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

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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

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Clumped isotope constraints on fluid processes and heat advection during late Variscan brittle failure of carbonate rocks

Paul Dennis1, Daniel Myhill1, Neil Allanach1, Alexandra Forman1 and Alina Marca1

1Stable Isotope Laboratory, School of

Environmental Sciences, University of East Anglia, Norwich, Norfolk, UK Daniel.Myhill@uea.ac.uk

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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
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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
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What are clu lumped is isotopes?

  • Ordering of heavy isotopes within the carbonate

(CaCO3) lattice (Eiler, 2007)

Heavy Light

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What are clu lumped is isotopes?

  • Clumping of heavy isotopes is inversely proportional

to temperature so therefore acts as a thermometer.

  • Measure Δ47 of CO2 (13C18O16O) as contains the

‘clumped’ isotopes

  • Measured clumped isotope value are compared to

empirical calculations based on known carbonate standards

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What are clu lumped is isotopes?

Summary of what we measure:

  • δ13C and δ18O of carbonate
  • Precipitation Temperature (TΔ47)

We can then calculate:

  • Fluid δ18O from which carbonate precipitated
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(SEPM STRATA, 2013)

Study Location and Geology

Clare Basin

  • Co. Clare, Ireland
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Clare Basin, Co. Clare, Ireland

Fisher Street

Study Location and Geology

(McNamara and Hennessy, 2010)

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Clare Basin, Co. Clare, Ireland

Study Location and Geology

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Clare Basin, Co. Clare, Ireland

Study Location and Geology

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Clare Basin, Co. Clare, Ireland

Study Location and Geology

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Clare Basin, Co. Clare, Ireland

Study Location and Geology

  • Dominant NNE-SSW strike of vein Calcite

(Gillespie et al., 2001 and Moore & Walsh, 2013)

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Adapted from Frazer et al. (2014)

South Pennine Orefield, Peak District, United Kingdom

Study Location and Geology

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South Pennine Orefield, Peak District, United Kingdom

Study Location and Geology

Adapted from Frazer et al. (2014)

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Fluorite dominant Baryte dominant Calcite dominant Copper dominant

South Pennine Orefield, Peak District, United Kingdom

Study Location and Geology

Adapted from Quirk, 1993 and Ford and Quirk, 1995)

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Dirtlow Rake, South Pennine Orefield, Peak District, UK

Study Location and Geology

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Dirtlow Rake, South Pennine Orefield, Peak District, UK

Study Location and Geology

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Ecton Hill, South Pennine Orefield, Peak District, UK

Study Location and Geology

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Ecton Hill, South Pennine Orefield, Peak District, UK

Study Location and Geology

D A B C E

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Geochemistry ry – Cla lare Basin, Ireland

0.5 1 1.5 2 2.5 15 17 19 21 23 25 δ13C(VPDB) (‰) δ18O(VSMOW) Carbonate (‰)

  • <0.4‰ variation in majority of δ13C values
  • 3‰ variation in δ18O
  • Carbon content is host rock buffered
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Precip ipitation Temperatures: Cla lare Basin, Ireland

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Geochemistry ry – Dir irtlow Rake, South Pennine Orefield

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5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 Host Lst

20.5 21 21.5 22 22.5 23 1.5 2 2.5 3 3.5 4 δ13C(VPDB) (‰) Calcite δ18O(VSMOW) (‰)

Geochemistry ry – Dir irtlow Rake, South Pennine Orefield

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Precip ipitation Temperature: Dir irtlow Rake, South Pennine Orefield

40 50 60 70 80 90 100

  • 3
  • 2
  • 1

1 2 3 4 5 TemperatureΔ47 (°C) Fluid δ18OVSMOW (‰)

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Precip ipitation Temperature: Dir irtlow Rake, South Pennine Orefield

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Geochemistry ry – Ecton Hill, ill, South Pennine Orefield

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Precip ipitation Temperature: Ecton Hill, ill, South Pennine Orefield

1. 2. 3. 4.

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Conceptual Model

Carboniferous Limestone

σ1 σ1 σ1 σ1

Isotopically evolved, hot fluid sourced from depth Inter-granular pore water Isotopically depleted, cool fluid sourced from above

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  • Clumped isotopes (Δ47) 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 160oC 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

Key Poin ints

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  • 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

Acknowledgements

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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.

References

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Thank you for listening Any Questions?

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