William R. Morgan

Halifax, N. S.

B. Sc. Honours Thesis

⁴⁰Ar/³⁹Ar Dating of Silurian-Devonian Rocks from the Gander and Botwood Zones of Newfoundland and their Paleomagnetic Implications

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Paleomagnetic poles recently reported by Lapointe, Murthy, and others are widely divergent from poles of similar age from cratonic North America. Two of the units from Newfoundland have each yielded two widely separated paleopoles. These units are the Mount Peyton Batholith (Botwood Zone) and a suite of diabase dikes from the Wesleyville area (Grander Zone).

Detailed ⁴⁰Ar/³⁹Ar stepwise outgassing measurements were made on a number of biotite and hornblende samples from these two units in an attempt to determine if age differences accounted for the observed variance in paleopoles. Results from the Wesleyville dikes yielded age spectra with plateaus at about 390 Ma. This is consistent with previously reported ages of 332 + 42 Ma for the younger Newport Pluton (Bell et al., 1979). However, it conflicts with the reported 300 + 18 Ma age for the Locker's Bay Pluton which is cut by the dikes. The freshest hornblendes and biotites from the Mount Peyton diorite yield an age plateau of about 425 Ma. Diorite inclusions from within the late granite phase yield distinctly younger ages corresponding to a 390 Ma age reported by Bell (personal communication). Similarity with the granites in age and pole location for the inclusions, suggests the ages and magnetizations have been reset during the granite emplacement.

Paleomagnetic data for the Northern Appalachians during the Silurian-Devonian yield two spatially distinct groups. From the paleomagnetic data, it would appear that the Botwood and Gander Zones of Newfoundland may have moved relative to the rest of Appalachia during these times.

Keywords: paleomagnetics;  ⁴⁰Ar/³⁹Ar; Gander Zone; Botwood Zone; Newfoundland; Mount Peyton Batholith; Wesleyville; diabase; dikes; paleopoles; stepwise outgassing; Appalachia; Silurian-Devonian.
Pages: 105
Supervisors: P.H. Reynolds

Bill is now retired and living in Canmore, AB with his wife of 31 years, Ingrid.