ion microprobe evidence for the mechanisms of stable isotope retrogression in high grade metamorphic rocks retrograde interdiffusion is widely proposed as the dominant factor in producing the stable isotopic fractionation among minerals in slowly cooled igneous and metamorphic rocks mineral zonation consistent with interdiffusion of stable isotopes has never been directly observed however leaving doubt as to the mechanism responsible for the bulk mineral isotopic compositions commonly measured ion microprobe analyses of oxygen isotope ratios in magnetite were combined with conventional bulk mineral analyses and diffusion modeling to document the relationship between mineral zonation and the mechanism of retrogression inferred from bulk mineral data two samples of magnetitebearing quartzo feldspathic lyon mountain gneiss from the adirondack mountains n y were studied in detail conventional stable isotope analysis of both samples indicates that isotope thermometers are discordant and were reset by as much as 200 c from the estimated peak temperature of 750 c the relative order of apparent temperatures recorded by various thermometers differs between the two samples however with t qtz fsp t mt qtz and t mt fsp in one sample and t qtz fsp t mt qtz and t mt fsp in the other diffusion modeling using the fast grain boundary model shows that the former pattern of apparent temperatures is consistent with closed system interdiffusion during cooling whereas the latter is not the modeling predicts that 0 5 mm diameter magnetite grains common to this rock type will contain isotopic zonation of 1 rims lower in 18 o than cores and that the cores of smaller 0 1 mm grains will be similarly lower than to the cores of large 0 5 mm grains ion microprobe analysis reveals that the zoning patterns of magnetite grains from the first sample contain clear core to rim zonation in multiple grains core rim 1 1 0 4 and predicted grain size vs core composition variations consistent with diffusion controlled resetting of bulk mineral fractionations in contrast the second sample shows irregular inter and intra granular variations over an 8 range consistent with open system alteration these results provide direct documentation of the importance of interdiffusion in affecting stable isotope distributions in slowly cooled rocks the correlations of bulk mineral resetting with zonation show that bulk mineral data when interpreted with detailed modeling can be used to determinate what processes controlling retrogression

recent warming in eastern canada inferred from geothermal measurements borehole temperature measurements from several sites in eastern canada were analyzed to determine recent step changes in ground surface temperature inversion of the data suggests a warming by 1 to 2 c in the last 100 years for most of the sites analyzed

assessment of grain scale homogeneity and equilibration of carbon and oxygen isotope compositions of minerals in carbonate bearing metamorphic rocks by ion microprobe abstract nineteen samples of metamorphosed carbonate bearing rocks were analyzed for carbon and oxygen isotope ratios by ion microprobe with a 5 15 m spot three from a regional terrain and 16 from five different contact aureoles contact metamorphic rocks further represent four groups calc silicate marble and hornfels 6 brucite marble 2 samples that contain a reaction front 4 and samples with a pervasive distribution of reactants and products of a decarbonation reaction 4 the average spot to spot reproducibility of standard calcite analyses is 0 37 2 standard deviations sd for 18 o and 0 71 for 13 c ten or more measurements of a mineral in a sample that has uniform isotope composition within error of measurement can routinely return a weighted mean with a 95 confidence interval of 0 09 0 16 for 18 o and 0 10 0 29 for 13 c using a difference of 6sd as the criterion only four of 19 analyzed samples exhibit significant intracrystalline and or intercrystalline inhomogeneity in 13 c at the 100 500 m scale with differences within individual grains up to 3 7 measurements are consistent with carbon isotope exchange equilibrium between calcite and dolomite in five of six analyzed samples at the same scale because of relatively slow carbon isotope diffusion in calcite and dolomite differences in 13 c can survive intracrystalline homogenization by diffusion during cooling after peak metamorphism and likely represent the effects of prograde decarbonation and infiltration all but 2 of 11 analyzed samples exhibit intracrystalline differences in 18 o up to 9 4 intercrystalline inhomogeneity in 18 o up to 12 5 and or disequilibrium oxygen isotope fractionations among calcite dolomite calcite quartz and calcite forsterite pairs at the 100 500 m scale inhomogeneities in 18 o and 13 c are poorly correlated with only a single mineral dolomite in a single sample exhibiting both because of relatively rapid oxygen isotope diffusion in calcite intracrystalline inhomogeneities in 18 o likely represent partial equilibration between calcite and fluid during retrograde metamorphism calcite is in oxygen isotope exchange equilibrium with forsterite in one of four analyzed samples in equilibrium with dolomite in none of six analyzed samples and in equilibrium with quartz in neither of two analyzed samples there are no samples of contact metamorphic rock with analyzed reactants and products of an arrested metamorphic reaction that are in oxygen isotope equilibrium with each other the degree of departure from equilibrium in analyzed samples is variable and is often related at least in part to alteration of 18 o of calcite during retrograde fluid rock reaction in situ sub grain scale carbon and oxygen isotope analyses of minerals are advisable in the common applications of stable isotope geochemistry to metamorphic petrology correlation of sub mm scale stable isotope data with imaging will lead to improved understanding of reaction kinetics reactive fluid flow and thermal histories during metamorphism

reconstruction of high resolution ground temperature histories combining dendrochronological and geothermal data in an attempt to obtain robust records of past climatic variations geothermal temperature depth data have been combined with dendrochronological data to yield high resolution ground temperature histories since the resolution of the dendrochronological record and the ground temperature history inferred from geothermal data are different comparison of these records is made possible by multiplying the dendrochronological data by the model resolution matrix for the geothermal data inversion under this condition we find that a simple transformation between tree ring indices and ground temperature changes allows us to interpret tree ring widths in terms of ground temperatures thus yielding a high resolution ground temperature history which explains the observed subsurface temperature regime the linear transformation relating the ground temperature changes and average variations from the tree ring chronology was found to be tg 9 93 iaverage

