structure and emplacement of the alpine type peridotites from beni bousera rif morocco a polyphase tectonic interpretation abstract the beni bousera peridotite antiform in the southern branch of the gibraltar orocline exhibits a lherzolitic core containing thin pyroxenite layers surrounded by harzburgites then by dunites and garnet bearing dunite in the peripheral areas the amount of pyroxenite greatly increases by the development of garnet pyroxenite veins these data indicate a gradient of partial melting increasing upward we conclude that a reversed geothermal gradient was temporarily established in the upper part of the peridotite just under its migmatitic roof kinzigite aureole then sillimanite gneiss study of ductile penetrative structures and discussion of the later cold structures show that the foliation of the tectonites was originally flat with a nw se trending stretching lineation orthopyroxene crystals are used as tectonic markers isostrain zones indicate that simple shear and finite strain increase upward we conclude that a ductile shear zone acted between peridotite and gneiss strain heating along this shear zone probably has been responsible for partial melting of the upper part of the peridotite in our model the peridotite emplacement into the mid continental crust began during crustal extension then as comparison with the ronda massif suggests an intracrustal thrusting stage was followed by high temperature and relatively low pressure metamorphism and by intrusion of acidic dikes the uplift of the mantle slab continued by compressive upthrusting and isostatic doming this complex polyphase evolution probably extended beyond the alpine orogeny as suggested by kornprobst

late cretaceous paleomagnetism of the tombstone district and vicinity evidence for a rotational domain boundary in southeastern arizona paleomagnetic data are presented for late cretaceous volcanic and intrusive rocks in the tombstone district and dos cabezas mountains of southeastern arizona the resultant paleopole 73 n 224 e a95 8 is similar to a late cretaceous reference pole for north america 82 n 210 e a95 7 implying that these rocks have not been significantly rotated about vertical or near vertical axes relative to the continental interior generally concordant results have also been published for pennsylvanian terra rosa paleosols within the black prince limestone at localities in the nearby gunnison hills whetstone mountains and naco hills together however these carboniferous data indicate a 9 7 clockwise rotation with respect to north america similar to that determined for the colorado plateau 5 14 since the mid cretaceous published paleomagnetic data for rocks south and west of the tombstone vicinity indicate much larger clockwise rotations ranging from 25 to 60 implying that a rotational domain boundary runs between the mustang mountains and canelo hills to the southeast and between the silver bell and tucson mountains to the northwest this boundary roughly coincides in part with the sawmill canyon fault zone and is parallel to other northwest trending strike slip faults in the region that were active during the laramide orogeny the clockwise rotations in southern arizona are likely part of a larger pattern of dextral shear along the western margin of north america during the late cretaceous and early tertiary caused by northward oblique subduction of oceanic plates relative to the stable craton

ophiolite emplacement by collision between the sula platform and the sulawesi island arc indonesia much of the tectonic complexity displayed in eastern indonesia results from a series of neogene collision events between island arcs continental fragments and the australian continent here we examine the emplacement of a large ophiolite belt resulting from the miocene collision between the sulawesi island arc and a continental fragment the sula platform we present the results of several marine geophysical expeditions to the sw molucca sea and the nw banda sea plus gravity and geology on the east arms of sulawesi the batui thrust separates the ophiolite from sedimentary rocks deformed along the leading edge of the sula platform we mapped this thrust eastward from sulawesi along the southern margin of the gorontalo basin the latter is floored by oceanic crust and its south edge is uplifted against the thrust thus the sulawesi ophiolite can be traced offshore to its origin as basement of the gorontalo basin the ophiolite is composed of harzburgite in the southeast arm and passes upward through a complex of gabbros and diabase dikes in the east arm ophiolite melange underlies the harzburgites on the southeast arm beneath low angle thrust contacts where seen our local observations show the melange to be composed of thrust packets of both serpentine and red shale matrix varieties the packets are several hundred meters thick and the melange where studied has a moderate north to northeast dipping foliation this orientation if regionally representative of the melange fabric is consistent with a significant northward component of movement of the lower plate probably the sula platform or its margin where the ophiolite is in contact with rocks of the central schist belt it dips under the schist but where it encounters melange or mesozoic or paleogene sedimentary rocks the ophiolite is thrust over them the tectonic overlap sequence from west to east is schist over ophiolite over older sediments or melange the ophiolite appears to have been emplaced by oblique convergence of the sula platform along the southern edge of the gorontalo basin we suggest that the gorontalo basin represents a forearc basin and the ophiolite is its basement analogous to a number of other forearc settings deformation of the ophiolite may have occurred in part on the seafloor prior to emplacement but we feel that much of the deformation occurred during emplacement the sulawesi ophiolite is only one of a number of ophiolites in the indonesian region each of which has a very different origin and tectonic history

evaluation of paleomagnetism as a correlation criterion for mogollon datil ignimbrites southwestern new mexico paleomagnetic and rock magnetic data show that 36 24 ma ignimbrite outflow sheets in the mogollon datil volcanic field carry thermoremanent magnetizations trms that provide useful reliable correlation criteria over 90 of 404 ignimbrite sites exhibit well grouped 95 500 m intracaldera ignimbrite sequences agree in polarity with associated outflow sheets but show less consistent trm directions probably reflecting syncooling secular variation and discrepancies between eutaxitic foliations and the syncooling paleohorizontal mean virtual geomagnetic pole positions vgps of normal and reverse polarity ignimbrites are nearly antipodal 175 6 apart showing no evidence of long term differences in the zonal harmonics of the normal and reverse polarity states less antipodal mean vgps 161 2 apart from normal and reverse polarity lavas are interpreted as defects in the data set probably including incompletely removed normal polarity viscous overprints the mean paleomagnetic pole position for mogollon datil ignimbrites n 68 independent unit mean vgps is located at 78 8 n 166 6 e k 19 8 a95 4 0 18 2

extension during continental convergence with application to the tibetan plateau the tibetan plateau is the product of crustal thickening caused by the collision between india and asia and is the largest active example of extensional tectonics in a zone of continental collision throughout most of the tertiary the tectonics of the plateau were dominated by north south shortening a significant proportion of which took place on east west striking thrust faults for the last 5 m y or so the plateau has been thinning by the mechanism of extension on north south trending normal faults previous investigations of the collision have been able to account for the large scale features of the tertiary deformation but have failed to explain the transition in the late tertiary to quaternary strain rate field of the plateau from north south compression to east west extension the transition could in principle be effected by a reduction in the rate of convergence between india and asia or by a uniform reduction in strength of the whole continental lithosphere of asia it could not however be effected by a reduction in strength of the elevated region alone this produces increased compressional strain rates in the weakened zone an alternative explanation for the transition to extension comes from considering the thermal evolution of thickened continental lithosphere the lower part of the lithosphere consists of a thermal boundary layer which when thickened by horizontal shortening is colder and denser than its surroundings convective instability of the thickened thermal boundary layer and its replacement by hot asthenosphere would rapidly raise the surface elevation and gravitational potential energy of the overlying part of the lithosphere the convective instability would happen in a time brief compared with the collision time scale 50 m y in the case of india and asia but would only occur after there had already been substantial thickening of the lithosphere numerical experiments show that for a range of lithospheric parameters the increase in surface height as much as 2 km and of potential energy 5 to 10 1012 n m 1 resulting from convective instability of the lower lithosphere are sufficient for east west extension to replace north south compression as the dominant feature of the stress field of the tibetan plateau

paleomagnetism of the front range colorado morrison formation and an alternative model of late jurassic north american apparent polar wander a paleomagnetic study of the upper jurassic morrison formation in the front range of central colorado yields high unblocking temperature dual polarity magnetizations with respect to known paleohorizontal the inclinations absolute mean 57 3 degree 95 confidence interval 52 3 degree to 63 1 degree n 8 sites pass tilt and reversal tests whereas the dispersion in declinations can be attributed to apparent or real tectonic rotations and sedimentary processes the site centered colatitudinal locus of possible front range morrison poles partially overlaps the upper pole but it excludes the lower pole from the morrison formation on the colorado plateau as well as the 151 ma glance conglomerate pole from the basin and range province of southeastern arizona the authors offer various explanations for these disparities and suggest an alternative model of late jurassic north american apparent polar wander through approximately 70 degree n which is supported by late jurassic european poles with positive stability tests transferred to north american coordinates

the use of quartz grain microtextures in the study of the origin of sand terrains in western australia the origin of extensive sand terrains which lie inland from the coastal margin of western australia is contentious with the debate centering around an in situ vs an aeolian origin to resolve this debate the shape and surface features of sand grains are reported for sandplains sand dunes and bedrock for the victoria plateau sandplain which lies in the central west coastal region of western australia all three components of the victoria plateau are similar in grain shape and microtexture quartz grains show a combination of chemical dissolution and precipitation micromorphology characteristics of dissolution include etch patterning triangular shaped etch pits and solution features precipitation forms include edge rounding silica veneers and plate and sheet like structures features such as peeling plates complex precipitation forms projecting from grain surfaces adhering particles and preserved grain contact faces indicate stability rather than a transport dominated environmental history the combination of preserved dissolution and precipitation forms a dearth of mechanically derived features and a correspondence between grains in rock and overlying sands points to local siliceous sedimentary rocks as the source of the sands

