weathering of mars antarctic analog studies abstract terrestrial analog studies of potential martian weathering processes are reported four major weathering environments are identified i hydrothermal alteration of impact melt sheets and impact breccias ii solid gas and related reactions iii subpermafrost intrusion of lavas involving liquid water and iv subaerial extrusion of lavas in the absence of liquid water weathering in environments i iii has been discussed by other authors this report discusses weathering in environment iv an analog of which is antarctica we conclude that weathering is geologically slow in the absence of liquid water and that zeolites predominate over clays as secondary minerals on volumetric grounds it appears that hydrothermal alteration of impact melt sheets should be the most important time averaged weathering mechanism provided that h2o was present as liquid or permafrost such hydrothermal alteration should operate predominately on ancient crustal material gas solid reactions and photochemical weathering should also operate primarily on ancient crustal material on a time averaged basis weathering products of younger subpermafrost or subaerially erupted basalts should be subordinate to hydrothermal alteration and gas solid reactions it appears that the present martian regolith as analyzed by the viking landers contains a major contribution from ancient crust as typified today by the southern cratered highlands with a lesser contribution from the younger hemispherically restricted basaltic lavas

the effect of salt crust on the thermal conductivity of one sample of fluvial particulate materials under martian atmospheric pressures 1 a line heat source apparatus was used to measure thermal conductivities of a lightly cemented fluvial sediment salinity 1 1 g kg 1 and the same sample with the cement bonds almost completely disrupted under low pressure carbon dioxide atmospheres the thermal conductivities of the cemented sample were approximately 3 higher over the range of atmospheric pressures tested than the thermal conductivities of the same sample after the cement bonds were broken a thermal conductivity derived particle size was determined for each sample by comparing these thermal conductivity measurements to previous data that demonstrated the dependence of thermal conductivity on particle size actual particle size distributions were determined via physical separation through brass sieves when uncemented 87 of the particles were less than 125 m in diameter with 60 of the sample being less than 63 m in diameter as much as 35 of the cemented sample was composed of conglomerate particles with diameters greater than 500 m the thermal conductivities of the cemented sample were most similar to those of 500 m glass beads whereas the thermal conductivities of the uncemented sample were most similar to those of 75 m glass beads this study demonstrates that even a small amount of salt cement can significantly increase the thermal conductivity of particulate materials as predicted by thermal modeling estimates by previous investigators

experimental melting of biotite plagioclase quartz muscovite assemblages and implications for crustal melting abstract in order to understand the role of mica rich rocks as a source of granite magmas a series of melting experiments was performed on two different starting materials the first composition is a model biotite gneiss consisting of 30 wt biotite 30 wt plagioclase and 40 wt quartz the second composition is a model two mica pelites consisting of 15 wt biotite 15 wt muscovite 30 wt plagioclase and 40 wt quartz experiments were performed under vapor absent conditions at 1 0 gpa and between 750 o and 950oc with only biotite in the starting material the volume of melt is always less than 15 vol below 900oc and reaches 25 vol at 950oc in experiments that involve both biotite and muscovite in the starting material the melt proportion increases up to 28 vol at 825oc and reaches 60 vol at 950oc for the biotite plagioclase quartz bpq assemblage the solidus is located at 800oc at 1 0 gpa the melting reaction produces a metaluminous granitic liquid and leaves a residuum consisting of garnet biotite orthopyroxene plagioclase quartz in addition the experiments show that at 1 0 gpa biotite can be stable above 950oc with both micas in the starting material bpqm the solidus at 1 0 gpa is located at 750oc the melting reactions produce a peraluminous granitic liquid and leave a residuum of garnet sillimanite biotite quartz plagioclase kfeldspar in experiments below 900oc at 950oc the residuum consists of garnet orthopyroxene biotite plagioclase the melt fraction is determined by the proportions of the hydrous phases and of the amount of feldspar relative to quartz mineral modes of the source rocks particularly the amount of quartz are at least as important as the amount of available h20 in controlling the melt fraction generated during crustal anatexis

trace element zoning in garnet as a monitor of crustal melting x ray composition maps of sc y p and cr in garnet have been measured using the electron microprobe zoning is discontinuous and is correlated with fluid absent crustal melting reactions the magnitude of the discontinuity is a function of the amount of muscovite that melts and the partition coefficients of solids versus melt trace element zoning is apparently not modified by diffusive processes so the zoning can be used to monitor the extent of melting and to examine kinetics of melting and the participation of accessory phases in crustal anatexis

metamorphic consequences of thrust emplacement fall mountain new hampshire metamorphic pressure temperature p t paths from the upper and lower plates of the fall mountain nappe southwest new hampshire reveal different thermal histories in the two structural levels upper plate rocks experienced early low p high t contact metamorphism to peak p t conditions of 700 750 c 3 4 5 kbar these p t conditions were followed by loading to approximately 5 6 kbar and then by nearly isobaric cooling to approximately 500 c 4 5 kbar upper plate rocks then experienced minor heating with unloading and finally cooling the lower plate rocks also experienced early low p high t contact metamorphism but only to p t conditions of 480 510 c 2 3 5 kbar nappe emplacement resulted in nearly isothermal loading to 500 c 5 6 kbar which was followed by either heating or cooling depending on the proximity of the sample to the upper plate the early pressures recorded in both the upper and lower plate rocks suggest a depth of approximately 10 km for origination of the nappe the post nappe pressures 5 6 kbar imply a total tectonic thickness of approximately 20 km or a doubling of the overburden thickness diffusion calculations suggest that the emplacement of the nappe took less than approximately 10 m y and u pb chronology on zircon suggests that it occurred between 400 and 410 ma 4o ar 39 ar cooling ages on micas indicate that the terrane was cooled to approximately 300 c by 340 ma

major and trace element zoning in garnets from calcareous pelites in the nw shelburne falls quadrangle massachusetts garnet growth histories in retrograded rocks

geochronology and trace element geochemistry of zircon monazite and garnet from the garnetite and or associated other high grade rocks implications for palaeoproterozoic tectonothermal evolution of the khondalite belt north china craton abstract it is well documented that the khondalite belt of the north china craton formed by the collision of the yinshan and ordos blocks during ca 1 95 ga but the onset of the post collisional exhumation stage has not been well dated the garnetite and garnet bearing quartz rich lens that are regarded as residue melt phases occur occasionally in the foliated metasedimentary rocks in the jining terrane of the khondalite belt they are free of regional gneissosity and may be generated during the post collisional exhumation stage zircon u pb dating monazite chemical dating and trace element analyses of zircon monazite and garnet have been carried out on the garnetites and associated other high grade metamorphic rocks the geochronological results reveal a major age group of ca 1890 ma from the zircon grains overgrowths and inclusion type monazites within the garnet poikiloblasts in the garnetites the trace elements analyses show that zircon hosted in the mantle of the garnet poikiloblasts in the garnetite contains the highest hree and y contents whereas zircon hosted in the garnet rims shows higher hree and y contents than matrix zircon grains inclusion type monazite in the garnetite shows higher lan smn ratio than matrix monazite grains large garnet poikiloblasts in the garnetite exhibit bell shaped hree and y zoning profiles attributed to rayleigh fractionation during their growth compared to garnet poikiloblasts coronal garnet shows higher gro cr and li contents but lower xmg sm hree zn and zr contents and weaker eu negative anomalies reflecting their different formation environments based on evidences from microstructural analyses ree concentrations and patterns hree partition coefficients and the ti in zircon thermometer it is proposed that most of the zircon grains overgrowths in the garnetite formed coevally with garnet poikiloblasts consequently ca 1890 ma represents the timing of garnet poikiloblast growth during the partial melting of the protolith coronal garnet or zn rich spinel plus cordierite coupled with the matrix type monazite formed after garnet poikiloblasts growth during near isothermal decompression given the high metamorphic temperature and pressure revealed by the garnetite 820 850 c and up to 950 c 8 5 9 5 kbar it is suggested that the ca 1890 ma age group represents the beginning of extension exhumation event in the khondalite belt which is also recorded in the associated other high grade rocks such as the garnet bearing quartz rich lenses sillimanite garnet bearing quartzo feldspathic gneisses garnet bearing quartzo feldspathic gneisses and a pure quartz vein

monazite xenotime garnet equilibrium in metapelites and a new monazite garnet thermometer prograde suites of pelitic rocks were examined with electron microprobe introduction and laser ablation inductively coupled plasma mass spectrometry to monazite ce la th po4 plays an important role in determine the systematics of element partitioning between coexisting studies of igneous and metamorphic petrogenesis foremonazite xenotime and garnet monazite grains that grew in most monazite is used to date specific events in a equilibrium with xenotime are enriched in y and dy compared with petrogenetic sequence e g parrish 1990 harrison et al monazite that grew in xenotime absent assemblages y and heavy 1997 hawkins bowring 1999 foster et al 2000 rare earth element contents of monazite coexisting with xenotime monazite may contain a large percentage of the sample increase with rising temperature monazite xenotime y gd and rare earth element ree budget and thus exert an y dy partitioning is systematic within a metamorphic grade and important influence on the evolution of melt composition increases slightly with increasing metamorphic grade suggesting wark miller 1993 bea 1996 the thermobarometric that monazite xenotime pairs approached partitioning equilibrium potential of monazite coexisting with xenotime has been garnet and monazite in both xenotime bearing and xenotime absent recognized leading to calibration of monazite geoassemblages show a strong r 0 94 systematic relationship thermometers gratz heinrich 1997 1998 heinrich between inverse temperature and ln keq for the net transfer equiet al 1997 andrehs heinrich 1998 in addition the librium yag oh ap 25 4 qtz 5 4 grs 5 4 an recognition that nearly all lead in monazite is radiogenic 3ypo4 mnz 1 2h2o suggesting that garnet and monazite parrish 1990 montel et al 1994 has led to development crystallized in compositional equilibrium the following temand application of electron microprobe monazite dating perature keq relationship for the equilibrium above has been derived techniques suzuki adachi 1991 montel et al 1996 williams et al 1999 t c 1 45p bars 447772 32052 567 40 rln keq 273 15 full realization of monazite as a thermochronometer requires detailed understanding of the specific reactions responsible for its formation previous studies of monazite with a precision of some 30 c for temperature estimates our petrogenesis have focused on monazite compositional observations suggest that major and accessory phases interact in a zonation zhu o nions 1999a 1999b monazite coupled fashion during metamorphism and also approach a state growth kinetics ayers et al 1999 behavior of monazite of compositional equilibrium as reactions proceed during hydrothermal alteration poitrasson et al 1996 crowley ghent 1999 and melting events watt 1995 or to a limited extent the influence of major phase mineral assemblage in monazite reactivity zhu

