an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

constraints on the kinematics of post orogenic extension imposed by stretching lineations in the aegean region abstract new kinematic data from shear zones of tertiary age in the metamorphosed basement of the aegean region in combination with published kinematic lithological and palaeomagnetic data have enabled us to determine a detailed kinematic evolution of the region during post orogenic extension in the aegean three distinct stages are recognised firstly extension of both the western and eastern aegean started in the late oligocene early miocene 36 25 ma ago initially in an 023 direction stage two started shortly after this with the division of the aegean crust into the west aegean block a coupled assemblage of small blocks bound on its northwestern and southeastern margins by the scutari pec line and mid cycladic lineament fracture zones respectively between 25 ma and 3 ma the west aegean block underwent 30 clockwise rotation whilst the eastern aegean underwent on average 19 anticlockwise rotation rotation of the west aegean block as a semi coherent block was aided by the relative coolness of the block compared to the warmer eastern aegean region as the crust thinned and rotated the nw se trending faults which characterise the west aegean block were cross cut by e w trending faults in the latest miocene pliocene the thermal front migrated westwards into the west aegean block and the mid cycladic lineament ceased activity the final kinematic stage marked the start of the subdivision of the west aegean block into two portions in the pliocene the southeastern portion nw cycladic area coupled with the sw cycladic area to form a central aegean block that started to translate southwest the northern and western portion rotated a further 10 15 clockwise whilst the southeastern rim rotated anticlockwise these data demonstrate that aegean post orogenic extension is not dominated by a single block rotation or radial spreading event but is characterised by the sequential formation and reformation of lithospheric scale blocks that have developed in response to large scale partitioning of rotational strain

loess stratigraphy in central china abstract loess sequences in central china provide a detailed record of climate changes during the last 2 5 million years at least 44 major shifts from glacial to interglacial conditions occurred during this time in china prolonged loess deposition lasting more than 40 millennia occurred eleven times with only four of these intervals in brunhes chron the climate oscillations took place with increased frequency between 2 4 and 0 5 ma compared to the last half million years major shifts toward cooler and drier climates occurred at about 2 4 ma 1 2 ma and 0 5 ma while less pronounced shifts are dated to 1 65 ma 0 8 ma and 0 2 ma three of the last four reversals of the earth s magnetic field whose lithostratigraphic position has been detail are recorded in a glacial deposit the low field magnetic susceptibility of loess and soils which reflects the concentration of ultrafine magnetite is related to the degree of pedogenesis and serves as a proxy measure of climate the accumulation rate of the magnetite was fairly constant throughout the last 1 2 million years and can serve as a measure of time susceptibility records from localities near xifeng and luochuan located 160 km apart are compared and used to define informal lithostratigraphic units in the loess plateau of china

developments in oil shale in 1982 oil shale development activities continue at an impressive level both in the united states and elsewhere but the activity is somewhat reduced compared to prior years the current soft economic environment is probably the cause for the less aggressive development posture of many project developers

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

regional implications of geochemistry and style of emplacement of miocene i type diorite and granite delos cyclades greece abstract the miocene plutons of the cyclades were emplaced in a subduction setting during regional back arc extension of continental crust that led to flat lying mid crustal detachment faulting mapping of the island of delos shows that quartz diorite and tonalite were emplaced as dykes in country rock of schist and marble within shear zones parallel to the extension direction mafic magmas were followed by numerous small batches of felsic magma with magmatic and ductile deformation synchronous with magma emplacement late granite dykes occupy brittle fractures in the more deformed rocks mafic and intermediate rocks show a bimodal distribution of incompatible trace elements with one group of broadly tholeiitic character and the other with substantial enrichment in sr nb and hfse but low th and ba these differences appear to be inherited from two distinct mafic sources that are different from the mafic source for the plutons of the eastern cyclades voluminous granodiorite results from these mafic magmas fractionating and or mixing with felsic crustal material some of which was derived by anatexis of a sedimentary protolith indicated by high b and mn some late granites appear derived from partial melting of hercynian paragneiss regionally the shear zones appear to be feeders to more extensive granitic plutons located at space produced at ramps in detachment fault zones the shear zones parallel the mid cycladic lineament a broad zone of displacement between two crustal blocks rotating in opposing directions as rollback took place at the hellenic subduction zone distinctive geochemical features in miocene igneous rocks suggests that these two blocks had quite different geological histories the localisation of plutonism and core complexes near the mid cycladic lineament suggests that this crustal scale shear played a role in bringing subduction derived magmas to mid crustal levels the heat supplied by the mafic magmas promoted ductile deformation high in the crust where extension was concentrated leading to the formation of core complexes the regional extension resulted in progressive shallowing of the position of the granite solidus within the crust leading to welding of the mid cycladic lineament which is no longer seismically active

