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

lithostratigraphy of a cenozoic intra continental basin guadiana basin sw spain by using clay mineral assemblages and geophysical properties in the iberian peninsula alpine tectonics built several cenozoic basins that were mainly filled with continental deposits the guadiana basin is located halfway between two of the most important cenozoic basins of the sw of spain the tajo and the guadalquivir basins in this paper both geophysical and mineralogical studies have been carried out in order to establish the lithostratigraphy of the guadiana basin a combination of electric resistivity properties and variations in clay mineral assemblage content of the basin infill was used to identify several depositional sequences within the cenozoic deposits of the basin three depositional sequences ds1 ds2 and ds3 characterized by differentiated clay content and mineral assemblages were distinguished the lower depositional sequence ds1 consists of reddish siltstones and clays that scarcely crop out in the basin clay content of the 2 m fraction is dominated by illite averaging 60 of the total clay content with kaolinite and a few amount of smectite ds2 deposits lie unconformably over ds1 and the variscan basement and consist of a siliciclastic succession where carbonate units occur at bottom and at the top of the depositional sequence smectite dominates throughout the entire succession except in the basal carbonate unit where up to 70 of palygorskite is found in the younger sequence ds3 kaolinite is the dominant clay mineral electrical resistivity imaging helped in the physical characterization and horizontal and vertical distribution of each unit and provided good insight on the structure of the guadiana basin allowing to infer the basin structure due to high resistivity contrast between the basement and the sedimentary rocks in addition in areas where the lower sedimentary units do not crop out and borehole information is not available the geophysical response of the resistivity units imaged can be used to infer the corresponding depositional sequence the joint interpretation of the clay mineral assemblages and geophysical properties of the sedimentary units showed to be a useful tool to gather a reliable identification of depositional sequences in basins characterized by scarcity of good outcrops lack of borehole information and similarity of sedimentary rocks this is very important to properly correlate the different sedimentary units mapped as well as to infer the basin structure and its evolution through time

determination of present day stress tensor and neotectonic interval in the spanish central system and madrid basin central spain a brittle deformation tectonic analysis was performed in central spain spanish central system and madrid basin in order to decipher and understand the deformation processes that take place in a typical intracontinental zone 1174 fault slickensides obtained in materials with ages between late cretaceous and quaternary have been analyzed by means of fault population analysis methods to reconstruct paleostress tensors nine earthquake focal mechanisms have been determined with magnitudes ranging between 3 and 4 1 with regard to regional structural features and sedimentary record data the characteristics of present day and neotectonic stress fields have been figured out which determine the neotectonic period for this region thus we have established that the intraplate zone represented by central spain has been subjected to a stress field from the middle miocene until the present day with a largest horizontal shortening direction shmax located between n130e and n160e finally three paleostress maps with the main active structures are presented for a middle miocene to late miocene the period when the spanish central system was mainly formed b late miocene to quaternary and c the present day stress field deduced from earthquake focal mechanisms

cenozoic deformation of iberia a model for intraplate mountain building and basin development based on analogue modeling 1 inferences from analogue models support lithospheric folding as the primary response to large scale shortening manifested in the present day topography of iberia this process was active from the late oligocene early miocene during the alpine orogeny and was probably enhanced by reactivation of inherited variscan faults the modeling results confirm the dependence of fold wavelength on convergence rate and hence the strength of the layers of the lithosphere such that fold wavelength is longest for fast convergence rates favoring whole lithosphere folding folding is associated with the formation of dominantly pop up type mountain ranges in the brittle crust and thickening of the ductile layers in the synforms of the buckle folds by flow the mountain ranges are represented by upper crustal pop ups forming the main topographic relief the wavelengths of the topographic uplifts both in model and nature suggest mechanical decoupling between crust and mantle moreover our modeling results suggest that buckling in iberia took place under rheological conditions where the lithospheric mantle is stronger than the lower crust the presence of an indenter inducing oblique shortening in response to the opening of the king s trough in the north western corner of the atlantic iberian margin controls the spacing and obliquity of structures this leads to the transfer of the deformation from the moving walls towards the inner part of the model creating oblique structures in both brittle and ductile layers the effect of the indenter together with an increase on the convergence rate produced more complex brittle structures these results show close similarities to observations on the general shape and distribution of mountain ranges and basins in iberia including the spanish central system and toledo mountains

