major types and time space distribution of mesozoic ore deposits in south china and their geodynamic settings the ore deposits of the mesozoic age in south china can be divided into three groups each with different metal associations and spatial distributions and each related to major magmatic events the first event occurred in the late triassic 230 210 ma the second in the mid late jurassic 170 150 ma and the third in the early mid cretaceous 120 80 ma the late triassic magmatic event and associated mineralization is characterized by peraluminous granite related w sn nb ta mineral deposits the triassic ore deposits are considerably disturbed or overprinted by the later jurassic and cretaceous tectono thermal episodes the mid late jurassic magmatic and mineralization events consist of 170 160 ma porphyry skarn cu and pb zn ag vein deposits associated with i type granites and 160 150 ma metaluminous granite related polymetallic w sn deposits the late jurassic metaluminous granite related w sn deposits occur in a ne trending cluster in the interior of south china such as in the nanling area in the early mid cretaceous from about 120 to 80 ma but peaking at 100 90 ma subvolcanic related fe deposits developed and i type calc alkaline granitic intrusions formed porphyry cu mo and porphyry epithermal cu au ag mineral systems whereas s type peraluminous and or metaluminous granitic intrusions formed polymetallic sn deposits these cretaceous mineral deposits cluster in distinct areas and are controlled by pull apart basins along the south china continental margin based on mineral assemblage age and space time distribution of these mineral systems integrated with regional geological data and field observations we suggest that the three magmatic mineralization episodes are the result of distinct geodynamic regimes the triassic peraluminous granites and associated w sn nb ta mineralization formed during post collisional processes involving the south china block the north china craton and the indo china block mostly along the dabie sulu and songma sutures jurassic events were initially related to the shallow oblique subduction of the izanagi plate beneath the eurasian continent at about 175 ma but i type granitoids with porphyry cu and vein type pb zn ag deposits only began to form as a result of the breakup of the subducted plate at 170 160 ma along the nne trending qinzhou hangzhou belt also referred to as qin hang or shi hang belt which is the neoproterozoic suture that amalgamates the yangtze craton and cathaysia block a large subduction slab window is assumed to have formed in the nanling and adjacent areas in the interior of south china triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic w sn mineralization a relatively tectonically quiet period followed between 150 and 135 ma in south china from 135 ma onward the angle of convergence of the izanagi plate changed from oblique to parallel to the coastline resulting in continental extensional tectonics and reactivation of regional scale ne trending faults such as the tan lu fault this widespread extension also promoted the development of ne trending pull apart basins and metamorphic core complexes accompanied by volcanism and the formation of epithermal cu au deposits granite related polymetallic sn w deposits and hydrothermal u deposits between 120 and 80 ma with a peak activity at 100 90 ma

petrography and reservoir physics ii relating thin section porosity to capillary pressure the association between pore types and throat size porosity in reservoir rocks is configured into a few types of pores whose size and shape are controlled by depositional fabric and postdepositional processes the size shape and abundance of each pore type can be objectively determined from thin section using image analysis and pattern recognition procedures each pore type tends to be associated with a limited range of throat sizes the association between pore type and throat size can be determined using regression procedures linking pore type data obtained from thin section with capillary pressure data to do so a set of samples is required wherein the association between pore type and throat size is fixed but where pore type proportions vary between samples this condition is met by a sample suite representing res rvoir facies from a single core or in many cases from a single field the relationship between pore type and throat size is an effective means to relate reservoirs in terms of the efficiency of the porous microstructure to multiphase flow parameters derived from the relationship can be used to construct accurate physical models that subdivide physical response in terms of the contributions of each pore type

geochemistry of the lublin formation from the lublin coal basin implications for weathering intensity palaeoclimate and provenance abstract the lublin formation upper westphalian a and westphalian b is the main coal bearing series of the lublin coal basin lcb so far few geochemical studies of the carboniferous of the lcb have been performed and there is almost no data on the geochemistry of this series this paper presents geochemical data for 118 samples from the lublin formation from the central part of the lcb major oxide concentrations al2o3 sio2 fe2o3 p2o5 k2o mgo cao na2o k2o mno tio2 cr2o3 ba were obtained using an x ray fluorescence spectrometry trace and major elements zr th sc la u cu sr rb ni fe mn ca mg k na were analysed using inductively coupled plasma mass spectrometry concentrations of the major and trace elements showed significant diversity especially in the westphalian b deposits the chemical index of alteration plagioclase index of alternation and weathering index of parker values as well as the rb sr sr cu c and th u ratios of the studied samples suggest a high degree of chemical weathering of the source rocks and a prevailing warm humid climate with some arid episodes based on indicators such as al2o3 tio2 tio2 zr and la th it is suggested that all the studied samples from the lublin formation of the lcb were derived from felsic to intermediate igneous rocks while the th sc ratio suggests a mixed source for these sediments

petrogenesis and tectonic implications of early cretaceous s and a type granites in the northwest of the gan hang rift se china the gan hang rift trending at least 450 km in a ne sw direction is a part of a mesozoic basin and range province in southeastern china detailed shrimp zircon u pb chronology major and trace element and sr nd hf isotope data of three granitic plutons and a diabasic dike in the northwest of the gan hang rift are used to explore the origin of these granites and their relationship to the evolution of the gan hang rift shrimp zircon u pb dating shows that the granitic plutons and diabasic dike were emplaced in the early cretaceous 122 129 ma the tongshan and damaoshan plutons close to the gan hang rift consist mainly of weakly peraluminous granitic rocks which show a2 subtype affinity these granites have initial 87sr 86sr ratios of 0 7080 0 7103 end t values of 1 4 to 5 6 and ehf t in situ zircon values of 3 8 to 1 2 detailed elemental and isotopic data suggest that they were formed by partial melting of granulitized mesoproterozoic metamorphic basement including metasedimentary and metaigneous rocks in the shallow 30 km crust at a high temperature 823 c these pure crustal melts underwent crystal fractionation of biotite plagioclase and k feldspar forming the more felsic end member of granitic rocks the ehu pluton more distant from the gan hang rift is composed of two mica granites which are strongly peraluminous and are s type granites these granites have higher initial 87sr 86sr ratios 0 7162 0 7191 and lower end t 7 1 to 7 4 and ehf t 6 8 in situ zircon values than the tongshan and damaoshan granites detailed elemental and isotopic data suggest that the ehu granites were formed by partial melting of paleoproterozoic metasedimentary basement in the deep 40 50 km crust at a relatively low temperature 757 c with no fractional crystallization and mantle derived magma mixing in their evolution the coeval diabasic dike is calc alkaline and has initial 87sr 86sr ratio of 0 7085 end t value of 0 9 and ehf t in situ zircon value of 7 1 suggesting that it was derived from the asthenospheric mantle wedge that had been metasomatised via addition of subducted sediment derived melt with monazite in the residual phase the association of early cretaceous 122 129 ma s and a type granites in the northwest of the gan hang rift marks the onset of back arc extension or intra arc rift with ongoing extension the crust and lithospheric mantle became progressively thinned the upwelling of asthenosphere triggered partial melting of both metasedimentary and metaigneous rocks in the more thinned crust close to the gan hang rift forming the a type granitic magmas such as tongshan and damaoshan whereas partial melting of metasedimentary rocks in the less thinned crust farther from the gan hang rift formed the s type granitic magmas such as ehu the red sediments with the total thickness more than 10 000 m have been successively deposited in the gan hang rift valley since the late early cretaceous 105 ma suggesting that this region experienced the most back arc extension

late triassic melting of a thickened crust in southeastern china evidence for flat slab subduction of the paleo pacific plate abstract the dashuang complex in zhejiang province of southeast china is composed of two distinct lithologies syenite in the west and quartz monzonite in the east they record similar zircon u pb ages of 224 3 ma syenite and 226 2 ma and 227 1 ma quartz monzonite respectively but are notably different in petrography magnetic susceptibility whole rock chemistry zircon hf isotope and zircon trace element characteristics the west dashuang syenitic pluton the west body has high modal alkali feldspar high zircon saturation temperatures high whole rock and zircon mree hree ratios low fe mg ti contents and is depleted in ba sr and eu it also has low magnetic susceptibilities belongs to the ilmenite series and is a peraluminous and ferroan granitoid the east dashuang quartz monzonitic pluton the east body has abundant k feldspar megacrysts with hornblende titanite and biotite being the major ferromagnesian minerals in contrast to the west body the east body has lower zircon saturation temperatures lower whole rock and zircon mree hree ratios higher fe mg ti contents and shows no depletion in ba sr or eu the east body has higher magnetite contents high magnetic susceptibilities and belongs to the magnetite series it is a metaluminous and magnesian granitoid of arc affinity zircon hf isotopic data reveal that both bodies were derived from partial melting of paleoproterozoic igneous protoliths in the lower crust but the east body possibly incorporated subducted terrigenous sediments both bodies have higher melting temperatures and pressures than adjacent cretaceous granitoids reflecting their origin in a thickened hotter lower crust the most feasible model to explain their differences is variations in water content during crustal melting resulting in different melting and crystallization behaviors such melting in a triassic thickened crust with variable water involvement followed by cretaceous magmatism in an extensional setting is consistent with the flat slab subduction model proposed for south china the model involves crustal thickening and partial melting with mantle and lower crustal metasomatism during flat slab propagation in the triassic early jurassic and crustal thinning and extension from the mid jurassic to the cretaceous

