sulfur isotopic studies of the dunka road cu ni deposit duluth complex minnesota the dunka road deposit is one of a series of cu ni occurrences located within troctolitic rocks of the southern portion of the duluth complex minnesota sulfide minerals principally pyrrhotite chalcopyrite cubanite and minor pentlandite occur interstitially with silicate minerals and average about 2 volume percent in ore grade horizons areas of sulfide concentrations in excess of 1 to 2 percent occur erratically throughout the troctolitic sequence but are in general concentrated near the basal contact with rocks of the metasedimentary virginia formation the delta 34 s values of sulfides in the troctolites range from 0 2 to 15 8 per mil with an average value near 7 5 per mil pyrrhotite in the underlying virginia formation hornfels and pyrite from unmetamorphosed virginia formation are characterized by a similar range in delta 34 s values the high positive delta 34 s values and similarity to values found in the virginia formation strongly suggest that most of the sulfur in the dunka road deposit was derived from the breakdown of pyrite in the virginia formation the sulfur isotopic compositions of minerals in the troctolites show no consistent lateral or vertical trends and are in general characterized by a high degree of variability such fluctuations in delta 34 s values indicate that sulfur isotopic homogenization was not attained throughout the troctolitic sequence several mechanisms may have contributed to the variations in delta 34 s values found within the troctolites including mixing of sedimentary and igneous sulfur assimilation of sedimentary sulfur characterized by variable delta 34 s values fractionation caused by fluctuations in oxidation states during sulfur volatilization and assimilation and periodic introduction of isotopically distinct magma batches in light of the erratic sulfide mineral and delta 34 s distributions the predominant mechanism is thought to be the introduction of both isotopically and spatially variable country rock sulfur into crystallizing troctolitic magma

geochemistry and zircon geochronology of the permian a type hasanrobat granite sanandaj sirjan belt a new record of the gondwana break up in iran the sanandaj sirjan metamorphic plutonic belt ssb in west central iran is a polyphase metamorphic terrain composed of dominantly greenschist grade metasedimentary and metavolcanic rocks and felsic to mafic plutons of neoproterozoic phanerozoic ages the hasanrobat granite in central ssb occurs as a single pluton 20 km 2 surface area with relatively consistent mineralogy and chemistry quartz alkali feldspars microcline and perthite sodic plagioclases and biotite are the main constituents commonly associated with minor amphibole accessory phases include zircon allanite apatite and magnetite the country rocks are upper carboniferous lower permian sandstones and dolomitic limestones scattered patches of skarn type assemblages dominated by tremolite and talc occur in the dolomitic limestones and sandstones are recrystallized to a coarse grained quartzite at contact with the granite the granite is metaluminous to slightly peraluminous and is distinguished by high feo t mgo ratios typical of ferroan a type granites the a type affinity is also reflected by high na 2o k 2o high ga al ratios high contents of large ion lithophile elements lile high field strength elements hfse and rare earth elements ree as well as low contents of sr and distinct negative eu anomalies the biotites are aluminous fe rich and plot near the siderophyllite corner in the quadrilateral biotite diagram they are further distinguished by high fluorine contents 0 61 to 1 33 wt amphibole is ferrohastingsite in composition ion microprobe analyses of zircon grains separated from a representative granite sample yielded concordant u pb ages with weighted mean 206 pb 238 u age of 288 3 3 6 ma the granite and the country rocks are cut by a set of mafic dykes with asthenosphere like geochemical signatures such association suggests anorogenic intraplate magmatism in lower permian in the region this provides further evidence for and significantly constrains timing of a major extension in upper paleozoic in iran previously inferred from the rock record the extension led to the gondwana break up and the opening of neotethys ocean between sanandaj sirjan and zagros in permian

did the great dying of life take 700 k y evidence from global astronomical correlation of the permian triassic boundary interval the cause of the great permian triassic p t boundary mass extinctions remains unknown a crucial step in identifying the cause involves a precise timing of the mass extinction interval mei in order to reconstruct the pattern of biotic evolution and the chronologic record of potential triggers here we present an estimate of the p t boundary mei duration based on astronomical tuning of multiple cyclic sedimentary records magnetic susceptibility data from shangsi southern china provide evidence for strong 405 k y orbital eccentricity forcing throughout the p t boundary interval radioisotope dating combined with 405 k y tuning provides an absolute time scale through the p t boundary interval at unprecedented high resolution an estimated 700 k y duration for the mei at shangsi is supported by eccentricity tuned estimates of four other sections in china and austria in addition at shangsi the onset of mass extinction occurred shortly following a coincidence of minima in the observed 1 5 m y 405 k y and 100 k y cycles a change in the magnetic susceptibility response to astronomical forcing occurred just prior to the onset of extinction with reduced 100 k y scale cyclicity continuing into the early triassic for more than 2 m y

