lunar global shape and polar topography derived from kaguya lalt laser altimetry a global lunar topographic map with a spatial resolution of finer than 0 5 degree has been derived using data from the laser altimeter lalt on board the japanese lunar explorer selenological and engineering explorer selene or kaguya in comparison with the previous unified lunar control network ulcn 2005 model the new map reveals unbiased lunar topography for scales finer than a few hundred kilometers spherical harmonic analysis of global topographic data for the moon earth mars and venus suggests that isostatic compensation is the prevailing lithospheric support mechanism at large scales however simple rigid support is suggested to dominate for the moon venus and mars for smaller scales which may indicate a drier lithosphere than on earth especially for the moon and venus

igneous and tectonic evolution of the batchawana greenstone belt superior province a u pb zircon and titanite study u pb isotopic dating of zircon and titanite from all the major litho tectonic units of the batchawana belt an archean greenstone belt of the abitibi subprovince of the superior province in canada shows that the belt evolved during a period of about 60 ma between about 2730 and 2670 ma ago the earliest date of 2729 3 2 ma was found in a predominantly tholeiitic metavolcanic sequence the base of which is intruded by a tonalite dated at 2716 2 ma younger ages of 2720 10 ma 2709 2ma 2711 2ma 2701 2ma and 2698 2 ma date rocks at increasingly higher stratigraphic levels of a mixed tholeiitic calc alkalic metavolcanic sequence which is itself overlain by a thick succession of clastic metasedimentary rocks subsequent deformation of the supracrustal sequences produced isoclinal folding and culminated in metamorphism ranging from lower greenschist to amphibolite facies and anatexis related to the intrusion of syn to late tectonic plutons four phases of which have ages of 2678 4 2ma 2677

caloris impact basin exterior geomorphology stratigraphy morphometry radial sculpture and smooth plains deposits the mariner 10 flybys revealed the eastern third of the caloris basin and demonstrated its importance as a chronostratigraphic marker for the geological history of mercury uncertain after that mission were the size of the basin the full distribution of materials deposited or modified during the impact process and the stratigraphic and age relationships between caloris and surrounding terrain images obtained during messenger s january 2008 flyby of mercury revealed that the caloris basin is 15 larger than previously estimated and moderately elliptical 1525 by 1315 km basin related sculpture and secondary craters are dispersed widely in areas surrounding the basin confirming the widespread significance of this event as a stratigraphic marker units mapped around caloris on the basis of mariner 10 data are generally recognized in regions observed for the first time by messenger including most facies of the caloris group the caloris montes odin formation and van eyck formation the only unit without obvious exposures in messenger images is the nervo formation which was originally interpreted as impact melt or fallback ejecta new measurements of the size frequency distribution of impact craters both within the caloris basin and on surrounding units particularly the odin formation support the hypothesis that the vast majority of circum caloris plains postdate the basin and are likely volcanic the messenger observations re emphasize the importance of understanding the exterior stratigraphy of the basin in order to utilize the caloris event as a discrete time horizon in the geological history of mercury

is the subtropical jet shifting poleward the tropics are expanding poleward at about 0 5 circ per decade in observations this poleward expansion of the circulation is consistently reported using hadley cell edge metrics and lower atmospheric tropical edge metrics however some upper atmospheric tropical metrics report smaller trends that are often not significant one such upper atmospheric metric is the subtropical jet latitude which has smaller trends compared to the hadley cell edge in this study we investigate the robustness of the weak trends in the subtropical jet position by introducing a new method for locating the subtropical jet and examining the trends and variability of the subtropical jet latitude we introduce the tropopause gradient method based on the peak gradient in potential temperature along the dynamic tropopause using this method we find the trends in the subtropical jet latitude are indeed much smaller than 0 5 circ per decade consistent with previous studies we also find that natural variability within the subtropical jet latitude would not prevent trends from being detected if they were similar to the hadley cell edge as trends greater than 0 24 circ per decade could reliably be detected using monthly data or 0 09 circ per decade using daily data despite the poleward expansion of the tropics there is no robust evidence to suggest the subtropical jet is shifting poleward in either hemisphere neither the current diagnostic methods nor natural variability can account for the small subtropical jet trends the most likely explanation which requires further investigation is that the subtropical jet position is not tied dynamically to the hadley cell edge

