formation of iron carbon alloys in basaltic magma at uivfaq disko island the role of carbon in mafic magmas two types of metallic iron were identified in a collection of samples from the tertiary iron bearing basalts of uivfaq disko island greenland high carbon iron has 2 9 4 0 wt carbon and eutectic textures of iron and cohenite fe 3 c similar to those of commercial white cast iron it occurs in approximately spherical bodies up to 15 mm in diameter that appear to have been immiscible metallic liquids within basaltic magma low carbon samples have 1 8 2 0 wt carbon and textures similar to those of commercial hypereutectoid steel they occur principally as large up to 22 tons cumulate masses both types of metal could have crystallized at low pressure from iron carbon liquids of their present bulk carbon contents fe ni co cu and p oxides in basaltic magma were reduced by carbon derived principally from assimilated cretaceous tertiary sediments niand ni cu ratios of the metal are similar to those of terrestrial basalts the magma contained excess carbon graphite so the metal formed as

siderophile geochemistry of ureilites a record of early stages of planetesimal core formation abstract new bulk compositional data including trace siderophile elements such as ir os au and ni are presented for 25 ureilites without exception ureilites have siderophile abundances too high to plausibly have formed as cumulates ureilites undoubtedly underwent a variety of smelting by which c was oxidized to co gas while olivine feo was reduced to fe metal however pressure buffered equilibrium smelting is not a plausible model for engendering the wide range 75 96 mol of mafic silicate core mg among ureilites the smelting reaction produces too much co gas even supposing a disequilibrium process with the smelt gas leaking out of the mantle none of the ureilites least of all the ureilite with the most reduced highest olivine core mg alh84136 has the high fe metal abundance predicted by the smelted cores model in principle the fe metal generated by smelting could have been subsequently lost but siderophile data show that ureilites never underwent efficient depletion of fe metal ureilites display strong correlations among siderophile ratios such as au ir ni ir co ir as ir se ir and sb ir ureilite siderophile depletion patterns loosely resemble siderophile fractionations presumably nebular in origin among carbonaceous chondrites however zn for an element of moderate volatility is anomalously high in ureilites a tight correlation between au and ni extrapolates to the low ni au side of the compositional range of carbonaceous chondrites from this mismatch mild but nonetheless significant depletions of refractory siderophile elements such as ir and os and moderate depletions of strongly siderophile weakly chalcophile elements such as ni and au we infer that the ureilite siderophile fractionations are largely the result of a non nebular process i e removal of s rich metallic melt possibly with minor entrainment of fe metal several lines of trace element evidence indicate that melt porosity during ureilite anatexis was at least moderate the ureilite pattern of very mild depletions of extremely siderophile elements but much deeper depletions of moderately siderophile chalcophile elements suggests that asteroidal core formation probably occurs in two discrete stages in general separation of a considerable proportion several wt of s rich metallic melt probably occurs long before and at a far lower temperature than separation of the remaining s poor fe metal apart from the fe metal itself only extremely siderophile elements wait until the second stage to sequester mainly into the core

comment on the nature and origin of ureilites by j l berkley et al abstract the record of primordial noble gases in ureilites imposes serious constraints on models of ureilite petrogenesis it is argued that the inhomogeneous distribution between different mineral phases and the low 40 ar 36 ar ratio in particular can only be satisfied with difficulties in the model proposed by berkley et al

spectral reflectance properties of ureilites abstract the 0 35 2 6 m reflectance spectra of 18 ureilites have been examined in order to improve our understanding of the spectral reflectance properties of this meteorite class across this spectral range ureilite spectra are characterized by a steep rise in reflectance over the 0 3 to approximately 0 7 m range low overall reflectance 25 and weak mafic iron silicate absorption bands in the 1 and 2 m region the weakness of these bands and the low reflectance are attributed to the presence of dispersed graphite and related carbonaceous phases metal and possibly shock wavelength positions of the mafic silicate absorption bands span a range of values but are consistent with the presence of pyroxene and olivine ureilite spectra generally exhibit blue slopes across the 0 7 2 6 m interval and exhibit many overall similarities to some carbonaceous chondrites the weak features and spectral diversity of ureilites make reflectance spectroscopy based identification of a ureilite parent body challenging as terrestrial alteration of ureilites is prevalent spectral studies of falls are most useful for determining the spectral properties of likely parent bodies

first paleomagnetic results from mio pliocene series of the hellenic sedimentary arc abstract paleomagnetic measurements have been conducted on the mio pliocene series along the external sedimentary hellenic arc in order to detect the presence or absence of rotational deformations in different sections of the arc in the central eastern part of the arc crete and rhodes paleomagnetic directions are very closely aligned along the north south direction showing that this portion of the arc has not undergone significant rotation since at least 7 m y for crete and 4 m y for rhodes in the western and northwestern parts results from south peloponnesos zakinthos kephallinia and corfu indicate that this section of the arc has undergone a clockwise rotation detailed analysis of the data from the three ionian islands shows that their rotation began about 5 m y b p and has proceeded since then at roughly 5 m y giving a total amplitude of about 26 it is suggested that the beginning of this rotation is related to the lower pliocene compressive phase which most probably initiated the tectonic activity of the present day ionian margin

highly siderophile elements in ureilites abstract the abundances of the highly siderophile elements hse ru pd re os ir and pt were determined by isotope dilution mass spectrometry for 22 ureilite bulk rock samples including monomict augite bearing and polymict lithologies this report adds significantly to the quantity of available pt and pd abundances in ureilites as these elements were rarely determined in previous neutron activation studies the ci normalized hse abundance patterns of all ureilites analyzed here except alha 81101 show marked depletions in the more volatile pd with ci chondrite normalized pd os ratios excluding alha 81101 averaging 0 19 0 23 2 this value is too low to be directly derived from any known chondrite group instead the hse bulk rock abundances and hse interelement ratios in ureilites can be understood as physical mixtures of two end member compositions one component best represented by sample alha 78019 is characterized by superchondritic abundances of refractory hse rhse ru re os ir and pt but subchondritic pd rhse and is consistent with residual metal after extraction of a s bearing metallic partial melt from carbonaceous chondrite like precursor materials the other component best represented by sample alha 81101 is rhse poor and has hse abundances in chondritic proportions the genesis of the second component is unclear it could represent regions within the ureilite parent body upb in which metallic phases were completely molten and partially drained or it might represent chondritic contamination that was added during disruption and brecciation of the upb removal of carbon rich melts does not seem to play an important role in ureilite petrogenesis removal of such melts would quickly deplete the ureilite precursors in re os and as au which is inconsistent with measured osmium isotope abundances and also with literature as au data for the ureilites removal of 26 al during silicate melting may have acted as a switch that turned off further metal extraction from ureilite source regions

ureilites trace element clues to their origin carbonaceous vein separates from kenna and havero as well as bulk kenna were analyzed by rnaa for ag au bi br cd cs ge in ir ni pd os rb re sb se te tl u and zn the data are reviewed together with four earlier chicago analyses of bulk ureilites linear regressions confirm the presence of two metal components with the following cl normalized ratios ir ni 14 6 1 ge ni 5 4 2 4 au ni 2 3 0 9 the high ir component is enriched in vein separates and hence belongs to veins the lowir component belongs to the ultramafic rock vein material is enriched in all elements analyzed by us except zn and accounts for most of the c noble gases and presumably siderophiles in the meteorite most of the properties of ureilites apparently can be explained by the cumulate model of berkley et al 1980 with certain modifications comparison of ureilites with three other ultramafic rocks from different planets earth s mantle lunar dunite and chassigny suggests that the ureilite parent body had a primitive chondritic composition similar to c3v chondrites but richer in metal and carbon it melted causing depletion of incompatibles to a mean abundance of 0 02 cl and incomplete segregation of metal fes and c fractional crystallization or melting of metal in the presence of s and c apparently can explain the fractionations of ir re ni au and perhaps ge obviating the need for extraneous sources of vein metal or unusual parent body compositions noble gases from the parent material may have been retrapped in carbon during magmatism provided the system was closed