a 700 ma sm nd garnet whole rock age from the granulite facies central kaoko zone namibia evidence for a cryptic high grade polymetamorphic history continental collision of the kalahari and the congo craton in africa and the rio de la plata craton in south america resulted in a structurally complex neoproterozoic belt system the kaoko dom feliciano ribeira belt it is uncertain whether these three cratons collided more or less simultaneously during one single orogenic event at 580 550 ma or whether the belt owe its structural and metamorphic features to several so far poorly constrained events the kaoko belt nw nambia representing the belt system between the southern congo craton and the rio de la plata craton is an ideal object to study these complexities within this belt high grade meta igneous and metasedimentary rocks of the sillimanite k feldspar zone contain large garnet porphyroblasts that grew at ca 730 10 c at 6 7 1 2 kbar during peak metamorphic granulite facies conditions a sm nd garnet whole rock errorchron n 7 mswd 6 0 obtained on a siliceous metasediment yielded an unexpected old age of 692 14 ma which is interpreted as an inherited metamorphic age of an older granulite facies event it is evident that the dated garnets survived the younger high grade granulite facies metamorphism that occurred between ca 570 and 520 ma and preserved their old sm nd isotope systematics implying that the closure temperature for sm nd in garnet is higher than ca 730 c in this case these results imply fast cooling rates at different times during the pan african orogeny that prevent isotopic homogenization at sample scale moreover it is suggestive that trace element ree diffusion in garnet is considerably slower than major element diffusion from a regional point of view it is possible that these specific siliceous metasedimentary rocks may be unrelated to the pan african metamorphic evolution of the kaoko belt between 570 and 520 ma and may represent lithological units that belong to so far unrecognized terranes in the kaoko belt 2007 elsevier b v all rights reserved

hydrothermally altered impact melt rock and breccia contributions to the soil of mars samples of melt rock and breccia from 12 terrestrial impact craters were examined to identify alteration minerals and their conditions of formation the dominant assemblage in most cases is clay silica k feldspar zeolite indicating hydrothermal alteration at low pressures and temperatures of 100 300 c the clays are predominantly fe chlorites and smectites in most cases depleted in al and enriched in fe and mg relative to their source rocks alteration of impact glass is often complete while alteration of crystalling melt rock is limited to a few percent of the rock volume impact breccia is altered to only a small extent compared to the alteration of glass impact induced hydrothermal alteration is to be expected at martian impact sites if significant quantities of ground ice and or water are present the alteration products are likely to resemble the clays found at terrestrial craters al fe fractionation similar to that observed on earth is strongly suggested by the viking soil analyses the quantitative contribution of hydrothermal clays to the soil of mars is estimated based on a model which predicts the generation of the equivalent of a 61 m thick blanket of impact melt planet wide the inefficiency of melt production in small craters and the inefficiency of alteration in large craters limit the expected production of clay to a few percent of this figure clays produced by impact induced hydrothermal alteration may be expected to contribute to the fines on mars but this contribution is probably not dominant relative to other suggested sources

sub millimeter heterogeneity of yttrium and chromium during growth of semi pelitic garnet x ray maps of yttrium and chromium in two garnets from a semipelitic schist from central nepal reveal parallel spiraling bands of high and low concentration 10 30 m wide this zoning mimics similar concentration bands defined by foliation in the matrix outside the garnets the garnets apparently incorporated the matrix zoning intact during growth at conditions up to lower amphibolite facies these observations and interpretations indicate that yand cr concentrations remained heterogeneous at the scale of tens of micrometers during breakdown of matrix minerals and growth of garnet this conclusion extends results of previous work which showed that y and cr do not homogenize at the centimeter to millimeter scale during metamorphism to amphibolite facies the width of the concentration bands in the garnets places a constraint on the maximum effective intracrystalline diffusion coefficient for both y and cr in garnet of about 10 21 cm 2 s for peak metamorphic conditions of about 9 kbar at 5708c different concentrations of yand cr at different positions around the rim of each garnet indicate disequilibrium for these elements between garnet and matrix phases the presence of an internal foliation defined by the yand cr concentration bands rules out pre kinematic garnet growth most useful in conjunction with other indicators zoning of these elements in garnet is thus a tool for deciphering the relative timing of deformation and garnet growth

hydrothermal jarosite and hematite in a pyroxene hosted melt inclusion in martian meteorite miller range mil 03346 implications for magmatic hydrothermal fluids on mars low temperature aqueous processes have been implicated in the generation of jarosite and hematite on the martian surface but little is known regarding the role that high temperature magmatic fluids may have played in producing similar assemblages on mars we have identified jarosite and hematite in a clinopyroxene hosted melt inclusion in martian meteorite mil 03346 that shows evidence of having been hydrothermally precipitated in addition to jarosite and hematite the melt inclusion contains titanomagnetite pyrrhotite potassic chlorohastingsite an iron rich silicate glass and possibly goethite these phases were identified and characterized using scanning electron microscopy sem con focal raman spectroscopy and electron probe microanalysis epma based on observed textural relationships and the compositions of the hosted phases we report that the jarosite bearing melt inclusion in mil 03346 has recorded a fluid rich history that began in the magmatic stage and continued to low temperatures this history begins at entrapment of a volatile rich silicate melt that likely reached fluid saturation after only minor crystallization within the melt inclusion this fluid rich in chlorine reacted with surrounding silicate material to produce the potassicchlorohastingsite as cooling proceeded the liquid phase eventually became more oxidized and reacted with the pyrrhotite sulfide oxidation resulted in so4 2 formation and concomitant acid production setting the stage for jarosite formation once the fluid cooled beyond the upper thermal stability of jarosite 200 c as the fluid cooled below 200 c jarosite continued to precipitate with hematite and or goethite until equilibrium was established or reactions became kinetically unfavorable this work suggests an additional jarosite hematite formation pathway on mars one that may be important wherever magmatic hydrothermal fluids come into contact with primary sulfide grains at the martian surface or subsurface moreover hydrothermal fluids rich in chlorine sulfur and iron are important for ore forming processes on earth and their indirect identification on mars may have important implications for ore formation on mars

different origins of garnet in high pressure to ultrahigh pressure metamorphic rocks abstract garnet in high pressure hp to ultrahigh pressure uhp metamorphic rocks in subduction zone commonly shows considerable zonation in major and trace elements as well as mineral inclusions which bears information on its growth mechanism via metamorphic or peritectic reactions in coexistence with relic minerals and metamorphic fluids or anatectic melts at subduction zone conditions it provides an important target to retrieve physicochemical changes in subduction zone processes including those not only in pressure and temperature but also in the durations of metamorphism and anatexis garnet from different compositions of hp to uhp metamorphic rocks may show different types of major and trace element zonation as well as mineral inclusions discrimination between the different origins of garnet provides important constraints on pressure and temperature and the evolution history for the hp to uhp metamorphic rocks magmatic garnet may occur as relics in granitic gneisses despite metamorphic modification at subduction zone conditions with spessartine increasing or flat major element profiles from inner to outer core and exceptionally higher contents of trace elements than metamorphic mantle and rim metamorphic garnet can grow at different metamorphic stages during prograde subduction and retrograde exhumation with spessartine decreasing from core to rim if the intracrystalline diffusion is not too fast the compositional profiles of metamorphic garnet in the abundances of grossular almandine and pyrope are variable depending on the composition of host rocks and co existing minerals peritectic garnet grows through peritectic reactions during partial melting of hp to uhp rocks with the composition of major elements to be controlled by anatectic p t conditions and the compositions of parental rocks and anatectic melts trace element profiles in garnet with different origins are also variable depending on the coexisting mineral assemblages the garnet forming reactions and the property of metamorphic fluids or anatectic melts mineral inclusions not only present key clues to identify the different origins of garnet but also serve as sound candidates for the temporal constraint on garnet growth

metamorphic thermal and tectonic evolution of central new england mountain skitchewaug and big staurolite nappes reactivation of a new detailed tectonic model is presented for the acadian orogenic this fabric during thrusting is recorded in some rocks of the big belt of central new england vermont and new hampshire that staurolite nappe by rotated garnets that grew during near isothermal accounts for a wide range of petrological and structural observations loading only the sillimanite isograd crosses the fall mountain three belts are considered the eastern vermont merrimack and skitchewaug nappe boundary metamorphic breaks across the skitintervening bronson hill belts specific observations in eastern chewaug big staurolite nappe boundary at the base of the big vermont that are accounted for in the model include the following staurolite nappe and at the margin of the keene and alstead domes p t paths are clockwise with maximum pressures near the athens require post metamorphic thrusting when p t conditions were in chester and strafford domes of 8 11 kbar but with maximum the greenschist facies these observations can be explained by a pressures decreasing to 3 5 kbar at the boundary with the bronson relatively simple model involving in sequence thrusting from east to hill belt differential exhumation of the vermont domes relative to west commencing in central new hampshire at 400 410 ma the rocks in easternmost vermont is required by the recorded differences preservation of the low grade belt along the vermont new hampin maximum pressure 5 6 kbar 15 20 km and the present day shire border requires that crustal thickening in vermont was not geographical separation 7 10 km specific observations in new caused by emplacement of new hampshire nappes onto eastern hampshire that are explained include the following p t paths in vermont and that the nappes of western new hampshire had time the merrimack belt are counter clockwise with maximum pressures to cool before final juxtaposition against the low grade belt cooling of 4 5 kbar and are related to high regional heat flow and heat ages constrain this final juxtaposition to have occurred in the transfer by early acadian plutons p t paths in the bronson hill carboniferous suggesting that the acadian was a prolonged event belt are intimately associated with structural position an early spanning as much as 100 myr contact metamorphism is evidenced in the skitchewaug and fall mountain nappes near contacts with the early acadian bethlehem gneiss 400 410 ma peak metamorphic temperature rises upwards in the nappe sequence an inverted metamorphic sequence

