origin of convex tetrads in rare earth element patterns of hydrothermally altered siliceous igneous rocks from the zinnwald sn w deposit germany the chondrite normalized rare earth element ree patterns of whole rock samples from evolved granitic systems hosting rare metal deposits sometimes show a split into four consecutive curved segments referred to as tetrads in the present contribution a rigorous statistical method is proposed that can be used to test whether geological significance should be attributed to tetrads that are only of limited size the method involves a detailed evaluation of element and sample specific random and systematic errors that are constrained on the basis of independent repeated preparations and analyses of sample and reference materials application of the proposed method to samples from the granite hosted zinnwald sn w deposit germany revealed that at least two tetrads in normalized whole rock ree patterns have to be analytically significant to rule out that fractional crystallization led to the unusual behavior of the rees based on the analysis of altered albite granite and greisen samples from the endocontact of the zinnwald granite massif it is demonstrated that the lanthanide tetrad effect is responsible for the formation of the convex tetrads geological and petrological evidence suggests that the tetrads in the samples developed prior to greisenization and related cassiterite precipitation in contrast to the endocontact samples the rhyolitic wall rocks are typified by normalized ree patterns having tetrads that are variable in size and frequently close to the limit of analytical significance the sizes of the tetrads apparently correlate with the intensity of albitization but show no relation to subsequent alteration processes including greisenization and low temperature argillization this observation proves that curved segments in normalized whole rock ree patterns can be introduced during hydrothermal fluid rock interaction

geochronologic and geochemical evidence for persistence of south dipping subduction to late permian time langshan area inner mongolia china significance for termination of accretionary orogenesis in the southern altaids the langshan area in inner mongolia is situated in the southern altaids between the beishan suture to the west and the solonker suture to the east this paper addresses the poorly known tectonic evolution that led to formation of the terminal solonker suture dating of deformed porphyries and undeformed dolerites and gabbros constrains the timing of the relevant ne e striking and north vergent deformation deformed granitic granodioritic porphyries in this area are characterized by high sio2 65 38 78 00 low tfe2o3 1 29 5 07 mgo 0 13 0 63 and variable k2o 0 53 4 14 and na2o 2 05 4 62 all samples have enriched lree la yb 6 18 and negative nb anomalies nbn thn0 09 0 48 but different eu anomalies eu

palaeomagnetic constraints on the collision and rotation of north and south china the eastern half of china is dominated by the north china block ncb and south china block scb separated by a complex fold system that trends roughly east west interpretation of the geology of this fold belt has led to a variety of estimates of the age of amalgamation of these two blocks1 7 palaeomagnetic results are few and have also been subject to conflicting interpretations8 11 here we present our own palaeomagnetic results for late permian rocks for both the scb and ncb and summarize other relevant palaeomagnetic data by reinterpreting the polarity given in some previous studies we are able to synthesize the results for the widespread emeishan basalts of the scb and to suggest a new model for the collision and relative rotation of the two blocks

tectonomagmatic characteristics of the back arc portion of the calama olacapato el toro fault zone central andes 1 post 20 ma magmatism in the central andes is either localized in the magmatic arc or distributed east of it on the altiplano puna plateau here there is a distinct concentration of magmatic centers on nw se trending lineaments such as the calama olacapato el toro cot that extends into the eastern cordillera to the east of the puna understanding the possible genetic relationship between prominent structures and magmatic centers on these lineaments is important to elucidate the tectonomagmatic evolution of the central andes we investigated the back arc area of the cot using remote sensing geological structural and petrochemical data our study demonstrates that this portion of the cot consists of nw se striking faults formed under overall left lateral transtension that decreases in activity toward the cot termini deformation on the cot occurred during and after activity of prominent n s striking transpressive fault systems and is coeval with magmatism which is focused on the central cot the most evolved magmatic rocks with an upper crustal imprint are exposed on the central cot whereas more primitive mantle derived mafic to moderately evolved magmatic rocks are found toward the cot termini this points to a genetic relationship between upper crustal deformation and magmatic activity that led to enhanced magma storage in the central cot cot magmas may result either from slab steepening or episodic delamination of the asthenospheric mantle

detrital record of mountain building provenance of jurassic foreland basin to the dabie mountains 1 the huangshi foreland basin developed on the southern margin of the dabie mountains as a result of tectonic loading during triassic collisional suturing between the north china and south china cratons modal and detrital zircon data for jurassic samples within the basin suggest a multicomponent source with input from both the south china craton and dabie orogen samples are predominantly quartz arenites derived on the basis of framework compositions from a recycled orogen source detrital zircons range in age from archean to triassic with a dominant component in the late paleoproterozoic between 1 9 1 7 ga and subsidiary components at 2 6 2 2 ga 0 8 0 7 ga 0 5 0 4 ga and 0 33 0 2 ga age data integrated with cathodoluminescence and trace element data for the zircons indicate that the archean and proterozoic detritus was derived from igneous and metamorphic sources that overlap with time equivalent pulses of such activity within the south china craton phanerozoic zircon ages overlap the times of the ordovician carboniferous and triassic high pressure metamorphism in the dabie mountains the provenance record integrated with paleocurrent and regional relations enables a paleogeographic reconstruction in which the huangshi basin was fed by a major axial flowing trunk river system carrying detritus from eastern and southern sources within the south china craton and was also fed by short south flowing tributaries supplying some detritus from the evolving dabie orogen the dominance of cratonic derived detritus within the provenance record of the huangshi basin contrasts with that of the hefei foreland basin that lies to the north of the dabie mountains which is dominated by neoproterozoic mesozoic detritus derived directly from the dabie mountains and lacks any significant older paleoproterozoic or archean components easterly extensions of the dabie sulu collisional suture and of the resultant huangshi basin occur in korea and japan over an along strike length of some 2000 km

