pacific interdecadal variability in this century s sea surface temperatures analysis of this century s sea surface temperatures over the pacific ocean reveals an interdecadal oscillation with a period of 15 20 years our results show that the well known 1976 77 climate regime shift is not unique but represents one of several phase transitions associated with this interdecadal oscillation also found around 1924 25 1941 42 and 1957 58 the oscillation s striking north south symmetry across the equator implies strong interactions between tropics and extratropics a mode with a period of approximately 70 years and an apparently different spatial pattern is also identified tentatively but has to be evaluated further using longer time series

topographic inversion and changes in the sediment routing systems in the variscan orogenic belt as revealed by detrital zircon and monazite upb geochronology in post collisional continental basins abstract the basal alluvial and fluvial siliciclastic successions within the late carboniferous intracontinental basins of the west central bohemian massif provide an intriguing sedimentary record of changes in paleotopography and paleodrainage systems during and after orogenic collapse we analyze this record using the u pb laser ablation icp ms detrital zircon and monazite geochronology five distinct age groups have been identified across the examined stratigraphic succession i archean paleoproterozoic ii late neoproterozoic iii cambro ordovician iv late devonian and v mid to late carboniferous these age groups indicate mixing of both local and distal extra basinal sources and also point to a two stage post convergent geodynamic evolution of the variscan belt the first stage followed collapse of the central bohemian orogenic plateau at around 346 337 ma and involved rapid cooling at ca 340 320 ma and removal of ca 2 3 km of sedimentary overburden from the top of the plateau no sedimentary record of this erosional event suggests that the river systems transported detritus radially outwards from the inner part of the orogen to its forelands a paleorelief inversion and thus major reorganization of the sediment routing systems were then associated with uplift in the southerly and southwesterly peripheral domains of the orogen at ca 330 310 ma in turn these uplifted domains occupied by rapidly unroofed voluminous granite plutons shed detritus into the bohemian sink this was represented by the former plateau collapsed to relatively low elevations but still with significant internal paleorelief dominated by a system of tens of kilometers long nne ssw trending paleovalleys some of the material was further transported in extensive river systems crossing the former plateau to the northerly variscan foreland basin thus the radial sediment routing system changed into axial unidirectional finally we suggest that these major inversions of paleorelief and changes in the surface processes and paleodrainage systems may have been linked to distinct late orogenic lithospheric mantle delamination events first stage delamination occurred beneath the center of the bohemian massif to cause the plateau collapse denudation and radial sediment transport whereas the second stage delamination occurred along its periphery to cause uplift sourcing the intracontinental basins and unidirectional sediment transport end of deposition and magmatic shutdown at around 305 ma may then define the very cessation of late orogenic vertical movements and the transition to a post orogenic intra plate setting

a nonlinear theory for el nino bursting abstract a new mechanism is proposed that explains two key features of the observed el nino southern oscillation enso phenomenon its irregularity and decadal amplitude changes using a low order enso model the authors show that the nonlinearities in the tropical heat budget can lead to bursting behavior characterized by decadal occurrences of strong el nino events la nina events are not affected a feature that is also seen in enso observations one key result of this analysis is that decadal variability in the tropics can be generated without invoking extratropical processes or stochastic forcing the el nino bursting behavior simulated by the low order enso model can be understood in terms of the concept of homoclinic and heteroclinic connections it is shown that this new model for enso amplitude modulations and irregularity although difficult to prove might explain some features of enso dynamics seen in more complex climate models and the observations

co 2 degassing in the hartousov mofette area western eger rift imaged by co 2 mapping and geoelectrical and gravity surveys strong subcontinental mantle dominated co2 degassing occurs in the hartousov and bublak mofette fields in the western eger rift the combination of co2 gas flux and soil gas measurements as well as gravity and geoelectric surveys provides insight into the surface and subsurface of this unique mofette area co2 soil gas and gas flux measurements reveal that large amounts of carbon dioxide are released via channels with diameters below 1 m carbon dioxide emissions of several tens and up to more than 100 kg day 1 are ejected via these small seeps measurements with small spacings are necessary to account for the point like focused gas discharge in the lesser degassing surrounding we estimate that between 23 and 97 tons of co2 are released over an area of about 350 000 m2 each day in the hartousov mofette field the application of widely used geostatistical tools leads to estimations of the co2 discharge with very high standard deviations due to the strong positive skewness of the data distribution geophysical investigations via electrical resistivity tomography and gravity measurements were carried out over areas of strong seepage and reveal distinct anomalies in the subsurface below mofettes indicating rock and sediment alterations and or sediment transport by pressurised ascending co2 and water mobilised by it this study reveals that the gas emanations only occur west of a morphological step which is related to a n s oriented fault zone the pocatky plesna fault zone the results of co2 mapping and the geophysical studies can track the course of this fault zone in this area our results fit into a tectonic model in which the mofette fields are in the centres of two independent pull apart basin like structures we hypothesise that the sinistral strike slip movement of the pocatky plesna fault zone leads to a pull apart basin like opening at which the strong mantle derived co2 degassing occurs nowadays since the hartousov and bublak mofette fields only illustrate examples along the n s striking pocatky plesna fault zone its role and other n s striking faults roles of the regensburg leipzig rostock zone for upper mantle degassing might have been underestimated previously

petrology magnetic fabric and emplacement in a strike slip regime of a zoned peraluminous granite the campanario la haba pluton spain

intrusion level of granitic massifs along the hercynian belt balancing the eroded crust abstract hercynian granitoid intrusions form a long 3200 km belt comparable in size to other batholiths in the world six massifs have been selected which encompass cabeza de araya extremadura spain guitiriz galicia spain pontivy and mortagne brittany france la marche massif central france and fichtelgebirge bavaria germany detailed gravity surveys over these massifs and subsequent inversion provide their shape at depth correlation of the deeper zones with internal structures determine the place of the root zones the shape of the massifs is examined along the strike of the chain the emplacement of individual massifs is controlled by local tectonics most granites are not deeply rooted but one massif cabeza de araya spain shows a root zone presently as deep as 14 km most have about half of their volume in the first 3 km below the present surface estimates of the magma volume transferred result in 1500 km 3 issued from one specific feeder yielding a total of 70 000 km 3 of magma intruded all along the chain the depth of emplacement of the granitic massifs does not show any significant trend along the strike of the chain the shallower massifs in the french massif central correspond to more deeply eroded areas in the center of the chain their root zone as well as the change in the dip of the walls are presently observed at depths ranging between 4 and 6 km in hercynian granites both variations are interpreted as being related to the brittle ductile transition at the time of emplacement gross thermal considerations place the transition at its former place during magma emplacement indicating that the upper crust has not been eroded by more than 6 8 km this estimate severely contrasts with models involving a doubled crust

seismically induced changes of the fluid signature detected by a multi isotope approach he co2 ch4 n2 at the wettinquelle bad brambach central europe 1 we present a study considering the systematics of gas and isotope compositions 3 he 4 he 13 c co2 13 c ch4 15 n of a permanent magmatic co 2 flux in the hydrothermal system of the spring wettinquelle in bad brambach and their relation to the seismic activity beneath the western eger rift the gas and isotope compositions were monitored for more than 3 years the time series includes periods before during and after a 4 month long seismically active period from the end of august to the end of december 2000 shifts due to admixture of crustal components were found for all monitored isotope ratios during and after the seismically active period in case of helium and nitrogen isotopic anomalies occurred already about 6 weeks before the beginning of the seismically active period contemporaneous with a water level anomaly of the well vl4 near the wettinquelle on the one hand preseismic deformations may be responsible for the observed isotope anomalies on the other hand coseismic fracturing processes in the surroundings of the hypocenters may play a role both effects produce greater permeability and result in the release of crustal fluids the migration and admixture of these crustal components to the permanent upper mantle derived fluid flux result in geochemical anomalies that persist for more than 2 years the results of the detailed isotope monitoring have proven to be an important contribution to understand the geodynamic processes that may presently be going on in the region vogtland nw bohemia

the mechanism of ascent and emplacement of granite magma during transpression a syntectonic granite paradigm we propose a model for syntectonic ascent and emplacement of granite magma based on structural relations in part of the northern appalachians in the study area in western maine strain was distributed heterogeneously during devonian acadian transpression metasedimentary rocks migmatites at high grades record two contrasting types of finite strain in zones that alternate across strike rocks in both types of zones have a penetrative moderately to steeply ne plunging mineral elongation lineation defined by bladed muscovite fibrolite sillimanite at high grades in straight belts of enhanced deformation rocks have s l fabrics that record apparent flattening to plane strain apparent flattening zones afzs but rocks between these belts have l s fabrics that record apparent constriction apparent constriction zones aczs at metamorphic grades above the contemporary solidus rocks in afzs developed stromatic structure in migmatite which suggests that percolative flow of melt occurred along the evolving flattening fabric stromatic migmatites are intruded by concordant to weakly discordant m scale composite sheet like bodies of granite to suggest magma transport in planar conduits through the afz rocks inhomogeneous migmatite is found in the intervening aczs which suggests migration of partially molten material through these zones en masse probably by melt assisted granular flow inhomogeneous migmatites are intruded by irregular m scale bodies of granite that vary from elongate to sub circular in plan view and seem cylindrical in three dimensions these bodies apparently plunge to the northeast parallel to the regional mineral elongation lineation to suggest magma transport in pipe like conduits through the acz rocks we postulate that the form of magma ascent conduits was deformation controlled and was governed by the contemporaneous strain partitioning magma ascent in planar and pipe like conduits through migmatites is possible because oblique translation during contraction displaces isotherms upward in the orogenic crust to form a thermal antiform within this hot corridor it is the difference in temperature between melt producing reactions in the anatectic zone and the wet solidus for granite melt that enables magma to migrate pervasively up through the orogenic crust without congealing heat advected with the migrating melt promotes amplification of the thermal antiform in a feedback relation that extends the zone of plastic deformation and pervasive melt migration to shallower levels in the crust at the wet solidus we suggest melt flows obliquely toward axial culminations in the thermal antiform which are sites of melt accumulation and perturbations from which magma may escape to form plutons batches of melt that escape from these perturbations may be trapped by tectonic structures higher in the crust or ascent may become inhibited with decreasing depth by thermal arrest and solidification if the rate of arrival of subsequent melt batches exceeds the rate of crystallization at the site of pluton construction melt pressure ultimately may lead to sub horizontal magma fracture or viscous flow of wall rocks may allow lateral spreading the resultant plutons have sub horizontal tabular geometries with floors that slope down to the ascent conduit as the thermal antiform decays the height of sub solidus crust that separates the deepest part of the pluton from the anatectic zone increases consequently pluton inflation declines and solidification leads to infilling of the magma feeder channel to form a root zone that passes downward into migmatite which may explain the difficulty of determining precisely the floor to these deeper segments of large plutons using gravimetry

