miocene rotations in the eastern alps palaeomagnetic results from intramontane basin sediments a palaeomagnetic study of late early miocene to late middle miocene sediments from the eastern alpine intramontane basins revealed counterclockwise rotations in the ennstal in the western part of the noric and in the lavanttal depressions for the basal strata of the basins declinations are between 273 and 315 while for the younger strata they are between 321 and 333 in perfect agreement with observations from the klagenfurt basin the results suggest synsedimentary rotation during the lateral tectonic extrusion of the eastern alps ca 17 13 ma which was also responsible for the formation of the mostly transtensional basins we propose a model in which domino shaped blocks separated by nnw sse trending dextral faults rotated counterclockwise due to faster eastward motion in the south relative to areas further north the protrusion of the bohemian spur inhibited eastward motion in the northern part of the study area thus creating a sinistral wrench corridor after lateral extrusion had ceased the counterclockwise rotation continued probably as en bloc rotation of ca 30 clockwise rotation was observed in the eastern part of the noric depression which appears to belong to a limited area with complex rotation pattern near the eastern margin of the alps this area is wedged between the counterclockwise rotated eastern alps and the similarly rotated north pannonian area in hungary 2000 elsevier science b v all rights reserved

palaeomagnetism of devonian ring complexes from the bayuda desert sudan new constraints on the apparent polar wander path for gondwanaland summary the approach of gondwana and or microplates derived from its northern margins towards laurentia and the closure of the intervening palaeo tethys is a controlling factor in the geodynamic evolution of the atlantic bordering continents during the early and mid palaeozoic however the currently available palaeomagnetic data for gondwana especially for the geodynamically critical silurian to devonian interval are still rather sparse and are compatible with a number of palaeogeographic scenarios in order to address this issue 114 samples 18 sites have been collected from a series of high level acidic intrusive rocks rhyolitic lavas and tuffs of mid devonian age 377 5 ma rb sr along the southern escarpment of the gilif hills sudan 17 83 n 32 67 e detailed demagnetization experiments revealed the presence of three directionally distinct components of magnetization labelled a b and c the overall mean direction of component a dec 0 9 inc 29 8 95 4 6 k 91 1 n 12 sites is indistinguishable from either the direction of the present field or the geocentric axial dipole field in northern sudan mixed polarities suggest a recent or pleistocene age of this component component b also displays mixed polarities the site mean directions for this component average to 6 5 declination 40 2 inclination with 95 7 0 and k 48 1 based on 10 sites and yield a palaeomagnetic pole at 48 8 s 23 5 e dp 5 1 1 dm 8 4 maghaemite and haematite have been identified to be the predominant magnetic phases in samples which carry component a and or b both a and b are the probable results of low temperature oxidation of magnetite although the age of component b can not be directly determined it is inferred by correlation with published data to reflect a late carboniferous overprint component c identified in 11 sites 39 samples is characterized by a very steep downward magnetization dec 296 2 inc 79 3 95 10 8 k 18 7 n 11 sites which corresponds to a palaeomagnetic pole position in the southwestern corner of libya 25 9 n 11 6 e dp 19 6 dm 20 6 maximum blocking temperatures of component c generally below 580 c are indicative of magnetite as carrier of this remanence the results of thermal remanent magnetization experiments demonstrate that component c is a thermo remanent magnetization probably primary and suggest this component to be representative for the direction of the earth s magnetic field during emplacement of the gilif hills volcanic rocks in mid devonian times the position of the resulting palaeomagnetic pole lends new support to geodynamic scenarios advocating the existence of a wide approx 5000 km pre hercynian ocean during devonian times the simplest reconciliation of component b with the reference apparent polar wander path is achieved by assuming it to be of carboniferous age and by invoking a westward cusp in the carboniferous part of the apparent polar wander path taken at face value the age of this cusp coincides with large scale post orogenic right lateral strike slip movements in hercynian europe and north africa this interpretation does not require the apparent polar wander apw loop and very high rates of plate motion implied by some alternative models however if it is valid it will require reinterpretation of the remanence age of one west african intrusive suite and of some eastern australian palaeozoic rocks

the palaeolatitude controversy in the silurian of newfoundland resolved new palaeomagnetic results from the central mobile belt abstract a detailed palaeomagnetic investigation of early silurian volcanics of the lawrenceton formation in the central mobile belt cmb of newfoundland reveals primary remanence that places the sampled part of the cmb on the margin of laurentia in low southerly latitudes in the early silurian the palaeomagnetic data indicate large vertical axis net clockwise rotations within the cmb and between the cmb and cratonic laurentia the volcanics were folded faulted and in places cleaved in silurian to early devonian times anisotropy of magnetic susceptibility measurements on lava flow samples verify field observations of a primary flow parallel foliation and confirm field measurements of the palaeo horizontal a well developed tectonic fabric was detected at one sampling site near the reach fault silurian redbeds of the big indian pond formation were also sampled for palaeomagnetic study the sediments are folded faulted and cleaved a statistically sound syn folding remanence was identified which in a tectonically corrected state is consistent in direction with the remanence in the silurian volcanics the sampled sediments are more intensely deformed than the volcanics and magnetic anisotropy measurements indicate both primary layering and secondary cleavage related fabrics in varying degrees from site to site it is possible that cleavage development resulted in remanence reorientation leading to the illusion of syn folding remanence when in fact the remanence was acquired prior to folding previously published palaeomagnetic investigations of silurian rocks in the cmb revealed a discrepancy in palaeofield inclination between volcanic and sedimentary rock types the sedimentary rocks yielded shallow inclinations and the volcanics intermediate inclinations inclination shallowing in the sediments was put forward as an explanation as well as contamination of the sedimentary results with a shallow overprint others argued that the results from the volcanics were in error the present investigation demonstrates that key volcanics carry a shallower remanence than previously thought bringing them into approximate agreement with the majority of the results from sediments steep results from the springdale volcanics and very shallow results from the king george iv lake sediments are at variance with the rest of the data the springdale result has large error limits that overlap with the other data the anomalous king george iv result remains an outlier

palaeomagnetic and rock magnetic reliability criteria in ophiolitic rocks a case study from the palaeozoic ballantrae ophiolite scotland abstract palaeomagnetic studies of the ballantrae ophiolite southwest scotland are assessed in the light of palaeomagnetic and rock magnetic reliability criteria the remanence directions are palaeomagnetically reliable but have only limited significance for apparent polar wander path construction rock magnetic reliability criteria are found to be ambiguous when treated in isolation original grain size effects are detected in magnetic properties across three sections through pillow lavas we propose that a systematic study of spatial magnetic property variations within pillow lavas can provide an additional field test in the assessment of reliability thermomagnetic analyses and microscopic observations suggest three remanence carrying magnetic phases exist within the extrusive layer of the ophiolite these are almost pure magnetite hematite and titanomaghemite palaeomagnetic rock magnetic and geological observations are best satisfied by a pre obduction magnetisation age this study links the remagnetisation of an ultra oceanic conglomerate to local hydrothermal circulation rather than to a pervasive remagnetisation event as previously suggested

palaeomagnetism of red beds from the kimberley group western australia implications for the palaeogeography of the 1 8 ga king leopold glaciation abstract the 1 8 ga king leopold glaciation in northwestern australia is recorded in the kimberley basin by subglacial erosional forms cut in an unconformity surface at the top of the speewah group and buried by glaciofluvial deposits at the base of the king leopold sandstone the lowest formation of the kimberley group the glaciofluvial deposits are conformably overlain by texturally mature locally glauconitic quartzarenite of shallow marine origin implying that glaciation occurred near sea level palaeomagnetic data for five sites 29 specimens in the hematite bearing elgee siltstone of the upper kimberley group in the northeastern kimberley basin gave a dip corrected mean direction of declination d 95 4 inclination i 13 8 95 9 7 indicating a palaeolatitude 7 0 5 3 5 0 results for red beds from five sites 28 specimens in the conformably overlying pentecost sandstone gave a dip corrected mean direction of d 94 1 i 13 0 95 11 7 6 6 6 4 5 9 combining our data for the elgee siltstone and pentecost sandstone with results for the elgee siltstone in the southeastern kimberley basin li z x 2000 palaeomagnetic evidence for unification of the north and west australian cratons by ca 1 7 ga new results from the kimberley basin of northwestern australia geophysical journal international 142 173 180 yielded a dip corrected mean direction for 17 sites of d 93 5 i 15 1 95 4 4 palaeolatitude 7 7 2 3 and an overall pole position at latitude p 5 4 s longitude p 211 8 e with confidence semi axes dp 2 3 and dm 4 5 a positive fold test at 99 confidence was obtained for the combined data for the 17 sites the basinwide concordance of results for the elgee siltstone and the positive fold test argue for an early magnetisation acquired prior to late palaeoproterozoic initial folding of the kimberley group and close to the time of deposition our results imply a low palaeolatitude for the kimberley group and the king leopold glaciation palaeomagnetic data for the 1 822 ga plum tree creek volcanics in the pine creek orogen to the east of the kimberley basin are consistent with northwestern australia being in low palaeolatitudes during the late palaeoproterozoic hence the enigma of glaciation near sea level in low palaeolatitudes which marks the neoproterozoic and early palaeoproterozoic applies also to the late palaeoproterozoic red beds from the lansdowne arkose of the speewah group also were studied but only directions ascribable to tertiary regolith weathering processes were found similar findings for the late palaeoproterozoic mcarthur basin in northern australia suggest some units in that basin also record tertiary regolith processes

the rotations of the variscides during the carboniferous collision paleomagnetic constraints from the vosges and the massif central france abstract this study aims at completing and refining results from previous paleomagnetic investigations carried out in various outcrops of the european variscan belt sampling was performed in visean effusive and intrusive rocks of the southern vosges basin and the northern massif central all emplaced in the time range 345 340 ma stepwise thermal demagnetization of 254 specimens from 13 sites of the doller valley and nine sites of the massif central has yielded a very similar paleomagnetic record for both areas with the exception of post carboniferous overprints isolated in the southern vosges two groups of directions with both normal and reversed polarity have been evidenced the first group of directions labelled c occurs in both areas and is characterized by scarce pre tectonic magnetizations two sites and by syn tectonic overprints five sites acquired during the late visean convergence i e in the time range 340 328 ma the mean pole co is 28 s 45 e k 139 95 5 the main group labelled b shows a negative fold test and a positive reversal test indicating that the magnetizations are post tectonic overprints acquired after the main tightening phase i e after 328 ma at a few sites in both areas were evidenced syn tectonic b magnetizations that are in favour of an overprinting in the context of post visean extension tectonics the mean post tectonic b direction of the doller valley southern vosges 62 25 k 52 95 6 n 11 vgp 8 n 127 e is consistent with the mean post tectonic b direction 72 23 k 126 95 5 n 6 vgp 3 n 114 e obtained from the tuffs the grey microgranite and the dyke intrusive into the microgranite of the massif central the occurrence of similar paleomagnetic records in the eastern and central variscides implies that from the massif central to the sudetes the belt has probably moved as one block since early carboniferous the change in inclination of the c components suggests a southward drift of the moldanubian and saxothuringien variscides in the late visean 340 328 ma according to geological features in the same time the rhenohercynian crust was underplating the saxothuringian arc and fore arc zone subsequent to 328 ma the drift turned into a rapid clockwise rotation by about 70 around a pole located on southeastern corner of baltica leading to the closure of the rhenohercynian oceanic basin in the namurian large scale overprinting b components likely related to post rotation extension affected the internal belt the convergence continuing the variscides underwent a second clockwise rotation by about 45 in the late namurian westphalian 320 305 ma stacking of the rhenohercynian sedimentary cover and thrusting over the london brabant basement may be related with this motion

