. Cruachan Group* | |
| 2. Ramascaig Group | 2. Bualintur Group | |
| 1. Beinn Edra Group | 1. Meacnaish Group | |
| Individual groups are probably geographically restricted (see, for example Anderson and Dunham, 1966, figure 13)
* The thick fluviatile conglomerates of the Allt Geodh a' Ghamhna site are at the base of this group. |
||
| 14 | Thin, alkali olivine basalts with scoriaceous tops | 7 m |
| 13 | Massive basaltic lava with pillow structures towards the base | 5 m |
| 12 | Thin white ash | 0.03 m |
| 11 | Coal | 0.05 m |
| 10 | Sandstone with obscure plant remains occurring as diffuse carbonaceous streaks
and rootlets, possibly seat earth |
0.2 m |
| 9 | Coal | 0.01–0.05 m |
| 8 | Conglomerate with well-packed, rounded pebbles and cobbles of granophyre, quartzite, porphyritic rhyolite and red arkose. Clasts have a maximum diameter of 0.10–0.15 m, and are set in a pale sandy matrix | 3.2 m |
| 7 | Sandstone with micaceous partings | 0.2 m |
| 6 | Coal | 0.02 m |
| 5 | Sandstone with plant remains | 1.8 m |
| 4 | Conglomerate with a more sandy matrix than Bed 2, and a smaller proportion of acid igneous to arenaceous sediments than Bed 8. Rare pebbles of amygdaloidal and feldspar macroporphyritic basalt. Clast size <0.30 m, averaging 0.10–0.15 m. Thin lenses of white sandstone in lower horizons | 2.3 m |
| 3 | Fine-grained sandstone, laminated base | 1.1 m |
| 2 | Massive conglomerate with densely packed, crudely imbricated clasts of red arkose up to 0.30 m in diameter. Contains green siltstones with a sandstone wedge thickening to the north | 2.75 m |
| 1 | Highly amygdaloidal basaltic lavas forming the top of the cliff at about 125 m elevation 10 m |
| Aureole beyond the skarn zones | Skarn zones Group 1 Primary skarns | Skarn zones Group 2
Boron-fluorine ore skarns |
|
| Talc | Grossular-andradite* | Magnetite* | Grossular-andradite |
| Tremolite | Wollastonite solid solutions* | Tremolite | Hydro grossular |
| Forsterite | Diopside-hedenbergite | Forsterite* | Idocrase |
| Diopside | Spinel | Diopside* | Bornite |
| Periclase | Plagioclase | Monticellite* | Chalcosite |
| Wollastonite | Idocrase | Cuspidine* | Covellite |
| Spinel | Xanthophyllite | Fluorite | Chalcopyrite |
| Idocrase | Phlogopite | Chondrodite* | Pyrite |
| Grossular | Orthite | Humite | Blende |
| Phlogopite | Clinozoisite-epidote | Clinohumite | Galena |
| Brucite | Prehnite | Ludwigite | Chessylite |
| Serpentine | Apophyllite | Fluoborite | Malachite |
| Chlorite | Pectolite | Szailbelyite | |
| Hydromagnesite | Xonotlite | Datolite | |
| Harkerite | |||
| * most abundant minerals |
| Granites of the Strath na Crèitheach Centre |
| Volcaniclastic deposits of Strath na Crèitheach dolerite cone-sheets |
| Coire Uaigneich Granite |
| Intrusive tholeiites of the Outer and Main Ridge Complexes |
| Inner Layered Series |
| Inner Layered Gabbros |
| (?vent agglomerates in Harta Corrie) |
| Inner Layered Eucrites |
| Inner Layered Allivalites |
| Druim nan Ramh Eucrite |
| Agglomerates and explosion breccias of diatremes |
| Dykes |
| (Gars Bheinn ultrabasic sill?) |
| Outer Layered Series |
| Outer Layered Gabbros |
| Outer Layered Eucrites |
| Outer Layered Allivalites |
| Layered Peridotites |
| Border Group (including White Allivalite) |
| Cone-sheets |
| Dykes |
| Outer Marginal Gabbros and Eucrites |
| ?Early Granites (may pre-date Palaeocene basalts of south-west Skye) |
| Basalt lavas |
| Torridonian sediments |
| Valley-filling pitchstone of the Sgurr of Eigg, and associated conglomerates Dolerite dykes |
| Lavas and fluviatile sediments of north-west Rum and Canna-Sanday, olivine basalts, hawaiites, mugearite (on Canna), including also tholeiitic basaltic andesite, icelandite (on Rum) |