primary igneous carbon in ureilites petrological implications the ureilite meteorites are carbonaceous olivine pyroxene achondrites they typically contain up to 4 wt carbon carbonaceous matrix as graphite diamond and lonsdaleite shock degradation has effectively obliterated primary textures in the carbonaceous matrix of previously described ureilites a factor that has hampered efforts to explain the origin of this material in contrast the antarctic ureilite alha78019 displays perfectly preserved primary textures in the carbonaceous matrix characterized by euhedral graphite blades intergrown with fe ni metal and sulfide diamonds are absent this petrographic feature suggests that most graphite in ureilites originated by crystallization from a c rich metallic phase assuming that fo2 is controlled by c co co2 reactions the compositions of silicates and metals in ureilites imply a two stage redox history the noble gases and rare earths of ureilites are discussed in light of this model

achondrites and igneous processes on asteroids the possible roles of partial melting and fractional crystallization in the formation of eucrite and ureilite achondrites are discussed summarizing the results of recent petrological investigations and theoretical modeling efforts typical data are presented graphically and it is found that there is as yet no consensus on the correct model of achondrite evolution and hence no agreement on the chemistry of the parent bodies assuming that the ureilites formed as adcumulates their properties support a role for fractionation in relatively small bodies even though the magmatic composition of the ureilite parent bodies is different from that of terrestrial cumulates

origin and evolution of the ureilite parent magmas multi stage igneous activity on a large parent body analyses of olivine and pigeonite cores interpreted as cumulate crystals in eight low shock ureilites show well defined correlations between fe x where x is one of the minor elements mn cr ca al ti p or ni and fe mg ratios for the lithophile minor elements these trends are linear with positive slope and pass through or near the origin indicating various degrees of feo reduction of the parent magmas the trends shown by p and ni are consistent with this interpretation and additionally require equilibrium crystallization of 20 27 mole metal graphite was most likely the reducing agent which implies that the ureilites equilibrated at different pressures because the graphite fo2 buffer is pressure dependent there is no evidence for fractionation of olivine or pryroxene in any of these trends the ca ti and al trends show significant scatter indicating that there must have been multiple parent magmas with very similar mg mn and mgcr ratios but different mgal mgca and mgti ratios cao al2o3 ratios vary by a factor of 3 among the eight magmas and are superchondritic 14 32 molar similar to lunar mare basalts we propose the following model for generation and crystallization of ureilite parent magmas upm chondritic material undergoes 10 25 partial melting leaving a plagioclase depleted residue the magma or magmas form a differentiated crust on the ureilite parent body upb with mafic cumulates and plagioclase cumulates spatially separated later remelting 10 of the mafic cumulates produced the upm siderophile elements indicate that the source region of the upm had not experienced segregation of metal such as would occur during core formation in the source region the pressure must have been at least 0 5 1 kb because only at pressures this high does the graphite buffer allow iron oxide to be the stable phase relative to metallic iron the graphite bearing upm were emplaced at various levels in the crust where they were reduced to various extents dependent on depth ureilites are early olivine pigeonite cumulates from these magmas compositions of interstitial low ca pyroxenes indicate that the trapped interstitial liquids from which they crystallized had lower mnmg crmg camg almg and namg ratios than the upm and indicate an abrupt change in liquid composition coincident with impact excavation of ureilites this interstitial material may be derived by mixing a shock melt of nearby olivine pigeonite cumulates with residual primary liquid our model predicts that the upb had a differentiated crust did not have a core and was at least 235 km in radius the lack of a ureilite like body among spectrally analyzed asteroids suggests that either the spectral signature of the upb is not that of ureilites themselves perhaps of carbon free feldspathic material instead that the upb is not intact or that ureilites did not originate in the asteroid belt

geological structures on the south cretan continental margin and hellenic trench eastern mediterranean abstract combination of recent seismic profiles obtained along the south cretan continental margin with previously published data has provided a basis for mapping the overall structure of this portion of the active hellenic margin two sectors are distinguished from western crete to 25 east the continental slope is crossed by post late miocene extensional features creating a series of sedimental marginal troughs and steep basement ridges the lower slope the trench and parts of its outer slope are areas of little sedimentation most of the sediments are trapped on the margin and of active deformation this area represents the eastern prolongation of the ionian branch matapan trench of the hellenic subduction zone and is interpreted in the light of ne directed compression from 25 e to eastern crete the geological structures of both the continental margin and the adjacent trenches differ from those to the west this difference possibly relates to interferences between the present day structural directions interpreted in relation to a left lateral transform motion and previous trends inherited from a preceding ns compression

petrology of chromite in ureilites deconvolution of primary oxidation states and secondary reduction processes abstract ureilites are ultramafic achondrites thought to be residues of partial melting on a carbon rich asteroid they show a trend of feo variation olivine fo from 74 to 95 that suggests variation in oxidation state whether this variation was established during high temperature igneous processing on the ureilite parent body upb or preserved from nebular precursors is a subject of debate the behavior of chromium in ureilites offers a way to assess redox conditions during their formation and address this issue independent of fo we conducted a petrographic and mineral compositional study of occurrences of chromite cr rich spinel in ureilites aimed at determining the origin of the chromite in each occurrence and using primary occurrences to constrain models of ureilite petrogenesis chromite was studied in lew 88774 fo 74 2 nwa 766 fo 76 7 nwa 3109 fo 76 3 hah 064 fo 77 5 lap 03587 fo 74 9 cms 04048 fo 76 4 lap 02382 fo 78 6 and eet 96328 fo 85 2 chromite occurs in lew 88774 5 vol nwa 766 early chromite also occurs in a melt inclusion in olivine in hah 064 and in a metallic spherule in olivine in lap 02382 lap 03587 and cms 04048 contain m sized chromite pyroxene symplectic exsolutions in olivine indicating high cr valence in the primary olivine eet 96328 contains a round grain of chromite that could be a late crystallizing phase tiny chromite grains in melt inclusions in eet 96328 formed in late closed system reactions for 7 of the 8 ureilites we conclude that the relatively oxidizing conditions evidenced by the presence of primary or early chromite pertain to the period of high t igneous processing the observation that such conditions are recorded almost exclusively in low fo samples supports the interpretation that the ureilite feo variation was established during igneous processing on the upb

structural sketch of the hellenic continental margin between the western peloponnesus and eastern crete a structural sketch of the hellenic continental margin and adjacent areas based on numerous seismic profiles obtained in the past few years shows two distinct structural domains an inner extensional domain characterizes most of the continental margin the offshore regions as well as the cretan sea an outer compressional domain extends over the trenches and part of their outer slope we believe that this perplexing pattern is related to the presence of an underlying evaporitic series progressively deformed and piling up against a resistant continental margin the completion of subduction and subsequent continental collision are also involved in this structural framework

