late paleoproterozoic 1900 1800ma nappe stacking and polyphase deformation in the hengshan wutaishan area implications for the understanding of the trans north china belt north china craton abstract the hengshan wutaishan area forms part of the trans north china belt developed in response to the final amalgamation of the north china craton the hengshan wutaishan domain and the adjacent fuping massif constitute the largest and the most representative rock exposure of the belt a structural study allows us to redefine the lithological and tectonic units that compose the architecture of the hengshan wutaishan domain and to propose that the trans north china belt was built up through a polyphase tectonic evolution within the period 1900 1800 ma the first event d1 corresponds to the emplacement of lower and upper nappes herein called the orthogneiss and volcanites unit ovu and the low grade mafic unit lgmu respectively the ovu mainly consists of rocks formed in an arc system and metamorphosed under amphibolite facies conditions whereas the lgmu represents oceanic crust rocks with an arc component that underwent greenschist facies metamorphism the syn metamorphic d1 deformation is characterized by a nw se stretching and mineral lineation with a top to the se sense of shear that corresponds to the sense of nappe motion u th pb epm chemical dating on monazite from three metapelites of the ovu gives isochron ages of 1884 11 ma 1886 5 ma and 1887 4 ma interpreted as the age of the prograde amphibolite facies metamorphism coeval with nappe stacking during the d1 event the d2 event corresponds to a widespread crustal melting of the ovu and underlying basement rocks in hengshan related to the exhumation of deep structures about 20 30 ma after nappe emplacement the migmatite contains blocks of retrograded eclogite or hp granulitic restites and is characterized by the development of a pervasive foliation and lineation a late d2 event represents the folding stage of the migmatitic foliation during the completion of a dome the orthogneiss and volcanics unit and the low grade mafic unit are unconformably covered by weakly metamorphosed to unmetamorphosed sediments belonging to the hutuo supergroup these rocks were deformed by a ductile d3 event characterized by a nw se trending stretching lineation south verging folds associated with an axial planar slaty cleavage and an e w crenulation lineation lastly a left lateral wrenching along the zhujiafang shear zone separates the northern and southern parts of hengshan our structural study shows that there is no significant difference between the southern part of hengshan and the lower part of wutaishan both areas belong to ovu and show a structural continuity we suggest that this polyphase deformation developed in response to a north westward subduction of an old ocean named the luliang ocean beneath the western block followed by collision with a micro continent named the fuping block at 1890 1880 ma

a subdivision of the precambrian of china abstract precambrian rocks are widely distributed in china the precambrian is divided into two time units i e the archaean and proterozoic eon each of these is separated into three chronological intervals also with the status of eras with the prefixes early middle or late the time boundary between the archaean and proterozoic eon is placed at 2500 ma according to the present isotopic data the proposed subdivision for the archaean of china is two fold the age of the fuping group is younger than 2800 2900 ma and that of the qianxi group and the corresponding stratigraphic units of eastern liaoning are older than 2800 ma so that 2800 ma is selected as the boundary between the early middle and late archaean based on the representative stratigraphic units the wutai and huto groups and an intervening major unconformity formed by the wutaiian orogeny at 2200 2300 ma the early proterozoic is further divided into two periods with a time demarcation at 2200 ma a major episode of orogeny known as the luliangian movement occurred at the end of the early proterozoic at 1900 ma this disturbance was very extensive and is in a way responsible for the difference in geological conditions between the lower and middle upper proterozoic in china the boundary 1900 ma that relates to the luliangian movement is more important than the boundary corresponding to the age of 1600 ma which is recommended as the time boundary between proterozoic i and ii so we propose to use 1900 ma as the boundary between the early and middle proterozoic in china the time boundary between the middle proterozoic including the changcheng system and the jixian system and the late proterozoic which is composed of the qingbaikou and sinian systems is 1000 ma the age for the boundary between cambrian and precambrian based upon the recent isochron data is inferred to be 610 ma