exhumation of the ultrahigh pressure continental crust in east central china cretaceous and cenozoic unroofing and the tan lu fault the orogenic architecture of the world s largest ultrahigh pressure exposure the hong an dabie mountains of the triassic qinling dabie orogenic belt is dominated by cretaceous and cenozoic structures that contributed to its exhumation from 30 km depth cretaceous magmatic crustal recycling 50 for the entire dabie and heating 250 to 700 c were most prominent in dabie and exhumation magmatism and cooling were all controlled by cretaceous transtension exhumation was accomplished principally by an asymmetric cordilleran type extensional complex in the northern dabie northern orthogneiss unit between 140 and 120 ma at rates as fast as 2 mm yr and average horizontal stretching rates of up to 6 mm yr cretaceous reactivation occurred within a regional transtensional strain field as a result of far field collisions and pacific subduction the onset of crustal extension was preceded and possibly facilitated by a reheating of the hong an dabie crust 140 ma coeval with the onset of voluminous magmatism in eastern china 145 ma which resulted from a change in pacific subduction from highly oblique to orthogonal the tan lu continental scale fault was a normal fault zone in the mid cretaceous 110 90 ma and underwent 5 4 km dip slip and 4 km throw in the cenozoic during the india asia collision the qinling dabie belt acted as the structural discontinuity between the strike slip dominated escape tectonics south of the qilian qinling dabie belt and the rifting dominated tectonism north of it the most prominent cretaceous and cenozoic structures of the hong an dabie the xiaotian mozitang and the jinzhai fault zones respectively reactivated major lithospheric structures of the triassic orogen i e the huwan detachment zone and the suture

the role of magmatic sulfides and mafic alkaline magmas in the bingham and tintic mining districts utah this paper reports the existence of abundant magmatic sulfides in introduction latite lava vitrophyres and vent facies dikes from the bingham and the eruption of sulfur rich magmas from el chichon tintic districts in central utah these dikes and flows appear to luhr et al 1984 and mt pinatubo westrich gerlach be comagmatic with the ore related monzonite intrusions in addition 1992 in recent years has attracted attention to the limited analytical data suggest that the magmatic sulfides contain most of solubility of sulfur in intermediate magmas and the factors the cu and ag present in the latites magmatic sulfides are preserved potentially responsible for the formation of magmatic only in the least oxidized and least degassed lavas and vitrophyres sulfides and anhydrite however the occurrence of magpetrography of comagmatic dikes and intrusions suggests that matic sulfides in intermediate magmas is not universal resorption and oxidation s degassing of the globules may make many volcanic suites appear to be sulfide unsaturated the metal content available to a magmatic ore fluid minette and inasmuch as magmatic sulfides may sequester chalcophile shoshonite lavas occur in subordinate amounts in the latitic volcanic metals what would their presence signify in magmatic fields associated with latite monzonite intrusions and hydrothermal systems that formed porphyry cu and mesothermal vein ore deposits of the tintic ag pb zn cu au and bingham deposits do they sequester a significant portion of the porphyry cu au mo districts utah the ages chemical and magmatic cu pb zn ag and au thereby restricting modal compositions and field relations of the mafic alkaline lavas metal availability of subsequent ore forming fluids suggest that such magmas mixed and fractionated at shallow crustal we have examined the volcanic rocks from the tintic levels to form the ore related latites and monzonites the unaltered and bingham mining districts fig 1 utah and found mafic alkaline lavas in these districts are some of the most cu rich that almost all of the volcanic units contain magmatic lavas in the great basin province sulfides some quenched dikes and intrusion margins also have preserved magmatic sulfides comparable with those in the volcanic rocks several lines of evidence indicate that the volcanic and intrusive rocks are comagmatic keith et al 1989 1991 waite 1996 the tintic district and east tintic sub district in utah have recorded over