geochemistry tectonic setting and metamorphism of mid triassic volcanic rocks of greece abstract mid triassic volcanic rocks are preserved in about eight localities in the nappes of the external hellenides and are also widespread in the pelagonian zone of central greece most have suffered low grade metamorphism immobile trace elements from 35 samples 80 major element analyses and pyroxene analyses show that these rocks are the product of an eastward dipping subduction zone the subducted ocean was perhaps analogous to the pennine zone of the alps the othris and pindos ophiolites are probably contemporaneous products of related back arc extension metamorphic mineral assemblages in volcanic rocks of the phyllite series of the external hellenides indicate high pressure low temperature conditions probably related to a second subduction that occurred prior to the main phase of hellenide nappe emplacement in the miocene

pedostratigraphy of chinese loess deposits and climatic cycles in the last 2 5 myr summary the pedostratigraphy and magnetostratigraphy of several sections in the loess plateau of north central china have been investigated and correlated the most complete and distinct loess paleosol sequence occurs in the baoji section of the southern part of the plateau thirty seven pedostratigraphic units are identifiable in the baoji section and correlated with those in other parts of the plateau the sequence represents thirty seven major cold to warm climatic cycles in the last 2 5 myr at about the time of the matuyama gauss magnetic reversal an abrupt climatic event occurred in north china represented by the shift of the well weathered red clay formation below the m g boundary to the alternating loess and paleosol units above marking the beginning of a new epoch in the course of climatic evolution in addition there are two other major shifts of dominant periods of climatic cycles recorded in the loess paleosol sequences one occurring at about 1 5 myr and another at about 0 8 myr the pedostratigraphy of loess deposits in north central china provides an independent measure of the world wide climatic fluctuations and is now the most complete and reliable record of the major climatic cycles in the last 2 5 myr

miocene detachment in crete and exhumation p t t paths of high pressure metamorphic rocks a major problem posed by the geology of crete is the horizontal contact of an upper unit without miocene metamorphism onto a metamorphosed lower one with early miocene high pressure low temperature hp lt parageneses this very sharp contact is roughly parallel to the major oligo miocene thrust planes which were reactivated as a large scale detachment which allowed exhumation of high pressure units we describe the extensional deformation and the metamorphic evolution of the lower plate most first order deformation features relate to the retrogression from high pressure to low pressure conditions a n s pervasive stretching is observed everywhere often associated with a top to the north sense of shear the extreme variation of thickness of the phyllite quartzite nappe upper part of the lower plate is probably the result of large scale boudinage similar to the one seen in large outcrops the most important observation is the systematic occurrence of fresh carpholite immediately below the base of the tripolitza nappe except in northwestern crete where a late extensional shear zone is present deeper in the nappe pile carpholite is systematically retrograded this observation reveals a drastically different pt history for the upper part of the phyllite quartzite nappe it also suggests that the late extensional shear zone found along the northern side of crete cuts inside the metamorphic structure and brings the nonmetamorphosed tripolitza nappe directly in contact with the deeper parts of the phyllite quartzite nappe pt t paths suggest a fast temperature decrease in the top of the phyllite quartzite during retrogression and hence during the top to the north shear the deeper part of the phyllite quartzite nappe shows a low temperature regime throughout but its pt path includes an isothermal decompression in the first stage we produce a tentative map of domains having experienced similar pt trajectories during decompression the overall cool regime is related to the continuous underthrusting of cola continental units during exhumation isothermal decompression observed in the core of the phyllite quartzite nappe implies fast exhumation during extension and the faster cooling of the upper part is related to a continuous displacement toward the north of a cooler unit during exhumation single grain 39ar 40ar ages obtained on phengites 15 25 ma in various structural sites are in good agreement with these conclusions and with the geological context suggesting that underthrusting of cold units at the front the accretionnary complex occurred contemporaneously with unroofing below a north dipping detachment near the top of the wedge the age of this detachment is bracketed between the end of the high pressure event 20 ma and the deposition of the breccia early to middle miocene in the neogene basins

