reappraisal of early paleogene ccd curves foraminiferal assemblages and stable carbon isotopes across the carbonate facies of perth abyssal plain bulk carbonate content planktic and benthic foraminiferal assemblages stable isotope compositions of bulk carbonate and nuttallides truempyi benthic foraminifera and non carbonate mineralogy were examined across 30 m of carbonate rich paleogene sediment at deep sea drilling project dsdp site 259 on perth abyssal plain off western australia carbonate content mostly reflecting nannofossil abundance ranges from 3 to 80 and generally exceeds 50 between 35 and 57 mbsf a clay rich horizon with a carbonate content of about 37 occurs between 55 17 and 55 37 mbsf the carbonate rich interval spans planktic foraminiferal zones p4c to p6b 57 52 ma with the clay rich horizon near the base of our zone p5 upper p6b throughout the studied interval benthic species dominate foraminiferal assemblages with scarce planktic foraminifera usually of poor preservation and limited species diversity a prominent benthic foraminiferal extinction event bfee occurs across the clay rich horizon with an influx of large acarinina immediately above the 13c records of bulk carbonate and n truempyi exhibit trends similar to those observed in upper paleocene lower eocene 57 52 ma sediment from other locations two successive decreases in bulk carbonate and n truempyi 13c of 0 5 and 1 0 characterize the interval at and immediately above the bfee despite major changes in carbonate content foraminiferal assemblages and carbon isotopes the mineralogy of the non carbonate fraction consistently comprises expanding clay heulandite zeolite quartz feldspar sodic or calcic minor mica and pyrolusite mno2 the uniformity of this mineral assemblage suggests that site 259 received similar non carbonate sediment before during and after pelagic carbonate deposition the carbonate plug at site 259 probably represents a drop in the ccd from 57 to 52 51 ma as also recognized at other locations

formation and tectonic evolution of the cretaceous jurassic muslim bagh ophiolitic complex pakistan implications for the composite tectonic setting of ophiolites the muslim bagh ophiolitic complex balochistan pakistan is comprised of an upper and lower nappe and represents one of a number of ophiolites in this region which mark the boundary between the indian and eurasian plates these ophiolites were obducted onto the indian continental margin around the late cretaceous prior to the main collision between the indian and eurasian plates the upper nappe contains mantle sequence rocks with numerous isolated gabbro plutons which we show are fed by dolerite dykes each pluton has a transitional dunite rich zone at its base and new geochemical data suggest a similar mantle source region for both the plutons and dykes in contrast the lower nappe consists of pillow basalts deep marine sediments and a me lange of ophiolitic rocks the rocks of the upper nappe have a geochemical signature consistent with formation in an island arc environment whereas the basalts of the lower nappe contain no subduction component and are most likely to have formed at a mid ocean ridge the basalts and sediments of the lower nappe have been intruded by oceanic alkaline igneous rocks during the northward drift of the indian plate the two nappes of the muslim bagh ophiolitic complex are thus distinctively different in terms of their age lithology and tectonic setting the recognition of composite ophiolites such as this has an important bearing on the identification and interpretation of ophiolites where the plate tectonic setting is less well resolved

lunar meteorite queen alexandra range 93069 a lunar highland regolith breccia with very low abundances of mafic components lunar meteorite que 93069 found in antarctica is a mature anorthitic regolith breccia with highland affinities that was ejected from the moon 0 3 ma ago the frequency distribution of mineral and lithic clasts gives information about the nature of the regolith and subregolith basement near the ejection site as well as about the abundances of rock types shocked to different degrees prior to the breccia formation thin section que 93069 37 consists of 67 5 vol fine grained 130 m constituents and 32 5 vol mineral and lithic clasts and an impact melt vein the most abundant types of these clasts are intragranularly recrystallized anorthosites and plagioclases together 26 3 vol and feldspathic fine grained to microporphyritic crystalline melt breccias 21 9 vol mafic crystalline melt breccias are extremely rare 1 3 vol granulitic lithologies are 10 4 vol recrystallized feldspathic melt breccias are 15 0 vol and glasses are 3 5 vol the impact melt vein cutting across the entire thin section was probably formed subsequent to the lithification process of the bulk rock at pressures below 20 gpa because the bulk rock never experienced a higher peak shock pressure lunar meteorite que 93069 has a higher abundance of clear glass occurring within melt spherules glassy fragments and an impact melt vein than lunar meteorites alha81005 y 791197 y 82192 3 y 86032 or mac 88104 5 the high abundance of melt spherules indicates that this lunar meteorite contains the highest content of typical regolith components mafic crystalline melt breccias are much rarer in que 93069 than in all other lunar highland regolith breccias the extremely low abundance of mafic components may constrain possible areas of the moon from which the breccia was derived the source area of que 93069 must be a highland terrain lacking significant mafic impact melts or mare components

getting over continent ocean boundaries the idea of a simple linear boundary between continental and oceanic crust at extended continental margins is widely recognized to be an oversimplification despite this such boundaries continue to be mapped because of their perceived utility in palinspastic and plate kinematic reconstructions to examine whether this perception is justified we review the data and models on which basis continent ocean boundaries are interpreted and map a set of such interpretations worldwide from more than 150 publications the maps show that the location of the continent ocean boundary is rarely consistently estimated within the 10 100 km observational uncertainty that might be expected of the geophysical data used for doing so that this is the case regardless of whether the transition zone behind the boundary is classified as magma rich or magma poor and that the geographical separation of estimates exceeds the width of single study continent ocean transition zones the average of global maximum separations across sets of three or more estimates is large 167 km and mostly a consequence of interpretations published over the last decade we interpret this to indicate an extra component of uncertainty that is related to authors understanding of the range of features that are interpretable at extended continental margins we go on to discuss the implications of this uncertainty for palinspastic and plate kinematic modelling using examples from the literature and from the south atlantic ocean we conclude that a precise continent ocean boundary concept with locational uncertainty defined from the ensembles is of limited value for palinspastic reconstructions because the reconstruction process tends to bunch the ensemble within a region that is i of similar width to the observational uncertainties associated with continent ocean boundary estimates ii narrower than the regions of uncertainty about rotated features implied by the propagation of uncertainties from plate rotation parameters and iii coincident within all the above uncertainties with the more easily mapped continental shelf gravity anomaly secondly we conclude that estimated continent ocean boundaries are of limited use in developing or testing plate kinematic reconstructions because i reconstructions built using them as markers do not within uncertainty limits defined from the ensembles differ greatly from those using more easily determined bathymetric or gravity anomaly contours and ii because it is impossible to segment and date them with useful precision to use as markers of the edges of rigid oceanic lithosphere outside of the constraints of a pre existing plate kinematic model

