fluid processes and heat advection during late Variscan brittle - PowerPoint PPT Presentation

Clumped isotope constraints on fluid processes and heat advection during late Variscan brittle failure of carbonate rocks Paul Dennis 1 , Daniel Myhill 1 , Neil Allanach 1 , Alexandra Forman 1 and Alina Marca 1 1 Stable Isotope Laboratory, School of Environmental Sciences, University of East Anglia, Norwich, Norfolk, UK Daniel.Myhill@uea.ac.uk

Contents • Justification • What are clumped isotopes ? • Study locations and geology: • Clare Basin , Ireland • South Pennine Orefield , Peak District, UK • Results from the Clare Basin • Results from the South Pennine Orefield • Conceptual Model • Key Points

Ju Justification • No constraints on fluid composition in geological record • Pitfalls of other methods – Oxygen Isotope Thermometry and fluid inclusions in carbonates • Understanding mineralisation processes – MVT deposits • Critical in developing carbon, capture and storage • Understanding hydrocarbon migration

What are clu lumped is isotopes? • Ordering of heavy isotopes within the carbonate (CaCO 3 ) lattice (Eiler, 2007) Heavy Light

What are clu lumped is isotopes? • Clumping of heavy isotopes is inversely proportional to temperature so therefore acts as a thermometer. • Measure Δ 47 of CO 2 ( 13 C 18 O 16 O) as contains the ‘clumped’ isotopes • Measured clumped isotope value are compared to empirical calculations based on known carbonate standards

What are clu lumped is isotopes? Summary of what we measure: • δ 13 C and δ 18 O of carbonate • Precipitation Temperature (T Δ 47 ) We can then calculate: • Fluid δ 18 O from which carbonate precipitated

Study Location and Geology Clare Basin Co. Clare, Ireland (SEPM STRATA, 2013)

Study Location and Geology Clare Basin , Co. Clare, Ireland Fisher Street (McNamara and Hennessy, 2010)

Study Location and Geology Clare Basin , Co. Clare, Ireland

Study Location and Geology Clare Basin , Co. Clare, Ireland

Study Location and Geology Clare Basin , Co. Clare, Ireland

Study Location and Geology Clare Basin , Co. Clare, Ireland • Dominant NNE-SSW strike of vein Calcite (Gillespie et al ., 2001 and Moore & Walsh, 2013)

Study Location and Geology South Pennine Orefield, Peak District, United Kingdom Adapted from Frazer et al . (2014)

Study Location and Geology South Pennine Orefield, Peak District, United Kingdom Adapted from Frazer et al . (2014)

Study Location and Geology South Pennine Orefield, Peak District, United Kingdom Copper dominant Fluorite dominant Calcite dominant Baryte dominant Adapted from Quirk, 1993 and Ford and Quirk, 1995)

Study Location and Geology Dirtlow Rake, South Pennine Orefield, Peak District, UK

Study Location and Geology Dirtlow Rake, South Pennine Orefield, Peak District, UK

Study Location and Geology Ecton Hill, South Pennine Orefield, Peak District, UK

Study Location and Geology Ecton Hill, South Pennine Orefield, Peak District, UK A B C D E

Geochemistry ry – Cla lare Basin, Ireland 2.5 2 δ 13 C (VPDB) (‰) 1.5 1 0.5 0 15 17 19 21 23 25 δ 18 O (VSMOW) Carbonate (‰) • <0.4‰ variation in majority of δ 13 C values • 3‰ variation in δ 18 O • Carbon content is host rock buffered

Precip ipitation Temperatures: Cla lare Basin, Ireland

Geochemistry ry – Dir irtlow Rake, South Pennine Orefield

Geochemistry ry – Dir irtlow Rake, South Pennine Orefield 23 30 22.5 10 Calcite δ 18 O (VSMOW) (‰) 35 45 40 22 55 15 50 60 20 21.5 25 Host Lst 65 75 80 70 21 0 5 20.5 1.5 2 2.5 3 3.5 4 δ 13 C (VPDB) (‰)

