paleogene island arc collision related conglomerates yarlung tsangpo suture zone tibet abstract coarse clastic rocks in the liuqu conglomerate formed in both terrestrial and subaqueous settings record a paleogene phase in the tectonic evolution of tibet facies changes are commonly abrupt with rapid changes in clast types grain size and stratal patterns sediments were derived from the leading northern edge of the indian margin and a late jurassic cretaceous intraoceanic island arc that lay within tethys the coarse clastic sedimentary rocks of the liuqu conglomerates are extremely proximal but are locally offset relative to their original source terranes they record aspects of the history of collision between these terranes and are interpreted to have been deposited in oblique slip basins that developed along the zone of collision the absence of clasts derived from terranes to the north of the yarlung tsangpo suture suggests that basins associated with deposition of the liuqu conglomerate developed prior to the final collision between india and asia

environmental context for late holocene human occupation of the south wellesley archipelago gulf of carpentaria northern australia a 2400 year record of environmental change is reported from a wetland on bentinck island in the southern gulf of carpentaria northern australia three phases of wetland development are identified with a protected coastal setting from ca 2400 to 500 years ago transitioning into an estuarine mangrove forest from ca 500 years ago to the 1940s and finally to a freshwater swamp over the past 60 years this sequence reflects the influence of falling sea levels development of a coastal dune barrier system prograding shorelines and an extreme storm cyclone event in addition there is clear evidence of the impacts that human abandonment and resettlement have on the island s fire regimes and vegetation a dramatic increase in burning and vegetation thickening was observed after the cessation of traditional indigenous kaiadilt fire management practices in the 1940s and was then reversed when people returned to the island in the 1980s in terms of the longer context for human occupation of the south wellesley archipelago it is apparent that the mangrove phase provided a stable and productive environment that was conducive for human settlement of this region over the past 1000 years

miocene volcanism in the lhasa block tibet spatial trends and geodynamic implications miocene ultrapotassic up shoshonitic p and calc alkaline ca volcanism is recognized widely over the tibetan plateau this volcanism occurred after the end of india s oceanic lithosphere subduction beneath the plateau ambiguities about the distribution and significance of this volcanism arise in part from a paucity of geochronologic and geochemical data we have sampled two volcanic fields in the lhasa block 1 the eastern edge of the zabuye salt lake central part of the block 2 the southwestern edge of the yangbajin graben major and trace elements display high k2o 6 06 6 54 over a wide range of sio2 75 03 55 30 na2o 1 32 3 30 and lree hree enrichment with a significant rare earth element fractionation 266 la yb n 6 42 as well as negative nb ta and ti anomalies these features indicate that our samples are chemically identical to the post collision miocene up to p volcanic rocks already identified all over the tibetan plateau and the southern plateau specifically but distinct from the ca rocks found in the lhasa block the miocene volcanics found in the lhasa block present greater chemical variation than the rest of the tibetan plateau 40 ar 39 ar ages on both sanidine and biotite gave ages ranging from 16 16 g 0 12 ma to 16 01 g 0 12 ma and 10 60 g 0 14 ma to 10 88 g 0 17 ma 2 c excluding systematic errors relative to fish canyon sanidine at 28 02 ma for zabuye salt lake and yangying geothermal field volcanics respectively these results are consistent with the range of previously published ages from this part of the tibetan plateau the presence of n s trending dikes and the location of the volcanic fields suggest that local e w extension in the lhasa block was coeval we propose that the synchronous up p and ca volcanism in the lhasa block between 23 and 8 ma is the result of progressively deepening northward subduction of indian continental lithosphere producing asthenospheric upwelling convective thinning delamination of lithospheric mantle fueled by the hot asthenosphere induced partial melting of an enriched sub continental mantle lithosphere as well as eclogitic lower crust this mechanism could also explain the local e w extension observed in the same period 18 10 ma we also propose that lateral migration of the deepening indian continental lithosphere mantle slab could explain the observed younger volcanism in the eastern part of the lhasa terrane

europium mass balance in polymict samples and implications for plutonic rocks of the lunar crust abstract from correlations of sm concentration and sm eu ratio with th concentration for a large number of polymict samples from various locations in the lunar highlands and the value of 0 91 g g for the mean th concentration of the highlands surface crust obtained by the orbiting gamma ray experiments we estimate the mean concentrations of sm and eu in the lunar surface crust to be between 2 and 3 g g sm and 0 7 and 1 2 g g eu the compositional trends indicate that there is no significant enrichment or depletion of eu on the average compared to sm relative to chondritic abundances i e there is no significant eu anomaly in average upper crust although rich in plagioclase 70 the upper crust does not offer evidence for a gross vertical separation of plagioclase from the final liquid from which it crystallized this and the chondritic ratio of eu al in average highlands material imply that the net effect of the processes that led to formation of the lunar crust was to put most of the al and incompatible elements in the crust the concentration of eu in most polymict samples from the highlands exceeds that which can be supplied by the fraction of kreep necessary to supply the incompatible trace elements plus the fraction of plagioclase necessary to supply the al if the plagioclase has the composition of that in ferroan anorthosite among plutonic rocks only plagioclase in rocks from the magnesian suite can supply the excess eu in the polymict rocks owing to the intermediate value of the mean mg fe ratio of the crust a significant fraction of the mafic rocks of the lunar highlands must have lower mg fe ratios than the norites and troctolites of the magnesian suite of plutonic rocks a large fraction of the plagioclase in the lunar crust is associated not with ferroan anorthosite but with more mafic rocks e g norite anorthositic norite there is little evidence in the eu data that the lunar crust ever consisted of a thick shell of nearly pure plagioclase as envisioned in some formulations of the magma ocean model of its formation

timing of tibetan uplift constrained by analysis of volcanic rocks the tibetan plateau has had a central role in the development of recent models for the mechanics of mountain belts1 2 and cenozoic global climate change3 the present elevation and extensional deformation of the plateau probably result from uplift owing to convective thinning of the underlying lithospheric mantle1 2 an age for the uplift would provide a valuable constraint on these models but because recently proposed indicators of uplift are all climate dependent they are equivocal possibly reflecting global cooling rather than regional uplift4 here we present new geochemical data on post mid miocene lavas from the plateau which show that the lavas were derived from the lithospheric mantle simple thermal arguments indicate that the generation of such magmas also necessitates thinning of the lithospheric mantle thus volcanism is coincident with uplift providing a climate independent means of dating the onset of uplift dating by the laser 40ar 39ar technique places the beginning of this volcanism and therefore the time of uplift of the tibetan plateau at 13 myr ago

age of initiation of the india asia collision in the east central himalaya abstract we document the stratigraphy and provenance of the lower tertiary terrigenous sections in the zhepure shan region of the tethyan himalaya southern tibet using petrographic and geochemical whole rock and single grain techniques the cretaceous early tertiary shelf deposits of shallow marine carbonates and siliciclastics of the former indian passive margin near the western end of the zhepure shan are conformably overlain by lower tertiary clastic rocks sandstones in the jidula formation paleocene mostly contain monocrystalline quartz grains of cratonic origin in contrast significant amounts of immature framework grains with a distinct ophiolitic and volcanic arc influence are present in the youxia early eocene and shenkeza post early eocene formations major trace and rare earth element concentrations in both sandstones and shales complement the petrographic data and indicate that the source of the jidula formation consisted primarily of quartzose basement rocks probably of indian con