composite nature of the north china granulite facies belt tectonothermal and geochronological constraints granulite facies rocks are intermittently exposed in a roughly e w trending belt that extends for approximately 2000 km across the north china craton from the helanshan qianlishan wulashan daqingshan guyang and jining complexes in the western block through the huai an hengshan xuanhua and chengde complexes in the trans north china orogen to the jianping western liaoning eastern hebei northern liaoning and southern jilin complexes in the eastern block the belt is generally referred to as the north china granulite facies belt previously interpreted as the lowest part of an obliquely exposed crust of the north china craton recent data indicate that the north china granulite facies belt is not a single terrane instead it represents components of three separate terranes the eastern and western blocks and trans north china orogen each of these units records different metamorphic histories and reflect the complex tectonic evolution of the ncc during the late archean and paleoproterozoic mafic granulites in the eastern block and the yinshan terrane western block underwent medium pressure granulite facies metamorphism at about 2 5 ga with anticlockwise p t paths involving near isobaric cooling following peak metamorphism reflecting an origin related to intrusion and underplating of mantle derived magmas pelitic granulites in the khondalite belt western block underwent medium pressure granulite facies metamorphism at about 2 0 1 9 ga with clockwise p t paths which record the paleoproterozoic amalgamation of the yinshan and ordos terranes to form the western block mafic and pelitic granulites in the trans north china orogen experienced high to medium pressure granulite facies metamorphism at 1 85 ga with clockwise p t paths involving nearly isothermal decompression following peak metamorphism which are in accord with the final collision between the eastern and western blocks to form the north china craton at 1 8 ga the ncgb cannot therefore represent a separate unique terrane instead it reflects the amalgamation of three separate granulite terranes that evolved independently and at different times d 2005 international association for gondwana research published by elsevier b v all rights reserved

linear iterative refinement method for the rapid simulation of borehole nuclear measurements part i vertical wells as a result of its high numerical accuracy and versatility to include complex tool configurations and arbitrary spatial distributions of material properties the monte carlo method is the foremost numerical technique used to simulate borehole nuclear measurements although recent advances in computer technology have considerably reduced the computer time required by monte carlo simulations of borehole nuclear measurements the efficiency of the method is still not sufficient for estimation of layer by layer properties or combined quantitative interpretation with other borehole measurements we develop and successfully test a new linear iterative refinement method to simulate nuclear borehole measurements accurately and rapidly the approximation stems from monte carlo derived geometric response factors referred to as flux sensitivity functions fsfs for specific density and neutron tool configurations our procedure first invokes the integral representation of boltzmann s transport equation to describe

inversion based method for interpretation of logging while drilling density measurements acquired in high angle and horizontal wells abstractwe introduce a sector based inversion method to improve the petrophysical interpretation of logging while drilling density measurements acquired in high angle and horizontal wells the central objective is to reduce shoulder bed effects on the measurements this approach is possible because of a recently developed technique to accurately and efficiently simulate borehole density measurements the inversion based interpretation method consists of first detecting bed boundaries from short spacing detector or bottom quadrant compensated density by calculating their variance representative of the measurement inflection point within a sliding window subsequently a correlation algorithm calculates dip and azimuth from the density image depth shifts that vary azimuthally and depend on relative dip angle together with the effective penetration length of each sensor refine previously selected bed boundaries next the inversion method combines sector based density measurements acquired at all measur

2 7 ga crustal growth in the north china craton evidence from zircon u pb ages and hf isotopes of the sushui complex in the zhongtiao terrane abstractthe major precambrian crustal growth in the north china craton ncc has been thought to have occurred at 2 5 ga here we present secondary ion mass spectroscopy sims and laser ablation inductively coupled mass spectrometry la icp ms zircon u pb ages and hf isotope compositions from dioritic and tonalite trondhjemite granodiorite ttg gneisses of the neoarchean paleoproterozoic metamorphic terrane in the central ncc zircons from the trondhjemitic samples yield emplacement ages at and ma those from the dioritic gneiss yield an age of ma the ttg gneisses are characterized by a na rich and k poor nature strongly fractionated rare earth element patterns high sr 418 318 and sr y 78 49 low y 5 4 6 4 and ybn 3 0 3 6 and low mgo 0 89 1 10 mg 47 42 cr 39 20 and ni 11 8 nb ta 16 12 which suggests that magmas were derived from the partial melting of a flatly subducted oceanic slab the dioritic gneiss shows higher mgo 3 17 mg 50 cr 44

