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The Plat Sjambok Anorthosite crops out near Prieska Copper Mines in the Namaqua-Natal Province of southern Africa. It is a massif-type anorthosite, previously regarded as a late-tectonic intrusion and part of the ca. 1100Ma bimodal Keimoes Suite. Our new ion probe U-Pb zircon data show that the Plat Sjambok massif intruded at 1259 +/- 5Ma, before the 1220Ma Namaqua collision events and is thus approximately 150million years older than the Keimoes Suite. Despite the proximity to Prieska Mines, the anorthosite is located in the Kaaien Terrane close to the Brakbos Fault, which is the boundary with the Areachap Terrane in which Prieska Mines is situated. We dated the Nelspoortjie Tonalite, the main country rock of the Plat Sjambok Anorthosite, by laser ablation ICPMS at 1273 +/- 13Ma. Both intrusions thus originated concurrently with the 1286-1241Ma volcanic rocks of the Areachap Group, which developed in a subduction-related arc setting, prior to its collision with the Kaaien Terrane and Kaapvaal Craton. Metamorphic zircon rims in the Plat Sjambok Anorthosite give an age of 1122 +/- 7Ma, a time that corresponds to a quiet period in the Areachap Terrane. We propose a tectonic model in which formation of the Nelspoortjie Tonalite and Plat Sjambok Anorthosite was driven by intrusions from the mantle into a back-arc related tensional environment within the Kaaien Terrane, possibly situated above an Archaean crustal tongue. This led to heating in a thickened crustal setting in which the tonalite originated as a partial melt of amphibolite. The anorthosite then formed as a mixture of mantle-derived gabbro and Archaean crustal rocks, which explains the 2100-2600Ma zircon-Hf crustal residence ages and the Sm-Nd trend towards an old crustal source. The anorthosite and its country rocks were only juxtaposed with the Prieska Copper Mining District by late-tectonic uplift and transpressional movements on the Brakbos Fault towards the end of the Namaqua tectogenesis.

The Sveconorwegian Province occupies the southwestern part of the Fennoscandian Shield. The easternmost tectonic unit of the Province is the 1710-1660 Ma parautochthonous Eastern Segment, which bears the imprint of at least two metamorphic events; the 1460-1380 Ma Hallandian and the 1150-970 Ma Sveconorwegian. However, the nature and extent of the Hallandian event have been difficult to access due to the Sveconorwegian, effectively masking earlier metamorphic assemblages, structures and relations between rock units. This thesis aims to characterize the Hallandian event by investigating pre-Sveconorwegian deformation and metamorphism in an area of the Eastern Segment that largely escaped later Sveconorwegian reworking. These results are then considered in a regional perspective and related to ~1.45 Ga magmatism and metamorphism observed elsewhere in Fennoscandia. Considering the compiled data from this time period, it now appears that the Hallandian event indeed was a true orogenic event that affected a large portion of the Fennoscandian Shield. In the study area, located within the Protogine Zone in the eastern part of the Eastern Segment near Jonkoping, Sveconorwegian reworking is restricted to discrete, N-S trending shearzones. Between these shear-zones, structures, mineral assemblages and geochronological information from pre-Sveconorwegian events are preserved. The first paper provides field, mineral and chemical characteristics, as well as a baddeleyite U-Pb crystallization age of 1455±6 Ma for the Jonkoping Anorthositic Suite which is abundant across the study area as small intrusive bodies. In these plagioclase-porphyritic and equigranular anorthositic rocks, deformation is restricted to thin, E-W-trending shear-zones. In the second paper we investigate the deformed country-rocks and date metamorphism and the development of the E-W to SE-NW trending gneissic fabric at 1450-1400 Ma, using U-Pb secondary ion mass spectrometric (ion probe) analysis of complex zircons. The folding event is bracketed between 1440 and 1380 Ma, corresponding to the ages of leucosome formation and the emplacement of a cross-cutting aplitic dyke. In the third paper, the gabbroic Moslatt dolerites are dated at 1269±12 Ma using the U-Pb system in baddeleyite. These have well-preserved magmatic parageneses in contrast to nearby metamorphosed mafic dykes of the 1450-1420 Ma Axamo Dyke Swarm. This precludes the Sveconorwegian event from having caused amphibolite facies metamorphism in the area. In the fourth paper, the first estimate of Hallandian pressure and temperature conditions is obtained from mineral assemblages in one of the E-W-trending shear-zones. Pressure-temperature estimates and hornblende microtextures collectively suggest deformation under conditions of 7-8 kbar and 500-550°C. In the fifth paper we constrain the age of the gneissic fabric in the granitoid country-rock at around 1422 Ma by dating a member of the syn-kinematic felsic Axamo dykes, using the U-Pb ion probe technique. It is suggested that the mafic and plagioclase-porphyritic members of the Axamo Dyke Swarm were emplaced coeval with the Jonkoping Anorthositic Suite. This thesis is the first contribution which recognizes the Hallandian as a regional scale orogenic event, acknowledging all the major features of that age in the Fennoscandian Shield. These features include ~1460 Ma rifting, deposition of clastic sediments and extrusion of continental basalts in central Fennoscandia, 1460-1440 Ma emplacement of Ito A-type granitoids in southern Fennoscandia, 1450-1420 Ma deformation and metamorphism in southern Sweden and on Bornholm, and 1410-1380 Ma post-kinematic pegmatite dykes and intrusions of granite, monzonite and charnockite in the Eastern Segment. The spatial and temporal trends of these features suggest a tectonic model in which the rifting and mafic magmatism to the north are the far-field effects of north-eastward subduction of an oceanic plate, with the subduction zone located to the southwest of present-day Fennoscandia. Collision with an unknown (micro-) continent led to crustal shortening as Fennoscandia overrode this unknown continent. Post-collisional collapse triggered decompressional melting of heated continental crust, resulting in the emplacement of post-kinematic dykes and plutons

