distribution of marine organisms and its geological significance in the modern reef complex of the ryukyu islands abstract extensive investigations of biota in the reef complex around the ryukyu islands have revealed ecologic specificity of many benthic organisms and have shown that characteristic assemblages are found in each of the topographic zones and sub areas the moat is divisible into a nearshore seagrass bed and an offshore sand bottom both inner reef flat and outer reef flat are characterized by abundant occurrences of hermatypic corals and nonarticulated coralline algae however the former is dominated by branching and foliaceous forms of corals and various large fleshy erect forms of algae whereas the latter is dominated by encrusting and tabular forms of corals lacking these algae corals and coralline algae are not present on the reef crest which is covered by rubble and gravel where algal turf and sargassum are spreading encrusting and tabular forms of corals flourish on the shallower part of the reef slope with high coverage while with increasing depth the coverage decreases and the dominating coral forms change with hemispherical and encrusting forms on the middle part of reef slope and foliaceous and encrusting forms on the deeper part of reef slope nonarticulated coralline algae are distributed throughout the reef slope the composition of coral and coralline algal assemblages changes dramatically with increasing depth foraminiferal algal nodules rhodoliths are the most abundant constituent on the island shelf commonly with cycloclypeus carpenteri there are likely to be two types of shelves in tropical to subtropical regions nutrient rich halimeda dominant and nutrient poor rhodolith dominant sediments abundant in bryozoan skeletons occur occasionally on the shelf

larger foraminifera distribution on a mesotrophic carbonate shelf in sw sulawesi indonesia larger symbiont bearing foraminifera typically live in shallow tropical seas in this study the fauna composition of patch reefs scattered over the spermonde shelf sw sulawesi indonesia a mesotrophic carbonate shelf is examined the foraminiferal fauna of the spermonde shelf is characterised by three assemblages a seaward slope a leeward slope and a reef base assemblage this is similar to the fauna composition at palau except that palau s reef flat assemblage is absent the samples group in six clusters the reef base deep exposed slope deep leeward slope shallow leeward slope shallow exposed slope and the southern near shore cluster of the four ecological zones that have been recognised on the spermonde shelf in corals and marine vegetation we cannot distinguish between the two outer shelf zones but we do recognise two near shore zones a northern and a southern one this latter part of the shelf within 4 km of the mainland coast has a less diverse foraminiferal fauna in which the reef base fauna is absent compared to areas with a deeper euphotic zone the deepest living species are absent whereas most other species occur in much shallower water neorotalia calcar and calcarina gaudichaudii however have been found in deeper water due to an absence of suitable habitat in the shallow areas other species like peneroplis planatus and calcarina hispida have only been found in the deepest part of their depth range as reported at okinawa these species show a greater flexibility in their habitat preference than has been observed so far we used our results to test hallock s trophic resource continuum model with actual occurrences of larger foraminifera the predictions of the model are met but patterns for example in calcarinids and peneroplids show that not all taxa react in the same way to the described environmental parameters seasonal climatic conditions in the spermonde archipelago mainly affect species with a long life cycle and deep living species a model is presented that explains why deep living species are more affected by seasonal changes in water transparency than shallow living species

sims zircon u pb and molybdenite re os geochronology hf isotope and whole rock geochemistry of the wunugetushan porphyry cu mo deposit and granitoids in ne china and their geological significance abstract the geodynamic setting of magmatic rocks and geodynamic mechanism of cu mo fe sn pb zn ag polymetallic mineralization in northeastern ne china are attracting increasing attention this study explores these issues by providing sims zircon u pb dating whole rock geochemical hf isotopic data of magmatic rocks and molybdenite re os dating exposed in the wunugetushan porphyry cu mo deposit ne china this deposit is located in the western part of the great xing an range on the southeastern margin of the mongol okhotsk orogenic belt molybdenite re os and sims zircon u pb dating of the host monzogranitic porphyry and the wall rock of biotite granite in the wunugetushan porphyry cu mo deposit indicate that the ore formation host porphyry and wall rock emplacement occurred at 180 5 2 0 ma 180 4 1 4 ma and 203 5 1 6 ma respectively and the mineralization of the wunugetushan porphyry cu mo deposit occurred during the same period as that of the host monzogranitic porphyry geochemically the wunugetushan granitoids are characterized by strong lree hree fractionation and pronounced negative nb ta and ti anomalies with slightly negative eu anomalies eu eu 0 71 0 97 of the host monzogranitic porphyry and pronounced negative eu anomalies eu eu 0 29 0 32 of the wall rock of biotite granite in situ hf isotopic analyses of zircons from the host monzogranitic porphyry and the wall rock of biotite granite yielded ehf t values ranging from 0 5 to 8 2 and from 6 9 to 5 9 respectively the geochemical and isotopic data for the wunugetushan granitoids imply that the primary magmas of the host monzogranitic porphyry could have originated by partial melting of a thickened lower crust with input of mantle components while the primary magmas of the wall rock of biotite granite could have been derived by partial melting of a thickened lower crust that mixed with ancient crustal materials based on the regional geological history geochemistry of the wunugetushan granitoids and new isotopic age data we suggest that the formation of the wunugetushan porphyry cu mo deposit was possibly induced in the early jurassic during the period of the southeastward subduction of the mongol okhotsk oceanic plate beneath the erguna massif

granite greenstone terranes in the pilbara block australia as coeval volcano plutonic complexes evidence from u pb zircon dating of the mount edgar batholith the mount edgar batholith in the pilbara block western australia consists in part of a gneiss complex that resembles other archean high grade gneiss terranes the complex is extensively intruded by variably foliated granitoids which also intrude the surrounding greenstone succession the warrawoona group the contact between the greenstone belt and the gneiss complex is tectonic field evidence indicates that the banded gneisses are the oldest part of the batholith zircon u pb ages for three samples are 3429 13ma 3443 10ma and3448 8ma all very similar to the age of zircons in the felsic volcanic rocks near the base of the greenstone succession pidgeon 1978 1 two granitoids representing pre and post tectonic phases respectively give zircon ages of 3304 10ma and3314 13ma thereby constraining the major structural events to be contemporary with granite magmatism consistent with a diapiric model for the tectonic evolution of the batholith collins 1989 2 these ages are similar to the zircon age for terminal volcanism in the warrawoona group pidgeon 1984 3 but are 100ma older than the precisely defined rb sr whole rock ages obtained throughout the batholith collins and gray 1989 4 batholith wide resetting or late closure of rb sr isotopic systems is implied possibly associated with late fluid circulation the temporal coincidence between plutonism and volcanism in the mount edgar region strongly suggests that the greenstone succession contains the extrusive equivalents of both the 3300ma granites and the 3440ma gneisses in the batholith the isotopic evidence combined with the structural data indicates that the granites cannot be derived from the surrounding greenstone belt further there is no compelling evidence for a sialic basement to the greenstone succession

boundary lines within petrologic diagrams which use oxides of major and minor elements use of some petrologic diagrams applied to analyses of volcanic rocks is unnecessarily difficult due to lack of data for construction of discriminant lines between rock series coordinates are provided for sufficient points to enable accurate plotting of the boundary lines within seven diagrams viz 1 tas total alkalies na2o k2o vs sio2 2 k2o vs sio2 3 afm 4 jensen 5 ktp k2o tio2 p2o5 6 fms feo mgo vs sio2 and 7 taktip k2o na2o k2o vs tio2p2o5 different versions of these boundaries are collated to indicate their variable position and it is demonstrated that inter laboratory analytical precision suffices to account for almost all of their spread on the tas and k2o vs sio2 diagrams

evolution of calc alkaline to alkaline magmatism through carboniferous convergence to permian transcurrent tectonics western chinese tianshan continuous magmatic activity occurred in the western chinese tianshan central asia from the carboniferous to the permian i e before and after the late carboniferous amalgamation of junggar and the yili blocks zircon u pb la icpms and ar ar data reveal a coincidence in time between regional wrench faulting and granitoid emplacement permian post collisional granitoids crop out within or at the margins of large scale dextral strike slip shear zones some of them show synkinematic fabrics the whole rock geochemical features of the early middle permian granitoids indicate an evolution from high k calc alkaline towards alkaline series in other places of the north tianshan alkaline magmatism occurred together with deep marine sedimentation within elongated troughs controlled by wrench faults therefore in contrast with previous interpretations that forwarded continental rift or mantle plume hypotheses the coexistence of diverse magmatic sources during the same tectonic episode suggests that post collisional lithosphere scale transcurrent shearing tightly controlled the magmatic activity during the transition from convergent margin to intraplate anorogenic processes

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

archean synsedimentary tectonic deformation a comparison with the quaternary observations from the 3 55 3 3 ga barberton greenstone belt indicate an important phase of shortening synchronous with the deposition of alluvial sediments the structural style is remarkably similar in scale and geometry to that now occurring on land in the convergent plate boundary zone in the north island of new zealand

peraluminous i type granites abstract s type granites always contain more al than the amounts of na ca and k in the rock required to form feldspars primarily owing to their derivation from source components that had previously been weathered those rocks are therefore always saturated in al or peraluminous many i type granites are also peraluminous despite i type source rocks typically not being saturated in al it has previously been suggested that this may result from the fractional crystallisation of amphibole however data from compositionally zoned high temperature plutons in the lachlan fold belt show that it is difficult to generate large quantities of peraluminous melt by removal of amphibole most of the i type granites 95 in the lachlan fold belt formed at lower temperatures and almost half of those rocks for which bulk chemical compositions are available are peraluminous among these granites there are 98 separate suites for which there are chemical data for two or more samples with 47 suites that include both metaluminous more mafic and peraluminous more felsic compositions the origin of those peraluminous compositions is fundamental to any understanding of i type granite petrogenesis in this region compositional variations caused by the assimilation or by partial melting of supracrustal rocks are very small as the isotopic variations within these rocks are dominantly between different suites not within suites the partial melting of more mafic source rocks rather than the fractional crystallisation of more mafic magmas is favoured for the origin of these rocks partial melting is the most likely process involved in the petrogenesis of felsic granites where broadly granodioritic monzogranitic batholiths are associated with lesser amounts of tonalite and very minor amounts of mafic rock experimental studies have shown that the melts generated by the partial melting of basaltic to andesitic rocks under crustal conditions are mostly peraluminous during the dehydrational melting of i type granite source rocks at pressures below the garnet stability field biotite and amphibole melt incongruently to yield pyroxenes the excess al is incorporated into the felsic liquid resulting in the generation of peraluminous melts in this instance the excess al in felsic i type granites is a function of the melting process and unrelated to the bulk composition of the source the observed gradation from peraluminous felsic granites to metaluminous compositions in less felsic rocks in largely isotopically closed systems could happen in two ways at higher temperatures of partial melting ca and other components of clinopyroxene could dissolve in the melt with the melt eventually becoming metaluminous alternatively minerals residual from partial melting dominantly pyroxenes and plagioclase could be incorporated in suspension in the melt so that the resulting bulk magma is metaluminous examples of these two extremes and of intermediate cases are well developed among the granites of southeastern australia