comparison of proterozoic and phanerozoic rift related basaltic granitic magmatism abstract this paper compares the 1 67 1 47 ga rapakivi granites of finland and vicinity to the 1 70 1 68 ga rapakivi granites of the beijing area in china the anorogenic 130 ma granites of western namibia and the 20 15 ma granites of the colorado river extensional corridor in the basin and range province of southern nevada in finland and china the tectonic setting was incipient aborted rifting of paleoproterozoic or archean continental crust in namibia it was continental rifting and mantle plume activity that led to the opening of southern atlantic at 130 ma the 20 15 ma granites of southern nevada were related to rifting that followed the triassic paleogene subduction of the farallon plate beneath the southwestern united states in all cases extension related magmatism was bimodal and accompanied by swarms of diabase and rhyolite quartz latite dikes rapakivi texture with plagioclase mantled alkali feldspar megacrysts occurs in varying amounts in the granites and the latest intrusive phases are commonly topaz bearing granites or rhyolites that may host tin tungsten and beryllium mineralization the granites are typically ferroan alkali calcic metaluminous to slightly peraluminous rocks with a type and within plate geochemical and mineralogical characteristics isotope studies nd sr suggest dominant crustal sources for the granites the preferred genetic model is magmatic underplating involving dehydration melting of intermediate felsic deep crust juvenile mafic magma was incorporated either via magma mingling and mixing or by remelting of newly hybridized lower crust in namibia partial melting of subcontinental lithospheric mantle was caused by the tristan mantle plume in the other cases the origin of the mantle magmatism is controversial for the fennoscandian suites extensive long time mantle upwelling associated with periodic migrating melting of the subcontinental lithospheric mantle governed by heat flow and deep crustal structures is suggested

improved estimation of mineral and fluid volumetric concentrations from well logs in thinly bedded and invaded formations abstractcalculation of mineral and fluid volumetric concentrations from well logs is one of the most important outcomes of formation evaluation conventional estimation methods assume linear or quasi linear relationships between volumetric concentrations of solid fluid constituents and well logs experience shows however that the relationship between neutron porosity logs and mineral concentrations is generally nonlinear more importantly linear estimation methods do not explicitly account for shoulder bed and or invasion effects on well logs nor do they account for differences in the volume of investigation of the measurements involved in the estimation the latter deficiencies of linear estimation methods can cause appreciable errors in the calculation of porosity and hydrocarbon pore volume we investigated three nonlinear inversion methods for assessment of volumetric concentrations of mineral and fluid constituents of rocks from multiple well logs all three of these methods accounted for the gen

extensional collapse and uplift in a polymetamorphic granulite terrain in the archaean and palaeoproterozoic of north china abstract the archaean granulite terrain in the datong huai an area north china comprises a basement complex of felsic and mafic granulite overlain by a sedimentary sequence dominated by metapelite and metapsammite both lithological associations are separated by a tectonic contact and structural textural and stratigraphic data indicate that the terrain was affected by two prominent tectono thermal cycles c a and c b associated with two granulite facies events m1 and m2 which probably occurred 2500 ma and 1800 ma ago respectively of these m1 events were dominant and associated with all major structures in the area in the basement gneiss m1 reached peak metamorphic conditions of 12 14 kbar and 800 900 c during a foliation forming event d 2ba which transposed an earlier s 1ba foliation of unknown age and origin in the allochthonous cover sediments m1 peak conditions of about 8 kbar and 800 c were reached after a prograde thickening event d 1co associated with the formation of a bedding parallel foliation while large amounts of s type granites were emplaced the localised d 2ba and d 1co structures are interpreted as spatially distinct responses at different crustal levels to one metamorphic event juxtaposition of basement and allochthonous cover along a large low angle normal shear zone occurred during d 3 this detachment zone accommodated extension after crustal thickening and allowed unloading of the footwall resulting in a rise of the basement rocks through 4 6 kbar as deduced from syn d 3 decompression textures coeval cooling textures in the allochthonous cover sequence indicate that lateral rather than vertical displacements occurred in the hanging wall of the detachment during c b m2 peak conditions of about 4 6 kbar and 650 700 c were reached coeval with the development of discrete left lateral strike slip zones d 4 that transect both basement and allochthonous cover and accommodated some uplift the deduced c a and c b p t paths have equivalents in many precambrian granulites in general decompressional paths like the one recorded in the basement rocks are linked to processes involving crustal thickening followed by extensional collapse in the datong huai an area it can be shown that low angle detachments may have played an important role in the uplift and cooling history of granulite belts as long ago as the archaean proterozoic boundary

