a large refined catalog of earthquake relocations and focal mechanisms for the island of hawai i and its seismotectonic implications we present high quality focal mechanisms based on a refined earthquake location catalog for the island of hawai i focusing on mauna loa and k lauea volcanoes the relocation catalog is based on first arrival times and waveform data of both compressional and shear waves for about 180 000 events on and near the island of hawai i between 1986 and 2009 recorded by the seismic stations at the hawaiian volcano observatory we relocate all the earthquakes by applying ray tracing through an existing three dimensional velocity model similar event cluster analysis and a differential time relocation method the resulting location catalog represents an expansion of previous relocation studies covering a longer time period and consisting of more events with well constrained absolute locations the focal mechanisms are obtained based on the compressional wave first motion polarities and compressional to shear wave amplitude ratios by applying the hash program to the waveform cross correlation relocated earthquakes overall the good quality defined by the hash parameters focal solutions are dominated by normal faulting in our study area especially in the active ka iki and h lea seismic zones k lauea caldera is characterized by a mixture of approximately equal numbers of normal strike slip and reverse faults whereas its south flank has slightly fewer strike slip events our relocation and focal mechanism results will be useful for mapping the seismic stress and strain fields and for understanding the seismic volcanic tectonic relationships within the magmatic systems

deep magma body beneath the summit and rift zones of kilauea volcano hawaii a magnitude 7 2 earthquake in 1975 caused the south flank of kilauea volcano hawaii to move seaward in response to slippage along a deep fault since then a large part of the volcano s edifice has been adjusting to this perturbation the summit of kilauea extended at a rate of 0 26 meter per year until 1983 the south flank uplifted more than 0 5 meter and the axes of both the volcano s rift zones extended and subsided the summit continues to subside these ground surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones kilauea s magmatic system is therefore probably deeper and more extensive than previously thought the summit and both rift zones may be underlain by a thick near vertical dike like magma system at a depth of 3 to 9 kilometers

focal mechanisms of earthquakes related to the 29 november 1975 kalapana hawaii earthquake the effect of structure models initial focal mechanism determinations for the 29 november 1975 kalapana hawaii earthquake indicated discrepancy between the mechanism determined from teleseismic data by ando and the mechanism determined using data from the local u s geological survey network surrounding the epicenter region the resolution of this difference is crucial to correctly understand this earthquake as well as to understand the tectonics of the south flank of kilauea volcano when a model with a low velocity layer at the base of the crust is used for projection back to the focal sphere for the local network mechanisms the discrepancy vanishes to further investigate this result focal mechanisms were determined using several contrasting models for a set of well recorded earthquakes a large number of these earthquakes have mechanisms identical to the main shock when the low velocity layer model is used dispersion of p and t axes is also minimized by use of this model a low angle slip direction favored for the main shock and typical of most other solutions exhibits remarkable stability normal to the east rift zone of kilauea our results suggest a tectonic model similar in nature to that proposed by ando in which the south flank of kilauea consists of a mobile block of crust which is relatively free to move laterally on a low strength zone at about 10 km depth forceful injection of magma along the rift zones provides the loading stress which is released by catastrophic failure in the weak horizontal layer in a cycle of perhaps 100 yr

the lost inca plateau cause of flat subduction beneath peru abstract since flat subduction of the nazca plate beneath peru was first recognized in the 1970s and 1980s a satisfactory explanation has eluded researchers we present evidence that a lost oceanic plateau inca plateau has subducted beneath northern peru and propose that the combined buoyancy of inca plateau and nazca ridge in southern peru supports a 1500 km long segment of the downgoing slab and shuts off arc volcanism this conclusion is based on an analysis of the seismicity of the subducting nazca plate the structure and geochemistry of the marquesas plateau as well as tectonic reconstructions of the pacific farallon spreading center 34 to 43 ma these restore three sub parallel pacific oceanic plateaus the austral tuamotu and marquesas to two farallon plate counterparts the iquique and nazca ridges inca plateau is apparently the sixth and missing piece in an ensemble of v shaped hotspot tracks formed at on axis positions we argue the mirror image of the inca plateau the marquesas plateau is an ancient edifice overprinted by recent volcanism in disagreement with the widely accepted young

an efficient algorithm for double difference tomography and location in heterogeneous media with an application to the kilauea volcano 1 improving our understanding of crustal processes requires a better knowledge of the geometry and the position of geological bodies in this study we have designed a method based upon double difference relocation and tomography to image as accurately as possible a heterogeneous medium containing seismogenic objects our approach consisted not only of incorporating double difference in tomography but also partly in revisiting tomographic schemes for choosing accurate and stable numerical strategies adapted to the use of cross spectral time delays we used a finite difference solution to the eikonal equation for travel time computation and a tarantola valette approach for both the classical and double difference three dimensional tomographic inversion to find accurate earthquake locations and seismic velocity estimates we estimated efficiently the square root of the inverse model s covariance matrix in the case of a gaussian correlation function it allows the use of correlation length and a priori model variance criteria to determine the optimal solution double difference relocation of similar earthquakes is performed in the optimal velocity model making absolute and relative locations less biased by the velocity model double difference tomography is achieved by using high accuracy time delay measurements these algorithms have been applied to earthquake data recorded in the vicinity of kilauea and mauna loa volcanoes for imaging the volcanic structures stable and detailed velocity models are obtained the regional tomography unambiguously highlights the structure of the island of hawaii and the double difference tomography shows a detailed image of the southern kilauea caldera upper east rift zone magmatic complex

using repeating earthquakes to correct high precision earthquake catalogs for time dependent station delays waveform cross correlation allows one to measure the relative arrival times of similar microearthquakes with errors of less than 1 10 of 1 sample location algorithms based on these measurements have greatly improved images of earthquake distribution for the northern california seismic network catalog however the relative location errors implied by the scatter of relocated repeating earthquakes sometimes 10s of meters is often considerably larger than the errors estimated from monte carlo simulations meters using a priori estimates of the cross correlation errors i find that most of this discrepancy arises from unmodeled time varying station delays by identifying many clusters of repeating earthquakes presumed to rupture the same source and assuming the measured arrival time differences between event pairs to be due to the difference in origin time plus the difference in station delay it is possible to invert for time dependent station corrections the method is robust in that these corrections are consistent over many kilometers of fault and greatly reduce the scatter and residuals when relocating earthquake clusters not used in the station correction determination many of the largest delay changes some approaching 2 samples 20 ms are associated with changing station electronics at several stations an annual cycle is also clearly seen with amplitudes up to 0 5 samples some m 4 7 earthquakes have produced comparable transient delay changes after applying the station corrections the scatter within clusters of repeating earthquakes is reduced to a few meters and the apparent seismogenic thickness of many kilometer long sections of faults is only 10 20 m manuscript received 31 may 2001

petrogenetic evolution of arc magmatism associated with late oligocene to late miocene porphyry related ore deposits in ecuador we present a data set on the geochemical and isotopic composition of mineralized porphyry intrusions se riate intrusions and arc volcanic formations spatially associated with late oligocene to late miocene porphyry related ore deposits in ecuador our aim is to constrain the petrogenetic evolution of these arc magmas to evaluate geodynamic and tectonic impact factors on arc magmatism and to explore the metallogenic signifi cance of these parameters we distinguish four petrogenetic groups associated with the investigated magmatic centers indicating dif ferent paths of low and high pressure crustal magma evolution tertiary ecuadorian arc magmas which dif ferentiated at higher crustal pressures are commonly characterized by adakite like compositions related to fractionation and or restite equilibration effects of amphibole garnet titanite particularly in hydrous silicic melts without concomitant or subsequent major plagioclase fractionation trace element distribution patterns of arc magmas through time are broadly systematic and indicate that crustal magma differentiation progres sively extends to higher pressures from the late oligocene to the late miocene possibly related to crustal thick ening locally adakite like features possibly related to high melt h2o contents or accessory phase fractiona tion are already observed in the early miocene in a regional setting otherwise dominated by low pressure magma evolution compositional differences between mineralized porphyry intrusions and spatially associated seriate precur sor intrusions in ecuador mostly reflect regional scale changes in magma composition through time and are not observed if the relative emplacement age difference is small where porphyry intrusions are associated with shallow crustal batholith systems in northern central ecuador their emplacement is commonly late with re spect to batholith magmatism intrusive compositions indicate that porphyry parental melts mostly evolved at higher crustal pressures where metallogenically favorable melt preconditioning might possibly occur

magmatic sulphides in quaternary ecuadorian arc magmas abstract new petrographic and geochemical data on magmatic sulphide inclusions msis are presented and discussed for 15 quaternary volcanic centers of the ecuadorian frontal main and back volcanic arc msis occur mostly in fe ti oxides magnetite and or magnetite ilmenite pair and to a lesser extent in silicate minerals amphibole plagioclase and pyroxene msis are present in all volcanic centers ranging in composition from basalt to dacite sio2 50 67 wt indicating that sulphide saturation occurs at various stages of magmatic evolution and independently from the volcano location along the volcanic arc msis also occur in dioritic gabbroic and hornblenditic magmatic enclaves of the volcanic rocks msis display variable sizes 1 30 m and shapes globular ellipsoidal angular irregular and occur mostly as polymineralic inclusions composed of fe rich and cu poor pyrrhotite and cu rich mostly chalcopyrite phases aerial sulphide relative abundances range from 0 3 to 7 ppm in volcanic host rocks and from 13 to 24 ppm in magmatic enclaves electron microprobe analyses of msis indicate maximum metal contents of cu 65 7 wt fe 65 2 wt ni 10 1 wt for those hosted in the volcanic rocks and of cu 57 7 wt fe 60 9 wt ni 5 1 wt for those hosted in magmatic enclaves relationships of the sulphide chemistry to the host whole rock chemistry show that with magmatic differentiation e g increasing sio2 the cu and ni content of sulphides decrease whereas the fe and s contents increase the opposite behavior is observed with the increase of cu in the whole rock because the latter is anti correlated with the sio2 whole rock content laser ablation icp ms analyses of msis returned maximum values of pges and noble metals of pd 30 ppm rh 8 1 ppm ag 92 8 ppm and au 0 6 ppm and pd 43 ppm rh 22 6 ppm ag 89 ppm and au 1 ppm for those hosted in volcanic rocks and magmatic enclaves respectively these pge contents display a different range of values with respect to those in previously investigated magmatic sulphides msis that are cu and pge cu rich are found in less evolved rocks i e lower sio2 contents that also display a lower amount of sulphide inclusions cu rich sulphide phases chalcopyrite bornite are mostly hosted by magnetite whereas pge rich ones consist of a cu poor phase pyrrhotite hosted by plagioclase however no systematic changes in the chemistry of the host silicate mineral are observed in coincidence with the occurrence of msis we use the results of our study to draw some implications on cu and other chalcophile elements behavior during arc magmatic processes potentially associated with the formation of porphyry type deposits

tremor genic slow slip regions may be deeper and warmer and may slip slower than non tremor genic regions slow slip events sses are observed worldwide and often coincide with tectonic tremor notable examples of sses lacking observed tectonic tremor however occur beneath k lauea volcano hawaii the boso peninsula japan near san juan bautista on the san andreas fault california and recently in central ecuador these sses are similar to other worldwide sses in many ways e g size or duration but lack the concurrent tectonic tremor observed elsewhere instead they trigger swarms of regular earthquakes we investigate the physical conditions that may distinguish these non tremor genic sses from those associated with tectonic tremor including slip velocity pressure temperature fluids and fault asperities although we cannot eliminate the possibility that tectonic tremor may be obscured in highly attenuating regions slip velocities of sses at k lauea volcano 10 6 m s and boso peninsula 10 7 m s are among the fastest sses worldwide k lauea volcano the boso peninsula and central ecuador are also among the shallowest sses worldwide and thus have lower confining pressures and cooler temperatures in their respective slow slip zones fluids also likely contribute to tremor generation and no corresponding zone of high vp vs has been noted at k lauea or boso we suggest that the relatively faster slip velocities at k lauea volcano and the boso peninsula result from specific physical conditions that may also be responsible for triggering swarms of regular earthquakes adjacent to the slow slip while different conditions produce slower sse velocities elsewhere and trigger tectonic tremor

mode and timing of terrane accretion in the forearc of the andes in ecuador the volcanic basement of the ecuadorian western cordillera pallatanga formation and san juan unit is made up of mafi c and ultramafi c rocks that once formed an oceanic plateau radiometric ages from these rocks overlap with a hornblende 40 ar 39 ar plateau age of 88 1 6 ma age obtained for oceanic plateau basement rocks of the pinon formation in coastal ecuador and with ca 92 88 ma ages reported for oceanic plateau sequences in the caribbean and western colombia these results suggest that the oceanic plateau rocks of the western cordillera and fl at forearc in ecuador are derived from the late cretaceous caribbean colombia oceanic plateau intraoceanic island arc sequences rio cala group overlie the plateau in the western cordillera and yield crystallization ages that range between ca 85 and 72 ma the geochemistry and radiometric ages of island arc lavas from the rio cala group combined with the age range and geochemistry of their turbiditic volcaniclastic products indicate that the arc was initiated by westward subduction beneath the caribbean plateau they are coeval with island arc rocks of coastal ecuador las orquideas san lorenzo and cayo formations and colombia ricaurte arc these island arc