trace element analysis of ureilites new constraints on their petrogenesis abstract six ureilites alha77257 alha81101 alh82130 pca82506 kenna and novo urei were analyzed using neutron activation analysis for ca sc cr mn fe co ni zn ga ree w re os ir and au we examined bulk samples as well as acid treated samples in the bulk samples the refractory siderophiles concentrations range from approximately 0 1 to 1 0 times ci chondrites while the volatile siderophiles range from about 0 07 to 0 3 times ci chondrites rare earth elements rees in ureilites are quite depleted and display light and heavy rare earth enrichments the antarctic meteorites display either much less pronounced v shaped patterns or no enrichment in the light rare earths at all in terms of the new trace element results ureilites do not fall into the coherent groups that other workers have defined by chemical or petrographic characteristics trace elements do provide additional constraints on the models for the petrogenesis of ureilites in particular the siderophile element abundances call for simplified models of chemical processing rather than the complex multistage processing called for in silicate fractionation models ree concentrations on the other hand imply multistage processing to produce the ureilites none of the ureilite petrogenesis models extant account for the trace element data these new data and the considerations of them with respect to the proposed ureilite petrogenesis models indicate that the direction of modelling should be toward contemplation of mixtures and how the components we observe in ureilites behave under such conditions

fractional melting and smelting on the ureilite parent body we investigate petrologic and physical aspects of melt extraction on the parent asteroid of the ureilite meteorites upb we first develop a petrologic model for simultaneous melting and smelting reduction of feo by c at various depths for a model starting composition determined from petrologic constraints to have been cv like except for elevated ca al 2 5 ci we determine 1 degree of melting 2 the evolution of mg 3 production of co co2 gas and 4 the evolution of mineralogy in the residue as a function of temperature and pressure we then use these relationships to examine implications of fractional vs batch melt extraction in the shallowest source regions 30 bars melting and smelting begin simultaneously at 1050 c so that mg and the abundance of low ca pyroxene initially pigeonite ultimately pigeonite orthopyroxene begin to increase immediately however in the deepest source regions 100 bars smelting does not begin until 1200 c so that mg begins to increase and low ca pyroxene pigeonite appears only after 21 melting the final residues in these two cases obtained just after the demise of augite match the end members of the ureilite mg range 94 76 in pyroxene abundance and type in all source regions production of co co2 by smelting varies over the course of melting the onset of smelting results in a burst of gas production and very high incremental gas melt ratios up to 2 5 by mass after a few s melting however these values drastically decline to 0 05 in the final increments physical modelling based on these relationships indicates that melts would begin to migrate upwards after only 1 2 melting and thereafter would migrate continuously fractionally and rapidly reaching the surface in a year in a network of veins dikes all melts produced during the smelting stage in each source region have gas contents sufficient to cause them to erupt explosively and be lost however since in all but the shallowest source regions part of the melting sequence occurs without smelting fractional melting implies that a significant fraction of upb melts may have erupted more placidly to form a thin crust 3 3 km thick for a 100 km radius body our calculations suggest that melt extraction was so rapid that equilibrium trace element partitioning may not have been attained we present a model for disequilibrium fractional melting in which ree partitioning is limited by diffusion on the upb and demonstrate that it produces a good match to the ureilite data the disequilibrium model may also apply to trace siderophile elements and might help explain the overabundance of these elements in ureilites relative to predictions from the smelting model our results suggest that melt extraction on the upb was a rapid fractional process which can explain the preservation of a primitive oxygen isotopic signature on the upb

the hellenic margin from eastern crete to rhodes preliminary results abstract complementary data on previously surveyed areas have been obtained and more than 3000 km of continuous seismic profiles along the eastern hellenic continental margin between eastern crete and rhodes have been made among the important preliminary observations we note the relatively great thickness due to probable coarse rapid fill of the margin sedimentary cover which is also intensively affected by extensional faulting the presence of a well defined sedimentary basin lying between the strabo and pliny trench where evaporitic strata exist but where the acoustic facies also suggest coarse fill is probably derived from surrounding topographical highs exposed to erosion during the messinian finally we observe a progressive and perplexing change of the strabo trench structural pattern from west to east which indicates a more complex tectonic regime than we expected we speculate that at the southern margin of the rhodes basin northward thrusting may now be occurring

are ureilites residues from partial melting of chondritic material the answer from magpox calculations performed using magpox show that no bulk compositions having chondritic ca al ratio and within the range of chondritic si mg ratios can produce the olivine pigeonite ureilites which constitute 65 of those for which modal abundances are known as residues of single stage equilibrium partial melting calcium aluminum ratios of 2 3 5 ci are required in addition all the ureilites could not have formed from a single composition at various degrees of reduction because they show no correlation between pigeonite olivine ratio and mg ratio materials with various al mg ratios ranging from subchondritic to superchondritic are required if these materials are primitive i e created by nebular processes rather than planetary igneous processes they are unknown in the meteorite record excess accretion relative to chondrites of 5 10 mol of a high temperature condensate component which was itself almost completely depleted in corundum due to early fractionation could create the necessary compositions the plausibility that such processes occurred on a parent body sized scale is difficult to assess in contrast lodranites can be produced as residues of 3 30 equilibrium partial melting of an average ordinary chondritic composition at the appropriate level of reduction although many features of ureilites suggest that they are relatively primitive residues produced by low degrees of melting of chondritic materials and thus resemble lodranites and other groups of primitive achondrites their predominantly pigeonite olivine mineralogy remains difficult to explain within this simple scenario

extensional compressional tectonics associated with the aegean arc comparison with the andean cordillera of south peru north bolivia extensional compressional tectonics are analysed along the convergent boundaries of the aegean arc and of the andean cordillera of south peru and north bolivia this paper deals only with deformations of miocene pliocene and pleistocene ages the prevailing regime in the aegean basin is extensional yet two compressional tectonic phases of u miocene l pliocene and of l pleistocene age have been recorded they are also known in many places all around the mediterranean thus forces that induce compressional tectonics in the aegean seem to have their origin outside the region they seem to be linked with changes in the conditions of convergence change in rate between the arabo african and eurasian plates beneath the andean cordillera of south peru north bolivia the subduction zone plunges at an angle of 25 30 as it does under the aegean arc there as in the aegean sea tectonics are predominantly extensional and several short lived compressional phases break up this extensional regime the latter may also be induced by changes of the conditions of convergence here between the nazca and south american plates beneath central peru north of the nazca ridge the subduction zone plunges at a small angle about 10 there neotectonic deformations are different in the recent they are essentially compressional or expressed by strike slip faulting geological data from the aegean and andes seem to demonstrate that the compressional deformation in the crust above subduction zones is strongly controlled by the stress conditions along convergent boundaries

mineralogy of meteorite groups approximately 275 mineral species have been identified in meteorites reflecting diverse redox environments and in some cases unusual nebular formation conditions anhydrous ordinary carbonaceous and r chondrites contain major olivine pyroxene and plagioclase major opaque phases include metallic fe ni troilite and chromite primitive achondrites are mineralogically similar the highly reduced enstatite chondrites and achondrites contain major enstatite plagioclase free silica and kamacite as well as nitrides a silicide and ca mg mn na cr k and ti rich sulfides aqueously altered carbonaceous chondrites contain major amounts of hydrous phyllosilicates complex organic compounds magnetite various sulfates and sulfides and carbonates in addition to kamacite and taenite iron meteorites contain carbides elemental c nitrides phosphates phosphides chromite and sulfides silicate inclusions in iab iiicd and iie iron meteorites consist of mafic silicates plagioclase and various sulfides oxides and phosphates eucrites howardites and diogenites have basaltic to orthopyroxenitic compositions and consist of major pyroxene and calcic plagioclase and several accessory oxides ureilites are made up mainly of calcic chromian olivine and low ca clinopyroxene embedded in a carbonaceous matrix accessory phases include the c polymorphs graphite diamond lonsdaleite and chaoite as well as metallic fe ni troilite and halides angrites are achondrites rich in fassaitic pyroxene i e al ti diopside minor olivine with included magnesian kirschsteinite is also present martian meteorites comprise basalts lherzolites a dunite and an orthopyroxenite major phases include various pyroxenes and olivine minor to accessory phases include various sulfides magnetite chromite and ca phosphates lunar meteorites comprise mare basalts with major augite and calcic plagioclase and anorthositic breccias with major calcic plagioclase several meteoritic phases were formed by shock metamorphism martensite 2 fe ni has a distorted body centered cubic structure and formed by a shear transformation from taenite during shock reheating and rapid cooling the c polymorphs diamond lonsdaleite and chaoite formed by shock from graphite suessite formed in the north haig ureilite by reduction of fe and si possibly from olivine via reaction with carbonaceous matrix material ringwoodite the spinel form of mg fe 2sio4 and majorite a polymorph of mg fe sio3 with the garnet structure formed inside shock veins in highly shocked ordinary chondrites secondary minerals in meteorite finds that formed during terrestrial weathering include oxides and hydroxides formed directly from metallic fe ni by oxidation phosphates formed by the alteration of schreibersite and sulfates formed by alteration of troilite

