provenance of marbles used in the heliocaminus baths of hadrian s villa tivoli italy abstract this paper aims to ascertain the provenance of white and greyish marbles used for decorating the heliocaminus baths one of the most ancient thermal complexes inside the hadrian s villa at tivoli italy fifteen marble samples have been macroscopically described and investigated by means of mineralogical and petrographic observations of thin sections xrf chemical analyses of major and some trace elements and stable isotope ratio analysis of carbon and oxygen the collected data show that the majority of the marbles analysed come mainly from the apuan alps basin carrara and subordinately from several greek mt penteli and thasos islands and turkish afyon and probably ephesus districts quarrying areas

petrogenesis p t t path and tectonic significance of high pressure mafic granulites from the jiaobei terrane north china craton abstract high pressure hp mafic granulites in the jiaobei terrane are composed predominantly of garnet mafic granulites garnet hypersthene granulites and garnet amphibolites and they are found as irregular lenses or deformed dike swarms within tonalitic trondhjemitic granodioritic gneisses and granitic gneisses the hp mafic granulites contain four distinct metamorphic assemblages of which the early prograde assemblage m 1 is represented by the cores of garnets together with mineral inclusions of clinopyxene plagioclase quartz and it formed at 740 770 c and 0 90 1 00 gpa in contrast the peak assemblage m 2 consists of high ca cores in garnet high al cores in clinopyroxene and high na cores in plagioclase in the matrix which formed under p t conditions of 850 880 c and 1 45 1 65 gpa the peak metamorphism was followed by near isothermal decompression m 3 which resulted in the development of orthopyroxene clinopyxene plagioclase quartz amphibole magnetitie symplectites or coronas surrounding some garnet grains with p t conditions of 780 830 c and 0 65 0 85 gpa surrounding some garnet grains are symplectites of amphibole plagioclase quartz magnetitie which formed during a cooling retrograde stage m 4 with p t conditions of 590 650 c and 0 62 0 82 gpa an integrated study involving laser raman analysis of mineral inclusions cathodoluminescence imaging and in situ u pb dating of zircons shows that the protolith ages of the hp mafic granulites are mainly 2550 2500 ma and that the timing of the peak metamorphism of the hp mafic granulites ranges from 1900 to 1860 ma as recorded by the cores of metamorphic zircons on the other hand the medium to low pressure granulite amphibolite facies retrogression occurred mainly at 1860 1820 ma as recorded by the rims of some single zircon grains and the zircon grains that contain inclusions of garnet orthopyroxene plagioclase sphene the combination of petrography mineral compositions metamorphic reaction history thermobarometry and geochronology defines a near isothermal decompressional clockwise p t t path for the jiaobei hp mafic granulites suggesting that the jiaobei terrane underwent initial crustal thickening during 1950 1860 ma followed by relatively rapid exhumation cooling and retrogression in the period 1860 1820 ma this tectonothermal path was probably generated by subduction and collision related tectonic processes

metamorphic evolution and zircon u pb geochronology of the mts huashan amphibolites insights into the palaeoproterozoic amalgamation of the north china craton abstract exposed in the southernmost terminal of the palaeoproterozoic trans north china orogen tnco the garnet bearing amphibolites in the mts huashan metamorphic complex preserve three generations of mineral assemblages including the prograde peak and retrograde metamorphic stages the prograde metamorphic stage m1 is recognized as inclusion type mineral assemblages hornblende plagioclase quartz biotite ilmenite preserved in the garnet porphyroblasts the peak metamorphic assemblages m2 are represented by the garnet porphyroblasts and matrix minerals hornblende plagioclase quartz biotite ilmenite the retrograde metamorphic assemblages m3 are characterized by the symplectitic intergrowth minerals hornblende plagioclase quartz orthopyroxene biotite ilmenite rimming decomposed relict garnet porphyroblasts known as the white eye socket reaction textures calculated by geothermometers and geobarometers the p t conditions of these three metamorphic stages are estimated to be of 5 7 6 0 kbar 660 760 c for the prograde stage m1 6 6 7 7 kbar 700 820 c for the peak stage m2 and 4 5 6 7 kbar 720 760 c for the retrograde stage m3 respectively therefore these three metamorphic stages define clockwise p t paths including nearly isothermal decompression itd processes geochronological studies of zircons from the amphibolites indicate that the protolith of the amphibolites formed at 2 3 ga and the metamorphism occurred at 1 87 1 85 ga and the metamorphic period was further deciphered to be of 1 96 1 80 ga when considering our previous reports it is therefore proposed that the southernmost terminal of the tnco was also involved in the subduction and collision processes between the eastern and western blocks of the north china craton at least as early as 1 96 ga and continued as late as 1 80 ga followed by rapid uplift and exhumation the available data suggest that the palaeoproterozoic tectono metamorphic event of the southernmost terminal of the trans north china orogen not only started earlier but also continued longer than the other terranes in the middle and northern sections elsewhere in the orogen

zircon sims u pb geochronology of the lushan terrane dating metamorphism of the southwestern terminal of the palaeoproterozoic trans north china orogen high resolution sims u pb dating of metamorphic zircons of the ttg gneisses gneissic granitoid and amphibolites of the lushan terrane taihua metamorphic complex suggests that the metamorphism had taken place at least as early as 1 96 1 86 ga these new dates along with reference data demonstrate that the southern and middle terranes of the trans north china orogen had been involved in the continent continent collision between the western block and the eastern block of the north china craton this orogenic process started as early as 1 96 ga and lasted as late as 1 80 ga

fractionation of bulk rock composition due to porphyroblast growth effects on eclogite facies mineral equilibria pam peninsula new caledonia chemically zoned porphyroblasts in metamorphic rocks indicate that diffusional processes could not maintain equilibrium conditions on a grain scale during porphyroblast growth or establish it afterwards an effect of this inability to maintain equilibrium is the progressive removal of elements forming garnet cores from any metamorphic reaction that occurs at the porphyroblast boundaries or in the matrix of the rock to examine this effect on mineral assemblages the bence albee matrix correction was applied to x ray intensity maps collected using eclogite samples from northern new caledonia in order to determine the chemical composition of all parts of the sample the manipulation of these element maps allows a quantitative analysis of the fractionation of the bulk rock composition between garnet cores and the matrix a series of calculated equilibrium volume compositions represents the change in matrix chemistry with progressive elemental fractionation as a consequence of prograde garnet growth under high p conditions pressure temperature pseudosections are calculated for these compositions in the cao na2o feo mgo al2o3 sio2 h2o system assemblages modal proportions and mineral textures observed in the new caledonian eclogites can be closely modelled by progressively removing elements forming garnet cores from the bulk rock composition the pseudosections demonstrate how chemical fractionation effects the peak metamorphic assemblage prograde textures and the development of retrograde assemblages

empirical garnet biotite plagioclase quartz gbpq geobarometry in medium to high grade metapelites on the basis of the net transfer reactions among garnet biotite plagioclase and quartz for both mg and fe end member models the garnet biotite plagioclase quartz gbpq geobarometer was empirically calibrated under physical conditions of p 1 0 11 4 kbar and t 515 878 c based on the input garnet biotite temperatures and garnet aluminosilicate plagioclase quartz gasp pressures of 224 natural aluminosilicate bearing metapelitic samples collated from the literature the calibrations are internally consistent with the asymmetric quaternary solid solution model of garnet the symmetric quaternary solid solution model of biotite and the al avoidance ternary solid solution model of plagioclase in calibrating the garnet biotite geothermometer and the gasp geobarometer the resulting two gbpq barometer formulae reproduce the input gasp pressures well within 1 0 kbar mostly within 0 5 kbar for both aluminosilicate bearing and aluminosilicate absent metapelites the two gbpq barometry formulae yielded identical pressures whether the sample was included or not included in calibrating the gbpq barometry the random error of the gbpq barometry may be expected as 1 2 kbar the dp dt slopes of these two gbpq formulae are close to that of the gasp barometer in p t space applications of the gbpq barometry of aluminosilicate absent metapelites to the rocks within a thermal contact aureole or rocks within a limited geographical area without post metamorphic structural discontinuity show no obvious pressure change it may be concluded that the two gbpq barometry formulae derived in this study may be used as practical tools for metamorphic pelites under the conditions of 515 878 c and 1 0 11 4 kbar in the composition range of xgros 3 in garnet xan 17 in plagioclase and x bio 3 in biotite application of the gbpq barometer beyond the calibration range should be undertaken with caution

