Hostname: page-component-78c5997874-mlc7c Total loading time: 0 Render date: 2024-11-10T11:18:41.738Z Has data issue: false hasContentIssue false
  • English
  • Français

Low-grade metamorphism in the Scottish Southern Uplands terrane: deciphering the patterns of accretionary burial, shearing and cryptic aureoles

Published online by Cambridge University Press:  03 November 2011

R. J. Merriman  and
B. Roberts
R. J. Merriman
Affiliation:
R. J. Merriman, British Geological Survey, Keyworth, Nottingham NG12 5GG, U.K.
B. Roberts
Affiliation:
B. Roberts, Department of Geology, Birkbeck College, Malet Street, London WC1E 7HX, U.K.
Get access Rights & Permissions [Opens in a new window]

Abstract

ABSTRACT

Systematic studies of metapelitic grade linked with the geological re-survey of the Southern Uplands have been used to generate a contoured metamorphic map currently covering nearly two-thirds of the terrane. These studies, based on approximately one pelite sample per 2·5 km2, have used XRD measurements of clay mineral reaction progress, particularly illite crystallinity, to delineate zones of diagenesis and low-grade metamorphism in the imbricated Ordovician and Silurian strata. The regional pattern revealed by metapelitic zonal sequences does not agree with earlier observations that grade increases across the strike, from SE to NW. Instead, the map shows considerable variations in metamorphic trends, including patterns of grade increasing from older into younger strata, indicative of accretionary burial. Other patterns identified include those generated by high strain rates in the Moniaive Shear Zone (MSZ), and by extensive low-temperature cryptic aureoles associated with late granitic intrusions. The present pattern is the result of uplift that generated normal movement on reactivated thrust faults and differential block movement on NW-trending faults.

Regional metamorphic patterns were generated by burial and underplating in an accretionary thrust stack. Subduction was initiated in the early Caradoc and probably ceased in the early Wenlock. Metapelitic patterns suggest that two levels of accretion are exposed in the terrane. Strata accreted to the toe of the prism and stacked above the décollement zone are typically at late diagenetic grade. Underplated strata below the décollement are typically at anchizonal grades with moderate to well-developed slaty cleavage. Coherent thrust-bounded tracts of strata at both levels were rotated and buried to produce a syntectonic depth-controlled pattern of meta-morphism. Shear zone metamorphism at depths of 12 km or more was probably confined to the underplated lower level of the thrust stack, and Devonian granitic intrusions were also emplaced mainly within the underplated strata.

Keywords

illite crystallinitymetapelitic zonessubductiontectonic burialunderplating
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 91 , Issue 3-4: The Southern Uplands Terrane: Tectonics and Biostratigraphy within the Caledonian Orogen , 2000 , pp. 521 - 537
Copyright
Copyright © Royal Society of Edinburgh 2000