carboniferous inherited grain and age zoning of monazite and xenotime from leucogranites in far eastern nepal constraints from electron probe microanalysis chemical th u total pb isochron method chime of monazite and xenotime from three leucogranites in far eastern nepal revealed the presence of carboniferous inherited grains of monazite and intense intrusion of leucogranites around 18 16 ma in the high himalaya in garnet bearing sillimanite muscovite biotite leucogranite most monazite grains have inherited cores with the chemical dates of 504 418 and 342 272 ma which were overgrown by early miocene mantles and rims of 17 9 1 5 ma early ordoviciain and carboniferous ages are rarely found in the same euhedral subhedral cores in addition to the previously recognized early paleozoic magmatism monazite cores with carboniferous ages in early miocene leucogranites provide evidence for two periods of magmatism at the base of the high himalaya prior to the cenozoic himalayan orogeny in muscovite biotite leucogranite no inherited domains were observed in monazite and xenotime grains they yielded the chime monazite and xenotime dates of 16 1 2 0 and 19 8 6 5 ma respectively monazite grains adjacent to xenotime have significantly lower concentrations of uo 2 and y 2 o 3 compared to those isolated from xenotime these results imply that xenotime influences y and u contents in monazite reflecting local equilibrium system in aplitic leucogranite monazite grains yielded the mean of apparent chemical date of 18 0 2 2 ma the chime monazite ages of 18 16 ma in three leucogranites reflect the timing of melt crystallization

the crystalline units of the high himalayas in the lahul zanskar region northwest india metamorphic tectonic history and geochronology of the collided and imbricated indian plate in the high himalayan belt of northwest india crustal thickening linked to palaeogene collision between india and eurasia has led to the formation of two main crystalline tectonic units separated by the syn metamorphic miyar thrust the high himalayan crystallines sensu stricto hhc at the bottom and the kade unit at the top these units are structurally interposed between the underlying lesser himalaya and the very low grade sediments of the tibetan nappes they consist of paragneisses orthogneisses minor metabasics and chiefly in the hhc leucogranites the hhc registers a polyphase metamorphism with two main stages designated as m1 and m2 a metamorphic zonation with high temperature recrystallization and migmatization at middle structural levels and medium temperature assemblages at upper and lower levels in contrast the kade unit underwent a low temperature metamorphism rb sr and u th pb isotope data point to derivation of the orthogneisses from early palaeozoic granitoids while the leucogranites formed by anatexis of the hhc rocks and were probably emplaced during miocene time most of the complicated metamorphic setting is related to polyphase tectonic stacking of the hhc with the cooler kade unit and lesser himalaya during the himalayan history however a few inconsistencies exist for a purely himalayan age of some ml assemblages of the hhc as regards the crustal derived leucogranites the formation of a first generation mixed with quartzo feldspathic leucosomes was possibly linked to melt lubricated shear zones which favoured rapid crustal displacements at upper levels they intruded during stage m2 and the latest movements along the syn metamorphic miyar thrust but before juxtaposition of the tibetan nappes along the late metamorphic zanskar fault

expansion of the hadley cell under global warming winter versus summer abstracta scaling relationship is introduced to explain the seasonality in the outer boundary of the hadley cell in both climatology and trend in the simulations of phase 3 of the coupled model intercomparison project cmip3 in the climatological state the summer cell reaches higher latitudes than the winter cell since the hadley cell in summer deviates more from the angular momentum conserving state resulting in weaker upper level zonal winds which enables the hadley cell to extend farther poleward before becoming baroclinically unstable the hadley cell can also reach farther poleward as the itcz gets farther away from the equator hence the hadley cell extends farther poleward in solstices than in equinoxes in terms of trend a robust poleward expansion of the hadley cell is diagnosed in all seasons with global warming the scaling analysis indicates this is mostly due to an increase in the subtropical static stability which pushes poleward the baroclinically unstable zone and hence the polewar

nappe tectonics extension and metamorphic evolution in the indian tethys himalaya higher himalaya se zanskar and nw lahul in the southern part of the indian tethys himalaya between se zanskar and nw lahul nappe tectonics with transport toward the wsw during the main deformation phase has been ascertained if the stratigraphy of the different units considered as nappes is combined it results in a composite section ranging from lower cambrian to middle cretaceous a metamorphism of amphibolite facies in the lowest unit is associated with the nappe stacking the lower miocene cooling ages of metamorphic biotite and muscovite suggest that the nappe emplacement starts at the oligocene or at the oligocene eocene boundary after the compressional phases an extension provokes the reactivation of older main thrusts as normal fault and the formation of a steeply dipping normal fault this interpretation is based on detailed mapping

