error analysis for the determination of tectonic rotation from paleomagnetic data appendix b is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b83 001 2 50 payment must accompany order recent determinations of tectonic rotation and flattening from paleomagnetic data have exaggerated the size of the confidence limits or error bars by about 25 this has been caused by the misuse of conventional error propagation formulas to derive one degree of freedom error bars from a two dimensional cone of confidence 95 an analytical calculation which is valid when error bars are small shows that the correct error bars are 75 to 80 of the values derived in previous studies i have used numerical integration to check on the applicability of the analytical solution and to calculate error bars when the analytical approximation cannot be used the analytical approximation may be used whenever 95 is less than 10 and the mean inclination is not too close to vertical confidence limits given for tectonic rotation and flattening in recent literature are too large and should be reduced by 20 25 narrowing the error bars in this way permits a more accurate interpretation of paleomagnetic data

thermal history of the ecstall pluton from 40ar 39ar geochronology and thermal modeling abstract new 40ar 39ar thermochronology results and thermal modeling support the hypothesis of hollister et al 2004 that reheating of the mid cretaceous ecstall pluton by intrusion of the coast mountains batholith cmb was responsible for spatially variable remagnetization of the ecstall pluton 40ar 39ar ages from hornblende and biotite from 12 locations along the skeena river across the northern part of the ecstall pluton decrease with proximity to the quottoon plutonic complex the nearest member of the cmb to the ecstall pluton the oldest 40ar 39ar ages are found farthest from the quottoon plutonic complex and are 90 3 ma for hornblende and 77 9 1 2 ma for biotite the youngest 40ar 39ar ages are found closest to the quottoon plutonic complex and are 51 6 1 2 ma for hornblende and 45 3 1 7 ma for biotite no obvious relationship between grain size and age is seen in the ecstall pluton biotites spatial trends in 40ar 39ar ages are consistent with model results for reheating by a thermal wall at the location of the quottoon plutonic complex although no unique solution is suggested our results indicate that the most appropriate thermal history for the ecstall pluton includes both reheating and northeast side up tilting of the ecstall pluton associated with intrusion of the quottoon plutonic complex estimates of northward translation from shallow paleomagnetic inclinations in the western part of the ecstall pluton are reduced to 3000 km consistent with the baja bc hypothesis when northeast side up tilting is accounted for

northward motion of the whitehorse trough paleomagnetic evidence from the upper cretaceous carmacks group reply the upper cretaceous carmacks group 70 4 2 4 ma comprises gently dipping basaltic and andesitic lava flows overlying volcaniclastic deposits of the intermontane belt in the whitehorse trough the sampling area is in southern yukon and northern british columbia it lies west of the tintina northern rocky mountain trench fault and teslin suture zone and east of the denali shakwak fault volcanic sections were sampled in three regions spread over 300 km providing the first paleomagnetic data from pre tertiary volcanic rocks in the northern canadian cordillera alternating field and thermal demagnetization revealed stable magnetization for 18 of the 27 sites collected the overall mean direction d 166 7 i 71 4 k 53 95 4 8 n 18 sites is pre folding and is most probably primary latest cretaceous this gives a paleopole at 109 4 e 82 1 n k 21 a95 7 8 a critical evaluation of north american cratonic data yields a reference paleopole for the latest cretaceous at 185 8 e 77

age of emplacement and basement character of the cache creek terrane as constrained by new isotopic and geochemical data new u pb and rb sr isotopic and major and trace element geochemical data are reported for late triassic to eocene granite bodies that intrude the cache creek and stikine terranes in the atlin bennett area of northwestern british columbia the u pb isotopic age data help constrain closure of the cache creek ocean and obduction of the cache creek terrane to before 172 ma middle jurassic low 87sr 86sr initial ratios 0 7037 0 7046 and lack of evidence for inheritance in zircons suggest that rocks underlying the cache creek terrane are largely primitive in nature with derivation of intrusive rocks predominantly from unevolved sources a genetic link between late triassic granitic plutons and stuhini arc volcanics of stikinia is supported by trace and rare earth element data which indicate generation of magma in a volcanic arc setting geochemical patterns for postaccretion middle jurassic and late cretaceous to early tertiary age plutons are similar to those of the late triassic indicating that middle ju

