NEW APPROACHES TO LONG-STANDING PROBLEMS: EXAMPLES FROM THE NORTHERN APPALACHIANS

The basic framework of the Appalachian orogen and many details of its evolution are known from 200 years of mapping, but intractable questions remain at all scales. New analytical and imaging techniques will undoubtedly help, but so too can strategic application of tested methods to such local and regional problems as:

The most basic problem: not enough outcrop. Lobby for wind farm construction.

Formation ages and correlation: Much of northern New England is underlain by similar sandstone units of presumed Silurian through Early Devonian age – presumed because of the absence of fossils. However, primitive vascular plant remains found during a pilot study in the Fredericton trough suggest a new way to resolve long-standing debates.

Nature of lithotectonic boundaries: Regional seismic transects are prohibitively expensive but short reflection lines targeting specific problems can resolve some problems, particularly if coupled with detailed magnetic and gravity studies.

Existence of cryptic basement blocks: Geochemical studies of granitoids that sample local basement blocks have been instructive, but most focus on only one or two parameters. Distribution of rocks with similar isotopic, major and trace element, and age profiles can delimit the orogen’s basement blocks, reveal cryptic blocks not exposed at the surface, and identify areas where basement and surface rocks have been decoupled.

Relationships between basin fill and source regions: recent detrital zircon studies have clarified (or clouded) some problems, but combining age studies of detrital zircons and white micas can characterize individual basins for comparison with proposed source areas.