paleomagnetism of the tulemalu dykes northwest territories canada easterly trending tulemalu diabase dykes that cut an area of predominantly archean rock in southern keewatin were magnetized more than 2200 ma ago thirteen of the sampled sites dykes exhibit a southeast down remanent magnetization and five sites give a more poorly grouped direction that is reversed to this their combined pole is at 122 4 e 0 5 s m 10 4 p 6 0 six northeasterly trending kazan dykes which are probably correlatives of the kaminak dykes give a metamorphic pole at 94 2 w 30 7 n m 35 p 31 the age of their magnetization is thought to be between 1900 and 2000 ma the pole for the tulemalu dykes lies within a group of poles of similar age derived from basic rocks of the slave province it is about 30 away from the pole for the mackay dykes which occur north of great slave lake and which have an easterly trend similar to that of the tulemalu poles whose ages range between 1900 and 2200 ma and that are derived from the slave western churchill and superior provinces al

formation of chlorite during thrust fault reactivation record of fluid origin and p t conditions in the monte perdido thrust fault southern pyrenees the chemical and isotopic compositions of clay minerals such as illite and chlorite are commonly used to quantify diagenetic and low grade metamorphic conditions an approach that is also used in the present study of the monte perdido thrust fault from the south pyrenean fold and thrust belt the monte perdido thrust fault is a shallow thrust juxtaposing upper cretaceous paleocene platform carbonates and lower eocene marls and turbidites from the jaca basin the core zone of the fault about 6 m thick consists of intensely deformed clay bearing rocks bounded by major shear surfaces illite and chlorite are the main hydrous minerals in the fault zone illite is oriented along cleavage planes while chlorite formed along shear veins 50 m in thickness authigenic chlorite provides essential information about the origin of fluids and their temperature 18o and d values of newly formed chlorite support equilibration with sedimentary interstitial water directly derived from the local hanging wall and footwall during deformation given the absence of large scale fluid flow the mineralization observed in the thrust faults records the p t conditions of thrust activity temperatures of chlorite formation of about 240 c are obtained via two independent methods chlorite compositional thermometers and oxygen isotope fractionation between cogenetic chlorite and quartz burial depth conditions of 7 km are determined for the monte perdido thrust reactivation coupling calculated temperature and fluid inclusion isochores the present study demonstrates that both isotopic and thermodynamic methods applied to clay minerals formed in thrust fault are useful to help constrain diagenetic and low grade metamorphic conditions

chloritisation along the thanewasna shear zone western bastar craton central india its genetic linkage to cu au mineralisation abstract the cu au mineralisation of thanewasna bastar craton central india is hosted in quartz chlorite veins traversing granitoid rocks mineralisation and associated alteration are controlled by a nw se trending brittle ductile shear zone large scale alkali magmatism in the form of k rich granite emplacement is found in the vicinity of the shear zone the emplacement of this granite 1587 14 ma along the northern shoulder of the godavari rift produced a high geothermal gradient resulting in intense chloritisation and mineralisation field and petrographic studies show that the chlorite formed in two possible modes viz a replacement of ferromagnesian minerals of the host rock and or b precipitated directly from hydrothermal solutions mineral chemistry epma coupled with sem and xrd studies reveals that chamosite with minor clinochlore varieties of chlorite is commonly associated with cu and au mineralisation chlorite shows variation in fe fe mg ratios from 0 54 to 0 60 0 55 to 0 64 and 0 49 to 0 55 and al iv from 1 88 to 2 40 1 91 to 2 50 and 1 80 to 1 94 apfu respectively at the surface and in the sub surface mineralisation and host rock empirical and thermodynamic geothermometers have been used to determine the temperature of chlorite formation based on chemical composition six empirical methods based on al iv al vi and fe fe mg ratio showed a temperature range of 187 c to 381 c temperatures of chlorite formation have also been determined by the thermodynamic solid solution method the thermodynamic equations of three intra crystalline equilibria at 2 kbar pressure show that temperature ranges from 215 to 454 c for low si contents 2 8 apfu the thermodynamic method of vidal et al 2001 and 2005 was not so compatible for an estimation of temperature of hydrothermal fe rich chlorites associated with cu au mineralisation at the thanewasna copper deposit tcd the temperature of chlorite formation increases from the host rock mean 201 c to proximal mineralisation zone mean 234 c to distal k na alteration zone mean 251 c integrating field and laboratory results suggested that tcd chlorite is part of a structurally controlled high sulphidation epithermal system this characterization would help in the regional exploration for base and precious metals and the results are applicable for the entire western bastar craton wbc of central india and similar deposit elsewhere

very low grade metamorphism of sedimentary rocks of the meliata unit western carpathians slovakia implications of phyllosilicate characteristics the meliata unit represents a melange like accretionary wedge containing blueschist facies tectonic blocks and slices in a triassic and jurassic sedimentary matrix the blueschist facies rocks are tectonic remnants of the subducted parts of the meliata hallstatt branch of the tethys the phyllosilicate assemblages in very low grade metapelites represent metastable disequilibrium stages which the assemblages have reached during reaction progress therefore temperature and pressure values of low t metamorphism of the sedimentary series and the late stages of decompressional cooling of blueschist facies rocks obtained by phyllosilicate crystallinity chlorite thermometric and white k mica geobarometric methods can be regarded as semiquantitative estimates however results of chlorite white mica thermobarometry suggest that local equilibrium was approached at a microscopic scale for deciphering the age relations of prograde and retrograde events k ar isotope geochronological methods were applied the sedimentary series and related basalts of the meliata unit experienced high t anchizonal prograde regional metamorphism the temperature and pressure of which can vary between ca 280 and 350 c and ca 2 5 and 5 kbar white k mica b geobarometry suggests possible minimal pressures of ca 1 5 to 3 kbar the mylonitic retrogression of blueschist facies phyllites is characterised by 340 c and 4 kbar minimal p the low t prograde metamorphism was synchronous with the retrograde metamorphism of the blueschists the ages of these two events may be between ca 150 and 120 ma culminating most probably at around 140 145 ma thus the upper jurassic lowermost cretaceous very low grade metamorphism of the meliata unit is younger than the subduction related 160 155 ma blueschist facies event and definitely older than the cretaceous 100 90 ma metamorphism of the footwall gemer palaeozoic

fuzzy classification of soil profiles and horizons from the lockyer valley queensland australia abstract this paper examines the application of fuzzy classification and ordination to the characterization of soil units recognized in the alluvial plain of the lockyer valley in southeast queensland australia soil profile classes and soil stratigraphic units were recognized initially using field criteria data from soil profiles and horizons at 133 equally spaced sites on a 3 4 km transect were analysed the analyses aimed to assess how similar or separate profiles and horizons were regardless of their position along the transect and to scrutinise field assumptions of a typical alluvial soil landscape sequence centroids of fuzzy groups classes were generated together with fuzzy group memberships for each profile or horizon distribution of fuzzy group membership on the transect and data patterns developed using ordination procedures were found to reflect changes in landscape position soil profile classes soil stratigraphic units and soil factors related to internal drainage analysis corroborated most soil stratigraphic units and profile classes recognized in the field but some profile classes were shown to be in need of re examination the distribution of horizon groups generated by fuzzy classification was generally unrelated to the distribution of profile fuzzy groups it is suggested that for these soils it would be difficult to create a fixed number of profile classes based on homologous relationships between horizons classification of soil by horizons appears to be more meaningful than the classification of profiles but profile fuzzy group distribution along the transect was more mappable and easily interpreted than horizon fuzzy group distribution

crustal shortening during the paleoproterozoic can it be accommodated by paleomagnetic data abstract in the last 130 million years perhaps as much as 2000 km of intra continental shortening has taken place within asia during 10 000 km of convergence between siberia and india with 8000 km being accommodated by oceanic subduction given that earth was hotter during the paleoproterozoic crustal shortening at this time may have been equally if not more significant compared to today warranting a search of the paleomagnetic data base for any supporting evidence paleomagnetic data from units on either side of the paleoproterozoic trans hudson orogen in canada have been chosen because this orogen bears close similarity both in size and history to the india siberia one the data do not prove but can accommodate continental crustal shortening between the archean slave and superior provinces of about 3000 1000 km the results allow crustal shortening to have been a significant component of continental collision in the paleoproterozoic an important issue in any re assembly of precambrian continents if true the present dimensions of precambrian shields may be significantly different compared to those existing in earlier times

late tectonic and metamorphic evolution of the piedmont accretionary wedge queyras schistes lustres western alps evidences for tilting during alpine collision this paper addresses the contribution of extension in the upper crust during syncollisional exhumation of subducted material we present structural data based on the analysis of ductile brittle ductile and brittle deformation features in metapelitic schists and meta basalts from the schistes lustres nappe stack in the piedmont zone of the western alps to link the structures with synkinematic pressure and temperature estimates geothermobarometry was performed using fluid inclusion investigation in quartz together with temperature estimations based on metamorphic chlorite composition samples used for geothermobarometry were collected taking into account the structural framework within veins associated with extensional structures observed at the regional scale the early generation of veins associated with boudinage occurred at 415 345 c and 6 2 5 kbar and subsequent incipient normal faulting occurred at temperatures of 315 235 c and pressures 1 7 kbar the transition from ductile to brittle extension occurred between ca 27 ma and ca 10 ma these results indicate a continuous extension in the upper crust during exhumation and continuous deformation associated with regional scale tilting of the exhumed schistes lustres tectonic pile the extensional tectonic regime in greenschistfacies conditions remains active today in most of the internal alpine zones as the alpine collision continues

microstructures mineral chemistry and geochronology of white micas along a retrograde evolution an example from the aar massif central alps switzerland abstract this study investigates gneissic tectonites of different mechanical origins and aims at unravelling the link between microstructures white mica chemistry and k ar data the highest temperature mylonitic deformation which is investigated is dominated by dislocation creep in monomineralic quartz and viscous granular flow in polymineralic domains these mylonites show homogenous mineral chemistry resulting in robust and consistent k ar age data the lowest temperature deformation investigated is that of a retrograde brittle deformation producing cohesionless fault gouges within the cohesionless fault gouges frictional granular flow is considered as the main deformation mechanism the k bearing phases inside the fault gouges record no chemical resetting during this brittle overprint but contain mechanically fragmented k bearing micas and significant amounts of newly produced smectite this yields k ar ages inside of a gouge that are in the range of adjacent mylonite ages and may not represent the timing of gouge formation in an effort to understand these uncertainties in k ar ages detailed observations of the microstructural context of k bearing white mica were made microstructural criteria in combination with quantitative element mapping allowed for the discrimination of five important mica related processes 1 fracturing recrystallization of white mica 2 re precipitation of new fine grained white mica inside the deforming rock matrix 3 pseudomorphic replacement of precursor minerals by white mica and chlorite 4 pseudomorphic replacement of pre existing white mica without grain size reduction and 5 remnant grains the combination of these different processes led to a high variability in mineral chemistry and isotope data for tectonites which relates directly to variations in the size of the equilibrium volumes despite the samples being highly deformed in the presence of fluids inherited sheet silicates may survive if inherited sheet silicates are present they contribute to an increase in both the chemical heterogeneity and the apparent k ar ages of a sample

