comparison of the geochemistry of ophiolitic pyroxenites with a strongly fractionated dyke of pyroxenite from the sakhakot qila ophiolite pakistan abstract exceptionally strong fractionation has been found amongst the pyroxenite dykes crosscutting the ultramafic rocks of the sakhakot qila ophiolite pakistan one such dyke an fe websterite is particularly fractionated and anomalously feenriched and mg depleted this is supported by the data from whole rock analyses of major trace and rare earth elements as well as by the mineral chemistry of the constituent chromian spinel olivine clinopyroxene orthopyroxene and magmatic amphibole secondary sulphides of the fe websterite include troilite pentlandite instead of the awaruite heazle woodite pentlandite assemblage typical of all the other ultramafic rocks of the host ophiolite the non cumulate parent liquid of the magnesian pyroxenites crystallized in an initial episode when the surrounding cumulates were still hot in a belated second episode the fe websterite may have crystallized in isolated pockets after its differentiation to an extent much greater than that known from most pyroxenite dykes in ophiolites

ferro andesites in the grande ronde basalt their composition and significance in studies of the origin of the columbia river basalt group flows from the grande ronde basalt of the columbia river basalt group include several with the chemical composition of ferro andesites these flows have sio2 55 mgo 4 and also have higher fe mg than the average value for grande ronde basalt they are also distinctly richer in cs rb k ba la ce th and u than the remainder of the grande ronde basalt flows and possess small negative eu anomalies their pb isotopic compositions define a mixing line with a negative slope on a 206pb 204pb versus 207pb 204pb plot their nd isotopic compositions lie between 143nd 144nd 0 51252 and 0 51264 and their sr isotopic compositions lie between 87sr 86sr 0 7055 and 0 7060 these values define the enriched end of the columbia river basalt group spectrum on a sr nd epsilon diagram excluding the saddle mountains basalt these ferro andesite flows also form a compositional end member of the columbia river basalt group and are sufficiently distinctive to warrant special consideration we compare them with

highly variable coastal deformation in the 2016 mw7 8 kaikōura earthquake reflects rupture complexity along a transpressional plate boundary abstract coseismic coastal deformation is often used to understand slip on offshore faults in large earthquakes but in the 2016 m w 7 8 kaik ura earthquake multiple faults ruptured across and sub parallel to the coastline along 110 km of coastline a rich dataset of coastal deformation comprising airborne lidar differencing field surveying and satellite geodesy reveals highly variable vertical displacements ranging from 2 5 to 6 5 m these inform a refined slip model for the kaik ura earthquake which incorporates changes to the slip on offshore faults and inclusion of an offshore reverse crustal fault that accounts for broad low amplitude uplift centered on kaik ura peninsula the exceptional detail afforded by differential lidar and the high variability in coastal deformation combine to form the highest resolution and most complex record of coseismic coastal deformation yet documented this should prompt reassessment of coastal paleoseismic records that may not have considered multi fault ruptures and high complexity deformation fields

geochemistry of muong nong type tektites iv selected trace element correlations muong nong type tektites are distinct from other tektites in their shape size petrographical characteristics and chemistry volatile elements are enriched but other trace elements do not show large differences when compared to normal splash form tektites an analysis is made of nineteen muong nong type tektites for 40 50 elements fifteen nonvolatile elements are discussed in this paper it is shown that the muong nong type tektites are very restricted in chemical composition and are almost indistinguishable from the australasian tektites elemental ratios calculated from the data reported here show the same genetic connection all elementary abundances and ratios are fully consistent with terrestrial sediments the nonvolatile elements may record more about the conditions of the origin

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

nd and sr isotopic systematics of central australian granulites chronology of crustal development and constraints on the evolution of lower continental crust nd and sr isotopic data are reported for a granulite terrain in the proterozoic arunta block of central australia sm nd data from a wide range of rock types define a crust formation age of 2 070 125 ma and provide further evidence for voluminous crustal growth in the proterozoic an nd value of 1 5 0 8 indicates a depleted mantle source for this crustal segment and there is no evidence for a large component of significantly older sialic crust field relationships geochemistry and rb sr data for mafic and felsic granulites indicate that intracrustal differentiation and polyphase deformation were followed by granulite facies metamorphism rb depletion at 1 800 ma rb sr data for strongly retrogressed granulites define an age of 1 700 ma which is interpreted as the time of retrograde biotite growth partial melting at the presently exposed crustal level and anatexis at deeper crustal levels were broadly coeval with the retrograde metamorphism sm nd and rb sr isotopic systematics of minerals indicate that the terrain cooled slowly did not experience significant uplift until 1 000 ma and remained at temperatures above 320 c until the late palaeozoic the mineral data are consistent with geological relationships and petrological evidence for a prolonged period of isobaric cooling followed by uplift late in the metamorphic evolution of the terrain the granulite protoliths appear to have formed in a rift which closed within 280 ma of initial separation deformation and granulite facies metamorphism at 1 800 ma are interpreted to be a consequence of collision between the continental blocks which defined the rift regional retrogression and granitoid magmatism at 1 700 ma are attributed to underthrusting of the granulites by lower grade rocks in the final stages of collision subsequent events in the cooling and uplift history appear to have been controlled by the presence of long lived major faults in the crust and a prolonged history of episodic compression in the continental lithosphere the results of this study suggest that granulite terrains in general cannot be equated with lower continental crust but instead represent assemblages of mainly supracrustal rocks which in some instances have been involved in major collision events

rb cs fractionation a link between granulite metamorphism and the s process abstract high grade metamorphism of pelitic sediments produces large cs losses with little k and rb depletion island arc volcanics contain an enhanced cs component relative to k and rb we suggest a connection between these two processes whereby fluids or melts removed from feldspar bearing subduction assemblages under high grade metamorphic conditions are enriched in cs relative to k and rb these cs enriched components infiltrate subarc mantle and lead to ubiquitous cs enrichment in arc volcanics normal oceanic magmatism is not effective in fractionating rb cs therefore the canonical oceanic basalt value of 85 for rb cs is distinctive relative to processes involving sediments recycling fluid melt metamorphism and arc volcanism

complex rupture of the 13 november 2016 m w 7 8 kaikoura new zealand earthquake comparison of high frequency and low frequency observations abstract we apply a back projection analysis to determine the locations and timing of the sources of short period 0 5 to 2 s energy generated by the 13 november 2016 mw 7 8 kaikoura new zealand earthquake using data from australian and southeast asia the sources of strong short period energy are distributed northeast of the epicenter at distances of 70 to 80 km during the time period of 70 to 80 s after the initiation the locations of sources of long period energy derived from global seismic and local gps data are close to the northeastern edge of the source area and complementary to the areas of short period energy which occur in the converging region of the upper kowhal papatea and jordan thrust faults the obvious frequency dependence might be attributed to complexities in fault geometry possible rupture in the subduction interface or varying focal mechanisms during the earthquake

geochemical effects of decoupled fractional crystallization and crustal assimilation most models of crustal assimilation assume that the amount of assimilant added to the magma is proportional to each infinitesimally small amount of solid removed during crystallization afc in some magmatic systems however assimilation and crystallization are not strictly related and the mass assimilated is decoupled from and therefore varies independently of the mass crystallized fca the geochemical consequences of fca are examined and compared to those of afc the behavior of incompatible elements is identical during afc and fca and ratios of these elements do not allow discrimination between the two processes major oxide least squares mass balance models do not discriminate between afc and fca at f 0 7 f fraction of melt remaining however fca yields magmas richer in compatible elements and with higher sr isotopic ratios than afc at a given value of f repeated cycles of fca and afc combined with magma mixing fam may result in unusual geochemical trends such as the evolution of a calc alkaline basaltic parent to a tholeiitic daughter magma or the evolution of low and medium k calc alkaline basalts to high k andesites dacites trachyandesites or trachydacites lavas erupted by the volcano micro profitis ilias on santorini hellenic arc greece provide an example of magmas which evolved by combined fractionation assimilation by fca and mixing

geochemistry and petrogenesis of early proterozoic amphibolites west central colorado u s a abstract early proterozoic supracrustal rocks exposed in west central colorado include amphibolites intimately associated with felsic volcanics and associated volcaniclastic sediments three successions are recognized the dubois succession 1770 1760 ma is comprised chiefly of amphibolites and felsic volcanics the amphibolites exhibit low concentrations of light ree and hfse and are broadly similar in composition to tholeiites from immature island arcs and in some respects to nmorb the cochetopa succession 1745 1730 ma includes large amounts of felsic volcanics and volcaniclastic sediments together with amphibolites that exhibit variable but slight incompatible element enrichment similar to basalts from evolved island arc systems and associated back arc basins the black canyon succession is coeval with the cochetopa succession and is comprised chiefly of volcaniclastic sediments with minor amphibolite these amphibolites exhibit significant incompatible element enrichment similar to basalts from continental margin arc systems geochemical modeling indicates that the amphibolites evolved by closed system fractional crystallization of depleted for the dubois succession to variably enriched parental basalts for the cochetopa and black canyon successions chiefly at shallow depths incompatible element distributions in the amphibolites indicate that mantle sources changed with time from relatively depleted 1770 1760 ma to variable but slightly enriched 1745 1730 ma a provisional model calls upon the dubois succession forming in an island arc system followed by collision with the archean wyoming province at 1750 ma the cochetopa succession was deposited in an intra arc basin developed within a new continental margin arc and the black canyon succession formed in a back arc basin associated with this arc

1891 1883 ma southern bastar cuddapah mafic igneous events india a newly recognized large igneous province abstract a newly recognized remnant of a paleoproterozoic large igneous province has been identified in the southern bastar craton and nearby cuddapah basin from the adjacent dharwar craton india high precision u pb dates of 1891 1 0 9 ma baddeleyite and 1883 0 1 4 ma baddeleyite and zircon for two se trending mafic dykes from the bd2 dyke swarm southern bastar craton and 1885 4 3 1 ma baddeleyite for a mafic sill from the cuddapah basin indicate the existence of 1891 1883 ma mafic magmatism that spans an area of at least 90 000 km2 in the south indian shield this record of 1 9 ga mafic ultramafic magmatism associated with concomitant intracontinental rifting and basin development preserved along much of the south eastern margin of the south indian shield is a widespread geologic phenomenon on earth similar periods of intraplate mafic ultramafic magmatism occur along the margin of the superior craton in north america 1 88 ga molson large igneous province and in southern africa along the northern margin of the kaapvaal craton 1 88 1 87 ga dolerite sills intruding the waterberg group existing paleomagnetic data for the molson and waterberg 1 88 ga large igneous provinces indicate that the superior and kalahari cratons were at similar paleolatitudes at 1 88 ga but a paleocontinental reconstruction at this time involving these cratons is impeded by the lack of a robust geological pin such as a limpopo like 2 0 ga deformation zone in the superior province the widespread occurrence of 1 88 ga intraplate and plate margin mafic magmatism and basin development in numerous archean cratons worldwide likely reflects a period of global scale mantle upwelling or enhanced mantle plume activity at this time