far field effects of alpine plate tectonism in the iberian microplate recorded by fault related denudation in the spanish central system abstract apatite fission track analysis was performed on 56 samples from central spain to unravel the far field effects of the alpine plate tectonic history of iberia the modelled thermal histories reveal complex cooling in the cenozoic indicative of intermittent denudation accelerated cooling events occurred across the spanish central system scs from the middle eocene to recent these accelerated cooling events resulted in up to 2 8 0 9 km of denudation in the western sierra de gredos and 3 6 1 0 km in the central and eastern gredos assuming a paleogeothermal gradient of 28 5 c and a surface temperature of 10 c the greatest amount of denudation 5 0 1 6 km occurred in the sierra de guadarrama accompanying rock uplift was 4 7 1 0 and 5 9 1 6 km in the eastern gredos and guadarrama respectively most denudation in the gredos occurred from the middle eocene to the early miocene and can be related to the n s stress field induced by the pyrenean compression in the guadarrama the greatest denudation was pliocene to recent of age and seems related to the ongoing nw se betic compression the fact that the formation of the e w trending gredos coincides with the n s pyrenean compression and the creation of the present day morphology of the ne sw trending guadarrama with the younger nw se betic compression indicates that they record the far field effects of alpine plate tectonics on iberia the trend of pre existing lineaments was of major importance in influencing the style and magnitude of these of far field effects

granulite facies metamorphism in the anatectic complex of toledo spain late hercynian tectonic evolution by crustal extension the anatectic complex of toledo consists of a heterogeneous suite of high grade metamorphic rocks mainly granulitic migmatites of pelitic composition and orthogneisses and different types of syn orogenic granitoids with minor associated basic rocks none of the metamorphic rock types records evidence of the early prograde history and only the peak and retrograde p t conditions can be estimated the intrusion of the syn orogenic granitoids is either slightly before or synchronous with the metamorphic climax these rock types thus can be used to make p t estimates of the peak and retrograde conditions microtextural analysis of reaction textures in conjunction with a petrogenetic grid has enabled construction of an incomplete clockwise p t path that is characterized by an isothermal decompression after or during the metamorphic peak temperatures the peak estimates from different geo thermobarometers are 800 50 c and 4 6 kbar the highest temperatures recorded in this part of the iberian hercynian belt it is proposed that this high t low p metamorphism is at least partially related to an extensional process possibly due to gravitational collapse of previously thickened crust

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

thermal history of the sabero coalfield southern cantabrian zone nw spain as revealed by apatite fission track analyses from tonstein horizons implications for timing of coalification apatite fission track aft central ages from carboniferous stephanian tonsteins of the sabero coalfield nw spain range from 140 8 7 5 to 65 8 8 1 ma cretaceous with mean c axis projected track length values ranging from 12 5 to 13 4 m mean random vitrinite reflectance rr of these samples ranges from 0 91 to 1 20 which can be translated into maximum palaeotemperatures of ca 130 to 180 c all analysed samples experienced substantial post depositional annealing the considerably younger aft ages compared to the depositional ages of the samples and rr data indicate the certainty of the occurrence of at least one heating event after the deposition of strata the unimodal track length distributions the relatively short mean track length and the rather low standard deviation sd 1 0 1 6 m indicate a relatively simple thermal history that could be related to the post late variscan heating event followed by prolonged residence in the apatite partial annealing zone apaz geological data combined with thermal models of aft data indicate that stephanian strata reached the maximum palaeotemperatures in the permian period which was therefore the major time of the coalification processes the permian magmatic activity was responsible for a high heat flow which with the added effect of sedimentary burial could account for the resetting of the aft system it appears that the fault related hydrothermal activity could have redistributed heat in areas of significant subsidence cooling occurred in the triassic cretaceous times after a high heat flow permian regime a post permian maturation of the stephanian organic matter is not very likely since there is no evidence of a high mesozoic burial that was sufficient to cause a significant increase in the palaeotemperatures finally exhumation and associated erosion rates may possibly have been faster in the tertiary causing the present exposure of the studied rocks

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

thermochronology of lower cretaceous source rocks in the idaho wyoming thrust belt lower cretaceous organic rich source rocks that are thermally mature to postmature crop out on the absaroka darby and prospect plates in linear belts that run parallel to the trace of the thrusts in the idaho wyoming portion of the idaho wyoming utah thrust belt although the common assumption is that burial by thrust plates and the synorogenic sediments derived from them have been responsible for thermal maturation of the organic rich strata commercial amounts of hydrocarbons have not been found in structural traps in this portion of the thrust belt in a companion paper burtner and nigrini demonstrated that gravity driven fluid flow in the idaho wyoming portion of the thrust belt was responsible for moving large amounts of heat from the depths of the early cretaceous foreland basin eastward toward the stable platform in this paper we demonstrate through the application of organic maturation indicators and a new refinement of the apatite fission track technique that this process heated lower cretaceous organic rich source rocks to temperatures sufficient to generate hydrocarbons hydrocarbon generation and migration occurred prior to the development of the thrusts that are often assumed to have played a major role in the generation and entrapment of hydrocarbons in this portion of the thrust belt