geodynamic controls on tertiary arc magmatism in ecuador constraints from u pb zircon geochronology of oligocene miocene intrusions and regional age distribution trends abstract we obtained u pb zircon ages of late tertiary intrusions in the northern andes to provide robust time calibration points for the intrusive geochronologic framework of ecuador which is mostly based on k ar data magmatism associated with intrusion emplacement ranges from 31 to 7 ma with ages mainly pooling in the late oligocene early miocene where both k ar and u pb data exist for a given intrusive system ages obtained by the different methods are usually concordant within 1 4 m y suggesting that k ar ages are accurate indicators for the timing of tertiary arc magmatism on a regional multi m y scale except for a single sample the investigated intrusions completely lack externally inherited zircons in agreement with dominantly zircon poor oceanic crustal basement domains spatio temporal distribution trends of tertiary arc magmatism inferred from screened u pb k ar and zircon fission track geochronologic data allow tracking of the progressive along arc broadening of a flat slab segment below southernmost ecuador in the mid to late miocene and of moderate slab shallowing in northern central ecuador in the late miocene these regional arc migration patterns correlate in time with the subduction of the buoyant inca plateau and the carnegie ridge seamount chain the temporal distribution of tertiary ecuadorian arc magmatism indicates a late oligocene early miocene arc magmatic flare up event comprising widespread ignimbrite eruption and batholith construction initiation of the flare up event coincides in time with accelerating less oblique farallon nazca south america plate convergence suggesting a positive feedback between convergence rates asthenospheric melt production mantle crust melt flux and upper crustal arc magmatic productivity in ecuador

role of plate kinematics and plate slip vector partitioning in continental magmatic arcs evidence from the cordillera blanca peru new structural and geochronological data from the cordillera blanca batholith in the peruvian andes coupled with nazca south american plate slip vector data indicate that oblique convergence and associated strike slip partitioning strongly influenced continental magmatic arc evolution both the strain field and mode of magmatism plutonism vs volcanism in the late miocene peruvian andes were controlled by the degree to which the arc parallel component of the plate slip vector was partitioned into the arc strong strike slip partitioning at ca 8 ma produced arc parallel sinistral shear strike slip intercordilleran basins and east west oriented tension fractures that facilitated emplacement of the cordillera blanca batholith ca 8 2 0 2 ma periods during which the strike slip component was not partitioned into the arc ca 10 and ca 7 ma were associated with roughly arc normal contraction and ignimbrite volcanism the data thus support the contention that contraction within continental magmatic arcs favors volcanism whereas transcurrent shear favors plutonism the tie between oblique convergence and batholith emplacement in late miocene peruvian andes provides a modern analogue for batholiths emplaced as the result of transcurrent shear in ancient arcs

slip parallel seismic lineations on the northern hayward fault california a high resolution relative earthquake location procedure is used to image the fine scale seismicity structure of the northern hayward fault california the seismicity defines a narrow near vertical fault zone containing horizontal alignments of hypocenters extending along the fault zone the lineations persist over the 15 year observation interval implying the localization of conditions on the fault where brittle failure conditions are met the horizontal orientation of the lineations parallels the slip direction of the fault suggesting that they are the result of the smearing of frictionally weak material along the fault plane over thousands of years

block tectonics of the island of hawaii from a focal mechanism analysis of basal slip the southern third of the island of hawaii is composed of at least three rigid blocks kilauea volcano s south flank mauna loa volcano s southeast flank and mauna loa volcano s west flank analysis of earthquake focal mechanisms suggests that kilauea s south flank the most mobile of these blocks is moving seaward perpendicular to its east rift zone along a southeasterly course at an azimuth of 155 5 mauna loa s southeastern flank is also moving in a southeasterly direction although at a slightly more easterly azimuth of 140 5 although data are sparse on the western flank of mauna loa due to low seismicity and inadequate seismic network station density the available data suggest that this region is translating seaward along a generally westerly azimuth relative differences in these translational azimuths may represent oblique opening across the boundaries between these regions the active rift zones of kilauea and mauna loa volcanoes

deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of kilauea dense microearthquake swarms occur in the upper south flank of kilauea providing multiplets composed of hundreds of events the similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters a simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically relocation of these events greatly improves the definition of the seismic image of the fault that generates them indeed relative relocations define a plane dipping about 6 northward although corresponding absolute locations are widely dispersed in the swarm a composite focal mechanism built from events providing a correct spatial sampling of the multiplet also gives a well constrained northward dip of about 5 to the near horizontal plane this technique thus collapses the clouds of hypocenters of single event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies we cannot conclude that all south flank earthquakes collapse to a single plane there may locally be several planes perhaps with different dips and depths throughout the south flank volume the 6 northward dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of hawaii this plane is probably an important feature that characterizes the basal slip layer below the upper south flank of kilauea volcano differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane the present work illustrates how high precision relative relocations of similar events in dense swarms combined with the analysis of geodetic measurements can help to describe deep fault plane geometry systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well instrumented highly seismic areas to provide reliable basic information especially useful for understanding of earthquake generation processes

an autochthonous geological model for the eastern andes of ecuador abstract we describe a traverse across the cordillera real and sub andean zone of ecuador poorly known areas with very little detailed mapping and very little age control the spine of the cordillera comprises deeply eroded triassic and jurassic plutons the roots of a major arc emplaced into probable palaeozoic pelites and metamorphosed volcanic rocks the w flank comprises a jurassic submarine basaltic andesitic volcanic sequence which grades up into mixed jurassic cretaceous volcanic and sedimentary rocks of the inter andean valley the sub andean zone on the e flank of the cordillera comprises a newly recognized cretaceous basin of cleaved mudrocks quartz arenites and limestones east of the syndepositional cosanga fault the cretaceous basin thins into a condensed sequence that is indistinguishable from the rocks of the adjacent hydrocarbon bearing oriente basin the principal penetrative deformation of the cordillera real was probably latest cretaceous palaeocene it telescoped the magmatic belts but shortening was largely partitioned into the pelites between plutons the plutons suffered inhomogenous deformation some portions completely escaped tectonism the pelites conserve two foliations the earliest comprises slaty cleavage formed under low or sub greenschist conditions the later is a strong schistosity defined by new mica growth it largely transposed and obliterated the first both foliations may have developed during a single progressive deformation we find inappropriate recent terrane models for the cordillera real and sub andean zone of ecuador instead we find remarkable similarities from one side of the cordillera to the other including a common structural history in place of sutures we find mostly intrusive contacts between major plutons and pelites triassic to cretaceous events occurred on the autochthonous western edge of the archaean guyana shield the latest cretaceous paleocene deformation is interpreted as the progressive collision of an oceanic terrane s with the south american continent young fault movements have subsequently juxtaposed different structural levels through the cordillera real orogen

implications of diverse fault orientations imaged in relocated aftershocks of the mount lewis ml 5 7 california earthquake 1 we use seismic waveform cross correlation to determine the relative positions of 2747 microearthquakes near mount lewis california that have waveforms recorded from 1984 to 1999 these earthquakes include the aftershock sequence of the 1986 ml5 7 mount lewis earthquake approximately 90 of these aftershocks are located beyond the tips of the approximately north striking main shock defining an hourglass with the long axis aligned approximately with the main shock surprisingly our relocation demonstrates that many of these aftershocks illuminate a series of near vertical east west faults that are 0 5 1 km long and separated by as little as 200 m we propose that these structures result from the growth of a relatively young fault in which displacement across a right lateral approximately north striking fault zone is accommodated by slip on secondary left lateral approximately east striking faults we derive the main shock induced static coulomb failure function f on the dominant fault orientation in our study area using a three dimensional 3 d boundary element program to bound viable friction coefficients we measure the correlation between the rank ordering of relative amplitudes of f and seismicity rate change we find that likely friction coefficients are 0 2 0 6 and that the assumed main shock geometry introduces the largest uncertainties in the favored friction values we obtain similar results from a visual correlation of calculated f contours with the distribution of aftershocks viable rate and state constitutive parameters bound the observed relationship between magnitude of f and seismicity rate change and for our favored main shock model a maximum correlation is achieved when f is computed with friction coefficients of 0 3 0 6 these values are below those previously cited for young faults

paleozoic and triassic conodonts from the northwind ridge of the arctic ocean abstract conodonts are present in the basal part of six arctic ocean sediment cores recovered from the northwind ridge in the chukchi borderland area of the western arctic ocean the conodonts include species typical of the upper cambrian lower and middle ordovician middle to upper pennsylvanian probable lower middle and upper permian and lower triassic most of the conodont elements including a few of the cambro ordovician and all of the upper permian species were recovered from the sand fraction of the northwind breccia in the basal 1 5 m of core 92 p34 other ordovician and younger paleozoic conodont specimens occur in carbonate clasts incorporated in the northwind breccia the talus breccia occurs in the lower part of the early pliocene miocene unit a undifferentiated and is overlain unconformably by pleistocene age sediment a few paleozoic and triassic conodonts also occur in clasts recovered from the basal parts of five other northwind ridge cores upper permian specimens are the most numerous of the conodont elements and occur together with an abundant ichthyolith assemblage in addition the sand fraction of the northwind breccia contains poorly preserved foraminifera holothurians and sponges spicules that are common in all arctic ocean plio pleistocene sediment occurrence of conodonts in what is interpreted to be talus derived from bedrock indicates that the enigmatic northwind ridge is a true continental fragment that includes marine strata of at least paleozoic and triassic age the nature of the conodonts and other fossils recovered from the breccia suggests that the northwind ridge originated as part of the canadian arctic islands

genesis of the datuanshan stratabound skarn cu mo deposit middle lower yangtze valley eastern china constraints from geology re os geochronology mineralogy and sulfur isotopes stratabound deposits are the most abundant and economically significant ore type in the middle lower yangtze river valley one of the most important metallogenic belts in china the datuanshan deposit is one of the largest and most representative stratabound cu mo deposits in the tongling district of the middle lower yangtze river metallogenic belt all the orebodies of the datuanshan deposit occur around mesozoic quartz monzodiorite and are tabular or semi tabular bodies along bedding parallel faults within upper permian to lower triassic strata however discordant and crosscutting relationships e g the host rocks crosscut by skarn and quartz sulfide veins with alteration halos around the veins have also been found especially along the skarn host contact and orebody host contact indicating that skarnitization and mineralization postdated the deposition of the host sediments the skarn consists mainly of prograde garnet and pyroxene and retrograde alteration assemblages of amphibole epidote and chlorite as well as quartz and sulfides electron microprobe analyses show that the garnets and pyroxenes are grossular andradite and hedenbergite diopside series respectively and all samples plot in the field of typical skarn copper deposits worldwide molybdenite samples from stratiform copper ores yield re os model ages of 138 2 139 9 ma with a weighted mean age of 139 2 0 9 ma this is reasonably consistent with the ages of the stratiform mo ores 138 0 140 8 ma and genetically related quartz monzodiorite 135 2 139 3 ma in the datuanshan deposit indicating that the stratiform cu and mo mineralization was contemporaneous with emplacement of the quartz monzodiorite magmas in the early cretaceous fifteen 34s values for sulfides range from 1 8 to 4 7 with a mean of 0 5 indicating that the sulfur was derived mainly from a magmatic source moreover the sulfur isotope values of the ores are consistent with those of mesozoic intermediate acid intrusions but are different from those of sediments in the shizishan orefield based on these lines of evidence we conclude that the datuanshan stratabound cu mo deposit is the result of replacement related to mesozoic magmatic rocks and is not a product of submarine exhalative sedimentary processes

precursors to the kalapana m 7 2 earthquake the kalapana hawaii earthquake of november 1975 had a rupture length of 40 to 50 km and was located on the south flank of the active volcano kilauea the source mechanism was dip slip normal faulting on a plane dipping 20 degrees to the se with the greatest principal stress oriented in that direction and accumulated by volcanic intrusions into kilauea s rifts the source area of the 1975 earthquake was subject to intensive geological and geophysical research for many years before this earthquake because of its proximity to the volcano we studied the distribution of epicenters for small earthquakes from 1962 to 1975 seven seismographs located within 3 km of the aftershock area had been in operation for 3 to 10 years before the mainshock and geodetic triangulations and trilaterations in the source area had been carried out repeatedly since 1914 we found that precursory changes occurred throughout most of the rupture area but in two distinctly different patterns in the larger outer anomalous area the seismicity rate was decreased by 50 during the 3 8 years before the mainshock in addition several geodetic lines indicated anomalous strain release during this time within two inner areas the seismicity remained high then increased shortly before the mainshock in one of the inner areas a p wave travel time delay of 0 2 s could be detected which began about 3 5 years before the mainshock within the other inner anomalous area geodetic strain was accumulating until the first half of 1975 when 3 5 10 4 strain 35 bars was released aseismically by contrast the outer anomalous volume was experiencing strain softening from 1970 1971 on we interpret these observations as indicating that strain softening by fault creep in the outer anomalous area transferred stress into two major asperities locked portions of the fault a velocity decrease and foreshocks were observed in one asperity and high stress accumulation in the other implying that dilatancy of the crust probably occurred our model is qualitatively supported by the independent evidence of strong motion records which show that the kalapana earthquake was a complex multiple rupture we conclude that the kalapana earthquake was preceded by a preparatory process which lasted 3 8 0 3 years and which had dimensions of 45 10 km covering approximately the aftershock area