the dagpazari carbonate platform mut basin southern turkey facies and environmental reconstruction of a coral reef system during the middle miocene climatic optimum abstract plate tectonics and climate change have deeply influenced the evolution of coral reef systems of the mediterranean during the miocene most of this information is based on studies of coral reefs from the western and central sectors of the mediterranean this study reports facies analyses sr isotope stratigraphy and environmental reconstructions of the dagpazari coral reef system located within the mut basin in southern turkey stratigraphic correlations and sr isotope ratios on several oyster shells date the dagpazari reef to the early langhian ten different facies have been recognized and their arrangement has led to the identification of two main depositional units interpretation of the biotic associations indicates that the dagpazari depositional system developed constantly within the euphotic zone the reef framework was mainly built by massive faviid and poritid zooxanthellate corals whereas loose grain sediments were essentially produced by halimeda coralline red algae or influenced by the presence of seagrass colonizations this study highlights for the first time the great importance of halimeda as sediment producer in the eastern mediterranean coral reef systems this role is related to the common occurrence of halimeda plates within almost all the reef facies but especially to the presence of large in situ bioherms dominated by the algal segments dagpazari langhian halimeda bioherms also represent the oldest of these structures so far recorded in the fossil record the development of the dagpazari platform was mainly controlled by eustatic fluctuations of the sea level and by the morphology of the antecedent substrate in particular the occurrence of a pre existent topographic high promoted the constant presence of shallow water environments throughout the depositional history of the reef system with the production of euphotic carbonates both landward and basinward and the consequent formation of a small elliptical platform 87sr 86sr ages place the dagpazari reef system exactly within the middle miocene climatic optimum phase the most recent warm phase of the earth this suggests that zooxanthellate corals were able to exert their reef building capacity in shallow water settings even during periods of global warming thus being not exclusively an adaptation to cooling climates as proposed in the recent debates

habitats of larger foraminifera on the upper reef slope of sesoko island okinawa japan larger foraminifera living in the upper 50 m in front of the fringing coral reef northwest off sesoko island japan show strong habitat differences this study closely examines the distributions of larger foraminifers and relates these to a number of key environmental factors using rigorous statistical methods since all larger foraminifera house symbiotic algae light attenuation by the water column is the most important limiting factor that must be dealt with wall structures water energy is also countered by test structure the local topography is responsible for different intensities of hydrodynamic forces which are expressed in various substrates mostly coral rubble and coarse grained sand the genus peneroplis very common on the reef flat clearly prefers hardgrounds of the shallowest slope parts down to 30 m while dendritina is restricted to sandy bottoms and avoids the uppermost meters of the slope it can be found down to 50 m at least alveolinella shows a similar depth distribution to dendritina but is common on hard bottom the distribution of parasorites which is restricted to sandy substrates starts at 20 m and extends to 80 m sorites on the other hand was found only on firm substrates between the reef edge and 50 m the same depth distribution was recorded for amphisorus but this genus is not correlated with specific substrates most of the amphistegina species prefer hardgrounds while amphistegina radiata is also common on sand the calcarinids capable of withstanding high water energy are abundant on firm substrates close to the reef edge only baculogypsinoides inhabits deeper parts of the slope on sandy bottom and avoids the shallowest parts sections with hard substrates are settled by heterostegina even down to 80 m although this genus was occasionally found on sandy bottoms nummulites in contrast is restricted to sands between 20 and 70 m operculina starting at 20 m also prefers sandy substrates but rare individuals were detected on coral rubble and macroids

constraints on the age of the warrawoona group eastern pilbara block western australia abstract zircons from mafic and felsic volcanic rocks in the type area of the warrawoona group the basal archaean greenstone succession of the eastern pilbara block have been dated precisely using the ion microprobe shrimp the results allow two alternative time frames for the duration of the warrawoona group dependent on how the dated zircons are considered to relate to the volcanic rocks our favoured interpretation requires a hiatus of 135 5 ma between the duffer formation at 3 46 ga and the overlying felsic volcanic rocks of the wyman formation and a hydrothermal or later magmatic origin for zircons of age 3 33 ga within one duffer formation sample and the underlying metabasalts the alternative time frame requires a short time for deposition of the entire group less than 15 ma at 3 33 ga and a xenocrystic origin for the 3 46 ga zircons of the duffer formation outside the type area of the warrawoona group the age of an intrusive granodiorite requires that greenstones be older than 3 43 ga and the group formed over an interval of 120 ma visibly different zircons within one of the duffer formation samples were found to be palaeozoic in age and presumably constitute hydrothermal growth of new zircon within the rock at low temperature similar zircons were found within samples from other rock units but with a spread of proterozoic ages

habitat heterogeneity reflected in mesophotic reef sediments abstract modern reef sediments reflect the physical and chemical characteristics of the environment as well as the local reef fauna analysis of sedimentary reef facies can thus provide a powerful tool in interpreting ancient reef deposits however few studies have attempted to differentiate sedimentary facies in mesophotic coral ecosystems low light habitats defined as residing 30 150 m below sea level the low angle shelf mesophotic coral ecosystem south of the northern u s virgin islands usvi consists of reefs with different structural characteristics ideal for studying the relationship between habitat variability and sedimentary facies textural compositional and geochemical analyses of surface sediments were used to identify mesophotic reef subfacies associated with distinct benthic communities and structural habitats sediment grain composition and bulk geochemistry were found to broadly record the distribution and abundance of coral and macroalgae communities foundational mesophotic reef benthic organisms overall sediment composition was found to be a good indicator of specific reef environments in low angle mesophotic reef habitats sedimentological analyses indicate that hydrodynamic forces do not transport a significant amount of allochthonous sediment or potentially harmful terrigenous material to usvi mesophotic reefs episodic maximum current velocities prevented deposition of most silt size grains and smaller but biological processes were found to have a greater influence on subfacies partitioning than hydrodynamic processes results provide a new analog for studies of ancient mesophotic coral ecosystem geological history and document the relationship between mesophotic reef subfacies structural complexity and habitat heterogeneity they also demonstrate how mesophotic reefs along the same shelf system do not always share similar sedimentary characteristics and thus record a diverse set of ecological and environmental conditions

fringing reef growth on a terrigenous mud foundation fantome island central great barrier reef australia the leeward fringing reef at fantome island central great barrier reef province is a carbonate body which has developed under the influence of terrigenous sedimentation the reef flat is up to 1000 m wide and is surfaced by mobile sand and gravel with almost all live corals restricted to the seaward rim the reef slope has coral columns and heads on the upper part but below 5 m water depth it is a muddy substrate with scattered mounds of branching corals three high recovery cores show the reef is up to 10 m thick and developed over a gently sloping terrace of weathered pleistocene alluvium three post glacial stratigraphic units are recognised i carbonate reef top unit of coral rudstone and framestone including sinuluriu spiculite 2 lower slope unit of coral floatstone in a terrigenous muddy matrix and 3 transgressive basal unit of skeletal arkosic sand the acid insoluble content of matrix and of individual corals increases downwards coral growth rates decrease downwards reflecting slower growth in muddier environments radiocarbon dating shows that the reef prograded seaward at almost stable sea level an average vertical accumulation rate of 6 7 mm yr is indicated two age reversals are interpreted as material transported by storms or by erosion in response to a late holocene sea level fall the carbonate reef top unit has developed adjacent to and is environmentally compatible with a muddy terrigenous lower slope unit terrigenous influx has not changed during the holocene and terrigenous content of sediments is controlled by deposition on the reef slope of fine sediment winnowed from the reef flat and concentration of coarse sediment in the transgressive basal sheet

seagrass related carbonate ramp development at the front of a fan delta burdigalian new caledonia insights into mixed carbonate siliciclastic environments abstract past shallow water carbonate environments of the main island of new caledonia nc have been subject to high terrigenous influx derived from the erosion of ultramafic obducted nappes and are therefore a relevant case study for characterizing neritic carbonate production in mixed carbonate siliciclastic systems under a tropical climate more particularly we focused on burdigalian carbonate sedimentary records cropping out on the western coast of nc in the nepoui area based on a comprehensive sedimentological study of cores and outcrops we established a new depositional model of an alluvial fan to carbonate ramp transition shallow water euphotic carbonate production was dominated by seagrass related biota and corals derived from small sized bioconstructions extensional tectonics and associated normal faulting driven by post obduction isostatic rebound favored carbonate ramp aggradation and preservation the carbonate ramp was incised by conglomerate filled terminal distributary channels which indicate that terrigenous inputs remained significant during marine transgression and did not inhibit the development of seagrass and scleractinian carbonate factories phytal substrates induced by seagrass and or macro algae seafloor colonization strongly controlled the nature of carbonate production and promoted the accumulation of foraminiferal coralline algal sediments seagrass development at the front of the fan delta is interpreted to have controlled the preservation of a diverse and significant carbonate production by reducing water turbidity and by limiting the risk of suffocation for filter feeding biota in such a high terrigenous influx setting

internal structure and accretionary history of a nearshore turbid zone coral reef paluma shoals central great barrier reef australia abstract nearshore environments directly influenced by fluvial sediments and dominated by terrigenoclastic sedimentation are generally considered marginal for coral reef growth there are however a growing number of examples from the modern and fossil record that clearly show that reef building and terrigenous sedimentation are not mutually exclusive although a number of descriptive accounts of nearshore turbid zone reefs have emerged in recent years our understanding of the accretionary architecture and history of such reefs remains extremely limited here we detail the depositional facies and accretionary history of an inshore turbid zone coral reef complex paluma shoals on the central great barrier reef shelf of australia high turbidity 40 ntu for over 30 of the time and terrigenous sedimentation both at levels close to the perceived limits for coral growth are episodically important influences at paluma shoals despite these potentially limiting conditions paluma shoals exhibits high live coral cover 50 60 but locally up to 80 with the intertidal reef flats compositionally dominated by g aspera microatolls and galaxea sp and porites sp colonies seventeen cores from 5 cross reef transects reveal that the internal reef structure comprises an unconsolidated detrital coral rubble framework 2 0 2 7 m thick dominated by fragments of acropora pulchra t frondens and m mollis these occur within a mixed terrigenoclastic carbonate sediment matrix basal facies in particular contain a high 60 proportion of terrigenoclastic sediment radiocarbon dating indicates that the reef initiated above pleistocene clays 1600 cal yr bp the present reef flat was emplaced within the last 150 100 cal yr bp within the last 60 years areas of the north shoal have become partially smothered as a result of intertidal sandflat progradation the depositional sequence at paluma shoals shows 1 that long term millennial timescale reef accretion has occurred under conditions dominated by terrigenoclastic sediment accumulation 2 that relatively rapid vertical reef growth and progradation can occur in these marginal settings and 3 that these reefs are susceptible to natural episodic mortality events associated with the remobilisation of intertidal and shallow subtidal sediments this study provides important insights into coral reef development where environmental conditions are perceived to be marginal for hermatypic coral growth

equatorial carbonates an earth systems approach the hypothesis here is that an earth systems processes to products approach can be used to better develop predictive models for the recognition and assessment of under evaluated equatorial carbonate systems warm temperatures together with common clastic fresh water and nutrient influx as well as basinal settings in the equatorial tropics all have a major impact on carbonate deposition and diagenesis specific features of equatorial carbonate systems resulting from the combination of processes acting in the region include common occurrence of photoautotrophs and heterotrophs aragonitic and or calcitic dominant mineralogies lack of coated grains or aggregates common associations with clastics lack of associations with evaporites and diversity of platform types including oligophotic ones additional diagenetic characteristics include common micritization and bioerosion paucity of marine cements extensive vadose dissolution and concomitant phreatic cementation there is also significant replacement of aragonite by calcite in regions of meteoric groundwater flow common burial compaction and leaching as well as localized massive dolomitization via sea water or continental derived groundwater flow although equatorial carbonates fall into the warm water photozoan association many of the features described above are at odds with models derived from their warm water arid zone counterparts instead a range of the equatorial carbonate features show some similarities with those formed in cool waters and there have been difficulties separating carbonates from these two very different climatic regimes recommendations for the recognition of phanerozoic regional equatorial carbonate development are i a diversity of calcitic and or aragonitic photoautotrophs plus ii common elements of the heterozoan association plus iii independent for example isotopic evidence for warm temperatures 22 c additional indicators towards a humid equatorial setting are iv situation in appropriate palaeolatitudes v lack of association with sedimentary evaporites coated grain or aggregates and vi geochemical evidence for reduced marine salinity and or nutrient upwelling the aim is that this work will lead to greater awareness and understanding of equatorial carbonate systems and contribute to the development of globally predictive models to better understand past and likely future environmental change

