Paper No. 230-7
Presentation Time: 10:30 AM
AGES OF MAGMATISM IN THE CENTRAL SVERDRUP BASIN, CANADIAN ARCTIC ISLANDS, FROM VOLCANOGENIC ROCKS, GEOCHRONOLOGY, AND PALEO-DEPTHS OF SAUCER-SHAPED SILLS
Representative and well-constrained ages for magmatism are needed to clarify the tectonic history of the Amerasia and Canada basins. We use field evidence, map compilation, geochemistry, geochronology, and potential field data to document six intervals of Cretaceous magmatism in the central Sverdrup Basin. These are: 1) mid-Hauterivian (ca. 130 Ma) volcaniclastic rocks in the lower Isachsen Formation; 2) 126.6 ± 1.2 Ma (U-Pb zircon) intrusion of gabbro; 3) 120.8 ± 0.8 Ma (U-Pb baddeleyite) intrusion of diabase; 4) 105.40 ± 0.22 Ma (U-Pb detrital zircon) pyroclastic deposition at the top of Invincible Point Member, Christopher Formation; 5) upper Albian (ca. 103 Ma) hydroclastic breccia in the upper Christopher Formation; and 6) uppermost Albian (ca. 101 Ma) volcanic breccia in the Hassel Formation. Whole rock geochemical data show that magmatic rocks are similar to previously documented HALIP tholeiitic basaltic magmatism, but analyses of fresh glass in tuffs reveal evolved ferroandesite to dacite compositions rarely recorded in whole rock data. Intrusive rocks include a newly recognized occurrence of saucer-shaped sills. Approximate ages of saucer-shaped sills are inferred from the relationship of sill width to depth of emplacement, indicating at least three intervals of sill emplacement between 130 and 120 Ma, and possibly an additional younger interval. The interpreted ages of emplacement are consistent with ages of magmatism determined independently from U-Pb age determination and the stratigraphic position of volcanogenic rocks. The new data show that volcanism in the Sverdrup Basin was of greater spatial extent, and that magmatism occurred more frequently, than previously recognized. Comparing the new central Sverdrup Basin data and interpretations with other data sets from the Sverdrup Basin, Svalbard, and Franz Joseph Land, it appears that HALIP magmatism occurred with much greater frequency in the Sverdrup Basin than other regions.