lunar highland meteorites and the composition of the lunar crust abstract major minor and trace element data obtained by neutron activation techniques and by spark source mass spectrometry ssms on two lunar meteorites mac88104 and mac88105 are reported both mac samples were also analysed for their contents and isotopic compositions of rare gases additional ssms data were obtained on four lunar highland meteorites previously found in antarctica alha81005 y791197 y82192 and y86032 mac88104 and mac88105 are very similar in chemistry suggesting that they are pieces of a single fall event the bulk chemical composition of mac88104 5 is not very different from the other lunar highland meteorites highly aluminous with relatively low contents of ree and siderophile element concentrations slightly above 1 of a ci chondritic level however mafic element concentrations mg cr mn etc are slightly lower in mac88104 5 than in the other lunar highland meteorites the contents of solar rare gases in the two mac samples are low indicating only a small regolith contribution in agreement with rare petrographically identifiable regolith components the mac samples and also y82192 and y86032 are classified as fragmental breccias with negligible regolith components in contrast to alha81005 and y791197 which are regolith breccias with high solar wind derived rare gas contents there is no correlation among lunar meteorites between peak shock pressures and solar gas contents indicating that peak shock pressures of up to 25 gpa do not lead to gas loss a low 26al activity vogt et al 1990 and high contents of cosmogenic rare gases in mac88104 5 suggest a long exposure 400 000 years in the lunar sub surface k ar ages are in excess of 3 9 by lunar highland meteorites and compositionally similar granulitic rocks from the apollo 16 and 17 landing sites contain about 1 of a ci chondritic component according to siderophile and volatile element contents but independent of the amount of regolith components apparently the major fraction of meteoritic elements in these rocks was not provided by micrometeorites impacting the regolith the abundances of siderophile e g ir and volatile elements may therefore reflect the last spike of accretion of the moon after the formation of the anorthositic crust lunar meteorites of highland origin are chemically different from the bulk of the apollo 16 highland samples in having higher fe mg ratios and lower contents and less fractionated patterns of incompatible and siderophile elements since lunar highland meteorites are associated with at least three but probably four different fall events and since they are not derived from chemically exotic front side terranes they may represent a better sampling of the average chemical composition of the lunar crust than previous estimates based on returned lunar samples and remote sensing data a comparison between an average highland composition derived by taylor 1982 and an estimate based on lunar highland meteorites shows that the taylor composition contains higher concentrations and more fractionated incompatible elements mainly because of a substantial amount of kreep a trace element rich highly fractionated component from the front side of the moon not present at the sites from which the lunar meteorites come

climate and geomorphology in the uppermost geomorphic belts of the central mountain range taiwan abstract the central mountain range of taiwan is in its lower parts exposed to strong denudation by mass movements caused by extreme rainfalls and active tectonics even though the uppermost regions of the mountains are also influenced by earthquakes and typhoon rains present geomorphic activity is low investigations based on field work and air photo study in nanhuta shan 3742 m and yushan 3952 m and the analysis of climate data indicate the presence of a periglacial belt with a lower limit at 3600 3700 m the upper limit of the periglacial belt in taiwan is not met ground temperature measurements in nanhuta shan show that freeze thaw activity at 3560 m during the winter is restricted to the top few centimetres of the ground and the maximum frost depth is 25 cm the only indicator landforms within the periglacial belt are smooth slopes the high relief energy and a lack of fine material account for the absence of other periglacial landforms relict solifluction terraces debris cones and slope failures found between 3400 and 3600 m in nanhuta shan are strong evidence for a period of increased slope activity during the holocene which in two cases were dated by osl to approx 3 ka at least one solifluction unit developed during a cooler phase between 3 ka and today

a ferroan region of the lunar highlands as recorded in meteorites mac88104 and mac88105 macalpine hills 88104 and 88105 mac88104 5 are paired meteorites of noritic anorthosite composition from the lunar highlands mac88105 is a breccia composed mainly of melt breccia clasts in a fine grained fragmental and partly glassy matrix the most abundant melt lithologies are feldspathic and are similar in composition to the bulk meteorite other melt lithologies include feldspathic melt rocks mafic melt breccias and a rare melt breccia relatively enriched in incompatible trace elements subordinate lithic clasts are granulitic breccias and ferroan relatively low mg mg fe igneous lithologies including troctolitic anorthosite anorthositic norite gabbronorite and anorthosite igneous clasts having mafic mineral compositions more magnesian than fo55 and en60 were not observed rare fragments of glass spheres and shards as well as glass clasts indicate that the meteorite was derived from an immature regolith the bulk composition of mac88105 is characterized by a molar mg mg fe ratio of 0 62 at the extreme low end of the range for meteorites from the lunar highlands its low concentrations of incompatible trace elements and feldspathic bulk composition 29 al2o3 suggest that it like the other lunar meteorites formed at a site far removed from the areas sampled by the apollo missions similarities in mineral compositions among the different lithologies of the breccia melt breccia clasts granulitic breccias igneous fragments and the distribution of mineral fragments suggest that most components of the meteorite were derived from a crustal section dominated by material with a noritic anorthosite composition and an affinity to the ferroan suite of plutonic rocks the mafic melt breccias have roughly peritectic melt compositions similar to many low k fra mauro melt breccias in the apollo collection but much more ferroan and represent a source material distinct from the noritic anorthosite moderate ce anomalies both positive and negative occur in some separated clasts and to a lesser extent in some small chips dominated by matrix but not in powder prepared from 20 g of bulk meteorite these anomalies are almost certainly terrestrial weathering effects one granulitic breccia clast is rich in siderophile elements as a result of a large amount of fe ni metal the auir ratio of the clast 0 64 ci normalized is distinctly different from that of metal rich impact melts from apollo 16 3 ci normalized the compositional range observed among the nonmare lunar meteorites alha81005 y791197 y82192 3 y86032 and mac88104 5 is equivalent to that observed among representative samples of 1 mm fines from apollo 16 thus compositional data provide little constraint on the number of impacts required to eject these meteorites from the moon