origins of microspherules from the permian triassic boundary event layers in south china abstract volcanism and impact scenarios are two of the most plausible ways of interpreting the causes of the largest biological mass extinction at the end permian microspherules have previously been widely reported from tens of different permian triassic boundary ptb sections in south china and some other regions these microspherules have been interpreted as either the product of volcanic eruptions or an impact event in order to test these scenarios we collected 60 samples from 12 intensively studied ptb sections in south china in addition four soil samples close to these ptb layers were also collected for comparison our investigation indicates that abundant microspherules with mosaic or dot shape crystals on rounded surface are present in the surface samples in the ptb layers at meishan meili and shatian sections and most soil background samples in south china those microspherules consist of four different types based on their main chemical composition surface features and internal structure including iron magnetite silicate glassy pyrite microspherules and framboids in contrast microspherules have not been found in a few sections in remote areas such as the selong xishan section in tibet and the dalongkou section in xinjiang northwest china in the deeply excavated samples at the shangsi section and the hard tuff layers around the ptb at the xiaochehe section in guiyang microspherules decrease in abundance with depth in ptb clay beds all these microspherules except the pyrite microspherules and framboids are found in both the ptb layers and the nearby soil background samples the iron microspherules are pure iron oxides such as magnetite hematite or maghemite and contain low concentrations of nickel and chromium and lack an ni fe core and general extraterrestrial mineral wustite all these external and chemical characteristics suggest that most of iron microspherules previously reported from ptb sections in south china are modern industrial fly ashes a low ratio of fe 3 fe total in crystals of magnetite silicate microspherules and high zno contents can identify them as industrial contaminants the pyrite microspherules and framboidal pyrite found from bed 24e and bed 26 at the meishan sections are of depositional or and diagenetic origins and only the rounded quartz and the fragments containing extremely high sio 2 and tio 2 are possibly of volcanic origin

analysis of sulfides in whole rock matrices by elemental analyzer continuous flow isotope ratio mass spectrometry abstract potential matrix effects in the sulfur isotopic analysis of whole rocks by elemental analyzer continuous flow isotope ratio mass spectrometry ea cfirms have been investigated by measuring mixtures of a well calibrated laboratory sulfide reference mineral and common rock forming minerals mixtures of sulfide and quartz orthoclase plagioclase kaolinite olivine magnetite ilmenite garnet halite fluorite calcite and graphite show consistent s yields and 34s values generally within 0 2 of the measured pure sulfide value however erratic results are obtained for mixtures of reference sulfide and pyroxene amphibole or biotite these minerals may suppress sample peaks cause extreme peak tailing and prohibit isotope ratio measurements pure sulfide minerals introduced after the mixtures also showed suppressed sample peaks suggesting so2 adsorption on mineral and residual ash surfaces removal of the residual ash resulted in normal measurements for reference sulfide minerals whole rocks with s concentrations in excess of 100 ppm can be successfully analyzed using ea cfirms provided that measurements are carefully monitored for evidence of so2 retention during and after combustion

did the great dying of life take 700 k y evidence from global astronomical correlation of the permian triassic boundary interval comment huang et al 2011 1 have produced a valuable astro chronological framework across the permian triassic boundary in china and austria however in doing so they define a mass extinction interval mei and prolonged extinction lasting in all cases 700 k y the mei in their study ranges from

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

40ar 39ar dating of strike slip motion on the tan lu fault zone east china abstract ne trending sinistral ductile shear belts in the southern part of the tan lu fault zone east china are exposed along the eastern edge of the northern dabie belt and southern zhangbaling belt three hornblende three phengite and 12 biotite separates from greenschist facies mylonites in the shear belts were dated by the 40ar 39ar method in this study a hornblende plateau age of 143 3 ma is interpreted as representing the time of sinistral motion on the zhangbaling part of the tan lu fault zone seven biotite samples from the same part yield 40ar 39ar cooling ages from 137 to 125 ma a phengite plateau age of 138 8 ma from the eastern edge of the dabie belt is considered as being close to the time of deformation in the tan lu strike slip zone five biotite 40ar 39ar ages from 120 to 110 ma and one phengite age of 121 ma from the same area represent cooling ages after the sinistral faulting it is concluded on the basis of these 40ar 39ar ages that the sinistral ductile shear belts in the southern part of the tan lu fault zone were produced in earliest early cretaceous this sinistral motion on the tan lu fault zone is considered to be related to high speed highly oblique subduction of the pacific plate at this time

zr th and ree rich biotite differentiates in the a type granite pluton of suzhou eastern china the key role of fluorine

the transition from amphibolite facies mylonite to chloritic breccia and role of the mylonite in formation of eocene epizonal plutons bitterroot dome montana the bitterroot mylonite is a ductile deformed amphibolitefacies mylonite a mylonite abruptly capped by ductile to brittle deformed greenschist facies mylonite g mylonite the movement picture of the a mylonite from its lineation and s c surfaces is strongly focused the average orientation for the g mylonite is similar but much more diffuse

early cretaceous granitoids and their implications for the collapse of the dabie orogen eastern china shrimp zircon u pb dating and geochemistry abstract two stages of early cretaceous post orogenic granitoids are recognized in the dabie orogen eastern china which recorded processes of extensional collapse of the orogen the early stage granitoids 132 ma are foliated hornblende quartz monzonites and porphyritic monzogranites they are of high k calc alkaline series and metaluminous to weakly peraluminous with high k 2 o and low mgo contents mg values 32 0 46 0 they contain high sr low y and heavy rare earth elements hree and have high sr y and la yb n ratios without clear negative eu sr and ti anomalies the early stage deformed granitoids have adakitic geochemical compositions and are equilibrated with residues rich in garnet and poor in anorthite rich plagioclase and thus indicate the existence of an over thickened 50 km crustal root beneath the orogen at 132 ma the later stage granitoids 128 ma are undeformed fine grained monzogranites fine grained k feldspar granites and coarse grained k feldspar granite porphyry they belong to a peraluminous and high k calc alkaline to shoshonite series and display a flat hree pattern and have strong negative eu sr and ti anomalies with low sr y and la yb n ratios the late stage granitoids are equilibrated with residues rich in anorthite rich plagioclase hornblende ilmenite titanite and poor in garnet indicating that the crust of the dabie orogen became thinner

