an early carboniferous paleomagnetic pole for gondwanaland new results from the mount eclipse sandstone in the ngalia basin central australia paleomagnetism of fourteen diamond drill cores from the uppermost devonian lower carboniferous mount eclipse sandstone in the ngalia basin central australia has been studied the samples were oriented using the borehole directions bedding planes identified in the drill cores and regional bedding attitudes three magnetic remanent components have been revealed 1 a drilling induced low to moderate temperature remanence c1 from all the drill cores which is oriented parallel to the drill cores and is most likely a combination of isothermal remanent magnetization and piezoremanent magnetization 2 a moderate to high temperature syndeformational overprint c2 d 226 7 i 82 3 95 6 2 k 68 9 in 65 samples from nine drill cores which was probably acquired during the mid to late carboniferous mount eclipse movement and 3 a moderate to high temperature likely primary remanence c3 d 057 1 i 36 9 95 9 6 k 29 6 from 64 samples in nine drill cores which exhibits a positive fold test c2 and c3 are found only in reddish siltstones and sandstones whereas c1 is best developed in grey reduced sandstones and siltstones a palynological examination gives an early to mid visean early carboniferous age of deposition for samples carrying the interpreted primary component c2 gives a mid to late carboniferous pole at 32 1 s 119 5 e with a95 11 9 which is in agreement with results of a previous study on surface outcrops c3 when combined with results from one drill core in a previous study gives a visean pole at 37 6 s 52 6 e with a95 8 7 this pole suggests a south polar position for central africa during the early carboniferous and therefore indicates the existence of a large ocean between gondwanaland and laurussia at that time the paleo south pole shifted from central africa in the early carboniferous 340 5 ma to east antarctica in the mid to late carboniferous 310 10 ma with a minimal continental drifting rate of 15 20 cm yr

physicochemical evolution of a porphyry breccia system a laser ablation icp ms study of fluid inclusions in the mount leyshon au deposit queensland australia the evolution of magmatism brecciation alteration and mineralization is described for the mount leyshon intrusive complex queensland australia using p t v x analysis and major to trace element analysis of single fluid inclusions using laser ablation icp ms the 290 ma mount leyshon intrusive complex is a subvolcanic porphyry breccia system mined for 97 metric tons t au 70 mt at 1 4 g t au between 1986 and 2000 the mount leyshon intrusive complex is characterized by several generations of genetically related breccias and magmatic intrusions both alteration and mineralization can be traced to specific intrusive events the earliest phase of brecciation was followed by widespread biotite magnetite alteration stage 1 fluid inclusions associated with stage 1 were trapped at 350 c and 145 bars and were anomalously k and fe rich this stage was followed by the emplacement of rhyolite to dacite stocks and coeval breccia pipes stage 2 fluids exsolved from these magmas simultaneously exsolved na k fe mn rich brine 60 wt nacl equiv and dilute vapor at 500 bars 2 km paleodepth and 600 c pressures likely oscillated between lithostatic and sublithostatic conditions in response to the transient rupture and sealing of intrusions and wall rocks hydrothermal fluids infiltrating breccia pore space produced base metal mineralization stage 3 stage 3 fluid inclusions contain 2 to 10 wt percent nacl equiv and were trapped at 300 to 400 c below 500 bars stage 3 fluids were depleted in k fe and mn and enriched in ca sr and ba relative to stage 2 brines this trend is consistent with the transition from potassic alteration in stage 2 to feldspar destructive phyllic alteration in stage 3 cu zn and pb were conservative elements above 350 c and precipitated nonselectively as sulfides below 350 c in a bulk ratio very similar to that measured in fluid inclusions subsequent emplacement of andesite to rhyodacite dikes stage 4 was marked by au and additional base metal sulfide mineralization in veins and breccia cavities stage 4 fluids are chemically similar to stage 3 but contain several mol percent co2 perhaps suggesting a more mafic co2 charged magma source relative to earlier intrusive pulses in addition to fluid cooling the destabilization of au bisulfide complexes attending phase separation of h2o co2 nacl fluids below 400 c and 400 bars was the likely cause for au precipitation mount leyshon appears to indicate that co2 can play a crucial role in the transport of gold bearing solutions from a magmatic source at depth into much shallower hydrothermal environments

evolution of pangea paleomagnetic constraints from the southern alps italy abstract a new early late triassic paleopole for adria has been obtained from the val sabbia sandstone in the southern alps as early permian and jurassic cretaceous paleomagnetic data from para autochthonous regions of adria such as the southern alps are consistent with african apwps 1 2 paleomagnetic data from this region can be used to bolster the west gondwana apwp in the poorly known late permian triassic time interval the southern alpine paleopoles are integrated with the west gondwana and laurussia apwps of van der voo 1 and used to generate a tectonic model for the evolution of pangea the early permian overall mean paleopole for west gondwana and adria in conjunction with the coeval laurussia paleopole support pangea b of morel and irving 3 the late permian early triassic and the middle late triassic paleopoles from adria and laurussia support pangea a 2 of van der voo and french 4 the phase of transcurrent motion between laurasia and gondwana 5 that caused the pangea b to a 2 transition occurred essentially in the permian at the end of variscan orogeny with an average relative velocity of approximately 10 cm yr finally the late triassic early jurassic paleopoles from west gondwana and laurussia agree with pangea a 1 of bullard et al 6 the widely accepted pangea configuration at the time of the jurassic breakup

