steepest descent integration a novel method for computing wavefields radiated from borehole sources borehole sources which include chemical explosives air gun water gun piezoelectric transducers in the borehole generate seismic waves both in and outside the borehole modeling the wave field inside and outside the borehole is of key importance in acoustic logging crosshole tomography mining geophysics and deep sounding seismic for interpretation of amplitude information of real data and prediction of energy radiation pattern the classical methods for wavefield modeling inside the borehole such as real axis integration are challenged by highly oscillatory integrals outside the borehole we present a novel method called steepest descent integration sdi which evaluates the oscillatory wavenumber integration by numerically integrate along the steepest descent path the oscillation along the new integration path is extremely reduced the contribution of poles and branch cuts are added if they are located between the steepest descent path and the real axis the sdi is applicable to arbitrary freq

experimental studies of electrokinetic conversions in fluid saturated borehole models experimental and theoretical studies show that there are electromagnetic em fields generated by seismic waves with two kinds of conversion mechanisms in a fluid saturated porous medium within a homogeneous formation the seismic wave generates a seismoelectric field that exists only in the area disturbed by the seismic wave and whose apparent velocity is that of the seismic wave at an interface between differing formation properties the generated seismoelectric wave is a propagating em wave that can be detected everywhere an electrode used as a receiver on the ground surface can detect the propagating em wave generated at an interface but cannot detect the seismoelectric field generated in a homogeneous formation when the electrode is in a borehole and close to a porous formation it can detect both the em waves and the seismoelectric field in this paper electrokinetic measurements are performed with borehole models made of natural rocks or artificial materials experimental results show that

a new early jurassic ca 183 ma fossil lagerstatte from ya ha tinda alberta canada lagerstatten deposits of exceptionally preserved fossils offer vital insights into evolutionary history to date only three konservat lagerstatten are known from early jurassic marine rocks osteno posidonia shale and strawberry bank all located in europe we report a new assemblage of exceptionally preserved fossils from alberta canada the first marine konservat lagerstatte described from the jurassic of north america the ya ha tinda assemblage includes articulated vertebrates fish ichthyosaurs crinoids crustaceans brachiopods abundant mollusks coleoids with soft tissues ammonites gastropods bivalves wood and microfossils paired bioand chemostratigraphies show that lagerstatte deposition occurred during the late pliensbachian through early toarcian capturing the carbon isotope excursion associated with the toarcian oceanic anoxic event therefore the panthalassan ya ha tinda biota is coeval with toarcian lagerstatten from the tethys ocean posidonia shale and strawberry bank comparisons among these deposits permit new insights into the diversity ecology and biogeography of jurassic marine communities during a time of pronounced biological and environmental change e g expanded subsurface anoxia warming and extinctions they also highlight the possibility that mesozoic oceanic anoxic events are temporal foci of exceptional preservation

jurassic ophiolite formation and emplacement as backstop to a subduction accretion complex in northeast turkey the refahiye ophiolite and relation to the balkan ophiolites the eastern mediterranean region within the tethyan realm shows a high concentration of ophiolites with contrasting times of formation and emplacement along the belt in the balkans the ophiolites formed during the early to medial jurassic and were obducted during the late jurassic whereas in turkey and farther east structurally intact jurassic ophiolites are rare and jurassic ophiolite obduction is unknown here we report a structurally intact large ophiolite body of early jurassic age from ne turkey the refahiye ophiolite located close to the suture zone between the eastern pontides and the menderes taurus block the refahiye ophiolite forms an outcrop belt 175 km long and 20 km wide and is tectonically bound by the late cretaceous ophiolitic melange to the south and by the north anatolian transform fault against the triassic low grade metamorphic rocks to the north early to medial jurassic very low to low grade metamorphic rocks interpreted as intraoceanic subduction accretion complexes occur either beneath the ophiolite or as thrust slices within it the ophiolite body within the studied section is made up of mantle peridotite clinopyroxene bearing harzburgite and minor dunite crosscut by up to 20 cm thick veins of clinopyroxenite and later dikes pods stocks of gabbro ranging in size from 2 m to several hundreds of meters the gabbro is represented by two distinct types i cumulate gabbro and ii non cumulate gabbro with locally well developed igneous foliation within the non cumulate gabbro or enclosing peridotite there are up to 5 m and 50 cm thick veins of trondhjemite and pegmatitic gabbro respectively la icp ms dating on zircons from two trondhjemite samples yielded weighted mean ages of 184 4 ma and 178 4 ma 2 respectively suggesting formation during early jurassic time formation in a suprasubduction zone forearc setting is inferred from i wide ranging pyroxene and spinel compositions in the peridotites as documented in most suprasubduction zone ophiolites ii arc tholeiitic signature of the non cumulate gabbros and iii association of the ophiolite with the coeval subduction accretion complexes emplacement of a trapped forearc ophiolite above its own subduction accretion complex as a backstop is proposed based on a series of field relationships such as i intimate association of the unsubducted suprasubduction zone ophiolite with coeval accretionary complexes ii absence of unambiguous relationship to the southern atlantic type continental margin and iii absence of any stratigraphic indications for the ophiolite obduction in the southern atlantic type continental margin during jurassic time this is a clear difference from the jurassic ophiolites in the balkans that were obducted over the atlantic type continental margin this difference in mode of emplacement is most probably related to the greater distance of the intra oceanic subduction zone to the atlantic type continental margin than it was in the balkans which is commensurate with the greater width of the tethys in the east during jurassic time

