petrology mineral chemistry and geochemistry of late triassic ni cu ore bearing mafic ultramafic intrusions hongqiling northeastern china petrogenesis and tectonic implications the hongqiling magmatic ni cu sulfide deposit situated on the southern margin of the eastern central asian orogenic belt caob is composed of over 30 mafic ultramafic intrusions these ore beari

armoring and sorting simulation in alluvial rivers formulations for bed armoring and hydraulic sorting of bed sediments in alluvial streams are developed and an application to missouri river bed evolution is presented a relation for the areal coverage factor for armoring on a plane bed is first formulated as a function of degradation depth and bed material characteristics and is then modified by introducing correction factors for the effect of bed forms and the stochastic nature of sediment motion for the simulation of hydraulic sorting bed sediments are assumed to be mixed homogeneously in a mixed layer depth approximately equal to average bed form height and the composition of mixed layer materials is adjusted to satisfy the continuity equation for each sediment size fraction these formulations are applied in a 20 year simulation of bed degradation in the middle missouri river reach downstream of gavins point dam it is found that the simulated bed sediment composition including the two layer structure comprising the top armor coat and the underlying finer sediments is in good agreement with the observed missouri river bed characteristics

boundary shear in smooth rectangular channels the results of some experiments are reported concerning the boundary shear stress and boundary shear force distributions in a smooth channel of rectangular cross section an empirically derived equation is presented which gives the percentage of the total shear force carried by the walls as a function of the breadth depth ratio ancillary equations are presented giving the mean wall bed and bed center line shear stresses as functions of aspect ratio a comparison is made between boundary shear stress distributions in open channel and closed conduit flows at comparable aspect ratios certain differences are noted in both the distributions and the mean resistance coefficients on account of different secondary flow structure the results will be useful to those engaged in resistance sediment or dispersion studies

mapping the distribution of melt during anatexis at the source area of crustal granites by synchrotron μ xrf proyecto fapa universidad de los andes bogota colombia centro nacional de pesquisa em energia e materiais brazilian synchrotron light laboratory lnls proposal n xafs1 17105 cariparo cassa di risparmio di padova e rovigo project makearth european union s horizon 2020 research and innovation programme under the marie sklodowska curie grant agreement no 654606

do extrusion ages reflect magma generation processes at depth an example from the neogene volcanic province of se spain the high k calc alkaline volcanic rocks along the neogene volcanic province of se spain represent crustal anatectic melts mixed with mantle components during the opening of the alboran sea partially melted metapelitic enclaves along with the geochemical signature provide evidence of their crustal source u pb shrimp geochronology on monazite and zircon from enclaves and their hosting lavas in the localities of el hoyazo mazarron and mar menor reveals variable delays between the melting at depth and the eruption of the volcanics these data indicate that 1 the most important event of anatexis in the neogene spanned at least the 3 m y interval between 12 and 9 ma 2 there is no trend in age of crustal melting and 3 the delay between magma generation and extrusion varies from more than 3 m y at el hoyazo to 0 5 m y and possibly 2 5 m y at mar menor with no significant delay measurable at mazarron the variable time delay between anatexis and lava extrusion indicates that radiometric ages of volcanics may provide misleading information on the timing of magma genesis occurring at depth this highlights the pitfall of basing detailed geodynamic models on volcanic extrusion ages alone

tracking bubble evolution inside a silicic dike abstract pressure estimates from rapidly erupted crustal xenoliths constrain the depth of intrusion of the silicic lavas hosting them this represents an opportunity for tracking magmatic bubble s evolution and quantifying the variation in bubble volume during rapid magma ascent through a volcanic dike just prior to eruption the petrology stable isotope geochemistry and x ray micro tomography of dacites containing crustal xenoliths erupted from a neogene volcano in se spain showed an increase in porosity from 1 7 to 6 4 from 19 to 13 km depth at nearly constant groundmass and crystal volumes this result provides additional constraints for experimental and numerical simulations of subvolcanic magma crust degassing processes in silicic systems and may allow the characterization of volcanic eruptive styles based on volatile content

prediction of discharge coefficients for sluice gates equipped with different geometric sills under the gate using multiple non linear regression mnlr abstract gates in dams and irrigation canals are used for controlling discharge and for water regulation to determine the discharge under a gate the discharge coefficient cd must be quantified this study investigates the effect of sill shape under a vertical sluice gate on cd the study also includes the influence of height the investigated shapes are comprised of polyhedral and non polyhedral sills multiple nonlinear regression mnlr is applied to predict cd values and the results show that circular sills under the gate can increase cd by 23 31 a circular sill with a 3 cm diameter has the highest cd and trapezoidal sills have the lowest cd on the other hand semicircular sills have moderate values of cd the most influential parameters affecting cd are h1 p and z g where h1 is the upstream head over the sill crest p is the sill wetted perimeter z is the height of sill and g is the gate opening using dimensionless parameters and regression analysis an equation for predicting cd in free flow conditions with and without a sill is presented the equation agrees with previously published results and can be implemented for predicting cd in sluice gates with and without sills to within 6 accuracy

formation of spinel cordierite feldspar glass coronas after garnet in metapelitic xenoliths reaction modelling and geodynamic implications spinel cordierite k feldspar plagioclase glass form coronas around garnet in metapelitic xenoliths at el hoyazo and mazarron two localities of the neogene volcanic province nvp of se spain the presence of fresh glass quenched melt in all phases shows that corona development occurred under partial melting conditions algebraic analysis of mass balance in the nckfmash system suggests the reaction grt sil bt pl spl crd kfs melt as the most plausible model for the development of coronas in the el hoyazo sample and indicates that biotite was required as reactant for the formation of cordierite the p t conditions for the formation of coronas are estimated at 820 50 c 4 5 0 6 kbar at el hoyazo and 820 50 c 4 0 0 4 kbar at mazarron the el hoyazo xenoliths record a complex p t history characterized by early melt production during heating and additional melting during decompression a local cooling event characterized by minor retrograde reaction and melt crystallization preceded ascent and eruption this study shows that detailed xenolith analysis may be used to track magma evolution in a chamber

crustal thinning and mafic underplating beneath the neogene volcanic province betic cordillera se spain evidence from crustal xenoliths three metapelitic xenolith suites in the neogene volcanic province nvp of se spain from sw to ne el hoyazo mazarron and mar menor originated by partial melting at different crustal depths decreasing from 20 25 km in the sw to 9 12 km in the ne peak temperatures reached c 900 c the xenolith source level is equated with the base of a felsic upper crust of high melting potential fertility at el hoyazo this matches a thin intracrustal low velocity zone recently inferred from seismic studies isostatic calculations indicate that this zone increases in thickness from sw to ne a model of increasing upper crustal thinning from sw to ne in the nvp accompanied by mafic underplating is consistent with the 9 ma petrological data with current heat flow seismic data and gravimetry it is concluded that significant crustal extension occurred in the nvp in the late miocene i e after the main phase of widespread extension exhumation of high pressure rocks and formation of the alboran sea

crustal thickness and velocity structure across the moroccan atlas from long offset wide angle reflection seismic data the sima experiment the crustal structure and topography of the moho boundary beneath the atlas mountains of morocco has been constrained by a controlled source wide angle seismic reflection transect the sima experiment this paper presents the first results of this project consisting of an almost 700 km long high resolution seismic profile acquired from the sahara craton across the high and the middle atlas and the rif mountains the interpretation of this seismic data set is based on forward modeling by raytracing and has resulted in a detailed crustal structure and velocity model for the atlas mountains results indicate that the high atlas features a moderate crustal thickness with the moho located at a minimum depth of 35 km to the s and at around 31 km to the n in the middle atlas upper crustal shortening is resolved at depth through a crustal root where the saharan crust underthrusts the northern moroccan crust this feature defines a lower crust imbrication that locally places the moho boundary at 40 41 km depth in the northern part of the high atlas the p wave velocity model is characterized by relatively low velocities mostly in the lower crust and upper mantle when compared to other active orogens and continental regions these low deep crustal velocities together with other geophysical observables such as conductivity estimates derived from mt measurements moderate bouguer gravity anomaly high heat flow and surface exposures of recent alkaline volcanism lead to a model where partial melts are currently emplaced at deep crustal levels and in the upper mantle the resulting model supports the existence of a mantle upwelling as mechanism that would contribute significantly to sustain the high atlas topography however the detailed moho geometry deduced in this work should lead to a revision of the exact geometry and position of this mantle feature and will require new modeling efforts

back reaction between restite and melt implications for geothermobarometry and pressure temperature paths partial melting is an important process in high grade metamorphism and is responsible for the production of large volumes of melt in the earth9s crust unless melt extraction is complete in situ crystallizing melt back reacts with the restite upon cooling in the northampton block western australia spinel formed by high temperature 850 c partial melting of metapelites is separated from leucosome by garnet sillimanite or cordierite sillimanite coronas formation of the coronas by back reaction with a silica undersaturated melt is inferred because 1 textural evidence indicates that quartz was exhausted as a result of progressive dehydration melting before formation of spinel melt 2 the coronitic phases are never in direct contact with quartz of the leucosome 3 barometry on cordierite and garnet bearing equilibria with spinel gives conflicting pressures 8 0 0 5 and 3 3 0 2 kbar respectively at 850 c if reactions with quartz are assumed but pressure estimates converge on 6 5 0 5 kbar at lower silica activity a sio 2 0 85 0 02 these results indicate that the use of corona textures for the derivation of pressure temperature p t conditions and pressure temperature vectors in migmatites should be reconsidered such coronas may result from a heating cooling cycle without substantial change in pressure back reaction with residual melt is likely to be an important process in migmatites generally affecting both the solid residuum and the leucosome composition

