T344 Exhumation of Continental Ultrahigh-Pressure Terranes

Thursday, 9 October 2008
8:00 AM - 12:00 PM

Zircon Geochronology and Tectonostratigraphy of Liverpool Land, East Greenland: Evidence for a Caledonian Lower-Crustal Continental Suture

Paper number: T344-6
Program: Technical Sessions
Time: 9:10 AM – 9:25 AM

Authors

Abstract

The East Greenland Caledonides consists of several west-directed thrust sheets that formed from 460–360 Ma as Baltica subducted westward beneath Laurentia, and offer a unique opportunity to investigate continental ultrahigh-pressure (UHP) processes. The (U)HP Liverpool Land gneiss complex, exposed in a hinterland window ~100 km east of the nearest Caledonian gneisses, is split into three tectonostratigraphic units including, from the bottom up: 1) the eclogite + peridotite-bearing Tvaerdal Orthogneiss, 2) the granulite-facies Jaettedal Paragneiss, both below the normal-sense Hurry Inlet Detachment, and, above the Hurry Inlet Detachment, 3) the Hurry Inlet Granites and associated Kalkdal Paragneiss. We present new LA–MC–ICPMS U–Pb zircon geochronology from Liverpool Land for correlation with Caledonian tectonostratigraphy and metamorphic events in Greenland and in Norway.

Zircons from the Tvaerdal Orthogneiss yield metamorphic rims that cluster in age from 409–403 Ma and overgrow magmatic cores of 1676 and 1663 Ma in two samples, and range from ~1750–1000 Ma in a third sample. In contrast, zircons from three samples in the Jaettedal Paragneiss and two samples in the Kalkdal Paragneiss yield metamorphic rims that cluster in age from 438–418 Ma with Archean–Early Neoproterozoic detrital cores. Archean–Early Neoproterozoic detrital zircons associated with 440–420 Ma metamorphism in the Liverpool Land paragneisses suggests correlation with the Hagar Bjerg Thrust Sheet of Laurentian affinity, whereas Mesoproterozoic magmatic cores, which have not been identified elsewhere in Greenland, and ~400 Ma (U)HP deformation suggests correlation of the Tvaerdal Orthogneiss with the Western Gneiss Complex in Norway and of Baltican affinity (e.g., Augland et al., 2007). As such, the contact between the Tvaerdal Orthogneiss and the Jaettedal Paragneiss records an initial stage of (U)HP exhumation prior to displacement along the upper-crustal Hurry Inlet Detachment, and may represent a Caledonian lower-crustal suture between Baltica and Laurentia.