Quantitative Modeling of Thermal History at Extensional Terrains Involving Lithospheric Detachments--Constraints from Apatite Fission Track Analysis (AFTA)

Kerry A. Hegarty, Andrew J. W. Gleadow, Paul F. Green, Ian R. Duddy

Models of major detachment faults (or zones) penetrating the entire continental lithosphere have proven remarkably successful in accounting for the often complex structure across several conjugate passive margins and across extending continental terrains. Inherent in lithospheric-detachment-fault (LDF) models is a complementary asymmetry in the structural evolution at margin pairs during and following active extension. LDF models also require that opposing margins exhibit complementary asymmetry in their heating history. Our modeling shows that significantly different thermal histories on opposing margins will be recorded by fission tracks in grains of apatite within basement rocks and overlying sediments. Apatite Fission Track Analysis provides constraints on the magnitu e and timing of the thermal perturbation related to extension and also on the geometry of the detachment fault.

Using quantified LDF models which include instantaneous rifting and planar low-angle detachment faulting, we show that fission track parameters (age and length) are a sensitive indicator of upper and lower plate behavior. Examples from Australia's Southeast Highlands, southern margin, and Antarctica are consistent with LDF models.

Model results show that relatively hotter and uplifted upper-plate terrains are characterized by significantly lower apparent fission track ages and different length distributions than their lower plate counterpart. In addition, fission track parameters can be used to assess the maturation history and hydrocarbon potential in sedimented regions of upper and lower plate terrain pairs.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.