crustal structure of the western part of the southern granulite terrain of indian peninsular shield derived from gravity data abstract the southern granulite terrain sgt is composed of high grade granulite domain occurring to the south of dharwar craton dc the structural units of sgt show a marked change in the structural trend from the dominant north south in dc to east west trend in sgt and primarily consist of different crustal blocks divided by major shear zones the bouguer anomaly map prepared based on nearly 3900 gravity observations shows that the anomalies are predominantly negative and vary between 125 mgal and 22 mgal the trends of the anomalies follow structural grain of the terrain and exhibit considerable variations within the charnockite bodies two dimensional wavelength filtering as well as zero free air based zfb analysis of the geoid corrected bouguer anomaly map of the region is found to be very useful in preparing regional gravity anomaly map and inversion of this map gave rise to crustal thicknesses of 37 44 km in the sgt crustal density structure along four regional gravity profiles cutting across major shear zones lineaments plateaus and other important geological structures bring out the following structural information the bavali shear zone extending at least up to 10 km depth is manifested as a plane separating two contrasting upper crustal blocks on both sides and the gravity high north of it reveals the presence of a high density mass at the base of the crust below coorg the steepness of the moyar and bhavani shears on either side of nilgiri plateau indicates uplift of the plateau due to block faulting with a high density mass at the crustal base the bhavani shear zone is manifested as a steep southerly dipping plane extending to deeper levels along which alkaline and granite rocks intruded into the top crustal layer the gravity high over palghat gap is due to the upwarping of moho by 1 2 km with the presence of a high density mass at intermediate crustal levels the gravity low in periyar plateau is due to the granite emplacement mid crustal interface and the thicker crust the feeble gravity signature across the achankovil shear characterized by sharp velocity contrast indicates that the shear is not a superficial structure but a crustal scale zone of deformation reaching up to mid crustal level

the rare earth element ree mineralisation potential of highly fractionated rhyolites a potential low grade bulk tonnage source of critical metals abstract the rare earth elements ree have become crucial for modern industry technology and medicine with the increase in demand for these elements over the past few years currently being met by relatively few well known mineral deposits this lack of a secure supply of the ree has led to increased research into potential alternative sources of these in demand elements the primary fractionation processes involved in the petrogenesis of highly fractionated high silica rhyolites can cause the magmas that form these units to become preferentially enriched in the ree especially in the more valuable heavy ree hree although this is dependent on the mineral assemblages fractionated by the system in question a factor that is in turn a function of the source and tectonic setting of a given magmatic event the mineralogy of the ree is also important with volatile exsolution and vapour phase activity within highly evolved rhyolite systems potentially having a key role in concentrating the ree and other elements into concentrations and more importantly potentially acid leachable and therefore processable minerals that may be economically viable to extract this combined with the fact these rhyolites are often enriched in other critical and or economically important metals e g y nb ta be li f sn rb th and u means that these volcanic units should be considered as potential sources of these critical metals in addition the large volume nature of these rhyolites combined with the fact they frequently crop out at the earth s surface makes them ideally suited for more economical bulk open pit extraction this suggests that these high silica ree enriched rhyolites should be considered potential ree analogues of bulk tonnage low grade porphyry cu deposits warranting further investigation to determine whether these rhyolites are a viable new source of the ree especially the hree and are potential targets for future mineral exploration

loop current cycle coupled response of the loop current with deep flows abstract although the upper layer dynamics of the loop current and eddies in the gulf of mexico are well studied the understanding of how they are coupled to the deep flows is limited in this work results from a numerical model are analyzed to classify the expansion shedding retraction and deep coupling cycle the loop current cycle according to the vertical mass flux across the base of the loop stage a is the loop reforming period with downward flux and deep divergence under the loop current stage b is the incipient shedding with strong upward flux and deep convergence stage c is the eddy migration with waning upward flux and deep throughflow from the western gulf into the yucatan channel because of the strong deep coupling between the eastern and western gulf the loop s expansion is poorly correlated with deep flows through the yucatan channel stage a is longest and the mean vertical flux under the loop current is downward therefore because the net circulation around the abyssal

metallogenic evolution of convergent margins selected ore deposit models abstract metallogenic patterns in convergent margin arcs are related to thickness of the arc crust and its petrologic evolution which are themselves linked by a positive correlation between average silica content of arc rocks and average thickness of arc crust in general tin mercury antimony and fluorine are most abundant in areas of thickest crust although the composition of ore deposits is strongly controlled by deep crustal and mantle features the actual form and type of many ore deposits is controlled by upper crustal features particularly the relative abundance of carbonate and silicate country rock for instance epithermal precious metal deposits are commonly associated with subaerial silicic volcanism which generally forms in the later stages of arc evolution deposits of this type will be absent if arc volcanism is terminated prematurely or removed if subduction of thickened or hot oceanic crust causes extreme uplift and consequent erosion of the upper parts of the arc similarly chimney manto limestone replacement lead zinc silver deposits are common only in terranes with extensive thick limestone units which are commonly formed in shallow shelf environments several important types of convergent margin deposits remain poorly understood acid sulfate deposits in primitive oceanic volcanic arcs are associated with bimodal volcanic suites that appear to have formed at an early stage in the evolution of the arc alkaline porphyry copper deposits are closely associated with calc alkaline porphyry copper deposits commonly in the same volcanic arc although they appear to have formed farther back from the trench or during periods of oblique subduction or arc reversal massive iron oxide deposits and related base and precious metal mineralization are closely associated with silicic magmas that form during later stages of arc evolution in addition to tectonic and petrologic factors metallogenic patterns probably reflect global forcing mechanisms the most important of which are global seawater anoxia and plate reorganizations global anoxia produces deep water environments that favor sedex mineralization and can promote subsurface ore deposition where anoxic bottom waters recharge underlying aquifers plate reorganizations can lead to ore deposition by providing extensional environments in the upper crust and possibly by facilitating partial melting of oceanic crust that has been modified by earlier subducting slabs

