temporal spatial distribution and tectonic implications of the batholiths in the gaoligong tengliang yingjiang area western yunnan constraints from zircon u pb ages and hf isotopes abstract considerable progress has recently been made regarding temporal and spatial distribution of magmatism in the lhasa terrane however the eastward and southeastward correlation of these tibetan magmatic suites in western yunnan and burma remains poorly constrained this paper reports zircon u pb dating and hf isotopic compositions of granites in the gaoligong tengliang yingjiang area west yunnan it reveals three episodes of plutonism and more importantly a southwestward magmatic migration the gaoligong batholiths in the northeast were mainly emplaced during early cretaceous 126 121 ma and comprised predominantly s type granites with negative zircon ehf values ehf 2 12 the tengliang granites situated southwest of the gaoligong belt were emplaced in late cretaceous 68 76 ma and also displayed a strong peraluminous affinity and negative ehf 5 14 indicating a provenance from a proterozoic sedimentary source with little mantle contribution the youngest phase of magmatism 52 66 ma occurred in yingjiang southwestmost of the study area it is composed of s type granites ehf 2 12 in east yingjiang and i type granites ehf 4 6 in west yingjiang near the china burma border the late cretaceous early cenozoic plutons in the tengliang and yingjiang area are thus considered as the northern continuation of the late cretaceous magmatic arc west which comprises i type granites and andesitic rocks and of the belt of predominant s type granites east in burma thailand and malaysia such a chemical polarity of the dual i type and s type granites is strongly reminiscent of the northern american cordillera indicating a cordilleran style continental margin during the late cretaceous early cenozoic while the magmatic arc was related to eastward subduction of the neo tethys beneath the asian continent the s type granites represented the melting products of thickened crust in the hinterland in response to subduction induced decrease in lithospheric strength and compressive plate convergence forces and to a less degree to the collision between burma and sundaland blocks the gaoligong early cretaceous granites which bear strong similarities in lithology geochemistry and emplacement age to those in the northern magmatic belt in the lhasa terrane are also the magmatic expression of crustal thickening this crustal thickening may have stemmed from the collision between the lhasa block and the qiangtang block in late jurassic and early cretaceous the magmatism in western yunnan thus recorded a long term subduction of the neo tethyan plate enhanced by continental collisions at different time

impact cratering in sandstone the memin pilot study on the effect of pore water abstract planetary surfaces are subjected to meteorite bombardment and crater formation rocks forming these surfaces are often porous and contain fluids to understand the role of both parameters on impact cratering we conducted laboratory experiments with dry and wet sandstone blocks impacted by centimeter sized steel spheres we utilized a 40 m two stage light gas gun to achieve impact velocities of up to 5 4 km s 1 cratering efficiency ejection velocities and spall volume are enhanced if the pore space of the sandstone is filled with water in addition the crater morphologies differ substantially from wet to dry targets i e craters in wet targets are larger but shallower we report on the effects of pore water on the excavation flow field and the degree of target damage we suggest that vaporization of water upon pressure release significantly contributes to the impact process

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

geochemistry and u pb geochronology of the wagone and hermyingyi a type granites southern myanmar implications for tectonic setting magma evolution and sn w mineralization abstract tin tungsten associated granites occur widely in the dawei region of the southeast asian tin belt in this contribution we present a detailed study of zircon u pb geochronology and whole rock and zircon elemental geochemistry for the wagone and hermyingyi granites in southern myanmar with the aim of determining their petrogenesis mineralization associations and tectonic setting these granitic rocks which belong to the high k calc alkaline series a2 type granites are characterized by high concentrations of sio2 75 2 82 5 rb 264 927 ppm th 18 4 58 3 ppm u 10 4 18 3 ppm and y 33 5 212 ppm but low contents of tfeo 0 57 3 45 cao 0 23 0 86 mgo 0 02 0 19 mno 0 01 0 38 tio2 0 01 0 10 p2o5 0 003 0 012 ba 3 162 ppm and sr 4 3 34 4 ppm hydrothermal zircons from the mineralized wagone pluton show an anomalous lack of zoning and vermicular spongy internal structures and they contain high concentrations of ti y u and light rees but low th u ratios mostly

depletion of light rare earth elements in felsic magmas contrary to simple generalizations about their behavior light rare earth elements lree do not act as incompatible elements in very felsic magmas in fact lree concentrations typically decrease often drastically during differentiation of such magmas the simplest explanation for this depletion involves the separation of minute easily overlooked quantities of an extremely lree rich accessory mineral either monazite or allanite our data indicate that felsic liquids with 50 ppm lree may be saturated in either of these accessories and that the concentration required for saturation decreases in increasingly felsic liquids this accounts for incompatible behavior of lree even at high concentrations in mafic magmas in contrast to compatible behavior at low concentrations in felsic magmas partitioning of lree into solid rather than liquid has important implications for trace element and nd isotope modeling of crustal anatexis as well as for magma differentiation

a strain based porosity model for use in hydrocode simulations of impacts and implications for transient crater growth in porous targets numerical modelling of impact cratering has reached a high degree of sophistication however the treatment of porous materials still poses a large problem in hydrocode calculations we present a novel approach for dealing with porous compaction in numerical modelling of impact crater formation in contrast to previous attempts e g p alpha model snowplow model our model accounts for the collapse of pore space by assuming that the compaction function depends upon volumetric strain rather than pressure our new e alpha model requires only four input parameters and each has a physical meaning the model is simple and intuitive and shows good agreement with a wide variety of experimental data ranging from static compaction tests to highly dynamic impact experiments our major objective in developing the model is to investigate the effect of porosity and internal friction on transient crater formation we present preliminary numerical model results that suggest that both porosity and internal friction play an important role in limiting crater growth over a large range in gravity scaled source size

how old are young lunar craters 1 the accurate definition of the lunar cratering chronology is important for deriving absolute model ages across the lunar surface and throughout the solar system images from the lunar reconnaissance orbiter narrow angle cameras and wide angle camera and the selene kaguya terrain camera provide new opportunities to investigate crater size frequency distributions csfds on individual geological units at lunar impact craters we report new csfd measurements for the copernican aged craters north ray tycho and copernicus which are crucial anchor points for the lunar cratering chronology we also discuss possible reasons for an age discrepancy observed between the impact melt and ejecta units our csfds for north ray and tycho crater ejecta deposits are consistent with earlier measurements however for copernicus crater and one of its rays we find significantly lower cumulative crater frequencies than previous studies our new results for copernicus crater fit the existing lunar absolute chronologies significantly better than the previous counts our derived model ages of the ejecta blankets of north ray tycho and copernicus agree well with radiometric and exposure ages of the apollo 16 17 and 12 landing sites respectively and are generally consistent with a constant impact rate over the last 3 ga however small variations of the impact rate cannot be resolved in our data and require further investigations

eocene break off of the neo tethyan slab as inferred from intraplate type mafic dykes in the gaoligong orogenic belt eastern tibet article i nfo eocene 40 42 ma basaltic dykes in the gaoligong tengliang belt eastern tibet are characterized by high na2 o 2 4 in contrast with the widespread post collisional potassic and ultrapotassic rocks in the tibetan plateau despite the ubiquitous negative nb anomalies these dykes have relatively high nb and zr contents making them distinct significantly from the gangdese arc magmas all these together with the positive nb anomaly in some samples indicate an intraplate affinity for the gaoligong tengliang dykes specifically the gaoligong dykes represent the asthenosphere derived melts which has been contaminated to various degrees by the lithosphere mantle derived melts whereas the tengliang samples were directly derived from an enriched lithosphere mantle the thin lithosphere b80 km inferred from basalt geochemistry is unusual in tibet thus demanding a peculiar mechanism to thin lithosphere a slab break off model is preferred given the geochemical contrast between pre 40 ma and post 40 ma magmas in tibet and the temporal correlation among this intraplate magmatism the termination of gangdese arc magmatism and regional thermally driven metamorphism therefore the occurrence of intraplate type magmas in the gaoligong orogenic belt likely represents magmatic expression of the detachment of subducting neo tethyan slab from the indian continental plate during the eocene in the light of the slab break off concept and thermo mechanical modeling the eocene slab break off furthermore suggests the onset of the india asia collision between 52 and 57 ma

he ar and s isotopic constraints on the relationship between a type granites and tin mineralization a case study of tin deposits in the tengchong lianghe tin belt southwest china abstract the tengchong lianghe tin belt in western yunnan province southwest china is the most important tin mineralization belt in the sanjiang tethyan metallogenic domain stmd there are two large tin deposits in this belt the paleogene lailishan and the late cretaceous xiaolonghe deposits the two deposits are spatially and temporally associated with the lailishan and xiaolonghe granitic plutons respectively recent studies suggest that the lailishan and xiaolonghe granitic plutons exhibit most of the mineralogical and geochemical characteristics of a type granites in this study we discuss the he ar and s isotopes of pyrite samples from the two large tin deposits to trace ore forming fluids and elements we also review the relationship between a type granites and tin deposits from a new perspective the 34scdt values of the lailishan tin deposit range from 4 9 to 6 7 with an average value of 5 53 the 34scdt values of the xiaolonghe tin deposit range from 5 0 to 8 1 with an average value of 6 33 these values are slightly higher than those of the granites 0 to 5 7 in the tengchong lianghe area indicating mainly magmatic sources for the sulfur of ore forming fluids with a small amount of s from the wall rocks the lailishan tin deposit has 3he 4he values of 1 57 3 46 ra with an average value of 2 078 ra and 40ar 36ar values of 382 00 622 99 with an average value of 459 67 the xiaolonghe tin deposit has 3he 4he values of 0 53 0 88 ra with an average value of 0 686 ra and 40ar 36ar values of 301 06 348 43 with an average value of 322 04 these values suggest that ore forming fluids of the lailishan and xiaolonghe tin deposits have mixed crustal mantle and a small volume of meteoric water sources in different proportions the mantle 4he values and 3he 4he values of the lailihsan tin deposit 26 44 1 57 3 46 ra are markedly higher than those of the xiaolonghe tin deposit 8 15 0 53 0 88 ra implying increased crust mantle interaction in the paleogene relative to the late cretaceous in western yunnan this interaction may be attributed to the upwelling of the asthenosphere through the break off of the neo tethyan slab during the main collisional period 65 41 ma of india asia

