synchronous detachment folds and coeval sedimentation in the prepyrenean external sierras spain a case study for a tectonic origin of sequences and systems tracts this paper reports on the structural and sedimentary evolution of the middle to late eocene of the prepyrenean external sierras southern pyrenees spain the initiation duration and kinematics of a set of growth structures that developed in a shallow marine depositional setting is documented the detailed analysis of the syntectonic marine sediments not only confirms the already known east to west progression of deformation but also reveals the continued growth of the early formed structures as later ones propagate towards the foreland the sedimentary units coevally deposited with these growth structures are arranged in four depositional sequences their boundaries correspond to flooding surfaces which grade basinwards into correlative conformities they are also indicated by the presence of both angular unconformities and onlap geometries each depositional sequence generally consists of two systems tracts the lower one or transgressive systems tract is formed by up to 400 m of azoic marls deposited in outer ramp areas the upper one or highstand systems tract mainly consists of shallow siliciclastic and carbonate facies up to 200 m thick deposited in middle to inner ramp areas these depositional sequences are interpreted to be controlled by regional tectonic pulses an increase of tectonic activity resulted in the flooding of the basin and in the subsequent deposition of a thick succession of nearly azoic blue marls i e transgressive systems tract the overlying highstand systems tract developed following periods of diminished tectonism with the consequent growth and progradation of shallow carbonate platform facies

electron microprobe and la icp ms study of monazite hydrothermal alteration implications for u th pb geochronology and nuclear ceramics this paper presents new data that quantify the response of magmatic monazite to three main types of hydrothermal alteration namely sericitization chloritization and greisenization the samples were taken from three paleozoic granites the st nectaire granite massif central france the carnmenellis granite cornwall england and the skiddaw granite lake district england fluid inclusion thermometry and hydrothermal parageneses indicate that alteration took place at temperatures ranging from 260 to 340 c and salinities from 3 to 18 wt nacl equivalent possible monazite alteration mechanisms found in the course of this study using backscattered scanning electron microscopy bse sem electron microprobe laser raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry la icp ms include cationic substitutions monoclinic to hexagonal structure transition accompanied by chemical exchanges selective th removal dissolution reprecipitation and dissolution with replacement by a different mineral these results show that despite the compositional and crystallographic simplicity of monazite it exhibits varied chemical responses to different mineral fluid interactions elemental and isotopic measurements by la icp ms for the unaltered monazites yield statistically significant 232th 208pb and 238u 206pb magmatic crystallization ages in some cases it was possible to give a reasonable estimate of the age of mineral fluid interaction using the altered parts of the monazites or newly precipitated crystals for other minerals 232th 208pb and 238u 206pb systematics were strongly disturbed by variable inputs and or depletions of u th and pb the data suggest that monazite like nuclear waste forms would be good hosts for tetravalent actinides but may release the lanthanides and actinides with lower and higher valencies especially if the fluids are oxidizing or tend to dissolve monazite

experimental resetting of the u th pb systems in monazite abraded fragments 200 400 m of a large chemically homogeneous and non metamict brazilian monazite crystal characterised by a concordant u pb ages of 474 1 ma 208pb 206pb 19 5 were hydrothermally treated at varying temperatures with solutions of different compositions product monazites were analysed with scanning electron microscope sem electron microprobe emp secondary ion mass spectrometer sims and isotope dilution thermal ionisation mass spectrometer id tims experiments with pure water over a temperature range of 800 1200 c at 700 mpa and durations ranging from 5 to 60 days showed that even at 1200 c any dissolution and recrystallization of new monazite is confined to the outermost surface of the grain neither pb diffusion at the emp scale nor significant discordancy were observed we performed experiments at 800 and 1000 c for different durations using different fluid compositions at quartz saturation a 10 wt cacl2 fluid a 10 wt srcl2 fluid a 10 wt nacl fluid and a fluid containing nbs 982 pb standard 208pb 206pb 1 for all runs emp traverses revealed no pb diffusion profiles significant overgrowths of newly formed monazite are documented by sem analyses they occurred only in the 1000 c experiments when either cacl2 or pb bearing fluids were present in the cacl2 experiment two zones could be distinguished within the crystal a core possessing the initial monazite composition and a rim consisting of newly formed monazite produced by dissolution precipitation which was enriched in ca and pb free id tims dating of single grains treated with srcl2 and cacl2 solutions at 1000 c are significantly discordant experiments employing the nbs pb standard produced sub concordant monazite for which the 207pb 206pb apparent age has become older than prior to the experiment 544 ma at 800 c and 495 ma at 1000 c the newly grown monazite rim had obviously incorporated pb from the fluid none of our reaction products contained a detectable diffusion profile the only resetting mechanism we detected involved dissolution precipitation the extent of the dissolution precipitation process depends on fluid composition and is a more efficient mechanism than diffusion for controlling the resetting of monazite in natural rocks

pb isotopic composition colour and microstructure of monazites from a polymetamorphic rock in antarctica a moderate to high grade regionally metamorphosed paragneiss from antarctica contains monazites of several different colours brown yellow and grey each colour type has a distinctive u pb isotopic composition which appears to result from different proportions of radiogenic pb loss isotopic differences are neither related to la nd ce p ca ti and or ba nor to u or th content all colour types have similar structures at the submicron scale as determined by both conventional and high resolution transmission electron microscopy tem these show that the grains are essenttially non metamict but are composed of 100 a crystalline domains misoriented from each other by no more than 2 10 3 radians and separated by narrow confused boundary regions where misorientation is probably accommodated by imperfect atomic arrangements these regions of mismatch form potential zones of high permeability diffusivity which are believed to be fundamental to the isotopic and colour differences between grains colour type is apparently related to the capacity of different minerals to shield included monazite grains from fluids circulating in the rock system

