The geology of northeastern Mozambique has been remapped at 1:250 000 scale. Proterozoic rocks, which make up the bulk of the area, form a number of gneiss complexes defined on the basis of their lithologies, metamorphic grade, structures, tectonic relationships and ages. The gneiss complexes, which contain both ortho- and paragneisses, range from Palaeo- to Neoproterozoic in age, and were juxtaposed along tectonic contacts during the late Neoproterozoic to Cambrian Pan-African Orogeny. In this paper we describe the geological evolution of the terranes north of the Ludo Belt, a major tectonic boundary which separates the complexes described in this paper from the Nampula Complex to the south. The Marrupa, Nairoto and Meluco Complexes are dominated by orthogneisses of felsic to intermediate compositions. Granulitic rocks, including charnockites, are present in the Unango, M'Sawize, Xixano and Ocua Complexes (the last forms the centre of the Lurio Belt). The Neoproterozoic Geci and Txitonga Groups are dominated by metasupracrustal rocks at low metamorphic grades and have been tectonically juxtaposed with the Unango Complex. Geochemical data integrate and support: a model of terrain assembly in northeast Mozambique, which is largely published and mainly derived from our new geochronological, lithostratigraphic and structural work. This model shows the contrast between the mainly felsic lower tectonostratigraphic levels (Unango, Marrupa, Nairoto and Meluco Complexes) and the significantly more juvenile overlying complexes (Xixano, Muaquia, M'Sawize, Lalamo and Montepuez Complexes), which were all assembled during the Cambrian Pan-African orogeny. The juxtaposed terranes were stitched by several suites of Cambrian late- to post-tectonic granitoids.

Pan-African high-pressure granulites occur as boudins and layers in the Lurio Belt in north-eastern Mozambique, eastern Africa. Mafic granulites contain the mineral assemblage garnet + clinopyroxene + plagioclase + quartz +/- magnesiohastingsite. Garnet porphyroblasts are zoned with increasing almandine and spessartine contents and decreasing grossular and pyrope contents from core (Alm(46)Prp(32)Grs(21)Sps(2)) to rim (Alm(52)Prp(26)Grs(19)Sps(3)). This pattern is interpreted as a retrograde diffusion zoning with the preserved core chemistry representing the peak metamorphic composition. Mineral reaction textures occur in the form of monomineralic and composite plagioclase +/- orthopyroxene +/- amphibole +/- biotite +/- magnetite coronas around garnet porphyroblasts. Thermobarometry indicates peak metamorphic conditions of up to 1.57 +/- 0.14 GPa and 949 +/- 92 degrees C (stage I), corresponding to crustal depths of similar to 55 km. Zircon yielded an U-Pb age of 557 +/- 16 Ma, inferred to date crystallization of zircon during peak or immediately post-peak metamorphism. Formation of plagioclase + orthopyroxene-bearing coronas surrounding garnet indicates a near-isothermal decompression of the high-pressure granulites to lower pressure granulite facies conditions (stage II). Development of plagioclase + amphibole-coronas enclosing the same garnet porphyroblasts shows subsequent cooling into amphibolite facies conditions (stage III). Symplectitic textures of the corona assemblages indicate rapid decompression. The high-pressure granulite facies metamorphism of the Lurio Belt, followed by near-isothermal decompression and subsequent cooling, is in accordance with a long-lived tectonic history accompanied by high magmatic activity in the Lurio Belt during the late Neoproterozoic-early Palaeozoic East-African-Antarctic orogeny.

Granulite-facies metamorphism is extensively reported in Late Neoproterozoic/Early Palaeozoic time during formation of the East-African-Antarctic orogen (EAAO). Metamorphic data acquired from the Pan-African orogen of central Dronning Maud Land (cDML) are compared with data from northern Mozambique. The metamorphic rocks of cDML are characterised by Opx±Grt-bearing gneisses and Sil+Kfs-bearing metapelites which indicate medium-P granulite-facies metamorphism. Peak conditions, which are estimated to 800-900ºC at pressures up to 1.0 GPa, were followed by near-isothermal decompression during late Pan-African extension and exhumation. Granulite-facies lithologies are widespread in northern Mozambique, and Grt+Cpx-bearing assemblages show that high-P granulite-facies conditions with PT reaching 1.55 GPa and 900ºC were reached during the Pan-African orogeny. Garnet is replaced by symplectites of Pl+Opx+Mag indicating isothermal decompression, and the subsequent formation of Pl+amphibole-coronas suggests cooling into amphibolite facies. It is concluded that high-T metamorphism was pervasive in EAAO in Late Neoproterozoic/Early Paleozoic time, strongly overprinting evidences of earlier metamorphic assemblages.

