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Loughermore MountainLondonderry
Disused quarry, west of Loughermore Forest, Co. Londonderry.
Summary Full report
Site Type: Quarry (disused)
Site Status: PASSI
District:
Grid Reference: C606151
Rocks
Rock Age: Precambrian (Dalradian)
Rock Name: Claudy Formation, Southern Highlands Group
Rock Type: Greywacke, Metagreywacke, Psammite
Interest
Other interest: No data, No Data

Summary of site:

This small quarry on Loughermore Mountain contains typical rocks of the ancient Dalradian Claudy Formation.

The Dalradian rocks were formed around 600 million years ago near the South Pole on a vast supercontinent. The Dalradian has two major divisions, the Argyll Group, topped by the Southern Highland Group. The lowest of the three formations in the Southern Highland Group is the Claudy Formation, typified by medium to coarse quartz and feldspar-rich metamorphosed sands and gravels with well rounded grains. The quartz gives a blue tinge to the rock which is distinctive. There is also a hint of graded bedding (beds of mixed grain size in which the larger grains settled first, the finest last) which could indicate whether the rocks are the right way up or overturned but structures superimposed during regional metamorphism (large scale alteration by heat and pressure) make this less than certain. The rocks were deposited in an ocean basin and show features of near-shore environments as well as deep water turbidites (rocks churned up in submarine sediment slides). The rocks are so altered that a clear interpretation is impossible. The metamorphism took place around 465 million years ago in a continental collision that buried them, subjecting them to high pressures and temperatures. In the overall scale of intensity of metamorphic alteration these rocks fall at the lower end in a division called greenschist facies. There is a giant fold in the Dalradians, over 40 km wide, that has been overturned to the south. This quarry exposes rocks on the north limb which are therefore the right way up. This site is valuable because it shows typical rocks of the Claudy Formation with possible sedimentary structures and a clear metamorphic fabric. The quarry is small and had some dumping at the time of survey. It is recommended that it be cleared and the face cleaned of obscuring vegetation.


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