palaeomagnetism of the late precambrian vadso and barents sea groups varanger peninsula norway abstract a palaeomagnetic study has been made on neoproterozoic rocks from the varanger peninsula northernmost norway several of the formations studied contain a stable magnetization of diagenetic origin two main groups of directions were obtained one a with a steep southeasterly positive direction the other b with a shallow northern direction the group a direction is not in accordance with the stratigraphic age of the rocks and the fennoscandian apparent polar wander path hence it may reflect a remagnetization the group b direction yields a late riphean early vendian palaeopole at 24 n 207 e dp 5 dm 11 n 11 in good agreement with data from contemporary rocks of the kola peninsula the varanger peninsula is transected by the trollfjord komagelv fault which divides the peninsula into the allochthonous barents sea region and the autochthonous varangerfjord region previous palaeomagnetic studies have suggested that the barents sea region has moved 500 to 1000 km to its present position this study indicates that the movement has been less than 250 km which is in better agreement with geological information

paragenesis of sodic pyroxene bearing quartz schists implications for the p t history of the sanbagawa belt sodic pyroxene jadeite content x jd 0 1 0 3 occurs locally as small inclusions within albite porphyroblasts and in the matrix of hematite bearing quartz schists in the sanbagawa sambagawa metamorphic belt central shikoku japan the sodic pyroxene bearing samples are characteristically free from chlorite and their typical mineral assemblage is sodic pyroxene subcalcic or sodic amphibole phengitic mica albite quartz hematite titanite epidote spessartine rich garnet occurs in mn rich samples sodic pyroxene in epidote bearing samples tends to be poorer in acmite content average x acm 0 26 0 50 than that in the epidote free samples x acm 0 45 0 47 x jd shows no systematic relationship to metamorphic grade and is different among the three sampling regions saruta gawa asemi gawa and bessi besshi the average x jd of the saruta gawa samples 0 21 0 29 is higher than that of the asemi gawa 0 13 0 17 and bessi 0 14 0 23 the p t conditions of the asemi gawa and bessi regions are estimated at 5 5 6 5 kbar 360 c in the chlorite zone 7 8 5 kbar 440 15 c in the garnet zone and 8 9 5 kbar 520 25 c in the albite biotite zone metamorphic pressure of the saruta gawa region is systematically 1 1 5 kbar higher than that of the asemi gawa and bessi regions and materials of the saruta gawa region have been subducted to a level 3 5 km deeper than materials that underwent metamorphism at equivalent temperatures and are now exposed in the asemi gawa and bessi regions pressure slightly increases toward the north structurally high levels through the sanbagawa belt of central shikoku two types of zonal structure were observed in relatively coarse grained sodic pyroxenes in the matrix one type is characterized by increasing x jd from core to rim the other type by decreasing x jd from core to rim both types of zoned pyroxenes show an increase in x fe 2 fe2 fe2 mg from core to rim the first type of zoning was observed in a sample from the chlorite zone of lowest grade whereas the latter occurs in the garnet and albite biotite zones of higher grade the contrast in zonal structure implies that dp dt during prograde metamorphism decreased with increasing metamorphic grade and may have been negative in some samples from the higher grade zones the estimated dp dt of the prograde stage of the chlorite zone is 3 2 kbar 100 c and that of the garnet and albite biotite zones is 1 8 to 0 9 kbar 100 c the variation of dp dt at shallow and deep levels of a subduction system probably reflects the difference of heating duration and or change in thermal gradient of the subduction zone by continuous cooling of the surrounding mantle

the sedimentary expression of oceanic anoxic event 1b in the north atlantic abstract the aptian albian oceanic anoxic event 1b contains the record of severalperturbations in the global carbon cycle and multiple black shale levels particularly in the western tethys the local lithological expression of anoceanic anoxic event depends on palaeogeographical and depositional settingas well as on regional palaeoclimate marine sediments at a particular locationmay therefore be more or less organic rich or not at all and they may consistof different lithologies in most studies however much of the lithologicalvariability associated with oceanic anoxic events is left unaccounted for and thus the exact processes leading to the enrichment of organic matter in thesemarine sediments and their subsequent preservation in the geological recordare unknown this study focuses on the local sedimentary processes behindthe deposition of organic rich sediments at deep sea drilling project site 545and ocean drilling program sites 1049 and 1276 in the north atlantic duringoceanic anoxic event 1b although speci cally dealing with the sedimentsdeposited during this particular event at these localities it is expected that thesame processes were responsible for determining the exact sedimentaryproducts at localities in similar settings as well as during other similar eventsin the mesozoic here it is shown that the deposition of organic richsediments during oceanic anoxic event 1b was a consequence of theenhanced productivity favoured by upwelling and by riverine nutrientinput or aeolian fertilization of the euphotic zone depending ongeographical location slope instability processes resulted in the transfer ofpart of these organic rich sediments from the shelf to deep sea depocentres asmud laden organic rich turbidites especially in the northern north atlantic the so called black shales are much more varied than their name implies the end product of sedimentation during an oceanic anoxic event at aparticular location is commonly the result of several equi nal processes actingon a local scale rather than the direct result of basinal or even globalmechanisms keywords aptian albian kilian event north atlantic oae 1b oceandrilling program oceanic anoxic event paquier event

characterization of an early metamorphic stage through inclusions in zircon of a diamondiferous quartzofeldspathic rock from the erzgebirge germany about 1000 zircon grains from a diamondiferous quartzofeldspathic rock of the saxonian erzgebirge were investigated for inclusions using optical microscopy and confocal laser raman spectroscopy cathodoluminescence imagery was applied to characterize the growth zone of zircon where the inclusions occurred the most abundant inclusion minerals are microdiamonds coesite was not detected however garnet and jadeite occur as rare inclusions in zircon cores where diamonds are lacking jadeite was detected for the first time in quartzofeldspathic rocks from the crystalline complex of the erzgebirge the compositions of the pristine garnets in the zircons are similar to those of core areas of millimeter sized garnets but the original garnet composition of the early metamorphic stage is only preserved in zircon intracrystalline diffusion at temperatures as high as 1000 c resulted for instance in higher ti concentrations in garnet cores compared with garnet enclosed in zircon rutile quartz and the compositions of jadeite and garnet inclusions in zircon and of phengite inclusions in cores of large garnets were applied for geothermobarometry the results related to an early metamorphic stage are 650 c and 18 kbar which represent conditions at the base of a thickened continental crust before deeper subduction

igneous and metamorphic petrology of the eclogitic seljeneset meta anorthosite and related jotunites western gneiss region norway abstract the seljeneset meta anorthosite consists of deformed and metamorphosed anorthosite and mafic rocks is situated in the high grade western gneiss region wgr of norway and is adjacent to the 1 52 ga flatraket quartz monzonite mangerite the wgr was metamorphosed to eclogite fades during caledonian tectonism 414 16 ma ago the meta anorthosite contains 46 57 wt sio 2 and displays chondrite normalized ree patterns typical of anorthosite indicating that metamorphism did not significantly affect ree abundances norms indicate that igneous anorthosite consisted of 90 modal plagioclase minor mafic silicates and 1 fe ti oxide mafic rocks 43 48 wt sio 2 are rich in total fe 2 o 3 13 20 tio 2 3 4 and p 2 o 5 1 3 poor in cr jotunites which are characteristic of proterozoic anorthosite mangerite complexes jotunite originally consisted of 50 modal andesine 25 mafic silicates 10 fe ti oxide and up to 7 apatite ree patterns of jotunite are highly variable which reflects variable igneous abundances and modification by metasomatism filter pressing of residual liquid trapped between cumulus plagioclase may have been important in the evolution of anorthosite and jotunite anorthosite contains ultramafic xenoliths high mgo cr and ni and depleted in lree which suggests that some mantle derived peridotite was present in the baltic crust by mid proterozoic time this may extend the crustal history of norwegian garnet peridotites by over one billion years seljeneset rocks display evidence of retrogression from eclogite through amphibolite facies meta anorthosite consists of ovoidal clots of margarite quartz plagioclase and relict kyanite set in a matrix of zoisite clinozoisite plagioclase quartz hornblende and biotite phase equilibria analysis of sequential assemblages shows that meta anorthosite records a retrograde p t path from 15 17 kbar to 4 3 8 2 kbar at 450 600 c mafic rocks vary from moderately well preserved eclogite through varieties containing symplectite to dynamically recrystallized amphibolite in one sample the rare na ca amphibole magnesio alumino taramite appears to be part of the eclogite assemblage calculations indicate eclogite formation at p 16 18 kbar at 750 c some mafic rocks contain veins and segregations of biotite muscovite pyrite allanite and zircon that considered together with geochemical data indicate metasomatic introduction of k rb ba ga s and rare earth and other high field strength elements by channelized fluids during retrogression the seljeneset meta anorthosite associated jotunites and adjacent flatraket quartz monzonite likely constitute a single complex here named the nordpollen plutonic complex this complex was emplaced 1 52 ga ago metamorphosed to eclogite facies during silurian continent continent collision largely retrograded to amphibolite facies during uplift of the orogen and locally metasomatised during retrogression

a geothermobarometric investigation of garnet peridotites in the western gneiss region of norway in the western gneiss region of norway are found numerous peridotite lenses which have been extensively recrystallized under amphibolite fades conditions during the caledonian orogeny however evidence for an earlier caledonian high pressure metamorphism has been recorded by abundant eclogite and granulite relicts within gneiss and by the presence of at least ten garnet perioditite bodies preserved within chlorite peridotites two garnet bearing ultramafic assemblages have been recognized olivine orthopyroxene clinopyroxene garnet and olivine ortho pyroxene pargasitic amphibole garnet

