deep crustal structure of northwestern part of turkey abstract the deep crustal structure of the polatli nallihan karasu nw turkey area was investigated by magnetotelluric and transient electromagnetic measurements all measurements were acquired as part of a national project called crustal structures of turkey undertaken by the general directorate of mineral research and exploration of turkey mta magnetotelluric data were collected from 44 stations located along a 250 km northwest to southeast profile crossing in succession the istanbul zone intra pontid suture sakarya continent izmir ankara suture tavsanli zone the tauride anatolide belt intra pontid suture and sakarya continent after decompositional analysis and strike direction estimation static shift is corrected by using transient electromagnetic data from mt apparent resistivity data the processed mt data were inverted to derive a two dimensional geoelectrical model the estimated model is interpreted with the help of gravity data observed along the mt lines and using earthquake epicenter which occurred around mt measurement lines four layers with distinctive resistivity values dominate the geoelectrical section the uppermost layer having resistivity values of 5 35 ohm m can be interpreted as the sedimentary fill this layer reaches down to about 10 km depth in haymana basin the second layer has resistivity values higher than 110 ohm m and reaches 27 km depth the first and second layers can be inferred as constituting the upper crust in the general model of the earth s lithosphere the third layer underlying the upper crust has resistivity values of 10 30 ohm m corresponding to the lower crust the fourth layer having high resistivity values 225 ohm m can be considered as the upper mantle the depth of the boundary separating the crust from the upper mantle moho varies between 20 and 40 km high conductive zones between the istanbul zone and sakarya continent sakarya continent and tavsanli zone coincide with high bouguer gravity anomaly values it can be inferred from these properties that these zones correspond to the intra pontide suture and the izmir ankara suture noticeable differences in tectonic characteristics are observed between the southern and northern part of sakarya continent in the geoelectrical section the northern part of the continent is separated by high dip slip faults while the faults in the southern part do not affect the high resistive zone in the deeper part of the section these faults controlled the development of the haymana basin but they do not alter the high resistive zone to form separate blocks the majority of these faults which are clearly seen in the geoelectrical section are not evident in the sedimentary fill these buried faults have not been studied in detail prior to the present study

petrofabrics of high pressure rocks exhumed at the slab mantle interface from the point of no return in a subduction zone sivrihisar turkey the highest pressure recorded by metamorphic rocks exhumed from oceanic subduction zones is 2 5 gpa corresponding to the maximum decoupling depth mdd 80 10 km identified in active subduction zones beyond the mdd the point of no return exhumation is unlikely the sivrihisar massif turkey is a coherent terrane of lawsonite eclogite and blueschist facies rocks in which assemblages and fabrics record p t fluid deformation conditions during exhumation from 80 to 45 km crystallographic fabrics and other features of high pressure metasedimentary and metabasaltic rocks record transitions during exhumation in quartzite microstructures and crystallographic fabrics record deformation in the dislocation creep regime including dynamic recrystallization during decompression and a transition from prism slip to activation of rhomb and basal slip that may be related to a decrease in water fugacity during decompression 2 5 to 1 5 gpa phengite lawsonite and omphacite or glaucophane in quartzite and metabasalt remained stable during deformation and omphacite developed an l type crystallographic fabric in marble aragonite developed columnar textures with strong crystallographic fabrics that persisted during partial to complete dynamic recrystallization that was likely achieved in the stability field of aragonite p 1 2 gpa results of kinematic vorticity analysis based on lawsonite shape fabrics are consistent with shear criteria in quartzite and metabasalt and indicate a large component of coaxial deformation in the exhuming channel beneath a simple shear dominated interface this large coaxial component may have multiplied the exhuming power of the subduction channel and forced deeply subducted rocks to flow back from the point of no return

partial high pressure aragonitization of micritic limestones in an accretionary complex tavsanli zone nw turkey pelagic micritic limestones within an upper cretaceous accretionary complex in the tavsanli zone nw turkey preserve textures indicating incomplete prograde transformation of micritic calcite to aragonite representing the only known example of this type aragonitization starts at the central parts of the micritic limestone beds and advances towards the lower and upper parts of the layers at the expense of micrite micrite is very fine grained 0 003 mm and contains radiolaria foraminifera and thin shell fragments aragonite forms large crystals up to 3 cm across with straight grain boundaries and c axis mostly subparallel to the carbonate beds relict micritic portions are devoid of any aragonite grain stylolites characterized by the accumulation of clay minerals fe mn hydroxides and quartz are concentrated in the upper and lower parts of the beds stylolite formation precedes aragonitization conditions of aragonitization are estimated as 200 50 c and 0 45 0 65 gpa based on metamorphic mineral assemblages observed in associated basalts several features such as i constant composition of micritic calcite 98 99 mol caco3 throughout individual beds ii enormous grain size difference between micritic calcite and aragonite up to 1200 times and iii absence of any aragonite grains within the relict micritic portions suggest that kinetic rather than thermodynamic factors controlled selective aragonite formation in the central portions of carbonate layers

