changes in the 300 mb north circumpolar vortex 1963 2001 abstract the mean monthly polar stereographic map analyses of the free university of berlin terminated at the end of 2001 this paper summarizes the changes in size of the 300 mb north circumpolar vortex and quadrants for the full period of record 1963 2001 where the size has been defined by planimetering the area poleward of contours in the jet stream core a contracted vortex has tended to be a deep vortex in winter but a shallow vortex in summer during 1963 2001 there was a statistically significant decrease in vortex size of 1 5 per decade the decrease in size of western hemisphere quadrants being twice that of eastern hemisphere quadrants a significant increase in arctic oscillation ao index accompanies the significant decrease in vortex size but since the vortex contracts appreciably in all four seasons whereas the positive trend in the ao index is mainly in winter the vortex cannot serve as a proxy for the ao index the evidence for vortex contraction at the time of the 1976 77 regime

constraining lithologic variability along the alleghanian detachment in the southern appalachians using passive source seismology polarities and amplitudes of intracrustal p sv conversions p waves converted to vertically polarized shear waves in receiver functions from the southeastern suture of the appalachian margin experiment array and usarray transportable array provide new constraints on the origin of seismic reflectivity delineating the alleghanian detachment in the southern appalachians eastern united states forward modeling of receiver functions is consistent with a 3 5 km thick high shear wave velocity vs 3 9 km s section of deformed paleozoic platform metasedimentary rocks beneath the blue ridge at 3 6 5 km depth in the inner piedmont conversions from the top and base of a low vs zone 3 1 km s at depths of 5 9 km are interpreted as a package of metasedimentary rocks or a shear zone characterized by radial anisotropy the detachment continues to the southeast beneath the carolina terrane where high amplitude negative conversions at 10 13 km depth are consistent with arc rocks vs 4 0 km s overlying sheared rocks with lower vs 3 2 km s southeast dipping conversions at 5 10 km depth mark the boundary between the inner piedmont and carolina terrane this study demonstrates that relatively high frequency receiver functions up to 3 hz though still lower in frequency than p wave energy analyzed for reflection profiling 20 hz can provide important links between surface geology and active source experiments to better constrain models of crustal structure

cocorp seismic profiling of the appalachian orogen beneath the coastal plain of georgia a southeastward extension onto the coastal plain of an earlier cocorp traverse which confirmed large scale thin skinned thrusting of crystalline rocks of the southern appalachians has provided some of the most spectacular reflections yet seen in crustal seismic data most of the reflectors can be interpreted as either fault surfaces or as metamorphosed strata of late precambrian early paleozoic age they are consistent with the hypothesis that a major detachment extends eastward beneath this part of the orogen although other interpretations with a more complex pattern of detachments or sutures are also possible large scale overthrusting provides a mechanism for incorporating sedimentary rocks into the lower crust and may help to explain many of the layered features on crustal seismic data reflections from deep beneath the coastal plain indicate that the structural configuration of the rocks is complex and that the remains of a collision zone are being observed several east dipping horizons which bear strong similarities to thrust faults in valley and ridge sedimentary rocks are seen in the basement at shallow and mid crustal levels beneath the coastal plain the augusta fault for example displays a reflection which extends at a low angle some 80 km or more southeast of its surface position in conjunction with surface geologic information these new data demonstrate that late paleozoic compressive deformation was pervasive and resulted in lateral movements in the upper crust extending from the valley and ridge to the crystalline rocks beneath the coastal plain a distance of 400 km or more a large antiform cresting at about 2 3 sec or about 6 km below the surface and other structures beneath the coastal plain of georgia deserve further consideration for petroleum exploration although metamorphism may have eliminated petroleum from these rocks refracted arrivals and fault geometries indicate two triassic rift basins beneath coastal plain sedimentary rocks one of which has apparently not been recognized previously

the influence of el nino southern oscillation events on the northern hemisphere 500 hpa circumpolar vortex the relationship between el nino the southern oscillation and their joint effect enso and northern hemisphere 500 hpa midlatitude circulation for the 1946 1994 observational record is determined seasonally standardized vortex positions at a spatial resolution of 5 longitude are correlated with an equatorial pacific sea surface temperature anomaly index and the southern oscillation index soi the 500 hpa circumpolar vortex is consistently expanded over the central pacific during and for the entire year following warm enso periods the vortex is contracted over north america concurrently with warm enso and to a lesser degree during the following season expansion contraction variability is also evident over east asia although the linkages to warm or cold enso are weak sea surface temperatures have a stronger association with the vortex than does the soi

elliptical diagnostics of stratospheric polar vortices diagnostics based on the spatial moments of isopleths of a long lived tracer or of potential vorticity are presented that enable the structure and evolution of stratospheric polar vortices to be concisely summarized and quantified the area centre aspect ratio and orientation of the equivalent ellipse of the vortex on an isentropic surface are defined using the second and lower order spatial moments of contours within the vortex edge region by examining the variations of these elliptical diagnostics with time and altitude the temporal evolution and vertical structure of the polar vortices can be quantified the usefulness of the diagnostics is assessed by examining nitrous oxide data from the geophysical fluid dynamics laboratory skyhi general circulation model the diagnostics show and quantify several differences between the arctic and antarctic vortices in the skyhi model the arctic vortex moves further off the pole is generally more elongated and has a more complicated vertical structure than the antarctic vortex with larger variations of both the vortex centre and elongation with height the elliptical diagnostics also identify the occurrence of large scale rossby wave breaking events both at the vortex edge and in the subtropics in the model

jointing within the outer arc of a forebulge at the onset of the alleghanian orogeny the oldest joint set in devonian rocks of western new york state has an atypical ns strike and predates regionally more abundant nw striking and ene striking joints driven by hydrocarbon related fluid decompression the ns joints originated in higher modulus diagenetic carbonate and were driven initially by a different mechanism either joint normal stretching and or thermoelastic contraction the origin of these joints in higher modulus carbonate concretions indicates the presence of a tensile stress produced by uniform regional extensional strain upper devonian shale hosting the ns joints crops out in that area of the appalachian basin where a morrowan erosional unconformity marks the region of maximum upward lithospheric flexure of an early alleghanian forebulge the ns strike of these early joints points to a forebulge stretching axis oriented approximately east west and associated in time and space with crustal loading that drove both the northfieldian orogeny and the underplating of the bronson hill anticlinorium in new england ultimately subsidence of the morrowan forebulge buried the upper devonian shale succession to the oil window during the latter part of the alleghanian tectonic cycle resulting in the propagation of fluid driven nw and ene trending joints in black shale

