transition from a singly vergent to doubly vergent wedge in a young orogen the greater caucasus the greater caucasus mountains due to their youth 5 ma provide an opportunity for insight into the early stages of orogen development during continent continent collision however their recent tectonic evolution and first order architecture remain unclear here we investigate the evolution of the orogen by integrating new observations of the fluvial geomorphology and neotectonics of the range with prior work on seismicity geodetic strain bedrock geology and foreland basin structure we find that the range contains four zones along strike that differ in structural architecture topography and first order tectonic history in particular two south directed singly vergent zones at the western and eastern tips of the orogen are separated by both a central doubly vergent zone that is dominated by north directed deformation and an eastern doubly vergent zone in which south directed thrusting dominates we hypothesize that the along strike changes in vergence and locus of deformation reflects different stages in the development of a doubly vergent orogen with the tips of the range preserving an early singly vergent form and the center recording a more advanced orogen the differences between the two doubly vergent zones seem to be driven by the initial stages of collision between the structurally thickened crust of the greater and lesser caucasus orogens which initiated at 5 ma

the influence of climate on the tectonic evolution of mountain belts simple physical arguments analogue experiments and numerical experiments all suggest that the internal dynamics of actively deforming collisional mountain ranges are influenced by climate however obtaining definitive field evidence of a significant impact of climate on mountain building has proved challenging spatial correlations between intense precipitation or glaciation and zones of rapid rock uplift have indeed been documented in numerous mountain ranges and are consistent with model predictions more compelling evidence such as tectonic changes in response to rather than just coincident with climate change has however rarely been documented triggered by a climate driven increase in erosion rate friction dominated mountain ranges are expected to show a number of simultaneous responses a decrease in the width of the range a temporary increase in sediment yield a persistent increase in the rate of rock uplift and a reduction in the subsidence rate of surrounding basins the most convincing field evidence for such a coordinated response of a mountain range to climate change comes from the european alps and the st elias range of alaska field studies and experimental research during the past two decades have provided considerable evidence for a significant influence of climate on tectonics recent advances suggest that model predictions can guide future fieldwork aimed at substantiating this view

topography relief and trmm derived rainfall variations along the himalaya 1 along the southern himalayan topographic front the indian summer monsoon modulates erosive processes and rates to investigate the influence of topography and relief on rainfall generation and resultant erosion we processed satellite rainfall amounts for the last 8 years 1998 2005 from the tropical rainfall measurement mission trmm based upon a spatial resolution of 5 5 km for the himalaya we identify 1 the spatial distribution of rainfall and 2 the large scale relationships between topography relief and rainfall locations our results show two distinct rainfall maxima along strike in the himalaya the first outer rainfall peak occurs along the southern margin of the lesser himalaya within a narrow band of mean elevation 0 9 0 4 km and mean relief 1 2 0 2 km the second discontinuous inner band typically occurs along the southern flank of the greater himalaya elevation and relief both 2 1 0 3 km

microbes play an important role in the alteration of oceanic crust microbes have been identified within altered parts of the glass rims of pillow lavas in the upper oceanic crust 237 m below the top of the volcanic basement of odp hole 896a at the costa rica rift their presence is verified by spherical and vermicular microbodies containing dna the elemental composition of the microbially processed areas differ from the parent glass further the microbially processed parts showing different morphological forms also show different elemental composition extreme k enrichment indicate that microbes are presently active in the alteration process the carbon isotopic composition of disseminated carbonates within the basaltic section of the hole 504b 1 km distance from hole 896a also give evidence for microbial activity during rock alteration the 13c values of most of these trace carbonates are very low reflecting metabolic control of the carbon cycle in these rocks microbial alteration of basaltic glass comprising a substantial volume and surface area of the upper oceanic crust may thus play an important role in the element exchange between oceanic crust and seawater

linear prediction of sea ice anomalies stationary and cyclostationary statistical models are developed to predict arctic and antarctic sea ice anomalies using as predictors previous sea ice atmospheric and oceanic anomalies a prediction model hierarchy is developed by using first internal i e sea ice predictors including persistence lateral advection and diffusion and a cyclostationary model that allows the prediction coefficients to vary seasonally an external cyclostationary model hierarchy is developed next to investigate the ability of atmospheric winds heat flux proxies air temperatures and sea surface temperatures sst s to predict sea ice extent in the arctic the highest skill was generally achieved by the cyclostationary internal model attempts to forecast the ice data at 1 2 month intervals after removal of its autoregressive component using external predictors gave nonsignificant models at longer lead times e g 3 months the sst in the north pacific was superior to persistence for sea ice prediction in the western bering sea in the southern ocean especially off east antarctica the model that included lateral advection and diffusion outperformed both persistence and the cyclostationary internal model in the weddel sea and the ross sea persistence proved to be the best sea ice predictor no external models were tested for antarctic sea ice because of insufficient data

climatic control on rapid exhumation along the southern himalayan front abstract along the southern himalayan front shf areas with concentrated precipitation coincide with rapid exhumation as indicated by young mineral cooling ages twenty new young 80 of the annual precipitation aft cooling ages reveal a coincidence between rapid erosion and exhumation that is focused in a 50 70 km wide sector of the himalaya rather than encompassing the entire orogen assuming simplified constant exhumation rates the rocks of two age vs elevation transects were exhumed at 1 4 0 2 and 1 1 0 4 mm a with an average cooling rate of 40 50 c ma during pliocene quarternary time following other recently published hypotheses regarding the relation between tectonics and climate in the himalaya we suggest that this concentrated loss of material was accommodated by motion along a back stepping thrust to the south and a normal fault zone to the north as part of an extruding wedge climatically controlled erosional processes focus on this wedge and suggest that climatically controlled surface processes determine tectonic deformation in the internal part of the himalaya

controls on the strength of coupling among climate erosion and deformation in two sided frictional orogenic wedges at steady state 1 many important insights regarding the coupling among climate erosion and tectonics have come from numerical simulations using coupled tectonic and surface process models however analyses to date have left the strength of the coupling between climate and tectonics uncertain and many questions unanswered we present an approximate analytical solution for two sided orogenic wedges obeying a frictional rheology and in a condition of flux steady state that makes explicit the nature and sensitivity of the coupling between climate and deformation we make the simplifying assumption that the wedge grows in a self similar fashion consistent with airy isostasy such that topographic taper is invariant with orogen width tectonic influx rate and climate we illustrate first how and why the form of the erosion rule matters to orogen evolution and then derive a physically based orogen scale erosion rule we show that steady state orogen width crest elevation and crustal thickness are controlled by the ratio of accretionary flux to erosional efficiency to a power dictated by the erosion process remarkably we show that for most combinations of parameters in the erosion law rock uplift rate is more strongly controlled by erosional efficiency than it is by the accretionary flux further assuming frontal accretion with no underplating the spatial distribution of erosional efficiency dictates the relative rock uplift rates on the pro wedge and retro wedge and the time averaged trajectories of rocks through the orogen the restriction to invariant frictional properties is conservative in these respects systems subject to positive feedback between erosion and rheology will exhibit even stronger coupling among climate erosion and deformation than shown here

