translation invariant attributes for effective lithofacies discrimination this study introduces translation invariant attributes using the hadamard and rapid transforms of seismic data to discriminate lithofacies unlike the fourier transform which projects the data onto a set of orthogonal sinusoidal waveforms the hadamard transform projects data onto a set of square waves called walsh functions the hadamard transform is particularly good at finding repeating stacked vertical sequences crossplot analysis indicates translation invariant attributes for horizon based time windows are less sensitive to horizon interpretation errors in the reservoir interval therefore translation invariant attributes can be used to find a particular geologic pattern of interest in a reservoir interval these attributes have been applied successfully to discriminate the lithofacies in a reservoir interval of interest for a 3d seismic survey in the upper assam basin of india the sand shale thickness ratio at the drilled locations within the reservoir interval is used to define the lithofacies categories using the discriminant function analysis of each of the conventional seismic principal component and translation invariant sets of attributes we create a corresponding discriminant score map the probability density function pdf of the discriminant score at the drilled locations transforms the pdf to lithofacies categories the comparative analysis presented in this study indicates that translation invariant attributes are superior to conventional seismic and principal component attributes in discriminating the lithofacies

postcollisional magmatism in the south tien shan variscan orogenic belt kyrgyzstan evidence for high temperature and high pressure collision abstract the south tien shan collisional belt consists of two segments divided by the largest in the central asia talas fergan diagonal dextral strike slip fault the narrow eastern kokshal segment where the late carboniferous collision was followed by continental subduction of the precambrian tarim platform beneath the caledonian kazakh continent is characterized by overthickened 60 65 km crust and ultrahigh pressure coesite eclogite regional metamorphism the permian postcollisional magmatism is represented there by a small volume of relatively cool two mica peraluminous leucogranites moderate volumes of k rich calk alkaline transitional from i to s type granites and several large plutons of a type rapakivi granites the latest could have formed by a two step process involving 1 syncollisional submersion of the tarim platform granulitic basement into the mantle accompanied by considerable heating of the source rocks 2 rapid postcollisional exhumation accompanied by decompression and extensive high degree of melting in the western alay segment which is much wider the collision was not followed by continental subduction the thickness of crust decreases westward dramatically from 60 to 45 km the alay segment is characterized by the high temperature low pressure regional metamorphism and significant volume of permian shoshonitic ultrapotassic magmatism connected with postcollisional strike slip tectonics the shoshonitic magmatism is indicative of lithosphere delamination and input of mantle derived melts and heat into the crust in contrast to the kokshal segment the postcollisional granitic magmatism in the alay segment is represented by relatively hot cordierite and sillimanite bearing strongly peraluminous s type granites locally rooted in the high temperature low pressure metamorphic rocks and large volume of calc alkaline i type granitoides of mixed crust mantle origin

the role of arc arc collision in accretionary orogenesis insights from 320 ma tectono sedimentary transition in the karamaili area nw china

early mesozoic southward subduction history of the mongol okhotsk oceanic plate evidence from geochronology and geochemistry of early mesozoic intrusive rocks in the erguna massif ne china abstract in this paper we present new zircon u pb ages hf isotope data and whole rock major and trace element data for early mesozoic intrusive rocks in the erguna massif of ne china and we use these data to constrain the history of southward subduction of the mongol okhotsk oceanic plate and its influence on ne china as a whole the zircon u pb dating indicates that early mesozoic magmatic activity in the erguna massif can be subdivided into four stages at 246 ma 225 ma 205 ma and 185 ma the 246 ma intrusive rocks comprise a suite of high k calc alkaline diorites quartz diorites granodiorites monzogranites and syenogranites with i type affinities the 225 ma intrusive rocks consist of gabbro diorites and granitoids and they constitute a bimodal igneous association the 205 ma intrusive rocks are dominated by calc alkaline i type granitoids that are accompanied by subordinate intermediate mafic rocks the 185 ma intrusive rocks are dominated by i type granitoids accompanied by minor amounts of a types these early mesozoic granitoids mainly originated by partial melting of a depleted and heterogeneous lower crust whereas the coeval mafic rocks were probably derived from partial melting of a depleted mantle modified by subduction related fluids the rock associations and their geochemical features indicate that the 246 ma 205 ma and 185 ma intrusive rocks formed in an active continental margin setting related to the southward subduction of the mongol okhotsk oceanic plate the 225 ma bimodal igneous rock association formed within an extensional environment in a pause during the subduction process of the mongol okhotsk oceanic plate every magmatic stage has its own corresponding set of porphyry deposits in the southeast of the mongol okhotsk suture belt taking all this into account we conclude the following 1 during the early mesozoic the mongol okhotsk oceanic plate was subducted towards the south beneath the erguna massif but with a pause in subduction at 225 ma and 2 the southward subduction of the mongol okhotsk oceanic plate not only caused the intense magmatic activity but was also favorable to the formation of porphyry deposits

geochemical and isotopic constraints on the evolution of late paleozoic dyke swarms in west junggar xinjiang china abstract there are two sets nw and ne trending of basic to intermediate dykes emplaced into both the carboniferous volcanic sedimentary strata and undeformed plutons in the west junggar northern xinjiang china the early to middle permian nw trending dykes are mainly diorite and diorite porphyrite characterized by moderate mg 55 66 1 belonging to calc alkaline series the late permian ne trending dykes are diabase and diabase porphyritic belonging to tholeiitic series with low mg 41 4 58 3 both sets of dykes exhibit enriched liles depleted nb ta hrees and highly depleted isotopic signatures end 5 1 8 1 isr 0 70379 0 70675 trace element and isotopic data indicate that the nw trending dykes were generated by partial melting of a recently metasomatized subducted cold lithospheric mantle sclm coupled with variable assimilation of juvenile crustal materials whereas the ne trending dykes were derived from the partial melting of a similar sclm with lower degree of metasomatism than the nw trending dykes which were subsequently subjected to magma modification by the fractional crystallization of olivine pyroxene and or plagioclase the arc signatures exhibited by the trace element patterns of both sets of dykes in north xinjiang imply a recently metasomated mantle in this region formed during subduction prior to late paleozoic the mafic dyke swarms in this region are the products of phanerozoic continental growth in north xinjiang indicating widespread lithospheric extension