gold mineralization of the chencai suichang uplift and tectonic evolution of zhejiang province southeast china abstract a metallogenic model is proposed in which gold and base metal mineralization in se china is related to plate interactions along the pacific margin with southeast asia from about 900 to 70 ma all depositional orogenic and metallogenic processes can be explained by subduction events along northeast trending zones with progressive accretion and cratonization along the continental margin these subduction zones moved southeast for a distance of less than 150 km as a result the area is one of crustal reworking in which the rocks and mineral deposits of earlier events have been repeatedly modified the chencai suichang uplift is an uplifted crustal block in central zhejiang province of mainland china in which the proterozoic basement is exposed as tectonic windows in overlying mesozoic volcanics several gold and base metal deposits are located in these proterozoic windows as well as in the younger volcanics most economic deposits were formed during the last major tectono magmatic event affecting the area the yanshanian 160 170 ma event although there is evidence for earlier mineralization that has been remobilized during the yanshanian it is suggested that crustal reworking was particularly important in remobilising and upgrading gold mineralization the model presented is supported not only by local geology and isotopic data but also by the regional distribution of gold deposits which are arranged in a 50 km wide belt parallel to the yanshanian subduction zone three major episodes of mineralization occurred during 1 a subduction related period of metamorphism partial melting and mesothermal fluid generation and mineralization in the lower crust during the caledonian 2 subduction related volcano plutonic activity with epithermal mineralization during the early yanshanian and 3 hydrothermal mineralization during late yanshanian tectono magmatic event in the third two main categories of metallogenic control are recognized namely 1 hydrothermal fluid generation in the lower crust and 2 upper crust structural and lithological controls on mineralization

revolution in cretaceous sea level analysis a thorough analysis of the geographical distribution of sea level changes throughout cretaceous time reveals that besides normal tectono eustasy there were large scale latitudinal eustatic sea level changes these represent south to north migrating geoidal eustatic highs and lows or gravitational drop motions this is a novel factor in sea level analyses it implies that global eustasy is an illusion and that regional eustasy should be the new key phrase

cretaceous pacific plate movement beneath se china evidence from episodic volcanism and related intrusions abstract extensive late mesozoic igneous rocks in se china have been widely considered to be generated under the paleo pacific tectonic regime the plate subduction model however remains controversial this study focuses on the cretaceous volcanic rocks in northwestern zhejiang province zircon u pb age determination indicates that cretaceous volcanism in northwestern zhejiang took place at three episodes of 140 130 130 127 and 123 118 ma in good agreement with the coeval lower volcanic series in southeastern zhejiang but lacking the episode at 110 88 ma corresponding to the upper volcanic series the cretaceous volcanic rocks in zhejiang therefore show an oceanward younging trend in situ zircon hf isotope analyses of three episodes of volcanics yield e hf t values of 11 2 to 8 7 4 8 to 2 4 and 4 4 to 2 2 respectively the entire sequences display typical isotopic features of magma mixing implying progressive involvement of juvenile component based on systematical researches on the cretaceous volcanic rocks and a series of granitoid plutons in zhejiang it is also identified that the juvenile component involvement gradually occurred from the inland to the coast under an enhanced lithospheric extensional tectonic setting all the observations in this study indicate the northwestward paleo pacific plate subduction with episodic slab rollback which triggered the arc system to retreat towards the pacific ocean rather than the southwestward subduction related to the ridge subduction along the lower yangtze river belt

re os geochronology and systematics in molybdenite from the endako porphyry molybdenum deposit british columbia canada precise re os molybdenite ages for the endako porphyry molybdenum deposit and the nithi mountain occurrence british columbia canada yield new information on the timing of molybdenite deposition three episodes of mineralization are indicated 1 154 ma 2 148 to 146 ma and 3 145 ma re os dates agree well with new u pb and 40 ar 39 ar data from granitoids of the nithi phase 155 2 1 5 ma the endako phase 148 4 1 5 ma and a preore dike 147 4 0 6 ma and the casey phase 145 1 0 2 ma plus hydrothermal biotite 144 5 0 75 ma villeneuve et al 2001 the excellent correlation between the re os dates from molybdenite and the ages of granitoids from the area indicates a direct genetic relationship between these plutons and molybdenite mineralization these re os data also provide further insight into the systematics and robustness of re os in molybdenite the endako molybdenum deposit is the product of two episodes of mineralization both associated with moderate salinity 5 15 wt nacl equiv and high temperature 440 c fluids a third low temperature 190 300 c hydrothermal event is associated with eocene faulting selby et al 2000 the clear distinction between two of the re os molybdenite dates in the deposit and the close agreement of these dates to the ages of granitoid intrusions suggest that the re os system in molybdenite is not reset by high temperature 440 c moderate salinity hydrothermal fluids in contrast magmatic biotite in a 147 ma preore dike has a 40 ar 39 ar age of 145 ma identical to the age of the hydrothermal biotite indicating that 440 c fluids reset the ar ar system in biotite hence we interpret that the re os isotope system in molybdenite is resistant to resetting by high temperature fluids 440 c in contrast to the 40 ar 39 ar system in biotite the re os system in molybdenite is also unaffected by postore hydrothermal fluids these data show that molybdenite can provide critical information in understanding sulfide mineral deposition in ore systems which is not recorded by other isotopic systems in alteration minerals

zircon u pb geochronology and geochemistry of two episodes of granitoids from the northwestern zhejiang province se china implication for magmatic evolution and tectonic transition abstract granitoids 175 80 ma representing a prominent yanshanian jurassic to cretaceous magmatic event in south china widely intrude the precambrian crystalline basement and paleozoic strata here we report zircon u pb age data geochemical characteristics and sr nd isotopes of the late jurassic and early cretaceous granitoids from the northwestern zhejiang province zxb of southeastern china our results reveal two distinct episodes for the yanshanian magmatism the jiemeng and datongkeng granodiorites formed at 148 6 1 1 ma whereas the huangshitan jiuligang and ruhong aluminous a type granites were generated between 129 0 0 6 ma and 126 1 1 1 ma the two magmatic phases represent a tectonic transition from an active continental margin to post orogenic setting during the late jurassic ca 150 ma to early cretaceous ca 128 ma geochemically these intrusions are granodioritic to granitic in composition and show an affinity of s type and a type granitoids respectively the s type granodiorites of jiemeng and datongkeng are characterized by moderate sio 2 65 0 69 6 wt high k 2 o na 2 o 5 0 7 6 wt k 2 o na 2 o 1 2 1 5 zr 31 109 ppm sr 71 190 ppm and high field strength elements low to intermediate mg and moderate nb depletion the a type granites of huangshitan jiuligang and ruhong are characterized by high sio 2 72 7 77 2 wt k 2 o na 2 o 6 9 8 8 wt k 2 o na 2 o 1 3 2 1 fe t fe t mg ga 17 29 ppm 20 ppm commonly zr 96 197 ppm and sr 8 45 ppm with slight nb depletion the s type granodiorites have higher mg a nk sr sr ba sr y la yb n and lree hree and lower sio 2 k 2 o na 2 o ga and zr with weak negative eu anomalies compared to those of the a type granites with negative eu anomalies all these rocks show y nb ratios 1 2 high initial 87 sr 86 sr i sr ratios and low e nd t and are depleted in nb ti and sr indicating crustal origin with subduction zone signatures we suggested that the zxb s type granitic bodies might have been derived from the mesoproterozoic metamorphic basement rocks through partial melting induced by mantle derived magma followed by limited fractional crystallization the zxb aluminous a type granites were also derived from a similar magma source but underwent fractional crystallization at higher crustal levels the a type granites in the zxb correlate with a post orogenic tectonic setting a geological comparison between zxb and adjacent areas indicates that the geochemical features of the zxb a type granites are comparable with the baijuhuajian a type granites and also the adjacent areas a type granites but are distinct from the late cretaceous a type granites 105 90 ma distributed along the southeastern coastal area of south china we correlate the formation of the zxb s type granodiorites to inland compression associated with the subduction and collision of the paleo pacific plate in the late jurassic 170 145 ma in contrast the a type granites formed under a post orogenic setting during the early cretaceous period 145 120 ma resulting from lithospheric thinning and continent extension accompanied by slab roll back of the paleo pacific plate following the subduction collision event

