aftsolve a program for multi kinetic modeling of apatite fission track data aftsolve is a computer program for deriving thermal history information from apatite fission track data it implements a new fission track annealing model that takes into account the known kinetic variability among different apatite species to fully utilize this model a fission track worker must obtain data that can be used to infer the kinetic characteristics of each apatite grain from which a measurement was taken such data can consist of etch figure lengths or chemical composition the benefit of this overall approach is that it allows useful information to be derived from previously unusable analyses extends the practical range of geological temperatures constrained by fission track analyses and increases overall confidence in model predictions aftsolve also incorporates the effects of fission track orientation relative to the apatite crystallographic c axis variation in initial track length and the biasing effect of 2 5 2 cf irradiation for enhancing confined horizontal track length detection aftsolve is written for windows operating systems and has a graphical interface that allows interactive input of thermal histories and real time generation of estimates for fission track length distributions and ages for up to six simultaneously modeled kinetic populations it also includes procedures for estimating the range of time temperature histories that are statistically consistent with a data set and constraints entered by the user

petrology geochemistry and geochronology of the post collisional triassic mangerite and syenite in the gwangcheon area hongseong belt south korea abstract the gwangcheon intrusive rocks occur in the hongseong collision belt of south korea which is thought to represent the eastern extension of the dabie sulu collision zone of china the central part of the gwangcheon intrusive complex consists of orthopyroxene bearing monzonite mangerite and the marginal part is composed of syenite north of the gwangcheon mangerite the post collisional 233 2 ma haemi biotite granite contains syenite enclaves shrimp u pb zircon analysis yields ages of 232 3 ma for the mangerite and 230 3 ma for a syenite enclave within the haemi biotite granite the mangerite syenite complex and syenite enclaves exhibit a shoshonitic affinity with a total alkalinity na2o k2o of 7 38 9 64 wt high k2o mg ba sr cr ni and lree contents and insignificant negative eu anomalies geochemical data indicate that the mangerite syenite intrusion and the syenite enclaves are post collisional igneous rocks formed by the partial melting of an enriched lithospheric mantle the heat for this melting was derived from asthenospheric upwelling following oceanic slab break off the shrimp age data suggest that both the gwangcheon intrusives and the syenite enclaves formed after the triassic continental collision of the north and south china blocks in korea

indosinian dextral ductile fault system and synkinematic plutonism in the southwest of the ogcheon belt south korea reply abstract the structure of the mylonite belt in the southwestern part of the ogcheon belt has been investigated and interpreted in the light of recent radiometric data the shear belt is composed of several en echelon dextral shear zones relayed by compressional or extensional tectonic bridges the dextral displacement along the fault system which may be extended to the hida zone of japan is of the order of 200 km it has brought into contact the ryeongnam block and its cambrian middle ordovician cover of north china affinity with the southwestern margin of the ogcheon belt characterized by cambrian middle silurian rift facies and shelf deposits of south china affinity synkinematic plutons are emplaced within the shear belt which is postdated by uppermost triassic unfoliated granitoids at the surface the shear belt generated elongated intermontane coal basins initiated as transtensional half grabens because of its post permian pre early jurassic age and its dextral kinematics we correlate the shear belt with the late stages of the akyioshi indosinian collisional orogeny of the east asian margin the synkinematic plutonism that accompanied the shear zone may be due to post collisional crustal stretching and subsequent anatexis at the mantle crust interface

mineralogical and geochemical characterization of the riopar non sulfide zn fe pb deposits prebetic zone se spain abstract the present paper reports the first detailed petrological and geochemical study of non sulfide zn fe pb deposits in the riopar area prebetic zone of the mesozoic betic basin se spain constraining the origin and evolution of ore forming fluids in riopar both sulfide and non sulfide zn fe pb calamine ores are hosted in hydrothermally dolomitized lower cretaceous limestones the hypogene sulfides comprise sphalerite marcasite and minor galena calamine ores consist of zn carbonates smithsonite and scarce hydrozincite associated with abundant fe hydr oxides goethite and hematite and minor pb carbonates cerussite three smithsonite types have been recognized i sm i consists of brown anhedral microcrystalline aggregates as encrustations replacing sphalerite ii sm ii refers to brownish subhedral aggregates of rugged appearance related with fe oxi hydroxides in the surface crystals which replace extensively sphalerite and iii sm iii smithsonite appears as coarse grayish botryoidal aggregates in microkarstic cavities and porosity hydrozincite is scarce and appears as milky white botryoidal encrustations in cavities replacing smithsonite also two types of cerussite have been identified i cer i cerussite consists of fine crystals replacing galena along cleavage planes and crystal surfaces and ii cer ii conforms fine botryoidal crystals found infill porosity calcite and thin gypsum encrustations were also recognized the field and petrographic observations of the riopar non sulfide zn fe pb revealed two successive stages of supergene ore formation under meteoric fluid processes i gossan and red calamine formation in the uppermost parts of the ore with deposition of fe hydr oxides and zn and pb carbonates sm i sm ii and cer i occurring as direct replacements of zn pb sulfides and ii gray calamine ore formation with deposition of sm iii cer ii and hydrozincite infilling microkarst cavities and porosity the stable isotope variation of riopar smithsonite is very similar to those obtained in other calamine ore deposits around the world their c o isotope data 18 o 27 8 to 29 6 v smow 13 c 6 3 to 0 4 v pdb puts constrains on i the oxidizing fluid type which was of meteoric origin with temperatures of 12 to 19 c suggesting a supergene weathering process for the calamine ore formation under a temperate climate and ii the carbon source that resulted from mixing between two co 2 components derived from the dissolution of host dolomite 13 c enriched source and vegetation decomposition 13 c depleted component

geological setting and age of australopithecus sediba from southern africa we describe the geological geochronological geomorphological and faunal context of the malapa site and the fossils of australopithecus sediba the hominins occur with a macrofauna assemblage that existed in africa between 2 36 and 1 50 million years ago ma the fossils are encased in water laid clastic sediments that were deposited along the lower parts of what is now a deeply eroded cave system immediately above a flowstone layer with a u pb date of 2 026 0 021 ma the flowstone has a reversed paleomagnetic signature and the overlying hominin bearing sediments are of normal polarity indicating deposition during the 1 95 to 1 78 ma olduvai subchron the two hominin specimens were buried together in a single debris flow that lithified soon after deposition in a phreatic environment inaccessible to scavengers

erosional denudation of the british columbia coast ranges as determined from fission track ages of detrital zircon from the tofino basin olympic peninsula washington in this study we use up section changes in fission track ft ages of detrital zircons to infer the tectonic evolution of the source region that fed sediments to the tofino basin a tertiary forearc basin in northwestern washington state and southwestern british columbia we have dated 50 grains from each of eight samples from a 6 km thick section that ranges in age from 40 to 19 ma the detrital zircons have not been reset and thus preserve information about the thermal and denudation history of the source region from which the sediments were derived each of our eight samples contains a distinct set of grain age populations or peaks indicating that the source region contained several ft source terrains the number of peaks and their lag time peak age minus depositional age contain thermochronologic information about these source terrains in this study there is little evidence of active volcanism in the source region thus the ft ages reflect cooling during denudation of the source regions the oldest sample in our suite from the upper eocene lyre formation shows a dominant peak at ca 40 ma coincident with cooling ages of denuded metamorphic rocks of the leech river schist on southern vancouver island this interpretation is supported by paleocurrent directions indicating a source in the vicinity of vancouver island the development of a late eocene unconformity across much of southern vancouver island and western washington and the predominance of lithic detritus in this part of the section samples from strata above the lyre formation are feldspathic and they presumably reflect erosional denudation of a plutonic source terrain peaks in samples from the lower part of this feldspathic interval have widely scattered jurassic to mid cretaceous ft ages young zircons are notably absent up section peak ages in samples from the upper part of the feldspathic section form a dominant peak that gets progressively younger with time while the age of the dominant peak becomes younger in younger samples the lag time for this peak remains constant at 40 m y this peak can be recognized in a compilation of zircon ft ages from modern exposures of the canadian coast mountains we infer that zircons in our samples were derived from progressive erosional denudation of the coast plutonic complex which had based on our results a constant rate of denudation of 250 m m y the scatter of ages in the older samples from the feldspathic interval may indicate the unroofing of a high level sedimentary basin containing the cretaceous nanaimo and burrard groups that used to overlie parts of the coast plutonic complex our study along with others shows that up section studies of ft ages of detrital zircons can be effective in resolving the long term denudation history of continental source regions

