permian triassic red stained albitized profiles in the granitic basement of ne spain evidence for deep alteration related to the triassic palaeosurface extensive areas of the variscan granitic basement in ne spain display profiles of red stained albitized facies characterized by albitization of ca plagioclase chloritization of biotite and microclinization of orthoclase along with the alteration of igneous quartz to secondary cl dark quartz these profiles have a geopetal structure beneath the triassic unconformity with a very intense and pervasive alteration in the upper part that progressively decreases with depth to 150 200 m where the alteration is restricted to the walls of fractures the red albitized facies contains secondary maghemite and hematite that indicate oxidizing conditions dating of microclinized orthoclase and secondary monazite that have formed in the red stained albitized facies yielded k ar and u th pbtotal ages of 240 and 250 ma respectively suggesting that the alteration developed during the permian triassic period the geopetal disposition of the red albitized profile with respect to the triassic unconformity its large regional extent and the fracture controlled alteration in the lower part of the profile indicate groundwater interaction the 18o values of albitized plagioclase 11 microclinized orthoclase 13 and secondary cl dark quartz 12 suggest that the alteration temperature was about 55 c this low temperature suggests that the alteration occurred during interaction of the granitic rocks with na rich fluids below a surficial weathering mantle on the permian triassic palaeosurface the latter is possibly related to triassic evaporitic environments in long lasting stable landscapes in which na rich solutions infiltrated deep regional groundwaters

long term and annual influence of aswan reservoir egypt on the local seismicity a spatio temporal statistical analysis earthquakes continue to occur in the kalabsha embayment region near the aswan reservoir for more than three decades these earthquakes including the 1981 mainshock m 5 3 have been considered to be reservoir triggered and pore pressure appears to be the main factor for their occurrence however influence of reservoir water levels on the earthquakes of the region which is significant in the initial period is reported to be weakening with time we statistically analyse the influence of the reservoir water levels on spatio temporal distribution of the earthquakes for the period 1982 2013 we divided the seismicity of various zones in different time windows depending upon their clustering and employed the power spectrum and singular spectrum analysis ssa the influence of long term and annual variations in the water level on the seismicity is very much apparent in ssa in the 45 years of reservoir filling history episodes of water levels more than 170 m which lead to filling of the embayment region appear to be correlated with the increase in seismicity of the aswan region in the power spectrum analysis a strong annual peak is found for water level time series however in the earthquake time series on an average a moderate and weak annual period cycle is present in the initial 1982 1988 and in the later 2001 2013 period respectively in the intermediate period 1989 2000 when the water level was the least in the embayment area a very weak annual cycle is present non consideration of spatio temporal variation in the seismicity leads to erroneous and misleading results of no or weaker reservoir influence in the later period this also highlights that the time and space dependent pore pressure diffusion process is likely responsible for earthquake triggering in the aswan region

a time scale for granitoid emplacement in the archean murchison province western australia by single zircon geochronology abstract in the late archean murchison province of western australia four major granitoid suites intruded into two stratigraphically distinct supracrustal sequences the luke creek and mount farmer groups single zircon u pb ages from five granitoid samples representing three of the four suites were measured by ion microprobe the earliest of the suites the pegmatite banded gneiss intruded luke creek group greenstones at 2919 12 ma 1 the luke creek group and the pegmatite banded gneiss protolith were subsequently deformed and then overlain by mount farmer group greenstones large volumes of monzogranite then intruded greenstones throughout the province two samples from this suite gave crystallization ages of 2704 51 and 2681 6 ma this package of greenstones gneiss and monzogranite was folded and metamorphosed and then intruded by two suites of post folding granitoids two samples from the more southern of these suites gave ages of 2641 5 and 2602 14 ma two additional samples were collected from a tonalite pluton previously assigned to the northern post folding granitoid suite they gave crystallization ages of 2760 8 and 2784 22 ma 1 this tonalite is now interpreted as a subvolcanic pluton associated with the andesite and dacite volcanism which produced the nearby mount farmer group greenstones no xenocrystic zircons with ages significantly in excess of 3 0 ga were found in any of the seven samples implying that little or no mid archean or older rocks are present in the region lower concordia intercept ages and 207 pb 206 pb ages from individual analyses indicate the presence of mid to late proterozoic activity throughout the murchison province concordia intercept ages were calculated using a least squares fit of a plane in three dimensions this approach obviates both the need to assign a common lead isotopic composition and the assumption that no pre recent events have disturbed the population s u pb system a further refinement of the data assessment process involved the use of the internal scan by scan scatter for defining the precision of the individual pb pb isotopic ratios compared with the observed scatter ion counting error estimates were found to frequently underestimate the uncertainties in the 207 pb 206 pb and 204 pb 206 pb ratios

role of fluids in the earthquake occurrence around aswan reservoir egypt 1 continuing seismicity for about 30 years near a large western embayment of the lake nasser about 50 km from the aswan high dam in egypt has led to a debate about the possibility of its relation with the reservoir impoundment the largest event in the region occurred on 14 november 1981 m 5 3 20 km beneath the wadi kalabsha embayment a westward extension of the lake aswan since then continuous monitoring of seismic activity has given an excellent opportunity to study the spatiotemporal distribution of seismicity in the area most of the immediate aftershocks of the 1981 main shock were located in the gebel marawa area at depths between 15 and 30 km depths of almost all earthquakes away from this zone were shallower than 12 km to quantify the effect of the reservoir impoundment on the seismicity of the aswan area we calculated changes in stress and pore pressure due to the reservoir impoundment using green s function approach the change in coulomb stress s is calculated on the fault planes responsible for majority of the seismicity of the region we found that for all the seismogenic faults s is negative i e stabilizing when we consider the effect of the reservoir load only whereas it is positive i e destabilizing when we include pore pressure for example at the hypocenter of the main earthquake shear stress normal stress and pore pressure due to reservoir operation are estimated as 5 5 13 2 and 13 5 kpa respectively which suggest that s is 3 1 kpa when we do not consider the effect of pore pressure and 5 7 kpa when contribution from pore pressure is considered hence the seismicity in the aswan lake region is driven by the pore pressure due to reservoir impoundment

some isotopic constraints on the evolution of the granulite and upper amphibolite facies terranes in the eastern musgrave block central australia abstract the central to eastern musgrave block central australia consists of the meso to neoproterozoic fregon and mulga park subdomains that are separated by a zone of mylonites and pseudotachylytes known as the woodroffe thrust the subdomains were previously considered to have undergone different geological histories but the differences relate mainly to metamorphic grade the fregon subdomain attained at least transitional granulite facies metamorphic conditions and the mulga park subdomain reached upper amphibolite facies felsic gneisses from both the fregon and mulga park subdomains contain zircons that are structured with euhedral centres overgrown by round elongate rims ion microprobe u pb analyses of the cores yield ages of 1557 24 and 1554 28 ma respectively and are interpreted to represent the time of igneous crystallization these ages place a maximum age constraint on the deposition or emplacement of the gneiss precursor high grade metamorphism grading from upper amphibolite to granulite facies took place between 1200 and 1150 ma and prior to the intrusion of several granitoid suites at around 1150 ma the kulgera adamellite and ayers ranges adamellite granitoid suites of the fregon subdomain yield ion microprobe u pb crystallization ages of 1150 12 and 1152 11 ma respectively a concordant u pb isotope dilution analysis on the ayers ranges adamellite yields a more precise age of 1152 3 ma the porphyritic suite intruding the mulga park subdomain yield an ion microprobe u pb magmatic age of 1159 20 ma these emplacement ages indicate extensive grenvillian felsic magmatism not previously recognized in australia the woodroffe thrust formed during a period of substantial crustal shortening the petermann orogeny 550 ma when the fregon subdomain was thrust onto the mulga park subdomain synkinematic muscovite and biotite record k ar and rb sr ages between 560 and 520 ma this petermann event is not recorded in the fregon subdomain due to confinement of the strain and associated mineral recrystallization to the underlying mulga park subdomain we suggest that the granulites were not exposed prior to the petermann orogeny as the basal quartzites of the amadeus basin occur only on the amphibolite facies mulga park subdomain

recognition of 3850 ma water lain sediments in west greenland and their significance for the early archaean earth a layered body of amphibolite banded iron formation bif and ultramafic rocks from the island of akilia southern west greenland is cut by a quartz dioritic sheet from which shrimp zircon 206pb 207pb weighted mean ages of 3865 11 ma and 3840 8 ma 2 sigma can be calculated by different approaches three other methods of assessing the zircon data yield ages of 3830 ma the bifs are interpreted as water lain sediments which with a minimum age of approximately 3850 ma are the oldest sediments yet documented these rocks provide proof that by approximately 3850 ma 1 there was a hydrosphere supporting the chemical sedimentation of bif and that not all water was stored in hydrous minerals and 2 that conditions satisfying the stability of liquid water imply surface temperatures were similar to present carbon isotope data of graphitic microdomains in apatite from the akilia island bif are consistent with a bio organic origin mojzsis et al 1996 extending the record of life on earth to 3850 ma life and surface water by approximately 3850 ma provide constraints on either the energetics or termination of the late meteoritic bombardment event suggested from the lunar cratering record on earth

archean magmatism in the kaminak lake area district of keewatin northwest territories ages of the carbonatite bearing alkaline complex and some host granitoid rocks u pb zircon data obtained on the ion microprobe shrimp have yielded an age of 2700 11 ma for tonalite of the kaminak batholith where it is intruded by a carbonatite bearing alkaline complex at kaminak lake northwest territories canada and a crystallization age of 2659 5 ma for the alkaline intrusion relatively undisturbed age spectra determined by laser probe 40ar 39ar analysis of hornblende from a gabbro and from a second tonalite of the batholith yielded cooling or minimum ages of 2727 14 and 2599 9 ma respectively spectra for hornblendes from two other gabbros suggest overprinting more recent than 2 04 ga with a minimum cooling age of 2 69 0 09 ga in one case and with incorporation of excess argon a maximum cooling age of 2 80 0 03 ga in the other correlation of these data with those recently reported by other workers indicates that the volcanic sequence and the plutonic granitoid units of the kaminak lake granitoid greenstone belt are approximately coeval plutonic units bot

tracking the sources of icebergs with lead isotopes the provenance of ice rafted debris in heinrich layer 2 the provenance of ice rafted debris ird deposited in the north atlantic before during and after heinrich event 2 has been determined through measuring the lead isotopic composition of single feldspar grains and multiple grain composites from the larger than 150 m size fraction from cores from the eastern and western north atlantic and from the labrador sea single grain analyses are used to identify the specific continental sources of the ird whereas composite samples are used to assess the relative ird contributions from different sources all single grains from heinrich layer 2 h 2 as well as h 2 composites plot along a correlation line on a 207pb 204pb versus 206pb 204pb diagram characteristic of the churchill province of the canadian shield this is yet another strong piece of evidence that this heinrich event was dominated by a massive iceberg discharge of the laurentide ice sheet lobe located over hudson bay in contrast single grains from the ambient glacial sediment above and below h 2 have multiple sources many of them also lie along the correlation line with h 2 grains but many others have pb signatures consistent with derivation from the grenville province and the appalachian range in north america and possibly from scandinavia and greenland composites from the ambient sediment generally lie well to the right of the h 2 reference line in agreement with the results of the single grain analyses the evidence provided by lead isotopes regarding the dominant role played by the hudson bay lobe of the laurentide ice sheet in the development of the heinrich events lends support to the binge purge model advanced by macayeal 1993a b that invokes trapping of geothermal heat by the base of the icecap and subsequent basal melting as the mechanism that triggered the heinrich events

infrared microspectroscopy analysis of water distribution in deformed and metamorphosed rocks infrared microspectroscopy has been applied to thin sections of various deformed and metamorphosed rocks in order to investigate water content of quartz in these rocks the broad ir band absorbance around 3400 cm 1 probably due to fluid inclusion molecular water h2o was used to calculate water contents deformed granitic rocks from the yanazawa kamimura area near the median tectonic line mtl showed an increase of water content in quartz from about 300 ppm to 2500 ppm toward the mtl with increasing degree of deformation metacherts from sambagawa metamorphic rocks asemigawa route showed a systematic decrease of water content in quartz from about 1000 ppm to 200 ppm with increasing metamorphic degree from chlorite garnet albite biotite to oligoclase biotite zones an archaean metachert from the napier complex granulite facies has only 40 ppm water comparing this with an inuyama unmetamorphosed chert sample having water contents of 3500 to 7000 ppm a starting point of metamorphism the systematic decrease of water in quartz with increasing metamorphic grade may extend from unmetamorphosed cherts to the highest grade metacherts water contents in high pressure metamorphic rocks in japan are mostly of the order of 500 ppm 300 700 ppm except for those from kurosegawa with a water content as high as 1700 ppm these results represent an exploratory analysis of intragranular water contents in quartz in various deformed and metamorphosed rocks further micro ft ir studies of the distribution of water in crustal rocks will provide a quantitative basis for examining the geochemical cycle of water in the earth s crust

