petrology and geothermobarometry of granulite facies metapelites from the hisoy torungen area south norway new data on the sveconorvegian p t t path of the bamble sector the high grade rocks metapelite quartzite metagabbro of the hisoy torungen area represent the south westernmost exposures of granulites in the proterozoic bamble sector south norway the area is isoclinally folded and a metamorphic p t t path through four successive stages m1 m4 is recognized petrological evidence for a prograde metamorphic event m1 is obtained from relict staurolite chlorite albite staurolite hercynite ilmenite cordierite sillimanite fine grained felsic material quartz and hercynite biotite sillimanite within metapelitic garnet the phase relations are consistent with a pressure of 3 6 0 5 kbar and temperatures up to 750 850 c m1 is connected to the thermal effect of the gabbroic intrusions prior to the main m2 sveconorwegian granulite facies metamorphism the main m2 granulite facies mineral assemblages quartz plagioclase k feldspar garnet biotite sillimanite are best preserved in the several metre wide al rich metapelites which represent conditions of 5 9 9 1 kbar and 790 884 c these p t conditions are consistent with a temperature increase of 80 100 c relative to the adjacent amphibolite facies terranes no accompanying pressure variations are recorded up to 1 mm wide fine grained felsic veinlets appear in several units and represent remnants of a former melt formed by the reaction bt sil qtzgrt lq this dehydration reaction together with the absence of large scale migmatites in the area suggests a very reduced water activity in the rocks and xh2o 0 25 in the c o h fluid system was calculated for a metapelitic unit a low but variable water activity can best explain the presence or absence of fine grained felsic material representing a former melt in the different granulitic metapelites the strongly peraluminous composition of the felsic veinlets is due to the reaction grt former melt silcrd bt qtz h2o which has given poorly crystalline cordierite aggregates intergrown with well crystalline biotite the cordierite and biotite producing reaction constrains a steep first stage retrograde relative to m2 uplift path decimetre to metre wide strongly banded metapelites quartz plagioclase biotite garnet sillimanite inter layered with quartzites are retrograded to m3 amphibolite facies assemblages a p t estimate of 1 7 5 6 kbar 516 581 c is obtained from geothermobarometry based on rim rim analyses of garnet biotite plagioclase sillimanite quartz assemblages and can be related to the isoclinal folding of the rocks m4 greenschist facies conditions are most extensively developed in millimetre wide chlorite rich calcite bearing veins cutting the foliation

retrograde net transfer reaction insurance for pressure temperature estimates retrograde net transfer reactions significantly affect compositions of metamorphic minerals yet are rarely considered when determining pressure temperature p t conditions two natural amphibolite facies metapelites from the central himalaya of nepal exhibit extremely common compositional patterns including increases in mn and fe fe mg at the rims of garnets which are the result of retrograde garnet dissolution and fe mg exchange with biotite however typical thermobarometric approaches for these rocks result in errors of hundreds of degrees and 3 6 kbar compared with thermobarometry of nearby rocks and petrogenetic grids these large errors result because dissolution of high fe garnet has strongly affected the fe mg ratio of matrix biotite x ray maps help evaluate the extent and chemical effects of retrograde reactions in these samples by identifying mineral regions that retain highest t compositions or through a new data processing approach by permitting correction of mineral compositions to original high t values these approaches ensure against retrograde net transfer reactions and should be applied routinely in thermobarometric studies they ultimately yield p t estimates that are more petrologically reasonable and permit rapid screening of samples for those least affected by retrograde reactions reconsideration of thermobarometry in the central and eastern himalaya indicates that retrograde net transfer reactions are extremely common therefore previous thermobarometric studies based on garnet major element compositions from that region should be reevaluated

on the pacific ocean regime shift the temporal variability of pacific ocean upper ocean heat content is examined for the 1948 1998 period using gridded objectively analyzed temperature anomaly fields results indicate a regime shift in upper ocean temperature structure occurred in conjunction with the atmospheric shift in sea level pressure around 1975 leading to warming cooling in the eastern western equatorial pacific the shift is a basin wide phenomenon affecting the thermal structure from 60 s to 70 n eof analysis of the pacific ocean heat content 0 125 m shows a shift from a relatively cool to a warm state in the equatorial pacific during the mid 1970s further analysis of the gridded temperature anomaly fields shows equatorial warming to be as much as 1 5 c and a cooling in the north pacific of 1 c down to 250 meters after the mid 1970s overall the analysis indicates the regime shift continues through 1998 with no signs of returning to a cooler phase

