fault slip bed length and area variations in experimental rollover anticlines over listric normal faults influence in extension and depth to detachment estimations abstract to check the behaviour of physical experiments of simple rollover anticlines over listric normal faults several fault slip bed length and area parameters are measured for different beds in two stages of evolution of two physical experiments given a certain amount of extension the heave and dip of the displacement vary for different beds whereas the throw is approximately constant for small amounts of extension and the displacement remains constant for high amounts of extension neither bed lengths nor areas beneath beds remain constant with increasing extension a number of techniques allow amounts of extension and detachment depth to be estimated given one or more marker horizons the portion of the fault between hanging wall and footwall cut off points the depth to detachment and or the shear angle these techniques are applied to the physical experiments of listric normal faults analysed since many of these techniques rely on parameters measured on the physical experiments such as fault slip bed length and area the influence of these parameters on the different magnitudes of extension and detachment depths estimated using different techniques is discussed and the accuracy of the results is compared

evolution of mg fe ratios in late variscan plutonic rocks from the external crystalline massifs of the alps france italy switzerland late variscan plutonic bodies are widespread in the external raumer et al 1993 menot et al 1994 from south to crystalline massifs of the alps argentera pelvoux belledonne north they are the argentera pelvoux belledonne grandes rousses mont blanc aiguilles rouges aar gotthard grandes rousses mont blanc and aiguilles rouges they can be classified on the basis of their mg fe mg ratio massifs western alps and the aar and gotthard massifs and mafic mineral content expressed by the b fe mg central alps fig 1 they appear as dome like structi parameter together with available ages of emplacement this tures of crystalline basement surrounded by a mostly classification highlights the existence of two plutonic suites one mesozoic sedimentary cover as a whole they define an early visean 330 340 ma and highly magnesian the other arcuate structure possibly inherited from the variscan later mainly stephanian 295 305 ma and more ferriferous orogeny bogdanoff et al 1991 this evolution from a magnesian plutonism to a more ferriferous during the variscan orogeny the ecm were part of one which also occurs in other variscan massifs e g corsica the helvetic moldanubian terrane of the internal zone might be accounted for by a combination of factors related to the of the variscides von raumer neubauer 1993 nature of the source of the magmas the physical and chemical precambrian metamorphic units and precambrian to conditions of melting and the late variscan geodynamic setting palaeozoic sediments interlayered with volcanic and as a basis for these considerations a comprehensive review is ultramafic rocks display in most areas a polymetamorphic presented of all the external crystalline massifs and their history and underwent a highly complex pre variscan late variscan intrusions and variscan evolution although they share a number of similarities the ecm each have also specific characteristics von raumer et al 1993 in addition to orthogneisses deriving from early palaeozoic plutonic and volcanic protoliths bussy von

the crystalline units of the high himalayas in the lahul zanskar region northwest india metamorphic tectonic history and geochronology of the collided and imbricated indian plate in the high himalayan belt of northwest india crustal thickening linked to palaeogene collision between india and eurasia has led to the formation of two main crystalline tectonic units separated by the syn metamorphic miyar thrust the high himalayan crystallines sensu stricto hhc at the bottom and the kade unit at the top these units are structurally interposed between the underlying lesser himalaya and the very low grade sediments of the tibetan nappes they consist of paragneisses orthogneisses minor metabasics and chiefly in the hhc leucogranites the hhc registers a polyphase metamorphism with two main stages designated as m1 and m2 a metamorphic zonation with high temperature recrystallization and migmatization at middle structural levels and medium temperature assemblages at upper and lower levels in contrast the kade unit underwent a low temperature metamorphism rb sr and u th pb isotope data point to derivation of the orthogneisses from early palaeozoic granitoids while the leucogranites formed by anatexis of the hhc rocks and were probably emplaced during miocene time most of the complicated metamorphic setting is related to polyphase tectonic stacking of the hhc with the cooler kade unit and lesser himalaya during the himalayan history however a few inconsistencies exist for a purely himalayan age of some ml assemblages of the hhc as regards the crustal derived leucogranites the formation of a first generation mixed with quartzo feldspathic leucosomes was possibly linked to melt lubricated shear zones which favoured rapid crustal displacements at upper levels they intruded during stage m2 and the latest movements along the syn metamorphic miyar thrust but before juxtaposition of the tibetan nappes along the late metamorphic zanskar fault

oblique slip deformation in extensional terrains a case study of the lakes tanganyika and malawi rift zones the east african rift system ear is the archetypal continental rift and a widely proposed analogue for the early stages of evolution of passive continental margins the three dimensional structure of parts of the ear has been recently elucidated by a multifold seismic mfs survey of lakes tanganyika and malawi project probe analysis of fault geometries displayed on the probe mfs data coupled with the more extensive 28 khz echosounder data has improved understanding of the geometry and kinematics of the linked fault systems that underlie the lakes in particular it has been recognized that profiles across i e at high angles to the rift elongation commonly display fault geometries that are not readily retrodeformable there must therefore be significant displacement out of the plane of what would conventionally be regarded as dip lines that is perpendicular to rift elongation and parallel to the tectonic transport or extension direction careful determination of fault plane dip and the dip of synrift reflectors in the hanging wall demonstrates that the dip directions of the shallowest faults and the steepest hanging wall sediment dips are oriented either nw or se this defines the direction of maximum fault block rotation and therefore the direction of extension or tectonic transport as nw se oblique to the trend of the regional rift axis and to the apparent strike of many of the major border faults in the survey area the border faults and many other faults imaged on the probe mfs data must therefore have significant components of strike slip motion and the tanganyika and malawi rift zones have undergone extension oblique to and not perpendicular to their axes near dip slip normal faults steeply dipping oblique slip faults and subvertical strike slip or transfer faults have all been recognized in a complex linked fault system that accomplishes the extension the overall orientation of the rift lakes and their internal segmentation are influenced by major preexisting subvertical fault zones within the basement complex accommodation zones act principally as transfer zones that allow switches in gross polarity of the border fault system the detailed geometries of the accommodation zones result from the specific relations between juxtaposed half graben and the strike and internal geometry of the influencing basement structure the variations in fault geometry subsidence water depth and basin or rift morphology can be better explained by an oblique slip extensional model influenced by basement structures than by a simple orthogonal extensional model

u pb ages and morphologies of zircon in microgranitoid enclaves and peraluminous host granite evidence for magma mingling granites of the s type wilson s promontory batholith lachlan fold belt australia contain zircons which are euhedral and relatively large their age is 395 ma which can be considered as the best available estimate of the crystallysation age of the granites contrary to their dominance in other s type granites of the lachlan fold belt very few zircon cores give inherited ages varying between 500 and 1700 ma microgranitoid enclaves contained within the granites contain a zircon population that is dominated by relatively small anhedral or elongated crystals these give ages that are indistinguishable from the crystallisation age of the granite some enclaves which are characterised by the presence of megacrysts contain a proportion of larger euhedral zircons these zircons give inherited ages similar to the zircons from the granitic host rocks the data are in agreement with a magma mingling origin for the microgranitoid enclaves the large euhedral zircons are interpreted to have been introduced into the enclave magma during a hybridisation event which also introduced quartz and plagioclase megacrysts into the magma the relatively high proportion of inherited cores within the large zircon population of the enclaves is related to the timing of mixing between enclave and host magma this mixing event took place before the majority of the magmatic zircons crystallised in the granitic magma the small anhedral zircons within the enclaves crystallised during quenching of the globules of enclave magma against the cooler granitic magma

the transient atmospheric circulation response to north atlantic sst and sea ice anomalies abstract the objective of this study is to investigate the transient evolution of the wintertime atmospheric circulation response to imposed patterns of sst and sea ice extent anomalies in the north atlantic sector using a large ensemble of experiments with the ncar community climate model version 3 ccm3 the initial adjustment of the atmospheric circulation is characterized by an out of phase relationship between geopotential height anomalies in the lower and upper troposphere localized to the vicinity of the forcing this initial baroclinic response reaches a maximum amplitude in 5 10 days and persists for 2 3 weeks diagnostic results with a linear primitive equation model indicate that this initial response is forced by diabatic heating anomalies in the lower troposphere associated with surface heat flux anomalies generated by the imposed thermal forcing following the initial baroclinic stage of adjustment the response becomes progressively more barotropic and increases in both spatial extent an

improving the resolution of single grain u pb dating by use of zircon extracted from feldspar application to the variscan magmatic cycle in the central alps abstract the usual discordant u pb zircon age patterns for intrusives in orogenic belts impede and exact determination of the time of emplacement they are the product of multiple overprinting and of the presence of inherited zircon dating of monophase zircons crystallized during a single event may yield higher age resolution and results that are easier to interpret during magma crystallization zircon is generated over a range of ptx conditions whereas rock forming minerals grow under more limited conditions and their relative ages can be determined petrographically zircons formed during earlier stages of magma crystallization and included in such mineral constituents are shielded from subsequent reactions outside the carrier mineral following partial melting of the protolith or xenolith assimilation newly crystallizing rock forming minerals may include zircon xenocrysts as individual grains using this insight and to facilitate the analysis of monophase zircons included in petrogenetically defined constituent minerals we have introduced additional steps in the mineral separation procedure we found the effort worthwhile in that the magmatic zircons extracted from plagioclase yielded the most concordant intrusive ages in contrast to zircons from microcline or from the interstices also inherited zircons occurring as individual grains in magmatic feldspar appear to have preserved some rudimentary morphology and a less disturbed radiogenic pb composition which allows us to distinguish provenance from discrete protoliths we were thus able to resolve small but structurally supported age differences between two groups of variscan intrusives in the central swiss alps we obtained 299 4 1 2 ma for the crystallization age of the granite gneiss in the gotthard massif with inherited zircons that suggest generation from late proterozoic 735 ma and mid proterozoic 1760 ma protoliths the massive leucocratic granites on the margin of the granite gneiss yielded an intrusive age of 294 3 1 1 ma with an inherited grain implying a source of caledonian vintage

