toward understanding the post collisional evolution of an orogen influenced by convergence at adjacent plate margins late cretaceous tertiary thermotectonic history of the apuseni mountains 1 the relationship between syn to post collisional orogenic shortening and stresses transmitted from other neighboring plate boundaries is important for understanding the kinematics of mountain belts but has received little attention so far the apuseni mountains are an example of an orogen in the interference zone between two other subduction systems located in the external carpathians and dinarides this interference is demonstrated by the results of a combined thermochronological and structural field study that quantifies the post collisional latest cretaceous tertiary evolution the exhumation history derived from apatite fission track and u th he thermochronology indicates that the present day topography of the apuseni mountains originates mainly from latest cretaceous times modified by two tectonic pulses during the paleogene the latter are suggested by cooling ages clustering around 45 ma and 30 ma and the associated shortening recorded along deep seated fault systems paleogene exhumation pulses are similar in magnitude 3 5 km and are coeval with the final collisional phases recorded in the dinarides and with part of the carpathian rotation around the moesian promontory these newly quantified paleogene exhumation and shortening pulses contradict the general view of tectonic quiescence subsidence and overall sedimentation for this time interval the miocene collapse of the pannonian basin did not induce significant regional exhumation along the western apuseni flank nor did the subsequent carpathian collision this is surprising in the overall context of pannonian basin formation and its subsequent inversion in which the apuseni mountains were previously interpreted as being significantly uplifted in both deformation stages

a new model for the emplacement of columbia river basalts as large inflated pahoehoe lava flow fields extensive flows of the columbia river basalt crb group in washington oregon and idaho are dominantly inflated compound pahoehoe sheet lavas early studies recognized that crb lavas are compound pahoehoe flows with textures suggesting low flow velocities but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks however small volume 1 km compound pahoehoe flows on kilauea hawai i demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger 10 20 km3 pahoehoe flows in iceland the vertical distribution of vesicles and other morphologic features within crb lava flows indicate that they grew similarly by inflation small pahoehoe lobes at the base and top of many crb pahoehoe lava flows indicate emplacement in a gradual piecemeal manner rather than as a single flood we propose that each thick crb sheet flow was active for months to years and that each group of flows produced by a single eruption a flow field was emplaced slowly over many years

miocene facies associations and sedimentary evolution of the southern transylvanian basin romania implications for hydrocarbon exploration abstract the transylvanian basin is a mature hydrocarbon province of romania characterized by two petroleum systems mesozoic thermogenic and miocene biogenic an extensive outcrop based sedimentological and micropaleontological study correlated to seismic and well data discusses the elements of the miocene petroleum system the facies associations are indicative of alluvial fandelta shallow and deep marine settings these are grouped into four different depositional systems evaporite mud carbonate sand mud and sand gravel their evolution in time and space shows large differences between various parts of the basin that have important consequences for exploration the transylvanian gas is formed by more than 99 methane of bacterial origin this is sourced by low quality the largest traps typically have multistory up to 20 pay zones with a total of 100 bcf to 1 tcf reserves exploration to date has focused on structural traps but most of the obvious structures have been drilled it is argued that significant exploration potential lies in stratigraphic plays including confined submarine fans slope channels detached lowstand prograding wedges incised valleys diapir flanks salt tectonics related unconformities and various sub volcanic plays risks of the petroleum system elements associated to these plays in different areas of the basin are discussed

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

neogene kinematics of the transylvanian basin romania the transylvanian basin is a major sedimentary basin located in the eastern part of the european alpine orogenic system it has a sedimentary fill more than 5 km up to 8 km in some small areas thick of upper cretaceous to upper miocene deposits it represents the main gas producing province in romania and central eastern europe in this article we analyze seismic lines and structural data from the basin as well as from its northern eastern and southeastern borders these data indicate a tectonic origin for the neogene structures from the transylvanian basin these structures include 1 northeast and southwest dipping thrust faults and 2 east northeast and west northwest striking strike slip faults having normal or reverse slip secondary structures such as salt diapirs and folds are related to these faults structural data from the basin and its border indicate a neogene overall compressional transpressional regime having maximum principal stress oriented north to northeast daniel ciulavu received a diploma in geology and geophysics at the university of bucharest in 1989 and his ph d in geology at the vrije universiteit amsterdam netherlands in 1999 he worked two years for geasol s a romania in hydrogeology coal and alluvial gold exploration since 1991 he has been on the staff of the university of bucharest where he teaches the courses on structural geology in the department of geophysics and kinematic analysis for master s students corneliu dinu received a diploma in geology in 1966 and his ph d in 1976 at the university of bucharest romania after graduation he worked as field geologist for prospectiuni s a romania since 1970 he has been on the staff of the university of bucharest where he is professor of structural geology and basin analysis since 1990 he has served as the dean of sciences at the faculty of geology and geophysics university of bucharest alexandru szakacs received a diploma in geology in 1974 and his ph d in 2000 at the university of bucharest romania he is senior geologist at the romanian institute of geology he has 25 years of experience in studying the neogene volcanism of the carpathian pannonian area he has also worked on the neogene volcanism of the cordillera betica spain dorin dordea received a diploma in geology in 1974 at the university of cluj romania his field of activity is remote sensing he has worked in several areas in africa and romania since 1999 he has served as the chief geologist of prospectiuni s a bucharest romania he is now working on the application of remote sensing in mining exploration

ar ar dating of adularia a tool in understanding genetic relations between volcanism and mineralization baia mare area gutii mountains northwestern romania

the transylvanian basin romania and its relation to the carpathian fold and thrust belt insights in gravitational salt tectonics abstract interpretation of regional seismic profiles stratigraphic and sedimentologic data improved insights in the evolution of the transylvanian basin the basin evolution was coeval with the post mid cretaceous to recent deformation of the carpathian mts four tectonostratigraphic megasequences are differentiated upper cretaceous rift paleogene sag lower miocene flexural basin and middle to upper miocene backarc sequence dominated by gravitational tectonics the mid miocene continental collision in the eastern carpathians is associated with the rising carpathians this uplift enhanced the differential load which together with the high heat flow induced by late miocene to pliocene arc volcanism triggered large scale mio pliocene gravity spreading of the salt overburden this mega slide comprises three structural domains as follows extensional weld upslope contractional folds central and contractional toe thrust downslope the diapirs in the east indicate a pre shortening reactive passive growth stage the central folds are mostly the result of late shortening basement involved thrusting uplifted the toe thrust domain by the late pliocene the late neogene to recent carpathians uplift backarc volcanism and gravity spreading are largely coeval