structural and sedimentological development of footwall growth synclines along an intraforeland uplift east central bighorn mountains wyoming structural sedimentological and provenance data from paleogene synorogenic deposits of the east central flank of the bighorn mountains provide new information about the development of footwall growth synclines the evolution of fault related folds and the erosional unroofing history of intraforeland uplifts three conglomerate units the upper conglomerate member of the fort union formation and the kingsbury and moncrief members of the wasatch formation are incorporated within an asymmetric east verging growth syncline in the footwall of the main range bounding thrust system three stages of footwall deformation are recorded within these conglomerates analysis of mapped progressive unconformities retrodeformed balanced cross sections and conglomerate clast composition data define these stages as part of a continuum of deformation associated with the development of footwall growth synclines development of an anticline syncline pair marked the earliest stage of growth syncline formation stage i rotation of the shared fold limb resulted in amplification of the growth syncline fine grained synorogenic sediment derived from easily eroded mesozoic mudstone bypassed the growth syncline during this stage by the end of lebo shale deposition an average of 12 1 of shortening and 6 46 km of uplift had occurred along the range margin continued growth syncline development was marked by the deposition of the kingsbury conglomerate the kingsbury conglomerate was derived from resistant middle and lower paleozoic carbonate strata in the uplifted source terrane intraformational unconformities recording as much as 55 of bed rotation were developed within the kingsbury conglomerate as fold limb rotation occurred coeval with deposition cross sections indicate that during this early stage of fault related folding an average of 16 9 shortening and 8 12 km of uplift occurred along the eastern flank of the bighorn mountains end of stage i the intermediate stage stage ii of footwall growth syncline development involved partial truncation of the growth syncline by the advancing thrust faults and deposition of the moncrief conglomerate the lower portion of the moncrief conglomerate was rotated basinward in the developing growth syncline the final stage of deformation stage iii was dominated by the thrust faulting of middle and lower paleozoic strata eastward over steeply dipping mesozoic strata and rotated eocene synorogenic conglomerate during this stage of deformation the moncrief conglomerate was deformed as the initially blind thrusts propagated into the near surface conglomerate deposits truncated the entire footwall syncline and overrode the synorogenic conglomerate package cross sections in areas where this final stage of deformation is well developed indicate that an average of 24 1 shortening and 9 7 km of uplift had occurred along the eastern margin of the bighorn mountains the caliber of synorogenic deposition in the powder river basin was linked directly to the lithologic composition of the bighorn mountains approximately half of the 3 6 km thick source stratigraphic section of the eastern bighorn mountains was eroded prior to accumulation of conglomerate the majority of this eroded material was derived from mesozoic mudstone and poorly indurated sandstone that were incapable of generating coarse detritus the first paleogene conglomerates deposited along the east central bighorn mountains therefore do not represent the initiation of laramide uplift but instead represent the exposure of coarse clast forming rock types from the lower half of the hanging wall stratigraphic section i e the mississippian madison limestone and ordovician bighorn dolomite

flexural to broken foreland basin evolution as a result of variscan collisional events in northwestern spain the variscan cantabrian zone of northern spain records the transition from passive margin sedimentation to foreland basin deposition during the late devonian initiation of the foreland basin system is refl ected in the evolution of a hinge line that separated the foredeep from the adjacent peripheral bulge bulge erosion provided siliciclastic detritus that was deposited in the evolving foredeep after cessation of sedimentary input the foredeep achieved starved conditions during the earliest tournaisian these events were a long distance effect of initial subduction of the iberian continental margin prior to collision between northwestern gondwana and north america during the namurian propagation of the deformation front and the rise of the orogen led to increasing input of detritus that began to fithe foredeep during the late namurian and the early westphalian deformation started to affect the cantabrian zone the palencian nappes were emplaced onto the valsurvio dome after which thick wedge top deposits formed the curavacas conglomerate when the esla nappe and the valsurvio dome became involved in deformation and approached the rigid lithosphere of the cantabrian block anticlinal stacks began to form and the lithosphere broke two major faults developed the leon fault and the ruesga fault which dissected the lithosphere to accommodate further compression the resulting topography led to the gravitationally induced gliding of the palencian nappes into the pisuerga carrion unit where sedimentation and deformation continued under broken foreland basin conditions the cantabrian mountains preserve a foreland basin system that in its early stage was formed under fl exural deformation of the lithosphere induced by subduction when deformation affected the autochtho

leaching and differential recrystallization of metamict zircon under experimental hydrothermal conditions we report results of hydrothermal experiments on four alluvial zircons from sri lanka which cover a wide range of radiation damage at 450 c and 1 3 kbar for 744 h with 2 m cacl2 solution as reactive fluid after the hydrothermal treatment the most metamict samples show micrometer thick reaction rims which surround apparently unreacted zircon as revealed by cathodoluminescence cl and nomarski differential interference contrast ndic images these rims have sharp curved and transgressive boundaries with unreacted zircon and are in some cases spread out along cracks the thickness of reaction rims increases with increasing cumulated dosage of the starting materials the reaction rims are strongly enriched in ca up to 7000 ppm and a water species and depleted in radiogenic pb zr and si as revealed by electron microprobe analyses a significant th loss from the reaction rims was detected in the case of the most metamict sample whereas u remained in the structure ft infrared spectrometry and x ray diffraction measurements revealed that the bulk run products were recrystallized using micro raman spectrometry we were able to demonstrate that differential recrystallization took place the reaction rims are strongly recrystallized whereas the unreacted grain interiors underwent only minor recrystallization recrystallization of the rims is accompanied by an enhancement of the integral cl intensity it is suggested that recrystallization in the reaction rims was catalyzed by water infiltration and ion exchange and prevented significant congruent zircon dissolution under the given experimental conditions previous zircon studies have shown that 1 a transgressive morphology 2 a reduced th u ratio and 3 an enhanced cl emission are also characteristics of rims in zircons from high grade metamorphic rocks based on these similarities between natural and experimentally produced rims it is suggested that leaching catalyzed recrystallization is an important alteration process in zircon under wet geological conditions and can account for many complex core rim structures found in natural zircons furthermore the strong enrichment of ca in the reaction rims supports previous assumptions that high ca concentrations in natural zircons are of secondary origin it is suggested that lower u pb concordia intercept ages obtained from single phase zircons with high ca contents date a leaching event

growth stratal architectures associated to decollement folds and fault propagation folds inferences on fold kinematics abstract in many thrust and fold belts asymmetric folds with overturned or steeply dipping forelimbs and gently dipping backlimbs are commonly interpreted as thrust related folds determining the folding mechanism exclusively from the final fold geometry in the pre growth units is possible only for a limited suite of structures the nature of fold thrust interaction in shallow structures can be inferred by coupling the fold geometric analysis with the study of the syntectonic sediment stratal architectures several factors such as axial surface activity fold uplift limb rotation and limb widening rates together with sedimentation and erosion rates control growth strata patterns because the evolutionary path of most of these parameters depends on the folding kinematics different growth stratal architectures are expected for different thrust related anticlines in this paper we examine the influence of the above factors on growth stratal geometries associated to a simple kink band and then we apply the same approach to kinematic models of decollement folding and fault propagation folding four geometric approaches are used to account for the geometry and kinematics of anticlines located at the tip of a blind thrust fault propagation folding with no excess layer parallel shear fault propagation folding with progressive layer parallel shear constant limb length decollement folding and variable limb length decollement folding whereas fault propagation folding with no excess layer parallel shear is a self similar folding mechanism the other three types involve limb rotation coherent geometries between growth and pre growth sequences develop at high sedimentation rates in the crest of fault propagation folds and incoherent ones in decollement folds minor differences within growth strata patterns occur at low sedimentation rates and when erosion affects the crest of the anticlines

