geophysical geological transect and tectonic evolution of the swiss italian alps a complete alpine cross section integrates numerous seismic reflection and refraction profiles across and along strike with published and new field data the deepest parts of the profile are constrained by geophysical data only while structural features at intermediate levels are largely depicted according to the results of three dimensional models making use of seismic and field geological data the geometry of the highest structural levels is constrained by classical along strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units because the transect is placed close to the western erosional margin of the austroalpine nappes of the eastern alps it contains all the major tectonic units of the alps a model for the tectonic evolution along the transect is proposed in the form of scaled and area balanced profile sketches shortening within the austroalpine nappes is testimony of a separate cretaceous age orogenic event west directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the meliata hallstatt ocean further to the east considerable amounts of oceanic and continental crustal material were subducted during tertiary orogeny which involved some 500 km of n s convergence between europe and apulia consequently only a very small percentage of this crustal material is preserved within the nappes depicted in the transect postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments both detachments nucleating at the interface between lower and upper crust large scale wedging of the adriatic or apulian lower crust into a gap opening between the subduced european lower crust and the pile of thin upper crustal flakes alpine nappes indicates a relatively strong lower crust and detachment between upper and lower crust

role of horizontal thermal conduction and finite time thrust emplacement in simulation of pressure temperature time paths abstract comparison of metamorphic thermal histories produced by 1 one vs two dimensional conductive models and 2 instantaneous vs finite emplacement time thrusting indicates that the simple 1d or instantaneous models applied by many petrologists generally produce pressure temperature pt paths with topologies similiar to those generated by 2d time transitive models however maximum temperatures attained by footwall rocks are significantly lower in 1d than in 2d conductive models leading us to recommend that 2d thermal effects be incorporated into models whenever possible pt paths produced by instantaneous and finite duration thrust emplacement differ significantly during the synthrusting period but the peak metamorphic conditions t max and pressure at t max eventually attained by footwall rocks during erosional unroofing are the same within minimum analytical uncertainties 50 k 100 mpa on geothermobarometric data thus if erosion begins only after the end of the thrusting event instantaneous thrusting is a reasonable simplifying assumption that introduces relatively little inaccuracy into pt models devised to examine peak metamorphic conditions

past present and future of thermochronology in one form or another geochronologists have been practicing thermochronology 1 the use of radioisotopic dating to constrain thermal histories of rocks and minerals for over 40 years building from lessons learned over these four decades thermochronology continues to evolve due to technical developments increasingly sophisticated theoretical models and an expanding range of applications in geologic and planetary science most recently interest in earth surface processes and interactions between tectonics erosion and climate has drawn attention to techniques that can address the timing and rates of processes operating at temperatures below about 300 c the purpose of this rimg volume is to assess the current state of thermochronology as of circa 2005 which is coincidentally the 100th anniversary of the first radioisotopic date rutherford 1905 1906 excellent review papers and books on specific topics within this field have been published but no single volume has yet provided a comprehensive review of current practices basic theory and illustrative examples the motivation for this volume stems from these considerations knowing that in a fast developing field a book like this can quickly become dated we tried to include sufficient review of fundamentals and the literature to offer students and new users a useful introduction to thermochronology that may have some staying power in this chapter we first review the salient points of thermochronology s history before assessing our current capabilities and challenges and then taking the risk of suggesting where the field is headed we do not provide a comprehensive history of the method that does full justice to the work of the large and growing cohort of thermochronologists in this short space we instead opted to give our perspectives on where the intellectual and technological roots of the discipline lie which run deeper and go back farther than is sometimes appreciated

two dimensional modeling of the p t t paths of regional metamorphism in simple overthrust terrains quantitative modeling of metamorphic p t t paths in thrust belts has so far been limited to one dimensional simplification we have developed a two dimensional time dependent finite element procedure capable of tracing and updating fault and strata boundaries during faulting for modeling thermal evolution of overthrust terrains we show that the two dimensionality of an overthrust and the speed and duration of thrusting have significant effects on the p t t paths of rocks in orogenic belts the results suggest that petrological studies of p t paths of rocks from different lateral positions in an orogenic belt along with two dimensional modeling procedure can put strong constraints on models of regional tectonic processes

thermal effects of linked lithospheric and upper crustal scale processes insights from numerical modeling of the cenozoic central catalan coastal ranges ne spain processes influencing the thermal state of the continental crust such as heat upwelling related to rifting and isotherm reorganization due to mass redistribution by erosion deposition and fault tectonic transport operate at different scales and their effects overlap in this paper we use lithospheric as well as crustal scale numerical modeling tools in order to quantify the contributions of these various factors to the geothermal field establishing their relative relevance we apply the models to address the thermal evolution of the catalan coastal ranges ne spain during the cenozoic a period that is characterized by a change in tectonic style from pyrenean compression to extension related to the western mediterranean rifting results of the lithospheric scale thermal model for extensional basins show an increase in the geothermal surface gradient of about 11 c km in the catalan coastal ranges during the neogene related to extensional thinning of the lithosphere in the valencia trough western mediterranean predictions of the upper crustal scale thermal model incorporating fault motions and surface mass redistribution erosion and sedimentation point to little changes in the isotherms due to fault block movements in the paleogene and neogene in contrast erosion appears to have a significant effect on the then nal history of basement rocks sited in the shallowest crust comparison of the integrated lithospheric and upper crustal scale modeling results with apatite fission track and apatite u th he thermochronology data reveals larger amounts of neogene to present cooling than predicted by the models on the basis of this unresolvable mismatch we suggest that similar to present forced fluid convection along fault planes played an important role in the evolution of the geothermal field during the neogene stage of rifting copyright 2007 by the american geophysical union

pressure temperature time paths from two dimensional thermal models prograde retrograde and inverted metamorphism two dimensional thermal models of time transitive crustal thickening and subsequent unroofing in large scale overthrust terrains generate pressure temperature time ptt paths that generally resemble those produced by earlier one dimensional instantaneous models but that differ in detail these differences in ptt path morphology are most pronounced proximal to major fault zones where postthrusting geotherms are characterized by large temperature inversions in one dimensional models but generally lack inversions in two dimensional models tests using the two dimensional fault model developed here indicate that 1 burial rate proportional to dp dt not thrust fault geometry dip angle controls the topology of synthrusting pt paths but plays only a minor role in determining the maximum temperature that rocks attain during the later unroofing stage in their thermal histories 2 normal ranges of thrusting and erosion rates and fault parameters result in pt paths with the usual sense clockwise on conventional pt diagrams counterclockwise in our diagrams 3 the amount of heating and duration of heating following the end of thrusting are a function of the rate of unroofing dp dt during this period 4 fast unroofing rates lead to the attainment of lower maximum temperatures after greater amounts of unroofing 5 the initial thermal state of the lithosphere prior to thrusting has a profound effect on pt path morphologies and on the peak metamorphic conditions attained by samples 6 for excess heat distributed across the entire lithosphere e g due to increased background thermal gradients a plot of peak temperatures experienced by metamorphic rocks versus structural depth tmax plot closely represents the initial geotherm 7 excess heat in the crust only e g increased radioactive heating in a layer yields a different result with the tmax plot corresponding to the initial geotherm only near the top of the hanging wall tmax plots for both 6 and 7 show no temperature inversion which exceeds the nominal uncertainties 50 k for geothermometric data 8 shear heating can lead to significant temperature inversions at the fault zone if the frictional coefficient is 0 6 or greater and 9 simultaneous thrusting and erosion produce pt loops significantly narrower than those resulting from sequential thrusting and erosion suggesting that any formulation which fails to account for some degree of simultaneity between thrusting and erosion represents a far endmember model forward models like those presented here provide important guidelines for understanding the sensitivity of metamorphic ptt paths to various thermal mechanical and geometric factors related to tectonism but they are generally inappropriate for reconstructing metamorphic thermal histories from actual petrologic and geochronologic data analytical inversion techniques that use a postthrusting thermal regime consistent with two dimensional forward models and that integrate values of dp dt dt dt and radioactive heating rates extracted from suites of metamorphic rocks provide the best hope for furthering our understanding of the thermal evolution of metamorphic terrains

geomagnetic excursions and paleointensities in the matuyama chron at ocean drilling program sites 983 and 984 iceland basin 1 we report natural remanent magnetization nrm directions and geomagnetic paleointensity proxies for part of the matuyama chron 0 9 2 2 ma interval from two sites located on sediment drifts in the iceland basin at ocean drilling program sites 983 and 984 mean sedimentation rates in the late matuyama chron are 15 9 and 11 5 cm kyr 1 respectively for the older part of the record 1 2 ma oxygen isotope data are too sparse to provide the sole basis for age model construction the resemblance of the volume susceptibility record and a reference 18o record led us to match the two records to derive the age models this match based on site 983 984 susceptibility is consistent with available site 983 984 benthic 18o data paleointensity proxies were derived from the slope of the nrm versus anhysteretic remanent magnetization plot for alternating field demagnetization in the 30 60 mt peak field range paleointensity lows correspond to polarity reversals at the limits of the jaramillo olduvai cobb mountain and reunion subchrons and to seven excursions in nrm component directions magnetic excursions defined here by virtual geomagnetic polar latitudes crossing the virtual geomagnetic equator are observed at 932 1048 1115 1190 1215 cobb mountain subchron 1255 1472 1480 1567 1575 gilsa subchron and 1977 ka the results indicate that geomagnetic directional excursions associated with paleointensity minima are a characteristic of the matuyama chron and probably of polarity chrons in general

cenozoic thermal evolution and tectonics of the coast mountains of british columbia 1 fission track dating apparent uplift rates and patterns of uplift the high relief of the coast mountains of british columbia has been produced in part by rapid late neogene uplift the relationship of this uplift to the presently diverse and complex plate tectonic regime off the west coast of british columbia however is not clear cut to study this problem the areal patterns rates and total amounts of cenozoic uplift from 50 to 55 n have been determined by using fission track dating of zircon and apatite separated from rocks collected at high and low altitudes along several traverses through the mountains accepting closure temperatures of 105 c 10 c and 175 c 20 c for apatite and zircon respectively and a likely closure temperature difference between zircon and apatite of 70 15 c paleogeothermal gradients have been measured at kemano c km 35 ma ago and near ocean falls king island c km 20 ma ago subcrustal heat flow is suggested to have significantly increased in the late neogene near king island uplift rates in the axial part of the northern 52 55 n coast mountains were 0 1 0 2 km ma from 25 to 15 ma ago this uplift was temporally and tectonically related to part of the subsidence in the adjacent queen charlotte basin uplift rates increased somewhat in the late miocene to about 0 4 km ma probably due to passage of the anahim hot spot beneath the area late miocene recent erosion in the north 52 55 n has reduced summit altitudes and been more extensive than farther south despite this relicts of miocene river valleys and topography are still locally preserved partly beneath 7 10 ma basalts the area of the present southern 50 to 52 n coast mountains was near sea level and experienced very low uplift rates 0 5 km ma of the southern coast mountains the profile of this uplift was broadly plateaulike and this uplift led to the inversion of the miocene coastal topography middle cenozoic uplift from 52 to 55 n was probably the result of denudation and diminishing uplift after the terminal paleocene eocene orogenic episode which grossly thickened the crust this middle cenozoic erosion resulted in the restoration of a normal crustal thickness late neogene uplift in the coast mountains was the result of thermal expansion in the mantle caused by a mantle hot spot near 53 n and changes in the geometry of the subducted slab farther south