geochemistry and petrogenesis of amphibolites kolar schist belt south india evidence for komatiitic magma derived by low percentages of melting of the mantle the kolar schist belt of the dharwar craton of south india is an archean greenstone belt dominated by metavolcanic rocks the mafic metavolcanic rocks occur as komatiitic and tholeiitic amphibolites the komatiitic amphibolites occur along the margins of the n s trending synformal belt they are much less abundant than the tholeiitic amphibolites and have 14 to 21 3 wt per cent mgo the komatiitic amphibolites from the west central part of the belt have two distinctive ree patterns 1 those enriched in the middle to light ree but depleted in ce relative to nd and 2 those with patterns that are convex up i e depleted in both light and heavy ree although more depleted in the light ree associated tholeiites have light ree depleted to flat ree patterns komatiitic and tholeiitic amphibolites from the eastern part of the belt have enriched light ree patterns the tholeiitic amphibolites from the kolar schist belt are similar to the th i and th ii types of archean tholeiites of condie 1981 the komatiitic amphibolites are similar to komatiites and komatiitic basalts of barberton mountainland but have higher feo and tio 2 abundances and lower yb gd ratios the petrogenetic interpretations for these rocks are based primarily on a modification of the mgo feo diagram of hanson langmuir 1978 and modelling of zr ni and ree all of the rocks have undergone some fractionation while the modelling does not give accurate temperatures pressures compositions and extents of melting of the mantle sources for the various amphibolites it does present an approach which can be used for estimating these parameters for example the komatiitic amphibolites appear to be derived from melts generated by 10 to 25 per cent melting of the mantle over a range of depths and temperatures greater than 80 km and 1575 c the variation in the p t conditions of magma generation is possibly due to adiabatic melting in mantle diapirs with a range of feo mgo ratios if the tholeiitic amphibolites are derived from similar mantle sources it is not clear that they are their parent melts may have been generated by similar extents of melting but at depths of less than 80 km the komatiitic amphibolites from the west central part of the belt were generated from light ree depleted mantle whereas those from the eastern part of the belt appear to have been generated from light ree enriched mantle the sources for the komatiitic amphibolites in both areas were significantly enriched in feo relative to pyrolite thus a light ree depleted and a light ree enriched source appear to have provided mafic volcanics with similar major element chemistry to this belt during its evolution

geochemistry and petrogenesis of proterozoic mafic dykes in north kerala southwestern indian shield preliminary results abstract mafic dyke intrusions occur in three distinct orientations nnw sse nw se and ne sw in north kerala region the southwestern part of the indian shield dating of two nnw sse trending dykes by k ar method has yielded middle proterozoic ages ca 1660 ma and ca 1420 ma respectively our initial geochemical results on these dyke rocks 0 65 0 15 wt k 2 o 0 37 0 38 wt p 2 o 5 3 30 1 00 wt tio 2 11 1 p p m rb 250 90 p p m sr 230 40 p p m ba 160 40 p p m zr and 30 10 chondrite rare earth elemental abundances indicate a transitional character between abyssal and plateau tholeiites petrogenetic modelling suggests that the dyke compositions have been derived by different degrees of partial melting of a heterogenous source mantle the mantle sources with accessory amphibole and or garnet variably enriched in lree and lil elements is compatible with the observed geochemical data

two regions of seafloor deformation generated the tsunami for the 13 november 2016 kaikoura new zealand earthquake the 13 november 2016 kaikoura new zealand m w 7 8 earthquake ruptured multiple crustal faults in the transpressional marlborough and north canterbury tectonic domains of northeastern south island the hikurangi trench and underthrust pacific slab terminate in the region south of kaikoura as the subdution zone transitions to the alpine fault strike slip regime it is difficult to establish whether any coseismic slip occurred on the megathrust from on land observations the rupture generated a tsunami well recorded at tide gauges along the eastern coasts and in chatham islands including a 4 m crest to trough signal at kaikoura where coastal uplift was about 1 m and at multiple gauges in wellington harbor iterative modeling of teleseismic body waves and the regional water level recordings establishes that two regions of seafloor motion produced the tsunami including an m w 7 6 rupture on the megathrust below kaikoura and comparable size transpressional crustal faulting extending offshore near cook strait

the scourie dyke suite petrogenesis and geochemical nature of the proterozoic sub continental mantle the petrogenesis of bronzite picrite olivine gabbro norite and quartz tholeiite dykes which make up the 2 39 b y scourie dyke swarm cutting the archaean lewisian gneisses of n w scotland is interpreted on the basis of their major and trace element geochemistry most of the dykes bear primary amphibole and or phlogopite and with one exception are all hypersthene or quartz normative apart from one tholeiite dyke which shows relative light rare earth element depletion all the dykes show enrichment in light rare earths and large ion lithophile elements they do not however show an equivalent enrichment in other incompatible high field strength ions such as nb and ta and in this respect resemble island arc and calc alkaline basalts the different dyke types have distinctive rare earth patterns and other trace element ratios which are maintained over a range of major element compositions

regional o sr and pb isotope relationships in late cenozoic calc alkaline lavas of the andean cordillera quaternary recent volcanism in the andes has occurred in three regions 45 33 s 28 16 s and 2 s 5 n each of which has a distinct plate tectonic setting and contains volcanic suites with different chemical and isotopic characteristics isotope ratios of o and sr are lowest and those of pb least variable in the southern volcanic zone svz where medium k lavas have isotopic characteristics equivalent to volcanics from intraoceanic arcs where continental crust is absent the svz lavas were probably derived from an asthenospheric mantle source above a shallow benioff zone parental basaltic magmas rose largely unmodified through thin continental crust where differentiation occurred by low pressure crystal fractionation without concurrent modification of isotopic composition the slight enrichment of 206 pb in the northern volcanic zone nvz where the crust is thin and the benioff zone deep suggests a greater subduction zone component for parental medium k magmas the slight 18 o enrichment suggests a small amount of lower crustal interaction isotope ratios of o and sr are highest and those of pb most variable in the central volcanic zone cvz parental magmas in the cvz were probably generated within the same mantle source region as those in the svz and nvz subsequently during transit through the exceptionally thick continental crust of the central andes high k magmas were produced by a combination of bulk contamination in the lower crust and later low pressure fractional crystallization assimilation processes in the upper crust which altered both chemical and isotopic compositions

influence of palaeoclimate and hydrothermal activity on organic matter accumulation in lacustrine black shales from the lower cretaceous bayingebi formation of the yin e basin china abstract the lacustrine black shales of the lower cretaceous bayingebi formation are an important hydrocarbon source rock in the yin e basin it is important to understand the mechanism of organic matter accumulation in these shales to reconstruct the palaeoenvironment and palaeoclimate in the early cretaceous in northwestern china and search for potential oil and gas resources based on petrological elemental geochemical and organic geochemistry analyses of typical field profile samples the influence of palaeoclimate and hydrothermal activity on organic matter accumulation in different sedimentary units unit i ii and iii is revealed unit ii has the highest total organic matter abundance tocavg 5 95 mainly type i kerogen lamalginite which is in the immature to low mature stage organic carbon isotope data 13corg element ratios sr cu and c value and weathering indexes including cia ciw and pia together revealed that the region experienced a semihumid to semiarid palaeoclimate in the middle of the early cretaceous the increase in rainfall in unit ii enhanced the abundance of lake algae and surrounding terrestrial vascular vegetation and elevated the lake level which contributed to adequate sources and favourable preservation conditions for organic matter accumulation several lines of evidence including high sulfur contents the combination of vein pyrite and micritic dolomite positive eu anomalies and element geochemical correlations confirm the existence of intermittent low temperature white smoker type hydrothermal activity the decrease of oxygen content in lake bottom water may be related to the input of hydrothermal fluid which provided necessary nutrient elements for biological productivity according to palaeontological and radioisotope dating data it can be inferred that the black shales of the bayingebi formation are the product of the combined effect of global palaeotemperature rise in the early aptian stage of the early cretaceous and intermittent low temperature hydrothermal activity

the mineral chemistry of new titanates from the jagersfontein kimberlite south africa implications for metasomatism in the upper mantle new members of the crichtonite mineral series are described in which k ba ca and ree are in significant concentrations 5 wt oxides filling the a formula position in am21o38 these phases are chromium 16 wt cr2o3 titanates 58 wt tio2 enriched in zro2 5 wt and constitute a mineral repository for refractory and large ion lithophile elements in the upper mantle the mineral senes coexists with mg cr ilmenite nb cr rutile and ca cr nbzr armalcolite that have equally unusual chemistries kimberlitic crichtonites are depleted in the intermediate lanthanides but highly enriched in lree and hree with chondrite normalized abundances of 103 to 105 crichtonite armalcolite and nb cr rutile occupy a compositional range in tio2 contents bridging the gap between ilmenite and rutile two minerals having a widespread distribution in kimberlites and mantle derived nodule suites in common with other associations and based on similarities in mineral chemistry it is concluded that these minerals formed at p 20 30 kb 900 1100 c by reaction of peridotite with metasomatizing fluids kimberlitic crichtonite may be expressed as spinel cr ferropseudobrookite and armalcolite is equivalent to cr geikielite rutile in the system femg tio2 cr2o3 this system contains a number of cr ti compounds not found as minerals but it is proposed that the ubiquitous occurrence of ilmenite intergrowths in kimberlitic rutile results from decomposition of high pressure pbo2 type crystallographic shear structures the new minerals have exotic chemistries and the high k affinities broaden the scope for the origin of alkalic rocks the generation of highly potassic magmas in the upper mantle and suggest that alkali metasomatism may be pervasive

trace element geochemistry and genesis of precambrian sub alkaline mafic dikes from the central indian craton evidence for mantle metasomatism abstract precambrian mafic dikes transect the archaean granite gneisses of the southern bastar craton central india on the basis of high field strength elements the bastar mafic dike swarms were sub divided into an earlier bd1 and a later bd2 system the bd1 set comprises amphibolites whereas the bd2 set consists of dolerites metadolerites on the basis of field relationships and available age data for enveloping granite rocks the bd1 dikes are regarded as middle archaean in age and bd2 dikes are paleoproterozoic 1 8 ga the silica and total alkalis contents of dikes of both swarms classified them mostly as sub alkaline basalts the bd1 dikes are low ti fe and high mg olivine to quartz normative rocks whereas the bd2 dikes are predominantly quartz normative with relatively high ti fe and low mg contents the high field strength element concentrations are relatively higher in the bd2 dikes than in the bd1 dikes for comparable values of mgo and or cr judging from the geochemical data these dikes probably were not contaminated by crustal components the geochemistry and field observations clearly suggest a continental rift environment for the emplacement of both bd1 and bd2 dikes rare earth element patterns and compatible incompatible trace element modelling suggest that the two swarms were derived from distinctly different sub alkaline basaltic magmas the middle archaean bd1 dikes were derived from 15 20 batch melting of a depleted lherzolite mantle source in contrast the paleoproterozoic bd2 dikes were derived from 7 10 batch melting of a relatively enriched mantle source a post archaean increase in the thickness of metasomatized mantle lithosphere is the probable cause of mantle enrichment

