hydrothermal dolomitization of jurassic cretaceous limestones in the southern alps italy relation to tectonics and volcanism dolomitization has affected up to 750m of the jurassic and cretaceous pelagic carbonate sequence of the southern continental margin of the alpine tethys the sequence crops out in the southern alps of italy monti lessini late paleocene to miocene extrusion of basaltic tuffs breccias and lavas was contemporaneous with the dolomitization was was associated with extensive tectonism in an ancient back arc basin more than 200 samples were analyzed by x ray diffraction cathodoluminescence scanning electron microscopy stable isotope ratios carbon oxygen strontium and clay mineralogy the dolomite contains 40 to 50 mgco sub 3 in thin sections the crystal size distribution is unimodal about 100 mu m possibly indicating a single nucleation for the main crystallization phase the delta sup 13 c of the dolomite is not appreciably different from the undolomitized pelagic limestone 1 0 per thousand to 2 0 per thousand peedee belemnite pdb the delta sup 18 o variation 5 0 per thousand to 13 0 per thousand pdb is due to temperature variation in the system the sup 87 sr sup 86 sr ratio in the dolomite 0 70839 0 70867 is consistent with the ratio in late oligocene miocene marine water clay minerals in limestone and dolomite differ in the presence of neoformed mg chlorite indicating a maximum temperature of about 150c for dolomitization the dolomite is suggested more to have a hydrothermal origin the heat flow associated with the volcanism allowed marine water to penetrate the system and circulate in convective cells through the tectonic breccias locally dolomitizing the limestone less

late cretaceous and cenozoic tectonics of the malay peninsula constrained by thermochronology abstract new thermochronological analyses of granites from the malay peninsula record the region s thermal history during the late mesozoic and cenozoic 40 ar 39 ar and u th sm he analyses are combined with existing fission track data to provide a comprehensive set of temperature and time data fully and partially reset k feldspar and biotite mica 40 ar 39 ar analyses indicate a significant period of thermal perturbation between 100 and 90 ma and a second lesser perturbation between 51 and 43 ma zircon u th sm he analyses and existing fission track data indicate exhumation of the malay peninsula in the cretaceous and renewed localised exhumation in the early paleogene apatite u th sm he and fission track data indicate rapid exhumation of the region in the late eocene and oligocene late cretaceous tectonism is linked to the reversal of a regional dynamic topographic low following the cessation of subduction along the sundaland margin in the late cretaceous causing regional uplift and exhumation and the addition of significant heat into the crust via mantle upwelling early paleogene exhumation may reflect the continuation of cretaceous tectonism or a discrete phase of paleocene exhumation linked to localised transpressional tectonics eocene tectonism is coincident with major subsidence offshore of the malay peninsula interpreted to reflect regional block faulting in response to north south compression driven by the resumption of subduction along the southern margin of sundaland in the eocene

structurally controlled hydrothermal dolomites in albian carbonates of the ason valley basque cantabrian basin northern spain abstract shallow marine carbonate sedimentation dominated during the albian in the western part of the basque cantabrian basin in northern spain forming the large ramales platform this platform originated on a less subsiding tectonic block facing deeper and more subsiding areas to the south and east which were created by tectonic activity in the basin fracture related hydrothermal dolomites hosted in these albian carbonates are well exposed in the ason valley area mapping in the studied area revealed several dolomite bodies related to main faults that cut the stratification almost at right angles the bodies show a vertical development along fault strike up to 900 m thick from which kilometre scale branches expand following the stratification dolomitization is pervasive and independent of the limestone facies main dolomite facies are fine replacive sucrosic and saddle petrography c o and sr isotopes and fluid inclusion analysis support a polyphase hydrothermal dolomitization at fluid temperatures between 75 c and 240 c and highly variable salinity of up to 22 wt nacl fine dolomite replaced limestone first and then sucrosic and saddle dolomites replaced part of the first dolomite and cemented newly created fracture porosity together with different calcite cements zebra dolomites and hydroclastic breccias are products of this later stage burial analysis of the host rock supports maximum burial temperatures of 80 c and intense tectonic activity from the albian to turonian with a latest albian peak subsidence albian stretching of the crust and subsequent ascent of the isotherms in the area is suggested to have produced sufficient heat to the dolomitizing fluids the structural analysis indicates a strong transtensional tectonic activity in the studied area during albian to turonian time with the creation of an overstep between w e trending and n s trending faults fluids moved from subsiding areas to fractured uplifted parts of the ramales platform enhanced by diapiric activity

late cretaceous early palaeogene tectonic development of se asia abstract the late cretaceous early palaeogene history of the continental core of se asia sundaland marks the time prior to collision of india with asia when se asia from the tethys in the west to the palaeo pacific in the east lay in the upper plate of subduction zones in myanmar and sumatra subduction was interrupted in the aptian albian by a phase of arc accretion woyla and mawgyi arcs and in java eastern borneo and western sulawesi by collision of continental fragments rifted from northern australia subsequent resumption of subduction in the myanmar thailand sector explains 1 early creation of oceanic crust in the andaman sea in a supra subduction zone setting 95 ma 2 the belt of granite plutons of late cretaceous early palaeogene age starting 88 ma in western thailand and central myanmar and 3 amphibolite grade metamorphism between 70 and 80 ma seen in gneissic outcrops in western and central thailand and 4 accretionary prism development in the western belt of myanmar until glancing collision with the ne corner of greater india promoted ophiolite obduction deformation and exhumation of marine sediments in the early palaeogene the ranong strike slip fault and other less well documented faults were episodically active during the late cretaceous palaeogene time n to nw directed subduction of the palaeo pacific ocean below southern china vietnam and borneo created a major magmatic arc associated with rift basins metamorphic core complexes and strike slip deformation which continued into the late cretaceous the origin and timing of termination of subduction has recently been explained by collision of a large luconia continental fragment either during the late cretaceous or palaeogene evidence for such a collision is absent from the south china sea well and seismic reflection record and here collision is discounted instead relocation of the subducting margin further west possibly in response of back arc extension which created the proto south china sea is preferred lying between the two subduction related arcs the khorat basin is of predominantly late jurassic early cretaceous age but stratigraphic and apatite fission track data also indicates deposition of 1 2 km of late cretaceous sediments the synformal basin geometry probably arose due to the dynamic topography created by converging tethyan and palaeo pacific subduction zones the aptian albian slowing of basin subsidence and onset of evaporite deposition coincides with collision of the mawgyi and woyla island arcs extensive palaeogene deformation and exhumation 3 km in places affected all margins of the khorat plateau deformation includes folds of the phu phan uplift and strike slip faults thrusts and folds on the southern and eastern margins south of the khorat plateau outcrop and seismic reflection data from the ton le sap basin cambodia and the gulf of thailand indicate syn depositional fault controlled subsidence was important during cretaceous deposition the hot thickened crust developed during the late cretaceous palaeogene events follows the weak indosinian crustal scale inthanon and sukhothai zones which persistently guided the location of later structures including cenozoic extensional and post rift basins and influenced the widespread occurrence of low angle normal faults metamorphic core complexes and eastern gulf of thailand super deep post rift basins

using surface waves recorded by a large mesh of three element arrays to detect and locate disparate seismic sources author posting the authors 2018 this article is posted here by permission of the royal astronomical society for personal use not for redistribution the definitive version was published in geophysical journal international 215 2018 942 958 doi 10 1093 gji ggy316

model for dolomite formation in northwest florida abstract petrographic methods are used to examine the nature of the floridan post oligocene unconformity and diagenetic responses in the associated carbonate units the study addresses the depositional environment and the character of sediments associated with the unconformity types and timing of diagenetic changes and mode of dolomitization for the suwannee limestone dolomites and basal hawthorn group dolosilts the purpose of the study is to determine if the original texture of geologic materials is preserved more frequently in rocks deposited in a supratidal environment in the uppermost floridan carbonates to examine possible sources of magnesium for the dolomitization that has occurred in the floridan aquifer and to determine the chemical environment of dolomite formation on the basis of lithology the tri county study area can be divided into two regions one in which the uppermost floridan carbonate is calcareous or locally silicified and one in which the aquifer system is capped with dolomite lateral interfingering between the two regions is apparent and it is inferred that the boundary between the limestone and dolomite represents a geochemical boundary between a mixed marine and freshwater environment and a subaerially exposed freshwater environment where dolomite has replaced the uppermost suwannee limestone the dolomite is overlain by a thin unit of dolosilt the predominant source of magnesium for the dolomitization that occurred in the study area is probably seawater

dolomitization a critical view of some current views the principal models in vogue today for dolomitization are the mixing zone and the sabkha models despite the wide acceptance of these models there has been little critical assessment of their validity such an assessment is the objective of the present paper a close look at the dorag mixing zone model badiozamani 1973 reveals several serious weaknesses 1 the range of freshwater seawater mixtures that meet the dorag requirement for dolomitization shrinks to a small window if the geologically more realistic disordered dolomite is used in the calculations instead of the ordered dolomite on which the model is based 2 in none of the known modern coastal mixing zones in limestone or lime sediments has replacement by dolomite been observed 3 in a number of dolomites interpreted to be of mixing zone origin dolomite has precipitated without dissolution of the calcite substrate evidence that negates the fundamental premise of the dorag model in addition to these weaknesses isotope and trace element data used to identify mixed water dolomite are inadmissible because 1 isotopic fractionation factors for dolomites remain unresolved 2 isotope values uncorrected for temperature for a host of dolomites interpreted to be of different origins overlap 3 nonisomorphous trace elements such as na in dolomite cannot on theoretical grounds be relied on to identify dolomitizing fluids similar overall objections can be brought against folk and land9s 1975 schizohaline version of mixing zone dolomitization in summary mixing zone models have such weak underpinnings that they should be questioned as viable explanations for massive dolomitization contemporaneous dolomite formation in modern sabkhas is well documented but the important question of whether the mechanism of dolomite formation is replacement or direct precipitation remains to be resolved in the well studied sabkha at abu dhabi brine chemistry changes have been used as evidence of a replacement origin for the dolomite but it is shown here that this evidence is far from unequivocal an alternative origin of direct precipitation of dolomite is offered an origin in keeping with dolomite precipitation known from other modern sabkhas and saline lakes and in line with our laboratory experience with dolomite synthesis moreover it is suggested here that in general contemporaneous dolomite will form at low temperatures only by direct precipitation a mechanism that requires special conditions of highly super saturated waters of high mg ca ratio and elevated co 3 hco 3 concentrations this may explain why modern dolomite is mainly restricted to evaporitic environments a bias not shared by ancient dolomites in contrast replacement dolomite appears to require at low temperatures long reaction times or 10 4 yr a requirement that is mainly to be met in large regional groundwater flow systems both marine and nonmarine a third dolomitization model considered here is that of baker and kastner 1981 based on the experimental finding that sulfate ions inhibit or retard dolomitization a number of modern sedimentary dolomites are not in accord with this model in that they are forming from brines with large sulfate concentrations 2 to 70 times that of seawater thus the baker kastner model should be held in abeyance until these serious contradictions are resolved the current emphasis on mixing zone and sabkha dolomitization has diverted attention from other promising avenues of approach to the dolomite problem four of these avenues each of which deemphasizes the special water approach are briefly addressed and are as follows 1 influence of temperature and time 2 mass transfer processes 3 burial diagenesis of epigenetic dolomites 4 fluid inclusion studies at elevated temperatures the dolomite problem essentially disappears ordered dolomite can be made in the laboratory in days at 100 degrees c what is more at temperatures above 60 degrees c ca rich waters become dolomitizing fluids which makes most natural subsurface waters capable of dolomitization at low temperatures time may be the key element so that seawater will become a major dolomitizing fluid only where stable circulation systems such as kohout convention can drive seawater through carbonate platforms for many thousands to millions of years this paper has tried to show that currently favored models of dolomitization carry serious uncertainties enough to warn us to look more critically at the validity of these models and also it is hoped enough to spur new efforts to find new solutions to the problems of dolomitization

