formation mechanism and tectonic significance of millipede microstructures in the nw himalaya abstract this article focuses on the origin and tectonic significance of millipede inclusion trail microstructures preserved within garnet porphyroblasts of typical barrovian type schist from the swat region of the himalayas in pakistan two possible kinematic models are assessed envisaging bulk coaxial shortening and progressive simple shear 3d microstructural analysis of three samples hosting the millipedes reveals a poly phase deformation history that produced three suborthogonal foliations called sx sy sz successive inclusion of sx and sy in garnet porphyroblasts produced two sets of millipedes with distinctive subvertical and subhorizontal orientations respectively this kinematic reconstruction is supported further with a numerical simulation using finite difference code of millipede formation in a spherical porphyroblast subjected to a superposition of two orthogonal shortening directions measurements of inclusion trail curvature axes or fia foliation intersection inflexion axes in porphyroblasts in 61 additional samples from the study area which contain straight sigmoidal or spiral inclusion trails reflect two principle orogenic episodes during the first episode fias developed with wnw ese set 1 and e w set 2 trends associated with thrusting and collision tectonics a younger fia set 3 with nne ssw trend developed as a result of subsequent bulk e w crustal shortening and associated regional scale folding sigmoidal or straight inclusion trails defining this fia set can be correlated with the millipede microstructures based on their similar trends and timing relative to matrix fabrics these results are consistent with the meso and macro scale structures in the region and significant in terms of establishing relative timing of formation of different structures in the region well developed preferred vertical and horizontal orientations of both sigmoidal and millipede inclusion trails imply that their development involved limited or no relative rotations between porphyroblasts sigmoidal trails formed in zones where bulk shearing caused progressively reoriented matrix foliations around stable garnets while millipedes formed simultaneously in local coaxial strain pods

evolution of the sanbagawa and shimanto high pressure belts in sw japan insights from k ar ar ar geochronology abstract the sanbagawa belt sensu lato in japan is one of the world s classical high pressure hp metamorphic belts and has long been considered to be a coherent hp belt of the cretaceous age however recent progress in detrital zircon geochronology together with the accumulation of abundant phengites k ar ar ar ages revealed that the belt is comprised of two petrotectonic belts sanbagawa sensu stricto hp belt and shimanto hp belt these two belts have distinctly different ages of peak metamorphism and different p t conditions of metamorphism the sanbagawa schists sensu stricto were metamorphosed in the conditions of the pumpellyite actinolite facies through the epidote blueschist to epidote amphibolite facies and up to the eclogite facies during a prograde stage in a subduction zone at 120 115 ma phengite k ar geochronology revealed that the subsequent exhumation after the peak metamorphism took placed in a manner that the higher grade rocks exhumed more rapidly in comparison with the lower grade rocks this is supported by a positive correlation between age and apparent metamorphic gradient that have formed during the post metamorphic peak hydration recrystallization moreover the schists have experienced intense ductile deformation and long term exhumation it took longer than 31 m y to reset the phengite k ar system in contrast the shimanto hp schists were metamorphosed in the epidote blueschist greenschist transitional facies to the epidote amphibolite facies and have experienced a short term deformation for less than 13 m y this short deformation formed a negative correlation between k ar age and apparent metamorphic gradient these two contrasting age temperature relationships suggest different exhumation processes between the two hp belts most likely due to a change in subducting oceanic plates in the cretaceous along the paleo japanese convergent margin

felsic magmatic phases and the role of late stage aplitic dykes in the formation of the world class cantung tungsten skarn deposit northwest territories canada abstract a field and petro chemical classification of felsic magmatic phases fmps at the world class cantung w skarn deposit was undertaken to document the evolution of magmatism and the relationships between different fmps metasomatism and mineralization early fmps include moderately differentiated zr hf 18 26 ti zr 14 15 biotite monzogranitic plutons and early biotite rich granitic dykes and compositionally similar quartz feldspar porphyry dykes late highly fractionated zr hf 8 17 ti zr 3 13 fmps sourced from a deeper monzogranitic intrusion include 1 leucocratic biotite or tourmaline bearing dykes derived from localized entrapments of residual magma and 2 sub vertical ne trending aplitic dykes derived from a larger segregation of residual fluid and incompatible element enriched magma the aplitic dykes have textures morphologies spatial associations and a pervasive calcic metasomatic mineral assemblage ca plagioclase quartz or clinozoisite indicative of syn mineralization emplacement very late stage overpressuring and initiation of sub vertical fractures into the overlying plutonic carapace and country rocks by supercritical magmatic fluid led to an interaction with calcareous country rocks that resulted in an increased aca2 in the fluid and the concurrent precipitation of w skarn residual magma also ascended with and quenched in equilibrium with the magmatic fluid to from the aplitic dykes then was metasomatized by the fluid as it interacted with calcareous country rocks overall highly fractionated and moderately to very highly undercooled fmps at cantung provide evidence for a large and evolving felsic magmatic system at depth that segregated and maintained a stable fluid and incompatible element enriched residual magma until the latest stages of crystallization the detailed study of fmps associated with magmatic hydrothermal mineral deposits allow us to refine our understanding of these mineralizing systems and better define metallogenic and exploration models for intrusion related mineralization

petrology of chloritoid ilmenite rich rocks in the indus suture melange of pakistan implications for the cretaceous paleolatitude of kohistan abstract the indian plate and kohistan island arc are juxtaposed to the north of peshawar along the indus suture which is characterized by a tectonic melange consisting of ultramafic mafic and a variety of sedimentary rocks within metavolcanic greenstones there are small lensoid bodies comprising quartz white mica up to 4 5 wt feo chlorite pseudothuringite to ripidolite pyrite and abundant chloritoid up to 60 and ilmenite these lenses consist essentially of sio 2 tio 2 al 2 o 3 and iron oxide there is a clear petrographic and geochemical major trace and re element transition from these rocks to their host greenstones suggesting a common parentage the greenstones contain high tio 2 fe 2 o 3 and p 2 o 5 their chondrite normalized patterns show enrichment in light ree depletion in heavy ree negative eu and positive yb anomalies because the greenstones have probably been altered the present set of data is not capable of deciphering the tectonic setting of these rocks but previous geochemical studies have suggested an island arc setting for volcanic rocks in the melange by chemical analogy with lateritized basalts the chloritoid rich rocks are considered to be the product of weathering of basalts in tropical probably equatorial conditions before the northward drift of kohistan melange formation and greenschist facies metamorphism occurred during the collision of the indian plate and the kohistan magmatic arc to its north in the late cretaceous early tertiary

arsenic in bedrock soil and groundwater the first arsenic guidelines for aggregate production established in finland abstract concern over arsenic as rich drinking water has gained worldwide attention since the 1990s when the problem was discovered in west bengal in india and in bangladesh since then authorities and research institutes have focused on risk assessment and management for as in finland nationwide geochemical mapping projects determined background levels and revealed regions with a higher than average as content in bedrock and soil approximately 10 of the citizens in finland use drinking water from private wells groundwater especially from drilled bedrock wells may contain as concentrations higher than 10 g l the european union quality guideline for as in drinking water here we present the outcome of two european union projects ramas and asrocks which based their conclusions on nationwide databases and thousands of samples both ramas and asrocks focused on the tampere hame region of southern finland where bedrock and soil contain more as than in other parts of finland on average over 1000 groundwater samples revealed that drilled bedrock wells may contain as rich water in certain geological units naturally occurring as in bedrock and soil may also cause the mobilization of as during rock aggregate production and construction activities potentially impacting on groundwater aquifers surface waters and biota arsenic concentrations in aggregate production and construction exceeded the regional background levels in some bedrock and aggregate product samples but during leaching tests as concentrations were found to be low based on the results risk management tools were revised and guidelines for the rock aggregate industry were established in cooperation with authorities companies and other stakeholders to our knowledge the guidelines established were the first in the world the guidelines for as for the aggregate and construction industries can be applied in other countries and adapted to local conditions

chemical features of white micas from the piemonte calc schists western alps and implications for k ar ages of metamorphism abstract anomalously large chemical ranges in muscovite paragonite and muscovite celadonite systems are observed in white micas from the piemonte calcschists in the chisone valley area internal western alps the petrographical and chemical observations on white mica strongly suggest that most mica crystals with high na k ratios in the chlorite zone are of detrital origin and were derived from the pre alpine high temperature metamorphic sequence such the caledonian and or variscan submicroscopic muscovite ms paragonite pg composite aggregates occur in the chlorite zone and their epma analyses give an apparent chemical composition range from ms 0 6 pg 0 4 to ms 0 2 pg 0 8 in the rutile zone the paragonite content of the white micas is less than 20 suggesting that the white micas have been homogenized during the alpine metamorphism even if detrital white micas existed metamorphic mica is also very heterogeneous the total range in si content becomes wider with increasing of metamorphic grade 3 22 3 39 pfu for the chlorite zone 3 07 3 45 pfu for the chloritoid zone and 3 06 3 59 pfu for the rutile zone this clearly indicates that the micas have experienced significant retrogressive chemical reactions during cooling and exhumations of the host schists the detrital white mica in the chlorite zone has not reset well in its k ar system during the alpine subduction related metamorphism the wide range of the white mica k ar ages from 115 to 41 ma must be due to a mixture of various amounts of detrital white mica in the separates this feature is also observed in the chloritoid zone though the age variation is not so large as that in the chlorite zone in contrast the mica in the rutile zone which was higher than 450 c has been reset completely during alpine hp metamorphism

geology mineralogy and human welfare the complex sciences of geology and mineralogy couple the focused sciences of physics chemistry and biology to the diffuse disciplines of ecology and the environment for this colloquium 18 papers have been selected on matters related to human welfare particularly health and both physical and mental wellbeing to demonstrate the importance of new research plans and new instrumentation emerging chemical microscopes using neutrons synchrotron x rays and electrons allow physicochemical characterization of mineral surfaces and adsorbed molecules and ions in soils 1 plant growth depends on subtle interactions between mineral surfaces saline fluids and microbes incorporation of good trace elements into food depends on the interaction of organic and inorganic components as does that of toxic ones one quarter of the wheat and rice crops are lost to mn oxidizing bacteria soils become contaminated with mobile toxic elements including pb cd se and as which can affect plant growth and food safety 2 4 mineral dust blown from drying geological basins pervades the atmosphere and falls to earth with both good results loess soil in central europe china and north america was important for early agriculture and still supports large populations and bad ones air pollution causes lung problems 5 chemical microscopes provide physicochemical analysis of tiny particles particularly useful for distinguishing the natural and industrial components 6

a re evaluation of the stratigraphy and evolution of the kohistan arc sequence pakistan himalaya implications for magmatic and tectonic arc building processes new field mapping and structural data combined with published geochemical data from the kohistan arc in the nw himalaya enable a re evaluation of the arc stratigraphy key lithological units and their relationships are more clearly defined permitting the construction of a revised magmatic tectonic history for the arc the oldest units are transitional oceanic type basalts which form the basement to the subduction related sequence arc type gabbroic sheets and plutons intrude the oceanic basalts together these form the kamila amphibolite belt metasediments and basaltic lavas were deposited within an extensional basin onto the kamila amphibolite belt basement this sequence exposed across the arc forms a distinct stratigraphic unit which is formally defined here as the jaglot group sediment charged turbidity currents transported material into the basin whilst submarine eruptions contributed the basaltic component this period of extension culminated in the eruption of high mg boninites of the chalt volcanic group which overlie the rocks of the jaglot group the earliest granitoids of the kohistan batholith predate suturing and intrude the jaglot and chalt sequences at c 100 ma kohistan sutured to asia suturing being accompanied by thickening of the arc with the development of major intra arc shear zones and a penetrative regionally developed steep cleavage at c 85 ma intra arc rifting permitted the emplacement into the arc of the voluminous gabbronorites of the chilas complex which clearly intrudes the kamila amphibolite belt to the south and the jaglot group to the north the chilas complex has been regarded as part of the pre suturing juvenile arc sequence field evidence summarized here show this to be not so heat advection associated with emplacement of the complex caused amphibolite facies regional metamorphism melting of the lower arc and plutonism some of the resultant granitoid plutons were unroofed and eroded during a compressional phase at between 80 and 55 ma before emplacement of further plutons and extrusion of basaltic through to rhyolitic volcanic rocks at between 55 and 40 ma at least three phases of extension and rifting each separated by short lived phases of compression charac terized arc evolution much of the magmatism is controlled by extensional tectonics within the overriding plate of the kind commonly associated with a retreating subduction zone

