Palaeoproterozoic U-Pb ages of autochthonous and allochthonous granites from the northern Swedish Caledonides - regional and palaeogeographic implications

• In the Silurian, Baltica and Laurentia collided to form the Caledonian orogenic belt. During this process, nappes derived from the pre-collisional Baltic margin, from outboard terranes of Baltica, and from exotic terranes of probable Laurentian origin, respectively, were thrust upon the indenting Baltica. The Middle Allochthon is a tectonostratigraphic level inferred to represent the rifted Neoproterozoic margin of Baltica and is heterogeneously composed of telescoped fault-controlled sedimentary basins and subjacent basement plinths. In the Akkajaure area of northern Sweden, the Middle Allochthon consists mainly of granites (Akkajaure Nappe Complex). The Ritsem Granite, a part of the (para-) authochthonous basement below the nappe complexes, yields a U-Pb zircon and titanite age of 1871 +/- 11 Ma. Granite and felsic dykes in the lowermost thrust-sheet in the Middle Allochthon yield ages of 1800 +/- 2 Ma and 1795 +/- 4 Ma, respectively. The granite of the overlying thrust-sheet is 1781 +/- 2 Ma old and crosscutting dykes are 1779 +/- 7 Ma. These ages constrain the pre-Caledonian position of the nappe complex to the general region west of Lofoten, northwestern Norway, substantiating a link with the Transscandinavian Igneous Belt (TIB) of the Fennoscandian Shield. (C) 2004 Elsevier B.V. All rights reserved.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

Nyckelord

Palaeoproterozoic

U-Pb ages

caledonides

allochthonous

granitoids

basement

Sweden

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art (ämneskategori)

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