relation between depositional environment and the elemental composition of early diagenetic siderite early diagenetic siderites from marine and fresh water depositional environments are characterized by distinctive compositional trends siderite from fresh water environments is often relatively pure i e greater than 90 mol feco sub 3 and commonly attains end member composition siderite from marine environments however is always extremely impure and has extensive substitution of mg up to 41 mol and to a lesser extent ca up to 15 mol for fe in the siderite lattice in addition marine siderite generally contains less mn and has a higher mg ca ratio than fresh water siderite this compositional variation appears to result from differences in the chemistry of early marine and meteoric pore waters inasmuch as early marine pore waters generally have a higher mg sup 2 ca sup 2 ratio and contain less mn sup 2 and fe sup 2 and more ca sup 2 and mg sup 2 than meteoric waters

elemental and sr nd isotopic geochemistry of permian emeishan flood basalts in zhaotong yunnan province sw china this study presents new whole rock elemental and isotopic data for the basalts from the zhaotong area located in the intermediate zone of the 260 ma emeishan large igneous province elip the zhaotong basalts belong to high ti series with tio2 from 2 93 to 5 26 and ti y from 519 to 974 the parental magma was subjected to minor crustal contamination as indicated by slight nb ta depletion nb la 0 72 1 10 meanwhile the relatively invariable sr nd isotopes end t 0 74 to 2 86 mostly 1 10 to 2 86 87sr 86sr i 0 7050 0 7072 and the light rare earth elements lree enrichment la yb 10 3 19 1 of the basalts prefer a mantle plume origin a garnet dominated peridotite mantle source was further suggested on the basis of the ree distribution patterns and high sm yb and high la yb ratios this study further confirms the geochemical zoning of the high ti basalts in the elip which is in accordance with both the spatial distribution and the thickness of the basalts the high ti basalts in the intermediate and outer zones of elip e g zhaotong and guizhou share similar sr nd isotopic and elemental compositions suggesting that they originated directly from the emeishan mantle plume by contrast the high ti basalts in the inner zone e g longzhoushan and binchuan have variable compositions indicating a rather heterogeneous mantle source possibly involved with subcontinental lithospheric mantle sclm components

the mid cretaceous earth paleogeography ocean circulation and temperature atmospheric circulation a reconstruction of the global paleogeography of the mid cretaceous 100 m y ago including adjustment of continental outlines to account for microplate movements cmstal shortening and accretion in mid cretaceous and later orogenic regions is described and a map presented on the modified continents coastlines and significant mountain ranges are added this paleogeography is used as a framework for a reconstruction of ocean surface circulation and temperature distribution then the main features of the atmospheric circulation are deduced using the paleogeography and ocean temperatures as boundary conditions relative to the present these features are a much weaker westerly wind belt and greater seasonality of wind patterns leading to more extreme surface climates over the continents slightly equatorward positions of the subtropical anticyclones and monsoonal regimes over the continental margins bordering tethys and the central atlantic a comparison of the results with climatic evidence from t

experimental zircon melt and zircon garnet trace element partitioning and implications for the geochronology of crustal rocks garnet is the most commonly used mineral in thermobarometry whereas zircon is the most robust chronometer to date high grade metamorphic rocks to provide a basis for correlation of zircon and garnet growth we determined experimentally the trace element partitioningbetweenzircon ahydrousgraniticmeltandgarnetat20kbarand800 1000 cforp y rareearthelements ree zr hf th andu inrespecttomelt zirconpreferentiallyincorporatesallinvestigatedelementsapartfromreewithatomicnumberlowerthansm at this pressure and in the chosen composition the distribution coefficient between zircon and melt d zrn melt for ree increases with increasingatomicnumberofthereeandwithdecreasingtemperature dyb is 20at1000 c butmorethananorderofmagnitude higher at800 c the solubilityofzrinhydrousgraniticmelts buffered by zirconisabouta factoroftwo lower at20kbar than what has been previously established for mid crustal pressures large garnet produced in the experiments allowed determination of garnet melt trace element partitioning d grt melt at temperatures of 800 1000 c conditions relevant for partial melting of crustal rocks there is a systematic increase indree with decreasing temperature zircon contains significantly more heavy ree than garnet at temperatures of 800 850 c zircon garnetpartitioncoefficientsofheavy reedecreasewithincreasingtemperaturefromdlu of12at800 cto 1 4at1000 c middle reepartitioningisclosetounityforthewholeinvestigatedtemperaturerange differentempiricallydetermined zircon garnet partition coefficients from granulites and ultra high temperature granulites can potentially be explained by the experimentallydeterminedchangeofpartitioningasafunctionoftemperature thesedatacanassistinestablishingequilibriumbetween garnetandzirconzonesinnaturalrocks andintheconstructionofdetailedpressure temperature timepathsinhigh grademetamorphic rocks

age and duration of the emeishan flood volcanism sw china geochemistry and shrimp zircon u pb dating of silicic ignimbrites post volcanic xuanwei formation and clay tuff at the chaotian section abstract the age and duration of the emeishan basalts sw china remain poorly constrained largely due to the severe thermo tectonic overprinting of the ar ar system and failure to obtain zircon separates from erupted basalts in an attempt to solve this problem geochemical analyses and shrimp zircon u pb dating have been carried out on rare felsic ignimbrite in the uppermost of the emeishan lava succession the xuanwei formation which immediately overlies the emeishan basalts and a clay tuff at the middle late permian boundary at the chaotian section clastic rocks of the lowermost xuanwei formation group 1 in eastern emeishan large igneous province lip have a geochemical affinity to the emeishan felsic volcanic rocks whereas the overlying sediments group 2 are compositionally more akin to mafic components of the emeishan traps this is the reverse of volcanic sequence of the central emeishan lip where the felsic extrusives sit above predominant mafic rocks it is likely that the clastic rocks are water transported sediments resulting from erosion of the volcanic rocks in the center of the emeishan lip this interpretation is further supported by the general agreement between the age of the lowermost xuanwei formation 257 4 ma 260 5 ma and that of the silicic ignimbrite 263 4 ma and the clay tuff at the middle late permian boundary at chaotian 260 5 ma these ages interpreted as the termination age of the emeishan volcanism are indistinguishable within error from the middle late permian boundary age 260 4 0 4 ma and the main stage 259 262 3 ma of the emeishan volcanism inferred from dating of mafic and alkaline intrusions in the emeishan lip all these suggest that the emplacement of the emeishan volcanism took place over a very short interval moreover the temporal link and geochemical analyses suggest that the chaotian clay at the middle late permian boundary was genetically related to the emeishan silicic volcanism this together with the fact at that both the emeishan basalts and the chaotian clay rest on the maokou formation leads us to infer that the emeishan basalt was emplaced at the middle late permian boundary in this sense the emeishan volcanism can be regarded as a boundary event and its age is presumed at 260 ma although more precise dating is required both stratigraphic correlation and chronologic data presented in this paper lend supports to the notion that the emeishan volcanism was one of likely causes of the end guadalupian mass extinction