palaeomagnetism of the stephano autunian lower tiguentourine formations from stable saharan craton algeria summary palaeomagnetic studies have been carried out in a stephano autunian formation of the saharan craton despite the presence of a strong recent magnetic overprint some samples give a well defined characteristic remanent magnetization direction moreover a new approach using the remagnetization circles has been used to confirm the significance of this direction the obtained stephano autunian pole 35 3 s 60 3 e allows a substantial improvement of the apparent polar wander path apwp for stable africa this apwp clearly shows that the clockwise rotation of africa which occured during the hercynian orogeny was stopped during the stephano autunian period

magnetic overprinting in southeastern australia and the thermal history of its rifted margin the magnetizations of many rock units in southeastern australia have been severely overprinted interpretation of early work was hindered by this and one of the aims of the current research is to ascertain the nature of the overprint mechanism its geological significance and its regional extent results from three igneous bodies from the sydney basin which have been studied previously in a reconnaissance fashion have provided a new insight into the reason for such widespread magnetic overprinting the hornsby breccia hb and milton monzonite mm yield similar magnetic signatures both containing discrete high and low temperature magnetizations with directions of dec 72 inc 83 95 4 and dec 13 inc 76 95 2 respectively for hb and dec 60 inc 78 95 4 and dec 348 inc 79 95 6 respectively for mm the corresponding pole positions are 29 s 166 e a95 7 and 59 s 139 e a95 4 for hb and 22 s 171 e a95 7 and 55 s 158 e a95 11 for mm the paleomagnetic direction and pole from the third body studied the mogo hill basalt mh are dec 241 inc 81 95 5 and 41 s 130 e a95 9 this pole position and the two low temperature overprint pole positions from hb and mm are consistent with ages ranging from 100 m y to approximately 70 m y when compared to the late mesozoic apparent polar wander path we relate the overprinting to uplift erosion and rapid supracrustal cooling of the southeastern margin of australia associated with initial phases of marginal rift development prior to seafloor spreading in the tasman sea the temperatures of rocks now exposed may have reached 200 c or higher before the rapid cooling blocked and stabilized the overprint magnetizations

paleomagnetism and paleothermometry of the sydney basin 1 thermoviscous and chemical overprinting of the milton monzonite the early triassic 245 ma milton monzonite of the sydney basin australia has four distinct components of natural remanent magnetization nrm with only slightly overlapping ranges of unblocking temperatures the low temperature lt component the first to be thermally demagnetized is thought to be a late cretaceous 100 ma thermoviscous overprint acquired in slow cooling during uplift the high temperature ht component the second to be demagnetized is probably the primary thermoremanent magnetization trm of the milton intrusion but could possibly be a jurassic overprint lt and ht are usually carried by magnetite and occasionally by pyrrhotite samples from nine sites have a further nrm component which unblocks at higher temperatures than ht but below the magnetite curie temperature of 580 c this component is argued to be a chemical remanent magnetization crm because of its discrete range of high unblocking temperatures above those of the thermal components ht and lt and is called crm1 crm1 has almost the same direction as lt and is likely carried by authigenic magnetite produced during uplift 100 ma samples from five sites have a fourth nrm component with a direction resembling that of ht but carried by hematite this fourth component could be a primary trm but is more likely a crm and is therefore called crm2 the ht crm2 mean direction is d 50 i 75 5 defining a paleopole at 16 s 172 e the ht crm2 paleopole falls near 150 ma on the australian apparent polar wander path but is a considerable distance from paleopoles of permian and early triassic age there is no known tectonic or other remagnetizing event in the sydney basin around 150 ma for this reason we propose that the ht crm2 paleopole defines a new triassic segment of the australian polar wander path the lt crm1 mean direction is d 348 i 79 with a paleopole falling at 56 s 1580 e near 100 ma on the polar wander path this age is consistent with uplift and cooling related to initial rifting of the tasman sea