thermochronologic evidence for orogen parallel variability in wedge kinematics during extending convergent orogenesis of the northern apennines italy analysis of 146 new apatite u th he ages six new apatite fi ssion track ages and 165 previously published apatite fi ssiontrack aft ages from the northern apennine extending convergent orogen reveals a signifi cant along strike change in post late miocene wedge kinematics and exhumation history east of 11 30 e age patterns and age elevation relationships are diagnostic of ongoing frontal accretion and slab retreat consistent with a northeastward migrating orogenic wave enhanced erosion rates of 1 mm yr over a period of 3 5 ma are recorded on the contractional pro side of the orogen and 0 3 mm yr on the extending retro side west of 11 30 e ongoing exhumation has been restricted to the range core since at least ca 8 ma at rates of 0 4 mm yr increasing to 1 mm yr in the pliocene ca 3 ma accompanied by post pliocene tilting and associated faulting this pattern can be attributed to either continued convergence but a switch in the transfer of material into the wedge to a regime dominated by underplating or out of sequence shortening or a slowdown or cessation of frontal accretion and slab retreat with enhanced pliocene uplift and erosion triggered by a deeper seated process such as lithospheric delamination complete slab detachment or slab tear these fi ndings emphasize that no single model of wedge kinematics is likely appropriate to explain long term northern apennine orogenesis and synconvergent extension but rather that different lithospheric geodynamic processes have acted at different times in different lateral segments of the orogen

influence of thrust belt geometry and shortening rate on thermochronometer cooling ages insights from thermokinematic and erosion modeling of the bhutan himalaya advancements in thermochronology and numerical modeling offer the potential to associate the age of thermochronometric samples to both exhumational and deformational processes however understanding how these components are related in compressional systems requires linking the geometry and magnitude of fault slip to the distribution and amount of erosion to address this we apply a 2 d thermokinematic model to a forward modeled balanced cross section to quantify the cooling history in fold thrust belt settings the restored cross section provides a kinematic path of rocks and structures necessary to reproduce the surface geology by assigning ages to displacement amounts we produced a range of potential velocity vectors used to calculate heat transport erosion and rock cooling we test the predicted ages against a suite of previously published thermochronometric data from the bhutan himalaya to explore the utility of the data to constrain the timing rate and geometry of fault motion as well as variations in the exhumation rate we evaluate the cooling history associated with a constant rate of shortening of 18 mm yr rates that are 2 0 1 5 0 75 and 0 5 times the constant rate and rates that vary with time to determine which kinematic history best matches the measured cooling ages the combination of relatively old apatite fission track and zircon u th he measured ages and younger 15 9 ma 40ar 39ar ages from white mica is best matched with faster rates relative to constant rates between 11 5 and 8 ma and slower than constant rates from 17 to 11 5 ma and 8 ma to present

global changes in intensity of the earth s magnetic field during the past 800kyr recent advances in palaeomagnetic and dating techniques have led to increasingly precise records of the relative intensity of the earth s past magnetic field at numerous field sites the compilation and analysis of these records can provide important constraints on changes in global magnetic field intensity and therefore on the earth s geodynamo itself a previous compilation for the past 200 kyr integrated 17 marine records into a composite curve1 with the geomagnetic origin of the signal supported by an independent analysis of 10be production made on different cores2 the persistence of long term features in the earth s magnetic intensity or the existence of long term periodic changes cannot however be resolved in this relatively short time span here we present the integration of 33 records of relative palaeointensity3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 into a composite curve spanning the past 800 kyr we find that the intensity of the earth s dipole field has experienced large amplitude variations over this time period with pronounced intensity minima coinciding with known excursions in field direction reflecting the emergence of non dipole components no stable periodicity was found in our composite record and therefore our data set does not support the hypothesis that the earth s orbital parameters have a direct and strong influence on the geodynamo

simulation of foreland basin stratigraphy using a diffusion model of mountain belt uplift and erosion an example from the central alps switzerland foreland basin stratigraphy can be considered as the result of three interacting processes thrust deformation which builds the tectonic load sedimentary and erosional processes which redistribute that load and the flexural response of the lithosphere the resultant stratigraphy of foreland basins is commonly composed of a small number of shallowing and coarsening upward cycles bounded by regional unconformities to understand the development of these unconformities we present a simple model of these three processes coupling an evolving thrust wedge on a linear elastic plate with erosion and sedimentation defined by the diffusion equation applied to topography our model demonstrates the development of regional unconformities without recourse to either eustasy or complex viscoelastic models for the continental lithosphere the model describes the thrust wedge foreland basin system in terms of four parameters 1 the effective elastic thickness of the foreland plate te 2 the sediment transport coefficient k 3 the thrust wedge advance rate 4 the surface slope of the thrust wedge the model is applied to the oligocene miocene north alpine foreland basin nafb of eastern switzerland the stratigraphy of the nafb can be simplified into two large scale shallowing upward cycles separated by an unconformity at the base of the burdigalian 22 ma geological information is taken from the nafb to estimate suitable values for the parameters listed above assuming a linear elastic lithospheric rheology the te value is estimated at 10 5 km from decompacted sediment columns data to constrain the sequential development of the thrust wedge come from structural geology the early stages 40 24 ma of compression involved a relatively low angle thrust wedge with an advance rate of approximately 2 4 mm yr at about 24 ma the wedge advance slowed down and thickened by underplating crystalline basement of the foreland plate the value for the transport coefficient has been estimated from previous studies prior to attempting to simulate the broad scale geometry of the nafb the role of each parameter was assessed individually the values for te and k are held constant throughout the simulation of the nafb at 7 5 km and 500 m yr respectively the geometry of the base burdigalian unconformity is reproduced by variations in the parameters describing the thrust wedge the surface slope angle of the wedge is increased from 2 5 to 4 over 0 2 m y and the rate of thrust advance is decreased from 2 mm yr to 0 2 mm yr during the thickening event between 24 and 23 8 ma the rejuvenation of the internal parts of the thrust load causes backtilting of the foreland basin sediments and after a time lag erosion of the distal stratigraphy over the forebulge so simulating the base burdigalian unconformity

secular variation of the geomagnetic dipole during the past 2000 years we have constructed a very simple model of a time varying geocentric dipole based on the archeomagnetic records obtained at four widely separated sites on the globe for the past 2 ka the predictions of the model in terms of directional variations have been tested against actual archeomagnetic data from 12 sites distributed over the globe they were also compared with the hongre et al 1998 time varying spherical harmonic model and with the cals7k 2 model by korte et al 2005 we find that the misfits between the predictions of our simple dipole model and the data are equivalent to those of the spherical harmonic models for the european sites and not strikingly larger for the rest of the world many discrepancies can be accounted for by uncertainties inherent to the archeomagnetic records which along with the small number and poor geographical distribution of sites leads us to conclude that the present state of the database does not allow the extraction of secular variations described by terms going beyond degree 2 it appears also that dipole tilt could be responsible for the main part of the secular variation associated with time constants exceeding 102 years in a second step we used the paleointensity records contained in the same database to construct the curve depicting the variations of the true dipole moment the present decrease of the dipole did not begin prior to 1000 years ago and the dipole was actually increasing from 0 until a d 500 the dipole moment of cals7k is lower than the present estimate probably due to large repartition of energy to higher harmonics to minimize the misfit between the inversion and the data the tilt and strength of the dipole can predict the dipole field at any site and were used to derive the contribution of the nondipole field to values of paleointensity at paris during the past 2 ka the results show that the archeomagnetic jerks are associated with various configurations depending on the phase relationship between the nondipolar and dipolar parts of the field

dominant dipole effect embedded in paleomagnetic secular variation in taiwan region over the past 7500 years abstract to study the holocene paleomagnetic field in taiwan area we performed a series of magnetic experiments to a marine sediment core or1 715 21 obtained from the offshore of eastern taiwan during the or1 715 cruise analyzed magnetic properties show that the remanent magnetization carriers of the core are uniformly dominated by single domain and pseudo single domain magnetite revealing a suitable material for relative paleointensity rpi estimation the stable and well defined characteristic remanent magnetization chrm provides the reliable determination of the inclination and declination dipole moments were further calculated by using the rpi and inclination data the variation of the dipole moments compares well to the cals10k 1b model a continuous model of archaeomagnetic and lake sediment data for the past 10000 years implying the dominance of the dipole field in taiwan area though the real declination is unavailable because of lacking core orientation during coring we could correct the values based on some critical conditions if the paleosecular variation psv is considered the virtual geomagnetic pole vgp is generally suggested to vary between 80 n and 90 n instead of coinciding with the geography north pole to fit the condition considering the psv effect the chrm declination had to be rotated 180 to get the corrected declination as a result variation patterns of the paleo inclination declination and paleointensity could be suitably determined in the study outcomes of these analyses reveal that the paleomagnetic field in taiwan region should be dominantly driven from the dipole field under the psv effect for the last 7500 years

continuous geomagnetic field models for the past 7 millennia 2 cals7k 1 we present two continuous global geomagnetic field models for recent millennia cals3k 2 covering the past 3000 years and cals7k 2 covering 7000 years from 5000 bc to 1950 ad the models were determined by regularized least squares inversion of archeomagnetic and paleomagnetic data using spherical harmonics in space and cubic b splines in time they are derived from a greatly increased number of paleomagnetic directional data compared to previous efforts and for the first time a significant amount of archeointensity data is used in this kind of global model allowing the determination of evolution of geomagnetic dipole strength while data accuracy and dating uncertainties remain a limitation reliable low resolution global models can be obtained the results agree well with previous results from virtual axial dipole moment vadm studies from archeomagnetic intensity data apart from a systematic offset in strength a comparison of model predictions with the previous 3000 year model cals3k 1 gives general agreement but also some significant differences particularly for the early epochs the new models suggest that the prominent two northern hemisphere flux lobes are more stationary than cals3k 1 implied extending considerably the time span of stationary flux lobes observed in historical models between 5000 bc and 2000 bc there are time intervals of weak dipole moment where dipole power is exceeded by low degree nondipole power at the core mantle boundary model coefficients and evaluation code can be obtained from the earthref digital archive erda together with animations and snapshots plots for every 100 years at http www earthref org detailed urls for the different material are listed in appendix a

rotation and exhumation of a thrust plane apatite fission track data from the glarus thrust switzerland apatite fission track ages and track length measurements are presented from 22 samples from the glarus alps eastern switzerland where maximum temperatures of 100 to 350 c along an alpine thrust plane were reached during late tertiary metamorphism with the exception of the northernmost sample apatite ages are fully reset and range between 5 and 12 ma apatite fission track data along a vertical profile and a horizontal profile indicate that isothermal planes were oriented parallel to the glarus thrust plane and that the thrust plane cooled below a mean apatite fission track closure temperature of 110 c at 9 ma the metamorphic pattern and fission track data indicate a south dipping thrust plane during the times of peak metamorphic conditions postmetamorphic thrusting over a distance of 10 km and gradational exhumation of the plane to a horizontal position at ca 9 ma ongoing rotation of the plane is reflected by the present dip of about 7 nnw

geomagnetic field for 0 3 ka 1 new data sets for global modeling 1 paleomagnetic and archeomagnetic records are used in both regional and global studies of earth s magnetic field we present a description and assessment of five newly compiled data sets also used in the companion paper by korte et al 2009 to produce a series of time varying spherical harmonic models of the geomagnetic field for the last 3000 years data are drawn from our compilation of lake sediment records and from the online database geomagia50v2 the five selections are available from the earthref digital archive at http earthref org cgi bin erda cgi n 944 data are grouped according to the source of material and we conducted separate assessments of reliability for archeomagnetic artifacts and lava flows the arch3k dat data set and for sediments sed3k dat the overall number of data is 55 greater than in previous compilations constrained data sets were selected using different criteria for each group winnowing of archeological data was based on uncertainties supplied by the original data providers the lake sediment data assessment relied on preassigned age uncertainties and one or more of the following comparisons with archeomagnetic data from the same region regional consistency among several lakes and consistency with global archeomagnetic models we discuss relative merits of a larger unconstrained data set or a smaller possibly more reliable one the constrained data sets eliminate a priori up to 35 of the available data in each case and rely on potentially subjective assessments of data quality given the limited data available our analyses indicate that iterative rejection of a small number 1 1 5 of outlying data during global field modeling is a preferable approach specific regional comparisons among the models and data support the conclusion that korte et al s outlier free cals3k 3 model based on all available measurements from sediments and archeological artifacts currently provides the best global representation of the 0 3 ka field the arch3k 1 model provides a better fit to the denser european archeomagnetic data and may be better in that region

nanoscale chemical zoning of chlorite and implications for low temperature thermometry application to the glarus alps switzerland abstract a combination of adapted chlorite thermometry and high spatial resolution analytical techniques tem edx fib shows that the low grade metamorphic chlorites of the glarus alps central alps switzerland do not record the peak metamorphic conditions as commonly assumed in previous studies of this reference area for low grade metamorphism chlorites have rather recorded several stages of the retrograde path through an intracrystalline nanometric scale compositional zoning the consistency of the nanoscale zoning patterns observed both within sample and along the transect suggests that local equilibrium was achieved at this spatial scale and maintained during growth or re equilibration applying recent thermobarometers we highlight that chlorites recorded a distinct behaviour between the northern and southern part of the studied transect the south of the glarus area displays a regular p t exhumation path from 3 0 0 2 kbar and 310 20 c for maximum p t estimated with conventional thermometers to 0 8 kbar and 220 c according to chlorite crystal core analysis and to 0 3 kbar and 190 c according to chlorite crystal rim analysis on the contrary the north of the glarus area shows an apparent break in the exhumation with p estimates from chlorite crystal rims 1 3 kbar higher than from chlorite crystal cores 0 8 kbar even if the absolute pressure values are fraught with large uncertainty their contrasting core rim pattern is not model dependent we try to correlate these new thermobarometric results with independent data to refine the exhumation scenario of the north helvetic flyschs confirming differential uplift along the transect this reappraisal of glarus chlorite thermometry demonstrates that an adapted thermometry analysis protocol opens new prospects for investigating the evolution of low grade metamorphic terranes

relation between rock uplift and denudation from cosmogenic nuclides in river sediment in the central alps of switzerland 1 a north south traverse through the swiss central alps reveals that denudation rates correlate with recent rock uplift rates in both magnitude and spatial distribution this result emerges from a study of in situ produced cosmogenic 10be in riverborne quartz in central alpine catchments as a prerequisite we took care to investigate the potential influence of shielding from cosmic rays due to snow glaciers and topographic obstructions to calculate a possible memory from last glacial maximum lgm glaciation and to identify a watershed size that is appropriate for systematic sampling mean denudation rates are 0 27 0 14 mm a for the alpine foreland and 0 9 0 3 mm a for the crystalline central alps the measured cosmogenic nuclide derived denudation rates are in good agreement with post lgm lake infill rates and are about twice as high as denudation rates from apatite fission track ages that record denudation from 9 to 5 ma in general denudation rates are high in areas of high topography and high crustal thickness the similarity in the spatial distribution and magnitude of denudation rates and those of rock uplift rates can be interpreted in several ways 1 postglacial rebound or climate change has introduced a transient change in which both uplift and denudation follow each other with a short lag time 2 the amplitude of glacial to interglacial changes in both is small and is contained in the scatter of the data 3 both are driven by ongoing convergence where their similarity might hint at some form of long term quasi steady state or 4 enhanced continuous quaternary erosion and isostatic compensation of the mass removed accounts for the distribution of present day rock uplift

mechanical model for the tectonics of doubly vergent compressional orogens a mechanical model of crustal shortening and deformation driven by the relative convergence of rigid underlying mantle plates explains many features of convergent orogens results based on numerical models and supported by sandbox models show that a coulomb crustal layer subject to basal velocity boundary conditions corresponding to asymmetric detachment and subduction of the underlying mantle passes through three stages of orogenic growth 1 block uplift bounded by step up shear zones 2 development of a low taper wedge over the underthrusting mantle plate and 3 development of a low taperwedge overlying the overthrusting mantle plate and verging in the opposite direction when modified by isostasy basal viscous flow surface erosion and denudation and sedimentation the resultant model orogens exhibit a variety of styles with characteristics in common with small rapidly denuded orogens large orogens with plateaus and extensional characteristics and active subduction margins with doubly vergent accretionary wedges and deformed fore arc basins