mesozoic basin development and tectonic evolution of the dabieshan orogenic belt central china 1 the dabieshan orogenic belt is a zone of long lived shortening with late stage extension that formed during mesozoic time in central china regional basin analysis coupled with structural cross sections provides a means of reconstructing the paleogeography of the region from triassic continental collision through early tertiary extension the overall distribution of different basin types in the orogenic belt indicates that there was a prolonged period of shortening throughout the mesozoic that became less intense over time meanwhile extension became more common from jurassic into tertiary time either compression or extension was isochronous but limited to different geographic regions and or crustal levels or alternated repeatedly orogen wide through time nonetheless the orogen underwent gradual transition from overall shortening and crustal thickening to dominantly extension and rift basin formation although these events overlapped in time from the jurassic through early cretaceous penecontemporaneous compression and extension across the orogen may reflect long term 100 m y shortening and crustal thickening leading to gravitational spreading of the resultant thick crustal welt we suspect that this prolonged history of shortening across two nearby 100 km apart suture zones played some role in the exhumation of ultrahigh pressure rocks from beneath the dabieshan

are discontinuous chondrite normalized ree patterns in pegmatitic granite systems the results of monazite fractionation abstract all 14 stable rare earth elements rees in biotite muscovite granite and tourmaline rich granite of the harney peak granite black hills south dakota usa have been analyzed using inductively coupled plasma mass spectrometry chrondrite normalized ree patterns of the tourmaline rich granites are discontinuous between nd and sm the discontinuity was modeled successfully by the fractional crystallization of monazite from a biotite muscovite granite initial composition this explanation may also apply to the development of such discontinuous patterns in other highly evolved rocks

unusual rare earth element fractionation in a tin bearing magmatic hydrothermal system normalized rare earth element patterns of rock and mineral samples from evolved granitic systems and associated hydrothermal tin deposits frequently show an unusual split into four consecutive curved segments referred to as tetrads in the present contribution the simultaneous occurrence of complementary convex and concave tetrads is described for the first time for vein fluorite suggesting that this unusual trace element signature may develop during a single evolutionary stage within the hydrothermal environment based on geochemical analysis of vein fluorite fluid inclusion studies and thermodynamic modeling it is shown that fractionation of the rare earth elements can be linked to fluid immiscibility and preferential partitioning of these elements between vapor and coexisting liquid the findings provide the first direct evidence constraining the geological conditions responsible for the occurrence of the tetrad effect in tin bearing magmatic hydrothermal systems and require a reassessment of the current understanding of the origin of tin deposits

tetrad effect in rare earth element distribution patterns a method of quantification with application to rock and mineral samples from granite related rare metal deposits abstract in some geological environments the tetrad effect can be observed as a split of rare earth element ree patterns into four rounded segments a new method is proposed to quantify the sizes of the individual segments and for the first time the significance of observed tetrad effects is evaluated by taking analytical errors into account the outlined method was applied to lanthanide patterns of whole rock and fluorite samples collected from granite related rare metal deposits the ree patterns of the granite and greisen samples investigated exhibit significant tetrad effects that may not be accounted for by analytical uncertainties it is shown that the study of whole rock samples is insufficient to determine whether this effect is developed during fractional crystallization or is due to other processes such as fluid rock interaction a concave tetrad effect mirroring the pattern of the whole rock samples was not observed in the ree patterns of related vein fluorite samples therefore it is unlikely that the convex tetrad effect in the samples from the magmatic environment can be explained by removal of a respective complementary ree pattern by a coexisting hydrothermal fluid as previously suggested it is proposed that the tetrad effect formed within the magma fluid system before emplacement in the subvolcanic environment where phase separation caused a split of this system into fluid and magma subsystems alternatively the tetrad effect may also be inherited from an external fluid influencing the system during or after the emplacement of the magma on the basis of the fluorite data it is shown that the behavior of eu in the fluids is not related to the tetrad effect consequently different physico chemical factors control the occurrence of both phenomena y was found to be strongly enriched in samples precipitating from hydrothermal fluids that experienced prolonged interaction with the wall rocks whereas the tetrad effect in the fluids vanished with time and increasing distance from the ore bearing granite thus these different geochemical parameters can be used to reconstruct different aspects of the fluid evolution within this type of deposit

