seismicity of the aegean and surrounding area abstract seismicity parameters based on instrumental and historical data are given for 36 seismic sources of shallow earthquakes and for 6 seismic sources of intermediate depth earthquakes in the aegean and surrounding area 34 n 43 n 18 e 30 e these parameters are of two categories parameters of the first category are useful for seismic hazard evaluation a and b values of the frequency magnitude relation maximum earthquake magnitude number of shocks larger than certain magnitude per year while parameters of the second category are proper for describing the spatial distribution of seismicity mean return period most probable magnitude in a certain time period moment rate shallow seismicity is highest along the convex side of the hellenic arc but close to the coast ionian islands south peloponnesus south of crete south of karpathos and rhodos in central greece patraikos corinthiakos evoikos gulfs thessalia and along a seismic belt which includes the northwestern anatolia fault zone the northernmost part of the aegean sea and the serbomacedonia zone the intermediate depth seismic activity is distributed in two parts of the benioff zone which dips from the convex side eastern mediterranean to the concave side aegean sea of the hellenic arc the one part shows a low dip angle and includes earthquakes with focal depths between 70 km and 100 km this part has a high seismicity earthquake magnitudes up to 8 0 and is situated below the inner slope of the sedimentary part of the hellenic arc eastern peloponnesus north of crete rhodos based on the fact that this part of the benioff zone is a continuation of the seismic zone of shallow earthquakes along the hellenic arc and that both zones have the same seismicity it is concluded that they constitute a continuous seismic belt on which coupling occurs between the subducted eastern mediterranean lithosphere and the overthrusted aegean lithosphere the other inner part of the benioff zone shows low seismicity maximum earthquake magnitude up to 7 1 with earthquakes of focal depths between 100 km and 180 km it dips at a mean angle of 38 below the volcanic arc of the southern aegean sea and is the result of the subduction of the front part of the eastern mediterranean lithosphere without coupling with the aegean lithosphere

accelerated preshock deformation of broad regions in the aegean area twenty four regions where accelerating deformation has been observed for a few decades before corresponding strong m 6 0 7 5 mainshocks are identified in the broader aegean area to a first approximation these preshock regions have elliptical shapes and the radius r in km of a circle with an area equal to the corresponding ellipse is related to the moment magnitude m of the mainshock by the equation log r 0 42 m 0 68 the dimension of each preshock region is about seven to ten times larger than the rupture zone fault length of the corresponding mainshock the time variation of the cumulative benioff strain was satisfactorily fitted by a power law relation which is predicted by statistical physics if the mainshock to which accelerating strain rates leads is considered as a critical point the duration t in years of the accelerating benioff strain release period is given by the relation log t 5 94 0 75 log s r where s r is the mean benioff strain rate release per year for 104 km2 in the preshock region calculated by the complete available data m 5 2 for the entire instrumental period 1911 1998 the importance of identifying and investigating such regions for better understanding the dynamics of the active part of the lithosphere as well as for earthquake prediction and time dependent seismic hazard assessment is discussed

the origin of the palaeoproterozoic amcg complexes in the ukrainian shield new u pb ages and hf isotopes in zircon the ukrainian shield hosts two palaeoproterozoic anorthosite mangerite charnockite granite amcg complexes the korosten and korsun novomyrhorod complexes that intruded palaeoproterozoic continental crust in north western and central parts of the shield respectively we report results of u pb zircon and baddeleyite dating of 16 samples from the korosten plutonic complex kpc and 6 samples from the korsun novomyrhorod plutonic complex knpc fifteen zircon samples from both complexes were also analysed for hf isotopes these new together with previously published data indicate that the formation of the kpc started at c 1815 ma and continued until 1743 ma with two main phases of magma emplacement at 1800 1780 and 1770 1758 ma each of the main phases of magmatic activity included both basic and silicic members the emplacement history of the knpc is different from that of the kpc the vast majority of the knpc basic and silicic rocks were emplaced between c 1757 and 1750 ma the youngest stages of the complex are represented by monzonites and syenites that were formed between 1748 and 1744 ma both ukrainian amcg complexes are closely associated in space and time with mantle derived mafic and ultramafic dykes the hf isotope ratios in the zircons indicate a predominantly crustal source for the initial melts with some input of juvenile hf from mantle derived tholeiite melts the preferred model for the formation of the ukrainian amcg complexes involves the emplacement of large volumes of hot mantle derived tholeiitic magma into the lower crust this resulted in partial melting of mafic lower crustal material mixing of lower crustal and tholeiitic melts and formation of ferromonzodioritic magmas further fractional crystallization of the ferromonzodioritic melts produced the spectrum of basic rocks in the amcg complexes emplacement of the ferromonzodioritic and tholeiitic melts into the middle crust and their partial crystallization caused abundant melting of the ambient crust and formation of the large volumes of granitic rocks present in the complexes

plio pleistocene lacustrine stromatolites from lake turkana kenya morphology stratigraphy and stable isotopes abell p i awramik s m osborne r h and tomellini s 1982 plio pleistocene lacustrine stromatolites from lake turkana kenya morphology stratigraphy and stable isotopes sediment geol 32 1 26 a sequence of fossil stromatolites from lake turkana in kenya was examined for 51so and 513c content these stromatolites ranging in age from holocene 10 000 yrs b p to middle pliocene 3 m y showed a variety of growth forms from oncolitic columnar layered to bulbous heads the stromatolites used in our study contain filamentous blue green algae of one morphological type and rare coccoids thus the stromatolites are considered biogenic the stable isotope ratios for oxygen and carbon indicate changing climatic conditions ranging from a cool wet climate prior to ca 1 9 m y to much drier warmer conditions around 1 4 m y followed in turn by a somewhat cooler and wetter climate at the end of the pleistocene