paired lunar meteorites mac88104 and mac88105 a new fan of lunar petrology abstract new lunar meteorite mac88104 5 represents an exciting new opportunity to study a potentially unsampled region of the moon we have analyzed six thin sections by electron microprobe and three bulk samples by instrumental neutron activation ina in order to determine the chemical characteristics of this new lunar sample lunar meteorite macs 8104 5 is dominated by lithologies of the ferroan anorthosite fan suite and contains abundant granulitized highland clasts devitrified glass beads of impact origin and two small clasts which appear to be of basaltic origin one of these asaltic clasts clast e in mac88105 84 is probably mesostasis material whereas the second larger clast clast g may be similar to the very low ti vlt or low ti high alumina mare basalts impact melt clasts mac88105 69 and 72 have major and trace element compositions similar to the bulk meteorite there is little evidence of any lkfm low k fra mauro or low k kreep contribution to this meteorite as mac88104 5 and other brecciated lunar meteorites are fe rich and poor in the incompatible elements relative to apollo 16 regolith and feldspathic breccias while the exact site of origin for the lunar meteorites cannot be pinpointed it is evident that they were derived from a relatively kreep free ferroan anorthosite terrain

multiple sources for volcanic rocks dredged from the western australian rifted margin abstract igneous rock samples recovered during the 2008 09 australian southwest margin marine reconnaissance survey ga 2476 off the western australian coast from perth to the wallaby plateau come from a variety of tectonic settings reflecting a complex magmatic history of this margin cretaceous rhyolite and basaltic andesite samples most likely erupted in a continental extensional setting while younger volcanic samples reflect a transition to a mature passive continental margin with the generation of mid ocean ridge basalt during the last phase of volcanism a series of volcanic cones and mounds with ocean island basalt geochemical signatures formed along the margin the pre rift sedimentary rocks sampled on the wallaby plateau support the viewpoint that it is an extended block of continental crust overlain by syn rift and post rift volcanic rocks

the banda celebes sulu basin a trapped piece of cretaceous eocene oceanic crust the banda celebes and sulu basins are poorly understood marginal seas located at the junction of the eurasian indian australian and pacific philippine sea plates the incompleteness of the data sets the complex geology of the surrounding islands and the late cenozoic evolution involving subduction rifting transform faulting and island arc collision have complicated tectonic interpretation of the region the banda basin is underlain by oceanic crust1 3 bowin et al 2 and lapouille et al 3 have suggested that it is a trapped oceanic basin which was once continuous with the late jurassic argo abyssal plain off north west australia similarly the celebes and sulu basins are also underlain by oceanic crust4 6 on the basis of newly identified magnetic reversal ages fig 1 heat flow data and on land geological studies we suggest that the celebes and sulu seas may have been continuous with the banda basin this cretaceous eocene basin has been dissected into its present configuration by tertiary tectonic processes

late jurassic early cretaceous evolution of the eastern indian ocean adjacent to northwest australia over 9700 km of new aeromagnetic data were acquired off the northwest coast of australia and combined with existing magnetic data to map magnetic isochrons in the eastern indian ocean the isochrons were used to constrain a tectonic model of the evolution of the seafloor in the argo cuvier and gascoyne abyssal plains a complete set of anomalies from m26 through m16 was found in the argo abyssal plain trending generally n70 e spreading commenced in the center of the basin at or prior to m26 and propagated outward until at least m24 time anomalies m10 mo recording the separation of australia and india were found in the cuvier and gascoyne abyssal plains with a trend of about n30 e a significant crustal age discontinuity occurs in the vicinity of the joey rise where the two lineation sets converge because there appears to be no overlap of isochron ages in the two groups it is not necessary to postulate that a triple junction existed off northwest australia as has been previously suggested at m4 m5 time a 10 clockwise change in spreading direction occurred on the cuvier gascoyne spreading system this event triggered ridge jumps that transferred two pieces of the indian plate to the australian plate overlapping spreading on the forming and dying ridges curved fracture zones and lineations as well as fanned lineation trends suggest that the ridge jumps occurred by ridge propagation and that the transferred lithospheric blocks behaved as microplates for a brief interval of approximately 1 2 m y

reconstruction of the east africa and antarctica continental margins the early jurassic separation of antarctica from africa plays an important role in our understanding of the dispersal of gondwana and pangea previous reconstruction models contain overlaps and gaps in the restored margins that reflect difficulties in accurately delineating the continent ocean boundary cob and determining the amount and distribution of extended continental crust this study focuses on the evolution of the african margin adjacent to the mozambique basin and the conjugate antarctic margin near the riiser larsen sea satellite derived gravity data have been used to trace the orientations and landward limits of fracture zones a 3 d gravity inversion has produced a crustal thickness model that reliably quantifies the extent and amount of stretched crust crustal thicknesses together with fracture zone terminations reveal cobs that are significantly closer to the african and antarctic coasts than previously recognized correlation of fracture zone azimuths and identified cobs suggests antarctica began drifting away from africa at approximately 171 ma in a roughly sse direction an areal balancing method has been used to restore the crust to a uniform prerift thickness so as to perform a nonrigid reconstruction for both nonvolcanic and volcanic margins both margins reveal a trend of increasing extension from east to west our results suggest africa underwent extension of 60 120 km while antarctic crust was stretched by 105 180 km various models tested to determine the direction of extension during rifting suggest that antarctica moved away from africa in a wnw ese direction during the period between 184 and 171 ma prior to the onset of seafloor spreading