interannual and decadal variability of the subsurface thermal structure in the pacific ocean 1961 90 heat content anomalies are analyzed to understand subsurface variability on both aparticular focus on the evolving basinwide patterns and oceanic connections between the extratropics and tropics various analyses indicate two distinct modes one interannual and the other decadal that involve the tropics and the north pacific subtropical gyre respectively interannual variability is associated with el nino in the tropics with a prominent see saw pattern alternately on and off the equator and in the east and west respectively the interannual cycle features a coherent propagation of subsurface signals around the tropical pacific eastward along the equator but westward off the equator at 10 15 n decadal signals are dominant in the subtropics and midlatitudes but also have a tropical component that appears to be independent of interannual variations an oceanic connection can be seen between subsurface anomalies in the midlatitudes in the subtropics and tropics on decadal time scales subsurface thermal anomalies associated with midlatitude decadal variability can propagate through the subtropics into the tropics which may modulate the intensity of interannual variability in the tropics for example in the middle and late 1970s a significant warm temperature anomaly appeared to penetrate into the western and central tropics at depth warming the tropical upper ocean and depressing the thermocline during the development of el nino therefore an extratropically preconditioned subsurface state e g an enhanced positive heat content anomaly in the western and central tropical pacific would favor a warmer sea surface temperature anomaly in the eastern equatorial pacific potentially increasing the intensity of ocean atmosphere coupling these changes in the thermocline structure and possibly in the coupling strength can further alter the very character of tropical air sea interactions this may help to explain decadal variability of el nino evolution in the tropical pacific as observed in the 1980s our subsurface variability analysis presents observational evidence for the detailed space time structure of decadal oceanic links between the extratropics and the tropics

interdecadal change of the structure of the enso mode and its impact on the enso frequency in the late 1970s the enso cycle exhibited frequency change the oscillation period increased from 2 4 yr high frequency during 1962 75 to 4 6 yr low frequency during 1980 93 observations suggest that this frequency change was accompanied by a significant change in the structure of the coupled enso mode in comparison with the high frequency regime the structure of the coupled mode in the low frequency regime shows three distinctive features during the warm phase of enso the eastward shift of the westerly anomalies the meridional expansion of the westerly anomalies and the weaker intensity of the easterly anomalies in the eastern pacific to test the robustness of the relationship between the oscillation period and the structure of the coupled mode the authors designed empirical atmospheric models based on observations and coupled them with the ocean model of zebiak and cane numerical experiments demonstrate that the enso period is sensitive to changes in the wind anomaly pattern in a way much like the observed enso frequency structure relation the increase of the enso period after 1980 is mainly due to the eastward shift of the zonal wind stress with respect to the sst anomalies physical explanations of the dependence of enso frequency on the structure of the coupled mode are provided by diagnosing the relative contributions of the thermocline feedback and zonal advection feedback on enso evolution

how different wind stress patterns affect the tropical subtropical circulations of the upper ocean abstract an oceanic gcm is used to investigate the response of the tropical and subtropical thermocline circulation and structure to different wind stress patterns although the subtropical winds do not affect the transport or the speed of the equatorial undercurrent significantly they do change the equatorial temperature field in the lower part of the equatorial thermocline significantly a weaker subtropical wind curl causes a cooling of the subsurface equatorial region and hence an intensification of the equatorial thermocline a weakening of the subtropical wind curl by a factor of 2 cools the equatorial lower thermocline water by 2 c

interdecadal sea surface temperature variability in the equatorial pacific ocean part ii the role of equatorial off equatorial wind stresses in a hybrid coupled model abstract many modeling studies have been carried out to investigate the role of oceanic rossby waves linking the off equatorial and equatorial pacific ocean although the equatorial ocean response to off equatorial wind stress forcing alone tends to be relatively small it is clear that off equatorial oceanic rossby waves affect equatorial pacific ocean variability on interannual through to interdecadal time scales in the present study a hybrid coupled model hcm of the equatorial pacific between 12 5 s and 12 5 n was developed and is used to estimate the magnitude of equatorial region variability arising from off equatorial poleward of 12 5 latitude wind stress forcing the hcm utilizes a reduced gravity ocean shallow water model and a statistical atmosphere derived from monthly output from a 100 yr australian bureau of meteorology research centre now the centre for australian weather and climate research coupled general circulation model integration the equatorial region wind stress forcing i

the relationship between length and width of plutons within the crustal scale cobequid shear zone northern appalachians canada the lengths and widths have been measured for 69 component bodies of composite plutons along the cobequid shear zone plutons on major fault strands those with mylonite zones 0 1 km wide exhibit evidence of multiple intrusion of magma batches small plutons along short faults in stepover zones appear related to rapid emplacement of magma in bodies 1 5 4 km long by 0 1 2 km wide such small plutons show low enrichment in incompatible elements in older component bodies but increasing amounts in younger bodies as a result of progressive magma expulsion from crystal mush during crystallization and shear enhanced compaction in fault zones wider plutons generally occur along longer fault strands accommodating more strain and penetrating deeper into the crust and show enrichment in incompatible elements the width of the mylonitic fault zone is about 15 of the width of these plutons the length to width ratio of component bodies and composite plutons varies between 2 and 11 the best fit line describing these data has a slope of 1 056 which implies scaling behavior between plutonism and tectonic processes scalar properties of plutonic bodies are similar to those of faults but scalar relationships observed in component bodies do not apply to composite plutons

ventilation of the subtropical north pacific abstract the ventilation of the subtropical north pacific is studied using a simple analytical model the model is forced by winter mixed layer density and depth calculated from the levitus climatology and wind stress curl from the hellerman and rosenstein wind stress data the wind driven gyre in the north pacific is shallow no more than 1 4 km the gross feature of the subduction rate is very similar to the results by huang and qiu based on data analysis of the levitus climatology with a total ventilation rate of 31 3 sv sv 106 m3 s 1 including 20 8 sv due to the vertical pumping and 10 5 sv due to lateral induction the age of water within the ventilated thermocline is relatively young it is no more than 10 years old except near the southeast corner of the basin the young age indicates a fast communication between the atmosphere and the upper ocean on a timescale of less than 10 years the vertical mass partition is slightly different from the results based on analysing climatology by huang a

origin of upper ocean warming and el nino change on decadal scales in the tropical pacific ocean the cause of decadal scale variability in the tropical pacific ocean such as that marked by the 1976 77 shift in the el nino southern oscillation1 2 3 4 5 6 7 is poorly understood unravelling the mechanism of the recent decade long warming in the tropical upper ocean is a particularly important challenge given the link to el nino variability but establishing the hypothesized interannual decadal oceanic connections between middle latitudes and tropics has proved elusive8 here we present observational evidence that pacific upper ocean warming and decadal changes in the el nino southern oscillation after 1976 may originate from decadal mid latitude variability in the middle 1970s the north pacific ocean is observed to have undergone a clear phase transition a see saw subsurface temperature anomaly pattern that rotates clockwise around the subtropical gyre at middle latitudes a subsurface warm anomaly formed in the early 1970s from subducted surface waters and penetrated through the subtropics and into the tropics thus perturbing the tropical thermocline and driving the formation of a warm surface water anomaly that may have influenced el nino in the 1980s the identification of this teleconnection of extratropical thermal anomalies to the tropics through a subsurface ocean bridge may enable improved prediction of decadal scale climate variability

should felsic magmas be considered as tectonic objects just like faults or folds abstract integrated studies that correlate gravity data with magmatic structures or geochemical analysis reveal that the organization of granitic plutons shape and feeder varies according to the tectonic regime brittle or ductile and type extension strike slip or compression under which magma was generated deformation clearly controls granite emplacement it also has influence during the ascent segregation of melt and indirectly during the phase of initial melting because of the contrast of viscosity between melt and its plastic matrix strain partitioning develops during magma ascent that facilitates melt flow which bears consequences for the chemical evolution of the magma fast rate of melt extraction out of the source may lead to chemical disequilibrium at a larger scale petrochemical zoning of plutons is described as a dynamic process that results from the competition between the rate of magma emplacement the rate of the room provided by deformation and the rate of magma delivery