ultra high pressure metamorphism of carbonate rocks in the dabie mountains central china abstract widespread ultra high p assemblages including coesite quartz pseudomorphs after coesite aragonite and calcite pseudomorphs after aragonite in marble gneiss and phengite schist are present in the dabie mountains eclogite terrane these assemblages indicate that the ultra high p metamorphic event occurred on a regional scale during triassic collision between the sino korean and yangtze cratons marble in the dabie mountains is interlayered with coesite bearing eclogite and gneiss and as blocks of various size within gneiss discontinuous boudins of eclogite occur within marble layers marble contains an ultra high p assemblage of calcite aragonite dolomite clinopyroxene garnet phengite epidote rutile and quartz coesite coesite quartz pseudomorphs after coesite aragonite and calcite pseudomorphs after aragonite occur as fine grained inclusions in garnet and omphacite phengites contain about 3 6 si atoms per formula unit based on 11 oxygens similar to the coesite bearing eclogite marble exhibits retrograde recrystallization under amphibolite greenschist facies conditions generated during uplift of the ultra high p metamorphic terrane retrograde minerals are fine grained and replace coarse grained peak metamorphic phases the most typical replacements are symplectic pargasitic hornblende epidote after garnet diopside plagioclase an18 after omphacite and fibrous phlogopite after phengite ferroan pargasite plagioclase and actinolite formed along grain boundaries between garnet and calcite and calcite and quartz respectively the estimated peak p t conditions for marble are comparable to those for eclogite garnet clinopyroxene geothermometry yields temperatures of 630 760 c the garnet phengite thermometer gives somewhat lower temperatures the minimum pressure of peak metamorphism is 27 kbar based on the occurrence of coesite such estimates of ultra high p conditions are consistent with the coexistence of grossular rich garnet rutile and the high jadeite content of omphacite in marble the fluid for the peak metamorphism was calculated to have a very low xco2 0 03 the p t conditions for retrograde metamorphism were estimated to be 475 550 c at 7 kbar

diamond from the dabie shan metamorphic rocks and its implication for tectonic setting diamond occurs in ultrahigh pressure metamorphic rocks from dabie shan anhui province eastern china diamond bearing rocks include eclogite gamet pyroxenite and jadeitite diamond occurs in a mineral assemblage with coesite and jadeite the diamonds and diamondiferous rocks of dabie shan are interpreted to be the products of ultrahigh pressure metamorphism in the underthrust basement of the yangtze continental plate during the early mesozoic at greater than 4 0 gigapascals and 900 c this interpretation is based on the distribution of rock units the stability field of diamond and isotopic data indicating a crustal origin for the rocks most diamonds occur as euhedral inclusions in garnets and are 10 to 60 micrometers across although some are up to 700 micrometers across

cretaceous ongonites topaz bearing albite rich microleucogranites from ongon khairkhan central mongolia products of extreme magmatic fractionation and pervasive metasomatic fluid rock interaction abstract ongonites were defined at their type locality at ongon khairkhan central mongolia as pristine magmatic topaz bearing albite quartz keratophyres with up to 4 wt f and containing phenocrysts of albite k feldspar quartz and rare mica and topaz hosted in a groundmass composed of the same minerals however detailed petrographic and sem eds studies indicate that these rocks underwent considerable subsolidus exchange with deuteric fluids as evidenced by the presence of albitic plagioclase ab 100 and end member orthoclase or 100 secondary li fe rich mica zinnwaldite enriched in rare metals sn w ta nb pitted feldspars containing fluid inclusions and disseminated fluorite the 120 ma old dyke rocks emplaced at a high structural level in the crust are strongly peraluminous leucogranites characterized by high al and alkalis that are also enriched in rb cs ga and ta depleted in mg ca zr ba sr and eu and have anomalous k rb rb sr zr hf and nb ta ratios compared to the average continental crust however the suite has nd isotopic ratios nd 120 1 similar to those of contemporaneous a type granites of the mongolian transbaikalian igneous province of the central asian orogenic belt the inferred primary 18 o 6 to 7 and pb isotopic values are consistent with a granitic parent magma and interaction with orthomagmatic fluids the ongonites and constituent minerals record 1 an extensive and protracted crystal fractionation history in part due to the presence of volatiles particularly f which depressed the solidus temperature of the felsic rocks and extended its duration of crystallization and 2 subsolidus exchange with fluids which includes late flux of heated meteoric water as indicated by modified whole rock 18 o values 0 5 to 2 7 the interaction of the ongonites with internally derived orthomagmatic fluids is considered to result in enrichment and or redistribution of several incompatible elements but not to have greatly modified their original major element chemistry which indicates that this suite represents the last stages of fractionation of a highly differentiated f rich granitic magma the escape of these evolved melts from the apical part of the underlying pluton is now represented by the ongonite dykes late stage magmatic water rich fluids enriched in incompatible elements including nb ta sn and w were responsible for the late to post magmatic alteration and associated w mineralization

zircon u pb o and hf isotopic constraints on mesozoic magmatism in the cyclades aegean sea greece compared to the well documented cenozoic magmatic and metamorphic rocks of the cyclades aegean sea greece the geodynamic context of older meta igneous rocks occurring in the marble schist sequences and melanges of the cycladic blueschist unit is as yet not fully understood here we report o hf isotopic compositions of zircons ranging in age from ca 320 ma to ca 80 ma from metamorphic rocks exposed on the islands of andros ios sifnos and syros with special emphasis on triassic source rocks ion microprobe shrimp ii single spot oxygen isotope analysis of pre cretaceous zircons from various felsic gneisses and meta gabbros representing both the marble schist sequences and the melanges of the study area yielded a large range in 18o values varying from 2 7 to 10 1 vsmow with one outlier at 0 4 initial ehf values 12 5 to 15 7 suggest diverse sources for melts formed between late carboniferous to late cretaceous time that record derivation from mantle and reworked older continental crust in particular variable 18o and ehf t values for triassic igneous zircons suggest that magmatism of this age is more likely rift than subduction related the significant crustal component in 160 ma meta gabbros from andros implies that some jurassic gabbroic rocks of the hellenides are not part of ssz type supra subduction zone ophiolites that are common elsewhere along the margin of the pelagonian zone

genesis of the xiaolonghe quartz vein type sn deposit sw china insights from cathodoluminescence textures and trace elements of quartz fluid inclusions and oxygen isotopes abstract quartz textures revealed by scanning electron microscope cathodoluminescence sem cl images suggest that quartz in the xiaolonghe sn deposit formed in at least three fluid episodes quartz q1 in the pre ore silicification zone has homogeneous texture high cl intensity and high ti content 19 53 ppm fluid inclusions hosted in q1 are vapor rich v1 type and homogenized as supercritical fluid at 570 c quartz q2 in the syn ore topaz cassiterite quartz veins has lower cl intensity and is characterized by euhedral growth zones with lower ti content 1 3 12 ppm fluid inclusions hosted in q2 topaz and cassiterite are liquid rich fluid inclusions of moderate salinity 15 wt nacl equiv l1 type which homogenized at 423 c the post ore quartz q3 closely associated with sericitization of topaz generally crosscuts q2 and has dark cl intensity and much lower ti concentration the upper limits of t p conditions of pre ore and syn ore stage are constrained by the intersection of nacl h2o fluid inclusion isochores and ti in quartz isopleths and the lower limits are based on microthermometry results of fluid inclusions combined with the 18ofluid value 8 3 of q1 it indicates that the pre ore supercritical fluid was directly exsolved from a granitic magma at t 570 600 c and p 0 70 0 77 kbars corresponding to a maximum depth of 2 8 km under lithostatic pressure the syn ore subcritical fluid 8 0 18ofluid 6 3 mixed with some meteoric water was under 423 450 c 0 32 0 45 kbars the transition from the pre ore supercritical fluid to the syn ore subcritical fluid indicates boiling condition probably at 512 c 0 62 kbars which was likely caused by hydraulic fracturing under high pressure both the fluid boiling and fluid mixing contribute to the cassiterite precipitation in xiaolonghe sn deposit in the post ore stage the coexisting s type and v2 type fluid inclusions in q3 indicates a second fluid boiling at 269 c 0 05 kbars which was probably caused by decompression due to rapid denudation of the overlain strata the low salinity 5 5 wt nacl equiv l2 type fluid inclusions hosted in fluorite homogenized at 199 c and

generation of leucogranites via fractional crystallization a case from the late triassic luoza batholith in the lhasa terrane southern tibet abstract leucogranites are important in understanding intracrustal differentiation and regional tectonic evolution but how these rocks form remains a matter of much debate the luoza batholith in the central lhasa subterrane provides an important opportunity to address these issues as this batholith consists of normal calc alkaline s type granodiorites group 1 and highly fractionated s type leucogranites group 2 laser ablation inductively coupled plasma mass spectrometry zircon u pb dating indicates that these rocks were emplaced at ca 221 205 ma the group 1 samples ca 205 ma have low sio2 content 64 67 wt and low differentiation index values di 75 76 and are slightly depleted in ba p sr and ti compared to the group 2 samples ca 221 ma and 213 ma which have high sio2 content 74 75 wt high differentiation index values 91 94 and are significantly depleted in ba p sr and ti samples from group 1 and group 2 exhibit similar zircon ehf t values 15 6 to 1 4 both of which are significantly higher than melts from the pure ancient basement in the central lhasa subterrane 20 5 to 10 6 the group 1 samples can be interpreted as having been derived from the partial melting of metagreywacke within the ancient basement in the central lhasa subterrane with contributions from mantle or juvenile crust derived components whereas the group 2 samples may have formed via varying degrees of fractional crystallization of different minerals e g plagioclase k feldspar biotite zircon allanite monazite titanite and apatite from the parental magmas represented by the granodioritic samples in group 1 in shallow crustal magma chambers in combination with sedimentary records the high temperature and low pressure conditions indicated by the group 1 samples can be geodynamically linked to a back arc extensional setting in response to the southward subduction of the bangong nujiang tethys ocean seafloor our work implies that fractional crystallization is likely a feasible mechanism for the development of leucogranites and for explaining the compositional diversity of the granite during intracrustal differentiation

geochemical and geochronological characteristics of late cretaceous to early paleocene granitoids in the tengchong block southwestern china implications for crustal anatexis and thickness variations along the eastern neo tethys subduction zone abstract the tengchong block of southwestern china is key to tracing the eastward subduction of neo tethys and collision between indian and asian continents the block contains a magmatic belt that represents the southeastward continuation of the gangdese belt produced by the eastward subduction of eastern neo tethyan oceanic lithosphere in this paper we present geochemical and geochronological data of late cretaceous to early paleocene 64 ma granitic rocks of the guyong and husa batholiths in the tengchong block these can be subdivided into high silica peraluminous granites and low silica metaluminous granodiorites and all belong to the high k calc alkaline series are enriched in lile and depleted in hfse the guyong granitoids have high initial sr ratios of 0 706511 0 711753 negative e nd t values of 9 2 to 11 6 two stage model ages of 1 39 1 55 ga and pb isotopic compositions that indicate a crustal affinity the husa granodiorites also have high initial sr ratios of 0 716496 negative e nd t value of 16 5 two stage model age of 1 89 ga variable e hf t values of 3 4 to 18 1 and pb isotopic compositions similar to lower crustal values these geochemical and isotopic data indicate that the guyong granitoids were likely derived from partial melting of ancient crustal metapelite or mixed pelite greywacke sources while the husa granodiorites were derived from the partial melting of lower crustal mixed sources involving metasedimentary and metaigneous rocks to understand the thermal state and architecture of the late cretaceous to early paleocene magmatic arc crust the crust derived intermediate to acidic igneous rocks of the southern central lhasa and tengchong blocks and eastern himalayan syntaxis are compared we infer that partial melting of crust occurred at great depth in the southern lhasa block intermediate depths in the eastern himalayan syntaxis and shallow depths in the central lhasa and tengchong block sr y ratios indicate that the tengchong block was characterized by thin crust while the eastern himalayan syntaxis and northernmost part of southern lhasa block contained crust of normal thickness and the southernmost part of the southern lhasa block contained thickened crust

