concentration of h si cl k fe and th in the low and mid latitude regions of mars 1 we report maps of the concentrations of h si cl k fe and th as determined by the gamma ray spectrometer grs on board the 2001 mars odyssey mission for 45 latitudes the procedures by which the spectra are processed to yield quantitative concentrations are described in detail the concentrations of elements determined over the locations of the various mars landers generally agree well with the lander values except for fe although the mean of the grs fe data agrees well with that of martian meteorites the water equivalent concentration of hydrogen by mass varies from about 1 5 to 7 5 by mass with the most enriched areas being near apollinaris patera and arabia terra cl shows a distribution similar to h over the surface except that the cl content over medusae fossae is much greater than elsewhere the map of fe shows enrichment in the northern lowlands versus the southern highlands silicon shows only very modest variation over the surface with mass fractions ranging from 19 to 22 over most of the planet though a significant depletion in si is noted in a region west of tharsis montes and olympus mons where the si content is as low as 18 k and th show a very similar pattern with depletions associated with young volcanic deposits and enrichments associated with the tes surface type 2 material it is noted that there appears to be no evidence of significant globally distributed thick dust deposits of uniform composition

rock magnetic and remanence properties of synthetic fe rich basalts implications for mars crustal anomalies abstract we characterized the magnetic mineral assemblage and remanence properties of a set of synthetic samples patterned on the meteorite derived basalt composition a which contains 18 9 total feo basalts were synthesized at conditions that track 4 oxygen fugacity f o 2 buffer curves from 3 4 log units below the quartz fayalite magnetite qfm buffer to 5 log units above qfm and 6 cooling rates from 10 5 to 3 c h the resulting array of samples was characterized using magnetic hysteresis loops temperature dependence of saturation magnetization and saturation remanence 10 to 1000 k and the acquisition and demagnetization of anhysteretic remanent magnetization arm and thermoremanent magnetization trm the magnetic mineral assemblage characteristics are strongly dependent on f o 2 samples synthesized at the iron wustite iw buffer have a very low concentration of remanence carrying grains which are likely near the superparamagnetic stable single domain boundary samples synthesized at the qfm and nickel nickel oxide nno buffers contain a slightly higher concentration of remanence carrying grains which are stable single domain to fine pseudo single domain particles respectively samples synthesized at the manganese oxide mno buffer contain the highest concentration of magnetic grains which are up to 100 m in diameter the dominant fe ti oxide produced is an mg and al bearing titanomagnetite with 2 4 2 7 fe cations per formula unit the curie temperatures of the qfm samples are consistent with their electron microprobe derived compositions those of the nno sample set are very slightly elevated with respect to their electron microprobe derived compositions the curie temperatures of the mno samples are elevated up to 200 c above what they should be for their composition we attribute the curie temperature elevation to high temperature nonstoichiometry of the titanomagnetite the iw sample set acquired very weak trms with intensities of 0 02 to 0 5 a m this intensity of remanence is a factor of 50 500 too low to generate the observed 1000 nt anomalies detected on mars by the mars global surveyor mag er experiment the qfm nno and mno samples acquired trms up to 40 a m in a 10 t applied field and up to 200 a m in a 50 t field with little or no dependence on cooling rate our results suggest that fe rich melts that crystallize extensive titanomagnetite can generate an intensely magnetized layer in the martian crust even if the remanence was acquired in a weak field the qfm sample set can easily account for the observed 1000 nt mars magnetic anomalies even in a magnetized layer as thin as 15 30 km

petrology of the ispendere malatya ophiolite from the southeast anatolia implications for the late mesozoic evolution of the southern neotethyan ocean

comparisons between tethyan anorthosite bearing ophiolites and archean anorthosite bearing layered intrusions implications for archean geodynamic processes

structure and geochemistry of tethyan ophiolites and their petrogenesis in subduction rollback systems suprasubduction zone ssz ophiolites in orogenic belts represent oceanic crust generation in subduction rollback cycles during the closing stages of basins prior to terminal continental collisions mantle flow and slab rollback result in one or more episodes of arc splitting and basin opening producing a collage of protoarc and forearc oceanic lithosphere in suprasubduction zone settings the jurassic cretaceous ssz tethyan ophiolites in the eastern mediterranean region i e mirdita pindos troodos kizildag oman generally have penrose type oceanic crust and contain well developed sheeted dike complexes indicative of magmatic extension beneath narrow rift zones during their seafloor spreading evolution igneous accretion of these ssz tethyan ophiolites involved upper plate extension and advanced melting of previously depleted asthenosphere in host basins showing a progressive evolution from morb like to iat island arc tholeiite to boninitic extremely refractory protoarc assemblages however there are some distinct differences in the geochemical evolution of these tethyan ophiolites that appear to have resulted from variations in their subduction zone geodynamics whereas a major part of the kizildag and troodos lavas shows island arc affinity similar to their counterparts in the pindos and mirdita ophiolites a significant component of the oman lavas indicates morb affinity and the majority of the kizildag and oman data plot within the mantle array between n morb and e morb on the nb yb th yb discriminant diagram furthermore the troodos and oman lavas do not show any particular th enrichment in their multi element patterns suggesting that fluid melt input from subducted sediments was not that significant in generation of their magmas although all ophiolites exhibit geochemical features indicating increased subduction influence during the melt evolution of their younger extrusive sequences and dike intrusions as evidenced by their negative nd values their overall characteristic trace element patterns seem to have been strongly affected by the maturity of the subduction systems in which they developed

the supra ophiolitic sedimentary cover of the asbestos ophiolite quebec canada first geochemical evidence of transition from oceanic to continental sediment flux abstract the 473 5 3 myr asbestos ophiolite complex of the quebec appalachians was formed in a forearc basin and obducted on a margin of laurentia 460 myr ago the complex together with its sedimentary cover is well exposed at burbank hill 130 km sw of quebec city where eight distinct lithologies have been identified 1 pyroxenites and wehrlites with minor dunitic layers 2 fractured gabbros 3 breccia containing gabbro and diabase fragments 4 polygenic conglomerates 5 red mudstone chert sandstone succession 6 tuffs with intercalated grey chert 7 greenish grey mudstones and 8 slates and sandstones of the saint daniel melange the gabbroic and mafic volcanic rocks show the characteristics of arc tholeiites tio2 0 8 0 85 wt and boninites tio2 45 la sm n 1 9 3 3 these rock types also occur as mafic fragments in the polygenic conglomerate the mafic fragments crystals and rocks within the conglomerate and the ophiolitic sandstones also show the same greenschist facies metamorphism as the mafic igneous rocks of the complex the conglomerate was probably formed after the forearc crust was fragmented by pre obduction normal faults these fault scarps would have promoted the erosion of the oceanic crust leading to the accumulation of diverse detritus in grabens the sedimentary lithologies which overlie the conglomerate exhibit a gradual increase in continent derived material la sm n 5 and la yb 20 and a decrease in ophiolitic material moving upward in the stratigraphic sequence the sedimentary rocks at the bottom of the sequence group 3 are mostly composed of ophiolite material with only 20 of crustal material they also have a high content of cr and mgo with values of 350 480 ppm and 5 7 8 respectively the rocks of the uppermost part of the pile group 1 which contain up to 80 crustal material have low abundances of cr and mgo 30 100 ppm and 2 7 4 5 wt continental detritus on the top of the asbestos ophiolite suggests the complex formed near the laurentian continental margin and that the eroded continental material had access to the basin where the ophiolite was formed this is consistent with the obduction of the asbestos and thetford mines ophiolites on the laurentian margin shortly after their formation the proximity of thick laurentian continental crust near the trench could explain why the subduction zone blocked up soon after the ophiolites formation