seismic evidence of mylonite reflectivity and deep structure in the kettle dome metamorphic core complex washington the first direct test of the seismic reflectivity of mylonites is provided by a seismic reflection profile over a mylonite zone exposed in the kettle dome metamorphic core complex northeastern washington the mylonite zone developed at mid crustal levels and has undergone a minimum of retrogression and cataclasis during uplift downdip projection of the exposed mylonite zone into the seismic profile indicates that the compositionally layered mylonite zone is reflective and traceable to at least 5 km depth as a complex zone of multicyclic reflections the seismic data also show that the crust beneath the kettle dome is characterized by abundant strongly reflective moderately dipping layers down to at least 18 km these layers can be interpreted in terms of compressional or extensional orogenic events or a combination of both models for the structure and genesis of metamorphic core complexes must take these data into account

signal penetration in the cocorp basin and range colorado plateau survey seismic sections from cocorp s 1982 survey from the eastern basin and range to the colorado plateau of central utah exhibit distinct cutoff times after which reflections are rare to nonexistent in the eastern basin and range this cutoff time is approximately 11 s 33 km but beneath the central colorado plateau it exceeds 15 s 45 km these depths appear to correspond to the base of the crust moho with the lack of reflections from greater depths indicating mantle homogeneity in general absence of deeper reflections may be due either to geologic homogeneity or to lack of signal penetration cocorp line 3 in the colorado plateau basin and range transition zone shows that variations in penetration are significant on line 3 few reflections are evident below the structurally complex sedimentary cover which extends to only 4 s 8 km and virtually none are identifiable later than 7 s 21 km lateral variations in the temporal decay of source generated energy together with estimates of correspondin

polyphase reactivation history of the towaliga fault central georgia implications regarding the amalgamation and breakup of pangea abstractthe towaliga fault southern appalachians contains fault rocks that formed under various p t conditions revealing a complex reactivation history it trends 070 along the northwest flank of the pine mountain window changes to 035 at the northeast end of the window and continues northeastward into the inner piedmont isolated kilometer scale rhomboidal pods of silicified cataclasite along the towaliga fault likely represent ancient dilational step overs which acted as conduits for hydrothermal fluid flow during faulting and consequently are sites of concentrated mineralization towaliga fault garnet grade mylonite formed during large displacement alleghanian 295 ma dextral strike slip while geometric and kinematic evidence suggests dilational step overs formed in a small displacement sinistral strike slip system mutually overprinting crosscutting relationships with mesozoic diabase dikes confirm cataclasis occurred 200 ma silicified dilational step overs are present along both fault o

a geophysical study of the earth s crust in central virginia implications for appalachian crustal structure a regional seismic reflection line i 64 across the virginia piedmont has provided a stacked section suitable for an integrated interpretation of geophysical data in the region a highly reflective upper crust an allochthonous blue ridge province underlying thrust sheets including the blue ridge master decollement and a basal decollement at a depth of about 9 km 3 s are confirmed on the seismic data immediately east of the blue ridge province appalachian structures plunge to as much as 12 km 4 s depth the evington group hardware terrane and chopawamsic metavolcanic rocks carolina terrane crop out in the piedmont province and numerous eastward dipping reflections originate from these rocks in the subsurface these eastward dipping reflectors overlie a gently west dipping 10 15 highly reflective zone that varies in depth from 1 5 s 4 5 km beneath the goochland terrane to 4 s 12 km beneath the rocks of the evington group some of the overlying eastward dipping reflections apparently root in this zone the zone may include decollement surfaces along which the overlying rocks were transported relatively few reflections originate from within autochthonous grenville basement at the western end of the profile the goochland granulite terrane is interpreted to be a westward thrust nappe structure that has overridden a portion of the chopawamsic metavolcanic rocks a broad zone of east dipping 20 45 reflections bounds the goochland terrane on the east these reflections may originate from deformation zones and continue to moho depths they appear to be correlative with similar events seen on other appalachian lines the pervasiveness of the zone of east dipping events on other seismic reflection lines and the continuity of the adjacent piedmont gravity high suggest continuity of crustal features along the length of the appalachians a major conclusion of this study is that crustal thinning is responsible for the main components of the gravity field in virginia that is the appalachian gravity gradient and the piedmont gravity high the crust thins from about 52 km beneath the appalachian mountains to about 35 km beneath richmond virginia and then rethickens by up to 10 km beneath the zone of east dipping reflections mylonites east of richmond the i 64 seismic data also contain a sequence of reflections at about 9 12 s indicative of lower crustal layering the base of this zone of reflections coincides almost exactly with the mohorovicic discontinuity interpreted from earlier refraction work the layering extends about 70 km west from richmond virginia and is interpreted as a lower crustal transition zone that is believed to persist across most of virginia

high resolution sequence stratigraphic analysis and sea level interpretation of the middle and upper jurassic strata of the nyurolskaya depression and vicinity southeastern west siberia russia abstract in this article we present the first application of high resolution sequence stratigraphic analysis to the jurassic vasyugan deposits of west siberia on the basis of wireline logs lithologies and sedimentary facies we identified a series of third order depositional sequences that formed on a low gradient siliciclastic ramp in shallow marine to paralic environments our sequence stratigraphic framework helped to properly distinguish specific stratigraphic units productive sand beds while enhancing stratigraphic correlation sequence stratigraphic procedures particularly aided in recognition of fluvial channels and prograding shorelines in marginal parts of positive structures that usually represent the most favorable reservoir zones the depositional architecture of sequences throughout the entire area of study was primarily controlled by synchronous oscillations of relative sea level comparison of interpreted sea level changes with our quantified eustatic curve qec derived from russian platform stratigraphy revealed close correspondence of timing of sea level events for the late bathonian late oxfordian interval this indicates that sea level events occurred simultaneously in west siberia and the russian platform and suggests that eustasy was the main factor controlling sedimentation in southeastern west siberia during that time interval in addition it supports the validity of the late bathonian late oxfordian interval of the qec demonstrating its utility for further application to west siberia and other sedimentary basins