fluid rock interactions related to metamorphic reducing fluid flow in meta sediments example of the pic de port vieux thrust pyrenees spain in orogens shortening is mainly accommodated by thrusts which constitute preferential zones for fluid rock interactions fluid flow mass transfer and mineralogical reactions taking place along thrusts have been intensely investigated especially in sedimentary basins for petroleum and uranium research this study combines petrological investigations mineralogical quantifications and geochemical characterizations with a wide range of analytical tools with the aim of defining the fluid properties nature origin temperature and redox and fluid host rock interactions mass transfers recrystallization mechanisms and newly formed synkinematic mineralization in the pic de port vieux thrust fault zone pyrenees spain we demonstrate that two geochemically contrasted rocks have been transformed by fluid flow under low grade metamorphism conditions during thrusting the hanging wall triassic red pelite was locally bleached while the footwall cretaceous dolomitic limestone was mylonitized the results suggest that thrusting was accompanied by a dynamic calcite recrystallization in the dolomitic limestone as well as by leaching of iron via destabilization of iron oxides and phyllosilicate crystallization in the pelite geochemical and physical changes highlighted in this study have strong implications on the understanding of the thrust behavior tectonic and hydraulic and improve our knowledge of fluid rock interactions in open fluid systems in the crust

fluid rock reaction weakening of fault zones the presence of weak phyllosilicates may explain the low shear strengths of fault zones if they define well developed fabrics the growth of phyllosilicates is favored in meteoric water dominated granitic fault systems where mineral aqueous fluid equilibria predict that modal phyllosilicate will increase via feldspar replacement reactions in deeper more alkaline rock dominated regimes the reactions reverse and feldspars tend to replace phyllosilicates in mg rich mafic rocks however phyllosilicates chlorite biotite can replace stronger framework and chain silicates in both shallower approximately 10 km meteoric h sub 2 o dominated and in deeper alkaline rock dominated regimes where these phyllosilicates precipitate in active fault zones they contribute directly to reaction softening because low temperature deformation of phyllosilicates is not governed by frictional processes alone but can occur by pressure independent dislocation glide the strength of phyllosilicate rich fault rocks can be low at all depths low strain rate creep during interseismic periods can align phyllosilicate grains in foliated gouge and phyllonites where preferred orientations are strong and contiguity of phyllosilicates is large strengths of rocks within fault zones may approach minimum strengths defined by single phyllosilicate crystals fault zones containing localized high concentrations of phyllosilicates with strong preferred orientations in well defined folia can exhibit aseismic slip especially where mafic mg rich rocksmore occur along the fault like parts of the san andreas fault 104 refs 6 figs 1 tab less

stabilization and reactivation of cratonic lithosphere from the lower crustal record in the western canadian shield new u pb geochronology for an extensive exposure of high pressure granulites in the east lake athabasca region of the western canadian shield is consistent with a history characterized by 2 55 ga stabilization of cratonic lithosphere 650 million years of lower crustal residence and cratonic stability and 1 9 ga reactivation of the craton during lithospheric attenuation and asthenospheric upwelling high precision single grain and fragment zircon data define distinctive discordia arrays between 2 55 and 1 9 ga u pb ion microprobe spot analyses yield a similar range of u pb dates with no obvious correlation between date and cathodoluminescence zonation we attribute the complex u pb zircon systematics to growth of the primary populations during a 2 55 ga high pressure granulite facies event 1 3 gpa 850 c recorded by the dominant mineral assemblage of the mafic granulite gneisses with subsequent zircon recrystallization and minor secondary zircon growth during a second high pressure granulite facies event 1 0 gpa 800 c at 1 9 ga the occurrence of two discrete granulite facies metamorphic events in the lower crust separated by an interval of 650 million years that included isobaric cooling for at least some of this time suggests that the rocks resided at lower crustal depths until 1 9 ga we infer that this phase of lower crustal residence and little tectonic activity is coincident with an extended period of cratonic stability detailed structural and thermochronological datasets indicate that multistage unroofing of the lower crustal rocks occurred in the following 200 million years extended lower crustal residence would logically be the history inferred for lower crust in most cratonic regions but the unusual aspect of the history in the east lake athabasca region is the subsequent lithospheric reactivation that initiated transport of the lower crust to the surface we suggest that a weakened strength profile related to the 1 9 ga heating left the lithosphere susceptible to far field tectonic stresses from bounding orogens that drove the lower crustal exhumation an ultimate return to cratonic stability is responsible for the preservation of this extensive lower crustal exposure since 1 7 ga

timescales and significance of high pressure high temperature metamorphism and mafic dike anatexis snowbird tectonic zone canada new geochronological isotopic and geochemical data for a spectacular swarm of deep crustal migmatitic mafic dikes offer important insight into processes operative during 1 9 ga high pressure high temperature metamorphism along the snowbird tectonic zone in northern saskatchewan high precision u pb zircon dates reveal anatexis of chipman mafic dikes at 1 896 2 0 3 ma during syntectonic and synmetamorphic intrusion at conditions of 1 0 1 2 gpa 750 c u pb zircon dates of 1 894 1 891 ma for cross cutting pegmatites place a lower bound on major metamorphism and deformation at the currently exposed crustal levels the persistence of elevated temperatures for 14 m y following peak conditions is implied by younger u pb titanite dates and by sm nd whole rock isotopic data that suggest the derivation of the pegmatites by melting of a mafic source limited melting of the host felsic gneiss at 1 9 ga despite high temperature is consistent with evidence for their previous dehydration by granulite facies metamorphism in the archean spatial heterogeneity in patterns of mafic dike and tonalitic gneiss anatexis can be attributed to lateral peak temperature and compositional variability we correlate 1 896 ma chipman mafic dike emplacement and metamorphism with substantial 1 9 ga mafic magmatism over a minimum along strike extent of 1 200 km of the snowbird tectonic zone this suggests a significant continent wide period of asthenospheric upwelling that induced incipient continental rifting extension was subsequently terminated by hinterland contraction associated with trans hudson accretion and orogenesis little activity in the lower crust for ca 650 m y prior to proterozoic metamorphism and mafic magmatism implies an extended interval of cratonic stability that was disrupted at 1 9 ga this episode of destabilization contrasts with the record of long term stability in most preserved cratons and is important for understanding the lithospheric characteristics and tectonic circumstances that control the destruction or survival of continents

1891 1883 ma southern bastar cuddapah mafic igneous events india a newly recognized large igneous province abstract a newly recognized remnant of a paleoproterozoic large igneous province has been identified in the southern bastar craton and nearby cuddapah basin from the adjacent dharwar craton india high precision u pb dates of 1891 1 0 9 ma baddeleyite and 1883 0 1 4 ma baddeleyite and zircon for two se trending mafic dykes from the bd2 dyke swarm southern bastar craton and 1885 4 3 1 ma baddeleyite for a mafic sill from the cuddapah basin indicate the existence of 1891 1883 ma mafic magmatism that spans an area of at least 90 000 km2 in the south indian shield this record of 1 9 ga mafic ultramafic magmatism associated with concomitant intracontinental rifting and basin development preserved along much of the south eastern margin of the south indian shield is a widespread geologic phenomenon on earth similar periods of intraplate mafic ultramafic magmatism occur along the margin of the superior craton in north america 1 88 ga molson large igneous province and in southern africa along the northern margin of the kaapvaal craton 1 88 1 87 ga dolerite sills intruding the waterberg group existing paleomagnetic data for the molson and waterberg 1 88 ga large igneous provinces indicate that the superior and kalahari cratons were at similar paleolatitudes at 1 88 ga but a paleocontinental reconstruction at this time involving these cratons is impeded by the lack of a robust geological pin such as a limpopo like 2 0 ga deformation zone in the superior province the widespread occurrence of 1 88 ga intraplate and plate margin mafic magmatism and basin development in numerous archean cratons worldwide likely reflects a period of global scale mantle upwelling or enhanced mantle plume activity at this time

ore lead and sulphur isotope pattern from the low temperature veins of the catalonian coastal ranges ne spain the lead isotopic composition of galenas from low temperature veins of the catalonian coastal ranges ne spain displays a small but distinct range of values 18 318 206pb 204pb 18 678 15 678 207pb 204pb 15 767 and 38 534 208pb 204pb 39 189 the data define a linear trend in the 208pb 204pb versus 206pb 204pb diagram that can be interpreted in terms of mixing of lead from different reservoirs the lead appears to be derived from a solution that preferentially leached granites of late hercynian age sulphur isotopic compositions of the galenas range from 8 5 to 7 3 but variations in a single deposit are small 1 2 pointing to different sources of sulphur in a 34s versus 206pb 204pb plot no clear correlation trends appear lead isotope data from deposits of similar characteristics situated within the hercynian orogenic belt as the linares la carolina district s spain and the inglesiente sulcis area sardinia show slight differences indicating a source area of similar lead isotopic composition in the ccr and linares la carolina districts the main source of lead is related to the hercynian granites of each area although small contributions from metasediments cannot be ruled out the contribution of lead from metasedimentary rocks is particularly seen in the sardinian hercynian vein type ores

origin and behavior of clay minerals in the bogd fault gouge mongolia we analyzed twelve fault gouge samples from the bogd fault in south western mongolia to understand the origin and behavior of clay minerals the investigation relies on x ray powder diffraction xrd scanning electron microscopy sem transmission electron microscopy tem and high energy synchrotron x ray diffraction methods to investigate microstructure and preferred orientation smectite montmorillonite illite smectite mixed layers illite mica and kaolinite are the major clay components in addition to quartz and feldspars which are present in all samples the observations suggest that the protoliths and the fault rocks were highly altered by fluids the fluid rock interactions allow clay minerals to form as well as alter feldspars to precipitate kaolinite and montmorillonite thus newly formed clay minerals are heterogeneously distributed in the fault zone the decrease of montmorillonite component of some of the highly deformed samples also suggests that dehydration processes during deformation were leading to illite precipitation based on synchrotron x ray diffraction data the degree of preferred orientation of constituent clay minerals is weak with maxima for 001 ranging from 1 3 to 2 6 multiples of a random distribution m r d co existing quartz and feldspars have random orientation distributions microstructure and texture observations of the gouges from the foliated microscopic zone alternating with micrometric isotropic clay rich area also indicate that the bogd fault experienced brittle and ductile deformation episodes the clay minerals may contribute to a slip weakening behavior of the fault

