Thermochronological and petroleum generation studies next to dikes in the upper Jurassic-lower Cretaceous Strzelecki Group, Onshore Gippsland Basin, Australia

Conference · Tue Dec 31 04:00:00 EST 1996

OSTI ID:425407

Barker, C E; Lewan, M D ^[1]; Bone, Y ^[2]

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1. Geological Survey, Denver, CO (United States)
2. Univ. of Adelaide, Adelaide (Australia); and others

Fluid inclusion, apatite fission track analysis (AFTA{reg_sign}) annealing, mean random vitrinite reflectance (Rv-r) data and heat flow modeling studies of nine basalt dikes ranging from 0.06 m to 40 in thick in the Strzelecki Group were used to constrain the conditions of contact metamorphism of coaly sedimentary organic matter (SOM) to investigate it as an extended-duration natural analog to hydrous pyrolysis experiments. Thermal history reconstruction suggests that at the time of dike intrusion the host rock was at a paleotemperature of 100 to 120{degrees}C. Reequilibrated fluid inclusions in the host rocks next to thin dikes (< 3.4 m thick) suggest maximum temperature (T{sub peak}) systematically increases towards the dike margin to around 550{degrees}C. These T{sub peak} data are in fair agreement with those predicted by a conductive heat flow model and measured Rv-r. AFTA indicates the time of uplift and cooling as mid to Late Cretaceous and that paleotemperatures were too high for heating duration information to be recorded by annealing of tracks in apatite near the dikes. The estimated T{sub peak} next to some larger dikes (20 to 40 m thick) as indicated by an extended zone of elevated Rv-r did not fit the pattern seen next to the thin dikes. Heat flow modeling along with whole rock elemental and isotopic data suggest that the extended zone of increased Rv-r is caused by convection of heated fluids. This is in contrast to the apparent advection effects found adjacent to thin dikes. Laboratory hydrous pyrolysis compares well with contact metamorphism next to thin dikes with respect to the composition of the free hydrocarbons except in samples very close to the dike. Close to the dike, fluid inclusion evidence indicates a water vapor or super-critical phase in the rock making the organic geochemistry results diverge from.

• OSTI ID: 425407
• Report Number(s): CONF-960527--
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
58 GEOSCIENCES
CRETACEOUS PERIOD
JURASSIC PERIOD
MATURATION
ORGANIC MATTER
ORIGIN
PETROGENESIS
PETROLEUM
SEDIMENTARY BASINS