New data on the age and geographic distribution of Neoproterozoic plutons near Saint John, New Brunswick

New U-Pb zircon and titanite ages for four plutons from the Brookville and Mascarene blocks of the Saint John region suggest that the age distribution of Neoproterozoic intrusions in the Mascarene block resembles that in the Caledonia block, with older plutons emplaced at similar to 630-620 Ma (Brit tain Creek, 625 +/- 2 Ma, U-Pb zircon and titanite; Lingley, 629.3 +/- 0.9 Ma, U-Pb zircon), and younger plutons emplaced at about 550 Ma. Older pluto ns are more fractured and altered than younger ones, but not everywhere mor e strongly foliated. Within the Brookville block, the Hanson Stream pluton gives an age of 532 +/- 1/-3 Ma (U-Pb zircon), demonstrating that Ar-40/Ar- 39 ages as young as ca. 518 Ma from this pluton (Dallmeyer and Nance 1992) indicate postemplacement disturbance. The A-type Harvey Hill pluton, previo usly thought to be the youngest pluton in the Brookville block, gave a U-Pb zircon age of 544 +/- 4 Ma, similar to that of the geochemically similar B onnell Brook pluton of the Caledonia block Combined with presence of a dist inctive Cambro-Ordovician siliciclastic cover (Saint John Group), these dar es indicate that the Mascarene and Caledonia blocks originated in the same continental fragment. Western parts of the Brookville and Mascarene blocks were affected by a Cambrian thermal event (520-510 Ma), which may also be r epresented in the Caledonia block. Tectonic models based on these data sugg est that the Saint John region underwent repeated subduction in Neoproteroz oic time and diverse transcurrent movements from Silurian to Carboniferous time.