palaeozoic amalgamation of central europe new results from recent geological and geophysical investigations abstract multidisciplinary studies of geotransects across the north european plain and southern north sea and geological reexamination of the variscides of the north bohemian massif permit a new 3 d reassessment of the relationships between the principal crustal blocks abutting baltica along the trans european suture zone tesz accretion was in three stages cambrian accretion of the bruno silesian lysogory and malopolska terranes end ordovician early silurian accretion of avalonia and early carboniferous accretion of the armorican terrane assemblage ata palaeozoic plume influenced metabasite geochemistry in the bohemian massif explains the progressive rifting away of peri gondwanan crustal blocks before their accretion to baltica geophysical data faunal and provenance information from boreholes and dated small inliers and cores confirm that avalonian crust extends beyond the anglo brabant deformation belt eastwards to northwest poland the location and dip of reflectors along the tesz and beneath the north european plain suggest that avalonian crust overrode the baltica passive margin marked by a high velocity lower crustal layer on shallowly southwest dipping thrust planes forming the heligoland pomerania deformation belt the variscan orocline of southwest poland masks two junctions between the armorican terrane assemblage ata and previously accreted crustal blocks to the east is a dextrally transpressive contact with the bruno silesian and malopolska blocks accreted in the cambrian while to the north is a thrust contact with easternmost avalonia deeply buried beneath younger sedimentary cover in the northeast bohemian and rhenohercynian massifs devonian early variscide deformation dominated by wnw and nw directed thrusting records closure of ordovician devonian seaways between detached islands of the ata and avalonia

aluminous granulites from the pulur complex ne turkey a case of partial melting efficient melt extraction and crystallisation abstract in the pulur complex ne turkey a heterogeneous rock sequence ranging from quartz rich mesocratic gneisses to silica and alkali deficient fe mg and al rich melanocratic rocks is characterized by granulite facies assemblages involving garnet cordierite sillimanite ilmenite spinel plagioclase quartz biotite corundum rutile and monazite textural evidence for partial melting in the aluminous granulites particularly leucosomes is largely absent or strongly obliterated by a late stage hydrothermal overprint however inclusion relations high peak p t conditions the refractory modes bulk and biotite compositions of the melanocratic rocks strongly support a model of partial melting the melt was almost completely removed from the melanocratic rocks and crystallised within the adjacent mesocratic gneisses which are silica rich bear evidence of former feldspar and show a large range in major element concentrations as well as a negative correlation of most elements with sio2 peak conditions are estimated to be 800 c and 0 7 0 8 gpa subsequent near isothermal decompression to 0 4 0 5 gpa at 800 730 c is suggested by the formation of cordierite coronas and cordierite spinel symplectites around garnet and in the matrix sm nd rb sr and 40ar 39ar isotope data indicate peak conditions at 330 ma and cooling below 300 c at 310 ma

ordovician metagranitoid from the anatolide tauride block northwest turkey geodynamic implications we report a middle ordovician metagranitoid from the northern margin of the anatolide tauride block the basement of which is generally characterized by voluminous latest proterozoic to early cambrian granitoids the ordovician metagranitoid forms an 400 m thick body in the marbles and micaschists of the tavsanli zone the whole sequence was metamorphosed in the blueschist facies during the late cretaceous c 80 ma zircons from the metagranitoid give a middle ordovician pb pb evaporation age of 467 0 4 5 ma interpreted as the age of crystallization of the parent granitic magma the micaschists underlying the metagranitoid yield cambro ordovician 530 450 ma and carboniferous c 310 ma detrital zircon ages indicating that the granitoid is a pre or syn metamorphic tectonic slice the ordovician metagranitoid represents a remnant of the crystalline basement of the anatolide tauride block and provides evidence for ordovician magmatism at the northern margin of gondwana prismatic carboniferous detrital zircons in the micaschists indicate that during the triassic the northern margin of the anatolide tauride block was close to variscan terranes

pre alpine evolution of a segment of the north gondwanan margin geochronological and geochemical evidence from the central serbo macedonian massif abstract the serbo macedonian massif smm represents a composite crystalline belt within the eastern european alpine orogen outcropping from the pannonian basin in the north to the aegean sea in the south the central parts of the massif i e southeastern serbia southwestern bulgaria eastern macedonia consist of the medium to high grade lower complex and the low grade vlasina unit new results of u pb la icp ms analyses coupled with geochemical analyses of hf isotopes on magmatic and detrital zircons and main and trace element concentrations in whole rock samples suggest that the central smm and the basement of the adjacent units i e eastern veles series and struma unit originated in the central parts of the northern margin of gondwana these data provided a basis for a revised tectonic model of the evolution of the smm from the late ediacaran to the early triassic the earliest magmatism in the lower complex vlasina unit and the basement of struma unit is related to the activity along the late cadomian magmatic arc 562 522 ma subsequent stage of early palaeozoic igneous activity is associated with the reactivation of subduction below the lower complex and the eastern veles series during the early ordovician 490 478 ma emplacement of mafic dykes in the lower complex due to aborted rifting in the middle ordovician 472 456 ma and felsic within plate magmatism in the early silurian 439 2 ma the third magmatic stage is represented by carboniferous late to post collisional granites 328 304 ma these granites intrude the gneisses of the lower complex in which the youngest deformed igneous rocks are of early silurian age thus constraining the high strain deformation and peak metamorphism to the variscan orogeny the permian triassic 255 253 ma stage of late to post collisional and within plate felsic magmatism is related to the opening of the mesozoic tethys