beyond threshold hillslopes channel adjustment to base level fall in tectonically active mountain ranges numerous empirical and model based studies argue that in general hillslopes and river channels increase their gradients to accommodate high rates of base level fall to date however few data sets show the dynamic range of both these relationships needed to test theoretical models of hillslope evolution and river incision here we utilize concentrations of 10 be in quartz extracted from river sand on the eastern margin of the tibetan plateau to explore relationships among short term 10 2 10 5 a erosion rate hillslope gradient and channel steepness our data illustrate nonlinear behavior and a threshold in the relationship between erosion rate and mean hillslope gradient confi rming the generalization that hillslopes around the world are limited by slope stability and cease to provide a metric for erosion at high rates 0 2 mm a the relationship between channel steepness index and erosion rate is also nonlinear but channels continue to steepen beyond the point where threshold hillslopes emerge up to at least 0 6 mm a demonstrating that channel steepness is a more reliable topographic metric than mean hillslope gradient for erosion rate and that channels ultimately drive landscape adjustment to increasing rates of base level fall in tectonically active settings

landscape form and millennial erosion rates in the san gabriel mountains ca abstract it has been long hypothesized that topography as well as climate and rock strength exert first order controls on erosion rates here we use detrital cosmogenic 10 be from 50 basins ranging in size from 1 to 150 km 2 to measure millennial erosion rates across the san gabriel mountains in southern california where a strong e w gradient in relief compared to weak variation in precipitation and lithology allow us to isolate the relationship between topographic form and erosion rate our erosion rates range from 35 to 1100 m ma and generally agree with both decadal sediment fluxes and long term exhumation rates inferred from low temperature thermochronometry catchment mean hillslope angle increases with erosion rate until 300 m ma at which point slopes become invariant with erosion rate although this sort of relation has been offered as support for non linear models of soil transport we use 1 d analytical hillslope profiles derived from existing soil transport laws to show that a model with soil flux linear in slope but including a slope stability threshold is indistinguishable from a non linear law within the scatter of our data catchment mean normalized channel steepness index increases monotonically though non linearly with erosion rate throughout the san gabriel mountains even where catchment mean hillslope angles have reached a threshold this non linearity can be mostly accounted for by a stochastic threshold incision model though additional factors likely contribute to the observed relationship between channel steepness and erosion rate these findings substantiate the claim that the normalized channel steepness index is an important topographic metric in active ranges

mantle lithosphere delamination driving plateau uplift and synconvergent extension in eastern anatolia eastern anatolia is the site of lithospheric thinning plateau uplift heating and synconvergent extension using numerical geodynamic experiments we test the hypothesis that these tectonic anomalies are all related and the consequence of delamination of the mantle lithosphere our findings indicate that delamination during plate convergence results in 2 km high plateau uplift the removal of mantle lithosphere induces distinct regions of contraction and thickening as well as extension and thinning of the crust the latter occurs even within a regime of plate shortening although it is muted with increasing plate convergence detachment of the delaminating slab results in minor surface topographic perturbation but only above the delamination hinge the plateau uplift and pattern of surface contraction and or extension are consistent with a topographic profile at 42 e and geologically interpreted zone of synconvergent extension at eastern anatolia

decoupling of modern shortening rates climate and topography in the caucasus the greater and lesser caucasus mountains and their associated foreland basins contain similar rock types experience a similar two fold along strike variation in mean annual precipitation and were affected by extreme base level drops of the neighboring caspian sea however the two caucasus ranges are characterized by decidedly different tectonic regimes and rates of deformation that are subject to moderate less than an order of magnitude gradients in climate and thus allow for a unique opportunity to isolate the effects of climate and tectonics in the evolution of topography within active orogens there is an apparent disconnect between modern climate shortening rates and topography of both the greater caucasus and lesser caucasus which exhibit remarkably similar topography along strike despite the gradients in forcing by combining multiple datasets we examine plausible causes for this disconnect by presenting a detailed analysis of the topography of both ranges utilizing established relationships between catchment mean erosion rates and topography local relief hillslope gradients and channel steepness and combining it with a synthesis of previously published low temperature thermochronologic data modern climate of the caucasus region is assessed through an analysis of remotely sensed data trmm and modis and historical streamflow data because along strike variation in either erosional efficiency or thickness of accreted material fail to explain our observations we suggest that the topography of both the western lesser and greater caucasus are partially supported by different geodynamic forces in the western lesser caucasus high relief portions of the landscape likely reflect uplift related to ongoing mantle lithosphere delamination beneath the neighboring east anatolian plateau in the greater caucasus maintenance of high topography in the western portion of the range despite extremely low 2 4 mm y modern convergence rates may be related to dynamic topography from detachment of the north directed greater caucasus slab or to a recent slowing of convergence rates large scale spatial gradients in climate are not reflected in the topography of the caucasus and do not seem to exert any significant control on the tectonics or structure of either range

structural geometries and magnitude of shortening in the eastern kura fold thrust belt azerbaijan implications for the development of the greater caucasus mountains 1 the greater caucasus are the northernmost extent of the arabia eurasia collision and are thought to represent the main locus of shortening within the central portion of the collision zone between 40 and 48 e recent work suggests that in detail since the plio pleistocene much of the shortening in the eastern portion of the caucasus system has been focused within the kura fold thrust belt along the southeastern margin of the greater caucasus here we present new field mapping and stratigraphic investigations of the eastern termination of the kura fold thrust belt in azerbaijan to better constrain the structural geometries magnitude of shortening and initiation age for this portion of the fold thrust belt our work suggests that this area of the fold thrust belt exhibits significant along strike variations in structural style and evolution and can effectively be divided into two distinct domains at 48 e the western domain is characterized by a subcritical median surface slope and isolated folds and thrusts propagating out of sequence whereas the eastern domain is dominated by a single duplex structure and a history of in sequence development in a critically tapered wedge we hypothesize that these variations result from changes in relative rates of syn tectonic sedimentation erosion and convergence velocity along strike we find that within the western domain the fold thrust belt has accommodated 12 km of total shortening an unconformity within the western domain brackets the initiation age of this portion of the fold thrust belt to between 1 8 and 0 88 ma yielding permissible average shortening rates of between 6 7 and 13 6 mm yr comparison of these average shortening rates to the geodetically measured shortening rate of 8 mm yr indicates that since initiation the fold thrust belt has accommodated 83 100 of convergence between the greater and lesser caucasus at this longitude

