Orbicular Granite, Youanmi Terrane
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This site records the orbicular granite from Boogardie quarry 35 km west of Mount Magnet in Western Australia. More about it can be found at: http://www.nationalrockgarden.org.au/rock-collection-2/rock-listing/show/11 . Here, I record some interesting features: a) how some of the orbicles have an amphibolite clast in its core, b) how some orbicles impinge and mould into one another, c) how some of them are broken up by other orbicles, and d) most importantly, how they seem to be associated with a bimodal, composite dykes comprised of a felsic rim and a mafic core.
 Orbicular granite cut by a composite dyke with pegmatite margins and mafic fine-grained. |
 Orbicular granite cut by a co-magmatic intrusion of granite and fine-grained diorite. |
 Orbicular granite. |
 Orbicles with amphibolite fragment in the core. Many have these fragments but the majority does not. |
 Orbicles with amphibolite fragment in the core. Note one of them has a fractured rim intruded by magma. |
 Broken up orbicle in the centre of the photo. Note a truncated half an orbicle in the lower right, as if broken up. |
 Orbicular granite intruded by pegmatite. Notice two orbicles impinging on to each other. |
 Broken up orbicle. |
Co-magmatic granitic rock and fine-grained darker diorite(?). The granitic layer has one orbicle. The relationship between the mafic and felsic magma is similar to that of the first photograph, but there the co-magmatic intrusion cut across the orbicular granite. |