crustal response to continental collisions between the tibet indian south china and north china blocks geochronological constraints from the songpan garze orogenic belt western china we report shrimp u th pb monazite conventional u pb titanite sm nd garnet and rb sr muscovite and biotite ages for metamorphic rocks from the danba domal metamorphic terrane in the eastern songpan garze orogenic belt eastern tibet plateau these ages are used to determine the timing of polyphase metamorphic events and the subsequent cooling history the oldest u th pb monazite and sm nd garnet ages constrain an early barrovian metamorphism m1 in the interval c 204 190 ma coincident with extensive indosinian granitic magmatism throughout the songpan garze orogenic belt a second higher grade sillimanite grade metamorphic event m2 recorded only in the northern part of the danba terrane was dated at c 168 158 ma by a combination of u th pb monazite and titanite and sm nd garnet ages it is suggested that m1 was a thermal event that affected the entire orogenic belt while m2 may represent a local thermal perturbation rb sr muscovite ages range from c 138 100 ma whereas rb sr biotite ages cluster at c 34 24 ma these ages document regional cooling at rates of c 2 3 c myr 1 following the m1 peak for most of the terrane however those parts of the terrane affected by the higher temperature m2 event e g the migmatite zone experienced initially more rapid c 8 c myr 1 cooling after peak m2 before joining the regional slow cooling path defined by the rest of the terrane at c 138 ma regional slow cooling between c 138 and c 30 ma is thought to be the result of post tectonic isostatic uplift after extensive crustal thickening caused by collision of the south and north china blocks the clustering of biotite rb sr ages marks the onset of rapid uplift across the entire terrane commencing at c 30 20 ma this cooling history is shared with many other regions of the tibet plateau suggesting that uplift of the tibet plateau including the songpan garze orogenic belt occurred predominantly in the last c 30 myr as a response to the continuing northwards collision of india with eurasia

biodurability of chrysotile and tremolite asbestos in simulated lung and gastric fluids chrysotile mg 3 si 2 o 5 oh 4 and tremolite ca 2 mg 5 si 8 o 22 oh 2 asbestos represent two distinct mineralogical categories of regulated asbestos commonly evaluated in epidemiological toxicological and pathological studies human respiratory and gastric systems are sites of asbestos deposition where chrysotile and tremolite asbestos are undersaturated with respect to biological fluids and dissolution kinetics control the persistence of these minerals in biological environments here we examined the biodurabilities i e the resistance to dissolution of chrysotile and tremolite asbestos in simulated body fluids as a function of mineral surface area over time batch experiments in simulated gastric fluid sgf hcl and nacl solution at ph 1 2 and simulated lung fluid slf modified gamble s solution at ph 7 4 were performed at 37 c over 720 h to evaluate the dissolution of chrysotile vs tremolite asbestos in acidic and near neutral biological fluids the rate limiting step of si release for both minerals was used to obtain rate constants k and reaction orders n allowing comparisons of mineral dissolution rates both chrysotile and tremolite asbestos are less biodurable in sgf low ph compared to slf near neutral ph based on equivalent surface area comparisons the surface chemistry of tremolite is more reactive in lung fluid than chrysotile and vice versa in digestive fluid however the relative biodurabilities of these asbestos silicates from most to least are tremolite slf chrysotile slf tremolite sgf chrysotile sgf when accounting for the greater surface area of chrysotile per mass or per fiber compared to tremolite overall this study illustrates the importance of surface area and fiber morphology considerations when evaluating the biodurabilities of asbestiform minerals

origin and evolution of the thermal waters from the pamukkale geothermal field denizli basin sw anatolia turkey insights from hydrogeochemistry and geothermometry abstract the pamukkale geothermal field pgf of the denizli basin sw turkey is one of the most distinguished active geothermal fields known in the world the thermal waters from the pgf are subdivided into two groups group 1a ca hco3 and group 1b ca so4 types the cold waters are also classified into two groups group 2a ca hco3 and group 2b mg hco3 types the hydrogeochemical properties of the pgf thermal waters suggest interactions with the basal metamorphic rocks of the menderes massif tectonically overriding by the carbonate rocks of the lycian nappes and sedimentary rocks of the neogene formations the bedrock units are stratigraphically overlain by the neogene sedimentary units of the denizli group the thermal springs of the pgf are affected by several hydrothermal processes including mixing water rock interaction and input of mantle volatiles the thermal water plots of the pgf deviate from the full equilibrium line indicating a low water maturity and or mixing processes mixing models and na k mg ternary diagram suggest mixing between meteoric and thermal waters during the uprising of the deep originated fluids the water rock interaction leads saturation of calcite and induces travertine precipitation in the discharge area low tritium this study proposes a conceptual hydrogeological hydrogeochemical tectonic model for the pgf the thermal waters are derived from the infiltration of rainwater through fractures and faults in high recharge areas to the deep hot reservoir heating produced by the high geothermal gradient is interpreted in relation with the regional crustal thinning thermal waters upwell along wnw ese trending deep faults and fractures the pamukkale fault system that act as hydrothermal pathways favouring migration of a huge amount of co2 rich gas from deep geothermal reservoir the geochemical and isotopic data of the thermal waters and gas indicate that the degassing of both metamorphic co2 and mantle derived co2 occurs in the pgf helium isotope data indicate that mantle volatiles produce possibly an upwelling into asthenosphere and ascent along these tectonic discontinuities in this context the pgf is one of the best example of geothermal fields as an interaction of active magmatism in the actively extending crustal setting

continuous metamorphic gradient documented by graphitization and k ar age southeast otago new zealand the chrystalls beach brighton coastal section southwest of dunedin new zealand exposes otago schist including the weakly metamorphosed triassic accretionary melange of the chrystalls beach complex and higher grade rocks of a largely felsic arc derived provenance melange zones contain pelagic sediments some of which are manganiferous and metabasites the grade of metamorphism increases progressively from southwest to northeast four mineral zones are recognized largely on the basis of mineral assemblages in psammitic and semipelitic rocks pumpellyite chlorite pumpellyite actinolite epidote actinolite and biotite d 002 data for carbonaceous material b 0 values for phengite and metamorphic phengite k ar ages are reported for 32 pelitic and semipelitic samples remarkably tight correlations are revealed between d 002 for progressively graphitized carbonaceous material k ar ages that range from 184 6 to 138 7 ma and linear distance along the section both the d 002 values and the k ar ages decrease progressively toward the northeast through the four mineral zones and with progressive textural changes all rocks cropping out in the section have undergone a coherent episode of progressive metamorphism associated with terrane collision and have not been disturbed by any later major displacements a convex trend for phengite b 0 values plotted against advancing graphitization suggests p t conditions during metamorphism as in the high pressure intermediate facies series the age of the metamorphic peak is inferred to be 175 155 ma middle to late jurassic with cooling to the mica closure temperature at 155 135 ma late jurassic to early cretaceous unloading denudation and cooling were accompanied by localized hydrothermal events the oldest covering strata were deposited at ca 100 ma and denudation was completed by ca 75 80 ma middle triassic radiolarian nodules in melange zones are dated as preceding the metamorphic peak by about 65 ma associated turbidites contain suspected late middle to early late triassic tube fossils

petrology of the dykes from the waziristan ophiolite nw pakistan abstract the waziristan ophiolite is located in the suture zone between the indian plate to the east and afghan block to the west it is highly dismembered and divisible into three main sheets or nappes which from east to west are the vezhda sar nappe entirely comprised of pillow basalts the boya nappe made up of ophiolitic melange with an intact section in its basal part and the datta khel nappe consisting mainly of sheeted dykes with smaller proportions of other components faunal evidence suggests that the ophiolite is of tithonian valanginian age it was thrust over the mesozoic shelf slope sediments of the indian plate to the east during the paleocene and is unconformably overlain by sedimentary rocks of early to middle eocene age to the west beside the sheeted dykes best exposed in the hanging wall of the datta khel thrust ene of datta khel the ophiolite also contains isolated dykes these are doleritic and basaltic in composition the dykes contain high na 2 o contents and high feo t mgo and lile hfse ratios and low tio 2 2 o contents non depletion of nb and high lile hfse ratio negate respectively an island arc or mid ocean ridge setting for these dykes enrichment in the lile suggests the involvement of a crustal component driven by fluids along the subduction zone several geochemical parameters suggest that the dykes of waziristan ophiolite have transitional characteristics between mid ocean ridge basalt and island arc tholeiite it is therefore proposed that these dykes may have originated in a back arc basin tectonic setting

hydrochemical characterization of pamukkale travertines denizli turkey for remediative measures the unesco world heritage snow white travertines in pamukkale w turkey are discolored as a consequence of algae growth at the surface the first act to restore the travertines was to abandon the activities and facilities that found to provide nutrients discoloration has continued after the pollution sources were abandoned because the nutrients were sorpted onto the travertine material the subsurface water was found to be contaminated by desorption of the nutrients sorption desorption characteristics of the travertines had to be quantified in order to achieve an effective remediation and restoration this study was carried out to determine the sorption desorption characteristics of the travertines by batch and column experiments batch experiments revealed that the sorption isotherms of the pamukkale travertine fit a linear model for nitrate and freundlich isotherm model for phosphate the distribution coefficients k d for nitrate and phosphate were calculated from the isotherms as 24 1 and 181 l kg respectively incorporating k d values the retardation factors were calculated as 142 for nitrate and 1553 for phosphate thus the relative velocity of nitrate and the phosphate was calculated as 7 3 10 2 and 6 7 10 3 m day respectively the data obtained from the column experiment evaluated by fitting a theoretical curve the results from the column experiment were then interpreted in terms of flushing of nitrate by pore volumes and suggested that the travertines can be cleaned up by flushing at least four pore volumes

excess 40ar free phengite in ultrahigh pressure metamorphic rocks from the lago di cignana area western alps abstract ar ar analyses of phengites and paragonites from the ultrahigh pressure metamorphic rocks zoisite clinozoisite schist garnet phengite schist and piemontite schist in the lago di cignana area western alps were carried out with a laser probe step heating method using single crystals and a spot dating method on thin sections eight phengite and two paragonite crystals give the plateau ages of 37 42 ma with 96 100 of 39 ar released each rock type also contains mica crystals showing discordant age spectra with age fractions 20 35 ma significantly younger than the plateau ages phengite inclusions in garnet give ages of 43 2 1 1 ma and 44 4 1 5 ma which are significantly older than the spot age 36 4 1 4 ma from the matrix phengites and the plateau ages from the step heating analyses inclusion ages 43 and 44 ma are consistent with a zircon shrimp age 44 1 ma in this area these results suggest that the oceanic materials that underwent a simple subduction related uhpm form excess 40 ar free phengite and that the peak metamorphism is ca 44 ma or little older we suggest that matrix phengites experienced a retrogression reaction changing their chemistry contemporaneously with deformation related to the exhumation of rocks releasing significant radiogenic 40 ar from the crystals this has lead to the apparent ages of the matrix phengites that are significantly younger than the inclusion age

