the present day stress field of australia abstract the unusual present day crustal stress pattern of the australian continent has been the subject of scientific debate for over 25 years the orientation of maximum horizontal present day stress s hmax in continental australia is unlike all other major tectonic plates in that the stress pattern shows regional variability and it is not oriented sub parallel to the direction of absolute plate motion previous studies on the stress pattern of australia revealed that the complex stress pattern of the continent is controlled at a first order by the superposition of plate tectonic forces exerted at the plate boundaries however prior analysis of the contemporary australian crustal stress pattern have been unable to model or explain the stress pattern observed in most of eastern australia and has not extensively addressed the numerous smaller scale variations in stress orientation the recent development of unconventional reservoirs in australia has resulted in a greatly increased amount of new data for stress analysis in previously unstudied or poorly constrained areas in eastern australia in addition stress analysis in conventional hydrocarbon mineral and geothermal exploration in all other parts of the continent provides the opportunity to review and update the australian stress map asm this study presents the new release of the asm with a total of 2150 stress data records in australia increased from 594 data records in 2003 the 2016 asm contains 1359 data records determined from the interpretation of drilling related stress indicators 650 from earthquake focal mechanism solutions 139 from shallow engineering measurements and two from geological indicators the results reveal four distinct regional trends for the s hmax orientation in australia including a nne ssw s hmax trend in northern and northwestern australia which rotates to a prevailing e w orientation in most western and south australia the orientation of s hmax in eastern australia is primarily ene wsw and swings to nw se in southeastern australia a comparison between the new asm database and neotectonic features further confirms the role of contemporary stress in recent deformation of the australian crust the 2016 asm reveals significant discrepancies between newly observed s hmax orientations and predictions by published geomechanical numerical models for the australian continent forces generated at the boundary of indo australian plate remain the major control on the regional crustal stress pattern in continental australia however the increased data density particularly in eastern australia reveals numerous local perturbations of the stress field that were not previously clearly captured hence the key findings of the new release are that local intra plate stress sources are more significant than previously recognized particularly in eastern australian basins and cause substantial local scale rotations of the present day crustal stress pattern that have not been factored into existing australian stress models

proterozoic contraction extension tectonics of the southern sao francisco region minas gerais brazil the southern sao francisco region comprises the southern portion of the sao francisco craton which is underlain by archean basement and its fringing proterozoic orogenic belts included in this region are three geologic provinces the quadrilatero ferrifero qf the sao francisco basin and the cordilheira do espinhaco we synthesize preliminary results of ongoing structural analysis reconnaissance field studies and published reports to provide a concise review of the geology of the region and to propose a working tectonic model for its proterozoic evolution interpretation of superimposed folds faults and foliations leads to the conclusion that the southern sao francisco region records the effects of four principal tectonic events that occurred subsequent to deposition of the lower proterozoic minas supergroup the first event resulted in formation of a northwest verging fold thrust belt the second event led to development of high angle reverse faults open folds and basement uplift the third event is manifested in the qf by the formation of normal faults and by the intrusion of mafic dikes these extensional structures may be associated with formation of the sedimentary basins east and south of the sao francisco craton the final event resulted in formation of a west verging fold thrust belt that affected the qf the cordilheira espinhaco and the sao francisco basin the events that we describe can be tentatively associated with regionally recognized orogenic periods trans amazonian uruacuano brasiliano

the pyrope coesite rocks and their country rocks at parigi dora maira massif western alps detailed petrography mineral chemistry and pt path both the coarse and fine grained varieties of the partly coesite bearing pyrope quartzites their interlayered jadeite kyanite rocks and the biotite phengite gneiss country rock common to all of them were subjected to detailed petrographic and textural studies in order to determine the sequence of crystallisation of their mineral constituents which were also studied analytically by microprobe prior to pyrope and coesite growth the mg rich metapelites were talc kyanite chlorite rutile ellenbergerite schists which upon continued prograde metamorphism developed first pyrope megacrysts in silica deficient local environments at the expense of chlorite talc kyanite and subsequently the smaller pyrope crystals with coesite inclusions from reacting talc kyanite based on geobarometrically useful mineral inclusions as well as on experimentally determined phase relations a prograde pt path simplified for water activity 1 is constructed which passes through the approximate pt conditions 16 kbar and 560 c 29 kbar and 720 c and finally up to 37 kbar at about 800 c where the mg rich metapelite was a pyrope coesite rock with phengite kyanite and talc still present during the retrograde path pyrope was altered metasomatically either into phlogopite kyanite quartz or at a later stage to chlorite muscovite quartz both assemblages yield pt constraints the latter about 7 9 kbar 500 600 c the country rock gneisses have also endured high pressures of at least 15 kbar but they provide mostly constraints on the lowest portion of the uplift conditions within the greenschist facies about 5 kbar 450 c microprobe data are presented for the following minerals pyrope ellenbergerite dumortierite unusually mgti rich jadeite vermiculite formed after na phlogopite paragonite and for several generations of phengite chlorite talc phlogopite dravite and glaucophane in the high pressure rocks as well as for biotite chlorite phengites epidote garnet albite and k feldspar in the country rock gneisses an outstanding open problem identified in this study is the preservation of minerals as inclusions within kyanite and pyrope beyond their pt stability limits

deformation volume and cleavage development in metasedimentary rocks from the ballarat slate belt psammites from the ballarat slate belt in se australia exhibit well developed differentiated or spaced cleavage defined by alternating phyllosilicate and quartz rich domains termed p and q domains respectively strain estimates derived from independent microstructural and chemical observations suggest that the p q fabrics developed in response to plane strain deformation dominated by solution transfer with the principal finite shortening in the p domains approximately twice that in the adjacent q domains significant finite extensions are indicated by ubiquitous quartz albite chlorite overgrowths in both p and q domains while pressure shadow development around syntectonic pyrite porphyroblasts suggest finite extension of at least 100 this estimate is comparable with the extension predicted for constant volume deformation and consequently there appears to have been no significant bulk material loss or gain on the hand specimen scale these observations are consistent with solute transfer scales as little as a few centimetres via diffusion in a stationary fluid and do not require although do not necessarily preclude large scale advective fluid transport through the slate belt during cleavage formation as suggested in previous studies