a regional gradient in the composition of metamorphic fluids in pelitic schist pecos baldy new mexico two metamorphic isograds cut across graphitic schist near pecos baldy new mexico the southern isograd marks the first coexistence of staurolite with biotite whereas the northern isograd marks the first coexistence of andalusite with biotite the isograds do not record changes in temperature or pressure instead they record a regional gradient in the composition of the metamorphic fluid phase ortega quartzite which contains primary hematite lies immediately north of the graphitic schist mineral compositions within the schist change gradually toward the quartzite reflecting gradients in mu text o text 2 and mu text h text 2 text o the chemical potential gradients locally as high as 72 cal m in mu text o text 2 and 9 cal m in mu text h text 2 text o controlled the positions of the two mapped isograds the staurolite biotite isograd records where x text h text 2 text o fell below 0 80 at f text o text 2 near 10 23 bars the andalusite biotite isograd records where x text h text 2 text o fell below 0 25 at f text o text 2 near 10 22 bars dehydration and oxidation were coupled by graphite fluid equilibrium the chemical potential gradients apparently formed during metamorphism as graphite in schist reacted with hematite in quartzite local oxidation of graphite formed co2 which triggered dehydration reactions along the schistquartzite contact this process created a c o h fluid which infiltrated into overlying rocks upward infiltration local fluid rock equilibration and additional infiltration proceeded until the composition of the infiltrating fluid evolved to that in equilibrium with the infiltrated rock this point occurs very close to the staurolite biotite isograd pelitic rocks structurally above this isograd show no petrographic evidence of infiltration even though calculations indicate that volumetric fluid rock ratios may have exceeded 15 and thin rare calc silicate beds show extensive k metasomatism and quartz veining

metamorphism in the olary block south australia compression with cooling in a proterozoic fold belt the sedimentary and igneous rocks comprising the lower proterozoic olary block south australia were deformed and meta morphosed during the mid proterozoic olar ian orogeny the area is divided into three zones on the basis of assemblages in metapelitic rocks higher grade conditions occurring in the south east mineral assemblages developed during peak metamorphism which accom panied recumbent folding include andalusite in zones i and i1 and sillimanite in zone 111 upright folding and overprinting of mineral assemblages occurred during further com pression the new mineral assemblages includ ing kyanite in zone i1 and kyanite and sillimanite in zone 111 the timing relationships of the aluminosilicate polymorphs together with the peak metamorphic and overprinting parageneses imply an anticlockwise p t path for the olarian orogeny pressure increasing with cooling from the metamorphic peak

revised empirical garnet biotite muscovite plagioclase geobarometer in metapelites the garnet biotite muscovite plagioclase gbmp barometer was empirically revised for p t conditions of 1 14 kbar and 450 840 c using 263 metapelitic rock samples from all over the world this barometer is based on activity models for garnet biotite and plagioclase identical to those of the well calibrated garnet biotite thermometer and the garnet aluminosilicate plagioclase quartz gasp barometer the gbmp barometer is less temperature dependent than the gasp barometer and can be applied to either al2sio5 absent or al2sio5 bearing metapelites the total error of the gbmp barometer is estimated to be about 1 2 kbar on considering input temperature error and analytical errors of chemical compositions of the phases involved the random error of the gbmp barometer is evenly distributed with respect to pressure temperature and mineral composition simultaneous application of the gbmp barometer and the garnet biotite thermometer identifies the correct stability field for al2sio5 bearing metapelites application of the gbmp barometer to metapelitic rocks within the same geological terranes or thermal contact aureoles yielded similar pressures within error a spreadsheet for implementing the proposed gbmp geobarometer is supplied on the journal s website

metamorphism at a late mesozoic accretionary margin a study from the coast belt of the north american cordillera the late mesozoic and cenozoic metamorphic evolution of the western north american continental margin is recorded in a belt of homogeneous metapelitic rocks the kluane metamorphic assemblage kma in the northern coast belt of yukon territory a record of late cretaceous medium pressure and temperature c 7 kbar 500 c metamorphism m1 is preserved in ca rich garnet and na rich plagioclase cores in rocks that were little affected by later events m1 was synchronous with mylonitization and is attributed to accretion of the kma to the ancient continental margin isothermal decompression during rapid uplift was followed by early eocene emplacement of the ruby range batholith rrb part of a magmatic arc produced by subduction of the kula plate the intrusion of the rrb led to a contact metamorphic overprint m2 producing a 5 6 km wide aureole in which the grade ranges from subgarnet zone to garnet cordierite k feldspar zone pressure and temperature estimates for m2 calculated from mineral equilibria are 3 5 4 5 kbar and 530 720 c generally consistent with the stability limits of the observed mineral assemblages comparison of mineral assemblages and p t conditions in the kma with those in the mclaren glacier metamorphic belt in alaska does not support the correlation of the two metamorphic sequences this weakens the hypothesis proposing 400 km of dextral slip along the denali fault zone

