an 40ar 39ar thermochronology of the ofoten troms region implications for terrane amalgamation and extensional collapse of the northern scandinavian caledonides fifteen 40ar 39ar cooling ages are reported for metamorphic hornblende and muscovite from far traveled terranes constituting the ofoten nappe stack of northern norway eight cooling ages on hornblende range from 425 to 394 ma and seven muscovite ages from the same or nearby outcrops as the hornblendes range from 400 to 373 ma these data are compared with 40ar 39ar ages from over a large part of the northern caledonides to evaluate regional mineral cooling patterns results indicate that 1 scandian silurian devonian metamorphism was predominant 2 most of the nappes investigated contain some vestige of pre scandian tectonism and or metamorphism 3 hornblende and muscovite cooling ages are progressively younger to the west and south which suggests a hinged to the east mineral cooling pattern and 4 a late out of sequence thrust is the only disruption of this cooling pattern synmetamorphic amalgamation of the nappes resulted from scandian a type subduction the hinged to the east mineral cooling pattern implies isostatic adjustment and exhumation of the footwall of a west dipping crustal scale extensional fault located somewhere west of the present norwegian coast during late synorogenic gravitational collapse the late out of sequence fault formed contemporaneously with uplift in the hinterland implying a kinematic and temporal connection with east directed contractional faulting in the foreland

u pb dating of prograde and retrograde titanite growth during the scandian orogeny u pb ages of metamorphic titanite from high grade gneisses of the nasafjallet window in the north central scandinavian caledonides record growth over an 20 m y interval during the late silurian to early devonian biotite amphibolite gneisses located near the basement cover boundary contain metamorphic titanite in two microtextural settings one as lenticular grains distributed throughout a recrystallized matrix of metamorphic phases and one as plate like grains enclosed within biotite grains these distinct morphological populations exhibit core overgrowth relationships with compositionally similar cores and overgrowths but the plate like titanite grains have a much higher proportion of overgrowth and give slightly younger ages cores and overgrowths in both types are inferred to have formed along the prograde ca 413 ma and retrograde ca 395 ma paths respectively of a single metamorphic cycle associated with the burial and exhumation of a slice of baltic basement during the caledonide orogeny baltica laurentia collision the existence of polygenic u pb systematics in metamorphic titanite demonstrates the potential usefulness of titanite to reveal multiple metamorphic and deformational episodes and to constrain the duration of metamorphic events

patterns rates and possible causes of saltmarsh erosion in the greater thames area uk the estuary dominated coast of the greater thames in england has experienced rapid lateral erosion and internal dissection of saltmarshes this paper provides an overview of saltmarsh development in this area and re examines the role of environmental and human forcing factors it draws on documentary evidence including historical maps survey data and time series data of forcing factors lateral marsh retreat began in the 19th century in the medway and blackwater estuaries followed by other estuaries in the greater thames region at the beginning of the 20th century the outer estuaries and the wider parts of the inner estuaries especially have experienced erosion erosion has been modest in wave sheltered areas e g the colne and the inner crouch in the 1960s and more widely the 1970s a phase of rapid erosion took place with erosion rates of up to ca 16 ha year 1 per site notably along the open coast of dengie and foulness and in the blackwater and thames estuaries at all sites vertical sediment accretion was well able to keep up with sea level rise over the past century evidence indicates that there may have been several causes for the erosion of saltmarshes these are notably land claim and embankment construction increasing the tidal range and current velocities and a continuous rise of especially high and extreme water levels the latest episode of rapid erosion in the 1970s is largely attributed to changes in the wind wave climate for example erosion at wave exposed sites coincided with a peak in high magnitude waves combined with a high incidence of southeasterly waves the study shows that many factors including natural forcing factors and human activities have to be taken into account when explaining saltmarsh development

multistage zircon and titanite growth and inheritance in an archean gneiss complex winnipeg river subprovince ontario abstract the paper presents results from a u pb isotopic investigation of zircon and titanite from three phases of the archean sioux lookout gneiss complex at the margin of the gneissic plutonic winnipeg river subprovince wrs of the superior province the data reveal an intricate data pattern caused by inheritance and multistage crystallization and record the timing of two major orogenic events followed by a protracted post metamorphic evolution a zircon age of 2889 3 ma for a foliated pink granite correlates with that of similar units elsewhere in the superior province and reflects one of the first major episodes of crustal assembly in the pre kenoran evolution of the region tonalite and diorite from the same site yield zircon and titanite ages of 2704 2 and 2705 5 ma which correspond to the timing of major magmatism related to kenoran collision of the wrs with the adjacent wabigoon volcanic domains tonalite and diorite both contain abundant xenocrystic zircon moreover the late kinematic diorite also includes xenocrystic titanite which has a minimum age of 2730 ma and coexists with younger ca 2705 ma titanite and zircon two generations of titanite are also present in both the tonalite and the granite the earliest one reflects the 2704 ma plutonic metamorphic event whereas the second one indicates post metamorphic crystallization at 2650 and 2627 ma caused by superimposed hydrothermal activity and retrogression the data support the concept that the titanite can remain a closed system to pb diffusion at elevated temperatures as long as the crystals escape magmatic or metamorphic recrystallization conversely they also show that titanite can easily be produced by low temperature processes hence generalized interpretation of titanite ages in terms of regional cooling can be inappropriate

geochronology and trace element geochemistry of titanite in the machangqing cu mo dominated polymetallic deposit yunnan province southwest china abstract the machangqing cu mo dominated polymetallic deposit is a porphyry skarn epithermal cu mo au metallogenic system located in the middle part of the jinshajiang ailaoshan alkaline porphyry metallogenic belt the skarn mineralization of the machangqing deposit mainly occurs along the contacts between the alkalic porphyry intrusions and the surrounding lower ordovician xiangyang formation rocks we present la icp ms u pb ages and trace element data for titanite from the machangqing deposit in order to investigate the origin of this deposit based on mineral textures and assemblages two types of titanite are recognized in machangqing magmatic titanite type i from the granite porphyry and hydrothermal titanite from the mineralized skarn the coarse grained magmatic titanite is euhedral and occurs as discrete grains in the interstices of feldspar quartz and biotite whereas fine to medium grained hydrothermal titanite crystals type ii are euhedral to subhedral and occur in association with skarn minerals such as garnet pyroxene and magnetite magmatic titanite has lower feo al2o3 f and nb ta but higher tio2 th u hfses and lu hf than hydrothermal titanite the magmatic titanite has higher lree hree ratios and total ree contents with stronger negative eu anomalies than its mineralized skarn counterpart trace elemental characteristics of hydrothermal titanite in machangqing are consistent with relatively low f contents and oxygen fugacities when compared to the neighboring beiya gold dominated polymetallic deposit in the same metallogenic belt the weighted average 206pb 238u age of 34 3 1 2 ma of hydrothermal titanite is within error but slightly younger than the age of magmatic titanite 37 5 4 1 ma indicating that the skarn mineralization followed the emplacement of the granite porphyry and was broadly coeval with the porphyry mineralization the porphyry and skarn types of mineralization at machangqing were formed from the same metallogenic system different ore forming conditions such as oxygen fugacities and f contents might be responsible for different metal enrichments at the machangqing and beiya deposits