petrology chemistry and origin of apollo 15 regolith breccias abstract variations in modal petrology mineral compositions and bulk compositions were determined for ten apollo 15 regolith breccias for comparison with local soils and assessment of the intrasite petrologic variability of the apollo 15 regolith based on the above criteria the breccias are of local origin and mimic the soils from the corresponding sampling stations with the exception of station 2 breccia 15205 this sample formed from an anomalous regolith and although not considered exotic to the site is not representative of the soil at the site kreep basalt and green glass components vary from trace amounts to dominant in the breccias evidence that these materials entered the regolith prior to formation of the breccias breccias from the edge of hadley rille are modally richer in highland fragments than the soils whereas at the base of hadley delta the reverse is true this is explained by the loss of material into the rille to be replaced by basalt derived material making the soils more basalt rich at the base of hadley delta highland material is accumulating and the soils are becoming more highland rich over billions of years these processes have developed differences between the present day evolving soils and fossil non evolving soils represented by the regolith breccias this shows that there has been little change in the geology and the morphology of the apollo 15 site probably since the eruption of mare basalts at the site 3 3 b y

stratigraphic and sedimentological constraints on the age and tectonic evolution of the neotethyan ophiolites along the yarlung tsangpo suture zone tibet

the lunar regolith chemistry mineralogy and petrology the lunar regolith a several meter thick layer of unconsolidated debris forms the interface between the moon and its space environment the regolith forms from lithic sources by the destructional processes of comminution and the constructional processes of agglutinate formation in this manner a steady state soil can develop and will remain in a type of dynamic equilibrium until the system is disturbed by burial or mixing with new soil mixing takes place mainly on a local scale vertically through meters and horizontally over several kilometers lateral transport is a relatively inefficient process and therefore most of the lunar soil components were derived locally there is no evidence for preferential transport of the finer soil fractions relative to the coarser fractions the truly exotic derived at distances of tens of kilometers component is generally in low abundance 1 therefore remotely sensed data should provide a reasonably accurate picture of bedrock geology the chemical composition of the regolith varies with grain size the 10 m fraction is chemically fractionated from the bulk soil in most cases the 10 m fraction is enriched in al2o3 cao na2o k2o light rare earth elements and th and depleted in mgo feo mno and sc these systematics are largely a result of simple comminution with feldspar and friable mesostasis from local source rocks concentrating in the finest fraction there is evidence that agglutinate glass forms preferentially by fusion of the finest soil fractions therefore agglutinate glass like the 10 m soil fraction appears to be fractionated from bulk soil compositions highland soils are distinct from mare soils both chemically and petrologically soil samples collected near mare highland contacts are mixtures of the two lithologies mineral chemical systematics of monomineralic fragments in the lunar soil provide important clues to soil provenance they can in some cases sort out the highland mare contributions and in special cases can even further pinpoint a lithic source in theory lunar regolith cores can serve as solar probes recording the sun s activity over billions of years in practice this has generally not been the case the formation and evolution of most cores is still poorly understood for most we have not established how they formed for example how many depositional and erosional events were involved what the time span involved in the accretion of the sampled soil column was and how long that soil column has remained in situ without this information it is difficult if not impossible to read the sun s record more interdisciplinary studies on cores must be carried out before they can be used as solar probes

understanding the lunar surface and space moon interactions the surface of the moon is a critical boundary that shapes our understanding of the moon as a whole all geologic mapping and remote sensing techniques utilize only the outermost portion of the moon before leaving the moon for study in our laboratories all lunar samples that have been studied existed at or very near the surface with the exception of the deeply probing geophysical techniques our understanding of the interior of the moon is derived from surficial but not superficial information coupled with boundary of the lunar crust it is the lower boundary layer of the tenuous lunar atmosphere and constitutes both a source and a sink for atmospheric gases the surface is also where the moon interacts with the space environment causing changes in the physical nature of lunar materials and provides a laboratory for the study of processes that occur on all airless bodies the data obtained remotely by the galileo clementine and lunar prospector missions as well as data derived from lunar meteorites have resulted in major changes to our understanding of global distributions of chemistry and rocks this chapter summarizes the current understanding of this critical interface the surface of the moon in its role as the lower boundary of the lunar atmosphere the upper boundary of the crust and the window through which we view through remote sensing the composition of the crust and the history of the moon in this post lunar prospector time the view of the moon has changed lending new perspectives to lunar samples and lunar processes but the new view will likely remain in flux as we continue to digest the results from these recent space missions and move forward to a new era of lunar exploration despite the freshness of our perspective this is an important moment to capture

evolution of intra oceanic arc trench systems abstract intra oceanic island arc trench systems represent a locus of crustal thickening through the addition of mantle derived magmas which form the volcanoes and subjacent stratiform plutons the crust of immature island arcs and adjacent back arc basins is oceanic in chemistry in that it is dominated by mafic e g tholeiitic magmas a magma sequence is recognized in many arc systems which progress from boninite to arc tholeiite to calc alkaline and in some arcs to shoshonites the adjacent back arc basins are formed of morb like tholeiite arc systems may be dominated by extension rather than compression if the subducted and overriding plates are decoupled extension of the arc system may be associated with seaward retreat or roll back of the trench axis alternate cycles of extension and compression of the arc system can lead to both tectonic erosion of the fore arc and accretion of fragments from the incoming sea floor the izu bonin mariana tonga yap and palau trench arc systems are examples of different stages in a dynamic process which starts when subduction begins along old fracture zone traces crustal extension causes both fore arc subsidence and opening of back arc basins island arc volcanic chains and back arc basins are new crust formed largely of fractional melts of the mantle the evolution of an arc system may stop when blocking of the subduction zone or changes in relative plate motion causes overthrusting of back arc lithosphere on to former volcanic arcs many ophiolites preserve remnants of arc system crust and upper mantle

shoshonitic magmas in nascent arcs new evidence from submarine volcanoes in the northern marianas volcanoes in the northern mariana arc between uracas lat 20 n and minami iwo jima 24 n are very active yet entirely submarine in contrast to the predominantly low k basaltic magmas of the central mariana arc the northern mariana arc is dominated by more siliceous melts in the south and by shoshonites in the north the northern arc melts have enrichments in ba 800 ppm rb 70 ppm sr 1000 ppm ce 50 ppm and ce yb n 24 which increase to the north as far as iwo jima lavas from volcanoes north of iwo jima lack these enrichments and are indistinguishable from those of the central maranas the shoshonites are unusual in occurring along the magmatic front of a primitive intra oceanic arc we hypothesize that they represent the reconstruction of a magmatic arc following melting of enriched mantle due to the propagation of the mariana trough spreading center northward through the volcano arc shoshonites thus may characterize the initial stages of arc construction after an episode of back arc rifting and need not be restricted to the mature stages of arc evolution this situation contrasts with subduction zone initiation where first melts may be boninites or low k tholeiites these differing initial melts converge toward tholeiitic and calc alkaline compositions as arcs evolve