seismic properties of subducting oceanic crust constraints from natural lawsonite bearing blueschist and eclogite in sivrihisar massif turkey abstract investigating the seismic properties of natural lawsonite lws bearing blueschist and eclogite is particularly important for constraining the seismic interpretation of subducting oceanic crust based on seismological observations to achieve this end we analyzed in detail the mineral fabrics and seismic properties of foliated lws blueschist and lws eclogites from sivrihisar massif in turkey in both blueschists and eclogites the lawsonite fabric is characterized by three different patterns 0 0 1 axes aligning sub normal to foliation and 0 1 0 axes aligning sub parallel to lineation normal type 0 0 1 axes aligning sub parallel to lineation and 1 0 0 axes aligning sub normal to foliation with a girdle sub normal to lineation abnormal type and 0 0 1 axes aligning both sub normal to foliation and sub parallel to lineation 0 1 0 axes aligning sub parallel to lineation and 1 0 0 axes aligning sub normal to foliation transitional pattern in contrast glaucophane and omphacite mostly present consistent axial fabrics with the 0 0 1 axes aligning to lineation these mineral fabrics produce whole rock seismic anisotropies with similar patterns however the variations in seismic anisotropies are mainly controlled by the rock type to a lesser extent are determined by the lawsonite fabric type and to only a small extent are affected by mineral fabric strength despite the constructive abnormal type lawsonite fabric on whole rock seismic anisotropies because of their weaker mineral fabric strength or deformation degree the abnormal type lws blueschist still exhibit comparatively lower seismic anisotropies than those normal type lws blueschist from other localities based on the calculated seismic anisotropies and velocities we estimated that when oceanic crust transforms from lws blueschist to lws eclogite with increasing subduction depth 1 p wave and max s wave polarization anisotropies reduce about 70 and 40 respectively and 2 variations of vp and vs contrasts relative to mantle peridotites are about 7 to 3 and 8 to 6 respectively these results corroborate the important roles of lws bearing blueschist and eclogite in interpreting the existence and gradual weakening of low velocity layers in subducting oceanic crust during the subduction process

blueschist metamorphism in an active subduction zone the high pressure low temperature metamorphic rocks known as blueschists have long been considered to form in subduction zones where the descent of a relatively cold slab leads to the occurrence of unusually low temperatures at mantle pressures until now however the link between blueschist facies rocks and subduction zones has been indirect relying on a spatial association of blueschists with old subduction complexes and estimates of the geothermal gradients likely to exist in subduction zones here we strengthen this link by reporting the discovery of blueschist facies minerals lawsonite aragonite sodic pyroxene and blue amphibole in clasts from a serpentinite seamount in the forearc of the active mariana subduction zone the metamorphic conditions estimated from the mineral compositions are 150 250 c and 5 6 kbar 16 20 km depth the rocks must have been entrained in rising serpentine mud diapirs and extruded from mud volcanoes onto the sea floor further study of these rocks may provide new insight into the tectonics of trench forearc systems and in particular the processes by which blueschist facies clasts come to be associated with forearc sediments in ancient subduction complexes

lawsonite composition and zoning as tracers of subduction processes a global review abstract lawsonite is an abundant hydrous mineral in oceanic crust sediments and metasomatic rocks at depths of 45 to 300 km in most subduction zones but it is rarely preserved in the geologic record because it commonly transforms to epidote and other minerals during prograde or retrograde metamorphism owing to the significance of lawsonite for water and element cycling in subduction zones occurrences of fresh lawsonite in blueschist and more rarely eclogite provide important opportunities to determine lawsonite composition zoning and inclusion suites and to use this information to reconstruct reaction history during subduction and exhumation in this review we use new and published data to document lawsonite composition in eight of the nine known lawsonite eclogite localities in which fresh lawsonite coexists with garnet omphacite in the rock matrix as well as the composition of lawsonite inclusions in six of seven known sites in which lawsonite occurs only as inclusions in garnet in eclogite facies rocks that lack matrix lawsonite as lawsonite blueschist is much more common than lawsonite eclogite we survey the composition of lawsonite in representative localities of blueschist including blueschist associated with eclogite lawsonite bearing epidote bearing and blueschist not associated with eclogite at current exposure levels included in this review are metabasaltic rocks silica and carbonate rich metasedimentary rocks metasomatic rocks and lawsonite rich veins this dataset demonstrates that lawsonite composition is a sensitive indicator of reaction history during subduction and exhumation and specifically of fluid rock interaction with implications for element cycling in subduction zones furthermore most exhumed lawsonite eclogite records slab surface conditions that correspond to the location where the slab mantle interface transitions from decoupled to coupled and therefore provides key insights into the thermal history and dynamics of subduction zones

