Figure 1
From: Chromitite layers indicate the existence of large, long-lived, and entirely molten magma chambers
A notable lack of textural evidence for gravity settling of chromite crystals within a UG1 chromitite of the Bushveld Igneous Complex, South Africa. (a) Location and generalized geological map of the Bushveld Complex emphasizing its enormous size. Note that this is just an erosional remnant of the complex so that its original size was even larger. The immense lateral extent of the chromitite layers (> 350–400 km) in this complex is illustrated here by the UG1 chromitite that occurs at the top of the Critical Zone. Also indicated are places from which the studied samples were obtained. The map is compiled from many open sources5,16,25,28,30,31,34 and is prepared using CorelDRAW (version 18.1.0.690). (b) Panoramic view of a few sublayers of the UG1 chromitite in the anorthosite footwall at the Dwars River, Eastern Limb. c, A close-up photograph of the top part of the UG1 chromite sublayer. Note large plagioclase oikocrysts enclosing numerous small crystals of cumulus chromite (chadacrysts). (d,e) Photographs of a thin-section (under plane polarized light) of the UG1 chromitite showing isolated chromite grains and their loose clusters enclosed by a single large oikocryst of plagioclase. Red arrows emphasize that chromite grains show no tendency to gravitate downwards despite a high porosity of the framework (~ 65 vol.%). Also note that most chromite crystals in (e) are touching each other along crystal faces. Sample HX-07–153.33, Mototolo mine, Eastern Limb.
