The stratigraphy of the central Pine Creek Geosyncline has been
simplified into a three-fold subdivision comprising the Batchelor, Frances
Creek and Finniss River Groups. The Batchelor Group consists of a
sequence of shallow water coarse clastics and crystalline carbonates and
is conformably overlain by the marine carbonaceous shale dominated
Frances Creek Group. Interbedded within the carbonaceous shale are
turbidites, iron formation, tuffs, carbonate and non carbonaceous shale.
The Finniss River Group is a flysch sequence of greywacke and
mudstone. The stratigraphic and structural evolution and igneous history are all
interrelated. Although the Batchelor Group may have formed in a
tensional regime, it is likely that regional compression and accompanying
thin skinned deformation began during deposition of the Frances Creek
Group. Continued compression resulted in D2 folding d6collement
deformation, wrench faulting in compressional zones and thrust faulting.
Occasional relaxation of compression is marked by a number of periods
of basic intrusion and perhaps distal volcanism. The style of deformation within sediments varies away from granitic
basement highs and is similar to that observed around salt domes and
found in experimental diapiric models. Sedimentary facies changes also
indicate local emergence of basement highs during sedimentation. As compression continued, the deposition of thick sequences of the
Finniss River and El Sherana Groups brought about regional
metamorphism. Relaxation of compression and waning of associated
subsidence resulted in a relative increase in the rate of uplift and partial
melting of diapiric sialic basement. In places, granitic magma moved
upwards and crystallised forming grossly concordant bodies. Other
masses moved laterally and formed extensive granitic sills. Later compression periods caused mainly brittle deformation which
may have been strongly influenced by underlying basement fabric.