| —Period of profound erosion during which the Rum central igneous complex was unroofed and eroded— |
| The Rum Layered Igneous Complex: |
| Central Series: feldspathic peridotites, including breccias and some layered allivalites and peridotites |
| Western Layered Series (WLS): feldspathic peridotites and gabbroic rocks at Harris |
| Eastern Layered Series (ELS): layered feldspathic peridotite and allivalite, also gabbroic |
| and ultrabasic intrusive bodies |
| (The WLS and ELS above may be coeval) |
| Dolerite and basalt dykes (some also post-date the Layered Igneous Complex) |
| Dolerite and basalt cone-sheets on Rum |
| Early phase of acid igneous activity: |
| Western Granite, also granite at Papadil and Long Loch |
| Porphyritic felsite (ignimbrites, in caldera, and intrusions) |
| Tuffisites (some may post-date porphyritic felsite) |
| Volcaniclastic breccias - probably a mixture of explosion breccias and breccias formed by caldera wall collapse |
| Dolerite and basalt dykes (some intruded after breccias and prior to felsites) |
| Initiation of the Main Ring Fault System: movement on this system of arcuate faults probably continued at least until emplacement of the ELS/WIS and was a major tectonic feature during the early acid phase of igneous activity. |
| Lavas of Eigg and Muck, and those involved in the Main Ring Fault on Rum. Principally olivine basalts, feldspar-phyric olivine basalts and mugearites on Eigg. The dykes cutting these lavas belong to the main post-felsite and granite phase of dyke intrusion on Rum. Thin sedimentary layers occur in the Eigg and Muck successions. |
| Thickness | Distinctive features | |
| Upper Ruinsival Series | ~ 330 m | Both Ruinsival series show an upwards gradation from olivine cumulates often with feldspar to feldspar-olivine cumulates often with pyroxene. |
| Lower Ruinsival Series* | ~ 500 m | Exposure is generally poor and the sequence is complicated by transgressive later intrusions, zones of igneous breccia and structural disturbances. In places, gravity stratification, rhythmic layering and slump structures occur. |
| Transition Layer | ~ 0.5 m | Olivine-feldspar cumulate. Variable dips (5°-50°) in all directions but predominantly in general easterly direction. |
| Dornabac Series | ~ 130 m | Olivine-feldspar and feldspar olivine cumulates often with streaky or rhythmic layering and frequently with slump structures and evidence of gravity stratification. Layering dips at 35° to 40° to the east and southeast. The rocks show similarities to the allivalites of the Hallival–Askival area. Feldspathic peridotite breccia at the base of the Central Series cuts transgressively across all Western Layered Series units. |
| Ard Mheall Series | ~ 400 m | Olivine and olivine-feldspar cumulates with rhythmic layering throughout. Harrisitic cumulates are intimately associated with normal cumulates and are very prominent within the lower half to two-thirds of the sequence and they are also locally important higher in the series. The layering has a general dip of 5° to 10° (exceptionally 15°) to the south-east or east. |
| Transition Series | ~ 50–60 m | Olivine-feldspar cumulates, often with pyroxene, of both harrisitic and normal types. Olivine is more abundant than in the Harris Bay Series, while the content of feldspar is higher than in the Ard Mheall Series. |
| Harris Bay Series | ~130–140 m | Essentially eucritic mesocumulates in texture with olivine, feldspar and ubiquitous pyroxene as cumulus phases. Olivine is the most abundant phase and forms distinctive tabular crystals exhibiting igneous lamination in the normal cumulates. Intercalations of generally thin harrisitic cumulates (crescumulates) richer in feldspar and pyroxene than those of the Ard Mheall Series occur. Layering dips at low angles (5–10°) to the north-east. |
