Is the Liverpool Land Eclogite Terrane, Eastern Greenland Caledonides, Baltican, Laurentian, or Both?

Abstract:

The Liverpool land Eclogite Terrane (LLET) is a small (≈200 km²) high pressure metamorphic terrane at the southern tip of the Eastern Greenland Caledonides. Recent publications propose the LLET is a subducted Baltic terrane that underplated the Eastern Greenland Caledonides during the ca. 400 Ma Scandian Orogeny and was stranded in Greenland (Laurentia) during the opening of the Atlantic. However Johnston et al. (2011) proposed the LLET is actually a composite terrane comprised of a mid-crustal, high-pressure (granulite facies) terrane, the Jaettedal Complex, tectonically juxtaposed during the Scandian orogeny against a higher pressure (eclogite-facies), peridotite-bearing, metamorphic terrane, the Tvaerdal complex. The composite Tvaerdal/Jaettedal Terrane (now the LLET) was subsequently exhumed from beneath a Laurentian plutonic continental arc terrane, the Hurry Inlet Complex. U-Pb Precambrian ages from the Tvaerdal Complex obtained by LA-ICPMS from detrital zircons (this study) as well as published zircon dates do not distinctly match the published Proterozoic zircon age patterns of basins and crystalline complexes from either Laurentia or Baltica, therefore not resolving the provenance of the Tvaerdal Complex. However, Paleozoic zircon U-Pb dates (this study and the literature) demonstrate the Tvaerdal Complex underwent relatively short-lived high pressure/ultrahigh pressure metamorphism and subsequent anatectic melting between 415-385 Ma while recent work by Johnston et al. (2014) indicates the Jaettedal Complex underwent an earlier, much longer evolution between 460-412 Ma. The older ages from the Jaettedal coincide with ages obtained from the overlying Hurry Inlet Complex as well as other Greenland igneous terranes suggesting the Jaettedal Complex is a Laurentian terrane involved in the lengthy evolution of a continental arc complex along the eastern Greenland margin during the closure of Iapetus. The paucity of concordant 460-412 ages from the Tvaerdal Complex suggests it was not part of the Laurentia, but is consistent with earlier proposals that it was part of the eastern Baltica passive margin. Thus the LLET is composite; composed both of both Laurentian and Baltican complexes.

Johnston et al., 2011, Earth and Planetary Science Letters 297, 512-524: Johnston et al., 2014, in prep.