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

evolution of the west siberian basin the west siberian basin is one of the largest intracratonic basins of the world and an important hydrocarbon province of russia perhaps the most important geologic event in siberia was the emplacement of basalts around 250 ma i e permo triassic boundary covering an area of about 5 10 6 km 2 this volcanism may be responsible for a mass extinction that occurred around permian triassic time the prebasaltic rifting event was limited to the north northeastern sector of the basin initial basin wide subsidence took place in the jurassic as a result of which the western part of siberia became the west siberian basin bounded by uplifts to the east and to the west one of the surprising aspects of the west siberian basin is the abundance of subvertical faults believed to be result of strike slip movement while intraplate inversions and fault reactivation structures have been observed in many cratons subvertical faults observed in the west siberian basin are unique because of their geometries and abundance the differentiation between the effects of tectonics and eustasy in cratonic basins is simple the global eustatic signal is basin wide with regional and local tectonics playing an overprinting role thus the middle jurassic turonian first second and third order cycles in the west siberian basin were primarily driven by eustasy the middle jurassic turonian series can be subdivided into two second order and 16 third order transgressive regressive cycles within dataset extent fourth order cycles appear to be controlled by delta shifting although extensively studied a number of fundamental questions regarding the origin and evolution of the west siberian basin remain unresolved or poorly documented in the literature

new field evidence for an exposure of the appalachian decollement at the east end of the pine mountain terrane georgia detailed field mapping at the east end of the pine mountain terrane in central georgia indicates that the box ankle fault is an 4 km thick ductile shear zone separating grenvillian basement of laurentian affinity in the footwall from allochthonous accreted terranes in the hanging wall fabric data from the box ankle fault indicate that it is a gently southeast dipping northwest vergent thrust fault recently discovered structural relations together with geochronological data indicate that the box ankle fault is of late paleozoic age we argue that the box ankle fault is a surface exposure of the appalachian decollement the east end of the pine mountain terrane may be the only place in the entire orogen where this fundamentally important structure is exposed for study

acadian dextral transpression and synorogenic sedimentary successions in the appalachians the successive seboomook littleton northern appalachians and catskill pocono central appalachians clastic wedges suggest oblique convergence and southwestward migration of acadian orogeny beginning in early devonian and continuing into early mississippian wrench fault movement in maritime canada coincided with deposition of all but the earliest components of the catskill pocono clastic wedge and continued into the pennsylvanian contrasts between a thin lower to middle devonian shallow shelf facies in the alabama appalachian fold thrust belt and a time equivalent thick shallowing upward sedimentary to volcanic succession in the adjacent talladega slate belt are interpreted to reflect a wrench fault basin a wrench fault setting for devonian rocks in alabama integrated with manifestations of oblique convergence during the acadian orogeny in the central and northern appalachians can be accommodated in dextral transpression along the entire length of the acadian appalachian orogen

2 d image of seismic attenuation beneath the deep seismic sounding profile quartz russia we present a 2 d image of the upper mantle attenuation using nuclear explosion data from the ultra long refraction reflection profile quartz our analysis is based on a modified common spectrum technique followed by least squares inversion for q and iterative ray tracing in the velocity structure obtained earlier the resulting attenuation structure corroborates the earlier model for northern eurasia as well as our recent estimate based on the analysis of the long range p n phase and provides significantly more detail than the existing models the resulting upper mantle attenuation structure is characterised by q values ranging from 400 to 1800 down to the depths of 150 190 and probably 400 km the attenuation increases horizontally in se direction away from the baltic shield our model exhibits strong 2 d vertical and horizontal attenuation contrasts a high attenuation layer in the depth range of 120 150 to 160 180 km can apparently be associated with the presence of a partial melts within the base of the lithosphere

development of interlaced mylonites cataclasites and breccias example from the towaliga fault south central appalachians abstract a variety of cataclastic rocks from crush breccias to cataclasites and silicified breccias are associated with retrograde mylonites along the towaliga fault zone of south central appalachians in georgia a zone of alternating breccias and quartz ultra mylonites bordered by quartz mylonites that are roughly laminated with mm scale mica rich bands of cataclasites occur subparallel to the mylonitic foliation elsewhere along the fault zone evidence for plastically deformed microfractures is found in discussing the mechanical evolution of these rocks two possibilities are considered a the cataclasis is an overprint representing deformation in an entirely brittle regime and b cataclasis and mylonitization occurred at t 300 c in a predominantly plastic regime within the framework of the latter model it is suggested that the cataclasite bands are either due to the relaxation of dilational stresses following downward propagation of seismic ruptures or represent strain induced seismic instabilities during plastic shearing

contraction of the 300 mbar north circumpolar vortex during 1963 1997 and its movement into the eastern hemisphere the size of the 300 mbar north circumpolar vortex and its partition into western and eastern hemispheres and quadrants 0 90 w 90 w 180 90 e 180 and 0 90 is estimated by planimetering the area poleward of contours in the main belt of westerlies on the polar stereographic mean monthly analyses of the institute of meteorology of the free university of berlin during 1963 1997 the trend in annual vortex size is a significant 1 4 decade vortex contraction but with the trend in the western hemisphere portion of the vortex a significant 2 1 decade compared to 0 7 decade in the eastern hemisphere portion signifying a movement of the vortex farther into the eastern hemisphere thus while on average 52 of the vortex was in the eastern hemisphere during 1963 1997 this value increased by a significant 0 4 decade during the period resulting in a substantial increase in vortex eccentricity in winter and spring the vortex has moved mainly into the asian quadrant 90 e 180 whereas in summer the vortex has become elliptical with less of a decrease in size of quadrants 90 e 180 and 0 90 w and in autumn there has been a decrease in size of quadrant 90 w 180 relative to the other quadrants the standard deviation of the annual quadrant size anomalies has decreased significantly during 1963 1997 indicating a decrease in the annual displacements of the vortex center from its mean location as the eccentricity increases and the vortex contracts on the basis of a 41 station northern hemisphere radiosonde network during 1963 1997 the annual 850 300 mbar temperature increased by a significant 0 12 c decade in the northern hemisphere as a whole and by a significant 0 17 c decade in the western half and by 0 06 c decade in the eastern half of the hemisphere the resulting association of a 1 decade decrease in 300 mbar vortex size with about an 0 1 c decade increase in 850 300 mbar temperature differs by a factor of 2 from what would be expected hydrostatically a difference that would be eliminated by an 0 4 mbar decade increase in midlatitude surface pressure during 1963 1997

the nature of seismic reflections from deep crustal fault zones deep seismic reflection profiles have recorded reflections from ductile shear zones within the crystalline basement perhaps the best example is the consortium for continental reflection profiling cocorp wind river line in wyoming which shows the wind river thrust fault to be a strong reflector from the surface to depths of about 30 km to identify the physical properties responsible for the seismic reflections from fault zones we report measurements of compressional wave velocity and velocity anisotropy in mylonites recovered from exhumed ductile shear zones these rocks are characterized by extensive ductile deformation of plastic minerals brittle deformation of the more rigid minerals grain size reduction and development of a strong fabric average velocity and density were not found to change significantly and systematically between the mylonites and the adjacent undeformed rock seismic anisotropy of 7 or greater is present in several mylonites dependent upon their composition and fabric using our data on mylonite properties and models for the crustal structure near the wind river line we compute true amplitude synthetic reflection seismograms and compare them to true amplitude plots of the cocorp wind river reflection data when anisotropy and the finely laminated structure of the fault zone are considered our modeling indicates fairly strong reflections from mylonite zones in most cases we also show that elevated pore pressure in shear zones may produce strong reflections however a permeability of the order of 10 16 darcy is required to maintain sufficient pore pressure to produce a velocity anomaly in a fault zone which has long been inactive