tracking meteoric infiltration into a magmatic hydrothermal system a cathodoluminescence oxygen isotope and trace element study of quartz from mt leyshon australia the oxygen isotope and trace element composition of hydrothermal quartz has been integrated with scanning electron microscope cathodoluminescence sem cl images and fluid inclusion properties to track fluid sources and hydrothermal processes in the mt leyshon an deposit australia oxygen isotope and trace element data were collected on parallel traverses across the same quartz sections using secondary isotope mass spectrometry sims and laser ablation inductively coupled plasma mass spectrometry la icp ms respectively with sem cl images obtained before analysis for petrographic context over the 280 to 650 degrees c quartz precipitation range suggested by fluid inclusion microthermometry delta o 18 quartz varies from 0 0 to 14 4 o corresponding to a wide range of equilibrium delta o 18 fluid values from 6 1 to 10 2 o vs v smow the delta o 18 quartz signature varies systematically among distinct sem cl quartz generations both within and between samples and can be correlated with variations in temperature and fluid composition but is independent of intra generational oscillatory zoning in contrast al and li concentrations correlate broadly with cl intensity in oscillatory quartz whereas their concentration is unpredictable in sealed fractures and overgrowths concentrations of b mg na p cl k ti mn fe ge and sn are independent of al li and oscillatory cl features but ti correlates with quartz precipitation temperature although no systematic correlation between delta o 18 quartz and trace element concentrations was found complementary patterns exist in narrow overgrowths of low delta o 18 quartz similar to 0 o and high al g 10 000 ppma these quartz zones likely formed during the incursion of o 18 depleted meteoric water into the magmatically dominated mt leyshon hydrothermal system we interpret the highest al concentrations as the result of high quartz precipitation rates triggered by depressurisation of the hydrothermal cell the decoupling of oxygen isotope and trace element patterns in quartz leads to the suggestion that 1 under most circumstances temperature and fluid chemistry dominate delta o 18 quartz and 2 the trace element record and in particular al and li is influenced by the superimposed effects of quartz precipitation rate c 2007 elsevier b v all rights reserved

validation of a new global 30 min drainage direction map abstract digital drainage direction maps are a prerequisite for analyzing the flow of water on the land surface of the earth for continental or global studies the most appropriate and most frequently used resolution for such data sets appears to be 30 longitude by latitude in this paper we present the new global drainage direction map ddm30 a 30 raster map of surface drainage directions which organizes the earth s land area into drainage basins and provides the river network topology ddm30 was generated by first upscaling two drainage direction maps ddms at higher resolutions the resulting map was then extensively corrected in an iterative manner by comparison against vectorized high resolution river maps and other geographic information finally it was co referenced to the locations of 935 gauging stations provided by the global runoff data centre grdc which again involved manual corrections ddm30 was validated against drainage basin areas from the literature against the given upstream areas of the grdc stations and most importantly against information from hydro1k a data set based on a hydrologically corrected 1 km digital elevation model which is thought to afford the best information on surface drainage currently available at the global scale in the course of the validation the quality of ddm30 was compared to three other 30 ddms the validation results show that ddm30 provides a more accurate representation of drainage directions and river network topology than the other 30 ddms

a tectonic model for the location of palaeozoic ring complexes in air niger west africa the fir region in niger is one of the largest peralkaline granite provinces in the world in addition to the granites some plutons are characterized by an abundance of plagioclase rich cumulates gabbros troctolites and anorthosites with subordinate metaluminous granites and quartz syenites these anorogenic ring complexes were intruded along a 400 km zone near the 9 e meridian the province formed during a major magmatic event newly dated at around 407 8 ma and comprises 28 plutons which range from 0 8 to 65 km in diameter and show no correlation between distribution and age remote sensing over the whole fir massif demonstrates the existence of two main trends of faults or lineaments n50 e n90 e and n120 e n150 e autocorrelation analysis of the ring complexes reveals three large parallel high density strips orientated n20 e based on the structural and geological setting coupled with map analysis a new tectonic model for the location of the complexes is presented we propose a dextral n5 e shear zone model where the emplacement of the ring structures is controlled by n20 e dextral riedel shear r with a secondary n50 e tensional gash t this tectonic model implies a control by lithospheric structures for the emplacement of the ring complexes as well as a relationship between a transtensional tectonic regime and intra plate alkaline magmatism the new geochronological data on the ayir massif allow us to derive a silurian devonian palaeomagnetic pole representative for gondwana which fits data for the other continents better than previous estimates

a pure dipole analysis of the gondwana apparent polar wander path paleogeographic implications in the evolution of pangea the paleogeography of prebreakup pangea at the beginning of the atlantic spreading has been a subject of debate for the past 50 years reconciling this debate involves theoretical corrections that cast doubt on available data and paleomagnetism as an effective tool for performing paleoreconstructions this 50 year old debate focuses specifically on magnetic remanence and its ability to correctly record the inclination of the paleomagnetic field in this paper a selection of paleopoles was made to find the great circles containing the paleomagnetic pole and the respective sampling site the true dipole pole tdp was then calculated by intersecting these great circles effectively avoiding nondipolar contributions and inclination shallowing in an innovative method the great circle distance between each of these tdps and the paleomagnetic means show the accuracy of paleomagnetic determinations in the context of a dominantly geocentric axial and dipolar geomagnetic field the tdps calculated allowed a bootstrap analysis to be performed to further consider the flattening factor that should be applied to the sedimentary derived paleopoles it is argued that the application of a single theoretical correction factor for clastic sedimentary derived records could lead to a bias in the paleolatitude calculation and therefore to incorrect paleogeographic reconstructions the unbiased apwp makes it necessary to slide laurentia to the west in relation to gondwana in a b type pangea during the upper carboniferous later evolving during the early permian to reach the final a type pangea configuration of the upper permian 2017 american geophysical union all rights reserved