two stage gold mineralization of the axi epithermal au deposit western tianshan nw china evidence from re os dating s isotope and trace elements of pyrite the axi gold deposit is one of the largest epithermal deposits in northwestern china and is characterized by multistage generations of pyrite associated with gold mineralization genetic models for superjacent epithermal au and porphyry cu systems involve either contemporaneous or episodic mineralization implying different metal sources and ore forming events nine pyrite separates from disseminated ores associated with pyrite sericite quartz alteration in the axi deposit yield a re os isochron age of 350 10 ma mswd 5 1 initial 187os 188os ios 0 20 0 11 this age likely reflects a mixed contribution of two subtypes of disseminated pyrite py1 based on zoned pyrite crystals the isochron age of 353 6 ma mswd 1 6 ios 0 107 0 021 n 6 excluding samples with pyrite cores overlaps previous ages for andesite from the dahalajunshan formation ca 356 ma indicating that the early mineralization event occurred shortly after the formation of host rocks ca 353 ma pyrite from disseminated ores shows little variation of sulfur isotopic compositions 2 9 to 4 0 and has high cu co ni and v contents which favors a magmatic hydrothermal origin pyrite grains from gray quartz veins yield a younger re os isochron age of 332 8 ma mswd 0 22 n 4 vein hosted pyrite shows characteristics of a mantle derived magma source ios 0 171 0 024 34s 0 10 3 10 which result from the intrusion driven convective hydrothermal circulation accompanying fluid exsolution and metal remobilization from basement and wallrocks our data demonstrate that the axi gold deposit was formed during two temporally separated hydrothermal events this model of ore formation may apply to other epithermal porphyry deposits within the axi tawuerbieke district disseminated au and porphyry style au cu mineralization occurred shortly after magmatic activity 356 353 ma whereas epithermal style au mineralization occurred at ca 332 ma

sediments of the lomonosov ridge and makarov basin a pleistocene stratigraphy for the north pole sediments of 16 short cores taken as part of the lomonosov ridge experiment lorex can be organized into the first pleistocene stratigraphy for the north polar region this stratigraphy can be correlated with stratigraphic units described from the alpha chukchi areas 300 km distant the lorex cores include at least 12 sedimentary subunits differentiated by texture color and carbonate content the units are silty and arenaceous lutites and are principally glacial marine benthic and planktonic foraminifera degree of bioturbation and fe mn micro nodule abundance generally are positively correlated foraminifera in core b 8 from 3 956 m in the makarov basin may have been affected by ccd fluctuations that did not affect fossils in core b 24 from 1 600 m on the crest of the lomonosov ridge the 12 stratigraphic units were deposited during the late pleistocene and represent the same major sedimentary events as those of stratigraphic units k l and m of the amerasian basin this correlation is excellent evidence for the remarkable and widespread uniform depositional style of glacial marine sediment times of major glacial ice transport reflect deglaciation events in the central arctic ocean surface currents during deglaciation transport glacial ice in a more or less uniform pattern over at least 50 of the arctic ocean even thin sedimentary units deposited during relatively long time intervals are correlated over 500 000 km 2

the interpretation of inverse isochron diagrams in 40 ar 39 ar geochronology abstract the concepts involved in the construction and interpretation of inverse isochron diagrams used in 40 ar 39 ar geochronology are reviewed the diagrams can be useful as a means of recognising atmospheric argon and excess 40 ar incorporated in the mineral lattice which cannot be recognised from 40 ar 39 ar spectra the age established using an inverse isochron plot unlike that yielded by a spectrum is not affected by trapped argon 40 ar 36 ar ratios that are different from the atmospheric argon ratio e g due to excess 40 ar and may contribute to a better age interpretation however a heterogeneous distribution of excess 40 ar or heterogeneous argon loss can cause false isochrons with axial intercepts indicating an incorrect age and an incorrect trapped argon composition inconsistency between the ages from a spectrum and from the associated inverse isochron plot may indicate the degree of inaccuracy of isochrons however it is possible that both the spectrum and inverse isochron yield the same incorrect age the importance of considering all possible interpretations before assigning an age to a specimen is stressed

location of long period events below kilauea volcano using seismic amplitudes and accurate relative relocation 1 we present methods for improving the location of long period lp events deep and shallow recorded below kilauea volcano by the permanent seismic network lp events might be of particular interest to understanding eruptive processes as their source mechanism is assumed to directly involve fluid transport however it is usually difficult or impossible to locate their source using traditional arrival time methods because of emergent wave arrivals at kilauea similar lp waveform signatures suggest the existence of lp multiplets the waveform similarity suggests spatially close sources while catalog solutions using arrival time estimates are widely scattered beneath kilauea s summit caldera in order to improve estimates of absolute lp location we use the distribution of seismic amplitudes corrected for station site effects the decay of the amplitude as a function of hypocentral distance is used for inferring lp location in a second stage we use the similarity of the events to calculate their relative positions the analysis of the entire lp seismicity recorded between january 1997 and december 1999 suggests that a very large part of the lp event population both deep and shallow is generated by a small number of compact sources deep events are systematically composed of a weak high frequency onset followed by a low frequency wave train aligning the low frequency wave trains does not lead to aligning the onsets indicating the two parts of the signal are dissociated this observation favors an interpretation in terms of triggering and resonance of a magmatic conduit instead of defining fault planes the precise relocation of similar lp events based on the alignment of the high energy low frequency wave trains defines limited size volumes

the use of earthquake rate changes as a stress meter at kilauea volcano stress changes in the earth s crust are generally estimated from model calculations that use near surface deformation as an observational constraint but the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues although this possibility has considerable appeal because seismicity data are routinely collected and have good spatial and temporal resolution the method has not yet proven successful owing to the non linearity of earthquake rate changes with respect to both stress and time here however we present two methods for inverting earthquake rate data to infer stress changes using a formulation for the stress and time dependence of earthquake rates application of these methods at kilauea volcano in hawaii yields good agreement with independent estimates indicating that earthquake rates can provide a practical remote sensing stress meter

metallogenic features of miocene porphyry cu and porphyry related mineral deposits in ecuador revealed by re os 40ar 39ar and u pb geochronology mineralization and alteration events at ten miocene porphyry cu and porphyry related epithermal mineral deposits in southern central and northern ecuador were dated by means of molybdenite re os biotite and alunite 40ar 39ar and titanite u pb geochronology most of these hydrothermal events show a spatio temporal correlation with porphyry intrusion emplacement as constrained by zircon u pb ages the total age range for these events spans the 23 5 6 1 ma period without displaying systematic along or across arc age distribution trends while epithermal deposits tend to be spatially associated with volcanic rocks of a similar age porphyry cu deposits in ecuador are frequently spatially associated with deeper seated basement units and batholith scale precursor intrusive systems assembled over 5 m y time periods in most cases formation of the porphyry cu deposits is related to the youngest magmatic hydrothermal event in a given area postdating batholith construction at a regional scale the majority of miocene deposits occurs in southern ecuador where areally extensive post mineralization late miocene to recent volcanic sequences with the potential to conceal mineralization at depth are lacking only few miocene deposits occur in northern central ecuador where they mainly crop out in the western cordillera west of the productive present day volcanic arc the surface distribution of post mineralization arc volcanism reflects along arc variations in subducting slab geometry porphyry cu and epithermal deposits in ecuador define a miocene metallogenic belt broadly continuous with its coeval counterpart in northern central peru although both belt segments were formed in an overall similar tectonomagmatic and metallogenic setting their respective metal endowments differ significantly

erratum to 40ar 39ar dating of the rajahmundry traps eastern india and their relationship to the deccan traps earth planet sci lett 208 2003 85 99

how accurately can we date the duration of magmatic hydrothermal events in porphyry systems an invited paper determining the absolute duration of magmatic hydrothermal events leading to the formation of porphyry systems i e including porphyry copper skarn and epithermal deposits is one of the key questions in ore geology this is so because the duration of magmatic hydrothermal events in porphyry systems is instrumental to the development of genetic models necessary to explore a category of mineral deposits that provide most of the copper and significant amounts of base and precious metals to our economy the problem of determining the absolute duration of magmatic hydrothermal events in porphyry systems has been addressed through thermal modeling of cooling intrusions and time needed to precipitate specified metal amounts from active hydrothermal systems with known metal concentrations and fluid fluxes both these methods have shown that the likely duration of hydrothermal systems is on the order of a few tens of kilo annum ka isotopic dating in contrast is the only possible way to determine the life span of magmatic hydrothermal events in fossil porphyry systems analytical and methodological developments during the last decade in the fields of the most robust isotopic systems commonly used for absolute dating u pb 40ar 39ar re os allow us to date minerals with internal precisions 0 2 2 for a 10 ma old mineral this corresponds to a 20 ka uncertainty which is marginally sufficient to discriminate the duration of hydrothermal systems at the tens of kilo annum scale however many geochronological studies on fossil porphyry systems have shown that these are most often formed through repeated cycles of several intrusion events which extend the overall life of the porphyry systems to a few 0 x and up to 2 ma in some cases internal precisions of the above mentioned dating methods allow us in theory to comfortably discriminate events at the 0 x scale and the combination of u pb 40ar 39ar and reos geochronology is a tool widely used by ore geologists to bracket the duration of cyclic magmatic hydrothermal events in porphyry systems in this review we discuss some fundamental problems that are systematically overlooked in most geochronological studies trying to bracket the life span of porphyry systems we show that if these problems are not adequately taken into account and tackled the result will be that fundamentally wrong life spans of porphyry systems will be estimated we also provide basic guidelines to follow when trying to resolve the duration of magmatic hydrothermal events in porphyry systems with the highest accuracy and precision currently achievable

new insights into kilauea s volcano dynamics brought by large scale relative relocation of microearthquakes 1 we investigated the microseismicity recorded in an active volcano to infer information concerning the volcano structure and long term dynamics by using relative relocations and focal mechanisms of microearthquakes there were 32 000 earthquakes of the mauna loa and kilauea volcanoes recorded by more than eight stations of the hawaiian volcano observatory seismic network between 1988 and 1999 we studied 17 000 of these events and relocated more than 70 with an accuracy ranging from 10 to 500 m about 75 of these relocated events are located in the vicinity of subhorizontal decollement planes at a depth of 8 11 km however the striking features revealed by these relocation results are steep southeast dipping fault planes working as reverse faults clearly located below the decollement plane and which intersect it if this decollement plane coincides with the pre mauna loa seafloor as hypothesized by numerous authors such reverse faults rupture the pre mauna loa oceanic crust the weight of the volcano and pressure in the magma storage system are possible causes of these ruptures fully compatible with the local stress tensor computed by gillard et al 1996 reverse faults are suspected of producing scarps revealed by kilometer long horizontal slip perpendicular lineations along the decollement surface and therefore large scale roughness asperities and normal stress variations these are capable of generating stick slip large magnitude earthquakes the spatial microseismic pattern observed in the south flank of kilauea volcano and hilina type instabilities rupture intersecting the decollement surface causing its large scale roughness may be an important parameter controlling the growth of hawaiian volcanoes

characteristics of deep 13 km hawaiian earthquakes and hawaiian earthquakes west of 155 55 w 1 high precision relocation of earthquakes recorded by the hawaiian volcano observatory hvo seismic network provides new information on the characteristics of seismic faulting at this oceanic hot spot using waveform cross correlation we have measured correlation coefficients and travel time differences for a set of 14 605 deep 13 km earthquakes recorded from 1988 to 1998 we find that about half of the analyzed earthquakes are in similar event clusters that delineate fault zones in the lower crust and upper mantle we suggest that much of this deep seismicity reflects rupture in the brittle lithosphere away from the magma pathways although at kilauea the stresses from magma movement may additionally help trigger mantle earthquakes on preexisting faults in regions with high differential ambient stresses focal mechanisms of similar event clusters throughout hawaii display characteristic patterns and appear consistent with the hypothesis that deep earthquakes on preexisting faults reflect the stresses due to volcano loading and flexure we also present the results of applying cross correlation analyses and relocation to 7000 earthquakes at all depths located west of 155 55 w and recorded from 1988 to 1998 the pattern of relocated earthquakes at the kealakekua fault zone is consistent with the presence of a low angle detachment on the west flank of mauna loa

comparison of orientations of stress and strain tensors based on fault plane solutions in kaoiki hawaii the stress tensor orientation was estimated based on inversion from 238 first motion fault plane solutions of earthquakes with mostly m 3 5 0 6 located in the 10 km radius kaoiki crustal volume separate inversions for subvolumes containing 20 50 events yielded the same results in several adjacent volumes suggesting that the stress tensor is homogeneous in those parts of the kaoiki area and that the inversion results are stable and meaningful five spatial subsets of the data were found for which the orientation of at least one of the principal axes was different from that in the other sets by 20 80 and at confidence levels exceeding 95 the volcano summits of kilauea and mauna loa and their rift systems are identified as the source of stress in the kaoiki crust because the greatest principal stress points to kilauea and mauna loa in addition the strain tensor due to energy released by these 238 earthquakes was computed for the kaoiki area and several subvolumes of it by summing the moment tensors the moment tensor of each earthquake was constructed from the individual fault plane solutions and from an estimate of the scalar moment derived from the moment magnitude relationship a comparison of the directions of strain and stress tensors showed close agreement for subvolumes with predominantly strike slip faulting in these volumes the inversion process for stress directions led to misfits of approximately equal size for the conjugate near vertical nodal planes these observations are interpreted to show that in the strike slip regime of the upper part of the crust neither of the nodal planes is preferred for faulting rupture probably occurs along the nw and along the nh striking nodal planes in separate earthquakes subvolumes with more decollement faulting showed significant differences of 30 40 between the principal strain and stress directions in these volumes the near horizontal nodal planes showed noticeably smaller misfits in the inversion for the stress directions these facts are interpreted to indicate that the decollement plane is weak allowing slip on it even if the principal stresses are inclined at a large angle to it it is proposed that comparison of strain and stress tensor calculations may be able to differentiate between tectonic regimes uniform in strength no well developed fault plane and regimes in which a fault with low frictional strength dominates as a function of time significant rotations of the strain tensor by approximately 45 can be observed which seem to be related to the occurrences of kaoiki mainshocks during three background periods of about 7 years each the average strain tensor showed an orientation typical for predominant decollement faulting while two premainshock periods of 2 5 years each showed an orientation closer to strike slip faulting it is proposed that this pattern may be repeated before the next kaoiki mainshock the strain released seismically is less than the geodetically observed strain by approximately an order of magnitude stress strain fault plane solutions hawaii

