Structural evolution of the Western Papuan Fold Belt , Papua New Guinea
File(s)
Author(s)
Mason, Russell A.
Type
Thesis
Abstract
New Guinea forms the northern margin of the Australian Plate which is now
characterised by a zone crustal deformation and accreted terranes. The present day
configuration is the result of global tectonics in the southwestern Pacific since the
Triassic. The Papuan Fold Belt is located within Papua New Guinea, the eastern half of
New Guinea, and comprises deformed basement, platformal and basinal Mesozoic and
Tertiary sediments. Deformation within the fold belt commenced possibly as early as
Middle to Late Miocene and is currently continuing.
The structure of the western part of the Papuan Fold Belt is characterised by thin skinned
thrusting and basement involved structures, the latter attributed to inversion of
extensional faults active in the Tertiary and the Mesozoic. Inversion is thought to have
post-dated the initiation of thin skinned thrusting by approximately 5 Ma. Continued
basement shortening may be due to the current high convergence rate between the
Australian and Pacific Plates.
The Alice Anticline formed due to inversion of a Tertiary extensional fault system.
Three-dimensional restoration of the Alice Anticline makes use of a series of balanced
cross-sections and is based on a line length method. Paradoxically, this restoration
reveals non-plane strain in the balanced cross-sections upon which it relies. However, the
restoration also reveals and quantifies a component of rotation about vertical axes which
would not be obvious by application of conventional methods of structural analysis. Two
transfer zones associated with the original extensional geometry acted as obstructions to
deformation and have effectively pinned contractional structures during their formation
causing the rotations about vertical axes.
A general fracture system is developed in rocks in the Alice Anticline area. This typically
comprises two sets of conjugate shear fractures and a third set, interpreted as extensional,
which is sub-nonnal to the acute bisector of the two conjugate sets. Unfolding of bedding
using the three-dimensional restoration results in a symmetrical geometric relationship
between the general fracture system and folds. The mechanical interpretation of
fractures, their geometric relationships and the timing constraints on their formation are
consistent with folding.
The structure of the Ok Tedi mine area is complicated by the presence of approximately
syn-tectonic intrusive bodies. The development of the Parrots Beak and Taranaki Thrusts
as floor and roof thrusts respectively constitutes shortening estimates in the mine area which are consistent with those determined regionally. Striation analysis of rnesoscale faults from country rocks in the mine area reveals a reduced stress tensor compatible with
the regional shortening direction. Reduced stress tensors determined for the Fubilan
Monzonite Porphyry are related to emplacement processes and would be consistent with development of radial and concentric fracture sets.
characterised by a zone crustal deformation and accreted terranes. The present day
configuration is the result of global tectonics in the southwestern Pacific since the
Triassic. The Papuan Fold Belt is located within Papua New Guinea, the eastern half of
New Guinea, and comprises deformed basement, platformal and basinal Mesozoic and
Tertiary sediments. Deformation within the fold belt commenced possibly as early as
Middle to Late Miocene and is currently continuing.
The structure of the western part of the Papuan Fold Belt is characterised by thin skinned
thrusting and basement involved structures, the latter attributed to inversion of
extensional faults active in the Tertiary and the Mesozoic. Inversion is thought to have
post-dated the initiation of thin skinned thrusting by approximately 5 Ma. Continued
basement shortening may be due to the current high convergence rate between the
Australian and Pacific Plates.
The Alice Anticline formed due to inversion of a Tertiary extensional fault system.
Three-dimensional restoration of the Alice Anticline makes use of a series of balanced
cross-sections and is based on a line length method. Paradoxically, this restoration
reveals non-plane strain in the balanced cross-sections upon which it relies. However, the
restoration also reveals and quantifies a component of rotation about vertical axes which
would not be obvious by application of conventional methods of structural analysis. Two
transfer zones associated with the original extensional geometry acted as obstructions to
deformation and have effectively pinned contractional structures during their formation
causing the rotations about vertical axes.
A general fracture system is developed in rocks in the Alice Anticline area. This typically
comprises two sets of conjugate shear fractures and a third set, interpreted as extensional,
which is sub-nonnal to the acute bisector of the two conjugate sets. Unfolding of bedding
using the three-dimensional restoration results in a symmetrical geometric relationship
between the general fracture system and folds. The mechanical interpretation of
fractures, their geometric relationships and the timing constraints on their formation are
consistent with folding.
The structure of the Ok Tedi mine area is complicated by the presence of approximately
syn-tectonic intrusive bodies. The development of the Parrots Beak and Taranaki Thrusts
as floor and roof thrusts respectively constitutes shortening estimates in the mine area which are consistent with those determined regionally. Striation analysis of rnesoscale faults from country rocks in the mine area reveals a reduced stress tensor compatible with
the regional shortening direction. Reduced stress tensors determined for the Fubilan
Monzonite Porphyry are related to emplacement processes and would be consistent with development of radial and concentric fracture sets.
Version
Open Access
Date Issued
2006
Date Awarded
2006
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Coward, Mike
Sponsor
Ok Tedi Mining
Publisher Department
Geology
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)
Author Permission
Permission granted