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Petrology and U-Pb geochronology of buried Avalonian plutonic rocks on southeastern Cape Cod

January 1, 1993

Plutonic rocks have been intersected by two separate drill holes on southeastern Cape Cod. Hole CC2 is located at Chatham Harbor about 7 km south of the Nauset anomaly, an east-northeast-trending magnetic lineament that was considered to separate the distinct plutonic zones of Avalon terrane. This drill hole intersected weakly foliated, fairly homogeneous biotite granite. Zircons from this granite give a U-Pb age of 584+9/-8 Ma. Hole CC1 is located near North Eastham, about 12 km north of the Nauset anomaly. The drill core intersected foliated, sheared, biotite granodiorite and biotite-hornblende-clinopyroxene-quartz gabbro, metamorphosed to greenschist facies. The deformed and altered state of these rocks, as well as their geochemistry, suggest that their origin and possibly their ages are distinct from the granite in hole CC2. No datable zircons were obtained from rocks in CC1. The age of 584 Ma for the CC2 granite sample is within the range of published ages for plutonic rocks of the Avalon terrane and confirms the suggestion of Hutchinson et al. (1988) that the southern plutonic zone is a part of the Avalon terrane. The data also indicate that the Nauset anomaly is not the Avalon-Meguma terrane boundary in this area.

Citation Information

Publication Year 1993
Title Petrology and U-Pb geochronology of buried Avalonian plutonic rocks on southeastern Cape Cod
DOI 10.4138/1993
Authors G. W. Leo, J.K. Mortensen, B. Barreiro, J. D. Phillips
Publication Type Article
Publication Subtype Journal Article
Series Title Atlantic Geology
Index ID 70017944
Record Source USGS Publications Warehouse
USGS Organization Geology, Geophysics, and Geochemistry Science Center