discrete plio pleistocene phases of tilting and counterclockwise rotation in the southeastern aegean arc rhodos greece early pliocene formation of the south aegean left lateral strike slip system the island of rhodos represents an uplifted block in the largely submerged southeastern aegean forearc it has a complex history of subsidence uplift and counterclockwise rotation during the plio pleistocene in response to the interplay between large scale geodynamic processes in this paper we present a new chronostratigraphic framework for the continental pliocene apolakkia basin of southwestern rhodos we combine these time constraints with recently published chronostratigraphic data from the marine plio pleistocene basins of northeastern rhodos to reconstruct rotational and vertical motions our palaeomagnetic results identify two rotation phases for rhodos c 10 9 6 counterclockwise ccw rotation between 3 8 and 3 6 ma and c 17 6 ccw rotation since 0 8 ma between these phases rhodos tilted to the se drowning the southeastern coast to a depth of 500 600 m between 2 5 and 1 8 ma then to the nw which resulted in the re emergence of the drowned relief between 1 5 and 1 1 ma we relate the rotations of rhodos to incipient formation of the south aegean sinistral strike slip system and the foundering of the rhodos basin the previously shown absence of messinian evaporites in the deep marine rhodos basin in combination with the 3 8 ma onset of ccw rotation of rhodos constrains the onset of the formation of the south aegean strike slip system between 5 3 and 3 8 ma the formation of this strike slip system is probably related to the interplay of oblique collision between the southeastern aegean region and the northward moving african plate the westward motion of anatolia gravitational spreading of the overthickened aegean lithosphere and the recently postulated southwestward retreat of the african subducted slab along a subduction transform edge propagator fault

deformation of western greece during neogene clockwise rotation and collision with apulia following an early miocene phase of n s extension affecting the entire hellenides 50 clockwise rotation affected western greece modern gps analyses show rapid southwestward motion in southwestern greece over subducting oceanic lithosphere and no motion in the northwest where greece collided with apulia we aim to identify the deformation history of western greece associated with the rotation and the collision with apulia the timing of the various phases of deformation is constrained via detailed analysis of vertical motions based on paleobathymetry evolution of sedimentary sequences overlying the evolving structures the results show that accompanying the onset of rotation compression was re established in western greece in the early langhian around 15 ma subsequently western greece collided with the apulian platform leading in the late miocene to a right lateral strike slip system running from the aliakmon fault zone in northern greece via the kastaniotikos fault and the thesprotiko shear zone to the kefallonia fault zone offshore western greece ne sw compression and uplift of the ionian islands was accompanied by ne sw extension in southwestern greece associated with faster southwestward motion in the south than in the north this led in the middle pliocene around 3 5 ma to collision without further shortening in northwestern greece from then onward nw se to n s extension east of apulia and gradually increasing influence of e w extension in the south accommodated motion of the hellenides around the apulian platform as a result curved extensional basin systems evolved including the gulf of amvrakikos sperchios basin gulf of evia system and the gulf of corinth saronic gulf system

new constraints on the active tectonic deformation of the aegean 1 site velocities from six separate global positioning system gps networks comprising 374 stations have been referred to a single common eurasia fixed reference frame to map the velocity distribution over the entire aegean we use the gps velocity field to identify deforming regions rigid elements and potential microplate boundaries and build upon previous work by others to initially specify rigid elements in central greece the south aegean anatolia and the sea of marmara we apply an iterative approach tentatively defining microplate boundaries determining best fit rigid rotations examining misfit patterns and revising the boundaries to achieve a better match between model and data short term seismic cycle effects are minor contaminants of the data that we remove when necessary to isolate the long term kinematics we find that present day aegean deformation is due to the relative motions of four microplates and straining in several isolated zones internal to them the rms misfit of model to data is about 2 sigma very good when compared to the typical match between coseismic fault models and gps data the simplicity of the microplate description of the deformation and its good fit to the gps data are surprising and were not anticipated by previous work which had suggested either many rigid elements or broad deforming zones that comprise much of the aegean region the isolated deforming zones are also unexpected and cannot be explained by the kinematics of the microplate motions strain rates within internally deforming zones are extensional and range from 30 to 50 nanostrain year nstrain year 10 9 year 1 to 2 orders of magnitude lower than rates observed across the major microplate boundaries lower strain rates may exist elsewhere within the microplates but are only resolved in anatolia where extension of 13 4 nstrain year is required by the data our results suggest that despite the detailed complexity of active continental deformation revealed by seismicity active faulting fault geomorphology and earthquake fault plane solutions continental tectonics at least in the aegean is to first order very similar to global plate tectonics and obeys the same simple kinematic rules although the widespread distribution of aegean seismicity and active faulting might suggest a rather spatially homogeneous seismic hazard the focusing of deformation near microplate boundaries implies the highest hazard is comparably localized

along strike changes in the structural evolution over a brittle detachment fault example of the pleistocene corinth patras rift greece abstract the patras corinth and northern saronic gulfs occupy a 200 km long n120 trending pleistocene rift zone where peloponnese drifts away from mainland greece the axes of patras and corinth basins are 25 km apart and linked by two transfer fault zones trending n040 the older one defines the western slope of panachaikon mountain and the younger one limits the narrow rion patras littoral plain between these two faults the ca 4 km thick rion patras series dips 20 30 ssw it is part of the patras gulf synrift deposits which pile in an asymmetric basin governed by a fault dipping ca 25 35 nne located in the southern gulf of patras mapping of this fault to the east in northern peloponnese shows that it is an inactive north dipping low angle normal fault 0 to 30 n called the northern peloponnese major fault npmf the structural evolution of the npmf was different in the gulfs of patras and corinth in the gulf of patras it is still active in northern peloponnese footwall uplift and coeval southward tilting flattened the fault and locked its southern part steeper normal faults formed north of the locked area connecting the still active northern part of the npmf to the surface after several locks the presently active normal faults psathopyrgos aigion helike trend along the southern shore of the gulf of corinth this migration of faults caused the relative 25 km northward shift of the corinth basin and the formation of ne sw trending transfer faults between the corinth and patras gulfs

role of plate kinematics and plate slip vector partitioning in continental magmatic arcs evidence from the cordillera blanca peru new structural and geochronological data from the cordillera blanca batholith in the peruvian andes coupled with nazca south american plate slip vector data indicate that oblique convergence and associated strike slip partitioning strongly influenced continental magmatic arc evolution both the strain field and mode of magmatism plutonism vs volcanism in the late miocene peruvian andes were controlled by the degree to which the arc parallel component of the plate slip vector was partitioned into the arc strong strike slip partitioning at ca 8 ma produced arc parallel sinistral shear strike slip intercordilleran basins and east west oriented tension fractures that facilitated emplacement of the cordillera blanca batholith ca 8 2 0 2 ma periods during which the strike slip component was not partitioned into the arc ca 10 and ca 7 ma were associated with roughly arc normal contraction and ignimbrite volcanism the data thus support the contention that contraction within continental magmatic arcs favors volcanism whereas transcurrent shear favors plutonism the tie between oblique convergence and batholith emplacement in late miocene peruvian andes provides a modern analogue for batholiths emplaced as the result of transcurrent shear in ancient arcs