simulation of the borehole quasistatic electric field excited by the acoustic wave during logging while drilling due to electrokinetic effect acoustic logging while drilling lwd is an important commercial technology for oil and gas exploration however the collar wave in the full waveform has been found to interfere with signals from the formation making it difficult to obtain formation compressional and shear velocities from acoustic lwd signals we investigated seismoelectric lwd to solve this problem we focused on the feasibility of obtaining the formation acoustic compressional and shear velocities from electric signals that go with acoustic waves near the borehole due to the electrokinetic effect the theoretical full waveform of the seismoelectric lwd was simulated by one way conversion approximation the full waveform of acoustic pressure was simulated first with a viscoelastic formation medium the pore pressure was then estimated by confining pressure the electric field excited by the elastic wave was seen as quasistatic and was simulated by solving the poisson equation under the borehole conditions with an inhomogeneous term generated by the acoustic disturbance in the full waveform of the synthesized electric field there was a signal traveling with the collar wave speed as well as signals accompanying compressional shear and similar guided wave groups the converted electric collar wave signal was weaker than its acoustic counterpart in terms of their amplitudes relative to other wave groups in their respective full waveforms

discovery of the late triassic middle carnian rhaetian radiolarians in the volcano sedimentary sequences of the kocali complex se turkey correlation with the other tauride units abstract the kocali complex in se turkey includes pelagic sediments pelagic limestones cherts etc basic volcanic rocks of oceanic crust origin together with platform derived sediments its depositional age was previously assigned as late jurassic early cretaceous in order to study the radiolarian contents of volcano sedimentary sequences in this complex six stratigraphic sections have been measured mainly at the ne and nw adiyaman city radiolarian faunas from these stratigraphic sections reveal that the age of these sequences ranges from middle carnian to rhaetian based on these data the depositional age of the complex is older than the previously assigned lithological characteristics widespread triassic basic volcanic rocks associated with pelagic sediments and radiolarian contents of these sequences have close similarities with the sequences of the alakircay nappe of the antalya nappes in western and central taurides based on taxonomic studies 99 taxa have been determined of which one genus adiyamanium and four species monocapnuchosphaera kocaliensis paronaella speciosa ferresium okuyucui and adiyamanium crassum are described as new

pre mesozoic alpine basements their place in the european paleozoic framework prior to their alpine overprinting most of the pre mesozoic basement areas in alpine orogenic structures shared a complex evolution starting with neoproterozoic sediments that are thought to have received detrital input from both west and east gondwanan cratonic sources a subsequent neoproterozoic cambrian active margin setting at the gondwana margin was followed by a cambrian ordovician rifting period including an ordovician cordillera like active margin setting during the late ordovician and silurian periods the future alpine domains recorded crustal extension along the gondwana margin announcing the future opening of the paleotethys oceanic domain most areas then underwent variscan orogenic events including continental subduction and collisions with avalonian type basement areas along laurussia and the juxtaposition and the duplication of terrane assemblages during strike slip accompanied by contemporaneous crustal shortening and the subduction of paleotethys under laurussia thereafter the final pangea assemblage underwent triassic and jurassic extension followed by tertiary shortening and leading to the buildup of the alpine mountain chain recent plate tectonic reconstructions place the alpine domains in their supposed initial cambrian ordovician positions in the eastern part of the gondwana margin where a stronger interference with the chinese blocks is proposed at least from the ordovician onward for the visean time of the variscan continental collision the distinction of the former tectonic lower plate situation is traceable but becomes blurred through the subsequent oblique subduction of paleotethys under laurussia accompanied by large scale strike slip since the pennsylvanian this global collisional scenario has been replaced by subsequent and ongoing shortening and strike slip under rising geothermal conditions and all of this occurred before all these puzzle elements underwent the complex alpine reorganization