petrogenesis of metaluminous a type granitoids in the tengchong lianghe tin belt of southwestern china evidences from zircon u pb ages and hf o isotopes and whole rock sr nd isotopes abstract the tengchong lianghe tin belt is the most importantpart of the tin metallogenic belt in southwest china s sanjiang metallogenic province in this district two a type granite plutons that are spatially associated with the tin deposits have recently been discovered these granitoids are dominated by biotite granites with weakly peraluminous to metaluminous compositions high sio2 contents 73 3 76 2 wt and high alkali contents k2o na2o 8 3 9 17 wt trace element spider diagrams show that these granitoids are also clearly enriched with the large ion lithophile elements rb th u and k but are markedly depleted in ba and sr they are significantly depleted in the high field strength elements nb and ti but are enriched with zr and hf these rocks have relatively high zircon saturation temperatures 774 833 c high zr nb ce y contents 272 416 ppm and 10 000 ga al ratios almost 2 7 that are typical of a type granites they also have high total rare earth element ree contents 174 404 ppm and relatively flat chondrite normalized ree patterns with significantly negative eu anomalies la icp ms zircon u pb dating results indicate that the emplacement of these two granite plutons occurred during the early tertiary 52 7 0 3 53 0 0 4 ma and the late cretaceous 73 3 0 5 73 3 0 5 ma periods respectively isotopic compositions show that the granitoids have highly variable 87sr 86sr i ratios 0 7182 0 7457 relatively constant low end t values 11 2 to 12 4 and ancient nd and hf model ages 1 56 1 88 ga suggesting that they were derived from the partial melting of the paleoproterozoic continental crust their zircon 18o values 6 6 8 5 and ehf values from 8 6 to 11 3 also suggest that these granitoids mainly originated from the middle lower continental crust consisting of mafic and metasedimentary rocks such geochemical characteristics indicate that these two a type granite plutons were generated by the partial melting of paleoproterozoic mafic and the metasedimentary basement of the tengchong block in a post collisional or syn collisional extensional setting of the neo tethy anorogenic zone during the late cretaceous early cenozoic the late cretaceous granitoids were probably associated with the subduction of the neo tethyan plate under the post collisional extension of the western burma and tengchong microplates collision during the jurassic early cretaceous the early tertiary granitoids might be the syn collisional product of stretching relaxation during the middle and late main collisional period 55 41 ma between india and asia

ries and chicxulub impact craters on earth provide insights for martian ejecta blankets terrestrial impact structures provide field evidence for cratering processes on planetary bodies that have an atmosphere and volatiles in the target rocks here we discuss two examples that may yield implications for martian craters 1 recent field analysis of the ries crater has revealed the existence of subhorizontal shear planes detachments in the periphery of the crater beneath the ejecta blanket at 0 9 1 8 crater radii distance their formation and associated radial outward shearing was caused by weak spallation and subsequent dragging during deposition of the ejecta curtain both processes are enhanced in rheologically layered targets and in the presence of fluids detachment faulting may also occur in the periphery of martian impacts and could be responsible for the formation of lobe parallel ridges and furrows in the inner layer of double layer and multiple layer ejecta craters 2 the ejecta blanket of the chicxulub crater was identified on the southeastern yucatn peninsula at distances of 3 0 5 0 crater radii from the impact center abundance of glide planes within the ejecta and particle abrasion both rise with crater distance which implies a ground hugging erosive and cohesive secondary ejecta flow systematic measurement of motion indicators revealed that the flow was deviated by a preexisting karst relief in analogy with martian fluidized ejecta blankets it is suggested that the large runout was related to subsurface volatiles and the presence of basal glide planes and was influenced by eroded bedrock lithologies it is proposed that ramparts may result from enhanced shear localization and a stacking of ejecta material along internal glide planes at decreasing flow rates when the flow begins to freeze below a certain yield stress

petrogenesis of the early eocene i type granites in west yingjiang sw yunnan and its implication for the eastern extension of the gangdese batholiths abstract this study reports new zircon u pb and hf isotopes and whole rock elemental and sr nd isotopic data for the gneissic granite and leucogranite from the nabang metamorphic zone yingjiang area west yunnan sw china the metamorphosed granitoids crystallized during the early eocene 55 50 ma with zircons showing ehf t values from 11 to 5 3 and crustal model ages of 1 5 to 0 42 ga comparable to those of coeval i type granitoids from the gangdese batholith southern lhasa the rocks are characterized by metaluminous and weakly peraluminous hornblende bearing gneissic granites with a cnk 0 95 1 09 na2o k2o coupled with low initial sr isotopic values of 0 7049 0 7070 and high end t values from 1 1 to 7 1 the rocks were derived from crustal materials involving ancient upper crust sedimentary and juvenile mantle derived rocks together with available data from nearby regions it is proposed that the early eocene granitoids in the nabang and tengliang area can be correlated to the gangdese granitoids and represent the southeastward continuation of the magmatic arc resulting from the neotethyan subduction in southern tibet the petrogenesis of early eocene granitoids in western yunnan was probably related to the rollback of the subducting neotethyan slab that caused the remelting of the crustal materials newly modified by the underplated basaltic magma

kinematics of the tengchong terrane in se tibet from the late eocene to early miocene insights from coeval mid crustal detachments and strike slip shear zones abstract it is generally believed that the extrusion of se tibet was bounded by the dextral gaoligong and the sinistral ailaoshan red river strike slip shear zones from the oligocene to early miocene this study integrates field mapping structural analysis and geochronology in western yunnan china where foliated precambrian basement rocks and late cretaceous to early eocene plutons are exposed to the west of the gaoligong shear zone we found that late eocene to early miocene flat lying ductile shear zones were kinematically related to steeply dipping strike slip shear zones four elongated gneiss domes donghe guyong yingjiang and sudian are cored by high grade metamorphic rocks and pre kinematic granite plutons and bounded by top to ne detachments and ne trending dextral strike slip shear zones zircon u pb ages from la icp ms analysis and 40 ar 39 ar ages of micas and hornblende demonstrate that the flat lying donghe detachment 35 15 ma and the nabang dextral strike slip shear zone 41 19 ma were sites of prolonged mostly coeval ductile deformation from amphibolite to greenschist facies metamorphism the gaoligong shear zone experienced dextral shearing under similar metamorphic conditions between 32 and 10 ma consistent 40 ar 39 ar ages of hornblende from the three shear zones indicate their contemporaneity at mid crustal depth causing the rapid exhumation and sw ward extrusion of the tengchong terrane the strain geometry and shear zone kinematics in the tengchong terrane are interpreted with folding of the anisotropic lithosphere around a vertical axis i e the northeast corner of the indian plate since 41 ma the newly discovered ne trending sudian yingjiang and lianghe strike slip shear zones are subordinate ductile faults accommodating the initially rapid clockwise rotation of the tengchong terrane the detachments caused mid crustal decoupling and faster sw ward extrusion below the sedimentary cover whereas the strike slip shear zones accommodated extrusion and clockwise rotation of the tengchong terrane around the proto eastern himalayan syntaxis since the late eocene

application of nondestructive testing methods to study the damage zone underneath impact craters of memin laboratory experiments within the framework of the multidisciplinary experimental and modeling impact research network memin research group the damage zones underneath two experimentally produced impact craters in sandstone targets were investigated using several nondestructive testing ndt methods the 20 20 20 cm sandstones were impacted by steel projectiles with a radius of 1 25 mm at approximately 5 km s 1 resulting in craters with approximately 6 cm diameter and approximately 1 cm depth ultrasound us tomography and vibrational analysis were applied before and after the impact experiments to characterize the damage zone and micro computer tomography l ct measurements were performed to visualize subsurface fractures the newly obtained experimental data can help to quantify the extent of the damage zone which extends to about 8 cm depth in the target the impacted sandstone shows a local p wave reduction of 18 below the crater floor and a general reduction in elastic moduli by between approximately 9 and approximately 18 depending on the type of elastic modulus the results contribute to a better empirical and theoretical understanding of hypervelocity events and simulations of cratering processes

petrogenesis of the early cretaceous granitoids and its mafic enclaves in the northern tengchong terrane southern margin of the tibetan plateau and its tectonic implications abstract cretaceous granites are widely exposed in the tengchong terrane that is the southern extension of the tibetan plateau resulting from the evolution of the tethys they therefore play a critical role in deciphering the tethys evolution and the growth of the tibetan plateau in this paper we present new zircon u pb dating and hf isotopic results along with whole rock elemental and sr nd isotopic data of the granitoids from the lushui pianma lp batholith and its mafic enclaves and the strongly deformed granites from the gaoligong shear zone in the northern tengchong terrane the dating results show that both the lp granitic batholith and the strongly deformed granites in the gaoligong shear zone formed in the early cretaceous of 122 110 ma they are composed of granodiorite quartz monzodiorite and monzogranite with minor gabbroic enclaves mineralogically and geochemically the granitoids in the lp batholith particularly for the less evolved ones display a metaluminous nature and an affinity to i type granite all the granitoids are characterized by similar rare and trace patterns and whole rock nd and zircon hf isotopic compositions indicating a common origin the sodium rich feature for the less evolved dioritic rocks and the predominantly negative zircon ehf t and whole rock end t values for all the granitoids demonstrate that they were derived mainly from the partial melting of the mesoproterozoic metabasic rocks likely the basement rocks of the gaoligong group in the lower crust of the tengchong terrane in the case of the mafic enclaves they share similar mineralogical assemblages and nd hf isotopic compositions to its host granodiorite indicating a cognate origin with the latter in combination with previous data for the granitoids in the tengchong terrane our study further illustrates that the early cretaceous granitic rocks are dominated by metaluminous i type granites with minor highly fractionated peraluminous i type granites rather than the dominant s type granites as assumed before the new identification of the myitkyina meso tethys ophiolitic suite in eastern myanmar together with regional early cretaceous magmatic and sedimentation patterns indicate that these early cretaceous magmatic rocks were the products of the evolution of the myitkyina tethys ocean which was related to post collisional slab breakoff

nb ta fractionation in peraluminous granites a marker of the magmatic hydrothermal transition in their late stages of evolution peraluminous granitic melts exsolve large amounts of fluidswhich can modify the chemical composition of granitic whole rock samples the niobium tantalum nb ta ratio is expected to decrease during the magmatic differentiation of graniticmelts but the behavior of both elements at the magmatic hydrothermal transition remainsunclear using a compilation of whole rock geochemical data available in the literature wedemonstrate that fractional crystallization alone is not sufficient to explain the distribution ofnb ta in most peraluminous granites however we notice that most of the granitic samplesdisplaying evidence of interactions with fluids have nb ta 5 we propose that the decreaseof the nb ta ratio in evolved melts is the consequence of both fractional crystallization andsub solidus hydrothermal alteration we suggest that the nb ta value of 5 fingerprints themagmatic hydrothermal transition in peraluminous granites furthermore a nb ta ratio of 5appears to be a good marker to discriminate mineralized from barren peraluminous granites