B. Bingen, G. Viola, W. L. Griffin, J. Jacobs, R. Boyd, R.J. Thomas, E. Daudi, I.H.C. Henderson, E. Beyer, O. Skar, A. Engvik, R.M. Key, A. Solli, J.S. Sandstad, M. Smethurst, E. Tveten, T. Bjerkgard, V.A. Melezhik, D. Jamal, R. Smith, L.M. Hollick, P. Feito 1. Geological Survey of Norway, 7491 Trondheim, Norway, bernard.bingen@ngu.no 2. Department of Earth and Planetary Sciences, Macquarie University, NSW 2109 Australia 3. Department of Earth Science, University of Bergen, 5007 Bergen, Norway 4. British Geological Survey, NG125GG Keyworth, UK 5. National Directorate for Geology, Maputo, Mozambique 6. Eduardo Mondlane University, Maputo, Mozambique

Magnetic and gravity anomalies within the northern Norwegian margin, 67 degrees to 71 degrees N are generally interpreted in terms of a complex series of uplifted and rotated basement blocks. Some of the basement highs were previously not identified on seismic reflection data because they lie below basalt Bows. Several shifts in polarity occur along the faults in the continental shelf and the adjacent onshore area. This is most pronounced along the Ribban and Vestfjorden Basins and further to the northeast along the Vestfjorden-Vanna fault complex. The individual segments of the fault complexes are connected by transfer zones, which occur as either: (1) transverse faults, e.g. the Lenvik transfer zone, or (2) twist zones, e.g. the Vesteralen transfer zone. The Vestfjorden Basin consists of two subbasins or half-grabens: one to the north with a border fault to the east and one to the south with a border fault to the west. Several basement faults on the continental shelf can be traced onto the mainland. Reactivation of old shea zones is commonly observed. The Senja Fracture Zone is a reactivation of the Proterozoic Bothnian-Senja fault complex. A palaeomagnetic study of Vesteralen, Senja and Kvaloya has furnished temporal constraints on the near-shore fault activity. On Senja and Kvaloya, two phases of faulting and brecciation have been identified. A young phase, associated with the formation of fault-gouges, is recent-Tertiary in age, whereas an older phase, associated with brecciation, is of Permian age. The lack of Cretaceous/Jurassic faulting along the central Vestfjorden-Vanna fault complex indicates that there may have been a westward shift of the regional fault activity in the Nordland-Troms area from the Carboniferous-Permian to the late Jurassic-early Cretaceous.

Magnetic and gra vi ty anomalies within the northern Norwegian margin, 67° to 71 oN are generally interpreted in terms of a complex series of uplifted and rotated basement blocks. Some of the basement highs were previously not identified on seismic reftection data because they Iie below basalt ftows. Several shifts in polarity occur along the faults in the continental shelf and the adjacent onshore area. This is most pronounced along the Ribban and Vestfjorden Basins and further to the northeast along the Vestfjorden-Vanna fault complex. The individual segments of the fault complexes are connected by transfer zones, which occur as either: (l) transverse faults, e.g. the Lenvik transfer zone, or (2) twist zones, e.g. the Vesterålen transfer zone. The Vestfjorden Basin consists of two subbasins or half-grabens: one to the north with a border fault to the east and one to the south with a border fault to the west. Several basement faults on the continental shelf can be traced onto the mainland. Reactivation of old shear zones is commonly observed. The Senja Fracture Zone is a reactivation of the Proterozoic Bothnian-Senja fault complex. A palaeomagnetic study of Vesterålen, Senja and Kvaløya has furnished tempora! constraints on the near-shore fault activity. On Senja and Kvaløya, two phases of faulting and brecciation have been identified. A young phase, associated with the formation of fault-gouges, is recent-Tertiary in age, whereas an older phase, associated with brecciation, is of Permian age. The Jack of Cretaceous/Jurassic faulting along the central Vestfjorden-Vanna fault complex indicates that there may have been a westward shift of the regional fault activity in the Nordland-Troms area from the Carboniferous-Permian to the late Jurassic-early Cretaceous.