lawsonite zone blueschists and a sodic amphibole producing reaction in the tavsanli region northwest turkey the petrology and mineralogy of lawsonite zone metabasites have been studied northeast of town of tavsanli nw turkey in the field the metabasites are characteristically green and lack foliation the essential mineral assemblage being sodic pyroxene lawsonite chlorite quartz sodic amphibole sodic pyroxene of aegirine jadeite composition occurs as pseudomorphs after magmatic augite lawsonite and chlorite are the other two dominant minerals sodic amphibole forms progressively from a reaction between sodic pyroxene chlorite and quartz and an isograd representing the first abundant occurrence of sodic amphibole in basic rocks has been mapped the widespread occurrence of sodic pyroxene pseudomorphs in other blueschist terrains indicates that the inferred sodic amphibole producing reaction is of general significance for blueschist metabasites

a large amplitude traveling ionospheric disturbance produced by the may 18 1980 explosion of mount st helens a remarkable long lived large scale traveling ionospheric disturbance tid excited by the may 18 1980 explosion of mount st helens has been detected in total electron content monitor data oscillatory perturbations in the electron column density of the ionosphere with amplitudes about 10 of the nominal daytime content were detected at three stations whose ionospheric penetration points lie between 1610 and 1890 km from mount st helens smaller perturbations were detected at five of six additional stations between 3760 and 4950 km away the period of the tid increased linearly with great circle distance from mount st helens ranging from 37 min at the nearest station to 116 min at the most distant one the tid persisted for at least four cycles at the three close stations and three cycles at the more distant stations and was qualitatively similar to tids produced by the low altitude thermonuclear detonations of the 1960 s the disturbance front of this tid accelerated from an average velocity of 350 m s between mt st helens and the close stations to an average velocity of 550 m s to the more distant ones in analogy with the bomb excited disturbances this tid is interpreted as the ionospheric fluctuations induced by a gravity wave excited by the explosion of mount st helens propagating in the neutral atmosphere a model based on the free wave response of an isothermal atmosphere to a point disturbance provides a good fit to the data at the three closest stations but no such model can account for all of the data modeling of the long distance behavior of the mount st helens tid in terms of upper atmosphere guided gravity waves is complicated by the requirement of exciting them by a ground level explosion a comprehensive explanation would probably include the propagation of energy to ionospheric heights in free modes and the excitation thereby of guided modes there was no evidence for a strong supersonic shock wave in the ionosphere as a result the mount st helens disturbance may prove to be a cleaner test of detailed theories of the point excitation and propagation of gravity waves in a realistic atmosphere than were tids excited by thermonuclear weapons

metamorphic petrology of a high pressure low temperature subduction complex in west central baja california mexico the western baja terrane wbt of west central baja california is an uplifted subduction complex that is divided into smaller subterranes on the basis of bounding faults and petrological differences each subterrane contains coherent early jurassic to early cretaceous sedimentary and mafic volcanic rocks not melange that have been metamorphosed under blueschist facies conditions key phases in metabasites and metaturbidites include jadeitic to acmitic clinopyroxene sodic amphibole lawsonite aragonite chlorite titanite and white mica pressure indicators include the jadeite content of clinopyroxene and the presence of aragonite temperature indicators include the presence of lawsonite the absence of greenschist facies minerals and results from vitrinite reflectance studies conditions at the peak of metamorphism were 8 kbar 225 325 c for subterrane 1 7 8 kbar 170 220 c for subterrane 2 and 5 6 kbar 175 200 c for subterrane 3 these correspond to cold geothermal gradients 6 9 km vein assemblages that include aegerine jadeite and aegerine albite aragonite lawsonite and sodic amphibole indicate uplift during continued cold conditions probably during steady state subduction