composition of the cayley formation at apollo 16 as inferred from impact melt splashes chemical data for impact melt splashes ims collected at the apollo 16 landing site show that ni concentrations and feo ni cr ni and co ni correlations are consistent with a chondritic meteoritic component present at levels between approximately 1 5 and 11 wt like apollo 16 soils the ims are intermediate in composition to apollo 16 rocks the chemical data for the ims are consistent with two main compositional groups the group a ims 28 samples are chemically distinct from local apollo 16 soils and are very similar to mixtures of anorthosite and low sc vha lscvha impact melt rocks calculated to a meteorite free basis their average sc concentration la sc mgo sc and tio2 mgo ratios and mg value are 6 1 ug g 1 94 9800 0 066 and 0 74 respectively the group b ims seven samples have chemical equivalents among the soils five samples are chemically very similar to mature apollo 16 soils from the central and southern parts of the landing site two are more similar to soils 67601 and 67941 from north ray crater generally the group b ims and soils are enriched in a composition similar to anorthositic norite 67215 or mixtures thereof with anorthosite as compared to the group a ims the average sc concentration la sc mgo and tio2 mgo ratios and mg value for the subgroup of five are 9 3 ug g 1 41 5780 0 124 and 0 66 respectively the corresponding values for the subgroup of two are 7 5 ug g 1 04 7400 0 090 and 0 71 respectively the group b ims and most soils have a minor high ti component not present in the group a ims if this component is high ti mare basalt its average concentration is approximately 1 6 wt the seven group a ims that have been dated by rare gas methods all have approximately 2 m y exposure ages an age generally associated with south ray crater these seven and potentially most group a ims are likely quenched samples of the melt volume produced by the south ray impact the chemical signature of the impacting projectile is chondritic and its average concentration for the group a ims is 7 3 wt like large coherent melt sheets from terrestrial impacts the impact melt volume of the south ray impact as represented by the group a ims is homogeneous with respect to target lithologies target lithologies at south ray crater which are represented by the host rocks for the ims include anorthosite lscvha impact melt rocks hscvha impact melt rocks and dimict breccias with the exception of 61016 the melt portion of analyzed dimict breccias has the hscvha composition implying that the dimensional scales of lscvha type of rocks and anorthosite in the south ray target do not extend to the 1 10 cm scale observed for the hscvha dimict breccias the compositional difference between group a ims and surface soils from the southern part of the landing site implies stratigraphic variation in the dominant type of vha impact melt rock within the cayley formation chemical data and mixing model results are consistent with a model in which hscvha rocks dominate lscvha rocks in the surface layer the lscvha rocks dominate hscvha rocks in the layer beneath the south ray impact penetrated both layers as both types of vha impact melt rocks are traceable as ejecta material its impact melt volume was formed primarily from the lower layer to give the observed composition of the group a ims that the north ray impact also sampled the lower layer is indicated by the chemical affinities of soils 67601 and 67941 with the lscvha composition away from north ray crater most soils have chemical affinities with the hscvha composition reflecting soil development primarily from the surface layer estimated average compositions give tio2 mgo sc and la concentrations of 0 69 and 7 1 wt and 10 5 and 21 2 ug g respectively for the surface cayley layer and 0 38 and 5 9 wt and 6 1 and 11 8 ug g respectively for the subsurface cayley layer an average composition estimated for the descartes formation from soil compositions has tio2 mgo sc and la concentrations of 0 25 and 3 5 wt and 7 7 and 2 2 ug g respectively the cayley formation is more kreepy more magnesian and less aluminous than the descartes formation

lunar and martian meteorite delivery services launch mechanisms for lunar and martian meteorites have been investigated by integrating physical modeling constraints geochemical cosmic ray exposure cre constraints and petrologic constraints the potential source region for lunar meteorites is remarkably small compared to the final crater volume cre constraints indicate that most launches start at depths of 3 2 m and cratering theory implies derivation of suitably accelerated objects from a subvolume with diameter only about 0 3 the final crater diameter the shallow depth provenance is probably related to shock wave interference enhanced by the lunar regolith s extremely low compressional wave velocity cre constraints alone imply that four to five separate launch events are represented among the eight well studied lunar meteorites most of the lunar meteorites are regolith breccias which tend to show only limited compositional diversity within any kilometer scale region of the moon several others are polymict breccias which also show relatively subdued compositional diversity compared to igneous rocks the observed diversity among these samples in terms of abundances of mare basalt and kreep and in mg mg fe ratio implies that among eight well studied lunar meteorites only two potential source crater pairings are plausible between asuka 881757 y 793169 most probable and between y 793274 eet875721 altogether these eight lunar meteorites apparently represent at least six separate source craters including three in the past 105 years and five in the past 106 years cre constraints imply that snc meteorites are launched from systematically greater depths than lunar meteorites sncs are also systematically bigger and all nine well studied sncs are uncommonly young by martian standards mafic igneous rocks comparison between viking and apollo results reveals that rocks the size of common meteorites are remarkably scarce in the martian regolith probably due to pervasive weathering a plausible explanation for these trends is that most old small and shallow rocks on mars have been weakened by a two stage process of brecciation followed by pervasive weathering to the point where they seldom survive the stresses of spallation off the planet the scarcity of source crater pairing among the lunar meteorites implies that these objects can be launched from craters much smaller than previously estimated and tends to support the suggestion of rabinowitz 1993 astrophys j 407 412 427 that present day cratering rates for the earth moon region may be higher than previously estimated

lunar ferroan anorthosites mineralogy compositional variations and petrogenesis detailed petrologic study of a suite of lunar ferroan anorthosites indicates that their mineral compositional variations are generally consistent with derivation of these anorthosites from a common parent magma there are continuous compositional variations in major elements and smooth trends in minor elements mg fe in plagioclase al ti cr in pyroxene relict textures zoning and possible primary trends of mineral compositional variations are preserved in many of the anorthosites the presence of heterogeneous bimodal and or trimodal pyroxene compositions suggests that some of the anorthosites are polymict rocks however they are composed entirely of ferroan anorthosite suite lithologies some aspects of the mineral composition data suggest that complex processes operated during formation of the ferroan anorthosites the lack of a well defined positive or negative trend of pyroxene mg mg fe versus plagioclase anorthite content the homogenization of mineral compositions in some anorthosites and the varied and apparently enriched mn contents of pyroxenes in some anorthosites suggest that original igneous compositional characteristics have been altered during and or after crystallization processes operative during anorthosite formation may have included some mixing of different melts trapping of variable amounts of intercumulus liquid postcrystallization redistribution of elements or perturbations both during adcumulus growth and subsequent to crystallization by impact events feo and mgo contents of the highly calcic plagioclase typical of these anorthosites suggest that the plagioclase melt distribution coefficients for these elements need to be reassessed

