sequence stratigraphy tectonics and depositional history in eastern thrace basin nw turkey abstract the eastern thrace basin forms the eastern portion of the turkish thrace basin in nw turkey the pre tertiary crystalline basement shows platform and deep basin depositional morphology which results in facies pattern and thickness distribution localization during the early stages of basin development in middle to late eocene time normal fault controlled early and lateral reverse fault controlled later stage tectonic events characterize basin geometry and the present topography respectively the early stage normal faulting caused subsidence and sediment accumulation in the late eocene and early oligocene while later stage tectonic events caused intense deformation and structuration in the early to middle miocene as a result southeastern and northern regions were folded or uplifted and deeply eroded outcrop well log core and reflection seismic studies reveal that the sedimentary succession can be subdivided into five characteristic depositional sequences bounded at their base by unconformities these unconformities were dated using paleontological data the sequence boundaries underlying consecutively sequences 1 2 3 and 5 were dated at 39 5 36 30 and 25 5 ma from older to young in order of succession corresponding to the major erosional breaks between the middle and upper eocene the upper eocene and the lower oligocene the lower and upper oligocene and the upper oligocene and the lower miocene the sequence boundary underlying sequence 4 was determined to lie within the late oligocene succession and as an age designation could not be assigned it was termed intra sequence boundary isb the first two sequences correspond to relative sea level rises and a normal fault controlled tectonism coincides with them reefal carbonates coarse grained clastics and marine shales with abundant volcanic flows or layers represent the sedimentary facies of these two early sequences the third and fourth sequences correspond to either a decreased relative rise of sea level or a relative still stand of sea level and a sediment induced subsidence related to thermal relaxation provides accommodation prograding delta sediments of varying extent constitute the sedimentary packages of these two sequences the depositional sequence 5 which makes up the uppermost part of the sedimentary succession in the basin corresponds to a relative sea level fall and a tectonic style shaped by lateral and inversion faulting characterizes this period nonmarine alluvial fan fluvial channel and various lagoonal deposits constitute the sedimentary facies of this last sequence porous reefal limestones and shallow marine beach sandstones of sequence 1 and deltaic sandstones of sequences 3 and 4 provide good reservoir rocks for the hydrocarbons produced in the study area the marine shales and marls of the second and the third sequences provide good source rocks as they are rich in disseminated organic matter content although the non marine alluvial and fluvial channel deposits of sequence 5 are good reservoirs they lack effective seals the time interval in which sequence 5 was deposited represents a period of major structural and trap development in the basin

reconciling heterogeneity in crystal zoning data an application of shared characteristic diagrams at chaos crags lassen volcanic center california isotope trace element and textural crystal zoning patterns record heterogeneity in magmatic systems not resolved by whole rock analyses these zoning data are used to infer crystal residence times magma mixing and other magmatic processes in many magmatic systems we present the shared characteristic diagram scd as an organizational framework for crystal zoning data that compares information from different phases and chemical tracers in a common framework an example from chaos crags in the cascade arc produces three main results 1 anorthite zoning profiles in plagioclase have fewer shared characteristics in mafic inclusions than in the host rhyodacite 2 single crystal 87sr 86sr data from previous studies tepley et al 1999 are consistent with more shared history between crystals than in anorthite profiles this difference reflects a more homogeneous distribution of 87sr 86sr than the intensive parameters controlling plagioclase composition 3 the chaos crags system exhibits a layer of heterogeneity in crystal populations that is not represented in whole rock analyses that indicate only simple binary mixing the inconsistency between 87sr 86sr and anorthite zoning data highlights decoupling between compositionally controlled and temperature water controlled zoning in plagioclase from chaos crags

petrological geochemical and statistical analysis of eocene oligocene sandstones of the western thrace basin greece and bulgaria abstract the rhodopian orogen developed since the late cretaceous early eocene during accretionary processes following the closure of the vardar ocean basin a branch of neotethys through a multidisciplinary approach including sandstone petrology and geochemistry of the clastic and volcanoclastic sediments we reconstruct the unroofing history of the rhodopian orogen and characterize the formation and the evolution of the western portions of the thrace basin in greece and bulgaria between the late eocene and oligocene detrital modes of 127 sandstone samples provide evidence of three distinctive petrofacies quartzolithic quartzofeldspathic and volcanoclastic the petrographic composition gives evidence of contributions from three key source areas corresponding to the three main tectonic units the circum rhodope belt the variegated complex ultramafic complex and the gneiss migmatite complex the three petrofacies reflect multiple provenance from different tectonic settings as they evolve from quartzolithic to quartzofeldspathic to volcanoclastic corresponding to collisional orogen crustal block uplift and volcanic arc settings respectively geochemical data on major elements and trace elements are used to discuss the efficacy of tectonic setting discrimination diagrams and compare them to the dickinson model as well as to distinguish and characterize i petrographically homogeneous gneiss supplied subbasins and ii volcanic contributions to sandstone composition multivariate statistical techniques are used to unravel the complex web of factors controlling sediment composition biplot analysis highlights the influence of two independent processes 1 mixing between carbonate and silicate phases and 2 evolution from mafic to felsic source rocks the latter indicates progressively increasing supply rates from deeper crustal levels the compositional evolution of the sandstone suites of thrace basin in ne greece and se bulgaria is strictly related to various geodynamic stages of the rhodope region provenance analysis of thrace sandstones provide an example of the changing nature of orogenic belt sand associate basins through time and may contribute to the general understanding of similar geodynamic settings

age and sr isotopic signature of the catoctin volcanic province implications for subcrustal mantle evolution variations in chemical and sr isotopic signatures of a series of basaltic flows have been correlated with newly mapped stratigraphic sections in the upper precambrian catoctin flood basalts in the central appalachians element mobility through fluid interaction is commonly observed in flows with a well developed fabric but some samples with more massive textures commonly in the cores of thicker flows still retain relict clinopyroxene and igneous textures and show only minor element redistribution five whole rock samples with relict igneous textures and a clinopyroxene mineral separate yield an isochron with an age of 570 36 ma 2sigma and a strontium initial ratio of 0 7035 1 this age is consistent with recent paleontological evidence for a latest precambrian time for catoctin volcanism and along with isotopic age determinations of 680 710 ma for other rift related magmatism suggests either a two stage or a very long protracted episode of continental rifting paleogeographic reconstruction indicates that the original site of eruption for the lavas must have been at least 56 km to the east in the same geographic location from which the mesozoic appalachian tholeiite terrane evolved variations in sr isotopic signatures and differences in major element abundances between these two sequences suggest mantle heterogeneitiesmore that must have developed beneath the eastern north american craton during the interim 400 m y less

a rapid mechanism to remobilize and homogenize highly crystalline magma bodies the largest products of magmatic activity on earth the great bodies of granite and their corresponding large eruptions have a dual nature homogeneity at the large scale and spatial and temporal heterogeneity at the small scale this duality calls for a mechanism that selectively removes the large scale heterogeneities associated with the incremental assembly of these magmatic systems and yet occurs rapidly despite crystal rich viscous conditions seemingly resistant to mixing here we show that a simple dynamic template can unify a wide range of apparently contradictory observations from both large plutonic bodies and volcanic systems by a mechanism of rapid remobilization unzipping of highly viscous crystal rich mushes we demonstrate that this remobilization can lead to rapid overturn and produce the observed juxtaposition of magmatic materials with very disparate ages and complex chemical zoning what distinguishes our model is the recognition that the process has two stages initially a stiff mushy magma is reheated from below producing a reduction in crystallinity that leads to the growth of a subjacent buoyant mobile layer when the thickening mobile layer becomes sufficiently buoyant it penetrates the overlying viscous mushy magma this second stage rapidly exports homogenized material from the lower mobile layer to the top of the system and leads to partial overturn within the viscous mush itself as an additional mechanism of mixing model outputs illustrate that unzipping can rapidly produce large amounts of mobile magma available for eruption the agreement between calculated and observed unzipping rates for historical eruptions at pinatubo and at montserrat demonstrates the general applicability of the model this mechanism furthers our understanding of both the formation of periodically homogenized plutons crust building and of ignimbrites by large eruptions

the thrace basin in the rhodope province of ne greece a tertiary supradetachment basin and its geodynamic implications abstract detailed tectonic analysis and geological mapping on the tertiary molassic and volcanosedimentary rocks of the thrace basin in northeastern greece allowed us to reconstruct the structural evolution of the basin and its geotectonic setting as well as the orientation of the regional paleostress field sedimentation was linked with a calc alkaline and locally shoshonitic magmatism associated with the tertiary syn to late orogenic extension in the rhodope province we interpret the molassic tertiary greek part of the thrace basin as a supradetachment basin associated with sedimentary and volcanic infilling five 5 deformational events t1 to t5 have been distinguished during basin evolution from eocene to quaternary time t1 is related to a low angle normal detachment fault zone with a top to the sw to ssw sense of movement and initial basin subsidence during middle late eocene to oligocene time simultaneously with uplift and exhumation of the footwall rhodope metamorphic rocks stacking and crustal thickening in the more external parts of the hellenic orogenic belt have taken place during the same time t2 evolved during oligocene miocene time it was characterized by transpressional tectonics and formation of large strike slip faults and extensional fractures as well as conjugate thrust faults and folds with n nw or s se sense of movement during miocene pliocene time the third t3 event took place it was responsible for the high angle normal faults dismembering the eocene oligocene molassic basin into neogene grabens the t4 event affected the neogene sediments of the basin with minor reverse strike slip faults as well as normal faults the following t5 event is related to large normal active faults they coincided with the active tectonics of the study area defined by the earthquake focal mechanisms

