TY - JOUR
T1 - South African crustal fracture fluids preserve paleometeoric water signatures for up to tens of millions of years
AU - Heard, Andrew W.
AU - Warr, Oliver
AU - Borgonie, Gaetan
AU - Linage, Borja
AU - Kuloyo, Olukayode
AU - Fellowes, Jonathan W.
AU - Magnabosco, Cara
AU - Lau, Maggie C.Y.
AU - Erasmus, Mariana
AU - Cason, Errol D.
AU - van Heerden, Esta
AU - Kieft, Thomas L.
AU - Mabry, Jennifer C.
AU - Onstott, Tullis C.
AU - Sherwood Lollar, Barbara
AU - Ballentine, Chris J.
N1 - Funding Information:
For this study we would like to thank the management and staff of the Driefontein gold mine (Sibanye-Stillwater), the Masimong gold mine (Harmony Gold Mining Co. Ltd.), Star (Petra Diamonds), Zondereinde platinum mine (Northam Platinum Ltd.) and Tau Tona gold mine (AngloGold Ashanti Ltd.) for providing access, training, logistical support and assistance during sampling of their subsurface fractures. Support for sample collection was provided by NSF Grants EAR-0948335 to TLK and EAR-0948659 to TCO and National Geographic Society Grant 8990-11 to TCO. We acknowledge funding from the Deep Carbon Observatory Grant DCO-DGR00840 . Donald Porcelli and Peter Barry are thanked for providing insightful comments on an early version of the manuscript. Reika Yokochi is thanked for helpful discussions about radiocarbon dating which greatly improved the quality of the Appendix. This manuscript benefited from detailed reviews by Miquela Ingalls and an anonymous reviewer.
Funding Information:
For this study we would like to thank the management and staff of the Driefontein gold mine (Sibanye-Stillwater), the Masimong gold mine (Harmony Gold Mining Co. Ltd.), Star (Petra Diamonds), Zondereinde platinum mine (Northam Platinum Ltd.) and Tau Tona gold mine (AngloGold Ashanti Ltd.) for providing access, training, logistical support and assistance during sampling of their subsurface fractures. Support for sample collection was provided by NSF Grants EAR-0948335 to TLK and EAR-0948659 to TCO and National Geographic Society Grant 8990-11 to TCO. We acknowledge funding from the Deep Carbon Observatory Grant DCO-DGR00840. Donald Porcelli and Peter Barry are thanked for providing insightful comments on an early version of the manuscript. Reika Yokochi is thanked for helpful discussions about radiocarbon dating which greatly improved the quality of the Appendix. This manuscript benefited from detailed reviews by Miquela Ingalls and an anonymous reviewer.
Publisher Copyright:
© 2018 Elsevier B.V.
PY - 2018/8/20
Y1 - 2018/8/20
N2 - Fracture fluids in Earth's crust may remain isolated for millions to billions of years, and contain information on paleohydrogeology, subsurface microbial life, and conservative components that help elucidate the atmospheric evolution of the early Earth. Examples include fluids in the South African Kaapvaal craton which host chemolithoautotrophic microbial communities that survive independent of the photosphere, and billion-year-old fluids in the Canadian Shield, which preserve the Xe isotopic signature of an evolving early atmosphere. Stable isotope analyses of the aqueous phase combined with isotopic analyses of the dissolved noble gases provide unrivalled insight into the time-alteration history of aqueous fracture fluids. Here we report stable isotope and noble gas data for fracture fluids in the Witwatersrand Basin and Bushveld Igneous Province systems, South Africa. We determine closed-system radiogenic noble gas residence times of 0.77–97 million years (Myr). Open-system residence times range between 6.0 kyr and 10.8 Myr. One sample from Masimong Mine has a mean closed-system residence time of 85 Myr, making it one of oldest paleometeoric waters ever recorded. The δ2H and δ18O of water in this sample, and in previously reported samples from the same mining district that are shown to have similar ages, require an isotopically depleted source of groundwater recharge. This could reflect a recharge regime at a higher paleolatitude, elevation, or with higher rainfall, established up to tens of Myr ago, and perhaps similar to the recharge regime in the modern Lesotho Highlands. These data suggest that groundwater isotopes can provide useful paleoclimatic information for many Myr.
AB - Fracture fluids in Earth's crust may remain isolated for millions to billions of years, and contain information on paleohydrogeology, subsurface microbial life, and conservative components that help elucidate the atmospheric evolution of the early Earth. Examples include fluids in the South African Kaapvaal craton which host chemolithoautotrophic microbial communities that survive independent of the photosphere, and billion-year-old fluids in the Canadian Shield, which preserve the Xe isotopic signature of an evolving early atmosphere. Stable isotope analyses of the aqueous phase combined with isotopic analyses of the dissolved noble gases provide unrivalled insight into the time-alteration history of aqueous fracture fluids. Here we report stable isotope and noble gas data for fracture fluids in the Witwatersrand Basin and Bushveld Igneous Province systems, South Africa. We determine closed-system radiogenic noble gas residence times of 0.77–97 million years (Myr). Open-system residence times range between 6.0 kyr and 10.8 Myr. One sample from Masimong Mine has a mean closed-system residence time of 85 Myr, making it one of oldest paleometeoric waters ever recorded. The δ2H and δ18O of water in this sample, and in previously reported samples from the same mining district that are shown to have similar ages, require an isotopically depleted source of groundwater recharge. This could reflect a recharge regime at a higher paleolatitude, elevation, or with higher rainfall, established up to tens of Myr ago, and perhaps similar to the recharge regime in the modern Lesotho Highlands. These data suggest that groundwater isotopes can provide useful paleoclimatic information for many Myr.
KW - Crustal fracture fluids
KW - Groundwater dating
KW - Noble gases
KW - Paleohydrogeology
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U2 - 10.1016/j.chemgeo.2018.06.011
DO - 10.1016/j.chemgeo.2018.06.011
M3 - Article
AN - SCOPUS:85048964636
SN - 0009-2541
VL - 493
SP - 379
EP - 395
JO - Chemical Geology
JF - Chemical Geology
ER -