experimental geochemical mineralogical and o isotope constraints on the late magmatic history of the fichtelgebirge granites germany mineralogical experimental geochemical and stable isotope data give evidence for an aqueous late stage fluid which develops increasingly from the less to the more highly evolved granites of the fichtelgebirge g1 g4 in less evolved granites particularly g1 only minor chloritization and sericitization minor hydration and corrosion of zircons low leachable fractions of sr and zr the nearly chondritic ratios of zr hf and y ho and rare earth element ree patterns lacking the tetrad effect provide evidence of a less differentiated granitic melt system poor in complexing agents and water with insignificant late magmatic fluid rock interaction the subsequent low temperature alteration which is suggested by oxygen isotope composition of quartz and biotite did not affect the whole rock chemical composition in the highly evolved granites particularly g4 albitization sericitization and fluoritization ubiquitous hydration and corrosion of zircons high leachable fractions of sr and zr zr hf and y ho ratios very different from the chondritic ratios and ree patterns showing a marked tetrad effect point to the presence of a highly specialized fluid system rich in water and complexing agents such as fluorine leading to a marked magmatic hydrothermal alteration the oxygen isotopes also indicate alteration by high temperature fluids which were likely exsolved during the final stage of crystallization

successive granitic magma batches during pluton emplacement the case of cabeza de araya spain we present a dynamic scenario of granite emplacement in the upper introduction crust for the pluton of cabeza de araya extramadura spain various mechanisms have been suggested to account for based on interpretations of gravity data internal structures and the emplacement of granitic bodies they range from geochemical variations the three dimensional shape of the pluton forceful intrusion via diapirism cruden 1988 or dyking is derived from the inversion of gravity data and the magma flow clemens mawer 1992 to permitted intrusion assisted structures are obtained by mapping the rock anisotropy of magnetic by deformation hutton 1982 castro 1985 guinesusceptibility the deepest zones of the pluton which also correspond berteau et al 1987 hutton et al 1990 between these to vertical lineations are interpreted as feeder zones from which modes ballooning brun et al 1990 nested diapirs magma upwelled these feeders form small distinct areas connected bouchez diot 1990 paterson vernon 1995 to the pluton s floor 6 km below the present surface level we propose stoping paterson fowler 1993 and also recognition that the two main feeders of the pluton represent tension gashes that of the ubiquity of syntectonic magmatism hutton 1997 formed at the base of the brittle crust and served as conduits for call for a competition depending on the crustal level the magma that was ready to be tapped in the southern half of of observation between mechanisms driven by magma the pluton granite type a is cross cut by type b in the magmatic pressure and those involving tectonic accommodation state these magmas show a continuum in their chemistries attributed evidence for the original segregation and ascent of to progressive differentiation a fine grained leucocratic granite more felsic magmas now frozen as plutons is difficult to evolved chemically cross cuts the surrounding facies and crops out observe in the field as a consequence these processes above the southern feeder zone it is interpreted as a late magma have to be inferred from petrological and rheological batch coming from a different source that intruded into the models of both the magma and country rock e g cruden incompletely crystallized surrounding facies the normal petrographic 1988 weinberg podladchikov 1994 stages of magma zoning of the massif of cabeza de araya is therefore viewed as a generation and transport have however little influence succession of continuous and discontinuous infillings sequentially on the mode of the final ponding of the magma which permissive and forceful of increasingly evolved magma batches into in turn is not directly observable in the field in addition a reservoir that opened at varying rates within the brittle crust to considerations from regional geology information from

constraints on the origin of zonation of the granite complexes in the fichtelgebirge germany and czech republic evidence from a gravity and geochemical study compositional zoning of granitic plutons is a common feature but the spatial variation of zoning is rarely studied in detail it is suggested that important additional information can emerge if the compositional zoning is regarded with relation to the root zones i e with the granite shape at depth a combined geochemical and gravity investigation was performed on the hercynian fichtelgebirge granites which are composed of an older intrusive complex oic and younger intrusive complex yic the oic and yic are distinct from each other with respect to magma origin differentiation pattern shape of the granite complexes at depth and the zonation pattern in relation to the root zone the oic shows normal compositional zoning whereas the yic both reverse yic 1 and normal zoning yic 2 the general zonation pattern of the oic and the yic is the result of a combination of multiple injections of single magma batches and in situ differentiation during magma emplacement in addition to the general zonation pattern local zonation in individual granite bodies of the yic was caused by sidewall crystallisation producing a less differentiated marginal facies g2 and a more differentiated core facies g3 and g4 it is suggested that the complex zonation patterns of the fichtelgebirge granite complexes reflect interactions between the rate of magma output which is partly governed by their rheological properties and the rate of deformation which provides the room for the magma to be emplaced

long term hydrographic changes at 52 and 66 w in the north atlantic subtropical gyre caribbean abstract in july september 1997 two hydrographic lines were done in the western n atlantic along longitudes of 52 and 66 w as part of the woce one time hydrographic survey of the oceans each of these two lines approximately repeated earlier ones done during the international geophysical year s igy and the mid 1980s because of this repeated sampling long term hydrographic changes in the water masses can be examined in this report we focus on temperature and salinity changes within the subtropical gyre mainly between latitudes of 20 and 35 n and compare our results to those presented by bryden et al 1996 who examined changes along a zonal line at 24 n most recently occupied in 1992 since this most recent 24 n section in 1992 substantial changes have occurred in the western part of the subtropical gyre at the depths of the labrador sea water lsw in particular we see clear evidence for colder fresher labrador sea water throughout the gyre on our two recent sections that was not yet present in 1992 at similar longitudes along 24 n at shallower depths inhabited by waters that are an admixture of mediterranean mw and antarctic intermediate waters aaiw our recent survey shows an increase in salinity which can only be attributed to changes in water masses on potential temperature or neutral density surfaces furthermore waters above the mw aaiw layer and into the deeper part of the main pycnocline have continued to become saltier and warmer throughout the 40 year period spanned by our sections these latter changes have been dominantly due to a vertical sinking of density surfaces as t s changes in density surfaces are small but depths of individual t s horizons have increased with time the net change since the igy shows a mean temperature increase between 800 and 2500 m depth at a rate of 0 57 c century with a corresponding steric sea level rise of 1 mm yr and a net downward heave with small values near the top and bottom and a maximum rate of 2 7 m yr at 1800 m depth changes in the deep caribbean indicate a warming since the igy due to temperature increases of the inflowing source waters in the subtropical gyre at 1800m depth but no significant change in the deep salinity

fractured hydrothermal dolomite reservoirs in the devonian dundee formation of the central michigan basin the middle devonian dundee formation is the most prolific oil producing unit in the michigan basin with more than 375 million bbl of oil produced to date reservoir types in the dundee formation can be fracture controlled or facies controlled and each type may have been diagenetically modified although fracture controlled reservoirs produce more oil than facies controlled reservoirs little is known about the process by which they were formed and diagenetically modified in parts of the dundee preexisting sedimentary fabrics have been strongly overprinted by medium to coarse grained dolomite dolomitized intervals contain planar and saddle dolomite with minor calcite anhydrite pyrite and uncommon fluorite fluid inclusion analyses of two phase aqueous inclusions in dolomite and calcite suggest that some water rock interaction in these rocks occurred at temperatures as high as 120 150c in the presence of dense na ca mg cl brines these data in conjunction with published organic maturity data and burial reconstructions are not easily explained by a long term burial model and have important implications for the thermal history of the michigan basin the data are best explained by a model involving short duration transport of fluids and heat from deeper parts of the basin along major fault and fracture zones connected to structures in the precambrian basement these data give new insight into the hydrothermal processes responsible for the formation of these reservoirs

microthermometric study of silicate melt inclusions in variscan granites from se germany volatile contents and entrapment conditions melt inclusions in granitic rocks are generally crystalline and must oberpfalz regions along the northern margin of the be homogenized to glass before analysis we employ a simple kinetic bohemian massif some of these granites particularly in technique with microthermometry to estimate total volatile contents the german erzgebirge are highly evolved geochemically and p t conditions of trapping of the melts from their hoand famous for the tin and uranium mineralization mogenization behaviour this information complements chemical associated with them several publications have condata from microprobe or ion probe analysis and can be obtained centrated on the geology geochemistry and ore from inclusions too small for direct analysis we present here values associations of the granites forster tischendorf 1994 for volatile contents as equivalent wt h2o trapping temperatures seltmann 1994 tischendorf forster 1994 hecht et and trapping pressures derived from studies of melt inclusions in some al 1997 siebel et al 1997 but their magmatic volatile variscan granites of the erzgebirge fichtelgebirge and oberpfalz contents and emplacement level are difficult to determine germany the volatile concentrations range from 3 to 10 equiv wt and have not often been addressed the granites from h2o microprobe analysis shows that the most volatile rich these regions contain abundant melt inclusions and these inclusions contain up to 8 wt f estimates of trapping offer the potential of constraining melt water contents pressures and temperatures suggest that crystallization began at an and conditions of trapping emplacement level of 3 6 5 km near 700 c with normal biotite all three regions contain composite plutons or plutonic and two mica granites and ended with topaz albite granite complexes which range in composition from un 650 c and pegmatitic phases down to 520 c this wide differentiated biotite granites to more highly evolved tworange of trapping temperatures and volatile contents is a general mica granites and finally to extremely evolved granites feature of melt inclusions in granites many of the granites studied containing li micas and topaz in some cases this comare highly evolved geochemically but the extreme volatile enrichment positional range is covered by different units of a single typical for these also occurs locally in the unspecialized granites pluton e g falkenberg granite oberpfalz whereas in other places individual plutons are more restricted in composition the erzgebirge region is particularly rich

geology of the devonian dundee reservoir west branch field michigan 1 west branch field located near the center of the michigan basin is a low relief asymmetric northwest southeast trending anticline since 1934 the dundee reservoir middle devonian dundee and rogers city limestones has produced more than 12 million bbl 2 million m 3 of oil from this field dundee sediments were deposited on a carbonate ramp that dipped gently to the northwest core studies and log correlations show that the reservoir is dominated by normal marine somewhat lenticular beds of skeletal peloidal grainstones and packstones crinoids are very abundant comprising nearly 100 of the grains in some intervals the uppermost dundee consists of micritic carbonates with a restricted faunal assemblage the dundee rogers city contact is a disconformity that ppears to be a pyritized extensively bioeroded hardground the overlying rogers city limestone is a dark nodular wackestone with rare packstone interbeds trace amounts of dolomite are common throughout the field however pervasive dolomite is common only in the top 10 15 ft 3 4 5 m of the dundee this dolomite generally has high porosity 5 15 but very low permeability 0 1 0 md primary interparticle porosity in limestones accounts for most of the reservoir porosity although previous workers have concluded that fracture controlled dolomites are responsible for porosity and permeability in this field we conclude that such dolomites are not important we also conclude that at west branch field there is no evidence for reefal growth over a pre existing fold as has been reported in other dundee rogers city reservoirs