precise radiolarian age constraints on the timing of ophiolite generation and sedimentation in the dazhuqu terrane yarlung tsangpo suture zone tibet well preserved abundant radiolarians provide high precision biostratigraphic age constraints on the timing of the eruption of ophiolitic basalts exposed along the yarlung tsangpo suture zone in southern tibet dazhuqu terrane ophiolites were generated in an intra oceanic supra subduction zone setting within a relatively short

the dras arc two successive volcanic events on eroded oceanic crust abstract the dras arc is recognized as a volcanic arc system in the western part of the indus suture zone and it constitutes the link between the ladakh batholith and the kohistan arc this study is based on detailed mapping of the area between dras kargil and sanku which revealed the following 1 1 the ultramafics of dras and thasgam can be followed across the suru dras ridge and are not intrusive into the arc volcanics but instead constitute the most probably oceanic substratum of these volcanics 2 2 successive volcanic events are distinguished 2 1 a dras i is a variable volcaniclastic series rich in slates and carbonates which can probably be assigned to the albo cenomanian as dated by orbitolines this series is intruded by gabbro diorite and granite and is deformed essentially in the northern part it is unconformably overlain by 2 2 b the dras ii pyroclastics which grade southward into volcanic breccia and thus enable the location of the centres of volcanic activity during this younger period

a jurassic cretaceous island arc in the ladakh himalayas abstract the ladakh mesozoic ophiolite belt western himalaya contains a pile of volcanic thrust sheets dras unit which differ significantly in structure and composition from the ophiolitic melange zones the dras unit is composed of pillow lavas doleritic sills very irregular basaltic basaltic andesites and dacitic flows intercalated with pyroclastics volcanoclastic sediments and radiolarian cherts according to fossil evidence this volcanism must have been active between upper jurassic and upper cretaceous the presence of relict primary minerals such as magnesiochromite clinopyroxene hastingsitic hornblende and ti magnetite as well as distinctive bulk chemistries suggests that the volcanics belong to island arc tholeiite and to calc alkaline rock series typical of present island arcs in the caribbean and pacific model calculations incorporating probed phenocryst phases indicate that in addition to olivine clinopyroxene and plagioclase amphibole and titanomagnetite are crucial fractionating phases in the development of the dacites from a primitive tholeiitic melt the latter process must have taken place at about 1000 c and at moderate depth of 5 15 km within or underneath the island arc today hornblende bearing mafic cumulates appear in the vicinity of kargil within and close to the dras volcanics in a sr evolution diagram the dras volcanics have yielded a pseudo isochron with a low initial 87 sr 86 sr ratio of 0 7035 0 0003 which is in the same range as the mean of modern island arc volcanics however a geologically unrealistic age of 263 m y is obtained from the slope of this isochron the upper mantle is regarded as the source material for the island arc tholeiitic magmas enrichment in k ba sr and lree supports the involvement of components derived from dehydration or incipient melting of subducted tethyan oceanic crust in the mantle

neotethys and the india asia collision insights from a palaeomagnetic study of the dazhuqu ophiolite southern tibet since 1999 independently derived geophysical and geological models have been published arguing for an intra oceanic subduction system along essentially the entire width of the india eurasia collision belt this idea conflicts with earlier proposals where in the eastern part of the convergence zone neotethyan mid ocean ridge generated lithosphere directly north of the indian craton was consumed beneath eurasia in tibet in an andean type plate configuration new palaeomagnetic data are reported from three barremian aptian 120 ma sequences of chert siliceous mudstones and volcaniclastic rocks these rocks form the uppermost part of the dazhuqu supra subduction zone ophiolite terrane which crop out along substantial portions of the india eurasia yarlung tsangpo suture zone in southern tibet the declination data provide little regionally useful tectonic information they are dominated by local rotations presumably related to the dazhuqu terrane s initial obduction onto the india plate in the palaeocene and subsequent movement s as india later collided and indented into eurasia the inclination data are however useful because they yield consistent sub equatorial formation sites 2 7 s 3 0 7 9 n 2 7 1 4 n 5 7 which correspond with the location of the neotethyan intra oceanic subduction system inferred from the seismic tomographic data at the time these dazhuqu terrane rocks formed the intra tethyan subduction zone would have been about 2500 km south of eurasia

the dras arc complex lithofacies and reconstruction of a late cretaceous oceanic volcanic arc in the indus suture zone ladakh himalaya abstract the purpose of this paper is to give an integrated description and interpretation of mainly volcaniclastic sediments related to excellently exposed oceanic volcanic arc successions in the ladakh himalayas the mainly late cretaceous aptian paleocene dras arc complex in the indus suture zone n india is reconstructed as an oceanic arc passing southwards into a proximal to distal forearc apron the arc complex comprises three structural units from west to east these are the suru unit the naktul unit and the nindam formation the suru unit and the naktul unit are unconformably underlain by dissected late jurassic oceanic crust and mantle the suru unit preserves the interior of the arc and is divided into dras 1 and dras 2 sub units the dras 1 sub unit of mid late cretaceous age was intruded by arc plutonics deformed then unconformably overlain by the poorly dated dras 2 sub unit lower tertiary the dras 1 sub unit comprises arc extrusives volcaniclastic and tuffaceous sedimentary rocks and mainly redeposited shallow water limestones the dras 2 sub unit is dominated by coarse volcaniclastics and lava flows passing up into rhythmically layered acidic extrusives with interbedded turbiditic siltstones and siliceous pelagic limestones further east the naktul unit is mainly clastic with large volumes of massive volcaniclastic talus thick bedded debris flows volcaniclastic turbidites and reworked shallow water carbonates pillowed extrusives and ribbon radiolarites are present mainly low in the succession in some areas while pelagic carbonates are abundant near the top the naktul unit is interpreted as a proximal forearc apron the nindam formation in the east is dominated by deep water volcaniclastic turbidites tuffaceous sediments and pelagic carbonates with subordinate debris flows and is interpreted as a distal deep water forearc succession cyclical alternations of mainly volcaniclastics and pelagic carbonates in the nindam formation are thought to reflect relative sea level changes of tectono magmatic and or global eustatic origin the oceanic dras arc complex formed within neotethys in the mid late cretaceous above an assumed northward dipping subduction zone around 79 ma campanian the oceanic arc underwent collisional deformation possibly related to accretion to the trans himalaya ladakh block and or the southern margin of eurasia to form an andean type active continental margin the suru unit in the west dras 1 sub unit was deformed then overlain by the mainly acidic dras 2 sub unit however there is no direct evidence that the nindam formation in the east was deformed until the early eocene when final collision of india and eurasia took place with southward thrusting of the dras arc complex this was followed by partial erosion during deposition of the indus molasse and then back thrusting and folding related to uplift of the high himalayas in the later tertiary

