a transitional alkalic dolerite dike suite of mesozoic age in southeastern new england dike rocks from the new england platform of rhode island and adjacent massachusetts consist of premetamorphic and post metamorphic suites the older group includes metamorphosed dolerite minette and schistose dioritic rocks post metamorphic dikes consist of dolerite and sparse monchiquite the post metamorphic dolerites are of comparable age to the eastern north american dolerite suite associated with the mesozoic basins along the eastern seaboard of north america however the southeastern new england dolerites exhibit mineralogy and chemistry more typical of a transitional alkalic suite compared to the more subalkalic tholeiitic dolerites of the eastern north american suite both suites are compatible with a rift tectonic setting but the more alkalic dolerites may represent a deeper source of small volume melts compared to the eastern north american dolerites these more alkaline melts may have concentrated at local centers or they may be typical of flank dolerites as opposed to the less alkalic varieties that occur within the central axial rift

internal reflecting horizons in spitsbergen glaciers a single pronounced internal reflecting horizon has been observed on radio echo sounding from over 30 glaciers in spitsbergen they are often present along the entire length of the glacier remaining at a fairly constant depth 100 200 m below the ice surface echo strength data from radio echo sounding have been used to obtain reflection coefficients for these horizons of between 15 and 25 db combined with results of ice core studies the possible causes of this internal layer are investigated the presence of water is found to be the most likely explanation indicating the existence at depth of a layer of temperate ice

new pieces the acquisition and distribution of volcanic glass sources in northeast china during the holocene abstract little is known about the diversity of volcanic glass sources used in prehistoric northeast china although preliminary research established the presence of a number of sources in archaeological sites from this area the exact location of these sources was not known jia et al 2010 a recent geoarchaeological survey of three source areas and new data derived from portable x ray fluorescence elemental analysis pxrf has revealed not only the location and use of two new geological sources in northeast china but also extended our understanding of the geologic context of volcanic glass from tianchi paektusan volcano the major geological source of volcanic glass in northeast china furthermore understanding the geological history of these new sources clarifies why they were only found in archaeological sites dated to the holocene

reflection polarity of the midcrustal surrency bright spot beneath southeastern georgia testing the fluid hypothesis a small reflection seismic experiment with an explosive source was conducted in southeastern georgia to determine the polarity of an unusually strong midcrustal reflector the surrency bright spot sbs which was found at a depth of approximately 16 km during earlier cocorp profiling in the region in addition to being very bright the sbs is notable for being unusually flat and horizontal for about half of its 4 km length as these characteristics are similar to those of fluid caused reflections at shallow depths it has been suggested that the sbs may be caused by in situ midcrustal fluids if caused by fluid enclosed in fracture porosity in solid rock the reflection would be expected to exhibit a negative polarity from the top of the porous zone the vibroseis data however gave ambiguous results with regard to polarity due to the limited bandwidth and inherent uncertainties about the phase of the source signal the new experiment consisted of four dynamite shots each recorded at three receiver stations by seismic group recorders sgr borrowed from amoco production company comparison of the dynamite records with geophone polarity tests indicate that the sbs is characterized by a positive reflection coefficient at its top this result itself does not negate the fluid hypothesis a fluid fluid interface could cause the positive reflection as well as the flat spot nature of the reflector waveform modeling shows that the sbs is caused by two or more thinly spaced reflectors a relatively high impedance layer about 120 m thick provided a good match to the observed dynamite data but requires a lower boundary having a slightly smaller reflection coefficient than the upper boundary 0 7 versus 1 0 a 150 m thick porous zone model also provided a relatively good fit to the observed dynamite data but in this model the polarity test requires that the initial sbs reflection of positive polarity be caused by a fluid fluid interface within the porous zone and that the top of the porous zone be relatively non reflective though these observations do not preclude the fluid hypothesis they certainly make the high impedance model the simpler of the two alternatives presented here the additional constraints imposed by the modeling also suggest that the sbs is more complex than these simple two interface models in either of these cases wavelet tuning contributes in part to the unusually large amplitude of the sbs reflection

estimation of relative water content in a sub polar glacier using surface penetration radar radar sounding data taken at uversbreen glacier svalbard are used to estimate the relative water content of the temperate part of the glacier the relative change in water content is estimated from the strength of the backscattered radar energy without knowing the size of the scatterers the main findings are that the water content is increasing gradually with depth below the cold temperate interface the water content is on average changing by a factor of five in the ice with the exception of some bright spots believed to stem from larger water moulins the general trend is also that the water content is increasing with lower altitude the applied technique may be a useful method for large scale mapping of the relative water content variation in temperate and polythermal glaciers

