Eclogites in the Tromsø area, northern Norway, are intimately associated with meta‐supracrustals within the Uppermost Allochthon of the Scandinavian Caledonides (the Tromsø Nappe Complex). The whole sequence, which includes pelitic to semipelitic schists and gneisses, marbles and calc‐silicate rocks, quartzofeldspathic gneisses, metabasites and ultramafites, has undergone three main deformational/metamorphic events (D 1 /M 1 , D 2 /M 2 and D 3 /M 3 ). Detailed structural, microtextural and mineral chemical studies have made it possible to construct separate P–T paths for these three events. Chemically zoned late syn‐ to post‐D 1 garnets with inclusions of Bt, Pl and Qtz in Ky‐bearing metapelites indicate a prograde evolution from 636°C, 12.48 kbar to c. 720°C, 14–15 kbar. This latter result is in agreement with Grt–Cpx geothermometry and Grt–Cpx–Pl–Qtz geobarometry on eclogites and trondhjemitic to dioritic gneisses. Maximum pressures at c. 675°C probably reached 17–18 kbar based on Cpx–Pl–Qtz inclusions in eclogitic garnets, and Grt–Ky–Pl–Qtz and Jd–Ab–Qtz in trondhjemitic gneisses. Post‐D 1 / pre‐D 2 decompressional breakdown of the high‐ P assemblages indicates a substantial drop in pressure at this stage. Inclusions and chemical zoning in syn‐ to post‐D 2 garnets from metapelites record a second episode of prograde metamorphism, from 552°C, 7.95 kbar, passing through a maximum pressure of 10.64 kbar at 644°C, with final equilibration at c. 665°C, 9–10 kbar. The corresponding apparently co‐facial paragenesis Grt + Cpx + Pl + Qtz in metabasites yields c. 635°C, 8–10 kbar. In the metapelites post‐D 3 , Grt in apparent equilibrium with Bt, Phe and Pl yield c. 630°C, 9 kbar. The D 1 /M 1 and D 2 /M 2 episodes are exclusively recorded in the Tromsø Nappe Complex and must thus pre‐date the emplacement of this allochthonous unit on top of the underlying Lyngen Nappe, while the D 3 /M 3 episode is common for the two units. A previously published Sm–Nd mineral isochron (Grt–Cpx–Am) on a partly retrograded and recrystallized ecologite of 598 ± 107 Ma represents either the timing of formation of the eclogites or the post‐eclogite/pre‐D 2 decompression stage, while a Rb–Sr whole rock isochron of an apparently post‐D 1 /pre‐D 2 granite of 433 ± 11 Ma is consistent with a K–Ar age of post‐D 1 /pre‐D 2 amphiboles from a retrograded eclogite of 437 ± 16 Ma which most likely record cooling below the 475–500°C isotherm after the M 3 metamorphism.
Summary Continental Middle Devonian sediments of the Kvamshesten district have recently been interpreted as a thrusted block. However, although basal contacts in the E of the district are mylonitized, contacts in the W can be interpreted as depositional unconformities. Coarse alluvial-fan breccias (Markavatn Formation) in the district's northern margins interdigitate with fluviatile sandstones (Heilefjell Formation) towards the basin's centre. Syndepositional tectonism is demonstrated by the geometry of the coarse marginal deposits.
hic gneisses of Nordfjord are similar to the oceanic tholeiites in their low content of titanium, ferric iron, potassium, and phosphorus. The chemical composition of the eclogites varies, how ever, within wide limits, and it is probable that alterations of bulk chemical compositions have taken place if the eclogites were indeed formed by transformations from other basic rocks. The garnets contain 36-50% Alm, 0.4-1.9% Spess, 23-43% Py, 0.3-2.1% And, and 13-25% Gross. Clinopyroxenes contain 3-9% Ac, 23-42% Jd, 8-13% Tsch, 3-7% Hd, and 38-56% Di. Titanium, nickel, chromium, and strontium are concentrated in dino pyroxene relative to garnet, while cobalt, manganese, scandium, and zir conium are relatively concentrated in garnet. Eclogites from gneiss of Nordfjord differ from the eclogites endosed in ultrabasites of Sunnmore bothin bulk chemistry, composition of garnet and clinopyroxene, and in the partition of elements between garnet and dinopyroxene. The ultrabashes occur in leetonised zones and might represent rocks which are tectonically emplaced, but the eclogites enclo3ed in gneiss are Iikely to be original crustal rocks. They occur as disrupted layers or boudins in paragneiss in harmony with a formation from dry basic igneous and sedimentary rocks endosed in a thick geosynclinal pile of supracrustals which were rapidly buckled down to great depths and metamorphosed there. Elements that could not easily be accommodated
Summary Early Palaeozoic metamorphism is represented in several of the nappes of the Scandinavian Caledonides, although it is often severely overprinted by late Silurian-early Devonian events. It is defined particularly in N Norway where the Finnmarkian phase probably reached peak conditions at about 535 Ma with extensive cooling and uplift at about 485 Ma. On Spitsbergen there was a phase of low- to high-grade metamorphism of jadeite-glaucophane type prior to the late Ordovician-Silurian.
ABSTRACT A structure illustrated as a sand volcano in the recent textbook of Reineck and Singh (1973) is interpreted as a patterned conical pit formed by water welling up through unconsolidated coarse silt, i.e., formed with geometry opposite that of a volcano. Corresponding pits with patterned sides have since been found in situ. The patterned cones and pits occur in sandstones assumed to have formed in a braided stream/floodplain environment, close to coarse alluvial fans, where it is very likely that artesian water could have been produced.
Various isolated bodies of gabbro in the Old Red Sandstone Series at Hers vikbygda in Solund (Fig. l) were regarded by Kolderup (1916, 1925, 1926a) as erosional fragments of a once continuous sheet, 30-80 metres thick and at least 7 km2 in extent. He interpreted this as a thrust, but Nilsen (1968) claimed that the gabbro bodies occurred at more than one stratigraphic level and that there was only little mylonitization or disturbance at their contacts. Nilsen suggested that the gabbro bodies actually were intrusive sills associated with the quartz keratophyres (Kolderup 1926a, b) which occur in the same area. Either of these interpretations have serious implications for our under standing of the waning stages of the Caledonian orogeny in Norway. Thrust ing had already been inferred when Vogt (1929) defined the late-orogenic 'Svalbardian' phase and the presence of such a thrust sheet could be applied elsewhere, for the apparently enormous thicknesses of the Devonian rocks in other districts (Bryhni 1964) could be explained as a sequence of such thrusts. On the other hand, Nilsen's explanation would require that igneous activity during or after deposition of the Old Red Sandstone Series in Norway was much more significant than hitherto recognized.
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