heat flow and thermal history of the anadarko basin and the western oklahoma platform abstract the average geothermal gradient in the anadarko basin and the oklahoma platform estimated from 856 corrected bottom hole temperatures bhts is 21 c km analysis of previously published thermal maturation data indicates that the anadarko basin has undergone from 1 to 3 km of erosion starting about 40 to 50 ma the average thermal gradient at the time of maximum burial was in the range of 22 to 25 c km there is no evidence that the thermal state of the anadarko basin has changed significantly since the late paleozoic 250 ma to estimate heat flow in the anadarko basin and the oklahoma platform we made 652 thermal conductivity measurements on drill cuttings from 9 oil and gas wells all measurements were corrected for the effects of anisotropy temperature and porosity matrix conductivities perpendicular to bedding at 22 c range from 1 7 w m 1 k 1 for permian age sandstone and shale to 2 6 w m 1 k 1 for devonian silurian age limestone and shale in situ thermal conductivities vary from 1 3 w m 1 k 1 to 1 9 w m 1 k 1 estimated heat flow 20 ranges from 30 mw m2 to 42 mw m2 with a mean of 36 mw m2 we found no evidence for heat flow to increase significantly from the anadarko basin in the south to the oklahoma platform to the north these results contradict a previous study which found heat flow increases from south to north with heat flow in the oklahoma platform as much as 50 greater than heat flow in the anadarko basin at the present time we do not know if these differences are related to spatial variations or reflect methodological errors if our results are averaged with those reported in previous work mean heat flows in the anadarko basin and oklahoma platform are 39 mw m2 and 51 mw m2 respectively

pre observational evolution of surface temperature in romania as inferred from borehole temperature measurements temperature data from nine boreholes in the carpathian orogen in romania were used to obtain information on the ground surface temperature history gsth in the last 250 years the temperature measurements were taken with a thermistor probe sensitivity in the 10 mk range using the stop and go technique at 10 m intervals in the depth range of 20 580 m the least squares inverse modelling approach of tarantola and valette j geophys 50 159 170 1982 was used to infer the gsth long term air temperature records available from the romanian weather station network were used as a comparison term for the first 100 150 years of the gsth and as a forcing function in a pom sat model that combines borehole temperature profiles btps and meteorological time series surface air temperature sat to produce information on the so called pre observational mean pom results from a global circulation model for the romanian area are incorporated in the discussion as well

early triassic conodont palynological biostratigraphy of the meishan d section in changxing zhejiang province south china the lower triassic consisting of the yinkeng fm helongshan fm and the lower part of the nanlinghu fm is well developed at the meishan d section of changxing county zhejiang province south china based on detailed study of the conodont biostratigraphy from the interval of the permian triassic boundary and the lower triassic in the meishan d section 8 conodont zones are recognized in ascending order as follows the neogondolella changxingensis yini hindeodus praeparvus zone beds 24a 24e top of the changxing fm the neogondolella meishanensis meishanensis hindeodus eurypyge zone beds 25 27b base of the yinkeng fm the hindeodus parvus zone beds 27c 27d first conodont zone of triassic the global index for the base of triassic the isarcicella staeschei zone beds 28 29a lower part of the yinkeng fm i isarcica zone beds 29b 51 lower part of the yinkeng fm the neogondolella tulongensis n planata zone beds 52 72 from upper part of the yinkeng fm to lower part of the helongshan fm the neospathodus kummeli zone beds 73 92 middle part of the helongshan fm and the neospathodus cristagalli n dieneri zone beds 93 111 from upper part of the helongshan fm to the base of the nanlinghu fm at the meishan d section the palynological biostratigraphy is also studied herein the palynological assemblage of lundbladispora taeniaesporites equisetosporites is found in the intervals which contain the conodont isarcicella isarcica zone and the lower part of the neogondolella tulongensis n planata zone

estimations of the past groundwater recharge rate from deep borehole temperature data abstract in order to estimate the past groundwater recharge rates from deep borehole temperature data observed temperature depth profiles are compared with the profiles calculated from heat conduction convection equation under the condition of linear increase in surface temperature due to global warming and urbanization in tokyo metropolitan area the results show the increase in groundwater recharge rate from the 1890s to 1940s and it decreased from the 1940s to 1990s these estimations agree well with the precipitation record in tokyo during the last 100 years therefore the deep borehole temperature data can be used for estimating not only surface temperature history but also the past groundwater recharge rate in tokyo area

climate change in india inferred from geothermal observations 1 temporal variations in surface ground temperature impart a signal to the subsurface thermal regime that is captured in borehole temperature depth profiles seventy temperature depth profiles in india located between 12 and 28 n are analyzed to infer past changes in ground temperature these profiles exhibit predominantly positive anomalous temperatures relative to the background thermal regime beginning at depths of 75 150 m and increasing toward the surface this pattern is consistent with warming over the past century an interpretation in terms of linear surface temperature change indicates warming of about 0 9 0 1 c over the past 150 years relatively complete surface air temperature sat records from meteorological stations near the boreholes indicate similar rates of warming over the last century a combined analysis of borehole temperatures and sat records yields a long term preobservational mean temperature 0 8 0 1 c lower than the 1961 1990 mean sat when the most recent decade is included directly in the analysis the average total warming in india from the early 1800s to the late 1990s is 1 2 c

formation of al rich titanite catisio4o caalsio4oh reaction rims on ilmenite in metamorphic rocks as a function of fh2o and fo2 abstract reaction rims of titanite on ilmenite are described in samples from four terranes of amphibolite facies metapelites and amphibolites namely the tamil nadu area southern india the val strona area of the ivrea verbano zone northern italy the bamble sector southern norway and the northwestern austroalpine otztal complex the titanite rims and hence the stability of titanite catisio4o and al oh titanite i e vuaganatite hypothetical end member caalsio4oh are discussed in the light of fh2o and fo2 buffered equilibria involving clinopyroxene amphibole biotite ilmenite magnetite and quartz in the systems cao feo fe2o3 tio2 sio2 h2o o2 cftsh and cao feo fe2o3 al2o3 sio2 h2o o2 cfash present in each of the examples textural evidence suggests that titanite reaction rims on ilmenite in rocks from tamil nadu val strona and the bamble sector originated most likely due to hydration reactions such as clinopyroxene ilmenite quartz h2o amphibole titanite and oxidation reactions such as amphibole ilmenite o2 titanite magnetite quartz h2o during amphibolite facies metamorphism or as in the case of the otztal complex during a subsequent greenschist facies overprint overstepping of these reactions requires fh2o and fo2 to be high for titanite formation which is also in accordance with equilibria involving al oh titanite this study shows that in addition to p t bulk rock composition and composition of the coexisting fluid fo2 and fh2o also play an important role in the formation of al bearing titanite during amphibolite and greenschist facies metamorphism

temperature trends over the past five centuries reconstructed from borehole temperatures for an accurate assessment of the relative roles of natural variability and anthropogenic influence in the earth s climate reconstructions of past temperatures from the pre industrial as well as the industrial period are essential but instrumental records are typically available for no more than the past 150 years therefore reconstructions of pre industrial climate rely principally on traditional climate proxy records each with particular strengths and limitations in representing climatic variability subsurface temperatures comprise an independent archive of past surface temperature changes that is complementary to both the instrumental record and the climate proxies here we use present day temperatures in 616 boreholes from all continents except antarctica to reconstruct century long trends in temperatures over the past 500 years at global hemispheric and continental scales the results confirm the unusual warming of the twentieth century revealed by the instrumental record but suggest that the cumulative change over the past five centuries amounts to about 1 k exceeding recent estimates from conventional climate proxies the strength of temperature reconstructions from boreholes lies in the detection of long term trends complementary to conventional climate proxies but to obtain a complete picture of past warming the differences between the approaches need to be investigated in detail

ground temperature histories for central and eastern canada from geothermal measurements little ice age signature deep borehole temperature profiles have been analyzed to determine ground temperature histories in central and eastern canada clear signs of a cold period between 1500 and 1800 a d corresponding to the little ice age have been found a warming trend after 1800 a d was detected throughout eastern and central canada temperature profiles from western ontario are consistent and were inverted simultaneously to yield a regional ground temperature history the recent warming appears to be correlated with the increase of atmospheric co2 reported for a greenland ice core

precision logging of temperature gradients and the extraction of past climate abstract with new equipment it is now possible to obtain borehole logs which allow resolution of temperature gradients differing by 0 1 0 2 mk m over a distance of about 0 5 m at a logging rate of 8 m min since such a detailed profile of temperature gradient versus depth is easily obtained disturbances to the equilibrium gradient can now be readily identified in order to identify the forms of surface temperature variation which disturb the equilibrium regime in boreholes to depths of more than 100 m some tests are proposed in which a polynomial curve is fitted to the observed temperature gradient the real roots of the first and second derivative equations of this fitted curve are then used to estimate the types of surface thermal disturbances aplication of these tests to a well characterized borehole indicates that there were increases in temperature of 1 k approx 250 years ago 3 6 k approx 25 years ago and 5 0 k approx 8 years ago the first disturbance may be associated with the ending of the little ice age while the last two are associated with the completion of large buildings nearby in 1958 and 1967

in situ 40k 40ca double plus sims dating resolves klokken feldspar 40k 40ar paradox abstract the 40k 40ca decay system has not been widely utilized as a geochronometer because quantification of radiogenic daughter is difficult except in old extremely high k ca domains even these environments have not heretofore been exploited by ion microprobe analysis due to the very high mass resolving power mrp of 25 000 required to separate 40k from 40ca we introduce a method that utilizes doubly charged k and ca species which permits isotopic measurements to be made at relatively low mrp 5000 we used this k ca double plus approach to address an enduring controversy in 40ar 39ar thermochronology revolving around exsolved alkali feldspars from the 1166 ma klokken syenite southern greenland ion microprobe 40k 40ca analysis of klokken samples reveal both isochron and pseudoisochron behaviors that reflect episodic isotopic and chemical exchange of coarsely exsolved perthites and a near end member k feldspar until 719 ma and perhaps as late at 400 ma feldspar microtextures in the klokken syenite evolved over a protracted interval by non thermal processes fluid assisted recrystallization and thus this sample makes a poor model from which to address the general validity of 40ar 39ar thermochronological methodologies

north american climate of the last millennium underground temperatures and model comparison general circulation models gcms are currently able to provide physically consistent simulations of millennial climate variability in which estimations of external forcing factors are incorporated as boundary conditions climate reconstruction attempts to recover as faithfully as possible past climate variability using a variety of independent and climate sensitive sources of information by deriving strategies of comparison between gcm simulations and proxy data or directly recorded data such as subsurface thermal profiles the agreement between model and observations can be assessed thermal profiles obtained from the boreholes of north america were grouped into eight geographically discrete ensembles and averaged to form robust representative profiles the gridded output from the three distinct integrations of the gcm echo g were similarly averaged by region these simulated millennial paleoclimatic histories were then forward modeled to arrive at the subsurface thermal profiles that would result from the temperature trends at the surface these forward modeled profiles were then compared with the borehole average thermal anomaly profile in each region in most of the regions studied the externally forced runs from echo g are in better agreement with underground temperature anomalies than with the control run suggesting that boreholes are sensitive to external forcing not only do echo g simulations demonstrate better agreement with borehole data when considering variable external forcing factors but echo g also appears to broadly describe qualitative aspects of long term climatic trends at a regional scale

the carthage colton mylonite zone adirondack mountains new york the site of a cryptic suture in the grenville orogen u pb ages were determined on metamorphic sphenes and monazites from the late proterozoic adirondack highlands and lowlands in the vicinity of the carthage colton mylonite zone monazites were extracted from metapelites and sphenes were separated from marbles calc silicate gneisses and granite gneisses in order to determine the timing and the duration of metamorphism as well as the cooling histories for rocks on either side of the mylonite zone monazite ages from the lowlands range from 1171 1137 ma sphene ages in the lowlands range from 1156 1103 ma those from the highlands immediately to the east of the mylonite zone range from 1050 982 ma the ages indicate that the last high grade metamorphism in the highlands is ca 100 m y younger than in the lowlands and that both terranes had separate cooling histories at least until ca 1000 ma sphenes from within the carthage colton mylonite zone yield ages of about 1098 ma which are distinct from sphene ages on either side of the shear zone the mineral