modal composition and detrital clinopyroxene geochemistry of lithic sandstones from the new england fold belt east australia a paleozoic forearc terrane the new england fold belt of southeast australia is divided by the peel fault system into two time equivalent zones showing contrasting depositional structural and metamorphic histories these are inferred to represent a western magmatic arc frontal arc succession and an eastern subduction complex assemblage the composition of the early to middle paleozoic clastic rocks from both east and west of the peel fault system indicates derivation from an undissected volcanic arc detrital quartz is absent or present only in minor amounts and always as monocrystalline grains lithic fragments are almost exclusively volcanic and normally dominant over feldspar which is invariably plagioclase now largely albitized to the west of the fault the distribution of lathwork microlitic felsitic and vitric rock fragments as well as variation in the amount of detrital quartz indicates changes in provenance through time and two cycles of basaltic to silicic volcanic activity have been identified the composition of detrital calcic clinopyroxene grains particularly their low ti and al contents and their ti mn na ratios indicates that they crystallized mainly from subalkaline probably calc alkaline volcanic arc magmas the dominantly volcanogenic provenance of sandstone from east of the fault and the low ti content of most detrital clinopyroxene grains indicate that the volcanic chain that lay to the west of the peel fault was the most likely source for the major portion of the clastic debris in the eastern rocks however the presence of ti rich detrital clinopyroxenes identical in composition to those in the metabasalts of the subduction complex indicates that uplifted segments of the complex provided an additional sediment source

a lower crust origin of some flood basalts of the emeishan large igneous province sw china abstract high seismic velocity layers within the lower crust i e 40 km of the yangtze block are interpreted as mafic underplated rocks derived from the late permian emeishan mantle plume however the region experienced a previous magmatic event during the neoproterozoic 800 ma that produced the kangdian basalts and associated mafic intrusions and therefore the lower crust seismic velocity layers may represent a mixture of two different magmatic episodes the identification of inherited neoproterozoic i e 750 to 850 ma zircons within emeishan magmatic rocks indicates either assimilation of older material during emplacement or that the rocks could be derived from a mafic neoproterozoic precursor equilibrium partial melt modeling of neoproterozoic kangdian basalts can produce compositions similar to emeishan basalt at a pressure of 1 2 gpa i e 40 km depth it is suggested that the injection of high temperature picritic magmas into the lower crust of the yangtze block could be sufficient to induce high degrees of melting of the lower crust and produce magmas that are similar in composition to some emeishan mafic rocks and or produce melts that could contaminate pristine emieshan magmas

late permian basalts in the yanghe area eastern sichuan province sw china implications for the geodynamics of the emeishan flood basalt province and permian global mass extinction abstract we report the finding of a 20 m thick sequence of massive pyroxene plagioclase phyric basalt lava flows in the yanghe area of the northeastern sichuan basin within the yangtze craton of sw china which were previously considered to be located outside the emeishan flood basalt province this basaltic sequence above the middle permian maokou formation fm is overlain by the late permian longtan fm thus the yanghe basalts should be stratigraphically correlated with the emeishan flood basalts the yanghe basalts show typical oceanic island basalt oib affinity and geochemically resemble emeishan basalts especially in the case of high ti ht basalts from the eastern domain of the emeishan flood basalt province the rocks have low age corrected 87sr 86sr t t 260 ma ratios 0 704158 0 704929 and pb isotopic ratios 206pb 204pb t 18 264 18 524 207pb 204pb t 15 543 15 58 and 208pb 204pb t 38 147 38 519 and positive end t values 3 15 to 3 61 suggesting that the lavas have not undergone any significant crustal contamination the crystallization temperature of clinopyroxene is estimated to be 1368 1420 c suggesting anomalously thermal inputs from a mantle source and a possible plume head origin the fractionation of middle rare earth elements mree to heavy ree hree suggests that these rocks were produced by small degrees of partial melting of mantle peridotite within the garnet spinel transition region the stratigraphic relationships and similar geochemical signatures with the emeishan flood basalts suggest that the yanghe basalts are part of the emeishan flood basalt province and can be considered as the northeastern limit of the emeishan flood basalt province our finding extends the diameter of the emeishan flood basalt province to 1200 1400 km covering an area of up to 7 105 km2 two times more than previously estimated the larger areal extent and giant eruption volume incorporating the sichuan basin lend support to the correlation between the end guadalupian mass extinction and the emeishan flood basalt province

rhyolites in the emeishan large igneous province sw china with implications for plume related felsic magmatism abstract in the emeishan large igneous province elip western yangtze block sw china minor amounts of silicic volcanic rocks 5 are spatially and temporally associated with flood basalts the distribution and origin of these silicic rocks are keys to understanding the processes associated with mantle plume activities in the binchuan and panzhihua areas southwestern elip there are nb ta poor and nb ta rich rhyolites nb ta poor rhyolites interlayered with basalts in the binchuan area occur in the lower part of the emeishan volcanic sequence and have a crustal origin they are characterized by negative nb ta anomalies low end t and high 87sr 86sr i values and zircon saturation temperatures 836 852 c nb ta rich rhyolites are associated with the main phase of the emeishan volcanic sequence in the binchuan and panzhihua areas and are characterized by positive nb ta anomalies oceanic island basalt oib like trace element ratios low 87sr 86sr i ratios positive end t and ehf t values and high a cnk ratios and fe s in addition they have high ga al ratios high field strength elements hfses and high zircon saturation temperatures 920 c typical of aluminous a type silicic rocks similar to the spatially distributed syenitic intrusions of the elip these nb ta rich rhyolites are best interpreted as hybrid products of crystal fractionation of high ti basaltic magmas coupled with minor crustal assimilation 6 14 on the basis of rhyolite melts and ec afc simulations the temporal and spatial distributions of these two types of rhyolite reflect various extents of thermal and mass exchange between mantle derived basaltic magma and crustal material above a mantle plume when the plume head reached the base of the western yangtze block enriched components in the lithospheric mantle were melted and the melts partially ponded near the crust mantle boundary or in the lower crust where they induced partial melting of crustal materials to form nb ta poor rhyolites during the main phase of volcanism large magma chambers and extensive plumbing systems developed due to decompressional melting of the mantle plume in this stage abundant mafic ultramafic and felsic intrusions were formed and nb ta rich rhyolites and a type granites were emplaced

evolution of a plume influenced source to sink system an example from the coupled central emeishan large igneous province and adjacent western yangtze cratonic basin in the late permian sw china abstract source to sink paleogeography in a time constrained sequence stratigraphic framework has been reconstructed for the non marine to marine transitional lopingian strata late permian in the western yangtze cratonic basin wycb and the adjacent inner zone of the emeishan large igneous province elip in order to reveal the evolution of a mantle plume influenced cratonic basin the lopingian coal bearing strata can be subdivided into seventeen 4th order sequences and three 3rd order composite sequences representing 6 76 myr paleogeographic reconstructions of the wycb demonstrate the existence of n s trending terrestrial transitional and marine facies belts distributed west to east away from the central elip geomorphological analysis indicates that the western boundary of the source area coincided with the major axis of the uplifted central elip based on sediment flux estimates and modeling bqart model relief of the central elip increased from near sea level in the earliest late permian and reached equilibrium at about 200 m in the latest permian sediment volume backfilling analysis indicates that total tectonic uplift of the central elip in the late permian was more than 500 m evolution of the coupled central elip and wycb can be subdivided into three stages pre eruptive uplift stage pre and syn eruptive subsidence stage and syn and post eruptive uplift stage post eruptive basin filling was controlled by sediment supply that was related to tectonic uplift drainage topography and climate change and basin accommodation that was related to sea level fluctuations and plume induced syn sedimentary tectonics