the influence of crustal structure on compositions of subduction related magmas abstract a survey of sr isotopic ratios and other compositional features of subduction related magma suites reveals significant correlations between these averaged parameters and characteristics of the underlying crust i e thickness composition and age these observations lead to the conclusion that crust and or mantle rocks in the hanging walls of subduction zones are involved in modification of primary mafic magmas typically basalt or basaltic andesite it is proposed that mafic magmas will stagnate within the crust or uppermost mantle where they may differentiate and react with wall rocks the extent to which such processes manifest themselves will depend upon details of the local crustal structure in particular the composition and age of the crust will strongly influence such parameters as sr nd and pb isotopic compositions such data strongly indicate the involvement of crustal rocks in locales underlain by old sialic crust e g central andes depending upon the level of magma stagnation and evolution within the crust different trends in isotopic composition may result these isotopic trends may be enhanced by partial melting of the wall rocks to produce relatively silicic anatectic magmas and locally they may reflect subduction of continental sediments interpretation of the isotopic data may be more ambiguous in locales underlain by younger and more mafic continental crust cascades e eleutians and those underlain by oceanic crust owing to the similarity in isotopic composition of primary magmas and the latter crustal materials yet some degree of crustal involvement in magmatic evolution seems highly probable even in these more primitive terranes consequently most island arc magmas and especially those more evolved than basalt are probably not primary in the sense that they do not represent direct melts of the upper mantle studies of arc volcanic rocks may yield misleading conclusions concerning processes of magma generation related to subduction unless evolutionary processes are defined and their effects considered it appears that modern volcanic arcs provide a poor analog for models of early crustal development because the modern mantle derived magmatic components are more mafic in composition than average continental crust

evolution of the lithosphere in pakistan abstract the geological setting of pakistan in the framework of the modern concept of plate tectonics is unique in the sense that within an area of about 800 000 km 2 critical tectonic junctions of different interacting plates and microplates are present in an environment where field exposures are excellent here we discuss the dynamics of these various plate boundaries two types of active plate boundaries are conspicuous 1 convergent boundaries characterized by continent continent collision obduction and thrusting in the northern region of the himalaya and by oceanic crust subduction with a volcanic arc and a wide accretionary wedge in the southern region of chagai and makran 2 a transform boundary the chaman transform zone characterized by very large strike slip and lesser thrusting the chaman transform zone connects the makran convergence zone where oceanic lithosphere is being subducted beneath the lut and afghan microplates with the himalayan convergence zone where the indo pakistan lithosphere is underthrusting eurasia the chaman zone is at present an intracontinental plate boundary with oblique motion characterized by north south strike slip faults and eastward thrusting and folding in the kirthar sulaiman mountain belt this mountain belt the northwestern margin of the indo pak subcontinent was an atlantic type margin from the late paleozoic until the cretaceous in the cretaceous the continental margin became a plate boundary a thrust belt was formed in the paleocene and fragments of the oceanic crust were obducted either as thrust sheets muslimbagh or as an ophiolitic melange bela and waziristan

rbsr dating of the kohistan arc batholith in the trans himalaya of north pakistan and tectonic implications the kohistan arc batholith in northern pakistan is situated between the indus suture and the northern suture it belongs to the trans himalayan belt which continues eastwards as the ladakh arc batholith in northwest india and the kangdese batholith in southern tibet in kohistan the island arc consists upward sequence of the chilas stratiform complex of norites noritic gabbros and chromite layered dunites which formed in the sub arc magma chamber plutons of tonalite and diorite one of which has a rbsr isochron age of 102 12 ma the chalt volcanics of basaltic tholeiites succeeded by andesites to rhyolites and the yasin group sediments which formed in overlying intra arc basins and which contain albian aptian faunas all these rocks were deformed by major fold structures which are correlated with the formation of the northern suture ne sw trending basic jutal nomal dykes north of gilgit cross cut all the above structures and have a39ar 40ar hornblende age of 75 ma thus the northern suture must have formed in the period 102 12 to 75 ma with the island arc attached to the eurasian plate further northward subduction of the tethyan plate gave rise to an andean type batholith two plutons of which have rbsr isochron ages of 54 4 ma and 40 6 ma the dir utror group of calc alkaline lavas and sediments with eocene fossils are remnants of the volcanic cover of the andean type batholith we suggest that late cretaceous blueschists formed during subduction under the active continental margin and that continental collision and formation of the indus suture was in the eocene the batholith was intruded by layered aplite pegmatite sheets at 34 14 ma and 29 8 ma rbsr ages in post collisional times the87sr 86sr initial ratios of all the dated rocks range between 0 7039 and 0 7052

the new england batholith eastern australia geochemical variations in time and space the new england batholith australia is part of the upper paleozoic new england fold belt with most plutons intruded into the deformed trench complex metasedimetary rocks in the southeast part of the fold belt the batholith was emplaced in two major periods of plutonism the first during the upper carboniferous and the second during the upper permian and triassic with a major phase of metamorphism and deformation including westward overthrusting of the trench complex sedimentary rocks between the two periods on the basis of petrography geochemistry and isotopic characteristics the granitoids of the batholith are subdivided into five named intrusive suites and a group of leucoadamellites the differences between the six groups are considered to reflect differences in their source rock types the carboniferous granitoids are peraluminous s type and are divided into the bundarra plutonic suite a belt of very coarse grained adamellites with cordierite garnet and the hillgrove plutonic suite a belt of biotite rich garnet deformed adamellites and granodiorites both suites have 18o greater than 10 negative 34s 87sr 86sr initial ratios about 0 706 are ilmenite bearing and have low feo3 ratios the bundarra plutonic suite however is consistently sio2 rich greater than 70 contains cordierite and has higher 18o than the hillgrove plutonic suite the two s type suites are inferred to have formed by partial melting of the deepest parts of a wedge of trench complex sedimentary rocks oceanwards of an andean volcanic chain to the west analagous to the lower tertiary s type plutons of the sanak baranof plutonic belt of southern alaska of the remaining four groups of plutons emplaced during the upper permian and triassic two are metaluminous i type granitoids one the clarence river plutonic suite new name a group of k poor granodiorites and tonalites with low 87sr 86sr initial ratios average 0 7035 and the other the moonbi plutonic suite a group of k rich adamellites with low 87sr 86sr initial ratios average 0 7045 18o less than 10 and 34s positive the clarence river plutonic suite is inferred to have formed from the partial melting of a large ion lithophile element poor gabbro source region and the moonbi plutonic suite from a large ion lithophile element rich shoshonite source region a third group the uralla plutonic suite is less metaluminous has higher 87sr 86sr initial ratios average 0 706 18o only just less than 10 and negative 34s and is considered to have formed in a region containing a physical mixture of metaluminous and peraluminous source rocks gabbro and metasedimentary rocks plutons of the fourth group are leucoadamellites largely emplaced after the other suites with low 18o indicating an i type source it is argued that this group has resulted from low degrees of dry partial metling of an i type source region that had undergone an earlier melting event these four groups of plutons are largely confined to a narrow belt parallel to but 100 km west of the present rifted margin of australia their origin may be related to crustal thickening attendant on the overthrusting that occurred early in the permian and or a temperature increase in the lower crust due to the recovery of normal continental geotherms following the cessation of subduction

carbonaceous material in pelitic schists of the sanbagawa metamorphic belt in central shikoku japan abstract carbonaceous material in pelitic schists of the sanbagawa metamorphic belt in central shikoku japan was separated from the host rocks and its x ray diffraction and chemical composition were studied its crystal structure and chemistry change continously with increasing metamorphic grade and approach those of well ordered graphite near the biotite isograd as graphitization is a rate process the temperature of complete graphitization differs from one metamorphic terrain to another as a function of the duration of metamorphism in an individual metamorphic terraan however the degree of graphitization is a useful indicator of relative metamorphic temperature in lower grade rocks

collision and rifting in the tethys ocean geodynamic implication abstract the tethys ocean was formed 250 m y ago when gondwana collided with laurasia since then and up to its closure about 40 50 m y ago the development of the ocean was dominated by repeated jumps of the spreading axes to the passive margin of gondwana splitting of microcontinents their transportation across the ocean and accretion to the active margin of eurasia it appears that jumps of the spreading centre and rifting of the passive margin coincided with periods of major collisions on the active margin several epochs of collision and rifting are described the late permian mid late triassic late jurassic early cretaceous end of the early cretaceous late eocene the simultaneous occurrence of rifting and collision has important geodynamic implications and it cannot be explained if only the forces applied to plate margins i e slab pull and ridge push are considered as the plate drying forces slab pull did not act in times of collision when the subduction zone was blocked by continental fragments and the ridge push creates compression but not extension on the passive margin it is suggested instead that the conveyor belt process of transportation of continental masses from the passive to the active margin of tethys was governed by north directed convective flow in the asthenosphere in times of collision when lithospheric plates were unable to move with the flow the latter created great tensile stresses in the overlying lithosphere that led to formation of rifts and then to new spreading centres

health effects of mineral dusts other than asbestos this article reviews the health effects from occupational exposure to mineral dusts citations include those providing both clinical evidence of disease and support by epidemiological data in many instances these associations have been studied experimentally to establish the etiological agents the health effects of the following mineral and rock dusts will be reviewed the three polymorphs of silica quartz cristobalite and tridymite coal sepiolite palygorskite kaolinite talc vermiculite non figrous amphiboles mica chlorite erionite wollastonite fuller s earth 200 refs 4 figs 13 tabs

transpressional folding and associated cross fold jointing controlling the geometry of post orogenic vein type w sn mineralization examples from minas da panasqueira portugal the world class w sn panasqueira deposit consists of an extensive subhorizontal vein swarm peripheral to a late orogenic greisen cupola the vein swarm consists of hundreds of co planar quartz veins that are overlapping and connected laterally over large distances various segmentation structures a local zigzag geometry and the occurrence of straight propagation paths indicate that they exploited a regional joint system a detailed orientation analysis of the systematic joints reveals a geometrical relationship with the subvertical f2 fold generation reflecting late variscan transpression the joints are consistently orthogonal to the steeply plunging s0 s2 intersection lineation both on the regional and the outcrop scale and are thus defined as cross fold or ac joints the joint system developed during the waning stages of the variscan orogeny when already uplifted to an upper crustal level veining reactivated these cross fold joints under the conditions of hydraulic overpressures and low differential stress the consistent subperpendicular orientation of the veins relative to the non cylindrical f2 hinge lines also when having an inclined attitude demonstrates that veining did not occur during far field horizontal compression vein orientation is determined by local stress states variable on a meter scale but with the minimum principal stress consistently subparallel to fold hinge lines the conspicuous subhorizontal attitude of the panasqueira vein swarm is thus dictated by the geometry of late orogenic folds which developed synchronous with oroclinal buckling of the ibero armorican arc