sveconorwegian massif type anorthosites and related granitoids result from post collisional melting of a continental arc root article i nfo two magmatic suites were emplaced during the post collisional evolution of the sveconorwegian orogeny an anorthosite mangerite charnockite suite amc suite and an hornblende and biotite bearing granitoids suite hbg suite the amc suite is exclusively located in the westernmost and warmest part of the orogen in granulite facies gneisses whereas the hbg suite intruded in the rest of the orogen but not in the granulite domain new u pb zircon geochronological data confirm previous age determinations 970 932 ma hbg suite and 933 916 ma amc suite the mafic facies of the two post collisional magmatic suites have similar geochemical compositions but the hbg differentiation trend displays higher cao sr u and th as well as lower k2o and feot mgo than the amc differentiation trend the hbg suite is hydrous and has a broadly higher fo2 whereas the amc suite is anhydrous the inferred parent magmas of both suites have overlapping initial sr nd and pb isotopic compositions with increasing differentiation the two trends point towards two different crustal contaminants together with the recent recognition of a major crustal shear zone located just east of the amc suite this difference suggests that the suites were emplaced in two different lithotectonic units using published experimental constraints and geochemical modeling we suggest that the mafic facies of both suites were produced by partial melting of lower crustal sources which were previously underplated probably during the evolution of a long lasting convergent margin later these lower crustal sources were modified by the regional granulite facies metamorphism 1 035 to 0 97 ga prevailing in the westernmost part of the orogen thus producing an anhydrous lower crustal source for the amc suite accordingly we conclude that the sveconorwegian massif type anorthosites result from partial melting of the continental arc root this process if accepted for other amcg anorthosite mangerite charnockite granite complexes was possible in the proterozoic because of a sufficiently high temperature but not in the archean because in subduction zones the main transfer to the crust was then felsic tonalites granodiorites and not basaltic we thus further suggest that the onset of massif type anorthosites at the beginning of the proterozoic may mark the time when plate tectonics began to operate in a similar way as today

first paleomagnetic results from mio pliocene series of the hellenic sedimentary arc abstract paleomagnetic measurements have been conducted on the mio pliocene series along the external sedimentary hellenic arc in order to detect the presence or absence of rotational deformations in different sections of the arc in the central eastern part of the arc crete and rhodes paleomagnetic directions are very closely aligned along the north south direction showing that this portion of the arc has not undergone significant rotation since at least 7 m y for crete and 4 m y for rhodes in the western and northwestern parts results from south peloponnesos zakinthos kephallinia and corfu indicate that this section of the arc has undergone a clockwise rotation detailed analysis of the data from the three ionian islands shows that their rotation began about 5 m y b p and has proceeded since then at roughly 5 m y giving a total amplitude of about 26 it is suggested that the beginning of this rotation is related to the lower pliocene compressive phase which most probably initiated the tectonic activity of the present day ionian margin

chemical characteristics of plagioclase and pyroxene megacrysts and their significance to the petrogenesis of the nain anorthosites abstract unmetamorphosed anorthosites of the nain plutonic suite in labrador are divided into a noritic pale facies to the west and south and a troctolitic dark facies to the east and north two large intrusions along tikkoatokhakh bay tik are taken as representative of the noritic suite and massif anorthosites at kikkertavak island kik and port manvers run pmr represent the troctolitic suite in this study plagioclase and pyroxene megacrysts from the tik bodies are distinguished from those of the kik and pmr intrusions by many element concentrations and ratios most tik plagioclase megacrysts an 42 54 have lower an values than found at kik pmr an 51 61 associated pyroxene megacrysts have lower x mg in the tik bodies than in kik pmr continuous variations of element concentrations and ratios support fractionation within each suite but a discontinuity between tik and kik pmr argues against fractionation from one suite to another and favors different magma compositions instead different pyroxene megacrysts suggest that pmr with cpx and kik with opx crystallized from different troctolitic magmas the plagioclase megacrysts resemble their enclosing rocks in composition and are therefore consanguineous reliable discriminants between plagioclases of noritic and troctolitic suites appear in plots of fe an fe ti fe ti an k rb and in values of k and sr the dark color of the troctolitic facies plagioclase is accompanied by a higher fe content and higher fe ti suggesting incorporation of tetrahedral ferrous iron at relatively reduced conditions k rb is highly scattered between 1200 and 4000 and ba k is scattered between 5 and 8 sr ca correlates strongly with k in a linear array in contrast to the kiglapait trend which is concave up at low values of k the difference between the two trends is attributed to hypersthene saturation at depth in the nain liquids the plagioclase ree patterns are highly enriched in lrees with ce yb n around 36 in the tik bodies and 12 27 in the kik pmr samples the least evolved pattern from pmr matches a plagioclase from the lower zone of the nearby kiglapait intrusion high alumina hypersthene megacrysts occur in the tik intrusions but not in the kik pmr bodies the presence of a chilled margin on the west edge of the tik bodies suggests that the high alumina contents are probably due to rapid growth in place rather than decompression from great depth the most aluminous opx megacrysts are also enriched in both incompatible zr and compatible cr but not compatible ni in conflicting testimony bearing on the rapid growth hypothesis the megacryst compositions can be used to discriminate and characterize magma types that produced massif anorthosite with adequate partition coefficients still lacking for many important elements they can also be used to calculate magma compositions explicitly by inversion within limits imposed by the scatter