kinematic setting and structural control of arc volcanism abstract the evaluation of the kinematic setting and the structural control of volcanic arcs are important in defining the tectono magmatic processes along convergent plate boundaries however our knowledge is fragmented and the available data highlight different behaviours this study analyzes the kinematic setting the structural control and the volcanic productivity of 16 arcs these arcs are characterized by predominant extensional compressional strike slip or oblique motions there is an overall coupling between the normal vs parallel motions along the arc and those of the underlying slab therefore the higher the trench normal or parallel component of the subduction rate the higher is the amount of arc normal or parallel motion this relation confirms that strain partitioning is in general feasible at many convergent settings involving also the volcanic arc portion the arc normal motion may be characterized by extension or compression as a function of the increase in the trench normal convergence or subduction velocity the lack of an evident relation between the subduction rate or convergence rate and the volcanic productivity of the arc is partly inconsistent with previous studies which highlight a relation between the subduction rate and melt production below arcs this discrepancy mainly suggests that different processes control the generation rise and eruption of magma at different depths varying the intrusive extrusive ratio along arcs the structure of the arc does not control the distribution of the volcanoes however it does control the volcanic output through different processes even though regional or local extension associated with strike slip or compressive structures is the ultimate requisite in any setting in general the higher the amount of extension the higher is the output rate along the arc

the effect of changing regional tectonics on an arc volcano methana greece abstract the peninsula of methana has the longest recorded volcanic history of any volcanic centre in the south aegean arc regional fault patterns in the arc changed during the pliocene quaternary with e w striking listric faulting increasingly important through the quaternary as recorded in well dated sedimentary basins this study investigates how the geochemistry and eruptive style of volcanic products is influenced by regional tectonics the volcanic stratigraphy of methana was refined using radiometric dating lithogeochemistry and field observations that included recording deformational structures and enclave abundance small n s striking pliocene domes and a central volcano of uncertain type phase a were eroded to produce a widespread volcaniclastic apron phase b in the early quaternary an explosive central volcano with flank eruptions of andesite developed phase c dacite domes and small andesitic stratovolcanoes formed throughout the mid and late quaternary phases d h basaltic andesite and andesite of phase c are the least evolved rocks characterised by high tio 2 rocks that have experienced important assimilation and fractional crystallisation in the crust have a high abundance of enclaves th u and alkalies na k ni and cr are abundant in phase a andesites due to crystallisation and entrainment of olivine and pyroxene whereas phase h andesites have the highest relative abundance of ba rb and sr from crystallisation and entrainment of hornblende and biotite pliocene domes of phase a were emplaced on n s striking listric faults during regional e w extension onset of ne sw faulting arguably crustal scale and strike slip in character led to the eruption of the least evolved rocks of phase c thereafter e w striking faults controlled the location of volcanism volcanism in phases f and g was particularly voluminous and was synchronous with the onset of steep normal faulting in the gulf of corinth 150 km west of methana these steep faults cross cut older lower angle listric faults it is times of changes in regional fault patterns as in phases c f and g that have the greatest influence on the eruptive style and abundance of volcanic products

first paleomagnetic results from mio pliocene series of the hellenic sedimentary arc abstract paleomagnetic measurements have been conducted on the mio pliocene series along the external sedimentary hellenic arc in order to detect the presence or absence of rotational deformations in different sections of the arc in the central eastern part of the arc crete and rhodes paleomagnetic directions are very closely aligned along the north south direction showing that this portion of the arc has not undergone significant rotation since at least 7 m y for crete and 4 m y for rhodes in the western and northwestern parts results from south peloponnesos zakinthos kephallinia and corfu indicate that this section of the arc has undergone a clockwise rotation detailed analysis of the data from the three ionian islands shows that their rotation began about 5 m y b p and has proceeded since then at roughly 5 m y giving a total amplitude of about 26 it is suggested that the beginning of this rotation is related to the lower pliocene compressive phase which most probably initiated the tectonic activity of the present day ionian margin

the structures stratigraphy and evolution of the gulf of corinth rift greece summary a multichannel seismic and bathymetry survey of the central and eastern gulf of corinth goc greece reveals the offshore fault geometry seismic stratigraphy and basin evolution of one of earths most active continental rift systems active right stepping en echelon north dipping border faults trend ese along the southern gulf margin significantly overlapping along strike the basement offsets of three akrata derveni sithas and xylocastro are linked the faults are biplanar to listric typically intermediate angle 35 in the centre and 45 48 in the east near the surface but decreasing in dip and or intersecting a low or shallow angle 15 20 in the centre and 19 30 in the east curvi planar reflector in the basement major s dipping border faults were active along the northern margin of the central gulf early in the rift history and remain active in the western gulf and in the subsidiary gulf of lechaio but unlike the southern border faults are without major footwall uplift much of the eastern rift has a classic half graben architecture whereas the central rift has a more symmetric w or u shape the narrower and shallower western gulf that transects the 40 km thick crust of the hellenides is associated with a wider distribution of overlapping high angle normal faults that were formerly active on the peloponnesus peninsula the easternmost sector includes the subsidiary gulfs of lechaio and alkyonides with major faults and basement structures trending ne e w and nw the basement faults that control the rift architecture formed early in the rift history with little evidence other than the vrachonisida fault along the northern margin in the marine data for plan view evolution by subsequent fault linkage several have maximum offsets near one end crestal collapse graben formed where the hanging wall has pulled off the steeper onto the shallower downdip segment of the derveni fault the dominant strikes of the corinth rift faults gradually rotate from 090 120 in the basement and early rift to 090 100 in the latest rift reflecting a 10 rotation of the opening direction to the 005 presently measured by gps the sediments include a locally 1 5 km thick early rift section and a late rift section also locally 1 5 km thick that we subdivide into three sequences and correlate with seven 100 ka glacio eustatic cycles the gulf depocentre has deepened through time currently 700 mbsl as subsidence has outpaced sedimentation we measure the minimum total horizontal extension across the central and eastern gulf as varying along strike between 4 and 10 km and estimate full values of 6 11 km the rift evolution is strongly influenced by the inherited basement fabric the regional nnw structural fabric of the hellenic nappes changes orientation to ese in the parnassos terrane facilitating the focused north south extension observed offshore there the basement penetrating faults lose seismic reflectivity above the 4 14 km deep seismogenic zone multiple generations and dips of normal faults some cross cutting accommodate extension beneath the goc including low angle 15 20 interfaces in the basement nappes the thermally cool forearc setting and cross orogen structures unaccompanied by magmatism make this rift a poor analogue and unlikely precursor for metamorphic core complex formation