the formation of plagioclase chains during convective transfer in basaltic magma the basaltic rock in the lower part of the thick holyoke lava flow in connecticut and massachusetts has been shown to have a remarkable texture with crystals of feldspar linked together in a continuous three dimensional network of chains1 heating experiments have revealed that this network persists to temperatures where the rock is 75 liquid2 and therefore the network was interpreted to have formed at an early stage of crystallization and to have played an important role in the compaction of crystal mush in the lower part of the flow3 4 despite the texture s importance to our understanding of how such basalt flows form the origin of the texture has remained uncertain1 2 3 here we show that although the network is present in the lower third of the flow it was actually formed in the upper solidification front and was transported down in plumes of dense crystal mush convection of this type has been postulated for intrusive magma chambers but corroborative field evidence has been equivocal especially in lava lakes and flows preservation of the roof generated texture in the lower part of a thick flood basalt flow therefore constitutes important evidence for the role of convection in the solidification and differentiation of a simple magma sheet

the age of the sarmatian pannonian transition in the transylvanian basin central paratethys abstract a marked paleoenvironmental change took place at the beginning of the late miocene in the central paratethys with dominantly marine sarmatian successions grading rapidly into mainly brackish pannonian deposits a long and excellently exposed section comprising the sarmatian pannonian transition has been investigated at oarba de mures in the transylvanian basin romania in this paper we focus on both radiometric and magnetostratigraphic dating to provide a chronology for the sarmatian pannonian transition in transylvania two volcaniclastic layers located approximately 40 m below the sarmatian pannonian transition yield excellent 40ar 39ar ages the weighted mean plateau age for biotite and sanidine separates provided isotopic ages of 11 62 0 12 ma and 11 65 0 13 ma this implies deposition during the magnetic chron c5r 2r which is in agreement with the magnetostratigraphic results of the oarba de mures composite section rock magnetic analyses indicate greigite as the main magnetic carrier with characteristics very similar to the magnetosomal greigite found in the carpathian foredeep the newly obtained chronology at oarba de mures constrains the age of the sarmatian pannonian transition in the transylvanian basin to 11 3 0 1 ma slightly younger than the 11 61 ma postulated in the styrian and vienna basins

the onset of the volcanism in the ciomadul volcanic dome complex eastern carpathians eruption chronology and magma type variation abstract combined zircon u th pb and u th he dating was applied to refine the eruption chronology of the last 2 myr for the andesitic and dacitic pilisca volcano and ciomadul volcanic dome complex cvdc the youngest volcanic area of the carpathian pannonian region located in the southernmost harghita eastern central europe the proposed eruption ages which are supported also by the youngest zircon crystallization ages are much younger than the previously determined k ar ages by dating every known eruption center in the cvdc repose times between eruptive events were also accurately determined eruption of the andesite at murgul mare 1865 87 ka and dacite of the pilisca volcanic complex 1640 37 ka terminated an earlier pulse of volcanic activity within the southernmost harghita region west of the olt valley this was followed by the onset of the volcanism in the cvdc which occurred after several 100s kyr of eruptive quiescence at ca 1 ma a significant change in the composition of erupted magma occurred from medium k calc alkaline compositions to high k dacitic baba laposa dome at 942 65 ka and shoshonitic magmas malnas and bixad domes 964 46 ka and 907 66 ka respectively noteworthy eruptions of magmas with distinct chemical compositions occurred within a restricted area a few km from one another these oldest lava domes of the cvdc form a nne ssw striking tectonic lineament along the olt valley following a brief ca 100 kyr hiatus extrusion of high k andesitic magma continued at dealul mare 842 53 ka after another ca 200 kyr period of quiescence two high k dacitic lava domes extruded puturosul 642 44 ka and balvanyos 583 30 ka the turnul apor lava extrusion occurred after a ca 200 kyr repose time at 344 33 ka whereas formation of the haramul mic lava dome 154 16 ka represents the onset of the development of the prominent ciomadul volcano the accurate determination of eruption dates shows that the volcanic eruptions were often separated by prolonged ca 100 to 200 kyr quiescence periods demonstration of recurrence of volcanism even after such long dormancy has to be considered in assessing volcanic hazards particularly in seemingly inactive volcanic areas where no holocene eruptions occurred the term of volcanoes with potentially active magma storage illustrates the potential of volcanic rejuvenation for such long dormant volcanoes with the existence of melt bearing crustal magma body

some seismic signatures in the romanian crust abstract some new seismic reflection data in the w of the moesian platform focsani depression and transylvania depression show seismic patterns which reflect the local structure and evolution of the each area these local areas were affected by subsidence which over printed the changes on the old pattern the old and more or less reflective lower crust was fractured and some rigid blocks have preserved the reflectivity up to the present the ba ilesti section illustrates a transparent or diffractive upper crust and a well marked lower crust by an alternation of reflective and non reflective zones the crystalline crust of the r mnicu sa rat section has two patterns one relatively reflective near the bottom of the depression the w side whilst the other on the e flank of depression is transparent the e flank seems to be more fractured due to some tensile fractures originating in the bending stress during subsidence the t rgu muressection has a specific crustal pattern a near transparent crystalline crust overlies a very large crust mantle transition zone which is fragmented in alternated reflective and transparent blocks