new results from physical modelling of arc continent collision in taiwan evolutionary model abstract both the analysis of the geological data and the results from 2d and 3d experimental modelling of arc continent collision in taiwan reveal the following major stages in this process 1 failure and thickening of the subducting crust of the chinese continental margin under the frontal part accretionary prism of the philippine sea plate psp since ca 6 7 ma 2 uplift squeezing and exhumation of the subducted crustal slice of the chinese margin and initiation of the central range about 5 ma ago 3 flexural buckling subsidence of the luzon arc fore arc under strong horizontal compression and sedimentary infilling of this area by the material shed from the growing and exhuming central range 4 failure of the psp along the west vergent longitudinal valley fault dipping beneath the arc and closure of the fore arc 5 subduction reversal and stoppage of continental subduction which has already occurred in northern taiwan and propagates to the south the southward propagation of the collision is not stationary currently occurring initial collision in southern taiwan and offshore to the south does not follow the same described above evolution as in central and northern taiwan the evolution of the collision in time and space should be considered in the framework of a 3d model where the psp rupture is preparing in the central and northern taiwan during a long time passing through a number of evolutionary stages once it has occurred the rupture longitudinal valley fault rapidly propagates to the south into the domain which did not undergo the pre rupture evolution the rupture front is currently located near 21 30 n

remote laser induced breakdown spectroscopy libs for lunar exploration 1 laser induced breakdown spectroscopy libs is an active analytical technique that makes use of a laser pulse to analyze materials of interest at a distance by creating a plasma which emits photons at characteristic emission line wavelengths we validate the technique for planetary exploration under vacuum conditions we review the capability and advantages of the libs technique for lunar regolith analysis at 1 5 m distance from a lunar rover and we characterize its potential for the detection of resources for future exploration such as the determination of regolith water content the limits of detection determined for the major elements typically 1 wt help to determine regolith parent material such as feldspathic highland rocks rocks from the ancient magmatic high magnesian suite mg suite fe rich mare basalts or potassium rare earth element and phosphorus rich kreep rich samples compositional parameters commonly used to classify lunar regoliths such as tio2 al2o3 and k2o abundances are readily determined by libs certain elements support regolith analysis for example ba and zr can be used to confirm kreep like composition while quantifying the ni and co content can be used to infer the amount of meteoritic material finally it is shown that the ice content of lunar soil produces strong h emissions with the libs techniques at the 25 wt h2o level while measurements on altered basalts give a limit of detection of about 1 wt for h2o content this demonstrates that the 5 6 wt water content detected by the recent lcross experiment should be easily detectable and quantifiable by libs analysis

the zedong terrane a late jurassic intra oceanic magmatic arc within the yarlung tsangpo suture zone southeastern tibet an overturned sequence of igneous and volcaniclastic rocks crops out along the yarlung tsangpo suture zone ytsz in southeastern tibet these rocks are remnants of an intra oceanic island arc the zedong terrane that once lay between india and asia 40ar 39ar dating and u pb ion microprobe analyses reported here reveal that this arc was active during the jurassic u pb dating of zircon from a dacite breccia from the middle portion of the zedong terrane yields an age of 161 2 3 ma 1 40ar 39ar dating of hornblende from a cross cutting andesite dyke yields the youngest age of 152 2 3 3 ma 1 40ar 39ar results from hornblende from andesite dykes and an andesite breccia from the upper portion yield a mean age of 156 0 3 ma 1 additional u pb and 40ar 39ar dating of zircon and hornblende from quartz diorite yields a mean age of 156 8 0 8 ma 1 geochronological data reported here and other published work indicate that the intra oceanic subduction system to which the zedong terrane belonged was active from at least late jurassic to early to mid cretaceous

chemistry of the apollo 11 highland component chemical data 28 major minor and trace elements were obtained by instrumental neutron activation analysis inaa for 38 hand picked highland fragments 1 20 mg from coarse fines 10085 the apollo 11 highland chemical groups are represented by a range of petrographic types six major chemical highland groups are identified in the apollo 11 fragments these are 1 high k kreep 2 anorthosite e g 15415 60015 with 10 chondrite rare earth elements ree abundances a positive eu anomaly anorthosite with 30 chondrite abundances and a positive eu anomaly 3 anorthosite norite troctolite ant 67075 4 low k fra mauro lkfm 77135 5 anorthositic gabbro 68415 with no eu anomaly anorthositic gabbro 65055 67955 with a positive eu anomaly and anorthositic gabbro 68516 60015 with a negative eu anomaly and 6 apollo 11 dominant highland component 2 10 chondrite ree abundances with a positive 10 14 chondrite eu anomaly there are three newly recognized groups in the apollo 11 highland suite based on the ree patterns these are a ant with 5 chondrite la 22 chondrite abundances and a positive eu anomaly b 10 chondrite flat pattern with 14 chondrite positive eu anomaly and c 2 3 chondrite flat pattern with 10 chondrite positive eu anomaly the apollo 11 highland suite is very low in potassium non kreepy overall the apollo 11 highland suite is quite similar to the apollo 16 suite most previously recognized highland chemical groups are represented in the apollo 11 highland component

chemistry and petrology of apollo 12 drive tube 12027 modal and chemical data for 31 major minor and trace elements obtained by inaa for soils from four 5 cm depth intervals of drive tube 12027 show three compositional units within the core the upper 2 5 cm of 12027 represent part of the sharp crater rim crest deposit which has a total thickness of 23 cm chemical differences are attributed to addition of local mare rocks to the upper 2 cm and kreepy material to the lower stratigraphic layer 14 17 cm depth the coarser fractions 1000 90 90 20 and 20 10 pm are compositionally similar to each other but quite different from the 10 m fine fractions which are more feldspathic and enriched in incompatible lil elements correlation between fused soil contents and lil enrichments of the coarse fractions strongly suggests that agglutinates are derived from the fine fraction thus supporting the fusion of the finest fraction f3 model the trench soil 12033 from 15 cm depth is very similar to the 15 5 16 cm soil of core 12027 indicating that the apollo 12 regolith exhibits kreep enrichments at various depths and that exotic kreepy ejecta are wide spread at the apollo 12 site

constraining the source regions of lunar meteorites using orbital geochemical data lunar meteorites provide important new samples of the moon remote from regions visited by the apollo and luna sample return missions petrologic and geochemical analysis of these meteorites combined with orbital remote sensing measurements have enabled additional discoveries about the composition and age of the lunar surface on a global scale however the interpretation of these samples is limited by the fact that we do not know the source region of any individual lunar meteorite here we investigate the link between meteorite and source region on the moon using the lunar prospector gamma ray spectrometer remote sensing data set for the elements fe ti and th the approach has been validated using apollo and luna bulk regolith samples and we have applied it to 48 meteorites excluding paired stones our approach is able broadly to differentiate the best compositional matches as potential regions of origin for the various classes of lunar meteorites basaltic and intermediate fe regolith breccia meteorites are found to have the best constrained potential launch sites with some impact breccias and pristine mare basalts also having reasonably well defined potential source regions launch areas for highland feldspathic meteorites are much less well constrained and the addition of another element such as mg will probably be required to identify potential source regions for these