kinematics of post orogenic extension and exhumation of the taku schist ne peninsular malaysia abstract recent studies imply that the formation and evolution of many se asian basins was driven by extensional detachments or systems of low angle normal faults that created significant crustal exhumation in their footwalls in this context the architecture of the triassic indosinian orogen presently exposed in peninsular malaysia is compatible with significant extension post dating the orogenic event in this study we performed a kinematic analysis based on fieldwork and microstructural observations in the taku schist kemahang granite and the surrounding gua musang sediments of northern peninsular malaysia in order to shed light on processes related to the build up and subsequent demise of the indosinian orogen the first three phases of deformation were related to an overall period of e w oriented contraction and burial metamorphism these phases of deformation are characterized by isoclinal folding with flat lying axial plane cleavages d1 asymmetrical folding top to the w sw shearing d2 and upright folding d3 all are in general agreement with observations of the previously inferred permo triassic indosinian orogeny during these times the taku schist a sequence of paleozoic clastic sediments with mafic intercalations was metamorphosed to amphibolite facies these rocks are most likely equivalent to the ones exposed in the bentong raub suture zone structural relations suggest that the triassic kemahang pluton is syn kinematic which provides important constraints for the timing of these contractional events we demonstrate that the overall shortening was followed by a hitherto undescribed extension in nw se direction resulting in the formation of a large scale detachment the taku detachment in northern peninsular malaysia extension probably reactivated the former subduction plane as a detachment and exhumed previously buried and metamorphosed rocks of similar lithological composition to the neighboring bentong raub suture zone such a mechanism is similar to that observed in other regions such as the aegean apennines dinarides or the betics rif system where exhumation of high pressure metamorphic rocks is largely controlled by detachments or low angle normal shear fault systems

rb sr sm nd and u pb geochronology of the rocks within the khlong marui shear zone southern thailand abstract in southern thailand the khlong marui shear zone is dominated by a nne ssw striking high topographic lozenge shaped area of ca 40 km long and 6 km wide between the khlong marui fault and the bang kram fault the geology within this strike slip zone consists of strongly deformed layers of mylonitic meta sedimentary rocks associated with orthogneisses mylonitic granites and pegmatitic veins with a steeply dipping foliation the strike slip deformation is characterized by dextral ductile deformation under amphibolite facies and low to medium greenschist facies in situ u pb ages of inherited zircon cores from all zircons in the khlong marui shear zone indicate that they have the same material from the archean late triassic to late cretaceous ages obtained for zircon outer cores of the mylonitic granite are probably related to a period of magmatic activity that was significantly influenced by the west burma and shan thai collision and the subduction along the sunda trench the early dextral ductile deformation phase of the khlong marui shear zone in the early eocene suggested by u pb ages of zircon rims and the later dextral transpressional deformation in the late eocene indicated by mica rb sr ages rb sr sm nd and u pb dating correlation implies that the major exhumation period of the ductile lens was in the eocene this period was tectonically influenced in the se asia region by the early india asia collision

classification of dolomite rock textures abstract dolomite rock textures can be classified according to crystal size distribution and crystal boundary shape the classification scheme presented here is largely descriptive but carries genetic implications because size distribution is controlled by both nucleation and growth kinetics and crystal boundary shape is controlled by growth kinetics size distributions are classified as unimodal or polymodal crystal boundary shapes are classified as planar or nonplanar if the evidence permits a complete classification includes a description of recognizable allochems matrix and void filling allochems and preexisting cements may be unreplaced partially replaced replaced mimically or replaced nonmimically allochems may be dissolved leaving molds matrix can be unreplace partially replaced or replaced by a unimodal or polymodal size dolomite unimodal size distributions generally indicated a single nucleation event on a unimodal substrate polymodal sizes can be formed by multiple nucleation events on a unimodal or polymodal substrate or differential nucleation on an originally polymodal substrate planar crystal boundaries develop when crystals undergo faceted growth and nonplanar boundaries develop when crystals undergo nonfaceted growth nonplanar boundaries are characteristic of growth at elevated temperature 50 c and or high supersaturation both planar and nonplanar dolomite can form as a cement replacement of caco3 or neomorphism of a precursor dolomite

mechanisms for quasi stationary behavior in simulated heavy rain producing convective systems abstract in this study idealized numerical simulations are used to identify the processes responsible for initiating organizing and maintaining quasi stationary convective systems that produce locally extreme rainfall amounts of particular interest are those convective systems that have been observed to occur near mesoscale convective vortices mcvs and other midlevel circulations to simulate the lifting associated with such circulations a low level momentum forcing is applied to an initial state that is representative of observed extreme rain events the initial vertical wind profile includes a sharp reversal of the vertical wind shear with height indicative of observed low level jets deep moist convection initiates within the region of mesoscale lifting and the resulting convective system replicates many of the features of observed systems the low level thermodynamic environment is nearly saturated which is not conducive to the production of a strong surface cold pool yet the convection qui

petrogenesis of malaysian granitoids in the southeast asian tin belt part 1 geochemical and sr nd isotopic characteristics the malaysian granitoids of the southeast asian tin belt have been traditionally divided into a permian to late triassic i type dominated arc related eastern province indochina terrane and a late triassic s type dominated collision related main range province sibumasu terrane separated by the bentong raub paleo tethyan suture that closed in the late triassic the present study however shows that this model is oversimplified and that the direct application of chappell and white s 1974 i and s type classification cannot account for many of the characteristics shared by malaysian granitoids despite being commonly hornblende bearing as is typical for i type granites the roof zones of the eastern province granites are hornblende free in addition the main range province granitoids contain insignificant primary muscovite and are dominated by biotite granites mineralogically similar to many of the plutons of the eastern province in general the malaysian granitoids from both provinces are more enriched in high field strength elements than typical cordilleran i and s type granitoids the mineralogy and geochemistry of the eastern province granitoids and their relationship with contemporaneous volcanics confirm their i type nature the bulk liquid lines of descent of both granitic provinces largely overlap with one another sr nd isotopic data further demonstrate that the malaysian granitoids especially those of the main range were hybridized melts derived from two end member source regions one of which is isotopically similar to the kontum orthoamphibolites and the other akin to the kontum paragneisses of the indochina block however there are differences in the source rocks for the two provinces and it is suggested in this paper that these are related to differing proportions of igneous and sedimentary protoliths the incorporation of sedimentary sourced melts in the eastern province is insignificant which allowed the granites in this belt to maintain their i type nature the presence of minor primary tin mineralization in the eastern province compared to the much more significant tin endowment in the main range is considered to reflect the incorporation of a smaller proportion of sedimentary protolith in the melt products of the former

the response of simulated nocturnal convective systems to a developing low level jet some recent numerical experiments have examined the dynamics of initially surface based squall lines that encounter an increasingly stable boundary layer akin to what occurs with the onset of nocturnal cooling the present study builds on that work by investigating the added effect of a developing nocturnal low level jet llj on the convective scale dynamics of a simulated squall line the characteristics of the simulated llj atop a simulated stable boundary layer are based on past climatological studies of the llj in the central united states a variety of jet orientations are tested and sensitivities to jet height and the presence of lowlevel cooling are explored the primary impacts of adding the llj are that it alters the wind shear in the layers just above and below the jet and that it alters the magnitude of the storm relative inflow in the jet layer the changes to wind shear have an attendant impact on low level lifting in keeping with current theories for gust front lifting in squall lines the changes to the system relative inflow in turn impact total upward mass flux and precipitation output both are sensitive to the squall line relative orientation of the llj the variations in updraft intensity and system relative inflow are modulated by the progression of the lowlevel cooling which mimics the development of a nocturnal boundary layer while the system remains surfacebased the below jet shear has the largest impact on lifting whereas the above jet shear begins to play a larger role as the system becomes elevated similarly as the system becomes elevated larger changes to systemrelative inflow are observed because of the layer of potentially buoyant inflowing parcels becoming confined to the layer of the llj

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

diagenetic evolution of tortonian temperate carbonates close to evaporites in the granada basin se spain abstract the granada basin se spain is a small basin located in the central part of the betic cordillera structured as such in the late tortonian and initially connected to the atlantic ocean and to the mediterranean sea during the late tortonian normal marine conditions prevailed leading to the deposition of skeletal carbonate sediments on platforms around structural highs the marine connections were later interrupted first to the atlantic ocean and then to the mediterranean sea and a thick evaporite sequence marking the transition from marine to continental conditions was deposited during the latest tortonian in this work the diagenetic evolution of the tortonian temperate carbonates ttc underlying and close to the evaporite bodies is revealed and discussed the diagenetic study includes petrographic analyses conventional petrography cathodoluminescence and fluorescence geochemical analyses major minor and trace elements and 13c and 18o stable isotopes and microthermometry of fluid inclusions in the ttc marine diagenetic processes such as micritization and fibrous calcite cement precipitation and mechanical compaction took place during or just after deposition eogenesis an initial burial event mesogenesis 1 is characterized by 1 stabilization of the temperate water carbonates by freshwater and 2 porosity occlusion via precipitation of low mg bladed and syntaxial mosaic calcite cements the ttc were then subaerially exposed or got close to the surface during evaporite deposition and underwent pedogenesis mg smectite infiltration and pyrite formation telogenesis 1 subsequent brine related diagenetic alterations such as dolomitization and silica halite and sylvite replacements of carbonate grains occurred during a second burial episode mesogenesis 2 concomitant with the messinian lacustrine deposition this being followed by chemical compaction stylolite formation finally the area was uplifted and the ttc exhumed microstalactitic dripstone and fibre whisker calcite cement precipitation and extensive dissolution relate to this pliocene quaternary late event telogenesis 2 in the study case diagenetic history is closely linked to basin evolution as diagenetic pathways of carbonate rocks were related to major geodynamic events including basin restriction leading to evaporite deposition and several episodes of subsidence and uplift up to now only very few diagenetic studies have attempted to demonstrate this correlation between diagenetic history and basin evolution

fault controlled and stratabound dolostones in the late aptian earliest albian benassal formation maestrat basin e spain petrology and geochemistry constrains this study was developed under the exxonmobil fc2 alliance fundamental controls on flow in carbonates the authors wish to thank exxonmobil production company and exxonmobil upstream research company for providing funding the views in this article by sherry l stafford are her own and not necessarily those of exxonmobil this research was supported by the sedimentary geology research group of the generalitat de catalunya 2014sgr251 we would like to thank andrea ceriani and paola ronchi for their critical and valuable reviews and associated editor piero gianolla for the editorial work

fault controlled dolomitization at swan hills simonette oil field devonian deep basin west central alberta canada the partly dolomitized swan hills formation middle upper devonian in the simonette oil field of west central alberta underwent a complex diagenetic history which occurred in environments ranging from near surface to deep 2500 m burial five petrographically and geochemically distinct dolomites that include both cementing and replacive varieties post date stylolites in limestones depths 500 m these include early planar varieties and later saddle dolomites fluid inclusion data from saddle dolomite cements th 137 190 c suggest that some precipitated at burial temperatures higher than the temperatures indicated by reflectance data tpeak 160 c thus at least some dolomitizing fluids were hydrothermal fluorescence microscopy identified three populations of primary hydrocarbon bearing fluid inclusions and confirms that saddle dolomitization overlapped with upper cretaceous oil migration the source of early dolomitizing fluids probably was devonian or mississippian seawater that was mixed with a more 87sr rich fluid fabric destructive and fabric preserving dolostones are over 35 m thick in the swan hills buildup and basal platform adjacent to faults thinning to less than 10 cm thick in the buildup between 5 and 8 km away from the faults this plume like geometry suggests that early and late dolomitization events were fault controlled late diagenetic fluids were in part derived from the crystalline basement or palaeozoic siliciclastic aquifers based on 87sr 86sr values up to 0 7370 from saddle dolomite calcite and sphalerite cements and 206pb 204pb of 22 86 from galena samples flow of dolomitizing and mineralizing fluids occurred during burial greater than 500 m both vertically along reactivated faults and laterally in the buildup along units that retained primary and or secondary porosity