evidence for northward thrusting south west of the rhodes basin models of convergence between the major african and european plates involve a stretching aegean plate whose present motion relative to africa is south west1 3 this motion has resulted in subduction of eastern mediterranean sea floor as shown by seismicity volcanism and morphology the southern boundary of the aegean plate is formed by the hellenic trench intensive study culminating in the use of submersibles and multibeam echo sounding as part of the hellenic arc and trench program4 has outlined the complexity of this boundary detailed reflection profiling which we carried out in autumn 1980 of the eastern portion of the hellenic trench system shows arcward verging thrusting south west of the rhodes basin we conclude that collision of the african continental margin with the hellenic arc is now in progress causing overriding by the mediterranean ridge along the southeastern branch of the hellenic trench system

primary magmatic carbon in ureilites evidence from cohenite bearing metallic spherules metallic spherules containing cohenite fe ni metal sulfides and rare phosphorus bearing minerals occur as inclusions within olivine and pigeonite grains in five low shock ureilites the bulk compositions mineralogy and textures of these spherules indicate that they represent fe ni c s alloys that existed as droplets of immiscible metallic liquid in the magma s from which ureilites crystallized at magmatic temperatures these alloys were carbon saturated and probably coexisted with graphite in the magma this is consistent with the occurrence of graphite crystals as inclusions in olivine in some ureilites and supports the view that graphite in ureilites was a primary magmatic component graphite could have been a residue from the solid source materials that melted to produce the ureilite parent magma s or could have crystallized from the magma s the metallic liquids separated into immiscible fe c liquids and fe s liquids after they were trapped within silicates the fe c liquids contained 4 5 wt c and 3 7 wt ni cohenite was the liquidus phase and started to crystallize at 1200 1225 c forming euhedral and subhedral crystals at the eutectic 1175 c iron containing 7 9 ni and 1 8 c crystallized along with cohenite at lower temperatures the iron exsolved cohenite and possibly iron

the structure and regional significance of the talea ori crete abstract on the basis of detailed geological mapping in the talea ori of crete metamorphic rocks previously interpreted as basement to the plattenkalk series are re interpreted as down faulted parts of the overlying phyllite quartzite series nappe a supposed unconformity separating these two units is shown to be a high angle fault the phyllite quartzite series and overlying nappes were affected by two major deformational phases whereas the plattenkalk series has a simpler structural history and was folded and imbricated by southwards directed overthrusting which emplaced the phyllite quartzite series nappe and other overlying nappes in the oligocene we reject previous models of a huge inversion of the plattenkalk series and we also consider that considerable local inversion by tight to isoclinal folding and thrusting means that the stratigraphic thickness is much less than previously appreciated the differences between the structural and sedimentological histories of the plattenkalk series and the overlying nappes implies that they were separated by a major crustal discontinuity such as a transform or transcurrent fault before the oligocene overthrusting

fish tanks of eastern crete greece as indicators of the roman sea level abstract the ancient fish tanks and fish traps of crete are relics of the roman domination of the island they were usually constructed near the major urban centers of that period the direct relationship of their various functional characteristics with past sea levels and the relatively accurate determination of their construction dates establish them as sensitive indicators of sea level change through space and time the fish tanks presented in detail in this study namely those of matala chersonissos mochlos and sitia and the fish trap in the gulf of zakros have all been reported recorded and or interpreted in regard to their operation by previous researchers in the absence of a comprehensive interdisciplinary approach to the issue uneven methodologies inaccurate data and wrong measurements have led to erroneous conclusions about sea level during their operation and about the size and direction of vertical tectonic movements in eastern crete during the upper holocene the present study is based on a new underwater survey in the course of which the architectural and functional features of the ancient constructions were reexamined precisely their depth from modern sea level was measured and their relationship with coastal landforms indicative of a past sea levels was investigated a review of their manner of operation and their modern submerged position allowed the definition of a roman mean sea level 1 24 m 0 09 m below the present one the submersion of the central and eastern parts of crete included in the same tectonic block with a total length of at least 150 km at an average tectonic rate of 0 65 mm year during the last 1900 100 years occurred as is shown by historical evidence during a paroxysmal tectonic event probably related to the strong earthquake of 1604

the tectonic development of the hellenic arc and the sea of crete a synthesis abstract we use field analyses together with interpretation of aerial photographs orbital imagery and sea beam data to define more accurately the geometry of fault systems in the hellenic arc the tectonics of the area are dominated by extensional processes related to normal faulting we then use sea beam data previous oceanographic studies and extrapolation of field analyses on surrounding islands to describe the fault pattern of the cretan sea basin which is found consistent with the land fault pattern the mechanisms of the late neogene and quaternary deformation of the central and southern aegean region are analysed in terms of stress trajectories as revealed by field studies of fault populations we then examine the subsidence of the sea of crete in terms of a model of uniform stretching of the lithosphere the opening of the sea of crete was cylindrical and did not result in bending of crete this leads us to modify the southern portion of an earlier kinematic reconstruction of aegea in agreement with recent paleomagnetic results the implications of the opening of the sea of crete on the tectonic evolution of the straits to the west and east of crete are discussed finally the uplift of the outer arc is explained by underplating due to subduction

miocene detachment in crete and exhumation p t t paths of high pressure metamorphic rocks a major problem posed by the geology of crete is the horizontal contact of an upper unit without miocene metamorphism onto a metamorphosed lower one with early miocene high pressure low temperature hp lt parageneses this very sharp contact is roughly parallel to the major oligo miocene thrust planes which were reactivated as a large scale detachment which allowed exhumation of high pressure units we describe the extensional deformation and the metamorphic evolution of the lower plate most first order deformation features relate to the retrogression from high pressure to low pressure conditions a n s pervasive stretching is observed everywhere often associated with a top to the north sense of shear the extreme variation of thickness of the phyllite quartzite nappe upper part of the lower plate is probably the result of large scale boudinage similar to the one seen in large outcrops the most important observation is the systematic occurrence of fresh carpholite immediately below the base of the tripolitza nappe except in northwestern crete where a late extensional shear zone is present deeper in the nappe pile carpholite is systematically retrograded this observation reveals a drastically different pt history for the upper part of the phyllite quartzite nappe it also suggests that the late extensional shear zone found along the northern side of crete cuts inside the metamorphic structure and brings the nonmetamorphosed tripolitza nappe directly in contact with the deeper parts of the phyllite quartzite nappe pt t paths suggest a fast temperature decrease in the top of the phyllite quartzite during retrogression and hence during the top to the north shear the deeper part of the phyllite quartzite nappe shows a low temperature regime throughout but its pt path includes an isothermal decompression in the first stage we produce a tentative map of domains having experienced similar pt trajectories during decompression the overall cool regime is related to the continuous underthrusting of cola continental units during exhumation isothermal decompression observed in the core of the phyllite quartzite nappe implies fast exhumation during extension and the faster cooling of the upper part is related to a continuous displacement toward the north of a cooler unit during exhumation single grain 39ar 40ar ages obtained on phengites 15 25 ma in various structural sites are in good agreement with these conclusions and with the geological context suggesting that underthrusting of cold units at the front the accretionnary complex occurred contemporaneously with unroofing below a north dipping detachment near the top of the wedge the age of this detachment is bracketed between the end of the high pressure event 20 ma and the deposition of the breccia early to middle miocene in the neogene basins