paleoproterozoic basement cover infolding and thick skinned thrusting in hearne domain nunavut canada intracratonic response to trans hudson orogen enveloped by orogenic belts during the assembly of laurentia 2 0 1 7 ga the rae and hearne domains of the western churchill province experienced a complex sequence of tectonic events historically referred to as the hudsonian orogeny in hearne domain diverse thick skinned intraplate structures developed in response to accretionary processes in trans hudson orogen these structures include infolds of archean basement and paleoproterozoic cover and broken foreland thrusts in central hearne domain an intracratonic basin succession of continental to shallow marine strata hurwitz group 2 45 1 91 ga is exposed in outliers that constitute the keels of doubly plunging basement cover synclinoria defining a fold train with wavelengths of 35 45 km with the exception of local out of syncline shear zones basement and hurwitz group are welded formed under greenschist facies conditions the basement cover infolds are open concentric and commonly display complex structures in their interiors in the poorfish windy outlier southwestern hearne domain continental rift deposits of the kiyuk group unconformably overlie the hurwitz group in contrast to basement cover infolding to the north and east archean basement the hurwitz group and the kiyuk group are imbricated by thick skinned northwest vergent thrusts and folds thrusting in the poorfish windy belt was completed by 1815 10 ma as indicated by new u pb data from hydrothermal metamorphic titanite recovered from recrystallized cements at the top of the kiyuk group we interpret that shortening from shallow level basement cover infolding is balanced at depth by intrabasement faulting and distributed ductile strain and that the geometric link between central hearne basement cover infolding and poorfish windy thrusting is via intrabasement faults that cut to the surface the main controls on thick skinned deformation were the high competency of the lower hurwitz group previous thermal weakening basement heterogeneities and possibly shallow subduction preceding terminal collision in trans hudson orogen 2002 elsevier science b v all rights reserved

the effect of calcium ions in pore water on the residual shear strength of kaolinite and sodium montmorillonite this paper reviews the literature concerning the effects of pore water chemistry on residual shear strength it presents the results of index limit and residual shear strength testing undertaken on kaolinite and sodium montmorillonite using concentrations of calcium chloride similar to the calcium levels measured in groundwaters obtained from landslipped calcareous mudrock of the fuller s earth formation the residual shear strength of the sodium montmorillonite increased markedly for the sample treated and tested with 80 mg 1 cat compared with that tested with deionized water greater concentra tions of ca2 resulted in only a marginal further increase in the residual shear strength these changes were also reflected in the interpreted parameters or and c the liquid limit of the montmorillonite decreased dramatically when the samples were treated with 80 mg 1 ca2 and this effect persisted and or was slightly enhanced when the concentration of ca2 was increased the residual shear strength

scandinavia s north atlantic passive margin 1 the tectonics of the eastern passive margin of the north atlantic are reexamined the scandinavian north atlantic passive margin includes not only the offshore exploration and basin domain but also large portions of the onshore domains of the scandinavian caledonides combined information from structural geology potential field data regional geology basin development and geomorphology made it possible to propose a new definition of the passive margin the rift shoulder is formed by linked faults defining the present rift flank these faults are the extensional structures located furthest to the east onshore norway sweden that can be linked to the rifting that led to the formation of the north atlantic this innermost boundary fault system ibf is formed by a set of normal west dipping crustal faults it extends over a distance exceeding 2000 km from the north sea across the caledonian mountain belt to the barents sea the passive margin width between the continent ocean boundary and the ibf ranges from 550 km in the south to over 700 km in mid norway to 165 km north of lofoten rifting and faulting on the ibf started in permo carboniferous and a succession of rift phases eventually culminated in continental breakup and the formation of the north atlantic basin development between permian and cretaceous was toward the future breakaway fault but faulting was also active on land from mesozoic to present onshore offshore crustal scale cross sections show the geometry of the passive margin the dip orientation of the major faults and the changes in crustal thickness

the remarkable re os chronometer in molybdenite how and why it works the re os rhenium osmium chronometer applied to molybdenite mos2 is now demonstrated to be remarkably robust surviving intense deformation and high grade thermal metamorphism successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite unique to each sample such that recognized spatial decoupling of 187re parent and 187os daughter within individual molybdenite crystals is overcome highly precise accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry id ntims spatial decoupling of parent daughter precludes use of the laser ablation icp ms microanalytical technique for re os dating of molybdenite the use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons the rb sr k ar and 40ar 39ar chronometers are susceptible to chemical and thermal disturbance particularly in terranes that have experienced subsequent episodes of hydrothermal magmatic activity and therefore should not be used as a basis for establishing accuracy in re os dating of molybdenite as has been done in the past re os ages for molybdenite are almost always in agreement with observed geological relationships and when available with zircon and titanite u pb ages for terranes experiencing multiple episodes of metamorphism and deformation molybdenite is not complicated by overgrowths as is common for some minerals used in u pb dating e g zircon monazite xenotime nor are re and os mobilized beyond the margins of individual crystals during solid state recrystallization moreover inheritance of older molybdenite cores incorporation of common os and radiogenic os loss are exceedingly rare whereas inheritance common pb and pb loss are common complications in u pb dating techniques therefore molybdenite ages may serve as point in time markers for age comparisons