transient response of an atmospheric gcm to north atlantic sst anomalies abstract a high resolution atmospheric general circulation model gcm is used to evaluate the atmospheric response to north atlantic sea surface temperature sst anomalies the transient evolution of the response is studied in detail the linear and nonlinear effects can thus be contrasted and separated by their different time scales baroclinic patterns related directly to the surface anomalies quickly reach their maximum manifestation however barotropic patterns related to the mid and upper troposphere eddy vorticity fluxes have longer time scales with much more important amplitude able to gradually replace the initial baroclinic response this study thus provides an evolutional picture of the two types of response in a gcm

zircon in amphibolites from naxos aegean sea greece origin significance and tectonic setting we report u pb zircon ages of c 700 550 ma 262 220 ma 47 38 ma and 15 14 ma from amphibolites on naxos island in the aegean extensional province of greece the zircon has complex internal structures based on cathodoluminescence response zoning and crosscutting relationships a minimum of four zircon growth stages are identified inherited core magmatic core inner metamorphic rim and an outer metamorphic rim trace element compositions of the amphibolites suggest igneous differentiation and crustal assimilation zircon solubility as a function of saturation temperatures zr content and melt composition indicates that the zircon did not originally crystallize in the mafic bodies but was inherited from felsic precursor rocks and subsequently assimilated into the mafic intrusives during emplacement zircon inheritance is corroborated by the complex xenocrystic nature of the zircon in one sample ages of c 700 550 ma and 262 220 ma are assigned to inherited zircon available geochemical data suggest that the 15 14 ma metamorphic rims grew in situ in the amphibolites corresponding to a high grade metamorphic event at this time however the geochemical data cannot conclusively establish if the c 40 ma zircon rims also grew in situ or whether they were inherited along with the xenocrystic cores two scenarios for emplacement of the mafic intrusives are discussed i intrusion during late triassic to jurassic ocean basin development of the aegean realm in which case the 40 ma zircon rims would have grown in situ and ii emplacement in the miocene as a result mafic underplating during large scale extension in this case only the 15 14 ma metamorphic outer rims would have formed in situ in the amphibolitic host rocks

u pb zircon dating of granulite metamorphism in the sludyanskiy complex eastern siberia abstract conventional multigrain and single grain zircon u pb ages were obtained for syn and post metamorphic granitoids from the sludyanskiy complex in the south western baikal region regarded as a classical precambrian terrain in the eastern siberia single grains of magmatic zircon from the syn metamorphic hypersthene bearing biotite trondhjemite and two pyroxene trondhjemite have yielded concordant u pb ages of 488 5 0 6 ma and 488 0 5 ma concordant u pb data for zircons of metamorphic origin in the syn metamorphic two pyroxene trondhjemite yield an age for the peak of the granulite facies metamorphism in the sludyanskiy complex as 477 6 2 ma the pattern of multigrain magmatic zircon samples from syn metamorphic granitoids reflects significant pb loss during the metamorphic episode this came to an end before 471 1 2 ma as demonstrated by concordant zircon data for the intrusion of post metamorphic amphibole two pyroxene quartz syenite our zircon data establish that the granulite facies reworking of the sludyanskiy complex took place during the palaeozoic and not during the paleoproterozoic as was previously suggested the age span between the intrusions of syn metamorphic and post metamorphic granitoids constrains the duration of the metamorphic episode to about 20 ma

geochronological constraints on the emplacement history of an anorthosite rapakivi granite suite u pb zircon and baddeleyite study of the korosten complex ukraine u pb zircon baddeleyite ages obtained for the korosten anorthosite rapakivi granite complex ukrainian shield suggest that different magmatic phases were emplaced during a period of ca 30 million years as a series of distinct igneous episodes the earliest 1789 1 2 0 ma anorthosites were followed by 1781 3 3 2 ma dykes of plagiogranite porphyries the emplacement of a major rapakivi granite phase took place at 1767 4 2 2 ma and was followed by emplacement of layered intrusions of anorthosites gabbronorites diabases and ultrabasic rocks between 1761 and 1758 ma the minimum duration of magmatism of about 30 million years the 6 15 million years interval between igneous pulses and alternation of discrete episodes of basic and felsie magmatism are common features of major anorthositemangerite charnockite rapakivi granite complexes temporal distribution of igneous activity in the korosten complex shows that the gabbro anorthosites and the granites are not comagmatic although they are possibly cogenetic and that at least four portions of granitic and basic magmas were generated during a relatively long period of at least 30 million years the time gap of about 20 25 million years between early basic and later and more voluminous granitic magmatism characteristic of the korosten pluton wiborg and salmi batholiths probably reflects the duration of extensional processes before the generation of large volumes of magma in the lower crust

influence of the north atlantic sst on the atmospheric circulation using the monthly coads dataset and nmc ncar archives we show that significant anomalies of the atmospheric circulation are related to previous sst anomalies in the north atlantic a signal over the northwest labrador sea in late spring is associated with the dominant mode of sst variability during the preceeding winter it is more clearly seen in the mid troposhere than at sea level and appears to be related to the anomalous surface heat exchanges that slowly damp the sst anomalies in addition a nao like signal in early winter is associated with sst anomalies east of newfoundland and in the eastern subtropical north atlantic during the preceeding summer

local wintertime tropospheric response to oceanic heat anomalies in the nordic seas area abstracta regression analysis between observed summertime atlantic water temperature anomalies at the entrance to the barents sea and atmospheric fields in the following winter from the ncep ncar reanalysis in the period 1982 2006 is carried out it shows that the ocean plays a key role in shaping wintertime tropospheric variability in the nordic seas greenland iceland norwegian and barents seas region the oceanically driven atmospheric circulation anomaly around the nordic seas marginal ice zone is intensified at the surface as a result of a thermally direct baroclinic adjustment frictional convergence in the cyclonic disturbance corresponding to warm ocean temperature anomalies forces ascending motion at the top of the planetary boundary layer and a compensating divergence aloft which over the barents sea is extreme at the tropopause a quasi meridional overturning circulation anomaly is closed by descending motion south of the cyclonic disturbance in addition an equivalent barotropic flow anomal

hornblende k ar ages and the climax of tertiary metamorphism in the lepontine alps south central switzerland an old problem reassessed abstract twenty five new k ar ages for amphiboles from the tertiary barrovian type metamorphic terrain of the central alps were determined these results lead to the conclusion that the meso alpine metamorphism reached its peak condition and maximum expanse about 26 3 m y ago along a profile of increasing grade of alpine metamorphism in both basement and cover rocks the following observations can be made 1 pre alpine hornblendes in the zone of greenschist facies show ages ranging from 639 to 152 m y the implied open system behavior may be related to the observed mineralogical instability of these hornblendes during the alpine overprint in contrast two greenschist facies hornblendes which grew in pennine mesozoic rocks during the alpine metamorphism yield ages of 23 2 and 29 3 m y 2 on both sides of the boundary marking the first occurrence of alpine staurolite pre or early alpine hornblende k ar ages are not fully reset unless the rocks were completely recrystallized for one rock specimen which clearly exhibits two generations of hornblende an age two times greater was obtained for the smaller crystals oriented parallel to the foliation than for the structurally younger hornblende porphyroblasts which overgrew the preexisting texture 3 in the high grade area of alpine metamorphism only young alpine ages between 23 and 28 m y were found for hornblendes which grew syn to postkinematically with respect to the last penetrative deformation one amphibolitic inclusion not affected by this deformation yielded a significantly older hornblende age of 32 1 m y these results suggest that temperature controlled ar diffusion is not the main factor governing the k ar system of metamorphic hornblendes we conclude that these hornblende ages should not be interpreted as cooling ages from a structurally ill defined earlier event instead they indicate that the high grade metamorphism responsible for the well known isograd pattern in the lepontine area persisted until some 23 m y ago

crystallization and age of zircon from corsican ophiolitic albitites consequences for oceanic expansion in jurassic times abstract in corsica albitites and albite granites are considered to be the latest products of an ophiolitic magma two albitites have been selected for a study of the morphology typology and age of their zircons applying for the first time the u pb method to western tethyan ophiolites both samples come from the rospigliani series possibly formed in a transform fault zone the first one shows a cumulate texture whereas the second has features indicative of more rapid cooling zircons have precipitated at the end of the fractional crystallization process after a strong enrichment in alkali and incompatible elements in a typological diagram they plot at high temperature and high agpaicity indexes these abundant large euhedral to subhedral zircons sometimes with fine zoning may also contain inclusions of granitic composition which testifies to k fractionation in ophiolitic magmas the u pb age of 161 3myr is in the range of the ages obtained for alpine and apennines ophiolites all these ophiolitic remnants belonging to the liguro piedmont basin may represent a portion of the central atlantic ocean created during middle and upper jurassic times

combined high precision chronometry and geochemical tracing using accessory minerals applied to the central alpine bergell intrusion central europe abstract the behaviour of nd u th and pb isotopes in granitic rocks is usually controlled by accessory minerals in this study an approach is adopted which uses the initial 143 nd 144 nd as a geochemical tracer together with high precision u th pb geochronology for accessory phases and their respective whole rock this combination of techniques is applied to zircon allanite sphene apatite and thorite from both a tonalite and a granodiorite from the tertiary alpine bergell intrusion inherited isotopic signatures have been identified in bulk zircon fractions by inverse discordance in the u pb system in the case of the granodiorite the initial nd in the zircon is 1 77 units lower than the bulk rock this result indicates that nd isotopes in zircon may serve as a useful tool for tracing crustal precursors in silicic rocks all other accessories yield an initial nd equal to their respective whole rock and u th pb ages equal to or lower than the respective intrusion ages this indicates either the absence of inherited cores or that such cores have exchanged their nd and pb in the case of apatite also sr by diffusion where available experimental mineral melt equilibria and diffusion models are consistent with this behaviour u pb geochronology of carefully selected core free zircons yields a precise intrusion age of 31 88 0 09 ma for the tonalite in contrast granodioritic zircons are partially reset due to radiation damage caused by high u concentrations however an alternative means of dating young intrusions is to use 232th 208pb ages of allanite in the case of allanite the presence of a large excess of 206pb derived from 230th indicates that no total pb loss has occurred since crystallization and the nd isotopes indicate the absence of inheritance using both the allanite age and a 238u 206pb age for sphene an intrusion age of 30 13 0 17 ma is indicated for the granodiorite taken together with an allanite th pb age for the tonalite these results strongly support the high closure temperatures for the allanites studied here 700 800 c at high post magmatic cooling rates all other accessory mineral ages are reset to values similar to hornblende 39ar 40ar ages and reflect the effect of post magmatic cooling superimposed on post metamorphic cooling