paleomagnetism of the newcastle range northern queensland eastern gondwana in the late paleozoic 1 the newcastle range is an extensive 2500 km2 and well exposed caldera system erupted on the trailing edge of eastern gondwana between 325 and 295 ma paleomagnetic samples were collected from ignimbrites and associated microgranitoid intrusions from the central northern and southern calderas from which three components of magnetization are recognized component 1 is considered to be a viscous magnetization acquired during the brunhes chron a presumed permian component c2 is found in seven paleomagnetic sites with a mean pole at 30 9 s 139 7 e k 13 9 a95 16 8 asd 21 7 agreeing with previously reported permian data from australia carboniferous units have a well defined characteristic component c3 distinguished by dual polarity predominantly reversed and moderate to steep inclination directions paleomagnetic polarities in the newcastle range volcanics are formation dependent and new constraints on the timing of carboniferous volcanism 325 317 ma are consistent with recent reanalysis of the base of the permo carboniferous reversed superchron pcrs a mean paleomagnetic pole calculated from 15 vgps lies at 63 4 s 125 e k 26 22 a95 7 6 asd 15 8 suggesting that australia remained at midlatitudes into the middle carboniferous this paleomagnetic pole is consistent with similarly aged poles from western gondwana the conformity of which indicates contributions from nondipole components of the earth s paleofield were probably not significant in the time immediately preceding the pcrs

paleomagnetism and the evolution of pangea we present new apparent polar wandering apw paths for the latest carboniferous to middle jurassic of europe northern asia north america and gondwana the paths have been constructed by ordering the paleopoles into a time sequence and calculating running averages globally this statistical analysis cannot be carried back before the latest carboniferous because the paleomagnetic record becomes inadequate the polar paths have all been rotated along with the land masses from which they have been observed into the classical configuration of wegener pangea a as quantified by later workers the mean paleopoles agree in the early jurassic but disagree in the latest carboniferous permian and early triassic this result is insensitive to reasonable choices made regarding the arrangement of the continents within gondwana it is true either for results from gondwana as a whole or from africa and south america alone this disagreement in apw paths suggests but does not prove that pangea a lasted for only a short interval of time in the early to middle jurassic 190 170 m y and perhaps the latest triassic 200 m y alternatively we may say either that the paleomagnetic record is biassed by sampling inadequacies or by systematically incorrect age assignments or that the earth s field has been non dipolar we regard these explanations as less likely although they cannot be discounted the polar paths can be reconciled by rotating gondwana anticlockwise by about 35 relative to laurasia placing africa beneath europe and south america beneath eastern north america this configuration is called pangea b pangea b could be a valid reconstruction for the latest carboniferous and early permian approximately 290 260 m y pangea b provides a statistically satisfactory resolution of the paleomagnetic problem it also provides a symmetrical arrangement of the continents bordering the appalachian hercynian fold belt for the late paleozoic which pangea a does not it provides a satisfactory framework for the early evolution of the gulf of mexico and it provides an explanation of the absence of geological evidence for a tethys ocean in the paleozoic the transition between b and a cannot be accurately reconstructed from the paleomagnetic data because the resolution of the record is as yet inadequate but it presumably occurred by a 3500 km minimum dextral megashear between laurasia and gondwana during the late permian and triassic approximately 250 200 m y without the formation of ocean between them and was accompanied by lesser motions between north america and europe the sense of megashear is the same as that invoked by arthaud and matte 1977 on geological grounds but the magnitude and timing are different our interpretation favors the idea that continental drift is a continuous process not confined to jurassic and later times but extending backwards into the triassic and permian we suggest that pangea was not an immobile configuration as envisaged by wegener and most subsequent workers but that it evolved more or less continuously

evidence for late paleozoic and mesozoic non dipole fields provides an explanation for the pangea reconstruction problems abstract paleomagnetic pole positions have long been calculated with the assumption that the ancient geomagnetic field was purely that of a geocentric dipole but in recent years it has become a concern that this assumption is not always valid because of long term contributions from non dipole fields in particular octupole fields we tested for the presence of a zonal octupole field in the late carboniferous permian mesozoic and early tertiary by comparing the observed paleomagnetic paleolatitude distributions for the laurentian north america and greenland and european landmasses with those predicted from the mean paleopoles such a test is possible for a good sized continent not subsequently deformed when numerous and reliable paleomagnetic results exist from sites that cover a wide range of paleolatitudes if the field were purely dipolar coeval results should form a coherent dataset such that a regression line through the individual points in an observed versus predicted paleolatitude plot has a slope of 1 if the slopes of regression lines are systematically different from 1 0 for successive time intervals and granted that the earth s radius stayed the same then it is likely that non dipole fields can be held responsible regression line slopes standard errors for three intervals analyzed are 0 78 0 04 200 300 ma 0 93 0 11 120 200 ma and 0 82 0 06 40 120 ma as might be expected with a non dipole contribution to the total geomagnetic field paleomagnetic results from the most northerly areas of laurentia and europe i e ellesmere greenland and svalbard show clearly anomalous paleolatitudes because of the agreement between the equatorial locations determined independently by paleomagnetism and equatorial rain forest occurrences d v kent p e olsen earth planet sci lett 179 2000 311 324 we argue that long term quadrupole fields are less likely than octupole fields to be the cause of the paleolatitude discrepancies estimates of the magnitude of the octupole dipole field ratio are not very precise but center around 0 1 which could cause errors in conventional paleopole determinations using the dipole formula of 7 5 because of the antisymmetry of octupole fields a comparison of paleomagnetic poles from mid northern and mid southern hemisphere locations could thus be off by as much as 15 the well known misfit between the paleomagnetic results from the laurentia european and gondwana continents in a classical pangea a configuration could be explained by such errors due to octupole fields this explanation would negate the need to seek tectonic pangea b type solutions for the misfit these solutions have generally remained unacceptable in terms of the geology of the gondwana laurussia borderzone