pre orogenic upper crustal softening by lower greenschist facies metamorphic reactions in granites of the central pyrenees pre kinematic greenschist facies metamorphism is often observed in granites and basement units of mountain belts but rarely dated and accounted for in orogenic cycle reconstructions studying pre kinematic alteration is challenging because of its usual obliteration by subsequent syn kinematic metamorphism often occurring at conditions typical of the brittle ductile transition it is however to be expected that pre kinematic alteration has major implications for the rheology of the upper crust in the 305 ma old variscan basement of the bielsa massif located in the axial zone of the pyrenees successive fluid rock interaction events are recorded in granites below 350 c combined microstructural and petrographic analysis low t thermobarometry and in situ u th pb dating of anatase titanite and monazite show extensive pre orogenic pre alpine and pre kinematic alteration related to feldspar sericitization and chloritization of biotite and amphibole at temperatures of 270 350 c at 230 300 ma this event is followed by a second fluid rock interaction stage marked by new crystallization of phyllosilicates at 200 280 c and is associated with the formation of mylonitic shear zones and fractures parallel to the shear planes u pb anatase and monazite ages as well as the microtextural relationships of accessory minerals suggest an age for this event at 40 70 ma consistent with independent regional geology constraints the variscan basement was therefore softened at late to post variscan time at least 150 200 ma before the main alpine shortening while alpine age compression c 35 50 ma leads to the formation of a dense net of mylonites the associated deformation both distributed at the scale of the bielsa massif and localized at decametric scale in mylonitic corridors precedes the strain localization along the major thrusts of the axial zone the bielsa massif is a good example where inherited pre orogenic upper crustal softening controls the deformation patterns in granitic basement units through low grade metamorphic reactions

low p t caledonian resetting of u rich paleoproterozoic zircons central sweden uranium rich zircons from a paleoproterozoic high grade deformation zone in the fennoscandian shield central sweden show an almost complete resetting of the u pb system in early phanerozoic time a mylonitic gneiss in the deformation zone contains two types of highly discordant 70 u rich zircons large brown cloudy prisms and small milky white irregularly shaped grains the gneiss also contains mostly clear prismatic zircon of lower u content with mildly discordant to concordant u pb ages laser raman spectroscopy reveals that the dark cathodoluminescent areas in brown zircons have a highly metamict crystal structure whereas the structures of both the dark cathodoluminescent milky white grains and the bright cathodoluminescent clear prisms have higher degrees of crystallinity age dates obtained by u pb sims analysis of 40 zircons of the three types described above range continuously from concordant at 1871 11 ma to 98 discordant at 384 15 ma the strongly discordant zircons clearly have suffered severe disturbance at about the time of the caledonian orogeny however caledonian metamorphic temperatures and pressures in this region did not exceed 150 200 c and 1 3 kbar too low to strongly disturb the u pb systematics in non metamict zircon by thermal means alone independent evidence indicates that saline fluids were circulating in the paleoproterozoic basement rocks at this time possibly driven by hydrological gradients generated in front of the encroaching caledonian orogenic wedge these low temperature saline fluids are inferred to be responsible for causing both strong pb loss in the mostly metamict brown zircons via a diffusive process and the formation of small milky white zircon via a low temperature recrystallization or dissolution re precipitation process

constraints on hydrothermal processes and water exchange in lake vostok from helium isotopes lake vostok the largest subglacial lake in antarctica is covered by the east antarctic ice sheet which varies in thickness between 3 750 and 4 100 m ref 1 at a depth of 3 539 m in the drill hole at vostok station sharp changes in stable isotopes and the gas content of the ice delineate the boundary between glacier ice and ice accreted through re freezing of lake water2 unlike most gases helium can be incorporated into the crystal structure of ice during freezing3 making helium isotopes in the accreted ice a valuable source of information on lake environment here we present helium isotope measurements from the deep section of the vostok ice core that encompasses the boundary between the glacier ice and accreted ice showing that the accreted ice is enriched by a helium source with a radiogenic isotope signature typical of an old continental province this result rules out any significant hydrothermal energy input into the lake from high enthalpy mantle processes which would be expected to produce a much higher 3he 4he ratio based on the average helium flux for continental areas the helium budget of the lake leads to a renewal time of the lake of the order of 5 000 years

an inventory of active subglacial lakes in antarctica detected by icesat 2003 2008 through the detection of surface deformation in response to water movement recent satellite studies have demonstrated the existence of subglacial lakes in antarctica that fill and drain on timescales of months to years these studies however were confined to specific regions of the ice sheet here we present the first comprehensive study of these active lakes for the antarctic ice sheet north of 868 s based on 4 5 years 2003 08 of nasa s ice cloud and land elevation satellite icesat laser altimeter data our analysis has detected 124 lakes that were active during this period and we estimate volume changes for each lake the icesat detected lakes are prevalent in coastal antarctica and are present under most of the largest ice stream catchments lakes sometimes appear to transfer water from one to another but also often exchange water with distributed sources undetectable by icesat suggesting that the lakes may provide water to or withdraw water from the hydrologic systems that lubricate glacier flow thus these reservoirs may contribute pulses of water to produce rapid temporal changes in glacier speeds but also may withdraw water at other times to slow flow

early ordovician u pb metamorphic ages of the eclogite bearing seve nappes northern scandinavian caledonides eclogite grade metamorphism of the seve nappe complex snc in norrbotten sweden records the attempted subduction of the baltic continental margin during the early palaeozoic evolution of the iapetus ocean metamorphic titanite sampled from several calcsilicate gneisses of the snc in norrbotten occurs as part of a prograde eclogite facies metamorphic mineral assemblage and yields concordant to nearly concordant u pb ages of 500 475 ma later structural disruption of these rocks occurred during the siluro devonian scandian phase of the caledonide orogeny but the u pb systematics show no evidence of a second generation metamorphic or recrystallized of titanite or of post early ordovician disturbance through pb loss hence the u pb ages are believed to record the time of prograde mineral growth during eclogite facies metamorphism of the snc these results support earlier sm nd and 40ar 39ar studies indicating an early ordovician metamorphic age for the eclogitic norrbotten snc and confirm the early ordovician destruction of at least this segment of the palaeozoic passive margin of baltica these results indicate that the snc in the northern scandinavian caledonides was subducted and metamorphosed to high grade some 50 70 myr prior to the high grade metamorphism of the snc in the central scandinavian caledonides this result requires significantly different early palaeozoic tectonic histories for rocks mapped as snc in the northern caledonides and those in the central caledonides despite a seemingly similar tectonostratigraphic position and broadly similar high grade metamorphism