anatomy of a pressure induced ferromagnetic to paramagnetic transition in pyrrhotite implications for the formation pressure of diamonds 1 meteorites and diamonds encounter high pressures during their formation or subsequent evolution these materials commonly contain magnetic inclusions of pyrrhotite because magnetic properties are sensitive to strain pyrrhotite can potentially record the shock or formation pressures of its host moreover pyrrhotite undergoes a pressure induced phase transition between 1 6 and 6 2 gpa but the magnetic signature of this transition is poorly known here we report room temperature magnetic measurements on multidomain and single domain pyrrhotite under nonhydrostatic pressure magnetic remanence in single domain pyrrhotite is largely insensitive to pressure until 2 gpa whereas the remanence of multidomain pyrrhotite increases 50 over that of initial conditions by 2 gpa and then decreases until only 33 of the original remanence remains by 4 5 gpa in contrast magnetic coercivity increases with increasing pressure to 4 5 gpa below 1 5 gpa multidomain pyrrhotite obeys neel theory with a positive correlation between coercivity and remanence above 1 5 gpa it behaves single domain like yet distinctly different from uncompressed single domain pyrrhotite the ratio of magnetic coercivity and remanence follows a logarithmic law with respect to pressure which can potentially be used as a geobarometer owing to the greater thermal expansion of pyrrhotite with respect to diamond pyrrhotite inclusions in diamonds experience a confining pressure at earth s surface applying our experimentally derived magnetic geobarometer to pyrrhotite bearing diamonds from botswana and the central african republic suggests the pressures of the pyrrhotite inclusions in the diamonds range from 1 3 to 2 1 gpa these overpressures constrain the mantle source pressures from 5 4 to 9 5 gpa depending on which bulk modulus and thermal expansion coefficients of the two phases are used

magnetic and petrologic characterization of synthetic martian basalts and implications for the surface magnetization of mars 1 a suite of synthetic martian basalts is generated with the objective of providing fundamental material properties data for use in modeling and interpretation of mission data we systematically evaluate the effects of major element composition oxygen fugacity fo2 and cooling rate on phase chemistry and magnetic mineralogy grain size and intensity of remanent magnetization the range of experimental compositions and fo2 are chosen to bracket the range expected in the martian crust our results should therefore span the range of possible mineralogies textures and magnetic properties in rapidly cooled mars crustal materials two starting compositions are used for the sample synthesis 1 an fe rich al poor composition patterned after snc basaltic meteorites and 2 a composition based on thermal emission spectrometer tes data with a much lower fe al ratio the resulting magnetic phase in samples generated at the quartz fayalite magnetite qfm buffer is a spinel structured oxide with varying amounts of cr ti mg and al compositional differences depend on bulk composition cooling rate differences in crystallization sequence and the kinetics of silicate mineral nucleation and growth oxide abundance and magnetic intensity are most strongly influenced by fo2 with more subtle composition and cooling rate effects moderately oxidizing qfm conditions result in an intense magnetization 2 3 10 5 am2 kg 1 to 1 4 10 2 am2 kg 1 especially in the meteorite derived basalts however an increase of magnetic grain size into the multidomain range meteorite type and or low unblocking temperatures resulting from increased cr substitution tes type may affect the long term stability of the remanence in qfm samples

chassigny petrogenesis melt compositions intensive parameters and water contents of martian magmas abstract the snc meteorites are a class of eight basaltic achondrites that have extremely young crystallization ages 1 3 ga chassigny a unique snc meteorite is a dunite containing fo68 olivines and rare poikilitic ca pyroxenes it is one of the most primitive snc meteorites and thus is most likely to reveal information about the snc basalt source region this study presents a detailed examination of partially crystallized melt inclusions in cumulus olivine grains in chassigny these trapped melts are argued to be representative samples of the melt that existed when chassigny crystallized this melt has been modified however by interaction with the host olivine and by closed system crystallization the phases inside the melt inclusions include hydrous ti rich amphibole kaersutite biotite two pyroxenes and rhyolitic and alkali feldspar glasses all phases have been extensively analyzed with an electron microprobe the new mineralogical information is combined with a complementary experimental study of kaersutite melt equilibria this combined data set can be used to formulate a system of linear equations which can then be solved to determine the composition of the originally trapped melt this calculation reveals that the trapped melt was an feo rich and al2o3 poor basalt the melt composition is shown to be consistent with the crystallization sequence both inside the melt inclusions and in the rock matrix the major element chemistry of this liquid closely resembles terrestrial boninite lavas the new data also allow the intensive conditions temperature total pressure and water fugacity of chassigny crystallization to be estimated two pyroxene geothermometry indicates that equilibration temperatures were 1000 50 c although amphibole does not coexist with melt until t 960 c the trapped liquid initially contained 1 5 wt dissolved water crystallization of anhydrous phases caused water to buildup in the trapped melt prior to kaersutite crystallization the melt must have contained at least 4 wt dissolved water suggesting that a minimum of 1 5 kbar total pressure is required a maximum total pressure cannot be inferred but all available data are consistent with low pressure 5 kbar crystallization finally x h2o in the fluid in the melt inclusion is estimated to have been at least 0 8 in order to stabilize amphibole without plagioclase implying that the water fugacity was 1480 bars the existence of hydrous melts and conditions appropriate for amphibole crystallization suggest that evolved sio2 rich lavas exist on the chassigny parent body mars

grain size dependence of the magnetic behavior of pyrrhotite during its low temperature transition at 34 k the grain size dependent behavior of pyrrhotite during a magnetic lt transition at 34 k is suitable for granulometric purposes cycling down to liquid helium temperature suppresses soft md jrs more than hard sd jrs so that it may be effective in removing soft secondary nrm components the domain structure of large pyrrhotite grains changes from md at room temperature to sd or psd below the lt transition