lake lewis basin central australia environmental evolution and osl chronology abstract lake lewis is the furthest from the coast of australia s salt lakes and lies at the southern edge of influence of the australian monsoon regime the macdonnell ranges south of the lake intercept moist air masses crossing the region and efficiently deliver water and sediment to the lake and its surrounding alluvial plain we describe lacustrine fluvial and aeolian environments of the basin and report optically stimulated luminescence osl dates from representative sediments a long period of generally wetter conditions during most of the pleistocene is represented by thick uniform lacustrine clay beneath and near lake lewis this is overlain by more heterogeneous lacustrine sediments deposited since hydrologic closure of the basin which indicate fluctuating climatic conditions osl results show that dune building in the basin commenced before 95 ka when salinity at the depocentre was high dune building peaked around 23 21 ka osl ages of fluvial deposits show that floods occurred during the last 20 ka following the last phase of maximum aridity in the region

onset of aridity and dune building in central australia sedimentological and magnetostratigraphic evidence from lake amadeus abstract sediments from lake amadeus a groundwater discharge playa in central australia comprise a surface playa sequence the winmatti beds varying between 0 6 and 3 m in thickness overlying a long sequence of fairly uniform fluvial lacustrine clays the uluru clay the latter extends down to at least 15 m the maximum depth cored during this study and possibly down to 65 m below the present playa surface in the cores studied the brunhes matuyama boundary 0 73 ma was identifiable in all the upper sediments typically at a depth of between 1 and 2 m but below this there are two plausible chronological interpretations of the palaeomagnetic data deposition rates are very low typically no more than 1 5 cm ka in the uluru clay beds and down to 0 2 cm ka in the winmatti beds these rates suggest that the fluvial lacustrine phase lasted for at least 5 ma the boundary between the uluru clay and the winmatti beds bears a close correspondence to the boundary between the blanchetown clay a lacustrine sequence and the tyrrell beds a playa sequence in palaeo lake bungunnia in what is now the murray basin in southeastern australia however the transition occurs at about 0 9 ma or possibly 1 6 ma at lake amadeus whereas it has been dated palaeomagnetically at less than 0 73 ma probably 0 5 ma in lake bungunnia records from other locations in southeastern australia likewise support a major change from wetter to drier conditions at or shortly after the matuyama brunhes polarity transition thus the current evidence from lake amadeus indicates that in central australia the onset of aeolian and saline gypseous deposits characteristic of arid zone facies may have pre dated the corresponding change in the southeastern part of the continent by about 0 4 ma or possibly by about 1 1 ma in common with most playas in central australia lake amadeus is surrounded by a ring of gypseous dunes derived from material deflated from the surface of the playa magnetostratigraphic evidence from auger island in the middle of lake amadeus suggests that the oldest gypseous dune formation on the island must have pre dated the start of the jaramillo subchron at 0 98 ma or possibly the start of the brunhes epoch 0 73 ma thus making these the oldest dated dunes in australia the age of the auger island dunes is probably characteristic of other gypseous dunes around the margins of playas in central australia

mesozoic ash flow caldera fragments in southeastern arizona and their relation to porphyry copper deposits jurassic and upper cretaceous volcanic and associated granitic rocks in southeast arizona are remnants of large composite silicic volcanic fields characterized by voluminous ash flow tuffs and associated calderas presence of 10 15 large caldera fragments is inferred primarily from 1 ash flow deposits more than 1 km thick having features of intracaldera ponding 2 exotic block breccias within a tuff matrix interpreted as caldera collapse megabreccias and 3 local granitic intrusions along arcuate structural boundaries of the thick volcanic sequences several porphyry copper deposits are associated with late granitic intrusions within the calderas or along their margins

hydroclimatic interpretation of quaternary shorelines on south australian playas abstract the catchment of lake eyre is one of the world s largest internally drained basins the playas near its depocentre the driest region of australia contain a partial record of quaternary climatic and hydrologic events for the last full glacial cycle and probably beyond ancient beach ridges marginal to lakes eyre frome callabonna and blanche have been dated using thermoluminescence tl to provide evidence for major changes in the hydrological regime of the basin beach ridges around lake eyre provide evidence of high lake stands up to 27 m above the present lake floor during what probably corresponds to the middle to latter part of marine oxygen isotope stage 5 there is evidence also for even higher lake stands associated with earlier isotope stages three tl dates identify a period of aeolian activity during stage 4 and a further 5 tl dates from lakes eyre and frome indicate that high lake stands occurred between about 55 and 40 ka corresponding with stage 3 the stage 5 and stage 3 high stands both relate to periods of enhanced fluvial activity previously identified in the lake eyre basin and elsewhere in australia in contradiction with other work a few tl dates from some playas suggest a possible major episode of high lake levels immediately preceding or at the start of the last glacial maximum lgm 26 22 ka this may relate to a sharp temperature suppression and an increase in runoff by rivers fed from monsoons in the north while a set of relatively low elevation late holocene beaches have been dated on two of the playas a period of enhanced precipitation and stream flow in the early to mid holocene appears not to have formed higher beaches possibly due to high temperatures and evaporation rates at that time the filling of lake eyre during and since stage 5 appears to have been to no more than to a level of 12 m australian height datum ahd possibly due a spillway at about this elevation in the form of the warrawoocara channel connecting lake eyre with playas to the southeast lakes gregory blanche callabonna and frome such overflows from one large basin to another would have had a major impact on the hydrology of the region in addition to enhanced runoff essential for the maintenance of high lake levels must have been local temperatures and evaporation rates significantly reduced from present day levels

paleomagnetism of jurassic volcanic rocks in the patagonia mountains southeastern arizona implications for the north american 170 ma reference pole paleomagnetic study of middle jurassic volcanic and volcaniclastic rocks in southeastern arizona yields a paleomagnetic pole located at 61 8 n 116 0 e k 49 6 95 6 2 these rocks from corral canyon represent an autochthonous segment of the jurassic cordilleran magmatic arc and were deposited directly on upper paleozoic carbonates of the cratonic miogeocline rock magnetic experiments demonstrate that the natural remanent magnetization of these rocks is dominantly a single component magnetization carried in both magnetite and hematite phases and is interpreted as a primary thermoremanent magnetism rb sr isotope geochemistry on whole rock samples from eight welded ash flow tuffs yields an isochron age of 172 2 5 8 2 ma the corral canyon pole falls between poles from newark trend group ii 179 3 ma and glance conglomerate 151 2 ma

evidence for a submerged and displaced continental borderland north banda sea indonesia the banda sea is separated into two oceanic fragments the south and north banda basins by a large intervening region of ridges and basins called the banda ridges the north and south banda basins appear to be trapped pieces of pre tertiary oceanic crust whereas the banda ridges are a submerged and displaced continental borderland structurally very similar to the southern california offshore borderland analysis of dredged rocks from the banda ridges suggests an origin from western irian jaya

basement character and basin formation in gorontalo bay sulawesi indonesia new observations from the togian islands we present a new stratigraphy for the togian islands sulawesi and interpret the age character and evolution of gorontalo bay at its western end the bay is underlain by continental crust the central part is underlain by eocene to miocene oceanic and arc rocks although the area south of the togian islands could have continental crust of the banggai sula microcontinent thrust beneath this and the east arm ophiolite gorontalo bay was not a significant deep bathymetric feature before the miocene field relationships indicate a latest miocene to pliocene age for inception of the basin medium k to shoshonitic volcanism in the togian islands is not due to subduction but reflects crustal thinning and extension in the pliocene and pleistocene causing the underlying mantle to rise decompress and melt extension is continuing today and is probably the cause of volcanism at una una volcanic activity migrated west with time and volcanic products have been offset by dextral strike slip displacement along the balantak fault extension and subsidence was driven by rollback of the subduction hinge at the north sulawesi trench with a possible contribution due to flow of the lower crust 2011 the geological society of london

zircon u th pb and whole rock rb sr age patterns of lower mesozoic igneous rocks in the santa rita mountains southeast arizona implications for mesozoic magmatism and tectonics in the southern cordillera volcanic and plutonic rocks and associated sediments in the santa rita mountains southeast arizona represent one of the most complete mesozoic sections in the cordillera zircon from the lower member of the mt wrightson formation the oldest of the dated units has lost radiogenic lead and contains a component of older zircon accordingly only an imprecise maximum age of 220 ma could be obtained for an andesite from near the middle of this unit the lower member is intruded by the piper gulch granodiorite which gave a concordant zircon u th pb age of 188 2 2 ma complex isotopic systematics of zircon from dacite in the middle member of the mt wrightson formation allow its age to lie between 172 and 190 ma because the piper gulch is interpreted to also cut the base of the middle member a hiatus of no longer than 30 m y is likely to separate the lower and middle members this stratigraphic break marks the change from early predominantly basaltic and andesitic volcanism to later dacitic to rhyolitic lavas and tuffs the silty to conglomeratic red beds and minor volcanic rocks of the gardner canyon formation for which we obtained a nearly concordant u th pb age of 200 5 ma on an abraded fraction of zircon may identify a rift dominated tectonic regime and mark the transition to felsic volcanism a second cycle of andesite and rhyolitic volcanism and sedimentation represented by the temporal and bathtub formations was dated at 151 5 2 ma by the whole rock rb sr isotopic method compared to previous age estimates our results suggest an earlier initiation of arc magmatism in this part of the cordillera apparently by the late triassic this area was already an uplifted continental arc margin analogous to the present day andes shedding volcanic material to what is now the colorado plateau the volcanic rocks we dated fall within the range of ages measured for cobbles of similar lithology from the upper triassic chinle formation in the colorado plateau therefore it is not necessary to invoke the tectonic removal of an early mesozoic arc terrane along the proposed mojave sonora megashear

