Late Permian age of ammonium-bearing illite in Pennsylvania anthracites: Temporal constraints on coalification in the central Appalachians
- Chevron Petroleum Technology Co., La Habra, CA (United States)
K/Ar dating of authigenic NH4-bearing illite in coal from the Anthracite region of eastern Pennsylvania yields apparent ages of 253-236 Ma ({+-}8 m.y.). The oldest K/Ar date of 253 Ma ({+-}8 m.y.) is a minimum age for the thermal event associated with anthracite formation and illite authigenesis. This date is probably within {approx}10 m.y. of the time at which coal-bearing rocks experienced peak temperatures, which suggests an age range of 265-255 Ma for this event. Age dates for authigenic NH{sub 4}-bearing illite reflect the approximate age of late-stage coalification (formation of anthracite-rank coal) because this mineral formed only during late-stage coalification (T=200-275{degrees}C) from a kaolinite (potassium-free) precursor, and the K/Ar data suggest that NH{sub 4} does not significantly influence the closure temperature of illite. K/Ar dates, in conjunction with paleomagnetic and vitrinite reflectance data, constrain the thermal pulse and deformation associated with the Alleghanian orogenic episode to a time period of 25-35 m.y., beginning in Early Permian time ({approx}285 Ma) after coal deposition, and concluding by Late Permian time ({approx}260-250 Ma). Syn- and post-folding secondary chemical remanent magnetizations constrain Alleghanian folding in the Central Appalachians to Late Permian time, which coincides with the postulated time range of 265-255 Ma for NH{sub 4}-bearing illite authigenesis and anthracite formation derived from the K/Ar data. The similar time range for anthracite formation and Alleghanian folding is consistent with vitrinite reflectance data that suggests anthracite formation was a syn-folding thermal event.
- OSTI ID:
- 425499
- Report Number(s):
- CONF-960527-; TRN: 96:004994-0132
- Resource Relation:
- Conference: Annual convention of the American Association of Petroleum Geologists, Inc. and the Society for Sedimentary Geology: global exploration and geotechnology, San Diego, CA (United States), 19-22 May 1996; Other Information: PBD: 1996; Related Information: Is Part Of 1996 AAPG annual convention. Volume 5; PB: 231 p.
- Country of Publication:
- United States
- Language:
- English
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