|Résumé||(disponible en anglais seulement)|
The 2008 German CASE11-Pearya expedition to the northernmost part of Ellesmere Island, Canada, included onshore geological work combined with an
onshore/offshore aeromagnetic survey. The work was carried out to improve the understanding of the exotic terrane or microcontinental plate called "Pearya" on the North American continental margin.
The aeromagnetic survey was designed to map
regional-scale geological structures using a survey-line spacing of 2 km. The new survey ties existing magnetic surveys flown by the National Research Council of Canada in the 1990s as part of the Polar Margin Aeromagnetic Program (PMAP). Over
onshore mountainous terrain, survey flights were flown in a "draped" mode trying to keep the distance to ground at approximately 450 m, the same as over the offshore areas. The survey area covered a 40 to 50 km wide swath offshore roughly parallel to
the north coast of Ellesmere Island from Yelverton Inlet in the west to Cape Columbia in the east, the northernmost point of Canada. Between Yelverton Inlet and the western boundary of the Quttinirpaaq National Park (M'Clintock Inlet) the survey
extended about 40 to 50 km inland. The aeromagnetic survey operations for the CASE11-Pearya Project took place in a 4-week period in May/June 2008 prior to the geological work, due to more favorable weather conditions for the helicopter flying.
Altogether close to 8000 km on aeromagnetic line data were acquired, covering an area of 12000 km2.
The map of the total magnetic field anomalies shows distinct areas with different magnetic character.
The onshore areas are dominated by a
broad magnetic low, while in the offshore areas (mainly in the west) the magnetic field is dominated by high amplitude long wavelength positive anomalies. Generally, the offshore magnetic anomalies have longer wavelengths, attributed to increased
The onshore magnetic low correlates with Mesoproterozoic to Neoproterozoic crystalline basement of Pearya (Succession 1) and Neoproterozoic to Ordovician metasediments of Pearya Succession 2. In the central and eastern portion of
the survey area, this magnetic low continue offshore, suggesting that Pearya Succession 2 continues to the northern limit of mapping (>50km). Within this inland region isolated high amplitude positive magnetic anomalies are observed. These generally
correlate with Paleozoic intrusive rocks (eg. Cape Fanshaw Martin Pluton). The most notable of these isolated magnetic anomalies (>3900 nT) is observed east of southern M'Clintock Inlet. Although the feature is tentatively correlated with the
M'Clintock West Ultramafic Massif, it lies outside the extent of the unit on the published geological maps. A magnetic high extends from the mouth of M'Clintock Inlet, across Bromley Island and Cape Richards, to Ayles Fiord. This feature correlates
with Ordovician units of Pearya Successions 3 and 4, which are dominated by volcanic rocks, including the Cape Richards Intrusive Complex. The magnetic high north of Disraeli Fiord is interpreted to be a continuation of the Pearya Successions 3 and 4
At the western end of the survey, the onshore low and the offshore high are separated by a ridge of high amplitude N-S oriented positive anomalies extending from the mouth of Yelverton Inlet to north of Milne Fiord. This feature appears to
be a continuation of the magnetic anomaly chain on central Wootton Peninsula produced by Early Cretaceous igneous rocks (Hansen Point volcanics and Wootton intrusives). North of Ayles Fiord, this magnetic high separates into individual E-W oriented
positive magnetic anomaly chains which cross-cut the longer wavelength anomalies caused by the Peary basement rock. This suggests that Early Cretaceous igneous rocks are present all along the near-shore portion of the margin. The broad
long-wavelength offshore magnetic high is probably related to the Alpha Ridge as part of the Cretaceous High Arctic Large Igneous Province.