laboratory assessment of the equivalent apertures of a rock fracture hydraulic electrical and tracer test results are presented for a natural fracture in granite the hydraulic and electrical apertures of the fracture are similar and suggest minimal fracture surface to surface contact tracer aperture exceeds hydraulic aperture indicating transport at a rate less than that predicted on the basis of hydraulic aperture numerical simulation of tracer transport reveals that transport within the fracture is not explicable in terms of parallel plate flow and that transport occurs locally at rates in excess of the overall rate defined by tracer aperture

late cenozoic deformation of the hellenide foreland western greece the late cenozoic structural evolution of western greece involved the shortening of mesozoic passive continental margin and cenozoic foreland basin sequences in a foreland propagating fold and thrust system and superimposed neotectonic deformation related to the development of an active island arc although the pre apulian zone has been regarded as the undeformed western foreland to the thrust belt three dimensional exposures in the ionian islands of kephalonia and zakinthos afford evidence of significant late neogene and quaternary shortening including thrusting on reactivated normal faults time relations and fault kinematics show that these structures are compatible with the westward migration of the locus of hellenide thrusting beyond its previously recognized limit and outer arc compression related to active subduction the presence of the pre apulian zone in the west contrasts with other aegean foreland areas where no such intermediate block lay between the thrust pile and old mesozoic oceanic crust consequently the pre apulian block took up continued hellenide shortening in the late miocene while oceanic crust was being overridden subducted in southern parts of the arc to the east the pre apulian zone subsequently overrode the ocean floored ionian sea during the late neogene the confusion in determining driving mechanisms for late cenozoic deformation in western greece and the apparent conflict between evidence for the age of initial subduction in different parts of the arc are explained by this model which is consistent with regional considerations including structuration in adjacent areas and important paleomagnetic rotations in the arc

active tectonics of the north and central aegean sea summary in this paper we examine the connection between the westward motion of turkey relative to europe and the extension in and around the aegean sea the principal new data available since the last attempt to synthesize the tectonics of this region by mckenzie 1978 are much improved focal mechanisms of earthquakes constrained by p and sh body wave modelling as well as by first motions these mechanisms show that the faulting in the western part of the aegean region is mostly extensional in nature on normal faults with a nw to wnw strike and with slip vectors directed nnw to nne there is evidence from palaeomagnetism that this western region rotates clockwise relative to stable europe in the central and eastern aegean and in nw turkey distributed right lateral strike slip is more prevalent on faults trending ne to ene and with slip vectors directed ne palaeomagnetic data in this eastern region is more ambiguous but consistent with very small or no rotations in the northern part and possibly anticlockwise rotations relative to europe in the south the strike slip faulting that enters the central aegean from the east appears to end abruptly in the sw against the nw trending normal faults of greece the kinematics of the deformation is controlled by three factors the westward motion of turkey relative to europe the continental collision between nw greece albania and the apulia adriatic platform in the west and the presence of the hellenic subduction zone to the south as the right lateral slip on the north anatolian fault enters the aegean region it splays out becoming distributed on several parallel faults the continental shortening in nw greece and albania does not allow the rotation of the western margin of the region to be rapid enough to accommodate this distributed e w right lateral shear and thus leads to e w shortening in the northern aegean which is compensated by n s extension as the southern aegean margin can move easily over the hellenic subduction zone the dynamics of the system once initiated is self sustaining being driven by the high topography in eastern turkey and by the roll back of the subducted slab beneath the southern aegean the geometry of the deformation resembles the behaviour of a system of broken slats attached to margins that rotate in spite of its extreme simplicity a simple model of such broken slats is able to reproduce quantitatively most of the features of the instantaneous velocity field in the aegean region including the slip vectors and nature of the faulting in the eastern and western parts the senses and approximate rates of rotation the overall extensional velocity across the aegean and the distribution of strain rates as seen in the seismicity and topography or bathymetry and using geodetic measurements as part of this study we re examined the relation between the surface faulting and the focal parameters determined seismologically for the three large 1981 gulf of corinth earthquakes and reassessed the evidence for associating particular earthquakes in the sequence with observed surface faulting an important result is that in one of the events there is a resolvable discrepancy between the slip vector measured at the surface and that determined from the seismic body waves

paleomagnetic stratigraphy and radiometric dating of the pliocene volcanic rocks of aegina greece the island of aegma includes some of the oldest volcanic rocks in the south hellenic arc previous radiometric dates range from 3 87 to 4 4 ma the volcanic sequence is divided into nine units on the basis of field relations petrography and geochemistry and the characteristic paleomagnetic polarity of each unit has been determined two new radiometric dates 2 1 and 3 9 ma show that the volcanism spans the pliocene a detailed chronology is proposed using the paleomagnetic data which places the most voluminous volcanism in the mid pliocene

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

the methana volcano geothermal resource greece and its relationship to regional tectonics abstract geophysical methods of analysis were applied in order to investigate the deep structure and the geothermal potential of the methana volcano ne peloponnesus greece the study is based on a re evaluation and reinterpretation of legacy magnetotelluric mt data with modern analysis methods as well as 3 d inversion of aeromagnetic data constrained by in situ measurements of magnetic susceptibility magmatic systems are located in regions of active tectonic processes that often play a controlling role the mt method is effective in delineating low resistivity functional elements of volcanic systems such as magma chambers vents thermal fluid reservoirs and thermal fluid circulation conduits the latter two of which are typically associated with active faults the aeromagnetic data can assist in mapping the configuration hence emplacement modes of volcanic rocks at depth accordingly the joint interpretation of these lines of evidence together with structural and geochemical information is expected to allow insight into the influence of contemporary tectonics on the inception and evolution of the volcano the contemporary stress field is mainly extensional nne ssw oriented and overall homogeneous in the area of methana it allows for the formation of wnw ese north easterly dipping normal faults w e faults consistent with the synthetic dextral r shear direction of riedel s shear theory and nw se faults consistent with the antithetic sinistral r shear direction all such features have been mapped on methana peninsula the magnetotelluric data imaged a significant geothermal reservoir developing around an intersection of the three active fault zones normal r and r at depths of 1 1 5 km below the centre of the peninsula as well as elongate epiphenomenal conductivity anomalies associated with the circulation of thermal fluids along all three fault zones the 3 d magnetic susceptibility model strongly suggests that the intrusion and emplacement of magmas were guided by the same active fault zones with particular reference to the r and r shears whose influence is imprinted on the configuration of volcanic rocks at depth the joint interpretation of all lines of evidence indicates that magmatism and volcanism at methana are almost completely controlled by tectonic activity in a manner analogous to the situation of the large santorini volcanic complex it also indicates that the reservoir is replenished through the weak permeable zone created by the intersection of the r and r shears which is very probably collocated with the main vent of intrusive magmatic activity and may connect with a shallow magma chamber at depths greater than 4 5 km the apparently common origin and similarities differences in the circulation paths of thermal fluids may amply explain both the individual characteristics and similarities differences in the chemical composition of thermal spring discharges which have been reported by hitherto geochemical investigations

