A B C D E F G H I 500 1000 HEIGHT (M) HORIZONTAL DISTANCE (M) A B C NM3590 9752 CROSS SECTION 'ABC' OF THE CENTRAL AND WESTERN SUITE OF THE ISLE OF RUM NM3500 9843 LONG LOCH FAULT NM3650 9744 1:10000 NW SE ESE 500 500 400 300 200 100 0 -100 -200 -300 400 300 200 100 0 -100 -200 -300 500 400 300 200 100 0 -100 -200 -300 500 400 300 200 100 0 -100 -200 -300 500 HEIGHT (M) HORIZONTAL DISTANCE (M) 1:10000 LONG LOCH FAULT CROSS SECTION 'CDE' OF THE CENTRAL SUITE OF THE ISLE OF RUM D C E SW NE/NW SE NM3500 9843 NM3662 9754 NM3684 9733 DONE BY: ANDREW MOYLE 51228528 47 46 49 40 48 54 50 28 42 36 30 40 42 48 48 38 24 18 18 20 22 24 52 40 58 38 56 33 31 40 42 38 44 40 48 22 18 48 12 12 22 11 18 18 30 19 40 38 30 34 25 28 40 30 36 30 28 49 48 37 24 28 16 42 20 26 18 28 24 38 44 28 44 44 48 62 22 34 20 24 24 18 24 52 62 74 70 72 54 28 31 35 36 37 35 36 37 01 00 99 98 97 01 00 99 98 97 LOCATION TOPOGRAPHY GEOLOGICAL ZONES OF RUM SOLID GEOLOGY OF THE WESTERN AND CENTRAL IGNEOUS SUITE OF ISLE OF RUM , INNER HEBRIDES, SCOTLAND STEREONET SHOWING DISTRIBUTION OF POLES TO FRACTURE PLANES ALONG THE N-S LONG LOCH FAULT [NM36372 00209] TO [NM36189 96940] STEREONET SHOWING THE 3 MOST COMMON FRACTURE PLANES ALONG THE N-S LONG LOCH FAULT [NM36372 00209] TO [NM36189 96940]. N N n=382 n=382 1 2 3 1- Most common fracture plane 3- least common fracture plane R P R' Fig 1.) Reidel Model for strike-slip faults (Fossen 2010) The 3 major fracture planes show a very similar pattern to the Reidel Model of a Dextal Strike Slip Fault. In the Reidel Model (fig 1.), the first sets of fractures to form in an overall strike-slip zone are shear fractures. One set, known as Reidel shear fractures or R-fractures, make a low angle with the overall shear zone and show the same sense of slip. P-Shear Fractures (P) usually develops after the establishment of R-fractures, and development is probably related to temporal variations in the local stress field along the shear zone as offset accumulates. A third set of shear fractures (anitithetic fractures) make a high angle to the zone. These are called R’-shear fractures, and are generally less well developed than R-fractures. (Fossen 2010) ϕ ϕ = angle of internal friction HORIZONTAL DISTANCE (M) 1:10000 CROSS SECTION 'FG' OF THE CENTRAL AND WESTERN SUITE OF THE ISLE OF RUM NW SE F G NM35000 98599 NM35480 96920 HEIGHT (M) 500 400 300 200 100 0 -100 -200 -300 500 400 300 200 100 0 -100 -200 -300 1000 500 1500 NG35000 99920 NG36380 99920 strike-slip fault HEIGHT (M) 500 400 300 200 100 0 -100 -200 -300 500 400 300 200 100 0 -100 -200 -300 500 1000 CROSS SECTION 'H-I' OF THE CENTRAL AND WESTERN SUITE OF THE ISLE OF RUM HORIZONTAL DISTANCE (M) 1:10000 H I W E KEY LITHOLOGIES Basic Dyke (Basalt/Dolerite) Basic Plug (Dolerite) Olivine Gabbro Ultrabasic Plug (Peridotite(P) and Feldspathic Peridotite (FP)) Rock Y (Troctolite) Ultramaifc Breccia (Feldspathic Peridotite and Troctolite Breccia in Feldspathic Peridotite Matrix) Feldspathic Peridotite Intrusive Grandodiorite-Ash Microgranite Intrusive Breccia (Red Sandstone and Felsic Breccia in Ash Matrix) Red Sandstone Gneiss 50 70 19 A Long Loch Fault reactivates as dextral strike-slip fault, further displacing sandstone, microgranite, the ring fault and the layered igneous suite. Minor faults along the Long Loch Fault form Unconformity Gneiss: gneissic banding is disguished by light bands (quartz and plagioclase rich, lacking hornblende) and dark bands (quartz and plagioclase rich, hornblende rich). Structures observed in the gneissic banding include folding,stretching, brittle fracturing, normal and reverse faults, minigrabens, an echleon structures. These structure are possibly formed dring the uplift of the gneiss Red Sandstone member is composed of <60% Quartz, <30% K-feldspar, <10% Micas. Crystalline around the aurioles of doleritic plugs, indicating contact