We present major and trace element data for eighteen 1.71–1.66 Ga granitoid samples, and Sm–Nd whole‐rock isotope data for eleven of these samples, in a transect across the border between the Transscandinavian Igneous Belt (TIB) and the Eastern Segment in central southern Sweden. The geochemistry of the granitoids varies from alkalic to alkali‐calcic and peraluminous in the east to predominantly calc‐alkaline and metaluminous in the west. Rocks in the west also have lower SiO2contents. Trace element signatures favour formation in an active continental margin setting. Nd isotope data are completely overlapping along the transect and initialεNdvalues are mildly depleted in the range +0.3 to +2.6. The combined data suggest that the magmas were derived mainly from juvenile, pre‐existing crust, increasingly mafic and less alkaline towards the west. Copyright © 2011 John Wiley & Sons, Ltd.

Between 1271 and 1246 Ma, dolerite dykes and sills of the Central Scandinavian Dolerite Group intruded into the Fennoscandian Shield during three distinct magmatic pulses. They are distributed around five large magmatic complexes extending from Sweden to western Finland and record large-scale intracratonic tensional stress. Coeval plutonism is observed in the westernmost terrane of the Sveconorwegian orogen in southern Norway, but differs in the sense of a bimodal character and uncertain Fennoscandian ancestry of the host terrane. We report a U-Pb baddeleyite age of 1269 +/- 12 Ma for a gabbronoritic member of an E-trending set of dykes, called the Moslatt Dolerites, near Lake Vattern in southern Sweden, much farther to the south than any previously known Central Scandinavian Dolerite Group rock. A similar age of approximately 1275 Ma is obtained for a metadolerite sheet in the Borgefjell basement window in the Scandinavian Caledonides in Mid-Norway. The initial epsilon-Hf values for these two dykes are +3.9 and +10.1, respectively, and correspond to the range of values for other occurrences of the Central Scandinavian Dolerite Group (+4.7 to +10.3). They add to the evidence that the Central Scandinavian Dolerite Group is characterized by more positive epsilon values (depleted source) than other mafic Proterozoic suites in Fennoscandia. These results extend the distribution of c. 1270-1245 Ma mafic magmatism in Fennoscandia, particularly when accounting for significant Caledonian shortening. The Central Scandinavian Dolerite Group and coeval bimodal magmatism in S Norway may represent distal magmatic events related to a Mesoproterozoic subduction along the western margin of Fennoscandia rather than hotspot (mantle plume) activity as previously suggested.

The Eastern Segment abutting the Transscandinavian Igneous Belt (TIB) mostly consists of rocks with overlapping igneous ages. In the Eastern Segment west of Lake Vättern, granitoids of clear TIB affinity exhibit strong deformational fabrics. This article presents U–Pb zircon ages from 21 samples spanning the border zone between these deformed TIB rocks in the east, and more thoroughly reworked rocks in the west. Magmatic ages fall in the range 1710–1660 million years, irrespective of the degree of deformation, confirming the overlapping crystallization ages between deformed TIB rocks and orthogneisses of the Eastern Segment. A common history is further supported by leucocratic rocks of similar ages. Prolonged orogenic (magmatic) activity is suggested by continued growth of zircon at 1.66–1.60 Ga. Six of the weakly gneissic rocks show zircons with cathodoluminescence-dark patches and embayments, possibly partly replacing metamict parts of older magmatic crystals, with 207Pb/206Pb ages dominantly between 1460 and 1400 million years, whereas three of the gneisses have zircon rims with calculated ages of 1440–1430 million years. Leucosome formation took place at 1443 ± 9 and 1437 ± 6 Ma. The minimum age of SE–NW folds was determined by an undeformed 1383 ± 4 million years crosscutting aplitic dike. Sveconorwegian zircon growth was not found in any of the samples from the studied area. To our knowledge, 1.46–1.40 Ga metamorphism affecting the U–Pb zircon system has not previously been reported this far northeast in the Eastern Segment. We suggest that the E–W- to SE–NW-trending deformation fabrics in our field area were produced during the Hallandian–Danopolonian orogeny and escaped later, penetrative Sveconorwegian reworking.