petrogenetic interpretation of granitoid rock series using multicationic parameters abstract granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la roche and his coworkers this shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors these suggest that most granitoid series result from a two stage process first fractional crystallisation of clinopyroxene olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition this magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series

marine biota response to clastic sediment influx a quantitative approach abstract there have been few quantitative studies of the effects of siliciclastic and volcaniclastic sediment influx on carbonate producing organisms from the geological record this study presents the results of quantitative field petrographic and acid digestion analyses of samples from three cenozoic shallow water mixed carbonate volcani siliciclastic depositional environments the miocene wonosari formation of south java the miocene batu putih limestone of east borneo and the eocene collsuspina limestone of northeast spain carbonate production in these systems is dominated by larger benthic foraminifera coralline algae and corals analyses of the quantity grainsize and type of volcani siliciclastic sediment within these mixed successions have allowed assessment of the influence of these factors on shallow water carbonate producers larger benthic foraminifera and coralline algae exhibit the greatest tolerance to siliciclastic sediment influx abundant up to 55 and 38 wt respectively at a range of grain sizes to coarse sand platy corals are also present within sediments containing a large proportion of insoluble material geologically averaged rates of clastic accumulation and their potential influences on carbonate producers inferred herein may be difficult to compare directly with the daily and seasonal fluctuations experienced by modern clastic influenced systems however this study may aid our understanding of the likely effects of increased clastic influx today commonly anthropogenically related to marine carbonate environments over longer time periods

development of equatorial delta front patch reefs during the neogene borneo abstract miocene patch reefs formed in turbid waters associated with high siliciclastic input at the seaward margin of the equatorial mahakam delta in eastern borneo se asia patch reefs were initiated on unstable substrates on localized low relief bathymetric highs associated with delta front channels or distributary mouthbars in the process of abandonment patch reefs developed only in shallow waters formed low relief buildups lacked rigid frameworks and had gently sloping margins although the biodiversity of the patch reefs may be comparable with that of clear water systems all the organisms present were adapted to turbid water areas associated with siliciclastic and sometimes nutrient influx the patch reefs were transient features and their demise was influenced by increased siliciclastic and nutrient input perhaps at times associated with deepening carbonate production and bioherm or patch reef development can occur in turbid water delta front areas as localized or more regionally extensive units during any phases of eustatic sea level however development and preservation of turbid water carbonates is most likely during relative transgression or perhaps late lowstand periods this is in contrast with common highstand carbonates from clear water shelves where nearly pure carbonates interdigitate with siliciclastics it is the interplay between factors such as tectonics eustasy delta lobe switching shelf currents and amount and size fraction of siliciclastic influx that ultimately controlled carbonate development and preservation

extensional structures during deposition of the 3460 ma warrawoona group in the eastern pilbara craton western australia abstract structures in the granite greenstone terrain of the eastern pilbara were mapped in both the coongan belt greenstones and shaw batholith granitoids important structures that are coeval with an early magmatic event in both the granitoids and the greenstones were identified in the coongan greenstones a brittle extensional fault array is syn kinematic with felsic volcanics of the duffer formation dated at 3452 16 ma pidgeon 1978a in the underlying shaw batholith a major ductile shear zone was mapped at the contact with the coongan belt although the foliation in the shear zone forms part of a domal structure the stretching lineations constantly plunge to the ene the sense of shear as recorded in the shear zone is consistently east up with subsidiary sinistral strike slip movement on the e w trending part and dextral movement on the n s trending part a wedge shaped granitoid intruded into the shear zone during deformation this granitoid is part of the north shaw suite which has been dated at 3467 6 ma mcnaughton et al 1988 the structures in the greenstones and in the batholith have therefore formed during the same event at different crustal levels the structural kinematic magmatic metamorphic and geochronological data are consistent with a model in which these structures represent the downdip part of a dome with a core complex type of geometry in turn this implies that the domal geometry of the shaw batholith was initiated at mid crustal levels at a very early stage namely during deposition of the warrawoona group in the evolution of the pilbara craton as extension occurred during intrusion and extrusion of large volumes of magma the original distribution and thickness of granitoid bodies and greenstones were probably largely determined by the extensional geometry the initial domal shape of the shaw batholith has been enhanced during later deformation phases which caused steepening of n s trending structures

large benthic foraminifera from the deep photic zone of a mixed siliciclastic carbonate shelf off east kalimantan indonesia abstract living large benthic foraminifera lbf were analyzed from three transects of boxcores taken on a shelf off the coast of east kalimantan just north of the mankalihat peninsula the transects were located at different distances to the mouth of the berau river in 45 boxcores of which 28 contained living lbf 20 species were recognised they occurred in moderate to high density outside the pro delta i e outside the area with high clay and silt sedimentation lbf characteristic of sandy substrates can be divided into two or possibly three assemblages shallow 15 50 m deep 50 85 m and possibly very deep 85 m the latter is poorly developed in the study area few lbf were recorded in one of the three transects possibly because of either sediment instability or physical or chemical parameters of the sediment grain size analysis of samples in the other transects indicates that lbf occurrence strongly modify the habitat after colonisation grain size increases creating more opportunities for other species and higher densities of lbf

recurrent patterns of coral community and sediment facies development through successive phases of holocene inner shelf reef growth and decline abstract coral community decline and resultant turn off of reef accretion potential are commonly predicted outcomes of the increasing environmental stresses experienced by many coral reefs the potential for coral reef communities to re establish once environmental conditions ameliorate or new substrates for colonisation become available are however less well understood here we discuss data from a fringing reef at dunk island an inner shelf high island on australia s great barrier reef gbr although this reef is spatially contiguous detailed coring and dating reveal it was constructed in two discrete temporal phases the inner part of the reef flat formed first during the late stages of the post glacial marine transgression early sea level highstand 6 9 4 5 k cal yr b p whereas the outer fringe developed after the late holocene sea level regression from 1 6 k cal yr b p to present a hiatus of almost 3000 years separates the two reef growth phases data from this reef thus provide a same site perspective on the degree of temporal continuity that exists where an actively growing reef slows and eventually ceases to accrete for an extended period before re establishing and growing again a temporal transition equivalent to reef turn off followed by renewed reef turn on the depositional architectures of the two phases of reef growth are very similar as are patterns of facies and coral assemblage development this study suggests that reefs over the timescales at which cycles of reef turn on and turn off operate the centennial to millennial timescale can not only re establish successfully but also that regrowth may be characterised by the establishment of near identical reef building communities and the development of near identical depositional structures these findings thus have direct relevance to the on going debate about whether and in what form reef communities will be able to re establish themselves following periods of suppressed growth such as those projected for the near future

ecological tolerances of miocene larger benthic foraminifera from indonesia abstract to provide a comprehensive palaeoenvironmental reconstruction based on larger benthic foraminifera lbf a quantitative analysis of their assemblage composition is needed besides microfacies analysis which includes environmental preferences of foraminiferal taxa statistical analyses should also be employed therefore detrended correspondence analysis and cluster analysis were performed on relative abundance data of identified lbf assemblages deposited in mixed carbonate siliciclastic mcs systems and blue water bw settings studied mcs system localities include ten sections from the central part of the kutai basin in east kalimantan ranging from late burdigalian to serravallian age the bw samples were collected from eleven sections of the bulu formation on central java dated as serravallian results from detrended correspondence analysis reveal significant differences between these two environmental settings cluster analysis produced five clusters of samples clusters 1 and 2 comprise dominantly mcs samples clusters 3 and 4 with dominance of bw samples and cluster 5 showing a mixed composition with both mcs and bw samples the results of cluster analysis were afterwards subjected to indicator species analysis resulting in the interpretation that generated three groups among lbf taxa typical assemblage indicators regularly occurring taxa and rare taxa by interpreting the results of detrended correspondence analysis cluster analysis and indicator species analysis along with environmental preferences of identified lbf taxa a palaeoenvironmental model is proposed for the distribution of lbf in miocene mcs systems and adjacent bw settings of indonesia

growth and demise of cenozoic isolated carbonate platforms new insights from the mozambique channel seamounts sw indian ocean although long term evolutions of isolated shallow water carbonate platforms and demise episodes leading to guyot formation have been the subject of numerous studies during the last decades their driving processes are still the subject of active debates the mozambique channel sw indian ocean is characterized by several flat topped seamounts ranging from 11 s to 21 s in latitudes based on a comprehensive geomorphologic study and on dredged samples analysis we show that these features correspond to tropical isolated shallow water carbonate platforms coupling strontium isotopy and foraminifera biostratigraphy well constrained chronostratigraphy results indicate that shallow water carbonate production started in the mozambique channel during distinct cenozoic periods ranging from paleocene to early miocene our data also demonstrate that these carbonate platforms were subsequently characterized by different evolutions locally marked by tectonic and rejuvenated volcanism while some of them kept developed until present days forming modern carbonate systems some others were drowned during late neogene and subsided to form guyots although different factors can be discussed tectonic and volcanism appear as good potential triggers for demise episodes during late miocene early pliocene times chronology and location of this geodynamical activity tend to emphasize influence of east african rift system until southern mozambique channel

gliding and overthrust nappe tectonics in the barberton greenstone belt abstract regional recumbent folds inverted stratigraphy nappes and olistostromes are described from the southern part of the 3 3 3 5 ga barberton greenstone belt overthrusting of thin rigid silicified slabs with minimum dimensions of 25 km2 and up to 500 m in thickness occurred over minimum distances of 86 km more ductile and coherent units were overfolded up to at least 2 km during their emplacement the glide planes on which these nappes travelled were zones of high fluid pressures related to hydrothermal fluid circulation patterns driven by heat sources from igneous intrusions the upwelling areas of the geothermal convection cells were sites of mud pools and hydrothermal vents which may mark the trailing edges pull aparts of the overthrust units progressive silica and carbonate precipitation due to decreasing temperatures within the zones of fluid migration distant from the areas of high heat flow probably acted as built in braking systems below the travelling slabs active sedimentation and metasomatism during this tectonism indicates a protracted history for the evolution of the greenstone belt the recognition of nappe and overthrust tectonics in the barberton belt processes which may have been commonplace in archaean terrains necessitates a re evaluation of the stratigraphy of this belt

cenozoic palaeogeographic evolution of sulawesi and borneo abstract sulawesi and borneo are located in the middle of the indonesian archipelago an area which has been extremely tectonically active throughout the cenozoic this paper compiles current knowledge on the geology and palaeogeography of this complex region and includes the first attempt to synthesise palaeogeographic data onto plate tectonic reconstructions construction of palaeogeographic maps helped to identify some of the strengths and weaknesses of current plate tectonic models for the region thereby highlighting areas where further geological research is required palaeogeographic maps presented using plate tectonic reconstructions as a base illustrate the evolution of borneo and sulawesi and highlight important changes in the environment during the cenozoic the tertiary geological history of eastern borneo and sulawesi is inextricably linked to the progressive accretion of continental and oceanic material from the east onto the eastern margin of sundaland and to the resultant development of volcanic arcs large tracts of western sulawesi eastern borneo the east java sea and the makassar straits formed an extensive basinal area throughout much of the tertiary implications for plate tectonics exploration for natural resources and biogeography are discussed from the palaeogeographic reconstructions of sulawesi and borneo