dating deposition and low grade metamorphism by in situ upb geochronology of titanite in the paleoproterozoic timeball hill formation southern africa abstract titanite coexists with zircon in a felsic tuff in the paleoproterozoic timeball hill formation southern africa two generations of titanite are preserved euhedral brown crystals with apatite inclusions and colorless matrix filling cement the brown titanite has elevated u th and fe and low al consistent with a magmatic origin whereas the colorless titanite has higher al and f contents suggestive of a metamorphic paragenesis in situ shrimp geochronology of zircons extracted from a polished thin section of the tuff bed suffer from inheritance and pb loss and yield an imprecise date 2259 35 ma whereas coexisting brown titanites give a weighted mean 207pb 206pb age of 2278 7 ma this date is consistent with u pb zircon ages for tuffs in the same stratigraphic unit from a nearby drill hole the brown titanite is interpreted to be magmatic and to provide a reliable estimate for the age of deposition in situ u pb dating of matrix filling titanite cement from the same stratigraphic interval yields an age of 2145 12 ma which corresponds with previous estimates for a low grade tectonothermal event in southern africa our results demonstrate that titanite is a versatile chronometer that can be used to constrain depositional ages and those of low grade metamorphism thus increasing the number of sedimentary rocks that can be dated and elucidating the low temperature geological history of depositional basins

polyphase growth of accessory minerals during continental collision geochemical evidence from ultrahigh pressure metamorphic gneisses in the sulu orogen abstract an integrated study of petrology geochronology and geochemistry was performed for ultrahigh pressure metamorphic gneisses in the sulu orogen the results are used to elucidate the polyphase growth of such metamorphic minerals as zircon titanite and garnet in response to pressure temperature changes and fluid melt action during continental collision this provides insights into the property of metamorphic fluid melt and their effects on trace element mobility a combined result from ree patterns mineral inclusions and ti in zircon temperatures indicates three stages of zircon growth prograde growth occurred at 237 ma primarily at eclogite facies retrograde growth at 222 ma mostly at eclogite facies and the last growth at 205 ma at granulite facies the three stages of zircon growth are deciphered by distinct ree patterns and trace element compositions reflecting the differences in the property of metamorphic fluid melt the episodic growth of metamorphic zircon is primarily dictated by the episodic concentration of zr and si in metamorphic fluid melt relict domains of magmatic titanite are distinguished from metamorphosed and metamorphic domains by their distinctive ree patterns and trace element compositions the metamorphic titanite exhibit variably elevated nb contents and nb ta ratios suggesting nb ta fractionation due to breakdown of amphibole and or biotite during metamorphism polyphase growth of garnet is suggested by an integrated analysis of mineral inclusions and major and trace elements in large garnet grains trace element abundances vary in different zones of garnet which is ascribed to changes in the paragenesis and composition of matrix minerals involved in garnet forming reactions at different p t conditions therefore the metamorphic growth of zircon titanite and garnet would have occurred not only during prograde subduction but also during retrograde exhumation in the continental collision zones both metamorphic dehydration and partial melting would have taken place episodically during the collisional orogeny the breakdown of hydrous minerals at high to ultrahigh pressure conditions is a key to fluid liberation and element supply for the growth of these accessory minerals

metamorphism in basement rocks and the implications for the tectonic evolution nasafjall window scandinavian caledonides the rocks of the nasafjall window comprise proterozoic granitoids with a metasedimentary cover of late precambrian to ordovician age the mierkenis group the metamorphic grade in the window varies from greenschist facies in the eastern part of the window to amphibolite facies in the western part the metamorphic maximum is syn to post kinematic in relation to the formation of the thrust related pervasive foliation this suggests a rapid basement heating in response to the late silurian to early devonian nappe emplacement the caledonian metamorphism terminated in middle devonian times and the retrograde phase was characterized by decompression this implies that the later stage of the thrusting was not associated with an increase in thickness of the nappe pile above the rocks of the nasafjall window

inherited pb components in magmatic titanite and their consequence for the interpretation of upb ages abstract the occurrence of inherited radiogenic pb components in 35 ma old magmatic titanite is reported here for the first time the about 810 ma age of the inherited components is identical to that contained in zircon from the same amphibole bearing syenite sample in both minerals the precambrian components were not totally reset during magmatic new growth at 35 ma this age pattern substantiates that the u pb chronometer in titanite is resistant to temperatures in excess of 712 c as is already known for zircon and monazite in consequence u pb ages from crystalline titanites have to be interpreted as the age of mineral formation or re crystallization rather than the time of u pb system closure during cooling of the rock

in situ la icpms trace elements and u pb analysis of titanite from the mesozoic ruanjiawan w cu mo skarn deposit daye district china abstract in this paper we present u pb ages and trace element compositions of titanite from the ruanjiawan w cu mo skarn deposit in the daye district eastern china to constrain the magmatic and hydrothermal history in this deposit and provide a better understanding of the u pb geochronology and trace element geochemistry of titanite that have been subjected to post crystallization hydrothermal alteration titanite from the mineralized skarn the ore related quartz diorite stock and a diabase dike intruding this stock were analyzed using laser ablation inductively coupled plasma mass spectrometry la icpms titanite grains from the quartz diorite and diabase dike typically coexist with hydrothermal minerals such as epidote sericite chlorite pyrite and calcite and display irregular or patchy zoning these grains have low lree hree and high th u and lu hf ratios coupled with negative eu and positive ce anomalies the textural and compositional data indicate that titanite from the quartz diorite has been overprinted by hydrothermal fluids after being crystallized from magmas titanite grains from the mineralized skarn are texturally equilibrated with retrograde skarn minerals including actinolite quartz calcite and epidote demonstrating that these grains were formed directly from hydrothermal fluids responsible for the mineralization compared to the varieties from the quartz diorite stock and diabase dike titanite grains from the mineralized skarn have much lower ree contents and lree hree th u and lu hf ratios they have a weighted mean 206 pb 238 u age of 142 2 ma mswd 0 7 2 in agreement with a zircon u pb age of 144 1 ma mswd 0 3 2 of the quartz diorite and thus interpreted as formation age of the ruanjiawan w cu mo deposit titanite grains from the ore related quartz diorite have a concordant u pb age of 132 2 ma mswd 0 5 2 which is 10 12 ma younger than the zircon u pb age of the same sample and thus interpreted as the time of a hydrothermal overprint after their crystallization this hydrothermal overprint was most likely related to the emplacement of the diabase dike that has a zircon u pb age of 133 1 ma and a titanite u pb age of 131 2 ma the geochronological results thus reveal two hydrothermal events in the ruanjiawan deposit an early one forming the wu cu mo ores related to the emplacement of the quartz diorite stock and a later one causing alteration of the quartz diorite and its titanite due to emplacement of diabase dike it is suggested that titanite is much more susceptible to hydrothermal alteration than zircon results from this study also highlight the utilization of trace element compositions in discriminating titanite of magmatic and hydrothermal origins facilitating a more reasonable interpretation of the titanite u pb ages

