major types and time space distribution of mesozoic ore deposits in south china and their geodynamic settings the ore deposits of the mesozoic age in south china can be divided into three groups each with different metal associations and spatial distributions and each related to major magmatic events the first event occurred in the late triassic 230 210 ma the second in the mid late jurassic 170 150 ma and the third in the early mid cretaceous 120 80 ma the late triassic magmatic event and associated mineralization is characterized by peraluminous granite related w sn nb ta mineral deposits the triassic ore deposits are considerably disturbed or overprinted by the later jurassic and cretaceous tectono thermal episodes the mid late jurassic magmatic and mineralization events consist of 170 160 ma porphyry skarn cu and pb zn ag vein deposits associated with i type granites and 160 150 ma metaluminous granite related polymetallic w sn deposits the late jurassic metaluminous granite related w sn deposits occur in a ne trending cluster in the interior of south china such as in the nanling area in the early mid cretaceous from about 120 to 80 ma but peaking at 100 90 ma subvolcanic related fe deposits developed and i type calc alkaline granitic intrusions formed porphyry cu mo and porphyry epithermal cu au ag mineral systems whereas s type peraluminous and or metaluminous granitic intrusions formed polymetallic sn deposits these cretaceous mineral deposits cluster in distinct areas and are controlled by pull apart basins along the south china continental margin based on mineral assemblage age and space time distribution of these mineral systems integrated with regional geological data and field observations we suggest that the three magmatic mineralization episodes are the result of distinct geodynamic regimes the triassic peraluminous granites and associated w sn nb ta mineralization formed during post collisional processes involving the south china block the north china craton and the indo china block mostly along the dabie sulu and songma sutures jurassic events were initially related to the shallow oblique subduction of the izanagi plate beneath the eurasian continent at about 175 ma but i type granitoids with porphyry cu and vein type pb zn ag deposits only began to form as a result of the breakup of the subducted plate at 170 160 ma along the nne trending qinzhou hangzhou belt also referred to as qin hang or shi hang belt which is the neoproterozoic suture that amalgamates the yangtze craton and cathaysia block a large subduction slab window is assumed to have formed in the nanling and adjacent areas in the interior of south china triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic w sn mineralization a relatively tectonically quiet period followed between 150 and 135 ma in south china from 135 ma onward the angle of convergence of the izanagi plate changed from oblique to parallel to the coastline resulting in continental extensional tectonics and reactivation of regional scale ne trending faults such as the tan lu fault this widespread extension also promoted the development of ne trending pull apart basins and metamorphic core complexes accompanied by volcanism and the formation of epithermal cu au deposits granite related polymetallic sn w deposits and hydrothermal u deposits between 120 and 80 ma with a peak activity at 100 90 ma

evidence from precise earthquake hypocenters for segmentation of the san andreas fault in san gorgonio pass we use precise hypocenter patterns and focal mechanisms to investigate the presence or absence of a continuous strike slip fault at depth connecting the san bernardino strand of the san andreas fault with the coachella valley segment of the banning fault we inverted 560 000 arrival times from 23 000 earthquakes 1981 1993 for high quality hypocenters and three dimensional p wave velocity structure in a 1 by 2 area centered on the san gorgonio pass cross sectional plots of relocated earthquakes reveal an abrupt 5 to 7 km high step in the maximum depth of hypocenters the step riser defines a near vertical locally curved surface that extends westerly more than 60 km from the coachella valley segment of the san andreas fault to the san jacinto fault a hypothetical continuous vertical san andreas fault through san gorgonio pass would cross the step at an oblique angle we suggest that the step is the expression of the contact between different basement rock types juxtaposed by large scale right slip motion on the ancestral san andreas fault south of the step in peninsular ranges type basement intrusives brittle failure occurs down to about 20 km depth while north of the step in san bernardino type basement pelona schist brittle failure occurs to only about 13 km depth the step provides a piercing plane that should be offset about 3 km right laterally by an active continuous vertical san andreas fault within the resolution of our mapping the step is not offset in this manner implying either that there has not been a throughgoing vertical fault at depth that a throughgoing fault has not experienced enough slip to offset the step or that a throughgoing fault is not vertical and dips north over the top of the step hypocentral patterns and focal mechanisms indicate distributed deformation thrust normal and strike slip faulting over a large volume in the san gorgonio pass region there is no evidence of hypocenter or slip vector alignments that would indicate a throughgoing continuous near vertical san andreas fault in summary we find no evidence indicating a continuous fault at seismogenic depth connecting the san bernardino strand and coachella valley segment of the san andreas fault zone we speculate that this is because the 3 km of right slip on the san bernardino stand of the san andreas fault and coachella valley segment of the banning fault has not been sufficient to form a single new structure through the 15 to 20 km gap between the two previously unconnected segments this implies that large earthquake rupture on the san andreas fault may be inhibited from propagating through san gorgonio pass thus limiting the maximum magnitudes on the southern san andreas fault

high resolution seismic velocities and shallow structure of the san andreas fault zone at middle mountain parkfield california a 5 km long high resolution seismic imaging survey across the san andreas fault saf zone and the proposed san andreas fault observatory at depth safod drill site near parkfield california shows that velocities vary both laterally and vertically velocities range from 4 0 km sec probably correspond to granitic rock of the salinian block which is exposed a few kilometers southwest of the saf the depth to the top of probable granitic rock varies laterally along the seismic profile but is about 600 m below the surface at the proposed safod site we observe a prominent lateral low velocity zone lvz beneath and southwest of the surface trace of the saf the lvz is about 1 5 km wide at 300 m depth but tapers to about 600 m wide at 750 m depth at the maximum depth of the velocity model 750 m the lvz is centered approximately 400 m southwest of the surface trace of the saf similar velocities and velocity gradients are observed at comparable depths on both sides of the lvz suggesting that the lvz is anomalous relative to rocks on either side of it velocities within the lvz are lower than those of san andreas fault gouge and the lvz is also anomalous with respect to gravity magnetic and resistivity measurements because of its proximity to the surface trace of the saf it is tempting to suggest that the lvz represents a zone of fractured crystalline rocks at depth however the lvz instead probably represents a tectonic sliver of sedimentary rock that now rests adjacent to or encompasses the saf such a sliver of sedimentary rock implies fault strands on both sides and possibly within the sliver suggesting a zone of fault strands at least 1 5 km wide at a depth of 300 m tapering to about 600 m wide at 750 m depth fluids within the sedimentary sliver are probably responsible for observed low resistivity values

a unique association of scheelite and magnetite in the tiemuli w fe skarn deposit implications for early cretaceous metallogenesis in the nanling region south china abstract the tiemuli scheelite magnetite deposit in the central part of the nanling region south china is genetically related to a porphyritic biotite granite pluton the w fe orebodies are hosted within upper cambrian calcareous sandstone or impure limestone in the external zones la icp ms u pb dating of zircons from the granite yielded a weighted mean age of 136 6 1 1 ma the main ore minerals are magnetite scheelite and arsenopyrite and the gangue minerals are clinopyroxene grossularite vesuvianite amphibole and mica three paragenetic stages of skarn formation have been recognized i a skarn stage ii a retrograde stage and iii a quartz sulphide calcite stage massive magnetite and scheelite orebodies associated with hydrous minerals formed during stage ii molybdenite grains separated from tiemuli skarns yielded re os model ages of 136 3 133 8 ma with a weighted mean age of 135 1 0 8 ma biotite associated with fine grained magnetite from the ores has a 40 ar 39 ar plateau age of 132 67 0 43 ma these three independent dating techniques show that the granitic magmatism and tungsten mineralization were coeval within error whereas the late stage alteration recorded by biotite could be ca 2 m y younger than the early stage the granite is classified as an a type body on the basis of its geochemistry and mineralogy zircon grains from the granite show negative ehf t values of 7 7 to 2 3 and molybdenite grains from the skarn ores contain low re contents of 0 93 to 2 97 ppm these data indicate that the magma and ore forming components at tiemuli were derived mainly from crustal materials although mafic xenoliths in the granites are consistent with some mantle contribution the tiemuli deposit was produced by crust mantle interaction in an extensional regime possibly caused by rollback of the subducting paleo pacific plate during early cretaceous the skarn scheelite and magnetite association formed by interaction between magmatic fluids and calcite bearing sandstone or impure limestone of the host strata