gold and metal enrichment in natural granitic melts during fractional crystallization metal evolution in a composite granitic pluton was tracked by analyzing melt inclusions in 11 quartz samples from 7 zones at the timbarra gold deposit australia we present the first quantitative microanalyses of gold au in granitic silicate melt inclusions using laser ablation inductively coupled plasma mass spectrometry and show how au and other metals become enriched during fractional crystallization in a granite intrusion au was enriched during fractionation from a monzogranite to a highly fractionated alkali feldspar granite similar enrichment behavior for other metals implies that no gold enriched precursor melt is required and fractional crystallization can enrich the au concentration to economic levels the low content of accessory oxides and sulfides the absence of early cl bearing fluids the volatile content in the melt and a prolonged crystallization constitute important factors for extensive metal enrichment during crystal fractionation these characteristics play a crucial role in felsic highly fractionated plutons and their associated deposits such as intrusion related au deposits the gold enrichment during fractionation also implies that au is directly sourced from the granites

an evolving magmatic hydrothermal system in the formation of the mesozoic meishan magnetite apatite deposit in the ningwu volcanic basin eastern china abstract the meishan iron deposit contains 338 mt of iron ore reserves at 39 fe and represents the largest magnetite apatite deposit in the ningwu basin of eastern china controversy has long existed about whether this deposit had a hydrothermal or iron oxide melt origin iron mineralization is genetically related to plutons that are composed of gabbro diorite which were emplaced at 130 1 ma these rocks have sio2 contents of 51 72 54 60 wt na2o contents of 3 47 4 04 wt k2o contents of 2 02 2 69 wt and k2o na2o ratios of 0 51 0 73 these rocks are enriched in liles and lrees and depleted in nb ta and ti which indicates that the magma originated through partial melting of an enriched lithospheric mantle source in a subduction environment a pattern of decreasing initial sr isotopic ratios and increasing end t values with time in early cretaceous magmatic rocks of the ningwu basin may indicate incorporation of increasing proportions of asthenospheric mantle material into the source magma which is consistent with the processes of lithospheric thinning and asthenospheric upwelling in eastern china related to mesozoic subduction of the paleo pacific plate two stages of magnetite are found in the gabbro diorite 1 early crystallized magnetite as euhedral subhedral crystals in larger clinopyroxene crystals and 2 later crystallized magnetite and accompanying ilmenite grains in the voids between plagioclase and clinopyroxene crystals the formation of magnetite before clinopyroxene combined with the results of fe ti oxide geothermometry and analysis of magnetite v content indicates that the oxygen fugacity of the source magma was greater than fmq 2 2 at an early stage 640 c but decreased to fmq 2 66 as abundant magnetite crystallized at a later stage 489 c the early crystallization of magnetite at a high oxygen fugacity does not support a fenner evolution trend for the primitive magma and diminishes the likelihood of liquid immiscibility which could have generated an iron rich melt and is thus inconsistent with an iron oxide melt origin for the meishan iron deposit the 34s values of pyrite 6 6 15 1 and anhydrite 15 6 16 9 in the deposit and the occurrence of evaporites under the volcanic rocks likely indicate that the iron ores and alteration rocks of the meishan deposit were formed by the circulation of fluids of evaporitic origin driven by heat from the hypabyssal gabbro diorite intrusives in the late magmatic stage oxygen fugacity decreased to a reducing range triggering the reduction of sulfate to reduced sulfur and leading to local gold and pyrite mineralization

coesite bearing eclogite from the dabie mountains in central china coesite and coesite pseudomorphs are recognized in eclogite from the dabie mountains a collision zone between the sino korean and yangtze cratons in central china this third known occurrence of coesite in deep crustal rocks is within an archean gneiss terrane and is the first locality where coesite has been identified as an inclusion in both omphacite and garnet crystals at the same location coesite bearing eclogite is estimated to form at pressures of 28 kbar and temperatures from 600 to 710 c the dabie mountains eclogite underwent retrograde metamorphism to amphibolite facies after its formation the preservation of coesite in eclogite is found to be strongly controlled by the pressure temperature time path that coesite bearing eclogite followed during its uplift and retrograde metamorphism

the carancas meteorite impact crater peru geologic surveying and modeling of crater formation and atmospheric passage the recent carancas meteorite impact event caused a worldwide sensation an h4 5 chondrite struck the earth south of lake titicaca in peru on september 15 2007 and formed a crater 14 2 m across it is the smallest youngest and one of two eye witnessed impact crater events on earth the impact violated the hitherto existing view that stony meteorites below a size of 100 m undergo major disruption and deceleration during their passage through the atmosphere and are not capable of producing craters fragmentation occurs if the strength of the meteoroid is less than the aerodynamic stresses that occur in flight the small fragments that result from a breakup rain down at terminal velocity and are not capable of producing impact craters the carancas cratering event however demonstrates that meter sized stony meteoroids indeed can survive the atmospheric passage under specific circumstances we present results of a detailed geologic survey of the crater and its ejecta to constrain the possible range of impact parameters we carried out numerical models of crater formation with the isale hydrocode in two and three dimensions depending on the strength properties of the target the impact energies range between approximately 100 1000 mj 0 024 0 24 t tnt by modeling the atmospheric traverse we demonstrate that low cosmic velocities 12 1 4 kms 1 and shallow entry angles 20 are prerequisites to keep aerodynamic stresses low 10 mpa and thus to prevent fragmentation of stony meteoroids with standard strength properties this scenario results in a strong meteoroid deceleration a deflection of the trajectory to a steeper impact angle 40 60 and an impact velocity of 350 600 ms 1 which is insufficient to produce a shock wave and significant shock effects in target minerals aerodynamic and crater modeling are consistent with field data and our microscopic inspection however these data are in conflict with trajectories inferred from the analysis of infrasound signals

trace inheritance clarifying the zircon o hf isotopic fingerprint of i type granite sources implications for the restite model abstract early to mid carboniferous i type granites distributed in a broad meridional belt west of sydney southeastern australia represent the last phase of granite magmatism in the southern lachlan fold belt rare inherited zircon in the granites in combination with zircon precipitated from the melt phase of the magmas provides direct evidence of the nature and age of the source rocks from which the granites were derived and the isotopic compositions of those rocks most granites from the north and central parts of the belt represented by the wuuluman home rule oberon and lett plutons 334 3 328 4 339 2 and 328 2 ma respectively are characterized by scarce inherited zircon dominantly of siluro devonian age consistent with all being derived from a common zircon poor source rock of mid to late devonian age based on the isotopic compositions of the igneous zircon rims that source was relatively homogeneous and immature 18ozrn 6 7 ehf t 0 4 two samples of the tarana pluton 331 2 ma near the centre of the belt show evidence for heterogeneity in that source and the presence of a more evolved component that is also more zircon rich together with the lett pluton from the same geochemical suite their zircon rim compositions define a mixing array between more and less evolved end members 18ozrn 5 5 9 5 ehf t 4 4 only in the southern chapmans creek pluton 327 3 ma is there clear evidence that the source of the granite also contained a minor component with a similar older protolith to the lfb early palaeozoic sediments that host most of the lfb pre carboniferous granites presence of that component which overwhelmingly dominates the inheritance in the pre carboniferous granites is also reflected in a slightly elevated whole rock initial 87sr 86sr 0 7050 and igneous 18ozrn ca 7 5 but not in the igneous zircon ehf t ca 2 the amount of restitic zircon in granite is determined by not only the proportion of restite present but also the zircon contents of the various source rock components the process of restite unmixing does not necessarily mean that more mafic restite rich granites will contain more inherited zircon

experimental melts from crustal rocks a lithochemical constraint on granite petrogenesis abstract many studies of experimental petrology have devoted to partial melting of crustal rocks in order to provide lithochemical constraints on granite petrogenesis this paper presents a compilation and synthesis of available experimental data for the major element compositions of felsic melts derived from partial melting of natural or synthetic materials in the compositional range of crustal rocks the experimental melts are categorized into four types according to the species of hydrous minerals in starting materials i amphibole bearing ii amphibole and biotite bearing iii biotite bearing and iv biotite and muscovite bearing if dehydration melting takes place at normal crustal conditions p 5 10 kbar t 1000 c experimental melts are rich in sio 2 but poor in mgo feo t except those from amphibole bearing sources a comprehensive comparison of compositions between experimental melts and starting materials indicates that geochemical fractionation is variable for different major elements and their ratios source composition and melting temperature exert stronger controls on the compositional variations of experimental melts than pressure and fluid by comparing the experimental melts with natural granites the following insights into granite petrogenesis can be got 1 while peritectic assemblage entrainment may be the dominant mechanism for the compositional variations of garnet cordierite rich s type granites fractional crystallization of diverse melts from heterogeneous metasedimentary precursors probably governs the compositional variations of garnet cordierite poor s type granites 2 relatively k 2 o rich mafic to intermediate rocks are appropriate sources for calc alkaline i type granites the compositional variations of calc alkaline granites are jointly controlled by peritectic assemblage entrainment and subsequent fractional crystallization 3 while dehydration melting at t 950 c is appropriate for the production of ferroan and alkali rich granitic melts from intermediate magnesian tonalite or granodiorite it is also possible for ferroan alkali rich and fluorine rich granitic melts to be produced by dehydration melting of moderately magnesian mica bearing materials at t 900 c nevertheless the low t melts are more peraluminous than the high t ones therefore the composition of source rocks exerts the first order control on the composition of granitic melts in closed systems in addition the dehydration melting of crustal rocks under different conditions is also responsible for variations in the composition of granites

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

the memin research unit scaling impact cratering experiments in porous sandstones the memin research unit multidisciplinary experimental and modeling impact research network is focused on analyzing experimental impact craters and experimental cratering processes in geological materials memin is interested in understanding how porosity and pore space saturation influence the cratering process here we present results of a series of impact experiments into porous wet and dry sandstone targets steel iron meteorite and aluminum projectiles ranging in size from 2 5 to 12 mm were accelerated to velocities of 2 5 7 8 km s 1 yielding craters with diameters between 3 9 and 40 cm results show that the target s porosity reduces crater volumes and cratering efficiency relative to nonporous rocks saturation of pore space with water to 50 and 90 increasingly counteracts the effects of porosity leading to larger but flatter craters spallation becomes more dominant in larger scale experiments and leads to an increase in cratering efficiency with increasing projectile size for constant impact velocities the volume of spalled material is estimated using parabolic fits to the crater morphology yielding approximations of the transient crater volume for impacts at the same velocity these transient craters show a constant cratering efficiency that is not affected by projectile size

geochronological geochemical and sr nd hf isotopic constraints on the petrogenesis of late cretaceous a type granites from the sibumasu block southern myanmar se asia abstract the late cretaceous to paleogene granitoids occur widespread in the sibumasu block within myanmar se asia which show a close association with tin tungsten mineralization however the precise timing petrogenesis and tectonic significance of these granitoids are poorly constrained so far in this study we present a detailed study on geochronology elemental and sr nd hf isotopic geochemistry for the hermyingyi and taungphila granites in southern myanmar with the aim of determining their petrogenesis and tectonic implications la icp ms u pb dating of zircon grains from the two granites yield ages of 69 70 ma indicating a late cretaceous magmatic event these granitic rocks are weakly peraluminous and belong to the high k calc alkaline series they are both characterized by high sio2 k2o na2o feot feot mgo and ga al ratios and low al2o3 cao mgo p2o5 and tio2 contents enriched in rb th u and y but depleted in ba sr p and eu suggesting an a type granite affinity moreover they display prominent tetrad ree patterns and non charac trace element behavior which are common in late magmatic differentiates with strong hydrothermal interaction or deuteric alteration the granites belong to a2 type and probably formed at a high temperature and anhydrous condition they have zircon ehf t values from 12 4 to 10 0 and whole rock end t values from 11 3 to 10 6 with paleoproterozoic tdm2 ages 1741 1922 ma for both hf and nd isotopes geochemical and isotopic data suggest that these a type granites were derived from partial melting of the paleoproterozoic continental crust dominated by metaigneous rocks with tonalitic to granodioritic compositions without significant input of mantle derived magma and followed by subsequent fractional crystallization by integrating all available data for the regional tectonic evolution in se asia and adjacent regions we attribute the formation of the late cretaceous a type granites to a back arc extension in the hinterland behind the subduction zone which is induced by the rollback of the flat neo tethyan subducting slab around ca 70 ma

