indicators of aqueous alteration in cm carbonaceous chondrites microtextures of a layered mineral containing fe s o and ni a petrographic and transmission electron microscopy study of the mighei murchison and murray cm carbonaceous chondrites shows that much of the cm matrix material was probably produced by aqueous alteration of olivine pyroxene sulfide and metal the amount of cm matrix appears to be proportional to the degree of alteration as suggested by mcsween 1979 and microtextures of pcp poorly characterized phase provide evidence of the progressive alteration pcp is divided into two major types one occurs in chondrules and aggregates and consists largely of an fe ni s o phase type i and the other occurs in matrix and consists of the fe ni s o phase and cronstedtite in various proportions type ii microtextures of pcp suggest that it resulted from a three stage alteration process 1 1 type i was produced by alteration of kamacite in chondrules and aggregates presumably early in the parent body regolith 2 2 as the alteration advanced olivine and pyroxene were converted to serpentine type i pcp separated from chondrules and aggregates into the matrix during regolith gardening simultaneously the fe ni s o phase reacted with si released by alteration of olivine and pyroxene producing well formed platy cronstedtite and coherent intergrowths of the fe ni s o phase and cronstedtite the fe ni s o phase also recrystallized into platy and pod like crystals fe s ni cr and p were leached out of type i pcp and were deposited as small grains of fe ni sulfides magnetite chromite and a mineral unidentified containing fe ni cr and p as a result pcp came to consist primarily of the fe ni s o phase and cronstedtite i e type ii pcp 3 3 during continued alteration the well formed crystals of the fe ni s o phase cronstedtite and their intergrowths in type ii pcp were replaced by poorly formed fibers in comparison to other cm chondrites mighei murchison and murray are relatively unaltered their matrices retain abundant amounts of the fe ni s o phase and cronstedtite commonly as distinctive pcp grains which account for a large proportion of the fe in these meteorite matrices in more altered cm chondrites much of the fe ni s o phase was probably consumed to produce cronstedtite magnetite and sulfides with further alteration cronstedtite itself reacted with the serpentine to form ferroan serpentine thus the cm matrix was increasingly enriched in mg with alteration and pcp was increasingly degraded and intimately mixed with the magnesian phyllosilicates

the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

on the formation of fe ni metal in renazzo like carbonaceous chondrites the fe ni metal within chondrites has been postulated to have originated either through condensation or as a byproduct of chondrule formation to test these hypotheses we studied metal in three renazzo like carbonaceous cr2 chondrites from three petrographic settings inside chondrules on chondrule rims and in the matrix abundances of fe ni co cr and p were determined in situ by electron microprobe and those of os ir pt and au were measured by a newly developed ion microprobe technique the refractory platinum group elements os ir and pt behave coherently in cr2 metal they are either all enriched all depleted or unfractionated with respect to fe and cosmic ratios metal with approximately ci os fe ir fe and pt fe occur primarily in chondrule interiors all metal grains have essentially ci values of ni fe and co fe almost all metal grains have lower than ci ratios of the volatile elements au and p we also estimated the bulk compositions via analyses of phases and modal recombination of a subset of the chondrules whose metal we analyzed the bulk compositions of chondrules are generally unfractionated relative to ci chondrites for elements more refractory than cr but are depleted in more volatile elements abundances of siderophile elements correlate strongly with the metal abundance in the chondrules which implies that siderophile depletions are due to expulsion of metal from the chondrule melts the metal most likely originated during melting via reduction of oxides by c that was part of the chondrule precursor during chondrule heating molten metal efficiently extracted siderophile elements from the silicate melt rim metal consists of two types one is like metal in chondrule interiors and was in the process of being expelled when the chondrules were quenched the other shows systematic depletions in os ir and pt relative to fe and higher concentrations of au and p than interior metal this metal is attributed to recondensation from a vapor depleted in refractory siderophiles a vapor most likely derived via evaporation from chondrules large isolated matrix metal grains comprise the same two groups as rim grains and have the same origins bulk chondrule compositions and siderophile abundance patterns in metal indicate that the precursors of cr2 chondrules had ci like abundances of refractory and moderately volatile elements but was likely depleted in the more volatile elements

microchondrules in three unequilibrated ordinary chondrites we report on a suite of microchondrules from three unequilibrated ordinary chondrites uocs microchondrules a subset of chondrules that are ubiquitous components of uocs commonly occur in fine grained chondrule rims although may also occur within matrix microchondrules have a variety of textures cryptocrystalline microporphyritic radial glassy in some cases their textures and in many cases their compositions are similar to their larger host chondrules bulk compositions for both chondrule populations frequently overlap the primary material that composes many of the microchondrules has compositions that are pyroxene normative and is similar to low ca pyroxene phenocrysts from host chondrules primary material rarely resembles olivine or plagioclase some microchondrules are composed of feo rich material that has compositions similar to the bulk submicron fine grained rim material these microchondrules however are not a common compositional type and probably represent secondary feo enrichment microchondrules may also be porous suggestive of degasing to form vesicles our work shows that the occurrence of microchondrules in chondrule rims is an important constraint that needs to be considered when evaluating chondrule forming mechanisms we propose that microchondrules represent melted portions of the chondrule surfaces and or the melt products of coagulated dust in the immediate vicinity of the larger chondrules we suggest that through recycling events the outer surfaces of chondrules were heated enough to allow microchondrules to bud off as protuberances and become entrained in the surrounding dusty environment as chondrules were accreting fine grained rims microchondrules are thus byproducts of cyclic processing of chondrules in localized environments their occurrence in fine grained rims represents a snapshot of the chondrule forming environment we evaluate mechanisms for microchondrule formation and hypothesize a potential link between the emergence of type ii chondrules in the early solar system and the microchondrule bearing fine grained rims surrounding type i chondrules

magmatic evolution of a volcano studied by 230th 238u disequilibrium and trace elements systematics the etna case age determinations of several lava flows from etna through 230th 238u disequilibrium internal isochrons yield a precise chronology of the volcano s history for the last 200 000 years and emphasize the main episodes in the formation of this huge complex strato volcano study of 230th232th 0 initial ratios of lavas together with their trace element compositions yields a consistent model of magmatic evolution implying the existence for 200 000 years of a deep reservoir of alkalic magma periodically mixed with magmas of tholeiitic affinity these short periods of mixing appear to be related to the formation of the large calderas of etna in addition to these processes affecting the deep reservoir fractional crystallization also occurred in more superficial levels of the volcanic edifice thereby yielding several series of differentiation of relatively short duration as for its geochemistry etna s volcanism is of oceanic type but with its own characteristics and in a peculiar geodynamic context at the edge of the african plate

widespread oxidized and hydrated amorphous silicates in cr chondrites matrices implications for alteration conditions and h2 degassing of asteroids abstract the cr chondrites carry one of the most pristine records of the solar nebula materials that accreted to form planetesimals they have experienced very variable degrees of aqueous alteration ranging from incipient alteration in their matrices to the complete hydration of all of their components in order to constrain their chemical alteration pathways and the conditions of alteration we have investigated the mineralogy and fe oxidation state of silicates in the matrices of 8 cr chondrites from type 3 to type 1 fe l edge x ray absorption near edge structure xanes was performed on matrix fib sections using synchrotron based scanning transmission x ray microscopy stxm the fe 3 fe ratio of submicron silicate particles was obtained and coordinated with tem observations in all the least altered cr chondrites que 99177 eet 87770 eet 92042 lap 02342 gra 95229 and renazzo we find that the matrices consist of abundant submicron fe rich hydrated amorphous silicate grains mixed with nanometer sized phyllosilicates the fe 3 fe ratios of both amorphous and nanocrystalline regions are very high with values ranging from 68 to 78 in the most altered samples al rais and gro 95577 fine grained phyllosilicates also have a high fe 3 fe ratio around 70 whereas the coarse micrometer sized phyllosilicates are less oxidized down to 55 and have a lower iron content these observations suggest the following sequence submicron fe2 amorphous silicate particles were the building blocks of cr matrices after accretion they were quickly hydrated and oxidized leading to a metastable amorphous gel like phase nucleation and growth of crystalline phyllosilicates was kinetically limited in most type 3 and 2 crs but increased as alteration became more extensive in al rais and gro 95577 the decreasing fe 3 fe ratio is interpreted as a result of the transfer of fe3 from silicates to oxides during growth while aqueous alteration progressed higher temperature longer duration change of fluid composition in a fully closed system equilibrium thermodynamics suggest that the water to rock ratios typically assumed to be low fe 3 fe ratio such a high fe 3 fe value could be accounted for however if the system was partially open at least with respect to h2 and other gases as well rapid degassing of the fluid would have favored more oxidizing fluid conditions recently proposed scenarios involving some degree of water d h increase through rayleigh isotopic fractionation are supported by these results

