Structure of the Deep Freeze Range–Eisenhower Range of the Wilson Terrane (North Victoria Land, Antarctica): emplacement of magmatic intrusions in the Early Palaeozoic deformed margin of the East Antarctic Craton
In North Victoria Land (Antarctica), the Wilson Terrane is a portion of the palaeomargin of the East Antarctic Craton, deformed during the Late Cambrian–Early Ordovician Ross Orogeny. Crustal deformation, from westward subduction of the palaeo Pacific plate and terrane accretion on this palaeomargin, gave rise to the development of a transpressive fold belt and a wide magmatic arc. In the inner portion of the Wilson Terrane, (Deep Freeze Range–Eisenhower Range) a large portion of this magmatic arc is made up of intrusions and dyke systems. Intrusive rocks range from large unfoliated plutons to well foliated sheet intrusions emplaced in low and medium–high grade metamorphic rocks respectively. Field and structural data on intrusive rocks and metamorphic host rocks, coupled with parameters relative to deformation mechanism and magmatic processes (crystallization and cooling) rates, make it possible to outline an episode of diffuse synkinematic magmatism in the Wilson Terrane. The emplacement of intrusions in both the middle and upper crust was coeval and related to the development of transpressional and transtensional structures along dextral strike-slip shear zones. Furthermore the development of foliated or unfoliated fabrics is related to competition between rates of deformation and magmatic processes, which is a function of the thermal state of the host rocks.(Received December 7 1998)
(Accepted December 1 1999)
Key Words: Antarctica; intrusive magmatism; North Victoria Land; Ross Orogen; transpressional tectonics.