post collisional adakite like magmatism in the agvanis massif and implications for the evolution of the eocene magmatism in the eastern pontides ne turkey abstract in the anatolia the caucasus and northwest iran the eocene epoch is characterized by widespread basic to acidic magmatism whose temporal and spatial evolutions and origin are poorly understood in this paper we provide geochronological and geochemical data on a suite of early eocene intrusions from northeast turkey and discuss their origin within a regional tectonic framework post to late collisional moderate to small bodies of quartz diorite and leucogranodiorite as well as later dacite porphyries intrude permo triassic low grade metamorphic rocks in the southern part of the eastern pontides very close to the neo tethyan izmir ankara erzincan suture in places the intrusives display well developed subsolidus foliations indicating on going penetrative deformation during and shortly after emplacement different emplacement depths were inferred based on the contact metamorphic mineral assemblages al in hornblende barometry and igneous textures quartz diorite 14 16 km vs dacitic porphyries 7 km biotite and hornblende ar ar and zircon u pb data indicate that the compositionally and texturally different intrusives were emplaced at 51 ma ypresian three lines of evidence indicate that the early eocene represents a tectonically active time with high exhumation rates 0 6 cm a 1 i the quartz diorite and dacitic porphyries were emplaced at different crustal depths ii the emplacement ages of these texturally distinct intrusive rocks are geochronologically undistinguishable and iii intrusive rocks locally show a well developed foliation the intrusive rocks display high abundances of al 2 o 3 sr ba lrees and low abundances of y sc and hrees and are similar to high silica adakites from supra subduction zone settings the geochemical features imply a residual and or fractionating assemblage rich in hornblende garnet pyroxene and poor in plagioclase all rock types display similar sr nd isotopic characteristics with initial e nd and 87 sr 86 sr values ranging from 1 0 to 1 1 and from 0 70421 to 0 70494 respectively these three coeval rock groups quartz diorite leucogranodiorite and dacite porphyries were generated from a similar source by variable degrees of partial melting and fractionation these data together with those from the literature clearly reveal that the adakitic signature is common in paleocene to early eocene igneous rocks in northern turkey on both sides of the izmir ankara erzincan suture but disappears towards the middle eocene regional geological constraints indicate that the continental collision between the pontides and the anatolide tauride block occurred in the paleocene and that the middle eocene represents a period of major extension characterized by a marine transgression we therefore suggest that the early eocene adakitic magmatism in northern turkey resulted from the presence of a thickened continental crust following the continental collision along the neo tethyan izmir ankara erzincan suture whereas the voluminous middle eocene magmatism was related to extensional collapse of a thickened orogen

evolution of late neoproterozoic to early paleozoic tectonic elements in central and southeast european alpine mountain belts review and synthesis abstract late neoproterozoic to early paleozoic cadomian tectonic elements are widespread in the southeastern alpine mediterranean mountain belts with discontinuous exposure extending from the alps to the menderes massif in turkey the sequences include voluminous plutonic island and continental arc successions some ophiolites of variable late neoproterozoic and cambrian to early ordovician ages high to medium grade metamorphic sequences and subordinate metasediments geological and geochronological data suggest that these cadomian elements partly experienced tectonothermal activity including metamorphism and magmatism between ca 650 and 600 ma followed by further i and s type plutonism in an andean type continental margin setting ca between 570 and 520 ma subsequently a major rift zone developed which resulted in continental stretching and subsequent formation of a back arc basin which is dated as late cambrian rifting is followed by oceanic spreading which commenced ca at the cambrian ordovician boundary possibly in a back arc setting this tectonic scenario suggests that alpine mediterranean cadomian tectonic elements were accreted to gondwana during early cadomian events ca 600 650 ma subsequently they were likely part of a long lasting outer subduction zone of gondwana at the margin of a panthalassa type ocean during late neoproterozoic iii and cambrian due to back arc spreading continental pieces started to split off from gondwana ca at the cambrian ordovician boundary

theoretical simulation of the multipole seismoelectric logging while drilling this erratum corrects a type error in the text of guan et al 2013 the continuity condition at the borehole wall of the electric field in the r direction er e o r which was given in the eighth line of the paragraph after eq 20 on p 1242 of guan et al 2013 should be that of the electric current density jr j o r the original results in guan et al 2013 are unchanged because they are calculated by using the correct continuity condition of jr j o r

contrasting geochemical patterns in the 3 7 3 8 ga pillow basalt cores and rims isua greenstone belt southwest greenland implications for postmagmatic alteration processes abstract pillow basalts from the early archean 3 7 to 3 8 ga isua greenstone belt west greenland are characterized by well preserved rims and concentric core structures the pillow rims and cores have different mineral assemblages and chemical and isotopic compositions the rims have systematically higher contents of fe2o3 mgo mno k2o rb ba ga y and transition metals than the cores in contrast the cores possess higher concentrations of sio2 na2o p2o5 sr pb u nb and the light rare earth elements rees than the rims these compositional variations in the rims and cores are likely to reflect the mobility of these elements during posteruption alteration variations of many major and trace element concentrations between the rims and cores of the isua pillow basalts are comparable to those of modern pillow basalts undergoing seafloor hydrothermal alteration al2o3 tio2 th zr and the heavy rees display similar values in both rims and cores suggesting that these elements were relatively immobile during postemplacement alteration in addition the rims and cores have distinctive sm nd and rb sr isotopic compositions in that the rims are characterized by higher 143nd 144nd and 87sr 86sr ratios than the cores the pillow basalts yield 2569 170 ma and 1604 170 ma errorchron ages on 143nd 144nd vs 147sm 144nd and 87sr 86sr vs 87rb 86sr diagrams respectively the sm nd errorchron age may correspond within errors to a late archean tectonothermal metamorphic event recorded in the region the sm nd errorchron may have resulted from a combination of isotopic homogenization and preferential loss of nd relative to sm during late archean metamorphism although the rb sr errorchron age overlaps with the timing of an early to mid proterozoic tectonothermal metamorphic event recorded in the region because of a considerably large mean square of weighted deviates value and scatter in 86sr 87sr and 87rb 86sr ratios this age may not have a precise geological significance the 1 6 ga rb sr errorchron is likely to have resulted from the loss of radiogenic 87sr collectively the sm nd and rb sr data obtained from the 3 7 3 8 ga isua pillow basalt rims and cores are consistent with disturbances of the sm nd and rb sr systems by tectonothermal metamorphic events long after their eruption in contrast to the sm nd and rb sr systems the lu hf system appears to be largely undisturbed by metamorphism five core samples and three rim samples yield a 3935 350 ma age within error of the approximate age of eruption 3 7 to 3 8 ga two rim samples that have gained lu give an age of 1707 140 ma within error of the rb sr errorchron age initial 176hf 177hf ratios of the undisturbed samples at 3 75 ga lie within 1 e unit of the chondritic value suggesting no long term depletion in the mantle source of the basalts