bimodal magmatism produced by delamination geochemical evidence from late palaeozoic volcanic rocks from the yili block western tianshan northwestern china

approaches to defining reservoir physical properties from 3 d seismic attributes with limited well control an example from the jurassic smackover formation alabama much industry interest is centered on how to integrate well data and attributes derived from 3 d seismic data sets in the hope of defining reservoir properties in interwell areas unfortunately the statistical underpinnings of the methods become less robust in areas where only a few wells are available as might be the case in a new or small field especially in areas of limited well availability we suggest that the physical basis of the attributes selected during the correlation procedure be validated by generating synthetic seismic sections from geologic models then deriving attributes from the sections we demonstrate this approach with a case study from appleton field of southwestern alabama in this small field dolomites of the jurassic smackover formation produce from an anticlinal feature about 3800 m deep we used available geologic information to generate synthetic seismic sections that showed the expected seismic response of the target formation then we picked the relevant horizons in a 3 d seismic data volume that spanned the study area using multiple regression we derived an empirical relationship between three seismic attributes of this 3 d volume and a log derived porosity indicator our choice of attributes was validated by deriving complex trace attributes from our seismic modeling results and confirming that the relationships between well properties and real data attributes were physically valid additionally the porosity distribution predicted by the 3 d seismic data was reasonable within the context of the depositional model used for the area results from a new well drilled after our study validated our porosity prediction although our structural prediction for the top of the porosity zone was erroneous these results remind us that seismic interpretations should be viewed as works in progress which need to be updated when new data become available

geochronology and geochemistry of the triassic bimodal volcanic rocks and coeval a type granites of the olzit area middle mongolia implications for the tectonic evolution of mongol okhotsk ocean abstract the olzit volcanism in middle mongolia comprises a bimodal suite of basalts and peralkaline rhyolites adjacent to the main mongolia lineament the basalts are characterized by enrichment in lile and lree and depletion in hfse with typical sr nd isotopic signatures end t 2 50 to 0 38 and 87sr 86sr i 0 7058 0 7063 indicating they were likely derived from partial melting of an enriched lithospheric mantle modified by subducted slab derived fluids the rhyolites show a close affinity to a type granites with enrichment in lile and lree and depletion in nb ta and ti they also show a significant negative eu anomaly and have end t values ranging from 0 50 to 1 38 and initial 87sr 86sr ratios ranging from 0 7022 to 0 7200 suggesting the rhyolites stem from partial melting of crustal rocks rather than fractional crystallization of the basaltic melt the rhyolite porphyry yields a shrimp zircon u pb age of 207 2 ma mswd 1 42 indicating the bimodal volcanic suite formed in the late triassic the miarolitic per alkaline granite and biotite bearing granite which are associated with the bimodal volcanic rocks show typical a type granitic geochemical affinity with end t 0 89 0 91 and 87sr 86sr i 0 7021 0 7043 indicating they are likely generated by partial melting of crustal rocks similar to the rhyolitic end member of bimodal suite the miarolitic per alkaline granite and biotite bearing granite yielded shrimp zircon u pb ages of 209 2 ma mswd 0 91 and 213 3 ma mswd 1 65 respectively which are nearly coeval with the age of the bimodal volcanic suites in view of the new geochemical and chronological data in this study we suggest the olzit late triassic bimodal volcanic rocks together with the coeval a type granites represent a back arc basin extensional environment which probably related to the roll back of mongol okhotsk oceanic plate during the southward subduction under the central mongolia microcontinent

an early paleoproterozoic high k intrusive complex in southwestern tarim block nw china age geochemistry and tectonic implications abstract systematic geochronologic geochemical and nd isotopic analyses were carried out for an early paleoproterozoic high k intrusive complex exposed in southwestern tarim nw china the results provide a better understanding of the paleoproterozoic tectonic evolution of the tarim block zircon u pb age dating indicates two paleoproterozoic magmatic episodes occurring at ca 2 41 ga and ca 2 34 ga respectively which were followed by a ca 1 9 ga metamorphic event the 2 41 ga granodiorite adamellite suite shares characteristics of late to post orogenic metaluminous a type granites in its high alkalinity na2o k2o 7 6 9 3 total ree 410 788 ppm zr 370 660 ppm and y 21 7 58 4 ppm contents end t values for the suite range from 3 22 to 4 71 and accordingly the nd modal ages t2dm vary between 3 05 ga and 3 17 ga based on geochemical data the 2 34 ga suite can be subdivided into two sub suites namely a type and s type however both types have comparable nd isotope compositions end t 0 41 to 2 08 and similar narrow t2dm ranges 2 76 2 91 ga geochemical and nd isotopic data for the high k intrusive complex in conjunction with the regional geological setting suggest that both the 2 41 ga suite and the 2 34 ga a type sub suite might have been produced by partial melting of the archean mafic crust in a continental rift environment the s type sub suite is thought to have formed by partial melting of felsic pelites and or metagreywackes recycled from archean crust ttg gabbro enclaves with positive end t value 2 15 have been found to be intermingling within the 2 34 ga suite ca 2 34 2 36 ga gabbroic dykes and adamellites have previously been documented in eastern tarim these observations indicate that the high k intrusions may reflect the emergence of depleted mantle upwelling beneath the tarim block at that time we suggest a three stages model for the precambrian crustal evolution in the tarim block 1 the formation of proto crust ttg by ca 2 5 ga 2 episodes of felsic magmatism possibly occurring in continental rift environments at ca 2 41 ga and ca 2 34 2 36 ga and 3 ca 1 9 ga metamorphism that may represent the solidification of the precambrian basement of the tarim block