phase relationships in buchan facies series pelitic assemblages calculations with application to andalusite staurolite parageneses in the mount lofty ranges south australia low pressure medium to high temperature buchan type regional metamorphism of pelitic rocks in the mount lofty ranges south australia is defined by the development of biotite staurolite andalusite fibrolite prismatic sillimanite and migmatite zones k feldspar makes its first appearance in the prismatic sillimanite zone and here we restrict our discussion to lower grade assemblages containing prograde muscovite concentrating particularly on well developed andalusitestaurolite parageneses in general the spatial distribution and mineral chemical variation of these assemblages accord with the predictions of petrogenetic grids and p t and t xfe pseudo sections constructed from the internally consistent data set of holland and powell 1990 in the system kfmash assuming a h2o 1 although analysed white mica compositions are systematically more aluminous than predicted importantly the stability ranges of most critical assemblages predicted by these grids and pseudo sections coincide closely with p t estimates calculated using the data set of holland and powell 1990 from the mount lofty ranges assemblages with the exception of mn in garnet and zn in one staurolite cordierite muscovite assemblage non kfmash components do not significantly appear to have affected the stability ranges of the observed assemblages an apparent local reversal in isograd zonation in which andalusite first appears down grade of staurolite suggests a metamorphic field gradient concave towards the temperature axis and together with evidence for essentially isobaric heating of individual rocks is consistent with the exposures representing an oblique profile through a terrain in which heat was dissipated from intrusive bodies at discrete structural levels

geological and geophysical review of results of the arco 1 paul gibbs well flathead county montana abstract the arco 1 paul gibbs well was drilled to a depth of 17 774 ft within the cordilleran fold and thrust belt of northwest montana from september 1983 to october 1984 this well was a test for subthrust paleozoic hydrocarbon source and reservoir rocks below metasedimentary rocks of the proterozoic belt supergroup the well drilled only metasedimentary rocks of the middle proterozoic prichard formation and intrusive diabasic sills within the middle and lower prichard formation the several diabasic sills account for a gravity anomaly over the purcell anticlinorium where the well was drilled as well as for the extensive seismic reflectors felt by many to represent paleozoic rocks where penetrated by the gibbs well the prichard formation consists of about 14 000 ft of metasiltstones and quartzites intruded by several diabasic sills totaling about 3 900 ft thick two of the sills are more than 1 000 ft thick the well penetrates a 500 ft thick duplex zone of the pinkham thrust near 17 000 ft and it appears that the lower portion of the lower prichard formation has been thrust over the lower part of the middle prichard formation a throw of about 7 000 ft gas shows were present in the well for considerable thicknesses within the prichard formation particularly where extensive tectonic brecciation created fracture porosity source rock studies of the well cuttings indicate that the prichard formation contains intervals with sufficient organic carbon to have acted as a hydrocarbon source rock for much of its greater than 1 300 m y existence and possibly even since laramide tectonism and overthrusting it is believed that the gas shows in the prichard formation are indigenous to the prichard formation and may well represent the oldest indigenous hydrocarbons drilled to date in the world in the range from 1 430 to 1 300 m y old the area of the belt supergroup is felt to represent a new hydrocarbon province with potential for future di coveries within its proterozoic metasedimentary rocks end of article last page 1042

potential field imaging of palaeozoic orogenic structure in northern and central europe abstract the trans european suture zone tesz is the most fundamental lithospheric boundary in europe separating the ancient crust of the fennoscandian shield east european craton from the younger crust of central europe and extending deep into the mantle geophysical potential field images provide an overview of the entire palaeozoic orogenic system of northern and central europe for the first time the tesz is largely concealed by sedimentary basins of permian cenozoic age geological observations are largely restricted to local basement highs and deep boreholes and the coverage of deep seismic surveys is widely spaced despite experiments recently acquired within the europrobe programme by contrast the potential field data offer a relatively detailed coverage of standardised observations throughout the tesz while some features of the images may be sourced in the near surface particularly in the gravity image much of their content reflects the structure of the underlying palaeozoic basement at the scale presented the images highlight the most fundamental features of the crustal structure of the tesz these include the strong contrast between the highly magnetic crust of the east european craton and the less magnetic palaeozoic accreted terranes of central europe the lateral continuity of terranes and their internal structure particularly where arc magmatic complexes are involved and the location and geometry of the terrane boundaries oceanic sutures and strike slip zones that separate them

high pressure phengite decomposition in the weissenstein eclogite munchberger gneiss massif germany the petrography mineral chemistry and petrogenesis of a sample from the weissenstein eclogite bavaria germany has been investigated the total mineral assemblage comprises garnet clinopyroxenei ii quartz amphibolei ii rutile phengite epidote allanite plagioclase biotite apatite pumpellyite titanite sphene zircon alkali feldspar and calcite textural observations combined with geothermobarometry fe mg distribution between clinopyroxene garnet and phengite garnet jadeite content of omphacite si content of phengite and an content of plagioclase provide indications of two different stages in the metamorphic evolution of the rock the main phengitequartz eclogite mineral equilibration occurred at minimum p 13 17kbar minimum t 620 50 c the retrograde symplectite stage clinopyroxeneii amphiboleii biotite plagioclase occurred at ptotal between 12 and 8 5 kbar

stratigraphic and structural constraints on the proterozoic tectonic history of the olary block south australia abstract the lower proterozoic of the olary block is divided into five rock suites defining a conformable stratigraphic sequence correlated with the willyama supergroup of the broken hill block which has a probable depositional age no greater than 1800 ma the sequence was deformed and metamorphosed during the olarian orogeny at 1580 ma definition of the stratigraphy permits regional structural analysis and the resolution of two folding events an initial recumbent fold terrain redeformed by upright folds with a near vertical axial surface the olarian orogeny comprises a single regional compression axis with both folding events indicating a se direction of transport the described tectonic fabrics are consistent with simple shear deformation generating the early recumbent terrain

the seismicity of the adelaide geosyncline south australia a network of seismograph stations has been operational in south australia since 1963 a magnitude 2 event is locatable practically anywhere in the state presently about 250 earthquakes yr are being located the greatest concentration of earthquakes occurs in the flinders ranges of the adelaide geosyncline the other major zones are eyre peninsula and the southeast corner of the state in the last 100 yr south australia has experienced 10 earthquakes of magnitude larger than 5 the most recent being in 1986 the largest earthquake to have occurred in the state s history was the beachport kingston earthquake of 1897 ml 6 1 2 the focal depths for most south australian earthquakes are quite shallow being confined to the upper crust focal mechanisms have been obtained for six earthquakes occuring in the central flinders ranges the predominant principal stress is northeast southwest compression this is consistent with surface uplift of the ranges causing crustal thickening the population center of adelaide has the highest earthquake risk of any capital city in australia the 1954 ml 5 adelaide earthquake involved 30 000 insurance claims totalling 11 million u s currency epicenters for microearthquakes in the adelaide region show a correlation with known faults seismicity here appears to be associated with normal block faulting of the st vincent gulf graben structure