late quaternary slip rates on the acireale piedimonte normal faults and tectonic origin of mt etna sicily abstract mt etna is located along the east coast of sicily near the boundary between the continental crust of the hyblean plateau and the mesozoic oceanic crust of the ionian basin the main active faults near mt etna cut the base of its eastern flank forming a 30 km long system of nne and nnw trending ene chelon fault segments the acireale piedimonte system showing dip slip and oblique right lateral motion most segments are associated with shallow depth seismicity and all have late pleistocene to holocene vertical slip rates ranging between 1 and 2 mm yr typical of major active normal faults worldwide eruptive fissures arranged in nne to ne trending zones cut the highest slopes of the volcano on the footwall of the normal fault system structural analysis suggests that current motions along both the active faults and eruptive fissures are kinematically compatible and simply linked with ongoing wnw ese directed regional extension such extension characterizes at a greater scale the active tectonics of southern italy where all large shallow historical earthquakes have remained confined within a narrow normal fault belt or rift zone stretching from the northern calabrian arc to southeastern sicily the southernmost west dipping faults of that rift zone in calabria aspromonte cut across the calabro peloritan thrust belt to join the mostly east dipping acireale piedimonte faults along the western boundary of ionian oceanic lithosphere which continues southwards as the malta escarpment we thus relate magmatism at etna to dilational strain on the footwall of an east facing crustal scale normal fault at the bend where the siculo calabrian rift zone veers 60 eastwards as it begins to cross the calabrian arc leaving the east facing margin of the ionian sea to catch up with the west facing margin of the tyrrhenian sea farther north

volcanism and mantle crust evolution the etna case abstract mount etna is located in a particular region of convergence of african and eurasian plates where intense post collisional tectonics caused considerable uplift however we present arguments supporting the hypothesis that volcanism and associated seismic activity would result from a local mantle uprise leading to a horst probably linked to a deep rooted hot spot it ensued deformation and fracturing of the overlying crust with emission of aphyric tholeiitic basalts directly from their mantle source and subsequent development of a deep reservoir or complex of intrusions at the top of a mantle diapir near 30 km depth this is advocated by the appearance of porphyritic alkaline lavas whose mineral equilibria and differentiation processes are consistent with an 8 10 kbar pressure and by the development of central volcanoes the horst itself appears to have begun in the sw sector of the present volcanic area its uplift was greater westward as seen from the trend of the terraces along the simeto river and became later obvious toward the se these differential movements produced fractures and faults which are to day evident in the southern area of mt etna the growth of the horst then proceeded in a ne direction following the regional tectonic lines and with a greater intensity along the side facing se crossed by the regional nnw sse line aeolian maltese escarpment the seismicity and ground deformation registered over the last twenty years support the proposed model earthquakes are unfrequent in the lower southern and western areas of the volcano whereas they are numerous and stronger to the north east in the summit area above 1600 m a s l and in the eastern sector along the nw se faults and fractures finally a digital elevation model recently published reveals the existence of two tectonic domains the first one is associated with the horst and contains prevalently ne sw oriented faults whereas the second is mainly linked to regional tectonics with nnw sse and nw se faults and fractures

tomographic images and 3d earthquake locations of the seismic swarm preceding the 2001 mt etna eruption evidence for a dyke intrusion 1 on july 12 2001 mt etna experienced a sudden increase of seismic activity heralding one of the most intense eruptions of the past 30 years between july 12 and july 18 when the eruption started thousands of small magnitude earthquakes occurred and were recorded by a dense seismic network run by the istituto nazionale di geofisica e vulcanologia sezione di catania ingv ct hypocentral depths of earthquakes were very shallow mostly located above 3 km b s l and clustered near the summit area the high quality seismic dataset gives us the unique opportunity to study the process of magma migration before the eruption in this study we present the three dimensional earthquake locations and the velocity structure obtained by a tomographic inversion the shallowness of seismicity allowed us to enhance the details of the structure beneath the summit craters in a volume poorly defined by previous tomographic studies the presence of a high vp body previously observed at mt etna is confirmed at shallow depth beneath the southeastern part of the summit area the earthquakes preceding the eruption onset concentrated at its western border a low vp vs anomaly is found at 0 1 km depth just at the top of the volume where the magma intruded before the eruption this anomalous zone can be considered as molten material wealthy in gas the relocated seismicity occurs in a cylinder below the vents activated along the fracture system and exhibited an upward migration until the eruption all these results show evidence for the emplacement of a near vertical dyke striking about n s and a few kilometres south of the summit craters

opaque minerals in the matrix of the bishunpur ll3 1 chondrite constraints on the chondrule formation environment abstract the chemistry and mineralogy of a group of opaque mineral assemblages in the matrix of the bishunpur ll3 1 ordinary chondrite provide insight into the nebular environment in which they formed the assemblages consist of a kamacite fe ni core that is rimmed by troilite fes and fayalite fe2sio4 accessory phases in the rims include silica sio2 chromite fecr2o4 whitlockite ca3 po4 2 maricite fenapo4 magnetite fe3o4 and tetrataenite feni we suggest that the metal melted in and equilibrated with an igneous chondrule under high temperature reducing conditions in this environment the molten alloys incorporated varied amounts of si ni p cr and co depending on the oxygen fugacity and temperature of the melt some of the metal was subsequently expelled from the chondrule interiors into the surrounding nebular gas as the temperature dropped the alloy solidified and volatile elements corroded the metal the main reaction products were troilite and fayalite thermodynamic equilibrium calculations are used to constrain the conditions under which these two phases can form simultaneously in the solar nebula kinetic factors are used to place a lower limit on the formation temperature we determine that the metal corroded between 1173 and 1261 k at a total pressure in the range of 10 5 0 to 10 4 1 bars and a dust gas ratio of 302 to 355 x relative to solar composition these conditions are consistent with our model that the metal corroded in a dust rich region of the solar nebula that was cooling after a chondrule formation event

recent seismicity and tomographic modeling of the mount etna plumbing system the monitoring of seismic activity in eastern sicily southern italy has been recently improved in the framework of the poseidon project to investigate both tectonics and volcanic processes of mount etna this effort has produced a homogeneous and complete data set which we use to image the deep structure of the volcano and to define the space and time distribution of the recent seismicity encompassing the 1995 eruption diffuse eruptions between 1995 and 1997 a further magma intrusion started in 1997 and an increase of volcanic activity in july 1998 we inverted p wave arrival times from 307 selected local earthquakes to obtain a three dimensional velocity model of the volcano with a simultaneous inversion for hypocenters and velocity parameters the new tomographic images permit us to define the structure beneath the volcano from the surface down to 18 km depth the main structural feature revealed by our inversion is a high velocity body located beneath the central craters whose lateral extent increases from 6 km between 18 and 9 km depth to 12 km between 9 and 3 km depth near the surface the fast anomaly branches in two separate high vp regions which are located below the summit craters and the eastern flank valle del bove respectively the high velocity features are interpreted as high density cumulates of solidified magma that intruded the shallow crust we hypothesize that magma ascends the crust within the relatively small high velocity conduit below 9 km depth and is stored at depth shallower than 9 km within the broad high velocity region as also suggested by petrological data a sharp increase of seismicity in 1997 with earthquakes occurring at the border of the high velocity body suggests that mount etna sustained recent episodes of intrusions which possibly herald future eruptions no large low velocity anomaly interpretable as a melted magma chamber is imaged in the upper 18 km of the crust while a broad low velocity anomaly in the uppermost mantle revealed by regional seismic data possibly indicates the magma source region at depth earthquake occurrence from the deep source to the shallow intrusive area helps to trace the magma migration and the feeding of the volcanic system

long term uplift rate of the etna volcano basement southern italy based on biochronological data from pleistocene sediments the eastern flank of mt etna volcano rests on pleistocene marine sediments which unconformably cover the apenninic maghrebian chain units a quantitative biostratigraphic analysis was carried out based on the calcareous nannofossil content of the pleistocene deposits outcropping along the s and ne periphery of the volcano sediments were constrained to the mnn19e and mnn19f biozones deposited from 1 2 to 0 589 ma according to the depth of deposition and the present altitude of the pleistocene succession uplift rates are estimated between 1 1 and 1 7 mm yr 1 for the northeastern sector of the etna edifice and between 0 36 and 0 61 mm yr 1 for the southern one this inhomogeneous long term uplift rate affecting the etna region probably results from a buried thrust below the northern flank of etna which is related to the post tortonian geodynamic evolution of ne sicily

long term behaviour of the late quaternary normal faults in the straits of messina area calabrian arc structural and morphological constraints abstract the calabrian arc is located in the peri tyrrhenian orogenic belt of southern italy and is characterised by intense post collision dynamics this consists of rapid regional uplifting combined with active normal faulting affecting the tyrrhenian side of calabria and the ionian coast of sicily the siculo calabrian rift zone the effects of the two combined processes are well exposed in the straits of messina area that represent a major transfer zone located between two opposing sets of normal faults characterising the southern calabria and the northeastern sicily branches of the rift in the straits of messina region the distribution and elevation of the upper quaternary marine terraces suggest a southward propagation of the normal fault belt from calabria to sicily it occurred at about 125 ka after a long period of tectonic quiescence and was triggered by huge elastic releases in southern calabria the long term behaviour recorded on the distinct fault segments of the rift is to relate to the presence of a crustal barrier that influenced both the geometry and the fault propagation along the rift zone

seismic heterogeneity of mt etna structure and activity a dense seismic array maintained temporarily for 7 weeks provides an approach to deducing the 3 d heterogeneity of the structure of the upper crust beneath mt etna volcano from the inversion of p and s wave arrivals of local earthquakes independent data from a different source array geometry using waves generated by distant shots at sea confirm a main lateral variation a high velocity body underlies part of the volcano its contrast with the surrounding thick sedimentary pile and its location extending from the present summit to the southeast suggests that it may have been built by the development and migration of past eruptive centres followed by caldera collapse local low velocity anomalies near its sharp western edge may be associated with presently active features

