North America during the Lower Cretaceous: new palaeomagnetic constraints from intrusions in New England

Abstract

SUMMARY Six Late Aptian and Albian intrusions in Maine, New Hampshire and Vermont, dated between 113 and 100 Ma, were sampled for palaeomagnetic analysis. The majority of samples unblock between 550 C and 580 C, and Curie temperatures fall in a discrete interval between 556 C and 580 C. This indicates that the dominant remanence carrier is a TRM and is carried by titanomagnetite, which crystallized from the magma or was produced by deuteric oxidation alteration during post-magmatic cooling. Titanomagnetite occurs as discrete Cl-C3 grains, as exsolution lamellae in the silicates, and as fine reaction rims on the silicates. The palaeomagnetic results are combined with additional data from four Barremian and Early Aptian intrusions in southern Maine to produce nine reliable virtual geomagnetic poles. These possess a higher latitude than most published poles for the Lower Cretaceous. Ar4O/Ar3, ages on biotite and hornblende from these intrusions demonstrate three intrusive pulses at approximately 120 Ma, 111 Ma and 100 Ma, constraining the ages of the calculated VGPs. The corresponding palaeopoles are 72.3 ON, 198.2 E, A,, = 3.3 ; 74.5 ON, 195.2 E, A,, = 3.8; and 76.6 ON, 167.5 E, A,, = 5.3. Based on new palaeomagnetic data reported here, significant changes to the North American Mesozoic APW path are necessary. These changes constrain the palaeoposition of the North American plate in the Lower Cretaceous.