frontal surveys with a towed profiling conductivity temperature depth measurement package seasoar in april 1986 rv oceanus participated in the frontal air sea interaction experiment fasinex1 in the region 27 29 n 68 71 w the objective was to survey a pronounced oceanic front2 4 and its effect on the oceanic and atmospheric boundary layers although moorings have yet to be recovered and much of the data analysis is as yet only preliminary it is possible to report here the typical density structure of a front as derived from seasoar5 6 fig 1a observations which were analysed within a few hours of collection previously unreported detail is revealed including subducted pycnostads areas of weak vertical density gradient with anomalous temperature salinity signature splitting of the frontal jet and three dimensional structure not apparent in the surface temperature field

the seasat altimeter data and its accuracy assessment the seasat satellite launched on june 27 1978 carried a radar altimeter designed to measure the altitude of the satellite above the ocean surface the surface wave height and the ocean surface backscatter coefficient from which wind speed can be inferred postlaunch engineering assessment indicated that the seasat altimeter met the performance specification for 10 cm precision noise in the altitude measurements however to determine the accuracy of this measurement as well as the accuracy of the wave height and wind speed measurements a significant calibration validation and model development effort was required this summary describes the instrument atmospheric and geophysical effects which influence the radar altimeter measurement accuracies and the attendant correction models adopted for the altimeter geophysical data record also summarized are the activities of the seasat altimeter precision orbit determination experiment team directed towards the validation and improvement of these models as well as the investigations required to assess the accuracy of the altimeter measurement and the computed satellite altitude ephemeris finally an accuracy assessment is made for the various altimeter measurement corrections which are included on the altimeter geophysical data record

faulting apparently related to the 1994 northridge california earthquake and possible co seismic origin of surface cracks in potrero canyon los angeles county california apparent southward dipping reverse fault zones are imaged to depths of about 1 5 km beneath potrero canyon los angeles county california based on their orientation and projection to the surface we suggest that the imaged fault zones are extensions of the oak ridge fault geologic mapping by others and correlations with seismicity studies suggest that the oak ridge fault is the causative fault of the 17 january 1994 northridge earthquake northridge fault our seismically imaged faults may be among several faults that collectively comprise the northridge thrust fault system unusually strong shaking in potrero canyon during the northridge earthquake may have resulted from focusing of seismic energy or co seismic move ment along existing related shallow depth faults the strong shaking produced ground surface cracks and sand blows distributed along the length of the canyon seismic reflection and refraction images show that shallow depth faults may underlie some of the observed surface cracks the relationship between observed surface cracks and imaged faults indicates that some of the surface cracks may have devel oped from nontectonic alluvial movement but others may be fault related imme diately beneath the surface cracks p wave velocities are unusually low 400 m sec and there are velocity anomalies consistent with a seismic reflection image of shallow faulting to depths of at least 100 m on the basis of velocity data we suggest that unconsolidated soils 800 rrdsec extend to depths of about 15 to 20 m beneath our datum 25 m below ground surface the underlying rocks range in velocity from about 1000 to 5000 m sec in the upper 100 m this study illustrates the utility of high resolution seismic imaging in assessing local and regional seismic hazards

genetic relationship between granitic magmatism and w mineralization recorded in the nanling scientific drilling sp nlsd 2 in the pangushan w mining district south china abstract the nanling region in south china hosts numerous w dominated polymetallic deposits that are related to mesozoic granites although considerable amounts of age data have been obtained the genetic relationship between granitic magmatism and w mineralization remains unclear the nanling scientific drilling sp nlsd 2 in the pangushan w deposit has penetrated upper devonian sedimentary rocks 4 1 721 9 m sinian sedimentary rocks 721 9 1287 9 m and mesozoic granite 1287 9 2012 1 m the drill hole clearly reveals a zonation including exocontact w bearing quartz veins alkali autometasomatic zone and primary k feldspar granite the k feldspar granite at the depth of 1880 m and rocks of potassium autometasomatic zone at 1414 m and greisenized zone at 1288 m have magmatic zircon grains with u pb ages of 164 8 1 4 ma 161 7 1 6 ma and 153 8 1 2 ma respectively molybdenite re os ages of endocontact mineralization at the depths of 1302 m and 1291 m are 155 9 3 1 ma and 155 0 2 3 ma respectively muscovite ar ar ages of exocontact mineralization at the depths of 1050 and 885 m are 154 9 1 5 ma and 154 0 3 0 ma respectively and molybdenite re os age of exocontact quartz vein type mineralization at 860 m is 152 0 2 6 ma these new ages indicate that the granite emplacement potassium autometasomatism greisenization and w mineralization occurred at 164 8 ma 161 7 ma 153 8 ma and 155 9 152 ma respectively the w mineralization was approximately 9 13 myr younger than the hosting granite the whole rock and feldspar chemical compositions of k feldspar granite potassium autometasomatic zone greisenized zone and feldspar quartz veins indicate the sequence of metal transportation and concentration to form the zonation the granite crystallized from high k calcalkaline metaluminous to peraluminous highly differentiated magmas that were enriched in w and bi during crystallization the magmas underwent potassium autometasomatism caused by post magmatic fluids which were rich in k fe w and rare earth elements ree but poor in na and ca and formed the potassium autometasomatic zone the evolved post magmatic fluids became rich in k si ca ree and w but poor in na and fe and initiated greisenization to generate the greisenized zone which almost exhausted ca ree na and fe of the fluids the later crystallization of feldspar quartz veins exhausted k and caused the residual post magmatic fluids to be rich in si and w the fluids formed w bearing quartz veins with decreasing temperature and pressure the main reason for w enrichment in the hydrothermal fluids was due to the successive crystallization of minerals rather than autometasomatism

triggered surface slips in the coachella valley area associated with the 1992 joshua tree and landers california earthquakes the coachella valley area was strongly shaken by the 1992 joshua tree 23 april and landers 28 june earthquakes and both events caused triggered slip on active faults within the area triggered slip associated with the joshua tree earth quake was on a newly recognized fault the east wide canyon fault near the south western edge of the little san bernardino mountains slip associated with the land ers earthquake formed along the san andreas fault in the southeastern coachella valley surface fractures formed along the east wide canyon fault in association with the joshua tree earthquake the fractures extended discontinuously over a 1 5 km stretch of the fault near its southern end sense of slip was consistently right oblique west side down similar to the long term style of faulting measured offset values were small with right lateral and vertical components of slip ranging from 1 to 6 mm and 1 to 4 mm respectively this is the first documented historic slip on the east wide canyon fault which was first mapped only months before the joshua tree earthquake surface slip associated with the joshua tree earthquake most likely de veloped as triggered slip given its 5 km distance from the joshua tree epicenter and aftershocks as revealed in a trench investigation slip formed in an area with only a thin 3 m thick veneer of alluvium in contrast to earlier documented triggered slip events in this region all in the deep basins of the salton trough a paleoseismic trench study in an area of 1992 surface slip revealed evidence of two and possibly three surface faulting events on the east wide canyon fault during the late quaternary probably latest pleistocene first event and mid to late holocene second two events about two months after the joshua tree earthquake the landers earthquake then triggered slip on many faults including the san andreas fault in the southeastern coachella valley surface fractures associated with this event formed discontinuous breaks over a 54 km long stretch of the fault from the indio hills southeastward to durmid hill sense of slip was right lateral only locally was there a minor 1 mm vertical component of slip measured dextral displacement values ranged from 1 to 20 mm with the largest amounts found in the mecca hills where large slip values have been measured following past triggered slip events

