--> Abstract: NW Composite Terrane of Svalbard Revisited: U-Pb Zircon Dating Provides Evidence for the Presence of Ordovician Metasedimentary Strata, by Friedhelm Henjes-Kunst; #90177 (2013)

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NW Composite Terrane of Svalbard Revisited: U-Pb Zircon Dating Provides Evidence for the Presence of Ordovician Metasedimentary Strata

Friedhelm Henjes-Kunst

The Caledonian basement in Albert I Land and Haakon VII Land of NW Svalbard (“NW composite terrane”) is largely built up by lithological units thought to record a two-stage geological history: latest Mesoproterozoic metasedimentary strata (Krossfjorden group) associated with c. 960 Ma old metagranitoids were tectonometamorphically reworked about 430- 420 Ma ago during the Caledonian Orogeny and intruded shortly thereafter by the posttectonic Hornemantoppen Granite. So far, only the Richarddalen complex is interpreted to have experienced a different geological history. Within the jigsaw of the Caledonian orogenic system, the NW composite terrane of Svalbard is correlated with the Pearya terrane of north Ellesmere Island (CA). New U-Pb zircon and monazite age data demonstrate that the geological history of the migmatite complex and its metasedimentary cover in the NW composite terrane east of the Raudfjorden Fault (Haakon VII Land) and south of Liefdefjorden is different to that of basement rocks to the west (Albert I Land). LA ICP-MS zircon dating of the migmatite and its metasedimentary cover reveals a small but significant group of concordant Early Paleozoic to late Neoproterozoic ages interpreted to date formation age of the youngest detrital components within the rocks. Major age clusters further constrain the significance of early Neopreterozoic (Grenvillian) and older source rocks. A large gneiss xenolith within the migmatite complex showing an earlier generation of migmatisation not found in the surrounding migmatites also bears evidence of early Paleozoic and older detrital zircons. Additionally, there is a coherent group of zircon ages at 466 ± 2 Ma (n=12; MSWD 0.8) with in part very low Th/U interpreted to date migmatisation in this xenolith. Since migmatisation in the xenolith predates its emplacement into the protolith of the migmatite complex, a maximum Middle Ordovician sedimentation age can be inferred. The protolith of the migmatite complex can best be described as a Middle to Upper Ordovician diamictite. One may speculate about an origin of this diamictite as a Hirtanian tillite. Thus, migmatites and overlying metasedimentary rocks of Haakon VII Land cannot be correlated with migmatites and metasedimentary rocks of the Krossfjorden group in Albert I Land or equivalents in northernmost Haakon VII Land north of Liefdefjorden. Single grain zircon and monazite TIMS dating of syntectonic granite veins partly from within a prominent high-strain shear zone constrains the time of late-metamorphic formation of large-scale shear zone in Haakon VII Land south of Liefdefjorden to c. 422 – 415 Ma. The new findings strengthen the correlation of the NW composite terrane of Svalbard with the Pearya terrane of NE CA. In both regions, c. 960 Ma old meta-igneous basement is associated with early Paleozoic metasedimentary strata (Pearya: succession 4).

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013