mesozoic and cenozoic exhumation history of the sw iberian variscides inferred from low temperature thermochronology abstract the post paleozoic tectonothermal evolution of the sw iberian variscides is poorly known mainly due to the scarce low temperature geochronological data available we have obtained new apatite fission tracks and apatite u th he ages to constrain the mesozoic and cenozoic tectonic evolution of this portion of the iberian massif located just north of the betic rif alpine orogen we have obtained nine apatite fission track ages on samples from variscan and pre variscan granitoids these ages range from 174 4 10 8 to 54 1 4 9 ma with mean track lengths between 10 3 and 13 9 m we have also performed 5 u th he datings on some of the same samples obtaining ages between 74 6 1 6 and 18 5 1 4 ma time temperature path modeling of these low temperature geochronological data leads us to envisage four post paleozoic tectonically controlled exhumation episodes in the sw iberian variscides three of these episodes occurred in mesozoic times middle triassic to early jurassic early cretaceous and late cretaceous at rates of 1 1 to 2 5 c ma 1 separated by periods with almost no cooling we relate these mesozoic cooling events to the formation of important marginal reliefs during the rifting and opening of the central and northern atlantic realm the fourth exhumation episode occurred in cenozoic times at rates of 3 2 to 3 6 c ma 1 being only recorded in samples next to faults with topographic escarpments these samples cooled below 80 c at 20 ma at rates of 3 13 c ma 1 due to roughly n s oriented compressional stresses affecting the whole iberian plate which in the particular case of sw iberia reactivated some of the previous late paleozoic thrusts

triassic southeastward subduction of north china block to south china block insights from new geological geophysical and geochemical data abstract lithospheric subduction prior to the assembly of the south china and north china blocks is traditionally considered to be directed northward however some critical geological and geochemical data cannot be reconciled with this northward subduction this paper presents new lines of evidence against the traditional models and proposes a new and revolutionary tectonic model to explain the distribution and exhumation of high pressure hp ultrahigh pressure uhp metamorphic rocks of the dabie sulu belt we emphasize the following 1 the triassic tectonic environment of the southern margin of the north china block was passive not active based on the stratigraphy 2 in the southern margin of the north china block no arc magmatism was recorded 3 many paleoproterozoic slices of jiaobei affinity of the jiao liao ji belt in the north china block were located in the triassic sulu orogen 4 many 1 85 ga metamorphic zircons are preserved in the dabie sulu high pressure ultra high pressure hp uhp metamorphic rocks 5 the geometric asymmetry of many structural patterns in the hp uhp slices indicates top to the northwest thrusting during the exhumation of hp uhp slices 6 blueschists occur in the south of the uhp eclogite slices 7 in the eastern segment of the north qinling orogen no components with an affinity of the south china block have been found along the shangdan suture of the qinling orogen has been recorded an apparent northward subduction we consider that the suture is just a lateral subduction zone rather than a major collisional zone along the shangdan suture the rarity of i type plutonism can be attributed to a transform type continental margin the bureya jiamusi khanka block has an affinity to the south china block based on its similarity regarding the paleozoic history of deformation and triassic blueschist metamorphic facies metamorphism the bureya jiamusi khanka block could be the northern extension of the dabie sulu belt and this gigantic belt could be interpreted as an orocline related to the southeastward subduction of the north china block beneath the greater south china block

subsidence history and continental margin evolution of the western pyrenean and basque basins abstract we have studied cretaceous sedimentary sequences of four sedimentary basins along the european and north iberian continental margins of the western pyrenean realm and the basque basin the depression intermediaire sare vera basin and ulzama basin in the western pyrenees and the zumaya basin along the southern margin of the bay of biscay the formation of these basins was largely due to upper cretaceous sinistral strike slip tectonics during iberian plate motion resulting in wrench basins oblique slip and pull apart basins a detailed biostratigraphic framework and paleobathymetric calculations based on sedimentologic and benthic foraminiferal data were used to construct decompacted and backstripped subsidence history curves for each basin from these curves two major changes in subsidence history are apparent 1 increased subsidence since late albian and 2 decrease in subsidence and or initial uplift since early campanian these changes are closely related to plate tectonic events namely spreading in the bay of biscay followed by european iberian plate convergence

mesozoic thermal history of the prebetic continental margin southern spain constraints from apatite fission track analysis apatite fission track analysis was applied to triassic and cretaceous sediments from the south iberian continental margin to unravel its thermal history apatite fission track age populations from triassic samples indicate partial annealing and point to a maximum temperature of around 100 110 c during their post depositional evolution in certain apatites from cretaceous samples two different fission track age populations of 93 99 and around 180 ma can be distinguished track lengths associated with these two populations enabled thermal modelling based on experimental annealing and mathematical algorithms these thermal models indicate that the post depositional thermal evolution attained temperatures 70 c which is consistent with available vitrinitereflectance data thermal modelling for the cretaceous samples makes it possible to decipher a succession of cooling and heating periods consisting of a a late carboniferous permian cooling followed by b a progressive heating episode that ended approximately 120 ma at a maximum tof around 110 c the first cooling episode resulted from a combination of factors such as the relaxation of the thermal anomaly related to the termination of the hercynian cycle the progressive exhumation of the hercynian basement and the thermal subsidence related to the rifting of the bay of biscay reactivated during the late permian jurassic thermal evolution deduced from the inherited thermal signal in the cretaceous sediments is characterized by progressive heating that ended around 120 ma this heating episode is related to thermal subsidence during jurassic rifting in agreement with the presence of abundant mantle derived tholeiitic magmas interbedded in the jurassic rocks the end of the jurassic rifting is well marked by a cooling episode apparently starting during neocomiam times and ending at surface conditions by albian times

timing of triassic tectonic division and postcollisional extension in the eastern part of the jiaodong peninsula abstract the jiaodong peninsula is a key region for researching the interaction between the north and south china plates tectonic relationships between collision exhumation of ultra high pressure uhp slabs strike slip faulting and gold mineralization are still ambiguous the eastern part of the jiaodong peninsula eastern jiaodong which includes triassic intrusions and is less affected by the tan lu fault zone is a key area to examine exhumation dynamics in detail systematic field mapping and zircon u pb dating of triassic intrusions establishes that 1 the uhp wedge in the eastern part of the jiaodong peninsula can be divided into the lateral and frontal ramps of a thrust and nappe system dating of samples from donglinghou 244 7 4 2 ma and qingyutan 233 8 8 1 ma areas indicates that the collision happened at or before the middle triassic 2 postcollisional extension intrusions including the shidao granitoid 216 2 2 4 ma and the chengshantou granitoid cut by a dolerite dyke dated at 210 5 1 0 ma generally strike ne and occurred in a metamorphic core complex below the upper jiashan xiangshui detachment u jsxs 3 regional faults in the jiaodong peninsula exploited syncollisional foliations of the uhp wedge which resulted in faults dipping towards the nw and se the reactivation of the lower jiashan xiangshui shear zone l jsxs and its overprinting upon the tan lu fault system may have caused another major episode of exhumation of the syncollisional wedge and could have been responsible for an extensional environment that favored gold mineralization

a comparison of the age and composition of the shelburne dyke nova scotia and the messejana dyke spain new 40ar 39ar age determinations on biotite from the shelburne dyke of nova scotia and from the messejana dyke of spain are identical at 203 2 ma in addition both dykes have similar chemical compositions and probably represent similar magma sources petrogenetic processes and tectonic settings related to an early phase of opening of the north atlantic ocean