shrimp u pb zircon ages of granitoid rocks in the luliang complex implications for the accretion and evolution of the trans north china orogen abstract the luliang complex is situated in the central segment of the trans north china orogen tnco a continent continent collisional belt along which the discrete eastern and western blocks amalgamated to form the basement of the north china craton the complex consists of supracrustal and granitoid rocks of which the latter can be subdivided into pre tectonic ttg gneisses including the yunzhongshan guojiazhuang and chijianling guandishan gneisses syn tectonic gneissic granites represented by the huijiazhuang gneissic granite and post tectonic granites including the luyashan charnockite luchaogou porphyritic granite and tangershang guandishan massive granite the pre tectonic ttg gneisses are mostly calc alkaline and considered to have formed in a magmatic arc environment shrimp u pb analyses reveal that the yunzhongshan gneisses were emplaced at 2499 9 ma representing the earliest arc related magmatic event in the luliang complex this was followed by the intrusion of the guojiazhuang gneisses at 2375 10 ma the most widespread arc related magmatic event in the region was the emplacement of the chijianling guandishan granitoid gneisses of which the tonalitic granodioritic and monzogranitic gneisses were emplaced at 2199 11 ma 2180 7 ma and 2173 7 ma respectively metamorphic zircon overgrowth rims from a tonalitic gneiss yielded a weighted mean 207 pb 206 pb age of 1872 7 ma consistent with the metamorphic age range of 1880 1820 ma defined by metamorphic zircons from various high grade rocks in the tnco thus the evolution of the luliang complex involved emplacement of the yunzhongshan granitoids at 2499 ma the guajiazhuang granitoids at 2375 ma and the chijianling guandishan granitoids at 2199 2173 ma with the final collision between the eastern and western blocks in this area occurring at 1872 7 ma the whole series of magmatic events lasting nearly 650 ma this suggests that the trans north china orogen represents a long lived magmatic arc the new shrimp zircon data combined with structural and petrological studies also reveal the existence of both syn and post collisional granites in the luliang complex the former is represented by the huijiazhuang gneissic granite that was emplaced at 1832 11 ma whereas the latter include the 1815 5 ma luyashan charnockite 1807 10 ma luchaogou porphyritic granite 1798 11 ma guandishan massive granite and 1790 14 ma tangershan massive granite

decompressional coronas and symplectites in granulites of the musgrave complex central australia abstract in granulite facies metapelitic rocks in the musgrave complex central australia reaction between s1 garnet and sillimanite involves the development in s2 of both garnet cordierite hercynitic spinel biotite and hercynitic spinel cordierite sillimanite biotite the s2 assemblages occur either in coronas and symplectites mainly around garnet or in rocks in which s2 is more strongly developed as recrystallized assemblages ignoring the presence of biotite and ilmenite the mineral textures can be accounted for qualitatively by a consideration of the model system feo mgo al2o3 sio2 fmas the textural relationships accord with decompression accompanying the change from s1 to s2 however since biotite and ilmenite are involved in the assemblages the parageneses are better accounted for in terms of equilibria in the expanded model system k2o feo mgo al2o3 sio2 h2 tio2 fe2o3 kfmashto i e afm tio2 fe2o3 the coronas reflect the tectonic unroofing of at least part of the musgrave complex from peak s1 conditions of about 8 kbar to s2 conditions of about 4 kbar

zircon u pb ages of paleoproterozoic mafic granulites from the huai an terrane north china craton ncc implications for timing of cratonization and crustal evolution history abstract the north china craton ncc is considered to have been incorporated into the columbia supercontinent during late paleoproterozoic the huai an terrane located in north central part of the ncc is an important tectonic window to investigate the paleoproterozoic crustal evolution history of this craton particularly due to the wide occurrence of high grade metamorphic rocks including retrograded eclogites and high pressure granulites available data show two controversial peak metamorphic ages of these rocks as 1 95 1 90 or 1 85 1 80 ga thus determining the precise timing of metamorphism of the high pressure granulites is important in reconstructing the collisional history in this study we present zircon u pb ages bulk chemistry and mineral inclusions in zircons and matrix mineral assemblages from the high pressure granulites to evaluate the timing of metamorphism our results reveal ca 2 05 2 0 ga ages from magmatic zircons in these rocks representing the timing of emplacement of mafic magmas the metamorphic zircons yield two groups of ages at 1 95 1 90 and 1 85 1 80 ga clinopyroxene plagioclase titanite and apatite occur as common mineral inclusions within the 1 85 1 80 ga metamorphic zircons the chemical compositions of clinopyroxene and plagioclase occurring as inclusions are very similar to those of the rim compositions of those minerals in the matrix suggesting their formation during retrograde granulite metamorphism and are distinctly different from those of the core domains of the minerals in the matrix which represent high pressure granulite metamorphism these results indicate that the metamorphic zircons formed during retrograde granulite metamorphism dated as 1 85 1 80 ga and the age range of 1 95 1 90 ga corresponds to high pressure granulite metamorphism the dual nature of the geological and geochronological features suggest that the archean gray gneisses in the huai an terrane represent the basement rocks detached from the khondalite belt of the ncc after collision integrating with published data a double side collision with scissor like suturing model is proposed for the paleoproterozoic cratonization of the ncc

spatial distribution of 1950 1800 ma metamorphic events in the north china craton implications for tectonic subdivision of the craton abstract great progress has been made in the last twenty years in understanding the unification of the north china craton according to a prevailing model it developed by amalgamation of four sub blocks by three spatially and temporally separate orogenic belts the first at 1950 ma formed the western block the second at 1900 ma created the eastern block and the third at 1850 ma unified the eastern and western blocks however new data show that the 1950 ma orogen was affected by granulite facies reequilibration at 1800 ma and parts of the 1850 ma orogen have evidence of metamorphism at 1950 1900 ma new zircon u pb ages enable the paleoproterozoic metamorphic events to be statistically sub divided into four at 1955 ma m 1 1920 ma m 2 1885 ma m 3 and 1850 ma m 4 the m 1 2 events always appear together mainly in two belt areas including the helanshan qianlishan northern ordos yinshan liangcheng huai an lushan jiaobei and liaodong regions whereas the m 3 4 events are distributed over larger areas and were superimposed on the m 1 2 activities this age distribution is inconsistent with previous models of three separate orogens it should also be noted that the igneous rocks contemporary with the regional ultra high temperature high pressure granulite facies metamorphisms m 1 2 were previously described as arc related series i e the gabbro norites i s type granites and trimodal volcanics based on the spatial distribution of the paleoproterozoic metamorphic events m 1 4 and of the coeval igneous rocks we speculate that the assembly of the ncc was created by one orogen which formed between the eastern and western cratons in two tectonic stages two marginal arcs the korean and xuwujia developed against both eastern sides of the two sub cratons and were both accreted and deformed at 1965 1900 ma m 1 2 subsequently the amalgamation of the two sub cratons resulted in metamorphism on the western side of the eastern craton and in metamorphism that was superimposed on both accreted arcs at 1900 1790 ma m 3 4

ree activated cathodoluminescence of calcite and dolomite high resolution spectrometric analysis of cl emission hrs cl abstract cathodoluminescence cl investigations of phanerozoic marine limestones sinter calcites and saddle dolomites of hydrothermal veins indicate that in contrast to previous knowledge rare earth element ree activated cl in sediments is common the methods of high resolution spectrometric analysis of cl emission hrs cl combined with hot cathode cl microscopy are able to prove qualitatively some ree below the detection limits of electron microprobe and proton induced x ray emission analysis pixe our investigations document sm3 dy3 tb3 and probably ho3 activated cl in calcite and eu3 activated cl in a saddle dolomite of hydrothermal veins sometimes the ree activated cl is hidden by dominant mn 2 emission in such cases the ree emission spectrum may be obtained by subtracting a spectrum of luminescence produced only by mn2 the occurrence of only one ree in natural samples is uncommon in all observed samples ree are present in groups