origin and tectonic setting of some melange units in turkey a geologic study of three different melange belts in turkey revealed that the melange units in these belts were formed by gravity sliding in basins underlain by continental basement rather than by tectonic crushing in trenches mafic volcanic activity is a characteristic feature of such basins which are located on continental margins adjacent to tectonically active belts the peridotite and gabbro blocks of the melange units were transported but some of the basalts radiolarites and mudstones originated within the basins and hence are not part of an ophiolite suite

eo alpine metamorphism in the uppermost unit of the cretan nappe system petrology and geochronology the uppermost unit of the cretan nappe system consists of ophiolites on the top and an ophiolitic melange at the base

the prina complex in eastern crete and its relationship to possible miocene strike slip tectonics abstract the basal neogene formations in the ierapetra region eastern crete are strongly influenced by a late serravallian tectonic phase which resulted in the breakup of pre existing palaeogeographic patterns important vertical movements caused the southward emplacement of neogene sediments together with parts of the underlying pre neogene nappe pile the resulting chaotic association of exotic blocks and sediments known as the prina complex has the properties of a sedimentary melange it can be traced for more than 15 km from north to south in the north a relatively coherent accumulation of large slide masses overlies deformed neogene coarse clastics and pre neogene rocks distally it comprises a poorly stratified sequence of breccias and intermixed finer grained sediments which locally contains olistostromes and debris flows and interfingers to the south with submarine fan deposits the intricate relation of faulting and gravity sliding in a rapidly subsiding basin can be explained by generation in a strike slip setting it is suggested that the ierapetra basin and its offshore extension the south cretan trough were initiated by sinistral movements along a ne sw oriented fault zone implications of this model for the geodynamic evolution of the south aegean area are discussed

extension and exhumation of the hp lt rocks in the hellenic forearc ridge localized intensive ductile and ductile brittle extension of along the arc orientation is prominent in phyllite quartzite unit pqu rocks in kythera and the adjacent southeastern peloponnese but declines in prominence to the north and to the south along the cretan peloponnese ridge using zircon and apatite fission track dating we find that this structural characteristic is correlated with the youngest zircon fission track cooling ages of 14 to 9 ma and with the highest pressure temperature condition recorded in the metamorphic rocks below the structural detachment the cooling ages of the high pressure phyllite quartzite unit pqu rocks along the hellenic forearc ridge show that exhumation migrated from both crete and from the peloponnese to the area with the youngest ages in kythera and the southeastern peloponnese starting in the early miocene and continuing to the present trench rollback and slab retreat expanded the hellenic arc and this bending of the arc from an initial more rectilinear geometry increased areas of oblique convergence and we suggest this localized the subsequent arc parallel extension and local enhanced exhumation of hp rocks the zircon fit exhumation ages from the arc parallel stretching episode restrict the ductile part of this episode in exposed rocks to between about 14 and 9 ma apatite ft ages suggest brittle along arc extension continued to about 7 ma this episode is proposed to be the result of a temporary higher rate of rollback and slab retreat younger normal faults including those which define the margins of the present hellenic arc show return to arc normal extension

sm nd and rb sr isotopic systematics of ureilites abstract sm nd and rb sr isotopic data are reported for seven ureilites on the basis of sm nd isotopic systematics these ureilites are divided into three groups 1 alh82130 pca82506 and meta78008 2 kenna novo urei and alha77257 3 lew85440 group 1 whole rock samples of these ureilites are highly depleted assemblages 147 sm 144 nd 0 33 0 35 having sm nd model ages consistent with 4 55 ga their rb sr isotopic systematics however require that radiogenic sr present day 87 sr 86 sr 0 716 0 721 was introduced into these rocks at some time later than 4 55 ga group 2 whole rock samples of kenna novo urei and alha77257 and a pyroxene separate from kenna plot on a sm nd isochron with an age of 3 74 0 02 ga and an initial 143 nd 144 nd ratio of 0 50945 2 whole rock samples of these ureilites are heterogeneous mixtures of an unidentified lree enriched component and a lree depleted olivine pyroxene assemblage the lree enriched component is volumetrically minor but has lree abundances sufficiently high to dominate whole rock sm and nd abundances and sm nd ratios our best estimate indicates that it has nd 8ppm and 147 sm 144 nd 0 115 variation in the quantity of lree enriched component present in whole rock samples accounts for most of the variation in their sm nd ratios second order variation is due to varying olivine pyroxene ratios the possibility that 3 74 ga is the crystallization age of kenna novo urei and alha77257 cannot be ruled out however we favour the interpretation that the 3 74 ga isochron records an event in which lree enriched material a metasomatic fluid which was the precursor of the present lree enriched component reacted with a preexisting highly depleted 147 sm 144 nd 0 51 ultramafic assemblage the sr isotopic compositions of eleven samples of kenna whole rocks and various separated fractions are virtually identical 87 sr 86 sr 0 7086 regardless of rb sr ratio there is a positive correlation between sr concentration and degree of lree enrichment in these samples suggesting that the lree enriched component is also sr rich the sr data for kenna could be explained by introduction of radiogenic sr along with the lree enriched material at 3 74 ga and a subsequent rb free history all present rb would have to be terrestrial contamination in this interpretation the sr isotopic compositions of novo urei and alha77257 are not however the same as that of kenna group 3 lew85440 neither has a model sm nd age of 4 55 ga nor plots on the 3 74 ga isochron of the kenna group it might have had an evolution similar to that of the kenna group but involving different times and or isotopic compositions if some samples of group 1 ureilites contain a lree enriched component then this component must have been generated and mobilized on the ureilite parent body or bodies at least twice in the interval 4 55 3 74 ga there is no apparent correlation between oxygen isotopic systematics and sm nd or rb sr isotopic systematics

late miocene to recent tectonic evolution of crete greece geological observations and model analysis abstract using a numerical model we focus on the late middle miocene to recent kinematic evolution of the cretan segment of the hellenic arc geological observations of crete are given a quantitative interpretation in terms of tectonic mechanisms controlling the evolution of the active arc boundary this was achieved by calculating intra plate stress fields for various possible distributions of forces and comparing the models with observations the models address specific questions concerning important changes in the observed horizontal stress patterns we deal with the question of what caused extension to initiate modelling results of the collapse of an earlier formed topography and extensional forces acting on the plate boundary are compared with a newly reconstructed tectonostratigraphy of crete our results suggest that arc normal pull is the dominant force that generates the late miocene extension in the cretan segment of the overriding plate although arc normal pull in combination with intra plate spreading forces cannot be excluded the observed transform motions in the pliny and strabo trenches led us to incorporate experiments with additional resistance on the eastern levantine segment of the hellenic arc the models performed with a transform resistance along the trenches are in agreement with the cretan deformation for the pliocene to recent period the stress fields for the short duration compressional periods around the middle late miocene and the miocene pliocene boundary are modelled by assuming resistive instead of tensional forces acting at the overriding margin