eoarchaean crustal growth in west greenland itsaq gneiss complex and in northeastern china anshan area review and synthesis eoarchaean crust in west greenland the itsaq gneiss complex 3870 3600 ma is 80 by volume orthogneisses derived from plutonic tonalite trondhjemite granodiorite ttg suites 3850 c 3810 and c 3710 mahave some compositional similarities to modern island arc basalts iab suggesting their origin by hydrous fluxing of a suprasubduction zone upper mantle wedge most of the eoarchaean tonalites match in composition highsilica low magnesian adakites whose petrogenesis is dominated by partial melting of garnetiferous mafic rocks at high pressure however associated with the tonalites are volumetrically minor more magnesian quartz diorites whose genesis probably involved melting of depleted mantle to which some slab derived component had been added this assemblage is evocative of suites of magmas produced at phanerozoic convergent plate boundaries in the case where subducted crust is young and hot thus eoarchaean subduction first gave rise to short lived episodes of mantle wedge melting by hydrous fluxing yielding iablike basalts boninites in the hotter eoarchaean earth flux dominated destructive plate boundary magma generation quickly switched to slab melting of subducted oceanic crust this latter process produced the voluminous tonalites that were intruded into the slightly older sequences consisting of tectonically imbricated assemblages of iab like pillow lavas sedimentary rocks gabbros and upper mantle peridotite slivers zircon datingshows that eoarchaean ttg production in the itsaq gneiss complex was episodic 3870 3850 3840 3820 3810 3795 3760 3740 3710 3695 and 3660 ma in each case emplacement of small volumes of magma was probably followed by 10 40 maquiescence which allowed the associated thermal pulse to dissipate this explains why greenland eoarchaean crustal growth did not have granulite facies metamorphismdirectly associated with it instead 3660 3600 ma granulite facies metamorphism s in the itsaq gneiss complex were consequential to collisional orogeny and underplating upon termination of crustal growth similar eoarchaean crustal history is recorded in the anshan area of china where a few wellpreserved rocks as old as 3800 ma have been found including high mgo quartz diorites for 3800 ma rocks this is a rare if not unique situation outside of the itsaq gneiss complex the presence of volumetrically minor 3800 mamantle derived high mgo quartz diorites in both the itsaq gneiss complex and the anshan area indicates either that eoarchaean subduction zones were overlain by a narrow mantlewedge or that the shallow subduction trapped slivers of upper mantle between the conserved and consumed plates the geological society of london 2009

stability of zircon u pb systematics in a greenschist grade mylonite an example from the rockfish valley fault zone central virginia usa the mid paleozoic greenschist grade rockfish valley fault zone rvfz of central virginia cuts the grenville aged pedlar river charnockite suite prcs and contains zircons that underwent brittle failure during ductile deformation electron microprobe analyses and scanning electron microscope sem backscattered electron bse imaging show that zircons from the protolith prcs are concentrically zoned with alternating u hf rich and u hf poor bands and contain numerous radial microcracks zircons from the rvfz mylonite are unzoned fragmented show no internal microfractures and have low u and hf concentrations relative to the prcs zircons u pb isotopic studies of zircons from the mylonites and from the charnockitic protolith demonstrate that no preferential pb loss occurred in the zircons from the mylonite and that the 207 pb 206 pb ages of the mylonite zircons are identical to those of the protolith zircons the loss of primary zoning from the zircons of the rvfz ultramylonites can be explain

setting and origin for problematic rocks from the 3 7 ga isua greenstone belt southern west greenland earth s oldest coarse clastic sediments abstract whether or not coarse detrital sedimentary rocks occur within the 3 7 ga isua greenstone belt igb southern west greenland has been debated for some time repeated regional metamorphic deformational and metasomatic events have obscured most protolith lithologies leading to misunderstandings about the stratigraphy and environments of deposition rocks here interpreted as meta conglomerate crop out in a fault bounded structural domain that is lower in strain relative to adjacent domains the meta conglomerate has a strike length of 1 km and is 10 m thick bed thickness ranges from 10 cm to more than 1 m and beds may be either framework or matrix supported a poorly sorted and variably rounded polymict assemblage of framework clasts consisting of meta chert bif and a variety of mafic volcanic rock fragments are set into a matrix of biotite quartz garnet schist clast compositions indicate reworking of adjacent stratigraphic units a lack of structural similarity in framework clasts range of grain sizes range of rounding and polymict composition demand a primary sedimentary origin for the deposit inferred depositional processes include traction and debris flow which would be consistent with subaerial or shallow subaqueous environments although the limited extent of the meta conglomerate warrants interpretational caution

multiparametric statistical investigation of seismicity occurred at el hierro canary islands from 2011 to 2014 abstract a detailed statistical investigation of the seismicity occurred at el hierro volcano canary islands from 2011 to 2014 has been performed by analysing the time variation of four parameters the gutenberg richter b value the local coefficient of variation the scaling exponent of the magnitude distribution and the main periodicity of the earthquake sequence calculated by using the schuster s test these four parameters are good descriptors of the time and magnitude distributions of the seismic sequence and their variation indicate dynamical changes in the volcanic system these variations can be attributed to the causes and types of seismicity thus allowing to distinguish between different host rock fracturing processes caused by intrusions of magma at different depths and overpressures the statistical patterns observed among the studied unrest episodes and between them and the eruptive episode of 2011 2012 indicate that the response of the host rock to the deformation imposed by magma intrusion did not differ significantly from one episode to the other thus suggesting that no significant local stress changes induced by magma intrusion occurred when comparing between all them therefore despite the studied unrest episodes were caused by intrusions of magma at different depths and locations below el hierro island the mechanical response of the lithosphere was similar in all cases this suggests that the reason why the first unrest culminated in an eruption while the other did not may be related to the role of the regional local tectonics acting at that moment rather than to the forceful of magma intrusion

high precision 207pb206pb zircon geochronology using a small ion microprobe abstract a small geometry ion microprobe cameca ims 4f has been successfully used for the routine measurement of 207 pb 206 pb ratios in individual zircons with a spatial resolution of 20 m in spite of the lower sensitivity of the small ion microprobe resulting from operating at high mass resolution m m 4600 in order to resolve isobaric molecular interferences we can discern archean components whose ages differ by 50 ma a single measurement requires 90 min of data acquisition thus a comprehensive study of a zircon population can be accomplished in a few days three sets of precambrian zircons analyzed earlier by other techniques yielded ages which are within 2 of their true values as our first unknown we analyzed zircons from a sample of orthogneiss collected from the aravalli craton of northwestern india for this sample we obtained a minimum age of 3281 3 ma 1 which we believe closely approximates the time of crystallization of the gneiss s igneous protolith

hydromechanics of the koyna warna region india continuous reservoir induced seismicity has been observed in the koyna warna region in western india following the beginning of impoundment of koyna and warna reservoirs in 1961 and 1985 respectively this seismicity includes 19 events with m 5 0 which occurred in 7 episodes i vii between 1967 and 2005 at non repeating hypocentral locations in this study we examined the first six episodes the seismicity occurs by diffusion of pore pressures from the reservoirs to hypocentral locations along a saturated critically stressed network of ne trending faults and nw trending fractures we used the daily lake levels in the two reservoirs from impoundment to 2000 to calculate the time history of the diffused pore pressures and their daily rate of change at the hypocentral locations the results of our analysis indicate that episodes i and iv are primarily associated with the initial filling of the two reservoirs the diffused pore pressures are generated by the large 20 45 m annual fluctuations of lake levels we interpret that critical excess pore pressures 300 kpa and 600 kpa were needed to induce episodes i iii and episodes iv vi respectively suggesting the presence of stronger faults in the region the exceedance of the previous water level maxima stress memory was found to be the most important although not determining factor in inducing the episodes the annual rise of 40 m or more rapid filling rates and elevated dp dt values over a filling cycle contributed to the rapid increase in pore pressure

tectonic implications of palaeoproterozoic post collisional high k felsic igneous rocks from the kimberley region of northwestern australia abstract palaeoproterozoic high k i type granites high level porphyry intrusions and felsic volcanic rocks of the whitewater volcanics dominate the hooper and lamboo complexes in the kimberley region of northwestern australia the granites porphyries and volcanic rocks are gradational into each other in the field and they have the same mineralogy similar major and trace element abundances and indistinguishable shrimp u pb zircon ages of 1865 1850 ma there is evidence of widespread mingling between the granites and coeval gabbros magma mixing may be important in the formation of some of the mafic granites but most of the rocks probably formed from felsic parent magmas that underwent variable degrees of fractional crystallization the felsic igneous rocks may have formed by partial melting of intermediate to felsic calc alkaline rocks along the southern and eastern margins of the kimberley craton following accretion of various earlier palaeoproterozoic terranes to the craton therefore models for palaeoproterozoic high k granites in northern australia that invoke intracratonic rifting of a stable archaean craton may need to be revised

u th pb systematics of individual perovskite grains from the allende and murchison carbonaceous chondrites ion microprobe u th pb isotopic measurements have been made of individual perovskite grains from the allende cv3 and murchison cm2 chondrites these are the first chronological data reported for murchison refractory inclusions several generations of perovskite were identified in polished thin sections of fluffy type a inclusions 3529 44 and 4691 from allende of which only the largest anhedral perovskites 20 m were analysed with the ion microprobe the allende perovskites are characterised by low u typically 3 ppm but ranging up to 12 ppm in grain 7 1 from 3529 44 and th u of around 4 in 3529 44 and 10 in 4691 the204pb concentrations in the allende perovskites range from 6 to 140 ppb a precise age measurement could be obtained on grain 7 1 only the u pb systematics of this grain are concordant with a207pb 206pb age of 4565 34 2 ma two of the murchison perovskites occurred as individual 20 m inclusions in spinel grains 7 309 7 a52 while the third perovskite bearing inclusion was a spherule dominated by perovskite with interstitial spinel 7 396 u concentrations range from 3 6 to 15 ppm with th u less than 0 5 and204pb concentrations ranging from 61 to 369 ppb all analyses of the murchison perovskites are consistent with a single formation age of 4569 26ma the ages determined by ion microprobe from these perovskites show good agreement with previous age estimates of allende refractory inclusions measured by conventional mass spectrometric techniques there is no evidence in the u pb systematics of allende and murchison refractory inclusions for material that substantially predates the formation of the solar system

sm nd studies of archaean metasediments and metavolcanics from west greenland and their implications for the earth s early history metasedimentary and metavolcanic rocks from the archaean of west greenland have been examined for evidence of crustal components greater than 3 8 ga in age and for their compatibility with the presently adopted bulk earth sm nd parameters sm nd isotopic data have been obtained for the garbenschiefer metagabbro unit metasediments from the isua supracrustal belt gneisses interior to the isua belt and metasediments from the malene supracrustal belt using estimates of emplacement age t of between 3 77 and 3 67 ga for the parental volcanics to the garbenschiefer unit initial143nd 144nd ratios yield positiveendt values between 1 0 and 3 1 relative to the chur parameters for seven out of eight samples model sm nd ages for the isua gneisses and metasediments are only compatible with their estimated stratigraphic ages if their sources were ca 2end relative to chur at those times similarly model sm nd ages for the malene samples are only compatible with stratigraphic age constraints when based on a source evolution with positiveendt implications of these results for the early development of the earth s mantle are discussed

combined high precision chronometry and geochemical tracing using accessory minerals applied to the central alpine bergell intrusion central europe abstract the behaviour of nd u th and pb isotopes in granitic rocks is usually controlled by accessory minerals in this study an approach is adopted which uses the initial 143 nd 144 nd as a geochemical tracer together with high precision u th pb geochronology for accessory phases and their respective whole rock this combination of techniques is applied to zircon allanite sphene apatite and thorite from both a tonalite and a granodiorite from the tertiary alpine bergell intrusion inherited isotopic signatures have been identified in bulk zircon fractions by inverse discordance in the u pb system in the case of the granodiorite the initial nd in the zircon is 1 77 units lower than the bulk rock this result indicates that nd isotopes in zircon may serve as a useful tool for tracing crustal precursors in silicic rocks all other accessories yield an initial nd equal to their respective whole rock and u th pb ages equal to or lower than the respective intrusion ages this indicates either the absence of inherited cores or that such cores have exchanged their nd and pb in the case of apatite also sr by diffusion where available experimental mineral melt equilibria and diffusion models are consistent with this behaviour u pb geochronology of carefully selected core free zircons yields a precise intrusion age of 31 88 0 09 ma for the tonalite in contrast granodioritic zircons are partially reset due to radiation damage caused by high u concentrations however an alternative means of dating young intrusions is to use 232th 208pb ages of allanite in the case of allanite the presence of a large excess of 206pb derived from 230th indicates that no total pb loss has occurred since crystallization and the nd isotopes indicate the absence of inheritance using both the allanite age and a 238u 206pb age for sphene an intrusion age of 30 13 0 17 ma is indicated for the granodiorite taken together with an allanite th pb age for the tonalite these results strongly support the high closure temperatures for the allanites studied here 700 800 c at high post magmatic cooling rates all other accessory mineral ages are reset to values similar to hornblende 39ar 40ar ages and reflect the effect of post magmatic cooling superimposed on post metamorphic cooling