the role of transcurrent intra arc tectonics in the configuration of a volcanic arc summary field investigations show that plio quaternary mexican and quaternary ecuadorian volcanic arcs are coeval with intra arc transcurrent or transtensional tectonics with motions along faults parallel or subparallel to the arc this relationship can also be observed in the quaternary kamchatka arc these arcs have an anomalously wide distribution of volcanic centres which cannot be explained simply by a low dip in the subducting lithosphere comparison with the intra arc tectonics and geometry of other quaternary arcs reveals that strike slip fault zones parallel to the arc favour magma rising in a broad surficial zone and may channel magma feeding mainly huge stratovolcanoes

post early messinian counterclockwise rotations on crete implications for late miocene to recent kinematics of the southern hellenic arc most geodynamical models for the kinematics of the central mediterranean recognise that major tectonic rotations must have played an important role during the neogene the hellenic arc is believed to have been subjected to clockwise rotations in the west and counterclockwise rotations in the east while the southern part crete shows no rotations kissel and laj 1988 many qualitative and quantitative models are based on the idea that crete did not rotate we present new palaeomagnetic data which show that post early messinian counterclockwise rotations have occurred on crete the amount of counterclockwise rotation generally varies between 10o and 20o but in central crete much larger rotations up to40o counterclockwise were found only a few sections did not show any rotation the anisotropy of magnetic susceptibility ams shows lineations which are consistently wnw ese throughout crete indicating post rotational wnw ese extension or nne sse compression the observed counterclockwise rotations are consistent with the results of tectonic modelling by ten veen and meijer 1998 the latter study compares the late middle miocene to recent kinematics with modelled intra plate stresses for various possible distributions of plate boundary forces observations reveal that motion along left lateral and right lateral faults occurred during the pliocene the model analysis shows these motions to be consistent with transform resistance along the eastern segment of the overriding margin the counterclockwise block rotations observed by us are probably a consequence of displacements along the left lateral and right lateral faults and could reflect a similar tectonic regime that involved transform resistance 1998 elsevier science b v all rights reserved

east west extension and holocene normal fault scarps in the hellenic arc examination of surface fault traces with spot images and in the field corroborates the inference that the active tectonics of southern peloponnesus and crete are dominated by approximately north south normal faulting and approximately east west extension the heights of holocene normal fault scarps yield first order regional estimates of fault slip rates between 0 1 and 2 3 mm yr most of the surface scarps probably ruptured during past earthquakes such as that which destroyed sparta in 464 b c on the sparta fault the holocene average slip rate and the recurrence time of large earthquakes may be 1 mm yr and 3000 yr respectively the regional pattern of quaternary faulting suggests that the east west extension near the hellenic subduction zone is fast about 5 10 m y the change from north south to east west extension in the late pliocene 2 4 ma implies that the aegean is starting to collide with the northern margin of africa

magnetic fabric and palaeomagnetic analyses of the plio quaternary calc alkaline series of aegina island south aegean volcanic arc greece abstract the south aegean volcanic arc represents the magmatic expression of active subduction of the african plate beneath eurasia in the region of greece plio quaternary calc alkaline dacite and andesite lava flows exposed on the island of aegina have been sampled for palaeomagnetic analyses to determine whether the western arc area has experienced vertical axis rotations in addition these units allow an assessment of the use of magnetic fabric anisotropy of magnetic susceptibility ams data as indicators of lava flow directions in silicic extrusive rocks providing a complement to the existing literature on ams of basaltic flows the magnetic mineralogy of both dacites and andesites is dominated by fine grained magnetite ti poor titanomagnetite sampled flows are characterised by oblate magnetic fabrics at site level which are co axial to flow surfaces although most sites also contain specimens with prolate ams ellipsoids where magnetic lineations are developed they are systematically aligned either parallel or orthogonal to average exposure scale lava flow directions magnetic lineations in these rocks therefore may be interpreted in terms of flow directions only when the latter are known a priori observed variability in the directions of remanent magnetisation recorded by the aegina lava flows may be explained wholly in terms of geomagnetic variations several sites record spot readings of the geomagnetic field during polarity transitions scatter of directions at the remaining sites is consistent with that expected from secular variation post eruption tilting of magnetisation vectors is shown to be limited the in situ mean direction of magnetisation of the non transitional sites is indistinguishable from the geocentric dipolar field used as a reference direction for these young

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

tectonic deformation and microseismicity of the saronikos gulf greece we deployed an on offshore seismic network consisting of 36 three component stand alone digital stations in the saronikos gulf and surrounding area and observed the microseismic activity from 17 august to 9 december 2001 the geometry and location of the network were designed to observe the offshore activity to connect known active faults onshore with those offshore an average of 15 events per day were recorded by a minimum of six stations the focal parameters of 739 events could be defined within the network area we located 306 events with an rms travel time residual of about 0 2 sec the epicenters in the saronikos gulf are aligned mainly along an east west trending fault with a length of nearly 30 km this fault is located north of aegina and could produce earthquakes as large as ms 6 5 it is the offshore continuation of a seismic zone located in east corinthia a second active fault was identified east of aegina trending northeast southwest it is probably linked to the northeast southwest striking zone of the salamis fili seismic region activated by the september 1999 event of athens outside the network we mapped an active area at the parnis mountain still active after the ms 5 9 event and a second one further northeast at the western coast of evia this zone is close to chalkis and the recently active psachna area the network also mapped intense activity at the northeastern coast of evia close to the city of kymi and the area of skyros which was seriously damaged by an ms 5 8 earthquake in 2001 the onshore offshore local network identified several regions of very high seismic activity not detectable by regional networks and demonstrated once more the advantage of deploying local seismic networks for mapping active deformation in very short periods of time