a systematic spatiotemporal test of the critical point hypothesis for large earthquakes 1 the critical point hypothesis for large earthquakes predicts two different precursory phenomena in space and time an accelerating moment release and the growth of the spatial correlation length the objective of this work is to investigate both methods with respect to their predictive power a systematic statistical test based on appropriate random earthquake catalogs allows to quantify the correlations of a precursory pattern with the subsequent mainshock activity the analysis of target earthquakes in california since 1960 with magnitudes m mcut reveals that these correlations increase systematically with growing mcut and correlations at greater than 95 confidence are observed for mcut 6 5 in the case of the spatial correlation length in particular the seismicity patterns are found to be significantly correlated with each of the largest earthquakes m 7 0 individually the acceleration of the moment release has a similar trend but is less significant

sequence of tuffs between the kbs tuff and the chari tuff in the turkana basin kenya and ethiopia this paper describes a sequence of tuffs between the kbs and the chari tuff of omo group formations in kenya and ethiopia these tuffs have recently been shown to be 1 87 0 02 ma and 1 38 0 03 ma in age respectively the sequence of tuffs that is derived is consistent with 40 ar 39 ar ages reported separately and provides the stratigraphic framework for interpreting those ages further new correlations are established to the konso formation in southern ethiopia as drainage from the ethiopian rift to the omo turkana basin developed after deposition of the konso formation pumice clasts in tuffs of the omo turkana basin probably were transported there by the omo river the tuffs are divided into five groups on the basis of their stratigraphic position in relation to extensive ash layers the sequence of tuffs has import for the placement and age of archaeological sites in the koobi fora formation and for ages of mammalian faunas including hominids many tuffs were deposited during a 90 ka interval during which mediterranean sapropels are lacking suggesting that nile flow was reduced and that the level of a lake that occupied the omo turkana basin at the time was low thus the record of climatic influence on deposition in the omo turkana basin previously shown for the kibish formation 200 ka extends at least to early pleistocene time

seismic coupling and structure of the hellenic subduction zone in the ionian islands region abstract the western hellenic arc has been commonly considered as a largely aseismic subduction zone from the comparison of a small rate of shortening derived from the seismic moment release with a large rate of convergence inferred from geology complete seismic coupling would instead be expected from models that consider a control by plate tectonic forces because of the trenchward velocity of the hellenic aegean upper plate now confirmed with gps measurements in the region of the ionian islands a subduction interplate boundary has been recently imaged and its seismogenic downdip width suggested to be moderate from reflection seismic profiling and local earthquake tomography in the appropriate model for such an earthquake source region which considers a single interplate fault and takes into account these features the moderate seismic moment release is found consistent with complete seismic coupling of this subduction the shallow downdip limit of the seismogenic zone can be interpreted as due to the interplate boundary being overlain there by the ductile deeper crust of the orogenically thickened hellenides

pyroxene megacrysts in proterozoic anorthosites implications for tectonic setting magma source and magmatic processes at the moho abstract proterozoic anorthosites from the 1630 1650 ma mealy mountains intrusive suite grenville province canada the 1289 1363 ma nain plutonic suite nain churchill provinces canada and the 920 949 ma rogaland anorthosite province sveconorwegian province norway all entrain comagmatic cumulate high alumina orthopyroxene megacrysts haoms the orthopyroxene megacrysts range in size from 0 2 to 1 m and all contain exsolution lamellae of plagioclase that indicate the incorporation of an excess ca al component inherited from the host magma at pressures in excess of 10 kbar at or near moho depths 30 40 km suites of haoms from each intrusion display a large range in 147sm 144nd 0 10 to 0 34 making them amenable for precise age dating with the sm nd system sm nd isochrons for haoms give ages of 1765 12 ma mealy mountains 1041 17 ma rogaland and 1444 100 ma nain all of them older by about 80 to 120 m y than the respective 1630 1650 920 949 and 1289 1363 ma crystallization ages of their host anorthosites internal mineral sm nd isochrons between plagioclase exsolution lamellae and the orthopyroxene host for haoms from the rogaland and nain complexes yield ages of 968 43 and 1347 6 ma respectively identical within error to the ages of the anorthosites themselves this age concordance establishes that decompression exsolution in the haom was coincident with magmatic emplacement of the anorthosites 100 m y after haoms crystallization at the moho correspondence of pb isotope ages 206pb 204pb vs 207pb 204pb with sm nd ages and other strong lines of evidence indicate that the older megacryst ages represent true crystallization ages and not the effects of time integrated mixing processes in the magmas nd isotopic evolution curves afc mixing calculations and the age relations between the hoams and their anorthosite hosts show that the haoms are much less contaminated with crustal components and are an older part of the same magmatic system from which the anorthosites are derived modeling of these anorthositic magmas with melts indicates that their ultramafic cumulates would have sunk in the magma and been sequestered at the moho where they may have sunk deeper into the mantle resulting in large scale compositional differentiation the haoms thus represent a rare example of part of a cumulate assemblage that was carried to the upper crust during anorthosite emplacement and together with the anorthosites illustrate the dramatic influence that magma ponding and differentiation at the moho has on residual magmas traveling towards the surface the new geochronologic and isotopic data indicate that the magmas were derived by melting of the mantle forming magmatic systems that could have been long lived e g 80 100 m y a geologic setting that would fit these temporal constraints is a long lived andean type margin