early palaeozoic foreland thrusting and basin reactivation at the palaeo pacific margin of the southeastern australian precambrian craton a reappraisal of the structural evolution of the southern adelaide fold thrust belt abstract regional and detailed structural mapping kinematic analysis and balancing and restoration of cross sections has lead to a re interpretation of the adelaide fold belt in south australia in this belt sedimentary rocks of the late proterozoic adelaidean and early cambrian normanville and kanmantoo sequences were deposited during at least two episodes of subsidence related to major crustal attenuation contraction and crustal thickening accompanied by granitoid intrusions are related to the cambro ordovician delamerian orogeny during this event both basins were reactivated inverted and the sedimentary rocks are now incorporated in a wnw verging foreland fold and thrust belt at the margin of the proterozoic southeast australian craton maximal shortening of the orogen was around 55 within the adelaidean basin shortening is dominantly accommodated by major mylonitic shear zones and reverse faults in the cambrian kanmantoo basin several thrusts are demonstrably reactivated growth faults across which thickness changes of cambrian sedimentary rocks are revealed by balancing and restoration of cross sections owing to the steep easterly dips of these faults in the western part of the kanmantoo basin lateral shortening of up to 58 is largely accommodated by intense folding and fold axial planar flattening strain further east strain magnitudes wane and the overall shortening of around 30 is accommodated by both discrete thrust zones and regional folds the basin reactivation along the australian part of gondwana s palaeo pacific craton margin reflects the rapid transition from passive to active tectonism which possibly is a consequence of the disintegration of the formerly conjugate margins of gondwana and laurentia

high pressure melting of eclogite and the p t x history of tonalitic to trondhjemitic zoisite pegmatites munchberg massif germany summary the zoisite pegmatites provide an excellent example of theonset of metabasite melting at eclogite facies conditions such conditions can be expected in a down going oceanicslab as well as in collision zones the newly produced meltin a metabasaltic rock of morb composition is tonalitic to trondhjemitic and shares some characteristics withthe ttg series or with adakites the amount of melt forming at a temperature of less than 7508c however is small as a result of the combined effect of relatively lowtemperature and restricted availability of water and themelt does not separate from the rock unit only if themelt fraction increases will the melt segregate and mightmigrate upwards influencing melting in the overlyingmantle wedge because of the poor outcrop situation ofthe mu nchberg area in the variscan chain of centraleurope it is unfortunately impossible to give an estimateof the amount of melt produced this will be a crucialquestion to solve at what degree of melting at whattemperature in a given composition andat what geological mechanical conditions the melt will effectively separate our data suggest the following model high pressurepartial melting and pegmatite formation occurred at con ditions only slightly above the water saturated solidus andcan be a fluid conserving or fluid recycling process any fluid released from hydrous minerals such as zoisite epidote or amphibole is trapped in small fractions offully to nearly water saturated siliceous melt for truedehydration melting a free fluid phase never exists neither the fluid nor the siliceous melt will separate andmigrate into the overlying rock units during uplift cool ing and crystallization the water which is stored in thesiliceous melt is again liberated and encounters a dehy drated eclogite facies assemblage here it hydrates theeclogite facies assemblage leading to crystallization ofhydrous minerals such as amphibole or mica this modelof fluid conservation or fluid recycling implies also thatthe trace element budget of the whole rock does notchange during melting and subsequent crystallization the pegmatites from the hangendserie of the mu nchbergarea still preserve some trace element signatures of theirindividual protoliths which means that the partial meltsdid not mix andwere not homogenized element transportoccurs onlyona restricted scale of probably much lessthanthe present thickness of the hangendserie the coarse grain size of the pegmatitic rocks is how ever a good condition to preserve textural disequilibriumand to record different stages of the uplift and coolinghistory reheating is indicated in the pegmatites by partialresorption of zoisite and crystallization of a second andthird generation with distinctly different composition this observation is in line with the idea that upliftoccurred during the collision event and shortly afteror simultaneously with stacking of the nappes that is in a short time frame which is in many cases close to thetime resolution of available geochronometric methods

partially retrograded eclogites of the munchberg massif germany records of a multi stage variscan uplift history in the bohemian massif eclogites with a wide range in bulk composition are present in the munchberg massif part of the variscan basement of the bohemian massif in north east bavaria new analyses of the primary phases garnet omphacite phengite and amphibole as well as the secondary phases clinopyroxene ii various amphiboles biotite phlogopite plagioclase margarite paragonite prehnite and pumpellyite reveal a complex uplift history new discoveries were made of samples with very jadeite rich primary omphacite as well as a secondary omphacite in a symplectite with albite various geothermobarometric techniques together with thermodynamic databases incorporating separately determined activity composition values and experimental data have clustered the minimum conditions for the primary assemblages to the p t range 650 60 c 14 3 1 kbar however jadeite in omphacite kyanite paragonite in phengite and zoisite grossular in garnet kyanite quartz relationships suggests pressures of 25 28 kbar at the same temperatures the fact that the secondary omphacite plagioclase assemblage yields pressures within a few hundred bars of the minimum pressures for the plagioclase free assemblages strongly suggests that the minimum values are serious underestimates zoning inclusion suites and breakdown reactions of primary phases in addition to new minerals formed during uplift define a polyphase metamorphic evolution which from geochronological evidence occurred solely within the variscan cycle the complex breakdown in other bohemian massif eclogites and the distinct variation in their temperatures during uplift suggest a multi stage thrusting model for the regional evolution of the eclogites such an evolution has significance with respect to incorporation of mantle slices into crustal sequences and fluid derivation from successively subducted units possibly driving the breakdown reactions

the early exhumation history of the western tianshan uhp metamorphic belt china new constraints from titanite u pb geochronology and thermobarometry the national natural science foundation grant award number 41330210 41702052 china postdoctoral science foundation funded project grant award number 8201400768

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

palaeozoic terranes and their lithospheric boundaries within the trans european suture zone tesz a review the trans european suture zone tesz is a broad and complex zone of terrane accretion separating ancient lithosphere of the baltic shield and east european craton eec from the younger lithosphere of western and southern europe there is debate about the number of terranes involved and their origins the most significant terrane boundaries originally oceanic sutures are poorly exposed and are defined using faunal provinciality prominent geophysical lineaments may represent sub terrane boundaries within composite terranes the avalonia composite terrane was amalgamated to baltica in latest ician time the provenance of the malopolska and moravo silesian terranes whose neoproterozoic basement is suspect with respect to baltica but with which they nonetheless share faunal affinities is still debated the extent of the variscide rhenohercynian zone defines the southern limit of the early palaeozoic accreted terranes terranes within the bohemian massif exhibit hp metamorphism recording subduction driven collision prior to incorporation in the tesz collage itself associated with a hp event in romania the saxothuringian zone and rheic suture are directly juxtaposed with the eec and the crustal structure of the tesz has been much modified by post palaeozoic tectonism deep seismic reflection data where available show that the oceanic sutures are frequently associated with inclined reflectivity zones irz in the lithospheric mantle here inferred to mark relict subduction zones interpreting the age of subduction is complicated by offset of originally coplanar mantle and crustal segments of the irz resulting from early orogenic lithospheric delamination at the moho interface and or post orogenic reordering processes the mantle irz appear to indicate a n directed polarity for early palaeozoic subduction apparently incompatible with the geological evidence which indicates subduction of the tornquist sea beneath avalonia and a large amount of underthrusting of avalonia by baltica possible explanations for these apparently incompatible observations are evaluated

