time frequency seismic data de noising marine seismic data are always affected by noise an effective method to handle a broad range of noise problems is a time frequency de noising algorithm in this paper we explain details regarding the implementation of such a method special emphasis is given to the choice of threshold values where several different strategies are investigated in addition we present a number of processing results where time frequency de noising has been successfully applied to attenuate noise resulting from swell cavitation strumming and seismic interference our seismic interference noise removal approach applies time frequency de noising on slowness gathers p domain this processing trick represents a novel approach which efficiently handles certain types of seismic interference noise that otherwise are difficult to attenuate we show that time frequency de noising is an effective amplitude preserving and robust tool that gives superior results compared to many other conventional de noising algorithms for example frequency filtering p or fx prediction as a background some of the physical mechanisms responsible for the different types of noise are also explained such physical understanding is important because it can provide guidelines for future survey planning and for the actual processing

early miocene change in direction of least principal stress southwestern united states conflicting inferences from dikes and metamorphic core detachment fault terranes previous investigations have suggested that the direction of least principal stress in the western united states has shifted from northerly to easterly between 50 to 30 ma an effort is made to more tightly constrain the time of this shift using igneous dike host rock systems in which the isotopic age of both host and dike is known and differs by less than 10 ma in such systems the possibility that magma intruded along old fractures unrelated to the state of stress at the time of intrusion is minimized and the axis of least principal stress is considered to be normal to the strike of the subvertical dike during the time interval between the ages of the dike and host rock these systems indicate that a northerly least principal stress orientation persisted more recently than previously believed until probably after 30 ma possibly about 26 ma and conceivably as recently as 18 ma in some areas the data are insufficient and too loosely bracketed in time to decide how fast the change in state of stress occurred in any one place and if by systematic rotation or abrupt shift however the change could be diachronous earlier in the southeast and later in the northwest major easterly trending magmatic and tectonic elements of tertiary age in the great basin of utah and nevada are compatible with the dike data however numerous metamorphic core complexes and detachment fault terranes seem to indicate more or less easterly extension throughout the time period represented by the dikes this inconsistency is not clearly resolvable but may reflect differences between the regional plate stress field and gravitational stresses in a crust overthickened by mesozoic compression

geodynamic setting of volcano plutonic rocks in so called paleo accretionary prisms fore arc activity or post collisional magmatism the shimanto belt as a case study abstract the cretaceous tertiary shimanto belt of southwestern japan is usually considered to be a simple accretionary prism taira et al 1982 ogawa 1985 whereas based on structural and sedimentological evidences charvet and fabbri 1987 and charvet et al 1990 proposed an alternative model in which a collision with an unknown microblock followed the formation of the accretionary prism and induced the early miocene main tectonism one characteristic of the shimanto belt is the occurrence of well developed magmatic bodies of middle miocene age 14 1 ma which can be used for testing the model they show numerous peculiarities 1 they consist predominantly of acidic volcano plutonic complexes mafic sills or lavas are present in a lesser amount 2 with respect to the supposed position of the subduction trench during miocene time and to the northern location of the setouchi volcanics considered as a volcanic front ca 13 ma this magmatism is a near trench magmatism 3 various tectono magmatic affinities are present the basaltic sills or lavas have mostly t to e morb type affinities an alkaline complex is present at ashizuri cape the most abundant magmatism consists of calc alkaline volcano plutonic bodies typically peraluminous in the southern part of shimanto and metaluminous near the northern border of the belt 4 metamorphic enclaves inter alia are often included in the calc alkaline complexes their highest p t conditions range between 0 7 0 8 gpa and 630 860 c a simple subduction model is not able to explain all these features the first necessity is to find a mechanism which develops a high thermal anomaly allowing the formation of magmas close to the trench according to thermal modelling the subduction of an oceanic plate even young does not provide enough heat secondly in well known mature accretionary prisms e g the barbados one the thickest part of the complex does not exceed 15 km in such conditions it is difficult to obtain pressures ranging from 0 7 to 0 8 gpa this is much more difficult if we consider that some granitic rocks were formed in the youngest part of the so called prism in the thinnest portion finally a simple subduction model does not explain the various magmatic affinities geochemical data show that the magmatic source of the ashizuri alkaline complex is likely to be an enriched mantle comparable to oib sources on the other hand the calc alkaline rocks may have been derived by mixing between mantellic components and crustal ones or in some cases by pure anatectic processes the upwelling of a hot asthenospheric mantle from which the ashizuri suite could have been derived may represent a heating source strong enough to make crustal materials melt the proposed collision model could explain 1 the heating source 2 the various magmatic affinities and also 3 the 0 7 0 8 gpa pressure invoking crustal thickening induced by the collisional event

