Butterlope Glen
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Geology & landscape
Geological Feature: Rock Outcrop · Mining / Industrial: Quarry · Geological Period: Precambrian · Rock Type: Chert, Limestone, Quartzite, Schist
Landscape processes: Glacial, Volcanic / Igneous
Description
Butterlope Glen Dalradian, Structural The area is of special scientific interest because of its' important geology. The site is important for understanding Dalradian stratigraphy, a geological rock series, both within Ireland and between Ireland and Scotland. The east side of the Glen exposes a section through representative lithologies of the Dungiven Formation and the lowest levels of the Dart Formation. The rocks are Precambrian in age forming part of the Argyll Tayvallich Subgroup and Southern Highland Groups from the upper Dalradian. Structural evidence indicates the sequence is part of the Sperrln fold, related to rocks in Donegal, north east Antrim and the southwest Highlands of Scotland. Butterlope Glen itself is a glacial meltwater channel that formed toward the end of the last Ice Age, around 13,000 years ago. At this time, meltwater had accumulated to the south, in Glenelly Valley. When the water eventually found a route to the north, it scoured Butterlope Glen into the country rock as it drained. The Glen cuts across the Sperrin Mountains and rock is exposed over approximately 800m, mainly along the eastern side of the valley. The succession dips toward the north and is structurally inverted such that the youngest rocks outcrop at the south end of the site with progressively older strata occurring down dip towards the north of the Glen. The youngest rocks are from the Dart Formation and are silver-grey to green amphibolite schists of the Glenga Amphibolite Member, which is particularly well exposed in the south west section of the site. Moving north, the Dart Formation continues with interbedded psammites and semipelites, amphibolite schist with chert, stratified tuffs and locally graded hyaloclastite. The rocks are deformed as is shown by thick units of pink-buff coloured quartzite with graded bedding and micaceous psammite which form the hinge of a large flat-lying, downwards facing fold. The Dart Formation is succeeded by the Dungiven Formation with typical limestones exposed in a disused quarry. The limestone, somewhat altered by heat and pressure, is interbedded with thin units ofdark grey schist and black graphitic pelite. At the north end of the site, natural outcrop exposes highly deformed volcanogenic rocks. These include stretched pillow lavas interbedded with tuffaceous amphibolitic schist with selvages of black chert and hyaloclastic shards. The rocks were originally deposited in a submarine, unstable rift setting at the margin of the ancient continent Laurentia. Evidence of crustal thinning is found in the basic volcanic rocks found in the upper part of the Argyll Dart Formation and lower part of the Southern Highland Group Dungiven Formation. The rocks were subsequently deformed during the Caledonian Orogeny, a mountain building event of which the Sperrins are a remnant part. https://www.daera-ni.gov.uk/publications/butterlope-glen-assi