opaque phases in type ii chondrules from cr2 chondrites implications for cr parent body formation abstract we report the results of a detailed study of sulfide bearing opaque assemblages from the mac 87320 eet 92011 and renazzo cr carbonaceous chondrites the objectives of this study are to 1 characterize sulfide and associated phases within cr2 chondrites 2 determine the petrographic relationship between sulfides metals and chondrules 3 constrain the history of type ii chondrules 4 ascertain the environments in which type ii chondrules formed and were altered and 5 unravel the formation and alteration history of the cr parent body as recorded in sulfide bearing assemblages sulfide bearing opaque assemblages occur primarily within type ii feo rich chondrules the sulfide assemblages are concentrated near the chondrule edges assemblages in mac 87320 are composed of troilite phosphate and ni rich metal eet 92011 contains assemblages composed of pentlandite troilite and ni rich metal the assemblages in renazzo contain tochilinite magnetite troilite pentlandite and phosphate in all of the assemblages in renazzo the tochilinite is fine grained and intimately mixed with troilite pentlandite or magnetite opaque assemblages in cr chondrites record a complex history that includes both high and low temperature processes the morphology and composition of sulfides in cr2 chondrites suggests that the sulfide bearing assemblages originally formed in gas solid reactions in the nebula at temperatures above the fe fes eutectic 988 c many of the assemblages were subsequently aqueously altered on the cr chondrite parent body to various degrees at temperatures from 50 to 200 c we combine these observations and interpretations to provide a detailed model of the history of the cr parent body

the formation and alteration of the renazzo like carbonaceous chondrites i implications of bulk oxygen isotopic composition abstract to better understand the role of aqueous alteration on the cr chondrite parent asteroid a whole rock oxygen isotopic study of 20 meteorites classified as renazzo like carbonaceous chondrites cr was conducted the cr chondrites analyzed for their oxygen isotopes were dhofar 1432 elephant moraine eet 87770 eet 92042 eet 96259 gao guenie b graves nunataks gra 95229 gra 06100 grosvenor mountains gro 95577 gro 03116 lapaz ice field lap 02342 lap 04720 meteorite hills met 00426 north west africa nwa 801 pecora escarpment pca 91082 queen alexandra range que 94603 que 99177 and yamato 793495 y 793495 three of the meteorites asuka 881595 a 881595 gra 98025 and met 01017 were found not to be cr chondrites the remaining samples concur petrographically and with the well established oxygen isotope mixing line for the cr chondrites their position along this mixing line is controlled both by the primary oxygen isotopic composition of their individual components and their relative degree of aqueous alteration combined with literature data and that of this study we recommend the slope for the cr mixing line to be 0 70 0 04 2 with a 17 o intercept of 2 23 0 14 2 thin sections of al rais shisr 033 renazzo and all but 3 samples analyzed for oxygen isotopes were studied petrographically the abundance of individual components is heterogeneous among the cr chondrites but feo poor chondrules and matrix are the most abundant constituents and therefore dominate the whole rock isotopic composition the potential accreted ice abundance physico chemical conditions of aqueous alteration e g temperature and composition of the fluid and its duration control the degree of alteration of individual cr chondrites combined with literature data we suggest that lap 02342 was exposed to lower temperature fluid during alteration than gra 95229 with only two falls terrestrial alteration of the cr chondrites complicates the interpretation of their whole rock isotopic composition particularly in the most aqueously altered samples and those with relatively higher matrix abundances we report that que 99177 is the isotopically lightest whole rock cr chondrite known 18 o 2 29 17 o 4 08 possibly due to isotopically light unaltered matrix which shows that the anhydrous component of the cr chondrites is isotopically lighter than previously thought although it experienced aqueous alteration que 99177 provides the best approximation of the pristine cr chondrite parent body s oxygen isotopic composition before aqueous alteration took place using this value as a new upper limit on the anhydrous component of the cr chondrites water rock ratios were recalculated and found to be higher than previously thought ratios now range from 0 281 to 1 157 we also find that according to their oxygen isotopes a large number of cr chondrites appear to be minimally aqueously altered although sample heterogeneity complicates this interpretation

relationships between type i and type ii chondrules implications on chondrule formation processes in unequilibrated chondrites the ferromagnesian silicates in chondrules exhibit wide ranges of mg mg mg fe allowing to sub divide porphyritic chondrules into either type i mg 0 9 or type ii mg 0 9 although both chondrule types formed under oxidizing conditions relative to the canonical solar nebula it is generally inferred that type ii chondrules formed in more oxidizing conditions than type i in order to check whether this redox difference was established during chondrule formation or reflects differences in their precursors we have undertaken a set of experiments aimed at heating type i olivine rich a chondrule proxy i e forsterite fe metal ca mg si al glass mixtures under oxidizing conditions we show that high temperature isothermal oxidation of type ia like assemblages is a very efficient and rapid process e g few tens of minutes to form textures similar to type iia chondrules due to the rapid dissolution of fe metal blebs a feo increase in the melt and in combination with the dissolution of magnesian olivine allows the melt to reach ferroan olivine saturation crystallization of ferroan olivine occurs either as new crystal in the mesostasis or as overgrowths on the remaining unresorbed forsterite grains relicts interruption of this process at any time before its completion by rapid cooling allows to reproduce the whole range of textures and chemical diversity observed in type a chondrules i e from type i to type ii several implications on chondrule formation processes can be inferred from the presented experiments type i chondrules or fragments of type i chondrules are very likely the main precursor material involved in the formation of most type ii chondrules formation of porphyritic olivine type ii chondrules is very likely the result of processes generating crystal growth by chemical disequilibrium at high temperature rather than processes generating crystallization only by cooling rates this questions the reliability of chondrule thermal history e g cooling rate values hitherto inferred for producing porphyritic textures from dynamical cooling rate experiments only type a chondrule formation can be a very fast process after periods of sub isothermal heating or slow cooling 103 104 k h in order to preserve their glassy mesostasis such inferred thermal history being at odds with nebular shock models we thus advocate that impacts on planetesimals causing rapid melting and vaporization may provide the high density and highly volatile enriched gaseous environments required to form chondrules in this scenario chondrules and their diversity should result from various degrees of interaction of the ejected fragments with the impact vapor plume the most oxidizing conditions recorded in type iia chondrules being very likely the closest to those imposed by the impact vapor plume

the formation and alteration of the renazzo like carbonaceous chondrites ii linking o isotope composition and oxidation state of chondrule olivine abstract to better understand the formation conditions of type i and type ii chondrules in the renazzo like carbonaceous cr chondrites an in situ major and minor element and o isotope study was conducted twenty one ferromagnesian chondrules from three cr chondrites gra 95229 gra 06100 and que 99177 were analyzed to establish an internally consistent data set from this study we infer that type ii chondrule precursors contained enhanced s bearing dust and ice abundances relative to type i chondrules there is a relationship between the o isotope composition and oxidation state of olivine which may be related to the amount of 16 o poor ice and reduced carbon accreted by chondrule precursors before melting type ii chondrules formed under h 2 o h 2 ratios of 230 740 times solar in contrast type i chondrules formed under more reducing conditions with lower h 2 o h 2 ratios of 10 100 times solar we find a relationship between type ii chondrule petrology relict free vs relict grain bearing and o isotope composition which is due to degree of melting and exchange with a 16 o poor gas reservoir the 16 o poor gas that interacted with both type i and type ii chondrules is estimated to have an isotopic composition between 18 o g 13 27 and 17 o g 10 22 different from the o isotope composition of the water accreted by the cr chondrite parent body due to partial melting type i chondrules and relict grain bearing type ii chondrules exchanged with the 16 o poor gas to a lower degree than relict free type ii chondrules

patterns of tectonic stress in sicily from borehole breakout observations and finite element modeling the orientation of in situ tectonic stress was deduced from borehole breakout analysis of 22 wells from onshore sicily the results allow us to distinguish the stress field of different geological units 1 a nearly nnw 148 orientation is detected in the hyblean plateau 2 a nne shmax direction characterizes the gela area to the north within the thrust belt around mount judica the shmax direction swings to ne in the northeastern segment of the foredeep the catania plain the direction of shmax is roughly parallel to the ne trending grabens that mark the northern margin of the hyblean plateau 3 the southwestern segment of the foredeep has no preferential shmax orientation and may act as a transition zone with isotropic horizontal stresses 4 in western sicily a shmax orientation from n s to nw se is observed this fits well the kinematics of the se migrating egadi and adventure thrust belts and the direction of shortening inferred from the modern seismicity of the area a three dimensional finite element modeling including the most important tectonic features was performed modeling results of the stress field indicate that the nnw trending shmax is locally influenced by the variation of crustal thickness and local zones of weakness in addition the pantelleria rift causes a rotation of the regional nw se stress orientation to nne along the northern rim of the rift system including large on shore areas in the adjacent central south sicily