mantle convection and early crustal evolution abstract the existence of peridotitic komatiites in the archaean suggests that the archaean mantle was significantly hotter than the modern mantle this evidence is contradicted by estimates of archaean continental geothermal gradients based on the pressure and temperature recorded in metamorphic rocks which suggest that there is no marked difference between archaean and modern continental geothermal gradients numerical modelling shows that small changes in the mantle temperature can have an important influence on convection if the average temperature of the upper mantle is increased by 200 c convection within the mantle becomes chaotic and an upper mantle partial melt zone encircles the globe the crust formed during this period will be komatiitic in composition but will be unstable and will be mixed back into the mantle by subduction later when the mantle temperature falls to 100 c above its present level the upper mantle partial melt zone contracts away from subduction areas it is suggested that the first primitive felsic magmas were generated at subduction zones the appearance of these magmas at 3 8 ga permitted the formation of buoyant continents and eventually led to crustal thickening as a consequence of this thickening the proto continents consisting of a bimodal suite of basalts and sodic granodiorites contained two types of latent energy 1 radioactive energy held in elements such as th k and u and 2 potential energy resulting from the elevation of the continents above sea level the potential energy of the continents led to sedimentation the increase in the rate of sedimentation during the archaean resulted from increased crustal buoyancy at the same time heat released by radioactive elements in the deep crust built up under the insulating blanket of the upper crust this caused a major metamorphic metasomatic and crustal melting event which produced the potassic granites of the late archaean once the radioactive elements had been removed from the lower crust that region of the continent become tectonically stable the proterozoic shelf sediments were deposited at the margins of these stable cratons convection models of the archaean mantle show hot diapirs rising from the boundary layer above the core mantle interface we suggest that these diapirs began to melt at a depth of 450 km giving rise to komatiitic magmas this model requires the average temperature of the archaean upper mantle to be 100 c above that of the modern mantle the similarity between archaean and modern continental geothermal gradients can be explained if archaean continents formed above subduction zones raising the temperature of the archaean mantle by 100 c 1 halves the thickness of the oceanic lithosphere 2 increases the oceanic geothermal gradient at the mid point of a convection cell 3 decreases the viscosity of the mantle by at least an order of magnitude the combination of these effects produces a marked decrease in the strength of the archaean lithosphere and mantle thus the form of archaean tectonics can be expected to have been very different from modern tectonics

the 2016 kaikōura earthquake simultaneous rupture of the subduction interface and overlying faults abstract the distribution of slip during an earthquake and how it propagates among faults in the subduction system play a major role in seismic and tsunami hazards yet they are poorly understood because offshore observations are often lacking here we derive the slip distribution and rupture evolution during the 2016 mw 7 9 kaik ura new zealand earthquake that reconcile the surface rupture space geodetic measurements seismological and tsunami waveform records we use twelve fault segments with eleven in the crust and one on the megathrust interface to model the geodetic data and match the major features of the complex surface ruptures our modeling result indicates that a large portion of the moment is distributed on the subduction interface making a significant contribution to the far field surface deformation and teleseismic body waves the inclusion of local strong motion and teleseismic waveform data in the joint inversion reveals a unilateral rupture towards northeast with a relatively low averaged rupture speed of 1 5 km s the first 30 s of the rupture took place on the crustal faults with oblique slip motion and jumped between fault segments that have large differences in strike and dip the peak moment release occurred at 65 s corresponding to simultaneous rupture of both plate interface and the overlying splay faults with rake angle changes progressively from thrust to strike slip the slip on the papatea fault produced more than 2 m of offshore uplift making a major contribution to the tsunami at the kaik ura station while the northeastern end of the rupture can explain the main features at the wellington station our inversions and simulations illuminate complex up dip rupture behavior that should be taken into consideration in both seismic and tsunami hazard assessment the extreme complex rupture behavior also brings new challenges to the earthquake dynamic simulations and understanding the physics of earthquakes

origin of basal dolomitic claystone in the marsili basin tyrrhenian sea abstract red brown dolomitic claystones overlay the marsili basin basaltic basement at odp site 650 sequential leaching experiments reveal that most of the elements considered to have a hydrothermal or hydrogenous origin in a marine environment such as fe cu zn pb co ni are present mainly in the aluminosilicate fraction of the dolomitic claystones their vertical distribution content and partitioning chemistry of trace elements and ree patterns suggest enhanced terrigenous input during dolomite formation but no significant hydrothermal influence from the underlying basaltic basement positive correlations in the c and o isotopes in the dolomites reflect complex conditions during the dolomitization the stable isotopes can be controlled in part by temperature variations during the dolomitization majority of the samples however form a trend that is steeper than expected for only temperature control on the c and o isotopes the latter indicates possible isotopic heterogeneity in the proto carbonate that can be related to arid climatic conditions during the formation of the basal dolomitic claystones in addition the dolostones stable isotopic characteristics can be influenced by diagenetic release of heavier 18o from clay dehydration and or alteration of siliciclastic material strontium and pb isotopic data reveal that the non carbonate fraction the dye of the dolomitic claystones is controlled by saharan dust 75 80 and by material with isotopic characteristics similar to the aeolian arc volcanoes 20 25 the non carbonate fraction of the calcareous ooze overlying the dolomitic claystones has a sr and pb isotopic composition identical to that of the dolomitic claystones indicating that no change in the input sources to the sedimentary basin occurred during and after the dolomitization event combination of climato tectonic factors most probably resulted in suitable conditions for dolomitization in the marsili and the nearby vavilov basins the basal dolomitic claystone sequence was formed at the initiation of the opening of the marsili basin 2 ma which coincided with the consecutive glacial stage the glaciation caused arid climate and enhanced evaporation that possibly contributed to the stable isotope variations in the proto carbonate the conductive cooling of the young lithosphere produced high heat flow in the region causing low temperature passive convection of pore waters in the basal calcareous sediment we suggest that this pumping process was the major dolomitization mechanism since it is capable of driving large volumes of seawater the source of mg2 through the sediment the red brown hue of the dolomitic claystones is terrigenous contribution of the glacially induced high eolian influx and was not hydrothermally derived from the underlying basaltic basement the detailed geochemical investigation of the basal dolomitic sequence indicates that the dolomitization was most probably related to complex tectono climatic conditions set by the initial opening stages of the marsili basin and glaciation

transpressional rupture cascade of the 2016 mw 7 8 kaikoura earthquake new zealand large earthquakes often do not occur on a simple planar fault but involve rupture of multiple geometrically complex faults the 2016 m w 7 8 kaikoura earthquake new zealand involved the rupture of at least 21 faults propagating from southwest to northeast for about 180 km here we combine space geodesy and seismology techniques to study subsurface fault geometry slip distribution and the kinematics of the rupture our finite fault slip model indicates that the fault motion changes from predominantly right lateral slip near the epicenter to transpressional slip in the northeast with a maximum coseismic surface displacement of about 10 m near the intersection between the kekerengu and papatea faults teleseismic back projection imaging shows that rupture speed was overall slow 1 4 km s but faster on individual fault segments approximately 2 km s and that the conjugate oblique reverse north striking faults released the largest high frequency energy we show that the linking conway charwell faults aided in propagation of rupture across the step over from the humps fault zone to the hope fault fault slip cascaded along the jordan thrust kekerengu and needles faults causing stress perturbations that activated two major conjugate faults the hundalee and papatea faults our results shed important light on the study of earthquakes and seismic hazard evaluation in geometrically complex fault systems

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

the lithospheric geodynamics of plate boundary transpression in new zealand initiating and emplacing subduction along the hikurangi margin and the tectonic evolution of the alpine fault system abstract in contrast to the normal wilson cycle sequence of subduction leading to continental collision and associated mountain building the evolution of the new zealand plate boundary in the neogene reflects the converse initially a period of continental convergence that is followed by the emplacement of subduction plate reconstructions allow us to place limits on the location and timing of the continental convergence and subduction zones and the migration of the transition between the two plate boundary regimes relative plate motions and reconstructions since the early to mid miocene require significant continental convergence in advance of the emplacement of the southward migrating hikurangi subduction a sequence of tectonism seen in the present plate boundary geography of hikurangi subduction beneath north island and convergence in the southern alps along the alpine fault in contrast to a transition from subduction to continental convergence where the leading edge of the upper plate is relatively thin and deformable the transition from a continental convergent regime with its associated crustal and lithospheric thickening to subduction of oceanic lithosphere requires substantial thinning removal of upper plate continental lithosphere to make room for the slab the simple structure of the wadati benioff zone seen in the present day geometry of the subducting pacific plate beneath north island indicates that this lithospheric adjustment occurs quickly associated with this rapid lithospheric thinning is the development of a series of ephemeral basins younging to the south that straddle the migrating slab edge based on this association between localized vertical tectonics and slab emplacement the tectonic history of these basins records the effects of lithospheric delamination driven by the southward migrating leading edge of the subducting pacific slab although the new zealand plate boundary is often described as simply two subduction zones linked by the transpressive alpine fault in actuality the present is merely a snapshot view of an ongoing and complex evolution from convergence to subduction

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

pre breakup continental extension in east gondwanaland and the early opening of the eastern indian ocean abstract extension of continental crust by up to 360 km on a north northeast azimuth in the great australian bight occurred prior to the middle cretaceous 96 ma onset of seafloor spreading between australia and antarctica this large amount of continental extension is constrained to the late jurassic 160 ma middle cretaceous interval about a pole estimated to lie about 40 southeastward of southeastern australia using bathymetric data combined with seismic and magnetic determinations of the continent ocean boundaries off australia india and antarctica we determine a revised fit of east gondwanaland prior to continental extension and at various stages thereafter in the first stage from 160 to 132 5 ma m11 india australia rotated from antarctica with continental crustal extension between australia and antarctica and largely transform motion between the coromandel coast margin of india and the kron prins olav kyst margin of antarctica in the second stage from 132 5 to 96 ma india rotated northwestward away from australia antarctica producing m10 and younger magnetic anomalies along the western margin of australia continental extension was greatest between australia and antarctica during this stage the newly determined 132 5 96 ma rotation between india and australia provides an improved fit between the orientation of observed m10 m0 magnetic anomalies and the southward decrease in spreading rate off the western australian margin together with bathymetry the new rotation parameters lead to identification of the abandoned 96 ma spreading ridge along the lost dutchmen and dirck hartog ridges the naturaliste fracture zone is found to lie nearly parallel to the early cretaceous transform direction between india and antarctica suggesting that slow seafloor spreading required between australia and antarctica to accommodate the continental extension further east occurred between naturaliste fracture zone and the m4 m0 anomalies adjacent to the naturaliste plateau the revised fit of india in east gondwanaland reduces the eastward extent of greater india to 95 e but does not change its extent as far north as the cape range fracture zone the new pole determined for the early cretaceous rotation between india and australia antarctica lies within 15 of the southern tip of india significantly closer than in previous determinations thereby reducing the amount of seafloor spreading generated between africa and antarctica by the india antarctica rotation and thus offering a possible solution to the perceived spreading rate problems between m11 and m0 in the somali mozambique and antarctic basins