palaeomagnetism and age of mid palaeozoic ring complexes in niger west africa and tectonic implications summary detailed af and thermal demagnetization has been performed on 185 oriented samples from 36 sites in a series of basic to acid subvolcanic ring complexes in central and southern niger published rb sr whole rock and mineral isochrons from acid members of the suite range north to south from 480 ma to 320 ma two distinct vectors have been isolated by linear regression of demagnetization data 1 a due north and negative inclination rarely reversed component is present in basic rocks from 12 sites in four distinct northern complexes published rb sr ages date from 480 ma to 420 ma this component is carried by single domain magnetite occasionally also by titanhaematite and is considered to be primary acquired during the terminal stages of this igneous episode 40ar 39ar dating of biotite from three samples used in the palaeomagnetic study yield 435 myr ages 2 a due north and positive inclination rarely reversed direction is present as a second component in some of the basic suite sites and is the predominant component in most sites in syenitic to granodioritic rocks primary fe ti oxides are rare in these acid igneous rocks and the feldspars within them are usually pervasively altered this component carried primarily by haematite is believed to be either a modern day vrm or a secondary tcrm acquired during hydro thermal activity associated with widespread quaternary volcanism in the southern air the primary component gives a mean south pole at 43 4s 08 6e n 12 k 50 95 6 2 located southwest of cape town this position requires a rapid southward excursion of the gondwana a p w path in early silurian time but it is generally consistent with most of the other silurian devonian palaeomagnetic data from gondwana these however are from the lachlan fold belt in southeast australia whose relation to the australian craton in early palaeozoic time is not clear integrating all stratigraphic palaeoclimatic tectonic and other palaeomagnetic data for early and middle palaeozoic time suggests that the proto atlantic closed during the silurian period if a late devonian early carboniferous gondwana pole in central africa is valid the ocean may have opened again before the final closure and reassembly of gondwana in the late carboniferous

behavior of the paleosecular variation during the permian carboniferous reversed superchron and comparisons to the low reversal frequency intervals since precambrian times we investigated the paleo latitudinal dependence of angular dispersion sets of virtual geomagnetic poles vgps for the permian carboniferous reversed superchron pcrs 262 318 ma in order to analyze the paleosecular variation during this period we prepared different paleomagnetic datasets from scientific databases and recent literature based on selection criteria which provided high degree of refinement model g of mcfadden et al 1988 was fitted to the vgp dispersion data providing the shape parameters a and b which were further compared with similar results for the cretaceous normal superchron cns and other periods of different geomagnetic reversal rates throughout the last 3 ga our results indicate high similarity between the angular vgp dispersion from the pcrs and cns a low vgp dispersion at low paleolatitudes and strong paleolatitudinal dependence in contrasting difference for periods of higher reversal rates the last 5 ma despite the geodynamic differences related to both phanerozoic superchrons such evidence could point out similar heat flux conditions in the cmb which may favor compatible stability conditions throughout these magnetozones notably two additional observations which arose from the shape parameters relations for both phanerozoic superchrons and precambrian datasets demand further investigation i a pattern of increase for the b a ratio throughout the 0 5 1 6 ga interval was observed which could be partially explained by the maya superchron recently proposed by gallet et al 2012 ii the b a relationship for both phanerozoic superchrons and the 2 45 2 82 ga interval pointed to the presence of one or more long term magnetozones throughout the paleoproterozoic

magnetic polarity stratigraphy and paleolatitude of the triassic jurassic blomidon formation in the fundy basin canada implications for early mesozoic tropical climate gradients a magnetic polarity stratigraphy is established for a continuously cored 360 m thick section of the entire cyclical lacustrine sequence and part of the sandy fluvial and eolian basal sequence of the late triassic blomidon formation in the fundy basin in nova scotia canada in conjunction with published results for the newark and dan river basins the fundy basin record allows us to precisely map the spatio temporal distribution of climate sensitive continental lithofacies along a paleolatitudinal transect in eastern north america corresponding to the tropics of pangea in the late triassic indicators of high humidity such as coals and black shales tend to occur within 5 of the paleoequator and eolian dunes and other evidence of aridity occurs within 10 of the paleoequator although steep the latitudinal climate gradient in the interior of the pangea supercontinent is not that different from the average modern zonal variation in the balance of evaporation to precipitation even though the distribution of continents was radically different and there is no evidence of continental ice sheets in the late triassic we suggest that the common perception of a dry paleoequator in the triassic is largely an artifact of observational bias because compilations of paleoclimate proxies usually have spatio temporal resolutions that are inadequate to delineate narrow zonal climate belts giving an aliased impression of ancient climate fl 2000 elsevier science b v all rights reserved