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

pangea s complex breakup a new rapidly changing stress field model over the years numerous proposals have been presented describing the relationship between the central atlantic magmatic province camp and the break up of pangea recent proposals have focused on refuting the original proposal of a mantle plume origin for the large igneous province and attendant dikes and instead propose an upper mantle or passive cause for the break up and camp in this paper we examine the fundamental assumption that the multiple dike orientations associated with the break up are geographically or temporally delimited new mapping and compilations of older local maps demonstrate that multiple dike orientations ranging from nw to ne trending were intruded throughout the western carolinas and are not geographically limited further new plagioclase 40 ar 39 ar dates indicate that all three orientations observed were emplaced within a 2 ma period c a 199 197 ma based on this information we propose that a rapidly rotating stress field must be responsible for the emplacement of multiple dike orientations in the carolinas and the break up of pangea and go on to propose several new tectonic models to account for this rotating stress field d 2005 elsevier b v all rights reserved

moving sources a preliminary study of volcanic glass artifact distributions in northeast china using pxrf recent studies have highlighted the long distance transport of obsidian from the paektusan tianchi or baitoushan in chinese volcano on the border between china and north korea to eastern russia and korea but little is known about the role of the local population in the production and movement or exchange of this important raw material this paper addresses this data lacuna by presenting sourcing results of 440 artifacts from 18 late paleolithic sites located in northeast china a portable xrf enabled rapid non destructive characterization of samples the results show that although paektusan obsidian was widely transported throughout northeast asia material from at least three other sources was also used in particular we highlight the significance of basaltic glass artifacts with the same geochemistry as sources found in the primorye region of far east russia in sites from northeast china this result indicates a two way movement of volcanic glass artifacts between primorye and the northeast of china rather than a unidirectional long distance exchange system originating from paektusan volcano

water storage and subglacial drainage conditions inferred from borehole measurements on gornergletscher valais switzerland measurements of change in length of a borehole or displacements of poles and of subglacial water pressure were combined with drainage tests and electrode tests in boreholes in experiments near the northern margin of gornergletscher valais switzerland at the upstream side of an overdeepening the measurements suggest that the subglacial drainage system consisted of discrete conduits at that location presumably linked cavities on clean bedrock changes in subglacial water pressure were followed by variations in subglacial water storage together with similar variations in elevation of a pole the variations in subglacial water storage caused changes in cross sections of subglacial passageways and thereby changed the frequencies of slug test oscillations similar experiments conducted near the center line of the glacier revealed different subglacial conditions impeded drainage through a sediment layer and different depths of water levels in different boreholes these results are discussed in relation to previous studies

on the thermal regime of an arctic valley glacier a study of white glacier axel heiberg island n w t canada from 1974 to 1981 a total of 32 bore holes was drilled on white glacier and vertical ice temperature profiles measured the data obtained allowed the construction of three longitudinal and four transverse profiles of the two dimensional temperature distributions thus an extensive layer of temperate or near temperate ice was discovered close to the bedrock in the lowest part of the glacier tongue it was also found that the temperature distribution cannot be in a steady state since there is a temperature minimum 100 150 m below the glacier surface in the accumulation area a simple numerical model calculation shows that this minimum can be mostly explained by the general climatic warming since 1880 the 10 m temperatures show diffuse relations to climatic conditions and balance zones a simple scheme for extrapolating surface temperatures is discussed

sources of archaeological obsidian on sakhalin island russian far east abstract instrumental neutron activation analysis was performed on 79 obsidian tools and flakes from 35 sites on sakhalin island dating from upper paleolithic c 19 000 bp to early iron age c 2000 800 bp due to the absence of volcanic glass on sakhalin island raw materials from the nearest obsidian sources on hokkaido island such as oketo shirataki tokachi mitsumata and akaigawa were also analysed a strong correlation between the chemical compositions of obsidian artefacts from sakhalin and volcanic glass sources from hokkaido was discovered in particular the oketo and shirataki sources were used for tool manufacturing throughout all of sakhalin island s prehistory the distances between sources and archaeological sites range from 200 1000 km the intensive exchange of raw materials continued and even intensified after the appearance of the la perouse soya strait between hokkaido and sakhalin about 10 000 8000 bp the sakhalin island populations were deeply involved in the obsidian exchange network centered on hokkaido

