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ABSTRACT: Thermal history of Australian passive margin cover sequences accreted to Timor during Late Neogene arc-continent collision, Indonesia

Harris, Ron1, James Kaiser2, and Tony Hurford3
(1) Brigham Young University, Provo, UT 
(2) Exxon, Houston, TX 
(3) University College London, London, United Kingdom

Paleotemperature indicators, and apatite fission track analysis of Australian continental margin cover sequences accreted to the active Banda arc-continent collision, indicate little to no heating during rapid late Neogene uplift and exhumation. Thermal maturation patterns of vitrinite reflectance, conodont alteration and illite crystallinity show that peak paleotemperatures (PPT) increase with stratigraphic and structural burial. The highest PPT is found in the northern hinterland of the accretionary wedge. Major discontinuities in the pattern of PPT are associated with the position of major thrust ramps such as those forming the Ramelau/Kekneno Arch (RKA). PPT for upper Triassic to Neogene strata south of the RKA are 60 to 80 degrees C. Permian to lower Triassic sedimentary strata thrust over younger units near the RKA have PPT of 100 to 220 degrees C. Thrust sheets accreted beneath the upper plate have PPT approximately 90 degrees C higher than those frontally accreted. Thrust stacking yields an inverted thermal profile of PPT decreasing discontinuously downward and to the south (towards the foreland). Apatite fission track ages from mostly Triassic continental margin cover sequences yield ages mostly coeval with deposition and show little evidence of thermal annealing. In contrast, ages from Lower Triassic units are almost completely annealed and range from 1.8+0.5 Ma to 19.2+9.7 Ma. The clustering of apatite fission track ages into two distinct groups indicates that the upper boundary of the partial annealing zone has remained for some time at a Triassic stratigraphic interval in the slope and rise deposits of the NW Australian continental margin. These data preclude pre-Late Miocene tectonic burial or pre-Pliocene exhumation of the NW Australian continental margin.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia