structures and way up criteria in migmatites with application to the velay dome french massif central abstract a detailed structural analysis has been applied to the migmatite sequence of the southern limb of the velay dome france in an attempt to study the structural implications of the occurrence of metatexites and diatexites metatexites have a plastic behaviour presumably dominated by the solid skeleton which largely takes up the deformation in contrast diatexites have a predominantly viscous behaviour because the solid framework has been disrupted and they are dominated by the granitic melt rather than the solid component therefore the metatexite to diatexite transition has a major rheological and tectonic importance because it separates regions that record plastic stable deformation from regions that record viscous unstable deformation where gravitational instabilities may develop mesoscopic syn migmatitic way up criteria which assume that melt migration is partly driven by gravity give evidence for a southward overturning of the velay dome this overturning is supported by sedimentary and plutonic way up criteria seen in schists and granitic plutons respectively the n s asymmetry of the velay dome is related to late variscan asymmetric extension on a regional scale consistency of data provides further evidence that syn migmatization way up criteria are regionally reliable structural tools applicable to other migmatitic terrains

provenancing and archaeology of roman millstones from the mediterranean area abstract roman rotary grain mills in the mediterranean area are mainly of two styles hourglass shaped pompeian style mills and flatter cylindrical millstones many of these millstones are made of igneous rocks imported to the sites where the mills are found and they may therefore be important indicators of resource procurement and trade if the source of the rock of manufacture can be traced three types of igneous rock were used to make millstones 1 reddish rhyolitic ignimbrite 2 leucite phyric lavas and 3 generally fresh grey vesicular lavas of basic intermediate composition potential source rocks and millstones of all three types of rock were characterized using petrographic examination in thin section and chemical analysis for major and 15 trace elements determined by low dilution fusion wavelength dispersive x ray fluorescence analysis one hundred and forty six millstones and lavas from archaeological contexts were studied and 113 of these were successfully assigned to geological sources sixteen areas of igneous rocks were used by the romans for millstone production these include the basic and intermediate composition grey vesicular lavas of olot northeast spain agde southern france volvic and possibly the le puy area central and southeast france respectively vulture italy etna and monti iblei in sicily pantelleria sardinia ustica the aeolian islands nisyros aegean libya and the middle atlas and rif areas of morocco the red rhyolite was quarried at the village of mulargia in sardinia and the leucite phyric rocks originated on the italian mainland including the quarry of orvieto in umbria there is a wide variation in size and style of millstones from individual production centres and some were exported in unfinished form grey vesicular millstones were traded up to at least 820 km from their sources and fall into four mainly separate distributions in the mediterranean the mulargia rhyolite and the leucitites were moved mainly from north to south were traded further than the grey vesicular rocks and were probably the most desirable types they are found 1350 and 1500 km distant from their sources respectively the millstones were moved mainly by sea perhaps on grain collecting ships on outward voyages from italy to the south and west of the mediterranean

orogen parallel and orogen perpendicular extension in the central nepalese himalayas north dipping gravitationally driven extensional structures that unroof the high grade core of the himalayas have been recognized in several parts of the orogen recent work in west central nepal demonstrates that the extensional history at the top of the greater himalayan metamorphic sequence in this region is laterally variable in the upper marsyandi valley there is evidence for three generations of early to middle miocene west directed orogen parallel extensional structures the study area consists of two tectonostratigraphic sequences the lower sequence consists of a 12 km thick section of high grade metasedimentary rocks of the greater himalayan sequence the higher sequence consists of a 4 km thick section of medium grade marble of the tibetan sedimentary sequence it overlies the greater himalayan sequence in the marsyandi valley along a northwest dipping ductile shear zone the chame detachment mylonitic fabrics in footwall rocks show evidence of west directed displacement at sillimanite grade through greenschist grade conditions a cataclastic zone indicates progressively more brittle deformation at the eastern end of the outcrop trace of the chame detachment in the dudh khola valley 15 km west of the marsyandi valley the tibetan sedimentary sequence is juxtaposed with the greater himalayan sequence by an early miocene north dipping ductile shear zone the dudh khola detachment that has well developed north trending stretching lineations formed during sillimanite grade metamorphism north directed orogen perpendicular extension in the dudh khola region is interpreted as coeval with west directed orogen parallel extension in the marsyandi region along strike variations in the orientation of extensional strain at the top of the greater himalayan sequence may be explained by lateral crustal thickness gradients

structural analysis of sheath folds with horizontal x axes northeast canada abstract early proterozoic supracrustal rocks occur below a thick nappe of archaean basement gneiss in the melville peninsula where sheath folds are exposed in a wide zone of middle proterozoic dynamothermal metamorphism outcrop patterns of truncated isoclinal sheath folds resemble cylindrical folds except in relatively small areas around the paraboloidal caps bulk extension axes are parallel to strike in the belt as shown by isoclinal sheath folds with horizontal central axes x axes as well as similarly aligned mullion structure and rotated scapolite prisms extension axes converge from northeast to southwest in the apparent flow direction

the spatial and temporal variability of convective storms over the northeast united states during the warm season abstract a spatial and temporal climatology of convective storms over the northeast united states during the warm season april september is presented using composite national operational weather radar nowrad data at 2 km grid spacing from 1996 to 2007 as well as cloud to ground lightning from the national lightning data network nldn on a 10 km grid from 2001 to 2007 there are preferred regions for convective storms within new york s hudson river valley western and southeastern pennsylvania central new jersey and across the delmarva peninsula a favored initiation area during the early afternoon is the immediate lee of the appalachians with a tendency for these convective systems to move eastward to the coast by late evening there is a sharp gradient in convective frequency within 20 km of the coast on average as a result of the relatively stable marine boundary layer but as the sea surface warms by midsummer this convective activity increases near the coast with a nocturnal 0600 1200 utc c

geodynamic evolution of the pan african belt in central africa with special reference to cameroon the pan african belt in central africa has benefited from the many petrographic structural and geochronological studies in the recent years that have improved our understanding of the belt however those studies have also produced various and often divergent evolutionary models for the belt some of which do not even involve well defined cratons following a review of the available data in cameroon we propose a model of continent continent collision that involved the congo craton and the north central cameroon active margin showing archean to paleoproterozoic inheritances this model is based among others on i the prominent role of the congo craton as demonstrated by the regional extension of external nappes on its northern edge and the concomitant exhumation of the 620 ma granulitic rocks believed to have formed at the root of the collision zone and ii the late development of a strike slip fault system in central cameroon as the result of horizontal movement following the multistage collision

upb and smn edvidence for eburnian and pan african high grade metamorphism in cratonic rocks of southern cameroon abstract u pb analyses of zircons and sm nd mineral and whole rock analyses of samples from southern cameroon document three distinct rock forming or high grade metamorphic events 2900 ma 2050 ma and 600 ma zircons from the ebolowa charnockite in southern cameroon yield an age of 2896 7 ma consistent with published rb sr total rock data for the region sm nd crustal formation ages for these rocks are 3000 ma indicating that the granitoids and ntem series gneisses in the north end of the congo craton formed 2900 ma ago and do not contain major contributions from older archean crust a second metamorphic event of eburnian age is identified from re equilibration of sm and nd in gneisses and metadolerites of the ntem complex at 2050 ma zircons from the younger nyong series gneisses are a complex mixture of cores and overgrowths the overgrowths in most cases formed during a high grade metamorphic event between 2100 and 2000 ma and clearly postdate the ebolowa charnockite the ages of the cores are not precisely known but we believe most represent detrital zircons from 2900 ma protoliths sm nd crustal formation ages for samples of the nyong series gneisses are generally 2500 to 2900 ma indicating that their precursors were apparently derived mainly from the archean craton with variable amounts of younger component sm nd garnet total rock isochrons for metamorphosed mafic rocks in the nyong series yield ages of 2050 ma and zircons from one of them yield an upper intercept age of 2037 10 ma further documenting the existence of a major event with magmatism and charnockitization at 2000 to 2100 ma we interpret the nyong series metasedimentary gneisses as post 2900 ma cratonic cover that was deformed and metamorphosed during the 2000 to 2100 ma eburnian orogeny we cannot define precise limits on the ages of sedimentation preliminary data on metamorphosed intrusive rocks associated with the yaounde series yield u pb concordant ages around 620 ma consistent with sm nd garnet whole rock ages from the same series this dates the pan african tectono metamorphic activity in the southern end mobile belt the pan african lower intercepts of zircons and sm nd garnet whole rock ages from thnyong series are the consequences of this event which is further represented by a 590 ma zircon age from a late syenitic pluton results from cameroon are consistent with recent results from the western part of the congo craton farther south and from the northeastern part of the sao francisco craton in brazil one interpretation of these results is that the congo and sao francisco cratons were joined during the ebumian trans amazonian orogeny 2100 ma and are bordered to the north by a late mesoproterozoic rift basin that was closed during the pan african brasiliano orogeny 600 ma

sedimentological proof and dating of the early holocene volcanic eruption of ulmener maar vulkaneifel germany a minerogeniclayer occurs in early postglacial organic sediments from five maar lakes west eifel volcanic field germany the mineralogy and stratigraphic position of this tephra suggests that it is related to the youngest german volcano ulmener maar nearby radiocarbon dating of wood from the base of the ulmener maar tephra at two locations provide ages in agreement with an accelerator mass spectrometer 14c date for the minerogenic layer from sediments of lake holzmaar situated 13 km south west of ulmener maar the mean radiocarbon age is 9 560 years bp dating by varve chronology provides an age of 10017 years vt varve time in years before 1950 or 10 895 years corrected vt based on palynology the ulmener maar tephra was deposited at the end of the preboreal high values of natural remnant magnetization intensity typical of pyroclastic material confirm that this minerogenic layer differs in composition from other clastic deposits of the sedimentary record geochemical analyses reveal increased values of total trace elements for the laacher see tephra and ulmener maar tephra an isopach map based on thickness variations of the ulmener maar tephra at five investigated maar lakes indicates that the tephra was mainly transported to the south west

palaeogeographical reconstructions of the pan african brasiliano orogen closure of an oceanic domain or intracontinental convergence between major blocks abstract a reconstruction of the pan african brasiliano orogen has become possible thanks to new data from the southern pan african belt and by using published data geological mapping which included structural thermobarometric and geochemical studies in togo and neighbouring countries have enabled to define the existence of a preorogenic continental rift whose closure followed soon after its opening continental crust convergence induced an oblique collision that caused nappe stacking this involved external nappes thrust over the west african craton intermediate nappes including metabasic rocks with eclogitic assemblages and internal nappes composed of highgrade anatectic gneiss and intrusive granite and charnockite comparison with data from other regions hoggar adrar des iforas northeastern brazil nigeria central africa has led to the recognition of a pre orogenic continental rift that bordered the west africa sao francisco congo cratons in the southern part of the chain farther north in the hoggar and adrar des iforas this continental rift opened on a wider oceanic domain which involved a passive margin along the west african craton and an active margin to the east after these rifting and subduction stages continental collision followed that was dominated by strike slip movement oblique to the plate boundaries the general organization of the pan african brasiliano belt can be considered as the result of a confrontation between three major continental domains these were the west african and sao francisco congo cratons and a reworked shield composed in its inner part of polycyclic basement rocks and bounded by a fringe of monocyclic metasedimentary thrust belts that faced the cratons

improving geochronological framework of the pan african orogeny in cameroon new sims zircon and monazite u pb age constraints abstract high precision geochronological framework is crucial to understanding of the evolution of orogenesis as part of the pan african north equatorial fold belt the neoproterozoic fold belt of cameroon nfbc involved polyphase deformation d1 to d4 phases metamorphism up to granulite facies and widespread crustal anatexis and magmatism while a general geochronological framework has been established controversy still exists on the temporal evolution of the metamorphic and magmatic events associated with polyphase deformation in particular the accurate age and geodynamic manifestations underlining the end of the orogeny are yet to be well constrained we conduct in this work integrated analyses of sims u pb zircon and monazite dating and in situ zircon hf o isotopes on the orthogneiss leucosome and granite samples from wum and yaounde of southwestern cameroon in order to provide further constraints on temporal evolution of the nfbc our high precision sims u pb age data demonstrate that the magmatic protoliths of orthogneisses from wum and yaounde were emplaced synchronously at ca 620 ma they were generated by partial melting of the thickened paleoproterozoic crustal basement rocks with zircon hf tdmc model age of ca 1 9 2 0 ga metamorphic zircons and two generations of monazites from an in situ leucosome within the granulitic paragneiss of the yaounde group yield indistinguishable ages of ca 610 ma these new results in combination with previous isotopic data suggest that the yaounde group supracrustal rocks with zircon hf tdmc model age of ca 1 7 ga experienced a very rapid evolution from sedimentation at

u pb zircon evidence for a pan african granulite facies metamorphism in the central african republic a new interpretation of the high grade series of the northern border of the congo craton abstract the results of u pb zircon and sm nd whole rock analyses are reported on three meta igneous granulitic samples from the central african republic basement formerly ascribed to an archaean complex u pb data point to late proterozoic ages 833 66 ma 652 19 ma and 639 3 ma and sm nd model ages in the 1700 2200 ma range preclude an exclusive derivation from an archaean source whatever their precise geologic significance either first crystallization of zircons at the time of igneous emplacement or complete resetting during metamorphic recrystallization the u pb data clearly rule out an archaean age for the high grade event in contrast with previous opinion indeed the granulite facies metamorphism cannot be older than late proterozoic this is in good agreement with the recent recognition of a major collision type orogen oubanguides belt of pan african age in this area it is proposed that two main generations of granulitic rocks occur at the northern margin of the congo craton an archaean one in the foreland of the oubanguides belt e g ntem complex cameroon and a pan african one in the internal zones of this orogen

structural characterization of the misaje granitic pluton nw cameroon constraints from magnetic and field observations the misaje granitic pluton emplaced between 569 and 560 ma in an amphibolitic and gneissic host rock comprises four petrographic units namely biotite hornblende granite bhg granodiorite gd biotite granite bg and leucocratic granite lg four major tectonic events have been described in the studied area a d1 early tectonic event responsible of the e w flat foliation which has been progressively transposed by a d2 tectonic event a d2 event has developed heterogeneous simple shear in a dextral transpressive context with moderate to strong dipping ne sw striking foliation a d3 tectonic event has lead to a sinistral n s ductile shear characterized by n to ene striking foliation and e w strike slip shear corridors and a d4 tectonic event that developed n s dextral ductile strike slip deformation the magnetic study of the pluton based on the ams parameters reveals the coexistence of both paramagnetic dominated by iron bearing silicates 54 of sites and ferromagnetic due to the occurrence of psd and md grains of magnetite or other ferromagnetic minerals 46 of sites behaviors magnetic foliation shows best poles at 55 82 for the whole pluton 95 32 in bhg and 273 83 in bg and the magnetic lineation trends are mostly nne ssw with best lines at 210 8 198 19 and 36 3 respectively the trend of the magnetic lineation in bg indicates an s shape trajectory suggesting a sinistral sense of shear motion along discrete e w corridors situated at the northern and southern ends kinematic indicators in bg point to a sinistral sense of shear suggesting its emplacement during the d3 event the close relationship between k1 and k3 points to a syn kinematic emplacement and crystallization of the misaje granitic pluton during the pan african event and the tectonic evolution of the study area is considered to be coeval with the tectonic evolution of the trans saharan pan african belt of eastern nigeria

kilometre scale sheath fold at mattmark and implications for transport direction in the alps folds were the first tectonic features of rocks to be studied and as such are taken as a reference for the interpretation of other structures intuitively fold axes were assumed to be subperpendicular to the direction of transport nevertheless many studies of metamorphic belts showing intense ductile deformation describe folds with axes close to the transport direction in particular sheath folds1 9 are highly curvilinear folds elongated parallel to the direction of transport we discuss here a spectacular large sheath fold situated in a crustal shear zone in the monte rosa nappe swiss alps our analysis implies that both the geometry and significance of folds in the internal alps must be re examined we further demonstrate the existence of crustal ductile shear zones in an area of the alps where previously emphasis was generally placed on fold nappes the movements on these shear zones is often tens of kilometres

orogen parallel extension and oblique tectonics the relation between stretching lineations and relative plate motions many collisional orogens exhibit two distinct deformation phases the first and relatively early phase forms within an obliquely subducting continent and is characterized by regionally consistent stretching lineations subparallel to the orogen and to associated isoclinal and sheath folds second phase folds and stretching lineations develop during and after imbrication of the subducting plate into the overriding plate and they become progressively disharmonic with stretching lineations oriented perpendicular to the orogen structural morphology and stretching lineations indicate that a fundamental kinematic transition occurs as material is imbricated from footwall to hanging wall kinematic modeling based on modern oblique convergent boundaries and considerations of buoyancy forces suggest that only the relatively early structures reflect the relative plate motion but that the correspondence is not simple in particular the orientation of stretching lineations is a function of finite strain kinematics of deformation and angle of subduction and convergence and it will consistently underestimate the angle of oblique convergence second phase structures reflect isostatic emergence of the hanging wall and are independent of relative plate convergence examples are drawn from the south central canadian rockies the western alps the variscides of ireland and france and the himalaya

geochemical provenance analyses of roman lava millstones north of the alps a study of their distribution and implications for the beginning of roman lava quarrying in the eifel region germany abstract in roman times rotary querns and different types of millstones driven either by horse capstan or water power were produced in the lava quarries of the quaternary volcanic eifel region and exported to many parts of the empire the geographic distribution of roman lava millstones from the eifel region provides important information about trade patterns and in cases of well dated millstones also allows an estimate as to when the roman lava quarrying in the eifel region began sixty two millstones from germany france and austria were sampled and analyzed for major and trace elements by x ray fluorescence to determine their provenance the millstone data was evaluated by a combination of geochemical discrimination and cluster and discriminant analyses using an extensive and detailed database of all roman lava quarries in the eifel region an eifel provenance could be confirmed for forty four artefacts and furthermore determined down to the exact lava flow the affiliation of the other artefacts to other possible regions where millstones of comparable lava were extracted was carried out on the basis of geochemical data from the literature however because of insufficient data only assumptions about the regional provenance can be made the origins of the other finds are assumed to be the vogelsberg region the massif central orvieto and possibly the pannonian basin a preliminary map of the distribution of eifel millstones in roman times based on these data is presented the beginning of roman lava quarrying can be constrained to 8 7 bc

crustal growth in the mesoarchean plutonic belt from the memve ele area ntem complex southwestern cameroon evidence of early earth transpressional tectonics abstract the mesoarchean crust of the plutonic belt of the memve ele area lies in the southwestern part of the ntem complex ntc cameroon emplacement of these rocks resulted from both gravity and tectonic driven vertical flow perpendicular to the direction of shortening at the time of partial melting and magmatic accretion such deformation patterns suggest the occurrence of a long lived hot orogen and may explain a nearly isobaric retrograde pressure temperature p t path recorded within high t low to medium p metamorphic rocks however in the memve ele shear zone msz a metamorphic gradient runs from granulite to green schist facies structural analysis reveals four continuous ductile deformations the first stage is characterized by the emplacement of dome and basin structures the second stage is marked by coeval diapiric movements and a transpressional shear zone the third stage is marked by both transpressional and lateral flow regimes and the last stage is marked by horizontal constrictional strain these features indicate that the mesoarchean crust is affected by a long lived horizontal shortening deformation d1 d3 coeval with vertical movements in which concentric cleavages occur around domes thus the studied area can be considered as exemplifying an early earth style tectonics the structural patterns in the msz contain zone of high strain rocks belonging to the deep and shallow mid crusts that have recorded transpressional tectonics the compressional strain regime in which results coeval steep to shallow dipping structural features and dome and basin geometries associated to msz activities contributed to maintaining a stable crustal thickness in the memve ele area during mesoarchean orogeny

tectonometamorphic evolution of ghana togo and benin in the light of the pan african brasiliano orogeny abstract the south pan african belt of west africa ghana togo and benin province can be divided into three domains 1 1 the external nappes thrust over the west african craton derived from passive margin sedimentary deposits middle to late proterozoic and displaying middle to high pressure metamorphism such as the kante and atacora nappes 2 2 the intermediate nappes including the suture zone rocks with eclogitic assemblages protoliths ca 800 ma and mainly monocyclic metasedimentary rock and orthogneiss that are found in central togo and northwest benin 3 3 the internal nappes composed of high grade commonly anatectic gneiss anatexis ca 600 ma including orthogneiss eburnian plutons elongated granulite belts reworked archean basement and an intrusive granite and charnockite association ca 600 ma which are exposed in benin and nigeria the p t t d paths calculated from rocks in these three domains show a prograde retrograde evolution 1 1 an initial clockwise evolution related to an early burial stage hp ht in the intermediate nappes followed by oblique thrusting in a sw direction that caused nappe stacking and subsequent uplift 2 2 a second anti clockwise evolution with late temperature and pressure increases only recorded in the more internal units this temperature increase was a consequence of the previous crustal thickening with subsequent doming extension and anatexis the pressure increase was related to movement along the kandi fault working as a dextral strike slip fault with a transpressional component under late e w shortening the retrograde trend corresponds to the final uplift the evolution of the belt can thus be divided into three successive stages 1 1 a first stage was characterized by an oblique collision inducing sw oblique thrusting with associated syn foliation reverse metamorphism 2 2 during a second stage anatectic doming took place followed by 3 3 a third stage at still high temperature with dextral wrench faulting and associated n s post foliation folding under late e w shortening comparison between the west african north brasiliano and central african late proterozoic belts shows very strong similarities between their lithology kinematics and metamorphism and indicates that the pan african brasiliano chain resulted from collision between three major continental domains the west african and sao francisco congo cratons and a late proterozoic mobile domain

devonian orogen parallel opposed extension in the central norwegian caledonides late orogenic early to middle devonian extension in the scandinavian caledonides was unidirectional in western norway new data from two detachment zones hoybakken and kollstraumen north of the more trondelag fault complex show that bidirectional opposed orogen parallel extension dominated in this region at this time the fault complex acted as a transfer zone for the hoybakken detachment extension and uplift in central norway triggered significant magmatic activity in contrast to the lack of granite intrusions during exhumation of western norway

vergence and facing patterns in large scale sheath folds the careful geometric analysis of minor structural detail elucidates the relationships and evolution of associated large scale curvilinear hinge geometries developed during wnw directed caledonian thrusting exposed in neoproterozoic moine psammites of the moine nappe reversals in the polarity of structural facing associated with minor folding mark the position of major sheath folds which parallel transport upwardly convex sheaths closing in the direction of thrust transport cored by older gneissose basement inliers are termed culminations whilst those opening in the transport direction and cored by moine psammites are termed depressions sheath folds are bisected by transport parallel and foliation normal culmination depression surfaces which separate not only the reversals in facing but also delineate zones of minor fold hinge obliquity into clockwise and anticlockwise domains relative to the transport direction the sense of obliquity of minor z and s folds is thus dependent on position with respect to the surfaces of culmination and depression and not the fold axial surfaces surfaces of culmination and depression may be superimposed on original overturned antiformal and synformal folds to produce a variety of dome culmination on antiform saddle depression on antiform inverted saddle culmination on synform and basin depression on synform configurations the curvilinear hinges of minor folds may also be asymmetrical about the transport direction and within the plane of the regional foliation to define patterns of fold hinge line vergence classical concepts of fold limb vergence may thus relate to larger antiformal and synformal hinges whilst the fold hinge line vergence defines major curvilinear hinges associated with culminations and depressions major sheath folds may therefore be interpreted in terms of both minor fold hinge line and limb vergence coupled with fold axis obliquity and reversals in the polarity of structural facing the ability to recognise consistent and reliable structural relationships between facing and hinge obliquity at small scales indicates that the regional deformation process forms a linked and coherent system through several orders of magnitude 1999 elsevier science ltd all rights reserved

geochemistry and trade of eastern mediterranean millstones from the neolithic to roman periods millstones and grindstones of the prehistoric to roman periods include saddle querns rectangular hopper rubber mills rotary querns and pompeian style donkey mills many of these were manufactured from igneous rocks which can be provenanced to their geological sources using chemical analysis giving information about trade contacts of sites sixty nine samples of 10 20 g each were removed from broken parts of lava millstones of prehistoric and early historic date from sites in israel syria egypt greece and turkey these were analysed for major and trace elements using x ray fluorescence and petrological features were examined in thin section the millstones were all young generally fresh lavas ranging from vesicular basalt to porphyritic andesite potential sources occur in younger volcanics of mainland greece the aegean turkey and the levant israel syria and jordan and in egypt thirty four geological samples from israel syria and turkey were collected and analysed in the same way as the archaeological samples and an intensive literature survey carried out to supplement these by published analyses comparison of archaeological samples with source data is done by using a series of discrimination graphs following a simple flow diagram the archaeological samples were of two types within plate lavas and island arc or other subduction related lavas all samples were successfully assigned to sources and results show use of the source areas as follows during the prehistoric period neolithic bronze age pre 6th century bc iron age samples saddle querns in mainland greece were made of aegina andesire while sites in north syria used local syrian lavas and in israel basalts from near lake tiberias and from the dead sea area were used earlier work by the authors and others has shown import of levant millstones to cyprus in the late bronze age hopper rubbers of the 5th century bc onwards were made at specialized quarries in aegean islands on nisyros kimolos and santorini and exported to mainland greece western turkey egypt and cyprus less well finished hopper rubbers were made and used in western turkey and in israel roman pompeian style mills were made of levant lavas from several sources particularly around lake tiberias and were transported within israel as well as to cyprus as shown by earlier studies rotary querns were made of lavas from santorini and probably nisyros and of locally used west anatolian rocks rotary querns of roman and later 10th 12th century ad dates were also produced at several sources in the levant again around lake tiberias and probably in north syria and within the dead sea volcanics for use within israel olive crushing trapeta used in turkey and greece were manufactured from andesites from anatolia and aegina respectively west anatolian lavas mill types unknown have also been identified at roman sites in the eastern desert of egypt millstone distributions increased in complexity and extent over time with hopper rubbers being traded up to 820 km from sources and roman rotary millstones up to 1300 km the three major source areas aegean anatolia and the levant were in apparent competition by the roman period when there is extensive overlap of distributions from different sources with aegean and anatolian products traded the furthest the millstone trade in the eastern mediterranean is separate from that of the west mediterranean west of greece except for one hopper rubber of nisyros lava identified in a shipwreck off mallorca this dichotomy is in marked contrast to the distribution of amphorae within which west mediterranean italian products were widely used in the east from at least the 2nd century bc stylistically east mediterranean millstones also show differences from those in the west in the prevalence of hopper rubbers and later in decorative features common on pompeian style mills

tectonic evolution of the yaounde segment of the neoproterozoic central african orogenic belt in southern cameroon the deformation history of the neoproterozoic central african orogenic belt in southern cameroon is well recorded in the low to high grade rocks outcropping in the area around yaounde the fabrics in these rocks are con sistent with two main ductile deformation events d1 and d2 d 1 predated emplacement of calc alkaline dioritic bodies and caused the formation of nappes that resulted in high pressure granulite metamorphism of soft sediments a strong overprinting of these nappes during d2 symmetric extension probably associated with large scale foliation boudinage and or gneissic doming and intense magmatic underplating gave rise to regional flat lying fabrics the latter were further buckled by d3 and d4 folding phases defining a vertical constriction occurring with a major east west to nw se shortening direction the corresponding f3 and f4 folds trend north south to ne sw and east west to nw se respectively and represent the main regional strain patterns based on the east west to nw se maximum shortening orientation indicated by f3 folds it is proposed that the nappe stacking phase d 1 occurred in the same direction the deformation history in the area can thus be described as corresponding principally to alternating east west to nw se contractions and north south to ne sw orogenic parallel extensions at the regional scale this could be due to the transaharan east west collisional system

gneiss domes and orogeny many gneiss domes record positive feedback between decompression and partial melting of orogenic middle crust exhumed orogens are riddled with gneiss domes cored by migmatites that underwent dehydration melting during decompression the decreasing buoyancy associated with increasing melt fraction drives further decompression at near isothermal conditions as the partially molten crust rises diapirically this combination of processes may explain the generation and retention of large volumes of crustally derived melt recorded in many deep seated migmatite terranes and inferred for active orogens in exhumed orogens the signature of the rapid ascent of partially molten crust is a gneiss dome cored by migmatite granite the large volume of material involved in the vertical transfer of partially molten crust indicates that the formation of gneiss domes is an efficient mechanism for heat advection during orogenesis

modes of superposed buckling in single layers controlled by initial tightness of early folds in a series of experiments with soft test models superposed buckling folds were produced in a competent layer resting on a slab of incompetent painter s putty the angle between the hinge lines of the first set of cylindrical folds f1 and the direction of the second compression p2 was varied in the different experiments the experiments showed that with an increase in the initial tightness of f1 there was a transition from one mode of superposed buckling to another when the interlimb angle of f1 was very large the superposed deformation gave rise to a dome and basin pattern the first mode of superposed buckling the second mode with small f2 folds riding over larger f1 folds developed when the initial interlimb angle ranged roughly between 135 and 90 the third mode was observed when the f1 interlimb angle was less than about 90 but the fold was not very tight in the third mode a set of non plane non cylindrical folds developed however the sinuous hinge line of the non cylindrical structure was newly created by replacing the old f1 hinge when f1 was very tight or isoclinal the fourth mode of superposed buckling led to the development of non plane non cylindrical folds without concomitant hinge replacement

petrology of high pressure granulite facies metapelites and metabasites from tchollire and banyo regions geodynamic implication for the central african fold belt cafb of north central cameroon the tchollire and banyo high pressure granulites occur mainly as highly strained small lenses bands or elongated bodies interbedded with gneisses and migmatites in the central african fold belt cafb in north central cameroon they were previously attributed to palaeoproterozoic but are now shown to be pan african these granulites are made up of two occurrences of metapelites with garnet kyanite sillimanite cordierite biotite quartz plagioclase and metabasites containing garnet clinopyroxene orthopyroxene hornblende quartz plagioclase eight samples were analysed in detail by electron microprobe for mineral chemistry parageneses in both metapelites and metabasites highlight three main stages witnessed by prograde peak and retrograde mineral assemblages the prograde stage is preserved as well defined inclusion trails of kyanite biotite plagioclase quartz and rutile within porphyroblasts of garnet in metapelites or with more or less clinopyroxene hornblende plagioclase quartz ilmenite rutile and apatite within porphyroblasts of garnet in metabasites the peak stage displaying heterogranular granoblastic texture is characterised by porphyroblastic garnet kyanite k feldspar biotite in metapelites and garnet clinopyroxene plagioclase quartz in metabasites this was followed by decompression and cooling during the retrograde stage marked by aggregate of sillimanite prisms presumably after kyanite and cordierite corona around garnet in metapelites and by symplectites or vermicular structures of orthopyroxene plagioclase and orthopyroxene corona around garnet in metabasites geothermobarometric study shows that granulite facies metapelites and metabasites from both tchollire and banyo regions recrystallised under peak pressure temperature conditions of 13 14 kbar and 800 900 c they experienced similar clockwise p t path with nearly isothermal decompression our results provide evidence for a substantial crustal thickening during the pan african continent continent collision but show that there is no significant isothermal decompression as commonly observed in recent collisional orogens the reconstructed p t paths are in some ways reminiscent of the ones reported in precambrian mixed hot orogens

roman lava quarries in the eifel region germany geochemical data for millstone provenance studies roman millstones of assumed eifel origin were produced and exported in huge quantities to many parts of roman europe and can be used as tracers for trade patterns in roman times this study presents for the first time a raw material centred geochemical definition of the 13 well known roman basaltic lava quarries in the quaternary east and west eifel volcanic fields the aim is to find a way to characterize the individual exploitation sites precisely by means of their geochemical composition and to recommend a standard procedure for further millstone provenance analysis based on major and trace element composition analyses by xrf a differentiation of each quarry is achieved by using a combination of geochemical discrimination and cluster and discriminant analysis therefore for provenance analysis of a unknown millstone sample the following procedure is recommended 1 geochemical discrimination to check if it actually belongs to the volcanic eifel quarries 2 cluster analysis to check to which quarry or cluster of quarries the millstone can be affiliated and 3 discriminant analysis to assign the sample to its quarry of origin with a certain confidence

tubular folds and sheath folds definitions and conceptual models for their development with examples from the grapesvare area northern sweden abstract two parameters are used in the classification of highly non cylindrical folds the hinge line angle and the ratio of the length of the cone axis to that of the long axis of the cross section of the structure at the position where the hinge angle was measured if in a non cylindrical fold a cross section can be selected so that the hinge angle w measured where the cross section cuts the cone is less than 90 and the length of the cone axis x is more than a quarter of the length of the long axis y of the cross section the fold is a sheath fold a tight sheath fold with w x y 1 can be termed a tubular fold a tubular fold is thus an extreme type of sheath fold while sheath folds with w 20 but x y 0 25 but tubular folds from the grapesvare area comply to the definition given above and they occur in a structural setting that is consistent with the models described

the influence of initial fold geometry on type 1 and type 2 interference patterns an experimental approach abstract experiments on superposed folding were performed in a plane strain pure shear rig using paraffin wax as an analogue for rocks a series of pre formed cylindrical folds were refolded with the compression direction acting parallel to the initial fold hinge direction the intermediate axis perpendicular to the first fold axial plane and the extension direction parallel to the first fold axial plane and perpendicular to its axis type 1 interference geometry roundness tightness and amplitude were varied to investigate the influence of first fold geometry on the interference patterns experimental folding of an initially planar layer oriented parallel to the first fold envelope provides a reference geometry for comparison the results suggest that hinge roundness has less influence on the interference pattern than other factors close initial folds refold into type 2 interference patterns which become even more pronounced as the tightness increases open folds produce type 1 interference patterns folds with the same interlimb angle and the same roundness produce different interference patterns depending on relative amplitude folds with relatively large amplitude are refolded into type 2 patterns whereas folds with small amplitude give clear dome and basin structures in a second set of experiments the compression direction also acted parallel to the first fold hinge but the orientations of the intermediate and extension axes were interchanged the interference patterns obtained are very similar to those in type 1 interference geometry suggesting that the major factor in determining whether type 1 or type 2 interference patterns develop is the initial fold geometry and not the kinematics of the second deformation