relation of size and displacement of the 300 mbar north circumpolar vortex to qbo el nino and sunspot number 1963 2000 the size of the 300 mbar north circumpolar vortex and its eastern western date line and greenwich hemisphere components is estimated for the period 1963 2000 by planimetering the area poleward of 300 mbar contours in the main belt of westerlies on the mean monthly polar stereographic analyses of the institute of meteorology of the free university of berlin on the basis of the superposed epoch method there is little evidence of a relation between vortex size and phase of the qbo but significant at the 90 level or better is the tendency for the vortex to be less displaced into the eastern hemisphere in the east wind phase of the qbo for the vortex to be expanded near the time of nino 3 sea surface temperature maximum el nino but contracted 3 4 seasons after and for the vortex to be displaced farther into the date line hemisphere when there is an el nino there is also an impressive tendency for the winter vortex to be less displaced into the eastern hemisphere at the time of el nino the tendency for the vortex to be contracted near sunspot maximum and expanded near sunspot minimum is significant at only about the 80 level because of the small sample size

ocmulgee fault the piedmont avalon terrane boundary in central georgia the ocmulgee fault is a fundamental boundary within the piedmont of central georgia separating north american piedmont terrane rocks from exotic rocks of the avalon carolina terrane contrasts in stratigraphy metamorphic grade and aeromagnetic signature coincide with the fault trace the fault comprises a broad zone ca 2 km of foliation dipping steeply southeast and containing localized syn and post thermal peak right lateral strike slip shear zones oblique dextral convergence between the avalon and peidmont terranes most likely around 350 ma produced the steep zone and its attendant dextral shear zones steep foliation within the fault zone resulted in its predisposition to later faulting

relation between 300 mb north polar vortex and equatorial sst qbo and sunspot number and the record contraction of the vortex in 1988 89 abstract the size of the 300 mb north circumpolar vortex and quadrants has been estimated between 1963 and 1989 by planimetering the area poleward of contours in the main belt of westerlies on the 300 mb mean monthly polar stereographic maps analyzed by the meteorological institute free university of berlin the annual mean vortex was most contracted in 1989 6 4 less than average size and next most contracted in 1988 4 6 less than average size there have been three extensive vortex displacements during this period the last toward the north pacific and associated with the strong el nino of 1982 83 based on 108 seasonal deviations there has been a significant correlation of 0 39 between sea surface temperature sst in the eastern equatorial pacific and vortex size three seasons later that is the vortex has tended to be contracted following el nino there has been a highly significant correlation of 0 45 between this sst and the size of quadrant 90 w 180 in the same season that is this el n

basement influence on foreland thrust and fold belt development an example from the southern urals abstract the reactivation of two sets of pre existing basement faults provided strong control on the geometric and kinematic evolution of the paleozoic south urals foreland thrust and fold belt pre existing basement faults oriented subparallel to the uralide structural grain were related to several stages of precambrian deformation reactivation focused the deformation along these earlier faults resulting in the subsequent incorporation of crystalline basement thrust sheets in the thrust belt at an early stage of its evolution pre existing basement faults oriented subperpendicular to the developing thrust belt structural grain were related to aulacogens in the archean crystalline basement that were filled by variable thickness of riphean aged sediments these influenced the localisation and development of numerous structures in the thrust belt that caused along strike structural changes related to lateral ramps recognition of these features and their influence on the geometric and kinematic evolution of the south urals foreland thrust and fold belt are important for understanding seismic reflection fabrics in the south urals thrust belt and for potential field 3 d geological and kinematic modelling

tectonic implications of subthrust structures revealed by seismic profiling of appalachian ouachita orogenic belt a growing body of deep seismic reflection profiles across the appalachian ouachita orogenic belt reveals subthrust structures which have been previously interpreted as products of continental rifting of later thrusting or of some combination of rifting and thrusting the subthrust features can be placed into three general categories 1 small normal faults which offset lower plate shelf sequences and basement in the foreland and have been attributed to thrust loading perhaps reactivating earlier rifting faults 2 moderately dipping seismic events which lie entirely below lower plate shelf sediments in the foreland interpreted in part as strata deposited during the earlier rifting and 3 hinterland dipping reflection sequences beneath more interior portions of the mountain belt previously interpreted as thrust faults which imbricate sediments and basement related to the earlier rifted margin these interpretations are evaluated through a comparison of reflection profiles across the orogenic belt to previously interpreted seismic lines across modern extensional and compressional settings the comparisons suggest that although some normal fault offsets of lower plate shelf sequences may be original or reactivated rifting faults the dipping events entirely beneath the shelf sequence are more diagnostic of the rifting process these dipping sequences are therefore consistent with previous interpretations that large portions of the earlier rifted margin are preserved in an undeformed state beneath thrust sheets in the appalachian foreland the comparisons also suggest an alternative to interpretations of the hinterland dipping sequences as thrust related in that the sequences are similar in seismic appearance to that of volcanic wedges commonly observed in the narrow zone separating continental from oceanic basement on modern passive margins the implication of this new interpretation is that the actual continent ocean boundary related to the earlier rifted margin may be preserved on the lower thrust plate beneath interior portions of the appalachians and ouachitas

early jointing in coal and black shale evidence for an appalachian wide stress field as a prelude to the alleghanian orogeny early ene striking joints present coordinates within both pennsylvanian coal and devonian black shale of the central and southern appalachians reflect an approximately rectilinear stress field with a dimension 1500 km this appalachian wide stress field awsf dates from the time of joint propagation when both the coal and shale were buried to the oil window during the 10 15 m y period straddling the pennsylvanian permian boundary the awsf was generated during the final assembly of pangea as a consequence of plate boundary tractions arising from late stage oblique convergence where maximum horizontal stress s h of the awsf was parallel to the direction of closure between gondwana and laurentia after closure the awsf persisted during dextral slip of peri gondwanan microcontinents when sh appears to have crosscut plate scale trans current faults at around 30 sup o following 10 m y of dextral slip during tightening of gondwana against laurentia the awsf was disrupted by local stress fields associated with thrusting on master basement decollements to produce the local orocline shaped alleghanian map pattern seen today