cretaceous to miocene thrusting and wrenching along the central south carpathians due to a corner effect during collision and orocline formation field studies in the romanian south carpathians longitude 22 5 to 24 2 e and latitude 45 2 to 45 6 n demonstrate 1 cretaceous top to ne shearing parallel to the present strike of the thrust system connected with coaxial flattening within the generally northwest dipping foliation 2 paleogene ductile brittle dextral wrenching e w compression 1 87 15 and basin formation petrosani basin along the cerna jiu fault system 3 large scale miocene dextral wrenching along the northern margin of moesia 1 143 16 and 4 probably pliocene early pleistocene n s compression 1 205 25 we discuss the tectonics of the south carpathians stressing the corner effect of the moesian foreland promontory during convergence and formation of the carpathian orocline up to the late early cretaceous subduction of oceanic crust was active between europe moesia on one side and east carpathia rhodopia on the other side collision and intracontinental deformation occurred during the late early and late cretaceous the pinning of the thrust front at the western tip of moesia and the foreland recess north of it caused superposition of thrusting and wrenching during collision and lateral translation tangential stretching during orocline formation and spreading into the recess further convergence during the early tertiary resulted in dislocation of the previously welded east carpathian rhodopian and moesian fragments along the cerna jiu fault system and the further northeast translation of the western segment the intramontane petrosani basin opened as a northeasterly propagating transient pull apart structure along the cerna jiu fault system which acquired a curved northwesterly convex transtensional trace due to the shape of the moesian promontory tightening of the carpathian orocline and or rearrangement of the microplate geometry during the formation of the pannonian basin system led to large scale dextral wrenching along the northern margin of moesia pliocene n s compression reflects final shortening in the carpathian system before ongoing convergence between europe and africa was transferred to the mediterranean rotation of material lines around the moesian corner is corroborated by paleomagnetic studies

the neogene evolution of the outer carpathian flysch units poland ukraine and romania kinematics of a foreland fold and thrust belt system abstract various techniques of geometric and kinematic analyses including cross section balancing and forward modeling have been applied successfully to the outer carpathian flysch units along regional geologic profiles crossing the belt from its undeformed foreland to the pieniny klippen belt western carpathians poland or to the central east carpathian allochthon eastern carpathians ukraine and romania the amounts of neogene shortening as well as the mode and the location of basement consumption are discussed on the basis of balanced cross sections compiled along the three most representative regional traverses in addition the complete kinematic evolution of complex carpathian structures such as the fore dukla triangle zone southeastern poland the borislav pokut duplexes ukraine and the marginal folds romania are described in more detail by using a forward modeling approach major results concern the tectonic heritage of laramian inverted structures mesozoic normal faults reactivated as reverse faults during the late cretaceous paleocene compression or transpression in the development of the neogene outer carpathian edifice pre eocene deformation and erosion effectively induce discontinuities in the mid cretaceous blackshale detachment horizon and help to localize the neogene deformations in complex triangle zones the thrust sequence itself evolves alternatively in a piggyback or in an out of sequence mode clearly the critical taper of the outer carpathians is preserved by a constant balance between erosion and thrust reactivations in the inner part of the wedge and sedimentation and tectonic accretion at its front

fission track constraints on the thermal and tectonic evolution of the apuseni mountains romania new zircon and apatite fission track ft data including apatite thermal modelling are combined with an extensive literature survey and reconnaissance type structural fieldwork in the eastern apuseni mountains this leads to a better understanding of the complex structural and thermal history of a key area at the boundary between two megatectonic units in the balkan peninsula namely the tisza and dacia mega units following late jurassic obduction of the transylvanian ophiolites onto a part of the dacia mega unit that is the biharia nappe system both units were buried to a minimum of 8 km during late early cretaceous times when these units were underthrust below the tisza mega unit consisting of the present day codru and bihor nappe systems tisza formed the upper plate during early cretaceous austrian east facing orogeny turonian to campanian zircon ft cooling ages 95 71 ma from the bihor and codru nappe systems and the biharia and baia de aries nappes at present the structurally lowest part of the dacia mega unit record exhumation that immediately followed a second cretaceous age i e turonian orogenic event thrusting during this overprinting event was nw facing and led to the overall geometry of the present day nappe stack in the apuseni mountains zircon ft ages combined with thermal modelling of the apatite ft data show relatively rapid post tectonic cooling induced by a third shortening pulse during the latest cretaceous laramian phase followed by slower cooling across the 120 60 c temperature interval during latest cretaceous to earliest paleogene times 75 60 ma cenozoic age slow cooling 60 40 ma was probably related to erosional denudation postdating laramian large scale updoming

crustal constraints on the origin of mantle seismicity in the vrancea zone romania the case for active continental lithospheric delamination abstract the vrancea zone of romania constitutes one of the most active seismic zones in europe where intermediate depth 70 200 km earthquakes of magnitude in excess of m w 7 0 occur with relative frequency in a geographically restricted area within the 110 bend region of the southeastern carpathian orogen geologically the vrancea zone is characterized by a a laterally restricted steeply nw dipping seismogenic volume 30 70 200 km situated beneath b thickened continental crust within the highly arcuate bend region of the carpathian orocline and c miscorrelation of hypocenters with the position of known or inferred suture zones in the carpathian orogenic system geologic data from petroleum exploration in the eastern carpathians published palinspastic reconstructions and reprocessing of industry seismic data from the carpathian foreland indicate that 1 crust of continental affinity extends significantly westward beneath the external thrust nappes sub carpathian marginal folds and tarcau of the eastern carpathians 2 cretaceous to miocene strata of continental affinity can be reconstructed westward to a position now occupied by the transylvanian basin and 3 geologic structure in the carpathian foreland including the moho is sub horizontal directly to the east and above the vrancea seismogenic zone taken together these geologic relationships imply that the vrancea zone occupies a region overlain by continental crust and upper mantle and does not appear to originate from a subducted oceanic slab along the length of the carpathian orogen accordingly the vrancea zone appears to potentially be an important place to establish evidence for active lithospheric delamination

the mid langhian flooding in the eastern central paratethys integrated stratigraphic data from the transylvanian basin and se carpathian foredeep the mid langhian badenian flooding fully reconnected the semi isolated central paratethys realm with the mediterranean and thereby drastically changed the middle miocene paleogeography of central europe due to the scattered stratigraphic record and scarcity of independent age constraints in some areas the precise age and underlying mechanism are still debated we present integrated chronostratigraphic data from five sections in the eastern part of the system to reconstruct the flooding event distal from the strait to the mediterranean by applying modern mediterranean biochronology planktonic foraminifera and calcareous nannofossils supplemented by an 40ar 39ar age on a tuff we demonstrate that the widespread open marine settings in the nw transylvanian basin were definitely installed after 14 9 ma mmi4d biozone and in most areas before 14 4 ma in the marginal study area in the se carpathian foredeep fully marine conditions likely set in slightly later 14 6 14 4 ma there short lived marine incursions into the brackish environment occurred since the latest burdigalian pre flooding phase the new ages overlap with the flooding in the majority of the central paratethys 14 9 14 4 ma and with marine overflow into the black sea 14 85 ma we suggest that the transgression was driven by subsidence of the pannonian basin by creating accommodation space and diminishing barriers between sub basins but was likely enhanced by a global sea level rise finally we speculate that the scarcity of all calcareous material in the se carpathian foredeep before the mid langhian flooding might be related to pulses of nutrient rich brackish and low ph water from the neighboring black sea basin