the timing of partial melting barrovian metamorphism and granite intrusion in the naxos metamorphic core complex cyclades aegean sea greece abstract the relationship between partial melting and granite intrusion in a classic barrovian metamorphic terrane has been assessed thirteen samples were dated by shrimp u pb zircon geochronology from the island of naxos greece one of the aegean metamorphic core complexes the effect of partial melting during peak barrovian metamorphism on naxos is recorded by fine

middle miocene graben development in crete and its possible relation to large scale detachment faults in the southern aegean the linkage between the development of south facing cretan graben and large scale detachment faulting in the southern aegean is unknown widespread serravallian deposits in the ierapetra graben of crete supply constraints to middle miocene graben development in the southern aegean the ierapetra graben and by inference the cretan graben in general were hitherto believed to have formed as a result of sinistral transpression during n s shortening we argue that the formation of the cretan graben is due to n s extension the south dipping n s extending kritsa normal fault served as the master fault controlling graben development in the ierapetra graben the kritsa normal fault is either an antithetic fault related to the top n cretan detachment or a synthetic fault associated with the top s ios detachment the overall geometry and timing relationships lead us to favour a connection with the ios detachment which in turn implies a large scale displacement on the ios detachment

the pelagonian zone in greece a polyphase deformed fragment of the cimmerian continent and its role in the geotectonic evolution of the eastern mediterranean data from macedonia greece correlated with those reported from the pontides turkey indicate that the pelagonian zone of the hellenides represents a fragment of the cimmerian continent which separated the paleo tethys and neo tethys oceans a permo triassic age is suggested for separation of the paleozoic continent and initial rifting in the two oceanic basins as the pelagonian zone represented the northwestern european end of the cimmerian continent the paleo tethys and the northern branch of neo tethys would have been very close to each other on either side of this zone thus both oceans at their european end closed within a short time of each other in the late jurassic early cretaceous the sequential development of the two oceans outlines a model for the geotectonic evolution of the internal hellenides in which a correlation of thrusting and folding phases is also given

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

baoji type pedostratigraphic section loess plateau north central china abstract the baoji section is judged to be the most complete pedostratigraphic section on the loess plateau of north central china it is located about 5 km north of the city of baoji and consists of 37 paleosols formed during more than the last 2 5 ma it is designated here as the type pedostratigraphic section with formally named geosols following the rules of the north american commission on stratigraphic nomenclature geochronological control is based largely on magnetostratigraphy with the brunhes matuyama and gauss epochs and jaramillo and olduvai events clearly recognized the baoji geosols can be correlated with equivalent pedostratigraphic units throughout the loess plateau by a combination of magnetostratigraphy and character position and the association of the pedostratigraphic units within the quaternary succession the variation of the geosols suggests climatic cycles of varying intensity and duration but generally warmer and moister conditions when compared with the loess units that suggest colder and drier periods

