The nature of groundwater flow in fractured rock: Evidence from the isotopic and chemical evolution of recrystallized fracture calcites from the Canadian Precambrian Shield

Journal Article · Wed Jan 01 04:00:00 EST 1992 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(92)90139-A· OSTI ID:7206228

Bottomley, D J ^[1]; Veizer, J ^[2]

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1. Univ. of Ottawa, Ontario (Canada)
2. Univ. of Ottawa, Ontario (Canada) Ruhr Univ., Bochum (Germany)

The isotope geochemistry of fracture calcites in three Precambrian plutons on the Canadian Shield has been investigated in order to understand the paleohydrogeological conditions in fractured crystalline rock. Fracture calcites of ancient hydrothermal origins in the Chalk River and East Bull Lake plutons exhibit {sup 18}O enrichment and {sup 13}C depletion trends resulting from recent low-temperature calcite recrystallization under open-system conditions for oxygen, but semiclosed for carbon, and under extremely variable time-integrated, water/rock (calcite) ratios. This process causes recycling of elements with calcite distribution coefficients > 1 (rare earths, manganese, and possibly iron) from the precursor calcite to younger calcites as well as calcite control over the {sup 87}Sr/{sup 86}Sr ratio of the groundwater within the Chalk River pluton. The large but variable water/rock (calcite) mole ratios calculated from the shifts in the stable isotopic composition of fracture calcites are compatible with fracture flow models that invoke flow channeling within single fractures that also contain regions of immobile porosity. Quantification of isotopic shifts resulting from recrystallization requires that the initial isotopic composition of the precursor hydrothermal calcite be well constrained. Unlike the Chalk River and East Bull Lake plutons, hydrothermal fracture calcites in the White Lake pluton, which intrudes marble-rich country rocks of the Grenville Supergroup, have highly variable {delta}{sup 13}C and {delta}{sup 18}O values. This is attributed to mixing of carbon from magmatic and sedimentary reservoirs, and to oxygen isotopic exchange between hydrothermal fluids and carbonate country rocks at the time of intrusion.

• OSTI ID: 7206228
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 56:1; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540210 -- Environment
Terrestrial-- Basic Studies-- (1990-)
58 GEOSCIENCES
580000* -- Geosciences
ALKALI METAL ISOTOPES
ALKALINE EARTH ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CALCITE
CANADA
CARBON 13
CARBON ISOTOPES
CARBONATE MINERALS
CHEMICAL ANALYSIS
CHEMISTRY
DATA
DEPTH
DEVELOPED COUNTRIES
DIMENSIONS
ELECTRON CAPTURE RADIOISOTOPES
ELECTRON MICROPROBE ANALYSIS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
FLOW MODELS
FLUID FLOW
FRACTURED RESERVOIRS
GEOCHEMISTRY
GEOLOGIC HISTORY
GEOLOGY
GROUND WATER
HOURS LIVING RADIOISOTOPES
HYDROGEN COMPOUNDS
HYDROLOGY
HYDROTHERMAL ALTERATION
IGNEOUS ROCKS
INFORMATION
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
LIQUID FLOW
MASS SPECTROSCOPY
MATHEMATICAL MODELS
MICROANALYSIS
MINERALS
NONDESTRUCTIVE ANALYSIS
NORTH AMERICA
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
OXYGEN 18
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PLUTONIC ROCKS
RADIOISOTOPES
RECRYSTALLIZATION
ROCKS
RUBIDIUM 87
RUBIDIUM ISOTOPES
SPECTROSCOPY
STABLE ISOTOPES
STRONTIUM 86
STRONTIUM 87
STRONTIUM ISOTOPES
WATER
YEARS LIVING RADIOISOTOPES