testing 87sr 86sr as a paleosalinity indicator on mixed marine brackish water and terrestrial vertebrate skeletal apatite in late paleocene early eocene near coastal sediments mississippi abstract mixed marine brackish water and terrestrial vertebrate skeletal apatite is found in the late paleocene early eocene tuscahoma and bashi formations of mississippi the co occurrence in these near coastal marine deposits of skeletal apatite with different provenances offers a unique opportunity for unraveling the effects of diagenesis on apatite 87sr 86sr composition with bearings on the use of this isotope pair as paleosalinity indicator the results show that the sr isotopes of all originally poorly ordered phases of skeletal apatite have extensively re equilibrated with pore water with significantly lower 87sr 86sr ratios than late paleocene early eocene seawater for example marine shark and ray teeth from the bashi formation all have clearly nonmarine 87sr 86sr ratios 0 7073 0 7075 compared with a coeval seawater ratio in the range 0 7077 0 7078 however separated shark tooth enamel with a high original crystallinity appears to have retained all or most of its in vivo sr isotopic signature until the present here we also show that 87sr 86sr results on recent vertebrate skeletal material from different environments are in good agreement with expected values for respective habitat earlier analyses of calcite material from the bashi formation indicated the existence of a shift in seawater 87sr 86sr to a lower value at the paleocene eocene boundary the strong influence of pore water with low nonmarine 87sr 86sr on the apatite in the bashi formation suggests that the proposed isotopic shift may be an artifact related to diagenetic processes

origin of fibrous gypsum in the newark rift basin eastern north america abstract cores from the red beds constituting the upper triassic passaic formation a syn rift sequence in the newark basin display subhorizontal fractures veins filled with satin spar gypsum such veins are apparent in the shallow subsurface 100 300 m below present ground level but are not observed in outcrops or in quarries because of groundwater dissolution these fractures are roughly parallel to the present ground surface in the basin suggesting topographic influence on their formation fractures observed in cores are seen to crosscut stratigraphic boundaries indicating that the veins formed after stratal tilting and faulting and thereby post date the early late jurassic the gypsum crystals making up the vein fill grew perpendicular to the fracture walls suggesting that opening and filling of the fractures was contemporaneous and that the fractures are extensional that gypsum crystallizes from meteoric and connate waters and is derived by dissolution of associated evaporites is reflected in the d 18o 34s and 87sr 86sr isotopic compositions of the sulfate fractures are interpreted to be a result of unloading and exhumation fractures were initiated after major depositional and tectonic events took place and post date the late jurassic satin spar precipitated in those fractures carried in by gypsum saturated brines derived either by dissolution of the near surface sulfate evaporites or rehydration of more deeply buried anhydrite such satin spar veins are not evaporites but are composed of chemically remobilized sulfate

development of slaty cleavage and degree of very low grade metamorphism a review illite crystallinity ic and other indicators of the grade of very low grade metamorphism associated with the appearance of various stages of slaty cleavage in phyllosilicate rich rocks have been compiled from a wide variety of terranes ic values have been converted to a kubler equivalent standard scale but the diverse characterizations of the cleavage fabrics in published descriptions do not always allow an unequivocal identification of equivalent stages of cleavage development nevertheless there exists a distinct relationship between grade and the appearance of various stages of cleavage development 1 indications of incipient slaty cleavage such as s0 s1 pencil structure appearance of primary s1 crenulation cleavage and of closely spaced cleavage without parallel fabric in the microlithons is associated with a wide range of mostly medium and high grade diagenetic ic values 2 the appearance of smooth cleavage with a strong parallel fabric in the microlithons and or quartz mica beards and the chlorite mica stacks shortened at a high angle to 001 and of irregular cleavage in sandy beds is associated with a much narrower range of predominantly low and medium grade anchimetamorphic grades rarely high grade diagenetic the first appearance of these stages of cleavage development with higher grades can often be related to post kinematic magmatic heating polymetamorphism pre cleavage metamorphism or static recrystallization without cleavage formation for example in low strain zones there exists a relationship between finite strain fabric and metamorphic grade in mudstones and slates in coarser clastic rocks the same finite strain fabric relationship occurs at appreciably higher grades a relationship between finite strain in carbonate rocks and ic in the nearby rocks has been reported from the helvetic zone of the swiss alps the earlier stages of cleavage formation are associated with little improvement in ic the narrow range of ic associated with smooth cleavage is concluded to represent recrystallization and grain growth concurrent with cleavage formation

pre caledonian granulite and gabbro enclaves in the western gneiss region norway indications of incomplete transition at high pressure the western gneiss region of norway is a continental terrane that experienced caledonian high pressure and ultrahigh pressure metamorphism most rocks in this terrane show either peak caledonian eclogite facies assemblages or are highly strained and equilibrated under late caledonian amphibolite facies conditions however three kilometre size rock bodies flatraket ulvesund and krakenes in outer nordfjord preserve pre caledonian igneous and granulite facies assemblages and structures where these assemblages are preserved the rocks are consistently unaffected by caledonian deformation the three bodies experienced high pressure conditions 20 23 kbar but show only very localized about 5 eclogitization in felsic and mafic rocks commonly related to shear zones the preservation of pre caledonian felsic and mafic igneous and granulite facies assemblages in these bodies therefore indicates widespread 95 metastability at pressures higher than other metastable domains in norway late caledonian amphibolite facies retrogression was limited the degree of reaction is related to the protolith composition and the interaction of fluid and deformation during the orogenic cycle whereby metastability is associated with a lack of deformation and lack of fluids either as a catalyst or as a component in hydration reactions the three bodies appear to have been far less reactive than the external gneisses in this region even though they followed a similar pressure temperature evolution the extent of metastable behaviour has implications for the protolith of the western gneiss region for the density evolution of high pressure terranes and hence for the geodynamic evolution of mountain belts

a late middle stone age artifact assemblage from sibudu kwazulu natal comparisons with the european middle paleolithic abstract it has been suggested that many behavioral innovations said to appear during the late middle stone age in sub saharan africa facilitated the expansion of anatomically modern humans from africa and the near east into europe at about 50 kyr the process eventually led to the replacement of neanderthals by modern humans and the emergence of the upper paleolithic however assemblages in this time range are little known in south africa in fact the transition from middle to the later stone age in southern africa is controversial the early appearance in south africa of many innovations such as sophisticated knapping techniques e g the use of soft hammer or indirect percussion in blade production of composite tools of microlithic and bladelet technologies remains to be established through technological analysis we present here the first results of a project designed to carry out detailed technological studies of several lithic assemblages in south africa and france dated to the transition period at this time we have completed the study of a post howiesons poort assemblage from the rock shelter site of sibudu the 2 m deep stratigraphic sequence of sibudu extends from howiesons poort at its base to final middle stone age directly under iron age layers we have analyzed in detail layer rsp ca 53 kyr 1 m above the howiesons poort levels which has provided a large assemblage of several thousand stone artifacts compared to published msa assemblages this industry is unusual for the very high proportions of retouched pieces 15 the technology is not very elaborate and there is no strong standardization of the end products there are no flakes of predetermined shapes retouch is used to modify irregular flakes to obtain desired edges knapping of flakes and blades is done by hard hammer soft hammer is used only for retouching tools interestingly the older howiesons poort blades were produced on the same raw materials by soft hammer raw material hornfels and dolerite was procured from distances of less than 20 km unifacial points are the dominant type and there is strong evidence of hafting and use as spear armatures detailed comparisons with middle paleolithic assemblages of western europe show that the late middle stone age technology in south africa is very similar to that of the middle paleolithic in fact we see no fundamental differences between the two entities as far as lithic technology is concerned implications for the out of africa hypothesis are discussed

diaphyseal cross sectional geometry of near eastern middle palaeolithic humans the tibia external osteometric assessments of near eastern middle palaeolithic human tibial diaphyseal robusticity have been used to argue for significant differences in locomotor loading regimes between late archaic and early modern humans from the middle palaeolithic of that region reassessment of tibial diaphyseal strength using cross sectional geometry of their shafts scaled against biomechanically appropriate measures of body mass and beam length reveals no significant difference between the near eastern late archaic human and qafzeh skhul early modern human samples this is in agreement with other assessments of their comparative levels of locomotor strength and endurance indicating similar levels of summed loads upon their lower limbs once body mass and beam length are appropriately incorporated into the analysis at the same time there are no systematic differences in either relative cortical area within cross sections or the biomechanically relevant distribution of bone indicated by perpendicular second moments of area between these samples what emerges from a consideration of appropriately scaled measures of strength of these nemp tibiae however precise the estimates employed is that contrary to previous assessments there are no grounds for inferring a significant change in locomotor activity levels or patterns between late archaic and early modern humans in the near eastern middle palaeolithic

experimentally determined stability of clinopyroxene garnet corundum in the system cao mgo al 2 o 3 sio 2

metamorphic evolution of kyanite staurolite bearing epidote amphibolite from the early palaeozoic oeyama belt sw japan early palaeozoic kyanite staurolite bearing epidote amphibolites including foliated epidote amphi bolite fea and nonfoliated leucocratic or melanocratic metagabbros lmg mmg occur in the fuko pass metacumulate unit fpm of the oeyama belt sw japan microtextural relationships and mineral chemistry define three metamorphic stages relict granulite facies metamorphism m1 high p hp epidote amphibolite facies metamorphism m2 and retrogression m3 m1 is preserved as relict al rich diopside up to 8 5 wt al2o3 and pseudomorphs after spinel and plagioclase in the mmg suggesting a medium p granulite facies condition 0 8 1 3 gpa at 850 c an unusually low variance m2 assemblage hbl czo ky st pg rt ab crn occurs in the matrix of all rock types the presence of relict plagioclase inclusions in m2 kyanite associated with clinozoisite indicates a hydration reaction to form the kyanite bearing m2 assemblage during cooling the corundum bearing phase equilibria constrain a qualitative metamorphic p t condition of 1 1 1 9 gpa at 550 800 c for m2 the m2 minerals were locally replaced by m3 margarite paragonite plagioclase and or chlorite the breakdown of m2 kyanite to produce the m3 assemblage at 0 5 gpa and 450 500 c suggests a greenschist facies overprint during decompression the p t evolution of the fpmmay represent subduction of an oceanic plateau with a granulite facies lower crust and subsequent exhumation in a pacific type orogen

