Harts Range, Central Australia: the brain and diapirism

The brain (top half of the image): a circular body in Central Australia (the Entia Dome, see Buick, I. 1988, Ph.D. Thesis, Mawby, J., Ph.D. thesis, Adelaide University), comprised of Palaeoproterozoic granite and sedimentary rocks showing an internal flow geometry akin to the pattern of internal convection similar to those in ascending spherical diapirs as Cruden, Schmeling and Weinberg showed in the early 90s. Notice also the presence of a granitic tail in the SW quadrant, and how the country rocks turn norhwards (upwards?) on either side of the tail. Notice also how dark rocks (Ordovician basalts) seem to wrap around the dome. Metamorphism reached amphibolite facies (Arnold, J., Sandiford, M., Wetherly, S., 1995, Metamorphic events in the Eastern Arunta Inlier, Part 1. Metamorphic petrology, Precambrian Research, 71, 183-205). Scale: the dome is approximately 30 km wide on its widest E-W section.

Interpretation: this is a potential example of internal circulation in a diapiric body of granite+sediment, rising obliquely to the NE through a denser carapace of basalts, leaving its pathway behind. The age difference between the older granite and younger basalt carapace suggests that diapirism took place in the solid state. Rock dating can be found in Hand, Mawby, Kinny, Foden, J. 1999. SHRIMP evidence for multiple high-T Palaeozoic events in the Arunta Inlier, central Australia. Geological Society of London Journal, 156, 715-730.