the history of a continent from upb ages of zircons from orinoco river sand and smnd isotopes in orinoco basin river sediments abstract we report shrimp u pb ages of 49 zircons from a sand sample from the lower orinoco river venezuela and nd model ages of the fine sediment load from the main river and tributaries the u pb ages reflect individual magmatic or metamorphic events the sm nd model ages reflect average crustal residence ages of the sediment sources together they allow delineation of the crust formation history of the basement precursors of the sediments the u pb ages range from 2 83 to 0 15 ga and most are concordant or nearly so discrete age groupings occur at 2 8 2 1 and 1 1 ga the oldest group contains only three samples but is isolated from its closest neighbors by a 600 ma age gap larger age groupings at 2 1 and 1 1 ga make up about a third and a quarter of the total number of analyses respectively the remaining analyses scatter along concordia and most are younger than 1 6 ga the 2 8 and 2 1 ga ages correspond to periods of crust formation of the imataca and trans amazonian provinces of the guyana shield respectively and record intervals of short but intensive continental growth these ages coincide with 2 9 and 2 1 ga nd model ages of sediments from tributaries draining the archean and proterozoic provinces of the guyana shield respectively indicating that the u pb ages record the geological history of the crystalline basement of the orinoco basin zircons with ages corresponding to the major orogenies of the north atlantic continents the superior at 2 7 ga and hudsonian at 1 7 1 9 ga were not found in the orinoco sample the age distribution may indicate that south and north america were separated throughout their history nd model ages of sediments from the lower orinoco river and andean tributaries are 1 9 ga broadly within the range displayed by major rivers and dusts this age does not coincide with known thermal events in the region and reflects mixing of sources with different crust formation ages the igneous and metamorphic history of these sources as recorded by the detrital zircons is that of the orinoco basin basement this implies that despite evidence of fast sedimentary recycling global similarities in nd crustal residence ages and the probability of cross continent mixing through continental drift the sedimentary material carried by individual rivers is mainly derived from the crystalline basement in the basin the global semblance in nd isotope ratios in major river sediments and atmospheric dusts results from the averaging effect of large scale sampling of the continents which are heterogeneous in age on smaller regional scales a large portion of the continental crust in the orinoco basin formed during the trans amazonian orogeny at 2 0 2 1 ga and smaller portions formed both earlier at 2 8 ga and later after 1 6 ga these observations which are consistent with the relative sizes of crustal age provinces in the orinoco basin indicate that sediments from the lower orinoco and andean tributaries contain 25 35 of material added to the crust since trans amazonian times nd model ages of these sediments underestimate the average crust formation age of the basement of the orinoco basin by only about 10 if this relationship holds in other river basins then nd model ages of major rivers and wind blown particulates indicate that the mean age of the continental crust is 1 9 2 ga

dynamical characterization of the 1982 2015 seismicity of aswan region egypt abstract in this study the seismicity that occurred in aswan region from 1982 to 2015 is investigated using robust statistical methodologies the completeness magnitude estimated by using two different methods maxc and gft is 2 5 for the whole catalog with b 1 07 by using the expectation maximization algorithm two depth classes of events were identified with a threshold at about 12 km the events deeper and shallower than the threshold could be likely generated by the same mechanism the loading unloading operation of the lake nasser reservoir we suggest that the shallow seismicity occurs on shallow small fractures in correspondence of the intersection of n s faults with e w faults which may form a minor pull apart basin the deep events mainly occur along the right lateral strike slip e w kalabsha fault and the seismicity is characterized by mainshock aftershocks sequences that mask the annual periodicity if not properly aftershock depleted indeed before applying the declustering on the seismic catalog the analysis of the time clustering properties of the shallow earthquakes reveals already the presence of annual modulation that is not evident in the time dynamics of the deep earthquakes furthermore the shallow events are featured by the allan factor scaling exponent measuring the strength of the time clustering in an earthquake sequence lower than that of the deep events indicating a tendency of the time dynamics of the shallow earthquakes to behave more regularly than the deep ones the detrended fluctuation analysis of the magnitude series suggests that the earthquake series are weakly persistent characterized by the tendency of events of similar value of magnitude to follow each other

tertiary mineralization and magmatism east greenland lead isotope evidence for remobilization of continental crust abstract well defined lead isotope signatures of sulphides from mineral occurrences associated with tertiary igneous rocks in east greenland fall in two distinct groups 1 sulphide samples from the region south of scoresby sund kangerlussuaq igneous complex have lead characterized by retarded uranogenic evolution and slightly elevated thorogenic isotopic ratios 2 sulphide samples from the region north of scoresby sund werner bjerge kap simpson and kap broer ruys igneous complexes have lead compositions typical of modern average terrestrial lead these distinct signatures in both conventional and 208 pb 204 pb 207 pb 204 pb diagrams lie within linear trends defined by previously published lead isotope data for unmineralized tertiary basalts and intrusive rocks the linear trends are mixing lines between the lead in the tertiary mantle derived magmas and lead remobilized from continental crust tertiary magmas in the region south of scoresby sund remobilized and incorporated lead from low high 208 pb 204 pb crustal sources similar in isotope composition to archaean high grade metamorphic gneisses exposed in the area non to sub parallel distinct lead mixing lines in the 208 pb 204 pb 206 pb 204 pb diagram for the tertiary igneous complexes in this region suggest strong heterogeneity of the remobilized crust more than one half of the lead from sulphide mineral occurrences within the kangerlussuaq alkaline intrusive complex may be derived from local continental crust in the region north of scoresby sund the tertiary magmas remobilized moderately radiogenic lead from local basement and sedimentary basins palaeoproterozoic mesoproterozoic gneisses neoproterozoic ordovician sediments caledonian granites and palaeozoic mesozoic sediments these crustal rocks lack the very low 206 pb 204 pb and 207 pb 204 pb ratios typical of the gneisses from the kangerlussuaq region and mixing trends between mantle derived and crustal lead are therefore much less extensive however because the mantle derived magmas had very low total lead contents even small additions of crustal lead are traceable sulphide mineralized alkaline intrusive complexes are shown to be highly contaminated with crustal lead and it is further shown that the pre tertiary rocks of north east greenland are likely local crustal sources of lead for contaminated tertiary plateau basalts many stratabound sediment hosted hydrothermal base metal occurrences in the palaeozoic mesozoic jameson land basin are thought to be tertiary in age but do not appear to contain tertiary igneous derived lead on the contrary the hydrothermal alteration zones associated with several of the mineralized tertiary igneous complexes attest to extensive fluid rock mass transfer lead and other base metals were leached from the country rocks homogenized and incorporated into sulphide minerals

resetting of smnd systematics during metamorphism of 3 7 ga rocks implications for isotopic models of early earth differentiation abstract new sm nd isotopic results for sixteen samples from the garbenschiefer amphibolite unit of the 3700 ma isua supracrustal belt of west greenland are reported the data illustrate the difficulty in identifying primary nd t values in poly metamorphic and poly deformed rock sequences the investigated samples are interpreted as derived from a mg and al rich igneous protolith which can be argued to have been essentially isotopically homogeneous at least on the outcrop scale at the time of its emplacement however the data do not give uniform nd t values even from single outcrops the wide variation of nd t which we obtain 1 0 to 5 0 demonstrates that the sm nd systematics of the samples were disturbed by one or more metamorphic event s which took place some considerable time after the original crystallization of the isua belt a sm nd isochron age of 2849 116 ma has been obtained on plagioclase and amphibole separates which represent the oldest metamorphic assemblage now preserved at isua this result indicates that the earliest amphbolite facies metamorphism of the isua belt for which pressure and temperature conditions can be obtained p 5 kbar t 500 600 c is late archaean and not early archaean as had been assumed earlier by some authors 2850 ma is also thought to represent the main time of disturbance of the sm nd system in the garbenschiefer amphibolite unit a consideration of available isotopic data suggests that many of the rocks from isua underwent some nd isotopic re equilibration and or fractionation of their 147 sm 144 nd ratio during the 2850 ma metamorphic episode in these rocks the computed nd t are apparent values only and need not represent either the primary isotopic composition of their protoliths or early archaean mantle values only nd rich rocks 20 ppm such as some felsic schists and the grey gneisses adjacent to the belt are arguably sufficiently robust to retain nd t values which are close to their original composition these average 2 0 which may represent a close approximation of the nd value of the earth s mantle at 3800 ma the results presented in this paper show that great care should be exercised in the use of sm nd data from very early archaean rocks as constraints for isotopic models of early earth s evolution particularly in terranes which have been affected by several metamorphic episodes

u pb investigations on zircons from pre variscan gneisses i a study from the schwarzwald west germany abstract field observations in the schwarzwald indicate that pre variscan rocks were formed by the following events 1 1 intrusion of granitic to granodioritic magma into sediments 2 2 a sequence of two anatectic events with an intervening regional metamorphism and development of a gneissic schistosity the absolute chronology of these older gneisses and migmatites has not yet been satisfactorily resolved we collected several samples of a coarse grained homogeneous orthogneiss of granodioritic composition and one sample of a metasedimentary source rock related to this orthogneiss body in the einetwald forest north of steinach kinzig valley the metasedimentary rock corresponds to the biotitepoor paragneisses in the schwarzwald the zircons in the latter sample are detrital and only very small specimens 45 m are euhedral the zircons from the orthogneiss samples are euhedral some are zoned and some have dark inclusions analyses of the three coarser fractions of the paragneiss form a linear array on a concordia diagram with upper and lower intercepts of about 2000 myr and 524 20 myr respectively the 2000 myr value is interpreted as the average age of the sedimentary source rocks for this material the 524 myr intercept defines an event responsible for most of the lead loss in the zircons as well as new zircon growth analyses of the zircons from the orthogneiss samples do not show a linear array on the concordia diagram because of inclusions of older inherited zircons stepwise leaching of two zircon fractions shows newly grown u rich zircon rims around old cores a 207 pb 206 pb age of 517 15 myr was found for the first dissolution steps about 50 of the zircons dissolved in subsequent steps with progressive dissolution of the residue 207 pb 206 pb age increased to 950 myr the u pb zircon data for the paragneiss and the orthogneiss establish an age of 520 15 myr for the magma intrusion

the zircon geochronology of the akilia association and isua supracrustal belt west greenland the akilia association and the isua supracrustal belt are interpreted as both derived from a single volcano sedimentary sequence because they occupy the identical position in local stratigraphic sequences show a similar association of lithologies and are both intruded by geologically and geochronologically correlated orthogneisses zircon from the akilia association yields a concordia intersection age of3587 38ma while that from the isua supracrustal belt gives 3813 14 21 ma the isua supracrustal date is close to the original age of crystallisation of the zircon while the akilia intercept age results from the resetting of the zircon date by granulite facies metamorphism close to 3600 ma ago

the hydrothermal stability of zircon preliminary experimental and isotopic studies experimental investigations of the stability of the u pb isotopic system in nonmetamict zircons show that appreciable losses of pb and u can be induced at amphibolite grade conditions 400 c to 600 c 4 to 6 kb in 2 m nacl and 2 hno sub 3 solutions the severity of u loss and to a lesser extent pb loss varies with solution composition in this case the 2 m nacl solution induced more pb and u loss than the 2 hno sub 3 solution at the same p t conditions scanning electron microscopy of the run products also revealed a range of corrosion related surface features which suggests that some of the observed trends in pb and u loss must be attributed to zircon dissolution backscattered electron bse imaging of the run products further suggests that partial homogenization of chemical zoning patterns occurred during the experiments microprobe analyses of treated and untreated grain show that both populations have a similar range of hf contents thus the apparent loss of sharp well defined zoning features is most likely due to small scale smearing out of formerly sharp chemical gradients and is perhaps related to the annealing of lattice defects caused by alpha recoil damage thus experimentally induced u pb isotopicmore discordance in zircon is a complex function of zircon stability and annealing effects less