genesis of the carbonatite hosted fluorite deposit at amba dongar india evidence from fluid inclusions stability isotopes and whole rock mineral geochemistry the amba dongar carbonatite complex is located approximately 400 km northeast of bombay india and consists of a carbonatite ring dike and a number of syenitic intrusions which were emplaced into late cretaceous bagh sandstones and early to late eocene deccan volcanic rocks hydrothermal activity associated with intrusion of the carbonatite was responsible for fenitization of the surrounding sandstones and deposition of economic quantities of fluorite 11 6 mt of 30 caf 2 fluorite mineralization occurs as veins and vug fillings localized along fractures within the calcite carbonatite near its contact with the sandstone fluid inclusions in fluorite indicate a low temperature low salinity 42 and 3 5 respectively the presence of al and s in the fluid the molar equivalence of na and cl and the positive deviation of 18 o and d from the meteoric water line point to a small contribution from orthomagmatic fluids a model is proposed in which the intrusion of a carbonatite magma at high crustal levels caused faulting and fracturing of the surrounding country rocks and was accompanied by the release of orthomagmatic fluids expressed as extensive k and na metasomatism of the surrounding sandstones with the decline of orthomagmatic activity a meteoric water dominated hydrothermal system was initiated by the heat of the intrusion the interaction of ca bearing meteoric fluids with the last vestiges of f bearing orthomagmatic nacl brines caused deposition of large quantities of fluorite at the site of mixing

magnetostratigraphy of the lower triassic beds from chaohu china and its implications for the induan olenekian stage boundary a magnetostratigraphic study was performed on the lower 44 m of the west pingdingshan section near chaohu city anhui province china in order to provide a magnetic polarity scale for the early triassic data from 295 paleomagnetic samples are integrated with a detailed biostratigraphy and lithostratigraphy the tilt corrected mean direction from the west pingdingshan section passes the reversal and fold tests the overall mean direction after tilt correction is d 299 9 i 18 3 305 2 95 1 9 n 19 the inferred paleolatitude of the sampling sites 31 6 n 117 8 e is about 9 4 consistent with the stable south china block scb though the declinations indicate some 101 counter clockwise rotations with respect to the stable scb since the lower triassic low field anisotropy of magnetic susceptibility indicates evidence of weak strain the lower part of the yinkeng formation is dominated by reversed polarity with four normal polarity magnetozones wp2n to wp5n with evidence of some thinner 0 5 m thick normal magnetozones the continuous magnetostratigraphy from the yinkeng formation provides additional high resolution details of the polarity pattern through the later parts of the induan into the lowest olenekian the magnetostratigraphic and biostratigraphic data show that the conodont marker for the base of the olenekian first presence of neospathodus waageni is shortly prior to the base of normal magnetozone wp5n this provides a secondary marker for mapping the base of the olenekian into successions without conodonts this section provides the only well integrated study from a tethyan section across this boundary but problems remain in definitively relating this boundary into boreal sections with magnetostratigraphy

remanent magnetization mapping a tool for greenfields magmatic ni cu pge exploration undercover part 1 abstract there are many challenges for greenfields exploration particularly in vast sparsely populated partially covered terrains e g a paucity of prior exploration data and difficulties in gaining access to land however in many cases good aeromagnetic coverage is freely available and for some styles of mineralization e g magmatic ni cu pge aeromagnetic data alone can provide critical insights into the age size and depth of multiple targets across large regions early in the exploration life cycle this study investigates whether an understanding of remanent magnetization from three suites of mafic intrusions exposed in the huckitta area nt australia can be utilized to provide a first pass exploration tool for exploration under shallow cover to the east the study demonstrates that although the measured remanent magnetization vectors present were complex in some cases the majority are sub parallel oriented steep down to the south which implies a common mode of acquisition it was found that the magnetizations were acquired during the alice springs orogeny ca 450 300 ma with the dominant magnetization occurring at ca 330 ma therefore the magnetizations present do not relate to cooling of the parent magmas but rather to cooling of lower crustal rocks from temperatures above the curie point 580 c during exhumation of the host terrain whilst this knowledge does not allow discrimination of the three suites remotely based purely on their remanent magnetization vectors the recognition of a common magnetization vector present in all mafic rocks does allow us to better map mafic rocks under cover and better constrain magnetic modelling and exploration targeting as discussed in the second paper

self reversal of chemical remanent magnetization a palaeomagnetic example summary an anomalous region with complicated thermal demagnetization characteristics has been observed in siluro devonian andesites from the contact aureole of a 6 2 m wide tertiary dyke in the mull dyke swarm scotland outside this anomalous region rocks from the contact aureole carry a simple two component remanence the existence of a self reversed crm in samples from between 75 cm and 182 cm from the contact has been inferred from thermal demagnetization data this magnetization has blocking temperatures greater than the peak temperatures reached in the aureole and causes a beak shape in the vertical projection of vector plots of thermal demagnetization data the self reversed remanence is presumed to be carried by titanohaematite x 0 03 with a curie point of 650 660 c not isolated as a separate phase and its blocking temperatures overlap with those of a primary siluro devonian remanence and a normal tertiary crm overprint carried by hematite the suggested mechanism for this self reversed crm is the transformation of maghaemite to haematite where super exchange across the phase boundary causes the self reversal this is probably the best documented geological example of such a self reversal

miocene pliocene tectonic evolution of the slovenian periadriatic fault implications for alpine carpathian extrusion models the periadriatic line pal is a remarkable several hundred kilometer long fault system of the alpine orogen its dextral character was documented by several authors using diverse criteria but detailed kinematics and timing of movements had not been investigated along its whole length structural and paleomagnetic measurements mapping and stratigraphic and sedimentological studies have helped to unravel the miocene pliocene evolution of the slovenian segment of the pal brittle deformation was characterized by nw se to n s compression and perpendicular tension deformation has resulted in dextral strike slip faulting folding and tilting of beds the first transpressional event corresponds to the first phase of lateral extrusion of the east alpine western carpathian northern pannonian block in the early miocene 24 17 5 ma after a short period of transtension during the karpatian 17 5 16 5 ma dextral transpression reoccurred during the middle miocene to pliocene and lasted up to the quaternary middle miocene dextral slip can be connected to the second phase of extrusion the highly deformed rocks within the dextral shear zones show variable clockwise sometimes counterclockwise rotations the mechanism of rotation seems to be complex ranging from regional rotation to local folding due to pure or simple shear domino type rotation

palaeomagnetism magnetic fabrics and the structural style of the hornelen old red sandstone western norway the old red sandstone of the hornelen district western norway forms part of a major fold terrane and the principal magnetization is associated with the late devonian to early carboniferous svalbardian solundian orogeny the present fault margins of the hornelen massif claimed by various authors to represent subordinate devonian splay faults associated with megashearing in the north atlantic or lateral ramps in a regional extensional tectonic setting are shown to be post devonian structures and the present outline of the hornelen massif is a mesozoic jurassic graben

ediacaran palaeomagnetism and apparent polar wander path for australia no large true polar wander summary we report new palaeomagnetic data for red beds from the ediacaran brachina and wonoka formations in the adelaide geosyncline south australia and discuss their place with previously determined poles in the ediacaran apparent polar wander path for australia both formations behave similarly on thermal demagnetization displaying high temperature components that decay to the origin at 680 c consistent with haematite being the only magnetic mineral present restoring the strata to the palaeohorizontal yielded positive fold tests for both units at 99 per cent confidence indicating that acquisition of magnetization occurred before the early palaeozoic delamerian orogeny for the brachina formation n 91 specimens the mean direction after unfolding is declination d 178 2 inclination i 22 6 95 4 4 indicating a palaeolatitude 11 8 2 5 and a pole position at latitude p 46 0 s longitude p 315 4 e with confidence semi axes dp 2 4 and dm 4 6 the mean direction for the wonoka formation after unfolding n 70 is d 255 9 i 23 7 95 6 4 indicating 12 3 3 8 3 4 and a pole position at latitude p 5 2 s longitude p 30 5 e dp 3 6 and dm 6 8 the mean directions for these units and other ediacaran units in the adelaide geosyncline are significantly different from each other which excludes blanket remagnetization of the units before delamerian folding and therefore gives strong preference to their magnetization dating from close to the time of deposition the late cryogenian ediacaran cambrian apparent polar wander path for south australia spans 150 myr from 635 to 490 ma and places australia in low palaeolatitudes throughout the interval studied the poles differ significantly from each other suggesting australia underwent continual drift during that time whereas the directional difference between the late cryogenian elatina formation and early ediacaran nuccaleena formation is mainly in inclination for most other contiguous stratigraphic units the differences are mainly in declination with minor inclination differences indicating australia was rotating about a nearby euler pole in low palaeolatitudes the large and perhaps rapid polar shifts at 615 590 and 575 565 ma in the laurentian apparent polar wander path are not evident in the ediacaran apparent polar wander path for australia because true polar wander should be recorded globally in the absence of evidence for any major stratigraphic break in the south australian succession we conclude that large true polar wander did not occur during the ediacaran

magnetostratigraphic correlations in two cores from the late triassic lunde formation beryl field northern north sea uk the magnetostratigraphy of two cores from the late triassic lunde formation of the northern north sea are compatible with the calibrated magnetostratigraphy for the norian stage determined by gallet et al 1993 from tethyan carbonates the polarities of the cores indicate a lower to upper norian age for core 9 13a 36 and lower to middle norian age for core 9 13a a45 the isolated characteristic magnetizations are due to a triassic detrital remanent magnetization which is partially overprinted with a drilling induced remanence of two origins the drilling induced remanences are associated with 1 the main coring procedure producing an overprint which is oriented downcore and 2 the subsample coring procedure which produces an overprint parallel to the subsample core axis and directed outwards from the main core axis the elimination of those specimens with a significant drilling induced remanence is important for the determination of the magnetostratigraphy in these cores

