TIBOOBURRA GRANODIORITE, WESTERN NEW-SOUTH-WALES - EMPLACEMENT HISTORY AND GEOCHEMISTRY

The Tibooburra Inlier, in the Thomson Fold Belt in northwestern New So uth Wales, forms a morphological dome-like structure, comprising a plu ton, the Tibooburra Granodiorite, enclosed by greenschist grade and lo cally hornfelsed metasediments, the Easter Monday beds, The inlier is surrounded by Mesozoic, Tertiary and Quaternary sedimentary rocks that unconformably overlie the Easter Monday beds. The inlier is part of t he Tibooburra Block, which is separated from the Milparinka Block by t he north-northwest-trending Warratta Fault. Structural investigation o f the Easter Monday beds revealed two deformational events. The princi pal deformation (D-1), represented by a northwest-trending S-1 fabric with horizontally plunging, upright to inclined, tight F-1 folds, was followed by a second event (D-2), characterised by F-2 folds, West-sou thwest-trending F-2 kink bands and brittle deformation. The Tibooburra Granodiorite comprises a main granodiorite pluton, dacite, aplite and pegmatite dykes, and shows brittle deformation of the same style as t hat in the Easter Monday beds. Structural relationships show that the granodiorite intruded the Easter Monday beds syntectonically late in D -1. The age of the granodiorite is around 410 Ma based on mineral Sr d ata. Geochemical and whole-rock Sr-isotopic investigations of the Tibo oburra Granodiorite revealed an I-type character for the parent magma. The initial Sr-87/Sr-86 ratios lie in the range 0.7050-0.7053 and are thus in good agreement with the geochemistry. It is suggested that th e Tibooburra Granodiorite was derived from a deep crustal, igneous sou rce, and has been emplaced in an intracontinental setting.