were non avian theropod dinosaurs able to swim supportive evidence from an early cretaceous trackway cameros basin la rioja spain a fundamental question remaining unanswered in dinosaur behavior is whether they had the ability to swim we report the discovery of an exceptional swimming dinosaur trackway with 12 consecutive footprints in lacustrine nearshore sediment from the early cretaceous cameros basin la rioja spain the singular morphology of these footprints strongly suggests a fl oating animal clawing the sediment as it swam diagnostic traits of theropod dinosaur footprints are identifi able in these peculiar elongated s shaped ichnites paleoenvironmental reconstruction indicates an upper shoreface setting with a maximum water depth of 3 m substantiating the swimming hypothesis ichnological analysis of the trackway shows that this theropod used a pelvic paddle motion similar to that of modern bipeds and swam with amplifi ed asymmetrical walking movements to maintain direction into a leftward water current after recent hints of swimming dinosaurs this new evidence persuasively demonstrates that some non avian theropod dinosaurs were swimmers

establishment of a continuous gps network across the kephalonia fault zone ionian islands greece abstract we report on the establishment of a continuous gps network across the kephalonia fault zone kfz central ionian islands greece the kfz is an important segment of the boundary zone between the rapidly moving aegean microplate and the apulian platform italy repeated gps measurements carried out between the northern ionian islands and the island of crete have shown rates of crustal motion of the aegean reaching 35 mm a oriented sw relative to southern italy the kfz coincides with a maximum shear strain rate 180 nano strain a and a very high level of seismicity in order to monitor the ongoing deformation across the kfz and correlate the strain accumulation with earthquakes a continuous gps network has been installed operating at a sampling rate of 5 s this paper describes the instrumental set up the data logging strategy and first preliminary results

gps derived strain rate field within the boundary zones of the eurasian african and arabian plates we use the gps velocity field 1988 1998 for eastern mediterranean and asia minor to determine the crustal deformation strain rate field in an area bounded by 35 n and 43 n and 20 e and 48 e we calculate the normal and shear strain rate components associated with the major faults and compare these qualitatively with seismological data uncertainties in the calculation of the strain rates reach 50 nstrain yr 1 in sparsely observed parts of anatolia whereas we estimate errors 20 nstrain yr 1 in the aegean and marmara regions the largest compressional strain rate components in the eastern part of the study area occur along the greater caucasus mountain front reaching 70 nstrain yr 1 1 nstrain yr 1 0 0317 10 15 s 1 the north anatolian fault zone is the clearest feature in the shear strain rate field it is expressed as a pronounced dextral strike slip fault zone reaching rates of up to 170 nstrain yr 1 this holds true also for the izmit area where the august 17 1999 earthquake occurred central anatolia is almost strain free whereas extension prevails in western anatolia the principal axes of extension vary around the n s direction with strain rates of up to 85 nstrain yr 1 these extensional areas coincide with graben features and normal faulting earthquakes the central and southwestern aegean sea is strain free with values far below 40 nstrain yr 1 the seismic cluster around the dodekanissa islands southeastern aegean sea coincides with nw se oriented extension attaining strain rates of up to 90 nstrain yr 1 this area of extension also exhibits recent active volcanism the entire hellenic arc shows compressional strain rates perpendicular to the arc the pliny strabo troughs along the eastern segment of the arc show left lateral shear strain rates reaching 80 nstrain yr 1 significant extension is found in central greece with a nne ssw oriented maximum of 120 nstrain yr 1 centered around the gulf of corinthos the kephalonia fault zone in nw greece is a distinct dextral fault zone separating apulia from the rapidly moving aegean microplate right lateral shear strain rates reach 150 nstrain yr 1

lower crustal cumulate nodules in proterozoic dikes of the nain complex evidence for the origin of proterozoic anorthosites

precise 40ar 39ar geochronology for the upper koobi fora formation turkana basin northern kenya the plio pleistocene koobi fora formation about 560 m thick crops out east of lake turkana and is part of the much larger depositional system of the omo turkana basin the upper half of the koobi fora formation from just below the kbs tuff to above the chari tuff is particularly notable for its wealth of hominid fossils and archaeological sites silicic tuffaceous horizons have provided the basis for stratigraphic subdivision and correlation pumice clasts within the tuffs contain anorthoclase phenocrysts ideal for 40ar 39ar single crystal dating feldspars from pumice clasts in about 15 tephra within the stratigraphic interval from the kbs tuff to the silbo tuff have yielded precise ages that allow much finer definition of the numerical time framework for the sedimentary sequence between the kbs tuff 1 869 0 021 ma and the chari tuff 1 383 0 028 ma and to yet higher in the sequence to the silbotuff 0 751 0 022 ma these results provide a precise and accurate time scale for the upper part of the sequence in the whole of the omo turkana basin a number of these tuffs are recognized elsewhere in east africa thus ages determined at koobi fora also apply to the wider region

comment on bybee et al 2014 pyroxene megacrysts in proterozoic anorthosites implications for tectonic setting magma source and magmatic processes at the moho