robust characteristics method for modelling multiphase visco elasto plastic thermo mechanical problems abstract we have extended our previous 2d method gerya t v yuen d a 2003 characteristics based marker in cell method with conservative finite differences schemes for modeling geological flows with strongly variable transport properties phys earth planet interiors 140 295 320 which is a combination of conservative finite differences with marker in cell techniques to include the effects of visco elasto plastic rheology self gravitation and a self consistently derived evolving curvilinear planetary surface this code is called i2elvis and can solve a new class of computationally challenging problems in geodynamics such as shear localization with large strains crustal intrusion emplacement of magmas bending of realistic visco elasto plastic plates and core formation by vigorous shell tectonics activities related to a global rayleigh taylor instability of a metal layer formed around silicate rich lower density primordial core during planetary accretion we discuss in detail the computational strategy required the rheological constraints to be satisfied at each time step and spatial location we show analytical benchmarks and examples drawn from comparing between numerical and analogue experiments in structural geology subducting slab bending with a visco elasto plastic rheology and equilibrium spherical configurations from self gravitation we have also tested possibilities of future applications by addressing 3d geometries based on multigrid method and including inertial effects in the momentum equation with tracers in order to simulate meteoritic impact events and eventually earthquake instabilities

the remarkable re os chronometer in molybdenite how and why it works the re os rhenium osmium chronometer applied to molybdenite mos2 is now demonstrated to be remarkably robust surviving intense deformation and high grade thermal metamorphism successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite unique to each sample such that recognized spatial decoupling of 187re parent and 187os daughter within individual molybdenite crystals is overcome highly precise accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry id ntims spatial decoupling of parent daughter precludes use of the laser ablation icp ms microanalytical technique for re os dating of molybdenite the use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons the rb sr k ar and 40ar 39ar chronometers are susceptible to chemical and thermal disturbance particularly in terranes that have experienced subsequent episodes of hydrothermal magmatic activity and therefore should not be used as a basis for establishing accuracy in re os dating of molybdenite as has been done in the past re os ages for molybdenite are almost always in agreement with observed geological relationships and when available with zircon and titanite u pb ages for terranes experiencing multiple episodes of metamorphism and deformation molybdenite is not complicated by overgrowths as is common for some minerals used in u pb dating e g zircon monazite xenotime nor are re and os mobilized beyond the margins of individual crystals during solid state recrystallization moreover inheritance of older molybdenite cores incorporation of common os and radiogenic os loss are exceedingly rare whereas inheritance common pb and pb loss are common complications in u pb dating techniques therefore molybdenite ages may serve as point in time markers for age comparisons

thermal limitations on incorporation of wall rock into magma incorporation of solid wall rocks is an oft cited process in the evolution of magmas but this process is severely limited by the energy required to dissolve xenoliths disaggregation without melting has been proposed as an alternative process for incorporating xenoliths into magma because disaggregation avoids expending the energy required for melting analysis of these processes using enthalpy composition diagrams shows that both processes rapidly lead to high crystal contents in the hybrid magma for example incorporation of 25 granite at 400 c into basalt magma at 1125 c produces a hybrid magma at 1050 c with 50 crystals if the granite disaggregates without melting the crystal content is 65 70 once the crystal content reaches 50 the viscosity of the magma is too high to allow further magma movement or xenolith incorporation thus both processes are self limiting and probably restricted in natural systems to at most a few tens of percent incorporation of xenoliths

the tertiary geodynamical evolution of the aegean arc a paleomagnetic reconstruction abstract the paleomagnetic results obtained in the last 5 6 years from tertiary formations in the aegean domain indicate that the lower miocene arc was almost rectilinear with an e w trend and that its curvature has been acquired tectonically in two major phases during the middle miocene a first phase of deformation is characterized by rotations occurring at the two terminations of the arc clockwise in the west epirus anticlockwise in the east southeastern anatolia a second phase of rotation occurring in the last 5 ma about a pole situated in the southern adriatic sea has affected only the northwestern part the data also indicate that the antalya basin has not been involved in the geodynamical evolution of the arc so that the bey daglari represent its easternmost unit a more complex rotational pattern is observed in the internal zones the large rotations measured in evia 48 and skyros 26 probably occurred in the last 5 ma and result from rotation of fault bounded blocks in a shear zone connecting the north aegean trough to the external arc in the izmir region in the karaburun peninsula of western anatolia and in the island of lesbos significant counterclockwise clockwise or null rotations of coherent blocks have taken place during the neotectonic extensional regime furthermore the values of the inclination obtained from both sedimentary and volcanic oligo miocene formations are systematically shallower than expected on the basis of a geocentered dipole field this suggests that the entire studied area has undergone a northward drift of over 1000 km since the middle miocene

maximum and minimum water contents of granitic melts implications for chemical and physical properties of ascending magmas new results obtained by the investigation of liquidus and solidus phase relations in the system qz ab or and by the determination of h2o solubility in haplogranitic melts are used to discuss the evolution of granitic quartzo feldspathic magmas during their ascent in the crust particular attention is given to the role of h2o and its effect on physical properties of ascending magmas the evolution of melt fraction h2o content of the melt and viscosity of melt and magma during ascent are discussed for several examples adiabatic ascent ascent with cooling ascent with crystal fractionation it is shown that decompression melting processes may be very important significant increase of the melt proportion especially at low pressure in magmas ascending along adiabats or with slow cooling rates the comparison of the discussed examples shows that melts formed at low t are significantly less viscous than at high t although the degree of melting may remain very low in the case of dehydration melting at low temperature the low viscosity of the generated melts may enhance the extraction of these melts from the source area to produce leucogranites

petrogenesis of cogenetic nepheline and quartz syenites and granites northern damara orogen namibia enriched mantle versus crustal contamination abstract geochemical and nd sr o whole rock isotope data and pb isotope data from leached feldspars for a suite of synorogenic ca 540 ma syenites and granites from the northern part of the proterozoic damara orogen namibia constrain their sources and petrogenesis major rock types are mildly potassic nepheline syenites and quartz syenites that were primarily generated by fractional crystallization from a mantle derived alkaline magma even the most primitive samples show pronounced depletion in nb ti sr and p on a primitive mantle normalized diagram indicating the involvement of a recycled crustal component in the source extrapolation of the sr nd pb o isotope composition of the syenites back to a hypothetical parental melt with 8 wt 10 wt mgo suggests derivation from a moderately enriched lithospheric upper mantle documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage t

lateral variation of the crust in the iberian peninsula new evidence from the betic cordillera abstract new results from a seismic refraction wide angle reflection survey carried out in the betic cordillera in autumn 1989 contribute to a better picture of its deep structure one nw se profile cuts across the iberian massif the external and internal betics the structure of the crust in the iberian massif shows characteristics similar to those found in previous experiments the lower crust is found as a distinct layer 12 km thick with an average velocity of 6 8 km s 1 the moho is found at about 35 km depth this structure extends southeastward until a 3 4 km upwelling of the moho about 30 km north of the present day surface boundary between the external and internal betic units further southeast the moho deepens to 38 km and the lower crust is no longer seismically detected the absence of differentiated lower crust beneath part of the external betics may be related with the mesozoic rifting of the south iberian passive margin instead this absence under the internal betics may be caused by rifting in conjunction with the collisional evolution of the orogen a wnw ese profile lying in the internal betics shows the presence of a prominent reflector at 10 12 km depth this seems to be a widespread feature in the internal betics and may be interpreted as a detachment surface the moho is found at 38 km depth rising strongly in the easternmost betics seismic data suggest a thin crust in the offshore area southwest of malaga probably containing a massive zone of high velocity rocks which is also supported by available geophysical and geological data

characterization and origin of aluminous a type granites from the lachlan fold belt southeastern australia the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are a distinctive group of igneous rocks on the basis of chemical and mineralogical criteria those granites that contain 65 72 sio2 can be distinguished from other types on the basis of higher abundances of fetotal fetotal mg high field strength elements trivalent rare earth elements ga and zn mineralogically they contain fe rich hydrous mafic minerals and primary ilmenite and hence are reduced relative to the ni nio buffer however the extremely felsic a type granites sio2 72 have the same chemical and mineralogical characteristics as felsic fractionated i type granites recent analyses indicate that the lachlan fold belt a type granites have sc f alkali element trace transition element and h2o contents similar to those of other unfractionated i type granites rb sr and nd sm isotopic compositions are highly variable probably reflecting source region heterogeneity the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are distinct from peralkaline rocks in terms of chemical composition petrography and field associations although these rocks have been grouped together as a single type in current classification schemes we propose that the metaluminous to weakly peraluminous a type granites such as those of the lachlan fold belt should be defined as aluminous a type granites and should not be grouped with peralkaline granites the lachlan fold belt aluminous a type granites have relatively high calculated zircon saturation temperatures we suggest that these granites were produced by high temperature partial melting of a felsic infracrustal source

dynamics of magma flow near the vent implications for dome eruptions abstract magma erupting out of a volcanic vent into a flow or a dome is subjected to a marked change of boundary conditions which strongly affects the distribution of gas pressure and stress within the flow a numerical code is implemented to study the role of degassing induced crystallization the 2 d governing equations for a compressible viscous liquid are solved with a fully axially symmetric finite element model for different crystal contents and vent geometrical shapes the potential effects of gas pressure deformation rates and elongational stresses on the stability of endogenous dome growth are studied for two shallow vent structures for common eruption conditions values of the internal gas pressure at the vent may be as large as 2 mpa the magnitude of gas pressure at the vent is sensitive to the amount of crystallization and to the shape of the shallow conduit beneath the vent high tensile stresses of 2 mpa are generated at the vent which may account for ring fracturing of the dome and gas escape through shallow fissures such failure conditions may also lead to a change of exit conditions from lateral spreading to the vertical protrusion of a lava spine