aluminous titanite sphene from the eclogite zone south central tauern window austria abstract highly aluminous titanite with al 2 o 3 contents up to 14 wt 50 of the caalsio 4 f oh end member occurs in siliceous dolomites from the eclogite zone south central tauern window austria 140 chemical analyses of titanites from 13 samples from the eclogite zone and adjacent tectonic units reveal that al is incorporated into titanite primarily by the mechanism ti o al f oh there is also a strong positive correlation between al and f content of these titanites indicating that the combined substitution is enhanced by the presence of f al contents of titanite vary between tectonic units with the most aluminous varieties occurring in the high pressure eclogite zone variations also occur from sample to sample within a single tectonic unit and both between and within individual grains in a single sample complex zoning with sharp chemical and optical discontinuities is observed with al 2 o 3 variations of up to 6 wt within a single sample individual grains generally have low al cores mantled by high al zones and rimmed by low al edges it is suggested that the incorporation of al into titanite is favoured by high p low t and high f activity

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

are systematic variations in thrust belt style related to plate boundary processes the western alps versus the carpathians within the mediterranean region cenozoic deformation of the western alps and the west to east carpathians has resulted in two different styles of foreland fold and thrust belt the most prominent difference between the two belts is the presence carpathians or absence western alps of contemporaneous back arc extension but other important differences in structure topography and metamorphism also exist these differences in thrust belt style developed mainly during the final stages of thrust belt evolution and appear to reflect fundamental differences in the tectonic settings of the western alps and the carpathians in middle and late cenozoic time in particular they appear to be the result of convergence that is in the first case driven primarily by major plate motions and in the second case only by local motions of small lithospheric flakes or fragments we suggest that the structural styles developed in these two mountain belts may be useful in identifying mountain belts that have evolved in similar tectonic settings elsewhere in the world in this respect the western alps and the carpathians can be regarded as typical examples of two different styles of foreland fold and thrust belt or more properly as end member examples within a broad spectrum of foreland fold and thrust belt styles we propose that continental subduction zones and orogenic belts can be loosely divided into segments that show no major back arc extensional deformation adjacent to the belt the western alps and segments that exhibit back arc extension contemporaneously with thrusting the carpathians the former are found in areas where the rate of overall plate convergence exceeds the rate of subduction and are commonly typified by extensive involvement of crystalline basement in thrusting exposure of high grade metamorphic rocks at the surface high topographic elevation and large amounts of erosion tens of kilometers the latter are found in areas where the rate of subduction exceeds the rate of overall plate convergence and are commonly typified by thrust belts with little to no involvement of crystalline basement in thrusting low grade to no metamorphism low topographic elevation little erosion and in some instances an anomalously deep foredeep basin system

coesite in clinopyroxene in the caledonides and its implications for geodynamics coesite is reported for the first time from the caledonide orogen it occurs as inclusions in clinopyroxene in the dolomite eclogite at grytting norway and provides valuable new evidence to support the hypothesis of extremely high pressure 30 kbar in certain norwegian eclogites this finding has implications for the geodynamics and kinetics of the concepts of microscale intracrystalline tectonic overpressure and of macroscale local or regional tectonic overpressure and for the hypotheses of subduction and obduction involving a more than 100km vertical component of transport

reaction textures and fluid behaviour in very high pressure calc silicate rocks of the munchberg gneiss complex bavaria germany calc silicate rocks occur as elliptical bands and boudins intimately interlayered with eclogites and high pressure gneisses in the munchberg gneiss complex of ne bavaria core assemblages of the boudins consist of grossular ric h garnet diopside quartz zoisite clinozoisite calcite rutile and titanite the polygonal granoblastic texture commonly displays mineral relics and reaction textures such as post kinematic grossular rich garnet coronas reactions between these mineral phases have been modelled in the cao al 2 0 3 si02 c 02 h 20 system with an internally consistent thermodynamic data base high pressure metamorphism in the calc silicate rocks has been estimated at a minimum pressure of 31 kbar at a temperature of 630 c with x osq gi small volumes of a c02 n2 rich fluid whose composition was buffered on a local scale were present at peak metamorp hic conditions the p t conditions for the onset of the amphibolite facies overprint are about 10 kbar at the same temperature a co of the h20 rich fluid phase is regarded to have been 0 03 during amphibolite facies conditions these p t estimates are interpreted as representing different stages of recrystalliza tion during isothermal decompression the presence of multiple generations of mineral phases and the preservation of very high pressure relics in single thin sections preclude pervasive post peak metamorphic fluid flow as a cause of a re equilibration within the calc silicates the preservation of eclogite facies very high pressure relics as well as amphibolite facies reactions textures in the presence of a fluid phase is in agreement with fast tectonically driven unroofing of these rocks

statistical estimation of the seismicity level change around hokkaido northern japan the temporal seismicity change in two seismically active zones around hokkaido northern japan was investigated using the statistical estimate of the seismicity level sesl 09 procedure hypocenter data provided by the japan meteorological agency from 1960 to 2013 were analyzed the seismicity of two geographically different zones formed by pacific plate subduction and amurian plate convergence showed different statistical characteristics low cross correlation values between the two zones also suggest independent seismic processes for each area however an anomalously high cross correlation period was identified from 1996 to 2000 with a time lag of 8 weeks a 6 month seismic quiescence period before the strongest hokkaido toho oki earthquake 4 october 1994 mj 8 2 was observed on the pacific side

p t evolution of glaucophane omphacite bearing hp lt rocks in the western tianshan orogen nw china new evidence for alpine type tectonics the late palaeozoic western tianshan high pressure low temperature belt extends for about 200 km along the south central tianshan suture zone and is composed mainly of blueschist eclogite and epidote amphibolite greenschist facies rocks p t conditions of mafic garnet omphacite and garnet omphacite blueschist which are interlayered with eclogite were investigated in order to establish an exhumation path for these high pressure rocks maximum pressure conditions are represented by the assemblage garnet omphacite paragonite phengite glaucophane quartz rutile estimated maximum pressures range between 18 and 21 kbar at temperatures between 490 and 570 c decompression caused the destabilization of omphacite garnet and glaucophane to albite ca amphibole and chlorite the post eclogite facies metamorphic conditions between 9 and 14 kbar at 480 570 c suggest an almost isothermal decompression from eclogite to epidote amphibolite facies conditions prograde growth zoning and mineral inclusions in garnet as well as post eclogite facies conditions are evidence for a clockwise p t path analysis of phase diagrams constrains the p t path to more or less isothermal cooling which is well corroborated by the results of geothermobarometry and mineral textures this implies that the high pressure rocks from the western tianshan orogen formed in a tectonic regime similar to alpine type tectonics this contradicts previous models which favour franciscan type tectonics for the southern tianshan high pressure rocks