application of vertebrate trace fossils to palaeoenvironmental analysis abstract this is a review of the main uses of vertebrate trace fossils ichnofabrics and ichnofacies in the palaeoenvironmental analysis of sedimentary sequences the article accounts for the significant developments produced in the last three decades including the application of the ichnofacies concept to vertebrate trace fossils recognition of footprints in cross sectional view and their distinction from inorganic structures and burrow fills is first discussed the response of different substrates showing contrasting water content and imprinted by different animals or devices is compared in terms of the morphology of the resultant footprint trackways with sand crescents are typical of aeolian cross strata and are absent in associated flat lying to low angle deposits thick packages of highly bioturbated sandy dune and interdune sediments have been interpreted as reflecting periods of increased rainfall neoichnological observations in modern lake basins suggest that distinct zones can be recognized in the margins of fossil ponds and lakes including onshore shoreline and shallow subaqueous zones abundant flamingo like footprints and flamingo nest mounds are good indicators of alkaline and or saline lake waters hippopotamus trails are found closely associated with modern and fossil freshwater wetlands dinosaur and pterosaur swim traces from lacustrine and fluvial deposits can be used to estimate water depth turtle crocodile amphibian hippopotamus and fish swim traces allow one to infer a subaqueous substrate certain modern intertidal fish feeding traces are oriented with the predominant tidal current and can be used as palaeocurrent indicators the preferential orientation of tetrapod trackways in lacustrine and fluvial deposits is analyzed vertebrate trace fossils can help to infer discharge variability in fluvial channels the descriptions of vertebrate ichnofabrics are commonly limited to heavily bioturbated beds due to trampling by vertebrates and to a few examples of ichnofabrics with discrete trace fossils the nature and implications of the recognized vertebrate ichnofacies are still being debated and have a limited utility in palaeoenvironmental analysis the distinction of a potential vertebrate burrow ichnofacies in carbonate bearing palaeosols is proposed to represent well drained soils developed under arid or semiarid climate

a partisan review of proterozoic anorthosites most anorthosites of the massif type crystallized in the episode 1 7 1 2 gyr with a pronounced peak of the age distribution near 1 4 gyr they were emplaced anorogenically at depths as shallow as 7 km where the ambient temperature of country rocks was probably less than 250 c depths of emplacement may have been as great as 25 km or more in rare cases the greater depths of equilibration estimated from granulite facies metamorphism may be incorrectly interpreted as emplacement depths but in any case they are demonstrably not required or characteristic of anorthosite emplacement penetrative deformation and metamorphism of anorthosites are post emplacement accidents of the local geologic history and are not directly caused by the presence of anorthosites granitic rocks mangerite charnockite suite associated with anorthosite are in general later or contemporaneous products of crustal anatexis with chemical and isotopic signatures distinct from the anorthosites and their residua such granitic rocks should not therefore be summed with the anorthositic rocks to obtain bulk compositions the magmas that produced most anorthosites were dry as shown by high temperature mineralogy and anhydrous mineral assemblages in contact aureoles residua from their crystallization are ferrodiorites to ferrosyenites typical of closed system fractionation these residua were locally and frequently ejected into contemporaneously molten granite where they formed pillows and cooled rapidly the overall chemistry of anorthosites and residua is broadly tholeiitic and consistent with derivation from the mantle olivine bearing magmas locally ranged from leucotroctolite anorthosite to later but coexisting picrite or melatroctolite in the same pluton confirming a wide spectrum of magma types a signal feature of troctolitic and noritic magmas is their low augite content implying high content of spinel component large anorthosite complexes such as nain and harp lake consist of many plutons representing repeated injections of separate magma batches with varying chemistry the abundant true anorthosites richer in plagioclase than magmas cosaturated with a mafic phase must represent plagioclase enrichment by either mechanical or chemical processes or both the role of kinetics in nucleation and solidification of such rocks may be centrally important it is proposed that hyperfeldspathic plagioclase supersaturated liquids were generated by quasi isothermal extraction of mafic minerals from tholeiitic magma enroute to and at the site of emplacement and that such a kinetic process was uniquely permitted in an environment of aborted continental rifting anorthositic rocks may have much to say about the episodic versus continuous geochemical evolution of the earth s mantle

crustal evolution and the temporality of anorthosites abstract types of rock such as komatiite which formed entirely or dominantly during restricted time periods in solar system history are important indicators of how planetary bodies evolved in deep time in this paper we characterize three different types of temporally restricted anorthosites and discuss their significance to the broad scale evolution of planetary processes primordial anorthosites which constitute the bulk of the lunar crust were sampled during apollo and luna missions and have subsequently been identified in our meteorite collections they are characterized by very calcic plagioclase an93 98 and all have magmatic crystallization ages 4 3 ga suggesting that the earliest planetary crust forming processes on the moon and possibly elsewhere involved substantial if not total melting the magma ocean hypothesis which has endured for nearly 50 years argues that the lunar anorthositic rocks represent global flotation cumulates of plagioclase which crystallized after extensive precipitation and sinking of olivine and pyroxene another possibility revitalized by critical filtering of age data involves serial magmatism whereby the lunar crust was constructed by younger smaller episodic magmatic events on earth two distinct types of temporally restricted anorthosites offer opportunities to understand the evolution of terrestrial geodynamics tectonics and magmatic processes archean megacrystic anorthosites formed only between 3 73 and 2 49 ga as small bodies