petrology of the tekirova antalya ophiolite southern turkey evidence for diverse magma generations and their tectonic implications during neotethyan subduction the sw antalya complex is an assemblage of mesozoic carbonate platform margin and ophiolitic rocks which record the formation and tectonic emplacement of a small mesozoic ocean basin the late cretaceous ophiolitic rocks are located at two localities namely the relatively intact tekirova ophiolite to the east of kemer zone and the dismembered godene ophiolite to the west of kemer zone the tekirova antalya ophiolite comprises harzburgitic tectonites ultramafic to mafic cumulates isotropic gabbros and sheeted dikes numerous isolated dikes ranging in thickness from 5 cm to 10 m intruded the crustal rocks at different structural levels the isotropic gabbros are represented by gabbro diorite and quartz diorite rocks with granular to ophitic subophitic textures the isolated dikes are characterized by dolerite diabase and microdiorite with ophitic intersertal and microgranular textures these rocks exhibit tholeiitic to alkaline compositions new geochemical data presented in this paper from the isolated dikes and isotropic gabbros suggest that there are three main types of parental basic magmas that form the oceanic crustal rocks of the tekirova antalya ophiolite these are 1 iat series which can be referred to the group i isolated dikes and isotropic gabbros 2 low ti boninitic series characterized by the group ii isolated dike and isotropic gabbros and 3 oib type including the group iii isotropic gabbros the geochemical evidence suggests that the crustal rocks of the tekirova antalya ophiolite were generated from a progressive source depletion from island arc tholeiites iat to boninites therefore a fore arc tectonic setting seems likely for the generation of the crustal rocks from the tekirova antalya ophiolite in the southern branch of neotethys during the late cretaceous the oib type alkaline isotropic gabbros are thought to have resulted from either 1 a late stage magmatic activity fed by melts that originated within an asthenospheric window due to slab break off or 2 subduction of a ridge system which generated oib source across the asthenospheric window that has been no influence of fluids from the subducted slab into the overlying mantle wedge shortly before the emplacement of the tekirova antalya ophiolite onto the tauride platform

mesozoic tertiary tectonic evolution of albania in its regional eastern mediterranean context abstract research carried out since the opening of albania to the western geological community in the 1990s allows the geology and tectonics of this small balkan country to be integrated into an overall interpretation of neotethys in the eastern mediterranean region specifically greece and the former yugoslavia region albanian geology is most famous for the occurrence of contrasting ophiolites of jurassic age the country is sub divided into three main geotectonic units those in the west i e sazani ionian kruja krasta cukali and the albanian alps relate to the western margin of apulia effectively part of north africa from early mesozoic time onwards in the east is the korabi zone interpreted as a microcontinent located further northeast within neotethys between the two is the mirdita zone dominated by two contrasting jurassic ophiolites the western type ophiolite and the eastern type ophiolite taking account of evidence from greece and former yugoslavia the following tectonic evolution is proposed from early mesozoic time onwards neotethys in albania existed as a northward continuation of the pindos oceanic basin in greece pindos mirdita ocean a korabi microcontinent was rifted off apulia in the early mid triassic followed by passive margin subsidence until late middle jurassic time a rifted slow spreading mor type ophiolite formed within the western pindos mirdita oceanic basin in late triassic early late jurassic time using present co ordinates the shkoder peje scutari pec lineament in the north of albania is interpreted as an important transform fault zone that influenced the regional tectonic evolution during the entire mesozoic early tertiary rift drift emplacement history of the pindos mirdita ocean taking account of evidence from the greek and former yugoslavia ophiolites the easterly albanian ophiolites formed within the pindos mirdita ocean above a westward dipping intra oceanic subduction zone in the early late jurassic metamorphic soles were formed during initial intra oceanic displacement ca 162 174 m y and underlying melanges originated as subduction accretion complexes the mor western type ophiolite evolved into the iat boninitic eastern type ophiolite after subduction began during tithonian berriasian time trench margin collision emplaced the ophiolites eastwards over the korabi margin coupled with redeposition of ophiolitic and continental margin material as exotic blocks debris flow deposits and turbidites these were emplaced onto the upper surface of the ophiolitic thrust sheet during the latest stages of emplacement onto the korabi microcontinent following collision in the east oceanic crust remained within a small remnant pindos mirdita oceanic basin passive conditions were restored in the mid late cretaceous with shallow water carbonate deposition on microcontinental units and both pelagic and redeposited carbonates in basinal settings from the maastrichtian onwards africa eurasia convergence resulted in large scale westward thrusting deforming the apulian foreland in oligo miocene time the suture zone was re activated in oligo miocene time as the albanie thassalie piggy back type basin in central and southern albania albania as a whole was rotated 45 clockwise as part of the western aegean arc in post eocene time coastal and offshore albania experienced strong subsidence after early miocene time forming the periadriatic basin including the tirana depression interpreted as a foredeep related to continuing regional convergence southern albania experienced extensional tectonics in plio quaternary time related to southward roll back of the aegean active margin

geochemical characteristics of the cretaceous ophiolitic rocks of ikaria island greece scattered occurrences of ophiolitic rocks are widespread in the cyclades islands of greece and are important for understanding the later mesozoic ocean spreading and collisional history of the region which has been obscured by cenozoic nappe stacking metamorphism plutonism and extension ophiolitic rocks in the upper tectonic unit of ikaria are preserved in a melange underlying triassic limestones in the kefala unit and in a coarse grained conglomerate at faros directly overlying the mid crustal detachment fault the geochemistry of these rocks has been determined their mineralogy investigated by electron microprobe and k ar radiometric dating was carried out sole rocks are amphibolite of alkaline basalt protolith most ophiolitic samples from ikaria consist of hornblende gabbro with morb geochemistry that underwent sea floor hydration deformation and metamorphism the large variation in degree of deformation grade of metamorphism and radiometric ages suggest syn spreading extensional deformation at a slow spreading ridge the ophiolitic melange on ikaria because it is unaffected by younger metamorphism provides clear evidence for late cretaceous ocean crust formation in the cyclades region

evolution of boninites and island arc tholeiites in the pindos ophiolite greece whole rock geochemical and sm nd isotope data are presented for a representative suite of crustal rocks from the pindos ophiolite in order to resolve the origin of the geochemical signature of the boninites comparison is made with triassic morb from the avdella melange and with other ophiolitic rocks of northwestern greece hydrothermal alteration results in large scatter in sr and k and some variability in ba th and u the pindos boninites contain high zr and hf with respect to ree characteristic of many boninites pb la sm and nb decrease with decreasing tio 2 from morb to iat but then increase in the boninites nd isotopic values expressed as e nd decrease systematically with decreasing tio 2 from 7 8 in iat to 0 6 3 0 in boninites as mantle wedge harzburgite became increasingly depleted another magma source contributed significant amounts of pb ree and probably nb the pb and other large ion lithophile elements may have been transported in aqueous solutions from the subducting slab but the ree and nb imply an ocean island basalt oib type source within the mantle wedge this oib source is a consequence of mantle plume activity during late triassic rifting

spinel in martian meteorite sau 008 implications for martian magnetism shergotty nakhla chassigny snc meteorites provide the only available samples of martian material the stable permanent magnetization of snc meteorites has been traditionally attributed to magnetite fe3o4 or pyrrhotite fe7s8 on the basis of rock magnetic microscopic and electron microprobe analyses on rock chips and mineral separates we suggest that a new material fe cr ti spinel is responsible for the stable paleomagnetic record of martian meteorite sau 008 it is possible that sau 008 acquired a primary remanence of thermal origin from the martian crustal field however this proposition requires further testing because the effect of shock events on fe cr ti spinel is unknown d 2004 elsevier b v all rights reserved