tectonic setting petrology and geochronology of jadeite glaucophane and chloritoid glaucophane schists from north west turkey the north west turkish blueschists represent a subducted passive continental margin sequence dominated by metaclastic rocks and marble the depositional age of the blueschist protoliths are probably palaeozoic to mesozoic while the age of the high pressure low temperature metamorphism is late cretaceous blueschists are tectonically overlain by a volcanosedimentary sequence made up of accreted oceanic crustal material that locally shows incipient blueschist metamorphism and by spinel peridotite slices the metaclastic rocks with regional jadeite and glaucophane which comprise the lower part of the blueschist unit make up an over 1000 m thick coherent sequence in the kocasu region of north west turkey rare metabasic horizons in the upper parts of the metaclastic sequence with sodic amphibole iawsonite but no garnet indicate lawsonite blueschist facies metamorphism the blueschist metaclastics in the kocasu region are practically free of calcium and ferric iron and closely approximate the nfmash system in bulk composition two low variance mineral assemblages with quartz and phengite are jadeite glaucophane chlorite paragonite and chloritoid glaucophane paragonite the metaclastics comprise up to several metres thick layers of jadeite schist with quartz phengite and nearly 100 mol jadeite phase relations in the metaclastics show that the chloritoid glaucophane assemblage even in fe2 rich compositions is stable in the jadeite stability field in the nfash system the above assemblage without the accompanying garnet has a narrow thermal stability field mineral equilibria in the metaclastics involving chloritoid glaucophane jadeite paragonite and chlorite indicate metamorphic p t conditions of 20 2 kbar and 430 30 d c yielding geothermal gradients close to 5d c km 1 one of the lowest geotherms recorded blueschists in the kocasu region which have been buried to 70 km depth are tectonically overlain by the volcanosedimentary sequence and by peridotite buried not deeper than 30 km phengites from two jadeite schists were dated by ar ar laser probe they give an age of 88 5 0 5 ma interpreted as the age of metamorphism blueschists and the overlying peridotite bodies are intruded by 48 53 ma old granodiorite bodies that were emplaced at 10 km depth this suggests that the exhumation of blueschists by underplating of cold continental crust and normal faulting at the blueschist peridotite interface occurred during the late cretaceous to palaeocene 88 53 ma

incipient blueschist metamorphism and metasomatism in the tavsanli region northwest turkey volcano sedimentary rocks in an imbricate tectonic zone around a peridotite massif have been studied northeast of the town of tavsanli in northwest turkey basic volcanic rocks which are the dominant rock type in this zone show incipient blueschist metamorphism and associated metasomatism while the igneous textures of the volcanic rocks are retained augites are partially to completely replaced by sodic pyroxene and plagioclase is albitised resulting in rocks with 6 8 wt na2o the volcanic rocks are cross cut by numerous veins of calcite aragonite quartz pumpellyite albite lawsonite and sodic pyroxene pelagic limestones which are interbedded with the basic volcanic rocks consist of coarse aragonite grains showing partial replacement by calcite the occurrence of aragonite lawsonite and albite indicates conditions of metamorphism for the whole zone in the range of 5 8 kb and 150 200 c metasomatism probably related to high pressure serpentinization has occurred contemporaneously with the incipient high pressure metamorphism

pressure temperature evolution of lawsonite eclogite in sivrihisar tavsanli zone turkey abstract the cretaceous blueschist belt tavsanli zone representing the subducted and exhumed northern continental margin of the anatolide tauride platform is exposed in western anatolia the sivrihisar area east of tavsanli is made up of tectonic units consisting of i metaclastics and conformably overlying massive marbles coherent blueschist unit ii blueschist eclogite unit iii marble calcschist intercalation and iv metaperidotite slab the metaclastics are composed of jadeite lawsonite glaucophane and jadeite glaucophane chloritoid schists phengite phyllites and calcschists with glaucophane lawsonite metabasite layers the blueschist eclogite unit representing strongly sheared deeply buried and imbricated tectonic slices of accreted uppermost levels of the oceanic crust with minor metamorphosed serpentinite bodies consists of lawsonite bearing eclogitic metabasites approximately 90 of the field lawsonite eclogites metagabbros serpentinites pelagic marbles omphacite glaucophane lawsonite metapelites and metacherts the mineral assemblage of the lawsonite eclogite garnet omphacite 70 is omphacite garnet lawsonite glaucophane phengite and rutile lawsonite eclogite lenses are enclosed by garnet lawsonite blueschist envelopes textural evidence from lawsonite eclogites and country rocks reveals that they did not leave the stability field of lawsonite during subduction and exhumation the widespread preservation of lawsonite in eclogitic metabasites and eclogites can be attributed to rapid subduction and subsequent exhumation in a low geothermal gradient of the oceanic crust material without experiencing a thermal relaxation peak p t conditions of lawsonite eclogites are estimated at 24 1 kbar and 460 25 c these p t conditions indicate a remarkably low geotherm of 6 2 c km corresponding to a burial depth of 74 km