dynamic and thermodynamic characteristics of atmospheric response to anomalous sea ice extent in the sea of okhotsk abstract influence of sea ice extent anomalies within the sea of okhotsk on the large scale atmospheric circulation is investigated through an analysis of the dynamic and thermodynamic characteristics of the response in an atmospheric general circulation model to specified anomalous sea ice cover significant response appears not only around the sea of okhotsk but also downstream over the bering sea alaska and north america in the form of a stationary wave train in the troposphere this remote response associated with wave activity flux emanating from the okhotsk area to the downstream is regarded as a stationary rossby wave generated thermally by the anomalous turbulent heat fluxes from the ocean surface as a result of the anomalous sea ice cover the pacific storm track in the model that extends zonally at 35 n is located too far south of the sea of okhotsk to exert substantial feedback forcing on the local and remote response since a similar stationary wave train is identified in the composite di

magma generation by slab steepening and breakoff beneath a subduction accretion complex an alternative model for collision related volcanism in eastern anatolia turkey 1 eastern anatolia is regarded as one of the best examples of continental collision represented by a 2 km high plateau it displays shallow and diffuse seismicity indicating that the crust is still being actively deformed perhaps the most striking aspect of eastern anatolia is the volume and compositional variability of collision related volcanic products erupted during the neogene and quaternary time a number of models have been proposed for the genesis of this volcanism in the region however recent geophysical studies have revealed that a mantle lithosphere is almost completely absent beneath a greater portion of the region which makes us question the validity of the previous models in this paper we propose a new model for magma genesis slab steepening and breakoff beneath a large subduction accretion complex this model holds that a northward subducting oceanic lithosphere beneath the eastern anatolia accretionary prism gets steepened and eventually detached from the continental lithosphere of the bitlis poturge massif following the continent accretionary complex collision this brings the asthenospheric mantle in contact with the accretionary complex at shallow depths e g around 50 km resulting in rapid regional uplift and extensive melting which leads to collisional volcanism

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

considerations of hydration rind dating of glass artefacts alteration morphologies and experimental evidence of hydrogeochemical soil zone pore water control sem edax textural chemical alteration morphologies of man made glass from egypt and modern soda lime glass are compared to literature data for obsidian and sideromelane rhyolitic and basaltic glass a series of laboratory experiments using soda lime glass slides held at 90 c for 3 21 days in baths using different salt solutions mgcl2 licl nacl cacl2and kcl in various concentrations provides compelling evidence that for any particular glass composition the style of glass corrosion hydration dissolution is dependent on solution geochemistry two fundamental styles of glass corrosion occur pitting dissolution and gel lamination hydration glasses of different compositions may behave differently in similar anthrosols reaction style and kinetics and hydration dissolution rates are controlled by soil temperature glass and soil water geochemistry and ultimately alkali exchange between the glass artefact and the soil zone pore water glass and gel thickness loss through dissolution reactions may compromise hydration dating and may be responsible for a variety of reported apparent chronological inconsistencies future studies with obsidian and sideromelane under bath conditions and in the natural environment are needed to assess their response to variable soil zone solution geochemistry

on steady states in mountain belts the dynamic system of tectonics and erosion contains important feedback mechanisms such that orogenic systems tend toward a steady state this concept is often invoked but the nature of the steady state is commonly not specified we identify four types of steady state that characterize the orogenic system and illustrate these cases by using numerical model results and natural examples these types are 1 flux steady state 2 topographic steady state 3 thermal steady state and 4 exhumational steady state they refer to the erosional flux the topography the subsurface temperature field and the spatial pattern of cooling ages respectively models suggest that the topography will reach a steady mean form at the scale of an orogenic belt but perfect topographic steady state is unlikely to be achieved at shorter length scales thermal steady state is a precondition for exhumational steady state and in the case of temperature dependent deformation topographic steady state exhumational steady state is characterized by reset age zones spatially nested according to closure temperature as illustrated in natural systems from new zealand the cascadia accretionary margin and taiwan

tomographic evidence of slab detachment beneath eastern turkey and the caucasus summary teleseismic phase readings from the eastern turkey seismic experiment etse have been inverted using teleseismic tomography in order to create a 3 d image of the underlying mantle beneath eastern turkey the aim was to investigate the existence of an upper mantle negative velocity anomaly that is used to explain the uplift of eastern anatolian plateau and the potential pieces of detached oceanic slabs related to neo tethyan subduction suggested by previous studies using teleseismic waveforms from the 29 stations of the eastern turkey seismic experiment 2926 direct p phases from 146 events were picked by using adaptive stacking techniques in order to increase the station coverage and resolve the surrounding area the phase readings from the international seismological center isc bulletin have also been added the data set consists of 9571 p and pkp phase readings of 79 stations from 503 teleseismic events this study develops the first highresolution 3 d upper mantle p wave tomographic model for this region the tomographic results show the existence of an upper mantle negative velocity anomaly to a depth of 200 km beneath the eastern anatolian accreationary complex eaac as commonly observed in the previous studies that suggest a shallow partially molten asthenosphere the slab like high velocity anomalies beneath the eaac pontides and caucasus are interpreted as the detached southern and northern neo tethys slabs

northern caucasus basin thermal history and synthesis of subsidence models abstract burial histories of the eastern central and western parts of the northern caucasus basin are reconstructed on the basis of well data and seismic sections subsidence began in the early triassic after the late carboniferous permian orogeny triassic sediments were mainly removed during late triassic early jurassic uplift and erosion platform cover began to form in the middle jurassic and albian sediments covered the whole territory of the basin thermal modelling shows that jurassic eocene subsidence was mainly controlled by late triassic early jurassic intrusive warming this heating event induced thermal uplift of the whole territory followed by exponentially decelerating subsidence due to cooling of the lithosphere in the southern areas adjacent to great caucasus subsidence was also affected by caucasian extensional and compressional events in the oligocene early miocene the eastern and the central basins underwent rapid long wavelength subsidence maikopian subsidence the geodynamic cause of this subsidence is probably associated with the mantle flow appearance after cessation of the tethyan subduction due to reequilibration of subducted slab while in the late miocene quaternary times the eastern and the western basins underwent foreland type asymmetrical subsidence due to loading of the great caucasus orogen the central basin was uplifted according to flexural modelling the main component of orogen loading was the lithospheric root load delamination of the latter under the central caucasus caused rapid uplift of the orogen and adjacent basin

