Uncertainties in breakup markers along the Iberia-Newfoundland margins illustrated by new seismic data

Annabel Causer, Lucia Perez Diaz, Jurgen Adam, Graeme Eagles

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Plate tectonic modellers often rely on the identification of break-up markers to reconstruct the early stages of continental separation. Along the Iberian-Newfoundland margin, so-called break-up markers include interpretations of old magnetic anomalies from the M-series, as well as the J-anomaly. These have been used as the basis for plate tectonic reconstructions on the belief that these anomalies pinpoint the location of first oceanic lithosphere. However, uncertainties in the location and interpretation of break-up markers, as well as the difficulty in dating them precisely, has led to plate models that differ in their depiction of the separation of Iberia and Newfoundland.

We use newly available seismic data from the Southern Newfoundland Basin (SNB) to assess the suitability of commonly used break-up markers along the Newfoundland margin for plate kinematic reconstructions. Our data shows that basement associated with the younger M-Series magnetic anomalies is comprised of exhumed mantle and magmatic additions, and most likely represents transitional domains and not true oceanic lithosphere. Because rifting propagated northward, we argue that M-series anomaly identifications further north, although in a region not imaged by our seismic, are also unlikely to be diagnostic of true oceanic crust beneath the SNB. Similarly, our data also allows us to show that the high amplitude of the J Anomaly is associated to a zone of exhumed mantle punctuated by significant volcanic additions, and at times characterised by interbedded volcanics and sediments. Magmatic activity in the SNB at a time coinciding with M4 (128 Ma), and the presence of SDR packages onlapping onto a basement fault suggest that, at this time, plate divergence was still being accommodated by tectonic faulting.

We illustrate the differences in the relative positions of Iberia and Newfoundland across published plate reconstructions and discuss how these are a direct consequence of the uncertainties introduced into the modelling procedure by the use of extended continental margin data (dubious magnetic anomaly identifications, breakup unconformity interpretations). We conclude that a different approach is needed for constraining plate kinematics of the Iberian plate pre M0 times.
Original languageEnglish
JournalSolid Earth
Early online date30 Sept 2019
Publication statusE-pub ahead of print - 30 Sept 2019

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