observing silicic magma transport in dykes at depths of 8 19 km evidences from crustal xenoliths and numerical modelling abstract within the context of magma transport processes in a dyke this paper integrates petrography and thermodynamic modelling together with fluid dynamics to model the melting of the wall rock in three magma dykes at crustal depths from 8 to 19 km using this combination we explore the interaction between thermal and mechanical processes during silicic magma ascent and the implications for the relative abundance of different crustal xenoliths erupted at the surface we utilize a two dimensional thermal model of dacitic magma injection and flow in dykes of different thickness lengths and depths and associated partial melting of the wall rock and compare the results with field examples from the neogene volcanic province se spain the modelling results open the possibility to relate the range of observed xenoliths information microstructures size distribution at the surface p t evolution to their position in a transient thermal regime in the wall rock of a magma conduit and to the time spent immersed in magma in addition the effects of the modelled stress in the wall rock during magma ascent by the presence or absence of planar features in the xenoliths reveal that the stress patterns are independent of the dyke length and thickness

geochemistry of a type granites in the huangshaping polymetallic deposit south hunan china implications for granite evolution and associated mineralization abstract the huangshaping granites in hunan province south china were investigated for their geochemical characteristics three types of granites have been petrographically identified quartz porphyry granophyre and granite porphyry whole rock geochemistry suggests that the huangshaping granites especially the granite porphyry exhibit typical a type granite characteristics with their enrichment in si rb u th and nb and significant depletion in ba sr ti eu and p based on the al y and zr contents as well as the ree patterns of the rocks investigated the quartz porphyry and the granophyre are classified as a1 type alkaline granites whereas the granite porphyry is considered as a2 type aluminous granite whole rock and quartz feldspar o isotope data yields a wide range of 18osmow values 11 09 26 32 the granites are characterized by high radiogenic pb isotopic composition the present day whole rock pb isotopic ratios are 206pb 204pb 18 706 19 155 207pb 204pb 15 616 15 711 and 208pb 204pb 38 734 39 296 combining the o pb isotope compositions with major trace and ree geochemistry and regional geology characteristics the huangshaping granites were determined to resemble within plate granites that were mainly derived from a felsic infracrustal source related to continental extension the magma source of the quartz porphyry and the granophyre may have been generated from deeper depths and then ascended rapidly with limited water content and low oxygen fugacity which contributed to cu pb and zn mineralization on the other hand the magma that generated the granite porphyry may have ascended relatively slower and experienced pronounced crystal fractionation upper crustal basement rock contamination assimilation and wall rock interaction producing the sn and w rich granite porphyry this study reveals the crustal extension process and associated magmatic metallogenic activities during 180 150 ma in south hunan

lithospheric structure beneath the alboran basin results from 3d gravity modeling and tectonic relevance a three dimensional gravity modeling combined with integrated heat flow and elevation modeling is conducted to map out the crustal and lithospheric mantle thickness in the alboran basin in the westernmost mediterranean a sediment corrected bouguer anomaly has been derived using a depth to the basement map and densities determined from well logs and seismic data the gravity effect of the base of the lithosphere has been removed from the sediment corrected bouguer anomaly to obtain a crustal bouguer anomaly which has been inverted for crustal thickness the resulting lithospheric structure is further constrained by elevation data under the assumption of local isostasy the low residual elevation anomalies obtained 100 m in average suggest that the area is in local isostasy particularly the medium and long wavelength topography features variations in crustal thickness range from 36 km underneath the betic and rif chains to 12 km beneath the easternmost part of the alboran sea basin in the transition to the south balearic basin in western alboran the moho lies at a rather constant depth of 18 km deepening sharply toward the gibraltar strait down to 30 32 km the base of the lithosphere shallows from 140 km depth in the gibraltar strait to 45 km depth in the easternmost alboran sea lithospheric thinning penetrates to the southeastern side of the iberian margin crosscutting topographic highs of the central and eastern betic chain our results favor mantle delamination produced by detachment and subsequent peeling away of the lithospheric mantle rather than convective removal of the lithospheric mantle either by orogenic collapse or detachment and sinking of a lithospheric slab

teleseismic p residual study in the iberian peninsula abstract teleseismic p wave residuals cleared of the effects of various source regions and deep mantle paths reflect the composition and structure of the lithosphere and asthenosphere beneath seismological stations we use a method with which we compute two components of the relative residuals for each station namely a directionally independent average and azimuth incidence angle dependent terms and also the ach 3 d inversion method the representative averages show consistent variations over the iberian peninsula with a relatively steep gradient in some areas the iberian massif and the betic cordillera these changes attain values around 1 s over a distance of about 200 km the lateral variations of these residual averages are transformed into a tentative model of the lithosphere thickness a thick lithosphere is observed beneath the iberian massif the pyrenees and beneath part of the betic cordillera waves from events at different teleseismic distances and various azimuths provide consistent residual patterns and a systematic directional dependence of the relative residuals especially at stations in the betic cordillera

geochronology and geochemistry of the cuihongshan fe polymetallic deposit northeastern china implications for ore genesis and tectonic setting the lesser xing an range is located in the eastern segment of the central asian orogenic belt it hosts an important polymetallic metallogenic belt that contains more than 20 large to small scale porphyry mo epithermal au and skarn fe polymetallic deposits the cuihongshan fe polymetallic deposit is one of the largest polymetallic deposits in ne china to better understand the formation of the cuihongshan fe polymetallic deposit we investigated the geological characteristics of the cuihongshan deposit and applied geochemistry and geochronology to constrain the timing of the mineralization and characteristics of the magmas and ore forming minerals zircon u pb dating of the alkali feldspar granite and monzogranite yielded weighted mean 206pb 238u ages of 495 1 6 ma and 203 1 ma respectively re os dating on molybdenite yielded an isochron age of 203 2 1 4 ma and 40ar 39ar dating on phlogopite yielded an age of 203 4 1 3 ma these data suggest that mineralization occurred during the late tri

petrogenetic interpretation of granitoid rock series using multicationic parameters abstract granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la roche and his coworkers this shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors these suggest that most granitoid series result from a two stage process first fractional crystallisation of clinopyroxene olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition this magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series

diagenesis and metallogenetic mechanisms of the tuanjiegou gold deposit from the lesser xing an range ne china zircon u pb geochronology and lu hf isotopic constraints abstract the tuanjiegou gold deposit is a large sized breccia hosted epithermal gold deposit in heilongjiang province eastern china and was discovered in the late 1950s the scale and unusual metallogenic setting of this gold deposit have made it the focus of many previous studies we systematically analyzed ore samples and volcanic and granitic rocks that are associated with the formation of the deposit by single zircon u pb dating obtaining three distinct concordant groups of u pb ages from dacitic pyroclastic rocks and lavas 119 3 3 3 n 2 113 2 1 1 n 13 and 109 1 1 4 ma n 8 four groups of concordant u pb ages from an ore bearing granite porphyry 112 5 2 2 n 2 107 0 1 2 n 4 103 0 0 70 n 10 and 99 9 1 1 ma n 4 two groups of concordant u pb ages from a pyrite rich quartz vein cemented brecciated and silicified granite porphyry 104 23 0 51 n 16 and 101 3 1 3 ma n 2 and five groups of concordant u pb ages from pyrite rich quartz vein cemented brecciated or chunky ore samples 139 4 to 144 3 n 2 127 4 n 1 113 8 2 1 n 8 101 3 3 4 n 3 and 91 3 ma n 1 combining the whole rock and lu hf isotope geochemistry with the geology of the mining area and these new u pb dates we have redefined the ore deposit related temporal history of the area with formation age of the magma associated with the ningyuancun stage volcanics being 119 1 4 ma and eruption of the volcanics at 113 1 1 ma the granodiorite porphyry and granite porphyry were emplaced at 107 0 1 2 ma and 103 102 ma respectively with ore deposit formation at 102 100 ma the magmato hydrothermal interaction that formed the deposit was closely related to late mesozoic crust mantle interaction with the early stage calc alkaline and high k calc alkaline magmatism in this area potentially being derived from interaction between asthenospheric mantle material and the underplated lower crust however the magmas associated with late stage intrusive calc alkaline and high k calc alkaline magmatism may have been generated during interaction between adakite like magmas derived from the subduction of an oceanic plate and lower crustal material here we suggest that the fluids that formed this deposit formed by interaction with both early and late stage mantle derived magmas and the lower crust with subsequent aggregation after significant igneous differentiation during ore formation the area was in a back arc initial passive rift and continental margin island arc tectonic environment associated with late mesozoic subduction of the pacific plate with metallogenesis occurring during a change in the tectonic environment between the latest early cretaceous and the late cretaceous

sr and o isotope constraints on source and crustal contamination in the high k calc alkaline and shoshonitic neogene volcanic rocks of se spain the neogene volcanic province of se spain nvps is characterized by calc alkaline ca high k calc alkaline kca shoshonitic sh ultrapotassic up and alkaline basaltic ab volcanic series all these series except the ab have high lilerlree lilerhfse and brbe ratios and high but variable sr pb and o isotope compositions the kca and sh lavas contain metapelitic xenoliths whose mineralogical and chemical composition are typical of anatectic restites the geochemical characteristics of ca kca sh and up series suggest that they originated from the lithospheric mantle previously contaminated by fluids derived from pelagic sediments additionally the presence of restite xenoliths in the kca and sh lavas indicates some sort of interaction between the mantle derived magmas and the continental crust trace element and isotope modeling for the kca and sh lavas and the restites point towards the existence of two mixing stages during the first stage the lithospheric mantle was contaminated by 1 5 of fluids derived from pelagic sediments which produced

