tectonic evolution of the sanga sanga block mahakam delta kalimantan indonesia the sanga sanga block contains four large to giant hydrocarbon fields in mid to upper miocene deltaic sandstones of the mahakam delta eastern kalimantan indonesia these fields occur in the northeast trending mahakam fold belt which is characterized by long tight fault bounded anticlines and broad synclines and cored by overpressured shales onshore sections of the fold belt are strongly deformed uplifted and eroded whereas the eastern offshore sections are little deformed and buried by the progradational delta wedge section balancing of depth converted seismic lines together with scaled analog modeling was used to develop a new tectonic model of inverted delta growth faults for the evolution of the mahakam fold belt section balancing shows that the fault bounded anticlines of the sanga sanga block are formed by contractional reactivation of early delta top extensional growth faults the change from gravity driven extension to regional contraction occurred at around 14 ma anticlinal folds controlled local sedimentation patterns and influenced the distribution of the reservoir channel sands in the main hydrocarbon fields scaled analog models of progradational loading above a ductile substrate produced delta top extensional growth faults and depobelts together with delta toe fold thrust contraction inverted the extensional growth faults and depobelts producing tight fault bounded anticlines the results support the model of delta inversion and thus the most viable explanation for the geometric kinematic and mechanical evolution of the structures in the sanga sanga block the inverted delta model has applications to other hydrocarbon bearing deltas around borneo and in other contracted delta systems

diagenesis of a se asian cenozoic carbonate platform margin and its adjacent basinal deposits abstract this study provides insights into the diagenesis of a se asian tertiary carbonate platform and the variations in alteration that occur across platform top margin slope and adjacent basinal deposits a petrographic cathodoluminescent and stable isotopic study allowed evaluation of the diagenesis of the kedango limestone of borneo the kedango carbonate platform developed as a predominantly low to moderate energy system in the semi enclosed marine embayment of the kutai basin during the eocene to miocene early alteration through pervasive micritisation and minor isopachous fringing syntaxial overgrowth and bladed to radiaxial cements was due to marine diagenesis on the basis of limited relatively enriched stable isotope compositions and non luminescent cathodoluminescent cl characters minor early marine cementation formed just in the shallowest platform top and margin deposits and was likely promoted in high energy portions of the platform due to wave and or current activity dissolution cavities banded calcite cements with variable cl characteristics and depleted stable isotope compositions micritic sediment infiltration and alveolar textures are minor features but together are indicative of localised subaerial emergence and meteoric diagenesis the most prevalent and pervasive diagenetic feature of the deposits is the neomorphic alteration and replacement of metastable bioclasts and micritic matrix together with contiguous calcitisation of pore spaces burial fluids with a marine character are inferred as the parent diagenetic fluid since stable isotope compositions for the neomorphic spar is largely consistent with precipitation from se asian oligocene miocene seawater in a burial environment tectonic subsidence the protected semi enclosed marine embayment setting and probably terrestrial runoff together with component variability reflecting local environmental variations are inferred to have been major controlling influences on the diagenesis of the kedango platform variations in diagenesis across bathyal slope and shallow platform deposits of the kedango limestone are not as marked as in other platforms from the region

fault reactivation and structural inversion backarc and intraplate compressive deformations example of the eastern sunda shelf indonesia the tectonic evolution of the eastern sunda platform in indonesia is revealed by the study of seismic profiles and comprises three general tectonic periods during the cenozoic extension with graben infill from the paleogene to the early miocene a tectonically quiet period with only broad subsidence and a middle miocene recent period of folding inversion and thrusting these structures reveal changes in the intraplate stress field which was controlled by the changes in the boundary conditions of the plates collisions on the northern and eastern sides and interplate coupling southward along the java subduction zone inversions often occurred without reactivation of pre existing normal fault planes at the upper levels of these faults the factors controlling these deformations are discussed with special interest placed on the conditions for the potential reactivation of cohesionless normal faults inversion and reactivations were mostly controlled by the orientation of the pre existing fault planes in relation with the regional stress field and by the tectonic stress regime in a strike slip regime effective principal stresses 1 and 3 horizontal with 1 2 3 the optimum conditions for reactivation in isotropic rocks are pre existing faults that strike close to the potential two vertical conjugate failure planes the same mechanical properties as for pre existing fault prevail in such conditions strike slip movements and reverse strike slip movements and associated en echelon folds were generally observed in a compressive regime 1 and 2 horizontal with 1 2 3 typical steeply dipping normal faults are difficult to reactivate by slip movements we suggest that reverse slip movements occurred in the deeper levels of faults and were accommodated by flexure above the pre existing fault planes and the inversion of grabens the strongly inverted grabens are those whose orientation is perpendicular to the regional compression nevertheless with strong regional shortening large uplifts and thrust faults were observed with reactivation in the form of reverse or reverse strike slip movements along pre existing steeply dipping normal fault planes

mapping the buraburi granite in the himalaya of western nepal remote sensing analysis in a collisional belt with vegetation cover and extreme variation of topography abstract the aim of the present study is to define the most suitable methodologies for aster data pre processing and analysis in order to enhance peraluminous granitoid rocks in rugged and vegetated areas the research started with raw image data pre processing and continued with a comparison of satellite field and laboratory data the masking technique adopted to isolate rocky pixels was of fundamental importance to perform further analysis an integration of density sliced images and false colour composite images of band ratio relative absorption band depth and principal component analysis allowed us to generate a geological map that highlights a new granitoid body buraburi granite and the surrounding host rocks in the dolpo region western nepal the buraburi granite was mapped and sampled integrating remotely sensed aster data with analysis of rocks and minerals spectral signatures the innovative approach that we have adopted considers the absorption features of particular lichen species acidophilic the results highlight the importance of considering acidophilic lichen means of detecting granitoid rocks furthermore since peraluminous granitoids i e buraburi granite have a considerable al2o3 bulk rock content the muscovite al oh absorption peaks centred in the 6th aster band were also considered an important parameter for their detection field observations confirm the results of remote sensing analysis showing the intrusive relationship between the newly discovered 110 km 2 granitoid body and the wall rocks of the higher himalayan crystalline and the tibetan sedimentary sequence in conclusion the proposed methods have great potential for granitoid mapping in vegetated and rough terrains particularly those with climatic and geological conditions similar to the ones of the southern himalayan belt