geology and genesis of the toongi rare metal zr hf nb ta y and ree deposit nsw australia and implications for rare metal mineralization in peralkaline igneous rocks the toongi deposit located in central nsw australia hosts significant resources of zr hf nb ta y and ree within a small ca 0 3 km2 rapidly cooled trachyte laccolith toongi is part of regional late triassic to jurassic alkaline magmatic field but is distinguished from the other igneous bodies by its peralkaline composition and economically significant rare metal content that is homogenously distributed throughout the trachyte body the primary ore minerals are evenly dispersed throughout the rock and include lueshite natroniobite and complex na fe zr nb y ree silicate minerals dominated by a eudialyte group mineral egm the egm occurs in a unique textural setting in the rock commonly forming spheroidal or irregular shaped globules herein called snowballs within the rock matrix the snowballs are often protruded by aegirine and feldspar phenocrysts and contain swarms of fine aegirine and feldspar grains that often form spiral or swirling patterns within the snowball secondary ore minerals include ree carbonates y milarite catapleiite and gaidonnayite that fill fractures and vesicles in the rock based on bulk rock geochemical and nd isotope data and thermodynamic modelling of magma fractionation the alkaline rocks of the region are interpreted to represent extrusive to hyperbyssal products of mantle derived magma that ponded at mid crustal levels ca 0 3 gpa and underwent extensive fractionation under low oxygen fugacity conditions the high na2o peralkaline nature of the toongi deposit trachyte developed via extensive fractionation of an alkali olivine basalt parental magma initially in the mid crust and subsequently at shallow levels ca 0 1 gpa this extended fractionation under low fo2 and relatively low h2o activity conditions limited volatile release and allowed build up of rare metal contents to ore grades we speculate that the ore minerals may have originally formed from rare metal rich sodic silicate melt that formed immiscible globules subsequently crystallized to egm in the magma shortly before emplacement and rapid cooling subsequent hydrothermal alteration caused relatively limited and localized remobilization of some ore metals into fractures and vesicles in the rock

geometry amount and sequence of thrusting in the subalpine molasse of western austria and southern germany european alps in this paper we review the structure of the most external thrust belt of the alps between the rhein valley and salzburg based on a new tectonic map and the re interpretation of seismic sections specifically we address the correlation between deformation in the subalpine molasse and the alpine thrust belt in general and focus on the control of sedimentary facies on the structural style a dramatic change in architecture from a ramp flat structure to buckle folding is related to a change from coarse grained fans to fine grained deposits within the subalpine molasse additionally the interaction of escape tectonics with postcollisional shortening controls the decrease of late early miocene and younger shortening within the subalpine molasse from 50 km near the rhine valley to almost zero near salzburg transfer of shortening into the hinterland which is the zone of lateral escape ended foreland propagation of the alpine thrusts and initiated a general break back sequence of thrusting throughout this time the thrusts remained active in such a scenario tectonic units on top of the subalpine molasse are expected to undergo clockwise rotation around vertical axes as thrusting in the subalpine molasse is closely related to contemporaneous transport and shortening within the tectonically higher helvetic thrust sheets amounts of miocene differential shortening and related clockwise vertical axis rotation are minimum amounts true clockwise vertical axis rotation is probably larger than the 12 deduced from the subalpine molasse thrust belt

time of formation and peak of variscan hp ht metamorphism of quartz feldspar rocks in the central erzgebirge saxony germany the variscan erzgebirge represents an antiform with a core of gneisses and mica schists surrounded by a phyllitic mantle the gneiss eclogite unit geu in the central part is a composite tectonometamorphic assemblage characterized by a hp ht imprint and comprises migmatitic para and orthogneisses ht mylonites hp granulites eclogites and garnet peridotites it is tectonically sandwiched between two major units with distinctly lower pt histories the geu experienced a characteristic kinked retrograde pt path after hp ht equilibration with 1 strong near isothermal decompression at high temperatures 2 extensive re equilibration at medium pressures followed 3 by rapid cooling during continued uplift we dated zircons pb pb evaporation from granitoid orthogneisses and metapelites of the geu the orthogneisses contain euhedral long prismatic zircons of igneous origin that provided protolith ages between 470 and 524 ma metapelites retain well preserved granulite facies mineral assemblages and contain spherical multifaceted metamorphic zircons that grew near the peak of hp ht metamorphism inclusions of prograde hp phengite 15 kbar and rutile are included in one such zircon metamorphic zircons of three samples from different localities yielded identical 207pb 206pb ages of 340 5 0 7 ma 341 2 0 5 ma and 341 6 0 5 ma respectively consideration of these zircon ages with published 39ar 40ar white mica ages suggests fast cooling and uplift rates in excess of 50 c ma and 4 km ma this is typical for large scale extensional tectonic unroofing of the ultra deep part of a fossil thickened variscan continental crust 60 km during continuing continental collision and orogenic collapse

early crustal evolution in the western yangtze block evidence from u pb and lu hf isotopes on detrital zircons from sedimentary rocks abstract in situ u pb and lu hf data on detrital zircons from paleo to neoproterozoic sediments have been used to gain a clearer picture of the regional tectonic background and crustal evolution in the western part of the yangtze block the youngest concordant zircon ages for sedimentary units suggest maximum depositional ages of 1014 ma for the kunyang group 750 649 ma for the sinian sequences and 525 ma for the cambrian sediments the yinmin formation previously assigned to the middle part of the kunyang group was actually deposited after 1667 ma and contains zircons whose ages are dominantly from late archean to paleoproterozoic 2 8 2 7 ga 2 5 2 3 ga and 1 85 ga the heishantou formation in the lower part of the kunyang group has two major age populations of 1 0 ga and 1 8 1 6 ga the sinian and cambrian sedimentary rocks are dominated by neoproterozoic zircons with age peaks at 760 ma and 825 ma consistent with the ages of widespread igneous rocks around the yangtze block the lu hf isotope data suggest that a significant juvenile input took place during archean and neoproterozoic times respectively while crustal reworking was dominant during the paleoproterozoic time the archean paleoproterozoic detritus is isotopically distinct from the archean paleoproterozoic basement exposed in the northern part of the yangtze block suggesting that a subarea of old crust lies beneath the young sediments covering the craton the presence of abundant 1 85 ga zircons suggests that the yangtze block was probably part of the columbia supercontinent during paleoproterozoic time comparisons to the other parts of columbia suggest that the yangtze block could have been adjacent to the north china craton and or australia