preserved zr temperatures and u pb ages in high grade metamorphic titanite evidence for a static hot channel in the himalayan orogen abstract titanite grains from 800 c gneisses of the c 6 km thick greater himalayan sequence of central nepal were analyzed for zr in titanite temperatures and u pb ages to investigate the formation and evolution of a former weak mid crustal channel in the himalaya laser ablation icp ms depth profiles and spot analyses of titanite zr and u pb isotopic compositions are inconsistent with diffusional reequilibration on scales greater than 1 2 m and instead data appear to faithfully record both temperature and age titanite records protracted heating from 700 750 c at 37 ma to 775 c at 24 ma and possibly slight cooling to 765 c at 20 ma such temperatures exceed partial melting reactions in associated metapelites and imply profoundly weak rheologies i e a hot channel yet predate initiation of the bounding main central thrust and south tibetan detachment systems by as much as 15 myr evidently thick but weak crustal channels may remain stationary with respect to the convergence direction for 10 myr even during one of earth s biggest continent continent collisions

inherited zircon and titanite upb systems in an archaean syenite from southwestern australia implications for upb stability of titanite abstract inherited zircon and titanite have been identified in a syenite from the archaean of southwestern australia conventional and shrimp analyses on euhedral zoned zircon and zoned rims on complex grains define a crystallisation age of 2654 5 ma for the syenite in addition shrimp analyses on zircon cores and unzoned subhedral zircons show that zircon has a ca 3250 ma inherited component conventional u pb ages on titanite also fall between ca 3250 ma and ca 2650 ma demonstrating that inherited titanite as well as zircon is present in the syenite the syenite has been affected by regional upper amphibolite facies metamorphism at an estimated temperature of 625 650 c retention of the inherited radiogenic pb in the titanite is evidence that the closure temperature for titanite is greater than 650 c the presence of inherited titanite and zircon also demonstrates a crustal source component for the syenite and indicates it originated by partial assimilation of crustal rocks by a potassic magma at

saltmarsh soil evolution after land reclamation in atlantic estuaries bay of biscay north coast of spain abstract tidal wetland soils exhibit particular physical chemical properties governed mainly by tidal dynamics on the atlantic seaboard of the iberian peninsula a great swath of tidal wetlands which correspond to semi confined estuaries represents land reclaimed from the 18th century to the first half of the 20th century and used for urban development or agricultural production these interventions led to the end of tidal flooding in extensive areas of salt marshes causing a drop in the water table that triggered pyrite oxidization processes leaching of cations and salts and soil acidification in many cases these transformations have given rise to environmental problems such as the development of acid sulphate soils a resulting decrease in ph and the leaching of carbonates the organic carbon storage capacity has also been altered and the release of metal cations from sediments has caused toxic waters to appear in order to investigate the alterations caused by the historic reclamation of estuarine soils on the north coast of spain natural and reclaimed lands were mapped in two estuaries villaviciosa and san vicente de la barquera and zoned in accordance with flood frequency the different evolutionary paths of the two studied estuarine sites after reclamation can be assessed through the description and analysis of their soils despite reclamation some parts i e lower areas of the reclaimed lands do not remain fully isolated from tidal dynamics whose influence varies throughout the soil profiles that have developed since the strength of the morphological e g genetic horizons chemical ph metal cation concentration and functional balance of the carbon budget changes suffered by the original soils seem to depend strongly on the remaining tidal influence as well as the land use of the area

evidence for the stability of the potential nuclear waste host sphene over geological time from uranium lead ages and uranium series measurements abstract a sphene based glass ceramic material is being investigated as a potential host for canadian nuclear fuel recycle waste the ability of sphene to retain certain radionuclides over geological time is examined using observed properties and age measurements of natural sphenes the long term stability of sphene is determined by comparing u th pb isotopic age data for sphene from the literature with ages determined for zircon and other minerals better internal agreement is found between u th pb sphene ages than for zircon ages indicating the resistance of sphene to daughter radionuclide loss over periods as long as 3000 ma excellent agreement was observed between sphene ages and the estimated age of crystallization of the host rocks or vein infillings except where subsequent metamorphim had reset the sphene age complete lead loss was generally found to accompany high grade metamorphic conditions when temperatures exceeded 500 c stability over shorter periods of geological time was found for vein infilling and mineral separates of sphene using uranium series disequilibrium analysis conditions of secular equilibrium in the decay chain 238 u 234 u 230 th 226 ra were observed for most of the 21 sphenes studied indicating that no radionuclide migration had occurred over periods as long as the last 1 ma exceptions to this were four sphenes that had 234 u deficiencies between 6 and 24 and two sphenes that showed 226 ra 230 rh disequilibrium no correlation was found between the extent of radiation damage suffered by the sphenes and the presence of uranium series disequilibrium the presence of alteration products in three sphenes did correlate however with measured disequilibrium indicating that some 234 u and 226 ra had been lost or gained by these samples in the last 1 ma and 8 ka respectively

