Palaeomagnetism and K-Ar ages of triassic igneous rocks from the Ischigualasto-Ischichuca Basin and Puesto Viejo Formation,Argentina

The palaeomagnetism of Middle Triassic (224 ± 5 m.y.) igneous rocks from the Ischigualasto-Ischichuca Basin (67°40′W, 30°20′S) was investigated through 86 oriented hand samples from 11 sites. At least one reversal of the geomagnetic field has been found in these rocks. Nine sites yield a palaeomagnetic pole at 239°E, 79°S (α₉₅ = 15°, k = 13).The K-Ar age determinations of five igneous units of the Puesto Viejo Formation give a mean age of 232 ± 4 m.y. (Early Triassic). The palaeomagnetism of six igneous units of the Puesto Viejo Formation (68°W, 35°S) was investigated through 60 oriented samples. These units, two reversed relative to the present magnetic field of the Earth and four normal, yield a pole at 236°E, 76°S (α₉₅ = 18°, k = 14).Data from the Puesto Viejo Formation indicate, for the first time on the basis of palaeomagnetic and radiometric data, that the Illawarra Zone, which defines the end of the Kiaman Magnetic Interval, extends at least down to 232 ± 4 m.y. within the Early Triassic. The palaeomagnetic poles for the igneous rocks of the Ischigualasto-Ischichuca Basin and Puesto Viejo Formation form an “age group” with the South American Triassic palaeomagnetic poles (mean pole position: 239°E, 77°S; α₉₅ = 6.6°, k = 190). The Middle and Upper Permian, Triassic and Middle Jurassic palaeomagnetic poles for South America would define a “time group” reflecting a quasi-static interval (mean pole position: 232°E, 81°S; α₉₅ = 4°, k = 131).     

A new palaeomagnetic result from East Africa and estimates of the Mesozoic palaeoradius

Of 16 sites collected in the Taru grits (Permian) and Maji ya Chumvi beds (Permo-Triassic) of East Africa only 6 sites from the Maji ya Chumvi sediments gave meaningful palaeomagnetic results. After thermal cleaning the 6 sites (32 samples) give an Early Triassic pole at 67°N, 269°E with A₉₅ = 17° in excellent agreement with other African Mesozoic poles. There are now 26 Mesozoic palaeomagnetic poles for Africa from widely diverse localities ranging in present latitude from 35°N to 30°S. The poles subdivide into Triassic (17 poles) and Cretaceous (9 poles) groups whose means are not significantly different. The palaeomagnetic pole for Africa thus remained in much the same position for 170 m.y. from Early Triassic to Late Cretaceous. The data form an especially good set for estimating the palaeoradius using Ward's method. Values of 1.08 ± 0.15 and 1.03 ± 0.19 times the present radius are deduced for the Triassic and Cretaceous respectively with a mean value of 1.08 ± 0.13 for all the Mesozoic data combined. The analysis demonstrates that hypotheses of earth expansion are very unattractive.     

Palaeomagnetism of upper cretaceous volcanic rocks in Sicily

From Upper Cretaceous volcanic rocks of Southeast Sicily 107 cores from 19 sites were collected giving a mean palaeomagnetic pole position at 62°N, 223°E, A₉₅ = 5.4° after AF-cleaning. This pole agrees with the Upper Cretaceous pole of Northern Africa indicating that no large post-Cretaceous relative motion has occurred between Africa and Sicily.     

Palaeomagnetic directions in Precambrian basic intrusives of the Mount Isa Province,Australia

Palaeomagnetic investigation of basic intrusives in the Proterozoic Mount Isa Province yields three groups of directions of stable components of NRM after magnetic cleaning in fields up to 50 mT (1 mT= 10 Oe). The youngest group (IA) includes results from the Lakeview Dolerite, and yields a palaeomagnetic pole at 12°S, 124°E (A₉₅ = 11°). The second group (IB) has a palaeomagnetic pole 53°S, 102°E (A₉₅ = 11°). The third group (IC) is derived from the Lunch Creek Gabbro and contains normal and reversed polarities of magnetization with a palaeomagnetic pole at 63°S, 201°E (A₉₅ = 9°). Some samples from the gabbro have anomalously low intensities of remanent magnetization in obscure directions attributed to the relative enhancement of the non-dipole component of the palaeomagnetic field during polarity reversal. The present attitude of the igneous lamination is probably of primary, not tectonic origin.     