modern style plate subduction preserved in the palaeoproterozoic west african craton the timing of onset of modern style plate tectonics on earth is debated analysis of rocks in the west african metamorphic province which is more than 2 gyr old reveals that some minerals formed under conditions similar to those in modern day subduction zones suggesting that subduction occurred on the palaeoproterozoic earth

thermal effects of linked lithospheric and upper crustal scale processes insights from numerical modeling of the cenozoic central catalan coastal ranges ne spain processes influencing the thermal state of the continental crust such as heat upwelling related to rifting and isotherm reorganization due to mass redistribution by erosion deposition and fault tectonic transport operate at different scales and their effects overlap in this paper we use lithospheric as well as crustal scale numerical modeling tools in order to quantify the contributions of these various factors to the geothermal field establishing their relative relevance we apply the models to address the thermal evolution of the catalan coastal ranges ne spain during the cenozoic a period that is characterized by a change in tectonic style from pyrenean compression to extension related to the western mediterranean rifting results of the lithospheric scale thermal model for extensional basins show an increase in the geothermal surface gradient of about 11 c km in the catalan coastal ranges during the neogene related to extensional thinning of the lithosphere in the valencia trough western mediterranean predictions of the upper crustal scale thermal model incorporating fault motions and surface mass redistribution erosion and sedimentation point to little changes in the isotherms due to fault block movements in the paleogene and neogene in contrast erosion appears to have a significant effect on the then nal history of basement rocks sited in the shallowest crust comparison of the integrated lithospheric and upper crustal scale modeling results with apatite fission track and apatite u th he thermochronology data reveals larger amounts of neogene to present cooling than predicted by the models on the basis of this unresolvable mismatch we suggest that similar to present forced fluid convection along fault planes played an important role in the evolution of the geothermal field during the neogene stage of rifting copyright 2007 by the american geophysical union

plate tectonics before 2 0 ga evidence from paleomagnetism of cratons within supercontinent nuna laurentia the core of paleo to mesoproterozoic supercontinent nuna has remained largely intact since assembly 2 0 to 1 8 billion years ago ga for earlier times previous paleomagnetic data on poorly dated paleoproterozoic mafic intrusions yielded ambiguous estimates of the amount of separation between key cratons within nuna such as the slave and superior recent developments in paleomagnetism and u pb baddeleyite geochronology including new results reported herein yield sufficiently precise data to generate partial apparent polar wander paths for both the slave and superior craton from 2 2 to 2 0 ga our new apparent polar wander comparison confirms earlier speculations that processes similar to plate tectonics with relative motion between the slave and superior cratons were operative leading up to the final assembly of supercontinent nuna

sequence stratigraphy and plate tectonic significance of the transvaal succession of southern africa and its equivalent in western australia the transvaal succession in the northeastern part of the kaapvaal province of southern africa is the erosional remnant of four 2 7 to 2 1 ga unconformity bounded stratigraphic units or sequences each of which is 102 to 103 m thick and spans 107 to 108 years three of these phanerozoic like cratonic sequences occur in the western part of the kaapvaal province and in the pilbara province of western australia thus the two provinces once were part of the same continent vaalbara the stratigraphically lowest sequence historically assigned to the transvaal succession is part of the ventersdorp supergroup in kaapvaal and the upper part of the fortesque group in pilbara it consists predominantly of arkosic sandstone and basaltic andesite it probably is 2687 2 ma the second sequence contains the quartz arenites dolomites and banded iron formations of the transvaal and griqualand west successions in the kaapvaal and the hamersley group in the pilbara the span of ages 2684 6 to 2432 31 ma lithologies and geographic extent of this sequence imply that the limpopo orogeny which welded the zimbabwe province to vaalbara is 2 47 ga not 2 67 0 05 ga the third sequence the pretoria and postmasburg groups in the kaapvaal and the lower part of the wyloo group in the pilbara probably is the clastic wedge generated by the limpopo orogeny the fourth sequence dominated by the felsites of the rooiberg group is restricted to northeastern kaapvaal sequence stratigraphy lithostratigraphy and lithofacies indicate that the pilbara rifted from the southern edge of western kaapvaal the penge iron formation in northeastern kaapvaal the asbesheuwels iron formation in southwestern kaapvaal and the brockman iron formation in the pilbara are the same formation in which cyclothemic units 0 6 to 15 0 m thick extended 1200 km

u pb baddeleyite ages of the kerns and triangle mountain intrusions nipissing diabase ontario u pb ages have been determined for two diabase intrusions from kerns and hudson townships that are part of the nipissing diabase suite from the proterozoic southern province canada the ages of the kerns and triangle mountain intrusions are 2217 2 4 and 2209 6 3 5 ma respectively based on analysis of primary baddeleyite from both intrusions together with a published u pb age for the castle mine intrusion these data indicate that the nipissing sills were emplaced separately over a time span of 2 8 1 6 ma given by the maximum and minimum overlap of errors on the u pb ages

patterns of mineral transformations in clay gouge with examples from low angle normal fault rocks in the western usa abstract neoformed minerals in shallow fault rocks are increasingly recognized as key to the behavior of faults in the elasto frictional regime but neither the conditions nor the processes which wall rock is transformed into clay minerals are well understood yet understanding of these mineral transformations is required to predict the mechanical and seismogenic behavior of faults we therefore present a systematic study of clay gouge mineralogy from 30 outcrops of 17 low angle normal faults lanf s in the american cordillera to demonstrate the range and type of clay transformations in natural fault gouges the sampled faults juxtapose a wide and representative range of wall rock types including sedimentary metamorphic and igneous rocks under shallow crustal conditions clay mineral transformations were observed in all but one of 28 faults one fault contains only mechanically derived clay rich gouge which formed entirely by cataclasis clay mineral transformations observed in gouges show four general patterns 1 growth of authigenic 1m d illite either by transformation of fragmental 2m 1 illite or muscovite or growth after the dissolution of k feldspar illitization of fragmental illite smectite is observed in lanf gouges but is less common than reported from faults with sedimentary wall rocks 2 retrograde diagenesis of an early mechanically derived chlorite rich gouge to authigenic chlorite smectite and saponite mg rich tri octahedral smectite 3 reaction of mechanically derived chlorite rich gouges with mg rich fluids at low temperatures 50 150 c to produce localized lenses of one of two assemblages sepiolite saponite talc lizardite or palygorskite chlorite quartz and 4 growth of authigenic di octahedral smectite from alteration of acidic volcanic wall rocks these transformation groups are consistent with patterns observed in fault rocks elsewhere the main controls for the type of neoformed clay in gouge appear to be wall rock chemistry and fluid chemistry and temperatures in the range of 60 180 c

microstructural analyses of a giant quartz reef in south china reveal episodic brittle ductile fluid transfer abstract a long lived hydrothermal system at the heyuan fault south china has led to the development of a giant quartz reef now partially exhumed along its length for more than 40 km systematic analyses and focused microstructural studies have been undertaken to unravel a complex formation history of repeated fracturing hydrothermal fluid flow and sealing cycles resulting in a dynamic permeability across the fault zone the change in morphology and decreasing grain size with time further indicates the move from slow ductile opening to fast seismic events quartz reef formation has been estimated to occur within a range of 200 350 c based on evaluation of i quartz deformation microstructures ii chlorite and mica geothermometry and iii review of comparable quartz reef studies additionally a set of physico chemical formation conditions have been identified which compose the quartz reef window these are i significant volume of fluid ii fluid sources from meteoric metamorphic and or from mantle origin iii considerable time integrated fluid fluxes iv sio2 oversaturation due to a temperature change b sudden pressure drop or c chemical change e g fluid mixing v accommodation space to grow the reef vi channel permeability and vii cap rock seal to trap the fluid flow the mechanism of quartz reef growth is here interpreted as the brittle ductile analogue of the brittle fault valve model

the neogene structure of the eastern iberian margin structural constraints on the crustal evolution of the valencia trough western mediterranean abstract the presence of a thinned crust beneath the valencia trough has been recognized for a long time however to date no attempt to link this thinning inferred from geophysical data with the superficial structures has been made a quantification of the neogene extensional processes in the crustal evolution of the valencia trough is presented as a consequence of the complexity of the betic balearic domain the analysis has been done for the catalan valencian domain northwestern areas of the trough crustal and superficial data in this area show that neogene extension was accommodated by a listric normal fault system detached in a deep upper crustal level 13 15 km in the marginal zone of the domain quantitative analysis of the neogene structure shows the incoherence between the upper crustal thinning inferred from the geometric analysis of the superficial structures factor 1 4 1 5 and from geophysical data 1 8 although the latter value agrees with that deduced from the analysis of neogene subsidence this incoherence suggests that the present thinned crust would be partially inherited from the mesozoic extension in this way mesozoic subsidence analysts and the recognized mesozoic structure show that the mesozoic extension was almost as important as the neogene one

discovery of archaean crust within the akitkan orogenic belt of the siberian craton new insight into its architecture and history abstract the akitkan orogenic belt separates the aldan and anabar superterranes of the siberian craton and was previously suggested to consist exclusively of palaeoproterozoic juvenile crust foliated granitoids in the baikal basement salient within the akitkan belt were studied geochronologically and geochemically thermal ionisation mass spectrometry tims analysis of six zircons of a tonalite sample yielded a discordia line with an upper concordia intercept age of 2884 12 ma which is interpreted as the time of tonalite emplacement geochemical data of the foliated granitoids confirm their affinity to the tonalite trondhjemite granodiorite ttg series they are characterized by high al2o3 contents 14 4 17 2 wt high sr y ratios 18 99 and show significant rare earth element ree fractionation with lan ybn 11 89 the nd t values vary from 1 6 to 0 8 and nd mean crustal residence ages range from 3 23 to 3 07 ga geochemical and isotopic data confirm their genesis through interaction of mantle and crustal material under high pressure near the base of thickened crust either after accretion of ancient continental crust and an oceanic plateau or after underplating of oceanic plateau like basaltic magmas the akitkan orogenic belt is a composite crustal unit of archaean and palaeoproterozoic age we propose two possible scenarios of its evolution in the first scenario palaeoproterozoic complexes developed along the active margin of the archaean anabar superterrane at 2 1 2 0 ga alternatively archaean and palaeoproterozoic components of the akitkan belt could have a distal origin and were accreted to the anabar superterrane these accretional processes were followed by a major collision of the aldan and anabar superterranes at 1 9 ga finalised by post collisional granitoid magmatism at 1 87 1 84 ga