evidence for multiphase deformation in the archean basal warrawoona group in the marble bar area east pilbara western australia abstract the results of a structural analysis of the marble bar greenstone belt in the mcphee reward area of the eastern pilbara block in western australia indicate that the area has undergone a multiphase deformation on shears which approximately parallel the trace of stratigraphy cf primary igneous layering around the talga talga anticline early extensional movements were associated with the formation of the warrawoona group chiefly the duffer formation and indicate a wnw ese extensional direction similar to the syn warrawoona extension found in the area of the north shaw batholith extension was followed by thrusting with transport to the east the talga talga anticline is a culmination which formed during this event by thrust stacking a major shear in the area the duffada shear was reactivated during granodiorite emplacement with transport to the ne in their present geometry the shears have thrust movements on the south side of the talga talga anticline but normal movements on the north side after the reactivation came a nw se shortening which was accompanied by conjugate shear activity on north trending sinistral and west trending dextral shears and constrained to 2950 ma in the north shaw area the final movements were associated with a n s shortening which resulted in an e w trending thrust which cuts the northern flank of the talga talga anticline and nw and ne trending conjugate faults there is no evidence of radially oriented stretching lineations or slickensides which would be expected if the granitoid bodies which make up the mount edgar batholith were emplaced by a solid state diapiric process the net result of deformation was tectonic disruption of the stratigraphic stacking within the type ara of the talga talga subgroup in the warrawoona group this may offer an additional explanation for anomolously young dates of the talga talga subgroup with respect to the duffer formation and also indicates that the type section for the talga talga subgroup is a lithotectonic sequence

late paleozoic underplating in north xinjiang evidence from shoshonites and adakites abstract shoshonitic series volcanic rocks ssvr and adakites are widely distributed in the permian terrestrial volcanic strata of the yishijilike awulale range of west tianshan north xinjiang china isotopic dating yields permian ages of 280 250 ma the ssvr include absarokite shoshonite and banakite which are characterized by enrichment of alkalis particularly in k combined with lower ti higher al a nkc 0 70 0 99 metaluminous and fe2o3 feo the ssvr that are rich in lile with high ree contents and eu eu range from 0 59 to 1 30 they are rich in lree la yb n 2 15 11 97 and depleted in nb ta and ti tnt negative anomalies the adakites are metaluminous to weakly peraluminous a nkc 0 85 1 16 and belong to the high sio2 type of adakite hsa sio2 62 71 they are characterized by lower ree with strong lree enrichment la yb n 13 35 pronounced positive eu anomalies eu eu 1 02 1 27 very low yb contents and distinct tnt negative anomalies are evident the ssvr have end t 1 28 to 4 92 and 87sr 86sr i 0 7041 0 7057 that are similar to adakites in the regions which are characterized by end t 0 95 to 5 69 and 87sr 86sr i 0 7050 0 7053 trace element ree and sr nd isotopic compositions suggest that both ssvr and adakites possess similar source regions associated with underplated mantle derived basaltic materials lithosphere extension driven by magmatic underplating was responsible for the generation of both the ssvr and adakites this magmatism serves as a petrological indicator of underplating during the permian obviously thickened crust 62 52 km a complex moho discontinuity high heat flow 100 mw m 2 widespread contemporary alkali rich granites basic dike swarms k ar ages of 187 271 ma ar ar ages of 174 270 ma and rb sr ages of 255 28 ma end t 1 84 to 10 1 87sr 86sr i 0 7035 and 0 7065 and basic granulites shrimp u pb age of 268 279 5 6 ma provide additional evidences for the underplating event in this area during permian

sedimentology of archean greenstone belts signatures of tectonic evolution abstract stratigraphic styles in archean greenstone belts are compared to those of modern and phanerozoic depositional basins in order to test the conformity of tectonic style through time six lithological associations in greenstone belts are recognized 1 mafic ultramafic volcanic 2 calc alkaline volcanic 3 bimodal volcanic 4 quartz arenite iron formation or carbonate 5 conglomerate wacke and 6 conglomerate arenite examples of the associations are described from the kaapvaal superior and zimbabwe provinces and the pilbara block each association differs only slightly between the four regions thereby emphasizing a common tectonostratigraphic theme sedimentary rocks are a minor component of the mafic ultramafic volcanic association they were deposited in two types of volcanic basin environments one similar to barred lagoons and bays around oceanic volcanic islands and the other similar to sediment starved platforms adjacent to coalesced volcanoes in inter arc intra arc and back are basins in contrast sedimentary rocks in the calc alkaline volcanic association comprise thick wedges of epiclastic and volcaniclastic detritus deposited in elongate sedimentary basins and thick wedges of pyroclastic and volcaniclastic detritus deposited adjacent to volcanic centers sedimentary facies were identical to those of forearc trench and marine volcanoplutonic arc settings chemogenic lithofacies in both volcanic associations were deposited in shallow to deep marine waters although shallow water profiles were selectively preserved in some terrains sedimentary rocks of the bimodal volcanic association are thick wedges of siliciclastic and volcaniclastic deposits interbedded with subaerial to submarine erupted flows of komatiite basalt and rhyolite depositional environments ranged from braid plain and braid delta to coastal marine and submarine fan starved basin deposits include banded iron formation and sulfidic black shale the association is identical to that of cratonic extensional basins in arc continent and intracontinental rifts sedimentary rocks of the quartz arenite iron formation or carbonate association onlap weathered basement or bimodal volcanic association rocks depositional environments were either transitional from fluvial to siliciclastic and carbonate marginal marine to offshore pelagic hemipelagic or from inshore intrabasinal clastic and volcaniclastic to offshore pelagic hemipelagic siliciclastic deposits are supermature two tectonic sites are represented those with siliciclastic facies represent continent adjacent syn to post rift stable shelves and those dominated by banded iron formation with volcaniclastic deposits represent arc adjacent post rift stable shelves sedimentary rocks of the conglomerate wacke association are represented by thick wedges of siliciclastic or volcaniclastic sandstone with minor volcanic components these were deposited in braid plain braid delta and submarine fan environments within elongate sedimentary basins coastal plain and pelagic basin facies are also present siliciclastic detritus was derived from syndepositional magmatic and metasedimentary thrust belts two stratigraphic styles are preserved one that records a flysch like stage of deep to marginal marine environments and the other that records a molasse like stage of marginal marine to fluvial environments the association is identical to that of compressional foreland basins of arc continent collisional and compressional arc tectonic affinities the conglomerate arenite association is preserved in elongate structural basins that transgress crustal components and all other supracrustal units it is dominated by thick wedges of siliciclastic sandstone although bimodal volcanic and volcaniclastic rocks can also be present depositional environments ranged from talus and alluvial fan and braid plain to either lacustrine or coastal marine local basin margins often show lateral offsets from source terrains and vertically skewed facies patterns longitudinal facies geometries are typical the association is similar to that of strike slip collisional graben in hinterland tectonic escape and terrane accretion orogens the examples show that despite all the ramifications of secular geophysical geothermal and geochemical global change the stratigraphic style of sedimentary rocks in archean greenstone belts can be matched with modern tectonic analogues thereby emphasizing the conformity of stratigraphic style through time the inseparable link between stratigraphic and tectonic styles implies that the tectonic style of greenstone belts was not temporally unique major differences exist with regards to the chemical composition of certain magmatic and sedimentary products but these are compensated for by their constant stratigraphic function in terms of depositional processes depositional environments and tectonic sites

archaean basin margin geology and crustal evolution an east pilbara traverse a palinspastic reconstruction of a 100 km long traverse through archaean rocks of the east pilbara western australia includes new observations of the deformation preceding the now visible greenstone belt pattern the restoration is time calibrated with all available u pb datings between incompletely preserved basin sequences two superposed palaeoarchaean volcano sedimentary basins the coongan and salgash basins are separated by an eastwards time transgressive interface tentatively interpreted as an onlap surface for over 140 ma the basin margin architecture was structurally controlled by superposed extensional growth fault arrays d 1 with associated dyke swarms in a curved pattern spatially not related to that of the actual distribution of granite domes and greenstone belts the basins are interpreted to have formed by collapse after arching above hotspots due to phase transitions by mini subduction of slabs of cooled water saturated basalt towards the base of an originally c 45 km mafic crust at c 3 31 ga the extension was replaced by plate driven regional nw se compression d 2 inferred from nw over se shear and ramp and flat thrusts partly reversing offsets of the d 1 extension the recognition of widespread d 2 pre doming compression is important because it triggered the c 3 18 ga start of formation of the dome and keel pattern d 3 visible today which culminated at c 2 9 ga supplementary material eight figures numbered supplementary material fig a h and a gps list of observation sites are available at https doi org 10 6084 m9 figshare c 3808243

the descriptive nomenclature and classification of growth fabrics in fossil scleractinian reefs abstract framework sensu stricto is a concept originally relating to modern reefs and is defined by structural ecological and sedimentological criteria however in the geological literature the term framework has come to be applied to almost any organically influenced in situ accumulation including non calcareous non rigid facies associated with sea grasses this drastic departure from the original meaning is misleading and scientifically unhelpful the concept of wave resistance is integral to that of framework but in the geological record it is not easy to evaluate and the term may be of little comparative use between reef environments it is suggested that the term growth fabric be generally applied as a descriptive term for the presence of aggregated in situ corals or other organisms in growth position within a facies the term growth fabric should be used as an alternative to framework as a purely descriptive term the term framework should be restricted to its original definition and used only where the criteria for framework can be clearly demonstrated two end member types of scleractinian growth fabric genesis are recognised termed superstratal and constratal terms adapted from gili e masse j p skelton p w 1995 rudists as gregarious sediment dwellers not reef builders on cretaceous carbonate platforms palaeogeogr palaeoclimatol palaeoecol 118 245 267 in a superstratal growth fabric the constituent organisms collectively projected decimetres to metres above the substratum creating positive topographic relief in contrast constratal growth is where vertical organic accretion occurred at a similar rate to sediment accumulation hence the majority of the skeletal material remained continuously embedded in the sediments and only a small proportion of the skeleton projected centimetres above the sediment surface the architectural palaeoecological sedimentological and diagenetic implications of different types of growth fabric genesis is discussed a review of the classification of reef fabrics suggests that there is currently no adequate system to describe fossil scleractinian growth fabrics the most commonly used classification of reefal fabrics is that of embry and klovan 1971 embry a f klovan j e 1971 a late devonian reef tract on northeastern banks island northwest territories bull can pet geol 33 730 781 there are a number of shortcomings in this scheme which may be grouped into three categories 1 the interpretative nature of the classification 2 problems in interpreting biological effect from form and 3 insufficient categories to adequately describe mesozoic and cenozoic growth fabrics moreover there appears to be a lack of a standardised nomenclature for growth fabrics which has hindered meaningful comparisons of scleractinian growth fabrics through time and space a descriptive system based on a modification and expansion of the embry and klovan system 1971 is proposed and a revised nomenclature for growth fabrics presented the system is designed to be flexible in its application it can be used simply to describe a growth fabric or through the use of genetic and non genetic modifiers to imply types of reef building processes and growth fabric heterogeneity although the concepts and terminology discussed in this paper relate to scleractinian growth fabric they are equally applicable to fabrics comprising other organisms

formation of hp lt rocks and their tectonic implications in the western tianshan orogen nw china geochemical and age constraints the western tianshan high pressure low temperature metamorphic belt in northwestern china formed within a paleozoic accretionary wedge on the south side of the yili central tianshan plate it comprises various lithologies including mafic metavolcanic rocks metavolcaniclastic rocks metagreywacke marble and serpentinite the metavolcanics comprise eclogite omphacitite epidosite and blueschist the trace and rare earth element characteristics of these rocks indicate morb to oib affinities suggesting a seamount like setting for the protoliths of these rocks the end value of the eclogite 8 9 indicates that the protolith was derived from a long term depleted mantle i e an n morb source supporting the trace and rare earth element characteristics of these samples sm nd isochron dating of 343 44 ma omp gln grt wr and an age of 346 3 ma grt gln were determined using an eclogite boudin within blueschist a well defined 40ar 39ar plateau age of 344 1 ma was obtained for crossite from an omphacite phengite bearing blueschist and is concordant with the sm nd isochron age for the eclogite suggesting that neither argon loss nor excess argon affected the crossite a well defined 40ar 39ar plateau age of 331 2 ma was determined for phengite from the same sample the high pressure metamorphic rocks were formed by the b type subduction of a paleozoic south tianshan ocean about 344 ma ago they were however exhumed to higher crustal levels during the collision of the tarim and yili central tianshan plates about 331 ma ago similar to an alpine type tectonic regime