Lead,uranium, strontium,potassium and rubidium in inclusion-bearing diamonds and mantle-derived xenoliths from Southern Africa

Measurements are reported of K, Rb and Sr levels and Sr isotopic compositions in silicate inclusions in diamonds, and of U, Th and Pb levels and Pb isotopic compositions in sulphide inclusions in diamonds. Samples are from the Premier Mine (Transvaal), the Finsch Mine (northern Cape Province) and the Kimberley mines (northern Cape Province). The isotopic composition of Pb in sulphide inclusions indicates that the diamonds containing these inclusions are xenocrysts in the host kimberlite. Model Pb ages for the sulphide inclusions in the diamonds from Finsch and Kimberley are in excess of 2 b.y., although the host kimberlites are Cretaceous. The sulphide inclusions from Premier, however, have a model age similar to the emplacement age of the Premier kimberlites (approximately 1.2 b.y.).In addition, K, Rb, Sr, U and Pb concentrations and Sr and Pb isotopic compositions in clinopyroxenes from 14 mantle-derived xenoliths were measured. Samples were eclogites from the Roberts Victor Mine (Orange Free State), peridotites from the Matsoku Pipe (Lesotho) and diopside megacrysts from the four mines in Kimberley. The samples from the Roberts Victor Mine define a large spread in Sr and Pb isotopic composition. The slope of a regression line through the Pb data in the 207/204 vs. 206/204 plot defines an age of roughly 2.5 b.y. The Matsoku samples have⁸⁷Sr/⁸⁶Sr ratios around 0.704. One group of samples (“fertile peridotites”) shows uniform, anomalously radiogenic Pb isotopic compositions, and bears evidence of a young event involving isotopic homogenisation. Lead isotopic heterogeneity, indicating an old age, has persisted in another group (“common peridotites”). The megacrysts from the four Kimberley mines have⁸⁷Sr/⁸⁶Sr ratios around 0.704 and uniform, anomalously radiogenic Pb isotopic compositions, indicating a young age. Their Pb isotopic uniformity contrasts with the spread shown by kimberlites in Kimberley, and shows that the megacrysts did not crystallise in equilibrium with their host kimberlites.The similarity between the Pb isotopic data obtained on clinopyroxenes from xenoliths and the data obtained on sulphide inclusions in diamonds from Finsch and Kimberley suggests that these diamonds might be cogenetic with old rock provinces in the subcontinental mantle.     

Lower Jurassic palaeomagnetic results from Yorkshire,England, and their implications

Palaeomagnetic study of Middle Liassic siltstones shows a stable magnetization with a mean direction of D = 12.3°, I = 64.6° (N = 60, k = 26, α₉₅ = 3.9°) corresponding to a palaeomagnetic pole at 79.8°N, 125.6°E, similar to that for southern Germany and confirming predictions based on palaeogeographic reconstructions using North American data. Sideritic concretions of Lower Liassic age show a higher magnetic stability with a mean direction of D = 12.6°, I = 61.4° (N = 125, k = 50, α₉₅ = 1.8°) which is not significantly different from the siltstones. This confirms the sedimentological evidence that suggests that such concretions grew very shortly after deposition, i.e. within the Liassic, and suggests that similar concretions of other ages could thus be used for palaeomagnetic studies. Although the Liassic palaeomagnetic pole (76.9°N, 134.7°E), based on this work, appears valid it is still not possible to evaluate a sensible Mesozoic polar wandering curve for the North Atlantic bordering continents.     