paleomagnetism of the ocotillo badlands southern california and implications for slip transfer through an antidilational fault jog abstract the right lateral coyote creek fault is the southernmost segment of the san jacinto fault zone in california at the ocotillo badlands an anticlinorium of locally updomed material is exposed at a step over between echelon segments of the fault here uplift and deformation most probably result from multiple slip increments transferred across the antidilational fault jog under the assumption that material away from the jog region deforms by rigid body translation within the 2 km wide fault jog contraction has occurred by folding of the quaternary sedimentary strata about east west trending hinge lines structural analysis of this deformation shows that folding has accommodated 800 m of fault slip transferred through the antidilational jog by comparison total right slip on the coyote creek fault is 2 5 km measured 25 km to the northwest at coyote ridge a magnetostratigraphic study of the deformed strata was undertaken to determine the longevity of this fault discontinuity at the ocotillo badlands the eroded core of the updomed material at the ocotillo badlands exposes a 325 m thick sequence of sedimentary rock made up by the lacustrine borrego formation 200 m and the overlying conglomeratic ocotillo formation 125 m stepwise thermal demagnetization of samples from the exposed strata suggests that the formation boundary also marks a magnetic polarity reversal of reversed field to normal field as one travels upwards through the composite section the inferred primary magnetization is probably produced by a detrital remanent magnetization drm and is often overprinted with a weak viscous present field component comparison with magnetostratigraphy of the borrego badlands 10 km to the northwest indicates that the reversal sampled is the onset of the jaramillo event 0 97 ma the presence of a 20 angular unconformity within the upper portion of the exposed stratigraphy shows that deformation within the ocotillo badlands began during deposition of the ocotillo formation shortly after the time of the field reversal if total slip on the coyote creek fault at the ocotillo badlands is greater than 800 m it appears that the fault jog has been a transitory feature within the fault zone with slip alternately bypassing it or being transferred across it such switchyard behavior of slip transfer through the fault jog has important implications for understanding structural controls on earthquake rupture

paleomagnetic evidence for low temperature emplacement of the phreatomagmatic peperino albano ignimbrite colli albani volcano central italy the peperino albano approximately 19 36 ka old is a phreatomagmatic pyroclastic flow deposit cropping out along the slopes of the associated albano maar colli albani volcano italy the deposit exhibits lateral and vertical transitions from valley pond to veneer facies as well as intracrater facies we present the results of a paleomagnetic study of thermal remanent magnetization trm of the lithic clasts of the peperino albano ignimbrite that provide quantitative estimates of the range of emplacement temperatures across the different facies of the ignimbrite emplacement temperatures estimated for the peperino albano ignimbrite range between 240 and 350 c with the temperatures defined in the intracrater facies being generally lower than in the valley pond and veneer facies this is possibly due to the large size of the sampled clasts in the intracrater facies which when coupled with low temperature at the vent were not completely heated throughout their volume during emplacement the emplacement temperatures derived from the paleomagnetic results are in good agreement with the presence of un burnt plants at the base of the ignimbrite indicating that the temperature of the pyroclastic flow was lower than the temperature of ignition of wood paleomagnetic results from the peperino albano confirm the reliability of the paleomagnetic approach in defining the thermal history of pyroclastic flow deposits

mid cretaceous paleomagnetic reference field for north america restudy of 100 ma intrusive rocks from arkansas we have obtained new paleomagnetic data from three middle cretaceous alkalic intrusive complexes in central arkansas magnet cove and potash sulfur springs intrusions about 100 ma 20 sites and granite mountain stock about 88 ma 6 sites out of 254 specimens measured 147 from 20 sites were accepted the remainders have scattered magnetization directions which experiments indicate were caused by lightning occurring during frequent electrical storms in this region the geologic evidence indicates that the intrusions have not been tilted since emplacement the directions of magnetization calculated with respect to present day horizontal yield a mean paleopole at 192 5 e 74 1 n n 20 k 34 a95 5 7 this does not differ at 95 confidence from that determined previously by scharon and hsu but the error is diminished by half the angular dispersion sd of site virtual geomagnetic poles vgps is 13 6 similar to the value of sd about 15 predicted by current paleosecular variation models the revised arkansas paleopole is combined with four other cratonic north american paleopoles of mid cretaceous age to yield a revised middle cretaceous reference pole at 196 e 71 n a95 4 9 the mean of nine paleopoles derived from overprints in rock units from the craton and craton margin which range in age from proterozoic to jura cretaceous is 202 e 68 n a95 8 2 this is not different from the reference paleopole indicating that overprinting was very widespread across north america in mid cretaceous time

paleomagnetic estimates of temperatures reached in contact metamorphism a paleomagnetic study of some silurian devonian lavas from the lorne plateau scotland locally reheated by the intrusion of small tertiary dikes has shown that a laboratory equivalent of the actual peak temperature reached in the reheating can be accurately determined theoretically derived corrections are applied to the experimentally determined temperatures to obtain an estimate of the actual peak temperatures reached in a series of samples across the contact zones these corrected experimental profiles can be compared with peak temperature profiles calculated from heat conduction models the two profiles fit well when the temperatures of the lavas immediately prior to the intrusion are taken into account ambient temperature estimates of 75 25 c and 150 25 c have been obtained for the lavas before intrusion by a normally magnetized dike and a reversely magnetized dike respectively

linear and planar structure in ordered multivariate data as applied to progressive demagnetization of palaeomagnetic remanence summary consider a sequence of say 10 to 20 vector observations in threedimensional space it is suspected that a few subsets of consecutive observations are made up of collinear points the purpose of this paper is to construct a statistically based algorithm to find such linear segments and to assess their accuracy a similar assessment is made for coplanar sets of points this algorithm is applied here to palaeomagnetic data and is claimed to be superior to previous methods of palaeomagnetic analysis in terms of completeness and balance of analysis treatment of measurement errors and other sources of scatter criteria for identification of linear and planar sets of points and statistical rigour stability spectra with statistically based confidence limits are obtained as a by product 1 palaeomagnetic analysis background to the geometrical problem the natural remanent magnetization nrm in rocks is known in general to have originated in one or more relatively short time intervals during their formation and subsequent history i e during rock forming or metamorphic events during which nrm is frozen in stabilized by falling temperature grain growth etc the nrm acquired during each such event is a single vector magnetization parallel to the then prevailing geomagnetic field and is called a component of nrm rocks which have suffered more than one event of this kind are therefore liable to carry multi component nrm in the laboratory these components can be identified by demagnetizing the rock step by step usually by thermal alternating field or chemical demagnetization which involves the analysis of the distribution of blocking rzmperature coercivity and chemical leaching respectively resistance to these treatments is called stability of remanence and the range of treatment over which a particular component is removed is called the stability range of the component the various discrete

palaeomagnetism palaeogeography and the multicomponent analysis of middle and upper cambrian rocks of the barrandian in the bohemian massif abstract with a view to the importance of the barrandian in the bohemian massif for global palaeogeographic reconstructions considerable attention has been devoted to palaeomagnetic stability tests and multicomponent analysis of rocks of the pre variscan formations using substantially improved laboratory techniques this study is devoted to samples of upper cambrian andesite and middle cambrian sediments alternating and thermal fields were used for magnetic cleaning a thermal demagnetizer fitted with a newly developed inductor of high sensitivity the rocoma rotating coil magnetometer with a sensitivity of 0 1 to 0 2 nt was used the whole newly built and fully tested mavacs system magnetic vacuum control system guaranteed a high degree of compensation of the magnetic field in a volume of 5 1 to a value not exceeding 2 nt as numerous laboratory experiments have shown the high magnetic vacuum was necessary to derive the palaeomagnetic directions of rocks of the older formations affected significantly by the variscan orogenic phase the position of the upper cambrian pole 28 6 s 131 2 e should be considered tentative because it was derived using samples from only three andesite outcrops two other andesite outcrops preserved carboniferous or permo carboniferous palaeomagnetic directions the position of the middle cambrian pole 11 3 s 154 0 e was determined using samples of sediments mainly greywackes and shales from ten outcrops some of which represent extensive rock cross sections by combining multicomponent analysis with fold tests the mean direction of the pre variscan magnetization could be derived the very low values of the moduli of the natural remanent magnetization of the middle cambrian sediments and the considerable amount of magnetically soft components required special care to be taken in the laboratory procedures the palaeozoogeographic zones of the barrandian are related to palaeogeographic latitudes of about 40 s derived from palaeomagnetic data cold water is characteristic for the bohemian fauna but arctic conditions can be ruled out due to the amount of primary red sediments mostly of continental origin

the variscan belt of northern france southern belgium geodynamic implications of new palaeomagnetic data abstract palaeomagnetic investigations were carried out in devonian early carboniferous rocks of the variscan foreland chain of northern france southern belgium in order to reveal the origin of its arcuate shape the brabant parautochthon was sampled in the boulonnais near calais and near tournai while the ardenne allochthon was sampled near maubeuge and in the givet area all the sampled localities yielded characteristic remanent magnetization as a result of stepwise demagnetization and component analysis fold or tilt tests were possible for three localities with negative results indicating pervasive remagnetization the tectonic position was sub horizontal at two localities while the tilt was monoclinal for the rest therefore the acquisition time of the magnetic signals was estimated by comparing the palaeolatitude computed from each magnetic component to the palaeolatitudes of variscan europe calculated after van der voo 1993 three components showing a a southern b a near equatorial and c a northern palaeolatitude are recognized from our data since a pre variscan age of component a observed only in boulonnais at 10 sites is not supported by data it is assigned to an early phase of deformation component b 16 sites was acquired during the peak of the variscan tectonics late westphalian while component c five sites originated during permian times regardless of the palaeolatitudes declinations fall between 190 and 210 thus being conformable with the declinations expected for variscan europe the declinations show no correlation with the arcuate shape of the belt neither are they different in the paraauthochthon and in the allochthon nor in the different components arc formation by moulding of the allochthon on the brabant parautochthon is therefore not supported by these data since this mechanism requires substantial opposed rotations on both wings of the arc the available palaeomagnetic data are conformable with a pre formed arc simply docking to the brabant obstacle of similar shape variable offsets along a main thrust make possible a third model which slightly unfolds the former passive arc

miocene humid intervals and establishment of drainage networks by 23 ma in the central sahara southern libya terrestrial and lacustrine neogene and quaternary sediments in the libyan fezzan provide key evidence for paleoclimate changes in the central sahara associated with lake megafezzan understanding of holocene and late pleistocene deposits is resolved but the age of older sediments is not we provide the first high resolution chronology and stratigraphy of the neogene deposits in the fezzan basin and so also the central sahara the sediments are divided into three unconformity bounded units the oldest unit comprising the shabirinah and brak formations is dated using magnetostratigraphy the shabirinah formation is a succession of lacustrine and fluvial units locally with humid and arid paleosols which progressively show evidence of increasing aridity up through the succession the overlying brak formation is a pedogenically modified palustrine limestone at basin margin locations all these units are dated to the early aquitanian to late serravallian in the early to mid miocene having formed prior to major volcanic fields to the east during the mid late aquitanian widespread stromatolitic lake sediments developed in se fezzan in the late burdigalian palustrine carbonate units developed that typically pass laterally into mixed clastic paleosol carbonate units that characterise basin margin situations the serravallian aged brak formation is a highstand deposit developed during maximum lake extent which formed due to restriction of basin drainage to the north and east due to growth of the jabal as sawda volcanic centre and uplift of the sw shoulder of the sirte basin gradual aridification of the central sahara occurred from the early miocene but this trend was periodically interrupted by humid phases during which lake megafezzan developed the hyperaridity of the central sahara must have developed after 11 ma and the main drainage networks from the fezzan basin were established before 23 ma in the oligocene indicating the great antiquity of major central saharan river basins