cenozoic rotation history of borneo and sundaland se asia revealed by paleomagnetism seismic tomography and kinematic reconstruction se asia comprises a heterogeneous assemblage of fragments derived from cathaysia eurasia in the north and gondwana in the south separated by suture zones representing closed former ocean basins the western part of the region comprises sundaland which was formed by late permian triassic amalgamation of continental and arc fragments now found in indochina the thai penisula peninsular malaysia and sumatra on borneo the kuching zone formed the eastern margin of sundaland since the triassic to the se of the kuching zone the gondwana derived continental fragments of sw borneo and east kalimantan accreted in the cretaceous south china derived fragments accreted to north of the kuching zone in the miocene deciphering this complex geodynamic history of se asia requires restoration of its deformation history but quantitative constraints are often sparse paleomagnetism may provide such constraints previous paleomagnetic studies demonstrated that sundaland and fragments in borneo underwent vertical axis rotations since the cretaceous we provide new paleomagnetic data from eocene miocene sedimentary rocks in the kutai basin east borneo and critically reevaluate the published database omitting sites that do not pass widely used up to date reliability criteria we use the resulting database to develop an updated kinematic restoration we test the regional or local nature of paleomagnetic rotations against fits between the restored orientation of the sunda trench and seismic tomography images of the associated slabs paleomagnetic data and mantle tomography of the sunda slab indicate that sundaland did not experience significant vertical axis rotations since the late jurassic paleomagnetic data show that borneo underwent a 35 counterclockwise rotation constrained to the late eocene and an additional 10 counterclockwise rotation since the early miocene how this rotation was accommodated relative to sundaland is enigmatic but likely involved distributed extension in the west java sea between borneo and sumatra this late eocene early oligocene rotation is contemporaneous with and may have been driven by a marked change in motion of australia relative to eurasia from eastward to northward which also has led to the initiation of subduction along the eastern sunda trench and the proto south china sea to the south and north of borneo respectively

diagenesis of neogene delta front patch reefs alteration of coastal siliciclastic influenced carbonates from humid equatorial regions abstract this study offers insights into the diagenetic alteration of coastal carbonates that formed coevally with nearly continuous siliciclastic influx in a humid equatorial setting a multi disciplinary petrographic cathodoluminescent stable isotope trace element and major element investigation allowed characterization of diagenetic features paragenetic sequencing and an interpretation of diagenetic environments from neogene patch reefs of the samarinda region mahakam delta borneo se asia marine cements are absent from the patch reefs with grain micritization the only marine diagenetic feature recognized the predominant diagenetic feature within the patch reefs is pervasive neomorphic stabilization and cementation of aragonite reef components to calcite that pre dates all compaction features meteoric aquifer flow derived from the adjacent landmass is inferred as the main parent diagenetic fluid since 18o v pdb values of calcite cements of 3 6 to 11 7 are consistent with precipitation from se asian freshwater and inconsistent with a wholly marine origin late stage fracturing cementation and chemical compaction are relatively minor features and attest to a changing paleohydrologic and diagenetic environment evidence for a shallow to moderate burial diagenetic regime for these later features are maximum temperature of 53 c and burial depths 1000 m inferred from stable isotope values of calcite and late dolomite cements dolomite crystal fabrics the onset depth of stylolite or dissolution seam formation and regional geothermal gradients the humid tropical environment and ever wet conditions on the island of borneo together with rapid cenozoic uplift likely led to paleoaquifer flow with fluids focused through adjacent deltaic units into the reef carbonates in these coastal carbonates from the humid samarinda region continental groundwater flow has resulted in pervasive stabilization and calcitization features rare in arid or temperate counterparts

neogene sediment thickness and miocene basin floor fan systems of the celebes sea abstract in the celebes sea basin the middle miocene turbidites were correlated from odp site 767 throughout the studied area differences in their regional thickness variations and distribution indicate two source areas the middle miocene turbidite fan complexes of the central and southern celebes sea basin are controlled by the paleo tarakan delta system the tectonic events and the basin floor morphology respectively the main source area for the time correlative turbidites along the southern sulu arc is assumed to be mindanao the correlation of the middle miocene to pleistocene sequences exhibit tentative ages for the development of the accretionary wedges along the cotabato trench and along the north sulawesi subduction a post middle miocene to pre pliocene age is inferred for the cotabato wedge and a plio pleistocene age is assumed for the north sulawesi wedge