geochemistry of major and trace elements in permian coal with an emphasis on no 8 coal seam of zhuji coal mine huainan coalfield china a better understanding on geochemistry of elements in coal has both environmental and geological implications in this study 53 coal samples were collected from no 8 coal seam of the zhuji coal mine huainan coalfield the concentrations of 49 elements ash yield and total organic compound toc as well as mineralogical phases in coal were determined as compared with chinese the usa and world coals si k se cd sn sb and w in studied coal seam are higher whereas zn as and lu are lower the enrichment factor and concentration coefficient show that se cd sn sb and w are preferably enriched in studied coals the enrichment of se and cd is probably attributed to their higher proportions of organic forms most major and trace elements tend to concentrate in either the upper or lower sections of coal seams which suggest that depositional micro environment was important in controlling elements migration and enrichment the correlation analysis of elements with ash yield shows that the behavior of elements in coal follows the periodic change of metallic activity the modes of occurrence of major and trace elements are elaborated by statistical methods silicon is mainly in form of montmorillonite or presents as free quartz iron is associated with chlorite siderite lepidocrocite and other iron bearing minerals ti shows obviously organic association three groups of elements are divided in accordance with the cluster dendrogram group 1 sc hree be y v co cu p sr b sn se bi toc s ba as group 2 lree zn al mn li na th cr fe mg and group 3 ca mo si w ad ti pb k many trace elements including li sc v cr zn sr la ce nd sm eu gd tb lu pb bi and th correlate positively with al suggesting their occurrence mainly in clay such as kaolinite and chlorite ree in the studied coalfield was primarily supplied by terrestrial clastics coming from north china coal basin the differentiation of lree and hree is probably attributable to their different physicochemical characterisitcs and specific paleo sedimentary environment various indexes e g b content ash index c value and the existence of certain minerals suggest a reducing and anoxic sedimentary environment of coal swamp with a stable supply of terrigenous detrital materials in a moist environment the origins of enriched elements are primarily derived from the source rock sedimentary environment and thermally contact metamorphism or possibly magmatic hydrothermal fluids

tectonics magmatism hydrothermalism and sets of flat joints locally filled by snw aplite pegmatite and quartz veins southeastern border of the serra de estrela granitic massif beira baixa portugal abstract sets of flat joints controlling barren or sn w mineralized veins with aplite pegmatite and or quartz fillings form an interesting but difficult and controversial problem in fact at least three more or less independent parameters influence the formation of these vein type deposits 1 the creation of flat sets 2 the origin of opening s and 3 their filling s relatively few studies have been made of these domains and even if their authors did determine similar successions of events i e creation opening and filling of the joints they disagreed and even came to drastically contrary conclusions concerning the mode of the origin and the opening of flat joints these different hypotheses are summarized and compared with our own results the latter were obtained from observations of flat joint sets and of mineralized or unmineralized quartz and or aplite pegmatite veins occupying parts of these sets on the southern flank of the serra de estrela and by comparison with already known flat sets locally with veins of the iberian variscan belt the following conclusions are drawn 1 1 sets of flat joints are very common structures in the iberian variscan chain 2 2 the sets are locally opened and filled by veins either with or without mineralization which is present only in close proximity of granitic intrusions especially near late well differentiated leucogranitic cupolas elsewhere the joints remain closed and barren 3 3 the genetic history of the flat joints is clearly independent of their opening s and filling s these joints originated long before the opening and infilling the later having been two sub synchronous or penecontemporaneous mechanisms namely the consequence of shrinkage of the granites and hydraulic over pressuring of different fluids clearly several genetic stages were involved 4 4 the origin of flat joint systems can be related to shearing movements associated with weak to very weak tectonics which developed when the main structuration of the belt by the first syn metamorphic phase of folding was already achieved and when the belt was partially uplifted and eroded 5 5 the formation of the flat joints terminated just before the intrusion of the latest granites stephanian leucogranites and thus before the injection of the residual magmatic liquids aplites pegmatites or of hydrothermal sn w mineralizing fluids in fact some late biotitic leucogranites filled some scarcely opened joints

ocean plate stratigraphy in east and southeast asia abstract ancient accretionary wedges have been recognised by the presence of glaucophane schist radiolarian chert and melange recent techniques for the reconstruction of disrupted fragments of such wedges by means of radiolarian biostratigraphy provide a more comprehensive history of ocean plate subduction and successive accretion of ocean floor materials from the oceanic plate through offscraping and underplating reconstructed ocean floor sequences found in ancient accretionary complexes in japan comprise from oldest to youngest pillow basalt limestone radiolarian chert siliceous shale and shale and sandstone similar lithologies also occur in the melange complexes of the philippines indonesia thailand and other regions this succession is called ocean plate stratigraphy ops and it represents the following sequence of processes birth of the oceanic plate at the oceanic ridge formation of volcanic islands near the ridge covered by calcareous reefs sedimentation of calcilutite on the flanks of the volcanic islands where radiolarian chert is also deposited deposition of radiolarian skeletons on the oceanic plate in a pelagic setting and sedimentary mixing of radiolarian remains and detrital grains to form siliceous shale in a hemipelagic setting and sedimentation of coarse grained sandstone and shale at or near the trench of the convergent margin radiolarian biostratigraphy of detrital sedimentary rocks provides information on the time and duration of ocean plate subduction the ages of detrital sediments becomes younger oceanward as younger packages of ops are scraped off the downgoing plate ops reconstructed from ancient accretionary complexes give us the age of subduction and accretion direction of subduction and ancient tectonic environments and is an important key to understanding the paleoenvironment and history of the paleo oceans now represented only in suture zones and orogenic belts

overview of naturally occurring earth materials and human health concerns abstract the biosphere and the earth s critical zone have maintained a dynamic equilibrium for more than 3 5 billion years except for solar energy almost all terrestrial substances necessary for life have been derived from near surface portions of the land hydrosphere and atmosphere if aggregate biological activities are less than the rate of nutrient supply and or resource renewal sustained population growth is possible where the replenishment rate of a life sustaining earth material is finite usage may reach a condition of dynamic equilibrium in which biological consumption equals but on average cannot exceed the overall supply although large most natural resources are present in finite abundances for such commodities excessive present day human utilization reduces future availability and thus the ultimate planetary carrying capacity for civilization intensive use of earth materials has enhanced the quality of life especially in the developed nations still natural background levels and earth processes such as volcanic eruptions as well as human activities involving agriculture construction and the extraction refining and transformation of mineral resources have led to harmful side effects involving environmental degradation and public health hazards among naturally and anthropogenically induced risks are bioaccessible airborne dusts and gases soluble pollutants in agricultural industrial and residential waters and toxic chemical species in foods and manufactured products at appropriate levels of ingestion many earth materials are necessary for existence but underdoses and overdoses have mild to serious consequences for human health and longevity this overview briefly sketches several natural resource health hazards included are volcanic ash aerosols gases mineral dusts non volcanic aerosols nanoparticles asbestos fibrous zeolites arsenic fluorine iodine uranium thorium radium radon polonium selenium mercury copper lead chromium and cadmium also noted are health effects of natural disasters and an obligatory future sustainable consumption of natural resources not treated are the overwhelming adverse effects of malnutrition lack of potable water inadequate sanitation fossil fuel usage mining manufacturing and agricultural pollution or environmental pathogens nor are the important impacts of complex mixtures of earth materials considered with rise of the worldwide information network economic globalization and the industrial thrust of developing nations the achievement of natural resource sustainability has emerged as a strategic imperative accompanying increased rates of earth materials consumption and attendant environmental change substantially improved universal public health will require a major global effort integrating collaborations among geoscientists medical researchers and epidemiologists governments and ngos must provide important support of such cooperative efforts and both health and earth scientists must cross disciplinary and national boundaries

apatite fission track and u th he ages from the higher himalayan crystallines kaghan valley pakistan implications for an eocene plateau and oligocene to pliocene exhumation abstract apatite fission track and apatite and zircon u th he ages were obtained from high and ultra high pressure rocks from the kaghan valley pakistan four samples from the high altitude northern parts of the valley yielded apatite fission track ages between 24 5 3 7 and 15 6 2 1 ma and apatite u th he ages between 21 0 0 6 and 5 3 0 2 ma these data record cooling of the formerly deeply subducted high grade metamorphic rocks induced by denudation and exhumation consistent with extension and back sliding along the reactivated normal acting main mantle thrust overlap at around 10 ma between fission track and u th he ages is recognised at one location besal showing that fast cooling occurred due to brittle reactivation of a former thrust fault widespread miocene cooling is also evident in adjacent areas to the west deosai plateau tso morari most likely related to uplift and unroofing linked to continued underplating of the indian lower crust beneath ladakh and kohistan in the late eocene to oligocene in the southernmost part of the study area near naran two significantly younger late miocene to pliocene apatite fission track ages of 7 6 2 1 to 4 0 0 5 ma suggest a spatial and temporal separation of exhumation processes these younger ages are best explained by enhanced late miocene uplift and erosion driven by thrusting along the main boundary thrust

cenozoic and mesozoic metamorphism in the longmenshan orogen implications for geodynamic models of eastern tibet new zircon u pb and mica 40ar 39ar dating combined with structural studies in the longmenshan orogen confirm that most of the upper crustal deformation in the eastern margin of tibet is mesozoic however at lower structural levels apatite u pb and monazite electron microprobe dating reveals a previously unknown domain of cenozoic ca 65 ma barrovian type metamorphism and deformation this discovery shows that the crust in the eastern margin of tibet was already a substantial thickness around the time of the india asia collision associated deformation has a n s oriented stretching lineation implying that deformation was not driven by topographic gradients in the tibetan plateau the observed moderate amounts of distributed postmetamorphic e w shortening can probably explain the present thickness of the continental crust in the area these results do not support models of crustal thickening caused by solid state lateral flow of midcrustal metamorphic rocks

middle ordovician high pt metamorphic rocks in eastern australia evidence from k ar ages phengite separated from a metagabbro three blueschist and one metabasite that occur as blocks in serpentinite melange in the new england fold belt eastern australia has yielded k ar ages of 465 480 ma significantly older than the age of most components of the belt the schists and metabasite contain either glaucophane and or crossite intergrown with the phengite providing the first conclusive evidence for early paleozoic subduction accretion associated with the east gondwana margin the tectonic affinity of the blocks is uncertain they and other small early paleozoic convergent margin elements in the new england fold belt may be allochthonous remnants of an arc system accreted in the devonian or carboniferous or they may be related to early paleozoic convergent margin components found farther inboard in the paleozoic fold belts of eastern australia

geochemistry and petrogenesis of the fiskenaesset anorthosite complex southern west greenland nature of the parent magma abstract the petrogenesis of the fiskenaesset anorthosite body has been investigated using major and trace element data for a large range of rock types from each zone of the complex the chemistry of these ultramafic to anorthositic cumulates is interpreted in terms of crystal fractionation of a parental trace element impoverished tholeiitic magma involving crystallisation of the cumulus phases olivine orthopyroxene clinopyroxene and dominant plagioclase feldspar amphibole appears not to have been a significant cumulus phase at any stage of crystallisation of the body the abundant amphibole found in the rocks of the complex being produced by primary intercumulus crystallisation supplemented by secondary metamorphic recrystallisation similarly magnetite is unlikely to have been a significant early cumulus phase although together with chromite it crystallised as a cumulus phase at high stratigraphic levels in the complex the metamorphism appears to be largely isochemical although sub solidus metamorphic re equilibration of the ree can be demonstrated on a grain size scale the spatial and temporal association between the anorthosite complex and the bordering metavolcanic amphibolites is matched by a strong similarity between the observed trace element chemistry of the amphibolites and the trace element chemistry of calculated successive liquids for the complex this is taken to suggest a genetic relationship between the evolution of the anorthosite complex and enclosing amphibolites the presence of trace element impoverished amphibolites which are not cumulates with trace element abundances comparable to those of the suggested parental liquid to the anorthosite complex is used to derive a major element composition for the primary fiskenasset magma this composition approximates a moderately aluminous tholeiitic basalt which may have been generated by hydrous fusion of previously depleted mantle this primary magma underwent crystal fractionation under low pressure conditions allowing the development of extensive plagioclase cumulates the fiskenaesset anorthosite and similar bodies cannot represent a cumulate residue complementary to the enclosing voluminous tonalitic gneisses which have a calc alkaline chemistry controlled by high pressure crystal liquid fractionation rather the association between the cumulate layered complex and bordering supracrustal sequence may imply an ancient ocean crust analogue for the development of this component of archaean high grade terrains it is suggested that slices of such archaean ocean floor may be emplaced laterally into the base of the continental crust during subduction of oceanic lithosphere at cordilleran type continental margins