volatile transport in a convecting magma column implications for porphyry mo mineralization we propose that convection in a column of silicic magma allows transport of volatile components from large 50 km3 magma chambers to the sites of shallow 3 km porphyry type mo deposits using constraints from the henderson and pine grove systems we show that even at temperatures as low as 700 c a granitic magma with 30 vol phenocrysts can flow through a magma column with a 150 m radius at a rate 10 km3 yr enough magma to contribute the mo necessary to form an ore deposit in a geologically reasonable time frame this process requires an efficient mechanism for bubble separation at the top of the magma column to produce degassed magma that can descend down through the column it also requires slow rates of crystallization in the silicic magma consistent with experimental studies hydrothermal fluids released from the convecting magma column can explain many geologic features of the deposits

geophysical investigations of the geology and structure of the pangushan tieshanlong tungsten ore field south jiangxi china evidence for site selection of the 2000 m nanling scientific drilling project sp nlsd 2 abstract the pangushan tieshanlong tungsten ore field located in the center of southern jiangxi province eastern nanling region contains many granitic plutons both exposed and concealed and hosts numerous tungsten polymetallic ore deposits despite many previous geological studies the deep geology and structure of the field are poorly known because few geophysical measurements have been undertaken in this study we carried out a variety of geophysical measurements including gravity magnetic field detection magnetotelluric sounding mt and high resolution seismic reflection to better outline the nature of the ore field and to aid in site selection for the 2000 m nanling scientific drilling project sp nlsd 2 to be carried out by the chinese sinoprobe program four granitic intrusives the tangcun pangushan huangsha and bai e plutons crop out independently at the surface but were found to be parts of a large batholith at depth the tangcun composite pluton which at the surface consists chiefly of caledonian granite and minor early yanshanian intrusive material was found to be chiefly early yanshanian granite concealed beneath the lower part of the caledonian granite the bai e pluton initially decreases in size with depth and then expands as it merges with the major batholith the pangushan and huangsha plutons are domes on the inferred batholith four granitic magma channels and a considerable number of faults have been identified due to its favorable geological conditions the top of the pangushan pluton is predicted to be the best candidate for ore prospecting it is basically a granite cupola with many cross cutting and parallel faults in addition it is characterized by a high gravity anomaly a high magnetic anomaly and locally a low electrical resistivity anomaly

descriptive oceanography during the frontal air sea interaction experiment medium to large scale variability medium and large scale oceanographic variability in the sargasso sea is examined during the frontal air sea interaction experiment fasinex focusing primarily on processes that influence the formation of subtropical fronts from fall to spring the mean meridional gradient of meridional ekman transport in the subtropical convergence zone stcz enhances the meridional sea surface temperature ts gradients between 26 o and 32on in the presence of this enhanced mean gradient baroclinic eddies with zonal wavelengths of 800 km and periods of 200 days exert the dominant influence on the formation of subtropical fronts at medium and large scales these eddies generate westward propagating ts anomaly features with the same dominant wavelengths and periods they are confined between 26 o and 32on and have amplitudes that occasionally exceed ioc ts fronts tend to be found within bands 200 km wide that roughly follow the periphery of these anomaly features deformation in the horizontal eddy current field is primarily responsible for the existence of these frontal bands the migration of the strong front originally bracketed by the fasinex moored array was related to the westward propagation of the larger scale eddy anomaly frontal band pattern the moored array was located within a warm anomaly feature during most of the experiment which produced exceptionally warm conditions in the upper ocean these anomalies are confined between 26 o and 32on not only because the relatively large seasonal mean tsy there allows horizontal eddy currents to force strong anomalies but also because the baroclinic eddies with wavelengths of 800 km and periods of 200 days are confined to the stcz large meridional variability exists in many properties of the eddy field much of which can be traced to the influence of the sargasso sea mean current field on eddy variability

discussion on metallogenic setting and time difference between magmatism and mineralization of molybdenum deposits in east china east china was intensely affected by the marginal pacific metallogenic domain in mesozoic most molybdenum deposits along border areas of different tectonic units or regional deep faults are dominantly distributed in such metallogenic belts as east qinling yanshan liaoning middle lower reaches of the yangtze river nanling and da hinggan mountains combined with previous studies this paper discusses metallogenic settings of these regions exemplified by typical ore deposits and draws the conclusion that mo mineralization in these me tallogenic belts probably resulted from the extensional setting of post collision and or subduction of the pacific plate according to isotopic data of mineralization and ore related rocks collected from some typical mo deposits in east china the authors investigated in detail and quantitatively determined the characteristics of time diffe rence between magmatism and mineralization for mo deposits mo mineralization in east china occurred contemporaneously with or immediately after ore related granitoids time differences of the two peaking stages of mo mineralization are within 0 10 0 ma and 0 15 0 ma respectively for a single mo deposit the time differences are concentrated in 0 14 0 ma with a mean of 4 1 ma in order of porphyry type mo deposits porphyry skarn complex mo deposits skarn type mo deposits quartz vein type mo deposits the time differences seem gradually increase which is consistent with the observed geological facts of the magmatic hydrothermal ore formational process

fluid rock interaction is decisive for the formation of tungsten deposits tungsten mineralization is typically associated with reduced granitic magmas of crustal origin while this type of magmatism is widespread economic tungsten deposits are highly localized with 90 produced from only three countries worldwide therefore the occurrence of reduced magmatism while necessary for tungsten enrichment seems to be insufficient to form such rare deposits here we explore the mechanisms that lead to wolframite precipitation and evaluate whether they may exert a decisive control on tungsten global distribution tungsten differs from other rare metals enriched in magmatic hydrothermal ore deposits because it is transported as an anionic species precipitation of the main tungstate minerals scheelite cawo 4 and wolframite fe mn wo 4 thus depends on the availability of calcium iron or manganese we demonstrate quantitatively that magmatic fluids at panasqueira portugal provide tungsten in solution whereas the host rock contributes the iron required to precipitate wolframite the combination of special source conditions with specific reactive host rocks explains why major wolframite deposits are rare and confined to a few ore provinces globally

molybdenite re os and muscovite 40ar 39ar dating of the xihuashan tungsten deposit central nanling district south china abstract the xihuashan tungsten deposit in the central nanling region south china is an important vein type ore deposit hosted in cambrian strata and mesozoic granitic intrusions wolframite and molybdenite are the principal ore minerals the gangue minerals are mainly quartz and muscovite wolframite and molybdenite are products of the first stage hydrothermal activity whereas muscovite formed dominantly at the second stage molybdenite re os and muscovite 40ar 39ar dating have been carried out to investigate the age of mineralization re os isotopic dating for molybdenite associated with wolframite yield a precise well constrained isochron age of 157 8 0 9 ma mswd 1 5 ar ar isotopic analyses of muscovite yield a plateau age of 152 8 1 6 ma in agreement with an inverse isochron age of 152 8 1 6 ma which is 5 mys younger than the re os age the molybdenite re os age is interpreted as the age of tungsten mineralization this age coincides well with the zircon u pb age of the host granitic intrusion reported previously the 5 mys difference between molybdenite re os and muscovite 40ar 39ar ages probably represents the duration of hydrothermal activity the results show that the xihuashan tungsten deposit is one of many important tungsten tin deposits formed during 150 to 160 ma associated with large scale lithospheric extension in south china

ocean frontal variability in the frontal air sea interaction experiment oceanographic observations during the frontal air sea interaction experiment fasinex in the sargasso sea indicate that upper ocean fronts in the subtropical convergence are strongly surface intensified coherent flow structures which have a preferred orientation and translation speed fronts grow as they propagate in this region such that currents roughly double in strength in a time that they translate by twice their width while currents are dominated by geostrophic momentum balance the rossby number of these flows can reach a few tenths mixed layer water from the cold side of fronts appears to subduct under warm side near surface waters since isolated lenses of water with cold side temperature and salinity characteristics are found embedded in the seasonal thermocline on the warm side of fronts although plausible vertical speeds were observed no actual rates of subduction could be estimated typical frontal widths temperature contrasts horizontal currents vertical shears vertical currents and translation speeds of fronts in the region studied are 20 km 1 c 0 5 m s 1 0 005 s 1 0 0005 m s 1 and 0 2 m s 1 respectively