analogue modelling of orthogonal and oblique rifting abstract the three dimensional progressive development of orthogonal and oblique rift systems has been simulated using scaled analogue sandbox models the orientation of the zone of rifting where angle between the rift axis and the extension direction was varied systematically from 90 orthogonal rifting to 75 60 and 45 oblique rifting completed models were impregnated and sectioned both vertically and horizontally orthogonal rift models are characterized by long straight rift border faults and intra rift faults perpendicular to the extension direction oblique rift models are characterized by shorter segmented rift border faults and intrarift faults in the oblique models the rift border faults formed en echelon arrays parallel to the inderlying zone of basement stretching whereas the intra rift faults formed at a high angle to the extension vector increased extension in the moderately oblique and oblique rift systems 60 and 45 caused the intra rift faults to rotate towards parallelism with the rift border faults no strike slip or oblique slip transfer faults were found in any experiments rift border faults and intra rift faults in the models are segmented along strike with relay ramp structures formed between overlapping fault tips along the strike of the rift variations in half graben polarities and offsets of depocentres are accomplished by accommodation zones formed by interlocking conjugate fault arrays the experimental fault patterns compare well with the fault architectures found in those modern or relatively young rift systems where well defined basement controlled strike slip or oblique slip transfer faults are absent an accommodation zone model consisting of interlocking conjugate extension faults is proposed for the along strike switching of half graben asymmetries and offsetting of depocentres in rift systems the fault geometries in the analogue models can be used as templates for recognition of fault styles in both orthogonal and in oblique rift environments

major and trace element geochemistry of tourmalines from archean orogenic gold deposits proxies for the origin of gold mineralizing fluids abstract orogenic style gold mineralizations in the archean hattu schist belt e finland are present in all major host rock lithologies including epiclastic sedimentary and volcanogenic rocks as well as felsic intrusives the gold mineralizations occur as dissemination in altered wall rocks and within hydrothermal quartz veins hydrothermal tourmalines are often associated with the gold mineralizations occurring in the quartz veins as alteration minerals in contacts of the metasedimentary host rocks and quartz veins but also within mineral assemblages of the metasedimentary and magmatic rocks we characterize and compare the major trace and rare earth element chemistry of these tourmalines in order to evaluate their suitability as a petrogenetic tool for tracing the fluid sources of the hydrothermal system by comparing the chemistry of tourmalines from gold mineralization with those from metamorphic and magmatic host rocks we test whether tourmaline composition can be used to identify the source rocks of the gold transporting hydrothermal fluids all analyzed tourmalines belong to the alkali super group and plot along the schorl dravite join the hydrothermal tourmalines have li sr and v concentrations comparable to metamorphic tourmalines and clearly distinct from magmatic tourmalines because the concentrations of ni pb cr mn ga zn and sn show a wide overlap between magmatic metamorphic and hydrothermal tourmalines these elements do not permit to discriminate between different source rocks the co variations of many elements in hydrothermal tourmalines when plotted against li show more similarity to metamorphic tourmalines and the whole rock compositions of metasedimentary and metavolcanic host rocks than to their magmatic counterparts this indicates that the major and trace element composition of hydrothermal tourmalines in the hattu schist belt is predominantly controlled by the host rocks and local fluid rock interactions and does not reflect the distal fluid sources the effect of local fluid rock interaction is also manifested by the ree patterns of tourmalines the magmatic tourmalines have distinct lree enriched patterns resembling the whole rock ree patterns of granitic intrusives while the metamorphic and hydrothermal tourmalines have flat or weakly fractionated patterns similar to metavolcanic and metasedimentary host rocks taken together the tourmaline data suggest that hydrothermal tourmalines associated to gold mineralizing fluids are most likely genetically related to metamorphic rock sources without important contributions of magmatic fluids and that local fluid rock interaction exerted a major control on tourmaline chemistry

production of carbonic fluids during metamorphism of graphitic pelites in a collisional orogen an assessment from fluid inclusions abstract fluid inclusions in quartz veins within proterozoic metamorphic rocks in the black hills south dakota were examined by microthermometry and raman spectroscopy to assess the evolution of fluid compositions during regional metamorphism of organic rich shales and late orogenic magmatism both of which were related to the collision of the wyoming and superior crustal blocks fluid inclusions occur in veins that began to be generated before or during regional compression and metamorphism that reached at least garnet grade conditions and in veins within the aureole of the harney peak granite hpg where temperatures reached second sillimanite grade conditions early veins in the schists have undergone recrystallization during heating and deformation that modified the composition of early ch4 or co2 and n2 dominated inclusions these fluids were apparently trapped under conditions of immiscibility with a saline aqueous fluid phase they are interpreted to represent components generated during maturation of organic matter and dehydration of phyllosilicates during incipient metamorphism at reducing fo2 conditions most inclusions in the quartz veins are however secondary co2 bearing they imply a transition to higher fo2 conditions with increasing temperature of regional metamorphism the fo2 conditions may have been controlled by the mineral assemblage in the host metapelites the prevalence of bimodal distributions of trapped co2 n2 and aqueous endmembers in the biotite and garnet zones also suggests that two immiscible fluid phases existed during the regional metamorphism in the aureole of the hpg graphite was evidently consumed by influx of magmatic fluids co2 h2o fluid inclusions dominate but they have significantly less n2 than inclusions at lower metamorphic grades all inclusions define secondary trails in mostly unstrained quartz the bimodality of inclusion compositions is not as well defined as at lower grades with many inclusions containing intermediate co2 h2o compositions this suggests that a single fluid phase existed at the high temperatures in the granite aureole but then unmixed during cooling a set of late quartz veins with graphitized and tourmalinized selvages in the granite aureole contains ch4 bearing inclusions with little n2 the existence of ch4 in these inclusions is attributed to complexing of magmatic b with hydroxyl anions taken from the co2 h2o fluid phase effectively causing reduction in fo2 and promoting precipitation of graphite