relationships between atmospheric internal variability and the responses to an extratropical sst anomaly abstract the january and february responses of a gcm to an imposed extratropical pacific sst anomaly are compared with the patterns of the model s internal variability relevant patterns of internal variability are diagnosed from ensembles of model control runs by regressing monthly mean geopotentials and temperatures against low level temperatures in the vicinity of the sst anomaly and by eof analysis these patterns are found to play a significant role in determining the local and the remote responses to the sst anomaly different responses to the sst anomaly in the gcm s january and february climates are largely explained by the differences in the regression patterns and in the leading eof the gcm response may be considered as comprising a direct linear response to low level heating that is local to the forcing and baroclinic and an eddy forced component that closely resembles patterns of the model s internal variability it is equivalent barotropic and extends over the entire hemisphere the results

the anatomy of a pull apart basin seismic reflection observations of the dead sea basin the dead sea basin dsb located along the african arabian plate boundary constitutes a good example of a pull apart basin because of its large dimensions its structural simplicity and its active subsidence a coherent three dimensional picture of the dsb has been constructed on the basis of analysis of seismic stratigraphy together with the interpretation of previously published geological and geophysical data despite the large known vertical offsets across the basin deformation takes place mainly along the transverse and longitudinal faults and the intervening sediments are relatively undeformed and are hardly tilted comparison between e w seismic lines indicate that the basin has widened by the collapse and tilting of arcuate blocks from the western margin but that its original shape is a full graben the southern and central parts of the basin are divided into equidistant segments 20 30 km long by transverse faults activity along these faults commenced only during the pleistocene long after the dead sea strike slip fault system was formed and migrated northward with time a likely scenario for the development of the dsb is one in which the basin grows northward with time by a simultaneous propagation of the southern strand of the dead sea fault and a retardation of the northern strand

effects of ekman transport on the nao response to a tropical atlantic sst anomaly abstract a recent study showed that a tropical atlantic sea surface temperature sst anomaly induces a significant coupled response in late winter february april fma in a coupled model in which an atmospheric general circulation model is coupled to a slab mixed layer ocean model agcm ml the coupled response comprises a dipole in the geopotential height like the north atlantic oscillation nao and a north atlantic tripole in the sst the simulated nao response developed 1 or 2 months later in the model than in observations to determine the possible effects of ekman heat transport on the development of the coupled response to the tropical forcing an extended coupled model agcm eml including ekman transport in the slab mixed layer ocean is now used large ensembles of agcm eml experiments are performed parallel to the previous agcm ml experiments with the model forced by the same tropical atlantic sst anomaly over the boreal winter months september april the inclusion of ekman heat tra

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

an eifelian u pb zircon date for the enagh tuff bed from the old red sandstone of the munster basin in nw iveragh sw ireland the first geochronological data from the minister basin sw ireland contradict the accepted biostratigraphical maximum age late givetian early frasnian of the oldest alluvium in the basin depocentre magmatic zircons from the enagh tuff bed a sub plinian air fall tuff within fluviatile old red sandstone of nw iveragh give a pb pb isotope age of 384 9 0 7 ma this confirms middle devonian probably eifelian sedimentation and allows possible early devonian basin initiation associated second cycle gravels suggest a pre 385 ma minimum age for the caherbla group of the dingle basin correlation with alluvium containing tetrapod trackways indicates a pre 385 ma age for the trace maker

tectonic evolution of the northumberland basin the effects of renewed extension upon an inverted extensional basin the northumberland sedimentary basin has a history of repeated extensional and contractional tectonic phases and a study of the deformation interference pattern and sedimentary record allows the identification of the tectonic state through time initial rifting is represented by a thick dinantian sedimentary fill but carboniferous extension is thought to have ceased by the early namurian in order to explain the development of certain facies patterns during the westphalian thermal subsidence phase of the evolution of the northumberland basin some syn depositional extensional fault movements are required at other times in the westphalian compaction induced subsidence was the dominant control on facies distribution a single phase of e w to se nw variscan compression commenced during or after late westphalian times and ceased prior to the intrusion of the whin sills and dykes subsequent permo mesozoic extension with a right lateral shear component re activated pre existing normal fault lines these later structures may be interpreted as being listric in form shallowing onto decollement surfaces within the carboniferous basin fill and overlie the buried faulted margin at the southern side of the basin

the general circulation model response to a north pacific sst anomaly dependence on time scale and pattern polarity abstract a general circulation model was integrated with perpetual january conditions and prescribed sea surface temperature sst anomalies in the north pacific a characteristic pattern with a warm region centered northeast of hawaii and a cold region along the western seaboard of north america was alternately added to and subtracted from the climatological sst field long 1350 day runs as well as short 180 day runs each starting from different initial conditions were performed the results were compared to a control integration with climatological ssts the model s quasi stationary response does not exhibit a simple linear relationship with the polarity of the prescribed sst anomaly in the short runs with a negative sst anomaly over the central ocean a large negative height anomaly with an equivalent barotropic vertical structure occurs over the gulf of alaska for the same sst forcing the long run yields a different response pattern in which an anomalous high prevails over northern canada and

two high precision u pb zircon ages for the sudbury nickel irruptive two independent u pb zircon ages were measured using norite samples from the north and south ranges of the sudbury nickel irruptive ages of and ma were obtained with a probability of fit within experimental error of 51 and 57 respectively previous determinations by the rb sr whole rock method gave ages between about 1700 and 2000 ma with errors of the order of 100 ma the difference in precision is inherent in the two methods zircons from the norite are highly radiogenic and almost concordant whereas rb sr whole rock ages are determined by very small increments in radiogenic 87sr the two zircon ages have completely different discordia so that all simple models for lead loss by continuous diffusion can be excluded

the modeled atmospheric response to midlatitude sst anomalies and its dependence on background circulation states abstract the atmospheric response to a midlatitude sst anomaly in the north pacific and its dependence on background flow are examined in a gcm experiments are conducted using the same warm sst anomalies but two different model states perpetual january and perpetual february the atmospheric responses to the sst anomalies are statistically significant in both january and february but are completely different the anomalous circulation in january is characterized by a trough decaying with height immediately downstream of the sst anomalies in february the anomalous circulation is dominated by a downstream ridge growing with height the patterns of the anomalous heights in the two months are nearly orthogonal vorticity and thermodynamic budgets are diagnosed to illustrate how the anomalous circulations are maintained over the sst anomalies low level convergence and ascent are observed in both months in january the anomalous convergence is balanced by a residual due primarily to the forcing by submont

rollovers in salt tectonics the inadequacy of the listric fault model abstract rollover anticlines are syn sedimentary extensional structures common in salt tectonics that are classically considered to result from layer bending during hangingwall displacement above a listric normal fault however theoretical considerations and seismic images of natural examples put in question the validity of the listric fault model from which rollover growth is steady state by nature and controlled by the relative displacement of two blocks we used laboratory experiments of gravity driven deformation of brittle ductile models simulating salt tectonics processes to study in which circumstances rollovers are obtained both in time and space it is argued that rollover growth is a nonsteady process that results from a mechanical instability whose critical lifetime can be divided in three characteristic stages birth growth and decay in kinematic terms the development of a synthetic or antithetic rollover requires a three block system an upslope block and a downslope block that move downslope and that separate from each other on top of an extending decollement layer lying above a basement block synthetic and antithetic rollovers developed with upward concave shapes whatever the sense of shear in the salt layer and can pass laterally to each other without transform fault this points out that the concave shape of a rollover base is not an argument in favour of listric faulting the concave shape simply results from the connection between a steeply dipping normal fault and a flat lying or gently dipping decollement

segmentation and along strike asymmetry of the passive margin in socotra eastern gulf of aden are they controlled by detachment faults on the island of socotra the southern passive margin of the gulf of aden displays along its strike two different types of asymmetric structures western socotra is made up of a series of southward tilted blocks bounded by consistently northward dipping normal faults eastern socotra consists of a broad asymmetric anticline with a steep northern limb and a gently dipping southern limb a zone of ne sw striking strike slip and normal faults separates the two areas the overall structure is interpreted as representing two rift segments separated by a transfer zone the along strike juxtaposition of crustal scale asymmetric structures on the southern margin of the gulf of aden is complemented by the asymmetry of the conjugate margins on either side of the gulf whereas the western socotra margin is narrow and characterized by oceanward dipping normal faults the conjugate oman margin is broader and dominated by horsts and graben considering that asymmetric structures in the upper crust are often associated with synthetic shear zones at deeper ductile levels we propose that the western and eastern socotra margin segments were controlled at depth by two detachment faults with opposite dips and senses of shear the normal faults of western socotra would sole out into a top to the north ductile shear zone whereas the asymmetric anticline of eastern socotra would be associated with a top to the south detachment fault

