halogen contents of eclogite facies fluid inclusions and minerals caledonides western norway primary multiphase brine fluid inclusions in omphacite and garnet from low to medium temperature eclogites have been analysed for cl br i f li and so4 halogen contents and ratios provide information about trapped lower crustal fluids even though the major element na k ca contents of inclusion fluids have been modified by fluid mineral interactions and step daughter crystal formation after trapping halogens in the inclusion fluids were analysed with crush leach techniques cl br and cl i mass ratios of eclogite fluids are in the range 31 395 and 5000 33 000 respectively most fluids have a cl br ratio lower than modern seawater and a cl i ratio one order of magnitude lower than modern seawater fluids with the lowest cl br and highest cl i ratios come from an eclogite that formed by hydration of granulite facies rocks and may indicate that br and i are fractionated into hydrous minerals reconstructions indicate that the inclusion fluids originally contained 500 4000 ppm br 1 14 ppm i and 33 438 ppm li electron microprobe analyses of eclogite facies amphibole biotite phengite and apatite indicate that f and cl fractionate most strongly between phengite f cl mass ratio of 1469i1048 and fluid f cl mass ratio of 0 008 and the least between amphibole and fluid the chemical evolution of cl and br in pore fluids during hydration reactions is in many ways analogous to cl and br in seawater during evaporation the cl br ratio remains constant until the ah2o value is sufficiently lowered for cl to be removed from solution by incorporation into hydrous minerals

the formation environment of potassic chloro hastingsite in the nakhlites mil 03346 and pairs and nwa 5790 insights from terrestrial chloro amphibole potassic chloro hastingsite has been found in melt inclusions in mil 03346 its paired stones and nwa 5790 it is some of the most chlorine rich amphibole ever analyzed in this article we evaluate what crystal chemistry terrestrial analogs and experiments have shown about how chlorine dominant amphibole chloro amphibole forms and apply these insights to the nakhlites chloro amphibole is rare with about a dozen identified localities on earth it is always rich in potassium and iron and poor in titanium in terrestrial settings its presence has been interpreted to result from medium to high grade alteration 400 c of a protolith by an alkali and or iron chloride rich aqueous fluid ferrous chloride fluids exsolved from mafic magmas can cause such alteration as can crustal fluids that have reacted with rock and lost h2o in preference to chloride resulting in concentrated alkali chloride fluids in the case of the nakhlites an aqueous alkali ferrous chloride fluid was exsolved from the parental melt as it crystallized this aqueous chloride fluid itself likely unmixed into chloride dominant and water dominant fluids chloride dominant fluid was trapped in some melt inclusions and reacted with the silicate contents of the inclusion to form potassic chloro hastingsite

micro scale element migration during eclogitisation in the bergen arcs norway a case study on the role of fluids and deformation abstract understanding chemical element mobility during high pressure metamorphism is paramount to the knowledge of the transformations occurring during the course of eclogite facies metamorphism in particular the role of deformation and fluid circulation appear essential in order to better decipher this role we investigated two eclogite facies samples from the lindas nappe in the bergen arcs norwegian caledonides which are related to a fluid deformation metamorphic event this study based on detailed microtextural investigations coupled with major and trace element analyses either in situ empa and la icp ms or by conventional icp ms nebulisation on mineral fractions illustrates the complexity of chemical reactions accompanying the eclogite and amphibolite facies metamorphism a single eclogite facies mineral species two eclogite facies i e phengite and epidote depicts various chemical features depending on its textural location at thin section scale the correlation with the mineralogical reaction occurring in each textural site demonstrates that the compositional variations are inherited from the precursor minerals thus the composition of eclogite facies minerals is locally controlled by the composition of few hundred micron domains on the contrary alteration phases of the amphibolite facies symplectite and calcic amphibole display clear enrichment in lile pb sr and lree compared to their precursor minerals omphacite and garnet this supports that the transport of elements at hand sample scale was enhanced during the retrogression and elements were efficiently delocalised from one textural site to another the contrasting behaviour of element mobility between peak eclogite facies metamorphism and retrogression can be explained in terms of rate processes and fluid deformation activity during eclogitisation deformation allows the formation of textural and mineralogical microdomains contemporaneously the fluid circulation favours the development of heterogeneities by transport of elements in excess towards areas protected from deformation where phengite bearing quartz lenses crystallise this together with the very fast recrystallisation of eclogite facies minerals results in a heterogeneous redistribution of elements at sample scale and in a chemical disequilibrium between different microdomains of hundred micron size during retrogression in the amphibolite facies coeval with long term ductile deformation the fluids act as an efficient vector to redistribute the elements from a given textural site to another and thus allow to reach at hand sample scale a new chemical equilibrium between the different crystallising phases