application of strontium isotopes to understanding the hydrology and paleohydrology of the altiplano bolivia peru abstract strontium concentrations and strontium isotopic ratios were measured in natural waters and carbonate sediments from throughout the bolivian and peruvian altiplano in order to improve hydrologic and paleohydrologic mass balances with the ultimate goal of better understanding the paleoclimatic history of the central andes rivers flowing into lake titicaca have a wide range of strontium isotopic ratios that exhibit spatial patterns consistent with the lithologies of the different drainage basins because of the limited exchange of water between the two main sub basins of lake titicaca lago grande and lago huinaimarca and between the sub basins of lago huinaimarca there are significant differences in strontium isotopic ratios between the sub basins calculated elemental balances of strontium in lake titicaca are in reasonable agreement with previously published budgets of water and major elements however the strontium isotopic budget indicates that the lake is not in isotopic steady state this also implies that the major element budgets are unlikely to be in steady state lake titicaca had a higher than modern strontium isotopic ratio during the early and middle holocene elevated values persisted in lago grande until at least 2000 cal yr bp consistent with other evidence that modern hydrologic conditions namely overflow were not established until that time an isotopic budget calculated for late pleistocene paleolake tauca in the central altiplano suggests that between 70 and 83 of its riverine inputs were derived from lake titicaca overflow this calculated flow represents about a 30 fold increase over the average discharge of the modern rio desaguadero at desaguadero or a seven fold increase over its average discharge into lago poopo the strontium isotopic budget if complete precludes the possibility that decreased evaporation alone could have accounted for the existence of paleolake tauca

seawater 87sr86sr for the late permian delaware basin evaporites new mexico u s a abstract the delaware basin southeastern new mexico u s a contains a thick section of marine evaporites the three uppermost units all of ochoan age of evaporites are in ascending order castile formation salado formation and rustler formation the castile consists predominantly of bedded and massive anhydrites the salado of massive halite with numerous interbeds of anhydrite sylvite and minor other units and the rustler of impure anhydrites gypsums halites silty and clayey units dolomites and others the previously established seawater 87 sr 86 sr curve for the late latest permian is marked by a dramatic increase from 0 7068 at 250 ma ago to 0 7072 by the permian triassic boundary data are not shown for rocks of approximate ochoan age however the results of our study show the following average 87 sr 86 sr values for the rocks samples castile 0 706880 0 000005 salado 0 70688 0 000004 and rustler 0 706976 0 000008 thus a systematic increase in 87 sr 86 sr is observed from castile to salado and especially to rustler consistent with a previous prediction these data are submitted for the seawater curve for the ochoan group upper evaporites of late permian age

linking lacustrine cycles with syn sedimentary tectonic episodes an example from the codo formation late aptian northeastern brazil the codo formation exposed in the eastern grajau basin northeastern brazil consists mostly of black shales limestones and evaporites arranged into several shallowing upward cycles formed by progradation of lake deposits three ranks of cycles are distinguished the lower rank cycles correspond to millimetric interbeddings of bituminous black shales with evaporites calcimud stones or peloidal wackestone packstone grey green shale with calcimudstone peloidal wackestone packstone or ostracodal wackestone grainstone and ostracodal wackestone grainstone and or calcimudstones with cryptomicrobial mats and ooidal pisoidal packstones the intermediate rank cycles average 1 7 m in thickness and are formed by complete and incomplete cycles complete cycles show a transition from central to intermediate and then to marginal facies associations and include two types c1 cycle with central lake deposits consisting of evaporites and black shales and c2 cycle with central lake deposits formed by grey green shale complete cycles were produced by the upward gradation from central to marginal environments of the lake or saline pan sabkha system incomplete cycles are those where at least one facies association is lacking having been formed by successions either with central and intermediate facies associations i1 or intermediate and marginal facies associations i2 the higher rank cycles are on average 5 2 m thick and consist of four depositional units that display shallowing upward successions formed by complete and incomplete intermediate rank cycles that vary their distribution upward in the section and are bounded by sharp surfaces while the lower rank cycles display characteristics that reveal their seasonal signature detailed sedimentological characterization and understanding of stratal stacking patterns related to the intermediate and higher rank cycles support a genesis linked to syn sedimentary tectonic activity this is particularly suggested by the high facies variability limited lateral extension and frequent and random thickness changes of the intermediate rank cycles additionally the four higher rank cycles recognized in the codo formation match with stratigraphic zones having different styles of soft sediment deformation structures attributed to seismic activities therefore the several episodes of lake shallowing recorded in the codo formation are linked to seismic pulses that alternated with sediment deposition this process would have created significant changes in the lake water level and resulted in sharply bounded successions with upward gradation from deeper to relatively shallower facies associations

strontium isotope record of paleohydrology and continental weathering eocene green river formation wyoming sr isotope ratios in carbonate rich lacustrine strata provide highly resolved and geo graphically specific records of past changes in weathering and regional drainage patterns the eocene green river formation is perhaps the best documented pre quaternary la custrine unit in the world therefore these strata are ideally suited for studying the be havior of sr the 87 sr 86 sr ratios measured for primary carbonate in lake expansion contraction cycles of the laney member are directly linked to changing lake facies four distinct cycles are preserved in a 6 4 m interval of the arco washakie basin no 1 core each represented by a vertical succession of transgressive stromatolite facies containing dolomicritic intraclasts laminated micrite facies deposited during lake highstands and lake marginal dolomicrite facies which represent subsequent lowstands initial 87 sr 86 sr ratios range from 0 711 99 to 0 713 31 the least radiogenic isotope compositions are as sociated with laminated micrite that records increased regional runoff from phanerozoic marine carbonate and tertiary volcanic rocks during lacustrine highstands the most radiogenic isotope compositions are associated with dolomicrite recording a higher pro portion of runoff from basin bounding precambrian uplifts and the exposed lake plain during lacustrine lowstand the observed 87 sr 86 sr variations may also be due in part to changes in differential weathering of the surrounding landscape where drier climates are associated with decreased differential weathering and therefore higher 87 sr 86 sr in runoff

origin of satin spar veins in evaporite basins abstract satin spar fibrous gypsum veins occur in rocks overlying evaporites in the amadeus basin australia appalachian basin usa cheshire basin england elk point basin canada palo duro basin usa paradox basin usa and zechstein basin england these antitaxial veins which are characterized by central partings and near vertical fibers fill horizontal and inclined fractures most satin spar veins occur in highly fractured or brecciated clastic strata that overlie or are associated with bedded halite anhydrite and gypsum saline springs are commonly present indicating that halite dissolution is active the similarities in morphology and occurrences of these veins suggest a common genesis satin spar veins result from several simultaneously active processes recharge of low salinity surface water results in dissolution of shallow 200 m to 750 m deep halite development of cavernous porosity and formation of extensional fractures in the rock column overlying salt dissolution zones greater solubility of anhydrite than gypsum at low temperatures and at salinities below halite saturation causes hydration of anhydrite to gypsum which takes place without significant volume change once groundwater is saturated with respect to gypsum any further anhydrite hydration and solution must result in supersaturation and the excess caso4 carried by ground water flowin from dissolution zones precipitates as gypsum in open high permeability fractures

the metamorphic evolution of the high pressure mafic granulites of the bacariza formation cabo ortegal complex hercynian belt nw spain abstract the high pressure mafic granulites of the bacariza formation outcrop in the two uppermost structural units of the cabo ortegal complex la capelada unit and cedeira unit were separated by a variscan thrust in both cases they appear as heterogeneous metabasites in normal contact between ultramafic rocks and other more homogeneous and less differentiated metabasic rocks also affected by catazonal metamorphism the main difference between the mafic granulites in the two units is the degree of deformation which is higher in the underlying cedeira unit petrologie and mineralogical data indicate that the high pressure hp granulites gt cpx amp pl qtz scp rt ilm czo are already retrograde m2 stage post dating an earlier eclogite facies metamorphism ml stage characterised by the mineral associations gt cpx amp ky qtz rt and gt cpx amp qtz zo rt the main structure relatted to the exhumation processes is the development of a general mylonitic foliation that although initiated in granulite facies conditions was mainly equilibrated in amphibolite facies m3 stage this foliation was affected by isoclinal folds which led to the formation of the variscan thrusts responsible for the present stacking position thrust conditions were transitional between amphibolite and greenschist facies m4 stage thermobarometric data point to different p t exhumation paths in the two units estimated p t conditions were higher in la capelada unit during ml p 13 kbar 860 c and m2 15 kbar 800 c than in the cedeira unit ml p 11 kbar 770 c m2 12 kbar 750 c temperatures for the m3 stage were comparable 720 c in both units but rocks from the cedeira unit show a much bigger drop in pressure this resulted in an isothermal decompression type path for the cedeira unit while both p and t decreased more steadily in la capelada rocks these were always located at deeper level than the cedeira rocks before the variscan stacking the difference in the two paths is related to different exhumation rates higher in rocks from the cedeira unit than in those from la capelada exhumation processes coeval with underthrusting and a different location of the rocks with respect to the main shear zone responsible for the exhumation would account for the distinct paths