fluid immiscibility in natural processes use and misuse of fluid inclusion data ii interpretation of fluid inclusion data in terms of immiscibility abstract phase equilibrium analysis of the relevant systems together with the application of the principles of chemical equilibrium put severe constraints on the interpretation of fluid inclusion data in terms of immiscibility in part i following from that point the major limits on the accuracy and even the validity of fluid inclusion quantitative data and their interpretation in terms of fluid composition and density are briefly discussed the practical implications of the general constraints temperature pressure topology of the fluid systems are envisaged emphasis is laid on some important consequences such as the use of isochore intercepts and the possible resulting interpretation of fluid mixing rather than unmixing the case of highly saline inclusions the identification and interpretation of heterogeneous trapping the composition and density constraints on coexisting fluids are presented and illustrated by natural examples taking into account all the measurable parameters in fluid inclusions volume temperature and nature of phase transitions more or less complete individual spectroscopic analyses all the available experimental data and all the theoretical constraints may be long and difficult however it is most generally very informative and productive although part of these data is often sufficient to deny unmixing nevertheless a final example on metamorphic fluids demonstrates how such an approach can prove and also characterize a fluid unmixing during a geologic process

syn collisional transform faulting of the tan lu fault zone east china origin of the continental scale tan lu fault zone tlfz east china remains controversial about 550 km sinistral offset of the dabie orogenic belt dob and sulu orogenic belt sob is shown along the ne nne striking tlfz syn collisional sinistral ductile shear belts in the tlfz have been identified thirteen phengite bulk separates from the mylonites were dated by the 40ar 39ar method they gave cooling ages of the 198 181 ma for the shear belts along the eastern margin of the dob and 221 210 ma from the western margin of the sob distribution of the foreland basin deposits suggests that sinistral offset of the dob and sob by the tlfz took place prior to deposition of the upper triassic strata the marginal structures around the dob and sob support syn collisional faulting and indicate anticlockwise rotation of the dob during the displacement the folding and thrust faulting related to crustal subduction coeval with the tan lu faulting is older than the foreland basin deposition related to the orogenic exhumation several lines of evidence demonstrate that the tlfz was developed as a syn collisional transform fault during latest middle to earliest late triassic time when the dob and sob experienced crustal subduction of the south china block scb eastward increase of the crustal subduction rates is believed to be responsible for the sinistral transform faulting

pb pb and u pb zircon dating of subvolcanic rhyolite as a time marker for hercynian granite magmatism and sn mineralisation in the eibenstock granite erzgebirge germany considering effects of zircon alteration tin mineralisation is closely related to rhyolite stocks and dykes which occur in the endo and exocontact of the eibenstock granite erzgebirge germany the same structures which cut the granite control the rhyolite emplacement and the location of ore bearing greisen bodies albitisation and greisenisation related to tin mineralisation as well as sericitisation and argillic alteration may be traced by changes in chemical and mineralogical composition of both rhyolite and granite wall rock comprehensive zircon studies by scanning electron microscopy secondary and backscattered electron as well as cathodoluminescence imaging edx measurements reveal that zircon from rhyolite and from the enclosing granite shows significant changes in chemical composition and crystallinity including distortion of the u pb isotope system when affected by greisenisation single evaporation analysis of zircon from rhyolite with little or no greisenisation gave a 207pb 206pb age of 290 5 ma whereas zircon from little altered granite gave a 207pb 206pb age of 320 8 ma the single evaporation age of zircon from rhyolite is confirmed by 238u 206pb shrimp ages of 297 8 ma the significant time gap of at least 20 ma between granite intrusion and rhyolite formation suggests that the late magmatic evolution of the eibenstock granite cannot be regarded as a source for tin ore forming fluids as previously assumed

a detrital record of continent continent collision in the early middle jurassic foreland sequence in the northern yangtze foreland basin south china abstract the mesozoic northern yangtze foreland basin system was formed by continental collision between the north china and south china plates along the mianlue suture synorogenic stratigraphic sequences of late triassic to early middle jurassic age were developed in the northern yangtze foreland basin the upper middle jurassic shaximiao formation consists mainly of thick bedded terrestrial successions that serve as the main body of the basin filling sequences suggesting intense tectonism in the peripheral orogeny of the foreland basin laser icp ms u pb analysis of 254 detrital zircon grains from sandstone samples and several published lower middle jurassic samples detrital compositions petrofacies and paleocurrent reconstructions in the northern yangtze foreland basin indicate that discrete source areas included the qinling dabieshan ranges and the mianlue suture zone to the north and the south china plate to the south the stratigraphic succession and sediment provenance of the foreland basin imply that the early mianlue oceanic basin magmatic arc and nonmarine molasse foreland basin during the period of deposition were modified or buried by the subsequent continent continent collision between the north china qinling dabieshan plate and the yangtze plate during the jurassic which followed the oblique amalgamation between these plates during the middle late triassic

