The geology, petrology and geochemistry of the Tommys Gap area in the Giles Creek Synform, MacDonnell Ranges, south-eastern Arunta Block, Northern Territory

Abstract

The study area is located within the Giles Creek Synform, approximately 80km east of Alice Springs. Basement rocks are the Tommys Gap Metamorphics which are a part of the Division 2 group of rocks of the Arunta Inlier. These have been intruded by the Atnarpa Igneous Complex and overlain unconformably by the Heavitree Quartzite and Bitter Springs Formation of the Amadeus Basin Sequence. The igneous rocks comprise of granite, tonalite, diorite and a coarse crystalline basic rock.

The main aim of the study was to determine the magma origin and fractionation history of the igneous rocks using petrographical and geochemical techniques. Data indicate that all the igneous rocks were formed by fractional crystallization, rather than the restite model of White and Chappell (1977), and have calc-alkaline affinities. Unfortunately, the lack of analyses makes it difficult to conclude whether they are a consanguineous suite or not.

Using the U/Pb isochron dating method, an age determination was performed on zircons from the tonalite and found to be 1863+/-31 Ma.