the structure and timing of lateral escape during the scandian orogeny a combined strain and geochronological investigation in finnmark arctic norwegian caledonides abstract determining the timing duration and mechanism of tectonic events within an orogenic cycle such as ocean subduction continent continent collision or gravitational collapse is challenging especially in ancient orogenic belts variations in the tectonic transport direction however can be used as a guide to these stages of orogeny while thrust sheets within the caledonian allochthon in north norway were emplaced broadly eastwards perpendicular to the trend of the orogen many features indicate material transport in other orientations one dominant feature of the mageroy nappe sitting above and infolded with the kalak nappe complex is the development of a strong n s lineation orthogonal to the main transport direction strain measurements in part determined by a new method are used in the context of the regional structural data to identify the critical stage in orogeny when compressional forces are balanced by orogen parallel lateral escape quantitative 3 d strain estimation in the mageroy nappe indicates prolate deformation with c 50 horizontal shortening parallel to the thrusting direction e w and c 200 extension along the orogenic strike n s with c 30 vertical shortening temporal constraint on this fabric is provided by ar ar isotopic analysis of undeformed white mica in cross cutting granitic pegmatites these data show that prolate deformation occurred before the white mica cooling age of 416 4 ma while the previously determined depositional age of the hellefjord schist indicates that it occurred after 438 4 ma a granitic pegmatite that intruded the hellefjord schist after an initial deformation phase but during or prior to a later deformation has been dated at 431 2 ma by u pb zircon a previous lower age constraint on this deformation of 428 5 ma is given by metamorphic zircon overgrowths on fractured grains these results constrain the continental collision between baltica and laurentia in finnmark to the interval c 431 428 ma placed in a regional context these results indicate that lateral escape was orthogonal to the thrusting direction and occurred during the continent continent collision stage in the scandian orogeny before gravitationally driven collapse

deciphering the sedimentological imprint of paleoseismic events an example from the aptian codo formation northern brazil abstract a stratigraphic horizon bearing several styles of soft sediment structures occurs sandwiched within entirely undisturbed deposits in the lacustrine codo formation aptian located in the eastern part of the grajau basin northern brazil these deposits show a variety of sedimentary features distinguished according to their deformation style as follows from bottom to top a zone 1 consisting of widespread molar tooth structures i e fine grained spar filled cracks that are interconnected with small scale faults fissures and stylolites inclined at a high angle to bedding b zone 2 represented by complex convolute folds with lateral gradation of smooth synclines and anticlines into isoclinic folds and internal layers that retain the normal bedding features recumbent folds nappe folds with associated thrust faults pseudonodules and mound and sag structures c zone 3 consisting of normal faults and fissures that are vertical to near vertical show ragged morphology with small delicate peaks taper both downward and upward after a few centimeters and are associated with large up to 2 5 m long collapsed boulders and d zone 4 characterized by shales with irregular convolute folds these deformation zones are interpreted to reflect sediment rheology and alternating periods of sediment accumulation and deformation under the influence of synsedimentary seismic events as suggested mostly by 1 occurrence between undeformed deposits 2 lateral correlation for several kilometers of distance 3 similarity with other features formed in areas affected by seismic activity 4 presence of structures attesting to sediment deformation in an unconsolidated to semi consolidated state and 5 complex association of brittle and ductile deformation structures hence zone 1 records small scale cracking and faulting of early cemented cohesive deposits zone 2 is dominated by ductile deformation structures formed on water saturated unconsolidated sediments probably as a reflex of compressional stress zone 3 records a change in tectonic style to dominantly distension as evidenced by the horizon with normal faults finally zone 4 shows structures attributed to ductile deformation of water saturated muds which was probably formed during the same episode of deformation responsible for the faults and fissures in zone 3 this succession of deformation events appears to be consistent with transtensional and compressional shear stresses during the sedimentary evolution of the grajau basin

sedimentary facies depositional environments and palaeogeographic evolution of the neogene denizli basin sw anatolia turkey abstract the denizli basin southwestern anatolia turkey contains a record of environmental changes dating since the early miocene detailed facies analysis of the neogene formations in this half graben enables us to document successive depositional regimes and palaeogeographic settings sedimentation commenced in the early miocene with the deposition of alluvial fan and fluvial facies kizilburun formation at this stage alluvial fans sourced from elevated areas to the south prograded towards the basin centre the middle miocene time saw the establishment of marginal lacustrine and wetland environments followed by the development of a shallow lake sazak formation the uppermost part of this unit consists of evaporitic saline lake and saline mudflat facies that grade upward into brackish lacustrine deposits of late miocene pliocene age kolankaya formation the lake became shallower at the end of the pliocene time as is indicated by expansion shoreface foreshore facies in the early quaternary the denizli basin was transformed into a graben by the activation of ese trending normal faults alluvial fans were active at the basin margins whereas a meandering river system occupied the basin central part oxygen isotope data from carbonates in the successive formations show an alternation of wetter climatic periods when fresh water settings predominated and very arid periods when the basin hosted brackish to hypersaline lakes the neogene sedimentation was controlled by an active ese trending major normal fault along the basin s southern margin and by climatically induced lake level changes the deposition was more or less continuous from the early miocene to late pliocene time with local unconformities developed only in the uppermost part of the basin fill succession the unconformable base of the overlying quaternary deposits reflects the basin s transformation from a half graben into a graben system

40ar39ar whole rock dating and the age of cleavage in the finnmark autochthon northernmost scandinavian caledonides abstract four variably cleaved samples of red shale slate were collected from the nyborg formation vestertana group exposed in the finnmark autochthon northernmost scandinavian caledonides quartz normalized illite crystallinity values suggest metamorphism varied between upper diagenesis lower anchizone east and lower anchizone middle anchizone west the samples display similarly discordant 40 ar 39 ar whole rock age and k ca spectra with total gas ages ranging between 606 and 661 ma spectra complexity is a result of evolution of gas from relatively non retentive chlorite white mica and relatively refractory detrital plagioclase apparent ages defined by intermediate temperature increments are relatively constant within each sample but show marked intersample variations 550 575 to 635 650 ma three size fractions 1 2 2 4 and 4 8 m were separated from the sample containing the least chlorite the two coarser fractions contain numerous rock fragments and display 40 ar 39 ar age and k ca spectra similar to the whole rock the 1 2 m fraction is largely comprised of individual mineral grains gas increments evolved between 375 and 495 c record similar k ca ratios but systematically increasing apparent ages between 637 and 783 ma these results suggest that the 1 2 m fraction is composed of detrital white mica grains which were affected by a diagenetically related geologic disturbance at 635 ma although the affects of a late cambrian early ordovician orogenic event finnmarkian orogeny have been locally described from portions of the overlying caledonian allochthons no clear record of correlative tectonothermal activity has been documented within samples from the finnmark autochthon

p t evolution and fluid inclusion characteristics of retrograded eclogites munchberg gneiss complex germany kyanite eclogites occur as part of the munchberger nappe pile in ne bavaria west germany eclogites are overprinted by subsequent amphibolite facies metamorphism the preservation of primary eclogitic textures as well as symplectitic textures are indicative of rapid decompression eclogite formation is estimated to have occurred under conditions of high h2o activities at pressures between 20 and 26 kbar and temperatures ranging between 590 and 660 c as is shown by the coexistence of omphacite jd 50 kyanite zoisite and quartz minimum pressure estimates independent of the water activity range between 9 and 16 kbar at the relevant temperatures detailed studies of fluid inclusion reveal two predominant groups of aqueous brine inclusions high salinity 14 17 wt nacl equiv and low salinity 0 8 wt nacl equiv inclusions fluid compositions of both groups of inclusions yield isochores passing close to the estimated amphibolite facies pt field the compositions of these fluids are in good agreement with fluid compositions considered from mineral equilibria none of the fluid inclusions has densities appropriate for eclogite facies metamorphism but probably reflect later amphibolite facies metamorphism

a tectonic model for the metamorphic evolution of the basal gneiss complex western south norway a review of currently available information relevant to the basal gneiss complex bgc of western south norway combined with the authors own observations leads to the following conclusions 1 most of the bgc consists of proterozoic crystalline rocks and probably subordinate lower palaeozoic cover 2 the last major deformation of these rocks was during the caledonian orogeny and involved large scale thrusting recumbent folding and doming the structural development of the bgc is closely tied in with that of the caledonian allochthon 3 the whole eclogite bearing part of the bgc has suffered a high pressure metamorphism with conditions of between 550 c 12 5 kbar sunnfjord and about 750 c 20 kbar more og romsdal at the metamorphic climax 4 this metamorphism was of caledonian age probably rather early in the caledonian tectonic history of the bgc and is considered to have been a rather transient event by setting these conclusions in a framework provided by geophysical evidence for the deep structure of the crust in southern norway we have constructed a geotectonic model to explain the recorded metamorphic history of the bgc it is suggested that considerable crustal thickening was caused by imbrication of the baltic plate margin during continental collision with the greenland plate this resulted in high pressure metamorphism in the resulting nappe stack progradation of the suture caused underthrusting of the baltic foreland below the eclogite bearing terrain causing it to emerge at the earth s surface aided by tectonic stripping and erosion application of isostacy equations to the model shows that eclogites can be formed by in situ metamorphism in crustal rocks and reappear at the land surface above a normal thickness of crust in a single orogenic episode of approximately 65 70 ma duration

precise dating of low temperature deformation strain fringe analysis by 40ar 39ar laser microprobe pyritized graptolites from the welsh basin united kingdom slate belt acted as rigid bodies during cleavage formation and epizonal white micas formed within the resulting strain shadows orthogonal to the principal stress orientation although the quantities of mica are small they are a pure synkinematic mineral and have been dated by ar 40 ar 39 infrared laser microprobe as a means to dating cleavage four samples of strain fringe mica from different hand samples yielded ages ranging from 394 4 3 1 to 397 8 1 8 ma 2sigma with a mean age of 396 1 1 4 ma 2sigma by focusing on minerals that are unequivocally synkinematic this technique provides a novel solution to the problems of isotopically dating slaty cleavage previous studies have predominantly relied on dating whole rock slate samples or separated illite grains by ar 40 ar 39 techniques problems encountered included 1 separating the effects of isotopic contamination by detrital phases 2 ar 39 loss during the irradiation of illite mineral separates and 3 thermally induced ar 40 loss in nature from fine grained minerals by circumventing these problems this new method provides the first unequivocal and high precision age data for acadian deformation in the well characterized welsh basin slate belt with such precision the method may afford geologists the opportunity to track tectonic fronts across orogens and assess the rates of accretion processes in areas that are peripheral to sites of continent continent collision