cogenetic rock fragments from a lunar soil evidence of a ferroan noritic anorthosite pluton on the moon abstract the impact that produced north ray crater apollo 16 landing site exhumed rocks that include relatively mafic members of the lunar ferroan anorthositic suite bulk and mineral compositions indicate that a majority of 2 4 mm lithic fragments from sample 67513 including impact breccias and monomict igneous rocks are related to a common noritic anorthosite precursor compositions and geochemical trends of these lithic fragments and of related samples collected along the rim of north ray crater suggest that these rocks derived from a single igneous body this body developed as an orthocumulate from a mixture of cumulus plagioclase and mafic intercumulus melt after the plagioclase had separated from any cogenetic mafic minerals and had become concentrated into a crystal mush 70 wt plagioclase 30 wt intercumulus melt we present a model for the crystallization of the igneous system wherein system is defined as cumulus plagioclase and intercumulus melt the initial accumulation of plagioclase is analogous to the formation of thick anorthosites of the terrestrial stillwater complex however a second stage of formation is indicated involving migration of the cumulus plagioclase intercumulus melt system to a higher crustal level analogous to the emplacement of terrestrial massif anorthosites compositional variations of the lithic fragments from sample 67513 are consistent with dominantly equilibrium crystallization of intercumulus melt the highly calcic nature of orthocumulus pyroxene and plagioclase suggests some reaction between the intercumulus melt and cumulus plagioclase perhaps facilitated by some recrystallization of cumulus plagioclase bulk compositions and mineral assemblages of individual rock fragments also require that most of the mafic minerals formed in close contact with cumulus plagioclase not as separate layers the distribution of compositions and by inference modes has a narrow peak at anorthosite and a broader larger peak at noritic anorthosite characteristics of the samples and their geochemical trends imply an origin in a system that was large relative to the unknown size of the impact that produced the brecccas of ferroan noritic anorthosite composition that were excavated later by the formation of north ray crater and they appear to be consistent with an origin of the suite within a perched plagioclase cumulate if the moon s crust formed by accumulation of plagioclase in a magma ocean ferroan noritic anorthosite formed as an orthocumulate is an alternative to extensive adcumulus formation of ferroan anorthosite 90 vol plagioclase this provides a relatively mafic ferroan anorthositic component 15 vol mafics which is required by mass balance models of compositions of polymict lunar crustal materials the inferred bulk composition of the system of cumulus plagioclase and intercumulus melt is similar to that of ferroan regolith breccia macalpine hills 88104 5 a lunar highland meteorite and may represent a common and widespread component of the moon s early highland crust

origin of lunar meteorite alha 81005 clues from the presence of terrae clasts and a very low titanium mare basalt clast petrographic data and pyroxene compositions indicate that meteorite alha 81005 is a breccia from the terrae of the earth s moon thin section alha 81005 9 includes ferroan anorthositic clasts a lone clast of mg suite plutonic composition fragments which are intermediate in composition between ferroan anorthosite and mg suite plutonics and a clast of very low titanium mare basalt fragments of norite and harzburgite have mineral compositions like ferroan anorthosite and a clast of ferroan anorthosite has pyroxenes with lower molar mg mg fe than in known pristine rocks the mg suite protoliths for the clasts of intermediate composition are inferred to be magnesian troctolites spinel troctolites and feldspathic lherzolites although clasts of these lithologies are not present in alha 81005 9 mineral fragments from them are present a single basaltic clast is of mare origin based on the molar mg mg fe ratio and cr content of its pyroxenes the composition of its plagioclase and the molar ti ti cr ratios of its pyroxenes indicate that the clast is a fragment of very low titanium vlt mare basalt if this basalt is significantly younger than the last basin forming impact event 3 9 109 years ago its presence probably constrains the source crater for alha 81005 to be within a hundred kilometers of a vlt mare basalt flow

antarctic meteorite alha81005 not just another lunar anorthositic norite seven subsamples of meteorite alha81005 a regolith breccia from the lunar highlands were analyzed by inaa for 32 elements four of them were also studied petrographically in bulk composition the rock corresponds to anorthositic norite with a very small component of kreep and is very similar to estimates of average lunar highlands surface compositions of the white clasts and the dark matrix are similar but the clasts are more magnesian and 30 50 as rich in kreep related elements the white clasts have fine grained granulitic textures and are generally similar to apollo 16 and 17 granulitic anorthositic norites but are more magnesian and only 20 as rich in kreep related elements some granulitic clasts are dominated by a magnesian anorthositic norite component not represented among the pristine apollo samples