on the valency state of radiogenic lead in zircon and its consequences in zircon u pb systematics extreme robustness up to the temperatures of granulite facies and anatexis contrasts with apparently easy loss of radiogenic pb at low temperatures often without any metamorphic event being in evidence here we propose that this paradoxical behaviour can be understood with the hypothesis that radiogenic pb in zircon is tetravalent we review data and arguments in favour of this hypothesis diffusion profiles calculated for pb sup 2 in a 25 micro m radius zircon xenocryst in a melt at 1000 c combined with the incompatibility of pb sup 2 or for a zircon core inside a younger zircon rim at this temperature show age effects that should have been observed in sims dating further in zircon evaporation as well as in leaching experiments common pb is generally released preferentially to radiogenic pb after removal of less radiogenic pb the evaporation record generally shows pure radiogenic pb during the final evaporation steps the distribution of residual pb in a leached titanite revealed by pixe is similar to that of ti lastly xanes spectra of a 1 ga old titanite predominantly radiogenic pb and an alpine one predominantly common pb are significantly different although the former does not resemble that ofmore pbo sub 2 the arguments why radiogenic pb should be tetravalent are based on analogies with studies relating to the tetravalent state of sup 234 th and the hexavalent state of sup 234 u which show that alpha recoil in silicates generates a strongly oxidizing environment at the site where the recoiling nucleus comes to rest further a zircon grain being small should remain highly oxidizing in its interior by the constant loss of beta particles maintaining the 4 state of radiogenic pb from its effective ion radius similar to that of zr sup 4 and its charge pb sup 4 has to be compatible in the zircon lattice also by analogy with u sup 4 th sup 4 and hf sup 4 its diffusivity should be several orders of magnitude lower than that measured for pb sup 2 in zircon these factors can account for the extreme retentivity of u pb clocks even at high temperatures on the other hand radiogenic pb situated in alpha recoil damaged sites could be leached out by any electrolyte solution that reduces it to the divalent state making it both incompatible and soluble thus discordia can be generated in weathering the curious observation that discordant archaean zircon suites generally define trends to lower intercepts at up to 800 ma instead of zero appears to reflect a c 14 to 28 better average accessibility to leaching of radiogenic sup 207 pb compared to sup 206 pb in accord with the somewhat higher recoil energy of the last branched alpha decays in the sup 235 u chain less

gneiss greenstone relationships in the ancient gneiss complex of southwestern swaziland southern africa and implications for early crustal evolution the ancient gneiss complex agc of swaziland is made up of a variety of archaean gneisses derived from granitoid intrusions of ttg composition emplaced between 3 6 and 3 2 ga ago and infolded amphibolite grade greenstone remnants locally referred to as dwalile supracrustal suite dss the greenstones were considered to postdate the oldest phases of the agc known as ngwane gneiss and this is now confirmed by conventional u pb zircon geochronology and shrimp single zircon ages on detrital grains from dwalile clastic metasediments suggesting that these rocks were derived from a granitoid source some 3 42 to 3 57 ga in age trondhjemitic ngwane gneiss structurally underlying the greenstones has a zircon age of 3521 23 ma and contains a 3683 10 ma old xenocryst this together with nd tdm model ages between 3 7 and 3 9 ga and a pronounced negative euanomaly for the metasediments strongly argues for the presence of very old crustal components in the agc nd isotopic systematics of dwalile metavolcanics suggest these rocks to be contaminated with older crustal material of ngwane type and resulting nd model ages 3 60 3 99 ga are likely to be too old the major and trace element chemistry of the dwalile metavolcanics is remarkably similar to that of onverwacht group rocks in the nearby barberton greenstone belt bgb and this together with a similar age for these two suites points to a genetic link and a similar mechanism of formation our data as well as field relationships do not favour an intra oceanic origin for the dss as has been inferred for the onverwacht group nor do they support a juvenile origin for the exposed ngane gneisses of the agc the ngwane precursors were apparently derived from older crustal protoliths whose subsequent modification particularly through remelting and deformation gave rise to the various compositional varieties now seen in the ngwane suite

are earthquakes predictable summary the answer to the above question depends on the definition of earthquake prediction we discuss several definitions and possible classifications of earthquake prediction methods we also consider various measures of prediction efficiency review several recent examples of earthquake prediction and describe the methods that can be used to verify prediction schemes we conclude that an empirical search for earthquake precursors that forecast the size of an impending earthquake has been fruitless despite considerable effort in several countries no statistically rigorous validation of proposed precursory phenomena is available therefore reported cases of precursors can be explained by random noise or by chance coincidence we present evidence that earthquakes are non linear chaotic scale invariant phenomena the most probable consequence of earthquake self similarity is a lack of earthquake predictability as popularly defined that is a forecast of a specific individual earthquake many small earthquakes occur throughout any seismic zone demonstrating that the critical conditions for earthquake nucleation are satisfied almost everywhere apparently any small shock can grow into a large event thus it is likely that an earthquake has no preparatory stage this sceptical view of current earthquake prediction efforts should not be interpreted as a statement that any further attempts to mitigate the destructive effects of earthquakes are futile the seismic moment conservation principle when combined with geodetic deformation data offers a new way to evaluate the seismic hazard not only for tectonic plate boundaries but also for areas of low seismicity that is the interiors of continents earthquake clustering with a power law temporal decay omori s law can be used to estimate the rate of future earthquake ocurrence realtime seismology can facilitate relief efforts after large earthquakes and eventually provide an immediate warning of severe shaking a few seconds or tens of seconds before the shaking starts

zircon reaction and stability of the u pb isotope system during interaction with carbonate fluid experimental hydrothermal study the interpretation of metamorphically induced u pb isotopic discordance requires a thorough understanding of zircon fluid interactions with this aim we have studied the behaviour of metamict and crystalline zircon phases and their u pb systems by cathodoluminescence after treatment by 2m na2co3 solution at t 200 800 c and p 1 5 kbar for 3 14 days x ray diffraction microprobe and isotope dilution analysis the data indicate that zircon transformation under hydrothermal conditions depends on the experimental conditions and the degree of structural damage reconstitution of defective and impurity enriched zones of metamict zircon homogenization of impure element concentrations and increase of crystallinity was observed at 400 c and p 1 kbar considerable lead and uranium loss occurred under these conditions as a result of zircon dissolution newly formed baddeleyite accommodating u from 2m na2co3 solution and zr na silicate were recognized this process intensified with increasing pressure study of crystalline zircon indicates that migration of u and pb took place only during dissolution of zircon at t above 650 c in the presence of carbonate ions essential u and pb amounts are lost from metamict zircon at a lower p t than is typical for greenschist facies metamorphism

earth s oldest preserved unconformity prospect of a beginning in the tectono sedimentary continental cycle abstract earth s oldest preserved conglomerates and basaltic pillow lavas at isua greenland provide robust field evidence for deep and shallow water environments on our planet within the first billion years of its formation the conglomerates represent the first paleoarchaean archive of sub aerial erosion and shallow water sedimentation these ca 3700 million year old sedimentary rocks now metamorphosed at amphibolite grade comprise units of rounded quartz pebbles set in a sandy to muddy matrix that unconformably overlie an ophiolite sequence the pillow lavas of the ophiolite are variolitic and essentially vesicle free indicative of formation in a deep water environment locally an unconformity separates the conglomerates from the deformed ophiolite related rocks elsewhere the contact between these units is tectonic such field relationship between deep and shallow water environments resemble those preserved in younger orogenic belts where obducted oceanic crust has been tectonically emplaced across terrestrial platforms or subaerial parts of forearc and backarc basins

cambrian granitoids in pre alpine basement of crete greece evidence from u pb dating of zircon the pre alpine basement of eastern crete consists of at least three sub complexes which show differences in age and grade of pre alpine metamorphism u pb analyses of zircons of two orthogneisses yielded upper intercepts in the concordia diagram at 511 16 ma chamezi crystalline complex and 514 14 ma myrsini crystalline complex these values are interpreted as protolith ages of the gneisses suggesting that parts of the basement underwent cadomian pan african imprints at the northern margin of gondwana the lower intercept ages are attributed to alpine subduction which led to high pressure low temperature metamorphism t ca 300 c brittle ductile deformation and hydrothermal fluid activity due to pervasive alpine fluid migration the zircons of the chamezi crystalline complex display disturbed zonation and solution resulting in 87 radiogenic pb loss ca and al gain and zr depletion

the complex age of orthogneiss protoliths exemplified by the eoarchaean itsaq gneiss complex greenland shrimp and old rocks abstract field studies integrated with cathodoluminescence petrography and shrimp u pb dating of zircons from 150 orthogneisses and metatonalites from the eoarchaean itsaq gneiss complex southern west greenland shows that only a minority contain 3840 ma zircons whereas the majority carry only younger ones rocks containing 3840 ma zircons vary from very rare single phase metatonalites to more common complexly banded tonalitic migmatites the former metatonalites have simple oscillatory zoned 3840 ma zircon with limited recrystallisation and overgrowth whereas the more common migmatites have much more complicated zircon populations with both 3840 ma and 3650 3600 ma oscillatory zoned zircon more extensive recrystallisation and widespread complex core rim multiple growth relationships with only 100 160 ppm zr in the tonalites and likely melt generation temperatures of 1000 c the experimentally determined zircon solubility melt composition relationships established by other workers shows that the precursor melts to the itsaq complex tonalites were strongly undersaturated in zircon thus any entrained xenocrystic zircon would have been rapidly dissolved therefore the 3840 ma oscillatory zoned zircons crystallised out of tonalitic melt and gives magmatic age of the rock in which they occur with an established igneous age of 3840 ma established from such relationships we interpret the correlated variation between the field nature of these rocks and their zircon petrography age structure as due to superimposition onto 3840 ma tonalite protoliths of variable amounts of heterogeneous strain heterogeneous distribution of melt patches formed during in situ anatexis at up to 800 c plus granitic veining this explains why geologically simple metatonalites have simple zircon populations whereas complex orthogneisses have complex zircons the large amount of integrated field geochemical and zircon data rule out an alternative interpretation that the 3840 ma zircons represent an igneous xenocrystic component present in younger rocks to varying degrees if this were true then the structurally simple less reworked rocks should still display complex zircon populations gneisses with 3840 ma zircon are commonest on akilia and neighbouring islands in itilleq fjord 65 km east akilia and on the north of ivisaartoq 150 km northeast of akilia these include from itilleq a 3891 6 ma gneissic tonalite with minor neosome which is currently the oldest rock recognised in the itsaq gneiss complex overall the 3840 ma tonalites are a widespread and unevenly distributed in the itsaq gneiss complex and they are a volumetrically minor component compared with 3800 3750 and 3700 ma tonalite generations using the subset of our data covering itilleq and the neighbouring fjords migmatite samples with 3800 ma igneous zircon are mutually exclusive from migmatite samples with 3700 ma igneous zircon this suggests that prior to an amalgamation event followed by 3660 3600 ma high grade metamorphism 3840 ma tonalites might have resided in a terrane discrete from 3700 ma tonalites this is in accord with interpretation of the non migmatised part of the complex in the isua area where a terrane of 3800 ma tonalites with a minor associated 3840 ma component and a terrane with 3700 ma tonalites were tectonically juxtaposed at 3660 ma