rapid magma evolution constrained by zircon petrochronology and 40ar 39ar sanidine ages for the huckleberry ridge tuff yellowstone usa understanding the time scales of magmatic differentiation storage and eruption of large volume silicic magmas is a primary goal of igneous petrology within the huckleberry ridge tuff hrt idaho usa representing the earliest and largest caldera forming eruption associated with yellowstone volcanic activity zircon morphological zoning patterns coupled to strongly correlated changes in ti in zircon thermometry and trace element indicators of progressive differentiation provide a proxy record for the evolution of the hrt member b magma body tandem in situ and isotope dilution u pb dating of single zircon crystals demonstrates an absence of pre pleistocene xenocrysts but reveals the presence of antecrysts recycled from pre caldera rhyolites in the hrt magma the petrochronologic interpretation of autocrystic zircon thermal chemical and temporal characteristics suggests that hrt member b differentiated over 10 k y prior to eruption at 2 0794 0 0046 ma as defined by new astronomically calibrated single crystal total fusion 40 ar 39 ar sanidine analyses this refined eruption age demonstrates that the transitional polarity preserved by hrt member b does not record the reunion subchron but rather a separate younger geomagnetic event our novel approach places the thermal and chemical regime of silicic magmas within a temporal context and demonstrates the rapid evolution of a large volume of silicic magma

high latitude meteoric δ18o compositions paleosol siderite in the middle cretaceous nanushuk formation north slope alaska siderite bearing pedogenic horizons of the nanushuk formation of the north slope alaska provide a critical high paleolatitude oxygen isotopic proxy record of paleoprecipitation supplying important empirical data needed for paleoclimatic reconstructions and models of greenhouse world precipitation rates siderite 18 o values were determined from four paleosol horizons in the national petroleum reserve alaska npr a grandstand 1 core and the values range between 17 6 and 14 3 peedee belemnite pdb with standard deviations generally less than 0 6 within individual horizons the 13 c values are much more variable ranging from 4 6 to 10 8 pdb a covariant 18 o versus 13 c trend in one horizon probably resulted from mixing between modified marine and meteoric phreatic fluids during siderite precipitation groundwater values calculated from siderite oxygen isotopic values and paleobotanical temperature estimates range from 23 0 to 19 5 standard mean ocean water smow minor element analyses show that the siderites are impure having enrichments in ca mg mn and sr minor element substitutions and mg fe and mg ca mg ratios also suggest the influence of marine fluids upon siderite precipitation the pedogenic horizons are characterized by gleyed colors rare root traces abundant siderite abundant organic matter rare clay and silty clay coatings and infillings some preservation of primary sedimentary stratification and a lack of ferruginous oxides and mottles the pedogenic features suggest that these were poorly drained reducing hydromorphic soils that developed in coal bearing delta plain facies and are similar to modern inceptisols model derived estimates of precipitation rates for the late albian of the north slope alaska 485 626 mm yr are consistent with precipitation rates necessary to maintain modern peat forming environments this information reinforces the mutual consistency between empirical paleotemperature estimates and isotope mass balance models of the hydrologic cycle and can be used in future global circulation modeling gcm experiments of greenhouse world climates to constrain high latitude precipitation rates in simulations of ancient worlds with decreased equator to pole temperature gradients

equable climates during earth history eocene and cretaceous climate model experiments demonstrate that regardless of conditions of warm polar oceans differences in pole to equator surface temperature gradient or topography above freezing surface temperatures in winter for continental interiors at middle to high latitudes cannot be maintained continental interiors will have cold winter temperatures even during globally warm periods unless currently unrecognized forcing factors influenced past climates if model simulations of eocene and cretaceous climates are accurate the term equable as it applies to paleoclimate should be reconsidered

zircon u pb and hf isotope constraints on crustal melting associated with the emeishan mantle plume abstract shrimp zircon u pb dates combined with in situ hf isotopic data provide new constraints on the petrogenesis and protolith of peralkaline metaluminous and peraluminous intrusions and rhyolitic tuffs in the emeishan large igneous province with significant bearing on crustal melting associated with mantle plumes syenite and a type granitic intrusions from huili miyi and taihe in the center of this large igneous province yield u pb dates at 260 ma consistent with the ages obtained for mafic layered intrusions in the same province zircon from these rocks exhibits a wide range of initial hf isotope ratios ehf t 1 4 to 13 4 with corresponding tdm1 of 400 900 ma the highest ehf t value is only marginally lower than that of depleted mantle reservoir at 260 ma suggesting that their source is primarily juvenile crust added during emeishan volcanism with incorporation of variable amounts of neoproterozoic crust the trigger of crustal melting is most likely related to advective heating associated with magmatic underplating in contrast the 255 251 ma peraluminous granites from ailanghe and 238 ma rhyolitic tuff from binchuan have negative initial ehf values of 1 3 to 4 4 and of 7 7 to 14 respectively hf isotopic model ages and presence of inherited zircons indicate their derivation from mesoproterozoic and paleoproterozoic crust respectively given the time lag relative to the plume impact 260 ma and insignificant mantle contribution to 255 238 ma magmatism conductive heating is suggested as the trigger of crustal melting that resulted in formation of delayed felsic magmas the involvement of older crust in younger felsic magmas is consistent with upward heat transfer to the lithosphere during plume impregnation if the age of crust is inversely stratified i e changes from paleoproterozoic to mesoproterozoic to neoproterozoic to permian with increasing depth such crust may have resulted from episodic downward crustal growth during the evolution of the western yangtze craton

paleobotanical evidence for cool north polar climates in middle cretaceous albian cenomanian time mid cretaceous albian cenomanian floras are abundant and diverse on the north slope of alaska the older floras consist of conifers cycadophytes ferns ginkgophytes and sphenophytes horsetails angiosperms appeared in latest albian time and rapidly diversified the preserved floras consist entirely of deciduous plants with the exception of a microphyllous conifer ferns and sphenophytes deciduousness is evidence for strong seasonality which for these floras might be variations in either light or temperature or both cool temperatures are suggested by the prevalence of toothed leaves among the angiosperms and the presence of large leaved conifers the paleobotanical evidence points to a mid cretaceous climate that was no warmer than cool temperate on the north slope of alaska

late cretaceous early tertiary palaeoclimates of northern high latitudes a quantitative view analyses of plant community structure vegetational and leaf physiognomy and growth rings and vascular systems in wood provide qualitative and quantitative data that can be combined to define non marine palaeoclimatic parameters with better resolution than is available from other principally sedimentological methods application of these techniques to cenomanian through paleocene floras from high palaeolatitudes 75 85 n indicates a polar light regime similar to that of the present plant data suggests cenomanian sea level mean annual air temperatures mats of 10 c and mats of 13 c 5 c and 6 7 c in the coniacian maastrichtian and paleocene respectively evapotranspirational stresses at sea level were low and precipitation was in most part uniform throughout the growing season in the cenomanian with possible seasonal drying occurring by the maastrichtian maastrichtian winter freezing was likely but periglacial conditions did not exist at sea level permanent ice was likely above 1700 m at 75 n in the cenomanian and above 1000 m at 85 n in the maastrichtian these near polar data provide critical constraints on global models of late cretaceous to early tertiary climates