identification of wrench faults using subsurface structural data criteria and pitfalls 1 many structures imaged with reflection seismic can resemble a wrench fault system because of the great structural diversity of strike slip faults and the wide range of contractional and extensional features associated with these faults because of these resemblances numerous faults are misidentified as wrench faults by workers using subsurface structural data credible identification requires combinations of profile and map criteria 1 narrow long straight throughgoing solitary master fault or zone of deformation 2 steep to moderate dip of the master fault at depth 3 offset of the top of basement 4 changes in relative upthrown side separation sense and or fault dip direction at depth or along the strike of the master fault 5 narrow fault slices within the master fault zone that steepen and join at depth negative and positive flower structures 6 different separation sense and orientation of relative upthrown side at these fault slices and 7 coeval en echelon flanking structures the identification should be confirmed with other criteria that refute alternative interpretations the main pitfalls to a reliable identification are not considering alternative structural styles and the misinterpretation of features or patterns that superficially resemble wrench systems the profile geometries of basement involved reverse or normal faults particularly those with structural inversion can resemble the single strand of convergent or divergent wrench faults profile geometries of flower structures can be mimicked by narrow contractional horsts or narrow extensional grabens complexly faulted anticlines or synclines splay faults fault zones intruded by salt or shale and overprinted structures pitfalls in interpreting map relationships are possible when structural patterns combine several tectonic influences are controlled by rock anisotropy or include elements hat are not coeval and if the patterns characteristic of other styles are misinterpreted many erroneous identifications of wrench faults can be eliminated by demonstrating that the investigated fault or feature lacks a straight trace lateral length or throughgoing continuity

a note on the depth recurrence and strain release of large vrancea earthquakes the large 1940 vrancea event with body wave magnitude mb 7 3 was investigated in terms of the depth of rupture initiation and extent it was found that the rupture started at 150 km depth and propagated downwards the ruptured zones of the 1977 1986 and 1990 vrancea events were estimated from the distribution of aftershocks located with the joint hypocentre determination method their depth ranges are 90 110 km 130 150 km and 70 90 km respectively because the body wave magnitudes mb were saturated for the last three events and the surface wave magnitudes ms were underestimated not being corrected for depth we chose the moment magnitudes to quantify the four events 7 7 1940 7 4 1977 7 1 1986 and 6 9 1990 respectively the depth interval 110 130 km is found to be unbroken since at least 1838 or 1802 and therefore is expected to accommodate the next large moment release mw 7 0 to 7 4 the strain in the vertical and in the se nw directions is about 0 0003 giving a moderate strain rate of about 10 13 s 1 a correlation between the depth interval of the large events and the year of occurrence in a century is suggested offering a physical basis to the observed quasi cyclicity

vrancea99 the crustal structure beneath the southeastern carpathians and the moesian platform from a seismic refraction profile in romania the vrancea99 seismic refraction experiment is part of an international and multidisciplinary project to study the intermediate depth earthquakes of the eastern carpathians in romania as part of the seismic experiment a 300 km long refraction profile was recorded between the cities of bacau and bucharest traversing the vrancea epicentral region in nne ssw direction the results deduced using forward and inverse ray trace modelling indicate a multi layered crust the sedimentary succession comprises two to four seismic layers of variable thickness and with velocities ranging from 2 0 to 5 8 km s the seismic basement coincides with a velocity step up to 5 9 km s velocities in the upper crystalline crust are 5 9 6 2 km s an intra crustal discontinuity at 18 31 km divides the crust into an upper and a lower layer velocities within the lower crust are 6 7 7 0 km s strong wide angle pmp reflections indicate the existence of a first order moho at a depth of 30 km near the southern end of the line and 41 km near the centre constraints on upper mantle seismic velocities 7 9 km s are provided by pn arrival times from two shot points only within the upper mantle a low velocity zone is interpreted travel times of a plp reflection define the bottom of this low velocity layer at a depth of 55 km the velocity beneath this interface must be at least 8 5 km s geologic interpretation of the seismic data suggests that the neogene tectonic convergence of the eastern carpathians resulted in thin skinned shortening of the sedimentary cover and in thick skinned shortening in the crystalline crust on the autochthonous cover of the moesian platform several blocks can be recognised which are characterised by different lithological compositions this could indicate a pre structuring of the platform at mesozoic and or palaeozoic times with a probable active involvement of the intramoesian and the capidava ovidiu faults especially the intramoesian fault is clearly recognisable on the refraction line no clear indications of the important trotus fault in the north of the profile could be found in the central part of the seismic line a thinned lower crust and the low velocity zone in the uppermost mantle point to the possibility of crustal delamination and partial melting in the upper mantle

source side shear wave splitting and upper mantle flow in the romanian carpathians and surroundings we present shear wave splitting measurements from 5 earthquakes that occurred in the vrancea seismic zone of the carpathian arc s waves from these events all with magnitudes 5 4 mw and deeper than 88 km were recorded at broadband stations of the global seismic network and the geoscope and geofon networks and used by us to measure shear wave splitting corrected for sub station splitting and anisotropy in order to carry out these corrections we used published shear wave splitting parameters thus isolating contributions to observed splitting from the vrancea source region and upper mantle surrounding the carpathian arc the resulting 32 good observations of source side shear wave splitting along with 54 null splitting observations which yield two potential splitting directions clearly show that upper mantle anisotropy is strongly variable in the region of the tightly curved carpathian arc shear waves taking off from vrancea along paths that sample the east and southern carpathians have fast anisotropy axes parallel to these ranges whereas those leaving the source region to traverse the upper mantle beneath the transylvanian basin i e mantle wedge side trend ne sw shear waves sampling the east european and scythian platforms are separable into two groups one characterized by fast shear trends to the ne sw and a second deeper group with trends to nw se also the majority of null splits occur along paths leaving vrancea in these ne e azimuths we interpret these results to indicate the presence of at least three distinct upper mantle volumes in the carpathians region the upper mantle beneath the carpathian arc is strongly anisotropic with fabrics parallel to the local arc strike the transylvanian basin upper mantle fabrics trend ne sw and the anisotropy beneath the westernmost east european platform may be characterized by a shallow nw se trending fabric concentrated in the cratonic lithosphere of the east european platform and a second deeper fabric with e w trend marking asthenospheric flow beneath the craton s base this more complex anisotropy beneath the western edge of the east european platform would account for both the variability of observed splitting of waves that sample this volume and also the strong prevalence of nulls observed along eastward departing azimuths