multi phase cooling of early cretaceous granites on the jiaodong peninsula east china evidence from 40 ar 39 ar and u th he thermochronology abstract the jiaodong peninsula at the southeastern periphery of the north china craton ncc has undergone complex changes since the mesozoic a striking feature of the ncc is the widespread distribution of late mesozoic magmatic rocks predominantly characterized by granitic intrusions these igneous plutons are economically important due to their polymetallic mineralization and significant as geodynamic tracers of the regional tectonic evolution two representative early cretaceous granites the yashan and yuangezhuang plutons on the jiaodong peninsula were selected for multiple thermochronometer studies to constrain a complete thermal history from their emplacement to near surface conditions we obtained biotite 40ar 39ar ages of two granites on the new generation argus vi noble gas mass spectrometer two biotites registered identical 40ar 39ar plateau ages of 117 ma which are consistent within the error with their zircon u pb ages this suggested that the two granites were emplaced at the same time and cooled rapidly to about 300 c the single crystal zircon u th he zhe dating for the two samples gave weighted mean ages of 93 5 4 5 ma and 93 3 5 0 ma combined with previously published geochronological data and the thermal inversion of the zircon low temperature thermochronological data three phases of rapid cooling were identified for the two studied plutons 1 the early cretaceous 117 110 ma 2 the late cretaceous 100 90 ma and 3 the early tertiary 65 50 ma the early cretaceous phase of cooling occurred in a regional extensional regime on the ncc characterized by various extensional structures the late cretaceous cooling is consistent with the third episode of the yanshan movement which caused a regional basin inversion event on the ncc in comparison to the first two phases of rapid cooling the early tertiary cooling was more gradual this phase corresponded to a widely developed eocene rift on the ncc and the reactivation of major boundary faults such as the giant tan lu fault zone and the taihangshan fault

environmental magnetism a practical guide j walden f oldfield j and smith eds technical guide no 6 quaternary research association london 1999 243 pp price 17 00 9 00 to qra members isbn 0 907780 42 3

the reunion subchronozone at odp site 981 feni drift north atlantic abstract at ocean drilling program site 981 the reunion subchron is recorded from the marine isotopic stage mis 81 82 boundary to mis 79 as a single normal polarity zone spanning the 2 115 2 153 ma interval according to the age model produced by matching the site 981 18 o record to an orbitally tuned reference record the duration of the reunion subchron 38 kyr is almost four times that assumed in current geomagnetic polarity timescales high interval sedimentation rates 18 cm kyr during mis 81 at site 981 have resulted in an unusually detailed record of the subchron virtual geomagnetic poles during the onset and demise of the reunion subchron trace a series of mainly anticlockwise loops over eastern asia

the lower limb and mechanics of walking in australopithecus sediba the discovery of a relatively complete australopithecus sediba adult female skeleton permits a detailed locomotor analysis in which joint systems can be integrated to form a comprehensive picture of gait kinematics in this late australopith here we describe the lower limb anatomy of au sediba and hypothesize that this species walked with a fully extended leg and with an inverted foot during the swing phase of bipedal walking initial contact of the lateral foot with the ground resulted in a large pronatory torque around the joints of the foot that caused extreme medial weight transfer hyperpronation into the toe off phase of the gait cycle late pronation these bipedal mechanics are different from those often reconstructed for other australopiths and suggest that there may have been several forms of bipedalism during the plio pleistocene

tectonic and geochronological constraints on late archaean and palaeoproterozoic stratigraphic correlation within and between the kaapvaal and pilbara cratons recent radiometric dating of carbonates and banded iron formations on the kaapvaal craton southern africa has suggested that late archaean and palaeoproterozoic carbonate sedimentation was diachronous across the craton we present new shrimp u pb zircon ages of 2583 5 ma and 2588 7 ma for two samples of a tuff bed 320 km apart in the upper oak tree formation transvaal supergroup these ages in conjunction with published data support previously established sequence stratigraphic correlations that show the temporal equivalence of late archaean carbonates in the region a review of the sequence stratigraphy and geochronology of the mount bruce megasequence set on the pilbara craton western australia and the newly named highveld megasequence set on the kaapvaal craton indicates a remarkably similar geohistory both cratons are characterized by a divergent megacycle hamersley range and vaal megasequences followed by a convergent megacycle chichester range and drakensberg megasequences our data show that the megasequence boundary is marked by drowning of both cratons at approximately the same time c 2590 ma which permits more meaningful geotectonic correlations between them

postcollisional extension of the caledonide orogen in scandinavia structural expressions and tectonic significance the scandinavian caledonides are much more affected by postcontractional devonian extension than previously thought the extensional deformation is not restricted to the internal parts of the orogen but can be traced for more than 200 km from the west coast of norway toward the foreland it involved significant reactivation of the basal thrust zone as a low angle extensional detachment whic consequently contains abundant top to the north west sense of shear indicators the extensional deformation involved substantial backsliding of the orogenic wedge eduction of the baltic shield together with stretching of the basement by west dipping extensional shear zones after 30 km of backsliding the extensional detachment splayed to penetrate the overlying orogenic edifice in the coastal region in southern norway which led to inactivation of the main portion of the basal thrust zone as an extensional detachment

sulfur and lead isotope systematics implications for the genesis of the riopar zn fe pb carbonate hosted deposit prebetic zone se spain abstract the zn fe pb deposits of the riopar area prebetic zone se spain are hosted by dolostones that replace berriasian to valanginian upper jurassic lower cretaceous limestones mineralization consists of hypogene sphalerite marcasite and galena and supergene calamine zones the hypogene ores are associated with a saddle dolomite gangue the ore bodies occur as discordant and stratiform lenses ore cemented breccias cm to mm wide veins and veinlets disseminations and stylolite porosity filling within the host dolomites the main ore controls include stratigraphy and or lithology tectonics faults fractures and breccias and availability of metals and sulfur the morphologies and epigenetic character of the hypogene ore bodies are consistent with the classification of this mineralization as a mississippi valley type mvt deposit the ga ge geothermometer in sphalerite yielded a temperature range of 194 252 c which represents the temperature of the source region of the ore solution this value is comparable to the temperature obtained in the ore deposition site 159 15 c from the 34s geothermometer in sphalerite galena pairs this similitude points to a hydrothermal fluid that did not cool down significantly during flow from the fluid reservoir area to the precipitation site 34s values of base metal sulfides 7 5 to 3 5 are consistent with thermochemical reduction of triassic sulfate seawater and or derived from dissolution of evaporites by interaction with organic compounds e g hydrocarbons methane which reduced sulfate to sulfide in the deposition site the lead isotope ratios 206pb 204pb 18 736 18 762 207pb 204pb 15 629 15 660 208pb 204pb 38 496 38 595 of galena suggest that pb and probably other metals as zn is derived from continental crustal rocks on the other hand these relations points to a unique metal source probably derived from the paleozoic basement rocks the relationship between bedding parallel stylolites dolomitization sulfide precipitation and alpine tectonic affecting the mvt ore suggests a relative timing range for the mineralization in the riopar area of 95 20 ma upper cretaceous tertiary the sulfide mineralization and the associated dolomitization are thus explained by the contribution of two fluids that mixed in different proportions during dolomitization and mineralization i a fluid probably derived from cretaceous seawater saturating mesozoic sediments fluid a characterized by being dilute and initially low temperature which should have contained organic rich compounds in the ore deposition site e g hydrocarbons and ch4 dissolved gas and ii a high salinity hydrothermal brine fluid b rich in both metals and sulfate circulated through the paleozoic basement during the pre ore dolomitizing stage the fluid phase was dominated by the diluted fluid fluid a fluid b whereas in a later fluid pulse the proportion of the high salinity fluid increased fluid a

crustal structure of the dabie orogenic belt eastern china inferred from gravity and magnetic data abstract in order to better characterize the crustal structure of the dabie orogen and its tectonic history we present a crustal structure along a 500 km long profile across the dabie orogenic belt using various data processing and interpretation of the gravity and magnetic data source depth estimations from the spectral analysis by continuous wavelet transform cwt provide better constraints for constructing the initial density model the calculated gravity effects from the initial model show great discrepancy with the observed data especially at the center of the profile more practical factors are then incorporated into the gravity modeling first we add a high density body right beneath the high pressure metamorphic hpm and ultrahigh pressure metamorphic uhpm belt considering the exposed hpm and uhpm rocks in the mid of our profile then the anomalous bodies a b and c inferred from the cwt based spectral analysis results are fixed in the model geometry in the final crustal density structure two anomalous bodies b and c with high density and low magnetization could possibly be attributed to metasomatised mantle materials by sio2 rich melt derived from the foundering subducted mafic lower crust under the extensional environment in the early cretaceous the upwelling metasomatised mantle was partially melted to produce the parental magma of the post collisional mafic ultramafic intrusive rocks as for the low density body a with strong magnetization located in the lower crust right beneath the hp and uhp metamorphic belt it is more likely to be composed of serpentinized mantle peridotite smp this serpentinized mantle peridotite body smpb represents the emplacement of mantle derived peridotites in the crust accompanying the exhumation of the uhp metamorphic rocks