non destructive pxrf analysis of museum curated obsidian from the near east abstract non destructive pxrf has the potential to expand sample populations of archaeological provenancing studies by facilitating access to museum collections of artefacts in this study we use museum curated obsidian for the sites of tell brak mersin yumuktepe and tell arpachiyah and geological obsidian samples from central turkey to demonstrate that non destructive pxrf is comparable to other techniques in differentiating between near eastern obsidian sources secondly we use multivariate analysis to evaluate whether non destructive pxrf is sufficiently accurate and precise to enable comparison with legacy datasets from previous analysis using pixe and icp ms multivariate analyses show that instrumental offsets between the results from pxrf and other analytic techniques are less than source to source variation typical for most anatolian obsidian outcrops and pxrf identified geochemical groups are directly comparable to legacy datasets non destructive pxrf analysis indicates that during the chalcolithic east gollu dag and nenezi dag continued to be the major sources of obsidian to communities in central anatolia and the bingol range and mountains surrounding lake van supplied sites east of the levant variations in the analysed assemblages suggest a number of obsidian exchange networks existed during this period

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

the puzzle of the primary obsidian source in the region of paektusan china dpr korea abstract since the 1990s a characteristic obsidian geochemistry has linked widespread archaeological assemblages spanning the russian far east korean peninsula and northeast china referred to as pnk1 the source of this material has yet to be identified as a contribution to solving this enduring puzzle we report here analyses of a commercial specimen of obsidian exported from chongjin in dpr north korea a combination of neutron activation analysis naa and potassium argon dating enable us to compare this piece with a large obsidian database for northeast asia we find that the chongjin sample is identical to pnk1 lithics from archaeological collections while the exact source of the chongjin sample remains unknown we can more confidently locate the primary source for pnk1 lithics in dpr korea based on an exhaustive literature review of the geology and geochemistry of volcanic glasses and other volcanic rocks in the northern part of the korean peninsula and drawing on our own unpublished data we suggest that the pnk1 source is most likely located south of paektusan volcano this corroborates the existing evidence for the long range transport of the material

the thermal regime of sub polar glaciers mapped by multi frequency radio echo sounding radio echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale radar signals of 320 370 mhz penetrate ice at sub freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water radar signals of 5 20 mhz on the other hand see through both the cold and the temperate ice down to the glacier bed radio echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in svalbard kongsvegen uversbreen midre lovenbreen and austre broggerbreen in the ablation area of kongsvegen a cold surface layer 50 160m thick was underlain by a warm basal layer which is advected from the temperate accumulation area the surface ablation of this cold layer may be compensated by freezing at its lower cold temperate interface this requires that the free water content in the ice at the freezing interface is about 1 of the volume the cold surface layer is thicker beneath medial moraines and where cold based hanging glaciers enter the main ice stream on uversbreen the thermal regime was similar to that of kongsvegen a temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between kongsvegen and uversbreen where meltwater accumulates during the summer near the subglacial lake setevatnet 250 m a s l lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer up to 50m thick was fed by temperate ice from two cirques on austre broggerbreen a temperate basal layer was not detected by radio echo soundings but the basal ice was observed to be at the melting point in two boreholes

magmatic rifting of pangaea linked to onset of south american plate motion abstract the causes of the transition from amagmatic to magmatic rifting during continental break up are not always clear and have been often linked to the break through of a plume however stress fields recorded in the crust may offer new insights into the relationship between changes in the stress field and the onset of magmatism in this paper stress fields recorded in the crust of north america are used to test possible causes of the break up of pangaea and the transition from amagmatic to magmatic rifting finite element models reveal that the most likely scenario for the break up involves the initial northwest motion of north america at 230 ma followed by a south southeast motion of south america at 200 ma with the initiation of magmatism and finally a weakened area between north and south america sometime soon after 200 ma which resulted in north america being dominated by northwest motion once again it was also determined that plate boundary structure and orientation play a large part in the recorded stress fields and must be taken into consideration when modeling continental break ups and rifting