origin of atoll garnets in eclogites and implications for the redistribution of trace elements during slab exhumation in a continental subduction zone detailed electron and ion microprobe analyses were carried out on atoll shaped and normal garnets in ultrahigh pressure uhp metamorphic eclogite from dabie east central china compositional profiles of both normal garnets and rings of atoll garnets show well preserved growth zoning with a decrease in mn ca and heavy rare earth elements hrees and an increase in mg toward rims manganese and middle rare earth element mree enrichments are observed near garnet rims island and peninsula shaped garnet inside atolls are homogeneous in major elements and show the same composition as garnet rims whereas the hree concentrations are similar to those of the normal garnet cores electron back scatter diffraction ebsd analyses show that the island and peninsula shaped garnet fractions inside atolls have crystallographic orientations identical to that of the atoll rings these observations suggest that the atoll garnets were formed by the consumption of earlier formed cores by fluid released from both hydroxyl exsolution from the nominally anhydrous minerals nams and lawsonite decomposition at the onset of exhumation i e garnet breakdown was from the inside and re growth from outside to inside though somewhat restricted this study reveals that because garnet and zircon act as sinks for hrees and zr respectively the majority of released hrees and zr were likely re incorporated into newly grown garnet and zircon during the dabie uhp metamorphic slab exhumation

monazite behaviour and age significance in poly metamorphic high grade terrains a case study from the western musgrave block central australia abstract integrated in situ textural chemical and electron microprobe age analysis of monazite grains in a migmatitic metapelitic gneiss from the western musgrave block central australia has identified evidence for multiple events of growth and recrystallisation during poly metamorphism in the mesoproterozoic garnet sillimanite bearing metapelite underwent partial melting and segregation to palaeosome and leucosome during metamorphism between 1330 and 1296 ma with monazite grains in leucosome recording crystallisation at 1300 ma monazite breakdown during melting is inferred to have occurred in the palaeosome during a subsequent granulite facies event at 1200 ma deformation and metamorphism of leucosome and palaeosome resulted in partial disturbance of ages and potential minor growth on 1300 ma monazite in leucosome growth of new high y hree monazite in palaeosome domains occurred during garnet breakdown in the presence of sillimanite to cordierite and spinel as a result of post peak isothermal decompression diffusive enrichment of resorbed garnet rims in y hree suggests garnet breakdown occurred slower than volume diffusion of ree monazite in both palaeosome and leucosome were subsequently partially to penetratively recrystallised during a retrogression event that is suggested to have occurred at 1150 1130 ma the intensity of recrystallisation and disturbance of ages appears linked to proximity to retrogressed garnet porphyroblasts and their occurrence in the relatively reactive or fertile local environments provided by the palaeosome mesosome volumes which caused localised changes in retrogressive fluids towards compositions more aggressive to monazite like reaction textures it is apparent that domainal equilibrium and reaction may control or at least strongly influence monazite ree and u th pb chemistry and hence ages

geochemistry and trace element behaviors of eclogite during its exhumation in the xitieshan terrane north qaidam uhp belt nw china abstract the xitieshan terrane located in the central part of the north qaidam ultrahigh pressure uhp metamorphic belt china is mainly composed of orthogneiss and paragneiss and a few intercalated eclogite layers and boudins based on their bulk rock tio 2 contents the eclogites can be subdivided into a high ti group tio 2 2 and a low ti group tio 2 e nd t and restricted i sr values and therefore provide further evidence for the formation of the protoliths of the eclogites in an oceanic environment on the other hand the sr nd isotopes of high ti eclogites show mainly positive but also some negative e nd t values and relatively broadly distributed i sr values indicating minor crustal contamination of the ocean floor basalts considering available 750 877 ma protolith ages preserved in zircon cores it is inferred that some of the eclogites derived from neoproterozoic protoliths were emplaced onto the crust far ahead of the paleozoic deep subduction while the other eclogites originate from a different oceanic crust e g the paleo qilian ocean indicating multiple orogenies in the geological history of the xitieshan terrane china whole rock and in situ la icp ms mineral trace element analyses of eclogites revealed two stages of fluid behavior during retrogression that correspond to the two exhumation stages uncovered by phase equilibrium calculations the mineral scale trace element distributions and trace element inheritance of newly formed amphibole from its precursors indicate that at the peak metamorphic stage m1 and at the earlier eclogite facies overprint m2 the fluid was internally controlled by the rock itself within a mafic lens the amount of water soluble elements e g rb sr ba u pb and lree observed in the whole rock compositions as well as in amphiboles increases from the core phengite bearing eclogite to the rim amphibolite and implies an external fluid source for the amphibolite facies retrogression m3 which should be helpful for the final exhumation of uhp eclogite

yttrium zoning in metamorphic garnets abstract yttrium zoning has been measured in garnets from the straits schist connecticut usa using the synchrotron x ray fluorescence sxrf microprobe sxrf compositional maps for mn and fe show that the major elements are concentrically zoned about the gannet core in the classic bell shaped profiles considered indicative of growth zoning yttrium however displays oscillatory zoning which varies three orders of magnitude in abundance from about 3 to 4000 ppm and is correlated with textural zoning in garnet the major element abundances by contrast display no visible inflection related to textural zoning at this time it is not possible to unequivocally identify the mechanism which has produced this oscillatory zoning most likely this reflects either the breakdown of y enriched phases changes in the rate of garnet growth with time or changes in the effective y concentration of matrix phases due to breakdown and reprecipitation of garnet as the equilibrium reactions involving gannet change this study demonstrates that the sxrf microprobe provides excellent spatially resolved compositional maps for trace elements in porphyroblasts something other analytical techniques have been unable to do it also suggests that the diffusion rates for y in garnet are probably significantly slower than those for major cations such as mn fe mg and ca as a result trace element mapping potentially provides a clearer record of the reaction history of the rock provides details of how chemical zoning in garnet is produced and allows evaluation of assumptions about chemical equilibrium between minerals

mineral leucosome trace element partitioning in a peraluminous migmatite a laser ablation icp ms study abstract low pressure peraluminous migmatites from the pena negra complex central spain stayed partially molten for 5 10 ma until the latest hercynian deformations allowed the segregation of melt as discordant leucosome veins due to long residence within its source the melt had time enough to equilibrate with residual phases other than accessories included within major refractory minerals we estimated crystal melt partition coefficients as the concentration ratios between leucosome samples appearing to be pure melts and mesosome minerals which were analyzed for trace elements with a laser probe coupled to an icp mass spectrometer our data reveal that when biotite is stable li rb cs tl sc v cr ni nb and ta become strongly compatible the role of biotite in fractionating y th u and the ree is insignificant cordierite strongly fractionates li and be and also has some effect on the hree and u garnet produces extreme fractionation of sc y and the hree the ree partition coefficients for ferromagnesian silicates increase with the atomic number this effect being progressively more important through biotite cordierite and garnet k feldspar strongly fractionates ba and pb but plays a secondary role to biotite for rb and cs k feldspar fractionation does not change the lree hree ratio but plagioclase fractionation produces a significant decrease in the lree hree ratio both feldspars greatly fractionate sr and eu monazite fractionation produces a dramatic depletion in ree th and u as well as a decrease in the lree hree and th u ratios apatite also fractionates the ree although in contrast with monazite it increases the lree hree ratio and does not affect the th u ratio zircon fractionation like apatite and garnet produces a strong depletion in the hree and a concomitant increase in the lree hree ratio in contrast with monazite zircon fractionation causes the th u ratio to increase

terrestrial analogues of the surface rocks of mars the pathways of chemical weathering processes on earth and the virtual absence of them on the moon are well characterized because we have direct access to samples of primary igneous rocks their upper mantle sources and derivative sedimentary rocks and soil forming the regolith tracing chemical changes on the surface of mars however is more difficult because of limited access to samples from mars terrestrial rocks and minerals are continually being sought which might serve as analogues for martian materials evidence presented here suggests that hisingerite iddingsite and several ferric sulphate minerals derived from deuteric alteration of iron rich basalts may provide clues to the evolutionary history of the surface of mars

jarosite formation by an amd sulphide oxidizing environmental enrichment implications for biomarkers on mars abstract the formation of jarosite in acid mine drainage amd accompanies microbial oxidation of reduced sulphidic minerals such as pyrite fes 2 and pyrrhotite fe 1 x s found in mining waste materials the discovery of jarosite at meridiani planum mars has been used to interpret past hydrologic conditions as episodically wet acidic and evaporative based on evidence from jarosite formed abiotically or through microbial iron oxidation to date no study has specifically assessed jarosite formation via microbial sulphide oxidation the most likely pathway in amd or the mineral stability of any jarosite formed via this pathway here using both aerobic and anaerobic conditions to control iron and sulphide oxidation metabolisms we demonstrate that oxidation of pyrrhotite a putative mars mineral by a sulphur oxidizing environmental amd enrichment produces crystalline jarosite at a higher ph than previously described we further show that jarosite produced via microbial sulphide oxidation is stable under the drying heating and wet aging conditions shown to impact abiotic and microbial iron oxidation derived jarosite our results indicate that preservation of microbially produced jarosite via pyrrhotite associated sulphide oxidation does not require the evaporitic conditions that have been proposed to date if water is established to have persisted on mars then this new evidence signals that the occurrence of stable crystalline jarosite at meridiani planum may itself be a clear biomarker indicating that not only water occurred at some time s on mars but also life

early cretaceous migmatitic mafic granulites from the sabzevar range ne iran implications for the closure of the mesozoic peri tethyan oceans in central iran terra nova 22 26 34 2010 abstract the ophiolitic melange of the sabzevar range northern iran is a remnant of the mesozoic oceanic basins on the northern margin of the neotethys that were consumed during the arabia eurasia convergence history occurrence of km scale dismembered mafic hp granulitic slices is reported in this study granulites record an episode of amphibole dehydratation melting and felsic tonalite throndhjemite melt segregation at c 1 1 gpa and 800 c in situ u th pb geochronology of zircon and titanite grains hosted in melt segregations points to an early cretaceous albian age for the metamorphic climax results of this study i impose reconsideration of the current palaeotectonic models of the neothetyan convergent margin during the early cretaceous and ii argue that punctuated events of subduction of short lived back arc oceanic basins accompanied the long lasting history of the neotethyan subduction in the region