We present detailed microstructural and chemical analyses from an initially dry anorthositic rock deformed during wet amphibolite facies conditions. Three different domains representing the microstructural variation of the deformed samples are investigated in detail in terms of fracture morphology and mode, grain characteristics and chemistry of present phases. Results show transient deformational behaviour where a close interaction between brittle, plastic and fluid-assisted deformation mechanisms can be observed. Our analysis allows us to describe the succession, interrelationships and effects of active mechanisms with progressively increasing strain in three so-called stages. In Stage 1, initial fracturing along cleavage planes promoted fluid influx that caused fragmentation and chemical reactions, producing fine-grained mineral assemblages in the fractures. Deformation twins and dislocations developed in clast pieces due to stress relaxation. Passive rotation of conjugate fracture sets and interconnection of intracrystalline fractures formed micro-shear-zones, constituting Stage 2. Microstructures and grain relationships indicate the activity and fluctuation between fracturing, dissolution-precipitation creep, grain boundary sliding and locally dislocation creep, reflecting the transient behaviour of brittle and plastic deformation mechanisms. Further rotation and widening of fractures into overall foliation parallel shear-bands (Stage 3) promoted strain partitioning into these areas through increased fluid influx, influence of fluid-assisted grain boundary sliding, phase mixing and presence of weak phases such as white mica. We suggest that local differences in fluid availability, volume fraction of weak phases produced by fluid present metamorphic reactions coupled with volume increase and local variations in stress concentration induced transient brittle-plastic behaviour. The studied shear-zone represents an example of the transformation of a rigid dry rock to a soft wet rock during deformation through syntectonic fracturing.

Deformation and recrystallisation of plagioclase in the brittleductile transition zone during fluid-present conditions. Deformation mechanisms, Rheology and Tectonics, Liverpool

The Jönköping Anorthositic Suite (JAS) in S. Sweden has characteristics typical for (Proterozoic) massif-type anorthosites. The interstitial liquid of these plagioclase-porphyritic rocks solidified at 1,455 ± 6 Ma, as determined by U–Pb isotope analysis of baddeleyite. The JAS developed during a regional 1.47–1.44 event in Fennoscandia that generated widespread mafic magmatism (basalts, and diabase dykes and sills) in the north and emplacement of felsic plutons in the south. The event of 1.47–1.44 Ga magmatism in Fennoscandia largely coincides in age with dynamic high-grade metamorphism in SW Sweden and was probably related to convergent active-margin processes during the Danopolonian orogeny.

Abstract The Habo Volcanic Suite is situated in the southwestern part of the Småland-Värmland batholiths of the Transscandinavian Igneous Belt (TIB), Sweden. It comprises mainly intermediate to mafic pyroclastic and redeposited volcanic rocks and is distinct from other, more felsic, volcanic rocks of the Småland-Värmland batholiths. The Habo Volcanic Suite has been intruded by a TIB-granite, here dated at 1660±9 Ma. U-Pb ages of zircon from the Habo Volcanic Suite fall into two groups; 1795±14 Ma for domains with Th/U >0.2 and 1694±7 Ma for rims with Th/U <0.2. The 1795±14 Ma age is interpreted as the crystallization age of the Habo Volcanic Suite, linking it to other Småland volcanic rocks, whereas the 1694±7 Ma rims are interpreted to reflect a thermal event related to intrusions of younger TIB rocks. These interpretations are supported by LA-ICPMS REE analyses which show flatter REE patterns and Th/U <0.2 for metamorphic zircon; and positive Ce anomalies for magmatic zircon. Two geochemically different groups of the Habo Volcanic Suite can be distinguished. The first consists of primitive, alkaline mafic rocks whereas the second group comprises felsic to intermediate, subalkaline compositions. Mixing or crustal assimilation between a juvenile basaltic magma and an upper-crustal component is likely to have formed the second group. The mixing, as well as the geochemical signatures and the great abundance of intermediate volcanic rocks strongly suggest an active continental margin setting for the Habo Volcanic Suite, supporting previously suggested theories of an Andean-type convergent continental margin setting for the TIB.