inference of ground surface temperature history from subsurface temperature data interpreting ensembles of borehole logs ground surface temperature histories gsths inferred from borehole temperaturedepth t z data are often degraded to a various extent by random or systematic noise in thet z data and in the measurements of thermophysical properties of the earth to minimize the effects of noise and hence improve the fidelity of the inferred gsth a plausible approach is to perform a simultaneous inversion of thet z logs in a region or alternatively to invert the individualt z logs and then average the resulting gsths averaging and simultaneous inversion are conceptually different whereas an averaging can always be peformed a simultaneous inversion is predicated on the assumption of a common transient component of the gsth in all thet z logs in this work we examine and compare the two approaches using a time domain inverse formulation based on the method of least squares we consider a set of scenarios a multiplet z logs from a single borehole b multiple boreholes from a single site c multiple boreholes in similar climatological settings and d multiple boreholes in different climatological settings we show that for a b and c averaging and simultaneous inversion yield nearly identical results for boreholes in different settings the assumption of a common transient gsth may be invalid and averaging and simultaneous inversion give divergent results

adirondack highlands northwest lowlands boundary a multiply folded intrusive contact with fold associated mylonitization the boundary between the adirondack highlands and the northwest lowlands near harrisville new york is a multiply folded intrusive contact between metamorphosed sedimentary rocks of the lowlands and metamorphosed intrusive rocks of the diana complex in the highlands this is shown by detailed geologic mapping and analysis of stratigraphy and minor structural features regionally developed protomylonitic foliation in the diana complex is an axial plane foliation formed during isoclinal folding of dry quartz syenite at granulite facies metamorphic grade lack of major post intrusive fault displacement along the diana complex northwest lowlands boundary is demonstrated by correlation of xenoliths in the diana complex with immediately adjacent metamorphosed sedimentary rock units of the northwest lowlands and by continuity of major folds across the boundary a stratigraphic succession consisting of seven rock units has been recognized in northwest lowlands rocks of the harrisville area rocks in these units include from oldest to youngest 1 garnet sillimanite cordierite gneiss 2 rusty pelitic gneiss with biotite gneiss pyroxene amphibolite and quartzite 3 graphitic calcite marble 4 siliceous marble 5 rusty calc silicate rocks 6 diopside gneiss and 7 calc silicate granulite four phases of folding are evident in these stratigraphic units but only the last three phases affect intrusive quartz syenite gneisses of the diana complex first phase isoclinal folds in bedding have a pervasive axial plane foliation which is the regional foliation associated regional lineations are parallel to first phase fold axes foliation and lineation formed during the first phase of folding were deformed by second phase isoclinal folds which have a weak to strong axial plane foliation or slip cleavage quartz syenite of the diana complex intruded folded metamorphosed sedimentary rocks early during second phase folding and was itself isoclinally folded somewhat later during the second phase isoclinal folding of quartz syenite gneiss is associated with development of protomylonitic to mylonitic axial plane foliation which is most intense in the northwest border zone of the diana complex due to lithic contrast with rocks northwest of the border third phase folds are isoclinal to open and are locally characterized by axial plane slip cleavage or fracture cleavage the axial surfaces of folds associated with the first three phases of deformation have a general northeasterly trend and northwesterly dip but their axes have varied plunges two dimensional heart and anchor and hook patterns are a product of interference of second and third phase folds fourth phase deformation resulted in northwest trending open folds with locally developed axial plane slip or fracture cleavage interference of third and fourth phase folds is manifest in dome and basin patterns that are elongate to the northeast and overturned to the southeast similar to dome and basin patterns throughout the northwest lowlands late stage ductile shearing produced very fine grained thin mylonite and ultramylonite in shear zones that transect the preexisting protomylonite foliation in quartz syenite gneiss later brittle deformation resulted in closely spaced fractures quartz and epidote veins and local minor faults however no evidence for major faulting has been observed along this part of the adirondack highlands northwest lowlands boundary

vadose zone fluid flow estimates calculated from temperature measurements taken in the southern albuquerque basin at tome new mexico 1 closely spaced temperature measurements taken across the vadose zone at tome new mexico suggest upward and or horizontal fluid flow between 58 and 30 m depth the temperature depth profile is an independent data set that in the present example is best fitted by the exponential expression characterizing vertically upward water flow in addition expressions representing horizontal flow and combined horizontal and vertical flow also provide relatively good fits to the temperature data a unique hydrogeologic environment is present at the tome site where a thick clay layer straddles the water table at 59 m depth neutron and bulk density porosity logs indicate the clay porosity is largely liquid phase water filled it is suggested that matrix potential and perhaps osmosis are able to drive an uncommonly large vertical fluid flow for southwestern u s desert vadose zone sites because the presence of the saturated clay layer straddling the relatively shallow water table provides ideal conditions the vertical specific discharge estimate is 0 09 m yr 1 liquid water horizontal flow may also be possible in the clay layer and is estimated as 23 m yr 1 both the vertical and horizontal flow estimates are not untypical for the saturated zone in the albuquerque basin

a review of least squares inversion and its application to geophysical problems geophysical inversion involves the estimation of the parameters of a postulated earth model from a set of observations since the associated model responses can be nonlinear functions of the model parameters nonlinear least squares techniques prove to be useful for performing the inversion a common type of inversion applies iterative damped linear least squares through use of the marquardt levenberg method traditionally this method has been implemented by solving the associated normal equations in conventional ways however singular value decomposition svd produces significant improvements in computational precision when applied to the same system of normal equations iterative least squares modeling finds application in a wide variety of geophysical problems two examples illustrate the approach 1 seismic wavelet deconvolution and 2 the location of a buried wedge from surface gravity data more generally nonlinear least squares inversion can be used to estimate earth models for any set of geophysical observations for which an appropriate mathematical description is available

