27. VOLCANIC ROCKS OF THE SOUTHEAST GREENLAND MARGIN IN COMPARISON WITH OTHER PARTS OF THE NORTH ATLANTIC TERTIARY IGNEOUS PROVINCE¹

Lotte Melchior Larsen,² J. Godfrey Fitton,³ and Miranda S. Fram⁴

ABSTRACT

The lavas drilled during Ocean Drilling Program Leg 152 on the southeast Greenland Margin cover almost the whole compositional variation found in the North Atlantic volcanic province, ranging from picrites to dacites. Evidence for high-MgO melts, indicating a hotter than normal (plume) mantle is now found in several widespread areas, regardless of the distance to the assumed plume center. In most areas of the North Atlantic, several parallel fractionation trends are present, indicating several independent magma types and magma generation events. Fe- and Ti-enriched fractionated three-phase cotectic basalts are characteristic of the North Atlantic province but are not present at the southeast Greenland Margin except for one young sill. The Tertiary basalts are richer in FeOT and poorer in Na₂O than normal mid-ocean-ridge basalts (MORB), indicating melting of hot plume material under a continental/lithospheric lid. The lavas from the southeast Greenland Margin, the Hatton Bank Margin, and the British Isles apparently formed from less hot mantle than the rest. Parts of this southern mantle were more depleted in incompatible elements than the mantle in other areas. The lavas from Hatton Bank and Site 918 have unusually high Sc contents, unparalleled in modern MORBs.

All seaward-dipping reflector sequences drilled up to now (Vøring Margin, Hatton Margin, southeast Greenland Margin) include crustally contaminated rocks in the oldest parts of the sequences. Thick Tertiary dacite successions formed only over the peripheral parts of the mantle plume head. The crustal contaminant at the southeast Greenland Margin is similar to that in the British Isles and Kangerlussuaq and is in strong contrast to the crustal component in the Hatton Bank lavas. This is in accordance with the situation of these areas in different Precambrian structural and age provinces in the North Atlantic region.

¹Saunders, A.D., Larsen, H.C., and Wise, S.W., Jr. (Eds.), 1998. Proc. ODP, Sci. Results,152: College Station, TX (Ocean Drilling Program).
²Geological Survey of Denmark and Greenland, and Danish Lithosphere Centre, Thoravej 8, DK-2400 København K, Denmark. LmL@geus.dk
³Department of Geology and Geophysics, Grant Institute, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, United Kingdom.
⁴Department of Geology, University of California, Davis, CA 95616, U.S.A.