T13C-3029
A Sm-Nd eclogite and U-Pb detrital zircon study of a probable Baltic HP-UHP metamorphic terrane in the Greenland Caledonides
Monday, 14 December 2015
Poster Hall (Moscone South)
Hannes K Brueckner1, Elena A Belousova2, L Gordon Medaris Jr.3, Scott M Johnston4, William L Griffin5, Ebbe H Hartz6, Sidney R Hemming1 and Richard Bubbico7, (1)Lamont-Doherty Earth Observatory of Columbia University, New York City, NY, United States, (2)Macquarie University, Department of Earth and Planetary Sciences, Sydney, Australia, (3)University of Wisconsin Madison, Department of Geoscience, Madison, WI, United States, (4)California Polytechnic State University San Luis Obispo, San Luis Obispo, CA, United States, (5)Macquarie University, Sydney, Australia, (6)University of Oslo, Physics of Geological Processes, Oslo, Norway, (7)Queens College of CUNY, Flushing, NY, United States
Abstract:
Liverpool Land, at the southern tip of the Greenland Caledonides, exposes the small eclogite-facies, peridotite-bearing Tvaerdal complex tectonically juxtaposed against the mid-crustal, high-pressure granulite facies Jaettedal complex. Recent literature supports a Laurentian origin for the Jættedal complex, but the structurally lower Tværdal complex has been tentatively correlated with Baltica. Their juxtaposition raises the possibility of lower plate to upper plate terrane transfer during continental subduction. Pressure-temperature estimates from Tvaerdal eclogites indicate ultrahigh pressure (UHP) metamorphic conditions during recrystallization. Sm-Nd mineral isochrons from the eclogites indicate UHP recrystallization occured ≈400 millions years ago, the same time HP/UHP metamorphism occurred in the Western Gneiss Complex of the Scandinavian Caledonides. Almost half of detrital zircons collected from a modern stream channel within the Tvaerdal complex give LA-ICPMS U-Pb ages of 1.68 and 1.3-0.95 Ma ages, which are dates characteristic of both Baltic and Laurentia. However, none of the detrital zircons give the Archean or ≈1.8 Ga Proterozoic ages that are also characteristic of Laurentia. Most of the remaining detrital zircons from the Tvaerdal Complex give younger U-Pb ages that range between 411-375 Ma which contrast with the older 450-410 Ma ages obtained from the Jaettedal as well as from other gneiss terranes in the southern Greenland Caledonides. The different age patterns provide compelling evidence that the Tvaerdal Complex is indeed an orphaned Baltic Terrane. The Jaettedal complex took part in the lengthy evolution of a compressional continental arc complex along the eastern Laurentian margin during the closure of Iapetus while the Tvaerdal complex was a fragment of the approaching Baltic passive margin. Eclogite-facies metamorphism of the Tvaerdal Complex occurred when Iapetus closed and the edge of Baltica subducted to UHP mantle conditions beneath Laurentia. We propose that a fragment of the eclogitized, subducted Baltic continental crust was transferred to the base of the overriding Laurentian crust through trans-mantle wedge diapirism. A journey through the hot mantle wedge may explain the presence of abundant granitic intrusions within the Tvaerdal Complex.