aqueous alteration in cr chondrites meteorite parent body processes as analogue for long term corrosion processes relevant for nuclear waste disposal aqueous alteration of carbonaceous chondrites is one of the fundamental processes on accreting planetesimals that changes pristine materials from the formation of the solar system the study of mineralogical petrological and chemical changes resulting from this alteration provides insight into the physical and chemical setting of forming planetesimals cr chondrites provide samples for all stages of aqueous alteration from type 3 to 1 entirely hydrated and are thus suited to study the alteration of pristine materials in a coherent sequence vitrification is a common way to store and stabilize fission products and minor actinides resulting from the reprocessing of nuclear spent fuel in a nuclear boro silica glass in steel containers the waste material has to be stored safely for a period of at least 105 106 years in a clay rich geological repository laboratory experiments being too short to follow the long term evolution of these materials we analyzed the mineralogical petrological and chemical changes in a series of cr chondrites renazzo cr2 al rais cr2 and gro 95577 cr1 to serve as analogues rims of secondary materials around metal grains in contact to the fine grained matrix serve as analogue to the interface between steel containment and the surrounding clay rich geological layer while chondrule glassy mesostasis is used as a proxy of the nuclear glass with increasing degree of aqueous alteration in the sequence renazzo al rais gro 95577 the size of the rims increase fe rich alteration rims are 10 m in thickness around metal grains in the fine grained matrix in renazzo in al rais multi layered structures of interchanging fe s and p ca rich layers appear with a thickness of up to 30 m in the highly altered gro 95577 extensive inner and external rims of secondary phases reach up to 200 m into the surrounding matrix in chondrules metal in contact with the altered mesostasis shows similar trends but with thinner alteration rims altered mesostasis is similar to the surrounding fine grained matrix consisting of serpentine and smectite however the chemistry has not completely equilibrated as indicated by e g a remaining high al contents 2 2 wt fine grained matrix and altered mesostasis show a trend towards decreasing fe with progressing alteration matrix is also the main source of s in the alteration system most of the dissolved species stays close to the source the main source for fe ni p and also ti cr and mn is the altered metal these findings confirm the model for long term corrosion of nuclear disposal sites alteration rims of iron oxides form around the steel containments whereas dissolved species fe al and si diffuse into the surroundings

mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites abstract the degree of compositional variation of fine grained minerals displayed by the members within any carbonaceous chondrite group i e ci cm cv cr is a direct reflection of the range of aqueous alteration assemblages present matrix and fine grained chondrule rims within any particular carbonaceous chondrite are mineralogically nearly identical to one another but not necessarily similar in bulk elemental composition even though they have subsequently experienced post accretional secondary processing aqueous alteration under identical conditions this may indicate preferential alteration of one component brecciation exchange of components between rims and matrix and or accretion of matrix and rims from mineralogically or compositionally distinct materials we propose that co chondrites experienced parent body conditions of low f o2 low water rock ratios and temperatures below 50 c cr chondrites experienced higher water rock ratios potentially higher temperatures 150 c and a wide range of f o2 the alteration mineralogy of cv chondrites indicates water rock ratios at the high end at least of the range for cr chondrites essebi and mac 87300 cm chondrites experienced temperatures below 50 c low f o2 and low water rock ratios except eet 83334 which probably experienced relatively higher f o2 and b 7904 and y 86720 which experienced postalteration temperatures in the range 500 700 c most ci chondrites experienced temperatures between 50 and 150 c relatively high water rock ratios and variable f o2 with a late stage increase in the latter due possibly to brecciation and consequent release of methane y 82162 witnessed post alteration heating possibly as high as 400 c

the cr chondrite clan implications for early solar system processes in this paper we review the mineralogy and chemistry of calcium aluminum rich inclusions cais chondrules feni metal and fine grained materials of the cr chondrite clan including cr ch and the metal rich cb chondrites queen alexandra range 94411 hammadah al hamra 237 bencubbin gujba and weatherford the members of the cr chondrite clan are among the most pristine early solar system materials which largely escaped thermal processing in an asteroidal setting bencubbin weatherford and gujba may be exceptions and provide important constraints on the solar nebula models these constraints include 1 multiplicity of cai formation 2 formation of cals and chondrules in spatially separated nebular regions 3 formation of cais in gaseous reservoir s having o 16 rich isotopic compositions chondrules appear to have formed in the presence of o 16 poor nebular gas 4 isolation of cais and chondrules from nebular gas at various ambient temperatures 5 heterogeneous distribution of al 26 in the solar nebula and 6 absence of matrix material in the regions of cai and chondrule formation

crustal structure and seismotectonics of central sicily southern italy new constraints from instrumental seismicity summary in this paper we propose a new model of the crustal structure and seismotectonics for central sicily southern italy through the analysis of the depth distribution and kinematics of the instrumental seismicity occurring during the period from 1983 to 2010 and its comparison with individual geological structures that may be active in the area the analysed data set consists of 392 earthquakes with local magnitudes ranging from 1 0 to 4 7 we defined a new detailed 1 d velocity model to relocate the earthquakes that occurred in central sicily and we calculated a moho depth of 37 km and a mean vp vs ratio of 1 73 the relocated seismic events are clustered mainly in the area north of caltanissetta e g mainland sicily and in the northeastern sector madonie mountains of the study area only minor and greatly dispersed seismicity is located in the western sector near belice and along the southern coast between gela and sciacca the relocated hypocentral distribution depicts a bimodal pattern 50 per cent of the events occur within the upper crust at depths less than 16 km 40 per cent of the events occur within the middle and depth crust at depths between 16 and 32 km and the remaining 10 per cent occur at subcrustal depths the energy release pattern shows a similar depth distribution on the basis of the kinematic analysis of 38 newly computed focal plane solutions two major geographically distinct seismotectonic domains are distinguished the madonie mountain domain with prevalent extensional and extensional oblique kinematics associated with upper crust late pliocene quaternary faulting and the mainland sicily domain with prevalent compressional and compressional oblique kinematics associated with thrust faulting at mid to deep crust depth along the north dipping sicilian basal thrust sbt the stress inversion of the mainland sicily focal solutions integrated with neighbouring mechanisms available in the literature highlights a regional homogeneous compressional tensor with a subhorizontal nnw sse striking 1 axis in addition on the basis of geodetic data the mainland sicily domain may be attributed to the sse ward thrusting of the mainland sicily block along the sbt plane seismogenic shearing along the sbt at mid crustal depths was responsible for the unexpected belice 1968 earthquake mw 6 1 with evident implications in terms of hazard assessment

three dimensional p wave velocity structure of mt etna italy the three dimensional p wave velocity structure of mt etna is determined to depths of 15 km by tomographic inversion of first arrival times from local earthquakes recorded by a network of 29 permanent and temporary seismographs results show a near vertical low velocity zone that extends from beneath the central craters to a depth of 10 km this low velocity region is coincident with a band of steeply dipping seismicity suggesting a magmatic conduit that feeds the summit eruptions the most prominent structure is an approximately 8 km diameter high velocity body located between 2 and 12 km depth below the southeast flank of the volcano this high velocity body is interpreted as a remnant mafic intrusion that is an important structural feature influencing both volcanism and east flank slope stability and faulting

nwa 1152 and sahara 00182 new primitive carbonaceous chondrites with affinities to the cr and cv groups we have investigated the mineralogy petrography bulk chemistry and light element isotope composition of the ungrouped chondrites north west africa nwa 1152 and sahara 00182 nwa 1152 contains predominantly type 1 porphyritic olivine po and porphyritic olivinepyroxene pop chondrules chondrule silicates are magnesium rich fo98 8 1 2 n 36 fs2 3 2 1 wo1 2 0 3 n 23 matrix comprises 40 vol of the sample and is composed of a micron sized silicate groundmass with larger silicate sulfide magnetite and fe ni metal ni 50 wt grains phyllosilicates were not observed in the matrix refractory inclusions are rare 0 3 vol and are spinel pyroxene aggregates or amoeboid olivine aggregates melilite is absent from the refractory inclusions sahara 00182 contains predominantly type 1 po chondrules pop chondrules are less common most chondrules contain blebs of and are often rimmed with fe ni metal and sulfide chondrule phenocrysts are magnesium rich fo92 2 0 6 n 129 fs4 4 1 8 wo1 3 1 1 n 16 matrix comprises 30 vol of the meteorite and is predominantly sub micron silicates with rare larger silicate gains matrix fe ni metal mean ni 5 8 wt and sulfide grains are up to mm scale no phyllosilicates were observed in the matrix refractory inclusions are rare 1 1 vol and melilite is absent the oxygen isotope composition of nwa 1152 falls within the range of the cv chondrites with 17o 3 43 18o 0 70 and is similar to sahara 00182 17o 3 89 18o 0 19 grossman and zipfel 2001 based on mineralogical and petrographic characteristics we suggest nwa 1152 and sahara 00182 show many similarities with the cr chondrites however oxygen isotopes suggest affinity with the cvs thus neither sample can be assigned to any of the currently known carbonaceous chondrite groups based on traditionally recognized characteristics both samples demonstrate the complexity of inter and intra group relationships of the carbonaceous chondrites whatever their classification nwa 1152 and sahara 00182 represent a source of relatively pristine solar system material