early tectonic evolution of china abstract at least four tectogenetic cycles are recognized in the early precambrian tectonic evolution of china they brought profound changes to the tectonic regime and delineate different evolutionary stages these are the qianxi an 3 1 2 9 ga and fuping ian 2 6 2 4 ga in the archaean and the wutai an 2 1 2 0 ga and luliang ian 1 8 1 7 ga of the early proterozoic time it is illustrated through the above four stages that the mode of tectonic processes has probably changed with time developing in a non uniformitarian fashion each stage of crustal evolution was characterized by specific tectonic regimes that reflect the response of the crust to the gradual changes of the physical conditions in the lithosphere and underlying mantle major crustal forming events occurred at the end of the archaean through which large crustal segments centering around north china and talimu came into existence these protocontinents were subsequently disrupted during extensive proterozoic reworking but by the end of early proterozoic time general consolidation of proto platforms of sub continental proportions was brought about and the main tectonic framework of chinese continental crust acquired its shape

palaeozoic pre and post collision calc alkaline magmatism in the qinling orogenic belt central china as documented by zircon ages on granitoid rocks based on large scale reconnaissance mapping we identified two calc alkaline plutonic assemblages from the northern qinling orogenic belt central china the older assemblage of intrusions closely associated and deformed coevally with their host volcanic arc sequences seems to represent the fractionation product of basaltic arc magma it therefore predates the collision of the north china block with the central qinling island arc system that developed in a sw pacific type oceanic domain south of the north china block single zircon 207pb 206pb evaporation dating yielded early to middle ordovician ages for this assemblage with a relatively small range from 487 2 1 1 to 470 2 1 3 ma intrusions of the younger assemblage are largely undeformed and truncate structures shown in rocks of the older assemblage they are interpreted as post collisional calc alkaline granitoids single zircon dating provided an age of 401 8 0 8 ma for the younger assemblage consistent with earlier work that defines an age range from c 420 to 395 ma our data favour a tectonic model involving formation and amalgamation of island arc and microcontinent terranes between ca 490 and 470 ma ago to create the central qinling zone which subsequently collided with the north china block prior to c 400 ma ago a late precambrian age of 762 0 0 7 ma for a granitoid gneiss at the northern margin of the yangtze block supports a gondwana affinity for this large continental block

tectonic evolution of the east qinling mountains china in the palaeozoic a review and new tectonic model east asia is a composite assemblage built up from various plates and the qinling mountains are prominent among the orogenic belts dividing these plates because of its complex and prolonged history interpretation of the geology of the qinling mountains has led to a variety of tectonic models we review and summarize recently published data and previous work and develop a new tectonic model for the eastern part of this mountain range four tectonic zones are recognized from north to south the lesser qinling the north qinling the central qinling and the south qinling zones the lesser and north qinling zones are interpreted as a late proterozoic to early palaeozoic passive continental margin bordering the north china block the central qinling separated from the lesser north qinling zone by a suture zone mainly consists of volcanic arcs and a high grade metamorphic complex the south qinling zone forms part of the northern margin of the yangtze block and has a long latest proterozoic to middle triassic depositional history as revealed by its sedimentary cover available data do not support the hypothesized existence of a major suture divide between the central and the south qinling zones these two zones seem to have collectively formed an early palaeozoic destructive continental margin on the northern edge of the yangtze block with the central qinling as an island arc system and the south qinling as a wide highly attentuated marginal basin late ordovician to early silurian collision between the north china and the yangtze block built up the palaeozoic orogenic belt in the northern part of the qinling and gave rise to the embryonic east asian continent yet the south qinling was transformed to a remnant basin and remained undeformed until the late triassic when the palaeo tethys collision to the south of the yangtze block drove the yangtze block to move northeastwards deformation in a transpressive regime during this late event largely reconstructed the qinling belt and hence further complicated its tectonics