gravity model improvement for seasat analysis of the data from the seasat altimeter a 10 cm precision instrument requires accurate knowledge of the radial position of the spacecraft for oceanographic applications such as the study of tides and ocean circulation as well as for geodetic applications initial orbit determinations using the best available geodetic and force models gave radial errors approaching 5 m the dominant source of this radial error was the gravity field model improvements in the gravity modeling were made by successively incorporating the seasat laser and unified s band ground tracking data the geos 3 altimeter data and finally the seasat altimeter data with the most recent model a set of spherical harmonic coefficients complete to degree and order 36 seasat ephemerides have been computed for an orbital arc length of 12 days with an rms radial accuracy of about 70 cm

a preliminary model for geosat altimeter data errors noise power spectral densities psds are derived from the analysis of geosat altimeter data from segments of nearly collinear repeat tracks the difference time series which are analyzed using autoregressive ar modeling techniques contain primarily time varying oceanographic signals and altimeter noise since geoid content is canceled by the differencing process an average noise psd obtained from eight independent repeat track psds is fitted closely by a first order markov model with a white noise floor the geosat average noise psd is compared with analogous spectra derived earlier for geos 3 and seasat in general the geosat noise psd is the same as the seasat noise spectrum at wavelengths greater than about 100 km but has a lower noise level at shorter wavelengths

nearly contemporaneous evolution of the a and s type fractionated granites in the krusne hory erzgebirge mts central europe abstract the krusne hory erzgebirge mountains is one of the best known provinces of granite magmatism and associated metallogenesis in europe variscan magmatic activity in the krusne hory erzgebirge area spanned the period from 330 to 295 ma for much of this time two types of magma were generated and emplaced in close proximity in this province strongly peraluminous p rich s type melts were formed alongside slightly peraluminous p poor melts a type two suites of strongly peraluminous p f li rb cs u sn rich and zr th y hree poor magmas were intruded in rapid succession over a period of about 10 ma about 330 320 ma over the entire region of the krusne hory several peraluminous rhyolitic dykes near gottesberg mark an isolated event at about 295 ma slightly peraluminous f li rb cs sn zr y hree rich and p poor magmas were intruded in several events separated in space and time 325 295 ma both magmatic episodes culminated with strongly fractionated subvolcanic granite intrusions accompanied by explosive brecciation and followed by sn w mineralization of greisen type successive volcanic eruption of rhyolites and dacites of s type and rhyolites of a type form the fill of the altenberg teplice caldera atc thus demonstrating the close temporal and spatial relationship between these two types of magma when these two geochemically distinct types of rock are in direct contact then the rocks of a type are always younger the absolute time difference between the two types can range from less than 1 ma the first eruption of the teplice rhyolite versus the schonfeld dacite in the atc to about 15 ma eruption of rhyolites at gottesberg versus emplacement of the eibenstock granite the assumed protolith of all late variscan granites in the area of krusne hory erzgebirge is a mixture of fertile quartzo feldspathic rocks with micaceous metapelites enriched in lile and sn w the differences in chemical composition of s and a type melts originated from local changes in the proportion of quartzo feldspathic and pelitic lithologies different pt conditions of melting the degree of melting and the degree of metamorphic dehydratation of the protolith prior to the melting

mesozoic metallogeny in east china and corresponding geodynamic settings an introduction to the special issue abstract the giant east china mesozoic metallogenic province hosts some of the world s largest resources of tungsten tin molybdenum antimony and bismuth ores of gold silver mercury lead zinc copper uranium and iron are also of major importance the province and its constituent metallogenic belts or regions south china middle lower yangtze river valley east qinling dabie interior of north china craton yan liao and north east china are the products of several pulses of igneous activity and mineralisation between 240 and 80 ma each successive stage has produced a distinctive suite of deposits that can be readily related to the geodynamic evolution of the region during the mesozoic this geodynamic evolution is linked to a complex series of tectonic events involving far field subduction plate collisions crustal thickening post collision collapse and rifting

temporal consistency between granite evolution and tungsten mineralization in huamei ao southern jiangxi province china evidence from precise zircon u pb molybdenite re os and muscovite 40ar 39ar isotope geochronology abstract the large huamei ao tungsten deposit with total wo 3 reserves of 67 400 tons at an average grade of 1 334 wo 3 is located in the convergent zone of the eastern nanling e w trending tectono magmatic belt and the western wuyishan nne ssw trending tectono magmatic belt in southern jiangxi province china the tungsten mineralization in this deposit is mainly found in quartz wolframite veins with most orebodies distributed at the outer contact zone between concealed late jurassic granitic stocks and sinian weakly metamorphosed sandstones and phyllites zircons collected from medium to fine grained biotite granite in a diamond drill hole at a sea level of ca 10 m yield a crystallization age of 159 9 1 2 ma through laser ablation multicollector inductively coupled plasma mass spectrometry la mc icp ms u pb dating molybdenite and muscovite that were both separated from quartz wolframite veins yield a re os isochron age of 158 5 3 3 ma and an 40 ar 39 ar weighted plateau age of 157 9 1 1 ma respectively these dates obtained via three independent geochronological techniques constrain the ore forming age of the huamei ao deposit and link the genesis of the ore and the underlying granite analyses of available high precision zircon u pb molybdenite re os and muscovite 40 ar 39 ar radiometric ages of major w sn deposits in southern jiangxi province indicate that there is no significant time interval between w sn mineralization and its intimately associated parent granite emplacement interval of 0 6 ma these deposits formed over three intervals during the mesozoic 240 210 170 150 and 130 90 ma with large scale w sn mineralization occurring mainly between 160 and 150 ma the majority of w sn deposits in this region are located in southern jiangxi and southern hunan provinces

late paleozoic sedex deposits in south china formed in a carbonate platform at the northern margin of gondwana abstract sedex sulfide deposits hosted in black shale and carbonate are common in the south china block the dajiangping pyrite deposit is the largest of these deposits and is made up of stratiform orebodies hosted in black shales sandstone interlayered with stratiform orebodies contains detrital zircon grains with the youngest ages of 429 ma pyrite from the orebodies has a re os isochron age of 389 62 ma indicative of formation of the hosting strata and syngenetic pyrite ores in the mid late devonian the hosting strata is a transgression sequence in a passive margin and composed of carbonaceous limestone in the lower part and black shales in the upper part the ore hosting black shales have high toc total organic carbon mo as pb zn and cd indicating an anoxic euxinic deep basin origin the high redox proxies v v ni 0 6 and v cr 1 and the positive correlations of toc with mo and v in black shales are also consistent with an anoxic depositional environment the dajiangping deposit is located close to the ne trending wuchuan sihui fault which was active during the devonian the mid late devonian mineralization age and the anoxic euxinic deep basinal condition of this deposit thus imply that the formation of this deposit was causally linked to hydrothermal fluid exhalation in an anoxic fault bounded basin that developed in a carbonate platform of the south china block the regional distribution of many devonian stratiform carbonaceous sediment hosted sulfide deposits along the ne trending fault bounded basins in south china similar to the dajiangping deposit indicates that these deposits formed at a basin developed in the passive margin setting of the south china block during the devonian this environment was caused by the break up and northward migration of the south china block from gandwana

