Empleo directo

The field relationships of the Ardara appinite suite require a knowledge of the lithologies into which they were emplaced. The succession consists of Dalradian metasediments comprising quartzites, limestones, semi-pelites andpelites. The stratigraphy used is that defined by Iyengar et. al. (1954), see Fig 3.3. Pitcher and Shackleton (1966) correlated the succession with that of the Creeslough succession of NW Donegal and with

Fig 3.2 (a) General map of the Ardara area showing the main villages and loughs referred

the Ballachulish succession (Appin group) in Argyllshire on the basis of similarities of

facies and lateral stratigraphic continuity.

1500m 1000m 500m 0m CLEENGORT PELITES

Massive dark grey pelite with rare calcareous horizons

PORTNOO LST Massive marble, often schistose MAAS

SEMIPELITE

Grey pelitic schists with semipelitic and quartzitic intercalations

MULNAMIN CALC SILICATE FLAGS

Calc-silicate flags, quartzose in places.

MULNAMIN FLAGS Siliceous flags, muddy bands COR QUARTZITE Massive quartzite

Fig 3.3. Stratigraphic column of the metasediments present in the study area (after Iyengar et al. 1954), with thicknesses as seen in the type area of Maas shown in metres.

3.3.1 The Cor Quartzite

This is the lowermost member of the succession and outcrops in the east of the

area, with a maximum thickness of 70m. The best outcrops are seen in two places:

a) Crockard Hill (G7920 9720)

Here the quartzite is relatively undeformed, it dips steeply to the north and is white to dull grey in colour with pink feldspar grains within a highly siliceous matrix which often weather out to give a pock-marked appearance. No muddy bands are found. Bedding ranges from 1cm-lm, with occasional fine laminae of muscovite mica.

b) South Meenalargan Hill (G8087 9690)

Although this is a mega-enclave caught up in the Meenalargan complex diorites it has similar textures to the type area of Crockard Hill stretching from (G8200 9775 to G8000 9650), a distance of >800m. It is creamy white but it has more micaceous bands as well as cross bedding in the larger beds, indicating that it is the correct way up. Deformation associated with the emplacement of the Ardara pluton and MDG takes the form of intense stretching, with formation of rod-like mullions parallel to the extension direction. A pervasive stretching lineation is developed along 060°, plunging 20° south­

west. The two outcrops seem to be linked structurally to a faulted anticline and although their stratigraphic relations are unclear as the outcrop on Meenalargan Hill is a large roof enclave, both quartzites have very similar mineralogical characteristics.

3.3.2 Mulnamin Siliceous Flags

Immediately overlying the Cor quartzite to the north of Crockard hill are the horizons of the Mulnamin siliceous flags. They form boggy ground around L. Nagamaman (G7930 9770), striking west towards the Maas river (7740 9790) and east to L. Nacroaghy (G8258 9840). Outcrops of the flags are poor but where visible they comprise thinly bedded muddy quartzite, yellowy brown in colour up to 83m in thickness. No cross bedding was seen. Around L. Nagarnaman the flags form a broad anticlinal structure disrupted by a late dextral wrench fault.

3.3.3 Mulnamin Calc Silicate Flags

This group is probably best seen along part of the southern margin of the Mulnamin intrusion, (G7890 9885) where it reaches up to 250m in thickness. It is also an important horizon found at the western end of the Meenalargan intrusion (G7880 9690), especially around Lough Laragh. In this area it forms thinly bedded brown pelitic horizons with abundant patches of pale green actinolitic and epidote rich bands in siliceous and calc siliceous bands, possibly caused by a metasomatic reaction with the appinitic magma. Iyengar et al. (1954) noted several distinct tracer horizons of pure limestone and quartzite around Ranny Point (G9720 9930). Most notable of these is a basal creamy yellow, blocky calcite limestone up to 10m thick. This was not seen in the Meenalargan area, the succession being disclosed by the pelitic and calc silicate nature of the majority if the succession.

3.3.4 Maas Semi-Pelite

This rather homogeneous group is only found close to the Ardara pluton, near Maas, where it forms grey semi-pelitic, finely laminated beds. It also outcrops along the northern margin of the Mulnamin intrusion and isolated on Carrickfad (B7250 0050) and Inishkeel Island (B7050 0030). In total it forms over 300m of exposed semi-pelite.

3.3.5 Portnoo Limestone

This group is thought to be transitional from the underlying Maas semi-pelite, *as a thin limestone band is found at the top of the semi-pelite. No contact is seen in the Maas area due to a dislocation (Iyengar et al. 1954). As the name suggests the Portnoo Limestone is best seen around the type area of Portnoo. Here it takes the form of a variable muddy limestone up to 160m thick. It varies in colour from pale cream to yellow and grey. It may show a high mica content, giving it a schistose appearance e.g. east of Dunmore Hill

(G6910 0005). Local development of garnet along the Narin-Portnoo foreshore is due to the thermal effects of the Ardara granite. The limestone forms a hilly swathe of grassy ground striking east from the coast west of Dunmore (6900 9991) to the low grassy hills of Drumshantony and the saltmarsh at Clashagh (G7620 9870).

3.3.6 Cleengort Pelites

The passage from the underlying Portnoo Limestone appears relatively rapid with no obvious transition. The majority of the pelite is a dark grey to brown micaceous pelite often hornfelsed with occasional semi-pelite and calcareous bands within it. This group is found mainly in the west of the area and is thought to form up to 260m of metasediment (Iyengar et al 1954). It also forms the hills immediately north of the Ardara pluton, and is in contact with the granite where it records the thermal metamorphism of the intrusion. The mineralogy of the pelite shows increasing grade from chlorite-biotite- andalusite-sillimanite-cordierite as the contact is approached.