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

transport of uranium thorium and lead in metamict zircon under low temperature hydrothermal conditions abstract understanding the stability of radiation damaged zircon under low temperature hydrothermal conditions is crucial to the application of zircon for u pb geochronology and as a host phase for the disposal of plutonium waste we report the results of an investigation of the stability of partially metamict zircon by leaching experiments at 175 c with a 2 m alcl 3 and a 1 m hcl cacl 2 solution as hydrothermal fluids for 1340 h cathodoluminescence cl and backscattered electron bse images show that the zircon grains have developed a reaction rim several micrometers thick or deeply penetrating reticulated alteration zones with sharp boundaries to unaltered metamict zircon these zones have experienced severe loss of si u th and pb and gain of al or ca and a water species as revealed by electron microprobe sensitive high resolution ion microprobe shrimp analyses and infrared spectroscopy micro raman and infrared measurements on the altered areas show that disordered crystalline remnants of the partially metamict zircon structure were partially recovered whereas recrystallization of the embedding amorphous phase was not observed no detectable structural or chemical changes were detected inside the unaltered areas intensive fracturing which was most intense in the hcl cacl 2 experiment occurred inside the altered areas due to the volume reduction associated with the recovery of the disordered crystalline material and probably with the leaching reactions we explain the formation of deep penetrating alteration zones by a percolation type diffusion model which is based on the assumption that percolating interfaces or areas of low atomic density between crystalline and amorphous regions as well as between amorphous domains exist along which fast chemical transport is possible the idea of the existence of fast diffusion interfaces is supported by the sharp chemical gradients at the margin to unreacted zircon the model was used to estimate for the first time diffusion coefficients for u th and pb diffusion in amorphous zircon at 175 c by assuming that volume diffusion inside the amorphous domains is the loss rate limiting process these estimates show that volume diffusion in metamict zircon can cause significant loss of u th and especially loss of radiogenic pb over geological time scales even at temperatures as low as 175 c our results show that recent pb loss discordias can be generated 1 by predominate pb loss from metamict zircon through volume diffusion at low temperatures where thermal healing of the structure is insignificant and 2 by leaching of pb and u and th from metamict zircon through an external fluid

the age and pb loss behaviour of zircons from the isua supracrustal belt as determined by ion microprobe ion microprobe uthpb analyses of zircons from a conglomeratic metavolcanic unit in the isua supracrustal belt of west greenland show that their magmatic age is3807 1ma and failed to detect any older zircon cores or xenocrysts low u areas within zircons at a 30 m scale lost only small amounts of radiogenic pb and only in the recent past whereas high u areas within grains lost much greater proportions of their pb both recently and as early as the archaean some areas in the zircons have concordant upb and thpb ages the ion probe results agree with earlier determinations for the isua supracrustals and clarify minor discrepancies between previous multigrain and single crystal analyses

space time clustering of seismicity in california and the distance dependence of earthquake triggering 1 using two recent high resolution earthquake catalogs i examine clustering in california seismicity by plotting the average rate of earthquakes as a function of both space and time from target events of m 2 to 5 comparisons between pre and post target event activity can be used to resolve earthquake to earthquake triggering associated with target events of different magnitudes the results are more complicated than predicted by computer simulations of earthquake triggering that begin with background events occurring at random times in particular at least some of the temporal clustering of seismicity at short scales 0 1 to 5 km does not appear to be caused by local earthquake triggering but instead reflects an underlying physical process that temporarily increases the seismicity rate such as is often hypothesized to drive earthquake swarms earthquake triggering for m 4 5 earthquakes is only resolvable in average seismicity rates at times less than about one day and to distances of less than about 10 km and its linear density decreases as r 1 5 to r 2 5 significantly steeper than some previous studies have found

3820 ma zircons from a tonalitic armisoq gneiss in the godthab district of southern west greenland abstract zircons from a sample of the tonalitic amitsoq gneisses near godthhb west greenland exhibit several stages of crystal growth measurements of the u th pb isotopic composition of 30 m areas within individual grains using the ion microprobe shrimp reveal that components of magmatic zircon from the original igneous protolith are at least 3822 5 ma l old slightly but significantly older than the age of zircons from a fclsic volcanic unit in the isua supracrustal belt as measured at high precision by the same technique and older than all ages previously determined by mineral and whole rock isotopic techniques for amitsoq gneisses at godthab and at isukasia overgrowths of younger zircon formed at ca 3630 ma coinciding with an episode of major pb loss from the older grains these results indicate that previous whole rock isochron ages refer to later isotopic redistribution and or that other phases of the amitsoq gneisses intruded during this later period and dominate the isotopic systematics comparison of the ion probe results with previous conventional u th pb data for the same zircon sample demonstrates the strong influence of discordant high uranium parts of zircon on the mean isotopic composition of multi grain samples

possible juvenile palaeoarchaean ttg magmatism in eastern india and its constraints for the evolution of the singhbhum craton high precision shrimp u pb zircon dating yields a late palaeoarchaean age 3290 8 6 ma for a large unmetamorphosed weakly peraluminous ttg body the keonjhargarh bhaunra pluton in the singhbhum craton of eastern india one inherited subhedral zircon grain gave a concordant age of 3495 9 5 3 ma and nd isotope characteristics show a juvenile trend with end t 0 and t dm 3395 3453 ma the data support a model of typical archaean crustal evolution until late palaeoarchaean times for the singhbhum craton which is in contrast to the more southerly bastar craton where palaeoarchaean non ttg granites have been identified these data demonstrate the diachronous development of continental crustal blocks now forming the basement of the eastern and central peninsular of india

earthquake cycle fault zones and seismicity patterns in a rheologically layered lithosphere we study the coupled evolution of earthquakes and faults in a model consisting of a seismogenic upper crust governed by damage rheology over a viscoelastic substrate the damage rheology has two types of functional coefficients 1 a generalized internal friction separating states associated with material degradation and healing and 2 damage rate coefficients for positive degradation and negative healing changes the evolving damage modifies the effective elastic properties of material in the upper crust as a function of the ongoing deformation this simulates the creation and healing of fault systems in the upper seismogenic zone in addition to the vertically averaged thin sheet approximation we introduce a green function for three dimensional elastic half space for the instantaneous component of deformation the formulation accounts in an internally consistent manner for evolving deformation fields evolving fault structures aseismic energy release and spatiotemporal seismicity patterns these developments allow us to simulate long histories of crustal deformation and to study the simultaneous evolution of regional earthquakes and faults for various model realizations to focus on basic features of a large strike slip fault system we first consider a simplified geometry of the seismogenic crust by prescribing initial conditions consisting of a narrow damage zone in an otherwise damage free plate for this configuration the model generates an earthquake cycle with distinct interseismic preseismic coseismic and postseismic periods model evolution during each period is controlled by a subset of physical properties which may be constrained by geophysical geodetic rock mechanics and seismological data in the more generic case with a random initial damage distribution the model generates large crustal faults and subsidiary branches with complex geometries the simulated statistics depend on the space time window of the observational domain the results indicate that long healing timescale h describing systems with relatively long memory leads to the development of geometrically regular fault systems and the characteristic frequency size earthquake distribution conversely short h relatively short memory leads to the development of a network of disordered fault systems and the gutenberg richter earthquake statistics for intermediate values of h the results exhibit alternating overall switching of response from periods of intense seismic activity and the characteristic earthquake distribution to periods of low seismic activity and gutenberg richter statistics

dating the lower crust by ion microprobe ion microprobe uthpb ages of zircons from granulite facies lower crustal xenoliths from north queensland australia correlate well with the ages of major orogenic episodes manifest at the earth s surface about half of the xenoliths contain proterozoic zircons which are similar in age to the episodes of high grade metamorphism of the older surface rocks all the xenoliths contain late paleozoic zircons which show a real 100 ma range in206pb238 u ages from 320 to 220 ma which is attributed to granulite facies metamorphism followed by slow cooling in the deep crust the paleozoic zircon ages coincide in time with the prolonged episode of eruption of voluminous felsic ash flows and intrusion of high level granites in this region 320 270 ma mineral and melt inclusions in the zircons provide clues to the origin of some of the xenoliths and coupled with the age information can be used to infer the geological processes operating in the lower crust the zircons from two mafic xenoliths contain felsic and intermediate melt inclusions implying at least a two stage history for these rocks involving either partial melting of a more felsic protolith or crystal accumulation from an evolved melt some of the zircons from the felsic xenoliths contain co2 rich fluid inclusions indicating that those zircons grew during high grade metamorphism the isotopic and chemical data for the whole rock xenoliths show that they originate from a segment of the lower crust which is a heterogeneous mixture of supracrustal and mafic mantle derived lithologies the major orogenic event responsible for the formation of that crust occurred in the late paleozoic when proterozoic supracrustal rocks were emplaced into the lower crust possibly along thin skinned thrust slices this was accompanied by intrusion of high temperature mantle derived melts which caused partial melting of pre existing crust the most likely setting for such tectonism is a continental margin subduction zone

chemical characteristics and genesis of the quartz feldspathic rocks in the archean crust of greenland a total of 108 samples of meta tonalites metagranodiorites granites and meta tholeiites representing groups of early to late archean age and different metamorphic history from sw and se greenland have been analyzed for ca k and 28 trace elements there is no systematic change of the chemical composition with age observable the results support petrologic experiments which suggest that tonalites and granodiorites the most abundant rocks of the archean crust are partial melting products of a mafic lower crust modelling suggest that this crust consisted of garnet amphibolite derived from a source with a bulk composition resembling a slightly enriched rather than depleted mantle the cen ybn ratio is above 10 in the majority of tonalites most samples have no eu anomaly because of a balanced contribution from the minerals of a mafic rock or a plagioclase free source the positive eu anomaly of some granodiorites and of a minor proportion of tonalites can be explained as being caused by plagioclase accumulation during differentiation or by partial melting of plagioclase rich fractions modelling with zn excludes an origin of tonalitic melts by differentiation of basaltic to dioritic magmas the archean meta diorites meta tonalites and meta granodiorites from greenland have generally lost some k and s relative to their suggested magmatic protoliths loss of rb tl pb and k and relative gain of ca sr ba and sc connected with granulitization of meta tonalites can be explained in the majority of cases by separation of about 25 percent granitic partial melt high k rb k pb zn cd and nb th ratios of granulites plus low ratios of granites are almost in balance with intermediate ratios of amphibolite facies tonalites retrogression of granulites into amphibolites was accompanied by introduction of pb tl rb ba sr and k from na cl rich brines circulating on fractures a comparison of the abundance of 24 elements characterized by different compatibility in the archean crust of greenland with the present bulk crust reflects only minor changes th nb if at all in the chemical composition of the continental crust since the archean

nanosims study of seismically deformed zircon evidence of y yb ce and p redistribution and resetting of radiogenic pb lattice defects in zircon can cause trace elements redistribution and disturbance of isotopic systems this study investigates in detail how seismically induced deformation microstructures in zircon correlate with trace element and isotope re equilibration felsic mylonites with pseudotachylyte veins from the ivrea verbano zone in northern italy were studied with special focus on deformed zircon we have revealed the following post growth deformation microstructures planar deformation bands pdbs planar fractures pfs non planar fractures both healed and open and finite strain patterns pdbs are planar portions of crystal lattice that are strictly parallel to 100 crystallographic planes and are rotated to up to 3 with respect to the host grain they are from 0 5 to 1 m wide and have average spacing of 5 m pdbs originate in seismically active environment at elevated differential stress strain rate and temperature several grains in which pdbs are observed were analyzed with ion microprobe ion maps indicate redistribution of radiogenic pb isotopes associated with pdb formation isotopic redistribution preferably occurs in pdbs with larger crystallographic misorientation profiling demonstrated clear spatial correlation of pdbs with variations of ree abundances both gain and loss and possible correlations with increased and decreased hf ti and p abundances trace elements can be depleted or enriched compared to the abundance in surrounding matrix in deformed domains depending on the spacing of pdbs and the proximity of the analyzed volume to grain boundary or to detrital core 207 pb 206 pb ratio demonstrates systematic pb loss in the pdb bearing lattice domains with respect to pdb free domains in some cases pb gain is observed where the pdbs source radiogenic pb from older detrital cores our study has important implications for geochronology and microchemistry of zircon from seismically deformed sections of ivrea verbano zone and from other paleo seismic zones of the world zircon found in seismically deformed rocks near pseudotachylyte veins may demonstrate distorted and even reset isotopic ages and altered trace element abundances enhanced trace element exchange between deformed zircon and host mylonite can influence mass balance calculations for the bulk rock

reverse age zonation of zircon formed by metamictisation and hydrothermal fluid leaching abstract understanding the stability of radiation damaged zircon is crucial to the application of zircon to u pb geochronology especially for zircons rich in radioactive nuclides electron microprobe and laser raman spectral analyses show that zircons from the ejinao sodalite syenite in southeast china are composed of cores without zonation and oscillatory rims the cores are rich in uranium and have experienced increased metamictisation an internal sieved structure and radial cracks were formed by radiation damage and radiation induced volume expansion infrared spectral analyses show that zircon from the ejinao sodalite syenite contains large amounts of oh and h 2 o this finding suggests that the zircon crystals experienced hydrothermal alteration the pb loss of zircons is ascribed to their interaction with a hydrothermal fluid derived from the ejinao syenite radiogenic pb 4 situated in recoil damaged sites has been significantly reduced to pb 2 by the hydrothermal fluid becoming incompatible in the crystal lattice and highly mobile in solution consequently it has been leached out from the zircon this pb loss leads to diverse 206 pb 238 u ages from 134 ma to 147 ma and severe pb loss from the inner core even produces reverse age zonations with cores approximately 5 ma younger than the rims the real crystallisation age for zircons from the ejinao sodalite syenite should be approximately 145 ma considering the entire range of analytical data obtained by both the shrimp and la icpms methods