spatial dependence and classification of the soil along a transect in northeast scotland abstract this paper analyses a problem common to almost all general purpose soil surveys namely how to classify the soil of a region so that each class is both reasonably homogeneous with respect to soil profile and occurs as reasonably large parcels of land a spatial analysis and a classification have been made of the soil along a transect in northeast scotland semi variograms of subsoil properties were computed from sample data at 20 m intervals they showed spatial dependence extending to about 360 m for some properties in particular colour and ph and little or no spatial dependence in others notably the particle size fractions and organic matter content the form of the first group of semi variograms suggested that there were several discontinuities on the transect i e boundaries between distinct soil types these were identified by two segmentation techniques thereby providing a spatial classification the results were then compared with an optimal classification of the same data irrespective of position on the ground there was close agreement between the two classifications in some parts of the transect particularly where the soil was strongly gleyed elsewhere segments contained mixtures of non spatial classes

tectonothermal evolution of the northeastern margin of iberia since the break up of pangea to present revealed by low temperature fission track and u th he thermochronology a case history of the catalan coastal ranges abstract the catalan coastal ranges ccr form part of the northeastern iberian mediterranean margin this margin typifies the transition zone between the thickened crust of the pyrenees and ebro basin 32 to 40 km and the extremely thinned continental crust of the offshore valencia trough 8 km despite intensive geological research in recent decades the issue of the unsolved thermochronological history has hardly been addressed for the catalan margin this study provides for the first time a continuous low temperature thermochronological dataset covering the period from late paleozoic to present day more than 100 analyses have been performed in an area less than 200 km long by 50 km wide zircon and apatite fission track zft and aft results of the hercynian basement yield cooling ages between 254 41 104 16 ma and 223 27 16 3 ma respectively apatite u th he ages range between 58 3 and 2 0 0 2 ma these thermochronological data provide evidence for a very active geothermal past revealing above all an important thermal period coeval with the triassic early jurassic break up of pangea hereby we discuss and suggest various mechanisms responsible for the elevated crustal temperatures detected this new dataset also provides new constraints on the allocation of areas where exhumation uplift occurred synchronous with some tectonic phases the widespread presence of hydrothermal mineralizations and the present day overmaturity state of the mesozoic sediments with regard to oil potential in the ccr despite the local scale of the catalan margin the very detailed study here presented sheds some light on the geological implications of results from other more regional thermochronological studies on the iberian microplate studies that yield similar mesozoic thermochronological record for areas that also experienced extensional fracturing and subsidence during the break up of pangea

sedimentology of proterozoic cratonic sheet sandstones of the eastern canadian shield sims formation labrador canada abstract the upper lower proterozoic to middle proterozoic sims formation rests unconformably on lower proterozoic strata of the knob lake group of the labrador trough sequence the 700 m thick sims formation consists of basal fluvial arkoses and conglomerates about 100 m and an upper sheet like sand body about 600 m thick composed of quartz arenites and minor quartz clast conglomerates this upper unit is interpreted as beach shoreface tidal and shallow shelf deposits the lowest 70 m of the quartz arenite unit appear to be of fluvial origin but probably were formed by reworking of quartzose sands produced in coastal environments during a period of elevated sea level the lower sims formation probably represents molasse shed from either the hudson or labrador orogens rivers flowed northwest away from these upland areas the upper part of the sims formation records deposition during a period of slow steady sea level rise in an ocean that deepened to the west the sims formation outliers are remarkably similar to outliers of the sakami formation of northern quebec a unit that has a poorly constrained early to middle proterozoic age if these units are correlative a hypothesis supported mainly by identical facies and facies sequences then the transgressive quartz arenites would originally have covered an area of at least 200 000 km2

paleomagnetism of ca 2 13 2 11 ga indin and ca 1 885 ga ghost dyke swarms of the slave craton implications for the slave craton apw path and relative drift of slave superior and siberian cratons in the paleoproterozoic of 35 archean cratons that have been identified around the globe only one the superior craton of the canadian shield has a reasonably well defined apparent polar wander apw path for much of paleoproterozoic time based on key i e well defined and precisely dated paleopoles as a result it has been difficult to compare the drift of these cratons or reliably test continental reconstructions of the archean cratons in the paleoproterozoic based on paleomagnetism in this study we report key paleopoles for the 2 13 2 11 ga northwest to north northwest trending indin dyke swarm 36 n 76 w a 95 7 and the 1 885 ga northeast to north northeast trending ghost swarm 2 n 106 w a 95 6 of the yellowknife region of the slave craton u pb baddeleyite ages have been determined at paleomagnetic sampling sites and baked contact tests establish that the remanences are primary combined with paleopoles from other precisely dated dyke swarms of the slave craton these data define a rudimentary apw path between ca 2 23 and 1 885 ga and permit a comparison of the drift of the slave and superior cratons over this interval both the indin and ghost poles are precisely matched in age with key poles on the superior apw path the slave and superior paths are not superimposed demonstrating that the two cratons were not in their present relative locations they have different overall shapes indicating relative drift during at least a portion of the period however the earlier 2 23 2 21 ga portions of the tracks appear broadly similar and could permit the two cratons to be on a single tectonic plate at that time although separated by a great distance a comparison of the ghost pole and a coeval key pole for siberia permits a 1 88 ga reconstruction with southern siberia facing the northern slave laurentia margin broadly similar to reconstructions that have been proposed at least as late as 1 38 ga although the distance between the cratons is still poorly constrained

paleomagnetism and u pb geochronology of the lac de gras diabase dyke swarm slave province canada implications for relative drift of slave and superior provinces in the paleoproterozoicgeological survey of canada contribution 20080350 lac de gras diabase dykes trend north to nne across the central slave province of the canadian shield u pb baddeleyite ages of 2023 2 and 2027 4 ma are interpreted as dyke emplacement ages th

paleomagnetism of the komatiitic basalts of the ottawa islands n w t the komatiitic basalts of the ottawa islands in eastern hudson bay are on strike with and believed to form a continuation of similar units of the cape smith belt 150 km to the northeast units sampled in the ottawa islands all dip gently to the west and hence are not suitable for an internal fold test of their age of magnetization however before correcting for the tilt of the lavas the dominant magnetization direction d 207 6 i 61 9 k 168 95 3 7 does not differ significantly from the uncorrected magnetization direction reported from the steeply dipping northwest facing units at cape smith d 218 i 60 k 47 95 4 this negative fold test suggests that the remanence at both locations was acquired after folding comparison with the north american precambrian apparent polar wander path implies that overprinting is related to the hudsonian orogeny a second stable magnetization directed to the west with a shallow inclination is superimposed on the dominant component at a numbe

mesozoic fluorite veins in ne spain record regional base metal rich brine circulation through basin and basement during extensional events abstract basinal brines are commonly involved in the formation of hydrothermal base metal ore deposits in sedimentary basins although in many instances the source of metals is often thought to be the underlying basement rocks the evidence of brine infiltration through the basement is sometimes directly found in vein systems in fracture zones crosscutting the basement that is the case of the fluorite barite base metal veins found throughout the hercynian basement of europe north africa and the appalachians a geochemical study of brines trapped in these veins can reveal their origin and evolution but also their mineralizing potential and coupled with the timing of fluid circulation can give clues to elucidate the role of these or similar brines in the genesis of base metal mineralizations together with their possible links to tectonic events the sm nd dating of fluorite samples from one of these veins in ne spain the rigros fluorite vein has yielded an age of 137 25 ma 2 mswd 0 40 the vein formation took place during the late jurassic early cretaceous rifting event in the western european basins which is related to the opening of the atlantic inclusion fluids in samples from rigros and another vein system from the same region the berta fluorite vein have been studied with microthermometry crush leach and la icp ms the brines trapped in the two studied vein systems are na ca cl k mg brines with homogenization temperatures 120 c and salinities up to 25 equiv mass nacl the source of this salinity is related to evaporated seawater at least in the halite precipitation field and to the leaching of mesozoic halite and gypsum sequences by seawater and or meteoric water the basinal brines later evolved through water rock interaction with the crystalline basement resulting in some sodium loss and potassium calcium strontium the latter inferred from isotope data and barium enrichment the analyzed brines have concentrations of zn between 3 and 790 ppm of pb between 3 and 995 ppm and of fe between 27 and 2639 ppm which are similar to those reported in comparable hydrothermal veins and mississippi valley type deposits but higher than in most present day sedimentary brines despite the fact they were able to transport large amounts of metals no significant precipitation of sulfides occurred in the veins and consequently the mineralizing potential of these brines was still preserved after fluorite vein formation

unraveling multiple thermotectonic events accommodated by crustal scale faults in northern iberia spain insights from k ar dating of clay gouges

malley diabase dykes of the slave craton canadian shield u pb age paleomagnetism and implications for continental reconstructions in the early paleoproterozoic1geological survey of canada contribution 20110114 the ne trending malley dyke swarm dated herein at 2231 2 ma u pb baddeleyite extends from the central slave craton to the vicinity of the kilohigok basin and may continue farther to the nort

baked contact test demonstrates primary nature of dominant n1 magnetisation of nipissing intrusions in southern province canadian shield abstract nipissing diabase sills cone sheets and dykes define a major episode of igneous intrusion in the southern province of the canadian shield at about 2200 ma the dominant n1 remanence of these intrusions has been established in several palaeomagnetic studies and hence is a key tie point for the north american apparent polar wander path yet the age of this magnetisation remains very controversial positive baked contact tests reported for the n1 remanence have often been dismissed as inconclusive and the n1 palaeopole attributed to overprinting during the hudsonian orogeny 1900 1800 ma due to its position on a widely accepted polar wander path for north america previous baked contact studies utilise sediments of the huronian supergroup as host rock the remanence of these sediments is often difficult to interpret in this study a positive baked contact test is described for an n1 nipissing sill or cone sheet using stably magnetized mafic dykes of the matachewan swarm as host thus the n1 remanence is primary and no longer supports the time calibration of polar wander paths which assume that it is a 1900 1800 ma overprint