a simple model of the mass exchange between the subtropical and tropical ocean abstract a simple ventilated thermocline model is used to study the subtropical tropical mass exchange it is found that the water subducted in the western subtropical gyre recirculating window tends to recirculate within the subtropical gyre while the water subducted in the eastern part exchange window tends to penetrate equatorward the exchange window expands with an increased easterly wind or basin width on the southern boundary of the subtropical gyre but shrinks with an increased wind curl within the subtropical gyre furthermore the total exchange transport increases with the easterly wind or the width of the basin on the southern boundary of the subtropical gyre but it is independent of subtropical wind the ventilation mechanism is important in supporting the exchange transport for wind with realistic strength at the southern boundary the reduction of the exchange transport is about 15 30 of the ekman transport finally relative to the exchange transport in the interior of the ocean

earthquake impact on iron isotope signatures recorded in mineral spring water we investigated the iron isotope signatures of dissolved fe in the water of the wettinquelle mineral spring bad brambach germany by time series sampling covering seismically active periods related to tectonic activity near the eger rift system in central europe our objective was to test whether fe isotopes trace earthquake induced abiotic and biotic changes in the fluid rock interaction of the deep fissured granitic aquifer we found that the dissolved fe isotope signatures in spring water are distinct from the granitic source signature 56fe 0 09 particularly we discovered that water 56fe values are remarkably stable 0 01 0 11 2sd n 4 before and during a strong seismic swarm period in 2000 local magnitudes ml 3 while o2 and h2 concentrations in water decrease and dissolved fe content increases later recurring events of lower 56fe values down to 0 3 are observed in the period from 2001 to 2003 with intermittent seismic events 1 ml 2 6 the observations indicate a time lag between tectonic forcing and fe isotope response the role of abiotic fluid rock interaction and fe utilizing bacteria identified in the mineral spring water on fe isotope fractionation is discussed we explain recurring changes towards isotopically lighter values by a combination of fe dissolution from deep granite and admixture of isotopically light fe generated by a complex combination of abiotic and biotic processes operating in the aquifer when disturbed by swarm earthquakes events we propose a conceptual model scenario of earthquake triggered changes in biogeochemical processes

granite petrogenesis revealed by combined gravimetric and radiometric imaging in peneplaned terranes it is often impossible to get a full 3d view of geological objects in the case of granitic plutons for which intrusive relationships between constituent units can provide first order information regarding their petrogenesis this lack of 3d field evidence is a major issue indirect observations can be provided by geophysical surveys here we interpret field gravity data and airborne gamma ray radiometric maps with whole rock geochemistry data in order to obtain information on granite petrogenesis first we test our proposed combined geophysical and geochemical approach on the huelgoat variscan intrusion armorican massif france and we show that ternary radiometric maps are a good proxy for the distribution of k u and th radioelements then we apply our method to the lizio and questembert variscan granitic intrusions armorican massif and show that some features characteristic of the intrusions such as the feeding zones can be localised by geophysical imaging indeed radiometric maps constitute a frozen image of the latest stage of the magmatic building of plutons

links between the structure of the mantle lithosphere and morphology of the cheb basin eger rift central europe the cheb basin chb located in the western part of the eger rift er and the western bohemian massif is characterized by earthquake swarms neotectonic crust movements and emanations of co2 dominated gases of mantle origin deep structure of the region can be characterized as junction of three domains of mantle lithosphere with different olivine fabrics revealed by consistent orientations of seismic anisotropy the domains represent mantle components of the major tectonic units micro plates saxothuringian st tepla barrandian tb and moldanubian md which were assembled during the variscan orogeny the st tb boundary reactivated during the cenozoic extension controlled the position and development of the er and the chb we show that the chb originated above the rejuvenated mantle suture between the st and tb though the basin is located within the st crust domain which is thrust over the mantle junction it is the mantle suture that controls the chb shape and its development through the allochthonous st crust the seismically active marianske lazn fault limits the basin against the uplifted block of the erzgebirge crystalline complex the most subsided parts of the er and chb developed above the centre of the mantle transition whereas a well expressed morphology developed above its flanks our study documents a long memory of the mantle lithosphere assembly inherited from the variscan orogeny it is possible that other continental regions also contain some of intra plate basins that originated above healed palaeo plate mantle boundaries

late variscan magmatism revisited new implications from pb evaporation zircon ages on the emplacement of redwitzites and granites in ne bavaria pb evaporation zircon analyses coupled with a detailed cathodoluminescence cl study on the complete series of granitoids from the northern oberpfalz ne bavaria provide new evidence for the commencement and timing of late variscan magmatism all granitoids analysed in this study were dated before by rb sr and or k ar methods investigated samples comprise medium grained i type dioritic rocks redwitzites i s type granites leuchtenberg marktredwitz g1 zainhammer and s type granites falkenberg liebenstein mitterteich friedenfels steinwald flossenburg barnau the zircon evaporation technique reveals three groups of 207pb 206pb ages which are interpreted to represent magmatic crystallisation 1 ages of 324 321 ma are found in all analysed redwitzites and in almost all i s type granites 2 the granites of falkenberg and liebenstein yield ages of 315 ma 3 ages between 312 and 310 ma are recorded in the mitterteich friedenfels steinwald and flossenburg granites titanite crystals from different redwitzite bodies yield conventional u pb ages of 325 322 ma identical to the pb evaporation zircon data of these rocks the s type granites of groups 2 and 3 contain zircons with relict cores but only a small number of them yield older ages indicating that some of the cores must have lost their radiogenic pb from the geochronological data we infer that metamorphic conditions of the variscan crust produced different granite types at different times the data support a model involving an early period of mantle related magmatism which postdates the final convergence stage of the variscan orogen this magmatic activity was at the same time as the thermal peak of regional metamorphism and is followed by a late period of crustal anatexis which is probably related to post collisional extension of the thickened variscan crust

geochemical and isotopic composition and inherited zircon ages as evidence for lower crustal origin of two variscan s type granites in the nw bohemian massif geochemical and nd sr isotopic compositions and u pb zircon ages of two variscan granites neunburg and oberviechtach from southern oberpfalz nw bohemian massif have been investigated in order to place constraints on their formation and on the crustal reworking both granites exhibit similar mineralogical chemical and isotopic characteristics they have peraluminous compositions a cnk ratios 1 2 1 3 and display high k2o na2o ratios of 2 2 2 3 consistent with typical s type granites in terms of trace elements they show an enrichment of lree and strong fractionation between lree and hree lan ybn ratios 46 to 60 compared with the primordial mantle distinct negative anomalies of several trace elements ba sr nb and ti are also observed in both granites they are further characterised by low initial end values of 6 2 to 8 2 and high initial 87sr 86sr ratios of 0 7114 to 0 7147 zircon u pb data indicate that the intrusion of both granites shortly post dates the ht lp metamorphism of the moldanubian basement and crystallised at about 320 ma the samples studied contain zircons mostly having xenocrystic cores with diverse morphologies these inherited zircons have early proterozoic to early palaeozoic ages this points to melting of sources comprising substantial sedimentary rocks the lan ybn and tbn ybn ratios of both granites are the highest so far reported from granitoids within this region melting of lower crustal rocks leaving garnet as a restite phase in the source provides a viable mechanism to reproduce the ree characteristics

adjustment of the ventilated thermocline the time dependence of the ventilated thermocline is examined via analytical and numerical means the original henderschott model is modified such that the outcrops all occur on the same geopotential surface rather than at staggered geopotential surfaces this model has the advantage that the ocean interior can be ventilated directly by the sverdrup flow rather than by western boundary processes the propagation of disturbances governed by linearized forms of the three layer or four layer modified henderschott model nonlinear solutions of the full modified henderschott model and numerical solutions of the planetary geostrophic equations are considered low frequency disturbances are predicted by the linear models to move on characteristics jointly set by advection and wave dynamics it is shown that perturbations due to wind stress anomalies project strongly onto the first mode and propagate westward similarly to the classical first baroclinic rossby mode they do not experience much interaction with the mean flow the so called non doppler effect on the other hand perturbations generated by buoyancy anomalies have strong projections onto the second or third modes and propagate along pathways very close to the mean circulation their speed is somewhat slower than the current speed however these properties appear in the linearized and simplified nonlinear models and their occurrence in planetary geostrophic results argues the relevance of the henderschott model also these properties are consistent with results from other studies

climate variability induced by anomalous buoyancy forcing in a multilayer model of the ventilated thermocline climate variability induced by surface cooling in a four moving layer model of the ventilated thermocline is studied the perturbations propagate within the characteristic cones defined by streamlines in individual layers where the potential vorticity anomaly is created each time the characteristic cones cross a new outcrop line the number of characteristic cones doubles thus climate variability in a multilayer model can have very complicated structure in the horizontal plane with anomalies of alternating sign the vertical structure of such perturbations defines a class of dynamical thermocline modes