u pb zircon and chime monazite dating of granitoids and high grade metamorphic rocks from the eastern and peninsular thailand a new report of early paleozoic granite abstract in order to understand the age and tectonic framework of eastern to peninsular thailand from the viewpoint of basement metamorphic and plutonic geology the la icp ms u pb zircon dating and the chemical th u total pb isochron method chime monazite dating were performed in the khao chao hub kapong to pran buri and khanom areas in eastern to peninsular thailand the la icp ms u pb zircon dating of the garnet hornblende gneiss from the khao chao area gave 229 3 ma representing the crystallization age of the gabbro and that of the garnet biotite gneisses gave 193 4 ma representing the timing of an upper amphibolite facies metamorphism the chime monazite dating of pelitic gneiss from the khao chao gneiss gave scattered result of 68 22 ma due to low pbo content and rejuvenation of older monazite grains during another metamorphism in the late cretaceous to tertiary time the u pb ages of zircon from the hua hin gneissic granite in the hub kapong to pran buri area scatter from 250 ma to 170 ma on the concordia granite crystallization was at 219 2 ma followed by the sillimanite grade regional metamorphism at 185 2 ma monazite in the pelitic gneiss from this area also preserves early to middle jurassic metamorphism and rejuvenation by later contact metamorphism by non foliated granite or by another fluid infiltration event in the late cretaceous to tertiary time the khao dat fa granite from the khanom area of peninsular thailand gave a u pb zircon age of 477 7 ma this is the second oldest granite pluton ever reported from thailand and is a clear evidence for the sibumasu block having a crystalline basement that was formed during the pan african orogeny the khao pret granite gives u pb zircon concordia age of 67 5 1 3 ma which represents the timing of zircon crystallization from the granitic melt and accompanied sillimanite grade contact metamorphism against surrounding metapelites and gneisses metamorphic rocks in the doi inthanon area also share the similar plutono metamorphic history with the khanom and the hub kapong to pran buri areas this suggests that these three areas belong to the sibumasu block and the sibumasu block records similar plutono metamorphic history from northern to peninsular thailand relative abundance of oceanic components in the khao chao gneiss their late triassic magmatic ages and the early jurassic metamorphic ages prefer the interpretation that the khao chao gneiss belongs to the sukhothai arc

paleomagnetism of peninsular malaysia abstract paleomagnetic results from upper jurassic to paleocene rocks in peninsular malaysia show counter clockwise ccw rotations while clockwise rotations cw are predominantly found in older rocks continental redbeds of the upper jurassic to lower cretaceous tembeling group have a post folding remagnetization giving a vgp at n54 e29 corresponding to approximately 40 of ccw rotation relative to eurasia and 60 ccw relative to the indochina block khorat plateau samples from cretaceous to paleocene mafic volcanics of the kuantan dike swarm and the segamat basalts give vgps at n59 e47 and n34 e36 respectively these malayasian data are indistinguishable from the late eocene and oligocene vgps reported for borneo and the celebes sea and are similar to the eocene vgps reported for southwest sulawesi and southwest palawan the occurrence of ccw deflected data over this large region suggests that much of malaysia borneo sulawesi and the celebes sea rotated approximately 30 to 40 ccw relative to the geocentric axial dipole gad between the late eocene and the late miocene although not necessarily synchronously nor as a single rigid plate these regional ccw rotations are not consistent with simple extrusion based tectonic models cw declinations have been measured in late triassic granites permian to triassic volcanics and remagnetized paleozoic carbonates the age of this magnetization is poorly understood and may be as old as late triassic or as young as middle or late cretaceous the plate or block rotations giving rise to these directions are correspondingly weakly constrained

simulated convective lines with parallel stratiform precipitation part i an archetype for convection in along line shear abstract this article the first of two describing convective lines with parallel stratiform ps precipitation addresses the basic kinematic and precipitation features of these systems the ps mode appears to be the preferred organizational structure in environments with line parallel vertical wind shear this archetype for long lived convective systems has received relatively little attention to date and yet it is frequently implicated in flash flooding because it entails both the along line movement of hydrometeors and back building convective development as a reality check this paper presents conventional observations of the wind and reflectivity fields associated with an archetypal ps system from 2 may 1997 thereafter analyses of idealized numerical simulations serve as the basis for a more detailed investigation of ps systems internal structures and processes the observations and simulations suggest several unique aspects of the ps structure the environment s vertically sheared 3d wind prof

late palaeozoic and mesozoic palaeogeography of southeast asia abstract southeast asia comprises a complex assemblage of allochthonous terranes derived directly or indirectly from gondwana land and assembled between the late palaeozoic and cenozoic the continental core of the region is made up of four principal continental blocks south china indochina sibumasu and east malaya south china indochina and east malaya were rifted from northeast gondwanaland during the silurian or devonian and amalgamated to each other during the early carboniferous sibumasu remained attached to northwest australian gondwana land until the late early permian when it rifted away as part of the elongate cimmerian continent collision between sibumasu and indochina east malaya probably occurred in the early triassic forming the continental core of southeast asia other small terranes including mount victoria land sikuleh natal semitau and southwest borneo were accreted to this core during the jurassic and cretaceous to form sundaland a series of palaeogeographic maps are presented showing interpreted palaeopositions of the various southeast asian terranes in the late palaeozoic and mesozoic which are consistent with the current geological and geophysical constraints

linking process dimension texture and geochemistry in dolomite geobodies a case study from wadi mistal northern oman understanding the distribution and geometry of reservoir geobodies is crucial for net to gross estimates and to model subsurface flow this article focuses on the process of dolomitization and resulting geometry of diagenetic geobodies in an outcrop of jurassic host rocks from northern oman field and petrographic data show that a first phase of stratabound dolomite is crosscut by a second phase of fault related dolomite the stratabound dolomite geobodies are laterally continuous for at least several hundreds of meters 1000 ft and probably regionally and are one half meter 1 6 ft thick based on petrography and geochemistry a process of seepage reflux of mesosaline or hypersaline fluids during the early stages of burial diagenesis is proposed for the formation of the stratabound dolomite in contrast the fault related dolomite geobodies are trending along a fault that can be followed for at least 100 m 328 ft and vary in width from a few tens of centimeters to as much as 10 m 1 33 ft petrography geochemistry and high homogenization temperature of fluid inclusions all point to the formation of the dolomite along a normal fault under deep burial conditions during the middle to late cretaceous the high 87sr 86sr ratio in the dolomite and the high salinity measured in fluid inclusions indicate that the dolomitizing fluids are deep basinal brines that interacted with crystalline basement the dolomitization styles have an impact on the dimension texture and geochemistry of the different dolomite geobodies and a modified classification scheme compared to the one from jung and aigner 2012 is proposed to incorporate diagenetic geobodies in future reservoir modeling

organization and environmental properties of extreme rain producing mesoscale convective systems this study examines the radar indicated structures and other features of extreme rain events in the united states over a 3 yr period a rainfall event is defined as extreme when the 24 h precipitation total at one or more stations surpasses the 50 yr recurrence interval amount for that location this definition yields 116 such cases from 1999 to 2001 in the area east of the rocky mountains excluding florida two kilometer national composite radar reflectivity data are then used to examine the structure and evolution of each extreme rain event sixty five percent of the total number of events are associated with mesoscale convective systems mcss while a wide variety of organizational structures as indicated by radar reflectivity data are seen among the mcs cases two patterns of organization are observed most frequently the first type has a line often oriented east west with training convective elements it also has a region of adjoining stratiform rain that is displaced to the north of the line the second type has a back building or quasi stationary area of convection that produces a region of stratiform rain downstream surface observations and composite analysis of rapid update cycle version 2 ruc 2 model data reveal that training line adjoining stratiform tl as systems typically form in a very moist unstable environment on the cool side of a preexisting slow moving surface boundary on the other hand back building quasistationary bb mcss are more dependent on mesoscale and storm scale processes particularly lifting provided by storm generated cold pools than on preexisting synoptic boundaries

organizational modes of midlatitude mesoscale convective systems this paper discusses common modes of mesoscale convective organization using 2 km national composite reflectivity data the authors investigated linear mesoscale convective systems mcss that occurred in the central united states during may 1996 and may 1997 based upon the radar observed characteristics of 88 linear mcss the authors propose a new taxonomy comprising convective lines with trailing ts leading ls and parallel ps stratiform precipitation while the ts archetype was found to be the dominant mode of linear mcs organization the ls and ps archetypes composed nearly 40 of the studied population in this paper the authors document the characteristics of each linear mcs class and use operational surface and upper air data to describe their different environments in particular wind profiler data reveal that the stratiform precipitation arrangement associated with each class was roughly consistent with the advection of hydrometeors implied by the mean middle and upper tropospheric storm relative winds which were significantly different among the three mcs modes case study examples are presented for both the ls and ps classes which have received relatively little attention to this point as well the authors give a general overview of the synoptic scale meteorology accompanying linear mcss in this study which was generally similar to that observed by previous investigators

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

late paleogene rifting along the malay peninsula thickened crust abstract sedimentary basins often develop above internal zones of former orogenic belts we hereafter consider the malay peninsula western sunda as a crustal high separating two regions of stretched continental crust the andaman malacca basins in the western side and the thai malay basins in the east several stages of rifting have been documented thanks to extensive geophysical exploration however little is known on the correlation between offshore rifted basins and the onshore continental core in this paper we explore through mapping and seismic data how these structures reactivate pre existing mesozoic basement heterogeneities the continental core appears to be relatively undeformed after the triassic indosinian orogeny the thick crustal mega horst is bounded by complex shear zones ranong klong marui and main range batholith fault zones initiated during the late cretaceous early paleogene during a thick skin transpressional deformation and later reactivated in the late paleogene the extension is localized on the sides of this crustal backbone along a strip where earlier late cretaceous deformation is well expressed to the west the continental shelf is underlain by three major crustal steps which correspond to wide crustal scale tilted blocks bounded by deep rooted counter regional normal faults mergui basin to the east some pronounced rift systems are also present with large tilted blocks western thai songkhla and chumphon basins which may reflect large crustal boudins in the central domain the extension is limited to isolated narrow n s half grabens developed on a thick continental crust controlled by shallow rooted normal faults which develop often at the contact between granitoids and the host rocks the outer limits of the areas affected by the crustal boudinage mark the boundary towards the large and deeper andaman basin in the west and the malay and pattani basins in the east at a regional scale the rifted basins resemble n s en echelon structures along large nw se shear bands the rifting is accommodated by large low angle normal faults lanf running along crustal morphostructures such as broad folds and mesozoic batholiths the deep andaman malay and pattani basins seem to sit on weaker crust inherited from gondwana derived continental blocks burma sibumasu and indochina the set of narrow elongated basins in the core of the region khien sa krabi and malacca basins suffered from a relatively lesser extension

tectonic evolution of the malay peninsula abstract the malay peninsula is characterised by three north south belts the western central and eastern belts based on distinct differences in stratigraphy structure magmatism geophysical signatures and geological evolution the western belt forms part of the sibumasu terrane derived from the nw australian gondwana margin in the late early permian the central and eastern belts represent the sukhothai arc constructed in the late carboniferous early permian on the margin of the indochina block derived from the gondwana margin in the early devonian this arc was then separated from indochina by back arc spreading in the permian the bentong raub suture zone forms the boundary between the sibumasu terrane western belt and sukhothai arc central and eastern belts and preserves remnants of the devonian permian main palaeo tethys ocean basin destroyed by subduction beneath the indochina block sukhothai arc which produced the permian triassic andesitic volcanism and i type granitoids observed in the central and eastern belts of the malay peninsula the collision between sibumasu and the sukhothai arc began in early triassic times and was completed by the late triassic triassic cherts turbidites and conglomerates of the semanggol formation were deposited in a fore deep basin constructed on the leading edge of sibumasu and the uplifted accretionary complex collisional crustal thickening coupled with slab break off and rising hot asthenosphere produced the main range late triassic earliest jurassic s type granitoids that intrude the western belt and bentong raub suture zone the sukhothai back arc basin opened in the early permian and collapsed and closed in the middle late triassic marine sedimentation ceased in the late triassic in the malay peninsula due to tectonic and isostatic uplift and jurassic cretaceous continental red beds form a cover sequence a significant late cretaceous tectono thermal event affected the peninsula with major faulting granitoid intrusion and re setting of palaeomagnetic signatures

reservoir quality textural evolution and origin of fault associated dolomites fault associated dolomitized carbonates are proven hydrocarbon reservoirs in the subsurface yet their origins and spatial variability in reservoir quality are poorly understood fault associated dolomitization has affected a 4 8 km 2 5 5 mi wide strip of inner platform carbonates of the oligocene miocene taballar limestone exposed onshore northeastern borneo where they are juxtaposed against deep marine shales of the eocene maliu mudstone on textural grounds planar dolomites postdating compaction and from the predominance of monophase aqueous inclusions replacive dolomite rhombs and later dolomite cements appear to have formed at about 50 60c and at shallow burial depths up to 0 5 1 km 0 3 0 6 mi isotopic and inclusion data indicate that the most likely dolomitizing fluid was dominated by neogene seawater for dolomites 18ov pdb 5 9 to 10 3 consistent with the precipitation from southeast asian oligocene miocene seawater 18o 1 5 to 4 2 at temperatures of 40c up to a maximum of about 50 75c 87sr 86sr 0 708566 0 708697 from tm 2 1 3 4 wt nacl however replacement and remobilization of the precursor limestone also contributed to the isotopic signature of the dolomites 87sr 86sr 0 708115 0 708197 whereas an evolved formation water component cannot be ruled out dolomitizing fluids used faults and fractures as conduits to move into and alter the limestone migrating farthest into the most permeable strata the likely driver for fluid movement was convective flow caused by nearby neogene igneous activity perhaps in combination with tectonically induced hydrologic drive related to fault reactivation close to the main fault late stage dolomite cements occlude pore throats reducing porosity 5 and permeability 5 md the best reservoir quality occurs in medium to coarsely crystalline idiotopic mosaics of dolomite that have completely replaced the limestone 0 5 2 km 0 3 1 2 mi away from the main fault where the late stage cements did not form these dolomites have 12 20 intercrystalline porosity and moderate to good permeability tens of millidarcys fracturing has had variable impact on reservoir quality where late fractures remained open permeability is enhanced tens to hundreds of millidarcys whereas brecciation and fault gouges result in sealing and reduced permeability the textures reservoir quality characteristics and mechanisms of dolomitization show similarities to the few other detailed studies in the literature this study refines the types of predictive reservoir models used in hydrocarbon exploration for subsurface faulted and dolomitized carbonates and increases the understanding of dolomitizing mechanisms of equatorial carbonates

