Facies associations in the
Okiduse Volcanics, woodlark island,
suggest that two major volcanic centres
erupted synchronously during the Middle
Miocene. These centres are referred to
as the Watou Mountain Eruptive Centre
and the Uvarakoi Caldera. The Watou
Mountain Eruptive Centre, centred on
Boganuse Mountain in the Okiduse Range,
was a typical, moderate-sized composite
volcano (or stratovolcano). The seq-
uence is readily divisible into lava
(Boganuse lava unit), breccia (Nikuben
breccia unit) and epiclastic (Talpas
sandstone unit) dominant facies,
typical of composite volcanoes. These
facies girdle Boganuse Mountain and
they are interpreted to represent vent,
cone forming and ring plain associat-
ions, respectively. These facies
indicate a reconstructed volcano of
approximately 1,700m height with a
basal diameter of 7km. The presence of
limited exposures of intrusive
associated with the vent facies
(Kuike'beimmicrodiorite) suggests that
the volcano is only partially
dissected. The Uvarakoi Caldera is a
felsic volcanic system contrasting with
the mafic Watou Mountain centre.