assessing the applicability of portable x ray fluorescence spectrometry for obsidian provenance research in the maya lowlands recent innovations in portable energy dispersive x ray fluorescence pxrf spectrometry have increased its utility for the geochemical characterization of obsidian artifacts for archaeological provenance research however concerns over the utility of pxrf instrumental analyses have been raised focused on the validity and reliability of the geochemical data produced here we adopt the framework of richard hughes on reliability validity and scale in obsidian sourcing research 1998 whereby reliability addresses instrument stability and issues of measurement while validity pertains to an instrument s ability to discern geochemical source provenance this is done in order to test the utility of pxrf instruments for archaeological provenance research k means cluster analysis was used to test the accuracy of pxrf through statistical comparison of data acquired via laboratory and portable energy dispersive xrf instruments multivariate analysis was employed to demonstrate obsidian source representation at two classic maya archaeological sites in southern belize uxbenka and ek xux and to test the validity of data obtained from a pxrf instrument in answering archaeological research questions pertaining to regional interactions between lowland maya polities results suggest that portable xrf instruments produce internally consistent results however data acquired from a pxrf instrument are not statistically equivalent to other xrf instruments this is to say that while pxrf is not a reliable technique it is valid for questions pertaining to geochemical source representation

mechanisms of fast flow in jakobshavns isbrae west greenland part i measurements of temperature and water level in deep boreholes several holes were drilled to depths of 1500 1630 m along a profile across jakobshavns isbrae 50 km upstream from the calving front drilling was by hot water and required approximately 20 h the holes were rapidly closed by refreezing but it was possible to instrument them with thermistors and tilt sensors before this occurred near the margins of the ice stream the holes reached the bed and connected with the subglacial drainage system water level changes recorded in these holes are discussed in terms of the basal hydraulic system the temperature measurements show that the glacier is temperate based moreover extrapolation of a measured temperature profile and its curvature suggests that a temperate layer of substantial thickness may exist at the bed near the center of the ice stream there is a striking difference in the shapes of temperature profiles measured at different locations beneath the center line the temperature minimum is at a considerably smaller relative depth than near the margins but it is nearly the same in magnitude 22 1 c this may indicate a disproportionately large vertical stretching of the basal ice in the center of the ice stream since the basal ice is warmer and much less viscous than the ice above a thickening of that layer would cause a corresponding increase of surface velocity we presume that this mechanism contributes to the fast flow of jakobshavns isbrae

olivine normative dolerite dikes from western south carolina mineralogy chemical composition and petrogenesis this investigation describes five mesozoic dolerite dikes which intrude paleozoic metamorphic and igneous rocks of the inner piedmont of western south carolina the dikes are vertical or nearly so and strike approximately n40 w three major northeast trending faults also occur in the study area left lateral displacement of one dolerite is documented at a locality near cleveland south carolina elsewhere several of the dolerite dikes appear to terminate at or near the faults the dolerite dikes have subophitic to microporphyritic textures and consist principally of plagioclase generally an70 80 olivine dominantly fo80 90 and augite with subordinate pigeonite titanomagnetite chromite and brown partly glassy mesostasis in one dike pyroxene compositions trend from augite to ferroaugite in contrast to an augite subcalcic augite pigeonite trend characteristic of the other dolerites the contrasting trends primarily result from differences in sio2 abundance in the dolerite magmas major and trace element analyses indicate the presence of two different olivine normative dolerite magma types the two magma types are not related by near surface crystal fractionation models for genesis of the olivine normative dolerite magmas by partial melting of a plagioclase peridotite upper mantle source region are presented the models require that the source region be enriched in lree and incompatible elements such as rb ba hf and th relative to cl chondritic abundances one magma type appears to represent a primary dolerite magma that ascended from the source region with little subsequent compositional change the second magma type most likely experienced assimilation of clinopyroxene garnet eclogite during ascent thereby acquiring a ree pattern with a less steep negative slope for the lree and a slight positive slope in the hree