shear zone related syenites in the damara belt namibia the role of crustal contamination and source composition geochemical and nd sr pb o isotope data for a suite of syn collisional ca 520 ma syenites associated with a major shear zone in the proterozoic damara orogen namibia constrain their sources and petrogenesis major rock types from within and outside the shear zone range from highly potassic nepheline syenites to quartz syenites and were primarily generated by fractional crystallization from a mantle derived alkaline magma even the most primitive samples show pronounced depletion in nb ti sr and p on a primitive mantle normalized diagram indicating the involvement of a recycled crustal component in the source extrapolation of the sr nd pb o isotope composition of the syenites from within the shear zone back to a hypothetical parental melt with 10 wt mgo suggests derivation from a moderately enriched lithospheric upper mantle 87sr 86sr 0 705 e nd 2 18o 6 206pb 204pb 19 40 207pb 204pb 15 82 more evolved quartz syenites show increasing 87sr 86sr ratios increasing 18o values but less radiogenic e nd values and pb isotopes with decreasing mgo indicating assimilation of ca 10 archaean to proterozoic local lower crust with unradiogenic e nd high 87sr 86sr and low u pb for samples from outside the shear zone a hypothetical parental melt with 10 wt mgo has distinctly more radiogenic sr but less radiogenic nd isotopic composition 87sr 86sr 0 712 e nd 13 with strongly unradiogenic pb isotope ratios 206pb 204pb 17 40 207pb 204pb 15 50 suggesting another strongly enriched lithospheric mantle source for these rocks differentiated syenites from outside the shear zone show decreasing 87sr 86sr increasing 18o values more radiogenic e nd values and pb isotope ratios with decreasing mgo indicating interaction with a lithospheric component with low rb sr but high sm nd and u pb

geochronology and metallogenesis of porphyry mo deposits in east central jilin province china constraints from molybdenite re os isotope systematics abstract the east central part of jilin province located on the eastern continental margin of northeast china along the eastern xing meng orogenic belt hosts more than 10 large and medium scale mo deposits the major types of mineralization include porphyry skarn and quartz vein to better understand the formation and distribution of porphyry mo deposits in this area we investigated the geological characteristics of the deposits and applied molybdenite re os isotope dating to constrain the age and source of mineralization the results combined with existing data show that a the daheishan mo deposit yields an isochron age of 168 7 3 1 ma b the shuangshan mo deposit yields an isochron age of 171 6 1 6 ma c the liushengdian mo deposit yields a weighted mean model age of 168 7 1 4 ma d the jiapigou mo deposit yields a weighted mean model age of 196 4 ma and e the sancha mo deposit yields a weighted mean model age of 183 1 1 8 ma therefore the mo mineralization occurred in the early middle jurassic 196 167 ma during the late stages of magmatism or during the late evolution of magma chambers the geodynamic setting at this time was dominated by subduction of the paleo pacific plate beneath the eurasian continent the rhenium content of molybdenite varies from 0 2 to 99 7 ppm suggesting that the ore forming materials may come from a crustal source or a mixed crustal and mantle source

a porphyry skarn metallogenic system in the lesser xing an range ne china implications from u pb and re os geochronology and sr nd hf isotopes of the luming mo and xulaojiugou pb zn deposits abstract the luming porphyry mo deposit and the xulaojiugou skarn pb zn deposit are located in the southeast lesser xing an range ne china they are about 15 km apart and are both related to monzogranite mo orebodies in the luming deposit are hosted within the medium to fine grained monzogranite while pb zn orebodies in the xulaojiugou deposit are hosted by the contact zone between the medium grained monzogranite and the marbles of the early cambrian qianshan formation la icp ms zircon u pb dating of the ore related monzogranite in the luming deposit yields crystallization age of 180 7 1 6 ma and the medium grained and porphyritic monzogranites from the xulaojiugou deposit yield crystallization ages of 181 2 1 1 ma and 179 9 1 0 ma respectively analyses of seven molybdenite samples from the luming deposit display re os isochron age of 177 9 2 6 ma these results indicate that the mineralization in the luming and xulaojiugou deposits occurred at about 181 178 ma these two deposits are genetically linked and belong to a porphyry skarn metallogenic system combined with the previously reported geochronological data for ore deposits in adjacent areas we consider that the early jurassic is an important epoch for mo and pb zn mineralization in the lesser xing an range the monzogranites from the luming and xulaojiugou deposits are enriched in and rb th u pb and light rare earth elements lrees and are depleted in ba nb ta p ti and eu they have positive ehf t values of 1 0 4 0 with two stage hf model ages tdm2 of 868 1033 ma whole rock sr and nd isotopes show restricted ranges of initial compositions with 87sr 86sr i between 0 706346 and 0 707384 and end t between 3 5 and 1 8 these data indicate that their primary magmas originated from the partial melting of a depleted lithospheric mantle which had been metasomatized by subducted slab derived fluids melts the early jurassic magmatic metallogenic events in the lesser xing an range are interpreted as a response to the subduction of the paleo pacific plate

the spinel and quartz associations in high grade xenoliths from tallante s e spain and their potential use in geothermometry and barometry remarkable spinel quartz associations are observed in some xenoliths found in the basaltic rocks from tallante the main primary parageneses are quartz plagioclase sillimanite spinel garnet ilmenite graphite quartz plagioclase garnet orthopyroxene spinel ilmenite

degradation downstream from a sluice gate variation of bed and sediment characteristics with time and discharge abstract results observed from a laboratory study concerning the degradation of an alluvial channel owing to the flow of clear water are reported two sizes of sand of median diameter 0 47 mm and 0 79 mm and geometric standard deviation 4 65 and 3 54 respectively are used as a bed material this paper focuses on studying the variation of the surface layer size with time and distance the variation of sediment discharge with time the sediment size of the armoured layer and the time required for stabilization of the channel bed some useful equations for predicting the sediment size of the armoured layer and the total time for the degradation are also given

formation of elliptical garnet in a metapelitic enclave by melt assisted dissolution and reprecipitation metapelitic residual enclaves in the neogene volcanic province of se spain are residues left after melt extraction glass quenched melt of granitic composition occurs as inclusions in most minerals and as intergranular pockets the most common enclave types show one stage of garnet growth that is interpreted to have occurred at the same time as glass production some of these show a well developed foliation outlined by fibrolite biotite graphite and glass which wraps around elongate garnet crystals that have aspect ratios up to 10 1 based on microstructures and chemistry the garnet within these rocks shows clear core and mantle structure the core has an average composition of alm76 prp08 sps14 grs03 and contains primary inclusions of biotite and melt trapped during garnet growth a thin c 100 lm irregular mantle overgrows the garnet core enclosing oriented fibrolite inclusions in strain caps and biotite in strain shadows in places the overgrowths form skeletal elongated arms which extend parallel to the foliation the garnet mantle contains less mn and higher xmg but both core and mantle display flat mn profiles the contact being a sharp break ternary feldspar and grt bt thermometry yield temperatures in the range 800 900 c with no systematic differences among the different microstructural domains of elliptical garnet based on the observed intracrystalline microstructures the high amount of melt extraction in the rock by flattening component strain and the chemical zoning of garnet the formation of elliptical garnet is modelled by a multistage sequence this involves pressure solution and reprecipitation of the core followed by post kinematic partly mimetic growth of the garnet mantle

age distribution of lamproites along the socovos fault southern spain and lithospheric scale tearing lithospheric scale tearing is commonly linked to the lateral termination of subduction rollback and slab segmentation the upper crustal expression of this process can be associated with the development of arcuate orogenic belts oroclines generated by a combination of vertical axis block rotations and strike slip faulting however the link between such strike slip faults and slab tearing is relatively poorly constrained we show here an example from the gibraltar arc in the westernmost mediterranean where lithospheric scale tear faulting during the late miocene accommodated westward subduction rollback the dextral strike slip socovos fault in the eastern betics may represent one of the surface expressions of this process we document a high concentration of mantle derived volcanic rocks lamproites along the socovos fault which were intruded as dikes during the late miocene phlogopite and whole rock 40ar 39ar ages of lamproites along the socovos fault show a spatial age zonation with older ages 9 3 8 2ma in the east and younger ages 7 3 7 1ma in the west this age distribution of the lamproites along the socovos fault is compatible with the westward retreat of the lithospheric slab that was active beneath the eastern betics in the late miocene we therefore hypothesize that tearing allowed pathways for lamproite melts in the subcontinental lithospheric mantle and lower crust with the socovos fault channelizing these magmas in the upper crust

partial crustal melting beneath the betic cordillera se spain the case study of mar menor volcanic suite abstract the neogene volcanic province nvp within the betic cordillera se spain consists of three main metapelitic enclave suites from sw to ne el hoyazo mazarron and mar menor since the nvp represents a singular place in the world where crustal enclaves were immediately quenched after melting their microstructures provide a photograph of the conditions at depth just after the moment of the melting the thermobarometric information provided by the different microstructural assemblages has been integrated with the geophysical and geodynamical published data into a model of the petrologic evolution of the mar menor enclaves they were equilibrated at 2 3 kbar 850 900 c and followed a sequence of heating melt producing reactions a local cooling event evidenced by minor melt crystallization preceded the eruption the lower crustal studies presented in this work contribute to the knowledge of i the partial melting event beneath the mar menor volcanic suite through a petrologic detailed study of the enclaves ii how the microstructures of fast cooled anatectic rocks play an important role in tracing the magma evolution in a chamber up to the eruption and how they can be used as pseudothermobarometers iii the past and current evolution of the alboran domain betic cordillera and mediterranean sea and how the base of a metapelitic crust has melted within an active geodynamic setting