the integration of gravity magnetic and seismic data in delineating the sedimentary basins of northern sinai and deducing their structural controls abstract the sinai peninsula is a part of the sinai sub plate that located between the southeast nubian arabian shield and the southeastern mediterranean northward the main objectives of this investigation are to deduce the main sedimentary basin and its subdivisions identify the subsurface structural framework that affects the study area and determine the thickness of sedimentary cover of the basement surface the total intensity magnetic map bouguer gravity map and seismic data were used to achieve the study aims structural interpretation of the gravity and magnetic data were done by applying advanced processing techniques these techniques include reduce to the pole rtp power spectrum tile derivative and analytical signal techniques were applied on gravity and magnetic data two dimensional gravity and magnetic modeling and interpretation of seismic sections were done to determine the thickness of sedimentary cover of the study area the integration of our interpretation suggests that the northern sinai area consists of elongated troughs that contain many high structural trends four major structural trends have been identified that reflecting the influence of district regional tectonic movements these trends are 1 ne sw trend 2 nnw sse trend 3 ene wsw trend and 4 wnw ese trend there are also many minor trends e w nw se and n s structural trends the main sedimentary basin of north sinai is divided into four sub basins 1 northern maghara 2 northeastern sinai 3 northwestern sinai and 4 central sinai basin the sedimentary cover ranges between 2 km and 7 km in the northern part of the study area

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

element mobility and volumetric strain in brittle and brittle viscous shear zones of the superdeep well ktb germany abstract mass balance studies of brittle and brittle viscous shear zones of the superdeep well ktb germany show that element mobility and associated volumetric strain is markedly different in metabasites and paragneisses shear zones in metabasites show thickening and volume increase due to mineralization of prehnite epidote calcite within open fractures and pore space gains in al 2 o 3 cao and sio 2 are compatible with these observations shear zones in paragneisses show either constant volume or volume loss volume loss of the paragneiss shear zones can be explained by pressure solution of quartz and by retrograde mica forming reactions associated with significant gains in potassium group elements k rb ba and losses in sio 2 the differences in volumetric strain between paragneiss and metabasite shear zones can be explained by the different deformation mechanisms and rheology of paragneiss and metabasite at t ca 250 350 c the rigid metabasites supported long lived open fractures and pores where new minerals could precipitate from a fluid phase the paragneisses on the other hand were weak because of increasing amounts of crystal plasticity and pressure solution of quartz which is typical for the brittle viscous transition of quartz bearing rocks open fractures and pores were rapidly closed hampering the deposition of new minerals graphite enrichment has been found in both paragneiss and metabasite shear zones there is clear evidence that graphite enrichment results from fluid phases which carried c into the shear zones from external sources suggesting that c was largely mobile during the shearing processes

contrasting scales of element mobility in metamorphic rocks near harney peak granite black hills south dakota outcrop scale and regional dispersion patterns of rare elements help establish origins of fluid components mechanisms of fluid flow and the scale of element mobility in metamorphic rocks near the harney peak granite enrichment of granite derived elements sn b w li cu f p adjacent to a quartz vein 3 5 km north of the granite indicates that fracture controlled flow was one mechanism for movement of magmatic fluids graphitization of wall rocks and co2 ch4 fluid inclusions in vein quartz show that c was also transported by the vein forming fluid mixing of h2o rich magmatic fluid and co2 ch4 bearing metamorphic fluid within a concealed intrusive below the vein is proposed based on the observation of late stage graphite in several exposed pegmatite bodies in the area other wall rock alteration includes small relative gains of rb k and al toward the vein and relative losses of na sr ca si fe mg mn and possibly ti changes in p k al and si and reequilibration of whole rock 18o are confined to a 50 cm wide zone next to the vein additions of c sn w and cu and depletion of ca na and sr reach 100 150 cm from the vein boron reaches a maximum 25 150 cm from the vein and drops to background levels between 150 and 250 cm in contrast to these elements li is three times the regional background level throughout the outcrop at least 600 cm from any known veins and f and rb remain at elevated levels comparing these results with a regional geochemical profile away from the harney peak granite and published results on dispersion around rare element pegmatites documents the extent of element redistribution on a broader scale for example rb and f can be affected up to 100 m from local fluid sources whereas li appears to record interaction with granite derived fluids in rocks that are 500 m or more from map scale fluid sources thus regional dispersion patterns of li and other rare elements provide a minimum estimate of the volume of mid crustal rock that interacted with granite derived fluids in the harney peak area

new insights on the late pleistocene holocene lithic industry in east kalimantan borneo the contribution of three rock shelter sites in the karstic area of the mangkalihat peninsula this paper aims to present some aspects of the late pleistocene holocene lithic industry in the inland east kalimantan region by studying the assemblages found in three rock shelter sites in the karstic area of the mangkalihat peninsula this study analyzes these assemblages in their regional techno complex taking into consideration the environmental components it focuses on certain aspects of stone flaking technology and the trends in the reduction sequences of the assemblages our results shows that the reduction sequences flaking technology and the typology of the blanks and tools persisted across the pleistocene holocene boundary as revealed in liang abu where the lithic artifacts were found throughout the stratigraphic sequence over at least 20 000 years other excavations in liang jon and liang pemalawan have confirmed this continuity until the historical eras in addition this research emphasizes the potential influence of the environmental and climatic stability persistence of the rain forest during at least the last 40 000 years in this region as well as the inland geographical location on the continuity of the local stone flaking technology

