A PLATE MODEL AND KEY UNCERTAINTIES FOR PERI-GONDWANAN TERRANES IN RELATION TO WEST AFRICA CRATON, BALTICA AND AMAZONIA

This model spans 900 Ma to 550 Ma and describes peri-Gondwana terranes (especially Avalonia, Ganderia, and Carolinia) and their relationship to Baltica (BAL), Amazonia (AMZ) and West Africa craton (WAC). It is based on published tectonostratigraphic histories and DZ ages, leveraging existing plate models for cratons. Its 550 Ma endpoint is consistent with many 550-450 Ma terrane models, thus viable for subsequent terrane history.

The model starts at 900 Ma with WAC, AMZ and BAL joined. Ocean-opening dates are a key uncertainty. In this model they are: WAC-AMZ (Clymene) 850 Ma; WAC-BAL (Miravoi) 850 Ma; AMZ-Laurentia (Puncoviscana) 700 Ma; AMZ-BAL (Tornquist) 620 Ma.

The initial location of key Peri-Gondwana terranes and rationale are as follows. Avalonia originates along the margin of BAL facing WAC. Avalonia has BAL affinity based on DZ ages and Hf isotope values. Placing Avalonia across from WAC allows tectonic interaction between them as suggested the similar tectonostratigraphic history of Avalonia and Anti-Atlas. Grand Manan Island and Islesboro Block (Ganderia) originate on WAC, indicated by DZ ages.

The Roanoke Rapids terrane of Carolina and Hermitage Flexure of Ganderia originate on AMZ facing Puncoviscana. These terranes have 675 Ma arcs, older than modeled Tornquist opening and lacking the early arcs of Avalonia and Anti-Atlas, indicating a different location. The model location is common to many post-550 Ma models. The remainder of Ganderia is on AMZ at the western end of the AMZ-BAL suture, based on Grenville crust and DZ ages.

During Miravoi opening the “Gadel Block” (Mauritanides) separates from WAC. Volcanic arcs initiate on the BAL margin and rift away toward WAC. These are on Avalonia and outboard Anti-Atlas. They collide with “Gadel Block” ca. 720 Ma, then WAC ca. 650 Ma. Subduction resumes under the composite margin ca. 620 Ma.

From ca. 590-550 Ma, subduction converts to transform, and Avalonia and Islesboro/Grand Manan traverse from WAC to AMZ. A subduction zone topped by Cary Arc of Carolinia leads the way through the Tornquist. At 550 Ma, this arc collides with the Charlotte arc of Carolinia. Carolinia, Ganderia and Avalonia have assembled on AMZ.

A key uncertainty is the age of Tornquist opening. Opening prior to 720 Ma allows Avalonia to form there but does not explain interactions with Anti-Atlas and WAC.