trace element systematics of the neoarchean fiskenaesset anorthosite complex and associated meta volcanic rocks sw greenland evidence for a magmatic arc origin abstract new major and high precision icp ms trace element data on the neoarchean ca 2970 ma layered fiskenaesset complex and associated volcanic rocks southern west greenland provide new constraints on the petrogenesis and geodynamic setting of the complex the complex appears to have been emplaced as multiple sills of magma and crystal mush into oceanic crust tholeiitic basalts and gabbros forming an association of ca 550 m thick anorthosite leucogabbro gabbro and peridotite layers the fiskenaesset complex and the associated volcanic rocks were intruded by neoarchean tonalite trondhjemite and granodiorite ttg sheets during thrusting that was followed by several phases of isoclinal folding despite the intense deformation and amphibolite to granulite facies metamorphism primary cumulate textures and igneous layering are locally well preserved throughout the complex the presence of calcic plagioclase an75 95 and igneous amphibole in anorthosites gabbros and leucogabbros and hornblendite veins in peridotites suggests a hydrous magma source s the major and trace element compositions of tholeiitic basalts amphibolites suggest that they are petrogenetically related to the fiskenaesset complex by fractional crystallization the trace element systematics of the least altered anorthosites gabbros leucogabbros peridotites tholeiitic basalts and calc alkaline high magnesian andesites hma is collectively consistent with a supra subduction zone geodynamic setting on the log transformed tectonic discrimination diagram including la th sm th yb th and nb th ratios tholeiitic basalts display a trend projecting from mid ocean ridge basalt morb field to island arc basalt iab field this trend is interpreted as reflecting a transition from the neoarchean depleted upper mantle to a subarc mantle wedge following the initiation of intra oceanic subduction and arc migration collectively on the basis of field relationships petrographic features and geochemical characteristics the fiskenaesset complex is interpreted as a fragment of a neoarchean oceanic island arc on the basis of ree patterns anorthosites are divisible into four major groups 1 group 1 displays moderately depleted to slightly enriched lree and hree patterns 2 group 2 possesses strongly enriched lree and moderately depleted hree patterns 3 group 3 has strongly enriched lree and depleted hree patterns and 4 group 4 garnet anorthosite exhibits concave upward ree patterns that appear to have resulted from contamination of anorthositic magma by basaltic rocks or magma the different ree patterns in group 1 2 and 3 anorthosites are interpreted to reflect various depths of partial melting and variably enriched in incompatible elements source compositions the majority of anorthosites and leucogabbros were derived from depths above the garnet stability field

interpreting noble gas concentrations as proxies for salinity and temperature in the world s largest soda lake lake van turkey in this work we present noble gas concentration profiles measured in the water column and in the sediment pore water of the earth s largest soda lake lake van eastern anatolia turkey the concentrations of noble gases in particular ar kr and xe in the water body deviate significantly from the expected equilibrium concentrations calculated from the in situ temperature and salinity using existing solubility functions for seawater the specific chemical composition of the water of the soda lake seems to be responsible for the observed deviations our measurements allow the identification and quantification of salinity factors that can be applied to correctly calculate the noble gas equilibrium concentrations for the lake these salinity factors provide a solid and robust empirical basis for the interpretation of noble gas concentration signals measured in the sediment pore water of lake van in terms of palaeosalinity and palaeotemperature

tectono metamorphic evolution of high p t and low p t metamorphic rocks in the tia complex southern new england fold belt eastern australia insights from k ar chronology the tia complex in the southern new england fold belt is a poly metamorphosed late paleozoic accretionary complex it consists mainly of high p low t type pumpellyite actinolite facies rare blueschist facies schists phyllite and serpentinite t 300 c and p 5 kbar and low p high t type amphibolite facies schist and gneiss t 600 c and p 5 kbar associated with granodioritic plutons tia granodiorite white mica and biotite k ar ages distinguish carboniferous subduction zone metamorphism and permian granitic intrusions respectively the systematic k ar age mapping along a n s traverse of the tia complex exhibits a gradual change the white mica ages become younger from the lowest grade zone 339 ma to the highest grade zone 259 ma in contrast si content of muscovite changes drastically only in the highest grade zone the regional changes of white mica k ar ages and chemical compositions of micas indicate argon depletion from precursor high p low t type phengitic white mica during the thermal overprinting and recrystallization by granitoids intrusions our new k ar ages and available geological data postulate a model of the eastward rollback of a subduction zone in early permian the eastward shift of a subduction zone system and subsequent magmatic activities of high mg andesite and adakite might explain formation of s type granitoids hillgrove suite and coeval low p high t type metamorphism in the tia complex

crustal structure of southwest japan revealed by the integrated seismic experiment southwest japan 2002 abstract a multi purpose seismic experiment named the 2002 integrated seismic experiment southwest japan was conducted in 2002 along a more than 240 km long line across southwest japan from the pacific coast to the japan sea coast its profile provides the first crustal scale cross section across the japanese island arc which highlights a number of significant points related to the structural development of the arc major outstanding points are that the japanese island arc is composed of two completely different crusts juxtaposed by the median tectonic line mtl and that the mtl started its activity associated with lower crustal thinning and formation of an upper crustal scale half graben in late cretaceous

comment on does the manning orocline exist new structural evidence from the inner hinge of the manning orocline eastern australia by li and rosenbaum 2013 gondwana research the manning orocline is an enigmatic structure that has been the subject of much speculation with those advocating its existence korsch and harrington 1987 glen and roberts 2012 rosenbaum et al 2012 to those sceptical of its existence lennox et al 2013 in their recent contribution li and rosenbaum in press provide evidence for this structure by analysing the geometry of the structural fabrics in the armidale walcha area an area that they suggest comprises a less deformed part of the subduction accretion complex of the southern new england orogen in their study area the rocks show what appears to be a slaty cleavage s1 that the authors suggest delineates an oroclinal structure formed in the permian however as shown in the following discussion their s1 fabric can be either s1 or s2 and therefore cannot be correlated across outcrops as a single surface thus the structural history is far more complex than implied by li and rosenbaum in press and that the trends of the fabric they interpreted as s1 in the innermost hinge of the manning orocline are a mixture of fabrics formed during separate deformation and metamorphic events we will present evidence in the following sections that show that preoroclinal structures have not been obliterated and that the area of interest has inherited a complex structural metamorphic history related to the carboniferous subduction accretion history of the rocks in addition we will show that careful petrographic and field studies are essential to confirm the type and timing of cleavage formation before any model can be proposed finally we will comment on some statements

petrogenesis of late cretaceous lava flows from a ceno tethyan island arc the raskoh arc balochistan pakistan abstract the raskoh arc is about 250 km long 40 km wide and trends in an ene direction the oldest rock unit in the raskoh arc is an accretionary complex early to late jurassic which is followed in age by kuchakki volcanic group the most wide spread unit of the raskoh arc the volcanic group is mainly composed of basaltic to andesitic lava flows and volcaniclastics including agglomerate volcanic conglomerate breccia and tuff with subordinate shale sandstone limestone and chert the flows generally form 3 15 m thick lenticular bodies but rarely reach up to 300 m they are mainly basaltic andesites with minor basalts and andesites the main textures exhibited by these rocks are hypocrystalline porphyritic subcumulophyric and intergranular the phenocrysts comprise mainly plagioclase an 30 54 in nok chah and an 56 64 in bunap they are embedded in a micro cryptocrystalline groundmass having the same minerals apatite magnetite titanomagnetite and hematite occur as accessory minerals major trace and rare earth elements suggest that the volcanics are oceanic island arc tholeiites their low mg 42 56 and higher feo total mgo 1 24 2 67 ratios indicate that the parent magma of these rocks was not directly derived from a mantle source but fractionated in an upper level magma chamber the trace element patterns show enrichment in lile and depletion in hfse relative to n morb their primordial mantle normalized trace element patterns show marked negative nb anomalies with positive spikes on k ba and sr which confirm their island arc signatures slightly depleted lree to flat chondrite normalized ree patterns further support this interpretation the zr versus zr y and cr versus y studies show that their parent magma was generated by 20 30 melting of a depleted mantle source the trace elements ratios including zr y 1 73 3 10 ti zr 81 59 101 83 ti v 12 39 30 34 la yb n 0 74 2 69 ta yb 0 02 0 05 and th yb 0 11 0 75 of the volcanics are more consistent with oceanic island arcs rather than continental margin arcs it is suggested that the raskoh arc is an oceanic island arc which formed due to the intra oceanic convergence in the ceno tethys during the late cretaceous rather than constructed on the southern continental margin of the afghan block as claimed by previous workers it is further suggested that the semail zagros chagai raskoh muslim bagh and waziristan island arcs were developed in a single but segmented cretaceous ceno tethyan convergence zone

palaeozoic and mesozoic tectonic evolution and palaeogeography of east asian crustal fragments the korean peninsula in context east and southeast asia comprises a complex assembly of allochthonous continental lithospheric crustal fragments terranes together with volcanic arcs and other terranes of oceanic and accretionary complex origins located at the zone of convergence between the eurasian indoaustralian and pacific plates the former wide separation of asian terranes is indicated by contrasting faunas and floras developed on adjacent terranes due to their prior geographic separation different palaeoclimates and biogeographic isolation the boundaries between asian terranes are marked by major geological discontinuities suture zones that represent former ocean basins that once separated them in some cases the ocean basins have been completely destroyed and terrane boundaries are marked by major fault zones in other cases remnants of the ocean basins and of subduction accretion complexes remain and provide valuable information on the tectonic history of the terranes the oceans that once separated them and timings of amalgamation and accretion the various allochthonous crustal fragments of east asia have been brought into close juxtaposition by geological convergent plate tectonic processes the gondwana derived east asia crustal fragments successively rifted and separated from the margin of eastern gondwana as three elongate continental slivers in the devonian early permian and late triassic late jurassic as these three continental slivers separated from gondwana three successive ocean basins the palaeo tethys meso tethys and cenotethys opened between these and gondwana asian terranes progressively sutured to one another during the palaeozoic to cenozoic south china and indochina probably amalgamated in the early carboniferous but alternative scenarios with collision in the permo triassic have been suggested the tarim terrane accreted to eurasia in the early permian the sibumasu and qiangtang terranes collided and sutured with simao indochina east malaya in the early middle triassic and the west sumatra terrane was transported westwards to a position outboard of sibumasu during this collisional process the permo triassic also saw the progressive collision between south and north china with possible extension of this collision being recognised in the korean peninsula culminating in the late triassic north china did not finally weld to asia until the late jurassic the lhasa and west burma terranes accreted to eurasia in the late jurassic early cretaceous and proto east and southeast asia had formed palaeogeographic reconstructions illustrating the evolution and assembly of asian crustal fragments during the phanerozoic are presented d 2005 international association for gondwana research published by elsevier b v all rights reserved