interaction of two successive alpine deformation fronts constraints from low temperature thermochronology and structural mapping nw iberian peninsula the lateral termination of the alpine pyrenean orogen relief onshore is located in the nw iberian peninsula it overlies a variscan basement iberian massif where the sedimentary record of the alpine tectonic is very scarce thus the characterisation of the tectonic evolution of the lateral termination is difficult and timing and geometries of the main tectonic structures remain unclear combining the tectonothermal histories obtained by modelling of the apatite fission track data aft with structural mapping allows for a comparative study of the different tectonic scenarios and deformation transfer in the lateral termination of an orogen aft ages for the studied area vary from 53 5 12 9 and 222 12 ma from late triassic to early eocene the beginning of the cenozoic cooling episodes is in agreement with the infilling of the tertiary basins late eocene or oligocene calculated uplift for the alpine orogeny is around 2 400 m the cantabrian mountains were uplifted and emplaced southwards and the main period of exhumation began in the palaeogene at rates of 0 02 mm a and continued during the neogene at rates of 0 06 mm a however the galaico leoneses mountains located to the south of the studied area were uplifted and emplaced northwards during the neogene showing more rapid uplift rates of 0 08 mm a suggesting that the western termination of the alpine pyrenean orogen relief is the result of the successive interaction of two alpine deformation fronts

multiple rind structure in pillow lava as an indicator of shallow water multiple rind structure is common among shallow water pillows with diameters larger than about 1 m in oamaru new zealand on the columbia plateau usa and elsewhere a rind consists of sideromelane tachylyte and tachylytic basalt a multiple rind is a concentric set of repeated rinds in various forms e g a portion of a broken rind thrust under another part a series of short and detached subparallel rinds or a pouch shaped depression transitions and combinations of these three forms are common multiple rind structure develops at any part of the pillow perimeter but does not cover the pillow completely it is always accompanied by a rupture in the outermost rind up to 13 rinds have been observed but two to four rinds are most common the multiple rind structure is formed by implosion resulting from condensation of exsolved h2o when h2o condenses a pressure difference between the interior and exterior of a pillow is created above a certain threshold pressure difference the outer skin of a pillow is torn at weak points such as radial joints and thrusts under the neighboring skin buckles to form a pouch shaped depression or produces some variation of these one set of multiple rinds is thus formed further exsolution and condensation of h2o in solidifying pillows may cause development of additional rinds h2o exsolution and condensation and subsequent implosion are limited to low pressure environments so that multiple rind structure is characteristic of shallow water pillow lava

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

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

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

subaqueous volcanism in the etnean area evidence for hydromagmatic activity and regional uplift inferred from the castle rock of acicastello abstract the subalkaline rocks outcropping at the acicastello castle rock catania sicily and on its abrasion platforms are related to the oldest etnean volcanism 500 300 ka gillot p y kieffer g romano r 1994 the evolution of mount etna in the light of potassium argon dating acta vulcanol 5 81 87 here submarine lavas with pillows closely packed onto each other are associated with heterogeneous and poorly sorted volcaniclastic breccia levels with sub vertical sharp boundaries the present day attitude was previously interpreted as due to a local tilt di re m 1963 hyaloclastites and pillow lavas of acicastello mt etna bull volcanol 25 281 284 kieffer g 1985 evolution structurale et dynamique d un grand volcan polygenique stades d edification et activite actuelle de l etna sicile clermont ferrand iidoctorat etat tesi clermont ferrand ii or to the seaward sliding of the entire eastern etnean flank borgia a ferrari l pasquare g 1992 importance of gravitational spreading in the tectonic and volcanic evolution of mount etna nature 357 231 235 on the assumption of originally horizontal boundaries on the contrary our observations do not match the hypothesis of a significantly tilted succession and lead us to conclude that apart from the strong regional uplift the present castle rock exposure did not suffer any substantial change of its attitude