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

polygenetic titanite records the composition of metamorphic fluids during the exhumation of ultrahigh pressure metagranite in the sulu orogen

estuarine fluvial floodplain formation in the holocene lower tagus valley central portugal and implications for quaternary fluvial system evolution abstract we present a brief synthesis of the quaternary fluvial record in the lower tagus basin central portugal concentrating on factors controlling infill and incision the holocene part of the record forms the focus of this paper and guides the questioning of the basic assumptions of the established quaternary fluvial evolution model in particular the link between sea level change and fluvial incision deposition we suggest that several incision aggradation phases may have occurred during glacial periods major aggradation events may overlap with cold episodes while incision appears to concentrate on the warming limb of climate transitions the complex stratigraphy of the quaternary record in the lower tagus valley is influenced by repeated base level and climate changes this paper submits the first chronostratigraphic framework for valley fill deposits in the lower tagus area sea level rise forced aggradation and controlled deposition of the fine grained sedimentary wedge underlying the low gradient lower tagus floodplain investigations have focused on the lower muge tributary where rapidly aggrading estuarine and fluvial environments were abruptly established 8150 cal bp as sea level rose base level at the valley mouth controlled the upstream extent of the fine grained backfill tidal environments disappeared abruptly 5800 cal bp when the open estuary at the muge confluence was infilled by the tagus river the decrease and final still stand of sea level rise led to floodplain stabilisation with peat 6400 5200 cal bp and soil formation 5200 2200 cal bp localised renewed sedimentation 2200 200 cal bp is linked to human activity

timing structural assembly metamorphism and cooling of caledonian nappes in the ofoten efjorden arca north norway tectonic insights from u pb and40ar 39ar geochronology u pb and 40ar 39ar geochronology from part of the northern norwegian caledonides indicates a cooling and unroofing history different from that inferred for the caledonides in southwest norway in the ofoten efjorden area of north norway the narvik nappe complex nnc represents the basal portion of the composite caledonian allochthon and consists of amphibolite facies oceanic affinity metasedimentary rocks intruded by numerous pretectonic felsic dikes two of these dikes yield indistinguishable u pb zircon ages of 437 1 ma providing a maximum age for tectonic assembly metamorphism and deformation at this structural level u pb ages of metamorphic monazite 432 2 ma and zircon 431 7 0 5 ma from pelitic schist and migmatite yield robust estimates of the age of peak metamorphism combined with structural evidence for transport parallel stretching and subvertical attenuation of the rock mass at the time of metamorphism these ages suggest that local and or episodic extensional modification of the

radar based subglacial lake classification in antarctica 1 subglacial lakes in east antarctica can be separated into four categories specified by radar reflection properties definite lakes are brighter than their surroundings by at least 2 db relatively bright and both are consistently reflective specular and have a reflection coefficient greater than 10 db absolutely bright dim lakes are relatively bright and specular but not absolutely bright indicating nonsteady ice dynamics fuzzy lakes are both relatively and absolutely bright but not specular and may indicate saturated sediments or swamps indistinct lakes are absolutely bright and specular but no brighter than their surroundings lakes themselves and the different classes of lakes are not arranged randomly throughout antarctica but are clustered around ice divides ice stream onsets and prominent bedrock troughs with each cluster demonstrating a different characteristic lake classification distribution the lake classification algorithm expands on previous studies and demonstrates a novel way to characterize ice water interactions in east antarctica

application of in situ titanite u pb geochronology to volcanic hosted magnetite deposit new constraints on the timing and genesis of the zhibo deposit western tianshan nw china abstract the awulale metallogenic belt within the western tianshan orogenic belt of northwestern china includes four large iron oxide deposits with a total resource of 1000 million metric tons mt fe among these the zhibo deposit is a large 337 mt at 26 68 wt fe volcanic hosted magnetite deposit where massive ti poor magnetite ores are hosted in the carboniferous volcanic and volcaniclastic sequences here we use in situ u pb analyses of titanite and zircon by laser ablation icp ms to place tight constraints on the timing and genesis of iron mineralization at zhibo titanite in the magnetite ore are closely associated with magnetite and ca alteration assemblages consisting of actinolite epidote and calcite the dated titanite exhibit strongly fractionated ree patterns with heavy ree enrichment neutral to negative eu anomalies and have low th and u concentrations and low th u ratios the textural and geochemical characteristics indicate that the titanite are hydrothermal in origin and coeval with magnetite in the paragenetic sequence titanite from three magnetite ores yield weighted mean 207pb corrected 206pb 238u ages of 310 3 1 8 ma mswd 0 17 310 1 1 8 ma mswd 0 30 and 315 3 2 5 ma mswd 0 26 constraining the iron mineralization at zhibo to a time interval between 315 ma and 310 ma magmatic zircon from a host andesite sample yield u pb age of 316 3 3 4 ma mswd 0 079 the overlapping ages for magnetite ores and the host volcanic rocks confirm a genetic relationship between them and are consistent with a magmatic contribution to the mineralization system as also indicated by fe and o isotope data of magnetite in previous work these new u pb results are also consistent with age estimates for mineralization and igneous activity in other major magnetite deposits in the awulale iron metallogenic belt indicating a significant iron mineralization event related to the ca 315 300 ma volcanism combined with previous geological and geochemical evidence we conclude that the zhibo magnetite deposit was formed mainly by iron rich fluids derived from a mafic to intermediate magma in a volcano plutonic structure

laser ablation icp ms titanite u th pb dating of hydrothermal ore deposits a case study of the tonglushan cu fe au skarn deposit se hubei province china abstract titanite from the tonglushan cu fe au skarn deposit daye district eastern china has been successfully dated by laser ablation inductively coupled plasma mass spectrometry la icp ms hydrothermal titanite from both skarn ores and calcite veins cutting the ore bodies are characterized by having much lower ree and th u and lu hf ratios compared to their magmatic equivalents from the ore related yangxin quartz diorite intrusion and a late stage albitite dike titanite from the yangxin quartz diorite and an albitite dike which intrudes both the quartz diorite intrusion and ore bodies yield weighted mean 206pb 238u ages of 136 0 1 5 ma and 120 6 2 3 ma 2 respectively in agreement within analytical uncertainty to their 208pb 232th ages in situ analysis of epidote enclosed hydrothermal titanite in thin sections of a skarn ore sample yields a mean 206pb 238u age of 135 9 1 3 ma and 208pb 232th age of 138 2 4 5 ma whereas titanite in calcite from a calcite dominated vein cross cutting the skarn ore body has consistent 206pb 238u and 208pb 232th ages of ca 121 ma the data thus reveal two independent hydrothermal events the earlier event was responsible for the known cu fe au skarn mineralization at tonglushan and throughout the daye district and was caused by coeval magmatism that has resulted in the emplacement of the yangxin quartz diorite the later event previously unrecognized was associated with a second magmatic pulse as represented by the albitite dikes and provides potential for discovering new mineral deposits at tonglushan and possibly over the daye district this study represents the first direct dating of skarn deposits using titanite u th pb geochronometer and signifies the utilization of titanite for precise dating of hydrothermal ore formation