700 ma rift event in the blue ridge province of virginia a unique time constraint on pre iapetan rifting of laurentia discovery of compositionally distinctive rhyolites produced from a peralkaline volcanic center within the late neoproterozoic robertson river batholith and which are intercalated with terrestrial deposits of the previously undated mechum river formation indicates that rift related sedimentation and magmatism were ongoing at 702 705 ma about 130 m y before the breakup of laurentia recognition of late neoproterozoic age rhyolites in central virginia indicates that rift related magmatism was more widespread along the incipient eastern present coordinates margin of laurentia than previously thought neoproterozoic rifting in the blue ridge province of virginia appears to have been part of a broad scale process that affected most if not all of the preserved margins of laurentia the association of similar extension related terrestrial deposits and compositionally distinctive felsic rocks elsewhere may provide a unique marker for testing proposed predrift configurations of the late neoproterozoic supercontinent rodinia

ophiolitic detritus in cretaceous clastic formations of the dinarides nw croatia evidence from cr spinel chemistry cr spinel is a common heavy mineral in the sandstones of cretaceous synorogenic sedimentary formations of the nw dinarides croatia the rocks occur in isolated exposures in the uplifted basement units of medvednica ivanscica umberak and samobor mountains near zagreb in this area evidence of the early alpine evolution of the dinarides is obscured due to strong dismemberment of pre tertiary tectonostratigraphic units resulting from an intense tectonic history as well as due to the widespread sedimentary cover of the pannonian basin electron microprobe analyses of detrital cr spinels from the ostrc formation reveal that in the early cretaceous the ophiolitic source area was predominantly composed of harzburgite peridotites and associated cumulate rocks which developed in a supra subduction zone setting the supply of cr spinels with the same chemical signature remained dominant until the end of the cretaceous suggesting that exposed remnants of the same ophiolite belt persisted through the cretaceous and or that recycling was significant similarities with data reported from the northern calcareous alps and the transdanubian central range imply that a rather extensive harzburgitic ophiolite belt probably extended along the adriatic margin during the early cretaceous a slight trend of increasing variation in the cr is observed from the early to the latest cretaceous suggesting that the source areas became more heterogeneous with the ongoing cretaceous tectonic evolution differences in cr spinel compositions in two contemporaneous latest cretaceous formations are well in line with existing data on heavy mineral proportions which together identify contrasting hinterland geology for these formations and strongly suggest the coeval existence of two separate basins

u pb and 40ar 39ar geochronology of the symvolon granodiorite implications for the thermal and structural evolution of the rhodope metamorphic core complex northeastern greece north aegean continental lithosphere was thickened by southwest vergent thrusting and continental subduction within the alpine collisional orogen but has subsequently been greatly extended on a northeast southwest axis in the back arc of the hellenic subduction zone crosscutting relationships with two granodiorite bodies emplaced at 31 33 ma the xanthi and eastern vrondou plutons constrain a pre mid oligocene origin of alpine convergent structures in northeastern greece post alpine thinning of the north aegean nappe pile began in earliest miocene time and has been accommodated by a succession of distinct structural systems the earliest of these the symvolon shear zone appears to represent a midcrustal coaxial rupture of the falakron marble series a carbonate platform 5000 m thick that was subducted northeastward beneath high grade rocks of the rhodope metamorphic province in late alpine time zircon and titanite u pb dates and hornblende 40ar 39ar dates obtained in this study constrain the intrusion and incipient mylonitization of the symvolon or kavala granodiorite within the symvolon shear zone at 21 22 ma following its emplacement the symvolon body resided at temperatures between 300 c and 500 c for 5 7 m y during which coaxial deformation may have continued within a widening symvolon rupture the strymon valley detachment a regionally south west dipping low angle normal fault succeeded the symvolon shear zone in middle miocene time southwestward displacement of the serbo macedonian gneiss complex by as much as 80 km in the hanging wall of this detachment facilitated the unroofing of the rhodope metamorphic core complex including the falakron marble series and several tertiary plutons in its footwall biotite and k feldspar 40ar 39ar dates from 11 1 0 2 ma to 15 5 0 3 ma yielded by symvolon granodiorite samples document the cooling of the rhodope core complex below 150 c 300 c during its southwestward progressive exhumation in the footwall of the strymon valley detachment

the time scales of magma mixing and mingling involving primitive melts and melt mush interaction at mid ocean ridges we have studied the chemical zoning of plagioclase phenocrysts from the slow spreading mid atlantic ridge and the intermediate spreading rate costa rica rift to obtain the time scales of magmatic processes beneath these ridges the anorthite content mg and sr in plagioclase phenocrysts from the mid atlantic ridge can be interpreted as recording initial crystallisation from a primitive magma 11 wt mgo in an open system this was followed by crystal accumulation in a mush zone and later entrainment of crystals into the erupted magma the initial magma crystallised plagioclase more anorthitic than those in equilibrium with any erupted basalt evidence that the crystals accumulated in a mush zone comes from both 1 plagioclase rims that were in equilibrium with a sr poor melt requiring extreme differentiation and 2 different crystals found in the same thin section having different histories diffusion modelling shows that crystal residence times in the mush were 11 wt partial equilibration in some crystals can be modelled as starting 1 year prior to eruption but for others longer times are required for complete equilibration this variety of times is most readily explained if the mixing occurred in a mush zone none of the plagioclase phenocrysts from the costa rica rift that we studied have mg contents in equilibrium with their host basalt even at their rims requiring mixing into a much more evolved magma within days of eruption in combination these observations suggest that at both intermediate and slow spreading ridges 1 the chemical environment to which crystals are exposed changes on annual to decadal time scales 2 plagioclase crystals record the existence of melts unlike those erupted and 3 disaggregation of crystal mush zones appears to precede eruption providing an efficient mechanism by which evolved interstitial melt can be mixed into erupted basalts

the structural geometry and evolution of foreland thrust systems northern virginia seismic reflection data reveal that the structural geometry of the central appalachians of northern virginia consists of three distinct thrust systems each thrust system is characterized by a unique internal geometry the blue ridge thrust sheet is a composite thrust sheet composed primarily of imbricated precambrian crystalline rocks it over rode cambrian ordovician carbonates and formed a sheared basement cored fault bend fold thrusts within the sheet may be taconic and earliest alleghanian whereas final thrusting and emplacement of the sheet were probably slightly younger but still early alleghanian the north mountain thrust sheet is characterized by imbricated cambrian ordovician carbonates that are deformed into large amplitude mode ii fault bend folds and fault propagation folds rocks of this sheet were transported more than 60 km across a similar section of carbonates the leading edge of the north mountain thrust sheet was deformed into a fold with a mode ii fault bend fold geometry and was juxtaposed against middle paleozoic rocks the middle paleozoic rocks occur in a ramp across which displacement along the north mountain thrust was transferred to a higher detachment more than 60 km of cover rocks displaced during the emplacement of the north mountain thrust sheet either were transported across this ramp and thrust over a similar section in the western valley and ridge province or were backthrust above the sheet the timing for imbrication and emplacement of the north mountain thrust sheet is probably main phase alleghanian the lower carbonate duplex extends from beneath the blue ridge and north mountain thrust sheets westward across the western valley and ridge province the lower carbonate duplex is characterized by imbricated cambrian ordovician carbonates that form low amplitude fault bend folds this thrust system also probably formed during main phase alleghanian deformation

effects of chaotic advection on the timescales of cooling and crystallization of magma bodies at mid crustal levels we numerically define the thermochemical evolution of a subduction related crystal bearing magmatic mass at mid crustal levels 0 7 gpa 20 25 km two main dynamic mechanisms are considered 1 a pure buoyancy driven system where the convective flow is induced by density changes during magma cooling 2 a buoyancy driven convective system governed by chaotic advection the non newtonian rheology of natural magmas is taken into account linking the herschel bulkley formulation with the results of fractional crystallization experiments of magmas with the same composition and at the same conditions of temperature and pressure of the studied system the latent heat of crystallization is also considered in order to address the thermal release in the system induced by the crystallization results indicate that the development of chaotic advection generates a complex thermochemical evolution of the system speeding up the crystallization process and the timing required to reach the jamming condition relative to the pure buoyancy driven convective system nearly 2 times faster our results have important implications for both the rheological history of the magmatic body and the refilling of shallower magmatic systems in particular 1 a time dependent composition ranging from basalt to andesite can be extracted from an initial basaltic magmatic batch 2 at the attainment of the maximum packing fraction i e just before the jamming condition homogeneous andesitic melts can be potentially extracted from the system and 3 the development of chaotic advection within the system allows for the extraction of andesitic melt in shorter times compared to a buoyancy dominated system

detrital supply from subduction accretion complexes to the eocene oligocene post collisional southern thrace basin nw turkey and ne greece abstract the thrace basin is a large mostly eocene oligocene post collisional sedimentary basin which developed following the closure of the vardar izmir ankara oceanic domain latest cretaceous paleocene sandstone petrologic data framework and heavy mineral analyses and the synthesis of preexisting and new sedimentological observations along representative stratigraphic sections show that the basin fill of the southern thrace basin was mostly derived from the izmir ankara and biga intra pontide subduction accretion complexes to the south proximal facies consistently show northward paleocurrents whereas most paleocurrent indicators measured downcurrent point to an eastward paleoflow likely the result of the deflection of primary gravity flows originated along the southern margin of the basin detrital contributions from the rhodopian basement complex to the west are virtually absent within the southern thrace basin fill conversely rhodopes derived eocene proximal facies in northeastern greece are characterized by a series of coarse grained fan deltas prograding eastward and likely feeding the basin plain turbidites of the depocentral portion of the thrace basin now concealed in the subsurface to the north of our study area arenites of the southern thrace basin are mostly lithic arkoses and arkosic litharenites provenance from the izmir ankara and biga suture zones to the south is characterized by ophiolitic granitoid gneissic low grade metamorphic and extrabasinal carbonate rock fragments as well as by picotite and glaucophane the application of detailed petrographic observations for discriminating paleo vs neovolcanic and penecontemporaneous vs noncoeval terrigenous sands lead to a substantial revision of the geodynamic interpretation of the thrace basin formerly considered a forearc basin a significant penecontemporaneous volcanic component is common in the upper eocene lower oligocene section and can be related to extensive post collisional volcanism following the closure of the vardar izmir ankara ocean the coexistence of pure neovolcanic layers crystal tuffs and cinerites and hybrid arenites rich in penecontemporaneous carbonate grains with sands derived from a continental basement and ophiolitic suites indicates the presence of episutural basins where shallow water carbonates were deposited on top of the exhuming subduction accretion prism these carbonates were mixed with penecontemporaneous neovolcanic and terrigeneous components and redeposited in deeper marine environments