Palaeomagnetism of Cretaceous and Jurassic volcanic rocks in west Sicily

The mean palaeomagnetic pole position obtained from Upper Cretaceous rocks in west Sicily is at 21°N, 100°E (A₉₅ = 15°), and at 38°N, 67°E (A₉₅ = 31°) obtained from Middle Jurassic rocks. These pole positions are completely different from comparable pole positions for southeast Sicily and Africa and imply a clockwise rotation of west Sicily since the Upper Cretaceous of about 90° relative to southeast Sicily and Africa and also a clockwise rotation of about 60° relative to “stable” Europe. The sense of rotation of west Sicily is opposite to any known rotation of other crustal blocks in the central Mediterranean.     

Emplacement temperatures of pyroclastic and volcaniclastic deposits in kimberlite pipes in southern Africa

Palaeomagnetic techniques for estimating the emplacement temperatures of volcanic deposits have been applied to pyroclastic and volcaniclastic deposits in kimberlite pipes in southern Africa. Lithic clasts were sampled from a variety of lithofacies from three pipes for which the internal geology is well constrained (the Cretaceous A/K1 pipe, Orapa Mine, Botswana, and the Cambrian K1 and K2 pipes, Venetia Mine, South Africa). The sampled deposits included massive and layered vent-filling breccias with varying abundances of lithic inclusions, layered crater-filling pyroclastic deposits, talus breccias and volcaniclastic breccias. Basalt lithic clasts in the layered and massive vent-filling pyroclastic deposits in the A/K1 pipe at Orapa were emplaced at >570°C, in the pyroclastic crater-filling deposits at 200–440°C and in crater-filling talus breccias and volcaniclastic breccias at <180°C. The results from the K1 and K2 pipes at Venetia suggest emplacement temperatures for the vent-filling breccias of 260°C to >560°C, although the interpretation of these results is hampered by the presence of Mesozoic magnetic overprints. These temperatures are comparable to the estimated emplacement temperatures of other kimberlite deposits and fall within the proposed stability field for common interstitial matrix mineral assemblages within vent-filling volcaniclastic kimberlites. The temperatures are also comparable to those obtained for pyroclastic deposits in other, silicic, volcanic systems. Because the lithic content of the studied deposits is 10–30%, the initial bulk temperature of the pyroclastic mixture of cold lithic clasts and juvenile kimberlite magma could have been 300–400°C hotter than the palaeomagnetic estimates. Together with the discovery of welded and agglutinated juvenile pyroclasts in some pyroclastic kimberlites, the palaeomagnetic results indicate that there are examples of kimberlites where phreatomagmatism did not play a major role in the generation of the pyroclastic deposits. This study indicates that palaeomagnetic methods can successfully distinguish differences in the emplacement temperatures of different kimberlite facies.     

Palaeomagnetism of the dyke swarms of the Gardar Igneous Province,south Greenland

In the western part of the Gardar Igneous Province of southern Greenland, lamprophyre dykes intruded at ca. 1276-1254 m.y. RbSr biotite ages yield a palaeomagnetic pole at 206.5°E,3°N (nine sites, dψ = 5.1°, d_χ = 10.1°) Slightly younger dolerite dykes with RbSr biotite ages in the range 1278-1263 m.y. give a pole at 201.5°E,8.5°N (24 sites, dψ = 4.7°, d_χ = 9.4°), and the syeno-gabbro ring dyke of the Kûngnât complex (RbSr isochron age 1245 ± 17 m.y.) cutting both of these dykes swarms, gives a pole at 198.5°E, 3.5°N (four sites, dψ = 2.3°,d_χ = 4.4°). All these rock units have the same polarity and the poles are identical to those from Mackenzie and related igneous rocks of North America (1280-1220 m.y.) after closure of the Davis Strait; they confirm that this part of the Gardar Province is a lateral extension of the Mackenzie igneous episode within the Laurentian craton.In the Tugtutôq region of the eastern part of the Gardar Province 47 NNE-trending dykes of various petrologic types, and intruded between 1175 ± 9 and 1168 ± 37 m.y. (RbSr isochron ages) yield a palaeomagnetic pole at 223.9° E, 36.4°N (dψ = 4.1°, d_χ = 6.1°). Fifteen other dykes in this swarm were intruded during a transitional phase of the magnetic field which, however, does not appear to have achieved a complete reversal over a period of several millions of years. The majority of dykes studied are highly stable to AF and thermal demagnetisation and contain single high blocking temperature components with single Curie points in the range 380–560°C.Palaeomagnetic poles from the Gardar Province between ca. 1330 and 1160 m.y. in age define the earlier part of the Great Logan apparent polar-wander loop; they correlate closely with contemporaneous North American results and confirm the coherence of the Laurentian craton in Upper Proterozoic times.     