moissanite sic with metal silicide and silicon inclusions from tuff of israel raman spectroscopy and electron microscope studies abstract here we present studies of natural sic that occurs in situ in tuff related to the miocene alkaline basalt formation deposited in northern part of israel raman spectroscopy sem and fib assisted tem studies revealed that sic is primarily hexagonal polytypes 4h sic and 6h sic and that the 4h sic polytype is the predominant phase both sic polytypes contain crystalline inclusions of silicon sio and inclusions of metal silicide with varying compositions e g si58v25ti12cr3fe2 si41fe24ti20ni7v5zr3 and si43fe40ni17 the silicides crystal structure parameters match si2tiv5 pm 3m space group cubic fesi2ti pbam space group orthorhombic and fesi2 cmca space group orthorhombic respectively we hypothesize that sic was formed in a local ultra reduced environment at respectively shallow depths 60 100 km through a reaction of sio2 with highly reducing fluids h2o ch4 h2 c2h6 arisen from the mantle hot spot and passing through alkaline basalt magma reservoir sio2 interacting with the fluids may originate from the walls of the crustal rocks surrounding this magmatic reservoir this process led to the formation of sic and accompanied by the reducing of metal oxides to native metals alloys and silicides the latter were trapped by sic during its growth hence interplate hot spot alkali basalt volcanism can now be included as a geological environment where sic silicon and silicides can be found

ultra reduced phases in apollo 16 regolith combined field emission electron probe microanalysis and atom probe tomography of submicron fe si grains in apollo 16 sample 61500 the lunar regolith contains a variety of chemically reduced phases of interest to planetary scientists and the most common metallic iron is generally ascribed to space weathering processes lucey et al 2006 reports of silicon metal and iron silicides phases indicative of extremely reducing conditions in lunar samples are rare anand et al 2004 spicuzza et al 2011 additional examples of fe silicides have been identified in a survey of particles from apollo 16 sample 61501 22 herein is demonstrated the utility of low kev electron probe microanalysis epma using the fe ll x ray line to analyze these submicron phases and the necessity of accounting for carbon contamination we document four fe si and si0 minerals in lunar regolith return material the new fe si samples have a composition close to fe ni 3si whereas those associated with si0 are close to fesi2 and fe3si7 atom probe tomography of fe ni 3si shows trace levels of c 60 ppma and nanodomains enriched in c ni p cr and sr these reduced minerals require orders of magnitude lower oxygen fugacity and more reducing conditions than required to form fe0 documenting the similarities and differences in these samples is important to constrain their formation processes these phases potentially formed at high temperatures resulting from a meteorite impact whether carbon played a role in achieving the lower oxygen fugacities and there is evidence of nearby carbonaceous chondritic material it remains to be proven that carbon was the necessary component for the unique existence of these si0 and iron silicide minerals

discovery of moissanite in a peralkaline syenite from the azores islands abstract our discovery of moissanite grains in a peralkaline syenite from the agua de pau volcano sao miguel azores islands portugal represents the first report of this mineral in present day oceanic geodynamic settings raman spectroscopy and single crystal x ray diffraction show the presence of both the 6h and 4h polytypes with the predominance of the first one the distribution of trace elements is homogeneous except for al and v azorean moissanite often hosts rounded inclusions of metallic si and other not yet identified metallic alloys a process involving a flushing of ch4 h2 ultra reducing fluids in the alkaline melts might be considered as a possible mechanism leading to the formation of natural sic thus calling for strongly reducing conditions that were locally met in the crust mantle beneath the sao miguel island

a model for predicting the volumes of vesicles in submarine basalts the total volume percentage of vesicles in submarine pillow basalt rinds can be modelled by the exsolution of h o and co vapor using available solubility determinations for these components in basalt in accordance with observations on natural samples co is predicted to be the major vapor component in vesicles at eruption depths 1 2 km only small initial contents of co 0 1 0 2 wt are consistent with the vesicle volumes observed in most deep sea pillow lavas h o is important only at shallow depths crystallization of pillow interiors can lead to more extensive vesiculation inside of pillow lavas than in the vesicle poor outer rinds

the madrid basin and the central system a tectonostratigraphic analysis from 2d seismic lines abstract data from deep boreholes seismic surveys and surface geology are used to reconstruct the sedimentary infilling of the cenozoic madrid basin eight main depositional sequences and seismic units are recognised from the paleogene the latter four of these sedimentary sequences were deposited in a continental environment under the influence of tectonic activity in the central system the toledo mountains the iberian chain and the sierra de altomira the sedimentary infill shows an overall coarsening upward trend from upper cretaceous formations to syn tectonic conglomerate deposits followed by a fining upward sequence and moderate reactivation of some faults during the late miocene pliocene the syn tectonic sediments are oligocene early miocene in age the foredeep is oriented northeast southwest and shows a sediment thickness of up to 3800 m in areas close to the central system several types of tectonic structures are recognised including imbricate thrust systems thrust triangle zones fault propagation folds back thrust systems and pop up structures the frontal thrusts were subjected to significant erosion and late miocene sediments onlap the anticlines of the onshore foreland nw se trending positive flower structures have been recognised in the eastern part of the basin the total northwest southeast shortening across the contact between the madrid basin and the central system is approximately 5 km of which 2 3 km occurred across the southern border thrust the simultaneous basement uplift of the central system and the tectonic escape of the sierra de altomira have been interpreted as a consequence of constrictive deformation within the pyrenean foreland of the iberian microplate