accelerated seismic release and related aspects of seismicity patterns on earthquake faults observational studies indicate that large earthquakes are sometimes preceded by phases of accelerated seismic release asr characterized by cumulative benioff strain following a power law timeto failure relation with a term tf t m where tr is the failure time of the large event and observed values of m are close to 0 3 we discuss properties of asr and related aspects of seismicity patterns associated with several theoretical frameworks the subcritical crack growth approach developed to describe deformation on a crack prior to the occurrence of dynamic rupture predicts great variability and low asymptotic values of the exponent m that are not compatible with observed asr phases statistical physics studies assuming that system size failures in a deforming region correspond to critical phase transitions predict establishment of long range correlations of dynamic variables and power law statistics before large events using stress and earthquake histories simulated by the model of ben zion 1996 for a discrete fault with quenched heterogeneities in a 3 d elastic half space we show that large model earthquakes are associated with nonrepeating cyclical establishment and destruction of long range stress correlations accompanied by nonstationary cumulative benioff strain release we then analyze results associated with a regional lithospheric model consisting of a seismogenic upper crust governed by the damage rheology of lyakhovsky et al 39 over a viscoelastic substrate we demonstrate analytically for a simplified 1 d case that the employed damage rheology leads to a singular power law equation for strain proportional to t f t 1 3 and a nonsingular power law relation for cumulative benioff strain proportional to t f t 1 3 a simple approximate generalization of the latter for regional cumulative benioff strain is obtained by adding to the result a linear function of time representing a stationary background release to go beyond the analytical expectations we examine results generated by various realizations of the regional lithospheric model producing seismicity following the characteristic frequency size statistics gutenberg richter power law distribution and mode switching activity we find that phases of asr exist only when the seismicity preceding a given large event has broad frequency size statistics in such cases the simulated asr phases can be fitted well by the singular analytical relation with m 1 3 the nonsingular equation with m 0 2 and the generalized version of the latter including a linear term with m 1 3 the obtained good fits with all three relations highlight the difficulty of deriving reliable information on functional forms and parameter values from such data sets the activation process in the simulated asr phases is found to be accommodated both by increasing rates of moderate events and increasing average event size with the former starting a few years earlier than the latter the lack of asr in portions of the seismicity not having broad frequency size statistics may explain why some large earthquakes are preceded by asr and other are not the results suggest that observations of moderate and large events contain two complementary end member predictive signals on the time of future large earthquakes in portions of seismicity following the characteristic earthquake distribution such information exists directly in the associated quasi periodic temporal distribution of large events in portions of seismicity having broad frequency size statistics withrandom or clustered temporal distribution of large events the asr phases have predictive information the extent to which natural seismicity may be understood in terms of these end member cases remains to be clarified continuing studies of evolving stress and other dynamic variables in model calculations combined with advanced analyses of simulated and observed seismicity patterns may lead to improvements in existing forecasting strategies

search for reliable precursors a case study of the seismic quiescence of the 2000 western tottori prefecture earthquake 1 how to search for reliable precursors is one of the key problems of the study on earthquake forecast in this paper a method is presented to judge whether or not a precursor is reliable before a potential anomaly can be nominated as a reliable precursor it should pass or be proved by the following tests or analyses whether or not it is an artificial anomaly whether or not it correlates with an investigated event whether or not it is a random anomaly as a case study i have investigated the reliability of seismic quiescence for an m 7 3 earthquake which occurred in the western region of tottori prefecture japan on 6 october 2000 the earthquake data 1975 2000 of the japan meteorological agency jma were used in this study after analyzing the completeness of the catalog and removing aftershocks a statistical method which is called the rtl region time length algorithm and takes into account the information of magnitude occurrence time and location of earthquakes was applied to the above preprocessed earthquake data a clear seismic quiescence anomaly was detected before the 2000 western tottori prefecture earthquake close investigation indicated that the above anomaly is not due to artifacts of the selections of model parameters after quantifying the anomaly and making statistical analysis over the whole investigated spatiotemporal domain reasonable correlation between the above anomaly and the main shock in 2000 was recognized the stochastic test using synthetic randomized catalogs showed the above anomaly is unlikely due to chance thus the above seismic quiescence anomaly before the 2000 main shock should be a significant and reliable precursor and the research method revealed in this study can enhance the reliability of precursors

ion microprobe u th pb isotopic studies of zircons from three early precambrian areas in the u s s r abstract ion microprobe u th pb dating of zircons from three polymetamorphic archaean terranes in the soviet union has provided some precise estimates of protolith and metamorphic ages which confirm that the ages inferred previously from conventional zircon u pb analysis are broadly correct the gneisses of the novopavlovsk complex intersected by drilling in the eastern ukrainian shield contain pyroxenite enclaves zircons in one pyroxenite give 3450 8 ma and in a nearby enderbite give 3441 10 ma two pyroxenites from another drill hole contain zircons as old as 3633 16 ma and 3640 11 ma respectively in addition to clearly metamorphic zircons interpreted to be 2901 34 ma and 2664 68 ma old in one and 2595 92 ma old in the other the tonalitic orthogneiss host to these two enclaves is 3609 5 ma old and was metamorphosed at 2826 16 ma the zircons in the pyroxenites are probably not primary but grew when the pyroxenites were incorporated into the magmatic precursors of the orthogneisses zircons in a leucocratic orthogneiss from the aulandjha block in the omolon massif soviet far east are interpreted to be mostly 3481 18 ma old but a minor metamorphic population gives 2667 29 ma a recently reported age of 3900 ma from the daldin series in the anabar shield in central siberia was not confirmed the zircon age of an enderbite from the daldin series is interpreted to be 3164 32 ma

depositional age and provenance of the marboo formation from shrimp u pb zircon geochronology implications for the early palaeoproterozoic tectonic evolution of the kimberley region western australia abstract the marboo formation is the oldest rock unit in the hooper complex in the west kimberley region of western australia the complex forms an elongate belt 350 km long and at least 100 km wide of deformed and metamorphosed palaeoproterozoic low to high grade metasedimentary rocks and mafic and felsic igneous rocks the marboo formation consists of a sequence of turbiditic metasedimentary rocks derived from the northwest an area of crust now buried beneath the unconformably overlying speewah and kimberley basins shrimp u pb dating of detrital zircons from a low grade quartz wacke indicate that the provenance terrain contributed zircons dated at around 2500 to 2400 ma 2300 ma 2200 to 2050 ma 1970 ma and 1910 ma the mount joseph migmatite formed by in situ melting of the marboo formation and zircons interpreted as detrital in origin give ages of 2500 to 2000 ma a maximum depositional age is provided by a population of zircon cores dated at 1872 9 ma growth of rims on zircons is dated at 1861 5 ma and is interpreted as the age of high grade metamorphism a minimum age for deposition is provided by the richenda microgranodiorite which forms a high level intrusive stock into the marboo formation and is dated at 1858 5 ma comparison with recent shrimp ages from the halls creek group in the east kimberley indicates that the turbidites of the marboo formation were deposited deformed metamorphosed and intruded by granitoid before the majority of the turbiditic metasedimentary rocks in the olympio formation were deposited this is not consistent with deposition of the turbiditic rocks in the same basin the assumption of contemporaneous turbidite deposition throughout the kimberley region has been taken as evidence of intracratonic palaeoproterozoic orogeny however these results provide support for plate tectonic models and the recognition of tectonostratigraphic terranes within the kimberley region detrital zircons from the marboo formation suggest that unexposed crust beneath the speewah and kimberley basins is largely early palaeoproterozoic in age rather than archaean as previously assumed the spread in ages indicates that the time period between formation of late archaean basement in northern australia and the formation of palaeoproterozoic orogens was marked by ongoing crust formation and was not a period of quiessence

long term earthquake clustering summary we analyse statistically the long term properties of several instrumental earthquake catalogues complete catalogues exhibit both short and long term clustering for earthquakes of all depth ranges after accounting for the effect of short term clustering we find that in residual declustered catalogues long term clustering not periodicity characterizes the occurrence of all earthquakes shallow intermediate and deep the degree of clustering in residual catalogues is the same for earthquakes in different depth ranges circumstantial evidence indicates that the long term v ariation of seismicity is governed by a power law temporal distribution as in short term clustering it is scale invariant the fractal dimension of an earthquake set on the time axis is of the order of 0 8 0 9 therefore mainshock occurrence is closer to a stationary poisson process than standard aftershock sequences of shallow earthquakes

a long lasting relaxation of seismicity at aswan reservoir egypt 1982 2001 the aswan reservoir seismicity is accepted as an example of reservoir induced seismicity with the m 5 4 event of 1981 which occurred 15 years after the reservoir impoundment started during the 1982 2001 period the aswan seismicity separates into shallow and deep seismic zones between 0 and 15 and 15 and 30 km respectively these two seismic zones behave differently over time as indicated by the seismicity rate depth migration b value and spatial clustering for the deep events the rate decreases with time the depth remains at a constant or increasing depth and the b value is lower than for the shallow events which migrate toward the surface with a close to constant seismicity rate of all the previous parameters only the seismicity rate correlates with seasonal variations of the lake level this is positive evidence for the aswan reservoir seismicity to be reservoir triggered in the 1982 2001 period clustering over time and space expresses that numerous after shock sequences are activated that is a minimum of 35 of the seismicity similarly to tectonic seismicity the observed decrease of the b value with depth is also a property suggested for natural events our results suggest that the aswan seismicity emerges both from the water level loading and the interplay between induced earth quakes themselves through numerous standard aftershock sequences this latter pro cess induces stochastic fluctuations in the seismicity patterns that inhibit a recovery of a simple seismic response to water level changes even though aftershock se quences dominate the temporal fluctuations of seismicity this does not negate the importance of influence of the reservoir in sustaining this unusual long lasting seis mic episode during the 1982 2001 period the aswan seismicity appears as a power law relaxation response to the 1981 m 5 4 shock this response being decorated by long term larger than 100 days water level changes

recent ground deformation around lake nasser using gps and insar aswan egypt abstract the rate of seismic activity around lake nasser rapidly increased after the creation of the high dam the largest earthquake was of magnitude ml 5 6 it occurred on november 14th 1981 60 km southwest of the aswan high dam we use 16 years of gps measurements collected around the northern part of lake nasser represented by 27 gps sites plus eight years of envisat sar scenes 35 descending scenes to estimate the recent ground movement of this area gps and insar showed a land subsidence localized around lake nasser the subsidence has a magnitude of 1 2 mm yr therefore we model the earth s response to water level changes using full daily water level variations starting from 1982 to 2016 our loading model captures a similar deformation pattern like ones estimated from gps and insar around the lake with comparable amplitudes with respect to stable nubia most of gps sites around the lake show a negligible north to northeast motion of

strontium neodymium and lead isotope variations of authigenic and silicate sediment components from the late cenozoic arctic ocean implications for sediment provenance and the source of trace metals in seawater proven ance changes of silicate sediment deposited during the late cenozoic 5 0 ma on the alpha ridge central arctic ocean are determined from variations in strontium lead and neodymium isotope compositions whereas strontium and lead isotope compositions are relatively invariant from 5 to 1 7 ma end values start to increase at 3 ma subsequently s7sr 86sr and 2 6pb z 4pb ratios progressively increase and end values progressively decrease from 1 7 ma to the present day from these isotope variations three different endmember compositions for sediment source regions are defined the two endmember compositions defined by sediment that was deposited by sea ice from 5 to 1 7 ma are consistent with a significant component being derived from the east siberian shelf the progressive change in isotope compositions from 1 7 to 0 ma correlates with an increase in coarse detritus deposited by icebergs over this time period the isotope data are consistent with a progressive increase in the proportion of sediment that was deposited in the central arctic ocean since 1 7 ma having been derived from the northern canada or queen elizabeth island region changes in the strontium neodymium and lead isotope compositions of arctic seawater are determined by analyzing the oxide fractions of fe mn micronodules strontium isotope compositions of the microno dule oxide fractions are similar to published late cenozoic seawater data and indicate that 97 of the sr is seawater derived but minute contributions of sr from silicate detritus prohibit using the hydrogenous fractions for chronostratigraphic purposes neodymium and lead isotope compositions of the micronodule oxide fractions which reflect those of arctic seawater follow the isotope variations of the silicate components throughout the late cenozoic these relations indicate that river water can not be the primary source of rare earth elements and pb to the dissolved reservoir in arctic seawater and that ice rafted detritus by dissolution or exchange processes is an important source of trace elements to seawater in ice covered oceans copyright 1997 elsevier science ltd