adjoint sensitivity studies of loop current and eddy shedding in the gulf of mexico 1 adjoint model sensitivity analyses were applied for the loop current lc and its eddy shedding in the gulf of mexico gom using the mit general circulation model mitgcm the circulation in the gom is mainly driven by the energetic lc and subsequent lc eddy separation in order to understand which ocean regions and features control the evolution of the lc including anticyclonic warm core eddy shedding in the gom forward and adjoint sensitivities with respect to previous model state and atmospheric forcing were computed using the mitgcm and its adjoint since the validity of the adjoint model sensitivities depends on the capability of the forward model to simulate the real lc system and the eddy shedding processes a 5 year 2004 2008 forward model simulation was performed for the gom using realistic atmospheric forcing initial and boundary conditions this forward model simulation was compared to satellite measurements of sea surface height ssh and sea surface temperature sst and observed transport variability despite realistic mean state standard deviations and lc eddy shedding period the simulated lc extension shows less variability and more regularity than the observations however the model is suitable for studying the lc system and can be utilized for examining the ocean influences leading to a simple and hopefully generic lc eddy separation in the gom the adjoint sensitivities of the lc show influences from the yucatan channel yc flow and loop current frontal eddy lcfe on both lc extension and eddy separation as suggested by earlier work some of the processes that control lc extension after eddy separation differ from those controlling eddy shedding but include yc through flow the sensitivity remains stable for more than 30 days and moves generally upstream entering the caribbean sea the sensitivities of the lc for sst generally remain closer to the surface and move at speeds consistent with advection by the high speed core of the current while sensitivities to ssh generally extend to deeper layers and propagate more slowly the adjoint sensitivity to relative vorticity deduced from the sensitivities to velocity fields suggests that advection of cyclonic positive relative vorticity anomalies from the yc or the lcfes accelerate the lc eddy separation forward model perturbation experiments were performed to complement and check the adjoint sensitivity analysis as well as sampling the predictability and nonlinearity of the lc evolution the model and its adjoint can be used in four dimensional variational assimilation 4d var to produce dynamically consistent ocean state estimates for analysis and forecasts of the circulation of the gom

numerical study of circulation dispersion and hydrodynamic connectivity of surface waters on the belize shelf a nested grid ocean circulation modeling system is used to examine the circulation dispersion and hydrodynamic connectivity of surface waters on the belizean shelf the nested grid system consists of a coarse resolution 19 km outer model of the western caribbean sea an intermediate resolution 6 km middle model of the southern meso american barrier reef system mbrs and a fine resolution 2 km inner model of the belizean shelf the nested system is forced by climatological monthly mean surface forcing and integrated over 5 years the near surface circulation on the belize shelf produced by the inner model is characterized by a strong and persistent northwestward flow as a direct influence of the caribbean current on the northwestern shelf and a weak and spatially variable flow on the inner and southern shelf the monthly mean model currents are used to calculate retention and dispersion of conservative near surface particles carried by the ocean currents the near surface dispersion is relatively higher in areas seaward east of lighthouse and glovers reef atolls and lower on the inner shelf particularly within the inner channel and in the vicinity of south water cay to examine hydrodynamic connectivity of reefs in the surface waters of the belize shelf we calculate upstream and downstream retention areas for coral reefs at turneffe islands and glovers reef atolls the potential sources of passive near surface particle supply reaching these two reef atolls within 30 days include both the shallow waters surrounding the two sites the deep waters between them and the coastal waters of the bay islands honduras the 30 day downstream retention areas of the turneffe and glovers reef atolls cover the central and southern belize shelf respectively

flow structure and transport in the yucatan channel 1 the direct ocean current observations across the yucatan channel collected during the canek program allow the best description to date of the exchange between the caribbean sea and the gulf of mexico a net transport of 23 8 1 sv 1 sv 106m3s 1 95 confidence interval flowed through the yucatan channel from the caribbean sea into the gulf of mexico during the period between september 1999 and june 2000 this is about 20 percent less than the 30 sv accepted as the nominal transport of the florida current and less also than the 28 sv assumed for yucatan in closing the transport budgets for caribbean passages the discrepancy may be an imbalance due to fluctuations in the transports through other passages of the system especially the old bahama and northwest providence channels which remain poorly known our data corroborate the principal features of the flow through the yucatan channel the northerly surface yucatan current and its southerly under current off mexico and the southerly surface cuban counter current near cuba but previously unobserved mean currents are found to exist at depth especially on the eastern side of the channel fluctuations seen in the deep flows are related to volume anomalies over the gulf of mexico a transport through the yucatan channel smaller than previously thought has significant implications for the dynamics of the gulf of mexico and its modeling since this transport is the principal forcing of its circulation the circulation budgets in the western subtropical atlantic should be revised considering these new results