growth and persistence of hawaiian volcanic rift zones hawaiian volcanic rift zones are modeled by representing the rifts and adjacent volcano flanks as long ridges with the geometry of flattened triangular prisms the intrusion of dikes along the axis of a rift requires a mechanism to generate the appropriate dike trapping stress field within the prism possible factors that affect the state of stress in the prism include multiple dike intrusion along the ridge axis faulting and gravitational sagging of the topography in extreme models with very steep slopes and high poisson s ratio corresponding to the gelatin models of rift zones by fiske and jackson 1972 results of finite element calculations indicate that gravity induced stresses are sufficient to trap a dike into propagating within the prism and parallel to the rift zone as proposed by fiske and jackson however the mechanism does not work for gently sloping flanks or a more acceptable poisson s ratio of about 0 25 additionally trapping stresses in the gravity loading and density stratification models will not persist after a few dike injection episodes therefore in mature hawaiian rift zones with possibly thousands of dikes additional processes must act to control the stresses that permit continued dike intrusion and rift persistence it is proposed that accommodation to dike emplacement occurs by slip on deep faults possibly of the type proposed for the 1975 kalapana hawaii earthquake as suggested by others for this earthquake the faults could coincide with the contact of the volcano with the seafloor within the weak seafloor sediments such faulting not only provides a means for the flanks to adjust continuously to intrusions but also generates the stress patterns needed to constrain future dikes to propagate along the rift axis other possible faulting mechanisms such as shallow gravity slides and normal faulting of the flanks do not appear to favor rift zone persistence in this model the horizontal stress generated by a standing column of magma at the time of dike emplacement the stresses in the ridges and the fault strength are coupled this results in a feedback between the maximum height that magma can rise along the rift fault friction and fault width through this feedback the slope of the volcano flank is controlled by the fault friction when applied to kilauea volcano the model yields an estimate for the coefficient of fault friction as high as 0 39 assuming normal hydrostatic pore fluid pressure an implication of this model supported by other studies is that rift intrusion and lateral spreading could be major contributors to volcano growth

focal mechanisms and locations of earthquakes in the vicinity of the 1975 kalapana earthquake aftershock zone 1970 1979 implications for tectonics of the south flank of kilauea volcano island of hawaii the november 29 1975 kalapana earthquake of magnitude 7 1 on the south flank of kilauea volcano hawaii represents a major rift tectonic event it is generally understood that the earthquake resulted from movement on a nearly horizontal fault plane with the crustal block south of kilauea s east rift zone moving south southeastward up to several meters well recorded earthquakes on the south flank of kilauea from 1970 to 1979 were analyzed and focal mechanisms determined to obtain a better understanding of the details of south flank tectonics included are a large number of earthquakes from the aftershock sequence of the 1975 earthquake hypocenters are distributed in a subplanar zone that dips 2 to 3 to the west at a depth of about 8 9 km depth we interpret this pattern to coincide with a portion of the slip plane of the kalapana earthquake and to be consistent with the notion of the slip plane occurring in a weak layer at the top of the old oceanic crust focal mechanisms are remarkably constant throughout this time period both before and after the 1975 event and closely agree with the mainshock mechanism p axis azimuths and slip vectors for the low angle fault planes are normal to the middle and lower east rift zones of kilauea there is suggestion of a change in the orientation of p axes from shallower to steeper plunge at the time of the kalapana earthquake such a change is consistent with a general reduction in the horizontal compressional stress normal to the rift zone at the time of the large earthquake no other evidence of precursory reorientation of the stress field was found and the precise predictability of this event remains in doubt however a general model of the tectonics of the volcanic rift system is now available that satisfies a number of geological and geophysical observations

collision related genesis of the sharang porphyry molybdenum deposit tibet evidence from zircon u pb ages re os ages and lu hf isotopes article i nfo sharang is a low fluorine calc alkaline porphyry mo deposit hosted mainly in a granite porphyry of a multi stage plutonic complex in the northern gangdese metallogenic belt largely with stockwork and ribbon textured mineralization the observed age estimates suggest that the formation of the magmatic host complex 52 9 51 6 ma and the ore deposit itself 52 3 ma occurred during the main stage of the india asia collision the host rocks are characterized by lower zircon ehf t values than those of the pre ore and post ore rocks this suggests that the lhasa terrane basement might play an important role in the formation of sharang ore forming intrusions in view of the framework of magmatic metallogenic events we suggest that slab roll back may have induced melting of juvenile crust and ancient continental complexes during the india asia collision this proposal focuses exploration for additional molybdenum deposits on the collision zone

evolution of permian conodont provincialism and its significance in global correlation and paleoclimate implication the main components of asselian through artinskian conodont faunas found around the world are basically the same and the provincialism is indicated only by less common endemic elements such as gondolelloides and new genus a henderson in north pangea sweetognathus bucaramangus around the equator and vjalovognathus in eastern gondwana provincialism is marked by differences at the species level of mesogondolella neostreptognathodus and sweetognathus during the kungurian and becomes very distinct with differences at the genus level during the guadalupian and lopingian three provinces of permian conodonts referred to as the north cool water province ncwp the equatorial warm water province ewwp and the peri gondwana cool water province gcwp are recognized the ncwp is marked by gondolelloides in the early cisuralian dominance of neostreptognathodus and no or rare sweetognathus in the late cisuralian dominance of merrillina and mesogondolella and absence of sweetognathus in the guadalupian and dominance of merrillina and mesogondolella and absence of iranognathus in the lopingian the ewwp is characterized by the absence of gondolelloides and vjalovognathus in the cisuralian abundance of sweetognathus and pseudosweetognathus in the kungurian late cisuralian jinogondolella and sweetognathus in the guadalupian and clarkina and iranognathus in the lopingian the gcwp is marked by vjalovognathus merrillina in the cisuralian vjalovognathus merrillina and mesogondolella in the guadalupian and vjalovognathus and merrillina in the lopingian mixed faunas are recognized in regions bordering between the ewwp and gcwp including western timor during the artinskian pamirs during the kungurian and the salt range during the guadalupian and lopingian three different conodont zonations are proposed one for each of the three conodont provinces four potential horizons for inter provincial correlation of permian conodonts are recognized they are in ascending order 1 the first appearance of sweetognathus whitei which is closely related to the last occurrence of carboniferous type conodonts such as streptognathodus and adetognathus 2 the first appearance of neostreptognathodus pequopensis 3 the base of the jinogondolella nankingensis zone and 4 the base of the clarkina postbitteri iranognathus erwini zone the spatial and temporal distribution pattern of permian conodonts suggests that temperature is the primary controlling factor evolution of permian conodont provincialism reveals a glaciation during the asselian and sakmarian a global warming during the artinskian a climate cooling in north pangea during the kungurian a continuation of kungurian climate trends in the guadalupian a relatively minor warming during the wuchiapingian a returned cooling in the changhsingian and lower and middle griesbachian and a global warming in the late griesbachian which ended the permian conodont lineage

tomographic image of p velocity structure beneath kilauea s east rift zone and south flank seismic evidence for a deep magma body we present first results from the analysis of p wave arrival time data recorded from november 11 to december 31 1999 by a temporary 29 station network installed across kilauea volcano s east rift zone erz and south flank sf on hawaii augmented by data from the permanent network of the hawaiian volcano observatory starting with the inversion result for a minimum 1d velocity model we use arrival time data from 135 local earthquakes to invert for the 3d p velocity structure the resulting tomographic image shows evidence for a deep magma body beneath the erz just east of its southward bend and a smaller magma body at about 5 km depth beneath the wnw ese trending segment of the erz we also observe a drastic change in velocities south of the hilina fault system from velocities around 5 5 km s in the west to 6 5 km s to the east

timing of porphyry cu mo and base metal zn pb ag cu mineralisation in a magmatic hydrothermal system morococha district peru the morococha district in central peru is characterised by economically important cordilleran polymetallic zn pb ag cu vein and replacement bodies and the large toromocho porphyry cu mo deposit in its centre u pb re os and 40ar 39ar geochronology data for various porphyry related hydrothermal mineralisation styles record a 3 5 ma multi stage history of magmatic hydrothermal activity in the district in the late miocene three individual magmatic hydrothermal centres were active the codiciada toromocho and ticlio centres each separated in time and space the codiciada centre is the oldest magmatic hydrothermal system in the district and consists of a composite porphyry stock associated with anhydrous skarn and quartz molybdenite veins the hydrothermal events are recorded by a titanite u pb age at 9 3 0 2 ma and a molybdenite re os age at 9 26 0 03 ma these ages are indistinguishable from zircon u pb ages for porphyry intrusions of the composite stock and indicate a time span of 0 2 ma for magmatic hydrothermal activity the small ticlio magmatic hydrothermal centre in the west of the district has a maximum duration of 0 3 ma ranging from porphyry emplacement to porphyry mineralisation at 8 04 0 14 ma 40ar 39ar muscovite cooling age the toromocho magmatic hydrothermal centre has a minimum of five recorded porphyry intrusions that span a total of 1 3 ma and is responsible for the formation of the giant toromocho cu mo deposit at least two hydrothermal pulses are identified post dating a first pulse of molybdenite mineralisation wide spread hydrous skarn covers an area of over 6 km2 and is recorded by five 40ar 39ar cooling ages at 7 2 6 8 ma these ages mark the end of the slowly cooling and long lived toromocho magmatic hydrothermal centre soon after last magmatic activity at 7 26 0 02 ma district wide 50 km2 cordilleran base metal vein and replacement bodies post date the youngest recorded porphyry mineralisation event at toromocho by more than 0 5 ma polymetallic veins 5 78 0 10 and 5 72 0 18 ma 40ar 39ar ages and the manto italia polymetallic replacement bodies 6 23 0 12 and 6 0 0 2 ma 40ar 39ar ages are interpreted to have been formed by a single hydrothermal pulse hydrothermal activity ceased after the formation of the base metal vein and replacement bodies overlapping monazite u pb 8 26 0 18 ma and muscovite 40ar 39ar ages 8 1 0 5 ma from the early base metal stage of one cordilleran vein sample in the sulfurosa area provide evidence that a discrete hydrothermal pulse was responsible for polymetallic vein formation 2 6 ma prior to the district wide polymetallic veins these ages pre date those of toromocho porphyry cu mo formation and show that zn pb ag cu mineralisation formed during several discrete magmatic hydrothermal pulses in the same district

slow slip and tremor search at kilauea volcano hawaii 1 kilauea volcano hawaii has hosted a long series of slow slip events observed since the installation of the continuous gps network in 1996 kilauea s slow slip events are inferred to occur on the decollement fault at 8 km depth beneath its south flank with a location updip of the epicenters of large regular earthquakes fault slip typically lasts about two days and the events have magnitudes equivalent to mw 5 3 6 0 while slow slip events in subduction zones are commonly accompanied by tectonic tremor also called nonvolcanic tremor no tremor has yet been reported in association with kilauea s slow slip events instead there are swarms of small triggered earthquakes which is a characteristic only seen at select subduction zones e g boso and hikurangi a temporary array of seismometers was installed at kilauea in 2007 in anticipation of a slow slip event here we use several established methods to perform a systematic search for tectonic tremor during geodetically defined slow slip events as well as searching for tremor triggered by teleseismic surface waves we do not detect tectonic tremor using any of these methods although we are able to detect episodes of previously identified deep offshore volcanic tremor at 15 20 km depth and volcanic tremor from kilauea although kilauea s seismic network may not be adequate to observe tectonic tremor because hawaii is seismically noisy and its crust is highly attenuating it is also possible that the specific fault conditions on kilauea s decollement are not conducive to such tremor generation