a mantle derived bimodal suite in the hercynian belt nd isotope and trace element evidence for a subduction related rift origin of the late devonian brevenne metavolcanics massif central france in the brevenne series ne massif central a low grade bimodal association of metabasalts and metarhyolites is exposed together with intrusive trondhjemite bodies zircon u pb dating constrains their magmatic emplacement at 366 5 ma and 358 1 ma respectively the metabasalts are characterized by a distinct enrichment in incompatible elements e g th and lree and positive ndi from 5 to 8 combined isotope and trace element systematics rule out crustal contamination of mafic melts as a suitable cause of the lile large ion lithophile element enrichment rather a mixing process between a component similar to mid ocean ridge basalts and an enriched end member with ndi 5 is suggested an enriched mantle source of ocean island basalt affinity is precluded by the relative depletion of high field strength elements especially nb which shows negative anomalies in chondrite normalized patterns on the contrary a subduction related origin for the lile enrichment would be more consistent it may be inferred that arc like melts enriched in th and lree light rare earth elements and depleted in nb with ndi 5 were produced through partial melting of a depleted mantle source to which a small amount of crustally derived component had been added the metarhyolites are enriched in lile and have a close genetic relationship with the metabasalts as evidenced by their high ndi from 4 7 to 6 8 although the chemical evidence remains ambiguous it is suggested that fractional crystallization accompanied by subordinate assimilation is the petrogenetic process most consistent with the data the trondhjemites are isotopically distinct from the metarhyolites their ndi values from 1 0 to 2 2 reflect an important contribution of continental crust to their genesis and disprove their inferred cogenetism with the felsic volcanics a review of modern environments in which such bimodal suites are exposed shows that settings involving incipient rifting of a volcanic arc fringing a continental margin or built upon young thin continental crust might provide suitable analogues geodynamic reconstructions are complicated by subsequent tectonic events which disrupted the initial patterns and by mesozoic cenozoic sedimentary cover however this subduction related magmatism enlarges the growing body of evidence for southward subduction processes until the late devonian during the evolution of the northern flank of the european variscides as a general implication it is suggested that the combined use of the sm nd system with incompatible elements relatively resistant during alteration and low grade metamorphism ree th zr nb may provide diagnostic criteria for recognizing the tectonic setting of bimodal metaigneous suites in ancient orogenic belts

monazite as a metamorphic chronometer south of the grenville front western quebec monazite was utilized as a chronometer to examine the effects of high grade metamorphism across the parautochthonous belt and allochthon boundary thrust of the grenville province in western quebec this study in addition to previous geo chronological studies indicates an archean component in the gneisses which is consistent with the presence of more than one set of peak metamorphic conditions single grain monazite analyses from metasedimentary gneisses from four locations within the parautochthonous belt yielded grenvillian u pb dates of 1000 5 to 1006 2 ma the location farthest to the northwest 45 km southeast of the grenville front included monazite with a distinct archean signature southeast of this point an archean signature was not detected in the monazite at 70 km southeast of the grenville front monazite yielded two discrete ages of 1005 2 and 1020 3 ma xenotime from one location indicated that the closure temperature of this mineral may be equivalent to that of monazite 725 25

u pb dating of major and accessory minerals formed during metamorphism and deformation of metapelites abstract u pb isotope analyses on major and accessory minerals from pelitic schists in of southwestern connecticut are used to date metamorphism and deformation most of the major minerals have 206 pb 204 pb ratios less than 100 however u pb mineral isochron and mineral whole rock isochrons constructed using aliquots of the same mineral yield concordant ages with uncertainties as low as 5 ma staurolite kyanite and garnet are older than metamorphic monazites and zircons these data are summarized below 5 mineral 206 pb 204 pb system the straits schist trap falls fm monazite zircon 207 pb 206 pb 379 384 ma 380 2 ma staurolite 48 623 238 u 206 pb 394 400 ma 398 5 ma garnet 22 46 238 u 206 pb 383 ma 414 10 ma 235 u 207 pb 418 ma 207 pb 206 pb 623 ma kyanite 21 27 238 u 206 pb 399 ma chlorite anatase ilmenite 20 27 238 u 206 pb 350 370 ma apatite quartz kspar 18 19 transposed pegmatitic intrusions in the straits schist yield monazites with u pb ages analytically indistinguishable from those of metamorphic monazites and zircons in the schists growth of monazite and zircon in the schists may be related to high t fluid influx associated with pegmatite intrusion age discordance in the garnets from the straits schist is most consistent with continuous loss of intermediate daughter products of the 238 u decay chain from about 420 ma to 380 ma garnets from the adjacent trap falls formation do not display this behavior

growth and propagation of buckle folds determined from syntectonic sediments the ubierna fold belt cantabrian mountains n spain abstract the geometry of syntectonic tertiary sediments in the ubierna fold belt can be explained using the buckling folding theory the geometric features of the fold train in the pre orogenic succession also agree with a buckling process each fold grew with progressive and coeval rotation of both limbs although rotation was asymmetric and greater on the forelimb than the backlimb the diachroneity of synrotational sequences progressive unconformities through different folds indicates that fold propagation migrated towards the foreland however the initial folds were tightened during a later deformation stage synchronous with the development of younger folds

differential response of u pb systems in coexisting accessory minerals winnipeg river subprovince canadian shield implications for archean crustal growth and stabilization the u pb isotopic systems of zircon monazite titanite and some apatite and the pb isotopic composition of k feldspar have been investigated in three areas of the winnipeg river subprovince wrs of the superior province canada in order to define the timing of magmatic and metamorphic processes in this archean gneissic granitoid terrain