Precip ipitation Temperature: Dir irtlow Rake, South Pennine Orefield 100 90 Temperature Δ 47 (°C) 80 70 60 50 40 -3 -2 -1 0 1 2 3 4 5 Fluid δ 18 O VSMOW (‰)

Precip ipitation Temperature: Dir irtlow Rake, South Pennine Orefield

Geochemistry ry – Ecton Hill, ill, South Pennine Orefield

Precip ipitation Temperature: Ecton Hill, ill, South Pennine Orefield 3. 1. 2. 4.

Conceptual Model σ 1 σ 1 Isotopically depleted, cool fluid sourced from above Carboniferous Limestone Inter-granular pore water σ 1 σ 1 Isotopically evolved, hot fluid sourced from depth

Key Poin ints • Clumped isotopes (Δ 47 ) offers a new and unique window into hydrothermal temperatures and fluid processes • Example of Variscan fluids in the South Pennine Orefield and Clare Basin show temperatures in the range 35 to 160 o C following a linear, two end-member mixing line • Evidence of pulsed fluids with rapid advection of heat and mineral precipitation due to disequilibrium with host rock • Interconnected, high permeability path for fluid-flow and mixing due to brittle failure in carbonate rocks • Interaction between stress field , pore pressure and faulting/hydraulic fracturing (e.g. gas pulsars (Cathles, 2007), seismic pumping (Sibson,1975), seismic valve (Sibson, 1981)) – evident at Dirtlow Rake with pulsed

Acknowledgements • Tectonics Studies Group – funding my trip to EGU • John Barnett (Peak District National Parks Authority) – for leading trips into Ecton Mine • Peter Kennett (Ecton Mine Education Trust) – allowing access to the mines in the Peak District • Natural England and English Heritage for allowing access and sampling in the Peak District

References Cathles, L.M., 2007, Changes in sub-water table fluid flow at the end of the Proterozoic and its implications for gas pulsars and MVT lead-zinc deposits. Geofluids 7 , pp209-226, doi: 10.1111/j.1468- 8123.2007.00176x. Eiler , J.M., 2007, “Clumped - isotope” geochemistry – The study of naturally-occurring multiply-substituted isotopologues. Earth and Planetary Science Letters 262 , pp309-327. Ford, T.D. and Quirk, D.G., 1995, Mineralisation of the South Pennines. Geology Today 11 , (5), pp177-181. Frazer, M., Whitaker, F. and Hollis, C., 2014, Fluid expulsion from overpressurised basins: Implications for Pb-Zn mineralisation and dolomitisation of the East Midlands platform. Geology , pp1-19. Gillespie, P.A., Walsh, J.J., Watterson, J., Bonson, C.G. and Manzocchi, T., 2001, Scaling relationships of joint and vein arrays from The Burren, Co. Clare, Ireland. Journal of Structural Geology 23, pp183-201. McNamara, M.E. and Hennessy, R.W., 2010, Stone water and ice – The Geology of the Burren region, Co. Clare, Ireland. First Edition, Ennistymon: The Burren Connect Project. Moore, J.McM. and Walsh, J.J., 2013, Analysis of fracture systems and their impact on flow pathways in Irish bedrock aquifers. Groundwater Newsletter 51 , pp28-33. Quirk, D.G., 1993, Origin of the Peak District Orefield. Bulletin of the Peak District Mines Historical Society 12 . pp4-15. SEPM STRATA, 2013, Clare Basin Upper Carboniferous Deepwater Sediments, http://www.sepmstrata.org/page.aspx?&pageid=154&2, Accessed: 11/10/14 Sibson, R.H., Moore, J.McM. and Rankin, A.H., 1975, Seismic pumping – a hydrothermal fluid transport mechanism. Journal of the Geological Society of London 131 , pp653-659.

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