multiple phase fracture and fault controlled burial dolomitization upper devonian wabamun group alberta abstract recent data from the subsurface tangent eaglesham and normandville fields located east of the peace river arch in northern alberta indicate that these wabamun group subtidal carbonates have undergone a complex diagenetic history related to multiple stages of fracturing and faulting burial dolomitization which generated mainly matrix dolomites was responsible for the development of porous reservoir rocks which are spatially highly variable primary porosity was reduced by marine and early burial diagenesis which formed micrite syntaxial overgrowths granular blocky and coarse fracture filling calcite cements minor amounts of microdolomite and floating dolomite rhombs formed during shallow burial further porosity reduction by mechanical compaction and cementation except for minor dissolution and initial fracturing resulted in predominantly tight limestones matrix dolomitization is associated with the second most extensive phase of fracturing which greatly increased both the porosity and permeability of the tightly cemented wabamun limestones dolostones which comprise 85 matrix dolomite are the principal reservoir rock but have highly variable porosity large dissolution cavities developed locally after formation of the matrix dolomites the third phase of fracturing crosscuts the matrix dolomites in the tangent field these fractures locally form irregular cavity systems which are partly filled with finely crystalline and saddle dolomites these fine crystalline dolomites probably represent dolomite silt and sand derived from brecciation of the earlier matrix dolomite during faulting renewed faulting was responsible for rotation of breccia clasts saddle dolomite was precipitated during at least two phases on the sides and undersides of some clasts and in fractures late stage bladed anhydrites and fracture filling coarse calcites precipitated during hydrocarbon generation presumably in the late cretaceous except locally where source rocks may have been heated by ascending hot brines the timing of dolomitization and fracturing is difficult to determine early fractures most likely occurred in the late devonian to early carboniferous during early burial and mechanical compaction the second phase of fracturing probably occurred during the mississippian to pennsylvanian when the normandville and dunvegan faults underwent movement during the foundering of the peace river arch the third phase of fracturing is linked to the more rapid subsidence and burial by the cretaceous and early tertiary clastic wedge which presumably reactivated some of the earlier faults the combined stratigraphic petrophysical and geochemical data support the following interpretations 1 early dolomite rhombs and patches resulted from the movement of seawater through semi lithified sediment near the sediment water interface or during early compaction 2 matrix dolomites formed at temperatures of between 40 and 65 c and depths of about 500 to 1500 m probable fluid sources for matrix dolomites were devonian brines buried with these and underlying sediments and expelled by mechanical compaction possibly aided by seismic pumping along stage ii fracture fault conduits 3 sucrosic saddle and reworked dolomites postdate stage iii fractures and occurred during deep burial most saddle dolomites formed at temperatures around 100 c but a few formed near 200dc these dolomites formed from warm highly saline basin brines and or from hot brines that ascended along fractures and faults and other stratigraphic conduits from deeper parts of the basin and or the crystalline basement

the granites of the southeast asian tin belt four granite provinces have been delineated each with its own distinctive pattern of mineralization 1 the main range province endogenous greisen bordered vein swarms of cassiterite and wolframite 2 the eastern province magnetite cassiterite skarns base metal sulphides with antimony in thailand 3 the western peninsular thailand burma province endogenous greisen bordered vein swarms and pegmatites of cassiterite and wolframite 4 the north thailand migmatitic province endogenous vein and skarn replacement scheelite and fluorite deposits with some tin and local antimony in all provinces but particularly in the main range granitoids designated as two phase variants have been recognized where xenocrysts and xenoliths of coarse primary texture granite are enclosed in and corroded by an invasive equigranular quartzo feldspathic matrix these rocks form an essential part of the granite sequence in all provinces and have probably resulted from the infiltration and disruption of the host granite by late stage magmatic fluids whole rock geochemistry from peninsular malaysia shows that the granites from the main range and eastern provinces comprise two contrasted suites which correspond approximately to the i and s type categories advocated by chappell white 1974 in addition it is shown that individual plutons within batholiths in the two provinces have distinctive geochemical parameters variation diagrams of plutons having the intrusive sequence primary texture granite two phase granite microgranite show linear trends with increasing sio 2 na 2 o rb w sn and u and decreasing sr ba th and all other major elements

estimating mass and momentum fluxes in a line of cumulonimbus using a single high resolution doppler radar we present a method to derive the vertical wind field at a scale of 1 2 km from a high resolution doppler radar by performing vertical scans in the plane of the mean wind and tracking turbulent features on a scale of several hundred metres in the radial velocity field between consecutive scans the method is applied to a line of cumulonimbus clouds observed by the high resolution chilbolton radar in southern england the storm was not a squall line since it was propagating parallel rather than perpendicular to its length a sequence of scans was taken over an hour long period from these scans we derive the u and w components of the wind updraughts of up to 15 m s 1 are found from these observations the mass flux of a typical storm cell was estimated over the 50 min lifetime of the cell the total mass of air transported from the boundary layer to the upper troposphere was found to be around 50 megatonnes the profile of hour averaged momentum flux against height was then calculated and compared to the vertical shear of the mean horizontal wind it was found that above 4 5 km the momentum flux was down gradient with an equivalent eddy diffusivity of around 103 m2s 1 below this height however the flux was counter gradient with an equivalent eddy diffusivity of around 103m2s 1 we propose a mechanism to explain this behaviour involving the prevalence of precipitation cooling and descent on the downshear side of convergence lines a synthesis of the major wind flows in the storm reveals that despite superficial appearance the storm did not fit the usual multi cell paradigm in which gust fronts play a key roll in triggering new cells downwind rather the convergence lines associated with the convection were more akin to warm frontal surfaces that remain tied to the base of each cell new cells tending to form upwind of older cells copyright 2008 royal meteorological society

dolomite reservoirs porosity evolution and reservoir characteristics systematic analyses of the published record of dolomite reservoirs worldwide reveal that the majority of hydrocarbon producing dolomite reservoirs occurs in 1 peritidal dominated carbonate 2 subtidal carbonate associated with evaporitic tidal flat lagoon 3 subtidal carbonate associated with basinal evaporite and 4 nonevaporitic carbonate sequence associated with topographic high unconformity platform margin buildup or fault fracture reservoir characteristics vary greatly from one dolomite type to another depending upon the original sediment fabric the mechanism by which dolomite was formed and the extent to which early formed dolomite was modified by postdolomitization diagenetic processes e g karstification fracturing and burial corrosion this paper discusses the origin of dolomite porosity and demonstrates the porosity evolution and reservoir characteristics of different dolomite types

stratigraphy and palaeoenvironmental evolution of the mid to upper palaeozoic succession in northwest peninsular malaysia abstract the stratigraphy of the devonian to permian succession in northwest peninsular malaysia is revised the timah tasoh formation consists of black mudstone containing graptolites and tentaculitids indicating a pragian or earliest emsian age the sanai limestone overlies the timah tasoh formation at sanai hill b and contains conodonts indicating a late devonian frasnian to possibly early famennian age in other places late tournaisian chert of the telaga jatoh formation overlies the timah tasoh formation the overlying kubang pasu formation is predominantly composed of mudstone and sandstone and can be divided into 3 subunits from oldest to youngest 1 chepor member 2 undifferentiated kubang pasu formation 3 uppermost kubang pasu formation the ammonoid praedaraelites tuntungensis sp nov is reported and described from the chepor member of bukit tuntung pauh the genus indicates a late visean age for part of the subunit dropstones and diamictites from the chepor member indicate a glacial marine depositional environment the carbo permian undifferentiated kubang pasu formation consists of similar interbedded mudstone and sandstone the uppermost kubang pasu formation of kungurian age consists of coarsening upward cycles of clastics representing a shallow marine wave and storm influenced shoreline the permian chuping limestone also represents shallow marine wave and storm influenced deposits a mid palaeozoic unconformity separating early late devonian rocks from overlying late devonian carboniferous deposits probably marks initiation of rifting on sibumasu which eventually led to the separation of sibumasu from australian gondwana during the late sakmarian early permian

mineralogy nucleation and growth of dolomite in the laboratory and sedimentary environment a review dolomite camg co3 2 forms in numerous geological settings usually as a diagenetic replacement of limestone and is an important component of petroleum reservoir rocks rocks hosting base metal deposits and fresh water aquifers dolomite is a rhombohedral carbonate with a structure consisting of an ordered arrangement of alternating layers of ca2 and mg2 cations interspersed with co32 anion layers normal to the c axis dolomite has r3 symmetry lower than the caco3 r3 c symmetry of calcite primarily due to ca mg ordering high magnesium calcite also has r3 c symmetry and differs from dolomite in that ca2 and mg2 ions are not ordered high magnesium calcite with near dolomite stoichiometry 50 mol mgco3 has been observed both in nature and in laboratory products and is referred to in the literature as protodolomite or very high magnesium calcite many dolomites display some degree of cation disorder ca2 on mg2 sites and vice versa which is detectable using transmission electron microscopy and x ray diffractometry laboratory syntheses at high temperature and pressure as well as studies of natural dolomites show that factors affecting dolomite ordering stoichiometry nucleation and growth include temperature alkalinity ph concentration of mg and ca mg to ca ratio fluid to rock ratio mineralogy of the carbonate being replaced and surface area available for nucleation in spite of numerous attempts dolomite has not been synthesized in the laboratory under near surface conditions examination of published x ray diffraction data demonstrates that assertions of dolomite synthesis in the laboratory under near ambient conditions by microbial mediation are unsubstantiated these laboratory products show no evidence of cation ordering and appear to be very high magnesium calcite elevated temperature and elevated pressure experiments demonstrate that dolomite nucleation and growth always are preceded by very high magnesium calcite formation it remains to be demonstrated whether microbial mediated growth of very high magnesium calcite in nature provides a precursor to dolomite nucleation and growth analogous to reaction paths in high temperature experiments

tertiary diachronic extrusion and deformation of western indochina structural and 40ar 39ar evidence from nw thailand the wang chao and three pagodas fault zones cut the western part of the indochina block and run parallel to the red river fault evidence of intense ductile left lateral shear is found in the lansang gneisses which form a 5 km wide elongated core along the wang chao fault zone dating by 40 ar 39 ar shows that such deformation probably terminated around 30 5 ma the wang chao and three pagodas faults offset the north striking lower mesozoic metamorphic and magmatic belt of northern thailand 40 ar 39 ar results suggest that this belt suffered rapid cooling in the tertiary probably around 23 ma these results imply that the extrusion of the southwestern part of indochina occurred in the upper eocene lower oligocene it probably induced rifting in some basins of the gulf of thailand and in the malay and mekong basins in the oligo miocene the continuing penetration of india into asia culminated with the extrusion of all of indochina along the ailao shan red river fault this occurred concurrently with the onset of e w extension more to the south plotting in a geographical reference frame the diachronic time spans of movement on left lateral faults east and southeast of tibet implies that the northward movement of the indian indenter successively initiated new strike slip faults located farther and farther north along its path