geochemical and sr nd pb isotopic compositions of cretaceous granitoids constraints on tectonic framework and crustal structure of the dabieshan ultrahigh pressure metamorphic belt china abstract the dabie orogenic belt can be divided into four tectonic and lithological units they are from north to south the north huaiyang nhy unit the northern dabie complex ndc unit the ultrahigh pressure uhp metamorphic unit and high pressure hp metamorphic unit cretaceous granitoids from the four tectonic units irrespective of tectonic unit and lithology show surprisingly similar major and trace element and particularly sr nd pb isotopic compositions indicating a similar crustal source for their magma genesis they have initial 87 sr 86 sr t values of 0 7068 0 7091 and nd depleted mantle model ages of 1 6 2 4 ga and e nd t values at the time of their emplacement 120 ma ranging from 13 to 26 their present day pb isotopic compositions are 206 pb 204 pb 15 62 17 06 207 pb 204 pb 15 21 15 44 and 208 pb 204 pb 36 59 37 81 with comparison to the sr nd pb isotopic compositions of the basement rocks in the dabie orogenic belt the isotopic compositions of the cretaceous granitoids indicate a source that is similar to the northern dabie complex but distinct from the ultrahigh pressure metamorphic unit this strongly suggests that the exposed northern dabie complex extends in the deep crust southward beneath the uhp hp metamorphic units and northward beneath the north huaiyang unit the northern dabie complex is best interpreted as the core of a dome within the dabie orogenic belt the uhp hp metamorphic unit is only a thin skinned slab confined in shallower crustal levels over the northern dabie complex present tectonic framework for the uhp hp terrain was formed by extensional tectonics and post the uhp hp metamorphism the northern dabie complex has an affinity to the yangtze craton the similar source for the cretaceous granitoids also suggests that the suture between the north china and the yangtze cratons is marked by the xiaotian mozitang fault separating the north huaiyang unit and the northern dabie complex rather than the previously thought wuhe shuiko fault which separates the northern dabie complex and the uhp unit

u pb zircon ages of granitoid rocks in the north dabie complex eastern dabie shan china the north dabie complex ndc comprises a high temperature metamorphic suite dominated by amphibolite facies granitoid orthogneiss intruded by voluminous granites u pb zircon dating on these rocks yields the following new results 1 two of the granitoid orthogneiss samples have early cretaceous protolith emplacement ages of 133 7 2 3 ma and 134 0 2 8 ma 2 an undeformed granodiorite intrusive into granitoid gneiss yields an emplacement age at 125 6 0 3 ma these early cretaceous ages entirely post date late triassic early jurassic continental subduction and exhumation evident in the neighboring ultrahigh and high pressure metamorphic terrains to the south in the dabie shan hence they do not support previous tectonic models that infer paleozoic or triassic protolith emplacement ages for these granitoid orthogneisses 3 a mylonitic granite from the northern boundary of the ndc yields a concordant age of 756 6 0 8 ma which is interpreted as magma emplacement age the concordance of this late

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

a new look at stable isotope thermometry interdiffusion between coexisting minerals affects all rocks and causes resetting and discordance of stable isotope geothermometers that is commonly observed in slowly cooled igneous and metamorphic rocks the fast grain boundary fgb model describes the stable isotope fractionations and intracrystalline zonation which result from closed system interdiffusion eiler et al 1991 1992 this model assumes that grain boundary diffusion is much faster than volume diffusion and it accounts for exchange among all minerals in a rock previous models of closure temperature violate mass balance restrictions and will be inaccurate in most rocks modeling results are described for amphibolites and hornblende granites and gneisses biotite granites schists and gneisses pelitic and semi pelitic rocks garnet peridotites anorthosites gabbros pyroxenites and related rocks and calc silicate rocks examples of mineral pairs and specific rock types that allow accurate stable isotope thermometry include plagioclase pyroxene in pyroxene bearing anorthosites and garnet quartz in garnetiferous quartzites in contrast the same mineral pairs in related rocks such as pyroxenites and pelitic schists will exhibit reset apparent temperatures closed system processes are capable of producing a variety of patterns of stable isotope resetting discordance mineral zonation and fractionation reversals examples include large reversals of quartz feldspar fractionations in micaceous rocks and oscillatory zonation in feldspar from some quartz rich rocks these results permit reinterpretation of many studies of stable isotope thermometry speedometry and retrograde alteration history fgb modeling of mineral zonation provides an important new guide to applying recently developed micro analytical tools to slowly cooled rocks application of the fgb model to quartzo feldspathic gneisses from the adirondack mountains new york demonstrates the usefulness of diffusion modeling in discriminating closed system diffusion controlled retrogression from open system retrogression and illustrates the possible importance of incorporating the effect of water activity on mineral diffusivity