origin of the early middle devonian magmatism in the sakarya zone nw turkey geochronology geochemistry and isotope systematics abstract a unique example of isotopically dated devonian metagranitoid the camlik metagranite okay et al 1996 crops out in the biga peninsula nw turkey although its contact relationships with the country rocks and geodynamic setting have remained to be enigmatic so far our field work however has shown that a number of metagranitoid bodies similar to the camlik metagranite intruded the country rocks and developed contact metamorphic zones consisting of andalusite and calcsilicate hornfelses garnet epidote and diopsite wollastonite skarns the country rocks of these metagranitoids are made up of regionally metamorphosed metaclastic successions with subordinate metacarbonate metachert metabasites the kalabak formation intercalated with tectonic slices of meta serpentinites the metagranitoids and the kalabak formation are collectively termed here the havran unit which forms a ne sw trending 20 km wide and 80 km long belt in the biga peninsula the havran unit is unconformably overlain by the late triassic shallow marine sediments and is in tectonic contact with the permo triassic karakaya complex interpreted as the palaeotethyan subduction accretion complex u pb shrimp ii and la icp ms dating of the zircons from four individual plutons yielded crystallization ages ranging from 389 1 2 6 to 401 5 4 8 ma i e early to middle devonian based on their geochemical characteristics the metagranitoids are divided into two groups named the camlik and yolindi metagranitoids both granitoids display distinct subduction signature and plot in the volcanic arc granite and post collisional granite fields on tectonic discrimination diagrams 87 sr 86 sr t values of these intrusions vary between 0 707367 and 0 715588 while their 143 nd 144 nd t values range from 0 51166 to 0 51187 very low values of end t from 5 3 to 9 1 imply that the lower to mid devonian metagranitoids in the havran unit might have been generated by partial melting of lower continental crust probably driven by a major magma underplating event delamination and or slab breakoff models are considered to be the most plausible mechanisms for the genesis of these metagranitoids the data obtained in this study has shown for the first time the widespread existence of devonian and older basement in nw turkey regional geological correlations imply that this basement may be an exotic terrane in the sakarya zone emplaced during the late triassic prior to its amalgamation with the palaeotethyan karakaya complex

silurian anorogenic basic and acidic magmatism in northwest turkey implications for the opening of the paleo tethys abstract the sakarya zone northern turkey is a gondwana derived continental block accreted to northern laurussia during the carboniferous and is regarded as the eastward extension of armorica timing of its detachment from the northern margin of gondwana thus opening of the paleo tethys is poorly known here we report on metagranite and amphibolite with silurian igneous crystallization ages from the early carboniferous high temperature middle to low pressure amphibolite facies metamorphic rocks of the saricakaya massif within the sakarya zone nw turkey the metagranite amphibolite complex is exposed mainly along the southern margin of the saricakaya massif over an area of ca 12 km by 1 5 km the metagranite contains preserved domains of porphyric texture indicative of derivation from a former granite porphyry the amphibolite is devoid of any relict igneous texture both the metagranite and amphibolite are crosscut by late up to 50 cm thick felsic veins uranium pb dating on igneous zircons from both metagranite and amphibolite yielded silurian ages of ca 419 6 to 434 7 ma 2 and on those from a felsic vein an age of 319 5 ma 2 late carboniferous geochemically amphibolite displays anorogenic transitional tholeiitic to alkaline signatures initial ehf values of the igneous zircons from both metagranite and amphibolite show a large variation with medial values of 16 to 9 and 3 to 6 respectively thus the protoliths of amphibolite were derived from melts of depleted mantle and those of the metagranite on the other hand from melts of reworked crustal material we suggest that the silurian anorogenic magmatism is related to a rifting event at the northern margin of gondwana leading to the detachment of the sakarya zone and hence placing an age on the initial opening of the paleo tethys this interpretation is based on i the presence of late silurian to devonian deep sea sedimentary blocks in the paleo tethyan accretionary complexes and ii the resemblance of the u pb age spectra of detrital zircons in the metaclastic sequence of the saricakaya massif to those of cambro ordovician sandstones in jordan gondwana and iii the local occurrence of anorogenic a type granites of late ordovician silurian age in the anatolide tauride block a continental block which rifted from gondwana during the early triassic wholly anorogenic nature of the late ordovician to silurian igneous rocks in the saricakaya massif and reported in literature does not support the opening of the paleo tethys as back arc ocean as suggested in most paleogeographic reconstructions