hydrogen and oxygen isotope geochemistry of a type granites in the continental margins of eastern china hydrogen and oxygen isotope studies of both whole rock and mineral separates were carried out for five representative atype granites in eastern china from north to south the whole rock d d and d 18 o values vary from 2145 to 282 and from 21 2 to 5 0 for nianzishan pluton from 2135 to 2110 and from 1 6 to 6 7 for shanhaiguan pluton and from 2145 to 2111 and from 1 5 to 9 1 for laoshan massif respectively the highest whole rock dd and d 18 o values are observed in suzhou pluton and range from 281 to 259 and from 3 5 to 9 2 respectively homogeneous d d and d 18 o values are found in kuiqi massif ranging from 2113 to 299 and from 5 6 to 8 5 respectively the results show that the large variabilities in the hydrogen and oxygen isotope ratios are mainly related to the diverse processes of magma evolution such as magma degassing fractional crystallization as well as post magmatic alteration by local meteoric water under subsolidus conditions the initial d d and d 18 o values of the a type granites in eastern china are constrained to be about 250 5 and 7 5 1 0 respectively this is consistent with mantle like protoliths for granitoid rocks and thus precludes the possibility that the a type granites is derived from the anatexis of the 18 o rich upper crust however recycling of crustal materials by earlier subduction cannot be excluded in the processes of generating the a type granitic magmas the variation in the ddepletion of the granites with latitude implies that the paleogeographic localities of the a type granites have not changed significantly since the mesozoic q 2000 elsevier science b v all rights reserved

use of volume based 3 d seismic attribute analysis to characterize physical property distribution a case study to delineate sedimentologic heterogeneity at the appleton field southwestern alabama u s a abstract in this paper we illustrate the use of 3 d seismic attribute studies for predicting the distribution of physical properties in the subsurface using a data set consisting primarily of digital logs and seismic data we show how correlations can be made between seismic attributes and physical properties porosity and how those relationships can be exploited to predict the distribution of the property of interest in three dimensions the results of these studies 1 provide quantitative site specific 3 d models of physical properties that are of more use for applied studies than qualitative 2 d models commonly derived from facies modeling or sequence stratigraphic analysis 2 are generally more geologically reasonable than studies based on geostatistics alone 3 can provide sedimentary geologists with fundamental insights into depositional and or diagenetic controls on the distribution of properties of interest 4 need to be rigorously evaluated by integrating other types of data and analyses and 5 are best thought of as supplementing rather than replacing conventional geologic analyses the concepts and methods we illustrate may have application in various branches of sedimentary geology our study area is appleton field in southern alabama at this location we predict the 3 d distribution of porosity in carbonates of the upper jurassic smackover formation using a probabilistic neural network and a combination of four attributes our results suggest that porosity was best developed and preserved in thrombolite facies of the reef front

using multi attribute neural networks classification for seismic carbonate fades mapping a workflow example from mid cretaceous persian gulf deposits abstract seismic facies mapping in large seismic surveys can be time consuming even if only a basic overview of the facies distribution is needed therefore this study outlines an approach for the use of volume based seismic attributes from 2d surveys for automated seismic facies mapping within carbonate settings the study area is located in the central persian gulf offshore iran the interval of interest is the mid cretaceous sarvak formation which is part of the extensive cretaceous shallow water carbonate platform of the eastern arabian plate a set of nine volume based seismic attributes calculated from time amplitude and frequency information of post stacked 2d seismic data was chosen to characterize geological information within the interval of interest the volume based attributes were supplemented by two grid based attributes to highlight structural elements the geological significance of each attribute was evaluated by comparing it with results of seismic sedimentological geomorphological studies furthermore statistical methods were applied to highlight direct relationships amongst the attributes the results of these tests were then used to choose a limited set of attributes for neural network based multi attribute classifications the results show that seismic attributes derived from 2d surveys can be used to map basic seismic facies types in carbonate settings and that the outlined general approach might be applied in other studies

geochronology and geochemistry of the heilongjiang complex and the granitoids from the lesser xing an zhangguangcai range implications for the late paleozoic mesozoic tectonics of eastern ne china abstract an integrated study on two subduction related units the heilongjiang complex and magmatic rocks in the lesser xing an zhangguangcai range was carried out to explore the paleozoic to early mesozoic tectonic framework of the eastern northeast china with a focus on the jiamusi block the heilongjiang complex which is considered as the suture between the jiamusi and songliao blocks is composed of blueschist amphibolite and ultramafic rocks the blueschist from the yilan area shows geochemical features similar to oib and has a 206pb 238u age of 288 2 ma which is interpreted as the crystallization age of protolith formed in an ocean island setting in contrast amphibolite from the xiachengzi area shows geochemical features similar to n morb zircons in this amphibolite show magmatic character and yield a 206pb 238u age of 248 4 ma which is interpreted as the protolith age calcic amphiboles in the amphibolite give a 40ar 39ar plateau age of 195 3 ma which is interpreted as the metamorphic age of the heilongjiang complex magmatic rocks in the lesser xing an zhangguangcai range mostly belong to i type granites that were formed in an active continental margin setting zircon u pb ages of these granites range from 200 ma to 174 ma with a westward younging trend shown as two groups of emplacing ages of 200 ma in the east and 180 ma in the west our new data support an early occurrence likely since the early permian of a large ocean namely the mudanjiang ocean in the area whose subduction resulted in the metamorphic unit the heilongjiang complex and the magmatic unit the lesser xing an zhangguangcai range in the jurassic

potential risks when using seismic attributes as predictors of reservoir properties the advance of our ability to generate seismic attributes and the growing emphasis on production geophysics has led to the widespread use of seismic attributes as predictors of reservoir properties in many cases we can show using seismic modeling or rock physics a physically justifiable relationship between a seismic attribute and the reservoir property of interest when this is true we are able to greatly reduce the uncertainty of interwell predictions of reservoir properties