the new nb p aplite at reinhardsrieth a keystone in the lateral and depth zonations of the hagendorf pleystein pegmatite field se germany abstract the hagendorf pleystein pegmatite field hppf is the largest pegmatite concentration in central europe which has been intensively studied for its mineralogy mainly at hagendorf south pegmatite stock it was not until recently that the lateral and depth zonations of the hppf could be clarified when the newly discovered tabular aplite at reinhardsrieth aplite has been found at transition into the so called barren zone devoid of rare metals thereby the theory of the derivation of the hppf felsic mobilizates as a result of a successive differentiation of a pegmatitic melt from the flossenburg granite has to be discarded from the structural and lithological point of view stock like well zoned pegmatites e g hagendorf south developed in the hinge zone whereas tabular aplites such as reinhardsrieth evolved along the limb zone of strongly folded basement rocks in the latter case the accommodation space was smaller and the cooling of the felsic mobilizates much faster giving rise to fine grained aplitic rather than coarse grained felsic mobilizates chilled margin effect during the incipient stages of the evolution in the hppf at reinhardsrieth a stronger impact of granitization can be determined than at the neighboring aplites and pegmatites based upon the ree fractionation a tripartite subdivision may be established for the various pegmatites and aplites in the hppf 1 barren zone minor amounts of lree in a system otherwise dominated by feldspar and quartz 2 marginal zone mainly fe al phosphates plus columbite fe 3 central zone fe zn li phosphates plus columbite fe the afore mentioned zonation shows an e w trend and a bilateral symmetric arrangement of the various areas there are significant indications of an oxidizing facies to substitute for a more reducing facies at the transition from the central into the marginal zone of the hppf the key mineral for the primary pegmatite mineralization in the marginal and central zones is columbite fe its mn fe ratios plotted vs the ta nb ratios allow for an assessment to what extent metamorphic and magmatic processes have contributed to the built up of the pegmatites and aplites in the hppf even the most primitive nigrine hosted columbites fit well into this pattern forming a lithochemical halo in the roof rocks of the pegmatites the heavy mineral aggregated of rutile ilmenite nigrine giving host to the columbite as armored relicts got released from the basement rock on top of the pegmatites into the stream sediments where they are operative as an ore guide the morphology of zircon in the stream sediments has been utilized as an economic ore indicator the zr silicate is also indicative of the temperature of formation and closely supports the tripartite zonation established above manganiferous apatite is a good depth of emplacement indicator for each aplite and pegmatite respectively the higher the feo mno content of apatite the shallower the depth of emplacement of its host pegmatite or aplite vivianite in turn marks the onset of the hydrothermal alteration of the pegmatites and aplites and its mn contents relate to the depth where alteration has taken place or emplacement of the secondary phosphates the higher the mn content the shallower the depth of alteration peculiar element ratios were selected to design some key diagrams so as to corroborate the field based mineralogical and geological results in terms of zonation of genetic economic geology as well as to cater for applied economic geology as proximity indicators and ore guides when exploring for rare element pegmatite

on the predominant nonlinear response of the extratropical atmosphere to meridional shifts of the gulf stream abstractthe north atlantic atmospheric circulation response to the meridional shifts of the gulf stream gs path is examined using a large ensemble of high resolution hemispheric scale weather research and forecasting model simulations the model is forced with a broad range of wintertime sea surface temperature sst anomalies derived from a lag regression on a gs index the primary result of the model experiments supported in part by an independent analysis of a reanalysis dataset is that the large scale quasi steady north atlantic circulation response is remarkably nonlinear about the sign and amplitude of the sst anomaly chosen over a wide range of gs shift scenarios the nonlinear response prevails over the weak linear response and resembles the negative north atlantic oscillation nao the leading intrinsic mode of variability in the model and the observations further analysis of the associated dynamics reveals that the nonlinear responses are accompanied by the shift of the north atlantic eddy

mechanisms determining the atmospheric response to midlatitude sst anomalies abstract previous gcm experiments demonstrated that a model atmosphere produces two different responses to a midlatitude warm sst anomaly over the pacific under perpetual january and february conditions to elucidate the mechanisms responsible for the different gcm responses and their dependence on the background flow experiments with two idealized models are conducted experiments with a linear baroclinic model reveal that the gcm responses at equilibrium are primarily maintained by the anomalous eddy forcing the anomalous flow induced directly by an idealized initial heat source exhibits little sensitivity to the background flow eddy feedbacks on the heating induced anomalous flow are examined using a linear storm track model the anomalous eddy forcing produced by the storm track model is sensitive to the basic state the eddy forcing in january acts to shift the heating induced upper level ridge toward the northeast of the gulf of alaska while in february it acts to reinforce the ridge this sugge

u pb geochronologic constraints on the crustal evolution of the long range inlier newfoundland the long range mountains of newfoundland expose the northeastern most basement inlier of the appalachian orogen u pb results for two samples of basement gneiss reveal crustal formation ages of 1466 10 ma western brook pond charnockite and 1530 8 ma cat arm road gneiss indicating an affinity with pinwarian magmatism 1510 1450 ma in labrador a third sample of basement gneiss from the cat arm road dam site yielded a minimum formation age of 1631 ma these basement gneisses were intruded by granite plutons during two periods of grenvillian magmatism group i at 1032 1022 ma and group ii at 993 985 ma group i intrusions include the 1032 0 1 5 ma lomond river granite and the 1022 0 2 0 ma lake michel igneous suite group ii intrusions include the 999 4 ma potato hill charnockite 993 7 ma horse chops granite 984 9 1 6 ma cloud river granite and may include the apsy granite the metamorphic history of the long range inlier is complex and three discrete proterozoic metamorphic events can

kinematics and age of syn intrusive detachment faulting in the southern alps evidence for early permian crustal extension and implications for the pangea a versus b controversy permian basin formation and magmatism in the southern alps of italy have been interpreted as expressions of a wsw ene trending dextral megashear zone transforming early permian pangea b into late permian pangea a between 285 and 265 ma in an alternative model basin formation and magmatism resulted from n s crustal extension to characterize permian tectonics we studied the grassi detachment fault a low angle extensional fault in the central southern alps the footwall forms a metamorphic core complex affected by upward increasing top to the southeast mylonitization two granitoid intrusions occur in the core complex the synmylonitic val biandino quartz diorite and the postmylonitic valle san biagio granite u pb zircon dating yielded crystallization ages of 289 1 4 5 ma for the former and 286 8 4 9 ma for the latter consequently detachment related mylonitic shearing took place during the early permian and ended at 288 ma but kinematically coherent brittle faulting continued considering 30 anticlockwise rotation of the southern alps since early permian the extension direction of the grassi detachment fault was originally n s even though a dextral continental wrench system has long been regarded as a viable model at regional scale the local kinematic evidence is inconsistent with this and rather supports n s extensional tectonics based on a compilation of 200 u pb zircon ages we discuss the evolution and tectonic framework of late carboniferous to permian magmatism in the alps

influence of the meridional shifts of the kuroshio and the oyashio extensions on the atmospheric circulation abstract the meridional shifts of the oyashio extension oe and of the kuroshio extension ke as derived from high resolution monthly sea surface temperature sst anomalies in 1982 2008 and historical temperature profiles in 1979 2007 respectively are shown based on lagged regression analysis to significantly influence the large scale atmospheric circulation the signals are independent from the enso teleconnections which were removed by seasonally varying asymmetric regression onto the first three principal components of the tropical pacific sst anomalies the response to the meridional shifts of the oe front is equivalent barotropic and broadly resembles the north pacific oscillation western pacific pattern in a positive phase for a northward frontal displacement the response may reach 35 m at 250 hpa for a typical oe shift a strong sensitivity since the associated sst anomaly is 0 5 k however the amplitude but not the pattern or statistical significance strongly depends on the lag and an

the evolution of the polymetamorphic basement in the central alps unravelled by precise u pb zircon dating the u pb age determinations of zircon and rutile from the aar massif reveal a complex evolution of the central alpine basement the oldest components are found in zircons of metasediments which bear cores of archean age the u pb age of discordant prismatic zircons of the same rocks ranges between 580 and 680 ma an age that is typical for pan african metamorphism the zircons are interpreted as pan african detritus with archean inheritance the provenance region of the pan african zircons is assumed to be a terrane of gondwana affinity i e the w african craton or the pentevrian microplate the caledonian metamorphism left a pervasive structural imprint in amphibolite facies on the rocks of the aar massif it is dated at 456 2 and 445 ma by zircons of a layered migmatitic gneiss and a migmatitic leucosome respectively both occurring in the northernmost zones of the massif hercynian metamorphism never exceeded greenschist facies conditions and is recorded by zircon in a garnet amphibolite and by rutile in a meta psammite that yield an age of 330 ma both zircon and rutile are considered to be products of retrograde mineral reactions and therefore do not date the peak conditions of hercynian metamorphism the gastern granite at the western end of the aar massif is a contaminated granite that intruded at 303 4 ma contemporaneously with the wide spread late hercynian post collisional i type magmatism the study demonstrates the potential of isotope dilution u pb dating of single grains and microfractions in deciphering complex evolutionary histories of polymetamorphic terrains

observed impact of atlantic sst anomalies on the north atlantic oscillation the large scale patterns of covariability between monthly sea surface temperature sst and 500 mb height anomalies z500 in the atlantic sector are investigated as a function of time lag in the ncep ncar reanalysis 1958 97 in agreement with previous studies the dominant signal is the atmospheric forcing of sst anomalies but statistically significant covariances are also found when sst leads z500 by several months in winter a panatlantic sst pattern precedes the north atlantic oscillation nao by up to 6 months such long lead time covariance is interpreted in the framework of the stochastic climate model reflecting the forcing of the nao by persistent atlantic sst anomalies a separate analysis of midlatitudes 208 708n and tropical 208s 208n sst anomalies reveals that the bulk of the nao signal comes from the midlatitudes a dipolar anomaly with warm sst southeast of newfoundland and cold sst to the northeast and southeast precedes a positive phase of the nao and it should provide a prediction of up to 15 of its monthly variance several months in advance since the forcing sst pattern projects significantly onto the tripole pattern generated by the nao these results indicate a positive feedback between the sst tripole and the nao with a strength of up to 25 mk 21 at 500 mb or 2 3 mb k21 at sea level additionally a warming of the tropical atlantic 208s 208n roughly symmetric about the equator induces a negative nao phase in early winter this tropical forcing of the nao is nearly uncorrelated with and weaker than that resulting from the midlatitudes and is associated with shorter lead times and reduced predictive skill

