a palaeomagnetic approach to the origin of the black sea summary available palaeomagnetic data for the circum black sea region are reviewed with the object of evaluating the geodynamical evolution of the black sea jurassic data from the south of the stara planina forebalkan zone south of the moesian platform in bulgaria which was then part of the east european platform place the region at about 39 latitude while the pontides the northernmost tectonic unit of turkey were at a lower latitude 10 15 palaeomagnetic investigations on upper cretaceous magmatic rocks sampled in different parts of the srednogorie tectonic unit southern boundary of the stara planina forebalkan indicate that the region was at 39 palaeolatitude during the upper cretaceous while the pontides had moved northward to 23 palaeolatitude since early cretaceous time the great caucasus domain of the ussr was welded to eurasia by coniacian time and had a palaeolatitude of 36 calculated palaeopole positions for the above mentioned geological times for the pontides fit well with the african palaepoles but largely deviate from the eurasian ones taken together these observations indicate that the pontides were not part of eurasia instead they were separated from the east european platform by the early mesozoic tethys this conclusion does not favour the rifted back arc hypothesis for the formation of the black sea during cretaceous time as suggested by some researchers adamia et al 1977 hsii et al 1977 sengor yilmaz 1981

new results and a palaeomagnetic overview of the pontides in northern turkey summary palaeomagnetic results are reported from 16 sites within volcanic and volcano sedimentary rocks of cretaceous and eocene age from the central pontides in northern turkey the sampled area is bounded by the north anatolian fault naf to the south and the black sea to the north the palaeomagnetic data collected demonstrate the presence of both non rotated and anticlockwise rotated regions i declination directions including lower upper cretaceous and eocene sites do not indicate any significant rotations north of where the naf exhibits an arcuate shape ii 20 anticlockwise rotation was observed in the sinop peninsula the northernmost extremity of the central pontides iii in the west of the central pontides two sites with normal and reversed antipodal directions indicate a 20 anticlockwise rotation and iv another region lies to the east of the study area and shows a rotation in an anticlockwise sense of about 5 30 the upper cretaceous and eocene directions reported in this paper and other palaeomagnetic studies show that there is not much difference between the inclination values of the upper cretaceous i 40 1 95 7 2 and the eocene sites i 39 6 95 8 1 furthermore the values of the inclination available from both sedimentary and volcanic upper jurassic lower cretaceous formations are shallower than the upper cretaceous ones this suggests that the entire pontides have undergone a northward drift of over 2000 km since the upper jurassic

snow avalanche penetration into mature forest from timber harvested terrain clear cut logging in british columbia canada is creating new avalanche start zones from which snow avalanches sufficient in size to penetrate and destroy mature forest cover can initiate in addition to creating new start zones the presence of these logging cut blocks can augment the destructive potential of previously existing avalanche paths forest penetrating avalanches can pose a significant risk to down slope structures and resources this study is the first to develop and utilize a database containing information on penetration distances and lateral spread from avalanches that have penetrated forest cover the study area for this research spans the southern coast and columbia mountains of british columbia canada analysis focuses on terrain characteristics related to forest penetration and the resultant destruction of mature standing forest physical terrain and vegetation characteristics in the avalanche starting zone track and runout zone of 45 forest penetrating avalanches are described m

paleomagnetic implications on the evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we first re examined the apparent polar wander curves for stable eurasia and africa since the triassic these curves were then combined together with curves of north and south america according to the kinematics of the atlantic ocean and a synthetic polar wander curve was given then most of the paleomagnetic results from the tethys mobile belt from the atlantic to the pamirs were analysed several groups of plates microplates and blocks can be seen first relatively stable regions like maghreb and sicily which have not moved much then we have a group formed by iberia sardinia italy and to a lesser extent corsica and the western and central alps for these blocks movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of africa but they are sometimes stronger to the east a major change takes place the north of the aegean sea and the ionian zone are clockwise rotated and these rotations are recent oligocene miocene for the first part pliocene to the present for the second part a major problem arises in turkey caucasus and iran paleomagnetic results indicate a position far to the south of eurasia and at the same time geological evidence is in favour of a position close to eurasia we discuss these discrepancies