petrography and geochemistry of fault controlled hydrothermal dolomites in the riopar area prebetic zone se spain abstract the present paper reports the first detailed petrographical and geochemical studies of hydrothermal dolomites related to mvt zn fe pb deposits in the riopar area mesozoic prebetic basin se spain constraining the nature origin and evolution of dolomitizing and ore forming fluids mapping and stratigraphic studies revealed two stratabound dolostone geobodies connected by other patchy bodies which replace carbonate units of upper jurassic to lower cretaceous ages these dolostones are associated to the w e trending san jorge fault indicating a main tectonic control for fluid flow seven different dolomite types were identified i matrix replacive planar s red i ii matrix replacive planar e red ii iii planar e sucrosic cement sud iv non planar grey saddle dolomite cement sad i pre dating zn fe pb sulfides v non planar milky to pinkish saddle dolomite cement sad ii post dating zn fe pb ores vi ore replacive planar e porphyrotopic pod and vii planar s cloudy cement ced meteoric calcite types were also recognized the different dolomite types are isotopically characterized by i depleted 18 o from 25 1 to 27 6 v smow and 13 c from 2 3 to 0 9 v pdb values compared to upper jurassic to lower cretaceous limestone signature 18 o 27 6 to 30 9 v smow 13 c 0 5 to 3 2 v pdb and ii 87 sr 86 sr ratios for the main dolomitization phases red and sud 0 70736 0 70773 close to the jurassic and cretaceous carbonate values 0 70723 0 70731 whereas more radiogenic values 0 70741 0 70830 for saddle dolomites sad related to the zn fe pb sulfide mineralization prevailed after fluid interaction with rb bearing minerals microthermometrical studies on two phase liquid and vapor fluid inclusion populations in planar and non planar dolomites and sphalerite show homogenization temperatures between 150 and 250 c these data indicate that both planar and non planar dolomite textures formed at high temperatures under hydrothermal conditions in deep burial diagenetic environments the main dolomitizing phase red i red ii and sad i shows low to moderate fluid inclusions salinity 5 14 wt eq nacl whereas the dolomitization related to ore precipitation sphalerite and sad ii spreads to higher salinity values 5 25 wt eq nacl these data may respond to a mixing between a low salinity fluid fluid a less than 5 wt eq nacl and a more saline brine fluid b more than 25 wt eq nacl at different fluid proportions

criteria for identifying bone modification by termites in the fossil record three geographically dispersed middle and later stone age cave sites in south africa and a middle stone age cave site in ethiopia share a similar taphonomic signature that includes destruction of bones associated with variable forms of star shaped features clusters of microscopically visible sub parallel striations edge gnawing pits and etching of the bone surface similar traces preserved on plio pleistocene fauna are interpreted by different authors as the possible work of termites or ants considering that ambiguity exists in the interpretation of these traces and that there are no modern examples available for comparison we set out to create a reference collection of bones modified by southern african termites here we present the results of an actualistic experiment conducted with the harvester termite trinervitermes trinervoides sjostedt isoptera termitidae in the sterkfontein valley south africa results show that within six months all bones were approximately half covered with a dark surface residue had an etched surface appearance and recorded boreholes and destruction particularly of less dense elements and epiphyses star shaped marks edge gnawing and clusters of sub parallel striations on the periosteal surface were faint after six months but became clearly visible and more plentiful after 12 months a finding attributed to the termites being more active in austral autumn and spring this result demonstrates the pertinence of insect modification studies to our understanding of regional palaeoenvironment palaeoecology and palaeoclimate this experiment has demonstrated that t trinervoides can destroy bone in all stages of preservation favouring fresh thin cortical and spongy bone with meat and marrow the presence of appreciable quantities of calcium carbonate in termite mounds suggests that termites may be drawn to dolomitic cave sites and the calcium rich bones they contain to satisfy their mineral requirements they therefore have the potential to bias taxonomic and element representation minimum number of individuals and age profiles in a faunal assemblage and may account in part for the patchy preservation of faunal remains including hominins in fossil deposits and or the lack of bone artefacts at some middle stone age cave sites preserving long sequences of occupation

the endocast of mh1 australopithecus sediba the virtual endocast of mh1 australopithecus sediba obtained from high quality synchrotron scanning reveals generally australopith like convolutional patterns on the frontal lobes but also some foreshadowing of features of the human frontal lobes such as posterior repositioning of the olfactory bulbs principal component analysis of orbitofrontal dimensions on australopith endocasts mh1 sts 5 and sts 60 indicates that among these mh1 orbitofrontal shape and organization align most closely with human endocasts these results are consistent with gradual neural reorganization of the orbitofrontal region in the transition from australopithecus to homo but given the small volume of the mh1 endocast they are not consistent with gradual brain enlargement before the transition

termites and necrophagous insects associated with early pleistocene gelasian australopithecus sediba at malapa south africa abstract this study focuses on two early pleistocene australopithecus sediba hominin specimens and associated fauna from malapa south africa these specimens have been interpreted as having fallen through a shaft opening into a cave where they died and likely mummified before being washed into a lower chamber in order to better understand the taphonomy of the fossils and to identify the invertebrate agent s responsible for damage we examined the fossils using high resolution imagery and studied the site and associated breccia blocks in the laboratory for traces of invertebrate activity we also conducted bone modification experiments with termites and hide beetles results show the presence of blowfly puparia within the cranium of the juvenile male mh1 indicating that flies visited the facial orifices of the freshly decomposing corpse blowflies which have a requirement to oviposit in daylight imply that the body was exposed to sunlight for part of the day a shaft opening that admitted sunlight is supported by the presence of a fossil fungus garden associated with mh2 fungus gardens occur subsurface and sprout mushrooms in areas with dappled light analysis of the fossil surfaces revealed a pattern comprising 14 damage types that were made on relatively fresh bone a bone modification experiment conducted with resident termites at the site showed that they created the same suite of microscopic surface features as those observed on the fossils the features are mostly the result of harvesting symbiotic fungi from fresh bones and mineral rich coatings from fossils damage resulting from the activity of hide beetles is similar to that of termites apart from invasive edge gnawing produced by the beetles this research highlights the importance of insect activity in the modification of fossils in the cradle of humankind world heritage site area and calls for consideration of this agent at other fossil sites in the region

lithosphere dynamics and tectono stratigraphic evolution of the mesozoic betic rifted margin southeastern spain abstract quantitative subsidence analysis demonstrates that mesozoic sediments in the eastern betic cordilleras have been deposited on a thermally subsiding rifted margin the dynamics of rifting are related to regional trans tension in the atlantic realm modelling of this phase of rifting at the southern iberian margin shows that the associated stretching of the lithosphere significantly altered its geometrical and mechanical structure and exerted a major control on subsequent convergence tectonics the mesozoic stretching led to the formation of a ramp at the margin due to strong lateral variations in the effective elastic thickness eet of the lithosphere and the thickness of the crust in a direction perpendicular to the margin the existence of a ramp structure in the late mesozoic at the iberian margin which is also supported by stratigraphic and structural data is important for the style of subsequent deformation of the lithosphere in late cretaceous tertiary times the lateral variations in eet inferred from forward modelling of rifted margin stratigraphy could explain the observed multiple collapse of the betic margin and the partitioning of deformation between the converging units involved in the betic orogeny modelling of depth dependent palaeo rheological profiles of the margin shows that the mechanical properties of the lithosphere after stretching differed distinctly from those before stretching lithospheric deformation in the betic cordilleras during the tertiary orogeny seems therefore to be largely controlled by the previous rifting phase a comparison of the palaeo and present day rheologies in terms of estimates for eet during late cretaceous and present times indicates that the mechanical properties of the lithosphere underlying the betic orogen were also affected by rifting during late oligocene aquitanian times this phase of rifting is coeval with extension in the valencia trough the gulf of lions and the west european rift system which supports a causal relation with regional lithospheric processes the lateral and spatial variations in thermo mechanical properties of the lithosphere underlying the betics therefore reflect the dynamics of lithospheric extension on a larger scale

australopithecus sediba at 1 977 ma and implications for the origins of the genus homo newly exposed cave sediments at the malapa site include a flowstone layer capping the sedimentary unit containing the australopithecus sediba fossils uranium lead dating of the flowstone combined with paleomagnetic and stratigraphic analysis of the flowstone and underlying sediments provides a tightly constrained date of 1 977 0 002 million years ago ma for these fossils this refined dating suggests that au sediba from malapa predates the earliest uncontested evidence for homo in africa