seismic and acoustic signatures of surficial mass movements at volcanoes abstract surficial mass movements such as debris avalanches rock falls lahars pyroclastic flows and outburst floods are a dominant hazard at many volcanoes worldwide understanding these processes cataloging their spatio temporal occurrence and detecting tracking and characterizing these events would advance the science of volcano monitoring and help mitigate hazards seismic and acoustic methods show promise for achieving these objectives many surficial mass movements generate observable seismic and acoustic signals and many volcanoes are already monitored significant progress has been made toward understanding modeling and extracting quantitative information from seismic and infrasonic signals generated by surficial mass movements however much work remains in this paper we review the state of the art of the topic covering a range of scales and event types from individual rock falls to sector collapses we consider a full variety of volcanic settings from submarine to subaerial shield volcano to stratovolcano finally we discuss future directions toward operational seismo acoustic monitoring of surficial mass movements at volcanoes

timing of tectonic events in the menderes massif western turkey implications for tectonic evolution and evidence for pan african basement in turkey the menderes massif forms the western of the two large metamorphic culminations within the turkish alpide orogen it has three major lithologic units with a gneissic core at the base and a schist and a marble envelope overlying it successively although relations between them have been largely obscured by the polymetamorphic and structurally complex history of the massif we present a review of the available stratigraphic evidence and combine it with new isotopic ages from the central and southern parts of the massif to constrain the timing of major tectonic events that shaped the massif since the late proterozoic pt3 in the southern part of the massif sensu stricto three episodes of deformation and metamorphism are distinguished whereas in its northern part there are four the first episode occurred at 500 10 ma with intense deformation and metamorphism at high grade amphibolite facies with local anatexis in the central part of the massif the 470 9 ma old now highly deformed tonalitic and granitic intrusions mark the end of this episode on a cambrian reconstruction of continents around the eastern mediterranean the menderes massif forms the southern end of the pan african orogenic collage of northeastern africa and arabia the area of earliest palaeozoic deformation in the menderes may connect with the northwest african orogenic collage along the strike via the bozburun and saricicek diabases arkoses and schists in the center of the karacahisar dome interpreted herein as fragments of a pan african suture the earliest palaeozoic deformations to affect the rocks were probably related to the last pan african collisions and associated postcollisional convergence the southern part of the massif was undeformed from early ordovician to the early later eocene whereas the northern part was deformed metamorphosed and intruded possibly during the late triassic related to the closure of the karakaya marginal basin of palaeo tethys the next major event affecting the whole of the massif was the intense deformation and widespread metamorphism that reached high amphibolite grade in the structurally lower parts and only greenschist grade in the outermost envelope this metamorphism here called the main menderes metamorphism mmm is biostratigraphically constrained between early eocene and early oligocene time rb sr isotopic data show a spread of ages between 60 ma and 25 ma with the greatest number of determinations around 35 5 ma this number is in excellent agreement with the stratigraphic evidence and shows that mmm took place during latest eocene time or at the transition from eocene to oligocene time along the northern border of the massif deformation and metamorphism had already taken place during the late cretaceous in a high pressure low temperature hp lt metamorphic belt northernmost part of menderes massif sensu lato which was then covered by palaeocene molasse the evolution of the hp lt belt was probably related to the obduction of the bozkir ophiolites from the izmir ankara branch of the neo tethys ocean and preceded terminal collision in the evolution of the massif the mmm was a product of the latest palaeocene collision across neo tethys and the consequent internal imbrication of the menderes taurus block that resulted in the burial of the menderes massif area beneath the lycian nappe complex a low grade metamorphic event dated at 10 to 5 ma is interpreted to be related to the extensional deformation in the aegean and western turkey which has been dated stratigraphically to have begun during the tortonian 11 5 ma