gulf of mexico circulation within a high resolution numerical simulation of the north atlantic ocean 1 the gulf of mexico circulation is examined from the results of a high resolution 1 12 north atlantic simulation using the miami isopycnic coordinate ocean model the motivation for this paper is twofold first we validate the model s performance in the gulf of mexico by comparing the model fields to past and recent observations and second given the good agreement with the observed gulf of mexico surface circulation and loop current variability we expand the discussion and analysis of the model circulation to areas that have not been extensively observed analyzed such as the vertical structure of the loop current and associated eddies especially the deep circulation below 1500 m the interval between successive model eddy sheddings is 3 to 15 months the eddy diameters range between 140 and 500 km the life span is about 1 year and the translational speeds are 2 3 km d 1 in good agreement with observations areas of high cyclonic eddy occurrence in the model are southwest of florida the loop current boundary and the western campeche bay area the cyclonic eddy diameters range between 50 and 375 km the orbital speeds range between 1 and 55 cm s 1 the translational speeds range between 0 5 and 14 km d 1 and the eddy life spans range between 1 and 3 months the vertical structure of the temperature and salinity of each modeled eddy from the moment it is shed until it disintegrates in the western gulf of mexico is in agreement with the few available observations below 1500 m deep cyclonic eddies are associated with the surface loop current anticyclones the eddy variability is consistent with rossby waves propagating westward and there is bottom intensification of the flow close to steep topography overall we show that this very high horizontal resolution isopycnic coordinate ocean model which is able to produce a quite realistic surface circulation for the north and equatorial atlantic is also able to reproduce well the smaller scale basin wide intricate dynamics such as the gulf of mexico variability

loop current and deep eddies abstract in contrast to the loop current and rings much less is known about deep eddies deeper than 1000 m of the gulf of mexico in this paper results from a high resolution numerical model of the gulf are analyzed to explain their origin and how they excite topographic rossby waves trws that disperse energy to the northern slopes of the gulf it is shown that north of campeche bank is a fertile ground for the growth of deep cyclones by baroclinic instability of the loop current the cyclones have horizontal vertical scales of about 100 km 1000 2000 m and swirl speeds 0 3 m s 1 the subsequent development of these cyclones consists of two modes a and b mode a cyclones evolve into the relatively well known frontal eddies that propagate around the loop current mode a cyclone can amplify off the west florida slope and cause the loop current to develop a neck that sometimes leads to shedding of a ring this process is shown to be the loop current s dominant mode of upper to deep variability

comparisons between a continuous 3 year current meter observation at the sill of the yucatan strait satellite measurements of gulf loop current area and regional sea level from october 1977 through november 1980 a current meter mooring was maintained in the yucatan strait the meter was moored halfway between mexico and cuba 145 m above the sill or in 1895 m of water motions of low frequency 14 1 cycles day are oriented approximately parallel to the isobaths 021 030 true net drift for 3 years is to the ssw at an average velocity of 1 8 cm s sustained southward flows at intervals of 8 months which persisted for several months each have average velocities of 5 cm s with randomly spaced bursts as high as 15 cm s energy in subtidal frequency bands has significant peaks near 38 1 and 19 1 cycles day with a broad band of energy between 300 1 and 200 1 cycles day the latter peak is consistent with the approximately 8 month interval between the southward flow events comparison with weekly areal coverage of the gulf loop current from geostationary operational environmental satellite infrared observations shows little covariation except that 8 months is typical of some anticyclonic eddy generation there is little coherence of sill depth velocities with naples sea level at subtidal frequencies but with miami there is coherence at several frequencies notably 38 1 and 19 1 cycles day in the higher frequencies the principal tidal motions are diurnal and are oriented somewhat across the isobaths toward the northwest 346 349 true with counterrotating o1 and k1 constituents no semidiurnal inertial or fortnightly energy is observed above the background continuum

deep flows in the yucatan channel and their relation to changes in the loop current extension 1 the first attempt to establish a relation between the loop current extension and deep flows in yucatan channel was made by maul et al 1985 it was unsuccessful probably because of the low spatial resolution of their observations from september 8 1999 to june 17 2000 eight moorings with acoustic doppler current profilers current meters and thermometers were deployed across the yucatan channel the data from these arrays were used to compute time series of the transports below the level of the deepest isotherm observed in the florida straits as required by a simple box model that restricts deep exchanges with the gulf of mexico to the yucatan channel the surface extension of the loop current was inferred from 3 day advanced very high resolution radiometer imagery from october to may when temperature gradients were sufficient to map the warm water unambiguously the deep transports appear at first unrelated to the rate of change of the loop current extension but filtering the series with a 20 day running mean increases the correlation between the low pass series to 0 62 and up to 0 83 with a lag of 8 5 days with loop current changes leading the deep flows the cumulative deep transport a quantity that favors lower frequencies is very well related correlations 0 9 to the surface extension of the loop current also with a lag of about a week these lags are not statistically significant but suggest a timescale for internal adjustment processes in the gulf of mexico the empirical orthogonal function of the current best related to the area extension of the loop current represents a unidirectional flow across the entire deep section flowing either toward or from the gulf of mexico and includes a strong expression of the yucatan undercurrent