heat flow variations in a deep borehole near sept iles quebec canada paleoclimatic interpretation and implications for regional heat flow estimates a deep 2000m borehole in the sept iles intrusion on the north shore of the saint lawrence river in quebec canada was repeatedly logged for temperature systematic variations of the temperature gradient with depth are not correlated with the thermal conductivity we interpreted the temperature profile as follows 1 during the last glacial maximum the temperature at the base of the ice sheet was cold 5 c 2 when the region was below sea level between 10 and 5ky b p the ground surface temperature was warm 6 c 3 the average ground surface temperature dropped to 2 c at 5ky b p when the region rebounded above sea level 4 the long time averaged ground surface temperature before the last glacial maximum was 0 1 c 5 the reference heat flow 36 37mw m 2 is 4 5mw m 2 higher than estimated from the upper 1000m of the heat flow profile this interpretation can not be extrapolated to the entire region covered by the laurentide ice sheet except for extremely deep 1500m boreholes the small uncertainty 15 affecting heat flow estimates can not be eliminated

geothermics and climate change 1 analysis of borehole temperatures with emphasis on resolving power temperature depth data from six boreholes in western utah and nine boreholes in southeastern utah are reanalyzed for evidence of ground surface temperature gst histories we invert the temperature depth data using the functional space inverse algorithm of shen and beck 1991 1992 which we prefer over previous inversions of these data because of its greater sophistication and flexibility in suppressing noise gst histories for western and southeastern utah are generally consistent and suggest that temperatures in the mid 1800s are on average cooler than previous centuries followed by about 0 6 c of warming in this century attention is given to the temporal resolution of our gst solutions showing the time smearing effects of heat conduction on the solutions gst solutions represent an average ground temperature over a time window that expands as we look farther into the past the size of the time window is a function of measurement and geologic noise and limits the ultimate resolution of gst reconstructions

high resolution p t t paths from δ18o zoning in titanite a snapshot of late orogenic collapse in the grenville of new york we characterize oxygen isotope zoning within single titanite crystals from the carthage colton mylonite zone ccmz adirondack mountains new york state united states by ion microprobe smooth gradients of 18 o up to 0 6 over 90 m resulted from diffusive exchange of oxygen during cooling from peak metamorphic temperatures of 650 700 c modeling of the observed profile indicates punctuated cooling rates of 30 60 c m y along the ccmz set within long periods of much slower cooling these results indicate a previously unrecognized period of rapid cooling along the ccmz that is interpreted to result from the post ottawan collapse of the grenville mountain belt and exhumation of the central adirondack highlands at ca 1050 ma

deriving century long trends of surface temperature change from borehole temperatures we have employed a few parameter estimation fpe technique to derive information on past surface temperature variations from present day borehole temperatures synthetic experiments show that the fpe technique can separate reasonably well information on century long trends of surface temperature change from borehole temperatures within a wide range of noise levels the technique also allows a simple illustration and comparison of the inversion results both spatially and temporally we illustrate this technique by analyzing seventeen borehole temperature profiles from eleven sites in northeast usa and southeast canada utilizing a ground surface temperature model of five ramps of century long duration

ground surface temperature history in southern canada temperatures at the base of the laurentide ice sheet and during the holocene abstract we use temperature profiles from 7 deep 2000 m boreholes located in southern canada to infer ground surface temperature histories gsth during the last glacial maximum lgm and the holocene visual inspection of the heat flow and of the reduced temperature depth profiles reveals significant regional differences with some sites showing conspicuous signs of post glacial warming and other indicating only very small changes in ground surface temperature these differences are confirmed by the inversions of the temperature profiles the most prominent variations in gst are found at the sudbury ontario sites where the present ground surface temperature is high with the exception of sept iles quebec the other sites only show moderate or no variation in gst for all the sites except possibly sept iles temperatures at the base of the ice sheet during the lgm were at or slightly below the melting point of ice temperatures might have been lower a few degrees below 0 c at sept iles these results are consistent with field observations and model predictions suggesting high velocity basal flows in the ice sheet above the studied regions these new data on basal temperatures will provide better quantitative constraints on glacier flow dynamics the inversions give a chronology for the retreat of the ice sheet comparable to other proxies inversion and direct modeling show that following the ice retreat there was a warm period between 2 and 5 ka with temperatures 1 2 k higher than present the inversion yields a time for this episode 1 2 kyr more recent than that inferred by other proxies for the holocene climate optimum hco

reconstruction of the 500 year ground surface temperature history of northern awaji island southwest japan using a layered thermal property model abstract changes in the ground surface temperature gst propagating underground can be recorded as thermal perturbations to the background thermal field this paper presents a forward model of conductive propagation of gst in a layered material model with uniform thermal properties in each layer and a series of step functions as gst history this model which is expressed using the same mathematical form of that for a uniform thermal property model with a series of step functions as gst history calculates subsurface temperature perturbations that originate from the gst change by superimposing numerically solved solutions of the model with surface boundary condition of a unit function using this model we reconstruct the recent 500 year gst history from borehole temperature data in northern awaji island southwest japan by bayesian inversion the reconstructed gst history shows the onset of warming in the mid 18th century to the early 19th century and an increase of 1 1 1 3 k up to the mid 20th century from the middle to late 20th century the gst decreased by about 0 2 k the gst change in the 20th century fits the trend of mean annual surface air temperature records in kobe opposite the coast of northern awaji island the gst history in northern awaji island differs from that in ulsan in the southeastern republic of korea which is located at the same latitude as northern awaji island differences of the gst histories of these regions most likely reflect differences in sea surface temperatures in these regions