chronology of quaternary shoreline progradational sequences related to eustatic sea level changes sedimentation and subsidence in saronikos gulf greece abstract the stacking pattern of shoreline progradational sequences in subsiding basins have been used as a chronologic tool in the mediterranean region most previous studies have used a few key seismic lines seaward of deltas where the record is complicated by deltaic distributary switching southeastern saronikos gulf in the western aegean sea at the northwestern end of the south aegean arc lacks large river input of sediment the ene wsw and nw se trending neotectonic aegina and methana basins lie between the tectonically active gulf of corinth and the relatively stable cyclades plateau new high resolution seismic profiles from southeastern saronikos gulf have been interpreted according to the principles of seismic and sequence stratigraphy alpine basement and marine pliocene sediments have been recognized in the surrounding basin margins and more than 300 m and 150 m of unconsolidated sediments have been mapped in aegina and methana basin respectively progradational clinoforms that toplap against transgressive surfaces have been traced along strike leading to the establishment of a robust chronostratigraphic framework further controlled by sedimentation rates as extracted from cores southeastern saronikos gulf poses an outstanding example of development of progradational wedges formed within a microtidal wave dominated regime of low sedimentation rates between 2 8 cm ka and 3 2 cm ka within the framework of low subsiding basins with rates between 0 03 and 0 31 m ka in this environment more than 180 well preserved shoreline progradational units with attributes similar to the ones reported from the aegean and eastern mediterranean seas have been mapped and correlated to sea level lowstands back to 866 ka deeper mid pleistocene progradational units are also recognized tentatively back to 1 4 ma subsidence rate shows a dramatic decrease in the last 1 ma and significant numbers of faults became inactive during the last 130 ka in early middle quaternary methana basin was an isolated lake and extended terrestrial areas were shaped in the poros agios georgios plateau during sea level lowstands aegina basin was continuously connected to the aegean through the agios georgios fault valley this study demonstrates the robustness of chronology based on stacked shoreline progradational sequences and its applicability to determining rates of tectonic subsidence

tectonics of nisyros island greece by field and offshore data and analogue modelling abstract we use new on land and offshore structural data and scaled analogue models to analyse the fault tectonic pattern at nisyros island greece which has an active caldera that shows a complicated network of faults fractures and volcano tectonic structures we measured 157 faults that show dominant dip slip normal motions along planes mainly striking ne sw nne ssw and nnw sse inside the caldera dykes necks and morphometric parameters of volcanic domes explosion craters and fumarole pits indicate the control by ne striking discontinuities on magma and gas paths the nnw and ne striking faults bound a major block that underwent repeated downthrow and uplift movements during the late pleistocene holocene experiments with scaled models of caldera resurgence and two magma chambers indicate the formation of an hourglass shaped fault pattern as seen in plan view with an asymmetric increase in the fault offset and a widening of the fault divergence towards the volcano flank all these data suggest that regional fault tectonics and stress state strongly guided magma upwelling and the emplacement of volcanic centres whereas periodical bulging due to the overpressure of a second magma chamber located northwest of the caldera combined with faulting due to tectonic stresses can account for the overall deformation field

distribution and dispersal of clay minerals on the western continental shelf of india abstract sediment samples distributed over a distance of 1700 km from the inner continental shelf of western india were analysed for their clay mineral content by x ray diffraction the clay minerals present in the sediments in order of abundance are montmorillonite kaolinite illite chlorite and gibbsite based on the abundance of montmorillonite and kaolinite four clay mineral provinces on the continental shelf have been demarcated these are 1 the montmorillonite kaolinite illite chlorite province off the gulf of kutch 2 the montmorillonite rich zone off the gulf of cambay 3 a transition zone on the central parts of the shelf and 4 a relatively montmorillonite poor gibbsite province on the southwestern part of the shelf source rock influence on clay mineral composition appears to be more important than physical transport the southwest monsoon drift in the present case in the northwestern part of the study area the high velocity tidal streams of the macrotidal gulf of kutch act as dynamic barriers to longshore sediment dispersal leading to distinct clay mineral assemblages on the shelf north and south of the gulf mouth

reconciling the geological history of western turkey with plate circuits and mantle tomography abstract we place the geological history since cretaceous times in western turkey in a context of convergence subduction collision and slab break off to this end we compare the west anatolian geological history with amounts of africa europe convergence calculated from the atlantic plate circuit and the seismic tomography images of the west anatolian mantle structure western turkish geology reflects the convergence between the sakarya continent here treated as eurasia in the north and africa in the south with the anatolide tauride block atb between two strands of the neotethyan ocean convergence between the sakarya and the atb started at least 95 90 myr ago marked by ages of metamorphic soles of ophiolites that form the highest structural unit below sakarya these are underlain by high pressure low temperature metamorphic rocks of the tavsanli and afyon zones and the oren unit which in turn are underlain by the menderes massif derived from the atb underthrusting of the atb below sakarya was since 50 ma associated with high temperature metamorphism and widespread granitic magmatism thrusting in the menderes massif continued until 35 ma after which there is no record of accretion in western turkey plate circuits show that since 90 ma 1400 km of africa europe convergence occurred of which 700 km since 50 ma and 450 km since 35 ma seismic tomography shows that the african slab under western turkey is decoupled from the african plate this detached slab is a single coherent body representing the lithosphere consumed since 90 ma there was no subduction re initiation after slab break off atb collision with europe therefore did not immediately lead to slab break off but instead to delamination of subducting lithospheric mantle from accreting atb crust while staying attached to the african plate this led to asthenospheric inflow below the atb crust high temperature metamorphism and felsic magmatism slab break off in western turkey probably occurred 15 myr ago after which overriding plate compression and rotation accommodated ongoing africa europe convergence slab break off was accommodated along a vertical ne trending subduction transform edge propagator step fault zone accelerating southwestward slab retreat of the aegean slab the se aegean slab edge may have existed already since early miocene times or before but started to rapidly roll back along the southeastern aegean step in middle miocene times penetrating the aegean region in the pliocene

linking changes in tectonic style with magmatism in northern europe during the late carboniferous to latest permian abstract early carboniferous to permian magmatism associated with rifting within the northern foreland of the variscan orogen was widespread across europe during the long period of magmatic activity the regional tectonic setting changed across the region from early carboniferous extension and basin formation to a rifting wrenching style of deformation in the late carboniferous stephanian to early permian wrenching and faulting were accompanied by widespread voluminous and episodic magmatic extrusion intrusion and underplating this was followed by thermal relaxation and the development of the northern and southern permian basins in later permian times thermal relaxation was punctuated by a permo triassic phase of extension and graben formation 40ar 39ar ar step heating dating for mineral separates and whole rock samples of magmatic rocks from southern scandinavia oslo graben and south sweden and rugen north germany provides further radiometric evidence for three of the proposed periods of magmatic activity in the region latest carboniferous to earliest permian ages c 300 310 ma were obtained for volcanic rocks in the oslo graben and dolerite sills and dykes in south sweden and north germany this phase can be time correlated with magmatic activity that occurred throughout europe during large scale dextral wrenching that followed the variscan orogeny a second phase of alkaline intrusions is confined to the oslo graben and related to caldera collapse around c 275 ma the third permo triassic phase c 250 ma is considered to be related to a new tectonic cycle involving extension that triggered minor melting of enriched fertile mantle