geochronology of the karadere basement nw turkey and implications for the geological evolution of the istanbul zone earlier geological work in the istanbul zone western pontide tectonic belt has revealed the presence of extensive basement outcrops exposed underneath palaeozoic and mesozoic to tertiary cover sequences the basement of suspected neoproterozoic age plays an important role in understanding the crustal accretion process in nw turkey we report the first results of a detailed pb pb and u pb zircon study complemented by nd sr whole rock and mineral data from basement rocks exposed in the karadere valley safranbolu area five samples were selected for this study comprising three metagranitoids and two metasediments zircon geochronology indicates that the metagranitoids were formed during late proterozoic pan african magmatic events between 590 and 560 ma the rocks are of tonalitic and granitic composition and have low nb y ratios and ti contents consistent with those of arc rocks a continental arc setting is supported by their sr and nd isotope data that indicate a contribution of a mantle source as well as crustal assimilation during magma genesis the metasediments can clearly be distinguished from the metagranitoids by their higher 87sr 86sr ratios and lower end values at 580 ma which supports the suggestion that the arc was underlain by mature continental crust zircons from the metasediments yield a range of pb pb ages between 1 860 and 710 ma thirty per cent of them fall between 890 and 710 ma possibly suggesting a derivation from gondwana afro arabian regions a sm nd garnet whole rock analysis obtained on a metagranite gives an age of 559 8 ma which either reflects pre metamorphic magmatic growth of garnet in a felsic melt or a syntectonic high temperature metamorphic event uplift and cooling of the basement is further constrained by rb sr biotite ages of 548 545 ma these lower cambrian mineral ages demonstrate that the istanbul zone was not thermally reactivated during the hercynian cimmerian or alpine orogeny in contrast to its neighbouring tectonic zones confirming its role as a suspect terrane in the modern western pontide tectonic belt

mineral chemistry and crystallization sequences in kimberlite and lamproite dikes from the sisimiut area central west greenland precambrian and eocambrian ultramafic and ultrapotassic dike rocks from the sisimiut holsteinsborg area of west greenland can be grouped into three main types each showing characteristic mineral parageneses micaceous kimberlites contain macrocrysts and phenocrysts of olivine and phlogopite set in a groundmass of olivine phlogopite diopside perovskite and spinels leucite lamproites contain olivine leucite pseudomorphed and phlogopite macrocrysts and phenocrysts in a matrix of phlogopite leucite diopside and rutile amphibole lamproites contain phenocrysts of diopside in a fine grained matrix of phlogopite diopside sanidine richterite ilmenite rutile and quartz olivine in the leucite lamproites have compositions fo93 to fo89 while olivine in the kimberlites have compositions fo90 to fo80 diopside in the kimberlites are calcic and contain relatively high al when compared to the diopside in the lamproites phlogopite in the kimberlites contain relatively high al and low ti and are deficient or low in calculated fe3 phlogopite in the lamproites contain relatively high ti and significant amounts of fe3 ilmenite xenocrysts from the kimberlites are magnesian with relatively high hematite contents whereas the groundmass ilmenites from the amphibole lamproites are manganoan ilmenites with low hematite and magnesium the spinels range compositionally from titaniferous magnesiochromite to titanomagnetite amphiboles are mainly potassium titanian richterites leucite is mostly pseudomorphed to k feldspar other phases present in variable amounts in the groundmass of the dikes are carbonate minerals chlorite serpentine apatite amphiboles actinolite arfvedsonite and a riebeckite like phase priderite sulphides and zircon mg ilmenites and pyrope garnets are considered xenocrystic while most olivine phlogopite and leucite macrocrysts are believed to be cognate the primary kimberlite and lamproite magmas originated in the mantle and were emplaced at a low level in the upper crust where they consolidated at contrasting levels of t h2o co2 o2 aal2o3 and asio2 the kimberlites crystallized olivine phlogopite spinels and perovskite as early phases the two lamproite types are related to different levels of volatile pressure a low h2o type crystallized leucite phlogopite and olivine at a pressure below 0 5 kbar and liquidus temperatures ranging from 1260 to 900 c a relatively high h2o type crystallized diopside phlogopite richterite rutile and ilmenite at a pressure above 1 kbar and liquidus temperatures most likely from 1150 to 950 c the crystallization of perovskite and al rich phlogopite points to a relatively low asio2 in the kimberlite magmas higher asio2 appears to have prevailed in the leucite lamproites constrained by the leucite orthoclase and perovskite rutile silica buffers the sanidine bearing amphibole lamproites record a relatively high asio2 with zircon and quartz crystallization in the groundmass the oxygen fugacities in the kimberlites are suggested from the appearance of olivine and magnetite in the groundmass to have been controlled by a fmq oxygen buffer the compositions of the richterites ilmenites and rutiles in the lamproites point to a relatively low fe3 and o2 in the melts