source regions of granites and their links to tectonic environment examples from the western united states this review in honor of ilmari haapala s retirement reflects on lessons learned from studies of three granitic systems in western north america 1 mesoproterozoic samples from west texas and east new mexico 2 laramide granitic systems associated with porphyry copper deposits in arizona and 3 granites of the colorado mineral belt the studies elucidate relationships amongst tectonic setting source material and magma chemistry mesoproterozoic basement samples are from two different felsic suites with distinct elemental and isotopic compositions the first suite the plutonic province is dominantly magnesian calc alkalic to alkali calcic and metaluminous it has low k2o na2o and rb sr and nd model ages of 1 56 to 1 40 ga the second suite the panhandle igneous complex is magnesian metaluminous alkalic and is part of the mesoproterozoic belt of magmatism that extends from finland to southwestern united states samples from the panhandle igneous complex demonstrate three episodes of magmatism the first pulse was intrusion of quartz monzonite at 1380 to 1370 ma the second was comagmatic epizonal granite and rhyolite at 1360 to 1350 ma both of these rock types are high k to slightly ultra high k the third pulse at 1338 to 1330 ma was intrusion of ultra high k quartz syenite nd model ages 1 94 to 1 52 ga are distinct from those of the plutonic province and systematically older than crystallization ages implying a substantial crustal input to the magmas at the sierrita porphyry copper deposit in the mazatzal province of southeastern arizona trace element sr and nd isotopic compositions were determined for a suite of andesitic and rhyolitic rocks 67 ma intruded by granodiorite and granite isotopic composition and chemical evolution are well correlated throughout the suite andesite has the least negative initial end 4 3 and lowest 87sr 86sri 0 7069 it is also the oldest and chemically most primitive having low concentrations of rb sio2 and high concentrations of transition elements these parameters change through the system to the youngest unit granite which has the most negative end 8 5 the highest 87sr 86sri 0 7092 and is chemically most evolved correlation between chemical and nd isotopic evolution probably resulted from a continuous process of progressive assimilation in which mafic magmas invade and incorporate continental crust deposits in arizona with end values more negative than the 8 5 of sierrita lie in the older yavapai province in the northwestern part of the state the difference in the most negative epsilon nd implies that nd isotopic signature is sensitive to the age of the precambrian domain the granites from the colorado mineral belt were emplaced during the transition from laramide convergence to mid tertiary extension three different groups of granites are recognized the first is laramide and was formed during assimilation fractional crystallization involving lower crustal mafic source materials the second and third groups are mid tertiary and represent intracrustal melting of heterogeneous sources this change in source regions and melt regimes in transition from convergence to extension is fundamental to the mesozoic and cenozoic evolution of western north america

evidence for the episodic turn on and turn off of turbid zone coral reefs during the late holocene sea level highstand terrigenous sediment accumulation within nearshore marine environments is regarded as a major factor inhibiting carbonate production and coral reef accretion while recent ecological and geological research into reef development under long term terrigenous sediment influence questions the overly simplistic nature of such views understanding of the time scales of reef initiation and growth and the morphodynamics of reef accretion in these settings remains limited here we present evidence to support recent suggestions that once established rapid reef accretion and progradation is possible but that the restricted accommodation windows in which such reefs develop often result in short lived ephemeral phases of reef building specifically we describe two discrete periods of reef growth within one small 600 m wide coastal embayment around a high island on the terrigenous sediment dominated inner shelf of the central great barrier reef australia these reef building phases occurred at either end of the holocene sea level highstand the first during the late postglacial marine transgression and early highstand 6900 4500 calibrated cal yr b p the second following the late holocene regression and stillstand 1600 cal yr b p to present an 3000 yr hiatus occurred between these events probably as a function of subtle changes in sea level and associated shoreline morphodynamics

coralline algae corallinales rhodophyta in western and central mediterranean messinian reefs abstract coralline algae are common components in messinian reefs in the sorbas basin in se spain and in the salento peninsula southern italy they occur encrusting coral skeletons and other bioclasts forming rhodoliths and as fragments in back reef reef framework and proximal to middle slope facies corallines also occur in halimeda boundstones associated to coral reefs in contrast no coralline algae have been recorded in the fine grained distal slope deposits in both areas and in lagoonal marly limestones in salento the relative abundance of corallines in reefs and their species richness is significantly higher in the salento platform than in the intermontane sorbas basin which was affected by terrigenous influx neogoniolithon brassica florida and spongites fruticulosus dominate the shallow water assemblages lithophyllum records peak at the base of reef core and upper slope deposits around 20 m palaeodepth and phymatolithon calcareum and species of lithothamnion are most abundant in deeper slope facies the main components of the messinian mediterranean reef coralline assemblages are extant species common in the mediterranean and along the north atlantic coast from morocco and the canary islands to the british islands a few such as spongites fruticulosus and phymatolithon calcareum have been living in the mediterranean region for more than 25 ma four species still live in the indo pacific but disappeared from the mediterranean during the messinian salinity crisis the typical components of present day indo pacific coral reefs do not occur in the mediterranean messinian reefs the mediterranean atlantic character of the messinian reef corallines reflects the decrease in tropical biotas in the mediterranean throughout the miocene probably related to global cooling and isolation of the mediterranean from the indian ocean since the middle miocene

upb zircon geochronology of archaean felsic units in the marble bar region pilbara craton western australia abstract archaean supracrustal rocks that are well exposed in the marble bar region pilbara craton have been assigned to the warrawoona group and younger sequences the predominantly volcanic warrawoona group previously dated at 3300 to 3500 ma is largely basaltic with locally intercalated thick felsic volcanic units the supracrustal rocks have been folded and are distributed around the margins of large roughly circular to ovoid granitic gneissic batholiths a u pb zircon geochronology study was undertaken to obtain precise age constraints for some of the ore deposits in the area especially the big stubby north pole barite and miralga creek zn pb cu au deposits in support of efforts to improve archaean lead isotope models the results also help significantly in interpreting stratigraphic relationships and crustal evolution in the area the new conventional zircon u pb data indicate that most of the warrawoona group from the duffer formation upwards was deposited over a period of 20 ma from 3470 ma to 3450 ma the age of the duffer formation is closely constrained by results of 3471 5 ma and 3465 3 ma and the age of the upper salgash subgroup appears to be established at 3454 1 ma the panorama formation at the southern margin of the north pole dome is 3458 1 9 ma unless the duffer formation was deposited over a period of at least 10 ma this casts doubt on a previously suggested panorama duffer correlation the age of the lower part of the north pole succession is greater than 3458 ma consistent with the correlation of the basal greenstones at north pole with the talga talga subgroup the north pole chert barite unit which is well known for its preservation of early archean stromatolites microfossils and evaporite sediments is clearly older than 3458 ma the 3325 ma age now established for the wyman formation shows that this unit must be excluded from the warrawoona group the age of the talga talga subgroup remains uncertain a felsic schist in the mount ada basalt which has been dated at 3449 3 ma is interpreted to be a sill probably related to the 3450 ma granitoid bodies an age 3724 ma for a zircon xenocryst in the panorama formation is the oldest obtained so far for zircon from the pilbara granite greenstone terrane and indicates the existence of pre pilbara supergroup sialic basement ages of 3465 3 ma and 3449 2 ma applied to previous pb isotope data for the big stubby and miralga creek deposits respectively in combination with comparable data for other syngenetic archaean sulphide deposits yield a general single stage pb evolution model with the parameters t0 4560 ma a0 9 0818 b0 9 9002 and c0 29 343 this gives model ages in accord with known constraints for many archean deposits a model lead age of 3490 ma for the north pole deposit which is older than 3457 ma may be too great but attempts to directly date this deposit have not yet succeeded there are striking parallels between the warrawoona group ages reported here and those recently obtained for the barberton region kaapvaal craton south africa the talga talga subgroup and lower onverwacht tjakastad subgroup sequences have approximately equivalent constraints and an age for the upper salgash subgroup agrees closely with those for the hoogenoeg formation of the upper onverwacht group geluk subgroup

platy corals from the middle triassic of upper silesia poland implications for photosymbiosis in the first scleractinians abstract coral patch reefs from middle triassic upper pelsonian lower illyrian strata in the upper silesia region of southern poland germanic domain of the peri tethys are rare examples of the first scleractinian buildups the shallowing upward succession in the tarnow opolski quarry records a transition from sponge to coral patch reefs interbedded with bioclastic limestones coral pillarstones built by thin branching volzeia szulci are succeeded by platy pamiroseris silesiaca constructing two platestone layers each up to 50 cm thick serial sections through platestones revealed flat to undulose growth form of p silesiaca the maximum observable dimension of the coral plates is 24 cm wide typically up to 12 cm while thickness of most plates is 1 1 5 cm coral plates are interlayered with crinoidal wacke to packstone and microbialites which are locally important component of the platestone platy corals grew in a shallow turbid water environment with changing but dominantly moderate hydrodynamics net sedimentation was low as indicated by the epibionts encrusted to the undersides of the coral plates and locally common microbial fabrics growth interruptions of p silesiaca record events of storm induced sediment input and resuspension of carbonate mud based on the euphotic floor model the flattened morphology of p silesiaca is interpreted as an optimal growth form in a turbid low light environment platy scleractinian assemblages from silesia are the oldest occurrences of this ecological coral group mostly representing deeper mesophotic habitats and support the hypothesis that some of the earliest scleractinians had photosymbionts like modern zooxanthellae

zircon u pb dating and hf isotope analysis on the taihua complex constraints on the formation and evolution of the trans north china orogen abstract precise age determination and source tracing of the granitic and pegmatitic gneisses of the taihua complex in the xiaoqinling area are important to address the debates on the timing and processes of the amalgamation of the western and eastern blocks along the trans north china orogen this paper conducted zircon dating of metamorphic rocks from the xiaoqinling area the results demonstrate that the collision between the western and eastern blocks occurred in the paleoproterozoic laser ablation inductively coupled plasma mass spectrometry la icpms zircon uranium lead u pb analyses yielded consistent results the early paleoproterozoic the first period age of 2346 28 ma was determined for granitic gneiss in the taihua complex and 2328 14 ma for the xiaohe granite pluton that intruded into the granitic gneiss the gneissose pegmatitic granite and granitic veins that intruded into the granitic gneiss yielded la icp ms zircon ages of 1881 24 and 1866 19 ma respectively these paleoproterozoic ages strongly indicate that the ocean between the eastern and western blocks were completely subducted at 1 85 ga the hf t values of the zircons from the granitic gneiss can be divided into a positive group 0 44 to 3 77 and a negative group 3 11 to 1 27 the two stage hafnium hf model ages tdm2 hf corresponding to the positive values are between 2672 and 2887 ma the hf t values of the zircons from the xiaohe granite range from 2 49 to 2 58 with the hf isotope model ages ranging from 2742 to 3022 ma thus the xiaohe granite could have resulted from the partial melting of the late archean lower crust caused by subduction and the presence of juvenile mantle material the primary magma of the granitic gneiss of the paleoproterozoic taihua complex was derived from the differentiation of the depleted late archean mantle source with a small portion derived from the remelting of the subducted lower crust