research on snow and ice this review unlike its predecessor martinelli et al 1979 is an intentionally selective survey of recent advances in selected areas of snow and ice research i have chosen to concentrate on studies relating to large scale aspects of the cryosphere and to consider their wider significance for other disciplines results obtained by new measurement techniques and the application of remote sensing methods are also stressed at the same time the broad lines of advance in glaciological research as represented in books conference themes and major field or laboratory programs are noted and a detailed bibliography is appended

dominance of tectonics over climate in himalayan denudation landscape denudation in actively deforming mountain ranges is controlled by a combination of rock uplift and surface runoff induced by precipitation whereas the relative contribution of these factors is important to our understanding of the evolution of orogenic topography no consensus currently exists concerning their respective infl uences to address this question denudation rates at centennial to millennial time scales were deduced from 10be concentrations in detrital sediments derived from 30 small basins 10 600 km2 in an 200 km wide region in central nepal along a northward strike perpendicular transect average denudation rates sharply increase from 0 5 mm yr in the lesser himalayas to 1 mm yr when crossing the physiographic transition and then accelerate to 2 3 mm yr on the southern flank of the high peaks in the greater himalayas despite a more than five fold increase in denudation rate between the southern and northern parts of this transect the corresponding areas display similar precipitation rates the primary parameter that presents a signifi cant co variation with denudation is the long term rockuplift rate that is interpreted to result from the ramp fl at transition along the main himalayan thrust we propose that in this rapidly uplifting mountain range landscapes adjust quickly to changing climatic conditions such that denudation is mainly limited by the rate at which material is pushed upward by tectonic processes and made available for removal by surface processes in this particular context variations in precipitation appear to have only a second order role in modulating the denudation signal that is primarily set by the background rock uplift rate 2014 geological society of america

review of the neotectonics of the eastern turkish armenian plateau by geomorphic analysis of digital elevation model imagery digital elevation model dem images provide synoptic views of the earth s surface allowing the analysis of landforms of still active tectonic and volcanic structures at regional scale a dem at 250 m pixel size constitutes regional scale data particularly efficient to investigate the late miocene quaternary deformation of the eastern turkish armenian plateau in the arabian eurasian area of convergence geomorphic analysis of the dem image associated with review of fault plane solutions of earthquakes show that faults are mostly strike slip with small vertical component here we show that the orientations of the tectonic and volcanic structures fit with a tectonic regime characterized by n s shortening and e w lengthening consistent with westward escape of anatolia perpendicular to the direction of the arabia eurasia shortening the uniform uplift of the plateau the predominance of strike slip faulting the lack of major thrusts and the occurrence of normal faults do not support a model of going on crustal thickening due to intracontinental convergence on the contrary our observations can be better interpreted in terms of lithospheric thinning and mantle upwelling related to gravity escape of anatolia

leucocratic and gabbroic xenoliths from hualalai volcano hawai i a diverse range of crustal xenoliths is hosted in young alkali basalt lavas and scoria deposits erupted 3 5 ka at the summit of hual alai leucocratic xenoliths including monzodiorites diorites and syenogabbros are distinctive among hawaiian plutonic rocks in having alkali feldspar apatite zircon and biotite and evolved mineral compositions e g albitic feldspar clinopyroxene mgnumber 67 78 fine grained diorites and monzodiorites are plutonic equivalents of mugearite lavas which are unknown at hual alai these xenoliths appear to represent melt compositions falling along a liquid line of descent leading to trachyte a magma type which erupted from hual alai as a prodigious lava flow and scoria cone at 114 ka inferred fractionating assemblages melts modeling pyroxene geobarometry and whole rock norms all point to formation of the parent rocks of the leucocratic xenoliths at 3 7 kbar pressure this depth constraint on xenolith formation coupled with a demonstrated affinity to hypersthenenormative basalt and petrologic links between the xenoliths and the trachyte suggests that the shift from shield to post shield magmatism at hual alai was accompanied by significant deepening of the active magma reservoir and a gradual transition from tholeiitic to alkalic magmas subsequent differentiation of transitional basalts by fractional crystallization was apparently both extreme culminating in 5 5 km of trachyte and rapid at 2 75 10 m magma crystallized year

a cost surface model of volcanic glass quarrying and exchange in hawai i abstract the spatial distribution of artifacts from the pu u wa awa a volcanic glass source north kona district hawai i island shows a pattern of direct access by those living in the immediately vicinity of the source with subsequent down the line exchange most quarrying and exchanges likely occurred within a single day s travel from sites where artifacts were deposited the exception to this is the discovery of non local direct access evident in assemblages from the extreme southern end of hawai i island these visits may have involved voyages by canoe while people did not often travel far for volcanic glass they nonetheless appear to have had unfettered accessed to source material and freely conducted inter community exchanges this implies volcanic glass was treated as a common pooled resource and the existence of informal exchange relationships

late cenozoic base level variations of the caspian sea a review of its history and proposed driving mechanisms abstract the caspian sea is characterized by significant variations in its base level during the late cenozoic and provides an important repository for long term records of both regional climate and tectonics due to its position within the interior of the eurasian continent and at the northern margin of the ongoing arabia eurasia collision zone the caspian also serves as an important moisture source for eastern eurasia including the northern tibetan plateau and thus the history of caspian base level variations represents an important and poorly understood constraint on paleoclimate reconstructions throughout eurasia prior work in the caspian region has largely focused on developing biostratigraphic age divisions and investigating the history of connection between the caspian black and mediterranean seas as well as the global ocean recent geochronologic work in the caspian and related basins has questioned previous correlations of hydrologic events in these different basins as a result prior estimates of the chronology and magnitude of caspian sea level variations may be incorrect here we synthesize previous work to develop a new caspian base level curve starting at the beginning of the meotian regional stage 7 ma we also present a new synthesis of potential driving mechanisms for the large variations in caspian base level and speculate on a possible cause for the enigmatic akchagyl transgression this synthesis highlights the dynamic range of caspian sea level which varied from 200 m above to in excess of 1000 m below its current level during the late cenozoic and provides a basis for future work investigating the tectonic and climatic drivers behind variations in caspian base level