why is it so difficult to classify renazzo type cr carbonaceous chondrites implications from tem observations of matrices for the sequences of aqueous alteration abstract a number of different classifications have been proposed for the cr chondrites this study aims at reconciling these different schemes mineralogy based classification has proved particularly challenging for weakly to moderately altered crs because incipient mineral replacement and elemental mobilization arising from aqueous alteration only affected the most susceptible primary phases which are generally located in the matrix secondary matrix phases are extremely fine grained generally sub micron and heterogeneously mixed with primary nebular materials compositional and isotopic classification parameters are fraught with confounding factors such as terrestrial weathering impact processes and variable abundance of clasts from different regions of the cr parent body or from altogether different planetary bodies here detailed tem observations from eighteen fib sections retrieved from the matrices of nine antarctic cr chondrites eet 96259 gra 95229 gro 95577 gro 03116 lap 02342 lap 04516 lap 04720 mil 07525 and mil 090001 are presented representing a range of petrologic types amorphous fe mg silicates are found to be the dominant phase in all but the most altered cr chondrite matrices which still retain significant amounts of these amorphous materials amorphous fe mg silicates are mixed with phyllosilicates at the nanometer scale the ratio of amorphous fe mg silicates to phyllosilicates decreases as 1 the size of phyllosilicates 2 abundance of magnetite and 3 replacement of fe ni sulfides increase carbonates are only abundant in the most altered cr chondrite gro 95577 nanophase fe ni metal and tochilinite are present small abundances in most cr matrices based on the presence abundance and size of phyllosilicates with respect to amorphous fe mg silicates the sub micron features of cr chondrites have been linked to existing classification sequences and possible reasons for inconsistencies among classification schemes are discussed

active tectonic features and structural dynamics of the summit area of mt etna italy revealed by soil co2 and soil temperature surveying project cgl2005 07509 cli ministry of education and science of spain dpc ingv project flank istituto nazionale di geofisica e vulcanologia osservatorio etneo sezione di catania

mineralogy of fine grained rims in the alh 81002 cm chondrite abstract the mineralogy of fine grained rims in alh 81002 a relatively primitive cm carbonaceous chondrite has been determined by using transmission electron microscopy the most abundant phase is mg rich serpentine which occurs in small 20 nm crystals with cylindrical or fibrous morphologies cronstedtite an fe rich phyllosilicate occurs as relatively large 100 to 2500 nm platy crystals some cronstedtite is coherently intergrown with tochilinite in many cases cronstedtite has been partially altered to serpentine the compositions and textures of these two phases provide a mineralogical and morphologic alteration sequence that parallels the known compositional trend for cm chondrite matrix accessory minerals embedded within the phyllosilicates include chlorite pentlandite gypsum olivine kamacite taenite and chromite regions containing only anhydrous minerals also occur the hydrated and anhydrous regions are in direct contact with each other suggesting that the rims accreted material from multiple reservoirs

compositional and genetic relationship between chondrules chondrule rims metal and matrix in the renazzo chondrite individual chondrules coarse and fine grained metal chondrule rims and matrix samples were separated from the renazzo chondrite cr2 and studied by instrumental neutron activation analysis both renazzo chondrule and matrix fractions have ci cr mg concentration ratios unlike chondrules from other classes of chondrites which have fractionated cr mg ratios this and other arguments suggest that renazzo chondrules and matrix formed in the same nebular region in renazzo fine grained metal the dominant metal component is mostly located inside chondrules or in chondrule rims matrix contains few coarse metal grains both types of metal fine and coarse exhibit similar chemical signatures comparatively high in cr and low in ni suggesting a genetic relationship although metal is mostly contained in chondrules chondrules and matrix of renazzo have similar common siderophile lithophile abundance ratios this may imply that renazzo chondrules and metal were formed by reduction of oxidized precursors compositionally similar to ci chondrites the ci like concentrations of sc mg se and zn in renazzo matrix are consistent with this inference the differences in siderophile element pattern between chondrules chondrule metal and matrix indicate evaporation and recondensation of volatile elements during chondrule formation recondensation of evaporated elements was incomplete and the degree of recondensation correlates with element volatility the higher than ci k mg na mg and ga fe ratios of renazzo matrix may reflect recondensation of k na and ga into the matrix the ci se sc and zn sc concentration ratios of the matrix however reflect very limited degrees of recondensation of se and zn into matrix the presence of abundant phyllosilicates and organic material in renazzo matrix requires a low background temperature 200 k during formation of the renazzo meteorite partial recondensation of volatile elements in a cold nebular environment implies instantaneous agglomeration of the renazzo chondrite following chondrule formation

the relationship between late quaternary deformation and volcanism of mt etna eastern sicily new evidence from the sedimentary substratum in the catania region abstract stratigraphical and structural analyses have been carried out on the late quaternary foredeep succession forming the etnean substratum in the catania region eastern sicily in order to investigate in detail the chronology of deformation events that have accompanied a significant period of the eruptive activity of mt etna i e from 240 ka to the present this episode was characterised at about 200 ka by a main change of the petrochemical features of the emitted products from sub alkaline to alkaline this can be related to an evolving mantle diapir located beneath the volcano the new stratigraphical and structural field data presented in this paper constrain the development from 240 to 125 ka of nw se trending dextral faults associated with minor e w to ne sw oriented accommodation thrusts and nnw sse trending normal faults that originated in a dominant transpressive regime strike slip tectonics were active during the earlier emissions of sub alkaline lavas 320 200 ka old and part of the ancient alkaline products 180 100 ka old from scattered eruptive systems which developed in local transtensive zones distributed throughout the whole etnean region a major change in the mode of deformation since 125 ka bp was related to the propagation of a normal fault belt along the ionian coast of the catania region and the eastern sectors of the etnean edifice this process was associated with the growth of open folds that deformed the entire foredeep sequence exposed along the southern boundary of the etnean edifice during this period eruptive activity concentrated along the main extensional features where steady and very efficient feeding systems originated this resulted in a rapid increase in the volume of emitted alkaline products that gave rise to the construction of the modern stratovolcano during the last 80 ka the collected data emphasise some main aspects of the relationship between tectonic deformation at a regional scale and volcanism in the etna area firstly the mode of deformation at the onset of etnean volcanism seems to be inadequate to explain the emplacement at depth of a mantle diapir related to the occurrence of a hotspot almost independent from the local crustal dynamics on the other hand the late quaternary structural assemblages recognised on the surface can be interpreted as direct effects of the europe africa convergence rather than as the products of deformation induced by the emplacement of the mantle diapir in the different stages of etnean evolution a direct relationship exists between the mode of deformation and the distribution as well as the capacity of the feeding systems in particular the amounts of emitted products in the different stages depend on the intensity of crustal stretching associated with deformation rather than the volume of available molten material at depth these conclusions represent a new perspective for the interpretion of the early stages and subsequent evolution of the volcanic activity of mt etna the proposed model also represents an useful tool in deciphering the relationship between the deformation path seismicity and volcanic activity of mt etna

tectonic stresses and volcanism in situ stress measurements and neotectonic investigations in the etna area italy abstract mt etna has been building up for about 500 000 years on the eastern margin of sicily at the external border of the apenninic maghrebian mountain chain and at the crossing of several important regional fault systems the tholeiitic and alkaline magmatism of mt etna represents the northernmost manifestation of present day volcanism which was continuous in space and time from the upper miocene to the lower pleistocene in central eastern sicily in situ stress measurements and neotectonic investigations have been carried out on mt etna on its periphery and on the hyblean mountains to obtain a better understanding of the stress field which is connected to the present day activity of the volcano and a clearer picture of the regional geodynamical evolution the investigations allow a comparison of the present stress field with that acting during the quaternary the neotectonic analysis has given evidence of strong compressional stresses exerted on the pleistocene sediments overlying the substratum of the volcano and its immediate surroundings in addition to evidencing the already known extensional deformation the compressional forces were oriented approximately n s at the beginning of the volcanic activity the in situ stress measurements show now that this n s compression is today active only in the northernmost part of the etna area whereas in the remaining area extensional stresses oriented approximately wnw ese prevail it is concluded that the compressional stresses near the surface today limited to the northernmost part of the etna area had a much more widespread distribution at the beginning of the volcanic activity this conclusion is important for understanding the deep seated magmatic process focal mechanisms of earthquakes indicate a complex tectonic situation with normal faulting down to a depth of 5 km and reverse faulting at deeper levels

opaque assemblages in cr2 graves nunataks gra 06100 as indicators of shock driven hydrothermal alteration in the cr chondrite parent body we have studied the petrologic characteristics of sulfide metal lodes polymineralic fe ni nodules and opaque assemblages in the cr2 chondrite graves nunataks gra 06100 one of the most altered cr chondrites unlike low petrologic type cr chondrites alteration of metal appears to have played a central role in the formation of secondary minerals in gra 06100 differences in the mineralogy and chemical compositions of materials in gra 06100 suggest that it experienced higher temperatures than other cr2 chondrites mineralogic features indicative of high temperature include 1 exsolution of ni poor and ni rich metal from nebular kamacite 2 formation of sulfides oxides and phosphates 3 changes in the co ni ratios and 4 carbidization of fe ni metal the conspicuous absence of pentlandite may indicate that peak temperatures exceeded 600 c opaques appear to have been affected by the action of aqueous fluids that resulted in the formation of abundant oxides fe rich carbonates including endmember ankerite and the sulfide silicate phosphate scorzalite we suggest that these materials formed via impact driven metamorphism mineralogic features indicative of impact metamorphism include 1 the presence of sulfide metal lodes 2 the abundance of polymineralic opaque assemblages with mosaic like textures and 3 the presence of suessite initial shock metamorphism probably resulted in replacement of nebular fe ni metal in chondrules and in matrix by ni rich co rich fe metal al ti cr rich alloys and fe sulfides while subsequent hydrothermal alteration produced accessory oxides phosphates and fe carbonates an extensive network of sulfide metal veins permitted effective exchange of siderophile elements from pre existing metal nodules with adjacent chondrules and matrix resulting in unusually high fe contents in these objects