melting reactions of gneissic inclusions with enclosing magma at voisey s bay labrador canada implications with respect to ore genesis the voisey s bay ni cu co sulfide deposit is associated with a 1 333 ga troctolitic gabbroic intrusion which transects the 1 85 ga collisional boundary between tasiuyak paragneiss of the proterozoic aged churchill province to the west and orthogneiss of the archean aged nain province to the east the intrusion comprises an upper chamber to the east the eastern deeps subchamber a lower chamber to the west the reid brook subchamber and a conduit connecting them sulfide mineralization is closely associated with a breccia which occurs close to the basal contact of the eastern deeps subchamber and within the conduit the breccia is composed of abundant tasiuyak paragneiss inclusions with a troctolitic gabbroic matrix the gneiss inclusions have reacted extensively with the enclosing magma in general the degree of reaction increases from the reid brook subchamber through the conduit to the eastern deeps subchamber in the course of this reaction garnet has been oxidized to form hercynite and magnetite with the release of sio2 to the magma cordierite has been dehydrated to form hercynite with the release of sio2 hypersthene and k feldspar have reacted together to produce hercynite with the release of sio2 and k2o plagioclase has broken down to produce corundum losing sio2 and na2o to the magma and itself becoming enriched in anorthite and the corundum has subsequently reacted with feo and mgo from magma to form hercynite the color of the hercynite changes progressively from beige in the reid brook subchamber through green within the conduit to black in the eastern deeps subchamber this color change reflects an increase in feal2o4 at the expense of the mgal2o4 in the hercynite the inclusions in the eastern deeps subchamber characteristically show a series of reaction rims ranging from labradorite through biotite to hypersthene it is seen that reaction with the gneiss inclusions results in the addition of sio2 k2o and na2o to the magma this felsification of magma has resulted in a decrease in its ability to dissolve sulfide and therefore has promoted sulfide immiscibility

pattern of marine mass extinction near the permian triassic boundary in south china the meishan section across the permian triassic boundary in south china is the most thoroughly investigated in the world a statistical analysis of the occurrences of 162 genera and 333 species confirms a sudden extinction event at 251 4 million years ago coincident with a dramatic depletion of 13ccarbonate and an increase in microspherules

geochronology of the karadere basement nw turkey and implications for the geological evolution of the istanbul zone earlier geological work in the istanbul zone western pontide tectonic belt has revealed the presence of extensive basement outcrops exposed underneath palaeozoic and mesozoic to tertiary cover sequences the basement of suspected neoproterozoic age plays an important role in understanding the crustal accretion process in nw turkey we report the first results of a detailed pb pb and u pb zircon study complemented by nd sr whole rock and mineral data from basement rocks exposed in the karadere valley safranbolu area five samples were selected for this study comprising three metagranitoids and two metasediments zircon geochronology indicates that the metagranitoids were formed during late proterozoic pan african magmatic events between 590 and 560 ma the rocks are of tonalitic and granitic composition and have low nb y ratios and ti contents consistent with those of arc rocks a continental arc setting is supported by their sr and nd isotope data that indicate a contribution of a mantle source as well as crustal assimilation during magma genesis the metasediments can clearly be distinguished from the metagranitoids by their higher 87sr 86sr ratios and lower end values at 580 ma which supports the suggestion that the arc was underlain by mature continental crust zircons from the metasediments yield a range of pb pb ages between 1 860 and 710 ma thirty per cent of them fall between 890 and 710 ma possibly suggesting a derivation from gondwana afro arabian regions a sm nd garnet whole rock analysis obtained on a metagranite gives an age of 559 8 ma which either reflects pre metamorphic magmatic growth of garnet in a felsic melt or a syntectonic high temperature metamorphic event uplift and cooling of the basement is further constrained by rb sr biotite ages of 548 545 ma these lower cambrian mineral ages demonstrate that the istanbul zone was not thermally reactivated during the hercynian cimmerian or alpine orogeny in contrast to its neighbouring tectonic zones confirming its role as a suspect terrane in the modern western pontide tectonic belt