seismic behavior of the southern san andreas fault zone in the northern coachella valley california comparison of the 1948 and 1986 earthquake sequences moderate earthquakes in 1948 and 1986 that occurred along the southern san andreas fault zone are examined to help understand the subsurface geometry and seismic behavior of active fault segments in the northern coachella valley the 1986 north palm springs earthquake occurred between the banning and mission creek traces of the san andreas fault zone based on data from both portable and permanent stations aftershocks of the 1986 event define a nearly planar surface that strikes about n60 to 70 w is about 15 km long and dips northeast from near the banning surface trace at about 45 to 50 relocation of the mainshock using revised station corrections and a local velocity model inverted from the aftershock arrival times indicates a location at 34 n00 26 116 w36 34 and a focal depth of 10 4 km the first motion focal mechanism for the mainshock indicates pure right slip on a plane dipping northeast at 40 to 45 with a strike of n60 w previous moment tensor solutions e g hartzell 1989 exhibit significant oblique reverse slip on a plane with a more westerly strike and a seismic moment of 1 4 to 1 7 1018 n m mw 6 1 actual and synthetic wood anderson recordings indicate a local magnitude of ml 6 0 the 1948 desert hot springs earthquake produced waveforms similar to 1986 although amplitudes for 1948 are typically 20 to 30 larger the 1948 mainshock is relocated at 33 n55 2 116 w28 9 with a focal depth of 12 km a revised magnitude of ml 6 3 and an estimated seismic moment of 2 to 3 1018 n m based on arrival time information from close 20 km portable stations deployed in 1948 to 1949 the 1948 aftershock distribution is about 15 km long 8 to 10 km wide and abuts the 1986 aftershock sequence to the southeast along the banning fault the 1948 aftershock zone is consistent with a focal mechanism that exhibits predominantly right slip motion rake 169 on a plane that strikes n55 w and dips more steeply northeast at 60 to 70 in 1986 the horizontal extent of the rupture may have been controlled by secondary cross faults and possible changes in fault geometry while the down dip extent may have been controlled by the presence at depth of a regional detachment in 1948 the rupture likely had a steeper dip than in 1986 and extended southeast as far as the northern indio hills where the surface trace of the banning fault undergoes an approximate 7 change in strike these results indicate that the banning fault is nonvertical is likely segmented according to fault dip as well as fault strike and has been the primary locus of recent moderate sized earthquake activity in the northern coachella valley

the mesoscale spatial structure and evolution of dynamical and scalar properties observed in the northwestern atlantic ocean during the polymode local dynamics experiment abstract dynamical properties examined in this paper are the dynamic height and the pressure on an isopycnal scalars are the salinity and the oxygen concentration on an isopycnal the sea surface temperature and salinity are also examined these properties are obtained from the spatially uniform and densely sampled hydrographic surveys conducted during a two month period of the polymode local dynamics experiment in 1978 near 31 n 69 5 w the spatial maps of the dynamic height and the pressure of an isopycnal show that the baroclinic current in this area sometimes intensifies to a jetlike flow and at other times has the shape of elongated eddies the current flows primarily in the ne sw direction westward propagation occurs but varies in time and with depth eddies that transport water properties are also observed in this area the salinity and the oxygen on an isopycnal are found to be correlated with itself and with each other from the surface to the 18 c water layer within a 200 db range in the ther

timing of large earthquakes since a d 800 on the mission creek strand of the san andreas fault zone at thousand palms oasis near palm springs california paleoseismic investigations across the mission creek strand of the san andreas fault at thousand palms oasis indicate that four and probably five surface rupturing earthquakes occurred during the past 1200 years calendar age estimates for these earthquakes are based on a chronological model that incorporates radiocarbon dates from 18 in situ burn layers and stratigraphic ordering constraints these five earthquakes occurred in about a d 825 770 890 mean 95 range a d 982 840 1150 a d 1231 1170 1290 a d 1502 1450 1555 and after a date in the range of a d 1520 1680 the most recent surface rupturing earthquake at thousand palms is likely the same as the a d 1676 35 event at indio reported by sieh and williams 1990 each of the past five earthquakes recorded on the san andreas fault in the coachella valley strongly overlaps in time with an event at the wrightwood paleoseismic site about 120 km northwest of thousand palms oasis correlation of events between these two sites suggests that at least the southernmost 200 km of the san andreas fault zone may have ruptured in each earthquake the average repeat time for surface rupturing earthquakes on the san andreas fault in the coachella valley is 215 25 years whereas the elapsed time since the most recent event is 326 35 years this suggests the southernmost san andreas fault zone likely is very near failure the thousand palms oasis site is underlain by a series of six channels cut and filled since about a d 800 that cross the fault at high angles a channel margin about 900 years old is offset right laterally 2 0 0 5 m indicating a slip rate of 4 2 mm yr this slip rate is low relative to geodetic and other geologic slip rate estimates 26 2 mm yr and about 23 35 mm yr respectively on the southernmost san andreas fault zone possibly because 1 the site is located in a small step over in the fault trace and so the rate is not be representative of the mission creek fault 2 slip is partitioned northward from the san andreas fault and into the eastern california shear zone and or 3 slip is partitioned onto the banning strand of the san andreas fault zone

complexities of the san andreas fault near san gorgonio pass implications for large earthquakes 1 geologic relationships and patterns of crustal seismicity constrain the three dimensional geometry of the active portions of san andreas fault zone near san gorgonio pass southern california within a 20 km wide contractional stepover between two segments of the fault zone the san bernardino and coachella valley segments folds and dextral reverse and dextral normal faults form an east west belt of active structures the dominant active structure within the stepover is the san gorgonio pass garnet hill faults a dextral reverse fault system that dips moderately northward within the hanging wall block of the san gorgonio pass garnet hill fault system are subsidiary active dextral and dextral normal faults these faults relate in complex but understandable ways to the strike slip faults that bound the stepover the pattern of crustal seismicity beneath these structures includes a 5 8 km high east west striking step in the base of crustal seismicity which corresponds to the downdip limit of rupture of the 1986 north palm springs earthquake we infer that this step has been produced by slip on the linked san gorgonio pass garnet hill coachella valley banning sgp gh cvb fault this association enables us to construct a structure contour map of the fault plane the large step in the base of seismicity downdip from the sgp gh cvb fault system probably reflects a several kilometers offset of the midcrustal brittle plastic transition u th he thermochronometry supports our interpretation that this south under north thickening of the crust has created the region s 3 km of topographic relief we conclude that future large earthquakes generated along the san andreas fault in this region will have a multiplicity of mostly specifiable sources having dimensions of 1 20 km two tasks in seismic hazard evaluation may now be attempted with greater confidence first the construction of synthetic seismograms that make useful predictions of ground shaking and second theoretical investigations of the role of this complexity in retarding the propagation of future seismic ruptures

high resolution seismic images and seismic velocities of the san andreas fault zone at burro flats southern california abstract to better understand the structure of the san andreas fault saf at burro flats in southern california we acquired a three dimensional combined set of seismic reflection and refraction profiles centered on the main active trace at burro flats in this article we discuss the variation in shallow depth velocities along each seismic profile with special emphasis on the 1500 m sec p wave velocity contour which can be an indicator of shallow depth water saturated unconsolidated sediments along the four seismic profiles minimum depths of the groundwater table as inferred from 1500 m sec velocity contour range from 10 to about 20 m the largest variations in depth to the top of the groundwater table occur in areas near mapped faults suggesting that the groundwater flow in burro flats is strongly affected by the locations of fault traces we also used the seismic data to develop seismic reflection images that show multiple strands of the saf in the upper 60 m reflectors above the 10 m depth probably correspond to holocene alluvial deposits reflectors below the 15 m depth probably arise from velocity or density variations within the precambrian gneiss complex likely due to weathering apparent vertical offsets of reflectors are observed along profiles lines 1 and 2 that are normal to the saf indicating minor apparent vertical offsets on the saf at shallow depths along line 2 the apparently vertically offset reflectors correlate with zones of relatively low p wave velocity along the central part of lines 1 and 2 the faults form a flower structure which is typical of strike slip faults such as the saf

geological characteristics and metallogenic epoch of pangushan w bi te ore deposit in yudu county jiangxi province the pangushan tungsten ore deposit is a large size wolframite quartz vein type w bi te ore deposit in the exocontact zone of the buried rock body within the eastern part of the nanling metallogenic belt the authors collected molybdenite samples from the w bearing quartz veins of different geological modes of occurrence re os isotopic dating yielded isochron ages of molybdenite 157 75 0 76 ma mswd 0 99 and 158 8 5 7 ma mswd 1 7 the ages indicate that these two mineralized veins belong to the same product and were formed in the same period i e early yanshanian the study also provides useful evidence that the ore deposit is the product of nanling ew trending tectonic magmatic belt