structural evolution of the transylvanian basin romania a sedimentary basin in the bend zone of the carpathians abstract the transylvanian basin with its up to 10 km thick upper cretaceous to pliocene fill is one of the most important sedimentary basins of southeastern europe upper cretaceous coarse grained clastics lie unconformably on basement strongly tectonized during early cretaceous and older stages upper cretaceous sediments were mainly deposited along roughly n s trending grabens and were subsequently folded before the end of the paleocene eocene to middle oligocene rocks record mostly quiet sedimentation n s tension and extension took place in the oligocene and was followed by widespread nw se compression and contraction important thrusts are associated with this phase in the northwestern and southeastern parts of the basin widespread n s contraction followed during the early miocene in association with s vergent thrusting in the northern part of the basin a southward thinning clastic wedge developed during this stage the badenian basal unconformity marked a major change in the sedimentary and tectonic pattern of the transylvanian basin with new depocenters developing in the central parts of the present day basin late miocene e w extension affected vast areas and caused some important normal faulting in the southeast the youngest deformation recorded is associated with e w contraction and is of pliocene or younger age

tectonic significance of changes in post subduction pliocene quaternary magmatism in the south east part of the carpathian pannonian region the south eastern part of the carpathian pannonian region records the cessation of convergence between the european platform moesia and the tisza dacia microplate plio quaternary magmatic activity in this area in close proximity to the vrancea zone shows a shift from normal calc alkaline to much more diverse compositions adakite like calc alkaline k alkalic mafic na alkalic and ultrapotassic suggesting a significant change in geodynamic processes at approximately 3 ma we review the tectonic setting timing petrology and geochemistry of the post collisional volcanism to constrain the role of orogenic building processes such as subduction or collision on melt production and migration the calc alkaline volcanism 5 3 3 9 ma marks the end of normal subduction related magmatism along the post collisional c limani gurghiu harghita volcanic chain in front of the european convergent plate margin at ca 3 ma in south harghita magma compositions changed to adakite like calc alkaline and continued until recent times 0 03 ma interrupted at 1 6 1 2 ma by generation of na and k alkalic magmas signifying changes in the source and melting mechanism we attribute the changes in magma composition in front of the moesian platform to two main geodynamic events 1 slab pull and steepening with opening of a tear window adakite like calc alkaline magmas and 2 renewed contraction associated with deep mantle processes such as slab steepening during post collisional times na and k alkalic magmas contemporaneous post collisional volcanism at the eastern edge of the pannonian basin at 2 6 1 3 ma was dominated by na alkalic and ultrapotassic magmas suggesting a close relationship with thermal asthenospheric doming and strain partitioning related to the adriatic indentation similar timing magma chamber processes and volume for k alkalic shoshonitic magmas in the south apuseni mountains 1 6 ma and south harghita area at a distance of ca 200 km imply a regional connection with the inversion tectonics

crustal properties from s wave and gravity data along a seismic refraction profile in romania vrancea 99 is a seismic refraction line that was carried out in 1999 to investigate the deep structure and physical properties of the upper lithosphere of the southeastern carpathians and its foreland it runs from the city of bacau to the danube river traversing the vrancea epicentral area of strong intermediate depth seismicity and the city of bucharest interpretation of p wave arrivals led to a velocity model that displays a multi layered crust with velocities increasing with depth the range of p wave velocities in the sedimentary cover increases from n to s and a structuring of the autochthonous basement of the moesian platform is observed the crystalline crust displays thickness variations but at the same time the lateral velocity structure along the seismic line remains almost constant an intra crustal boundary separates an upper crust from the lower crust within the upper mantle a low velocity zone is detected at a depth of about 55 km the interpretation of observable s waves resulted in a velocity model that shows the same multi layered crust with s velocities increasing similarly with depth as the p waves the corresponding poisson s ratio is highly variable throughout the crust and ranges from 0 20 0 35 for the sedimentary cover to 0 22 0 25 for the crystalline crust the interpretation of the vp vs and poisson s ratio in petrological terms suggests a large variety of rocks from sand and clay to sandstone limestone and dolomite within the sedimentary cover within the crystalline crust the most probably rock types are granite granodiorite granite gneiss and or felsic amphibolite gneiss in the upper part and gneiss and or amphibolite in the lower part based on the 2 d seismic velocity model a density model is developed density values are assigned to each layer in agreement with the p wave velocity model and with values accepted for the geological units in the area after several iterations a good fit between the computed and observed bouguer anomalies was obtained along the seismic line

architecture of the focsani depression a 13 km deep basin in the carpathians bend zone romania 1 in front of the se carpathians bend a very deep basin focsani depression developed in miocene to recent times an important part of its subsidence occurred after the main stages of thrusting in the carpathians apparently the basin lies in the wrong place and evolved in the wrong time in this study we constrain its architecture and evolution by analyzing a large database consisting of more than 1000 km two dimensional seismic lines and more than 60 wells around 13 km thick badenian to quaternary 16 5 myr sediments were deposited in the central part of the focsani depression during the badenian 16 5 13 myr the foreland south of trotus fault underwent ne sw directed extension and nw trending basins opened in the eastern moesian platform a nw se oriented area of subsidence stretched from the transylvania basin through the focsani depression to the se of the moesian platform while thrusting was going on in the east european scythian platform east carpathians and getic depression starting with the sarmatian 13 10 myr the focsani depression depocenter moved out of the carpathian belt coeval with the exhumation of the south and the east carpathians north of the trotus fault the basin became wider and was tilted toward the belt tilting was accompanied by dextral shearing mainly along the intramoesian and peceneaga camena faults after sarmatian times subsidence occurred practically only sse of trotus fault during meotian pontian 10 5 myr subsidence slowed down stronger pliocene quaternary subsidence is coeval with normal faulting and shearing in moesian platform the western margin of the focsani depression was then tilted eastward coeval with the exhumation of the bend zone and opening of the intramontane basins in the inner part of the belt