paleohydrology of an upper aptian lacustrine system from northeastern brazil integration of facies and isotopic geochemistry abstract the codo formation records the initial evolutionary stages of an intracontinental rift system formed along the brazilian equatorial margin in the late aptian deposits of this unit exposed on the eastern margin of the grajau basin include gypsum bituminous black shales and limestones these lithologies were formed in a low energy well stratified anoxic and hypersaline lake system developed in a dominantly arid semi arid climate this lacustrine succession is internally organized into three categories of shallowing upward cycles with the first and second order cycles being related to seismic activity associated with fault reactivations and the third order cycles recording climatic fluctuations studies emphasizing petrography and analysis of the geochemical tracers fe mg sr mn na and ca helped to identify the sedimentary facies that kept a primary signal which were thus appropriate for isotopic investigations aiming paleoenvironmental and paleohydrologic reconstructions the results of this study revealed a wide distribution of dominantly low carbon and oxygen isotope values in carbonates ranging from 5 69 to 13 02 and from 2 71 to 10 80 respectively this paper demonstrates that at least in the particular case of oxygen the isotope ratios vary according to seismically induced shallowing upward cycles with values in general lower at their bases where central lake deposits dominate and progressively higher upward where marginal lake deposits are more widespread in addition to confirming a depositional signature for the analysed samples this behavior allowed the development of a seismic induced isotope model the lighter isotope ratios appear to be related to flooding events promoted by subsidence which resulted in the development of a perennial lake system while heavier isotope values are related to ephemeral lake phases favored by uplift and or increased stability furthermore the results show that a closed lake system dominated as indicated by the overall good positive covariance i e 0 42 to 0 43 between the carbon and oxygen isotopes though open phases are also recorded by negative covariance values of 0 36 during closed phases the 18 o displayed the highest range of variation i e 3 63 to 4 89 due to increased residence time while this variation was low i e 0 09 to 1 87 during open lake phases when there was a balance in the water isotope composition maintained by continuous basin inflow

reconstruction of the miocene western amazonian aquatic system using molluscan isotopic signatures abstract strontium isotopic ratios and sr contents of molluscs from the miocene pebas formation in colombian amazonia indicate that the bulk of the pebas formation was deposited in a freshwater environment predominantly draining the andes with minor contribution from the shield regions the molluscan oxygen and carbon isotopic composition does not provide a palaeosalinity proxy but points to a lacustrine palaeoenvironment the faunal character confirms such an interpretation sr isotopic ratios further suggest that a marine incursion that reached the area was composed of a mixture of shield derived freshwater and seawater with a maximum salinity of about 5 psu faunistic components of this incursion level support a shield seawater mixing the incursion most likely reached western amazonia from the north probably along the western guyana shield

tectonics of the scandian orogeny and the western gneiss region in southern norway two crust forming events dominate the precambrian history of the western gneiss region wgr at about 1800 1600 ma and 1550 1400 ma the influence of the sveconorwegian orogeny 1200 900 ma is restricted to the region south of moldefjord romsdalen a series of anorthosites and related intrusives are present possibly derived from the now lost western margin of the baltic craton that may have been emplaced in the wgr as an allochthonous unit before the ordovician

experimental evidence concerning spear use in neandertals and early modern humans abstract can a bimanual activity such as thrusting a spear during hunting produce bilateral asymmetries in the strength of the upper limbs this question is important to arguments about the predatory capabilities of neandertals and early modern humans to address this question we determined the magnitude and direction of reaction forces on the upper limbs during thrusting spear use we collected lateral video records of eight adults thrusting an instrumented aluminum rod into a padded target this spear was instrumented with two sets of four strain gauges placed at two positions along the shaft to register the force along the shaft and the distribution of those forces relative to the two limbs from the gauge output and video we were able to calculate loads experienced by the trailing limb holding the proximal spear and the leading limb holding the distal spear as well as approximate bending moments along the trailing limb the trailing limb provides a significantly greater portion of the force during spear impact and when the spear is held forcefully on the target the loads on this limb at spear impact are twice body weight and the bending moments on the trailing humerus are large and appear to occur primarily in the parasagittal plane these data in combination with fossil humeral cross sectional data and the lack of evidence for throwing spears among eurasian neandertals suggest that previously documented humeral strength asymmetries in eurasian neandertals and early upper paleolithic modern human males can be plausibly linked to spear thrusting

mixing properties and stability of jadeite acmite pyroxene in the presence of albite and quartz the stability of synthetic jadeite acmite pyroxene coexisting with albite and quartz has been determined at 600 700 and 900 c the end member reaction albite jadeite quartz has been determined to lie between 1 67 and 1 70 gpa at 600 c 1 88 and 1 90 gpa at 700 c and 2 44 and 2 48 gpa at 900 c jd78acm22 quartz is stable above 1 58 1 78 and 2 33 gpa at 600 700 and 900 c respectively jd61acm39 quartz is stable above 1 47 1 67 and 2 18 gpa at 600 700 and 900 c respectively addition of as much as 40 of acmite component in jadeite extends pyroxene stability by less than 300 mpa at 900 c unit cell parameters measured for synthetic jadeite acmite pyroxenes indicate linear volume composition relations the data are consistent with ideal mixing in jadeite acmite solutions

abu dhabi sabkha persian gulf revisited application of strontium isotopes to test an early dolomitization model a study of brines and diagenetically altered minerals from coastal sabkha of abu dhabi persian gulf was undertaken to test the flood recharge evaporative pumping model for early dolomitization using strontium isotopes as a tracer the sup 87 sr sup 86 sr ratio of the sabkha brines defines a pattern of both horizontal and vertical mixing of coastal seawater and continental ground water consistent with a previously proposed model the sup 87 sr sup 86 sr ratio of the diagenetic dolomites indicates early dolomitization by marine recharge waters the sup 87 sr sup 86 sr ratio of gypsum from the dolomitization area 1 4 to 4 4 km from high tide mark and seaward reflects precipitation from marine brines but more landward 6 to 9 km gypsum and anhydrite record a continental signal in the minerals suggests a paragenetic evaporative sequence dolomite yields gypsum yields anhydrite the dolomitizing fluid is evaporated seawater that recharges the sabkha aquifer during supratidal flooding and is afterward pumped upward through the saturated zone by evaporative processes

development of microbial carbonates in the lower cretaceous codo formation north east brazil implications for interpretation of microbialite facies associations and palaeoenvironmental conditions the study of microbial carbonates has acquired new significance with the recognition that they retain valuable information related to biomineralization processes associated with microbial activity throughout geological time additionally microbialites have a demonstrated economic potential to serve as excellent hydrocarbon reservoirs the lower cretaceous codo formation located in the parnaiba basin of north east brazil comprises a unique stratigraphic sequence of up to 20 m thick well preserved carbonate microbialites deposited in a continental basin during the initial break up and separation of south america from africa in the early cretaceous this lacustrine carbonate sequence provides an excellent example to investigate the palaeoenvironmental conditions controlling microbialite facies development based on macroscopic and microscopic observations of outcrop and drill core samples four microbialite facies stromatolite lamina massive and spherulite were defined and distinguished by textures and microbial fossil content changes in facies type are related to alternating palaeo water depths as reflected by 87sr 86sr cycles resulting from fluctuations in the sources of meteoric water clumped isotope measurements of stromatolitic fabrics yield precipitation palaeo temperatures with an average value of 35 c the 18 o values of bulk carbonate 6 8 to 1 5 vienna pee dee belemnite imply precipitation from water with calculated 18 o values between 1 6 and 1 8 vienna standard mean ocean water reflecting precipitation from variably modified meteoric waters the 13 c values of bulk carbonate 15 5 to 7 2 vienna pee dee belemnite indicate a significant input of carbon derived from aerobic or anaerobic respiration of organic matter combined the data indicate that the evolution of the codo formation occurred in a closed lacustrine palaeoenvironment with alternating episodes of contracting and expanding lake levels which led to the development of specific microbialite facies associations the results provide new insights into palaeoenvironmental settings biogenicity and early diagenetic processes involved in the formation of ancient carbonate microbialites and by extension improve the knowledge of the reservoir geology of correlative units in deep waters offshore brazil

polyorogenic 40ar 39ar mineral age record within the kalak nappe complex northern scandinavian caledonides the kalak nappe complex is composed of variably retrogressed middle proterozoic basement and imbricated polydeformed metasedimentary cover successions which at least in part appear to have originated within the late proterozoic early palaeozoic baltoscandian miogeocline mafic alkaline plutons seiland igneous suite occur within uppermost structural units of the nappe complex 40 ar 39 ar incremental release mineral ages suggest local differences in tectonothermal evolution within the kalak nappe complex post metamorphic cooling dates of c 490 ma are locally recorded by hornblende within the structurally highest tectonic unit suggesting significant orogenic activity occurred during and or immediately prior to the arenig a distinctly later metamorphic overprint occurred in the silurian and was of sufficient magnitude to everywhere rejuvenate ar systems in muscovite and nepheline and locally in hornblende this was followed by relatively rapid post metamorphic cooling through hornblende and muscovite ar closure temperatures between c 425 and 415 ma the complex tectonic history suggested for the kalak nappe complex is generally similar to that previously outlined for the central swedish caledonides together 40 ar 39 ar mineral ages from these widely separated areas indicate that significant tectonothermal activity occurred along the baltoscandian margin prior to the silurian this activity appears at least in part to have been associated with formation of a late cambrian early ordovician accretionary wedge over a westward dipping subduction zone during initial closure of the iapetus ocean