fluid inclusions muscovite ar ar age and fluorite trace elements at the baiyanghe volcanic be u mo deposit xinjiang northwest china implication for its genesis abstract the baiyanghe be u mo deposit is located in the late paleozoic xuemisitan kulankazi island arc of the northwestern margin of the junggar plate northwest china it is the largest be deposit 2 2 m tons of ore with grades ranging from 0 2 to 1 4 in asia orebodies in the deposit occur as fractures along contact zones between the yangzhuang granite porphyry intrusion and devonian pyroclastic country rocks and within the porphyry itself muscovite fluorite veins are closely associated with the be u mo mineralization a new ar ar dating of the muscovite in this study yields a plateau age of 303 0 1 6 ma which constrains the timing of the be u mo mineralization of the deposit three stages of fluorite of different colors have been identified at the deposit with the earliest dark purple fluorite more closely associated with the mineralization microthermometry of fluid inclusions obtained from the three stages of fluorite suggests that the fluorites were precipitated as veins from low temperature 120 150 c hydrothermal fluids with salinity ranging from 4 7 to 19 7 wt nacl eqv based on the trace elemental concentrations and ree patterns of the fluorite the style of veining and the low salinity and low temperature characters of the fluid inclusions it is suggested that be and u were most likely transported as fluoride complexes and mo as hydroxyl complexes pb isotopic compositions of the ores and country rocks as well as o and h isotopic characters of the ore related muscovite indicate mixing between magmatic and meteoric waters both contributed to formation of the ore forming fluids metallic be u and mo were most likely leached out from the granite porphyry by the fluids the fluid mixing led to the reduction of u mo and be and their precipitation at the deposit

the lanthanide tetrad effect and its correlation with k rb eu eu sr eu y ho and zr hf of evolving peraluminous granite suites lanthanide tetrad effects are often observed in ree patterns of more highly evolved variscan peraluminous granites of mid eastern germany central erzgebirge western erzgebirge fichtelgebirge and northern oberpfalz the degree of the tetrad effect te1 3 is estimated and plotted vs k rb sr eu eu eu y ho and zr hf the diagrams reveal that the tetrad effect develops parallel to granite evolution and significant tetrad effects are strictly confined to highly differentiated samples mineral fractionation as a cause for the tetrad effect is not supported by a calculated rayleigh fractionation which also could not explain the fractionation trends of sr eu and eu eu the strong decrease of eu concentrations in highly evolved rocks suggests that eu fractionates between the residual melt and a coexisting aqueous high temperature fluid mineral fractionation as a reason for the tetrad effect is even more unlikely as ree patterns of accessory minerals display similar tetrad effects as the respective host rocks the accessory minerals inherit the ree signature of the melt and do not contribute to the bulk rock tetrad effect via mineral fractionation these results point in summary to significant changes of element fractionation behavior in highly evolved granitic melts ionic radius and charge which commonly control the element distribution between mineral and melt are no longer the exclusive control the tetrad effect and the highly fractionated trace element ratios of y ho and zr hf indicate a trace element behavior that is similar to that in aqueous systems in which chemical complexation is of significant influence this distinct trace element behavior and the common features of magmatic hydrothermal alteration suggest the increasing importance of an aqueous like fluid system during the final stages of granite crystallization the positive correlation of te1 3 with bulk rock fluorine contents hints at the importance of ree fluorine complexation in generating the tetrad effect as the evolution of a ree pattern with tetrad effect m type implies the removal of a respective mirroring ree pattern w type the tetrad effect identifies open system conditions during granite crystallization

zircon u pb ages and geochemistry of the wenquan mo bearing granitioids in west qinling china constraints on the geodynamic setting for the newly discovered wenquan mo deposit abstract east qinling is the largest porphyry molybdenum province in the world these mo deposits have been well documented in west qinling however few mo deposits have been discovered although granitic rocks are widespread recently the wenquan porphyry mo deposit has been discovered in gansu province which provides an insight into mo mineralization in west qinling in this paper we report pb isotope compositions for k feldspar and sulfides s isotope ratios for sulfides the results obtained from petrochemical study and from in situ la icp ms zircon u pb dating and hf isotopes the granitoids are enriched in lile and lree with ree and trace element patterns similar to continental crust suggesting a crustal origin the mg 40 05 to 56 34 and cr and ni contents are high indicating a source of refractory mafic lower crust the e hf t values of zircon grains from porphyritic monzogranite range from 2 9 to 0 6 and from granitic porphyry vary from 3 3 to 1 9 the zircons have t dm2 of 1014 to 1196 ma for the porphyritic monzogranite and 954 to 1224 ma for the granitic porphyry implying that these granitoids were likely derived from partial melting of a late mesoproterozoic juvenile lower crust the pb isotope compositions of the granitoids are similar to granites in south china showing that the magma was sourced from the middle lower crust in the southern qinling tectonic unit the pb isotopic contrast between the mo bearing granitoids and ores shows that the pb in the ore forming solution was derived from fractionation of a triassic magmatic system 34 s values of sulfides are between 5 02 and 5 66 similar to those associated with magmatic hydrothermal systems la icp ms zircon u pb dating yields crystallization ages of 216 2 1 7 and 217 2 2 0 ma for the granitoids consistent with a previously reported molybdenite re os isochron age of 214 4 7 1 ma this suggests that the mo mineralization is related to the late triassic magmatism in the west qinling orogenic belt in view of these geochemical results and known regional geology we propose that both granitoid emplacement and mo mineralization in the wenquan deposit resulted from the triassic collision between the south qinling and the south china block along the mianlue suture since triassic granitoid plutons commonly occur along the qinling orogenic belt the triassic wenquan mo bearing granitoids highlight the importance of the triassic tectono magmatic belt for mo exploration in order to apply this metallogenic model to the whole qinling orogen further study is needed to compare the wenquan deposit with other deposits

textural and chemical variations of micas as indicators for tungsten mineralization evidence from highly evolved granites in the dahutang tungsten deposit south china