comment on mid cretaceous extensional fragmentation of a jurassic early cretaceous compressional orogen alaska by e l miller and t l hudson

seismic directional random noise suppression by radial trace time frequency peak filtering using the hurst exponent statistic radial trace time frequency peak filtering filters a seismic record along the radialtrace direction rather than the conventional channel direction it takes the spatial correlation of the reflected events between adjacent channels into account thus radial trace time frequency peak filtering performs well in denoising and enhancing the continuity of reflected events however in the seismic record there is often random noise whose energy is concentrated in certain directions the noise in these directions is correlative we refer to this kind of random noise that is distributed randomly in time but correlative in the space as directional random noise under radial trace time frequency peak filtering the directional random noise will be treated as signal and enhanced when this noise has same direction as the signal therefore we need to identify the directional random noise before the filtering in this paper we test the linearity of signal and directional random noise in time using the hurst exponent the time series of signals with high linearity lead to large hurst exponent value however directional random noise is a random series in time without a fixed waveform and thus its linearity is low therefore we can differentiate the signal and directional random noise by the hurst exponent values the directional random noise can then be suppressed by using a long filtering window length during the radial trace time frequency peak filtering synthetic and real data examples show that the proposed method can remove most directional random noise and can effectively recover the reflected events

thermal overprint on blueschists of the seward peninsula the lepontine in alaska on the seward peninsula alaska blueschists and greenschists of the nome group and amphibolites and granulites of the kigluaik group all formed during a single episode of continent arc collision high pressure low temperature mineral assemblages that initially developed in a structurally coherent package of miogeoclinal rocks were then variably overprinted during later uplift by lower p higher t barrovian facies series assemblages derived pressure temperature time p t t paths illustrate the early passage of both the nome and kigluaik groups through high pressure 12 kbar conditions subsequent nearly isothermal decompression of nome group blue schists and divergence during decompression of nested p t paths to amphibolite and granulite conditions in the underlying kigluaik group similar field occurrences are described from the lepontine alps and the greek island of naxos standard geobarometric techniques applied to medium grade kigluaik group rocks do not record the earliest burial phase and therefore underestimate peak pressures by 8 kbar

tin granites of seward peninsula alaska seven granite plutons spatially and genetically related to tin metalization are exposed in a 170 km long belt across northwestern seward peninsula alaska these plutons are cupolas and epizonal composite stocks that consist of several textural varieties of biotite granite including medium to coarse grained seriate biotite granite porphyritic biotite granite with an aplitic groundmass and fine to medium grained equigranular biotite granite the common accessory minerals are fluorite allanite apatite and zircon other accessory minerals that are locally present include tourmaline sphene opaque oxide minerals and late forming deuteric muscovite and chlorite the granites range in major element contents as follows sio 2 72 5 to 76 6 a1 2 o 3 12 7 to 14 3 na 2 o 2 9 to 4 0 k 2 o 3 9 to 5 6 and cao 0 6 to 1 2 the sum of feo fe 2 o 3 mgo ranges from 0 3 to 2 4 and the k 2 o to na 2 o ratio from 1 1 to 1 8 the 0 1 to 0 9 f and 0 01 to 0 2 cl reflect the over all volatile rich nature of the granites the granites contain average or below average concentrations of co sc cr and zn and generally above average to distinctly high concentrations of th u hf and ta the large cations emphasize the evolved nature of the granites the rb sr ratio is as high as 90 in some samples initial 87 sr 86 sr ratios range from 0 708 to as high as 0 720 the three rb sr isochrons defined by the data agree with k ar age determinations and show that the stocks were emplaced during the late cretaceous between about 70 and 80 m y ago the field petrologic and geochemical data indicate that the plutons had a multistage origin that involved large scale melting of sialic crust emplacement of magmas derived from batholithic fractionation at depth and subsequent evolution of these magmas to generate small volumes of more highly evolved residual magmas although evolution of the granite complexes was largely governed by crystal melt fractionation some minor element variations in the highly evolved granites cannot be explained by this process for example the distribution of rubidium and the light rare earths appears to have been influenced by volatile depletion at the final stages of crystallization the field data petrologic data and variation trends such as distinct shifts toward higher albite contents in the residual granites suggest that the coexistence of a volatile phase was important in their evolution these results require that models seeking to explain compositional gradients in high level granite rhyolite systems fully consider the role of a coexisting volatile phase