oxygen isotopic systematics of an open system magma chamber an example from the freetown layered complex of sierra leone abstract the freetown layered complex of sierra leone is a 7 km thick rift related tholeiitic intrusion that formed 193 ma ago during the opening of the middle atlantic ocean the complex was emplaced above archean basement gneisses granulites and schists of the kasila group at pressures of 2 8 to 5 1 kbar the 18o values of bulk cumulates 5 5 6 7 separated plagioclase 5 7 6 0 olivine 5 0 5 7 and clinopyroxene 5 1 5 8 spanning the entire stratigraphic section indicate that the complex has preserved its primary magmatic oxygen isotopic composition the 18o values of whole rocks are uniform in zone 1 average 5 74 0 01 but vary widely in zones 2 and 3 average 6 18 0 52 and 5 71 0 32 respectively variations in whole rock 18o with stratigraphic height correlate well with plagioclase mode with 18o values being highest in the strongly laminated anorthosites of zones 2 and 3 and lowest in olivine gabbro from the cyclically layered subzone of zone 3 the overall pattern of oxygen isotopic variation with stratigraphic height in the intrusion appears to the related to the accumulation of high 18o plagioclase rich rocks that are overlain by low 18o olivine or pyroxene rich rock types fractional crystallization in combination with mineral accumulation can explain the observed oxygen isotopic variations in the complex oxygen isotopic thermometry yields equilibration temperatures of 1040 to 1290 c which are similar to temperatures 1045 to 1381 c estimated from the plagioclase liquid thermometer applied to the freetown bulk magma for each zone obtained by geochemical summation the oxygen isotopic temperatures are highest where major influxes of new magmas have occurred indicating negligible subsolidus resetting of mineral compositions contemporary diabase dikes intruding the complex have whole rock and plagioclase 18o values of 6 6 and 6 7 respectively suggesting minimal interaction of the dikes with hydrothermal fluids archean gneisses from the kasila group have widely varying 18o values of 6 2 to 11 4 for whole rocks and 6 8 for quartz the whole rock 18o values for the gneisses suggest that the kasila group may have been selectively altered by hydrothermal fluids during retrograde m3 metamorphism associated with the pan african event however the kasila appears not to have significantly exchanged oxygen with the freetown magma the calculated average 18o value for the original freetown magma is 6 0 0 2 which is similar to the values reported for magmas parental to the kiglapait stillwater and duluth complex intrusions

early cretaceous low mg adakitic granites from the dabie orogen eastern china petrogenesis and implications for destruction of the over thickened lower continental crust it is generally accepted that the low mg adakitic rocks were derived from the partial melting of metabasalts eclogites in this study we demonstrate that the early cretaceous low mg adakitic granites in the north dabie complex ndc were generated by the partial melting of the ndc orthogneisses here we present in situ u pb and lu hf isotopes in zircon with whole rock geochemical and sr nd isotopic compositions were carried out for the tiantangzhai porphyritic monzogranites from the dabie orogen eastern china the monzogranites are characterized by high sr 576 988 ppm low y 7 3 19 0 ppm and depletion in hree yb 0 50 1 78 ppm thus resulting in high sr y 34 3 135 2 and la yb n 17 0 105 2 ratios without a negative eu anomaly they also exhibit high sio2 66 5 73 5 wt and k2o 2 7 4 7 wt and low mgo 0 4 1 6 wt or mg 28 2 45 3 mostly 40 values whole rock geochemical compositions suggest that the monzogranites represent low mg adakitic rock with high si and rich k features equilibrated with residues rich in garnet sr nd isotopic compositions end t 16 2 to 20 3 87sr 86sr i 0 707798 0 708804 tdm2 nd 2 3 2 6 ga of the monzogranites are distinct from that of the eclogites and amphibolites in the dabie orogen but similar to that of the neoproterozoic 700 800 ma gneisses in the ndc u pb dating of zircons gives a consistent age of 130 0 3 4 ma with discordia upper intercept age of 716 34 ma for inherited cores identified by cl imaging correspondingly in situ lu hf analyses of early cretaceous young age spots from zircons yield initial 176hf 177hf ratios from 0 281898 to 0 282361 ehf t values from 28 1 to 17 6 and two stage crust hf model ages tdm2 from 2293 89 to 2949 108 ma which are generally in agreement with values of 0 281891 to 0 282218 28 2 to 11 7 and 1927 87 to 2963 92 ma for the pre mesozoic inherited cores respectively as for individual core rim pairs in zircon th u ratios increase from the inherited cores to the young growth rims possibly due to variable degrees of partial melting whereas 176lu 177hf ratios greatly decrease because of the garnet effect in residues thus we suggest that the early cretaceous low mg adakitic granites were derived from the partial melting of the ndc neoproterozoic 700 800 ma gneisses and the foundering of the garnet bearing residues could have caused the destruction of the over thickened lower continental crust