the behaviour of nd and pb isotopes during 2 0 ga migmatization in paragneisses of the central zone of the limpopo belt south africa and botswana we have carried out major and trace element analyses and nd pb isotope measurements on different components of two migmatite outcrops in the limpopo belt lose quarry botswana and palala south africa in order to assess the effect of migmatization during a high grade metamorphic event on sm nd systematics and nd model ages the outcrops studied are located in the mahalapye tshipise straightening zone at the south western part of the limpopo central zone close to its contact with the kaapvaal craton leucosomes of peraluminous granitic composition were formed by incongruent biotite melting in an fe rich metagreywacke lose quarry and in a metapelite palala respectively monazite u pb and garnet sm nd ages yield close to 2 0 ga for the high grade event confirming other recent work in the central zone the chemical compositions of the main mineral phases feldspar biotite and garnet indicate minimum melt formation at t 750 c and low pressure isocon plots and pb isotope data indicate that the partial melts are locally derived however lil trace element distribution between the leucosomes and paleosomes indicate the incomplete equilibration of the nascent melts with the residual feldspars and biotite in the paleosomes sm nd results on leucosomes and paleosomes of the metagreywacke migmatite show considerable scatter when calculated back to 2 0 ga the paleosomes fall in a narrow range of nd 4 and give tdm model ages between 2 45 and 2 66 ga the nd values of leucosomes are on average four units lower causing them to have apparent tdm ages of 2 7 2 92 ga on average 250 ma older than those of the paleosomes the ree th p2o5 and zr budgets of paleosomes and leucosomes indicate dominance of the lree by monazite and the hree by apatite incorporation of proportionally more monazite than apatite into the melt is inferred as the cause for the nd isotope discrepancy and hence the uncertainty of the average protolith mantle derivation age in contrast pb pb results define an apparent age of 2025 29 ma reflecting nearly full pb isotope exchange in the case of the palala metapelitic migmatite the nd values at 2 0 ga of all but two migmatitic constituents cluster between 7 and 9 5 pointing out extensive nd isotope equilibration during migmatization whereas the pb isotopes yield an errorchron date of 2311 65 ma indicating incomplete pb isotope exchange here garnet dominates the hree distribution whereas the lree are controlled by feldspar and monazite considering that nd isotope equilibration was nearly reached during migmatization nd model ages on the whole rocks represent a good approximation of those of the original protolith 3 0 3 2 ga in the regional context the pb isotope data from the lose quarry locality combined with the nd model age uncertain but within the range of 2 5 2 9 are reminiscent of the northern marginal zone of the limpopo belt and the southern zimbabwe craton whereas the nd and pb isotope data from the palala locality are typical for the limpopo southern marginal zone and the northern kaapvaal craton

late stage orogenic loading revealed by contact metamorphism in the northern appalachians new york pelitic schists from contact aureoles surrounding mafic ultramafic plutons in westchester county ny record a high p 0 8 gpa high t 790 c contact overprint on a taconic regional metamorphic assemblage 0 5 gpa the contact metamorphic assemblage of a pelitic sample in the innermost aureole of the croton falls pluton a small 10 km 2 gabbroic body consists of quartz plagioclase biotite garnet sillimanite ilmenite graphite zn rich al spinel both k feldspar and muscovite are absent and abundant biotite plagioclase sillimanite quartz and ilmenite inclusions are found within subhedral garnet crystals unusually low bulk rock na and k contents imply depletion of alkalic components and silica through anatexis and melt extraction during contact heating relative to typical metapelites outside the aureole thermobarometry on nearby samples lacking a contact overprint yields 620 640 c and 0 5 0 6 gpa in the aureole sample wds x ray chemical maps show distinct ca enriched rims on both garnet and matrix plagioclase furthermore biotite inclusions within garnet have significantly higher mg concentration than matrix biotite thermobarometry using gasp and garnet biotite mg fe exchange equilibria on inclusions and adjacent garnet host interior to the high ca rim zone yield 0 5 0 1 gpa and 620 50 c pairs in the modified garnet rim zone yield 0 9 0 1 gpa and 790 50 c thermocalc average p t calculations yield similar results for core 0 5 0 1 gpa 640 80 c and rim 0 9 0 1 gpa 800 90 c equilibria the core assemblages are interpreted to record the p t conditions of peak metamorphism during the ta conic regional event whereas the rim compositions and matrix assemblages are interpreted to record the p t conditions during the contact event the high pressures deduced for this later event are inter preted to reflect loading due to the emplacement of taconic allochthons in the northern appalachians during the waning stages of regional metamorphism after c 465 ma and before contact metamor phism c 435 ma in the absence of contact metamorphism induced recrystallization it is likely that this regional scale loading would remain cryptic or unrecorded

trace element zoning in a metamorphic garnet trace element zoning has been measured in an amphibolite garnet from the tauern window austria by using an ion microprobe humps in the zoning profiles of na sc v y and the heavy rare earth elements mark a period of open system behavior these humps correspond to a part of the major element zoning profile that is interpreted as a p t reversal the source of the mass excesses of these elements remains ambiguous they were derived either on a thin section scale by the breakdown of trace element enriched refractory minerals or externally from unusual trace element enriched fluids p t paths determined from garnet zoning may require modification if open system behavior is important during garnet growth

interpretation of monazite ages obtained via in situ analysis abstract monazite grains from nepal and vietnam were compositionally analyzed with an electron microprobe and dated th pb with an ion microprobe five sources of uncertainty explain age distributions from single samples that appear inconsistent with a single population 1 pb loss due to diffusion 2 dissolution reprecipitation reactions along a retrograde path 3 analytical uncertainties 4 analyses of overlapping age domains and 5 episodic monazite growth the influence of these factors is sample dependent but can be evaluated 1 using peak metamorphic conditions and x ray element maps to assess potential polymetamorphism or retrogression 2 obtaining other geochronologic data including previous work or dating other minerals in the sample 3 evaluating any method related uncertainty including counting statistics for electron microprobe analyses or calibration reproducibility for ion microprobe analyses and 4 ascertaining the potential growth mechanism of the monazite grain including dissolution of detrital grains or production from rare earth element ree oxide or allanite chemical contents of monazite grains analyzed in this study fail to reflect timing information or mineral growth mechanisms instead of relying on monazite chemical composition major mn fe mg ca and minor y element garnet zoning patterns and peak p t conditions should be used to facilitate age interpretation this thermobarometric data records the sample s thermal history changes in garnet growth rate and mechanisms and accessory mineral breakdown

cosmogenic and nucleogenic isotopic changes in mars their rates and implications to the evolutionary history of martian surface abstract we present calculations of rates of production of several nuclides in the martian atmosphere and in the regolith due to nuclear interactions of cosmic ray and radiogenic particles and consider their implications to the evolutionary history of mars nuclides selected are those which considering their chemical properties may be useful as tracers for delineating the past histories of the martian atmosphere and regolith calculations are presented for different assumed atmospheric pressures the regolith production rates for the present thin martian atmosphere 20 g cm 2 are expected to be fairly robust because they are based primarily on observed cosmogenic effects in the moon for which semiempirical estimates of nuclide production rates have been provided earlier by reedy 1981 uncertainties which arise in the calculations of nuclide production rates for an earlier hypothetical martian atmosphere of 300 500 g cm 2 thickness are discussed compared to cosmic ray production rates the nucleogenic production rates are smaller by several orders of magnitude however the nucleogenic production extends to much deeper levels whereas the cosmogenic production is essentially confined to the top 750 1000 g cm 2 depth important examples of nucleogenic production are discussed isotopes of neon and argon appear to be very promising for delineating relative magnitudes of a number of planetary processes related to the temporal changes in the thickness of the atmosphere as well as their release from the regolith however quantification of the processes would require higher precision isotopic data for the atmosphere and also direct measurements of isotopic ratios in the martian regolith along with supplementary information on changes in the isotopic compositions of hydrogen carbon and nitrogen which are affected by a variety of mechanisms of escape of gases from the atmosphere cosmogenic effects are minimal in these cases we show that although we can at present draw but limited inferences the planet mars presents a unique opportunity to use cosmogenic nuclides as tools to delineate the evolutionary history of the planet as a whole as well as its regolith and the atmosphere this arises because of two factors minimal degassing of the planet and a fairly intense chemical weathering history of the upper surface consequently an appreciable fraction of some of the isotopes of volatile elements is contributed by nuclear reactions

exhumation of the main central thrust from lower crustal depths eastern bhutan himalaya geothermometry and mineral assemblages show an increase of temperature structurally upwards across the main central thrust mct however peak metamorphic pressures are similar across the boundary and correspond to depths of 35 45 km garnet bearing samples from the uppermost lesser himalayan sequence lhs yield metamorphic conditions of 650 675 c and 9 13 kbar staurolite kyanite schists about 30 m above the mct yield p t conditions near 650 c 8 10 kbar kyanite bearing migmatites from the greater himalayan sequence ghs yield pressures of 10 14 kbar at 750 800 c top to the south shearing is synchronous with and postdates peak metamorphic mineral growth metamorphic monazite from a deformed and metamorphosed proterozoic gneiss within the upper lhs yield u pb ages of 20 18 ma staurolite kyanite schists within the ghs a few metres above the mct yield monazite ages of c 22 1 ma we interpret these ages to reflect that prograde meta morphism and deformation within the main central thrust zone mctz was underway by c 23 ma u pb crystallization ages of monazite and xenotime in a deformed kyanite bearing leucogranite and kyanite garnet migmatites about 2 km above the mct suggest crystallization of partial melts at 18 16 ma higher in the hanging wall south verging shear bands filled with leucogranite and pegmatite yield u pb crystallization ages for monazite and xenotime of 14 15 ma and a 1 2 km thick leuco granite sill is 13 4 0 2 ma thus metamorphism plutonism and deformation within the ghs con tinued until at least 13 ma p t conditions at this time are estimated to be 500 600 c and near 5 kbar from these data we infer that the exhumation of the mct zone from 35 to 45 km to around 18 km occurred from 18 to 16 to c 13 ma yielding an average exhumation rate of 3 9 mm year 1 this process of exhumation may reflect the ductile extrusion by channel flow of the mctz from between the overlying tibetan plateau and the underthrusting indian plate coupled with rapid erosion