developments in oil shale in 1981 significant oil shale development activities are taking place in the united states principally in the piceance basin in colorado and the uinta basin in utah enthusiasm for development has declined somewhat during the year due to a worsening economic and institutional climate about 400 000 b d of shale oil production capacity is still in the planning stage for the piceance basin but a protracted development schedule is currently anticipated about 250 000 b d capacity is in the planning stage for the uinta basin completion of projects in both the piceance and uinta basins will depend on an attractive political economic and environmental climate additional worldwide shale oil production of over 250 000 b d is in the planning or development stage

developments in oil shale in 1984 oil shale development activities continued at a somewhat restricted pace during 1984 the activities reflect the continued soft economic environment in the petroleum industry and the uncertain future of synfuel development

extension and exhumation of the hellenic forearc ridge in kythera abstract detailed mapping and new structural observations on kythera demonstrate that there is a major detachment fault here termed the potamos detachment fault pdf exposed on the northern part of the island and bordering the domed structure of a metamorphic core complex the detachment forms the contact of contrasting metamorphic and nonmetamorphic units and both ductile and brittle structures are found related to its extensional development the earliest potamos mylonites as well as some other early ductile structures near the mapped detachment fault indicate initiation of the pdf under ne trending extension in mid to late miocene time later ductile ductile brittle and some brittle structures in the metamorphic unit near the detachment indicate in contrast a significant nw se extension along the forearc ridge the younger brittle structures indicate return to ne sw extension late miocene pliocene strata cover the detachment unconformably and are affected only by the late faults trench r

the fluctuations of fixed nh4 n content in the luochuan loess and its paleoclimatic significance abstract the fixed nh4 n content varies from 120 to 202 g g in luochuan loess paleosol sequences this content in the interstratified paleosols is significantly higher than that of the loess fixed nh4 n content in the loess l2 is the lowest varying between 144 to 147 g g whereas the highest in the paleosol s5 reaching 200 g g the distribution of fixed nh4 n is similar to that of the

asymmetrical pull aparts and foliation fish as kinematic indicators abstract from field observations asymmetrical boudins pinch and swell structures and ellipsoidal volumes of oblique foliation segments in anisotropic rocks lacking competent layers are potentially useful kinematic indicators in shear zones they are derived by the modification of initially symmetrical pull aparts and or layering by superposed layer parallel shearing the response of boudins to such shear is a synthetic flow of those corner volumes lying within the extensional quadrants of the kinematic framework of the deformation into the inter boudin gaps type 1 asymmetrical pull aparts the response of pinch and swell structure is a back rotation of the swells to form type 2 asymmetrical pull aparts discrete extensional shears in the pinches may be either absent type 2a or present type 2b analogues of types 2a and 2b asymmetrical pull aparts occur in anisotropic materials with no compositionally distinct competent members where ellipsoidal volumes contain back rotated foliation segments foliation fish the field based kinematic interpretation was successfully tested by laboratory experiment wherein initially symmetrical trains of pre formed competent internally anisotropic boudins and pinch and swell structures were deformed in bulk simple shear a mechanical model is presented in terms of two material properties of the inclusions competence viscosity and internal rheological anisotropy in an attempt to account for the observed flow in the experiments and the deduced flow and kinematic significance of the natural examples in the presence of angular corners and associated geometrical stress concentrations competence viscosity controls the response to shear in the boudins in the absence of angular corners internal anisotropy controls the response to shear in the pinch and swell structures and in the foliation fish

true and apparent geometric variability of en echelon vein arrays abstract the wide range of vein array angles reported for en echelon vein arrays can be attributed to both true and apparent geometric effects a survey of published figures supports a continuum of orientations rather than distinct populations related to different fracture mechanisms the results of the survey indicate a modal veinarray angle of less than 45 which indicates area increase as described by a displacement vector oriented outward from the array a stereometric analysis of the effects of exposure plane orientation on the apparent vein array angle is developed examples of vein arrays from the nambucca slate belt of eastern australia exposed on two differently oriented surfaces are shown these examples include non profile exposures with apparent vein array angles which are 1 less than 2 greater than 3 approximately equal to and 4 of opposite shear sense to the true vein array angle

