GEOCHRONOLOGY AND GEOCHEMISTRY OF PALEOZOIC INTRUSIVE ROCKS IN THE ROCKVALE REGION, SOUTHERN NEW-ENGLAND OROGEN, NEW-SOUTH-WALES

Palaeozoic intrusive rocks of the New England Batholith from the Rockv ale district in the southern New England Orogen form three distinct as sociations: (i) the Carboniferous Rockvale Adamellite, a member of the Hillgrove Suite of deformed S-type granitoids; (ii) a small I-type ig neous complex on the northwestern margin of the Rockvale Adamellite: s everal members of this complex have similar chemical compositions to t he most mafic members of the Moonbi Suite of New England Batholith I-t ypes; and (iii) a suite of dyke rocks ranging in composition from calc -alkaline lamprophyre through homblende and biotite porphyrite to apli te. Ion-microprobe U-Pb zircon analysis indicates intrusion of the Roc kvale Adamellite at 303 +/- 3 Ma (weighted mean Pb-206/U-238 U-238 age ; 95% confidence limits). Preliminary investigation of zircon inherita nce within the Rockvale Adamellite is consistent with chemical and iso topic indications of derivation of New England Batholith S-type granit oids from a relatively juvenile protolith. Deformation of the Rockvale Adamellite occur-ed after complete crystallization of the pluton and prior to emplacement of dykes and 1-type intrusives. K-Ar biotite and homblende ages show broadly synchronous intrusion of I-type magmas and lamprophyre dykes at ca 255 Ma, indicating that mantle magmatism asso ciated with lamprophyres was contemporaneous with the crustal producti on of 1-type melts. Chemical similarities between the most mafic Moonb i Suite members and calc-alkaline lamprophyres may also indicate a dir ect mantle contribution to some 1-type magmas.