jarosite and hematite at meridiani planum from opportunity s mossbauer spectrometer mossbauer spectra measured by the opportunity rover revealed four mineralogical components in meridiani planum at eagle crater jarosite and hematite rich outcrop hematite rich soil olivine bearing basaltic soil and a pyroxene bearing basaltic rock bounce rock spherules interpreted to be concretions are hematite rich and dispersed throughout the outcrop hematitic soils both within and outside eagle crater are dominated by spherules and their fragments olivine bearing basaltic soil is present throughout the region bounce rock is probably an impact erratic because jarosite is a hydroxide sulfate mineral its presence at meridiani planum is mineralogical evidence for aqueous processes on mars probably under acid sulfate conditions

formation of metamorphic and metamorphosed garnets in the low t uhp metagranite during continental collision in the dabie orogen abstract a combined study of major and trace elements in garnet was carried out for low t uhp metagranite in the dabie orogen the results show different fashions of element zoning in the garnet suggesting occurrence of both metamorphic and metamorphosed garnets three generations of garnet growth are distinguished on the basis of the assumption that ca contents mn contents and fe mg ratios of garnet in metagranites are a function of pressure and temperature the first generation of garnet grt i occurs in the core of a skeletal garnet showing homogeneously low x grs values and fe mg ratios but high x sps values this implies that the core garnet grew at the highest temperature but the lowest pressure representing a metamorphosed residue of magmatic garnet in protolith granite the second generation of garnet grt ii occurs in the mantles and cores of many garnet grains exhibiting increased x grs values but decreased fe mg ratios this is ascribed to a continuous increase in temperature and pressure till the peak pressure corresponding to metamorphic growth or overgrowth during the prograde subduction the third generation of garnet grt iii occurs in the rims of all garnet grains displaying decreased x grs values and fe mg ratios in response to a pressure decrease but a temperature increase till the peak temperature these rims overgrew subsequent to the peak pressure with continuous heating during the initial exhumation grt i shows steep mree hree patterns and profoundly negative eu anoalies consistent with growth from granitic melt this kind of metamorphosed garnet from protolith granite has still preserved very high contents of many trace elements such as ree rb ba sr pb th u nb and ta despite the low t uhp metamorphism grt ii and grt iii in one sample exhibit steep mree hree patterns with a continuous decrease in ree contents this suggests their growth from the almost same matrix of mineral assemblages plagioclase k feldspar muscovite during metamorphism however grt ii in the other sample displays flat to steep mree hree patterns with an increase of ree contents from core to mantle this implies that the matrix of mineral assemblages for grt ii changes from common rock forming minerals e g feldspar muscovite and biotite to ree rich minerals e g epidote allanite zircon amphibole apatite and titanite grt iii in the two samples all displays significantly lowered ree contents compared to those of grt i and grt ii this may be due to a decrease in pressure and an increase in temperature during the initial exhumation therefore the two stage growth of metamorphic garnet is evident in the low t uhp metagranite during the continental subduction zone metamorphism in addition the highest pressure occurs in the cores or mantles whereas the highest temperature occurs in the rims this suggests that the peak pressure p max did not occur contemporarily at the peak temperature t max corresponding to the hot exhumation

influence of ultramafic rocks and hot springs with travertine depositions on geochemical composition and baseline of soils application to eastern central greece abstract ultramafic rocks and hot springs which occur on almost every continent of our planet lead to enriching concentration to several elements including some potentially toxic ones to the soil groundwater fauna and flora and subsequently are posing potential risks to human health a geochemical and mineralogical soil survey was undertaken in eastern central greece an area characterised by the presence of ultramafic rocks of ophiolite complexes and hot springs with thermogenic travertine depositions the research aimed to investigate their influence on soil mineralogy and geochemistry and to establish the soil geochemical baseline values one hundred four soil samples were collected from 74 sites at depths of 0 25 cm and 25 50 cm they were found to be enriched in ca 5 17 fe 3 72 mg 2 08 co 28 mg kg cr 252 mg kg cu 32 mg kg and ni 267 mg kg relative to the median values of both greek and european soil and upper continental crust factor analysis revealed three main factors controlling the soil chemical composition reflecting the influence of ultramafic rocks ni co cr and fe pedogenesis processes ba al and k and thermogenic travertine deposits ca and sr all the factors showed a significant spatial correlation with the geological features within the study area geochemical baselines were estimated for three sub areas based on the three controlling factors revealed by the multivariance statistical analysis and spatial data calculating only one baseline value based on the total dataset would lead to incorrect baseline values for several elements the outcome of the present research could be used in future studies at regions with similar geological features i e serpentine soils and hot springs depositions providing a comparative example concerning the concentrations of several elements including some potentially toxic ones to the soil their host mineral phases and a scientific approach for setting pragmatic geochemical baseline values for pollution assessment

mineral chemistry of the shergottites nakhlites chassigny brachina pallasites and urelites the mineral chemistry is compared for selected achondrites olivine in the alha 77005 and eeta79001 shergottites olivine rich chassigny and brachina and the nakhlites contains ni indicative of oxidizing conditions whereas pallasitic and ureilitic olivines contain much lower ni due to reducing conditions the brachina olivine and pyroxene have distinctively higher fe mn than the shergottites and chassigny further indicating that brachina is unique the chassigny and 77005 olivines contain lower cr2o3 0 03 wt than the brachina and 79001 olivines values of fe mn for cumulus augites in nakhlites are higher than for the shergottites whereas those for ferropigeonites are not the 77005 shergottite contains troilite fes in contrast to 79001 shergotty zagami and chassigny which contain pyrrhotite further analyses are needed but the present survey indicates that at least brachina is not chemically cogenetic with the other oxidized achondrites and that the fe mn ratio of the cumulus augites in nakhlites is a problem for the assignment of the nakhlites shergottites and chassigny to a single genetic group

chemical composition of martian fines of the 21 samples acquired for the viking x ray fluorescence spectrometer 17 were analyzed to high precision compared to typical terrestrial continental soils and lunar mare fines the martian fines are lower in al higher in fe and much higher in s and cl concentrations protected fines at the two lander sites are almost indistinguishable but concentration of the element s is somewhat higher at utopia duricrust fragments successfully acquired only at the chryse site invariably contained about 50 higher s than fines no elements correlate positively with s except cl and possibly mg a sympathetic variation is found among the triad si al ca positive correlation occurs between ti and fe sample variabilities are as great within a few meters as between lander locations 4500 km apart implying the existence of a universal martian regolith component of constant average composition the nature of the source materials for the regolith fines must be mafic to ultramafic

implications of lightning charge moment changes for sprite initiation 1 we report impulse lightning charge moment changes defined as occurring in the first 2 ms after return stroke onset in all cloud to ground lightning strokes detected by the national lightning detection network in three storms during which above thunderstorm sprite video was recorded after analyzing strokes that both did and did not produce sprites and carefully accounting for lightning sprite delay times we found that sprite initiation on all three nights is consistent with a sharp charge moment threshold essentially all charge moment changes above and none below this threshold produced sprites with short delays 5 ms from the source lightning on two nights this threshold was approximately 600 c km and on the other it was approximately 350 c km this internight variability is probably due to expected variability in the nighttime mesospheric conductivity and the thresholds themselves are consistent with predictions of conventional breakdown theory additionally we found only one negative polarity lightning stroke from all three storms that exceeded this threshold indicating that the rarity of documented sprites produced by negative strokes may be largely explained by the lack of sufficiently big negative strokes in the u s high plains

jarosite in a pleistocene east african saline alkaline paleolacustrine deposit implications for mars aqueous geochemistry 1 jarosite occurs within altered tephra from the saline alkaline paleolake deposits of pliocene pleistocene olduvai gorge tanzania zeolites mainly phillipsite authigenic k feldspar and mg fe smectites dominate the mineral assemblage indicating saline alkaline diagenetic conditions ph 9 as jarosite is ordinarily an indicator of acidic conditions on earth and mars its association with such undisputed high ph indicators is unexpected of 55 altered tephra samples collected from the paleolake basin and margin deposits eleven contained jarosite detectable by x ray diffraction xrd 0 15 mossbauer spectroscopy fourier transform infrared reflectance ftir electron probe microanalysis epma x ray fluorescence xrf and scanning electron microscopy sem analyses confirm the presence and nature of the jarosite this paper documents this occurrence and presents mechanisms that could produce this unusual and contradictory mineral assemblage we favor a mechanism by which jarosite formed recently perhaps as modern ground and meteoric water interacted with and oxidized paleolacustrine pyrite providing local and temporary acidic conditions however local groundwater at modern springs has a ph 9 in recent studies of mars the presence of jarosite or other fe or mg sulfates is often used to indicate dominantly acidic conditions regardless the current study shows that jarosite can form in sediments dominated by alkaline minerals and solutions its coexistence with mg fe smectites in particular makes it relevant to recent observations of martian paleolakes

mossbauer parameters of iron in sulfate minerals although fe sulfate minerals occur only rarely on earth as alteration products of sulfidic basalts or in hydrothermal systems multiple lines of evidence point to the importance of fe and other sulfate minerals on the surface of mars one such martian data set comes from the mimos ii mossbauer spectrometers on the mars exploration rovers which acquired hundreds of spectra from the martian surface at two locations interpretation of those spectra has been limited by the lack of a comprehensive set of laboratory analog spectra of the broad range of naturally occurring sulfate minerals accordingly this study reports mossbauer data of 98 samples representing 47 different sulfate mineral species all containing six or higher coordinated fe the resultant mossbauer parameters are related to the local polyhedral environment around the fe cation in each mineral to explain variations in spectral characteristics results show that the size of the coordination polyhedron is the best predictor of quadrupole splitting which increases with both octahedral volume and mean bond length species within groups of structurally similar minerals are shown to have comparable spectral peaks that generally fall within small ranges although coordination polyhedron geometry is not necessarily unique to any particular mineral species or group mossbauer data can be used to help constrain mineral identifications from martian spectra the number of mineral species is large but the range of crystal structures and hyperfine parameters may be small so that in many cases individual minerals cannot be uniquely fingerprinted examples would include quenstedtite coquimbite kornelite and lausenite which have indistinguishable spectra as do apjohnite bilinite dietrichite and romerite overlap of mossbauer parameters is a particular complication for identification of fe 3 rich phases because the range of mossbauer parameters for fe 3 in any coordination number is so small previous analyses of martian mossbauer spectra reported the presence of jarosite klingelhofer et al 2004 morris et al 2004 and an unspecific ferric sulfate morris et al 2008 new data presented here indicate that botryogen metasideronatrite and slavikite exhibit mossbauer spectra similar to those attributed to jarosite at meridiani planum fibroferrite and rhomboclase have parameters similar to those observed at arad samra and copiapite and parabutlerite could be present at tyrone mount darwin and berkner island unique mineral identifications are generally not possible from mossbauer data alone particularly for paramagnetic phases although combining mossbauer results with other data sets enables a greater level of confidence in constraining mineralogy this study provides a new expansive data set for future interpretation of iron sulfates on mars