closing history of the southern tianshan oceanic basin western china an oblique collisional orogeny abstract the tianshan tien shan range is an important paleozoic collisional orogenic belt and the key to understand the central asia tectonic evolution this paper integrates our research results with the existing chinese and international literature on sedimentology geochemistry isotopic geochronology paleontonology and paleomagnetism of the tianshan and tarim regions to propose that the oblique collision may have played an important role in the late paleozoic closing of the southern tianshan oceanic basin as a result of the sinian latest proterozoic younger than 800 ma continental extension and rifting process the tarim and yili blocks separated from their parent continent in the late cambrian ordovician the southern tianshan oceanic crusts between the two blocks subducted northward beneath the southern margin of the yili block in the silurian during the devonian early carboniferous the tarim block rapidly drifted to the north and rotated about 46 clockwise this process induced the collision of the yili micro continent with the eastern segment present geographical position of the tarim continent in the late devonian and the southern tianshan oceanic crust evolved to be a west facing remnant oceanic basin during the late carboniferous early permian the tarim block located within an almost constant latitude range rotated about 26 clockwise with respect to the yili micro continent which ultimately closed the remnant oceanic basin in a scissors like manner from east to west and completed the tarim yili collision subsequent a type subduction of the tarim continental crust and lithosphere scale sinistral shearing generated a magmatic arc on the southern margin of the tarim yili suture zone the late permian early triassic clastics deposited in a peripheral foreland basin developed above the arc

age geochemistry and tectonic implications of a late paleozoic stitching pluton in the north tian shan suture zone western china the central asian orogenic belt is the largest tectonic assembly of continental and oceanic terranes on earth due to closure of the paleo asian ocean in the phanerozoic among major suture zones in the north xinjiang region of western china the north tian shan suture zone because of collision between the yili terrane in the south and the junggar terrane in the north contains the youngest ophiolitic rocks and may represent the terminal stage of development of the central asian orogenic belt in western china but the timing of the suture zone remains poorly constrained a sensitive high resolution ion microprobe shrimp zircon u pb age of 316 3 ma i e the beginning of the late carboniferous from the undeformed sikeshu pluton which crosscuts the suture zone places a crucial upperage bound for the time of collision between the yili and junggar terranes this event occurred later than or nearly concurrent with other accretion collision events in the north xinjiang region implying that fi nal terrane amalgamation was completed in the late carboniferous the sikeshu pluton shares geochemical characteristics of the widespread late carboniferous to permian postcollisional a type and i type granitoids with depleted mantle like sr nd isotopic signatures in the north xinjiang region they all occurred during a protracted ca 320 270 ma episode of postcollisional magmatism that may have been induced by basaltic under plating due to either slab breakoff or delamination of thickened mantle lithosphere beneath the central asian orogenic belt the same postcollisional magmatism also generated cu ni sulfi de bearing mafi c ultramafi c magmatic complexes adakites and porphyry type coppermolybdenum bearing magmatic rocks in the north xinjiang region

components facies and ramps redefining upper oligocene shallow water carbonates using coralline red algae and larger foraminifera venetian area northeast italy abstract chattian mixed carbonate siliciclastic deposits from two palaeogeographic units of southern alps the lessini shelf and venetian foreland basin of northeast italy are studied with respect to facies distributions and controlling ecological factors on dominant biogenic components these ramp depositional systems are located in the western southern alps on the lessini shelf and in the eastern southern alps in the venetian foreland basin the successions show an extensive geographic distribution of at least 150 km 40 km at the southern margin of the southern alps palaeoenvironments are inferred following microfacies characteristics and floral and faunal indicators especially those of coralline red algae and larger foraminifera an inner to middle homoclinal ramp morphology is reconstructed based on facies distributions and taxonomic and coralline algal growth form proxy data the distribution along depositional strike shows variation from thinner carbonate dominated sequence in the west monti berici and monti lessini to a more variable mixed carbonate siliciclastic dominated environment to the east vittorio veneto alpago facies character and occurrence are controlled by local hydrodynamic conditions and varying water turbidity of the studied ramp depositional system the general facies succession shows a transgressive sequence from the proximal inner to proximal middle ramp a shoal belt of trough cross bedded sandstones occurs in a proximal inner ramp position in all of the studied areas in a gentle dipping homoclinal ramp most benthic organisms inhabited the relatively quite environments off these shoals in a distal inner ramp setting basinward environments proximal middle ramp constitute areas of maximal carbonate production and consist primarily of larger foraminiferal facies and rhodolith pavements larger foraminifera represented by two larger foraminiferal assemblages are most diversified in the shallower settings near the fair weather wave base distal inner proximal middle ramp whereas coralline algae predominate in deeper areas proximal middle ramp constructing extensive rhodolith pavements rhodolith pavements are distinguished with respect to rhodolith shape size growth forms and coralline algal taxonomic composition larger foraminifera are interpreted with respect to shell structures shell architectures and comparable recent counterparts the analysed benthic communities thrived in a mesotrophic regime within trophic gradients constrained by fluvial influence coralline algal dominance and a moderately diverse larger foraminiferal assemblage suggest a tropical warm temperate transition the considerable stability imposed on sediments by the rhodolith pavement must also have significantly contributed to the maintenance of a middle ramp profile bulge this study will contribute to a better understanding of oligocene carbonates which have received less attention than their eocene or miocene counterparts

stratigraphy and sedimentology of an early archean felsic volcanic sequence eastern pilbara block western australia with special reference to the duffer formation and implications for crustal evolution abstract a sequence of early archean felsic volcanic and volcaniclastic rocks and chert is present in the upper half of the warrawoona group throughout greenstone belts in the eastern pilbara block western australia it includes three formations the duffer formation which makes up the bulk of the sequence consists of up to 5 km of metamorphosed dacitic to rhyolitic volcaniclastic breccia and lava and lesser amounts of tuffaceous rocks and mafic lava it is overlain in several sections by the sandy panorama formation and both are capped by silicified orthochemical and biogenic deposits of the towers formation including both the strelley pool and marble bar cherts these units are identifiable in at least six greenstone belts in the eastern pilbara block the duffer formation is divided into four facies a structureless and graded breccia b complexly organized conglomerate c turbiditic tuff breccia and tuff and d lava these facies represent deposition on predominantly subaqueous volcaniclastic aprons flanking felsic volcanic centers a three stage model of the evolution of these aprons includes 1 an early stage of felsic and mafic eruptions and subaqueous deposition 2 a middle stage during which the bulk of the sequence was deposited involving shallow water to subaerial felsic volcanism and subaqueous deposition and 3 a terminal stage of subaerial felsic eruptions and subaerial deposition post duffer felsic volcanism was marked by explosive pyroclastic activity which resulted in widespread deposition of ash in surrounding shallow water and subaerial systems this phase of activity is represented by the panorama formation after the cessation of volcanism erosion of the emergent vents and regional subsidence led to an interval of orthochemical and biogenic sedimentation represented by the towers formation paleocurrent and facies patterns in the duffer and panorama formations support earlier proposals that the intrusion of granitoid rocks in the eastern pilbara block was coeval with felsic volcanism it seems likely that this volcanism was the surficial expression of plutonism that represented early stages of cratonization in the eastern pilbara the calc alkaline volcanism and depositional styles represented by this sequence are similar to those associated with many phanerozoic arcs the abundance of shallow water facies closely spaced and possibly non linear distribution of felsic centers close association of felsic units with thick sequences of basalt erupted at or near sea level sparse syn volcanic deformation and lack of granitic detritus suggest however that the setting of this archean felsic volcanism was in many details unlike that of most modern arcs

mesophotic coral buildups in a prodelta setting late eocene southern pyrenees spain a mixed carbonate siliciclastic system lower priabonian coral bioherms and biostromes encased in prodelta marls clays occur in the ainsa jaca piggyback basin in the south central pyrenean zone detailed mapping of lithofacies and bounding surfaces onto photomosaics reveals the architecture of coral buildups coral lithosomes occur either isolated or amalgamated in larger buildups isolated lithosomes are 1 to 8 m thick and a few hundred metres wide clay content within coral colonies is significant stacked bioherms form low relief buildups commonly 20 to 30 m thick locally up to 50 m these bioherms are progressively younger to the west following progradation of the deltaic complex the lowermost skeletal rich beds consist of bryozoan floatstone with wackestone to packstone matrix in which planktonic foraminifera are abundant and light related organisms absent basal coral biostromes and the base of many bioherms consist of platy coral colonies floating in a fine grained matrix rich in branches of red algae corals with domal or massive shape locally mixed with branching corals and phaceloid coral colonies dominate buildup cores these corals are surrounded by matrix and lack organic framework the matrix consists of wackestone to packstone locally floatstone with conspicuous red algal and coral fragments along with bryozoans planktonic and benthonic foraminifera and locally sponges coral rudstone and skeletal packstone with wackestone to packstone matrix also occur as wedges abutting the buildup margins integrative analysis of rock textures skeletal components buildup anatomy and facies architecture clearly reveal that these coral buildups developed in a prodelta setting where shifting of delta lobes or rainfall cycles episodically resulted in water transparency that allowed zooxanthellate coral growth the bathymetric position of the buildups has been constrained from the light dependent communities and lithofacies distribution within the buildups the process product analysis used here reinforces the hypothesis that zooxanthellate corals thrived in mesophotic conditions at least during the late eocene and until the late miocene comparative analysis with some selected upper eocene coral buildups of the north mediterranean area show similarities in facies components and textures and suggest that they also grew in relatively low light mesophotic and low hydrodynamic conditions

tensile and compressive growth structures relationships between sedimentation deformation and granite intrusion in the archaean coppin gap greenstone belt eastern pilbara western australia1pii of original article s0301 9268 97 00065 x 1

volcanic sedimentary and tectonostratigraphic environments of the 3 46 ga warrawoona megasequence a review abstract the warrawoona megasequence comprises a 3 46 ga assemblage of tholeiitic and calc alkaline volcanic rocks interlayered with cherty sedimentary rocks deposition occurred in a range of shallow to deeper water environments ranging from the shoreline to distal deposits in sediment starved basins volcanism provided the dominant or only source of clastic sediment sedimentary rocks also contain evaporites probable stromatolites other evidence for the existence of microbial life and possible evidence of meteorite impact the tectonostratigraphic assemblage and its contained facies associations are most similar to those developed in younger volcanic arc or near arc settings the compositions of volcanic rocks are also comparable with those of younger tholeiitic and calc alkaline suites developed above subduction zones the calc alkaline suite has a complex petrogenesis which probably involves mantle derived basaltic melts intermediate to silicic melts derived from subducted mafic crust magma mixing and fractional crystallization intense hydrothermal alteration and a distinctive association of metal deposits are also compatible with the interpretation that the warrawoona megasequence contains examples of early archaean volcanic arc and near arc assemblages

microbial domes and megaoncoids in miocene reefs in the mahakam delta in east kalimantan indonesia abstract coral patch reefs in the miocene mahakam delta in east kalimantan borneo indonesia developed in shallow marine turbid waters these reefs grew in delta front to prodelta environments under fluctuating siliciclastic input langhian patch reefs are well exposed in limestone quarries of the air putih area near the city of samarinda and include two different types of microbial carbonates in two sections 2 km apart in the northern section microbialites occur as low relief domes up to 2 m wide and 0 5 m high the domes show internal lamination and coralline algae and encrusting foraminifers interlayered with microbial micrite they developed around large coral fragments at the transition from reef deposits to fine grained siliciclastics microbialites in the southern section formed decimetre to metre scale nodules here termed megaoncoids around nuclei of large coral fragments microbial micrite with laminated to digitate fabrics intergrew with coralline algae and encrusting foraminifers to form the thick covers of megaoncoids small nodules were bound together in larger ones which are usually strongly asymmetric internally megaoncoids accumulated in a carbonate breccia laterally changing into coral boundstones in both sections microbialites grew on the flanks of shallow water low relief patch reefs in poorly illuminated low energy conditions flat domed microbialites formed on a nearly horizontal stable seafloor seawards of the patch reef the megaoncoids in the southern section formed as a result of downslope displacement of coral fragments coated by microbialite coralline algal encrusting foraminifer crusts the slope of the patch reef s flank favoured the falling and rolling of encrusted corals with the continued growth of microbial crusts on all sides of nodules in contrast to quaternary and recent occurrences of microbialites in indo pacific and caribbean reefs the samarinda microbialites are not components of the reef framework nor formed in deep water instead they developed in shallow turbid waters of the miocene mahakam delta in periods of arrested siliciclastic input