submarine tumuli and inflated tube fed lava flows on axial volcano juan de fuca ridge a seafloor lava field was mapped within the summit caldera of axial volcano juan de fuca ridge using seamarc i sidescan sonor and submersible observations by analogy with similar subaerial features we infer that several volcanic seafloor features here formed by the process of lava flow inflation flow inflation occurs within tube fed lava flows when lava continues to be supplied to the interior of a flow that has ceased advancing thus uplifting the flow s rigid surface and creating a suite of characteristic surface structures inflated lavas require a feeder lava tube or tube system connected to a remote lava source and therefore we infer that inflated submarine lava flows contain lava tubes inflated flow features identified from sidescan sonar images elsewhere on axial volcano and within the axial valley of the southern juan de fuca ridge suggest that flow inflation is a widespread submarine volcanic process

not all moissanites are created equal new constraints on moissanite from metamorphic rocks of bulgaria abstract terrestrial moissanite sic is widely reported as an ultra high pressure mineral occurring in kimberlites diamonds and ultramafic mafic rocks of mantle origin however the conditions of crystallization remain largely unknown moreover dozens of sic occurrences have been reported from continental crust sources such as granitoids andesite dacite volcanic rocks and their breccia metasomatic and metamorphic rocks and even limestones the validity of many of these reports is still debated primarily due to possible contaminations from the widespread use of synthetic sic abrasives in samples preparation indeed reports of well documented in situ occurrences of moissanite in association with co existing minerals are still scarce the only condition of moissanite formation that is agreed upon is that extremely reducing media are required e g 4 5 6 log units below the iron wustite buffer here we report the new occurrence of moissanite that was found in situ within the garnet staurolite mica schists of topolovgrad metamorphic group of triassic age in southern bulgaria the 10 300 m moissanite crystals are situated within 0 1 1 2 mm isolated clusters filled with amorphous carbon and nanocrystalline graphite most of moissanite crystals are 15r rhombohedral and 6h hexagonal polytypes and one prismatic crystal found within them exhibits unusual concentric polytypical zoning with core 15r intermediate zone 6h and rim 3c cubic experimental data show that this type of polytypical zonation is likely due to a decrease in temperature or and pressure and changes in si c ratio indeed amphibolite facies metamorphism 500 580 c garnet staurolite zone followed by a subsequent cooling during the retrograde stage of green schist facies metamorphism 400 500 c could have provided a change in temperature the sic containing clusters exhibit evidence that they are pre metamorphic and we hypothesize that their protolith was a black shale material likely rich in carbon hydrocarbon and terrigenous silica the latter served as a source of isolated chemically reduced media which is required for sic formation other concepts to explain moissanite occurrences in metasedimentary rocks are also discussed importantly our findings show that the formation conditions of moissanite are likely more variable than previously recognized

variability of apatite fission track annealing kinetics ii crystallographic orientation effects a method is presented that permits the length of any horizontal confined fission track inclined at a specified angle to the crystallographic c axis in apatite to be converted to an equivalent track length parallel to the crystallographic c axis the model is based on the results of annealing experiments for six selected apatites five calcian fluorapatites and durango apatite representing a subset of the 15 total apatite specimens studied an iterative process of calculation is required to project fission track lengths onto the c axis and computer source code implementing the solution to this problem is presented this method of projecting apatite fission track lengths onto the crystallographic c axis is shown to remove effectively fission track length variation within single fission track populations due to anisotropic track length reduction for all 15 apatites studied in addition a model is developed that offers predictions that closely reproduce published experimental data concerning the relationship between fission track density etched fission tracks per unit area of apatite surface and the arithmetic mean fission track length finally it is shown that natural fission track populations exhibit fission track length anisotropy similar to that of fission track populations created and annealed in the laboratory this observation implies that the same process by which apatite fission tracks anneal in the laboratory is responsible for annealing of apatite fission tracks in the geological environment