decadal variability of temperature at a depth of 400 meters in the north pacific ocean the gyre scale structure and evolution of decadal ocean thermocline variability in the north pacific is described by analyzing historical temperature data at a depth of 400 meters decadal thermocline anomalies are characterized by a distinct see saw pattern in the midlatitudes and subtropics that appears to circulate coherently in the north pacific basin with a period on the order of 20 years there are coherent spatial and temporal relationships between temperature anomalies around the subtropical gyre with phase differences at depth and at the sea surface suggesting that thermocline variability evolves independently of local sst anomalies in the subtropics subsurface anomalies can be seen to propagate all the way across the basin and thereby lead sst anomalies providing a possible phase transition mechanism for sst the basinwide anomaly pathways suggest a clockwise advection of subsurface temperature anomalies around the subtropical gyre an active role played by the mean geostrophic flow in decadal variability

upper ocean thermal variations in the north pacific during 1970 1991 abstract a newly available extensive compilation of upper ocean temperature profiles was used to study the vertical structure of thermal anomalies between the surface and 400 m depth in the north pacific during 1970 1991 a prominent decade long perturbation in climate occurred during this time period surface waters cooled by 1 c in the central and western north pacific and warmed by about the same amount along the west coast of north america from late 1976 to 1988 comparison with data from coads suggests that the relatively sparse sampling of the subsurface data is adequate for describing the climate anomaly the vertical structure of seasonal thermal anomalies in the central north pacific shows a series of cold pulses beginning in the fall of 1976 and continuing until late 1988 that appear to originate at the surface and descend with time into the main thermocline to at least 400 m depth individual cold events descend rapidly 100 m yr 1 superimposed upon a slower cooling 15 m yr 1 the inter

devonian dundee formation crystal field michigan basin recovery of bypassed oil through horizontal drilling carbonate reservoirs of the devonian dundee formation represent the most productive interval in the michigan basin yet have suffered widespread abandonment due to improper early reservoir management and completion practices dundee carbonate reservoirs deposited in marginal marine and shallow marine environments have produced over 351 mmbbl oil from 137 fields most of which were discovered in the 1930s and 1940s initial potentials for many dundee wells ranged from 2000 to 9000 bbl day presumably due to high permeability fractures and solution enhanced porosity in some areas and excellent primary interparticle porosity in other areas crystal field discovered in 1935 at a depth of less than 3500 ft 1060 m was aggressively developed and produced at high rates causing widespread water coning such that 95 of the field was drilled and abandoned in less than 5 yr leaving considerable interwell reserves in the ground no cores or wireline logs existed for the field prior to 1995 when the field became the subject of a multiyear study aimed at determining the feasibility of employing horizontal drilling to recover bypassed reserves a vertical test portion of the tow 1 3 horizontal well located in a structurally elevated portion of the field cored and logged the entire reservoir interval yielding crucial new information on the basis of relevant data a horizontal leg was drilled resulting in an excellent producer with estimated recoverable reserves of 200 000 bbl two subsequent horizontal tests with poor results were drilled in downdip locations and oriented perpendicular to the tow well suggesting the importance of both structural position and azimuth selective use of horizontal drilling is considered an appropriate cost effective means for recovering bypassed reserves in dundee fields where sufficient geologic data exist to adequately characterize the reservoir and oil occurrence for some fields this may require new coring and logging operations

structure and cycle of decadal variability of upper ocean temperature in the north pacific abstract yearly upper ocean in situ temperature anomaly data for the period 1961 90 are analyzed to reveal spatial structure and evolution of decadal variability in the north pacific ocean an eof analysis has been performed on individual temperature anomaly fields at upper ocean standard levels as well as simultaneously on the entire upper ocean data to depict the combined three dimensional structure in a coherent manner time evolution of anomaly fields is depicted by using a regression analysis the analyses detect the principal basin scale structure of decadal warm period dwp and decadal cold period dcp there is a well defined subsurface thermal anomaly pattern characterized by a prominent seesaw structure with opposite anomaly polarity between the midlatitude north pacific and the subtropical regions during a dwp a positive temperature anomaly is found in the central midlatitude upper ocean with the maximum at about 100 m depth this is accompanied by a corresponding negative anomaly in the

sensitivity of an intermediate ocean atmosphere coupled model of the tropical pacific to its oceanic vertical structure an intermediate ocean atmosphere coupled model icm of the tropical pacific is used to investigate the sensitivity of the coupled system to the oceanic vertical structure the model consists of a three baroclinicmode tropical pacific ocean and a gill tropical atmosphere the mixed layer is similar to the zebiak and cane zc coupled atmosphere ocean model but uses a different parameterization for subsurface temperature derived from xbt data a 100 yr simulation is made and the long term variability of the icm is briefly discussed and compared with the the observations and the zc model the icm reproduces regular enso events with a spectrum peak centered at the period 3 5 yr the presence of higher order vertical modes in the oceanic component of the model allows for reduced off equatorial variability of zonal current and thermocline anomalies and for finer meridional scale for sst anomaly variability in comparison with a simulation with one baroclinic mode only the nature of the processes sustaining the oscillations in the icm is then investigated based on the coupled instabilities and delayed oscillator theories it

decadal thermocline variability in the north pacific ocean two pathways around the subtropical gyre yearly in situ temperature anomaly data in the north pacific ocean for 1961 90 have been analyzed along constant density surfaces isopycnals in order to better describe and understand decadal thermocline variability in the region various empirical orthogonal function analyses are performed on isopycnals to depict the dominant three dimensional patterns the major finding is of two preferential pathways associated with decadal temperature variability around the subtropical gyre a subduction pathway with a large signal in the upper thermocline originates from the north pacific central eastern outcrop regions about 408n 1508w and then basically follows the mean gyre circulation southwestward along isopycnals toward the western tropics a subtropical pathway extends from the eastern subtropical tropical and boundary regions and appears to continue predominantly westward across the southern part of the gyre between 158 and 308n and then along the kuroshio path toward the midlatitudes along these two pathways thermal anomalies show coherent phase relationships to one another in the surface layer and in the thermocline around the gyre with their source regions variability centers being out of phase on decadal timescales two examples of each type of anomaly pattern can be illustrated for the periods analyzed in the 1960s a negative temperature anomaly signal propagated predominantly westward across the subtropics followed by a subducted warm anomaly from the outcrop region in the early 1970s that subsequently moved southwestward along isopycnals toward the western tropics a similar pattern was observed in the late 1970s and in the 1980s but with the opposite sign a westward propagating positive temperature anomaly signal along the subtropics in the late 1970s through the 1980s and a subducted cold anomaly in the early 1980s that also made its way southwestward with the expected gyre circulation to the western tropics in the late 1980s it is suggested that the southwestward subduction pathway provides a mechanism that connects surface anomalies in the outcrop region to thermocline variations in the western subtropics and in the tropics and that the westward subtropical pathway presents a possible link of tropical subtropical variability to surface temperature anomalies around the kuroshio and its extension regions which may further force variations in the overlying atmospheric circulation in the midlatitudes the results provide an observational basis for verification of theoretical studies and model simulations

subduction of decadal north pacific temperature anomalies observations and dynamics abstract observations of oceanic temperature in the upper 400 m reveal decadal signals that propagate in the thermocline along lines of constant potential vorticity from the ventilation region in the central north pacific to approximately 18 n in the western pacific the propagation path and speed are well described by the geostrophic mean circulation and by a model of the ventilated thermocline the approximate southward speed of the thermal signal of 7 mm s 1 yields a transit time of approximately eight years the thermal anomalies appear to be forced by perturbations of the mixed layer heat budget in the subduction region of the central north pacific east of the date line a warm pulse was generated in the central north pacific by a series of mild winters from 1973 to 1976 and reached 18 n around 1982 after 1978 a succession of colder winters initiated a cold anomaly in the central north pacific that propagated along a similar path and with a similar speed as the warm anomaly then arrived in the west

transport of mantle volatiles through the crust traced by seismically released fluids a natural experiment in the earthquake swarm area vogtland nw bohemia central europe abstract vogtland which is located on the czech german border near the crossing of the eger rift and the marianske lazn fault zone is characterised by co 2 rich mineral springs fed by a magmatic source and swarm earthquake activity the free gas of the eisenquelle mineral spring was studied weekly from april 1994 to june 1996 a period which included a quake swarm on december 4 and 5 1994 comprising approximately 500 individual events m local 2 2 co seismic shifts in he content after about a month as well as in the 13 c of co 2 and 3 he 4 he after about 220 days were resolved from seasonal background variations the he concentration shift is assumed to originate near the discharge whereas the isotopic shifts are probably caused by the addition of crustal fluids released by crushing rocks within the hypocentre from the distance of 14 km between the hypocentre to the mineral spring the transport velocity of the released crustal fluids was determined to be at least 50 m day such a high speed indicates gaseous fluid transport along channel like conduits rather than being predominantly controlled by dissolution in water using a simple mass balance it is shown that the amount of crustal fluids potentially released by seismic activity strongly exceeds that required for the observed shifts in 3 he 4 he and 13 c this fact along with the coincidence of both shifts supports the hypothesis that magmatic fluids occurring in mineral waters of the eisenquelle environs flush the hypocentral crustal block by means of advectional transport

modification of the regional stress field by magma intrusion and formation of tabular granitic plutons granitic intrusions typically have large aspect ratios with an horizontal major axis about 4 8 times the vertical one combined structural and geophysical gravity data allows distinction between two main types of plutons flat floored plutons the most represented are rather thin 3 4 km and extend in every horizontal direction with a gently dipping floor toward several root zones these contrast with the thick 10 km wedge shaped plutons more elongated in one direction with a few root zones we interpret the shape of flat floored plutons as the result of a switch in the stress pattern caused by the emplacement of magma magma is preferentially emplaced into the plane 1 2 perpendicular to the least principal stress component 3 this plane is initially vertical except for compressional conditions this dilation causes a local re organization of the stress field by increasing the minor and intermediate principal stress components when they overcome the lithostatic load a drastic change in the orientation of the opening plane results switching from vertical to horizontal this constitutes a change from vertically oriented dike shaped intrusions to sub horizontal laccoliths crustal anisotropies vertical faults or horizontal zones of different rheology also contribute to modify the shape of the intrusions the continual exchange of the intermediate stress components also explains the rounded shape of intrusions in strongly extended regions our analysis suggests that the concept of magmas rising to a level of neutral buoyancy is not applicable to many settings rather we suggest that the feedback between displacements resulting from magma intrusion and the local stress pattern controls the geometry of magma emplacement