oxygen isotope zoning profiles in hydrothermally altered feldspars estimating the duration of water rock interaction the characterization of intragrain mineralogical and isotopic zoning patterns provides the basis for estimating the duration of fluid rock interaction associated with mineral replacement reactions in the rico colorado hydrothermal system oxygen isotope ratios in reaction rims on partially reacted plagioclase feldspar exhibit some of the largest gradients yet reported for individual grains to 15 o the extent of rim formation and accompanying isotopic exchange vary across the system as a function of temperature fluid isotope composition and the local fluid rock ratio distal feldspars show narrow rims with 1 8 o enrichments relative to pristine feldspars feldspars intermediate or proximal to the system s center have wide reaction rims or are completely exchanged and show 180 depletions formation times of reaction rims and associated isotopic patterns have been estimated with a coupled reaction diffusion model that suggests that hotter 250 350 c hydrothermal circulation was active for 100 300 k y in the center part of the system perhaps only while the igneous heat engine was still magma cooler 150 200 c circulation was widespread lasting for 1000 k y

carbon isotope thermometry in marbles of the adirondack mountains new york carbon isotope thermometry has been applied to coexisting calcite and graphite in marbles from throughout the adirondack mountains new york eighty nine calcite graphite pairs from the amphibolite grade nw adirondacks change systematically in temperature north westwards from 680 to 640 to 670 c over a 30 km distance reflecting transitions from amphibolite facies towards granulite facies to the north west and to the south east temperature contours based on calcite graphite thermometry in the nw adirondacks parallel mineral isograds with the orthopyroxene isograd falling above 675 c and indicate that regional metamorphic temperatures were up to 75 c higher than temperatures inferred from isotherms based on cation and solvus thermometry bohlen et al 1985 fifty five calcite graphite pairs from granulite grade marbles of the central adirondacks give regional metamorphic temperatures of 670 780 c in general agreement with cation and solvus thermometry data for amphibolite and granulite grade marbles show a 12 oo range in 13ccal and 13cgr a strong correlation between carbon isotopic composition and the abundance of graphite cgr crock indicates that the large spread in isotopic compositions results largely from exchange between calcite and graphite during closed system metamorphism the trends seen in 13c vs cgr crock and 13ccal vs 13cgr could not have been preserved if significant amounts of co2 rich fluid had pervasively infiltrated the adirondacks at any time the close fit between natural data and calculated trends of 13c vs cgr crock indicates a biogenic origin for adirondack graphites even though low 13c values are not preserved in marble delamination of 17 graphite flakes perpendicular to the c axis reveals isotopic zonation with higher 13c cores these isotopic gradients are consistent with new graphite growth or recrystallization during a period of decreasing temperature and could not have been produced by exchange with calcite on cooling due to the sluggish rate of diffusion in graphite samples located 2km from anorthosite show a decrease of 0 5 0 8 oo in the outer 100 of the grains while samples at distances over 8 km show smaller core to rim decreases of c 0 2 oo correlation between the degree of zonation and distance to anorthosite suggests that the isotopic profiles reflect partial overprinting of higher temperature contact metamorphism by later granulite facies metamorphism core graphite compositions indicate contact metamorphic temperatures were 860 890 c within 1 km of the marcy anorthosite massif if samples with a significant contact metamorphic effect cal gr 3 2 oo are not included then the remaining 38 granulite facies samples define the relation 13c cal gr 3 56 106t 2 k

geothermics and climate change 2 joint analysis of borehole temperature and meteorological data long period ground surface temperature variations contained in borehole temperature depth profiles form a complementary climate change record to high frequency but noisy surface air temperature sat records at weather stations we illustrate the benefits of jointly analyzing geothermal and meteorological data for two regions in utah where both high quality temperature depth measurements and century long sat records exist transient temperature depth profiles constructed from sat time series reproduce in considerable detail borehole transient ternperature depth profiles typical rms differences between these transient temperature profiles are less than 13 mk the analysis yields a preobservational mean pom temperature a parameter describing the long term mean surface temperature prior to the onset of sat measurements i e prior to the 20th century the average pom for these two regions is 0 6 0 2 c cooler than the 1951 1970 average sat suggesting that 20th century warming represents a real and significant departure from 19th century surface temperature values in certain cases borehole temperature profiles might be used as an independent check on long wavelength adjustments made to sat data

climate change on the colorado plateau of eastern utah inferred from borehole temperatures temperature profiles from boreholes on the colorado plateau of southeastern utah have been examined for evidence of climate change because these boreholes penetrate layered sedimentary rocks with different thermal conductivities bullard plots temperature versus integrated thermal resistance are used to estimate background heat flow and surface temperature intercepts reduced temperatures which represent departures from a constant heat flow condition are inverted for a surface ground temperature history at each borehole site using a singular value decomposition algorithm singular value cutoffs are selected by analyzing the spectral energy and the standard deviation of the model fit to the data as a function of the number of eigenvalues solutions are constructed from areas of large spectral energy and a cutoff where additional eigenvalues fail to improve the solution significantly the solution is parameterized in terms of 13 time steps increasing in duration and going back 400 years eight of nine borehole sites indicate between 0 4 and 0 8 c 0 2 c warming over the past 200 years with some evidence for accelerated warming in this century one borehole indicates local cooling over the same time period the amplitude of the warming inferred from borehole temperatures is less than that deduced from analysis of 100 year surface air temperature records at four of the five weather stations surrounding the borehole sites