electron microprobe dating of monazites from high grade gneisses and pegmatites of the kerala khondalite belt southern india monazites of five samples one leptynitic garnet biotite gneiss one khondalite one augen gneiss and two pegmatites from the central and northern part ponmudi unit of the kerala khondalite belt kkb in southern india were analyzed with the electron microprobe dating technique monazites in the augen gneiss and the pegmatites yield grain sizes between 200 800 m th abundances are rather low 10 wt and the distribution of th u and pb within single grains is fairly homogeneous contrasting to this monazites in the leptynitic gneiss and the khondalite are small 150 m they often display very complex th u pb patterns and contain high th concentrations up to 20 wt the statistical treatment of individual ages from the investigated samples revealed three populations of lower proterozoic 1 9 ga upper proterozoic 580 ma and ordovician age 470 ma as well as mid proterozoic ages between 0 8 1 7 ga which are not regarded to be of geological significance lower proterozoic ages are preserved in the cores of monazites from leptynitic gneisses and khondalites they fairly agree with sm nd model ages for similar rocks of the kkb and give a minimum age for first monazite growth or complete homogenization the prominent pan african population with mean values between 540 and 580 ma is present in the leptynitic gneiss the khondalite and the augen gneiss and in line with published isotope ages for the kkb the ordovician population finally marks the emplacement of granitic pegmatites subsequent to the pan african high grade metamorphic event there is an obvious discrepancy between khondalites and leptynitic gneisses on the one hand and augen gneisses on the other concerning the presence of lower proterozoic ages while these are abundant in the former often rimmed by upper proterozoic ages they are completely absent in the latter it appears unlikely that lower proterozoic ages were completely reset during a pan african event exclusively in the augen gneisses while they were preserved in leptynitic gneisses and khondalites it is further concluded that the augen gneisses are of magmatic origin and were derived from porphyritic granites thus the upper proterozoic age of 605 37 ma calculated for the investigated sample approximates the time of magma emplacement which slightly precedes the peak stage of pan african high grade metamorphism in the kkb and of monazite crystallization from the granitic melt a characteristic feature of the investigated monazites is the resetting of lower proterozoic and pan african ages to significantly younger values due to partial pb loss monazites not shielded by other minerals e g garnet suffered selective mobilization of pb along fractures or at their rims while th and u concentrations remained almost unchanged the results presented in this study indicate that this was mainly due to fluid rock interaction it is concluded that thermal diffusion of pb even at the suggested temperatures of 900 c only had minor influence on the th u pb composition in monazite and that the closure temperature for this system must be significantly higher than previously assumed 750 c

detection of inherited monazite in the manaslu leucogranite by 208pb232th ion microprobe dating crystallization age and tectonic implications abstract although leucogranites are among the least petrologically variable of all igneous rocks ironically they are among the most difficult to reliably date the high himalayan leucogranites have been the subject of numerous geochronological investigations because of their interrelationship with the most significant tectonic features of that mountain belt for a variety of reasons linked to the minimum melt composition of these leucogranites these dating studies have not been entirely successful we report results of a new ion microprobe dating method based on the decay of 232 th to 208 pb in monazite that has directly revealed the presence of inherited pb in monazite from the manalsu granite casting doubt on its previously accepted age monazite ages obtained from this leucogranite yield two distinct populations a large number of ages with a normal distribution and mean age of 22 4 0 5 ma 2 s e that we interpret to be the crystallization age and a smaller inherited fraction with an age of ca 600 ma because formation of the granite is thought to be related to slip on the main central thrust both this date and a second less precise result from a structurally similar pluton near mt everest indicate that the main central thrust was active in the interval 24 22 ma but do not constrain its initiation together with crosscutting relationships these data require that movement on the north himalayan fault occurred prior to 22 ma at both locations

low temperature exhumation history of variscan age rocks in the western cantabrian mountains nw spain recorded by apatite fission track data abstract this paper presents the first regional study of apatite fission track aft thermochronology to be undertaken in the western termination of the cantabrian mountains nw spain the mountains reach elevations of over 2600 m along the northern coast of spain and are comprised of a variscan crustal section uplifted due to cenozoic shortening along the northern iberian plate the study constrains the pattern and history of exhumation within the paleozoic bedrock over the past c 240 ma twenty one apatite fission track samples range in age from 246 7 26 9 ma to 78 1 3 7 ma with mean track lengths between 10 4 1 8 m and 12 4 1 4 m time temperature path modelling of the data indicates that different rates of continuous cooling took place during the three main tectonic events that affected the area a rapid cooling event that ended by the late jurassic corresponds to topographic decay during unroofing of the variscan orogen and the break up of pangea and is responsible for the largest amount of exhumation westernmost samples cooled coinciding with rifting in the north atlantic and bay of biscay during the late jurassic to early cretaceous by about 100 80 ma most samples had reached or passed through the upper boundary of the apatite partial annealing zone which indicate that regional denudation has not exceeded c 1 7 km since then for geothermal gradients 27 c km and a surface temperature of 15 c only three samples next to fault escarpments in the west cooled below 70 c since 80 ma reaching below 65 c before initiation of incipient subduction along the northern iberian margin by 46 ma an average cooling rate of 1 c ma reflects latest denudation as the new mountainous relief developed since then due to shortening and incipient subduction associated with convergence along the northern iberian plate the cantabrian mountains are one of the few natural examples of a coastal orogen in a juvenile stage of evolution

time calibration of a p t path from a variscan high temperature low pressure metamorphic complex bayerische wald germany and the detection of inherited monazite a temperature time path was constructed for high temperature low pressure ht lp migmatites of the bayerische wald internal zone of the variscan belt germany the migmatites are characterised by prograde biotite dehydration melting peak metamorphic conditions of approximately 850 c and 0 5 0 7 gpa and retrograde melt crystallisation at 800 c the time calibration of the pressure temperature path is based on u pb dating of single zircon and monazite grains and titanite separates on 40ar 39ar ages obtained by incremental heating experiments on hornblende separates single grains of biotite and k feldspar and on 40ar 39ar spot fusion ages of biotite determined in situ from sample sections additionally crude estimates of the duration of peak metamorphism were derived from garnet zoning patterns suggesting that peak temperatures of 850 c cannot have prevailed much longer than 2 5 ma the temperature time paths obtained for two areas approximately 30 km apart do not differ from each other considerably u pb zircon ages reflect crystallisation from melt at 850 800 c at 323 ma southeastern area and 326 ma northwestern area the u pb ages of monazite mainly coincide with those from zircon but are complicated by variable degrees of inheritance the preservation of inherited monazite and the presence of excess 206pb resulting from the incorporation of excess 230th in monazite formed during ht lp metamorphism suggest that monazite ages in the migmatites of the bayerische wald reflect crystallisation from melt at 850 800 c and persistence of older grains at these temperatures during a comparatively short thermal peak the u pb ages of titanite 321 ma and 40ar 39ar ages of hornblende 322 316 ma and biotite 313 309 ma reflect cooling through the respective closure temperatures of approximately 700 570 500 and 345 310 c published in the literature most of the feldspars ages 305 296 ma probably record cooling below 150 300 c while two grains most likely have higher closure temperatures the temperature time paths are characterised by a short thermal peak by moderate average cooling rates and by a decrease in cooling rates from 100 c my at temperatures between 850 800 and 700 c to 11 16 c my at temperatures down to 345 310 c further cooling to feldspar closure for ar was probably even slower the lack of decompressional features the moderate average cooling rates and the decline of cooling rates with time are not easily reconciled with a model of asthenospheric heating rapid uplift and extension due to lithospheric delamination as proposed elsewhere instead the high peak temperatures at comparatively shallow crustal levels along with the short thermal peak require external advective heating by hot mafic or ultramafic material