surface features of sand grains from the australian continental dunefield post depositional features dominate the surfaces of sand grains from the australian continental dunefield variations in the type and form of these features are evident among dunefields and also within individual desert regions these variations are used to differentiate between sediment sources and to provide evidence for the means of sediment transport into the deserts chemically precipitated features observed include previously unreported forms and are interpreted in terms of the environmental and climatic characteristics of the sand source regions these forms here termed type i sheet precipitation and type ii plate precipitation are believed to be intimately associated with the absence or presence respectively of significant quantities of clay or clay pellets within the dune system in the absence of clay the re precipitation of silica from pore waters leads to the formation of type i precipitated sheets type ii plate precipitation results when grain surfaces covered by clay coatings are overlain by a secondary cover of type i precipitated sheets such a cover would act as a resistant barrier to chemical attack and therefore protect the clay coatings from removal polygonal cracking found associated with type ii precipitation results from the dehydration of these underlying clay layers causing the disintegration of their silicate lattice structure the predominance of chemically produced surface features and the poorly rounded and irregular nature of most grains indicate that the majority of sand in the australian continental dunefield is currently stabilised and has not been transported long distances during its sedimentary history

reply to comment by robert f butler steven r may and david r bazard on high latitude paleomagnetic poles from middle jurassic plutons and moat volcanics in new england

back arc basin origin for the east sulawesi ophiolite eastern indonesia the east sulawesi ophiolite is one of the three largest ophiolites in the world it displays all the components of a typical sequence from residual mantle peridotites to cumulate gabbros sheeted dolerites and lavas of normal mid oceanic ridge basalt morb composition trace element data on the lavas and dolerites and particularly their depletion in nb compared to neighboring incompatible elements suggest a subduction zone environment for their origin the chemical similarity between the east sulawesi ophiolite lavas and those from the eocene celebes sea back arc basin crust together with their identical age strongly suggest a back arc tectonic environment for this ophiolite which represents a fragment of the eurasian plate obducted onto the east sulawesi basement of australian origin

short wavelength high amplitude gravity anomalies around the banda sea and the collapse of the sulawesi orogen abstract in eastern indonesia high density ophiolitic rocks outcropping on islands surrounding the banda sea are in many cases associated with strong gravity anomalies and steep gravity gradients however the relationships are not always straightforward bouguer gravity levels and gradients over the extensive east sulawesi ophiolite are generally relatively low although short wavelength high amplitude anomalies indicate rapid changes in thickness of high density rocks in a few places in the banda arc most local positive anomalies due to ophiolites are superimposed on a steep regional gravity gradient but in one case in western seram there is a distinct and important spatial separation between the two on buru west of seram a gradient of more than 10 mgal km testifies to the presence of very dense rocks in the near subsurface despite the absence of ophiolites in the outcrop gravity variations and ophiolite distribution around the banda sea are compatible with extension having occurred in the sulawesi region following and as a result of oligo miocene collision with an australian derived microcontinent similar histories have been proposed for many mediterranean deep basins of similar size shape and character and emplacement of some of the high density masses in the banda arc has probably resembled at least the later stages in the emplacement of peridotite massifs in the rif betic belt in both areas the present close association of the ultramafic rocks and their associated local anomalies with a strong regional gravity gradient is largely coincidental

paleomagnetism of late jurassic rocks in the northern canelo hills southeastern arizona the canelo hills volcanics are exposed in the canelo hills a northwest trending range in santa cruz county southeast arizona the formation is composed of silicic tuffs and flows as well as volcaniclastic conglomerates and sandstones strikes of the rocks are generally to the northwest with moderate dips to the southwest and northeast apparent age results from the sequence studied paleomagnetically include two published isotopic dates of 147 6 ma k ar biotite and 149 11 ma whole rock rb sr and a rb sr isochron age reported here which indicates an age of 151 2 ma paleomagnetic samples were collected from 17 cooling units in the northern canelo hills samples from most of these units responded to alternating field af demagnetization and secondary components were generally erased by peak af between 10 and 50 mt samples from five sites showed no response to af demagnetization thermal demagnetization of samples from these units produced no significant changes in direction of natural remanent magnetization nrm although within site clustering of nrm directions was improved data from two sites were rejected because of failure to isolate a well determined characteristic nrm of the remaining 15 sites 10 sites were of normal polarity while five sites showed reversed polarity intensities of the characteristic nrm ranged from 4 10 3 to 3 10 1 a m the data from these 15 cooling units yield a formation mean direction of i 29 9 d 334 9 with k 33 4 and 95 6 7 the resulting paleomagnetic pole is at 62 2 n 130 3 dp 4 1 dm 7 4 this pole is between poles obtained from the summerville and lower morrison formations the canelo hills pole is thus consistent both in position and age with the late jurassic episode of rapid apparent polar wander originally defined by paleomagnetic data from the summerville and morrison formations

paleomagnetism of the roskruge and gringo gulch volcanics southeast arizona paleomagnetic data were obtained from nine cooling units of the late cretaceous 72 ma roskruge volcanics and from 25 flows in the lower paleocene gringo gulch volcanics both from southeastern arizona alternating field demagnetization successfully erased the infrequent secondary components of magnetization the paleomagnetic pole position obtained from the roskruge volcanics is at 73 6 n 176 0 e with dp 6 2 and dm 8 8 the gringo gulch volcanics pole position is at 77 0 n 201 0 e with dp 1 2 and dm 1 7 in conjunction with other recently published paleocene and eocene paleomagnetic poles these data provide details of north american apparent polar wander during the laramide orogeny 80 to 40 ma an episode of rapid apparent polar wander from the cretaceous pole position in the bering strait to the eocene pole position near the present rotation axis occurred during that interval of time the initiation of this episode of apparent polar wander appears to be coincident with the major plate reorganizations which occurred at the onset of the laramide orogeny

hydrology of lake eyre australia el nino link abstract all major ephemeral rivers of australia lie in the lake eyre basin dry for years on occasions they carry enormous floods with annual volumes of 40 km 3 and instantaneous discharges of the order of 30 000 m 3 s 1 mean annual runoff of the basin is 4 km 3 or 3 5 mm significantly less than the 57 mm for the whole of australia this paper examines lake eyre and its drainage basin describing the historical hydrology of the catchment both in terms of instrument records and inflows hindcast using a model based on the technique of coral fluorescence palaeohydrological reconstruction coral fluorescence is a function of nearby river discharge and can be used to reconstruct annual river outputs reconstruction coral fluorescence is a function of nearby river discharge and can be used to reconstruct annual river outputs beyond the instrument period the burdekin river catchment runoff history is strongly paralleled by the volumes of lake eyre inflows during the period of common reliable instrument gaugings the burdekin runoff data have been extended back to 1735 a d using the correlation between river discharge and annual growth band fluorescence in an old coral from pandora reef off the north queensland coast for the instrument period 1952 to 1980 73 of the variance between coral fluorescence and burdekin discharge is common during the period 1949 1980 41 of the variance between coral fluorescence and lake eyre inflow data is common modelled inflows to lake eyre for the period 1885 1948 are based on the latter data set

carboniferous through jurassic paleomagnetic data and their bearing on rotation of the colorado plateau small yet systematic differences between paleomagnetic poles derived from strata on the colorado plateau and paleopoles determined from rocks on the north america craton have been interpreted to support the hypothesis of modest post late cretaceous clockwise rotation of the plateau as a quasi rigid body with respect to the craton using an iterative search for the best fit euler pole and rotation angle comparison of the best quality late carboniferous through late jurassic paleomagnetic poles from the colorado plateau and the north america craton gives a cumulative rotation estimate based on a rotation pole at 34 n 105 w of 7 4 3 8 95 confidence limits a similar comparison using subsets of the cratonic database from localities in 1 northeast north america and 2 the craton platform interior give larger 8 8 3 6 and smaller 5 1 3 8 estimates respectively reflecting the fact that poles from localities in northeast north america in particular those from triassic rift basins indicate a larger rotation as concluded in direct pole to pole comparisons the euler pole as determined by the paleomagnetic data only can lie anywhere within a relatively large area that encompasses locations in the western united states previously proposed from geological observations paleomagnetic data and geologic observations together or independently do not support the hypothesis of a large colorado plateau rotation of 11 to 15 if geologically reasonable previous estimates of significant 20 km dextral slip along the eastern margin of the plateau require a position for the euler pole east of the 105 w meridian

the structural evolution of the timor collision complex eastern indonesia abstract the structural style of timor is consistent with foreland fold belt processes and zones of frontal accretion and underplating can be recognized in the australian parautochthonous sequence the parautochthon is overlain by an allochthonous sequence which corresponds to the pre collisional oceanic forearc in northern timor the parautochthon has been underplated directly beneath the allochthonous basement unlike previous interpretations of timor in terms of foreland fold belt processes the timor foldbelt is here interpreted as having evolved in a fairly straightforward way from the pre collisional forearc by the sequential addition of thrust slices of australian continental crust to the front and base of the developing collision complex