u pb re os and 40ar 39ar geochronology of the nambija au skarn and pangui porphyry cu deposits ecuador implications for the jurassic metallogenic belt of the northern andes new u pb re os and 40ar 39ar dates are presented for magmatic and hydrothermal mineral phases in skarn and porphyry related ores from the nambija and pangui districts of the subandean zone southeastern ecuador nambija has been one of the main gold producing centers of ecuador since the 1980s due to exceptionally high grade ores average 15 g t but frequently up to 300 g t au pangui is a recently discovered porphyry cu mo district the geology of the subandean zone in southeastern ecuador is dominated by the i type subduction related jurassic zamora batholith which intrudes triassic volcanosedimentary rocks the zamora batholith is in turn cut by porphyritic stocks which are commonly associated with skarn formation and or porphyry style mineralization high precision u pb and re os ages for porphyritic stocks u pb zircon associated prograde skarn u pb hydrothermal titanite and retrograde stage skarn re os molybdenite from veins postdating gold deposition of the nambija district are all indistinguishable from each other within error 145 ma and indicate a late jurassic age for the gold mineralization previously gold mineralization at nambija was considered to be early tertiary based on k ar ages obtained on various hydrothermal minerals the new jurassic age for the nambija district is slightly younger than the 40ar 39ar and re os ages for magmatic hydrothermal minerals from the pangui district which range between 157 and 152 ma mineralization at nambija and pangui is associated with porphyritic stocks that represent the last known episodes of a long lived jurassic arc magmatism 190 to 145 ma a jurassic age for mineralization at nambija and pangui suggests that the northern andean jurassic metallogenic belt which starts in colombia at 3 n extends down to 5 s in ecuador it also adds a new mineralization style au skarn to the metal endowment of this belt

seismological evidence on the geometry of the orogenic system in central northern ecuador south america analysis of the spatial distribution of seismicity beneath central ecuador from a temporary network gives new insights on two main points of the ecuadorian tectonics major structures in the ecuadorian andes are east dipping late jurassic to paleogene sutures reactivated by present day compression the oceanic plate is plunging continuously down to a depth of about 200 km with a dip of 25 35 we also show that the coastal plain acts as a buttress transmitting stresses to the andes beneath which deformation is concentrated

kilauea slow slip events identification source inversions and relation to seismicity 1 several slow slip events beneath the south flank ofkilauea volcano hawaii have been inferred from transient displacements in daily gps positions to search for smaller events that may be close to the noise level in the gps time series we compare displacement fields on kilauea s south flank with displacement patterns in previously identified slow slip events matching displacement patterns are found for several new candidate events although displacements are much smaller than previously identified events one of the candidates 29 may 2000 is coincident with a microearthquake swarm as are all of the previously identified slow slip events the microearthquakes follow the onset of slow slip implying that they are triggered by stress changes during slip the new slow slip event brings the total number of events on kilauea between 1997 and 2007 to eight the smallest having m w 5 3 and the largest having m w 6 0 while the recurrence time between the four largest events is 2 11 0 01 years the repeat time for all eight events is 0 9 0 6 years we invert for the fault geometry and distribution of slip during the slow slip events the optimal source depths of 5 km assuming uniform slip dislocations in an elastic half space are considerably shallower than the accompanying swarm earthquakes 6 5 8 5 km which would place the earthquakes in a zone of decreased coulomb stress inversions including the effects of topography and layered elastic structure in the forward models favor depths comparable to microearthquake depths such that the earthquakes are located in a region of increased coulomb stress we also invert for time dependent fault slip directly from the 30 s gps phase observations constraining the source to the optimal uniform slip geometry on the basis of these inversions the larger events last between 1 5 2 2 days the data are unable to resolve migration of slip along the fault the temporal pattern of accompanying microearthquakes is consistent with the fault slip history assuming a seismicity rate theory based on rate and state friction making the swarm earthquakes coshocks and aftershocks of the slow slip events

crustal structure of mauna loa volcano hawaii from seismic refraction and gravity data abstract in october 1978 the u s geological survey established a 100 km long seismic refraction profile normal to the kona coast of hawaii island analysis of these data along with available gravity data suggest that the oceanic crust dips about 3 landward under the submerged flank of the island increasing to 8 5 under the kona coast maximum vertical deflection of the base of crust from beneath the deep ocean to a point beneath the summit of mauna loa is about 9 km high velocity high density rocks vp about 7 1 km sec density about 2 9 gm cm 3 comprise the bulk of the volcanic edifice and reach to within a few kilometers of the surface beneath the north flank of mauna loa the data also suggest that an elongate high velocity high density body lies parallel to the kona coast just below the surface this body probably represents an extinct buried rift zone

laramide porphyry cu mo mineralization in northern mexico age constraints from re os geochronology in molybdenite twenty five new re os molybdenite ages for nine porphyry copper molybdenum deposits from northern mexico constrain the timing of mineralization and the longevity of porphyry systems in this region the ages of all the deposits are between 50 and 61 ma i e paleocene to early eocene and are associated with the laramide orogeny the oldest deposits are those from the cananea district and include the el alacran prospect 61 ma the maria deposit 60 ma the current cananea mine and la colorada breccia 59 ma the age of mineralization at cumobabi also is 59 ma and it was followed by the emplacement of deposits at suaqui verde and cuatro hermanos at about 57 to 56 ma the malpica prospect the southernmost porphyry copper prospect in western mexico was emplaced at 54 ma the la caridad deposit in nacozari and the el creston prospect both have re os molybdenite ages of 54 ma the tameapa prospect has a protracted hydrothermal mineralization history with multiple molybdenite mineralization events at 57 52 to 53 and 50 ma total re and 187 os concentrations for molybdenites range from 10 424 to 26 ppm and from 6 641 to 14 ppb respectively the deposit with the highest re and os concentrations is el alacran and the lowest concentrations are found in el creston the ages determined support the formation of porphyry copper deposits in northern mexico during the laramide orogeny in general the ages of porphyry copper deposits in the north american province range from 76 ma at bagdad arizona to 50 ma at tameapa sinaloa the ages also show that porphyry copper mineralization occurred continuously between these two dates with two main episodes at 60 ma cananea district mexico and sierrita and copper creek united states and at 54 ma la caridad el creston malpica in mexico and morenci united states

physiographic and tectonic settings of high sulfidation epithermal gold silver deposits of the andes and their controls on mineralizing processes abstract gold and silver ores in the vast majority of andean high sulfidation epithermal au ag deposits occur at high present day elevations and typically 200 500 m below low relief landforms situated at 3500 to 5200 m a s l most deposits are middle miocene and younger and include el indio tambo pascua lama veladero el indio belt chile argentina cerro de pasco central peru pierina lagunas norte yanacocha northern peru quimsacocha ecuador and the california vetas mining district santander colombia jointly accounting for 130 moz au resources slightly older examples are only preserved in the atacama desert and include the middle eocene el guanaco and el hueso and the late oligocene early miocene la coipa deposits the absence of paleocene and older high sulfidation epithermal deposits can be explained by limited preservation potential imposed by transpressional tectonics within overall contractile episodes and surface uplift these conditions prevailed predominantly in segments of shallow angle subduction of the nazca or caribbean plate below the south american continent a tectonic setting also common for porphyry style cu au mo deposits stratovolcanoes are uncommon ore hosts and volcanic rocks coincident with mineralization are in most cases volumetrically restricted or absent recording the terminal stages of local arc magmatism however dacitic domes are important at e g yanacocha and la coipa at lagunas norte a small stratovolcano largely pre dating but temporally overlapping with mineralization occurs immediately east of the deposit and volcanic sector collapse may have occurred during hydrothermal activity mineralization is typically located near the backscarp of pediments or the heads of valleys incising now high elevation low relief surfaces in the california vetas mining district and el indio belt hydrothermal alunite ages become generally younger upstream along the incising valleys indicating that hydrothermal activity and by inference ore deposition were facilitated by erosion the lowering of the water table and reduction of hydrostatic and lithostatic pressure at these sites of high local relief are believed to have enhanced both boiling and mixing of magmatic with meteoric fluids ultimately enhancing ore deposition the host rock composition permeability and location of the water table control the distribution of alteration zones and ore intermediate volcanic rocks are the most common ore hosts but they typically pre date mineralization by several ma however high sulfidation epithermal mineralization can be hosted in any conceivable rock type including high grade metamorphic rocks california vetas mining district significantly older plutonic rocks pascua lama or quartzites lagunas norte large vuggy quartz alteration zones and commonly oxidized low grade large tonnage mineralization are best developed in relatively permeable volcaniclastic rocks or hydrothermal breccia bodies whereas coherent volcanic plutonic or metamorphic rocks may host fault and breccia controlled ores the near surface steam heated zone can attain a thickness of several hundred meters in dry climates e g veladero pascua lama tambo but is typically poorly developed and less than 20 m thick in humid climatic zones the physiographic and tectonic settings of high sulfidation epithermal deposits are distinct from low sulfidation epithermal districts such as those of patagonia el penon chile or fruta del norte ecuador the latter range to significantly older ages jurassic to early eocene occur at mainly lower elevations and were emplaced in extensional settings a temporal coincidence between uplift erosion and mineralizing processes as well as a spatial and temporal association with porphyry style mineralization is not evident for these low sulfidation districts

tectonic segmentation of the north andean margin impact of the carnegie ridge collision the north andean convergent margin is a region of intense crustal deformation with six great subduction earthquakes mw 7 8 this century the regional pattern of seismicity and volcanism shows a high degree of segmentation along strike of the andes segments of steep slab subduction alternate with aseismic regions and segments of flat slab subduction this segmentation is related to heterogeneity on the subducting nazca plate in particular the influence of the carnegie ridge collision is investigated four distinct seismotectonic regions can be distinguished region 1 from 6on to 2 5on with steep ese dipping subduction and a narrow volcanic arc region 2 from 2 5on to 1os showing an intermediate depth seismic gap and a broad volcanic arc region 3 from 1os to 2os with steep ne dipping subduction and a narrow volcanic arc region 4 south of 2os with flat subduction and no modern volcanic arc the carnegie ridge has been colliding with the margin since at least 2 ma based on examination of the basement uplift signal along trench parallel transects the subducted prolongation of carnegie ridge may extend up to 500 km from the trench as suggested by the seismic gap and the perturbed broad volcanic arc these findings conflict with previous tectonic models suggesting that the carnegie ridge entered the trench at 1 ma furthermore the anomalous geochemical adakitic signature of the volcanoes in the broad ecuador volcanic arc and the seismicity pattern are proposed to be caused by lithospheric tears separating the buoyant shallowly subducting carnegie ridge from segments of steep subduction in regions 1 and 3 it is further suggested that carnegie ridge supports a local flat slab segment similar to that observed in peru the impact of the carnegie ridge collision on the upper plate causes transpressional deformation extending inboard to beyond the volcanic arc with a modern level of seismicity comparable to the san andreas fault system the pattern of instrumental and historical seismicity indicates 1 great earthquakes on the northern and southern flanks of the colliding ridge 2 a slight reduction in observed seismicity at the trench ridge intersection 3 increased stress far into the continent and 4 a nne displacement of the n andes block to be further effects of the collision 1999 elsevier science b v all rights reserved

cenozoic continental arc magmatism and associated mineralization in ecuador most of the economic ore deposits of ecuador are porphyry cu and epithermal style gold deposits associated with tertiary continental arc magmatism this study presents major and trace element geochemistry as well as radiogenic isotope pb sr signatures of continental arc magmatic rocks of ecuador of eocene to late miocene 50 9 ma elm and late miocene to recent 8 0 ma lmr ages the most primitive elm and lmr rocks analyzed consistently display similar trace element and isotopic signatures suggesting a common origin most likely an enriched morb type mantle in contrast major and trace element geochemistry as well as radiogenic isotope systematics of the whole sets of elm and lmr samples indicate strikingly different evolutions between elm and lmr rocks the elm rocks have consistently low sr y increasing rb sr and decreasing eu gd with sio2 suggesting an evolution through plagioclase dominated fractional crystallization at shallow crustal levels 20 km and most likely at sub crustal levels 40 50 km the change in geochemical signatures of tertiary magmatic rocks of ecuador from the elm to the lmr type coincides chronologically with the transition from a transpressional to a compressional regime that occurred at 9 ma and has been attributed by other investigations to the onset of subduction of the aseismic carnegie ridge

flexure and seismicity beneath the south flank of kilauea volcano and tectonic implications we present a refined model for the tectonic behavior of kilauea volcano s south flank including flexure calculations and microearthquake data supportive of the model in our model the south flank moves seaward over the downwardly flexed ocean crust in a manner analogous to an accretionary prism in a subduction zone the flank is driven seaward by the gravitational stresses inherent in its shape this driving force is augmented by high density material in kilauea s rift zones elastic flexure calculations predict a configuration for the downwardly flexed crust which agrees with previous seismic refraction and gravity modeling this configuration in turn is consistent with the hypothesis that many earthquakes occur along the volcanic pile ocean crust interface focal mechanisms for these events predominantly indicate southeastward directed overthrusting we also propose a relationship between rift zone intrusion and south flank displacement including a suggestion that the decollement configuration controls the relative activity of kilauea s east and southwest rift zones

quaternary state of stress in the northern andes and the restraining bend model for the ecuadorian andes inversion of shallow focal mechanisms in the northern andes together with a neotectonic analysis of the ecuadorian andes shows that the state of stress is homogeneous in most of the northern andes e w trending 1 however north of 5 n 1 is roughly nw se trending this difference in state of stress is due to the force balance between the nazca caribbean and south american plates south of 5 n the state of stress appears to be mainly controlled by the nazca south american plate interaction while north of 5 n it appears to be mainly controlled by the caribbean south american plate interaction this state of stress difference from south to north is consistent with dextral motions along faults trending parallel to the chain south of 5 n and sinistral motions along faults trending parallel to the chain north of 5 n this inversion of shallow focal mechanisms also illustrates the incomplete strain partitioning of the oblique convergence between the nazca and south american plates along the ecuadorian southern colombian trench the convergence obliquity that increases northward controls the active transcurrent fault slip rate in the upper plate finally this convergence obliquity is responsible for the location of the seismicity in the upper plate in addition the andean block is considered in this paper as a large triple zone under constriction with one of its borders caribbean behaving partly as a free border