alteration assemblages in the miller range and elephant moraine regions of antarctica comparisons between terrestrial igneous rocks and martian meteorites the weathering products present in igneous terrestrial antarctic samples were analyzed and compared with those found in the four miller range nakhlite martian meteorites the aim of these comparisons was to determine which of the alteration phases in the miller range nakhlites are produced by terrestrial weathering and what effect rock composition has on these phases antarctic terrestrial samples mil 05031 and eet 96400 along with the miller range nakhlites mil 03346 and 090032 were found to contain secondary alteration assemblages at their externally exposed surfaces despite the difference in primary mineralogy the assemblages of these rocks consist mostly of sulfates jarosite in mil 05031 jarosite and gypsum in eet 96400 and iddingsite like fe clay as neither of the terrestrial samples contains sulfur bearing primary minerals and these minerals are rare in the miller range nakhlites it appears that so42 possibly along with some of the na k and ca in these phases was sourced from wind blown sea spray and biogenic emissions from the southern ocean cl enrichment in the terrestrially derived iddingsite of mil 05031 and mil 03346 and the presence of halite at the exterior edge of mil 090032 can also be explained by this process however jarosite within and around the olivine bound melt inclusions of mil 090136 is present in the interior of the meteorite and therefore is probably the product of preterrestrial weathering on mars

major and trace elements in pyrope almandine garnets as sediment provenance indicators of the lower carboniferous culm sediments drahany uplands bohemian massif abstract the lower carboniferous culm basin is part of the european variscan foreland basin garnet is an abundant heavy mineral at all stratigraphic levels of the culm sediments the protivanov rozstani and myslejovice formation from base to top this paper compares the major element electron microprobe and trace element la icp ms compositions of garnet for the purpose of studying the provenance of the culm sediments the polymict garnet assemblages ranging from the protivanov to lower part of the myslejovice formation goniatite zones pe go pass into oligomict ones dominated by pyrope almandine garnets uppermost part of the myslejovice formation goniatite zones go go as the predominant low grossular pyrope almandines from oligomict garnet assemblages are very uniform and homogeneous in major element composition we studied their trace element composition and zoning pyrope almandine garnets are poor in lree and show enrichment in hree the chondrite normalized patterns are almost flat from dy to lu and show a significant negative eu anomaly typical for granulite grade garnets major element compositions of detrital low grossular pyrope almandines can only be matched with some granulites and garnetiferous felsic gneisses of the bohemian massif garnets from granulites cropping out at the present day erosion level of the bohemian massif have usually higher ca and or lower mg contents the major and trace element compositions and zoning patterns of pyrope almandine garnets from the upper part of the myslejovice formation compare well with garnets from the miroslav granulites and small moldanubian granulite bodies west of the t ebic massif the moldanubian granulites are commonly associated with mantle derived peridotites and eclogites the presence of detrital cr spinels with high cr and low mg single grains of cr spinels and fine grained kelyphitic intergrowths of cr spinel with chlorite comparable with spinel types from moldanubian peridotites could indicate the joint occurrence of peridotites serpentinized peridotites and granulites at the erosion level of the bohemian massif during the deposition of the uppermost culm sediments 325 ma while the older culm sediments polymict garnet assemblages represent the accumulation of clastic material from the northern and north western areas moravo silesian and lugian zone the uppermost culm sediments oligomict garnet assemblages contain material from western and south western areas moldanubian zone and moravian nappe the general influx of clastic material changed as a result of clockwise rotation of the eastern part of the variscan belt during this time span 340 325 ma

near infrared spectral reflectance of mineral mixtures systematic combinations of pyroxenes olivine and iron oxides near infrared spectral reflectance data are presented for systematic variations in weight percent of two component mixtures of ferromagnesian and iron oxide minerals mixtures were chosen for application to the study of the dark materials on mars but the results are equally applicable to mafic and ultramafic assemblages elsewhere in the solar system olivine spectral features are greatly reduced in contrast by admixture of other phases but remain distinctive even for low olivine contents clinopyroxene and orthopyroxene mixtures show resolved pyroxene absorptions near 2 m the addition of limonite greatly modifies pyroxene and olivine reflectance but does not fully eliminate distinctive spectral characteristics using only spectral data in the 1 m region it is difficult to differentiate orthopyroxene and limonite goethite in a mixture additional spectral coverage or other evidence may be required for a unique interpretation all composite mineral absorptions observed in this study are either weaker than or intermediate in strength to the end member absorptions and have bandwidths greater than or equal to those for the end members in general spectral properties in an intimate mixture combine in a complex nonadditive manner with features demonstrating a regular but usually nonlinear variation as a function of end member phase proportions

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

mossbauer mineralogy of rock soil and dust at meridiani planum mars opportunity s journey across sulfate rich outcrop basaltic sand and dust and hematite lag deposits additonal co authors p gutlich e kankeleit t mccoy dw mittlefehldt f renz me schmidt b zubkov sw squyres re arvidson

residence and redistribution of ree y zr th and u during granulite facies metamorphism behaviour of accessory and major phases in peraluminous granulites of central spain accessory minerals are thought to play a key role in controlling the behaviour of certain trace elements such as ree y zr th and u during crustal melting processes under high grade metamorphic conditions although this is probably the case at middle crustal levels when a comparison is made with granulite facies lower crustal levels differences are seen in trace element behaviour between accessory minerals and some major phases such a comparison can be made in central spain where two granulite facies terranes have equilibrated under slightly different metamorphic conditions and where lower crustal xenoliths are also found differences in texture and chemical composition between accessory phases found in leucosomes and leucogranites and those of melanosomes and protholiths indicate that most of the accessory minerals in melt rich migmatites are newly crystallized this implies that an important redistribution of trace elements occurs during the early stages of granulite facies metamorphism in addition the textural position of the accessory minerals with respect to the major phases is crucial in the redistribution of trace elements when melting proceeds via biotite dehydration melting reactions in granulitic xenoliths from lower crustal levels the situation seems to be different as major minerals show high concentration of certain trace elements the distribution of which is thus controlled by reactions involving final consumption of al ti phlogopite a marked redistribution of hree y zr between garnet and xenotime where present and zircon but also of lree between feldspars k feldspar and plagioclase and monazite is suggested

anatomy of garnets in a jurassic granite from the south eastern margin of the north china craton magma sources and tectonic implications abstract the late jurassic jingshan granite located at the south eastern margin of the north china craton contains abundant garnets which can be subdivided into three types based on texture and composition i euhedral garnet in mafic biotite and garnet rich enclave grt i ii coarse grained garnet grt ii in the host granite and iii small euhedral garnet in aplite grt iii in general grt i has higher feo cao and lower mno contents than grt ii grt iii has higher mn but lower ca contents than others grt i has lower mree and hree contents than grt ii grt iii has prominent and distinctly negative eu anomaly as well as higher mree composition compared to the others systematic variations in oxygen isotope compositions are observed among the three garnet types with 18 o values of 4 7 in grt iii some of the grt ii and grt iii display two distinct zonings with cores having similar major and trace element compositions to grt i cathodoluminescence cl images revealed that the zircons from different garnet bearing samples possess fine scale oscillatory zoned magmatic rims with inherited cores in situ zircon u pb dating and trace element analyses show that the dark luminescent magmatic rims all have jurassic concordia ages 160 ma and similar trace element patterns most of the inherited cores also display similar triassic ages of 210 236 ma which is similar to the ages of ultrahigh pressure uhp metamorphic rocks of the dabie sulu orogen 230 ma in addition jurassic concordia ages were also found in a zircon inclusion in grt i implying that the grt i was formed shortly before the main magmatic event the age data suggest that the three different garnet types may be genetically related and modified by cogenetic magmatic events based on the zircon u pb ages from different garnet bearing samples the major element trace element oxygen isotope and zoning textures of the three kinds of garnet we suggest that grt i may be peritectic garnet whereas grt ii and iii are probably the results of magmatic dissolution precipitation processes and re equilibration of garnets with changing magmatic conditions during melting differentiation crystallization and cooling within the granite we conclude from the oxygen isotopic character of the garnets and ages of the zircons that the source rocks for the jingshan granites are from dabie sulu orogen representing the south china craton

primary crustal melt compositions insights into the controls mechanisms and timing of generation from kinetics experiments and melt inclusions abstract we explore the controls mechanisms and timing of generation of primary melts and their compositions and show that the novel studies of melt inclusions in migmatites can provide important insights into the processes of crustal anatexis of a particular rock partial melting in the source region of granites is dependent on five main processes i supply of heat ii mineral melt interface reactions associated with the detachment and supply of mineral components to the melt iii diffusion in the melt iv diffusion in minerals and v recrystallization of minerals as the kinetics of these several processes vary over several orders of magnitude it is essential to evaluate in nature which of these processes control the rate of melting the composition of melts and the extent to which residue melt chemical equilibrium is attained under different circumstances to shed light on these issues we combine data from experimental and melt inclusion studies first data from an extensive experimental program on the kinetics of melting of crustal protoliths and diffusion in granite melt are used to set up the necessary framework that describes how primary melt compositions are established during crustal anatexis then we use this reference frame and compare compositional trends from experiments with the composition of melt inclusions analyzed in particular migmatites we show that for the case of el hoyazo anatectic enclaves in lavas the composition of glassy melt inclusions provides important information on the nature and mechanisms of anatexis during the prograde suprasolidus history of these rocks including melting temperatures and reactions and extent of melt interconnection melt homogenization and melt residue equilibrium compositional trends in several of the rehomogenized melt inclusions in garnet from migmatites granulites in anatectic terranes are consistent with diffusion in melt controlled melting though trace element compositions of melt inclusions and coexisting minerals are necessary to provide further clues on the nature of anatexis in these particular rocks