archean granulite gneisses from eastern hebei province china rare earth geochemistry and tectonic implications the granulite gneisses and their retrograded products of the qianxi group from eastern hebei province china have been investigated for their isotope and trace element geochemistry a consistent age of about 2 5 ae has been obtained by the rb sr and sm nd whole rock isochron methods in agreement with the zircon u pb data pidgeon 1980 d y liu unpubl geochemical arguments from initial isotopic ratios isr and ind and elemental distribution patterns have led us to conclude that this age of about 2 5 ae represents the time of granulite facies metamorphism which must have followed closely the primary emplacement of their protoliths previous claims for early archean ages 3 5 ae of these granulites are not substantiated the mineral isotope systematics register an important thermal event at about 1 7 ae roughly corresponding to the time of the widespread luliang orogeny ma and wu 1981 or chungtiao movement huang 1978

lithotectonic elements and geological events in the hengshan wutai fuping belt a synthesis and implications for the evolution of the trans north china orogen the hengshan wutai fuping belt is located in the middle segment of the trans north china orogen a palaeoproterozoic continental collisional belt along which the eastern and western blocks amalgamated to form the north china craton the belt consists of the medium to high grade hengshan and fuping gneiss complexes and the intervening low to medium grade wutai granite greenstone terrane and most igneous rocks in the belt are calc alkaline and have affinities to magmatic arcs previous tectonic models assumed that the hengshan and fuping gneiss assemblages were an older basement to the wutai supracrustal rocks but recent studies indicate that the three complexes constitute a single long lived neoarchaean to palaeoproterozoic magmatic arc where the wutai complex represents an upper crustal domain whereas the hengshan and fuping gneisses represent the lower crustal components forming the root of the arc the earliest arc related magmatism in the belt occurred at 2560 2520 ma marked by the emplacement of the wutai granitoids which was followed by arc volcanism at 2530 2515 ma forming the wutai greenstones extension driven by widespread arc volcanism led to the development of a back arc basin or a marginal sea which divided the belt into the hengshan wutai island arc japan type and the fuping relict arc at 2520 2480 ma subduction beneath the hengshan wutai island arc caused partial melting of the lower crust to form the hengshan tonalitic trondhjemitic granodioritic ttg suites whereas eastward directed subduction of the marginal sea led to the reactivation of the fuping relict arc where the fuping tonalitic trondhjemitic granodioritic suite was emplaced in the period 2360 2000 ma sporadic phases of isolated granitoid magmatism occurred in the hengshan wutai fuping region forming 2360 ma c 2250 ma and 2000 2100 ma granitoids in the hengshan complex the c 2100 ma wangjiahui and dawaliang granites in the wutai complex and the 2100 2000 ma nanying granitoids in the fuping complex atc 1920 ma the hengshan wutai island arc underwent an extensional event possibly due to the subduction of an oceanic ridge leading to the emplacement of pre tectonic gabbroic dykes that were subsequently metamorphosed together with their host rocks to form medium to high pressure granulites at 1880 1820 ma the hengshan wutai fuping arc system was juxtaposed intensely deformed and metamorphosed during a major and regionally extensive orogenic event the l uliang orogeny which generated the trans north china orogen through collision of the eastern and western blocks the hengshan wutai fuping belt was finally stabilized after emplacement of a mafic dyke swarm at 1780 1750 ma