middle late cretaceous climate of the southern high latitudes stable isotopic evidence for minimal equator to pole thermal gradients a detailed 18 o and 13 c stratigraphy has been generated from analysis of well preserved albian early maastrichtian foraminifera from deep sea drilling project dsdp sites 511 and 327 falkland plateau 58 s 62 s paleolatitude in the southern south atlantic and cenomanian and coniacian santonian foraminifera from dsdp site 258 naturaliste plateau 58 s paleolatitude in the southern indian ocean these results when combined with previously published maastrichtian stable isotope data from ocean drilling program odp site 690 weddell sea 65 s paleolatitude provide new insight into the climatic and oceanographic history of the southern high latitudes during middle late cretaceous time the planktonic foraminifer 18 o curves reveal a gradual warming of surface waters from the albian through the cenomanian followed by extremely warm surface waters from the turonian through the early campanian long term cooling of surface waters began in the late early campanian and continued through the end of the maastrichtian the benthic foraminifer 18 o record generally parallels changes in the oxygen isotopic curves defined by shallow dwelling planktonic foraminifera the vertical oxygen and carbon isotopic gradients were relatively low during the albian cenomanian high from the turonian early campanian and then low during the late campanian and maastrichtian foraminiferal oxygen isotopic data from published sources and this study are averaged for each site corrected for latitudinal changes in salinity based on modern day surface water values and plotted versus paleolatitude for the late albian coniacian santonian and late maastrichtian differences between lowand high latitude surface water paleotemperatures are estimated at 14 c during the late albian and late maastrichtian but the coniacian santonian reconstruction reveals only a 0 4 c latitudinal temperature gradient uncertainty regarding cretaceous salinity gradients and possible diagenetic alteration of 18 o values introduce error into our estimates of paleolatitudinal thermal gradients however apparent low equator to pole temperature differences could indicate much higher poleward heat transport than at present

a temporal link between the emeishan large igneous province sw china and the end guadalupian mass extinction abstract previous studies have suggested that there were two mass extinction events in the late permian one that occurred at the permo triassic p t boundary 251 ma and a second smaller mass extinction that occurred 5 8 myr earlier at the end of the guadalupian many workers have argued that there is a causal relationship between large scale volcanic activity and mass extinctions the major mass extinction event at the p t boundary coincides with the outpouring of huge quantities of lava that formed the siberian flood basalt province in russia courtillot et al earth planet sci lett 166 1999 177 195 and wignall earth sci rev 53 2001 1 33 suggested that the earlier late permian mass extinction coincided with the eruption of the lavas that formed the emeishan flood basalt efb province in sw china however the age of eruption of the efb lavas is poorly constrained using the sensitive high resolution ion microprobe to analyze zircons we have established the age of the xinjie intrusion believed to be a feeder to the main phase of efb volcanism to be 259 3 ma hence the formation of the efb is coincident with a proposed extinction event at 256 259 ma this result supports a temporal link between the emeishan large igneous province and the end guadalupian mass extinction

tracking the evolution of large volume silicic magma reservoirs from assembly to supereruption the most voluminous silicic volcanic eruptions in the geological past were associated with caldera collapses above giant silicic magma reservoirs the thermal evolution of these subcaldera magma reservoirs controls the volume of eruptible magma and eruptive style here we combine high precision zircon u pb geochronology trace element analyses of the same mineral grains and mass balance modeling of zircon trace element compositions allowing us to track the thermal and chemical evolution of the oligocene fish canyon tuff magma reservoir colorado united states as a function of absolute time systematic compositional variations in u pb dated zircons record 440 k y of magma evolution an early phase of volumetric growth was followed by a period of cooling and crystallization during which the fish canyon magma approached complete solidifi cation subsequent remelting due to underplated andesitic recharge magmas began 219 45 k y prior to eruption and led to the generation of 5000 km3 of eruptible crystal rich 45 vol dacite age equivalent but compositionally different zircons in an andesite enclave from late erupted fish canyon tuff tie the growth and thermal evolution of the upper crustal reservoir to a lower crustal magma processing zone our results demonstrate that the combination of high precision dating and trace element analyses of accessory zircons can reveal invaluable information about the chemical and thermal histories of silicic magmatic systems and provides critical input parameters for fl uid dynamic modeling

emeishan large igneous province sw china in recent years there have been major advances in our understanding of the emeishan large igneous province lip of sw china following publication of a number of lip focused investigations of the terrain and associated rocks this paper reviews the current state of knowledge the volcanic and upper intrusive portion of the province is relatively small 0 3 106 km3 even when offset fragments eroded sections and buried portions are included in the volume calculation the most reliable radiometric age dates zircon u pb shrimp from an associated layered intrusive body several kilometers in area indicate generation at 259 ma consistent with the end guadalupian end middle permian stratigraphic age in addition several ar ar dating studies have been carried out mainly on the volcanic rocks with a number of reported dates 253 251 ma late permian but a consensus is emerging that these ages are problematic because they are in conflict with the stratigraphic data possibly due to a monitor standard miscalibration the ar ar investigations have also yielded a large number of secondary ages which are clustered at 175 142 98 and 42 ma and these are inferred to record sub regional tectonic events that affected the western yangtze block as east asia was assembled and later deformed by india s collision indentation into asia magnetostratigraphic data and field observations suggest that the bulk of the volcanic sequence formed within 1 2 my the geochemistry of the volcanic rocks and bio lithostratigraphic studies of the underlying maokou formation suggests a mantle plume generated the province the basalts can be classified into low and high ti groups with different parental magmas the low ti basalts are confined to the western part of the province and are overlain by the high ti basalts the low ti magmas formed at shallow mantle depths in the spinel garnet field transition zone 60 80 km whereas the high ti magmas formed by low degrees of partial melting within the deeper garnet stability field this observation suggests a deepening of the melting column as the lithosphere thickened due to under plating and a transition from peak basalt generation to the waning stage outstanding issues which might focus future studies are also outlined

silicic magmas from the emeishan large igneous province southwest china petrogenesis and their link with the end guadalupian biological crisis abstract the emeishan large igneous province in sw china comprises a bimodal mafic silicic suite with the silicic rocks occurring at the uppermost part of the thick lava sequence the silicic rocks have an age of 257 263 ma and are thus roughly coeval with the guadalupian loping g l boundary event most silicic rocks trachyte and rhyolite from the emeishan province have rather uniform e nd values 1 to 2 9 that are comparable with the uncontaminated high ti basalts this fact and the remarkably narrow ranges of incompatible element ratios e g zr nb of the basalt silicic suite indicate a genetic relationship between basalt and silicic members the significant difference between the emeishan rocks and the experimental melts of hydrated basaltic crust suggests the fractional crystallization of basaltic magma rather than crustal melting as the major petrogenetic process for the formation of silicic rocks indeed their major and trace element trends can be modeled by fractionation of the observed mineral phases feldspar clinopyroxene fe ti oxide and apatite in contrast to the virtually closed system differentiation processes associated with trachytes the rhyolites may have experienced interaction with upper crustal material during ascent the geochemical characteristics and recent assessment of timing of the emeishan volcanism suggest the emeishan rhyolites as the potential source of the widespread clay bed at the g l boundary in south china this enhanced the causal link between the emeishan eruption and the end guadalupian biological crisis