the age of the latest thermal overprint of tin and polymetallic deposits in the erzgebirge germany constraints from fluorite u th sm he thermochronology the erzgebirge region of germany records two major episodes of hydrothermal activity which includes a late carboniferous to early permian event associated with significant sn w mineralization that is related to late variscan granite magmatism and a mesozoic episode of polymetallic vein mineralization in contrast to the first event the age of the younger hydrothermal activity is poorly constrained for the latter various geochronological methods yielded a wide age range from permian to early tertiary here we apply fluorite u th sm he thermochronology fhe on both types of mineralization with a twofold goal 1 to investigate the sensitivity and applicability of the new fhe method evans et al 2005 and 2 to constrain the thermal history of ore deposits in the erzgebirge region two hundred and thirty three aliquots from seven mineralization localities have been dated fluorite from six deposits yielded cretaceous fhe ages between 112 to 79 ma which are independent of their paragenesis in contrast fluorite from the sadisdorf sn w deposit yielded an age of 234 ma the younger ages are interpreted as cooling ages indicating the time of the last thermal overprint including possible hydrothermal activity in the erzgebirge the oldest triassic fhe ages at sadisdorf indicate that the mesozoic thermal overprint only partially reset the u th sm he system of the late variscan mineralization thermal modeling based on fhe ages and he diffusion parameters in fluorite results in thermal histories comparable to the results from the well established apatite based thermal modeling this study emphasizes the applicability of fluorite u th sm he thermochronology which is especially suited for ore deposits where apatite is lacking

heterogeneous sources of the triassic granitoid plutons in the southern qinling orogen an e w tectonic division in central china 1 the qinling orogen is an important orogenic belt formed by the collision between the north and south china blocks along the mianlue suture during the triassic the orogen is customarily divided into the western and eastern qinling terranes however the boundary has long been a matter of debate there are many triassic granitoid plutons in the orogen especially in south qinling along the southern part of the shangdan suture systematic analysis of u pb ages and hf isotopes in zircons frxom six granitoid plutons including guangtoushan gaoqiaopu xiba laocheng dongjiangkou and zhashui from west to east allows us to trace their formation ages and source regions all plutons yield ages that vary only from 218 to 211 ma however zircon hf isotope data for these triassic plutons cluster in two distinct groups granitoids from the western segment i e guangtoushan gaoqiaopu and xiba of the south qinling belt have negative ehf t values 20 9 to 5 2 and relatively old two stage hf model ages 1 58 to 2 57 ga in contrast those from the eastern segment i e laocheng dongjiangkou and zhashui show higher ehf t values 5 4 to 6 8 and younger two stage hf model ages 0 82 to 1 60 ga integrating these analyses with published sr nd pb hf isotopic data we suggest that the division between the western and eastern south qinling segments is located near the taibai chenggu line between the baoji chengdu railway and 108 e longitude the integrated data suggest that the western south qinling segment separated from the north china block during the paleoproterozoic and early mesoproterozoic and then switched into continental convergence with the eastern south qinling segment northern margin of the yangtze block during the late mesoproterozoic to early neoproterozoic finally the two segments amalgamated during the late neoproterozoic

rare earth elements in sinters from the geothermal waters hot springs on the tibetan plateau china abstract the mineralogical and geochemical composition of sinters from the geothermal areas on the tibetan plateau was determined they occur as siliceous salty and calcareous sinters but biogenic siliceous sinters were also found the analyses indicate that there are no distinct inter element relationships between individual rare earth elements rees and other elements formed from the same geothermal water the mineralogical and chemical composition of the sinters is influenced by their genesis and formation conditions the ree distributions depend on the origin of the sinters fe mn phases in sinters tend to scavenge more rees from geothermal water neither the ree fractionation nor the ce anomaly seems to be associated with fe mn phases in the sinters the fourth tetrads of some sinters display weak w type concave effects in contrast the third tetrads present large effects in some sinters due to positive gd anomalies the origin of the positive eu anomalies in some sinters seems to be caused by preferential dissolution of feldspars during water rock interaction the complexing ligands in geothermal water may contribute significantly to the fractionation of rees in sinters the dominant co 3 2 and hco 3 complexing in geothermal water favors enrichment of heavy rees in calcareous sinters

petrogenesis of lingshan highly fractionated granites in the southeast china implication for nb ta mineralization abstract whole rock major and trace element and sr nd and hf isotope data together with zircon u pb hf and o isotope data are reported for the nb ta ore bearing granites from the lingshan pluton in the southeastern china in order to trace their petrogenesis and related nb ta mineralization the lingshan pluton contains hornblende bearing biotite granite in the core and biotite granite albite granite and pegmatite at the rim in addition numerous mafic microgranular enclaves occur in the lingshan granites zircon sims u pb dating gives consistent crystallization ages of ca 132 ma for the lingshan granitoids and enclaves consistent with the nb ta mineralization age of 132 ma indicating that mafic and felsic magmatism and nb ta mineralization are coeval the biotite granites contain hornblende and are metaluminous to weakly peraluminous with high initial 87 sr 86 sr ratios of 0 7071 0 7219 negative e nd t value of 5 9 to 0 3 e hf t values of 3 63 to 0 32 for whole rocks high 18 o values and negative e hf t values for zircons and ancient hf and nd model ages of 1 41 0 95 ga and 1 23 1 04 ga indicating that they are i type granites and were derived from partial melting of ancient lower crustal materials they have variable mineral components and geochemical features corresponding extensive fractionation of hornblende biotite and feldspar with minor fractionation of apatite existence of mafic microgranular enclaves in the biotite granites suggests a magma mixing mingling process for the origin of the lingshan granitoids and mantle derived mafic magmas provided the heat for felsic magma generation in contrast the nb ta mineralized albite granites and pegmatites have distinct mineral components and geochemical features which show that they are highly fractionated granites with extensive melt and f rich fluid interaction in the generation of these rocks the fluoride rich fluids induce the enrichment in nb and ta in the highly evolved melts therefore we conclude that the nb ta mineralization is the result of hydrothermal process rather than crystal fractionation in the lingshan pluton which provides a case to identify magmatic and hydrothermal processes and evaluate their relative importance as ore forming processes