climatic and tectonic sea level gauge for midcontinent pennsylvanian cyclothems new sedimentological determinations suggest that pennsylvanian sea level change ranged from as little as 40 m to as much as 160 m depending on which model establishes the deepest water facies of a midcontinent cyclothem average sedimentological estimates of sea level change for models of heckel and gerhard are 96 4 m and 86 0 m respectively in the midcontinent tectonic subsidence contributed 5 to 20 of the total pennsylvanian sea level change in platform areas and basin depocenters additional change in sea level was controlled by short term glacial eustasy nearly 70 of sea level change and long term climate change nearly 15 of sea level change these findings suggest that away from orogenic belts climatic change is the principal driving mechanism controlling sea level change whereas within orogenic belts climate becomes more subordinate to tectonic processes that influenced pennsylvanian sea level change even though indicators of climatic change reportedly are preserved

cyclic ramp to basin carbonate deposits lower mississippian wyoming and montana a combined field and computer modeling study abstract the lower mississippian lodgepole lower madison formations 20 225 m thick developed along a broad 700 km storm dominated pericratonic ramp three types of fifth order upward shallowing cycles are recognized across the ramp to basin transition peritidal cycles consist of very shallow subtidal facies overlain by algal laminated tidal flat deposits which are rarely capped by paleosol breccia layers shallow subtidal cycles consist of stacked ooid grainstone shoal deposits or deeper subtidal facies overlain by ooid skeletal grainstone caps deep subtidal cycles located along the outer ramp consist of basal sub storm wave base limestone argillite overlain by storm deposited limestone which are capped by hummocky stratified to massive skeletal ooid grainstone deep subtidal c cles pass downslope into ramp slope facies composed to rhythmically interbedded limestone and argillite with local deep water mud mounds no upward shallowing cycles occur within the ramp slope facies average cycle durations calculated along the outer ramp are between 30 110 ky the fifth order cycles are stacked to form three third to fourth order depositional sequences which are recognized by regional transgressive regressive facies trends and cycles stacking patterns ramp margin wedges rmw developed during long term sea level fall and lowstand and consist of cyclic crinoidal bank and oolitic shoal facies which pass downdip into deep subtidal cycles transgressive systems tracts tst which onlapped the ramp during long term sea level rise include thick shallow and deep subtidal cycles peritidal cycles are restricted to the inner ramp highstand systems tracts hst developed during long term sea level highstand and fall and along the ramp are composed of early hst shallow subtidal cycles overlain by late hst peritidal cycles shallow through deep subtidal cycles characterize the hst along the ramp slope two dimensional computer modeling of the cyclic sequences suggests that for the assumed water depths of facies fifth order sea level oscillations of at least 20 25 m were required to generate deep subtidal cycles along the ramp slope synthetic sequences run with fifth order sea level amplitudes end page 1194 and tst deposition a feature not observed in the actual sequences other factors in addition to fifth order sea level oscillations likely played a role in generating synchronous peritidal and deep subtidal cycles during hst deposition these factors may include short term climatic changes which influenced the depths to storm wave reworking the moderate amplitude sea level oscillations suggested by the cyclic sequences may reflect the initial effects of carboniferous glaciation that was occurring in gondwana

magmatism along the southeast margin of the yangtze block precambrian collision of the yangtze and cathysia blocks of china the time and the environment of formation of igneous rocks along the southern margin of the yangtze continental block in southern anhui province and northeastern jiangxi province china are discussed sm nd dating for samples from two ophiolite suites give ages of about 1 ga late proterozoic granodiorites in the study area have ages of about 0 9 ga and have normal intrusive relations against banxi group metamorphic country rocks trace element abundances and initial nd isotope ratios for ophiolite and proterozoic granodiorites are consistent with formation in an island arc environment in contrast sr and nd isotopes for mesozoic granitoids of the region suggest that they are products of remelting of crustal sources similar to the basement of the yangtze block these relations do not support a recently proposed mesozoic overthrust tectonic model for southeast china but rather favor a late precambrian collision history for the yangtze and cathysia blocks

quartz grain surface textures evidence for middle carboniferous glacial sediment input to the parrsboro formation of nova scotia scanning electron microscope examination of quartz grains obtained from lacustrine limestones marginal to an alluvial fan in the middle carboniferous parrsboro formation riversdale group reveals surface characteristics typical of glacial transport this suggests that a paleoclimate sufficiently cool to support mountain glaciation may have existed in the northeastern appalachians during middle carboniferous time this evidence of a cool paleoclimate is contrary to conventional interpretations of carboniferous paleoclimates which are considered to have been warm the glacially modified quartz grains may represent a paleoclimatic event that can be used in stratigraphic subdivision of middle carboniferous strata and can also be used to separate the canso and riversdale groups of the middle carboniferous of eastern canada the boundary between the canso and riversdale groups is at present recognized as being of a time transgressive nature

introduction to tectonics of china abstract the continental crust of china is a mosaic of cratonic blocks and orogenic belts containing small cratons and terranes with various tectonic settings they have diverse origins and complex histories of amalgamation and often suffered repeated reworking after multiple episodes of amalgamation in the last three decades extensive geological geochemical and geophysical investigations have been carried out on these cratonic blocks and intervening orogenic belts producing an abundant amount of new data and competing interpretations this provides important insights into understanding the formation and evolution of the chinese continents the papers assembled in this volume present a timely and comprehensive overview on major advancements and controversial issues related to the formation and evolution of continental crust in china complex tectonic histories were experienced not only by the large scale cratonic blocks and orogenic belts but also by small scale terranes and orogens between and inside these blocks nevertheless our understanding of lithotectonic units and geological processes has been greatly advanced by recent studies of zirconology and geochemistry for various rock types from major petrotectonic units in china it has been further advanced from integrated interpretations of geochemical and petrological data for petrogenesis of magmatic rocks an overview of these observations and interpretations provides new insights into understanding the continental plate tectonics and the chemical geodynamics of subduction zones

sea level curve for pennsylvanian eustatic marine transgressive regressive depositional cycles along midcontinent outcrop belt north america at least 55 cycles of marine inundation and withdrawal are recognized in the mid desmoinesian to mid virgilian midcontinent outcrop sequence in north america they range from widespread major cycles classic cyclothems with deep water facies extending across the northern shelf through intermediate cycles persisting as marine horizons across the shelf to minor cycles developed on the lower shelf or as parts of major cycles biostratigraphic differentiation of the cycles should establish interbasinal correlation on a scale fine enough to allow evaluation of differential tectonics and sedimentation sequential groupings of cycles are more irregular than proposed megacyclothems or mesothems but they may be obscured by the distinctness of the major cyclothems estimates of cycle periods range from about 40 to 120 x 10 sup 3 yr for the minor cycles up to about 235 to 400 x 10 sup 3 yr for the major cyclothems the range for all cycles corresponds well to the range of periods of earth s orbital parameters that constitute the milankovitch insolation theory for the pleistocene ice ages and it further supports gondwanan glacial control for the pennsylvanian cycles even though the dominant period of the major pennsylvanian cyclothems is up to four times longer than the dominant 100 000 yr period inmore the pleistocene the shapes of both curves display rapid marine transgression rapid melting of ice caps and slow interrupted regression slow buildup of ice caps which suggest similar linkages between the climatic effects of the orbital parameters and ice cap formation and melting at the two different scales widely separated in time 28 references 3 figures less