metamorphism. Grain description vary from: very fine to medium grain size, low to high sphericity, well to very well sorted, sub rounded to rounded grain shape, and well to very well sorted, but all have a general texture of being very gritty. Ocassional detrital quartz and k-feldspar can be seen, with size up to 2cm and 4cm in length respectively. Sedimentary structures such as grading, wavy and planar lamination, and occasion soft sediment deformation can be observed. The grain desciption along with structures could indicate a large fluvial environment. A microgranite intrusion occured. This felsic intrusion has a very glassy appearance and is observed in the central intrusion and west of the Western mafic intrusion boundary. Emplacement of ring fault due to microgranite uplifting sandstone, and then caldera collapse. Intrusive Breccia in an ash matrix. Formed as a result of caldera collapse. Breccia is made up of microgranite, gneiss, and sandstone. Breccias have a melted appearance and are angular in shape. Long Loch Fault - N-S Dextral strike-slip fault commences with intial displacement of microgranite, sandstone and main ring fault. Feldspathic peridotie enters the collapsed caldera through the Long Long Loch Fault. The mineral composition is <60% Olivine, <30% Pyroxene and <5-10% Plagioclase Feldspar. Generally equigranular with medium to coarse size minerals. Harrisite texture observed, indicating floor of basement. Harrisite crystals are arranged crudely to chaotic, inequigranular and medium to coarse crystal size (up to 10cm in length, 1cm thick). Mineral compositon of Harrisites are <60% pyroxene, <30% olivine and <5-10% Plagioclase Feldspar . Granodiorite- Ash intrusion occurs as a result of melting of the chamber walls composed of microgranite by feldspathic peridotite. The matrix has a chalky/glassy texture, white/grey in colour, and very dense. Mineralogy of the matrix: <30% Plagioclase, <20% K-Feldspar, <30% Quartz, <10% Hornblende, <2% Biotite Long Loch Fault movement pauses, formation submagmatic central graben. Ultramafic brecciation occurs. Breccia contained within a medium grained feldspathic peridotite matrix. Breccia is composed of feldspathic peridotite and troctolite. Length of breccia ranges from 0.5cm to 100cm, with an average length of 5cm. Smaller clasts are generally rounded, with larger clasts being angular. Rock Y (troctolite) forms as successive layers with feldspathic peridotite. Mineralogy: <60% plagioclase, <20-30% olivine, <2-10% Pyroxene. Crystal grains are equigranular and medium to coarse in size. Large olive clusters appear on some troctolite layers. Structures observed have the appearance of flow structure observed in sedimentary rocks, including wavy structures, deformed layering, grading, interlayering, flame structures, slumping and soft sediment deformation. Plugs of peridotite. Mineralogy: <80% olivine, <10% plagioclase feldpsar. The mineral grains are equigranular and medium sized. Wavy flow structures observed as well a vein of chromite. Basalt/Dolerite Dykes and Plugs intrude. Mineralogy: <60%: plagioclase, <30% pyroxene, <10% Olivibne. Minerals in dykes are equigranular and medium sized and have a glassy texture. (basalts darker than dolerite). Dolerite plugs are inequigranular with medium sized mineral grains with phenocrysts of plagioclase feldspar. GENERALISED VERTICAL SECTION OF THE WESTERN AND CENTRAL IGNEOUS SUITE OF THE ISLE OF RUM TERTIARY (PALAEOCENE) PRE-CAMBRIAN ARCHAEAN FP FP P Olivine gabbro observed as plugs and sheets. Mineralogy: <60% plagioclase, <30% pyroxene, <5-20% olivine. The mineral grains are equigranular where medium sized observed in plugs, and coarse to very coarse observed in sheets. Flow structures observed in sheets including éye structures´and grading. Plugs show no flow structures. Olivine clusters observed in plugs.