constraints of multiple dating of the qingshan tungsten deposit on the triassic w sn mineralization in the nanling region south china abstract the qingshan tungsten deposit is a quartz vein type ore deposit in the nanling region south china and consists of orebodies along the contact between ordovician sandstone and the mesozoic keshuling granitic pluton there are more than 54 ore bearing quartz veins controlled by ne and nne trending faults the principal ore minerals are wolframite and cassiterite with subordinate molybdenite which formed dominantly during the early oxide and oxide sulfide ore forming stage together with extensive greisenization adjacent to the w bearing quartz veins the gangue minerals are mainly quartz and muscovite zircon grains from the keshuling pluton have a u pb age of 231 9 1 0 ma mswd 4 0 molybdenite separates from the ore bearing quartz veins have a well defined 187re 187os isochron age of 228 7 2 5 ma mswd 0 36 with model ages ranging from 227 6 3 3 to 229 7 3 2 ma hydrothermal muscovite from the greisen between the granite and country rocks has a flat 40ar 39ar plateau age spectra yielding a 40ar 39ar plateau age of 229 4 1 4 ma mswd 0 34 the u pb re os and 40ar 39ar ages are nearly identical within analytical uncertainties and these ages together with the field relationships provide tight constraints on the w sn mineralization at around 230 ma this multiple dating study reflects that the duration of the hydrothermal activity could be less than several million years our new results suggest that the triassic large scale w sn mineralization occurred throughout the nanling region

two ages of porphyry intrusion resolved for the super giant chuquicamata copper deposit of northern chile by ela icp ms and shrimp zircon u pb ages measured in situ by excimer laser ablation inductively coupled plasma mass spectrometry ela icp ms and verified by sensitive high resolution ion microprobe shrimp on ore bearing felsic porphyries from the chuquicamata porphyry copper molybdenum deposit northern chile identify two discrete igneous events the volumetrically dominant east porphyry has an age of 34 6 0 2 ma whereas the bench and west porphyries yield ages of 33 3 0 3 ma and 33 5 0 2 ma respectively the age of the east porphyry is indistinguishable from a re os age for early molybdenite mineralization 35 ma and the oldest reported 40 ar 39 ar ages for hydrothermal alteration confirming a genetic link with mineralization previous geological studies and 40 ar 39 ar and re os geochronology identify two main hydrothermal events high temperature potassic alteration with chalcopyrite at 33 4 0 3 ma followed by lower temperature quartz sericite alteration with pyrite at 31 1 0 3 ma the ages of the west and bench porphyries match the ages for potassic alteration younger quartz sericite alteration may reflect an additional fourth intrusion concealed at depth the anomalously large size of chuquicamata appears to be due to a protracted igneous history resulting in the superposition of at least two temporally distinct magmatic hydrothermal systems

shrimp u pb zircon ar ar muscovite and re os molybdenite isotopic dating of the taoxikeng tungsten deposit south china block abstract the taoxikeng tungsten deposit is located in the jiangxi province in the southern part of china and is one of the largest wolframite quartz vein type tungsten deposits in the country the deposit is situated in sinian neoproterozoic to permian strata at the contact with the buried taoxikeng granite sensitive high mass resolution ion microprobe shrimp zircon u pb analysis of the granite has yielded dates of 158 7 3 9 and 157 6 3 5 ma which are interpreted as the emplacement age of the granite molybdenite separated from ore bearing quartz veins yields a re os isochron age of 154 4 3 8 ma and muscovite separated from greisen between the granite and country rocks yields 40ar 39ar plateau ages of 153 4 1 3 and 152 7 1 5 ma these dates obtained from three independent geochronological techniques constrain the ore forming age of the taoxikeng deposit and link the ore genesis to that of the underlying granite the taoxikeng deposit is an example of a jurassic regional scale tungsten tin ore forming event between 160 and 150 ma in the nanling region of the south china block the deposit s strikingly low rhenium contents 4 9 to 13 0 10 3 g g in molybdenite suggests that the ore was derived from a crustal source this conclusion is consistent with previously published constraints from s d and o stable isotopes sr nd systematics and petrogenetic interpretations of spatially related granites

from andesitic volcanism to the formation of a porphyry cu au mineralizing magma chamber the farallon negro volcanic complex northwestern argentina abstract the geological relations and geochemical composition of extrusive and subvolcanic intrusive rocks of the upper miocene farallon negro volcanic complex nw argentina were studied to reconstruct the evolution of a deeply eroded andesitic volcano over most its life history of some 3 5 my this paper is part of an integrated study of the processes that generate magmatic hydrothermal fluids responsible for the formation of porphyry cu au deposits here we present new data on bulk rock chemical and nd sr and pb isotopic compositions of unaltered volcanic and subvolcanic intrusive rocks for which geological relations and ages are constrained by field based stratigraphy and extensive ar ar geochronology the combined results indicate that voluminous volcanism started at ca 9 7 ma with the eruption of basaltic andesite to andesite lava flows and pyroclastic deposits this basic to intermediate volcanism persisted until 7 5 ma and was followed at 7 35 ma by the eruption of dacites as the last recorded major extrusive event the oldest andesitic intrusions emplaced at 9 0 ma were followed by hypabyssal intrusions of basaltic andesite andesite and dacite composition which intruded the volcanic sequence between 8 3 and 6 1 ma intrusions at 6 8 0 2 ma led to the formation of over 800 mt of porphyry cu au ore at bajo de la alumbrera it was formed by a large flux of magmatic hydrothermal fluids channeled through several phases of fractured dacitic porphyry which together with immediately following barren andesitic intrusions make up a composite stock after this magmatic hydrothermal event only minor rhyodacitic to rhyolitic intrusions were emplaced until magmatic activity ceased at 6 1 ma geochemical data for the magmatic rocks indicate that the evolution of the system was dominated by mixing of a mafic magma with a felsic magma that contained a component of crustal material as indicated by linear compositional correlations between compatible and incompatible elements initial strontium isotopic ratios vary between 0 7047 and 0 7118 while 143nd 144nd range from 0 5127 to 0 5124 and both isotopic variations correlate with each other and with sio2 content of the rocks after 8 5 ma a continuous increase in the silica content of intrusive rocks suggests the gradual formation of a magma chamber a substantial magma reservoir 7 km3 must have been established by the time of porphyry cu au mineralization to allow rapid release of a large volume of ore forming magmatic brine as a result of wholesale crystallization and de volatilization of the magma chamber

the complex hydrothermal history of granitic rocks multiple feldspar replacement reactions under subsolidus conditions recurring subsolidus re equilibration of granitic feldspars induced by fluid infiltration events provides a record of fluid rock interactions that affect large volumes of the earth s continental crust this has a direct bearing on the interpretation of the present day granitic rock mineralogy and geochemistry we examine palaeoproterozoic grey and red stained granitoids from the simpevarp and laxemar areas in se sweden particularly focusing on consecutive feldspar replacement reactions to provide an in depth understanding of subsolidus re equilibration of granitic rocks with hydrothermal fluids the apparently most unaltered grey granitoids contain highly porous oligoclase grains that enclose crystallographically continuous microcline relicts this texture suggests that the oligoclase is already secondary and may be a replacement product of original microcline oligoclase is progressively replaced by albite an9 along polysynthetic twinning and intragranular fractures the features of this replacement are characteristic of a dissolution reprecipitation mechanism finegrained mica sericite is closely associated with the albite porosity within micron sized pores observable with scanning electron microscopy as well as in nanopores imaged with transmission electron microscopy the reddening phenomenon in the vicinity of fractures is contemporaneously related to the k feldspathization of sericite which is restricted to the altered oligoclase submicron size hematite precipitation within orthoclase pores at the replacement front results in the red coloration the complex associations between the fluid feldspar reactions indicate that the replacement reactions may be due to sequential fluid infiltration events and that the granitoids have undergone extensive subsolidus re equilibration changing the original magmatic mineralogy therefore the effects of large scale re equilibrations of granitic rocks through hydrothermal convection systems should be more closely considered