controls on conduit magma flow dynamics during lava dome building eruptions 1 lava dome eruptions commonly display fairly regular alternations between periods of high and low or no activity with timescales typically of weeks to years and sudden transitions between effusive and explosive activity we develop a transient model of the magma flow in a volcanic conduit from an open system magma chamber with continuous replenishment the model incorporates gas exsolution bubble growth gas escape through the magma and decompression induced crystallization and considers variations in magma temperature water content conduit diameter phenocryst size chamber volume and magma rheology calculations show the presence of periodic variations in discharge rate due to the transition from a stable regime when discharge rate is low and crystals grow efficiently leading to high magma viscosity to another stable state when discharge rate is high and crystallization is negligible the difference in discharge rates between these regimes can be several orders of magnitude periods are similar to the observed timescales and mainly depend on the chamber volume the system shows strongly nonlinear responses to the variation of governing parameters if magma has a bingham rheology pauses in discharge rate occur between peaks of discharge and the peaks are much higher than for the case of newtonian rheology large changes in discharge rate and eruptive behavior can occur as the consequence of small changes in magma temperature water content phenocryst size distribution or conduit diameter the system can fluctuate between low and high discharge rates with transitions to explosive activity

biot number and thermos bottle effect implications for magma chamber convection thermal boundary conditions model the coupling between a convecting magmatic body and its host such conditions need to be considered in models of igneous systems that involve thermal histories crystallization and fractionation of melt formation of aureoles by contact metamorphism and any other processes in which transport of heat plays a role usually investigations of magmatic systems have tended to emphasize modeling the interior convective regime relative to treatment of the thermal coupling yet it is found that the thermal nature of an intrusion is likely to be influenced more by coupling to its host than by the details of internal convective flows evaluation of a parameter having the form of a biot number bi provides a basis for estimating which boundary conditions are most appropriate it is found that bi 0 1 constant heat flux limit for models of several caldera systems for such values of the biot number the host regime behaves somewhat like a thermos bottle by limiting the flow of heat through the magma host system so that convective stirring of magma has little effect on the cooling rate of the intrusion because of this insulating effect boundary temperatures assumed in convection models should approach magmatic values even if an active hydrothermal system is present however high boundary temperatures do not imply that melting and assimilation of host rock by magma must occur despite the thermos bottle effect magmatic convection can still be quite vigorous

geochronological and geochemical constraints on the genesis of the huanren skarn cu zn deposit northeast china abstract the huanren skarn cu zn deposit is located in southeastern liaoning on the eastern edge of the north china craton ncc in this paper we present a study on the geochronologic geochemical and sr nd hf and s isotopic data for the magmatic rocks and sulfide minerals exposed in the deposit laser ablation inductively coupled plasma mass spectrometry la icp ms dating of zircon grains from two mining pits in the monzodiorite yields ages of 128 2 1 1 ma and 128 6 1 5 ma these results indicate that the magmatism in the huanren cu zn deposit might have occurred in the early cretaceous geochemically the huanren monzodiorite belongs to the high k calc alkaline and shoshonitic series is enriched in rb ba and k and is depleted in nb ta and ti the rocks also have relatively high 87sr 86sr i 0 7091 0 7099 and low end t 13 2 to 10 3 and ehf t values 14 3 to 7 8 the sr nd hf isotopic data for the monzodiorite indicate that the magma may be derived from mixed sources of the crust and mantle the 34s values of chalcopyrite galena and pyrite range from 4 4 to 5 8 with an average of 5 1 indicating that the sulfur in the deposit was mainly derived from a magmatic source the huanren cu zn deposit resulted from the magmatism and mineralization induced by the rollback of the paleo pacific plate

magmagenesis at the eocene electric peak sepulcher mountain complex absaroka volcanic province usa abstract igneous rocks exposed on electric peak and sepulcher mountain represent the preserved intrusive and extrusive components of an early eocene calc alkaline eruptive center in the absaroka volcanic province avp of montana and wyoming usa the electric peak stock has an outcrop area of 1 km2 and consists of six discrete phases ranging in composition from quartz diorite to granite representing multiple small intrusions of compositionally distinct magmas lava flows and dikes on sepulcher mountain are basaltic andesitic to dacitic in composition with silicic rocks generally peripheral to mafic rocks important geochemical characteristics of the rocks from both localities include high ni and cr concentrations in andesitic and dacitic rocks lower rare earth element ree concentrations in evolved rocks relative to more mafic rocks and variable sr and nd isotopic ratios although petrographic evidence permissive of magma mixing is limited compositional data suggest that andesitic rocks are hybrids formed by mixing variably fractionated and contaminated mantle derived mafic magmas with diverse composition silicic crustal melts derived from partial melting of amphibolitic lower to mid crustal rocks isotopic and trace element systematics of mafic rocks such as high ratios of large ion lithophile to high field strength elements also suggest that parental magmas were derived from melting of subduction modified lithospheric mantle the significance of these results is that the calc alkaline nature of the center was inherited from crustal processes whereas the arc like trace element signature reflects generation of the magmas in a tectonic environment related to geometrically complex subduction of the farallon plate under the north american continent

petrological and geochemical variations of a turbidite like metasedimentary sequence over the metatexite to diatexite transition within the pampean orogen argentina large masses of turbidite systems have been metamorphosed in orogenic systems during earth s history under granulite facies conditions the transformation of turbidite sedimentary successions into metasedimentary sequences drives intracrustal differentiation by anatexis and melt residuum separation we report on a migmatite terrane developing from turbidite successions that were buried into the deep crust during the neoproterozoic to early cambrian pampean orogeny in central argentina at the exposed middle crustal paleodepths migmatites occur on the regional scale but lithological zones are characterized by 1 bedded migmatites 2 metatexite and 3 diatexite bedded migmatites are the low temperature part of the migmatite terrane where the alternating metapelite and metagreywacke layers are traceable among migmatites of different protoliths the temperature 790 c was sufficient high for melting the metapelite but not for melting the metagreywacke the majority of the migmatite terrane consists of stromatic metatexites in which the limit among different progenitors is either faint or erased by migmatization metatexite zone acts as melt transfer in the migmatite terrane in the stromatic migmatites the major oxide composition of leucosomes and tabular bodies of leucogranite resembles those of the glasses of experimental petrology however leucosomes and leucogranites are crystallized melts that have low zr th and lree contents and positive eu anomalies resulting from accessory mineral retention in melting residues the transformation of metatexite into diatexite is gradational over tens of metres and related to an accumulated melt fraction that dismembers the stromatic fabric the most abundant diatexite is mesocratic and has little or lacks k feldspar a subordinate proportion of diatexites is leucocratic contains k feldspar phenocrysts and shows igneous like textures leucogranites and leucocratic diatexites are the potential carriers of an anatectic melt rich component from granulite facies migmatite sequences toward shallow crustal levels turbidite successions are fertile protoliths that undergo widespread melting under low granulite facies temperature 850 c and the development of large diatexite massifs makes them suitable sources of granitic magmatism

experimental peridotite melt reaction at one atmosphere a textural and chemical study sieve textured clinopyroxene and spinel are common in mantle xenoliths and have been interpreted to be the result of partial melting mantle metasomatism and host magma xenolith reaction during transport in this paper we test the latter hypothesis with a series of reduced and oxidized experiments at 1 200 and 1 156 c at one atmosphere using a synthetic leucitite melt and discs of natural peridotite our results show that sieve texture development on clinopyroxene and spinel in mantle xenoliths is the result of a multistage reaction process in the first step orthopyroxene undergoes incongruent dissolution to produce a silica and alkali rich melt together with olivine as this melt migrates along grain boundaries it causes incongruent dissolution of clinopyroxene and spinel the incongruent dissolution mechanism involves complete dissolution of the clinopyroxene or spinel followed by nucleation and growth of a secondary clinopyroxene or spinel once the reacting melt is saturated the reaction of orthopyroxene clinopyroxene and spinel with infiltrated host magma results in a range of melt compositions that are very similar to those interpreted to be due to very small degrees of partial melting

the study of molybdenites through the187re 187os chronometer we determined the re and os concentrations in 11 molybdenites of various ages 30 2700 m y and from various areas no common osmium has been detected and os was found to be purely radiogenic therefore by comparing the concentrations we were able to determine 187 re 187 os ages for most samples these ages are in good agreement with those measured in surrounding rocks and probably correspond to the age of mineralization however two or three re os ages seem unreliable being probably related to some rhenium leaching through later metamorphic and or hydrothermal events this shows that the petrographic characteristics of ores and the type of crystallization of mos 2 are important in choosing samples suitable for dating re and os determinations combined with careful petrographic investigations may give important clues on the genesis and evolution of molybdenum ores

active continental subduction beneath the betic cordillera and the alboran sea p and s wave seismic tomography detect a low velocity anomaly in the upper mantle beneath the betic cordillera and the alboran sea region the anomaly is associated with the intermediate depth seismicity h

velocity profiles in steep open channel flows velocity measurements with a fiber optic laser doppler anemometer were conducted in steep open channel flows over smooth and imcompletely rough beds the channel slopes were changed from 1 500 and 1 25 by steps and as a result the froude number changed from 0 5 to 3 the law of the wall and the distributions of turbulence intensity were examined in more detail the von karman constant n in the log law was verified to be universally equal to 0 41 on the other hand the integral constant ia n in the log law coincided with the usual value of 5 29 in subcritical flows whereas it decreased with an increase of the bed slope in supercritical flows this decrease of ia n was explained by a decrease of the damping factor ib n in the van driest s mixing length formula the decrease of ib n was well correlated with an increase of the friction velocity and the roughness the streamwise turbulence intensity became smaller in the near wall region than the semiempirical universal formula as the friction velocity became larger