carbonado physical and chemical properties a critical evaluation of proposed origins and a revised genetic model abstract carbonado diamond is the most controversial of all diamond types and is found only in brazil and the central african republic bangui neither an affinity to earth s mantle nor an origin in the crust can be unequivocally established carbonado diamond is at least 3 8 ga old an age about 0 5 ga older than the oldest diamonds yet reported in kimberlites and lamproites on earth derived from neo to mid proterozoic meta conglomerates the primary magmatic host rock has not been identified discovered in 1841 the material is polycrystalline robust and coke like and is best described as a strongly bonded micro diamond ceramic it is characteristically porous which precludes an origin at high pressures and high temperatures in earth s deep interior yet it is also typically patinated with a glass like surface that resembles melting with exotic inclusions of highly reduced metals carbides and nitrides the origin of carbonado diamond is made even more challenging but the challenge is important because a new diamondiferous host rock may be involved and the development of a new physical process for generating diamond is possibly assured the combination of micro crystals and random crystal orientation leads to extreme mechanical toughness and a predicable super hardness the physical and chemical properties of carbonado are described with a view to the development of a mimetic strategy to synthesize carbonado and to duplicate its extreme toughness and super hardness textural variations are described with an emphasis on melt like surface features not previously discussed in the literature but having a very clear bearing on the history and genesis of carbonado selected physical properties are presented and the proposed origins diverse in character and imaginatively novel are critically reviewed from our present knowledge of the dynamic earth all indications are that carbonado is unlikely to be of terrestrial origin a revised model for the origin of carbonado is developed based on 1 new observations which show that white dwarf stars can have diamond cores 2 c rich exoplanets may have diamond bearing mantles and 3 new shock wave experiments on methane suggest that diamond may be present in large gaseous planets such as saturn uranus and neptune where diamond in the core is solid and in jupiter where liquid diamond may be present it is proposed that carbonado diamond was delivered to earth from extra solar sources during the episode of late heavy bombardment 4 1 3 8 ga if the currently held view that r process heavy elements were added as a late veneer to earth through the collision of white dwarfs in kilonova explosions then why not carbonado diamond during this epic event

the neotectonics of the aegean an alternative view minor reverse faults in widely dispersed neogene outcrops in the central aegean have led several people to suggest that the regional extension which started in the lower pliocene or earlier was interrupted by short periods of compression the durations of these postulated compressional episodes are short compared to the time scale on which convective forces acting on the base of the lithosphere can change thus possible mechanisms for driving such motions are limited in this paper we offer alternative explanations for these observations and in particular show that these apparently compressional episodes are probably not regional in extent and may not be truly compressional in origin in some places they are more likely to be a consequence of the considerable rotation that is found in extensional terranes the plio quaternary paleogeography of the central aegean is satisfactorily explained by uplift in the footwall blocks of normal faults and does not require regional compression studies of the faulting associated with recent large earthquakes suggest that the sort of microtectonic analysis which is typically carried out on small faults in surficial sediments is more likely to reflect the internal deformation of blocks bounded by major fault structures than be a reliable indicator of regional stress patterns

comment on parent body depth pressure temperature relationships and the style of the ureilite anatexis by p h warren maps 47 209 227 ureilites are carbon rich ultramafic olivine dominantly low ca pyroxene achondrites with poorly understood petrogenesis one major problem concerns the origin of extensive variation in feo content olivine core fo values ranging from approximately 75 to 95 among the individual ureilites the two main competing hypotheses to explain this variation are 1 equilibrium smelting in which ureilite fo values were established by pressure dependent depth linked carbon redox reactions on the ureilite parent body during partial melting or 2 nebular inheritance in which the variation in feo contents was derived from ureilite precursors and was preserved during partial melting the paper parent body depth pressure temperature relationships and the style of the ureilite anatexis by warren 2012 discusses a series of topics related to ureilite petrogenesis in each case an argument is presented within the context of smelting versus nonsmelting models collectively these arguments create the impression that there are many valid arguments against smelting the purpose of this comment is to point out flaws in some of these arguments and or to show that the issues they address are independent of smelting versus nonsmelting models both equilibrium smelting and nebular inheritance simple anatexis models face challenges in explaining all the properties of ureilites but both remain viable

tectonics of the hellenic trench a synthesis of sea beam and submersible observations abstract detailed bathymetric investigations were performed in four zones of the hellenic trench system in 1978 using the multi narrow beam echo sounder sea beam on r v jean charcot in 1979 a field study using the 3000 m submersible cyana was conducted in three of the four sites covered by sea beam we summarize here the principal tectonic results of these studies and publish the corresponding sea beam maps it is shown that compressional structures affect the sedimentary cover of the outer wall and trench whereas extensional tectonics is present on the inner wall in addition there is evidence that most of the upper sedimentary cover is not subducted but rather piles up in front of the trench to form the mediterranean ridge we suggest that the surface limit of the zone of mechanical decoupling occurs near the base of the inner wall we show that the gross structure of the trench as well as the strain pattern observed is controlled by the kinematics of subduction and we discuss its evolution since its initiation about 13 m y ago

early petrologic processes on the ureilite parent body we present a petrographic and petrologic analysis of 21 olivine pigeonite ureilites along with new experimental results on melt compositions predicted to be in equilibrium with ureilite compositions we conclude that these ureilites are the residues of a partial melting smelting event textural evidence preserved in olivine and pigeonite record the extent of primary smelting in pigeonite cores we observe fine trains of iron metal inclusions that formed by the reduction of olivine to pigeonite and metal during primary smelting olivine cores lack metal inclusions but the outer grain boundaries are variably reduced by a late stage reduction event the modal proportion of pigeonite and percentage of olivine affected by late stage reduction are inversely related and provide an estimation of the degree of primary smelting during ureilite petrogenesis in our sample suite this correlation holds for 16 of the 21 samples examined olivine pigeonite liquid phase equilibrium constraints are used to obtain temperature estimates for the ureilite samples examined inferred smelting temperatures range from 1150 c to just over 1300 c and span the range of estimates published for ureilites containing two or more pyroxenes temperature is also positively correlated with modal percent pigeonite smelting temperature is inversely correlated with smelting depth the hottest olivine pigeonite ureilites coming from the shallowest depth in the ureilite parent body the highest temperature samples also have oxygen isotopic signatures that fall toward the refractory inclusion rich end of the carbonaceous chondrite anhydrous mineral ccam slope 1 mixing line these temperature depth variations in the ureilite parent body could have been created by a heterogeneous distribution of heat producing elements which would indicate that isotopic heterogeneities existed in the material from which the ureilite parent body was assembled

