The Ebor Volcano in
north eastern New South Wales is an eroded example of a central-type intraplate volcanic-intrusive
complex. It is of Miocene age (19 - 20 Ma) and has
similarities to other central-type volcanoes in eastern Australia which
may
represent manifestations of
sub-lithospheric hotspot activity. Thick lava flows are exposed around
the Great Escarpment and are dominated by a tholeiitic basaltic suite, ranging
from ol-tholeiite to qz-tholeiite to icelandite with ages of 19.2 -
19.6 Ma. On its western edge, the tholeiitic lava suite probably overlies
remnants
of
basanite flows belonging to the Eocene (~48 Ma) Doughboy province, but
elsewhere, minor alkaline basaltic lavas may be coeval with the tholeiitic
suite. Several felsic bodies were emplaced into the volcano at ~19.0 -
19.2 Ma and include subalkaline and peralkaline types. The Crescent
Complex is a Miocene-age, strongly differentiated mafic to felsic intrusion in
basement rocks and centrally located in pre-erosion reconstructions of
the
Ebor Volcano.
It is interpreted to be a major feeder for the tholeiitic lavas based on age and
composition. Evolution of the dominant
tholeiitic suite proceeded from a parental ol-tholeiite
magma, through
qz-tholeiite, icelandite and small volumes of felsic rocks by fractionation of
plagioclase, olivine, clinopyroxene and titanomagnetite, accompanied by
enrichmentof
SiO2, FeOlMgO,
alkalies and
HFSE.