the gaosongshan epithermal gold deposit in the lesser hinggan range of the heilongjiang province ne china implications for early cretaceous mineralization abstract the newly discovered and large ca 99 ma gaosongshan gold deposit is located in the lesser hinggan or xinggan range to the west of the jiamusi massif the deposit is located at the border of the great hinggan range mongolian orogen with the circum pacific tectonic belt and has a resource of 22 t 6 3 g t au gaosongshan is classified as an adularia sericite epithermal deposit associated with the large tensional shaqihe fault and has a low sulfide content with a high concentration of gold hosted by pure chalcedonic quartz which makes the deposit both unique and economically important in the area early cretaceous volcanic rocks host the deposit as well as other gold deposits in the region the mineralization at gaosongshan includes au ag mo sb as pb and hg stable isotope studies of fluid inclusions associated with the mineralization suggest that the mineralizing fluid had a meteoric origin d v smow 129 to 111 18 o fluid 7 9 to 13 8 fluid inclusion thermography indicates that the mineralized fluid was between 150 and 310 c and had a low salinity 0 7 3 71 wt nacl low density 0 48 0 94 g cm 3 shallow metallogenic depth 430 1270 m and a large amount of reducing gaseous components ch 4 c 2 h 6 co n 2 and co 2 the presence of large quantities of flaky quartz adularia gas rich fluid inclusions low sulfide minerals and pure gold bearing chalcedonic quartz suggests that fluid boiling was the principal mechanism for the gold precipitation sulfur isotopic data 34 s 2 4 to 2 9 indicate a deep magmatic origin for the mineralization and the pb isotopes 206 pb 204 pb 18 14 18 46 207 pb 204 pb 15 51 15 57 208 pb 204 pb 38 01 38 40 also indicate that the metallogenic source of the deposit contained a significant mantle component the mineralizing fluid interacted with a late paleozoic ca 260 253 ma substrate and ca 141 91 ma volcanic host rocks the geological and geochemical characteristics of the deposit and the tuanjiegou dongan sandaowanzi and other large gold deposits represent an early cretaceous 114 80 ma epithermal mineralizing events in the lesser hinggan range the belt is controlled by the volcanic sunwu jiayin basin formed in a back arc extensional setting along an active continental margin in east china and the gold deposits in the belt have the same genesis as porphyritic au cu deposits along the continental margin in eastern jilin and heilongjiang provinces it is here proposed that the mineralization in both regions is related to the subduction of the paleo pacific plate

early jurassic porphyry copper mineralization in ne china a case study of the yanghuidongzi deposit abstract the yanghuidongzi cu deposit is located in the southeastern part of heilongjiang province in ne china and represents one of the few known early jurassic porphyry cu deposits within the eastern edge of the xing an mongolia orogenic belt here we present new whole rock major and trace element and sr nd isotopic data zircon u pb and hf isotopic data and molybdenite re os data for units associated with the deposit laser ablation inductively coupled plasma mass spectrometry la icp ms dating of zircons from the granodiorite porphyry in the study area yielded ages of 191 0 1 1 and 191 2 1 0 ma that are interpreted to be the emplacement age of this intrusion the molybdenite re os dating undertaken during this study yielded model ages of 192 7 187 0 ma an isochron age of 188 2 3 8 ma and a weighted mean model age of 190 2 2 6 ma representing the timing of formation of the cu mineralization in this area the yanghuidongzi granodiorite porphyry contains relatively high concentrations of sio 2 68 88 72 49 wt al 2 o 3 15 37 16 31 wt and sr 230 479 ppm but relatively low concentrations of y 7 97 9 87 ppm and yb 0 72 0 85 ppm suggesting that this intrusion has an adakitic affinity combining this with the positive end t 0 7 1 1 and ehf t values 4 0 6 9 low mg values 41 50 and the low concentrations of mgo 0 86 1 22 wt cr 3 17 4 37 ppm and ni 2 11 4 20 ppm within this intrusion suggests it formed from a magma generated by the partial melting of juvenile lower crustal material during the early jurassic subduction of the paleo pacific plate

the temporal evolution of chemical and physical properties of magmatic systems exactly 100 years ago the great canadian born petrologist n l bowen published two seminal works on the chemical differentiation of magmas in which he posed the basis for a physico chemical understanding of the fractionation of crystals from melts in molten rock a subsequent century of research and technological advances has enhanced our understanding of the physics and chemistry of magmatic systems and their temporal evolution the image of sub volcanic magmatic systems has evolved greatly in that time from a simple boiling vat concept of molten rock in which bubbles crystals and melt separate gravitationally to a recognition that magma vats are relatively rare and that most magmatic systems spend much of their lifetime in a partially molten or mushy state real magmatic systems appear to be organized into a series of storage regions periodically connected by feeding structures transferring magma and heat at different fluxes magma fluxes between the different portions of this plumbing system and the variation of the chemical and physical properties of magma as it rises through the crust exert essential controls on the eruptive modalities of volcanoes and the geochemistry of their products this book presents a collection of contributions that use petrology geochemistry geochronology and numerical modelling to identify the processes operating at different depths within magmatic systems and to characterize the fluxes of magma between them

effect of partial melting on vp and vs in crustal enclaves from mazarron se spain abstract the combination of compressional and shear wave velocity is an important tool in discriminating rock types and identifying residing melts within the continental crust here we report the laboratory measurements for vp and vs obtained in varying conditions up to those exceeding the beginning of melting 950 c at 500 mpa confining pressure on two residual garnet biotite sillimanite cordierite spinel metapelitic enclaves recovered from the neogene dacites of mazarron se spain the enclaves preserve widespread interstitial rhyolitic glass as evidence of primary melt extraction at 500 mpa the experimental vp ranges from 7 21 7 46 km s 1 at room temperature to 5 44 km s at 950 c the mean vs is 4 5 km s at room temperature with shear wave splitting of 0 25 0 3 km s measured along three mutually orthogonal directions when temperature increases the vs evidences a reversible slope change at about 650 c and the shear wave splitting reduces to zero isotropic material at 850 950 c where the sample vs is 3 0 km s the vp anisotropy is 7 10 up to 700 c increasing to 20 at 950 c while the vs anisotropy continuously decreases with temperature from 5 to 7 at room temperature to zero at 950 c no mineral reactions are observed up to 650 700 c however microstructure equilibrates due to the relaxation of the primary glass at the glass transition temperature between 850 c and 950 c a new melting reaction is observed producing biotite spinel ilmenite plagioclase melt at melting the rock becomes isotropic for vs and poisson s ratio increases to 0 30 our seismic data show that the seismic signature of high grade metapelitic rocks is similar to that of mafic materials the evolution of vp and vs at melting conditions is compatible with the geophysical data of the area supporting the hypothesis of the current existence of anatectic melts at intermediate depths of the alboran domain

magma ascent along a major terrane boundary crustal contamination and magma mixing at the drumadoon intrusive complex isle of arran scotland the composite intrusions of drumadoon and an cumhann crop out on the se coast of the isle of arran scotland and form part of the larger british and irish palaeogene igneous province a subset of the north atlantic igneous province the intrusions shallow level dykes and sills comprise a central quartz feldspar phyric rhyolite flanked by xenocryst bearing basaltic andesite with an intermediate zone of dark quartz feldspar phyric dacite new geochemical data provide information on the evolution of the component magmas and their relationships with each other as well as their interaction with the crust through which they travelled during shallow crustal emplacement the end member magmas mixed isotopic evidence shows that both magmas were contaminated by the crust prior to mixing the basaltic andesite magma preserves some evidence of contamination within the lower crust whereas the rhyolite mainly records upper crustal contamination the highland boundary fault divides arran into two distinct terranes the neoproterozoic to early palaeozoic grampian terrane to the north and the palaeozoic midland valley terrane to the south the drumadoon complex lies within the midland valley terrane but its isotopic signatures indicate almost exclusive involvement of grampian terrane crust therefore although the magmas originated at depth on the northern side of the highland boundary fault they have crossed this boundary during their evolution probably just prior to emplacement

on the longevity of large upper crustal silicic magma reservoirs understanding the processes involved in the formation and maturation of upper crustal magma reservoirs ultimately sourcing the largest volcanic eruptions on earth is one of the most fundamental aspects of volcanology while such reservoirs are known to assemble incrementally over extended periods of time debate persists regarding the time scales of melt preservation in the cold upper crust if rapid cooling individually freezes incoming replenishing intrusions accumulations of eruptible magma are impossible precluding the construction of voluminous volcanic reservoirs for all but the highest magma emplacement rates recent numerical thermal models have been used to assess the viability of upper crustal silicic magma survival and have suggested that supervolcanic reservoirs must form on geologically short time scales with anomalously high injection rates and subsist only ephemerally making their long term evolution less predictable motivated by geological observations suggesting the contrary we have improved upon these models by incorporating two fundamental features of natural systems not previously considered 1 a nonlinear crystallization temperature relationship adapted for upper crustal silicic magmas and 2 a temperature dependent thermal conductivity we demonstrate that the incorporation of both of these properties can allow an upper crustal reservoir to remain above its solidus for hundreds of thousands of years when fed by magma fluxes typical of large magmatic provinces while the crystallization temperature path plays the most significant role in maintaining a large pool of eruptible magma the incorporation of temperature dependent thermal properties significantly extends the lifetime of such reservoirs furthermore while deeper emplacement levels e g 10 km depth can both extend magma survival and increase melt availability we show that a 5 km depth can also provide an adequate magma storage environment these results provide strong support for long lived upper crustal mushes as a staging ground for accumulation of highly eruptible crystal poor silicic magmas and further assert the evolutionary link between volcanic and plutonic systems

characteristics of supercritical flow below sluice gate supercritical flow below a sluice gate in a horizontal smooth rectangular channel is investigated to explain the effect of the inflow condition on the characteristics of the hydraulic jump the movement of jump location to variations of tailwater level is also examined so the position of the jump in a horizontal apron can be stabilized the distributions of mean velocities and turbulence intensities were obtained with a laser doppler velocitymeter for a wide range of supercritical froude numbers the development of the turbulent boundary layer the water surface profile and the location of the critical point the point where the limit of the boundary layer crosses the water surface are predicted by an approach to the boundary layer analysis and the agreement of those observations with the experimental data is presented using the analyzed water surface profiles the movement of jump location to variations of tailwater level is predicted accurately and verified by laboratory experiments

