10 Neoproterozoic and Paleozoic Geological Connections Among Northwest Africa, Europe, and Eastern North America II – A Session Honoring the Career of Sandra M. Barr

Sunday, 17 March 2024
1:30 PM - 5:30 PM
Pemigewasset Room

A COMPARISON AMONG THE MEGUMA TERRANE OF EASTERN CANADA, THE SEHOUL BLOCK OF NW AFRICA, THE HARLECH DOME OF NORTH WALES, AND THE SOUTH PORTUGUESE ZONE OF SOUTHERN SPAIN AND PORTUGAL

Paper number: 10-3
Program: Symposia Sessions
Time: 1:55 PM – 2:15 PM

Authors

Abstract

The Meguma terrane of Canada, the Harlech Dome of Wales, the Sehoul Block of NW Africa, and the South Portuguese Zone of Iberia have previously been interpreted as part of a larger Gondwanan domain Megumia. We compare their characteristics based on published data. The Meguma terrane consists of primarily latest Ediacaran to Early Ordovician turbiditic metasandstone and slate, locally overlain by early Silurian to Early Devonian slate, quartzite and metavolcanic rocks. The Cambrian to Tremadocian rocks are similar to those of the Harlech Dome, but their post-Tremadocian histories diverge. In the Meguma terrane, Early to Middle Devonian greenschist to amphibolite facies metamorphism and folding were followed by mainly Late Devonian peraluminous granitic plutonism. The detrital zircon in various units of the Meguma terrane has a strong West African signature with large ~2.2–1.9 Ga and ~700–500 Ma populations, and minor ~1.5–0.9 Ga dates. Based on drill core data, the Meguma terrane extends offshore to the southeast.

The Sehoul Block primarily consists of Cambrian phyllite and metawacke. It was folded and metamorphosed prior to intrusion of the peraluminous 367±9 Ma Rabat granite. The Meseta domain to the south does not show the same deformation, metamorphism and plutonism, implying that the Sehoul Block was separated from NW Africa during that time. The Sehoul Block was juxtaposed with the Meseta domain in the Carboniferous along the Sehoul thrust. Detrital zircon of the Sehoul Block is dominated by 605–560 Ma ages with a smaller ~2.0 Ga population, and a few ~1.0 Ga grains.

The South Portuguese Zone consists of Middle Devonian (and older?) to Carboniferous metasedimentary and metavolcanic rocks. Detrital zircon shows a large 630–580 Ma population, with a smaller ~2.2–1.9 Ga population. Some of the rocks also show a significant Mesoproterozoic population, which has been interpreted as indicating an Avalonian origin. A 375–365 Ma population corresponds with ages of granites in the Meguma terrane and the Sehoul Block. By the Middle Devonian, the South Portuguese Zone may have been in proximity to, and derived zircon from Avalonia and/or elements of Megumia, but the origin of its basement remains unclear. We conclude that the Harlech Dome and Sehoul Block show similarities to the Meguma terrane, starting in the Cambrian.

Geological Society of America Abstracts with Programs. Vol. 56, No. 1

doi: 10.1130/abs/2024NE-397574

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