melts mush and more evidence for the state of intermediate to silicic arc magmatic systems understanding the physical state of intermediate to silicic arc magmatic systems is necessary for our petrologic models of these systems researchers have generated a plethora of data geophysical geochronological petrological theoretical over the past few decades these data have changed how we view arc magmatic systems leading to a model of crystal mush that is rejuvenated repeatedly over the lifespan of the magmatic system however much data are either circumstantial or incomplete paterson et al 2016 october issue use a combined set of textural geochemical and temporal data to demonstrate the changing physical state of the tuolumne intrusive complex in california over its 10 million year history they offer evidence for magmatic erosion and recycling along with the potential for a surge growth of the batholith that allows for significant volumes of magma to exist ephemerally under arc volcanoes most intermediate to silicic arc magmas henceforth arc magma are stored 3 km depth so direct observation is impossible instead this question has been approached in four main ways 1 geophysical inspections of active arcs 2 mineral geochronology 3 field observations of plutons and 4 thermal and physical modeling of magmatic systems each of these four avenues has their own strengths and shortcomings many times the interpretation of these data appears to be at odds some overarching observations can be made about what we know of the state of active intermediate to silicic arc magmatic systems geophysical observations such as seismic tomography have yielded little evidence for large bodies of fully molten magma persistently underneath arc volcanoes if anything only small lenses of partial melt are observed at

aegean tectonics strain localisation slab tearing and trench retreat abstract we review the geodynamic evolution of the aegean anatolia region and discuss strain localisation there over geological times from late eocene to present crustal deformation in the aegean backarc has localised progressively during slab retreat extension started with the formation of the rhodope metamorphic core complex eocene and migrated to the cyclades and the northern menderes massif oligocene and miocene accommodated by crustal scale detachments and a first series of core complexes mccs extension then localised in western turkey the corinth rift and the external hellenic arc after messinian times while the north anatolian fault penetrated the aegean sea through time the direction and style of extension have not changed significantly except in terms of localisation the contributions of progressive slab retreat and tearing basal drag extrusion tectonics and tectonic inheritance are discussed and we favour a model 1 where slab retreat is the main driving engine 2 successive slab tearing episodes are the main causes of this stepwise strain localisation and 3 the inherited heterogeneity of the crust is a major factor for localising detachments the continental crust has an inherited strong heterogeneity and crustal scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation the dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate successive slab ruptures from the middle miocene to the late miocene have isolated a narrow strip of lithosphere still attached to the african lithosphere below crete the formation of the north anatolian fault is partly a consequence of this evolution the extrusion of anatolia and the aegean extension are partly driven from below asthenospheric flow and from above extrusion of a lid of rigid crust

variations in the crustal structure beneath western turkey summary we use teleseismic receiver functions to investigate the crustal structure at two locations in westernturkey using seismic data recorded on small arrays of temporary broad band seismographs the results from these analyses are compared with receiver function results from the gdsn station anto on the anatolian plateau in central turkey the crust is 30 km thick in the region of western turkey where active normal faulting reveals present day extension in the upper crust and alkali basaltic volcanism reveals recent extension within the subcrustal lithosphere the crust is 34 km thick further east where crustal extension is still evident but less pronounced in the anatolian plateau which is not currently extending the crust is 38 km thick the level of extension estimated from these measurements of crustal thickness implies a b factor of 1 2 this value agrees with the amount of extension estimated in the upper crust from the integrated seismic strain rate b factor of 1 3 from surface faulting b factor of 1 25 and from the amount of extension in the subcrustal lithosphere estimated from the volcanism b factor 2 all indicating that the extension is approximately uniformly distributed vertically throughout the lithosphere the moho transition in this region appears to thin slightly as the degree of extension increases westwards

tectonic inversion and basement buttressing an example from the central appalachian blue ridge province abstract the structural geometry of the central appalachian blue ridge province is primarily the result of paleozoic contractional deformation however the tye river fault zone in the western blue ridge of central virginia preserves an extensional map pattern these ene wsw striking faults place neoproterozoic to early cambrian volcanic and sedimentary rocks over grenvillian granitic basement detailed mapping cross section restoration and balancing reveals partially inverted faults original half grabens and significantly thicker cover units on hanging walls the orientation and geometry of the tye river fault zone as well as the thickness changes in the cover rocks are inconsistent with extensional reactivation of paleozoic reverse faults during mesozoic rifting the extrusion and deposition of cover rocks was contemporaneous with normal displacement on the tye river fault zone and the formation of rift basins recording 5 crustal extension faults were reactivated as paleozoic contractional structures but an extensional map pattern is generally still preserved regional shortening of 10 20 was accomplished primarily by folding of the cover rocks rather than by reactivation of older faults the basement formed a rigid buttress that controlled the geometry of folding in the cover sequence

glacially influenced sedimentation in the late neoproterozoic mechum river formation blue ridge province virginia the late neoproterozoic ca 700 730 ma mechum river formation is exposed as a structural inlier within grenvillian basement in the blue ridge province of central virginia united states the southern portion of the mechum river belt preserves evidence of glaciomarine sedimentation at the margin and basinward of grounding line fans subaqueous glacial till coarse grained rhythmites and dropstones record the incursion of ice into the basin marine deposition is evidenced by persistent laminations cyclopsams in rhythmically bedded diamictite and possibly by tidally pumped distal turbidites in laminated mudstones glaciomarine sedimentation in the mechum river formation may have been coeval with sturtian rapitan glaciations in northwestern laurentia and australia and provides further evidence for a globally cold climate during the late neoproterozoic

linking fluid dynamics and olivine crystal scale zoning during simulated magma intrusion the compositional zoning styles of natural crystals produced during magma intrusion can be used to investigate the structure of magmatic plumbing systems and its relation to expressions of volcanic unrest seismic deformation volatiles however magma intrusion is a progressive dynamic process and yields non monotonic heterogeneities in physio chemical variables such as complex spatial variations in temperature and liquid composition with time such changes in variables are difficult to incorporate in models of crystal zoning in natural systems here we take another approach by integrating the results of a numerical multiphase simulation of melt arrival in an olivine rich reservoir with models of chemical re equilibration of olivine we evaluate the diversity of chemical zoning styles and the inferred time scales using fe mg diffusion in olivine for a limited range of system geometries and time composition temperature values although our models are still a large simplification of the processes that may occur in natural systems we find several time dependent and systematic relations between variables that can be used to better interpret natural data the proportions of zoned and unzoned crystals the zoning length scales and the calculated diffusion times from the crystals vary with time and the initial position of the crystal in the reservoir these relationships can be used for example to better constrain the plumbing structure and dynamics of mafic eruptions from monogenetic volcanoes by detailed studies of changes in the zoning of the crystal cargo with eruptive sequence moreover we also find that the time scales obtained from modeling of crystals at a single temperature and boundary condition tend to be shorter about 25 than the residence time which could also be tested in natural studies by combining crystal time scale records with monitoring datasets

the mechum river formation virginia blue ridge a record of neoproterozoic and paleozoic tectonics in southeastern laurentia neoproterozoic metasedimentary rocks of the mechum river formation crop out in an elongate northeast southwest trending belt in the central virginia blue ridge province the northwestern contact of the mechum river formation is nonconformable above mesoproterozoic basement whereas the southeastern contact is a set of steeply dipping brittle reverse faults that juxtapose basement against mechum river rocks the internal structure of the belt consists of northwest verging open to tight moderately to steeply plunging asymmetric folds although previous workers have interpreted the outcrop belt of the mechum river formation as a graben formed during laurentian rifting structural relations require that its present geometry is a structural inlier related to paleozoic contractional deformation strain analysis reveals that grain scale deformation processes produced up to 35 percent shortening during foliation development whereas map scale folds account for an additional 30 to 50 percent shortening restoration of the mechum river formation to its pre contractional geometry reveals little about the geometry of the original depositional basin the bounding reverse faults on the east side of the mechum river formation are interpreted as out of sequence structures that developed after regional folding metamorphism and foliation development that may be related to the emplacement of the blue ridge thrust sheet over a tectonic ramp sediment transport indicators are consistent with a source area to the east suggesting that the mechum river formation was separated from similar units in the eastern blue ridge by an asymmetric basement high that may have been produced by block rotation above listric normal faults

a review of tectonics and sedimentation in a forearc setting hellenic thrace basin north aegean sea and northern greece abstract exposure of the forearc region of the north aegean sea greece offers insight into evolving convergent margins the sedimentary fill of the thrace basin during the late eocene to oligocene time provides a record of subduction driven processes such as growth of magmatic arcs and construction of accretionary complexes this large sediment repository received sediment from two sources the southern outboard basin margin reflects the active influence of the exhumed accretionary prism e g pindic cordillera or biga peninsula while the northern inboard margin records the effect of the magmatic arc in the rhodope region the forearc basin sedimentary fills shoal upward into shallow marine strata but are dominated mainly by deep marine facies the depositional trend and stacking pattern are dominated by progradational patterns this trend which is observed in both basin margins is related to tectonic deformation rather than sea level fluctuations additional evidence for this tectonic uplift comes from the backstripping analysis the accretionary complex provided material into the forearc basin this material was transported northeast and formed a sand rich turbidity system that evolved upslope into shallow marine deposits stratigraphic data indicate that this turbidity system exhibits a successive landward inboard migration of the depocenter provenance data utilizing sandstone petrography conglomerate clast composition and bulk rock geochemistry suggest that this system reflects an increased influx of mafic material into the basin volcanic arc derived material was transported south and east and accumulated in deep marine settings both stratigraphic and provenance data indicate a seaward outboard migration of the basin depocenter and a significant increase in felsic detritus into the forearc

palaeomagnetism in greece cenozoic and mesozoic components and their geodynamic implications abstract an important number of palaeomagnetic data have been obtained in greece during the last 20 years these data can be schematically divided into two groups according to their age when plate movements are fairly well constrained the cenozoic provides a dense network of palaeomagnetic directions the general pattern displays eastward declinations broadly distributed over a large distance from the ionian islands to the western greek rhodope and westward declinations less accurately constrained in space and time in the southern and eastern aegean and in western anatolia emphasis is given to the evaluation of this dataset by comparing it with new concepts of the regional tectonics in the mesozoic palaeozoic more scarcely covered reliable information is provided about latitudinal movements resulting in a suggested palaeolatitude of 15 20 n for almost all studied areas a model proposing prevailing counterclockwise rotations in the internal hellenides and strong clockwise rotations for the external hellenides appears plausible finally issues for future research are outlined for example mio pliocene formations from central greece the pindos ophiolites and palaeocene upper cretaceous data should receive further attention