metamorphism in the olary block south australia compression with cooling in a proterozoic fold belt the sedimentary and igneous rocks comprising the lower proterozoic olary block south australia were deformed and meta morphosed during the mid proterozoic olar ian orogeny the area is divided into three zones on the basis of assemblages in metapelitic rocks higher grade conditions occurring in the south east mineral assemblages developed during peak metamorphism which accom panied recumbent folding include andalusite in zones i and i1 and sillimanite in zone 111 upright folding and overprinting of mineral assemblages occurred during further com pression the new mineral assemblages includ ing kyanite in zone i1 and kyanite and sillimanite in zone 111 the timing relationships of the aluminosilicate polymorphs together with the peak metamorphic and overprinting parageneses imply an anticlockwise p t path for the olarian orogeny pressure increasing with cooling from the metamorphic peak

grenvillian age decompression of eclogites in the glenelg attadale inlier nw scotland the glenelg attadale inlier is the largest basement inlier within the caledonian moine nappe of nw scotland in the eastern part of the inlier amphibolite facies retrogression of the eclogites is associated with tectonic fabrics and p t estimates indicate significant decompression c 20 km previous sm nd mineral whole rock dates indicated that peak eclogite facies metamorphism occurred around c 1 08 ga which was correlated with the grenvillian orogeny however the middle ree enrichment of the analysed garnets suggests the influence of apatite inclusions it is therefore likely that the interpretation of the c 1 08 ga age is complex possibly reflecting re equilibration at lower temperatures sampled eclogites contain zircon in a number of distinct textural forms that are mainly associated with pargasite and plagioclase and are part of the retrograde amphibolite facies assemblages titanite extensively replaces rutile and is clearly associated with the retrograde amphibolite facies event a second textural type of titanite forms anhedral grains with plagioclase and pargasite which is developed where the retrograde amphibolite facies assemblage overprints the eclogite mineralogy u pb dating has yielded the following ages zircon age of 995 8 ma and variably discordant rutile ages between 416 and 480 ma u pb and pb pb isochrons on titanite and plagioclase quartz separates yielded ages of 971 65 ma and 945 57 ma respectively in agreement with the zircon age analysed zircons and titanites are texturally part of the amphibolite facies assemblage the new zircon age demonstrates that amphibolite facies metamorphism during exhumation occurred at 995 8 ma the titanites could have closed with respect to pb at this time or alternatively at some time between c 1000 and 900 ma these data clearly demonstrate that parts of the scottish basement underwent major thick skinned tectonics during the grenvillian orogeny rutile is part of the eclogite facies paragenesis and yet has young ages these data are best explained by reheating producing near total pb loss related to emplacement of the late to post tectonic ratagain granite complex at c 425 ma at the end of the caledonian orogeny

fluid inclusions in epidote minerals and fluid development in epidote bearing rocks the widespread occurrence of epidote minerals in metamorphic and igneous rocks as well as in many ore deposit types makes it a promising candidate for fluid inclusion studies apart from high to very high temperature and low to intermediate pressure conditions epidote minerals are stable over a wide range of pressure and temperature in the continental and oceanic crust e g poli and schmidt 1998 yet fluid inclusion studies on epidote minerals are surprisingly scarce even in fluid saturated environments like certain vein type deposits or hydrothermal volcanic vugs and druses for example epidote minerals are not mentioned in the subject index of roedder s 1984 outstanding summary and review of fluid inclusion studies and occurrences which lists more than sixty different host minerals for fluid inclusions nonetheless more recent studies showed fluid inclusions in epidote minerals to be the only direct witness of the physiochemical and compositional fluid evolution during certain geodynamic processes mainly found in fossil geothermal systems ore deposits and high pressure to ultra high pressure rocks the aim of this review is to outline and summarize some aspects and interpretations of geodynamic processes which are based on temperature t pressure p molar volume v and composition x data from fluid inclusions in epidote minerals as well as associated host minerals from various geological environments the review starts with a chapter on some typical mixed volatile solid fluid equilibria involving epidote minerals which are relevant for the here discussed environments this is followed by a short introduction into the basic concepts of fluid inclusion research and the role of epidote minerals the next section covers fluid inclusion studies on epidote minerals from active and fossil geothermal systems as well as low grade metamorphic rocks and constraints on the p t x properties of the fluids present in these systems this is followed by a short introduction

retrograde evolution of eclogites evidences from microstructures and 40ar 39ar white mica dates munchberg massif northern bavaria phengites from eclogites and pegmatites 3t 2m1 coarse grained and recrystallized of the munchberg massif weissenstein and oberkotzau have been dated by the 40ar 39ar method 3t micas from the eclogites yielded plateau and isochron ages of 365 7 ma 2m1 micas show disturbed degassing spectra micas from pegmatites show a slight excess ar component with an isochron age of 353 to 351 3 ma an age component of approximately 300 ma was also detected in combination with age values from the literature the cooling history of the munchberg massif from eclogite facies conditions 390 ma to cooling below 350 c 350 ma is documented the age component of 300 ma is attributed to a low grade stage of mineral growth accompanied by a transitional ductile brittle deformation the petrological effects include formation of pumpellyite prehnite facies minerals frequently precipitated in microcraks and cleavage planes of earlier formed minerals this stage has to be seen in conjunction with the intrusions of the fichtelgebirge granite

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

origin of the western subbetic arc south spain palaeomagnetic and structural evidence abstract an integrated structural and palaeomagnetic study in late cretaceous eocene rocks of the western subbetic arc in the betic cordillera of southern spain shows that the change in fold trend around the arc is significantly greater than the variation in primary magnetic declination this suggests that the arcuate geometry is not primarily a consequence of differential rotation the area has experienced a regional clockwise rotation of at least 40 which was most probably imposed during oblique wnw directed convergence along the southern iberian margin in early miocene time before the arcuate structure was formed kinematic indicators associated with the arcuate folds and thrust traces arc for the most part consistently wnw directed suggesting that the arc is not primarily a result of variations in the direction of tectonic transport the arcuate structure was probably initiated without significant rotation by the wnw directed indentation of the curved western end of the alboran domain into the iberian margin and was then tightened involving up to about 35 of further rotation in different segments of the arc finally one sector in the arc was rotated anticlockwise by about 40 with respect to the rest of the region reorientating the magnetic declinations the fold trends and the kinematic indicators this rotation was associated with local sinistral shear

