Paleostress Analysis of Atlantic Crustal Extension in the Quebec Appalachians

A paleostress analysis using normal fault slip data and Jurassic dike trends has been conducted in the Quebec and New England Appalachians. Stress tensor analysis of fault slip by a numerical inversion method has distinguished homogeneous and directionally consistent E‐W‐ and NW‐SE‐oriented extensional stress regimes in the Quebec Appalachians and St. Lawrence Lowlands. The directions of extension compare well with the mean direction of extensional stress inferred from the Jurassic dolerite dike trend in New England. Both extensions are interpreted as the result of rift‐related stress associated with the separation of North America and Africa, early in the Late Triassic–Early Jurassic fragmentation of Pangea. The paleostress field configuration is assumed to be related to the direction of divergent plate motion. The N‐S and NE‐SW Late Proterozoic faults that bordered the Quebec Reentrant and Taconian‐Acadian structures of the Quebec Appalachians appear to have played a significant role in the distribution of later stress regimes in the upper part of the lithosphere. The NNE‐SSW‐trending regional and mesoscopic normal faults in southern Quebec are interpreted as linked to the formation of Mesozoic rift basins in Massachusetts and Connecticut and synchronous with Early and Middle Jurassic dike emplacement in the Quebec and New England Appalachians.