polyphase metamorphism and the development of the main central thrust along a cross section through the lesser and higher himalayan units at the kishtwar window area north west india a polyphase barrovian type metamorphism has been delineated in relation to the development of the main central thrust mct in the metapelitic mineral assemblages three metamorphic phases have been distinguished a conditions up to amphibolite grade at moderate to high pressures alm rut ilm kya qtz characterize the m1 phase b pressure release and or temperature increase as a result of movement along the mct and the formation of gneiss domes in the higher himalaya as expressed by oriented n70 100 e fibrolite defines the m2 phase and c finally during uplift of the kishtwar window area a retrogressive m3 phase is characterized by the assemblage quartz muscovite chlorite both optically zoned and single stage garnets have been examined with the electron microprobe to determine their element partitioning normal zoning has been found in samples below the mct in the lesser himalaya indicating prograde growth during the m2 phase whereas tectonically above in the higher himalaya unit the garnets reveal double stage growth with a complex zoning pattern due to reaction partitioning during m1 and m2 and reverse zoning at their rims during the retrogressive m3 phase geothermometry on metapelites along a cross section through the mct zone and the higher himalaya imply distinct readjustments of garnet biotite exchange equilibria and indicate isothermal conditions 500 600 c throughout the section during the m3 retrogression pressure calculations gro an kya qtz and alm rut ilm kya qtz suggest a decrease in pressure towards the top of the section 6 7 5 to 4 5 5 kbar as corroborated by fibrolite replacing kyanite the spatially inverse metamorphism exposed within the lesser himalaya of the kishtwar window is regarded as a product of polyphase metamorphism combined with ongoing thrusting and shearing and is reflected by condensed m2 isograds around the kishtwar window

geothermometry and geobarometry in pelitic rocks of north central wopmay orogen early proterozoic northwest territories canada pressure and temperature estimates for the pelitic schists and gneisses along the east flank of the hepburn batholith early proterozoic have been determined by means of an electron microprobe study of coexisting garnet biotite plagioclase and cordierite garnet biotite geothermometry using recent calibrations yields results between 560 and 765 c consistent in spatial distribution with andalusite sillimanite and sillimanite k feldspar metamorphic zones calibrations of the garnet cordierite equilibrium give temperature estimates on average 23 c lower both sets of temperature estimates for the garnet cordierite bearing assemblages are consistent with the theoretical stability field of these rocks geobarometry based on the 3 caal 2 si 2 o 8 ca 3 al 2 si 3 o 12 2 al 2 sio 5 sio 2 equilibrium outlines a broad pressure culmination with variation from 2 6 to 5 2 kbar the p culmination coincides with a structural plunge culmination as outlined by the change in plunge azimuth of folds of bedding by a re entrant in the trace half window of a major premetamorphic thrust fault and by a narrowing of the synmetamorphic funnel shaped hepburn batholith garnet cordierite geobarometric calibrations generally give pressure determinations in the same range as the grossular anorthite results the spread in the garnet cordierite pressure estimates from various calibrations however points to the need for considering the role of water when using the garnet cordierite geobarometer

femg partitioning between coexisting garnet and phengite at high pressure and comments on a garnet phengite geothermometer abstract the fe mg exchange reaction between coexisting garnet and phengite has been studied by reacting a natural phengite mg 67 in the presence of quartz and water at pressures of 20 35 kb and temperatures of 800 1000 c compositions of coexisting garnet and mica indicate a linear relation between both the inkd fe mg garnet fe mg phengite and temperature and inkd and pressure in the above p t range this fe mg exchange reaction between garnet and phengite is shown to be dependent on the ca content of the garnet and on the mg number of the bulk composition these two composition effects have been studied by usin phengitic mica mixes with mg numbers of 23 and 46 and by using a synthetic basaltic composition the overall results allow broad empirical calibration of separate geothermometers for pelitic and basaltic systems respectively however because of non ideality in the exchange reaction this geothermometer should not be used in any practical application outside the composition ranges studied also careful consideration of the presence of fe3 in phengite must be made if the fe3 content of the natural phengite is unknown then the temperatures obtained will be maximum temperatures only