structure and origin of the fleurieu and nackara arcs in the adelaide fold thrust belt south australia salient and recess development in the delamerian orogen abstract the regional map pattern of structural trends in the early paleozoic adelaide fold thrust belt of south australia resembles an upright letter s in general structures in the fold thrust belt verge toward the gawler craton to the west so the northern curve nackara arc of the s is a salient whereas the southern curve fleurieu arc is a recess the map view axial trace of the nackara arc coincides with the thickest portion of the adelaidean late proterozoic basin and the map view axial trace of the fleurieu arc coincides with the intersection between the adelaidean and kanmantoo cambrian basins our structural analysis of the adelaide fold thrust belt demonstrates that the cross sectional structural geometry of the nackara arc contrasts markedly with that of the fleurieu arc in the nackara arc the belt consists of open detachment folds that probably formed above an evaporite hosted decollement whereas in the fleurieu arc the belt consists of an imbricate fan of basement involved thrusts further the foreland edge of the nackara arc coincides with a blind ramp whose strike parallels fold axes of the arc whereas the foreland edge of the fleurieu arc coincides with emergent thrusts that cut obliquely across earlier formed folds of the arc in the transition region between the two arcs the fold thrust belt consists of an intensely sheared basal duplex overlain by open folds structural contrasts between the nackara and fleurieu arcs indicate that the two curves did not form in the same way we present a model for development of these curves based on a comparison of their structural features to those of curves in other fold thrust belts and based on previous studies of curve formation using sandbox analogs we suggest that curvature of the nackara arc reflects the control of basin stratigraphy on the width of a fold thrust belt while curvature of the fleurieu arc reflects oroclinal bending of the fold thrust belt when it impinged on the southeastern corner of the gawler craton our model explains the structural contrast between the two arcs and illustrates correlations between fold thrust belt curve formation and pre deformational basin geometry

effect of overburden thickness on thrust belt geometry and development laboratory sand models simulating development of thrust belts indicate that 1 distance between the backstop and the first formed thrust is a linear function of initial sand layer thickness 2 spacing between the first two thrusts is most likely a nonlinear function of initial sand layer thickness 3 initial dip of successive ramps decreases progressively toward the foreland because of variations in principal stress directions with depth and or changes of mechanical properties of sand with increasing overburden 4 faults to the hinterland steepen and become less active as hinterland thrust sheets undergo penetrative shear during sand wedge growth and 5 new ramp initiation occurs to the hinterland of the basal detachment tip line these observations can be interpreted both in context of area balance considerations and soil mechanics theory if initial sand layer thicknesses in our models represent syntectonic overburden in natural thrust belts i e distance between the ground surface and the detachment then our results suggest that locations of some thrust belt salients are controlled by along strike variations in stratigraphic thicknesses and that initial thrust spacing decreases progressively to the foreland if the thrust belt involves a foreland tapering basin furthermore our sand model observations suggest that the concept of a fixed rigid backstop in the hinterland of thrust belts may be misleading as a consequence of thickening the hinterland portion of the thrust belt becomes stabilized and effectively becomes the backstop itself

some geodynamic and compositional constraints on postorogenic magmatism postorogenic magmatic suites are common to many orogens in many cases apparently just postdating the cessation of deformation they differ from preceding orogenic suites in that they have higher temperatures more primitive isotopic signatures and bimodal natures and thus are compositionally similar to suites found in extensional regimes we propose that thinning of the lithospheric mantle which may be an automatic response to orogenic lithospheric thickening is responsible for these magmatic suites mantle lithospheric thinning moves the asthenospheric lithospheric thermal boundary higher in the lithospheric column thereby raising the overall thermal budget of the orogen and the likelihood of basaltic magmatism this removal of much of the dense lithospheric mantle root of the orogen also invokes uplift capable of producing horizontal orogenic buoyancy forces that will oppose and potentially terminate deformation extreme fractionation of the magmas is promoted by high temperatures and a noncompressional or tensional lithospheric stress regime to produce accompanying felsic a type magmas this model explains why the cessation of deformation is coincident with high temperature bimodal magmatism and inferred uplift as well as the long noted similarity and confusion between postorogenic and extensional magmatic suites this arises because both reflect thinning of the lithospheric mantle not because both reflect extensional tectonics we suggest that these magmatic episodes may be important in transferring lithospheric mantle material and its compositional signatures into the crust

the cordilleran foreland thrust belt in northwestern montana and northern idaho from cocorp and industry seismic reflection data cocorp and petroleum industry seismic reflection profiles in northwestern montana reveal the structure of the cordilleran foreland thrust belt the front ranges consist of thick thrust sheets containing precambrian belt supergroup and paleozoic miogeoclinal shelf rocks above a thin remnant of paleozoic rocks and gently westward dipping north american basement interpretation of the seismic data and results from a recent petroleum exploration well suggest that 15 22 km of precambrian belt supergroup sedimentary rocks are present in several thrust plates beneath the eastern purcell anticlinorium previous hypotheses of a large mass of paleozoic miogeoclinal sedimentary rocks or slices of crystalline basement located beneath the eastern purcell anticlinorium do not appear to be supported by the data the easternmost occurrence of allochthonous basement is interpreted to be in the western part of the anticlinorium near the montana idaho border comparison of the cordilleran foreland thrust belt in northwestern montana and southern canada suggests that a change in the deep structure of the purcell anticlinorium occurs along strike the anticlinorium in southern canada has been interpreted as a hanging wall anticline that was thrust over the western edge of thick proterozoic north american basement whereas in northwestern montana the anticlinorium appears to consist of a complex series of thrust sheets above highly attenuated north american basement

basement cover interaction in the adelaide foldbelt south australia the development of an arcuate foldbelt abstract the upper proterozoic to cambrian aged sedimentary and volcanic rocks comprising the adelaide foldbelt were deformed and in places metamorphosed during the cambro ordovician delamerian orogeny tectonic fabrics developed in the central portion of the foldbelt mt lofty ranges demonstrate westward transport during the orogeny the sigmoidal shape outlined by the kangaroo is mt lofty ranges olary portion of the foldbelt is interpreted to have been the result of dextral wrench faulting in the lower to mid proterozoic basement thus cover rocks overlying such basement wrench fault zones would have suffered a transpressional stress regime giving rise to the observed fold axis oriented at an oblique angle to the thrust boundary in the northern portion of the foldbelt northern flinders ranges wrench faulting is interpreted to have accommodated considerable basement shortening which initiated a basement cover decollement and resulted in thrust bound pop up structures in the cover

