AVALONIA'S FOUNDATION? PRELIMINARY PALEOMAGNETISM AND U-PB ZIRCON GEOCHRONOLOGY OF THE MID-NEOPROTEROZOIC BURIN GROUP, NEWFOUNDLAND

Submarine volcanic, sedimentary and intrusive rocks of the Burin Group are exposed in the southeastern Burin Peninsula, Newfoundland. On the basis of a single published U-Pb zircon age of 763 +/- 2 Ma on a gabbro sill (Wandsworth), the Burin Group is thought to be of mid-Neoproterozoic age and may therefore represent a remnant of the earliest history of Avalonia. This study reports further defines the Burin Group's tectonic setting, age, and possible paleogeographic relationships. The volcanic and intrusive rocks are confirmed to have a mafic island arc affinity. Reconnaissance paleomagnetic sampling of gabbro, dacite, pillow basalts and mafic dykes in twelve sites yields stable but not necessarily primary remanence in nine. At Epworth, located 8 km to the SW along strike from the published Neoproterozoic locality, moderately SW-dipping mafic dykes intrude gabbro which has a preliminary U-Pb zircon age of 764.5 +/- 2.1 Ma, confirming the occurrence of mid-Neoproterozoic magmatism throughout the Burin Group. A positive baked contact test of two dykes at this locality indicates that their remanence is primary. Upon simple tilt-correction to vertical the dykes have a SE and up remanence; the gabbro host, an E and down remanence. At the Burin locality, pillow basalts and interbedded SW-dipping marine sediments are cut by numerous NW-dipping dykes. The basalts and feeder dykes at Burin suffer from a strong steep down overprint, but at one site a characteristic direction is recovered which becomes SE and up after tilt correction. Taken together, the three reporting dyke sites at Epworth and Burin give a preliminary paleolatitude for the Burin Group of 29 degrees, but as yet have an unknown age. The ca. 764 Ma gabbro at Epworth gives a paleolatitude of 22 degrees, provided the tilt correction of the dykes is correct and appropriate. The low paleolatitudes in both cases are consistent with the low paleolatitudes found for Avalonia from mid- to Late Neoproterozoic time.