mount etna dense array local earthquake p and s tomography and implications for volcanic plumbing inversion for the three dimensional velocity structure of mount etna is performed with a data set of arrival times of p and s waves of local earthquakes from temporary dense arrays of three component seismographs a high v p body revealed by the original tomography without nearby stations is confirmed and its image is sharpened using new velocity constraints provided by refraction data synthetic tests of v p and v p v s and comparison with an independent artificial source tomography with a fundamentally different geometry consistently calibrate the significance threshold of the resolution indicators the trustworthy part of the image shows a high v p body centered under the southern part of valle del bove above the 6 km below sea level deep basement which extends towards sea level and may be rooted in or through the crust it has a large contrast of over 1 km s with the surrounding sediments and sharp lateral limits and can thus be regarded as made of intrusive material of magmatic origin the massive high v p body is heterogeneous in v p v s the regions inside it where v s is relatively low can then be suspected of containing a proportion of melt or be fractured and act as pressure links or transport zones such features may be structurally linked and appear to be activated in eruptive phenomena by taking into account the heterogeneities in structure and physical state retrieved by seismic tomography a succession of seismic events deformational episodes and geochemical variation in lavas can be discussed with respect to the well observed eruptions

seismic tomography of etna volcano abstract a 3 d velocity model beneath etna volcano has been obtained through inversion of p wave arrivals of local earthquakes about 300 seismic events distributed around this volcano from surface up to a depth of 20 km have been used to infer the p wave velocity structure high p wave velocity bodies have been found in the upper portion of the volcanic edifice in a region where positive values of bouguer anomalies have previously been found low velocity bodies are identified at depths lower than 10 km and may be related to magmatic reservoirs the spatial pattern of these deeper velocity anomalies appears to be correlated at surface with the distribution of spatter cones in the nw quadrant a high velocity anomaly is correlated to the presence of a deeper seismicity the distribution of relocated hypocenters is not homogeneous but shows some features apparently related to the presence of magmatic bodies

variations in the o isotope composition of gas during the formation of chondrules from the cr chondrites to better understand the environment of chondrule formation and constrain the o isotope composition of the ambient gas in the renazzo like carbonaceous cr chondrite chondrule forming region we studied the mineralogy petrology and in situ o isotope compositions of olivine in 11 barred olivine bo chondrules and pyroxene and silica in three type i porphyritic chondrules from the cr chondrites gao guenie b graves nunataks gra 95229 pecora escarpment pca 91082 and shisr 033 bo chondrules experienced a higher degree of melting than porphyritic chondrules and therefore it has been hypothesized that they more accurately recorded the o isotope composition of the gas in chondrule forming regions we studied the o isotope composition of silica as it has been hypothesized to have formed via direct condensation from the gas bo chondrules constitute 4 of the total cr chondrule population by volume on a three isotope oxygen diagram 17o vs 18o olivine phenocrysts in type i and type ii bo chondrules plot along slope 1 line with the exception of a type ii bo chondrule that plots along slope 0 5 line olivine phenocrysts in type i and type ii bo chondrules have similar but more restricted ranges of 17o values 3 8 to 1 3 and 0 8 to 1 4 respectively than those in type i and type ii porphyritic chondrules 4 6 to 0 3 and 1 8 to 0 9 respectively the observation that olivine grains in type i bo chondrules have similar chemical and o isotope compositions to those of olivine in their porphyritic counterparts argues against the hypothesis that olivine grains in type i porphyritic chondrules are xenocrysts and represent relict fragments of early formed planetesimals the compositional and o isotope data suggest that bo chondrules experienced more extensive but incomplete exchange with the ambient gas than porphyritic chondrules we suggest that cr chondrules formed from relatively 16o enriched solids in the presence of relatively 16o depleted gaseous h2o the o isotope compositions of chondrule olivine likely result from differences in the o isotope composition of both the chondrule precursors and the ambient gas during chondrule formation the inferred o isotope composition of this gas 17o ranges from 3 to 3 is inconsistent with a high abundance of water from the outer solar system which has been predicted to be isotopically heavy

quaternary evolution of the corinth rift and its implications for the late cenozoic evolution of the aegean summary we present geological and morphological observations at different scales to constrain rates of faulting and the distribution of deformation in the seismically active aegean region we focus first on the 130 km long corinth rift an asymmetric graben where a flight of terraces of marine origin are uplifted we show that the edges of the terraces lie in the footwall of the normal fault bounding the corinth rift and correspond to sea level highstands of laic pleistocene age using a detailed analysis of aerial and spot imagery supported by field observations we have mapped 10 terrace platforms and strandlines ranging in elevation from 10 to 400 m over distances of 2 to 20 km from the fault the elevation of the terraces inner edges was estimated at 172 sites with an error of 5m this data set contains a precise description of the uplift and flexure of 10 different palaeohorizontal lines with respect to the present sea level to date the deformation we correlate the corinth terraces with late pleistocene oxygen isotope stages of high sea level stands and with global sea level fluctuations using a thick elastic plate model consistent with our current understanding of the earthquake cycle and a boundary element technique we reproduce the geometry of the shorelines to constrain both mechanical parameters and the slip on the fault we show that the seismogenic layer behaves over the long term as if its elastic modulus were reduced by a factor of about 1000 all the terraces are fitted for fault slip increasing in proportion to terrace age and the component of regional uplift is found to be less than 0 3 mm yr 1 the best fits give a slip rate of 11 3 mm yr 1 on the main rift bounding fault over the last 350 kyr other geological and morphologic information allows us to estimate the total age of the main fault 1 ma and to examine the mechanical evolution of the corinth rift the minimum observed sediment thickness in the gulf places an extreme check on the results of the modelling and a lower bound on slip rate of 6 7 mm yr 1 40 per cent less than estimated with modelling even this slip rate is nearly 10 times higher than for comparable features in most of the aegean and elsewhere in the world at a larger scale the spacing and asymmetry of the rift systems in the aegean suggest strain localization in the upper mantle with slow extension starting 15 myr ago or earlier the more recent 1 myr rapid phase of rifting in corinth partly reactivated this earlier phase of extension the younger faulting in corinth appears to result from its present location in the inhomogeneous stress field process zone of the south westward propagating tip of the southern branch of the north anatolian fault we extend these relations to propose a mechanical model for the late cenozoic evolution of the aegean as the arabia europe collision progressed in eastern turkey it caused anatolia to move to the west and the north anatolian fault to propagate into the aegean where the early slow extension started to be modified about 5 ma ago the process of propagation dramatically increased the activity of some but not all of the earlier rifts the model we present is compatible with tectonic observations as well as with the seismicity the palaeomagnetic rotations and the displacement field now observed with gps and slr

plio quaternary tectonic evolution and structure of the catania foredeep the northern hyblean plateau and the ionian shelf se sicily abstract available multi and single channel seismic reflection profiles calibrated by onshore borehole data have been used for defining the structural styles in the shelf and slope of the ionian sea between catania and augusta se sicily the geological and geophysical data suggest that this area represents a segment of the foredeep foreland system which collapsed after late pliocene times the foundering was controlled by normal faults trending ne sw which flank the southern margin of the catania foredeep onland in outcrop these faults appear largely to be post dated by lower pleistocene sediments nearshore carbonates passing laterally into basinal clays which lie unconformably upon older substrata offshore close to the southern edge of the foredeep seismic lines allow recognition of two distinct units a syn rift wedge upper pliocene submarine tholeiites and sediments and a post rift sequence which can be correlated with lower pleistocene carbonates sands and clays recognisable on land both in outcrop and by borehole data the true frontal part of the thrust belt as detected by the seismic lines occupies the inner part of the area investigated and is buried by upper pliocene and lower pleistocene sediments however the compressive deformation seems to propagate toward the south southeast by means of growing detachment levels developing at depth within pleistocene marine clays for a length of about 10 km ahead of the present day thrust front offshore the faults trending ne sw are dissected towards the east by faults trending nnw sse subparallel to the malta escarpment which flank the edge of the submerged messina rise these faults originating in a steep scarp which drops eastwards to the deep ionian basin have triggered submarine slides and affected the present day seafloor sediments as shown by seismic lines and as stressed by the modern seismicity of the area some of the faults along the malta escarpment could be still active