the crust of cathaysia age assembly and reworking of two terranes abstract u pb dating and hf isotope data from detrital zircons have been used to analyse the crustal evolution of the eastern and western parts of the cathaysia block in se china zircons from the oujiang river in eastern cathaysia indicate that the basement is dominantly paleoproterozoic 1850 1870 ma 2100 2400 ma in age with minor archean components it was extensively reworked in jurassic cretaceous time 100 155 ma to produce the widespread yanshanian magmatic suite both the 1850 1870 ma event and the yanshanian magmatism show wide ranges in hf isotope composition consistent with mixing between crustal and juvenile magmas marked downstream changes in the relative proportions of zircon age populations emphasize the care required in using detrital zircon data to estimate continental growth rates zircons from the north river indicate that the crust of western cathaysia was generated mainly during neoproterozoic time although it contains some archean 2500 3500 ma to mesoproterozoic components this crust was strongly reworked during caledonian ca 450 ma indosinian ca 240 ma and early yanshanian ca 160 ma thermal events there is little evidence for juvenile crustal growth in any of these events although the yanshanian granitoids of the eastern and western parts of the cathaysia give similar mean hf model ages consistent with published nd model ages this is a coincidence they have different crustal sources the distinct patterns of crustal evolution suggest that eastern and western cathaysia may represent separate microcontinents accreted to the older yangtze craton and transposed by extensive strike slip faults

a review of anomalous rare earth elements and yttrium in coal abstract coal deposits have attracted much attention in recent years as promising alternative raw sources for rare earth elements and yttrium rey not only because the rey concentrations in many coals or coal ashes are equal to or higher than those found in conventional types of rey ores but also because of the world wide demand for rey in recent years has been greater than supply in addition to anomalies of enrichment or depletion of light medium and heavy rey in coal deposits normalized to upper continental crust post archean australian shale or north american shale composite anomalies of redox sensitive ce and eu and in some cases of non redox sensitive la gd and y could be used as geochemical indicators of the sediment source region sedimentary environment tectonic evolution and post depositional history of coal deposits factors controlling rey anomalies in coal deposits include the geochemistry of terrigenous source rocks ingress of hydrothermal fluids influence of marine environments percolating natural waters volcanic ashes and sedimentary environments of peat formation additionally the smoothness of a normalized rey distribution pattern provides a simple but reliable basis for testing the quality of rey chemical analyses for coal and other sedimentary rocks

the genesis of zr nb ree mineralisation at khalzan buregte western mongolia reconsidered abstract the sources and formation conditions of unconventional zr nb ree mineralisation ree rare earth elements presently found in increasing number worldwide are still poorly constrained one particular problem is the specific role of magmatic and hydrothermal processes active in various geological settings investigation of zr nb ree mineralisation at khalzan buregte and tsakhir western mongolia enables to evaluate magmatic processes preceding economic mineralisation and in a second step to compare similar ore forming processes developing in host rocks of contrasting rock composition low vs high silica rocks the genesis of the zr nb ree mineralisation is re assessed using field observations whole rock analysis chemical composition quantitative modal analysis by x ray diffraction and by the application of various transmitted light and electron microscopic techniques coarse grained intrusive bodies dikes and volcanic rocks of alkaline silica saturated composition were found to be contemporarily emplaced at subvolcanic to volcanic levels forming four alkaline massifs within the khalzan buregte area the whole rock composition of weakly altered magmatic rocks ranges from syenite to quartz monzonite and alkaline granite alkali feldspar syenite to alkali feldspar granite according to their modal composition magmatic and at least two subsequent hydrothermal processes contributed significantly to the formation of economic concentrations of high field strength elements hfse such as zr hf nb ta ree and y in the khalzan buregte deposit and in the nearby tsakhir prospect mixing of magma from at least three sources and the formation of potassium feldspar cumulates resulted in local enrichment of zr nb and light rare earth elements lree in the rocks up to sub economic levels there was no significant increase in y and heavy rare earth elements hree during magmatism multistage metasomatic alteration resulted in a pronounced chemical and mineralogical heterogeneity of associated alteration assemblages the main hosts of zr and hf in the ores are zircon and other zirconium silicates gittinsite catapleiite ca and elpidite the rare metals nb and ta are mainly contained in various types of pyrochlore khalzan buregte and to a lesser extent in fergusonite and other minerals tsakhir a large variety of ree and y bearing minerals have been identified including oxides fluorocarbonates and silicates early hydrothermal alteration by silica and carbonate rich fluids yielded extreme concentrations of zr nb and lree later alteration resulted in enrichment of y and hree in the latter case fluids were very rich in fluorine our preliminary genetic model assumes a carbonatite related fluid system responsible for the early alteration that occurred late during or postdating the intrusion extrusion of the silica saturated magmas a li f granite type fluid system was active during the late alteration the interplay of all these processes resulted in the formation of a complex economic zr nb ree mineralisation at khalzan buregte

