Abstract

The Meguma Zone is a very large block that is foreign to ancient North America. Paleoenvironments shoal upward from Cambro-Ordovician deep sea fans, through glaciomarine tillite to Silurian and Early Devonian paralic settings. The zone is a segment of an embankment of a continent that in the Early Mesozoic drifted to the southeast. Three candidates for this source-continent are discussed in this paper.

The Avalon microcontinent is in fault-contact with the Meguma Zone, and extends to the southwest into the Southern Appalachians, and to the northeast into Western Europe (Southern Britain, France and Iberia). The Avalon and Meguma Zones evolved in different areas, as indicated by sediment compositions, dispersal, environment, paleontology, structural geology, pluton chemistry, and metallogenic evidence. Neither the Avalon nor its European extensions are probable source areas for the Meguma.

Northwestern South America is a probable candidate as seen by paleomagnetic data, and general sedimentologic and tectonic patterns. Timing of both Early Paleozoic orogenic and glacial activity is difficult to determine with exactitude.

Northwestern Africa is the third candidate. Early Paleozoic rocks of northwestern Morocco are very similar to those of the Meguma Zone. At present, both areas occur within a distinctive, narrow, fault-bounded crustal strip; during Early Paleozoic time, both areas were exotic to their respective continents. Their sedimentary rock was deposited simultaneously in an identical environment by similar agents of mass transport which moved in a similar direction from a similar source area. Later these strata were metamorphosed, deformed in a similar stress field, and intruded by granitic plutons. Difficulties arise with the ages of the latter. Two new hypotheses are postulated in order to resolve these geologic and paleomagnetic questions.