crustally derived granites in dali sw china new constraints on silicic magmatism of the central emeishan large igneous province we have identified a new crustally derived granite pluton that is related to the emeishan large igneous province elip this pluton the wase pluton near dali shows two distinct shrimp zircon u pb age groups 768 and 253 ma as it has an intrusive relationship with devonian limestone the younger age is interpreted as its formation which is related to the elip event whereas the 768 ma neoproterozoic aged zircons were inherited from precambrian crustal component of the yangtze block implying the pluton has a crustally derived origin this is consistent with its peraluminous nature negative nb ta anomaly enrichment in light rare earth elements high 87sr 86sr i ratio 0 7159 0 7183 and extremely negative e nd i values 12 15 to 13 70 indicative of melts derived from upper crust materials the wase pluton intruded devonian strata lie stratigraphically below the shangcang elip sequence which is the thickest volcanic sequence 5400 m in the whole elip the uppermost level of the shangcang sequence contains laterally restricted rhyolite although the rhyolite has the same age as the wase pluton its geochemical features demonstrate a different magma origin the rhyolite displays moderate 87sr 86sr i 0 7053 slightly negative e nd i 0 18 and depletions in ba cs eu and sr implying derivation from differentiation of a mantle derived mafic magma source the coexistence of crustally and mantle derived felsic systems along with the robust development of dike swarms vent proximal volcanics and thickest flood basalts piles in dali shows that the dali area was probably where the most active emeishan magmatism had once existed

provenance of late permian volcanic ash beds in south china implications for the age of emeishan volcanism and its linkage to climate cooling abstract whole rock geochemistry and zircon trace element u pb and hf isotopic data for upper permian volcanic ash at shangsi show a significant change in source from the emeishan large igneous province lip to a convergent plate margin magmatic arc the lower stratigraphic samples display high al2o3 tio2 ratios strong negative eu anomalies and no depletion in high field strength elements zircons with ages of ca 260 ma from these ashes have a geochemical affinity to within plate type magmas and with felsic ignimbrites from the uppermost part of the emeishan volcanic succession at binchuan these features combined with relatively high ehf t values and low th nb ratios in the zircons imply a late stage felsic volcanic origin related to emeishan lip the upper stratigraphic samples at shangsi display significant depletion in nb and ti zircons separated from these volcanic ashes are chemically similar to those from arc related orogenic rocks indicative of a magmatic arc source combined with published high precision ca tims data for these volcanic ash layers the emeishan volcanism can be constrained to between ca 260 257 8 ma the age of emeishan volcanism is consistent with the wuchiapingian climate cooling event supporting a potential linkage between these two phenomena

late cretaceous terrestrial vegetation a near polar temperature curve quantitative estimates of terrestrial paleotemperatures near the north pole were derived from the physiognomy of the vegetation including leaf margin analysis from rocks of latest albian and late cretaceous age of the north slope of alaska during the latest albian and cenomanian mean annual temperature was approximately 10 3 c during the coniacian mean annual temperature may have been 2 3 c warmer than during the albian cenomanian but no higher than 13 c during the campanian and maastrichtian mean annual temperature would have been about 2 8 c although the ranges for the individual estimates overlap differences among the floras indicate that the relative changes in mean annual temperature did occur

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

tectonic history of a jurassic backarc basin sequence the gran canon formation cedros island mexico based on compositional modes of tuffaceous deposits the jurassic gran canon formation cedros island baja california mexico constitutes an unusually well preserved and exposed example of ancient backarc basin fill petrofacies analysis conducted on tuff aceous sandstone and tuff samples from this formation complement and reinforce prior lithofacies interpretations but with some modification when temporal and spatial trends in petrographic data detrital modes are analyzed and compared to mod els based on data collected from deep sea drilling project and ocean drilling pro gram cores the trends indicate a second heretofore unrecognized phase of backarc rifting basalt lavas interstratified with da citic pyroclastic rocks of the primary vol canic lithofacies previously interpreted to record the eruption of differentiated mag mas at the climax of growth of the gran canon island arc are now as a result of this study considered to be the product of arc extension and rifting our method of modal analysis uniquely combines the quantification of textural at tributes of pyroclastic and epiclastic debris that reflect eruption style and magma com position as well as the effects of reworking and mixing in marine settings this study demonstrates that detailed petrographic analysis is useful in the interpretation of ancient volcaniclastic deposits suspected of having formed in backarc basin settings

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

early wuchiapingian cooling linked to emeishan basaltic weathering abstract the last glaciation during the late paleozoic ice age commenced at around the guadalupian lopingian g l boundary and is synchronous with the emplacement of the emeishan large igneous province using ca tims zircon u pb dating we obtained an age of 259 51 0 21 ma for the uppermost tuff from the puan volcanic sequence in the eastern emeishan large igneous province constraining the timing of emeishan volcanism and providing another candidate age for the g l boundary in addition we determined an age of 259 69 0 72 ma for a basal claystone in the immediately overlying longtan formation from a drill core section in southwest south china these ages along with source weathering trends of mudstones from the lower longtan formation and compiled paleotemperature records indicate an earliest wuchiapingian cooling coinciding with the onset of the last permian glaciation this global cooling is associated with positive shifts in both organic and carbonate carbon isotopic records and likely a decrease in atmospheric pco2 a hypothesised causal linkage is proposed in which the rapid post eruptive basaltic weathering of the emeishan province in an equatorial humid belt may accelerate the atmospheric co2 consumption and lead to climate cooling our work supports the long term climate cooling effects of large igneous provinces

anatomy and evolution of a lower cretaceous alluvial plain sedimentology and palaeosols in the upper blairmore group south western alberta canada the lower cretaceous albian upper blairmore group is part of a thick clastic wedge that formed adjacent to the rising cordillera in south western alberta regional transgressive intervals are superimposed on the overall regressive succession alluvial conglomerates sandstones and mudstones were deposited in east north eastward draining fluvial systems orientated transverse to the basin axis five facies associations have been identified igneous pebble conglomerate thick sandstone interbedded lenticular sandstone and mudstone thick mudstone with thin sandstone interlayers and fossiliferous sandstone and mudstone the facies associations are interpreted as gravelly fluvial channels sandy fluvial channels sand dominated floodplains mud dominated floodplains and marine shoreline deposits respectively five types of palaeosols are recognized in the upper blairmore group based on lithology the presence of pedogenic features clay coatings root traces ferruginous nodules slickensides carbonate nodules and degree of horizonization the regional distribution of the various types of palaeosols enables a refinement of the palaeoenvironmental reconstruction permitting an assessment of the controls on floodplain evolution in source proximal areas palaeosol development was inhibited by high rates of sedimentation in source distal locations poor drainage resulting from high watertables low topography and lower rates of sedimentation also inhibited palaeosol development the best developed palaeosols containing bt horizons occur in intermediate alluvial plain positions tectonic hinge zone where the floodplains were most stable due to a balance between sedimentation erosion and subsidence rates extrapolating from the upper blairmore group suggests that the tectonic hinge zone of continental foreland basins can be established by palaeosol analysis at the hinge zone soil development is controlled primarily by climate and tectonics and their effect on sediment supply whereas closer to the palaeoshoreline relative sea level fluctuations resulting in poor drainage may have a more significant influence