tourmaline rich pseudomorphs in sillimanite zone metapelites demarcation of an infiltration front textural features combined with mineral chemistry preserved in metamorphic rocks provide insights into metamorphic reaction mechanisms as well as open vs closed system processes prograde tourmaline rich muscovite pseudomorphs after staurolite develop in sillimanite zone metapelites adjacent to peraluminous granitoid intrusives in nw maine tourmalines occur in discrete domains restricted to central regions of muscovite rich quartz poor pseudomorphs with biotite rich margins these tourmaline grains are relatively large 1 0 mm lack detrital cores and exhibit only minor compositional zoning in sharp contrast to matrix tourmaline from other samples these features suggest fluid infiltration as the causative mechanism for the formation of these tourmaline rich mica pseudomorphs after staurolite irreversible thermodynamic models of local reactions and material transport in combination with mineral chemistry allow evaluation of reaction mechanisms that produced these pseudomorphs thermodynamic models in the nkcmtfashob system mimic the observed textural features if a threestage process is used stage 1 staurolite replacement is initiated by infiltration of an aqueous phase that adds k na h2o to the rock with the concomitant removal of al fe because the system is initially undersaturated with respect to tourmaline a pseudomorph containing muscovite with minor biotite develops at the expense of staurolite stage 2 with continued infiltration concentration of b increases tourmaline saturation is exceeded tourmaline nucleates and grows local material transport constraints mandate that tourmaline precipitation be spatially restricted to regions of staurolite dissolution consequently tourmaline forms in clusters at sites containing the last vestiges of staurolite in the pseudomorph core also evidenced by staurolite inclusions within several tourmaline grains resultant domains of staurolite replacement during this stage contain about equal amounts of muscovite and tourmaline typical staurolite poikiloblast pseudomorphing reactions require silica transport matrix quartz dissolves from the surrounding host resulting in a local enrichment of biotite and plagioclase at the pseudomorph margin stage 3 small amounts of sillimanite nucleate and grow throughout the rock late stage aqueous fluids from the adjacent monzonitic intrusive are likely to be the primary b source theoretical textural and compositional modeling combined with observational data indicate that boron must have been derived externally from the rock that the modal amount of tourmaline is very sensitive to the b content of the fluid that tourmaline is stable throughout the sillimanite zone depending on other cation activities and ph of the fluid and that these pseudomorphs provide insight into b contents of metamorphic fluids and the timing of the b influx the outer geographic extent of the tourmaline bearing pseudomorphs marks the boundary of a reactive geochemical front and thus defines an advective isograd interpretation of subtle textural features preserved in the rock in conjunction with irreversible textural modeling provides a powerful tool with which to understand the chemical evolution of metamorphic rocks and the fluids involved

melt composition control of zr hf fractionation in magmatic processes zircon zrsio4 and hafnon hfsio4 solubilities in water saturated granitic melts have been determined as a function of melt composition at 800 and 1035 c at 200 mpa the solubilities of zircon and hafnon in metaluminous or peraluminous melts are orders of magnitude lower than in strongly peralkaline melt moreover the molar ratio of zircon and hafnon solubility is a function of melt composition although the solubilities are nearly identical in peralkaline melts zircon on a molar basis is up to five times more soluble than hafnon in peraluminous melts accordingly calculated partition coefficients of zr and hf between zircon and melt are nearly equal for the peralkaline melts whereas for metaluminous and peraluminous melts dhf dzr for zircon is 0 5 to 0 2 consequently zircon fractionation will strongly decrease zr hf in some granites whereas it has little effect on the zr hf ratio in alkaline melts or similar depolymerized melt compositions the ratio of the molar solubilities of zircon and hafnon for a given melt composition temperature and pressure is proportional to the hf zr activity coefficient ratio in the melt the data imply that this ratio is nearly constant and probably close to unity for a wide range of peralkaline and similar depolymerized melts however it changes by a factor of two to five over a relatively small interval of melt compositions when a nearly fully polymerized melt structure is approached for most ferromagnesian minerals in equilibrium with a depolymerized melt dhf dzr typical values of dhf dzr range from 1 5 to 2 5 for clinopyroxene amphibole and titanite because of the change in the hf zr activity ratio in the melt the relative fractionation of zr and hf by these minerals will disappear or even be reversed when the melt composition approaches that of a metaluminous or peraluminous granite it is thus not surprising that fractional crystallization of such granitic magmas leads to a decrease in zr hf whereas fractional crystallization of depolymerized melts tends to increase zr hf there is no need to invoke fluid metasomatism to explain these effects results demonstrate that for ions with identical charge and nearly identical radius crystal chemistry does not alone determine relative compatibilities rather the effect of changing activity coefficients in the melt may be comparable to or even larger than elastic strain effects in the crystal lattice

spatio temporal evolution of a tertiary carbonate platform margin and adjacent basinal deposits abstract the variability in low to moderate energy carbonate platform margins is poorly known from the geological record here the spatial and temporal evolution of platform margin and adjacent basinal deposits is evaluated from the little known tertiary kedango limestone that developed in a semi enclosed marine embayment in se asia the hypothesis here is that platform margin development will reflect regional and perhaps global influences such as tectonics eustasy or biotic change rather than windward leeward effects and storms that typically impact strongly upon open oceanic platforms the development of the carbonate platform was determined through logging petrography facies evaluation provenance and high resolution dating studies eleven carbonate facies were identified from the 30 km long western margin of the 600 m thick platform and its adjacent slope and basinal deposits larger benthic foraminifera and coralline algal packstones and wackestones dominated in shallow waters during the oligo miocene coral patch reef related floatstones rudstones and less commonly boundstones were also present on the platform top perhaps surprisingly for a low energy platform there was considerable variation along the platform margin and much reworking of material into slope and basinal deposits during the oligo miocene reworked material includes shallow water bioclasts clasts from older siliciclastics fresh feldspars lithified slope and platform top carbonate clasts some of the latter showing evidence for karstification the western platform margin varied laterally over a few kilometres from a gently sloping unrimmed platform to a probable bank top with in places coral fringed bypass and erosional faulted escarpment margins eustasy may have influenced shallowing and deepening trends on the platform top but apparently had little impact on mass wasting instead platform margin development was strongly impacted by tectonics including active faulting terrestrial runoff together with changes in carbonate producers and local variability on the platform top