new insight into a subduction related orogen a reappraisal of the geotectonic framework and evolution of the japanese islands abstract the geotectonic framework and the evolutionary history of the japanese islands need revision in accordance with the various geophysical geological evidence gathered by new methodologies in the recent years including seismic tomography vibroseis ground breaking seismic experiments and detrital zircon chronology these investigations have addressed various themes such as 1 seismic profile of the crust and mantle beneath the japanese islands 2 high precision ages of the protoliths of high p t metamorphic rocks and 3 provenance of terrigenous clastics the results have led to a number of important findings including 1 detection of a large mass of slab around the mantle boundary layer suggesting the long term oceanic subduction beneath japan 2 confirmation of the subhorizontal piled nappe structure for the entire crust of japan 3 finding a new high p t metamorphosed accretionary complex unit that represents the youngest blueschist in japan 4 finding of the oldest early cambrian arc batholith and cover sediments and 5 the identification of plural arc batholiths which have already been erased from the surface based on a synthesis of these new data this article presents a re evaluation of the conventional geotectonic subdivision of the subduction related orogen in japan re definition of the elements and their mutual boundaries and re consideration of the geotectonic evolution of the japanese islands in particular the historical change in provenance suggests that proto japan has experienced large scale tectonic erosion in multiple stages and the corresponding large amounts of continental crust materials were subducted for understanding the orogenic growth of japan during the last ca 500 million years the significance of tectonic erosion coupled with continental contraction as well as the oceanward accretionary growth requires further attention

extensional failure and hydraulic valving at minas da panasqueira portugal evidence from vein spatial distributions displacements and geometries abstract at panasqueira portugal exceptional exposure and demonstrable vein connectivity allow robust characterisation of brittle elastic failure mechanisms in intrusive related environments extensional failure was driven by cycles of fluid injection hydraulic valving and vein growth under conditions with v 1 and differential stress

petrotectonic significance of the chemistry of chromite in the ultramafic mafic complexes of pakistan abstract the suture zones which border the indian craton in pakistan are characterized by several large mafic ultramafic complexes from south to north these include 1 bela 2 muslimbagh zhob valley 3 waziristan 4 dargai skhakot qila 5 shangla mingora 6 jijal and 7 sapat besides these there is the huge 300x 40 km chilas mafic ultramafic complex in the cretaceous kohistan magmatic arc the sapat jijal shangla and dargai skhakot qila complexes are distributed along the indus suture the waziristan zhob valley and bela complexes lie along the suture on the western margin of the indian plate all these complexes were emplaced during late cretaceous paleocene time at ca 65 ma these complexes largely consist of ultramafic and mafic plutonic rocks ranging from dunite and peridotite to gabbro the mafic ultramafic rocks of the sapat chilas and jijal complexes are generally well layered and appear to be mainly cumulates in addition to cumulate plutonic rocks the remaining five complexes also contain abundant residual peridotites sheeted dykes a variety of lava flows locally pillowed and associated pelagic sediments disseminated and segregated chromite occurs in all the complexes on the basis of the chromium number cr 100 cr cr al of their chromite the complexes can be divided into three groups 1 the sapat and jijal complexes contain chromites with cr 60 2 the shangla mingora dargai skhakot qila waziristan muslimbagh zhob and bela rocks contain chromites that display a wide range of composition with cr varying from 15 to 90 and 3 rocks of the chilas complex are characterized by low cr chromites cr mostly the chromite compositions appear to indicate different tectonic settings for the origin of the complexes under consideration those with high cr chromite belong to an island arc type tectonic setting opinion differs on the origin of the group 2 chromite bearing complexes they may well be of complex origin with components which originated in different tectonic settings the chilas complex of group 3 contains low cr chromite similar to oceanic rocks supporting the idea that it is related to rifting within an island arc setting

full paleostress tensor reconstruction using quartz veins of panasqueira mine central portugal part i paleopressure determination abstract paleostress tensor restoration methods are traditionally limited to reconstructing geometrical parameters and are unable to resolve stress magnitudes based on previous studies we further developed a methodology to restore full paleostress tensors we concentrated on inversion of mode i fractures and acquired data in panasqueira mine portugal where optimal exposures of mineralized quartz veins can be found to carry out full paleostress restoration we needed to determine 1 pore paleo pressure and 2 vein attitudes the present contribution focuses specifically on the determination of pore pressure to these aims we conducted an extensive fluid inclusion study to derive fluid isochores from the quartz of the studied veins to constrain p t conditions we combined these isochores with crystallisation temperatures derived from geochemical analyses of coeval arsenopyrite we also applied the sphalerite geobarometer and considered two other independent pressure indicators our results point to pore pressures of 300 mpa and formation depths of 10 km such formation depths are in good agreement with the regional geological evolution the obtained pore pressure will be merged with vein inversion results in order to achieve full paleostress tensor restoration in a forthcoming companion paper

the contorted new england orogen eastern australia new evidence from u pb geochronology of early permian granitoids 1 a series of sharp bends oroclines are recognized in the paleozoic to early mesozoic new england orogen of eastern australia the exact geometry and origin of these bends is obscured by voluminous magmatism and is still debated here we present zircon u pb ages that confirm the lateral continuation of early permian 296 288 ma granitoids and shed new light on the oroclinal structure orogenic curvature is defined by the alignment of early permian granitoids parallel to the structural grain of the orogen as well as the curved geometry of sub vertical deformation fabrics forearc basin terranes and serpentinite outcrops alternative geometrical interpretations may involve two bends texas and coffs harbour oroclines three bends manning orocline or even four bends nambucca orocline we argue that the model involving four bends is most consistent with available data although further kinematic constraints are required to confirm the existence of the manning and nambucca oroclines a subsequent phase of younger magmatism 260 ma cuts across the curved structural grain providing a minimum age constraint for orocline development assuming a structure of four oroclines we suggest a tentative tectonic model that involves an early stage of subduction curvature during slab rollback at 300 285 ma followed by bending associated with dextral transpression a final tightening of the curved structures was possibly obtained by e w shortening during the late permian to triassic 265 230 ma hunter bowen orogeny

permian evidence for trans tasman relationships between east australia new caledonia and new zealand abstract basaltic to basaltic andesitic tuff breccias agglomerates and subordinate lavas together with cogenetic dacitic tuffs and glassy flows comprise the tectonomorphically anomalous early permian submarine volcanic sequence of the gympie group southeast queensland the least accumulative gympie basalts and basaltic andesites show geochemical features which typify island arc tholeiites the absence of andesitic eruptives i e the essential bimodality of the volcanic sequence together with low levels of large ion lithophile elements lile and the absence of compelling evidence for amphibole or garnet fractionation are consistent with an immature submarine tholeiitic stage of arc development on relatively thin oceanic crust by contrast the mid carboniferous to permian calc alkaline camboon arc to the west is inferred to have developed at least in part on early carboniferous continental crust the volcanics and overlying sediments of the gympie group are compared with those of the volcanic arc and adjoining formations of the nelson eglinton takitimu areas of new zealand to reveal some striking geochemical and lithostratigraphic similarities dacitic volcanics in new caledonia may also have formed a relatively young part of the same volcanic arc we analyse the overlying permian sediments to show further similarities and facial differences between the three regions essentially we propose new zealand was locus for an actively spreading mid ocean ridge dun mountain ultramafics and patuki ophiolite complex which received a substantial thickness of marine sediment gympie lay towards the end of the mid ocean ridge and new caledonia close to the terminus of the volcanic arc and received more terrestrial sediment we analyse original and subsequent spatial interrelationships that developed before and during the late cretaceous opening of the tasman sea and suggest that the history of separation was complicated by strike slip and or transform movements

does the manning orocline exist new structural evidence from the inner hinge of the manning orocline eastern australia the map view structure of the southern new england orogen in the eastern gondwanan margin is characterised by four tight orogenic scale curvatures texas coffs harbour manning and nambucca oroclines here we focus on the geometry of the manning orocline and examine whether the inner arc area of the oroclinal structure is expressed within the accretionary wedge rocks of the tablelands complex our observations from the tablelands complex armidale walcha area show that rocks were subjected to penetrative deformation d1 which resulted in a regional slaty cleavage s1 and related isoclinal folds this was followed by subsequent deformation d2 associated with minor gentle folds in a larger scale the steeply dipping s1 structural fabric shows a continuous map view curvature thus defining a macroscopic fold structure we interpret this macroscopic fold as the expression of the manning orocline within the accretionary wedge complex this interpretation is consistent with the contorted spatial distribution of other tectonic elements serpentinite belt forearc basin terranes and early permian granitoids which independently define the structure of the manning orocline our new structural data support the existence of the manning orocline and the quadruple oroclinal geometry of the whole southern new england orogen the origin of these oroclines is attributed to multiple stages of bending possibly associated with an earlier phase of curvature during slab rollback in the early permian followed by a subsequent middle late permian episode of contractional deformation that tightened the oroclinal structure

subduction products according to experimental prediction knowledge of the thermal structure and processes in subduction zones is so uncertain that our more extensive knowledge of source materials and phase relationships remains insufficient for prediction of magmatic products the phase relationships do provide important constraints for testing geophysical and petrogenetic models especially when considered along with geochemical constraints physical questions such as the behavior of partially molten rocks are intimately related to the compositions of magmas from source to eruption site tentative predictions and conclusions include 1 andesite is not a primary magma from oceanic crust 2 it is unlikely that liquids from subducted oceanic crust yield andesites by fractionation except by melting of amphibolite in an especially warm subducted crust 3 it is more likely that hydrous siliceous magmas from the crust leak into the overlying mantle 4 andesite magmas can be generated in peridotite only under exceptional circumstances 5 h2o undersaturated basic magmas from peridotite modified by aqueous fluids or hydrous magma may yield andesite by fractionation 6 phlogopite peridotite could escape melting and yield alkalic magmas at deeper levels 7 andesite magmas could be produced in continental crust only by extreme heating through underplating of basalts or by mixing of basalt and rhyolite derived from crust most of these conclusions need revision if convection in the asthenosphere wedge raises the temperature of the subducted slab to 1250 c at 100 km as proposed by marsh 1979a this demonstrates the dependence of experimental predictions on geophysical models

the himalayan passive margin from precambrian to cretaceous times abstract the himalaya passive margin should be separated into the indian himalaya and the pakistan himalaya divided by the nanga parbat haramosh basement uplift in the northwestern syntaxes the indian passive margin shows a complex history involving splitting of microcontinents off the northern gondwana margin from early paleozoic times until the jurassic in contrast the pakistan himalaya formed part of the stable indian shelf until separation from africa started in the jurassic each margin has a distinct stratigraphic history until the mid mesozoic after which they show similar histories until the tertiary the himalaya mountains in india consist of three distinct tectonic units juxtaposed during the neogene by southward thrusting of the northern indian precambrian to mesozoic passive margin the lesser himalaya on the south forms a late precambrian passive margin usually directly overlain by late cretaceous to tertiary clastics its stratigraphy is closest to that of the indian shield in contrast the high himalaya has a thin ordovician to carboniferous shelf sequence deposited after early ordovician deformation and granite intrusion above this thick permian and mesozoic shelf sequences mark the separation of continental blocks off the northern indian margin and the opening of the neotethys ocean the north himalaya formed the slope and basin of this ocean and consists of reactivated paleozoic gneiss domes overlain by thick mesozoic sediments which pass in the northeastern himalaya into an enormously thick sedimentary sequence resting on oceanic crust paleomagnetic and structural evidence indicates at least 500 km of southward thrusting along the main central thrust between the lesser and high himalaya this thrusting together with a further 250 km of erosion at the front of the nappes has removed the entire inner shelf of the himalaya passive margin and can explain the startling contrast between the high and lesser himalaya stratigraphic sequences but there are still discrepancies particularly in the eastern himalaya where precambrian basement is juxtaposed with the north himalaya mesozoic slope these discrepancies can be partly resolved by strike slip movements roughly parallel to the himalaya which have removed parts of the northern indian passive margin such faults of the requisite orientation displacement and age occur in southeast asia where their cumulative displacements can add up to several thousand kilometres similar faults of undoubted pre tertiary age occur in the pakistan himalaya here the passive margin shows a much simpler history of jurassic to miocene subsidence