calibration of the garnet biotite al2 sio5 quartz geobarometer for metapelites a garnet biotite al2sio5 quartz gbaq geobarometer was empirically calibrated using more than 700 natural metapelites with a broad compositional range of garnet and biotite under p t conditions of 450 950 c and 1 17 kbar in the calibration activity models of garnet and biotite identical to those in the garnet biotite geothermometer of holdaway 2000 were used therefore the gbaq geobarometer and the garnet biotite geothermometer can be simultaneously applied to iteratively estimate metamorphic p t conditions successful application of the gbaq geobarometer to natural metapelites certify its validity most importantly when plagioclase is absent or cao in garnet and or plagioclase are deficient this geobarometer may prove useful for estimating metamorphic pressures the random error of the present gbaq geobarometer is inferred to be around 1 8 kbar an electronic spreadsheet is available as table s4 to apply the gbaq geobarometer in combination with the garnet biotite geothermometer this article is protected by copyright all rights reserved

thermobarometry in granulites pitfalls and new approaches abstract computer models of cooling granulite facies rocks with the assemblage garnet biotite sillimanite k feldspar plagioclase quartz are presented that incorporate simultaneous reaction net transfer and exchange and multicomponent diffusion in garnet in models where cooling is accompanied by exchange reactions plus diffusion only the calculated garnet core matrix biotite temperature is always lower than the metamorphic peak by an amount that depends on the cooling rate the size of the garnet and the volumetric ratio of garnet to biotite maximum calculated core temperatures of approximately 700 750 c are to be expected from typical granulite facies garnet biotite assemblages and calculated core temperatures can easily be as low as 600 c in models where both net transfer and exchange reactions are possible calculated garnet core matrix biotite temperatures are typically higher than the metamorphic peak temperatures by more than 150 c for large garnets r 2 mm but may be lower than the metamorphic peak for small garnets r the composition of matrix plagioclase in equilibrium with garnet is very sensitive to the amount of modal plagioclase that reacts and hence calculated p t trajectories are very sensitive to the petrologic interpretation of this recrystallization history for models in which all the modal plagioclase reacts the core and rim pressures may be faithfully recovered provided that the temperature estimate for the core is reliable for models in which only a small percentage of the modal plagioclase reacts very small modal amounts of plagioclase may be in equilibrium with garnet rim which if incorrectly interpreted may lead to grossly erroneous p t path interpretations a method to test an inferred p t path model is presented that involves attempting to match the observed garnet and plagioclase zoning information with a forward model that involves simultaneous reaction and diffusion an example from western new hampshire usa is presented that closely matches the measured profile

excitation of resonant modes along the japanese coast by the 1993 and 1983 tsunamis in the japan sea we observed seiches at 55 ports in japan facing the japan sea and obtained dominant periods from their maximum spectral amplitudes these periods were mostly determined ranging from 10 to 40 minutes they were compared with dominant periods of the 1993 hokkaido nansei oki tsunami and the 1983 nihonkai chubu oki tsunami at the same ports as a result relations of dominant periods between seiches and tsunamis are classified into three types the first one is fundamental mode excitation the second is higher mode excitation and the third is no excitation plotting the maximum spectral amplitude normalized at an epicentral distance of 50 km versus the ratio of the tsunami dominant period to the seiche dominant period we obtained resonance curves having maxima at one this fact shows a contribution of resonance to the amplification thus it is recognized that the dominant period of seiching is an important factor in interpreting amplification and resonance of tsunami

geothermobarometric history of subduction recorded by quartz inclusions in garnet 1 burial histories of subduction zone rocks are often difficult to accurately constrain owing to a lack of robust mineral geobarometers applicable to high pressure mineral assemblages knowledge of the depth histories of subduction is however required for our understanding of global geochemical cycles subduction related seismicity and the evolution of destructive tectonic boundaries the high spatial resolution of quartz inclusion geobarometry can be used to determine pressure evolution during metamorphic growth of individual garnet crystals quartz inclusions in garnet from sifnos greece preserve such a record of the pressure of garnet growth allowing detailed reconstruction of the metamorphic evolution of these rocks pressure dependent raman spectra of quartz inclusions were combined with elastic modeling to infer the conditions at which they were trapped during garnet growth all measured inclusions suggest that garnet growth occurred between 19 and 20 5 kbars with little evidence for significant pressure variation during the garnet growth interval which is interpreted to record 100 c of heating coupled with thermometry and geochronology these results show that early cold burial was followed by a phase of rapid heating which immediately preceded exhumation garnet growth occurred primarily during this heating phase