geochronological and geochemical constraints on the luliang group in the luliang complex implications for the tectonic evolution of the trans north china orogen abstract the luliang complex is located at the western margin of the middle segment of the trans north china orogen along which the western and eastern blocks amalgamated to form the basement of the north china craton the complex consists of the late neoarchean to paleoproterozoic granitic plutons and meta supracrustal rocks of which the latter are subdivided into the jiehekou luliang yejishan and heichashan lanhe groups the luliang group is composed mainly of siliciclastic rocks in the lower part and volcanic rocks in the upper part all of which have been metamorphosed from greenschist to amphibolite facies u pb ages of detrital zircons from meta sedimentary rocks in the luliang group yield four populations of 3061 2920 ma 2790 2600 ma 2599 2280 ma and 2211 2202 ma suggesting that their provenances were derived mainly from the luliang and taihua complexes in the trans north china orogen the meta volcanic rocks give igneous zircon u pb ages of 2209 2178 ma and e hf t values of 0 8 to 3 6 geochemically they are subalkaline basalts and andesites that can be classified into two groups of which one group has flat lrees weak enrichment in lrees relative to hrees and flat hrees and displays e morb like spider diagrams with the exception of insignificantly negative nb ta zr hf and ti anomalies in contrast the other group displays stronger lree fractionation stronger enrichment in lrees relative to hrees and mildly fractionated hrees and is characterized by spiky spider diagrams similar to arc volcanic rocks the first group is interpreted to have originated from a neoarchean e morb source whereas the second group shows inputs of newly subduction derived fluids in the mantle source these geochronological and geochemical signatures indicate the existence of an 2 2 2 1 ga continental back arc system in the luliang complex of the trans north china orogen which is consistent with the model that the collision between the eastern and western blocks to form the coherent basement of the north china craton in the paleoproterozoic not at the end of neoarchean

new constraints on metamorphism in the rauer group prydz bay east antarctica granulite facies metapelites of the mather and filla paragneisses within the rauer group east antarctica possess markedly different compositions the metamorphic evolution of the two metapelite types has been interpreted as temporally distinct with the rauer group preserving at least two distinct granulite facies tectonothermal episodes calculated p t pseudosections and orthopyroxene al content indicate the revised maximum preserved p t conditions within the mather paragneiss to lie in the vicinity of 950 975 c and 10 10 6 kbar less extreme than previous estimates the range of possible p t paths for the mather paragneiss consistent with mineral textural relationships and pseudosections contoured for mineral proportion are significantly shallower dp dt than previous estimates a near isothermal decompression p t path and extreme peak metamorphic conditions are not necessary to explain the development of preserved mineral reaction textures the filla paragneiss contains pelitic assemblages less amenable to rigorous quantitative analysis nevertheless possibilities for the shared or otherwise metamorphic evolution of the mather and filla paragneisses may be postulated on the basis of calculated pseudosections in the context of existing geochronology for the rauer group and preserved microstructures a shared evolution most likely during pan african granulite facies metamorphism is plausible and consistent with mineral assemblage development geochronology and microstructures a revised interpretation of the rauer group s preserved metamorphic evolution may warrant the revision of existing tectonic models applicable also to the remainder of prydz bay more generally the employed approach may incite a revision of peak p t and p t paths in other granulite facies terranes

la icp ms u pb zircon ages of the qianlishan complex constrains on the evolution of the khondalite belt in the western block of the north china craton abstract the qianlishan complex is located in the westernmost part of the khondalite belt a continent continent collisional belt along which the yinshan block in the north and the ordos block in the south amalgamated to form the western block which then collided with the eastern block along the trans north china orogen to form the north china craton the complex is dominated by high grade supracrustal rocks and minor s type granites of which the supracrustals consist of graphite bearing sillimanite garnet gneiss garnet quartzite felsic paragneiss calc silicate rock and marble cl images reveal the existence of detrital and metamorphic zircons in major rocks of the qianlishan complex in most cases detrital zircons occur as either single grains with oscillatory zoning or oscillatory zoning cores typical of igneous origin which are surrounded by metamorphic overgrowth rims that are structureless high bright and low in th u ratio detrital zircons from the qianlishan complex yield nearly concordant 207 pb 206 pb ages ranging from 2 3 to 2 0 ga suggesting that the protoliths of the high grade supracrustal rocks in the qianlishan complex were deposited at some time after 2 0 ga metamorphic zircons yield two age populations with one at 1 95 ga and another at 1 92 ga of which the former is interpreted as the timing of the collision between the yinshan and ordos blocks to form the western block whereas the later is considered to be the age of subsequent post orogenic extensional event minor s type granites were emplaced at 1 88 ga as a result of partial melting of supracrustals at the stage of the exhumation of the qianlishan complex these new zircon ages combined with structural and metamorphic considerations enable resolution of the tectonothermal events involving the collision between the yinshan and ordos blocks to form the western block followed by the post collisional extension and subsequent exhumation of the khondalite belt

new data of 87sr 86sr ratio in classical marble an initial database for marble provenance determination abstract 87 sr 86 sr ratios are presented for white marbles collected from some of the most famous classical quarry areas of the mediterranean carrara paros naxos pentelikon dokimeion hymettus thasos and proconnesus these ratios range from 0 7071 to 0 7092 the ranges of the different quarry areas are notably superimposed this prevents a common adoption of this parameter in distinguishing the quarry locations for the classification of the provenance of marbles used during classical times for architectural and sculptural artefacts however some quarry areas show peculiar distributions of their isotopic values which could help to assign the provenance to an unknown marble artefact adding these new data to the scarce number of strontium isotopic compositions measured on white marbles and available in the relevant literature permits the creation of an initial database of 11 classical quarry locations this database confirms that the strontium isotope ratio could be used in marble provenance determination together with petrographic and geochemical methods as an ancillary technique

perturbation analysis of convective instability of oceanic lithosphere and initiation of subduction zones a linear perturbation analysis is made on convective instability of the oceanic lithosphere to understand the occurrence of subduction on the earth the oceanic lithosphere is modeled by the upper part of top thermal boundary layer in a convecting newtonian temperature dependent viscosity fluid thickening of oceanic lithosphere with its age due to cooling at the surface is modeled by thickening of the thermal boundary layer with time its thickening rate l is a measure of the rate with which temperature in the thermal boundary layer decreases with time and hence is a measure of the rate with which viscosity in the thermal boundary layer increases with time the linear perturbation analysis shows the possible excitation of plural eigenmodes to give rise to an instability in the thermal boundary layer depending on a threshold value rc of the local rayleigh number r of the thermal boundary layer further rc is shown to be a linearly increasing function of l which is treated as a free parameter from estimates of r and l appropriate for the major oceanic lithosphere denoted as robs and l obs respectively i find that rc l 0 robs rc l l obs the flow pattern of mantle convection depends strongly on which eigenmodes are excited by the convective instability in thermal boundary layer 1 when r is lower thanrc only the fundamental and the first higher modes at most are excited the resulting mantle convection manifests itself as the secondary convection 2 when r is higher than rc the modes higher than the first higher mode are also excited the resulting mantle convection involves lithospheric instability leading to large local deformation in the oceanic lithosphere and finally to subduction of the oceanic lithosphere this result implies that 1 subduction does not begin newly in the major oceanic lithosphere at present since lithospheric instability is suppressed by thickening of the major oceanic lithosphere neither by its high viscosity nor by its buoyancy 2 subduction will newly begin in the major oceanic lithosphere due to lithospheric instability in future when the oceanic lithosphere becomes so old that its thickening rate l decreases to sufficiently small value the latter result suggests that lithospheric instability is an important agent that maintains multiplate tectonics on the earth