compositional changes of minerals associated with dynamic recrystallizatin the rate of compositional and isotopic exchange between minerals may be enhanced significantly if the rock is deformed simultaneously the enhanced exchange rate may result from a reduction in grain size shorter distance for volume diffusion dissolution and growth of grains by diffusion creep pressure solution or the movement of high angle grain boundaries through strained grains during recrystallization in the dislocation creep regime the migration of high angle grain boundaries provides high diffusivity paths for the rapid exchange of components during recrystallization the operation of the latter process has been demonstrated by deforming aggregates consisting of two plagioclases an1 and an79 at 900 c 1 gpa confining pressure and a strain rate of 2x10 6s 1 the polygonal recrystallized grains were analyzed using an analytical transmission electron microscope and have a variable but often intermediate composition at the conditions of these experiments the volume interdiffusion rate of nasi caal is too slow to produce any observable chemical change and microstructural chemical relations indicate that the contribution from diffusion creep was insignificant except for initially fine grained 2 10 m aggregates these results indicate that strain induced recrystallization can be an effective mechanism for enhancing the kinetics of metamorphic reactions and for resetting the isotope systematics of minerals such as feldspars pyroxenes and amphiboles

ilmenite breakdown and rutile titanite stability in metagranitoids natural observations and experimental results rutile and titanite commonly form by replacement of ilmenite in metamorphic rocks exhumed orthogneiss from the western alps show that titanite is mostly stable below 1 gpa while rutile seems to dominate within rocks recrystallized under higher pressures we herein investigate phase relationships for four granitic compositions with variable cao content at medium to high pressure conditions 0 7 1 6 gpa 450 650 c with a focus on ilmenite breakdown and ti bearing species formation our piston cylinder experiments show that in the investigated p t range ilmenite reacts during metamorphism above 1 2 1 4 gpa to form rutile below this pressure titanite is the dominant ti bearing species for most granitoid compositions we also show that the position of this reaction curve is strongly influenced by the whole rock ca activity for low ca activities rutile may be stable down to 0 7 gpa and below within ilmenite pseudomorphs while the titanite stability field may extend to pressures 1 3 gpa for ca richer compositions both species may be stable in one single sample depending on the local ca activity gradients the finding of metamorphic rutile within metagranitoids with cao contents 2 wt can be considered under certain conditions as a reliable indicator of high pressure metamorphism this study also highlights the importance of improving our knowledge of the phase relationships between rutile and titanite as a function of p t x to better interpret the textural and tectonic history in natural samples as well as the meaning of age values yielded by rutile and titanite geochronometers

dating of subduction and differential exhumation of uhp rocks from the central dabie complex e china constraints from microfabrics rb sr and u pb isotope systems abstract the correlation of deformation fabrics and metamorphic reactions with geochronologic data of uhp metamorphic rocks demonstrate that the multistage subduction and exhumation history of the central dabie complex requires rapid subduction and rapid initial exhumation moreover these data show that volume diffusion is not the major resetting mechanism of radiogenic isotope systems thus our age data do not simply reflect a thermal cooling history in the investigated section the maximum age for uhp is given by the 244 3 ma 2 u pb age of a pre uhp titanite phenocryst that survived uhp metamorphism and subsequent tectonometamorphic events a minimum age for uhp is set by the 238 1 ma 2 238 u 206 pb mineral isochron age of titanite and cogenetic epidote these minerals formed from local partial melts during ascent and their age suggests fast exhumation and emplacement in the middle crust in the period of ca 238 218 ma the uhp terrain records ht metamorphism local partial melting and extensive pervasive strain below the eclogite jd grt stability field exhumation was polyphase with a first phase of fast exhumation succeeded by episodes of ht metamorphism and concomitant deformation at deep mid crustal level between 238 and 218 ma slow exhumation related to the final emplacement of tectonic units along greenschist facies shear zones did not cease before ca 209 204 ma the resetting and homogenization of radiogenic isotope systems were aided by dissolution precipitation creep which was the dominant deformation mechanism in quartz feldspar rocks in combination with fluid influx

constraints on pb closure temperature in titanite based on rocks from the ungava orogen canada implications for u pb geochronology and p t t path determinations on the basis of multiequilibrium metamorphic pressure temperature p t estimates we have determined that 660 700 c is a reasonable minimum estimate of the closure t of pb diffusion in titanite a temperature significantly higher than previously suggested activity corrected reactions that produce titanite define narrow t stability fields 40 c that correspond closely to metamorphic p t determinations derived for coronitic garnet clinopyroxene hornblende samples growth of titanite occurring between 1789 and 1814 ma in the underthrust archean basement of the paleoproterozoic ungava orogen northern quebec is associated with retrograde metamorphism during underthrusting of the archean basement approx 1 b y after formation of the original granulitic assemblages

thrust related metamorphism in basement windows of the central scandinavian caledonides the late caledonian metamorphic evolution of the basement beneath the caledonian allochthons of the central scandes has been determined by studying mafic schists and phyllonites of the crystalline basement and the overlying vendian and or cambrian sedimentary rocks the studied rocks occur along the caledonian front and in tectonic windows within the scandinavian caledonides a gradual westwards increase in metamorphic grade is recorded which varies from upper diagenetic conditions in the autochthonous rocks along the eastern thrust front of the caledonides to middle amphibolite facies in the western parts of the nasafjall and tomeras windows locally strain related deviations from this pattern occur further west the grade of caledonian metamorphism of the basement increases and reaches the eclogite and granulite facies the scandian metamorphic conditions in the basement rocks studied prevailed in the mid to late silurian at pressures of 8 2 kbar and temperatures of 550 50 c in the tommeras window and 7 2 kbar at 550 50 c in the nasafjall window uplift and cooling followed thereafter continuing into the devonian the final retrograde metamorphism was characterized by temperatures of 450 50 c at pressures of about 3 kbar in the nasafjall and tommeras windows the occurence of syn schistosity amphibolite facies assemblages implies heating of the basement rocks during nappe emplacement available time constraints suggest that this was a relatively rapid process in late silurian to early devonian the prograde phase was followed by uplift and erosion the metamorphic evolution also demonstrates that early devonian thrust movements were associated with a decrease in the thickness of the nappe pile