structural evolution of mesozoic peninsular malaysia field evidence from upper palaeozoic and mesozoic strata exposed in peninsular malaysia demonstrates that the structural style degree and orientation of folding axial plane cleavage and faulting in the triassic jurassic and cretaceous rocks of the central basin are remarkably similar in contrast the upper palaeozoic strata especially the carboniferous rocks exposed in the eastern part of the peninsula show multiple phase folding and regional metamorphism unlike anything seen in the mesozoic rocks these observations demonstrate that two important compressional events affected peninsular malaysia one in late permian times and the other in the mid to late cretaceous the late palaeozoic compressional event was a major orogenic mountain building phase with associated emplacement of major permo triassic granite plutons that form the eastern and main ranges no indications were found of the widely reported triassic orogenic compression the palaeotectonic and palaeogeographical implications of these discoveries are important for interpreting the evolution of eastern gondwana and tethys the raub bentong line was an important fault zone active during the mesozoic but does not appear to have been a major tectonic suture since the late palaeozoic we postulate that the permo triassic granites of the eastern belt and those presently exposed in the main range were originally about 30 50 km apart and that triassic and jurassic crustal attenuation and subsidence led to the separation of these two granitic belts by more than 100 km

the bentong raub suture zone abstract it is proposed that the bentong raub suture zone represents a segment of the main devonian to middle triassic palaeo tethys ocean and forms the boundary between the gondwana derived sibumasu and indochina terranes palaeo tethyan oceanic ribbon bedded cherts preserved in the suture zone range in age from middle devonian to middle permian and melange includes chert and limestone clasts that range in age from lower carboniferous to lower permian this indicates that the palaeo tethys opened in the devonian when indochina and other chinese blocks separated from gondwana and closed in the late triassic peninsular malaysia segment the suture zone is the result of northwards subduction of the palaeo tethys ocean beneath indochina in the late palaeozoic and the triassic collision of the sibumasu terrane with and the underthrusting of indochina tectonostratigraphic palaeobiogeographic and palaeomagnetic data indicate that the sibumasu terrane separated from gondwana in the late sakmarian and then drifted rapidly northwards during the permian triassic during the permian subduction phase the east malaya volcano plutonic arc with i type granitoids and intermediate to acidic volcanism was developed on the margin of indochina the main structural discontinuity in peninsular malaysia occurs between palaeozoic and triassic rocks and orogenic deformation appears to have been initiated in the upper permian to lower triassic when sibumasu began to collide with indochina during the early to middle triassic a type subduction and crustal thickening generated the main range syn to post orogenic granites which were emplaced in the late triassic early jurassic a foredeep basin developed on the depressed margin of sibumasu in front of the uplifted accretionary complex in which the semanggol formation rocks accumulated the suture zone is covered by a latest triassic jurassic and cretaceous mainly continental red bed overlap sequence

drainage basin and topographic analysis of a tropical landscape insights into surface and tectonic processes in northern borneo abstract we investigated the recent landscape development of borneo through geomorphic analysis of two large drainage basins rajang and baram basins the extraction of morphometric parameters utilizing digital terrain data in a gis environment focusing on hydrography stream length gradient index ratio of valley floor width to valley height and transverse topographic symmetry factor and topography local relief and relief anomaly was carried out in order to elucidate processes governing drainage and landscape evolution anomalously high and low values of stream length gradient indices of main tributary streams associated with faults and multiple knick points along the channel profiles are linked to deformation events the development of deeply incised v shaped valleys show enhanced incision capability of streams in response to steepening of hillslope gradients following tectonic inputs deflection of streams and probable dynamic reorganization of the drainage system through stream capture processes as feedbacks to tectonic uplift and orographic effect are observed local relief and relief anomaly maps highlight the presence of preserved elevation accordant relict portions of landscapes characterized by low amplitude relief nested between ridgelines in regions of complex folding our results reveal dynamic geomorphic adjustment of the landscape due to perturbations in tectonic and climatic boundary conditions the implication is that the landscape of north borneo experienced a tectonic phase of rapid uplift after 5 ma and undergoes active folding of the rajang group thrust belts in the present day active shortening combined with high rates of denudation in sarawak demonstrates transience emphasized by the drainage system attempting to adjust to tectonic and climatic forcing

multiscale analysis of a mature mesoscale convective complex abstract a multiscale analysis reveals diverse atmospheric structure and processes within a mesoscale convective complex mcc observed during the oklahoma kansas preliminary regional experiment for storm central pre storm experiment this midlatitude system was the second in a series of four mccs that developed and traveled along a quasi stationary frontal zone over the central united states on 3 4 june 1985 objectively analyzed mesoscale upper air soundings encompassing the mcc are interpreted in tandem with more detailed dual doppler radar measurements that disclose the storm s internal airflow and precipitation structure the mature mcc is found to include a variety of local environments and associated weather ranging from tornadic thunderstorms to more linear convective bands and widespread chilling rains a corresponding spectrum of mesoscale ver6cw motion profiles is documented these findings are related to previous composite based portrayals of mccs as well as detailed case studies of simple

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

transitional i s type characteristic in the main range granite peninsular malaysia the dominantly triassic main range granite of peninsular malaysia that occurs west of the paleo tethyan bentong raub suture zone was regarded exclusively as an s type granite the main range dominantly biotite granites are of batholithic proportion and host one of the world s largest tin provinces the s type characteristics include high initial 87sr 86sr isotope ratios 0 710 a narrow range in silica presence of ilmenite and occasional cordierite and andalusite and the presence of pelitic or quartzose meta sedimentary xenoliths however the present review shows that the main range granites also have many features that are more characteristic of i type granites such as the very large scale of plutonism the presence of primary titanite and amphibole occurrence of hornblende bearing mafic enclaves increasing peraluminosity towards the more differentiated end members of the suite and decreasing p2o5 with increasing sio2 contents the moderately peraluminous nature of the bulk main range granite without containing cordierite fe mg garnet or sillimanite is consistent with derivation from a meta sedimentary protolith that was itself undersaturated with respect to al2sio5

hydrothermal dolomite a product of poor definition and imagination abstract the latest dolomite bandwagon is the hydrothermal dolomite model in its present form this bandwagon is doomed or at least very much overstated for at least two reasons 1 there are several definitions of hydrothermal and hardly any author specifies which one s he is using 2 very few of the dolomites hitherto called hydrothermal have been demonstrated to be hydrothermal according to any definition except the worst as presently applied the term hydrothermal dolomite is confusing and or meaningless we suggest to use white s geol soc amer bull 68 1957 1637 time honored definition of hydrothermal as aqueous solutions that are warm or hot relative to its surrounding environment with no genetic implications regarding the fluid source hence a dolomite should be called hydrothermal only if it can be demonstrated to have formed at a higher than ambient temperature regardless of fluid source or drive furthermore this definition does not carry a lower or upper temperature limit even a dolomite formed at 40 c could be hydrothermal by extension dolomites formed at temperatures lower than ambient are not hydrothermal even if they formed at a rather high temperature for example groundwater may penetrate a rock sequence through a highly permeable pathway such that it is heated to 150 c at a depth where the surrounding rock has a temperature of 250 c we suggest to call dolomite formed from this water hydrofrigid dolomite formed in or near thermal equilibrium with the surrounding rocks may be called geothermal furthermore not all saddle dolomite formation requires advection fluid flow to transport mg saddle dolomite can be formed in at least three ways i e from advection local redistribution of older dolomite during stylolitization and as a by product of thermochemical sulfate reduction in a closed or semi closed system only the first and the last of these three possibilities have a chance of being hydrothermal almost all dolomites and dolostones in the western canada sedimentary basin have recently been re interpreted as hydrothermal applying the rationale outlined above reveals however that this basin contains very little hydrothermal dolomite rather most dolomites in this basin and almost all dolostones south of the peace river arch are geothermal and or the proof of a hydrothermal origin has not been made this has important implications beyond the various case studies at hand as attempts to tie dolomitization to orogenic events become moot at least in the southern part of the basin

tectonics and history of the andaman sea region abstract the andaman sea is an active backarc basin lying above and behind the sunda subduction zone where convergence between the overriding southeast asian plate and the subducting australian plate is highly oblique the effect of the oblique convergence has been formation of a sliver plate between the subduction zone and a complex right lateral fault system the late paleocene collision of greater india and asia with approximately normal convergence started clockwise rotation and bending of the northern and western sunda arc the initial sliver fault which probably started in the eocene extended through the outer arc ridge offshore from sumatra through the present region of the andaman sea into the sagaing fault with more oblique convergence due to the rotation the rate of strike slip motion increased and a series of extensional basins opened obliquely by the combination of backarc extension and the strike slip motion these basins in sequence are the mergui basin starting at 32 ma the conjoined alcock and sewell rises starting at 23 ma east basin separating the rises from the foot of the continental slope starting at 15 ma and finally at 4 ma the present plate edge was formed alcock and sewell rises were separated by formation of the central andaman basin and the faulting moved onshore from the mentawai fault to the sumatra fault system bisecting sumatra

the timing of strike slip shear along the ranong and khlong marui faults thailand 1 the timing of shear along many important strike slip faults in southeast asia such as the ailao shan red river mae ping and three pagodas faults is poorly understood we present 40ar 39ar u pb shrimp and microstructural data from the ranong and khlong marui faults of thailand to show that they experienced a major period of ductile dextral shear during the middle eocene 48 40 ma centered on 44 ma which followed two phases of dextral shear along the ranong fault before the late cretaceous 81 ma and between the late paleocene and early eocene 59 49 ma many of the sheared rocks were part of a pre kinematic crystalline basement complex which partially melted and was intruded by late cretaceous 81 71 ma and early eocene 48 ma tin bearing granites middle eocene dextral shear at temperatures of 300 500 c formed extensive mylonite belts through these rocks and was synchronous with granitoid vein emplacement dextral shear along the ranong and khlong marui faults occurred at the same time as sinistral shear along the mae ping and three pagodas faults of northern thailand a result of india burma coupling in advance of india asia collision in the late eocene 37 ma the ranong and khlong marui faults were reactivated as curved sinistral branches of the mae ping and three pagodas faults which were accommodating lateral extrusion during india asia collision and himalayan orogenesis

characteristics genesis and parameters controlling the development of a large stratabound htd body at matienzo ramales platform basque cantabrian basin northern spain abstract at matienzo basque cantabrian basin northern spain a large stratabound htd body 4 by 2 km 2 and 80 400 m thick delimited by two parallel sinistral strike slip faults is exposed in aptian carbonates the margins of the htd body are characterised by dolomite tongues indicating that some limestone beds were more prone to dolomitisation however no clear relationship between htd occurrence and precursor limestone facies can be established massive limestone beds as found at the top of the htd body act as barriers to hydrothermal processes since no dolomite is present in or above these beds three types of dolomites have been differentiated i e 1 matrix 2 coarse crystalline and 3 zebra dolomite the distribution of the dolomite types is attributed to ascending fluid flow and changing degree of dolomite oversaturation the dolomite body was formed by two dolomitisation phases under burial conditions no indications for a synsedimentary early diagenetic dolomitisation have been observed the first dolomitisation phase is characterized by ferroan dolomite and the second by non ferroan dolomite the two htd phases are characterised by depleted 18 o values ranging between 10 and 16 v pdb 13 c values similar to the aptian albian marine signature and homogenisation temperatures of primary fluid inclusions between 120 c and 150 c the dolomitising fluid was enriched in 87 sr compared to aptian seawater excluding the latter as an unmodified fluid source for dolomitisation microthermometry of primary fluid inclusions indicates that the dolomitising fluid evolved from a moderate saline 9 7 14 0 wt nacl to a more saline 10 9 21 0 wt nacl h 2 o nacl brine the dolomitising fluid likely originated from evaporated seawater fluid circulation through the dolomitised strata is inferred to have taken place during the tectonically active period of the late albian throughout which important sinistral strike slip movements along basement faults occurred

evolution of deformation styles at a major restraining bend constraints from cooling histories mae ping fault zone western thailand the c 500 km long mae ping fault zone trends nw se across thailand into eastern myanmar and has probably undergone in excess of 150 km sinistral motion during the cenozoic a large c 150 km long restraining bend in this fault zone lies on the western margin of the chainat duplex the duplex is a low lying region dominated by north south trending ridges of mesozoic and palaeozoic sedimentary metamorphic and igneous rocks flanked by flat post rift basins of pliocene recent age to the north and south a review of published cooling age data plus new apatite and zircon fission track results indicates that significant changes in patterns of exhumation occurred along the fault zone with time oldest uplift and erosion eocene occurred in the umphang gneiss region west of an inferred thrust dominated restraining bend setting from 36 ma to 30 ma exhumation was strongest north of the duplex along the nw se trending segment of the fault zone at the northern exiting bend of the chainat duplex this region of the fault zone is characterized by a mid crustal level shear zone 5 6 km wide lan sang gneisses that passes to the nw into an apparent strike slip duplex geometry the deformation is interpreted to have occurred during passage around the northern restraining bend which resulted in vertical thickening uplift erosion and extensional collapse of the northern side of the shear zone this concentration of deformation at the bends at the ends of the restraining bend is thought to be a characteristic of strike slip dominated restraining bends following late oligocene early miocene extension there is apatite fission track evidence for 22 18 ma exhumation in the chainat duplex that coincides with a phase of inversion in the phitsanulok basin to the north the miocene recent history of the chainat duplex is one of minor sinistral and dextral displacements related to a rapidly evolving stress field influenced by the numerous tectonic reorganizations that affected se asia during that time