evaluation of biotite garnet geothermometers application to the english river subprovince ontario in recent years there have been numerous calibrations of the biotite garnet fe mg exchange geothermometer the eastern lac seul region of the english river subprovince ontario provides an excellent field area in which to compare these calibrations

chlorine titanium and barium rich biotites factors controlling biotite composition and the implications for garnet biotite geothermometry barium cl and ti rich biotite occurs together with garnet plagioclase and amphibole within narrow shear zones in 1800 ma old noritic granulites in the flakstadoy basic complex lofoten north norway the granulite facies assemblage plagioclase clinopyroxene orthopyroxene biotite and ilmenite was replaced by an amphibolite facies mineral assemblage including ba cl and ti rich biotite during ductile deformation biotite shows complex compositional variations with respect to the contents of ba k cl ti al fe mg and si there are correlations between si aliv k ba and cl and between alvi and ti titanium and cl are uncorrelated the fe and mg are correlated to both cl and ti multivariate analysis shows that most of the compositional variation of biotite can be described by two exchange reactions this indicates that most of the variation in biotite composition was controlled by two chemical variables of the system the content of the first exchange component ti1 0 fe0 6 al 1 1 vi mg 0 8 in biotite can be related to the original distribution of ti bearing minerals in the igneous protolith the content of the second exchange component al 0 4 iv fe0 8 ba0 5 cl1 0 si 0 4 mg 1 0 k 0 5 oh 1 0 is related to compositional variations of an externally derived ba and cl bearing fluid in equilibrium with biotite the initially low cl content of the externally derived fluid was increasing during bioite forming reactions because oh was preferentially incorporated relative to cl into biotite continued hydration chloridisation reactions resulted in a gradual consumption of the free fluid phase resulting in local fluid absent conditions the composition of biotite reflects the composition of the last fluid in equilibrium with the mineral i e the composition of the fluid immediately before the grain boundaries were fluid undersaturated thus the variations in biotite composition reflect how the fluid was gradually consumed throughout the shear zone rock the correlations between fe mg ba k and cl can be attributed to differences between the structure of the crystal lattices and the sizes of the cation sites of oh phlogopite and cl annite the dependency of the fe mg ratios of biotite on the cl and ti content has a strong effect on the fe mg partitioning between biotite and garnet the relationship between lnkd x ti bt and x cl bt can be expressed by the regression equation lnk d 1 82 2 60x ti bt 5 67x cl bt

halogens in water from the crystalline basement of the gotthard rail base tunnel central alps abstract drilling of the new gotthard rail base tunnel central alps opened a large number of water conducting fractures in granite and gneiss of the crystalline basement the overburden reaches locally more than 2000 m and water and rock temperature is up to 45 c the tunnel crosses a series of steeply dipping fractured rock units that also crop out at the surface above the tunnel recharge water enters the fractured rocks in the high mountainous area migrates gravity driven to the sampling locality in the tunnel along its flow path it reacts with rocks exposed on the fractures where it dissolves the principal granite minerals resulting in high ph na 2 co 3 waters the tunnel waters contain unusually high concentrations of fluoride ranging from 5 to 29 mg l alteration of f bearing biotite to f free chlorite is one of the sources of fluorine the highest f concentrations result from the equilibration of low ca waters with fluorite fluoride concentration is strongly lithology dependent and sharp discontinuities in both concentration and saturation state with respect to fluorite occur at the contacts of the different gneiss and granite slabs chloride concentrations vary between 1 and 1300 mg l in contrast the cl br mass ratio exhibits small variations and centers around 110 suggesting a common source for the cl and br which is independent of the lithology in the northern part of the tunnel cl and br are chiefly derived from saline pore fluids of one lithology which is then mixed with low salinity water along flow paths cl br ratios of the waters in the southern part of the tunnel section are similar to those measured in experimental leachates from different tunnel rocks suggesting that leaching of metamorphic fluids in the pore space is the main source of both cl and br

