Devonian to Carboniferous collision in the Greenland Caledonides: U-Pb zircon and Sm-Nd ages of high-pressure and ultrahigh-pressure metamorphism

• Published in: Contributions to Mineralogy and Petrology
• Main Authors: Gilotti, Jane, Nutman, Allen, Brueckner, Hannes
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Springer
• Subjects: Keywords: collision zone; geochronology; Laurentia; orogeny; Paleozoic; ultrahigh pressure metamorphism; Arctic; Arctic and Antarctic; Caledonides; Eastern Hemisphere; Eurasia; Europe; Greenland; World; Antarctic; Work Point; Antarc*; East Greenland
• Online Access: http://hdl.handle.net/1885/86315; https://doi.org/10.1007/s00410-004-0600-4; https://openresearch-repository.anu.edu.au/bitstream/1885/86315/5/MigratedxPub15150_2004.pdf.jpg; https://openresearch-repository.anu.edu.au/bitstream/1885/86315/7/01_Gilotti_Devonian_to_Carboniferous_2004.pdf.jpg

A variety of eclogites from an east-west transect across the North-East Greenland eclogite province have been studied to establish the timing of high pressure (HP) and ultrahigh-pressure (UHP) metamorphism in this northern segment of the Laurentian margin. Garnet + omphacite ± amphibole + whole rock Sm-Nd isochrons from a quartz eclogite, a garnet + omphacite + rutile eclogite and a partially melted zoisite eclogite in the western HP belt are 401 ± 2, 402 ± 9 and 414 ± 18 Ma, respectively. Corresponding sensitive high-resolution ion microprobe (SHRIMP) 206Pb/238U ages of metamorphic zircon in the same samples are 401 ± 7, 414 ± 13, and 393 ± 10 Ma. Metamorphic zircon domains were identified using morphology, cathodoluminescence (CL) imaging, U, Th, Th/U and trace element contents. Zircon from the quartz eclogite and the garnet + omphacite + rutile eclogite are typical of eclogite facies zircon with rounded to subhedral shapes, patchy to homogenous CL domains, low U, and very low Th and Th/U. The partially melted eclogite contains euhedral zircons with dark, sector-zoned, higher U, Th and Th/U inherited cores. Three cores give a Paleoproterozoic 207Pb/206Pb age of 1,962 ± 27 Ma, interpreted as the age of the leucogabbroic protolith. CL images of the bright overgrowths show faint oscillatory zoning next to homogenous areas that indicate zircon growth in the presence of a HP melt and later recrystallization. Additional evidence that zircon grew during eclogite facies conditions is the lack of a Eu anomaly in the trace element data for all the samples. These results, combined with additional less precise Sm-Nd ages and our earlier work, point to a Devonian age of HP metamorphism in the western and central portions of the eclogite province. An UHP kyanite eclogite from the eastern part of the transect contains equant metamorphic zircon with homogeneous to patchy zoning in CL and HP inclusions of garnet, omphacite and kyanite. These zircons have slightly higher U, Th and Th/U values than the HP ones, no Eu anomaly, ...