location of the western pontides nw turkey during triassic time preliminary palaeomagnetic results summary this paper reports preliminary results of palaeomagnetic data obtained from the lower triassic schtian and mid triassic anisian rocks in the western pontides nw turkey the triassic rocks have been studied by applying thermal and or alternating field demagnetization the characteristic magnetization has a 50d mean inclination derived from 41 samples taken from three separate sites although the inclination values for the three sites are similar the corresponding declination angles indicate that the gumusdere site which lies to the north of istanbul city has undergone 68d anticlockwise rotation while the tavsancil and denizlikoy sites which are to the southeast of istanbul have rotated 40d clockwise on average the mean inclination 50d places the western pontides at the southern margin of laurasia during lower and mid triassic time

jurassic cretaceous paleomagnetism and paleogeography of the pontides turkey published paleomagnetic data from the pontides indicate anomalously low jurassic and early cretaceous paleolatitudes compatible with the southern neo tethyan african continental margin and significantly different from paleolatitudes predicted for the northern eurasian neo tethyan margin we present a new set of paleomagnetic data from 50 late cretaceous sites mainly from the western pontides and from the eastern pontides and 11 early jurassic sites mainly from the eastern pontides fold tests indicate that the characteristic magnetization components predate eocene folding late cretaceous site mean declinations are northerly in the eastern pontides and rotated to the west by a few tens of degrees in the western pontides late cretaceous site mean declinations are affected by local clockwise rotation in one sampling region close to the north anatolian fault the mean late cretaceous inclinations and resulting paleolatitudes are 41 1 23 5 n and 43 7 25 5 n for the western and eastern pontides respectively for the eastern pontides the early jurassic liassic mean inclination is 60 5 yielding a paleolatitude of 41 4 n considerably further north than previous paleolatitude estimates for the eastern pontides at this time the paleolatitude estimates for the western and eastern pontides are consistent with these units being close to the eurasian continental margin during liassic and late cretaceous time

paleomagnetic constraints on the tectonic evolution of the sakarya continent northwestern anatolia comment abstract thirteen sites were sampled in northwestern anatolia in order to gather paleomagnetic information concerning the tectonic evolution of this region through jurassic to early tertiary time an interval encompassing much of the history of the neo tethys in this area specifically information concerning the history and behaviour of a crustal block the sakarya continent was sought in order to place some constraints on geologic models that have been proposed for the region four jurassic sites are believed to exhibit early magnetization signatures that yield similar paleolatitudes for all sites these results when compared with paleolatitude information for eurasia suggest that sakarya lay in close proximity to the southern eurasian margin at least during the jurassic part of its history significantly different declinations from the same four sites are interpreted to reflect the deformation of sakarya when it docked with eurasia during the early tertiary these rotations are not attributed to motions of the north anatolian fault since results from three paleocene sites in the same area show no evidence of significant rotation with respect to eurasia