palaeomagnetism of vendian early cambrian sedimentary rocks from e finnmark norway abstract a palaeomagnetic study has been made on vendian early cambrian rocks of the tanafjord and vestertana groups from the varanger peninsula northernmost norway magnetic components of probably primary origin were isolated at two sites apparently unaffected by the finnmarkian scandian events of the caledonian orogeny sites situated in the caledonian gaissa nappe or close to its front were remagnetized and comparison with a tentative ordovician to devonian apparent polar wander path indicates that the remagnetization occurred during these periods

experimental tests of middle palaeolithic spear points using a calibrated crossbow abstract controlled experiments using a calibrated crossbow to thrust stone tipped spears into animal carcasses reveal a relationship between levallois point morphology and their performance as spear points a comparative study of morphometric variation of levallois points from levantine mousterian contexts supports the hypothesis that the demand for stone spear points was an important factor in levallois point production

using strontium isotopes to determine the age and origin of gypsum and anhydrite beds the variation of 87sr 86sr in seawater with time can be used to determine the age of calcium sulfate beds precipitated from brine derived from seawater the determination of a marine origin can be established by the consistency of strontium isotope results from samples at different stratigraphic levels in a single gypsum anhydrite bed collected at separated sites the scatter of strontium isotope results in the gypsum anhydrite samples examined here is interpreted to result from the contribution of meteoric strontium to the salina strontium isotope results from three evaporite settings the jurassic todilto formation from new mexico the permian blaine formation from blaine county oklahoma and the permian salado formation from new mexico are used to determine the age and origin of the parent brine for these gypsum anhydrite beds the calcium sulfate beds from each of these formations precipitated from salinas that originated with a marine flooding but show at different times and localities volume do

spring peas from new york state nucleation and growth of fresh water hollow ooliths and pisoliths abstract delicate hollow spheroids 1 to 2 mm composed of radially fibrous calcite occur in and on the surface of calcareous travertine being deposited from water of the orenda spring saratoga springs new york state field observations suggest that spheroids form by the precipitation of calcite on the surface of water droplets that contain newly formed bubbles of co2 although many of the spheroids subsequently disintegrate some grow by the addition of laminae consisting of radial bundles of fibrous calcite commonly separated by thin seasonal laminae of fine grained calcite and detritus these spheroids are either incorporated into laminar travertine sheets or grow by successive increments into fresh water ooliths and pisoliths with both a concentric and a radial structur

metastability of granulites and processes of eclogitisation in the uhp region of western norway the flatraket complex a granulite facies low strain enclave within the western gneiss region provides an excellent example of metastability of plagioclase bearing assemblages under eclogite facies conditions coesite eclogites are found 28 kbar unprecedented metastability of plagioclase and quartz is implied alternatively a tectonic break exists between the flatraket complex and uhp eclogites supporting the concept of a tectonic boundary to the uhp zone of the western gneiss region the distribution of eclogite and amphibolite facies metamorphic overprints demonstrates that the reactivity of the crust during deep burial and exhumation is strongly controlled by fluid availability and is a function of the protolith

40ar 39ar mineral dates related to devonian extension in the southwestern scandinavian caledonides abstract middle devonian sedimentary basins exposed in west central norway formed during post caledonian extension they developed along west dipping low angle normal faults which effected ductile shearing of pre caledonian basement units of the western gneiss region wgr kinematic indicators suggest that the west vergent ductile deformation overprinted older east vergent caledonian fabric elements ductile extensional deformation led to development of a 2 km thick shear zone beneath the devonian basins five amphibole and nine muscovite concentrates from rocks within the shear zone and from unaffected gneisses of the western gneiss region have been analyzed with 40ar 39ar incremental release dating techniques in an attempt to calibrate the timing of extensional events well defined plateau ages are recorded by muscovite concentrates within the shear zone amphiboles display disturbed plateau ages clearly related to extraneous argon outside the shear zone muscovite records caledonian ages results suggest that a late tectonometamorphic event affected the rocks within the shear zone this event which not exceed ca 500 c completely rejuvenated muscovite argon systems and perturbed argon distribution within amphiboles this metamorphism is correlated with the extensional deformation which effected exhumation of the caledonian high pressure rocks and controlled formation of devonian basins

high pressure relics in meta sediments intercalated with the weissenstein eclogite munchberg gneiss complex bavaria the mineral assemblages in the eclogites and meta sediments of the munchberg gneiss complex suggest minimum pressures of about 15 kbar and temperatures of 600 30 c for the eclogite facies metamorphism both rock types underwent a subsequent amphibolite facies metamorphism at almost the same temperature range in the weissenstein borehole the eclogites and meta sediments show an intimate interlayering on a centimetre scale contacts between the two rock types are often sharp and untectonized suggesting in situ metamorphism of the eclogites the following features indicate that the gneisses were subjected to eclogite facies metamorphism 1 phengite relics and phengite inclusions in garnet contain up to 3 45 si per formula unit while amphibolite facies phengites have considerably lower si contents 3 0 3 25 p f u 2 omphacite relics occur in the form of na augite 6 9 mol jadeite oligoclase symplectites 3 garnets with up to 40 mol of the pyrope component occur

marine to non marine sedimentation in the upper miocene evaporites of the eastern betics se spain sedimentological and geochemical evidence abstract several neogene basins in the eastern betics contain a record of thick upper miocene evaporites the inner basins those located distal to the mediterranean coast include evaporite units ranging from the late tortonian to the early messinian whereas the marginal basins those located in the vicinity of the mediterranean coast include evaporite units corresponding to the late messinian that are linked to the salinity crisis the sedimentological and geochemical comparison of the evaporites in the inner and marginal basins enable us to show their differences in the modes of deposition under local structural controls and differentiated palaeogeography in the inner basins of the murcia alicante region a number of evaporite units have been differentiated whose gypsum lithofacies have 1 variable strontium contents with mean values primary gypsum between 1121 and 2380 ppm 2 isotopic compositions of sulphur 34 s ranging from those characteristic of the tertiary marine water 20 3 to 25 5 to those characteristic of the triassic sulphates 8 0 to 16 0 the latter suggesting recycling of the sulphate anion in meteoric waters intermediate values 17 4 to 19 6 are attributed to mixed mother brines and 3 strontium ratios 87 sr 86 sr comprised between 0 70804 and 0 70888 these values range from those of the tertiary marine water to those exceeding the triassic sulphates suggesting additional continental contributions from country rocks and hydrothermal solutions the comparison between the sulphur and strontium isotopic compositions of the sulphates together with the study of the biota present in the marls associated with the gypsum allows us to distinguish between marine continental and mixed units in the marginal basins of the eastern betics where single evaporite units characterized by selenitic gypsum prevail 1 the strontium contents are more homogeneous with mean values primary gypsum between 493 and 625 ppm 2 the isotopic compositions of oxygen 18 o and sulphur 34 s are comprised between 12 2 and 14 8 and between 22 0 and 23 5 respectively and 3 the strontium ratios 87 sr 86 sr vary from 0 70890 to 0 70895 all these isotopic values reveal a marine origin and the lack of contribution of significant continental water during the late messinian evaporite deposition in the betic strait these characteristics are similar to those of the lower evaporite

excess argon 40are uptake during slate formation a 40ar 39ar uv laserprobe study of muscovite strain fringes from the palaeozoic welsh basin uk syn kinematic pure muscovite strain fringes grew around pyritized graptolites in response to the early devonian acadian closure and uplift of the peri gondwanan welsh basin they record ar isotope information on the timing of low temperature deformation and the mudrock to slate transition here we have applied three different 40ar 39ar laserprobe dating methods to strain fringes from the central welsh basin to test for variations in age and to explore the technical limitations of the method infrared laserprobe step heating analyses yielded only occasional plateau ages varying between ca 403 ma and 422 ma and strong evidence for discordance in the ar system likewise ages from infrared laserprobe total fusion analysis are scattered and range from ca 390 ma to 651 ma by contrast ultraviolet laserprobe intra fringe age profiles revealed a complex pattern of ages across individual strain fringes this is the highest spatial resolution technique available and the resulting age profiles consistently showed an oscillatory pattern comprising troughs or baseline ages that are all within error of ca 397 ma and peaks or apparent ages ranging up to ca 550 ma these apparent ages we interpret as the results of repeated periodic assimilation of excess 40ar 40are during deformation and the mudrock to slate transition here basinal fluids carrying 40are are driven through bulk mudrock during contractional phases of the acadian orogen and 40are is taken up by muscovite strain fringes the concentration of 40are varies with metamorphic grade and is inversely proportional to the temperature of metamorphism and we suggest is controlled by the solubility of ar in water which has potentially quite severe implications for 40ar 39ar dating of k bearing minerals in any mudrock these results provide a first record of ar isotope information in strain fringes and a first record of orogenically driven fluid flow through bulk deforming mudrock they also demonstrate how the high spatial resolution ultraviolet laserprobe 40ar 39ar method can access ar isotope information that is obscured by lower spatial resolution laser analysis or bulk sampling methods

cambrian skeletal halite crystals and experimental analogues a suite of unusual highly skeletal halite pseudomorphs is described from the lower middle cambrian rocks that crop out at ardmore in the georgina basin northern australia the pseudomorphs are preserved as both moulds and casts within a dark and light colour banded chert they are orientated parallel to bedding and represent halite crystal growth within a brine pool laterally equivalent rocks are characterized by sedimentary textures and structures indicative of periodic emergence and desiccation laboratory grown halite crystals are also described and compared with the pseudomorphs from ardmore experimentally produced halite crystals formed from either 1 brine solutions obtained as residues after organic matter extraction from phosphate rocks or 2 solutions of naci and distilled water both pyramidal rafted hoppers and floor nucleated cuboids formed in solutions containing only naci and distilled water whereas in the residue solutions that contained humic acids rafted pyramidal forms were absent and crystal nucleation was restricted to the floor of the evaporative dish as brine depth decreased the halite precipitation rate increased and resulted in a suite of excrescent highly skeletal crystals that formed as a result of brine evaporation to dryness the variable crystal morphology depended upon both the brine depth and slope of the evaporative dish floor horizontally orientated chevron halite crystals formed where the evaporative dish was inclined and precipitation preferentially occurred on cube faces pagoda reticulate ridge and dendritic forms represent an increasingly skeletal crystal suite characterized by the preferential precipitation of naci on cube edges and corners rather than faces using the experimentally grown crystals as analogues the pseudomorphs at ardmore are interpreted as forming in very shallow brine pools that evaporated to dryness