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Anderson, T. B. & Oliver, G. J. H. 1986. The Orlock Bridge Fault: a major Late Caledonian sinistral fault in the Southern Uplands terrane, British Isles. Transactions of the Royal Society of Edinburgh: Earth Sciences 11, 203–22.CrossRefGoogle Scholar
Barnes, R. P. (in press). The Geology of the Kirkcowan–Wigtown district—a concise account of the geology. Memoir of the British Geological Survey, Sheets 4E, 4W and part of 2 (Scotland). Keyworth, Nottingham: British Geological Survey.Google Scholar
Barnes, R. P., Lintern, B. C. & Stone, P. 1989. Timing and regional implications of deformation in the Southern Uplands of Scotland. Journal of the Geological Society, London 146, 905–908.CrossRefGoogle Scholar
Barnes, R. P., Phillips, E. R. & Boland, M. P. 1995. The Orlock Bridge Fault in the Southern Uplands of southwestern Scotland: a terrane boundary? Geological Magazine 132, 523–9.CrossRefGoogle Scholar
Barton, M. D., Staude, J-M., Snow, E. A. & Johnson, D. A. 1991. Aureole systematics. In Kerrick, D. M. (ed.) Contact Metamorphism, Reviews in Mineralogy 26, 723–847. Michigan, U.S.A.: Mineralogical Society of America.CrossRefGoogle Scholar
Batchelor, R. A. & Weir, J. A. 1988. Metabentonite geochemistry: magmatic cycles and graptolite extinctions at Dob's Linn, southern Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 79, 19–41.CrossRefGoogle Scholar
Boles, J. R. & Franks, S. G. 1979. Clay diagenesis in Wilcox sandstones of southwest Texas; implications of smectite diagenesis on sandstone cementation. Journal of Sedimentary Petrology 49, 55–70.Google Scholar
British Geological Survey 1992a. Kirkcowan, Scotland. Sheet 4W. Solid 1:50,000. Keyworth, Nottingham: British Geological Survey.Google Scholar
British Geological Survey 1992b. Wigtown, Scotland. Sheet 4E. Solid 1:50,000. Keyworth, Nottingham: British Geological Survey.Google Scholar
British Geological Survey 1993a. The Rhins of Galloway, Scotland. Sheets 1 and 3 with parts of 7 and 4W. Solid Geology 1:50,000. Keyworth, Nottingham: British Geological Survey.Google Scholar
British Geological Survey 1993b. Kirkcudbright, Scotland. Sheet 5W. Solid Geology 1:50,000. Keyworth, Nottingham: British Geological Survey.Google Scholar
British Geological Survey 1993c. Regional geochemistry of southern Scotland and part of northern England. Keyworth, Nottingham: British Geological Survey.Google Scholar
British Geological Survey 1993d. Dalbeattie, Scotland. Sheet 5E. Solid Geology 1:50,000. Keyworth, Nottingham: British Geological Survey.Google Scholar
British Geological Survey 1996. Thornhill, Scotland. Sheet 9E. Solid Geology 1:50,000. Keyworth, Nottingham: British Geological Survey.Google Scholar
British Geological Survey 1998. New Galloway, Scotland. Sheet 9W. Solid Geology 1:50,000. Keyworth, Nottingham: British Geological Survey.Google Scholar
Bucher, L. & Frey, M. 1994. Petrogenesis of Metamorphic Rocks, 6th edn. Berlin: Springer.CrossRefGoogle Scholar
Essene, E. J. & Peacor, D. R. 1995. Clay mineral geothermometry–a critical perspective. Clays and Clay Minerals 43, 540–53.CrossRefGoogle Scholar
Floyd, J. D. 1994. The derivation and definition of the ‘Southern Upland Fault’: a review of the Midland Valley–Southern Uplands terrane boundary. Scottish Journal of Geology 30, 51–62.CrossRefGoogle Scholar
Floyd, J. D. 1996. Lithostratigraphy of the Ordovician rocks in the Southern Uplands: Crawford Group, Moffat Shale Group, Leadhills Supergroup. Transactions of the Royal Society of Edinburgh: Earth Sciences 86, 153–65.CrossRefGoogle Scholar
Floyd, J. D. & Kimbell, G. 1995. Magnetic and tectonostratigraphic correlation at a terrane boundary: the Tappins Group of the Southern Uplands. Geological Magazine 132, 515–21.CrossRefGoogle Scholar
Frey, M. 1969. A mixed-layer paragonite/phengite of low-grade metamorphic origin. Contributions to Mineralogy and Petrology 14, 63–5.CrossRefGoogle Scholar
Frey, M. 1987. The reaction isograde kaolinite + quartz = pyrophyllite + H2O, Helvetic Alps, Switzerland. Schweizerische Mineralogische und Petrographische Mitteilungen 68, 171–83.Google Scholar