cenozoic episodic volcanism and continental rifting in northeast china and possible link to japan sea development as revealed from k ar geochronology abstract cenozoic volcanic rocks in northeast china comprise part of the volcanic belt of the western circum pacific rim and represent one of the presently active tectono magmatic regions of the world over 590 volcanoes with erupted basalts covering an area of 50 000 km 2 are exposed in the songliao graben and particularly on its flanks k ar dating of the volcanic rocks sampled from a selection of eruption sites over the region reveals that the volcanism occurred episodically through the entire cenozoic corresponding to the tectono magmatic interactions particularly between the india eurasia and pacific plates the volcanism initiated in the songliao graben in late cretaceous 86 ma and migrated flankward since 28 ma the magmatic propagation shows three major stages intimately associated with the evolution of japan sea and related to the geodynamic forcing of the india eurasia collision prior to japan sea rifting volcanic eruptions were restricted to the songliao basin during japan sea opening volcanism migrated into the lateral belts after cessation of japan sea opening at 15 ma volcanism with greatest intensity occurred on both flanks particularly along the yi yi fault system around 14 13 ma and subsequently the fu mi fault between 11 and 7 ma continuing this trend of migration eruptions scattered further away from the songliao basin in the last 4 5 ma we suggest that the cenozoic volcanic belt in northeast china and the japan sea backarc basin are competitive parts in the eastern marginal magmatic system of the eurasian plate the early stage of the volcanism in the songliao basin may have resulted from mantle upwelling beneath the songliao bohai basin belt rifting of the ne faults and relatively weak intensity of volcanism in northeast china during japan sea opening could be attributable to the lithospheric breakup in the japan sea and spreading of japan sea the subsequent strong volcanism in northeast china after cessation of the japan sea opening implicates the easiest pathway for the melts of the magmatic system in the plate margin the diversified volcanism in scattered localities during the quaternary may indicate localized melting processes or notable modifications in smaller sized individual domains and possibly a magmatically waning phase of the limited source in eastern china

the opening of the atlantic the mesozoic new england igneous province and mechanisms of continental breakup abstract plume and tensionally induced rifting models have been proposed as causes of continental rifting and breakup mantle plumes should produce early lithospheric doming events associated with alkaline magmatism however the triassic alkaline rocks on the east north american e n a margin are structurally localized the uplifts are mostly jurassic in age and voluminous plateau magmatism post dates the initiation of taphrogenesis by 10 to 20 ma in addition there are no chains of anorogenic igneous rocks leading to any of the postulated triassic plumes these facts argue against the plume generated rifting model for the e n a margin but are consistent with the predicted effects of the tensionally induced rifting model the genesis of linear chains of alkaline rocks has been attributed to passage of a lithospheric plate over a mantle plume this explanation has been proposed for the cretaceous monteregian and white mountain intrusive series and the kelvin seamount chain however these rocks are distributed along structurally controlled e w trending lineaments the monteregians are localized by the presence of a paleorift ottawa bonnechere graben in the underlying grenvillian basement and the kelvin seamounts are emplaced along the early jurassic kelvin fracture zone the structures localizing the southern white mountain lineament are less well defined the spatial temporal and geochemical relationships along and between these lineaments are consistent with an origin as a southeastward propagating tensional event the intra plate stresses are probably the result of shifts in the pole of rotation of the north american plate due to irregular northward extensions of seafloor spreading during the cretaceous

juxtaposed mesozoic diabase dike sets from the carolinas a preliminary assessment aeromagnetic anomaly maps of the north carolina piedmont provide confirming evidence of juxtaposed mesozoic diabase dike sets dikes in north carolina may be divided into four domains on the basis of dike orientations most dikes are olivine normative but there are apparent systematic differences in chemical compositions that are reflected in different orientations and ages two orientations dominate northwest and north south the northwest trending set dominates in the south carolina piedmont and the north south set extends through much of the central virginia piedmont and under the coastal plain in south carolina the north south dikes are part of a set that converges near charleston and georgetown south carolina and diverges northward into virginia preliminary information suggests that the north south dikes are younger than the more common northwest trending dikes current models proposed for stress regimes associated with the breakup of pangea can accommodate the northwest set but not the north south convergent set this convergent set may be evidence for crustal deformation above a mantle plume centered near charleston and georgetown in middle jurassic time it is possible that presumed mafic plutons under the coastal plain near charleston regional seismicity patterns and orientations of the diabase dikes are all related to an intersection of zones of crustal weakness inherited from mid mesozoic time the western margin of northwest trending dikes may be related to tectonic features inherited from pre mesozoic time

