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The Nature of Shear Zones Formed During Extension in Eastern Papua New Guinea


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Author Hill E J


Goodenough and Fergusson Islands, in eastern Papua
New Guinea, lie in an area of crustal extension on the
western end of the Woodlark Basin seafloor spreading
system. The islands are made up of a number of mountainous
domes of complexely deformed basement, and these are
intruded by large bodies of granodiorite. The domes are
bounded by curved shear zones and faults dipping outwards
at angles of around 25 to 45°. The cores of the domes contain
lower crustal rocks of eclogite and granulite facies, these
rocks have undergone retrograde metamorphism in the outer
sheared zones. Movement indicators on the shear zones
indicate a complex moverm.-It geometry which does not fit the
models proposed by earlier workers. These dome-like
structures are similar to the metamorphic core complexes of
the western United States Cordilleran region, however there
are a number of aspects which do not fit with the models
proposed for the development of metamorphic core
complexes. Uplift of the metamorphic basement probably
resulted from a combination of forces associated with the
extension of the crust and the intrusion and emplacement of
granodiorite plutons.