| * Now termed the Long Loch Group (of Volker and Upton, 1990). | ||
| Part of Central Series: Upper Ruinsval Series to Ard Mheall Series
Amended (1982) Western Layered Series: Ard Mheall Series to Transition Series |
| (youngest) |
| Late NNW-trending dolerite dykes |
| Centre 3 |
| Quartz monzonite |
| Tonalite |
| Fluxion biotite gabbro of Glendrain |
| Fluxion biotite gabbro of Sithean Mòr |
| Quartz-biotite gabbro |
| Quartz dolerite, granophyre-veined |
| Inner Eucrite |
| Biotite eucrite |
| Quartz gabbro, southern side of Meall an Tarmachain |
| Quartz gabbro of Meall an Tarmachain summit |
| Outer Eucrite |
| Great Eucrite |
| Cone-sheets of Centre 3 (sparse) |
| Porphyritic gabbro of Meall nan Con screen |
| Gabbro, south-east of Rudha Groulin |
| Gabbro of Plochaig |
| Fluxion gabbro of Faskadale |
| Quartz gabbro of Faskadale |
| (Migration of focus of activity to Achnaha area) |
| Centre 2 |
| Felsite, south of Aodann |
| Fluxion gabbro of Portuairk |
| Younger quartz gabbro of Beinn Bhuidhe |
| Quartz gabbro of Beinn na Seilg |
| Quartz gabbro of Loch Caorach |
| Eucrite of Beinn nan Ord |
| Inner cone-sheets of Centre 2 |
| Quartz dolerite of Sgurr nam Meann |
| Quartz gabbro of Aodann |
| Older quartz gabbro of Beinn Bhuidhe |
| Granophyre of Grigadale |
| Quartz gabbro of Garbh-dhail |
| Old Gabbro of Lochan an Aodainn |
| Hypersthene gabbro of Ardnamurchan Point |
| Glas Eilean vent |
| Outer cone-sheets of Centre 2 |
| (Migration of focus of activity to Aodann area |
| Centre 1 and the Ben Hiant vent* |
| Cone-sheets of Centre 1 (penecontemporaneous with the quartz dolerite intrusion of Ben Hiant) |
| Ben Hiant quartz dolerite |
| Composite intrusion of Beinn an Leathaid |
| Augite diorite of Camphouse |
| Quartz dolerite of Camphouse |
| Porphyritic dolerite of Ben Hiant |
| Granophyre west of Faskadale |
| Quartz gabbro west of Faskadale |
| Old Gabbro of Meall nan Con |
| Porphyritic dolerite of Glas Bheinn |
| Agglomerates of Northern Vents |
| Tuffs, agglomerates and lavas of Ben Hiant vents |
| Trachyte plug |
| (Igneous activity localized at Ben Hiant and also centred on a focus c. 1.3 km west of Meall nan Con) |
| Palaeocene basalt lavas and thin sediments |
| Jurassic and Triassic sandstones, shales, limestones, conglomerates |
| Moine metasediments |
| (oldest) |
| *The relative ages of many of the units assigned to Centre 1 and Ben Hiant are uncertain. (From Emeleus, in Sutherland, 1982, table 29.5). |
| (youngest) |
| Dykes were intruded throughout the sequence (Loch Bà-Ben More) |
| Loch Bà Centre (Centre 3; North-West or Late Caldera) |
| Loch Bà felsite ring-dyke (Allt Molach-Beinn Chaisgidle, Loch Bà–Ben More) |
| Hybrid masses of Sron nam Boc and Coille na Sroine (Loch Bà–Ben More) |
| Beinn a' Ghraig Granophyre (Loch Bà–Ben More) |
| Knock Granophyre (Loch Bà–Ben More) |
| Late basic cone-sheets (Loch Bà–Ben More) |
| Early Beinn a' Ghraig Granophyre and felsite (Loch Bà–Ben More) |
| Glen Cannel complex and some late basic cone-sheets |
| (Allt Molach-Beinn Chaisgidle, Loch Bà–Ben More) |
| Beinn Chaisgidle Centre (Centre 2) |
| Glen More ring-dyke (Loch Sguabain, Cruach Choireadail) |
| Late basic cone-sheets (Allt Molach–Beinn Chaisgidle), Loch Scridain sheets (intruded towards middle and end of Centre 2 and start of Centre 3) |
| Ring-dyke intrusions around Beinn Chaisgidle |
| ?Augite diorite masses of An Cruachan and Gaodhail (Loch Bà–Ben More) |
| Corra-bheinn layered gabbro (Loch Bà–Ben More) |
| Second suite of early basic cone-sheets |