late cretaceous early eocene tectonic development of the tethyan suture zone in the erzincan area eastern pontides turkey six individual tectonostratigraphic units are identified within the izmir ankara erzincan suture zone in the critical erzincan area of the eastern pontides the ayikayasi formation of campanian maastrichtian age is composed of bedded pelagic limestones intercalated with polymict massive conglomerates the ayikayasi formation conformably overlies the tauride passive margin sequence in the munzur mountains to the south and is interpreted as an underfilled foredeep basin the refahiye complex of possible late cretaceous age is a partial ophiolite composed of 75 by volume serpentinized peridotite mainly harzburgite 20 diabase and minor amounts of gabbro and plagiogranite the complex is interpreted as oceanic lithosphere that formed by spreading above a subduction zone unusual screens of metamorphic rocks e g marble and schist locally occur between sheeted diabase dykes the upper cretaceous karayaprak melange exhibits two lithological associations 1 the basalt radiolarite serpentinite association including depleted arc type basalts 2 the massive neritic limestone lava volcaniclastic association that includes fractionated intermediate composition lavas and is interpreted as accreted neotethyan seamount s the several kilometre thick karadag formation of campanian maastrichtian age is composed of greenschist facies volcanogenic rocks of mainly basaltic to andesitic composition and is interpreted as an emplaced upper cretaceous volcanic arc the campanian early eocene sutpinar formation 1500 m thick is a coarsening upward succession of turbiditic calcarenite sandstone laminated mudrock volcaniclastic sedimentary rocks that includes rare andesitic lava and is interpreted as a regressive forearc basin the late paleocene eocene sipikor formation is a laterally varied succession of shallow marine carbonate and siliciclastic lithofacies that overlies deformed upper cretaceous units with an angular unconformity structural study indicates that the assembled accretionary prism supra subduction zone type oceanic lithosphere and volcanic arc units were emplaced northwards onto the eurasian margin and also southwards onto the tauride gondwana related margin during campanian maastrichtian time further mainly southward thrusting took place during the eocene in this area related to final closure of tethys our preferred tectonic model involves northward subduction supra subduction zone ophiolite genesis and arc magmatism near the northerly eurasian margin of the mesozoic tethys

miocene remagnetisation of carbonate platform and antalya complex units within the isparta angle sw turkey abstract a palaeomagnetic study has been carried out within the mesozoic and tertiary units of the relatively autochthonous carbonate platforms and the allochthonous deep sea volcanics and sediments of the antalya complex exposed around the isparta angle sw turkey the antalya complex is interpreted as a mosaic of carbonate platforms basinal sediments volcanic and ophiolitic rocks which formed within a southerly strand of the neotethyan ocean adjacent to gondwana the results indicate a widespread remagnetisation event negative fold tests show that the remanence at most sites is of secondary origin e g within the cirali lavas the magnetisation is carried by magnetite of presumed authigenic origin the remagnetisation event is believed to have occurred in the early middle miocene burdigalian langhian it was possibly triggered by the migration of orogenic fluids ahead of the advancing lycian nappes during their emplacement onto the carbonate platforms subsequent to remagnetisation a large segment of the isparta angle underwent an anticlockwise rotation of 30 this rotation is attributed to the overall convergence and bending of the hellenic arc and the final stages of emplacement of the lycian nappes during the late miocene in agreement with previous studies previously southerly palaeolatitudes were inferred from late triassic extrusives of the godene zone calbali dag unit the post folding magnetisation identified here within the cirali lavas of the godene zone to the south implies that these low palaeolatitudes result from the inappropriate application of structural tilt corrections the available data cannot be used to substantiate an origin for the antalya units south of the equator in the early mesozoic instead a position close to the northern margin of gondwana is indicated