valid garnet biotite gb geothermometry and garnet aluminum silicate plagioclase quartz gasp geobarometry in metapelitic rocks abstract at present there are many calibrations of both the garnet biotite gb thermometer and the garnet aluminum silicate plagioclase quartz gasp barometer that may confuse geologists in choosing a reliable thermometer and or barometer to test the accuracy of the gb thermometers we have applied the various gb thermometers to reproduce the experimental data and data from natural metapelitic rocks of various prograde sequences inverted metamorphic zones and thermal contact aureoles we have concluded that the four gb thermometers perchuk l l lavrent eva i v 1983 experimental investigation of exchange equilibria in the system cordierite garnet biotite in saxena s k ed kinetics and equilibrium in mineral reactions springer verlag new york berlin heidelberg pp 199 239 kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 holdaway m j 2000 application of new experimental and garnet margules data to the garnet biotite geothermometer american mineralogist 85 881 892 model 6av kaneko y miyano t 2004 recalibration of mutually consistent garnet biotite and garnet cordierite geothermometers lithos 73 255 269 model b are the most valid and reliable of this kind of thermometer more specifically we prefer the holdaway holdaway m j 2000 application of new experimental and garnet margules data to the garnet biotite geothermometer american mineralogist 85 881 892 and the kleemann and reinhardt kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 calibrations due to their small errors in reproducing the experimental temperatures and good accuracy in successfully discerning the systematic temperature changes of the different sequences in addition after applying the gasp barometer to 335 natural metapelitic samples containing one kind of aluminosilicate and 33 natural metapelitic samples containing two kinds of aluminosilicate as well as to rocks in limited geographic areas and thermal contact aureoles we propose that the calibrations of holdaway holdaway m j 2001 recalibration of the gasp geobarometer in light of recent garnet and plagioclase activity models and versions of the garnet biotite geothermometer american mineralogist 86 1117 1129 and newton and haselton newton r c haselton h t 1981 thermodynamics of the garnet plagioclase al2sio5 quartz geobarometer in newton r c navrotsky a wood b j eds thermodynamics of minerals and melts new york springer verlag 131 147 based on kleemann and reinhardt s kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 thermometer are the most valid gasp barometers other gb thermometers and gasp barometers are not recommended

a shallow marine emergent sequence from the northwestern sector of the last british ice sheet portballintrae northern ireland abstract at portballintrae northern ireland a well preserved emergent facies sequence formed around 17 kyr b p as the late devensian ice sheet withdrew from the continental shelf three main lithofacies assemblages are recognised 1 at the base of the sequence a massive muddy diamict was formed by resedimentation of an unstable sedimentary apron deposited in a tidewater setting 2 rhythmically bedded sand and mud units contain a wide range of wave diagnostic features and are separated from the underlying diamict by both transitional and wave eroded planar contacts palaeowave calculations suggest deposition in a coastal tract open to atlantic waves the preservation and range of boreo arctic foraminifera present are also typical of a lower shoreface storm influenced setting 3 interbedded gravel and sand facies are separated from the underlying rhythmically bedded facies by a planar wave cut surface this facies occurs as crudely organised beds within cross cutting shallow scours which are associated with off shore directed storm induced sediment pulses overall the coarsening upwards sequence is explained by tidewater sedimentation during ice wastage rapid isostatic rebound and isostatic deceleration in the late glacial an isostatic tectonic model comprising a forebulge on the outer continental shelf and a peripheral trough on the inner shelf is presented to resolve the apparent discrepancies between onshore and offshore sea level data

chlorine stable isotope composition of granulites from lofoten norway implications for the cl isotopic composition and for the source of cl enrichment in the lower crust abstract the cl isotopic composition of lower crustal rocks as revealed from granulites from the lofoten islands northern norway centres around the value of standard mean ocean chloride smoc the investigated rocks and mineral separates of cl amphibole and cl biotite have 37 cl values 37 cl 35 cl normalized to smoc of 1 12 to 0 79 with most values concentrated in the range of 0 3 to 0 11 and an average of 0 15 samples from gabbroic and from dry granitic rocks magmatic mangerites and charnockites with highly cl enriched hydrosilicates and from a later amphibolite with low cl amphiboles show no distinct differences in their 37 cl values the results indicate that there was only minor involvement of mantle derived cl in fluid involving processes in the middle and lower crust assuming a 37 cl of 4 7 for the undegassed mantle 1 cl isotopic values of the granulites do not support the influx of significant amounts of mantle derived cl the maximum possible mantle contribution to the sample with the highest 37 cl is about 33 thus the common occurrence of cl enriched minerals in granulite facies terrains is regarded as a product of remobilized crustal cl either during magmatism or during later fluid activity the results support the hypothesis that the crust can be regarded as a reservoir with cl isotopic values very similar to smoc