debating the petrogenesis of proterozoic anorthosites reply to comments by vander auwera et al on pyroxene megacrysts in proterozoic anorthosites implications for tectonic setting magma source and magmatic processes at the moho we welcome the opportunity for discussion on the petrogenesis of proterozoic anorthosites stimulated by a recent comment by vander auwera et al 2014 in their comment vander auwera et al accept our new geochronologic and isotopic data on comagmatic high aluminum orthopyroxene megacrysts haoms and anorthosites bybee et al 2014 but provide an alternate interpretation of the data in line with their model of magma genesis through melting of a mafic lower crust in short they suggest that the similarity of the ages of the haoms and a potential lower crustal source for the rogaland anorthosite province rap is evidence that the haoms crystallized at 1 05 ga at the base of a thickened crust from the parent magma of the gabbronoritic feda suite they suggest that this hypothesis is supported by overlapping nd and pb isotopic compositions of the haoms and feda suite vander auwera et al s argument centers on their suggestion that the haoms observed in most proterozoic anorthosites are restitic source material entrained in the melts from their proposed gabbronoritic source this model relies on a two stage petrogenesis wherein an underplating event forms lower crustal gabbronoritic cumulates followed approximately 100 million years later by a lower crustal melting event that entrains haoms and then crystallizes vast amounts of plagioclase to form proterozoic anorthosites we strongly disagree with this interpretation of our geochronologic

the environment of the ethiopian highlands at the mid pleistocene transition fauna flora and hominins in the 850 700 ka sequence of gombore ii melka kunture abstract environment climatic change and human evolution have been debated over the last 50 years giving special attention to the plio pleistocene sites of the rift valley in this paper we discuss the environment and the limits of hominin adaptability based on evidence from melka kunture at 2000 m asl on the ethiopian highlands and specifically on the 850 ka to 700 ka sequence at sub site gombore ii human fossils and multiple acheulean occurrences as well as hippo remains and footprints combined with palynological analysis provide a highly detailed chronological resolution of the changing local environmental conditions during the last 150 ka of the mpt mid pleistocene transition including the sequence of events after a volcanic eruption layers containing footprints and fossils are evidence of near continuous occupation by hippos and their recolonization of the area after a disruptive volcanic eruption conversely acheulean implements and human fossils suggest that peopling by hominins occurred at a different and discontinuous pace even when the flora and fauna were re established and the environment was rather stable most notably the assembled evidence points to the limits of homo erectus s l adaptability apparently this hominin could no longer live at 2000 m asl when the climate deteriorated during glacial isotopic stage 20 becoming markedly colder than it is today but re colonized the area when the climate turned warmer again during isotopic stage 19

crustal deformation in the central ionian islands greece results from dgps and dinsar analyses 1995 2006 abstract ground deformation studies based on differential gps dgps and differential interferometric sar dinsar analyses have been conducted in the seismically active area of the central ionian islands local gps networks were installed in cephallonia 2001 and zakynthos 2005 the cephallonian network has been remeasured five times and zakynthos once as of july 2006 the studies have yielded detailed information regarding both local and regional deformations that are occurring in the area for lefkas island dinsar analysis march to september 2003 revealed 56 mm of uplift in the central and western parts and is attributed to the august 2003 earthquake mw 6 3 that occurred offshore to the west synthetic dinsar modelling of the magnitude and extent of deformation is consistent with the seismologically deduced parameters for the ruptured segment along the lefkas transform fault subsidence for cephallonia island dinsar analysis 1995 to 1998 indicated ground deformation up to 28 mm located in small sections of the island further interferometric analysis for the period 2003 to 2004 encompassing the occurrence of the lefkas earthquake in august 2003 indicated 28 mm of uplift in the northern part while during the next two years 2004 to 2005 further uplift of at least 56 mm had taken place at the western and northern part of the island dgps measurements for the period 2001 to 2006 revealed a clockwise rotation of the island with respect to a centrally located station on aenos mt the horizontal component of deformation generally ranged from 6 to 34 mm with the largest values at the western and northern parts of the island considering the vertical deformation two periods are distinguished the first one 2001 to 2003 is consistent with anticipated motions associated with the main geological and tectonic features of the island the second one 2003 to 2006 has been tentatively attributed to dilatancy in which relatively small uplift 20 40 mm occurred along the southern and southeastern parts of the island while larger magnitudes 50 mm happened at the western part paliki peninsula these large magnitudes of uplift over an extended area 50 km in conjunction with an accelerated benioff strain determined from the analysis of the seismicity in the broader region are consistent with dilatancy this effect commenced some time after 2003 and is probably centered in the area between zakynthos and cephallonia if this interpretation is correct it may foreshadow the occurrence of a very strong earthquake s sometime during 2007 to 2008 in the above designated region

a reappraisal of the geomagnetic polarity time scale to 4 ma using data from the turkana basin east africa recalibration of the pliocene and early pleistocene geomagnetic time scale using the k ar dated fluvial sequence of the turkana basin in east africa agrees with calibrations based on astronomical calculations ages estimated here are olduvai subchron 1 78 1 96 ma reunion subchrons 2 11 2 15 ma and 2 19 2 27 ma matuyama gauss boundary 2 60 ma kaena subchron 3 02 3 09 ma mammoth subchron 3 21 3 29 ma gauss gilbert boundary 3 57 ma