cenozoic vertical motions of the catalan coastal ranges ne spain the role of tectonics isostasy and surface transport 1 we analyze the cenozoic topographic evolution of the catalan coastal ranges ne spain and the role of fault activity erosion sedimentation and isostasy in controlling uplift and subsidence a forward numerical model constrained by an extensive geological and geophysical data set is used to examine the temporal and spatial record of cenozoic vertical motions we show that the effect of isostasy erosion and sedimentation is as important as the contribution of fault deformation to the topography of the catalan coastal ranges the model predicts that paleogene topography generation by thrusting was compensated by erosion up to 1 3 km and isostatic subsidence up to 1 2 km resulting in a 1 2 1 9 km high mountain range by the end of compression 29 ma during the neogene strong tectonic subsidence related to normal faulting and the consequent flexural uplift of 0 7 1 2 km surface erosion as much as 1 6 2 3 km and sedimentation up to 4 5 km led to the present landscape configuration extension rates along the barcelona fault controlled flexural uplift and in combination with erosion and sedimentation processes led to the migration of the topographic maximum of the prelitoral range toward the easternmost ebro basin

paleomagnetism and u pb geochronology of the 2 17 ga biscotasing dyke swarm ontario canada evidence for vertical axis crustal rotation across the kapuskasing zone u pb dates on baddeleyite yield ages of 2167 8 2 2 and 2171 6 1 2 ma on two northeast trending dykes west of the kapuskasing zone in ontario canada these ages identify the dykes as belonging to the biscotasing dyke swarm east of the kapuskasing zone which was previously dated at 2166 7 1 4 ma by u pb on baddeleyite and zircon the new dates show that the biscotasing swarm was emplaced over an area of at least 300 000 km2 much larger than hitherto suspected and in a geologically short period of time of about 5 million years a comparison of paleomagnetic data from biscotasing and 2 45 ga matachewan dykes on either side of the kapuskasing zone suggests that the western half of the superior province has rotated about 10 20 counterclockwise relative to the eastern half across the kapuskasing zone this movement may have been accompanied by rifting farther north which ultimately led to the paleoproterozoic embayment underlying hudson bay that gives the superior province its characteristic butter

magmatic evolution of the southern great bear continental arc northwestern canadian shield geochronological constraints the calc alkaline great bear continental arc in the wopmay orogen developed after a collision ca 1890 ma of the archean slave craton with the paleoproterozoic hottah terrane to the west u pb zircon dating of three volcanic and six intrusive rocks from the southern part of the arc shows four stages of development i intrusion of a few small sodic leucogranite plutons at 1873 2 ma into a previously folded metasedimentary sequence ii abundant calc alkaline felsic volcanism and subvolcanic intrusions during the period 1870 1866 ma bracketed by five ages iii intrusion of large calc alkaline granitic plutons including the marian river batholith dated by zircon and titanite from two samples at 1866 2 3 ma and iv emplacement of the potassic faber lake rapakivi granite at 1856 2 3 ma the arc was developed on the hottah terrane due to easterly subduction of an oceanic plate under the amalgamated slave craton hottah terrane the oldest exposed rocks in the southern part of the arc are remnants

mesozoic extensional tectonics stratigraphy and crustal evolution during the alpine cycle of the eastern iberian basin abstract sequence stratigraphy subsidence analysis and the integration of the basin fill data allow to the identification of four successive evolutionary stages in the basins of the eastern iberian margin during mesozoic extension 1 triassic rift late permian hettangian 2 early and middle jurassic postrift sinemurian oxfordian 3 late jurassic and early cretaceous rift kimmeridgian middle albian and 4 late cretaceous postrift late albian maastrichtian the present day crustal structure of the eastern iberian range and evidence of its evolution are deduced from the analysis of a new gravity map and other geophysical data a regional gravity low along the iberian range is interpreted in terms of crustal thickening beneath the orogen as a result of the collision between the ebro block and the iberian plate during the paleogene the boundary between these blocks coincides with a magnetic lineament that is interpreted as an inherited signature of the thinning that occurred during mesozoic extension a geodynamic scenario for the crustal evolution of the eastern part of the iberian peninsula based on the evaluation of mesozoic extensional tectonics and an analysis of the available geophysical data includes three main successive evolutionary stages 1 1 mesozoic crustal thinning 2 2 paleogene crustal thickening 3 3 neogene crustal thinning based on new geological and geophysical arguments this study offers an alternative and a more complete geodynamic history of the eastern iberian basins related to the evolution of the iberian plate and the central north atlantic

theoretical constraints on true polar wander 1 for the present geologic epoch true polar wander tpw is relatively small but simple theoretical considerations suggest that it could have been larger in other epochs in this work we use scaling arguments to assess the qualitative behavior of tpw and a simple maxwell model to analytically describe how changes in mass anomalies translate into tpw unlike previous work we derive simple analytical estimates of tpw based on the characteristic amplitudes and timescales for changes in the moment of inertia we find estimates for both the amplitude and speed of tpw as a function of earth properties the following four main factors influence how large the maximum tpw can be the geological timescale over which the desired tpw occurs tpw the viscosity structure of the mantle which yields a weighted average viscosity the characteristic amplitude of the nonhydrostatic changes in the moment of inertia c and the added moment of inertia due to the equatorial bulge c a for the nominal values 3 1022 pa s and c c a 0 003 the maximum tpw is 61 over 100 myr and 8 over 10 myr the maximum tpw speed is only sensitive to c and c a and is 2 4 myr 1 for the nominal values tpw is shown to act as a low pass filter rapid changes in moment of inertia produce smaller and delayed tpw a consequence of this is that inertial interchange tpw does not have a different character than tpw tpw can have an important contribution to plate motions over relatively long timescales but not over shorter timescales our simple approach allows us to assess whether multiple tpw events are possible but the major uncertainty continues to be the mantle viscosity structure

digital soil pattern recognition in the lower namoi valley using numerical clustering of gamma ray spectrometry data abstract digital soil mapping involves the use of ancillary data e g proximal and remotely sensed as surrogates for soil information to produce maps of soil type or classes two of the most popularly used sources of ancillary data are the proximally sensing electromagnetic em induction instruments and remotely sensed digital elevation model data dem however these data have limitations at the catchment level and are of limited use on predominantly flat alluvial landscapes respectively another option is the use of remotely sensed gamma ray ray spectrometry data which has successfully been used to map the regolith in this paper the use of ray spectrometry data i e potassium k uranium u thorium th and total count tc coupled with a numerical clustering algorithm i e fuzzy k means fkm algorithm is explored in order to identify geological and geomorphological units at the district and soil mapping units at a broader catchment level we do this by using the euclidean distance and the measures of fuzziness performance index fpi and normalized classification entropy nce to identify k 11 classes and a fuzziness exponent 2 0 for interpretation the k 11 classes produce contiguous classes which are consistent with geological and geomorphological interpretations of an eroded landscape alluvial lands and dust mantled alluvial lands at the district level at the sub catchment level the k 11 classes also match broad soil mapping units and also elucidate subtle differences of the alluvial lands which characterise the agriculturally significant parts of the lower namoi valley fuzzy canonical analysis shows that k and tc contribute most to the discrimination of the classes associated with the trachyte rich parts of the eroded landscape the alluvial lands and most of the dust mantled alluvial lands whilst u and th discriminate the basaltic outliers and other geomorphological units of the eroded lands we conclude that the approach allows soil management and landscape units to be identified with the information used as a first approximation to determine where soil sample locations need to be collected to validate the map units identified in order to better incorporate and characterise subsoil properties the inclusion of em signal data e g em38 or dualem 1 may also be appropriate

the nature and importance of phyllonite development in crustal scale fault cores an example from the median tectonic line japan abstract like many large crustal scale faults the median tectonic line mtl in sw japan has a long history of movement having been active predominantly as a strike slip fault since the mid cretaceous fault rock exposures in the core of the mtl preserve a history of deformation at a range of mid to shallow crustal depths ryoke mylonites 1 4 km north of the main contact record deeper level cretaceous top to the south sinistral movements the remainder of the fault zone core is surprisingly narrow exhibiting a wide variety of fault rocks that illustrate both the interaction and effects of syn tectonic fluid influx over a range of deformation conditions exposures within 50 m of the central slip zone display a progressive sequence in fault rock evolution from ultramylonite cataclasite foliated cataclasite phyllonite breccia gouge this sequence occurs because cataclasis in the vicinity of the fault core creates permeable pathways for the ingress of chemically active fluids into the fault zone this leads to the replacement of load bearing phases such as feldspar by fine grained foliated aggregates of intrinsically weaker phyllosilicates such as white mica and chlorite the grain size reduction associated with both cataclasis and mineral alteration creates conditions ideal for the operation of fluid assisted stress induced diffusive mass transfer mechanisms comparison with the findings of recent experimental studies suggest that the fault zone processes observed in the core of the mtl will lead to long term weakening provided the network of phyllosilicate rich fault rocks are able to form an interconnected thin layer of weak material on kilometre to tens of kilometre length scales

palaeomagnetism and u pb dates of the palaeoproterozoic akitkan group south siberia and implications for pre neoproterozoic tectonics

towards digital soil morphometrics article i nfo article history digital soil morphometrics is defined as the application of tools and techniques for measuring and quantifying soil profile attributes and deriving continuous depth functions this paper reviews how proximal soil sensing and other tools can be used in soil profile descriptions where techniques and toolkits have not changed in the past decades the application of such tools is compared to standard soil profile descriptions for 11 common attri butes horizons texture color structure moisture mottles consistence carbonates rock fragments pores and roots these attributes are extensively used in soil classification and are indicative of many soil functions there has been progress in distinguishing soil horizons texture and soil color mainly using vis nir gpr and electrical resistivity there is potential for in situ digital morphometrics for all attributes of a soil profile smaller depth increments can be sampled and analyzed and that gives continuous depth functions of soil properties the com bined use of in situ digital morphometrics and continuous depth functions of soil properties may enhance our pedological understanding it will take time before the toolbox of the field pedologists will be digitally enriched but we think that digital soil morphometrics has the potential to complement existing description and analytical methods it may yield new insights in soil horizonation how soils form and how they could be classified published by elsevier b v

an approach to the thermal field in northeastern spain temperature data from oil wells thermal springs and recent water wells have been compiled and used to construct a temperature gradient map for the northeastern part of the iberian peninsula this map shows a gentle increase in thermal gradient from north to south and west to east with individual areas displaying both cold and warm temperature data a very cold area near the ebro mouth and a nearby anomalously warm area offshore are the most important features of the gradient map these data are interpreted in terms of normal 30 35 mk m 1 geothermal gradient with conspicuous anomalies caused by groundwater circulation this interpretation differs from previously published models of the thermal regime in northeastern spain

