Detrital zircon populations from Silurian-Devonian clastic rocks of NW Svalbard were analysed by U-Pb laser ablation inductively coupled plasma mass spectrometry to investigate the pre-Caledonian provenance of Svalbard's Northwestern Terrane. Changes in the resulting age spectra suggest a major shift in sources from the Laurentian-Avalonian suture in the latest Silurian to the local metasedimentary basement of the Northwestern Terrane in the Late Silurian-Early Devonian, and in the Lochkovian to Grenvillian-Sveconorwegian sources. These data, together with structural, additional geochronological and metamorphic data from Svalbard, East Greenland and Avalonia, support the amalgamation of Svalbard as the result of long-distance transport along sinistral strike-slip faults. A unifying model for the final amalgamation of Svalbard, consistent with the stratigraphical and tectonothermal history of Svalbard, involves fragments from the Grampian orogen and Avalonian crust originally accreted to the Laurentian margin being subsequently transported northward along sinistral strike-slip faults during Scandian deformation.

Svalbard represents the uplifted and exhumed northwest corner of the Barents Sea Shelf. Pre-Carboniferous rocks of Svalbard are divided into the Eastern, Northwestern and Southwestern Terranes, were amalgamated during the Caledonian Orogen and are separated by north-south-trending strike-slip faults. Even though our knowledge of Svalbard’s pre-Carboniferous history has increased dramatically during the last two decades, a major issue remains: Where did the different tectonostratigraphic terranes of Svalbard originate? The answer to this question has profound significance for the entire eastern Laurentian margin, which spans two supercontinent cycles, from the amalgamation and breakup of Rodinia to the amalgamation of Pangea. This thesis constrains the tectonothermal evolution of Svalbard’s Northwestern Terrane (NWT) using ion microprobe and LA-ICP-MS U-Pb zircon geochronology and electron microprobe thermobarometry on metasediments, clastic rocks and granitoids. Detrital zircon age populations of metasediments from the NWT suggests that they (e.g. the Krossfjorden Group) were deposited at c. 1000 Ma in a remnant ocean basin setting outboard the Eastern Grenville Province and were subsequently deformed and intruded by Late Grenvillian granitoids during the final suturing of Rodinia. Thus, a northern branch of the Grenvillian/Sveconorwegian orogeny is not present. This older history of the NWT is extensively overprinted by Late Caledonian deformation and metamorphism, with peak metamorphic conditions of 850 °C at >6 kbars, and subsequent migmatization of the Krossfjorden Group at c. 420 Ma. Based on these data, together with the detrital zircon age population from overlying Late Silurian-Early Devonian clastic rocks, a unifying model is proposed involving fragments from the Grampian orogen and Avalonian crust originally accreted to the Laurentian margin, subsequently transported northwards along sinistral strike-slip faults during Scandian deformation.

U–Pb ion microprobe investigations of zircons from gneisses, granites and migmatites of the pre-Devonian Smerenburgfjorden and Richarddalen Complexes constrain the tectonic evolution and origin of Svalbard's Northwestern Terrane. Field relationships combined with U–Pb age data indicate that a late Meso- to Neoproterozoic metapelitic protolith was intruded by Tonian (c. 960 Ma) granitoids and suggest that the entire Northwestern Terrane is underlain by early Neoproterozoic granitoids intruding older metasediments. Both rock types were later involved in Caledonian deformation, with subsequent migmatization and granite genesis at c. 435–420 Ma. Ages of inherited zircons in granites and migmatites reflect anatexis of this late Meso- to Neoproterozoic protolith, with zircon xenocrysts ranging in age from c. 1030 to 1820 Ma. Pronounced lithological, geochronological and tectonothermal similarities to NE Svalbard (Nordaustlandet) and the Krummedal supracrustal sequence of East Greenland suggest a strong correlation between Svalbard and East Greenland prior to Caledonian orogenesis.

In the North Atlantic region, Caledonian and Grenvillian terrains are exposed on Svalbard, Greenland, Great Britain, Canada and Scandinavia. Reconstructing the original configuration of these terrains depends partly on determining the age and provenance of the sedimentary rocks overlying the basement. Provenance investigations using detrital zircon U-Pb ages are a powerful tool to explore the palaeogeography and can yield important information how the North Atlantic region evolved through the Grenvillian and Caledonian orogenies.