stress induced late stage subsidence anomalies in the pannonian basin abstract subsidence sedimentation and tectonic quiescence of the pannonian basin was interrupted a few million years ago by tectonic reactivation this recent activity has manifested itself in uplift of the western and eastern flanks and continuing subsidence of the central part of the pannonian basin low to medium magnitude earthquakes of the carpathian pannonian region are generated mostly in the upper crust by reverse and wrench fault mechanisms there is no evidence for earthquakes of extensional origin 2 d model calculation of the subsidence history shows that a recent increase in magnitude of horizontal compressional intraplate stress can explain fairly well the observed quaternary uplift and subsidence pattern we propose that this stress increase is caused by the overall europe africa convergence in late pliocene consumption of subductible lithosphere at the eastern margin of the pannonian basin was completed and the lithosphere underlying the pannonian basin became locked in a stable continental frame consequently extensional basin formation has come to an end and compressional inversion of the pannonian basin is in progress

40ar 39ar chronology and paleomagnetism of quaternary basaltic lavas from the persani mountains east carpathians abstract quaternary volcanism in the persani mountains forms an na alkali basaltic province inside the bend area of the carpathians in the southeastern part of europe previous k ar ages and paleomagnetic data reveal several transitional virtual geomagnetic poles which were tentatively associated with the cobb mountain subchron and a brunhes chron excursion we report a new paleomagnetic and rock magnetic study coupled with 40ar 39ar geochronology to better constrain the age of geomagnetic reversals or excursions that might be recorded and the timing of volcanism of the paleomagnetic directions obtained from sampled lava flows 4 are reversed polarity 19 are normal polarity and 16 have transitional polarity 40ar 39ar plateau ages determined from incremental heating experiments on groundmass indicate that two of the reversely magnetized lavas erupted at 1142 41 and 800 25 ka four of the normally magnetized lavas erupted at 1060 10 1062 24 684 21 and 683 28 ka and two transitionally magnetized lavas formed at 1221 11 and 799 21 ka both the new 40ar 39ar ages and the paleomagnetic data suggest at least five episodes of volcanic activity with the most active periods during the jaramillo and brunhes chrons this results shows that the last phases of alkalic and calc alkaline magmatism in the south east carpathians were contemporaneous the age of the older transitionally magnetized lava flow is within error of recent unspiked k ar and astrochronologic ages for the reversal that defines the onset of the cobb mountain normal polarity subchron the age of the younger transitional lava is similar to that of an excursion that preceded the matuyama brunhes polarity reversal and which has come to be known as the matuyama brunhes precursor omitting the excursion data the dispersion of the virtual geomagnetic poles around 19 is larger than the expected value around 45 n from the global compilation but closer to the value obtained only from the time averaged geomagnetic field initiative studies

paleostress characterization of the wallachian phase in its type area southeastern carpathians romania abstract the wallachian phase is defined in the east carpathians a convex to the east mountain belt in romania as a tectonic event occurring between pliocene and quaternary times this event formed folds and minor thrusts structures that are usually located in internal parts of the somewhat older fold and thrust belt structure this location contrasts with the location one would predict from their recent age and contrasts with the older cretaceous middle tortonian piggyback thrust mode of propagation in the southeastern carpathians this late overstep sequence of thrusting resulted from a modification in the stress field our data indicate that the direction of compression changed from nw se to n s during middle tortonian time this is further supported by stratigraphic dating of structures and thereby paleostresses indicating that the wallachian episode was not a brief event at the pliocene quaternary boundary but lasted from middle tortonian to early pleistocene

late miocene quaternary volcanism tectonics and drainage system evolution in the east carpathians romania abstract middle miocene sarmatian convergence created the fold and thrust belt of the eastern carpathians of romania which subsequently experienced post collisional crustal deformation combined with calc alkaline and alkalic basaltic volcanism in late miocene quaternary time this deformation led to the rise of the c limani gurghiu harghita volcanic mountains and to the subsidence of the n s oriented intramontane borsec bilbor gheorgheni ciuc and brasov pull apart basins and the e oriented monocline related f g ras basin the regional drainage network is the composite of 1 older e se and s flowing rivers which cross the carpathians radiate towards the foreland and were probably established during the middle miocene sarmatian collision event 2 a more recent drainage system related to the contemporaneous development of the volcanoes and intramontaneous basins which generally drains westward into the transylvanian basin since late miocene time and has been capturing the older river system the older river drainage system has also been modified by late pliocene quaternary folding thrusting and monoclinal tilting along the pericarpathian orogenic front and by reactivated transverse high angle basement faults which cross the eastern carpathian foreland

palaeomagnetism of the south harghita volcanic rocks of the east carpathians implications for tectonic rotations and palaeosecular variation in the past 5 ma summary lavasofpliocene quaternaryageweresampledinthesouthharghitamountains whichform the southern end of the cu alimani gurghiu harghita volcanic chain of the east carpathians the analyses of 68 volcanic sites in the south harghita mountains provided 62 sites with well constrained directional data n 5 and k 50 in an age interval ranging from 0 5 to 4 3ma the age and polarity for the 62 sites 38 normal and 24 reversed are consistent with the geomagnetic reversal time scale and support the model of the southward migration of the volcanism the distribution of the vgps is fisherian and the mean pole position both from all contributing sites and from the 53 sites older than 2 ma includes the spin axis this result is consistent with the absence of important vertical axis rotations after the emplacement of the volcanicrocksinagreementwithtectonicmodelsforthepliocene quaternaryevolutionofthe bending area of the east carpathians virtual geomagnetic pole dispersions are consistently high compared with global values obtained between 40 and 55 n but closer to the values obtained only from the time averaged geomagnetic field initiative studies for the same latitudinal band our data are compatible with the prediction of the statistical palaeosecular variationmodeltk03 theinclinationanomalyislessthan1 inaccordwiththetotalaverage field global data these palaeomagnetic data from the south harghita volcanic rocks are the first data from the southeastern europe which can be considered in the databases for time averaged field and palaeosecular variation from lavas analyses in the last 5 ma