menderes massif western turkey structural metamorphic and magmatic evolution a synthesis the menderes massif covers large areas in western turkey the better understanding of its tectono metamorphic history would provide insight for the alpine evolution of western turkey and the entire eastern mediterranean region this paper summarizes the available literature on the metamorphic rocks of western turkey and that of the menderes massif with special reference and emphasis to the papers presented in the special issue

effective bulk composition changes due to cooling a model predicting complexities in retrograde reaction textures diffusive processes are a strong function of temperature thus during cooling of rocks mineral grains may develop zoning profiles as successively larger parts of the grain close to the diffusive exchange with the rock one of the consequences of this process is that during cooling successively larger parts of zoned minerals depending on grain size are effectively removed from the reacting part of the rock volume thus the effective bulk composition of metamorphic rocks changes during cooling and the rate of its change will be a function of grain size because the sequence of metamorphic reactions seen by a given rock is a strong function of its bulk composition this process may have the consequence that two rocks of identical overall bulk composition but of different grain size may experience a different sequence of reactions qualitatively identical peak paragenesis may therefore react to form qualitatively different retrograde reaction textures the model is applied to examples in the pelitic system there garnet is usually the slowest diffusing phase developing zoning profiles during cooling and the effective removal of garnet from the reacting rock volume will cause changes of the effective bulk composition it is shown that during cooling of pelitic rocks from amphibolite facies conditions typical aluminous peak parageneses of garnet muscovite kyanite biotite may react to form either staurolite chlorite or muscovite or different combinations thereof depending on grain size during cooling from the granulite facies aluminous peak parageneses of garnet cordierite sillimanite may form biotite either on the expense of cordierite or garnet also depending on grain size the two examples are illustrated with a series of reaction textures reported for amphibolite and granulite terrains in the literature

th u pb monazite geochronology of the luliang and wutai complexes constraints on the tectonothermal evolution of the trans north china orogen abstract recent lithological metamorphic and geochronological studies show that the basement of the north china craton ncc formed by collision of two discrete archean to paleoproterozoic blocks eastern and western blocks along a paleoproterozoic orogen named the trans north china orogen however the timing of the collision is controversial and post collisional exhumation has not been precisely dated this study applies the electron microprobe th u pb monazite dating technique to determine the ages of the peak metamorphic event and subsequent exhumation of the low to medium grade luliang and wutai complexes in the trans north china orogen electron microprobe th u pb monazite data for the luliang complex reveal five tho 2 pbo age ranges 1 1940 1938 ma 2 1880 1847 ma 3 1795 1755 ma 4 1720 1703 ma and 5 1648 ma of these age ranges the first four have also been recorded in the wutai complex which yields tho 2 pbo ages of 1 1930 ma 2 1838 1822 ma 3 1793 ma and 4 1719 ma the oldest age range of 1940 1930 ma is interpreted to record the widespread emplacement of mafic dikes in rocks of the luliang and wutai complexes the age range of 1882 1822 ma is in accord with the shrimp u pb ages of metamorphic zircons and mineral sm nd and 40 ar 39 ar ages obtained for other complexes in the orogen and is interpreted as the age of the major metamorphic event caused by amalgamation between the eastern and the western blocks the age range of 1795 1755 ma is consistent with emplacement of large scale unmetamorphosed mafic swarms at 1800 1765 ma interpreted as the time of post orogenic extension the 1720 1703 ma and 1648 ma ages are considered to date later multiple stages of hydrothermal alteration since monazites with such young ages only occur along fractures in older monazite grains and at the rims these new monazite tho 2 pbo ages support the tectonic model for the evolution of the north china craton that envisages discrete eastern and western blocks colliding along the trans north china orogen at 1 85 ga and then undergoing post collisional extension in the period 1795 1755 ma

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

u pb and hf isotopic study of detrital zircons from the luliang khondalite north china craton and their tectonic implications two types of metasedimentary rocks occur in the trans north china orogen of the north china craton one type consists of highly metamorphosed supracrustal rocks with protoliths of mature cratonic shale called khondalites as found in the luliang complex rocks of the other type are also highly metamorphosed but less mature as represented by the wanzi supracrustal assemblage in the fuping complex u pb isotopic data for detrital zircons from khondalites show a provenance dominated by 1 9 2 1 ga palaeoproterozoic rocks these detrital zircons display a wide range of e hf values from 16 0 to 9 2 and give hf isotopic model ages mostly around 2 3 ga the high positive e hf values approach those for the depleted mantle at 2 1 ga highlighting a juvenile crustal growth event in palaeoproterozoic times hf isotopic data also imply that c 2 6 ga old crustal material was involved in the palaeoproterozoic magmatic event these data are similar to those for the khondalitic rocks from the interior of the western block of the north china craton suggesting a common provenance in contrast other metasedimentary rocks in the trans north china orogen such as the wanzi supracrustal assemblage in the fuping complex have a source region with both palaeoproterozoic and archaean rocks their detrital zircon hf isotopic data indicate reworking of old crustal material and a lack of significant juvenile palaeoproterozoic magmatic input these rocks are similar to the coevally deposited meta sedimentary rocks in the interior of the eastern block we propose that the luliang khondalites were deposited on the eastern margin of the western block in a passive continental margin environment and were thrust eastward later during collision with the eastern block other metasedimentary rocks in the trans north china orogen were deposited on the western margin of the eastern block in a continental arc environment our data support the eastward subduction model for the palaeoproterozoic tectonic evolution of the north china craton

shrimp u pb zircon geochronology of the liaoji granitoids constraints on the evolution of the paleoproterozoic jiao liao ji belt in the eastern block of the north china craton abstract the paleoproterozoic jiao liao ji belt lies at the eastern margin of the eastern block of the north china craton and is composed mainly of the liaohe group and the liaoji granitoids the liaoji granitoids are divisible into pre tectonic magnetite and hornblende biotite monzogranitic gneisses and post tectonic or anorogenic porphyritic monzogranites and alkaline syenites shrimp u pb zircon geochronology combined with cathodoluminescence cl imaging has enabled for resolution of magmatic and metamorphic events that can be directed towards understanding the history of the paleoproterozoic jiao liao ji belt shrimp u pb zircon analyses reveal that the pre tectonic magnetite monzogranitic gneisses were emplaced in the period 2176 2166 ma and metamorphosed at 1914 ma and the pre tectonic hornblende biotite monzogranitic gneisses were emplaced at 2150 2143 ma these data demonstrate that the pre tectonic monzogranitic gneisses of the liaoji granitoids were not younger than the deposition of the liaohe group as previously considered since the latter contains a large amount of 2100 2000 ma detrital zircons in contrast the pre tectonic monzogranitic gneisses of the liaoji granitoids or similar aged granitoids may have been an important component of the provenance for the liaohe group shrimp u pb zircon analyses also reveal that the post tectonic porphyritic monzogranites and granites in the jiao liao ji belt were emplaced at 1875 10 and 1856 31 ma respectively simultaneously with the emplacement of the alkaline syenites that was dated at 1857 20 and 1843 23 ma similar post tecotnic or anorogenic granites are not only limited to the jiao liao ji belt but are also found in the north and south korea suggesting that the 1 85 ga post tectonic or anorogenic granitic magmatic event may have occurred in both the korean peninsula and the eastern block of the north china craton the shrimp zircon ages of this study combined with lithological structural metamorphic and geochemical data is consistent with a rift closure model which suggests that the archean complexes on the northern and southern sides of the jiao liao ji belt were originally situated on a single continental block that underwent paleoproterozoic rifting associated with the formation of the liaohe group and liaoji granitoids and closed upon itself at 1 9 ga