paleomagnetic study of upper jurassic rocks from the sichuan basin tectonic aspects for the collision between the yangtze block and the north china block abstract a paleomagnetic study has been carried out on late jurassic redbeds in the sichuan basin at the northern part of the yangtze block upper jurassic brownish red sandstones and brownish red siltstones were collected in the penglaizhen formation at 26 sampling sites around jiangyang city 30 4 n 104 5 e thermal demagnetization isolated a high temperature magnetization component with a maximum unblocking temperature of about 690 c the primary nature of magnetization acquisition is ascertained through a 95 confidence level positive fold test as well as a positive reversal test the tilt corrected overall mean direction of 24 sites is d 25 9 i 26 7 95 4 7 leading to a paleomagnetic pole situated at 61 3 n 222 7 e a95 4 2 this pole position agrees with two other late jurassic poles from the sichuan basin indicating that this basin has behaved as a rigid block since late jurassic these three poles from the sichuan basin therefore provide a characteristic late jurassic pole for the stable part of the yangtze block 64 3 n 231 2 e a95 6 7 comparison of the late jurassic pole of the yangtze block with the contemporaneous pole for the north china block ncb identifies a significant difference implying that the relative movement between the yangtze block and the ncb continued during and probably after the late jurassic paleomagnetic and geological evidence reveals that the yangtze block collided first with the ncb during the early permian and continued to penetrate into it while undergoing a clockwise rotation until the early cretaceous

oblique closure of the northeastern paleo tethys in central china a branch of the paleo tethys ocean once separated the north china plate from the south china plate however the mode of closure of the northeastern paleo tethys ocean during the late paleozoic to early mesozoic has been debated one reason for this debate is that the collisional suture zone was later buried by large scale thrust faults in the southern qinling dabieshan orogen which made it difficult to reconstruct the amalgamation of the supercontinent in central china new regional geologic mapping provides stratigraphic and structural constraints on the mechanism of this ocean closure our results indicate that dextral transpressional suturing in the southern qinling dabieshan foreland fold thrust belt resulted in the formation of the northern yangtze foreland basin where the stratigraphy precisely shows the time transgressive closure of the ocean and the orogenic sediments shed over 1000 km westward from eastern china to the closing paleo tethys therefore we propose an oblique subduction model to describe the closure of the paleo tethys ocean our findings suggest that prolonged slab pull during the oblique subduction of the oceanic plate continued to drive deep continental subduction thereby forming high and ultrahigh pressure metamorphic rocks and leading to sustained ocean closure

nb ta ti sn oxide mineral chemistry as tracer of rare element granitic pegmatite fractionation in the borborema province northeastern brazil the borborema pegmatitic province bpp northeastern brazil is historically important for tantalum mining and also famous for top quality specimens of exotic nb ta oxides and more recently for the production of gem quality turquoise blue paraiba elbaite with more than 750 registered mineralized rare element granitic pegmatites the bpp extends over an area of about 75 by 150 km in the eastern part of the neoproterozoic serido belt the late cambrian pegmatites are mostly hosted by a sequence of neoproterozoic cordierite sillimanite biotite schists of the serido formation and quartzites and metaconglomerates of the equador formation the trace element ratios in feldspar and micas allow to classify most pegmatites as belonging to the beryl columbite phosphate subtype electron microprobe analyses empa of columbite tapiolite niobian tantalian rutile ixiolite and wodginite group minerals from 28 pegmatites in the bpp are used to evaluate the effectiveness of nb ta oxide chemistry as a possible exploration tool to trace the degree of pegmatite fractionation and to classify the pegmatites the columbite group mineral composition allows to establish a compositional trend from manganoan ferrocolumbite to manganocolumbite and on to manganotantalite this trend is typical of complex spodumene and or lepidolite subtype pegmatites it clearly contrasts with another trend from ferrocolumbite through ferrotantalite to ferrowodginite and ferrotapiolite compositions typical of pegmatites of the beryl columbite phosphate subtype large scatter and anomalous trends in zoned crystals partially overlap and conceal the two main evolution patterns this indicates that a large representative data set of heavy mineral concentrate samples collected systematically along cross sections would be necessary to predict the metallogenetic potential of individual pegmatites other mineral species e g garnets and or tourmaline with a more regular distribution than nb ta oxides would be more appropriate and less expensive for routine exploration purposes the currently available nb ta oxide chemistry data suggest the potential for highly fractionated ta li cs pegmatites in the bpp so far undiscovered and encourages further more detailed research

further evidence for 1 85 ga metamorphism in the central zone of the north china craton shrimp u pb dating of zircon from metamorphic rocks in the lushan area henan province abstract this paper reports shrimp zircon u pb dating of precambrian supracrustal and granitic rocks from the lushan area henan province in the southern portion of the central zone also referred to as the trans north china orogen of the north china craton a graphite garnet sillimanite gneiss sample tw0006 1 of the shangtaihua group gives a range of inherited zircon ages from 2 73 to 2 26 ga and a metamorphic zircon age of 1 84 0 07 ga a garnet bearing gneissic granitoid sample twj358 1 which is considered to intrude the shangtaihua group gives a magmatic zircon age of 2 14 0 02 ga and a metamorphic zircon age of 1 87 ga the metamorphic zircon ages of 1 87 1 84 ga obtained in this study indicate that an important tectonothermal event occurred at the end of the paleoproterozoic in the lushan area this supports the southern continuation of a central zone in the north china craton that workers have recently considered to result from continent continent collision it is also evident that the shangtaihua group was formed during the paleoproterozoic between 2 26 and 2 14 ga and not during the archean as previously considered