tracing the transhimalayan magmatic belt and the lhasa block southward using zircon u pb lu hf isotopic and geochemical data cretaceous cenozoic granitoids in the tengchong block yunnan china abstract a number of cretaceous cenozoic granitoid bodies in the tengchong block were analyzed for their u pb zircon ages lu hf zircon isotopic compositions and whole rock geochemistry zircons from six different granite bodies in the central tengchong block have weighted mean 206 pb 238 u ages ranging from 76 to 65 ma and negative e hf t values ranging from 2 7 to 15 5 with t dm c ranging from 1312 to 1928 ma one dextrally sheared and gneissic granodiorite sample of the nabang shear zone in the western tengchong block yielded a weighted mean 206 pb 238 u age of 19 7 0 4 ma and positive e hf t values ranging from 0 2 to 10 7 with t dm c ranging from 418 to 1092 ma the late cretaceous granites have metaluminous and peraluminous affinities with strong enrichment of u and th and significant negative anomalies of eu ba sr nb p and ti the miocene granodiorite displays strong negative anomalies of nb ta p and ti and a weak negative eu anomaly the data suggest that the late cretaceous granites in the tengchong block were derived from partial melting of ancient most likely proterozoic continental crustal material whereas the miocene gneissic granodiorite was derived from partial melting of juvenile crustal material possibly within a supra subduction setting and intruded synkinematically into the active nabang shear zone lu hf isotopic data of late cretaceous paleocene granites are indistinguishable from those of granites of the central lhasa block thus we tentatively correlate the late cretaceous granites of the tengchong block with those of the central lhasa block the boundary between the south and central lhasa blocks in western tengchong may be exposed in the nne striking dextral nabang shear zone along the chinese myanmar border region which hosts early eocene granitoids with e hf t values 0 the lu hf data of the zircons from the gneissic miocene granodiorite indicate a juvenile crustal substrate in the western tengchong block as well the synkinematic miocene granodiorite provides an important age constraint for dextral shear at mid crustal levels which was active until at least c 19 20 ma in the nabang shear zone this miocene intrusion may be a first indication that active margin tectonics lasted 20 25 ma longer than in the gangdese belt and possibly was associated with deformation partitioning in the hinterland produced by increasing obliquity of subduction during clockwise rotation of sundaland during the india asia collision

non intrusive measurements of crater growth abstract an experimental technique to measure crater growth is presented whereby a high speed video captures profiles of a crater forming after impact obtained using a vertical laser sheet centered on the impact point unlike previous so called quarter space experiments where projectiles were launched along a transparent plexiglas sheet so that growth of half a crater could be viewed the use of the laser sheet permits viewing changes in crater shape without any physical interference to the cratering process this technique indicates that for low velocity impacts 300 m s into 220 m glass beads that are without cohesion and where the projectile is not disrupted craters initially grow somewhat proportionally but that later their depths remain essentially constant while their diameters continue to expand in addition these experiments indicate that as the impact velocity increases the rate of growth and the transient depth to diameter ratio at the end of ejecta excavation decreases these last two observations are probably due to the large time of penetration of the projectile which becomes a significant fraction of the time of crater formation this is contrary to the expectations for the scaling rules which assumes a point source very high curtain angles 45 are also seen and could be due to the low friction angle of the target significant crater modification which is rarely seen in quarter space experiments is also observed and appears to be controlled by the dynamic angle of repose of the target these latter observations indicate that differences in target friction angles may need to be considered when determining near rim ejecta mass distributions and large scale crater modification processes on the planets

tectono magmatic evolution of the gaoligong belt southeastern margin of the tibetan plateau constraints from granitic gneisses and granitoid intrusions abstract the gaoligong belt is located in the southeastern margin of the tibetan plateau and is bound by the tengchong and baoshan blocks this paper presents new data from zircon geochronology geochemistry and whole rock sr nd pb hf isotopes to evaluate the tectonic evolution of the gaoligong belt the major rock types analysed in the present study are granitic gneiss granodiorite and granite they are metaluminous to peraluminous and belong to high k calc alkaline series laser ablation inductively coupled plasma mass spectrometry la icp ms analyses of zircons from nine granitic rocks yielded crystallization ages of 495 487 ma 121 ma 89 ma and 70 63 ma the granitoids can be subdivided into the following four groups 1 early paleozoic granitic gneisses with high e nd t and e hf t values of 1 06 to 3 45 and 1 16 to 2 09 and model ages of 1 16 ga to 1 33 ga and 1 47 ga to 1 63 ga respectively their variable 87 sr 86 sr and pb values resemble the characteristics of the early paleozoic pinghe granite in the baoshan block our data suggest that the rocks were derived from the break off of the proto tethyan oceanic slab between the outboard continent and the baoshan block which induced the partial melting of mesoproterozoic pelitic sources mixed with depleted mantle materials 2 early cretaceous granodiorites with low e nd t and e hf t values of 8 92 and 4 91 with nd and hf model ages of 1 41 ga and 1 49 ga respectively these rocks have high initial 87 sr 86 sr 0 711992 and lower crustal pb values suggesting that they were derived from mesoproterozoic amphibolites with tholeiitic signature leaving behind granulite residue at the lower crust 3 early late cretaceous granites with low e nd t and e hf t values of 9 58 and 4 61 with nd and hf model ages of 1 43 ga and 1 57 ga respectively these rocks have high initial 87 sr 86 sr 0 713045 and lower crustal pb isotopic values these rocks were generated from the partial melting of mesoproterozoic metapelitic sources resulting from the delamination of thickened lithosphere following the closure of the bangong nujiang ocean and collision of the lhasa qiangtang blocks 4 late cretaceous to paleogene granitic gneisses with low e nd t and e hf t values of 4 41 to 10 and 5 95 to 8 71 nd model ages ranging from 1 08 ga to 1 43 ga and hf model ages from 1 53 ga to 1 67 ga respectively these rocks show high initial 87 sr 86 sr 0 713201 and 714662 and lower crustal pb values the data suggest that these rocks are likely related to the eastward subduction of the neo tethyan oceanic slab which induced partial melting of mesoproterozoic lower crustal metagreywacke the results presented in this study from the gaoligong belt offer important insights on the evolution of the proto tethyan bangong nujiang and neo tethyan oceans in the southeastern margin of the tibetan plateau

the key role of mica during igneous concentration of tantalum igneous rocks with high ta concentrations share a number of similarities such as high ta nb low ti lree and zr concentrations and granitic compositions these features can be traced through fractionated granitic series formation of ta rich melts begins with anatexis in the presence of residual biotite followed by magmatic crystallization of biotite and muscovite crystallization of biotite and muscovite increases ta nb and reduces the ti content of the melt titanium bearing oxides such as rutile and titanite are enriched in ta and have the potential to deplete ta at early stages of fractionation however mica crystallization suppresses their saturation and allows ta to increase in the melt saturation with respect to ta and nb minerals occurs at the latest stages of magmatic crystallization and columbite can originate from recrystallization of mica we propose a model for prediction of intrusion fertility for ta

early cretaceous highly fractionated i type granites from the northern tengchong block western yunnan sw china petrogenesis and tectonic implications abstract western yunnan an important constituent of the southeastern segment of the east tethyan tectonic domain lies along a transformed orientation from the nww trending himalayan tethyan segment to the northerly trending southeast asian segment however the geodynamical setting of the early cretaceous tectonothermal magmatism along the bangong nujiang lushui luxi ruili belt as the tethyan branch in western yunnan sw china remains controversial the donghe granitoid which is located between the gaoligong and tengliang belts in the northern tengchong block reveals its petrogenesis and its tectonics both of which play a vital role in resolving previous disputes our zircon laser ablation inductively coupled plasma mass spectrometry u pb dating of granites from the donghe batholith yields ages of 119 9 0 9 130 6 2 5 ma these granites display features typical of highly fractionated i type granites high sio 2 contents 71 wt high k contents k 2 o 3 88 5 66 wt calc alkaline character slight peraluminosity a cnk 1 02 1 16 and a highly differentiated index ranging from 83 6 to 95 6 in addition as sio 2 contents increase the rare earth element ree abundances especially heavy ree abundances and ree pattern slopes change gradually but the negative eu anomalies increase sharply while the degree of enrichment in rb th u and pb and depletion in ba nb sr p and ti are enhanced these features indicate that k feldspar plagioclase biotite amphibole apatite sphene garnet and fe ti oxides such as ilmenite play the major role in the fractional crystallization process the high initial 87 sr 86 sr 0 7067 and 0 7079 and negative e nd t values 8 6 to 10 1 with t 2dm ranging from 1 39 to 1 49 ga indicate that the sources were mainly derived from the mature ancient middle to lower crust and minor mantle derived materials the initial 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios of 18 462 18 646 15 717 15 735 and 38 699 39 007 respectively signify that some subduction related material such as ocean island volcanic rocks and mature arc primitive rocks may be involved as sources based on an analysis of similar zircon saturated temperature and geochemical characteristics of typical highly fractionated i type granites in se and sw china and consideration of the regional geological setting we suggest that the parent magma may be derived from the ancient middle to lower continental crust and mantle derived basaltic magma these were generated in the setting of a westward subducted lushui luxi ruili llr tethyan oceanic slab where mantle wedge derived sources provided enough heat and material to melt the middle to lower ancient crust taking into account the temporal spatial distributions of early cretaceous magmatic rocks in the region we further suggest the existence of an andean type active continental margin from the lhasa block to the tengchong block along the bangong nujiang llr tethys ocean during the early cretaceous