the equilibration of high angle grain boundaries in dynamically recrystallized quartz the effect of crystallography and temperature abstract dynamically recrystallized and sutured quartz grains from metamorphic rocks with different strain intensities and temperature conditions ranging from ca 350 c to ca 700 c have been studied universal stage measurements on quartz quartz high angle grain boundaries show that they are never curved but always consist of straight segments which preferentially occupy specific crystallographic orientations in relation to both neighboring crystals with increasing temperature the segments preferentially concentrate in a decreasing number of orientations mainly near the rhombohedral 1011 planes the crystallographic data and the observations on grain boundary geometries suggest that i grain boundary orientations are strongly crystallographically controlled ii this control is the main factor on the textural equilibration of quartz quartz grain boundaries in metamorphic rocks and iii grain boundaries from dynamically recrystallized quartz should be regarded as annealed and equilibrated fabrics that are stable against subsequent annealing as long as the material is not re deformed

the lanthanide tetrad effect and its correlation with k rb eu eu sr eu y ho and zr hf of evolving peraluminous granite suites lanthanide tetrad effects are often observed in ree patterns of more highly evolved variscan peraluminous granites of mid eastern germany central erzgebirge western erzgebirge fichtelgebirge and northern oberpfalz the degree of the tetrad effect te1 3 is estimated and plotted vs k rb sr eu eu eu y ho and zr hf the diagrams reveal that the tetrad effect develops parallel to granite evolution and significant tetrad effects are strictly confined to highly differentiated samples mineral fractionation as a cause for the tetrad effect is not supported by a calculated rayleigh fractionation which also could not explain the fractionation trends of sr eu and eu eu the strong decrease of eu concentrations in highly evolved rocks suggests that eu fractionates between the residual melt and a coexisting aqueous high temperature fluid mineral fractionation as a reason for the tetrad effect is even more unlikely as ree patterns of accessory minerals display similar tetrad effects as the respective host rocks the accessory minerals inherit the ree signature of the melt and do not contribute to the bulk rock tetrad effect via mineral fractionation these results point in summary to significant changes of element fractionation behavior in highly evolved granitic melts ionic radius and charge which commonly control the element distribution between mineral and melt are no longer the exclusive control the tetrad effect and the highly fractionated trace element ratios of y ho and zr hf indicate a trace element behavior that is similar to that in aqueous systems in which chemical complexation is of significant influence this distinct trace element behavior and the common features of magmatic hydrothermal alteration suggest the increasing importance of an aqueous like fluid system during the final stages of granite crystallization the positive correlation of te1 3 with bulk rock fluorine contents hints at the importance of ree fluorine complexation in generating the tetrad effect as the evolution of a ree pattern with tetrad effect m type implies the removal of a respective mirroring ree pattern w type the tetrad effect identifies open system conditions during granite crystallization

nonlinear interdecadal changes of the el nino southern oscillation nonlinear interdecadal changes in the el nino southern oscillation enso phenomenon are investigated using several tools a nonlinear canonical correlation analysis nlcca method based on neural networks a hybrid coupled model and the delayed oscillator theory the leading nlcca mode between the tropical pacific wind stress ws and sea surface temperature sst reveals notable interdecadal changes of enso behaviour before and after the mid 1970s climate regime shift with greater nonlinearity found during 1981 99 than during 1961 75 spatial asymmetry for both sst and ws anomalies between warm el nino and cool la nina events was significantly enhanced in the later period during 1981 99 the location of the equatorial easterly anomalies was unchanged from the earlier period but in the opposite enso phase the westerly anomalies were shifted eastward by up to 25 according to the delayed oscillator theory such an eastward shift would lengthen the duration of the warm events by up to 45 but leave the duration of the cool events unchanged supporting evidence was found from a hybrid coupled model built with the lamont dynamical ocean model coupled to a statistical atmospheric model consisting of either the leading nlcca or cca mode

mesoscale eddies in the northwestern subtropical pacific ocean statistical characteristics and three dimensional structures mesoscale eddy properties in the northwestern subtropical pacific ocean are investigated by analyzing 22 567 cyclonic eddies ces and 26 365 anticyclonic eddies aes detected from 19 year altimetric sea level records eddy occurrence frequency and kinetic energy are prevailingly high in the subtropical countercurrent zonal band between 19 degrees n and 26 degrees n and further elevated near the luzon taiwan coast a general superiority of aes is observed at most latitudes except between 19 degrees n and 22 degrees n where the ce number is larger the modal radius and mean lifespan of the ces aes are 134km and 11 2weeks 121km and 10 9weeks respectively after generation most eddies propagate westward with a mean speed of 7 2cms 1 and deflect northward following the kuroshio along the luzon taiwan coast three dimensional eddy structures are further explored with composite eddy images in five subregions constructed by surfacing argo temperature salinity data into altimeter detected eddy areas due to the existence of mode waters in the main thermocline eddy induced temperature anomaly exhibits a double core vertical structure which is especially evident in ce images because of the vertical water mass distribution salinity anomaly features a sandwich like pattern which is more evident in ae images also revealed is the significant structure difference in these five subregions eddies are greatly intensified as they approach the western boundary inducing larger temperature and salinity anomalies and influencing deeper ocean along the luzon taiwan coast aes are preferentially strengthened by the northward background flow

heterogeneous nucleation as the predominant mode of crystallization in natural magmas numerical model and implications for crystal melt interaction crystallization of natural magmas is inherently a disequilibrium process which involves nucleation and growth kinetics melt crystal mechanical interactions and subsolidus modifications which are all recorded in the resulting rock texture we use a new high resolution three dimensional numerical model to address the significance and consequences of homogeneous versus heterogeneous crystal nucleation in silicate magmas with increasing amount of heterogeneous nuclei during crystallization initially equigranular textures evolve to porphyritic bimodal and spherulitic types the corresponding crystal size distributions csds become concave up curved the clustering index progressively decreases and the grain contact relationships record increased clustering concave up curved csds previously interpreted as resulting from multistage crystallization mixing of crystal populations grain agglomeration or size dependent growth are now predicted consistently with other size spatial and clustering parameters to form by heterogeneous crystal nucleation correlation relationships between various textural parameters and the fraction of heterogeneous nuclei are calibrated and used on representative volcanic and plutonic rocks including cumulate rocks to deduce the fraction of heterogeneous nuclei the results indicate that 60 to 99 of all nuclei are heterogeneous for plutonic and cumulate rocks the estimate of the heterogeneous nuclei fraction based on the clustering index is significantly lower than other estimates such discrepancies in general point to the occurrence of other processes and here the results imply that crystal mush compaction and interstitial melt extraction were involved during the magma solidification formation of crystals in clusters implicit for heterogeneous nucleation implies that greater efficiency of crystal melt separation is expected in these situations

structure and evolution of interannual variability of the tropical pacific upper ocean temperature n n yearly in situ temperature anomaly data for the period 1961 1990 are analyzed to reveal the dominant structure and evolution of interannual variability of the tropical pacific upper ocean we use multivariate empirical orthogonal function eof analyses to detect the principal three dimensional structure related to el nino there are well defined subsurface thermal patterns characterized by a prominent sea saw structure with opposite anomaly polarity in the equatorial and off equatorial tropical north pacific regions during an el nino year a positive temperature anomaly is found in the e astern and central tropical upper ocean this is accompanied by a corresponding negative anomaly at subsurface depths in the west with a maximum at 100 150 m off the equator unlike sea surface temperature whose variations are confined largely to the east with one dominant polarity temperature variations at 50 200 m depths have a dipole pattern with out of phase oscillations in the central equatorial pacific and in the western tropical north pacific a reverse pattern of these anomalies is observed during a la nina year evolution between el nino and la nina involves a significant zonal transfer of anomaly phase across the equatorial basin as well as across the off equatorial tropical north pacific showing consistent and coherent variations from west to east from subsurface to sea surface and from on the equator to off the equator this phase propagation is more evident at subsurface depths than that at the sea surface suggesting a continual movement of anomaly pattern in succession eastward along the equator and westward off the equator of the tropical north pacific with spatial inhomogeneities of zonal propagation in longitude our analyses present evidence of the manner in which temperature anomalies evolve at subsurface ocean depths in the tropical pacific thus providing an observational basis for evaluating theoretical studies and model simulations the dynamical implication of these results is also discussed

variscan sn w mo metallogeny in the gravity picture of the krusne hory erzgebirge granite batholith central europe abstract late variscan wolframite molybdenite and cassiterite wolframite greisen skarn and vein deposits occur in a close spatial association with the granites of the krusne hory erzgebirge batholith kheb in central europe we examined the distribution of the deposits in relation to the gravity field affected by late variscan granites using the data from previous gravity and metallogenic studies late variscan granites are differentiated into earlier biotite monzogranites low f granites and later biotite or lithium mica syenogranites high f granites in accordance with the previous classifications all the outcrops of granites in the kheb region and their hidden continuation are confined to the bouguer anomaly contour of 20 mgal the sn w mo rare metal deposits and occurrences are within the gravity contour of 30 mgal with the exception of the grossschirma stratiform tin deposit in the freiberg polymetallic ore district we constructed a geological model based on the gravity data along two profiles across the kheb showing the position of some rare metal deposits and of outcropping and hidden granite bodies the models show that the overlapping of earlier and later granites is in the areas of the most intense regional gravity minima these coincide with the eastern volcano plutonic complex altenberg minimum which encloses large volumes of felsic extrusives microgranite dikes and granites and the western plutonic complex eibenstock minimum with small volumes of felsic dikes and predominance of earlier and later granites with no extrusives preserved there is no distinct relationship between the masses of late variscan granites and the distribution and the sizes of associated w mo and sn w deposits we prefer the idea that rare metal mineralization was formed by hydrothermal fluids derived from outside of presently outcropping granites it originated in two cycles one connected with the formation of earlier granites producing w mo associations and the other one associated with later granites connected with sn w mineralization mineralizing fluids were probably generated by mantle crustal interaction in the crust near the mantle crust boundary as also indicated by lamprophyric intrusions coeval with the late variscan granitic magmatism