the influence of rivers on the geochemistry of shelf sediments southwestern coast of india geochemical and magnetic susceptibility studies of shelf sediments off mangalore were carried out to understand the influence of rivers on sediment geochemistry to study the elemental distribution patterns and to evaluate the importance of the shelf as a source sink for base metals the contents of cu pb mn fe and al in the surficial sediments are lower by factors of 1 6 5 6 except ca which is higher by a factor of 3 4 in relation to riverine suspended particulate matter spm this is due to the seaward decrease of terrigenous influx which is reflected in the offshore protrusion of contours of al fe cu zn ni and magnetic susceptibility values particularly off netravati and gurpur rivers lower mn content is also due to its remobilization from the anoxic sulphidic shelf sediments in contrast to the elements mentioned above ca increases seaward suggesting that it is biogenic the enrichment factor ef indicates that the surficial sediments are depleted in cu zn and mn compared to average shale and other anoxic sediments and marginally enriched with ni co and pb in relation to the average shale however a comparison between the ef of spm of netravati gurpur rivers in the hinterland and surficial sediments indicates that the latter are depleted in mn and co but enriched with ni pb and fe thereby suggesting a source and a sink for the former and latter elements respectively to the arabian sea

gas geochemistry and co2 output estimation at the island of milos greece abstract twenty gas samples have been collected from the natural gas manifestations of milos island the majority of which is found underwater along its coast furthermore three anomalous degassing fumarolic areas kalamos paleochori and adamas have been recognized on land almost all the gases are co2 dominated with co2 ranging from 88 to 99 vol for the samples taken underwater while the on land manifestations show a wider range 15 98 due to air contamination methane reaches up to 1 0 vol h2 up to 3 2 vol and h2s up to 3 5 vol indicating a hydrothermal origin of the gases the isotope composition of he points out to mantle contributions up to 45 while the c isotope composition of co2 from 1 9 to 1 3 vs v pdb with most of the values around 0 5 suggests a prevailing limestone origin isotope composition of ch4 ranging from 18 4 to 5 0 vs v pdb for c and from 295 to 7 vs v smow for h points to a geothermal origin with sometimes evident secondary oxidation processes additionally co2 flux measurements showed high values in the three fumarolic areas up to 1100 1500 and 8000 g m2 d at kalamos paleochori and adamas respectively with the highest co2 flux values up to about 23 000 g m2 d being measured in the sea at kanavas with a floating chamber the south western part of the island was covered with a lower density prospection revealing only few anomalous co2 flux values up to 650 g m2 d the total output of the island 30 5 t d is typical of quiescent closed conduit volcanoes and comparable to the other volcanic geothermal systems of the south aegean active volcanic arc nisyros kos nea kameni methana and sousaki

upper cenozoic stratigraphy and paleogeographic evolution of myrtoon and adjacent basins aegean sea greece abstract the southern aegean sea has undergone major subsidence as a result of back arc extension during the neogene the details of this subsidence and the resulting sedimentation patterns have been examined in the myrtoon basin and adjacent areas including the south evoikos saronikos and argolikos gulfs by comparing seismic stratigraphy and facies interpretation from multichannel seismic profiles with the stratigraphic and sedimentologic history of adjacent land areas a detailed seismostratigraphy has been developed for the whole area in the late neogene the messinian erosion surface is an important regional marker pliocene and early quaternary markers are dated by comparison of marine transgressions with dated sections along the coast and dated volcanic rocks on islands the region appears to have progressively subsided since the miocene myrtoon basin and saronikos gulf were lake basins in the messinian that were flooded to form deep water marine basins during the basal pliocene transgression south evoikos and argolikos basins were progressively flooded during the pliocene and early quaternary in most areas deep marine basins filled principally with hemipelagic sediment but a submarine fan developed in the early pliocene in the northern myrtoon basin and fan deltas built into the basin from the east and southwest opening of marine gateways as a result of subsidence led to enhanced oceanographic circulation and the formation of regional erosion surfaces at basin margins

late neogene evolution of the western south aegean volcanic arc sedimentary imprint of volcanicity around milos abstract the distribution and stratigraphy of volcanic rocks around the island of milos has been interpreted from seismic reflection profiles a consistent seismic stratigraphy can be recognised in the major basins which contain mostly hemipelagic to low energy gravitative sedimentation interrupted only locally by mass transport deposits despite the proximity to volcanic islands volcanic rocks have a distinctive rather incoherent acoustic signature and in places overlie stratified marine sediment their age is inferred from position relative to the messinian seismic marker and by correlation with volcanic episodes dated on land volcanic rocks underlie an area five times larger than the present outcrops of volcanic rocks on milos and adjacent islands the main phase of volcanism was of late pliocene age it locally overlies folded lower pliocene strata in places the volcanic rocks have been planed off by quaternary coastal erosion surfaces and have subsequently subsided at rates of 0 2 0 35 mm yr basin margins appear to have been generally stable probably as a consequence of the relatively shallow water depths volcano flank failure deposits do not appear to be a major component of the sedimentary architecture

magnetic susceptibility of bottom sediments and suspended particulates from mulki pavanje river estuary and adjoining shelf west coast of india magnetic susceptibility has been determined for sediments from the riverine estuarine and marine environments near mulki west coast of india to understand the behaviour of magnetic minerals as they enter the oceanic realm through the estuary in the riverine environment magnetic minerals are bimodally distributed magnetic susceptibility is positively correlated with the magnetite weight percentage the magnetic mineral content decreases from the river head to the river mouth well sorted sediments are rich in magnetic minerals it is seen that the susceptibility of samples is governed both by the type of minerals present and by their relative abundances several instances of the environmental regime process influencing the magnetic susceptibility and hence the magnetic mineral content are discussed deposition of magnetic minerals in meander loops anoxic conditions in the inner shelf etc