U-Pb laser ablation ICP-MS provenance study of zircons from Late Silurian and Early Devonian coarse siliciclastics of NW Svalbard indicate an east Greenland provenance. The decrease in 410-440 Ma ages and 2600-2800 Ma ages, combined with a large increase in 950-1000 Ma ages up-section suggests that sediment detritus was initially derived from exhumation of the Caledonian Orogen and subsequently from the Grenvillain Orogen.

The pre-Devonian rocks of Svalbard can be grouped into three Caledonian terranes separated by north-south trending strike-slip faults. The paleogeography of the Southwestern and the Eastern Terranes is fairly well constrained, whereas the origin of the Northwestern Terrane (NWT) remains enigmatic. One difficulty in determining the paleogeographic origin of NWT is the complex, polyphase metamorphic history this terrane has experienced. In an attempt to understand the tectonic evolution of the NWT, a U-Pb ion microprobe study of zircons from gneisses, granitoids and migmatites from the Smerenburgfjorden Complex and Richarddalen Complex has been carried out.

Field evidence supported by age dating indicates that a Mesoproterozoic metapelitic protolith was intruded by ca. 960 Ma granitic orthogneiss. These new ion microprobe data are comparable with ages from other parts of Northwest Svalbard, and suggest that the entire NWT is underlain by Grenvillian-age (940-1039 Ma) and older basement rocks. These units were later involved in Caledonian deformation with subsequent granite genesis and migmatization at c. 417 to 433 Ma. Inherited zircons in the Caledonian granites suggest that two different protoliths were involved in Caledonian anatexis: One sourced dominantly from Greenvillian-age basement (940-1039 Ma) and another from an older early Mesoproterozoic to Paleoproterozoic basement (1500-1900 Ma). The origin of the NWT will be discussed, in light of these results.

Svalbard’s Caledonian and older bedrock consists of three main exotic terranes separated by north-south trending strike-slip faults. Early in the 19th century Kulling (1930, 1934) noted the striking similarity between the Neoproterozoic and Early Paleozoic sedimentary rocks from East Greenland and Svalbard’s Eastern Terrane. After this pioneering work Harland et al. (1969) documented their remarkable similarities through detailed stratigraphic correlation of Neoproterozoic and Early Paleozoic sedimentary rocks. Recent work in the Northwestern and the eastern part of the Eastern terrane shows that this metasedimentary basement has a strong resemblance to the Krummedal and Smallefjord sequences of central East Greenland, with Grenville age (sensu lato) granitoid intrusion followed by Caledonian migmatization and granite genesis. We present the first LA-ICP-MS U-Pb zircon provenance study on quartzites and mica schists from the Kongsfjorden Group of the Northwestern Terrane of Svalbard. These results indicate a strong correlation with the Krummedal of central East Greenland and help to constrain paleogeographic reconstructions of the Northwestern Terrane.

Mineral-chemical data of metapelites from the Proterozoic Krossfjorden Complex constrain the Late Caledonian tectonic evolution of Svalbard’s Northwestern Terrane and record a clockwise P-T path. The oldest deformation event (D2) related to orogenesis in the Northwestern Terrane records crustal thickening and incipient melting of the crust at c. 430 Ma. Continued heating during prograde metamorphism at c. 420 Ma resulted in the main migmatization event (D3) and related granitoid genesis at c. 850 °C and >6 kbars. Following the peak P-T conditions, the crust was uplifted and cooled to 645-683 °C and 3-5k bars. Unconformably above the Late Silurian aged high-T rocks and granitoid intrusives are Early Devonian (c. 416-411) cover sequences indicating rapid exhumation of the crystalline basement. This suggests that the peak metamorphic conditions were followed by near isothermal decompression. The clockwise P-T-t path of the Krossfjorden Complex of Svalbard’s Northwestern Terrane is remarkably similar to rocks from the Krummedal Sequence and Smallefjord Sequence of central East Greenland, confirming the close link between these areas prior to the Late Caledonian orogeny.