fracture pattern analysis as a tool for constraining the interaction between regional and diapir related stress fields poza de la sal diapir basque pyrenees spain during diapir evolution the local stress field results from the interaction between diapirrelated and remote regional stress fields the fracture pattern hosted in the overburden can register this evolving interaction providing significant insights for the unravelling of the diapir kinematics in this work we present the example of the poza de la sal diapir which is a salt diapir that pierces the synorogenic deposits of the basque pyrenees the integrated analysis of mesostructural data which includes field collected faults joints and fracture traces digitalized on high resolution orthophotos allowed us to establish an evolutionary model for the stress field around diapirs the presented data support the idea that during diapir evolution stress fields evolve from mostly regional related to mostly diapir related contrasting with other geological data seismic data geological map and cross section we observe that different methods provide complementary information coherent with the proposed evolutionary model of the poza de la sal diapir the study of fracture development associated with the growth of salt diapirs is of interest for both academic and industrial purposes in fact fractures play an important role in fluid flow and its accumulation in salt diapir related reservoirs johnson bredeson 1971 koestler ehrmann 1987 davison et al 2000a b on the other hand the analysis of fracture patterns is useful to constrain the host structure evolution thorbjornsen dunne 1997 tavani et al 2008 and accordingly can provide useful information for understanding diapir kinematics alsop 1996 stewart 2006 yin groshong 2007 yin et al 2009 the fracture pattern associated with salt diapirs and in general with doming structures is characterized by two classes of elements radial and concentric fig 1a b e g parker mcdowell 1955 withjack 1979 squyres et al 1992 branney 1995 malthe sorenssen et al 1999 rowan et al 1999 2003 davison et al 2000a b freed et al 2001 stewart 2006 this pattern is documented in simple structures where the remote stress field is negligible in relation to the diapir related stress fields when such a condition is not verified the interaction of these two stress fields leads to the development of more complex patterns ode 1957 withjack scheiner 1982 studies of interacting regional and punctual stress fields e g ode 1957 indicate that the influence of diapir induced stress progressively reduces away from the dome i e the punctual structure as a consequence far from the diapir the fracture pattern responds to the remote stress field and approaching the diapir the fracture pattern tends to be radial and concentric fig 1c although these patterns have been observed by several authors in different structures withjack scheiner 1982 mege masson 1996 ernst et al 2003 there are no detailed field studies focusing on this topic in this work we present a simple 2d theoretical stress field model where the stress tensor resulting from the interaction between remote and diapirrelated stress fields is assumed to be for a fixed distance from the diapir centre a 2 2 matrix provided by the sum of the horizontal components of the two stress tensors the eigenvectors associated with this matrix are assumed to be the principal axes of the local stress field the working hypothesis is that if the stress field changes the azimuth of fractures joints developed under these stress fields also change by understanding interactions between diapir related and regional stress fields we can predict the azimuth of the developed fractures to test the validity of this theoretical model we have applied it to a well exposed salt diapir located at the western pyrenees poza de la sal diapir this is a near circular diapir with a mainly carbonate overburden affected by a complex pattern of fractures results of this comparison indicate that despite its simplicity the provided stress model is a useful tool for understanding the kinematics of salt diapirs accordingly in this paper we provide from alsop g i archer s g hartley a j grant n t hodgkinson r eds 2012 salt tectonics sediments and prospectivity geological society london special publications 363 521 532 http dx doi org 10 1144 sp363 25 the geological society of london 2012 publishing disclaimer www geolsoc org uk pub ethics guidelines to obtain a fracture pattern using the theoretical model presented to complement other techniques of investigation such as field work or 3d seismic interpretations

monazite th pb age depth profiling the significant capabilities of the ion microprobe for thermochronometric investigations of geologic materials remain largely unexploited whereas sup 208 pb sup 232 th spot analysis allows approximately 10 mm scale imaging of pb loss profiles or overgrowths in sectioned monazite grains the spatial resolution offered by depth profiling into the surface region of natural crystals is more than two orders of magnitude higher the authors document here the ability of the high resolution ion microprobe to detect sup 208 pb sup 232 th age differences of 1 m y with better than 0 05 micro m depth resolution in the outer micron of tertiary monazites from the hanging wall of the himalayan main central thrust age gradients on this scale are inaccessible to ion microprobe spot analysis or conventional thermal ionization mass spectrometry interpretation of the near surface sup 208 pb distributions with available monazite pb diffusion data illustrates the potential of the approach for recovering continuous high temperature thermal history information not previously available

electron microprobe observations of pb diffusion in metamorphosed detrital monazites electron microprobe analyses have been made on monazite grains from paragneiss samples in the andalusite sillimanite transition 620 15 c and sillimanite orthoclase 680 15 c zones of the cretaceous ryoke metamorphic belt southwest japan monazites from pelitic gneisses are of metamorphic origin euhedral to subhedral and chronologically homogeneous giving chemical th u total pb isochron chime ages of 98 8 3 3 98 0 3 2 ma two psammitic gneisses of individual metamorphic grade contain both metamorphic monazite grains and detrital ones as old as ca 1700 ma most detrital monazite grains are heterogeneous in the tho2 and uo2 concentrations and have multiple or single rims as young as ca 100 ma several detrital monazite grains are well rounded in form exhibit homogeneous th and u distributions and show a pb diffusion profile in the margin the width of the diffusion zones is approximately constant throughout grains from each psammitic gneiss 18 22 m for 620 c and 48 58 m for 680 c assuming the isothermal diffusion of pb from homogeneous monazite spheres during a 5 ma duration of peak metamorphism we obtain diffusion coefficients of 1 9 0 3 10 21 and 1 5 0 3 10 20 cm2 s at 620 c and 680 c respectively these data derive an activation energy of 2 44 2 85 1 26 105 j mol and a frequency factor of 3 4 10 7 8 5 10 12 2 2 107 cm2 s taking account of uncertainties of 15 c in the temperatures and of 20 in the diffusion coefficients the diffusion parameters obtained from natural samples in this study provide a reliable insight into the closure temperature for pb in monazite that has been poorly understood so far