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

evolution of ore fluids in the donggou giant porphyry mo system east qinling china a new type of porphyry mo deposit evidence from fluid inclusion and h o isotope systematics abstract the donggou mo deposit in the eastern qinling area china is a giant porphyry system discovered based on a targeting concept by using the tectonic model for collisional orogeny metallogeny and fluid flow cmf model mo mineralization is associated with the donggou aluminous a type granite porphyry and was formed during the early cretaceous in a tectonic regime of continental extension the orebodies mainly occur as numerous veinlets in the host rocks hydrothermal ore forming processes include at least three stages characterized by veinlets of 1 quartz k feldspar minor molybdenite 2 quartz molybdenite beryl and 3 quartz carbonate fluorite three types of fluid inclusions fis are distinguished in quartz and beryl in stages 1 and 2 i e aqueous w type carbonic aqueous c type and solid bearing s type with only aqueous fis observed in stage 3 minerals s type fis contain variable daughter minerals including halite chalcopyrite calcite and an unidentified transparent crystal but only halite can dissolve during heating halite bearing s type fis are mainly homogenized by halite dissolution at 182 416 c corresponding to salinities of 30 9 49 2 wt nacl equiv minor halite bearing s type fis are homogenized to liquid at 190 360 c via vapor disappearance with salinities of 29 1 36 2 wt nacl equiv other fis in minerals of stages 1 2 and 3 are homogenized at temperatures of 341 550 c 220 440 c and 125 225 c with salinities of 8 0 18 3 5 3 16 8 and 0 5 7 3 wt nacl equiv respectively the estimated minimum trapping pressures are up to 141 mpa in stage 1 and up to 81 mpa in stage 2 respectively corresponding to an initial mineralization depth of no less than 5 km the quartz in veinlets yields 18 o values of 8 5 10 0 corresponding to 18 o h 2 o values of 2 9 to 5 9 while the d h 2 o values of fluid inclusions range from 59 to 82 these data suggest that the ore fluids forming the donggou deposit changed from high temperature high salinity co 2 rich magmatic to low temperature low salinity and co 2 poor meteoritic fluids via boiling and mixing resembling those of other magmatic hydrothermal systems in qinling orogen and dabie shan this supports the notion that the porphyry systems generated in a post collisional tectonic setting were initially co 2 rich as indicated by abundant c type and co 2 bearing s type fluid inclusions

modeling late paleozoic glaciation late paleozoic glaciation on gondwana is associated with changes in geography solar luminosity and estimated co sub 2 levels to assess the relative importance of these boundary conditions the authors conducted a suite of climate model simulations for the periods before during and after peak mid carboniferous approximately 300 ma glaciation 340 300 and 255 and 225 ma respectively orbital insolation values favorable for glaciation and interglaciation were used for each time interval results indicate that changes in geography cause significant changes in snow area but the temporal trend is not consistent with the geologic record for glaciation combined co sub 2 plus geography changes yield the best agreement with observations in addition interglacial orbital configurations result in almost ice free conditions for the glacial interval at 300 ma at a time of low co sub 2 the large simulated glacial interglacial snowline fluctuations for permian carboniferous time may explain cyclothem fluctuations at these times overall results support the importance of the co sub 2 paradigm but also indicate that a fuller understanding of past climate change requires consideration of paleogeographic luminosity and orbital insolation changes

petrogenesis of early cretaceous post collisional granitoids at shapinggou dabie orogen implications for crustal architecture and porphyry mo mineralization abstract the shapinggou molybdenum deposit is located in the qinling tongbai hong an dabie orogen which accommodates the largest molybdenum ore belt in the world new laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating geochemical and sr nd hf isotope data for the granitoids at shapinggou are presented in this paper two stages of early cretaceous magmatism 138 128 ma and 116 114 ma took place at shapinggou in a post collisional setting these granitoids can be divided into four groups including the early stage granites 134 129 ma sio2 62 33 to 76 27 and intermediate rocks 129 128 ma sio2 52 41 to 60 72 and the late stage quartz syenite 116 ma sio2 64 09 to 65 12 and mo bearing granite porphyry 114 ma sio2 74 95 to 77 26 the early stage granites have high sr contents sr y and lan ybn ratios but low y yb and mgo contents showing low mg adakitic chemical features they were possibly generated by partial melting of the thickened mafic lower continental crust the early stage intermediate rocks have relatively high mgo contents 2 71 to 4 84 and mg values 46 to 60 but low sr y and lan ybn ratios which were likely derived from a hybrid mantle metasomatized by melts from foundered eclogitic lower continental crust and subsequent fractional crystallization the late stage quartz syenite shows chemical features of metaluminous a type granites including high abundances of alkalis hfse zr nb and trivalent ree the late stage mo bearing granite porphyry displays high sio2 alkalis zr ce contents and a cnk ratios but low ba sr p and ti showing affinity to highly fractionated i type granites the late stage quartz syenite and granite porphyry were possibly produced by partial melting of intermediate compositions of middle crust our results support the conclusion that there were three layer continental crusts in the dabie orogen prior to early cretaceous magmatism and suggest that post collisional granitoids in the dabie orogen were derived from not only lower crust but also middle crust the giant shapinggou porphyry mo deposit was most likely formed by effective transport of volatiles and mo in a convecting granitic magma column rather than by direct melting of mo enriched sources the mo bearing rocks at shapinggou are characterized by a high degree of magma differentiation close associations with a type granite and formation at the end of regional magmatism

timing of the yuchiling giant porphyry mo system and implications for ore genesis the yuchiling mo deposit is a recently discovered giant porphyry system in the east qinling mo belt china its apparent causative intrusion i e the yuchiling granite porphyry is the youngest intrusion phase 4 of the heyu multiphase granite batholith which was emplaced between 143 and 135 ma new robust constraints on the formation of the yuchiling porphyry mo system are provided by combined zircon u pb biotite 40ar 39ar and molybdenite re os dating zircon grains from the mo mineralized granite porphyry yield weighted 206pb 238u age of 134 0 1 4 ma n 19 2 error mswd 0 30 magmatic biotite from the same sample yield a 40ar 39ar plateau age of 135 1 1 4 ma 2 error and an inverse isochron age of 135 6 2 0 ma n 7 2 error mswd 10 8 which are effectively coincident with the zircon u pb age within analytical error three pulses of mineralization can be deduced from the molybdenite re os ages namely 141 137 and 134 ma which agree well with the zircon u pb ages of granitic phases 1 2 and the yuchiling porphyry phase 4 respectively these well constrained temporal correlations indicate that mo mineralization was caused by pulses of granitic magmatism and that the ore forming magmatic hydrothermal activity responsible for the yuchiling porphyry mo system lasted about 8 ma the yuchiling mo deposit represents a unique style of porphyry mo system formed in a post collision setting and associated with f rich high k calc alkaline intrusions which differ from convergent margin associated porphyry mo deposits

petrogenesis of cretaceous adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china implications for geodynamics and cu au mineralization both adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china are associated with cretaceous cu au mineralization the shaxi quartz diorite porphyrites exhibit adakite like geochemical features such as light rare earth element lree enrichment heavy ree hree depletion high al2o3 mgo sr sr y and la yb values and low y and yb contents they have low end t values 3 46 to 6 28 and high 87sr 86sr i ratios 0 7051 0 7057 sensitive high resolution ion microprobe shrimp zircon analyses indicate a crystallization age of 136 3 ma for the adakitic rocks most volcanic rocks and the majority of monzonites and syenites in the luzong area are k rich or shoshonitic and were also produced during the cretaceous 140 125 ma they are enriched in lree and large ion lithophile elements and depleted in ti and nb and ba and exhibit relatively lower end t values ranging from 4 65 to 7 03 and relatively higher 87sr 86sr i ratios varying between 0 7057 and 0 7062 the shoshonitic and adakitic rocks in the luzong area have similar pb isotopic compositions 206pb 204pb 17 90 18 83 207pb 204pb 15 45 15 62 and 208pb 204pb 38 07 38 80 geological data from the luzong area suggest that the cretaceous igneous rocks are distributed along ne fault zones e g tanlu and yangtze river fault zones in eastern china and were likely formed in an extensional setting within the yangtze block the shaxi adakitic rocks were probably derived by the partial melting of delaminated lower crust at pressures equivalent to crustal thickness of 50 km i e 1 5 gpa possibly leaving rutile bearing eclogitic residue the shoshonitic magmas in contrast originated mainly from an enriched mantle metasomatized by subducted oceanic sediments they underwent early high pressure 1 5 gpa fractional crystallization at the boundary between thickened 50 km lower crust and lithospheric mantle and late low pressure 1 5 gpa fractional crystallization in the shallow 50 km crust the adakitic and shoshonitic rocks appear to be linked to an intra continental extensional setting where partial melting of enriched mantle and delaminated lower crust was probably controlled by lithospheric thinning and upwelling of hot asthenosphere along ne fault zones e g tanlu and yangtze river fault zones in eastern china both the shoshonitic and adakitic magmas were fertile with respect to cu au mineralization