new features from the romblon island group key to understanding the arc continent collision in central philippines abstract a complete ophiolite sequence and melange are reported for the first time in the romblon island group located at the central part of the philippine archipelago the study area comprises tablas romblon and sibuyan islands built on amalgamated crust and mantle rocks that are typically fault bounded and stratigraphically disrupted the sibuyan ophiolite complex soc consists of harzburgite and dunite layered clinopyroxenite layered and isotropic gabbro diabase dike swarm and basaltic andesitic pillow lava and flow deposits a jurassic cretaceous age of formation and late early miocene age of emplacement are suggested for the soc by available data emplacement of these crust mantle units is believed to have been facilitated through displacements along east verging thrust faults developed consequent to the early miocene arc continent collision in central philippines along with recent k ar isotopic ages 12 ma obtained for some of the metamorphic rocks in the area these lithologic units and structural features provide critical information regarding the arc continent collision which is one of the significant events in the evolution of the philippine island arc system the usefulness of potential field geophysical methods to studying lithologic and structural relationships in an extremely disrupted terrane is evaluated in this study observed variations in gravity and magnetic values correlated with lithologic distributions and geologic structures higher relative bouguer and magnetic anomalies are observed over members of the complete ophiolite sequence and younger igneous materials exposed in tablas and sibuyan islands their geophysical characteristics contrast markedly with the less dense and magnetically inferior sedimentary rocks exposed only on tablas island on the other hand metamorphic units in tablas romblon and sibuyan islands display variable magnetic and gravity signatures that reflect differences in composition and alteration or weathering thrust faults related to the emplacement of the ophiolite as a result of the collision are inferred from sudden changes in gravity and magnetic values

tl chronology and stratigraphy of riverine source bordering sand dunes near wagga wagga new south wales australia abstract riverine source bordering dunes are found throughout the murray basin of southeastern australia at the eastern and northern margins of late quaternary palaeochannels the dunes are dominated by locally derived sand but often contain a minor calcareous clay component originating from a distant westerly source in the bedrock confined valley of the murrumbidgee river near wagga wagga the dunes occur as discrete mounds on the floodplain or as drapes over the marginal valley side slopes tl dating of three stratigraphic units within the dunes shows that phases of sand accumulation occurred between 15 and 25 ka in oxygen isotope stage 2 clarendon unit between 35 and 60 ka in stage 3 glenfield unit and between 80 and 120 ka in stage 5 yarragundry unit the tl ages here which show excellent agreement with those determined respectively for the yanco kerarbury and coleambally phases of palaeochannel activity on the riverine plain j quat sci 11 1996 311 extend the emerging regional model of late quaternary climatic and hydrologic change for southeastern australia

rise and fall of the eastern great indonesian arc recorded by the assembly dispersion and accretion of the banda terrane timor abstract new age petrochemical and structural data indicate that the banda terrane is a remnant of a jurassic to eocene arc trench system that formed the eastern part of the great indonesian arc the arc system rifted apart during eocene to miocene supra subduction zone sea floor spreading which dispersed ridges of banda terrane embedded in young oceanic crust as far south as sumba and timor in timor the banda terrane is well exposed as high level thrust sheets that were detached from the edge of the banda sea upper plate and uplifted by collision with the passive margin of nw australia the thrust sheets contain a distinctive assemblage of medium grade metamorphic rocks overlain by cretaceous to miocene forearc basin deposits new u pb age data presented here indicate igneous zircons are less than 162 ma with a cluster of ages at 83 ma and 35 ma 40ar 39ar plateau ages of various mineral phases from metamorphic units all cluster at between 32 38 ma these data yield a cooling curve that shows exhumation from around 550 c to the surface between 36 28 ma after this time there is no evidence of metamorphism of the banda terrane including its accretion to the edge of the australian continental margin during the pliocene these data link the banda terrane to similar rocks and events documented throughout the eastern edge of the sunda shelf and the banda sea floor

the tectonic emplacement of sumba in the sunda banda arc paleomagnetic and geochemical evidence from the early miocene jawila volcanics the island of sumba is a continental fragment in the fore arc region near the transition between the sunda arc and banda arc in southeastern indonesia paleomagnetic and geochemical evidence from the early miocene volcanics of the jawila formation in western sumba constrain the final drift stage and tectonic emplacement of the island the lavas range from predominantly andesites to dacites and display textural evidence for a weak metamorphism rock magnetic and mineral chemical data point to pseudo single to multi domain titanojmagnetite fe ti o with grain sizes up to 10 pm as the main carrier of remanence the jawila formation reveals a chrm direction with declination 4 6 inclination 19 2 c 9 9 and a paleolatitude of 9 9 s which corroborates earlier results chamalaun and sunata 1982 taking paleomagnetic evidence from other formations on the island into account we conclude that the sumba fragment has occupied approximately its present position since the miocene the talc alkaline affinity and trace element signatures of the lavas point to an origin in an arc environment this occurrence of subduction related volcanic activity in the early miocene on sumba implies that a volcanic arc existed south of the present day east sunda arc or that the island was located within the latter arc between sumbawa and eastern flores and still had a minor southward drift to cover

a dual doubly vergent orogen in the banda arc continent arc collision zone as observed on deep seismic reflection profiles new deep seismic reflection profiles across the banda arc of indonesia reveal reflectors in the uppermost 50 km of the lithosphere combined with existing earthquake hypocenter locations and focal mechanisms the new structural geometries inferred from the reflectors yield a more complete analysis of deformation during the past 10 m y and provide insights into how strain is partitioned across an orogenic belt in which volcanic arcs and continents converge a clearly defined wadati benioff zone and recent deformation of shelf sediments observed on older shallow seismic profiles indicated to previous workers that substantial convergence occurred at the timor trough a few focal mechanisms seafloor escarpments and recent geodetic surveying indicate that convergence at 7 cm yr 1 currently last 200 kyr occurs at the northern margin of the now inactive volcanic arc the wetar thrust zone reflectors on the new seismic profiles are interpreted as thrust faults and folds that occur throughout the crust and within the uppermost mantle between the timor trough and wetar thrust specifically basement reflectors beneath the toe of the accretionary complex have reverse sense offsets that imply blind thrusts the whole crust is horizontally shortened not only the sedimentary cover rocks that previously deformed into duplexes above a decollement reflectors dipping away from both margins of the forearc basin and at the northern margin of the volcanic arc are interpreted as evidence of thrusting thus each arc represents a doubly vergent fold and thrust belt but only the northern one is currently active crustal thicknesses inferred from seismic velocities reflectors and gravity anomalies are consistent with the merging of a thinned continental shelf margin with oceanic lithosphere to form an orogenic belt with at present 3 4 km of topographic relief in the region of eastern timor

a new late cretaceous paleomagnetic pole from the adel mountains west central montana north america s apparent polar wander path has been poorly defined between the mid cretaceous and paleocene reference pole positions existing data allowed 13 of apparent polar motion over about 22 m y 87 65 ma roughly coinciding with the beginning of laramide deformation 80 ma we report on a paleomagnetic study of the adel mountain volcanic rocks to refine the north american apparent polar wander path for this interval the shonkinite rocks of the adel mountain volcanic field are on the eastern edge of the cretaceous paleocene fold and thrust belt some of these structures disturb the western edge of the volcanic pile we obtained two new k ar dates from the adel rocks one date on biotite from a shonkinite dike that crosscuts most of the volcanic rocks is 71 2 2 7 ma the other a whole rock date from a flow deep in the volcanic pile is 81 1 3 5 ma we collected six to nine paleomagnetic samples from each of 34 sites in roadcuts and natural outcrops of flows dikes and laccoliths positive fold and conglomerate tests along with alternating field and thermal demagnetization indicate that our characteristic remanent directions are primary magnetizations acquired before late cretaceous to paleocene thrust belt deformation averaging the virtual geomagnetic poles from 26 reliable sites all of normal polarity yields a paleopole at 82 2 n 209 9 e 95 6 80 k 18 38 this pole is concordant with the paleocene reference pole 82 0 n 170 2 e 95 3 5 k 18 6 diehl et al 1983 and is 11 6 from the globerman and irving 1988 mid cretaceous pole at 71 n 196 e the youngest information in the cretaceous stillstand pole is from the niobrara formation shive and frerichs 1974 at about 85 89 ma if we take the average age of the adel mountain volcanics to be 76 ma then 12 of apparent polar motion occurred between 87 ma and 76 ma thus rapid apparent polar motion correlates well with the onset of laramide deformation

emplacement of the east sulawesi ophiolite evidence from subophiolite metamorphic rocks abstract a newly discovered high temperature metamorphic sole at the base of the extensive east sulawesi ophiolite in sulawesi indonesia yields new structural and petrological data with which to constrain the emplacement history the metamorphic sole is composed of a thin sequence of garnet and epidote amphibolite and basal greenschist metaclastics east dipping tectonite fabrics in the metamorphic sole amphibolite are coincident with those in subjacent basement mica schist and superjacent peridotite and indicate orthogonal east to west emplacement of the ophiolite in central sulawesi metabasite in the upper levels of the sole has morb geochemical characteristics was recrystallized at temperatures of about 700 c and yielded k ar radiometric ages of approximately 30 ma initial detachment of the ophiolite probably occurred at a ridge segment transform intersection in a back arc basin at the south east margin of sundaland detachment closely preceded nw directed overthrusting and orthogonal obduction on to the sundaland continental margin in the oligocene sinistral movement on a paleo transform boundary now the lawanopo fault may have facilitated obduction although the westernmost segments of ophiolite may represent younger more proximal slices of a marginal basin those further east probably represent successively older more distal slices of underthrust indian ocean back arc or forearc