chromium valences in ureilite olivine and implications for ureilite petrogenesis abstract ureilites are a group of ultramafic achondrites commonly thought to be residues of partial melting on a carbon rich asteroid they show a large variation in feo content olivine fo values ranging from 74 to 95 that cannot be due to igneous fractionation and suggests instead variation in oxidation state the presence of chromite in only a few of the most ferroan fo 75 76 samples appears to support such a model microxanes analyses were used in this study to determine the valence states of cr previously unknown in olivine cores of 11 main group ureilites the goal of this work was to use a method that is independent of fo to determine the oxidation conditions under which ureilites formed in order to evaluate whether the ureilite feo variation is correlated with oxidation state and whether it is nebular or planetary in origin two of the analyzed samples lew 88774 fo 74 2 and nwa 766 fo 76 7 contain primary chromite two others lap 03587 fo 74 4 and cms 04048 fo 76 2 contain sub micrometer sized exsolutions of chromite ca rich pyroxene in olivine and one eet 96328 fo 85 2 contains an unusual chromite grain of uncertain origin no chromite has been observed in the remaining six samples fo 77 4 92 3 chromium in olivine in all eleven samples was found to be dominated by the divalent species with valences ranging from 2 10 0 02 1 to 2 46 0 04 the non chromite bearing ureilites have the most reduced cr with a weighted mean valence of 2 12 0 01 i e cr2 cr3 7 33 all low fo chromite bearing ureilites have more oxidized cr with valences ranging from 2 22 0 03 to 2 46 0 04 eet 96328 whose chromite grain we interpret as a late crystallizing phase yielded a reduced cr valence of 2 15 0 07 similar to the non chromite bearing samples based on the measured cr valences magmatic 1200 1300 c oxygen fugacities fo2 of the non chromite bearing samples were estimated to be in the range iw 1 9 to iw 2 8 assuming basaltic melt composition consistent with fo2 values obtained by assuming olivine silica iron metal osi equilibrium for the primary chromite bearing ureilites the corresponding fo2 were estimated again assuming basaltic melt composition to be iw to iw 1 0 i e several orders of magnitude more oxidizing than the conditions estimated for the chromite free ureilites in terms of fo and cr valence properties ureilites appear to form two groups rather than a single cr valence or fo2 vs fo trend the chromite bearing ureilites show little variation in fo 74 76 but significant variation in cr valence while the non chromite bearing ureilites show significant variation in fo 77 95 and little variation in cr valence these groups are unrelated to petrologic type i e olivine pigeonite olivine orthopyroxene or augite bearing the chromite bearing ureilites also have lower contents of cr in olivine than most non chromite bearing ureilites consistent with predictions based on cr olivine melt partitioning in spinel saturated vs non spinel saturated systems under the assumption that at magmatic temperatures graphite gas equilibria controlled fo2 at all depths on the ureilite parent body we conclude 1 that ureilite precursor materials having the fo and cr valence properties now observed in ureilites are unlikely to have been preserved during planetary processing and 2 that the fo and cr valence properties now observed in ureilites are consistent with having been established by high temperature carbon redox control over a range of depths on a plausible sized ureilite parent body the apparent limit on ureilite fo values around 74 76 suggests that the precursor material s had bulk mg that of ll chondrites

map view restoration of aegean west anatolian accretion and extension since the eocene 1 the aegean region greece western turkey is one of the best studied continental extensional provinces here we provide the first detailed kinematic restoration of the aegean region since 35 ma the region consists of stacked upper crustal slices nappes that reflect a complex paleogeography these were decoupled from the subducting african adriatic lithospheric slab especially since 25 ma extensional detachments cut the nappe stack and exhumed its metamorphosed portions in metamorphic core complexes we reconstruct up to 400 km of trench perpendicular ne sw extension in two stages from 25 to 15 ma the aegean forearc rotated clockwise relative to the moesian platform around euler poles in northern greece accommodated by extensional detachments in the north and an inferred transfer fault se of the menderes massif the majority of extension occurred after 15 ma up to 290 km by opposite rotations of the western and eastern parts of the region simultaneously the aegean region underwent up to 650 km of post 25 ma trench parallel extension leading to dramatic crustal thinning on crete we restore a detachment configuration with the mid cycladic lineament representing a detachment that accommodated trench parallel extension in the central aegean region finally we demonstrate that the sakarya zone and cretaceous ophiolites of turkey cannot be traced far into the aegean region and are likely bounded by a pre 35 ma n s fault zone this fault became reactivated since 25 ma as an extensional detachment located west of lesbos island the paleogeographic units south of the izmir ankara sava suture however can be correlated from greece to turkey

petrology of the asuka 881931 ureilite with special reference to crystallization of interstitial silicate melt the asuka 881931 meteorite is an unbrecciated ferroan ureilite and consists mainly of equi granular olivine and pigeonite grains a metal sulfide network interstitial silicates and glass peripheral portions of equigranular olivine grains are often replaced by fine grained forsterite metal aggregates and sometimes by fine grained enstatite metal aggregates these aggregates may have been produced from the equigranular olivine by reduction peripheral portions of equigranular pigeonite grains also are sometimes replaced by fine grained orthopyroxene aggregates with tiny patches of si rich glass and may have been produced from the pigeonite by reduction reaction with silicate melt interstitial silicates are mainly orthopyroxene magnesian pigeonite high ca pyroxene diopside fassaite and cao poor enstatite and they crystallized from interstitial silicate melt interstitial glass is classified into two types si poor and si rich the si poor glass is always in contact with equigranular olivine but the si rich glass never contacts equigranular olivine and is in contact with pyroxene and the metal sulfide network both types of glass were produced from an original interstitial silicate melt but the si poor glass formed mainly by fractional crystallization of pyroxenes and the si rich glass may have formed by addition of si mainly from nearby metal sulfide melt as well as crystallization of pyroxenes the si poor and si rich melts were finally quenched as interstitial glasses under rapid cooling conditions

experimental constraints on ureilite petrogenesis abstract this experimental study explores the petrogenesis of ureilites by a partial melting smelting process experiments have been performed over temperature 1150 1280 c pressure 5 12 5 mpa and low oxygen fugacity graphite co gas conditions appropriate for a hypothetical ureilite parent body 200 km in size experimental and modeling results indicate that a partial melting smelting model of ureilite petrogenesis can explain many of the unique characteristics displayed by this meteorite group compositional information preserved in the pigeonite olivine ureilites was used to estimate the composition of melts in equilibrium with the ureilites the results of 20 experiments saturated with olivine pyroxene metal and liquid with appropriate ureilite compositions are used to calibrate the phase coefficients and pressure temperature dependence of the smelting reaction the calibrated coefficients are used to model the behavior of a hypothetical residue that is experiencing fractional smelting the residue is initially olivine rich and smelting progressively depletes the olivine content and enriches the pyroxene and metal contents of the residues the modeled residue composition at 1260 c best reproduces the trend of ureilite bulk compositions the model results also indicate that as a ureilite residue undergoes isothermal decompression smelting over a range of temperatures ca al values and cr 2 o 3 contents are enriched at lower temperatures below 1240 c and tend to decrease at higher temperatures therefore fractional smelting can account for the high ca al and cr 2 o 3 wt values observed in ureilites we propose that ureilites were generated from an olivine rich cpx bearing residue smelting began when the residue was partially melted and contained liquid olivine and carbon these residues experienced varying degrees of fractional smelting to produce the compositional variability observed within the pigeonite bearing ureilites variations in mineral composition modal proportions and isotopic signatures are best described by heterogeneous accretion of the ureilite parent body followed by minimal and variable degrees of igneous processing

early pliocene sedimentation in the cretan region implications for the timing and amount of vertical motion along the south hellenic arc eastern mediterranean abstract a boxcore taken from the top of a seamount south of crete on the outer south side of the hellenic trench contains allochtonous coarse clastics consisting mainly of rock fragments of alpine basement brecciated early middle pliocene marls and reworked older neogene sediments this mixture of lithologies is interpreted as an early middle pliocene mass flow deposit which can be correlated with similar deposits from adjoining on and offshore areas the wide distribution of these sediments may be related to a period of increased tectonic activity which caused substantial vertical movements in the south hellenic arc it is concluded that at the time of the formation of the mass flow deposits this part of the hellenic trench had not yet evolved