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

magmatic evolution of the alboran region the role of subduction in forming the western mediterranean and causing the messinian salinity crisis the magmatic evolution of the alboran region westernmost mediterranean contains important clues for improving our understanding of the origin of mediterranean style back arc basins and the desiccation of the mediterranean sea in the messinian we use new laser 40ar 39ar age and geochemical major and trace element and o sr nd pb isotope data from igneous rocks from southern spain the alboran sea and northern morocco to reconstruct the magmatic evolution of the westernmost mediterranean since the eocene lower oligocene dikes near malaga 33 6 0 6 ma and middle to upper miocene volcanic rocks from the alboran sea area 6 57 0 04 to 11 8 0 4 ma can be subdivided into two groups 1 lree depleted relative to n morb primarily tholeiitic series and 2 lree enriched primarily calc alkaline series volcanic rocks both groups are generally enriched in fluid mobile elements e g rb th u k and pb relative to fluid immobile elements e g nb ta lree the lree depleted group has 143nd 144nd 0 5128 0 5130 isotope ratios similar to atlantic morb but higher 87sr 86sr 0 7046 0 7100 in contrast the lree enriched group has less radiogenic nd 0 5121 0 5126 and tend to more radiogenic sr 0 7066 0 7205 isotopic composition pb isotope ratios are surprisingly uniform and have compositions similar to marine sediments analyses of mineral separates show that mafic melts with relatively low 18o 5 6 7 2 had high 87sr 86sr 0 7048 0 7088 7 4 10 6 14 1 and 8 4 40 0 49 3 modeling of the trace elements and sr nd pb o isotopic compositions provides compelling evidence for the contamination of the mantle source with hydrous fluids melts which can be explained through subduction of oceanic lithosphere beneath the alboran basin but not through detachment delamination of lithospheric mantle we present a geodynamic model that reconstructs the late eocene to quaternary evolution of the western mediterranean through westward roll back of subducted tethys oceanic lithosphere slab roll back resulted in a large scale reorganization of the western mediterranean paleogeography causing the closure of marine gateways linking the atlantic ocean to the mediterranean sea isolation of the mediterranean sea led to its desiccation causing the messinian salinity crisis

multistage magmatism resulting in large scale mineralizaion a case from the huojihe porphyry mo deposit in ne china abstract huojihe is a representative porphyry mo deposit in the lesser xing an range northeast china the major magmatic rocks in the ore district include granodiorite porphyritic granodiorite and monzogranite most of the orebodies are hosted within the granodiorite with minor within the monzogranite la icp ms zircon u pb dating of the granodiorite porphyritic granodiorite and monzogranite yields crystallization ages of 184 8 1 2 ma 184 9 1 3 ma and 182 1 1 9 ma respectively the re os model ages of the molybdenite range from 182 4 to 179 2 ma combined with the petrological evidences and previously published age data we suggest that the granodiorite and porphyritic granodiorite are different lithofacies of the same pluton and the huojihe mo deposit experienced two epoches of mineralization related to the granodiorite ca 185 ma and the monzogranite ca 182 ma respectively the granodiorite and monzogranite display consistent 87sr 86sr i ratios of 0 70677 to 0 70746 end t values of 2 1 to 0 5 ehf t values of 0 5 to 7 7 and two stage nd and hf model ages from 1167 to 711 ma indicating that they were generated by partial melting of a mixed source containing mantle derived juvenile materials and pre existed lower crust the magmatism and mineralization in the huojihe mo deposit were resulted from collision of the jiamusi and songnen blocks in response to the subduction of the paleo pacific plate multistage magmatism is beneficial for magmatic related mineralizaiton because it can result in the coupling of favorable structures heat energy and ore forming materials

seismic signature of intracrustal magmatic intrusions in the eastern betics internal zone se iberia 1 receiver functions at three broad band stations located in the most easterly inner betics have been analyzed to investigate the structure of its underlying crust and uppermost mantle these stations are located within a geologically distinctive block bounded by the palomares alhama de murcia faults which is characterized by high heat flow values widespread strike slip faulting and neogene volcanism our analysis shows that a low velocity zone pervades the uppermost mantle beneath the stations and that the overlying crust has a high vp vs ratio and a prominent intracrustal low velocity zone i between the palomares and alhama de murcia faults and ii east of murcia perhaps thermally perturbing the upper crust north and east of cartagena independent studies show that the seismic velocities of the intervening mantle lid are normal beneath the stations and we suggest that our observations result from rapidly ascending magma diapirs ponding at intracrustal levels within the distinctive block

thermal evolution rate of exhumation and tectonic significance of metamorphic rocks from the floor of the alboran extensional basin western mediterranean high grade metamorphic rocks drilled at ocean drilling program site 976 in the alboran sea show a pt path characterized by decompression from about 1050 mpa 40 km depth to 350 mpa 13 km depth accompanied by an increase in temperature from about 550 50 c to 675 25 c the ar ar dating on muscovite and apatite fission track analysis indicate that the final stage of exhumation and cooling occurred very rapidly in the interval 20 5 18 ma which coincides with the initiation of sedimentation in the alboran sea basin the alboran sea formed by miocene extension on the site of a late cretaceous to paleogene contractional orogen and extension coincided with thrusting in the peripheral parts of the betic rif arc which surrounds the basin on three sides thermal modeling of the pt path was carried out with the aim of constraining geodynamic models for the formation of the basin variables considered in the modeling included 1 the thickness and thermal gradient of the postorogenic lithosphere 2 the radiogenic heat production in the thickened crust 3 the time gap pause between the end of contractional tectonics and the start of extension 4 removal of lithospheric mantle below 125 75 or 62 5 km and 5 the rate of extension the only combinations of variables that produce modeled pt paths with the observed characteristics involve high radiogenic heat production combined with a significant postcontractional pause to produce high temperatures in rocks initially at 40 km depth removal of lithosphere below 62 5 km to produce further heating during decompression extension by a factor of 3 in 6 m y to delay the attainment of the maximum temperature until the rocks reached shallow depths and final exhumation and cooling in about 3 3 m y to satisfy radiometric and petrological constraints this gives a maximum of about 9 m y for exhumation from 40 km depth to the surface lithospheric stretching in response to plate boundary forces such as trench rollback without removal of lithosphere cannot explain the late onset of heating and the high temperatures reached by these rocks removal of lithosphere at depths significantly greater than 62 5 km cannot explain the combination of high temperatures reached by these rocks and the shallow depth at which they attained the maximum temperature only a combination of significant postcollisional radiogenic heating then wholesale removal of lithospheric mantle below the orogenic crust followed by rapid stretching can explain the observed pt path these results appear to support some form of lithospheric delamination as the primary cause for the formation of the alboran sea basin

melt producing and melt consuming reactions in the achankovil cordierite gneisses south india migmatitic cordierite gneisses within the achankovil zone az of southern pan african india record melt producing and subsequent melt consuming mineral reactions early mineral assemblages bt sil qtz and bt sil spl deduced from inclusion textures in garnet prophyroblasts break down via successive dehydration melting reactions to high t phase assemblages e g grt crd liq opx liq spl crd liq later back reactions between the restite and the in situ crystallizing melt resulted in thin cordierite coronas separating garnet from the leucosome and partial resorption of garnet to opx crd or crd bt qtz symplectites leucosomes generally display a moderate low strain gneisses to strong high strain gneisses depletion of alkali feldspar attributed to mineral melt back reactions partly controlled by the degree of melt segregation using a kfmash partial petrogenetic grid that includes a melt phase and qualitative pseudosections for microdomains of high and low al si ratios the successive phase assemblages and reaction textures are interpreted in terms of a clockwise p t path culminating at about 6 7 kbar and 900 950 c this p t path is consistent with but more detailed than published results which suggests that taking a melt phase into account is not only a valid but also a useful approach comparing p t data and lithological and isotopic data for the az with adjacent east gondwana fragments suggests the presence of a coherent metasedimentary unit exposed from southern madagascar via south india az and sri lanka wanni complex to the lutzow holm bay in eastern antarctica