petrogenesis of malaysian granitoids in the southeast asian tin belt part 2 u pb zircon geochronology and tectonic model in our complementary geochemical study part 1 the malaysian granitoids of the southeast asian tin belt were divided into a middle permian to late triassic i type dominated eastern province indochina terrane and a triassic to early jurassic transitional i s type main range province sibumasu terrane separated by the bentong raub suture zone which closed in the late triassic previous geochronology has relied on only a few u pb zircon ages together with k ar and whole rock rb sr ages that may not accurately record true magmatic ages we pre sent 39 new high precision u pb zircon ion microprobe ages from granitoids and vol canics across the malay peninsula our results show that ages from the eastern province granitoids span 289 220 ma with those from the main range province granitoids being entirely late triassic spanning 227 201 ma a general westerly younging magmatic trend across the malay peninsula is considered to refl ect steepening and roll back of the bentong raub subduction zone during progressive closure of paleo tethys the youngest ages of subduction related granites in the eastern province roughly coincide with the youngest ages of marine sedimentary rocks along the paleo tethyan suture zone our petrogenetic and u pb zircon age data support models that relate the eastern province granites to pre collisional andean type magmatism and the western main range province granites to syn and post collisional crustal melting of sibumasu crust during the late triassic tin mineralization was mainly associated with the latter phase of magmatism two alternative tectonic models are discussed to explain the triassic evolution of the malay peninsula the fi rst involves a second late triassic to jurassic or early cretaceous east dipping subduction zone west of sibumasu where subduction related hornblende and biotite bearing granites along sibumasu are paired with main range crustal melt tinbearing granites analogous to the bolivia cordilleran tin bearing granite belt the second model involves westward underthrusting of indochina beneath the west malaya main range province resulting in crustal thickening and formation of tin bearing granites of the main ranges cretaceous granitoids are also present locally in singapore ubin diorite on tioman island in the noring pluton of the stong complex eastern province and along the sibumasu terrane in southwest thailand and burma myanmar refl ecting localized crustal melting

active tectonic deformation along rejuvenated faults in tropical borneo inferences obtained from tectono geomorphic evaluation abstract the island of borneo is enveloped by tropical rainforests and hostile terrain characterized by high denudation rates owing to such conditions studies pertaining to neotectonics and consequent geomorphic expressions with regard to surface processes and landscape evolution are inadequately constrained here we demonstrate the first systematic tectono geomorphic evaluation of north borneo through quantitative and qualitative morphotectonic analysis at sub catchment scale for two large drainage basins located in sarawak the rajang and baram basins the extraction of morphometric parameters utilizing digital elevation models arranged within a gis environment focuses on hypsometric curve analysis distribution of hypsometric integrals through spatial autocorrelation statistics relative uplift values the asymmetry factor and the normalized channel steepness index hypsometric analysis suggests a young topography adjusting to changes in tectonic boundary conditions autocorrelation statistics show clusters of high values of hypsometric integrals as prominent hotspots that are associated with less eroded young topography situated in the fold and thrust belts of the interior highlands of borneo high channel steepness and gradients 200 m0 9 are observed in zones corresponding to the hotspots relative uplift values reveal the presence of tectonically uplifted blocks together with relatively subsided or lesser uplifted zones along known faults sub catchments of both basins display asymmetry indicating tectonic tilting stream longitudinal profiles demonstrate the presence of anomalies in the form of knickzones without apparent lithological controls along their channel reaches surfaces represented by cold spots of low hi values and low channel gradients observed in the high elevation headwaters of both basins are linked to isolated erosional planation surfaces that could be remnants of piracy processes the implication of our results is that borneo experiences active folding of the rajang group fold thrust belt to present and these events reactivated old major faults and minor related dislocations from geomorphic analysis associated with sedimentary record we posit that the terrain could have undergone high uplift rates since 5 ma or multi phased uplift with periodic intermittent pulses of high and low uplift rates

phanerozoic plate boundaries in mainland se asia the himalayas and tibet recently available geological data on tibet yunnan and burma facilitate recognition of phanerozoic subduction systems and two continental fragments of gondwanaland which extend through mainland se asia a cambrian subduction system and 5 mesozoic early caenozoic collision belts are identified in the region indochina eastern thailand and central tibet accreted to china in the early triassic western se asia and s tibet separated from gondwanaland in the permian or early triassic and collided with asia in the late triassic and the western burma island arc system collided with asia in the jurassic upper triassic flysch and schist in the eastern indoburman ranges were accreted to western burma in the jurassic early cretaceous during eastward subduction and formation of a back arc thrust belt following collision of greater india with arc complexes to the n in the cretaceous and with tibet in the early eocene western burma moved northwards about 450 km along the sagaing namyin ridge thrust transform fault formation of the 3 major belts of tin granites and the porphyry copper deposits in the region took place in specific tectonic settings within the subduction systems and collision belts

the basins of sundaland se asia evolution and boundary conditions abstract most of the basins developed in the continental core of se asia sundaland evolved since the late cretaceous in a manner that may be correlated to the conditions of the subduction in the sunda trench by the end of mesozoic times sundaland was an elevated area composed of granite and metamorphic basement on the rims which suffered collapse and incipient extension whereas the central part was stable this promontory was surrounded by a large subduction zone except in the north and was a free boundary in the early cenozoic starting from the palaeogene and following fractures initiated during the india eurasia collision rifting began along large faults mostly n s and nnw sse strike slip which crosscut the whole region the basins remained in a continental fluvio lacustrine or shallow marine environment for a long time and some are marked by extremely stretched crust phu khanh natuna n makassar or even reached the ocean floor spreading stage celebes flores western sundaland was a combination of basin opening and strike slip transpressional deformation the configuration suggests a free boundary particularly to the east trench pull associated with the proto south china sea subduction java sulawesi trench subduction rollback in the early miocene australian blocks reached the sunda subduction zone and imposed local shortening in the south and southeast whereas the western part was free from compression after the indian continent had moved away to the north this suggests an important coupling of the sunda plate with the indo australian plate both to se and nw possibly further west rollback had ceased in the java sumatra subduction zone and compressional stress was being transferred northwards across the plate boundary the internal compression is expressed to the south by shortening which is transmitted as far as the malay basin in the late miocene most of the sunda plate was under compression except the tectonically isolated andaman sea and the damar basins in the pliocene collision north of australia propagated toward the north and west causing subduction reversal and compression in the short lived damar basin docking of the philippine plate confined the eastern side of sundaland and created local compression and uplift such as in nw borneo palawan and taiwan transpressional deformation created extensive folding strike slip faulting and uplift of the central basin and arakan yoma in myanmar minor inversion affected many thailand rift basins all the other basins record subsidence the uplift is responsible for gravity tectonics where thick sediments were accumulated sarawak ne luconia bangladesh wedge

tectonic evolution of the sibumasu indochina terrane collision zone in thailand and malaysia constraints from new u pb zircon chronology of se asian tin granitoids three principal granite provinces are defined across se asia as follows 1 the western thailand myanmar burma province consists of hornblende biotite i type granodiorite granites and felsic biotite k feldspar garnet tourmaline granites associated with abundant tin mineralization in greisen type veins new ion microprobe u pb dating results from phuket island show zircon core ages of 212 2 and 214 2 ma and a thermal overprint with rims of 81 2 1 2 and 85 75 ma 2 the north thailand west malaya main range province has mainly s type biotite granites and abundant tin mineralization resulting from crustal thickening following collision of the sibumasu plate with indochina during the mid triassic biotite granites around kuala lumpur contain extremely u rich zircons up to 38000 ppm that yield ages of 215 7 and 210 7 ma 3 the east malaya province consists of dominantly permian triassic i type hornblende biotite granites but with subordinate s type plutons and a type syenite gabbros biotite k feldspar granites from tioman island off the east coast of malaysia also yield a zircon age of 80 1 ma showing cretaceous magmatism in common with province 1 geological and u pb geochronological data suggest that two east dipping in present day coordinates subduction zones are required during the triassic one along the bentong raub palaeo tethyan suture and the other west of the phuket burma province 1 belt supplementary material a full description of u pb analytical methods used and data tables are available at www geolsoc org uk sup18523

tectonic evolution of the mogok metamorphic belt burma myanmar constrained by u th pb dating of metamorphic and magmatic rocks 1 the mogok metamorphic belt mmb extends for over 1500 km along the western margin of the shan thai block from the andaman sea north to the eastern himalayan syntaxis previous geochronology has suggested that a long lasting jurassic early cretaceous subduction related event resulted in emplacement of granodiorites and orthogneisses 171 120 ma and a poorly constrained tertiary metamorphic event on the basis of new u pb isotope dilution thermal ionization mass spectrometry and u th pb laser ablation multicollector inductively coupled plasma mass spectrometer geochronology presented here we propose two tertiary metamorphic events affected the mmb in burma the first was a paleocene event that ended with intrusion of crosscutting postkinematic biotite granite dikes at 59 ma a second metamorphic event spanned late eocene to oligocene at least from 37 possibly 47 to 29 ma this resulted in the growth of metamorphic monazite at sillimanite grade growth of zircon rims at 47 43 ma sillimanite muscovite replacing older andalusite and synmetamorphic melting producing garnet and tourmaline bearing leucogranites at 45 5 0 6 ma and 24 5 0 7 ma these data imply high temperature sillimanite muscovite metamorphism peaking at 680 c and 4 9 kbar between 45 and 33 ma to around 606 656 c and 4 4 4 8 kbar at 29 3 0 5 ma the later metamorphic event is older than 24 5 0 3 ma the age of leucogranites that crosscut all earlier fabrics our structural and geochronological data suggest that the mmb links north to the unexposed middle or lower crust rocks of the lhasa terrane south tibet and east to high grade metamorphic core complexes in northwest thailand

structural controls on polyphase hydrothermal dolomitization in the kinta valley malaysia paragenesis and regional tectono magmatism abstract in the eastern side of the malay peninsula thick successions of limestone formations preserve important records of the mesozoic and cenozoic tectonic events here we investigate the strata and fracture bound hydrothermal dolomites in the palaeozoic carbonates of the kinta valley western peninsular malaysia based on their textural and morphologic characteristics structural relationships with the host rock different facies types and associations with hydrothermal calcite and low grade metamorphic marble we attempt to trace their polyphase origin and relationship with thermo tectonic events of the region a detailed evaluation of the nature of brecciation and crystallization of polyphase dolomites dolomitic limestones limestones and marble under the influences of episodic faulting is associated with the regional structural geology with emphasis on pre existing fault reactivations granitic emplacement and progressive thermal influence supply of mg2 from the host rock for dolomitization limited and episodic influx of circulating fluids and cessation of thermo tectonic evolution with progressive cooling are also inferred correlating the geological events in western peninsular malaysia with regional structural dynamics reveals that the major deformation episodes exerted first order controls on the loci of dolomite occurrences the occurrence geometry and structural relationships of the dolomites were controlled by successive magmatic events whereas the intensity of replacement dolomitization was controlled by host rock texture and varied bulk chemistry together with the nature of circulating fluids

the kinematic history of the khlong marui and ranong faults southern thailand abstract the khlong marui fault kmf and ranong fault rf are major nne trending strike slip faults which dissect peninsular thailand they have been assumed to be conjugate to the nw trending three pagodas fault tpf and mae ping fault mpf in northern thailand which experienced a diachronous reversal in shear sense during india eurasia collision it follows that the kmf and rf are expected to show the opposite shear sense and a slip sense reversal at a similar time to the tpf and mpf new field data from the kmf and rf reveal two phases of ductile dextral shear separated by campanian magmatism paleocene to eocene post kinematic granites date the end of this phase while a brittle sinistral phase deforms the granites and has exhumed the ductile fault rocks the timing of these movements precludes formation of the faults in response to himalayan extrusion tectonics instead they formed near the southern margin of a late cretaceous paleocene orogen and may have been influenced by variations in the rate of subduction ahead of india and australia north south compression prior to reactivation of the subduction zone around southern sundaland in the eocene caused widespread deformation in the over riding plate including sinistral transpression on the kmf and rf