cassiterite la mc icp ms u pb and muscovite 40 ar 39 ar dating of tin deposits in the tengchong lianghe tin district nw yunnan china the tengchong lianghe tin district in northwestern yunnan china is an important tin mineralization area in the sanjiang tethyan metallogenic domain there are three n s trending granite belts in the tengchong lianghe area with emplacement ages ranging from early cretaceous to late cretaceous and early cenozoic tin mineralization is spatially associated with these granitic rocks however the petrogenetic link between the tin deposits and the host granites is not clear because of the lack of age data for the tin mineralization we investigate the possibility of direct dating of cassiterite from three typical tin deposits in the tengchong lianghe tin district using laser ablation multicollector inductively coupled plasma mass spectrometry la mc icp ms in situ la mc icp ms dating of seven cassiterite samples from the lailishan lls 1 and lls 2 xiaolonghe xlh wds dsp and hjs and tieyaoshan tys tin deposits yielded well defined 206pb 207pb 238u 207pb isochron ages to assess the accuracy of the in situ u pb dating of cassiterite 40ar 39ar dating of coexisting muscovite in samples lls 1 dsp and tys was also performed the cassiterite in situ u pb ages 47 4 2 0 71 9 2 3 and 119 3 1 7 ma respectively are in excellent agreement with the coexisting muscovite 40ar 39ar ages 48 4 0 3 71 9 1 4 and 122 4 0 7 ma respectively the u pb ages of cassiterite combined with the 40ar 39ar ages of muscovite indicate that there are three tin mineralization events in this district the lailishan tin deposit at 47 4 2 0 to 52 2 7 ma the xiaolonghe tin deposit at 71 6 2 4 to 3 9 2 0 ma and the tieyaoshan tin deposit at 119 3 1 7 to 122 5 0 7 ma these ages are highly consistent with the zircon u pb ages of the host granites it is su ggested that the cretaceous tin mineralization might have taken place in a subduction environment while the early tertiary tin metallogenesis was in a postcollisional geodynamic setting

the extra large light gas gun of the fraunhofer emi applications for impact cratering research abstract the extra large light gas gun xllgg at the fraunhofer ernst mach institut emi efringen kirchen germany is a two stage light gas gun that can accelerate projectile masses of up to 100 g up to velocities of 6 km s 1 the accelerator s set up allows various combinations of pump and launch tubes for applications in different fields of hypervelocity impact research in the framework of the memin multidisciplinary experimental and modeling impact research network program the xllgg is used for mesoscale cratering experiments with projectiles made of steel and of iron meteorites and targets consisting of sandstone and other rocks the craters produced with this equipment reach a diameter of up to 40 cm a size unique in laboratory cratering research with the implementation of neural networks the acceleration process is being optimized currently yielding peak velocities of 7 8 km s 1 for a 100 g projectile here we summarize technical aspects of the xllgg

high silica granites terminal porosity and crystal settling in shallow magma chambers abstract high silica 70 wt sio2 granites hsgs are important carriers of highly incompatible elements thus understanding their origin is relevant to understanding how the composition of the continental crust evolves we examined a large scale geochemical study of plutons in the peninsular ranges batholith in southern california usa to better understand the petrogenetic relationships between hsgs and the batholith using highly incompatible and compatible elements we show that hsgs represent residual liquids within a felsic 69 72 wt sio2 magmatic crystal mush at crystal fractions of 50 60 and residual liquid fractions of 40 50 trace element systematics show that separation of the hsg liquid from the crystal mush is inefficient such that no more than 70 80 of the hsg is fully extracted and the remaining greater than 20 30 remains trapped in cumulate mush we find little evidence of more efficient liquid crystal segregation which suggests that compaction induced segregation may be too slow to be important on a large scale instead the terminal porosity of 20 30 coincides with theoretical maximum packing fraction of unimodal particles settled out of suspension 0 74 which may indicate that crystal settling perhaps in the form of hindered settling drives segregation of viscous silicic melts and crystals unlike compaction settling operates on timescales of 1 10 ky fast enough to generate large volumes of hsg and complementary cumulates with trapped melt before magma chambers freeze many felsic plutons may thus be cumulates but because of trapped melt they are difficult to geochemically distinguish from plutons whose compositions fall along liquid lines of descent the approach here using a combination of highly incompatible and compatible elements provides a way of identifying and quantifying trapped melt fractions finally we show that hsgs appear to form only in the shallow crust

tethys tectonic evolution and its bearing on the distribution of important mineral deposits in the sanjiang region sw china abstract the sanjiang region in se tibet plateau and nw yunnan is known to have formed by amalgamation of gondwana derived continental blocks and arc terranes as a result of oceanic subduction followed by continental collision from paleozoic to mesozoic in this paper we provide a synthesis of tectonic evolution magmatism and metallogeny in the region based on data from literatures early paleozoic ophiolites 473 439 ma in the changning menglian belt indicate the existence of a proto tethys ocean in this region two episodes of subduction related magmatism in the early paleozoic one occurred in the baoshan and tengchong blocks at 502 455 ma and the other occurred in the simao block at 421 401 ma are regarded as evidence for two different events of subduction of the proto tethys ocean at different locations the proto tethys was succeeded in early devonian by the paleo tethys which comprised the main ocean and three branches ailaoshan jinshajiang and garze litang the changning menglian main ocean existed from middle devonian to middle triassic the remnants of the oceanic crust are preserved in a few places in the longmu tso shuanghu suture as well as in the changning menglian ophiolite belt the eastward subduction of the main oceanic plate from early permian to early triassic formed a prominent arc terrane stretching 1500 km from yunnan to eastern tibet from the waning stage of subduction to post subduction numerous s type granite plutons with ages varying between 230 and 219 ma such as the lincang batholith in yunnan were emplaced at or close to the suture this event produced several hydrothermal w sn deposits in the region the tectonic evolution and associated magmatism of the jinshajiang and ailaoshan branch oceans are generally comparable to those of the main ocean however the branch oceans were subducted westward instead the garze litang branch ocean also underwent westward subduction from middle devonian to late triassic arc related high sr y porphyry intrusions and associated porphyry skarn cu mo au deposits are common in the jinshajiang ailaoshan region especially in the yidun arc which formed prior to jurassic the vms deposits in the sanjiang region formed in diverse tectonic settings including middle silurian back arc basins carboniferous oceanic islands paleozoic subduction zones and triassic post subduction rifting environments the mesozoic and early cenozoic evolution of the baoshan and tengchong blocks was largely influenced by eastward oceanic subduction of the meso and neo tethys from late permian to middle cretaceous and from late cretaceous to 50 ma respectively abundant early cretaceous granitoids and associated skarn type pb zn and sn fe deposits in the baoshan and tengchong blocks were produced in the background of the shan boundary oceanic slab subduction to the west and the break off of the nujiang bitu oceanic slab to the north the subduction of the neo tethys oceanic plate beneath the tengchong block from late cretaceous to paleogene formed abundant s type granitoids and many skarn type and greisen type sn w deposits granitoids formed at 105 to 81 ma and contemporaneous hydrothermal w mo ag and au deposits which temporally coincided with the subduction of the neo tethys are common in the yidun arc terrane

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

native titanium inclusions in the coesite eclogites from dabieshan china abstract microbeam analysis of eclogites from the ultrahigh pressure metamorphic belt in dabieshan china has revealed native titanium inclusions in garnets of coesite eclogite the inclusions are about 10 m in size have a submetallic luster from the thin oxidation film on the surface and are brown under reflected light this is the first report of native titanium inclusions in ultrahigh pressure eclogite

a crater and its ejecta an interpretation of deep impact we apply recently updated scaling laws for impact cratering and ejecta to interpret observations of the deep impact event an important question is whether the cratering event was gravity or strength dominated the answer gives important clues about the properties of the surface material of tempel 1 gravity scaling was assumed in pre event calculations and has been asserted in initial studies of the mission results because the gravity field of tempel 1 is extremely weak a gravity dominated event necessarily implies a surface with essentially zero strength the conclusion of gravity scaling was based mainly on the interpretation that the impact ejecta plume remained attached to the comet during its evolution we address that feature here and conclude that even strength dominated craters would result in a plume that appeared to remain attached to the surface we then calculate the plume characteristics from scaling laws for a variety of material types and for gravity and strength dominated cases we find that no model of cratering alone can match the reported observation of plume mass and brightness history instead comet like acceleration mechanisms such as expanding vapor clouds are required to move the ejected mass to the far field in a few hour time frame with such mechanisms and to within the large uncertainties either gravity or strength craters can provide the levels of estimated observed mass thus the observations are unlikely to answer the questions about the mechanical nature of the tempel 1 surface

trace element indicators of crystal accumulation in silicic igneous rocks abstract if fractional crystallization coupled with some crustal assimilation afc is the dominant process for generating evolved magmas in the earth s crust large quantities of igneous cumulates must be present in the rock record however despite some reported occurrences intermediate to silicic rocks characterized by an unambiguous crystal accumulation signature have remained elusive the signature is expected to be subtle in viscous silicic magmas and sensitive criteria need to be developed to test whether these cumulates are truly rare or simply difficult to discern we propose models that use specific trace element concentrations and ratios zr ba eu eu and zr hf within a well constrained framework for the physical extraction of liquid from crystals mostly occurring between 50 and 70 vol crystals to identify silicic cumulates the results of these models indicate that crystal accumulation or melt extraction has occurred in multiple natural examples around the world both in plutonic and volcanic realms however these examples were selected because they represent conditions that are most favorable high amount of melt extraction well constrained initial liquid compositions for unambiguously identifying cumulate residue in many cases we show that the trace element signature for crystal accumulation will remain largely concealed in addition the different liquid lines of descent related to the various tectonic settings on earth dry reduced in hot spots divergent margins and wetter more oxidizing in arc environments will lead to different trace element evolution and each criterion must be applied on a case by case basis despite these limitations the undeniable but subtle presence of silicic cumulates in the mid to upper crust lends support to the idea that igneous differentiation is dominantly driven by melt extraction from partially crystalline reservoirs

eoarchean to mesoarchean crustal evolution in the dharwar craton india evidence from detrital zircon u pb and hf isotopes abstract the formation and evolution of continental crust in the early earth are of fundamental importance in understanding the emergence of continents their assembly into supercontinents and evolution of life and environment the dharwar craton in southern india is among the major archean cratons of the world where recent studies have shown that the craton formation involved the assembly of several micro continents during meso to neoarchean through subduction accretion collision processes here we report u pb hf isotope data from detrital zircons in a suite of metasediments including quartz mica schist fuchsite quartzite and metapelite from the southern domain of the chitradurga suture zone that marks the boundary between the western and central dharwar craton morphology and internal structure of the zircon grains suggest that the dominant population was derived from proximal granitic felsic sources zircon u pb data are grouped into paleo mesoarchean and neoarchean to paleoproterozoic with peaks at 3227 ma and 2575 ma the age spectra of detrital zircon grains in combination with the lu hf isotopic analyses indicate sediment provenance from magmatic sources with model ages in the range of ca 3 67 to 2 75 ga a transition from dominantly juvenile to a mixture of juvenile and recycled crustal components indicate progressive crustal maturity the results from this study suggest major crustal growth events during ca 3 2 ga and 2 6 ga in dharwar our study provides insights into continental emergence weathering and detrital input through river drainage systems into the trench during eoarchean to mesoarchean

episodic growth of the gondwana supercontinent from hafnium and oxygen isotopes in zircon it is thought that continental crust existed as early as 150 million years after planetary accretion but assessing the rates and processes of subsequent crustal growth requires linking the apparently contradictory information from the igneous and sedimentary rock records for example the striking global peaks in juvenile igneous activity 2 7 1 9 and 1 2 gyr ago imply rapid crustal generation in response to the emplacement of mantle super plumes rather than by the continuous process of subduction yet uncertainties persist over whether these age peaks are artefacts of selective preservation and over how to reconcile episodic crust formation with the smooth crustal evolution curves inferred from neodymium isotope variations of sedimentary rocks detrital zircons encapsulate a more representative record of igneous events than the exposed geology and their hafnium isotope ratios reflect the time since the source of the parental magmas separated from the mantle these model ages are only meaningful if the host magma lacked a mixed or sedimentary source component but the latter can be diagnosed by oxygen isotopes which are strongly fractionated by rock hydrosphere interactions here we report the first study that integrates hafnium and oxygen isotopes all measured in situ on the same precisely dated detrital zircon grains the data reveal that crust generation in part of gondwana was limited to major pulses at 1 9 and 3 3 gyr ago and that the zircons crystallized during repeated reworking of crust formed at these times the implication is that the mechanisms of crust formation differed from those of crustal differentiation in ancient orogenic belts