propagating and incorporating the error in anisotropy based inclination corrections summary sedimentary rock palaeomagnetic inclinations that are too shallow with respect to the ambient field inclination may be restored using anisotropy based inclination corrections or techniques that rely on models of the past geomagnetic field one advantage of the anisotropy technique is that it relies on measured parameters declinations inclinations bulk rock magnetic fabrics and particle magnetic anisotropy that have measurement errors associated with them rather than relying on a geomagnetic field model and statistical treatment of the data sofar however theerrorassociatedwiththemeasurementshasnotbeenpropagatedthrough the corrections and the reported uncertainties are simply the 95 95 per cent confidence circles of the corrected directions in this paper we outline different methodologies of propagating the error using bootstrap statistics and analytic approximations using the case example of the shepody formation inclinationcorrection bothtechniquesareingoodagreementandindicateamoderate 15per cent uncertainty in the determination of the flattening factor f used in the correction such uncertainty corresponds to an 0 31 increase of the confidence cone and a bias that steepens the mean inclination by 0 32 for other haematite bearing formations realistic uncertainties for f ranging from 0 and 30 per cent were used together with an intermediate value of 15 per cent yielding a maximum expected increase in the confidence cones and steepening of the inclinationsof 1 suchresultsindicatethatformoderateerrorsoff theinclinationcorrection itself does not substantially alter the uncertainty of a typical palaeomagnetic study we also compare the uncertainties resulting from anisotropy based corrections to those resulting from the elongation inclination e i technique uncertainties are comparable for studies with a large sample number 100 otherwise the anisotropy based technique gives smaller uncertainties whenanisotropydataarenotavailable itispossibletoestimateacorrectionusingflattening factors f obtained from the literature a range of flattening factors has been observed for both magnetite and haematite bearing rocks 0 4 f 1 for haematite and 0 54 f 1f or magnetite but the exact value is specific to the anisotropy of the formation to evaluate the maximum effects of inclination shallowing the smallest f for magnetite or haematite should be used

a paleomagnetic test for northward tectonic transport of the eastern selwyn basin northern canadian cordillera data from the mid cretaceous ragged pluton ragged pluton is a member of the tungsten plutonic suite in the eastern selwyn basin this circular massive 97 ma granitic pluton is 5 km in diameter it intrudes deformed and metamorphosed clastic strata of the neoproterozoic to lower cambrian vampire formation thermal and alternating field step demagnetization data for 216 specimens from 21 plutonic sites isolated a stable characteristic remanent magnetization chrm direction at 20 sites of declination d 325 9 inclination i 80 4 95 2 7 k 142 thermal demagnetization and saturation remanence analysis show that the chrm is carried by both single domain pyrrhotite and magnetite ragged pluton s paleopole at 73 9 n latitude 191 4 e longitude dp 5 0 dm 5 2 is concordant with its co eval 97 ma north american reference paleopole showing at 95 confidence that the pluton has not been significantly rotated or translated relative to north america this paleomagnetic result favours tectonic models in which the eastern selwyn basin is

geochemical logging in the cajon pass drill hole and its application to a new oxide igneous rock classification scheme a new elemental oxide classification scheme for crystalline rocks is developed and applied to geochemical well logs from the cajon pass drill hole this classification scheme takes advantage of measurements of elements taken by a geochemical logging tool string it uses k 2o versus sio 2 al 2o 3 to distinguish between granites granodiorites tonalites syenites monzonites diorites and gabbros oxide measurements from cores are used to calibrate the elemental abundances determined from the well logs from these logs a detailed lithologic column of the core is generated the lithologic column derived from the well log classification scheme is compared with a lithologic column constructed from core samples and well cuttings in the upper 1295 m of the well agreement between the two columns is good discrepancies occur from 1295 to 2073 m and are believed to be caused by the occurrence of rock types not distinguished by the classification scheme and or the occurrence of secondary minerals despite these discrepancies the well log based classification scheme helps to distinguish changes in rock type and shows potential as an aid to the construction of lithologic columns in boreholes of crystalline rocks