archean crustal evolution in china u pb geochronology of the qianxi complex abstract the qianxi complex formerly the qianxi group in eastern hebei province is a key terrain for studying the archean crustal evolution of the sino korean craton in china the evolution of the complex involved several stages of supracrustal deposition and magmatic intrusion except for a few post tectonic intrusives all rock assemblages have been metamorphosed to high grade granulite and amphibolite facies the evolution of the complex has spanned more than 1 ga since about 3 5 ga ago in the present work two areas in the qianan region qianan county have been investigated for u pb age study 1 the caozhuang area in the south and 2 the shuichang yangyashan area in the north important tectonothermal events and magmatic episodes of the qianxi complex were identified by the u pb isotopic analyses of zircons extracted from various rock types the results of age determination and the most likely interpretation in terms of temporal evolution of the complex are summarized schematically the oldest zircons 3 65 3 67 ga of china have been found in a fuchsite bearing quartzite in association with the 3 5 ga sm nd isochron age amphibolites in the caozhuang area this emphasizes the existence of early archean sialic crust in the qianxi complex however no ages older than 2 9 ga have been revealed for grey gneisses enclosing the ca 3 5 ga amphibolite enclaves in the caozhuang area but a leptynite sample of dacitic composition gave a minimum 207pb 206pb age of 3 3 ga obtained by a single zircon stepwise evaporation analysis this age and the 3 5 ga sm nd isochron age for amphibolites suggest that the earliest deposition of supracrustal rocks took place about 3 5 3 3 ga ago the deposition of fuchsite quartzite could have taken place contemporaneously or in an earlier period up to 3 6 ga but its precise stratigraphic positions remains to be determined nevertheless the presence of very ancient zircons clearly advocate for the existence of sialic crust at least 3 6 ga in china in the shuichang yangyashan area a supracrustal sequence containing abundant banded iron formations was intruded by a granitic gneiss dated at 2 96 ga by the conventional multigrain zircon method sm nd model ages of about 3 3 ga were obtained for two amphibolite enclaves in a charnockitic gneiss it appears that supracrustal deposition of the qianxi complex might have migrated to the north and took place in the period of 3 3 3 0 ga in addition to supracrustal rocks the qianxi complex is characterized by polyphase granitoid intrusions except for the contaminated grey gneisses sm nd tdm 3 2 3 3 ga in the caozhuang area and the ca 3 ga granitic gneiss in the yangyashan area most granitoid intrusions are of late archean ages the period of 2 7 2 5 ga has undoubtedly recorded the most important tectonothermal events in the evolution of the sino korean craton the present zircon age study and available age data in the literature demonstrate that the archean crustal development in china culminated towards the end of the archean

systematic observation of westward propagating cloud bands over the arabian sea during indian ocean experiment indoex from meteosat 5 data 1 during the field experiment phase of the indian ocean experiment indoex linear cloud formations parallel to the west indian coast and propagating westward have been observed meteosat 5 images are used for the description of the life cycle of these events single cloud bands or main cloud bands followed by up to 10 secondary parallel cloud lines with a wavelike pattern have been observed daily during four periods in the dry season of 1999 15 january 16 19 february 27 february to 7 march and 1 3 april 1999 during these four periods one single cloud band or a packet of cloud bands is generated every day at nighttime their length reaches several hundreds of kilometers their width lies below 40 km and their duration in some cases exceeds 24 hours the smaller cloud lines observed behind the leading cloud line are narrower and are separated by a distance of 2 10 km cloud tops are about 3 8 c colder than the arabian sea corresponding to an altitude between 500 and 1200 m during the night and below 2500 m during daytime cloud bands travel westward over the arabian sea at a speed around 13 m s greater than the wind speed measured in the surrounding area the motion of the cloud band presents similarities with the wavelike propagation of atmospheric phenomena such as the australian morning glories common elements to the different cases are the following weak low level winds close to the southwestern indian coast when the cloud bands appear winds with a northerly component in the vicinity of the northwestern indian coast the presence of a sea land breeze circulation along the west indian coast and the presence of high concentrations of pollutants over the northeastern arabian sea however existing physical links between these elements if any still have to be investigated

quantitative interpretation of pulsed neutron capture logs part 1 fast numerical simulation pulsed neutron capture pnc logs are commonly used for formation evaluation behind casing and to assess time lapse variations of hydrocarbon pore volume because conventional interpretation methods for logs assume homogeneous formations errors may arise especially in thinly bedded formations when appraising petrophysical properties of hydrocarbon bearing beds there exist no quantitative interpretation methods to account for shoulder bed effects on logs acquired in sand shale laminated reservoirs because of diffusion effects between dissimilar beds logs acquired in such formations do not obey mixing laws between the responses of pure sand and pure shale end members of the sedimentary sequence we have developed a new numerical method to simulate pnc rapidly and accurately logs the method makes use of late time thermal neutron flux sensitivity functions fsfs to describe the contribution of multilayer formations toward the measured capture cross section it includes a correction procedure