origin and diagenetic evolution of ca mg fe carbonates in some coalfields of japan carbonate concretions lenses and bands in the pleistocene palaeogene and upper triassic coalfields of japan consist of various carbonate minerals with varied chemical compositions authigenic carbonates in freshwater sediments are siderite calcite ankerite dolomite ferroan magnesite in brackish water to marine sediments in the coal measures calcite dolomite ankerite siderite ferroan magnesite and in the overlying marine deposits calcite dolomite siderite most carbonates were formed progressively during burial within a range of depths between the sediment water interface and approximately 3 km the mineral species and the chemical composition of the carbonates are controlled primarily by the initial sedimentary facies of the host sediments and secondarily by the diagenetic evolution of pore water during burial based on the regular sequence and burial depth of precipitation of authigenic carbonates in a specific sedimentary facies three diagenetic stages of carbonates are proposed carbonates formed during stage i 2000 m are fe calcite and extremely high ca mg siderite the latter is exclusively in marine mudstones the supply of ca is partly from the alteration of silicates in the sediments at elevated burial temperatures after uplift calcite with low mg content precipitates from percolating groundwater and fills extensional cracks

voluminous silicic eruptions during late permian emeishan igneous province and link to climate cooling abstract silicic eruptive units can constitute a substantive component in flood basalts dominated large igneous provinces but usually constitute only a small proportion of the preserved volume due to poor preservation thus their environmental impact can be underestimated or ignored establishing the original volume and potential climate sensitive gas emissions of silicic eruptions is generally lacking for most large igneous provinces we present a case study for the 260 ma emeishan province where silicic volcanic rocks are a very minor component of the preserved rock archive due to extensive erosion during the late permian modal and geochemical data from late permian sandstones derived from the province suggest that silicic volcanic rocks constituted some 30 by volume of the total eroded emeishan volcanic source rocks this volume corresponds to 3 10 4 km 3 on the basis of two independent estimate methods detrital zircon trace element and hf isotopic data require the silicic source rocks to be formed mainly by fractional crystallization from associated basaltic magmas based on experimental and theoretical calculations these basalt derived 104 km3 silicic eruptions released 1017 g sulfur gases into the higher atmosphere and contribute to the contemporaneous climate cooling at the capitanian wuchiapingian transition 260 ma this study highlights the potentially important impact on climate of silicic eruptions associated with large igneous province volcanism

a simulation of mid cretaceous climate a series of general circulation model experiments utilizing genesis have been completed for the mid cretaceous based on geography variable atmospheric carbon dioxide concentrations 2 to 6 times present day concentrations and variable poleward oceanic heat flux 6 to 1 2 1015 w increased from present day by combining all three major variables co2 geography and oceanic heat flux the distribution of mid cretaceous temperatures can be achieved in the simulations increased co2 is required to promote global warmth and increased oceanic heat flux is required to prevent the tropics from overheating with higher levels of co2 four times present day co2 with 1 2 1015 w provided the best match to the distribution of mid cretaceous data the best match to the cretaceous observations was achieved with a globally averaged surface temperature increase of 6 2 c at the lower end of past estimates of mid cretaceous warmth this value may be a better estimate of mid cretaceous global warming finally the model experiments can be used to provide a paleocalibration of the global warming expected for a doubling of atmospheric carbon dioxide the best estimates for the mid cretaceous appear to be a 2 5 to 4 0 c sensitivity in the mid to upper range of the sensitivity of current climate models used to assess future global change

geologic geochemical and geophysical consequences of plume involvement in the emeishan flood basalt province prevolcanic kilometer scale lithospheric doming in the emeishan large igneous province southwest china allows us to evaluate the spatial and temporal consequences of uplift on the paleogeography geology geochemistry and geophysics of the region systematic spatial variations are observed across the domal structure in the distribution and thickness of clastic and carbonate sediments the extent of erosion thickness and chemistry of volcanic rocks and the crust mantle structure these features which are best explained by a mantle plume may be used to track older plume sites in the geologic record

silicic ash beds bracket emeishan large igneous province to 1 m y at 260 ma this research was supported by the open fund plc201404 of state key laboratory of oil and gas reservoir geology and exploitation chengdu university of technology the national natural science foundation of china 41502109 project funded by china postdoctoral science foundation 2015 m582528 and the fundamental research funds for the central universities chengdu university of technology

os pb and nd isotope geochemistry of the permian emeishan continental flood basalts insights into the source of a large igneous province abstract the nature of the source of continental flood basalts cfb is a highly debated topic proposed mantle sources for cfbs including both high and low ti basalts include subcontinental lithospheric mantle sclm asthenospheric mantle and deep plume related mantle re os isotope systematics can offer important constraints on the sources of both ocean island basalts oib and cfb and may be applied to distinguish different possible melt sources this paper reports the first re os isotope data for the late permian emeishan large igneous province lip in southwest china twenty one cfb samples including both low and high ti basalts from five representative sites within the emeishan lip have been analyzed for os nd and pb isotopic compositions the obtained os data demonstrate that crustal assimilation affected os isotopic compositions of some emeishan basalt samples with low os concentrations but not all of the samples and the emeishan basalts with high os contents likely experienced the least crustal contamination the low and high ti basalts yield distinct os signatures in terms of 187os 188os and os content the low ti basalt with the highest os concentration 400 ppt has a radiogenic os isotopic composition os t 6 5 similar to that of plume derived oib because the os isotopic composition of basalts with relatively high os concentrations typically 50 ppt likely represents that of their mantle source this result implies a plume derived origin for the low ti basalts on the other hand the high ti basalts with high os concentration over 50 ppt have unradiogenic os isotopic signatures os t values range from 0 8 to 1 4 suggesting that a subcontinental lithosphere mantle sclm component most likely contributed to the generation of these magmas combining pb and nd isotopic tracers with the os data we demonstrate that the low ti basaltic magmas in the emeishan cfb were mainly sourced from a mantle plume reservoir whereas the high ti basaltic magmas were most likely derived from a sclm reservoir or were contaminated by a significant amount of lithospheric mantle material during plume related magma ascent through the sclm