petrology of apollo 11 regolith breccias petrographic and mineral chemical data for 16 apollo 11 regolith breccias show that 1 the regolith breccias differ from soil 10084 with respect to a agglutinate content b glass population c plagioclase compositions and d proportions of high k mare and low k mare basalt components 2 the a 11 breccias and soil have highland components that are similar both in abundance and petrology and 3 lunar regolith breccias provide a better comparison with howardites than do lunar soils the data and observations are consistent with formation of the regolith breccias from immature soil it appears that little or no highland material has been added to the tranquillitatis regolith since the formation of the breccias

reconstruction of madagascar and africa evidence from the davie fracture zone and western somali basin new seismic reflection gravity and magnetic data from offshore east africa allow the davie fracture zone to be traced from 11 s to its intersection with the kenyan coast at 2 s constraining the relative motion of madagascar and africa seasat derived free air gravity anomalies and slope rise positive magnetic anomalies observed in shipboard data help to locate the continent ocean boundaries cob off the shore of east africa and madagascar seismic reflection data further document a diapirprovince off madagascar presumably conjugate to that observed off kenya and somalia the dhow and very large crude carrier vlcc basement ridges are complex features and do not appear to be simple fracture zones owing their existence entirely to the separation of madagascar and africa from these data we determine a predrift fit of madagascar and africa involving a 14 2 rotation of madagascar to africa about a pole at 10 n 150 e the geometry of the reconstruction adheres to seismic and potential field data indicating the oceanic nature and extent of the comoros basin and of the somali basin between kenya and the seychelles and it does not conflict with onshore or offshore stratigraphy timing of the opening of the western somali basin is constrained by mesozoic marine magnetic anomalies and extrapolation to the interpreted cob and occurred between approximately 165 and 130 ma

u pb zircon ages from the spontang ophiolite ladakh himalaya the spontang ophiolite in the ladakh himalaya consist of a thrust sheet of upper mantle and oceanic crustal rocks obducted onto the northern passive continental margin of india during the late cretaceous precise isotopic ages of himalayan ophiolites are presently unavailable u pb dating of zircons from a dioritic segregation in the high level gabbros of the spontang ophiolite shows that the complex formed at 177 1 ma mid jurassic and we suggest that it represents a fragment of neo tethyan oceanic crust this jurassic age contrasts with late cretaceous ages 91 95 ma previously reported for the formation of the troodos and oman ophiolite complexes further west along the neo tethyan suture zone and also predates the early to mid cretaceous masirah ophiolite c 150 ma and its alkaline volcanic seamounts 115 125 ma an andesitic rock from an arc sequence overlying the spontang ophiolite was also dated using as 88 5 ma this late cretaceous age constrains the minimum age of initiation of subduction beneath the spontang ophiolite the complex was emplaced during the turonian maastrictian some 80 ma after its formation when the indian continental margin collided with a cretaceous arc about 25 ma before the india asia collision the lack of a sub ophiolite metamorphic sheet beneath the spontang mantle sequence may be explained by the fact that the ophiolite was old and cold at the time of obduction

the yanbian terrane southern sichuan province sw china a neoproterozoic arc assemblage in the western margin of the yangtze block abstract the magmatic and tectonic history of the yangtze block and its possible affinity with other neoproterozoic arc terranes are important elements in the reconstruction of neoproterozoic plate tectonics the yanbian terrane in the western margin of the yangtze block is a typical arc assemblage composed of a flysch type sedimentary sequence intruded by gabbroic and granodioritic plutons the sedimentary sequence consists chiefly of tuffaceous material with interlayered chert sandstone and pillow basalts laser ablation icp ms u pb dating of detrital zircons from the sandstones yield ages as young as 840 ma the gaojiacun and lengshuiqing mafic intrusions are dated at 812 3 ma and 806 4 ma respectively using the shrimp zircon u pb technique geochemical data show that both the gaojiacun and lengshuiqing intrusions have arc signatures with nd t values of 1 5 to 6 0 initial 87 sr 86 sr ratios of 0 705 0 706 and pronounced negative nb ta and zr hf anomalies their geochemical variations are best explained by fractional crystallization without major crustal contamination the yanbian terrane represents a typical arc assemblage formed on the western edge of the yangtze block during neoproterozoic time the sedimentary sequence was deposited in an oceanic setting probably in a back arc basin environment the depleted subduction modified lithospheric mantle wedge above the subduction zone was the source of melts from which the mafic plutons were crystallized this scenario suggests subduction of oceanic lithosphere eastward present day orientation underneath the yangtze block

the zedong window a record of superposed tertiary convergence in southeastern tibet determining the timing magnitude and location of deformation due to the indo asian collision is widely acknowledged as an important step in understanding how the lithosphere responds during continental collision a puzzling result of geological investigations of the lhasa block over the past 2 decades has been the apparent lack of significant tertiary deformation there perhaps the most important structural feature of the lhasa block is the south directed gangdese thrust system which developed along its southern edge the thrust system which separates the andean type batholith of southern asia from rocks of indian affinity is obscured at most locations across southeastern tibet by back thrusts of the younger north directed renbu zedong thrust system the best documented site where both thrusts are exposed occurs near zedong zedong window systematic geochronologic analyses were conducted in this area u pb zircon dating of three samples of a synkinematically to postkinematically deformed hanging wall granitoid the yaja granodiorite cut by the gangdese thrust indicates a crystallization age of 30 4 0 4 ma 2 thus placing an upper bound on the initiation of the thrust u pb zircon dating of granitoid samples structurally higher in the gangdese hanging wall yields emplacement ages of 42 5 1 0 ma and 48 9 0 8 ma 2 similar to other magmatic complexes within the gangdese arc geochemical results are consistent with these plutons forming in the same environment as precollisional intrusions within the gangdese batholith suggesting a significant post collisional input of juvenile heat the 40ar 39ar thermochronology of samples from a vertical section through the hanging wall within the yaja granodiorite coupled with results of a numerical thermal model indicate an average slip rate along the gangdese thrust of 7 mm yr between 30 and 23 ma and a minimum displacement of 50 km farther east in the zedong window thermal effects produced by later north directed thrust sheets of the renbu zedong system appear to have obscured thermal history signatures in the gangdese hanging wall related to earlier south directed thrusting thermochronological results from this region indicate that thermal overprinting related to the north directed thrusting occurred between 25 and 10 ma consistent with previous estimates