the active submarine nw termination of the south aegean active volcanic arc the submarine pausanias volcanic field abstract methana peninsula shows the longest recorded volcanic history at the western end of the south aegean active volcanic arc including volcanic products from the upper pliocene to recent times the volcanic rocks comprise widespread dacite domes and andesite lava flows from several small volcanic centers and are only imprecisely dated in this paper the integrated analysis of swath bathymetry side scan sonar data and high resolution seismic reflection profiles correlated with core samples has allowed detailed mapping characterization and precise chronological identification of the pausanias submarine volcanic field activity offshore northern methana six volcanic cones or domes are recognized typically 1 3 km in diameter some elongated ne sw and some with a small central crater on their flanks the acoustically reflective volcanic rocks pass laterally into incoherent transparent seismic facies interpreted as volcaniclastic deposits possibly including hyaloclastites that interfinger with the regional basin sediments a sea bottom hummocky field is interpreted as volcanic avalanche and appears to be the submarine continuation of the volcaniclastic apron of northern methana peninsula a robust chronostratigraphic framework has been established based on the recognition of shoreline progradational units and their connection with quaternary eustatic sea level cycles relative dating of the different phases of submarine volcanic activity during the upper quaternary has been achieved by correlating the imaged volcaniclastic flows interlayered within the chronostratigraphically dated sediments dating by stratigraphic position relative to 2d imaged eustatic sea level clinoform wedges appears to be more precise than radiometric methods on land three main submarine volcanic events ve are recognized ve3 at 450 ka a less precisely dated interval at 200 130 ka ve2 and ve1 at 14 ka based on chronostratigraphic constraints subsidence rates of 0 16 0 008 m ka in between marine isotopic stages 6 and 12 and 0 19 0 009 m ka in between marine isotopic stages 12 and 16 were estimated for the marine basin north of methana the morphological similarity to the onshore volcanoes of methana peninsula implies that magmatic constructive processes were dominant regardless of whether in air or in water the upper quaternary submarine volcanic rocks of methana differ from those known from stratovolcanoes elsewhere in the mediterranean e g kos nisyros stromboli and in other volcanic arcs e g montserrat st vincent in the submarine development of domes or small cones the paucity of volcano flank failure deposits and the lack of explosive events pausanias volcanic products date the onset of ne sw faulting as well as the following tectonic phase of e w striking faults possibly related to basin inversion caused by a major rifting phase that also affected most of the south aegean arc and the adjacent gulfs of corinth and argolikos

rifting and shallow dipping detachments clues from the corinth rift and the aegean the corinth rift is superimposed on the hellenic nappe stack that formed at the expense of the apulian continental crust above the subducting african slab extension started in the pliocene and the major steep normal faults that control the geometry of the present day rift were born very recently some 600 kyr ago only they root into a shallow dipping zone of microseismicity recorded near the base of the upper crust the significance of this seismogenic zone is debated considering the northward dip of the zone of microseismicity the depth of microearthquakes and their focal mechanisms we observe a strong similarity with the northern cycladic detachments in terms of expected pressure temperature conditions and kinematics we herein show 1 that the formation of the corinth rift can be considered a part of a continuum of extension that started some 30 35 ma in the aegean and that was recently localised in a more restricted area 2 that the present day structure and kinematics of the corinth rift can be explained with a series of decollements relayed by steeper ramps that altogether formed a mechanically weak crustal scale detachment and 3 that the deformation fluid behaviour and metamorphic features seen in the northern cycladic metamorphic core complexes can be good analogues of the processes at work below the corinth rift

what triggered the early to mid pleistocene tectonic transition across the entire eastern mediterranean abstract subduction plays a fundamental role in plate tectonics and when interrupted it may trigger a series of geodynamic and sedimentary responses synchronous structural modifications recorded across the entire eastern mediterranean region are dated to a relatively short period early to mid pleistocene these deformations are documented within plates e g arabian sinai and african plates along plate boundaries e g dead sea and north anatolian faults and cyprus arc and in the mediterranean basin during the same period the northward subduction of the sinai plate was interrupted when the eratosthenes seamount cyprus arc collision initiated subduction collision processes of the eastern mediterranean serve as a unique modern analogue for similar settings worldwide understanding their association with accompanying neo tectonic processes is therefore predominantly important by fostering a detailed and comprehensive approach this research provides a coherent tectonic picture for the eastern mediterranean early to mid pleistocene tectonic transition in order to explore its triggering mechanisms since the neogene convergence across the eastern mediterranean was accompanied by eurasian indentation by arabia northward motion westwards anatolia escape and southwards aegean propagation this semi counterclockwise plate motion was temporarily interrupted by the incipient seamount arc collision which is suggested here as a trigger of the early to mid pleistocene tectonic transition

geodetic constraints on the tectonic evolution of the aegean region and strain accumulation along the hellenic subduction zone article i nfo we present evidence that gps velocity estimates of plate motions and fault slip rates agree to within uncertainties with geologic estimates during the most recent phase of the geologic evolution of the e mediterranean region post late miocene on this basis we use the gps differential velocities to estimate the timing of initiation of the principal structures in nw turkey the n aegean sea and central greece including the marmara sea the gulfs of evia goe and corinth goc and the kephalonia transform fault ktf we interpret these ages to indicate that the north anatolian fault propagated across the n aegean opening the goe and goc and initiating the ktf during the past 1 4 ma we further suggest that aegean extension that was earlier more distributed across the aegean basin became focused on this new fault system allowing the southern aegean and peloponnisos to translate sw with little internal deformation as observed today with gps this change in tectonic configuration may account for the clear geologic evidence for crustal thinning throughout the s aegean in apparent contradiction with low present day strain rates we further show that the low present day strain rate along the southern edge of the aegean micro plate requires substantial aseismic slip along the plate interface below crete consistent with the low level of historic subduction type earthquakes along this segment of the subduction zone

are s c structures duplexes and conjugate shear zones different manifestations of the same scale invariant phenomenon abstract by measuring s spacing c spacing and the s c angle in deformed rocks this paper investigates the geometry of previously published examples of s c and s c like structures on a scale range between micrometres and several hundred kilometres the results indicate that common s c fabrics of thin section hand specimen and outcrop scale and conjugate fault mylonite zones of map scale define a simple function c spacing 2 s spacing which depicts a scale invariant geometry over ten orders of magnitude logarithmic plots of cumulative frequency suggest that the s c fractal set d 0 13 is restricted to the scale range between 600 800 m and 1 km where genuine s c structures characterized by antithetic shear on the s planes can be formed below 600 800 m grain scale processes seem to influence the development of s c structures above the upper limit 1 km only s c like structures with duplex kinematics synthetic shear on s planes occur the s c and s c c fractals are envisaged as self similar structures where the foliations work as both s or c planes depending on which scale is considered