influence of the arctic circumpolar vortex on the mass balance of canadian high arctic glaciers abstract variability in july mean surface air temperatures from 1963 to 2003 accounted for 62 of the variance in the regional annual glacier mass balance signal for the canadian high arctic a regime shift to more negative regional glacier mass balance occurred between 1986 and 1987 and is linked to a coincident shift from lower to higher mean july air temperatures both the interannual changes and the regime shifts in regional glacier mass balance and july air temperatures are related to variations in the position and strength of the july circumpolar vortex in years when the july vortex is strong and its center is located in the western hemisphere positive mass balance anomalies prevail in contrast highly negative mass balance anomalies occur when the july circumpolar vortex is either weak or strong without elongation over the canadian high arctic and its center is located in the eastern hemisphere the occurrence of westerly positioned july vortices has decreased by 40 since 1987 the associat

tectonics of the southern and central appalachian internides the appalachian orogen was constructed along the ancient precambrian continental margin of eastern north america by a series of compressional events that began in the ordovician and episodically spanned much of the paleozoic era the processes of accretion of suspect and exotic terranes together with terrane collision and ultimately completion of the wilson cycle by continent continent collision resulted in construction of the appalachian orogen figure 1 these paleogeographic elements are rep resented by the various lithotectonic units visible today in the southern and central appalachians figure 2 these subdivisions represent the late precambrian rifted margin and early paleozoic platform that were formed directly upon north american grenvillian basement cumberland allegheny plateau valley and ridge and western blue ridge the offshore north american slope rise assemblage hamburg klippe southern appalachian eastern blue ridge and inner piedmont and higher thrust sheets of the maryland northern virginia piedmont and the exotic carolina or avalon and wilmington terranes the carolina ter rane contains the alleghanian high grade metamorphic core these elements form the basis for this analysis and review of the present state of knowledge of the tectonic history of the southern and central appalachian internides the appalachian orogen has been the subject of study by geologists at least since the early nineteenth century early fundamental concepts such as the geosynclinal theory of mountain building dana 1873 hall 1883

recent widening of the tropical belt evidence from tropopause observations 1 radiosonde measurements and reanalysis data are used to examine long term changes in tropopause behavior in the subtropics tropopause heights in the subtropics exhibit a bimodal distribution with maxima in occurrence frequency above 15 km characteristic of the tropical tropopause and below 13 km typical of the extratropical tropopause both the radiosonde and reanalysis data show that the frequency of occurrence of high tropopause days in the subtropics of both hemispheres has systematically increased during the past few decades so that tropical characteristics occur more frequently in recent years this behavior is consistent with a widening of the tropical belt and the data indicate an expansion of about 5 8 latitude during 1979 2005

wavelet analysis of polar vortex variability over the twentieth century recent increases in extreme weather events in the northern hemisphere have been linked to amplified planetary waves changes in planetary wave properties are linked to changes in climate hence finding a mechanism that links the planetary wave variability under climatic forcing and midlatitude blocking events has engendered a great deal of interest in this study wavelet analysis is applied to time series of planetary wave phase speeds at high latitudes as a first step to assessing the potential for identifying these mechanisms in the observational record a circumpolar multiannual cycle increase is found but signals also demonstrate a complex westward propagation pattern with periods of intense wave variability significant correlations between wavelet power at all time scales and albedo snow cover atmospheric ozone levels and surface air temperature are demonstrated

reflections from a mylonitized zone in central sweden dipping reflections imaged on a deep seismic reflection profile acquired within the baltic shield can be indirectly linked to strain induced acoustic impedance contrasts within a regional brittle ductile shear zone the singo shear zone measurements made at various scales and frequencies estimate rock velocity within the shear zone and correlate well with the ductile component of strain previously determined by structural analysis velocity measurements include some made on cored field samples at confining pressures of 0 4 gpa in a laboratory 10 mhz sensor frequencies and some made in situ using ultrasonic 54 khz sensors on exposures within the shear zone laboratory measurements show a 10 change in seismic anisotropy and a contrast of 0 5 km s 1 in bulk rock velocity between granitoid protolith and highly strained ultramylonite the in situ velocity measurements demonstrate that the velocity variations persist over considerable volumes including zones where strain and associated volume loss of silica remain elevated without mylonitization synthetic seismograms generated using a one dimensional velocity model of the shear zone show that velocity variations observed in the field were large enough in magnitude and of sufficient scale to produce reflections observable on the deep seismic reflection profile collected using 6 25 hz frequencies ray trace two dimensional forward modeling of a high density wide angle reflection section demonstrates that deep dipping reflections could result from strain induced acoustic impedance contrasts within the singo or similar nearby shear zones

accretionary complex structure and kinematics during paleozoic arc continent collision in the southern urals abstract the southern urals contain a well preserved accretionary complex that has overthrust the continental margin during arc continent collision between the east european craton eec and the magnitogorsk island arc in the late devonian within the accretionary complex we study three tectonic units that differ in deformation style and each provides a unique geodynamic implication the zilair nappe the largest and best exposed unit consists of 5 6 km of syncollisional arc derived upper devonian to lower carboniferous polymictic and graywacke turbidites that were deposited across the continental margin and incorporated by frontal accretion into the accretionary complex the zilair nappe is a bivergent thrust imbricate where the west vergent thrusts dominate and have associated kilometer scale ramp anticlines with well developed east dipping axial planar cleavage along its eastern contact however the cleavage fans until it dips moderately westward and the folds are east vergent following its emplacement west vergent basement involved thrusting that breached the whole accretionary complex imbricated the zilair nappe the timirovo duplex is structurally beneath the zilair nappe and outcrops for several tens of kilometers along its northwestern margin the duplex forms a west vergent thrust stack composed of a highly deformed and sheared lower and middle devonian reef carbonates of the former eec margin platform these rocks were shallowly underplated at the base of the accretionary complex during emplacement over the margin the suvanyak complex outcrops along the eastern contact of the zilair nappe and consists of polydeformed greenschist facies metasediments of the former eec slope that were offscraped underplated and incorporated at the rear of the accretionary complex

normal fault boundary of an appalachian basement massif results of cocorp profiling across the pine mountain belt in western georgia recent seismic reflection profiling in western georgia and adjacent eastern alabama conducted by the consortium for continental reflection profiling cocorp shows that reflections commonly associated with the appalachian detachment do not continue southeastward beneath the pine mountain belt rather these reflections terminate abruptly on the north side of the belt along the downdip projection of the towaliga fault this observation is difficult to reconcile with the basement duplex interpretation traditionally applied to the pine mountain belt and to all other appalachian interior basement massifs an alternative interpretation consistent with the reflection data and with local surface geologic relations is that the towaliga fault is at least in its later evolution a large northwest dipping normal fault that cuts the piedmont allochthon appalachian detachment and grenville basement where crossed by the cocorp profile this fault has an inferred average dip of about 54 and offsets grenville basement about 9 km this interpretation is consistent with the view that the pine mountain belt is a structural window through the piedmont allochthon however it implies that much of the structural relief on the basement exposed in the window is due to late normal faulting rather than to thrust imbrication alone if correct this has several important implications for appalachian geology 1 it implies that normal faulting of late paleozoic and or mesozoic age has played a much more important role in the development of the exposed southern appalachians than has generally been considered to date 2 grenville basement exposed in the pine mountain belt has been attached to north america since precambrian time it does not represent a paleozoic accreted terrane 3 the appalachian detachment may be exposed around the periphery of the pine mountain belt and hence may be available for direct observation at this locality