petrogenesis of mesozoic granitoids in the dabie uhp complex central china trace element and nd sr isotope evidence post collisional magmatism in the dabie orogen is characterized by the near contemporaneous intrusion of voluminous granitoids and minor mafic magmas in the late mesozoic 135 110 ma the granitoids are represented by three major batholiths in northern dabie zhubuyuan baimajian and tiantangzhai the largest zhubuyuan batholith comprises hornblende bearing intermediate rocks penghe suite and hornblende free granitic rocks huangbai suite the huangbai granites show limited variation in chemical composition but are highly variable in textures ranging from medium to coarse grained they have rather homogeneous sr and nd isotopic compositions with 87sr 86sr i 0 708 0 709 and end t 19 to 24 the penghe intermediate suite covers a wide spectrum of rock types including diorite monzodiorite quartz monzonite to monzogranitic rocks and all of them contain hornblende and mafic enclaves the existence of compositional and textural disequilibrium e g calcic and resorbed cores of plagioclase and the nature of chemical variation in these rock types indicate that magma mixing between an evolved mafic and a granitic magma was involved in their genesis fractional crystallization fc could have coupled with the process of magma mixing but with minor contamination by the upper continental crust during magma ascent isotopically the intermediate rocks show a variation in end t values from 13 7 to 18 while their 87sr 86sr i ratios vary from 0 7074 to 0 7088 the genesis and evolution of the dabie post collisional magmatic rocks may be summarized as follows intrusion of mantle derived mafic ultramafic magmas into thickened continental crust induced dehydration melting of the lower crust rocks with intermediate compositions and subsequent production of large amounts of granitic melts huangbai suite extensive interaction between the crustal and mantle derived melts through mixing produced a hybrid parental magma which subsequently underwent a fc process en route to higher crustal levels producing a wide variety of rock types as shown by the penghe intermediate rock suite injection of successive pulses of basic magma into upward mobile magma chambers could have resulted in the formation of the mafic enclaves as well as mafic dykes

tempo of the end permian event high resolution cyclostratigraphy at the permian triassic boundary the permian triassic p t boundary is marked by the most severe mass extinction in the geologic record high resolution cyclostratigraphy on a 10 4 yr scale across the p t boundary in a core from the carnic alps austria revealed significant cycles in the ratio 40 10 4 7 2 3 m identified with milankovitch cycles of 412 100 40 20 k y eccentricity 1 and 2 obliquity and precession wavelet analysis indicates continuity of deposition across the boundary with an average accumulation rate of 10 cm k y the dramatic faunal changes at the p t boundary can be constrained within an interval of 60 k y possibly 8 k y with the accompanying sharp negative global carbonisotope shift within 30 k y suggesting a catastrophic cause

paleoredox biotic and sulfur isotopic changes associated with the end permian mass extinction in the western tethys abstract detailed cm scale s toc total organic carbon 34ssulfide and pyrite morphological analysis of the permian triassic boundary beds at the bulla section northern italy suggests that marine waters at this site saw the influx of two dysoxic euxinic intervals that mark the end permian extinction event this suggests reduced oxygen conditions and the presence of h2s is the cause of the end permian extinction the bulla section also shows three troughs in 34ssulfate of which the latter two coincide with the dysoxic euxinic intervals this suggests that the latter two 34ssulfate troughs are the result of h2s oxidation in surface waters but the first trough is the result of a different mechanism we propose that h2s was oxidized in another region either to low 34ssulfate water or elemental s which then moved to the bulla area at the balvany section hungary there are two 34ssulfate troughs near the extinction and no evidence of euxinia a similar mechanism to the first bulla 34ssulfate trough is proposed with the suggestion that these waters were also depleted in oxygen in order to effect the extinction at balvany