uplift related retrogression history of aragonite marbles in western crete greece in the low grade high pressure 400 c 10 kbar metamorphic phyllite quartzite unit of western crete widespread occurrences of aragonite marbles have been discovered recently a sedimentary precursor is proved by relic structures bedding fossils partial or complete transformation of aragonite into calcite is ubiquitous compositional and microstructural features reflect the metamorphic history 1 the high pressure stage is documented by aragonite that is chemically characterized by incorporation of variable amounts of sr and the lack of mg the most sr rich aragonite has about 9 wt sro xsrarag 0 09 a compositional zoning observed in some aragonite crystals may be due to the prograde divariant calcite aragonite transformation in the system caco3 srco3 because the parent rocks probably were sr poor calcite limestones one can speculate that strontium has been supplied from an external source under high pressure conditions 2 during uplift calcite replacing aragonite did not equilibrate with unreplaced aragonite disequilibrium is indicated by highly variable compositions of calcite crystals that show topotactic relations to the host aragonite the calcite compositions range from that of the host aragonite sr rich and mg free to mg bearing and sr poor 3 calcite that recrystallized during retrogression is generally sr poor mean value ofxsr 0 005 mg bearing xmg 0 010 and chemically homogeneous because practically no sr remains in the calcite an interaction with a fluid phase is indicated in fine grained calcite marbles rich in solid organic matter microstructural features indicative of former aragonite may be present 4 the last stage of retrogression is documented by the appearance of radiating aragonite in veins and nodules this aragonite which shows neither deformation nor retrogression was probably formed metastably in a near surface environment

processing and interpretation of microbarograph signals generated by the explosion of mount st helens following the eruption of the mount st helens volcano on may 18 1980 atmospheric waves were recorded by a network of micrographs located over 7 000 km from the source analysis of these data requires the use of complex processing techniques based on a high resolution method to extract the signals produced by the st helens source from spurious waves or noise in each record this facilitates interpretation of the wave trains in terms of propagation modes it is thus shown that lamb mode l sub 0 is present in the low frequency part of all signals whereas acoustic modes more probably a prime sub 2 are needed to explain all the properties of the high frequency part which is clearly observed for a westward and a southward propagation

high pressure metasediments in central turkey constraints on the neotethyan closure history 1 the distribution of oceanic domains and continental blocks in central anatolia remains a challenge in understanding the alpine geodynamic evolution of the tethys realm the consumption of a neotethys oceanic branch at the mesozoic cenozoic boundary welded the central anatolian crystalline complex in central turkey and the anatolide tauride block in western turkey with the northerly eurasian margin whether those two regions constituted a single or two distinct continental masses is still matter of debate high pressure metamorphism has been locally evidenced in the afyon zone which was however defined as a greenschist facies metamorphic zone of the anatolide tauride block since the afyon zone composes a metamorphic equivalent of a continental margin exposed far south of the izmir ankara suture zone this encouraged us to reevaluate its metamorphic evolution in order to better understand the relation between western and central turkey our investigations reveal that the high pressure minerals fe mg carpholite and glaucophane are present in the entire afyon zone which we reconsider as a blueschist facies zone we additionally present a tectonic reconstruction stripping off the postcollisional tectonics it reveals that today s bending of the high pressure belt is consistent with an eocene collision of the anatolide tauride block around the southern edge of the central anatolian crystalline complex we argue that the central anatolian crystalline complex and the anatolide tauride block were two distinct continental masses separated by a neotethyan oceanic stripe the closure of which engendered subduction related metamorphism in the latter and arc volcanism and high grade metamorphism in the former by late cretaceous to early cenozoic

tracking physicochemical conditions of evaporite deposition by stable magnesium isotopes a case study of late permian langbeinites magnesium isotopic compositions of evaporite deposits may record information concerning brine evolution during deposition we report mg isotopic values delta mg 26 dsm3 measured from an evaporite deposit of langbeinite k2mg2 so4 3 found in the permian salado formation we used these data to model mg isotope fractionation between langbeinite and its parent brine in addition both measured and theoretical results are used to estimate precipitation temperature and interpret depositional environment the salado langbeinite delta mg 26 values are relatively low and fall within a relatively narrow range 4 12 0 03 parts per thousand to 3 81 0 07 parts per thousand equilibrium fractionation factors between langbeinite and aqueous mg2 solutions were calculated using quantum chemical density functional theory all computations were performed at the b3lyp 6 31 g d p level solvation effects were addressed using a solvent model water droplet approach and mineral structures were investigated using volume variable cluster models vvcm the equilibrium mg isotopic fractionation factors a between langbeinite and model brine solution we obtained are 1 0005 1 0004 and 1 0003 delta mg 26 langb water approximate to 10 3 ln alpha 0 473 parts per thousand 0 390 parts per thousand and 0 322 parts per thousand at 10 degrees c 25 degrees c and 40 degrees c respectively these relatively large equilibrium fractionation factors indicate significant mg isotope fractionation between langbeinite and its parent brine during precipitation as langbeinite preferentially incorporates the heavier mg 26 and mg 25 isotopes rayleigh distillation modeling of the salado langbeinite s relatively light mg isotopic composition requires delta mg 26 dsm3 values of 4 parts per thousand for the parent brine models favor a precipitation temperature as high as 40 degrees c under equilibrium conditions potential disequilibrium precipitation conditions suggested by mg isotopic data also imply rapid deposition in a hot arid sedimentary environment prevailing in the southwestern u s during the late permian

