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Abstract

A new gravity survey combined with ground-based
magnetic surveys have enabled detailed modelling of
basement structures in the Longford Basin of northern
Tasmania. This basin began to form in the mid-Jurassic, but
contains only Cainozoic sediments. The models suggest that
the basin has been formed by a series of predominately
northwest-trending Jurassic normal faults which have
produced a series of half-grabens in which blocks were
downthrown to both east and west with dips of up to 10" W.
The basin blocks incorporate Palaeozoic to Mesozoic
Parmeener Supergroup sedimentary rocks intruded by preto
syn-fault Jurassic dolerites. These units overlie an older,
geophysically distinct, Devonian fold-thrust terrane. Much
of the tectonic activity from the Palaeozoic to the Cainozoic
appears to have been controlled by the Tiers Fault system, a
major gravity and magnetic lineament within the Tasmanian
crust.
In contrast to many other Tasmanian Mesozoic-Cainozoic
basins, the Longford Basin is exclusively continental, with
up to 800 m of Paleocene to Quaternary fluvial sediments
having been drilled in two wildcat oil wells.
The basin also contains intercalated Late Eocene to
Pliocene basaltic volcanic rocks. Magnetic data indicate
three eruptive centres localised in reactivated Jurassic
faults. Massive flows, now lateritised, have infilled an Early
Eocene to Pliocene drainage system.

Item Type:	Article
Authors/Creators:	Direen, NG and Leaman, DE
Keywords:	geophysical modelling; gravity surveys; magnetic surveys; tectonostratigraphy; Tasmania; basins; Mesozoic-Cainozoic
Journal or Publication Title:	Exploration Geophysics
ISSN:	0812-3985
DOI / ID Number:	https://doi.org/10.1071/EG997029
Additional Information:	© ASEG 1997
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