paleomagnetism of borneo abstract the paleomagnetism of borneo remains controversial although the preponderance of results both from the island itself and from the surrounding regions suggest that counterclockwise ccw rotation has taken place ccw rotations are seen in minor intrusions in sarawak sabah and kalimantan which increase systematically with the age of the intrusion to a maximum value of 51 8 3 7 the rotation can be no older than 25 ma which is the age of the intrusion showing the maximum rotation the rotation appears to have neared completion by 10 ma similar ccw rotations are seen in sites from peninsular malaysia through borneo to sulawesi the celebes sea and palawan in the philippines but the ages of these rotations are for the most part unknown in mesozoic rocks in kalimantan and sarawak a stronger declination rotation of nearly 90 ccw is recorded at seven sites including sites which pass fold and reversal tests this strong rotation is no older than youngest cretaceous and although seen over a wide region in borneo it is not seen in peninsular malaysia nor in the celebes sea or palawan where only the weaker ccw rotation is seen the widespread occurrence of this strong rotation in western borneo suggests that it is essentially a rigid plate or microplate rotation and not a series of local rotations caused by distributed shear in limited deformation zones the rotation of borneo appears to be a consequence of convergence between the australian and eurasian plates which is accommodated by subduction along the northwest margin of borneo

b and li in proterozoic metapelites from the black hills u s a implications for the origin of leucogranitic magmas the abundance and distribution of b and li in metasedimentary rocks and in the harney peak granite hpg in the black hills south dakota u s a elucidate the behavior of these two elements during 1 regional metamorphism that began at 1760 ma 2 subsequent contact metamorphism associated with emplacement of the hpg and associated pegmatites at 1715 ma and 3 anatexis leading to production of the granite there is no clear evidence for changes in b and li concentrations with progressive regional metamorphism of the metapelites from chlorite biotite grade up to staurolite grade rocks outside the pegmatite aureole that surround the hpg have average b contents of 80 ppm there is no correlation of b with other elements in the pelitic schists which indicates that none of the major phases is the dominant host for b boron content is mainly controlled by small amounts of randomly distributed tourmaline that was identified in alpha track maps of thin sections in the aureole of the granite b concentrations are depleted in many samples the depletion is attributed to consumption of tourmaline during interaction of the rocks with alkalic fluids the average li contents in metapelites far away from the hpg are also 80 ppm near the hpg li concentrations reach roughly 190 ppm indicating significant metasomatism by fluids that emanated from the granite and pegmatites the concentrations of b and li in the low grade metapelites are sufficient to explain their abundances in the hpg if the granite formed by partial melting of the metapelites and if there was total breakdown of tourmaline stabilization of tourmaline in leucogranites is not necessarily related to sources enriched in b but may be related to its competition for fe and mg with biotite

regional stress alignments in the kutai basin east kalimantan indonesia a contribution from a borehole breakout study abstract borehole breakout data from 134 wells located within the kutai basin region east kalimantan were analyzed to determine the present day regional horizontal stress alignments the data were extracted from various types of dipmeter logs the study reveals that the majority of the data give a coherent picture of breakout orientation the mean azimuths for the entire unweighted ellipticity weighted and magnitude weighted data sets are preferentially aligned in the regional mean direction of 48 9 n or 128 9 n most of the data have a low dispersion value s o and the ranking of reliability in zoback s classification is a there is no significant azimuth variation with depth these relatively consistent alignments of breakout azimuths indicate that the maximum regional stress direction in the study area is nw se this regional mean of breakout azimuths deviates from the axis of the anticlinorium trends and from the strike of the thrust fault patterns in the region it is believed that these structural patterns are influenced by reactivation of weak zones related to sediment loading structural inversion

tertiary tectonic and magmatic evolution of western sulawesi and the makassar strait indonesia evidence for a miocene continent continent collision

stress near the surface of the earth over most of the earth s surface earthquake hypocenters are concentrated in the depth range 0 15 km that is in the upper half of the crust chen molnar 1983 the exception is the subduction zones where cold litho sphere is underthrust to greater depths as a first approximation the top 10 15 km of the crust can be regarded as a region of nearly elastic response to stress with brittle fracture under sufficient stress difference this is the depth range discussed in this review the lower crust appears to be characterized by some form of ductile response to stress in large areas of the upper crust the stress field is related to large scale tectonic processes and represents the tractions acting on the plate concerned however some decoupled crustal blocks are known and are noted herein caution is necessary in generalizing the stress in a region to the plate that contains it recent reviews of crustal stress are given by ranalli chandler 1975 wyss 1977 mcgarr gay 1978 and gay 1980 in the upper crust one principal stress is generally within 20 of the vertical except beneath very rough topography and this vertical principal stress jz is usually within 10 of the lithostatic pressure j pg dz due to overlying rock mcgarr gay 1978 the horizontal principal stresses generally increase with depth and may be less or greater than the vertical pressure within a few hundred meters of the surface the rock mass is divided into blocks by numerous fractures including large and small faults on which shear displacements can be identified and joints on which no shear movement can be seen if the ambient stress is comparable to the strengths of these