evidence against subduction related magmatism for the jiaoziyan gabbro northern dabie shan china the largest gabbroic intrusion jiaoziyan in the northern orthogneiss of the dabie shan was investigated to test whether such intrusions represent arc related or collision related magma as postulated in recent regional tectonic models the jiaoziyan intrusions comprise a gabbro monzogabbro suite and are locally characterized by cumulus textured anhydrous silicates petrologic indications against arc magmatism include 1 coexisting olivine plagioclase compositions beyond the documented range of arc gabbros and 2 a compositional trend of al ti ratios in the gabbroic clinopyroxenes that is significantly different from subduction related gabbros worldwide in contrast the jiaoziyan rocks are mineralogically similar to rift gabbros geochronologic and geometric arguments against collision related magmatism i e as a consequence of slab breakoff include the following 1 crystallization of the jiaoziyan mafic intrusion postdated the triassic 245 240 ma subduction and peak orogenic metamorphism by 100 m y and 2 the rocks of the dabie cretaceous magmatic suite including jiaoziyan are on the footwall plate rather than on the hanging wall of the triassic subduction zone framework and do not show a linear distribution these observations argue that the voluminous early cretaceous magmatism in the northern orthogneiss is geodynamically unrelated to the qinling dabie orogeny but was caused by extensional tectonism related to regional magmatic underplating beneath the thinned dabie crust

expanding the snow climate classification with avalanche relevant information initial description of avalanche winter regimes for southwestern canada existing snow climate classifications are primarily based on meteorological parameters that describe the average weather during the main winter months however field experience and measurements show that the characteristics of weak snowpack layers including type structure and details of formation are primary indicators of avalanches that form despite its importance in the characteristics of local avalanche activity weak layer information is currently not a formal part of any snow climate classification scheme the focus of this study is the analysis of persistent snowpack weak layers in southwestern canada observations from the industrial information exchange infoex of the canadian avalanche association are used to examine the frequency sequence and distribution of the most common types of snowpack weakness and their related avalanche activity the results show significant temporal and spatial variations in areas with the same snow climate characteristics the weak layer patterns observed in transitional snow climate areas are clearly more complex than a simple combination of maritime and continental influences avalanche winter regime is suggested as a new classification term that describes the snowpack structures relevant for local avalanche activity and complements the existing snow climate classification system three preliminary avalanche winter regimes are identified for southwestern canada

geochemistry and geochronology of carboniferous volcanic rocks in the eastern junggar terrane nw china implication for a tectonic transition the carboniferous tectonic setting of the junggar terrane northern xinjiang nw china has long been a matter of debate voluminous carboniferous volcanic rocks are widely distributed in the karamaili area the southern part of the eastern junggar terrane early carboniferous rocks comprise basalts and basaltic andesites with enrichment of lree and lile and depletion of hfse and uniformly high end t 3 7 to 4 0 late carboniferous rocks consist of basalts basaltic andesites rhyolites and minor dacites and can be subdivided into basic and felsic groups the basic rocks are depleted in hfse and show variable high end t 4 8 to 6 9 they have higher cr and ni and lower na2o u and th contents than early carboniferous basic rocks the felsic rocks show a type affinity with typical enrichment of alkalis lree and hfse and strong depletion in ba sr eu and ti they have high values of end t and zircon ehf t 11 6 to 17 9 new la icpms zircon u pb analyses constrain their emplacement to late carboniferous time 306 5 314 3 ma the carboniferous basic rocks show negative zr hf anomalies and low th ce 0 07 and th la 0 06 0 16 excluding significant crustal contamination during magma evolution they have low la ba 0 03 0 12 ce y 3 and tb yb n 2 and variable ba th 28 318 and ba la 3 1 34 suggesting that they were derived from a main spinel with minor garnet lherzolite mantle source metasomatized by slab derived fluids the late carboniferous felsic rocks were produced when upwelling asthenosphere triggered partial melting of juvenile lower crust the early carboniferous volcanism occurred in an island arc setting related to the southward subduction of the paleo junggar ocean plate whereas the late carboniferous rocks erupted in a post collisional extensional setting thus a rapid tectonic transition from arc to post collisional extension may have occurred between early and late carboniferous and probably resulted from slab break off or lithospheric delamination

seismic attributes a historical perspective a seismic attribute is a quantitative measure of a seismic characteristic of interest analysis of attributes has been integral to reflection seismic interpretation since the 1930s when geophysicists started to pick traveltimes to coherent reflections on seismic field records there are now more than 50 distinct seismic attributes calculated from seismic data and applied to the interpretation of geologic structure stratigraphy and rock pore fluid properties the evolution of seismic attributes is closely linked to advances in computer technology as examples the advent of digital recording in the 1960s produced improved measurements of seismic amplitude and pointed out the correlation between hydrocarbon pore fluids and strong amplitudes bright spots the introduction of color printers in the early 1970s allowed color displays of reflection strength frequency phase and interval velocity to be overlain routinely on black and white seismic records interpretation workstations in the 1980s provided

the kamusite a2 type granites in the karamaili tectonic belt xinjiang nw china tracing staged postcollisional delamination in the eastern junggar

seismic facies analysis based on speech recognition feature parameters abstractseismic facies analysis plays an important role in seismic stratigraphy seismic attributes have been widely applied to seismic facies analysis one of the most important steps is to optimize the most sensitive attributes with regard to reservoir characteristics using different attribute combinations in multidimensional analyses will yield different solutions acoustic waves and seismic waves propagating in an elastic medium follow the same law of physics the generation process of a speech signal based on the acoustic model is similar to the seismic data of the convolution model we have developed the mel frequency cepstrum coefficients mfccs which have been successfully applied in speech recognition as feature parameters for seismic facies analysis information about the wavelet and reflection coefficients is well separated in these cepstrum domain parameters specifically information about the wavelet mainly appears in the low domain part and information about the reflection coefficients