low angle detachment geometry of the late precambrian cambrian appalachian ouachita rifted margin of southeastern north america the late precambrian cambrian rifted margin of southeastern north america is framed by northeast striking rift segments offset by northwest striking transform faults palinspastically restored structural profiles thickness and composition of synrift rocks and thickness of postrift strata vary along the trace of the rifted margin the distribution of these variables suggests application of low angle detachment models of continental rifting including specific recognition of upper plate margins lower plate margins transform faults that offste the rift and transform faults that bound domains of oppositely dipping low angle detachments the trace of the mississippi valley rough creek rome intracratonic fault system suggests incipient rift segments offset by a transfer fault system

melt inclusions in detrital spinel from the se alps italy slovenia a new approach to provenance studies of sedimentary basins detrital spinel is a widespread heavy mineral in sandstones from the maastrichtian middle eocene sedimentary basins in the se alps chemistry of detrital spinels from the claut clauzetto and julian basins n italy and nw slovenia is used to constrain petrological and geochemical affinities and tectonic provenance of the source rocks in addition we have analysed melt inclusion compositions in the detrital volcanic spinels to better constrain the nature of their parental magmas this is the first study of melt inclusions in detrital spinels two principal compositional groups of detrital spinels are recognised based on their tio2 and fe2 fe3 one derived from peridotites the other from basaltic volcanics peridotitic spinels are more abundant and have tio2 0 2 better distinguish the differences between the compositions of their host spinels and help to further clarify the geodynamic provenance of extrusive source rocks several compositional groups of melt inclusions have been recognised and represent diverse magmatism of marginal basins including morb and subduction related geochemical types as well as magmas characteristic of early continental rifting these results combined with the data on regional ophiolitic complexes and tectonic reconstructions favour the internal dinarides of yugoslavia as a possible source area for the se alps sediments

eocene stratigraphic evolution of the thrace basin turkey abstract this paper explains the primary basin evolution processes of the thrace basin which started opening during early middle eocene stratigraphic and tectonic models for different parts of the basin have been constructed and basin scale stratigraphic correlations were established by using outcrop well and seismic data initial deposits of eocene in the thrace basin show irregular depositional patterns associated with various lithofacies deposited under the control of various tectonostratigraphic settings first a compressional regime started after the collision of the sakarya continent with the rhodope pontide fragment in late cretaceous paleocene enabled initiation of transtensional stress which was responsible for the creation of necessary accommodation space for deposition of the initial thrace sediments in the northern and eastern part of the thrace basin the lower middle eocene hamitabat formation was deposited in this kind of transtensional setting and can be divided into various lithostratigraphic units an unconformity identified within hamitabat formation from seismic and well data divides it to two major units in early eocene the thrace basin was deepening eastwards and deposition was initiated between finger shaped paleo highs aligned in an e w direction thus synchronous erosional and depositional events in different parts of the basin formed various facies associated with a variety of depositional environments during the same time interval a regional unconformity at the base of lower eocene between karaagac and hamitabat formations can be correlated from south to north moreover the unconformity between lower middle eocene deposits and the middle eocene limestones of southern thrace is correlative with the unconformity between the hamitabat formation and overlying upper eocene limestones at northern regions this unconformity has a correlative conformity within the gazikoy or kesan formations in central thrace where continuous deposition took place during eocene without interruption

multiple generations of extensional detachments in the rhodope mountains northern greece evidence of episodic exhumation of high pressure rocks abstract an integrated structural and petrological study shows that exhumation of high rocks of the rhodope occurred in several pulses the structurally uppermost kimi complex recording an early cretaceous high p metamorphism was exhumed between about 65 and 42 ma the sidironero kardamos and kechros complexes that record early tertiary high metamorphism at least 19 kbar at 700 c were exhumed at 42 30 ma exhumation occurred with isothermal decompression strain episodes depict thrusting of medium high grade above lower grade high p rocks syn thrusting extension and post thrusting extension polyphase extension created several generations of detachment zones which in sum excise about 20 km of material within the crustal profile this reduction in crustal thickness is consistent with a reduction of the present crustal thickness from more than 40 km to less than 30 km in the eastern rhodope we mapped the post thrusting xanthi low angle detachment system over 100km from its break up zone above the sidironero complex central rhodope into the eastern rhodope this detachment shows an overall ese dip with a ramp and flat geometry cutting across the earlier thrust structures the kimi complex is the hanging wall of all synand post thrusting extensional systems on top of the kimi complex marine basins were formed from the lutetian c 48 43 ma through the oligocene during extension successively at c 26 to 8 ma the thasos pangeon metamorphic core complexes were exhumed in these times representing the early stages of aegean back arc extension the strymon and thasos detachment systems caused crustal thinning in the western rhodope renewed heating of the lithosphere associated with magmatism and exhumation of hot middle crust from beneath the sidironero complex occurred we focusoxn the geometry timing and kinematics of extension and contraction structures related to the 42 30 ma interval and how these exhumed high p rocks we interpret high rocks exhumed in this interval as a window of the apulian plate beneath the earlier in the cretaceous accreted kimi complex

a fore arc origin for the thrace basin nw turkey hydrocarbon bearing thrace basin occupies much of the european part of turkey the middle eocene to oligocene sequence in the centre of the basin exceeds 9 km in thickness based on the stratigraphy structure and the regional context of this basin we propose that it developed as a fore arc basin between the medial eocene and the oligocene above the northward subducting intra pontide ocean its post miocene history has been dominated mainly by wrench tectonics resulting from the activity of the now deactivated northwestern strand of the present day north anatolian fault zone

evolution of the murphy synclinorium southern appalachian blue ridge usa abstract the western blue ridge allochthon of the southern appalachians is dominated by the 180 km long murphy synclinorium paired with anticlinoria to the northwest these are first generation northwest overturned doubly plunging large amplitude and wavelength 10 km isoclinal folds contemporaneous with peak neo acadian orogeny visian 335 345 ma regional metamorphism the synclinorium folds a regional unconformity separating neoproterozoic rift and lower paleozoic drift sequences from a younger successor basin sequence strain analysis of metaconglomerates from lithologic groups above and below the unconformity indicates coaxial low to moderate oblate to nearly plane strain in both groups the synclinorium evolved via nnw sse crustal shortening 32 combined with orthogonal nne ssw sub horizontal flow stretching 35 45 sub parallel to the developing fold axes differences in metamorphic grade and paleodepth 10 17 km of the exposed synclinorium had essentially no effect on strain magnitudes retrodeformation of the embedded regional unconformity reveals a very broad synclinal warping of the rift and drift facies units predating superposition of the murphy synclinorium suggesting tectonic inheritance in the latter structure s origin the earlier mild deformation is post early cambrian and may represent the only vestige of the dynamic effects of the middle ordovician taconic orogeny to be found in this region

coeval plutonism and metamorphism in a latest oligocene metamorphic core complex in northwest turkey a metamorphic core complex of latest oligocene age crops out in the kazdag mountain range in northwest turkey the footwall of the core complex consists of gneiss amphibolite and marble metamorphosed at 5 1 kbar and 640 50 c the average muscovite and biotite rb sr ages from the gneisses are 19 ma and 22 ma respectively and imply high temperature metamorphism during latest oligocene times the hangingwall is made up of an unmetamorphosed lower tertiary oceanic accretionary melange with upper cretaceous eclogite lenses the hangingwall and footwall are separated by an extensional ductile shear zone two kilometres thick mylonites and underlying high grade metamorphic rocks show a n trending mineral lineation with the structural fabrics indicat ing down dip top to the north shear sense the shear zone the accretionary melange and the high grade metamorphic rocks are cut by an undeformed granitoid with a 21 ma rb sr biotite age analytically indistinguishable from the rb sr biotite ages in the surrounding footwall gneisses the estimated pressure of the metamorphism and that of the granitoid emplacement indicate that the high grade metamorphic rocks were rapidly exhumed at 24 ma from a depth of 14 km to 7 km by activity along the shear zone the subsequent exhumation of the metamorphic rocks to the surface occurred during pliocene quaternary times in a transpressive ridge between two overstepping fault segments of the north anatolian fault zone the high grade metamorphic rocks of the kazdag range are surrounded by voluminous calc alkaline volcanic and plutonic rocks of late oligocene early miocene age which formed above the northward dipping hellenic subduction zone the magmatic arc setting of the core complex and stratigraphic evidence for subdued topography in northwest turkey prior to the onset of extension suggest that the latest oligocene regional extension was primarily related to the roll back of the subduction zone rather than to the gravitational collapse

cover stratigraphy and structure of the southernmost external basement massifs in the appalachian blue ridge evidence for two stage late proterozoic rifting