geochronology and geochemistry of the giant qian echong mo deposit dabie shan eastern china implications for ore genesis and tectonic setting abstract the qian echong mo deposit is a giant porphyry deposit in the dabie shan of eastern china molybdenum mo mineralization mainly occurs as numerous veinlets in altered schists with the development of potassic phyllic argillic and propylitic alteration assemblages a buried granite porphyry stock and locally exposed dikes are spatially and genetically related to the mo mineralization zircon crystals from exposed quartz porphyry rhyolitic porphyry and granite porphyry dikes as well as a buried granite porphyry dike yield weighted average 206 pb 238 u ages of 128 9 1 1 ma mswd 0 30 2 n 13 127 42 0 94 ma mswd 0 58 2 n 17 127 44 0 98 ma mswd 1 6 2 n 16 and 126 6 1 4 ma mswd 0 67 2 n 15 respectively the buried granite porphyry stock yields a zircon u pb weighted average age of 124 7 1 6 ma mswd 1 5 2 n 16 which is slightly younger than the exposed dikes but within error of the age of the buried granite porphyry dike five molybdenite samples from the ores yield re os isotope ages of 123 31 1 02 to 128 49 1 40 ma which are consistent with the u pb ages for the igneous rocks these age data constrain magmatic hydrothermal activity at the qian echong mo deposit to a period of about six million years from 129 to 123 ma this period overlaps the recognized regional mo mineralization event in the dabie shan of 142 111 ma which took place during the post collisional tectonism subsequent to amalgamation of the yangtze and north china blocks the qian echong granite porphyry stock and dikes have high contents of sio 2 k 2 o and al 2 o 3 and low contents of tio 2 mgo and cao showing a peraluminous high k calc alkaline to shoshonite affinity with obvious lree enrichment and a negative eu anomaly the rocks have a high initial 87 sr 86 sr of 0 70729 to 0 71788 and highly negative e nd t values of 16 2 to 26 1 with t dm2 nd ages of 2 24 to 3 03 ga their 206 pb 204 pb t 207 pb 204 pb t and 208 pb 204 pb t values range from 16 017 to 16 701 15 252 to 15 368 and 37 095 to 37 578 respectively this sr nd pb isotopic signature indicates that the causative granitic intrusions for the qian echong deposit were mainly melts with components of both the northern dabie complex and the taihua and xiong er groups that are part of the precambrian basement of the north china block the melts were generated during the tectonic extrusion of the dabie shan and their emplacement onto the basement of the north china block the qian echong mo deposit is unique based upon the crustal source for the causative porphyry localization of most mineralization in the surrounding schist country rocks and the co 2 rich ore forming fluid thus we propose the qian echong deposit to represent a new sub type of porphyry mo deposit herein termed collisional or dabie type porphyry deposit

changing patterns of pennsylvanian coal swamp vegetation and implications of climatic control on coal occurrence abstract improved regional and interregional stratigraphic correlations of pennsylvanian strata permit comparisons of vegetational changes in euramerican coal swamps the coal swamp vegetation is known directly from in situ coal ball peat deposits from more than 65 coals in the united states and europe interpretations of coal swamp floras on the basis of coal ball peat studies are extended to broader regional and stratigraphic patterns by use of coal palynology objectives of the quantitative analyses of the vegetation in relation to coal are to determine the botanical constituents at the peat stage and their environmental implications for plant growth and peat accumulation morphological and paleoecological analyses provide a basis for deducing freshwater regimes of coal swamps changes in composition of pennsylvanian coal swamp vegetation are quire similar from one paralic coal region to another and show synchrony that is attributable to climate paleobotany and paleogeography of the euramerican province indicate a moist tropical paleoclimate rainfall runoff and evapotranspiration were the variable climatic controls in the distribution of coal swamp vegetation peat accumulation and coal resources in relative terms of climatic wetness the pennsylvanian period is divisible into five intervals which include two relatively drier intervals that developed during the lower middle and middle upper pennsylvanian transitions the climate during early pennsylvanian time was moderately wet and the median in moisture availability early middle pennsylvanian was drier probably seasonally dry wet late middle pennsylvanian was the wettest in the midcontinent early late pennsylvanian was the driest and late late pennsylvanian was probably the wettest in the dunkard basin the five climatic intervals represent a general means of dividing coal resources within each region into groups with similar botanical constituents and environments of peat accumulation regional differences in basinal geology and climate were significant variables but the synchronous control of paleoclimate was of primary importance

relation of eustasy to stacking patterns of meter scale carbonate cycles late cambrian u s a abstract an interbasinal study of late cambrian cyclic carbonate successions in the appalachian and cordilleran passive margins suggests that superimposed orders of eustasy controlled the development of large scale depositional sequences and the component peritidal to subtidal meter scale cycles that comprise them the focus of this paper is on the small scale cyclicity its probable control by milankovitch forced sea level oscillations and how stacking patterns of meter scale cycles can be used to define internal components of larger scale sequences and estimate variations in relative sea level fining upward peritidal cycles showing evidence of episodic emergence grade seaward into coarsening upward subtidal cycles which lack evidence of emergence and form a continuum across the cambrian carbonate platforms eustasy appears to exert the dominant control on the simultaneous development of peritidal and subtidal cycles on late cambrian carbonate platforms evidence for milankovitch forcing of glacio eustatic sea level oscillations is provided by a 4 1 bundling of fifth order meter scale cycles 96 ky within fourth order cycles spanning tens of meters 440 ky within the big horse member of the orr formation in the house range of utah the 4 1 bundling may manifest the short e centricity to long eccentricity ratio of the milankovitch astronomical rhythms systematic changes in the stacking patterns of meter scale cycles can be used in conjunction with fischer plots to define long term sea level cycles on fischer plots of peritidal cyclic successions long term relative sea level rises are characterized by thick subtidal dominated cycles with thin laminite caps long term relative sea level falls are defined by stacks of thin laminite dominated cycles that show brecciated cycle caps and quartz sands toward the relative sea level lowstand on fischer plots of dominantly subtidal cyclic successions long term sea level rise is characterized by storm dominated open marine carbonate cycles or thick deep ramp shale based cycles falling segments of the fischer plot are characterized by thin shallow subtidal cycles compos d of restricted lithofacies cycle stacking patterns parasequence sets provide the crucial link between the meter scale cycles parasequences and the larger scale sequences and their component systems tracts one and two dimensional models of peritidal and subtidal cycle development indicate that whereas peritidal cycle thickness is primarily controlled by accommodation space deeper subtidal cycle thickness is primarily controlled by sedimentation rate lithofacies within peritidal cycles reflect the sedimentologic response to fluctuations in sea level lithofacies within subtidal cycles may be related to fluctuations in the zones of fairweather and storm wave reworking that oscillated in harmony with sea level fluctuations and may have acted as a subtidal limit to upward aggradation the 2 d modelling illustrates how stacked peritidal to deep subtidal carbonate cycles with thicknesses compositions and stacking patterns similar to the late cambrian of north america can be generated by ilankovitch driven composite eustasy

porphyry mo and epithermal au ag pb zn mineralization in the zhilingtou polymetallic deposit south china the zhilingtou polymetallic deposit south china provides an excellent opportunity to investigate the magmatic hydrothermal evolution of the porphyry mo to epithermal au ag pb zn ore spectrum new zircon u pb sphalerite 40ar 39ar and pyrite rb sr ages together with previous molybdenite re os ages indicate that the granitic magmatism and mo au ag pb zn mineralization were coeval and cogenetic in the early cretaceous 113 ma fluid inclusions and h o isotope results have established the evolution from an early high temperature h2o nacl magmatic fluid system mo mineralization to a medium temperature mixed fluid system of magmatic and meteoric water au ag mineralization to a peripheral late stage low temperature h2o nacl meteoric water fluid system epithermal au ag pb zn mineralization moreover the sulfur isotopic compositions 34s 2 1 7 8 of the sulfide minerals confirm a genetic link to the granitic magma lead isotope data from pyrite and the granite rhyolite porphyries are similar indicating that they share a common pb source the geochronological geochemical and isotopic lines of evidences consistently suggest that the porphyry mo and epithermal au ag pb zn mineralization formed in one magmatic hydrothermal system the porphyry epithermal mineralization model for zhilingtou has significant importance for prospecting work in south china where mo and associated pb zn ag resources are abundant

