PETROLOGY AND GEOCHEMISTRY OF CAMBRIAN VOLCANIC ROCKS FROM THE AVALON ZONE IN NEWFOUNDLAND AND NEW BRUNSWICK.

摘要

This thesis examines the petrology and geochemistry of Cambrian volcanic rocks from the Avalon Peninsula (Newfoundland) and southern New Brunswick as well as Silurian sills and Devonian (?) dikes from the Avalon Peninsula. The geochemistry of these rocks provides new information on Early Paleozoic tectonism affecting Avalonian terrane in eastern North America. The effects of low grade metamorphism on the primary geochemistry of each rock group are also discussed.;Silurian sills on Cape St. Mary's show primary textural, mineralogical and bulk-rock geochemical characteristics indicative of high volatile contents. Thermogravitative processes probably involving volatile complexing of some elements caused enrichment of these elements in the upper portions of the sills, or removal from the sill system as a whole. The parental sill magma was geochemically somewhat evolved, tholeiitic, and closely resembled compositions observed in flood basalt and rift provinces.;Dikes in the Cape St. Mary's study area show a range of bulk rock compositions representative of at least two batches of magma that underwent varying degrees of evolution. Some of the rocks appear to have alkaline characteristics whereas others have tholeiitic attributes, but all were probably produced in a tensional environment. These rocks resemble Devonian dikes around Bonavista Bay and could be time equivalent.;The Cape St. Mary's Cambrian basalts and their feeder pipes display (primary) whole-rock and mineralogical compositions representative of evolved alkali basalts. Lower to Middle Cambrian volcanic rocks in New Brunswick form a bimodal suite, the basaltic portion of which shows compositions ranging from relatively unevolved to highly evolved tholeiites. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI;Middle Cambrian basalts on Cape St. Mary's (Avalon Peninsula) were affected by two phases of alteration that resulted in the formation of chlorite and carbonate. The effects of the chlorite formation on element concentrations resemble those observed for basalt/seawater interaction, whereas the effects of carbonate addition are similar to those produced in high CO(,2) systems. Basalts in the Beaver Harbour area of New Brunswick show similar two-phase alteration, but phosphorous and yttrium were added during the carbonate addition phase suggesting that there were differences in the metasomatic solutions between the two areas.