Palaeomagnetism of Ketilidian metamorphic rocks of SW Greenland,and 1850-1600 m.y. apparent polar movements

Proterozoic supracrustal rocks of southwest Greenland and amphibolite dykes intruding the basement possess a thermal remanent magnetisation acquired during slow regional uplift and cooling between 1800 and 1600 m.y. following the Ketilidian mobile episode. Most samples from amphibolite dykes (mean palaeomagnetic pole 214°E, 31°N) possess a stable remanence associated with development of hematite during regional thermal metamorphism. Metavolcanics from the eastern part (eight sites, palaeomagnetic pole 230°E, 60°N, A₉₅ = 15°) and western part (twelve sites, 279°E, 59°N, A₉₅ = 17°) of Ars?k Island have magnetisations postdating folding and are related to KAr ages dating regional cooling (1700-1600 m.y.); magnetic properties are highly variable and partially stable remanence resides predominantly in pyrrhotite.These results agree in part with other palaeomagnetic results from the northern margin of the same craton, and currently available palaeomagnetic results assigned to the interval 1850-1600 m.y. are evaluated to define apparent polar wander movements. Two large polar movements are recognised during this interval with the possibility of a third at ca. 1800 m.y. It is concluded that apparent polar wander movements in Proterozoic times are most accurately described in terms of closed loops.     

A palaeomagnetic study of the coast-parallel Jurassic dyke swarm in southern Greenland

Results are reported from palaeomagnetic samples collected in two traverses across the coast-parallel dyke swarm of southern Greenland. This swarm probably resulted as the consequence of initial rifting between Greenland and Labrador, and a reversal of magnetisation has been found which is correlated on the basis of KAr age determinations (～168 m.y.) with the Mateke event of the Middle Jurassic (Bajocian). All of fifteen sites show significant grouping of directions after a.f. cleaning; three have anomalous directions of magnetisation while the remainder (nine normal, three reversed) give a combined mean direction of D = 336°, I = 66° (α₉₅ = 4.6°) with a palaeomagnetic pole at 191°E, 72°N. The dykes exhibit the same corelation between polarity and deuteric oxidation state as that found in Tertiary volcanics. There is a systematic change in magnetisation across the dyke swarm in south Greenland from normal to anomalous to reversed directions; this is interpreted as due to lateral migration of the response to the regional stress field with time. The pole position lies in the vicinity of Jurassic poles from North America after closing the Labrador Sea according to the reconstruction of Bullard, Everett and Smith, but the scatter of these latter poles precludes a confirmation of this reconstruction for Middle Jurassic and earlier times.     