petrogenesis of ore bearing porphyry from the tangjiaping porphyry mo deposit dabie orogen zircon u pb geochronology geochemistry and sr nd hf isotopic constraints abstract extensive early cretaceous post collisional igneous rocks especially the large volume of granitoids developed in the dabie orogen some of these granitic rocks are spatially temporally and genetically associated with economically important molybdenum deposits the tangjiaping large scale 0 1 million ton porphyry mo deposit is located in the northwest of the northern dabie complex unit the mo mineralization is mainly hosted in molybdenite bearing quartz veinlets and stockworks in the tangjiaping granite porphyry which intruded into proterozoic biotite plagioclase gneiss and amphibole plagioclase gneiss two alteration zones from the porphyry centre outwards and downwards can be recognized 1 k silicate alteration silicification zone 2 silicification phyllic alteration zone the tangjiaping ore bearing granite porphyry occurs as an individual stock with an outcrop of 0 4 km 2 la icp ms zircon u pb dating of the tangjiaping granite porphyry yields crystallization age of 115 1 ma which is consistent with the molybdenite re os age of the deposit given by previous studies the tangjiaping granitic rocks are metaluminous and belong to high k calc alkaline and shoshonitic series they are relatively enriched in light rare earth elements and have moderately negative eu anomalies geochemical and mineralogical characteristics indicate that the tangjiaping granite is an a type granite and was generated by partial melting of intermediate felsic rocks at pressures of ca 0 4 0 8 gpa there are high initial 87 sr 86 sr ratios ranging from 0 707367 to 0 709410 and negative e nd t values varying from 15 0 to 14 2 for the tangjiaping granite in situ zircon hf isotopic analyses show that the e hf t values of zircons from the tangjiaping granite porphyry vary from 17 0 to 6 0 the geochemical data and sr nd hf isotopes coupled with the neoproterozoic inherited zircon age 652 21 ma indicate that the tangjiaping granite porphyry was most likely derived from partial melting of the northern dabie gneiss with some relatively enriched mantle materials involved the tangjiaping mo ore forming granite porphyry was formed in an extensional setting the early cretaceous asthenospheric upwelling might have played an important role in the formation of the approximately coeval mo bearing magmas in the dabie orogen

proxy evidence from the gartnerkofel 1 core carnic alps austria for hypoxic conditions in the western tethys during the end permian mass extinction event abstract the most severe mass extinction in the phanerozoic in the latest permian period 251 9 ma has been attributed to environmental effects related to the massive coeval siberian flood basalt eruptions a potential causal link between the eruptions and the marine extinctions arises from lethal global warming from greenhouse gas emissions and the resulting development of widespread hypoxic conditions in the warm oceans the 331 m gartnerkofel 1 core carnic alps austria penetrated the permian triassic boundary interval in a western tethys shallow carbonate ramp setting we calculated u th ratios and element enrichment factors for u cr v co and ni using the previously published raw elemental data from the core these redox sensitive proxy calculations provide evidence for an 60 ky long episode of anoxic to euxinic ocean conditions in the shallow western tethys at the time of the abrupt end permian mass extinction epme subsequent fluctuating dysoxic conditions were coincident with a negative excursion of 13ccarb that is estimated to have lasted 450 ky in the earliest triassic at the gk 1 site these findings in a high deposition rate section support previous reports of widespread anoxia in the western tethys and in the oceans in general coincident with the epme and its aftermath

geochemical and isotopic studies of the lady of the lake intrusion and associated tobacco root batholith constraints on the genetic relation between cretaceous mafic and silicic magmatism in southwestern montana abstract small volumes of alkalic mafic intrusions are spatially associated with cretaceous to early tertiary granodioritic to granitic intrusions in the batholithic province of southwestern montana the mafic rocks generally occur near the contacts of the boulder pioneer and tobacco root batholiths with country rocks but their genetic relation with the batholiths is uncertain the lady of the lake intrusion is a small layered body composed of melagabbro and gabbro that occurs along the south central margin of the tobacco root batholith near its contact with archean country rocks a diorite unit spatially distinct from the granodiorite quartz monzonite of the batholith intrudes the gabbroic rocks of the lady of the lake intrusion zircon crystals from the melagabbro and diorite units give u pb ages that are very similar to that of the tobacco root batholith at 74 88 0 17 ma and 76 24 0 08 ma respectively mineral chemistry whole rock major and trace element compositions and oxygen and sulfur isotope ratios have been utilized to evaluate the genetic relation between the lady of the lake intrusion the diorite and the tobacco root batholith no significant variation in the composition of clinopyroxene is observed in different rock units of the lady of the lake intrusion minor olivine with fo 64 in the melagabbro unit is interpreted to represent early crystallization in the base of the intrusion whole rock major and trace element compositions as well as results from modeling using the melts program are consistent with the premise that the diorite was produced by fractional crystallization of the same magma that was parental to the gabbros of the lady of the lake intrusion both whole rock chemistry and oxygen isotopes support the interpretation that the parental magma was an uncontaminated mantle derived basaltic magma in contrast trace element and oxygen isotopes indicate that the quartz monzonitic and granodioritic rocks of the tobacco root batholith and the gabbroic rocks of the lady of the lake intrusion are not related to the same parental magma elevated d 18 o values of quartz 9 10 and feldspar 8 9 from the batholith are consistent with an origin involving partial melting of archean and proterozoic country rocks that was initiated by heat supplied by basaltic magma similar to that which was parental to the lady of the lake intrusion d 34 s values of the melagabbro range from 0 1 to 0 7 and support the premise that the mantle derived parental magma was uncontaminated in contrast d 34 s values of the gabbro and diorite units are elevated 0 6 to 6 5 and indicate that assimilation of country rock s occurred primarily via volatile transfer sulfur contents of the lady of the lake intrusion are low