laser ablation icp ms u pb and 40 ar 39 ar age constraints on neoarchean to paleoproterozoic magmatic and tectono metamorphic evolution of the link between hope bay and elu greenstone belts northeast slave craton nwt canada abstract the elu link connecting the neoarchean hope bay and elu granite greenstone belts in the bathurst block of the northeast slave craton consists of volcano sedimentary and gabbro granite rocks laser ablation icp ms zircon and titanite u pb dating was combined with mineral 40 ar 39 ar age data to date the elu link rocks and d 1 d 3 tectono metamorphic events as well as characterize the response to the thelon orogeny in the area the volcanic rocks are correlated with the ca 2716 ma flake lake suite in the adjacent hope bay belt whereas the sedimentary units have a minimum depositional age of 2684 11 ma nearly coinciding with the onset of d 1 deformation most gabbro granite bodies were emplaced between 2651 14 ma and 2577 13 ma coeval with the d 2 deformation whose accompanying metamorphism culminated at 2632 7 ma older ages up to 3042 22 ma retained by either the gabbro granite or their hosts are indicative of crustal contamination a few gabbro granites were also emplaced during the 2577 13 ma to 2494 21 ma d 3 deformation event however the 2494 21 ma intrusions are unusual and mark the archean paleoproterozoic transition the d 3 deformation was followed by erosional exhumation and localized thermal pulses associated with the emplacement of diabase dikes at 2228 8 ma 2128 11 ma and 802 75 ma the thelon orogeny imprint inferred from the 2054 11 ma to 1919 5 ma biotite ages corresponds to nearly isobaric low temperature

k ar geochronology of different tectonic units at the northwestern margin of the bohemian massif abstract the polymetamorphic moldanubian mo of the northeasthern margin of the bohemian massif has been thrust to the north onto the mainly paleozoic sedimentary saxothuringian of the fichtelgebirge fg these two units have undergone polyphase deformation and the last regional event to affect both units was a low pressure metamorphism in which temperatures decreased towards the north in contrast the nappe units of the erbendorf vohenstrauss zone zev and the erbendorf greenschist zone egz which partly cover the border of the moldanubian and the saxothuringian and the munchberg nappe pile mm which lies on the saxothuringian were in parts subjected to a late medium pressure metamorphic event the zev the egz the mo and the fg are intruded by late carboniferous granites conventional k ar analyses mainly of hornblendes and muscovites from the autochthonous fg and mo the units beneath the nappes have yielded exclusively carboniferous dates the oldest dates point to a regional cooling of the rocks which outcrop at the present day surface at about 330 320 ma i e at the early late carboniferous boundary the late carboniferous cooling history was largely governed by the thermal influence of the post kinematic granites 320 295 ma especially in the fg and the northern mo the high grade metamorphic rocks in the western part of the zev and in the upper three nappes of the mm mostly yield dates around 380 ma i e early devonian the results show a relatively wide scatter moreover biotites frequently appear to be older than the coexisting muscovites both observations indicate that the rocks underwent a later thermal influence whether some groups of older dates e g 400 ma are due to excess argon or to inherited argon is still open to discussion slightly scattered muscovite dates around 366 ma were obtained for the prasinite phyllite series one of the lower nappes of the mm a single hornblende from the egz gave the same age these two nappes have therefore probably been affected by a late devonian thermal and or tectonic event the muscovite dates obtained from the paleozoic bavarian lithofacies the lowermost nappe of the mm and the hornblende dates from the eastern part of the zev are indistinguishable from those of the autochthonous units fg and mo

calculation and application of clinopyroxene garnet plagioclase quartz geobarometers recently published thermodynamic and experimental data in a variety of chemical systems have been evaluated to derive gibbs free energies for hedenbergite and pyrope these were used to calculate the geobarometric equilibria

monazite in a variscan mylonitic paragneiss from the munchberg metamorphic complex ne bavaria records cadomian protolith ages small oval shaped unshielded monazite grains found in a variscan garnet muscovite bearing mylonitic paragneiss from the liegendserie unit of the munchberg metamorphic complex mmc in the northwestern bohemian massif central europe yield only pre variscan ages these ages determined with the electron microprobe have maxima at about 545 520 and 495 ma and two side maxima at 455 and 575 ma and are comparable with previously determined ages of detrital zircon reported from paragneisses elsewhere in the nw bohemian massif the pressure p temperature t history of this mylonitic paragneiss determined from contoured p t pseudosections involved an initial stage at 6 kbar 600 c reaching peak p t conditions of 12 5 kbar 670 c with partial melting followed by mylonitization and retrogression to 9 kbar 610 c the monazite representing detrital grains derived from igneous rocks of a cadomian provenance between 575 455 ma has survived these variscan metamorphic deformational events unchanged because this mineral has probably never been outside its p t stability field during metamorphism this article is protected by copyright all rights reserved

an interpretation of the tectonostratigraphic framework of the murray basin region of southeastern australia based on an examination of airborne magnetic patterns abstract new pixel map representations of regional total magnetic intensity data reveal previously unknown characteristics of the basement concealed beneath thin cainozoic sediments of the murray basin in southeastern australia interpretations of magnetic patterns in terms of structural features allow a revised interpretation of the nature of the tectonostratigraphic framework underlying and flanking the basin the magnetic data indicate that arcuate or curvilinear structural trends under the murray basin do not conform with those of the exposed lachlan fold belt to the east and suggest that the basement concealed beneath the basin together with that exposed in the victorian highlands to the south forms a distinct composite tectonostratigraphic terrane beneath the southwestern murray basin proterozoic lower cambrian metasediments of the padthaway ridge of the kanmantoo fold belt display a northwesterly trending structural grain and a previously unsuspected continuity of structural trend with adelaidean cambrian rocks of the mount lofty ranges to the west in the south cambrian volcanics of the black range and stavely greenstone belts have similar magnetic response and appear to be components of a single elongate and strongly magnetic domain which extends to the northwest for at least 400 km stavely belt to the north a similar but entirely concealed northeasterly trending magnetic domain can also be interpreted as volcanics lake wintlow belt together these two magnetic domains appear to form an arcuate zone of volcanics with a concave to the east configuration located at a possible suture between the lachlan and kanmantoo fold belts beneath the western murray basin in the south the magnetic imagery indicates that metasediments of the cambro ordovician stawell belt produce magnetic patterns distinct from those produced by the metasediments of the adjacent ordovician bendigo belt which can itself be subdivided into a number of areas of distinct magnetic pattern magnetic domains can be interpreted in terms of concealed proterozoic and palaeozoic structural belts and tectonostratigraphic terranes reconstructions suggest that much of the murray basin may be underlain by a former microcontinental block or rifted marginal plateau of precambrian crust now welded to the precambrian craton to the west deformation of the kanmantoo and adelaide fold belts adjacent to and beneath the western and southwestern margins of the basin can be attributed to late cambrian early ordovician convergence between the microcontinental block and the craton volcanics of the arcuate stavely and lake wintlow belts are interpreted to be located at the suture between the microcontinental block and the craton in addition the presence of concave to the east curvilinear magnetic trends in the cambro ordovician metasedimentary belts beneath the murray basin suggests that these successions as well as the volcanics of the heathcote and mount wellington belts may form allochthonous sheets these were possibly emplaced from the east during late ordovician devonian deformation possibly related to convergence of a further microcontinental block underlying the adjacent lachlan fold belt to the east of the murray basin

