Abstract

The Caledonian-Appalachian belt formed in the Early Palaeozoic by the assembly and dispersal of continental and oceanic crustal fragments of diverse provenance. The characterization of these terranes, and information on their origins, are essential in reconstructing the course of the orogeny. The region of northern Gudbrandsdalen in Norway is important for elaborating these questions as it represents an important geological transition in architectural style and composition of the Caledonian nappes and the meeting point of tectonic elements with diverse geological histories of both Baltic and exotic origins. In the past century this complexity has generated conflicting interpretations, which we have tested with new mapping and ID-TIMS U-Pb dating. The new data show that: (1) a meta-gabbro low in the tectonostratigraphy is 1497 ± 5 Ma, correlating with the Espedalen Complex of Telemarkian (1550-1480 Ma) affinity; (2) the structurally higher crystalline Rudihøe-Mukampen Suite (RMS) was metamorphosed at high grade during the Sveconorwegian Orogeny, mainly between 980 and 900 Ma, with older components pointing to a Gothian (1700-1600 Ma) affinity; (3) these ages and mapping indicate that the RMS is a lateral equivalent of the Upper Jotun Nappe; (4) the overlying, dominantly metasedimentary Steinhø Complex was metamorphosed in the Ordovician at about 473 ±3 Ma, and (5) both the RMS and Steinhø Complex were intruded by trondhjemite dykes at 430-427 Ma. These units are structurally overlain by the lowest elements of the Trondheim Nappe Complex, which includes serpentinite lenses and conglomerates, the products of hyperextension, locally with Ordovician fossils. The new results dispel some of the problematic interpretations proposed earlier and represent new firm elements that will anchor future tectonic reconstructions of the Caledonides in this region.

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