geochemical comparison of impact glasses from lunar meteorites alha81005 and mac88105 and apollo 16 regolith 64001 abstract most glasses that occur in lunar highland regolith are quenched droplets of impact melt the chemical compositions of these glasses are equivalent in the absence of volatile losses to the original target materials the compositional range of impact glasses in a regolith reflects the chemical diversity that existed throughout the region up to the time of system closure e g breccia formation since these glasses are a product of widespread and random sampling both in terms of space and time they can be used for geochemical exploration of the moon the major element compositions of impact glasses occurring in three samples of lunar feldspathic regolith alha81005 mac88105 apollo 16 64001 have been determined by electron microprobe the glass populations among these three unrelated samples are compositionally distinct while most of the impact glasses within each of these three samples are compositionally similar to the regolith in which they are found up to 40 of the impact glasses are different some of the compositionally exotic glasses were ballistically transported from other areas of the moon and thereby provide information about the compositional range of regoliths that exist elsewhere since the geological setting of the apollo 16 region is well known compared to the source areas of the lunar meteorites the apollo 16 glasses provide a ground truth for interpretations the thirty four impact glasses in meteorite alha81005 overlap the compositional range of feldspathic regoliths represented by all of the lunar highland meteorites i e y86031 y82192 y791197 mac88105 alha81005 and are compositionally distinct from highland regoliths sampled by apollo 14 apollo 16 apollo 17 and luna 20 a small proportion of alha81005 glasses contain a mare component no kreep glasses were observed due to their scarcity only ten impact glasses in lunar meteorite mac88105 were analyzed the spherules occur in two broadly defined compositional groups one group of glasses is similar to the bulk composition of mac88105 whereas the other group is more mafic all of these glasses are distinct from highland regoliths sampled by apollo 14 apollo 16 and apollo 17 and luna 20 a low ti mare glass was also analyzed in mac88105 no kreep glasses were observed the two hundred and fifty three aluminous impact glasses analyzed in apollo 16 regolith 64001 display a prominent grouping of compositions equivalent to the local regolith in addition about 10 of the glasses in 64001 are distinct from the local regolith and chemically resemble the lunar highland meteorites alha81005 mac88105 these glasses may record the chemical composition of an ancient regolith that occurred in the apollo 16 region prior to the arrival of kreep and mare components twentythree percent of the glasses in 64001 have high ti mare affinities these mare glasses are clearly exotic to the apollo 16 site and have been transported from distances of at least 300 km

compositional variation in apollo 16 impact melt breccias and inferences for the geology and bombardment history of the central highlands of the moon abstract high precision data for the concentrations of a number of lithophile and siderophile elements were obtained on multiple subsamples from 109 impact melt rocks and breccias mostly crystalline from the apollo 16 site compositions of nearly all apollo 16 melt rocks fall on one of two trends of increasing sm concentration with increasing sc concentration the eastern trend lower sm sc mg fe and sm yb ratios consists of compositional groups 3 and 4 of previous classification schemes these melt rocks are feldspathic poor in incompatible and siderophile elements and appear to have provenance in the descartes formation to the east of the site the western trend higher sm sc mg fe and sm yb ratios consists of compositional groups 1 and 2 these relatively mafic kreep bearing breccias are a major component 35 of the cayley plains west of the site and are unusual compared to otherwise similar melt breccias from other sites in having high concentrations of fe ni metal 1 2 the metal is the carrier of the low ir au 0 3 chondritic siderophile element signature that is characteristic of the apollo 16 site four compositionally distinct groups 1m 1f 2db and 2nr of western trend melt breccias occur that are each represented by at least six samples compositional group 1 of previous classification schemes the poikilitic or lkfm melt breccias can be subdivided into two groups group 1m represented by six samples including 60315 is characterized by lower al2o3 concentrations higher mgo and alkali concentrations and higher mg fe and cr sc ratios than group 1f represented by fifteen samples including 65015 group 1m also has siderophile element concentrations averaging about twice those of group 1f and ir au and ir ni ratios that are even lower than those of other western trend melt rocks ir au 0 24 0 03 ci normalized at the mafic extreme of group 2 vha melt breccias the melt lithology occurring as clasts in feldspathic fragmental breccias from north ray crater group 2nr is compositionally distinct from the melt lithology of dimict breccias from the cayley plains group 2db in having higher concentrations of sc cr and heavy rare earth elements and lower concentrations of siderophile elements the distinct siderophile element signature high absolute abundances low ir au ratio suggest that the four groups of mafic melt breccia are all somehow related ratios of some lithophile elements also suggest that they are more closely related to each other than they are to melt breccias from other apollo sites however none of the breccia compositions can be related to any of the others by any simple process of igneous fractionation or mixing involving common lunar materials thus the origin of the four groups of mafic melt breccia is enigmatic if they were produced in only one or two impacts then a mechanism exists for generating regimes of impact melt breccia in a single impact that are substantially different from each other in composition for various reasons including the problem of delivering large volumes of four different types of melt to the apollo 16 site it is unlikely that any of these breccias were produced in basin forming impacts if they were produced in as many as four crater forming impacts then the unusual siderophile element signature is difficult to explain possible explanations are 1 1 the four groups of melt breccia all contain metal from a single earlier impact 2 2 they were each formed by related metal rich meteoroids or 3 3 some common postimpact process has resulted in metal of similar composition in each of four melt pools within a compositional group most intrasample and intersample variation in lithophile element concentrations is caused by differences among samples in the proportion of a component of normative anorthosite or noritic anorthosite in most cases this compositional variation probably reflects variation in clast abundance for group 2db and probably 2nr differences in abundance of a component of ferroan anorthosite estimated al2o3 32 accounts for the compositional variation for groups 1m and 1f the anorthositic component is more mafic estimated al2o3 26 some group 2 samples may be related by a troctolitic component of varying abundance

late cretaceous early tertiary convergence between the indian and arabian plates recorded in ophiolites and related sediments abstract remnants of ocean floor forming the eastern ophiolite belt in oman and the western ophiolite belt in pakistan have a common plate tectonic history culminating in emplacement at the cretaceous tertiary boundary fragments of ocean floor in these two belts have ages between 150 and 65 ma and recorded tectonic events in the early indian ocean at 150 ma 130 120 ma 110 100 ma and 70 65 ma new radiometric and chronostratigraphic ages and paleomagnetic and sedimentary information are used to relocate these ophiolites in the frame of the evolving indian ocean which was characterised by the stepwise breakup of gondwana at 158 ma east and west gondwana 130 ma southern atlantic breakup of east gondwana 95 84 ma madagascar and india seychelles 65 ma india and seychelles and finally at 40 ma rifting between africa and arabia the 150 ma old oceanic rocks of masirah island in oman originally formed the extension of the basins now preserved along the eastern edge of the afro arabian plate masirah drifted together with india seychelles when a new ridge formed at approximately 130 ma separating microplates e g kabul block from the northern edge of greater india parts of this new ocean were later emplaced to form the western ophiolite belt in pakistan consumption of oceanic crust and emplacement of ophiolites during the closure of the neotethys occurred not only north of india seychelles but also along two or three subduction zones between the afro arabian plate and india seychelles documented by the formation of metamorphic soles beneath ophiolites relics of ocean floor formed approximately 65 70 ma ago now form the upper units in the western ophiolite belt of pakistan where they overlie an accretionary prism of pillow lavas of dominantly aptian albian age and sedimentary rocks the breakup of india and the seychelles at 65 ma was associated with the eruption of flood basalts deccan and seychelles and enhanced counter clockwise movement of india this breakup possibly caused the late jurassic early cretaceous fragments of ocean floor e g masirah to be thrust onto the eastern edge of oman the ophiolites which were emplaced onto the western edge of india drifted as part of this plate farther north where collision with eurasia and the accreted microplates occurred in the eocene 55 ma