Aspects of Caledonian palaeomagnetism and their tectonic implications

Palaeomagnetic results from the Lower Palaeozoic inliers of northern England cover the upper part of the (Middle Ordovician) Borrowdale Volcanic Series (palaeomagnetic pole 208°E, 18°S, A₉₅ = 9.4°), minor extrusive units relating to the Caradoc and Ashgill stages of Ordovician times, intrusive episodes of Middle Ordovician and Middle Silurian to Late Devonian age, and the Shap Granite of Devonian (393 m.y.) age (palaeomagnetic pole 313°E, 33°S, A₉₅ = 5.6°).A complete assessment of Ordovician to Devonian palaeomagnetic data for the British region shows that the pole was nearly static relative to this region for long intervals which were separated by shifts occupying no more than a few millions of years. The mean palaeomagnetic poles are: Ordovician (6°E, 16°S), Lower Silurian (58°E, 16°N), Middle Silurian/Lower Devonian (318°E, 6°N) and Middle/Upper Devonian (338°E, 26°S); the first two shifts separating these mean poles can be explained predominantly in terms of rotational movements of the crustal plate but the last involved appreciable movement in palaeolatitude.Comparison of Lower Palaeozoic palaeomagnetic data from the British region with contemporaneous data from continental Europe/North America on the Pangaean reconstruction reveals a systematic discrepancy in palaeolatitude between the two regions prior to Middle Devonian times. This discrepancy was eliminated during a few millions of years of Lower/Middle Devonian times (ca. 395 m.y.) and can be explained in terms of ca. 3500 km of sinistral strike-slip movement close to the line of the orthotectonic Caledonides. This motion is linked both in time and place to the impingement of the Gondwanaland and Laurentian supercontinents during the Acadian orogeny; this appears to have displaced the British sub-plate until it became effectively locked between the Baltic and Laurentian regions. Although movement of the dipole field relative to the British region in Lower Palaeozoic times is now well defined, nearly one fifth of the total data show that the geomagnetic field was more complex than dipolar during this interval. Until the significance of these anomalies is fully resolved, the tectonic model derived from the palaeomagnetic data cannot be regarded as unambiguous.     

Paleomagnetism of the Cambro-Ordovician McClure Mountain alkalic complex,Colorado

The Middle to Late Cambrian loop in the North American apparent polar wander path (APWP) has been variously attributed to tectonic rotations, remagnetizations and primary magnetizations. Although no primary thermal remanent magnetizations or primary detrital remanent magnetizations have as yet been demonstrated, the temporally self-consistent nature of the loop has been used as an argument for primary magnetizations. We have studied535 ± 5Ma nepheline syenites and syenites of the McClure Mountain alkalic complex, as well as495 ± 10Ma red trachyte dikes which intruded the complex, in an effort to find a primary TRM. Because Zijderveld analysis yielded consistent results for only one trachyte dike, remagnetization great-circle analysis was employed, giving a pole for the trachyte dikes at the tip of the loop (43°N, 114°E), while the syenites and nepheline synenites gave a pole at the base of the loop (18°N, 142°E). The magnetic carrier in the trachytes is hematite which apparently formed during a pervasive hydrothermal alteration. KAr whole rock dating of the trachytes suggests a Pennsylvanian age for the alteration, and thus a late Paleozoic remagnetization of the trachytes. Thus, the low-latitude Cambrian pole is confirmed, but we find no evidence in this study to support the primary nature of the Cambrian APWP.     

The palaeoposition of Madagascar: Palaeomagnetic evidence from the Isalo group

Palaeomagnetic results are reported from the continental facies of the Triassic-Jurassic Isalo Group of Madagascar. Stability of the magnetic remanence was tested using the alternating field and progressive thermal demagnetization techniques. Results from 8 sites, 6 located in northwestern Madagascar and 2 from the southwestern region, yield a palaeomagnetic pole at 74.2°S, 97.1°E (N = 8, A₉₅ = 6.3°). Three models previously proposed to describe the drift history of Madagascar relative to Africa are considered and the relevant geological and geophysical information is reviewed. The palaeomagnetic data are only consistent with the pre-drift model which places Madagascar off the east coast of Africa adjacent to Kenya and Tanzania. This is also the continental drift fit favoured on geological grounds.     