deglacial biogenic opal peaks revealing enhanced southern ocean upwelling during the last 513 ka abstract strength of southern ocean upwelling controls the exchange of carbon dioxide co 2 between deep ocean reservoirs and atmosphere as well as the communication of dissolved silicon with the euphotic zone of the southern ocean the silicon supply could limit diatom opal productivity in the high latitudes of southern ocean and the subsequent burial of biogenic opal in underlying sediments here we report a record of biogenic opal export off the prydz bay south of the polar front of the southern ocean indicating strengthened upwelling during the past five glacial terminations in all five terminations i v opal peaks occur in line with northern hemisphere summer insolation intensity as well as the existing irds indicating that freshwater injection associated with retreat of the northern hemisphere ice sheets could be the cause of enhanced upwelling in the southern ocean during terminations this could in turn promote co 2 outgassing finally accelerating the completion of the terminations in addition the enhanced upwelling could export the si rich deep water to low latitudes via antarctic intermediate water aaiw and subantarctic mode water samw potentially leading to deglacial opal peaks in subtropical north atlantic

re examination of the formation ages of the apollo 16 regolith breccias abstract the lunar regolith is exposed to irradiation from the solar wind and to bombardment by asteroids comets and inter planetary dust fragments of projectiles in the lunar regolith can potentially provide a direct measure of the sources of exogenous material being delivered to the moon constraining the temporal flux of their delivery helps to address key questions about the bombardment history of the inner solar system here we use a revised antiquity calibration after eugster et al 2001 that utilises the ratio of trapped 40 ar 36 ar parentless 40 ar derived from radioactive decay of 40 k against solar wind derived 36 ar to semi quantitatively calculate the timing of the assembly of the apollo 16 regolith breccias we use the trapped 40 ar 36 ar ratios reported by mckay et al 1986 our model indicates that the apollo 16 ancient regolith breccia population was formed between 3 8 and 3 4 ga consistent with regoliths developed and assembled after the imbrium basin forming event at 3 85 ga and during a time of declining basin forming impacts the material contained within the ancient samples potentially provides evidence of impactors delivered to the moon in the late imbrian epoch we also find that a young regolith population was assembled probably by local impacts in the apollo 16 area in the eratosthenian period between 2 5 and 2 2 ga providing insights to the sources of post basin bombardment the soil like regolith breccia population and the majority of local apollo 16 soils were likely closed in the last 2 ga and therefore potentially provide an archive of projectile types in the eratosthenian and copernican periods

new constraints on the india asia collision the lower miocene gangrinboche conglomerates yarlung tsangpo suture zone se tibet abstract lower miocene conglomerates crop out along the length of the yarlung tsangpo suture zone on the southern margin of the lhasa terrane these conglomerates known by various local names are correlated herein as the gangrinboche conglomerates all units exhibit broadly similar stratigraphic histories and a basal depositional contact upon an eroded surface of rocks of the lhasa terrane is ubiquitous at most localities the tops of sections are either removed by erosion or truncated by north directed thrusts these conglomeratic molasse units developed in response to the india asia collision and record aspects of its development in all units initial clast derivation was from the lhasa terrane on the northern margin of the yarlung tsangpo suture zone up section the first appearance of clasts derived from terranes within the suture zone and the northern margin of india all of which lie to the south of any outcrops of gangrinboche conglomerates is observed although these units were previously thought to be eocene analysis of fossil and structural constraints indicates early miocene deposition as development of the gangrinboche conglomerates records a significant phase in the evolution of the india asia collision understanding of their age and stratigraphic evolution has wider implications for regional tectonic models

geochemistry and petrogenesis of 270 ma ni cu pge sulfide bearing mafic intrusions in the huangshan district eastern xinjiang northwest china implications for the tectonic evolution of the central asian orogenic belt abstract the central asian orogenic belt caob is composed of remnants of microcontinents island arcs and ophiolites the presence of voluminous phanerozoic a type granites suggest that continental growth occurred through addition of juvenile crust and the presence of mafic ultramafic intrusions provides direct evidence for a mantle contribution the origin of the mafic ultramafic intrusions in the huangshan area eastern xinjiang has been debated because of the lack of precise age data or trace element and isotopic analyses we have studied the geology petrology geochemistry and geochronology of two of the intrusions the huangshanxi and huangshandong intrusions both are typical layered mafic ultramafic intrusions composed of diorite troctolite norite gabbronorite gabbro wehrlite websterite and lherzolite with systematic geochemical variations that are consistent with the following crystallization sequence ol chr ol pyx chr cpx pl and hbl bt igneous zircons separated from a diorite in the huangshanxi intrusion yield a 269 2 ma shrimp u pb age the rocks are enriched in rb ba u k sr relative to th and lree depleted in nb ta relative to th and exhibit positive end values 6 7 to 9 3 ni cu pge sulfide mineralization occurs in the lower parts of the intrusions primarily strata bound within wehrlite or lherzolite and locally stratiform along the margins of the intrusions the parental magmas appear to have been derived from a mantle source that was previously contaminated by subduction of oceanic crust and to have been variably contaminated by upper continental crustal components the intrusions appear to have formed by plume related activity within a continental setting likely related to post orogenic extension following carboniferous amalgamation of arc related terranes in the caob this plume activity was most likely also responsible for providing heat sources to generate large amounts of a type granites across the caob

tethyan subducted slabs under india abstract tomographic imaging of the mantle under tibet india and the adjacent indian ocean reveals several zones of relatively high p wave velocities at various depths under the hindu kush region in northeastern afghanistan and southern tajikistan a regional northward dipping slab is seen in the entire upper 600 km of the mantle and is apparently still attached to the lithosphere of the indian plate under northern pakistan this same slab shows a roll over structure with the deeper portion overturned and dipping southward as can also be seen in the distribution of earthquake hypocenters farther east southeast e g in the vicinity of nepal a well resolved anomaly below 450 km depth is connected to the slab under the hindu kush but seems to be separated from the lithosphere above 350 km these upper mantle anomalies are interpreted as the remnants of delaminated sub continental lithosphere that went down when greater india continued to converge northward with asia after 45 ma the deeper high velocity anomalies under the indian sub continent appear clearly separated from the shallower ones as well as from each other and are inferred to represent remnants of oceanic lithospheric slabs that have sunk into the lower mantle and were subsequently overridden by the indian plate they occur at depths between 1000 and 2300 km and occasionally descend down to the core mantle boundary the anomalies form three parallel wnw ese striking zones we interpret the two southern zones as remnants of oceanic lithosphere that was subducted when the neo tethys ocean closed between india and tibet in the cretaceous and earliest tertiary the northern deep mantle zone under northern afghanistan the himalayas and the lhasa block in southern tibet may represent the last subducted remnant of the paleo tethys ocean which is thought to have closed before the hauterivian stage of the early cretaceous the middle zone continues southeastward as a rather straight high velocity zone towards sumatra where it becomes convex southward and parallel to the subduction zone under the sunda arc comparison of this straight middle zone near india with the shallower upper 600 1000 km northern zone which displays a cusp like shape near the yunnan sw china syntaxis of the eastern himalayas supports the notion that the shallow northern zone represents later subduction than the deeper middle zone the suggestion of a counterclockwise rotation 20 of the indian plate during tertiary indentation of asia is supported by these features the present day latitudes of 5 35 n of the deep slabs under india and adjacent areas correspond to the approximate paleolatitudes of the cretaceous subduction zones the slab remnants in the middle mantle occur therefore near the ancient locations where they started their downward journey which implies that lateral movements in the deeper mantle were not large

upb geochronology of gangdese transhimalaya plutonism in the lhasa xigaze region tibet abstract a series of different plutons from the lhasa xigaze segment of the gangdese transhimalaya belt has been studied by high resolution u pb analyses of zircon using zircon fractions of 5 100 grains each selected upon specific grain characteristics for two diorites located east of xigaze dazhuka the zircons yield concordant ages of 93 4 1 0 and 94 2 1 0 m y respectively also concordant ages of 41 1 0 4 and 41 7 0 4 m y have been obtained for two granodiorites collected southwest of lhasa qushui the precision on the ages of two granites from the xigaze and lhasa area is limited by two factors the presence of inherited radiogenic lead and the occurrence of subsequent lead loss however some concordant zircons detected in both granites define approximate ages of about 67 and 53 m y respectively the inherited lead components show that melting of precambrian material was involved in magma genesis the u pb ages substantiate a magmatic activity lasting from mid cretceous cenomanian to eocene lutetian time such a period of plutonism at the southern margin of eurasia as well as the occurrence of magma generation from continental crust suggest that the gangdese range results from the subduction of tethys oceanic lithosphere indian plate underneath eurasia eurasian plate if this model is true the collision of india with eurasia along the lhasa xigaze sector postdates the emplacement of the 41 m y old gangdese granodiorites i e the collision occurred after lutetian time

paleocene eocene record of ophiolite obduction and initial india asia collision south central tibet 1 uppermost cretaceous to eocene marine sedimentary sequences occur both to the south and north of the yarlung zangbo suture in south central tibet they consist of indian margin strata of the northern tethyan himalaya and asian margin strata of the gangdese forearc both assemblages are characterized by major changes in depositional environment and sedimentary provenance at 65 ma and an appearance of detrital chromium rich spinel of ophiolite affinity tio2 generally 0 1 wt during the paleocene ophiolitic melange exposed along the suture could have provided a source for detrital spinel the melange occurs in the hanging wall of a north dipping south directed mylonitic shear zone which includes a tectonic sliver of mafic schist amphibole from the schist yields 40ar 39ar ages of 63 ma which we attribute to cooling during slip along the shear zone and southward obduction of the melange melange obduction was coeval with the development of an angular unconformity within the gangdese forearc basin to the north between late maastrichtian time and 62 ma upper paleocene to middle eocene sandstones in the northern tethyan himalaya yield 200 120 ma u pb detrital zircon ages and 190 170 ma 40ar 39ar detrital mica ages these detrital grains were most likely sourced from regions north of the yarlung zangbo suture suggesting that onset of india asia collision in south central tibet is middle eocene or older in age collectively our results support previous suggestions that oceanic rocks were obducted onto the northern margin of india during latest cretaceous earliest tertiary time coeval changes in gangdese forearc sedimentation raise the possibility that this obduction event marks onset of tectonic interaction between india and asia at 65 ma alternatively in concert with the conventional view of eocene collision initiation the obducted oceanic rocks may be of intraoceanic origin while coeval changes in gangdese forearc sedimentation may be a consequence of an increase in the rate of ocean continent convergence following the demise of the intraoceanic subduction zone

mid holocene aboriginal occupation of offshore islands in northern australia a reassessment of wurdukanhan mornington island southern gulf of carpentaria australia claims for mid holocene aboriginal occupation at the shell matrix site of wurdukanhan mornington island gulf of carpentaria australia are reassessed through an analysis of the excavated assemblage coupled with new surveys and an extensive dating program memmott et al 2006 pp 38 39 reported basal ages of c 5000 5500 years from wurdukanhan as the oldest date yet obtained for any archaeological site on the coast of the southern gulf of carpentaria and used these dates to argue for a relatively lengthy occupation since at least the mid holocene if substantiated with the exception of western torres strait these claims make mornington island the only offshore island used across northern australia in the mid holocene where it is conventionally thought that aboriginal people only re colonised islands after sea level maximum was achieved after the mid holocene our analysis of wurdukanhan demonstrates high shellfish taxa diversity high rates of natural shell predation and high densities of foraminifera throughout the deposit demonstrating a natural origin for the assemblage results are considered in the context of other dated shell matrix sites in the area and a geomorphological model for landscape development of the sandalwood river catchment

petrology and chemistry of apollo 12 regolith breccias petrographic mineral chemical and bulk chemical data are reported for the three large apollo 12 regolith breccias of the regolith breccia suite and for eight breccias handpicked from apollo 12 coarse fines two samples formed from non kreepy anorthositic regolith not presently found at the sampling site eight of the samples can be considered mixtures of local basalt and kreep components with minor anorthositic components mare kreep ratios indicated by chemical mixing models range from 86 7 to essentially endmember kreep one sample is unlike the others feo 23 7 mgo 21 7 and may be a new lithology or alternatively a nonrepresentative sample of the 11 samples studied 5 appear to be of local origin 3 are most likely exotic to the site and results for 3 others are inconclusive the anorthositic breccias formed from apollo 16 like regolith and may have been transported over several hundred kilometers from the non kreepy highlands to the east alternatively they may be of local origin formed from the material beneath the apollo 12 basalt flows

shoshonitic volcanism in the northern mariana arc 1 mineralogic and major and trace element characteristics petrographic and geochemical characteristics of samples dredged from 23 submarine volcanic edifices in the northern mariana and southern volcano arcs define two distinct rock series the central and northern mariana arc to 23 n and the northern volcano arc north of iwo jima are characterized by plagioclase clinopyroxene orthopyroxene titantomagnetite bearing subalkaline rocks including both low k and medium k series the northern mariana arc and southern volcano arc from 23 n to iwo jima are erupting rocks of a shoshonitic series with phenocrysts of plagioclase clinopyroxene olivine and biotite these rocks are less saturated than those of the subalkaline provinces and are substantially enriched in ba 400 900 ppm sr 600 1000 ppm k2o 1 4 5 and k2o na2o 0 4 1 2 relative to the subalkaline lavas ba y and ba zr increase by a factor of 3 to 4 in the shoshonitic rocks but k rb ba sr and k ba are relatively constant throughout the arc there is no relationship between degree of enrichment and volcano volume or degree of fractionation seamounts and islands within each province have the same range of compositions much of the intra edifice variation in lava composition can be modeled by 10 70 crystallization of plagioclase and clinopyroxene with smaller amounts of olivine orthopyroxene and titanomagnetite or by accumulation of 10 40 phenocrysts dominantly plagioclase the differences between parental lavas in the alkalic and subalkalic provinces require melting of two distinct mantle sources the occurrence of this enriched mantle in the northern marianas may be a consequence of the propagation of the mariana trough spreading center into the volcano arc