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

revisiting early middle jurassic igneous activity in the nanling mountains south china geochemistry and implications for regional geodynamics abstract early middle jurassic igneous rocks 190 170 ma are distributed in an e w trending band within the nanling tectonic belt and have a wide range of compositions but are only present in limited volumes this scenario contrasts with the uniform but voluminous middle late jurassic igneous rocks 165 150 ma in this area the early middle jurassic rocks include oceanic island basalt oib type alkali basalts tholeiitic basalts and gabbros bimodal volcanic rocks syenites a type granites and high k calc alkaline granodiorites geochemical and isotopic data indicate that alkaline and tholeiitic basalts and syenites were derived from melting of the asthenospheric mantle with asthenosphere derived magmas mixing with variable amounts of magmas derived from melting of metasomatized lithospheric mantle in comparison a type granites in the study area were probably generated by shallow dehydration related melting of hornblende bearing continental crustal rocks that were heated by contemporaneous intrusion of mantle derived basaltic magmas and high k calc alkaline granodiorites resulted from the interaction between melts from upwelling asthenospheric mantle and the lower crust the early middle jurassic magmatic event is spatially variable in terms of lithology geochemistry and isotopic systematics this indicates that the deep mantle sources of the magmas that formed these igneous rocks were significantly heterogeneous and magmatism had a gradual decrease in the involvement of the asthenospheric mantle from west to east these variations in composition and sourcing of magmas in addition to the spatial distribution and the thermal structure of the crust mantle boundary during this magmatic event indicates that these igneous rocks formed during a period of rifting after the indosinian orogeny rather than during subduction of the paleo pacific oceanic crust

definition of subsurface stratigraphy structure and rock properties from 3 d seismic data abstract this paper summarizes how three dimensional 3 d seismic technology is being used primarily in the petroleum industry to define subsurface structure stratigraphy and rock properties a 3 d seismic data volume a provides a more accurate image of the subsurface than can be obtained with 2 d seismic methods b is continuous and so has a much greater spatial sampling than is obtained with 2 d seismic or other subsurface data e g wells and c can be viewed and interpreted interactively from a variety of perspectives thus enhancing the interpreter s ability to generate an accurate description of subsurface features of interest seismic interpretation was once the almost exclusive realm of geophysicists however most 3 d seismic interpretation today is conducted by multidisciplinary teams that integrate geophysical geological petrophysical and engineering data and concepts into the 3 d seismic interpretation these factors plus proper survey design help to increase the chances of success of a 3 d seismic interpretation project although there are cases where the technology is not appropriate or cannot be applied for economic reasons or otherwise the general success of 3 d seismic has led it to become a mainstay of the petroleum industry the approach and technology first developed in that industry have potential applications in other applied and fundamental earth science disciplines including mining environmental geology structural geology and stratigraphy

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

timing of synorogenic granitoids in the south qinling central china constraints on the evolution of the qinling dabie orogenic belt abstract the ca 400 km long granitoid belt in the south qinling is believed to be a synorogenic product of the collision between the north and south china blocks along the qinling dabie orogenic belt in central china single and multigrain zircon u pb dating of six of these granitoid bodies indicate that the granitoids were formed between documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 220 pm 1 end document and documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage m

comparison of linear regression and a probabilistic neural network to predict porosity from 3 d seismic attributes in lower brushy canyon channeled sandstones southeast new mexico the lower brushy canyon formation of the delaware basin new mexico consists of a series of overlying sand filled channels and associated fans separated by laterally extensive organic siltstone and carbonate interbeds this laterally and vertically complex geology creates the need for precise interwell estimation of reservoir properties in this paper we integrate wireline log and 3 d seismic data to directly predict porosity in the area of an existing oil field in southeast new mexico the 3 d seismic data were used to interpret the location of major stratigraphic markers between wells and these seismic horizons were used to constrain a time window for a volume based attribute analysis stepwise regression and crossvalidation were used to combine seismic attributes to predict porosity in wells where the porosity was known from the well logs the results of a linear regression porosity model showed good correlation r2 0 74 between seven seismic attributes and the observed porosity logs at 11 wells in

rock property and seismic attribute analysis of a chert reservoir in the devonian thirty one formation west texas u s a in west texas fractured chert reservoirs of devonian age haveproducedmorethan700millionbarrelsofoil aboutthe same amount of mobile petroleum remains in place these reservoirsarecharacterizedbymicroporosity theyareheterogeneous and compartmented which results in recovery of less than 30 of the oil in place in this case study the objective was to use cores petrophysical logs rock physics and seismic attributes to characterize porosity and field scale fractures therelationsamongporosity velocity andimpedancewereexploredandalsoreactionsamongproduction impedance and lineaments observed in 3d attribute volumes laboratory core data show that gassmann s fluid substitution equation works well for microporous tripolitic chert also laboratry measurements show excellent linear correlation between p wave impedance and porosity volumetric calculations of reflector curvature and seismic inversion of acoustic impedance were combined to infer distribution of lithofaciesandfracturesandtopredictporosity statisticalrelationswereestablishedbetweenp wavevelocityandporosity measured from cores between p wave impedance and producing zones and between initial production rates and seismic fracture lineaments the strong quantitative correlation between thick bedded chert lithofacies and seismic impedance was used to map the reservoir a qualitative inverse relation between the first 12 months of production and curvaturelineamentswasdocumented