kinematics and geochronology of the proterozoic dongxiang shexian ductile shear zone with hp metamorphism and ophiolitic melange jiangnan region south china abstract a kinematic and geochronological analysis of the 10 20 km wide northeast trending dongxiang shexian ductile shear zone that trends along a length of 250 km in the eastern part of the jiangnan belt indicates a sinistral strike slip ductile shear that was formed during the neo proterozoic the zone experienced polyphase deformation related to tectonic collision between the huaiyu and the jiuling terranes geochronological data and kinematic analysis of macroscopic structures microscopic shear indicators and quartz c axes fabrics shows that a ductile southeastward thrusting occurred at about 950 900 ma followed by a sinistral strike slip shearing along a northeast trend at about 770 ma coarse clastic sedimentary rocks of sinian age were deposited unconformably on the entire jiangnan belt including the huaiyu and the jiuling terranes this paper emphasizes that the jiangnan belt in the se margin of yangzi plate is a neo proterozoic orogenic belt with hp metamorphism and ophiolitic melange not a late paleozoic mesozoic collisional orogen

pennsylvanian cyclothems methods of distinguishing tectonically induced changes in sea level from climatically induced changes analysis of tectonic subsidence permits calculation of the magnitude of tectonic processes and associated climatic effects which controlled changes in sea level during deposition of pennsylvanian cyclothems far field tectonic effects in response to regional orogenic movements influenced pennsylvanian sea level change in the midcontinent of north america and the illinois basin organization of virgilian and missourian midcontinent cyclothems into fourfold to fivefold bundles shows that sea level changes in midcontinent platform areas were influenced partly by milankovitch orbital parameters whereas desmoinesian sea level change apparently was influenced more strongly by tectonic subsidence sea level change associated with cyclothems in the central appalachian basin and the asturias basin of spain were controlled mostly by foreland basin subsidence and later strike slip faulting methods developed herein permit calculation of magnitudes of both tectonic and glacio eustatic components of sea level change influencing pennsylvanian cyclothem deposition and may be applicable to other cyclic sequences

fluid evolution of the yuchiling porphyry mo deposit east qinling china the yuchiling mo deposit east qinling china belongs to a typical porphyry mo system associated with high k calc alkaline intrusions the pure co2 pc co2 bearing c aqueous h2o naci w and

metallogenic geochronology of yuanzhuding cu mo deposit in western guangdong eastern guangxi metallogenic belt and its geological significance a large size porphyry cu mo deposit was recently discovered in yuanzhuding area of the western guangdong eastern guangxi metallogenic belt for the purpose of understanding geochronology of cu mo mineralization in this area the authors separated molybdenite samples from two borehole cores in the ore deposit re os dating of these molybdenite minerals from the two borehole cores has yielded eleven model ages ranging from 149 8 to 155 9 ma eight analytical results of borehole zk12 112 samples have yielded a re os isochron age of 157 3 4 3 ma 2 mswd 0 92 eleven analytical results from borehole zk12 112 and zk16 104 samples have yielded another re os isochron age of 155 6 3 4 ma 2 mswd 0 85 the two isochron ages are in accordance with the re os model ages within the range of error which demonstrates that the age results are reliable and the yuanzhuding porphyry cu mo deposit was formed in late middle jurassic the rhenium content of zk16 104 samples is very high suggesting that the metallogenic material of the yuanzhuding ore deposit originated from the mantle and this is further confirmed by the existence of many regional contemporaneous mafic intrusive rocks re os isotopic data of molybdenite from the yuanzhuding ore deposit may imply that izanagi plate with relatively buoyant topographic anomalies was subducted beneath the yuanzhuding area in early jurassic the variation of the subduction angle resulted in the tearing up of the subducting slab and the thickening of the lithosphere as a result a big slab window occurred or the partially over thickened lithospheric keel was delaminated and a series of ne striking extension belts with strong crust mantle interaction were formed which triggered the upwelling of the asthenosphere along the intersection of the nestriking deep fault and the former ew striking fault in mid late jurassic consequently many contemporaneous granitoids and mafic intrusives or enclaves as well as cu pb zn au ag deposits w sn polymetallic deposits and the yuanzhuding porphyry cu mo deposit related to these intrusives were formed in the western guangxi eastern guangdong region

pennsylvanian deposystems and paleoclimates of the appalachians abstract central appalachian basin rocks indicate major changes in source areas base level and climate for late mississipian through late pennsylvanian time through time dominant source areas change from craton and northeastern orogen to southeastern orogenic mountains the mississipian pennsylvanian uncomformity correlates with a worldwide eustatic event early pennsylvanian rocks contrast markedly with underlying mississippian mauch chunk redbeds in composition and texture yet the source areas and alluvial plain setting were similar seas transgressed northeastward during middle and earliest late pennsylvanian time along axes of the pocahontas and dunkard basins while fluvial dominant deltas prograded northwestward this progradation 1 progressively extended the coastal plain 2 provided coastal swamp environments for peat accumulation and 3 eventually cut off the narrow seaway of dunkard basin from the central interior by late pennsylvanian and transformed it into a large shallow freshwater lake redbeds calcium carbonate concretions and gilgai paleosol structures of late mississippian and late pennsylvanian rocks suggest seasonally dry tropical climate whereas the lithologies of the earlier pennsylvanian rocks are indications of everwet tropical climates with their quartz rich fluvial sandstones high quality coals and aluminum rich clay deposits streams change from predominantly bedload to suspended load generally from early to late pennsylvanian in response to changes in paleoslope gradient distance from source area unvegetated highland and change from everwet to intermittently dry tropical climate greater dryness is suggested for increased alkaline conditions observed in paleosols carbonates and coal beds of late pennsylvanian time but sufficiently wet to prevent evaporite deposition

karst controlled reservoir heterogeneity in ellenburger group carbonates of west texas petroleum production from restricted shelf carbonates of the lower ordovician ellenburger group is commonly considered to have been a result of a pervasive relatively homogeneous tectonic fracture system within the reservoir rock however regional facies and diagenetic paleokarst studies of ellenburger strata based on cores and wireline logs have demonstrated that significant reservoir compartmentalization was caused by karst modification in the upper part of the unit ellenburger group carbonates which attain a thickness of over 1 700 ft 520 m record sedimentation on a shallow water restricted shelf occupying most of west texas logging of over 10 000 ft 3 050 m of core from 63 wells has allowed recognition of six facies assemblages 1 lithic arenite 2 mixed siliciclastic carbonate packstone grainstone 3 ooid peloid grainstone 4 mottled mudstone 5 laminated mudstone and 6 gastropod intraclast packstone grainstone these facies assemblages record initial transgression and subsequent progradation and aggradation paleoslope was generally south and east from the texas arch toward the ouachita and marathon orogenic belts all facies assemblages with the local exception of the ooid peloid grainstone assemblage are characterized y very low intergranular and intercrystalline porosity porosity development in ellenburger group carbonates is directly related to a prolonged period of subaerial exposure that coincided with a middle ordovician eustatic lowstand prior to transgression of simpson group siliciclastics during this episode a widespread system of caves sinkholes joint controlled solution features and collapse breccias developed of particular importance to reservoir development was the formation of a regionally extensive cave system between 100 and 300 ft 30 and 90 m beneath the exposed ellenburger surface infill of this cave system by simpson group sand and clay segmented the upper ellenburger into three karst facies which are in descending order 1 cave roof dolomites fracture and mosaic breccias 2 laterally persistent cave fill facies siliciclastic matrix supported and carbonate matrix supported breccias and 3 lower collapse facies chaotic clast supported breccias of the cave floor pronounced vertical segregation of permeable zones defined by the three karst facies is evident in the emma andector martin block 13 and several other major ellenburger reservoirs lateral reservoir heterogeneities formed by localized laterally extensive collapse structures such as in the shafter lake reservoir also contribute to compartmentalization of producing zones within the upper ellenburger group secondary and tertiary recovery programs in these ellenburger reservoirs can be optimized by integrating concepts of lateral and vertical heterogeneity predicted by the karst model

