The BGS Lexicon of Named Rock Units — Result Details

South Charnwood Diorites

Computer Code: SCHD Preferred Map Code: notEntered
Status Code: Index Level
Age range: Ediacaran Period (AD) — Ediacaran Period (AD)
Lithological Description: A grey to pink, medium- to coarse-grained granophyric diorite with a distinctive "mottled" appearance caused by the clumping together of dark grey ferromagnesian minerals (mainly hornblende and chlorite) and grey-green hypidiomorphic plagioclase crystals. Both components are surrounded by a pink to grey granophyric mesostasis. The texture coarsens in places, but true pegmatites are rarely developed; green-grey aplite sheets cross the diorite in some quarries.
Definition of Lower Boundary: Where intrusive contacts are exposed (eg Cliffe Hill Quarry), the diorite fines progressively in grain size over about 10m, eventually developing a selvage 1.5m wide consisting of dark grey porphyritic andesite. The contact sharply truncates bedding in adjacent volcaniclastic rocks of the Charnian Supergroup, the latter developing thermal spots that are locally attenuated within the plane of a later cleavage. Many contacts are sheared and faulted.
Definition of Upper Boundary: Intrusive, as for the Lower Boundary; in places overlain unconformably by Triassic strata.
Thickness: c.1100m
Geographical Limits: The intrusion crops out discontinuously in Leicestershire, from beneath Triassic cover, from Stanton under Bardon [SK 457 108] southeastwards to the Groby Quarries [SK 526 082], and thence northeastwards to Bradgate Park [SK 535 102].
Parent Unit: Not Available (!)
Previous Name(s): South Charnwood Diorites Complex (-1166)
Alternative Name(s): none recorded or not applicable
Partial Type Section  Exposures in excavated faces along the northern and eastern margins of the "Old" Cliffe Hill Quarry, 500m southeast of the M1/A511 junction, Charnwood Forest (a RIGS). About 80m of stepped vertical sections are exposed, representing the western margin of the intrusion. Carney and Pharaoh, 2000. 
Partial Type Section  Markfield Quarry, off Hill Lane, 250m northwest of Markfield Church, Charnwood Forest (a RIGS). Approximately 100m of the intrusion is exposed. Worrsam and Old, 1988. 
Worssam, B C and Old, R A, 1988. Geology of the country around Coalville. Memoir of the British Geological Survey, Sheet 155 (England and Wales) 
Watts, W W, 1947. Geology of the ancient rocks of Charnwood Forest, Leicestershire. Leicester: Leicester Literary and Philosophical Society. 
Carney, J N and Pharaoh, T C P. 2000. Cliffe Hill Quarry. 122-126 in Precambrian Rocks of England and Wales. Geological Conservation Review Series No.20, Joint Nature Conservation Committee, Peterborough. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable