quantifying exhumation from apatite fission track analysis and vitrinite reflectance data precision accuracy and latest results from the atlantic margin of nw europe

fate of water transported into the deep mantle by slab subduction abstract the roles of water in the mantle transition zone lower mantle and the core mantle boundary are investigated the evidence for a wet mantle transition zone has been suggested based on hydrous mineral inclusions in diamond seismic wave velocity and electrical conductivity profiles together with mineral physics data are consistent with existence of stagnant slabs in a wet mantle transition zone the transition zone may contain continental crustal components in these stagnant slabs dense hydrous magmas may exist at the base of the upper mantle fluids or volatile rich magmas may also exist at the top of the lower mantle due to the large contrast in water contents between the mineral assemblages in the mantle transition zone and the lower mantle and the crossing of the convective descent of the cold hydrated materials dense magmas are not likely to be formed at the top of the lower mantle and hydrous magmas generated in this region move upwards and metasomatize the overlying mantle transition zone water can be transported deeper into the lower mantle by gravitational collapse of the stagnant slabs which supply water into the lower mantle including the core mantle boundary hydrous h solid solution may be the most important hydrous phase in lower mantle and existence of this phase reduces the aluminum content in coexisting bridgmanite and post perovskite and thus modifies the physical properties of the lower mantle hydrous h solid solution can accumulate at the base of the lower mantle the iron water reaction at the core mantle boundary can also create pyrite type feooh which can be a potential candidate material for the ultralow velocity zone ulvz

early tertiary paleo thermal effects in northern england reconciling results from apatite fission track analysis with geological evidence abstract the paleozoic lake district block in northwest england has traditionally been thought of as tectonically stable since the late paleozoic receiving only small thicknesses of late paleozoic to mesozoic cover although some workers have put forward different views apatite fission track analysis afta data from outcrop samples across the region reveal early tertiary paleotemperatures around 100 c requiring kilometre scale late paleozoic and mesozoic cover removed during tertiary uplift and erosion with no evidence for elevated basal heat flow in nw england during the early tertiary and no a priori justification for invoking it earlier studies favoured an explanation involving burial by up to 3 km of overburden removed during tertiary uplift and erosion this conclusion was met with scepticism by many workers and provoked a range of comments and criticisms with a variety of alternative interpretations put forward although these are also open to criticism results from the west newton 1 hydrocarbon exploration well on the northern flank of the lake district gave the first indication of a possibly more realistic interpretation involving a combination of elevated heat flow and more restricted burial but some aspects of the interpretation of these data were equivocal more detailed sampling was therefore undertaken in order to shed more light on the origin of the elevated early tertiary paleotemperatures observed across nw england new afta data in outcrop samples from different elevations around sca fell characterised by the highest elevations in the lake district with the summit of scafell pike at 978 m asl define an early tertiary paleogeothermal gradient of 61 c km and require around 700 m of section removed from the summit during tertiary uplift and erosion these results together with those from the west newton 1 well provide strong support for an interpretation involving early tertiary paleogeothermal gradients between 50 and 100 higher than present day values providing clear evidence of elevated basal heat flow during the early tertiary contrary to earlier assumptions combined with amounts of section removed during tertiary exhumation varying between 0 7 km from mountain peaks and 1 5 2 km from coastal plains and glacial valleys near sea level over the region this interpretation finally provides a geologically plausible mechanism for the origin of the observed early tertiary paleo thermal effects in nw england

results of recent cocorp profiling in the southeastern united states summary recently acquired cocorp profiles in the southeastern united states show that 1 reflections associated with the appalachian detachment are prominent beneath the inner piedmont of western georgia but do not extend further southeast beneath the pine mountain belt 2 the brunswick magnetic low is associated with a broad zone of crustal penetrating dipping reflections that probably marks the alleghanian suture in the southeastern u s 3 the south georgia basin is a composite feature consisting of several half graben locally containing 5 km of triassic e jurassic basin fill these basins occur within the interior of the alleghanian orogen but are not specifically associated with alleghanian suture 4 across strike crustal thickness variation and distribution and character of lower crust and moho reflections in the southern appalachians is grossly similar to that observed in other parts of the appalachiadhercynian orogenic belt global comparisons suggest that these regional variations are a consequence of post collisional extensional tectonics rather than a primary palaeozoic or older feature of the orogenic belt

timing and mechanisms for the generation and modification of the anomalous topography of the borborema province northeastern brazil abstract the results of apatite fission track analysis in 14 granitic gneissic samples from two regional transects across the borborema plateau northeastern brazil show evidence for two dominant paleothermal events a late cretaceous cooling event beginning sometime between 100 and 90 ma and a second cooling event in the neogene the distribution of the fission track results suggests that the cooling events have a broad regional expression and are consistent with the geologic record in the araripe basin western borborema province which attests to a post albian uplift of the whole region we hypothesize that the first event is due to the uplift and denudation of regional permanent topography generated after the breakup of brazil and africa such topography is predicted by models of continental margin extension in which continental lithosphere thinning is followed by thickening of the adjacent hinterland lithosphere and crust kusznir n j karner g d 2007 continental lithospheric thinning and breakup in response to upwelling divergent mantle flow application to the woodlark newfoundland and iberia margins in karner g d manatschal g pinheiro l eds imaging mapping and modeling continental lithosphere extension and breakup special publication 282 geological society london pp 389 419 in northeastern brazil this extension engendered topography may have been amplified by magmatic underplating related to the saint helena and ascension plumes the miocene cooling event 20 0 ma occurred at a time characterized by the transition from carbonate ramp to progradational clastic systems on the pernambuco paraiba margin and the offshore potiguar basin this same stratigraphic response characterizes the neogene stratigraphy of many passive margins and attests to a global increase in the delivery of clastics to margins the simplest explanation of which is a climate change that accentuated erosion of pre existing topography thus the present rugged landscape of northeastern brazil is interpreted to be a product of this younger denudation event a corollary of this study is that the history distribution and delivery of clastics to the northern and northeastern margins of brazil are a function of the regional development of the continental landscape during the late cenozoic

sound velocity measurements in dhcp feh up to 70 gpa with inelastic x ray scattering implications for the composition of the earth s core abstract we have determined the density evolution of the sound velocity of dhcp fehx x 1 up to 70 gpa at room temperature by inelastic x ray scattering and by x ray diffraction we find that the variation of vp with density is different for the ferromagnetic and nonmagnetic dhcp fehx and that only nonmagnetic dhcp fehx follows birch s law combining our results with birch s law for iron and assuming an ideal two component mixing model we obtain an upper bound of the hydrogen content in the earth s inner core 0 23 6 wt h corresponding to feh0 13 3 the iron alloy with 0 23 6 wt h can satisfy the density and compressional and shear sound velocities of the prem inner core assuming that there are no other light elements in the inner core

static compression of hydrous silicate melt and the effect of water on planetary differentiation abstract high pressure experiments using the sink float method have bracketed the density of hydrous iron rich ultrabasic silicate melt from 1 35 to 10 0 gpa at temperatures from 1400 to 1860 c the silicate melt composition was a 50 50 mixture of natural komatiite and synthetic fayalite water was added in the form of brucite mg oh 2 and was present in the experimental run products at 2 wt and 5 wt levels as confirmed by microprobe analyses of total oxygen buoyancy marker spheres were olivines and garnets of known composition and density the density of the silicate melt with 5 wt water at 2 gpa and 1500 c is 0 192 g cm 3 less than the anhydrous form of this melt at the same p and t this density difference gives a partial molar volume of water in silicate melt of 7 cm 3 mol 1 which is similar to previous studies at high pressure the komatiite fayalite liquids with 0 and 2 wt h 2 o have extrapolated density crossovers with equilibrium liquidus olivine at 8 and 9 gpa respectively but there is no crossover for the liquid with 5 wt h 2 o these results are consistent with the hypothesis that dense hydrous melts could be gravitationally stable atop the 410 km discontinuity in the earth the results also support the notion that equilibrium liquidus olivine could float in an feo rich hydrous martian magma ocean extrapolation of the data suggests that feo rich hydrous melt could be negatively buoyant in the earth s d region or atop the core mantle boundary cmb although experiments at higher pressure are needed to confirm this prediction

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

water transport into the deep mantle and formation of a hydrous transition zone abstract the phase relations in the peridotite water system to the top of the lower mantle reveal that a certain amount of water can be transported and stored in the transition zone by various hydrous minerals resulting in formation of a hydrous transition zone results of preliminary experiments to clarify the effect of water on kinetics of the olivine wadsleyite transformation are given and show that water enhances the transformation kinetics significantly there are potential dehydration sites in the deep mantle four sites along the descending slabs depending on their temperature profiles i e the mantle wedge of the subduction zone mantle transition zone top of the lower mantle where hydrous ringwoodite and superhydrous phase b decompose and deep in the lower mantle around 1200 1500 km depth where decomposition of phase d g occurs we also expect one site of dehydration melting at the base of the upper mantle where the hot mantle plume hydrated in the transition zone can be dehydrated the transition zone can serve as a water absorber for the mantle scale water circulation system some of the recent seismic works including the p wave tomography images reveal the existence of low velocity anomalies in the transition zone suggesting possibly a wet transition zone elevation of the 410 km discontinuity and lack of clear evidence for a metastable olivine wedge in cold slabs may be consistent with the equilibrium phase transformation from olivine to wadsleyite in cold and wet slabs on the basis of our kinetic study of the transformation under wet conditions

east asia seismotectonics magmatism and mantle dynamics abstract in this article we review the significant recent results of geophysical studies and discuss their implications on seismotectonics magmatism and mantle dynamics in east asia high resolution geophysical imaging revealed structural heterogeneities in the source areas of large crustal earthquakes which may reflect magma and fluids that affected the rupture nucleation of large earthquakes in subduction zone regions the crustal fluids originate from the dehydration of the subducting slab magmatism in arc and back arc areas is caused by the corner flow in the mantle wedge and dehydration of the subducting slab the intraplate magmatism has different origins the continental volcanoes in northeast asia such as changbai and wudalianchi seem to be caused by the corner flow in the big mantle wedge bmw above the stagnant slab in the mantle transition zone and the deep dehydration of the stagnant slab as well the tengchong volcano in southwest china is possibly caused by a similar process in bmw above the subducting burma microplate or indian plate the hainan volcano in southernmost china seems to be a hotspot fed by a lower mantle plume associated with the pacific and philippine sea slabs deep subduction in the east and the indian slab s deep subduction in the west down to the lower mantle the occurrence of deep earthquakes under the japan sea and the east asia margin may be related to a metastable olivine wedge in the subducting pacific slab the stagnant slab finally collapses down to the bottom of the mantle which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and cause the slab plume interactions some of these issues such as the origin of intraplate magmatism are still controversial and so further detailed studies are needed from now

aluminous hydrous mineral δ alooh as a carrier of hydrogen into the core mantle boundary 1 in situ x ray diffraction experiments were conducted to determine the stability field of the aluminous hydrous mineral alooh over the entire conditions of the lower mantle we observed alooh at pressures from 33 to 134 gpa at 1350 2300 k indicating that this hydrous mineral in the sediment layer of a subducting slab could transport hydrogen into the core mantle boundary cmb

heterogeneous exhumation in the inner moray firth uk north sea constraints from new afta and seismic data integration of regional seismic interpretation sonic velocity vitrinite reflectance and apatite fission track analysis afta studies has demonstrated that the western region of the moray firth rift arm uk north sea experienced pronounced exhumation during the cenozoic although this basin is usually considered to have experienced regionally uniform exhumation interpretation of new seismic data has revealed the presence of a major system of post jurassic normal faults with throws commonly in the range of 10 300 m and locally exceeding 1 km new high quality seismic data are used in combination with afta and vitrinite reflectance data to investigate the role of extensional faulting during exhumation of this basin results of this interpretation not only confirm the offsets across major faults but also show that greater exhumation and erosion occurred on their footwalls than on their hanging walls we conclude that the localized differential exhumation is the result of superposition of local or short spatial wavelength extensional tectonics upon regional long spatial wavelength exhumation these results suggest that differential exhumation might be characteristic of unroofed rift basins where normal faults subcrop the exhumation related unconformity and that in such cases thermal histories from footwall locations may yield inaccurate predictions of the burial history of hanging wall depocentres inaccurate burial histories will lead to a misrepresentation of the thermal history with an impact on the estimation of hydrocarbon source rock maturity for petroleum basins

u th systematics of dispersed young volcanoes in ne china asthenosphere upwelling caused by piling up and upward thickening of stagnant pacific slab abstract young 300 to 5500years old dispersed intraplate volcanism characterized by small volume of melt and large compositional variability occurred over ne china at jingbohu long gang tianchi and wudalianchi these young volcanic rocks provide ideal opportunities for investigating the mechanism of dispersed continental volcanism using short lived uranium series isotopes we present systematic u series nd sr pb isotope and trace element analyses of the young lavas from ne china jingbohu lavas display variable extents of 230th excesses 10 to 28 and moderately depleted nd isotopic compositions end 1 5 to 3 3 long gang lavas have pronounced 33 to 35 230th excesses and slightly depleted nd isotopic compositions end 0 5 to 0 7 the tianchi lavas display moderate 12 230th excesses and slightly enriched nd isotopic compositions end 1 0 to 1 1 230th enrichments in all these volcanic rocks are uncharacteristic of melts generated by subduction the strongest evidence against the involvement of subduction related fluids is derived from the long gang lavas having more than 30 230th excesses low u th sr th and ba th ratios and positive nb and ta anomalies the fluids released from the subduction of the pacific plate under the eurasian plate might have already been completely lost before the slab reached the mantle beneath ne china we postulate that in addition to the convective circulation process the continuous piling up and upward thickening of stagnant pacific slab in the mantle transition zone may help drive a broad asthenosphere upwelling far from the trench leading to mantle partial melting and the formation of the young volcanoes in ne china in addition our u th disequilibrium data provide constraints on magma evolution time the magma evolution time from low sio2 47 5 basalt to higher sio2 50 4 basalt at long gang is within 10 thousand years 10ka the magma evolution time from trachyte to rhyolite at tianchi volcano is also less than 10ka if the tianchi silicic rocks were evolved from long gang basaltic magmas with minor crustal assimilation then the magma evolution time from basaltic magma to silicic magmas is less than 110 thousand years

appraisal of u th he apatite thermochronology as a thermal history tool for hydrocarbon exploration an example from the taranaki basin new zealand the taranaki basin contains most of new zealand s commercial hydrocarbon reserves the southern parts of the taranaki basin underwent inversion during the late miocene with published afta apatite fission track analysis and vitrinite reflectance data suggesting approximately 2 5 3 km of section eroded from the structure on which the fresne 1 well was drilled consistent with estimates from reconstructions based on seismic sections the well constrained tectonic and thermal history framework for this well section established by earlier studies provides an ideal test bed for the thermochronological technique of apatite u th he dating helium ages determined in apatites from the earlier afta study decrease from about 6 ma at about 400 m depth to about 1 ma at 2465 m although these results are qualitatively consistent with late miocene cooling quantitative modeling of u th he ages based on best fit thermal histories derived from new afta analyses using improved methods suggests that cooling was protracted involving accelerated cooling during the pliocene possibly indicating a discrete pliocene inversion phase integration of afta and u th he dating can provide improved thermal history constraints in sedimentary basins particularly on cooling rates and or resolution of multiple thermal events by independently defining the timing of peak maturation in relation to formation of potential trapping structures this information offers the potential for improved assessment of hydrocarbon prospectivity and reduced exploration risk

evidence from apatite fission track analysis for the post devonian burial and exhumation history of the northern highlands scotland abstract devonian and older rock samples from outcrops in the northern scottish highlands have undergone protracted cooling since they reached palaeotemperatures of 110 c or more in the late palaeozoic to early mesozoic the results not only suggest that the northern highlands region has experienced kilometre scale exhumation since the late palaeozoic but also that devonian and possibly permo carboniferous sedimentation was probably more extensive than current outcrop patterns would imply a permian outcrop sample from the minches basin reached a maximum palaeotemperature of 70 90 c prior to the onset of cooling in the early tertiary while data from devonian and older samples suggest an acceleration in the rate of cooling in the early tertiary the magnitude of early tertiary palaeotemperatures on the mainland adjacent to the inner moray firth imf indicate similar amounts of tertiary exhumation to those derived from compaction analyses for the imf however to the west the magnitude of tertiary cooling cannot be solely ascribed to exhumation and a contribution of heating due to hydrothermal effects and or elevated heat flow associated with the tertiary igneous complex may also need to be invoked

thermal and tectonic evolution of the falkland islands implications for hydrocarbon exploration in the adjacent offshore region apatite fission track and vitrinite reflectance data combine to suggest that the falkland islands experienced three discrete episodes of heating and cooling during the phanerozoic each of which can be related to major changes in the plate tectonic setting of the islands combined with published data from the adjacent offshore areas the results provide unique insights into the behaviour of the region during the phases of convergent and divergent tectonic movements that have affected the region since the permian initial cooling of the falkland islands in the late permian was initially restricted to west falkland and was the result of differential uplift and erosion of west falkland relative to east falkland coinciding with d2 gondwanian deformation subsequent early jurassic cooling of both east and west falkland was associated with plume related thermal uplift preceding the separation of east and west gondwana and the development of the falkland plateau basin the falkland islands experienced renewed heating during the mesozoic probably due to increased burial suggesting that the offshore basins originally extended onto the present onshore region late cretaceous early tertiary cooling of the falkland islands was contemporaneous with the development of a transpressional plate boundary along the southern margin of the falkland plateau resulting in erosion of the islands that were situated on a flexural forebulge

in situ x ray diffraction study of post spinel transformation in a peridotite mantle implication for the 660 km discontinuity abstract we present the phase relations in anhydrous cao mgo feo al2o3 sio2 pyrolite to examine the influence of compositional difference between pyrolite and mg2sio4 on the post spinel phase transformation it is shown that in the pyrolite system the transformation occurs at about 0 5 gpa lower pressure relative to mg2sio4 we have carried out several in situ x ray diffraction experiments on ringwoodite to mg perovskite ferropericlase and backward transformations and found that post spinel transformation boundary can be expressed as p gpa 0 0005 t k 23 54 using the gold equation of state by tsuchiya t tsuchiya first principles prediction of the p v t equation of state of gold and the 660 km discontinuity in earth s mantle j geophys res 108 2003 doi 10 1029 2003jb002446 the interval for coexisting ringwoodite and mg perovskite was found to be 0 1 0 5 gpa the discrepancy between our data and the depth of the seismic discontinuity global average 654 km is about 20 km at 1850 k based on the results of in situ measurements we confirmed that the difference in chemical composition between pyrolite and mg2sio4 cannot modify the clapeyron slope of the post spinel transformation using experimental data and assuming the average mantle temperature 1850 k at 660 km we can account for only a half of variations in the depth of the 660 km discontinuity in subduction zones and at hot spots an additional explanation for the observed seismological variations at the 660 km discontinuity is required and may reflect influence of other minor components or volatiles

stability of hydrous silicate at high pressures and water transport to the deep lower mantle hydrous magnesium rich silicates play an important role in transporting water into the deep mantle when oceanic plates subduct as slabs but were thought to dissociate at pressures of 44 gpa in situ x ray measurements in conjunction with a multi anvil apparatus show that hydrous phases of magnesium rich silicate are stable under lower mantle conditions up to 50 gpa and may transport water to deeper layers of the mantle the presence of water strongly influences the structure composition and dynamics of the earth s deep mantle1 2 3 4 hydrous magnesium rich silicates play an important role in transporting water into the deep mantle when oceanic plates subduct as slabs the highest pressure form of such hydrous silicates phase d was reported to dissociate into an assemblage of nominally anhydrous phases plus water at pressures of about 44 gpa equivalent to 1 250 km depth5 in this way free water would be released in the middle region of the lower mantle which suggests that no water can reach the deeper regions of the lower mantle here we use in situ x ray measurements in conjunction with a multi anvil apparatus using sintered diamond anvils to show that hydrous phases are stable under lower mantle conditions up to 50 gpa we found that phase d transforms to an assemblage with another hydrous silicate mgsih2o4 named phase h at pressures above about 48 gpa our results suggest that phase h is the dominant hydrous silicate in descending slabs and may be found at depths far deeper than 1 250 km we conclude that a significant amount of water is retained in the descending slabs and may be delivered to the deepest part of the lower mantle

the thermal history of the eastern officer basin south australia evidence from apatite fission track analysis and organic maturity data the eastern officer basin in south australia contains a neoproterozoic to devonian succession overlain by relatively thin 500 m permian mesozoic and tertiary deposits within the basin fill there are several major unconformities representing uncertain amounts of erosion three of these surfaces are associated with regional deformational events regional unconformities formed between 560 and 540 ma petermann ranges orogeny approximately 510 490 ma delamerian orogeny 370 300 ma alice springs orogeny 260 150 ma and 95 40 ma afta results from 13 samples of neoproterozoic cambrian and permian sedimentary rocks in five wells giles 1 manya 2 5 and 6 and lake maurice west 1 show clear evidence for a number of distinct thermal episodes results from all samples are consistent with cooling from the most recent thermal episode beginning at some time between 70 and 20 ma maastrichtian miocene afta results from giles 1 indicate at least two pre cretaceous thermal episodes with cooling beginning between 350 and 250 ma carboniferous permian and between 210 and 110 ma late triassic albian results from manya 2 5 and 6 and lake maurice west 1 show evidence for at least one earlier higher temperature event with cooling from elevated paleotemperatures beginning between 270 and 200 ma late permian to late triassic these episodes can be correlated with other cooling erosional events outside the study area and the afta derived paleotemperatures are consistent with kilometre scale erosion for each of the episodes identified integration of the afta data with organic thermal maturation indicators mpi in the manya and giles 1 wells suggests that the cambrian and neoproterozoic successions in the northern part of the study area reached peak maturation prior to the permian while limited data from lake maurice west 1 allows peak maturation to have occurred as young as the late permian to late triassic thermal episode revealed by afta the approach outlined in this study is relevant to all ancient basins as it emphasises the importance of understanding events associated with neighbouring regions the thermal history of the officer basin as with most other ancient basins has been strongly affected by significant tectonic events throughout its history even though younger deposits are not preserved in the basin itself the recognition of these younger events and the implications of these events for the depositional history is important as it allows identification of the best regions for preservation of early generated hydrocarbons and in some cases suggests areas where generation of hydrocarbons could have occurred more recently than previously thought

the great west african tertiary coastal uplift fact or fiction a perspective from the angolan divergent margin 1 we explore exhumation in the coastal kwanza basin by combining analyses of tertiary hiatuses and apatite fission tracks planktonic biozones show five major hiatuses in the oligo miocene and plio pleistocene between gaps oligo miocene strata accumulated under marine conditions a marine setting refutes the idea of a massively raised coastal plateau in the mid tertiary marine conditions continued until 5 ma fission track data suggest three thermal events 150 ma during rifting and volcanism 100 70 ma during shortening and volcanism and 20 10 ma during exhumation tertiary uplift was spatially highly variable for the kwanza basin we infer that tertiary uplift on the west african margin is indeed a fact but that estimates of uplift timing and size are unreliable when extrapolated to adjoining areas massive uplift 2000 4000 m of the precambrian craton had little structural effect in the outer basin instead minor uplifts on the shelf drove late tertiary deformation on the slope