characterization of the devonian kharyaga carbonate platform russia integrated and multiscale approach abstract the devonian carbonate platform obj 2 of the kharyaga field russia has been operated by total since 1999 and produces 42 api oil rich in h2s a multidisciplinary sedimentological structural stratigraphic and geomechanical modeling and multiscale study was made of the field integrating seismic micro resistivity log and core data to characterize the reservoir the kharyaga carbonate platform is characterized by complex relationships among sea level variations subsidence and sedimentation rates the field is divided into a platform edge barrier zone in the southern area and back barrier and lagoon environments to the north each characterized by different facies distribution and dynamic behavior the platform shelf and the reef flat show dome shaped thrombolites the back barrier is characterized by grainstone shoals associated with columnar stromatolites whereas the lagoon comprises peloidal wackestones and packstones associated with laminated fenestral stromatolites significant and prolonged subsidence in both the lagoon and the platform edge is associated with partial emergence of the platform reef as shown by karst development seismic interpretation highlighted both underlying north south structures and syndepositional east west collapse faults along the southern barrier edge two dimensional and three dimensional sedimentological modeling of the obj 2 calibrated by well data and core analyses allowed the simulation of alternative scenarios to explain the evolution of the carbonate platform during the devonian and suggested the observed facies distribution is compatible with the presence of a fixed outer platform edge represented by east west faults the carbonate platform of the kharyaga field exhibits complex behavior hydrocarbon hc accumulation and flow is controlled by the interplay of primary porosity karst distribution and structural discontinuities faults and fractures besides the role of the karstification this paper mainly focuses on the role played by tectonic structures on the evolution of the carbonate platform and on the hc flow from drill stem test data east west faults and karsts are considered as major permeability heterogeneities but interference tests showed more complex fluid pathways at the smaller scale microresistivity images show dominant northeast southwest and northwest southeast fracture sets in the central barrier forming an interconnected flow network with the seismic faults geomechanical modeling suggests that these fractures are subseismic structures linked to inherited deep seated faults active at the time of fracturing in addition to the listric reservoir faults

intracontinental porphyry and porphyry skarn mineral systems in eastern china scrutiny of a special case made in china in this contribution we discuss a series of porphyry and porphyry skarn mineral systems which constitute important metallogenic belts along major lithospheric breaks and or collision zones that form the margins of the north china craton and the yangtze craton we describe a selection of porphyry and porphyry skarn deposits in the great xing an range in northeast china the yanshan liaoning xilamulum belts along the northern margin of the north china craton the qinling orogen and the middle lower yangtze river valley along the bonudaries between the north china and the yangtze cratons the occurrence of platform carbonate successions may have played some role in the evolution of ore fluids that resulted in the formation of porphyry skarn deposits the porphyry deposits of eastern china although sharing some common features with classic porphyry systems that are related to convergent margins do exhibit unusual features particularly in terms of ore fluid compositions the common presence of fluorite hydrothermal alteration assemblages which tend to be less hydrous than the porphyry at convergent margins on the other hand the porphyry mineral systems of eastern china have some similarities with the climax type porphyry a major tectonothermal event yanshanian which took place in the jurassic cretaceous affected eastern china and most of the eastern margin of asia this yanshanian event was responsible for the magmatism and associated mineral systems in the region the granitoid intrusions and accompanying porphyry and porphyry skarn deposits were developed along orogenic belts and major structural discontinuities mostly along the tectonic boundaries between the north china and yangtze cratons and between the northern margin of the north china craton and the mongolia siberia plate the porphyry and porphyry skarn deposits herein described include chalukou in the great xing an range orogen jiguanshan in the xilamulun metallogenic belt xiaojiayingzi lanjiagou chehugou yuanbaoshan in the yanshan liaoning belt nanninhu yuchiling jinduicheng lemeingou in the east qinling orogen tongchakoou shaxi from the middle lower yangtze river valley the role of mantle lithosphere dynamics in eastern china which led to the formation of these porphyry and porphyry skarn mineral systems is discussed and reviewed

geochemical and zircon u pb and hf isotopic study of the baijuhuajian metaluminous a type granite extension at 125 100 ma and its tectonic significance for south china abstract the early cretaceous baijuhuajian pluton is an a type granitic intrusion emplaced along the jiangshan shaoxing jssx fault zone in western zhejiang province se south china it intruded into a late jurassic volcanic basin bounded by proterozoic sandstone and siltstone the granite has a coarse grained porphyritic texture and is composed of alkali feldspar phenocrysts in a matrix of k feldspar quartz plagioclase and biotite the pluton has a clear a type geochemical signature e g it is metaluminous a cnk 1 0 and has high sio2 75 to 78 wt total alkalis na2o k2o 4 8 to 8 5 wt rare earth elements total ree 228 to 438 ppm hfse and fe feot feot mgo 0 87 to 0 97 on the other hand it is characterized by low cao 0 51 to 1 01 wt tio2 0 06 to 0 13 wt p2o5 below detection and sr 7 0 to 9 5 ppm the hypersolvus texture and fine grained groundmass indicate emplacement at a shallow depth shrimp u pb zircon dating yielded a weighted mean 206pb 238u age of 126 3 ma and zircons from this pluton give ehf t values between 0 52 and 4 24 suggesting the importance of juvenile material in the magma source most of the plutonic rocks in southeast china are calc alkaline subduction related intrusions of jurassic and cretaceous age previous studies suggested that the sparse a type granites in south china were emplaced in two episodes 190 155 ma in the inland area and 100 ma along the coastal area in se south china our study of the baijuhuajian granite together with the coeval suzhou a type granite 123 ma in jiangsu province defines an important extensional event between 125 and 100 ma considering the available data for the mesozoic igneous rocks in south china we suggest that subduction of the pacific plate in the mesozoic produced voluminous calc alkaline granitoids and volcanic rocks with a younging trend from west to east the a type granites were generated during periods of local extension at 190 155 ma and 125 100 ma perhaps corresponding to localized rollback of the pacific plate

zircon u pb geochronology and hf isotopic compositions of the mesozoic granites in southern anhui province china abstract mesozoic magmatism is extensively developed in eastern china along the eastern asian continental margin but the geochronological framework is not well understood for each area in this study seventy eight samples were collected from the mesozoic igneous rocks in south anhui province east central china in order to precisely constrain their formation ages and contributions to crustal growth zircon u pb age determination using ion probe and laser ablation techniques indicate that magmatism in the area can be divided into two separate stages at 150 136 and 136 120 ma respectively the first stage of granitic rocks not documented in other areas of eastern china is mostly composed of hornblende bearing i type granodiorite and monzogranite and is considered to be formed by slab tearing during pacific subduction the second stage of magmatism coeval to that in other areas of eastern china is characterized by the occurrence of a type granite and syenite and their volcanic counterparts although i type granitic rocks are also developed locally these rocks are mostly distributed around and within the fault controlled volcanic basins and some are closely related to detachment shearing indicating their formation in an extensional setting zircon hf isotopic analyses indicate that archean material might be present in the area but that the main episode of crustal growth took place during the mesoproterozoic with very little juvenile material in the mesozoic

re os isotopic dating of molybdenites in the xiaoliugou w mo deposit in the northern qilian mountains and its geological significance abstract the xiaoliugou is a large scale w mo deposit newly explored in the northern qilian mountains caledonian fold belt northwestern china it is a vein and skarn type deposit genetically associated with the xiaoliugou caledonian granodiorite stock re os isotopic dating for the molybdenite in the deposit yields an isochron age of 462 13 ma 2 and model ages of 436 to 496 ma these results suggest that w mo mineralization occurred before the collision of plates and mineralized substances mainly originated from the crust

cyclic sedimentation and climatically caused sea level changes in the late palaeozoic of central europe significant short term fluctuations are characteristic of geological history since precambrian times only the younger quaternary climatic fluctuations are known in more detail as a result of a high grade time resolution climatic change can also be postulated with respect to older cold periods during which polar inland ice sheets developed from a discussion of endogene and exogene interpretations it is shown that global climatic changes and the sea level changes induced by them as well as changes in the position and extent of climatic zones throughout the world provide a control mechanism for sedimentation which is consistent with cyclic sedimentation in late palaeozoic times and also if the basin subsides non cyclically the model allows an explanation of the development of the permo carboniferous sedimentary cycles without numerous short term vertical oscillations of the earth s crust in reality exogene and endogene controls on sedimentation act together in great variety of combinations