jurassic accretionary complex and ophiolite from northeast turkey no evidence for the cimmerian continental ribbon permian triassic and late cretaceous accretionary complexes ascribed to the consumption of two distinct oceans the paleo and neo tethys are exposed over extensive areas in the eastern mediterranean region however a separating continental ribbon the so called cimmeride continent between the paleo and neo tethys during early mesozoic time cannot be defined here we report a previously unknown early jurassic metamorphic oceanic accretionary complex and ophiolite from northeast turkey bounded by oceanic accretionary complexes of permian triassic and late cretaceous age to the north and the south respectively without a continental domain in between this special tectonic position and widespread coexistence of permian triassic and late cretaceous accretionary complexes alongside the izmir ankara erzincan suture imply that 1 the southern margin of laurasia in the eastern mediterranean region grew by episodic accretionary processes from late paleozoic to end mesozoic time without involvement of a cimmerian continental ribbon and 2 the paleo tethys and northern branch of the neo tethys were not distinct oceans in the eastern mediterranean region

the legacy of pleistocene glaciation and the organization of lowland alluvial process domains in the puget sound region article i nfo alluvial rivers of the eastern puget lowland a landscape shaped by scour and fill from the cordilleran ice sheet continue to respond to patterns of deposition and scour by the last glacial age ice sheet 18 000 years after deglaciation topography revealed by valley cross sections created from high resolution lidar digital elevation models shows that rivers are aggrading in valleys eroded by subglacial runoff and degrading in valleys incised by rivers post glaciation slope area analysis of river profiles shows that profile concavity varies systematically between river segments in the two valley contexts concavity indices in mountain headwaters 0 3b b0 9 compare to those of many world rivers 0 2b b1 0 but in the lowlands these indices differ between valleys created by subglacial fluvial erosion 5b b45 and post glacially incised river valleys that grade to base levels set by these relict glacial valleys or by post glacial sea levels 1b b7 dramatic differences in river pattern landforms and dynamics occur in valleys having contrasting aggrading vs degrading and incomplete responses to pleistocene glaciation creating discrete valley scale hetero geneities in fluvial process domains along and between rivers these results point to the importance of valley scale organization of alluvial process domains along and between rivers having profiles remaining in disequilibrium from pleistocene glaciation they also point to the potential usefulness of slope area analysis of longitudinal profiles in distinguishing among different river valley process domains in lowland alluvial landscapes

variscan amphibolite facies rocks from the kurtoglu metamorphic complex gumushane area eastern pontides turkey the kurtoglu metamorphic complex that forms part of the pre liassic basement of the sakarya zone in northern turkey consists of at least two tectonic units blueschist facies rocks of unknown metamorphic age in the southern part of the complex are tectonically overlain by variscan low pressure high temperature metamorphic rocks the latter comprise mica schists and fine grained gneisses cut by metaleucogranitic dikes as well as migmatitic biotite gneisses and subordinate amphibolite intercalations structural data indicate that metamorphism and penetrative deformation occurred after dyke intrusion peak metamorphic conditions of the mica schists fine grained gneisses and metaleucogranites are estimated to 650 c and 0 4 gpa based on phase relationships in the system nckfmash fe mg partitioning between garnet and biotite as well as garnet aluminosilicate quartz plagioclase gasp and garnet plagioclase biotite quartz gbpq barometry peak temperatures of the migmatitic biotite gneisses and amphibolite intercalations are not well constrained but might have been significantly higher 690 740 c as suggested from hornblende plagioclase thermometry 40ar 39ar incremental dating on muscovite and biotite fractions from the mica schists and fine grained gneisses yielded plateau ages of 323 ma significantly older model ages of 329 and 337 ma were obtained on muscovite fractions from two metaleucogranite samples these fractions contain both relict igneous and newly formed metamorphic muscovite

serbo macedonian revisited a silurian basement terrane from northern gondwana in the internal hellenides greece abstract new geochronological and geochemical data on basement orthogneisses from the vertiskos unit of the serbo macedonian massif smm internal hellenides northern greece are used in order to constrain the pre alpine tectonic history of the basement units in the metamorphic hinterland of the hellenides the prevailing rock types in the vertiskos crystalline basement are coarse grained biotite augengneisses with subordinate leucocratic muscovite gneisses and two mica gneisses zircon pb pb and u pb ages on 20 samples range from 425 9 4 2 ma to 443 4 5 5 ma with a mean of 432 2 3 2 ma and are interpreted as primary crystallisation ages of the basement granites on the basis of the magmatic internal structure of the zircon grains trace element and isotope geochemistry of the gneisses show that they originated in a magmatic arc setting but also contain material from pre existing continental crust the rocks are slightly peraluminous and some leucocratic gneisses are strongly depleted in incompatible trace elements the zircon ages document an early silurian magmatic phase in the internal hellenides the association of lithologies and ages is distinctly different from that of the adjacent basement massifs this difference in basement provenance and the fact that the vertiskos unit is bordered by ophiolitic material both to the west and to the east leads to the conclusion that this part of the smm is an exotic terrane of northern gondwanan origin which was finally accreted to its present position during the alpine orogeny the vertiskos terrane may have been part of the hun superterrane which evolved at the northern active continental margin of gondwana in the early palaeozoic and rifted away from it during the opening of the rheic ocean in the cambrian to silurian parts of this superterrane such as the vertiskos terrane are present throughout the variscan and alpine orogens