seismic image and origin of the changbai intraplate volcano in east asia role of big mantle wedge above the stagnant pacific slab abstract we determined p wave tomography of the crust and upper mantle under the changbai volcanic area in northeast asia by using 289 318 arrival time data from 4802 local earthquakes and 9599 teleseismic events a prominent low velocity anomaly is clearly imaged in the crust and upper mantle down to about 410 km depth beneath the changbai volcano a broad high velocity anomaly is revealed in the mantle transition zone and deep earthquakes occurred actively there suggesting that the subducting pacific slab is stagnating in the mantle transition zone under east asia our results suggest that the formation of the changbai and other intraplate volcanoes in northeast asia is related to the upwelling of hot and wet asthenospheric materials in the big mantle wedge above the stagnant pacific slab hence the active intraplate volcanoes in northeast asia are not hotspots related to deep mantle plumes but are caused by plate tectonic processes in the upper mantle

compositional influences on fission track annealing in apatite and improvements in routine application of afta reg sign use of apatite fission track analysis afta reg sign to reconstruct thermal histories in sedimentary basins relies critically on detailed knowledge of fission track annealing kinetics the influence of apatite cl content on annealing rates has long been recognized initial quantitative information on annealing rates came from a monocompositional apatite with approximately 0 45 wt cl subsequent work showed that annealing rates decrease with cl content so that pure fluorapatite are totally annealed at temperatures 10 to 20 degrees c less than those containing 0 5 wt cl we have recently completed a major investigation of compositional influences on fission track annealing using laboratory experiments and data from geological conditions using apatites from sedimentary sequences currently at their maximum burial depth in which afta parameters are dominated by the present day temperatures incorporation of vr data from the same sequences has assisted in confirming the simple nature of the thermal history in each well this study has included full investigation of compositional influences and has resulted in kinetic models for annealing which allow quantitatively for the influence of cl content this work has emphasized the importance of quantitatively allowing for compositional influences on fission track annealing in apatite in routine application of afta cl contents are now determined in everymore grain analyzed with data grouped into 0 1 wt cl divisions and interpreted using the kinetic models described above paleotemperatures and timing determined using this approach have improved precision and provide a well calibrated scale with which other paleotemperature dictators can be compared less

recognition of tectonic events in undeformed regions contrasting results from the midland platform and east midlands shelf central england apatite fission track and vitrinite reflectance data from central england demonstrate how these techniques can reveal otherwise unrecognized tectonic and or palaeothermal episodes in apparently tectonically stable areas the results document the transition from an inverted basinal region in the north east midlands shelf to a tectonically stable platform in the south midland platform afta data from the region reveal two discrete cooling episodes in the early and late tertiary maximum palaeotemperatures from afta and vr data in outcrop samples define a consistent increase from 50 c in lower cretaceous and upper jurassic units in the se to around 80 90 c in triassic and older units in the nw these early tertiary palaeotemperatures reflect a combination of deeper burial and elevated basal heat flow results from the rufford 1 well define an early tertiary palaeogeothermal gradient of 40 5 c km 1 32 50 c km 1 at 95 confidence limits corresponding to deeper burial by 1450 m of additional section 1 1 2 2 km at 95 confidence limits subsequently removed by tertiary erosion in contrast geological considerations suggest a maximum overburden of 800 900 m above the base of the lower jurassic in the vicinity of rugby where palaeotemperatures at outcrop are similar to those near the rufford 1 location the discrepancy between stratigraphic and palaeo thermal reconstruction of former burial depths often noted in earlier studies remains unresolved the late tertiary episode is much less well constrained but results from rufford 1 may require between 910 and 1650 m of eroded section thus much of the total amount of removed overburden may have been removed during the late tertiary results from the apley barn borehole oxfordshire reveal a late tertiary palaeothermal episode characterized by a highly non linear palaeotemperature profile which probably reflects local heating due to passage of hot fluids despite stratigraphic evidence for some early tertiary erosion results from this borehole show no evidence of early tertiary effects major early and late tertiary exhumation was limited to regions underlain by older palaeozoic basins while regions overlying palaeozoic basement were more stable experiencing significantly less exhumation we suggest this reflects the preferential reactivation of the weaker basinal regions as a result of compressional events at plate margins our results emphasize the importance of incorporating results from both inverted and non inverted areas in understanding the causal mechanisms of uplift and inversion and highlight the importance of testing apparent stability using palaeo thermal methods