field data validation of an algorithm for computing obsidian effective hydration temperature this paper describes an analysis to validate the effective hydration temperature eht algorithm for obsidian rogers a k 2007 effective hydration temperature of obsidian a diffusion theory analysis of time dependent hydration rates j arch sci 34 656 665 using hourly temperature data from the amargosa desert research site near beatty nv these data were used as input to a numerical model of the temperature dependent diffusion process and eht was calculated yearly and for the aggregate the same temperature data were processed to extract input parameters for the climatic model reported and used as input for eht computation eht as computed from recorded hourly data was found to be within 1 c of that computed from the climatic model it is also shown that computed eht differences between sites are not sensitive to whether air or surface temperature data are used as long as they are used consistently however surface temperature data must be used if depth corrections are to be made

monthly and seasonal variability in the ocean ice atmosphere systems of the north pacific and the north atlantic four regional indices of sea ice variability and thirty years of monthly sea surface temperature sst and sea level pressure slp data are used to evaluate the large scale interactions within the ocean ice atmosphere systems of the north pacific and the north atlantic a direct association between positive negative sst anomalies and light heavy ice in the bering sea is indicated the sst ice coupling in the northern alaskan waters is also statistically significant the sst anomalies in both the north pacific and the north atlantic appear as persistent responses to atmospheric forcing the slp distributions over both oceans correlate significantly with the arctic slp distribution although the midlatitude atmospheric circulation shows no systematic tendency to lead or lag the arctic circulation sea ice fluctuations correlate most highly with the atmospheric forcing over antecedent periods of approximately 9 months in the northern alaskan waters 3 4 months in the bering sea and 5 7 months in the east greenland sea the strength of the 9 month mean onshore air flow component describes over 70 of the northern alaskan ice variance

stratification on the eastern bering sea shelf revisited abstract the timing and magnitude of stratification can have profound influences on the marine ecosystem on the eastern bering sea shelf in the absence of strong wind mixing stratification can be initiated by the melting of seasonal sea ice or by springtime warming of the surface temperature and salinity both influence the stratification of the eastern bering sea shelf with their relative importance varying spatially and temporally in the northern middle shelf domain north of 60 n salinity stratification is often as important as temperature stratification on the southern middle shelf while the influence of temperature on stratification dominates during summer the influence of salinity stratification plays a role in the interannual variability mooring 2 m2 56 9 n 164 1 w has been deployed at 70 m depth in the southern middle shelf domain since 1995 data from this mooring show that stratification typically begins to set up in may and to break down in september october but these dates can vary by 30 d while no trend is found in the timing of the spring setup the fall stratification breakdown exhibited a trend toward later breakdown 2 d later per year from 1996 to 2009 results suggest that it may be difficult to forecast stratification on the eastern bering sea shelf from climate models as simple indices of wind mixing or heat fluxes are not correlated with stratification contrary to intuition the strength of summer stratification is not correlated with depth averaged temperature warm years such as 2000 and 2001 can have low stratification and cold years such as 2007 can have very high stratification this decoupling of stratification and temperature has implications for forecasting the ecosystem in the face of climate change as we cannot assume that projections of a warmer climate simply imply higher stratification in the future

simulated low frequency modes of circulation in the arctic ocean the variability of the arctic circulation is investigated for a 43 year period 1951 1993 from a coupled ice ocean model empirical orthogonal function eof analysis shows that the variability of the sea surface height ssh and vertically integrated transport is organized so that in the leading mode the whole arctic operates as a single gyre the mode is associated with the arctic oscillation ao thompson and wallace 1998 and it explains over 70 of the variance in the vertically integrated transport and 25 of the ssh variability the physical interpretation of this mode is derived to arise from its close connection to the atlantic inflow to the arctic the mode shows a major shift toward cyclonic circulation in the end of the 1980s which is associated with a large multiyear pulse of atlantic water to the arctic thus this event appears as the likely initiation of the atlantic layer warming observed during the recent years carmack et al 1995 overall the first mode shows strong decadal variability as reported by proshutinsky and johnson 1997 the second mode of the oceanic circulation which explains 9 of the variance in the transport contains two gyres with opposing cyclonicity in the eurasia and canada basins it projects onto the north atlantic oscillation nao pattern and displays a 14 year cycle which is known to exist in the midlatitude north atlantic surface temperatures deser and blackmon 1993 a further examination reveals that this mode describes the variability of the flow through the barents sea which is modulated by the water mass modification due to the local heat flux variability the apparent nao connection is provided by a simultaneous correlation between the time series of this second mode and the leading heat flux mode in the north atlantic which is associated with nao

a three dimensional stationary model of the thermal and thermoelastic fields of the caucasus abstract three dimensional geothermal and thermoelastic models of the caucasus have been produced application of the three dimensional approach to regions as complex as the caucasus has been justified the model calculations were made excluding the surface heat flow and could therefore be used to test the validity of the model the theoretical heat flow agreed well with the experimental model over the black and caspian sea areas and over the whole rioni kura depression as was expected areas of young volcanism presented exceptions charts of temperature and thermoelastic displacement were plotted for the granitic conrad and mohorovicic discontinuities

decoupling of erosion and precipitation in the himalayas the hypothesis that abrupt spatial gradients in erosion can cause high strain rates in active orogens has been supported by numerical models that couple erosional processes with lithospheric deformation via gravitational feedbacks1 2 3 most such models invoke a stream power rule in which either increased discharge or steeper channel slopes cause higher erosion rates spatial variations in precipitation and slopes are therefore predicted to correlate with gradients in both erosion rates and crustal strain here we combine observations from a meteorological network across the greater himalaya nepal along with estimates of erosion rates at geologic timescales greater than 100 000 yr from low temperature thermochronometry across a zone of about 20 km length spanning the himalayan crest and encompassing a more than fivefold difference in monsoon precipitation significant spatial variations in geologic erosion rates are not detectable decreased rainfall is not balanced by steeper channels instead additional factors that influence river incision rates such as channel width and sediment concentrations must compensate for decreasing precipitation overall spatially constant erosion is a response to uniform upward tectonic transport of greater himalayan rock above a crustal ramp

minimal climatic control on erosion rates in the sierra nevada california climate is widely thought to regulate erosion rates but the relationships among precipitation temperature and erosion rate have remained speculative because long term erosion rates have been difficult to measure we used cosmogenic nuclides to measure long term erosion rates at climatically diverse sites in the sierra nevada california spanning 20 180 cm yr in annual precipitation and 4 15 8c in mean annual temperature average erosion rates vary by only 2 5 fold across these sites and are not correlated with climate indicating that climate only weakly regulates nonglacial erosion rates in mountainous granitic terrain