rb sr mineral ages for the grenvillian metamorphic development of spilites from the dalsland supracrustal group sw sweden rb sr isotope systematics have been investigated of epidote actinolite albite and biotite concentrates from 4 spilite samples from the precambrian basement directly w of lake vanern in sw sweden the rocks belong to the dalsland supracrustal group whose basal conglomerate was deposited on an erosion surface with a maximum age of c 1 200 ma epidote wr and actinolite wr tie lines in a nicolaysen diagram give ages with an average of 990 10 la ma which is thought to represent the metamorphic culmination biotite wr lines yield an average age of 900 15 1 ma which indicates the time at which the rock complex cooled through the isotopic closure temperature of biotite estimated at c 250 c the average cooling rate in this period was very low 1 2 c ma initial sr isotopic ratios of the 4 spilite samples vary from 0 7040 to 0 7080 and are thought to reflect interaction of mantle derived basalts with seawater

the influence of recent lead loss on the interpretation of disturbed upb systems in zircons from igneous rocks in east greenland abstract a series of caledonian igneous rocks from east greenland have been dated by means of u pb isotope determinations on zircons all discordias obtained give too low intercept ages in one case more than 200 ma younger than the rb sr mineral isochron age from the same sample leach experiments show that recent or subrecent loss of lead is responsible for the geologically meaningless ages obtained further it is shown that the recent lead loss is not caused by laboratory treatment but must be related to natural processes x ray investigations combined with transmission electron microscope analyses show a correlation between recent lead loss and the chemistry of the investigated zircons

independent ages of magmatic and hydrothermal activity in alkaline igneous rocks the motzfeldt centre gardar province south greenland the motzfeldt centre is one of four major alkaline centres belonging to the igaliko complex part of the mid proterozoic gardar province of south greenland motzfeldt comprises syenites and nepheline syenites displaying complex magmatic and subsolidus histories ta nb and ree rich zones are associated with a pervasive hydrothermal alteration process in the north and east of the complex part of a subdivision of the centre called the motzfeldt so formation msf the zircons from the msf show textures that are both magmatic and altered whereas the textures of pyrochlore have a predominantly subsolidus chemistry we compare and contrast the radiogenic isotope geochemistry of the zircon and pyrochlore to obtain independent age estimates of the magmatic and hydrothermal episodes selected analyses of magmatic zircons are concordant with an age of 1 273 6 ma altered zircons are normally discordant with one intercept at 1 261 28 ma and the other at 349 49 ma this younger age would appear on face value to date the hydrothermal event at motzfeldt to 900 ma after the magmatism however the pb pb isotope systematics from altered pyrochlore define an isochron age of 1 267 6 ma for isotopic closure of the pyrochlore following alteration during the subsolidus there is no known magmatic event in southern greenland at 350 ma and discordant points have high common lead we therefore infer that the younger intercept age is spurious the overlap between the magmatic u pb zircon and the pb pb pyrochlore age suggests that alteration of the motzfeldt centre occurred shortly after magmatism

mass independent isotope effects in archean 2 5 to 3 8 ga sedimentary sulfides determined by ion microprobe analysis we report sulfur isotope anomalies with 33 s the deviation from a mass dependent fractionation line for the three isotope system 34 s 32 s vs 33 s 32 s ranging up to 2 within individual archean sedimentary sulfides from a variety of localities our measurements which are made in situ by multicollector secondary ion mass spectrometry unequivocally corroborate prior bulk measurements of mass independent fractionations mif in sulfur and provide additional evidence for an anoxic atmosphere on the earth before 2 ga this technique also offers new opportunities for exploring ancient sulfur metabolisms preserved in the rock record the presence of mif sulfur in sulfides from a 3 8 ga fe rich quartzite from akilia island west greenland is consistent with a marine sedimentary origin for this rock copyright 2003 elsevier science ltd

petrogenetic and tectonic significance of young leucogranites from the northwestern himalaya pakistan in the himalaya of northwestern pakistan small discordant bodies of leucogranite intrude metamorphosed basement of the indian crust as the first step in assessing the tectonic significance of these granites we have used the shrimp ion microprobe to obtain u pb dates on zircon zircons of igneous appearance are scarce in the leucogranites and with one exception are associated with xenocrystic components which occur as discrete grains and as cores rimmed by young zircon zircons of igneous appearance are high in u 5000 to 40 000 ppm low in th u 0 01 to 0 05 and frequently colored a distinct blue xenocrystic components give a range of proterozoic ages consistent with ages previously reported for indian crust in sharp contrast zircons of igneous appearance yield clusters of concordant tertiary ages two leucogranite dikes from southern localities yield rather old emplacement ages of about 35 ma swat and about 50 ma naran together with previously determined 40ar 39ar and fission track cooling ages these ages document immediate and rapid metamorphism and denudation following eocene collision three leucogranite dikes from northern localities within the nanga parbat haramosh massif are very young having emplacement ages of about 2 3 ma 5 ma and 7 ma the formation and emplacement of these leucogranites during the rapid late tertiary denudation of the nanga parbat region suggests to us that decompression melting may be a viable mechanism for leucogranite genesis

analysis of time dynamical features in intraplate versus interplate seismicity the case study of iquique area chile the intraplate and interplate seismic catalogues of iquique chile area were investigated by using seismological b value of the gutenberg richter law fractal allan factor and detrended fluctuation analysis and topological horizontal visibility graph methods the two catalogues show different stress state indicated by the different b value larger for the intraplate seismicity the interplate seismicity shows significant time clustering behavior of the earthquake occurrence times at large time scales while the time distribution of the intraplate earthquakes seems to be featured by random fluctuations without any significant sign of time clustering different role seems to be played by aftershocks in the two investigated seismic zones revealed by the different time distribution of the aftershock depleted catalogue of the intraplate zone which remains poissonian for most of the time scales and the interplate zone that still keeps its clustering phenomenon but at higher timescales thus shortening its clustering time scale range furthermore the interevent times of the interplate catalogue are characterized by persistent dynamics even after removing the aftershocks while uncorrelated fluctuations characterize the behavior of interevent intervals of the whole as well as aftershock depleted intraplate catalogue additionally the magnitudes of both catalogues are characterized by time reversibility before and after the aftershock removal while the interevent times of intraplate catalogue change their status from time irreversibility to time reversibility after removing the aftershocks the obtained results seem to evidence a different role played by the aftershocks in the intraplate and interplate zones that needs to be further explored

u pb ages of zircon and sphene for two gneiss terranes adjacent to the kolar schist belt south india evidence for separate crustal evolution histories orthogneisses adjacent to the kolar schist belt were emplaced as tonalitic to granodioritic magmas between 2630 and 2530 ma an orthogneiss unit east of the kolar schist belt apparently was a homogeneous granodioritic intrusion at about 2532 ma cooling to the blocking temperature of the u pb system in sphene by 2521 2517 ma gneisses on the west side of the kolar schist belt were emplaced as at least three separate intrusions dated at 2631 2610 and 2552 ma evidence from an older basement into which these rocks were intruded comes from inherited zircons with an age of 2800 ma rocks with zircons of the appropriate age to be part of this basement occur as tectonic fragments and inclusions in the area gneisses west of the kolar schist belt were last cooled through the blocking temperature of the u pb system in sphene at about 2552 ma synchronous with the last major intrusive event late felsic dikes and plutons apparently postdate deformation and yield sphene pb pb ages of 2480 ma a sample of muscov

uranium lead system in fragments of a single zircon grain since the demonstration that u pb analyses of zircon fractions1 from a few grains up to several thousand grains or fragments of grains2 or single zircon grains3 4 yield reliable radiometric age data this method has been widely applied to igneous metamorphic and sedimentary rocks the present investigation of u pb systems for a suite of distinct fragments of a single zircon grain from a 1 093 2118 myr old syenite of the pikes peak batholith colorado usa demonstrates that uranium is heterogeneously distributed in this zircon crystal most parts of the grain suffered various degrees of lead loss the others show a closed system behaviour we show that degrees of lead loss are not correlated with uranium concentrations of the fragments

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

discussion on a high precision u pb age constraint on the rhynie chert konservat lagerstatte time scale and other implications journal vol 168 863 872 we welcome the contribution of parry et al 2011 concerning the age of the globally important rhynie hot spring system aberdeenshire scotland however although we accept that they have provided a valuable and robust u pb age constraint for the milton of noth andesite and the rhynie outlier stratigraphic succession we do not accept that they have constrained the timing of hot spring activity as suggested the geophysical trace of the unexposed milton of noth andesite indicates that it lies immediately adjacent to the rhynie fault zone and runs parallel to it for some 2 km it may even lie within the rhynie fault zone see discussion by rice ashcroft 2004 its stratigraphic position is therefore uncertain parry et al 2011 stated that the exact stratigraphic position is not important because their preferred stratigraphic locations lie within the tillybrachty sandstone and dryden flags formations both of which have consistently yielded spores belonging to the polygonalis emsiensis spore assemblage biozone this assertion is not valid the polygonalis emsiensis spore assemblage biozone may have lasted several million years and thus potentially there could be a significant hiatus between eruption of the andesite and the onset of hot spring activity they further assume that the andesite was linked to an andesitic magma chamber at depth which powered the hydrothermal system this remains speculation accepting the uncertainty in the stratigraphic position and by asserting a maximum thickness of sediment between the andesite and the rhynie cherts and a conservative deposition rate parry et al 2011 attempted to temporally link the andesite to the cherts by calculating the time interval represented by the intervening sediment the estimation of time depends on the absence of unconformities disconformities and faulting with such assumptions and uncertainties casting doubt on the thickness of the intervening sediments

non uniform scaling features in central italy seismicity a non linear approach in investigating seismic patterns and detection of possible earthquake precursors 1 the detrended fluctuation analysis dfa is a powerful method for capturing scaling behavior in nonstationary time series using an appropriate instability index it is possible to identify and quantify deviations from uniform power law scaling which suggest the presence of changing dynamics in the system under study in this context the scaling behavior of the 1981 2007 seismicity in umbria marche central italy which is one of the most seismically active areas in italy was investigated significant deviations from uniform power law scaling in the seismic temporal fluctuations were revealed mostly linked with the occurrence of rather large earthquakes or seismic clusters

improved u th total pb dating of zircons by electron microprobe using a simple new background modeling procedure and ca as a chemical criterion of fluid induced u th pb discordance in zircon abstract we present a simple new background modeling method particularly for the determination of trace concentrations of pb u and th to date zircons chemically by electron microprobe this method reduces the acquisition time considerably and at the same time increases the precision of a single pb u and th analysis depending on the analytical conditions theoretical detection limits down to 45 ppm 99 confidence level for u th and pb could be obtained the final precision on age for a single measurement was between 8 and 35 l at pb concentrations between 100 and 200 ppm in proterozoic zircons precise u th and pb analyses however do not necessarily facilitate a straightforward chemical age calculation u th total pb data of zircons from four granites could not be objectively interpreted because of a severe disturbance of the u th pb system however it is shown that chemical ages derived only from zircon areas containing less than 0 2 wt cao agree very well with published conventional radiometric ages of these rocks we propose a model which explains the ca gain and pb loss of zircons which have not undergone any metamorphism after emplacement to be the result of a hydration of radiation damaged zircon domains through low temperature aqueous solutions it is suggested that the ca content can be used independently from u th and pb analyses as a chemical criterion to discriminate between altered zircon domains having suffered a low temperature fluid induced pb loss and non altered zircon domains for which there is a high probability that they will give concordant u th pb ages 2000 elsevier science b v all rights reserved

late archaean high k granite geochronology of the northern metacratonic margin of the archaean congo craton southern cameroon evidence for pb loss due to non metamorphic causes abstract high k granitoids in the archaean congo craton are products of crustal differentiation by partial remelting of archaean ttg and in addition the remelting of charnockites at its northern metacratonic margin the ntem complex in southern cameroon at the sangmelima region of this metacratonized complex high k granites mostly occur as small intrusions and as pods dykes and veins in ttg and charnockites zircon u pb analyses of these high k granites show an important radiogenic pb loss indicated by highly discordant u rich fractions pb loss in these smaller granitic intrusions appears to be due to continuous than discrete pan african diffusion and leaching that characterizes larger charnockitic and tonalitic intrusions in the region or a combination of both the contributive effect of leaching due to later reactivations during the phanerozoic cannot be ruled out these multiple pb loss causes and apparently disproportionate amounts of 206pb and 207pb loses probably explain the irregular clustering of the highly discordant u pb data however an upper intercept age of 2751 32 ma and a lower intercept age of 300 29 ma are obtained most of the zircons especially those from high k granite veins lost pb from the entire grain with no domains remaining that reflect the original pb isotopic composition it was therefore impossible to obtain meaningful 207pb 206pb evaporation ages for such grains thus caution should be taken against use of the evaporation method for zircons that experienced severe pb loss however some whole zircons and zircon domains from larger granite bodies apparently retained their primary pb isotopic composition and were dated successfully by the evaporation technique they yielded reproducible 207pb 206pb ages between 2717 9 ma and 2724 3 ma with a weighted mean of 2722 2 ma interpreted as the minimum estimate of the crystallization age of the sangmelima high k granites similar sr and nd isotope signatures and nd model ages 3 04 3 25 ga as for the ttg and charnockite protoliths indicate that the high k event did not add new juvenile material to the archaean crust of the congo craton but was the result of crustal differentiation