timing and temperature of cataclastic deformation along segments of the towaliga fault zone western georgia u s a abstract foliated cataclasite and breccia exposed along a segment of the towaliga fault zone tfz in western georgia u s a formed during two episodes of cataclastic deformation conventional k ar crystallization ages of muscovite collected along fractures in the foliated cataclasite at dixon mountain suggest that following mylonitization at about 296 ma pennsylvanian rocks along the tfz were elevated upward across the 300 c isothermal surface and ductile deformation via cataclastic flow was initiated fluid inclusion microthermometry and quartz microfabric in the cataclasite suggest that the temperature during this first cataclastic deformation which probably occurred at a depth greater than 8 km was between 140 and 300 c at around 237 ma late permian cataclastic deformation was dominated by brecciation and extensive vein sealing and formed the silicified breccias at dixon mountain muscovites from another cataclastic segment of the tfz give a relatively low apparent age of around 269 ma probably because of loss of argon or mixing with younger neocrystallized muscovite during cataclasis

magnetostratigraphy of the lower triassic volcanics from deep drill sg6 in western siberia evidence for long lasting permo triassic volcanic activity summary the deep drill hole sg6 in western siberia 66 n 78 5 e penetrated 1 1 km of lower triassic basalts which are possibly an extension of the central siberian permo triassic flood basalt province about 300 samples of these basalts were progressively demagnetized and measured principal component analysis often shows multiple magnetizations carried by haematite and magnetite the corrected mean inclinations are 77 and 77 for the haematite component a magnetostratigraphic scale was derived and showed a n r n r n succession this is quite diverent from the noril sk and taimyr typical polarity scale r n the basalts found in the sg6 deep drill hole are slightly younger than those of central siberia and taimyr they correspond to middle upper induan age whereas the noril sk and taimyr sections correspond to an uppermost permian and lower induan age altogether they indicate that after a high output rate of volcanic material near the permo triassic boundary this activity slowed down drastically on the siberian platform and taimyr but persisted for several million years in western siberia

post variscan evolution of the lithosphere in the rhine graben area constraints from subsidence modelling in the area of the cenozoic rhine rift system crustal and lithospheric thicknesses range between 24 and 35 km and 60 and 120 km respectively this rift system transects the deeply truncated variscan orogen and superimposed permo carboniferous wrench induced troughs and late permian and mesozoic thermal sag basins at the time of its westphlian consolidation the variscan orogen was probably characterized by 45 60 km deep crustal roots that were associated with its rheno hercynian saxo thuringian saxo thuringian bohemian and bohemian moldanubian sutures all of which are transected by the cenozoic rhine rift system during the stephanian early permian wrench induced disruption of the variscan orogen subducted lithospheric slabs were detached causing upwelling of hot mantle material during the resulting thermal surge partial delamination and or thermal thinning of the continental mantle lithosphere induced regional uplift at the same time the variscan orogenic roots were destroyed and crustal thicknesses reduced to 28 35 km in response to the combined effects of mantle derived melts interacting with the lower crust regional erosional unroofing of the crust and on a more local scale by its mechanical stretching towards the end of the early permian the potential temperature of the asthenosphere returned to ambient levels with this regional long term thermal subsidence of the lithosphere commenced controlling the development of a new system of late permian and mesozoic thermal sag basins however the evolution of these basins was repeatedly overprinted by minor short term subsidence accelerations that reflect the build up of far field stresses related to rifting in the tethyan and atlantic domains comparison of observed and modelled subsidence curves suggests that in the area of the rhine rift system the lithosphere had equilibrated with the asthenosphere at the end of the cretaceous at depths of 100 120 km before it became thermally destabilized again by cenozoic rifting and plume related magmatism modelled subsidence curves indicate that by the end of early permian times the thermal thickness of the remnant mantle lithosphere ranged between 10 and 50 km in areas that were later incorporated into mesozoic thermal sag basins this corresponds to mid permian thermal lithosphere thicknesses of 40 80 km the geological society of london 2004

reconstructing the end of the appalachian orogeny in contrast to crustal deformation observed in the actively forming himalayas where shallowly dipping crustal detachments extend over hundreds of kilometers prior work on the paleozoic southern appalachian orogeny inferred that the final continental collision occurred on a steeply dipping crustal suture permitting collision models that are dominated by strike slip motion here we use scattered seismic phases to instead reveal the appalachian alleghanian crustal suture as a low angle 15 southward dipping interface that soles into a flat lying mid crustal detachment the observed suture geometry implies more than 300 km of head on shortening across a plate boundary structure similar to the himalayan mid crustal detachment indicating that this mode of deformation has been fundamental in continental collisions over hundreds of millions of years

heterogeneity of the uppermost mantle beneath russian eurasia from the ultra long range profile quartz the 3850 km long deep seismic sounding profile quartz crosses six major geologic provinces in eurasia and is sourced by 3 nuclear and 48 chemical explosions we present the first interpretation of the entire data set using two dimensional 2 d ray tracing and inversion resolution analysis and 1 d amplitude modeling our interpretation shows a 42 km thick high velocity crust under the baltic shield a 29 km thick crust and high velocity upper mantle under the mezenskaya depression 52 km thick crust with high velocity lower crust and uppermost mantle under the urals and 40 km thick crust under the west siberian basin deepening to 45 km under the altay sayan fold belt high velocity 8 4 km s uppermost mantle is found under the mezenskaya depression and under the east flank of the urals one almost continuous upper mantle boundary occurs at 65 to 80 km depth and another with an approximately 40 km thick lvz occurs at 120 to 140 km depth the shallow upper mantle blocks and the two extensive interfaces indicate strong upper mantle heterogeneity resolution analysis based on direct multivariate model perturbations artificial neural network and principal component analysis indicate the depth uncertainty of the 410 km discontinuity within 6 km and also its trade off with dip and velocities above and below the discontinuity decreased near critical amplitudes of reflections from the 410 km and 660 km discontinuities indicate that these boundaries are most likely represented by gradient zones about 15 20 km thick lithosphere thins asthenospheric velocity decreases and the 410 km discontinuity dips to the se approaching the himalayan orogenic belt