first report of lower permian basalts in south tibet tholeiitic magmatism during break up and incipient opening of neotethys abstract the neo tethys ocean began to form at early permian times when continental flood basalts were emplaced in various areas of the newly formed indian passive margin exposed today in the so called tibetan sedimentary zone of the himalaya lower permian mafic volcanic rocks which have long been known from various himalayan localities from kashmir to arunachal pradesh are here for the first time reported to occur also in south tibet bhote kosi basalts of the gyirong county the basalts unconformably overlie lowermost permian diamictites with locally intervening black shales and debris flow deposits and are followed in turn by chert bearing quartzarenites and silty to phosphatic marls yielding brachiopods of roadian wordian age the age of the lavas can thus be bracketed as late early permian post sakmarian and pre roadian the geochemistry of these subalkalic tholeiites akin to morbs testifies to their similarity not only with the adjacent nar tsum spilites of central nepal but also with the panjal traps and abor volcanics of the western and eastern himalayas respectively the geochemical signature of lower permian volcanic rocks is in fact uniform all along the himalayan range and markedly different from that of basaltic rhyolitic alkalic products sporadically emplaced during the previous rifting stage rift volcanism in the tethys himalaya began in the early carboniferous and came to an end in sakmarian times in the early permian initial submergence of the rift shoulders and sediment starvation were followed by tholeiitic magmatism which is therefore interpreted as following break up and incipient sea floor spreading in the neotethys ocean roughly contemporaneous emplacement of continental flood basalts of similar geochemical signature along a 2000 km long rift axis would in fact suggest extensive mantle melting at the transition from continental rifting to break up and opening of the neotethys between northern gondwana and the peri gondwanian blocks

timing of normal faulting along the indus suture in pakistan himalaya and a case of major 231 pa 235 u initial disequilibrium in zircon we report age data by tims u pb la icp ms and 39ar 40ar techniques for main magmatic events in the lower swat region of pakistan in order to constrain the tectonic evolution of the northwestern himalaya the pre himalayan history of the indian continent is documented by single zircon u pb results from the peraluminous choga granite gneiss which yielded a 468 5 ma lower concordia intercept interpreted to approximate the time of magmatic emplacement the presence of a well defined 870 7 ma inherited component upper intercept suggests a plutonic or volcanic protolith residing at unexposed levels of the indian crust zircon data for the swat granite gneiss from the northern part of the loe sar dome give an emplacement age of 267 6 3 ma which is at variance with earlier correlations favoring an early paleozoic origin subsequent to metamorphic overprint by the himalayan orogeny the swat granite was intruded by late kinematic alkali granite dykes single zircons from one of these dykes show reproducible 206pb 238u data giving a precise mean age of 29 26 0 12 ma whereas the 207pb 235u ages scatter between 34 and 81 ma pointing to huge and variable enrichment in 207pb the unsupported 207pb can be explained by incorporation of 231pa an intermediate long lived daughter nuclide in the 235u decay chain in excess of the secular equilibrium ratio la icp ms measurements confirm the presence of unsupported 207pb but do not show any correlation between the latter and other selected trace element concentrations in these zircons a concordant ar ar muscovite age of 28 4 1 1 ma obtained for the same dyke postdates regional mica cooling ages and indicates a lack of younger regional events capable of resetting the k ar system in muscovite because the dyke is pre to synkinematic relative to normal faulting and related north vergent folds its emplacement age provides a maximum age for this event or reflects already ongoing local extension a lower limit of 15 ma has previously been established by apatite fission track analysis the 29 15 ma age bracket for normal faulting is coeval with extension along the south tibetan detachment system stds on the north side of the high himalaya this suggests that the indus suture in pakistan has acted as a western continuation of the stds and that related faulting was roughly contemporaneous over most of the himalaya