Palaeomagnetism of middle Ordovician volcanic rocks from Quebec

This palaeomagnetic study is centered on agglomerates and volcanic rocks from the western margin of the Appalachian belt in the Drummondville-Actonvale-Granby area, Quebec (long.: 72°30′W, lat.: 46°00′N). It involves a total of 36 oriented samples (111 speciments) distributed over eleven sites. Both thermal and AF cleaning techniques were used to isolate residual remanent components. The dispersion of the directions is slightly reduced after AF cleaning and thermal treatment.The palaeopole position obtained is 191°E, 6°N (d_m = 14°, d_p = 7°) after thermal treatment and 164°E, 19°N (d_m = 11°, d_p = 6°) after AF cleaning. The polarity of most of the sites (two exceptions) are reversed. The thermal-treated data appear to be relatively stable and an approximate value of the primary magnetization is extracted from them. The palaeopole obtained does not lie close to the tentatively defined position of the Cambrian and Ordovician poles from rocks of the North American plate; it is located near the Upper Cambrian and Lower Ordovician poles from eastern Newfoundland and the Lower Ordovician pole from the Caledonides in Europe.     

The palaeoposition of Madagascar: Remanence and magnetic properties of late Palaeozoic sediments

Palaeomagnetic results are reported from the predominantly green sediments of the Upper Permian to Lower Triassic Sakamena Group and the Upper Carboniferous to Lower Permian Sakoa Group of Madagascar. Secondary magnetizations could only be removed successfully through thermal demagnetization procedures and then only if the cleaning process was completed by 450°C. Heating in air caused extensive magnetochemical changes to occur above this temperature. Coercivity spectrum analysis and low-temperature characteristics of the heated and unheated green sediments indicate that considerable amounts of fine-grained single-domain magnetite are formed at 500°C or more from some non-magnetic mineral, probably the iron silicates. For this reason consistent palaeomagnetic data could only be obtained from about half the samples collected. Results from 4 sites (19 samples) of the Lower Sakamena Group give a palaeomagnetic pole at 64.9S, 113.9E (A₉₅ = 5.6°) and 3 sites (16 samples) from the Glacial Series of the Sakoa Group give a pole at 47.9S, 84.1E (A₉₅ = 8.1°). When compared with corresponding data from Africa these results confirm and strengthen our previous conclusions from the Triassic-Jurassic Isalo Group regarding the palaeoposition of Madagascar. All three poles are only consistent with the Smith and Hallam reconstruction which places Madagascar off the eastern coast of Africa adjacent to Kenya and Tanzania.     

Late Mesozoic palaeomagnetism from Spitsbergen; implications for continental drift in the Arctic

Thermal and alternating-current demagnetization combined with ore microscopy and measurements of the temperature dependence of saturation magnetization have been carried out on some Mesozoic, probably Cretaceous, basaltic lavas from two areas (Seidfjell and Sørlifjell) at Spitsbergen. The experimental studies suggest that the Seidfjell locality has undergone extensive oxidations, which resulted in remagnetization. The estimated palaeomagnetic pole for this area is 77°N 107°E, which suggests a remagnetization, probably some time in the Late Tertiary. On the other hand the experimental data from the Sørlifjell locality suggest that the magnetization is primarily of deuteric origin. The mean palaeomagnetic pole position for this latter formation is at 75°N 235°E, which is significantly different from previously published European Mesozoic data. However, closing the Neo-Arctic basin by rotating Spitsbergen towards the Lomonosov Ridge, makes the suggested Cretaceous pole coincide with poles of similar age from North-America. This suggests that the estimated pole from Sørlifjell is a good approximation for a Late Mesozoic palaeomagnetic pole for Europe and it also confirms that the process of continental separation in the Arctic has taken place in Tertiary time.     

Palaeomagnetic studies of Lower Jurassic rocks in England and Wales

Paleomagnetic data from late Lower Jurassic sediments from Dorset, Gloucestershire and Yorkshire confirm the existence of at least one interval of reversed geomagnetic polarity in Upper Toarcian time (about 175 m.y. ago). The mean pole position calculated from these data lies at 50°N, 37°E, but the field represented by this pole is believed to have been non-axial because of its incompatibility with Mesozoic faunal, palaeoclimatic and palaeomagnetic evidence throughout western Europe.Unstable remanent magnetization found in a large number of samples of various lithologies is shown to have originated during drilling. It is tentatively identified as partial TRM acquired during dissipation of heat from the drill tip. Alternative causes such as superficial contamination and vibration do not explain the majority of the observations.     