uranium lead zircon and titanite ages from the northern portion of the western gneiss region south central norway abstract the geochronologic history of the northern portion of the western gneiss region south central norway has been investigated by u pb analyses of zircon and titanite from various basement units and one supracrustal gneiss a six point four zircon and two titanite discordia line from a migmatite melt pod and its host gneiss astfjord migmatite gneiss defines upper and lower intercept ages of 1659 1 1 8 ma and 393 6 3 6 ma respectively the upper intercept age is interpreted as a time of tonalite emplacement and migmatite formation in the region a seven point three zircon and four titanite discordia line from the ingdal granite gneiss has similar upper and lower intercept ages 1652 9 1 7 ma and 396 1 4 9 ma respectively and the upper intercept age is interpreted as the time of granite crystallization the lower intercept age from both theastfjord migmatite gneiss and the ingdal granite gneiss is interpreted as the time of regional metamorphic resetting and is evidence for caledonian influence in the region titanite from these two gneiss units as well as from other tonalite granite and supracrustal gneisses throughout the western gneiss region displays a remarkably uniform pattern of discordance titanite discordance is variable from 6 to 100 and in general the degree of discordance is proportional to the caledonian metamorphic grade of nearby supracrustal schists episodic diffusional lead loss from titanite during caledonian metamorphism probably caused the discordance pattern but a combined mechanism of mixing and diffusional lead loss cannot be ruled out in any case the seventeen point titanite and zircon discordia line clearly indicates that 1 the bulk of the granitoid terrane in this portion of the western gneiss region was emplaced migmatized and cooled in a short time interval about 1657 ma ago 2 a second short lived thermal event that exceeded the blocking temperature of titanite occurred about 395 ma ago and 3 titanite and zircon in the region were not isotopically disturbed by comparable geologic events in the period from 1657 to 395 ma or at any time after 395 ma

titanite major and trace element compositions as petrogenetic and metallogenic indicators of mo ore deposits examples from four granite plutons in the southern yidun arc sw china major minor and trace element abundances in titanite crystals from four granitic plutons in southern yidun arc sw china have been determined using electron microprobe and laser ablation inductively coupled plasma mass spectrometry the selected plutons are the cretaceous xiuwacu cxwc pluton with quartz vein type mo mineralization economic mo the tongchanggou tcg pluton with porphyry type mo mineralization economic mo the triassic pulang pl pluton with porphyry type cu mineralization subeconomic mo and the triassic xiuwacu txwc pluton without any mo mineralization mo barren our study reveals that the chemical compositions of titanite crystals from these plutons such as ree sr ga delta eu delta ce fe2o3 al2o3 halogens and mo can be used to track magma compositions oxidation states metal fertility and crystallization history the data from this study also show that titanite crystals from these plutons with different potential of mo mineralization have similar mo contents and exhibit an irregular variation between mo and sr abundances indicating non mo enrichment in the residual melt during the progressive crystallization for some mo mineralized plutons our new observations support the recent hypothesis that high initial mo contents in magma and the enrichment of mo in residual melts formed by fractional crystallization are not the only requirements to form a granite related mo ore deposit efficient extraction of the residual melts possibly facilitated by high concentrations of magmatic f is also critical to the ore formation evidence for high f concentration in felsic magma which facilitates melt and fluid separation and economic mo mineralization during magma evolution may be traced by the presence of f rich titanite crystals in the two mo mineralized granite plutons cxwc and tcg these new findings from this study confirm that titanite is indeed a good petrogenetic and metallogenic indicator however in light of the limited contribution of metal fertility to mo mineralization we suggest that titanite mo concentrations should be used along with other crucial proxies such as titanite f contents and fe2o3 al2o3 ratios to better evaluate the mo mineralized potential of granites

radar reflections reveal a wet bed beneath stagnant ice stream c and a frozen bed beneath ridge bc west antarctica digital airborne radar data were collected during the 1987 88 antarctic field season in nine gridded blocks covering the downstream portions of ice stream b 6 km spacing and ice stream c 11 km spacing together with a portion of ridge bc between them an automated processing procedure was used for picking onset times of the reflected radar pulses converting travel times to distances interpolating missing data converting pressure transducer readings correcting navigational drift performing crossover analysis and zeroing remanent crossover errors interpolation between flight lines was carried out using the minimum curvature method maps of ice thickness estimated accuracy 20 m and basal reflection strength estimated accuracy 1 db were produced the ice thickness map confirms the characteristics of previous reconnaissance maps and reveals no new features the reflection strength map shows pronounced contrasts between the ice streams and ridge bc and between the two ice streams themselves we interpret the reflection strengths to mean that the bed of ice stream c as well as that of ice stream b is unfrozen that the bed of ridge bc is frozen and that the boundary between the frozen bed of ridge bc and the unfrozen bed of ice stream c lies precisely below the former shear margin of the ice stream

in situ la icp ms u pb geochronology and trace elements analysis of polygenetic titanite from the giant beiya gold polymetallic deposit in yunnan province southwest china abstract the beiya gold polymetallic deposit located in the middle of the jinshajiang ailaoshan alkaline porphyry metallogenic belt is one of the largest gold deposits in china the mineralization mainly occurs in skarn along the intrusive contacts between the alkaline porphyries and middle triassic limestone in this paper we present u pb age as well as major and trace element geochemistry of titanite from the beiya deposit and distinguish the titanite into a magmatic and a hydrothermal suite our study indicates that the titanite from the ore related porphyry and from the mineralized skarn is texturally and geochemically very different the euhedral envelope shaped titanite from the ore related porphyry has lower feo f hfses nb ta and lu hf together with higher tio2 and th u than the subhedral titanite from the mineralized skarn the titanite from the porphyry also displays higher lree hree and more subtle negative eu anomaly than its mineralized skarn counterpart this suggests a magmatic and a hydrothermal origin for respectively the titanite from the ore related porphyry and from the mineralized skarn in situ magmatic titanite u pb dating has yielded an eocene age of 36 0 5 9 ma consistent with the porphyry zircon u pb age 36 07 0 43 ma obtained in previous studies hydrothermal titanite has yielded a weighted average 206pb 238u age of 33 1 1 0 ma mswd 2 0 which represents the age of the retrograde skarn alteration and the maximum age for the gold mineralization together with the previous molybdenite re os age we have further constrained the beiya gold polymetallic metallogeny to 33 1 34 1 ma the mineralization age is slightly younger than the porphyry emplacement indicating that the beiya metallogeny was likely to be a post magmatic hydrothermal product of the himalayan orogenic event the ree characteristics of hydrothermal titanite also reveal that the ore forming fluids may have been derived from a highly oxidized magma