whole grain evaporation for 207 pb 206 pb age investigations on single zircons using a double filament thermal ion source a technique has been developed and tested to analyse 207pb 206pb apparent ages by thermal evaporation of radiogenic lead directly from untreated whole zircon grains 0 3 mm the evaporation analyses are performed in the double filament arrangement of a thermal ion mass spectrometer thims the method is a powerful tool to distinguish between different lead components occurring in the same grain because differing activation energies of the competing lead components cause their sequential evaporation from the zircons the evaporation of test samples results in 207pb 206pb apparent ages in good agreement with u pb ages known from literature single zircons from a granite of the marble mountains california yield an age of crystallization of 1 410 30 ma ceylon zircons from heavy mineral bearing gravels yield 560 40 ma as age of crystallization of the pegmatitic gravel sources individuals from a heterogeneous zircon population of a diatexite from the southern schwarzwald sw germany indicate metamorphic zircon formation around 500 ma and the existence of middle proterozoic relics 1 95 0 05 ga

preferential dissolution of 234u and radiogenic pb from α recoil damaged lattice sites in zircon implications for thermal histories and pb isotopic fractionation in the near surface environment abstract zircons from two archean samples a 2732 ma trondhjemite and a 2728 ma dacite both from the western superior province were washed in hydrofluoric acid hf at moderate temperatures zircon residues and hf wash solutions were analyzed for u pb isotope systematics and 234u 238u ratios in an attempt to study the effect of hf washing on selective dissolution of radiogenic isotopes in areas damaged by recoil on a conventional concordia diagram the datum from one analyzed wash solution plots below concordia near the array of discordant data from magnetic unabraded zircon fractions which record a lower concordia intersection of about 230 ma data points from hf wash residues of two different zircon fractions from the trondhjemite are also discordant and collinear with near concordant data from abraded unleached fractions which record the true age of crystallization however this array has a negative lower concordia intercept of 749 ma the residue and wash from hf treatment of a single zircon fraction from the dacite are collinear with the crystallization age of the sample as defined by near concordant data from unleached fractions this line has a lower concordia intersection of 1388 ma also negative but distinct from the trondhjemite residue line the discordance of strongly washed residues is proportional to the calculated recoil dosage of the grains leach residues show negative 234u 238u anomalies while the leaches themselves show 234u excess on the order of 10 these results can be explained by the bulk dissolution of altered and metamict crystal domains during the hf wash accompanied by leaching of 234u and radiogenic pb from recoil damaged lattice sites in alteration free zircon residues studies were also carried out on zircons washed in nitric acid these show small ca 0 5 negative 234u anomalies this suggests that small amounts of radiogenic pb can be leached from damaged lattice sites by nitric acid the negative age lower concordia intercepts of pb loss lines defined by hf leach residues can be explained if early radiation damage has been annealed so that only more recently formed radiogenic pb atoms are in damaged crystal lattice sites and are susceptible to leaching since this pb fraction is relatively young the residue pb is biased toward anomalously old values a model is proposed for early burial and heating of the rocks above the annealing temperature for recoil damage followed by uplift and cooling several hundred million years after crystallization this model predicts a cooling time of 2500 20 ma for the trondhjemite and 2295 35 ma for the rhyolite comparison with metamorphic and cooling histories from ar ar studies suggest that the long term annealing temperature for low levels of recoil damage in zircon is in the range 250 300 c approximately the same as for fission tracks these results demonstrate that hf and possibly to a small extent hno3 can preferentially leach radioactive daughter elements from damaged zircon lattice sites in addition to dissolving metamict domains the threshold recoil dosage for dissolution of damaged zircon appears to be slightly in excess of 1 5 1015 decay events mg the isotopic composition of the leached pb is sensitive to the annealing history of the zircon thus in addition to supplying the magmatic crystallization age of the sample the hf leaching of zircon might be useful for constraining its later low temperature thermal history leaching from recoil damaged sites also occurs in the natural environment and this may lead to significant enhancement of 206pb 204pb in groundwater

les facies de transgression du trias sur la bordure nord est du massif central francais la transgression triasique est suivie d est en ouest sur la bordure du massif central francais les formations sont de plus en plus recentes vers l ouest independamment de leur facies les limites du buntsandstein et du trias superieur semblent locales et d origine tectonique tandis que la limite du ladinien superieur parait plus generale et correspond a la periode ou le caractere marin de la transgression sur les massifs hercyniens etait le plus franc

unsupported radiogenic pb in zircon a cause of anomalously high pb pb u pb and th pb ages ion microprobe u th pb isotopic analyses of zircons from a granodioritic orthogneiss from the napier complex mount sones enderby land antarctica have identified an unambiguous example of unsupported radiogenic pb in a 3 950 ma old crystal at one 40 m spot on the crystal an unusually large heterogeneity in pb content was found the concentration of radiogenic pb ranging from 5 to 50 percent higher than could have been generated in 3 950 ma by radioactive decay of the co existing u and th this relative excess of radiogenic pb is attributed to pb gain rather than to u and th loss because first the pb content varied by more than the u or th contents and secondly changes in the pb u pb th and pb isotopic composition correlated directly with changes in the pb concentration the individual 207pb 206pb apparent ages ranged from 4 000 ma to 4 145 ma all greater than the inferred age of the crystal a correlation between 207pb 206pb and pb u shows that the pb excess has not resulted from recent pb movement the spot apparently gained radiogenic pb about 2 500 ma ago at the same time as the majority of the other zircons in the rock suffered substantial pb loss the pb movement occurred in response to a discrete geologic event reverse discordance is a phenomenon that must be considered when interpreting zircon u pb ages especially 207pb 206pb ages of single crystals or portions of crystals

a metamorphic history from micron scale 207pb 206pb chronometry of archean monazite ion microprobe measurements of pb isotope ratios in monazites have been obtained in situ from thin sections using the cambridge isolab 120 molecular interferences are sufficiently resolved at an rp of 6500 to allow 2 7pb z 6pb dating of monazite with precisions as low as 4 5 ma 2 r the results presented here provide important information on the chronological history of the late archean metamorphism of the wind river range wyoming usa matrix monazites and monazite inclusions in garnets from a metapelite from the northern wind river range have been analysed by sims in a previous study peak metamorphic conditions t 800 c p 8 1 kb were estimated using inclusion assemblages in garnets from this same sample isolated monazite inclusions in garnet yield 2 7pb z 6pb age estimates of 2781 6 to 2809 10 ma those along fractures yield lower ages 2603 2687 ma which are similar to tims and sims ages of matrix monazites a single large 500 xm monazite grain locally preserves growth zoning but has a recrystallised core and a resorbed recrystallised rim age estimates for these three regions are 2788 9 ma 2663 4 and 2523 6 ma respectively thus the inclusion assemblages of sharp and essene may record peak metamorphic conditions at ca 2 8 ga and indicate a phase of metamorphism that predates by over 100 ma the emplacement of the bridget batholith the major lithologic component of the northern wind river range the analysed monazite grains appear to preserve ca 300 ma history even within a single grain monazite inclusions in garnet that are fully armoured may provide estimates for the time of garnet growth even in high grade terranes where most chronometers are reset the age pattern preserved by the large monazite grain cannot be simply related to diffusion controlled closure instead a chronology is preserved which can be related to the petrographic setting of individual grains through in situ analysis

evolving fluvial architecture during a marine transgression upper buntsandstein triassic central spain abstract the sedimentation in central spain during the late anisian middle triassic limos y areniscas de rillo formation recorded the evolution from an alluvial environment into a coastal one with a diversity of environments this evolution was the result of one of the episodes of the tethys sea transgression over iberia during the first and second stages of this evolution mixed load low sinuosity channels evolved upwards into a distal braidplain with ephemeral run off and poorly defined channels during a third stage the characteristics of the sediments indicate the existence of both continental and marine waters in a transitional zone with seasonal hydrological fluctuations the fourth stage records the sedimentation in an upper intertidal to supratidal environment in a semiarid coastline with the presence of thin cryptalgal sheets and chicken wire textures the final evolution consists of an environment with a high percentage of fluvial channel deposits probably related to a meandering pattern this evolution has been correlated with the depositional sequences established for the ne of spain where the anisian transgressive event resulted in the formation of an inter to supratidal carbonate ramp so lowstand transgressive and highstand system tracts from depositional sequence 1 have been recognized in the centre of spain

statistical analysis of fractal properties of point processes modeling seismic sequences abstract fractal stochastic point processes are described by power law statistics and therefore are suited to model the time occurrence sequence of seismic events that are generally characterized by a time clustering phenomenon in this paper we quantified the temporal clustering in earthquake sequences by means of the fano factor and the allan factor that can be used to reveal the fractality of such processes these methods are applied to model the fractality of the 1983 1997 seismicity of one of the most seismically active area of southern apennine chain southern italy that has shown the presence of temporal clusterization

study of the temporal correlations in the magnitude time series before major earthquakes in japan a characteristic change of seismicity has been recently uncovered when the precursory seismic electric signals activities initiate before an earthquake occurrence in particular the fluctuations of the order parameter of seismicity exhibit a simultaneous distinct minimum upon analyzing the seismic catalog in a new time domain termed natural time and employing a sliding natural time window comprising a number of events that would occur in a few months here we focus on the minima preceding all earthquakes of magnitude 8 and 9 class that occurred in japanese area from 1 january 1984 to 11 march 2011 the day of the m9 tohoku earthquake by applying detrended fluctuation analysis to the earthquake magnitude time series we find that each of these minima is preceded as well as followed by characteristic changes of temporal correlations between earthquake magnitudes in particular we identify the following three main features the minima are observed during periods when long range correlations have been developed but they are preceded by a stage in which an evident anticorrelated behavior appears after the minima the long range correlations breakdown to an almost random behavior possibly turning to anticorrelation the minima that precede m 7 8 earthquakes are distinguished from other minima which are either nonprecursory or followed by smaller earthquakes furthermore it is discussed whether tsallis statistical mechanics in the frame of which it has been suggested that kappa distributions arise can capture the effects of temporal correlations between earthquake magnitudes

reply to comment by f corfu and d w davis on archaean hydrothermal zircon in the abitibi greenstone belt constraints on the timing of gold mineralisation

evidence of low magnitude continued reservoir induced seismicity associated with the pertusillo artificial lake southern italy the most common observations of reservoir induced seismicity ris by filling artificial lakes are generally associated with the initial impoundment of the lake or the lake level increase above a previous maximum rarely ris persists for many years without a decrease in frequency or magnitude if this occurs it is called protracted or continued seismicity pertusillo artificial lake in high agri valley southern italy is a small reservoir with a water column that fluctuates yearly by about 10 15 m on average corresponding to a pressure perturbation at the bottom of the lake of 0 10 0 15 mpa although the reservoir was filled in 1963 the microearthquake activity still occurring around the lake allows the categorization of such ris as continued seismicity we collected all microearthquakes m l 2 7 recorded near the reservoir by two different seismic networks from january 2005 to june 2012 and analyzed their frequency magnitude distribution which showed a b value b 1 40 much higher than that expected for the investigated area even though the spatial seismicity pattern shows two distinct clusters to the northeast and southwest of the lake we found that only the southwest seismicity is significantly correlated with the water level the findings suggest that the physical driving mechanism is the 1d pore fluid pressure diffusion along the northeast southwest fault zones connecting the reservoir to the southern termination of the monti della maddalena fault system with an average hydraulic diffusivity of 7 8 m2 s online material figures of magnitude comparisons between catalogs temporal occurrence of events rainfall versus number of earthquakes and number of events versus water level and animated 3d views of seismicity and reservoir

the stratigraphy of the 3 5 3 2 ga barberton greenstone belt revisited a single zircon ion microprobe study abstract recent field and geochemical studies indicate a need to test the stratigraphy of the ca 3 5 ga barberton greenstone belt as it is presently adopted 1 2 this work uses the ion microprobe shrimp to attempt such a test results show that 1 volcaniclastic sediments of the theespruit formation