the 3d crustal structure of the alps of eastern switzerland and western austria interpreted from a network of deep seismic profiles abstract a 3d crustal model of the alps of eastern switzerland and western austria was constructed a total of twenty two dimensional deep seismic reflection profiles recorded between 1986 and 1991 were two dimensionally interpreted based on depth migrated line drawings and using correlation with surface geology refraction derived velocity depth models and correlation with intersecting or neighboring profiles the network of crustal cross sections was then unified into 3d surfaces this analysis was restricted to four crustal discontinuities 1 the top of the european basement first european basement unit including the foreland encountered going downward from the topographic surface 2 the top of the lower crust 3 the top of the european moho transition zone and 4 the european moho simulation of the seismic profiles using 3d normal incidence and shot ray tracing enabled the quantification and correction of distortions caused by out of plane reflected energy the inferred 3d crustal configuration is likely the result of the latest phase of alpine shortening during the late tertiary it depicts a smooth sse dipping european moho overlain by a concordant lower crust in the external alpine domain and a presumably wedge shaped body of lower crust in the internal alpine domain in contrast to the lower crustal discontinuities the top of the european basement reveals a highly structured 3d geometry dominated by thrust tectonics the pronounced structural disharmony with respect to the lower crust implies an intracrustal decoupling mechanism during the formation of the external basement uplifts with the zone of decoupling possibly located near the top of the lower crust comparison of the top basement topography with the mapped surface geology indicates a close relation between the basement geometry and the shape of the austroalpine basal thrust delineating the prattigau halfwindow in the west and the engadine window in the east

miocene to holocene exhumation of metamorphic crustal wedges in the nw himalaya evidence for tectonic extrusion coupled to fluvial erosion the himalayan crystalline core zone exposed along the sutlej valley india is composed of two high grade metamorphic gneiss sheets that were successively underthrusted and tectonically extruded as a consequence of the foreland directed propagation of crustal deformation in the indian plate margin the high himalayan crystalline sequence hhcs is composed of amphibolite facies to migmatitic paragneisses metamorphosed at temperatures up to 750 c at 30 km depth between eocene and early miocene during early miocene combined thrusting along the main central thrust mct and extension along the sangla detachment induced the rapid exhumation and cooling of the hhcs whereas exhumation was mainly controlled by erosion since middle miocene the lesser himalayan crystalline sequence lhcs is composed of amphibolite facies para and orthogneisses metamorphosed at temperatures up to 700 c during underthrusting down to 30 km depth beneath the mct the lhcs cooled very rapidly since late miocene as a consequence of exhumation controlled by thrusting along the munsiari thrust and extension in the mct hanging wall this renewed phase of tectonic extrusion at the himalayan front is still active as indicated by the present day regional seismicity and by hydrothermal circulation linked to elevated near surface geothermal gradients in the lhcs as recently evidenced in the himalayan syntaxes active exhumation of deep crustal rocks along the sutlej valley is spatially correlated with the high erosional potential of this major trans himalayan river this correlation supports the emerging view of a positive feedback during continental collision between crustal scale tectono thermal reworking and efficient erosion along major river systems

numerical modelling of the thermal history of the nw himalayas kullu valley india abstract this paper demonstrates two dimensional time dependent finite difference modelling of himalayan metamorphism illustrated by the kullu s lahul area himachal pradesh after the collision between india and asia and the over thrusting of the higher himalayas over the lesser himalayas it is shown that a one dimensional model with crustal thickening by a single thrust cannot satisfy the observations present in the section along the kullu valley a two dimensional solution demonstrates that during thrust sheet emplacement at geologically realistic strain rates of several centimetres a year a temperature inversion does not occur in contrast to the inversion assumed by the one dimensional instantaneous thrust models therefore the variability of two other model parameters were explicitly considered i there is a significant conductivity contrast between the different types of rocks as conductivity layers function as a barrier to the transport of heat the conductivity limit should be variable for different regions in the grid ii rocks in the higher himalayas record a phase of metamorphism that preceded the movements on the main central thrust this observation together with the knowledge that rocks with different radiogenic heat production and conductivity are not uniformly distributed in the crust emphasizes that there were considerable horizontal temperature variations across the whole region for that reason the initial temperature profile too has to be adapted for a realistic model

the accretion of foreland basin sediments during early stages of continental collision in the european alps and similarities to accretionary wedge tectonics we present structural observations from foreland basin sediments that were incorporated into the orogenic wedge of the central european alps during early stages of continental collision our analysis focuses on the prograde evolution and considers the full history of the sediments ranging from their deposition in the basin to deep burial and metamorphism at temperatures of 320 c the tectonic evolution is matched with constraints on the diagenetic alteration of the sediments for this purpose we calculate the temperatures and depths of sediment compaction and illitization as well as the associated fluid liberation the data set highlights that the tectonic incorporation of the sediments into the orogenic wedge was strongly controlled by their diagenetic state earliest deformation took place during imbrication and frontal accretion of unconsolidated and fluid saturated sediments ductile folding of the sediments occurred already at this stage and was assisted by particulate flow with the progressive consolidation of the sediments the elastic strength increased which resulted in an overall embrittlement this rheological change is recorded by the onset of out of sequence thrusting brittle faulting and the formation of massive quartz calcite veins which took place in the approximate temperature range of the seismogenic zone i e 150 350 c moreover widespread pressure solution resulted in the formation of a penetrative cleavage and records slow but long lasting deformation at low background strain rates in summary the prograde tectonic evolution of the frontal alpine wedge exhibits many similarities with the structural and mechanical evolution of accretionary wedges at active subduction zones