u pb geochronology of zircon and monazite from mesoproterozoic granitic gneisses of the northern blue ridge virginia and maryland usa abstract mesoproterozoic granitic gneisses comprise most of the basement of the northern blue ridge geologic province in virginia and maryland lithology structure and u pb geochronology have been used to subdivide the gneisses into three groups the oldest rocks group 1 are layered granitic gneiss 1153 6 ma hornblende monzonite gneiss 1149 19 ma porphyroblastic granite gneiss 1144 2 ma coarse grained metagranite about 1140 ma and charnockite 1145 ma these gneisses contain three proterozoic deformational fabrics because of complex u pb systematics due to extensive overgrowths on magmatic cores zircons from hornblende monzonite gneiss were dated using the sensitive high resolution ion microprobe shrimp whereas all other ages are based on conventional u pb geochronology group 2 rocks are leucocratic and biotitic varieties of marshall metagranite dated at 1112 3 ma and 1111 2 ma respectively group 3 rocks are subdivided into two age groups 1 garnetiferous metagranite 1077 4 ma and quartz plagioclase gneiss 1077 4 ma 2 white leucocratic metagranite 1060 2 ma pink leucocratic metagranite 1059 2 biotite granite gneiss 1055 4 ma and megacrystic metagranite 1055 2 ma groups 2 and 3 gneisses contain only the two younger proterozoic deformational fabrics ages of monazite separated from seven samples indicate growth during both igneous and metamorphic thermal events however ages obtained from individual grains may be mixtures of different age components as suggested by backscatter electron bse imaging of complexly zoned grains analyses of unzoned monazite imaged by bse and thought to contain only one age component from porphyroblastic granite gneiss yield ages of 1070 1060 and 1050 ma the range of ages of monazite not reset to a uniform date indicates that the grenville granulite event at about 1035 ma did not exceed about 750 c lack of evidence for 1110 ma growth of monazite in porphyroblastic granite gneiss suggests that the short hill fault might be a grenvillian structure that was reactivated in the paleozoic the timing of proterozoic deformations is constrained by crystallization ages of the gneissic rocks d1 occurred between about 1145 and 1075 ma or possibly between about 1145 and 1128 ma d2 and d3 must be younger than about 1050 ma ages of mesoproterozoic granitic rocks of the northern blue ridge are similar to rocks in other grenville terranes of the eastern usa including the adirondacks and hudson highlands however comparisons with conventional u pb ages of granulite grade rocks from the central and southern appalachians may be specious because these ages may actually be mixtures of ages of cores and overgrowths

constraints on the petrogenesis of evros ophiolite extrusives ne greece abstract the incomplete and dismembered evros ophiolite is situated in thrace ne greece and belongs to the circum rhodope belt crb its age is considered to be jurassic lower cretaceous the geotectonic setting of the ophiolite was a volcanic arc marginal basin system in the vardar oceanic realm in the uppermost level of the ophiolitic sequence volcanic and pyroclastic rocks of tholeiitic composition are underlain massive and pillow lavas with a few tuffaceous rocks and lava breccia all these rocks were involved in intense deformation and low grade metamorphic events during and after their formation the underlying tholeiites were regionally metamorphosed to greenschist facies lower metavolcanics lmv whereas the upper lavas were extensively recrystallized mainly by ocean floor metamorphism of prehnite pumpellyite facies upper metavolcanics ree data and wide ranges in zr y ti zr and al ti ratios suggest that the parental magma of the upper metavolcanics underwent extensive fractional crystallization tholeiitic basalts and mainly basaltic andesites to andesites were formed at the initial stages of the differentiation by crystal fractionation which involved olivine cr spinel clinopyroxene and occasionally plagioclase subordinate dacites to rhyodacites were created when plagioclase became the main fractionating phase the oxygen fugacity remained nearly stable during the formation of the main volume of the rock association but it changed when rhyodacitic rocks started to crystallize the protoliths of the upper metavolcanics was boninitic produced in the forearc area by about 30 partial melting of an already depleted mantle source this partial melting was induced by aqueous fluids and or melts from the subducting oceanic crust and its sedimentary cover the depleted mantle source of the upper metavolcanics was the residue of an earlier partial melting event that had generated the magma of the lower metavolcanic protoliths in an extensional regime

short eruption window revealed by absolute crystal growth rates in a granitic magma giant volcanic eruptions occur when large volumes of magma accumulate in crustal reservoirs and do not cool and crystallize to form a solid pluton of rock within the crust geochronological dating of a pluton from elba italy shows that the magma solidified in the crust within just 10 40 thousand years of being injected into the crust implying that the time window for an eruption was short

rapid remobilization of magmatic crystals kept in cold storage we lack thermal histories for magma reservoirs but here the magma under mount hood oregon usa is shown to have been too cold to mobilize for most of the time it has been stored which implies that magma mobilizes at which point it can be imaged geophysically very quickly prior to eruption this paper presents a novel approach to constraining the thermal history of the subsurface magma bodies that feed eruptions by combining temporal information from a variety of sources kari cooper and adam kent combine timescales derived from uranium series disequilibria textural information and trace element zoning in crystals they show that at mount hood oregon only a small fraction of the total storage duration has been spent at temperatures above the critical crystallinity the point at which magma is easily mobilized they conclude that largely liquid bodies that could be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption the processes involved in the formation and storage of magma within the earth s upper crust are of fundamental importance to volcanology many volcanic eruptions including some of the largest result from the eruption of components stored for tens to hundreds of thousands of years before eruption1 2 3 although the physical conditions of magma storage and remobilization are of paramount importance for understanding volcanic processes they remain relatively poorly known4 5 eruptions of crystal rich magma are often suggested to require the mobilization of magma stored at near solidus conditions6 7 8 however accumulation of significant eruptible magma volumes has also been argued to require extended storage of magma at higher temperatures7 8 9 what has been lacking in this debate is clear observational evidence linking the thermal and therefore physical conditions within a magma reservoir to timescales of storage that is thermal histories here we present a method of constraining such thermal histories by combining timescales derived from uranium series disequilibria crystal sizes and trace element zoning in crystals at mount hood oregon usa only a small fraction of the total magma storage duration at most 12 per cent and probably much less than 1 per cent has been spent at temperatures above the critical crystallinity 40 50 per cent at which magma is easily mobilized partial data sets for other volcanoes also suggest that similar conditions of magma storage are widespread and therefore that rapid mobilization of magmas stored at near solidus temperatures is common magma storage at low temperatures indicates that although thermobarometry calculations based on mineral compositions may record the conditions of crystallization they are unlikely to reflect the conditions of most of the time that the magma is stored our results also suggest that largely liquid magma bodies that can be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption

the rhodope zone as a primary sediment source of the southern thrace basin ne greece and nw turkey evidence from detrital heavy minerals and implications for central eastern mediterranean palaeogeography detrital heavy mineral analysis coupled with a regional geological review provide key elements to re evaluate the distribution of the rhodope metamorphic zone se europe in the region and its role in determining the evolution of the thrace basin we focus on the eocene oligocene sedimentary successions exposed in the southern thrace basin margin to determine the dispersal pathways of eroded crustal elements of both oceanic and continental origins as well as their different contributions through time lithological aspects and tectonic data coupled with geochemistry and geochronology of metamorphic terranes exposed in the area point to a common origin of tectonic units exposed in nw turkey biga peninsula with those of ne greece and se bulgaria rhodope region the entire region displays 1 common extensional signatures consisting of comparable granitoid intrusion ages and a ne sw sense of shear 2 matching zircon age populations between the metapelitic and metamafic rocks of the circum rhodope belt ne greece and those of the camlica kemer complex and cetmi melange exposed in nw turkey detrital heavy mineral abundances from eocene oligocene sandstones of the southern thrace basin demonstrate the influence of two main sediment sources mostly of ultramafic ophiolitic and low to medium grade metamorphic lithologies plus a third volcanic source limited to the late eocene oligocene detrital cr spinel chemistry is used to understand the origin of the ultramafic material and to discriminate the numerous ultramafic sources exposed in the region compositional and stratigraphic data indicate a major influence of the metapelitic source in the eastern part gallipoli peninsula during the initial stages of sedimentation with increasing contributions from metamafic sources through time on the other hand the western and more external part of the southern thrace margin gokceada samothraki and limnos displays compositional signatures according to a mixed provenance from the metapelitic and metamafic sources of the circum rhodope belt camlica kemer complex and cetmi melange tectonic restoration and compositional signatures provide constraints on the palaeogene palaeogeography of this sector of the central eastern mediterranean region

provenance of sediments during subduction of palaeotethys detrital zircon ages and olistolith analysis in palaeozoic sediments from chios island greece abstract detrital zircon geochronology and analysis of fossiliferous olistoliths from chios island greece are used here to constrain terrane accretion processes and the provenance of crustal sources for sediments during the subduction of a branch of the palaeotethys ocean u pb ages obtained by ion microprobe shrimp ii analyses of detrital zircons from a carboniferous greywacke belonging to the tectonostratigraphic lower unit of chios gave major age groups of 2150 1890 ma 640 540 ma 505 475 ma and 365 322 ma detrital zircons from a permian triassic sandstone yielded prominent age clusters of 2200 1840 ma 1100 910 ma 625 560 ma and 385 370 ma the lack of zircon ages between 1 8 and 1 1 ga in both samples coupled with the occurrence of ca 2 ga old zircons imply a northern gondwana nw africa source the conodont fauna recovered from an orthoceras bearing limestone lens from the carboniferous succession of the lower unit indicates a late silurian age the fauna is typical of the ludfordian polygnathoides siluricus conodont zone the material has a conodont colour alteration index cai of about 1 2 indicating very low grade thermal alteration of less than 100 c the closest localities with similar conodont bearing limestones are to be found in the balkan region and in the istanbul zone of northern turkey the occurrence of orthoceras limestone can be used as an indicator of palaeosource reconstruction our new zircon ages in conjunction with provenance analysis of silurian to lower carboniferous olistoliths strongly suggest that the clastic succession of chios received its detritus from basement rocks of the sakarya microcontinent in western turkey and time and facies equivalents of palaeozoic units from the istanbul zone in northern turkey and the balkan region due to subduction of a branch of palaeotethys close to the southern active margin of eurasia in late palaeozoic times the multidisciplinary approach of this study underlines the importance of terrane accretion during stepwise closure of palaeotethys

reply to the discussion by maravelis and zelilidis on unravelling provenance from eocene oligocene sandstones of the thrace basin north east greece by caraccioloet al 2011 sedimentology 58 1988 2011

westward propagation of the north anatolian fault into the northern aegean timing and kinematics we present new evidence for the propagation processes of the north anatolian fault folding in the dardanelles straits region allows us to document the timing of the deformation preceding and the finite displacement after the passage of the propagating tip of the fault the accuracy of the observations is due to interplay between deformation and the sea level changes in the mediterranean the well known messinian regression followed by the pliocene transgression the long term kinematics around the sea of marmara pull apart total displacement of about 85 km over the past 5 m y is similar to the present day kinematics deduced from space geodesy at a larger scale westward propagation of the north anatolian fault over nearly 2000 km in the past 10 m y appears to be associated with strain recovery suggesting that the continental lithosphere retains long term elasticity