matching martian crustal magnetization and magnetic properties of martian meteorites magnetic properties of 26 of 32 unpaired martian meteorites sncs are synthesized to further constrain the lithology carrying martian magnetic crustal sources magnetic properties of ultramafic cumulates i e chassigny allan hills alh 84001 and lherzolitic shergottites alh 77005 lewis cliff lew 88516 are one or two orders of magnitude too weak to account for the crustal magnetizations assuming magnetization in an earth like field nakhlites and some basaltic shergottites which are the most magnetic sncs show the right intensity titanomagnetite is the magnetic carrier in the nakhlites 7 meteorites whereas in most basaltic shergottites 11 meteorites it is pyrrhotite dhofar dho 378 los angeles and nwa 480 1460 and 2046 are anomalous basaltic shergottites as their magnetism is mainly due to titanomagnetite pyrrhotite should be among the candidate minerals for the magnetized noachian crust

magnetic lineations in the ancient crust of mars the mars global surveyor spacecraft in a highly elliptical polar orbit obtained vector magnetic field measurements above the surface of mars altitudes 100 kilometers crustal magnetization mainly confined to the most ancient heavily cratered martian highlands is frequently organized in east west trending linear features the longest extending over 2000 kilometers crustal remanent magnetization exceeds that of terrestrial crust by more than an order of magnitude groups of quasi parallel linear features of alternating magnetic polarity were found they are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on earth but with a much larger spatial scale they may be a relic of an era of plate tectonics on mars

dike intrusion as a possible cause of linear martian magnetic anomalies a model in which the ancient 100 200 km wide magnetic lineations in the southern hemisphere of mars are formed by repeated dike intrusion is proposed on the basis of magnetizations observed at terrestrial mid ocean ridges a likely upper bound on the martian crustal magnetization is about 15 a m 1 this upper bound gives a minimum magnetized layer thickness of 35 60 km because the magnetic material is likely to be magnetite the long term stability of the anomalies probably requires ilmenite lamellae to have exsolved from the magnetite this exsolution process provides an upper bound on the cooling time available of 102 105 yr these bounds can be satisfied if the magnetic anomalies are created by successive intrusion of dikes from 20 to 2000 m wide production of a martian crust 35 60 km thick by rifting requires either mantle potential temperatures in excess of 1430 c or stretching factors greater than 5

tectonic significance of the geochemistry and petrology of ophiolites in southeast anatolia turkey abstract the southeast anatolian ophiolites form discontinuous linear belts of oceanic fragments immediately north of the bitlis zagros suture which marks a continental collision zone between the arabian platform to the south and the taurides to the north the late cretaceous ophiolites in the southeast anatolia are represented by the kizildag in the hatay area the goksun and the berit to the north of kahramanmaras ispendere in the malatya area and komurhan guleman in the elazig area the goksun berit ispendere komurhan and guleman ophiolites were attached to the base of the tauride platform i e the malatya keban along its northern active margin and intruded by the i type calc alkaline granitoids of late cretaceous age in contrast the kizildag hatay ophiolite was thrust over the arabian passive margin in the south the cumulate rocks in the ophiolites are represented by dunite wehrlite lherzolite olivine clinopyroxenite olivine gabbronorite olivine gabbro gabbronorite and gabbro highly magnesian olivines fo88 to 74 and pyroxenes mg 95 to 60 as well as highly calcic plagioclases an95 to 68 from the cumulate rocks differ from oceanic equivalents which mainly formed from a mor basaltic melt the order of crystallization in mineral phases whole rock and mineral chemistry data from the cumulates suggest that the primary magma is compositionaly similar to that observed in modern island arc tholeiitic sequences the volcanic and subvolcanic rocks exhibit tholeiitic compositions chondrite normalized ree n morb normalized multi element patterns and tectonic discrimination diagrams suggest the existence of two main types of parental basic magmas in the crustal rocks of the se anatolian ophiolites these are i iat series that characterize the kizildag goksun ispendere komurhan and guleman ophiolites and ii low ti boninitic series known only in the kizildag ophiolite the geochemistry of the crustal rocks suggests that they formed in a suprasubduction zone tectonic setting including arc forearc environments in the southern neotethys these well preserved plutonic oceanic crustal remnants mainly exhibit an intact ophiolite pseudostratigraphy and are overlain by a volcanic sedimentary unit made up of alternations of basic to acidic extrusive rocks debris flows volcaniclastic sandstones and pelagic limestones interpreted as a tholeiitic ensimatic island arc assemblage built on the suprasubduction zone type crust the metamorphism of some of the ophiolites i e berit in the se anatolia might be related to later stages of intraoceanic subduction during the evolution of the southern neotethys

the nature of triassic extension related magmatism in greece evidence from nd and pb isotope geochemistry the widespread triassic volcanic rocks of greece dismembered during the hellenide orogeny are used to interpret the nature of triassic rifting four assemblages of volcanic rocks are distinguished on geochemical criteria 1 a predominant subalkaline basalt andesite dacite series with a high proportion of pyroclastic rocks 2 minor shoshonites 3 alkali basalt and 4 morb the stratigraphic and palaeogeographic distribution of these rock types is synthesized new pb and nd isotopic data are used to discriminate between hypotheses suggesting that either subduction or extension was responsible for the triassic volcanism in the subalkaline basalt assemblage e nd is negative with depleted mantle model ages 1 5 ga pb isotopic compositions are mostly close to the very distinctive compositional field of cenozoic extensional rocks of the aegean area with very high 207 pb 204 pb for relatively low 206 pb 204 pb ratios these isotopic data confirm interpretations based on trace elements that subalkaline basalts were predominantly derived from melt depleted peridotite in the sub continental lithospheric mantle as a result of extension small areas of enriched hydrous mantle partially melted to yield shoshonitic magmas nd and pb isotopic compositions of the alkali basalts are quite different from those in other rock types and suggest a himu mantle source component derived from a small plume which also influenced morb compositions distribution of these various rock types is used to constrain palaeogeographic reconstruction of triassic micro continental blocks