kinetics of crystallization of igneous rocks the geochemistry of igneous rocks is discussed with the primary objectives of bringing together the theories underlying the kinetics of crystallization of igneous rocks and illustrating the use of these theories in understanding experimental and observational data the primary purpose of the chapter is to introduce current thinking about the kinetics of igneous rocks and to provide a basis for understanding other work a basic assumption made in the discussion is that the rate of any chemical reaction including the crystallization of igneous rocks is zero at equilibrium and proceeds at a finite rate only at a finite deviation from equilibrium as such an understanding of the processes operating in igneous rocks requires an understanding of how deviation from equilibrium affects the rates and mechanisms of the processes occurring during crystallization these processes are detailed with special emphasis given to nucleation and crystal growth jmt

structural stratigraphic models for extensional basins of half graben type abstract the equations describing subsidence in isostatically compensated basins formed by lithospheric stretching can be modified to define a notional depth to decollement which relates subsidence to the stretching factor in much the same way as the depth to a physical sole fault relates subsidence to extension in uncompensated thin skinned basins for a constant density basin fill this notional depth to decollement corresponds to the level of no vertical motion within the lithosphere in general the physical sole to a system of detached normal faults will not lie at the notional depth to decollement and must move vertically during extension this vertical movement must be implicitly corrected for before area bed length balancing is used to determine the depth to a physical sole fault the notional depth to decollement has been calculated numerically for an extensional basin loaded by sediments which follow a north sea shaly sand compaction law and increases with from 5 to 9 km a set of model half grabens has been constructed by combining subsidence curves generated by this shaly sand model with geometric relationships inherent in the rotated planar domino mechanism of upper crustal faulting for comparison a similar set of half grabens was constructed for an uncompensated basin with a sole fault at 7 5 km depth in both cases large fault to fault spacings give rise to large basement relief and consequent footwall uplift and erosion small fault spacings give rise to simple listric growth faults intermediate values generate more complex uplift subsidence histories which are capable of giving rise to such commonly observed features as rounded eroded fault block shoulders local regression followed by onlap or exponentially increasing subsidence at the crest of the fault block

the anomalous structures of atmospheric and oceanic variables associated with the frequency of north pacific winter blocking 1 from empirical orthogonal function eof analysis of the atmospheric and oceanic variables over the north pacific during the northern hemispheric winter 1960 2009 we were able to determine that the second mode of the eof is related to north pacific winter blocking our composite analysis reveals that the structures of the variables during winters with contrasting frequencies of blocking events are systematically different and show quite opposite pattern in the north pacific during winters with frequent blocking occurrence a north south dipole pattern of geopotential height anomaly is formed and the associated westerly winds are weakened strengthen north south of 35 n these factors bring variations of ocean advection and ocean surface heat flux resulting in a dipole pattern of sea surface temperature sst with a warm anomaly north of 35 n and a cold anomaly to the south the effect of sst on blocking is examined using an atmospheric general circulation model agcm experiment in the experiment the sst anomaly related to blocking is applied as a boundary forcing of the agcm to investigate the effect of sst on the formation of blocking from the experiment we also concluded that the winter blocking is not induced by north pacific sst forcing although consistent linkage between oceanic and atmospheric variables is evident

observed influence of north pacific sst anomalies on the atmospheric circulation abstract a lagged maximum covariance analysis mca of monthly anomaly data from the ncep ncar reanalysis shows significant relations between the large scale atmospheric circulation in two seasons and prior north pacific sea surface temperature sst anomalies independent from the teleconnections associated with the enso phenomenon regression analysis based on the sst anomaly centers of action confirms these findings in late summer a hemispheric atmospheric signal that is primarily equivalent barotropic except over the western subtropical pacific is significantly correlated with an sst anomaly mode up to at least 5 months earlier although the relation is most significant in the upper troposphere significant temperature anomalies are found in the lower troposphere over north america the north atlantic europe and asia the sst anomaly is largest in the kuroshio extension region and along the subtropical frontal zone resembling the main mode of north pacific sst anomaly variability in late winter

possible north atlantic origin for changes in enso properties during the 1970s the most intense el nino episodes in more than a century occurred after the 1970s climate shift previous studies show that the characteristics of the el nino southern oscillation enso phenomenon changed synchronously with the shift but the associated causes are not fully understood an analysis of the observed tropical pacific sea surface temperature sst anomalies shows that their increase in the eastern part of the basin after the 1970s is not related to the canonical enso pattern but to the tropical pacific meridional mode tpmm we present observational evidence which supports the hypothesis that the change in the tpmm was triggered by the great salinity anomaly gsa which manifested in the north atlantic during the late 1960s the gsa induced a weak labrador convection and a sst dipole south of greenland the associated atmospheric structure includes a north pacific oscillation sea level pressure dipole in the pacific sector this excites the tpmm which contributes to the intense el nino events and to the enhanced enso s asymmetry observed after the shift our results imply that if the gsa has not an anthropic origin as was suggested then the tropical pacific climate shift has a natural origin this is supported by the end of the north atlantic regime in the 1990s and by the rebound of the tropical pacific after 1998

timing of high pressure metamorphism in the yukon tanana terrane canadian cordillera constraints from u pb zircon dating of eclogite from the teslin tectonic zone zircon from eclogite near last peak in the teslin tectonic zone yielded a u pb isotopic age of 269 2 ma 2 the first precise age for such a rock in the yukon tanana terrane of the canadian cordillera both the morphology and geochemistry of the eclogitic zircons indicate a metamorphic origin and the u pb age therefore constrains the timing of peak high pressure metamorphism in this rock the u pb age demonstrates for the first time that an early permian high pressure metamorphic event occurred in rocks now making up the teslin tectonic zone and possibly elsewhere in the yukon tanana terrane this u pb age provides a new geochronologic pin in the evolution of the yukon tanana terrane prior to its mesozoic accretion to the north american continental margin and combined with recent 40ar 39ar muscovite data indicates that high pressure metamorphism at this time was a relatively short lived event

a response climatology of idealized midlatitude thermal forcing experiments with and without a storm track several gcm studies indicate that eddy activity may have a considerable influence on the atmospheric response to midlatitude sea surface temperature anomalies the effect of eddy activity on the atmospheric equilibrium response to idealized midlatitude thermal forcing is analyzed for an atmosphere with or without an idealized storm track experiments using a simplified global circulation model forced by thermal anomalies of different sign and location are discussed consistent with the linear theory the geopotential height field displays a baroclinic response with a shallow low high somewhat downstream of the warm cold anomaly farther downstream an equivalent barotropic response occurs with positive negative amplitude increasing with height eddy feedbacks have weak impact on the baroclinic part but the equivalent barotropic response is strongly enhanced if the bandpass filtered streamfunction tendency is in phase with the linear geopotential height response this is the case in an experiment with a warm anomaly near 408n located southwesterly of the idealized storm track in the corresponding experiment with a cold anomaly the two patterns are out of phase and the equivalent barotropic response is slightly reduced it is weakened strengthened if a warm cold anomaly is shifted about 108 poleward or equatorward relative to the idealized storm track midlatitude heat sources generate wave trains that extend equatorward and poleward developing large scale correlations between the flow at remote locations teleconnections the space time variability can be changed considerably by eddy feedbacks developing stronger variance for large scale retrogressive traveling and standing waves partially blocking like events develop

the transient atmospheric response to midlatitude sst anomalies abstract to study the transient atmospheric response to midlatitude sst anomalies a three layer quasigeostrophic qg model coupled to a slab oceanic mixed layer in the north atlantic is used as diagnosed from a coupled run in perpetual winter conditions the first two modes of sst variability are linked to the model north atlantic oscillation nao and eastern atlantic pattern eap respectively the dominant atmospheric modes in the atlantic sector the two sst anomaly patterns are then prescribed as fixed anomalous boundary conditions for the model atmosphere and its transient responses are established from a large ensemble of simulations in both cases the tendency of the air sea heat fluxes to damp the sst anomalies results in an anomalous diabatic heating of the atmosphere that in turn forces a baroclinic response as predicted by linear theory this initial response rapidly modifies the transient eddy activity and thus the convergence of eddy momentum and heat fluxes the latter transforms t

displacement distance methods in the analysis of fold thrust structures and linked fault systems a new method for analysing the internal strain in thrust sheets is described the displacement distance diagram can be used to quantify the relative shortening or relative stretch between the hangingwall and footwall beds of a thrust and is a useful way of analysing commonly occurring fold thrust structures the stretch is a function of the relative rates of thrust propagation and thrust slip the cumulative displacement distance diagram described here can be used to calculate the absolute shortening or extension when this is accommodated above a single decollement in a linked fault system this method offers a useful way of analysing duplex structures and large scale foreland thrust zones as well as extensional fault systems and can be used as an alternative to or in conjunction with balanced cross sections both methods can be used to quantify the variation in shortening above a single detachment zone this variation may be mechanically significant reflecting lithological control on thrust or normal fault growth

the geometry of listric normal faults and deformation in their hangingwalls abstract in cross sections containing listric extensional faults area balancing techniques for depth to decollement are usually based on either bed length conservation or displacement conservation listric fault geometry may be constructed from a hangingwall roll over profile using the chevron construction this construction based on conservation of heave necessitates a reduction in fault displacement with decreasing fault dip a modification of this construction utilizing conservation of fault displacement predicts a listric fault that detaches at a shallower depth a new construction based on slip lines uses fault perpendicular displacement segments to generate listric fault shape fault propagation strain may be responsible for anomalous hangingwall geometries and these can be predicted by forward modelling using either a modified chevron construction or a slip line construction

feedbacks of sea surface temperature to wintertime storm tracks in the north atlantic abstractin this study the lagged maximum covariance analysis is performed on winter storm track anomalies represented by the meridional heat flux by synoptic scale 2 8 days transient eddies and sea surface temperature sst anomalies in the north atlantic which are both derived from reanalysis datasets spanning the twentieth century the analysis shows significant seasonal and interannual coupling between storm track and sst variations on seasonal time scales it is found that sst anomalies in the preceding early winter november december which are expected to change the lower tropospheric baroclinicity can significantly influence storm tracks in early spring march that is an intensification and slight northward shift of storm tracks in response to a midlatitude sst dipole with a cold pole centered to the southeast of newfoundland and a warm pole in the western subtropical atlantic this storm track response pattern is similar to the storm track forcing pattern in early spring which resembl