linearity spectrum analysis of multi component magnetizations and its application to some igneous rocks from south eastern australia summary a method that enables the objective resolution of almost parallel multi component magnetizations is described and demonstrated a feature distinguishing this method from others is its simultaneous analysis of demagnetization data from a group of specimens rather than the analysis of data from one specimen at a time the only prerequisite is that the specimens are derived from a homogeneous source thus for a formation carrying a simple single component magnetization all specimens from the formation may be simultaneously reduced for a more complicated two component magnetization it is shown that only specimens from a particular site can be considered homogeneous and for a complex three component system each sample often requires undivided attention thus the workload is proportionally increased to achieve analyses of comparable reliability from data of variable quality new pole positions from mesozoic intrusions of the sydney basin nsw are from the marsden park breccia pipe 48 s 127 e a95 6 the st marys breccia pipe 46 s 150 e a95 8 the prospect dolerite 60 s 142 e a95 13 and 53 s 180 e a95 6 and from the dundas breccia pipe 58 s 162 e a95 36 and 31 s 195 e a95 16 the last two formations possess multi component magnetizations these pole positions are consistent with previous results from south eastern australia

reversal asymmetry in mesoproterozoic overprinting of the 1 88 ga gunflint formation ontario canada non dipole effects or apparent polar wander abstract eighty two palaeomagnetic samples of calcareous and jaspilitic grainstones iron formation or taconite and chert carbonate were collected from the 1 88 ga gunflint formation at 22 sites in the thunder bay area ontario twenty clasts of gunflint taconite also were sampled from the basal conglomerate of the overlying mesoproterozoic sibley group anisotropy of magnetic susceptibility measurements indicate the gunflint formation in the sampling area has not experienced regional dynamic metamorphism analyses by variable field translation balance and x ray diffraction show that the predominant magnetic mineral is hematite but a small amount of magnetite also is present in some samples altogether 213 gunflint specimens and 59 sibley conglomerate specimens were subjected to stepwise thermal demagnetisation and 74 gunflint specimens to stepwise alternating frequency demagnetisation the following components were isolated for the taconites gunflint magnetite normal declination d 293 4 inclination i 30 8 95 7 2 n 21 reverse d 86 7 i 54 6 95 5 8 n 29 gunflint hematite normal d 243 6 i 23 6 95 6 0 n 11 reverse d 70 3 i 51 4 95 3 2 n 79 sibley clasts magnetite normal d 282 7 i 33 4 95 7 6 n 20 sibley clasts hematite normal d 254 5 i 56 2 95 8 4 n 13 reverse d 110 6 i 55 7 95 8 3 n 11 none of these sets passed the reversal test with the normal component generally being the shallower fold tests were negative or inconclusive and the conglomerate test also was negative chert carbonate at one other site appears to have acquired a remanence carried by magnetite d 97 3 i 78 2 95 6 3 n 18 prior to folding related to keweenawan 1 1 ga logan diabase sill emplacement most of the components we identified match components for keweenawan sills volcanic rocks intrusions and baked contact rocks in the thunder bay area indicating that keweenawan magmatism caused widespread chemical remagnetisation of the proterozoic country rock in our sampling area although others have argued that asymmetry was a feature of the keweenawan geomagnetic field the declinations of our gunflint and sibley hematite and magnetite components are different suggesting that the components were acquired at significantly different times we conclude that the reversal asymmetry shown by our gunflint and sibley data may best be ascribed to apparent polar wander during keweenawan times

magnetostratigraphy of the sherwood sandstone group lower and middle triassic south devon uk detailed correlation of the marine and non marine anisian the sherwood sandstone group in south devon consists of the budleigh salterton pebble beds and the otter sandstone formation the otter sandstone formation comprises four lithostratigraphic sub units from the base labelled a d and contains tetrapods corresponding to the perovkan land vertebrate faunachron and is consequently a key european non marine anisian succession a total of 181 palaeomagnetic specimens from 92 horizons were measured to determine the palaeomagnetic signal the magnetic properties and characteristic remanence is predominantly carried by haematite most of which probably formed early in the depositional and diagenetic history the lower part of the sherwood sandstone group budleigh salterton pebble beds and otter sandstone formation unit a lower part of unit b has predominantly normal polarity magnetozones bs1 bs2 and bs3n with three thin reversed polarity magnetozones the lower part of unit b to the lower part of unit c of the otter sandstone formation is predominantly reverse polarity magnetozones bs3r bs4 and bs5 but includes three short normal polarity intervals the upper ca 50 m of unit c shows a mix of normal and reverse polarity bs6 bs7 with normal dominating the ca 15 m thick unit d is entirely of normal polarity bs8n the magnetostratigraphy allows unambiguous comparison with conodont and ammonite calibrated magnetostratigraphies from elsewhere in europe these show that the bs2 and bs3n magnetozones of the otter sandstone formation are lower aegean to middle pelsonian lower to middle anisian the bs3r to bs5r magnetozone interval is middle pelsonian to lower illyrian middle to upper anisian and the bs6 to bs8n magnetozone interval is middle illyrian to lower fassanian the top of unit d is correlated to an interval in the middle of the nevadites zone close to the anisian ladinian boundary consequently the otter sandstone formation correlates with the muschelkalk in the polish basin but is equivalent to only part of the germanic basin muschelkalk the continuous magnetostratigraphy from the sherwood sandstone group provides additional details of the polarity pattern through the pelsonian to illyrian interval which appears to be lacking in discontinuous marine sections a synthesis of adjacent european sedimentary basins in combination with the magnetostratigraphy suggests that the budleigh salterton pebble beds are probably late spathian to lower aegean

estimation and propagation of uncertainties associated with paleomagnetic directions principal component analysis pca is a well established technique in paleomagnetism and provides a means to estimate magnetic remanence directions from univectorial segments of stepwise demagnetization data derived directions constrain past geomagnetic field behavior and form the foundation of chronological and tectonic reconstructions pca of isolated remanence segments relies on estimates of the segment mean and covariance matrix which can carry large uncertainties given the relatively small number of demagnetization data points used to characterize individual specimens traditional pca does not however lend itself to quantification of these uncertainties and inferences drawn from paleomagnetic reconstructions suffer from an inability to propagate uncertainties from individual specimens to higher levels such as in calculations of paleomagnetic site mean directions and pole positions in this study we employ a probabilistic reformulation of pca that represents the unknowns involved in the data fitting process as probability density functions such probability density functions represent our state of knowledge about the unknowns in the fitting process and provide a tractable framework with which to rigorously quantify uncertainties associated with remanence directions estimated from demagnetization data these uncertainties can be propagated readily through each step of a paleomagnetic reconstruction to enable quantification of uncertainties for all stages of the data interpretation sequence removing the need for arbitrary selection rejection criteria at the specimen level rigorous uncertainty determination helps to protect against spurious inferences being drawn from uncertain data

magnetic carriers and remanence mechanisms in magnetite poor sediments of pleistocene age southern north sea margin pleistocene sedimentary sequences in the east anglian region of britain record both major and minor climatic oscillations and the impact of isostatic and eustatic variations intensively studied in terms of their lithology and biostratigraphy the sequences have been difficult to place in an absolute timeframe dating and correlation by magnetostratigraphy has been attempted over a num ber of years however these sediments are difficult to date by palaeomagnetic means because they are poor in detrital magnetite are subject to post depositional deformation and diagenesis and have unknown rates of sedimentation determining whether their natural remanence magnetisation nrm directions are reliable thus requires information on the mode and timing of remanence acquisition here we apply palaeomagnetic rock magnetic and mineralogical analyses to identify the nrm carriers in these sediments and hence their palaeomagnetic reliability within oxidised fluvial sediments the kesgrave formation the magnetic carriers appear to be relict magnetic minerals fer rian ilmenites chromites haematite and goethite which sometimes carry a reliable primary deposi tional remanence drm but often an overprinting viscous time varying remanence vrm within some reduced marine and intertidal sediments within the crag basin the iron sulphide greigite has been found to carry a reliable syn depositional chemical remanence crm in all the sediments magnetic inclusions within silicates are abundant are significant for the mineral magnetic signal but contribute little to any recoverable palaeomagnetic information copyright 2005 john wiley sons ltd

palaeomagnetism and magnetostratigraphy of the permian triassic northwest central siberian trap basalts abstract a detailed palaeomagnetic and magnetostratigraphic study of the permian triassic siberian trap basalts stb in the noril sk and abagalakh regions in northwest central siberia is presented thermal th and alternating field af demagnetisation techniques have been used and yielded characteristic magnetisation directions the natural remanent magnetisation of both surface and subsurface samples is characterised by a single component in most cases occasionally a viscous overprint can be identified which is easily removed by th or af demagnetisation the resulting average mean direction after tectonic correction for the 95 flows sampled in outcrops is d 93 7 i 74 7 with k 19 and 95 3 3 the corresponding pole position is 56 2 n 146 0 e unoriented samples from four boreholes cores in the same regions have also been studied they confirm the reversed normal succession found in outcrops the fact that only one reversal of the earth s magnetic field has been recorded in the traps can be taken as evidence for a rather short time span for the major eruptive episode in this region however there is evidence elsewhere that the whole volcanic activity associated with the emplacement of the stb was much longer and lasted several million years

palaeomagnetism of iron formation from the late palaeoproterozoic frere formation earaheedy basin western australia palaeogeographic and tectonic implications abstract oriented cores of unweathered frere formation 1 9 1 8 ga including shaly and peloidal iron formation were obtained from two holes drilled to 116 m depth on opposite limbs of an anticline in the southern earaheedy basin at the northeastern margin of the yilgarn craton anisotropy of magnetic susceptibility measurements indicated that the frere formation in this area was unaffected by regional metamorphism the predominant magnetic mineral in the iron formation is hematite but a small amount of magnetite also is present in some samples stepwise thermal demagnetisation was conducted for 263 specimens many specimens acquired spurious components of magnetisation after treatment to 300 500 c ascribable to the oxidation of siderite to magnetite on heating however other specimens displayed a stable high temperature 680 c dual polarity component a carried by hematite that gave a bedding dip corrected direction of d 314 3 i 24 8 k 38 5 95 2 6 n 78 a fold test was positive at 99 level of confidence indicating acquisition of remanence prior to stanley folding in the earaheedy basin that occurred at 1 78 ga near the end of capricorn orogenesis the presence of polarity reversals in the stratigraphic section from one drill hole and within some specimens argues for the identification of a dipole field axis and the sufficient averaging of secular variation to define a palaeopole for the frere formation located at 45 2 s 220 0 e dp 1 3 dm 2 4 component a is ascribed to a chemical remanent magnetisation crm acquired soon after deposition and indicates a palaeolatitude of 13 0 1 5 for the frere formation the frere pole plots adjacent to but is still significantly different from late to post capricorn orogeny overprint poles from the hamersley province of the southern pilbara however vertical axis relative anticlockwise rotation of 10 15 for the frere pole brings it close to these pilbara overprint poles the data imply that the earaheedy basin and possibly the yilgarn craton underwent clockwise rotation of 10 15 relative to the pilbara craton during stanley folding this finding accords with evidence for tectonic settings marked by sinistral strike slip deformation adjacent to the yilgarn pilbara cratonic boundary during deposition and subsequent folding in the earaheedy basin the data also imply that the west australian and north australian cratons were in close proximity by 1 8 ga