que94201 shergottite crystallization of a martian basaltic magma abstract basaltic shergottites are commonly described as having crystallized from magmas that contained entrained or cumulus pyroxenes complexly zoned clinopyroxenes in que94201 a newly recovered antarctic shergottite are similar to those formed during continuous growth in some lunar basaltic melts pyroxene cores have nuclei of magnesian pigeonite mantled by augite in turn rimmed by strongly zoned ferroan pigeonite with outer rims of pyroxferroite fe ti oxide compositions indicate that this meteorite crystallized under relatively reducing conditions more like lunar basalts than other shergottites ree and other trace element abundances in zoned pyroxenes maskelynite and phosphates are consistent with continuous pyroxene crystallization from an evolving magma punctuated by the appearance of new phases on the liquidus the higher proportion of maskelynite in que94201 suggests that its composition may be closer to multiple saturation with pyroxenes plagioclase than other shergottites and all pyroxene zones show negative eu anomalies thus this meteorite may represent the first example of a martian magma unaffected by crystal accumulation the fe fe mg ratio and proportions of incompatible elements reflected in 4 modal whitlockite are high implying that this is a fractionated melt the calculated bulk ree pattern shows extreme lree depletion suggesting either less contamination with enriched crustal materials or a more lree depleted source than other basaltic shergottites

shock experiments up to 30 gpa and their consequences on microstructures and magnetic properties in pyrrhotite 1 shock experiments with pressures ranging from 3 to 30 gpa have been conducted on a mixed assemblage of hexagonal and monoclinic pyrrhotite all samples were studied with respect to their particular shock induced microstructures and magnetic properties at high and low temperatures up to 8 gpa microstructures in shocked pyrrhotite are characterized by mechanical deformation producing a damage of the crystal structure at pressures of 20 gpa and upward amorphization and mechanical twinning are the dominant structural features induced by shock within the lower pressure range coercivity saturation isothermal remanent magnetization and coercivity of remanence increase with shock pressures in agreement with more single domain sd like behavior simultaneously the peak of hexagonal pyrrhotite decreases and the 34 k transition of monoclinic pyrrhotite broadens and is depressed magnetic hardening is triggered by grain size reduction but also by the formation of sd within discrete multidomain grains planar deformation features subdivide such multidomain grains into lath shaped domains with average sizes lying in the sd range the planar deformation features disappear at 20 gpa and irregular nanometer sized amorphous domains occur instead pressure release from 30 gpa finally triggers partial melting of pyrrhotite the sharp interfaces between molten and crystalline pyrrhotite document a rapid change of thermal conditions within molten pyrrhotite quenched iron crystals occur the presence of native iron strongly influences the magnetic properties depending on the particular amount in the studied sample and likely affects the magnetic properties of impact lithologies on earth and extraterrestrial material

influence of redox conditions on the intensity of mars crustal magnetic anomalies we evaluate the relationship between the intensity of remanent magnetization and fo2 in natural and synthetic mars meteorites the olivine phyric shergottite meteorite yamato 980459 y 980459 and a sulfur free synthetic analog y 98 of identical major element composition were analyzed to explore the rock magnetic and remanence properties of a basalt crystallized from a primitive melt and to explore the role of magmatic and alteration environment fo2 on mars crustal anomalies the reducing conditions under which y 980459 is estimated to have formed qfm 2 5 shearer et al 2006 were replicated during the synthesis of y 98 y 980459 contains pyrrhotite and chromite chromite is the only magnetic phase in y 98 the remanence carrying capacity of y 980459 is comparable to other shergottites that formed in the fo2 range of qfm 3 to qfm 1 the remanence carrying capacity of these low fo2 basalts is 1 2 orders of magnitude too weak to account for the intense crustal anomalies observed in mars s southern cratered highlands moderately oxidizing conditions of qfm 1 which are more commonly observed in nakhlites and noachian breccias are key to generating either a primary igneous assemblage or secondary alteration assemblage capable of acquiring an intense remanent magnetization regardless of the basalt character or thermal history this suggests that if igneous rocks are responsible for the intensely magnetized crust these oxidizing conditions must have existed in the magmatic plumbing systems of early mars or must have existed in the crust during secondary processes that led to acquisition of a chemical remanent magnetization

the hellenic ophiolites eastward or westward obduction of the maliac ocean a discussion ophiolitic bodies in the dinaro hellenic mountain belt are among the most important ones in the peri mediterranean alpine chains the characteristic feature of this ophiolitic belt is its middle to late jurassic age of obduction the ophiolitic bodies form two major belts on each side of the pelagonian zone an east pelagonian belt in the vardarian domain and a supra pelagonian ophiolitic belt spo to the west the different hypotheses relative to the origin of the spo present geodynamic evolution models accounting for most of the available data a mid triassic episode of rifting a ladinian jurassic episode of sea floor spreading forming notably the maliac ocean a middle to late jurassic convergent period with subduction and obduction episodes and finally a late episode of tertiary compressional deformation responsible for the westward thrusting of the jurassic ophiolitic nappes over the external zones despite many studies dating from the early 1970s the eastern or western pelagonian origin of these ophiolites especially the spo is still under dispute whatever the adopted hypothesis we consider that the main spo bodies n pindos vourinos othris evia argolis have the same origin because of their geographic continuity and of the similarities in their geological characteristics we propose that this ocean corresponds everywhere to the maliac ocean defined in othris from the well preserved sedimentary oceanic margin and ophiolitic nappes thrust during the late jurassic obduction onto the pelagonian platform there is strong evidence for the existence of two deep basins on both sides of the pelagonian continental ridge during triassic jurassic times they correspond respectively to the vardar area to the east and the pindos domain to the west one of these domains being at the origin of the spo the hypothesis of an eastward emplacement of the spo from the pindos domain is based mainly on sedimentological data from the margin series and on structural analyses of ophiolitic bodies however we conclude the westward obduction of the maliac ocean originating from the vardar area to be the best fitting model this westward model is supported by paleogeographic and structural constraints on regional scale notably the absence of obducted ophiolites in the jurassic series of the koziakas units units attributed to the western pelagonian margin and of the parnassus domain on the eastern side of the pindos basin is difficult to reconcile with an eastward obduction from the pindos domain other observations such as the distribution of ophiolitic detritus in the internal and external zones also promote the westward late jurassic obduction of the maliac ocean our preferred model offers a consistent explanation for the mechanism and timing of the emplacement of the spo as well as providing insight on the origin and emplacement of the vardarian ophiolites following this hypothesis there is no need for a clear boundary between the spo and the west vardarian ophiolitic bodies as they were obducted from the same oceanic basin and during the same jurassic tectonic event in this paper we develop evidence in favor of the eastern pelagonian origin for the spo our adopted model and provide discussion on the data supporting the main alternative hypothesis western origin for the spo

magnetic transition at 30 34 kelvin in pyrrhotite insight into a widespread occurrence of this mineral in rocks abstract a characteristic magnetic transition at 30 34 k is shown to provide a powerful tool for the identification of pyrrhotite with concentration down to 10 ppm through the same low temperature techniques as applied to magnetite and hematite extended down to liquid helium temperature a review of rock magnetic and petrological data on pyrrhotite suggests that this mineral should be considered as a major carrier of paleomatnetic signals unblocking temperature up to 350 c and extreme resistance against af may be encountered in fine grained pyrrhotite