metamorphic p t t paths retrieved from the amphibolites lushan terrane henan province and reappraisal of the paleoproterozoic tectonic evolution of the trans north china orogen abstract garnetiferous amphibolites preserving prograde inclusion assemblages m1 within garnet porphyroblasts metamorphic peak assemblages m2 and post peak symplectitic assemblages m3 have been found in the lushan terrane henan province taihua metamorphic complex southernmost section of the ns striking palaeoproterozoic trans north china orogen tnco geothermobarometric computation shows that the m1 m2 and m3 assemblages were formed under the p t conditions of 650 730 c 4 9 8 1 kbar 740 810 c 9 10 8 kbar and 750 760 c 5 0 7 7 kbar respectively suggesting that these amphibolites record clockwise p t paths including nearly isothermal decompression itd segments similar to the west alpine type p t paths indicative of being resulted from an orogenic process high resolution sims u pb dating of metamorphic zircons suggests that the metamorphism took place at ca 1 95 1 75 ga these data imply that the palaeoproterozoic collision between the eastern and western blocks of the north china craton along the southernmost terminal of the tnco not only started earlier but also continued longer than the middle and north sections of the tnco

improved methodology for identification of goktepe white marble and the understanding of its use a comparison with carrara marble abstract the provenance of marbles used for ancient statuary and architecture is of utmost importance for archaeologists art historians and archaeometrists the aim of this paper is to provide a comprehensive characterisation of the white marble exploited in antiquity in goktepe mugla province turkey to increase the reliability for identifying this marble in ancient artefacts a campaign of interdisciplinary archaeological and geological fieldwork undertaken by the marmora asiatica project is based on a multi method approach and on a representative set of samples used for the archaeometric analyses petrographic investigation showed that the goktepe marble is more variable with regard to fabrics and grain size than previously suggested whereas it is generally non luminescent and dolomite free stable c and o isotope and elemental analyses confirmed the results reported so far we also report for the first time for goktepe white marble the results of sr isotope measurements which in combination with elemental ratios e g sr mg and mn sr and 18o values greatly improve the discrimination among goktepe carrara and other fine grained white marbles applicability of these proxies was tested on artefacts from hadrian s villa for which carrara and goktepe provenance had been proposed the paper also reports new archaeological findings and results of estimates of stone extracted from the quarries which allowed for a recontextualization of the significance of quarries at goktepe high resolution topographic measurements performed for the first time with the use of a 3 d laser scanner combined with geological field study allowed for precise calculation of the volume of the white variety extracted in antiquity estimates of 17000 m3 is almost a half less than previously suggested moreover a careful study of the existing literature showed that in some instances assignment of white marble artefacts to the goktepe quarries may not be accurate verification of provenance for those problematic artefacts and a more reliable identification of goktepe marbles in the future can be achieved by application of the set of analyses proposed in this work which has a higher discrimination potential

paleoproterozoic structural evolution of the southern segment of the jiao liao ji belt north china craton abstract the paleoproterozoic jiao liao ji belt separates the eastern block of the north china craton into two small sub blocks the northern longgang and the southern rangrim blocks however it still remains unknown or controversial about the subduction polarity collisional deformation and kinematics between two sub blocks the southern segment of the belt consists of the paleoproterozoic fenzishan and jingshan groups and paleoproterozoic high pressure mafic granulites and serpentinites blocks which are located in the jiaodong complex all of which are separated from the jiaodong complex of neoarchean ttg gneisses by stz1 ductile shear zones structural analysis in this study indicates that most of the rocks in all the units of the southern segment of the jiao liao ji belt underwent three distinct episodes of folding d1 to d3 and two stage of ductile thrust shearing stz1 coeval to d1 and d2 stz2 between d2 and d3 the d1 deformation formed penetrative axial planar foliations s1 bedding parallel ductile shear zone mineral stretching lineations l1 and rarely preserved small isoclinal d1 folds in the jingshan and fenzishan groups in the jingshan group however penetrative deformational transposition resulted in stacking of sedimentary compositional layers which are separated by bedding parallel ductile shear zones stz1 at a period of about 1956 ma to 1914 ma the kinematic indicators of stz1 in the jingshan group with resultant prograde peak metamorphism up to granulite facies grade and the fenzishan group with peak metamorphism up to amphibolite facies grade indicate nw directed compression d2 resulted in crustal thickening with retrograded medium pressure granulite facies grade at about 1914 1893 ma the d2 deformation produced nw verging asymmetric and recumbent folds interpreted to have resulted from basement involved thicken skin structures the jiaodong complex was also involved into the development of wnw verging asymmetric tight folds associated with d2 in the jingshan and the fenzishan groups ongoing collision led to the development of transpressional ductile shearing stz2 forming the transpressional taipingzhuang dextral ductile shear zone between the jingshan group and the southern archean complex and the transpressional tading xiadian sinistral ductile shear zone between the jingshan group and the northern archean complex all three lithotectonic units were superposed during the late d3 deformation with amphibolite facies metamorphism the d3 deformation developed wnw trending open to tight upright folds at about 1893 1875 ma the structural pattern resulting from superimposition of d2 and d3 is a composite synform in the fenzishan and jingshan groups the structural events of d1 and stz1 and d2 and stz2 deformation were possibly responsible for fast syn collisional exhumation of the high pressure mafic granulites the structural patterns and deformational history of the fenzishan and jingshan groups suggest a southeastward directed oblique subduction beneath the northwestern margin of the rangrim block and that the final scissor shaped closure of the rift led to collision between the two blocks to form the coherent basement of the eastern block of the north china craton

high pressure granulites in the sanggan area north china craton metamorphic evolution p t paths and geotectonic significance high pressure basic granulites are widely distributed as enclaves and sheet like blocks in the huaian ttg gneiss terrane in the sanggan area of the central zone of the north china craton four stages of the metamorphic history have been recognised in mineral assemblages based on inclusion exsolution and reaction textures integrated with garnet zonation patterns as revealed by compositional maps and compositional profiles the p t conditions for each metamorphic stage were obtained using thermodynamically and experimentally calibrated geothermobarometers the low ca core of growth zoned garnet along with inclusion minerals defines a prograde assemblage m1 of garnet clinopyroxene plagioclase quartz yielding 700 c and 10 kbar the peak of metamorphism at about 750 870 c and 11 14 5 kbar m2 is defined by high ca domains in garnet interiors and inclusion minerals of clinopyroxene plagioclase and quartz kelyphites or coronas of orthopyroxene plagioclase magnetite around garnet porphyroblasts indicate garnet breakdown reactions m3 at conditions around 770 830 c and 8 5 10 5 kbar garnet exsolution lamellae in clinopyroxene and kelyphites of amphibole plagioclase around garnet formed during the cooling process at about 500 650 c and 5 5 8 kbar m4 these results help define a sequential p t path containing prograde near isothermal decompression itd and near isobaric cooling ibc stages the clockwise hybrid itd and ibc p t paths of the hp granulites in the sanggan area imply a model of thickening followed by extension in a collisional environment furthermore the relatively high pressures 6 14 5 kbar of the four metamorphic stages and the geometry of the p t paths suggest that the hp granulites together with their host huaian ttg gneisses represent the lower plate in a crust thickened during collision the corresponding upper plate might be the tectonically overlying khondalite series which was subjected to medium to low pressure mp lp 7 4 kbar granulite facies metamorphism with a clockwise p t path including an itd segment both the hp and the mp lp granulite facies events occurred contemporaneously at c 1 90 1 85 ga in a collisional environment created by the assembly process of the north china craton

thermobarometry in granulites pitfalls and new approaches abstract computer models of cooling granulite facies rocks with the assemblage garnet biotite sillimanite k feldspar plagioclase quartz are presented that incorporate simultaneous reaction net transfer and exchange and multicomponent diffusion in garnet in models where cooling is accompanied by exchange reactions plus diffusion only the calculated garnet core matrix biotite temperature is always lower than the metamorphic peak by an amount that depends on the cooling rate the size of the garnet and the volumetric ratio of garnet to biotite maximum calculated core temperatures of approximately 700 750 c are to be expected from typical granulite facies garnet biotite assemblages and calculated core temperatures can easily be as low as 600 c in models where both net transfer and exchange reactions are possible calculated garnet core matrix biotite temperatures are typically higher than the metamorphic peak temperatures by more than 150 c for large garnets r 2 mm but may be lower than the metamorphic peak for small garnets r the composition of matrix plagioclase in equilibrium with garnet is very sensitive to the amount of modal plagioclase that reacts and hence calculated p t trajectories are very sensitive to the petrologic interpretation of this recrystallization history for models in which all the modal plagioclase reacts the core and rim pressures may be faithfully recovered provided that the temperature estimate for the core is reliable for models in which only a small percentage of the modal plagioclase reacts very small modal amounts of plagioclase may be in equilibrium with garnet rim which if incorrectly interpreted may lead to grossly erroneous p t path interpretations a method to test an inferred p t path model is presented that involves attempting to match the observed garnet and plagioclase zoning information with a forward model that involves simultaneous reaction and diffusion an example from western new hampshire usa is presented that closely matches the measured profile