provenance of late triassic sediments in central lhasa terrane tibet and its implication abstract in southern tibet late triassic sequences are especially important to understanding the assembly of the lhasa terrane prior to indo asian collision we report new data relevant to the provenance of a late triassic clastic sequence from the mailonggang formation in the central lhasa terrane tibet petrographic studies and detrital heavy mineral assemblages indicate a proximal orogenic provenance including volcanic sedimentary and some ultramafic and metamorphic rocks in situ detrital zircon hf and u pb isotope data are consistent with derivation of these rocks from nearby triassic magmatic rocks and basement that comprise part of the newly recognized late permian triassic sumdo cuoqen orogenic belt the new data suggests correlation with the upper triassic langjiexue group which lies on the opposing southern side of indus yarlung ophiolite sediments from both the mailonggang formation and langjiexue group are interpreted to represent formerly contiguous parts of a sequence deposited on the southern flanks of the sumdo cuoqen belt

sensitivity of equatorial convection to horizontal resolution in aquaplanet simulations with a variable resolution gcm abstract climate simulations using idealized zonally symmetric boundary conditions an aquaplanet are performed in order to highlight possible deviations from zonality introduced by the spatial variations in resolution caused by the variable resolution technique simulations at three different uniform resolutions with spectral truncations t21 t63 and t106 are used as control simulations and analyzed in order to describe the zonal climate simulated by this version of the arpege climat general circulation model and establish its sensitivity to varying spatial resolution the model simulates a single equatorial precipitation maximum in which the activity of the convective cells is modulated by westward and eastward propagating equatorial waves depending on the resolution a simulation with the variable resolution technique using a truncation t63 and a stretching factor of 3 with the maximum resolution pole placed at the equator is then compared to the uniform resolution simulations deviations from the

climatic and volcanic forcing of tropical belt northern boundary over the past 800 years the position of the northern boundary of the tropical belt affects the hydroclimate of many arid and semi arid regions in the northern hemisphere widening of the tropical belt since the 1970s has largely been attributed to anthropogenic forcing however the relative influence of natural drivers of tropical belt expansion and contraction before this time is poorly understood here we use data on tree ring widths from five mid latitude regions in the northern hemisphere to reconstruct the movement of the northern boundary of the early spring tropical belt over the past 800 years ad 1203 2003 our reconstruction explains 45 of the interannual variance in the latitudinal extent of the hadley circulation a metric of the position of the tropical belt boundary we find that the tropical belt contracted expanded during positive negative phases of the el nino southern oscillation and pacific north american teleconnection patterns the tropical belt also contracted significantly following major volcanic events that injected sulfur into the stratosphere the longest period of persistent tropical belt expansion occurred in the late sixteenth century during one of the coldest periods of the little ice age our results warn of potential socio economic consequences of future variations in tropical belt width driven by natural climate variability or stratospheric aerosol injections whether volcanic or artificial climate variability and volcanic forcing both influenced the latitudinal migration of the tropical belt over the past 800 years according to an analysis of tree ring widths in the northern hemisphere

volcanism on mercury evidence from the first messenger flyby the origin of plains on mercury whether by volcanic flooding or impact ejecta ponding has been controversial since the mariner 10 flybys 1974 75 high resolution images down to 150 meters per pixel obtained during the first messenger flyby show evidence for volcanic vents around the caloris basin inner margin and demonstrate that plains were emplaced sequentially inside and adjacent to numerous large impact craters to thicknesses in excess of several kilometers radial graben and a floor fractured crater may indicate intrusive activity these observations coupled with additional evidence from color images and impact crater size frequency distributions support a volcanic origin for several regions of plains and substantiate the important role of volcanism in the geological history of mercury

on the discrepancies in tropical belt expansion between reanalyses and climate models and among tropical belt width metrics abstractthe arid subtropics are situated at the edges of the tropical belt where subsidence in the hadley cells suppresses precipitation any meridional shift in these edge latitudes could have significant impacts on surface climate recent studies have investigated past and future changes in the tropical belt width and have found discrepancies in the rates of expansion estimated with different metrics and between climate models and reanalyses here cmip5 simulations and four modern reanalyses are analyzed using an ensemble of objective tropical belt width metrics to reexamine if such inconsistencies exist the authors do not find sufficient evidence to demonstrate this discrepancy between models and reanalyses as reanalysis trends in the tropical belt width fall within the range of model trends for any given metric furthermore only metrics based on the hadley cells are found to exhibit robust historical and future expansion metrics based on the subtropical jet and the tropopause show no robust resp