juxtaposition of india and antarctica during the precambrian inferences from geochemistry of mafic dykes abstract there are several geological geochemical and geophysical evidences which corroborate reconstruction of gondwanaland and juxtaposition of india and antarctica petrology of the precambrian mafic dykes of east antarctica and central east india also support juxtaposition of india and antarctica mafic dykes of different generations are emplaced in the archaean granite gneisses of these regions these dykes appear to be an important tool to support juxtaposition of india and antarctica geological and petrological data of the central east india precambrian mafic dykes suggest four episodes of mafic magmatism in the region three tholeiitic and one noritic similarly east antarctica also comprises four dyke suites emplaced during three distinct periods these suites are 2 4 ga meta tholeiites 2 4 ga high mg tholeiites 1 8 ga dolerites and 1 2 1 4 ga dolerites geochemical compositions of these mafic dykes are compared and they show good relationships with each other similarities in petrological and geochemical characteristics of precambrian mafic dykes of east antarctica and central east india strongly support juxtaposition of these two continents

complex multifault rupture during the 2016 mw 7 8 kaikōura earthquake new zealand the 2016 moment magnitude m w 7 8 kaik ura earthquake was one of the largest ever to hit new zealand hamling et al show with a new slip model that it was an incredibly complex event unlike most earthquakes multiple faults ruptured to generate the ground shaking a remarkable 12 faults ruptured overall with the rupture jumping between faults located up to 15 km away from each other the earthquake should motivate rethinking of certain seismic hazard models which do not presently allow for this unusual complex rupture pattern science this issue p eaam7194 1 1 lookup doi 10 1126 science aam7194

a petrogenetic relationship between 2 37 ga boninitic dyke swarms of the indian shield evidence from the central bastar craton and the ne dharwar craton abstract the indian shield is cross cut by a number of distinct paleoproterozoic mafic dyke swarms the density of dykes in the dharwar and bastar cratons is amongst the highest on earth globally boninitic dyke swarms are rare compared to tholeiitic dyke swarms and yet they are common within the southern indian shield geochronology and geochemistry are used to constrain the petrogenesis and relationship of the boninitic dykes sio2 51 5 to 55 7 wt mgo 5 8 to 18 7 wt and tio2 0 30 wt to 0 77 wt from the central bastar craton bhanupratappur and the ne dharwar craton karimnagar a single u pb baddeleyite age from a boninitic dyke near bhanupratappur yielded a weighted mean 207pb 206pb age of 2365 6 0 9 ma that is within error of boninitic dykes from the dharwar craton near karimnagar 2368 5 2 6 ma and farther south near bangalore 2365 4 1 0 ma to 2368 6 1 3 ma rhyolite melts modeling indicates that fractional crystallization is the likely cause of major element variability of the boninitic dykes from bhanupratappur whereas trace element modeling indicates that the primary melt may be derived from a pyroxenite mantle source near the spinel garnet transition zone the nd isotopes end t 6 4 to 4 5 of the bhanupratappur dykes are more variable than the karimnagar dykes end t 0 7 to 0 6 but they overlap the variability of sr nd isotopes may be related to crustal contamination during emplacement or is indicative of an isotopically heterogeneous mantle source the chemical and temporal similarities of the bhanupratappur dykes with the dykes of the dharwar craton karimnagar penukonda chennekottapalle indicate they are members of the same giant radiating dyke swarm moreover our results suggest that the bastar and dharwar cratons were adjacent but likely had a different configuration at 2 37 ga than the present day it is possible that the 2 37ga dyke swarm was related to a mantle plume that assisted in the break up of an unknown or poorly constrained supercontinent

geochemical records of qionghai lake sediments in southwestern china linked to late quaternary climate changes abstract knowledge of the chemical weathering history under the subtropical monsoonal climate will help to resolve the discrepancies regarding how climate conditions constrain chemical weathering major element and rare earth element ree compositions of the qionghai lake sediments in sichuan province southwestern china were analyzed aiming to provide information on sediment source discrimination and history of chemical weathering intensities and its responses to variations of indian summer monsoon ism and paleoclimate conditions as revealed by the a cn k diagram and other provenance proxies including tio2 zr ratio th sc vs zr sc and la th vs hf diagrams as well as the ree characteristics the source of qionghai lake sediments was felsic rocks additionally these sediments were subjected to small changes in provenance sedimentary sorting and recycling and weak diagenesis after deposition and or metasomatism indicating original signals were maintained on the intensity of chemical weathering of source area the chemical weathering intensities inferred from cia chemical index of alteration values have significantly fluctuated over the past 28 kyr reflecting three stages of paleoclimate evolution which is consistent with grain size characteristics carbonate contents low frequency magnetic susceptibilities toc and biomarker proxy paq the cia values changed significantly during the typical warm and cold climate events including the last glacial maximum heinrich 1 cold event younger dryas and holocene climatic optimum and generally exhibited an increasing trend in amplitude correspondingly in concert with the climate shifting from cold and dry to warm and humid conditions generally warm and humid climate conditions suggest enhanced chemical weathering intensity whereas weak chemical weathering denotes cold and dry climate in the ism region in addition sequential variations of the cia values during the past 28 kyr may reflect changing chemical weathering processes in responses to the varying intensities of indian summer monsoon and the climate conditions forced by the northern hemisphere solar insolation

a model for continental crust genesis by arc accretion rare earth element evidence from the irish caledonides abstract the formation of continental crust is a complex problem with a paradox at its center continental material is believed to form by arc magmatism a model that does not reconcile the bulk mafic and light rare earth element lree depleted composition of intra oceanic arcs with the andesitic lree enriched composition of continents we present evidence supporting an arc origin for continental crust by demonstrating significant changes in magmatic chemistry during arc continent collision we use as an example the connemara region of the western irish caledonides where metamorphism and orogenesis of dalradian sedimentary sequences record the collision of the oceanic lough nafooey arc with the passive margin of laurentia at 475 ma arenig this arc was mafic and lree depleted during its oceanic activity during collision rhyolites more lree enriched than the surrounding continental crust were erupted while the mid crust was intruded by similarly lree enriched gabbro and diorite crystal fractionation caused lree enrichment to exceed that expected by assimilation of continental crust alone we propose that subsequent loss of the corresponding lower crustal cumulates into the mantle removed this lree depleted material from the net crust added to the continent the combined processes of crystal fractionation and lower crustal loss during arc continent collision drive the average bulk arc composition toward that of average continental crust

origins of stratiform and stratabound fe cu zn horizons in the lower proterozoic moran lake group labrador central mineral belt zn cu and fe are concentrated as stratiform and stratabound sulphide rich beds in the lower proterozoic warren creek formation moran lake group central labrador upper member sedimentary rocks have a hydrothermal like fe enrichment but a dominantly hydrogenous signature as indicated by high al2o3 relative to sio2 and high al and fe relative to mn the upper member shales and sulphide rich beds were deposited as fe rich pelagic sediments the paucity of mn and abundance of fe in typical shale samples and lack of cu pb and zn fractionation in stratiform massive sulphide beds that contain up to 4702 ppm zn 533 ppm cu and 15 ppm pb suggest that deposition occurred in restricted brine pools i e cu and zn were precipitated rapidly and were not fractionated stratabound sphalerite mineralization containing 3 7 zn and 121 ppm cu but no pb was deposited in a porous lithology at the top of the warren creek formation and represents a unique style of metal concentration the stratiform deposits proba

mafic and ultrapotassic rocks from the canyon domain central grenville province geochemistry and tectonic implications the canyon domain and the banded complex in the manicouagan area of the grenville province preserve a re cord of magmatic activity from 1 4 to 1 ga this study focuses on 1 4 1 2 ga mafic rocks and 1 ga ultrapotassic dykes geochemistry and sm nd isotopic signatures were used to constrain the origin of these rocks and evaluate the changing role of the mantle with time and tectonic setting from the late evolution of the laurentian margin to the grenvillian orogeny in the manicouagan area the mafic rocks include layers inferred to represent flows homogeneous bodies in mafic migma tite and deformed dykes all of which were recrystallized under granulite facies conditions during the grenvillian orogeny in spite of the complexities inherent in these deformed and metamorphosed mafic rocks we were able to recognize suites with distinctive geochemical and isotopic signatures integration of this data along with available ages is consistent with a 1 4 ga continental arc cut by 1 2 ga non arc basalts derived from depleted asthenospheric mantle with varied degrees of crustal contamination and inferred to represent magmatism in an extensional environment the 1 ga ultrapotassic dykes postdate the grenvillian metamorphism they are extremely enriched in incompatible elements have negative nb anomalies relatively unradiogenic sr isotopic compositions initial 87 sr 86 sr 0 7040 and nd 3t o 15 some dykes have composi tional characteristics consistent with derivation from the mantle ruling out crustal contamination as a major process in their petrogenesis the most likely source region for the ultrapotassic dykes is a metasomatized subcontinental lithospheric man tle with thermal input from the asthenosphere in association with post orogenic delamination

genesis of granitoid batholiths of peninsular malaysia and implications for models of crustal evolution evidence from a ndsr isotopic and upb zircon study nd sr and u pb isotopic data for the late triassic west coast province batholiths and permian to triassic east coast province batholiths of peninsular malaysia allow estimates of the ages of the crustal fragments comprising the peninsula to be made initial nd and sr values for granitoids from the west coast province range from 6 to 10 and 160 0 716 to 660 0 751 respectively nd model ages calculated based on a depleted mantle evolution model tdmnd range from 1300 ma to 1800 ma and are in general agreement with the mid proterozoic upper intersection ages of u pb zircon reverse discordia 1500 1700 ma initial nd and sr values for granitoids from the east coast province range from 0 8 to 6 and 10 0 705 to 130 0 714 respectively calculated tdmnd ages of 900 1400 ma for these granitoids are comparable to two u pb zircon reverse discordia intercepts that yield 800 ma and 1350 ma the general agreement of u pb zircon inheritance ages and tdmnd ages are interpreted to correspond to the proterozoic crust formation ages of the continental fragments represented by the west coast and east coast batholithic provinces mid proterozoic 1300 1900 ma crust formation ages are commonly shown by other phanerozoic continental margin plutonic and volcanic belts the ubiquitous mid proterozoic crust formation ages and the absence of archaean signatures suggest voluminous juvenile additions to the continental crust in the mid proterozoic such ages at continental margins would imply that many continental blocks had achieved very much their present day extent by the mid proterozoic