subsidence of the paris basin and its bearing on the late variscan lithosphere evolution a comparison between plate and chablis models abstract in this study two different models for the lithospheric thermal evolution are used to predict the long term subsidence of the paris basin the plate or chablis models have a constant temperature or constant heat flow at the base of the lithosphere these boundary conditions yield a different thermal relaxation time for a given equilibrium lithospheric thickness the final thermal steady state does not depend on the boundary condition fixed at the base of the lithosphere the thermal evolution of the lithosphere is computed taking into account temperature and pressure dependent thermal characteristics metamorphism in the crust top crustal erosion and phase transition in the mantle spinel garnet the long term tectonic subsidence of the paris basin constrains the mesozoic thermal evolution of the lithosphere and the amplitude of the initial thermal anomaly the chablis model including the effects of spinel garnet phase transition predicts present day lithospheric thickness in better agreement with observation than the plate model the chablis model involves a basal heat transfer of 37 mw m2 similar to the value beneath oceanic plates the long term subsidence of the paris basin obviously results from the decay of a thermal anomaly initiated during late variscan times we first assume that at 300 ma the lithosphere was less than 150 km thick and the thickened crust started returning to its present thickness 35 km by uniform lithospheric extension the subsidence data can be explained by short stephano autunian as well as long stephano triassic lasting extension these hypotheses both implicitly refer to extensional collapse of the variscan belt however the evolution of the variscan belt from 350 to 300 ma may have involved almost no crustal thickening but an anomalously thin lithosphere ca 55 km the corresponding thermal evolution of the lithosphere is computed using the chablis model with an initially high heat transfer of 61 mw m2 at the base of the base of the lithosphere at 280 ma this heat transfer is tuned to 40 mw m2 leading to lithospheric cooling from 280 to 30 ma which can also explain the paris basin subsidence for the short lasting extension hypothesis the late variscan lithospheric evolution predicted with the chablis model yields paleogeography magmatism and retrograde p t t paths in good agreement with those reported from areas around the paris basin conversely the plate model does not allow mantle melting during the end of carboniferous and permian times the long lasting extension hypothesis does not explain the paleogeographic evolution the timing of magmatism and retrograde p t paths showing isothermal decompression the hypothesis with a strong lithospheric delamination cannot be ruled out however it is less plausible than the extensional collapse hypothesis

late paleozoic post collisional magmatism in the eastern tianshan belt northwest china new insights from geochemistry geochronology and petrology of bimodal volcanic rocks abstract the late carboniferous to permian marks an important phase of terrane amalgamation through accretion collision in the central asian orogenic belt caob the tianshan belt forms part of this sequence where the post collisional event generated an e w trending bimodal volcanic zone that extends for ca 500 km from the southern bogda mt to the easternmost tianshan belt here we report the petrology geochemistry and geochronology of the bimodal volcanic rocks to characterize the post collisional tectonic evolution in late paleozoic the major element chemistry of the basalt and rhyolite samples indicates a bimodal high k calc alkaline affinity the basalts are characterized by high abundance in tio2 th u and pb and depletion in nb ta and p together with slight enrichment in lree contents and low hfse lree ratios the rhyolites show a close affinity to aluminous a type granites with enrichment in k na zr ce y and depletion in p nb ta and ti they also exhibit fractionated ree patterns with prominent negative eu anomalies the petrographic and geochemical data suggest that this bimodal rock series was generated in a post collisional setting the mafic rocks are likely derived from a metasomatized lithospheric mantle assimilation of different crustal components played a minor role in the genesis of these basaltic rocks the la icp ms analysis on zircons from four rhyolites and two basalts yielded similar ages ranging from 295 8 2 8 to 293 3 1 7 ma suggesting an early permian event zircons from the basalts show a wide ehf t range from 0 49 to 13 whereas those from the rhyolites show two groups of ehf t values from 5 to 3 and from 6 to 12 suggesting a mixing of crust mantle material the magmatic zircons from the bimodal volcanic rocks yielded two peaks of tdm2 between 600 820 ma and 1160 1360 ma probably representing two significant episodes of continental crust growth the bimodal volcanic rocks are correlated with the early stage of post collision our results suggest that vertical crustal growth through mantle derived magmas in post collisional setting also played a major role in the construction of the caob

geochronology geochemistry and deformation history of late jurassic early cretaceous intrusive rocks in the erguna massif ne china constraints on the late mesozoic tectonic evolution of the mongol okhotsk orogenic belt abstract this paper presents new zircon and sphene u pb ages biotite and hornblende 40 ar 39 ar ages hf isotopic data and geochemical data for five mesozoic plutons in the erguna massif of ne china these data are used to constrain the late mesozoic tectonic evolution of the mongol okhotsk orogenic belt this new dating when combined with previously published ages indicates that the late jurassic early cretaceous j 3 k 1 intrusive rocks can be subdivided into three stages that represent periods of magmatism during the late jurassic 155 ma early early cretaceous 137 ma and late early cretaceous 123 ma in addition the rocks have undergone later deformation recorded by peak ages of 137 and 123 ma the late jurassic and early early cretaceous intrusive rocks in the study area are dominantly syenogranites and are either a type granites or are classified as alkaline series suggesting that they formed in an extensional environment the late early cretaceous intrusive rocks in this area are generally monzogranitic and were emplaced as dikes in an extensional environment along with coeval bimodal volcanics these data combined with the presence of regional unconformities in the northern part of hebei province and western part of liaoning province and the spatial distribution of coeval volcanic rocks in ne china suggest the late jurassic and early early cretaceous magmatisms and the early early cretaceous deformation in this area occurred in an extensional environment related to the delamination of a thickened part of the crust after closure of the mongol okhotsk ocean in comparison the late early cretaceous deformation and magmatism occurred in an extensional environment related to either delamination of the previously thickened crust related to the mongol okhotsk tectonic regime or the subduction of the paleo pacific plate or the combined influence of these two tectonic regimes