tectonic control on the late stage exhumation of the aar massif switzerland constraints from apatite fission track and u th he data 1 we examine the hypothesis that pliocene exhumation of the external massifs in the central alps is controlled by climatic change new thermochronological data from the western gastern aar massif are used to investigate the timing extent and reasons for neogene exhumation our data reveal that exhumation was constant with 0 5 km ma over the last 10 ma in the north in the southern part exhumation was of the same order until 3 5 ma but then increased gradually toward the south to values of up to 1 2 km ma resulting in overall northward tilting of the western aar massif we explain this accelerated exhumation in the south after 3 5 ma mainly by tectonic denudation in the footwall of the rhone simplon fault and discuss changes in deep crustal configuration which may have triggered south directed normal faulting we propose that the rhone river was structurally trapped by the rhone simplon normal fault zone which additionally enhanced erosion in the southern section of the aar massif climatic forcing may have an impact in the very late stage of exhumation due to alpine glaciation in the late pliocene

a series of papers on fluid mineral equilibrium applied to mineral deposits preface the four papers that follow this brief introduction are examples of fluid mineral equilibrium geochemistry and chemical mass transfer as it is applied to mineral deposits a field pioneered by the late harold hal c helgeson november 13 1931 may 28 2007 although helgeson is best known as a geochemist he started his career as an economic geologist and it could be said that his time in the mines shaped his later geochemical contributions to the general field of economic geology hal was born in minneapolis and grew up in saint paul minnesota after completing a degree in geology at michigan state university he worked for a year as an exploration geologist for technical mine consultants in athabasca saskatchewan and at blind river ontario 1953 1954 he then served two years during the korean war as a photo radar intelligence officer in the 497th recon tech squadron of the u s air force in wiesbaden germany after his military service he spent four years as a mining and exploration geologist for anglo american

styles of crustal deformation in compressional orogens caused by subduction of the underlying lithosphere abstract crustal scale deformation is calculated for models in which the driving mechanism corresponds to the asymmetric detachment and underthrusting of the underlying mantle lithosphere the plane strain finite element model results provide indications of the styles of deformation to be expected in small compressional orogens in particular these styles occur where shortening of the mantle lithosphere is achieved by the nearly rigid convergence between lithospheric mantles and the subduction of one mantle beneath the other the crust is modelled using coulomb plastic frictional and thermally activated power law viscous rheologies and the effects of compositional layering and variable geothermal gradients are included results are presented for a range of models in which the strength of the coupling between the model crust and its basal boundary surface denudation partial and total subduction of the crust and compositional layering are examined the results show the development of inclined step up shear zones which are a consequence of conjugate thrusting in regions of coulomb controlled rheology these zones link to sub horizontal shear zones which occur where composition and temperature render the crust viscously weak the model strain fields are interpreted in terms of deformation on discrete planes and the seismic reflectivity fabric that may be associated with this discrete deformation finally we ask whether similar seismic reflectivity fabric can be recognized in observations from small compressional orogens

the evolution of illite to muscovite mineralogical and isotopic data from the glarus alps switzerland thirty five illite and muscovite concentrates were extracted from triassic and permian claystones shales slates and phyllites along a cross section from the diagenetic alpine foreland tabular jura and borehole samples beneath the molasse basin to the anchi and epimetamorphic helvetic zone of the central alps concentrates and thin sections were investigated by microscopic x ray infrared mossbauer thermal dta and tg wet chemical electron microprobe k ar rb sr 40ar 39ar and stable isotope methods with increasing metamorphic grade based on illite crystallinity data xrd and ir the following continuous changes are observed i the 1md 2m1 polymorph transformation is completed in the higher grade anchizone ii k2o increases from 6 8 wt diagenetic zone to 8 5 10 anchizone to 10 11 5 epizone reflecting an increase in the total negative layer charge from 1 2 to 2 0 iii a decrease of the chemical variation of the mica population with detrital muscovite surviving up to the anchizone epizone boundary iv a shift of an endothermic peak in differential thermal curves from 500 to 750 c v k ar and rb sr apparent ages of the fraction 2 m decrease from the diagenetic zone to the epizone k ar ages being generally lower than rb sr ages the critical temperature for total ar resetting is estimated to be 260 30 c k ar and rb sr ages become concordant when the anchizone epizone boundary is approached the stable isotope data on the other hand show no change with metamorphic grade but are dependent on stratigraphic age these results suggest that the prograde evolution from 1 md illite to 2m1 muscovite involves a continuous lattice restructuration without rupture of the tetrahedral and octahedral bonds and change of the hydroxyl radicals however this is not a recrystallization process this restructuration is completed approximately at the anchizone epizone boundary the isotopic data indicate significant diffusive loss of 40ar and 87sr prior to any observable lattice reorganization the restructuration progressively introduces a consistent repartition of ar and k in the mineral lattices and is outlined by the 40ar 39ar age spectra concordant k ar and rb sr ages of around 35 30 ma with concomitant concordant 40ar 39ar release spectra are representative for the main phase of alpine metamorphism calanda phase in the glarus alps a second age group between 25 and 20 ma can probably be attributed to movements along the glarus thrust ruchi phase while values down to 9 ma in regions with higher metamorphic conditions suggest thermal conditions persisting at least until the middle tortonian

