The BGS Lexicon of Named Rock Units — Result Details

Hascosay Slide Zone Mylonites

Computer Code: HSZM Preferred Map Code: SYMBOL
Status Code: Full
Age range: Cambrian Period (E) — Cambrian Period (E)
Lithological Description: Closely-packed masses of coarse-grained, dominantly hornblendic rocks, cut by and contained within, fine-grained and dominantly hornblendic blastomylonites.
Definition of Lower Boundary: On the western boundary, the rocks of the slide zone belong to the Shetland Boundary Zone. There is no lithological discordance at the junction but it is marked by a continuous and rapid increase in the intensity of the schistosity.
Definition of Upper Boundary: On the eastern boundary, the rocks to the east of the slide zone belong to the Dalradian of the East Mainland succession (Unst and Fetlar Succession). There is no lithological discordance at the junction, but it is marked by a continuous and rapid increase in the intensity of the schistosity.
Thickness: Up to 1 km in width.
Geographical Limits: It is about 15 km long and up to 1 km wide. It extends along the north-east coast of Yell and is offset 5 km dextrally by the Bluemull Sound Fault.
Parent Unit: Not Applicable (-)
Previous Name(s): Hascosay Slide (-2857)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Area  The eastern margin of the slide in the cliff top, southeast of Hascosay. Flinn, 1994. 
Type Area  The western margin of the slide, on the clifftop at Migga Ness. Flinn, 1994. 
Reference(s):
Flinn, D, 1994. Geology of Yell and some neighbouring islands in Shetland. Memoir of the British Geological Survey, Sheet 130 (Scotland). 
British Geological Survey, 1994. Yell, Scotland. Part of sheets 130 and 131. Solid and Drift geology, 1:50 000 (Keyworth, Nottingham: British Geological Survey). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
S130 S131