40ar 39ar geochronological constraints on the formation of the dayingezhuang gold deposit new implications for timing and duration of hydrothermal activity in the jiaodong gold province china abstract china s largest gold resource is located in the highly endowed northwestern part of the jiaodong gold province most gold deposits in this area are associated with the ne to nne trending shear zones on the margins of the 130 126 ma guojialing granite these deposits collectively formed at ca 120 5 ma during rapid uplift of the granite the dayingezhuang deposit is a large 120 t au orogenic gold deposit in the same area but located along the eastern margin of the late jurassic linglong metamorphic core complex new 40ar 39ar geochronology on hydrothermal sericite and muscovite from the dayingezhuang deposit indicate the gold event is related to evolution of the core complex at 130 4 ma and is the earliest important gold event that is well documented in the province the dayingezhuang deposit occurs along the linglong detachment fault which defines the eastern edge of the ca 160 150 ma linglong granite granodiorite massif the anatectic rocks of the massif were rapidly uplifted at rates of at least 1 km m y from depths of 25 30 km to form the metamorphic core complex the detachment fault with precambrian metamorphic basement rocks in the hangingwall and the linglong granitoids and migmatites in the footwall is characterized by early mylonitization and a local brittle overprinting in the footwall gold is associated with quartz sericite pyrite k feldspar altered footwall cataclasites at the southernmost area of the brittle deformation along the detachment fault our results indicate that there were two successive yet distinct gold forming tectonic episodes in northwestern jiaodong one event first reactivated the detachment fault along the edge of the linglong massif between 134 and 126 ma and then a second reactivated the shears along the margins of the guojialing granite both events may relate to a component of northwest compression after a middle early cretaceous shift from regional nw se extension to a ne sw extensional regime

long term thermo tectonic evolution of the montes de toledo area central hercynian belt spain constraints from apatite fission track analysis in the montes de toledo area located in the axial part of the central hercynian zone a long term thermo tectonic evolution can be deduced from apatite fission track aft data in conjunction with tight geological constraints derived from the knowledge of regional geology and other independent chronometers the area is composed of two different blocks separated by the toledo shear zone tsz the northern block is a granulite facies anatectic terrane the southern block is composed of greenschist facies paleozoic sediments intruded by a late hercynian granitic pluton a total of 13 samples have been recovered for aft analysis aft ages in both blocks cluster around 189 221 ma with mean confined track lengths between 11 4 m and 12 4 m modeling of the aft data indicates that the thermal history is broadly similar in both blocks which constrains the main movement of the tsz as essentially before the upper permian aft ages in the tsz cluster around 124 164 ma and the track lengths vary between 11 4 m and 12 4 m these data reveal that the fault must have been affected by a later thermal overprint as aft ages are significantly younger than those of the footwall and hangingwall blocks this differential thermal resetting is likely related to the advection of localized hydrothermal fluids that are responsible for the widespread pb zn mineralization along the tsz these results give an example of resetting aft data by hydrothermal events the long term evolution suggests a lack of important alpine tectonism in the montes de toledo block in clear contrast to other nearby hercynian areas such as the sierra de guadarrama where the important effect of alpine tectonism has almost totally erased the previous thermal signal in the aft system

recovery of strain rate variation from inversion of subsidence data despite considerable advances over the past 20 years in our understanding of continental lithospheric deformation see for example refs 1 and 2 we know little about the detailed spatial and temporal variations in strain rate at geologically relevant scales 102 104 km and 1 100 million years such measurements are needed to constrain dynamic models of lithospheric deformation3 although it is not yet obvious how detailed strain rate information can be obtained from mountain belts subsidence data from sedimentary basins should contain information about at least the vertical component of the strain rate tensor here i show that inverse theory can be used to calculate the temporal strain rate variation needed to fit observed subsidence patterns in extensional sedimentary basins no a priori information concerning either the duration of rifting or the total strain is required inverse calculations produce good fits to synthetic data and to subsidence data from the dolomites of northern italy calculated strain rates are not constant but vary between 10 18 and 10 15 s l error analysis shows that these results are significant and well resolved all of the stratigraphic sections studied exhibit a minimum in strain rate during extension a feature predicted by models of lithosphere deformation by power law creep

u pb zircon ages constrain the architecture of the ultrahigh pressure qinling dabie orogen china new shrimp and tims zircon ages 40ar 39ar ages and eclogite locations contribute significantly to our understanding of the ultrahigh pressure dabie shan 1 the geographic extent of the yangtze craton that was subducted to ultrahigh pressure extends to the northern edge of the dabie shan 2 the northern half of the dabie shan is a magmatic complex intruded over a 10 myr interval between 137 and 126 ma that accommodated 100 n s stretching of the pre existing collisional architecture 3 granitic orthogneisses and enclosing ultrahigh pressure paragneisses have indistinguishable zircon populations the population of triassic zircon ages ranges from 219 to 245 ma leading us to question the prevailing assumption that 219 ma zircons formed at ultrahigh pressure and to propose instead that they reflect late retrogression at crustal pressures following the bulk of exhumation

mid crustal detachment in the betic system of southeast spain abstract the tertiary orogenic belts of eastern spain can be interpreted using the principles of thin skinned thrusting with a fundamental detachment at mid crustal level in the eastern betics the compression involves an oblique restacking of a stretched continental margin much of the shortening is transmitted on permian and triassic detachments which emerge as forward and back thrust duplexes an interpretation of the guadarrama range of central spain is presented in which significant shortening is shown on a mid crustal detachment propagating from the southeast it is suggested that this represents the external limit of a compressive system linked to the betics the pyrenees and eastern cantabrians are a separate tertiary compressive system again resulting from restacking of an extensional basin during the collision of iberia and france previous authors have proposed mid crustal detachment in the pyrenees observation of the geological map of the iberian ranges suggests a broadly similar structural origin may apply in which case the iberian ranges may represent the most external zone of a major pyrenean system again linked by a mid crustal detachment thus it is suggested that the whole of eastern spain is made up of two major compressive systems linked at mid crustal level

cooling paths of the ne china crust during the mesozoic extensional tectonics example from the south liaodong peninsula metamorphic core complex abstract the south liaodong peninsula massif is the easternmost mesozoic metamorphic core complex recognized in eastern china it provides a good example of the combination of ductile shearing syn kinematic plutonism and polyphase exhumation the jurassic granodioritic plutons located at the footwall of the detachment normal fault and dated here at ca 160 ma recorded two different phases of cooling a slow cooling regime of about 3 10 c my prevailing before 122 ma was followed by a significant increase in cooling rate of about 40 55 c my after that time by contrast a single fast cooling path was recorded by the cretaceous monzogranite situated in the footwall of the detachment normal fault this result indicates that the jurassic and cretaceous plutons recorded different exhumation processes a jurassic slow or negligible exhumation and a cretaceous fast one assisted by normal faulting these two cooling stages correspond to distinct geodynamic processes during the jurassic and cretaceous extensional tectonics seems not significant before early cretaceous the second stage dominated by an extensional regime which develops after ca 120 ma is tentatively correlated to the lithosphere removal of the north china craton

quantitative subsidence analysis of the mesozoic evolution of the lusitanian basin western iberian margin abstract quantitative subsidence analysis of 26 wells in the lusitanian basin provides new constraints on the western iberian mesozoic passive margin development backstripped tectonic subsidence curves show a three fold subdivision of vertical motions from late triassic onward continental rifting was initiated during the late triassic and early jurassic from middle jurassic onward a distinct different behaviour is expressed in the subsidence curves for the north and the south lusitanian basin during the middle jurassic the south lusitanian basin records a stretching episode with stretching factors of about 1 08 while the north lusitanian basin typically has a middle jurassic hiatus this different development is also expressed in the late jurassic and early cretaceous sedimentary sequence when both the north and south lusitanian basin are subjected to another stretching episode with a more pronounced development of the southern than of the northern part of the basin the stretching factors for this last phase are about 1 03 for the northern part and 1 08 for the southern part of the area this north south difference during the middle jurassic to early cretaceous for which the transition roughly coincides with the location of the nazare fault zone is probably a result of differences in pre rift crustal composition or thickness late cretaceous sediments are mostly absent in the analysed wells in the southern part of the basin the absence of the cretaceous record is a consequence of erosion due to cenozoic inversion of the basin the generally low estimates for stretching factors suggest that the analysed eastern part of the lusitanian basin forms the distal part of the mid cretaceous continental breakup a comparison with subsidence curves of neighbouring basins of iberia reflects general patterns in mesozoic basin development and confirms the generally held view that the extension leading to continental breakup migrated from south to north during the middle jurassic to early cretaceous in west iberia

