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| Titel: |
The nature and tectonic significance of the crustal-scale Koolyanobbing shear zone, Yilgarn Craton, Western Australia |
| Auteur: |
Libby, J. Groves, D. I. Vearncombe, J. R. |
| Verschenen in: |
Australian journal of earth sciences |
| Paginering: | Jaargang 38 (1991) nr. 2 pagina's 229-245 |
| Jaar: |
1991-05 |
| Inhoud: |
The Koolyanobbing shear zone is one of a number of northwest-trending, crustal-scale, ductile shear zones located in the Archaean granitoid-greenstone terrains of the Yilgarn Craton, Western Australia. It is between 6 and 15 km wide and based on aeromagnetic data, may be in excess of 650 km long. At Koolyanobbing, in the Southern Cross Province, the shear zone is defined by an approximately 6 km wide zone of mylonitic rocks, formed by intense deformation of banded monzogranite to tonalite. The shear zone comprises a series of alternating zones of foliated granitoid, protomylonite, mylonite and ultramylonite that indicate a progressive increase in strain towards the centre of the shear zone. Within granitoid gneiss, to the north of Koolyanobbing, high- and low-strain zones appear to be symmetrically disposed about the centre of the Koolyanobbing shear zone. However, a zone of high strain also occurs adjacent to the Koolyanobbing greenstone belt. Kinematic indicators (asymmetrical pressure shadows, S-C and C-C fabrics and mica fish), and a shallowly plunging mineral-elongation lineation, indicate that the main phase of movement along the Koolyanobbing shear zone was essentially sinistral transcurrent, consistent with a major phase of east-west compression. Contact relationships and timing of regional peak metamorphism indicate that the shear zone probably formed between 2.7 and 2.65 Ga. At Lake Johnston, 180 km south of Koolyanobbing, the shear zone is defined by a 10-15 km wide zone of strongly recrystallized, banded and mylonitic gneiss, and strongly foliated amphibolite, that separate two contrasting Archaean terranes. The movement sense of the shear zone is obscured both by recrystallization of deformation fabrics during amphibolite facies metamorphism and by syn-tectonic emplacement of granitoids. Towards the southeast, the increase in width and metamorphic grade along the shear zone suggests a partial section through progressively deeper Archaean crustal levels. Despite its width and transcraton length, the Koolyanobbing shear zone does not appear to separate two major allochthonous blocks. |
| Uitgever: |
Taylor & Francis |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
Details van artikel 9 van 9 gevonden artikelen
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