bathozonal tilt corrections to paleomagnetic data from mid cretaceous plutonic rocks examples from the omineca belt british columbia the skelly creek batholith 49 4 n 116 6 w 94 99ma and summit stock 49 1 n 117 0 w 102 ma are intruded into the southern omineca belt of southeastern british columbia bathozonal mineral assemblages from contact aureoles of these plutons and others of the same age indicate that post emplacement tilting of the purcell anticlinorium has probably not exceeded about 5 whereas the summit stock has been tilted 24 down to the west the skelly creek batholith has a mean direction of magnetization d i with respect to present horizontal 349 74 13 sites k 53 95 6 the mean direction of magnetization of the summit stock is 48 72 nine sites k 290 95 3 and after correction for a westerly dip of 24 the mean direction becomes 318 74 directions of the skelly creek batholith and tilt corrected direction from the summit stock are in agreement with the reference field for cratonic north america evidently this part of the eastern omineca belt was close to the margin of ancestral north america in mid cretaceous time essentially where it is today

depleted arc volcanism in the alboran sea and shoshonitic volcanism in morocco geochemical and isotopic constraints on neogene tectonic processes abstract samples of volcanic rocks from alboran island the alboran sea floor and from the gourougou volcanic centre in northern morocco have been analyzed for major and trace elements and sr nd isotopes to test current theories on the tectonic geodynamic evolution of the alboran sea the alboran island samples are low k tholeiitic basaltic andesites whose depleted contents of hfs elements 0 5 n morb especially nb 0 2 n morb show marked geochemical parallels with volcanics from immature intra oceanic arcs and back arc basins several of the submarine samples have similar compositions one showing low ca boninite affinity 143nd 144nd ratios fall in the same range as many island arc and back arc basin samples whereas 87sr 86sr ratios on leached samples are somewhat more radiogenic our data point to active subduction taking place beneath the alboran region in miocene times and imply the presence of an associated back arc spreading centre our sea floor suite includes a few more evolved dacite and rhyolite samples with 87sr 86sr 0 up to 0 717 that probably represent varying degrees of crustal melting the shoshonite and high k basaltic andesite lavas from gourougou have comparable normalized incompatible element enrichment diagrams and ce y ratios to shoshonitic volcanics from oceanic island arcs though they have less pronounced nb deficits they are much less lil and lree enriched than continental arc analogues and post collisional shoshonites from tibet the magmas probably originated by melting in subcontinental lithospheric mantle that had experienced negligible subduction input sr nd isotope compositions point to significant crustal contamination which appears to account for the small nb anomalies the unmistakable supra subduction zone ssz signature shown by our alboran basalts and basaltic andesite samples refutes geodynamic models that attribute all neogene volcanism in the alboran domain to decompression melting of upwelling asthenosphere arising from convective thinning of over thickened lithosphere our data support recent models in which subsidence is caused by westward rollback of an eastward dipping subduction zone beneath the westernmost mediterranean moreover severance of the lithosphere at the edges of the rolling back slab provides opportunities for locally melting lithospheric mantle providing a possible explanation for the shoshonitic volcanism seen in northern morocco and more sporadically in se spain

a magnetostratigraphic and secular variation study of level mountain northern british columbia summary palaeomagnetic results are reported from 50 flows erupted by level mountain which is a composite volcano in northern british columbia fourteen magnetic polarity zones are represented and these allow a magneto stratigraphy to be established which indicates that eruptive activity began about 6 5 myr ago and continued up to very recent times with several hiatuses of up to 1 myr or more most of the flows yield acceptable normal or reversed palaeopoles but two of them record the gauss matuyama polarity transition and a further four yield a tight group of divergent directions which are here interpreted as a geomagnetic excursion near the base of the gauss epoch this observation lends support to an earlier suggestion bingham stone that the geomagnetic field was abnormally disturbed about 3 5 myr ago at least locally in north western north america the overall average palaeopole obtained after filtering out flows with high internal variance and those yielding divergent virtual geomagnetic poles vgps lies at 256 e 85 n n 38 a 7 2 a more representative palaeopole is obtained by combining the results with those of souther symons from mount edziza a closely related contemporaneous volcano some 100 km away this pole lies at 292 e 87 n n 92 ag5 4 1 and again includes the geographic pole within its 95 per cent confidence limits how ever the mean itself is not far sided as wilson s model predicts neither is it left handed as the analysis by merrill mcelhinny predicts the slight near sidedness observed agrees with the global compilation of wilson mcelhinny who show that the north western region of north america is the only area out of 15 regions worldwide to yield a near sided pole the dispersion of the vgps angular standard deviation 22 is a little higher than would be expected from global summaries and secular variation models this was also found to be the case in data from alaska doell cox the angular dispersion the occurrence of geomagnetic excursions and the