jurassic paleopole controversy contributions from the atlantic bordering continents the early early middle jurassic and early cretaceous mean paleopoles for north america europe south america and africa are very well grouped in appropriate continental reconstructions but the intervening late middle and late jurassic segment of the apparent polar wander path apwp is poorly defined and controversial the available paleopoles reconstructed for the partial opening of the central atlantic ocean form a scattered grouping with no coherent age patterns illustrating that they do not constitute a robust data set uncertainties in the reconstruction parameters between north america and europe also play a role however excellent paleomagnetic results exist for tectonic elements near the margin of west gondwana that are unlikely to have been significantly displaced with respect to cratonic africa and south america these results have not previously been used for apwp reconstructions because local rotations are thought to have deflected the paleopoles in many cases the inclinations of such results however can be used to determine a locus of paleopole positions paleopole loci for about 150 and 170 ma were determined from results from spain italy lebanon and the chilean andes and these were rotated with appropriate parameters to give locus intersections in north american coordinates a late middle jurassic early callovian best estimate of the paleopole in north american coordinates is located at about lat 70 n long 135 e and a late jurassic kimmeridgian best estimate is located at about 70 n 155 e the resulting jurassic early cretaceous apwp follows roughly the 70th parallel passing through the middle of the scattered individual paleopoles from the cratonic parts of the atlantic bordering continents

neogene history of bone gulf sulawesi indonesia abstract bone gulf is one of the inter arm basins of the unusual k shaped island of sulawesi its age character and origin are disputed this study is based on recently acquired 2d seismic lines seabed multibeam mapping and limited well data and is linked to stratigraphy on land the gulf is probably underlain by pre neogene volcanogenic sedimentary metamorphic and ultramafic rocks and includes crust of australian origin we favour basin initiation in the miocene rather than eocene by extension associated with strike slip deformation the main basin trends n s and is divided into several sub basins and highs the highs segment the gulf and their wnw ese orientations reflect pre neogene basement structures they are interpreted as strike slip fault zones active at different times in the neogene a southern high was active relatively early whereas further north there is evidence of young displacements during the late neogene these are visible on the seabed above a high linked to the kolaka fault on land early basin bounding faults are oriented nnw sse and record extension and strike slip movements like the sub parallel walanae fault of south sulawesi which can be traced offshore into extensional faults bounding the young and narrow selayar trough sediment in the basins came mainly from the north with contributions from both west and east carbonate deposits formed at the margins while deeper marine sediments were deposited in the axial parts of the gulf an early pliocene unconformity can be mapped across the study area marking major uplift of sulawesi and subsidence of bone gulf this regional event caused major influx of clastic sediments from the north development of a southward flowing canyon system and back stepping and drowning of carbonates at the basin margins hydrocarbons are indicated by seeps and bone gulf has potential sources reservoirs and seals but the complex faulting history is a risk

a neogene back arc origin for the banda sea basins geochemical and geochronological constraints from the banda ridges east indonesia abstract dredgings conducted during the french indonesian cruises banda sea ii and iii collected volcanic rocks from several ridges of the banda sea area tukang besi ridge site 218 lucipara ridge sites 214 and 305 nieuwerkerk emperor of china sites 219 and 220 with the exception of one 46 ma old n morb type basalt thought to belong to an ophiolitic complex k ar and ar ar datings indicate that all the dredged volcanics are neogene they range in age from ca 10 ma tukang besi back arc basalts to 8 7 ma nieuwerkerk emperor of china calc alkaline andesites and to 7 3 ma lucipara oib type transitional basalts and cordierite bearing andesites radiogenic isotopic signatures of andesites are consistent with an afc assimilation coupled with fractional crystallization process involving assimilation of continental crust 8 3 ma old calc alkaline volcanic activity is also recorded on the wetar segment an inactive part of the east sunda arc and corresponding isotopic compositions are also consistent with an afc process involving continental crust these features suggest that lucipara nieuwerkerk emperor of china ridges and the wetar segment were representing a single volcanic arc 8 7 ma ago the corresponding calc alkaline activity was related to the subduction of the indian oceanic lithosphere beneath continental blocks of australian origin back arc opening processes occurred from 6 to 3 ma as a multi rift opening for the wetar basin and as a single rift opening for the damar basin while subduction related magmatism was still active in the wetar segment volcanic activity stopped at 7 ma in the nieuwerkerk emperor of china ridge on lucipara ridge 6 3 ma volcanic activity emplaced concomitantly transitional basalts and cordierite bearing andesites the mineralogical and chemical features of the latter are consistent with an afc process involving assimilation of continental crust by mantle derived basaltic magmas the end of magmatic activity on both volcanic segments at 3 ma is thought to result from the collision of timor with the wetar segment of the sunda arc

mantle lithosphere bodies in the alboran crustal domain ronda peridotites betic rif orogenic belt abstract geological and geophysical data are used to demonstrate the existence of intracrustal high density high p wave velocity bodies in the western betics these bodies appear to correspond to buried peridotites similar to those that outcrop in the ronda area a gravity study shows how the gravity field is mainly the result of a combined effect of crustal thinning and the presence of ultramafic bodies the size of the buried high density body as interpreted from gravity and seismic results shows maximum dimensions of about 40 km in length nnw sse about 8 km in thickness and a lateral extension ene wsw of about 70 km the thinning of the crust from 32 35 km to 20 22 km takes place in a narrow area less than 35 km wide our results are compatible with an interpretation in terms of an unrooted peridotite slab dismembering of an initial slab of ultramafic rocks is a possible consequence of the extensional regime that originated the alboran basin

remagnetization of jurassic volcanic rocks in the santa rita and patagonia mountains arizona implications for north american apparent polar wander paleomagnetic poles for the jurassic corral canyon sequence and glance conglomerate in southern arizona have been used to construct apparent polar wander apw paths for the north american plate but they are controversial and conflict with higher latitude poles from new england lower jurassic dacites and ash flow tuffs of the mount wrightson formation in the santa rita mountains were initially sampled to provide an additional paleopole for southern arizona these rocks however have a predominantly reversed polarity characteristic magnetization in situ i 47 d 154 95 9 which is statistically indistinguishable from that for the nearby latest cretaceous elephant head pluton i 48 d 165 95 8 although magnetizations of both polarities are observed in the ash flow tuffs they are mostly carried by hematite and dual polarity components are observed within some specimens moreover widespread mineralization and a k ar age of 67 ma for altered rocks of the mount wrightson formation imply that these rocks were subjected to a prolonged episode greater than one polarity interval of low temperature alteration and remagnetization middle jurassic ash flow tuffs of the corral canyon sequence in the patagonia mountains to the south have a similar geologic setting they are exposed along strike amid mineralized rocks on the eastern flank of a mountain range cored by paleocene intrusions hematite is also the dominant remanence carrier in most of the corral canyon sequence and its predominantly normal polarity direction in situ i 51 d 326 95 9 is indistinguishable from that for the nearby patagonia granodiorite i 49 d 342 95 8 rocks of the corral canyon sequence therefore are likely remagnetized as well problems also exist with the glance conglomerate pole these rocks are situated within a caldera structure and have been potassium metasomatized this potassic alteration could have occurred shortly after emplacement or at a later time postdeformation the low latitude jurassic apw path for north america and j 2 cusp therefore are not well supported and may need revision

mantle core complexes and neogene extensional detachment tectonics in the western betic cordilleras spain an alternative model for the emplacement of the ronda peridotite abstract an alternative model for the emplacement of the ronda peridotite betic alpine orogenic belt southern spain is proposed involving mantle uprising during a major neogene extensional event the development of a detachment system and its further evolution by isostatic rebound and upward arching would have triggered the tectonic denudation of these ultramafic bodies forming what may be termed mantle core complexes mantle core complexes would represent a final step in the core complex forming processes once a complete separation of the upper and lower blocks has been achieved in a detachment system marking probably the transition from an intracontinental to a proto oceanic rift environment

late cretaceous paleomagnetism of the tucson mountains implications for vertical axis rotations in south central arizona the tucson mountains of southern arizona are the site of an upper cretaceous caldera from which the rhyolitic cat mountain tuff was erupted at about 72 ma two magnetic units within the cat mountain tuff are distinguished by paleomagnetic data in both the northern and southern tucson mountains the resurgent amole pluton 72 ma in the northern tucson mountains was emplaced soon after eruption of the cat mountain tuff but cooled and was magnetized after northeastward tilting 50 85 of the adjacent caldera fill sequence petrologic and paleomagnetic data indicate that the lower magnetic unit of the cat mountain tuff caps the silver bell mountains to the northwest a previous paleomagnetic investigation n 34 indicates that the silver bell mountains have been rotated clockwise 30 16 95 confidence level about a vertical axis relative to cratonic north america a similar paleomagnetic study of upper cretaceous volcanic volcaniclastic and intrusive units in the tucson mountains n 26 indicates that these rocks have been rotated 7 14 clockwise relative to stable north america a direct comparison of paleomagnetic directions for the lower unit of the cat mountain tuff shows a 17 10 clockwise rotation between the silver bell mountains and the tucson mountains which supports the relative accuracy of the absolute rotations determined for these two mountain ranges preliminary paleomagnetic directions for middle tertiary units from the silver bell and tucson mountains are consistent with clockwise rotation having occurred prior to deposition of these rocks clockwise rotation of crustal blocks in southern arizona likely was associated with strike slip movement on major northwest trending faults in the region and this movement may have been related to oblique subduction of oceanic plates along the western continental margin in late cretaceous and early tertiary time the available paleomagnetic data indicate that rocks in southern arizona have not remained unrotated with respect to north america since late cretaceous time and that vertical axis rotations may have played an important role in the region during laramide deformation