a cracked porous medium elastic wave theory and its application to interpreting acoustic data from tight formations rocks in the earth s crust usually contain pores and cracks typical examples include tight sandstone and shale rocks that have low porosity but contain abundant microcracks by extending the classic biot s poroelastic wave theory to include the effects of cracks we obtain an elastic wave theory for porous rocks containing cracks adding crack density and aspect ratio as two important parameters to the original theory because the flat or narrow shaped cracks can easily deform under acoustic wave excitation the acoustic property of a cracked porous rock is quite different for different saturation conditions the predicted fluid sensitivity is used to interpret acoustic velocity log data from tight sand and shale gas formations in both scenarios the new theory correctly predicts the trend of velocity variation with gas saturation the results confirm that the presence of cracks in tight rocks can give rise to significant hydrocarbon signature in the acoustic measurement data allowing for identifying hydrocarbons from the data

the formation of pangea abstract the making of pangea is the result of large scale amalgamation of continents and micro continents which started at the end of the neoproterozoic with the formation of gondwana as pieces were added to gondwana on its south american antarctica and australia side ribbon like micro continents were detached from its african and south chinese side cadomia in the late neoproterozoic avalonia and hunia in the ordovician galatia in the devonian and cimmeria in the permian cadomia was re accreted to gondwana but the other ribbon continents were accreted to baltica north china laurussia or laurasia finding the origin of these numerous terranes is a major geological challenge recently a global plate tectonic model was developed together with a large geological geodynamic database at the lausanne university covering the last 600 ma of the earth s history special attention was given to the placing of gondwana derived terranes in their original position using all possible constraints we propose here a solution for the variscan terranes another paper deals with the altaids the galatian super terrane was detached from gondwana in the devonian during the opening of paleotethys and was quickly separated into four sub terranes that started to by pass each other the leading terranes collided at the end of the devonian with the hanseatic terrane detached from laurussia in the carboniferous gondwana started to impinge onto the amalgamated terranes creating the variscan chain and the pangean super continent east of spain paleotethys remained opened until the triassic subducting northward under laurasia roll back of the paleotethyan slab triggered the collapse of most of the european variscan orogen which was replaced by series of permian rifts some of them becoming oceanized back arc basins during the triassic major force changes at the pangean plate limits at the end of the triassic provoked its break up through the opening of the proto caribbean central atlantic alpine tethys oceanic seaways

the birth of the rheic ocean early palaeozoic subsidence patterns and subsequent tectonic plate scenarios abstract new plate tectonic reconstructions of the gondwana margin suggest that the location of gondwana derived terranes should not only be guided by the models but should also consider the possible detrital input from some asian blocks hunia supposed to have been located along the cambrian gondwana margin and accreted in the silurian to the north chinese block consequently the gondwana margin has to be subdivided into a more western domain where the future avalonian blocks will be separated from gondwana by the opening rheic ocean whereas in its eastern continuation hosting the future basement areas of central europe different periods of crustal extension should be distinguished instead of applying a rather cylindrical model it is supposed that crustal extension follows a much more complex pattern where local back arcs or intra continental rifts are involved guided by the age data of magmatic rocks and the pattern of subsidence curves the following extensional events can be distinguished during the early to middle cambrian a back arc setting guided the evolution at the gondwana margin contemporaneous intra continental rift basins developed at other places related to a general post pan african extensional phase affecting africa upper cambrian formation of oceanic crust is manifested in the chamrousse area and may have lateral cryptic relics preserved in other places this is regarded as the oceanisation of some marginal basins in a context of back arc rifting these basins were closed in a mid ordovician tectonic phase related to the subduction of buoyant material mid ocean ridge since the early ordovician a new phase of extension is observed accompanied by a large scale volcanic activity erosion of the rift shoulders generated detritus armorican quartzite and the rift basins collected detrital zircons from a wide hinterland this phase heralded the opening of palaeotethys but it failed due to the silurian collision eo variscan phase of an intra oceanic arc with the gondwana margin during this time period at the eastern wing of the gondwana margin begins the drift of the future hunia microcontinents through the opening of an eastern prolongation of the already existing rheic ocean the passive margin of the remaining gondwana was composed of the galatian superterranes constituents of the future variscan basement areas remaining under the influence of crustal extension they will start their drift to laurussia since the earliest devonian during the opening of the palaeotethys ocean