observations and numerical simulations of the braking effect of forests on large scale avalanches although the disaster reduction effects of forest braking have long been known empirically they have not been known in detail down to recent in this study we ascertained forest braking effect by numerical simulations using the avalanche dynamics program titan2d to model large scale avalanches one of these avalanches occurred in the makunosawa valley myoko and damaged a cedar forest the others occurred on mt iwate and damaged a subalpine forest all avalanches damaged many trees and terminated within the forests in our simulations the resistance of the forests to avalanches is simulated using a larger bed friction angle fitting the observations from the makunosawa avalanche by trial and error a bed friction angle of 13 14 in the non forested area and of 25 in the forested area is obtained we conducted simulations of the mt iwate avalanches using the same method as for the makunosawa valley avalanche and obtained good agreement between observations and simulations simulations reveal that without the forest the avalanche would have traveled at least 200 m farther than the forest s actual end in the makunosawa valley and at least 200 m and possibly up to 600 m farther on mt iwate this study therefore clearly shows that forests provide a braking effect for avalanches

a new classification of the turkish terranes and sutures and its implication for the paleotectonic history of the region abstract the turkish part of the tethyan realm is represented by a series of terranes juxtaposed through alpine convergent movements and separated by complex suture zones different terranes can be defined and characterized by their dominant geological background the pontides domain represents a segment of the former active margin of eurasia where back arc basins opened in the triassic and separated the sakarya terrane from neighbouring regions sakarya was re accreted to laurasia through the balkanic mid cretaceous orogenic event that also affected the rhodope and strandja zones the whole region from the balkans to the caucasus was then affected by a reversal of subduction and creation of a late cretaceous arc before collision with the anatolian domain in the eocene if the anatolian terrane underwent an evolution similar to sakarya during the late paleozoic and early triassic times both terranes had a diverging history during and after the eo cimmerian collision north of sakarya the kure back arc was closed during the jurassic whereas north of the anatolian domain the back arc type oceans did not close before the late cretaceous during the cretaceous both domains were affected by ophiolite obduction but in very different ways north directed diachronous middle to late cretaceous melange obduction on the jurassic sakarya passive margin senonian synchronous southward obduction on the triassic passive margin of anatolia from this it appears that the izmir ankara suture currently separating both terranes is composite and that the passive margin of sakarya is not the conjugate margin of anatolia to the south the cimmerian taurus domain together with the beydaglari domain part of the larger greater apulian terrane were detached from north gondwana in the permian during the opening of the neotethys east mediterranean basin the drifting cimmerian blocks entered into a soft collision with the anatolian and related terranes in the eo cimmerian orogenic phase late triassic thus suturing the paleotethys at that time the taurus plate developed foreland type basins filled with flysch molasse deposits that locally overstepped the lower plate taurus terrane and were deposited in the opening neotethys to the south these olistostromal deposits are characterized by pelagic carboniferous and permian material from the paleotethys suture zone found in the mersin melange the latter as well as the antalya and mamonia domains are represented by a series of exotic units now found south of the main taurus range part of the mersin exotic material was clearly derived from the former north anatolian passive margin huglu type series and re displaced during the paleogene this led us to propose a plate tectonic model where the anatolian ophiolitic front is linked up with the samail baer bassit obduction front found along the arabian margin the obduction front was indented by the anatolian promontory whose eastern end was partially subducted continued slab roll back of the neotethys allowed anatolian exotics to continue their course southwestward until their emplacement along the taurus southern margin mersin and up to the beydaglari promontory antaya mamonia in the latest cretaceous paleocene the supra subduction ocean opening at the back of the obduction front troodos type ocean was finally closed by eocene north south shortening between africa and eurasia this brought close to each other cretaceous ophiolites derived from the north of anatolia and those obducted on the arabian promontory the latter were sealed by a maastrichtian platform and locally never affected by alpine tectonism whereas those located on the eastern anatolian plate are strongly deformed and metamorphosed and affected by eocene arc magmatism these observations help to reconstruct the larger frame of the central tethyan realm geodynamic evolution