a record of reversed polarity carried by the iron sulphide greigite in british early pleistocene sediments abstract palaeomagnetic measurements were made on samples extracted from a short sequence of early pleistocene estuarine clays now exposed in a sea cliff near sheringham on the north norfolk coast uk on the basis of earlier palynological work these clays had been ascribed a pastonian late tiglian age the clays show marked changes in colour from reddish brown at the top of the unit to blue grey in the middle and grey brown at the base the palaeomagnetic data vary in close association with these colour changes the top and basal brown clays show scattered normal directions of low intensity while the middle blue clays show strongly clustered reversed directions of much higher intensities some samples taken from the boundary between the middle blue and upper red clays show upon demagnetisation a normal overprint on a stable reversed polarity using high gradient magnetic extraction magnetic concentrates have been obtained from the strongly magnetic middle blue clays the presence of iron sulphide minerals in these concentrates was identified using energy dispersive x ray analysis during scanning electron microscopy more specifically x ray diffraction identifies greigite as the only detectable ferrimagnetic mineral in the magnetic concentrates rock magnetic measurements show clear qualitative differences in the magnetic mineralogies of the three clay subunits but absolute identification of the magnetic mineralogy of the weakly magnetic upper and basal brown clays has not yet been possible we interpret the sequence as a primary reversed polarity record this record is carried by the iron sulphide greigite as a chemical remanence acquired during syn depositional reduction of iron via the decomposition of organic material in these anoxic tidal clays subsequently the upper and basal subunits of the clay have been oxidised by permeation of groundwater from the adjacent coarse grained sediments most of the griegite in the oxidised margins of the clay has been altered as a result to a new less efficient magnetic recording material which thus carries a later scattered low intensity normal overprint

permian clockwise rotations of the ebro and corso sardinian blocks during iberian armorican oroclinal bending preliminary paleomagnetic data from the catalan coastal range ne spain abstract paleomagnetic investigations of early permian and triassic magmatic rocks from catalan coastal ranges provide three magnetic directions which are interpreted as primary magnetizations and partly as overprints the succession of magnetic directions is interpreted in terms of a succession of large scale clockwise rotations which bring the whole assembly of pyrenees catalonia corsica sardinia and maures esterel massifs from the southeast of the massif central to the west during permian this major movement is associated with clockwise rotation of northern limb of the iberian orocline during latest carboniferous and early permian 305 290 ma subsequently permian large scale dextral transtensional extensional shearing operated along aquitanian shear belt between the massif central in the northeast and the iberian variscan massifs in the southwest the latest phase of the rotation in the late permian early triassic is associated with alkaline magmatism probably linked to neo tethys opening activity in western europe

a palaeomagnetic study of the builth wells llandrindod wells ordovician inlier wales palaeogeographic and structural implications summary discrepancies exist in the southern british ordovician palaeomagnetic data set with individual studies indicating either high southerly or temperate southerly palaeolatitudes although previous palaeomagnetic investigations from the builth inlier have delineated a three component remanence structure doubts have been raised concerning i the magnetization age of the supposed primary component p ii the structural setting of the sampling area llanelwedd quarry within a zone of strike slip deformation and iii whether detailed step wise demagnetization has fully separated the various magnetization components in addressing these problems we present new palaeomagnetic results as follows i a positive palaeomagnetic conglomerate test establishing a pre late llanvirn age for component p ii an enlarged geographic sampling embracing several tectonic domains indicating that relative rotations linked to strike slip tectonism are minor within the builth sampling area and iii evidence that component p is uncontaminated by overprints at some sites suggesting the resulting palaeolatitude of 35 s to be representative for the builth inlier we also present evidence for local syn volcanic deformation within llanvirn volcanics and for intrusion related deformation of llanvirn shales when the revised llanvirn pole from the inlier 3 s 4 e is combined with other data from southern britain in a statistical spline analysis a mean palaeolatitude of 44 5 s is calculated for builth in llanvirn times a palaeoreconstruction for 468 474 ma c mid llanvirn is presented utilizing this analysis

two thousand years of geomagnetic field direction over central europe revealed by indirect measurements summary supplemented by 32 new directions the hungarian archaeomagnetic data set now consists of 217 archaeologically dated directions ranging in age from 300 bc to 1800 ad from this data set reference curves of secular variation of the geomagnetic field direction were computed using hierarchical modelling and curve estimation by moving average technique thanks to some of the new data the gap in the earlier reference curves around 500 ad has now been filled up for comparison s sake directional records of comparable length from central europe were also processed by the same curve building method for this purpose all dated directional data declination and inclination with statistics were drawn from the geomagia50 database for france germany the ukraine and moldavia bulgaria and italy and transferred via their virtual geomagnetic poles to a reference point of their respective countries the resulting reference curves including those for hungary show more or less similar temporal behaviour to the corresponding cals7k 2 model curves also available from the geomagia50 database but significant deviations from the low order cals7k 2 predictions are also discernible owing to the likely presence of additional higher order complications in the regional field therefore the regional field and its secular variation are suggested to be approximated by the reference rather than the predicted curves at any other location within the study area the direction of the regional field can be obtained by spatial interpolation from the reference curves as illustrated by isogonic and isoclinic maps shown for selected times local time series of interpolated directions for other central european countries lacking reference curves might serve as master curves for magnetic dating

tectonic and paleogeographic interpretation of the paleomagnetism of variscan and pre variscan formations of the bohemian massif with special reference to the barrandian terrane abstract paleomagnetic data from variscan and pre variscan formations of the bohemian massif bm have been interpreted tectonically and paleogeographically evaluated with respect to the european paleomagnetic results the interpretation of data from the bm was preceded by the evaluation of the effect of the trans european suture zone tesz on the dispersion of the european paleomagnetic pole positions during the variscan orogeny stability of the european lithospheric plate is well documented by paleomagnetic results for the early permian to the quaternary rocks of the regions between the ural mountains and great britain north of the alpine tectonic belt for the late carboniferous and earlier times the stable plate is defined in the regions ne of the tesz in the east european craton only late carboniferous and older rocks from the regions sw of the tesz largely occupied by the west european variscides show tectonic deformations controlled by prominent horizontal rotations these rotations can be studied on a theoretical model simulating the distribution of pole positions controlled by rotation of rock formations about a vertical axis in the bm horizontal paleotectonic rotations are well documented for variscan and pre variscan rocks they reach several tens of degrees up to 180 in extreme cases of mostly clockwise sense the study of the tectonics and paleogeography of cambrian to devonian formations of the barrandian area which is considered a peri gondwana terrane with affinities to armorica may serve as a case history of the study of a terrane incorporated into a stable lithospheric plate here the barrandian terrane became a part of the european plate as a component of the emerging pangea supercontinent in the final phase of the variscan orogeny high almost peri polar paleolatitudes for the cambrian rocks of the barrandian area are within the limits of data scatter in agreement with the presumed position of gondwana and armorica rocks of ordovician age did not produce consistent results they will require further paleomagnetic and paleoclimatologic studies in relation to the data for the late cambrian and early silurian rocks of the barrandian area the analysis of data presented here shows that paleomagnetic declinations of variscan and pre variscan formations reflect paleotectonic rotations following the formation of the respective rocks including rotations induced by the variscan orogeny and rotation of the european plate to which the rocks became incorporated therefore paleomagnetic declination of none of the pre variscan formations can be identified with paleotectonic rotation either of the barrandian terrane or even of the whole bm magnitudes of horizontal paleotectonic rotations in the bm affected by variscan tectonism are notably similar to those in the western carpathians affected by alpine deformation senses of rotation are however different with clockwise rotation prevailing in the bm and counterclockwise rotations prevailing in the western carpathians recognition of the effect of horizontal rotations of rock formations if located in tectonically mobile belts and incorporated into a stable plate during their later history should be respected while deriving the apparent polar wandering path apwp

paleomagnetism of the paleoproterozoic gowganda and lorrain formations ontario low paleolatitude for huronian glaciation abstract to further our understanding of the paleolatitudes of precambrian glaciations a paleomagnetic study has been conducted on the glaciomarine coleman member of the gowganda formation and the conformably overlying deltaic firstbrook member and lorrain formation huronian supergroup 2 4 2 3 ga in ontario canada many of the rocks notably the gray and grayish red argillic facies display unstable magnetization or overprints carried by magnetite and or hematite that give negative fold tests some red sandstones however have stable high temperature 690 c components marked by very shallow northerly or southwesterly directions five sites in pale red sandstone from the coleman member near elliot lake give a dip corrected a direction of d 216 3 i 5 5 95 6 7 n 30 and 17 sites in lorrain red sandstone near desbarats give a dip corrected a direction of d 5 4 i 5 5 95 5 9 n 75 unfavorable structural attitudes rendered fold tests inconclusive these very shallow directions may be ascribed to early chemical remanent magnetization crm because a some specimens display polarity reversals b such directions are unknown either as original or as overprint components in post huronian rocks of the region and c a prior site in coleman red beds gave a high temperature shallow nnw direction that is not significantly different from lorrain a and which a positive conglomerate test suggested is not an overprint the very shallow directions are near primary directions for the slightly older 2 45 ga matachewan dyke swarm in the region lorrain argillic rocks at five sites give a normal component b t 670 c d 18 6 i 59 6 95 6 1 n 16 dip corrected and a reverse component e t 500 c d 190 9 i 60 9 95 7 3 n 14 in situ which are close to a prefolding direction carried by magnetite previously identified in coleman gray argillites morris a however a primary origin for morris a is dubious because of the widespread occurrence of overprints carried by magnetite in coleman gray argillites and because the fold test employed folds formed during the penokean orogeny at 1900 1800 ma our results suggest that morris a lorrain b and lorrain e may data from immediately before and just after penokean folding respectively hence coleman sandstone a and lorrain a may be better estimates of original directions those components and matachewan paleomagnetic data constrain huronian paleolatitudes and suggest that huronian glaciation occurred within 11 and possibly within 4 of the paleoequator

palaeomagnetism of the torridonian of rhum scotland evidence for limited uplift of the central intrusive complex abstract the tertiary central intrusive of rhum was emplaced into the torridonian sandstone causing a heat influx into the sediment detailed progressive demagnetisation of sandstones from the thermal aureole of the intrusion show that they reached maximum temperatures which decrease systematically with distance in a manner indicative of conduction dominated cooling temperatures reached near to the intrusion are higher than would be predicted theoretically probably as a result of the presence of smaller plugs of magma at depth which are only rarely exposed at the surface the shape and magnitude of the thermal aureole suggest that upward movement of the central intrusive along the bounding fault was limited primary remanence in torridonian sandstones unaffected by the intrusion is carried by both magnetite and haematite often with both occurring in the same specimen it is suspected that only magnetite carries a truly primary detrital remanence the haematite probably formed diagenetically largely by oxidation of detrital magnetite at some time shortly after deposition