the formation and alteration of the renazzo like carbonaceous chondrites iii toward understanding the genesis of ferromagnesian chondrules to better understand the formation conditions of ferromagnesian chondrules from the renazzo like carbonaceous cr chondrites a systematic study of 210 chondrules from 15 cr chondrites was conducted the texture and composition of silicate and opaque minerals from each observed feo rich type ii chondrule and a representative number of feo poor type i chondrules were studied to build a substantial and self consistent data set the average abundances and standard deviations of cr2o3 in feo rich olivine phenocrysts are consistent with previous work that the cr chondrites are among the least thermally altered samples from the early solar system type ii chondrules from the cr chondrites formed under highly variable conditions e g precursor composition redox conditions cooling rate with each chondrule recording a distinct igneous history the opaque minerals within type ii chondrules are consistent with formation during chondrule melting and cooling starting as s and ni rich liquids at 988 1350 c then cooling to form monosulfide solid solution mss that crystallized around olivine pyroxene phenocrysts during cooling fe ni metal crystallized from the s and ni rich liquid and upon further cooling mss decomposed into pentlandite and pyrrhotite with pentlandite exsolving from mss at 400 600 c the composition texture and inferred formation temperature of pentlandite within chondrules studied here is inconsistent with formation via aqueous alteration however some opaque minerals fe ni metal versus magnetite and panethite present in type ii chondrules are a proxy for the degree of whole rock aqueous alteration the texture and composition of sulfide bearing opaque minerals in graves nunataks 06100 and grosvenor mountains 03116 suggest that they are the most thermally altered cr chondrites

relationships between organics water and early stages of aqueous alteration in the pristine cr3 0 chondrite met 00426 abstract in order to investigate the nature of organics at the time of their accretion into chondrite parent bodies as well as their subsequent evolution with aqueous alteration we have conducted a study of the morphologies spatial distribution and relationships between organic particles and the surrounding matrix phases in one of the most pristine carbonaceous chondrites currently known met 00426 cr which is therefore likely to contain the best preserved record of pre accretion features focused ion beam sections were extracted for transmission electron microscope observations from its matrix organic matter om shows a heterogeneous population of grains most of them smaller than 1 m diverse morphologies are observed such as compact rounded aggregates individual and aggregated nanoglobules and micron to nanometer sized veins a common feature is the systematic presence of cracks connected to the grains and filled with om the surrounding matrix groundmass consists of amorphous iron rich silicate particles intimately mixed with phyllosilicates sulfides and occasional tochilinite with sizes ranging from several hundreds of nanometers to below 10 nm a close spatial relationship is commonly observed between some of the organic matter particles and alteration phases such as tochilinite and phyllosilicates phyllosilicates sometimes occur intimately intercalated with organic matter at a scale below 10 nm we used tem eds techniques to quantify the water concentration in the matrix amorphous silicate material and the phyllosilicates the water contents of both materials are identical at 10 6 wt h 2 o and demonstrate that the amorphous silicate material in this meteorite is hydrated therefore even though these cr3 0 chondrites are the least altered objects from a mineralogical point of view their matrices contain significant amounts of water in the amorphous silicate this coupled in situ study of organics and aqueous alteration suggests that a significant population of the om accreted as a mixture of soluble and insoluble molecules together with water ice grains and that the om was mobile at the micrometer scale the spatial distribution of the om grains can therefore in part be attributed to parent body processes we suggest that as accreted ice melted hydration of the amorphous silicates and formation of tochilinite and phyllosilicates occurred in the immediate vicinity of the composite water ice organic matter grains the water soluble component of the organics was likely transported and redistributed in the surrounding porosity cracks grain boundaries as water circulated the textural settings suggest that some of the om material could have been polymerized during aqueous alteration and transformed into insoluble molecules perhaps during the last stages of alteration as water was consumed by silicate hydration reactions

oblique rifting in salina lipari and vulcano islands aeolian islands southern italy a structural analysis carried out on the volcanic products of the islands of salina lipari and vulcano aeolian archipelago points out that the large scale tectonic setting is dominated by nw se trending right lateral extensional strike slip faults and by n s to ne sw trending normal faults and fractures this fault pattern generates pull apart type structures developing between different right hand overlapping fault segments and a characteristic extensional imbricate fan geometry at the tip of the major strike slip faults all the structures representing the surface expression of an active crustal discontinuity which controls the evolutionary history of the magmatism of the three islands are kinematically compatible with a n100 e extension related to a rifting process affecting southern italy

quaternary normal faulting in southeastern sicily italy a seismic source for the 1693 large earthquake summary we present geological and morphological data combined with an analysis of seismic reflection lines across the ionian ovshore zone and information on historical earthquakes in order to yield new constraints on active faulting in southeastern sicily this region one of the most seismically active of the mediterranean is avected by wnw ese regional extension producing normal faulting of the southern edge of the siculo calabrian rift zone our data describe two systems of quaternary normal faults characterized by diverent ages and related to distinct tectonic processes the older nw se trending normal fault segments developed up to 400 kyr ago and striking perpendicular to the main front of the maghrebian thrust belt bound the small basins occurring along the eastern coast of the hyblean plateau the younger fault system is represented by prominent nnw sse trending normal fault segments and extends along the ionian ovshore zone following the ne sw trending avola and rosolini ispica normal faults these faults are characterized by vertical slip rates of 0 7 3 3 mm yr 1 and might be associated with the large seismic events of january 1693 we suggest that the main shock of the january 1693 earthquakes m 7 could be related to a 45 km long normal fault with a right lateral component of motion a long term net slip rate of about 3 7 mm yr 1 is calculated and a recurrence interval of about 550 50 yr is proposed for large events similar to that of january 1693

the gro 95577 cr1 chondrite and hydration of the cr parent body we carried out a petrologic and instrumental neutron activation analysis inaa whole chondrite compositional study of grosvenor mountains gro 95577 gro 95577 has many petrological similarities to the cr chondrites although the inaa data show patterns indicative of terrestrial weathering some of the elemental abundances are consistent with a relationship to cr chondrites the oxygen isotopic composition of gro 95577 plots close to the renazzo cr chondrite on the three isotope diagram however gro 95577 is remarkable in that the chondrules are completely hydrated consisting almost entirely of phyllosilicates magnetite and sulfides although gro 95577 is completely hydrated the initial chondrule textures are perfectly preserved the chondrules are in sharp contact with the matrix their fine grained rims are clearly visible and the boundaries of the dark inclusions can be easily discerned many chondrules in gro 95577 have textures suggestive of type i chondrules but the phenocrysts have undergone perfect pseudomorphic replacement by yellow to brownish serpentine rich phyllosilicate with sharp original crystal outlines preserved the chondrule mesostasis is a green aluminous chlorite rich material most likely a hydration product of the feldspathic mesostasis commonly found in anhydrous type i chondrules some chondrules contain magnetite spheres most likely formed by oxidation of metal we propose that gro 95577 be classified as a cr1 chondrite making it the first known cr1 chondrite and expanding the range of alteration conditions on the cr parent body

compositional evolution of the protoplanetary disk oxygen isotopes of type ii chondrules from cr2 chondrites chondrules are the dominant component of chondritic meteorites and attest to high temperature transient heating events within the protoplanetary disk they provide valuable constraint on the disk environments in which they formed and potentially the evolution of primitive planetary materials in the disk the oxygen isotopic composition of cr2 chondrite type ii chondrules was investigated our data show significant variation in the isotopic compositions of the chondrules with no petrographic or geochemical means to identify what chondrule will plot where on a three isotope diagram although we cannot rule out that these chondrules may have come from another chondrite forming region we argue in context of type i chondrules from cr2 chondrites that cr2 type ii chondrules record changes in solid and gas composition during formation due to the vaporization of icy bodies in localized regions of the inner disk

early deformations at a submarine compressive front the quaternary catania foredeep south of mt etna sicily italy abstract in the catania foredeep south of mt etna oil drilling has revealed the existence at depth of an allochthonous complex emplaced during the middle quaternary at the surface outcropping middle quaternary marine marly clays and sands display complex deformations which are partly synsedimentary and which can be correlated with the emplacement of this allochthonous complex most of these deformations are thought to result from gravitational gliding of slope sediment apron this process probably facilitated by high pore pressure would be in particular the cause of a semi penetrative shear deformation with an eastward vergence in the clays thus our study rules out the classical view of a shallow pre etnean gulf that was steadily filled in before emerging some 400 000 to 300 000 years ago this particular example of neotectonics shows the precocity and complexity of deformations occurring in sediments deposited along the compressive margin of a foreland basin or similarly at an accretionary prism front

deformation of the 125 ka marine terrace in italy tectonic implications in peninsular italy marine terraces and shorelines created during oxygenisotope substage 5e known historically as the tyrrhenian highstand provide a reliable and homogeneous datum of vertical motions during the past 125 000 years published accounts of 121 locations on the tyrrhenian inner edge were reinterpreted and used to calculate both local and regional uplift rates the data show arching of southern italy between the tyrrhenian and the adriatic coasts and of the calabrian arc between the sangineto and the longi taormina tectonic lineaments at rates of up to 1 2 mm yr for the past 125 ka they also suggest that the present configuration of the southern apennines is the product of post early pleistocene regional uplift superimposed on tortonian to early pleistocene thrusting uplift patterns are characterised by different wavelength in different geodynamic settings suggesting a close link with the depth of the causative tectonic sources

seismic tomography of the crust underneath the etna volcano sicily abstract a new tomographic inversion of the velocity structure and hypocenter parameters has been carried out in the etna area using a remarkably larger seismic dataset than used in the previous investigations the obtained v p and v p v s space distributions allow us to detail the already known structural features and to find new velocity anomalies a major aseismic high velocity body is recognized in the upper 10 km beneath the central crater area and the southeastern flank of the volcano interpreted as high strength magmatic rocks such as cumulites dike structures etc a high level of seismic activity and low v p values are found immediately to the west and the east of the high velocity body suggesting the presence of highly fractured weakness zones which also taking into account the local distribution of seismogenic stress can be supposed to include paths for magma rising and stationing clear evidence is also found of a shallow aseismic low velocity zone beneath the volcano s southwestern flank corresponding to the volume where previous investigators hypothesized the presence of a magma chamber on the grounds of geodetic data and seismic b value mapping