paleomagnetic results from saudi arabia and the permo triassic pangea configuration the pangea configuration for the interval of late carboniferous to early jurassic is still debated was it similar to the well known wegenerian pangea or did gondwanaland move with respect to laurussia along a major right lateral lineament of several thousand kilometres during the triassic as suggested by irving we try here to answer this important question with the paleomagnetic study of well dated permo triassic sediments from a borehole in saudi arabia sediments of the same age have also been sampled at the surface but proved to be remagnetized probably by a strong desert alteration the paleomagnetic study of the bore hole core yielded a high temperature component magnetization thought to be of primary origin carried either by magnetite late permian limestones or hematite early triassic red shales with antipodal normal and reversed inclinations its co latitude and pole directions compare well with those from a selection of south american african madagascar and moroccan poles a new reliable pole west gondwana with a mean age of 244 11 m y is derived 53 4 n 259 4 e a95 3 6 in west african coordinates and its comparison with the laurussian poles of same age window strongly suggests a pangea in which the northern part of south america was facing the east of north america pangea b of irving at the permo triassic boundary a large right lateral strike slip movement of some 3500 km during the triassic is thus required to reconstruct pangea to its jurassic pre atlantic opening position

palaeomagnetism of the brewer conglomerate in central australia and fast movement of gondwanaland during the late devonian summary palaeomagnetic analysis of 11 diamond drill cores from the late devonian brewer conglomerate in the northeastern part of the amadeus basin central australia yields three magnetic components a drilling induced remanence c1 acquired during the industrial drilling process a mid to late carboniferous syndeformational overprint c2 acquired during the alice springs orogeny and a primary remanence c3 c3 passes a fold test and gives a latest devonian pole bc at 47 1ds 041 0de with a95 6 4d the revised apwp for gondwanaland requires west gondwanaland to drift across the south pole during the late devonian with a speed of 20cm yr 1 while east gondwanaland remained at low latitude positions it is suggested that fast plate movement occurred far more often during the palaeozoic than has previously been thought

palaeomagnetism of the early permian mount leyshon intrusive complex and tuckers igneous complex north queensland australia summary this study provides reliable precisely defined and well dated early permian 286 6 ma palaeomagnetic poles for australia from the mount leyshon intrusive complex mlic and the tuckers igneous complex tic both complexes are associated with prominent negative magnetic anomalies indicating the presence of rocks carrying stable remanence of reverse polarity with a koenigsberger ratio greater than unity the characteristic remanence carried by the intrusive phases and by locally remagnetized contact metamorphosed host rocks is always of reverse polarity consistent with acquisition during the permo carboniferous kiaman reverse superchron the corresponding palaeopoles confirm that australia occupied high latitudes in the early permian the pole positions are mlic lat 43 2 s long 137 3 e dp 6 0 dm 6 4 q 6 tic lat 47 5 s long 143 0 e dp 6 0 dm 6 6 q 6 permian palaeomagnetic overprinting is detectable at considerable distances from the mlic 2 3 km well beyond the zone of visible alteration the primary nature of the early permian palaeomagnetic signature is established by full baked contact aureole tests at both localities other new data from australia are consistent with the poles reported here comparison of the australian african and south american apparent polar wander paths apwp suggests that mean permian and triassic poles from west gondwana particularly from south america are biased by remagnetization in the jurassic cretaceous and that the late palaeozoic mesozoic apwp for gondwana is best defined by australian data the australian apwp exhibits substantial movement through the mesozoic provided only that the time averaged palaeofield was zonal the early triassic palaeomagnetic data from australia provide an important palaeogeographic constraint that the south geographic pole was within or very close to se australia around 240 ma the new early permian poles are apparently more consistent with pangaea b type reconstructions of gondwana and laurussia than with the pangaea a2 configuration this may be partly an artefact of reconstruction problems within gondwana as systematic differences between approximately coeval apparently reliable permo carboniferous poles from africa south america and australia are evident in standard gondwana reconstructions these discordances require a tighter fit of the southern continents suggesting that some attenuation of continental margins not accounted for in the reconstructions has occurred during breakup of gondwana or that the fit between east and west gondwana needs to be substantially modified if stretching of continental margins during breakup of supercontinents is a general phenomenon it may help to ameliorate but not solve the long standing controversy regarding pangaea reconstructions although alternative pangaea reconstructions such as pangaea b may reconcile poles from laurussia with australian poles in the late carboniferous early permian no plausible reconstruction can bring the early triassic poles into agreement this suggests that persistent departures from a pure dipole field may have been present in the early triassic lesser but still significant non dipole effects may also have been present during the late carboniferous and permian and may help resolve the pangaea a versus b controversy without requiring substantial attenuation of continental margins or intracontinental deformation we suggest that the most parsimonious interpretation of the palaeomagnetic and geological information is that laurussia and gondwana remained in a pangaea a2 type configuration through the permian and triassic discordance between the apwps for these two supercontinents is attributable mainly to persistent non dipole components of the geomagnetic field which were most important in the early triassic

