TY - JOUR
T1 - Noble gases in Paleozoic shale fluids document tectonic events and fluid migration in the Upper Yangtze Block
AU - Liu, Rui
AU - Wen, Tao
AU - Pinti, Daniele L.
AU - Xu, Rui
AU - Hao, Fang
AU - Xu, Shang
AU - Shu, Zhiguo
N1 - Publisher Copyright:
© 2024 Elsevier B.V.
PY - 2025/1/13
Y1 - 2025/1/13
N2 - Major and noble gases of natural gas extracted from the low-permeability Paleozoic Wufeng-Longmaxi shale were measured to reconstruct the multi-stage, spatially varying tectonic evolution of the Upper Yangtze Block, China, one of the oldest parts of the Earth continents. The high gas dryness ratio [C1/(C2 + C3)] and high carbon isotopic ratios (δ13C-C1, δ13C-C2, δ13C-CO2) suggest a late mature thermogenic origin of shale gas. The highly fractionated atmospheric 20Ne/36Ar and 84Kr/36Ar ratios in our gas samples suggest they result from solubility-based partitioning of noble gases between oil and water followed by gas-water partitioning. Calculated volume ratios of oil, water, and gas phases vary spatially and temporally. In particular, the western Yangtze Block shows a lower reconstructed oil/water ratio, suggesting oil leakage promoted by the Triassic exhumation of Paleozoic shale, while a low gas/water ratio in the central-eastern Yangtze Block suggests gas leakage promoted by basin-wide Jurassic fold-thrust faulting. The lowest C1/36Ar volume ratio around faults at the basin edges indicates extensive gas expulsion. Delineated radiogenic 4He in gas samples are several orders lower than calculated in-situ produced radiogenic 4He, likely suggesting widespread 4He loss. Spatially-varying 4He/nucleogenic 21Ne ratios in the shale indicated that 4He loss in the western Yangtze Block predated that in the central-eastern portion. Such He loss was also coupled with the Triassic exhumation and the Jurassic fold-thrust faulting episodes. In summary, noble gas in pore fluids extracted from low-permeability shale can preserve reliable records of tectonic events produced during upper crust evolution.
AB - Major and noble gases of natural gas extracted from the low-permeability Paleozoic Wufeng-Longmaxi shale were measured to reconstruct the multi-stage, spatially varying tectonic evolution of the Upper Yangtze Block, China, one of the oldest parts of the Earth continents. The high gas dryness ratio [C1/(C2 + C3)] and high carbon isotopic ratios (δ13C-C1, δ13C-C2, δ13C-CO2) suggest a late mature thermogenic origin of shale gas. The highly fractionated atmospheric 20Ne/36Ar and 84Kr/36Ar ratios in our gas samples suggest they result from solubility-based partitioning of noble gases between oil and water followed by gas-water partitioning. Calculated volume ratios of oil, water, and gas phases vary spatially and temporally. In particular, the western Yangtze Block shows a lower reconstructed oil/water ratio, suggesting oil leakage promoted by the Triassic exhumation of Paleozoic shale, while a low gas/water ratio in the central-eastern Yangtze Block suggests gas leakage promoted by basin-wide Jurassic fold-thrust faulting. The lowest C1/36Ar volume ratio around faults at the basin edges indicates extensive gas expulsion. Delineated radiogenic 4He in gas samples are several orders lower than calculated in-situ produced radiogenic 4He, likely suggesting widespread 4He loss. Spatially-varying 4He/nucleogenic 21Ne ratios in the shale indicated that 4He loss in the western Yangtze Block predated that in the central-eastern portion. Such He loss was also coupled with the Triassic exhumation and the Jurassic fold-thrust faulting episodes. In summary, noble gas in pore fluids extracted from low-permeability shale can preserve reliable records of tectonic events produced during upper crust evolution.
KW - Fluid expulsion
KW - Noble gases
KW - Pore fluids
KW - Shale
KW - Tectonic deformation
KW - Yangtze Block
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U2 - 10.1016/j.coal.2024.104671
DO - 10.1016/j.coal.2024.104671
M3 - Article
AN - SCOPUS:85212538607
SN - 0166-5162
VL - 297
JO - International Journal of Coal Geology
JF - International Journal of Coal Geology
M1 - 104671
ER -