experimental determination of ree distributions between monazite and xenotime potential for temperature calibrated geochronology solid solutions of the ree y orthophosphates monazite and xenotime were synthesized hydrothermally between 300 c and 800 c at 2 and 5 kbar using ree y oxides and h3po4 as starting materials the ree bulk composition was similar to those found in metapelitic rocks all experiments produced two solid phases monoclinic monazite and tetragonal xenotime in volumetric ratios similar to relative abundances in metapelites ree concentrations of coexisting monazite xenotime pairs were determined by emp analysis and ree distribution coefficients dree xreemonazite xreexenotime were derived for the entire ree y suite values of dree depend strongly on ionic radii of the rees and on temperature the log dree vs ionic radius curve shows a nearly linear decrease from la to lu and comprises almost five orders of magnitude from dla 102 5 to dlu 10 2 between 450 and 800 c most dree values vary continuously by a factor of about 2 to 3 dnd decreases from 48 to 16 and dsm from 9 to 5 dtb increases from about 0 2 to about 0 4 ddy from 0 1 to 0 2 and dy from 0 06 to 0 12 along this temperature range experimentally determined values of dree are in close agreement with those derived from natural monazite xenotime pairs equilibrated between 400 and 700 c ree partitioning between monazite and xenotime is appropriate for geothermometry the most useful application is that equilibrium and disequilibrium partitioning of ree in metamorphic rocks are easily recognized in the case of equilibrium distributions u pb chronometry of single monazites or xenotimes provides a direct link to their growth conditions and information on temperature time paths equilibrium distributions of sm and nd expressed in molar fractions result in kd xsmmonazitexndxenotime xsmxenotimexndmonazite 0 2 to 0 3 from 600 to 800 c and sm nd chronometry should provide reasonable two mineral isochrons for such monazite xenotime pairs

metamorphism of the kisseynew gneisses and related rocks of the reindeer zone trans hudson orogen northern saskatchewan in the reindeer zone of saskatchewan the mostly metasedimentary kisseynew gneiss crops out in a 300 km wide belt extending from the tabbernor fault to the manitoba border metamorphic grade varies

thermoba raman try calibration of spectroscopic barometers and thermometers for mineral inclusions abstract mineral inclusions may develop residual pressures p incl during cooling and exhumation because of differential expansion and compression relative to the host entrapping mineral shifts to raman spectra as determined using laser raman microspectroscopy permit inference of p incl knowing the pressure temperature p t dependence of molar volumes from thermodynamic databases and the shear modulus of the host phase entrapment p at assumed t or entrapment t at assumed p can be calculated for a measured p incl this concept is developed theoretically to fit simplified empirical expressions of entrapment p t p incl or t p p incl for a wide range of common mineral host inclusion pairs typical residuals are quartz diamond graphite can preclude recovery of entrapment p s except for very high p s or rapid exhumation

equilibria within the mineral assemblage quartz muscovite biotite garnet plagioclase and implications for the mixing properties of octahedrally coordinated cations in muscovite and biotite interaction parameters derived using empirical calibration methods indicate strong non ideality in the mixing of octahedrally coordinated cations in muscovite and biotite the data set used for calibration comprises mineral compositions from 49 samples containing quartz muscovite biotite garnet plagioclase and al2sio5 kyanite or sillimanite pressures and temperatures in the data set were determined through the simultaneous application of geothermometry based on the garnet biotite femg1 exchange equilibrium and geobarometry based on the anorthite breakdown equilibrium two equilibria yielded simple expressions from which binary interaction parameters for octahedrally coordinated cations in biotite could be directly determined a four component fe2 mg al ti regular symmetric mixing model was assumed for biotite one equilibrium yielded a simple expression from which an interaction parameter for the mixing of the mgal celadonite component in muscovite could be directly determined two sets of calculations were performed utilizing different calibrations of the garnet biotite geothermometer and the anothite breakdown geobarometer and different garnet activity models both placed samples within or near the stability field of the al2sio5 phase present in each sample and both yielded similar values for the interaction parameters within narrow uncertainties indicating that the values are insensitive to differences in the underlying methods using the derived interaction parameters activity models were formulated for the annite phlogopite eastonite and siderophyllite components of biotite and for the mgal celadonite component of muscovite these were utilized for the empirical calibration of 45 fluid independent equilibria involving unique combinations of phase components from the mineral assemblage garnet plagioclase biotite muscovite quartz forty three of the equilibria may be applied as geobarometers to equilibrium assemblages of quartz muscovite biotite garnet plagioclase when care is taken to insure that applications are restricted to valid compositional ranges for these the calibrations yielded multiple correlation coefficients ranging from 0 953 to 0 998 and standard deviations of the residuals ranging from 597 to 118 bars