detrital record of late stage silicic volcanism in the emeishan large igneous province abstract silicic volcanic rocks generally constitute a minor but key product to track the magmatic evolution in mafic rock dominated large igneous provinces lips however for their generally late stage nature of the silicic volcanic rocks they have a poor preservation potential due to extensive post eruption erosion we track the eroded volcanic rocks from the 260 ma emeishan lip by analyzing the provenance of the lip derived sedimentary rocks sandstones from a cored succession of the late permian longtan formation in the northern youjiang basin are rich in volcanic rock fragments and associated mudstones have low al2o3 tio2 ratios detrital zircon grains from the longtan formation display typical unimodal u pb age spectra with a prominent peak at ca 260 ma these detrital zircons show an overall geochemical affinity akin to those crystallized from within plate anorogenic magmas such petrological and geochemical characteristics are consistent with a dominant source from the emeishan volcanic rocks through the sampled succession zircon grains of 260 ma from the lower longtan formation generally display lower u yb most

magnetostratigraphic constraints on two stage eruptions of the emeishan continental flood basalts temporal and spatial variations of high and low contents of ti basalts in the permian emeishan large igneous province elip of southwest china and vietnam are crucial for modeling of continental basalt formation and the nature of mantle lithosphere interaction a combined geochemical and magnetostratigraphic study was carried out at yanyuan in the inner zone of the elip geochemical results indicate that the basalts are low ti lt basalts ti y 484 2 511 4 in the luomapu section and high ti ht basalts ti y 558 2 658 9 in the gongmushan section systematic paleomagnetic sampling and stepwise thermal demagnetization demonstrate that the higher temperature component shows two distinct characteristic remanent magnetizations with northeasterly upward and sww downward directions these results indicate a simple magnetostratigraphic normal and reversed polarity pattern from the lower and upper parts of the section respectively by comparing with available magnetostratigraphic and paleomagnetic data carried out in the elip these results imply that the eruption of the emeishan basalts can be divided into early normal polarity subchron and late reversal subchron stages the early stage included lt basalts in the inner zone and most of the ht basalts in the intermediate and outer zones and the late stage contained a part of lt and ht basalts in the upper parts of the sections in the inner zone and a few in the intermediate zone of the elip correlating with available middle late permian magnetostratigraphy and the permian magnetic time scale the new magnetic polarity sequence result suggests that the elip formed over a very short time interval 1 myr

syncollisional rapid granitic magma formation in an arc arc collision zone evidence from the tanzawa plutonic complex japan the tanzawa plutonic complex tpc central japan is a suite of tonalitic gabbroic plutons exposed in a globally unique arc arc collision zone where an active intraoceanic izu bonin mariana ibm arc is colliding against the honshu arc the tpc has been widely accepted as an exposed middle crust section of the ibm arc chiefly because of geochemical similarities between the tpc and ibm rocks and previously reported precollisional miocene k ar ages however new zircon u pb ages show that the main pulse of tpc magmatism was syncollisional and that plutons were emplaced rapidly and cooled soon after pliocene collision trace element compositions of tpc zircon show distinctively elevated th nb ratios compared to zircon from other noncollisional ibm silicic plutonic rocks indicating the involvement of continental sediments from the honshu arc in their magma genesis

high resolution detection of geologic boundaries from potential field anomalies an enhanced analytic signal technique a high resolution technique is developed to image geologic boundaries such as contacts and faults the outlines of the geologic boundaries can be determined by tracing the maximum amplitudes of an enhanced analytic signal composed of the nth order vertical derivative values of two horizontal gradients and one vertical gradient the locations of the maximum amplitudes are independent of the ambient potential field this technique is particularly suitable when interference effects are considerable and or when both induced and remanent magnetizations are not negligible the corresponding depth to each geologic boundary can be estimated from the amplitude ratio of the enhanced and the simple analytic signals which provides a simple estimation technique such a method has been applied to magnetic data acquired in the ilan plain of taiwan located at the southwestern end of the okinawa trough the quantitative analysis shows that the underlying geologic boundaries deepen southward and slightly eastward the enlargement of the ilan plain in the direction of the okinawa trough and the existence of north northwest and west northwest trending faults near the city of ilan reveal a discontinuity between the okinawa trough backarc extension and the compressional process in taiwan

permian peralkaline peraluminous and metaluminous a type granites in the panxi district sw china their relationship to the emeishan mantle plume abstract numerous permian granitic intrusions plutons in the panxi region sw china are spatially and temporally associated with the emeishan large igneous province elip granites from the 260 ma panzhihua and taihe plutons are peralkaline asi 0 76 1 12 na k al 0 78 1 2 and have high fe values 0 92 0 99 with negative eu anomalies eu eu 0 22 0 98 contrasted with the peralkaline plutons syenites from the 260 ma woshui pluton are metaluminous asi 0 84 1 0 na k al 0 91 1 01 and have moderately high fe 0 79 0 81 and positive eu anomalies eu eu 0 82 1 91 both the peralkaline and metaluminous rocks have mantle isotopic signatures end t 1 3 3 2 and were derived from the elip mantle plume source the peralkaline rocks were likely derived by fractional crystallization of the temporally spatially and chemically associated layered mafic intrusions which host giant magmatic fe ti v oxide deposits the metaluminous granitic rocks although spatially related to the peralkaline granites and layered gabbros were likely generated by partial melting of underplated mafic rocks granites from the 251 ma ailanghe pluton are peraluminous asi 0 97 1 29 and have high fe 0 82 0 91 values and negative eu anomalies eu eu 0 10 0 37 their crustal isotopic signature end t 5 7 to 6 7 indicates possible derivation from melting of yangtze block basement rocks the ailanghe pluton is contemporaneous with other a type granites in the region supporting the view that elip magmatism was sporadic for at least 9 million years the coexistence of three chemically exclusive a type granites in the elip suggests that a variety of a type granites can be generated in the same tectonic setting

world peat occurrence and the seasonality of climate and vegetation abstract the climatic controls on present day peat formation are examined in order to develop a uniformitarian tool for refining paleoclimate studies and to create a retrodictive model for the coals of the geologic record a peat database has been compiled for the world and the resulting patterns are compared with aspects of precipitation and temperature drawn from a gridded data set precipitation continuity through the annual cycle is important for biologic productivity in the terrestrial realm it is expressed in terms of the number of months with average precipitation above 40 mm temperature is limiting at higher latitudes where the potential growing season may be defined by the number of months with mean temperature exceeding 10 c a map predicting the growing season has been constructed from these rainfall and temperature statistics which compares very well with actual vegetation persistence through the year as measured directly from satellite instruments however biologic production will not result in peat accumulation unless groundwater levels are maintained through the growing season our peat prediction map therefore shows the percentage of time that precipitation occurs during the potential growing season present day peat accumulations are well predicted by this map