short lived 1 9 ga continental margin and its destruction wopmay orogen northwest canada a 1 9 ga continental margin in the northwest of the canadian shield evolved in less than 15 m y from a zone of crustal stretching through a phase of passive margin subsidence to attempted subduction beneath an exotic microcontinent reversal of subduction polarity and generation of a major episutural magmatic arc occurred within 15 m y following microcontinental accretion terminal collision occurred 90 m y at most after initial rifting certain differences in detail between this collided margin and those of phanerozoic age may be related to subduction of newly rifted lithosphere rapid evolution of the orogen the contracted passive margin phase in particular is consistent with but does not prove more rapid recycling of oceanic plates at that time

temperature micro mapping in oscillatory zoned chlorite application to study of a green schist facies fault zone in the pyrenean axial zone spain oscillatory compositional zoning in minerals has been observed in hydrothermal magmatic and metamorphic environments and is commonly attributed to chemical or physical cyclical changes during crystal growth chemical zoning is a common feature of solid solutions which has been rarely reported in phyllosilicates in this study oscillatory zoning in chlorite is described in samples from the pic de port vieux thrust a minor thrust fault associated to the major gavarnie thrust fault zone central pyrenees spain the pic de port vieux thrust sheet comprises a 1 20 m thick layer of triassic red pelite and sandstone thrust over mylonitized cretaceous dolomitic limestone the thrust fault zone deformation comprises secondary faults and cleavage affecting the triassic pelite and sandstone an important feature responsible to this deformation is a set of veins filled by quartz and chlorite chlorite is present in crack seal extension veins and in shear veins both structures opened under the same stress conditions in some shear veins chlorite occurs as pseudo uniaxial plates arranged in rosette shaped aggregates these aggregates appear to have developed as a result of radial growth of the chlorite platelets oscillatory zoning has been imaged by backscattered scanning electron microscopy and by x ray quantitative micro mapping these oscillations correspond to chemical zoning with alternating iron rich and magnesium rich bands the chlorite composition ranges from a fe rich pole to a mg rich pole fe 3 fe values were measured in chlorite using xanes spot analyses and vary from 0 23 to 0 44 the highest values are in the fe rich area temperature maps built from standardized microprobe x ray images and redox state using the program xmaptools indicate oscillatory variations from about 310 to 400 50 c during chlorite crystallization these temperature variations are correlated with a fe 3 fe variation by al 3 fe 3 1 and di trioctahedral substitutions highlighted by mg and fe tot contents fe mg zoning chemical variations could be then explained by alternation of cooling times and cyclical pulses of a fluid hotter than the host rock it is however not excluded that kinetic effects influence the incorporation of mg or fe during chlorite crystallization

origin of the atrevida vein catalonian coastal ranges spain mineralogic fluid inclusion and stable isotope study atrevida is a ba f base metal vein located in the catalonian coastal ranges of spain about 100 km southwest of barcelona the vein cuts paleozoic metasediments and granites of the hercynian basement and triassic red beds at the base of an overlying transgressive sequence the atrevida vein can be divided into three parts on the basis of mineralogy the lower level contains sugarlike quartz fluorite minor barite the middle level contains a breccia of banded barite basement rocks cemented by a complex sulfide arsenide assemblage with galena ni sulfide ag sulfosalt and native silver veinlets the upper level contains symmetrical bands of white barite late calcite and marcasite are found in geodes the only alteration observed is quartz sericite chlorite after k feldspar and biotite where the vein cuts granite host rocks fluid inclusions in fluorite homogenize at 110 degrees c and have salinities of 21 wt percent nacl equiv inclusions in sphalerite homogenize at 90 degrees c and have salinities of 22 wt percent nacl equiv eutectic results in both minerals are as low as 59 degrees c indicating that the trapped fluids are complex cacl 2 bearing polysaline brines fluid inclusions in late calcite homogenize at 0 3 degrees c indicating that low salinity waters invaded the vein system during calcite deposition sulfur and oxygen isotope analyses reveal that vein barites have delta 34 s values of 14 to 17 9 per mil cdt and delta 18 o values of 9 5 to 12 2 per mil smow barite also occurs as cement in the triassic red beds with delta 34 s 15 3 per mil and delta 18 o 10 6 per mil both the sulfur and the oxygen isotope compositions are within the ranges reported for lower triassic to lower jurassic age evaporites banded galena from the middle level of the vein has delta 34 s values between 6 3 and 8 9 per mil and rimming anglesite has delta 34 s values of 21 to 30 9 per mil galena from the central breccia has delta 34 s values of 14 9 to 16 1 per mil and coexisting sphalerite is about 10 per mil quartz in the lower level of the vein has delta 18 o in the range 20 7 to 22 7 per mil we infer that sulfate in the vein was derived directly from seawater or from a solution which dissolved evaporites as it descended through the triassic section along the fault zone barite and sulfides were precipitated where the sulfate bearing solution mixed with an ascending ba rich brine the reduced sulfur found in the vein may have been carried by the ascending brine banded galena and may also have been produced by bacterial reduction of sulfate from a surficial source galena in breccia oxidizing nonmarine waters were introduced into the hydrothermal system giving rise to anglesite rims on galena mineralization took place in the late triassic during an extensional tectonic regime characterized by a high geothermal gradient atrevida and similar barite veins found throughout the catalonian coastal ranges formed along basin margin faults near a paleosurface formed on hercynian basement on a broader scale low temperature veins are known to occur throughout western europe and northern africa if atrevida is representative of the group then the formation of these veins may be linked to mesozoic extensional tectonics

evolution of the central catalan margin of the valencia trough western mediterranean abstract the evolution of the central catalan margin was conditioned by major fault activity and thermal processes generated by crustal thinning the continental margin structure is characterised by major ne sw striking southeast dipping basement faults which have given rise to a graben half graben and horst system these faults acted essentially as normal faults no major neogene strike slip activity has affected the continental margin although minor episodic variations from the dominant extensional regime to strike slip tectonics cannot be discounted two major structural evolutionary stages took place at the margin the transition from one stage to the other being gradual 1 rifting stage late oligocene to early burdigalian related to the opening of the valencia trough and from which originated both the barcelona and valles penedes half grabens 2 thermal subsidence stage late burdigalian to present generated by the subsequent crustal cooling and thinning fault activity during this stage was essentially concentrated in the major half graben bounding faults the sedimentary evolution of the central sector of the catalan margin was controlled by the tectonic and crustal evolution as well as by the successive sea level and paleoclimatic changes which affected the region drastic changes in the depositional systems took place during the transition from the rifting stage into the thermal subsidence stage during aquitanian langhian time characterized by an overall trend of pulsating encroachment of marine conditions over the continental margin a noticeable diversity of depositional systems alluvial lacustrine coastal evaporitic fan delta bay shelf carbonate platform systems developed from the latest serravallian up to the present the depositional framework was less varied due to a general lowering of sea level and to the final onlapping of most of older structural highs which are now buried below the miocene sediments two progradational terrigenous shelf talus systems separated by the messinian erosive surface developed during the latest serravallian tortonian and pliocene quaternary

compositions and parageneses of secondary minerals in the onikobe geothermal system japan abstract parageneses and chemical compositions of secondary minerals in many core samples of the onikobe geothermal system japan were investigated in detail in order to evaluate the controls of geothermal waters on alterations of andesitic dacitic rocks depth zonations of secondary minerals were delineated for cazeolites as mordenite laumontite yugawaralite wairakite and clay minerals as smectite alkaline smectite chlorite smectite chlorite compositional variations with depth hence temperature are apparent for smectite chlorite and illite chlorite interstratified clay minerals but not for wairakite both prehnite and epidote at depth have fe rich compositions and become more aluminous with increasing depth the ubiquitous occurrence of pyrite and rare magnetite and the absence of hematite suggest that the onikobe system had fs2 fo2 conditions within the pyrite stability field the occurrence of abundant calcite and ca zeolites indicates that thermal waters at depth are neutral to slightly alkaline and xco2 is very low to stabilize ca al silicates this conclusion is consistent with the production of a remarkable amount of alkaline high temperature steam and thermal waters in a newly drilled production well

p t deformation fe3 fe2 mapping at the thin section scale and comparison with xanes mapping application to a garnet bearing metapelite from the sambagawa metamorphic belt japan quantitative x ray maps of composition from a chlorite k white mica albite quartz and garnet bearing thin section from a sambagawa blueschist facies metapelite were combined with a multiequilibrium calculation method to calculate a p t fe3 fe2 deformation map at the millimetre scale the studied sample was chosen because elongated chlorite crystallization tails pressure shadows rimmed by phengite are present which is an appropriate assemblage for the quantification of the p t evolution chlorite temperature and fe3 content maps were calculated by successive iterations for each pixel analysis of fe3 until convergence of the four chlorite quartz h2o equilibria that can be written using the fe and mg amesite clinchlore daphnite and sudoite chlorite end members the calculated map of fe2 fe3 in chlorite is in good qualitative agreement with the in situ mapping of this ratio using xanes x ray absorption near edge structure techniques the temperature map indicates that high temperature chlorite zones with low fe3 contents alternate with lower temperature zones and higher fe3 contents in the crystallization tail late fractures perpendicular to the elongation axis of the tail are filled by very low temperature chlorite 250 c showing fe3 fetotal up to 0 4 groups of chlorite and mica pixels were then identified based on compositional and structural criteria and a p tdeformation map was calculated using representative analyses of these groups the calculated p tdeformation map suggests that in contrast to chlorite the composition of most mica did not change significantly during exhumation mica reequilibrated in late ew shear bands only ew shearing was already active at 0 1 gpa 500 c which corresponds to the peak temperature and probably pressure conditions at reduced redox conditions the intensity of deformation probably decreased with decrease in temperature to 350 400 c at this temperature a second main deformation event corresponding to a further ew stretching occurred and was still active below 250 c and more oxidizing conditions these results indicate that the scale at which p t data can be obtained is now close to the scale of observation of structural geologists a close link between deformation and mineral reaction is therefore possible at the microscopic scale which provides information about the relationship between deformation and mineral reactivity the modalities of deformation with time and the p t conditions at which it occurred

a chlorite solid solution geothermometer the los azufres mexico geothermal system chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites in the active geothermal system of los azufres mexico electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition correlation coefficients among chemical constituents were calculated it is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content and there is almost no correlation with the octahedral aluminium and magnesium content a procedure is proposed to select end members and substitution vectors and to give a general formula for these chlorites