possible lunar source areas of meteorite alha81005 geochemical remote sensing information antarctic meteorite alha 81005 is a regolith breccia apparently sent to earth by an impact event in the lunar highlands laboratory studies of this sample provide information that is used to understand the source region on the moon using remote sensing data the meteorites low thorium content is inconsistent with thorium values measured for the central lunar nearside from orbit with apollo gamma ray spectrometers similarly the mineral assemblages inferred from near ir spectra of small impact craters on the lunar nearside do not exhibit the significant component of olivine and fe bearing feldspar that is observed in the meteorite spectra the existing remote sensing data suggest the most probable source region for alha 81005 is the nearside limb or the lunar farside and that the composition of alha 81005 represents a surface unit that has not previously been extensively sampled

ocean crust vein mineral deposition rb sr ages u th pb geochemistry and duration of circulation at dsdp sites 261 462 and 516 abstract cation exchange experiments ammonium acetate and cation resin on celadonite smectite vein minerals from three dsdp holes demonstrate selective removal of common sr relative to rb and radiogenic sr this technique increases the rb sr ratio by factors of 2 3 to 22 without significantly altering the age of the minerals allowing easier and more precise dating of such vein minerals the ages determined by this technique site 261 121 4 1 6m y site 462a 105 1 2 8m y site 516f 69 9 2 4m y are 34 54 and 18 m y younger respectively than the age of crust formation at the site in the case of site 462a the young age is clearly related to off ridge emplacement of a massive sill flow complex at the other sites either the hydrothermal circulation systems persisted longer than for normal crust 10 15 m y or were reactivated by off ridge igneous activity celadonites show u and pb contents and pb isotopic compositions little changed from their basalt precursors while th contents are significantly lower celadonites thus have unusually high alkali u th ratios and low th u ratios if this celadonite alteration signature is significantly imprinted on oceanic crust as a whole it will lead to very distinctive pb isotope signatures for any hot spot magmas which contain a component of aged subducted recycled oceanic crust initial sr isotope ratios of ocean crust vein minerals smectite celadonite zeolite calcite are intermediate between primary basalt values and contemporary sea water values and indicate formation under seawaterdominated systems with effective water rock ratios of 20 200

the geological development of the passive margins of the exmouth plateau off northwest australia abstract the exmouth plateau is a very large sunken continental block off australia s northwest shelf whose culmination lies 800 m below sea level it is elongated in a northeasterly direction and bounded by abyssal plains on three sides its broad tectonic framework is controlled by mesozoic rifting and transform faulting which accompanied the breakup of australia and greater india after which the plateau sank to bathyal depths the pre breakup sequence consists of more than 5000 m of palaeozoic and early mesozoic shallow marine to terrestrial detrital sediments the post breakup sequence consists of about 2000 m of late mesozoic and cainozoic marine sediments mainly carbonates the northern margin came into existence in the callovian 155 m y ago when a continental fragment separated from it and moved off to the northwest an early phase of rifting gave rise to triassic jurassic intermediate and acid volcanics 213 192 m y ago which overlie a thick triassic paralic sequence steady subsidence north of an east west hinge line allowed several thousand metres of early and middle jurassic carbonates and coal measures to accumulate before breakup breakup occurred along a series of rifted and sheared segments and the margin is further complicated by northeast trending callovian horsts and grabens the horsts were planed off in late jurassic and early cretaceous times and the whole margin was covered by a few hundred metres of late cretaceous and cainozoic pelagic carbonate as it sank steadily to its present average depth of 2000 2500 m the northeast trending western margin formed by rifting in the neocomian 120 125 m y ago as greater india moved off to the northwest callovian normal faults parallel the margin a thick triassic paralic sequence is unconformably overlain by thin late jurassic and younger marine sequences indicating that the area was high in the early and middle jurassic thin late cretaceous and cainozoic pelagic carbonates cover the margin which now lies more than 2000 m below sea level the northwest trending southern margin formed by shearing in the neocomian at the same time as the western margin it is cut by northeast trending normal faults which formed in the late triassic and callovian and is paralleled by neocomian and later normal faults a thick triassic paralic sequence is unconformably overlain by a thick late jurassic and neocomian delta suggesting that the area was high in the early and middle jurassic but a depocentre before and afterwards there was thermal uplift of more than 1000 m during the neocomian period of shearing and igneous intrusions buttressed the margin later normal faulting lowered the outermost margin and turned the uplift into a marginal anticline trending northwest the anticline had sunk beneath the sea by late in the cretaceous and thereafter this margin was covered by a thin sequence of pelagic carbonate which now lies beneath more than 1500 m of water

origin of seaward dipping reflectors in oceanic crust off the norwegian margin by subaerial sea floor spreading a remarkable layered acoustic stratification is observed in the upper oceanic crust adjacent to the norwegian continental margin it comprises a seaward dipping complex of reflectors in the form of a wedge we suggest that it is a layered igneous sequence that results when crustal accretion occurs at a subaerial spreading axis and that this phenomenon may commonly occur during the earliest phase of ocean basin genesis