40 ar 39 ar thermochronology of white mica from the nome district alaska the first ages of lode sources to placer gold deposits in the seward peninsula

high frequency analysis of seismic background noise as a function of wind speed and shallow depth we used a deep 1500 m cased borehole near the town of datil in west central new mexico to study high frequency 1 hz seismic noise characteristics the remote site had very low levels of cultural noise but strong winds winter and spring made the site an excellent candidate to study the effects of wind noise on seismograms along with a three component set of surface sensors teledyne geotech gs 13 a vertical borehole seismometer gs 28 was deployed at a variety of depths 5 43 and 85 m to investigate signal and noise variations wind speed was measured with an anemometer event triggered and time triggered data streams were recorded on a reftek 72 02 data acquisition system located at the site our data show little cultural noise and a strong correlation between wind speed and seismic background noise the minimum wind speed at which the seismic background noise appears to be influenced varies with depth 3 m sec at the surface 3 5 m sec at 43 m in depth and 4 m sec at 85 m in depth for wind speed below 3 to 4 m sec we observe omni directional background noise that is coherent at frequencies below 15 hz this coherence is destroyed when wind speeds exceed 3 to 4 m sec we use a test event md 1 6 and superimposed noise to investigate signal to noise ratio snr improvement with sensor depth for the low q valley fill of the datil borehole dbh site we have found that snr can be improved by as much as 20 to 40 db between 23 and 55 hz and 10 to 20 db between 10 and 20 hz by deploying at a 43 m depth rather than at the surface at the surface there is little signal above noise in the 23 to 55 hz frequency band for wind speeds greater than 8 m sec thus high frequency signal information that is lost at the surface can be recorded by deploying at the relatively shallow depth of 40 m because we observe only minor further reductions in seismic background noise sbn at deeper depths 40 m is likely to be a reasonable deployment depth for other high frequency monitoring sites in similar environmental and geologic conditions

fallout of pyroclastic debris from submarine volcanic eruptions volcanic fallout deposits on land being widespread and accessible for study have received much attention and have revealed a great deal about subaerial eruption mechanisms in contrast virtually nothing is known about equivalent deposits produced by submarine volcanoes despite the probable abundance of such material in today s oceans and in accreted volcanic arc terrains many submarine deposits may form by the fallout of debris to the sea floor downcurrent from the umbrella region of submarine eruption columns experiments on water saturated pumice and pieces of rock lithics show that particles settling to the sea floor at terminal velocities of 10 to 50 centimeters per second will display conspicuous bimodality of particle diameters pieces of pumice may be five to ten times as large as codeposited lithic fragments similar material erupted into the air and deposited on land displays less well developed bimodality pumice diameters are generally two to three times as large as associated lithics submarine fallout deposits are therefore distinctive and may be used to indicate a subaqueous origin for some of the great thicknesses of nonfossiliferous volcanic debris contained in ancient volcanic terrains worldwide whose environment of deposition has been uncertain

early basin and range development in trans pecos texas and adjacent chihuahua magmatism and orientation timing and style of extension magmatism during early basin and range extension in trans pecos texas consisted of widespread but volumetrically minor alkali basalts 24 17 ma an alkalic mafic to intermediate composition stratovolcano 28 27 ma and a dominantly rhyolitic possibly bimodal caldera complex in adjacent chihuahua 31 28 ma this magmatism contrasted sharply with the much more voluminous and compositionally more diverse eocene oligocene magmatism the age and orientation of dikes emplaced during this magmatic episode have been used to determine the orientation of least principal stress 3 an ene orientation of 3 similar to early extension throughout the basin and range province can be well documented by 28 ma and possibly as early as 31 ma faulting consisting almost exclusively of movement along high angle normal faults was underway by 23 ma some initial extension was taken up along preexisting wnw trending structures oblique to ene oriented 3 the least principal stress probably changed to wnw as it did elsewhere in the basin and range province but the timing of this change is not well constrained in texas ene and ne striking silver copper lead veins in precambrian and cretaceous red beds may have formed during the later basin and range extension the present basin and range topography of this region is the result of movement along high angle and dominantly nnw trending faults established early under 3 oriented ene and reactivated after 3 changed to wnw