domainal variations of u pb monazite ages and rb sr whole rock dates in polymetamorphic paragneisses ktb drill core germany influence of strain and deformation mechanisms on isotope systems polyphase metamorphic paragneisses from the drill core of the continental deep drilling project ktb nw bohemian massif are characterized by peak pressures of about 8 kbar medium p metamorphism followed by strain accumulation at t 650 c initially by dislocation creep and subsequently by diffusion creep u pb monazite ages and rb sr whole rock data vary in the dm scale indicating ordovician and mid devonian metamorphic events such age variations are closely interconnected with dm scale domainal variations of microfabrics that indicate different predominant deformation mechanisms u pb monazite age variations dependent on microfabric domains exceed grain size dependent age variations in mylonitic domains recording high magnitudes of plastic strain dislocation creep and minor static annealing monazite yields concordant and near concordant lower ordovician u pb ages and the rb sr whole rock system shows isotopic disequilibrium at an mm scale in mineral growth mobilisate domains in which diffusive mass transfer was a major strain producing mechanism promoting diffusion creep of quartz and feldspar and in which static recrystallization annealing reduced the internal free energy of the strained mineral aggregates concordant u pb ages are mid devonian locally in such domains rb sr dates among mm3 sized whole rock slabs reflect post ordovician resetting in transitional domains the u pb ages are discordant we conclude that medium p metamorphism occurred at 484 2 ma and a second metamorphic event at 380 370 ma mid devonian caused progressive strain in the rocks dislocation creep at high rates even at high temperatures does not reset the rb sr whole rock system while diffusion creep at low rates and stresses i e low e deff ratios static annealing and the presence of intergranular fluids locally assist resetting at temperatures above 650 c diffusive pb loss did not reset ordovician u pb monazite ages and in domains of overall high imposed strain rates and stresses resetting was not assisted by dynamic recrystallization crystal plasticity however during diffusion creep at low rates pb loss by dissolution and precipitation recrystallization of monazite produces discordance and devonian concordant u pb monazite ages hence resetting of these isotope systems reflects neither changes of temperature nor directly the presence or absence of strain

geophysical constraints on the deep structure of a limited ocean continent subduction zone at the north iberian margin 1 late cretaceous to cenozoic convergence between iberia and europe led to the partial closure of the bay of biscay with limited southward subduction of oceanic crust below the north iberian margin inclined sub moho reflections and diffractions observed in deep seismic reflection profiles shot across the margin are especially well represented in two reflection profiles escin 3 2 and escin 3 3 these two profiles have been chosen to test if the sub moho reflections correspond to true primary deep events and provided that they are reflecting off the subduction zone to investigate its deep structure spectral analysis together with travel time estimation and migration allow us to characterize a number of these sub moho events as deep source low frequency 19 hz reflections and diffractions synthetic seismograms were generated by three dimensional seismic modeling of a sub moho southward dipping surface interpreted to correspond to the top of subducted oceanic crust comparison between the real and synthetic data show that inclined low frequency sub moho reflections in both escin 3 2 and escin 3 3 profiles may correspond to reflections from southward subducted bay of biscay oceanic crust geoid free air gravity and absolute topography modeling provides additional constraints on the lithospheric scale structure of this limited ocean continent subduction zone beneath the north iberian margin

subduction related structures in the north iberian margin the oblique convergence of eurasia and iberia since the early cretaceous caused the formation of the pyrenean intracontinental collisional orogen in the east and progressed to continent ocean collision with subduction of the bay of biscay oceanic crust beneath the north iberian margin in the west two deep multichannel seismic profiles iam 12 and escin 4 integrated with gravity modeling and other geological and geophysical data provide the crustal scale architecture of this margin and its tectonic evolution during the convergence the north iberian margin is modeled with a south or south southeast dipping oceanic crust beneath the outer part of the continental shelf mesozoic basins on the shelf were inverted during the tertiary and compressional activity continued until recent times in the escin 4 section while a shallower probably neogene age basin is subjected to active recent erosion in the iam 12 section in the oceanic areas a marginal trough deepens and widens toward the east as a result of the regional east dip of the oceanic basement the accretionary prism increases in size from west to east 18 56 km and its internal structure and morphology varies along strike the prism is buried by postcorivergence sediments in both sections and in the iam 12 section appears to have been active at least during lutetian to burdigalian times the crustal scale structure of the north iberian margin is that of an arrested subduction zone in which a remnant oceanic basin was being consumed near two continental plates that collided obliquely

the foreland deformation in the south western basque cantabrian belt spain abstract in the south western portion of the cenozoic basque cantabrian belt structural data collected in pre orogenic upper cretaceous limestones were combined with aerial images interpretation in flat lying areas observations about fracture strike type orientation and overprinting relationships both at the macro and mesoscales allow to constrain the pre thrusting and pre folding deformational sequence that affected the area when it was forming part of the foreland basin wnw ese striking extensional structures represent the oldest elements developed during the very late stages of the mesozoic rifting associated with the opening of the bay of biscay the onset of convergence is marked by the development of extensional structures striking roughly nnw sse and wsw ene which are associated with belt parallel stretching in the foredeep and outer arc extension in the peripheral bulge respectively and developed in a non fluid assisted environment these elements are postdated by a pre folding layer parallel shortening pattern which includes wsw ene striking pressure solution cleavages and reverse faults both of them frequently reactivating inherited early orogenic wsw ene striking extensional elements and right lateral reactivation of wnw ese striking pre orogenic extensional structures this stage was followed by a syn to post folding e w oriented belt parallel compression wnw ese striking left lateral faults being the most outstanding elements associated with this stage the presence of such elements in upper cretaceous sediments provides support to the idea that left lateral shear zones of the area related with a cenozoic intrabelt lateral extrusion tectonics our results indicate coherently with previously published works in the pyrenean orogen that most of the mesoscale deformation has been acquired before layer s tilting