on the motion of hawaii and other mantle plumes abstract the hawaiian hotspot and its prominent bend at 47 ma have figured prominently in the development of ideas on the nature of mantle plumes and plate motion here i review paleomagnetic analyses associated with ocean drilling program odp leg 197 which together with studies of plate circuits and geodynamic modeling results indicate southward motion of the hawaiian hotspot during formation of the emperor seamounts these analyses confirm the long posited idea that mantle plumes should be influenced by mantle flow moreover these results indicate that late cretaceous early paleogene hotspot motion was the dominant factor in forming the emperor track and thus the famous bend morphology an important corollary of this finding on hotspot motion is that long term polar wander of earth which has been inaccurately assessed by viewing paleomagnetic data in a fixed hotspot reference frame has been far less than previously thought salient points for future research raised by the odp leg 197 paleomagnetic results include the scale of mantle flow recorded by hotspot track segments and the underlying processes that cause track segments to be dominated by mantle flow rather than plate motion for given time intervals

palaeomagnetism and magnetic anisotropy of carboniferous red beds from the maritime provinces of canada evidence for shallow palaeomagnetic inclinations and implications for north american apparent polar wander summary a palaeomagnetic and magnetic anisotropy study was conducted on the lower middle carboniferous maringouin and shepody red bed formations of the maritime provinces of canada to detect and correct inclination shallowing because of the shallow inclinations commonly observed in red beds and the strong dependence of north america s palaeo mesozoic apparent polar wander apw on red beds inclination shallowing may substantially affect large portions of north america s apw path hematite is the primary magnetic mineral carrier in these red beds accompanied by secondary magnetite maghemite goethite and pigmentary hematite thermal and chemical demagnetization of the shepody fm successfully isolated characteristic remanence directions of d 177 i 20 4 95 6 5 n 19 and d 177 8 i 17 7 95 6 9 n 16 respectively thermal demagnetization of the maringouin fm isolated a characteristic remanence direction of d 178 7 i 24 9 95 14 5 n 9 high field anisotropy of isothermal remanence followed by alternating field and thermal cleaning on leached samples was used to isolate the fabric of hematite individual particle anisotropy was measured directly from magnetic separates using a new technique hematite s magnetic fabric and particle anisotropy were used to apply an inclination correction our inclination corrections indicate up to 10 of inclination shallowing corresponding to corrected palaeopole positions of 27 2 n 118 3 e a95 6 2 and 27 4 n 117 2 e a95 13 1 for the shepody and maringouin formations respectively this correction corresponds to a 6 increase in colatitude for carboniferous north america which translates into approximately a 650 km change in north america s palaeogeographic position the proposed position of north america supports a pangea b type reconstruction

late cretaceous age of the hutshi mount nansen and carmacks groups southwestern yukon territory and northwestern british columbia volcanic rocks of the hutshi mount nansen and carmacks groups occur in the southwestern yukon where they unconformably overlie the yukon crystalline terrane and deformed strata of the whitehorse trough the volcanic rocks are faulted and tilted locally altered and largely postorogenic the more basic carmacks volcanics locally overlie intermediate to acid rocks of the mount nansen group but are mostly in isolated exposures northwest of the hutshi and mount nansen volcanics hutshi mount nansen volcanics of the miners range are porphyritic partly vesicular calc alkaline andesite flows and flow breccias intruded by calc alkaline alkali rich rhyolite and two feldspar andesite dikes a low greenschist metamorphic overprint affects most rocks carmacks volcanics near carmacks are flows epiclastic breccias and sintered tuffs interbedded with immature volcanic sandstone one analysed breccia clast is calc alkaline andesite but the flows are potassic basalt trachybasalt and tristanite recent assignme