a middle carnian to early norian 225 ma paleopole from sediments of the newark basin pennsylvania paleomagnetic study of the middle carnian stockton formation upper carnian lockatong formation and the lower part of the norian passaic formation from 24 sites along 3 traverses perpendicular to strike in the newark basin of eastern pennsylvania shows that two hematitic magnetizations can be isolated from these rocks thermal demagnetization experiments reveal a distributed unblocking temperature typically 300 to 680 c magnetization with uniformly downward and northerly directions and a high unblocking temperature 660 c and above magnetization with shallow northerly normal polarity and southerly reversed polarity directions on the basis of a correlatable magnetic polarity stratigraphy between 3 traverses spanning 40 km along strike and within site directional scatter similar to that expected from paleosecular variation the high temperature magnetization was most probably acquired at or near the time of deposition the pole calculated from the high unblocking temperature magnetization 53 6 n 101 6 e a95 4 8 is consistent with other late triassic poles and indicates a paleolatitude of 3 8 n 3 0 the lower unblocking temperature magnetization is an overprint acquired at about the same time as the jurassic newark trend igneous n2 pole magnetization

late cretaceous paleomagnetism and clockwise rotation of the silver bell mountains south central arizona late cretaceous ash flow volcanism in the silver bell mountains of southern arizona 32 3 n 248 5 e was associated with caldera formation and porphyry copper mineralization oriented samples from 34 sites in volcanic volcaniclastic and intrusive units related to this episode of igneous activity 73 69 ma yield a mean paleomagnetic direction of i 61 2 d 24 0 95 7 6 primary remanent magnetizations are indicated by the presence of both normal and reversed polarities and by the significantly improved grouping 95 confidence level of site mean directions for a widespread tuff unit after structural correction a comparison of this direction with a direction at silver bell calculated from contemporaneous units for stable north america i 58 8 d 342 3 95 7 7 indicates a late cretaceous paleolatitude anomaly of 2 4 7 6 not significant at the 95 confidence level and a declination anomaly of 41 7 14 3 for the silver bell mountains previously determined paleomagnetic data for southeastern arizona suggest that this apparent clockwise rotation in the silver bell mountains is a local phenomenon although preliminary the average paleomagnetic direction for oligocene and lower miocene rocks in the silver bell area i 43 8 d 357 3 95 16 5 is similar to that calculated for stable north america i 50 2 d 352 2 95 3 9 implying that the observed rotation in the silver bell mountains occurred before 26 ma and was most likely associated with dextral strike slip movement along the ragged top and related wnw trending faults bounding the silver bell mountain block these data in conjunction with plate reconstructions and other paleomagnetic data from southwestern north america imply that wnw trending strike slip faults may have played an important role during late cretaceous to early tertiary deformation in southern arizona

paleomagnetism of three upper jurassic ash flow sheets in southeastern arizona implications for regional deformation a sequence of three petrologically distinct upper jurassic ash flow tuffs has been sampled for palcomagnetic analysis in the huachuca mountains canelo hills and mustang mountains of southeastern arizona site mean palco magnetic directions for these units indicate significant ver tical axis rotations between sampling localities 15o 40o and a comparison of these and previously published data with reference directions from the colorado plateau implies that the jurassic rocks in southeastern arizona have been rotated in a clockwise sense with respect to stable north america these new data are consistent with palcomagnetic results showing clockwise rotation of upper cretaceous rocks in south central arizona and further indicate that studies of north american apparent polar wander based on rocks from southern arizona could be subject to error the clockwise rotations in southern arizona are likely related to late cretaceous and early tertiary strike slip movement on northwest trending high angle faults in the region and this movement may be linked to an increase in oblique farallon north american plate conver gence at that time

aeolian and fluvial evidence of changing climate and wind patterns during the past 100 ka in the western simpson desert australia abstract sediments near finke in central australia provide evidence of late quaternary evolution and the interaction of aeolian and fluvial systems in response to changing climate in the western simpson desert thermoluminescence tl dating is used to develop a chronology of aeolian and alluvial activity and to identify differences in sand provenance quaternary alluviation in the finke valley at this location occurred at or prior to c 90 ka and with no surviving evidence of subsequent activity until the holocene in contrast to rivers in the eastern part of the lake eyre basin substantial alluviation took place here in the early to mid holocene probably due to reactivation of the northern monsoon and its partial penetration into central australia the regional dunefield near finke consists of linear dunes largely reworked and aligned during the last glacial 30 12 ka as part of the great anticlockwise whorl of dunes in central australia the oldest dated source bordering dunes from the finke river are bright red in colour were deposited at c 100 ka and are now buried beneath paler source bordering dunes the latter consist of two exposed units a lower one of unknown orientation that dates at 17 9 ka and an upper unit aligned to the northwest and parallel to the prevailing winds that dates at 5 0 ka the tl signature and sediment texture of the oldest source bordering dunes show them to have probably been derived from weathered alluvial red beds of similar or greater age nearby and to have contributed abundant sand to the regional dunefield immediately north of the river in contrast sand from the younger paler source bordering dunes appears to be from a different source and to have only recently extended into the regional field the finke region would seem to be in a pivotal position for the study of palaeowind patterns that have created and modified australia s whorl of continental dunes the 30 18 ka regional linear dunes near finke are oriented almost due north their cross sectional asymmetry steeper eastern slopes suggests a response to southwesterly or westerly sand transporting winds between 18 and 10 ka these winds appear to have shifted to their present southeast orientation during the past 5 ka from dune ages alignments and asymmetry it is proposed here that there was a northward shift in the wind pattern at finke by about 100 150 km 1 1 5 of latitude during the last glacial but that through this period the regional dune pattern has remained remarkably stable

tertiary tectonic and magmatic evolution of western sulawesi and the makassar strait indonesia evidence for a miocene continent continent collision

comment on high latitude paleomagnetic poles from middle jurassic plutons and moat volcanics in new england and the controversy regarding jurassic apparent polar wander for north america by mickey c van fossen and dennis v kent

thermoluminescence dating study of quartz in aeolian sediments from southeastern australia abstract using 90 125 m grains of quartz extracted from sediments the equivalent dose absorbed since burial was derived by exposing aliquots of quartz to a sunlamp regenerating the tl growth curve by artificial irradiation and comparing the natural tl of the sample being dated as well as that of an adjacent surface sample to this curve the age can then be calculated once the dose rate is known the method is tested successfully on known age aeolian sediments retaining their original bedding but reveals some difficulties in trying to use tl to date aeolian sediments for which the original bedding has been destroyed anomalous fading of tl in quartz is reported this latter difficulty was circumvented by using a delay of several weeks between the irradiation and heating of the quartz

jurassic ash flow sheets calderas and related intrusions of the cordilleran volcanic arc in southeastern arizona implications for regional tectonics and ore deposits volcanologic petrologic and paleomagnetic studies of widespread jurassic ash flow sheets in the huachuca southern dragoon mountains area have led to identification of four large source calderas and associated comagmatic intracaldera intrusions stratigraphic facies and contact features of the caldera related tuffs also provide constraints on the locations lateral displacements and very existence for some major northwest trending faults and inferred regional thrusts in south eastern arizona for example the intricate cochise thrust system as mapped by others in the southern dragoon mountains consists instead of primary depositional contacts within caldera fill megabreccia and the inferred regional thrusts do not exist at least as previously interpreted silicic alkalic compositions of the jurassic caldera related ash flow tuffs bimodal associated mafic magmatism and interstratified coarse sedimentary deposits provide evidence for synvolcanic extension and rifting within the cordilleran magmatic arc gold copper mineralization is associated with subvolcanic intrusions at several of the jurassic calderas

comparative uranium thorium and thermoluminescence dating of weathered quaternary alluvium in the tropics of northern australia abstract thermoluminescence tl age determinations of alluvial sediments in the tropics are evaluated by comparison with u th age determinations of pedogenic accumulations in the alluvium of the lower gilbert river a large fan delta in the wet dry tropics of northern queensland australia this study extends u th dating by applying it not only to calcretes but also to fe mn oxyhydroxide oxide accumulations while a direct correlation cannot be made between u th dates from secondary minerals and tl dates from the host sediments both sets of data show broad consistency in addition to providing a minima for acceptable tl ages u th dates are useful for determining the chronology of pedogenesis diagenesis they show that calcretes and ferricretes have formed under similar climatic conditions in the wet dry tropics of northern australia during the late pleistocene beneath about 5 12 m the gilbert fan delta consists of an extensive sand body older than 85 000 yr and probably about 120 000 yr in age representative of a period of major fluvial activity not repeated since this time above are muds and fine sandy muds that extend uninterrupted to the present surface except in the downstream fan where they are bisected by a thin unit of medium sand that tl dates at 40 000 50 000 yr b p a system of sandy distributary channels over the fan surface represents an early holocene fluvial phase probably more active than at present