a geophysical model of the variscan orogenic root bohemian massif implications for modern collisional orogens abstract a new model of the structure and composition of the variscan crust in the bohemian massif is proposed based on 3d gravity modelling geological data seismic refraction cel09 and reflection 9hr sections the bohemian massif crust is characterized by a succession of positive and negative anomalies of about 60 80 km wavelength for nearly constant moho depths the south western part of the bohemian massif displays a large negative bouguer anomaly corresponding to high grade rocks granulites and migmatites of the palaeozoic crustal root represented by the moldanubian domain the adjacent neo proterozoic bruno vistulian microcontinent displays an important gravity high reflecting mafic and intermediate medium grade metamorphic and magmatic rocks the deep crustal boundary between the root domain and the bruno vistulian microcontinent is represented by a strong gradient located 50 to 70 km westwards from the surface boundary between these units indicating that the high density basement rocks are covered by a thin sheet of low density granulites and migmatites north west from the moldanubian domain occurs an important gravity high corresponding to the neo proterozoic basement of the tepla barrandian unit limited in the north by southeast dipping reflectors of the tepla suture which is characterized by high density eclogites and ultramafics the footwall of the suture corresponds to low density felsic crust of the saxothuringian basement the reflection and refraction seismics and gravity modelling suggest a complex lithological structure of the moldanubian domain marked by a low density 5 10 km thick lower crustal layer located above the moho a 5 10 km thick heavy mafic layer a 10 km thick mid crustal layer of intermediate density and a locally developed 2 5 km thick low density layer at the surface the low density lower crust correlates well with low p wave velocities in the range 6 0 6 4 km s 1 in the cel09 section this complex geophysical structure and surface geology are interpreted as a result of carboniferous partial overturn of low density lower crust and high and intermediate density crust in the area of central root and by viscous extrusion of low density orogenic lower crust over the high density bruno vistulian continent comparison of these data with geophysical profiling of the andean and the tibetan plateaus suggests that modern orogenic systems reveal comparable deep crustal geophysical pattern based on these similarities we propose that the variscan root represents a deep crustal section of above mentioned plateaus which may have develop by the same orogenic process

evaluation of multiple emplacement mechanisms the huichizi granite pluton qinling orogenic belt central china three end member granite emplacement mechanisms host rock ductile shortening hrds host rock rigid displacement hrrd and magmatic absorption ma are identified in this study of the huichizi pluton the internal fabrics are mainly flattening typesona 0 4 0 9u and strain is highoesa 1 0 0 6u near the boundaries and lowoesa 0 7 0 30u toward the central parts of the pluton in the 1 5 km wide contact aureole extension e is measured in syn emplacement deformed veins and the calculated average shortening normal to the sides and tips of the pluton are 1 14 km and 0 74 km respectively from this we conclude that the hrds produced only about 20 space for the present volume of the pluton the regional hrrd derived from the uplift by about 8 km of the qinling group in a flower structure contributed 19 032 space ms including stoping and material transfer processes yielded another 37 space of this stoping contributed a minimum of 1 space estimated from the surface area of 2 8 km 2 covered by xenoliths transfer processes provided about 36 of the needed space deduced from the average 64 36 ratio of hybridization of mantle derived to crustal qinling group derived magma the three mechanisms may act nearly simultaneously as a multiple emplacement mechanism this situation may apply to many other plutons as well 2000 elsevier science ltd all rights reserved

compositional zonation of the shallow la gloria pluton central chile by late stage extraction redistribution of residual melts by channelization numerical modeling abstract the origin of highly evolved magmas e g rhyolites has been a long standing controversy in earth sciences they are commonly thought to be generated in the upper crust by melt extraction from mush zones but due to the rapid cooling of magma reservoirs in such shallow and typically cold environments high magma emplacement rates of intermediate magmas are thought to be necessary to maintain large silicic mushes above the solidus long enough for the high sio2 melts extraction to occur late stage redistribution of interstitial melts i e heat and mass by channels dikes within those mushes has been invoked as a mechanism to preserve silicic mushes above their solidi for longer periods i e delaying their final crystallization but the nature of this process and its implications on plutons zonation are still poorly understood here using time dependent numerical modeling we study the feasibility of late stage interstitial melt extraction redistribution by channels dikes from a crystalline mush our model accounts for magma fluid dynamics extraction of residual melts and thermal evolution of the crystallizing magma system and its hosting rocks considering the thermal effect of the redistributing material the model was applied to explain the anatomy of the well documented la gloria pluton lgp central chile which exhibits increasing contents of sio2 and abundant leucocratic dikes toward the margins interpreted as trapped residual melts generated elsewhere in the magma chamber our results suggest that favorable conditions for extracting late stage residual melts are reached at temperatures of 750 c 60 vol crystallinity at least for compositions similar to lgp dikes simulations correspond to 30 kyr of reservoir cooling when the concentric compositional zonation of lgp is reproduced after a short period of extraction

deciphering the late paleozoic to mesozoic tectono sedimentary evolution of the northern bohemian massif from detrital zircon geochronology and heavy mineral provenance from permian to late cretaceous the northern bohemian massif experienced a complex intra plate tectono sedimentary evolution involving development of at least four generations of sedimentary basins in different settings we examine this protracted evolution using stratigraphic changes in sediment provenance analyzed through heavy mineral assemblages and u pb detrital zircon geochronology by laser ablation icp ms in permian jurassic and late cretaceous successions the provenance data point to multiple temporally evolving sources ranging from local e g the west sudetic island through more distant from elsewhere in the bohemian massif to exotic likely derived from baltica the latter is interpreted as a trace of now completely eroded late jurassic to early cretaceous basin that once covered the lusatian lausitz block and received the baltica derived detritus from northerly fluvial and deltaic depositional systems we suggest that fill of this basin was recycled into the bohemian cretaceous basin during progressive unroofing of the west sudetic island a time slice reconstruction of the paleogeographic and tectono sedimentary evolution of the northern bohemian massif is then developed to show that periods of basin development and deposition early permian late early permian to early triassic middle jurassic early cretaceous and late cretaceous were interrupted by major depositional gaps middle triassic early jurassic mid cretaceous and post early campanian the mesozoic depositional episodes resulted from reactivation of major nw se strike slip fault zones due to stress transfer from the north atlantic rift during jurassic to early cretaceous overridden by the far field effect of convergence of iberia africa and europe during late cretaceous

the role of discontinuous magma inputs in felsic magma and ore generation for a long time granites have been considered as passive bodies ascending under intrinsic negative density and viscosity contrasts with their host rocks chemical variations within a granitic body resulted from in situ differentiation and crystal fractionation since the mid 1980s this global view has been significantly modified by i shifting melting from water saturated conditions to fluid absent reactions ii increasing the role played by the mantle during granite generation iii reassessing the rheology of partially molten rocks iv demonstrating stepwise segregation and ascent of magmas by analogue and numerical models v combining structural geophysical and geochemical studies to reveal the internal structures in granitic plutons it results that a granitic body is built up by a discontinuous accumulation of successive magma intrusions the discontinuous nature of magma emplacement has also significant consequences for its ability to generate ore the processes that lead to ore deposits are examined with a brief review of the magmatic and fluid phases that concentrate ore forming elements examples are taken from crustal derived granites and porphyry type deposits those are considered as the two end members of magmatic and hydrothermal ore deposits the source characteristics of the magma the emplacement mechanisms and magma mixing processes are the frame that controls the potential to carry base metals with the magma the distribution of elements is controlled by diffusion partition between minerals and melt solubility and redox conditions variations of those parameters are examined by considering their activation energy which controls the exponential dependence with temperature a characteristic length depending on the activation energy temperature variation and time is estimated for a characteristic time lag of 30 ka the intrusion of a magma into a magma chamber of similar composition hence temperature has few effects on diffusion partition coefficient and redox conditions because of a too low temperature contrast the intrusion of a mafic magma into a felsic one induces a variation of 300 c in both magmas the characteristic length of diffusion may vary by up to two orders of magnitude whereas the variation of partition coefficients is only one order of magnitude the redox conditions are about 2 5 log unit in the mafic magma but they can vary by 7 log units in the felsic magma hence a strong decrease in d values is observed in porphyry type deposits the effect is a removal of the elements with higher activation energy w sn zr from the mafic to the felsic magma deformation during the late stages of emplacement also controls ore formation