paleomagnetic evolution of the armorican massif in late paleozoic times in the light of overprints recorded in cadomian and paleozoic units abstract previous investigations have shown that in paleozoic outcrops of the variscides the major part of the paleomagnetic record consists of overprints after identification and dating of these overprints the magnetic record can be used to constrain the geotectonic evolution of the investigated area after the major tectonic event in order to test this hypothesis a paleomagnetic investigation was carried out on various volcanic and plutonic units from northern brittany 48 5 n 3 w emplaced and metamorphosed in the late proterozoic during the cadomian orogeny to calibrate the overprints in terms of their ages doleritic dykes intruded into the cadomian basement in the early paleozoic as well as early carboniferous intrusive and extrusive rocks were also sampled thermal demagnetization often shows multivectorial behaviour of most nrms and indicates a wide range of magnetic components characterized by various unblocking temperatures a large majority of the components isolated in cadomian units display directions that are consistent whith the results from the younger paleozoic units with exception of the d components mean vgp 7 s 152 e which are interpreted as being ordovician in age all other mean directions poles agree with results obtained from visean volcanic plutonic and metamorphic rocks of the central part of the variscan belt this means that no cadomian magnetization has survived the tectonic magmatic and metamorphic phases that have affected the cadomian basement during the paleozoic the major part of the magnetic overprints were acquired during the variscan orogeny particularly in relation to visean and westphalian magmatism the early carboniferous 340 328 ma cn 7 s 53 e co 29 s 60 e and cp 51 s 62 e components the middle carboniferous 328 310 ma b components 11 n 124 e the late carboniferous 310 300 ma a1 30 n 151 e the late permian a 51 n 154 e and the jurassic j1 overprints 72 n 107 e delineate an apparent polar wander path that can be interpreted in terms of geotectonic evolution since the late visean this evolution was the same as for the massif central the vosges the black forest and the odenwald spessart the variable inclinations of the c components suggest a northwestward tilting of the area north of saint brieuc and a possible latitudinal drift of the whole massif in late visean times the c b and b a1 segments of the apwp reveal two successive clockwise rotations by 70 80 in the latest visean and by 30 in the late namurian early westphalian the first rotation closed the rhenohercynian basin during the last rotation the variscan belt was tied to northern europe the a and j1 overprints give evidence of hydrothermal activity in northern brittany in the late permian and the early jurassic

permo triassic magnetostratigraphy in china northern tarim abstract the upper boundary of the permo carboniferous reversed polarity superchron has been identified in a palaeomagnetic study of the permo triassic of the northern part of the tarim basin china this boundary serves as an important marker horizon for correlation with other permo triassic sequences both in china and world wide a permo triassic palaeomagnetic pole for the tarim block is estimated to be at 71 8 n 187 6 e comparison with similar age poles from the adjacent blocks of china and asia suggests that the tarim was widely separated from the sino korean block in permo triassic times but was not yet sutured to kazakhstan

magnetostratigraphy of the lower triassic volcanics from deep drill sg6 in western siberia evidence for long lasting permo triassic volcanic activity summary the deep drill hole sg6 in western siberia 66 n 78 5 e penetrated 1 1 km of lower triassic basalts which are possibly an extension of the central siberian permo triassic flood basalt province about 300 samples of these basalts were progressively demagnetized and measured principal component analysis often shows multiple magnetizations carried by haematite and magnetite the corrected mean inclinations are 77 and 77 for the haematite component a magnetostratigraphic scale was derived and showed a n r n r n succession this is quite diverent from the noril sk and taimyr typical polarity scale r n the basalts found in the sg6 deep drill hole are slightly younger than those of central siberia and taimyr they correspond to middle upper induan age whereas the noril sk and taimyr sections correspond to an uppermost permian and lower induan age altogether they indicate that after a high output rate of volcanic material near the permo triassic boundary this activity slowed down drastically on the siberian platform and taimyr but persisted for several million years in western siberia

a palaeomagnetic investigation of the mashonaland dolerites north east zimbabwe summary earlier palaeomagnetic work on the mashonaland dolerite sills and dykes 1830 230 ma showed that they record a geomagnetic field reversal 28 new sites have been sampled in sills 26 and dykes 2 in north east zimbabwe detailed alternating field demagnetization afd is more effective in removing secondary components of remanence than thermal demagnetization td and enables an assumed primary remanence to be isolated at 16 sill sites combined with earlier results there are 11 sill sites with a positive inclination p d 287 i 53 k 40 and 18 with a negative inclination n d 114 i 47 k 35 the data lead to a positive class b reversal test field tests suggest that the n remanence is the younger and that the period of mashonaland igneous activity spanned a reversal of the earth s magnetic field from p to n the areal distribution of polarity is not random sills with only p remanence are found in the more elevated central region of the mashonaland igneous province whilst predominantly n bearing sills occupy the lower surrounding terrain

pyroclastic flow deposits from a kimberlite eruption the orapa south crater botswana abstract the orapa diamond mine republic of botswana exposes a bi lobate kimberlite pipe that erupted during the late cretaceous epoch 93 ma through archaean basement and volcano sedimentary rocks of the karoo supergroup geological mapping of the crater zone of the south pipe has revealed a 15 25 m thick in situ kimberlite pyroclastic flow deposit the pyroclastic deposit fills in the crater and completely drapes lower units indicating that the parent flow originated from an adjacent kimberlite pipe the unit comprises a basal coarse lithic concentration layer exhibiting imbricated clasts which grades upwards into massive poorly sorted lapilli tuff the tuff contains abundant sub vertical degassing structures defined by lithic enrichment and depletion in fine grained material degassing structures commonly emanate from blocks in the basal layer the presence of degassing structures and a coarse basal layer distinguishes this deposit from pipe filling massive volcaniclastic kimberlite which is typically homogeneous in terms of texture and clast size over distances on the order of 100s of metres studies of the thermal remanent magnetism in basalt clasts from the deposit together with serpentine diopside assemblages indicate that it was emplaced at elevated temperatures on the order of 200 440 c consistent with deposition from a pyroclastic flow the lithofacies characteristics can be explained by the interaction of the pyroclastic flow with the complex topography of a pre existing crater

in the wake of a counterclockwise rotating adriatic microplate neogene paleomagnetic results from northern croatia in northern croatia the neogene sediments cover complicated basement rocks which consist of alpine and dinaridic elements in the zagorje area and variscan alpine formations of the tisia tisza megatectonic unit in the slavonian mountains mts the neogene sediments were deposited in two separate basins before the karpatian but sedimentation became uniform from the karpatian onwards 17 5 ma of the 24 localities that we have studied so far paleomagnetically from northern croatia 16 localities are of karpatian or younger age while the rest are pre karpatian

palaeomagnetism and magnetic fabric in the freetown complex sierra leone summary about six separately orientated cores were collected at each of 14 sites distributed throughout the arcuate west dipping 6 km thick freetown layered igneous complex alternating field and thermal demagnetization both isolate a stable component of remanent magnetism which corresponds to a palaeomagnetic south pole from 13 sites nine reverse four normal polarity at 82 9 s 32 7 e a 95 5 6 this is indistinguishable from that reported in 1971 based on alternating field demagnetization of cores from 10 orientated hand samples the diverence between the freetown pole age 193 3 ma and other mid jurassic poles from west africa could be due to its greater age the diverence between the whole west african jurassic pole group and the karoo pole from southern africa however suggests moderate 10 d i verential rotation of west africa relative to the kaapvaal craton a prevalent magnetic foliation fabric coincides generally with the petrological layering as might be expected but a ubiquitous magnetic lineation is predominantly down dip this is compatible with a down dip pyroxene lineation reported to be present in some field outcrops and interpreted in terms of late stage deformation during the slow crystallization and cooling of the large igneous body however a fold test shows that the igneous layering had already achieved its present attitude before the complex cooled to 570 c the maximum blocking temperature of the characteristic remanence

magneto biostratigraphy of the middle to upper triassic transition central spitsbergen arctic norway palaeomagnetic and biostratigraphic data were obtained for the latest ladinian and most of the carnian botneheia formation to basal kapp toscana group from two sections in central spitsbergen svalbard archipelago thermal and alternating field af demagnetization reveals a magnetization of both normal and reversed polarities the mean directions pass reversal and fold tests and are similar to other european late triassic palaeopoles one of the sections displays 15 of vertical axis clockwise tectonic rotation on a decollement in the underlying botneheia formation the magnetostratigraphy is dominated by normal polarity in the uppermost botneheia formation and into the tschermakfjellet and basal de geerdalen formations a substantial hiatus characterizes the ladinian carnian boundary in central spitsbergen so reverse magnetozones identified in tethyan sections near this boundary are absent magnetostratigraphic correlation along with palynostratigraphic constraints indicates that most of the de geerdalen formation is lower carnian the magnetostratigraphy and palynology indicates that the isfjorden member upper unit of the de geerdalen formation is probably mid carnian in age change in the lithological architecture in the isfjorden member compared with the underlying parts of the de geerdalen fm suggests a hiatus near the base of the member which may represent a mid carnian unconformity not previously recognized on spitsbergen

early pleistocene sediments at great blakenham suffolk england abstract detailed investigation of a fine sediment sequence the college farm silty clay member that overlies the creeting sands early pleistocene in suffolk is presented the sedimentary sequence is thought to represent a freshwater pool accumulation in a small coastal embayment palaeobotanical investigation of the sediment indicates that it accumulated during the late temperate substage of a temperate interglacial event the occurrence of tsuga pollen associated with abundant remains of the water fern azolla tegeliensis indicate that the deposits are of early pleistocene age and are correlated with a later part of the antian bramertonian stage correlation with tiglian to substage in the netherlands sequence is most likely the sediments normal palaeomagnetic polarity reinforces the biostratigraphical correlation

paleomagnetism of pre grenvillian mafic rocks from the northeast grenville province labrador implications for the grenville track a paleomagnetic study of mafic plutonic rocks in the northeast grenville province found five magnetizations interpreted as grenvillian and later overprints components a b and c with the highest unblocking temperatures and distinct regional distributions have paleopoles that appear to lie on the grenville track component c with pole at 348 e 11 s p m 2 4 and mostly distributed in lower grade mafic rocks in the groswater bay terrane near the grenville front is interpreted as a post ca 970 ma grenville overprint predating components a and b the latter components nearly coextensive in distribution in the groswater bay and sandwich bay regions farther south have respective poles at 326 e 02 n n 9 sites p m 8 11 and 348 e 13 n n 13 sites p m 6 8 component b could be interpreted either as a grenville overprint or more likely as a later overprint of late neoproterozoic 615 ma to cambrian age due to rifting in the lake melville region if so many other so