correlated si isotope anomalies and large 13c enrichments in a family of exotic sic grains a suite of morphologically distinctive silicon carbide sic grains from the orgueil and murchison carbonaceous chondrite meteorites contains si and c of highly anomalous isotopic composition all of the sic grains in this suite are characterized by a distinctive platy morphology and roughly developed hexagonal crystal forms that allow them to be distinguished from other types of sic found in the host meteorites the 29 si and 30 si values of individual sic crystals deviate from those of normal solar material by more than 100 while the 13 c values range from 150 to 5200 isotopically normal c and si are not found in any of these sic crystals the sic grains belonging to this morphological suite are isotopically distinct from fine grained sic aggregates and other morphological types of sic in unequilibrated meteorites the 29 si 28 si and 30 si 28 si ratios of these platy grains are well correlated and define a linear array that does not pass through the composition of normal solar si this behavior contrasts sharply with the diverse and poorly correlated si isotopic compositions shown by the total sic population we suggest that the distinctive morphological characteristics and comparatively simple si isotope systematics identify the platy sic crystals as a genetically related family formed around a single isotopically heterogeneous presolar star or an association of related stars the enrichments in 13 c and the si isotope systematics of the platy sic are broadly consistent with theoretical models of nucleosynthesis in low mass carbon stars on the asymptotic giant branch the si isotope array most plausibly reflects mixing between 28 si rich material inherited from a previous generation of stars and material enriched in 29 si and 30 si produced in intershell regions by neutron capture during he burning 13 c is also produced in intershell regions by proton reactions on 12 c seed nuclei and is carried withs process nuclei to the stellar envelope by convection which penetrates down to the he shell the absence of a correlation between the si and c isotopic compositions of the sic suggests either episodic condensation of sic extending over several thermal pulses in the atmosphere of a single star or derivation of the sic from several stars characterized by different rates of 13 c production in the multiple star scenario the linear correlation of the 29 si 28 si and 30 si 28 si ratios among the platy sic indicates that these stars evolved from a common si seed composition under similar conditions of neutron capture nucleosynthesis the 29 si 30 si ratio of the sic inferred by us to be produced by neutron capture in the stellar interior is distinct from values calculated from models of nucleosynthesis in agb stars

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

magma water interactions in subaqueous and emergent basaltic in the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of 1 explosive release of magmatic volatiles 2 explosive expansion and collapse of steam formed at magma water contact surfaces 3 explosive expansion of steam following enclosure of water in magma or entrapment of water close to magma and 4 cooling contraction these processes named respectivelymagmatic explosivity contact surface steam explosivity bulk interaction steam explosivity andcooling contraction granulation can be enhanced by mutual interaction and feedback the first three explosive processes are limited at certain water depths hydrostatic pressures and become increasingly vigorous at shallower levels the depth of onset of magmatic explosivity depends largely on juvenile volatile content it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas at the depth where formation of clastic deposits becomes predominant over effusion of lavas magmatic explosivity is subordinate to steam explosivity as a clast forming process the upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it contact surface explosivity commonly requires initiation by a vigorous impact between magma and water and although no certain depth limit is known likelihood of such explosivity decreases rapidly with depth clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water which in sea water is at about 3 km cooling contraction granulation can occur in any depth of water but at shallow levels may be replaced by contact surface explosivity during continuous eruption under water tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur emergent volcanoes are characterized by distinctive steam explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material water and steam the water gets into the vent by flooding across or through the top of the tephra pile and violent explosions cease when this access is sealed the eruptions during emergence of surtsey and capelinhos typify the distinctive explosive activity the style and controls of which are different from those of maar volcanoes

local stress fields and intraplate deformation of iberia variations in spatial and temporal interplay of regional stress sources tertiary to present deformation in the interior of the iberian peninsula reflects spatial and temporal variations of the activity of the plate boundaries local deformation patterns observed in many of the numerous intraplate tertiary basins and their borders such as the madrid basin and the sierra de altomira are at first sight incompatible with the regional stress field under which they were formed we demonstrate however that they can be explained as the effect of several stress fields that acted on the iberian peninsula from earliest tertiary onward data on local deformation can constrain both magnitudes and directions of forces acting on the plate boundaries of iberia enabling us to estimate the relative importance of the different plate driving and deforming mechanisms providing further constraints on the tectonic evolution of iberia

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

lithospheric folding in iberia integration of stress indicator data gravity data crustal kinematics data and analysis of topography and recent vertical motions demonstrates the occurrence of consistently oriented spatial patterns of large scale alpine to recent intraplate deformation in iberia the inferred upper crustal and lithospheric deformation patterns and the timing of the associated expressions at or near the surface support the existence of a close coupling with plate boundary processes operating at the margins of iberia patterns of lithosphere and upper crustal folds are oriented perpendicular to the main axis of present day intraplate compression in iberia inferred from structural analysis of stress indicator data and focal mechanism solutions these findings suggest the presence of lithospheric folds with wavelengths compatible with theoretical predictions of folding wavelengths of variscan lithosphere stress induced intraplate deformation set up by plate interactions is compatible with indications for the absence of present day deep mantle lithosphere interactions inferred from seismic tomography