low limit of mn2 activated cathodoluminescence of calcite state of the art in the literature the lower limit for mn2 activated cathodoluminescence cl of calcite is variously reputed to over a very wide range of values above 10 ppm mn our spectroscopic investigations of the cl response in natural calcite reveal that below 10 ppm manganese content mn2 activation is also present using the quantitative high resolution spectral analysis of cl qhrs cl an activation by mn2 in the range of 700 ppb is proved which cannot be determined visually so if not quenched the minimum mn2 content for mn2 activation is one atom in the irradiated calcite crystal lattice volume as the intrinsic background blue luminescence is used to determine non altered biogenic calcite the limit of mn2 activation plays an important role in the interpretation of diagenetic processes our results of spectroscopic analyses require a revision of current opinions about the diagenesis of calcite as revealed by cl investigation

metamorphic records in the luliang metapelites of the jiehekou group implications for the tectonic evolution of the trans north china orogen north china craton abstract to further understand the metamorphic evolution of the trans north china orogen tnco a combined study of petrography pseudosection modeling and conventional thermobarometry was completed on garnet sillimanite bearing metapelitic rocks of the jiehekou group from the southern luliang metamorphic complex in the central segment of the tnco the luliang metapelitic rocks preserve peak assemblages of garnet biotite sillimanite plagioclase and quartz with or without k feldspar that reflect c 750 c and 7 0 kbar garnet has mostly homogeneous grain cores with sparse mineral inclusions enclosed successively by 1 rims of higher spessartine and lower pyrope content and 2 symplectitic intergrowths of cordierite biotite and plagioclase that present a spectacular white eye socket reaction microstructure quantitative phase equilibria modeling and traditional thermobarometric calculation results are consistent with this retrograde microstructure having developed during decompression to t 650 c and p

tectonic history of subduction zones inferred from retrograde blueschist p t paths many phanerozoic convergent plate junctions are marked by discontinuous blueschist belts reflecting relatively high pressure p prograde trajectories common blueschist paragneisses such as those of the western alps exhibit widespread overprinting by greenschist and or epidote amphibolite facies assemblages for this type of high p belt retrograde metamorphism involved fairly rapid nearly isothermal decompression some terranes underwent continued heating during early stages of pressure release uplift probably occurred as a consequence of the entrance of an island arc oceanic plateau or segment of continental crust into the subduction zone collision resulting in marked deceleration or cessation of underflow and buoyant approximately adiabatic rise of the stranded recrystallized subduction complex other high p belts such as the franciscan of western california preserve metamorphic aragonite and lack a low p overprint retrogression approximately retraced the prograde p t temperature path or for early formed high grade blocks occurred at even higher p t ratios parts of this type of metamorphic belt evidently migrated slowly back up the subduction zone in response to isostatic forces during continued plate descent and refrigeration upward motion took place as tectonically imbricated slices as laminar return flow in melange zones and perhaps partly a lateral spreading extension of the underplated accretionary prism retrograde p t trajectories of high pmore belts therefore provide important constraints on the tectonic evolution of convergent plate junctions less

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

timing of metamorphism in the paleoproterozoic jiao liao ji belt new shrimp u pb zircon dating of granulites gneisses and marbles of the jiaobei massif in the north china craton abstract the paleoproterozoic jiao liao ji belt lies in the eastern block of the north china craton with its southern segment extending across the bohai sea into the jiaobei massif high pressure pelitic and mafic granulites have been recently recognized in the paleoproterozoic jingshan group jiaobei massif new shrimp u th pb geochronology combined with cathodoluminescence cl imaging of zircon has been applied to the determination of the timing of the metamorphism of the high temperature and high pressure granulites and associated gneisses and marbles metamorphic zircons in these high pressure granulites gneisses and marbles occur as either single grains or overgrowth or recrystallization rims surrounding and truncating oscillatory zoned magmatic zircon cores metamorphic zircons are all characterized by nebulous zoning or being structureless with high luminescence and relatively low th u values metamorphic zircons from two high pressure mafic granulites yielded 207pb 206pb ages of 1956 41 ma and 1884 24 ma one metamorphic zircon from a garnet sillimanite gneiss also gave an apparent 207pb 206pb age of 1939 15 ma these results are consistent with interval of ages of c 1 93 1 90 ga already obtained by previous studies for the north and south liaohe groups and the laoling group in the northern segment of the jiao liao ji belt metamorphic zircons from a high pressure pelitic granulite and two pelitic gneisses yielded weighted mean 207pb 206pb ages of 1837 8 ma 1821 8 ma and 1836 8 ma respectively two diopside olivine phlogopite marbles yielded weighted mean 207pb 206pb ages of 1817 9 ma and 1790 6 ma these paleoproterozoic metamorphic ages are largely in accordance with metamorphic ages of c 1 85 ga produced from the ji an group in the northern segment of the jiao liao ji belt and c 1 86 1 80 ga obtained for the high pressure pelitic granulites from the jingshan group in the southern segment as this metamorphic event was coeval with the emplacement of a type granites in the jiao liao ji belt and its adjacent areas it is interpreted as having resulted from a post orogenic or anorogenic extensional event

metamorphism and geochronology of the luoning metamorphic terrane southern terminal of the palaeoproterozoic trans north china orogen north china craton abstract garnet bearing amphibolites and metapelites of the luoning metamorphic terrane taihua metamorphic complex southern terminal of the palaeoproterozoic trans north china orogen tnco preserve different metamorphic mineral assemblages formed at three metamorphic stages in the palaeoproterozoic the prograde mineral assemblages m1 comprise of hornblende plagioclase quartz biotite inclusions preserved in the garnet porphyroblasts in the amphibolites or quartz biotite plagioclase inclusions preserved in the garnet porphyroblasts in the metapelites the metamorphic peak mineral assemblages m2 are represented by the garnet porphyroblasts as well as the matrix minerals plagioclase hornblende biotite quartz in the amphibolites or quartz biotite plagioclase hornblende in the metapelites respectively the retrograde mineral assemblages m3 are the worm like fine grained white eye socket symplectitic assemblages formed between the relict garnet porphyroblasts and the matrix minerals consisting of plagioclase hornblende biotite intergrowths in the amphibolites or plagioclase biotite quartz intergrowths in the metapelites respectively geothermobarometric computation shows that the luoning terrane records clockwise p t trajectories including near isothermal decompression itd processes from 630 790 c 5 3 8 9 kbar through 720 820 c 8 9 10 7 kbar to 690 740 c 7 1 7 7 kbar sims u pb dating of zircons separated from the amphibolites and metapelites presents that the age of the protolith of the amphibolites is 2 32 ga and the metamorphism occurred during 1 97 1 94 ga suggesting that the subduction collision and the subsequent exhumation occurred in the late palaeoproterozoic combined with the literature data of the different discrete terranes within the trans north china orogen it is further deciphered that the tectono metamorphic event of the trans north china orogen started as early as 1 97 ga and lasted as late as 1 80 ga suggesting that the tectono metamorphic event of the orogen is a long and complex history