large scale deformation in a locked collisional boundary interplay between subsidence and uplift intraplate stress and inherited lithospheric structure in the late stage of the se carpathians evolution 1 the interplay between slab dynamics and intraplate stresses in postcollisional times creates large near surface deformation particularly in highly bent orogens with significant lateral variations in mechanical properties this deformation is expressed through abnormal foredeep geometries and contrasting patterns of vertical movements intraplate folding is often the controlling mechanism particularly when the orogenic belt is locked the study of these tectonic processes in the se carpathians indicates a generalized subsidence period during latest miocene pliocene times driven by the slab pull and an intraplate folding due to an overall quaternary inversion the latter accommodates 5 km ese ward movement of this area with respect to the neighboring units which creates complicated three dimensional deformation patterns potentially driven at a larger scale by the interaction between the adriatic indentor and the entire carpathians system the lithospheric anisotropy inherited from the subduction times concentrates strain and induces large scale deformation far away from the active plate margins this anisotropy is dynamic because of deep mantle processes related to the subducted slab during postcollisional times such as thermal reequilibration or increase in slab dip

sequence stratigraphy and paleogene tectonic evolution of the transylvanian basin romania eastern europe abstract the transylvanian basin of romania belongs to the 800 400 km wide pannonian domain of the european alpine megasuture bordered to the east and the north by the carpathians it represents a digitation of the epicontinental tethyan seaways locally connected during the palaeogene to the peripheral foredeep troughs during that time it was filled up by a 500 m thick sediment pile organized into three shallow marine and non marine facies alternations each evolved from alluvial fans to restricted marine and outer marine environments they are dated from lutetian to chattian times the study is focused on the lowermost alternation onlapping the basal post maastrichtian unconformity this alternation consists of the superimpossition of a thick retrogradational and a thin progradational depositional system the retrogradational depositional system grades upwards from stacked fault controlled deposits of alluvial fan ephemeral stream salina and sabkha and restricted marine bioclastic shales the progradational depositional system is composed of outer marine to estuarine sandstones and shales the two depositional systems are bounded at their tops by two baselevel change unconformities underlain by highly mobile low relief sandstone bodies that were deposited in shoal belts these two unconformities mark significant changes in the regime of the subsidence these are respectively a baselevel rise or drowning unconformity where the shoal deposits were associated with oolitic ironstones and glauconitic shales that typify basin starvation during a period of maximum basin drowning and a baselevel fall or uplifting unconformity where the bioclastic shoal deposits were buried by alluvial flood plain deposits that characterize periods of relief rejuvenation tentatively attributed to compressive events this bimodal succession is interpreted in terms of underfilled overfilled stages related to intraplate tectonic deformation the underfilled stage corresponds to the fault controlled drowning of the basin and the overfilled stage to the increasing flexural rigidity of the substrate culminating in differential uplift in the area three of these successions comprise the palaeogene sedimentary record of the transylvanian basin they attest to a large scale pulsating evolution of this continental microplate during its northward migration towards the european plate

interplay of tectonics and neogene post collisional magmatism in the intracarpathian region abstract distribution of the neogene calc alkaline magmatism of the carpathian arc is directly related in space and time to the kinematics of the two major terranes of the intracarpathian area alcapa tisia getia along the south eastern border of the european plate in the west carpathians and adjacent areas the volcanic activity occurred between 20 11 ma with large volumes of both acidic and intermediate rocks generally distributed randomly sometimes transversally to the orogenic belt and as rare small occurrences along the flysch belt in the east carpathians the volcanic rocks are distributed along the northern margin of the zemplin block the north easternmost part of the alcapa and eastward along the front of the getic block at the contact with european plate between tokaj slanske vihorlat up to northern calimani mountains the magmatism occurred between 14 9 ma and along the calimani harghita chain between 9 0 2 ma the calc alkaline magmatic rocks of the apuseni mountains are located in the interior of the tisia block and occurred between 14 9 ma the generation of the calc alkaline magmatism is considered here as the result of complex interplay between plate roll back and lithospheric detachment tectonic processes and the break off of the subducted plate mostly in a post collisional setting 1 the magmatites of the western carpathians and the pannonian basin were generated in direct relation to subduction roll back processes over the downgoing slab during the period of lateral extrusion and back arc extension in this area characterized by maximum crustal shortening we can infer further delamination processes to explain the generation of magmas 2 the magmatic rocks from the northern sector of the east carpathians tokaj slanske vihorlat up to the northern calimani mountains resulted after subduction roll back processes and an almost simultaneous break off of the descending plate all along the arc segment during main clockwise rotation of the intracarpathian terranes 3 in the eastern sector of the east carpathians calimani up to harghita mountains the magmatic rocks were generated through partial melting of the subducted slab followed by gradual break off of the subducted plate along strike north to south 4 the apuseni mts magmatic activity resulted in transtensional tectonic regime by decompressional melting of lithospheric mantle during the translation and rotation of tisia getia block

biostratigraphy and paleoenvironments of the late oligocene in the north western transylvanian basin revealed by the foraminifera assemblages abstract the paleoenvironmental evolution and biostratigraphy of the oligocene vima formation from the north western transylvanian basin maramure county romania is presented based on planktonic and benthic foraminiferal assemblages the deposits were assigned to late rupelian early chattian ages more precisely the globigerina angulisuturalis chiloguembelina cubensis crz o4 and paragloborotalia opima hoz o5 biozones the ecological preference of benthic foraminifera and statistical treatment of the raw data set were used to identify relationships between assemblages and reconstruct the ancient environments paleobathymetrical estimates indicate a deposition of the sediments in outer shelf to upper bathyal settings the shelf is characterized by alternating well oxygenated bottom waters and poor oxygen content indicated by low oxygen tolerant taxa the upper bathyal assemblages dominated by tubular agglutinated foraminifera suggest oligotrophic environments periodically disturbed by turbidite currents while the whole agglutinated communities suggest undersaturated bottom waters in respect to calcium carbonate and possible depletion in oxygen content due to water column stratification paleoclimatic reconstructions based on planktonic foraminifera suggest cool to temperate surface water temperatures with boreal influences the younger deposits of the f nt nele section indicate a warming trend at the surface waters the aggradational to progradational stacking pattern of the identified high frequency sequences suggest a high stand systems tract under the control of the regional tectonics