interdecadal variability of the pacific ocean model response to observed heat flux and wind stress anomalies variability of the pacific ocean is examined in numerical simulations with an ocean general circulation model forced by observed anomalies of surface heat flux wind stress and turbulent kinetic energy tke over the period 1970 88 the model captures the 1976 77 winter time climate shift in sea surface temperature as well as its monthly seasonal and longer term variability as evidenced in regional time series and empirical orthogonal function analyses examination of the surface mixed layer heat budget reveals that the 1976 77 shift was caused by a unique concurrance of sustained heat flux input anomalies and very strong horizontal advection anomalies during a multi month period preceding the shift in both the central pacific region where cooling occurred and the california coastal region where warming occurred in the central pacific the warm conditions preceding and the cold conditions following the shift tend to be maintained by anomalous vertical mixing due to increases in the atmospheric momentum flux tke input into the mixed layer which deepens in the model after the shift from the early 1970s to the late 1970s and 1980s since the ocean model does not contain feedback to the atmosphere and it succeeds in capturing the major features of the 1976 77 shift it appears that the midlatitude part of the shift was driven by the atmosphere although effects of midlatitude ocean atmosphere feedback are still possible the surface mixed layer heat budget also reveals that in the central pacific the effects of heat flux input and vertical mixing anomalies are comparable in amplitude while horizontal advection anomalies are roughly half that size in the california coastal region in contrast where wind variability is much weaker than in the central pacific horizontal advection and vertical mixing effects on the mixed layer heat budget are only one quarter the size of typical heat flux input anomalies

exploration in ordovician of central michigan basin deep wells in the central michigan basin have provided sufficient data to define two new mappable formations the foster formation and the bruggers formation recent conodont studies have corrected the age assignments of the strata containing these formations previously the lower section foster was classified as mostly cambrian and the upper unit bruggers was identified as early ordovician conodont identifications indicate an early and middle ordovician age for the foster formation and a middle ordovician age for the bruggers formation the michigan basin existed in embryonic form in the late cambrian but the full outline of the present day basin did not develop until early ordovician gas and condensate are produced from the bruggers formation as deep as 11 252 ft 3 429 m geothermal investigations suggest that gas production is possible to the base of the paleozoic section in the central basin 17 000 ft or 5 181 m paleotemperatures were higher during the paleozoic owing to 3 000 4 000 ft 914 1 291 m of additional sedimentary cover five wells are producing from the bruggers formation all are deeper tests in anticlines producing from devonian reservoirs discovered earlier the structures are the result of vertical movements of basement fault blocks activated by regional stresses

late winter generation of spiciness on subducted isopycnals the origins of density compensating anomalies of temperature and salinity spice are investigated using a model forced with the most realistic surface products available over the 40 years 1958 97 in this hindcast the largest interannual spiciness anomalies are found in the pacific ocean near the isopycnal s 0 5 25 5 where deviations as great as 1 28c and 0 6 psu are generated equatorward of winter outcropping in the eastern subtropics in both hemispheres these source regions are characterized by very unstable salinity gradients and low mean density stratification in winter two related signatures of winter mixing in the southeast pacific sep are density that is well mixed deeper than either temperature or salinity and subsurface density ratios that approach 1 all ocean basins in the model are shown to have regions with these characteristics and signatures however the resultant spiciness signals are focused on different isopycnals ranging from s 0 5 25 0 in the northeast pacific to s 0 5 26 5 in the south indian ocean a detailed examination of the sep finds that large positive anomalies are generated by diapycnal mixing across subducted isopycnals e g s 0 5 25 5 whereas negative anomalies are the result of a steady isopycnal advection moderated by vertical advection and heave there is considerable interannual variability in the strength of anomalies and in the density on which they occur historical observations are consistent with the model results but are insufficient to verify all aspects of the hindcast including the processes of anomaly generation in the sep it was not possible to relate isopycnal anomaly genesis to local surface forcing of any kind a complex scenario involving basinwide circulation of both the ocean and atmosphere especially of surface water through the subtropical evaporation zones is put forward to explain the decadal time scale evident in sep salinity anomalies on s 0 5 25 5 pacific anomalies generated on s 0 5 25 5 can be traced along mean geostrophic streamlines to the western boundary where decadal salinity variations at 78s are about 2 times as large order 60 1 psu as at 128n although there may be more variance on shallower isopycnals in the north at least portions of the s 0 5 25 5 signals appear to continue along the boundary to a convergence at the equator suggesting that the most robust sources of pacific spiciness variance coincide with equatorial exchange pathways

evidence for stronger el nino southern oscillation enso events in a mid holocene massive coral we present a 47 year long record of sea surface temperature sst derived from sr ca and u ca analysis of a massive porites coral which grew at 4150 calendar years before present b p in vanuatu southwest tropical pacific ocean mean sst is similar in both the modern instrumental record and paleorecord and both exhibit el nino southern oscillation enso frequency sst oscillations however several strong decadal frequency cooling events and a marked modulation of the seasonal sst cycle with power at both enso and decadal frequencies are observed in the paleorecord which are unprecedented in the modern record

climate variability inferred from a continuously stratified model of the ideal fluid thermocline climate variability in the subtropical gyre interior induced by anomalous surface thermal forcing ekman pumping mixed layer depth variability and anomalous subpolar water formation is examined using a continuously stratified model of the ideal fluid thermocline cooling heating induces a negative positive potential vorticity perturbation in the ventilated thermocline and the associated density perturbations propagate downstream in the form of second and higher baroclinic modes the second baroclinic mode resembles the traditional second baroclinic mode because it has a thermal structure with cooling warming in the upper thermocline and warming cooling in the lower thermocline anomalous ekman pumping can also induce density perturbations that propagate westward in the form of the first baroclinic mode in addition if the outcrop lines are nonzonal there are density perturbations that propagate downstream in the form of the second or third baroclinic modes perturbations in the sea surface elevation are mostly confined to the region of anomalous forcing on the other hand when the low potential vorticity anomaly in the subpolar mode water spreads into the subtropical basin both the unventilated and ventilated thermocline move downward consequently temperature at a given depth seems to increase

anti correlated variability in subduction rate of the western and eastern north pacific oceans identified by an eddy resolving ocean gcm analysis of results from an eddy resolving ocean general circulation model has revealed the existence of an anti correlated variability in subduction rate of the western and eastern north pacific oceans consistent with the leading mode of pacific decadal oscillation pdo a composite analysis shows that during the positive phase of pdo the winter mixed layer depth mld generally gets deeper in the west and shallower in the east being closely related to the variability in surface heat flux stemming from an enhanced aleutian low and the situation during the negative phase of pdo is reversed changes in mld are primarily responsible for the anti correlated variability in subduction rate though changes in subtropical gyre circulation also play a role the result also provides useful evidence for the interior and western boundary pathways through which variability in eastern subtropical mode water can be conveyed into the equatorial region citation chen j t qu y n sasaki and n schneider 2010 anti correlated variability in subduction rate of the western and eastern north pacific oceans identified by an eddy resolving ocean gcm geophys res lett 37 l23608 doi 10 1029 2010gl045239

subsurface granites in the franconian basin as the source of enhanced geothermal gradients a key study from gravity and thermal modeling of the bayreuth granite the franconian basin in ne bavaria is a region of gravity low between the bohemian massif in the east and the kraichgau terrane in the west borehole measurements have identified the northern part of the franconian basin as a regional geothermal anomaly and new heat flow calculations give values of 100 mw m2 distinct negative bouguer anomalies observed in this basin are modeled as granitic intrusions in the saxothuringian basement that underlies the permo mesozoic units the interpretation of gravity gradients in combination with the filtering of gravity data gives the possible depth constraints of the intrusive bodies the resulting depths were cross checked using microstructural studies of quartz veins in the basement rocks at 1341 m depth the quartz shows structures typical for low temperature plasticity and we infer a deformation temperature of ca 300 c this indicates a considerable pre permian uplift of at least 7 km for parts of the saxothuringian basement and supports depth estimates from gravity data the heat supply of granitic intrusions by radiogenic decay is modeled considering several scenarios for the geological conditions recovered by the obernsees borehole model for conductive heat transfer the 1390 m deep drillhole is in a marginal position to the most pronounced negative bouguer anomaly it could be shown that the saxothuringian basement including heat producing granites heat production rates 4 6 w m3 covered by the insulating sedimentary rocks 1 35 km of permian to lower jurassic units can account for the enhanced geothermal gradient 38 c km that were measured in the borehole

rift structure beneath the michigan basin from cocorp profiling cocorp consortium for continental reflection profiling surveys across the mid michigan gravity anomaly near the mcclure sparks no 1 deep well delineate a thick layered sequence of relatively strong reflectors that define a structural trough within the precambrian beneath the michigan basin these deep reflections which correlate spatially with the mid michigan gravity and magnetic high are interpreted to be a pile of basaltic extrusive rocks intercalated with clastic rocks and correlative with keweenawan volcanics exposed in the lake superior region to the northwest a reflection poor zone between the base of the paleozoic as found in the deep well and the top of the deep layered sequence probably corresponds to the upper keweenawan clastic assemblage direct evidence of faulting within the inferred volcanic sequence is lacking although sharp flexures structural benches and dips of as much as 10 suggest subsidence controlled by fault block motions reflections from beneath the inferred volcanic pile are rare the deepest clear event being at about 18 km there is no unequivocal evidence on these sections to indicate whether precambrian structures were reactivated to affect the overlying paleozoic strata of the michigan basin proper although data quality may be insufficient to detect such effects

evolution of interdecadal variability in sea level pressure sea surface temperature and upper ocean temperature over the pacific ocean abstract interdecadal variability in sea level pressure slp and sea surface temperature sst anomalies in the pacific ocean was quasiperiodic from 1900 91 the coherent variability of this phenomenon is investigated using gridded observational data from the turn of the century sst and slp and of upper ocean heat content hs from the recent two and a half decades the nominal cycle in atmosphere ocean variables is roughly two decades long but growth and decay can happen on a shorter timescale e g half a cycle or so the authors divide the full cycle into four phases an onset phase during which a weak slp anomaly pattern off japan takes approximately 2 4 yr to expand eastward leads to large slp anomalies in the region of the aleutian low a quasi stationary growth phase with the midlatitude slp anomaly pattern in the eastern ocean intensifies over a 2 4 yr period the persistent slp anomalies evolve in concert with large sst and hs anomalies of the same polarity located to the south sout