middle precambrian detrital monazite and zircon from the hida gneiss on oki dogo island japan their origin and implications for the correlation of basement gneiss of southwest japan and korea abstract monazite and zircon from seven paragneiss samples of the upper amphibolite facies grade from oki dogo island in the hida terrane western japan were analyzed for th u and pb on an electron microprobe most monazite grains are chronologically unzoned and give unequivocal chime chemical th u total pb isochron ages of 250 ma but some grains show a distinct core overgrowth relationship the cores retain evidence of pre 250 ma ages and are interpreted to be of detrital origin suggesting that monazite can be more immune to diagenetic and low grade metamorphic decompositions than had been thought previously zircon grains rounded to nearly euhedral give chime ages ranging from 3000 to 350 ma of particular interest are several rounded 3000 ma recycled zircons which perhaps originated from an archean terrain in the sino korean craton the youngest age of detrital zircons constrains that the gneiss protolith deposited after the 350 ma event the chime monazite and zircon ages for the paragneisses from oki dogo island and from the main part of the hida terrane reveal that the gneisses formed from permo carboniferous clastic sediments during a single metamorphism at ca 250 ma the results are in marked contrast to the current view that 1 the hida gneiss is a polymetamorphosed precambrian complex 2 the central part hida gneiss region and the eastern marginal part unazuki schist region of the hida terrane are correlative with the precambrian kyonggi massif and the paleozoic okchon zone in the korean peninsula respectively instead we consider that the okchon zone alone can be correlatable with the paleozoic hida terrane

modelling channelized surface drainage of supraglacial lakes supraglacial lakes can drain to the bed of ice sheets affecting ice dynamics or over their surface relocating surface water focusing on surface drainage we first discuss observations of lake drainage in particular for the first time lakes are observed to drain 70 km across the nivlisen ice shelf east antarctica inspired by these observations we develop a model of lake drainage through a channel that incises into an ice sheet surface by frictional heat dissipated in the flow modelled lake drainage can be stable or unstable during stable drainage the rate of lake level drawdown exceeds the rate of channel incision so discharge from the lake decreases with time this can prevent the lake from emptying completely during unstable drainage discharge grows unstably with time and always empties the lake model lakes are more prone to drain unstably when the initial lake area the lake input and the channel slope are larger these parameters will vary during atmospheric warming induced ablation area expansion hence the mechanisms revealed by our analysis can influence the dynamic response of ice sheets to warming through their impact on surface water routing and storage

widespread cretaceous inversion event in northern spain evidence from subsurface and palaeomagnetic data abstract in this paper we present geological evidence of a mid cretaceous inversion event in the polientes basin northern iberian plate based on geological data analysis of seismic profiles across the basin indicates that this tectonic event resulted in the uplift of the basin depocentre and the formation of an upright gentle anticline before cenomanian times the presence of a pre alpine syntectonic remagnetization in the jurassic and lower cretaceous rocks of the polientes basin allows us to define the geometry of the basin at the time between this early inversion event and the main alpine compressional period the early inversion in the polientes basin is consistent with a transpressional tectonic setting contemporaneous with the left lateral strike slip movement of iberia with respect to europe this study shows the successful use of two approaches to unravel the geodynamic scenario of the northern iberian plate during the cretaceous which was later obliterated during the tertiary pyrenean orogeny

geometric and numerical model of progressive limb rotation in detachment folds a simple area balanced geometric model of progressive limb rotation in detachment folds allows the quantification of displacement uplift and rotation and the assessment of their effect upon growth strata geometries translation of this geometric model into a velocity model of deformation allows the modeling of associated growth strata resulting from background sedimentation and local erosion transport and deposition we show that with constant displacement and sedimentation rate this model predicts a progressive unconformity indicating the onlap and eventual overlap of the fold limb caused by a decreasing uplift rate this decrease is a consequence of the kinematics of progressive limb rotation increases in displacement rate with sedimentation rate kept constant can lead to offlap and angular unconformities although subsequent onlap does not necessarily reflect a return to a lower displacement rate modeled growth strata geometries exhibit many of the features reported from the literature

origin structure and exposure history of a wave cut platform more than 1 ma in age at the coast of northern spain a multiple cosmogenic nuclide approach abstract along the asturian coast of northern spain an uplifted wave cut platform extends for 100 km east west the steep cliff which bounds the gently seaward dipping platform to the north increases in height from 30 m in the west to 100 m in the east and reflects the overall eastward increase in platform elevation the southern edge of the 2 4 km wide platform runs along the foothills of the cantabrian mountains as constrained by a high resolution digital elevation model the marine platform which was carved into deformed paleozoic bedrock with abundant quartzite beds is largely covered by weathered marine and continental sediments quartzite samples from flat bedrock outcrops which are currently not covered by sediment or soil yield cosmogenic nuclide concentrations 21ne 10be and 26al that demonstrate a long and complex exposure history including periods of burial with partial or complete shielding from cosmic rays the combination of multiple cosmogenic nuclides yields a minimum age of 1 2 ma for the platform taking into account i the horizontal and vertical extent of the platform ii the high resistance to erosion of the quartzitic bedrock and iii published data on the magnitude of past sea level fluctuations we suggest that the wave cut platform formed in the pliocene subvertical faults cutting the platform at high angles to the coastline offset the southern edge of the platform by 20 to 40 m and reactivate the pre existing anisotropy in the paleozoic bedrock uplift and crustal deformation of the coastal region have occurred after platform formation in the pliocene and may still be active the slow deformation of the northern edge of the iberian plate including the cantabrian mountains may result from the ongoing slow convergence at an incipient subduction zone extending along the coast of northern spain