the big flush paleomagnetic signature of a 70 ma regional hydrothermal event in displaced rocks of the northern canadian cordillera the 70 ma carmacks group a subaerial volcanic succession which once covered much of central southwest yukon has a paleomagnetic remanent direction which passes the fold test and the reversal test a new collection of 13 sites combined with 13 sites from a previous study renders a pole 088 6 e 78 4 n a95 7 8 which is far sided with respect to the pole for cratonic north america and implies a displacement from the south of 1900 700 km late triassic mandanna member red beds and early jurassic nordenskild formation tuffs deformed in the late jurassic fail the fold test and conglomerate test but pass a contact test with eocene dykes the postdeformational remanent direction is identical to that isolated from the carmacks group the magnetic signature contained in these older formations is probably an overprint produced by an extensive hydrothermal system active during carmacks extrusion geological work indicates that the carmacks group is plume related given its paleomagnetic latitude and geological nature we hypothesize that the carmacks group is a displaced segment of the yellowstone hot spot track and the hydrothermal system which remagnetized the older rocks was established by mantle upwelling below the region resume le groupe de carmacks go de 70 ma est une succession volcanique subaorienne qui couvrait jadis la majeure partie du centre sud ouest du yukon il possde une direction paloomagnotique romanente certifioe par le test du pli et le test des inversions une nouveau groupe de 13 sites combino 13 sites diune otude antorieure fournit un pule 088 6 e 78 4 n a95 7 8 qui est considorablement oloigno par rapport au pule du craton de liamorique du nord et qui implique un doplacement partir du sud de 1900 700 km les couches rouges du membre de mandanna du trias tardif et les tufs du formation de nordenskild du jurassique prococe qui subirent une doformation durant le jurassique tardif ont ochouo le test du pli et le test de conglomorat mais ils ont passo avec succs le test de contact avec les dykes de li ocne la direction romanente post tectonique est identique celle isoloe du groupe de carmacks la signature magnotique qui caractorise ces formations plus anciennes est probablement une roaimantation produite par un systme hydrothermal otendu qui fut actif durant liextrusion de carmacks liotude goologique rovle que le groupe de carmacks est apparento un panache tant donno sa latitude paloomagnotique et sa nature goologique nous avanaons lihypothse que le groupe de carmacks reprosente un segment doplaco du traco du point chaud de yellowstone et que le systme hydrothermal qui a roaimanto les roches les plus anciennes est ds liascension du manteau sous la rogion otudioe

yellowstone in yukon the late cretaceous carmacks group the late cretaceous carmacks group a thick subaerial volcanic succession that once covered much of southwest yukon was deposited on an uplifted terrane and is divisible into a lower fragmental unit and an upper flood basalt unit coeval hydrothermal activity resulted in widespread alteration and gold mineralization the lavas are shoshonites enriched in large ion lithophile and light rare earth elements but depleted in high field strength elements ankaramitic absarokite flows in the upper carmacks group range up to 15 wt mgo requiring a high liquidus temperature 1400 c at 1 bar dry high k 2 o contents 3 of these magnesian lavas indicate that the potassic character of the volcanic suite was established in the mantle although previously interpreted as subduction related the carmacks group was erupted during a cordilleran wide magmatic lull and lacks coeval calc alkalic batholiths the lavas are petrologically similar to plume related eocene to pliocene potassic lavas of the western united states new paleomagnetic collections combined with previous work place the carmacks group 17 2 6 5 1900 700 km south of its present position relative to the craton during deposition near the paleolocation of the yellowstone hotspot the spatial coincidence similarity of tectonic setting and lithologic similarity of the carmacks group and yellowstone volcanic successions suggest that the carmacks group is the 70 ma effusion of the yellowstone hotspot subsequent northward displacement of the carmacks group is attributed to coupling with the kula plate correlation of the carmacks group and the yellowstone hotspot fixes the paleolatitude and the paleolongitude of the terranes of the northern intermontane belt at 70 ma

additional k ar isotopic dates for the carmacks group upper cretaceous west central yukon three whole rock k ar analyses on andesites from the indian river area west central yukon yielded dates of 69 0 1 7 65 2 1 7 and 64 8 1 7 ma these confirm earlier dates indicating the carmacks group is late cretaceous in age a single date of 51 4 3 9 ma was obtained from a tuff in the sixty mile river area west central yukon suggesting an eocene age for these deposits however this date is considered equivocal because it is anomalous when compared with the other dates from the area