the geochemistry of manganese carbonate in panama basin sediments abstract the mn distribution in panama basin area sediments and interstitial waters is discussed striking surficial mn enrichments produced by a well known diagenetic recycling process characterize the sediments of the region thermodynamic solubility calculations indicate that in at least one core interstitial waters approach saturation with respect to mnco3 a mixed carbonate phase of composition mn48 ca47 mg5 co3 was recovered from an ash band in the same core the association of this material with the coarse volcaniclastic debris is thought to result from facile manganous carbonate precipitation in sediment horizons of coarser mean grain size since sulphate reduction in the upper two metres of panama basin sediments is fairly minor little increase in alkalinity is observed and it is postulated that significant production of carbonate alkalinity is not a prerequisite for manganous carbonate generation in hemipelagic sediments a more important factor appears to be the availability of mn oxides for solution during early diagenesis stable c isotopic analyses indicate that little c of organic origin is used in the precipitation reaction in either panama basin or loch fyne scotland sediments

complex layered deformation within the aegean crust and mantle revealed by seismic anisotropy continental lithosphere can undergo pervasive internal deformation often distributed over broad zones near plate boundaries however because of the paucity of observational constraints on three dimensional movement at depth patterns of flow within the lithosphere remain uncertain endmember models for lithospheric flow invoke deformation localized on faults or deep shear zones or alternatively diffuse viscous fluid like flow here we determine seismic rayleigh wave anisotropy in the crust and mantle of the aegean region an archetypal example of continental deformation our data reveal a complex depth dependent flow pattern within the extending lithosphere beneath the northern aegean sea fast shear wave propagation is in a north south direction within the mantle lithosphere parallel to the extensional component of the current strain rate field in the south central aegean where deformation is weak at present anisotropic fabric in the lower crust runs parallel to the direction of palaeo extension in the miocene the close match of orientations of regional scale anisotropic fabric and the directions of extension during the last significant episodes of deformation implies that at least a large part of the extension in the aegean has been taken up by distributed viscous flow in the lower crust and lithospheric mantle

a critical evaluation of depositional parameters controlling the variability of organic carbon in arabian sea sediments abstract organic carbon distribution in the surficial sediments of the arabian sea to some extent mirrors the surface productivity being both high in the peripheral portions and low in the central region suggesting that the productivity is a primary source of organic matter however a critical examination reveals that the organic enrichment on the slope of the indian margin is two to four higher max 16 71 than on the slope of the arabian peninsula max 7 54 while the productivity in the former region is three to four times lower than the latter this observation suggests that the influence of productivity on organic enrichment is of secondary importance high concentrations 4 of organic carbon exactly coincide with the oxygen minimum zone 150 1500 m water depth evidently reflecting the crucial role played by the anoxic bottom waters in the preservation of organic carbon incidently the organic rich band along the western indian slope is wide long and highly concentrated as compared to that of the slope of the arabian peninsula and no organic enrichment is found on other continental slopes of the arabian sea although an equally intense oxygen minima impinge on the floor of the slope such a variability of organic carbon on the slopes is attributed to various geological parameters such as texture of sediments rates of fine terrigenous sediment deposition shelf width slope gradient bottom currents and adsorption capacity of individual clay minerals all these observations suggest that the productivity is not an ultimate control for the organic enrichment of bottom sediments but it is the bottom water anoxia in conjunction with various depositional parameters which determine the degree of preservation

manganese fluxes from mississippi delta sediments abstract massive sediment deposition on the mississippi river delta establishes reducing conditions sufficient to bring about mn dissolution in the top millimeters of sediment as a result significant fluxes of dissolved mn pass from the delta sediments to the overlying water column this process is examined by study of chemical partitioning of mn in river particulates and delta sediments and from interstitial water chemistry remobilized mn is actively transported away from the delta area with aluminosilicate detritus thereby providing excess mn to the deep gulf of mexico at the expense of the delta sediments

climatic aridity over india 11 000 years ago evidence from feldspar distribution in shelf sediments abstract feldspars and quartz contents of sand and silt fractions of forty three samples from the western continental shelf of india were determined by the x ray diffraction method the results indicate that the feldspar content in the relict 9 000 12 000 yrs b p outer continental shelf sediments exceeds the feldspar content in modern inner continental shelf sediments the types of feldspar are maximum and intermediate microcline orthoclase and high albite the paleoclimatic inferences drawn from these data are that the climate during the late pleistocene and early holocene was arid these findings are in general agreement with the climate of other tropical areas for that period

quaternary neotectonics of the south aegean arc abstract the sedimentary and tectonic quaternary evolution of the south aegean arc has been interpreted from 8000 line km of sparker seismic reflection profiles the older parts of basins formed by e w trending faults and accumulated hemipelagic sediment younger active faulting trends nnw in the western part of the arc and ene in the eastern arc the ene trending faults record sinistral strike slip motion broadly parallel to the convergence direction of the aegean anatolian and african plates the north south faults in the western arc are similar to those on land in the south peloponnese chronology is estimated from sedimentation rates in cores and from stacked progradational units on basin margins controlled by eustatic changes in sea level the younger fault pattern developed at 0 6 0 8 ma in the western and central arc but progressively younger in the southeastern part of the arc the older basin fill with e w faults is of early quaternary and pliocene age an older regional unconformity corresponds to an early pleistocene unconformity in the cretan basin particularly in the area east of santorini faulting has resulted in startling changes in palaeogeography such that some areas were late pliocene basins positive features during the pleistocene and then subsided 600 m in the last 0 2 ma such rapid basin inversion resulted in uplift of stratified hemipelagic muds which were deformed by creep or failure so that debris flow deposits accumulated in valleys and ponded basins these fundamental tectonic changes in the past two million years indicate that much of the deformation resulting from the interaction of the eurasian african and anatolian aegean plates is taken up at the southern margin of the aegean microplate probably because subduction of the african plate has slowed as a result of collision of continental crust regional fault patterns are a consequence of spatially varying effects of subduction roll back

lateritisation of gabbro granophyre rock units of the ezhimala complex of north kerala india abstract laterites are ubiquitous in kerala and are developed over different rock types the laterite profiles developed over gabbro granophyre of the ezhimala complex are discussed here the principal mineral assemblages of the laterites are kaolinite gibbsite goethite hematite and quartz with minor amounts of zircon amorphous ferric hydroxide al hydroxide and al silicate are also present samples from various units of the weathering profile have been analysed for major and trace elements major element data show a steady depletion of si and enrichment of sesquioxides and tio2 during weathering it is also observed that the more the content of the mobile elements si mg ca k na in the parent rock the greater is its depletion during lateritisation the trace elements co cr v cu and ni show an enrichment while zn and ba show depletion over both the rock types pb shows almost a consistent behaviour