unique meteorite from early amazonian mars water rich basaltic breccia northwest africa 7034 we report data on the martian meteorite northwest africa nwa 7034 which shares some petrologic and geochemical characteristics with known martian meteorites of the snc i e shergottite nakhlite and chassignite group but also has some unique characteristics that would exclude it from that group nwa 7034 is a geochemically enriched crustal rock compositionally similar to basalts and average martian crust measured by recent rover and orbiter missions it formed 2 089 0 081 billion years ago during the early amazonian epoch in mars9 geologic history nwa 7034 has an order of magnitude more indigenous water than most snc meteorites with up to 6000 parts per million extraterrestrial h2o released during stepped heating it also has bulk oxygen isotope values of 17o 0 58 0 05 per mil and a heat released water oxygen isotope average value of 17o 0 330 0 011 per mil suggesting the existence of multiple oxygen reservoirs on mars

magnetic properties of martian meteorites implications for an ancient martian magnetic field the magnetic properties of samples of seven martian meteorites eet 79001 zagami nakhla lafayette governador valadares chassigny and alh 84001 have been investigated all possess a weak very stable primary natural remanent magnetization nrm and some have less stable secondary components in some cases the latter are associated with magnetic contamination of the samples imparted since their recovery and with viscous magnetization acquired during exposure of the meteorites to the geomagnetic field since they fell the magnetic properties are carried by a small content 1 of titanomagnetite and in alh 84001 possibly by magnetite as well the most likely source of the primary nrm is a thermoremanent magnetization acquired when the meteorite material last cooled from a high temperature in the presence of a magnetic field current evidence is that this was 1 3 ga ago for the nakhlites and chassigny and 180 ma for shergottites the time of the last relevant cooling of alh 84001 is not presently known preliminary estimates of the strength of the magnetizing field are in the range 0 5 5 ut which is at least an order of magnitude greater than the present field it is tentatively concluded that the magnetic field was generated by a dynamo process in a martian core with appropriate structure and properties

tectono stratigraphy and evolution of the mesozoic pindos ophiolite and related units northwestern greece the northwest pindos mountains expose mesozoic and tertiary thrust sheets which include the jurassic pindos ophiolite composed of ultramafic and mafic oceanic crustal rocks the tectono stratigraphy of these units is i mainly ultramafic ophiolitic thrust sheet and basal metamorphic sole dramala complex and loumnitsa unit ii late cretaceous platformal limestones orliakas group iii dismembered intrusive and extrusive ophiolitic rocks aspropotamos complex iv tectonic melange and olistostromes dominated by triassic jurassic volcanic and sedimtntary rocks avdella melange v coherent thrust sheets of late jurassic late cretaceous deep water sediments dio dendra group vi early tertiary flysch pindos flysch immobile trace element studies indicate that triassic and jurassic extrusives of the volcanic sedimentary melange formed mainly at within plate and or mid ocean ridge settings by contrast structurally overlying ophiolitic extrusives include boninitic volcanics and island arc tholeiites of supra subduction zone origin initial ophiolite displacement c 165 ma is recorded in metamorphic sole formation including basal peridotite mylonite amphibolites and greenschists the sole rocks have morb and wpb chemical affinities in our favoured model the pindos ophiolite formed above a mid jurassic westerly dipping intra oceanic subduction zone accompanied by accretion to form melange followed by collision and emplacement with the pelagonian margin final suturing of the pindos ocean however did not take place until early tertiary times

evidence for a reduced fe depleted martian mantle source region of shergottites estimates of the oxygen fugacity of the source regions of martian shergottites are obtained from coexisting fe ti oxides and from fe3 fe2 ratios in pyroxenes these estimates are one to four log10 units lower than previously reported values and indicate that the shergottite source region has an oxidation state about two or three orders of magnitude below the quartz fayalite magnetite qfm oxygen reference buffer an approximation of the major element composition of the shergottite source region is obtained utilizing the melts petrologic modeling software a bulk composition of the shergottite source region is derived which is consistent with the generation of sher gottites upon 3 partial melting at 10 kbar this composition is decidedly less enriched in na2o and feotot than previous estimates when compared to the bulk composition of the terrestrial mantle the source region of the shergottites is lower in cao al2o3 na2o and tio2 and higher in mgo

the jurassic south albanian ophiolites mor vs ssz type ophiolites abstract within the western belt of the southern albanian ophiolites the voskopoja ophiolite consists of three subunits voskopoja morava and rehove these are predominantly lherzolites with minor harzburgites and dunites in the mantle section above come ultramafic and mafic cumulates including wehrlites troctolites and olivine gabbros gabbronorites are restricted to the morava subunit isotropic clinopyroxene gabbros extrusives and sediments are present only in rehove and voskopoja the volcanic section is dominated by basaltic breccias including megablocks with sheeted dykes pillow lavas and isolated dykes the basaltic breccias grade upwards into sandstones in turn interlayered with argillites and cherts of jurassic age the basalts are predominantly clinopyroxene plagioclase basalts either aphyric or plagioclase phyric geochemically they are divided into four groups 1 an intermediate ti and zr group with low ni hereafter called low ni group 2 an intermediate ti zr group with high ni hereafter called high ni group 3 a high ti zr group and 4 a low ti zr group the high ni content in group 2 is interpreted as originating from olivine and spinel xenocrysts apart from the high ni content groups 1 and 2 are comparable with the volcanics of the low to high ti intermediate ophiolites by contrast group 3 is more comparable to the high ti ophiolitic extrusives in the western ophiolite belt of northern albania group 4 consists ssz type basalts and is widespread in the volcanics of the eastern ophiolite belt comparison of the ultramafic mafic cumulates and the basaltic volcanics with those in the northern part of the western belt in albania and the pindos ophiolite indicates that there is a systematic variation in petrography and geochemistry from north to south in the western belt with an increasingly distinct ssz signature towards the south ultramafic and mafic cumulates as well as basalts from the shebenik massif in the eastern belt are similar to those of voskopoja implying a genetic relationship

rotational deformation in the jurassic mesohellenic ophiolites greece and its tectonic significance abstract the jurassic pindos and vourinos ophiolites in the western hellenides of greece are part of the mesohellenic mafic ultramafic slab underlying the eocene miocene sedimentary basin mesohellenic trough the tectonic incorporation of this oceanic slab into the western edge of the pelagonian subcontinent occurred via trench passive margin collision in the late jurassic much of the tectonic architecture of these ophiolites particularly vourinos was acquired during progressive inhomogeneous deformation associated with the initial displacement of the jurassic oceanic crust from its original igneous environment of formation and its subsequent tectonic emplacement eastward onto the pelagonian margin the heterogeneous deformation in the mantle and crustal sequences of the pindos vourinos ophiolites occurred in ductile ductile brittle and brittle fields synchronously as the jurassic oceanic lithosphere was translated eastward it also resulted in differential horizontal rotations within the displaced oceanic slab areas retaining high temperature diapiric mantle fabric appear to have been passively translated by lower temperature ductile shearing commonly along mylonite zones individual dunite bodies in the harzburgite tectonites indicate movement distances of at least kilometer scale pervasively mylonitic domains within the upper mantle peridotites suggest elongation on the order of five to ten times in the direction of ophiolite emplacement seafloor spreading related high temperature mantle structures within the pindos and vourinos ophiolites are sub parallel imprinted ductile kinematic indicators and ductile shear zones pervasive to the mantle and lower crustal sections in both ophiolites are also sub parallel consistent with the direction of tectonic vergence and appear traceable across the sedimentary overburden of the mesohellenic trough these geometric relations imply that the pindos vourinos ophiolites retain their relative orientations from the time of cessation of ductile deformation within the ophiolitic slab more than 90 anticlockwise horizontal rotation of the vourinos ophiolite seems to have taken place during progressive simple shear deformation associated with the eastward emplacement of the jurassic oceanic lithosphere this kind of rotational deformation postdating the igneous accretion of ancient oceanic crust may be common in many ophiolites and should be carefully distinguished from tectonic extension related vertical rotational deformation developed during their seafloor spreading evolution

