Ld. Abbott, NEOGENE TECTONIC RECONSTRUCTION OF THE ADELBERT-FINISTERRE-NEW BRITAIN COLLISION, NORTHERN PAPUA-NEW-GUINEA, Journal of Southeast Asian earth sciences, 11(1), 1995, pp. 33-51
The Finisterre terrane is presently colliding with the Australian cont
inent in northern Papua New Guinea. The terrane is exposed in two dist
inct blocks - the Adelbert block and the Finisterre block. A elastic s
edimentary sequence in the suture zone provides constraints on the age
of initial collision for each block and on paleotectonic reconstructi
ons of New Guinea. Provenance shifts within the Finisterre block sedim
entary section date the collision of that block at 3.0-3.7Ma. Analysis
of the Adelbert block sedimentary section has not revealed similar pr
ovenance shifts. This absence of temporal trends in source area may be
caused by oblique collision of the Adelbert block with an allochthono
us terrane composed of oceanic crust. These factors would likely lead
to a ''soft'' collision involving little uplift and hence little disru
ption of the pre-collisional sedimentation patterns. In contrast, the
Finisterre block collided orthogonally with terranes composed of conti
nental crust. This ''hard'' collision has led to rapid uplift and sign
ificant modification of the pre-collisional depositional system. A dee
p water basin existed between the Adelbert block and the continent in
the Late Pliocene. Deep marine sediments deposited in this basin were
subsequently overthrust by older lithologies of the Adelbert block. Wh
en combined with geochemical, seismic and plate kinematic data publish
ed by other workers, these data suggest collision of the eastern porti
on of the Adelbert block in the Middle to Late Pliocene. The western p
ortion of the Adelbert block probably collided in the latest Miocene.
Many tectonic reconstructions of northern Papua New Guinea have favore
d collision of the Finisterre terrane over a doubly-subducting Solomon
Sea Plate in an extension of the modern tectonic configuration of the
Solomon Sea. The presence of continentally-derived sediment in the Fi
nisterre accretionary wedge casts doubt on this scenario. The trench o
f a southward-dipping subduction zone would be likely to block contine
ntally-derived sediment from reaching the Finisterre accretionary wedg
e. The Maramuni Are, the igneous association usually attributed to the
hypothesized southward-dipping subduction zone, appears to have erupt
ed on allochthonous terranes rather than on autochthonous crust. These
observations suggest that collision of the Adelbert block and most of
the Finisterre block occurred above a single, northward-dipping subdu
ction zone. The double subduction present in the Solomon Sea probably
never extended more than 200 km west of its present location.