low frequency eddy kinetic energy spectrum in the deep western north pacific the frequency spectrum for the low frequency eddy kinetic energy is estimated from a long term current meter record obtained in a deep layer in the western north pacific the eddy field is characterized by three time scales an annual scale with zonal dominance of eddy motions a temporal mesoscale with meridional dominance and a monthly scale with horizontal isotropy about two thirds of the eddy kinetic energy is contained in the temporal mesoscale

deep flow variability in the vicinity of the yucatan straits from a high resolution numerical simulation 1 the deep flow variability in the vicinity of the yucatan channel between the caribbean sea and the gulf of mexico is examined within a high resolution numerical simulation of the north atlantic ocean we focus on the 6 year integral cycle of loop current lc ring formation and we study the flow regimes both in the yucatan channel and farther north in the lc the circulation in the vicinity of the yucatan channel presents a high variability in the flow regimes and in the shedding period in good agreement with earlier observations the outflow toward the caribbean sea in the yucatan channel is shown to be controlled in part by a regular shift of the lc maximum velocity position in phase with the transport variations the outflow follows the inflow variations independently of the northward extension of the lc our analysis of the growth of the loop is also shown to be in good agreement with the ballooning process proposed by pichevin and nof 1997 and nof and pichevin 2001 to explain the lc ring formation moreover at the end of each cycle of ring formation a sudden deepening of the lc deepest layer occurs together with an intensification of the transport and of the currents in the deep layers beneath the lc this process is shown to be connected with the growth of cyclones in the deep layers they result from the bottom intensified instability of the lc ring and contribute to its separation from the lc

the integration of gravity magnetic and seismic data in delineating the sedimentary basins of northern sinai and deducing their structural controls abstract the sinai peninsula is a part of the sinai sub plate that located between the southeast nubian arabian shield and the southeastern mediterranean northward the main objectives of this investigation are to deduce the main sedimentary basin and its subdivisions identify the subsurface structural framework that affects the study area and determine the thickness of sedimentary cover of the basement surface the total intensity magnetic map bouguer gravity map and seismic data were used to achieve the study aims structural interpretation of the gravity and magnetic data were done by applying advanced processing techniques these techniques include reduce to the pole rtp power spectrum tile derivative and analytical signal techniques were applied on gravity and magnetic data two dimensional gravity and magnetic modeling and interpretation of seismic sections were done to determine the thickness of sedimentary cover of the study area the integration of our interpretation suggests that the northern sinai area consists of elongated troughs that contain many high structural trends four major structural trends have been identified that reflecting the influence of district regional tectonic movements these trends are 1 ne sw trend 2 nnw sse trend 3 ene wsw trend and 4 wnw ese trend there are also many minor trends e w nw se and n s structural trends the main sedimentary basin of north sinai is divided into four sub basins 1 northern maghara 2 northeastern sinai 3 northwestern sinai and 4 central sinai basin the sedimentary cover ranges between 2 km and 7 km in the northern part of the study area

ageostrophic fluctuations in cozumel channel 1 the cayman current flows to the west and most of it turns north as it approaches the yucatan coast producing a persistent northwesterly flow on both sides of cozumel island the transport between the yucatan peninsula and cozumel island i e through the cozumel channel is close to 5 sverdrups in the mean with velocities at midchannel ranging from 20 to 180 cm s a recent study of the subinertial flow and pressure difference across cozumel channel by chavez et al 2003 showed the existence of periods lasting over 1 month with large 3 day to 1 week ageostrophic fluctuations the flow was measured again for a year now at four locations around cozumel island including two instruments along the axis of the channel 8 6 km apart thus allowing estimations of the along channel velocity gradients the new measurements reveal that as suggested in the previous study the centripetal or curvature acceleration of the current is the most significant contribution in the departure from geostrophy indeed the curvature is at times so large that the pressure difference implies a geostrophic flow in the direction opposite to that of the actual flow that is the curvature is anticyclonic with amplitude in rossby number larger than unity measures of the intensity of suprainertial variations in pressure differences and velocity show that periods of ageostrophic fluctuations are consistently much richer in high frequency fluctuations than periods of nearly geostrophic behavior nonetheless the large scale reynolds stresses play an insignificant role throughout