horizontal tectonics pre dating upper gorge creek group sedimentation pilbara block western australia abstract the greenstone belt stratigraphy of the c 3500 ma old pilbara block has been subdivided into the lower dominantly volcanic warrawoona group and the upper mainly sedimentary gorge creek group regional mapping indicated that these units evolved as a near continuous succession with only minor internal unconformities and that both groups suffered their most intense tectonic imprint together as a result of granite diapirism however an upper gorge creek conglomerate a lalla rookh correlate with a basal angular unconformity contains felsic schist clasts derived from highly strained portions of the warrawoona group the folds in the conglomerate are upright as expected for diapirically generated structures and are as complex as any attributed to this process the schist clasts were therefore probably generated in a pre doming event high strain and high grade metamorphism are confined to the lower parts of the greenstone stratigraphy where a polyphase deformation history may be clearly defined the low strain low grade areas are generally regarded as having a simpler tectonic history but some examples contain very tight minor folds that pre date a widespread subhorizontal cleavage and both events pre date the doming in other low grade areas thrust structures are truncated by the angular unconformity at the base of the lalla rookh correlate and the thrust geometry suggests they formed in already folded rocks

siliciclastic and volcaniclastic influences on equatorial carbonates insights from the neogene of indonesia in active tectonic areas of humid equatorial regions nearshore shallow water environments are commonly sites of near continuous siliciclastic influx and or punctuated volcaniclastic input despite significant clastic influence neogene carbonates developed in se asia adjacent to major deltas or volcanic arcs and are comparable with modern mixed carbonate clastic deposits in the region research into delta front patch reefs from borneo and fore arc carbonate platform development from java is described and used to evaluate the effects of siliciclastic and volcaniclastic influx on regional carbonate sedimentation local changes in carbonate producing biota and sequence development regional carbonate development in areas of high siliciclastic or volcaniclastic input was influenced by the presence of antecedent highs changes in the amounts or rates of clastic input delta lobe switching or variations in volcanic activity energy regimes and relative sea level change a variety of carbonate producing organisms including larger benthic foraminifera some corals coralline algae echinoderms and molluscs could tolerate near continuous siliciclastic or volcaniclastic influx approximately equal to their own production rates these organisms adopted various strategies for coping with clastic input including a degree of mobility morphologies adapted to unstable substrate inhabitation or shedding sediment and shapes adapted to low light levels local carbonate production was also affected by energy regime clastic grain sizes and associated nutrient input clastic input influenced the inhabitable depth range for photoautotrophs the zonation of light dependent assemblages and the morphology and sequence development of mixed carbonate clastic successions this study provides data on the dynamic interactions between carbonate and non carbonate clastic sediments and when combined with information from comparable modern environments allows a better understanding of the effects of siliciclastic and volcaniclastic influx on carbonate production

lithostratigraphy and structure of the early archaean doolena gap greenstone belt east pilbara terrane western australia abstract the early archaean east pilbara terrane of the pilbara craton represents the archetypical granite dome greenstone keel terrain and preserves much of the primary geological features of dome and keel formation here we present the first detailed lithostratigraphic and structural transect from marginal gneisses of the muccan granitic complex through 6 km of steeply dipping strata of the western doolena gap greenstone belt based on overprinting relationships we identified five deformational events d1 d5 that can be correlated between four structural domains i marginal orthogneisses of the polyphase muccan granitic complex ii a dominantly mylonitic shear zone south muccan shear zone representing a granite dome greenstone keel detachment zone iii a central fold belt of dominantly mafic greenschists and iv a lower greenschist to sub greenschist facies southern low strain belt the d1 event in the low strain belt is recorded in syn depositional normal faulting f1 during eruption of deep water low vesicular pillow basalts of the ca 3 47 ga mount ada basalt followed by a conformable transition towards shallow water stromatolites in the duffer formation we interpret the d1 event as the result of upper crustal extension and subsequent uplift above the muccan granitic complex the d2 event shows the most intense deformation with syn anatectic tight folds within the muccan granitic complex and tight to isoclinal transposed folds f2 and fluid induced normal faults f2 within the central fold belt the d2 event resulted in a regional ew composite s1 2 foliation and in the development of the mylonitic south muccan shear zone along the dome keel interface and within the central fold belt mineral lineations l2 in conjunction with increasing southward d2 l tectonite this d2 event is not observed in a 1 km thick sandstone package ascribed to the we propose that the d1 and d2 events record locally significant initiation of muccan granitic complex doming and associated sagduction of greenstone keel rocks suggesting that partial convective overturn initiated early in the evolution of the east pilbara terrane

paleozoic tectonic evolution of the tianshan orogen northwestern china abstract the chinese tianshan orogenic belt which extends west east for about 1500 km is one of the most important paleozoic orogenic belts in central asia it includes parts of the tarim yili central tianshan and junggar plates which are microcontinental blocks with precambrian basements and meso cenozoic depositional covers the tarim plate is separated from the yili central tianshan plate by the southern central tianshan suture early carboniferous ophiolitic melanges and blueschists are widespread in this suture and are believed to be produced by the collision between a passive continental margin on the north side of the tarim plate and an active continental margin on the south side of the yili central tianshan plate the collision occurred at the end of early carboniferous the yili central tianshan and the junggar plates are separated by the northern central tianshan suture also considered as an early carboniferous collisional zone along which the middle ordovician ophiolitic melanges blueschists and late devonian early carboniferous ophiolites are exposed in early paleozoic times the subduction of the paleo junggar ocean took place in an active margin on the north side of the yili central tianshan plate along the northern central tianshan suture at the end of early carboniferous the north side of the yili central tianshan plate collided with the north tianshan arc along this suture the paleo oceanic crust in the tianshan and adjacent region was entirely consumed at the end of early carboniferous meanwhile the tarim yili central tianshan and junggar plates were accreted to eurasia epicontinental sediments were then deposited throughout the tianshan region during the middle late carboniferous times in the early permian tianshan began to uplift with accompanying volcanic eruption and granitic intrusion the uplift was accelerated in the late permian and continental molasse was extensively deposited

environmental reconstruction of a late burdigalian miocene patch reef in deltaic deposits east kalimantan indonesia abstract most studies of cenozoic shallow water mixed carbonate siliciclastic depositional systems have focused on their sedimentology to date however comprehensive analyses of biotas and biofacies of indo west pacific reefs that developed in mixed carbonate siliciclastic systems are lacking this study describes the palaeoenvironment and biodiversity of a late burdigalian patch reef that developed in a mixed carbonate siliciclastic depositional system the studied exposure is located at the northeast margin of the kutai basin near bontang indonesia and is approximately 80 m wide and 25 m thick multi taxon analysis of the most abundant fossil groups including larger benthic foraminifera corals coralline algae and bryozoans aims to provide a model for environmental interpretation that will allow comparison with similar deposits of indo west pacific region based on fossil content and lithology five different facies types have been distinguished foraminiferal packstone fp bioclastic packstone with foralgal communities bp thin platy coral sheetstone cs platy tabular coral platestone cp and shales s among larger benthic foraminifera smaller and more robust forms dominate in the fp and bp facies while larger and flatter forms are the most abundant in the cs and cp facies thin platy corals are dominant in the cs facies and gradually change into thicker platy tabular forms in the cp facies assemblages and growth forms of coralline algae show no major differences between the facies types and are dominated by melobesioids and sporolithon the majority of bryozoan species are encrusting and were found only in the cs facies light dependent organisms occurring in the reef indicate low light conditions typical for mesophotic reefs the relatively small size of this reef complex and quite distinct vertical changes in the facies types combined with the high siliciclastic content in most of the units points to strong terrigenous input affecting water transparency as the main factor controlling the reef growth

granite zircon u pb geochronology and geochemistry and the geological significance of the saibo copper deposit in the western tianshan mountains xinjiang province china abstract the discovery of the saibo copper deposit was a significant breakthrough in prospecting in the western tianshan mountains xinjiang province this deposit has great significance for studying the transboundary metallogenic belt because the deposit is associated with granitoids zircon dating by laser ablation inductively coupled plasma mass spectrometry la icp ms yield 206 pb 238 u ages of 385 9 1 3 ma and 387 2 1 4 ma for the granodiorite and granite porphyries from the deposit respectively indicating that the granitoids are the products of middle devonian magmatism in terms of their geochemistry these porphyries have high sio 2 contents between 62 60 and 67 47 and low tio 2 contents between 0 32 and 0 52 with aluminum saturation indexes asi between 0 76 and 0 90 these characteristics indicate a metaluminous medium potassium k calc alkaline i type granite that is enriched in large ion lithophile elements such as k and sr as well as in incompatible elements such as th and u and light rare earth elements lree is relatively depleted in high field strength elements such as na ta p and ti and lacks an obvious eu anomaly the zircon lu hf isotope ratios are relatively high with 176 hf 177 hf values varying between 0 28253 and 0 28272 and e hf t that varies between 0 4 and 6 5 mostly positive these features demonstrate that the granites were the products of co magmatic evolution originating from the depleted mantle and the partially melting of juvenile crustal material which occurred due to the north tianshan ocean subduction towards the southern yili block that led to magma ascent from the depleted mantle

origin of mesozoic adakitic intrusive rocks in the ningzhen area of east china partial melting of delaminated lower continental crust to the best of our knowledge modern adakites have not been documented in a nonarc environment we report geochemical and isotopic data for early cretaceous anjishan adakitic intrusive rocks that are in a continental setting unrelated to subduction the anjishan adakitic intrusive rocks which are exposed in the ningzhen area of east china have high sr y and la yb ratios coupled with low yb and y as well as relatively high mgo contents and mg numbers mg 0 4 0 6 similar to products from slab melting however low n d t values 6 8 to 9 7 and high 8 7 sr 8 6 sr i 0 7053 0 7066 are inconsistent with an origin by slab melting the tectonics and geochemistry lead us to conclude that adakitic magmas were most likely derived from partial melting of mafic material at the base of the continental crust high sr y and la yb ratios of the adakitic intrusive rocks suggest that garnet was stable as a residual phase during partial melting implying that the crustal thickness exceeded 40 km in the early cretaceous the present thickness of the crust in the ningzhen area is only 30 km and therefore the crust appears to have been thinned by at least 10 km since the early cretaceous the relatively high mgo contents and mg of the anjishan intrusive rocks suggest that adakitic magmas interacted with mantle rocks possibly coinciding with lower crustal delamination which would also account for the observed thinning

tectonic history of the barberton greenstone belt south africa 490 million years of archean crustal evolution rocks of the 3570 3080 ma barberton greenstone belt record a geological history of at least 490 million years m y and were affected by regional thermal perturbations for over 1500 m y small tectonic wedges of 3570 3511 ma schistose tonalite are the oldest rocks yet recognized but little is known about their tectonothermal history the earliest well recognized tectonothermal events 3490 3450 ma represent mid ocean ridge like processes these were followed by two periods of arc related and trench related processes separated by 160 m y the first 3445 3416 ma recording an intraoceanic suprasubduction like environment and the second 3260 3225 ma intra arc and interarc like processes culminating in arc amalgamation accretion like convergent processes dominated between 3230 ma and 3080 ma overlapping with the assembly of the kaapvaal craton at 3080 ma the barberton greenstone belt experienced a sudden shift from dominantly convergent to dominantly transtensional tectonism and was mineralized with mesothermal gold along a regional shear system soon afterward transtension became distributed across the entire kaapvaal craton heralding the onset of formation of the witwatersrand basin by 3070 ma