paleomagnetism of cretaceous volcanic rocks of the sverdrup basin magnetostratigraphy paleolatitudes and rotations the principal magnetization of lavas of the isachsen and strand fiord formations on axel heiberg island is shown to predate the eocene eurekan orogeny basalt flows of the strand fiord formation volcanigenic sandstone from the christopher formation and the uppermost flows of the isachsen formation are normally magnetized reversed magnetizations are found only in the isachsen formation occurring at two horizons which we suggest correspond to m and m of the m sequence of marine magnetic anomalies 1 18 123 ma it is possible therefore that we have located at least approximately the base of the cretaceous normal polarity superchron in these sections because inclinations are steep the analysis of directions of magnetization is not straightforward and has been done by two methods method i assumes that no relative rotations have occurred amongst sample localities and calculations on this basis show a 33 24 p 0 05 counterclockwise rotation with no paleolatitudinal displacement relative to north america the rotation is in agreement with the rotation of 36 8 p 0 05 determined earlier from the permian esayoo formation on ellesmere island analysis by method i assumes that the esayoo and the isachsen strand fiord sampling localities on axel heiberg and ellesmere island are contained within what is essentially one large structural domain the agreement using method i of paleolatitude with that of north america is consistent with standard plate reconstructions in which there is a gap of about 300 krn between greenland and ellesmere island however the dispersion of site mean directions is greater than that expected for paleosecular variation during the cretaceous and therefore some of the dispersion may be attributable to relative motions amongst collecting localities therefore by method 11 relative rotations amongst localities are assumed to have occurred and inclinations and declinations are analysed separately as with method i declinations are predominantly counterclockwise from that expected but by method i1 the mean inclination 74 f 2 standard error is significantly shallower than that expected 79 lo standard error this apparent flattening is consistent with the idea that the arctic islands were close to greenland in the cretaceous and that there was no gap along nares strait hence both methods of calculation yield similar counter clockwise rotation but each gives slightly different paleolatitudes the latter difference cannot at present be resolved

a palaeomagnetic study of recumbently folded and thermally metamorphosed torridon group sediments eishort anticline skye scotland two geologically significant palaeomagnetic components have been isolated in samples of torridon group sandstones from the kishorn nappe of nw scotland the samples were collected from the eishort anticline a large recumbent fold of caledonian age the softer component which is demagnetized by low temperatures and weak magnetic fields when in situ displays a steep upward direction typical of reversed tertiary magnetizations both polarities of the harder component which is demagnetized by high temperatures only are present and when dip corrected display either northwesterly upward or southeasterly downward directions characteristic of torridonian remanences it is suggested that the tertiary component is of chemical origin and the result of alteration of magnetite titanomagnetite grains the geographical distribution of these grains is irregular and as a result the distribution of the tertiary overprint is irregular the torridonian palaeomagnetic components from both limbs of the fold can be restored by rotation about the fold axis to internally consistent directions which lie close to previously published data from the caledonian foreland no correction is necessary for finite strain which suggests that the eishort anticline formed by a flexural slip mechanism however an anticlockwise rotation of 26 is required to reconcile the torridonian directions from the kishorn nappe with those of the caledonian foreland which suggests that during emplacement the thrust sheet rotated on the underlying fault surface

palaeomagnetic results from the late precambrian chela group of southwest angola abstract palaeomagnetic results from fourteen sites 56 samples in the late precambrian chela group of southwest angola are reported after alternating field demagnetization eight of the sites have mean directions closely grouped around d 123 i 44 1 2 the dispersion of these directions increases substantially after tectonic corrections suggesting magnetic overprinting intensive thermal demagnetization proved more effective than alternating field demagnetization in resolving magnetic components after removal of viscous components samples from five sites group i show a single component similar to that observed after alternating field demagnetization at four more sites group ii this same component is present together with another higher temperature component the mean direction for the component observed at all nine sites is d 119 7 i 45 9 with k 40 5 tectonic corrections produced little change in mean direction but reduced k to 4 5 the data supports the magnetic overprint hypothesis a high blocking temperature component was resolved by remagnetization circle analysis of three flat lying sites group iii and this component is similar to the higher temperature component observed at site dg group ii after tectonic correction has been made the component observed in group iii samples d 311 i 49 confirmed by some samples from group ii is similar to that observed in the nosib group just to the south in namibia it is suggested that the mean group iii result gives the primary direction of the chela group that the data support the correlation of the nosib and chela groups and that the chela rocks were overprinted magnetically during an event subsequent to their tilting

paleomagnetism of the 1 88 ga sokoman formation in the schefferville knob lake area quebec canada and implications for the genesis of iron oxide deposits in the central new quebec orogen abstract thirty nine oriented block samples of iron formation were collected at 13 sites including opposite limbs of major folds from the 1 88 ga sokoman formation knob lake group in the schefferville knob lake area of the central new quebec orogen northern quebec the samples assayed up to 80 24 fe2o3t 54 08 fe implying fe enrichment of the iron formation up to ore grade anisotropy of magnetic susceptibility measurements on 245 standard specimens indicate a well preserved bedding parallel fabric in the iron formation suggesting minimal alteration of the magnetic mineralogy since deposition and or a mimetic secondary magnetic mineralogy the iron formation has not been internally deformed since the magnetic mineralogy was established analyses by variable field translation balance and x ray diffraction showed that the predominant magnetic mineral is hematite but a small amount of magnetite also is present in most samples following low temperature pre treatment as appropriate stepwise thermal and alternating field demagnetization of 218 specimens revealed a low temperature post folding component maximum tub 400 c d 27 1 i 20 1 95 10 9 from seven sites pole position of 40 6 s 257 0 e and components carried by magnetite maximum tub 580 c d 35 8 i 3 9 95 9 1 from 10 sites pole position of 29 6 s 250 9 e and hematite maximum tub 680 c d 40 0 i 1 6 95 18 6 from seven sites pole position of 26 8 s 247 0 e the components carried by magnetite and hematite are pre syn and post folding depending on the sampling site indicating that the magnetization was acquired continuously with deformation in the new quebec orogen at 1 84 1 83 ga no evidence was found for acquisition of magnetization during the mesozoic when many of the iron oxide orebodies in the schefferville knob lake area are thought to have formed our findings imply that an episode of fe enrichment of iron formation in the sokoman formation involved the circulation of hydrothermal fluids related to late paleoproterozoic orogenesis such orogenic circulation of fluids may have contributed to the development of hematitic orebodies in the central new quebec orogen

superimposed recent permo carboniferous and ordovician palaeomagnetic remanence in the builth volcanic series wales the builth volcanic series of llanvirnian age in llanelwedd quarries mid wales carries three components of natural remanent magnetisation component p regarded as primary is a thermochemical remanence directed at d 181 7 i 54 5 95 4 4 relative to bedding component s is a secondary component with in situ d 178 7 i 6 7 95 5 4 and is believed to be a low temperature chemical remanence crm of permo carboniferous age component r is directed close to the present geomagnetic field and is believed to be a recent viscous remanence vrm the results are of interest for three reasons first they are an unusually good example of multi component nrm analysis the three components being so clearly discriminated by thermal demagnetisation because they have almost completely separate blocking temperature ranges second they provide evidence of a permo carboniferous event possibly a mild thermal or hydrothermal pulse promoting crm acquisition some 40 km north of the hercynian orogenic front third they illustrate very clearly the importance of detailed demagnetisation this work revises the pole position for these rocks by 10 and removes an obstacle to the palaeomagnetic recognition of the 1000 km wide iapetus ocean cutting britain in ordovician time

comments and reply on paleomagnetic evidence for a large 2 000 km sinistral offset along the great glen fault during carboniferous time

precambrian tidal and glacial clastic deposits implications for precambrian earth moon dynamics and palaeoclimate abstract over the past decade the study of precambrian clastic tidal rhythmites stacked laminae of sandstone siltstone and mudstone that display periodic variations in thickness reflecting a strong tidal influence on sedimentation has provided accurate palaeotidal and palaeorotational data palaeotidal records obtained from tidal rhythmites may be systematically abbreviated however and derived periods and frequencies can be misleading the validity of such values including past length of day can be assessed by testing for internal self consistency through application of the laws of celestial mechanics such a test supports the estimated length of day of 21 9 0 4 h derived from the late neoproterozoic 620 ma elatina reynella rhythmites in south australia and the indicated mean rate of lunar retreat of 2 16 0 31 cm year since 620 ma the validity of estimated lengths of day obtained from other precambrian tidal rhythmites remain unverified because the data sets contain only one primary value directly determined from the rhythmites the elatina reynella data militate against significant earth expansion at least since 620 ma and suggest that the free nutation or tipping of the earth s fluid core has undergone a resonance with the earth s annual forced nutation since the neoproterozoic glaciogenic deposits are readily distinguishable from ejecta resulting from impacts with earth crossing bodies palaeomagnetic data based on the geocentric axial dipole model for the geomagnetic field indicate that neoproterozoic and palaeoproterozoic glaciation and cold climate near sea level occurred in low palaeolatitudes this enigmatic finding may imply global glaciation or an increased obliquity of the ecliptic and is relevant to modelling the effect of ice sheet formation on the earth s obliquity history by obliquity oblateness feedback mechanisms through multidisciplinary studies clastic sedimentology and geophysics together can make substantial contributions to understanding precambrian earth moon dynamics and global palaeoenvironments

end of the kiaman superchron in the permian of sw england magnetostratigraphy of the aylesbeare mudstone and exeter groups the chronology of permian strata in sw england is fragmentary and largely based on radiometric dating of associated volcanic units magnetostratigraphy from the c 2 km of sediments in the exeter and aylesbeare mudstone groups was undertaken to define a detailed chronology using the end of the kiaman superchron and the overlying reverse and normal polarity in the middle and upper permian as age constraints the palaeomagnetic directions are consistent with other european permian palaeopoles with data passing fold and reversal tests the end of the kiaman superchron in the wordian occurs in the uppermost part of the exeter group the overlying aylesbeare mudstone group is early capitanian to latest wuchiapingian in age the changhsingian and most of the lower triassic sequence is absent magnetostratigraphic comparison with the southern permian basin shows that the exeter and aylesbeare mudstone groups are closely comparable in age with the havel and elbe subgroups of the rotliegend ii succession the altmark unconformities in these successions appear similar in age to the sequence boundaries in sw england indicating that both may be climate controlled clasts in the exeter group from unroofing of the dartmoor granite first occurred at a minimum of c 8 myr after formation of the granite supplementary material additional sampling magnetic fabric and palaeomagnetic data are available at http doi org 10 6084 m9 figshare c 3283400

palaeomagnetic signature of slow post orogenic cooling of the north east highlands of scotland recorded in the newer gabbros of aberdeenshire summary consideration of previous work and new data show a systematic distribution of the directions of high coercivity and high blocking temperature magnetization in the newer gabbros of aberdeenshire the site mean directions show a non fisherian distribution with the corresponding pole positions distributed along a published early palaeozoic apparent polar wander path for great britain the mean of the distribution closely agrees with the mean direction previously reported and widely quoted there is a close correlation of the site mean directions with the position of the sampling sites with respect to the contours chrontours of the k ar coolingage sites where stable nrm has se declinations and shallow 20 inclinations have the oldest chrontour ages 468 myr the mean palaeomagnetic direction progressively shifts and the sites with the youngest chrontour ages 428 myr have sw declinations with moderately steeper 45 inclination the relative age of magnetization determined from the position of the corresponding pole on the apparent polar wander path is consistent with the relative chrontour age the gabbros have therefore recorded the shift of the north east highlands with respect to the palaeomagnetic pole during the slow cooling of the terrain the slow cooling is presumably related to uplift and erosion and the resulting downward migration of isothermal surfaces a previously published suggestion that all magnetizations with southerly declinations and moderately downward inclination are the resultant of normal and reversed magnetizations with shallow inclination is shown to be incorrect