low and high ti ophiolites in northern pindos petrological and geological constraints ophiolites with different magmatic characteristics are closely associated in space with one another in northern pindos some have affinities with ocean floor magmas group i and others represent melts which are frequently strongly depleted in incompatible elements group ii group i is composed of cumulates dolerites and lavas whereas group ii occurs mainly as pillows and dykes and postdates group i the two groups have different geochemical mineralogical and petrographic features they exhibit different ti cr ni y zr p si and mg contents and clinopyroxenes and spinels of group i have higher ti al and ti mn ratios and lower cr cr al values respectively than those of group ii many rocks of group ii are chemically similar to boninites and associated rocks as well as to low ti basalts from other areas and ophiolitic complexes it is concluded that geochemical and mineralogical data alone do not allow a definitive answer about the original tectonic setting of the investigated rocks although a genesis above a subduction zone seems to be plausible hypothesis

sulfide mineralogy and redox conditions in some shergottites magmatic sulfide mineralogy has been studied in 2 olivine phyric shergottites dag 476 and sau 005 and 4 basaltic shergottites zagami shergotty los angeles and nwa 480 modal abundances of magmatic sulfides as estimated by image analysis on thin section are high 0 16 to 0 53 area percent and correlate positively with abundances of fe ti oxides sulfides are mesostasis minerals being mostly interstitial grains or locally enclosed in post cumulus melt inclusions e g sau 005 in olivine sulfides in shergottites are composed of major pyrrhotite containing pentlandite exsolutions associated with minor amounts of cu sulfides chalcopyrite and or cubanite hot desert finds e g dag 476 show abundant fracture filling iron oxy hydroxides of probable terrestrial origin unaltered sulfides show metal rich hexagonal pyrrhotite compositions with metal sulfur m s ratio ranging between 0 936 0 005 and 0 962 0 01 this compositional range corresponds to the two phase structural domain 2c nc of the fe s system however the high temperature disordered hexagonal 1c pyrrhotite structure would be in better agreement with magnetic properties of shergottites ni contents in pyrrhotite increase from los angeles 0 05 at to shergotty zagami and nwa 480 0 2 0 5 at and dag 476 and sau 005 up to 3 at the higher ni values of pyrrhotite in olivine phyric shergottites correlate with the abundance of pentlandite exsolutions both reflecting more primitive ni rich sulfide liquids where abundant olivine crystallized this result and the strong correlation between sulfide abundances and fe ti oxides argue for a primary magmatic origin of these sulfides although they reproduce the trend of magmatic oxygen fugacity conditions determined from fe ti oxide pairs observed pyrrhotite compositions are systematically more metaldeficient compared to those calculated from the fe s o system this suggests post magmatic oxidation during cooling on mars followed by terrestrial weathering for hot desert finds

controls on the sr and nd isotopic compositions of hydrothermally altered rocks from the pindos ophiolite greece abstract the sr and nd isotopic behaviour of hydrothermally altered basaltic rocks from the pindos ophiolite nw greece has been investigated samples were obtained mainly from rocks affected by intense hydrothermal alteration in field areas believed to represent hydrothermal discharge zones formed at a mesozoic seafloor spreading centre 87 sr 86 sr ratios in the altered rocks show a narrow range of values intermediate between those of seawater and fresh rock regardless of the degree of alteration this has been interpreted as the result of high overall water rock ratios which were sufficient to produce a homogeneous overprint throughout most of the hydrothermal cell a sr shift index which uses the sr isotopic composition and sr concentration of both rock and fluid has been derived to express the degree of sr exchange between rock and seawater it has been used to investigate the variations in water rock interaction between known hydrothermal systems and to compare ophiolite hosted with modern oceanic systems the results indicate that even when compared on such a uniform basis all the known present day hydrothermal systems are generally more rock dominated than those of pindos and other ophiolites 143 nd 14 nd ratios in the altered rocks are much less markedly affected but may show a shift from original magmatic values the results presented here suggest that this effect cannot simply be attributed to exchange with seawater nd these shifts must result from seawater transporting basaltic nd of a different isotopic composition from elsewhere in the volcanic pile into the zones of intense alteration this study has shown that sr and nd isotopes vary independently as a result of their different original distribution as well as their contrasting geochemical mobility

petrology and trace element geochemistry of tissint the newest shergottite fall the fall and recovery of the tissint meteorite in 2011 created a rare opportunity to examine a martian sample with a known short residence time on earth tissint is an olivine phyric shergottite that accumulated olivine antecrysts within a single magmatic system coarse olivine grains with nearly homogeneous cores of mg 80 suggest slow re equilibration many macroscopic features of this sample resemble those of lar 06319 including the olivine crystal size distribution and the presence of evolved oxide and olivine compositions unlike lar 06319 however no magmatic hydrous phases were found in the analyzed samples of tissint minor and trace element compositions indicate that the meteorite is the product of closed system crystallization from a parent melt derived from a depleted source with no obvious addition of a lree rich crustal component prior to or during crystallization the whole rock ree pattern is similar to that of intermediate olivine phyric shergottite eeta 79001 lithology a and could also be approximated by a more olivine rich version of depleted basaltic shergottite que 94201 magmatic oxygen fugacities are at the low end of the shergottite range with log fo2 of qfm 3 5 to 4 0 estimated based on early crystallized minerals and qfm 2 4 estimated based on the eu in pyroxene oxybarometer these values are similarly comparable to other depleted shergottites including sau 005 and que 94201 tissint occupies a previously unsampled niche in shergottite chemistry containing olivines with mg 80 resembling the enriched olivine phyric shergottite lar 06319 in its crystallization path and comparable to intermediate olivine phyric shergottite eeta 79001a depleted olivine phyric shergottite dag 476 and depleted basaltic shergottite que 94201 in its trace element abundances and oxygen fugacity the apparent absence of evidence for terrestrial alteration in tissint particularly in trace element abundances in the whole rock and individual minerals confirms that exposure to the arid desert environment results in only minimal weathering of samples provided the exposure times are brief