thermochronologic constraints on late cretaceous to cenozoic exhumation of the bendeleben mountains seward peninsula alaska in the bendeleben mountains seward peninsula mid cretaceous granites are exposed in an uplifted block bounded on its south side by an e w striking normal fault the bendeleben fault has well preserved scarps 4 7 m in height that offset holocene moraines seismic activity young normal faulting and quaternary basaltic volcanism are all evidence of active extension south of the bendeleben fault there is a 3 4 km deep basin fifteen apatite u th he ages from granitic samples of the footwall yield an eocene weighted mean age of 41 3 4 8 ma biotite 40ar 39ar ages from the country rock of the bendeleben pluton are 81 83 ma in spite of the young fault scarps hefty and pecube thermal modeling results illustrate that rapid exhumation of the bendeleben mountains occurred in the late cretaceous eocene and slowed since the oligocene a weak age elevation relationship of apatite he ages and a lack of correlation between age and distance from the fault indicate that exhumation was accomplished with minimal block rotation on a steeply dipping long lived normal fault timing of extension in the seward peninsula can be correlated with deformation in the offshore hope basin where seismic reflection lines document early tertiary large magnitude normal faulting followed by minor post miocene reactivation the faulting observed in the bendeleben mountains is part of an extensional system that spans a large portion of the bering strait region the tectonic model proposed in previous studies suggests that clockwise rotation of the bering block relative to north america is the cause of extensional deformation in western alaska

surface water productivity and sediment transport by bering strait throughflow in the chukchi shelf the western arctic ocean during the holocene diverse paleoceanographic proxies from three sediment cores gc12ex jpc35 and jpc30 collected from the chukchi shelf north of the bering strait elucidate the holocene paleoceanographic changes surface water productivity and sediment transport caused by the bering strait throughflow from the bering sea into the chukchi sea lithology of three sediment cores identified the same three units based on comparison and correlation to adjacent age dated cores as well as ams 14c dates of core gc12ex the boundary between unit 1 and unit 2a is dated about 8500 cal yr bp and the boundary between unit 2a and unit 2b is also dated about 4500 cal yr bp consistent down core profiles of the geochemical and isotopic properties among the three cores differentiate the paleoceanographic conditions corresponding to lithologic units based on the biogenic opal total organic carbon and 13c values unit 1 is characterized by low surface water marine productivity under relatively shallow water with weak transport of b

an assessment of 40ar39ar dating for the whole rock volcanic samples from the luzon arc near taiwan from electron microprobe petrographic and image analyses of samples from the northern tip of the luzon arc the effects of various alteration reactions phenocryst and groundmass assemblages on the whole rock 40ar39ar step heating spectra have been delineated the alteration of primary hornblende to an assemblage of zoisite chlorite sphene the palagonitization of glass and the crystallization of phillipsite tends to cause discordant 40ar39ar dates in the low temperature steps of the age spectra discordant 40ar39ar dates in the high temperature steps appear to result from degassing of inherited or trapped 40ar from coarse grained phenocrysts samples in which most of the k resides in groundmass plagioclase tend to yield meaningful plateau dates whereas samples in which most of the k resides primarily in palagonitized glass tend to yield meaningless plateau and isochron dates substantial loss of 39ar 13 40 occurred from irradiated samples prior to 40ar39ar step heating analysis which appears to be correlated with the abundance of groundmass and the degree of alteration this argon loss is attributed to thermally induced argon diffusion from the fine grained groundmass plagioclase glass and alteration phases during the pre step heating bakeout

submarine silicic volcanism and associated sedimentary and tectonic processes ramsey island sw wales lower ordovician marine strata formed in an ensialic marginal basin environment record early episodes of distant explosive silicic volcanism and a later volcanotectonic episode which was a precursor to the development of a wide variety of near to source submarine silicic volcanic phenomena the early episodes are represented by well bedded turbiditic tuffs these and older strata at least 770 m thick in normal stratigraphical succession are allochthonous and large scale wet sediment sliding with reworking of strata in cohesive debris flows reflects major disturbance of the sea floor during the emplacement of silicic magmas volcanotectonic uplift along a n s fault exceeded 1 km and led to the emergence and erosion of a rhyolitic volcanic island this was followed closely by submergence and in water depths perhaps of about 500 m there accumulated welded and non welded rhyolitic ash flow tuffs rhyolitic turbiditic tuffs rhyolite lavas and a wide variety of debris flow deposits shallow intrusions of 9low9 viscosity rhyolite were emplaced contemporaneously the more or less simultaneous emplacement of rhyolitic tuff with both 9low9 viscosity and high viscosity rhyolites is attributed to variable water content related perhaps to volatile fluxing in a magma body the location of the near to source extrusive rocks and consanguineous intrusions along the contemporary n s fault is considered to reflect channelling of magma initially along a deep crustal fracture