mount st helens eruption of 18 may 1980 air waves and explosive yield strong atmospheric acoustic gravity waves were recorded by sensitive microbarographs and seismographs at large distances from the mount st helens eruption of 18 may 1980 wave signatures were similar to those of waves from large nuclear explosions independent theoretical and empirical analyses indicate that the explosive yield of the eruption was approximately 35 megatons

recrystallization of high pressure marble sivrihisar turkey abstract in the sivrihisar massif turkey the southern margin of a blueschist facies terrane was affected by heating and deformation associated with later regional barrovian metamorphism creating a recrystallization front that can be observed in calcite microstructures calcite marble records a progression from high pressure h p textures in a northern domain to completely recrystallized greenschist to amphibolite facies textures in a southern domain with intermediate stages of partial recrystallization of the h p textures h p marble is characterized by rod shaped calcite aragonite pseudomorphs arranged in series with the long axis of each grain oblique to compositional layering obliquity varies from 50 to nearly parallel but high angles are most common in a narrow 200 m thick transition zone that contains partially retrogressed blueschist and eclogite the h p texture is partially overprinted by chains of small equant recrystallized grains that preserve the crystallographic orientation of the pre existing rod shaped calcite as revealed by electron backscatter diffraction analysis rod shaped crystals occur locally in a 100 m thick zone south of the transition zone all calcite grains are equant but have a crystallographic preferred orientation further south in the barrovian sequence recrystallized marble contains equant calcite that is randomly oriented the similarity in fabric elements foliation lineation of the two domains further shows the effect of barrovian related processes on the h p domain including the rotation of the calcite rods during shearing along foliation planes white mica 40 ar 39 ar ages for phengite in h p marble are 88 ma and for muscovite in barrovian marble are 59 ma indicating 30 ma time interval between initial exhumation and cooling of the h p rocks and final cooling of the rocks that were deformed and heated during the later metamorphic event

petrotectonics of lawsonite eclogite exhumation insights from the sivrihisar massif turkey 1 the sivrihisar massif of the tavsanli zone of turkey is 1 of less than 10 known lawsonite eclogite localities worldwide rocks of the sivrihisar massif consist of eclogite and blueschist in contact with metasedimentary host rocks and record decreasing maximum pressure conditions across three wnw ese striking belts from 16 24 kbar in the northern halilbagi belt to 14 16 kbar in the karacaoren belt and 8 10 kbar in the kertek belt where present sodic amphibole phengite chlorite and quartz define a pervasive s0 s1 foliation garnet omphacite and lawsonite define stretching lineations and kinematic indicators d1 and d2 structures are similar in the halilbagi and karacaoren belts but differ to those in the kertek belt d3 structures are uniform across the massif including fibrous calcite that occurs parallel to f3 fold axes shear sense indicators from field observations and asymmetric type i cross girdle of quartz c axes obtained from electron backscatter diffraction ebsd show top to the south thrusting throughout much of the massif d1 and d2 structures are interpreted to have formed during exhumation by extrusion along a 5 c km gradient the halilbagi and karacaoren belts were juxtaposed possibly as deep as 45 km within the subduction channel and exhumed by the arrival of the anatolide microcontinent at approximately 70 ma homogeneity of f3 axes and calcite fibers across the massif suggests that assembly occurred at blueschist conditions before exhumation through the aragonite calcite transition 350 c above 8 kbar