rapid early middle miocene exhumation of the kazdag massif western anatolia apatite fission track analyses indicate that the kazdag massif in northwestern anatolia was exhumed above the apatite partial annealing zone between 20 and 10 ma i e early middle miocene with a cluster of ages at 17 14 ma the structural analysis of low angle shear zones high angle normal faults and strike slip faults as well as stratigraphic analysis of upper plate sedimentary successions and previous radiometric ages point to a two stage structural evolution of the massif the first stage encompassing much of the rapid thermal evolution of the massif comprised late oligocene early miocene low angle detachment faulting and the associated development of small supradetachment grabens filled with a mixture of epiclastic volcaniclastic and volcanic rocks kucukkuyu fm the second stage plio quaternary has been dominated by i strike slip faulting related to the westward propagation of the north anatolian fault system and ii normal faulting associated with present day extension this later stage affected the distribution of fission track ages but did not have a component of vertical normal movement large enough to exhume a new partial annealing zone the thermochronological data presented here support the notion that neogene extensional tectonism in the northern aegean region has been episodic with accelerated pulses in the early middle miocene and plio quaternary

stratigraphy and tectonics of the virginia north carolina blue ridge evolution of a late proterozoic early paleozoic hinge zone late proterozoic 690 570 ma through ordovician rocks of the virginia north carolina blue ridge and valley and ridge record the evolution of an eastward facing passive margin and its subsequent deformation during continent arc collision taconic orogeny comparison of blue ridge stratigraphy with modern rifts and passive margins suggests that late proterozoic rifting involved substantial crustal attenuation in the eastern blue ridge the axial zone of the blue ridge from central virginia southward is occupied by a major fault system hayesville fries rock fish valley fault contrasts between rocks deposited east and west of this fault suggest that it is a reactivated hinge zone separating highly attenuated continental crust to the east from continental crust of more normal thickness to the west during rifting normal faulting and rapid subsidence of attenuating crust in the eastern blue ridge produced rift basins in which deep water clastic and volcanic rocks accumulated lynchburg group ashe formation landward of the hinge zone in the western blue ridge mainly terrestrial to shallow water clastic and volcanic rocks were deposited in a series of subaerial rift basins swift run catoctin grandfather mountain mount rogers formations the hinge zone not only controlled depositional patterns throughout the rift and passive margin history but it was also reactivated during the taconic collision when attenuated crust and its cover were thrust westward over the shelf edge turbidite dominated rift sequences of the eastern blue ridge are unlike typical rift deposits which are characterized by predominantly subaerial and shallow water sedimentation deep water rifts may be common on attenuated crust as in the bay of biscay however they are poorly known from the stratigraphic record because of their susceptibility to destruction during orogeny

comment on maravelis et al accretionary prism forearc interactions as reflected in the sedimentary fill of southern thrace basin lemnos island ne greece

open system dynamics and mixing in magma mushes magma in earth s crust is in a crystal rich mushy state yet must be fluidized before eruptions numerical simulations show that rapid injection of new magma into a reservoir creates a mixing bowl of fluid and crystals that are able to erupt

extensional and contractional deformation in the blue ridge province virginia basement rocks of the blue ridge anticlinorium in central and northern virginia were involved in two temporally distinct deformation episodes the older event is characterized by a locally pervasive low strain fabric and high strain shear zones a preferred grain shape orientation in recovered quartz feldspar and biotite combined with a poorly developed symmetric quartz c axis pattern defines the low strain fabric kinematic indicators are typically symmetric but where asymmetric they consistently indicate top down to the southeast extensional motion discrete shear zones are within and close to late proterozoic plutons kinematic evidence fron these zones records large noncoaxial strains also with a down to the southeast extensional shear sense feldspar microstructures range from cataclastic fractures to complete recovery suggesting that deformation occurred at greenschist to amphibolite grade both low strain foliations and high strain shear zones are cut by paleozoic thrust related tectonites on the basis of kinematic evidence and spatial association with late proterozoic plutons cross cutting relations with thrust related structures and regional geologic relations we suggest that extensional deformation is related to late proterozoic rifting of the laurentian margin the kinematic histories of the rockfish valley fault zone and related shear zones appear to be relatively simple and consistent with paleozoic west to northwest directed thrusting the rockfish valley fault zone does not separate distinctly different basement terranes and thus its displacement is thought to be small mylonitic rocks from this fault zone display crystal plastic deformation in quartz and cataclastic deformation in feldspars under lower to middle greenschist facies conditions solution transfer processes were an important deformation mechanism in these tectonites thrust related mylonitic rocks are overprinted by related cataclasite and semibrittle shear bands suggestive of a transition toward more brittle deformation as the thrust system cut higher in the crust the rockfish valley fault zone appears to predate the formation of the south mountain cleavage in the valley and ridge province but it may be part of a lengthy progressive thrust related deformation

plagioclase preferred orientation in layered mylonites evaluation of flow laws for the lower crust thesis s m joint program in marine geology and geophysics massachusetts institute of technology dept of earth atmospheric and planetary sciences and the woods hole oceanographic institution 2008

record of a palaeogene syn collisional extension in the north aegean region evidence from the kemer micaschists nw turkey in nw turkey the medium grade kemer micaschists of the biga peninsula record ne directed extension related to ductile to brittle ductile shearing during the palaeogene period a lower limit for their exhumation is given by the late maastrichtian age of the hp lt metamorphism of a similar nearby area camlica micaschists an upper limit is given by the early eocene intrusion age of the post kinematic karabiga granitoid dated as 52 7 1 9 ma using the u pb la icp ms method on xenotime correlations with the northeasterly rhodope region and integration into the geodynamic regional frame indicate that the kemer micaschists experienced an extensional deformation connected to a collisional context in latest cretaceous early tertiary times the kemer micaschists therefore represent a new area the first in turkey which suffered synorogenic extension in the north aegean domain at the very beginning of tertiary times

replenishment of magma chambers by light inputs magma chambers particularly those of basaltic composition are often replenished by an influx of magma whose density is less than that of the resident magma this paper describes the fundamental fluid mechanics involved in the replenishment by light inputs if denotes the uniform density of the resident magma and that of the input the situation is described by the reduced gravity g g the volume flux q and the viscosities of the resident and input magmas e and i respectively the nondimensional reynolds numbers ree g q3 1 5 e and rei g q3 1 5 i and chamber geometry then completely specify the system for sufficiently low values of the two reynolds numbers each less than approximately 10 the input rises as a laminar conduit for larger values of the reynolds numbers the conduit may break down and exhibit either a varicose or a meander instability and entrain some resident magma at still larger reynolds numbers the flow will become quite unsteady and finally turbulent the values of the reynolds numbers at which these transitions occur have been documented by a series of experiments with water glycerine and corn syrup if the input rises as a turbulent plume significant entrainment of the resident magma can take place the final spatial distribution of the mixed magma depends on the geometry of the chamber if the chamber is much wider than it is high the mixed magma forms a compositionally stratified region between the roof and a sharp front above uncontaminated magma in the other geometrical extreme the input magma is mixed with almost all of the resident magma if the density of the resident magma is already stratified the input plume may penetrate only part way into the chamber even though its initial density is less than that of the lowest density resident magma the plume will then intrude horizontally and form a hybrid layer at an intermediate depth this provides a mechanism for preventing even primitive basaltic magmas of minimum density from erupting at the surface by conducting an experiment using aqueous solutions we show that entrainment can lead to crystallization of the magma in the input plume by making it locally supersaturated all these effects are discussed and illustrated by photographs of laboratory experiments

provenance and tectonic setting of carboniferous triassic sandstones from the karaburun peninsula western turkey a multi method approach with implications for the palaeotethys evolution abstract carboniferous triassic siliciclastic sediments of the karaburun peninsula in western turkey were studied to unravel their provenance and the tectonic setting of depositional basins within the palaeotethyan realm a set of complementary techniques including petrography bulk rock geochemistry and single grain analysis of rutile garnet and chrome spinel were applied to provide a diverse dataset for testing existing palaeotectonic models using both established and recently published diagrams we show that tectonic discrimination diagrams of siliciclastic sediments based on major and trace element whole rock geochemical data do yield ambiguous results and are only partly in accordance with regional geological events chondrite normalised ree patterns of upper palaeozoic samples are characterised by enrichment of lree and a flat trend towards hree the degree of fractionation allows for discrimination between sandstones of karaburun lan ybn 8 00 14 79 and adjacent greek islands of chios 5 82 9 23 and inousses 7 40 9 95 petrographic observations and compositional data from single grain analysis indicate significant supply from low to medium grade metamorphic rocks of generally felsic character and minor input of ultra mafic detritus detrital chrome spinels in the lower triassic gerence formation are different in composition and shape compared to chrome spinels in carboniferous permian sandstones they were derived from a very proximal source and exhibit variable but generally high cr and mg numbers consistent with chrome spinels from podiform chromitites that have been formed in an intra oceanic back arc setting above a supra subduction zone we conclude that most of the carboniferous triassic successions were deposited along the southern active margin of eurasia in a continental arc environment during the time period when palaeotethys diminished in size and finally vanished large volumes of detritus were probably derived from rock units located in the present day balkan region and the sakarya zone or equivalent successions that are not present anymore

reply to comment by caracciolo et al on maravelis et al 2015 accretionary prism forearc interactions as reflected in the sedimentary fill of southern thrace basin lemnos island ne greece

dynamic plumbing system beneath volcanoes revealed by kinetic modeling and the connection to monitoring data an example from mt etna abstract our ability to monitor volcanoes using seismic signals ground deformation gas fluxes or other ground and satellite based observations as well as our understanding of melt reservoirs that feed eruptions have evolved tremendously in recent years the complex plumbing systems that are thought to feed eruptions are however difficult to relate to the monitoring signals here we show that the record preserved in compositional zoning of erupted minerals may be used to reconstruct sections of the plumbing system kinetic modeling of such zoning can yield information on the residence time of magma in different segments of the plumbing systems this allows a more nuanced evaluation of the link between observed monitoring signals or eruption styles and the magmatic processes and movement of batches of melts at depth the approach is illustrated through a study of the compositional zoning recorded in olivine crystals from the 1991 1993 se flank eruption products of mt etna sicily the zoning patterns in crystals reveal that the plumbing system of the volcano consisted of at least three different magmatic environments between which magma was transported and mixed in the year or two preceding the start of eruption quantification of this history indicates that two main pathways of melt migration and three timescales dominated the dynamics of the system combination of this information with the timing of observation of various monitoring signals allows a reconstruction of the dynamic evolution of this section of the plumbing system during the early stages of the 1991 1993 eruption it is seen for example how the migration of melt through the same sections of the plumbing system can cause pre eruptive triggering enhance strombolian activity and through the ensuing eruption cleanse and flush the plumbing system different kinds of mixing occur simultaneously at different sections of the plumbing system on different timescales a few days up to two years