polymetallic mineralization at the browns deposit rum jungle mineral field northern territory australia the rum jungle mineral field northern territory australia forms part of the paleoproterozoic pine creek orogen the geology of the area comprises two archean granitic basement domes overlain by a paleoproterozoic sequence of metasedimentary and subordinate metavolcanic rocks the rocks have been deformed and metamorphosed to greenschist facies during the 1880 ma barramundi orogeny but the original stratigraphic succession has been preserved the browns deposit browns and its extension browns east hosted within black carbonaceous pelites of the paleoproterozoic whites formation is the largest base metal deposit found to date in the pine creek orogen present resource estimates are 39 million metric tons mt at 0 44 percent cu 3 61 percent pb 0 11 percent co and 0 09 percent ni browns and 31 mt at 1 29 percent cu 1 28 percent pb 0 13 percent co and 0 13 percent ni browns east major sulfide minerals in the ore zone are galena sphalerite chalcopyrite pyrite and the main carrier of ni and co siegenite ni co 3 s 4 digenite group minerals and bornite ca bearing plumbogummite pbal 3 po 4 2 oh 5 h 2 o arsenopyrite and gersdorffite are present in minor quantities ore minerals occur as fine grained wisps parallel to the main bedding parallel foliation and as coarse grained mono and polyminerallic aggregates that crosscut the foliation total noncarbonate carbon contents of unaltered rocks range from 1 07 to 7 51 wt percent total sulfur contents range from 2 13 to 6 14 wt percent petrographic studies and raman spectroscopy identify three varieties of carbonaceous matter primary syngenetic premetamorphic epigenetic grain coating and postmetamorphic epigenetic uraniferous migrated altered rocks are rarely encountered values of 34 s for sulfides range from 5 to 15 per mil and are interpreted to reflect a combination of inorganic thermochemical reduction of seawater and bacterial activity no specific sulfur isotope patterns for individual minerals can be established indicating nonequilibrium conditions homogeneous lead isotope signatures of galena 206 pb 204 pb 16 20 16 22 207 pb 206 pb 15 48 15 51 208 pb 207 pb 35 86 35 92 suggest that all pb was derived from a single crustal source and paragenetically late crosscutting galena appears to have been remobilized from bedding parallel galena despite the occurrence of uranium in similar rocks nearby uranium is quantitatively insignificant in the browns deposit and is not genetically related to base metal mineralization instead it is linked to brittle deformation in the waning stages of orogenesis the browns deposit differs from other well known sediment hosted stratiform ore deposits both the zambian copperbelt and the polish kupferschiefer deposits are copper dominant and hosted in sedimentary sequences with significant psammitic components the pb zn ag deposits of the proterozoic australian zinc province also have significant carbonate in their host rocks e g carbonaceous dolomitic and siltstone at mcarthur river and lack economically interesting cu co and ni the nearby woodcutters pb zn ag deposit in rocks of similar age also differs in structural setting veins dominant metals and pb isotopes from the browns deposit

precambrian continental crust of india and its evolution the indian precambrian continental crust exhibits a variety of geological features fashioned at different times by different geotectonic processes the bulk of this crust was formed prior to 2600 m y ago and remobilized at least twice between 2600 2000 m y ago early proterozoic mobile belt epmb and 2000 1500 m y ago middle proterozoic mobile belt mpmb three early precambrian nucleii karnataka kn jeypore bastar jbn and singhbhum sn appear to have survived in the craton and are characterized by low grade supracrustals and tonalitic trondhjemite gneisses formed 3800 2600 m y ago the epmb event involved sedimentation amphibolite granulite facies metamorphism and co 2 k metasomatism and produced amphibolite facies rocks and k granites in the north and charnockite and other granulite facies rocks in the south gold sporadically distributed in the supracrustal rocks of the craton was remobilized during the epmb event k granites form a garland around the central dharwar craton sugg

mapping in the oman ophiolite using enhanced landsat thematic mapper images abstract the large areal extent and complex nature of the terrain has meant that previous largely field based mapping programmes in the oman ophiolite have produced maps of internally inconsistent quality recognition of subtle changes and minor outcrops across the area of a 1 1 map sheet is possible in the field only by unrealistically exhaustive mapping by using parts of the short wavelength infrared spectrum landsat thematic mapper data have the capacity to capitalize on distinctions in the spectral reflectances of different rock types and their weathering products and to allow consistent mapping across the whole ophiolite decorrelation stretching of these data produces images in which it is possible to recognize variations in gabbro composition to identify small acidic gabbroic and ultramafic intrusions to discriminate the uppermost mantle from the deeper mantle to locate the moho precisely and to delineate gossans and areas subject to chloritic epidotic alteration off axis plutonism is more widespread and dispersed than previously appreciated the significance of certain faults is reassessed in the light of new insights provided by the imagery such data could be a valuable mapping tool in similarly exposed terrains in arid and semi arid regions even where already mapped at the 1 100 000 scale

the influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern united states this paper reports systematic changes in mudrock composition through time on a single con tinental cmstal block the changes reflect both sediment recycling processes and changes through time in the composition of crystalline material being added to the sedimentary system and are related to tectonic evolution as the block matures from a series of accreted arc terranes to a stable craton the major and trace element distributions reflect different aspects of the provenance of the mudrocks in this study major elements record sediment recycling processes as well as changing proportions of sedi mentary and first cycle source rocks with the exceptions of kzo which tends to increase and sioz and a o3 which show no trend most major oxides tend to decline in relative abundance in younger mud rocks patterns shown by the index of compositional variability fe03 kro naao cao mgo mno tiojialro and by k20 a1203 indicate that the major oxide trends are due to decreasing proportions of nonclay silicate minerals and a concomitant increase in the proportion of clay minerals probably due to decreasing input of first cycle detritus coupled with recycling of sedimentary material excursions from progressive trends marked by increases in mgo k20 and cao reflect episodes of large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift the chemistry of low solubility trace elements in contrast is not sensitive to recycling effects and reflects the composition of first cycle input incompatible elements are progressively enriched relative to compatible elements in younger mudrocks and values for chondrite normalised rare earth elements also increase in addition the eu anomaly becomes systematically more negative in younger samples these trends cmnot be explained by diagenetic or weathering processes and therefore indicate that the proportion of fnc tionated granitic first cycle detritus being added to the sedimentary system becomes greater with time these results confirm the importance of tectonic setting in controlling mudrock chemistry and also demonstrate that there is a dynamic relationship between the tectonic evolution of a continental block and the composition of its sedimentary mantle

uranium thorium systematics of two canadian coals abstract a detailed study of u th distribution in two lower cretaceous coals in canada shows that for these coals formed in a continental fluvial and deltaic environment with no marine influence the u contents are in the range 0 07 7 5 ppm with th in the range 0 3 11 0 ppm average th u ratios are near 2 which indicates slight uranium enrichment the environments of the two coals show different degrees of weathering montmorillonite illite and kaolin gibbsite and u values are lowest in the more weathered environment in sedimentary profiles associated with the coals the maximum uranium values are not in the coals but in carbonaceoss clay sediments above and below coal seams uranium distribution patterns can be correlated cith ni cu rb pb sr and zr indicating contributions from heavy minerals plus more mobile species possibly simple organic compounds which are adsorbed or bonded onto claysor organic matter

geology geochemistry fluid inclusion and genesis of the guijeh qaleh ioa type iron ore deposit north of takab district northwestern iran abstract the guijeh qaleh iron deposit located in the takab district of northwestern iran contains ca 0 3 million metric tons mt of ore at 48 wt fe the host rocks are eocene to oligocene volcano sedimentary sequences consisting of andesite trachy andesite to basaltic andesite flows intruded by granites to granodiorite intrusions the hydrothermal alterations include argillic sericitic silicified carbonate and hematitic zones silicified and hematitic alteration zones are spatially associated with the mineralization and occur proximal to ore bodies whereas sericite carbonate and argillic alteration zones are distal to main ore bodies iron mineralization occurred as several quartz hematite specularite veins 0 5 to 5 m wide and 10 to 20 m long which were formed within and along normal and strike slip fault zones the mineralogy of ore bodies consists of hematite specularite pyrite subordinate magnetite and apatite together with minor malachite after chalcopyrite with open space filling disseminated massive and breccia textures geochemical analyses of high grade ore bodies show that fe concentration is strongly correlated with mo zn mn pb sio2 mgo tio2 and p2o5 the chondrite normalized ree patterns of the altered and mineralized ore bodies displays with lree hree ratio with a negative eu anomaly and low eu eu values characteristic of the kiruna type ioa deposits fluid inclusion studies from quartz occurring with the mineralization characterized mineralizing fluids with homogenization temperatures ranging from 133 to 464 c and apparent salinities between 0 2 to 23 2 wt nacl equ interpretation of fluid inclusion data suggest that mixing of magmatic and meteoric fluids and cooling caused ore precipitation geology mineralogy ore textures geochemistry and fluid inclusion data suggest that iron mineralization in the guijeh qaleh deposit is similar to kiruna type ioa deposits the presented data show that the takab district has the potential for hosting kiruna type ioa mineralization in the northwest of iran

age and origin of early proterozoic dolerite dykes in south west greenland samples of three dolerite dykes from south west greenland give a pooled weighted mean rb sr whole rock isochron age of 2 130 65 ma initial 87sr 86sr ratios are 0 70155 0 00018 for one of the dykes naujat and 0 70277 0 00012 for the other two torssut and akinaq a fourth dyke qaqarssuaq did not yield an isochron torssut samples have significantly lower initial 207pb 204pb ratios than samples from the naujat dyke indicating that the torssut dyke has been affected by crustal contamination

the joffre banded iron formation hamersley group western australia assessing the palaeoenvironment through detailed petrology and chemostratigraphy abstract the joffre member of the brockman iron formation is by volume the largest single known banded iron formation bif in the world here we present detailed petrology and chemostratigraphy through the entire 355 m core section of this 2 45 billion year old unit oxide bif and silicate carbonate oxide bif dominate the lithology with minor amounts of interbedded stilpnomelane mudrock stilpnomelane rich tuffaceous mudrock and calcareous mudrock besides chert and magnetite the prominent mineralogy is riebeckite ankerite hematite stilpnomelane and crocidolite the bif is characterized by an average of 50 wt sio 2 and 44 5 wt fe 2 o 3 and an overall low abundance of al 2 o 3 2 sn of 0 24 the rey patterns also show a positive la sn anomaly no ce sn anomaly and a weakly developed positive y sn anomaly iron isotopes 56 fe with positive 56 fe values of 0 04 to 1 21 suggest that a large part of the hydrothermal iron was partly oxidized in the upper water column and subsequently precipitated as ferric oxyhydroxides no epiclastic grains have been found rather submarine hydrothermal fluids and fine grained volcanogenic detritus controlled bif chemistry the former source is reflected through a constant positive eu sn anomaly throughout the core average eu sn anomaly of 1 6 with a peak of 2 1 between 100 and 155 m depth while the latter source is best reflected through the stilpnomelane rich tuffaceous mudrock consisting of volcanic ash fall tuff with relict shards set in a stilpnomelane matrix the mudrock is overlain by well preserved wavy laminae and laminae sets of stilpnomelane microgranules that likely originated from re worked volcanic ash formed either on the seafloor or in the water column prior to deposition an enriched hree to lree pattern a high iron content 30 wt and a 56 fe value of 0 59 collectively imply that the mudrock facies interacted with the fe rich seawater prior to deposition the tio 2 zr ratio of the bif and the associated mudrocks suggest a felsic only source related to the same style of volcanics as the slightly younger woongarra rhyolites given the observation that the dominant control on the seawater chemistry was associated with felsic volcanics we speculate that the fine grained pelagic ash particles may have sourced bio available nutrients to the surface water this would have facilitated enhanced biological productivity including bacterial fe ii oxidation which is now recorded as the positively fractionated 56 fe iron oxide minerals in the joffre bif alongside submarine hydrothermal input to the basin the dominant control on the ocean chemistry seems to have been through volcanic and pyroclastic pathways thereby making the joffre bif poorly suited as a chemical proxy for the study of atmospheric oxygen and its weathering impact on local landmasses

mineralogical characterization of rock surfaces formed by hydrothermal alteration and weathering application to remote sensing the value of 50 mu m was used as an approximate maximum penetration depth to include all mineral species which may contribute to a reflectance signal jarosite and alunite occur only in altered areas whereas hematite and goethite occur in both altered and unaltered areas incorporation of aluminum into hematite occurs only in unaltered areas the spectral shift to longer wavelengths which accompanies aluminum substitution should be useful in delineating mineralized zones modified journal abstract