early triassic potassic volcanism in the afyon zone of the anatolides turkey implications for the rifting of the neo tethys afyon zone which was derived from the anatolide tauride platform during closure of the neo tethys is made up of pre mesozoic basement and unconformably overlying triassic early tertiary cover series the afyon zone contains widespread metavolcanic rocks which are dominated by rhyolite dacite and trachyandesite they form a distinct volcanic succession which is separated from the underlying silurian lower carboniferous metacarbonates and meta siliciclastics by a regional unconformity trachyandesitic metavolcanics are made up of massive lava flows pyroclastics and epiclastics less frequently domes and dikes which were developed on a deeply eroded subaerial landmass u pb and pb pb zircon geochronology yielded lower triassic 250 ma ages which are interpreted as extrusion age of trachyandesitic volcanics based on the stratigraphic geochronological and geochemical data we suggest that these lower triassic magmatic rocks represent an extensional tectonic setting on the northern active margin of the gondwana which led to the development of the northern branch of the neo tethys

using borehole electroseismic measurements to detect and characterize fractured permeable zones in 1996 we measured stoneley wave induced electrical fields in an uncased water well drilled in fractured granite and diorite near hamilton massachusetts stoneley waves generated by sledgehammer blows to the surface casing produced a flow of pore fluid in permeable zones intersected by the borehole in turn this flow induced a streaming electrical field even though these electrical signals were very small tens of microvolts we were able to detect them using electrodes placed in the borehole after power line and telluric signals were canceled by remote referencing and notch filtering amplitude analysis of the electrical fields confirmed that they were induced by fluid flow in the fractured formation the normalized amplitudes of these electrical fields correlate with the fracture density log and agree with the theoretical model for this electroseismic phenomenon our biot theory based model predicts that borehole electroseismic measurements can be used to characterize permeable zones according t

neoproterozoic to early palaeozoic magmatic evolution in the gondwana derived austroalpine basement to the south of the tauern window eastern alps in the austroalpine basement to the south of the tauern window distinct suites of metabasites occur with orthogneisses in pre early ordovician units tholeiitic and alkaline within plate basalt type metabasites are associated with acid meta porphyroids in the post early ordovician thurntaler phyllite group according to their correlated trace element abundances metabasite zircons crystallized with their host rocks protolith pb pb zircon ages whole rock ta yb th yb and oxygen sr nd isotope data define two principal evolution lines an older evolution at elevated th yb typical of subduction related magmatism started by 590 ma n morb type and 550 530 ma volcanic arc basalt type basic suites which mainly involved depleted mantle sources it finished with mainly crustal source 470 450 ma acid magmatites an other evolution line by tholeiitic and 430 ma alkaline within plate basalt type suites in both pre and post early ordovician units is characterized by an intraplate mantle metasomatism and enrichment trend along multicomponent sources these magmatic evolution lines can be related to a plate tectonic scenario that involved terranes in a progressively mature neoproterozoic to ordovician active margin and a subsequent palaeo tethys passive margin along the north gondwanan periphery

variscan orogeny in the black sea region two gondwana derived paleozoic belts rim the archean paleoproterozoic nucleus of the east european platform in the black sea region in the north is a belt of paleozoic passive margin type sedimentary rocks which extends from moesia to the istanbul zone and to parts of the scythian platform the mois block this belt constituted the south facing continental margin of the laurussia during the late paleozoic this margin was deformed during the carboniferous by folding and thrusting and forms the variscan foreland in the south is a belt of metamorphic and granitic rocks which extends from the balkanides through strandja sakarya to the caucasus bassac block the protoliths of the metamorphic rocks are predominantly late neoproterozoic granites and paleozoic sedimentary and igneous rocks which were deformed and metamorphosed during the early carboniferous there are also minor eclogites and serpentinites mostly confined to the northern margin of the bassac block typical metamorphism is of low pressure high temperature type and occurred during the early carboniferous visean 340 330 ma coevally with that observed in the central europe volumetrically more than half of the crystalline belt is made up of carboniferous earliest permian 335 294 ma granites the type of metamorphism its concurrent nature over 1800 km length of the bassac block and voluminous acidic magmatism suggest that the thermal event probably occurred in the deep levels of a continental magmatic arc the bassac arc collided with laurussia in the mid carboniferous leading to the foreland deformation the ensuing uplift in the permian resulted in the deposition of continental red beds which are associated with acidic magmatic rocks observed over the foreland as well as over the bassac block in the black sea region there was no terminal collision of laurussia with gondwana during the late paleozoic and the laurussia margin continued to face the paleo tethyan ocean in the south

experimental measurements of seismoelectric signals in borehole models s u m m a r y an experimental system is built for the electrokinetic measurements with a small scaled seismoelectric detector and a high resolution digitizer 1 ms s 1 22 bits the acoustic and seismoelectric experiments are carried out in different boreholemodels at the high frequency of 90 khz in the laboratory all the localized seismoelectric signals that accompany compressional wave shear wave and stoneley wave are first clearly observed with a monopole source in sandstone boreholes that are saturated by tap water the amplitudes of these signals are measured in the range of 1 120 v which is useful for designing the seismoelectric logging instruments then the amplitude ratio of electric signal to acoustic pressure rep for each of the three waves is calculated and compared with the theoretical simulations based on the experimental data we find that seismoelectric logging signals as well as rep become stronger at the more permeable borehole model we also find that seismoelectric logging signals are more sensitive to permeability and porosity comparedwith acoustic logging signals therefore this study verifies the feasibility of seismoelectric well logging and further indicates that the seismoelectric logging technique might be a preferable method to estimate formation parameters in the field measurements