palaeoenvironments of the eifelian dolomites with earliest tetrapod trackways holy cross mountains poland abstract the eifelian dolomites in the zachelmie quarry holy cross mountains poland contain trackways and tracks of tetrapods 390 391 ma old and thus the oldest known so far the environments of the trackway bearing beds have been investigated using sedimentological palaeontological geochemical and palaeomagnetic methods the reconstructed tetrapod habitats comprised shallow water lagoons separated from an open marine basin by sparsely vegetated islands and spits the lagoonal waters were well aerated and a few metres deep at most undergoing periodic desiccation the dolomitic sediments primarily of microbial origin formed in tropical waters of slightly modified marine composition oxygen isotope data obtained from the dolomicrites suggest water temperatures around 30 c the seasonal semi arid to sub humid climate deduced from paleosol characteristics was probably of a tropical monsoonal type the degree of restriction of the lagoonal system evolved from relatively open evaporation dominated towards increasingly closed freshwater influenced the detailed observations of the footprint bearing beds as well as the characteristics of the tracks indicate that they were formed mostly under subaqueous conditions by wading walking on the bottom or swimming animals lack of tidal indicators in the restricted zachelmie lagoons argues against previous concept that tidal flats served as a food source for the early tetrapods nor is a hypothesis of flooded woodlands confirmed as a habitat promoting the fish to tetrapod transition we propose that functional limbs emerged among aqueous animals that acquired their locomotional capabilities in a shallow lagoonal water before attempting longer excursions on land

tracks made by swimming hippopotami an example from koobi fora turkana basin kenya here we report an ichnological surface close to koobi fora kenya in palaeontological collecting area 103 the surface is marked by hominin tracks as well as many traces from large animals a southern excavation of the surface some 70 m from the hominin tracks displays a diverse range of animal track typologies most of which appear to have been made by a four digit animal moving via punting or bottom walking in a shallow water body due to the track morphology and the associated fossil record the non hominin tracks are interpreted as being made by hippopotami potentially including pygmy species or juveniles the track typologies are explained using modern analogue observations of hippopotami sub aquatic locomotion this work provides important environmental context for adjacent hominin tracks and fossils as well as providing the first recorded description of fossilized swim tracks made by mammals the site has implications for the interpretation of swim tracks in the geological record particularly the widespread and controversial tracks made by sauropods and other dinosaurs

a middle pleistocene hippo tracksite at gombore ii 2 melka kunture upper awash ethiopia abstract in this paper we describe exceptionally well preserved evidence of hippo activity at gombore ii 2 a 700 000 year old site at melka kunture at 2000 m asl in the ethiopian highlands in the upper awash valley we excavated and made casts of footprints that had been left after a volcanic eruption the 3d casts provide a detailed record of the outer anatomy and soft tissues of pleistocene hippos they reveal for the first time the shape of the legs and feet of the animals gombore ii 2 also provides information on the behavior of past hippos this prominent species of the african wildlife affects the vegetation and the landscape and acts as a geomorphological agent the animals wallow beside bodies of water and erode deep trails linking them to pastures at gombore ii 2 the trampling marks converge toward an erosional feature that we interpret as a fossil trail documenting an early middle pleistocene behavior similar to that of today signs of trampling and erosional features interpreted as hippo trails have also been described in pliocene and early pleistocene levels at olduvai and koobi fora we further underline that the hippo population of this tract of the valley was resilient and re established itself not long time after the volcanic eruption

polybaric fractional crystallization of high alumina basalt parental magmas in the egersund ogna massif type anorthosite rogaland sw norway constrained by plagioclase and high alumina orthopyroxene megacrysts bulk analyses of plagioclase and high alumina orthopyroxene megacrysts decimetreto metre sized crystals with plagioclase lamellae from the late proterozoic egersund ogna massif type anorthosite rogaland anorthosite province swnorway are used to constrain the parental magma compositions and differentiation processes within this 30 km diameter diapir spatial compositional variations show that two types of anorthosite occur high sr 720 1090 ppm andesine anorthosite an48 4 in the centre of the intrusion and low sr 320 620 ppm labradorite anorthosite an59 6 in the margin two populations of orthopyroxene megacrysts are clearly discriminated by their mn and cr contents but display similar ranges of mg number 55 79 interpretation of trace element data and comparison with inversion models suggest that the two types of anorthosite result from crystallization of different parental magma compositions with high alumina basalt affinities and similar mg numbers but different wollastonite sr mn and cr contents a rayleigh fractional crystallization model of the trace element concentrations vs mgo content in orthopyroxene constrains the cotectic orthopyroxene plagioclase proportions to 0 33 0 67 in both magma types before the appearance of fe ti oxide minerals on the liquidus at f 0 7 where f is melt fraction polybaric crystallization is recorded by variable alumina contents in the orthopyroxene megacrysts 2 3 8 5 wt corresponding to crystallization pressures in the 3 13 kbar range as shown by experimental data this implies that the high alumina orthopyroxene megacrysts mainly crystallized en route during diapiric rise of the anorthositic mush modelling the plagioclase compositions with experimentally determined partition coefficients for ca k sr and ba confirms that pressure variation during polybaric crystallization is the main controlling factor on compositional variations in the anorthosite pluton