magmatic and hydrothermal r e e fractionation in the xihuashan granites se china the xihuashan stock south jiangxi china is composed of cogenetic granitic units granites xe a c d and b and emplaced during the yanshanian orogeny 153 0 2 ma they are two feldspars fe rich biotite garnet and slightly peraluminous granites primary accessory minerals are apatite 1 monazite zircon uranothorite xenotime in granites xe and a zircon uranothorite uraninite betafite xenotime 1 hydrothermal minerals are monazite altered into parisite and apatite 2 y rich parisite yttroparisite y rich fluorite and xenotime 2 in granites c and b petrographic observations major element ree y and rb sr isotropic data point to a magmatic suite granites xe and a granites c and d granite b distinct from hydrothermal na or k alteration of b from granite xe to granite b lree eu th and zr content are strongly depleted while hree y and u content increase during k alteration of b these variations are of minor importance major and accessory mineral evidences geochemical and fluid inclusion results indicate two successive alteration fluids interacting with b 1 a late magmatic f and co2 rich fluid and 2 a post magmatic aqueous and slightly saline fluid the depletion of lree and th content and the increase in hree y and u content correspond in the magmatic suite to the early fractionation of monazite in the granites where there is no hydrothermal alteration granites xe and e and to the hydrothermal alteration of monazite into parisite and secondary apatite intense new formation of yttroparisite y enrichment and u loss in the uranothorite and late crystallization of uraninite in the granites c and b moreover simulated crystallization of monazite and temperature of monazite saturation show early fractionation of monazite from the magma in the less evolved granites xe and e and prevailing hydrothermal leaching of monazite in the most evolved granites c d and b related to a late magmetic event the slight variations of ree y th and u content in the k altered granites compared to granite b emphazes the distinct chemical nature of the successive hydrothermal fluids rb sr and sm nd isotopic results point to a 30 ma period of time between the late magmatic and the post magmatic fluid circulation

constraints of in situ zircon and cassiterite u pb molybdenite re os and muscovite 40ar 39ar ages on multiple generations of granitic magmatism and related w sn mineralization in the wangxianling area nanling range south china abstract the nanling range in south china hosts numerous w sn rare metal deposits associated with several cycles of polygenetic granitic intrusions in the wangxianling area of the middle nanling range igneous intrusions include the wangxianling and hehuaping granite plutons and more than 20 granite porphyry dykes the wangxianling pluton has a central phase of medium grained tourmaline two mica granite and a marginal phase of medium grained tourmaline muscovite granite the pluton hosts several tungsten deposits including shuiyuanshan and yejiwo mineralization type is dominantly scheelite greisen with subordinate scheelite skarn and wolframite quartz veins the hehuaping pluton composed of coarse grained biotite granite and granite porphyry dykes to the east of the wangxianling pluton have an associated hehuaping tin deposit with tin skarn and subordinate porphyry and greisen mineralization in situ zircon and cassiterite u pb dating molybdenite re os and muscovite 40ar 39ar dating techniques are used to refine the age spectra of granitic rocks and w sn mineralization in the wangxianling area granites of the wangxianling pluton have zircon u pb ages of 224 ma tungsten bearing quartz veins from both the shuiyuanshan and yejiwo tungsten deposits have an average molybdenite re os isochron age of 224 ma and muscovite of scheelite greisen from the shuiyuanshan tungsten deposit yields a 40ar 39ar plateau age of 214 ma the two mineralization ages are consistent with the zircon u pb age of the wangxianling pluton indicating a close association between pluton emplacement and w mineralization in the late triassic both the hehuaping pluton and granite porphyry dykes have zircon u pb ages of 156 ma in situ la icp ms u pb dating of cassiterite in both the tin skarn and tin greisen yields an average age of 156 ma showing that the sn mineralization occurred at a similar time to the late jurassic granitic magmatism thus two mineralization events are identified in the wangxianling area and include an earlier w dominant mineralization event and a later sn dominant mineralization event the earlier event is related both spatially and temporally to intrusion of the late triassic s type wangxianling granite pluton whereas the later mineralization is associated both spatially and temporally with intrusion of the late jurassic hehuaping a2 type granite pluton and a2 type granite porphyry dykes

diachronous and independent histories of plutonism and mineralization in the cornubian batholith southwest england concordant u pb dates of magmatic monazites in the dominant coarse grained biotite muscovite granites of the late variscan cornubian batholith demonstrate that the emplacement of the six main plutons was diachronous ranging from 293 1 1 3 ma carnmenellis to 274 5 1 4 ma land9s end southern lobe 40 ar 39 ar age spectra for magmatic muscovites confirm that cooling to about 320 c at the present level of exposure was accomplished within 4 to 5 ma in each intrusion moreover age spectra for hydrothermal muscovites show that development of the major sn cu lodes of the south crofty mine commenced before 286 ma only 2 to 3 ma after cooling of the hosting cam brea granite a satellite of the carnmenellis pluton the older plutons had therefore approached ambient temperatures and had even experienced intense hydrothermal activity before emplacement of the youngest

reappraisal of the ages of neoproterozoic strata in south china no connection with the grenvillian orogeny the jiangnan fold belt separates the yangtze and cathaysia blocks in south china and has long been considered grenvillian in age in order to place south china in central rodinia it consists of deformed early neoproterozoic strata that are unconformably overlain by undeformed late neoproterozoic strata and intruded by undeformed and unmetamorphosed granitic plutons zircons from the early neoproterozoic strata yield u pb ages as young as 830 ma and one granitic pluton has a zircon u pb age of ca 827 ma the 830 ma mafic rocks along the southeastern margin of the yangtze block have arc affinity geochemical characters whereas mafic rocks younger than 830 ma have typical ocean island basalt oib like compositions thus we suggest that the early neoproterozoic strata were deposited on an active continental margin prior to amalgamation of the yangtze and cathaysia blocks at ca 830 ma the overlying late neoproterozoic strata were deposited in the intracontinental rifted nanhua basin at 820 730 ma and probably reflect backarc spreading above the long lived 950 735 ma oceanic subduction zone along the northern and western margin of the yangtze block this model is consistent with the secular tectonic evolution of south china during the neoproterozoic the jiangnan fold belt is therefore not a grenvillian feature as previously suggested and there is no evidence to place south china in central rodinia instead we believe that south china was located in a marginal position relative to this supercontinent

ocean surface topography measured by the geosat radar altimeter during the frontal air sea interaction experiment an objective analysis oa technique was used to analyze geosat geodetic mission residual sea height anomalies rsha for the frontal air sea interaction experiment fasinex conducted in the western north atlantic preprocessing of the geosat data included removal of a mean sea surface and orbit error and corrections for tides wave height inverse barometer and ionospheric and dry tropospheric effects geosat data were not corrected for water vapor central to the analysis was the computation of a spatially anisotropic time dependent autocorrelation function directly from the geosat data results show a single autocorrelation function peak having a diameter of 270 km at 0 day time lag a 15 month time series of rsha topography was constructed at 10 day intervals forming a set of 47 oa maps these maps show a field of topographic features propagating to the west at 4 km d 1 the features exhibited spatial and temporal scales of 200 km and 50 days respectively the root mean square rms of the oa derived feature amplitudes fluctuated slowly between 0 05 and 0 09 m with a period of 200 days over the 15 month interval these fluctuations appeared to be related to the passage of large scale northeast southwest trending sea surface temperature sst anomaly features reported for fasinex which were surface manifestations of large scale first mode baroclinic rossby waves the rms amplitude of the oa derived features was maximal minimal during periods of negative positive sst anomaly when the depths of the mixed layer and main thermocline in the upper ocean shoaled deepened the fluctuations also appeared to be correlated with the structure of the field periods of decreased feature amplitudes corresponded to a closely packed structure while during times of increased amplitudes the field structure became zonal with regions of alternating sign during fasinex january june 1986 the field was characterized by the closely packed structure and decreasing feature amplitudes this corresponded to the period of positive sst anomaly and high upper ocean heat content reported for fasinex