paleomagnetism of the middle jurassic summerville formation east central utah the paleomagnetism of the late callovian summerville formation was analyzed to obtain a late middle jurassic paleomagnetic pole for north america a total of 281 samples were collected from 35 sedimentary horizons sites in a single locality in the san rafael swell area of east central utah fifteen site mean characteristic remanent magnetization chrm directions pass the reversals test and define at least five polarity zones within 52 m of stratigraphic section suggesting that the chrm was acquired upon or soon after deposition magnetizations of some specimens are complex and several horizons yield anomalous site mean directions data analysis included filtering to provide different combinations of virtual geomagnetic poles for calculation of the paleomagnetic pole however editing the data did not change the pole position by more than 5 the preferred paleomagnetic pole position is 56 3 n 133 4 e a95 7 2 n 11 sites the summerville formation paleomagnetic pole is located near the 172 ma corral canyon pole and is statistically indistinguishable from the 151 ma glance conglomerate and 149 ma lower morrison poles the paleomagnetic pole from the summerville formation is located at a much lower latitude and more easterly longitude than the paleomagnetic pole obtained from the 165 ma moat volcanics of new england we propose that the jurassic north american apparent polar wander path is an age progressive band at 55 n to 65 n latitude extending from 11 e longitude at 172 ma to 150 e longitude at 149 ma

paleomagnetism of the chinle and kayenta formations new mexico and arizona paleomagnetic data were obtained from 22 sites 6 10 samples site in the upper shale member of the chinle formation 43 sites in the owl rock member of the chinle formation and 35 sites in the kayenta formation thermal demagnetization and data analyses indicate that within site dispersion is an important criterion for selecting sites which retain a high unblocking temperature characteristic remanent magnetization chrm site mean directions define at least four antipodal polarity zones within each member formation suggesting the chrm was acquired soon after deposition fifteen site mean virtual geomagnetic poles vgps from the upper shale member of the chinle formation yield an early norian paleomagnetic pole position of 57 4 n 87 8 e k 60 a95 5 0 eighteen site mean vgps from the owl rock member of the chinle formation yield a middle norian paleomagnetic pole position of 56 5 n 66 4 e k 183 a95 2 6 twenty three site mean vgps from the kayenta formation yield a pliensbachian pole position of 59 0 n 66 6 e k 155 a95 2 4 combined with paleomagnetic poles from the moenave formation and the shinarump member of the chinle formation these data record 30 m y of north american apparent polar wander apw within a regional stratigraphic succession during the camian and norian stages of the late triassic chinle poles progress westward during the hettangian through pliensbachian stages of the early jurassic the pattern of apw changed to an eastward progression even after correction for 4 clockwise rotation of the colorado plateau a sharp comer in the apw path j1 cusp is resolved near the pole from the hettangian sinemurian 200 ma moenave formation 59 4 n 59 2 e amongst other implications the sharp change in the apw path at the j1 cusp implies an abrupt change from counterclockwise rotation of pangea prior to 200 ma to clockwise rotation thereafter

paleomagnetism of the late cretaceous early tertiary north central montana alkalic province paleomagnetic results have been obtained from the late cretaceous early tertiary igneous complexes of the north central montana alkalic province data from 94 sites in eocene volcanic and intrusive rocks give a paleomagnetic pole located at 82 0 n 170 2 e a95 3 5 k 18 6 while 36 sites in paleocene intrusions yield a paleomagnetic pole at 81 8 n 181 4 e a95 5 4 k 20 2 these poles differ by only 1 6 and are not significantly different statistically the 130 site virtual geomagnetic poles show no significant elongation and suggest no significant apparent polar wander apw during the period of magnetization of the igneous centers postmagnetization structural complications in these rocks are minimal the presence of a single predominant polarity in these intrusive complexes reinforces the radiometric age data that suggest that igneous activity within individual centers was of short duration the northcentral montana data together with other early tertiary cretaceous and mid tertiary paleomagnetic results require modification of our earlier apw chronology diehl et al 1980 it now appears that apw relative to north america since the early cretaceous consists of a polar still stand during much of the cretaceous 120 75 m y b p a period of rapid movement in latest cretaceous time 75 65 m y b p and a period of slow polar movement thereafter the onset of this period of rapid apw correlates well with a major change in plate motions at 80 m y and the beginning of the laramide orogeny

evolution of a multi vent volcanic complex within a subsiding arc graben depression mount wrightson formation arizona the mount wrightson formation in the santa rita mountains south of tucson arizona is a homoclinally dipping section of lower jurassic volcanic subvolcanic hypabyssal and lesser sedimentary rocks that is 4 5 km thick and crops out over a strike length of 25 km the nature and distribution of volcanic lithofacies in the mount wrightson formation are interpreted to record the evolution of a multi vent volcanic complex that formed within a subsiding cratonal intra arc graben these lithofacies are grouped into the following facies assemblages 1 the near vent facies assemblage consisting of silicic to intermediate hypabyssal intrusive bodies and peperites and dacite lava flows 2 the proximal facies assemblage containing intermediate lava flows ignimbrites and debris flow deposits 3 the medial facies assemblage comprising ignimbrites debris flow deposits and reworked pyroclastic deposits and 4 the distal facies assemblage including nonwelded ignimbrites and fluvial deposits these facies assemblages are characteristic of stratovolcano complexes in the mount wrightson formation however the paucity of debris flow deposits and the burial of near vent facies assemblages by ignimbrites suggest that the formation was deposited in a low relief multi vent complex with no high standing central edifice some of the thickest most densely welded ignimbrites in the mount wrightson formation probably represent outflow from a more distant calders or calderas within the intro arc graben rather than being products of volcanism within the multi vent complex intro arc subsidence resulted in a complex juxtaposition of vent proximal medial and distal facies as vent areas were repeatedly buried by debris derived from adjacent vents in the multi vent complex and to a lesser extent by debris from calderas outside the complex this subsidence resulted in accumulation and preservation of a thick section of terrestrial volcanic and sedimentary rocks the mount wrightson complex evolved from predominantly effusive lower member to predominantly explosive middle member followed by waning volcanism upper member rapid intra arc subsidence resulted in burial of vent areas by craton derived eolian quartz arenites correlative with either the wingate or navajo sandstones on the colorado plateau this was particularly important as volcanism waned

deposition of franciscan complex cherts along the paleoequator and accretion to the american margin at tropical paleolatitudes red radiolarian cherts from three localities within the franciscan subduction complex of northern california contain three components of remanent magnetization which are best isolated by progressive thermal demagnetization the first component usually removed by 300 c has an in situ direction similar to the present axial dipole field and is probably a recently acquired thermoviscous overprint a second component generally removed between 300 and 630 c has constant normal polarity and direction within each section and is interpreted to have been acquired by low temperature chemical alteration during subduction and accretion at the continental margin the third component isolated between 560 and 680 c has both normal and reversed polarities passes a fold test and is inferred to have been acquired during or soon after deposition the available paleomagnetic biostratigraphic and geochemical data indicate deposition of these cherts along the paleoequator 0 2 n or s paleolatitude between pliensbachian and oxfordian time as the oceanic plate moved eastward relative to north america beneath the equatorial zone of high biologic productivity between bathonian and cenomanian time the chert sequences apparently moved progressively away from the paleoequator 2 15 n or s and were soon after accreted to the american continental margin plate reconstruction models for the farallon plate corroborate low paleolatitude trajectories from ridge crest to subduction zone for example from 3 s to 11 n and they imply subsequent northward translation of the franciscan complex 4 000 km by strike slip faulting related to relative motions between the farallon kula pacific and north american plates

paleomagnetic reconnaissance of early mesozoic carbonates from williston lake northeastern british columbia canada evidence for late mesozoic remagnetization three classic sections of middle and late triassic fossiliferous limestones cropping out around williston lake in british columbia canada were sampled for paleomagnetic study the objective was to test the suitability of these units for detailed magnetobiostratigraphic study with the aim of improving the reference triassic geomagnetic polarity time scale the williston lake characteristic magnetizations differ however from any triassic north america cratonic reference directions a satisfactory agreement is found instead with cretaceous early cenozoic north america cratonic reference directions the exclusive occurrence of normal polarity suggests that remagnetization likely occurred during the cretaceous long normal superchron remagnetizations may have been triggered by connate brines which moved along aquifers of porous sandstones and carbonates in the early stages of laramide folding resume trois sections fossiliferes classiques de calcaires trias moyen et tardif affleurant autour du lac williston en colombie britannique ont ete echantillonnees pour une etude paleomagnetique l objectif etait de s assurer de la pertinence de ces unites pour une etude magneto bio stratigraphique detaillee visant a ameliorer l echelle referentielle de temps de la polarite geomagnetique au trias les magnetisations caracteristiques du lac williston different toutefois de toute direction cratonique referentielle au trias en amerique du nord toutefois une correlation satisfaisante est etablie avec les directions cratoniques referentielles du cretace cenozoique precoce en amerique du nord l occurrence exclusive d une polarite normale suggere qu il y eut probablement une remagnetisation au cours du long superchron normal du cretace les remagnetisations peuvent avoir ete declenchees par des saumures connees qui se sont deplacees le long d aquiferes de gres et de carbonates poreux dans les premieres phases du plissement laramide