a model of palaeozoic obduction and exhumation of high pressure low temperature rocks in the southern urals abstract a new evolutionary geodynamic model of devonian continental subduction and exhumation of high pressure low temperature metamorphic rocks in the southern urals is proposed based on the results of physical modelling geological and geophysical data and on the comparison of this belt with other orogens the model includes the following principal phases 1 closure of the western uralian ocean by eastward intraoceanic subduction associated with the magnitogorsk volcanic arc 2 subduction of the european continental margin causing failure of the overriding plate in the arc area along a fault dipping eastward under the arc 3 subduction into the mantle of the fore arc block together with the underlying continental crust and sedimentary layer the sedimentary cover as well as the crustal and mantle fragments of this block are scraped off and accreted in front of and under the arc the continental crust shielded from the hot mantle by the fore arc block subducts to depths of more than 150 km remaining at a relatively low temperature the crust then fails at depths of several tens of kilometres 4 the subducted crustal slice starts to rapidly rise and intrude the interplate zone scraping and pushing up the sediments and slivers of the oceanic fore arc block previously dragged down to different depths 5 exhumation of the rising high pressure low temperature rocks within the uraltau dome separating the subduction accretionary complex from the magnitogorsk arc the eastern border of the uraltau dome coincides with the main uralian fault this fault represents a complex suture zone which at the stage of deep crustal subduction was associated with a major thrust subduction fault and at the exhumation stage with a major normal fault corresponding to the upper surface of the rising crustal sedimentary body

master decollement root zone beneath the southern appalachians and crystal balance a root zone of the southern appalachian master decollement is postulated to exist beneath kings mountain belt on the basis of an alternative interpretation of cocorp seismic profiles palin spastic restoration of the entire crust and earlier geological and geophysical interpretations mildly deformed cambrian metased imentary rocks beneath the decollement end beneath the piedmont in the vicinity of danielsville georgia reflections farther southeast are probably from ultramylonites weak subhorizontal reflections continue southeasterly to the kings mountain belt where a series of east dipping 30 reflections dominate the section to a depth of 20 km beneath the charlotte belt reflections southeast of the root zone are possibly all related to the structure in an accreted island arc

pine mountain terrane a complex window in the georgia and alabama piedmont evidence from the eastern termination the pine mountain terrane is exposed in a complex window within the piedmont of georgia and alabama the eastern end of the terrane is framed by three ductile faults of demonstrably different ages the polydeformed pre thermal peak box ankle fault is truncated to the south by the younger pre thermal peak goat rock fault and to the north by the even younger post thermal peak towaliga fault the three faults framing the eastern termination of the window are clearly neither 1 part of the same detachment nor 2 part of the appalachian detachment

contrasting tectonic history of the arc continent suture in the southern and middle urals implications for the evolution of the orogen the main uralian fault has been considered the original arc continent suture for 2000 km along the uralide orogen the symmetry of the tectonic units across it suggested a consistent east dipping polarity for the palaeosubduction zone which together with its topographic and aeromagnetic signature supported the idea of a single suture however several characteristics vary at different latitudes in the middle urals it is a strike slip fault zone with moderately deformed and metamorphosed volcanic arc fragments in its hanging wall and low grade metamorphic rocks of the east european craton in its footwall here it has a prominent nnw trending magnetic signature which cross cuts north trending anomalies in its hanging wall and a pronounced reflection seismic signature that can be traced to the top of the middle crust at c 5 s twt in the southern urals it is a serpentinite melange zone of ambiguous kinematics with a weakly deformed and metamorphosed volcanic arc in its hanging wall and moderately metamorphosed to high pressure rocks of the east european craton in its footwall in this part of the orogen it has a weak reflection seismic character and a magnetic signature that parallels that of its hanging wall on the basis of an integrated analysis of these different data sets we suggest that the main uralian fault as it is currently defined is not a single entity but rather the original arc continent suture in the south and the western strand of a strike slip fault system that reworked the original suture in the middle urals

integrating seismic reflection and geological data and interpretations across an internal basement massif the southern appalachian pine mountain window usa the southern appalachian pine mountain window exposes 1 1 ga grenvillian basement and its metasedimentary paleozoic cover through the allochthonous inner piedmont the issue of whether the crustal block inside the window was either transported above the master appalachian late alleghanian decollement or is an autochthonous block that was overridden by the decollement has been debated for some time new detrital zircon geochronologic data from the cover rocks inside the window suggest this crustal block was derived from gondwana but docked with laurentia before the alleghanian event reprocessed deep seismic reflection data from west central georgia pr and poststack noise reduction amplitude variation analysis and prestack depth migration indicate that a significant band of subhorizontal reflections occurs almost continuously beneath the window collinear with the originally recognized decollement reflections north of the window a marked variation in the decollement image from strong and coherent north of the window to more diffuse directly beneath the window is likely a partial consequence of the different geology between the inner piedmont and the window the more diffuse image beneath the window may also result from imaging problems related to changes in topography and fold of cover i e signal to noise ratio two alternative tectonic models for the pine mountain window can partially account for the observed variation in the decollement reflectivity 1 the pine mountain block could be truncated below by a relatively smooth continuation of the decollement the window would thus expose an allochthonous basement duplex or hors block thrust upward from the south along the late proterozoic rifted continental margin 2 the window represents localized exhumation of autochthonous basement and cover along a zone of distributed intrabasement shearing directly beneath the window either model is viable if only reflector geometry is considered model 1 is favored if both geometry and kinematics of blue ridge piedmont thrust sheet emplacement are incorporated in either model the southern margin of the window merges to the west with the iapetan early alleghanian central piedmont suture which juxtaposes north american affinity piedmont rocks to the north and exotic panafrican rocks of the carolina avalon terrane to the south immediately south of the window this suture dips southward and merges in the lower crust with the late alleghanian suture joining the appalachians with gondwana

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

new cocorp profiling in the southeastern united states part i late paleozoic suture and mesozoic rift basin new cocorp profiling in the southeastern united states has revealed a broad zone of dipping reflections that extends downward through the crust beneath the coastal plain in western georgia the zone is over 50 km wide and most of the reflections dip moderately steeply toward the south regional considerations suggest that this feature marks the late paleozoic suture between north america and africa where crossed by the cocorp survey the suture occurs beneath the north flank of the triassic early jurassic south georgia basin the main depocenter of the south georgia basin occurs about 90 km to the south and is formed by a large half graben containing more than 5 km of rift basin fill farther south the paleozoic suwannee basin sequence beneath northern florida is poorly imaged on the cocorp profiles however weak reflections suggest that these strata including basal felsic volcanics may have an aggregate thickness of about 6 km in north central florida at the northwest end of the cocorp traverse a prominent horizon imaged in the upper crust beneath the inner piedmont probably marks the southern appalachian detachment the detachment appears to be cut off by the towaliga fault implying that the towaliga fault is in part a down to the north normal fault intermittent moho reflections occur at 11 12 s two way time along the length of the cocorp survey indicating that the crust in the region has a roughly uniform thickness of about 33 36 km assuming an average crustal velocity of 6 km s

