Australia: The Land Where Time Began |
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Western Gawler Craton, Australia – Shear Zone architecture in the
Christie Domain, Geophysical Appraisal of an Orogenic Terrain that is
Poorly Exposed
In the Christie Domain of the northwest
Gawler Craton,
southern Australia large-scale crustal shear zones of
Proterozoic age
are partially exposed from beneath cover sequences. These structures are
allowed to be mapped under cover and the evaluation of their 3-D
geometry and kinematics by their being associated with gravity and
magnetic anomalies. It is indicated by gravity and magnetic modelling
that these shear zones form an imbricate oblique thrust stack with a
combined-to-the southeast, left-lateral transport. The longest shear
zones in the stack penetrate to at least 15 km into the crust, dipping
to the northwest at 70o; their inferred sense of motion are
consistent with kinematic indicators from sparse outcrops. The stack
includes crustal slices that are bound by the Karari Fault Zone,
Tallacootra and Blowout Shear Zones, Colona and Coorabie Fault Zones and
the Muckanippie Shear Zone, from the northwest to the southeast.
Discrete tectonometamorphic packages are separated by these structures
within the Christie Gneiss, which was previously undifferentiated, of
the Mulgathing Complex of Archaean age, which implies several
generations of the transport of material from the lower crust to the
middle crust.
The Muckanippie Shear Zone, which is a second-order splay of the
Coorabie Fault Zone, as is indicated by 3-D inversion of gravity data,
has an antithetic dip to the southeast, and is part of a positive flower
structure.
When coupled with recent reconnaissance geochronology, cross-cutting
relationships suggest that the western Gawler Craton is part of the
Mawson Continent, was under an oblique slip deformational regime which
was long lasting, after about 1,590 Ma. This tectonic reworking
correlates with episodic pervasive metamorphism, and deformation that
has been recorded elsewhere in the Gawler Craton between about 1,550 and
1,450 Ma (Coorabie Orogeny), which points to a complex history of
stabilisation in Proterozoic Rodinia.
Mesozoic age rift faults of the Southern Rift System cut the
Tallacootra, Colona and Coorabie structures at high angle to their
strikes, and may form piercing points in reconstructions of
Gondwana, as
well as earlier Rodinia configurations.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |