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Synorogenic crustal fluid infiltration in the Idaho‐Montana Thrust Belt
Author(s) -
Bebout Gray E.,
Anastasio David J.,
Holl James E.
Publication year - 2001
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2001gl013711
Subject(s) - geology , subaerial , paleogene , cretaceous , calcite , meteoric water , geochemistry , sedimentary rock , carbonate , fold and thrust belt , metamorphic core complex , metamorphic rock , paleontology , hydrothermal circulation , tectonics , extensional definition , materials science , metallurgy , foreland basin
Mississippian carbonates in the Sevier thrust belt in Idaho‐Montana show shifts in δ 18 O V‐SMOW , from marine carbonate values to as low as +11‰, which are best explained by exchange with externally‐derived, low‐δ 18 O fluids. Late‐stage, synkinematic calcite veins are depleted in 18 O relative to the host‐rocks and earlier‐formed veins, many having δ 18 O of +5 to +10‰. These veins could have equilibrated with H 2 O with δ 18 O of −7.5 to +2.5‰, perhaps reflecting infiltration of the Sevier thrust wedge by nearshore meteoric waters to depths of ∼10 km. Calcite veins in the hangingwall and footwall of the Pioneer Metamorphic Core Complex, produced during later Paleogene extension, have δ 18 O of −8.7 to +1.4‰ consistent with equilibration with meteoric waters with δ 18 O as low as −14‰. Transition from a Cretaceous crustal fluid regime influenced by the nearby Western Interior Seaway to one influenced by lower‐δ 18 O, more inland meteoric waters is consistent with seaway retreat during thrust wedge emergence and Paleogene uplift and subaerial volcanism.