climatology of ocean features in the gulf of mexico using satellite remote sensing data a climatology of various ocean features in the gulf of mexico gom was developed using the combination of satellite remote sensing and in situ data that spanned periods as long as 32 years twelve separate statistics were created some of which described characteristics of the loop current while others are involved with warm core rings that separate from the loop current and cold core rings these statistics examined the frequency with which the loop current was found in the gom the orientation of the loop current the frequency of intrusion of loop current water onto the west florida shelf and into the gom common water region ring separation period from the loop current ring dissipation ring speed ring path frequency of ring water in the western gom and the frequency of warm and cold core rings wcrs and ccrs respectively in the gom the results indicate that ccrs were principally responsible for mass and heat redistribution in the eastern gom egom and wcrs are responsible for mass and heat redistribution in the western gom wgom the average period for wcr separation from the loop current was 11 months and the range from 5 to 19 months wcrs moved through the wgom most often using the central path i e their trajectory was found between 24 and 26 n latitude and they decreased to about 55 of their initial size when they reach the western wall of the gom ccrs were most often found in the egom and their frequency of occurrence in the egom surpassed that of wcrs anywhere in the gom

impact of caribbean cyclones on the detachment of loop current anticyclones 1 the western boundary current in the north atlantic is characterized by an intense flow reaching 2 5 ms 1 at the surface that enters the caribbean sea through the lesser antilles passages crosses the entire caribbean and enters the gulf of mexico through the yucatan channel where it is known as the loop current a characteristic feature of the loop current is eddy shedding events i e the detachment of large anticyclonic eddies at irregular intervals moored current measurements between january 2005 and july 2009 in the loop current the yucatan channel and the caribbean coastal waters of mexico i e the western cayman sea along with aviso altimetry are used to evidence the northward propagation of cyclonic anomalies along the caribbean coast of mexico and the marked eastward displacement of the loop current at 23 n latitude just before several anticyclonic eddy shedding events after entering the gulf of mexico these cyclonic anomalies might initiate or enhance existing campeche bank cyclonic eddies which are related to many of the loop current detachment events sixteen of the twenty one detachments that occurred during the study period 76 are related to the cyclonic eddies in the western caribbean sea six of them were not reattached again to the loop current observations thus clearly indicate that cyclonic eddies in the western cayman sea contribute significantly to the loop current eddy shedding process which is complex and in principle not unique

tidal motions in the florida current abstract a linear relationship exists between sea level and the north component of the depth averaged tidal velocity in the straits of florida this relationship is used as a one dimensional model to predict barotropic tidal currents across the straits near 27 n predictions are independent of the choice of a sea level reference site between key west and patrick air force base the model when compared with three sets of depth averaged velocity obtained from current profilers can account for at least 70 of the variance in the diurnal and semidiurnal tidal bands the predicted diurnal tidal current is dominant and can account for more than 80 of the predicted tidal energy twice a year the one dimensional model yields a maximum amplitude of 12 cm s 1 3 5 cm s 1 rms this corresponds to a tidal transport of 5 1 106 m3 s 1 1 5 106 m3 s 1 5 1 sv

origin of rhyolitic lavas in the mesa central mexico by crustal melting related to extension the emplacement of a voluminous sequence of rhyolitic lava flows and domes characterizes oligocene volcanism in the mesa central mc of mexico its dominant effusive style of emplacement contrasts deeply with the predominantly explosive volcanism of the sierra madre occidental volcanic province toward the west whole rock geochemical major and trace elements and sr nd isotopic data of the mc oligocene rhyolitic lavas document a marked change in magma composition at around 30 ma allowing us to distinguish between a lower and an upper sequence lavas from the lower sequence are geochemically similar to the high k rhyolitic rocks of the eastern sierra madre occidental major and trace element variations are characteristic of mantle derived magmas evolving through fractional crystallization the initial 87 sr 86 sr and e nd values are nearly constant 0 70644 0 70770 and 1 2 to 2 1 respectively and indicate some contribution from crustal material lavas from the upper sequence are high silica peraluminous rhyolites with strong enrichment in fluorine and in some incompatible lithophile elements rb la sm yb y th u nb ta and strong depletion in the feldspar compatible elements sr ba eu initial 87 sr 86 sr ratios of the upper sequence lavas are high and variable 0 70812 0 72190 and decrease as silica content increases whereas the e nd values are relatively constant 1 4 to 2 8 the trace element behavior indicates an origin by variable degrees of non modal partial melting of granulitic low crustal rocks and chemical disequilibrium during melting processes the high and variable sr isotopic ratios could also be related to isotope disequilibrium melting processes if the isotopic heterogeneities between individual mineral phases were preserved during heating of the source rocks the changes in geochemical compositions are related to the onset of crustal extension at high strain rates documented for the mc crustal extension promoted crustal melting at high melting rates high melt segregation rates rapid ascent of low viscosity fluorine rich magmas and inhibited melt stagnation in magma chambers such conditions favored the effusive volcanic style and support the possibility of melting under disequilibrium conditions