extensional tectonics of the toledo ductile brittle shear zone central iberian massif abstract the toledo mylonite in the central area of the iberian massif represents a major ductile shear zone only a small part of which has been exposed to view mylonites derived largely from migmatite occupy a 300 350 m thick gently s dipping zone along the southern margin of the toledo crystalline massif the upper plate comprises palaeozoic lower grade metasedimentary rocks intruded by a late hercynian pluton the juxtaposition of the upper and lower plates with different structural and metamorphic conditions indicates that the shear zone is a significant structure with a large displacement progressive simple shear under conditions of a clearly decreasing confining pressure and temperature is supported by a microbrecciated mylonite cataclasite and ultracataclasite sequence overlying the mylonites the top of the ledge of cataclasites corresponds to the detachment fault part of the shear zone structural relations combined with meso and micro structural evidence stretching lineations and asymmetric shear sense indicators support the conclusion that the mylonites and cataclasites associated with the detachment faulting formed during a continuous extensional deformation detachment fault models developed for the formation of metamorphic core complexes can be applied in the toledo massif we propose a model that implies a transition from ductile to brittle deformation associated with extension at greater structural depths during lower permian time

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

large scale distributed deformation controlled topography along the western africa eurasia limit tectonic constraints in the interior of the iberian peninsula the main geomorphic features mountain ranges and basins seems to be arranged in several directions whose origin can be related to the n s plate convergence which occurred along the cantabro pyrenean border during the eocene lower miocene time span the iberian variscan basement accommodated part of this plate convergence in three e w trending crustal folds as well as in the reactivation of two left lateral nne ssw strike slip belts the rest of the convergence was assumed through the inversion of the iberian mesozoic rift to form the iberian chain this inversion gave rise to a process of oblique crustal shortening involving the development of two right lateral nw se shear zones crustal folds strike slip corridors and one inverted rift compose a tectonic mechanism of pure shear in which the shortening is solved vertically by the development of mountain ranges and related sedimentary basins this model can be expanded to nw africa up to the atlasic system where n s plate convergence seems also to be accommodated in several basement uplifts anti atlas and meseta and through the inversion of two mesozoic rifts high and middle atlas in this tectonic situation the microcontinent iberia used to be firmly attached to africa during most part of the tertiary in such a way that n s compressive stresses could be transmitted from the collision of the pyrenean boundary this tectonic scenario implies that most part of the tertiary eurasia africa convergence was not accommodated along the iberia africa interface but in the pyrenean plateboundary a broad zone of distributed deformation resulted from the transmission of compressive stresses from the collision at the pyrenean border this distributed intraplate deformation can be easily related to the topographic pattern of the africa eurasia interface at the longitude of the iberian peninsula shortening in the rif betics external zones and their related topographic features must be conversely related to more local driven mechanisms the westward displacement of the exotic alboran domain other than n s convergence the remaining nnw sse to nw se latest miocene up to present convergence is also being accommodated in this zone straddling iberia and morocco at the same time as a new ill defined plate boundary that is being developed between europe and africa

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

coherent intrusion complexes in large basaltic volcanoes a new structural model abstract highly concentrated coherent intrusion complexes consisting of thousands of small mafic intrusions occur in probably all major basaltic volcanoes and play an important role in volcano development magma excursions from the high level chamber travel laterally along a surface of neutral buoyancy at the margin of a complex and cause the complex to grow the limited distance however that narrow intrusions can propagate before becoming blocked causes complexes to be wedge like intrusive dike complexes underlie rift zones and asymmetric growth of the dike wedge causes rift zones of shield volcanoes to become non collinear and may initiate a third rift zone in the obtuse angle downbowing of stress trajectories across complexes causes dikes to be non vertical and results in axial subsidence intrusive sheet complexes form instead of dike complexes in volcanic systems that have a restricted ability to expand laterally and accommodate intrusions by expanding vertically instead downbowing of stress trajectories causes sheets to be non horizontal and this combined with subsidence increasing toward the thicker part of the sheet wedge produces the inward and inwardly increasing dip that characterizes cone sheet complexes this mechanism for cone sheets differs considerably from previously proposed mechanisms successive injections of sheets at the top of a sheet complex probably offers the most efficient means of powering a high intensity geothermal field such as the 5000 mw grimsvotn system in iceland it is inferred that similar mechanisms to those in major basaltic edifices operate in spreading ridges study of basaltic edifices has the potential to contribute significantly to the understanding of spreading ridges