space and time in granite plutonism granitic suites formed in the last 2500 ma are either calc alkaline or less commonly alkalic the space time trends of granitoid rocks from modern compressional arcs include variations towards more silicic and potassic products but even the most mature magmas of these arcs have fe mg ratios near to 1 in contrast with the strongly iron enriched alkalic suites that characterize zones of crustal extension both calc alkaline and alkalic suites are mainly mantle derived they evolved respectively from tholeiitic and alkali basalt parental magmas which have been subject in most examples to a two stage fractionation history other factors that may influence the evolution of these parental magmas include first the addition of variable but minor amounts of crustal melt and secondly the persistence of refractory mineral phases in the zone of melting contributions from subducted continental detritus are thought to be of minor significance a long term trend over the entire history of the crust from more sodic to more potassic calc alkaline magmatism may reflect the declining importance of subducted ocean lithosphere in magma generation and the increasing role of the overlying volatile fluxed mantle wedge this trend and in particular the widespread development of alkalic granite suites in mid proterozoic times may be linked to the declining vigour of tectonic and associated magmatic processes during the earth s history these alkalic suites may indicate a period when the continental lithosphere had become stable enough to resist fragmentation leading to intracontinental rift and swell zones of magmatism in some cases new plate cycles with more normal calcalkaline igneous rocks seem to have occurred in the same zones although much of the evidence favours the operation of plate tectonic and subduction processes in magma generation during archaean and early proterozoic times this link cannot be taken as proved except for the last ca 1000 ma

sensitivity of the eddy momentum flux to meridional resolution in atmospheric gcms abstract gcm experiments with zonally symmetric climates are used to demonstrate that the increase in the meridional eddy momentum fluxes and zonal surface winds that occurs when resolution is increased is primarily due to the increase in meridional rather than zonal resolution it is argued that the sensitivity to meridional resolution reflects the need to resolve the small scales generated in the rossby wave field as waves radiate from the midlatitude baroclinic eddy source region into regions with small mean winds some additional experiments highlight the sensitivity of surface winds and eddy momentum fluxes to the subgrid scale horizontal mixing formulation in low revolution models

petrogenesis of the flood basalts from the early permian panjal traps kashmir india geochemical evidence for shallow melting of the mantle article i nfo the early permian panjal traps of northern india represent a significant eruption of volcanic rocks which occurred during the opening of the neotethys ocean basaltic basaltic andesites dacitic and rhyolitic rocks collected from guryal ravine and pahalgam show evidence for subaerial and subaqueous eruptions indicating that they are contemporaneous with the formation of a shallow marine basin the major and trace element geochemistry of the basalts is consistent with a within plate setting and there are basalts which have high ti tio2 n 2 0 wt and low ti tio2 b 1 8 wt compositions the high ti basalts are similar to oib whereas the low ti basalts are similar to continental tholeiites the identification of high and low ti basalts within the panjal traps is analogous to other large igneous provinces e g karoo deccan parana emeishan the sr nd isotopic values end t 5 3 to 1 3 isr 0 70432 to 0 71168 of both types of basalts overlap indicating that the rocks may have originated from the same ancient subcontinental lithospheric i e emii like mantle source tdm 2000 ma the two groups of basalts can be modeled by using a primitive mantle source and different degrees of partial melting where the high tirocksare producedby 1 partial melting of a spinel peridotite source where as the low ti rocks are produced by 8 partial melting trace elemental and isotope modeling indicatesthat some of the basalts assimilated 10 crustal material in contrast the basaltic andesites are likely formed by mixing be tween basaltic magmas and crustal melts which produced rocks with higher sio2 55 wt content and enriched isotopic signatures end t 6 1 isr 0 70992 the panjal trap volcanism was likely due to partial melting of the sclm within a passive extensional setting related to the rifting of cimmeria from gondwana contemporaneous volcanic and plutonic granitic rocks throughout the himalaya are probably not petrogenetically related but are likely part of the same regional tectonic regime