extensional tectonics within a subduction type orogen the case study of the wugongshan dome jiangxi province southeastern china abstract in southeastern china the wugongshan massif consists of metamorphic rocks and granites generally considered as basement rocks formed during an early paleozoic orogeny our structural and radiometric reappraisal of this massif shows that it results from a mesozoic doming in the metamorphic rocks the foliation defines an e w elliptical shape and bears a n s stretching lineation the axial zone of the dome is occupied by oriented plutons the outer part of the dome consists of devonian quartzite carboniferous permian limestone and triassic jurassic sandstone ductile deformation observed in the permian carbonates and older units develops contrasting kinematics the northern and southern flanks present top to the north and top to the south motions respectively the same divergent pattern of motion is recorded from brittle structures up to the jurassic sandstone the late cretaceous red beds are undeformed in the axial zone coaxial flow indicated by symmetric pressure shadows and quartz fabrics predominates along the n and s flanks of the dome post folial recumbent folds are symmetrically overturned to the n and s respectively but at the two extremities of the dome the fold axes are parallel to the stretching lineation 40 ar 39 ar ages of biotite and muscovite from mylonite and granite suggest a late triassic age for the ductile deformation and an early cretaceous age for the final doming the wugongshan dome is similar to a metamorphic core complex formed in an extensional tectonic regime a model which emphasizes plutonism is discussed from permian to early cretaceous southeastern china was a subduction type orogen the crust of which was thickened by accretion of mantle derived magmas the emplacement of a large amount of mesozoic granitoids in southeastern china promoted thermal softening and gravitational instability that allowed the crust to extend the formation of the wugongshan dome and other metamorphic core complexes appears to be a the direct consequence of plutonic activity and crust rheology

anatomy of a world class epizonal orogenic gold system a holistic thermochronological analysis of the xincheng gold deposit jiaodong peninsula eastern china abstract xincheng is a world class orogenic gold deposit hosted by the early cretaceous guojialing granitoid in the jiaodong peninsula eastern china a zircon u pb age of 126 1 4 ma together with previous data constrain the emplacement of the guojialing intrusion to 132 123 ma the granitoid underwent subsolidus ductile deformation at 500 c following its intrusion the small difference in age between the youngest zircon u pb age of unaltered granitoid 123 ma and the ca 120 ma 40ar 39ar ages of sericite associated with breccias and gold mineralization within it indicate initial rapid cooling from magmatic temperatures to those prevalent during brittle deformation and associated gold mineralization at 220 300 c evidence of a direct association between granitic magmatism and gold mineralization such as at least localized near magmatic depositional temperatures and metal zoning evident in undoubted intrusion related gold deposits is absent the 40ar 39ar age of 120 ma coincides with the mineralization age of many other orogenic gold deposits along the jiaojia fault sixteen zircon fission track zft ages across the ore and alteration zones range from 112 9 3 4 to 99 1 2 7 ma the long period of cooling to the 100 ma zft closure temperatures recorded here suggests that ambient temperatures for hydrothermal alteration systems lasted to 100 ma possibly because of their focus at xincheng within the young guojialing granitoid as it cooled more slowly below approximately 300 c to 220 c however the restricted number of auriferous ore stages combined with the presence of cross cutting gold free quartz carbonate veins indicate that gold itself was only deposited over a restricted time interval at 120 ma consistent with studies of orogenic gold deposits elsewhere this highlights the complex interplay between magmatism deformation and the longevity of hydrothermal systems that cause genetic controversies based on apatite fission track aft ages the xincheng gold deposit was then uplifted and exhumed to near the surface of the crust at 15 ma probably due to movement on the crustal scale tan lu fault recognition of such exhumation histories along gold belts has conceptual exploration significance in terms of the probability of discovery of additional exposed or sub surface gold ore bodies as discovery is as much a function of preservation as formation of the deposits

flake tectonics in the sulu orogen in eastern china as revealed by seismic tomography 1 seismic tomographic image reveals a crocodile like p waves velocity structure beneath the sulu orogenic belt which marks the subduction collision zone between the sino korean block sk and yangtze block yz in eastern china it may imply that the upper crust of the yz was detached from its lower crust and thrust over the sk for a maximum of 400 km in the sulu region whereas the remnant of the subducted yangtze lithosphere was lay beneath the sk this crustal detached structure flake tectonics might have occurred after the triassic subduction collision

tectonics of the qinling belt build up and evolution of eastern asia the structure and history of the qinling range which separates the north and south china cratons are a key to the tectonic evolution of eastern asia the mountain range is composed of a northern palaeozoic belt and a southern mesozoic belt the palaeozoic orogeny probably involved the closure of an oceanic basin along a north dipping subduction zone followed by south vergent obduction of ophiolites and intracontinental thrusting during the devonian the mesozoic belt appears to be the product of purely intracontinental shallow crustal deformation over a large decollement with at least 100 km of horizontal transport since the devonian both belts have been sliced by huge east west sinistral strike slip faults

the liaonan metamorphic core complex southeastern liaoning province north china a likely contributor to cretaceous rotation of eastern liaoning korea and contiguous areas abstract the mesozoic liaonan metamorphic core complex mcc of the southeastern liaoning province north china is an asymmetric cordilleran style complex with a west rooting master detachment fault the jinzhou fault a thick sequence of lower plate fault related mylonitic and gneissic rocks derived from archean and early cretaceous crystalline protoliths has been transported ese ward from mid crustal depths u pb ages of lower plate syntectonic plutons ca 130 120 ma 40 ar 39 ar cooling ages in the mylonitic and gneissic sequence ca 120 110 ma and a cretaceous supradetachment basin attest to the early cretaceous age of this extensional complex the recent discovery of the coeval and similarly west rooting waziyu mcc in western liaoning darby b j davis g a zhang x wu f wilde s yang j 2004 the newly discovered waziyu metamorphic core complex yiwulushan western liaoning province north china earth science frontiers 11 145 155 indicates that the gulf of liaoning which lies between the two complexes was the center of a region of major crustal extension clockwise crustal rotation of a large region including eastern liaoning province and the korean peninsula with respect to a non rotated north china block has been conclusively documented by paleomagnetic studies over the past decade the timing of this rotation and the reasons for it are controversial lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 proposed that a clockwise rotation of 22 5 10 2 was largely post early cretaceous in age and was the consequence of extension within a crustal domain that tapers southwards towards the bohai sea of which the gulf of liaoning is the northernmost part paleomagnetic studies of early cretaceous strata ca 134 120 ma in the yixian fuxin supradetachment basin of the waziyu mcc indicate the non rotation of north china and the basin zhu r x shao j a pan y x shi r p shi g h li d m 2002 paleomagnetic data from early cretaceous volcanic rocks of west liaoning evidence for intracontinental rotation chinese science bulletin 47 1832 1837 such upper plate non rotation supports our conclusion that the lower plates of the waziyu and liaonan metamorphic core complexes were displaced ese ward in an absolute sense away from the stable north china block thus contributing to the rotation of korea and contiguous areas rotation is inferred to have affected only the upper crust above mid crustal levels into which we believe the jinzhou and waziyu detachment fault zones flattened if this is the case the regional tan lu fault that lies between the two core complexes was truncated at mid crustal depth since in areas to the south it forms the boundary between the north and south china lithospheric blocks it is noteworthy that the two extensional complexes lie not far north of the bohai bay the area proposed by lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 as the site of the pole of rotation for korea s clockwise displacement lin et al lin w chen y faure m wang q 2003 tectonic implication of new late cretaceous paleomagnetic constraints from eastern liaoning peninsula ne china journal of geophysical research 108 b 6 epm 5 1 to 5 17 were unaware of the liaonan and waziyu mcc s and argued that most of the regional block rotation was post early cretaceous and in part early cenozoic however the ca 130 120 ma ages of the two liaoning mcc s and a songliao basin mcc xujiaweizi the latter discovered only by recent drilling through its younger stratigraphic cover support our and some korean coworkers conclusions that most of the clockwise rotation was early cretaceous