formation of the late permian panzhihua plutonic hypabyssal volcanic igneous complex implications for the genesis of fe ti oxide deposits and a type granites of sw china the late permian 260 ma emeishan large igneous province of sw china contains numerous magmatic fe ti oxide deposits the fe ti oxide deposits occur in the lower parts of evolved layered gabbroic intrusions which are spatially and temporally associated with a type granitic rocks the 260 ma panzhihua layered gabbroic intrusion hosts one of the largest magmatic fe ti oxide deposits in china and is coeval with a peralkaline a type granitic pluton the granite has intruded the overlying emeishan flood basalts and fed at least one dyke which erupted onto the surface producing columnar jointed trachytes the presence of syenodiorite between the layered gabbro and granite is evidence for compositional evolution from mafic to intermediate to felsic rocks the syenodiorites have intermediate to felsic composition with sio2 61 to 65 wt mgo 0 27 to 0 6 wt and cao 1 0 to 2 5 wt as compared to the granite sio2 65 to 72 wt mgo 0 1 to 0 4 wt cao 1 eu eu 1 1 to 2 6 in the gabbroic intrusion to 1 in the syenodiorite eu eu 0 75 to 0 83 granites and trachytes eu eu 0 55 0 87 previously published end t values from clinopyroxenes end t 1 1 to 3 2 of the gabbroic intrusion match the whole rock values of the syenodiorite end t 2 1 to 2 5 granite and trachyte end t 2 2 to 2 9 suggesting that all rock types originated from the same mantle source melts and trace element modeling confirm that all rock types can be generated by fractional crystallization of high ti emeishan basalt the jump in sio2 from the gabbro to the syenodiorite is attributed to the en masse crystallization of the fe ti oxides the geological and geochemical data indicate that fractional crystallization of a common parental magma produced the layered gabbroic intrusion and fe ti oxide deposit the syenodiorite granites and trachyte of the panzhihua region which thus form a genetically related plutonic hypabyssal volcanic complex other granite gabbro complexes in the region likely formed in a similar manner

paleokarst on the top of the maokou formation further evidence for domal crustal uplift prior to the emeishan flood volcanism abstract the 260 ma emeishan large igneous province elip in southwest china has previously been demonstrated to provide compelling evidence for pre volcanic crustal doming in support of the mantle plume hypothesis however this has been questioned by ukstins peate and bryan 2008 by showing hydrothermal magmatic activity at the daqiao section to solve this argument a detailed characterization of the contact between the emeishan basalts and the maokou formation was carried out the contact is shown to be an unconformity which is characterized by paleokarst on top of the maokou formation including paleokarst relief sinkholes caves tower karst and its corresponding rocks such as kaolinite bauxite and ferruginous duricrust and collapsed breccias etc this paleokarst unconformity was in turn covered or infilled by the emeishan basalts and tuffs suggesting that uplift and erosion occurred prior to the eruption of the elip the extent of erosion of the maokou formation indicates the elip can be divided into three roughly concentric zones the inner intermediate and outer zones the paleokarst features on the top of maokou formation vary across the elip in the inner zone a likely sinkhole and an incision valley with 450 m relief in height are found in the intermediate zone various paleokarst landforms such as karst relief sinkholes and tower karsts are well developed some sinkholes that developed in the qixia formation below the maokou formation imply that the paleorelief is more than 350 m in height in the outer zone the paleokarstic surface is a paleo weathering layer with minor karstification and development of caves at 10 50 m this spatial variation of the paleokarst reflects variation of uplift height across the elip the extent of minimal uplift is estimated to be at least 450 m in the inner zone 350 m in the intermediate zone whereas uplift is minor tens 50 m in the outer zone the magnitude and shape of the uplift is roughly consistent with that predicted by mantle plume models the paleokarst was formed after the deposition of the maokou formation and the eruption of the emeishan basalts at the end guadalupian and indicates a short duration of uplift thus this study lends further support to domal uplift prior to the emeishan flood volcanism but also to the mantle plume initiation model for the generation of the elip

evidence for an albian hudson arm connection between the cretaceous western interior seaway of north america and the labrador sea numerous researchers have alluded to the existence of a cretaceous hudson arm connection between the labrador sea and the western interior seaway of north america however the evidence for this marine connection has been circumstantial in this paper we present sedimentary geochemical data that indicate a marine influence in the albian mattagami formation of the moose river basin james bay lowlands ontario the facies associations between dinoflagellate bearing laminated mudstones fluvial sandstones and early pyrite mineralization are interpreted to indicate deposition in the central basin of an estuary we use the facies association between the estuarine fill and coeval kaolinitic paleosols in the moose river basin and in similar deposits in quebec and labrador to reconstruct a southern shoreline of the albian hudson arm to the cretaceous western interior seaway we suggest that development of the hudson arm connection between the labrador sea and the cretaceous western interior seaway may be related to a regional extensional regime associated with rifting between labrador and greenland and the passage of eastern north america over cretaceous hotspots

recognition of interfluve sequence boundaries integrating paleopedology and sequence stratigraphy in shallow marine and coastal plain strata sequence boundaries are easily recognized at the base of incised valley fills between valleys however it is more difficult to recognize sequence boundaries where they are expressed as interfluve paleosols we suggest that interfluve paleosols can be most reliably identified using a combination of 1 stratigraphic position 2 field observations such as thickness structure color and degree of rooting and 3 micromorphological features such as bioturbation fabric clay coatings ferruginous features and siderite and barite only micromorphology permits recognition of temporal changes in drainage surface stability and protracted pauses in sedimentation that typify these surfaces this three part approach has been successfully employed to identify interfluve sequence bounding paleosols in the cenomanian dunvegan formation in alberta and british columbia canada

floodplain palaeosols of the cenomanian dunvegan formation alberta and british columbia canada micromorphology pedogenic processes and palaeoenvironmental implications

origin of k feldspar megacrysts in rhyolites from the emeishan large igneous province southwest china abstract silicic rocks occur in the uppermost units of the longest volcanic succession 5000 m thick in the binchuan area of the permian emeishan flood basalt province of sw china they are predominantly rhyolites and to a lesser extent trachytes both containing potassium feldspar megacrysts as the dominant phenocryst phase up to approximately 20 mm in size these megacrysts contain domains of albite arranged in vein like networks likely formed by post magmatic alteration crystal size distributions csd suggest that these megacrysts grew in a stable magmatic system consistent with relatively uniform core to rim compositional k 2 o 14 16 wt and isotopic profiles 208 pb 206 pb ratios 2 06 2 08 0 005 both whole rock trace elements and pb isotope ratios of these silicic rocks are similar to the emeishan basalts suggesting a common source for both mafic and felsic units and a limited role of crustal melting in genesis of the felsic units major and trace element models further indicate that these rocks could not have formed exclusively by re melting of old crust or solidified basaltic rock but must have formed through crystal fractionation from the flood basalts or possibly partial melting of basaltic rock followed by fractional crystallization k feldspar bearing rhyolites are also observed in the last stages of other large igneous provinces we suggest that they represent final melt fractions and their appearance in the magmatic system coincides with waning of voluminous magmatic activities

trace element composition of igneous zircon a thermal and compositional record of the accumulation and evolution of a large silicic batholith spirit mountain nevada hafnium u th and ree content of zircons from the spirit mountain batholith in southern nevada correlate with calculated temperatures from the ti in zircon thermometer to support field and petrologic evidence of rejuvenation of crystal mush and melt extraction events during the 2 million year accumulation of the granitoid batholith marked variation in zircon composition from sample to sample from grain to grain within individual samples and from zone to zone within individual grains documents in detail a history of fluctuating conditions with repeated episodes of replenishment reheating crystal mush rejuvenation fractional crystallization and melt segregation the zircons exhibit compositional and thermal variability indicative of variations in host melt composition due to 1 melt rejuvenation mixing and fractionation 2 coeval growth of other ree rich accessory minerals and possibly 3 fluctuation in fo2