u pb zircon geochronology of mesoproterozoic postorogenic rocks and implications for post ottawan magmatism and metallogenesis new jersey highlands and contiguous areas usa abstract postorogenic rocks are widespread in grenville terranes of the north central appalachians where they form small discordant largely pegmatitic felsic intrusive bodies veins and dikes and also metasomatic calcic skarns that are unfoliated and postdate the regional 1090 to 1030 ma upper amphibolite to granulite facies metamorphism related to the grenville ottawan orogeny zircons from magmatic and nonmagmatic rocks from northern new jersey and southern new york were dated to provide information on the regional tectonomagmatic and metallogenic history following ottawan orogenesis we obtained u th pb zircon ages of 1004 3 ma for pegmatite associated with the 1020 4 ma mount eve granite near big island new york 986 4 ma for unfoliated discordant pegmatite that intrudes supracrustal marble at the buckwheat open cut franklin new jersey 990 ma for a silicate borate skarn layer in the franklin marble at rudeville new jersey and 940 2 ma for a calc silicate skarn layer at lower twin lake new york this new data together with previously published ages of 1020 4 to 965 10 ma for postorogenic rocks from new jersey and southern new york provide evidence of magmatic activity that lasted for up to 60 ma past the peak of high grade metamorphism postorogenic magmatism was almost exclusively felsic and involved relatively small volumes of metaluminous to mildly peraluminous melt that fractionated from an a type granite parent source field relationships suggest the melts were emplaced along lithosphere scale fault zones in the highlands that were undergoing extension and that emplacement followed orogenic collapse by least 30 ma postorogenic felsic intrusions correspond to the niobium yttrium fluorine nyf class of pegmatites of cern 1992a geochronologic data provide a temporal constraint on late stage hydrothermal activity and a metallogenic event in new jersey at 990 to 940 ma that mineralized pegmatites with subeconomic to economic deposits of magnetite u th rare earth element ree and formed metasomatic calcic skarn bodies in marble and reactive carbonate rocks mineralization associated with this event overlaps the timing of pegmatite emplacement suggesting a petrogenetic relationship coeval metallogeny at 975 to 950 ma in the new york hudson highlands and 980 to 937 ma in the canadian grenville province implies that this event was widespread following the ottawan phase of the grenville orogeny

alkali calcic and alkaline post orogenic po granite magmatism petrologic constraints and geodynamic settings abstract the end of an orogenic wilson cycle corresponds to amalgamation of terranes into a pangaea and is marked by widespread magmatism dominated by granitoids the post collision event starts with magmatic processes still influenced by subducted crustal materials the dominantly calc alkaline suites show a shift from normal to high k to very high k associations source regions are composed of depleted and later enriched orogenic subcontinental lithospheric mantle affected by dehydration melting and generating more and more k and lile rich magmas in the vicinity of intra crustal magma chambers anatexis by incongruent melting of hydrous minerals may generate peraluminous granitoids bearing mafic enclaves the post collision event ends with emplacement of bimodal post orogenic po suites along transcurrent fault zones two suites are defined i the alkali calcic monzonite monzogranite syenogranite alkali feldspar granite association characterised by biotite plagioclase fractionation and moderate lile hfse enrichments and ii the alkaline monzonite syenite alkali feldspar granite association characterised by amphibole alkali feldspar fractionation and displaying two evolutionary trends one peralkaline with sodic mafic mineralogy and higher enrichments in hfse than in lile and the other aluminous biotite bearing marked by hfse depletion relative to lile due to accessory mineral precipitation alkali calcic and alkaline suites differ essentially in the amounts of water present within intra crustal magma chambers promoting crystallisation of various mineral assemblages the ultimate enriched and not depleted mantle source is identical for the two po suites the more primitive lile and hfse rich source rapidly replaces the older orogenic mantle source during lithosphere delamination and becomes progressively the thermal boundary layer of the new lithosphere present rock compositions are a mixture of major mantle contribution and various crustal components carried by f rich aqueous fluids circulating within convective cells created around magma chambers in favourable areas po suites pre date a new orogenic wilson cycle

40ar 39ar evidence for middle proterozoic 1300 1500 ma slow cooling of the southern black hills south dakota midcontinent north america implications for early proterozoic p t evolution and posttectonic magmatism 40ar 39ar total gas and plateau dates from moscovite and biotite in the southern black hills south dakota provide evidence for a period of middle proterozoic slow cooling early proterozoic 1600 1650 ma mica dates were obtained from metasedimentary rocks located in a synformal structure between the harney peak and bear mountain domes and also south of bear mountain metamorphic rocks from the dome areas and undeformed samples of the 1710 ma harney peak granite hpg yield middle proterozoic mica dates 1270 1500 ma two samples collected between the synform and bear mountain dome yield intermediate total gas mica dates of 1550 ma we suggest two end member interpretations to explain the map pattern of cooling ages 1 subhorizontal slow cooling of an area which exhibits variation in mica ar retention intervals or 2 mild folding of a middle proterozoic 1500 ma 300 c isotherm according to the second interpretation the preservation of older dates between the domes may reflect reactivation of a preexisting synformal structure and downwarping of relatively cold rocks during a period of approximately east west contraction and slow uplift during the middle proterozoic the mica data together with hornblende data from the black hills published elsewhere indicate that the ambient country rock temperature at the 3 4 kbar depth of emplacement of the hpg was between 350 c and 500 c suggesting that the average upper crustal geothermal gradient was 25 40 c km prior to intrusion the thermochronologic data suggest hpg emplacement was followed by a 200 m y period of stability and tectonic quiescence with little uplift we propose that crust thickened during the early proterozoic was uplifted and erosionally thinned prior to 1710 ma and that the hpg magma was emplaced into isostatically stable crust of relatively normal thickness we speculate that uplift and crustal thinning prior to hpg intrusion was the result of differential thinning of the subcrustal lithosphere beneath the black hills if so this process would have also caused an increase in mantle heat flux across the moho and triggered vapor absent melting of biotite to produce the hpg magma this scenario for posttectonic granite generation is supported in part by the fact that in the whole of the black hills the hpg is spatially associated with the deepest exposed early proterozoic country rock