geologic evolution of the betic cordilleras in the western mediterranean miocene to the present abstract the betic cordilleras were formed during the eo meso and neo alpine evolution of the western mediterranean area during the neo alpine stage the northward subduction of the african plate took place and the algerian provencal basin opened with the creation of oceanic floor associated space problems produced the expulsion and extensive stretching of the internal zones to the west which in turn disrupted and deformed the external zones of the betic and rif cordilleras these occurrences essentially took place in the burdigalian and continued with diminished intensity into the middle miocene following the suturing of the transcurrent contact between the internal and external zones important n60 90 e and nw se faults occurred the betic cordilleras are characterized as having been deformed by regional horizontal shortening compression oriented wnw ese or nw se which gradually rotated to the nnw sse in the late miocene when its most important intramontane neogene basins were formed the alboran basin with a thinned continental crust was formed as a western prolongation of the opening of the algerian provencal basin with its basic features already apparent in the burdigalian the volcanism present in the southeast of the betic cordilleras and in northeast morocco crossing the alboran basin is mainly late miocene in age it is linked to fracturing and exhibits chemistry related to the different thickness of the crust

sequence stratigraphy in the upper cretaceous of the basco cantabrian basin northern spain the sedimentary cycles of the cenomanian to maastrichtian were investigated in the basco cantabrian basin bcb in northern spain provinces of alava vizcaya and burgos the depositional area was a distally steepened carbonate ramp which extended from catalonia northwestwards to the basque country the investigated sediments range from calciturbidites and pelagic marls to marl limestone alternations deposited on a distal carbonate ramp shallow marine limestones marls and intertidal clastics and carbonates were deposited on the proximal part of the carbonate ramp the establishment of a regional sequence analysis is based on the investigation of seismic profiles well logs and outcrop sections examples of outcrop sections are interpreted in terms of sequence stratigraphy unconformities of third and second order cycles depositional geometries systems tracts the sequence stratigraphic interpretation of outcrop sections is based on facies analysis interpretation of observed depositional geometries and correlation of unconformities and marine flooding surfaces through the basin a biostratigraphic framework is established based on ammonites inoceramids planktonic and benthic foraminifera as a result a regional sequence stratigraphic cycle chart is presented and compared with published global cycle charts the correlation of the regional cycle chart with published cycle charts is good in the cenomanian and turonian several sequence boundaries in the bcb are shifted by up to one biozone compared with the global chart some type 1 boundaries of the standard chart are only type 2 in the bcb important type 1 boundaries in the bcb are top geslinianum zone with a 100 m lowstand wedge at the basis of the sequence sequence boundary 92 2 base petrocoriense zone with a 250 m shallowing upwards lowstand wedge at the basis sequence boundary 89 2 and within the syrtale zone sequence boundary 85 0

dating of subduction and differential exhumation of uhp rocks from the central dabie complex e china constraints from microfabrics rb sr and u pb isotope systems abstract the correlation of deformation fabrics and metamorphic reactions with geochronologic data of uhp metamorphic rocks demonstrate that the multistage subduction and exhumation history of the central dabie complex requires rapid subduction and rapid initial exhumation moreover these data show that volume diffusion is not the major resetting mechanism of radiogenic isotope systems thus our age data do not simply reflect a thermal cooling history in the investigated section the maximum age for uhp is given by the 244 3 ma 2 u pb age of a pre uhp titanite phenocryst that survived uhp metamorphism and subsequent tectonometamorphic events a minimum age for uhp is set by the 238 1 ma 2 238 u 206 pb mineral isochron age of titanite and cogenetic epidote these minerals formed from local partial melts during ascent and their age suggests fast exhumation and emplacement in the middle crust in the period of ca 238 218 ma the uhp terrain records ht metamorphism local partial melting and extensive pervasive strain below the eclogite jd grt stability field exhumation was polyphase with a first phase of fast exhumation succeeded by episodes of ht metamorphism and concomitant deformation at deep mid crustal level between 238 and 218 ma slow exhumation related to the final emplacement of tectonic units along greenschist facies shear zones did not cease before ca 209 204 ma the resetting and homogenization of radiogenic isotope systems were aided by dissolution precipitation creep which was the dominant deformation mechanism in quartz feldspar rocks in combination with fluid influx

dynamics of exhumation and deformation of hp uhp orogens in double subduction collision systems numerical modeling and implications for the western dabie orogen abstract the dynamics of formation and exhumation of high pressure hp and ultra high pressure uhp metamorphic orogens in double subduction collision zones remain enigmatic here we employ two dimensional thermo mechanical numerical models to gain insights on the exhumation of hp uhp metamorphic rocks as well as their deformation during the collision of a micro continent with pro and retro continental margins along two subduction zones a three stage collisional process with different convergence velocities is tested in the initial collisional stage a fold and thrust belt and locally rootless superimposed folds are developed in the micro continent and subduction channel respectively in the second exhumation stage of hp uhp rocks a faster convergence model results in upwelling of the asthenosphere which further leads to a detachment between the crust and lithospheric mantle of the micro continent a slower convergence model results in rapid exhumation of hp uhp rocks along the north subduction channel and a typical piggy back thrusting structure in the micro continent a non convergence model produces a slab tear off leading to the rebound of residual lithosphere of the micro continent in the third and final stage a series of back and ramp thrusts are formed in the micro continent with the pro continent re subducted based on an analogy of our numerical results with the western dabie orogen wdo we suggest that 1 slab tear off results in a rebound of residual lithosphere which controls the two stage syn collisional exhumation process of hp uhp rocks in the wdo and 2 in contrast to the single subduction collision system the exhumation range of the partially molten rocks with lower viscosity and density is restricted to a specific region of the micro continent by the mianlue and shangdan subduction zones which generated the complex deformation features in the wdo

high resolution clay mineralogy as a proxy for orbital tuning example of the hauterivian barremian transition in the betic cordillera se spain the response of clay mineral assemblages to potential orbital forcing is tested in mesozoic hemipelagic marl limestone rhythmites of the rio argos section betic cordillera southeastern spain along the section marls are pervasively enriched in kaolinite and illite whereas limestones are enriched in smectite rich illite smectite mixed layers suggesting that marl limestone alternations are produced by cyclic high frequency fluctuations of continental runoff spectral analyses show that clay mineral assemblages evolve accordingly to precession obliquity and eccentricity cycles durations of ammonite zones are assessed at 535 kyr for the late hauterivian pseudothurmannia ohmi zone and at 645 kyr and for the early barremian taveraidiscus hugii zone these durations are in agreement with other cyclostratigraphic estimates but significantly differ from the geologic time scale 2004 and 2008 clay minerals display enhanced amplitude of the eccentricity cycles during the faraoni oceanic anoxic event due to enhanced continental weathering conditions prevailing at that time sedimentary expression of the 405 kyr eccentricity is disturbed by palaeoclimate changes during the faraoni oae challenging the hypothesis of cretaceous oae triggered by eccentricity cycles although palaeoceanographic events e g faraoni oae may induce disturbances in the clay mineral record this study demonstrates the potential of these minerals to be used as a proxy for orbital calibration in mesozoic times

detrital zircons reveal no jurassic plateau in the eastern north china craton abstract u pb hf isotopic analyses have been carried out on detrital zircons from late permian jurassic strata in the western shandong bohai bay wsbb basins with aims of constraining the paleogeography and evolution of the eastern north china craton ncc four major groups of u pb ages namely 3 0 2 3 ga 2 2 1 4 ga 1250 430 ma and 410 150 ma are recognized for zircons from the fine grained sandstones the post paleoproterozoic zircons of the late permian sample show an age cluster of 344 255 ma with e hf t values of 18 to 8 being similar to those extracted from late paleozoic igneous rocks from the yinshan yanshan orogenic belt yyob on the northern margin of the ncc however the devonian jurassic zircons 390 150 ma from the jurassic sediments have e hf t values from 45 to 14 very similar to the mixture of phanerozoic zircons from the xing meng orogenic belt xmob and the yyob but significantly different from those of the liaodong peninsula jiaodong peninsula and the western shandong uplift in addition cambrian silurian zircons 535 430 ma of the jurassic samples have e hf t values from 27 to 7 resembling the early paleozoic zircons extracted from the northern qinling orogen nqo the u pb age spectra and hf isotope of devonian jurassic zircons as well as bulk nd isotopes suggest that the central eastern ncc received some juvenile materials from the xmob the yyob and the nqo during the jurassic this indicates widespread prototype basins and a low elevation during the jurassic arguing against the presence of a paleo plateau in the eastern ncc at that time the lack of evidence predicted by lithospheric delamination e g large scale elevation or doming after late triassic makes the delamination unlikely to be a viable mechanism of lithospheric thinning of the ncc the subsidence rather than elevation of the eastern ncc after late triassic might be related to thermo chemical erosion of the lithosphere by underlying convective mantle in a back arc setting