a chondrule like object captured by space exposed aerogel on the international space station abstract here we report on the mineralogy petrography and oxygen isotope compositions of a micrometeoroid captured on the international space station this micrometeoroid has the texture of a porphyritic olivine chondrule because hydrated phases were not identified in the micrometeoroid and because ni rich sulfide in it does not show exsolution of pentlandite on the tem scale the micrometeoroid probably escaped low temperature events such as aqueous alteration on its parent body however the mean value and standard deviation of cr2o3 wt in olivine in the micrometeoroid suggest that the micrometeoroid experienced weak thermal metamorphism oxygen isotope ratios of pyroxene and olivine in the micrometeoroid are similar to those of chondrule like objects in comet 81p wild2 and coarse grained crystalline micrometeorites as well as those in chondrules in major types of carbonaceous chondrites these data suggest that the micrometeoroid is a fragment of a chondrule like object that was derived from a primitive parent body that experienced thermal metamorphism

different styles of deformation in the calabrian arc southern italy implications for a seismotectonic zoning abstract the most recent seismic profiles in southern italy show the existence of a sudden thinning of the crust at the boundary between the chain and the tyrrhenian margin the abrupt change in thickness can be followed along a zone which has the same geometry in plan as the calabrian arc by considering these data and the gravimetric anomalies it is possible to associate this crustal anomaly with a deep seated shear zone which determines a crustal shortening of about 40 60 km which can only be a consequence of post tortonian tectonics the surface equivalents of the deep seated shear zone can be recognized from north to south in the alignment of the intra apenninic basins vallo di diano san arcangelo potenza in the crati mesima graben and in the mount kumeta alcantara fault zone the distribution of the seismicity and its connection with the surface structures shows that the largest earthquakes occur along the deep shear zone in particular shocks with the highest magnitude and the longest recurrence intervals are located in those areas where the deep shear zone is at an angle of about 90 with the direction of maximum shortening crati mesima graben the fault zones nearly parallel to the regional compression axis e g mount kumeta alcantara fault zone are characterized by earthquakes of lower magnitude taking into account the neotectonic evolution of the regional structures as well as the orientation of the stress field and its connection with the deep seated shear zone it is possible to distinguish the following seismotectonic zones upper crati mesima graben transverse throughs mount pollino mount raparo fault zone external ionian area san arcangelo basin zone of the external flysch sicani mountains mount kumeta alcantara fault zone caltanissetta basin and iblean plateau bradanic trough murge ridge the definition of the geometry of the shear zone at depth is one of the most important but still unresolved problems

the effects of entrained debris on the basal sliding stability of a glacier 1 new laboratory experiments exploring likely subglacial conditions reveal controls on the transition between stable sliding and stick slip motion of debris laden ice over rock with implications for glacier behavior friction between a rock substrate and clasts in ice generates heat which melts nearby ice to produce lubricating water an increase in sliding speed or an increase in entrained debris raises heat generation and thus meltwater production unstable sliding is favored by low initial lubrication followed by rapid meltwater production in response to a velocity increase low initial lubrication can result from cold or drained conditions whereas rapid increase in meltwater generation results from strong frictional heating caused by high sliding velocity or high debris loads strengthening of the interface healing during stick intervals between slip events occurs primarily through meltwater refreezing when healing and unstable sliding are taken together the experiments reported here suggest that stick slip behavior is common from motion of debris laden glacier ice over bedrock

late cenozoic subduction complex of sicily abstract besides remnants of hercynian deformations in the peloritani nappe and of pre oligocene alpine structures in the troiani nappe most compressive structures observed in the sicilian accretionary wedge result from the late cenozoic tortonian to present continental subduction of the apulia iblei block and are thus synchronous with distensive structures related to the opening of the tyrrhenian sea syntectonic deposits fill southward migrating foredeeps in a sequential fashion and the dating of these deposits helps to constrain the timing of deformation similarly plio quaternary sediments eroded from the accreted units rest on top of the allochthon in either compressive piggy back depressions or extensional basins the age and configuration of these overlap deposits constrain our reconstructions of the subsurface geometry of the underlying peri tyrrhenian detachment faults or s verging thrust faults post depositional erosion normal faulting and syntectonic filling of basins contribute to maintaining the critical taper of the prism whose geometry is continuously altered owing to frontal accretion underplating and isostatic uplift

the morphostructural setting of mount etna sedimentary basement italy implications for the geometry and volume of the volcano and its flank instability abstract the reinterpretation of more than 2500 subsurface data consisting of geoelectric and borehole prospecting undertaken at mount etna allows reconstructing the contour map of the sedimentary basement this reconstruction highlights a complex asymmetric topography due to the inhomogeneous long term updoming of the region and the interrelationship between the development of the drainage network and flank instability these different processes have produced a major morphological difference between the eastern sector characterised by a 17 km wide horseshoe shaped depression and the other flanks formed by palaeovalleys the origin of the wide horseshoe shaped depression can be attributed to the large scale flank instability processes involving the entire continental margin in the etna offshore this depression of the etna basement was generated by a series of coalescent landslides before the beginning of the eruptive activity of the timpe phase more than 220 ka ago this wide depression is the main cause of the flank instability that produced the gravitational slope failures of the valle del bove about 10 ka ago regarding mt etna s geometry we have estimated a total volume of about 532 km 3 that was emplaced during the past 330 ka resulting in an average rate of volcanic output of 0 0016 km 3 a the reconstruction of the temporal variation of the average eruptive rate highlights a drastic increase of volcanism during the last 100 ka in response to the gradual stabilization of the plumbing system in the etna region that led to the build up of the composite stratovolcano structure the data presented in this paper represent the state of knowledge of the sedimentary basement of etna which can be used for future studies aimed at developing a detailed understanding of the deep structure of the volcano s unstable flanks

silicon isotopic compositions of chondrule silicates in carbonaceous chondrites and the formation of primordial solids in the accretion disk abstract we determined the silicon isotopic compositions of silicates olivine and low ca pyroxene in type i and type ii chondrules of the carbonaceous chondrites allende kaba nwa northwest africa 5958 and mil miller range 07342 type i chondrule silicates show large mass dependent si isotopic fractionations with 30 si values ranging from 7 to 2 6 whereas the 30 si values of type ii chondrule silicates are close to zero and vary by less than 2 when present mg rich relict olivine grains in type ii chondrules show larger si variations than their feo rich counterparts in type i chondrules low ca pyroxenes yield systematically lighter 30 si values than mg rich olivines our results show that type i chondrules are complex objects whose si isotopic compositions derived from their precursors and sio rich gas melt interactions this corroborates that type i chondrules are nebular products that formed under open system conditions our data also suggest that at least some type ii chondrules derived from their type i counterparts overall this demonstrates that recycling was common during the evolution of the protoplanetary disk

the interaction of volcanic activity in quaternary times upon the evolution of the alcantara and simeto rivers mount etna sicily summary the interaction between volcanic and alluvial sequences is described for the alcantara and simeto valleys mount etna sicily this study provides valuable information on the stratigraphy for prehistoric lavas exposed on the lower western flanks of the volcano eight orders of terrace are recognised in the simeto valley the basal tholeiitic volcanics the oldest exposed lavas of etna are associated with terrace 7 of the simeto which is correlated with either the pre rianian nomentanan erosive phase or the early rianian stage of the pleistocene the earliest evidence of trachybasaltic volcanism in the simeto catchment occurs in terrace 4 which is considered to be of late maspinian age the oldest known volcanics in the north western part of the volcano are related to terrace 3 which is dated at around 20000 bp the alluvial deposits of these terraces provide a valuable sequence of italian quaternary sediments dating back over the last 300000 years the nature of these deposits is described and the probable conditions of their deposition considered the terraces in the upper part of the alcantara are quite different in their mode of formation from the lava capped cut and fill terraces of the simeto valley the current upper course of the alcantara river is considered to be quite youthful versilian in age and the terraces are bench features formed as the river cut down through the lava sequence

the feeding of the eruptive activity of etna volcano the regional stress field as a constraint to magma uprising and eruption an analysis of the structural lineaments as observed on the middle and upper slopes of etna volcano was made with the aim of checking stress distribution within the volcanic structure

the semarkona meteorite first recorded occurrence of smectite in an ordinary chondrite and its implications abstract semarkona is an unshocked unequilibrated ordinary chondrite much of the interchondrule matrix and the mesostases of some chondrules and clasts have been hydrothermally altered analyses of altered materials and opaque matrix are presented ca and fe have been redistributed from primary anhydrous phases into calcite and na fe smectite respectively in semarkona the process possibly requires open system behavior inconsistent with the conventional view of metamorphism of the ordinary chondrites the low petrologic type previously assigned to semarkona is the result of retrograde metamorphism under aqueous conditions of a higher temperature mineral assemblage semarkona and possibly bishunpur should be assigned to petrologic type 2