magmatic evolution of sulawesi indonesia constraints on the cenozoic geodynamic history of the sundaland active margin abstract tertiary and quaternary magmatic rocks from west sulawesi record the complex history of part of the sundaland margin where subduction and collision have been and are still active the present study based on petrographic data major and trace element chemistry and 40 k 40 ar dating aims to document the age and chemical characteristics of the magmatic formations from west sulawesi and to determine the corresponding constraints on the geodynamic evolution of the sundaland border the west sulawesi magmatic province includes the south arm of sulawesi ujung pandang area the western part of central sulawesi with the toraja and palu areas and finally the north arm extending from palu to manado which includes the tolitoli and manado areas paleocene magmatic activity seems to be restricted to an episode of calc alkaline magmatism in the ujung pandang area 61 59 ma the major eocene 50 40 ma magmatic event is tholeiitic and is documented in all areas except in ujung pandang it led to the emplacement of tholeiitic pillow lavas and basaltic dykes of back arc basin bab affinity these rocks are potential equivalents to the celebes sea basaltic basement from oligocene to miocene magmatic eruptions produced successively island arc tholeiitic iat and calc alkaline ca rock series the youngest iat activity occurred around 18 ma in the central part palu area and around 14 ma in the north arm tolitoli area while ca magmas were emplaced in the north arm at ca 18 ma tolitoli and manado areas typical calc alkaline activity resumed only in the north arm tolitoli and manado areas during the late miocene 9 ma and is still active in the manado region in other areas palu toraja and ujung pandang areas an important and widespread magmatic event occurred between 13 and 10 ma and emplaced k rich magmas either silica undersaturated alkali potassic basalts ak ultrapotassic basanites uk or shoshonites sh k rich activity continued in the south until the pleistocene 0 77 ma with alkali potassic ultrapotassic and shoshonitic magmas in central sulawesi toraja and palu areas the most recent magmatic event occurred between 6 5 and 0 6 ma the corresponding products are granitic rocks and widely distributed rhyolitic pyroclastic flow deposits all these rocks are acidic in character sio 2 60 with trace element and isotopic signatures sr nd pb typical of a strong continental imprint the most striking tectonic implication of this magmatic evolution is that west sulawesi can no longer be considered as a typical magmatic arc as previously assumed with the exception of the manado area beneath which subduction is still active calc alkaline and island arc tholeiitic lavas and plutonics are volumetrically minor with respect to k rich magmas their occurrence through time is also fairly restricted mostly to the period between 30 and 15 ma another important feature is the occurrence of island arc tholeiitic and calc alkaline magmas crosscutting an older terrane of bab affinity the tinombo formation manado tolitoli and palu areas as this formation is being regarded as an equivalent to the celebes sea floor the most likely explanation for this feature is the hypothesis of tectonic erosion linked to the nw dipping subduction beneath the north arm the late miocene high k magmatic activity in central and south sulawesi reflects the prevalence of a post collisional tectonic regime following the docking of microcontinents of australian origin to central sulawesi during neogene times the incompatible element enriched character of these high k rocks might reflect their derivation from a mantle source enriched through metasomatism related to a previous subduction event such a model cannot account for the plio pleistocene cak magmatism of central sulawesi the acidic composition of which does not support a derivation from an ultrabasic source the trace element patterns of the cak rocks are very similar to those of the high grade metamorphics of central sulawesi suggesting that the latter might represent their possible source such an anatectic model implies a collisional to post collisional tectonic regime limited to central sulawesi while a post subduction regime prevailed in the south

aeolian fluvial interaction evidence for late quaternary channel change and wind rift linear dune formation in the northwestern simpson desert australia in central australia the most easterly extent of the macdonnell ranges border the simpson desert dunefield where widely spaced strike ridges intercept and isolate pockets of broad crested linear dunes that reflect regional changes in late quaternary climate flow regime and channel avulsion an energetic todd river reworked the eastern part of camel flat basin from 75 65 ka until the last glacial maximum lgm when it shifted eastwards but with some flows persisting through the basin until about 10 ka resulting desert surfaces of different age facilitate temporal comparisons of linear dune formation fine grained red dunes 75 65 ka in age occur on the western floor of the basin and are ramped against the foot slopes of the range after the lgm and especially during the holocene the river s departure enabled small pale coloured closely spaced coarser textured linear dunes to form on the abandoned floodplain in the eastern basin their orientation 20 farther west than the larger and older red dunes this realignment indicates that the australian wind whorl shifted southwards some 160 km or 1 5 after the lgm linear dunes in the northwestern simpson desert were formed by wind rifting involving vertical accretion of sand from a proximal source not by long distance sand transport with linear extension the blocking ranges have caused negligible downwind sediment accumulation over the past 75 ka

aeolian fluvial interaction and climate change source bordering dune development over the past 100 ka on cooper creek central australia abstract this study provides an interpretation of interrelated quaternary fluvial and aeolian activity related to climate change on cooper creek in the lake eyre basin in southwestern queensland central australia the extensive muddy floodplain is characterised by buried sandy palaeochannels now almost entirely invisible but stratigraphically connected to source bordering dunes that emerge as distinctive sandy islands through the floodplain surface luminescence dating has identified pronounced periods of fluvial activity represented by abundant sandy alluvium from marine isotope stages mis 8 3 while all these sandy fluvial episodes on cooper creek were much more powerful than anything subsequent they appear to be ranked in order of declining activity mis 8 6 saw reworking of almost the entire floodplain whereas subsequent phases of reworking were far less extensive source bordering dunes were derived from active sandy channels in late mis 5 85 80 ka and mid mis 3 50 40 ka after 40 ka sand channel activity largely ceased and the floodplains and channels were inundated with mud isolating the dunes as emergent features although aeolian reworking of the upper parts of some dunes has continued to the present they show remarkable resilience having survived without appreciable migration for at least 40 ka whilst the channels once determined the location of source bordering dunes in an interesting role reversal the remnant dunes now determine the position of many contemporary flood channels and waterholes by deflection and confinement of overbank flows

gypsum ground a new occurrence of gypsum sediment in playas of central australia abstract there are many playas dry salt lakes in arid central australia regional rainfall about 250 mm y and pan evaporation around 3000 mm y highly soluble salts such as halite only appear as a thin several centimetres thick white ephemeral efflorescent crust on the dry surface gypsum is the major evaporite precipitating both at present and preserved in sediment sequences one type of gypsum deposit forms a distinctive surface feature which is here termed gypsum ground it consists of a thick up to 80 cm gypsum zone which rises from the surrounding smooth white playa surface and is overlain by a heaved brown crust the gypsum zone with an average gypsum content above 60 consists of pure gypsum sublayers and interlayered clastic bands of sandy clay the gypsum crystals are highly corroded especially in the direction parallel to the c axis and on the upper sides where illuviated clay has accumulated in corrosion hollows overgrowth parallel to the a and b axes is very common forming highly discoidal habits these secondary changes corrosion and overgrowth are well developed in the vadose zone and absent from crystals below the long term watertable depth around 40 cm these crystal characteristics indicate a rainwater leaching process at lake amadeus one of the largest playas 800 km2 of central australia such gypsum ground occupies 16 of the total area the gypsum ground is interpreted as an alteration of a pre existing gypsum deposit which probably extended across the whole playa before breaking down leaving a playa marginal terrace and several terrace islands within the gypsum ground this pre existing gypsum deposit preserved in the residual islands consists of pure pale sand sized lenticular crystals it is believed to have been deposited during an episode of high regional watertable causing active groundwater seepage and more frequent surface brine in the playa a later fall in watertable probably resulting from climatic change caused the degradation of the gypsum deposit by dissolution and leaching processes the common distribution of the gypsum ground and marginal terraces in the playas of central australia demonstrates the extent of this hydrologic and climatic history

structure and collision history of the buton continental fragment eastern indonesia although commonly reservoired within tertiary rocks hydrocarbons in eastern indonesia have generally been sourced from mesozoic sediments deposited on the continental margin of northern australasia fragments of this margin are now widely dispersed as allochthonous terranes throughout the area one of the most far traveled examples being the island of buton southeast of sulawesi asphalt reserves on buton support a significant local industry and exploration continues for oil and natural gas in common with other prospective australian derived terranes around the margins of the banda sea buton is now separated from australia by the active plate boundary marked by the java trench and the collision trace along the timor tanimbar and seram troughs buton differs from these other terranes in its distance from that boundary and its consequent insulation from the effects of the pliocene pleistocene collision between australia and the banda arcs reconstruction of the geological history of the buton terrane thus has an important role in guiding future exploration in the other australasian fragments in eastern indonesia geophysical studies of the buton region have used seismic reflection gravity and magnetic including paleomagnetic techniques seismic reflection images generally record extension rather than compression as dominating the recent history of the area gravity data define the present day western limits of the buton terrane and suggest that in the east the terrane includes the almost entirely submerged tukang besi platform the gravity surveys also demonstrate that the ophiolitic rocks exposed on buton are not attached to deep roots but are thin and isolated overthrust sheets therefore they do not mark a terrane boundary and their presence has little bearing on the prospectivity of the area paleomagnetic results document the independent movements of thrust sheets on buton during the pliocene pleistocene the combined data from buton record its separation from australia as part of a microcontinental block in the jurassic or late triassic followed by collision with the eurasian margin in southeastern sulawesi in the oligocene or early miocene collision was followed by extension as in sulawesi itself producing minor separation of tukang besi from buton and much greater dispersion of other fragments of the microcontinent some of which have since been incorporated in the new collision zone in the outer banda arc the oil seeps and asphalt deposits of buton are proof that hydrocarbons in the banda arc fragments can be sourced from within these fragments and are not necessarily derived from the underthrusting australian margin