cretaceous tectonic evolution of south china a preliminary synthesis abstract the cretaceous tectonic evolution of south china is characterized by widespread extensional basin and dome generation voluminous magma intrusion eruption and associated polymetallic mineralization all of which are of world wide interests that have stimulated the attention of geologists for more than half a century due to the lack of a comprehensive understanding of regional tectonic evolution and geodynamics of south china many controversies regarding the nature and origin of these features remain this paper attempts to make a review by synthesizing existing structural petrological geochronological and geochemical data of the cretaceous structures and magmas which guides us to propose a three stage tectono thermal evolutionary history of south china during the cretaceous period the earliest cretaceous 145 137 ma tectonic stage was characterized by syn orogenic shortening deformation and metamorphism under a nw se compressional setting which generated voluminous porphyry cu au ore bearing adakitic rocks in the lower yangtze river belt and gneissic granites in the coastal area its geodynamic origin was interpreted as combined effects of the pacific izanagi ridge subduction beneath the lower yangtze river belt and the pacific subduction beneath the cathaysia block this syn orogenic shortening stage was followed by a post orogenic stage 136 86 ma comprising two episodes of alternate extensional and shortening events the extension 136 118 ma in the earlier episode was dominated by a nw se extensional regime it led to significant taphrogenesis manifested by large scale extensional basins and voluminous magma intrusion eruption this extensional event was associated with a combination of the slab window opening during the ridge subduction and the rollback of the subducted pacific slab the subsequent nw se transpressional event led to cessation of active marginal magmatism and resulted in tectonic inversion of previous rift basins this transpression lasted from 117 ma to 108 ma and its driving mechanism was attributed to the collision between the eastern asian margin and the west philippine block the extension 107 86 ma in the later episode was dominated by a wnw ese extensional regime which led to a second phase of basin subsidence and produced numerous a and i type granites and bimodal volcanoes the tectonic regime then changed at ca 85 ma to wnw ese oriented transpression causing inversion of the late cretaceous rift basins and cessation of extension related magmatism the change of stress field from wnw ese extension to wnw ese transpression was related to the variations of the subducted slab dynamics i e the transition from either the ese ward retreat to wnw ward subduction of the pacific slab or the alternate stress during slab break off during the latest cretaceous a drastic change of regional tectonic stress orientation from wnw ese to n s occurred in south china the third stage predominated by n s extension was developed which caused a new phase of regional crustal subsidence along the youngest e w trending extensional structures

cretaceous magmatism and mo mineralization in the south china mo province u pb and re os geochronology constraints from the sanzhishu porphyry mo deposit abstract compared with the mesozoic w sn cu au pb zn ag mineralization in the south china mo province scmp detailed studies on mo deposits especially cretaceous mo deposits are rare due to limited exposures the sanzhishu porphyry mo deposit located in the scmp is characterized by disseminated and veinlet type molybdenite quartz veins within monzogranite zircon sims u pb analysis of the monzogranite yields a concordia age of 112 3 ma indicating that the emplacement of the sanzhishu monzogranite was in the early cretaceous six molybdenite samples yield re os ages between 111 and 112 ma with an isochron age of 111 6 4 ma which is consistent with the zircon age of the ore bearing monzogranite a new compilation of reliable re os isotope age data indicate that cretaceous mo mineralization in the scmp occurred during two major episodes at 130 145 ma and 90 120 ma with most deposits forming in the later episode during the cretaceous a back arc extensional setting in se china is evidenced by the occurrence of numerous high f mo deposits widespread a type granites and the development of pull apart basins the increasing trend in re contents of molybdenite from the early mo mineralization period to the late mo mineralization period in the scmp indicates that the area experienced stronger crust mantle interaction in the later mineralization episode based on geological evidence we propose that the early episode of mo mineralization formed in a tectonic setting associated with a metamorphosed subducted slab that experienced an increase in density and an increase in the gravitational pull on the slab itself which induced rollback of the subducting paleo pacific slab the late episode of mo mineralization developed in an extensional tectonic setting caused by the continued rollback and the eventual slab break off

u pb zircon ages of granites from the southern margin of the yangtze block timing of neoproterozoic jinning orogeny in se china and implications for rodinia assembly abstract neoproterozoic jinningian bendong granodiorite and sanfang and yuanbaoshan granites occurred in northern guangxi southern margin of the yangtze block se china and were generally considered to be of orogenic origin that is the collision between the yangtze and huanan blocks during the jinning orogeny these granites were intruded into the mesoproterozoic sibao metamorphic basement and covered unconformably by the neoproterozoic danzhou metasediments they are dominantly peraluminous asi 1 18 1 29 and have low initial end values of 4 8 to 7 6 indicating derivation from a supracrustal source with strong enrichment in rb k and th and relatively low zr hf and higher rare earth elements they are similar to post collision granites zircon u pb ages of 819 9 826 10 and 824 4 ma were obtained for the bendong granodiorite and the sanfang and yuanbaoshan granites respectively by both shrimp and conventional dating methods the age result precludes the existence of any late mesoproterozoic grenville age granitic magmatism in the southern margin of yangtze block together with previous age determinations of ophiolites along the southern margin of the yangtze block the jinning orogeny is referred to the neoproterozoic orogeny which took place between 1 0 and 0 80 ga and likely ended at 0 82 ga the granite formation age of 0 82 ga also supports the basal boundary age of 0 80 ga for the post orogenic sinian system which is probably stratigraphically correlated with the adeladean system in south australia as the link between australia east antarctica and laurentia in the configuration of the supercontinent rodinia the collision between the yangtze and huanan blocks during the neoproterozoic jinning orogeny probably marks the termination of the rodinia assembly

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent

petrogenesis and tectonic significance of a mesozoic granite syenite gabbro association from inland south china article i nfo a granite syenite gabbro association from inland south china has been studied for zircon u pb ages and hf isotopic compositions as well as whole rock elemental and sr nd isotopic compositions to constrain their sources and tectonic settings these rocks have distinctive crystallization ages the longyuanba biotite granites have a mean age of 240 ma the longyuanba two mica granites pitou alkali feldspar granites and amphibole bearing alkali feldspar granites tabei and huangbu syenites and chebu and chenglong gabbros have a similar age of 178 ma whereas the dafengnao syenite gives a mean age of 165 ma the longyuanba biotite granites and two mica granites exhibit s type characteristics probably derived from a neoproterozoic crustal source the chenglong gabbro has oib like trace element and highly depleted isotope compositions ehf t 10 0 1 3 end t 5 2 suggesting its parental melt to be of asthenospheric origin with insignificant crustal assimilation however crustal contamination is required to explain the isotopic compositions of the chebu gabbro the syenites are shoshonitic in composition and have depleted sr nd hf isotopic signatures which we interpret to have resulted from a mixed source of asthenospheric mantle and metasomatized lithospheric mantle as expected the signals of crustal assimilation are conspicuous in the petrogenesis of the more evolved syenites the pitou alkali feldspar granite and amphibole bearing alkali feldspar granite exhibit i type and a type characteristics respectively they are isotopically more depleted than the s type longyuanba granites we suggest that they may have formed through magma mixing of predominantly mantle derived melts with the neoproterozoic crust the jurassic granite syenite gabbro association was the product of asthenosphere lithosphere crust interactions which records the primary role of asthenospheric mantle upwelling in magma generation both in the mantle and in the crust in the early yanshanian time in south china they probably occurred in an intraplate rift like environment as a tectonic response to far field stress at plate margins during the early stage of the paleo pacific plate subduction the tectonic transition from the tethys orogenic regime to the paleo pacific regime was accomplished in the early jurassic and the early yanshanian magmatism should be genetically associated with the paleo pacific tectonic regime

new data on the development of the dunbarella marine marker horizon in the lublin coal basin poland abstract dunbarella marine marker horizon has significant stratigraphical importance for the lublin coal basin lcb poland it sets the boundary between westphalian a langsettian and b duckmantian and between paralic and limnic sedimentation at the same time this marker horizon is also the base of the lublin formation deposits where a main multi seam coal deposits can be found the horizon correlates with the clay cross marine band england the katharina horizon germany the netherlands and the quaregnon horizon belgium the paleontological material taken from recent boreholes provides new data about development of the dunbarella horizon of the lcb 32 bivalve species have been encountered and can be assigned to 28 genera edmondia posidonia sanguinolites polidevcia phestia and dunbarella are the most abundant in all profiles slightly less numerous are gastropods 9 genera represented mainly by glabrocingulum and euphemites and cephalopods 4 genera represented mainly by gastrioceras and anthracoceras very frequent although not so diverse are the brachiopods primarily inarticulate and represented almost exclusively by lingula studies of macrofauna showed the presence of marker species and faunal assemblages typical of the dunbarella horizon a distinctive feature of this horizon which was observed was the cyclic sedimentation and associated variability of the fauna spectrum this is typical for westphalian marine horizons of northwestern europe including those correlated with the dunbarella horizon