special paper major gold deposits and belts of the north and south american cordillera distribution tectonomagmatic settings and metallogenic considerations a compilation of economically viable gold concentrations containing 10 moz in the north and south american cordillera reveals the existence of 22 discrete belts in addition to five major isolated deposits most formed over the last 150 m y the gold concentrations are attributed to eight widely recognized deposit types of which porphyry sediment hosted and high sulfidation epithermal are economically the most important individual gold belts are typically several tens to hundreds of kilometers long dominated by single deposit types and metallogenically active for relatively brief periods 5 20 m y many of the gold belts and major isolated deposits were generated under extensional or transtensional tectonic conditions in either arc or back arc settings nevertheless the two main high sulfidation epithermal gold belts were generated in thickening or already thickened crust during low angle subduction eight other gold belts or districts also accompanied compression or transpression with two of them the main orogenic gold belts occupying fore arc sites there is a strong suggestion that the preeminent cordilleran gold concentrations formed either during or immediately following prolonged contraction the major gold deposits and belts occur along the craton edge as well as in adjoining accreted terranes but almost all are of postaccretionary timing many of the gold belts and isolated deposits were localized by crustal scale faults or lineaments which may be either parallel or transverse to the cordilleran margin the gold concentrations accumulated during active subduction commonly in close spatial and temporal association with intermediate to felsic medium to high k calc alkaline igneous rocks by contrast the low sulfidation epithermal gold deposits accompany bimodal volcanic pulses of calc alkaline tholeiitic or alkaline affinity however a gold alkaline rock association is uncommon a genetic link between gold mineralization and coeval magmatism is widely accepted for most of the deposit types the exceptions being the sediment hosted and orogenic gold deposits notwithstanding the small cumulative extent of the gold concentrations relative to the entire cordilleran margin there is a marked tendency for two or more belts or isolated deposits of different ages and genetic types to occur in close proximity within relatively restricted arc including fore and back arc segments in the case of the western united states for example six belts and four isolated major deposits make up a particularly prominent cluster if fortuity is discounted this clustering or pairing of gold concentrations must imply a predisposition of certain arc segments to gold mineralization an analogous situation is evident for other metals particularly copper and tin the reason for the recurrent generation of major deposits and belts dominated by one or more metals remains uncertain although heterogeneously distributed metal preconcentrations favorable redox conditions or other parameters somewhere above the subducted slab between the mantle wedge and upper crust are widely contemplated possibilities elucidation of the reason s for this metallogenic inheritance at the scale of limited arc segments poses an important and challenging series of research questions as well as being critical to the planning of potentially successful greenfield exploration programs

imaging the crustal magma sources beneath mauna loa and kilauea volcanoes hawaii three dimensional seismic p wave traveltime tomography is used to image the magma sources beneath mauna loa and kilauea volcanoes hawaii high velocity bodies 6 4 km s in the upper 9 km of the crust beneath the summits and rift zones of the volcanoes correlate with zones of high magnetic intensities and are interpreted as solidified gabbro ultramafic cumulates from which the surface volcanism is derived the proximity of these high velocity features to the rift zones is consistent with a ridge spreading model of the volcanic flank southeast of the hilina fault zone along the south flank of kilauea low velocity material

the andean orogenic period and its major structures in central and northern peru the andean orogenic period began in the albian and consisted of at least 6 discrete compressional phases which are albian to late miocene in age deformation migrated progressively toward the amazonian foredeep the major andean structures in central and northern peru are related to the eocene incaic early miocene quechua 1 and late miocene quechua 3 phases the maranon thrust and fold belt mtfb which bounds the western cordillera to the ne rose in the eocene it was reactivated partly by the quechua 1 phase which also folded the altiplano farther e and possibly part of the eastern cordillera the sub andean thrust and fold belt stfb is related to the quechua 3 phase in both mtfb and stfb the imbricate thrusts merge at depth in large decollement faults gravity sliding does not play a dominant role for these faults have to be rooted westward in the pre andean basement the corresponding crustal shortening played a significant part in the creation of the sialic root of the andes

neogene stratigraphy and andean geodynamics of southern ecuador abstract the present paper reviews tertiary volcanic and sedimentary formations in the inter andean region of southern ecuador between 2 s and 4 20 s in order to develop a geodynamic model of the region the formations occur in the southern shallow prolongation of the inter andean valley between the cordillera real to the east and the cordillera occidental and amotape tahuin provinces to the west one hundred fifty zircon fission track analyses has established a detailed chronostratigraphy for the sedimentary and volcanic formations and several small intrusions the paleogene to early miocene formations are dominated by intermediate and acidic volcanic and pyroclastic rocks in addition relics of eocene continental sedimentary series have been identified the neogene sedimentary series lie unconformably on deformed and eroded metamorphic sedimentary and volcanic formations they were deposited in two stages which are separated by a major unconformity dated at 10 9 ma 1 during the middle and early late miocene 15 10 ma marginal marine deltaic lagoonal lacustrine and fluvial environments prevailed which we group under the heading pacific coastal sequences they presumably covered a greater surface area in southern ecuador than their present occurrence in small topographic depressions we suggest that they were deposited in the shallow marine cuenca and loja embayments deposition in a marginal marine environment is also supported by the occurrence of brackish water ostracods and other fauna 2 above the regional angular unconformity the coastal facies are overlain by late miocene 9 5 ma continental alluvial fan and fluvial facies which are in turn covered by mainly airborne volcanic material they represent the intermontane sequences of the basins of cuenca giron santa isabel nabon loja and malacatos vilcabamba sedimentologic and stratigraphic results are used to discuss the tectonic setting of neogene sedimentation in the forearc and arc domain of the ecuadorian subduction system during the pacific coastal stage northward displacement of the coastal forearc block along the calacali pallatanga fault zone has driven crustal collapse in the inter andean region as a result extensional subsidence drove the eastward ingression of shallow seas into the cuenca and loja embayments from the manabi and progreso basins to the west tectonic inversion in the forearc area during the early late miocene at 9 5 ma reflects the initiation of w e oriented compression and uplift in the inter andean region and the establishment of smaller intermontane stage basins which host the continental sequences coeval topographic rise of the cordillera occidental is indicated by the onset of clastic input from the west the small intermontane basin of nabon 8 5 7 9 ma formed during the period of maximum compression the present data prove that the neogene andean forearc and arc area in southern ecuador was a site of important but variable tectonic activity which was presumably driven by the collision and coupling of the carnegie ridge with the ecuadorian margin since 15 9 ma

late pleistocene stratigraphy and micropaleontology of a part of the eurasian basin fram basin central arctic ocean during the 1979 lomonosov ridge experiment lorex 12 short gravity cores were collected from the fram basin part of the eurasian basin on the eastern flank of the lomonosov ridge sediments of these cores are organized into 11 lithologic units that constitute the first stratigraphy for any part of the deeper eurasian basin foraminifera are the same species that have been described elsewhere in the central arctic ocean but are abundant only in the uppermost part of the cores neogloboquadrina pachyderma is the most abundant species but the presence ofeponides tumidulus horvathi andstetsonia arctica in core ssk 2 provide a general chronologic framework for interpreting the fram basin sediment the stratigraphy a k is unique and is only partially correlated with other sediments of the north polar region including that of the adjacent lomonosov ridge and makarov basin amerasian basin differences in stratigraphies of the lomonosov area are interpreted to be at least in part the result of winnowing by turbidity currents and by currents crossing the ridge from the fram basin toward the makarov basin the sediment consists of silty lutites and sandy lutites as well as laminated lutites interpreted to have been deposited as a result of glacial marine and turbidite sedimentation these short cores document the same sedimentary processes in part of the arctic ocean east of the lomonosov ridge as have been previously reported for the western amerasian basin

development of the gulf of guayaquil ecuador during the quaternary as an effect of the north andean block tectonic escape 1 interpretation of industrial multichannel seismic profiles and well data are used to identify the main tectonic features of the gulf of guayaquil gg area these include two e w trending major detachments the posorja and the jambeli detachment systems which represent half grabens with oppositely dipping detachments to the south and to the north respectively the ne sw trending puna santa clara fault system developed as a transfer fault system between the posorja and the jambeli detachments the esperanza and the jambeli basins exhibit 3 4 km of sediment that accumulated during the past 1 6 1 8 myr the puna santa clara fault system bounds the esperanza and the jambeli basins evidencing that the evolution of these basins is tightly controlled by the two detachments at depth to the west the n s trending domito fault system bounding the posorja detachment system and the esperanza basin to the west acted as a transfer zone between the shelf area and the continental slope the pliocene series show no significant variations in thickness throughout the gulf of guayaquil area suggesting that no important tectonic deformation occurred from 5 2 to 1 8 1 6 ma the major period of tectonic deformation in the gulf of guayaquil area occurred during the pleistocene times three main tectonic steps are identified from early pleistocene to 180 ka major subsidence occurred along the esperanza and jambeli basins from 180 to 140 ka most of the gulf of guayaquil area was above sea level during the isotope substage 6 low stand from 140 ka to present tectonic activity is restricted along the normal faults bounding the esperanza basin the tenguel fault and the puna santa clara and domito fault systems a n s trending tensional stress regime characterizes the pleistocene times throughout the northward drifting of the north andean block is proposed to control the tectonic evolution and associated subsidence of the gulf of guayaquil area it is also accepted that the collision of the carnegie ridge with the trench axis has to play a major role in controlling the north andean block northward drift because the carnegie ridge subduction is possibly an ongoing process which began prior to the pliocene we postulate the along strike morphology of the ridge at the origin of interplate coupling variations the subduction of an along strike positive relief of the ridge is proposed at the origin of the major tectonic reorganization of the gg area occurring at 1 8 1 6 ma

lithospheric flexure under the hawaiian volcanic load internal stresses and a broken plate revealed by earthquakes several lines of earthquake evidence indicate that the lithospheric plate is broken under the load of the island of hawai i where the geometry of the lithosphere is circular with a central depression the plate bends concave downward surrounding a stress free hole rather than bending concave upward as with past assumptions earthquake focal mechanisms show that the center of load stress and the weak hole is between the summits of mauna loa and mauna kea where the load is greatest the earthquake gap at 21 km depth coincides with the predicted neutral plane of flexure where horizontal stress changes sign focal mechanism p axes below the neutral plane display a striking radial pattern pointing to the stress center earthquakes above the neutral plane in the north part of the island have opposite stress patterns t axes tend to be radial the m6 2 honomu and m6 7 kiholo main shocks both at 39 km depth are below the neutral plane and show radial compression and the m6 0 kiholo aftershock above the neutral plane has tangential compression earthquakes deeper than 20 km define a donut of seismicity around the stress center where flexural bending is a maximum the hole is interpreted as the soft center where the lithospheric plate is broken kilauea s deep conduit is seismically active because it is in the ring of maximum bending a simplified two dimensional stress model for a bending slab with a load at one end yields stress orientations that agree with earthquake stress axes and radial p axes below the neutral plane a previous inversion of deep hawaiian focal mechanisms found a circular solution around the stress center that agrees with the model for horizontal faults the shear stress within the bending slab matches the slip in the deep kilauea seismic zone and enhances outward slip of active flanks

distribution of porphyry copper deposits along the western tethyan and andean subduction zones insights from a paleotectonic approach abstract along the western tethyan and andean subduction zones the distribution of cretaceous and cenozoic porphyry cu deposits is not random and shows that they were emplaced in distinct regional clusters to understand the appearance of these clusters within their geodynamical contexts and identify kinematic features which would favor the genesis of porphyry type ore bodies we use a paleotectonic approach two clusters in the aegean balkan carpathian area which were emplaced in upper cretaceous and oligo miocene and two others in the andes which were emplaced in late eocene and miocene are sufficiently well constrained to be studied in detail it appears that they are associated with a specific polyphased kinematic context related to the convergence of tectonic plates this context is characterized by 1 a relatively fast convergence rate shortly followed by 2 a drastic decrease of this rate from these observations and assuming that the major part of plate convergence is accommodated along subduction zones we propose a two phase geodynamic model favoring emplacement of porphyry cu deposits 1 a high melt production in the mantle wedge followed by 2 an extensional regime or at least relaxation of the compressional stress in the upper plate promoting ascension of fertile magmas to the upper crust melt production at depth and the following extensional regime which would be related to variations in convergence rate are thus associated with variations in plate and trench velocities themselves being controlled by both plate kinematics at the surface and slab dynamics in the upper mantle in particular along strike folding behavior of the subducting slab may strongly influence trench velocity changes and the location of porphyry cu deposits metallogenic data suggest that periods of slab retreat which would favor mineralization processes during 40 myrs would be separated by barren periods lasting 10 to 20 myrs corresponding to shorter episodes of trench advance as observed in laboratory experiments these results confirm the control of the geodynamic context and especially subduction dynamics on the genesis of porphyry cu deposits this study also shows that the paleotectonic approach is a promising tool that could help identify geodynamic and tectonic criteria favoring the genesis of various ore deposits