k feldspar megacryst accumulations formed by mechanical instabilities in magma chamber margins asha pluton nw argentina abstract the asha pluton the oldest unit of the san blas intrusive complex early carboniferous exhibits impressive examples of magmatic structures formed by accumulation of k feldspar megacrysts enclaves and schlieren almost all recognized structures are meter scale vertically elongate bodies of variable shapes defined as fingers trails drips and blobs they preferentially developed near the external margin of the asha pluton and generally are superimposed by chamber wide magmatic fabrics they mostly have circular or sub circular transverse sections with an internal fabric defined by margin parallel inward dipping concentric foliation and steeply plunging lineation at upper parts and flat foliation at lower parts the concentration of megacrysts usually grades from upper sections where they appear in a proportion similar to the host granite to highly packed accumulations of k feldspar along with grouped flattened enclaves at lower ends these features suggest an origin by downward localized multiphase magmatic flow narrowing and log jamming and gravitational sinking of grouped crystals and enclaves with compaction and filter pressing as main mechanisms of melt removal crystal size distribution analysis supports field observations arguing for a mechanical origin of accumulations the magmatic structures of the asha pluton represent mechanical instabilities generated by thermal and compositional convection probably owing to cooling and crystallization near the pluton margins during early stages of construction of the intrusive complex

the effect of early alpine thrusting in late stage extensional tectonics evidence from the kulidzhik nappe and the pelevun extensional allochthon in the rhodope massif bulgaria abstract in the northeastern rhodope massif the kulidzhik nappe exposes a unique juxtaposition of a high grade basement allochthon onto a low grade mesozoic unit and the counterpart pelevun extensional allochthon belonging to the same unit the kulidzhik nappe tectonostratigraphy comprises structurally upward i a lower unit consisting of high grade basement orthogneisses ii a low grade greenschist phyllite unit consisting of jurassic extrusive rocks and metasedimentary rocks iii the nappe allochthon built by the lower high grade basement unit orthogneisses and iv eocene sedimentary rocks and oligocene volcanic cover rocks the pelevun extensional allochthon is heterogeneous and consists of mesozoic low grade unit marbles and greenschists and the upper high grade basement unit we have combined structure and kinematics with lithological information and 40 r 39 r geochronology to constrain the tectonic evolution and regional significance of the kulidzhik nappe and the pelevun extensional allochthon mineral chemistry reveals igneous phases of the granitic protolith of the allochthonous orthogneisses with textures related to ductile deformation and metamorphism higher than 500 c their trace element patterns are indistinguishable from the high grade basement orthogneisses in the eastern rhodope mineral chemistry of the metamorphic assemblage in the underlying greenschists is consistent with medium grade greenschist facies metamorphism at temperatures well below 450 c whose geochemistry defines transitional morb to iat affinities with a strong arc imprint the greenschist s composition is extremely similar to the composition of a supra subduction zone jurassic arc extrusive suite that occurs in the low grade unit of the eastern rhodope the structural elements in all of the tectono metamorphic units and the nappe surface indicate top to the nne tectonic transport deformation evolved from ductile to brittle conditions coevally with a progressive decrease from lower amphibolite to weak greenschist facies metamorphism towards the structural top two klippen gave plateau 40 r 39 r mica ages of 154 23 0 66 ma and 156 70 0 81 ma respectively which reflect cooling following the greenschist facies event below 350 c during shallow crustal level thrust emplacement and exhumation of the kulidzhik allochthon the hanging wall pelevun extensional allochthon preserves an internal nne directed ductile tectonic transport trend but is underlain by a ssw directed ductile brittle extensional detachment and has experienced ne sw brittle extension on high angle normal faults an amphibole 40 r 39 r inverse isochron age of 156 58 0 60 ma constrains a late jurassic upper greenschist facies tectono metamorphic event whereas a white mica plateau age of 39 66 0 47 ma provides evidence for middle eocene cooling and exhumation of the pelevun extensional allochthon in the hanging wall of the detachment we relate the kulidzhik nappe to late jurassic crustal deformation during arc continental margin collision that involved nne directed nappe staking and metamorphism of continental margin basement and island arc units the nappe shares a tectono metamorphic history with the nappes of the adjacent strandzha massif implying a region wide early alpine orogenic system our results reveal a record of early alpine thrust tectonics and show the significance of crustal accretion related assembly for the tectonic evolution of the rhodope massif both the late jurassic thrusting event and the subsequent cretaceous thrusting event thickened the rhodope crust creating crustal instability which influenced tertiary crustal extension

discussion unraveling the provenance of eocene oligocene sandstones of the thrace basin north east greece by caracciolo et al 2011 sedimentology 58 1988 2011

unravelling provenance from eocene oligocene sandstones of the thrace basin north east greece new sandstone petrology and petrostratigraphy provide insights on palaeogene middle eocene to oligocene clastics of the thrace basin in greece which developed synchronously with post cretaceous collision and subsequent tertiary extension sandstone petrofacies are used as a tool to unravel complex geodynamic changes that occurred at the southern continental margin of the european plate identifying detrital signals of the accretionary processes of the rhodope orogen as well as subsequent partitioning related to extension of the rhodope area followed by oligocene to present aegean extension and wide magmatic activity starting during the early oligocene sandstone detrital modes include three distinctive petrofacies quartzolithic quartzofeldspathic and feldspatholithic major contributions are from metamorphic basement units represented mostly by low to medium grade lithic fragments for the quartzolithic petrofacies and high grade metamorphic rock fragments for the quartzofeldspathic petrofacies volcaniclastic sandstones were derived from different volcanic areas with a composition varying from dominantly silicic to subordinate intermediate products mainly rhyolitic glass spherulites and felsitic lithics evolution of detrital modes documents contributions from three key source areas corresponding to the two main crystalline tectonic units i the variegated complex ultramafic complex in the initial stage of accretion quartzolithic petrofacies ii the gneiss migmatite complex quartzofeldspathic petrofacies and iii the circum rhodope belt the volcaniclastic petrofacies is interbedded with quartzofeldspathic petrofacies reflecting superposition of active volcanic activity on regional erosion the three key petrofacies reflect complex provenance from different tectonic settings from collisional orogenic terranes to local basement uplift and volcanic activity the composition and stratigraphic relations of sandstones derived from erosion of the rhodope orogenic belt and superposed magmatism after the extensional phase in northern greece provide constraints for palaeogeographic and palaeotectonic models of the eocene to oligocene western portions of the thrace basin clastic detritus in the following sedimentary assemblages was derived mainly from provenance terranes of the palaeozoic section within the strongly deformed rhodope massif of northern greece and south east bulgaria from the epimetamorphic units of the circum rhodope belt and from superposed late eocene to early oligocene magmatism related to orogenic collapse of the rhodope orogen the sedimentary provenance of the rhodope palaeogene sandstones documents the changing nature of this orogenic belt through time and may contribute to a general understanding of similar geodynamic settings

biostratigraphic data from the cetmi melange northwest turkey palaeogeographic and tectonic implications abstract the cetmi accretionary melange is cropping out in the biga peninsula of northwest turkey it is characterised by an isolated position relatively far from the accretion complexes of the nearest suture zones which raises the question of its lateral correlations a detailed biostratigraphic investigation of the limestone and radiolarite blocks and the matrix of the cetmi melange allowed to propose a solution for this palaeogeographic problem scarce red nodular limestones in the han bulog facies represent the oldest lithology in the melange their late scythian ladinian age is based on chiosella gondolleloides the co occurrence of gladigondolella sp and nicoraella cf kockeli and paragondolella fuelopi light grey limestone blocks are a characteristic feature of the cetmi melange they occur in two distinct facies facies a consists of packstone to grainstone and is characterised by unsorted and poorly washed pelbiosparites facies b consists of wackestone to packstone and is characterised by poorly washed biopelmicrites to biopelsparites the foraminiferal assemblage of facies a containing triasina hantkeni is of late norian to rhaetian age the foraminiferal assemblage of facies b never contains t hantkeni and is characteristic of a late triassic carnian to norian rhaetian age radiolarian cherts are widely distributed in the cetmi melange they record fully pelagic sedimentation from the upper bajocian to the aptian the matrix of the cetmi melange consists of brown to black shales sometimes silty or siliceous intercalated with dark grey greywackes palynomorphs of one sample of brownish silty shale yielded an early to middle albian age based on the co occurrence of several dinoflagellate cysts the age of the matrix representing the youngest lithology within the melange and of the unconformable overlaying section latest albian cenomanian indicate that the melange forming process stopped between the early albian and the latest albian cenomanian at a regional scale the cetmi melange has little in common with the melanges from the izmir ankara and intra pontide sutures of northwestern turkey precluding a direct correlation on the other hand the cetmi melange shares several characteristics with the melange like units of the eastern rhodope zone bulgaria and greece like a major cenomanian transgression the reworking of triassic limestones and middle jurassic lower cretaceous radiolarians and the absence of jurassic cretaceous passive margin lithologies the occurrence of rhodopian units on the biga peninsula suggests that the studied units represent an isolated fragment of the rhodope zone in nw turkey