the nature of the meteoritic components of apollo 16 soil as inferred from correlations of iron cobalt iridium and gold with nickel concentrations of co ni ir and au in small samples of submature and mature soil from apollo 16 are highly variable correlations of fe co ir and au with ni indicate that the variation in siderophile element concentrations results from variation in the concentration of fe ni metal from these correlations the mean composition of the metal is inferred to be 5 6 ni and 0 36 co for a ni co ratio of 15 5 0 7 i e dissimilar to the chondritic ratio of 20 21 the fe ni metal is also characterized by low ir ni and ir au ratios compared to metal in ordinary chondrites metal with a similar composition is also found in metal rich noritic impact melt breccias that occur as discrete rocks as well as small clasts in ancient regolith breccias at apollo 16 mass balance models using lithophile element concentrations indicate that about 35 of the soil is noritic impact melt the fe ni metal associated with this component is sufficient to supply virtually all the ancient fe ni metal found in the typical apollo 16 soil 0 4 0 5 i e no other source is required the soil also contains 1 2 carbonaceous chondrite the concentration of this component appears to be relatively constant from sample to sample and does not contribute significantly to the variation in siderophile element abundances these two meteoritic components contribute nearly equal concentrations of ni to the typical apollo 16 soil

prominent magnetic anomaly along the continent ocean boundary between the northwestern margin of australia exmouth and scott plateaus and the argo abyssal plain abstract a prominent positive magnetic anomaly with amplitude as great as 1400 nt lies along the lower slope between the northern exmouth plateau characterized seismically by faulted layered reflectors and the argo abyssal plain characterized by hyperbolic reflectors because the slope of the northern exmouth plateau is floored by continental crust as shown by triassic and early jurassic volcanics and sediments deposited before the middle jurassic inception of spreading in the argo abyssal plain the anomaly lies along the continent ocean boundary cob to the northeast of the northern exmouth plateau the anomaly here with an amplitude no greater than 700 nt is traced along the lower slope of the rowley terrace and scott plateau and across the expanded continental rise north of 13 s and indicates that the rowley terrace and the bulk of the scott plateau are continental and that only the lower part of the rise north of 13 s is oceanic in this area an oceanic ridge rises above the adjacent breakup unconformity in the scott plateau to impound a deep sedimentary basin like that impounded by the outer voring plateau off norway the cob anomaly is modelled as a shallow two dimensional magnetic body with rectangular cross section and 40 80 km wide that extends up to 20 km seaward of the cob and is interpreted as a complex of rift related dykes in the continental crust and adjacent oceanic crust

mineral compositions in pristine lunar highland rocks and the diversity of highland magmatism high precision electron microprobe analyses of olivine and pyroxene in pristine lunar highland rocks confirm the dichotomy between ferroan anorthosites and the mg suite ferroan anorthosites plot as coherent trends consistent with formation in a complex global magma system lack of coherent compositional trends in the mg suite rocks indicates derivation from numerous magmas

compositional implications regarding the lunar origin of the alha81005 meteorite geochemically alha81005 has all the attributes expected of a regolith sample from the lunar highlands most important is its fe mn ratio 77 within uncertainty the same as the mean lunar ratio there are significant differences however in comparison to previously sampled lunar regoliths the closest precedents are the apollo 16 and luna 20 regoliths particularly the latter but alha81005 has lower contents of na ti and incompatible elements feldspathic granulitic breccias such as 72559 which texturally resemble the most abundant type of clast in alha81005 are also similar compositionally from its low kreep and na contents we infer alha81005 originated well away from the k th and u rich region near the center of the nearside at least as far away as the eastern limb

antarctic meteorite alha 81005 a piece from the ancient lunar crust a 128 mg sample of the antarctic meteorite alha 81005 was analysed for major and trace elements by instrumental neutron activation techniques the meteorite or at least its major components may be older than 4 billion years and represent a piece of the ancient lunar crust before the formation of the large basins on the front side of the moon the evidence is derived from the low absolute content of incompatible elements and their slightly different fractionation pattern from kreep the dominant source for these elements on the front side the basically chondritic pattern of siderophile elements ni co ir au is clearly distinguished from younger basin related meteoritic components

stratigraphic evolution of mesozoic continental margin and oceanic sequences northwest australia and northern himalayas abstract during mesozoic time the northwest australian continental margin and the thakkhola region of north central nepal were adjacent passive margins off northeast gondwana the relatively sediment starved basins provide excellent opportunities for studying the early structural and depositional evolution of the indian ocean during the triassic jurassic rifting stages neo tethys and the jurassic cretaceous transition from rifting to drifting nepalese and australian paleomagnetic studies indicate subtropical paleolatitudes during the late triassic to early jurassic but higher latitudes of 35 40 s during the late jurassic to early cretaceous prior to the sustained northward flight of australia and greater india in the late cretaceous to cenozoic the latitudinal position of the basins and type of sediment are related principal continental margin formation along the northern edge of eastern gondwana started in late permian to triassic time by late triassic early jurassic time platform carbonates with thin lagoonal shales were laid down in a subtropical climate the carnian to rhaetian siliciclastics and carbonates show repeated shallowing upward sequences subsequent southward drift of greater india and australia during mid jurassic time replaced carbonates with more siliciclastic sediment input widespread erosion was caused during local uplift of parts of the northwest australian continental margin as a result of jurassic late rift block faulting a mid callovian early oxfordian hiatus in nepal is a submarine condensed sequence and non tectonic in origin in nepal the overlying 250 m thick organic rich dark shales which are correlated to the oxfordian kimmeridgian clays of circum atlantic hydrocarbon bearing basins can be traced along the northern himalayan range these shales probably represent an extensive continental slope deposit formed in a high productivity of organics belt the diverse foraminiferal microfauna of the belt was previously only known from boreal laurasia the callovian break up uncorformity off northwest australia is actually a post rift unconformity and precedes the onset of seafloor spreading by about 5 10 m y seafloor spreading leading to formation of the present indian ocean started in the argo abyssal plain around 155 ma ago in late jurassic time australia and greater india including northern nepal separated as early as in the late valanginian about 130 ma ago altered ash layers off northwest australia record an important volcanic phase in berriasian valanginian time mafic volcaniclastics in nepalese deltaic sediments also testify to continental margin volcanic activity which may be a precursor to the slightly younger rajmahal traps in eastern india an important tectonic event off northwest australia took place in aptian time 120 115 ma ago when hemipelagic sedimentation changed gradually into more pelagic sedimentation with sharply decreasing rates of deposition in nepal this marks the transition from coarse to fine grained organic rich terrigenous clastics leading eventually to more carbonate bearing strata during the mid cretaceous global sealevel highstand