intercrystalline stable isotope diffusion a fast grain boundary model we formulated a numerical model for stable isotope interdiffusion which predicts the temperatures recorded between two or more minerals and the intragranular distribution of stable isotopes in each mineral as functions of mineral grain sizes and shapes diffusivities modes equilibrium isotopic fractionations and the cooling rate of a rock one of the principal assumptions of the model is that grain boundaries are regions of rapid transport of stable isotopes this fast grain boundary fgb model describes interdiffusion between any number of mineral grains assuming that local equilibrium and mass balance restrictions apply on the grain boundaries throughout the volume modeled the model can be used for a rock containing any number of minerals and number of grain sizes of each mineral several grain shapes and any thermal history or domain size desired previous models describing stable isotope interdiffusion upon cooling have been based on dodson s equation or an equivalent numerical analogue the closure temperature of dodson is the average bulk temperature recorded between a mineral and an infinite reservoir by using dodson s equation these models have treated the closure temperature as an innate characteristic of a given mineral independent of the amounts and diffusion rates of other minerals such models do not accurately describe the mass balance of many stable isotope interdiffusion problems existing models for cation interdiffusion could be applied to stable isotopes with some modifications but only describe exchange between two minerals under specific conditions the results of fgb calculations differ considerably from the predictions of dodson s equation in many rock types of interest actual calculations using the fgb model indicate that closure temperature and diffusion profiles are as strongly functions of modal abundance and relative differences in diffusion coefficient as they are functions of grain size and cooling rate closure temperatures recorded between two minerals which exchanged stable isotopes by diffusion are a function of modal abundance and differences in diffusion coefficient and may differ from that predicted by dodson s equation by hundreds of degrees c either or both of two minerals may preserve detectable zonation which may in some instances be larger in the faster diffusing mineral rocks containing three or more minerals can record a large span of fractionations resulting from closed system processes alone the results of fgb diffusion modeling indicate that the effects of diffusive exchange must be evaluated before interpreting mineral fractionations concordant or discordant recorded within any rock in which diffusion could have acted over observable scales the predictions of this model are applicable to thermometry evaluation of open or closed system retrogression and determination of cooling rates or diffusion coefficients

intragrain oxygen isotope zoning in titanite by sims cooling rates and fluid infiltration along the carthage colton mylonite zone adirondack mountains ny usa oxygen isotopes are an attractive target for zoning studies because of the ubiquity of oxygen bearing minerals and the dependence of mineral 18 o 16 o ratios on temperature and fluid composi tion in this study subtle intragrain oxygen isotope zoning in titanite is resolved at the 10 lm scale by secondary ion mass spectrometry the patterns of d 18 o zoning differ depending on microstructural context of individual grains and reflect multiple processes including diffusive oxy gen exchange partial recrystallization grain size reduction and grain growth using the chrono logical framework provided by structural relations these processes can be related to specific events during the grenville orogeny titanite was sampled from two outcrops within the car thage colton mylonite zone ccmz a long lived shear zone that ultimately accommodated exhumation of the adirondack highlands from beneath the adirondack lowlands during the ott awan phase 1090 1020 ma of the grenville orogeny titanite is hosted in the diana metasyenite complex which preserves three sequentially developed fabrics an early nw dipping protomylonitic fabric s1 is crosscut by near vertical ultramylonitic shear zones s2 which are locally reoriented by a nnw dipping mylonitic fabric s3 texturally early titanite pre s2 shows diffusion domi nated d 18 o zoning that records cooling from peak ottawan granulite facies conditions numerical diffusion models in the program fast grain boundary yield good fits to observed d 18 o profiles for cooling rates of 50 20 cm a 1 which are considerably faster than the 1 5 cm a 1 cooling rates previously inferred for the adirondack highlands from regional thermochronology high cool ing rates are consistent with an episode of rapid shearing and exhumation along the ccmz during gravitational collapse of the ottawan orogen at c 1050 ma texturally later titanite syn s2 h as higher overall d 18 o and shows a transition from diffusion dominated to recrystallization dominated d 18 o zoning indicating infiltration of elevated d 18 o fluids along s2 shear zones and continued shear ing below the blocking temperature for oxygen 500 c for grain sizes at the study site the tex turally latest titanite post s3 h as growth dominatedd 18 o zoning consistent with porphyroblastic grain growth following cessation of shearing along the harrisville segment of the ccmz

possible ambiguities in subsurface temperature logs consideration of ground water flow and ground surface temperature change subsurface temperature regimes can commonly be influenced by both ground water flow in the saturated zone and ground surface temperature change both phenomena are widespread and one or the other may be unnoticed and or unanticipated in various temperature logs as a consequence it is often difficult to determine the relative impact of the two phenomena on the temperature depth data at a site a number of models for ground water flow ground surface temperature change and a combination of the two processes are fitted to two example temperature logs showing characteristic nonlinearity examples of the possible impact of one phenomenon on the parameters calculated for the other phenomenon demonstrate the potential interactive influence the analysis can be used to estimate potential uncertainties in calculations of ground water flow and ground surface temperature change from subsurface temperature data and therefore how interpretations of ground water flow and ground surface warming might be affected from the analysis presented the relative importance of the two phenomena may be further considered at different locations

recent warming in northwestern ontario inferred from borehole temperature profiles 1 we have used the temperature depth profiles available in the region north and northwest of lake superior in ontario canada to reconstruct the changes in ground surface temperature over the past 500 years the 49 temperature depth profiles used were obtained for heat flow measurements and are part of two different data sets one collected around 1980 the other one after 2000 we have discarded 16 of these profiles because of known nonclimatic perturbations lakes topography clear signs of groundwater circulation we have inverted the remaining 33 profiles to infer the variations in ground surface temperature individual and joint inversions consistently show a recent 150 200 years warming 1 2 k of the ground surface this warming trend is similar to that inferred for northern manitoba and saskatchewan to the northwest and in eastern ontario and quebec to the southeast however there is no clear indication that a cold episode preceded the warming of the past 200 years in northwestern ontario the mean increase in ground surface temperature for all boreholes measured between 2000 and 2003 is 1 3 0 8 k compared to 0 8 0 6 k for the 1980 data this difference suggests that the warming trend is persisting and might even have accelerated recently although the long term trend is climatic part of the recent warming may be due to deforestation by the logging industry

repeat temperature measurements in boreholes from northwestern utah link ground and air temperature changes at the decadal time scale 1 borehole temperature profiles provide a record of ground surface temperature gst change at the decadal to centennial time scale gst histories reconstructed from boreholes are particularly useful in climate reconstruction if changes in gst and surface air temperature sat are effectively coupled at decadal and longer time periods and it can be shown that borehole temperatures respond faithfully to surface temperature changes we test these assumptions using three boreholes in northwestern utah that have been repeatedly logged for temperature over a time span of 29 years we report 13 temperature depth logs at the emigrant pass observatory borehole gc 1 eight at borehole si 1 and five at borehole dm 1 acquired between 1978 and 2007 systematic subsurface temperature changes of up to 0 6 c are observed over this time span in the upper sections of the boreholes below approximately 100 m any temperature transients are within observational noise we difference the temperature logs to highlight subsurface transients and to remove any ambiguity resulting from steady state source of curvature synthetic temperature profiles computed from sat data at nearby meteorological stations reproduce both the amplitude and pattern of the transient temperature observations fitting the observations to within 0 03 c or better this observational confirmation of the strong coupling between surface temperature change and borehole temperature transients lends further support to the use of borehole temperatures to complement sat and multiproxy reconstructions of climate change