a late cretaceous felsic magmatic suite from the tengchong block western yunnan integrated geochemical and isotopic investigation and implications for sn mineralization the tengchong block within the sanjiang tethys belt in the southeastern part of the tibetan plateau experienced a widespread intrusion of a felsic magmatic suite of granites in its central domain during late cretaceous times here we investigate the guyong and xiaolonghe plutons from this suite in terms of their petrological geochemical and sr nd zircon u pb and lu hf o isotopic features to gain insights into the evolution of the neo tethys the guyong pluton 76 ma is composed of metaluminous monzogranites and the xiaolonghe pluton 76 ma is composed of metaluminous to peraluminous medium and fine grained syenogranite a systematic decrease in eu ba sr p and ti concentrations a decrease in zr hf and lree hree ratios and an increase in the rb ba and ta nb ratios from the guyong to xiaolonghe plutons suggest fractional crystallization of biotite plagioclase k feldspar apatite ilmenite and titanite they also show the characteristics of i type granites the negative zircon ehf t isotopic values 10 04 to 5 22 and high 18o values 6 69 to 8 58 and the negative whole rock end t isotopic values 9 7 to 10 1 and high initial 87sr 86sr ratios 0 7098 0 7099 of the guyong monzogranite suggest that these rocks were generated by partial melting of the precambrian basement without mantle input the zircon ehf t isotopic values 10 63 to 3 04 and 18o values 6 54 to 8 69 of the xiaolonghe syenogranite are similar to the features of the guyong monzogranite and this similarity suggests a cogenetic nature and magma derivation from the lower crust that is composed of both metasedimentary and meta igneous rocks the xiaolonghe fine grained syenogranite shows an obvious rare earth element tetrad effect and lower nb ta ratios which indicate its productive nature with respect to ore formation in fact we discuss that the sn mineralization in the region was possible due to sn being scavenged from these rocks by exsolved hydrothermal fluids we correlate the late cretaceous magmatism in the central tengchong block with the northward subduction of the neo tethys beneath the burma tengchong block

tracing magma mixing in granite genesis in situ u pb dating and hf isotope analysis of zircons in situ zircon u pb and hf isotopic data have been determined for mafic microgranular enclaves and host granitoids from the early cretaceous gudaoling batholith in the liaodong peninsula ne china in order to constrain the sources and petrogenesis of granites the zircon u pb age of the enclaves 120 1 ma is identical to that of the host monzogranite 120 1 ma establishing that the mafic and felsic magmas were coeval the hf isotopic composition of the enclaves ehf t 4 5 to 6 2 is distinct from the host monzogranite ehf t 15 1 to 25 4 indicating that both depleted mantle and crustal sources contributed to their origin the depleted mantle component was not previously revealed by geochemical and nd and sr isotopic studies showing that zircon hf isotopic data can be a powerful geochemical tracer with the potential to provide unique petrogenetic information some wall rock contamination is indicated by inherited zircons with considerably older u pb ages and low initial hf isotopic compositions hafnium isotopic variations in early cretaceous zircons rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead mixing of mantle derived mafic magmas with crustal derived felsic magmas coupled with assimilation of wall rocks is compatible with the data

origin and evolution of the tengchong block southeastern margin of the tibetan plateau zircon u pb and lu hf isotopic evidence from the meta sedimentary rocks and intrusions abstract u pb ages and hf isotopic data from detrital zircons of gaoligongshan metamorphic complex and the carboniferous menghong group and igneous zircons from intrusions constrain the origin tectonic affinity east gondwana crustal evolution processes and the properties of regional high grade metamorphic rocks in the tengchong block of southeastern china three granites intruded into the tengchong block at 72 ma 114 ma and 122 ma detrital zircons range in age from archean to late ordovician for both the carboniferous menghong group and the gaoligongshan metamorphic complex analyses for these two units yield similar age clusters at 2 5 ga 1 6 ga 1 17 ga 0 95 ga and 0 65 0 5 ga as well as parallel hf isotopic distributions the protolith of the studied gaoligongshan complex in the tengchong block should deposit in the late paleozoic detrital zircon age distribution patterns of the carboniferous menghong group and the gaoligongshan complex show dominant younger grenvillian age peaks at 0 95 ga indicating the strong paleogeographic connection of the tengchong block with the indian margin the hf isotopic comparison of both detrital and igneous dated zircon shows that the tengchong block can be represented by the post archean indian continental margin after 250 ma the intensive magma events affected the region and considerable juvenile material accreted to the crust of the tengchong block

geochemistry of tin bearing granitic rocks abstract the use of rb ba and rb sr ratios as guides to tin mineralization has only local interest because each of the correlations log rb ba log sn and log rb sr log sn of granitic series has a different slope in every area the ternary relation between rb ba and cs is useful to distinguish between sn bearing granitic rocks and non mineralized granitic rocks the sn bearing granitic rocks are late differentiates of anatectic melts s type with primary albite and muscovite and greisenized granites with metasomatic albite and muscovite they have high sn rb contents rb ba and rb sr ratios and low ba and sr contents the portuguese sn bearing muscovite granites aplites pegmatites and hypothermal quartz veins have muscovites richer in sn than those of greisenized granites f and sn of muscovites from portuguese sn bearing granitic rocks are positively correlated cassiterite crystallization seems to be independent of f h 2 o f in hf and favoured by a decrease in fo2

fractionation process of high silica magmas through the lens of zircon crystallization a case study from the tengchong block sw china abstract the generation of high silica magma is generally considered to occur as a result of liquid crystal segregation from a crystal mush yet whether high silica melts could undergo significant fractionation process after the segregation remains unclear this study contributes to this topic through the lens of zircon geochemistry of the 130 ma high silica granite in the tengchong block sw china the high silica granite with sio2 76 displays low zr hf and eun eu n and high rb sr ratios the zircons crystallized from the granite can be divided into two groups the group 1 zircons are characterized by lower hf 12 200 ppm and display elevated u values 936 2429 ppm averaging 1557 ppm and yb values 755 1556 ppm averaging 1134 ppm as well as lower eun eu n 0 01 0 1 the increasing hf content from group 1 to group 2 zircons presence of fluorite inclusions in high hf zircon and similarity in hf isotope between the two groups of zircon consistently support the high silica granite has witnessed a highly fractionated crystallization process the presence of these two groups of zircons is considered to reflect two stage in situ fractionation processes which display distinct ree rare earth elements compositions in the magma system in response to differing precipitated mineral assemblages in light of the change of zircon ree within each group the percentage of minerals co precipitating with zircons in each stage was estimated the results showed that 35 24 quartz 18 60 feldspar 0 25 apatite 0 14 zircon 0 12 allanite and 0 05 titanite fractionated in the early stage and 67 50 quartz 23 41 feldspar 0 15 zircon 0 10 allanite 0 07 apatite and 0 06 titanite fractionated in the second stage the discovery of different zircons and corresponding estimation in this study provide a new line of evidence for the fractionation of high silica melt

compositional variations of granitic rocks in continental margin arc constraints from the petrogenesis of eocene granitic rocks in the tengchong block sw china abstract in order to address the causes of compositional variations of crust derived granitic rocks in continental margin arc we focused on the petrogenesis of eocene granitic host rocks with enclosed mmes associated metagabbro fine grained quartz diorite in xima tongbiguan area the tengchong block which is a continental margin arc related to the subduction of neo tethys both the eocene granitic and mafic rocks are characterized by gradual increment in enriched compositions such as k rb th lree initial 87sr 86sr end t and ehf t but decreasing pb isotopic ratios from the west to the east of the tengchong block zircon u pb age data of granitic host rocks mmes metagabbro and fine grained quartz diorite reveal a similar age range of 55 50 ma the lithologies zircon hf compositions geochemical and isotopic signatures of host granitic rocks show that the origin of these host rocks are mainly controlled by magma mixing between felsic and mafic magma the products of the mafic magma are dominated by metagabbro fine grained quartz diorite and mmes enclosed in granitic rocks which are all resulted from the reaction and mixture between different mafic magmatic products and felsic magma the metagabbros could be the products of felsic magma mixing with early crystallized mafic magma and the fine grained quartz diorites could be the products of felsic magma mixing with crystal rich mafic magma and the mmes could be the products of felsic magma mixing with crystal poor mafic magma or melt the metagabbro has positive ehf t values of 1 8 to 10 9 which could provide the relative primitive lu hf isotopic compositions of mafic magma indicating that the mafic magma is derived from a depleted mantle the host granitic rocks have negative end t values of 5 2 to 6 5 indicating that the felsic magma is derived from partial melting of an ancient mafic lower crust furthermore there are excess reactions after magma mixing between the mafic and felsic magma such as multi stage reactions between solidified mmes and felsic magma and the disaggregation of mmes finally resulting in the basification of felsic magma magma mixing is therefore the main mechanism of the formation of granitic rocks in the tengchong block the compositional variation of intermediate to acid igneous rock in a continental margin arc is likely dominated by the characteristics of mafic magma because the intermediate to acid igneous rock is derived from mixing of crust derived granitic and different mantle sources derived mafic magma

the tectonic and metallogenic framework of myanmar a tethyan mineral system myanmar is perhaps one of the world s most prospective but least explored minerals jurisdictions containing important known deposits of tin tungsten copper gold zinc lead nickel silver jade and gemstones a scarcity of recent geological mapping available in published form coupled with an unfavourable political climate has resulted in the fact that although characterized by several world class deposits the nation s mineral resource sector is underdeveloped as well as representing a potential new search space for a range of commodities many of myanmar s known existing mineral deposits remain highly prospective myanmar lies at a crucial geologic juncture immediately south of the eastern himalayan syntaxis however it remains geologically enigmatic its mesozoic recent geological history is dominated by several orogenic events representing the closing of the tethys ocean we present new zircon u pb age data related to several styles of mineralization within myanmar we outline a tectonic model for myanmar from the late cretaceous onwards and document nine major mineralization styles representing a range of commodities found within the country we propose a metallogenetic model that places the genesis of many of these metallotects within the framework of the subduction and suturing of neo tethys and the subsequent himalayan orogeny temporal overlap of favourable conditions for the formation of particular deposit types during orogenic progression permits the genesis of differing metallotects during the same orogenic event we suggest the evolution of these favourable conditions and resulting genesis of much of myanmar s mineral deposits represents a single evolving mineral system the subduction and suturing of neo tethys