northward motion of the whitehorse trough paleomagnetic evidence from the upper cretaceous carmacks group discussion discordant paleomagnetic directions in mid cretaceous plutons of the coast plutonic complex and north cascades have been interpreted as indicating mid cretaceous paleolatitudes 2000 2500 km south relative to north america beck et al 1981 irving et al 1985 umhoefer 1987 but this magnitude of northward transport contradicts interpreted pre midcretaceous links between the north american miogeocline and westerly parts of the cordillera price and charmichael 1986 because paleohorizontal cannot be directly determined in plutonic rocks the discordant paleomagnetic directions may also be explained by tilting of the plutons about a horizontal axis primarily because of the consistent nature of the paleomagnetic discordance over a large region beck et al 1981 and irving et al 1985 have preferred the interpretation of northwards transport however butler et al 1989 recently pointed out geological evidence indicating that widespread northeast side up tilting may have affected the western portion of the coast plutonic complex and the north cascades resolution of this debate is of obvious importance to understanding the tectonic evolution of the canadian cordillera marquis and globerman reported results of a paleomagnetic study of the upper cretaceous carmacks group in the whitehorse trough the carmacks group is composed of gently dipping basaltic and andesitic lava flows that have been dated at 70 4 2 4 ma these rocks lie west of the tintina northern rocky mountain trench fault and the teslin suture zone because paleohorizontal can be unambiguously determined for these volcanic rocks the paleomagnetic data presented by marquis and globerman are potentially very important in resolving the tilt versus translation question marquis and globerman collected paleomagnetic samples in three regions spread over 300 km based on detailed laboratory studies they successfully isolated characteristic remanent magnetization chrm from 18 of 27 paleomagnetic sites flows the acquired paleomagnetic data pass a fold test of stability and contain sites of both normal and reversed polarity and magnetic properties indicate that the chrm is a primary thermoremanent magnetization the observed angular dispersion of virtual geomagnetic poles vgp s indicates some degree of required sampling of geomagnetic secular variation marquis and globerman determined a paleomagnetic pole from the carmacks group at 82 n 109 e with 95 confidence region ag5 of radius 7 8 using a 70 ma north american reference paleomagnetic pole of 77 7 n 185 8 e ag5 7 7 and the methods of beck 1980 as modified by demarest

emplacement ages and exhumation rates for intrusion hosted cu mo sb au mineral systems at freegold mountain yukon canada assessment from u pb ar ar and u th he geochronometers to decipher the thermal history of mineralized systems across the freegold mountain area yukon canada a combined geochronology zircon u pb and hornblende biotite and whole rock ar ar and thermochronology apatite and zircon u th he study was carried out previous u pb data combined with new u pb and ar ar data show that intrusive bodies across the freegold mountain were emplaced during two protracted episodes the first spanning from 109 6 to 98 ma and the second between 79 and 68 ma overprinting of the first intrusive event by a second magmatic hydrothermal event is suggested by a zircon u pb age of 108 7 0 4 ma for a chlorite altered dyke and a whole rock ar ar plateau age of 76 25 0 53 ma zircon u th he data are between 66 and 89 ma whereas apatite u th he data are scattered 38 7 109 9 ma and bracket the two magmatic emplacement events our combined data reveal a complex history of reheating that led to resetting of numerous chronometers in most of the investigated magmatic hyd

paleomagnetic dating of magmatic phases at the cantung tungsten deposit northwest territories canada the cantung tungsten copper w cu skarn orebodies are hosted by proterozoic and lower cambrian metasedimentary rocks next to the cretaceous mine stock monzogranite paleomagnetic analyses of 283

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

crossover plots a useful method for plotting sirm data in paleomagnetism the effective grain size of magnetic minerals and therefore domain type controls the saturation isothermal remanent magnetization acquisition and subsequent demagnetization response and can be used to create crossover plots for paleomagnetic specimens where sirm is plotted as a function of the field applied using a logarithmic scale this paper presents templates of such plots for magnetite pyrrhotite hematite and goethite onto which sample data can be plotted for conventional paleomagnetic specimens to characterize their magnetic mineralogy and effective grain size

internal flow structures in columnar jointed basalt from hreppholar iceland ii magnetic anisotropy and rock magnetic properties internal flow structures in columnar jointed basalt from hreppholar iceland ii magnetic anisotropy and rock magnetic properties