nagarparker granites showing rodinia remnants in the southeastern part of pakistan abstract the nagarparker area of the trans aravalli belt comprises precambrian igneous and metamorphic basement rocks predominantly granites these granites are subalkalic to alkalic a type containing riebeckite ferro richterite ferro edenite arvedsonite amphiboles and rutile zircon apatite allanite titanite titano magnetite ilmenite magnetite and fluorite accessory minerals the variations in nb y ce and ga and ga al ratios typify the granites of the area as post orogenic a2 type formed possibly by partial melting of the island arc crust in a rift related within plate tectonic setting the granites of the area yielded u th pb epma zircon and monazite radiometric ages between 1100 and 700 ma mostly concentrating around 750 ma based on petrological geochemical and geochronological resemblance of granites of the nagarparker area with those of the seychelles islands and the malani igneous suite it is inferred that being part of trans aravalli belt of the indian shield the nagarparker area might have shouldered the seychelles islands towards the western side of the rodinia before the supercontinent rifted in neoproterozoic

muscovite k ar ages of the sanbagawa schists japan and argon depletion during cooling and deformation seventy muscovites from schists in the sanbagawa terrain in central shikoku were dated by the k ar method the muscovite ages are consistently older with increasing metamorphic grade within the same zone the ages are significantly younger in schists which have been more severely deformed these k ar age variations could be due to systematic argon depletion during deformation i e to the dynamic recrystallization of muscovites during ductile deformation that formed a large scale recumbent fold during the uplift and cooling argon loss was greater in schists that were more extensively deformed and in the lower grade zone that experienced a longer period of low temperature deformation than the higher grade zone the relationships between age and grain size in a pelitic schist suggest that coarse grained muscovites lost more argon than the finegrained ones there was no significant resetting of ages in the vicinity of major strike slip faults such as the median tecotonic line or near thrust faults the combination of geochronological and geological data constrains the cooling rate of the sanbagawa schists to 9 12 c ma in the oligoclase biotite zone in central shikoku japan

characterization of respirable volcanic ash from the soufriere hills volcano montserrat with implications for human health hazards volcanic ash generated in the long lived eruption of the soufriere hills volcano montserrat is shown to contain respirable sub 4 m particles and cristobalite a crystalline silica polymorph respirable particles of cristobalite can cause silicosis raising the possibility that volcanic ash is a respiratory health hazard this study considers some of the main factors which affect human exposure to respirable volcanic ash namely the composition and proportions of respirable ash and the composition and concentrations of airborne suspended particulates the composition size distribution and proportion by weight of respirable particles in representative samples of the soufriere hills tephra dome collapse ash fall deposits dome collapse pyroclastic flow matrix vulcanian explosion ash and mixed ash have been characterized dome collapse ash fall deposits are significantly richer in respirable particles 12 wt than the other tephra samples in particular the matrices of dome collapse pyroclastic flow deposits 3 wt within the respirable fraction dome collapse ash contains the highest proportion of crystalline silica particles 20 27 number of which 97 wt is cristobalite compared with other primary tephra types 0 4 5 6 number this enrichment of crystalline silica in the dome collapse ash is most pronounced in the very fine particle fraction sub 2 m the results are explained as being due to significant size fractionation during fragmentation of pyroclastic flows resulting in a fines depleted dome collapse matrix and a fines rich dome collapse ash deposit for all sample types the sub 4 m fraction comprises 45 55 wt of the sub 10 m fraction aeolian deposit lahar deposit and airborne samples of suspended ash collected on filters were characterized these samples show enrichment of crystalline silica in the respirable fraction 10 18 number the results are consistent with ash in the environment having a mixed origin but originating predominantly from dome collapse eruptions the reworked ash however contains low proportions of respirable ash 3 wt compared to primary ash samples the concentration of ash particles re suspended by road vehicles on montserrat is found to decrease exponentially with height above the ground indicating higher exposure for children compared with adults pm4 concentration at 0 9 m height of two year old child is 3 times that at 1 8 m adult height the composition of the re suspended road particles is similar to that re suspended by the wind

orogenesis without collision stabilizing the terra australis accretionary orogen eastern australia the neoproterozoic to end paleozoic terra australis orogen extended along the gondwana margin of the paleo pacific ocean and it now provides a detailed record of orogenic activity and continental stabilization within an ongoing convergent accretionary plate margin new geochronological data from end paleozoic plutonic and volcanic rocks associated with the gondwanide orogeny in the new england region of eastern australia integrated with information on the nature and timing of associated sedimentation deformation and metamorphism allow resolution of a high fidelity record of orogenesis at the end of the carboniferous around 305 ma convergent margin magmatism which had been active along the western margin of the new england region terminated and was followed by a short pulse of regional compressional deformation and metamorphism marking the commencement of the tablelands phase of gondwanide orogenesis deformation was almost immediately followed by the onset of clastic sedimentation and local calc alkaline volcanism dated at 293 ma in the extensional barnard basin emplacement of the two new england s type granitic suites the bundarra and the hillgrove suites along with localized high temperature low pressure metamorphism was essentially contemporaneous ranging in age from 296 to 288 ma and overlapped in time with i type magmatism and the switch from regional compression to extension and barnard basin rifting the hunter bowen phase of the gondwanide orogeny commenced with contractional deformation resulting in termination of sedimentation in the barnard basin and regional deformation and metamorphism across new england and into the sydney and gunnedah basins to the west at around 265 260 ma contractional loading of the sydney and gunnedah basins resulted in their conversion from extensional to foreland basins which received ongoing pulses of sediment from the new england orogenic welt until 230 ma the hunter bowen phase was associated with widespread i type plutonism and volcanic activity in new england that ceased around 230 ma marking the termination of gondwanide orogenesis orogenesis occurred in an evolving convergent plate margin setting s and i type magmatic activity ranging in age from ca 300 to 230 ma represents a stepping out of arc magmatism from the western margin of new england prior to 305 ma into the preexisting arc trench gap there is no evidence that deformation was related to the collision of the convergent margin with a major lithospheric mass and the widespread development of extensional basins in the eastern third of australia in the early permian indicates control by phenomena acting on a continental scale probably changing plate kinematics associated with the amalgamation of pangea

hydrogeochemistry stable isotope composition and geothermometry of co2 bearing hydrothermal springs from western iran evidence for their origin evolution and spatio temporal variations abstract this study aims to hydrochemically characterise three co2 bearing springs representing distinct hydrofacies in nw gorveh western iran and interpret them in the light of their geological setting the results of laboratory measurements of elemental concentrations stable oxygen carbon and hydrogen isotopes dissolved and particulate organic and inorganic carbon dic doc poc pic and alkalinity are combined with in situ measurements of ph and temperature parameters such as alkalinity dic ca2 and pco2 concentration display strong positively correlated values with systematic decrease from the spring vent in down flow direction for the three spring systems the inverse correlation of ph and 13cdic is caused by co2 degassing the 18o and d values show no significant variation related to minor or no evaporation due to normal ambient temperatures the low concentration of poc pic and doc compared to that of dic and the lack of correlation between them reflect predominant inorganic carbon in these fluids spring i is oversaturated in calcite with additional dissolution of co2 and despite high concentrations of na and cl undersaturated in halite indicating a fluid of geothermal origin and or reflecting steady state dissolution this is related to water rock interaction processes with carbonate and evaporitic rocks that affected the isotopic signature of 18o which is shifted to the right of the global meteoric water line spring i also represents a partially equilibrated and mature deep chloride type water spring ii and iii are less saline and represent a different fluid circulation and or shorter residence time the two latter springs are characterized by peripheral shallow dilute chloride bicarbonate type waters decreasing key parameters especially in spring iii during the winter suggest that superficial mixing with rain and meteoric water results in high temporal variations cation and stable carbon isotope geothermometry applied to the studied springs reveals an average reservoir temperature of 210 110 and 90 c for spring i and ii and iii respectively the geochemical and isotopic data allowed to depict a conceptual model where the hydrothermal reservoir for spring i is residing in carbonate and evaporitic rocks most likely the qom formation situated at a depth of 3 4 km whereas those of spring ii and iii are likely sourced from a shallower depth 1 2 km in correspondence with carbonate and porous and permeable volcanic rocks integration of hydrofacies with conceptual hydrological and geological models forms the base towards a proper understanding of water circulation patterns increasingly important for sustainable water management and geothermal applications

characterization and timing of the different types of fluids present in the barren and ore veins of the w sn deposit of panasqueira central portugal the panasqueira w sn deposit is the largest quartz vein type deposit of the iberian peninsula and the most important wolframite deposit in western europe the ore veins are almost exclusively sub horizontal besides ore bearing sub horizontal veins the panasqueira mine also contains barren quartz veins there are essentially two generations of barren quartz quartz contemporaneous with the earliest regional metamorphism qi and recrystallized quartz contemporaneous with the thermal metamorphism related to the granite intrusion qii fluid inclusion studies microthermometry and raman were undertaken in order to distinguish fluids contemporaneous with the barren quartz from those contemporaneous with the ore bearing quartz qiii fluid inclusion data indicate that the barren and ore bearing quartz fluids are dominantly aqueous 93 to 98 mol h2o with a nearly constant bulk salinity 8 to 12 wt eq nacl with the quantity of volatile component determined by raman spectrometry higher in qiii but never greater than 5 mol however the co2 ch4 n2 ratio is different for each type of quartz volatiles are dominated by ch4 10 to 96 mol zch4 and or n2 3 to 87 mol zn2 in the barren quartz and by co2 60 to 73 mol zco2 in ore bearing quartz the bulk chemical composition of the fluids in qiii is comparable to that found commonly in hydrothermal fluids associated with wolframite mineralization where na k ca and hco3 cl so4 a dispersion in th 226 to 350 c found in qiii together with a variation in the degree of filling 0 5 to 0 7 and with the consequent variation of fluid densities 0 70 to 0 79 may result from changes in the fluid pressure regime below lithostatic pressure suggesting vein filling related to tectonic events

the tectonic evolution of the kohistan karakoram collision belt along the karakoram highway transect north pakistan the kohistan arc terrane comprises an intra oceanic island arc of cretaceous age separating the indian plate to the south from the karakoram asian plate to the north within the indus suture zone of north pakistan the intra oceanic arc volcanics chalt dras group were built on a foundation of dominantly mid ocean ridge basalt morb related amphibolites of the kamila group the subarc magma chamber is represented by multiple intrusions of a huge gabbro norite complex chilas complex which includes some ultramafic assemblages of residual mantle harzburgite and dunite layered cumulates and hornblendites cut by late stage dikes of hornblende plagioclase pegmatites the chilas complex norites intrude the gilgit metasediments of lower amphibolite and greenschist facies in northern kohistan which also form xenolithic roof pendants within the top of the chilas complex along the southern margin of kohistan jijal and sapat complex ultramafics dunites harzburgites and websterites form remnant suprasubduction zone ophiolitic mantle rocks along the hanging wall of the main mantle thrust the cretaceous obduction plane along which kohistan was emplaced onto indian plate rocks garnet granulites of the jijal complex formed at 12 14 kbars represent original magmatic lower crustal rocks subducted to depths of at least 45 km and metamorphosed during high pressure and high temperature subduction of earlier arc related rocks obduction of the sapat ophiolite and kohistan arc occurred between 75 and 55 ma the closure of the shyok suture zone separating kohistan from the karakoram plate must have occurred prior to 75 ma the age of the jutal basic dikes which crosscut the closure related fabrics mainly late north directed backthrusting in the lower hunza valley andean type granitoid gabbrodiorite granodiorite granite emplacement along the kohistan ladakh batholith ended at the time of india asia collision 60 50 myr ago postcollisional crustal thickening along the karakoram led to multiple episodes of metamorphism from latest cretaceous and throughout the tertiary sillimanite grade metamorphism in hunza was actually pre india asia collision and may have resulted from the earlier kohistan collision localized and sporadic crustal melting episodes across northern kohistan indus confluence and parri granite sheets and the southern karakoram hunza dikes and sumayar and mango gusar leucogranites occurred from 51 to 9 ma and culminated in the huge baltoro monzogranite leucogranite intrusion 25 21 myr ago a vast network of leucogranitic and pegmatitite dikes containing gem quality aquamarine muscovite tourmaline garnet biotite quartz are younger than 5 ma and form the final phase of intrusion in the haramosh area and parts of the southern karakoram area