the interpretation of the icelandic sea ice record the representativeness of the icelandic sea ice record one of the longest climate indicators for the north atlantic sector is assessed by statistical analysis correlation of the sea ice index with ice concentration data for the adjacent seas suggests that the index is a reasonable measure of the ice cover of a large area of the northern north atlantic sector associations with surface air temperature and sea level pressure are strong but regional rather than hemispheric in scale the immediate causes of the variable advance of ice onto the icelandic coasts are clear in the analysis of the atmospheric circulation data severe ice conditions are associated with enhanced anticyclonicity in the icelandic region and stronger northerly and westerly winds over the greenland sea it is concluded that the icelandic index is a useful indicator of the state of the atmospheric flow north of iceland and of the character of the east greenland current one of the major avenues of meridional heat exchange in the climate system

multiyear sea ice variability in the eastern bering sea an update time series of sea surface temperature sst percent ice cover degree day and surface wind anomalies are updated from niebauer 1980 for the period 1974 1982 from the eastern bering sea these data are used to provide further documentation of the recent short term 1977 present climatic warming trend in the region of the eastern bering sea the data analysis indicates that the warming trend is statistically significant and that it ended in 1979 details of the anomalies in sst ice and surface and 700 mbar winds are updated for the individual winters of 1979 82 are compared and contrasted to the recent multiyear warming trend and are discussed in relation to longer term studies of air ice sea interactions in this region

cenozoic recent tectonics and uplift in the greater caucasus a perspective from azerbaijan the greater caucasus is europe s highest mountain belt and results from the inversion of the greater caucasus back arc type basin due to the collision of arabia and eurasia the orogenic processes that led to the present mountain chain started in the early cenozoic accelerated during the plio pleistocene and are still active as shown from present gps studies and earthquake distribution the greater caucasus is a doubly verging fold and thrust belt with a pro and a retro wedge actively propagating into the foreland sedimentary basin of the kura to the south and the terek to the north respectively based on tectonic geomorphology active and abandoned thrust fronts the mountain range can be subdivided into several zones with different uplift amounts and rates with very heterogeneous strain partitioning the central part of the mountain range defined by the main caucasus thrust to the south and backthrusts to the north forms a triangular shape zone showing the highest uplift and fastest rates and is due to thrusting over a steep tectonic ramp system at depth the meridional orogenic in front of the greater caucasus in azerbaijan lies at the foothills of the lesser caucasus to the south of the kura foreland basin

expression of active tectonics in erosional landscapes understanding the manner and degree to which topography in active mountain ranges reflects deformation of the earth s surface remains a first order goal of tectonic geomorphology a substantial body of research in the past decade demonstrates that incising channel systems play a central role in setting relationships among topographic relief differential rock uplift rate and climatically modulated erosional efficiency this review provides an introduction to the analysis and interpretation of channel profiles in erosional mountain ranges we show that existing data support theoretical expectations of positive monotonic relationships between channel steepness index a measure of channel gradient normalized for downstream increases in drainage area and erosion rate at equilibrium and that the transient response to perturbations away from equilibrium engenders specific spatial patterns in channel profiles that can be used to infer aspects of the forcing these aspects of channel behavior lay the foundation for a series of case studies that we use to illustrate how focused quantitative analysis of channel morphology can provide insight into the spatial and temporal dynamics of active deformation although the complexities of river response to climate lithology and uplift patterns mean that multiple interpretations of topographic data alone will always possible we show that application of stream profile analysis can be a powerful reconnaissance tool with which to interrogate the rates and patterns of deformation in active mountain belts

criteria and tools for determining drainage divide stability abstract watersheds are the fundamental organizing units in landscapes and thus the controls on drainage divide location and mobility are an essential facet of landscape evolution additionally many common topographic analyses fundamentally assume that river network topology and divide locations are largely static allowing channel profile form to be interpreted in terms of spatio temporal patterns of rock uplift rate relative to base level climate or rock properties recently however it has been suggested that drainage divides are more mobile than previously thought and that divide mobility and resulting changes in drainage area could potentially confound interpretations of river profiles ultimately reliable metrics are needed to diagnose the mobility of divides as part of routine landscape analyses one such recently proposed metric is cross divide contrasts in a proxy for steady state channel elevation but cross divide contrasts in a number of topographic metrics show promise here we use a series of landscape evolution simulations in which we induce divide mobility under different conditions to test the utility of a suite of topographic metrics of divide mobility and for comparison with natural examples in the eastern greater caucasus mountains the kars volcanic plateau and the western san bernadino mountains specifically we test cross divide contrasts in mean gradient mean local relief channel bed elevation and all measured at or averaged upstream of a reference drainage area our results highlight that cross divide contrasts in only faithfully reflect current divide mobility when uplift rock erodibility climate and catchment outlet elevation are uniform across both river networks on either side of the divide otherwise a anomaly only indicates a possible future divide instability the other metrics appear to be more reliable representations of current divide motion but in natural landscapes only cross divide contrasts in mean gradient and local relief appear to consistently provide useful information multiple divide metrics should be considered simultaneously and across divide values of all metrics examined quantitatively as visual assessment is not sufficiently reliable in many cases we provide a series of matlab tools built using topotoolbox to facilitate routine analysis

discharge discharge variability and the bedrock channel profile long term bedrock incision is driven by daily discharge events of variable magnitude and frequency with ineffective events below an incision threshold we explore theoretically how this short term stochastic behavior controls long term steady state incision rates and bedrock channel profiles combining a realistic frequency magnitude distribution of discharge with a deterministic detachment limited incision model in which incision rate is a power function of basal shear stress above a critical shear stress our model predicts a power law relationship between steady state slope and drainage area consistent with observations the exponent of this power law is independent of discharge mean and variability while the amplitude factor which controls mountain belt relief is a power law function of mean runoff with an exponent of 0 5 and a complex function of runoff variability in accordance with evidence that incision occurs between 6 and 20 of time in rapidly incising rivers 1 mm yr our model predicts that channel steepness is virtually insensitive to runoff variability runoff variability can only decrease channel steepness for very slow incision rates and or weak lithologies the relationship between channel steepness and incision rate is always a power law whose exponent depends on the channel cross sectional geometry and runoff variability this contradicts models neglecting discharge stochasticity in which the steepness incision scaling is set by the incision law exponent our results suggest that changes in climate variability cannot explain an increase in bedrock incision rates during the late cenozoic within the context of a detachment limited model