geologic interpretation of space shuttle radar images of indonesia the national aeronautics and space administration nasa space shuttle mission in november 1981 acquired images of parts of the earth with a synthetic aperture radar system at a wavelength of 23 5 cm 9 3 in and spatial resolution of 38 m 125 ft this report describes the geologic interpretation of 1 250 000 scale images of irian jaya and eastern kalimantan indonesia where the all weather capability of radar penetrates the persistent cloud cover the inclined look direction of radar enhances subtle topographic features that may be the expression of geologic structures on the indonesian images the following terrain categories are recognizable for geologic mapping carbonate clastic volcanic alluvial and coastal melange and metamorphic as well as undifferentia ed bedrock regional and local geologic structures are well expressed on the images in the vogelkop region of irian jaya the major tectonic elements tamrau mountains sorong fault kemum block bintuni basin and lengguru foldbelt are readily mapped on the image of the sorong fault geomorphic features offset drainage shutterridges aligned notches provide clear evidence for left lateral strike slip displacement several lineaments on the image correlate with previously mapped faults other lineaments may be the expression of previously unrecognized faults on the image of the mainland of irian jaya a belt of metamorphic and melange terrain marks the zone of collision between the pacific plate and the australian plate the high central range of irian jaya is located south of the metamorphic and melange belt the generally homoclinal structure of the central range is interrupted in the paniai lake region by a series of southward directed thrust plates indicated by belts of carbonate terrain new guinea limestone group that alternate with belts of clastic terrain kembelangan formation in the image of eastern kalimantan several major foldbelts are clearly expressed these limited examples of space shuttle radar images demonstrate their value for geologic interpretation of indonesia it is recommended that future shuttle missions acquire complete radar coverage of the main islands of indonesia for use in geologic mapping and energy exploration shuttle radar images would also be valuable for other cloud covered forested regions

high heat flow effects on a coalbed methane reservoir east kalimantan borneo indonesia abstract the balikpapan formation miocene age in sangatta east kalimantan is thick 1500 m containing abundant coal seams that range in thickness from less than a meter to over 5 m coal seams are distributed throughout the section and may represent 5 to 7 of the total formation thickness measured gas contents range from

embaluh group turbidites in kalimantan evolution of a remnant oceanic basin in borneo during the late cretaceous to palaeogene turbidites crop out in large parts of nw borneo including kalimantan and sarawak the strata predominantly comprise the embaluh group in kalimantan and lateral equivalents the rajang group in sarawak collectively known as the rajang embaluh group previous interpretation of these rocks as the product of deep marine deposition and deformation as part of an accretionary prism during late cretaceous to palaeogene subduction implies south dipping thrusts northward stratigraphic younging the existence of a complete arc to trench system and significant deformation and metamorphism of the turbidites however new fieldwork described here established consistent southward stratigraphic younging in kalimantan no evidence for southward dipping thrusts and a lack of metamorphism and associated accretionary complex related deformation features furthermore all available palaeontological and radiometric age data indicate that deposition of the bulk of the rajang embaluh group postdates in board subduction related magmatism and thus a complete arc trench system cannot be demonstrated consequently the rajang embaluh group turbidites are re interpreted as having formed in either a post collisional foreland basin or a remnant ocean basin the lack of a identifiable mountain belt and linked thrust system and probable oceanic aynity of crust beneath the rajang embaluh group basin favour the latter interpretation borneo occupies a pivotal position within southeast asia this new model of a remnant oceanic basin setting for extensive turbidite units of borneo therefore has far reaching implications for the tectonic evolution of borneo the south china sea and se asia the new model is compared with older palaeozoic orogenic belts which also contain thick turbidites sequences

in defense of magmatic diapirs abstract diapirism as a crustal magma ascent mechanism has been recently criticized we contend that this reflects an overly simplistic view that diapirs must resemble modeled hot stokes diapirs and the perception that magma ascent in dikes is a more problem free mechanism for the construction of plutons we describe four cordilleran plutons that have characteristics much more compatible with diapirs than dike fed chambers these plutons were emplaced at depths ranging from 10 to 30 km and record different parts of diapiric ascent paths most ascended during complex visco elastic flow of host rock during regional deformation have narrow structural aureoles indicating power law behavior of host rock and were constructed of multiple batches of magma attributes enabling them to ascend greater distances than single hot stokes diapirs some features of these plutons are not typically attributed to diapirs and thus we introduce the term visco elastic diapir for bodies consisting of one or more batches of magma rising together with length to width ratios

the influence of basement reactivation on the extensional and inversional history of the kutai basin east kalimantan se asia the kutai basin east kalimantan is one of several large extensional basins formed in the middle to late eocene formed above an orogenic complex of late cretaceous early tertiary age basement fabrics oriented nw se and ne sw strongly influenced basin extension and inversion remote sensing data and fieldwork show basement fabric on the margins and tertiary cover are dominated by ne sw nw se and nne ssw trending structures similarly on a larger scale nw se narrow linear gravity lows cut nne ssw highs on the gravity data within the basin reconstruction of the basin architecture shows nne ssw basin bounding faults overlapping in a right stepping en echelon manner these overlaps relay ramps were breached by faults oriented ne sw through reactivation of the basement fabric opposing antithetic and synthetic half grabens were linked by highly oblique nw se transfer faults inversion utilized extensional faults as reverse faults however nw se oriented structures were reactivated as zones of lateral offset along the fold thrust belt whilst fault kinks oriented ne sw were reactivated as oblique slip reverse faults the kutai basin provides an example of the controls that basement heterogeneities play on both extension and inversion