water abundance of dunes in gale crater mars from active neutron experiments and implications for amorphous phases we report the water abundance of bagnold dune sand in gale crater mars by analyzing active neutron experiments using the dynamic albedo of neutrons instrument we report a bulk water equivalent hydrogen abundance of 0 68 0 15 wt which is similar to measurements several kilometers away and from those taken of the dune surface thus the dune is likely dehydrated throughout furthermore we use geochemical constraints including bulk water content to develop compositional models of the amorphous fraction for which little information is known we find the amorphous fraction contains 26 to 64 wt basaltic glass and up to 24 wt rhyolitic glass suggesting at least one volcanic source for the dune material we also find a range of hydrated phases may be present in appreciable abundances either from the incorporation of eroded aqueously altered sediments or the direct alteration of the dune sand

anatexis during high pressure crustal metamorphism evidence from garnet whole rock ree relationships and zircon rutile ti zr thermometry in leucogranulites from the bohemian massif in situ mineral garnet zircon trace element and garnet rock ree distribution data obtained on leucogranulites from the bohemian massif are consistent with an origin of these now strongly deformed rocks as migmatitic leucogranites formed through dehydration melting of muscovite bearing protoliths at high pressures during the variscan orogeny partial melting at p t conditions of 900 9408c and 1 6 1 8 gpa consumed mica and feldspar to produce peritectic kyanite and high ca 20 24 mol grossular high eu garnet along with leucogranitic melt dree grt rock values calculated from this garnet and its host rock are consistent with garnet melt equilibrium at these p t conditions ternary feldspar and rutile 2000 3200 ppm zr crystallized from the leucogranite melts in the migmatites at minimum temperatures of 4880 9208c these formed along with apatite prior to and accompanying the crystallization of garnet rims and the majority of the garnet that occurs in the leucogranulites this garnet is typified by strong depletion in eu and dree grt rock values consistent with garnet melt equilibrium only after the fractionation of apatite 50 3 wt and ternary feldspar 5 15 wt zircons in one leucogranulite are dominated by oscillatory zoned grains that yield pre variscan u pb ages 495 and 433 ma and crystallized from ti in zircon thermometry at 700 8108c in their original host magmas these xenocrystic grains are potentially preserved because of the short timespan of the high p t variscan event at 340 ma and the moderate amounts of leucogranitic partial melt present in the rocks estimated as at least 30 wt melt from zr mass balance the production of new zircon associated with the variscan event in this leucogranulite is limited to weakly zoned zircon rims characterized by flat heavy ree patterns that approach ree equilibrium with garnet rims this post peak zircon was formed at minimum p t conditions of 8408c and 0 8 1 0 gpa along the decompression cooling path defined by previous work for the bohemian massif granulites the garnet whole rock ree relationships observation of eu depletion between early and later garnet growth phases and zr ti thermometric estimates indicating temperatures of48408c for this evolution cannot be explained by the alternative interpretation of the leucogranulites as reworked and recrystallized pre variscan low p granitoids but support a model in which the bohemian leucogranulites were high p variscan age migmatites containing significant amounts of melt

overview of the opportunity mars exploration rover mission to meridiani planum eagle crater to purgatory ripple the mars exploration rover opportunity touched down at meridiani planum in january 2004 and since then has been conducting observations with the athena science payload the rover has traversed more than 5 km carrying out the first outcrop scale investigation of sedimentary rocks on mars the rocks of meridiani planum are sandstones formed by eolian and aqueous reworking of sand grains that are composed of mixed fine grained siliciclastics and sulfates the siliciclastic fraction was produced by chemical alteration of a precursor basalt the sulfates are dominantly mg sulfates and also include ca sulfates and jarosite the stratigraphic section observed to date is dominated by eolian bedforms with subaqueous current ripples exposed near the top of the section after deposition interaction with groundwater produced a range of diagenetic features notably the hematite rich concretions known as blueberries the bedrock at meridiani is highly friable and has undergone substantial erosion by wind transported basaltic sand this sand along with concretions and concretion fragments eroded from the rock makes up a soil cover that thinly and discontinuously buries the bedrock the soil surface exhibits both ancient and active wind ripples that record past and present wind directions loose rocks on the soil surface are rare and include both impact ejecta and meteorites while opportunity s results show that liquid water was once present at meridiani planum below and occasionally at the surface the environmental conditions recorded were dominantly arid acidic and oxidizing and would have posed some significant challenges to the origin of life copyright 2006 by the american geophysical union

ion microprobe determinations of trace element concentrations in garnets from anatectic assemblages abstract trace element data for garnet cordierite plagioclase alkali feldspar and tourmaline have been obtained by ion microprobe analysis of assemblages from a pelite derived leucogranite a sillimanite grade anatectic gneiss and a kyanite grade sub solidus schist from the high himalaya results confirm that for equilibrium melting residual plagioclase will cause depletion in sr and eu in the melt and residual garnet will result in strong depletion of y and hree consistent with their published partition coefficients all trace elements of interest are strongly incompatible in cordierite implying that for equilibrium fractional melting of pelites at shallow depths hree concentrations in garnets from metasediments are independent of metamorphic grade but the metamorphic garnets are significantly less enriched in hree than is the leucogranite garnet this suggests either that the leucogranite is derived from a source with lower modal abundances of garnet than the analysed metasediments or that garnet from the anatectic gneiss has not reached chemical equilibrium with a granitic melt the latter possibility is consistent with sluggish self diffusion rates in garnets for ree at temperatures of 5 kbar

phosphorus in s type magmas the p2o5 content of feldspars from peraluminous granites pegmatites and rhyolites

the nanophase iron mineral s in mars soil a series of surface modified clays containing nanophase np iron oxide oxyhydroxides of extremely small particle sizes with total iron contents as high as found in mars soil were prepared by iron deposition on the clay surface from ferrous chloride solution comprehensive studies of the iron mineralogy in these mars soil analogs were conducted using chemical extractions solubility analyses ph and redox x ray and electron diffractometry electron microscopic imaging specific surface area and particle size determinations differential thermal analyses magnetic properties characterization spectral reflectance and viking biology simulation experiments the clay matrix and the procedure used for synthesis produced nanophase iron oxides containing a certain proportion of divalent iron which slowly converts to more stable fully oxidized iron minerals the clay acted as an effective matrix both chemically and sterically preventing the major part of the synthesized iron oxides from ripening i e growing and developing larger crystals the precipitated iron oxides appear as isodiametric or slightly elongated particles in the size range 1 10 nm having large specific surface area the noncrystalline nature of the iron compounds precipitated on the surface of the clay was verified by their complete extractability in oxalate lepidocrocite gamma feooh was detected by selected area electron diffraction it is formed from a double iron fe ii fe iii hydroxy mineral such as green rust or ferrosic hydroxide magnetic measurements suggested that lepidocrocite converted to the more stable maghemite gamma fe2o3 by mild heat treatment and then to nanophase hematite alpha fe2o3 by extensive heat treatment after mild heating the iron enriched clay became slightly magnetic to the extent that it adheres to a hand held magnet as was observed with mars soil the chemical reactivity of the iron enriched clays strongly resembles and offers a plausible mechanism for the somewhat puzzling observations of the viking biology experiments their unique chemical reactivities are attributed to the combined catalytic effects of the iron oxide oxyhydroxides and silicate phase surfaces the reflectance spectrum of the clay iron preparations in the visible range is generally similar to the reflectance curves of bright regions on mars this strengthens the evidence for the predominance of nanophase iron oxides oxyhydroxides in mars soil the mode of formation of these nanophase iron oxides on mars is still unknown it is puzzling that despite the long period of time since aqueous weathering took place on mars they have not developed from their transitory stage to well crystallized end members the possibility is suggested that these phases represent a continuously on going extremely slow weathering process

an astrobiological perspective on meridiani planum sedimentary rocks exposed in the meridiani planum region of mars record aqueous and eolian deposition in ancient dune and interdune playa like environments that were arid acidic and oxidizing on earth microbial populations have repeatedly adapted to low ph and both episodic and chronic water limitation suggesting that to a first approximation the meridiani plain may have been habitable during at least part of the interval when deposition and early diagenesis took place on the other hand the environmental conditions inferred for meridiani deposition would have posed a challenge for prebiotic chemical reactions thought to have played a role in the origin of life on earth orbital observations suggest that the combination of sulfate minerals and hematite found in meridiani rocks may be unusual on the martian surface however there is reason to believe that acidity aridity and oxidizing conditions were broadly distributed on ancient mars when these conditions were established and how much environmental heterogeneity existed on early mars remain to be determined because sulfates and iron oxides can preserve detailed geochemical records of environmental history as well as chemical textural and microfossil signatures of biological activity meridiani planum is an attractive candidate for mars sample return