the f zone a negative velocity gradient near the inner outer core boundary might be adequately explained by the existence of heat producing elements in the region geochemically there should be about one third to more than a half of the earth s total resources of heat producing elements present below the upper mantle which is also consistent with observations of heat flux at the earth s surface the results of high pressure experiments further suggests that the heat producing elements would exist as dioxides which are chemically incompatible with the major mantle silicates under the temperature and pressure conditions prevailing in the lower mantle the great density of these heat producing dioxides probably greater than the liquid iron nickel core may cause them to be transported to the inner outer core boundary the f zone

reconstruction and interpretation of giant mafic dyke swarms a case study of 1 78 ga magmatism in the north china craton

the difference between oceanic and continental tholeiites a fluid dynamic explanation continental tholeiites have higher sio2 k2o and light rare earth element contents and more evolved isotopic characteristics than their oceanic counterparts these differences can be explained if the compositions of the parent magmas to both types of tholeiites are similar but if continental magmas assimilate significant amounts of continental crust en route to the surface although there is little doubt that most continental tholeiites have assimilated crustal material the lcoation and mechanism of assimilation remain uncertain longhi 1981 has argued that magmas derived directly from the mantle should crystallize little orthopyroxene the abundance of orthopyroxene in most continental layered intrusions suggests that they have crystallized from magmas which have assimilated continental crust since orthopyroxene is an early crystallizing phase in layered intrusions this assimilation must occur early before the magma enters the chamber assimilation can occur at the margins of the dykes which feed magma chambers depending on the nature of the flow if the flow is turbulent the high temperatures at the centre of the dyke will extend to the margins and the magma will erode the dyke walls if the flow is laminar a conductive profile develops at the margin and the flowing magma chills against the walls protecting them from thermal erosion the nature of flow in a dyke can be predicted from the reynolds number the criteria for turbulence reynolds number calculations suggest that the flow of primitive magmas in continental dykes will be fully turbulent and if this is the case assimilation of low melting point components in the walls of the dyke is inevitable it is therefore suggested that many of the geochemical characteristics of continental tholeiites result from melting at the walls of dykes as primitive magmas ascend through the crust

geochemical and isotopic disequilibrium in crustal melting an insight from the anatectic granitoids from toledo spain in the hercynian anatectic complex of toledo act the anatectic granitoids include leucogranitic leucosomes leucogranitic massifs and restite rich granites they show a broad range of initial sr and nd isotope ratios from 0 711 to 0 720 and 0 51164 to 0 51203 respectively which clearly indicate the absence of isotopic homogenization in the melts broadly the ranges reflect the isotopic variation of the metapelitic protoliths if crustal melting occurs under water undersaturated conditions as is the case of the act the generated melts do not isotopically and chemically equilibrate with the granulitic residuum the preservation of heterogeneities could arise through a number of processes 1 duration of the process in which the presence of melts with disequilibrium features and the high solid content of several of the granites in the act point to a very short lived magmatic system 2 limited diffusion in which poorly segregated and volatile undersaturated granitoids have a very restricted opportunity for isotopic and chemical homogenization and 3 magma dynamics in which the low melting rates the high restite and low water contents and the silica rich composition of these granites together with the small volume and high viscosity values of the melts seriously restrict the physical processes leading to homogenization

imaging the 2016 mw 7 8 kaikoura new zealand earthquake with teleseismic p waves a cascading rupture across multiple faults the 13 november 2016 mw 7 8 kaikoura new zealand earthquake was investigated using teleseismic p waves backprojection of high frequency p waves from two regional arrays shows unilateral rupture of at least two southwest northeast striking faults with an average rupture speed of 1 4 1 6 km s and total duration of 100 s guided by these backprojection results 33 globally distributed low frequency p waves were inverted for a finite fault model ffm of slip the ffm showed evidence of several subevents however it lacked significant moment release near the epicenter where a large burst of high frequency energy was observed a local strong motion network recorded strong shaking near the epicenter hence for this earthquake the distribution of backprojection energy is superior to the ffm as a guide of strong shaking for future large earthquakes that occur in regions without strong motion networks initial shaking estimates could benefit from backprojection constraints

dynamically triggered slip on a splay fault in the mw 7 8 2016 kaikoura new zealand earthquake we investigate the mw 7 8 2016 kaikoura new zealand earthquake using optical satellite imagery and seismology to reveal the main features of the rupture process correlation of landsat8 images reveals a 30 40 km surface rupture on the kekerengu fault and jordan thrust with up to 12 m of right lateral slip a previously unrecognized conjugate strike slip fault the papatea fault also slipped co seismically 3 4 m the global cmt centroid indicates both thrust and right lateral slip and is located 100 km ne of the mainshock epicenter the significant non double couple component of the gcmt 25 suggests the mainshock is not well represented by a single planar fault back projection of teleseismic p waves reveals two main bursts of seismic radiation 1 at 10 20 s near the mainshock epicenter and 2 at 70 s close to the observed surface ruptures we determine a finite source kinematic model of the rupture from the inversion of seismic waveforms we use two faults in our model defined to match the observed slip on the kekerengu fault and a deeper offshore fault with a lower dip angle to satisfy the long period seismological observations we compute the equivalent moment tensor from our finite source model and find it to be remarkably consistent with the gcmt solution although little is known about the geometry of these faults at depth if the kekerengu fault splays from the deeper thrust it provides a rare example where the contribution of slip on a splay fault can be clearly isolated in the seismological waveforms

metamorphic response and crustal architecture in a classic collisional orogen the damara belt namibia abstract the damara belt is a well exposed mid crustal section through a collisional orogen of cambrian age that closed the khomas ocean basin between passive margins on the congo and kalahari cratons collision resulted in a bi vergent orogen with a distinct paired metamorphic pattern of foreland vergent high p low t orogenic margins and a broad high grade low p high t orogen core spatial and temporal patterns of the metamorphic response to collision have been characterized for all parts of the belt using a large dataset n 240 of internally consistent quantitative pt determinations evolution of mineral parageneses and semi quantitative p t paths metamorphic mapping and quantitative metamorphic field gradients integration with deformation history structural profiles metamorphic chronology magmatic history and stratigraphy constrains a dynamic model of crustal architecture during peak metamorphic events the pattern of zonal metamorphic response is demarcated by three major metamorphic discontinuities md with steep pressure gradients inferring crustal scale structures that accommodated lateral exhumation of crustal wedges discontinuities are confirmed by deformation features in the field and metamorphic mineral growth indicates that vertical flattening at the peak of metamorphism progressing through ductile to brittle extensional structures crustal wedges along the orogenic margins experienced steep clockwise p t paths with peak pt conditions terminated by isothermal decompression during rapid exhumation in isostatic response to deep burial metamorphic chronology and over printing metamorphic fabrics constrain a sequence of foreland propagating out wedging of crustal thrust wedges that resulted in telescoping of the orogenic margins peak metamorphism at a geothermal gradient of 20 25 c km and 8 9 kb in the southern zone wedge i was attained between 517 530 ma followed by south directed out wedging at the uis pass suture accommodated by relative extension md1 at high structural levels near the boundary with the high grade orogen core out wedging of the southern zone further buried the southern margin zone wedge ii in the footwall below the uis pass suture peak metamorphism at 17 c km and 9 5 11 5 kb in the southern margin zone was attained at 517 4 ma and followed by out wedging on basal thrusts accommodated by vertical flattening and extensional reactivation of the uis pass suture md2 peak metamorphism at 17 c km and 10 5 kb in a high p low t crustal wedge in the northern margin wedge iii occurred at 510 4 ma peak metamorphism in this wedge was terminated by isothermal decompression during north directed thrusting accommodated by extension at higher structural levels near the high grade orogen core md3 granulite facies metamorphism in the high grade orogen core which formed the upper plate to the deeper thrust wedges occurred at significantly lower pressures 4 3 6 0 kb higher t depth ratios 38 47 c km and low p t clockwise p t paths indicating only moderate burial and protracted high grade conditions metamorphic chronology confirms high grade conditions 540 505 ma persisted beyond isostatic adjustment of the high p low t orogenic margins high heat flow conditions and long thermal lag are best explained by lithospheric breakoff during collision in contrast to the high p low t margins that experienced lateral exhumation in a convergent system the high grade orogen core was exhumed vertically as a broad core complex during extensional collapse of the orogen peak metamorphic conditions in the central part of the orogen core record higher pressures than marginal lower grade zones to both the north and south indicating vertical exhumation as a broad massif this post peak vertical exhumation of the central core occurred after 505 ma was accommodated by brittle extensional detachments at high stratigraphic levels with km scale omission of crustal section

reconciling the deformational dichotomy of the 2016 mw 7 8 kaikoura new zealand earthquake following the 2016 mw 7 8 kaikoura earthquake uncertainty over the nature of the coseismic rupture developed seismological evidence pointed to significant involvement of the subduction megathrust while geodetic and field observations pointed to a shallow set of intracrustal faults as the main participants during the earthquake the addition of tsunami observations and modeling as reported in bai et al 2017 places additional constraints on the specific location of coseismic slip which when combined with other observations indicates the simultaneous occurrence of shallow slip on the subduction interface and slip on overlying upper crustal fault structures this kaikoura style earthquake involving synchronous ruptures on multiple components of the plate boundary is an important mode of plate boundary deformation affecting seismic hazard along subduction zones

petrological and geochemical constraints on the evolution of the alkaline complex of koraput in the eastern ghats granulite belt india abstract the koraput alkaline complex in the high grade eastern ghats belt india is synkinematically emplaced in a pull apart structure and far from the bastar cratonic margin the suite comprises four distinct members namely mafic syenite felsic syenite nepheline syenite and perthite syenite fe rich orthopyroxene rims on olivine in mafic syenite indicate iron enrichment in the early stage of differentiation with plagioclase of andesine composition it could be described as alkali norite the plutonic equivalent of hawiite felsic syenite with both alkali feldspars and plagioclase of oligoclase composition could be described as two feldspar syenite the plutonic equivalent of mugearite albitic rims on nepheline indicates subsolvus reaction chemical trends in amphiboles and plagioclase feldspars progressively more ferroan and more sodic respectively are strong indications of mineral fractionation in the koraput suite chemical trends in the variation diagrams are compatible with feldspar fractionation in the koraput suite a weak fe enrichment trend in the early stage of differentiation as observed in the afm diagram is compatible with that of the alkali basalt series nb anomalies both positive and negative are indicative of crustal contamination as expected in synkinematic plutons in terms of gondwana assembly and break up the alkaline complexes are supposed to represent rift related magmatism along the continental margin in spite of petrological evidence of the magmatic character of the koraput complex anorogenic setting is contra indicated by mesoscopic and microscopic fabrics more akin to synkinematic intrusion during f 2 folding in the host country rocks the proterozoic alkaline complexes in the eastern ghats belt could alternatively trace the path of moving gondwana continent over mantle plumes