a stress controlled mechanism for the intensity of very large magnitude explosive eruptions abstract large magnitude explosive eruptions are the result of the rapid and large scale transport of silicic magma stored in the earth s crust but the mechanics of erupting teratonnes of silicic magma remain poorly understood here we demonstrate that the combined effect of local crustal extension and magma chamber overpressure can sustain linear dyke fed explosive eruptions with mass fluxes in excess of 10 10 kg s from shallow seated 4 6 km depth chambers during moderate extensional stresses early eruption column collapse is facilitated with eruption duration of the order of few days with an intensity of at least one order of magnitude greater than the largest eruptions in the 20th century the conditions explored in this study are one way in which high mass eruption rates can be achieved to feed large explosive eruptions our results corroborate geological and volcanological evidences from volcano tectonic complexes such as the sierra madre occidental mexico and the taupo volcanic zone new zealand

retrogression of eclogite facies shear zones by short lived fluid infiltration during the caledonian orogeny lofoten islands norway norwegian eclogite facies shear zones in the lofoten islands served as major pathways for short lived pulses of both 40 ar rich and 40 ar poor hot fluids during eclogitization and retrogression events related to the caledonian orogeny the open system for ar affected most of the minerals leading to old 40 ar 39 ar ages particularly in trioctahedral micas 40 ar concentration in the fluids appears to decrease during the amphibolite facies retrogression and ca rich amphiboles yield 40 ar 39 ar ages of c 415 ma scandian event late and post caledonian 40 ar 39 ar muscovite and k feldspar ages and rb sr biotite ages coincide with multiple extensional events fluid infiltration and thermal activity during the final exhumation of the crustal rocks potentially reflecting major tectonic episodes such as rifting of pangaea and seafloor spreading between europe and north america

the distribution of halogens f cl br in granitoid rocks abstract the halogen contents of granitoid rocks and their distribution between apatite biotite muscovite and amphibole from two different localities german part of the bohemian massif and central aegean greece are investigated in detail whole rock f and cl contents and f cl mass ratios vary systematically with the magmatic halogen bearing mineral assemblage in which biotite and apatite are present in all rock samples muscovite bearing granites are f rich mostly 1100 2000 g g but up to 3100 g g and are relatively cl poor 50 130 g g in contrast amphibole bearing rocks reach high cl contents 50 900 g g and are relatively f poor 500 1400 g g only biotite and apatite bearing granites show intermediate f 750 1100 g g and cl 120 350 g g contents bromine contents of all rock samples are below the detection limit of about 0 6 g g in general f and cl are preferentially incorporated in apatite over biotite and biotite usually contains higher amounts of f and cl than muscovite similarly biotite prefers f over amphibole but the distribution of cl between biotite and amphibole varies between different rock samples bromine contents in muscovite are below the detection limit of 0 4 g g but can reach up to 0 8 g g in biotite and up to 2 5 g g in apatite and amphibole near solidus effects such as fluid exsolution diffusive re equilibration and hydrothermal overprint may change the initial halogen distribution in the rock importantly significant amounts of the whole rock s f up to 60 and cl up to 90 may be accommodated in post magmatic alteration phases fluorite and na k ca bearing sheet silicates and fluid inclusions therefore great care has to be taken when interpreting halogen contents of whole rocks and the influence of post magmatic halogen carriers needs to be taken into account