Halliday, A. N., Stephens, W. E. & Harmon, R. S. 1980. Rb-Sr and Oisotopic relationships in three zoned Caledonian granitic plutons, Southern Uplands, Scotland: evidence for varied sources and hybridization of magmas. Journal of the Geological Society, London 137, 329–48.CrossRefGoogle Scholar
Hirono, T. & Ogawa, Y. 1998. Duplex arrays and thickening of accretionary prisms. An example from Boso Peninsula, Japan. Geology 26, 779–82.2.3.CO;2>CrossRefGoogle Scholar
Hirons, S. R., Roberts, B. & Merriman, R. J. 1997. Metamorphism of the Lower Palaeozoic rocks of the Carrick–Loch Doon region, southern Scotland. British Geological Survey Technical Report WG/97/25. Keyworth, Nottingham: British Geological Survey.Google Scholar
Hower, J., Eslinger, E. V., Hower, M. E. & Perry, E. A. 1976. Mechanisms of burial metamorphism of argillaceous sediment: 1 Mineralogical and chemical evidence. Geological Society of America Bulletin 87, 725–37.2.0.CO;2>CrossRefGoogle Scholar
Huff, W. D., Anderson, T. B., Rundle, C. C. & Odin, G. S. 1991. Chemostratigraphy, K–Ar ages, and illitization of Silurian K-bentonites from the Central Belt of Southern Uplands-Down-Longford terrane, British Isles. Journal of the Geological Society, London 148, 861–8.CrossRefGoogle Scholar
Jiang, W.-T. & Peacor, D. R. 1993. Formation and modification of metastable intermediate sodium mica, paragonite and muscovite in hydrothermally altered metabasites from northern Wales. American Mineralogist 78, 782–93.Google Scholar
Kemp, A. E. S., Oliver, G. J. H. & Baldwin, J. R. 1985. Low-grade metamorphism and accretion tectonics: Southern Uplands terrain, Scotland. Mineralogical Magazine 49, 335–44.CrossRefGoogle Scholar
Kimbell, G. & Stone, P. 1992. Geophysical evidence for a concealed Caledonian intrusive body at Sandhead, Wigtownshire. Scottish Journal of Geology 28, 19–25.CrossRefGoogle Scholar
Kisch, H. J. 1991. Illite crystallinity: recommendations on sample preparation, X-ray diffraction settings and interlaboratory standards. Journal of Metamorphic Geology 6, 665–70.CrossRefGoogle Scholar
Kübler, B. 1967a. La cristallinité de l'illite et les zones tout à fait supérieures du métamorphisme. In Étages tectoniques, Colloque de Neuchâtel 1966. Neuchâtel, Switzerland: À la Baconnière. 105–21.Google Scholar
Kübler, B. 1967b. Anchimetamorphisme et schistosité. Bulletin Centre Recherches Pau-SNPA 1, 259–78.Google Scholar
Kübler, B. 1968. Evaluation quantitative du métamorphism par la cristallinité de l'illite. Bulletin Centre Recherche Pau-SNPA 2, 385–97.Google Scholar
Leggett, J. K., McKerrow, W. S. & Eales, M. H. 1979. The Southern Uplands of Scotland: a Lower Palaeozoic accretionary prism. Journal of the Geological Society, London 136, 755–70.CrossRefGoogle Scholar
Li, G., Peacor, D. R., Merriman, R. J. & Roberts, B. 1994. The diagenetic to low grade metamorphic evolution of matrix white micas in the system muscovite–paragonite in a mudrock from Central Wales, U.K. Clays and Clay Minerals 42, 369–81.CrossRefGoogle Scholar
Lintern, B. C. & Floyd, J. D. 2000. The Kirkcudbright–Dalbeattie district—a concise account of the geology. Memoir of the British Geological Survey, Sheets 5W, 5E and part of 6W (Scotland). Keyworth, Nottingham: British Geological Survey.Google Scholar
Livi, K. J. T., Veblen, D. R., Ferry, J. M. & Frey, M. 1997. Evolution of 2:1 layered silicates in low-grade metamorphosed Liassic shales of Central Switzerland. Journal of Metamorphic Geology 15, 323–44.CrossRefGoogle Scholar
Maltman, A. J. 1998. Deformation structures from the toes of active accretionary prisms. Journal of the Geological Society, London 155, 639–50.CrossRefGoogle Scholar
McCurry, J. A. & Anderson, T. B. 1989. Landward vergence in the Lower Palaeozoic Southern Uplands-Down-Longford terrane, British Isles. Geology 17, 630–33.2.3.CO;2>CrossRefGoogle Scholar
MacKay, M. E. 1995. Structural variation and landward vergence at the toe of the Oregon accretionary prism. Tectonics 14, 1309–20.CrossRefGoogle Scholar