stratigraphy and sedimentology of the mid cretaceous deposits of the yukon koyukuk basin west central alaska the northeast trending yukon koyukuk basin of west central alaska consists of two subbasins the kobuk koyukuk subbasin to the north and east and the lower yukon subbasin to the southwest the subbasins are separated by an arcuate lower cretaceous volcanic pile the hogatza trend which is thought to be an accreted volcanic arc the oldest part of the sedimentary fill of the subbasins consists of valanginian to lower albian volcaniclastic rocks deposited on the flanks of the hogatza trend following subsidence of the hogatza trend mid cretaceous clastic sedimentary strata of mainly albian and cenomanian age and possibly as thick as 8000 m were shed into the basin these deposits were derived from surrounding uplands or borderlands in the seward peninsula to the west the brooks range to the north and the ruby geanticline to the southeast these mid cretaceous basin fill deposits can be divided into four main facies 1 basin margin conglomerate facies chiefly alluvial fan deposits that were transported basinward and rest in part unconformably on the surrounding uplands 2 shelf facies chiefly cross stratified and hummocky cross stratified sandstone deposited by wave generated currents on a shelf that rimmed the basin on its western and northern margins 3 deltaic facies chiefly sandstone and shale deposited in delta plain and delta front environments on a large constructional delta that prograded westward from the eastern basin margin across both subbasins and across the subsided southern part of the hogatza trend and 4 turbidite facies chiefly interbedded sandstone and shale deposited as elongate deep sea fans and related deep sea clastic systems by flows that transported sediment to the axial parts of both subbasins northeastward in the lower yukon subbasin and eastward to southward in the kobuk koyukuk subbasin sedimentation appears to have ended in the santonian followed by uplift folding and faulting of the basin fill less deformed lower tertiary nonmarine volcanic and volcaniclastic rocks unconformably overlie the more highly deformed cretaceous strata

dike swarms on seward peninsula alaska and their implications for the kinematics of cretaceous extension in the bering strait region late cretaceous dike swarms on seward peninsula northwestern alaska represent the youngest local manifestation of a 115 75 ma magmatic event in the bering strait region magmatism accompanied and followed high grade metamorphism and ductile deformation a late cretaceous extensional tectonic setting for the region is suggested by the thickness and seismic reflection characteristics of the crust regional basin development formation of high strain tectonites with subhorizontal foliations bimodal magmatism and dike swarms the orientation of the dike swarms is used to address the kinematics of extension a diabase dike swarm in the kigluaik mountains consists of dikes that strike northeast 040 and dip steeply phenocrysts include plagioclase clinopyroxene orthopyroxene and hornblende geochemical data indicate that sio2 ranges from 48 to 56 and k2o from 1 2 to 4 0 the dikes are geochemically similar to the mafic to intermediate root of the 90 ma kigluaik pluton sr and nd isotope data show that initial 87 sr 86 sr ranges from 0 7070 to 0 7077 and initial end ranges from 0 85 to 2 90 field relations and 40 ar 39 ar geochronology bracket the dike ages between 90 and 84 ma diabase dikes in the york mountains are associated with normal faults that strike east west to east northeast dikes in the bendeleben mountains are both mafic and felsic but their orientations are unknown alkalic dikes in the darby mountains strike 030 050 similar to those in the kigluaik mountains regional relationships including the orientation of dikes normal faults mineral stretching lineations and other shear sense indicators suggest that between 110 and 90 ma extension on seward peninsula was generally oriented north south to north northwest south southeast