inversion based petrophysical interpretation of logging while drilling nuclear and resistivity measurements abstractinterpretation of borehole measurements acquired in high angle ha and horizontal hz wells is challenging due to the significant influence of well trajectory and bed geometrical effects experience shows that accurate integrated interpretation of well logs acquired in ha hz wells requires explicit consideration of 3d measurement physics the most reliable alternative for interpretation of well logs in ha hz wells is with inversion techniques that correct measurements for shoulder bed undulating well trajectory and bed geometrical effects while taking advantage of high data resolution we discovered an efficient layer based inversion workflow for combined quantitative petrophysical and compositional interpretation of logging while drilling sector based nuclear density neutron porosity photoelectric factor gamma ray and array propagation resistivity measurements acquired in ha hz wells a challenging synthetic benchmark example confirmed improved formation evaluation with the layer based

linear iterative refinement method for the rapid simulation of borehole nuclear measurements part 2 high angle and horizontal wells based on previous research we developed and successfully tested a new linear iterative refinement method to rapidly simulate borehole nuclear measurements acquired in vertical wells the approximation considers 2d spatial properties of monte carlo derived flux sensitivity functions fsfs to simulate neutron and density measurements based on new research we implemented the linear iterative refinement method with explicit 3d spatial properties of fsfs to approximate nuclear borehole measurements acquired in high angle and horizontal ha hz wells we used generic neutron and density tools that are close to commercial tool designs to construct 3d fsfs in the proximity of a bed boundary between layers of contrasting petrophysical properties likewise to benchmark the approximation we consider adjacent layers of 5 and 30 porosity water saturated sandstone for the case of neutron measurements variations of azimuthal geometric factors are as large as 20 and 57 for the near and far detectors respecti

geochemical evolution and metamorphic development of the early precambrian in eastern hebei china abstract within the archaean qianxi group in eastern hebei china two roughly coeval tectonic units can be recognized the qian an granulite complex and the zunhua high grade greenstone belt both belong to the high grade terranes and have recorded almost the same history of metamorphism the granulite facies metamorphism was generally followed by a retrograde metamorphism of amphibolite facies and multistage anatexis despite the similar metamorphic histories the geochemical features of the two units are different 1 1 the protoliths of the qian an granulite complex consist of a calc alkaline volcanic series dominated by andesitic composition and a shallow water sedimentary series whereas that of the zunhua greenstone belt clearly show the character of a bimodal magmatic series 2 2 most metabasalts of the qian an complex belong to the continental basalt type and grade into andesite whereas in the zunhua belt they are characterized by a suite of high magnesian series low k2o tholeiites and a large amount of ultramafic mafic layered complexes 3 3 in terms of regional geochemistry the qian an complex is rich in potassium and potassium charnockites of autochthonous anatectic and intrusive origin are widespread in contrast the zunhua belt is rich in sodium and tonalitic gneisses of deep seated mixed origin are widespread finally a model for archaean crustal evolution of high grade terranes is suggested

joint petrophysical interpretation of multidetector nuclear measurements in the presence of invasion shoulder bed and well deviation effects abstractrecent advances in logging while drilling sigma measurements include three detector thermal neutron and gamma ray decay measurements with different radial sensitivities to assess the presence of invasion we have developed an inversion based work flow for the joint interpretation of multidetector neutron density and sigma logs to reduce invasion shoulder bed and well deviation effects in the estimation of porosity water saturation and hydrocarbon type whenever the invasion is shallow the procedure begins with a correction for matrix and fluid effects on neutron and density porosity logs to estimate porosity multidetector time decays are then used to assess the radial length of the invasion and estimate the virgin zone sigma while simultaneously reducing shoulder bed and well deviation effects density and neutron porosity logs are corrected for invasion and shoulder bed effects using two detector density and neutron measurements with the output from the time decay sigma inversion the f

fast modeling of borehole neutron porosity measurements with a new spatial transport diffusion approximation abstractthe quantitative integration of nuclear measurements into the in situ petrophysical and geophysical evaluation of rock formations has been elusive because of the lack of efficient algorithms to simulate them we discovered a new method for rapid numerical simulation of borehole neutron measurements using monte carlo mc derived spatial flux sensitivity functions fsfs and diffusion flux difference dfd approximations the method calculates spatial sensitivity flux perturbations using flux difference approximations of one group neutron diffusion models by invoking appropriate boundary conditions the one group time independent neutron diffusion solution is implemented for nonmultiplying systems in 2d and 3d cylindrical coordinates the solution is differentiated with respect to the neutron cross section to obtain an expression for flux difference due to cross section perturbations constant transport correction coefficients for cross section parameters are calculated with a flux fitting method