base of the kiaman its definition and global stratigraphic significance defining and dating the base of the kiaman the long period of reverse polarity that spans the time from the late carboniferous to the middle permian have proven difficult in an attempt to do this an integrated stratigraphic paleomagnetic and geochronologic study was undertaken in carboniferous rocks in the northern tamworth belt of the new england orogen eastern australia new paleomagnetic measurements at 145 horizons sites in the new england orogen of eastern australia provide an accurate record of the late namurian to westphalian geomagnetic field they have high unblocking temperatures satisfy tilt conglomerate and slump tests and show excellent agreement between a wide variety of igneous and sedimentary rock types indicating that magnetism was acquired at or soon after deposition magnetite and to a lesser degree hematite are the carriers of magnetization the record is contained in sequences of glaciogene sediments and arc derived volcano sedimentary units folded into broad structures in the late permian to triassic new isotopic dates for the volcanic units indicate ages from 321 to 306 ma late namurian to westphalian magnetizations are steeply inclined downward reversed polarity in the southern hemisphere except within the clifden formation of the rocky creek syncline where a change from normal to reverse polarity referred to as the wanganui reversal records the onset of the kiaman superchron integrating complex stratigraphic isotopic and paleomagnetic data we correlate the wanganui reversal to the top of n6 in the joggins section nova scotia canada and estimate that its age is between 318 and 316 ma further work may substantiate a younger normal zone in australia that would support a slightly younger age but within these limits these considerations indicate that the wanganui reversal occurs in the late namurian marsdenian and after the time of the mississippian pennsylvania boundary the mean direction of magnetization of the upper carboniferous australian sequences is declination d 195 3 inclination i 76 9 25 95 3 1 with a paleopole at 51 9 s 141 2 e 95 5 7 and a paleolatitude of 65 0 5 6 s p 0 05 this paleolatitude is consistent with the glacial origin of some of the sedimentary units

late mesozoic and cenozoic palaeomagnetism of australia iii bias corrected pole paths for australia antarctica and india summary palaeomagnetic results from part i of this study and their analysis in part ii are combined to eliminate bias from the cenozoic apparent polar wander path for australia a bias due to non dipole components in past geomagnetic fields or for poles calculated from hot spot data due to the motion of hot spots relative to the earth s rotational axis this path is extended in approximately bias free form to the late mesozoic and indicates a significant change in the drift direction of the continent between 26 and about 60 ma the bias corrected australian path is used first with seafloor spreading data for the southern ocean to derive a corresponding late mesozoic cenozoic pole path for antarctica the latter shows that the antarctic drift direction reversed in the early tertiary it is suggested that the early tertiary directional changes of both australia and antarctica are part of a global reorganization of plates during the eocene postulated by rona richardson cande mutter and patriat achache next the australian path is compared with hot spot data from the african and australian plates indicating a movement of the hot spots relative the earth s rotational axis during the cenozoic the direction of this movement is found to be consistent with previous results from other parts of the world finally the australian path is used together with non dipole components in the geomagnetic field to explain a prominent westward displacement of the mid and late cenozoic poles of india relative to those of australia because of uncertainties in the original poles and in the analysis the present results are likely to contain appreciable errors nevertheless their consistency with independent findings supports the dipole quadrupole model of part ii for mid and late cenozoic geomagnetic fields

geodynamical implications of a moscovian palaeomagnetic pole from the stable saharan craton illizi basin algeria abstract four different characteristic remanent magnetization chrm orientations have been isolated in the el adeb larache formation of the algerian sahara 27 45 n 8 9 e two of them are interpreted as overprints developed respectively during recent and permian times the two others give new moscovian 28 7 s 55 8 e and probably stephano autunian 38 5 s 57 5 e palaeopoles in good agreement with those previously obtained from the sahara but significantly different from the dwyka varves pole mcelhinny and opdyke 1968 comparison with lower carboniferous results shows that the latitudinal displacement of africa during the carboniferous is mainly related to a clockwise rotation about 25 around an axis close to the northeastern border of africa such a motion of africa agrees well with geological observations and with the pangea a2 hypothesis