mafic potassic lavas of the quaternary west eifel volcanic field major and trace element analyses for 103 volcanoes of the quaternary west eifel volcanic field show the lavas to be dominantly primitive mgo 7 wt and potassic na2o k2o 1 the rocks are divided into 1 a foidite f suite volumetrically dominant and consisting of four types leucitites and nephelinites melilite bearing foidites olivine free foidites sodalite bearing melilite free foidites and 2 a younger olivine nephelinite and basanite onb suite concentrated in the southeastern part of the field dominantly cpx phyric f suite magmas differ from the dominantly ol phyric onb suite mainly in higher k2o na2o and cao al2o3 ratios higher rb cu h2o co2 and lree concentrations and slightly lower sr ni and y contents most magmas have fractionated small amounts of olivine clinopyroxene and minor phlogopite systematic compositional variations within volcanoes or volcano groups are rare five more differentiated volcanoes 2 tephrites 3 phonolites occur in the center of the field their magmas are interpreted to have formed by fractionation within crustal magma chambers

hot orogens tectonic switching and creation of continental crust many granulite terrains were too hot to have formed during continental collision rather along with many high grade metamorphic terrains that typify continental crust most formed in accretionary orogens during tectonic switching when prolonged lithospheric extension was interrupted by intermittent transient contraction based on modern and ancient examples tectonic switching occurs when slab retreat induces upper plate extension causing arc splitting formation of microcontinent slivers and backarc basins then intermittent arrival of buoyant oceanic plateaus induces transient flat subduction or slab flip and crustal thickening during slab retreat basaltic magmas produced from decompressed asthenosphere advect into the extending orogen causing granulite facies metamorphism and granite generation but subsequent thickening during flat subduction cools the region thickening is focused in the thermally softened backarc region and if sediment filled a hot short lived 10 m y narrow 50 100 km orogenic belt forms such thickening is often misleadingly ascribed to arc or microcontinent collision once slab retreat mode is reestablished lithospheric extension recommences and a new arc backarc system forms generally outboard arrival of another plateau will reverse the procedure and another short lived hot orogen will form within the orogenic system cycles of tectonic switching efficiently produce continental crust

syn migmatization way up criteria abstract most geopetal way up structures are developed during primary formation or soon after in sedimentary or igneous rocks in migmatite terrains the possibly anomalous behaviour of rocks in which melt is present has often limited structural synthesis geopetal relationships may however be recognizable in at least some migmatites asymmetries in two structural relationships cauliflower structure and vein cluster involving neosome veins conformable with the main foliation of layered migmatites are interpreted as indicating the way up of these rocks when they were partially molten additional examples recognized in the literature suggest that similar structures can be seen in a wide range of geological environments these prove to be as reliable as sedimentary top and bottom features and suggest that the migmatites containing them were essentially sub horizontal while being strained and melted

origin and evolution of the late precambrian high grade yaounde gneisses cameroon abstract the yaounde series is composed of low to high grade garnet bearing schists and gneisses belonging to the pan african north equatorial fold belt the high grade rocks consist of kyanite garnet gneisses and garnet plagioclase gneisses containing layers of calcsilicate rocks marbles quartzites and magnetite rich orthopyroxenites the chemical patterns of these rocks are those of a sedimentary sequence of shales and greywackes and minor dolomite rocks dolomitic marls evaporitic beds quartzites and iron rich sediments some volcanogenic greywackes may have been of alkaline affinity this sequence was probably deposited in shallow water near shore semi barred conditions which can be related either to an intracontinental distensive environment or to a passive margin at the northern edge of the congo craton the yaounde gneisses were deformed during two main tectonic phases the first phase d1 is marked by a layering s0 s1 resulting from tectonic transposition the second one d2 corresponds to tangential tectonics with isoclinal folds and flat lying shear zones associated with a s2 schistosity and a l2 lineation a third phase late d2 is marked by the development of low temperature mylonitic shears scarce wrench faults indicate later e w compression the d1 d2 transition is characterized by the emplacement of mafic and ultramafic rocks and by the development of high pressure granulite facies conditions t 750 800 c p 10 12 kbar these peak metamorphic conditions triggered a widespread migmatization dated at 565 22 ma and coeval with the d2 event the gradual decrease of the metamorphic conditions toward the south and the existence of a syn d2 retrograde inverse metamorphic gradient suggest that the overall structure of the yaounde series is a large tectonic nappe thrust onto the congo craton a geotectonic scheme for the north equatorial fold belt is discussed