sudden death at the end of the mesozoic abstract a paleoecological analysis of the fossil record before and after the cretaceous tertiary boundary indicates that the widespread extinctions and biological stresses around the boundary are best explained in terms of a sudden significant but short temperature rise l alvarez and co authors having found an enrichment in iridium at the same boundary postulated that it was associated with the impact of an extraterrestrial body if this body struck the ocean the water injected into the atmosphere may have led to a transient increase in the global surface temperature this temperature pulse may have been primarily responsible for the effects observed in the biosphere the pattern of extinction of higher plant species suggests that splash down occurred in the northern pacific bering sea area

generation of normal and adakite like calc alkaline magmas in a non subductional environment an sr o h isotopic study of the apuseni mountains neogene magmatic province romania abstract neogene magmatism in the apuseni mountains of romania was active between 15 and 7 ma with an isolated final eruption at 1 6 ma several groups of magmatic rocks can be distinguished in the province on the basis of ages trace elements and isotopic compositions most are of calc alkaline affinity despite the fact that the region is located 200 km from the postulated carpathian subduction trench however adakite like calc alkaline magmas were also erupted and the youngest eruptions were of alkaline affinity magmatic rocks older than 13 5 ma are characterised by the highest 87sr 86sr 18o and d values in their phenocryst phases this early magmatism is considered to be a result of crustal melting related to the fast rotation of small crustal blocks volcanic rocks younger than 13 5 ma have lower 87sr 86sr and 18o ratios with a narrow range for pyroxene and amphibole mineral separates indicating closed system fractional crystallization a larger scatter of 87sr 86sr and 18o values is found in plagioclase phenocrysts and groundmasses indicating that a small amount of crustal assimilation also occurred the d values for hydrogen bearing phases such as amphibole biotite and groundmass indicate fractional crystallisation in a closed system and a trend of decreasing d in the source with time the magma source of normal calc alkaline adakite like magmas was not related to contemporaneous subduction but was likely due to melting of delaminated eclogitic mafic lower crust in contrast the late stage alkaline magmas were related to asthenospheric upwelling petrological analysis of the complex succession of magmas in the apuseni mountains province demonstrates that normal calc alkaline and adakite like magmatism can be generated in a non subductional environment in this case associated with an unusual extensional setting

seismic crustal structure between the transylvanian basin and the black sea romania abstract in order to study the lithospheric structure in romania a 450 km long wnw ese trending seismic refraction project was carried out in august september 2001 it runs from the transylvanian basin across the east carpathian orogen and the vrancea seismic region to the foreland areas with the very deep neogene focsani basin and the north dobrogea orogen on the black sea a total of ten shots with charge sizes 300 1500 kg were recorded by over 700 geophones the data quality of the experiment was variable depending primarily on charge size but also on local geological conditions the data interpretation indicates a multi layered structure with variable thicknesses and velocities the sedimentary stack comprises up to 7 layers with seismic velocities of 2 0 5 9 km s it reaches a maximum thickness of about 22 km within the focsani basin area the sedimentary succession is composed of 1 the carpathian nappe pile 2 the post collisional neogene transylvanian basin which covers the local late cretaceous to paleogene tarnava basin 3 the neogene focsani basin in the foredeep area which covers autochthonous mesozoic and palaeozoic sedimentary rocks as well as a probably permo triassic graben structure of the moesian platform and 4 the palaeozoic and mesozoic rocks of the north dobrogea orogen the underlying crystalline crust shows considerable thickness variations in total as well as in its individual subdivisions which correlate well with the tisza dacia moesian and north dobrogea crustal blocks the lateral velocity structure of these blocks along the seismic line remains constant with about 6 0 km s along the basement top and 7 0 km s above the moho the tisza dacia block is about 33 to 37 km thick and shows low velocity zones in its uppermost 15 km which are presumably due to basement thrusts imbricated with sedimentary successions related to the carpathian orogen the crystalline crust of moesia does not exceed 25 km and is covered by up to 22 km of sedimentary rocks the north dobrogea crust reaches a thickness of about 44 km and is probably composed of thick eastern european crust overthrusted by a thin 1 2 km thick wedge of the north dobrogea orogen

extreme methane deuterium nitrogen and helium enrichment in natural gas from the homorod seep romania abstract methane ch 4 in terrestrial environments whether microbial thermogenic or abiogenic exhibits a large variance in c and h stable isotope ratios due to primary processes of formation isotopic variability can be broadened through secondary post genetic processes such as mixing and isotopic fractionation by oxidation the highest and lowest 13 c and 2 h or d deuterium concentrations in ch 4 found in various geologic environments to date are defined as natural terrestrial extremes we have discovered a new extreme in a natural gas seep with values of deuterium concentrations d ch4 up to 124 that far exceed those reported for any terrestrial gas the gas seeping from the small homorod mud volcano in transylvania romania also has extremely high concentrations of nitrogen 92 vol and helium up to 1 4 vol carbon isotopes in ch 4 c 2 h 6 and co 2 and nitrogen isotopes in n 2 indicate a primary organic sedimentary origin for the gas a minor mantle component is suggested by the 3 he 4 he ratio r ra 0 39 both thermogenic gas formation modeling and rayleigh fractionation modeling suggest that the extreme deuterium enrichment could be explained by an oxidation process characterised by a d ch4 and 13 c ch4 enrichment ratio h c of about 20 and may be accounted for by abiogenic oxidation mediated by metal oxides all favourable conditions for such a process exist in the homorod area where increased heat flow during pliocene quaternary volcanism may have played a key role finally we observed rapid variations within 1 h in c and h isotope ratios of ch 4 and in the h 2 s concentrations which are likely caused by mixing of the deep oxidized ch 4 n 2 h 2 s he rich gas with a microbial methane generated in the mud pool of one of the seeps we hypothesize that the unusual features of homorod gas can be the result of a rare combination of factors induced by the proximity of sedimentary organic matter mafic metal rich volcanic rocks and salt diapirs leading to the following processes a primary thermogenic generation of gas at temperatures between 130 and 175 c b secondary alteration through abiogenic oxidation likely triggered by the neogene quaternary volcanism of the eastern transylvanian margin and c mixing at the surface with microbial methane that formed through fermentation in the mud volcano water pool the homorod gas seep is a rare example that demonstrates how post genetic processes can produce extreme gas isotope signatures thus far only theorized and that extremely positive d ch4 values cannot be used to unambiguously distinguish between biotic and abiotic origin