Multistage HALIP-related Magmatism on north Ellesmere Island and a Link to the Formation of Alpha Ridge - Evidence from Geochronological and Aeromagnetic data

Friedhelm Henjes-Kunst

Cretaceous circum-arctic volcanism on Svalbard, Franz Josef Land, the Canadian Arctic is¬lands, North Greenland, Bennett Island and the Alpha Ridge is interpreted as High Arctic Large Igneous Province (HALIP) which preceded and accompanied opening of the Amerasian Basin of the Arctic Ocean. Initial tholeiitic flood-basalt volcanism was followed by alkaline, rift-related igneous activity at Ellesmere Island and North Greenland c. 90 M ago. Duration, plume-origin, and extent of the HALIP, the pre-opening reconstruction of the related occurrences as well as the relationship between tholeiitic and alkaline igneous suites are still in discussion. The Canadian part of the HALIP comprises basalts of the Hauterivian to Aptian Isachsen Formation, the late Albian to Cenomanian volcanogenic Strand Fiord Formation, and basalts of the stratigraphically equivalent Hassel Formation exposed mainly on Axel Heiberg and Ellesmere islands. Related mafic dykes and sills are emplaced over the whole Sverdup Basin. Alkaline intrusive (Wootton Intrusive Complex, WIC) and extrusive (Hansen Point Volcanic Complex, HPVC) suites are known from north Ellesmere Island, where they are exposed within NE–SW trending fault zones. Thus, northern Ellesmere Island is the only place in the Arctic where both tholeiitic and alkaline igneous suites are found in close spatial association. This area was studied by combined geological field work (sampling for petrographic, geochemical and geochronological investigations) and an offshore-onshore helicopter-borne magnetic survey during joint expeditions of the German BGR and the Canadian GSC. A prominent feature of the magnetic anomaly map is a broad magnetic high over Yelverton Bay that also covers a small strip of the neighboured coastal area and that is most likely caused by deep-seated thick igneous units without onshore outcrops. A chain of small positive anomalies crossing the Wootton Peninsula and forming the SE margin of the Yelverton Bay high can be correlated with the alkaline suites (WIC, HPVC). Alkaline gabbro to granite of the WIC intruded at 92.1 ±0.1 Ma and related microgranite at 92.7 ±0.3 Ma (TIMS U-Pb single zircon and titanite ages). Alkaline basaltic to rhyolitic rocks of the HPVC were dated to c. 80 Ma (Rb-Sr isochron age, Ar-Ar feldspar and WR ages). Rhyodacite forms larger parts of the HPVC outcrops SW and NE of Yelverton Bay. It differs from the alkaline felsic WIC and HPVC rocks by lower eps. Nd(t) and higher Sr(t) isotope values indicating crustal influence. Preliminary LA-ICP-MS U-Pb zircon dating of a rhyodacite from SW of Yelverton Bay yielded an age of c. 100 Ma. The rhyodacite is probably an extrusive equivalent of granitic plutons magnetically reflected as part of the Yelverton Bay high. This high can be traced to the large Alpha-Mendeleev Ridge magnetic domain. Thus, the date for the rhyodacite may provide an estimate of the formation age of the Canadian end of the Alpha Ridge as part of the HALIP.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013