the first memin shock recovery experiments at low shock pressure 5 12 5 gpa with dry porous sandstone as part of the memin research program this project is focused on shock deformation experimentally generated in dry porous seeberger sandstone in the low shock pressure range from 5 to 12 5 gpa special attention is paid to the influence of porosity on progressive shock metamorphism shock recovery experiments were carried out with a high explosive set up that generates a planar shock wave and using the shock impedance method cylinders of sandstone of average grain size of 0 17 mm and porosity of about 19 vol and containing some 96 wt sio2 were shock deformed shock effects induced with increasing shock pressure include 1 already at 5 gpa the entire pore space is closed quartz grains show undulatory extinction on average 134 fractures per mm are observed dark vesicular melt glass of the composition of the montmorillonitic phyllosilicate component of this sandstone occurs at an average amount of 1 6 vol 2 at 7 5 gpa quartz grains show weak but prominent mosaicism and the number of fractures increases to 171 per millimeter two additional kinds of melt both based on phyllosilicate precursor could be observed a light colored vesicular melt and a melt containing large iron particles the total amount of melt all types increased in this experiment to 2 4 vol raman spectroscopy confirmed the presence of shock deformed quartz grains near the surface 3 at 10 and 12 5 gpa quartz grains also show weak but prominent mosaicism the number of fractures per mm has reached a plateau value of approximately 200 and the total amount of the different melt types has increased to 4 8 vol diaplectic quartz glass could be observed locally near the impacted surface in addition local shock effects most likely caused by multiple shock wave reflections at sandstone container interfaces occur throughout the sample cylinders and include locally enhanced formation of pdf as well as shear zones associated with cataclastic microbreccia diaplectic quartz glass and sio2 melt overall findings from these first experiments have demonstrated that characteristic shock effects diagnostic for the confirmation of impact structures and suitable for shock pressure calibration are rare so far they are restricted to the limited formation of pdf and diaplectic quartz glass at shock pressures of 10 gpa and above

weathering behaviour and construction suitability of dimension stones from the drei gleichen area thuringia germany the construction suitability of a dimension stone depends on its weathering properties along with the petrology and the petrophysical properties the aim of this study was to evaluate the suitability of the dimension stones from the drei gleichen area for construction and replacement purposes in total six sandstones ingersleben wachsenburg hindfelden seeberg rohnberg gleichenberg upper triassic as well as two carbonates wachsenburg sinter quaternary wandersleben dolomite middle triassic were analysed the results from our laboratory and on site studies of the dimension stones show that rocks from the same stratigraphic layer like the sandstones from the upper triassic can show major differences in their petrophysical and weathering properties these differences are attributed to their different diagenesis resulting e g in varying pore space water balance and strength properties the pore size distribution can be divided into four different groups based on their occurring maxima and micropore content the determined water balance properties as well as moisture expansion and salt attack depend on these groups next to this the mineralogical composition significantly influences the weathering resistance sandstones with a high content of altered lithoclasts show a high amount of moisture expansion low strength and in consequence a low weathering resistance against salt attack based on the results of the present study an evaluation of construction suitability could be accomplished from the analysed sandstones only the seebergen sandstone is suitable for construction purposes due to its good availability good strength properties high compressive and tensile strength low softening degree as well as a low porosity furthermore the wachsenburg sandstone also shows good petrophysical and petrological properties but exploitable deposits are too sparse to be of commercial interest from the carbonates the wachsenburg sinter shows very suitable rock parameters but only sparse outcrops occur which are not appropriate for mining

linking the tengchong terrane in sw yunnan with the lhasa terrane in southern tibet through magmatic correlation abstract new zircon u pb data along with the data reported in the literature reveal five phases of magmatic activity in the tengchong terrane since the early paleozoic with spatial and temporal variations summarized as cambrian ordovician 500 460 ma to the east minor triassic 245 206 ma in the east and west abundant early cretaceous 131 114 ma in the east extensive late cretaceous 77 65 ma in the central region and paleocene eocene 65 49 ma in the central and western tengchong terrane in which the cretaceous eocene magmatism migrated from east to west the increased zircon ehf t of the early cretaceous granitoids from 12 3 to 1 4 at ca 131 122 ma to 4 6 to 7 1 at ca 122 114 ma identified for the first time in this study and the magmatic flare up at ca 53 ma in the central and western tengchong terrane indicate increased contributions from mantle or juvenile crust derived components the spatial and temporal variations and changing magmatic compositions over time in the tengchong terrane closely resemble those of the lhasa terrane in southern tibet such similarities together with the data of stratigraphy and paleobiogeography enable us to propose that the tengchong terrane in sw yunnan is most likely linked with the lhasa terrane in southern tibet both of which experienced similar tectonomagmatic histories since the early paleozoic

early cretaceous na rich granitoids and their enclaves in the tengchong block sw china magmatism in relation to subduction of the bangong nujiang tethys ocean abstract the na rich intermediate to felsic granitic rocks provide insights into the generation of magmas in subduction zones this paper presents zircon la icp ms u pb ages as well as whole rock geochemical mineral chemical and in situ zircon hf isotopic data on na rich granitic rocks from the tengchong block sw china the granodiorites and associated mafic magmatic enclaves mmes from the menglian batholith yield zircon u pb ages of 116 1 0 8 to 117 8 0 6 ma and 117 7 0 7 ma respectively both host granodiorites and enclaves show calc alkaline and sodium rich nature enrichment in large ion lithophile elements liles and variable depletion in zircon hf isotopic compositions euhedral amphiboles in both granodiorites and associated enclaves are magnesian hornblende with high mg and ca and contain euhedral plagioclase inclusions of labradorite to andesine an36 57 composition the granodiorite was most likely derived through the mixing of partial melts derived from juvenile basaltic lower crust and a minor evolved component of ancient crustal sources the quartz monzodiorite granodiorites and associated mmes from the xiaotang mangdong batholith yield zircon u pb ages of 120 3 1 3 to 122 6 0 8 ma and 120 7 1 5 ma these rocks are also sodium rich and show calc alkaline trend with negative zircon hf isotopic compositions 5 55 to 0 58 the mmes in the host intrusions are monzogabbro with variable and depleted zircon hf isotopic compositions the amphiboles in the both host intrusions and the enclaves show al rich ferro tschermakite composition we infer that the quartz monzodiorite granodiorites were derived from magmas generated by the melting of ancient basaltic rocks in the lower arc crust induced by the underplating of mantle derived mafic magmas the formation of the different types of na rich granitic rocks is correlated to the subduction of bangong nujiang tethyan ocean a comparison with magmatism in the northern magmatic belt suggests that mantle derived magmas played an important role in the genesis of early cretaceous intrusions from tengchong to lhasa blocks although crustal melting is the dominant contributor

rare earth element tetrad effect and negative ce anomalies of the granite porphyries in southern qiangtang terrane central tibet new insights into the genesis of highly evolved granites abstract highly evolved granites are geochemically similar to the mature continental crust and are sometimes associated with w sn nb ta and rare metal mineralizations these rocks have important implications for tracing the compositional evolution of continental crust and magma metallogenesis they were commonly considered to have been produced by partial melting of crustal materials or by high degree fractional crystallization in this study we report on high sio2 granite porphyries in the xiabie co area of southern qiangtang terrane central tibet which provide new insights into the petrogenesis of the highly evolved granites zircon dating results indicate that they were generated in the late early cretaceous 107 1 ma they consist mainly of orthoclase albite and quartz with accessory minerals including zircon fluorite and fe ti oxides geochemically they have high sio2 but low mgo fe2o3t cao and p2o5 and are enriched in rb but depleted in ba sr eu and ti similar to highly evolved granitic rocks they are characterized by distinct rare earth element ree tetrad effects and negative ce anomalies they also have slightly higher end t values 0 99 to 0 36 than those of the adjacent early granites 2 05 to 3 01 and relatively high and variable zircon ehf t values ranging from 0 3 to 5 4 compared to typical highly evolved granites and petrological experiment data we suggest that the xiabie co granite porphyries represent highly evolved melts produced by fractional crystallization the interaction between fractionated melts and f rich aqueous fluids played an important role in the genesis of their ree tetrads effect involvement of meta sedimentary rocks that went through surficial chemical weathering into their source region is the predominant reason for the generation of negative ce anomalies this indicates that in addition to fractional crystallization the melt fluid interactions and partial melting of source materials also play important roles in the generation of highly evolved granites

crater morphology in sandstone targets the memin impact parameter study hypervelocity 2 5 7 8 km s 1 impact experiments into sandstone were carried out to investigate the influence of projectile velocity and mass target pore space saturation target projectile density contrast and target layer orientation on crater size and shape crater size increases with increasing projectile velocity and mass as well as with increasing target pore space saturation craters in water saturated porous targets are generally shallower and larger in volume and in diameter than craters from equivalent impacts into dry porous sandstone morphometric analyses of the resultant craters 5 40 cm in diameter reveal features that are characteristic of all of our experimental craters regardless of impact conditions i a large central depression within a fragile light colored central part and ii an outer spallation zone with areas of incipient spallation two different mechanical processes grain fragmentation and intergranular tensile fracturing are recorded within these crater morphologies zone i approximates the shape of the transient crater formed by material compression displacement comminution and excavation flow whereas ii is the result of intergranular tensile fracturing and spallation the transient crater dimensions are reconstructed by fitting quadric parabolas to crater profiles from digital elevation models the dimensions of this transient and of the final crater show the same trends both increase in volume with increasing impact energy and with increasing water saturation of the target pore space the relative size of the transient crater in percent of the final crater volume decreases with increasing projectile mass and velocity signifying a greater contribution of spallation on the final crater size when projectile mass and velocity are increased

strongly peraluminous fractionated s type granites in the baoshan block sw china implications for two stage melting of fertile continental materials following the closure of bangong nujiang tethys abstract strongly peraluminous fractionated s type granites are important indicators of compositional maturity of the continental crust here we report the finding of strongly peraluminous fractionated s type granites from the western baoshan block in the southeastern tibetan himalayan orogenic belt we present la icp ms zircon u pb ages from biotite and two mica granites which reveal two distinct periods of magmatism at 121 8 1 1 ma and 81 9 79 7 ma these cretaceous granites are strongly peraluminous a cnk 1 18 1 31 high k calc alkaline enriched in rb th k and pb and depleted in ba sr and ti they also show high normative corundum contents of 2 84 4 42 wt moderately high p2o5 content 0 22 0 28 wt and high differentiation index di of 93 1 96 8 similar to the features of fractionated s type granites the low total fe2o3t mgo tio2 contents

combining nd isotopes in monazite and hf isotopes in zircon to understand complex open system processes in granitic magmas mapping the age and trace element and sm nd isotope compositions of monazite grains from a peraluminous cretaceous granite using laser ablation split stream analysis reveals a wide range in nd isotope and rare earth element ree compositions within and between single grains these data corroborate isotopic variability indicated by hf isotope analysis of zircon in the same granite sample the ree variations indicate that monazite grew during fractional crystallization hf and nd isotopes indicate that the granitic magma was generated from at least two distinct proterozoic sources of approximately the same age one component that had highly radiogenic initial 176hf 177hf and 143nd 144nd and a second component that was notably less radiogenic this study highlights the utility of in situ ree and sm nd isotope data in monazite in magmatic systems further it refines the zircon based constraints on magmatic processes because of sensitivity of light rees to fractional crystallization lower probability of complications owing to inheritance and smaller analytical volumes required