cl scapolite cl amphibole and plagioclase equilibria in ductile shear zones at nusfjord lofoten norway implications for fluid compositional evolution during fluid mineral interaction in the deep crust abstract cl rich scapolite and amphibole formed during ductile shear deformation associated with the infiltration of an externally derived cl bearing fluid in a gabbroanorthosite of the flakstadoy basic complex lofoten norway amphibole and scapolite formed along the contacts between incompletely altered igneous mafic minerals orthopyroxene clinopyroxene biotite and ilmenite and plagioclase and internally in the grains of primary igneous plagioclase the secondary minerals show large compositional variations on thin section scale the cl content of scapolite varies between 0 3 and 0 95 apfu atoms per formula unit whereas amphibole shows cl concentrations from 0 to 1 5 apfu the primary igneous plagioclase an50 an60 underwent extensive recrystallization and alteration during the fluid rock interactions secondary plagioclase shows compositions in the range from an20 to an55 in general plagioclase did not equilibrate with the fluid phase during alteration due to the sluggishness of the cation exchange reactions between plagioclase and fluid occasionally however equilibrium among plagioclase scapolite and the fluid phase was attained the compositional variations of amphibole scapolite and plagioclase that equilibrated with the fluid are principally related to variations in the fluid activity ratios acl a co3 2 and acl aoh the large compositional variations of the minerals on thin section scale thus indicate steep gradients in the fluid activity ratios acl a co3 2 and acl aoh the activity gradients of the fluid phase developed as a result of the preferential extraction of water from the grain boundary fluid during the formation of hydrous silicates scapolite and the most cl enriched amphibole formed in equilibrium with an evolved fluid phase enriched in cl and co2

analysis of the compositional variations of biotite in pelitic hornfelses from northeastern minnesota mg mg fe 0 35 to 0 95 strong correlations among mg fe ti vi al and iv al principal components analysis shows that 98 of the total variance in compositions of biotite from the muscovite bearing assemblage can be ascribed to two substitutions with phlogopite biotite compositions from a particular assemblage might be sensitive indicators of the thermal gradient modified journal abstract

mineral zoning p t x m phase relations and metamorphic evolution of some adirondack granulites new york detailed petrologic analysis of ten meta anorthosites and related introduction rocks from the adirondack highlands new york has been used to the adirondack highlands of new york are one of constrain the p t history of the region metamorphic orthopyroxene the best studied granulite facies terranes of the world and clinopyroxene occur in aggregates of 1 mm diameter grains e g bohlen et al 1985 valley et al 1990 and that are zoned concentrically with decreasing al and fe fe mg references therein based on this considerable volume and increasing ca towards the rim moreover zoning is not related of work the peak metamorphic conditions in the to the presence of garnet zoning is interpreted to have been produced adirondack highlands have been fairly well constrained during growth by the reaction igneous pyroxene plagioclase at pressures of 7 8 kbar crustal depths of 25 30 metamorphic opx metamorphic cpx along a cooling path with a km and temperatures that range from 775 c in slope of 6 bars c starting at 850 c and 6 5 8 kbar garnet the central highlands to t 675 c in the southern occurs as isolated clusters of 5 25 grains of 1 mm diameter adirondacks e g bohlen et al 1985 p t paths have crystals and as necklaces of 1 mm diameter crystals surrounding been shown to follow nearly isobaric cooling trajectories metamorphic pyroxenes or oxides plagioclase quartz typically e g bohlen 1987 because of this wealth of inseparates garnet from pyroxene but locally garnet embays metaformation some fundamental questions about the origin morphic pyroxene suggesting that garnet grew at the expense of of the adirondack granulite facies terrane have emerged pyroxene garnet clusters have slightly lower fe fe mg than e g bohlen et al 1985 how did the crust achieve garnet in necklaces fe fe mg 0 73 and 0 75 0 78 rethe relatively high temperature conditions necessary to spectively and slightly higher grossular xgrs 0 20 vs 0 19 produce granulite facies rocks at depths of 25 30 km neither is zoned in mn and zoning towards increasing fe and what is the relative importance of magmatic fe mg is restricted to contacts with biotite and locally clinoheating vs continental burial in this process pyroxene biotite adjacent to garnet is zoned towards decreasing this study will present new data on mineral comfe fe mg production of garnet in necklaces is interpreted position and element zoning in garnet pyroxene to be the result of the continuous fe mg reaction opx pl biotite amphibole and plagioclase from adirondack grt cpx qtz p t x m modeling of this reaction reveals a meta anorthosite and related rocks with the goal of p t path with a slope of 6 bars c no evidence for early prefurther constraining the metamorphic evolution of this metamorphic peak garnet is observed which rules out any possibility terrane mineral compositions will be used to construct of early higher pressure metamorphism the p t path is therefore phase diagrams in an attempt to evaluate approach to inferred to be counterclockwise with loading to 6 5 8 kbar at a chemical equilibrium theoretical analysis will be used maximum temperature of 850 c occurring during or immediately to construct p t x m phase diagrams depicting how following an influx of heat presumably from early orogenic plutons mineral composition and modes change with p and t this theoretical analysis will then be applied to the mineral zoning to constrain the p t path and the results will be discussed in the context of a tectonic