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

combined u pb hafnium and oxygen isotope analysis of zircons from meta igneous rocks in the southern north china craton reveal multiple events in the late mesoarchean early neoarchean abstract we report the results of a comprehensive isotopic investigation of zircons from metamorphosed tonalites and amphibolites from lushan in the far south of the trans north china orogen of the north china craton that reveal the oldest rocks yet dated from the orogen a detailed investigation of the internal structures of zircons combined with targeted sims u pb and oxygen isotope analyses and icp ms hf zircon analyses has resulted in the discovery of previously unknown geological events in the north china craton magmatic zircon from the tonalite and amphibolite was found to be essentially coeval with a small spread of ages from 2829 18 ma to 2832 11 ma in the tonalites and from 2838 35 ma to 2845 23 ma in amphibolite hafnium isotope data suggest derivation of both tonalite and amphibolite from a depleted mantle source with minor crustal contamination oxygen isotope ratios in zircons range from 5 1 to 7 3 vsmow with high 18 o results recorded only from metamorphic domains the earliest stage of metamorphic zircon growth present in all four samples analyzed in this study occurred between 2772 17 22 in the tonalites and 2776 20 and 2792 12 ma in the amphibolites a younger metamorphic event at 2638 61 in the tonalite and between 2671 13 and 2651 13 ma in the amphibolites is recognized in zircons from three of the four samples investigated this is the first time that metamorphic events at either of these times have been recorded in the north china craton importantly there is no evidence for the 1 8 ga high grade metamorphic event that is manifest in the northern and central parts of the trans north china orogen

u pb and hf isotopic study of zircons of the helanshan complex constrains on the evolution of the khondalite belt in the western block of the north china craton abstract the helanshan complex is located at the westernmost segment of the khondalite belt a continent continent collisional belt along which the yinshan block in the north collided with the ordos block in the south to form the western block of the north china craton the complex consists of s type granites and high grade pelitic granulite gneiss felsic paragneiss quartzite calc silicate rock and marble together called the khondalite series rocks la q icp ms u pb geochronology and la mc icp ms lu hf isotopic data of zircons combined with cathodoluminescence cl imaging enable the resolution of magmatic and metamorphic events that can be directed towards understanding the formation and evolution of the khondalite belt in the western block of the north china craton cl images reveal the coexistence of magmatic type detrital zircons and metamorphic zircons in most of the khondalite series rocks of which the metamorphic zircons occur as either single grains or overgrowth rims surrounding and truncating magmatic type detrital zircon cores la q icp ms u pb analyses on magmatic type detrital zircons reveal two distinct age populations with one in the archaean 2 85 2 53 ga and the other in the palaeoproterozoic 2 2 2 0 ga suggesting that the sedimentary protoliths of the khondalite series rocks in the helanshan complex must have been deposited at some time after 2 0 ga the hf analyses show that the archaean detrital zircons possess negative ehf t values from 7 64 to 0 15 with depleted mantle model ages ranging from 3 34 to 3 10 ga this implies the existence of a paleo mesoarchaean 3 34 3 10 ga crust in the western block which underwent a recycling event in the period 2 85 2 53 ga nearly all palaeoproterozoic 2 2 2 0 ga detrital zircons possess positive ehf t values 0 86 9 38 with depleted mantle model ages of 2 45 2 15 ga suggesting a significant crustal growth event in the western block in the palaeoproterozoic metamorphic zircons yield two groups of age with one at 1 95 ga and the other at 1 87 ga of which the former is considered as the timing of the collision between the yinshan and ordos blocks to form the western block whereas the latter is consistent with the age of 1 86 ga from two s type granites which are considered to have formed by the partial melting of pelitic granulites gneisses at the stage of the exhumation of the helanshan complex

metallogeny of the north china craton link with secular changes in the evolving earth abstract the north china craton ncc has experienced a complex geological evolution since the early precambrian and carries important records of secular changes in tectonics and metallogeny here we synthesize the salient geological and tectonic features of the evolution and destruction of the ncc vis a vis major metallogenic events and the formation of potential ore deposits we identify a close relationship between the major geological events in the ncc and those reported elsewhere on the globe we trace the records of a regular change in the pattern of metallogeny mineral deposit character spatial distribution and genetic mechanisms which closely match the timing and styles of the major geological and tectonic events in this craton the ncc went through five major tectonic cycles 1 neoarchean crustal growth and stabilization 2 paleoproterozoic rifting subduction accretion collision with imprints of the great oxidation event goe 3 late paleoproterozoic neoproterozoic multi stage rifting 4 paleozoic orogenesis at the margins of the craton and 5 mesozoic extensional tectonics associated with lithospheric thinning and decratonization coinciding with these major geological events are five major metallogenic systems identified as follows 1 an archean bif system 2 paleoproterozoic cu pb zn and mg b systems 3 a mesoproterozoic ree fe pb zn system 4 a paleozoic orogenic cu mo system and 5 mesozoic intracontinental au and ag pb zn and mo systems the ore deposit types in each of these metallogenic systems show distinct characteristics and tectonic affinities from early precambrian through late precambrian to paleozoic and mesozoic the ncc records a transition from primitive to modern style plate tectonics evidence for imbricated oceanic plate stratigraphy in a subduction accretion setting and collisional orogenesis along at least three major zones of ocean closure are documented major transitions in tectonic style and surface environmental changes recorded in other parts of the world are also reflected in the geological history and metallogenic events in the ncc large scale gold deposits formed through intraplate tectonics during the mesozoic provide important insights into mantle dynamics and crust mantle interaction associated with lithospheric thinning and craton destruction the ncc provides one of the best examples for documenting secular changes in the geological history and metallogenic epochs of an evolving earth

metamorphic p t paths of the zanhuang amphibolites and metapelites constraints on the tectonic evolution of the paleoproterozoic trans north china orogen garnet bearing metapelites and amphibolites are exposed in the south and middle parts of the zanhuang complex which is located in the central segment of the nearly ns striking trans north china orogen these rocks preserve three metamorphic mineral assemblages forming at the prograde peak and post peak decompression stages the prograde metamorphic stage m1 is represented by mineral inclusions within garnet porphyroblasts the peak metamorphic stage m2 is represented by garnet rims and matrix minerals whereas the retrograde stage m3 is represented by amphibole plagioclase symplectite rimming garnet porphyroblasts in the amphibolites and biotite plagioclase symplectite rimming garnet porphyroblasts in the metapelites all garnet porphyroblasts in the metapelites preserve prograde chemical zoning except for the ubiquitous quite narrow zones from the underwent post peak decompression it has been determined through thermobarometric computation that the metamorphic conditions are 650 710 c at 8 2 9 2 kbar for the m1 inclusion assemblages 810 c at 12 5 kbar for the metamorphic peak m2 matrix assemblages and 660 680 c at 4 4 4 5 kbar for the retrograde m3 symplectite assemblages these rocks are thus determined to have undergone metamorphism with clockwise p t paths involving nearly isothermal decompression itd segments which is inferred to be related to the amalgamation of the eastern and western blocks to form the coherent basement of the north china craton along the trans north china orogen in the late paleoproterozoic 1 88 1 85 ga

the petrology of two distinct granulite types in the hengshan mts china and tectonic implications abstract the archean to proterozoic hengshan complex north china craton comprises tonalitic and granodioritic gneisses with subordinate mafic lenses pegmatites and granites amphibolite facies assemblages predominate although granulite facies relics are widespread and greenschist facies retrogression occurs in km wide shear zones mafic lenses locally abundant occur as strongly deformed amphibolite hornblende plagioclase boudins or sheets in contrast to previously published models we find two series of mafic rocks with distinctly different granulite facies evolutions in the north of the complex relict high pressure mafic granulites are garnet clinopyroxene bearing rocks with a secondary development of orthopyroxene around both garnet kelyphites and clinopyroxene coronas south of the newly defined central e w trending zhujiafang shear zone numerous mafic boudins and less deformed dykes exhibit a macroscopically visible magmatic texture with coronitic growth of metamorphic garnet full of quartz inclusions between the magmatic plagioclase and pyroxene domains additional orthopyroxene after magmatic augite and sodic rims to magmatic plagioclase clearly indicate medium pressure granulite facies metamorphism these findings suggest tectonic juxtaposition in this area of three different structural levels of the same proterozoic imprinted crust high pressure granulite grade in the northern hengshan medium pressure granulite grade in the southern hengshan and amphibolite to greenschist facies grade in the wutaishan to the se