hydrothermal activity in the lau back arc basin sulfides and water chemistry the submersible nautile completed 22 dives during the nautilau cruise r v nadir april 17 may 10 1989 for a detailed investigation of the southern lau basin near tonga the objective of the scientific team from france germany and tonga was to understand the process of sea floor ore formation associated with hydrothermal circulation along the valu fa back arc ridge behind the tonga kermadec trench the four diving areas between lat 21 25 s and 22 40 s in water 2000 m deep were selected on the basis of results from cruises of the r v jeancharcot and r v sonne the nadir cruise provided proof of hydrothermal activity in all four areas over more than 100 km as indicated by the widespread occurrence of hydrothermal deposits and by heat flow conductivity and temperature measurements near the sea bottom the most spectacular findings were high temperature white and black smokers and associated fauna and ore deposits hydrothermal water chemistry and sulfide composition data presented here indicate that this hydrothermal field is very different from the hydrothermal fields in oceanic ridges this difference is seen in the water chemistry of the hydrothermal fluid ph 2 and high metal content and the chemical composition of sulfides enrichment in ba as and pb

provenance of terrigenous detritus of the surface sediments in the bering and chukchi seas as derived from sr and nd isotopes implications for recent climate change in the arctic regions abstract strontium and nd isotope analysis of the detrital fractions extracted from the marginal sea sediments in the arctic was applied to examine regional and temporal changes in the inflow and transportation of terrigenous material in the chukchi and bering seas over the past 100 years regional distributions of the sr and nd isotopes of the surface sediments show higher sr isotope ratios and lower nd isotope ratios in the chukchi sea 87 sr 86 sr 0 7106 0 7150 e nd 10 1 to 8 3 and lower sr isotope ratios and higher nd isotope ratios in the eastern bering sea 0 7045 0 7109 8 6 to 3 0 in addition the rb and sr contents and ree patterns e g eu eu changed noticeably across the bering strait these variations mean that the sediments in the bering and chukchi seas have clearly distinct sources the terrigenous detritus in the chukchi sea is mainly derived from northeastern siberia 87 sr 86 sr 0 711 e nd 9 and bering strait inflow essentially from the yukon river and additionally from the mackenzie river basin including the canadian shield 0 732 0 734 14 the detritus in the eastern bering sea mainly consists of two components the continental material from the yukon river basin mainly underlain by mesozoic and paleozoic rocks in the alaskan mainland 0 708 0 709 9 to 8 and the aleutian arc volcanics 0 703 6 to 10 transported northward by the alaska coastal and bering shelf waters the eastern bering sediments over the past 100 years show slight variations of the sr isotope ratio and relatively wide variations of the nd isotope ratio and the variations and trends of the time series of the northeastern bering sea in the sr nd isotope diagram are probably controlled by changes in the grain size of the detritus from the yukon river basin some of the e nd time series show periodic fluctuations correlating with the annual mean surface air temperature sat for the arctic the e nd value is low in the high sat period and high in the low sat period in the warm period the yukon river was likely to supply a higher amount of the fine grain material with a relatively low e nd value such as surficial overburden probably because partial melting of continental glaciers and permafrosts in the alaskan mainland increased more detailed analysis with high time resolution is needed to clearly understand the effects the sat have on the arctic continental and marine environments

seismicity of the bering strait region evidence for a bering block newly compiled russian and u s seismological data support an independent bering block in motion relative to the north american plate this motion is likely to be driven by the westward extrusion of southwestern alaska resulting from compression in southern alaska due to subduction of the pacific plate and terrane accretion seismicity extends from central alaska through the bering strait and into chukotka in eastern chukotka several southwest trends are evident some of which continue through the koryak highlands to kamchatka the seismicity outlines the bering block which includes most of the bering sea chukchi peninsula seward peninsula and parts of western alaska focal mechanisms young basaltic volcanism and normal faults in western alaska and chukotka indicate that the bering strait is under northeast southwest extension this in conjunction with thrust faulting in the koryak highlands indicates that the bering block is rotating clockwise relative to the north american plate

strain collapsed metamorphic isograds in a sillimanite gneiss dome seward peninsula alaska unusually closely spaced barrovian series isograds have been described along the flanks of the kigluaik mountains seward peninsula alaska where they separate a high grade gneiss complex intruded by granites of cretaceous age from surrounding regionally developed blueschist to greenschist facies rocks structural mapping of the transition zone between the two metamorphic types indicates that their juxtaposition was aided by significant syn to late metamorphic solid state flow that served to attenuate the overlying rock column and thus collapse the field metamorphic gradient on the basis of field relations structural data petrography and geochronologic data strain appears to have accompanied the rapid adiabatic rise of high temperature rocks from several tens of kilometers to less than 10 km depth during the cretaceous in an event younger than the unrelated to high p metamorphism granite cored gneiss domes on the seward peninsula may have formed during extension of previously thickened continental crust resulting in the approximately 35 km thick crust and near sea level elevations of the region today