northern hemisphere circumpolar vortex trends and climate change implications 1 trends in the northern hemisphere circumpolar vortex at 700 500 and 300 hpa are examined to assess the relationship between circulation variability and air temperature a vortex climatology is developed for the period 1949 2000 at each pressure level three geopotential height contours are used to quantify the size and position of the vortex at 5 longitude resolution within and both north and south of the primary hemispheric baroclinic zone this combination of spatial specificity and the long temporal record makes this the most comprehensive vortex climatology to date the overall and seasonal vortex time series for the northern hemisphere are created for northern middle and southern contours at each of the three levels in the atmosphere from the beginning of the record until 1970 the vortex exhibits a statistically significant expansion but the vortex has been contracting significantly since then at all levels the pre 1970 expansion and subsequent contraction is strongest in the lower latitudes and weakest in the higher latitudes the trends are also stronger in the upper troposphere than in the lower troposphere spatial examination of the vortex indicates that the pre 1970 expansion and post 1970 contraction were driven primarily by expansion contraction over asia europe and north america with little change over the northern hemisphere oceans although significant climate change debate focuses on the discrepancy between positive trends in surface air temperature and little or no trends in microwave sounding unit msu satellite temperatures contraction of the circumpolar vortex at every level of the atmosphere implies that the atmosphere is warming at depth since 1970 comparisons with the msu temperature history indicate that the northern hemisphere circulation as a whole as represented by the circumpolar vortex accounts for almost two thirds of the interannual variability in midlatitude msu temperature indicating that vortex size and position are coupled strongly to atmospheric temperature and could be a good indicator of climate change on a latitude by latitude and level by level basis the lower latitudes are associated most strongly with msu temperature in the midtroposphere while the middle and higher latitudes are more closely associated with msu temperature in the upper troposphere the vortex trends are also similar to observed surface warming trends

displacements of the north circumpolar vortex during el nino 1963 83 abstract during the pronounced 1982 83 el nino the 300 mb north circumpolar vortex was displaced further toward japan from its mean seasonal locations than observed since the beginning of the vortex record in 1963 however during the strong 1972 73 el nino the vortex was displaced toward the 180th meridian and during the weaker 1965 66 el nino toward the eastern pacific so that vortex displacements are not indicated to have been the same for different el nino episodes based on the full 21 year record the vortex has tended to be displaced toward 90 w when sea surface temperature sst in the region 0 10 s 180 80 w was above average but toward the 180th meridian when the magnitude of sst deviation from average is considered

alleghanian development of the goat rock fault zone southernmost appalachians temporal compatibility with the master decollement the goat rock and associated bartletts ferry fault zones which mark the eastern margin of the pine mountain grenville basement massif are controversial due to the suggestion that they are rare exposed segments of the late paleozoic southern appalachian master decollement the controversy in part stems from reported middle paleozoic acadian radiometric dates postulated as the time of movement along these fault zones ultramylonite samples from the type area at goat rock dam yield a 287 plus minus 15 ma rb sr isochron interpreted as the time of sr isotopic rehomgenization during mylonitization this date is corroborated by late pennsylvanian early permian sup 40 ar sup 39 ar mineral ages on hornblende 297 288 ma and muscovite 285 278 ma from neomineralized and dynamically recrystallized rocks within and straddling the fault zone these late pennsylvanian early permian dates indicate the time of right slip movement alleghenian along the goat rock fault zone which is compatible with the timing suggested by cocorp for thrusting along the southern appalachian master decollement

crustal structures and the eastern extent of lower paleozoic shelf strata within the central appalachians a seismic reflection interpretation reprocessing of line pr3 proprietary seismic reflection data has delineated grenvillian paleozoic and mesozoic structures within the appalachian foreland blue ridge and piedmont of the central appalachians in virginia and west virginia the eastern portion of pr3 can be correlated along strike with the western portion of line i 64 reprocessed earlier at virginia tech the combined seismic reflection data image the crust from the eastern valley and ridge blue ridge piedmont and atlantic coastal plain provinces within the piedmont large as much as 10 km wide reflective structures imaged on both lines pr3 and i 64 are interpreted to be thrust sheets that might be composed of deformed catoctin evington group and possibly younger metamorphosed rocks a concealed extension of the green springs mafic mass intrudes a thrust sheet imaged along the pr3 profile the blue ridge piedmont allochthon was transported north west along the blue ridge thrust which ramps upward 12 km east of the surface exposure of the mountain run fault westward along line pr3 the blue ridge thrust maintains an undulating geometry the maximum thickness of the blue ridge allochthon is interpreted to be 4 5 km the blue ridge allochthon is generally acoustically transparent and overlies lower paleozoic shelf strata the maximum thickness of these strata is 8 km shelf strata are interpreted to extend in the subsurface 5 km east of the surface exposure of the mountain run fault the northeastward extension of the brevard fault zone where they are truncated by the blue ridge thrust at a depth of 10 5 km 3 5 s various folds and blind thrusts are imaged beneath the appalachian foreland however the foreland has not experienced the same degree of deformation as observed in the eastern provinces a basement uplift 45 km wide is imaged beneath the valley and ridge province and is interpreted as having formed prior to late cambrian time farther west reflections imaged beneath the glady fork anticline in the appalachian plateau are interpreted as a positive flower structure associated with wrench fault tectonics relatively few deep 9 km crustal reflections are imaged along line pr3 the majority of reflections that do exist at these depths are observed beneath the piedmont and eastern blue ridge the high reflectivity associated with the grenvillian basement in these areas might be the result of the paleozoic orogenies and extension related to late proterozoic and mesozoic rifting

imaging crustal structure beneath the southern appalachians with wavefield migration to constrain crustal structures in the southern appalachians and the suture zone with the gondwanan affinity suwannee terrane we applied the 2d grt wavefield migration method to the scattered incident p wavefield recorded by the earthscope southeastern suture of the appalachian margin experiment and adjacent transportable array stations we resolve the root of thickened crust beneath the high topography of the blue ridge mountains and estimate its density contrast with the mantle to be only 104 20 kg m3 a weak velocity contrast across the crustal root moho is observed and may be related to an ongoing crustal delamination event possibly contributing to local tectonic rejuvenation beneath the suwannee terrane we confirm prior observations of a gently south southeastward dipping crustal suture indicating the terminal collision of laurentia and gondwana involved several hundred kilometers of overthrusting

estimating crustal thickness using sspmp in regions covered by low velocity sediments imaging the moho beneath the southeastern suture of the appalachian margin experiment sesame array se atlantic coastal plain