late cretaceous subsidence history of the betic continental margin jumilla yecla region se spain abstract a combined approach of subsidence and tectono stratigraphic analyses is presented to document the vertical tectonic motions of the crust in the betic margin se part of the iberian plate during the late cretaceous late albian late maastrichtian when the basin was evoling from a passive margin into a convergent one the overall patterns of tectonic subsidence and paleogeography are characterized by the following phases 1 middle late albian regional tectonic pulse 98 ma major basin reorganization 2 latest albian early middle cenomanian relatively rapid subsidence wide carbonate platform development 3 late middle cenomanian early coniacian regional uplift and related tectonic pulses at 94 5 and 93 5 ma followed by a prolonged low subsidence phase 4 intra coniacian extensional tectonic event 88 5 ma 5 late coniacian late santonian interval relative tectonic quiescence and moderate subsidence rates wide carbonate platform development 6 latest santonian earliest campanian compressional tectonic event 83 5 ma restructuring of the betic margin 7 early campanian early maastrichtian low subsidence narrow mixed carbonate siliciclastic platforms 8 mid maastrichtian tectonic event 71 ma abrupt paleographic changes 9 late maastrichtian overall moderate subsidence high terrigenous influx and 10 latest maastrichtian regional tectonic event major basinal reorganization characterization of these periods which include the first compressional or transpressional tectonic phases of the alpine orogeny in the betic margin permits the integration of the late cretaceous tectono sedimentary evolution of the betic margin into the geodynamic evolution of iberia on the basis of this integration tectonic pulses and related changes in subsidence are interpreted as the result of variations on intraplate stresses which are superimposed on the general longer term subsidence of the passive margin these intraplate stresses were governed by 1 the north atlantic spreading and the consequent decrease in the sinistral relative motion between iberia and africa 2 the progressive opening of the bay of biscay between the late aptian and the early campanian and 3 the onset of the oblique convergence between africa and europe in the late cretaceous

a new concept on tectonic correlation between korea china and japan histories from the late proterozoic to cretaceous abstract the dabie sulu collision belt in china extends to the hongseong odesan belt in korea while the okcheon metamorphic belt in korea is considered as an extension of the nanhua rift within the south china block the hongseong odesan belt divides korea s gyeonggi massif into northern and southern portions the southern gyeonggi massif and the yeongnam massif are correlated with china s yangtze and cathaysia blocks respectively while the northern gyeonggi massif is part of the southern margin of the north china block the southern and northern gyeonggi massifs rifted from the rodinia supercontinent during the neoproterozoic to form the borders of the south china and north china blocks respectively subduction commenced along the southern and eastern borders of the north china block in the ordovician and continued until a triassic collision between the north china and south china blocks while subduction was occurring on the margin of the north china block high p t metamorphic belts and accretionary complexes developed along the inner zone of southwest japan from the ordovician to the permian during the subduction the hida belt in japan grew as a continental margin or continental arc collision between the north and south china blocks began in korea during the permian 290 260 ma and propagated westwards until the late triassic 230 210 ma creating the sinistral tanlu fault in china and the dextral fault in the hida and hida marginal belt in japan phanerozoic subduction and collision along the southern and western borders of the north china block led to formation of the qinling dabie sulu hongseong hida yanji belt

tectonic relation between northeastern china and the korean peninsula revealed by interpretation of grace satellite gravity data abstract the major continental blocks in northeastern asia are the north china block and the south china block which have collided starting from the korean peninsula geologic and geophysical interpretations reveal a well defined suture zone in northeastern china from qinling through dabie to jiaodong the discovery of high pressure metamorphic rocks in the hongseong area of the korean peninsula prominent evidence for the collision zone indicates extension of the collision zone in northeastern china into the korean peninsula interpretation of the grace satellite gravity dataset shows two prominent structural boundaries in the yellow sea one extends from the jiaodong belt in eastern china to the imjingang belt in the korean peninsula the other extends from near nanjing eastern china to hongseong tectonic movement in or near the suture zone may be responsible for seismic activity in the western korean peninsula and the development of the yellow sea sedimentary basin

the relationship between systematic metamorphic patterns and collisional processes along the qinling sulu odesan collisional belt between the north and south china cratons

a practical classification of gold deposits with a theoretical basis abstract well considered schemes that classify ore deposits can be effective contributors to exploration success understanding of deposit genesis mining geology engineering metallurgy property valuations and stock market analysis an effective classification scheme needs to be easy to apply without ambiguity and is much more powerful if based on sound scientific principles for deposits with economic gold a useful classification recognises gold only and gold plus deposits based upon whether they also have economic base metals the scheme is easy to apply and in most cases unambiguous for specific deposits and whole provinces the subdivision has a sound scientific basis that involves the chemistry of gold in relation to metal complexing salinity of ore forming fluids and redox state forward modelling from chemical principles can be integrated with inverse modelling from observations to add confidence in this classification and thus be used to create exploration opportunities the jiaodong gold province of eastern china comprises deposits mostly in granitic rocks with economic gold but low levels of base metals the inferred ore fluids are of low to moderate salinity from their gold only character several other aspects of their development can be inferred though the tectonic and metamorphic history remains unresolved the granitic host rocks appear to reflect a chemically and mechanically favourable site for deposition not a source for the gold or the ore fluid neither of which have been established yet

nature and composition of the lower continental crust in central spain and the granulite granite linkage inferences from granulitic xenoliths xenolith bearing alkaline ultrabasic dykes were intruded into the of the hercynian basement of the spanish central system in early mesozoic times the suite of lower crustal xenoliths in the dykes divided into three groups felsic peraluminous granulites metapelitic granulites and charnockitic granulites the felsic granulites form 95 of the total volume of the xenoliths whereas the charnockitic and metapelitic granulites are much less abundant 0 01 5 respectively thermobarometric calculations based on mineral paragenesis indicate equilibration conditions around 850 950 c 7 11 kbar thus the xenoliths represent lower continental crustal material superimposed on this high t high p assemblage is a high t low p paragenesis represented mainly by kelyphitic coronas reflecting re equilibration during transport in the clearly restitic mineral assemblages with up to 50 garnet and 37 sillimanite major and trace element modelling supports the idea that the late hercynian peraluminous granites of central spain represent liquids in equilibrium with restitic material of similar composition to the studied lower crustal xenoliths 87sr 86sr and end of the felsic xenoliths calculated at an average hercynian age of 300 ma are in the range 0 706 0 712 and 1 4 to 8 2 respectively these values match the isotopic composition of the outcropping late hercynian granites the sr isotopic composition of the xenoliths is lower than that of the outcropping mid crustal lithologies orthogneisses pelites a major contribution from the lower crust to the source of hercynian granites greatly reduces the necessity of invoking a large mantle contribution in models of granite petrogenesis the felsic nature of the lower continental crust in central spain contrasts with the more mafic lower crustal composition estimated in other european hercynian areas suggesting a non underplated crust in this region of the hercynian orogenic belt

revised ages for tuffs of the yellowstone plateau volcanic field assignment of the huckleberry ridge tuff to a new geomagnetic polarity event 40 ar 39 ar ages were determined on the three major ash flow tuffs of the yellowstone plateau volcanic field in the region of yellowstone national park in order to improve the precision of previously determined ages total fusion and incremental heating ages of sanidine yielded the following mean ages huckleberry ridge tuff 2 059 0 004 ma mesa falls tuff 1 285 0 004 ma and lava creek tuff 0 639 0 002 ma the huckleberry ridge tuff has a transitional magnetic direction and has previously been related to the reunion normal polarity subchron dating of the reunion event has been reviewed and its ages have been normalized to a common value for mineral standards the age of the huckleberry ridge tuff is significantly younger than lava flows of the reunion event on re union island supporting other evidence for a normal polarity event younger than the reunion event