glaucophane and barroisite eclogites from the upper kaghan nappe implications for the metamorphic history of the nw himalaya

projectile impact fractures and launching mechanisms results of a controlled ballistic experiment using replica levallois points abstract identifying the use of stone tipped projectile weapons in prehistory is important for understanding hominin strategic behavior and cognitive capacities such identifications are based on diagnostic impact fractures difs assumed to form as a result of collisions between the tips and organic materials in the prey body however demonstrating weapon use requires documenting an impact speed and or kinetic energy beyond those likely to occur accidentally or as a by product of other tasks we present a new experiment aimed at investigating the influence of speed on impact fracture formation in controlled conditions using an air gun we fired 234 nearly identical spears tipped with copies of a levallois point cast in soda lime glass into a composite target made of polyurethane bone like plates ballistic gelatin and leather the impact speed ranged from 7 to 30 m s and the impact angle ia varied in increments of 15 from 90 to 45 we show that realistic difs can be produced under these controlled conditions the frequency of longitudinal tip macrofractures is directly proportional to the impact speed but inversely proportional to the ia the relationship between the tip fracture type and the type of damage left on the target explains the contact conditions for the formation of different difs no relationship between either initiation or termination type and speed could be established therefore we conclude that step terminating bending fractures should not be considered diagnostic of weapon use without further supporting evidence further although fracture length increases with speed when ia is held constant a great deal of overlap exists between trials with different ias given the expected high variance in ia in real hunting situations large longitudinal macrofractures on the tips of archaeologically recovered lithics should not automatically be interpreted as resulting from the use of high speed projectiles we discuss the study s implications for the differentiation of prehistoric weapon delivery systems especially regarding recognizing stonetipped weapon use by neandertals

mid cretaceous strontium isotope stratigraphy of deep sea sections large variations exist between published mid cretaceous late barremian to early turonian stages seawater sr isotope stratigraphies this has resulted in disparate interpretations of crustal production rates we report on a detailed investigation of seawater sr isotope stratigraphy based on foraminifers and where available on inoceramid bivalves from 12 mid cretaceous deep sea drilling project and ocean drilling program sections the effects of diagenesis are assessed using scanning electron microscope observations and traceelemental analyses but are best distinguished by comparing the 87 sr 86 sr values of similarage samples from different sites strontiumisotope analyses compiled from 9 of 12 sites that have detailed age control define one band of common values this band is used as a composite curve which presumably represents seawater 87 sr 86 sr values the composite curve shows a trough of markedly lower 87 sr 86 sr values in the aptian and early albian stages higher but constant values for the middle albian cenomanian stages followed by a decrease in 87 sr 86 sr values in the early turonian

evaporites marine or non marine division of evaporites into those types that retain information about primary mineralogy textures and structures primary evaporites and those types so extensively altered that few or no primary features remain secondary evaporites only primary evaporites can give unequivocal data bout their marine or non marine origin to help evaluate such primary deposits they have been further divided using the following attributes 1 whether the depositional setting was marine or non marine 2 whether the source water was a seawater b meteoric c hydrothermal d diagenetic e volcanogenic or f mixed specific criteria for making distinctions are 1 kinds of fossils 2 sedimentology of the associated non saline facies 3 kinds of primary saline minerals 4 association of such saline minerals both in qualitative and quantitative terms 5 trace element isotope and fluid inclusion geochemistry of such saline minerals modified journal abstract

marine to nonmarine facies transition in permian evaporites of the palo duro basin texas geochemical response the late paleozoic palo duro basin evolved from a marine to nonmarine environment as it was infilled the evaporitic part of the sequence leonardian through ochoan is composed of regressive carbonate anhydrite halite cycles that displaced open marine environments toward the south during basin filling systematic vertical changes in evaporite geochemistry through the evaporite section include increasing 87sr 86sr ratios and decreasing altered from marine 34s in anhydrite decreasing recycled bromide content of the halite and increasing meteoric influence on the stable isotopic composition of fluid inclusions in halite geochemical changes correspond to changes in evaporite sedimentology and document the evolution from marine dominated to partly nonmarine evaporites geochemical tracers when used with sedimentological and facies analysis provide reliable indicators of the sources of water and solutes in an anhydrite halite facies tract perennial intermittently stratified and ephemeral brine pool conditions affect the amount of synsedimentary recycling variable rates of reflux and marine recharge control residence times of brines in the depositional environment these are two key processes in relating evaporite geochemistry to depositional environment

an upper aptian saline pan lake system from the brazilian equatorial margin integration of facies and isotopes facies and isotope sr and s data were combined in order to discuss the genesis and palaeohydrology of an upper aptian evaporite succession formed during the initial development of an intra continental rift from northern brazil comparison of facies distribution between two investigated areas shows i stable well stratified and hypersaline lakes with periods of anoxia and closure in the eastern margin of the basin where there was evaporite precipitation only in central lake environments and ii more ephemeral conditions in the eastern margin of the basin where a saline pan complex developed and evaporite precipitation took place mainly in marginal salinas and surrounding mudflats in both areas expansion contraction cycles developed as sedimentation took place accompanied by a decrease and then an increase in 87 sr 86 sr and d 34 s isotope values this combined with the wide distribution of sr and s isotope data within individual depositional cycles as well as petrographic and scanning electronic microscopic sem images led to the conclusion that diagenesis was not enough to obscure the primary geochemical signature a non marine brine source is suggested by 87 sr 86 sr ratios between 0ae707824 and 0ae709280 which are higher than those from upper aptian sea water i e between 0ae70720 and 0ae70735 the d 34 s value varies from 16ae12 to 17ae89 in the eastern margin of the basin which is in disagreement with upper aptian marine values 13 to 16 both geochemical tracers were influenced by facies characteristics and thus a model is provided where 87 sr 86 sr values respond to changes in expansion and contraction

stable δ13c δ18o and strontium isotopes through the paleocene at gebel aweina eastern tethyan region abstract stable 13 c 18 o and strontium 87 sr 86 sr isotopic records have been established through the paleocene section at gebel aweina in the eastern desert egypt the section has been formed in a shelf upper bathyal environment and spans the interval from planktonic foraminiferal zones p1d to p6a or p6b integrated evaluation of isotopic results and scanning electron microscope observations suggest that strontium and whole rock 13 c records reflect primarily original isotopic trends whereas 18 o and foraminiferal 13 c values have been severely affected by diagenesis the whole rock 13 c record exhibits a continuous increase of 4 from the early paleocene to middle late paleocene the increase is followed by a stepwise 13 c decrease of the same magnitude through the late late paleocene and onwards the gross trends of this 13 c record have earlier been registered in many coeval deep sea sections but there are also some significant disparities at aweina for example the paleocene carbon isotopic changes have a higher amplitude in the deep sea the mid to late paleocene 13 c increase has been interpreted to reflect high biological productivity and or changes in the global carbon mass balance the 13 c decrease in the upper part of the aweina section can be identified as the paleocene eocene transitional long term 10 3 kyr negative 13 c shift which may reflect a major reorganisation in global oceanic circulation patterns the well known latest paleocene deep sea benthic foraminiferal extinction event has been found in the upper part of the aweina section and coincides with a distinct and rapid 13 c decrease of 1 5 the benthic extinction event and the associated 13 c anomaly thus represent important stratigraphic markers also in more shallow environments the gebel aweina 13 c record shows considerably lower values compared to the global 13 c record during early and early late paleocene and in the latest paleocene in the early late paleocene foraminiferal zones p3a to the base of p4 the aweina 13 c values increase rapidly by 1 5 and converge with the global record thereafter the two records covary up to the benthic extinction event after which they diverge the convergence between the records may reflect sea level rise and more open water mass exchange between the eastern tethys and the world ocean the similarity of pilot 13 c records from greece and tunisia with the aweina record support this interpretation diagenetic processes however cannot be ruled out and further studies are required to determine the significance of the 13 c depletions in the eastern tethyan sediments the 87 sr 86 sr ratios through the paleocene at gebel aweina are remarkably invariable close to a value of 0 7077 this is the same trend that has been reported in some earlier detailed studies conducted on well preserved calcitic material from the paleocene indicating original sr isotopic signatures at gebel aweina the homogeneity of sr isotopic ratios throughout the paleocene contrasts with the prominent changes observed in the carbon isotope record indicating a decoupling of the mechanisms regulating the mass fluxes of these elements the invariable sr isotopic ratios suggest stable conditions as regards to relative changes in mass fluxes of riverine and or hydrothermal sr during the paleocene

a thermal tectonic model for high pressure rocks in the basal gneiss complex of western norway abstract the basal gneiss complex bgc of western norway is a segment of continental crust that was subjected to eclogite facies metamorphism during the caledonian orogeny and then was overprinted by amphibolite facies conditions numerical methods have been used to construct a model for thermal evolution of the bgc the calculated temperature depth time tzt paths for the bgc are in good agreement with the sequence of mineral assemblages that occur in metamorphosed mafic and ultramafic rocks however the thermal model indicates that retrograde zoning of minerals in the garnet bearing assemblages of eclogite and ultramafite may have developed metastably at pressures below 10 kbar numerical modeling of iron diffusion in garnet grains adjacent to olivine inclusions was used to calculate zoning profiles based upon the thermal model the calculated zoning profiles have shorter decay distances than the observed zoning profiles which may be due to uncertainties in the diffusion coefficients also discrepancies occur between the tzt paths and specific pt values calculated for eclogite and garnet ultramafite due either to the preservation of pre caledonian mineral assemblages or to utilization of geobarometers and thermometers which are based on different elements in different phases such as a1 in orthopyroxene and fe mg in olivine and garnet