preliminary report on the paleomagnetism of 1 88ga dykes from the bastar and dharwar cratons peninsular india abstract we report the results of a preliminary paleomagnetic study on well dated 1 9 ga dykes from the bastar craton india this suite of nw se trending dykes was linked to similarly aged magmatic activity in the dharwar craton and cuddapah basin in india as part of a large igneous province this igneous activity may have extended across many cratons in the columbia supercontinent including the north china craton laurentia baltica australia siberia and the kaapvaal and zimbabwe cratons southern africa the bastar dykes along with the cuddapah traps and dyke yield a dual polarity magnetization with d 126 i 15 2 k 27 95 11 9 and a corresponding paleomagnetic pole at 31 n 330 e dp 6 3 dm 12 2 the relatively robust paleomagnetic and geochronologic database at 1 85 1 90 ga allow us to test one of the configurations of the supercontinent columbia there are some critical differences between our paleomagnetically based reconstruction and the archetypal and geologically based columbia configuration of zhao et al 2004 most notably siberia india and australia cannot be linked to laurentia in the archetypal columbia fit proposed links between western australia and the kaapvaal and zimbabwe cratons are possible as is the fit between baltica and laurentia the robust paleomagnetic data reported in this paper require that either the columbia supercontinent did not exist at 1 9 ga or requires major modification given that our data provide only a snapshot on the paleoproterozoic we conclude that the columbia supercontinent remains a viable possibility although relationships between individual elements should be re evaluated as more data become available

rare earth elements as reactive tracers of biogeochemical weathering in forested rhyolitic terrain article rareearthelements rees were evaluatedaspotentialtracers of biogeochemicalweathering atpedon hillslope and catchment scales in the jemez river basin critical zone observatory jrb czo valles caldera national pre serve nm usa we investigated time series of ree patterns in precipitation soil pore water groundwater and stream water and related these data to ree composition of soil rock and atmospheric dust ree signatures in stream waters are dynamic reflecting processes that occur along hydrologic flowpaths during transport to the stream including organic matter complexation primary and secondary mineral weathering water soil bedrock interaction and atmospheric deposition strong compositional similarities for the ree between soil waters and stream waters during the initial snowmelt are consistent with shallow subsurface flows to streams most bio

origin of granites in an archean high grade terrane southern india archean deep level granites in southern india are similar geochemically to young granites from continentalmargin arc systems they exhibit light ree enriched patterns with variable but chiefly positive eu anomalies this is in striking contrast to the negative eu anomalies typical in high level archean granites in addition the deep level granites are relatively enriched in ba and sr and depleted in total ree and high field strength elements hfse one pluton the sankari granite has unusually low contents of ree and hfse most of the deep level granites appear to represent cumulates with variable amounts of trapped liquid and of minor phases resulting from fractional crystallization of a granitic parent such parental granitic magmas can be produced by batch melting of archean tonalite at middle to lower crustal depths the sankari granite requires a tonalitic source depleted in ree and hfse archean tonalites and tonalitic charnockites exhibit original igneous geochemical signatures and their average composition does not show a significant eu anomaly hence they cannot represent the positive eu anomaly complement to the negative eu anomaly high level granites our results suggest that archean deep level granites may represent this complement such granite may form in waterrich zones in the middle or lower crust and be produced in response to dehydration of the lower crust by a rising co2 rich fluid phase

long period analysis of the 2016 kaikoura earthquake abstract the recent m w 7 8 kaikoura new zealand earthquake involved a remarkably complex rupture propagating in an intricate network of faults at the transition between the alpine fault in the south island and the kermadec tonga subduction zone we investigate the main features of this complicated rupture process using long period seismological observations apparent rayleigh wave moment rate functions reveal a clear northeastward directivity with an unusually weak rupture initiation during 60 s followed by a major 20 s burst of moment rate to further explore the rupture process we perform a bayesian exploration of multiple point source parameters in a 3 d earth model the results show that the rupture initiated as a small strike slip rupture and propagated to the northeast triggering large slip on both strike slip and thrust faults the kaikoura earthquake is thus a rare instance in which slip on intraplate faults trigger extensive interplate thrust faulting this clearly outlines the importance of accounting for secondary faults when assessing seismic and tsunami hazard in subduction zones

breaking a subduction termination from top to bottom the large 2016 kaikōura earthquake new zealand abstract subduction systems globally terminate allowing plate motion to be transferred from the oceanic megathrust onto continental and or oceanic transform faults the mechanism of this kinematic transition over earthquake timescales is however poorly understood due to a lack of relevant data here we study the 2016 mw 7 8 kaik ura earthquake in new zealand the first large instrumentally recorded earthquake across a subduction termination to investigate this transfer mechanism in detail we find that the kaik ura earthquake unlike standard subduction earthquakes globally involved a predominance 80 of coseismic slip on upper plate faults and minor triggered slip on the underlying oceanic subduction thrust in the months following the earthquake the subduction thrust accommodated most of the earthquake s afterslip down dip of its co seismic rupture zone this top down strain release mechanism is in accord with local geological geodetic and historical seismicity data which suggest that the bulk of plate convergence 75 is accommodated in the upper plate we suggest therefore that this alternative strain release mechanism which is distinct from standard plate boundary earthquakes is characteristic of subduction terminations and results in the majority of seismic tsunami hazard being on steep near surface faults

geochemistry and geochronology of proterozoic tholeiite dykes of east antarctica evidence for mantle metasomatism two episodes of tholeiite dyke emplacement have been identified in archaean high grade metamorphics of the napier complex in enderby land middle proterozoic amundsen dykes are typical continental tholeiites and most of the chemical variation in individual suites can be explained in terms of different degrees of partial melting and low pressure crystal fractionation group i amundsen tholeiites were derived from a relatively homogeneous source region 1 190 200 m y ago whereas that of the group ii amundsen tholeiites was chemically and isotopically heterogeneous group ii dykes have various degrees of enrichment in incompatible elements and commonly show normalised trace element abundance patterns with negative nb anomalies these features imply variable metasomatism of the source region by a volatile rich fluid phase rather than a melt of any observed igneous composition enriched in k rb ba th and possibly la and ce early proterozoic 2 350 48 m y tholeiites were emplaced at considerable depths in the crust during the waning stages of granulite facies metamorphism and include a high mg suite of possible komatiitic affinity ranging in composition from hypersthene rich tholeiite norite to quartz rich tholeiite they tend to have higher ratios of highly to moderately incompatible elements e g k zr k ce and larger nb anomalies i e higher k nb compared with middle proterozoic tholeiites suggesting derivation from more enriched source regions isotopic data are not compatible with significant crustal contamination but constrain source metasomatism to a time immediately before emplacement metasomatism of the source region of the much younger group i tholeiites may have been contemporaneous with that of the high mg suite

impact glasses from zhamanshin crater u s s r chemical composition and discussion of origin three silica rich zhamanshinites and one irghizite from the zhamanshin impact crater northern aral area u s s r have been analyzed for up to 40 major minor and trace elements all data point to a clear distinction between these impact glasses and other tektites or impact glasses e g from the australasian strewn field halogens are generally enriched in the irghizites and zhamanshinites when compared to normal splash for tektites with zhamanshinites enriched more than irghizites the same holds also for the alkali metals and a number of other volatile elements like sb and as nickel and cobalt are enriched in the irghizite sample to a considerable degree suggesting meteoritic contamination this view is also supported by gold and selenium data but for quantifications other siderophile elements need to be considered chromium is not a valid indicator of meteoritic contamination because smallamounts of ultra basic igneous material may completely alter the picture the rare earth elements do show a sedimentary pattern consistent with two or three different source materials and a variation which is probably mostly due to dilution with silica rich materials the peak pressure and temperature experienced by the irghizites was lower than for australites or other splash form tektites and even lower for zhamanshinites which is revealed by the content of volatile elements and lesser homogeneity

the purana basins of southern cratonic province of india a case for mesoproterozoic fossil rifts abstract since its cratonization in the palaeoproterozoic southern peninsular india witnessed the development of a number of large intracratonic sedimentary basins traditionally referred to as purana basins spanning in age from late palaeoproterozoic through neoproterozoic the localization of these intracratonic basins namely pranhita godavari pg chattisgarh and cuddapah basins is apparently controlled by pre existing sutures and or weak zones the pg basin and the cuddapah basin host unconformity bound thick sediment dominated successions attesting to several cycles of fluvial shallow marine to shelf slope basin sedimentation deposition was punctuated by block uplifts resulting in local hiatuses and or volcanic upheavals leading to intercalation of thin but persistent basaltic flows and acid tuffs and ignimbrites basin margin deep faults apparently played a role in the facies distribution in these basins based on these features we propose that these basins initiated as continental rifts which however never opened up into a full fledged ocean basin but links with open seaway are evident from frequent occurrence of deposits representing tidal and storm influence particularly in upper part of the chattisgarh succession spatial distribution of facies and sediment thickness in the cuddapah and pg basins suggest that an open seaway existed to the east of the south indian cratonic province during the mesoproterozoic while similar criteria point to the existence of an open seaway north of the chattisgarh basin development history including nature of inversion suggest that the southern cratonic province of india existed as a single large continental mass since the mesoproterozoic in spite of episodes of supercontinent build up and fragmentation involving india and east gondwana during the proterozoic

tectonic environment of the devonian gramscatho basin south cornwall framework mode and geochemical evidence from turbiditic sandstones the portscatho formation within the allochthonous unit of the middle and upper devonian gramscatho group is a thick sequence of deep water sandstones and interbedded slates deposited by southerly derived turbidity currents into the gramscatho basin of south cornwall throughout an approximately 3 5 km thick sequence the portscatho formation is petrographically and chemically coherent except that the upper section shows a higher proportion of metamorphic clasts high but variable cr and low uniform zr abundances complementary framework mode and bulk geochemistry indicate that the sandstones were derived from a dissected continental magmatic arc of predominantly acidic composition similar to average upper continental crust but with an admixture of minor intermediate basic material flysch deposition took place in a fore arc setting the presence of an arc to the south of cornwall during the devonian implies that there was subduction at the margin of the gramscatho basin whose ultimate closure was accommodated by the northward stacking of flysch ophiolite nappes

mantle derived archaean monozodiorites and trachyandesites the 2 680 2 750 myr old1 5 intrusive granite greenstone terranes6 8 in the rainy lake region ontario and in and adjacent to the vermilion district minnesota of the superior province in north america include a wide variety of volcanic and intrusive rocks with initial pb sr and nd isotope ratios close to those for the mantle4 5 9 12 the isotopic constraints require the production of large volumes of silica oversaturated magmas from silica undersaturated mantle within 100 200 myr we present here geochemical data on monzodiorites and trachyandesites from the rainy lake area which are strongly enriched in large ion lithophile elements lile we conclude that they are derived by direct melting of the mantle at depths of 50km in either anhydrous or hydrous conditions their rare earth element ree abundances and initial 143nd 144nd ratios suggest that their mantle sources were enriched in lile shortly before melting the monzodiorites trachyandesites and their granodioritic derivatives may comprise up to 20 of the exposed igneous rocks in the rainy lake region and vermilion district if these rocks are as abundant in other archaean terranes a significant part of the early continental crust could have formed by direct melting of lile enriched mantle