volcanic rocks of the 1985 tibet geotraverse lhasa to golmud volcanic rocks encountered during the tibet geotraverse have been studied in the field in thin section and by major and trace element geochemistry in order to determine their most probable original eruptive environment rocks from a total of eleven distinct volcanic provinces were studied in this way they provide evidence for an active continental margin or post collision province of probable devonian early carboniferous age in the northern kunlun mountains an active continental margin of late carboniferous age in the southern lhasa terrane permian continental rifts in the central qiangtang and central kunlun terranes triassic volcanic arcs in the southern lhasa and northern qiangtang terranes a triassic active continental margin dyke swarm in the northern kunlun mountains a jurassic post collision or back arc rifting province in the southern qiangtang terrane a jurassic island arc in the northern lhasa terrane a cretaceous post collision province in the northern lhasa terrane possibly extending into the southern qiangtang terrane and a palaeogene active continental margin in the southern lhasa terrane an oligocene trachyte plug in the northern qiangtang terrane was the only evidence encountered during the geotraverse of volcanism post dating the palaeogene india eurasia collision however the composition of this plug coupled with new and published analyses from miocene volcanics in the southern lhasa terrane and from the pliocene recent volcanic province of northwest tibet places important constraints on models for post collision underplating of tibet by continental lithosphere any underplating is likely to have been a much later than the start of collision b directed beneath tibet from the north as well as the south and c limited in extent

an experimental investigation of agglutinate melting mechanisms shocked mixtures of apollo 11 and 16 soils mixtures of chemically contrasting lunar soils from a 11 and a 16 have been shocked at pressures ranging from 18 2 62 0 gpa 182 620 kb other than the generation of impact melts modal and textural changes caused by shock include destruction of pore space and fused soil clasts and conversion of plagioclase to maskelynite the loss of the fused soil component in these runs indicates that low agglutinate contents in shocked and or compacted regolith breccias cannot be considered by themselves to be evidence of formation from immature regolith from the petrographic and chemical data it appears that the impact glass formed mainly from the fine fraction and the fused soil component in the target with relatively minor contributions from the other coarse clasts the impact glasses exhibit the same chemical enrichments and depletions as their corresponding fine fractions and plot on or near a mixing line between the bulk and fine fraction of the soil in which they were formed from this as well as several other studies it appears that the fusion of the finest fraction f3 model is valid and that it accurately predicts the chemical systematics of impact glass formed from lunar soil in addition fusion of agglutinates present in the target soil is an important process

apollo 16 regolith breccias and soils recorders of exotic component addition to the descartes region of the moon abstract the subdivision of apollo 16 regolith breccias into ancient 4 b y and relatively younger samples on the basis of trapped 40 ar 36 ar ratios 1 makes possible with the present day soils as a third sample suite a petrologic and chemical determination of regolith evolution and exotic component addition at the a 16 site petrologic data for the ancient breccias show that the early regolith was composed of fragments of plutonic rocks and impact melt rocks and minerals and impact glasses derived from these lithologies the presence of kreepy glasses in the ancient breccias demonstrates that kreepy lithologies and impact melts formed early in lunar history comparison of the ancient breccias with the young breccias and the soils shows that the mare components mainly in the form of orange high tio 2 glass and green low tio 2 glass were mostly added to the site after formation of the ancient breccias and prior to formation of the young breccias the young breccias are petrologically similar to the soils the major change in the regolith since the formation of the young breccias is an increase in maturity the formation of fused soil particles with prolonged exposure to micrometeorite impacts by contrast the breccias formed at times when large impacts and soil mixing were dominant over small impacts and maturation

shoshonites in southern tibet record late jurassic rifting of a tethyan intraoceanic island arc abstract detailed field mapping combined with a petrologic and geochemical investigation of the zedong terrane within the yarlung tsangpo suture zone provides insights to the evolution of now mostly subducted portions of tethys during the late jurassic the terrane is dominated by volcanic rocks of shoshonitic affinity which were erupted in a submarine oceanic island arc setting the volcanic island arc was built on a basement of oceanic crust and the shoshonites locally overlie a thin section of pillowed island arc tholeiites and red ribbon bedded radiolarian cherts geochemistry of the shoshonites suggests that their development occurred in a setting analogous to that of late miocene to early pliocene fiji and was associated with an arc rifting we speculate that this event may have been a far field response to developments associated with gondwana breakup

the high k2o volcanism of northwestern tibet geochemistry and tectonic implications cenozoic volcanic rocks sampled during the 1989 sino french kunlun geotraverse have been analyzed to constrain the origin of widespread tertiary to neogene tibetan basic magmatism samples ranging from phonotephrites to trachyandesites are high k lavas k na always greater than 1 which exhibit typical calc alkaline characteristics although they are highly enriched in mobile trace elements and ree 600 times chondrites for la isotopic compositions exhibit radiogenic sr and pb 87sr 86sr 0 708 208pb 204pb 39 39 4 207pb 204pb 15 6 15 7 206pb 204pb 18 7 and unradiogenic nd 143nd 144nd 0 5123 0 5124 constancy of sr and nd isotopic values contrasts with variations in pb isotopes and highlights the problem of crustal contamination afc and simple mixing models are compatible with isotopic variations but were probably buffered by elemental concentration in sr and nd while pb isotopic values for the most primitive magmas are probably uncontaminated isotopic features are therefore proposed to be representative of a mantle source in which heterogeneity could be highlighted in the pb isotopic values such a source highly enriched in trace elements and radiogenic sr and pb is proposed to lay in the subcontinental mantle isolated from the overall convection movements the calc alkaline characteristics can date from the succession of enrichment phases linked to the numerous subduction events that have affected this part of asia while the isotopic characteristics are proposed to be the result of the aging of the concomitant lile enrichments the broad geographical geochemical and timing aspects of recent basic cenozoic magmatism are discussed in the light of our new data and we suggest that two mechanisms are acting together 1 a limited delamination of the base of the lithosphere or a thermal reequilibration of isotherms subsequent to thickening and 2 intracontinental subduction under the kunlun such mechanisms appear the most probable as they respect at the same time recent geophysical data and other geochemical studies

western oceanus procellarum as seen by c1xs on chandrayaan 1 we present the analysis of an x ray fluorescence xrf observation of the western part of oceanus procellarum on the moon s nearside made by the chandrayaan 1 x ray spectrometer on 10th february 2009 through forward modelling of the x ray spectra we provide estimates of the mgo sio2 and al2o3 sio2 ratios for seven regions along the flare s ground track these results are combined with feo and tio2 contents derived from clementine multispectral reflectance data in order to investigate the compositional diversity of this region of the moon the ground track observed consists mainly of low ti basaltic units and the xrf data are largely consistent with this expectation however we obtain higher al2o3 sio2 ratios for these units than for most basalts in the apollo sample collection the widest compositional variation between the different lava flows is in wt feo content a footprint that occurs in a predominantly highland region immediately to the north of oceanus procellarum has a composition that is consistent with mixing between low ti mare basaltic and more feldspathic regoliths in contrast to some previous studies we find no evidence for systematic differences in surface composition as determined through x ray and gamma ray spectroscopy techniques