Palaeomagnetism of the Msissi norite (Morocco) and the Palaeozoic reconstruction of Gondwanaland

Palaeomagnetic results are reported from eight sites in an Upper Devonian basic intrusion (the Msissi norite) in southeast Morocco. Specimens from one site are suspected of having been affected by lightning, but results from the other seven sites indicate the presence of a less-stable component, probably of viscous origin. The pole position corresponding to the stable component(0.5°S, 25°E, A₉₅ = 16.5) is interposed between the Middle Cambrian/Ordovician pole and the Lower Carboniferous pole on the African polar wander curve. When the southern continents are reassembled on the Smith/Hallam reconstruction of Gondwanaland the new Moroccan Devoniån pole is in excellent agreement with the corresponding portion of the main Australian polar-wander curve. This places additional constraints on the possible date of fusion of the separate Southeast Australian plate with the rest of Gondwanaland, postulated recently on palaeomagnetic grounds by M.W. McElhinny and B.J.J. Embleton (1974). The combined African/Australian polar-wander curve is compared with the South American curve, and two possible interpretations of available data are discussed, one involving possible relative tectonic motion between South America and the rest of Gondwanaland during the Lower and Middle Palaeozoic, and the other, favoured here, requiring a reassessment of the ages of several South American pole determinations.     

Palaeomagnetic study of the Swedish rapakivi suite: Proterozoic tectonics of the Baltic Shield

The major Proterozoic igneous intrusions in the Swedish sector of the Baltic Shield are the Ragunda complex (1293 m.y., palaeomagnetic pole 165°E, 54°N) and the Nordingrågabbro-granite-anorthosite complex (1385 ± 30 m.y.). The latter body has been partially remagnetised by later post-Jotnian dolerites (1254 m.y.), and sites influenced by the dolerites have a stable magnetisation with a mean direction D = 45°, I = ?39°, (α₉₅ = 4.3°). Elsewhere, the gabbro-anorthosite facies have a magnetisation of dual polarity predating the dolerite and recoverable at various stages of thermal and/or a.f. cleaning with a mean of D = 48°, I = 37° (α₉₅ = 5.3°); medium and high coercivity remanence resides in large magnetite grains and fine, predominantly hematite, rods in feldspar megacrysts. The Nordingrårapakivi granite yields a mean, also including dual polarities, of D = 221°, I = ?25° (α₉₅ = 13°), and the Gävle granite yields a mean of D = 26°, I = 17° (α₉₅ = 13°).New data define the a.p.w. path for the Baltic Shield after final uplift and cooling of the ca. 1800 m.y. Svecofennian mobile belt and prior to intrusion of the post-Jotnian dolerites at 1250 m.y.; this (ca. 1500–1200 m.y.) path defines a double loop similar in size and shape to the contemporaneous path for the Laurentian Shield and the paths can be superimposed to define relative positions of the shields. They were in juxtaposition prior to 1200 m.y. with the optimum reconstruction obtained by rotation of approximately 64° about a Euler pole at 1°E, 36°N. Pre-1500 m.y. palaeomagnetic data are also shown to fit this same unique reconstruction. The main geological correlations are an alignment of the Lower/Middle Proterozoic major strike-slip zones, the structural trends within the pre-1700 m.y. mobile belts, and the Grenville and Sveconorwegian (ca. 1100 m.y.) mobile belts. The anorogenic magmatism characteristic of Proterozoic times became gradually more restricted to one active margin of the continental reconstruction as temperature gradients decreased and the crust consolidated. All of these Proterozoic tectonic/magmatic trends are parallel to the long axis of the continental reconstruction.