mechanisms of thrust propagation some examples and implications for the analysis of overthrust terranes abstract evidence is presented for the existence of three fundamental mechanisms by which thrust sheets move the mechanisms are 1 failure of a stiff layer to form ramp flat geometry imbricated thrust sheets 2 detachment of a layer by folding decollement thrust sheets 3 differential layer parallel shortening lps thrust sheets the mechanisms are independent but may operate interactively to form families of hybrid thrust sheets since lps thrust sheets have not been previously described or documented data from the new york plateau deformed almost exclusively by differential lps is presented to demonstrate the physical characteristics of this thrust mechanism information from the plateau indicates that finite strain behavior closely reflects the geometric boundary conditions and is independent of temperature and depth of burial finite strain data are used to construct a set of iso strain maps in both the deformed and undeformed states the iso strain maps are in turn used to determine the displacement field for the thrust sheet the displacement field allows visualization of the effects of both lagrangian and eulerian transformations on an initially orthogonal grid utilizing sections from a number of overthrust belts it is shown that the three mechanisms occur universally although in various proportions lps is regionally developed throughout the central and northern appalachians the presence of the lps thrust sheets probably accounts for the failure of structural cross sections to bed length balance in these blind thrust terranes finally a series of examples drawn from the field as well as the literature are used to illustrate both the characteristics of hybrid thrust sheet families as well as to indicate how knowledge of their behavior can be utilized in developing strategies for the construction and balancing of structural cross sections

high density co2 n2 inclusions in eclogite facies metasediments of the munchberg gneiss complex se germany the eclogite facies metasedimentary rocks in the munchberg gneiss complex t 630 30 c p 17 24 kbar locally contain co2 n2 rich fluid inclusions of extremely low molar volumes 32 cm3 mol in quartz these fluid compositions are mainly found in rocks intercalated with calcsilicate bands densities were determined from low temperature phase transitions like stable or metastable homogenization l v l partial homogenization s l v s l and the transition s l l l liquid v vapour s solid the high fluid densities are in agreement with eclogite facies pressure and temperature and subsequent amphibolite facies co2 n2 inclusions were not observed in adjacent eclogites nor in non calcareous metasediments these rock types contain predominantly h2o rich inclusions correlating with amphibolite facies conditions the variation of fluid composition with lithological differences indicates local fluid gradients and speaks against a pervasive fluid flow during eclogite facies metamorphism

thirty years of seismic network recording in south australia selected results abstract the year 1993 marks 30 years of seismic network recording of earthquakes in south australia the network currently comprises 17 short period instruments of which six use digital recording and five employ triaxial sensors approximately 350 earthquakes are located within the state each year using a computerised seismic analysis system developed by the phillip institute of technology a duration based magnitude scale equivalent to the richter m l scale has been developed for most stations the pre network historical record of earthquake activity in south australia dates back to 1837 epicentres are available for just 45 earthquakes of these ten are of magnitude five or greater the instrumental data over the last 30 years show a similar trend in epicentral pattern to the historical earthquakes with the major zones being the flinders ranges eyre peninsula and the southeast there have been 40 earthquakes of magnitude four or greater since 1963 the largest earthquake being of magnitude six in the musgrave ranges during 1986 mine and quarry blasts within the state have been useful in calibration of the network both in terms of hypocentral location and amplitude studies the explosions have also furnished valuable information on the crustal velocity distribution epicentral co ordinates of mine blasts are generally good to within 3 5 km the explosions yield richter magnitudes of one charge size 1 or 2 tonnes to 2 5 charge size 50 tonnes the crustal s waves used in earthquake magnitude determinations exhibit an amplitude distance decay coefficient of 1 2 the p wave velocity function of the crust increases non linearly with depth from about 5 0 km s 1 near the surface to 6 4 km s 1 at 20 km depth where the gradient reduces with the velocity reaching a value of about 7 4 km s 1 at a depth of 40 km

the spar lake strata bound cu ag deposit formed across a mixing zone between trapped natural gas and metals bearing brine ore formation at the spar lake red bed associated strata bound cu deposit took place across a mixing and reaction zone between a hot oxidized metals transporting brine and a reservoir of sour h2s bearing natural gas trapped in the host sandstones fluid inclusion volatile analyses have very high ch4 concentrations 1 mol in most samples and a sample from the fringe of the deposit has between 18 and 36 mol ch4 the ratio of ch4 co2 in fluid inclusions appears to vary regularly across the deposit with the lowest ch4 co2 ratios from high grade chalcocite bearing ore and the highest from the chalcopyrite bearing fringe the helium r ra isotope ratios 0 23 0 98 and concentrations define a mixture between crustal and atmospheric helium the volatiles in fluid inclusions ch4 co2 h2s so2 h2 h2o and other organic gases and values of f o2 and temperature calculated from the volatiles data all show gradations across the deposit that are completely consistent with such a mixing and reaction zone other volatiles from the fluid inclusions hcl hf 3he 4he n2 ar characterize the brine and give evidence for only shallow crustal fluids with no magmatic influences the brine entered the gas reservoir from below and along the axis of the deposit and migrated out along bedding to the southwest northeast and northwest metals transporting brines may have been fed into the host sandstones from the east fault but that remains uncertain abundant ore stage fe and mn calcite cements from the reduced fringe have 13c values as low as 18 4 and many values less than 10 which indicate that significant carbonate was generated by oxidation of organic carbon from the natural gas the zone of calcite cements with very low 13c values approximately envelopes chalcocite bearing ore sulfur isotope data of cu pb and fe sulfides and barite indicate derivation of roughly half of the orebody sulfide directly from sour gas h2s that sour gas h2s had developed in steps known from other sedimentary basins starting with 1 bacterial sulfate reduction bsr of seawater sulfate having 34s of about 20 and sequestering of the sulfide in organic matter in source rocks stratigraphically below the deposit host rocks followed by 2 maturation of the sulfide bearing organic matter into liquid petroleum with relatively homogeneous sulfide having 34s of 5 5 then by 3 thermal cracking of the oil to ch4 and h2s with relatively homogeneous sulfide having 34s closely distributed about 6 the ch4 and h2s migrated and were trapped in sandstones of the upper member of the revett formation where they were later met by the 200 c metals transporting brine there was additional contribution of sulfide to ore from later thermochemical sulfate reduction tsr operating on sulfate 34s of 20 to 29 in both formation waters and metals transporting solutions a large range of 34s in sulfides resulted as the 6 sour gas sulfide was supplemented with varying proportions of 20 to 29 sulfide from tsr