McKerrow, W. S., Leggett, J. K. & Eales, M. H. 1977. Imbricate thrust model of the Southern Uplands of Scotland. Nature 267, 237–9.CrossRefGoogle Scholar
McMillan, A. A. 2001. Geology of the New Galloway and Thornhill district. Memoir of the British Geological Survey, sheets 9W and 9E (Scotland). Keyworth, Nottingham: British Geological Survey.Google Scholar
Merriman, R.J., Roberts, B., Peacor, D. R. & Hirons, S. R. 1995. Strain-related differences in the crystal growth of white mica and chlorite: a TEM and XRD study of the development of metapelite microfabrics in the Southern Uplands thrust terrane, Scotland. Journal of Metamorphic Geology 13, 559–76.CrossRefGoogle Scholar
Merriman, R. J., Roberts, B. & Hirons, S. R. 1997. Metamorphism of Lower Palaeozoic strata of the Kirkcowan and Wigtown districts (Sheet 4), SW Scotland. British Geological Survey Technical Report WG/97/4. Keyworth, Nottingham: British Geological Survey.Google Scholar
Merriman, R. J. & Frey, M. 1999. Patterns of very low-grade metamorphism is metapelitic rocks. In Frey, M. & Robinson, D. (eds) Low-Grade Metamorphism, 61–107. Oxford: Blackwell Science.Google Scholar
Merriman, R. J. & Kemp, S. J. 1998. Metamorphism of the Lower Palaeozoic rocks of the New Cumnock district, southern Scotland, 1:50K Sheet 15W. British Geological Survey Technical Report WG/ 98/9. Keyworth, Nottingham: British Geological Survey.Google Scholar
Merriman, R. J. & Peacor, D. R. 1999. Very low-grade metapelites; mineralogy, microfabrics and measuring reaction progress. In Frey, M. & Robinson, D. (eds) Low-Grade Metamorphism, 10–60. Oxford: Blackwell Science.Google Scholar
Merriman, R. J. & Roberts, B. 1985. A survey of white mica crystallinity and polytypes in pelitic rocks of Snowdonia and Llyn, N. Wales. Mineralogical Magazine 49, 305–19.CrossRefGoogle Scholar
Merriman, R. J. & Roberts, B. 1990. Metabentonites in the Moffat Shale Group, Southern Uplands of Scotland: geochemical evidence of ensialic marginal basin volcanism. Geological Magazine 127, 259–71.CrossRefGoogle Scholar
Merriman, R. J. & Roberts, B. 1992. Low grade metamorphism of Lower Palaeozoic strata on the Rhins of Galloway, SW Scotland, 1:50K Sheet 15W. British Geological Survey Technical Report WG/ 92/40. Keyworth, Nottingham: British Geological Survey.Google Scholar
Merriman, R. J. & Roberts, B. 1996. Metamorphism of the Lower Palaeozoic rocks. In Stone, P. (ed.) Geology in south-west Scotland: An excursion guide. Keyworth, Nottingham: British Geological Survey.Google Scholar
Moore, D. M. & Reynolds, R. C. Jr. 1997. X-ray Diffraction and Identification of Clay Minerals. Oxford University Press.Google Scholar
Moore, J. C., Diebold, J., Fisher, M. A., Sample, J., Brocher, T., Talwani, T., Ewing, J., von Hueue, R., Rowe, C., Stone, D., Stevens, C. & Sawyer, D. 1991. EDGE deep seismic reflection transect of the eastern Aleutian arc-trench layered lower crust reveals underplating and continental growth. Geology 19, 420–24.2.3.CO;2>CrossRefGoogle Scholar
Moore, J. C. & Bryne, T. 1987. Thickening of fault zones: A mechanism of melange formation in accreting sediments. Geologv 15, 1040–3.Google Scholar
Morse, J. S. & Casey, W. H. 1988. Ostwald processes and mineral paragenesis in sediments. American Journal of Sciences 288, 537–60.CrossRefGoogle Scholar
Murata, A. 1991. Duplex structures of the Uchinohae Formation in the Shimato Terrane, Kyusyu, southwest Japan. Geological Society of Japan Journal 97, 39–52.Google Scholar
Offler, R., McKnight, S. & Morand, V. 1998. Tectonothermal history of the western Lachlan Fold Belt, Australia: insights from white micas. Journal of Metamorphic Geology 16, 531–40.CrossRefGoogle Scholar
Ogawa, Y. 1998. Tectonostratigraphy of the Glen App area, Southern Uplands, Scotland: anatomy of an Ordovician accretionary complex. Journal of the Geological Society, London 155, 651–62.CrossRefGoogle Scholar
Oliver, G. J. H., Smellie, J. L., Thomas, L. J., Casey, D. M., Kemp, A. E. S., Evans, L. J., Balwin, J. R. & Hepworth, B. C. 1984. Early Palaeozoic metamorphic history of the Midland Valley, the Southern Uplands-Longford-Down massif and the Lake District, British Isles. Transactions of the Royal Society of Edinburgh: Earth Sciences 75, 259–73.Google Scholar