a geothermal climate change observatory first year results from emigrant pass in northwest utah temperature depth profiles measured in boreholes contain a temporal record of past changes in surface ground temperature and provide valuable constraints on climatic variations over the last few centuries however the linkage between ground temperature and meteorological variables including air temperature is imperfectly known to understand that linkage better and to document in detail how the surface ground temperature changes propagate into the subsurface where they are later measured in temperature depth logs in boreholes we have designed and installed a geothermal climate change observatory installed in arid northwest utah our emigrant pass observatory epo consists of an array of thermistor strings in the subsurface and a meteorological station at the borehole collar results from our first complete annual cycle november 1 1993 though october 31 1994 are presented ground and air temperatures generally track each other but with important time varying offsets the mean surface ground temperatures for the period are 11 3 c on the granite outcrop and 9 5 c for the partially shaded regolith site mean air temperature at a 2 m mast height above the ground is 8 8 c the ground air temperature differences are variable on timescales from days to seasons largely governed by level of absorbed solar radiation marginal precipitation 8 6 mm and ephemeral snow cover did not significantly disturb the ground air temperature difference during the year monitored instrumental measurement of air temperature has nonrandom sampling biases that present problems for observing long term changes the calculation of average annual air temperature at epo decreases by 0 34 k as the sampling rate of air temperature is decreased from 60 s to every 12 hours the attenuation and phase lag of thermal waves with depth confirm that heat conduction theory adequately describes the transient temperature field at this site and yield in situ estimates of thermal diffusivity a quantity needed to reconstruct surface ground temperature histories thermal diffusivity for the granite and regolith is 0 88 10 6 m2 s 1 and 0 45 10 6 m2 s 1 respectively energy flux calculations for the emigrant pass observatory site suggest that a geothermal climate change observatory has the capability of detecting a century scale energy perturbation that is one part in a million of the instantaneous flux

temperature and heat flux changes at the base of laurentide ice sheet inferred from geothermal data evidence from province of alberta canada using a previously published temperature log of the 2363 m deep borehole hunt well alberta canada and the results of its previous interpretation the new reconstructions of ground surface temperature and surface heat flux histories for the last 30 ka have been obtained two ways to adjust the timescale of geothermal reconstructions are discussed namely the traditional method based on the a priori data on thermal diffusivity value and the alternative one including the orbital tuning of the surface heat flux and the earth s insolation changes it is shown that the second approach provides better agreement between geothermal reconstructions and proxy evidences of deglaciation chronology in the studied region

rethinking the use of seabed sediment temperature profiles to trace submarine groundwater flow submarine groundwater fluxes across the seafloor facilitate important hydrological and biogeochemical exchanges between oceans and seabed sediment yet few studies have investigated spatially distributed groundwater fluxes in deep ocean environments such as continental slopes heat has been previously applied as a submarine groundwater tracer using an analytical solution to a heat flow equation assuming steady state conditions and homogeneous thermal conductivity these assumptions are often violated in shallow seabeds due to ocean bottom temperature changes or sediment property variations here heat tracing analysis techniques recently developed for terrestrial settings are applied in concert to examine the influences of groundwater flow ocean temperature changes and seabed thermal conductivity variations on deep ocean sediment temperature profiles temperature observations from the sediment and bottom ocean water on the scotian slope off eastern canada are used to demonstrate how simple thermal methods for tracing groundwater can be employed if more comprehensive techniques indicate that the simplifying assumptions are valid the spatial distribution of the inferred groundwater fluxes on the slope suggests a downward groundwater flow system with recharge occurring over the upper middle slope and discharge on the lower slope we speculate that the downward groundwater flow inferred on the scotian slope is due to density driven processes arising from underlying salt domes in contrast with upward slope systems driven by geothermal convection improvements in the design of future submarine hydrogeological studies are proposed for thermal data collection and groundwater flow analysis including new equations that quantify the minimum detectable flux magnitude for a given sensor accuracy and profile length

geothermal evidence from canada for a cold period before recent climatic warming three deep boreholes in a small area in quebec each having two high accuracy temperature logs separated by 22 years allow reliable determination of the ground surface temperature history during the past few centuries the temperature logs show that the recent climatic warming was preceded by a cold period near the end of the 19th century in this area the presence of such a cold period is also suggested by borehole temperature data from other areas in canada

heat flow density values and paleoclimate determined from stochastic inversion of four temperature depth profiles from the superior province of the canadian shield abstract it has long been recognized that terrestrial heat flow density observations from boreholes may be biased due to non steady surface temperature conditions this calls for paleoclimatic corrections which have conventionally been obtained by solving a forward problem based on the equation of heat conduction and models of the surface temperature history and the thermal properties structure while computationally convenient the forward method fails 1 1 to provide a stringent quantitative representation of all available data with confidence limits 2 2 to extract all available information in an optimum manner 3 3 to provide confidence limits on the parameters of interest a stochastic inverse method which overcomes these shortcomings is described the method treats the surface temperature history the thermal conductivity structure and the background heat flow as unknowns which have been constrained a priori with soft bounds the bounds ensure numerical stability and prevent unrealistic solutions when the a priori hypothesis is safe the technique is applied to geothermal data from four 600 m deep boreholes in the superior province of the canadian shield the examples show how it is possible to constrain simultaneously the recent surface temperature history and the steady state background heat flow from shallow geothermal data and furthermore show how uncertainty about the average ground temperature during the wisconsin glaciation may be taken into account