mantle fault zone beneath kilauea volcano hawaii relocations and focal mechanism analyses of deep earthquakes 13 kilometers at kilauea volcano demonstrate that seismicity is focused on an active fault zone at 30 kilometer depth with seaward slip on a low angle plane and other smaller distinct fault zones the earthquakes we have analyzed predominantly reflect tectonic faultingin the brittle lithosphere rather than magma movement associated with volcanic activity the tectonic earthquakes may be induced on preexisting faults by stresses of magmatic origin although background stresses from volcano loading and lithospheric flexure may also contribute

some aspects of the permian triassic boundary ptb and of the possible causes for the biotic crisis around this boundary abstract the first appearance datum fad of hindeodus parvus is an excellent datum very close to the base of the otoceras woodwardi zone priority base of the triassic for the first time it allows an exact correlation of the ptb in all marine facies and faunal realms the following features of the extinction and recovery patterns near the ptb are most important for the search for causes of the ptb biotic crisis 1 most strongly affected were the siliceous plankton radiolarians and the warm water benthos and nekton 2 most of the cold water faunas were not significantly affected 3 the recovery of the warm water benthos and siliceous plankton occurred only after an unusually long time during the late olenekian and middle triassic 4 the productivity of the terrestrial plants dropped strongly and the recovery was mainly in the upper olenekian and in the middle triassic 5 several terrestrial extinction events occurred at different levels within the upper permian considerable before the marine ptb at or close to the fad of lystrosaurus no extinction event in the terrestrial faunas can be observed 6 terrestrial faunal elements that survived the dzhulfian dorashamian extinctions were able to survive some months of extreme climatic conditions by hibernation like life stages vertebrates or by dry and freezing resistant eggs conchostracans 7 about 50 of the genera that disappeared at the ptb re appeared in the olenekian middle triassic interval lazarus taxa or in this time interval genera appeared that had undoubtedly evolved from genera that had disappeared at the ptb and 8 the ptb is preceded by mass occurrences of marine and continental fungi and the fungal spike ends abruptly a little before the ptb a scenario for the ptb biotic crisis is elaborated that takes into consideration the real not interpolated diversity patterns of different marine and continental fossil groups the exact correlation of bioevents in different faunal realms and facies the strong biotic crisis in the tethyan warm water faunas in contrast to the much weaker biotic event in cold water faunas the severe dzhulfian dorashamian climate in many parts of the world caused by the continent ocean configuration and by siberian trap volcanism the cooling of the boreal area by the northward drift of pangaea that interrupted the exchange of warm water benthos between the tethys and western north america during the guadalupian the extinction event at the guadalupian lopingian boundary that restricted most of the affected warm water faunas to the tethys the importance of lower scythian anoxia that reached an unusually shallow level and above all the effects of the contemporaneous huge volcanic events about 250 m y ago on the siberian platform and in the eastern tethys that caused a 3 6 months lasting volcanic winter with strong cooling in low latitudes followed by a strong global warming

u pb zircon and titanite systematics of the fish canyon tuff an assessment of high precision u pb geochronology and its application to young volcanic rocks a large data set of single and multi grain zircon and titanite analyses from a sample of the oligocene fish canyon tuff fct a voluminous ash flow from the san juan mountains of colorado and widely used 40ar 39ar geochronological standard has been used to evaluate the influence of various sources of analytical and geological uncertainty on the calculated age of this tuff by the isotope dilution u pb zircon method twenty three single zircon grains and seven small multi grain fractions of the fct yield an inverse variance weighted mean 206pb 238u date of 28 402 0 023 ma 2 mswd 0 93 and a slightly older weighted mean 207pb 235u date of 28 529 0 030 ma mswd 0 74 which are insensitive to common pb corrections initial 230th disequilibria calculated from a newly measured th u 2 2 for fct pumice shards indicate th deficiency for these zircons its correction brings the weighted mean 206pb 238u date to 28 478 0 024 mswd 0 97 minimizing the discordance of the fct zircon analyses these calculations culminate in concordia ages ludwig 1998 for the crystallization of the fct zircons of 28 476 0 029 ma mswd 1 50 without propagating decay constant errors or 28 498 0 035 ma mswd 1 03 with propagated decay constant errors these results are in close agreement with a previous single grain 206pb 238u zircon date of 28 41 0 05 ma for the fct oberli et al 1990 however they do not corroborate the discordia lower intercept date of 27 52 0 09 put forth by lanphere and baadsgard 2001 the 28 476 0 064 ma concordia age for fct zircons including systematic decay constant errors and uncertainty in pb u tracer calibration is substantially older than all published 40ar 39ar sanidine ages which range from 27 5 to 28 05 ma lanphere and baadsgaard 1997 renne et al 1998 a lengthy period 400 k y of zircon residence in the magma chamber before eruption is commonly called upon to explain the age discrepancy however fct titanite which may remain open to pb diffusive exchange until quenching upon eruption yield a minimum 230th disequilibrium corrected weighted mean 206pb 238u age of 28 395 0 049 ma 0 078 with tracer uncertainty weakening residence time arguments and supporting recent calls for re evaluation of the 40k decay constant and the accepted ages for commonly used 40ar 39ar mineral standards the fct zircon concordia age also provides an empirical constraint on the decay constants of the u isotopes indicating the relative accuracy of the currently accepted decay constants to within the original counting statistic errors of jaffey et al 1971

overlapping regions of coseismic and transient slow slip on the hawaiian decollement abstract earthquakes and slow slip are different faulting processes that release accumulated stress on different time scales despite nearly two decades of study it is still unclear whether the same section of fault is capable of hosting both slow aseismic and fast seismic slip here we jointly invert gps strong motion records and empirically corrected tsunami waveforms for the 2018 m7 1 hawai i earthquake our inversion results suggest the earthquake had a slow rupture speed of 1 2 km s with a maximum slip of 3 m south east of the hypocenter extending to the south west through an area known to regularly host slow slip events after exploring how the choice of fault geometry and regularization parameters affect the slip distributions of the earthquake and slow slip events we find strong evidence of overlap between the two additionally we perform numerical modeling to simulate fast and slow slip behavior due to the homogeneity of the hawaiian decollement differences in effective stress are likely an important factor that causes the diversity of slip we find that an earthquake can completely penetrate into the slow slip zone provided the effective stress differences between fast and slow slip zones is large enough to facilitate this our results reinforce the idea that an individual section of fault is capable of hosting a variety of distinct slip behaviors this is important for estimating earthquake rupture extent and for better ground motion and tsunami hazard assessment

a re os study of sulfide minerals from the bagdad porphyry cu mo deposit northern arizona usa rhenium and osmium isotopes in sulfide minerals from the bagdad porphyry cu mo deposit have been used to determine timing of mineralization and the source of osmium and by inference ore metals molybdenite chalcopyrite and pyrite were analyzed mainly from the quartz monzonite and porphyritic quartz monzonite units which are characterized by moderate to strong potassic alteration secondary biotite and k feldspar rhenium concentrations in molybdenite are between 330 and 642 ppm four re os analyses of two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite yield a weighted average age of 71 8 0 2 ma 2 analyses of a third sample from a molybdenite vein in precambrian rocks outside of the main ore zone yield a weighted average age of 75 9 0 2 ma 2 and provide evidence of two separate mineralization episodes chalcopyrite samples contain 6 to 12 ppt os and 1 7 to 4 1 ppb re 187os 188os initial ratios are between 0 1 and 0 8 pyrite samples have osmium and rhenium concentrations varying in the range 8 17 ppt and 3 9 6 8 ppb respectively analyses from these pyrite samples yield an eight point isochron with an age of 77 15 ma 2 and an initial 187os 188os ratio of 2 1 0 8 mswd 0 90 the results presented here add to the growing body of work indicating that porphyry type mineralization is produced by long term multiple episodes of magmatism and associated mineralization the data also support the hypothesis that a significant part of the metals and magmas may have a crustal source as has been suggested for other copper deposits and districts in arizona

longevity of porphyry copper formation at quellaveco peru metal introduction at the late paleocene to early eocene quellaveco porphyry copper molybdenum deposit in southern peru spans several phases of quartz monzonite porphyry emplacement and is bracketed by a precursor granodiorite pluton and a late mineral porphyry body that postdates essentially all copper introduction together the u pb ages of zircons from these intrusive rocks show that 1 08 0 58 m y elapsed between the precursor pluton and initiation of stock emplacement the porphyry system was active intermittently for at least 3 25 m y 4 07 0 82 m y and at least three quarters of the copper inventory was deposited in a maximum of 3 12 m y 2 51 0 61 m y recent u pb zircon dating of several other major central andean porphyry copper deposits in combination with other isotopic techniques suggests that 2 5 to 4 m y life spans are commonplace the longevity of porphyry copper systems implied by these studies appears to reflect the protracted time gaps between the multiple intrusions that intermittently replenished porphyry stocks other precise isotopic methods re os 40 ar 39 ar typically document shorter life spans because it is more difficult if not impossible to date the full sequence of events involved in porphyry copper formation

correlations between nazca farallon plate kinematics and forearc basin evolution in ecuador the tertiary evolution of the forearc basins of ecuador shows a close correlation between the changing convergence rate of the farallon and later nazca oceanic plates and continental south america the correlation occurs during the subduction of a relatively young slab and in the late miocene onset of the subduction of the carnegie aseismic ridge the ecuador forearc basins lie on a basement of oceanic crust known as the pinon terrane the accretion of this terrance occurred in the paleocene as the leading edge of the farallon plate the macuchi island arc collided with south america in the middle eocene this forearc terrane was the site of major pull apart basin formation and turbiditic sedimentation coincident with a phase of very rapid convergence between chron 21 and chron 13 48 37 ma this deformation was bounded by the trench and a major dextral strike slip fault zone and resulted in the northward translation of the forearc with respect to continental south america during the oligocene a phase of extension normal to the trend of the active margin occurred coincident with a phase of relatively slow convergence chron 13 to chron 6 37 20 ma this extension was followed in the middle miocene by inversion of most of the forearc basins coincident with a return to relatively fast convergence from chron 6 20 ma to the present day subduction of the carnegie aseismic ridge occurred during this period circa 8 ma to present and may have enhanced the compressive event further northward translation of the forearc silver accompanied this later deformation the relationships outlined for the forearc may be modeled in terms of a dynamic orogenic wedge which responds directly to changes in convergence rate at the subduction zone the convergence rate appears to be an important control on the coupling between the downgoing slab and overriding continental plate

creation of the cocos and nazca plates by fission of the farallon plate abstract throughout the early tertiary the area of the farallon oceanic plate was episodically diminished by detachment of large and small northern regions which became independently moving plates and microplates the nature and history of farallon plate fragmentation has been inferred mainly from structural patterns on the western pacific plate flank of the east pacific rise because the fragmented eastern flank has been subducted the final episode of plate fragmentation occurred at the beginning of the miocene when the cocos plate was split off leaving the much reduced farallon plate to be renamed the nazca plate and initiating cocos nazca spreading some oligocene farallon plate with rifted margins that are a direct record of this plate splitting event has survived in the eastern tropical pacific most extensively off northern peru and ecuador small remnants of the conjugate northern rifted margin are exposed off costa rica and perhaps south of panama marine geophysical profiles bathymetric magnetic and seismic reflection and multibeam sonar swaths across these rifted oceanic margins combined with surveys of 30 20 ma crust on the western rise flank indicate that i localized lithospheric rupture to create a new plate boundary was preceded by plate stretching and fracturing in a belt several hundred km wide fissural volcanism along some of these fractures built volcanic ridges e g alvarado and sarmiento ridges that are 1 2 km high and parallel to absolute farallon plate motion they closely resemble fissural ridges described from the young western flank of the present pacific nazca rise ii for 1 2 m y prior to final rupture of the farallon plate perhaps coinciding with the period of lithospheric stretching the entire plate changed direction to a more easterly nazca like course after the split the northern cocos part reverted to a northeasterly absolute motion iii the plate splitting fracture that became the site of initial cocos nazca spreading was a linear feature that at least through the 680 km of ruptured oligocene lithosphere known to have avoided subduction did not follow any pre existing feature on the farallon plate e g a fracture zone trail of a transform fault iv the margins of surviving parts of the plate splitting fracture have narrow shoulders raised by uplift of unloaded footwalls and partially buried by fissural volcanism v cocos nazca spreading began at 23 ma reports of older cocos nazca crust in the eastern panama basin were based on misidentified magnetic anomalies there is increased evidence that the driving force for the 23 ma fission of the farallon plate was the divergence of slab pull stresses at the middle america and south america subduction zones the timing and location of the split may have been influenced by i the increasingly divergent northeast slab pull at the middle america subduction zone which lengthened and reoriented because of motion between the north america and caribbean plates ii the slightly earlier detachment of a northern part of the plate that had been entering the california subduction zone contributing a less divergent plate driving stress and iii weakening of older parts of the plate by the galapagos hotspot which had come to underlie the equatorial region midway between the risecrest and the two subduction zones by the late oligocene