mineralogy composition and alteration of mars pathfinder rocks and soils evidence from multispectral elemental and magnetic data on terrestrial analogue snc meteorite and pathfinder samples major element multispectral and magnetic properties data were obtained at ares vallis during the mars pathfinder mission to understand the compositional mineralogical and process implications of these data we obtained major element mineralogical and magnetic data for well crystalline and nanophase ferric minerals terrestrial analogue samples with known geologic context and snc meteorites analogue samples include unaltered palagonitic and sulfatetic tephra from mauna kea volcano hydrolytic and acid sulfate alteration steam vent material from kilauea volcano hydrolytic alteration and impactites from meteor crater relithification salient results for mars pathfinder include 1 band depths bd530b and bd600 and the reflectivity ratio r800 r750 are consistent with the dominant ferric mineral being nanophase ferric oxide associated with an unknown amount of h2o and occurring in composite particles along with subordinate amounts of other ferric minerals hematite and hematite plus nanophase goethite are most consistent with the data but maghemite akaganeite schwertmannite and nanophase lepidocrocite are also possible interpretations ferric oxides that are consistently not favored by the data as sole alteration products are jarosites and well crystalline goethite and lepidocrocite 2 the strength of the ferric adsorption edge r750 r445 implies the fe3 fe2 values for pathfinder rock and soil are within the ranges 0 7 3 and 3 20 respectively 3 ferrous silicates are indicated for subsets of pathfinder rocks and soils one subset has a band minimum near 930 nm that can attributed to low ca pyroxene alternatively the band could be a second manifestation of certain ferric oxides including nanophase goethite maghemite akaganeite and schwertmannite another subset has a negative spectral slope from 800 to 1005 nm which could result from the high energy wing of a high ca pyroxene and or olivine band a mixture of bright and dark materials and for rocks thin coatings of bright dust on dark rocks 4 chemical data on pathfinder rocks and soils are consistent with two component mixtures between an andesitic rock with low mgo and so3 concentrations soil free rock and a global basaltic soil with high mgo and so3 concentrations rock free soil pathfinder rock free soil can be modeled as a chemical mixture of snc meteorites and the pathfinder soil free rock 5 pathfinder soil cannot be obtained by chemical alteration of pathfinder rocks by any of the hydrolytic and acid sulfate alteration processes we studied presumably global mixing has obscured and possibly erased the elemental signatures of chemical alteration 6 the strongly magnetic phase in palagonitic and sulfatetic tephra is titanomagnetite and possibly its oxidation product titanomaghemite fe ti spinels the saturation magnetization of the tephra samples 0 5 2 0 am2 kg is at or below the low end of the range inferred for martian dust 4 2 am2 kg implying that lithogenic fe ti spinels are a possible candidate for the martian strongly magnetic phase 7 the predominantly palagonitic spectral signature and magnetic nature of martian soil and dust are consistent with glassy precursors with imbedded fe ti spinel particles comparison with lunar glass production rates suggests that production of sufficient quantities of glassy materials on mars by volcanic and impact processes is sufficient to account for these observations

trace element zoning in garnet from the kwoiek area british columbia disequilibrium partitioning during garnet growth trace element zoning in garnets from two contact metamorphosed rocks from the kwoiek area british columbia hollister 1969a was measured with an ion microprobe zoning profiles have three distinct parts with chemical breaks defined by co variation of major and trace elements important features of the trace element zoning profiles are 1 roughly bell shaped zoning profiles for y and the hrees 2 an abrupt increase in ti at a point midway through each garnet with inflections in the zoning profiles of other elements li na cr v y zr and the hree and 3 irregular cr and v profiles unlike mn zoning the zoning profiles of most other trace elements cannot be easily modeled using simple rayleigh fractionation models ti activity in the two samples is buffered by phase relations with ilmenite garnets from a continuously heated contact metamorphic environment should display continuous ti zoning profiles if equilibrium was maintained and provided the ti buffering assemblage did not change during garnet growth the irregular ti profiles suggest disequilibrium behavior several elements cr v may indicate breakdown of a phase enriched in trace elements during metamorphism the source for the mass excess of these elements is probably the refractory cores of ilmenite grains either differing matrix transport rates of trace lements or interface kinetic controlled segregation could explain the unusual trace element behavior at the element inflection point the preferred explanation involves segregation of elements at the interface of the garnet that were trapped during episodes of rapid garnet growth

models of garnet differential geochronology abstract rayleigh distillation models are developed to describe theoretical growth zoning of lu hf rb sr sm and nd in typical garnet crystals from metapelites and metabasites effects of diffusion limited transport within the matrix and intracrystalline diffusion are also considered qualitatively theoretical zoning profiles show strong depletions of lu in garnet rims compared to cores but virtually invariant hf rb sr sm and nd profiles generally consistent with natural profiles for lu and hf and previously published models theoretical isochron diagrams for lu hf exhibit distinctive arcuate distributions and high mswds consistent both with himalayan data and with expectations that garnet growth durations exceed chronologic resolution by as much as an order of magnitude predicted isochron diagrams for sm nd and rb sr exhibit vertical arrays for garnet and high mswds that are generally lower than for lu hf in metapelites inherent chronologic resolution for bulk separates is best for lu hf in metapelites and rb sr but analytical considerations favor rb sr or sm nd for chronologic zoning studies diffusion limited transport in the rock matrix strongly influences zoning profiles but does not change the main trends on isochron diagrams intracrystalline diffusion will initially rotate lu hf isochrons to steeper slopes giving older apparent ages the natural himalayan data indicate growth of garnet in one rock from the greater himalayan sequence at 34 ma consistent with previously measured monazite ages from the same rock data from another himalayan rock suggest polymetamorphism that includes a paleozoic component

petrological and structural evolution of high grade metamorphic rocks from the floor of the alboran sea basin western mediterranean the metamorphic basement beneath the alboran sea a neogene introduction extensional basin drilled during ocean drilling program odp late orogenic extension of previously thickened conleg 161 site 976 consists of high grade pelitic schist overlying tinental lithosphere is a widely documented phenomenon migmatitic pelitic gneiss inferred assemblages in the high grade e g dewey 1988 malavieille 1993 ruppel 1995 schist evolved from garnet staurolite biotite muscovite but it is unclear whether the thermal evolution of the plagioclase assemblage 1 to biotite sillimanite k feldspar lithosphere in this situation differs significantly from that plagioclase garnet assemblage 2 to andalusite biotite associated with extension in non orogenic settings if k feldspar plagioclase assemblage 3 in the gneiss which extension is triggered by removal of part of the lower shows abundant migmatitic textures the present assemblage is biotite lithosphere e g england houseman 1989 there may andalusite sillimanite muscovite cordierite kbe a detectable rise in temperature during exhumation feldspar plagioclase garnet phase relations and thermoof rocks platt england 1994 whereas extension barometric calculations suggest that the high grade schist experienced caused by far field forces is likely to produce isothermal decompression accompanied by heating from 500 c at 10 5 kbar decompression paths followed by cooling ruppel et al through 600 30 c at 6 7 kbar assemblage 1 and thence 1988 platt et al 1999 decompression accompanied by to 650 700 c at 3 4 kbar assemblage 2 followed by cooling heating in extensional settings has been demonstrated in through 500 600 c at 2 kbar or less assemblage 3 peak the seward peninsula in alaska patrick lieberman temperature and melting occurred under low pressure conditions 1988 the cordillera darwin in the southern andes the widespread disequilibrium and overstepping of metamorphic kohn et al 1993 the tauern window in the alps reactions suggests that decompression was rapid the p t evolution selverstone et al 1984 the aegean buick holland is consistent with metamorphism in a late orogenic extensional 1989 the high himalaya inger harris 1992 and basin and suggests the existence of an external source of heat the betic cordillera van der wal vissers 1993 an probably indicating the complete removal of lithospheric mantle interesting related question is the significance of crustal beneath the extending region melting in extensional settings in principle partial melt

diffusion obstacles and opportunities in petrochronology many of the approaches in petrochronology are rooted in the assumption of equilibrium diffusion is an expression of disequilibrium the movement of mass in response to chemical potential gradients and isotopes in response to isotopic gradients it is extremely important that we be aware of how the effects of diffusion can place obstacles across our path towards petrochronologic enlightenment conversely the effects of diffusion also provide opportunities for understanding rates processes and conditions experienced by rocks the enormity of the field does not permit us to provide a comprehensive review of either the mathematics of diffusion or quantitative data that have been obtained relevant to the interpretation of diffusive processes in rocks and minerals many resources cover these topics including rimg volume 72 diffusion in minerals and melts zhang and cherniak 2010 and several textbooks crank 1975 glicksman 2000 particularly relevant to the discussion of petrochronology are summaries of the theory and controls on diffusion brady and cherniak 2010 zhang 2010 as well as diffusion rates in feldspar cherniak 2010a accessory minerals cherniak 2010b garnet ganguly 2010 mica pyroxene and amphibole cherniak and dimanov 2010 and melts zhang and ni 2010 zhang et al 2010 rather than duplicate that material our goal is to explore the obstacles and opportunities presented by the effects of diffusion as they inform the rates of petrologic processes to achieve this goal we emphasize key principles and illustrative examples quantitative interpretation of the effects of diffusion assumes predictability of numerous factors that may affect chemical or isotopic transport including temperature initial and boundary conditions water and oxygen fugacities activities of other components multiple mechanisms of diffusion and crystal chemistry coupling of the substitution of elements into different crystallographic sites additionally the extraction of meaningful ages durations of events and temperatures requires

temperature time paths from phosphate accessory phase paragenesis in the honey brook upland and associated cover sequence se pennsylvania usa abstract analysis of monazite bearing lithologies from the precambrian honey brook upland hbu and overlying metasedimentary paleozoic chester valley sequence cvs se pa usa reveals overprinting of primary major and accessory phase parageneses by texturally and compositionally disparate secondary accessory phase parageneses two pyroxene temperatures of 915 945 c for reconstituted pyroxene reflect emplacement temperatures of felsic plutonic rocks opdalite charnockite prior to mesoproterozoic metamorphism monazite in metavolcanic felsic gneiss yields three age domains at 1009 4 ma 2 s e 965 6 and 876 10 ma the first two domains record metamorphism of the hbu after anorthosite intrusion peak monazite xenotime temperatures for the monazite core domain are 700 c and high th u values in the second overgrowth age domain likely reflect a second high t monazite growth episode formation of cummingtonite coronas on orthopyroxene in opdalite constrains maximum 1010 ma metamorphic temperatures in the granulite facies terrane to 730 740 c evidence of increased cl fluid activity in the 965 ma metamorphism includes higher cl content of matrix apatite relative to garnet included apatite metavolcanics and cl bearing k hornblende succeeding cummingtonite in coronal overgrowths opdalite extreme monazite th u values 75 250 in the rim domain suggest growth during low t hydrothermal alteration in the opdalite secondary singe grain monazite and monazite xenotime metasomites in apatite yield ages of 714 24 and 586 88 ma temperatures of 325 425 c and are interpreted to reflect thermal disturbances associated with late proterozoic plutonic and volcanic activity in the upland this thermal disturbance may be recorded by rb sr age of 567 ma for biotite from a hbu gneiss monazite age domains in metaquartzite 378 28 272 44 ma suggest that low grade metamorphism 260 320 c mnz xno thermometry of the cvs is not a result of taconian orogenesis