composition of barian mica in multiphase solid inclusions from orogenic garnet peridotites as evidence of mantle metasomatism in a subduction zone setting multiphase solid inclusions in minerals formed at ultra high pressure uhp provide evidence for the presence of fluids during deep subduction this study focuses on barian mica which is a common phase in multiphase solid inclusions enclosed in garnet from mantle derived uhp garnet peridotites in the saxothuringian basement of the northern bohemian massif the documented compositional variability and substitution trends provide constraints on crystallization medium of the barian mica and allow making inferences on its source barian mica in the multiphase solid inclusions belongs to trioctahedral micas and represents a solid solution of phlogopite kmg3 si3al o10 oh 2 kinoshitalite bamg3 al2si2 o10 oh 2 and ferrokinoshitalite bafe3 al2si2 o10 oh 2 in addition to ba 0 24 0 67 apfu mica is significantly enriched in mg xmg 0 85 to 0 95 cr 0 03 0 43 apfu and cl 0 04 0 34 apfu the substitution vector involving ba in the i site which describes the observed chemical variability can be expressed as bafeivalclk 1mg 1si 1 oh 1 a minor amount of cr and vial enters octahedral sites following a substitution vector vi cr al 2 vi mg fe 3 towards chromphyllite and muscovite as demonstrated by variable ba and cl contents positively correlating with fe barian mica composition is partly controlled by its crystal structure textural evidence shows that barian mica together with other minerals in multiphase solid inclusions crystallized from fluids trapped during garnet growth the unusual chemical composition of mica reflects the mixing of two distinct sources 1 an internal source i e the host peridotite and its garnet providing mg fe al cr and 2 an external source represented by crustal derived subduction zone fluids supplying ba k and cl at uhp uht conditions recorded by the associated diamond bearing metasediments c 1100 c and 4 5 gpa located above the second critical point in the pelitic system the produced subduction zone fluids transporting the elements into the overlying mantle wedge had a solute rich composition with properties of a hydrous melt the occurrence of barian mica with a specific chemistry in barium poor mantle rocks demonstrates the importance of its thorough chemical characterization

short lived reheating events in the sommartuva shear zone hosted in cold crust ar diffusion modelling constraints for the exhumation of eclogites in flakstadoy lofoten islands norway abstract the exhumation of the norwegian lofoten eclogites formed during the continental collision of laurentia and baltica is mainly due to the reactivation of shear zones during the collapse of the caledonian orogen the current cooling history temperature time t t paths for the exhumation of these rocks as determined by 40 ar 39 ar dating and geothermometry involves a protracted period of slow cooling c 1 7 c ma 1 from high t the sommartuva shear zone hosted in a palaeoproterozoic anorthosite contains retrogressed eclogite and amphibolite facies lenses and served as an open system for ar with 40 ar rich and 40 ar poor hot fluid infiltration ca rich amphiboles from amphibolites contain excess ar and are mantled by phlogopites that yield ar diffusion loss profiles with plateau ages of 413 400 ma associated with an extensional event in lofoten locally the zone was intruded in its late stage history c 333 ma by a granitoid rock crystallizing annite and muscovite previously inferred to be injected synchronously with amphibolite facies metamorphism an alternative cooling path related to the exhumation of the eclogites was determined by a combination of i 40 ar 39 ar ages in minerals that grew during different thermal events ii thermal modelling of the ar systematics in these minerals and iii exploration of the thermal effects caused by the superposition of each event on pre existing mineral phases the best fit t t path as constrained by the ar data reveals that in order to preserve ar radiogenic and excess within the minerals the ambient t must have been relatively low 300 c over 80 ma 413 333 ma likewise the associated intrusion of the granitoid and the hot fluid that percolated the shear zone and crystallized the phlogopites were likely to have been short lived c 100 25 ka and at relatively moderate t 500 c in contrast to previous thermal models where the thermal events are represented as simple inflexions in a t t curve our cold crust model incorporates short lived thermal disturbances including estimates of the magnitude of their maximum temperature and duration superimposed on protracted periods of slow cooling from high t a new proposed t t path obtained for the exhumation of this terrane indicates that the eclogites resided for 80 ma 413 333 ma at relatively cool ambient temperatures c 300 c highlighting the enormous potential of coupling geochronological data from multiple isotopic systems with thermal modelling to identify and constrain the duration of short lived events