A Geological Interpretation of the Regional Gravity and Magnetic Features of North Queensland

Abstract

Using gravity and magnetic anomalies, I infer a regional geological framework for north Queensland. In the west are two almost-collinear, north-striking Proterozoic crustal rifts, each about 700 km long and 100 to 250 km wide, but with different geophysical anomaly patterns. The Mount Isa Geophysical Domain is the southern rift. These rifts are thought to be younger than most adjacent crust. To the east of these rifts the Proterozoic crust is of two types, magnetic and non-magnetic. Non-magnetic crust has lower amplitude magnetic anomalies at both short (< 3 km) and long wavelength. Basement of this type crops out only in the Croydon area. Magnetic crust is generally to the east, adjacent to the margin of the exposed Proterozoic crust, and it is extensively exposed in inliers. The magnetic and nonmagnetic Proterozoic crust originally had the same magnetization. Proterozoic and Palaeozoic thermal events/deformation subsequently magnetized the margin of the Proterozoic crust. The Palaeozoic crust along the southern margin of north Queensland can be subdivided into geophysical domains. The margins of these geophysical domains have similar geophysical anomalies to the margin of the Proterozoic crust to the north.