late cretaceous extension and exhumation of the stong and taku magmatic and metamorphic complexes ne peninsular malaysia fragmentation of large continental areas by post orogenic extension requires favourable geodynamic conditions and frequently occurs along pre existing suture zones or nappe contacts as exemplified by the stong and taku magmatic and metamorphic complexes of northern peninsular malaysia for this case we have employed a field and microstructural kinematic study combined with low temperature thermo chronology to analyse the tectonic and exhumation history the results show that the late palaeozoic triassic indosinian orogeny created successive phases of burial related metamorphism shearing and contractional deformation this orogenic structure was subsequently dismembered during a cretaceous thermal event that culminated in the formation of a large scale late santonian early maastrichtian extensional detachment genetically associated with crustal melting the emplacement of syn kinematic plutons and widespread migmatisation the emplacement of these magmatic rocks led to an array of simultaneously formed structures that document deformation conditions over a wide temperature range represented by amphibolite and greenschist facies mylonites and as well as brittle structures such as cataclastic zones and normal faults that formed during exhumation in the footwall of the detachment the formation of this detachment and a first phase of late cretaceous cooling was followed by renewed eocene oligocene exhumation as evidenced from our fission track ages we infer that an initial cretaceous thermal anomaly was responsible for the formation of an extensional gneiss dome associated with simple shear and rotation of normal faults these cretaceous processes played a critical role in the establishment of the presently observed crustal structure of peninsular malaysia

observations and simulation of elevated nocturnal convection initiation on 24 june 2015 during pecan abstractthe environment of elevated nocturnal deep convection initiation ci on 24 june 2015 is investigated using radiosonde data from the plains elevated convection at night pecan field experi

mesoscale organization of springtime rainstorms in oklahoma abstract radar reflectivity and raingage data obtained during six springtimes indicate the types of mesoscale organization that occur in association with major rain events in oklahoma at least 25 mm of rain in 24 h over an area exceeding 12 500 km2 in these storms the primary rain area is found to be a contiguous region of precipitation 10s to 100s of km in scale that consists partly of deep convection and partly of stratiform rain the patterns of rain formed by the convective and stratiform areas comprise a continuous spectrum of mesoscale structures about two thirds of the cases examined exhibited variations on the type of organization in which convective cells arranged in a moving line are followed by a region of stratiform rain storm organization was graded according to the degree to which it matched an idealized model of this leading line trailing stratiform structure the precipitation pattern was further graded according to whether its structure was relatively symmetric with respect to an a

hydrothermal dolomitization in platform and basin carbonate successions during thrusting a hydrocarbon reservoir analogue mesozoic of venetian southern alps italy abstract the early jurassic dolomitized carbonates in the venetian alp represent a surface analogue of the hydrocarbon exploration targets in adriatic offshore and po plain italy dolomitization affected the carbonate platform of monte zugna formation lower jurassic and the neptunian dikes breccia in the pelagic maiolica formation uppermost jurassic lower cretaceous improving the poro perm characteristics petrography stable isotope strontium isotope ratio trace element and fluid inclusion analyses were carried out on samples from the monte grappa anticline which is the direct analogue for subsurface the petrographic analyses showed a first pervasive replacement dolomitization phase d1 followed by volumetrically less important dolomite cement precipitation phases d2 d3 ds the same quite wide range of oxygen isotope 9 to 2 v pdb is observed in all dolomite types the 13 c range is in the positive field of marine derived carbonate from 0 5 to 3 2 pdb the trace element analysis showed a slight enrichment in fe and mn contents in the monte zugna dolostones with respect the original limestone the same dolomite precipitation temperature up to 105 c th was observed in the replacement and cement dolomites suggesting a unique dolomitization event this temperature largely higher than the maximum burial temperature about 50 c supports a hydrothermal origin of the dolomitizing fluids which had a seawater to brackish composition the data collected suggest a hydrothermal dolomitization occurring during to the south alpine thrusting according to the squeegee model the interpretation is consistent with the dolomitization model proposed for similar jurassic successions in the central southern alps this study indicates that the deformed foreland and thrust fold belts carbonates in po plain and adriatic offshore are suitable to be dolomitized and therefore reflect an efficient hydrocarbon exploration play

triggering and evolution of a deep convective system in the mediterranean sea modelling and observations at a very fine scale gaining a deeper physical understanding of the high impact weather events which repeatedly affected the western mediterranean basin in recent years on the coastal areas of eastern spain southern france and northern italy is strongly motivated by the social request to reduce the casualties and the economical impacts due to these highly localized and hardly predictable phenomena in october 2014 an extreme event hit genoa city centre less than 3 years after a very similar event which occurred in november 2011 taking advantage of the availability of both observational data and modelling results at the micro alpha meteorological scale this article provides insights about the triggering mechanism and the subsequent spatio temporal evolution of the genoa 2014 back building mesoscale convective system the major finding is the effect of a virtual mountain created over the ligurian sea by the convergence of a cold and dry jet outflowing from the po valley and a warm and moist low level southeasterly jet within the planetary boundary layer

cenozoic carbonates in southeast asia implications for equatorial carbonate development cenozoic equatorial carbonate production was at its most extensive and diverse in the seas of southeast asia yet the carbonates of this region remain poorly documented this paper presents the first published review of carbonate deposition during the cenozoic collating sedimentological data for carbonate successions throughout the region current models of warm water carbonate platform evolution sedimentation and facies distribution inspired by studies of the classic sub tropical areas provide inadequate analogues for the evaluation of modern or cenozoic equatorial carbonates in southeast asia the equatorial carbonates differ in being dominated by bioclasts coated grains and associations with evaporites or dolomites are rare the carbonate systems occur in a range of depositional settings which were often affected by coeval tectonism siliciclastic input or volcanism an understanding of the carbonate depositional environments spatial facies distributions and controls on deposition and diagenesis is essential in order to characterize equatorial carbonate development and to evaluate their considerable economic potential

epigenetic dolomitization and the origin of xenotopic dolomite texture abstract xenotopic texture which is commonly observed in pre cenozoic rocks is defined here as a mosaic of anhedral crystals with irregular or curved intercrystalline boundaries and usually undulatory extinction xenotopic dolomite texture is similar in appearance to neomorphic limestone textures idiotopic dolomite texture euhedral to subhedral crystals with straight intercrystalline boundaries contrasts with xenotopic texture and is commonly observed in both cenozoic and more ancient dolomites texture may be controlled by the temperature at which crystals grow crystal growth theory predicts that at low temperature a smooth crystal surface is energetically favored and atoms are added to crystal faces layer by layer with dislocations acting as nucleation sites this results in faceted crystals and euhedral to subhedral crystal mosaics above a critical roughening temperature crt a rough surface is energetically favored surface nucleation does not require dislocations and atoms are randomly added to the crystal surface resulting in nonfaceted growth and an anhedral crystal mosaic it is hypothesized that a critical roughening temperature exists for dolomite above 50 c xenotopic dolomites are produced by dolomitization of limestone and or neomorphic recrystallization of dolomite at elevated temperature above the crt after burial idiotopic dolomites are produced below the crt by near surface processes and are occasionally produced above crt if growth inhibiting effects of the solution or impurities stabilize crystal faces calcite has a crt below 25 c and therefore develops anhedral crystal mosaics characteristic of neomorphic texture both at near surface and at elevated temperatures synthetic xenotopic dolomite was produced in the laboratory at 250 c and 300 c by dolomitization of aragonite and calcite skeletal fragments and by recrystallization neomorphism of nonstoichiometric cenozoic dolomites xenotopic dolomite resulted from the metamorphic recrystallization of the idiotopic hueco dolomite permian texas near the marble canyon intrusion at temperatures between 350 c and 600 c hydrothermal dolomitization of periclase calcite marble near the intrusion also resulted in a xenotopic texture xenotopic dolomite in the galena group ordovician wisconsin was produced by neomorphism of a preexisting dolomite during the emplacement of lead zinc sulfides at temperatures between 80 c and 227 c in the trenton limestone ordovician michig n xenotopic dolomite replaced limestone during the migration of hot 50 c fluids along fracture systems xenotopic dolomite was not observed in cenozoic dolomites that were subjected to temperatures near surface values only

tectonic framework and phanerozoic evolution of sundaland abstract sundaland comprises a heterogeneous collage of continental blocks derived from the india australian margin of eastern gondwana and assembled by the closure of multiple tethyan and back arc ocean basins now represented by suture zones the continental core of sundaland comprises a western sibumasu block and an eastern indochina east malaya block with an island arc terrane the sukhothai island arc system comprising the linchang sukhothai and chanthaburi blocks sandwiched between this island arc formed on the margin of indochina east malaya and then separated by back arc spreading in the permian the jinghong nan uttaradit and sra kaeo sutures represent this closed back arc basin the palaeo tethys is represented to the west by the changning menglian chiang mai inthanon and bentong raub suture zones the west sumatra block and possibly the west burma block rifted and separated from gondwana along with indochina and east malaya in the devonian and were accreted to the sundaland core in the triassic west burma is now considered to be probably cathaysian in nature and similar to west sumatra from which it was separated by opening of the andaman sea basin south west borneo and or east java west sulawesi are now tentatively identified as the missing argoland which must have separated from nw australia in the jurassic and these were accreted to se sundaland in the cretaceous revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of sundaland and adjacent regions are presented

mechanical and fracture stratigraphy using examples from core studies this article shows that separate identification of mechanical stratigraphy and fracture stratigraphy leads to a clearer understanding of fracture patterns and more accurate prediction of fracture attributes away from the wellbore mechanical stratigraphy subdivides stratified rock into discrete mechanical units defined by properties such as tensile strength elastic stiffness brittleness and fracture mechanics properties fracture stratigraphy subdivides rock into fracture units according to extent intensity or some other observed fracture attribute mechanical stratigraphy is the by product of depositional composition and structure and chemical and mechanical changes superimposed on rock composition texture and interfaces after deposition fracture stratigraphy reflects a specific loading history and mechanical stratigraphy during failure because mechanical property changes reflect diagenesis and fractures evolve with loading history mechanical stratigraphy and fracture stratigraphy need not coincide in subsurface studies current mechanical stratigraphy is generally measurable but because of inherent limitations of sampling fracture stratigraphy is commonly incompletely known to accurately predict fractures in diagenetically and structurally complex settings we need to use evidence of loading and mechanical property history as well as current mechanical states

massive hydrothermal dolomites in the southwestern cantabrian zone spain and their relation to the late variscan evolution abstract large scale massive burial dolomitization affected upper carboniferous carbonates of the southwestern variscan cantabrian zone spain replacive and void filling dolomites formed and were post dated by calcite cementation the process of dolomitization was due to the circulation of hypersaline and hydrothermal marine derived brines controlled by rock anisotropies the dolomites probably formed in early permian time during post thrusting orocline formation in an extensional setting lithospheric delamination induced increased heat flow and allowed thermal convection of the fluids the dolomites from the cantabrian zone are excellently exposed and represent an interesting outcrop analogue for hydrocarbon reservoirs elsewhere in comparable geotectonic settings of the european variscan orogen large masses of similar dolomites could have formed if mg rich brines were available

modeled and observed variations in storm divergence and stratiform rain production in southeastern texas abstractstorm divergence profiles observed by an s band doppler radar are compared to ensemble simulations of 10 disparate precipitating systems occurring in warm season weakly baroclinic and strongly baroclinic environments in southeastern texas eight triply nested mesoscale model simulations are conducted for each case using single and double moment microphysics with four convective treatments i e two convective parameterizations and explicit versus parameterized convection at 9 km observed and simulated radar reflectivities are objectively separated into convective stratiform and nonprecipitating anvil columns and comparisons are made between ensemble mean echo coverages and levels of nondivergence lnds in both the model and observations storms occurring in less baroclinic environments have more convective rain area less stratiform rain area and more elevated divergence profiles the model ensemble and observations agree best for well organized leading line trailing stratiform systems

deformation history and u pb zircon geochronology of the high grade metamorphic rocks within the klaeng fault zone eastern thailand abstract in eastern thailand the klaeng fault zone includes a high grade metamorphic rock assemblage named nong yai gneiss which extends about 30 km in a nw se direction along the fault zone the rocks of this brittle fault strand consist of amphibolite to granulite grade gneissic rocks structural analysis indicates that the rocks in this area experienced three distinct episodes of deformation d1 d3 the first d1 formed large scale nw se trending isoclinal folds f1 that were reworked by small scale tight to open folds f2 during the second deformation d2 d1 and d2 resulted from ne sw shortening during the triassic indosinian orogeny before being cross cut by leucogranites d1 and d2 fabrics were then reworked by d3 sinistral shearing including shear planes s3 and mineral stretching lineations l3 la mc icp ms u pb zircon dating suggested that the leucogranite intrusion and the magmatic crystallization took place at 78 6 0 7 ma followed by a second crystallization at 67 1 to 72 1 0 6 ma both crystallizations occurred in the late cretaceous and it is suggested were tectonically influenced by se asian region effects of the west burma and shan thai sibumasu collision or development of an andean type margin the sinistral ductile movement of d3 was coeval with the peak metamorphism that occurred in the eocene during the early phases of the india asia collision