The Vesteralen-Lofoten area in northern Norway is a province of deep-seated origin with associated regional magnetic and gravimetric anomalies. A regional transition zone between amphibolite and granulite-facies gneisses has been examined in detail with regard to interpretation of aeromagnetic and gravimetric data in northern Fennoscandia. The location of this petrographical boundary is defined by the first appearance of orthopyroxene in the intermediate gneisses. This orthopyroxene isograd is situated within an approximately 3 km wide magnetic transition zone where the average magnetite content increases fairly gradually from approximately 0.05% in the amphibolite facies t-sigma 1.0% in the granulite facies. These estimates are based on in-situ susceptibility measurements which show an increase from 150.10(-5) SI to 3000.10(-5) SI. Magnetite is by far the most common Fe-oxide. The orthopyroxene isograd is situated approximately 500 m from the point where the susceptibility starts to increase. A few of the samples in the granulite facies have garnet occurring as coronas around Fe-Ti oxides and pyroxenes, indicating high-pressure retrograde metamorphism. Prograde textures, however, predominate.Density shows a moderate increase across the profile, varying from 2.75.10(3) kg/m3 in the amphibolite-facies rocks, through 2.77.10(3) kg/m3 in the transition zone, to 2.81.10(3) kg/m3 in the granulite-facies rocks. The Q-values are 2.0 for the amphibolite facies, 0.45 for the transition zone and 0.27 for the granulite facies. The remanence is predominantly viscous, and probably influenced by coarse-grained multidomain magnetite.Based on susceptibility measurements and thin section studies it is concluded that the prograde metamorphism occurred at the same time as or before the development of numerous fractures in which fluids such as CO2 had easy access. Sparse retrograde metamorphism in the granulite zone took place along more localized microshears that appear to have been carriers of H2O.

The region exposes an unusually deep section through the continental crust. Gravity and seismic surveys show a ridge-like NE-SW up-warping of the Moho to within 25 km of the surface. The oldest rocks are migmatitic gneisses of generally intermediate composition, probably largely of supracrustal origin; these were intruded by a granodiorite/granite pluton at about 2600 Ma. Pb isotope data indicate that the migmatites formed c. 2700 Ma ago, and the isotopic systems in some rocks have been disturbed by Proterozoic granulite-facies metamorphism. A Proterozoic supracrustal series is composed dominantly of felsic metavolcanic gneisses but includes marble, quartzite, graphite schist and iron formations. An Rb-Sr whole-rock isochron age of 1830 ±35 Ma is interpreted as the age of a metamorphism which reached intermediate-pressure granulite facies in the western part of the area. An early low-P, high-T event was followed by PT conditions near 900°C and 10 kbar at the metamorphic maximum. This thermal peak was essentially post-tectonic and coincided with the intrusion of gabbro, anorthosite and huge volumes of mangeritic to charnockitic magma between c. 1800 and c. 1700 Ma ago. A swarm of alkali-olivine dolerites was intruded shortly after the mangerites. The Lefdingen granitic batholith gives an Rb-Sr isochron age of 1380 ±80 Ma and may represent remobilized basement rocks. Pelitic schists of the Leknes Group were tectonically emplaced against the mangerites and gneisses, and metamorphosed in amphibolite facies 1140 ±135 Ma ago. Rb-Sr and K-Ar mineral ages suggest that the extensive retrograde metamorphism observed in the older rocks occurred at this time. Small granitic pegmatites were also emplaced during this episode. The Caledonian orogeny is recorded by some K-Ar mineral ages, the development of local W-dipping thrust zones, and the local intrusion of large pegmatites. Lofoten-Vesteralen was probably part of the Baltic plate during the Caledonian orogeny, but escaped deformation because it lay at a high tectonic level and consisted largely of massive granulite-facies rocks.