metallic phases and siderophile elements in main group ureilites implications for ureilite petrogenesis abstract metallic phases and siderophile elements are critical to understanding the petrogenesis of the enigmatic ureilite meteorites we obtained petrographic major and minor element and the first in situ trace element data for metallic phases metal sulfides phosphide carbide in 24 main group ureilites of various petrographic types with fo 75 95 the most abundant type of metal 1 3 vol occurs as 10 40 m wide strips along silicate grain boundaries ni contents of this metal range from 0 to 7 3 wt and are correlated with co among all samples ni co 0 64 ci a less abundant type of metal occurs as 5 150 m diameter metallic spherules consisting of cohenite fe 3 c metal phosphide and sulfide enclosed in silicates preferentially low ca pyroxene most samples contain 2 types of sulfide 1 low cr 2 s 4 and troilite abundances of 17 mostly siderophile elements were measured by la icp ms in grain boundary metal spherules graphite sulfides and silicates average compositions of grain boundary metal in 10 samples show decreasing ci normalized abundance with increasing volatility interrupted by depletions in w mo ni and zn and enrichments in au as ga and ge ci normalized os abundances range from 2 to 65 and are correlated with increasing os pt os ni and os pd ratios ci normalized pt os ratios range from 0 3 to 1 bulk cohenite bearing spherules have siderophile element abundances indistinguishable from those of grain boundary metal in the same sample ci normalized patterns of most siderophile elements in the metal are within error identical to those of the bulk rock at 25 40 higher abundances in each sample there are no correlations between siderophile element abundances and fo we infer that at t 1200 c ureilites contained immiscible fe c 3 4 wt c and fe s melts small samples of which were trapped as the spherules within silicates the fe s melt was largely extracted from the rocks and the bulk of the residual fe c melt is now represented by the grain boundary metal assuming that ureilite precursor materials had ci or cv abundances of siderophile elements the large fractionations of hse observed in metal in 7 of the 10 samples require extremely high degrees 98 of batch fe s melt extraction which implies very high x fes wt fes fe fes in the precursors furthermore at such high degrees of fractionation the hse are so strongly concentrated into the residual metal that to match their relatively low absolute abundances in the ureilite metal very high initial metal contents are required together these constraints would imply that ureilite precursors had abundances of fe metal and fes 20 35 wt each far exceeding those of known cc or oc these requirements could be relaxed permitting lower more plausible degrees of melting and lower initial metal and sulfide abundances if ureilite precursors were volatile depleted to a greater extent than bulk cv we suggest that ureilite precursors contained to various degrees an overabundance relative to chondrites of refractory enriched material such as cais excess cais could also account for observed depletions of w and mo otherwise difficult to explain in the ureilite metal and lead to the observed range of siderophile element patterns and abundances among samples such a model can potentially explain the lack of correlation between siderophile element abundances and feo or olivine fo and reconcile the metal and siderophile element data with a redox model for ureilite petrogenesis

application of modflow for simulating groundwater flow in the trifilia karst aquifer greece karst aquifers can have a complex flow as a result of the formation of large conduits from dissolution features as a result a three dimensional finite difference groundwater flow model equivalent porous media may not apply as the dual porosity nature of karst features and the effects of turbulent flow cannot be directly simulated statistical analysis of karst hydrographs of the trifilia aquifer in greece showed the existence of a slightly karstified mass with high primary porosity that regulates the flow an equivalent porous media model was developed to simulate the trifilia karst aquifer using modflow steady state and transient state calibration gave encouraging results for the equivalent porous media approach which does not consider pipe flow or turbulence detailed hydrogeological research conducted in the area helped define the aquifer hydraulic conductivity zones and extent and flux to from the aquifer only hydraulic conductivity and specific yield were adjusted during calibration as the flux to from the system was considered known and applied as boundary conditions small mean absolute and rms piezometric head error of the model under both steady and transient state conditions were achieved

the casanova complex of the northern apennines a melange formed on a distal passive continental margin abstract the cretaceous palaeocene casanova complex occurs in two thrust sheets of the eugeosynclinal ligurids of the northern apennines it is a sedimentary melange with ophiolitic and quartzose turbidites or limestone shale olistostrome submarine debris flows as matrix exotic blocks of ophiolite and granite serpentinite breccias and lenticular ophiolitic breccias and olistostromes contribute to the melange character of the complex deformational structures include soft sediment slump folds indicating a sw dipping palaeoslope and boudins a gradational slumped top to the melange small scale faults in chert blocks and deformation associated with the emplacement of the exotic slide blocks the blocks were shed as rotational slides from submarine fault scarps and are surrounded by haloes of debris created by submarine weathering the stacking pattern of the blocks with the originally stratigraphically highest ophiolite lithologies lowest in the pile of blocks is explained by a diverticulation model with progressively deeper erosion mechanical analysis shows that the blocks were stable when partly exposed resting on a soft sediment substratum criteria which distinguish the casanova complex from a tectonic melange and which may be of value in other melanges are discussed previous interpretations of the complex as a precursor olistostrome to northeastward nappe emplacement the bracco ridge model are rejected the melange is believed to have formed on ocean crust as a result of turbidite and debris flow sedimentation soft sediment deformation block faulting gravity sliding and submarine erosion at the distal edge of a uniformly sw dipping continental margin

shock post shock annealing and post annealing shock in ureilites the thermal and shock histories of ureilites can be divided into four periods 1 formation 2 initial shock 3 post shock annealing and 4 post annealing shock period 1 occurred 4 55 ga ago when ureilites formed by melting chondritic material impact events during period 2 caused silicate darkening undulose to mosaic extinction in olivines and the formation of diamond lonsdaleite and chaoite from indigenous carbonaceous material alkali rich fine grained silicates may have been introduced by impact injection into ureilites during this period about 57 of the ureilites were unchanged after period 2 during period 3 events impact induced annealing caused previously mosaicized olivine grains to become aggregates of small unstrained crystals some ureilites experienced reduction as feo at the edges of olivine grains reacted with c from the matrix annealing may also be responsible for coarsening of graphite in a few ureilites forming euhedral appearing idioblastic crystals orthopyroxene in meteorite hills met 78008 may have formed from pigeonite by annealing during this period the rb sr internal isochron age of 4 0 ga for met 78008 probably dates the annealing event at this late date impacts are the only viable heat source about 36 of ureilites experienced period 3 events but remained unchanged afterwards during period 4 7 of the ureilites were shocked again as is evident in the polymict breccia elephant moraine eet 83309 this rock contains annealed mosaicized olivine aggregates composed of small individual olivine crystals that exhibit undulose extinction ureilites may have formed by impact melting chondritic material on a primitive body with heterogeneous o isotopes plagioclase was preferentially lost from the system due to its low impedance to shock compression brief melting and rapid burial minimized the escape of planetary type noble gases from the ureilitic melts incomplete separation of metal from silicates during impact melting left ureilites with relatively high concentrations of trace siderophile elements

magnetism and mineralogy of almahata sitta polymict ureilite asteroid 2008 tc 3 implications for the ureilite parent body magnetic field the almahata sitta meteorite is the first case of recovered extraterrestrial material originating from an asteroid that was detected in near earth space shortly before entering and exploding in the high atmosphere the aims of our project within the 2008 tc 3 consortium were investigating almahata sitta s as magnetic signature phase composition and mineralogy focussing on the opaque minerals and gaining new insights into the magnetism of the ureilite parent body upb we report on the general magnetic properties and behavior of almahata sitta and try to place the results in context with the existing data set on ureilites and ureilite parent body models the magnetic signature of as is dominated by a set of low ni kamacites with large grain sizes additional contributions come from micron sized kamacites suessite cr troilite and daubreelite mainly found in the olivine grains adjacent to carbon rich veins our results show that the paleomagnetic signal is of extraterrestrial origin as can be seen by comparing with laboratory produced magnetic records irm four types of kamacite i iv have been recognized in the sample the elemental composition of the ureilite vein metal kamacite i particularly co clearly differs from the other kamacites ii iv which are considered to be indigenous element ratios of kamacite i indicate that it was introduced into the upb by an impactor supporting the conclusions of gabriel and pack 2009