tectono metamorphic evolution of the siliciclastic units in the middle tuscan range inner northern apennines mg carpholite bearing quartz veins related to syn metamorphic syn orogenic foliation abstract this paper accounts for a new finding of high pressure low temperature hp lt metamorphism documented in continental derived rocks exposed in the central part of the middle tuscan range representing the easternmost location in the tyrrhenian region where blueschist facies metamorphism has been documented it describes the development mechanism of mg carpholite bearing quartz veins in the framework of the deformational events described for the inner northern apennines the hp lt peak metamorphism can be estimated in p 1 1 gpa and t 370 420 c as supported by the mineralogical assemblage consisting of quartz muscovite chloritoid pyrophylite hematite chlorite paragonite ti oxides documented in the aluminous metasediments pelites and quartzose sandstones of the triassic verrucano succession this paragenesis defines the s 1 schistosity an axial planar tectonic foliation associated to map and mesoscale isoclinals folds f 1 s 1 schistosity is a composite foliation resulted from a non coaxial progressive deformation associated to the de 1 collisional event late oligocene early miocene mg carpholite bearing quartz veins developed as tension gashes in en echelon arrays within brittle ductile shear zones the development of quartz veins was guaranteed by the high volumes of si rich fluids produced by the dynamic recrystallization process on the siliciclastic rocks

tectonic evolution and paleogeography of the kirsehir block and the central anatolian ophiolites turkey in central and western anatolia two continent derived massifs simultaneously underthrusted an oceanic lithosphere in the cretaceous and ended up with very contrasting metamorphic grades high pressure low temperature in the tavsanli zone and the low pressure high temperature in the kirsehir block to assess why we reconstruct the cretaceous paleogeography and plate configuration of central anatolia using structural metamorphic and geochronological constraints and africa europe plate reconstructions we review and provide new 40ar 39ar and u pb ages from central anatolian metamorphic and magmatic rocks and ophiolites and show new paleomagnetic data on the paleo ridge orientation in a central anatolian ophiolite intraoceanic subduction that formed within the neotethys around 100 90 ma along connected n s and e w striking segments was followed by overriding oceanic plate extension already during suprasubduction zone ocean spreading continental subduction started we show that the complex geology of central and southern turkey can at first order be explained by a foreland propagating thrusting of upper crustal nappes derived from a downgoing dominantly continental lithosphere the kirsehir block and tavsanli zone accreted around 85 ma the afyon zone around 65 ma and taurides accretion continued until after the middle eocene we find no argument for late cretaceous subduction initiation within a conceptual inner tauride ocean between the kirsehir block and the afyon zone as widely inferred we propose that the major contrast in metamorphic grade between the kirsehir block and the tavsanli zone primarily results from a major contrast in subduction obliquity and the associated burial rates higher temperature being reached upon higher subduction obliquity

late cretaceous blueschist facies metamorphism in southern thrace turkey and its geodynamic implications a blueschist facies tectonic sliver 9 km long and 1 km wide crops out within the miocene clastic rocks bounded by the strands of the north anatolian fault zone in southern thrace nw turkey two types of blueschist facies rock assemblages occur in the sliver i a serpentinite body with numerous dykes of incipient blueschist facies metadiabase ii a well foliated and thoroughly recrystallized rock assemblage consisting of blueschist marble and metachert both are partially enveloped by an upper eocene wildflysch which includes olistoliths of serpentinite metadiabase upper cretaceous and palaeogene pelagic limestone upper eocene reefal limestone radiolarian chert quartzite and minor greenschist field relations in combination with the bore core data suggest that the tectonic sliver forms a positive flower structure within the miocene clastic rocks in a transpressional strike slip setting and represents an uplifted part of the pre eocene basement the blueschists are represented by lawsonite glaucophane bearing assemblages equilibrated at 270 310 c and 0 8 gpa the metadiabase dykes in the serpentinite on the other hand are represented by pumpellyite glaucophane lawsonite assemblages that most probably equilibrated below 290 c and at 0 75 gpa one metadiabase olistolith in the upper eocene flysch sequence contains the mineral assemblage epidote pumpellyite glaucophane recording p t conditions of 290 350 c and 0 65 0 78 gpa indicative of slightly lower depths and different thermal setting timing of the blueschist facies metamorphism is constrained to c 86 ma coniacian santonian by rb sr phengite whole rock and incremental 40 ar 39 ar phengite dating on blueschists the activity of the strike slip fault post dates the blueschist facies metamorphism and exhumation and is only responsible for the present outcrop pattern and post miocene exhumation 2 km the high p t metamorphic rocks of southern thrace and the biga peninsula are located to the southeast of the circum rhodope belt and indicate late cretaceous subduction and accretion under the northern continent i e the rhodope massif enveloped by the circum rhodope belt the late cretaceous is therefore a time of continued accretionary growth of this continental domain