geochronology of polygenetic monazites constrained by in situ electron microprobe th u total lead determination implications for lead behaviour in monazite abstract monazite grains are generally concordant and with an electron microprobe give th u total pb isochron ages in agreement with conventional u pb data monazites from four samples of post archean migmatite from the ivory coast record two main ages an archean age at 2 80 ga partly overprinted by a late migmatization event at 2 03 ga the in situ electron microprobe determination has also shown a third event that systematically appears at 2 72 ga for all the monazites from two of the four studied rocks the three events at 2 80 2 72 and 2 03 ga recorded by the th u total pb system in monazite were each obtained on independent homogeneous parts of a single grain with no sign of pb diffusion thus the oldest monazite remained closed during a high grade resetting migmatization at a temperature estimated at around 700 c and also remained closed during the growth of secondary monazite conventional u pb data isotope dilution on monazite from the same rocks did not allow precise age determinations because the representative points were highly up to 83 discordant and did not fit well along a chord in the concordia diagram the u pb isotope dilution method gave a lower intercept age of 2029 25 ma in agreement with the electron microprobe age although with an unusually high uncertainty due to a poor fit of the data the pb evaporation method gave an old archean age at 2830 7 ma and proterozoic ages ranging from 2417 10 to 2074 7 ma thus although the oldest archean age obtained with the pb evaporation and electron microprobe methods is similar within the analytical error the proterozoic ages obtained by the pb evaporation method are significantly older than the th u total pb proterozoic age obtained with the electron microprobe this discrepancy is presumed to be due to the influence in the pb evaporation method of radiogenic lead contained within archean zones of the monazite grains in other words it means that migmatization took place later than 2074 7 ma and probably around 2030 ma the second archean event at 2 72 ga revealed by high spatial resolution of the electron microprobe could not be determined by other methods the th u total pb method appears to be an inexpensive alternative method for dating simple monazites with a precision close to 20 ma even if the u pb isotopic dilution technique remains the reference method moreover owing to the very high spatial resolution 1 m of the electron microprobe it appears to have no competitor for dating complex polygenetic monazites especially when more than two events are recorded homogeneous zones of different ages coexist in a single grain with no major indication of lead diffusion a procedure for age and error calculations is defined

active faulting and growth folding in the eastern santa barbara channel california we develop new methods to identify blind thrust fault systems determine fault slip rates and estimate potential earthquake magnitudes and recurrence intervals in active fold and thrust belts these methods are applied to compressive folds along the offshore oak ridge and blue bottle trends which overlie active blind thrust faults in the eastern santa barbara channel these folds and their causative faults are interpreted using fault bend fold theory and are represented in balanced models and cross sections that integrate surface and subsurface data the structures are mapped using a new technique of axial surface mapping in seismic reflection grids which defines three dimensional structural geometries and shows changes in slip and subsurface fault geometry along strike analysis of syntectonic growth sediments yields pliocene and quaternary fault slip rates of 1 3 mm yr on a deep thrust 16 km and 1 3 mm yr on shallower faults 2 5 km the combined 2 6 mm yr slip rate represents only part of the 6 mm yr of shortening measured by geodesy across the channel and estimated from relative pacific north american plate motions across the transverse ranges additional shortening is probably accommodated on other active thrusts in the western transverse ranges and in the northern channel along the santa barbara coast deformed seafloor sediments and a swarm of axial surface seismicity along the fold trends indicate that the underlying thrusts are active and may pose significant earthquake hazards to coastal southern california unsegmented fault surfaces are used through empirical relationships between fault surface area and rupture magnitude to estimate the sizes of potential earthquakes this analysis suggests that a ramp in the channel islands fault beneath the offshore oak ridge trend is capable of rupturing in a m s 7 2 earthquake earthquakes of this magnitude may release 2 m of slip which when combined with the estimated slip rate 1 3 mm yr yields an earthquake recurrence interval of 1500 yr for this channel islands fault ramp

cenozoic right lateral wrench tectonics in the western pyrenees spain the ubierna fault system abstract a study of macro and mesostructural deformation patterns of the southern margin of the cantabrian area western pyrenees spain has revealed a complex cenozoic tectonic framework right lateral tectonics reactivated inherited wnw ese striking faults which developed during late paleozoic and early triassic events and late jurassic to early cretaceous main rifting stage the ubierna fault represents the southern boundary of the mesozoic basin during the oligocene even eocene to present day deformation this fault and the ventaniella fault located to the south in the study area acted as right lateral slightly transpressive elements forming a 120 km long and 15 km wide overstep area here named ubierna fault system where the cumulative right lateral displacement exceeds 15 km the cenozoic tectonic framework of the ubierna fault system includes reactivation along the wnw ese faults development of negative and mostly positive flower structures branch faults strike slip duplexes and releasing and restraining bends ne sw to ene wsw striking reverse faults and contractional horsetail terminations and nnw sse striking normal faults and joints are produced by the wnw ese right lateral strike slip motion the extensional elements are well developed and deformation progression implied their incorporation in the strike slip system as right lateral faults forming part of strike slip duplexes the abundance of flower structures striking wnw ese and paralleling the main strike slip faults together with the overall uplift of the overstep area testifies for a slight compressional component at a regional scale the ubierna fault system represents the most prominent element of a cenozoic transpressional belt which incorporates the western portion of the basque cantabrian basin and the asturian massif area lateral transition between this transpressive belt and the dip slip belt located to the east occurs across an area experiencing along strike shortening which developed to accommodate the eastward extrusion of the transpressional belt

radiation damage in zircon and monazite monazite and zircon respond differently to ion irradiation and to thermal and irradiation enhanced annealing monazite cannot be amorphized by 800 kev kr ions at temperatures greater than 175 c whereas zircon can be amorphized at temperatures up to 740 c the damage process i e elastic interactions leading to amorphization in radioactive minerals metamictization is basically the same as for the ion beam irradiated samples with the exception of the dose rate which is much lower in the case of natural samples the crystalline to metamict transition in natural samples with different degrees of damage from almost fully crystalline to completely metamict is compared to the sequence of microstructures observed for ion beam irradiated monazite and zircon the damage accumulation process representing the competing effects of radiation induced structural disorder and subsequent annealing mechanisms irradiation enhanced and thermal occurs at much higher temperatures for zircon than for monazite the amorphization dose expressed as displacements per atom is considerably higher in the natural samples and the atomic scale process leading to metamictization appears to develop differently ion beam induced amorphization data were used to calculate the decay event dose required for amorphization in terms of a critical radionuclide concentration i e the concentration above which a sample of a given age will become metamict at a specific temperature this equation was applied to estimate the reliability of u pb ages to provide a qualitative estimate of the thermal history of high u natural zircons and to predict whether actinide bearing zircon or monazite nuclear waste forms will become amorphous metamict over long timescales

3d fold growth rates geological folds are inherently 3d structures therefore they also grow in three dimensions here fold growth in all three dimensions is quantified by numerically simulating upright single layer folds in 3d newtonian media horizontal uniaxial shortening leads to a buckling instability which grows from a point like initial perturbation in all three dimensions by fold amplification vertical fold elongation parallel to fold axis and sequential fold growth parallel to shortening direction of secondary and further folds adjacent to the initial isolated fold the two lateral directions exhibit similar averaged growth rates leading to bulk fold structures with aspect ratios in map view close to 1 however fold elongation is continuous with increasing bulk shortening while sequential fold growth exhibits jumps whenever a new sequential fold appears and the bulk fold structure therefore suddenly occupies more space compared with the two lateral growth directions fold amplification exhibits a slightly higher growth rate