molluscan biostratigraphy of the koobi fora hominid bearing deposits since the discovery1 of late cenozoic hominid bearing deposits in the koobi fora area north kenya a variety of studies2 9 have been undertaken to provide a chronostratigraphical and palaeoenvironmental context for the important palaeoanthropological and early archaeological discoveries1 10 unfortunately although the exposures are areally extensive 1 000 km2 they are broken up into subareas fig 2 these local sections are often difficult to correlate with one another due to intervening bush cover and faulting here i summarize a molluscan biostratigraphical analysis which demonstrates serious stratigraphical miscorrelations between certain local sections including some previously indicated by vertebrate evidence these miscorrelations require substantial revisions to current stratigraphical interpretation of the koobi fora deposits in particular both the suregei and tulu bor tuff horizons actually represent different levels although the tulu bor is considered to overlie the suregei some exposures currently attributed to the tulu bor are actually older than some units previously mapped as the suregei fortunately the stratigraphical miscorrelations reported here do not significantly affect the relative placement of the mollusc faunas reported in a previous evolutionary analysis15 superpositional relationships in the areas from which these faunas were collected mainly collecting areas 102 103 110 123 202 and 203 are unaffected by the miscorrelations reported here

proterozoic massif type anorthosites as the archetypes of long lived 100 myr magmatic systems new evidence from the kunene anorthosite complex angola abstract proterozoic massif type anorthosites are voluminous plagioclase dominated plutonic suites with characteristic intermediate compositions an50 10 that represent mantle derived magmas ponded at moho depths and crystallized polybarically until emplacement at mid crustal levels we present new id tims and la icpms u pb ages as well as detailed field observations from the kunene anorthosite complex kac of sw angola our main objective in this work is to contextualize a variety of important petrographic and geochronological features of the kac that have implications for proterozoic anorthosite petrogenesis and the geological evolution of the sw congo craton high precision u pb zircon and baddeleyite ages for anorthositic rocks from across the complex n 11 range between 1376 and 1438 ma a period of 60 myr showing that such systems may be remarkably long lived dating of magmatic zircons from a comagmatic pegmatoidal enclave in the kac which also contains high al orthopyroxene megacrysts haom gives an age of 1500 ma indicating as much as 120 myr between some of the earliest and latest crystallization products of the system these enclaves provide a snapshot of the liquid line of descent of the anorthosites and are compelling evidence for the comagmatic nature of the haom field evidence for block structure magma mingling and extreme textural heterogeneity in the kac supports emplacement as multiple influxes of magma of various volumes carrying variable proportions of crystals and autoliths from below we infer that the kac represents a long lived mushy magmatic system that was likely emplaced in distinct pulses these observations refine our understanding of proterozoic anorthosite petrogenesis they also provide evidence for an array of magmatic processes operating at various levels of crystallinity that may create textural and chemical heterogeneity in evolving magma products at lower to mid crustal levels

earthquake rupture as a critical point consequences for telluric precursors abstract earthquakes are related to rupture phenomena in complex statistical systems of cracks we first review some available information suggesting that rupture in earthquakes is a critical point the consequences of this hypothesis on several phenomena are then discussed in particular we focus our attention on a simple theory of electroseismic activity based on mechano electrical transduction effects such as the piezoelectric or the pressure induced polarization effect the neighbourhood of the rupture threshold is characterized by a specific response which could correspond to telluric wave activity observed as precursors of earthquakes

predictive modeling of the seismic cycle of the greater san francisco bay region the seismic cycle for the san francisco bay region is synthesized by a model combining the pre and post 1906 seismic histories the long term acceleration of seismic release seismic moment benioff strain release or event count in the seismic cycle and the shorter term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique called time to failure analysis in which rate of seismic release is proportional to an inverse power of the remaining time to failure the exponent of time to failure in the accelerating sequences appears to be scale invariant and the length of the full cycle is estimated at 269 50 years the 1989 loma prieta earthquake which is the culmination of the first subcycle in the present long term seismic cycle should have been predictable with an uncertainty of 2 years in time and 0 5 in magnitude although the specific location at loma prieta was not predictable by this technique if our model is correct and if the loma prieta earthquake is the culmination of a subcycle the san francisco bay region should be entering a relatively long 20 50 years period of seismic quiescence above magnitude 6 a great earthquake such as the 1906 san francisco event would appear to be more than a century in the future

the 2003 lefkada earthquake field observations and preliminary microzonation map based on liquefaction potential index for the town of lefkada abstract a strong earthquake mw 6 2 occurred offshore the island of lefkada or lefkas on august 14 2003 the maximum intensity has been evaluated io viii ems at lefkada municipality while vi to vii intensities were evaluated at many other villages of the island the offshore nne ssw oriented strike slip right lateral fault was activated by the main shock this fault is the northern termination of the cephalonia transform fault the most characteristic macroseismic effects were extensive typical ground failures like rock falls soil liquefactions subsidence densification ground cracks and landslides these macroseismic effects are remarkably similar to those reported from some historical lefkada shocks e g 1704 1914 ms 6 3 and 1948 ms 6 5 sand boils and ground fissures with ejection of mud were observed at the seaside of the town of lefkada and in the villages of nydri and vassiliki in situ soil profiles are obtained based mainly on borings after the earthquake boreholes records with spt values standard penetration test are obtained and the simplified procedure originally developed by seed and idriss was employed to evaluate the liquefaction resistance of soils the results indicated that the silty sandy layer which lies beneath the artificial fill in the coastal zone in lefkada town had liquefied during the 14 august earthquake an attempt was also made to establish a preliminary microzonation map for lefkada town using the data from liquefaction potential index analyses our map was validated by the occurrence of liquefaction phenomena inside the town