circulation of the caribbean sea a well resolved inverse problem the caribbean sea is selected as a region where the large scale circulation is well determined by historical hydrographic measurements through application of the inverse method a simple example is used to illustrate the technique and to demonstrate how some physically relevant quantities may be well determined in the formally underdetermined inverse problem the geostrophic flow field in the caribbean is found by imposing mass and salt conservation constraints in seven layers separated by surfaces of constant potential density an unsmoothed solution is displayed that has weak dependence on an initial choice of reference level in addition a unique smoothed solution is shown above sigma sub theta 27 4 the total flow leaving the western caribbean is estimated to be 29 x 10 sup 6 m sup 3 s sup 1 in agreement with direct measurements this flow is made up of 22 x 10 sup 6 m sup 3 s sup 1 entering the caribbean from the east and flowing across the southern half of the basin as the caribbean current and 7 x 10 sup 6 m sup 3 s sup 1 in agreement with direct measurements this flow is made up of 22 x 10 sup 6 m sup 3 s sup 1 entering the caribbean from the east and flowingmore across the southern half of the basin as the caribbean current and 7 x 10 sup 7 m sup 3 s sup 1 entering from the north through windward passage both of these currents show small scale variability that diminishes with distance from the respective passages the deep flow has no net transport as required by the shallow exit but a well organized clockwise recirculation is found in the deep eastern caribbean less

a model study of the vertically integrated transport variability through the yucatan channel role of loop current evolution and flow compensation around cuba 1 in the paper a model study of the vertically integrated transport variability through the yucatan channel role of loop current evolution and flow compensation around cuba by lin et al journal of geophysical research 114 c08003 doi 10 1029 2008jc005199 2009 in the last sentence of paragraph 31 the word westward in drives enhanced westward should be eastward

controls and development of late quaternary periplatform carbonate stratigraphy in walton basin northeastern nicaragua rise caribbean sea the late quaternary sedimentary record in periplatform oozes and muds deposited on the northern nicaragua rise results from the interplay of four main controls 1 input of pelagic carbonates and bank derived fine aragonite and magnesian calcite 2 input of siliciclastic sediments 3 dispersal and removal of sediments by the caribbean current and 4 partial seafloor dissolution of metastable carbonates high accumulation rates of the calcite coarse sediment fraction throughout the study area demonstrate that planktonic foraminiferal productivity peaked during interglacial stages neritic carbonate productivity also peaked during interglacial stages when bank and shelf tops along the nicaragua rise were submerged within the photic zone because the bank and shelf tops remained mostly exposed during glacial stages the surface area available for the neritic carbonate productivity was drastically reduced to a narrow band along the margins of pedro bank and the southern shelf of jamaica a large volume of siliciclastic sediments transported from the coastal area of south america and the eastern and western regions of jamaica were deposited during glacial stages within the eastern and western deep extensions of walton basin this finding contrasts with the input pattern of siliciclastic sediments in walton basin itself where the largest input of siliciclastic sediments occurred at each of the interglacial climatic optima corresponding to intervals of maximum sea level transgression finally cores in water depths exceeding 1100 m display during interglacial stages aragonite accumulation rates systematically lower than rates in cores from water depths shallower than 1100 m this indicates that some bank derived aragonite and magnesian calcite has been partially removed by seafloor dissolution in areas from water depths exceeding 1100 m results from this study on the northeastern nicaragua rise indicate that not only do offbank transport and water column saturation state influence the late quaternary record but also that the variable strength of the caribbean current and the proximity of sources for siliciclastic sediments have played a major role in the development of the late quaternary periplatform high resolution stratigraphy

groundwater chemistry and mass transfers in the independence aquifer central mexico by using multivariate statistics and mass balance models in the light of progressive depletion of groundwater reservoir and water quality deterioration of the independence aquifer an investigation on chemical data of dissolved major and minor constituents in 246 recent groundwater samples was performed the main objective was the detection of processes responsible for the geochemical evolution and mineralization throughout the area multivariate techniques revealed different sources of solutes a dissolution of calcium and magnesium carbonate minerals b weathering of acid volcanic minerals c alteration of manganese containing alkaline silicates d leaching of halite deposits of meteoric origin e contamination from agricultural and urban wastewaters and f evaporative effects due to intensive irrigation although nitrate contamination is associated with pollution from intensive cultivated areas natural contamination plays an important role in the study area the investigation reveals that weathering of acid volcanic rocks rhyolite and oxidation of arsenic bearing sulfide minerals are the responsible processes for high fluorine up to 16 mg l and arsenic up to 0 12 mg l contents respectively exceeding the mexican maximum admissible concentration for drinking water except for kaolinite all recharge processes are dissolution oriented co2 calcite dolomite k feldspar plagioclase silicate precipitation amorphous silica and chalcedony is of growing importance in discharge zones cation exchange is not an important issue in the whole study area

the mean upper layer flow in the central gulf of mexico by a new method abstractprevious studies have found a puzzling disagreement between two large datasets and the results of numerical models in the central gulf of mexico the observations suggest an upper layer mean flow to the west of order 10 cm s 1 while the numerical models find no such mean flow a new technique is used here using 23 yr of satellite derived sea surface height data to estimate the mean flow this third independent set of data yields the same westward flow found in previous studies these findings require that there be sinking in the western gulf the details of the return flow remain an intriguing problem

