Deformation history of the Naraku Batholith, Mt Isa Inlier, Australia: implications for pluton ages and geometries from structural study of the Dipvale Granodiorite and Levian Granite

Plutons of the Naraku Batholith were emplaced into Proterozoic metasediment s of the northern portion of the Eastern Fold Belt of the Mt Isa inlier dur ing two intrusive episodes approximately 200 million years apart. Structura l relationships and geochronological data suggest that the older plutons (c a 1750 Ma) are contemporaneous with granites of the Wonga Batholith to the west. The Dipvale Granodiorite and the Levian Granite represent these older intrusive phases of the Naraku Batholith. and both contain an intense tect onic foliation, S-1. which is interpreted to have formed during the north-s outh shortening associated with D-1 of the isan Orogeny. The geometry of S1 form surfaces at the southern end of the Dipvale Granodiorite, and of the previously unrecognised sheeted contact, defines a macroscopic, steeply sou th-southwest-plunging antiform. which was produced by the regional D-2 Of t he Isan Orogeny. Si form surfaces in the Levian Granite define open F-2 fol ds With wavelengths of several hundred metres. The structural age of emplac ement of the Dipvale Granodiorite and the Levian Granite is interpreted to be pre- or syn- the regional Di. An intense foliation present in some of th e younger (ca 1505 Ma) granites that comprise the bulk of the Naraku Bathol ith is interpreted to represent S-3 of the Isan Orogeny. Foliations commonl y have similar styles and orientations in both the pre-D-1 and younger plut ons. This emphasises the simplicity with which regional fabrics can be, and probably have been, miscorrelated in the Eastern Fold Belt, and that the c lassification of granites in general on the basis of structural and geometr ic criteria alone is fraught with danger.