Selection of the paleomagnetic data base is fundamental to constructing an APW path, particularly as modelers increasingly rely on only a few studies. Substantial changes to recently constructed North American Mesozoic APW paths appear necessary based on the new data presented here. A southerly modification of the late Triassic-Early Jurassic segment of the APW path is supported by new data from the dual-polarity Late Triassic dikes in Rhode Island (paleopole 52.6$\sp\circ$N, 88.4$\sp\circ$E). The Jurassic portions of the paths are dominated by studies from the Colorado Plateau and Newark I and II poles from the east coast. Paleomagnetic data from Massachusetts and Connecticut diabases, a crucial part of the Newark I and II poles, indicate that these paleopoles should be reevaluated. The paleopoles from the early Jurassic diabases plot in three groups, one before (A) and two after (B, C) the J1 cusp: (A) 60.1$\sp\circ$N, 80.7$\sp\circ$E; (B) 66$\sp\circ$N, 92$\sp\circ$E; (C) 72.5$\sp\circ$N, 92$\sp\circ$E, all markedly different from the Newark I and II poles. From ten Cretaceous intrusions in Maine, New Hampshire, and Vermont, 514 samples were subjected to detailed thermal and alternating-field demagnetization, coupled with careful reflected-light microscopy. These have produced nine reliable VGP's of higher latitude than those previously published for the Cretaceous. Recent precise $\sp{40}$Ar/$\sp{39}$Ar ages on biotite and hornblende from the Cretaceous intrusions (Hubacher and Foland, 1991) show they are in three groups at approximately 120 Ma., 111 Ma., and 100 Ma. These constrain the calculated VGP's and the resultant paleopoles at 72.6$\sp\circ$N, 199.1$\sp\circ$E; 74.7$\sp\circ$N, 194.6$\sp\circ$E; and 76.9$\sp\circ$N, 167.4$\sp\circ$E, respectively, which in turn indicate the position of North America in the early to middle Cretaceous. When the new Cretaceous data are combined with new results from the Triassic and Jurassic rocks in New England, a considerably modified APW path for North America is indicated. Data from the Triassic and Early Jurassic intrusions is consistent with the J1 cusp. None of the data supports the J2 cusp. Instead the segment of the path from mid-Jurassic to Mid-Cretaceous is at higher latitude, and follows a smoother track toward Tertiary and younger poles.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-8586 |
| Date | 01 January 1993 |
| Creators | McEnroe, Suzanne Amy |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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