post aphebian uplift deduced from remanent magnetization yellowknife area of slave province remanent magnetization in five indin three dogrib two archean and one mackenzie dyke contact zone s from the yellowknife area of the canadian precambrian shield has been studied in order to establish the ambient temperature of the host rock and the depth of burial of the present erosion surface at the time of intrusion a positive baked contact test for an aphebian indin dyke demonstrates the primary nature of the dyke magnetization from this contact eight individual specimen determinations of the ambient host rock temperature at the time of intrusion yield an average of 211 c with a standard deviation of 18 c and probable error of 36 c assuming a paleogeothermal gradient of 44 c km 30 the estimated depth of burial of the present erosion surface is none of the remaining contacts yield estimates of the depth of burial however the results from the three dogrib contacts illustrate complications such as chemical overprinting that must be considered when analysis is made of magnetization

the effect of mineralogy and effective normal stress on frictional strength of sheet silicates abstract phyllosilicates are common constituents of upper crustal faults and subduction forearcs we studied the effect of mineralogy and controlled effective normal stress between 5 mpa and 100 mpa on frictional strength although the effect of mineralogy on frictional strength of single phase phyllosilicate gouges has been previously studied the influence of effective normal stress has not we conducted water saturated and vacuum dry frictional tests on single phase phyllosilicate gouges using a triaxial apparatus minerals included talc pyrophyllite kaolinite lizardite illite montmorillonite chlorite muscovite phlogopite and biotite particle size 20 mpa dry friction coefficients are constant and wet friction coefficients show a small increase this is attributed to loss of water and increased contact area the results indicate that frictional strength of clay rich faults increases at depths less than 1 km under hydrostatic pore fluid pressures

p t t estimation of deformation in low grade quartz feldspar bearing rocks using thermodynamic modelling and 40ar 39ar dating techniques example of the plan de phasy shear zone unit brianconnais zone western alps pressure temperature time p t t estimates of the syn kinematic strain at the peak pressure conditions reached during shallow underthrusting of the brianconnais zone in the alpine subduction zone was made by thermodynamic modelling and 40ar 39ar dating in the plan de phasy unit se of the pelvoux massif western alps the dated phengite minerals crystallized syn kinematically in a shear zone indicating top to the n motion by combining x ray mapping with multi equilibrium calculations we estimate the phengite crystallization conditions at 270 50 c and 8 1 2 kbar at an age of 45 9 1 1 ma combining this p t t estimate with data from the literature allows us to constrain the timing and geometry of alpine continental subduction we propose that the brianconnais units were scalped on top of the slab during ongoing continental subduction and exhumed continuously until collision

griffin gabbro sills 2 11 ga hurwitz basin nunavut canada long distance lateral transport of magmas in western churchill province crust circa 2 11 ga sills and rare dykes herein named the griffin gabbros extend discontinuously across an area 400 by 125 km in the hearne domain of the western churchill province in northern canada sills form poorly connected tongue like tabular bodies primarily within paleoproterozoic intracratonic basin deposits of the lower hurwitz group dykes are restricted to the southern limit of the griffin suite and have not been found in the interior of hurwitz basin or in archean basement incompatible element patterns and low end2111 values 0 1 1 0 indicate an enriched asthenosphere source similar to many modern hotspot related ocean island basalts the gabbros display enrichments in nb and la suggesting a mantle plume origin heavy rare earth element depletions and tio2 values averaging 3 40 wt suggest partial melting of a garnet peridotite source at depths of 70 100 km mgo values averaging 5 20 wt indicate fractionation after melting concentrations of both the incompatible and compatible elements scatter widely with respect to mg number indicating that compositional variation does not represent fractional crystallization from a common parent consistent with derivation from different magma chambers related to the same mantle plume the gabbros fail to show signs of an archean enrichment event recorded by other paleoproterozoic mafic rocks in the hearne domain this together with the absence feeder dykes in basement indicate derivation external to hurwitz basin we interpret that a mantle plume located beyond the present southern margin of the hearne domain was active during 2 1 ga rifting that led to opening of the manikewan ocean the griffin gabbros were likely injected because of the hydraulic head created by topographic doming above this plume analogous to the ferrar sills jurassic in antarctica the gabbros may have been fed by cryptic dykes in which magmas traveled laterally for at least 250 km across the southern hearne domain and then controlled by sedimentary layering spread as sills for hundreds of km within hurwitz basin

palaeogene evolution of deformation in the northeastern iberian peninsula during the palaeogene alpine compression three units were differentiated in the studied area south of the ebro basin the catalan coastal range dominated by ne sw major basement faults with a sinistral movement the iberian range where the important basement faults have a nw se direction and a reverse movement often with a dextral component the linking zone between these two ranges where an e w dominant structural direction is marked by an array of folds and thrusts with a northward vergence in the mesozoic cover from the analysis of both these major structures and the small scale structures it can be deduced that the compression in the studied area has evolved from a nw se direction lower middle eocene to a n s direction and to a ne sw one uppermost oligocene the major structures are due to the n s compression later the stress field progressively changed to a distensive regime we suggest a relation between the compressive phases and the displacement direction of the iberian plate with reference to the european plate

dehydration of dioctahedral aluminous phyllosilicates thermodynamic modelling and implications for thermobarometric estimates we propose a solid solution model for dioctahedral aluminous phyllosilicates accounting for the main compositional variations including hydration observed in natural smectites interlayered illite smectite illites and phengites from diagenetic to high grade metamorphic conditions the suggested formalism involves dehydrated micas and hydrated pyrophyllite like thermodynamic end members with these end members the equilibrium conditions of quartz water k bearing mica like phyllosilicates of fixed 2 1 composition are represented by a line in p t space along which the interlayer water content varies the relevant thermodynamic properties required for the calculation of equilibrium conditions were derived using a set of 250 natural data of known maximal temperature and pressure conditions which covers a range between 25 c and few mpa to 800 c and 5 gpa the temperatures calculated at fixed pressure with our model are in fair agreement with those reported in the literature for the 250 natural data at low temperature and pressure the amount of interlayer water in k deficient phengite and illite is predicted to reach 100 of the apparent vacancies which is consistent with previous values reported in the literature although the amount of interlayer water is predicted to decrease with pressure and temperature it is calculated to be significant in k deficient phengite from lt hp pelites metamorphosed at about 350 c 10 kbar the presence of molecular water in the interlayer site of such phengites has been confirmed by ftir mapping its implications for p t estimates are discussed

paleomagnetism and time stratigraphic correlation of proterozoic redbeds of the labrador trough and outliers of northern quebec one hundred and forty two oriented cores were collected from redbeds of the sakami formation near lg 4 85 dieter 19 cambrian 18 and snow ball 4 lakes all in quebec and from two outliers in labrador evening lake 6 and sims lake 10 a further 73 oriented drill cores were collected from the strongly folded chakonipau formation redbeds 44 in the labrador trough and undeformed redbeds near lac imbault 29 on the western edge of the trough thermal demagnetization of the trough redbeds yielded 52 core directions each of which showed good specimen end points and sufficient homogeneity of magnetization and 101 such core directions were obtained for the outlier redbeds in most of these samples there are no indications that the stable remanence is multi component and the fold test yields for lg 4 sakami formation and the chakonipau formation a significant 95 probability improvement of the dispersion parameter k thus the chakonipau formation remanence is probably pre hudsonian and th

two neoarchean supercontinents revisited the case for a rae family of cratons abstract a variety of early paleoproterozoic supercontinents or supercratons have been proposed including kenorland superia and vaalbara improved geologic knowledge of the churchill province canadian shield suggests that the classical kenorland configuration with linked rae and hearne cratons is invalid and represents a younger ca 1 9 ga nuna configuration we review the early paleoproterozoic tectonic history of the rae craton and propose that the ca 2 55 2 50 ga macquoid and 2 50 2 28 ga arrowsmith orogens represent critical piercing points for supercontinent reconstruction utilizing the stratdb and dateview databases we have identified nearly two dozen regions worldwide that show effects of these orogenic events including the rae gawler mawson peninsular india west africa amazonia north china and sask crustal blocks we propose that these cratonic blocks form a distinct rae family lineage utilizing new time space plots for the rae family and components of the superia and vaalbara supercratons we demonstrate that the rae family lacks the distinctive early paleoproterozoic depositional and glaciogenic record characteristic of superia and vaalbara but has an important contemporaneous record of juvenile crust formation and contractional orogenesis we propose the collective history of the rae family is best reconciled if it represents the now dispersed blocks of a third earliest paleoproterozoic supercraton that we term nunavutia in this model the magmatic and tectonometamorphic record of these cratons includes an early 2 55 2 45 ga period of interior collisional orogenesis in which the supercraton amalgamated and a later phase of long lived peripheral orogenesis 2 45 2 28 ga prior to its partial break up at ca 2 05 ga forming within an otherwise globally quiescent period the history of the rae family is important for assessment of constrasting models of early paleoproterozoic geodynamic activity

the late archean record a puzzle in ca 35 pieces abstract the global archean record preserves ca 35 large cratonic fragments and a less well defined number of smaller slivers most archean cratons display rifted margins of proterozoic age and therefore are mere fragments of supercratons which are defined herein as large ancestral landmasses of archean age with a stabilized core that on break up spawned several independently drifting cratons the tectonic evolution of individual archean cratons such as the slave craton of north america or the kaapvaal craton of southern africa should therefore always be considered in the context of their ancestral supercratons this is particularly true for many of the smaller cratons which are too limited in size to preserve the complete tectonic systems that led to their formation these limitations not only apply to the crustal geology of archean cratons but also to their underlying lithospheric mantle keels if these keels are archean in age as their broad correlation with ancient surface rocks suggests they also are rifted and drifted remains of larger keels that initially formed below ancestral supercratons the study of archean cratons and their lithospheric keels should thus be global in scope in the search for late archean supercratons a craton like the slave with three to four rifted margins has a ca 10 maximum probability of correlating with any of the ca 35 remaining cratons around the globe assuming wholesale recycling of archean cratons has been limited since ca 2 0 ga alternatively if the original number of independently drifting cratons was significantly larger the probability of successful correlations is much less due to repeated cycles of break up and plate tectonic dispersal since ca 2 0 ga the probability of correlation is probably independent of present day proximity unless there is independent evidence that two neighbouring cratons were only separated by a narrow ocean nevertheless most previously proposed craton correlations rely erroneously on present day proximity implicitly extrapolating relatively recent paleogeography back to the archean considering the fundamental differences between some of the better known cratons such as the slave superior and kaapvaal it seems likely that these cratons originated from independent supercratons sclavia superia vaalbara with distinct amalgamation and break up histories this is contrary to widely held opinion based largely on an idealized view of the supercontinent cycle that all cratons shared a common history in a single late archean supercontinent in contrast to the superior and kaapvaal cratons which are radically different from the slave craton and each other the dharwar craton of peninsular india the zimbabwe craton of southern africa and the wyoming craton of north america all show significant similarities to the slave craton it thus seems likely that at least some of these were nearest neighbours to the slave craton in the ca 2 6 2 2 ga sclavia supercraton