structures and dynamics of quasi 2d mesoscale convective systems abstract recently three distinct archetypes for midlatitude linear mesoscale convective systems mcss have been identified this article focuses on the fundamentals of two of these archetypes convective lines with trailing stratiform ts precipitation and convective lines with leading stratiform ls precipitation both the ts and ls modes typically exhibit quasi 2d reflectivity patterns and quasi 2d environmental storm relative wind fields ongoing work has revealed that there are three common flow structures for these quasi 2d mcss front fed ts systems which are sustained by front to rear storm relative inflow as well as front fed ls and rear fed ls systems which are sustained by rear to front storm relative inflow this paper summarizes the observed structures of the front fed ts front fed ls and rear fed ls modes and then outlines an idealized numerical experiment in which these modes were simulated the authors analyze the basic simulated kinematic and microphysical structures and provid

multistage hydrothermal dolomites in the middle devonian givetian carbonates from the guilin area south china pervasive dolomites occur preferentially in the stromatoporoid biostromal or reefal facies in the basal devonian givetian carbonate rocks in the guilin area south china the amount of dolomites however decreases sharply in the overlying frasnian carbonate rocks dolostones are dominated by replacement dolomites with minor dolomite cements replacement dolomites include 1 fine to medium planar e floating dolomite rhombs rd1 2 medium to coarse planar s patchy mosaic dolomites rd2 and 3 medium to very coarse nonplanar anhedral mosaic dolomites rd3 they post date early submarine cements and overlap with stylolites two types of dolomite cements were identified planar coarse euhedral dolomite cements cd1 and non planar saddle dolomite cements cd2 they post date replacement dolomites and predate late stage calcite cements that line mouldic vugs and fractures the replacementdolomiteshaved 18 ovalues from 13ae7to 9ae7 vpdb d 13 cvalues from 2ae 7t o 1 ae5 vpdb and 87 sr 86 sr ratios from 0ae7082 to 0ae7114 fluid inclusiondataofrd3dolomitesyieldhomogenizationtemperatures th of136 149 c and salinities of 7ae2 11ae2 wt nacl equivalent these data suggest that the replacive dolomitization could have occurred from slightly modified sea water and or saline basinal fluids at relatively high temperatures probably relatedtohydrothermalactivitiesduringthelatestgivetian middlefammenian and early carboniferous times compared with replacement dolomites cd2 cements yield lowerd 18 o values 14ae2to 9ae3 vpdb lowerd 13 c values 3ae0 to 0ae7 vpdb higher 87 sr 86 sr ratios 0ae7100 and higher th values 171 209 c whichcorrespondtotrappingtemperatures tr between260and300 c after pressure corrections these data suggest that the dolomite cements precipitated from higher temperature hydrothermal fluids derived from underlying siliciclastic deposits and were associated with more intense hydrothermal events during permian early triassic time when the host dolostones were deeply buried the petrographic similarities between some replacement dolomites and cd2 dolomite cements and the partial overlap in 87 sr 86 sr and d 18 o values suggest neomorphism of early formed replacement dolomites that were exposed to later dolomitizing fluids however the dolomitization was finally stopped through invasion of meteoric water as a result of basin uplift induced by the indosinian orogeny from the early middle triassic as indicated by the decrease in salinities in the dolomite cements in veins 5ae1 0ae4 wt nacl equivalent calcite cements generally yield the lowest d 18 ovalues 18ae5to 14ae3 vpdb variabled 13 cvalues 11ae3to 1ae2 vpdb andhighthvalues 145 170 c andlowsalinities 0 0ae2wt naclequivalent indicating an origin of high temperature dilute fluids recharged by meteoric water in the course of basin uplift during the indosinian orogeny faults were

outcrop analog for trenton black river hydrothermal dolomite reservoirs mohawk valley new york geochemical analysis and field relations of linear dolomite bodies occurring in outcrop in the mohawk valley of new york suggest that the area has undergone a significant fault related hydrothermal alteration the dolomite occurs in the lower ordovician tribes hill formation which is regionally a lower ordovician shaley limestone with patchy dolomitization the outcrop has an en echelon fault fracture and fold pattern a three dimensional 3 d ground penetrating radar gpr survey of the quarry floor has helped to map out faults fractures anticlines synclines and the extent of dolomitization most of the dolomitization occurs in fault bounded synclines or sags flanked by anticlines the dolomite structures are highly localized occurring around faults and are absent away from the faults and fractures trenches cut across the outcrop help relate offset along faults to the overall geometry of the dolomitized bodies geochemical analysis although helpful in characterizing the conditions of dolomitization does not define its origin absolutely this study uses fluid inclusions stable isotopes 3 d gpr core analysis and surficial observations which all show a link between faulting dolomitization and other hydrothermal alteration although the outcrop is much too small and shallow to act as a producing gas field it serves as a scaled analog for the trenton black river hydrothermal dolomite reservoirs of eastern united states it may therefore be studied to help petroleum geologists characterize existing gas plays and prospect future areas of exploration

dolomite characteristics and diagenetic model of the calcari grigi group asiago plateau southern alps italy an example of multiphase dolomitization a multidisciplinary study conducted over the carbonate platform deposits of the liassic calcari grigi group southern alps highlighted how the use of outcrop analogues can contribute to better define the distribution of dolomitic bodies related to fault networks to characterize the petrophysical properties of the dolomitic sequence and unravel a complex diagenetic history this study was carried out in the asiago plateau southernmost part of the eastern southern alps northern italy which provides excellent outcrops of the jurassic calcari grigi group the dolomitization of the jurassic sequence is variable in terms of stratigraphic extension and geographic distribution in the studied localities the dolomitization is generally limited to the mount zugna formation and is characterized by an undulatory front with sub vertical dolomitic chimneys along the major faults within this unit and often associated with faults stacked high porosity and permeability bed parallel dolomitic bodies are developed that show excellent petrophysical properties the dolomitic intervals are characterized by pervasive unimodal and patchy polymodal dolomite crystals thin section cathodoluminescence isotopic and fluid inclusion analyses were used to constrain the paragenetic evolution of the sequence which is similar in all the studied localities the first dolomitization stage is marked by zoned dolomite crystals with a dull luminescent core the porosity is thought to have increased after this stage with dark blue luminescent dolomite accompanied by the corrosion of older crystals the appearance of saddle dolomite marks the onset of the porosity reduction stage ending with the infilling of vugs and the remaining open pores with calcite cement the diagenetic evolution locally stopped at the saddle dolomite stage with the complete occlusion of the remaining pores paragenetic and fluid inclusion data suggest an evolutionary trend of increasing temperatures and decreasing salinity toward brackish fluids responsible for dolomite and calcite precipitation the integration of the available data seem to indicate that the diagenetic evolution of the study area is related to i the interplay between evolving fluids from marine to brackish ii the burial of the sequence increasing temperature and iii the evolution of the hydrogeological system fault and fracture network fluid mixing this complex paragenetic evolution is strongly linked to the evolution of the porosity framework that evolved from a good widespread network in the early stages of the burial history to a confined system in the later stages due to reduction of porosity by the deposition of late calcite and dolomite cements

granitic magmatism basement ages and provenance indicators in the malay peninsula insights from detrital zircon u pb and hf isotope data abstract the malay peninsula lies on two continental blocks sibumasu and east malaya which are intruded by granitoids in two provinces the main range and eastern previous models propose that permian triassic granitoids are subduction related and syn to post collisional we present 752 u pb analyses that were carried out on zircons from river sands in the malay peninsula of these 243 grains were selected for hf isotope analyses our data suggest a more complex sibumasu east malaya collision history 176hf 177hfi ratios reveal that permian triassic zircons were sourced from three magmatic suites a permian crustally derived granitoids b early middle triassic granitoids with mixed mantle crust sources and c late triassic crustally derived granitoids this suggests three permian triassic episodes of magmatism in the malay peninsula two of which occurred in the eastern province although the exact timing of the sibumasu east malaya collision remains unresolved current data suggest that it occurred before the late triassic probably in late permian early triassic our data also indicate that sibumasu and east malaya basements are chronologically heterogeneous but predominantly of proterozoic age some basement may be neoarchaean but there is no evidence for basement older than 2 8 ga finally we show that hf isotope signatures of triassic zircons can be used as provenance indicators

stratigraphic architecture and fracture controlled dolomitization of the cretaceous khami and bangestan groups an outcrop case study zagros mountains iran this work has been carried out as part of a joint study between norsk hydro now statoil and nioc national iranian oil company

nested strike slip duplexes and other evidence for late cretaceous palaeogene transpressional tectonics before and during india eurasia collision in thailand myanmar and malaysia the late cretaceous palaeogene structural and tectonic events in the northern region of sundaland represent a poorly known but potentially important orogenic development in se asia extensive late cretaceous s type granites extending from malaysia through thailand to myanmar have long been used to infer an episode of crustal thickening an inference supported by the presence of late cretaceous eocene ophiolites in myanmar however structural evidence for a well developed associated fold and thrust belt has been lacking apatite and zircon fission track studies of thailand indicate a broad regional uplift from about 80 ma to 40 ma suggesting an episode of crustal thickening but the uplift amount is modest and not that expected for a major fold and thrust belt left lateral motion on major nw se trending strike slip fault zones mae ping and three pagodas faults in myanmar and thailand has been attributed to himalayan tibetan escape tectonics this paper demonstrates that the fault zones are considerably more complicated than just nw se trends they are a network of branching faults with important north south trends as well as nw se trends they form large scale nested strike slip duplex structures and affect a region over 1000 km long and up to 250 km wide this diffuse branching network of strike slip fault trends may represent a substantial late cretaceous palaeogene transpressional belt himalayan escape tectonics represent later increments of deformation with both oligocene sinistral and late oligocene recent dextral reactivation

structurally controlled hydrothermal dolomite reservoir facies an overview structurally controlled hydrothermal dolomite htd reservoir facies and associated productive leached limestones are major hydrocarbon producers in north america and are receiving increased exploration attention globally they include multiple trends in the ordovician locally silurian and devonian of the michigan appalachian and other basins of eastern canada and the united states and in the devonian and mississippian of the western canada sedimentary basin they also occur in jurassic hosts along rifted atlantic margins in the jurassic cretaceous of the arabian gulf region and elsewhere hydrothermal dolomitization is defined as dolomitization occurring under burial conditions commonly at shallow depths by fluids typically very saline with temperature and pressure t and p higher than the ambient t and p of the host formation the latter commonly is limestone proof of a hydrothermal origin for htd reservoir facies requires integration of burial thermal history plots fluid inclusion temperature data and constraints on timing of emplacement hydrothermal dolomite reservoir facies are part of a spectrum of hydrothermal mineral deposits that include sedimentary exhalative lead zinc ore bodies and htd hosted mississippi valley type sulfide deposits all three hydrothermal deposits show a strong structural control by extensional and or strike slip wrench faults with fluid flow typically focused at transtensional and dilational structural sites and in the hanging wall transtensional sags above negative flower structures on wrench faults are favored drilling sites for htd reservoir facies saddle dolomite in both replacive and void filling modes is characteristic of htd facies for many reservoirs matrix replacive dolomite and saddle dolomite appear to have formed near contemporaneously and from the same fluid and temperature conditions the original host facies exerts a major influence on the lateral extent of dolomitization resultant textures pore type and pore volume breccias zebra fabrics shear microfractures and other rock characteristics record short term shear stress and pore fluid pressure transients particularly proximal to active faults high temperature hydrothermal pulses may alter kerogen in host limestones a process designated forced maturation basement highs underlying sandstone and or carbonate aquifers probably overpressured and overlying and internal shale seals and aquitards also may constrain or influence htd emplacement although many questions and uncertainties remain particularly in terms of mg and brine source and mass balance recognition and active exploration of the htd play continues to expand increasing use of three dimensional seismic imagery and seismic anomaly mapping combined with horizontal drilling oblique to linear trends defined by structural sags helps to reduce risk