implementation of magnetic gravity and resistivity data in identifying groundwater occurrences in el qaa plain area southern sinai egypt abstract el qaa plain is one of the areas that have been proved to be promising as to its soil and groundwater resources in the southwestern part of sinai this study was carried out to study the lateral and vertical variations in the subsurface lithologic properties in el qaa plain area and delineating the subsurface structure that affecting el qaa plain depression gravity magnetic data fifty one 51 vertical electrical sounding ves s and digital elevation model dem map were used two dimensional density modeling analytical signal tilt derivatives euler deconvolution techniques and interpretation of the resistivity data were applied on potential data this study concluded that el qaa plain is a ne sw depression confined by two normal faults and subdivided into five sedimentary units rock fragments and boulders derived to the plain from the surrounding highlands are the main components of the first surface unit that characterized by high resistivity values this layer is overly another unit composed of gravelly sand with thickness ranging between 10 and 140 m the third unit is composed mainly of sand with intercalations of clay with thickness ranging from 2 to 152 m a reefal limestone unit is a fourth unit interpreted from this study the fifth unit is composed of clay the water bearing formations in el qaa plain area are located principally in the second and the third layers finally the depth to the basement surface ranges from 400 m to more than 1 5 km below sea level also there are many minor structural trends interpreted from this study and affecting the el qaa plain are striking in n s e w and ne sw directions

analysis of flow variability in the yucatan channel 1 the structure and variability of the velocity and temperature fields in yucatan channel are analyzed using data from an eight mooring array deployed from august 1999 to june 2000 the area averaged kinetic energy and transport fluctuations spectra show that the extrema of these quantities do not coincide and that flow variability is dominated by highly energetic processes with weak transport contributions transport fluctuations peak in the 20 40 and 5 10 day period bands but show no clear correlation with the local wind stress forcing empirical orthogonal function eof analysis of the along channel velocity component shows that approximately 55 of the total velocity variance is retained in the first two eofs which depict tripolar the center of the channel is out of phase with the sides and dipolar structures a multivariate complex eof analysis of low passed temperature and velocity components suggests the tripole dipole structures are the components of irregular oscillations of the flow related to the northwestward propagation of anticyclones and cyclones through the channel the weak transport signal in these modes is consistent with the eddies being advected by the mean flow in contrast to other western boundary current regions the passage of eddies provides the predominant explanation for the variability in the yucatan channel however the processes controlling transport variability remain unclear

ages of epithermal deposits in mexico regional significance and links with the evolution of tertiary volcanism we present an analysis leading to a new space time classification of the mexican epithermal deposits based on new data and interpretations from seven deposits in central mexico and a new age for the la guitarra deposit temascaltepec district from the latter adularia from a barren stage of mineralization and from quartz bands of the main ore stage together with orthoclase phenocrysts from host monzogranites with a known late laramide age were analyzed by the 40ar 39ar method the ages obtained from adularia samples are 32 9 0 1 ma and 33 3 0 1 ma corresponding to the middle part of lower oligocene these ages are slightly younger than that of the ignimbrite succession exposed next to the study area and they suggest that the deposit is related to the crystallization of comagmatic intrusive rocks contrary to previous assumptions of a miocene age for several epithermal deposits in southern mexico the ages from la guitarra show that south of the trans mexican volcanic belt these deposits may be oligocene or older in addition the interpretation of a genetic link between intrusive rocks and epithermal mineralization is consistent with previous work on fluid geochemistry of the deposit to evaluate the obtained ages in a regional context we analyzed the geographic distribution and age of tertiary epithermal deposits in central mexico our study shows that mineral deposits coincide with the main volcanic pulses of the sierra madre occidental the distribution of epithermal deposits can be thus divided into three main groups 1 between 48 and 40 ma 2 between 36 and 27 ma and 3 between 23 and 18 ma within the first group are the batopilas and topia deposits that record the oldest ages found for epithermal deposits in mexico deposits of this age are hosted by the lower volcanic supergroup of the sierra madre occidental and are related to the laramide magmatism of the sierra madre occidental many of the epithermal deposits in mexico occur within the second time span in a northwest southeast belt from chihuahua to the mexico and guerrero states these deposits are related to the main episode of ignimbrite flare up of the sierra madre occidental the third group includes the bolanos san martin de bolanos and pachuca real del monte deposits plus possibly seven other epithermal deposits analyzed in this work these deposits are related to the last ignimbrite flare up of the sierra madre occidental with a general west northwest east southeast distribution recently documented in the southern sierra madre occidental

patterns of the loop current system and regions of sea surface height variability in the eastern gulf of mexico revealed by the self organizing maps the self organizing map som an unsupervised learning neural network is employed to extract patterns evinced by the loop current lc system and to identify regions of sea surface height ssh variability in the eastern gulf of mexico gom from 23 years 1993 2015 of altimetry data spatial patterns are characterized as different lc extensions and different stages in the process of lc eddy shedding the temporal evolutions and the frequency of occurrences of these patterns are obtained and the typical trajectories of the lc system progression on the som grid are investigated for an elongated northwest extended or west positioned lc it is common for the lc anticyclonic eddy lce to separate and propagate into the western gom while an initially separated lce in close proximity to the west florida continental slope often reattaches to the lc and develops into an elongated lc or reduces intensity locally before moving westward as a smaller eddy regions of differing ssh variations are also identified using the joint som wavelet analysis along the general axis of the lc ssh exhibits strong variability on time scales of 3 months to 2 years also with energetic intraseasonal variations which is consistent with the joint empirical orthogonal function eof wavelet analysis in the more peripheral regions the ssh has a dominant seasonal variation that also projects across the coastal ocean the som when applied to both space and time domains of the same data provides a powerful tool for diagnosing ocean processes from such different perspectives

fluid mixing leads to main stage cassiterite precipitation at the xiling sn polymetallic deposit se china evidence from fluid inclusions and multiple stable isotopes h o s the xiling sn deposit in eastern guangdong province comprises the fengdishan sn and the saozhoudi sn pb zn ore blocks and has long been regarded as a volcanic subvolcanic system related to sn polymetallic mineralization here we present fluid inclusion microthermometric data from different ore stages and h o s isotope data of hydrothermal minerals to constrain the genesis of the xiling deposit fluid inclusions from stage i have th values from 340 to 420 c and salinities from 15 to 17 wt nacl equivalent while homogenization temperatures of fluid inclusions from stages ii to v range from 150 to 320 c and salinities range between 1 and 6 wt equivalent the oxygen and hydrogen isotopic composition of quartz and cassiterite dfluid 65 18ofluid 3 6 to 6 3 suggest that the ore forming fluids from stage i have a distinct magmatic signature whereas those from stage ii through stage iv dfluid from 80 to 49 18ofluid from 3 7 to 2 5 show characteristics of mixing between meteoric and magmatic fluids moreover 34s values for sulfides from the fengdishan ore block have a narrow range of 0 6 to 2 5 with a mean close to 0 consistent with a magmatic sulfur source by contrast 34s values for ore minerals from the saozhoudi ore block range from 3 4 to 11 5 suggesting involvement of a sedimentary sulfur source in addition a previous geochronological study has shown that the volcanic subvolcanic host rocks have an age of 160 170 ma while the sn polymetallic mineralization has an age of about 145 ma our data support a model of mixing of magmatic brine from a hidden granitic intrusion with meteoric water the s isotope data and the observed temperature gradient of the fluid system suggest that the sn mineralization is developed in the central part of the ore system while the sn pb zn and pb zn mineralization occurs in the distal part this finding might have important implications for exploration in the region

yucatan channel flow observations versus clipper atl6 and mercator pam models 1 the statistical properties of the flow structure in the yucatan channel s main section based on 2 years of continuous observations august 1999 to june 2001 are compared with those simulated by the ocean parallelise opa primitive equation model in two different configurations the atl6 configuration from the clipper project the whole atlantic domain with a 1 6 resolution and the prototype atlantique mediterranee pam configuration from the mercator project the north atlantic domain with 1 12 resolution while the observed 2 year mean transport into the gulf of mexico is 23 06 sv atl6 has a 5 year mean of 27 49 sv and pam has a 3 year mean of 29 06 sv apart from this discrepancy in the mean transport both simulations are able to reproduce well in structure and magnitude details of the mean current and its variability features like the yucatan current core and the deep countercurrents in the yucatan and cuban sides are both well reproduced as is the presence of a minimum surface current variability at the center of the channel the two principal empirical modes of current variability which are related to the passage of eddies through the channel are also reproduced by the simulations the observed and simulated transports above and below the 6 c isotherm show no coherency at any frequency except for a significant coherent peak at a period around 20 days which we interpret as a first baroclinic kelvin mode between the two layers as in the observations the shedding of eddies by the loop current in the simulations is preceded by periods of diminished negative horizontal vorticity flux into the gulf of mexico

geochronology of mercury tin and fluorite mineralization in northern mexico this study was undertaken to obtain reconnaissance isotopic ages on tin mercury fluorine and antimony mineralization in northern mexico and to determine their temporal relation to the metallogenic evolution of the continental volcanic arc in this region deposits were dated using conventional k ar and 40 ar 39 ar analyses of whole rocks and phenocryst separates for altered and unaltered pre and postore samples ore related rhyolites in three tin deposits sombrerete la ochoa and cerro de los remedios formed at 30 to 31 m y ago and mineralization probably took place at the same time the guadalcazar stock which hosts disseminated cassiterite formed at about 28 m y ago mineralization in the canoas mercury district formed at 26 to 27 m y although mineralization in the other two districts studied sain alto and el cuarenta could be limited only to post 37 m y and post 40 m y respectively fluorite deposits hosted by limestone in the zaragoza and rio verde districts formed at 30 to 31 m y and smaller volcanic hosted deposits in the inde district could have formed as early as 38 m y the only radiometric age related to an antimony district obtained in this study was 36 m y for the granodiorite stock at santa maria de la paz north of the wadley district these ages demonstrate that the sn hg f sb mineralization was essentially contemporaneous with the latest phases of base and precious metal mineralization in northern mexico and suggest that formation of deposits containing these metals is a special stage in the metallogenic evolution of volcanic arcs which requires a relatively thick crust that is conducive to extensive magmatic differentiation and silicic volcanism