raman spectroscopy in heavy mineral studies abstract raman spectroscopy is an innovative tool with tremendous potential serving as a fun damental complement to a variety of provenance methods including heavy mineral analysis anddetrital geochronology because of its accuracy ef ciency and versatility the results of theraman technique are indispensable for fully reliable identi cation of heavy minerals in grainmounts or thin sections thorny long standing problems that cannot be solved con dently witha polarizing microscope alone such as the determination of opaque and altered heavy minerals of detrital grains as small as a few microns or of colourless crystals with uncertain orientationand rounded morphology can nally be addressed although the method can be highly automa tized the full ability and experience of the operator is required to combine raman data with theoptical information obtained under the microscope on the same grains which is essential for theef cient application of the method in provenance studies this article provides exemplaryramanspectrausefulforthecomparisonand determinationof over70 differentopaqueandtrans parent heavy mineral species commonly found in sediments conveying speci c information onthe genesis of their source rocks and thus is particularly useful in provenance diagnoses andpalaeotectonic reconstructions supplementary material detailed information on the lasers used and the origin of the analysedminerals is available at http www geolsoc org uk sup18615it is the scattering of light by atoms and moleculesthat gives us the light of the sky the blue colour ofthe deep sea and the delicate opalescence of largemasses of clear ice raman 1928 pp 368 369

jurassic to present thermal history of the central high atlas morocco assessed by low temperature thermochronology apatite fission track aft and u th he data from the high atlas have been obtained for the first time to constrain the tectono thermal evolution of the central part of the chain results from palaeozoic basement massifs indicate long residence at low temperatures consistently with their original location out of the deepest mesozoic rift troughs and indicating minor exhumation the best rocks for extracting the alpine history of the atlas mountains are jurassic intrusives which yield aft ages centred on c 80 ma thermal models based on aft data and constrained by u th he suggest that these ages are included in a slow cooling trend from intrusion age to c 50 ma ago that we attribute to post rift thermal relaxation this is followed by a stability period of c 30 ma and then by a final exhumational cooling until present exposure eocene intrusives yield aft ages similar to those of rb sr and k ar suggesting rapid emplacement in the uppermost crust

rock forming moissanite natural α silicon carbide we report the first occurrence of moissanite sic as a rock forming mineral 8 4 vol in one unique specimen of a terrestrial rock the sample has a homogeneous porphyritic texture and was found as a beach pebble thought to be derived from a tertiary volcanic province of the aegean sea region the matrix is bluish colored and consists of very fine grained brucite calcite and magnesite in which macrocrysts of quartz 25 3 vol and moissanite are found other accessory phases are phlogopite 3t magnesiochromite an fe rich phase cl bearing brucite al rich orthopyroxene and unidentified mgfe silicates 4 vol the bulk rock composition shows a kimberlitic chemistry 55 8 wt sio 2 28 5 wt mgo 1 4 wt cao 18 1 wt loi colorless gemmy and blue or black moissanite crystals are subhedral and display characteristic hexagonal symmetry 6h polytype most moissanite grains contain metallic si and fe silicide fe 3 si 7 inclusions and more rarely other fe silicides with varying amounts of al 24 5 wt ca 8 0 wt mn 6 8 wt ti 16 3 wt and ni 2 6 wt the 13 c value of the moissanite is 28 1 according to available data the f s o2 stability field of sic is five to six log units below the iron wustite iw buffer curve therefore the observed fe bearing silicates cannot have been equilibrated with sic under ambient pressure instead our finding indicates that the rock most likely formed at the ultrahigh pressure conditions of the upper mantle or transition zone

empirical evidence for the fractionation of carbon isotopes between diamond and iron carbide from the earth s mantle we have studied two samples of mantle diamond containing iron carbide inclusions from jagersfontein kimberlite south africa syngenetic crystal growth is inferred using morphological characteristics these samples provide an opportunity to investigate the isotopic partitioning of 13c in a terrestrial natural high pressure and high temperature hpht system the difference for the 13c values between the diamond and coexisting iron carbide averaged 7 2 1 3 these data are consistent with available data from the literature showing iron carbide to be 13c depleted relative to elemental carbon i e diamond we infer that the minerals formed by crystallization of diamond and iron carbide at hpht in the mantle beneath the kaapvaal craton it is unclear whether crystallization occurred in subcratonic or sublithospheric mantle in addition the source of the iron is also enigmatic nonetheless textural coherence between diamond and iron carbide resulted in isotopic partitioning of 13c between these two phases these data suggest that significant isotopic fractionation of 13c 12c 13c up to 7 can occur at hpht in the terrestrial diamond stability field we note that under reducing conditions at or below the iron iron wustite redox buffer in a cratonic or deep mantle environment in earth the cogenesis of carbide and diamond may produce reservoirs of 13c depleted carbon that have conventionally been interpreted as crustal in origin finally the large 13c for diamond iron carbide shown here demonstrates 13c for silicate metallic melts is a parameter that needs to be constrained to better determine the abundance of carbon within the earth s metallic core

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