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

atmospheric gcm response to an idealized anomaly of the mediterranean sea surface temperature the atmospheric response to an idealized 2 k cooling of the mediterranean sea is studied in a general circulation model gcm in the downstream region from the eastern mediterranean basin to the whole asian continent following the sub tropical jet stream a baroclinic response is produced with high pressure near the surface and low pressure in the upper layers it is the direct response to the mediterranean cooling and it needs only a few days to be established teleconnections with strong zonal characteristics are found following the sub tropical jet stream to the north pacific and north america propagating further across the north atlantic towards northern europe two remarkable remote features are the deepening of the aleutian low in the north pacific and the weakening of the icelandic low in the north atlantic these two teleconnections form and grow in several days in the north pacific and several tens of days in the north atlantic both have a quasi barotropic vertical structure it is believed that they are the consequence of complex interactions between the mean flow and the transient eddies in the atmosphere

cross section restoration and balancing as aid to seismic interpretation in extensional terranes structural cross sections in extensional terranes can be improved significantly by restoration and balancing principles originally developed for fold and thrust belts in rift basins and passive continental margins use of restoration techniques in analysis of growth faults elongate salt swells and other extensional structures results in geologically valid seismic interpretations sections must be in depth as opposed to two way time and oriented in the direction of material transport and decompaction must accompany restoration hanging wall deformation is characterized by different processes depending on the mechanical properties of the rocks being extended and can be approximated by various geometric and kinematic models antithetic faulting is analogous to antithetic shear combined antithetic and synthetic faulting is approximated by vertical shear domino style extension corresponds to rigid body rotation and flexural slip flow is modeled by bed length balance methods selection of the appropriate algorithm is crucial for proper restoration and balancing applications of these techniques illustrated here using seismic data from the gulf coast and north sea include 1 evaluating and adjusting seismic interpretations 2 projecting listric fault trajectories to depth 3 delineating more accurately the geometry and extent of hydrocarbon reservoirs 4 identifying new exploration leads 5 determining the deformation history of an area and 6 constraining the timing and direction of hydrocarbon migration and entrapment

improved accuracy of u pb zircon dating by selection of more concordant fractions using a high gradient magnetic separation technique abstract a loop of soft iron wire or a paper clip or a ferromagnetic grid mounted between the poles of an electromagnet picks up and allows further magnetic separation of zircons previously found to be non magnetic on a frantz isodynamic separator tests on previously analysed samples indicate that most such zircons that are fairly discordant say 10 can be picked up and isolated from associated grains that are more concordant tests on new samples indicate that even when most grains can be picked up the last few percent of the sample contain less uranium and are more concordant than the bulk sample the degree of discordance is the dominant factor affecting the uncertainty of u pb zircon ages both because of the error amplification in projections and because the assumption of a simple two stage system may not be valid only by eliminating or reducing discordance can errors approaching the uncertainty in a single analysis say 2 m y for 2700 m y rocks be achieved rutile normally concentrated with zircon as non magnetic has been successfully removed from a small amount of low uranium zircon using the high intensity separation technique

crustal thinning and subsidence in the north sea we present here the results of a detailed study of subsidence and crystal thinning across the central graben of the north sea basin two independent lines of evidence have been used to test how well the uniform extensional model1 2 can account for the evolution of the north sea basin a long range seismic profile was shot perpendicular to the central graben from edinburgh to southern norway and data were analysed from 11 exploration wells situated close to the seismic line fig 1 the estimates of the increase in surface area due to extension from the crustal structure determined using the seismic data and from the well subsidence patterns are both compatible with a simple uniform extensional mechanism for the post palaeozoic evolution of the north sea

transient atmospheric response to interactive sst anomalies abstract the transient atmospheric response to interactive sst anomalies in the midlatitudes is investigated using a three layer qg model coupled in perpetual winter conditions to a slab oceanic mixed layer in the north atlantic the sst anomalies are diagnosed from a coupled run and prescribed as initial conditions but are free to evolve the initial evolution of the atmospheric response is similar to that obtained with a prescribed sst anomaly starting as a quasi linear baroclinic and then quickly evolving into a growing equivalent barotropic one because of the heat flux damping the sst anomaly amplitude slowly decreases albeit with little change in pattern correspondingly the atmospheric response only increases until it reaches a maximum amplitude after about 1 3 5 months depending on the sst anomaly considered the response is similar to that at equilibrium in the fixed sst case but it is 1 5 2 times smaller and then slowly decays away

a modelling and observational study of the relationship between sea surface temperature in the north west atlantic and the atmospheric general circulation results from four pairs of 50 day wintertime integrations of the meteorological office s 5 level general circulation model with warm and cold sea surface temperature s s t anomalies of about 3 k in the northwest atlantic are described difference fields between the warm and cold integrations are statistically significant at the 1 level with positive geopotential height over the central north atlantic and weaker negative height over europe the storm track over the atlantic is displaced from its normal position results from four further pairs of integrations with halved s s t anomalies are also described the response is approximately linear with systematic differences in 500 mb geopotential height over the atlantic parts of which are just significant at the 10 level with half the full s s t anomaly overall however the model s response is weaker than could be obtained with tropical s s t anomalies of the same magnitude results from the model integrations are compared with results from an observational study of the relationship between wintertime s s t in the north west atlantic and mean sea level pressure and 500mb height two independent 30 year periods were chosen for study thus minimizing the influence of long term trends in s s t over the atlantic and europe the model results compared well with the observations with s s t data lagging the atmosphere by one month the observational study appears to show that the s s t anomalies are initially forced by perturbations in the atmospheric circulation with s s t data leading the atmosphere by one month results show that atmospheric and s s t anomalies are most persistent in the period october to december throughout the winter these lagged relationships are much weaker and not statistically significant diagnostics of e vector divergence from the gcm experiments are used to suggest that anomalous baroclinic wave activity over the atlantic is important as a momentum forcing for the anomalous time mean flow pattern on the other hand the role of thermal forcing provided by anomalous diabatic heating and transient eddy heat flux convergence may be important to substantiate this statement a simple linear steadystate two layer model of the response to extratropical thermal forcing is described with a suitable basic state flow and a mid tropospheric heat source given mainly by the transient eddy heat flux convergence the response is shown to be equivalent barotropic with a downstream ridge and ascent over the thermal source conversely results from an ocean mixed layer model are discussed which suggest that warm s s t anomalies could be maintained by a positive surface pressure perturbation positioned downstream of the anomaly through anomalous northward advection of warm ocean water by ekman drift currents this northward advection would balance the sensible and latent heat loss into the atmosphere over the s s t anomaly hence it is possible that some positive ocean atmosphere feedback may account for the persistence of such atmospheric and oceanic anomalies

hf isotope systematics in granitoids from the central and southern alps first initial hf isotopic compositions for samples from the alpine domain are presented and discussed the results are mainly based on zircons and a few whole rocks with ages between 30 and 450 ma of those so far analyzed the present day hf isotopic compositions of zircons from non metamorphic and metamorphic granitoid rocks vary between 0 2824 and 0 2829 zircon populations with concordant u pb ages have much higher initial 176hf 177hf than inversely discordant populations which have been contaminated with older zircons containing less radiogenic hf correlated nd hf crustal residence ages have been found involving model parameters of ehf end f lu hf f sm nd 1 6 for the depleted mantle and f lu hf f sm nd 1 2 for elemental fractionations in the crust the model implies 176lu 177hf of 0 017 for the bulk crust it is suggested that the granitoid rocks are the result of mixing of subcontinental mantle derived magmas with 1 7 ga old recycled and partially molten crustal material the continental mantle component mass ratio values for the granitoids range between 0 3 and 2

a joint statistical and dynamical assessment of atmospheric response to north pacific oceanic variability in ccsm3 abstract atmospheric response to north pacific oceanic variability is assessed in community climate system model version 3 ccsm3 using two statistical methods and one dynamical method all methods identify an equivalent barotropic low response to a warmer sea surface temperature sst anomaly in the kuroshio extension region koe during early midwinter while all three methods capture the major features of the response the generalized equilibrium feedback assessment method gefa isolates the impact of koe sst from a complex context and thus makes itself an excellent choice for similar practice

early archaean component 3 5 ga within a 3 05 ga orthogneiss from northern nigeria upb zircon evidence abstract conventional u pb analyses on selected single zircon grains and on zircon fractions from a granodioritic orthogneiss at kaduna northern nigeria show that the nigerian basement contains archaean components that have not been recognized until now a distinct u rich zircon group records an age of 3040 60 ma which is interpreted as the age of emplacement and crystallization of the granodioritic magma the occurrence of a magmatic event at ca 3000 ma is confirmed by the addition of core free abraded grains 3050 23 ma these ages are identical to the less precise value 2980 90 ma given by zircon fractions these results also demonstrate that zircons underwent pb loss during the pan african orogeny at 612 23 ma which is well supported by an identical age on a single monazite grain 618 8 ma moreover u pb analyses of abraded u poor core bearing crystals clearly identify the presence of source material of early archaean age 3500 ma the oldest age for crust initiating processes ever found in this area in contrast to earlier rb sr geochronology no evidence for an eburnean 2000 200 ma or kibaran 1100 200 ma orogeny is present in the u pb systems of these zircons