geochemistry and tectonic significance of the ongarbira metavolcanic rocks singhbhum district india abstract the volcanic sedimentary sequence of ongarbira occurs to the south of the singhbhum shear zone and rests uncomformably on a basement topographic low between the chakradharpur granite and the singhbhum granite structural analysis reveals that the ongarbira synform and other adjoining structures are kilometre scale first generation folds on e w striking axial planes these structures are in marked contrast with the corresponding kilometre scale first generation folds typical of the iron ore group synclinorium towards the south of the ongarbira belt the ongarbira metavolcanic rocks exhibit a limited range of tholeitic basalt compositions the basalts are grouped according to their mg and the details of their ree patterns groups i and ii are relatively unevolved and very similar to lree and lil depleted ocean ridge tholeiites the most evolved group iii with lree enrichment is most similar to lil enriched ocean floor basalts but may be contaminated with crustal materials in general the ongarbira volcanics evolve upward stratigraphically petrogenetic major element modelling of the ongarbira basalts suggests that the primary melt was generated by batch melting 30 of lherzolite at pressures of at least 1 5 gpa sequential fractionation of ol o1 cpx pl and cpx pl followed comparison of incompatible and compatible element distributions indicates a very similar batch m melting fractional crystallization sequence for ongarbira groups i and ii basalts group iii basalts may have been derived from a batch melt initially more enriched in incompatible elements trace element discrimination of the ongarbira basalts suggests that they were generated in an extensional environment primordial mantle normalized element distributions indicate that the basalts are similar to continental rift basalts but with oceanic affinities the chemical data along with the associated sediments indicate that the ongarbira basalts were probably emplaced in a mature continental rift although a back arc origin cannot be completely disregarded it is concluded that the ongarbira volcanics were emplaced as part of the same rifting event that resulted in outpourings of the proterozoic dalma and dhanjori volcanics implying that the ongarbira suite is proterozoic and not part of the archaean iron ore group the structural geometry of the ongarbira rocks is more conformable to that of the singhbhum mobile belt than to the iron ore group synclinorium in the singhbhum craton it is likely that the southern limit of the singhbhum mobile belt is defined by the interface of its e w structures with the nne structures of the iron ore group rocks thus the singhbhum shear zone does not mark the interface between the archaean singhbhum craton and the proterozoic singhbhum mobile belt in the eastern indian shield

the silurian passamaquoddy bay mafic dyke swarm new brunswick petrogenesis and tectonic implications the volcanic and sedimentary rocks of the passamaquoddy bay pb area of southeastern new brunswick are part of the silurian devonian coastal volcanic belt cvb an extensive belt of bimodal volca

geochemical and metallogenic relations in volcanic rocks of the southern slave province implications for late neoarchean tectonics late neoarchean volcanic belts in the southern slave province include 1 in the east the cameron river beaulieu river belts which are characterized by stratigraphically thin flow rich classic calc alkaline arc type sequences with accompanying syngenetic volcanogenic massive sulphide deposits and 2 in the west the yellowknife belt which is characterized by stratigraphically thick structurally complex pyroclastic rich adakitic back arc basin type sequences with accompanying epigenetic lode gold deposits the volcanic belt association bears persuasive chemical evidence of subduction initiated magma generation however the greenstone belts together with coeval matching patterned belts in superior province of the southern canadian shield bear equally persuasive evidence of prevailing autochthonous parautochthonous relations with respect to component stratigraphic parts and to older gneissic basement the eastern and western volcanic belts in question are petrogenetically ascribed to a westerly inclined present geography subduction zone s that produced shallower east to deeper west slab initiated mantle wedge generated parent magmas this early stage microplate tectonic process involved modest mantle subduction depths small tectonic plates and small sialic cratons in the larger context of earth s progressively cooling hence subduction deepening mantle this late neoarchean greenstone belt development 2 73 2 66 ga merged with the massive end archean tonalite trondhjemite granodiorite granite ttgg bloom 2 65 2 55 ga resulting in greatly enhanced craton stability successive subduction deepening plate craton enlarging stages with appropriate metallotectonic response across succeeding proterozoic time and beyond led to modern mode plate tectonics

magnetic fabrics and rock magnetism of the xiong er volcanic rocks and their implications for tectonic correlation of the north china craton with other crustal blocks in the nuna columbia supercontinent abstract the tectonic background of the paleoproterozoic xiong er volcanic rocks xvr is important for understanding the tectonic evolution of the north china craton ncc as well as its paleogeographic position during the assembly of the nuna columbia supercontinent here we report the results of the first anisotropy of magnetic susceptibility ams study of the xvr and use the interpreted flow directions to constrain the emplacement mechanism and to assess its geological significance for the reconstruction of the nuna columbia supercontinent thirty lavas were sampled from three sections in western henan province detailed rock magnetic analyses including measurements of hysteresis loops magnetization versus temperature curves and first order reverse curves were performed to identify the main magnetic phases and grain sizes the inferred directions from the ams results reveal a radial flow pattern with an eruption center probably located near xiong er mountain our data suggest that the xvr may have been emplaced in a triple conjugated continental rift on the south margin of the ncc probably initiated from a paleoplume based on this interpretation a comparison of geological and paleomagnetic results among the proposed crustal blocks in the nuna columbia supercontinent suggests a close linkage of the ncc with sao francisco congo rio de la plate and siberia

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

the mean life of continents estimates of continent recycling rates from nd and hf isotopic data and implications for mantle structure an analysis of the initial neodymium and hafnium isotopic compositions of modern and ancient mantle derived rocks shows that the divergence of the mantle 143nd 144nd and 176hf 177hf ratios from the chondritic ratios over the past 2 billion years has been much less than would be expected based on the sm nd and lu hf ratios of the mantle source of mid ocean ridge basalt the most likely explanation is that rock material from the continents has been recycled semi continuously back into the mantle over this time period the required rate of return of continents to the mantle calculated from a simple transport model is about 0 35 0 15 of the continental mass per billion years 2 5 km year this result is consistent with the hypothesis that the mass of the continents has been approximately constant since the late archean and implies that recycled continental material must be an important component of the upper mantle

petrograph a new software to visualize model and present geochemical data in igneous petrology a new software petrograph has been developed to visualize elaborate and model geochemical data for igneous petrology purposes the software is able to plot data on several different diagrams including a large number of classification and petrotectonic plots petrograph gives the opportunity to handle large geochemical data sets in a single program without the need of passing from one software to the other as usually happens in petrologic data handling along with these basic functions petrograph contains a wide choice of modeling possibilities from major element mass balance calculations to the most common partial melting and magma evolution models based on trace element and isotopic data results and graphs can be exported as vector graphics in publication quality form or they can be copied and pasted within the most common graphics programs for further modifications all these features make petrograph one of the most complete software presently available for igneous petrology research

intracrustal recycling and upper crustal evolution a case study from the pan african damara mobile belt central namibia abstract clastic sediments from the pan african damara mobile belt show a wide range in depositional nd nd 0 18 to 1 and several key trace element ratios notably th nd and la sm increase from 0 2 to 0 7 and 4 0 to 8 0 respectively with decreasing nd 0 such trace element ratio nd 0 data arrays are attributed to binary mixing within the sedimentary mass and the data array defined by the damara sediments is consistent with data from other regions the low nd 0 end member is characterised by high th nd th y la sm and hf zr ratios and reflects highly differentiated upper crust dominated by granitoids pb isotope data suggest that the low nd 0 end member also had relatively high time integrated th u 4 by contrast the high nd 0 end member reflects juvenile upper crust but this end member has la sm th nd and hf zr ratios 4 0 0 2 and 0 02 respectively slightly lower than those of taylor and mclennan s preferred model for bulk crust and significantly lower than those of the andesite model intracrustal differentiation is discussed in terms of bulk crust present day average upper crust post archaean shale and a highly differentiated low nd 0 end member trace element ratios which are not significantly fractionated during erosion and sedimentation e g th nd th y and la sm show relatively smooth increases between these reservoirs whereas other trace element ratios which are fractionated both by sedimentary and magmatic processes e g rb sr and rb zr increase dramatically in the more differentiated crustal reservoirs

geochemistry and geochronology of late mesozoic volcanic rocks in the northern part of the eastern pontide orogenic belt ne turkey implications for the closure of the neo tethys ocean abstract this paper presents 40ar 39ar and u pb age data sr nd isotopes whole rock and mineral compositions of upper cretaceous volcanic rocks from the ordu area of the eastern pontide orogenic belt epob in northeastern turkey the volcanic rocks exhibit a wide compositional range basalt basaltic andesites andesites and a rhyodacite suite they are characterized by subparallel light rare earth element lree enrichment relatively flat heavy rare earth element hree patterns with eu anomalies and moderate fractionation average la yb n 8 55 the geochemical results show that the volcanic rocks have calc alkaline affinity consistent with arc volcanic rocks erupted in an active continental margin initial 87sr 86sr values vary between 0 70569 and 0 70606 while initial 143nd 144nd values lie between 0 51244 and 0 51249 crustal contamination affected the mantle originated primary magma as indicated by increased 87sr 86sr and decreased 143nd 144nd ratios with increasing sio2 new precise laser ablation inductively coupled plasma mass spectrometer la icp ms 206pb 238u age analyses of zircon and 40ar 39ar age data of plagioclase from the volcanics enable a more precise reconstruction of the ebop the ages provide insight into the timing of arc formation in this region constrain the volcanic activity between 86 my coniacian and 75 my campanian and constrain the timing of closure of the neo tethys

multielement geochemistry of offshore sediments in the southeastern yellow sea and implications for sediment origin and dispersal abstract in total 116 surface sediments were collected from an offshore area of the southeastern yellow sea including a large mud belt southeastern yellow sea mud seysm and analyzed for grain size and geochemical composition organic carbon and 42 elements principal component analysis revealed that elemental compositions of the offshore sediments were mostly controlled by common aluminosilicate clay minerals and quartz most elements heavy minerals hf zr u th rare earth elements rees biogenic calcium carbonates ca sr feldspar and mica k ba pb and mn oxides mn oxide coatings on sand grains notably total ree concentrations may be associated with heavy minerals possibly zircon and monazite especially in silty grains even though heavy ree hrees concentrations are more strongly controlled by clay minerals in muddy sediments the diagnostic discrimination plots of geochemical compositions e g fe vs al mg vs al light ree vs hree and la lu ucc vs la y ucc suggested that the offshore sediments especially in seysm deposits were composed of a mixture of korean river derived silts and chinese river derived clays this demonstrated that chinese river sediments especially clay particles largely contributed to the formation of the giant mud belt in the korean coastal area furthermore the observed geochemical end members provide new markers of sediment provenance which can be used to track dispersal patterns and sediment limits from chinese and or korean rivers

investigations of the cerro colorado pluton northern chile using enhanced landsat thematic mapper images digitally enhanced landsat thematic mapper tm images of the cerro colorado pluton northern chile were studied the bulk of the intrusion is magnetic rich and laboratory spectra of the fresh surfaces of field samples are severely quenched weathering and oxidation of the magnetite has reduced the quenching effects allowing features due to the primary mineralogy of the rock to be resolved in the spectra of the weathered surfaces and consequently on the enhanced imagery in most cases the weathering alters the overall albedo of the rock and it may introduce additional features into the rock spectra due to iron hydroxides and clay minerals as yet it does not seem to the author that tm data alone could be used for lithological mapping some control is necessary in the form of fieldwork or pre existing maps