impact melt rock clasts in the hvittis enstatite chondrite breccia implications for a genetic relationship between el chondrites and aubrites the hvittis enstatite chondrite breccia contains 5 2 vol dark clasts which appear to be impact melt rocks the largest clast clast a is 2 5 cm in diameter it has an igneous texture no chondrules and is depleted in metallic fe ni and sulfide its fine grain size low ni kamacite and schreibersite and rare martensite resulted from rapid cooling the abundance of melt rock clasts in hvittis suggests that the breccia resided at its parent body surface however the apparent absence of el chondrites with solar wind implanted rare gases suggests that the el parent body was too small to develop a substantial regolith the bulk composition of clast a is very similar to that of average aubrites except for a sevenfold enrichment in s cr and mn these elements are concentrated in the sulfides it thus is possible that the clast was derived from one of the sulfide rich regions of the hvittis matrix if so then aubrites may be genetically related to el chondrites

statistical analysis of palaeomagnetic data from the last four centuries evidence of systematic inclination shallowing in lava flow records the main objective of this work is to compare directional declination and inclination volcanic and archaeomagnetic data for the last four centuries 1600 1990 with the historical geomagnetic predictions given by the gufm1 model which spans from 1590 to 1990 the results show statistical agreement between archaeomagnetic data and directions given by the geomagnetic field model however when comparing the volcanic data with the model predictions marked inclination shallowing is observed this systematically lower inclination has already been observed in local palaeomagnetic studies italy mexico and hawaii for the 20th century by comparing recent lava flows with the international reference geomagnetic field igrf model here we show how this inclination shallowing is statistically present at worldwide scale for the last 400 years with mean inclination deviation around 3 lower than the historical geomagnetic field model predictions

rethinking yellowstone in yukon and baja british columbia paleomagnetism of the late cretaceous swede dome stock northern canadian cordillera 1 paleomagnetic results obtained from the 69 8 ma swede dome stock emplaced into the pericratonic yukon tanana terrane ytt west of dawson yukon indicate a minimal northward translation of 360 575 km and a clockwise rotation of 20 23 with respect to north america in accord with the displacement of 425 km along the nearby tintina fault coeval carmacks group volcanics in contrast have previously indicated 1900 km northward translation and minimal rotation and have been proposed to be a displaced manifestation of the fixed yellowstone hot spot thus providing an independent estimate of the late cretaceous paleoposition of the baja british columbia terranes of western north america a compilation of recent mid and late cretaceous paleomagnetic results from the ytt and intermontane belt imb terranes reveals that the carmacks group paleomagnetic result is anomalous the ytt and imb terranes which form the bulk of baja british columbia appear instead to have experienced 1000 km northward translation with respect to north america since 70 ma consistent with geological estimates of motion along plausible accommodating faults in addition past mobility of the hawaii emperor hot spot implies that the pacific hot spots may have experienced 1200 km of southward motion from 81 to 47 ma if so then the paleoposition of the yellowstone hot spot if it existed at 70 ma would likely have produced the carmacks magmatism 1000 km north of yellowstone s current latitude consistent with a moderate 1000 km post 70 ma northward translation of the ytt and imb terranes to their present position in north america

eocene rotation of the coast plutonic complex and intermontane belt paleomagnetism of eocene plutons along the klondike highway paleomagnetic results are reported for the 59 ma skagway 54 ma fraser 53 ma summit lake and 48 ma clifton felsic plutons of the eastern coast plutonic complex cpc that outcrop along the south klondike highway in alaska and british columbia thermal and alternating field step demagnetizing methods yielded stable characteristic remanent magnetization chrm directions for all 29 sites of normal reversed and mixed polarity the chrm resides in single or pseudosingle domain magnetite and or pyrrhotite that is shown to be primary by contact tests with the 47 ma vertical white pass mafic dikes paleopoles from six 56 to 50 ma mean 52 2 ma intermontane belt yukon tanana terrane imb ytt units that cannot be explained by tectonic tilt are compared with nine clustered 59 to 46 ma mean 52 4 ma eastern cpc paleopoles both paleopole populations show nonsignificant poleward northward translation relative to north america imb ytt 3 7 5 3 n cpc 4 3 6 4 s overall 1 2 4 9 s ind

paleomagnetic and geobarometric study of the late cretaceous mount lorne stock southern yukon territory the 75 ma mount lorne monzodiorite stock has been studied paleomagnetically to estimate the tectonic motion of the northern canadian cordillera since the late cretaceous the stock is one of sever