Flow directions of Carboniferous ignimbrites, southern New England Orogen, Australia, using anisotropy of magnetic susceptibility

Abstract

Anisotropy of magnetic susceptibility (AMS) is used to define regional flow patterns and to locate possible source vents of Carboniferous ignimbrites in the Rocky Creek region, northern Tamworth belt, southern New England Orogen. The major axes of AMS fabrics from 115 sites are oriented in mainly eastward or northeastward directions, and the fabrics can be classified into three groups: normal, inverse, and intermediate. Comparisons between flow directions indicated by AMS fabrics and the alignment of feldspar laths in oriented thin sections from major ignimbrite units indicate a moderate to good level of agreement. The contoured intersections of flow lineations indicate a number of possible source regions, such as paleo-valleys, which controlled the dispersal of particular flows. When all trends from contoured intersections of flow lineations are combined, two major trends emerge, NE–SW and E–W. These trends converge within an area approximately 20 km west of the Mooki Thrust at the overthrust margin of the orogen. This convergent area is proposed as a possible major volcanic source region that may have existed during the late Carboniferous. Because of westward overthrusting, with a magnitude greater than 20 km, during the Late Permian to Early Triassic, this region is now probably located beneath Carboniferous forearc basin rocks of the Tamworth Belt.