NJG89-4-02
2009
Geochronology of magmatism in the Caledonian and Sveconorwegian belts of Baltica: synopsis for detrital zircon provenance studies
89
4
pp. 267-290
978-82-92394-57-1

A compilation of literature concerning U-Pb geochronological data recording magmatic events is presented for the Sveconorwegian and Caledonian belts of Baltica. It illustrates the episodic nature of magmatism along the western margin of Baltica from Archaean to Permian and helps identify primary zircon sources for detrital zircon provenance studies in North Atlantic regions. Archaean orthogneisses ranging from 2885 to 2635 Ma occur in basement windows in the northern Caledonides. Voluminous Palaeoproterozoic, mainly felsic, magmatism is regarded as part of the Transcandinavian Igneous Belt: it is dated at 1805-1770 Ma in the Nordland, Lofoten and Rombak windows, 1686-1621 Ma in the West Norway Gneiss Complex, and mainly 1797-1640 Ma in the Eastern Segment of the Sveconorwegian belt. As a first approximation, crystalline sheets in the Middle Allochthon mirror basement windows at equivalent latitudes. Voluminous Mesoproterozoic magmatism ranges from 1659 to 1517 Ma in the Idefjorden Terrane, 1572 to 1460 Ma in the Bamble and Kongsberg Terranes and 1555 to 1459 Ma in the Telemarkia Terrane. The Sveconorwegian belt hosts a variety of local to regional magmatic suites covering the entire time spans between 1473 and 1130 Ma and between 1060 and 914 Ma. Sveconorwegian post-collisional suites between 971 and 914 Ma are voluminous in the west of the belt and include anorthosites. Pre-Sveconorwegian (1257-1237 and 1190 Ma) and Sveconorwegian (976 to 891 Ma) intrusions are common in the southern part of the Caledonides, while, in the Northern Caledonides, minor 981-973 Ma granite plutonism is reported in the Kalak Nappes. The Caledonian and Sveconorwegian belts are poor in Cryogenian to Ediacaran magmatism, the only significant exceptions being the Seve and Kalak Nappes showing low volume suites at 876-825 Ma and 711-680 Ma and the 571-523 Ma Seiland Igneous Province. Cambro-Silurian magmatism ranging from 497 to 424 Ma and including Iapetan ophiolites and volcanic arcs is specific for the Upper and Uppermost Allochthons of the Caledonides. Scandian to late-Scandian pegmatites and minor intrusions range from 436 to 390 Ma in the basement windows and the Middle Allochthon. Dated magmatism in the Oslo rift ranges from 300 to 277 Ma. The compilation highlights the Mesoproterozoic signature of the Sveconorwegian belt. Erosion of primary magmatic sources in the Sveconorwegian belt can generate a whole range of Palaeoproterozoic to Mesoproterozoic detrital zircons ranging from ca. 1800 to 900 Ma, with only one clear gap between 1130 and 1060 Ma corresponding to the onset of the Sveconorwegian orogeny. Erosion of magmatic rocks in the Caledonides can produce a discontinuous distribution of detrital zircons characterized by a number of discrete modes ranging from Archaean to Devonian, and large gaps in the early Palaeoproterozoic (2500-1940 Ma), and in the Mesoproterozoic and Neoproterozoic. Primary magmatic source rocks contribute only marginally to the present day discharge from the Caledonides. This implies, not unsurprisingly, major sourcing in metasediments exposed in Caledonian allochthons and widespread sediment polycyclism.

bernard.bingen @ ngu.no
029-196X
Print