a possible triggering mechanism for large hawaiian earthquakes derived from analysis of the 26 june 1989 kilauea south flank sequence abstract examination of short period seismic data from the m l 6 1 kilauea south flank earthquake and aftershock sequence indicates that the rupture process in large hawaiian earthquakes is more complex than previously modeled in contrast to the low angle thrust solution determined for the mainshock from long period teleseismic body waves by other workers i find an intermediate to high angle reverse solution i find however that focal mechanisms for coastal aftershocks of m l 3 0 are similar to the teleseismic mechanism for the mainshock a difference in focal mechanisms determined from short period local network seismic data and from long period teleseismic data has been noted for other recent large hawaiian earthquakes both the mapping of surface cracks and the focal mechanism derived from short period seismic data for the m l 6 6 1983 kaoiki earthquake show strike slip motion whereas the centroid moment tensor solution shows low angle thrusting the focal mechanism calculated from short period seismic data for the m l 7 2 1975 kalapana mainshock shows low angle thrusting according to some workers but intermediate to high angle reverse faulting according to others whereas focal mechanisms calculated from long period seismic data show low angle thrusting this result suggests that rupture initiation in large hawaiian earthquakes as represented by the short period focal mechanisms differs significantly from the overall rupture process as represented by the teleseismic mechanisms i propose that small earthquakes trigger the large scale energy release at the bases of the volcanic edifices the type of energy release often observed in large hawaiian earthquakes these triggering events may occur along rupture surfaces that differ from those along which the long period moment release occurs and thus may represent release of a local stress concentration superposed upon the regional stress field

a quantitative approach to the dike intrusion process inferred from a joint analysis of geodetic and seismological data for the 1998 earthquake swarm off the east coast of izu peninsula central japan 1 a series of earthquake swarms off the east coast of izu peninsula central japan is typically associated with dike intrusion around active volcanoes numerous studies in this region have documented the seismic activity and ground deformations without fully resolving the process of dike intrusion this study involves a joint analysis of geodetic and seismic data from the most recent major activity in this region occurring in 1998 to reveal the process of dike intrusion quantitatively we combine data from a dense gps array including 10 temporary stations with seismic analysis published previously we estimate the location of the dikes from seismic data and the volume of intruded magma from geodetic data combined analysis of both data sets enables us to reveal the kinematic process of dike intrusion associated with the 1998 earthquake swarm the process of dike intrusion is quantitatively modeled using the time evolution of recorded dike volume and the use of seismic hypocenters as an indicator of the site of instantaneous dike intrusion on the basis of these observations we propose the following process of the dike intrusion the magma rose upward through a pathway aligned vertically and created a dike when it lost buoyancy we also evaluate the dike intrusion process quantitatively using a model of a circular dike that grows under a continuous magma supply from a deep magma reservoir from the observational data we infer the time evolution in the dike shape pressure distribution and magma viscosity in the dike the acquired viscosity increases over time and it may be reasonable because magma cools gradually however its value is too large compared to typical basaltic magma expected in this region it may represent magma within the dike that is nearly solidified otherwise the magma is supplied intermittently and the dike growth is mainly controlled by the magma supply rate from a deep reservoir the quantitative description of the dike intrusion process in nature described in this study is very rare and our results provide constraints on several parameters that have not been solved in many previous theoretical studies on the dike intrusion process

type of faulting and orientation of stress and strain as a function of space and time in kilauea s south flank hawaii earthquake focal mechanisms of events occurring between 1972 and 1992 in the south flank of kilauea volcano hawaii are used to infer the state of stress and strain as a function of time and space we have determined 870 fault plane solutions from p wave first motion polarities for events with magnitudes m l 2 5 and depth ranging between 6 and 12 km faulting is characterized by a mixture of decollement reverse and normal faults most large earthquakes with magnitude m 7 rupture the decollement plane since it is the only surface large enough to generate magnitude 7 or larger earthquakes the percentage of reverse faulting events is high compared to the decollement and normal faulting mechanisms for the period 1972 1983 the percentage of decollement type focal mechanisms becomes dominant after 1983 this pattern of faulting activity suggests that pressure was building up within kilauea s rift zone prior to the 1983 puu oo eruption overall a single stress orientation with the maximum compressive stress oriented se perpendicular to the rift and dipping at 45 is compatible with the coeval existence of decollement reverse and normal faults however in a crustal volume east of longitude 155 10 w we find a change of the orientation of 1 from nearly horizontal to plunging 45 se occurring in 1979 this stress rotation suggests magma movements within the aseismic part of kilauea s east rift zone the strain and stress orientations are coaxial in the south flank except within the volume where the stress rotation is observed we observe a change in the relationship between stress and strain directions caused either by the shifting of seismic activity from reverse faults to decollements while stress stays constant or by a rotation of stress while strain remains constant assuming that the model of a noncohesive coulomb wedge is appropriate for kilauea s south flank we find that high pore pressures are prevalent along the decollement and within the wedge for a coefficient of friction equal to 0 85

along strike variations in the thermal and tectonic response of the continental ecuadorian andes to the collision with heterogeneous oceanic crust oblique to strike geological segmentation in the andean chain has been previously recognised at various scales and is commonly attributed to changes in the convergence vectors of the oceanic and continental plates as well as the upperplate expressions of differing along strike subducted slab age strength and composition we present new white mica and biotite 40 ar 39 ar and zircon and apatite fission track data from several traverses across the cordillera real of ecuador in the northern andes that reveal distinct along strike differences in the timing of accelerated crustal cooling during the cenozoic the data record elevated cooling rates from temperatures of v380 c during v65 55 and v43 30 ma from all sampled regions of the cordillera real and at v15 ma and since v9 ma in the northern cordillera real each cooling period was probably driven by exhumation in response to the accretion and subduction of heterogeneous oceanic crust elevated cooling rates of up to v30 20 c myr were initiated during the palaeocene and eocene early oligocene along the entire contemporaneous margin of ecuador and were driven by the accretion of the oceanic pallatanga terrane and pin on macuchi block respectively onto northwestern south america both of these geological provinces originated at the southern parts of the leading and trailing boundaries of the caribbean plateau and accreted onto the margin during the approximately northeastward migration of the plateau into its current position within ecuador the development of higher topography and elevated cooling rates of up to 50 c myr at v15 ma and since v9 ma are restricted to the region north of 1 30ps and is situated above the postulated subducted flatslab section of the aseismic carnegie ridge plate convergence rate calculations suggest the carnegie ridge collided with the ecuador trench at v15 ma which caused the pre existing coastal provinces to displace to the northeast subsequently driving extension and marine ingressions in southern ecuador and compression and uplift in northern ecuador fl 2001 elsevier science b v all rights reserved

mio pliocene adakite generation related to flat subduction in southern ecuador the quimsacocha volcanic center abstract new geochemical and geochronological data on the miocene pliocene quimsacocha volcanic center qvc have led to the recognition of adakitic lavas generated by slab melting related to the flat slab subduction in southern ecuador and northern peru the qvc located in the presently inactive southern part of the ecuadorian arc was built up during three distinctive volcanic phases the first phase generated a basal edifice with mainly andesitic lava flows while the second phase is characterized by the emplacement of cryptodomes domes and related outflow breccias comprised of andesites and some dacites the last phase released rhyolitic ignimbrites associated with the formation of a large caldera which was later partly filled by dacitic rhyolitic domes geochemical data for the qvc indicate higher al2o3 tio2 na2o zr and sr contents and lower fe2o3 mgo y mree and hree abundances compared to other eruptive rocks of the plio quaternary volcanic front of ecuador such geochemical features as well as the frequent presence of an associated epithermal gold deposit are characteristic of the involvement of slab melts also known as adakites 1 2 in the generation of these magmas after a calc alkaline arc magmatism phase slab horizontalization in response to the subduction of a buoyant oceanic plateau results in increased involvement of a slab melting component in the magmas produced however pristine adakites were generated and emplaced during a relatively short period as indicated by zircon fission track ages then volcanic activity stopped and a volcanic gap formed the identification of these adakites their location and age support a model of slab melting associated with flat slab subduction m a gutscher et al geology 28 2000 535 538

u pb re os and 40ar 39ar geochronology of porphyry sn cu mo and polymetallic ag pb zn cu vein mineralization at bianjiadayuan inner mongolia northeast china implications for discrete mineralization events

rhenium behavior in molybdenite in hypogene and near surface environments implications for re os geochronometry abstract rhenium is concentrated mainly in molybdenite mos2 and occurs as a major cation in only a few rare minerals this affinity makes molybdenite an ideal mineral for re os geochronometry but research on the behavior of re in molybdenite is limited infrared microscope xrd back scattered electron bse and microprobe techniques have been used in this study to document re behavior in molybdenite affected by hypogene and near surface processes in the hypogene environment both 3r and 2h molybdenite can experience re loss during hydrothermal alteration which also causes increased infrared transparency ir alteration at temperatures as low as 150 c can cause re loss in the presence of advecting fluids and will affect re os dating if it occurs long after primary mineralization re loss in 3r and 2h molybdenite under supergene conditions does not increase ir transparency rhenium is not incorporated into supergene ferrimolybdite but is enriched in k al silicate intergrowths which may be illite these minute intergrowths are present in several samples and would not be detected in a simple optical examination in the supergene environment elemental os is stable whereas re is not rhenium in molybdenite may be removed by supergene fluids after some has decayed to 187os causing erroneously old ages or it may be adsorbed into the illite intergrowths creating ages which are too young in the weathering environment proterozoic molybdenites have altered to re enriched powellite which can be detected using back scattered electron imagery combined microprobe xrd bse and infrared microscopy can be successfully used to detect alteration in molybdenite prior to dating these techniques are non destructive and should be performed before any molybdenite is dated by the re os system

geodetic evidence for en echelon dike emplacement and concurrent slow slip during the june 2007 intrusion and eruption at kīlauea volcano hawaii 1 a series of complex events at k lauea volcano hawaii 17 june to 19 june 2007 began with an intrusion in the upper east rift zone erz and culminated with a small eruption 1500 m3 surface deformation due to the intrusion was recorded in unprecedented detail by global positioning system gps and tilt networks as well as interferometric synthetic aperture radar insar data acquired by the envisat and alos satellites a joint nonlinear inversion of gps tilt and insar data yields a deflationary source beneath the summit caldera and an ene striking uniform opening dislocation with 2 m opening a dip of 80 to the south and extending from the surface to 2 km depth this simple model reasonably fits the overall pattern of deformation but significantly misfits data near the western end of an inferred dike like source three more complex dike models are tested that allow for distributed opening including 1 a dike that follows the surface trace of the active rift zone 2 a dike that follows the symmetry axis of insar deformation and 3 two en echelon dike segments beneath mapped surface cracks and newly formed steaming areas the en echelon dike model best fits near field gps and tilt data maximum opening of 2 4 m occurred on the eastern segment beneath the eruptive vent although this model represents the best fit to the erz data it still fails to explain data from a coastal tiltmeter and gps sites on k lauea s southwestern flank the southwest flank gps sites and the coastal tiltmeter exhibit deformation consistent with observations of previous slow slip events beneath k lauea s south flank but inconsistent with observations of previous intrusions slow slip events at k lauea and elsewhere are thought to occur in a transition zone between locked and stably sliding zones of a fault an inversion including slip on a basal decollement improves fit to these data and suggests a maximum of 15 cm of seaward fault motion comparable to previous slow slip events

southern california hypocenter relocation with waveform cross correlation part 2 results using source specific station terms and cluster analysis we obtain precise relative relocations for more than 340 000 southern california earthquakes between 1984 and 2002 by applying the source specific station term ssst method to existing p and s phase picks and a differential lo cation method to about 208 000 events within similar event clusters identified with waveform cross correlation the entire catalog is first relocated by using existing phase picks a reference 1d velocity model and the ssst method of richards dinger and shearer 2000 we also perform separate relocations of imperial valley events by using a velocity model more suited to this region next we apply cluster analysis to the waveform cross correlation output to identify similar event clusters we re locate earthquakes within each similar event cluster by using the differential times alone keeping the cluster centroid fixed to its initial ssst location we estimate standard errors for the relative locations from the internal consistency of differential locations between individual event pairs these errors are often as small as tens of meters in many cases the relocated events within each similar event cluster align in planar features suggestive of faults we observe a surprising number of such faults at small scales that strike nearly perpendicular to the main seismicity trends in general the fine scale details of the seismicity reveal a great deal of structural com plexity in southern california fault systems

repeating earthquakes in the yellowstone volcanic field implications for rupture dynamics ground deformation and migration in earthquake swarms abstract we evaluated properties of yellowstone earthquake swarms employing waveform multiplet analysis thirty seven percent of the earthquakes in the yellowstone caldera occur in multiplets and generally intensify in areas undergoing crustal subsidence outside the caldera in the hedgen lake tectonic area the clustering rate is higher up to 75 the yellowstone seismicity follows a succession of two phases of earthquake sequence the first phase is defined between swarms it is characterized by a decay of clustering rate and by foreshock aftershock sequences the second phase is confined to swarms and is characterized by an increase in clustering rate and dominant aftershock sequences this phase reflects tectonic swarms that occur on short segments of optimally oriented faults for example the largest recorded swarm in yellowstone occurred in autumn 1985 on the northwest side of the yellowstone plateau which was initiated as a tectonic source sequence fitting experimental dependence of fluid injection with intrusion migration suggests that the 1985 swarm involved after 10 days hydrothermal fluids flowing outward from the caldera the 2008 2009 yellowstone lake swarm exhibited a high migration rate of 1 km day a decrease in clustering rate without a main shock and appears to be associated with magma injection of 1 to 5 m 3 s in a succession of migrating magma fronts that incrementally solidify and fracture at its brittle edges the 2010 madison plateau earthquake swarm on the west side of the caldera initiated as a tectonic sequence but the expansion of the swarm front was associated with hydrothermal fluid migration