provenance of tertiary volcanoclastic sediment in nw thrace bulgaria evidence from detrital amphibole and pyroxene geochemistry abstract detrital heavy mineral and bulk rock geochemistry and a review of sandstone petrographic data have been used to investigate the post collisional effusive magmatism that followed the closure of the vardar ocean and the generation of volcanic sediments in a complex and compositionally variable volcanic region available petrographic data gives evidence of contributions from three key source areas corresponding to the three main tectonic units the structurally lower gneiss migmatite complex byala reka kechros and kesebir kardamos domes and the upper variegated kimi complex both fringed by the low to medium grade mesozoic rocks of the circum rhodope belt besides the deposition of siliciclastic material volcanic contributions from both intermediate and acid products represent an important source of sediment in the area despite dominant intermediate to acid volcanic products volcanic lithic fragments in sandstones microlithic lathwork and brown vitric textures indicate main inputs from intermediate and basic intermediate products generating questions on the interpretation of volcanic detritus in reconstruction of provenance detrital amphibole and pyroxene chemistry is used to characterise the supply of volcanic material as well as the dispersal mechanisms and understand the role played by each of the volcanic centers present in the area in the infill of the north western thrace basin amphibole chemistry reveals high compositional heterogeneity according to both compositional variability of the numerous volcanic centres active at the time of deposition and presence of metamorphic amphibole 4 al and al t apfu values indicate that most of the amphiboles from the nerz are not of volcanic origin and their presence can only be attributed to the numerous amphibolite facies metamorphic rocks abundantly documented in the area detrital amphibole compositions from the zkvs indicate major contributions from the iran tepe and zvedzel volcanoes analysed detrital clinopyroxenes from the nerz are mostly diopside augite with no hedenbergite or fe augite detected the 4 al 6 al ratio is comparable with compositions of volcanic pyroxenes from the momchilgrad arda zkvs region and products from the pre caldera phase of the borovitza

the chemistry of detrital chromian spinels and its implications for the geodynamic evolution of the eastern alps detrital chromian spinel is a key mineral in paleogeographic reconstructions the chemical compositions of the spinels provide even more specific information about their host ophiolites because their chemistry is related to the degree of melting of the mantle peridotite and thus to the geotectonic environment of ocean crust formation

modeling of gas driven magmatic overturn tracking of phenocryst dispersal and gathering during magma mixing 1 we present a combined multiphase numerical and crystal tracking approach that provides a framework to investigate the transport and zoning of crystals associated with a gas driven mixing event mixing in compositionally intermediate to silicic magmatic systems is often initiated by gas exsolution in the recharging magma causing a density inversion and subsequent overturn the overturn is simulated for a range of bubble volume fractions bubbles and therefore indirectly for a range of reynolds numbers re all simulations show chaotic flow dynamics with fast overturn timescales of minutes to hours the large scale mixing is inefficient during a single overturn resulting in a continuously stratified system with respect to bubble volume fraction the crystal tracking algorithm provides us with information on the small scales i e 10 cm on this length scale we observe gathering of different crystals during the overturn that typically ranges on the order of tens of meters thus a complex crystal population may arise within a single overturn this gathering and dispersal of crystals is strongest and most uniform for high re for low re crystal populations are characterized by less gathering of crystals that originated from distal portions of the magma body during the overturn the crystals pass through environments of changing chemical potential we apply the damkohler number da which compares the crystallization or dissolution to the advection timescale results show an asymmetry between crystallization and dissolution crystallization times are too slow during gas driven overturn to record transient changes in chemical potential crystals most likely only record their initial as well as their final chemical environment in contrast dissolution and advection rates are of similar order suggesting potential dissolution during the overturn on the basis of the results for gas driven overturn we expect that slower physical mixing processes may be continuously recorded in the zonation pattern of the crystal phases as long as the changes in chemical potential produce crystal growth

stratigraphic model for timing the opening of the proto atlantic ocean in northern virginia theoretical rifting models suggest that rifting events have predictable stages time spans and characteristics the stratigraphy and sedimentary tectonics of northern virginia were compared with the theoretical models for the opening of ocean basins according to our model the rift valley stage of initial uplift and graben formation 0 10 m y after onset of rifting is represented in virginia by the lynchburg and equivalent formations the initiation of ocean crust formation immediately follows the rift valley stage 10 15 m y and is represented in virginia by the catoctin formation sedimentation on an unstable thermally subsiding continental margin youthful stage 10 60 m y is represented by the weverton and harpers formations the beginning of deposition on a stable continental margin occurs no later than 60 m y after onset of rifting according to the theoretical models and in virginia it is represented by the antietam formation a biostratigraphic age of early cambrian ca 570 ma for the antietam provides the datum for proposing that the rifting which opened the proto atlantic in virginia was initiated 60 m y before deposition of the antietam at most about 630 ma

petrology and u pb geochronology of the robertson river igneous suite blue ridge province virginia evidence for multistage magmatism associated with an early episode of laurentian rifting

crustal structures and the eastern extent of lower paleozoic shelf strata within the central appalachians a seismic reflection interpretation reprocessing of line pr3 proprietary seismic reflection data has delineated grenvillian paleozoic and mesozoic structures within the appalachian foreland blue ridge and piedmont of the central appalachians in virginia and west virginia the eastern portion of pr3 can be correlated along strike with the western portion of line i 64 reprocessed earlier at virginia tech the combined seismic reflection data image the crust from the eastern valley and ridge blue ridge piedmont and atlantic coastal plain provinces within the piedmont large as much as 10 km wide reflective structures imaged on both lines pr3 and i 64 are interpreted to be thrust sheets that might be composed of deformed catoctin evington group and possibly younger metamorphosed rocks a concealed extension of the green springs mafic mass intrudes a thrust sheet imaged along the pr3 profile the blue ridge piedmont allochthon was transported north west along the blue ridge thrust which ramps upward 12 km east of the surface exposure of the mountain run fault westward along line pr3 the blue ridge thrust maintains an undulating geometry the maximum thickness of the blue ridge allochthon is interpreted to be 4 5 km the blue ridge allochthon is generally acoustically transparent and overlies lower paleozoic shelf strata the maximum thickness of these strata is 8 km shelf strata are interpreted to extend in the subsurface 5 km east of the surface exposure of the mountain run fault the northeastward extension of the brevard fault zone where they are truncated by the blue ridge thrust at a depth of 10 5 km 3 5 s various folds and blind thrusts are imaged beneath the appalachian foreland however the foreland has not experienced the same degree of deformation as observed in the eastern provinces a basement uplift 45 km wide is imaged beneath the valley and ridge province and is interpreted as having formed prior to late cambrian time farther west reflections imaged beneath the glady fork anticline in the appalachian plateau are interpreted as a positive flower structure associated with wrench fault tectonics relatively few deep 9 km crustal reflections are imaged along line pr3 the majority of reflections that do exist at these depths are observed beneath the piedmont and eastern blue ridge the high reflectivity associated with the grenvillian basement in these areas might be the result of the paleozoic orogenies and extension related to late proterozoic and mesozoic rifting

mineral disequilibrium in lavas explained by convective self mixing in open magma chambers characteristic features of many porphyritic andesite and dacite lavas are that they are rich in crystals and display a range of disequilibrium features including reversely zoned crystals resorption surfaces wide ranges of mineral compositions and minerals which are not in equilibrium with the surrounding rock matrix these features are often interpreted as evidence of the mixing of magmas of contrasting composition temperature and origin1 2 here however we propose that such features can also be caused by convection within a magma body with a single composition that is heated from below and cooled from above we describe petrological observations of andesite lava erupted at the soufriere hills volcano montserrat which indicate a heating event and the intermingling of crystals that have very different thermal histories we present experimental data on a representative groundmass composition of this lava which indicate that it is difficult to explain the calcic compositions of plagioclase overgrowth rims and microphenocrysts unless parts of the magma were at temperatures much higher than the inferred average temperature the concept of convective self mixing allows us to explain the occurrence of compositions of minerals that apparently cannot coexist under equilibrium conditions

multiple reinjections and crystal mush compaction in the beacon sill mcmurdo dry valleys antarctica the beacon sill a member of the jurassic ferrar group of the transantarctic mountains south victoria land is a 150 m thick tholeiitic diabase intrusion uniform on a field and macroscopic scale it displays chemical and textural variability indicative of a sustained and complex history of emplacement and differentiation emplacement of the sill consisted of at least two and probably four discrete massive injections of magma each averaging 35 m thick over a time span of 100 years the final injection event is marked by a 30 m thick interval of significantly finer grained rock at the sill center these fine grained textures can be successfully reproduced by combining the results of thermal and crystal growth models but only if the sill was a multiple intrusion with the exception of a minor reinjection event captured in the chilled margin of the sill earlier reinjection events are not evident texturally most probably because of textural overprinting during prolonged cooling after initial crystallization the dominant process involved in the postemplacement differentiation of the beacon sill was compactiondriven redistribution of interstitial liquid transfer of residual liquid from the compacting lower solidification front to the dilating upper solidification front resulted in characteristic chemical and mineralogical effects such as the depletion of the lower half of the sill and the enrichment of the upper half of the sill in incompatible elements e g tio2 zr and modal granophyre based on thermodynamic models most of the compaction occurred at a crystallinity of roughly 33 geochemical profiles are distinctly segmented suggesting that the sill was repeatedly split and reinjected with fresh magma near the center after compaction had redistributed the interstitial liquid within the partially solidified magma the recognition of evidence for reinjection and compaction in a macroscopically uniform relatively quickly cooled sill suggests that these processes may be common in the construction of sills and other mesoscale igneous intrusions in general

application of actualistic models to unravel primary volcanic control on sedimentation taveyanne sandstones oligocene northalpine foreland basin abstract this work is focused on the taveyanne sandstones gres de taveyanne an oligocene volcaniclastic turbidite sequence cropping out in the northern alpine molassa between se france and central switzerland with the aim to investigate the temporal relationship between volcanic activity and sediment supply detailed stratigraphic sedimentological and petrographic xrd analyses on mudstones and point counts on sandstones studies conducted on three sections col de l oulette and flaine in se france taveyanne in sw switzerland allow a discrimination of three main facies among which only one is extremely enriched in volcaniclastic detritus and characterized by features similar to those of disaggregated pyroclastic density current deposits the other two facies are characterized by variable to no volcanic detritus but supplied by crystalline and sedimentary detritus such sediment trends are similar to those of modern volcanically controlled source to sink systems this allows a reinterpretation of the taveyanne sandstones as a syn volcanic turbidite system episodically supplied by large amounts of volcanic detritus which periodically modified the drainage paths moreover the well known temporal and spatial persistence of such modifications in modern settings leads to conciliate the syn volcanic supply with the location of the volcanic centers in the internal part of the alps without invoking particular climatic and tectonic conditions controlling foreland sedimentation