the early caledonian finnmarkian event reassessed in finnmark 40ar 39ar cleavage age data from nw varangerhalvoya n norway abstract the relative significance of early finnmarkian and late scandian caledonian deformation in n norway is uncertain early studies suggested pervasive finnmarkian deformation whilst later results indicated a restricted finnmarkian domain the present work suggests it was more widespread than accepted and that inter finnmarkian scandian deformation occurred 40 ar 39 ar dating of 2 6 and 6 11 m pelitic fractions from the lower to mid greenschist facies tanahorn nappe five samples base middle allochthon and the epizone lokvikfjellet and barents sea groups three samples north varanger region in the north scandinavian caledonides show slightly discordant spectra most spectra from the tanahorn nappe preserve possible evidence of an early caledonian event in the high temperature steps with recoil excess ar effects in the low temperature steps no pre caledonian relict component has been recorded the results indicate finnmarkian deformation continued to 460 ma with scandian reactivation at 425 415 ma from the north varanger region a strongly crenulated sample yielded plateau ages 444 442 ma means of combined young steps from weakly to uncrenulated samples gave 470 450 ma suggesting penetrative strike slip deformation occurred in the late finnmarkian to inter finnmarkian scandian period no scandian ages were recorded in the north varanger region reassessment of published data from the laksefjord nappe and gaissa thrust belt suggests they were affected by finnmarkian deformation

experimentally determined compositions of diopside jadeite pyroxene in equilibrium with albite and quartz at 1200 1350 c and 15 34 kbar abstract equilibrium compositions of diopside jadeite pyroxene coexisting with albite and quartz were experimentally determined at 25 different p t conditions using an electron microprobe for analysis the new data and the 600 c data of holland 1983 provided the following mixing properties of the diopside di jadeite jd solid solution j k g xs x jd x di 12600 9 45 t 12600 7 6 t x jd x di 21400 16 2 t x jd x di 2 the di jd solution is close to ideal above 1000 c but immiscible below 565 c the di jd solvus is slightly asymmetric with the crest at composition di 42 4 jd 57 6 excess enthalpy is positive but smaller than indicated by the enthalpy of solution measurements of wood et al 1980 disorder in the di jd solution is significantly smaller than complete disorder implied by the ionic two site model

late paleozoic collision delamination short lived magmatism and rapid denudation in the meguma terrane nova scotia canada constraints from 40ar 39ar isotopic data the meguma terrane consists of 8 15 km of early paleozoic stratified rocks deposited on a continental basement that were deformed and metamorphosed during the late paleozoic as a result of lithospheric plate collision the oldest cleavage previously published whole rock 40ar 39ar plateau ages of 415 395 ma dates the onset of crustal thickening which was followed by voluminous but short lived late devonian granitic and minor mafic magmatism 380 370 ma this magmatism may have been the product of delamination of the lower lithosphere and upwelling of asthenosphere which effected melting above the new moho and resulted in intrusion at depths of 5 12 km 40ar 39ar plateau ages of hornblende muscovite and biotite indicate that at the present erosion level most of the meguma terrane cooled through 300 c by 368 360 ma slightly earlier than for the southwestern meguma terrane ca 345 ma the present erosion level was exhumed by the latest devonian early carboniferous visean the age of the

a coherent lithostratigraphic unit in the coesite eclogite complex of dabie shan china geologic and petrologic evidence abstract as a contribution to the discussion about the in situ vs exotic origin of the ultrahigh pressure metamorphic uhpm rocks and to the real size of the exhumed tectonic units the wuhe pailou unit wpu in eastern dabie shan was studied the wpu typically consists of two micas epidote gneiss marble with minor eclogite and jadeite bearing granofels with rare garnetite and eclogite nodules these lithologies are enclosed within leucocratic granitic gneiss jadeite bearing granofels is the most peculiar lithology of the wpu being the only felsic rock in dabie shan still preserving extensive relics of the uhpm mineral assemblage the uhp peak assemblage is coesite jadeite garnet epidote phengite kyanite with accessory rutile apatite and zircon all eclogites consist of garnet omphacite quartz coesite rutile or high al titanite phengite clinozoisite kyanite two micas epidote gneiss associated with the jadeite bearing granofels typically consists of epidote muscovite biotite plagioclase k feldspar rare garnet and accessory rutile titanite apatite and zircon locally the wpu paragneiss contains garnet with inclusions of phengite kyanite rutile and amphibole na plagioclase symplectite after omphacite a clockwise p t path was inferred for the wpu which consists of an early prograde part up to coesite eclogite facies conditions p 3 3 gpa and t 720 c an early decompression stage and a late part characterised by a near adiabatic decompression down to medium pressure p 1 1 gpa t 670 c and to low pressure amphibolite facies conditions followed by a final cooling to greenschist facies conditions both field and laboratory data consistently suggest that the wpu characterised by the close association of paragneiss marble eclogite and granofels is a supracrustal metasedimentary sequence which underwent subduction uhpm and exhumation as a coherent tectonic unit therefore within collisional orogens large coherent slices of continental crust may be subducted at depths greater than 100 km

excess silica in omphacite and the formation of free silica in eclogite silica lamellae in eclogitic clinopyroxene are widely interpreted as evidence of exsolution during decompression of eclogite however mechanisms other than exsolution might produce free silica and the possible mechanisms depend in part on the nature and definition of excess silica excess silica may occur in both stoichiometric and non stoichiometric pyroxene although the issue has been debated we show that all common definitions of excess silica in non stoichiometric clinopyroxene are internally consistent interchangeable and therefore equivalent the excess silica content of pyroxene is easily illustrated in a three component condensed composition space and may be plotted directly from a structural formula unit or recalculated end members in order to evaluate possible mechanisms for the formation of free silica in eclogite we examined the net transfer reactions in model eclogites using a thompson reaction space we show that there are at least three broad classes of reactions that release free silica in eclogite i vacancy consumption in non stoichiometric pyroxene ii dissolution of ti phases in pyroxene or garnet iii reactions between accessory phases and either pyroxene or garnet we suggest that reliable interpretation of the significance of silica lamellae in natural clinopyroxene will require the evaluation not only of silica solubility but also of titanium solubility and the possible roles of accessory phases and inclusions on the balance of free silica

petrology of a margarite bearing meta anorthosite from seljeneset nordfjord western norway implications for the p t history of the western gneiss region during caledonian uplift abstract the western gneiss region of norway contains relics of eclogite and high pressure granulite that have been extensively overprinted by amphibolite facies assemblages a meta anorthosite from seljeneset nordfjord contains fine grained margarite quartz plagioclase muscovite clots set in a zoisite quartz plagioclase clinozoisite matrix in some clots relict kyanite is preserved equilibria modeled in the cash system indicate a retrograde p t path that begins in the kyanite zoisite field p 8 2 kbar passes through reaction 1 kyanite zoisite quartz anorthite h2o between 610 c and about 800 c and finally through reaction 2 kyanite anorthite h2o margarite quartz the sodic composition of plagioclase in reaction 1 suggests that pressures in excess of 15 17 kbar at 750 800 c may have been experienced during silurian eclogite facies metamorphism the simplified cash reaction 2 occurs between invariant points at 4 3 kbar 520 c and 8 2 kbar 610 c but polyvariance due to variable na solid solution broadens the reaction into a band about 150 c wide cooling through 500 c occurred about 410 ma ago this study provides the first well defined p t path for caledonian retrograde metamorphism at amphibolite facies conditions

deposition and early alteration of evaporites summary the depositional settings for primary and early diagenetic evaporite deposits generally fall into three categories marginal mixed shallow subaqueous and subaerial shallow and deep subaqueous these three environmental groupings hold for both marine and nonmarine settings although the details of continental evaporites may be far more complex than in most marine fed water bodies the primary evaporite morphologies from many continental playa hypersaline marine and marine marginal depositional settings are reasonably well understood because of the numerous detailed studies of recent holocene and cenozoic deposits that serve as models for sedimentary interpretation the sedimentological features that develop in deeper water settings are inferred based on examination of unaltered cenozoic deposits each environmental setting develops characteristic depositional features and patterns and one facies grades into the next because there may be significant physiochemical changes in water composition during deposition as well as sudden change s in both water depth and basinal circulation description and interpretation of evaporative rocks should not be based on mineralogy alone but on the distinct sedimentary characteristics of each part of a deposit in cases where sediments still reflect their primary mineralogy and morphology most of the environments can now be recognized however geochemical studies are commonly required to determine the source s of the original water the determinative geochemical techniques that presently serve as a support to sedimentologic study include studies of fluid inclusions bromine content of chloride salts and the stable isotopes of strontium sulphur carbon and oxygen only after these and perhaps other chemical analyses are considered can the full depositional history of a region be reasonably unravelled

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

coupling of oceanic and continental crust during eocene eclogite facies metamorphism evidence from the monte rosa nappe western alps high precision u pb geochronology of ru tile from quartz carbonate white mica rutile veins that are hosted within eclogite and schist of the monte rosa nappe western alps italy indicate that the monte rosa nappe was at eclogite facies metamorphic conditions at 42 6 0 6 ma the sample area indren glacier furgg zone dal piaz 2001 geology of the monte rosa massif historical review and personal comments smpm consists of eclogite boudins that are exposed inside a south plunging overturned synform within micaceous schist associated with the eclogite and schist are quartz carbonate white mica rutile veins that formed in tension cracks in the eclogite and along the contact between eclogite and surrounding schist intrusion of the veins at about 42 6 ma occurred at eclogite facies metamorphic conditions 480 570 c 1 3 1 4 gpa based on textural relations oxygen isotope thermometry and geothermobarometry the