spatial temporal relationships of mesozoic volcanic rocks in ne china constraints on tectonic overprinting and transformations between multiple tectonic regimes abstract la icp ms zircon u pb ages and geochemical data are presented for the mesozoic volcanic rocks in northeast china with the aim of determining the tectonic settings of the volcanism and constraining the timing of the overprinting and transformations between the paleo asian ocean mongol okhotsk and circum pacific tectonic regimes the new ages together with other available age data from the literature indicate that mesozoic volcanism in ne china can be subdivided into six episodes late triassic 228 201 ma early middle jurassic 190 173 ma middle late jurassic 166 155 ma early early cretaceous 145 138 ma late early cretaceous 133 106 ma and late cretaceous 97 88 ma the late triassic volcanic rocks occur in the lesser xing an zhangguangcai ranges where the volcanic rocks are bimodal and in the eastern heilongjiang jilin provinces where the volcanics are a type rhyolites implying that they formed in an extensional environment after the final closure of the paleo asian ocean the early middle jurassic 190 173 ma volcanic rocks both in the erguna massif and the eastern heilongjiang jilin provinces belong chemically to the calc alkaline series implying an active continental margin setting the volcanics in the erguna massif are related to the subduction of the mongol okhotsk oceanic plate beneath the massif and those in the eastern jilin heilongjiang provinces are related to the subduction of the paleo pacific plate beneath the eurasian continent the coeval bimodal volcanic rocks in the lesser xing an zhangguangcai ranges were probably formed under an extensional environment similar to a backarc setting of double direction subduction volcanic rocks of middle late jurassic 155 166 ma and early early cretaceous 145 138 ma age only occur in the great xing an range and the northern hebei and western liaoning provinces limited to the west of the songliao basin and they belong chemically to high k calc alkaline series and a type rhyolites respectively combined with the regional unconformity and thrust structures in the northern hebei and western liaoning provinces we conclude that these volcanics formed during a collapse or delamination of a thickened continental crust related to the evolution of the mongol okhotsk suture belt the late early cretaceous volcanic rocks widely distributed in ne china belong chemically to a low to medium k calc alkaline series in the eastern heilongjiang jilin provinces i e the eurasian continental margin and to a bimodal volcanic rock association within both the songliao basin and the great xing an range the volcanics in the eastern heilongjiang jilin provinces formed in an active continental margin setting related to the subduction of the paleo pacific plate beneath the eurasian continent and the bimodal volcanics formed under an extensional environment related either to a backarc setting or to delamination of a thickened crust or both late cretaceous volcanics limited to the eastern heilongjiang jilin provinces and the eastern north china craton ncc consist of calc alkaline rocks in the eastern heilongjiang jilin provinces and alkaline basalts in the eastern ncc suggesting that the former originated during subduction of the paleo pacific plate beneath the eurasian continent whereas the latter formed in an extensional environment similar to a backarc setting taking all this into account we conclude that 1 the transformation from the paleo asian ocean regime to the circum pacific tectonic regime happened during the late triassic to early jurassic 2 the effect of the mongol okhotsk suture belt on ne china was mainly in the early jurassic middle late jurassic and early early cretaceous and 3 the late early cretaceous and late cretaceous volcanics can be attributed to the subduction of the paleo pacific plate beneath the eurasian continent

development and prediction of bed armoring the major purposes of this study are to use available data to predict 1 the development of bed armoring and 2 the final composition of grain size distribution first the different factors influencing the incipient motion for nonuniform sediment size distribution are examined then the procedures for simulating the grain size distribution of the armor layer are developed based on modifications of gessler s procedure and einstein s hiding factor three regression equations are derived to predict the median size d d3 d0 and d d8 d4 of the final armor bed given the initial sediment bed size distribution and flow conditions a modified shields diagram for incipient motion for nonuniform sediment sizes is also suggested

petrological and structural evolution of high grade metamorphic rocks from the floor of the alboran sea basin western mediterranean the metamorphic basement beneath the alboran sea a neogene introduction extensional basin drilled during ocean drilling program odp late orogenic extension of previously thickened conleg 161 site 976 consists of high grade pelitic schist overlying tinental lithosphere is a widely documented phenomenon migmatitic pelitic gneiss inferred assemblages in the high grade e g dewey 1988 malavieille 1993 ruppel 1995 schist evolved from garnet staurolite biotite muscovite but it is unclear whether the thermal evolution of the plagioclase assemblage 1 to biotite sillimanite k feldspar lithosphere in this situation differs significantly from that plagioclase garnet assemblage 2 to andalusite biotite associated with extension in non orogenic settings if k feldspar plagioclase assemblage 3 in the gneiss which extension is triggered by removal of part of the lower shows abundant migmatitic textures the present assemblage is biotite lithosphere e g england houseman 1989 there may andalusite sillimanite muscovite cordierite kbe a detectable rise in temperature during exhumation feldspar plagioclase garnet phase relations and thermoof rocks platt england 1994 whereas extension barometric calculations suggest that the high grade schist experienced caused by far field forces is likely to produce isothermal decompression accompanied by heating from 500 c at 10 5 kbar decompression paths followed by cooling ruppel et al through 600 30 c at 6 7 kbar assemblage 1 and thence 1988 platt et al 1999 decompression accompanied by to 650 700 c at 3 4 kbar assemblage 2 followed by cooling heating in extensional settings has been demonstrated in through 500 600 c at 2 kbar or less assemblage 3 peak the seward peninsula in alaska patrick lieberman temperature and melting occurred under low pressure conditions 1988 the cordillera darwin in the southern andes the widespread disequilibrium and overstepping of metamorphic kohn et al 1993 the tauern window in the alps reactions suggests that decompression was rapid the p t evolution selverstone et al 1984 the aegean buick holland is consistent with metamorphism in a late orogenic extensional 1989 the high himalaya inger harris 1992 and basin and suggests the existence of an external source of heat the betic cordillera van der wal vissers 1993 an probably indicating the complete removal of lithospheric mantle interesting related question is the significance of crustal beneath the extending region melting in extensional settings in principle partial melt

flow conditions of undular hydraulic jumps in horizontal rectangular channels the flow conditions of undular jumps for fully developed inflow condition have been investigated systematically if the inflow froude number is larger than 1 2 an undular jump has lateral shock waves near the toe of the jump for a narrow channel the shock waves cross upstream of the first wave crest and the flow conditions of undular jumps depend on the aspect ratio and the inflow froude number in contrast for a wide channel the shock waves do not cross upstream of the first wave crest and the flow conditions of undular jumps are independent of the aspect ratio the flow conditions of undular jumps are classified by considering the cross position of the lateral shock waves and the inflow froude number also the hydraulic conditions for the formation of nonbreaking and breaking undular jumps are determined the effect of the reynolds number on undular jump formations is discussed and changes of the flow conditions with the reynolds number are described

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

closure temperatures of intracrystalline ordering in anatectic and metamorphic hercynite fe2 al2o4 ab stra c t the closure temperature tc of the intracrystalline ordering of mg hercynite is estimated with a comparative crystal chemical approach the single crystals were selected from two distinct geological environments that represent extremely different cooling rates the fast cooled setting refers to anatectic metapelitic enclaves that occur in the high k calc alkaline lavas of the neogene volcanic province of se spain the slow cooled setting refers to metabauxite from the anga metamorphic complex lake baikal parameters sensitive to tc include the oxygen fractional coordinate u and the inversion parameter i experimental equilibration data on the spinel and hercynite end members and on their solid solution are fitted to equations where tc is given as a function of the hercynite content hc of the solid solution and of u or i the unavoidable simplifications made in this empirical approach are discussed a reasonable value for tc 400 c was obtained for the slow cooled metamorphic hercynite from the oxygen fractional coordinates in contrast an unreasonably high value of tc 600 c was obtained from the inversion parameters in the case of the fast cooled anatectic samples tc calculated from the two structural parameters are comparable the five crystals show a range in the calculated values for tc over 250 c from 700 to 950 c which is reasonable considering the known diversity of cooling rates exhibited by their volcanic host rocks

re os and u pb geochronology of the shazigou mo polymetallic ore field inner mongolia implications for permian triassic mineralization at the northern margin of the north china craton abstract the recently discovered polymetallic shazigou mo w pb zn ore field is located at the northern margin of the north china craton this integrated metallogenic system is comprised of quartz vein mineralization in three deposits shazigou mo w jindouzishan pb zn and mantougou pb zn the total reserves are estimated to be 50 kt mo 626 t wo3 244 kt pb and 150 kt zn molybdenite re os dating of five quartz vein type ores yielded a mean model age of 243 8 1 6 ma mswd 0 81 and hydrothermal zircons yielded a concordant u pb age of 245 2 6 ma mswd 0 65 these results suggest that the mineralization was formed in the early triassic and could be related to paleo asian ocean subduction microthermometry and quartz fluid inclusion compositions indicate that fluids related to the mo w mineralization were mainly derived from magmatic sources and precipitated under relatively high temperature 280 340 c and salinity conditions 6 9 wt nacl equiv whereas subsequent pb zn mineralization related fluids may have been modified by metamorphic and meteoric waters the discovery of the shazigou ore field suggests conditions may be favourable for more extensive mineralization in the western xilamulun mo metallogenic belt at the northern margin of the north china craton

assimilation of felsic crust by basaltic magma thermal limits and extents of crustal contamination of mantle derived magmas basaltic magma is the most widely used probe of mantle chemistry and structure chemical characterization of the sources for mantle derived magma is possible only after quantitative evaluation of possible contamination by crustal wall rocks the most commonly invoked contamination mechanisms are the combined processes of crustal assimilation and magmatic fractional crystallization afc because of the energetic link between these processes predicting assimilation and crystallization progress requires modeling both heat and mass transfer in the magma country rock system using the melts software package we modeled isenthalpic heat balanced afc between two common types of basaltic magma and several types of felsic crust at 1 kbar our simulations show that during the early stages of isenthalpic afc the ratio of rates of assimilation to crystallization r may be substantially greater than one 2 0 2 7 allowing assimilation of a mass of country rock up to 5 18 of the initial magma mass with only 3 7 crystallization the second stage of afc beginning with plagioclase and or pyroxene saturation is characterized by lower r 0 5 1 0 the initial high r stage results from suppression of crystallization associated with the change in magma composition as assimilation progresses under certain conditions even small degrees of crystallization of olivine alone coupled with cooling of the magma can accommodate relatively large amounts of crustal assimilation and cause large shifts in isotopic and trace element geochemical indices with little differentiation

melt producing versus melt consuming reactions in pelitic xenoliths and migmatites abstract melt producing reactions have operated both in pelitic xenoliths and in pelitic migmatites but melt consuming reactions related to in situ melt crystallization are largely restricted to migmatites hence xenolith reaction textures may provide clues on the relative roles of both reaction types in migmatites a comparison of xenoliths and migmatites results in a catalogue of textural and chemical features some of which are argued to be diagnostic the results have implications for the identification of restite in igneous rocks and for the relative importance of prograde and retrograde processes in different domains of layered migmatites