cretaceous isochron ages from k ar and 40ar 39ar dating of eclogitic rocks in the tso morari complex western himalaya india abstract the tso morari complex which is thought to be originally the margin of the indian continent is composed of pelitic gneisses and schists including mafic rock lenses eclogites and basic schists eclogites studied here have the mineral assemblage grt omp ca amp zo phn pg qtz rt they also have coesite pseudomorph in garnet and quartz rods in omphacite suggesting a record of ultrahigh pressure metamorphism they occur only in the cores of meter scale mafic rock lenses intercalated with the pelitic schists small mafic lenses and the rim parts of large lenses have been strongly deformed to form the foliation parallel to that of the pelitic schists and show the mineral assemblages of upper greenschist to amphibolite facies metamorphism the garnet omphacite thermometry and the univariant reaction relations for jadeite formation give 13 21 kbar at 600 c and 16 18 kbar at 750 c for the eclogite formation using the jadeite content of clinopyroxene x jd 0 48 phengites in pelitic schists show variable si al and na k ratios among grains as well as within single grains and give k ar ages of 50 87 ma the pelitic schist with paragonite and phengite yielded k ar ages of 83 5 ma k 4 9 wt for paragonite phengite mixture and 85 3 ma k 7 8 wt for phengite and an isochron age of 91 13 ma from the two dataset the eclogite gives a plateau age of 132 ma in ar ar step heating analyses using single phengite grain and an inverse isochron age of 130 39 ma with an initial 40 ar 36 ar ratio of 434 90 in ar ar spot analyses of phengites and paragonites the cretaceous isochron ages are interpreted to represent the timing of early stage of exhumation of the eclogitic rocks assuming revised high closure temperature 500 c for phengite k ar system the phengites in pelitic schists have experienced retrograde reaction which modified their chemistry during intense deformation associated with the exhumation of these rocks with the release of significant radiogenic 40 ar from the crystals the argon release took place in the schists that experienced the retrogression to upper greenschist facies metamorphisms from the eclogite facies conditions

geochemistry of the chagai raskoh arc pakistan complex arc dynamics spanning the cretaceous to the quaternary abstract the chagai raskoh arc is located in western pakistan and extends into iran and afghanistan the arc forms an elongate body trending ew and is roughly 500 km long by 150 km wide activity along the arc began in the late cretaceous and continued through into the quaternary the oldest volcanic rocks in the arc belong to the sinjrani and kuchakki formations these rocks are primarily basalts and andesites which form both pillow sequences and massive flows geochemically these units are very similar they are tholeiitic lavas with typical island arc characteristics and an n morb source for example when normalized to n morb they are large ion lithophile element lile enriched high field strength element hfse depleted and have negative nb and ti anomalies also within the sinjrani formation are a sequence of senonian basalt dacite lavas that were generated from an n morb type mantle source and although they are initially tholeiitic the more evolved lavas are calc alkaline trace element data indicates these lavas have a very minor continental affiliation the generation of these lavas may mark the increasing proximity of the afghan continental block the youngest units in this study belong to the quaternary koh e sultan and the miocene koh e dalil these units have a calc alkaline fractionation trend and contain more silicic lavas including dacites than the older lavas chemically these units are very similar they both contain continental arc signatures and were generated from low degrees of partial melting of an enriched source current theories to explain the multiple phases of volcanism in the chagai raskoh arc propose that these lavas are the result of intra oceanic convergence in the neo tethys our data supports this model in that the initial phases of volcanism are entirely formed in an oceanic arc however the increasing proximity of the afghan block ca 65 ma is evidenced by increasing continental signatures in the lavas followed by much younger continental arc volcanism we suggest the north south distribution of oceanic versus continental signatures indicates that the location of the afghan block makran accretionary complex boundary is beneath the chagai raskoh arc

folding of granite and cretaceous exhumation associated with regional scale flexural slip folding and ridge subduction kitakami zone northeast japan abstract the early cretaceous granitic plutons intrude the kitakami zone northeast japan whose southern and northern regions consist of forearc basin and accretionary complex rocks respectively all country rock of the kitakami zone exhibit prominent pressure solution cleavage and associated folds formed during shortening with a small component of sinistral shear whereas most plutons show only igneous textures the kesengawa granite and some other plutons however have foliations that cut the pluton boundaries and are continuous with those observed in surrounding sedimentary rocks we document a tectonic fold with axial planar foliation in part of the kesengawa granite the metamorphic minerals associated with the contact aureole and country rocks of the kesengawa and other deformed plutons indicate an increase in metamorphic grade toward the pluton showing that deformation of the pluton and country rock took place as the plutons cooled the kesengawa pluton and country rocks of the southern kitakami zone are deformed into regional scale upright folds with parasitic asymmetric folds that verge toward regional anticlinal axes whereas regional scale folds in the northern kitakami zone are overturned and verge to the east the kitakami basement is not bounded by normal or reverse faults so the style of regional exhumation does not resemble the upright or inclined extrusion noted in other regions nor is the exhumation associated with extensional doming instead the vergence of parasitic folds toward the regional fold hinges indicates flexural slip deformation at least in the late stages of exhumation and exhumation occurred in the cores of regional scale anticlines the regional shortening of accretionary prism forearc basin and older forearc basement was associated with intrusion of adakitic plutons that thermally weakened the forearc basin and enhanced the deformation and exhumation the adakitic magmatism and forearc shortening resulted from subduction of the buoyant izanagi kula ridge a regional event known as the oshima orogeny

exhumation of triassic hp lt rocks by upright extrusional domes and overlying detachment faults ishigaki jima ryukyu islands abstract the tomuru formation of ishigaki jima in the southernmost part of the ryukyu arc comprises blueschist facies subduction complex rocks metamorphosed in triassic time d1 structures related to subduction blueschist facies mineral growth and possibly early stages of exhumation are deformed by d2 structures that appear to reflect the last stage of exhumation d2 structures define several anticlines with parasitic overturned folds verging away from anticlinal axes the shortening recorded by this deformation appears to reflect upward extrusion relative to flanking material the anticlines are flanked by detachment faults with normal sense of shear parallel to d2 vergence hanging wall rocks that include the fusaki formation an accretionary prism with early cretaceous metamorphic ages and late eocene limestone conglomerate and andesitic volcanics the eocene strata contain metamorphic detritus derived from the tomuru and fusaki formations indicating pre late eocene surface exposure of these units ultramafic rocks and gabbro blocks of the tomuru formation were incorporated by sedimentary sliding into the trench prior to subduction and high pressure metamorphism rather than being emplaced as diapirs along a post metamorphic fault as previously proposed geochronologic metamorphic and thermal considerations suggest exhumation of the tomuru formation to relatively shallow crustal depths prior to or concurrent with early cretaceous metamorphism of the fusaki formation arcward vergent thrusting may have placed the younger and formerly structurally lower subduction complex fusaki formation over the older one tomuru formation d2 extrusional doming began after the emplacement of the fusaki formation at high structural levels the d2 transport directions are subparallel to the strike of the orogen suggesting that the upright extrusion may have occurred along a forearc strike slip fault system this final stage of exhumation concluded in the late eocene with extensional collapse and the development of detachment faults the progression from initial exposure of the tomuru and fusaki formations deposition of late eocene strata extrusional doming and late detachment faulting may have been associated with migrating step overs rather than changes in regional tectonics

structural metamorphic evolution of the tia complex new england fold belt thermal overprint of an accretion subduction complex in a compressional back arc setting rocks in the tia complex underwent a simple clockwise p t t deformation path moving from mid crustal levels at blueschist facies conditions d1 d2 6 kbar 200 c to upper crustal levels at high t amphibolite facies conditions d4 d5 2 5 kbar 600 c in a relatively short time 15 ma the rocks remained under these conditions for approximately 40 ma d6 before they cooled and were brought to the surface d7 d8 during d6 permian rift basins were opening as thermal gradients in the tia complex reached a maximum d1 2 deformation was associated with accretion subduction processes and was followed by progressively less intense mainly e w oriented compression and uplift during d3 5 bringing the rocks to within 2 kbars of the surface d6 is characterized by limited extensional deformation and final uplift took place during d7 8 along shear zones that have orientations similar to d3 5 thrusts the shift from subduction dominated processes to thermally dominated processes occurred during d3 4 uplift of 4 kbar around 310 300 ma this coincided with a change in tectonic setting of the tia complex from an accretionary prism to a back arc position as the subduction zone stepped eastward an increased heat flow associated with back arc processes gradually caused thermal weakening of the lithosphere which due to external subduction related compressive forces resulted in uplift d3 with continued heating of the crust thermal doming resulted and uplift stopped d4 5 whilst thermal weakening led to limited crustal collapse as permian basins opened d6 the extremely high heat flow that was maintained for 40 ma suggests a heat source external to the crust possibly associated with thermal relaxation dehydration and detachment of the remnant stab left beneath the new england orogen after the subduction zone shifted east a stable crustal thermal structure was re established by 260 ma as the crust strengthened and could further support subduction induced compressional structures d7 8

palaeomagnetic study of cretaceous red beds from the eastern hindukush ranges northern pakistan palaeoreconstruction of the kohistan karakoram composite unit before the india asia collision we report palaeomagnetic results obtained from cretaceous red bed samples collected from the eastern hindukush mountains northern pakistan rock magnetic studies revealed specular haematite as the dominant remanence carrier while pigmentary haematite magnetite and goethite are responsible for the acquisition of secondary magnetizations thermal treatment generally revealed three components of magnetization the most unstable component a was removed between 200 c and 500 c which corresponds to the local present field direction the intermediate component b was generally separated between 200 c and 660 c the omnipresence of this complex secondary component across the northern suture zone suggests that movement of chemically active orogenic fluids at or slightly before the time of the india asia collision was probably responsible for the authigenic remagnetization processes the characteristic component c was generally unblocked between 600 c and 685 c the characteristic directions from 12 sites fall into two groups the sites from the purit formation give a tilt corrected mean direction of d 311 2 i 4 4 k 12 4 95 17 8 indicating a counter clockwise rotation of about 66 and 15 relative to eurasia and india respectively the tilt corrected mean direction for the reshun and drosh formations is d 263 0 i 2 2 k 52 7 95 10 6 which indicates that the sampling area experienced a counter clockwise rotation of about 114 and 63 with respect to eurasia and india respectively in both cases the palaeomagnetic rotation is consistent with the regional superstructure of the hindukush pamir karakoram syntaxial bend the difference in rotation between these two groups is probably due to local tectonic movement caused by the net rotation of thrust sheets along the northern suture zone the palaeolatitudes calculated for purit and reshun drosh formations are 2 2 s and 1 1 n respectively this indicates that about 4000 km of convergence has taken place since the mid cretaceous of which about 90 per cent post dates the india asia collision the late cretaceous inclination values across the northern suture zone are almost identical which indicates that suturing had been completed at the time of chrm acquisition