crustose coralline algae from the flower garden banks northwestern gulf of mexico controls on distribution and growth morphology abstract the east and west flower garden banks in the northwestern gulf of mexico represent the northernmost tropical coral reefs and caribbean coralline algal flora on the north american continental shelf coralline algae are the dominant framework builders and sediment contributors below 50 m on the banks on the basis of growth form and taxonomic composition coralline algae on the flower garden banks can be divided into four overlapping depth zones upper coral reefs 20 30 m madracis algal ridges 30 40 m algal nodule zone 45 80 m and deep algal reefs 50 90 m corallines on the upper coral reefs are dominated by hydrolithon lithophyllum and porolithon their growth form as thick laterally restricted crusts and knobs results from intensive grazing by parrotfish and urchins grazing is diminished on the madracis algal ridges below the upper reefs and corallines grow here as laterally extensive plates binding coral rubble dominant corallines on the ridges are lithophyllum paragoniolithon and tenarea algal nodules rhodoliths o the deeper bank slopes are the most widespread algal growth form on the flower garden banks on the basis of shape internal structure and composition rhodoliths are divided into an upper zone where they have a spherical shape with concentric laminae and a lower zone discoidal shape with irregular laminae diminishing current velocity with increasing depth controls nodule morphology the red alga peyssonnelia and the foraminifer gypsina are two non coralline components that contribute substantially to nodule growth reduced current velocity in the lower nodule zone enables corallines and peyssonnelia to develop laterally extensive pavements and 1 2 m high algal reefs taxonomic composition high framework porosity and irregular internal growth morphology f the deep algal reefs distinguish these structures from shallow algal ridges described elsewhere the 90 m isobath at the flower garden banks approximates the upward limit of a turbid nepheloid layer composed of continually resuspended sediment reefal structures within this water layer are dead and are now covered by fine sediment

palaeogeographic and tectonic evolution of the pilbara craton northwestern australia abstract two regional unconformities have been confirmed and followed throughout the greenstone belts of the pilbara craton the unconformities are usually low angle ones but each was preceded by considerable erosion in some areas granitoids are truncated at the younger unconformity a thick development of cherty banded iron formation bif and fine grained sediment has been used by most previous authors for correlations between greenstone belts when this unit and both unconformities which sandwich it are used as marker horizons considerable changes are required to the distribution of the major stratigraphic groupings as shown in most syntheses and regional maps for instance where volcanic units are in continuity of deposition with the bifs and sediments they are now grouped together the terms warrawoona gorge creek and whim creek groups are retained but they vary significantly from the accepted correlations this has engendered a new tectonic framework and history of evolution for the craton the warrawoona group is restricted to a possible protocontinent in the southeast overlapped by the gorge creek group but the whim creek group is developed essentially frontally to the protocontinent the observed distribution of tin nickel and some copper and pge mineralisation is consistent with the major tectonic provinces of the pilbara craton

development patterns of an isolated oligo mesophotic carbonate buildup early miocene yadana field offshore myanmar abstract the development history of an oligo mesophotic early miocene isolated carbonate system 160 m in thickness forming the uppermost part of the oligo miocene yadana buildup northern andaman sea has been evidenced from the integration of sedimentological core studies from 4 wells cumulated core length 343 m well correlations seismic interpretation and analysis of the ecological requirements of the main skeletal components three types of carbonate factory operated on the top of the platform depending on water depth turbidity and nutrient level 1 a scleractinian factory developing under mesophotic conditions during periods of high particulate organic matter supplies 2 an echinodermal factory occupying dysphotic to aphotic area of the platform coevally with the scleractinian factory 3 a large benthic foraminiferal coralline algal factories prevailing under oligo mesophotic and oligo mesotrophic conditions the limited lateral changes in facies between wells together with the seismic expression of the yadana buildup suggest deposition on a flat topped shelf carbonate production and accumulation on the yadana platform was mainly controlled by light penetration nutrient content and hydrodynamic conditions scleractinian rich facies resulted from transport of coral pieces derived from mesophotic environments mounds and deposited in deeper low light mud rich environments in which lived abundant communities of suspension feeders such as ophiuroids changes in monsoonal intensity terrestrial runoff from the irrawaddy river upwelling currents and internal waves activity during the early miocene are likely responsible for significant variations in water turbidity and nutrient concentration in the andaman sea thus promoting the development of an oligo mesophotic incipiently drowned platform

scleractinian assemblages under sediment input their characteristics and relation to the nutrient input concept abstract in the geological record scleractinian dominated turbid water bioconstructions that accumulated under substantial terrigenous input along with shallow neritic marls rich in well preserved corals are common these occurrences indicate that beyond some threshold the ecologic and taphonomic effects of sedimentation prevail over the effects of nutrification field data and experiments on recent corals show that some taxa cope well with terrigenous turbidity and sedimentation and acclimate to increased heterotrophy colonial corals resilient to sediment input commonly are massive to platy forms of high skeletal plasticity and with large polypars to effectively reject sediment or are branched species providing a very small sedimentation area cleaned by feeble currents or small polyped massive taxa that tolerate intermittent veneering by sediment these corals may comprise siltation assemblages of recent turbid water reefs and level bottoms in siliciclastic environments conversely excess input of even low amounts of dissolved inorganic nutrients into clear waters adversely affects many coral species fossil turbid water bioconstructions twb were situated in inner shelf to shore zone settings or near storm wave base on shelves or ramps did not stack into reef complexes mostly show a cluster to segment fabric are scarce in or devoid of frame pores with marine cement and lacked a high carbonate slope relative to fossil clear water buildups preserved in pure limestone successions fossil twb contain moderately diverse coral assemblages with an increased proportion of sediment resistant forms aside from coral behaviour that is elusive in fossils the sediment resistance of corals was mainly determined by colony shape and polypar size but small polyped sediment tolerant corals became common since the early cretaceous late jurassic to cretaceous turbid water coral assemblages are dominated by plocoid or thamnasterioid forms corresponding cainozoic assemblages consist mainly of cerioid and plocoid taxa in fossil twb bioerosion and encrustation are similar or higher than in contemporaneous clear water buildups under higher sediment input accumulation of discrete twb was quenched and level bottoms of both corals and soft substrate biota formed in the resulting coral marls depending on turbidity sedimentation and substrate stability the coral fauna consists largely of both solitary corals and mainly sediment resistant pseudocolonial colonial forms or is dominated by solitary corals many corals show growth anomalies resulting from partial mortality due to episodic rapid sedimentation and unstable substrate in coral marl environments because of terrigenous input nutrient levels probably were elevated yet macroboring and encrustation are very scarce beyond some threshold of terrigenous sediment input and accumulation the ecologic and taphonomic effects of sedimentation and unstable substrate prevail over the effects of nutrient enrichment during the meso cainozoic evolution of scleractinians increasing photoautotrophy and progressive invasion of oligotrophic environments is in contrast to a late cretaceous to cainozoic increase in the relative number of reefs in marginal marine siliciclastic settings this trend may be explained by second order sea level fall and shrinking of epicontinental carbonate seas and isolated platforms driving corals to more narrow attached shelves and by a wider total trophic range in which distinct coral assemblages can thrive as a result of coral evolution and diversification

sequence stratigraphy of the archaean supracrustal belts of the pilbara block western australia abstract the stratigraphic succession of the 3580 2770 m y old granite greenstone terrain of the pilbara block is re assessed by the first and second order sequence stratigraphic techniques that are the standard for phanerozic terrains with the view to testing the conformity of stratigraphic cause and response a holistic tectonostratigraphic framework is presented that pairs the supracrustal and crustal rock records the resulting sequence scheme is tested against the cause of first order sequence cycles viz global sea level responses to supercontinent breakup and assembly three first order inter regional unconformities divide the stratigraphic succession of the supracrustal belts into four units of first order megasequence status in order of decreasing age these are named the warrawoona gorge creek roebourne and mount negri megasequences a total of 17 second order supersequences are also named although some may represent supersequence sets the megasequences and or their genetic crustal equivalents represent the preserved rock record of four megacycles of forearc arc and or back arc geotectonic evolution associated with the convergent margins of a pilbara continent individual supersequences are the rock record of separate second order basins or basin phases and reflect the different geotectonic components of each megasequence the four megacycles had respective longevities from oldest to youngest of 150 m y 230 m y 160 m y and 180 m y they are identical in their stratigraphic successions and predicted first order sea level cycles to phanerozoic first order tectono eustatic cycles and are interpreted as the same response to global tectonic change the warrawoona and gorge creek megacycles and the roebourne and mount negri megacycles are tectonogenetic pairs of the east pilbara and the west pilbara megacycle sets respectively the east pilbara megacycle set evolved over a period of 380 m y from 3490 ma to 3110 ma whereas the west pilbara megacycle set evolved over a period of 340 m y from 3110 ma to 2770 ma the two megacycle sets are identical in their longevity geotectonic components and predicted sea level cycles to convergent margin wilson and supercontinent cycles and are thereby interpreted individually as the oldest established records of the supercontinent cycle the implication of this interpretation is that a steady state global tectonic regime has been in operation from early in earth s history which has important consequences for theoretical modelling of the earth s early tectonic style and secular changes in its geochemical regime

oxidized magnetite series rapakivi type granites of carajas brazil implications for classification and petrogenesis of a type granites abstract the varying geochemical and petrogenetic nature of a type granites is a controversial issue the oxidized magnetite series a type granites defined by anderson and bender anderson j l bender e e 1989 nature and origin of proterozoic a type granitic magmatism in the southwestern united states of america lithos 23 19 52 are the most problematic as they do not strictly follow the original definition of a type granites and approach calc alkaline and i type granites in some aspects the oxidized jamon suite a type granites of the carajas province of the amazonian craton are compared with the magnetite series granites of laurentia and other representative a type granites including finnish rapakivi and lachlan fold belt a type granites as well as with calc alkaline i type orogenic granites the geochemistry and petrogenesis of different groups of a types granites are discussed with an emphasis on oxidized a type granites in order to define their geochemical signatures and to clarify the processes involved in their petrogenesis oxidized a type granites are clearly distinguished from calc alkaline cordilleran granites not only regarding trace element composition as previously demonstrated but also in their major element geochemistry oxidized a type granites have high whole rock feo t feo t mgo tio 2 mgo and k 2 o na 2 o and low al 2 o 3 and cao compared to calc alkaline granites the contrast of al 2 o 3 contents in these two granite groups is remarkable the cao feo t mgo tio 2 vs cao al 2 o 3 and cao feo t mgo tio 2 vs al 2 o 3 diagrams are proposed to distinguish a type and calc alkaline granites whole rock feo t feo t mgo and the feo t feo t mgo vs al 2 o 3 and feo t feo t mgo vs al 2 o 3 k 2 o na 2 o diagrams are suggested for discrimination of oxidized and reduced a type granites experimental data indicate that besides pressure the nature of a type granites is dependent of o 2 conditions and the water content of magma sources oxidized a type magmas are considered to be derived from melts with appreciable water contents 4 wt originating from lower crustal quartz feldspathic igneous sources under oxidizing conditions and which had clinopyroxene as an important residual phase reduced a type granites may be derived from quartz feldspathic igneous sources with a metasedimentary component or alternatively from differentiated tholeiitic sources the imprint of the different magma sources is largely responsible for the geochemical and petrological contrasts between distinct a type granite groups assuming conditions near the nno buffer as a minimum for oxidized granites magnetite bearing granites formed near fmq buffer conditions are not stricto sensu oxidized granites and a correspondence between oxidized and reduced a type granites and respectively magnetite series and ilmenite series granites is not always observed