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- AFTA thermal history solutions (solid path) for Grant Fm sample
GC35-1. The red fields show the AFTA-derived time temperature
constraints.
- Cooling from maximum palaeotemperatures of 105-125°C beginning
some time in the Late Triassic to Early Cretaceous (230-180 Ma).
With cooling from a lower peak in palaeotemperatures of 75 to
95°C beginning at some time in the Early Cretaceous to Early
Tertiary (130 to 60 Ma).
- The dashed path shows the Default Thermal History for this sample.
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- Reconstructed thermal history for White Hills-1 using a constant
palaeogeothermal gradient of 31°C/km and palaeo-surface temperature
of 20°C for the entire history, as derived from the AFTA and
VR results.
- The history illustrated (solid lines) shows a heating period
following each of two most recent thermal episodes, this is not
constrained by AFTA, and a range alternative histories with less
heating are also possible, limited by the dashed paths.
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- This figure shows variation of maturity with time for White
Hills-1 derived from the reconstructed thermal history illustrated
in the above Figure.
- The grey columns represent the three thermal episodes revealed
by AFTA. The figure shows cessation of active source rock maturation
in the entire drilled section at 200 Ma (230-180 Ma allowed by
AFTA) due to cooling as a response to kilometre-scale uplift and
erosion attributed to the Fitzroy Movement. The recognition that
heat flow during this tectonic event was not elevated is consistent
with this event being associated with a major strike-slip structural
event.
- Early Cretaceous and Tertiary thermal episodes have no effect
on the source rock maturation history, as palaeotemperatures during
these episodes were less than those during the Late Triassic-Early
Jurassic.
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