geochemistry and petrogenesis of ophiolites from northern pindos greece the ophiolitic complex of northern pindos greece contains ocean floor basalts and low ti mafic rocks the former rocks are similar to recent mid ocean ridge basalts with a light ree depletion and a la yb ratio 2 the low ti rocks resemble boninites in their high mg and very low ti and zr contents and in their ree patterns which have convex downwards shape with a slight light ree enrichment however their zr ti ti v and zr y ratios are lower than in boninites both rock types could be generated by dynamic partial melting of a rising upper mantle diapir slight enrichment in light ree sr rb and ba in low ti rocks could be the result of either metasomatic or alteration processes although a subduction zone origin of the sequence is possible the geochemical data do not necessarily imply such a setting

isua supracrustal belt greenland a vestige of a 3 8 ga suprasubduction zone ophiolite and the implications for archean geology abstract the mafic ultramafic units of the 3 8 ga isua supracrustal belt isb in greenland occur in a two armed arcuate zone eastern and western arms and are grouped into two major tectonostratigraphic units based on their lithological and geochemical characteristics 1 undifferentiated amphibolites ua and 2 garbenschiefer amphibolites ga the ua contains all major lithological units of a typical penrose type complete ophiolite sequence the ga is composed dominantly of volcaniclastic and volcanic rocks commonly found in immature island arcs the available geochemical data from ua and ga show distinct differences between the two units compared with the geochemical evolution of some of the well known phanerozoic ophiolites the pillow lavas and associated dikes of the ua show a compositional range that is similar to typical morb type ligurian ophiolites in the western alps apennines and those displayed by lip type caribbean ophiolites the ga is characterized by island arc tholeiite iat to boninite like rocks and defines a magmatic evolution that is comparable to that of suprasubduction zone ssz ophiolites in the mediterranean region our proposed geodynamic model for the isb suggests that the ua was built by primary to differentiated mantle generated melts during seafloor spreading little to moderately affected by subduction processes and that the iat to boninitic like rocks of the ga formed at a later stage by melting from a strongly subduction affected depleted and hydrated mantle our interpretation of the isb is that the ua and ga represent early and late stages respectively in the formation of a ssz ophiolite this implies that phanerozoic type plate tectonic processes such as seafloor spreading and subduction were operating by 3 8 ga in the palaeoarchean

structural classification of chromite pods in southern new caledonia a structural classification of podiform chromite orebodies from southern new caledonia results in a division of deposits into three major types discordant subconcordant and concordant with penetrative structures foliation and lineation in the enclosing peridotite discordant deposits are very irregular in shape and clearly crosscut banding and foliation subconcordant deposits are generally tabular in shape and lie within 10 degrees to 25 degrees in strike and or dip to the foliation concordant deposits are also tabular and lie parallel to foliation in peridotite pyroxene lineation in host peridotite always indicates the elongation direction of these deposits within subconcordant and discordant deposits chromite lineations are often oblique to those in the surrounding rocks they follow local variations in the orebody shape and indicate possible deposit extensions at depth the classification of chromite bodies corresponds to three stages of increasing deformation as evidenced by chromite ore textures discordant deposits which are the least deformed are characterized by primary textures such as the nodular one the foam texture the chromite net and the occluded silicate texture within subconcordant and mainly concordant deposits massive disseminated and antinodular ores show evidence of strong deformation the lack of geochemical distinctions between the different deposit types supports such an hypothesis these chromite deposits in ophiolitic harzburgites are thought to have been formed beneath an oceanic spreading ridge if the discordant pods are considered as representative of the original situation it is proposed that the chromite has crystallized and has been dynamically concentrated along steep conduits traversing the enclosing harzburgite and feeding a magma chamber next the chromite enriched pipes are caught up by plastic deformation in the mantle and tectonically reoriented toward the foliation the chromite deposits in the massif du sud are located within a domain about 1 5 km thick in the harzburgites and dunite zones this domain is limited upward by the first cumulates and gabbros and downward by the transition to a different plastic flow regime in the harzburgites finally some guides to chromite prospecting and exploration are cited applicable at different geologic scales and based on lithologic and structural criteria

evidence for a contribution from two mantle plumes to island arc lavas from northern tonga lavas from the islands of tafahi and niuatoputapu at the northern end of the active tonga kermadec arc in the southwest pacific were erupted at a convergent plate margin yet they can be shown to contain a contribution from two different mantle plumes high concentrations of nb relative to other high field strength elements in these lavas compared to other tonga lavas reflect an ocean island basalt component in the mantle wedge derived from the nearby samoa mantle plume pb isotope compositions indicate that most of the pb in these lavas is derived from the oceanic crust of the plume generated louisville seamount chain which is being subducted beneath the tonga arc these two plume components were thus introduced into the arc lavas in very different ways and provide insight into upper mantle dynamics and magma generation processes occurring in an active arc back arc system

valence state partitioning of vanadium between olivine liquid estimates of the oxygen fugacity of y980459 and application to other olivine phyric martian basalts the valence state of vanadium v2 v3 v4 and v5 is highly sensitive to variations in redox conditions of basaltic magmas differences in valence state will influence its partitioning behavior between minerals and basaltic liquid using partitioning behavior of v between olivine and basaltic liquid precisely calibrated for martian basalts we determined the oxidation state of a primitive olivine rich high mg no martian basalt y980459 near its liquidus the behavior of v in the olivine from other martian olivine phyric basalts sau005 dag476 and nwa1110 was documented the combination of oxidation state and incompatible element characteristics determined from early olivine indicates that correlations among geochemical characteristics such as f o2 lree hree initial 87sr 86sr and initial end observed in many martian basalts is also a fundamental characteristic of these primitive magmas these observations are interpreted as indicating that the mantle sources for these magmas have a limited variation in f o2 from iw to iw 1 and are incompatible element depleted moreover these mantle derived magmas assimilated a more oxidizing iw 3 incompatible element enriched lower crustal component as they ponded at the base of the martian crust

controls on uranium and thorium behaviour in ocean floor hydrothermal systems examples from the pindos ophiolite greece abstract a suite of hydrothermally altered basaltic rocks from the jurassic pindos ophiolite of greece was analysed for its u and th content samples taken from different levels within the ophiolite display variable degrees of hydrothermal alteration ranging from low water rock ratio recharge zone alteration to high water rock ratio discharge zone alteration most samples analysed exhibit constant u th ratios regardless of the degree of alteration however neither of these two elements correlate with any other immobile element zr y ti ree these results suggest that both u and th have been mobile during high temperature ocean floor hydrothermal alteration and indicate a common probably mineralogical control for both elements the chemical composition of hydrothermal fluids from modern tectonic settings equivalent to that of the pindos ophiolite east pacific rise guaymas basin was used to predict theoretical aqueous speciation and solubility of u and th during water rock interaction in these environments the results of this treatment agree with the above conclusions drawn from rock studies and indicate that oxide mineral phases uraninite thorianite control u and th solubility during hydrothermal alteration at oceanic spreading environments