high pressure granulites formation recovery of peak conditions and implications for tectonics high pressure granulites are characterised by the key associations garnet clinopyroxene plagioclase quartz in basic rocks and kyanite k feldspar metapelites and felsic rocks and are typically orthopyroxene free in both basic and felsic bulk compositions in regional metamorphic areas two essential varieties exist a high to ultrahigh temperature group and a group representing overprinted eclogites the high to ultrahigh temperature type formerly contained high temperature ternary feldspar now mesoperthite coexisting with kyanite is associated with garnet peridotites and formed at conditions above 900 c and 1 5 gpa clinopyroxene in subordinate basic rocks is al rich and textural evidence points to a high pressure high temperature melting history the second variety contains symplectite like or poikilitic clinopyroxene plagioclase intergrowths indicating former plagioclase free i e eclogite facies assemblages this type of rock formed at conditions straddling the high pressure amphibolite high pressure granulite field at around 700 850 c 1 0 1 4 gpa importantly in the majority of high pressure granulites orthopyroxene is secondary and is a product of reactions at pressures lower than the peak recorded pressure in contrast to low and medium pressure granulites which form at conditions attainable in the mid to lower levels of normal continental crust high pressure granulites of nonxenolith origin mostly represent rocks formed as a result of short lived tectonic events that led to crustal thickening or subduction of the crust into the mantle short times at high temperature conditions are reflected in the preservation of prograde zoning in garnet and pyroxene high pressure granulites of both regional types although rare are known from both old and young metamorphic terranes e g c 45 ma namche barwa e himalaya 400 340 ma european variscides 1 8 ga hengshan china 1 9 ga snowbird saskatchewan and 2 5 ga jianping china this spread of ages supports proposals suggesting that thermal and tectonic processes in the lithosphere have not changed significantly since at least the end of the archean

palaeoproterozoic metamorphic evolution and geochronology of the wugang block southeastern terminal of the trans north china orogen abstract amphibolites of the wugang block in the taihua metamorphic complex which is located in the southeastern terminal of the palaeoproterozoic trans north china orogen tnco preserve three generations of metamorphic mineral assemblages i e the prograde m 1 peak m 2 and retrograde m 3 assemblages forming during the palaeoproterozoic tectono metamorphic event these amphibolites record metamorphic p t conditions of 4 8 6 7 kbar 720 750 c m 1 9 0 10 6 kbar 710 780 c m 2 and 7 1 8 5 kbar 700 780 c m 3 which define clockwise p t paths involving isothermal decompression itd the metamorphic peak reached upper amphibolite facies and high resolution in situ sims u pb dating of metamorphic zircons suggests that the peak metamorphism took place at 1 96 1 92 ga in the wugang block the present new data suggest that the wugang block was also involved in the continental collision between the eastern and western blocks of the north china craton ncc in the palaeoproterozoic combining metamorphic and geochronological data concerning the tnco obtained by previous scholars it may be anticipated that the middle and southern sections of the tnco were involved in a long lived continental collision and the collision event can be possibly traced back to as early as 1 96 ga and lasted to as late as 1 80 ga

an exposed hercynian deep crustal section in the sila massif of northern calabria mineral chemistry petrology and a p t path of granulite facies metapelitic migmatites and metabasites in the sila massif of northern calabria a continous section is exposed through a segment of a hercynian deep continental crust which has been interpreted by previous workers as a stack of basement nappes monte gariglione complex the section consists essentially of metapelitic migmatites and subordinate metabasites and marbles which were metamorphosed at medium pressure high temperature granulite facies conditions a continuous metamorphic gradient through the exposed segment can be deduced from the systematic change in the compositions of ferromagnesian minerals in divariant metapelitic assemblages this gradient is partly supported by conventional geothermobarometry and by applying the tweequ method however peak metamorphic conditions are better defined by dehydration melting reactions which reveal similar to4 kbar and 740 degreesc at the top and similar to6 kbar and 770 degreesc at the base of the section therefore the exposed rocks represent a former crustal depth range of similar to 14 21 km at the thermal peak of metamorphism the metamorphic evolution of the former deep crustal rocks has been reconstructed from reaction textures the prograde p t path took place in the stability field of sillimanite the retrograde path is characterized by a stage of isothermal uplift after peak metamorphism to mid crustal levels 10 15 km followed by near isobaric cooling to greenschist facies conditions the deep crustal section in northern calabria resembles that of the serre massif in southern calabria which represents the lowermost part of an exposed tilted cross section through the hercynian continental crust postkinematic mineral growth reaction textures and isotopic age constraints indicate that the thermal conditions in the calabrian crust during the hercynian orogeny were mainly controlled by advective heat input through magmatic intrusions as in southern calabria large granitic bodies were emplaced between the granulite facies lower crust monte gariglione complex and the amphibolite to greenschist facies upper crust during regional metamorphism

p t t evolution of orogenic belts and the causes of regional metamorphism barrow 1893 introduced three important ideas that furthered understanding of metamorphic processes i the use of critical index minerals in argillaceous rocks to define metamorphic zones and elucidate spatial features of regional metamorphism ii the concept of progressive metamorphism and iii the concept of magmatic advection of heat as a possible cause of regional metamorphism this article expands upon these themes by reviewing our understanding of the dynamic evolution of orogenic belts as interpreted from the p t t paths of metamorphic rocks and by considering the likely causes of the different kinds of regional metamorphism that we observe within orogenic belts understanding metamorphic rocks allows the distinction of two fundamentally different types of orogenic belt defined by relative timing of maximum t and maximum p orogenic belts characterized by clockwise p t paths achieved maximum p before maximum t the metamorphic peak normally post dated early deformation within the belt and additional heating above the normal conductive flux has been related to the amount of overthickening by contrast orogenic belts characterized by counterclockwise p t paths achieved maximum t before maximum p the metamorphic peak normally pre dated or was synchronous with early deformation within the belt and additional heating above the normal conductive flux has been related to the emplacement of plutons techniques used to constrain portions of p t t paths include the use of mineral inclusion suites in porphyroblasts and reaction textures thermobarometry the use of fluid inclusions thermodynamic approaches such as the gibbs method radiogenic isotope dating fission track studies and numerical modelling we can utilize specific mineral parageneses in suitable rocks to determine individual p t t paths and a set of p t t paths from one orogenic belt allows us to interpret the spatial variation in dynamic evolution of the metamorphism recent advances are reviewed with reference to collision metamorphism high temperature low pressure metamorphism granulite metamorphism and subduction zone metamorphism and some important directions for future work are indicated

u pb and hf isotopic study of detrital zircons from the yejishan group of the luliang complex constraints on the timing of collision between the eastern and western blocks north china craton abstract the trans north china orogen is a recently recognized continent continent collisional belt along which the discrete eastern and western blocks amalgamated to form the coherent basement of the north china craton however there is a hot debate on the timing of the collision between the two blocks with one school of thought arguing the collision occurred at 2 5 ga whereas others believe it took place at 1 85 ga u pb ages and hf isotopic data of detrital zircons from foreland basins in the trans north china orogen can provide rigorous constraints on this controversial issue one of such foreland basins is represented by the yejishan group in the luliang complex in the middle sector of the western margin of the trans north china orogen the group consists of conglomerates quartz wackes sandstones and minor limestones most of which contain large amounts of detrital zircons cl images reveal that nearly all detrital zircons from the yejishan group possess oscillatory zoning with th u ratios of 0 2 2 34 typical of an igneous origin the 207 pb 206 pb ages of detrital zircons range between 3 24 and 1 81 ga with most having paleoproterozoic ages of which the youngest group ages are around 1 87 1 81 ga this indicates that the foreland basin in which the yejishan group was deposited must have formed not earlier than 1 87 1 81 ga thus supporting the collision between the eastern and western blocks at 1 85 ga not at 2 5 ga