superimposed w and ag pb zn cu au mineralization and deep prospecting insight from a geophysical investigation of the yinkeng orefield south china abstract the yinkeng orefield is located in the eastern nanling region south china the nanling region hosts numerous w sn dominant polymetallic deposits related to the widely distributed mesozoic granites making it one of the most important w sn polymetallic metallogenic belts in the world in this study we utilized multiple geophysical methods including gravity magnetic audio frequency magnetotelluric sounding amt and high resolution reflection seismic techniques to detect the underground distribution of granites strata and structures our aims are to understand better the ore controlling mechanisms for the large scale w ag au pb zn aggregation to establish a metallogenic model for this type of mineralization and to supplement a 3000 m scientific drilling program in the nanling region for the chinese sinoprobe program project sp nlsd 1 in the yinkeng orefield an ore controlling ne trending nappe structure is composed of several thrust faults at shallow depths f1 and f2 which merge into a single major fault at depth the pre sinian sedimentary rocks of the hanging wall of these faults have much higher velocities densities and wave impedance than the carboniferous permian sedimentary rocks of the footwall the slip surface of the nappe which appears to have low resistivity extends downward to a two way travel time of more than 2 5 s equivalent to a depth of more than 4000 m thrusting was from se to nw and the fault flattens at depth the nappe structure may have provided channels for magmas and mineralized hydrothermal fluids granites in the yinkeng area which are spatially associated with the w ag pb zn orebodies generally show high resistivity low polarizability low seismic velocity and medium magnetism and their geophysical characteristics have revealed their distribution at depth specifically the gaoshanjiao granodioritic pluton closely related to precious metal mineralization is characterized by low density and high magnetism allowing us to identify a large buried part of the pluton se of the exposed body the jiangbei granitic pluton which typically hosts w mineralization has lower magnetism that reveals a ne trending extension about 2 2 2 8 km wide at a depth of 16 6 km one completely concealed granite the yinkeng pluton lies below the nappe structure it is geophysically similar to the jiangbei granitic pluton but has an obviously higher magnetic signature the high magnetism may be due to stratiform polymetallic bodies which could represent a good exploration target for porphyry skarn type w cu polymetallic deposits drilling site for sp nlsd 1 combined with surface mapping the geophysical data collected in this study allow us to propose a deep exploration model that can serve as a guide for w polymetallic ore prospecting in the nanling and adjacent regions

large scale sst variability in the western north atlantic subtropical convergence zone during fasinex part i description of sst and wind stress fields abstract we describe properties of large scale fluctuations in the wind field represented by two analyses fnoc and noaa atoll and in the sst field represented by maps derived from 5 day composite avhrr images within an 11 longitude by 10 latitude domain during fasinex january through june 1986 fnoc and atoll wind and wind stress time series were highly correlated with each other 0 8 over the entire domain and they were also highly correlated with time series measured at the fasinex site 0 89 at periods of 2 13 days clockwise energy exceeded anticlockwise energy by an order of magnitude while the energy was nearly partitioned equally at periods of 13 40 days mean atoll winds were everywhere more eastward than mean fnoc winds probably in part because the atoll fnoc analyses are intended to represent 850 mb 19 5 m winds the 850 mb winds are expected to be more eastward due to the thermal wind balance with the mean southward air temperature gradient the sst maps represented large s

large scale sst variability in the western north atlantic subtropical convergence zone during fasinex part ii upper ocean heat balance and frontogenesis abstract we analyzed the influence of wind deriven horizontal heat advection on the large scale o 1000 km wavelength variability of both the upper ocean mixed layer heat content and the subtropical frontal zone sfz within an 11 by 10 domain in the western north atlantic ocean during fasinex january through june 1986 by estimating heat advection due to both ekman transport and interior geostrophic sverdrup minus ekman transport from a slab mixed layer heat balance equation using satellite derived sea surface temperature ts and wind analysis maps it was found that these processes could not account for the observed variability in either beat content or the sfz the annual cycle of surface vertical heat flux had the dominant influence on the heat content even when the average heat balance was analyzed during a 4 month time interval when the net influence of the annual cycle was nearly zero mid january to mid may 1986 westward propagating ts spatial anomaly features with peak to peak scales

westward propagating sst anomaly features in the sargasso sea 1982 88 abstract sea surface temperature ts maps of the region from 59 5 to 75 5 w 22 5 to 33 5 n containing the western north atlantic subtropical convergence zone stcz were derived from avhrr 2 images the 7 year mean annual cycle was removed and the maps were filtered in space and time to represent anomaly variability with wavelengths 220 km and periods 50 days warm and cold anomaly features were observed cast of 71 w between 26 and 32 n that propagated westward at 3 4 km day 1 and that occasionally exceeded 1 c in amplitude they are generally strong and persistent from fall to spring and are only marginally detectable during summer during 1981 82 1982 83 and 1985 86 individual features could be followed through the entire fall spring interval during 1983 84 1986 87 and 1987 88 they could typically be followed for 2 4 months and during 1984 85 for only 1 2 months the features were anisotropic during all fall spring intervals except 1986 87 and they had characteristic wavelengths of 80

genetic types mineralization styles and geodynamic settings of mesozoic tungsten deposits in south china abstract south china hosts the most abundant and largest tungsten w deposits in the world being a famous w metallogenic region located at the eastern part of the south china block which was formed by amalgamation of the yangtze and cathaysia blocks during the neoproterozoic these w deposits were mainly formed during the mesozoic the w mineralization is dominanted by greisen quartz vein skarn and porphyry types all of which are genetically related to the evolution of highly fractionated granitoids four episodes of w mineralization are recognized 1 late triassic 230 210 ma in the central and western parts of south china 2 middle jurassic ca 170 ma to early cretaceous ca 140 ma in the interior of south china with the mineralization being concentrated in southern jiangxi province between 165 and 150 ma 3 early cretaceous 136 120 ma with deposits across south china and 4 late cretaceous 100 80 ma mainly in the southwestern parts of south china these four periods of mineralization are closely related to the closure of paleo tethys and subduction of the paleo pacific plate in the late triassic these two events caused local extensional environments facilitating emplacement of the peraluminous granitoids and formation of the w deposits in the middle jurassic break off of the subducting oceanic plate resulted in emplacement of highly fractionated granites in the nanling region later anticlockwise rotation of the paleo pacific plate created widespread s type granitoids and associated middle jurassic to early cretaceous w mineralization in the interior of south china since 136 ma rollback of the subducting pacific plate resulted in weak w mineralization across south china finally a change of direction in the retreating plate from se to ese resulted in intensive mineralization of the southwestern part of south china

magmatic to hydrothermal crystallization in the w sn mineralized mole granite nsw australia part i crystallization of zircon and ree phosphates over three million years a geochemical and u pb geochronological study abstract zircon monazite and xenotime crystallized over a temperature interval of several hundred degrees at the magmatic to hydrothermal transition of the sn and w mineralized mole granite magmatic zircon and monazite thought to have crystallized from hydrous silicate melt were dated by conventional u pb techniques at an age of 247 6 0 4 and 247 7 0 5 ma respectively xenotime occurring in hydrothermal quartz is found to be significantly younger at 246 2 0 5 ma and is interpreted to represent hydrothermal growth from associated fluid inclusions it is concluded that it precipitated from a hydrothermal brine 600 c which is below the accepted closure temperature for u pb in this mineral these data are compatible with a two stage crystallization process precipitation of zircon and monazite as magmatic liquidus phases in deep crustal magma followed by complete crystallization and intimately associated sn w mineralization after intrusion of the shallow sill like body of the mole granite later hydrothermal formation of monazite in a biotite fluorite topaz reaction rim around a mineralized vein was dated at 244 4 1 4 ma which distinctly postdates the mole granite and is possibly related to a younger hidden intrusion and its hydrothermal fluid system obtaining precise age data for magmatic and hydrothermal minerals of the mole granite is hampered by uncertainties introduced by different corrections required for multiple highly radiogenic minerals crystallising from evolved hydrous granites including 230 th disequilibrium due to th u fractionation during monazite and possibly xenotime crystallization variable th u ratios of the fluids from which xenotime was precipitating elevated contents of common lead and post crystallization lead loss in zircon enhanced by the fluid saturated environment the data imply that monazite can also survive as a liquidus phase in protracted magmatic systems over periods of 10 6 years the outlined model is in agreement with prominent chemical core rim variation of the zircon