interaction of permo triassic and jurassic extensional fault blocks during the development of the northern north sea the main structural elements resulting from late permian early triassic extension have been resolved across the total width of the northern north sea the northern segment of the basin north of 61 n bounded to the west by the hutton fault and to the east by the norwegian mainland was occupied by four westerly tilted half grabens 25 35 km in width prior to jurassic extension the central segment of the basin 60 20 61 n exhibits a full graben beneath the jurassic horda platform flanked by half grabens tilted towards the basin margins the change in permo triassic fault block configuration defining structural domains is largely constrained by a basement discontinuity which runs diagonally ne sw across the basin maximum jurassic extension is represented by several centres of subsidence aligned nne ssw across a n s oriented and broader permo triassic basin jurassic extension was concentrated within the viking graben proper south of 60 n which in this area is represented by single westerly tilted en echelon half graben segments 20 25 km wide the area affected by jurassic extension becomes progressively wider to the north again governed by the basement discontinuity eventually encompassing the total width of the basin c 200 km north of 61 n the central segment of the northern north sea displays the greatest contrast in permo triassic and jurassic structural styles and basin geometry jurassic stretching and faulting was negligible to the east horda platform precisely the area which had been the site of maximum permo triassic stretching and fault activity it has generally been assumed that jurassic fault configuration along the eastern margin of the central segment of the viking graben to a large extent reflects the reactivation of major permo triassic faults this study demonstrates the interference of permo triassic and jurassic basin geometries in this area due to major faults of the two generations dipping in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin and c 20km in width is underlain by a wider c 35 km and w tilted permo triassic fault block

the influence of basement faults during extension and oblique inversion of the makassar straits rift system insights from analog models analog models were used to investigate the influence of cross trending basement faults on inverted rift systems similar to those located in the makassar straits multilayer models composed of sand silicone putties and a silicone plasticine mixture were constructed so that laterally offset rift basins would form on either side of a preexisting basement fault transfer zones comprising a series of en echelon normal faults that connect downward with the basement fault formed to link the laterally offset rift basins during the extension phase subsequent oblique inversion of the models resulted in a general progression starting with broad folding followed by the development of small scale inversion anticlines associated with reactivated rift faults to thrust faulting and finally to the formation of cross trending wrench faults rift fault reactivation and wrench fault development were prominent in the transfer zones because of the orientation of the constituent faults oblique to the shortening direction and their connection with the underlying basement fault the addition of an intrasedimentary detachment layer which represents a thick overpressured shale present in the vicinity of the economically important mahakam delta allowed gravitational collapse and extensional faulting to occur on structural highs the cross trending basement fault was again the locus for inversion structures both above and below the detachment layer in the latter case which may have influenced the distribution of petroleum in the region

diagenesis and fracturing of a large scale syntectonic carbonate platform abstract the influence of coeval tectonics on carbonate platform development is widely documented yet the diagenesis of such syntectonic platforms is barely evaluated an outcrop petrographic and geochemical study details here for the first time the diagenesis of the tonasa limestone formation developed in an extensional regime in central indonesia this equatorial carbonate system was affected by block faulting tilt block rotation differential uplift and subsidence throughout its eocene to early miocene history wilson 1999 wilson et al 2000 the tonasa carbonate platform is dominated by alteration in shallow to deeper burial depths by fluids with predominantly marine precursor origins mechanical and chemical compaction features are common as are a range of mainly burial related granular mosaic blocky and equant calcite cements earlier marine cements and meteoric influences are rare being highly localised to block faulted highs and or bathymetrically upstanding platform margin areas early marine micritisation of allochems was common on the platform top tectonic uplift together with a major oceanic throughflow current are thought to be key influences on localised karstification meteoric diagenesis and marine cementation the distribution and orientation of faults fractures and calcite veins together with evidence for their relative timing are the strongest manifestation of tectonism coeval with diagenesis there is concordance in the orientation and timing of structures affecting the tonasa platform with those basin wide with the potential for reactivation of pre existing basement fabrics tectonic subsidence including fault associated differential subsidence controlled the degree of burial diagenesis impacting different areas of the platform a predominance of burial diagenetic features and dearth of earlier marine or meteoric cementation is seen in other tertiary equatorial platforms and is partly attributed to 1 predominance of non framework building larger benthic foraminifera and or algae that are prone to remobilisation have low production rates and limited potential to build to sea level and 2 high runoff due to the equatorial humid climate contributing to lowered marine salinities in se asia underlying tectonic reasons for the preponderance of a regional diagenetic signature over a syntectonic one fracturing excepted are 1 development on the flanks of a backarc basin not on typical continental crust 2 key platform influencing structures are oblique to the main extensional direction in the basin and 3 development in an overall subsiding tectonic regime post dating basin initiation the aim here is that this study will contribute to understanding diagenetic alteration of syntectonic carbonate platforms and those from equatorial regions

structural controls on the evolution of the kutai basin east kalimantan abstract the kutai basin formed in the middle eocene as a result of extension linked to the opening of the makassar straits and philippine sea seismic profiles across the northern margin of the kutai basin show inverted middle eocene half graben oriented nne ssw and n s field observations geophysical data and computer modelling elucidate the evolution of one such inversion fold nw se and ne sw trending fractures and vein sets in the cretaceous basement have been reactivated during the tertiary offset of middle eocene carbonate horizons and rapid syn tectonic thickening of upper oligocene sediments on seismic sections indicate late oligocene extension on nw se trending en echelon extensional faults early middle miocene n7 n8 inversion was concentrated on east facing half graben and asymmetric inversion anticlines are found on both northern and southern margins of the basin slicken fibre measurements indicate a shortening direction oriented 290 310 ne sw faults were reactivated with a dominantly dextral transpressional sense of displacement faults oriented nw se were reactivated with both sinistral and dextral senses of movement leading to the offset of fold axes above basement faults the presence of dominantly wnw vergent thrusts indicates likely compression from the ese initial extension during the middle eocene was accommodated on nne ssw n s and ne sw trending faults renewed extension on nw se trending faults during the late oligocene occurred under a different kinematic regime indicating a rotation of the extension direction by between 45 and 90 miocene collisions with the margins of northern and eastern sundaland triggered the punctuated inversion of the basin inversion was concentrated in the weak continental crust underlying both the kutai basin and various tertiary basins in sulawesi whereas the stronger oceanic crust or attenuated continental crust underlying the makassar straits acted as a passive conduit for compressional stresses