field examples of the joint petrophysical inversion of resistivity and nuclear measurements acquired in high angle and horizontal wells abstracta recently introduced interpretation workflow has confirmed that inversion based interpretation is more reliable than conventional well log analysis in high angle ha and horizontal hz wells because the former accounts for well trajectory and shoulder bed effects on well logs synthetic examples show that the inversion workflow could improve the estimation of hydrocarbon volumes by 15 and 10 in ha and hz intervals respectively using field examples of thinly interbedded calcite cemented siltstone formations we document results of the joint petrophysical inversion of logging while drilling multisector nuclear neutron porosity density natural gamma ray photoelectric factor and multiarray propagation resistivity measurement for improved formation evaluation in ha hz wells under the assumption of multilayer formation petrophysical models the inversion approach estimates formation properties by numerically reproducing the available measurements subsequently inversion derived hydrocarbon

a review on the huoqiu banded iron formation bif southeast margin of the north china craton genesis of iron deposits and implications for exploration abstract the huoqiu iron ore field in northwest anhui province is located in the north china craton ncc as a large banded iron formation bif iron ore field ore bodies occur in a middle high grade of neoarchean metamorphic formation forming a banded silicon iron series from north to south the main ore bodies can be divided into two sub belts from bottom to upper layers i e the a b ore belt consisting of leptynite schist magnetite quartz formation and the d ore belt consisting of schist marble hematite quartz formation based on a dataset from geological settings geophysical and geochemical exploration ore forming conditions and structural analysis of the iron deposit we discuss structural types sedimentary environments deep tectonic and ore controlling factors as well as characteristics and distribution of this colossal bif ore field in the huoqiu region using la icp ms techniques we obtained the oldest u pb age of ca 2 7 ga for plagioclase amphibolite as its original rock and 1 8 ga for magmatic granite in the huoqiu group the hf isotopes of zircon were also determined resulting in the oldest hf model age of 3 5 ga geochemical data indicate that the protolithes of amphibolites belong to a series of subalkaline rocks with enrichments of large ion lithophile elements and depletions of high field strength elements which are typical volcanic arc rocks the amphibolites have low k 2 o concentrations with low ratios of ti v 22 7 to 25 9 averaging 24 5 similar to island arc tholeiite this suggests that the iron deposit and bif are of the superior type in the huoqiu region

3 5 ga old amphibolites from eastern hebei province china field occurrence petrography sm nd isochron age and ree geochemistry amphibolite blocks frequently occur in association with grey gneisses within a small area near the villages of caozhuang and huangbaiyu in eastern hebei they are interpreted as remnants of an earlier bimodal suite now engulfed in late archaean k rich granitic magma and are further cut by pegmatite dykes they are considered together as giant enclaves within late archaean granite plutons u pb zircon ages 2 5 2 6 ga the amphibolites have been dated by the sm nd isochron method the results yielded t 3470 107 ma ind 0 50827 11 and nd t 2 7 0 6 this age represents the time of protolithic basalt eruption and possibly suggests a period of formation of primitive mafic crust this is the oldest reliable age so far obtained for the archaean rocks of china the sm nd results of grey gneiss samples yielded model ages tdm of about 3 24 ga it is not clear whether this younger age in comparison with that of the amphibolites indicates the intrusive nature of these rocks or is a result of contamination by later granite about 2 5 ga ago the rb sr and common pb isotopic systems have been highly disturbed and no isochron ages could be established the common pb data show retarded growth of radiogenic pb and hence imply reduction of u pb ratios in the past this is consistent with the petrographic study which suggests that the amphibolites have undergone an earlier period of granulite facies metamorphism and were subsequently retrogressed to the present amphibolite facies mineral assemblages the positive nd t value of 2 7 for the amphibolites implies that the protolithic basalt magmas were generated from mantle sources which had undergone long term depletion in light rare earth elements lree the depletion event must have taken place prior to 4 ga ago if their source had a chemical nature similar to the modern oceanic mantle it could have occurred as early as 4 5 ga ago if their source was less impoverished in lree if the mantle depletion was related to extraction of continental or sialic material the sm nd data of the caozhuang amphibolites lend support to the existence of sialic crust if not of a continental size before 4 ga ago