NENA in Nuna: Paleomagnetic confirmation of a long-lived (1800-1100 Ma) connection between Laurentia and Baltica
|Location||International Geological Congress,oslo 2008|
|Author||Evans, David۱; Raub, Theresa M.D.۲|
|Holding Date||08 October 2008|
A wide variety of proposed pre-Rodinian cratonic reconstructions have been proposed, but only a few of them have been paleomagnetically tested. The pre-Rodinian supercontinent (Nuna, also called Columbia or Hudsonland) is defined by 1900-1800 Ma orogeny that is assumed to represent the suturing of far-traveled blocks. Within Nuna, several cratonic juxtapositions have been proposed, including one in which Northern Europe is joined to North America (acronym NENA; Gower et al., 1990). Testing NENA, or other proposed reconstructions involving Laurentia, has been difficult because there is controversy in the Laurentian paleomagnetic database on whether the craton occupied high or low paleolatitudes at 1830-1800 Ma. Here we summarize an extensive review of the relevant published literature bearing on this debate, as well as present our new paleomagnetic data from the Dubawnt Supergroup, overlapping the Rae and Hearne cratons in central Canada.
Careful examination of published high-paleolatitude poles from the Trans-Hudson orogen between 1900 and 1750 Ma, indicates that most suffer from either inadequate tilt control on the sampled rock units, unconstrained age of magnetization, or biases due to component mixing. We suggest that most, if not all, of these high-paleolatitude data are unreliable. Our new data from the unmetamorphosed and only fault-tilted strata of the Dubawnt Supergroup, representing similar ages from 1830 to ca.1700 Ma, all imply moderate to low paleolatitudes for this part of Laurentia. Paleogeographic comparisons with other cratons should thus utilize the low-latitude option for Laurentia during and after the time of Nuna’s assembly.
In recent years, Baltica has yielded several new "key" paleomagnetic poles from the 1770-1270 Ma interval. Superposition of the Baltic apparent polar wander path with that from Laurentia during the same interval (employing the low-paleolatitude option) results in an “absolute” reconstruction between the two blocks (i.e., constrained in both relative paleolatitude and paleolongitude) that is strikingly similar to NENA, which was proposed according to geological comparisons. This quantitative verification of NENA is inconsistent with 1830-Ma poles from both cratons, suggesting that NENA assembled between 1830 and ca.1760 Ma. However, the Baltica 1830-Ma pole from the Haukivesi lamprophyres must be tested for its primary nature to verify this conclusion. New data from the ca.1120-Ma Salla Dyke in northern Finland are also broadly consistent with our quantitative NENA reconstruction, but ca.1050-Ma poles from both cratons are not. This implies that NENA broke up ca.1100 Ma.
A modern style of plate tectonics, with internally rigid plates in periods of relative motion alternating with periods of conjunction in supercontinents, is thus supported by paleomagnetic data with this high-quality example from the Paleo-Mesoproterozoic interval.