Three phases of cooling and unroofing in the Appalachian Basin, Pennsylvania: Implications for flexural control

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5809995

Blackmer, G C; Gold, D P ^[1]; Omar, G I ^[2]

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1. Pennsylvania State Univ., University Park, PA (United States). Dept. of Geosciences
2. Univ. of Pennsylvania, Philadelphia, PA (United States). Geology Dept.

Apatite fission-track ages of 111--184 Ma and mean lengths of 10.7--13.1 [mu]m with unimodal, negatively skewed length distributions indicate slow cooling of Ordovician through Permian rocks in an area extending from the Anthracite Basin to the western Appalachian Plateau. Cooling histories modeled from fission-track data show that cooling began immediately following the Alleghanian Orogeny at 250--240 Ma. Ordovician rocks in the Juniata Culmination began to cool slightly earlier at 265 Ma, probably reflecting synorogenic unroofing of this area during formation of the Valley and Ridge duplex. Unroofing histories were modeled from cooling histories using the one-dimensional heat flow equation. Cooling and unroofing histories can be divided into three periods. The initial period of relatively rapid cooling and unroofing extended from the end of the Alleghanian Orogeny into the Jurassic and represents post-orogenic unroofing due to flexural rebound as orogenic load was removed through erosion. Initial unroofing rates are higher in eater Pennsylvania than in the west, consistent with a flexural model. A period of little to no unroofing from the Jurassic into the Miocene began contemporaneously with the inception of drift at the Atlantic continental margin. As the new continental margin subsided, the remaining load dropped below sea level and was no longer subject to removal, resulting in the cessation of flexural rebound and suppression of unroofing in the foreland. The most rapid unroofing occurred from the Miocene to the present. The nature of this event is unknown; however, it is also observed in increased sedimentation rates in the middle Atlantic offshore basins.

• OSTI ID: 5809995
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
APATITES
APPALACHIAN BASIN
COOLING
DEVELOPED COUNTRIES
EROSION
FISSION TRACKS
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
MINERALS
NORTH AMERICA
OROGENESIS
PARTICLE TRACKS
PENNSYLVANIA
PHOSPHATE MINERALS
SEDIMENTARY BASINS
USA