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

climate induced rebound and exhumation of the european alps foreland basins record the regional isostatic compensation of mountain belts during periods of crustal thickening they subside and when erosion unloads the mass of the mountains the basins rebound and are eroded in order to evaluate this mechanism for rebound it is critical that the timing and magnitude of erosion are documented we present data estimating the timing and magnitude of late orogenic or postorogenic erosion in the north alpine foreland basin of switzerland mineral cooling ages demonstrate that the basin underwent 1 3 km of erosion soon after 5 ma this erosion coincided with a decline in structural deformation in the swiss alps and a doubling of sediment accu mulation rates in surrounding depocenters we propose that accelerated erosional un roofing of the swiss alps triggered isostatic rebound and erosion of the foreland basin after 5 ma a projection of the isostatic rebound of the basin into the mountains suggests that at least 6 5 km of erosion should have occurred in the high topography of the aar massif accelerated erosion in the swiss alps at that time is explained by an increase in atmospheric moisture driven by an intensification of the atlantic gulf stream at 4 6 ma consequently we propose that the changing erosional capacity of the climate triggered late orogenic to postorogenic mass reduction and isostatic rebound of the swiss alps and their neighboring foreland basin

fission track and numerical thermal modeling of differential exhumation of the glarus thrust plane switzerland abstract geometry and differences in metamorphic grade along the glarus thrust external european alps can be explained by a restoration of the hanging wall some 10 km toward the south and back rotation of the thrust plane into a ramp flat ramp geometry the apatite fission track ft age pattern from the area suggests that isotherms were parallel to the thrust plane during cooling of the rocks along the thrust plane below the apatite closure temperature two forward modeling programs that both produce time temperature paths are used to constrain the thermal and structural evolution of differential exhumation along the glarus thrust a a two dimensional finite difference thermal model is used to examine differential exhumation of the thrust plane starting from an assumed horizontal position of the middle part of the glarus thrust at some 10 ma when parallel to the paleo isotherms five locations in the crustal section corresponding to locations on a final horizontal and vertical sampling traverse record their time temperature t t history during exhumation along particle paths the near surface temperature distribution is strongly influenced by the development of a simplified step like topographic relief which causes all modeled samples to reach the surface at the end of the modeled time period b the calculated t t paths of these five modeled samples were used to forward model apatite ft data based on an existing annealing model by comparison between synthetically generated ft data and actual measured ft samples the exhumation history of the glarus alps was evaluated with respect to its thermal and temporal brackets several parameters such as the location of the rotation point the thermal gradient and the topography have significant influence on model results best fit models produce results that are consistent with independent geological and geophysical information

tectonic assembly of inverted metamorphic sequences inverted metamorphic sequences are characterized by peak metamorphic temperatures that increase structurally upward with isograds that are typically parallel to associated thrust faults a fully coupled thermal mechanical model for convergent orogens shows how an inverted sequence can be tectonically assembled in a crustal scale ductile shear zone at moderate to high rates of synorogenic erosion model inverted sequences form by tectonic juxtaposition of points with widely differing initial positions that reach peak temperatures at different times and in different places within the model orogen and thus do not represent metamorphic or thermal gradients inverted crustal isotherms are not required to produce model inverted isograds model results agree well with metamorphic pressure temperature data from the main central thrust zone of the central nepal himalayas

variable late neogene exhumation of the central european alps low temperature thermochronology from the aar massif switzerland and the lepontine dome italy 1 several recent studies proposed an important increase in exhumation rate in the western european alps since circa 5 4 ma in order to assess potential spatial differences in exhumation histories we present new apatite fission track aft and apatite u th he ahe ages from the central aar massif guttannen area switzerland and the western lepontine dome formazza area italy internal u th zoning in apatites explains alpha ejection corrected ahe ages that are older than the corresponding aft ages in this study a qualitative interpretation of aft and ahe age elevation relationships suggests a two phase 9 7 and 5 3 ma exhumation scenario affecting the central alps with a stronger expression of the pliocene signal in the formazza area however a quantitative evaluation of exhumation scenarios using the 3 d heat equation solver pecube highlights the existence of several other likely scenarios casting doubt on the validity of a qualitative interpretation of the age elevation relationships in formazza scenarios suggested by quantitative modeling include continuous denudation at a rate of 750 m ma and a one step exhumation rate change from 300 to 1000 m ma at 5 ma in guttannen they include continuous denudation at a rate of 400 m ma with valley deepening and two periods of higher exhumation rate increasing from 300 to 700 m ma repeatedly at 9 7 and at 5 3 ma contingent upon further flexural isostatic modeling the magnitude of exhumation recorded in the axial region of the alps since circa 5 ma does not appear sufficient to solely explain the denudation recorded in the north alpine foreland basin

kinematics exhumation and sedimentation of the north central andes bolivia an integrated thermochronometer and thermokinematic modeling approach quantifying mountain building processes in convergent orogens requires determination of the timing and rate of deformation in the overriding plate in the central andes large discrepancies in both timing and rate of deformation prevent evaluating the shortening history in light of internal or external forcing factors geologic map patterns age and location of reset thermochronometer systems and synorogenic sediment distribution are all a function of the geometry kinematics and rate of deformation in a fold thrust belt foreland basin ftb fb system to determine the timing and rate of deformation in the northern bolivian andes we link thermokinematic modeling to a sequentially forward modeled balanced cross section isostatically accounting for thrust loads and erosion displacement vectors in 10 km increments are assigned variable ages to create velocity fields in a thermokinematic model for predicting thermochronometer ages we match both the pattern of predicted cooling ages with the across strike pattern of measured zircon fission track apatite fission track and apatite u th he cooling ages as well as the modeled age of fb formations to published sedimentary sections results indicate that northern bolivian ftb deformation started at 50 ma and may have begun as early as 55 ma acceptable rates of shortening permit either a constant rate of shortening 4 5 mm yr or varying shortening rates with faster rates 7 10 mm yr at 45 50 ma and 12 8 ma significantly slower rates 2 4 mm yr from 35 to 15 ma and indicate the northern bolivian subandes started deforming between 19 and 14 ma