paleomagnetism u pb geochronology and geochemistry of marathon dykes superior province and comparison with the fort frances swarm we report the first detailed study of the paleomagnetism u pb geochronology and major element geochemistry of paleoproterozoic north trending marathon dykes north of lake superior the paleomagnetic and geochemical results demonstrate that marathon dykes can be divided into two subsets one of normal magnetic polarity the other of reverse polarity normal and reverse marathon paleomagnetic poles at 43 n 196 e dm 9 dp 7 number of dykes n 16 and 51 n 175 e dm 9 dp 6 n 12 respectively are statistically distinct and may indicate different ages of normal and reverse dyke emplacement a u pb baddeleyite age of ma has been obtained at a normally magnetized marathon paleomagnetic site the reversely magnetized marathon dykes are undated but have a paleopole rather close to that of the reversely magnetized ma fort frances dykes and major element geochemical signatures as portrayed on jensen plots that are identical to those of the fort frances swarm therefore reverse marathon an

reconnaissance paleomagnetic study of igneous rocks from the eastern sector of the labrador trough a paleomagnetic study has been carried out on 75 samples of metagabbro and metaperidotite from 14 sites in the labrador trough the sites were distributed over a distance of 500 km and are situated

crystallochemical indexes and geothermobarometric calculations as a multiproxy approach to p t condition of the low grade metamorphism the case of the san luis formation eastern sierras pampeanas of argentina abstract in this work crystallochemical indexes and geothermobarometric calculations are used together to estimate the p t condition in low grade metamorphic units of the san luis formation from sierra de san luis eastern sierras pampeanas of argentina phyllites and slates from this formation record at least two episodes of white mica wm and chlorite chl growth associated with main d1 s1 wm2 chl1 and local d2 s2 wm3 chl2 stages mean kicis values of 0 30 western belt and 0 23 2 eastern belt were determined for the the identification of increasing p t condition paths in low grade metasedimentary successions is not easy in the absence of higher grade rocks in these situations a systematic sampling and analysis of dozens of samples must be carried out the very good correlation between crystallochemical index values kubler index and white mica b parameter and thermobarometric calculations empirical and semi empirical chlorite thermometers and thermobarometry for chlorite white mica quartz h2o equilibrium presented in this work argues in favor of the development of a multiproxy study strategy in this type of low grade metasedimentary successions that involve 1 a systematic sampling of metapelite levels for x ray diffraction study mineralogical and crystallochemical indexes with a rapid implementation allowing a dense systematic sampling 2 the recognition of variations in the p t conditions from ki and b parameter values and the consequent selection of metapelitic samples for analyzing mineral chemistry and thermobarometric calculations in order to facilitate these calculations a user friendly spreadsheet for crystallochemical indexes and chlorite thermometry calculations is also provided

recurrent hydrothermal activity induced by successive extensional episodes the case of the berta f pb zn vein system ne spain abstract a mineralogical and geochemical fluid inclusion stable and radiogenic isotopes study of the berta f pb zn vein system has identified the source and temperature of the fluid reservoirs involved and proved the existence of two separate hydrothermal events at the mine scale which reflect distinct periods of regional fluid circulation main stage minerals fluorite i sulphides calcite i and barite i precipitated by mixing between a polysaline h 2 s bearing 34 s 11 brine up to 23 nacl eq salinity and a more dilute fluid 18 o from 3 2 to 0 at temperatures between 80 and 150 c the progressive increase in 87 sr 86 sr ratio from the early precipitated minerals 0 71242 in calcite i to the late ones 0 71894 in fluorite ii is mainly but not exclusively due to a difference in age separating the two hydrothermal events the assumed genetic model for the main stage fluorite i is based on a convective circulation of surficial waters leaching the crystalline basement rocks acquiring a high salinity high 87 sr 86 sr ratios and a high temperature these fluids then mixed with low salinity low temperature waters having a low 87 sr 86 sr ratio an at least jurassic age is suggested for the main period of vein filling contemporaneous with the extensional regime during the mesozoic when fluid circulation was probably enhanced by crustal thinning during the early burdigalian lower miocene a new period of important extension in this area took place hydrothermal activity related to this new and younger extensional regime is geochemically different and produced a distinctive mineralogical record developing a set of veinlets filled with green octahedral fluorite fluorite ii calcite ii and barite ii the sr isotope compositions of these late stage vein minerals are compatible with leaching the granodiorite host rocks during recent times the existence of successive hydrothermal events in the same area is not surprising as geothermal systems like la garriga samalus are still active and currently precipitating fluorite

crustal scale structure of south tien shan implications for subduction polarity and cenozoic reactivation based on new structural and petrological investigations we present two crustal scale cross sections of the kyrgyz south tien shan and correlations of main faults and units between kyrgyzstan and china the overall structure corresponds to a doubly vergent mountain belt the kyrgyz and chinese areas exhibit identical structural and metamorphic histories to the west the atbashi range comprises high pressure oceanic and continental units stacked by north verging thrusts above a low metamorphic accretionary prism high pressure hp gneisses are bound to their south by a south dipping detachment exhibiting mantle relicts the high pressure oceanic and continental units underwent similar pressure temperature p t paths with peak conditions of around 500 c 20 kbar followed by rapid exhumation the overall south dipping structure and kinematics indicate a south dipping subduction of the central tien shan ocean at 320 310 ma ending with the docking of the tarim block to the kazakh continent to the east the pobeda massif shows a narrow push up structure a major north vergent thrust exhumes deep crustal level granulites constituting the highest summits which were thrust towards the north onto low grade devonian carboniferous schists the southern part of south tien shan is made up of a south verging thrust stack that formed later during ongoing convergence reactivated throughout post 30 ma phases

diagenetic and oil migration history of the kimmeridgian ascla formation maestrat basin spain abstract the marine limestones of the kimmeridgian ascla formation in the maestrat basin reached more than 3500 m in burial depth during the cretaceous era despite containing organic rich intervals mature in parts of the basin its potential as oil source rock has been either overlooked or questioned a petrographic geochemical and fluid inclusion fi study of the cements of the ascla was performed in order to unravel its diagenetic and thermal evolution we particularly sought evidence of oil migration and its timing three sequences of cement were distinguished sequence 1 fills the primary porosity and began with fe poor calcites with geochemistry and fis consistent with precipitation from marine derived waters during shallow burial these calcites were followed by burial cements including ferroan calcite dolomite and minor celestite and barite sequence 2 consists of mg rich fracture filling calcite cement zones the earlier ones are ferroan and contain primary aqueous and oil fis with homogenization temperatures suggesting precipitation at temperatures as high as 117 c sequence 3 is dominated by fracture filling calcites with geochemistry and fis indicating precipitation at low temperatures less than 50 c from meteoric waters cross cutting relationships with compressional microstructures indicate that sequence 3 formed after the eocene oligocene tectonic inversion of the basin oil fis in sequence 2 provide evidence that light oils migrated through the ascla formation via fractures and microfractures these oils were likely generated in the organic rich marls of the basal part of the ascla the paragenetic sequence and burial history are consistent with oil generation when the ascla was at or close to maximum burial depth but before the eocene alpine tectonism which likely formed the structural traps in the basin oil generation and migration occurred long before this event therefore it is probable that early traps were breached by the alpine structures and that potential in this basin sector is low

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

uplift estimated from remanent magnetization munro area of superior province since 2150 ma ago a method for determining depth of burial from remanent magnetization was applied to three igneous contacts of two different ages in munro township of the superior province of the canadian shield sampling profiles perpendicular to the contact of a 2150 ma diabase dike one collected in an older 2690 ma diabase dike and a second in gabbro country rock yielded ambient temperatures for the present erosion surface at the time of dike emplacement of 219 23 and 181 7 c respectively a third sampling profile perpendicular to a 2690 ma dike failed to provide a usable magnetic contact zone a secondary magnetic component with shallow inclination and easterly declination was detected in individual samples collected from both dikes as well as from the surrounding country rock converging remagnetization circles indicate that this component acquired some time after emplacement of the younger 2150 ma dike has the direction d 70 i 39 and corresponding paleopole 39 e 4 s

long term fluid circulation in extensional faults in the central catalan coastal ranges p t constraints from neoformed chlorite and k white mica the neoformation of chlorite and k white mica in fault rocks from two main faults of the central catalan coastal ranges the valles and the hospital faults has allowed us to constrain the p t conditions during fault evolution using thermodynamic modeling crystallization of m1 and m2 muscovite and microcline occured as result of deuteric alteration during the exhumation of the pluton 290 c t 370 c in the permian after that three tectonic events have been distinguished the first tectonic event attributed to the mesozoic rifting is characterized by precipitation of m3 and m4 phengite together with chlorite and calcite c1 at temperatures between 190 and 310 c the second tectonic event attributed to the paleogene compression has only been identified in the hospital fault with precipitation of low temperature calcite c2 the shortcut produced during inversion of the valles fault was probably the responsible for the lack of neoformed minerals within this fault finally the third tectonic event which is related to the neogene extension is characterized in the valles fault by a new generation of chlorite associated with calcite c4 and laumontite formed at temperatures between 125 and 190 c in the absence of k white mica differently the hospital fault is characterized by the precipitation of calcite c3 during the syn rift stage at temperatures around 150 c and by low temperature fluids precipitating calcites c5 c6 and pc1 during the post rift stage during the two extensional events mesozoic and neogene faults acted as conduits for hot fluids producing anomalous high geothermal gradients 50 c km minimum

the paleomagnetic significance of new u pb age data from the molson dyke swarm cauchon lake area manitoba u pb geochronology paleomagnetism and petrography indicate that the molson dyke swarm along the western margin of the superior craton is a composite of at least two ages of intrusion the more extensive younger dyke set the molson swarm sensu stricto generally has a 030 trend is mainly pyroxenitic to noritic with subordinate diabase and has been related to rifting in a back arc environment during closure of the manikewan ocean at about 1920 1800 ma which culminated in the trans hudson orogen a u pb zircon age from one of these dykes located at cauchon lake indicates emplacement at 1877 7 150 4 similar to two previous u pb age determinations on molson dykes another dyke from cauchon lake yields a baddeleyite zircon u pb date of 2091 2 ma and appears to be part of an older mainly diabasic suite of east northeast trending dykes that may represent a continental rifting episode that preceded the opening of the manikewan ocean the new u pb age data require a revision to the interpretation of