concentration gradients and growth decay characteristics of the seasonal sea ice cover the growth and decay characteristics of sea ice in the northern and southern hemispheres are presented quantitatively by using brightness temperature data from the nimbus 5 electrically scanning microwave radiometer the areal extent of 15 ice cover follows a basically symmetrical seasonal cycle in the northern hemisphere ranging from 8 106 km2 in summer to 16 106 km2 in winter in contrast the seasonal cycle in the southern hemisphere is asymmetrical with longer periods of growth than decay and areal extent ranging from 4 106 km2 in summer to 20 106 km2 in winter at different longitudes the occurrences of the maximum rates of advance of the ice edge differ by up to 2 months and similarly for retreat the distribution of the rate of change in the latitudinal position of the ice edge using as a reference point the 50 ice concentration line near the ice ocean boundary follows a quasi gaussian function with peak at about 60 km month and with a standard deviation of about 120 km month however for some months rates as large as a 940 km month change in the latitudinal position are observed when the movement of the ice edge tends to be in the eastward or westward direction as for example in the weddell sea the gradient of ice concentration near the ice edge has considerable variability following a poisson distribution with peaks at about 0 89 ice concentration per kilometer as derived from the 3 day averages and 0 62 ice concentration per kilometer from the monthly averages during the growth cycle the dominant change in ice cover is the advance of consolidated ice behind the advancing ice edge while during decay the retreat of the ice edge is accompanied by massive reduction of ice concentration within the ice pack the monthly changes in ice edge position in the southern hemisphere are also shown to have good correlation with the rates of advance and retreat of the 271 k surface temperature isotherms inferred from climatological temperature data

the exhumation of the western greater caucasus a thermochronometric study this study provides 39 new thermochronometric analyses from the western part of the greater caucasus a region in which existing data are extremely limited and of questionable quality the new results are consistent with field studies that identify triassic to middle jurassic cimmerian and oligo miocene alpine orogenic erosional events an inverse relationship between the fission track and depositional ages of oligo miocene sedimentary samples also implies some degree of eocene erosion of the greater caucasus and intermediate sediment storage cooling ages and field relationships within the core of the range west of mt elbrus require 5 km of permo triassic exhumation and restrict the overall amount of cenozoic exhumation to 2 5 km current exhumation rates are typically low and do not support a plio pleistocene increase in climate driven denudation high 1 km ma 1 rates of exhumation are restricted to the southern flank of the range in northwest georgia despite a general lack of significant seismicity within the study region this exhumation peak is close to the largest instrumentally recorded earthquake in the caucasus ms 7 0 this may suggest that exhumation is associated with the decoupling of the sedimentary succession from its crystalline basement in the southern part of the range and the inversion of the largely jurassic fill of the greater caucasus basin rates of exhumation are compatible with this being driven by active shortening further sampling and analysis are required to provide a higher resolution low temperature thermochronology of alpine exhumation to isolate the drivers for palaeogene dziruli massif cooling and uplift and to constrain better the extent of the current localized phase of rapid exhumation

late cenozoic reorganization of the arabia eurasia collision and the comparison of short term and long term deformation rates the arabia eurasia collision deforms an area of 3 000 000 km2 of continental crust making it one of the largest regions of convergent deformation on earth there are now estimates for the active slip rates total convergence and timing of collision related deformation of regions from western turkey to eastern iran this paper shows that extrapolating the present day slip rates of many active fault systems for 3 7 million years accounts for their total displacement this result means that the present kinematics of the arabia eurasia collision are unlikely be the same as at its start which was probably in the early miocene 16 23 ma or earlier in some but not all active fault systems short term 10 year and long term 5 million year average deformation rates are consistent there is little active thickening across the turkish iranian plateau and possibly the interior of the greater caucasus these are two areas where present shortening rates would need more than 7 million years to account for the total crustal thickening and where there are structural and or stratigraphic data for pre late miocene deformation we suggest that once thick crust up to 60 km built up in the turkish iranian plateau and the greater caucasus convergence took place more easily by crustal shortening in less elevated regions such as the zagros simple folded zone the south caspian region and foothills of the greater caucasus or in other ways such as westward transport of turkey between the north and east anatolian faults the time and duration of this changeover are not known for certain and are likely be diachronous although deformation started or intensified in many of the currently active fault systems at 5 2 ma

two sided orogen collision and erosion from the sandbox to the southern alps new zealand in continental collision zones the indentor is of approximately the same vertical dimension as the material being deformed thereby allowing material to move over the indentor and out of the deforming orogen this simple constraint on the height of the indentor differs from that imposed by the bulldozer model of wedge deformation and results in the formation of an orogen with two opposite dipping topographic slopes these two wedges are mechanically coupled and the mechanics are strongly influenced by the erosion conditions imposed on the wedge where the growing mountains perturb prevailing moisture laden winds the erosion pattern is highly asymmetric erosional work being concentrated at the toe of the steep wedge facing the indentor the inboard wedge concentration of erosional energy results in concentration of mechanical energy in the same region and produces the distinctive geological and geophysical patterns associated with continental collision these include rapid uplift and exposure of deep crustal assemblages adjacent to the indentor accompanied by high crustal heat flow and anomalously low seismicity the outcrop pattern along the inboard wedge evolves from that of a crustal cross section currently exposed in the southern alps to one dominated by repetitive nappe structures consisting predominantly of lower crustal units as in the western alps of europe the other wedge the outboard wedge undergoes relatively little erosion is broad with a more gentle surface slope and maintains an outcrop pattern consisting of upper crustal material