palaeomagnetic results from the tibetan plateau palaeomagnetic measurements were carried out on 1325 oriented samples collected from 246 sites on a traverse of the tibetan plateau from lhasa to golmud in 1985 crossing the lhasa terrane qiangtang terrane and kunlun terrane high blocking temperature high coercivity statistically grouped magnetizations were isolated from the following units lhasa terrane cretaceous takena formation mid cretaceous nagqu volcanics mid cretaceous qelico volcanics qiangtang terrane norian batang group volcanics kimmeridgian yanshiping group paleocene to eocene fenghuoshan group kunlun terrane visean to namurian dagangou formation dykes of the triassic igneous province the triassic data from the kunlun terrane triassic and lower tertiary data from the qiangtang terrane and the cretaceous data from the lhasa terrane indicate palaeolatitudes ca 20 s of their present position within the eurasian frame of reference a possible interpretation is that the terranes successively accreted to eurasia and remained in the southern position until the convergence of india drove them northward via a process of tectonic shortening and or displacement of continental crust the carboniferous data from the kunlun terrane are consistent with moderate southern hemisphere latitude well separated from eurasia which was in the northern hemisphere at this time implying the existence of ocean crust between these blocks during the carboniferous

palaeomagnetic studies within the ballantrae ophiolite southwest scotland magnetotectonic and regional tectonic implications abstract the early arenig slockenray formation within the ballantrae ophiolite southwest scotland displays a multivectorial magnetisation structure two components s and m are identified delineated by differing blocking temperature coercivity spectra component s is removed around 200 c 10 mt and is regarded to be of recent viscous origin component m forms the characteristic formation magnetisation and resides in both magnetite and haematite extensive sampling of all exposed lithologies reveals an in situ non fisherian distribution of the characteristic magnetisation defining an envelope from se moderate positive to sw shallow negative directions a negative infra formation conglomerate test identifies this component as a pervasive overprint a second conglomerate test performed in the overlying benan conglomerate of llandeilo age reveals dispersely directed magnetisation with a stability range equivalent to that of component m this field test therefore defines a maximum remagnetisation window of 30 million years for the characteristic remanence hard viscous magnetisations are identified both in the benan conglomerate and at some sites within the slockenray formation structurally corrected site mean results from the slockenray formation define a non fisherian distribution and form a small circle partial arc centred on a vertical axis nw moderate positive to sw moderate positive directions a combined palaeomagnetic fold and fault test suggests that acquisition of component m pre dates both folding and faulting the resulting palaeolatitude of remanence acquisition 28 8 s implies a tectonic position close to the southern laurentian margin for the ballantrae ophiolite in arenig times

a multicomponent dual polarity palaeomagnetic regional overprint from the moine of northwest scotland abstract palaeomagnetic remanence may be reset by orogeny in a manner analogous to isotopic systems the heavy mineral seams and associated psammite in the deformed and metamorphosed lower morar division of the moine assemblage of northwest scotland have a palaeomagnetic signature that is characteristic over a wide area the various components of the magnetization are resolved by detailed thermal demagnetization these components are post tectonic as they are not affected by any structural fabric they may be classified according to blocking temperature and when statistically distinguishable show a systematic change of direction from high to lower temperature possibly associated with apparent polar wander comparison to the european palaeomagnetic record suggests a late silurian to early devonian age of magnetization for the localities south of the strath conon fault the distribution of remanance directions and blocking temperatures is not consistent with the pattern of potassium argon ages in this part of the british caledonides if the magnetization is purely of thermal origin the palaeomagnetic record indicates higher temperatures at later time than does the potassium argon record this remagnetization event is related to the closing stages of the caledonian orogeny

a new devonian palaeomagnetic pole for the russian platform and baltica and related apparent polar wander summary of published palaeomagnetic data from the russian platform and britain for mid palaeozoic times places an ocean between the two of the order of 2000 km latitudinal width this contradicts geological evidence which favours contiguity between the two continental units by devonian times we propose that this discrepancy can be attributed to the incorrect dating of palaeomagnetic remanence we strove to remedy this situation by conducting a new palaeomagnetic investigation of silurian and devonian sediments in west ukraine ussr latitude 48 7 n longitude 26 e that investigation uncovered a pervasive upper palaeozoic remagnetization corresponding to a palaeomagnetic pole at lat 45 8 s long 348 2 e dpldm 1 6 3 1 n 25 sites reversed polarity a second primary or near primary devonian remanence was identified with pole at lat 3 7 n long 325 5 e dpldm 5 2 8 7 n 25 samples mixed polarity the age determination for this devonian result is based on its dual polarity evidence for a detrital remanent mode and early host mineral phase haematite the new devonian result for the russian platform is conformable with the devonian parts of the british apparent polar wander paths and therefore eliminates the aforementioned discrepancy between palaeomagnetic and geological evidence for the timing of assembly of the old red continent

paleomagnetism and magnetostratigraphy of the traps from western taimyr northern siberia and the permo triassic crisis abstract the siberian traps were emplaced near the permo triassic boundary and are among the largest continental igneous provinces a 1750 m thick section of traps from the western taimyr 72 9 n 84 e has been sampled this section is equivalent to the lower and middle part of the total siberian traps section thirty one oriented hand samples were studied and demagnetised by alternating fields and heating cycles a stable characteristic component passes the fold test and is thought to be primary the mean direction is d 84 i 75 with 95 10 n 29 and the corresponding pole is 59 n 150 e the bottom part 660 m is of reversed polarity the middle part 900 m is normal and the uppermost level 150 m is mixed correlations with reference permo triassic magnetostratigraphic timescales are discussed the most probable correlation indicates an age quite close to the permian triassic boundary and a duration for the volcanism of less than 1 m y the data are therefore consistent with the hypothesis that this volcanism triggered the permian triassic crisis

palaeomagnetic resetting in the barrovian zones of scotland and its relationship to the late structural history the haematite schists in the lowest kyanite and the staurolite barrovian zones exposed in glen lethnot and glen esk angus scotland have a characteristic magnetization with blocking temperatures generally greater than 600 c and less than 695 c and coercivity greater than 200 mt the mean palaeomagnetic direction derived from 54 samples collected from n 10 sites isd 159 i 45 k 47 95 7 1 with the associated south pole position oflat 3 long 22 e dp 5 7 anddm 9 0 this magnetization is younger than folds of d3 generation and older than folds of d4 generation the pole position falls on the aberdeenshire polar wander track in a place consistent with an average kar biotite chrontour age of 455 m y a comparison of the blocking temperatures of magnetization to the estimated peak temperature of metamorphism suggest the magnetization is a chemical remanent magnetization crm possibly acquired during the metamorphic chemical reactions

biomagnetostratigraphy of the vikinghogda formation svalbard arctic norway and the geomagnetic polarity timescale for the lower triassic a bio magnetostratigraphy for the lower triassic is constructed using the ammonoid biostratigraphy from arctic boreal successions combined thermal and alternating field demagnetisation determines the triassic magnetic field polarity in 86 of specimens with 36 showing linear trajectory line fits and the remainder great circle trends towards the characteristic magnetisation mean pole directions for the deltadalen 50 159 dp dm 3 9 5 1 lusitaniadalen 56 163 dp dm 4 4 5 4 and vendomdalen 57 143 dp dm 4 4 5 4 members fall close to the european lower triassic apparent polar wander path mean directions for two of these member means pass the reversal test the remanence is predominantly carried by magnetite the polarity stratigraphy when integrated with the ammonoid and meager conodont data is similar to that determined from successions in the sverdrup basin canada the permian triassic boundary post dates a pronounced palynofloral turnover and pre dates a short duration reverse magnetozone lt1n 1r in the correlated shangsi section in s china lt1n 1r occurs after the fad of h parvus but in the arctic is within the otoceras boreale zone the late griesbachian to early smithian is mostly reverse polarity with three normal polarity intervals overlain by mid and late smithian normal polarity the spathian contains four reverse polarity intervals the oldest one within the early spathian with the remainder in the late spathian transition into the anisian is within the uppermost reverse magnetozone a feature documented in other sections of this age the polarity pattern is correlated to other marine sections indicating the robustness of the bio magnetostratigraphic composite and its utility in calibrating lower triassic time

rapid precise and high sensitivity acquisition of paleomagnetic and rock magnetic data development of a low noise automatic sample changing system for superconducting rock magnetometers among earth sciences paleomagnetism is particularly linked to the statistics of large sample sets as a matter of historical development and logistical necessity because the geomagnetic field varies over timescales relevant to sedimentary deposition and igneous intrusion while the fidelity of recorded magnetization is modulated by original properties of rock units and by alteration histories ideal paleomagnetic results measure remanent magnetizations of hundreds of samples at dozens of progressive demagnetization levels accompanied by tests of magnetic composition on representative sister specimens we present an inexpensive open source system for automating paleomagnetic and rock magnetic measurements using vacuum pick and place technology and a quartz glass sample holder the system can in one hour measure remanent magnetizations as weak as a few pam2 of 30 specimens in two vertical orientations with measurement errors comparable to those of the best manual systems the system reduces the number of manual manipulations required per specimen 8 fold

palaeomagnetism of the ejecta bearing bunyeroo formation late neoproterozoic adelaide fold belt and the age of the acraman impact abstract a new palaeomagnetic study has been conducted on haematitic shales and siltstones of the late neoproterozoic bunyeroo formation in the adelaide fold belt geosyncline south australia which host an extensive horizon of shock deformed rock fragments and microtektite like material of probable impact origin thermal step demagnetisation of 116 samples of red shale and siltstone from six sections sites revealed a high temperature component with a bedding corrected site mean direction of remanence of d 56 6 i 29 3 95 10 7 that gives a pole at 18 1 s 16 3 e dp 6 5 dm 11 8 the high temperature component provides a positive tectonic fold test 99 level of confidence the bunyeroo high temperature remanence direction is near the remanence direction d 50 i 40 indicated by modelling the subsurface magnetic source of the central high amplitude anomaly at acraman australia s largest confirmed meteorite impact structure 220 350 km west of the adelaide fold belt and also is close to the mean direction d 48 3 i 54 7 95 5 2 determined for surface melt rock from acraman statistical tests show that the virtual geomagnetic poles indicated by the directions for the subsurface central magnetic source and surface melt rock at acraman may be regarded as subsets of the bunyeroo palaeomagnetic pole position indicating that the three pole positions are statistically indistinguishable the results imply that the subsurface magnetic source and surface melt rock acquired their remanence in the ambient geomagnetic field during cooling after the impact when structural disturbance had ceased while the bunyeroo formation was accumulating the agreement among the various remanence directions argues strongly that the ejecta horizon in the bunyeroo formation was derived from acraman the present findings confirm that the acraman impact occurred in the late neoproterozoic about 590 ma which is the age of the bunyeroo formation provided by rb sr whole rock shale dating of equivalent and contiguous strata in the adelaide fold belt region the bunyeroo palaeomagnetic data give a palaeolatitude of 15 indicating a low palaeolatitude for the acraman impact and supporting other findings that the adelaide fold belt occupied low to equatorial palaeolatitudes during the late neoproterozoic