Petrology of the sedimentary and igneous rocks from the Strathmore district (Sheet 57), Scotland Integrated Geological Survey (North) Internal Report IR/04/125 BRITISH GEOLOGICAL SURVEY INTERNAL REPORT IR/04/125 Petrology of the sedimentary and igneous rocks from the Strathmore district (Sheet 57), Scotland Emrys Phillips The National Grid and other Ordnance Survey data are used with the permission of the Controller of Her Majesty’s Stationery Office. Ordnance Survey licence number GD 272191/2004 Key words Petrology, sedimentary and igneous rocks, Strathmore, Scotland Bibliographical reference PHILLIPS, E. R. 2004. Petrology of the sedimentary and igneous rocks from the Strathmore district (Sheet 57), Scotland. British Geological Survey Internal Report, IR/04/125. 21pp. © NERC 2004 Keyworth, Nottingham British Geological Survey 2001 BRITISH GEOLOGICAL SURVEY The full range of Survey publications is available from the BGS Keyworth, Nottingham NG12 5GG Sales Desks at Nottingham and Edinburgh; see contact details 0115-936 3241 Fax 0115-936 3488 below or shop online at www.thebgs.co.uk e-mail: [email protected] The London Information Office maintains a reference collection www.bgs.ac.uk of BGS publications including maps for consultation. 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Forde House, Park Five Business Centre, Harrier Way, Sowton, Exeter, Devon EX2 7HU 01392-445271 Fax 01392-445371 Geological Survey of Northern Ireland, 20 College Gardens, Belfast BT9 6BS 028-9066 6595 Fax 028-9066 2835 Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB 01491-838800 Fax 01491-692345 Parent Body Natural Environment Research Council, Polaris House, North Star Avenue, Swindon, Wiltshire SN2 1EU 01793-411500 Fax 01793-411501 www.nerc.ac.uk IR/04/125; Draft 0.1 Last modified: 2004/07/15 10:47 Foreword This report is the published product of a study by the British Geological Survey (BGS) on the regional geology of the Midland Valley of Scotland. It is part of the Science Budget funded programme which forms part of the core programme of BGS. This core programme is designed to undertake a multidisciplinary geological survey to meet user and strategic needs for geological information. Contents Foreword.........................................................................................................................................i Contents...........................................................................................................................................i Summary........................................................................................................................................ii 1 Introduction............................................................................................................................ 3 2 Petrology ................................................................................................................................. 3 2.1 Montrose Volcanic Formation........................................................................................ 3 2.1.1 Olivine-clinopyroxene phyric basalt ...........................................................................3 2.1.2 Medium- to coarse-grained basalt and basaltic andesite.............................................4 2.1.3 Olivine microgabbro ...................................................................................................4 2.1.4 Andesite and basaltic andesite.....................................................................................5 2.1.5 Pilotaxitic basaltic and andesitic rocks........................................................................6 2.1.6 Carbonate replaced basaltic or andesitic rock.............................................................6 2.1.7 Highly altered andesitic or microdioritic rock ............................................................6 2.1.8 Volcaniclastic or pyroclastic rocks .............................................................................6 2.1.9 Ophimottled basalt......................................................................................................7 2.2 Catterline Conglomerate Formation ............................................................................... 7 2.2.1 Matrix-rich wacke sandstone......................................................................................7 2.2.2 Quartzose litharenite...................................................................................................8 2.2.3 Volcaniclastic microconglomerate..............................................................................8 2.3 Auchmithie Conglomerate Member ............................................................................... 9 2.3.1 Sandstone ....................................................................................................................9 2.3.2 Clasts within the conglomerates..................................................................................9 2.4 Trappean Conglomerate, Scone Sandstone Formation................................................... 9 2.5 Cromlix Mudstone Formation ...................................................................................... 10 2.6 Teith Sandstone Formation........................................................................................... 10 i IR/04/125; Draft 0.1 Last modified: 2004/07/15 10:47 2.7 Glenvale Sandstone Formation..................................................................................... 11 2.8 Scone Sandstone Formation ......................................................................................... 11 2.9 Pittendriech Limestone................................................................................................. 12 2.10 Dundee Flags Formation............................................................................................... 12 2.10.1 Quartzose litharenites.............................................................................................12 2.10.2 Siltstones................................................................................................................13 2.10.3 Pebbly sandstone or microconglomerate ...............................................................13 3 Plate captions........................................................................................................................ 13 Glossary........................................................................................................................................ 14 Summary This report describes the mineralogy and petrology of a suite of basaltic to andesitic volcanic rocks and sedimentary rocks as part of the regional mapping of the Strathmore district (Sheet 57). ii IR/04/125; Draft 0.1 Last modified: 2004/07/15 10:47 1 Introduction This report describes the mineralogy and petrology of a suite of basaltic to andesitic volcanic rocks and sandstones, microconglomerates and associated sedimentary rocks of the Strathmore district (sheet 57). A total of 108 thin sections have been examined with the work forming part of a multidisciplinary project being undertaken by the British Geological Survey to examine the evolution of the Midland Valley of Scotland. This work forms part of the British Geological Survey’s Integrated Geological Survey (North) programme. 2 Petrology 2.1 MONTROSE VOLCANIC FORMATION 2.1.1 Olivine-clinopyroxene phyric basalt In thin section these basalts are typically fine-grained, anhedral granular, holocrystalline to hypocrystalline, micro- to macroporphyritic rocks (S335; S3787; S54048; S54049; S54046; S54045; S54053; S54056; S54104; S54108; S53566; S57011; S37081; S22139; S54109; S3780). They comprise an inequigranular mineral assemblage dominated by plagioclase, clinopyroxene and olivine (Plate 1) with minor to accessory opaque minerals and apatite. Phenocrysts within the basalts range up to 3.5 mm in size (typically ≤ 2.0 mm in size) and are composed of olivine (Plate 1a and b) and clinopyroxene with variable amounts of plagioclase (Plate 1c and d). These phenocrysts may exhibit a preferred shape alignment parallel to a pilotaxitic fabric locally developed within the groundmass. Olivine forms small anhedral to subhedral microphenocrysts that are variably altered to, or pseudomorphed by mesh textured chlorite, serpentine, bowlingite and iddingsite (Plate 1a and b). The pseudomorphs after olivine are typically enclosed within a rim of opaque oxides, with thin veinlets of opaque minerals also preserving fractures within the pre-existing relict olivine. These pseudomorphs after