effects of el nino southern oscillation and north pacific weather patterns on interannual variability in the subarctic bering sea extraordinary interannual variability in ice cover air and sea surface temperatures sst and surface winds in the eastern bering sea have been observed over recent years to investigate the causes of this interannual variability long term 20 30 years time series of air ocean and ice parameters from the bering sea were cross correlated with the southern oscillation index soi an index of el nino southern oscillation enso events in the tropical southern hemisphere as well as with an index of pacific north american pna events in the north pacific five to thirty percent of the interannual variability linear regression with various smoothing in the bering sea data sets with the exception of surface winds is explained by the soi when the bering sea data lags the soi for comparison 29 52 of the variability in the sst off south america can be explained by the soi the signs of the correlations all suggest that warming in the bering sea follows negative anomalies in the soi that is enso events positive anomalies in the soi which tend to precede el nino events were found to precede cooling in the bering sea significant correlation persists for 18 20 months higher order polynomial regressions between the soi and bering sea data can explain up to 40 of the bering sea variability the mechanism for the connection between enso events and bering sea interannual variability appears to be of atmospheric nature and is associated with the winter position and intensity of the aleutian low the aleutian low is intensified and eastward of normal in association with el nino i e warm events but is weaker and westward of normal during cool events it is the regional winds associated with the variable position of the aleutian low that cause the regional warming and cooling events this seesaw in the aleutian low is also used to explain the out of phase ice conditions between the bering sea and the sea of okhotsk pna events are also associated with an intensified aleutian low as well as 700 mbar ridging over northwestern north america causing southerly flow over alaska however while correlation between enso events and pna was significant the correlation between the bering sea and pna was marginal except for surface winds here surface winds from the north were significantly correlated with the pna this apparent inconsistency as well as the lack of correlation of surface winds with the soi is explained by the lack of preferred site of the aleutian low during enso events this lack of preferred site helps explain why the major el nino event of 1982 1983 had little apparent effect on the bering sea

a chronometric tool for hawaiian archaeology the hydration dating of pu u wa awa a trachytic glass the pu uw a awa a trachytic glass deposit located on the big island of hawai i was a source of lithic tools for much of hawaiian prehistory routinely encountered at habitation sites the glass has the potential to provide absolute dates based upon the degree of surface hydration infrared photoacoustic spectroscopy and secondary ion mass spectrometry were used to monitor the diffusion of water in archaeological and experimental samples accelerated laboratory hydration experiments show that water diffusion in trachytic glass containing a structural water content of 0 16 0 03 is linear with time application of the calibration to trachytic glass artifacts from the kahalu u habitation cave have produced chronometric dates in the 17the18th centuries these age estimates are in agreement with radiocarbon dates and artifactual data that bracket the site occupation however the glass dates do not correlate well with site stratigraphy and this suggests that slight sample imperfections that retain water may be one factor that results in ages that are too early for later occupation levels

bioalteration of basaltic glass in the oceanic crust 1 bioalteration of quaternary to early cretaceous basaltic glass from pillow lavas of the upper oceanic crust can be documented in deep sea drilling project ocean drilling program dsdp odp samples from shallow to deep drill holes from the north to central atlantic ocean lau basin and costa rica rift a wide range of marine settings biogenerated textures are rooted in fractures and occur as two main types a granular type and a tubular type the granular type common at all depths within the volcanic pile appears as solid bands semicircles or irregular patches of individual and or coalesced spherical bodies mostly 0 2 0 6 m in diameter with irregular protrusions into the fresh glass the tubular type is more common at deeper levels in the crust and consists of thin tubes sometime branching bodies mostly 20 30 m long and are more common at deeper levels the upper crust displays a large variability in the relative importance of biotic to abiotic alteration and the degree of bioalteration appears to decrease with depth thus the fraction of bioalteration of the total alteration of the glass ranges from 20 90 in the upper 300 m down to a maximum of 10 at about 500 m depth this might be due to a natural variability in the abundance of bioaltered glass or to biased sampling from low drilling recovery of relatively young crust the proportion of bioaltered to abiotically altered glass does not show any systematic variations with age of the crust thus bioalteration lasts as long as abiotic alteration i e for as long as water is available to the hydration of the oceanic crust evidence from heat flow measurements suggests that hydrothermal circulation lasts until at least 70 ma and thus the deep biosphere is likely to expand at least into crust of this age

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

rapid pliocene exhumation of the central greater caucasus constrained by low temperature thermochronometry 1 constraining the timing of onset and rates of deformation within the greater caucasus mountains is key to understanding their role in accommodating deformation across the arabia eurasia orogen we present new low temperature thermochronometric constraints on the cenozoic thermal evolution of the central greater caucasus that elucidate a three phase cooling history between 50 and 30 ma cooling within the range was negligible in oligocene time cooling rates throughout the range increased to 4 c myr these rates remained constant until the early pliocene time when they increased again reaching 25 c myr along the axial part of the range rates and timing of oligocene exhumation are consistent with previous results from the western greater caucasus and are proposed to result from onset of subduction of the greater caucasus back arc basin rapid exhumation of the greater caucasus beginning in pliocene time contrasts with previously reported thermal histories for other portions of the range pliocene exhumation of the central greater caucasus appears to be tectonically driven and coincides with widespread evidence for a major reorganization of the arabia eurasia plate boundary we hypothesize that this exhumation and regionally observed plate reorganization results from the collision of the lesser caucasus with eurasia completing the subduction of oceanic lithosphere across this segment of the arabia eurasia plate boundary

the growth of a mountain belt forced by base level fall tectonics and surface processes during the evolution of the alborz mountains n iran abstract the idea that climatically modulated erosion may impact orogenic processes has challenged geoscientists for decades although modeling studies and physical calculations have provided a solid theoretical basis supporting this interaction to date field based work has produced inconclusive results the central western alborz mountains in the northern sectors of the arabia eurasia collision zone constitute a promising area to explore these potential feedbacks this region is characterized by asymmetric precipitation superimposed on an orogen with a history of spatiotemporal changes in exhumation rates deformation patterns and prolonged km scale base level changes our analysis suggests that despite the existence of a strong climatic gradient at least since 17 5 ma the early orogenic evolution from 36 to 9 6 ma was characterized by decoupled orographic precipitation and tectonics in particular faster exhumation and sedimentation along the more arid southern orogenic flank point to a north directed accretionary flux and underthrusting of central iran conversely from 6 to 3 ma erosion rates along the northern orogenic flank became higher than those in the south where they dropped to minimum values this change occurred during a 3 myr long km scale base level lowering event in the caspian sea we speculate that mass redistribution processes along the northern flank of the alborz and presumably across all mountain belts adjacent to the south caspian basin and more stable areas of the eurasian plate increased the sediment load in the basin and ultimately led to the underthrusting of the caspian basin beneath the alborz mountains this underthrusting in turn triggered a new phase of northward orogenic expansion transformed the wetter northern flank into a new pro wedge and led to the establishment of apparent steady state conditions along the northern orogenic flank i e rock uplift equal to erosion rates conversely the southern mountain front became the retro wedge and experienced limited tectonic activity these observations overall raise the possibility that mass distribution processes during a pronounced erosion phase driven by base level changes may have contributed to the inferred regional plate tectonic reorganization of the northern arabia eurasia collision during the last 5 ma