| Second suite of early acid cone-sheets |
| Explosion vents (numerous at margin of the South-East Caldera) (Loch Bà–Ben More) |
| Glen More Centre (Centre 1; including the Early or South-East Caldera) |
| Ben Buie layered gabbro |
| Loch Uisg granophyre-gabbro |
| First suite of early basic cone-sheets (Loch Bà–Ben More) |
| Early acid and intermediate cone-sheets (Loch Bà–Ben More) |
| Acid explosion vents containing porphyritic rhyolite material (Loch Bà–Ben More) |
| Glas Bheinn and Derrynaculen granophyres (Loch Spelve–Auchnacraig) |
| Updoming and folding in south-east Mull as a result of rising diapir (Loch Spelve–Auchnacraig). |
| Lava eruption on to eroded surface of Mesozoic and older rocks. Latest flows overlap in time with formation of the South-East Caldera where pillow lavas are found. (Lavas: Bearraich, Ardtun, Carsaig Bay, Loch Bà–Ben More. Pillow lavas: Loch Sguabain, Cruach Choireadail) |
| (oldest) |
| Mull Memoir (Bailey et al., 1924) | Beckinsale et al. (1978) | Morrison (1978) Thompson et al. (1982) Morrison et al. (1985) Thompson et al. (1986) |
| Central Group (= NPCMT) (Includes pillow lavas in central complex) | Not dealt with in detail | Some samples analysed, all zeolitized or hydrothermally altered. |
| Plateau Group (majority = PMT)
Pale Group of Ben More (= PMT) (with interlayered mugearite and Big-Feldspar Basalt) |
Group 1 olivine basalts (mainly sampled in north-west Mull) and Group 3 olivine basalts (mainly sampled around Lochaline, Morven) | Mull Plateau Group (MPG)
Note that many are transitional between alkali basalt and tholeiite, and compare closely with Skye Main Lava Series. Some lower crust contamination. |
| (Staffa Type at base = NPCMT) | Group 2 of south-west Mull | Staffa Magma Type (SMT) Variably enriched in lower and upper crustal contaminants. |
| (NPCMT = Non-Porphyritic Central Magma Type) later = tholeiitic basalt
(PMT = Plateau Magma Type) later = alkali olivine basalt but many flows are in fact transitional between alkali basalt and tholeiite Total thickness of Mull lavas estimated about 2000 m (Bailey et al., 1924) |
||
| Rock type | Position within sill | Petrological features |
| (a) Crinanite | Central = forms the bulk of the intrusion | Plagioclase, analcite, olivine, ophitic Al-, Ti-rich augite. Zeolites. Analcite, secondary after nepheline and of hydrothermal origin. Olivine up to 12 vol.% about 10–15 m above base. |
| (b) Teschenite | Marginal facies = fine-grained margins showing quench textures | Lacks fresh olivine, substantial amounts of analcite, zeolites and calcite. Margins have skeletal Ti-augites. |
| (c) Augite teschenite | Patches within crinanites, especially towards base. | Augite, plagioclase, analcite. Alignment of augite suggests cumulate texture. Fe-Ti oxides more abundant than in crinanite. |
| (d) Pegmatite(i) | At several horizons throughout sill, centimetres to metres in thickness | Brown augite with emerald-green rims (Na-rich), plagioclase, analcite, Fe-oxides, apatite, rare blue riebeckitic amphibole and rare olivine pseudomorphs. Variant of augite teschenite. |
| (e)Pegmatite (ii) | As pegmatite (i) | Mineralogically as (i) but has less pyroxene and is much coarser grained. Skeletal magnetite and ophitic augite, rather than euhedral as in (i). |
| Pleistocene glaciation |
| Palaeocene igneous activity |
| Basaltic and composite (acid and basic) inclined sheets and dykes |
| Conachair Granite |
| Mullach Sgar Complex (mixed magma (basic-acid) intrusions) |
| Glen Bay Granite |
| Glen Bay Gabbro |
| Breccias of gabbro and dolerite |
| Western Gabbro (layered in places) |
| No pre-Palaeocene rocks are exposed, but the complex is thought to be intruded into Lewisian gneisses. |