amino acid distribution in a loess palaeosol sequence near luochuan loess plateau china abstract the distribution and abundance of potentially mobile amino acids in loess and palaeosols from the luochuan section have been determined amino acids in quantities significantly above laboratory background were detected in all samples ranging in age from recent to upper pliocene the highest concentration was measured in the recent soil forming the top 1 2 m below which yields fell away sharply declining by 98 at the bottom of the 130 m section average yields were smaller than those obtained earlier using a different method of sample preparation differences in abundance between neutral acidic and basic amino acids may be explained in terms of charge characteristics molecular weight and mode of interaction with mineral constituents amino acids as such or complexed with humus appear to be largely associated with caco 3 in the loess and with clay in the paleosols more of these compounds could thus be released from the loess than the palaeosols more of the amino acids was probably microbial in origin and ultimately derived from plant residues accumulating during the formation and development of individual palaeosols under a savannah open woodland vegetation the bulk of amino acids in loess would have come from the overlying palaeosols by water leaching and downward migration of clay and humus particles potentially mobile amino acids are more abundant in the loess layers than in the palaeosol horizons and hence can be used as one of a range of criteria for recognizing the occurrence of ancient soil development

micromorphology and genesis of paleosols in the luochuan loess section china pedostratigraphic and environmental implications the loess paleosol sequence in the well known potou section near luochuan covers the entire pleistocene back to 2 5 ma in a much more complete sequence than any known from europe or north america to deduce a record of the pleistocene climatic history an understanding of the genesis of the paleosols is important main diagnostic features normally observable in surface soils have disappeared in the case of fossil soils therefore micromorphology is of outstanding importance because it enables the reconstruction of original properties and polygenetic soil development especially in pedocomplexes the upper part of the loess paleosol sequence can well be compared with the 18o record shown in the specmap curve of the brunhes epoch although the sequence of paleosols shows partly an even more detailed record of cold and warm stages and allows more specific informations regarding the paleoclimate of the interglacial periods cf fig 2 the last four paleosols represented by the s1 pedocomplex the upper part of the s2 and the s3 are genetically well comparable with the natural holocene soil indicating a similar climate with a tall grass steppe vegetation the s6 is a steppe soil also whereas the five soils of the s4 the s5 complex and the s7 are forest soils indicating more moist and partly warmer interglaciations than the holocene the loess paleosol sequence of the matuyama epoch seems to give more paleoclimatic informations than the deep sea cores known so far the lishi loess below the b m boundary down to 84 m in the section contains two more soils s11 and s13 which are developed under steppe vegetation in interglaciations similar to the present one and four forest soils the s8 complex the upper soil of the s9 and the s10 indicating again more moist interglaciations than the holocene most of the numerous soils in the wusheng loess are probably formed synsedimentarily as alternation of soil formation and addition of loess the red clay at the basis consists of four intensively developed but truncated paleosols the parent material of at least the lower part must be regarded as pliocene loess

developments in oil shale in 1983 oil shale development activities continued at a somewhat restricted pace during 1983 the activities reflect the continued soft economic environment in the petroleum industry

late pleistocene chronology of loess deposition near luochuan china abstract loess near luochuan was sampled for thermoluminescence tl dating simultaneously with magnetic susceptibility measurements to provide the first independent age estimates on a susceptibility record from the loess plateau of china tl age estimates on late pleistocene loess l1 are stratigraphically consistent with no statistical difference in tl ages by the total or partial bleach techniques or by measuring ultraviolet or green wavelengths in the tl analysis loess below the last interglacial soil s1 yielded disparate results and is in many localities in central and eastern china unsuitable for tl dating because of complications of tl saturation and uncertainties in estimating the environmental radiation tl age estimates on the l1 loess are consistent with previously reported tl ages for sites near beijing and xian as well as in general agreement with age models for loess deposition based on paleomagnetics and magnetic susceptibility the convergence of a variety of geochronologic indices indicate that the last major period of loess deposition in central china began 70 000 10 000 yr b p and terminated