nao ocean circulation interactions in a coupled general circulation model the interplay between the north atlantic oscillation nao and the large scale ocean circulation is inspected in a twentieth century simulation conducted with a state of the art coupled general circulation model sig nificant lead lag covariance between oceanic and tropospheric variables suggests that the system supports a damped oscillatory mode involving an active ocean atmosphere coupling with a typical nao like space structure and a 5 years timescale qualitatively consistent with a mid latitude delayed oscillator paradigm the two essential processes governing the oscillation are 1 a negative feedback between ocean gyre circulation and the high latitude sst meridional gradient and 2 a positive feedback between sst and the nao the atmospheric nao pattern appears to have a weaker projection on the ocean meridional overturning compared to the gyre cir culation which leads to a secondary role for the thermohaline circulation in driving the meridional heat transport and thus the oscillatory mode

transient eddy forcing of the time mean flow as identified by geopotential tendencies abstract the forcing of the time mean flow by transient eddies is examined within the framework of a quasi geostrophic equation relating the geopotential tendency to the convergence of transient eddy transports of heat and vorticity the forcing functions of this equation are computed using observed circulation statistics for the wintertime northern hemisphere and solutions are sought for the three dimensional structure of geopotential and temperature tendencies associated with eddies of different time scales in general the geopotential tendencies associated with vorticity fluxes are of the same sign within a given atmospheric column whereas the polarity of the geopotential tendencies associated with heat fluxes in the lower troposphere is opposite to that in the upper troposphere the geostrophic wind tendencies associated with synoptic scale eddies with periods between 2 5 and 6 days are strongest in the vicinity of the oceanic storm tracks the enhanced poleward heat transports by active disturbanc

uranium lead system in fragments of a single zircon grain since the demonstration that u pb analyses of zircon fractions1 from a few grains up to several thousand grains or fragments of grains2 or single zircon grains3 4 yield reliable radiometric age data this method has been widely applied to igneous metamorphic and sedimentary rocks the present investigation of u pb systems for a suite of distinct fragments of a single zircon grain from a 1 093 2118 myr old syenite of the pikes peak batholith colorado usa demonstrates that uranium is heterogeneously distributed in this zircon crystal most parts of the grain suffered various degrees of lead loss the others show a closed system behaviour we show that degrees of lead loss are not correlated with uranium concentrations of the fragments

variability of the baroclinic and barotropic transient eddy forcing associated with monthly changes in the midlatitude storm tracks abstract the heat and vorticity transports by synoptic scale eddies at various levels between 1000 and 100 mb have been compiled for each winter month of the 1966 84 period using time filtered daily analyses produced by the u s national meteorological center these circulation statistics were used to compute the three dimensional distributions of the quasigeostrophic geopotential tendency and vertical motion induced by baroclinic and barotropic eddy processes in individual months the latter fields serve as the basis for describing the synoptic scale eddy forcing associated with the leading modes of month to month variability of the storm tracks over the north pacific and north atlantic these modes are associated with the meridional displacements of the storm track axes from their climatological positions the placement of a storm track at a certain latitude in a certain month is accompanied by enhanced convergence of eddy heat fluxes poleward of in the tropospheric column poleward of the storm tra

zircon inheritance in an igneous rock suite from the southern adamello batholith italian alps zircons from a suite of basic to acidic calcalkaline igneous rocks from the southern adamello batholith s ab southern alps n italy display complex u pb isotopic patterns which are mainly due to the presence of variable amounts of isotopically heterogeneous inherited radiogenic pb and to minor postmagmatic loss of pb inherited pb is mainly composed of 1 a 1100 ma pb component located in zircons devoid of visible cores and 2 a 450 ma component associated with conspicuous bubble rich turbid cores in concordia representation the data points conform to lower intercept ages of 40 ma a linear fit of three samples devoid of visible cores from the granodiorite defines an intrusion age of 39 3 ma u pb systematics of zircon in particular u content and crystal morphology are clearly related zircons of type g1 which form relatively late in the zircon crystallization sequence consistently show the highest u contents in each zircon population these late zircons however are not devoid of inherited radiogenic lead in a population from a granodiorite cores are randomly distributed throughout the morphological spectrum the presence of old inherited zircon components in all investigated samples furnishes proof for involvement of crustal material in the genesis of the s ab rocks samples characterized by crustal nd and sr values usually show enhanced zircon inheritance inheritance varies with differentiation and reaches a maximum for intermediate to acidic members these compositions show the highest zr saturation temperatures calculated for the rock spectrum studied textural relations between zircon and major phases indicate that the magmas of the leucocratic rocks were saturated with zr at an early stage of crystallization on the other hand zr solubilities and textural relations consistently show that melts of basic to intermediate rocks were not saturated with zr extension of the zr solubility model to mineral melt mixtures of tonalitic bulk composition demonstrates that zr solubility in the residual melt is drastically reduced by crystallization of plagioclase and amphibole survival of xenocrystic zircons in the mafic to intermediate rocks of the s ab can best be explained in terms of dissolution kinetics since temperature and h2o content of these zr undersaturated melts were favourable for relatively rapid zircon dissolution inherited zircons in particular trace element rich unstable cores cannot have been exposed to such conditions over extended time periods therefore the tonalitic or more basic magmas of the s ab cannot have been derived from crustal sources by slow processes such as burial metamorphism

morphology versus upb systematics in zircon a high resolution isotopic study of a zircon population from a variscan dike in the central alps upb isotopic measurements on individual zircon crystals combined with morphological analyses permit the identification of three distinct components within the zircon population of the saedelhorn diorite a variscan dike from the western gotthard central alps switzerland i 94 of the grains in the zircon population are elongate crystals with pronounced skeletal morphology indicative of rapid growth from a supercooled melt ii 5 of the population consist of turbid mostly subhedral zircons frequently showing d type morphology classification according to pupin and turco 1 and elevated uranium contents compared to the skeletal variety single crystal and multi grain upb isotopic data of group i and ii zircons define an intrusion age of 293 5 4 m y for the dike iii rare transparent zircon crystals 1 of the zircon population yield apparent upb ages in the range of 370 490 m y and display morphological and isotopic characteristics closely resembling those of a caledonian orthogneiss intruded by the dike this implies presence of assimilated wall rock components in the macroscopically homogeneous dike sample a comparison of the data obtained by conventional analysis of multi grain zircon fractions and those obtained by grain by grain analysis demonstrates that age resolution is considerably improved by single crystal upb dating furthermore quantitative identification of zircon components assimilated by the ascending magma along its path to the present level of exposure is feasible by the latter technique since it is likely that such zircon grains are common to a broad variety of magma types valuable information on age and composition of crustal layers not accessible to direct observation may readily become available by application of precise micro analytical techniques low initial143nd 144nd end 2 7 at the time of intrusion of the saedelhorn dike requires the magma to be derived partially or totally from a crustal source for this crustal precursor a model age of 1050 m y tdm is obtained indicating that proterozoic crust was involved in the petrogenesis of the variscan intrusives of the gotthard area

u th pb systematics of morphologically characterized zircon and allanite a high resolution isotopic study of the alpine rensen pluton northern italy abstract the rensen pluton is a typical member of the tertiary calc alkaline plutonic suite structurally connected to the periadriatic lineament it intrudes the austroalpine polymetamorphic basement of the eastern alps southwest of the tauern window northern italy zircons and allanites from tonalitic quartz dioritic and monzogranitic lithologies were studied systematically on the basis of refined grain by grain microanalytical techniques high resolution isotope analyses show that morphology and u pb systematics of zircon are highly correlated with magma evolution zircons from the main tonalitic part of the intrusion display a gradual increase of u content from early stage s type morphology to late stage g1 type morphology most of the zircon crystals include premagmatic seeds derived from old crustal sources unevolved s type zircons contain inherited components of late proterozoic early paleozoic apparent age whereas late stage g1 type zircons show inheritance of early proterozoic apparent age both types of inherited components are present in zircons from a fine grained tonalitic domain located at the center of the pluton which shows restitic structures the crustal affinity of this rock is corroborated by its relatively low e nd value 6 0 as compared to values obtained for the main tonalite 3 9 and the quartz diorite 3 5 the accuracy of cainozoic zircon ages is affected by initial radioactive disequilibrium in the u pb decay chains particularly uncertain is the fractionation behavior of protactinium which could be enriched in zircon due to the high stability of the pa 5 oxidation state because the th pb system is devoid of long lived intermediate radioactive nuclides the best approximation to the emplacement age of the rensen pluton is given by allanite th pb ages of 31 70 0 25ma 95 c l for the main tonalite and by a slightly younger age of 31 09 0 32ma for quartz diorite

on the feedback of the winter nao driven sea ice anomalies satellite derived sea ice concentration sic and re analysed atmospheric data are used to analyse the potential feedback of the north atlantic oscillation nao driven sea ice anomalies in winter onto the atmosphere during 1979 2013 a maximum covariance analysis shows that this feedback can be detected with monthly data when sic leads the covariability between atlantic sic and the euro atlantic atmospheric circulation in february is statistically significant but shows intra seasonal differences the december sic influence is dominated by anomalies east of greenland with maximum amplitude in the greenland sea gs while the january sic influence is dominated by anomalies west of greenland in the davis strait labrador sea dl region the lagged atmospheric anomalies are likewise different a reduction of sic over gs in december is followed in february by a negative nao like pattern near the surface and a hemispheric signature in the upper troposphere thus acting as a negative feedback on the other hand a reduction of sic over dl in january is followed by an atmospheric anomaly over the north atlantic that projects on the positive phase of the east atlantic pattern the dynamics associated with these atmospheric anomalies is described indicating that transient eddy activity is likely at work in settling the large scale patterns the role of concomitant north atlantic sea surface temperature anomalies is discussed

