Abstract

The Yilgarn Block of Western Australia consists mainly of Archean granite-greenstone terrain with oval areas of granitoid rocks fringed by arcuate greenstone belts. In a typical part of this terrain the outcrop pattern is shown to result from large-scale dome-and-basin fold interference structures rather than diapiric emplacement of steep-sided batholiths.

The greenstones and underlying granitoid rocks were initially deformed together in a subhorizontal tectonic regime. As a result, the granitoid rocks recrystallized and a gneissosity developed subparallel to the stratigraphy of the greenstones. Thick subhorizontal monzogranite sheets were later emplaced into the lower part of the greenstone sequence. Subsequent deformation generated two successive sets of folds with vertical axial surfaces at a high angle to each other. These folds formed dome-and-basin interference structures ranging from a few centimetres to more than 50 km in diameter.

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