Oliver, G. J. H. & Leggett, J. K. 1980. Metamorphism is an accretionary prism: prehnite–pumpellyite facies metamorphism of the Southern Uplands of Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 71, 235–46.CrossRefGoogle Scholar
Peacor, D. R. 1992. Diagenesis and low-grade metamorphism of shales and slates. In Buseck, P.R. (ed.) Minerals and Reactions at the Atomic Scale: Transmission Electron Microscopy Reviews in Mineralogy 27, 335–80. Michigan, U.S.A.: Mineralogical Society of America.CrossRefGoogle Scholar
Phillips, E. R., Barnes, R.P., Boland, M. P., Fortey, N. J. & McMillan, A. A. 1995. The Moniaive Shear Zone: a major zone of sinistral strike-slip deformation in the Southern Uplands of Scotland. Scottish Journal of Geology 31, 139–49.CrossRefGoogle Scholar
Phillips, E. R., Smith, R. A. & Floyd, J. D. 1999. The Bail Hill Volcanic Group: alkaline within-plate volcanism during Ordovician sedimentation in the Southern Uplands, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 89, 233–47.CrossRefGoogle Scholar
Roberts, B., Morrison, C. & Hirons, S. 1990. Low grade metamorphism of the Manx Group, Isle of Man: a comparative study of white mica ‘crystallinity’ techniques. Journal of the Geological Society, London 147, 271–7.CrossRefGoogle Scholar
Roberts, B., Merriman, R. J. & Pratt, W. 1991. The relative influences of strain, lithology and stratigraphical depth on white mica (illite) crystallinity in mudrocks from the district centred on the Corris Slate Belt, Gwynedd-Powys. Geological Magazine 128, 633–45.CrossRefGoogle Scholar
Roberts, B., Merriman, R. J., Hirons, S. R., Fletcher, C. J. N. & Wilson, D. 1996. Synchronous very low grade metamorphism, contraction and inversion in the central part of the Welsh Lower Palaeozoic Basin. Journal of the Geological Society, London 153, 277–86.CrossRefGoogle Scholar
Robinson, D., Warr, L. N. & Bevins, R. E. 1990. The illite ‘crystallinity’ technique: a critical appraisal of its precision. Journal of Metamorphic Geology 8, 333–44.CrossRefGoogle Scholar
Rushton, A. W. A., Stone, P. & Hughes, R. A. 1996. Biostratigraphical controls of thrust models for the Southern Uplands of Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 86 (for 1995), 137–52.CrossRefGoogle Scholar
Sample, J. C. & Moore, J. C. 1987. Structural style and kinematics of an underplated slate belt, Kodiak and adjacent islands, Alaska. Geological Society of America Bulletin 99, 7–20.2.0.CO;2>CrossRefGoogle Scholar
Stone, P. 1995. The Geology of the Rhins of Galloway district. Memoir of the British Geological Survey, sheets 1 and 3 (Scotland). Keyworth, Nottingham: British Geological Survey.Google Scholar
Stone, P., Floyd, J. D., Barnes, R. P. & Lintern, B. C. 1987. A sequential back-arc and foreland basin thrust duplex model for the Southern Uplands of Scotland. Journal of the Geological Society, London 144, 753–64.CrossRefGoogle Scholar
Stone, P., Green, P. M., Lintern, B. C., Simpson, P. R. & Plant, J. A. 1993. Regional geochemical variations across the lapetus Suture zone: tectonic implications. Scottish Journal of Geology 29, 113–21.CrossRefGoogle Scholar
Stone, P., Cook, J. M., McDermott, C., Robinson, J. J. & Simpson, P. R. 1995. Lithostratigraphic and structural controls on distribution of As and Au in southwest Southern Uplands, Scotland. Transactions of the Institution of Mining & Metalurgy (Section B: Applied Earth Science) 104, 111–19.Google Scholar
Velde, B. 1968. The effects of chemical reduction on the stability of pyrophyllite and kaolinite in pelitic rocks. Journal of Sedimentary Petrology 38, 13–16.CrossRefGoogle Scholar
Vrolijk, P. 1990. On the mechanical role of smectite in subduction zones. Geology 18, 703–7.2.3.CO;2>CrossRefGoogle Scholar
Warr, L. N., Greiling, R. O. & Zachrisson, E. 1996. Thrust related very low grade metamorphism in the marginal part of an orogenic wedge, Scandinavian Caledonides. Tectonics 15, 1213–29.CrossRefGoogle Scholar