seismic attribute based characterization of coalbed methane reservoirs an example from the fruitland formation san juan basin new mexico the fruitland formation of the san juan basin is the largest producer of coalbed methane in the world production patterns vary from one well to another throughout the basin reflecting factors such as coal thickness and fracture and cleat density in this study we integrated conventional p wave three dimensional 3 d seismic and well data to investigate geological controls on production from a thick continuous coal seam in the lower part of the fruitland formation our objective was to show the potential of using 3 d seismic data to predict coal thickness as well as the distribution and orientation of subtle structures that may be associated with enhanced permeability zones to do this we first derived a seismic attribute based model that predicts coal thickness we then used curvature attributes derived from seismic horizons to detect subtle structural features that might be associated with zones of enhanced permeability production data show that the best producing wells are associated with seismically definable structural features and thick coal although other factors e g completion practices and coal type affect coalbed methane production our results suggest that conventional 3 d seismic data integrated with wire line logs and production data are useful for characterizing coalbed methane reservoirs

a type granite and adakitic magmatism association in songpan garze fold belt eastern tibetan plateau implication for lithospheric delamination abstract the songpan garze fold belt covers a huge triangular area 200 000 km2 confined by the south china yangtze north china and tibetan plateau continental blocks in the songpan garze fold belt triassic adakitic granitoids have been identified however whether there are triassic a type granites is unclear here we report our first finding of an a type granite nianbaoyeche which occurs in the central part of the songpan garze fold belt the nianbaoyeche granite 820 km2 is characterized by arfvedsonite in its mineral assemblage using both la icpms and tims u pb zircon dating methods we obtain a magma crystallization age of 211 1 ma which is slightly younger than triassic adakitic granitoids 216 221 ma in the songpan garze fold belt the nianbaoyeche granite is enriched in si k na rb ree hfse nb ta zr hf with elevated feotot feotot mgo and ga al ratios but is depleted in al mg ca ba and sr the ree compositions show moderately fractionated patterns with la yb n 2 67 7 54 and eu eu 0 09 0 34 these geochemical characteristics indicate that the nianbaoyeche granite has an a type affinity geochemical data and u pb zircon age combined with regional studies show that the nianbaoyeche granite formed in a post collisional tectonic setting sr nd isotopic data for the granite exhibit isr 0 7090 0 7123 and end t 2 72 to 4 26 with tdm 1 15 1 51 ga suggesting that the magma has a dominantly crustal source though a minor contribution from the mantle cannot be ruled out melting to produce an a type granite may have resulted from triassic lithospheric delamination after triassic crustal thickening of the songpan garze fold belt due to convergence between the yangtze north china and north tibet continental blocks the lithospheric delamination model also helps to explain the triassic adakitic magma generation in the songpan garze belt we conclude that association of a type granite and adakitic granitoids in post collisional environment could be a useful indicator of lithospheric delamination

age petrogenesis and tectonic implications of early devonian bimodal volcanic rocks in the south altyn nw china abstract in this paper we report zircon u pb dating hf isotopes geochemical and sr nd isotopic data with the aim the petrogenesis and regional tectonic evolution of early devonian bimodal volcanic rock in the south altyn nw china new la icpms zircon u pb isotopic data constrained them at ca 406 ma the mafic samples are characterized by high fe cr and ni contents low ti and mg contents slightly enriched lree patterns and low la yb n la nb and la ta ratios and positive e nd t values 3 3 to 3 4 indicating that they were likely derived from strong batch melting of the asthenosphere in the spinel facies field the felsic rocks show an a type affinity with high alkalis fe ga zr nb ce and y contents low mg sr content high rb sr and ga al ratios enrichment in lile e g rb k th u and lree and depletion in ba sr nb ta p and ti and fractionated ree patterns with very strong negative eu anomalies these features along with distinct e nd t values 0 5 to 2 3 and mostly positive e hf t 0 29 to 5 18 indicate that the felsic rocks were mainly generated by partial melting of the crust in low pressure and high temperature conditions and simultaneously underwent slight magma mixing of such melts with mantle magma according to the petrogenetic schemes and geological background of the early devonian bimodal volcanic rocks tholeiite and a type dacite rhyolite they should have formed in a post collisional extensional setting moreover on the basis of spatial and temporal distribution and formation mechanism the tectonic magmatic evolution of the early paleozoic south altyn tagh could be divided into three stages 505 472 ma continental collision the magmatite formed under high pressure conditions due to the deep subduction and initial tearing of continental slab 467 450 ma continental slab break off the magmatite formed at high temperature and low pressure in virtue of felsic upper crust uplifting and mantle magma underplating and 432 385 ma post collisional extension the magmatite consists of a type granites and bimodal volcanic rocks which are the products of the interaction between mantle and crust and asthenosphere upwelling

variscan collisional magmatism and deformation in nw iberia constraints from u pb geochronology of granitoids u pb geochronology of variscan granitoid rocks from the west asturian leonese zone of the nw iberian belt documents the episodic nature of magmatism in this section of the western european variscides each magmatic episode is characterized by granitoids with distinct features and has a duration on the scale of several millions of years the ages of these granitoids place new constraints on the age and duration of magmatic and tectonic events that are consistent with previous structural studies and proposed models for the tectonic evolution and migration of deformation in the nw iberian variscan belt granitoid rocks in this zone belong to two main magmatic episodes syn and post tectonic relative to the variscan orogeny and are broadly representative of the granitoid types found in the nw iberian variscan belt the syntectonic association is formed by i tonalite granodiorite monzogranite intrusions emplaced synchronously with the main phase of crustal deformation d 2 at c 325 ma and ii younger leucogranite intrusions emplaced synchronously with syn convergence extensional structures at c 320 310 ma the post tectonic association is composed of i volumetrically dominant tonalite granodiorite monzogranite intrusions and associated minor mafic intermediate rocks emplaced at c 295 290 ma and ii scarce leucogranite intrusions emplaced at c 290 285 ma