cold ice in the ablation zone its relation to glacier hydrology and ice water content 1 cold ice within a polythermal ice body controls its flow dynamics through the temperature dependence of viscosity and affects glacier hydrology by blocking water flow paths lakes on the surface linked by persistent deeply incised meltwater streams are hallmark features of cold ice in the ablation zone of a glacier or ice sheet ice radar is a convenient method to map scattering from internal water bodies present in ice at the pressure melting temperature pmt consequently lack of internal scatters is indicative of cold ice we use a helicopter borne 30 mhz ice radar to delineate the extent of cold ice within grenzgletscher zermatt swiss alps the inferred thermal structure is validated with temperature measurements in 15 deep boreholes showing excellent agreement the cold ice occupies 80 90 of the total ice thickness in a 400 m wide flow band along the central flow line quantitative interpretation of ice radar scattering power indicates a decrease of ice water content between pmt and 0 5 k below pmt as predicted by theory and observed in the laboratory the cold ice which emerges at the surface in the lower ablation zone is impermeable to water and is thus devoid of moulins if not crevassed the surface water from melt and rain is routed through deeply incised persistent streams and lakes and cryoconite holes are frequent in stark contrast to the adjacent temperate ice from other tributaries the cold ice thus has a strong control on glacier hydrology but is likely to change due to continued warming

timescale and evolution of the intracontinental tianchi volcanic shield and ignimbrite forming eruption changbaishan northeast china abstract around the tianchi eruption cone the junjianshan formation which builds the tianchi basalt shield can be divided into three units they are from bottom to top the toudao baishan and laofangzixiaoshan units respectively individual basaltic flows of the tianchi shield vary significantly in volume and in spatial distribution from a few to dozens of kilometers in length hundreds to thousands of meters in width and a few to dozens of meters in thickness k ar age data indicate that the tianchi shield was formed within a very short time period between 2 77 0 08 and 0 31 0 002 ma our detailed mapping in combination with the k ar dating shows that the toudao unit erupted at 2 77 1 99 ma the baishan unit at 1 64 1 11 ma and the laofangzixiaoshan at 0 31 0 58 ma the huge millennium eruption from the tianchi volcano sustained a 35 km high column h t and lasted a few days producing the comenditic ignimbrite around the volcano wiggle matching measurements of a sample series of charcoal wood indicate the millennium eruption might have happened around 1024 ad features of eruptions stemming from the same source surrounding the tianchi volcano plus the volcanic evolution from effusive flows to explosive eruption are interpreted to reflect crustal thickening within this intracontinental tectonic environment field observations and lava compositional variations suggest that crystal fractionation and magma mixing or mingling process must have played an important role in the development and evolution of the tianchi volcano

a search in north greenland for a new ice core drill site a new deep ice core drilling site has been identified in north greenland at 75 12 n 42 30 w 316 km north northwest nnw of the grip drill site on the summit of the ice sheet the ice thickness here is 3085 m the surface elevation is 2919 m the north grip ngrip site is identified so that ice of eemian age 115 130 ka bp calendar years before present is located as far above bedrock as possible and so the thickness of the eemian layer is as great as possible an ice flow model similar to the one used to date the grip ice core is used to simulate the flow along the nnw trending ice ridge surface and bedrock elevations surface accumulation rate distribution and ratio echo sounding along the ridge have been used as model input the surface accumulation rate drops from 0 23 m ice equivalent year 1 at grip to 0 19 m ice equivalent year 1 50 km from grip over the following 300 km the accumulation is relatively constant before is starts decreasing again further north ice thickness up to 3250 m bring the temperature of the basal ice up to the pressure melting point 100 250 km from grip the ngrip site is located 316 km from grip in a region where the bedrock is smooth and the accumulation rate is 0 19 m ice equivalent year 1 the modeled basal ice here has always been a few degrees below the pressure melting point internal radio echo sounding horizons can be traced between the grip and ngrip sites allowing us to date the ice down to 2300 m depth 52 ka bp an ice flow model predicts that the eemian age ice will be located in the depth range 2710 2800 m which is 285 m above the bedrock this is 120 m further above the bedrock and the thickness of the eemian layer of ice is 20 m thicker than at the grip ice core site