crustal structure of the anza graben from gravity and magnetic investigations abstract the area of the present study constitutes the northeastern sector of the anza graben in this sector the graben is about 130 km wide and is characterized by a linear negative anomaly with an amplitude about 40 mgal geophysical data mainly gravity and magnetic were analysed quantitatively including modelling in an effort to determine the subsurface structure of the graben the study covered a strike length of about 320 km the results of the modelling indicate that in the area of the study two major basins with opposite dips exist the northern basin dips southwestwards the southern one northeastwards the density contrast assigned to the sediments in the final gravity model is 300 kg m3 suggesting a maximum sediment thickness of about 8 km the modelling of the magnetic data however favours a maximum thickness of over 10 km it is proposed that intrusives occur at some depth below sections of the graben shoulders and that the graben has a gentle northwesterly regional plunge

late jurassic half graben control on the siting and structure of hydrocarbon accumulations uk norwegian central graben abstract the late jurassic structure of the central graben is discussed both in terms of the extensional features developed at this time and their subsequent controls on younger inversion structures the regional kinematics of the north sea rift suggest that during the late jurassic the central graben opened approximately orthogonally to the main nnw sse fault trend within the basin some evidence that triassic extensional faults were reactivated at this time is seen towards the basin margins and a significant triassic extensional history is inferred the late jurassic basin comprises the axial c 100 km of the central graben s l the basin axis is offset progressively to the se by both transfer zones and discrete transfer faults footwall uplift of the basin margins during extension provided the source for the upper jurassic reservoir sands encountered by exploration drilling these sands were probably preferentially fed into the basin at transfer zones in the margins salt structures are ubiquitous within the central graben and their siting is everywhere controlled by the underlying fault block topography salt structures form preferentially towards the crests of half graben or buttressed against their boundary faults inversion structures in the norwegian sector reactivated with a reverse sense of displacement late jurassic extensional faults a model is proposed which shows the two main inversion structures feda graben norway tail end graben denmark to be detached on antithetic reverse faults riding in the salt these faults terminate at tip folds within major salt walls the geometry of the inversion structures can be understood only when considered together with the geometry of the underlying late jurassic half graben

equilibrium atmospheric response to north atlantic sst anomalies abstract the equilibrium general circulation model gcm response to sea surface temperature sst anomalies in the western north atlantic region is studied a coarse resolution gcm with realistic lower boundary conditions including topography and climatological sst distribution is integrated in perpetual january and perpetual october modes distinguished from one another by the strength of the midlatitude westerlies an sst anomaly with a maximum of 4 c is added to the climatological sst distribution of the model with both positive and negative polarity these anomaly runs are compared to one another and to a control integration to determine the atmospheric response in all cases warming cooling of the midlatitude ocean surface yields a warming cooling of the atmosphere over and to the east of the sst anomaly center the atmospheric temperature change is largest near the surface and decreases upward consistent with this simple thermal response the geopotential height field displays a baroclinic

low frequency variability in the southern ocean region in a simplified coupled model 1 patterns of interannual variability of the ocean atmosphere coupled system in the southern hemisphere extratropics are studied with a simple dynamical model in order to determine the basic physical processes of interaction independently of tropical forcing the model used is an atmospheric quasi geostrophic model coupled to a slab oceanic mixed layer which includes mean geostrophic advection by the antarctic circumpolar current acc the ocean atmosphere coupling occurs through surface heat fluxes and ekman current heat advection in a fully coupled simulation the atmospheric part of the model which includes high frequency transient eddies at midlatitudes exhibits a strong southern annular mode sam as the first mode of variability at interannual timescales the sam related wind anomalies induce ekman currents in the mixed layer which produce sea surface temperature anomalies these are then advected along by the acc a forced mechanism where the ocean role is reduced to advect the sea surface temperature sst appears sufficient to reproduce the main features of the variability nevertheless a positive feedback of the ocean was also found it operates through anomalous ekman currents heat advection and contributes to the maintenance of the sst anomaly

stationary atmospheric responses to an idealized sea surface temperature anomaly in the southern ocean abstractthe stationary atmospheric response to an idealized sea surface temperature anomaly ssta is studied with a quasigeostrophic atmospheric model of the southern hemisphere sensitivity of the stationary response to the midlatitude ssta location is determined and responses are decomposed on vertical modes the ssta almost directly forces baroclinic responses inducing warm air anomalies 40 50 downstream eastward to the ssta these baroclinic responses arise from an equilibrium between the ssta induced anomalous vortex stretching and i advection by the quasi stationary flow and ii dissipation by high frequency eddies the barotropic response consists of a midlatitude ridge trough and a south pole trough ridge for sstas localized from the drake passage to the western indian ocean from south of australia to the center of the pacific ocean this response can be further decomposed into i a zonally asymmetric component a quasi stationary wave train forced by a barotropic ridge downstream of

sea surface temperature anomalies planetary waves and air sea feedback in the middle latitudes the mechanisms that contribute to the generation and damping of large scale mid latitude sea surface temperature sst anomalies are discussed the sst anomalies reflect primarily the response of the upper ocean to the changes in air sea fluxes that are associated with daily weather fluctuations heat flux forcing is dominant in the lower middle latitudes while wind driven entrainment may be most effective in the high latitudes advection by anomalous ekman current is generally less important and ekman pumping is negligible the sst anomalies decay in part because of entrainment effects associated with mixed layer deepening and oceanic mixing and in part because of heat exchanges with the atmosphere the three approaches commonly used to model the evolution of sst anomalies are reviewed case studies based on monthly or seasonal anomaly maps of the large scale sst and atmospheric anomalies numerical simulations with one dimensional mixed layer models and stochastic forcing models we stress the similarities in the different approaches and discuss their main advantages and limitations the response of the atmosphere to mid latitude sst anomalies is considered first we discuss the poorly known relationship between sst anomalies and diabatic heating using a crude assumption for the air sea coupling we consider a two layer quasi geostrophic channel model and discuss the stationary wave response to sst anomaly forcing and the resulting air sea feedback it is found that the back interaction of the sst anomalies onto the atmosphere causes a weak sst anomaly damping at large scales and a strong one at small scales the air sea coupling should also act as an eastward propagator for the sst anomalies the response of more realistic linear wave models to prescribed diabatic heating is then reviewed and it is suggested that realistic mid latitude sst anomalies have a weak influence on the atmospheric circulation corresponding to changes in the geopotential height of 10 30 m at most this order of magnitude is consistent with the results of general circulation model experiments and with the limited climate predictability associated with mid latitude sst anomalies

red sea related history of extension and magmatism in the jizan area southwest saudi arabia indication for simple shear during early red sea rifting the tectonic and magmatic history of the jizan coastal plain of the red sea tihama asir in southwest saudi arabia is dominated by sw ne extension this extension manifests itself by a basic dike swarm and several generations of normal faults that trend roughly nw se the oldest synrift deposits are non marine clastics and bimodal volcanics of the jizan group which were intruded by basic dikes gabbros and granophyres of the tihama asir magmatic complex tamc radiometric ages for the tamc rocks range from 26 to 18 ma rifting in the southern part of the red sea system therefore is certainly older than 26 ma between 26 and 20 ma the southwestern arabian margin was affected by a monoclinal downwarp flexure the oldest extensional features in the jizan area are n s to nnw sse striking dikes and normal faults which were overprinted by other nw se striking extension structures an array of en echelon extensionzones is linked by complex patterns of transfer faults mainly wnw ese striking dextral strike slip or oblique slip faults the observed superposition of dikes and normal faults of different orientations was not necessarily caused by a counterclockwise rotation of the regional stress field but more likely reflects the clockwise rotation of individual faultbounded blocks between the two phases of extension uplift of the graben shoulder east of the jizan coastal plain is probably younger than 14 ma and its development coincides with a major rearrangement of the kinematics along the red sea this new kinematic pattern probably led to the onset of strike slip movement along the aqaba levant transform at the same time extension and volcanism ceased in the jizan area or shifted further to the west after a long hiatus of about 10 ma renewed extension facilitated extrusion of alkali olivine basalts since 2 ma ago

organization of storm track anomalies by recurring low frequency circulation anomalies abstract from previous studies it is known that anomalous momentum fluxes by bandpass eddies are important in maintaining long lasting tropospheric flow anomalies evidence is presented that suggests that these anomalous fluxes do not occur at random but happen because the structure of storm track activity is modified by the presence of prominent low frequency large scale circulation anomalies this behavior is noted in an extended integration of a perpetual january simulation with a general circulation model gcm because nonlinear feedbacks between low and high frequency variability make it difficult to establish causal relationships between these two ranges of variability a model is constructed that approximates the storm track activity that would be expected to accompany a given low frequency without including the feedback of the high frequencies onto the low frequency state this model is based on the linearized primitive equations and uses a series of short integrations from random initial condi

the role of rossby wave breaking in shaping the equilibrium atmospheric circulation response to north atlantic boundary forcing abstract the role of rossby wave breaking rwb is explored in the transient response of an atmospheric general circulation model to boundary forcing by sea ice anomalies related to the north atlantic oscillation nao when the ncar community climate model version 3 was forced by an exaggerated sea ice extent anomaly corresponding to one arising from a positive nao a localized baroclinic response developed and evolved into a larger scale equivalent barotropic pattern resembling the negative polarity of the nao the initial baroclinic response shifted the phase speeds of the dominant eddies away from a critical value equal to the background zonal flow speed resulting in significant changes in the spatial distribution of rwb the forcing of the background zonal flow by the changes in rwb accounts for 88 of the temporal pattern of the response and 80 of the spatial pattern of the zonally averaged response although results here focus on one experiment this rwb critical line mechanism appears to be