paleomagnetism of permian sedimentary rocks from tanzania and the permian paleogeography of pangea abstract we report new paleomagnetic results from karoo permian rocks in tanzania k1 and k3 redbeds and k5 siltstones and limestones from the songwe kiwira basin ndeke redbeds from the mikumi basin and group viii redbeds from the nyakatitu basin were sampled and thermally demagnetized palynologic data and lithologic correlations suggest that the k1 redbeds are lower permian and that the k3 ndeke and group viii redbeds as well as the k5 siltstones and limestones are upper permian stable magnetic directions were obtained from the k3 ndeke and group viii redbeds yielding an upper permain pole at 26 n 267 e characteristic remanence directions were also obtained from the k5 siltstones and limestones however because these directions define a pole 66 n 269 e that is very close to the upper cretaceous pole for africa and significantly different from the upper permian redbed poles these rocks may have been remagnetized the k1 redbeds did not yield stable results using our new results together with published permian poles for africa and the other gondwanan continents we revise the mean lower and upper permian poles for africa west gondwana and gondwana and investigate whether or not these revised poles can discriminate between the various pangea reconstructions proposed for the permian with any greater certainty than previous unrevised mean poles when compared to the mean lower and upper permian poles for laurussia we find that our revised west gondwanan and gondwanan poles do not necessarily provide stronger support for any particular pangea reconstruction than the previous poles therefore even though this study improves the paleomagnetic data base for gondwana for the permian it is not clear that the combination of our results with other paleomagnetic data from the gondwanan continents yields significant new insights about the permian configuration of pangea as suggested previously strong non dipole fields during the permian may provide an explanation for why it is not easy to discriminate with certainty between the various permain pangea reconstructions even with new paleomagnetic results

pangea in permian to jurassic time the apparent polar wander paths apwps for the northern and southern continents have been redetermined using revised time scales and data when plotted on the conventional pangea pangea a the paths are distinct but essentially linear and parallel from late carboniferous to late permian time both paths then undergo a sharp change in direction and converge so as to overlap in early to middle jurassic time if the permo triassic magnetic field was an axial dipole then paleomagnetic data show that pangea was mobile during most and possibly all of the mid triassic to mid jurassic interval because of the uncertainties in pole ages and positions and errors in measurements the new apwps are consistent with a range of pangeas in particular the data are compatible with two paleomagnetic pangeas a2 and a new class of pangea here named the d pangeas these resemble morel and irving s 1981 pangea b and the c pangeas of smith et al 1981 unlike the a2 pangeas the b c and d pangeas all require large 2000 km relative motion between the northern and southern continents geological data require the transition from an earlier pangea to pangea a to take place along a transform zone here named the pangea transform zone or ptz the ptz is considered to be technically analogous to the great glen fault of scotland four types of possible ptz are examined passing through either the western or eastern end of the brunswick magnetic anomaly of eastern north america or north and south of iberia the geological data suggest that those pangeas that require large displacements on ptzs that pass east of the brunswick magnetic anomaly are improbable b and c pangeas are snapshots giving precise paleomagnetic reconstructions d pangeas fit long stretches of the apwps as well as possible a2 pangeas fit the apwps moderately well but also require the geological displacement to be smaller the differences in displacement between the d and a2 pangeas reflect geometrical relationships between euler poles ptz curvature and the apwps the general geological evidence suggests that d pangeas are less probable than a2 pangeas but that they cannot be rejected transition from a2 to a is most likely to have occurred via a sequence of rotations about different poles rather than a single rotation in detail the conventional pangea requires modification africa must be broken into at least two fragments along the benue trough and its northern continuation northwest africa then fits more tightly into northern south america which modifies the apwps and reduces the gap between them by including the effects of continental extension and using detailed geological data the gap can be reduced to one in which the a63 circles touch or overlap non dipole fields or an expanding earth need not be invoked to explain the mismatch of the apwps on the conventional pangea the finite rotation required for the older pangea to pangea a is very close to van der voo and french s 1974 single rotation for a2 to a but is actually the sum of three smaller rotations that reflect the modification to pangea a continental extension and the postulated ptz displacement of the possible ptzs a ptz parallel to the west african continental magnetic anomaly with a displacement of about 170 km gives a better fit of this anomaly to the east coast magnetic anomaly of north america further refinements to pangea a2 will depend on a better knowledge of stretching factors on the passive continental margins of the modified pangea a and incorporation of rotations due to major faults such as the south atlas fault in morocco

juxtaposed and superimposed paleomagnetic primary and secondary components from the folded middle carboniferous sediments in the reggane basin saharan craton algeria abstract a paleomagnetic study was carried out on the middle carboniferous sediments of the eastern margin of the reggane basin of algeria seven sites 108 samples in the lower serpukhovian and 11 sites 129 samples in the upper serpukhovian bashkirian and lower moscovian levels were investigated besides a common but generally limited viscous remanent magnetization component a and a recent chemical remanent magnetization of reversed polarity a two main components were identified one of these component b is characterized by a negative fold test and has been identified as a lower jurassic remagnetization the associated paleomagnetic pole obtained in the seven zones by combining characteristic remanent magnetization directions chrm and great circles 71 1 n 251 4 e a95 3 8 k 254 lies in the vicinity of the nw african poles of similar ages the second component c displays both normal and reversed polarities also determined by the combination of chrm or stable end points and remagnetization circles it yields a positive fold test which constrains the magnetization acquisition time and a positive reversal test which argues in favor of a non composite nature of the component c the normal polarities observed in the lower serpukhovian levels represent the latest normal event observed in africa before the kiaman superchron the paleomagnetic south pole calculated from 10 sites n 64 data gathered in four large areas 26 5 s 44 7 e a95 4 7 k 383 is the first african carboniferous pole founded on both positive reversal and fold tests it lies only slightly apart from other middle carboniferous poles previously published for the northern part of africa where no intraformational test were available to constrain the magnetization age