the morphology of mercury s caloris basin as seen in messenger stereo topographic models a digital terrain model 1000 m effective spatial resolution of the caloris basin the largest well characterized impact basin on mercury was produced from 208 stereo images obtained by the messenger narrow angle camera the basin rim is far from uniform and is characterized by rugged terrain or knobby plains often disrupted by craters and radial troughs in some sectors the rim is represented by a single marked elevation step where height levels drop from the surroundings toward the basin interior by approximately 2 km two concentric rings with radii of 690 km and 850 km can be discerned in the topography several pre caloris basins and craters can be identified from the terrain model suggesting that rugged pre impact topography may have contributed to the varying characteristics of the caloris rim the basin interior is relatively smooth and shallow comparable to typical lunar mascon mare basins supporting the idea that caloris was partially filled with lava after formation the model displays long wavelength undulations in topography across the basin interior but these undulations cannot readily be related to pre impact topography volcanic construction or post volcanic uplift because errors in the long wavelength topography of the model cannot be excluded confirmation of these undulations must await data from messenger s orbital mission phase

the evolution of mercury s crust a global perspective from messenger mapping the distribution and extent of major terrain types on a planet s surface helps to constrain the origin and evolution of its crust together messenger and mariner 10 observations of mercury now provide a near global look at the planet revealing lateral and vertical heterogeneities in the color and thus composition of mercury s crust smooth plains cover approximately 40 of the surface and evidence for the volcanic origin of large expanses of plains suggests that a substantial portion of the crust originated volcanically a low reflectance relatively blue component affects at least 15 of the surface and is concentrated in crater and basin ejecta its spectral characteristics and likely origin at depth are consistent with its apparent excavation from a lower crust or upper mantle enriched in iron and titanium bearing oxides

geology of the caloris basin mercury a view from messenger the caloris basin the youngest known large impact basin on mercury is revealed in messenger images to be modified by volcanism and deformation in a manner distinct from that of lunar impact basins the morphology and spatial distribution of basin materials themselves closely match lunar counterparts evidence for a volcanic origin of the basin s interior plains includes embayed craters on the basin floor and diffuse deposits surrounding rimless depressions interpreted to be of pyroclastic origin unlike lunar maria the volcanic plains in caloris are higher in albedo than surrounding basin materials and lack spectral evidence for ferrous iron bearing silicates tectonic landforms contractional wrinkle ridges and extensional troughs have distributions and age relations different from their counterparts in and around lunar basins indicating a different stress history

regional changes in the annual mean hadley circulation in recent decades previous studies suggest that the zonally averaged hadley circulation zahc has experienced a robust poleward expansion and its trend in intensity displays inconsistency among different data sets this study examines changes in regional hc intensity and poleward edge using six reanalyses outgoing longwave radiation and precipitation data sets hcs in six regions including africa afhc the indian ocean iohc the western pacific wphc the eastern pacific ephc south america sahc and the atlantic athc are investigated intensity trends in the northern hemisphere nh wphc and athc and the southern hemisphere sh ephc and athc are in agreement with each other in the six reanalyses furthermore regional hcs in these domains appear to be intensifying although not all of the reanalyses show statistically significant trends for the poleward edge its trend in the nh afhc iohc ephc sahc and athc is significantly larger than zero and the northern hc poleward edge exhibits uniform poleward migrations in these five regions in the sh only the trend in the sahc poleward edge is significantly different from zero furthermore the trend in the sh sahc poleward edge is significantly larger than those in the sh afhc iohc and athc the results indicate that the poleward migration of the southern zahc poleward edge during recent decades that has been identified by previous studies may be attributed mainly to the poleward migration of the southern sahc poleward edge further analyses suggest that changes in regional hc poleward edges could have a significant impact on regional precipitation anomalies

unscrambling the stratigraphy of an archean greenstone belt a upb geochronological study of the favourable lake belt northwestern ontario canada abstract new zircon and baddeleyite u pb ages show that the major units of the archean favourable lake greenstone belt in the northern superior province were formed by episodic magmatism spanning more than 250 ma and demonstrate that the original stratigraphy is disrupted by thrusts that juxtaposed older supracrustal rocks on top of younger ones the oldest rocks of the area are a 2950 ma gneissic tonalite and a 3000 2960 ma granodiorite clast from a ca 2725 ma conglomerate five distinct volcanic and sedimentary groups formed during presumably short lived episodes at 2925 ma i 2870 ma ii 2858 ma iii 2734 ma iv and 2725 ma v the youngest group contains the thickest sedimentary unit a turbiditic and alluvial fluvial sequence compression caused thrusting that placed groups i and v on top of iv iii on v and ii on iii the thrust complex was subsequently isoclinally folded compression was accompanied by major plutonism that emplaced the bulk of the bounding batholiths between 2732 and 2711 ma ago the late tectonic mo mineralized setting net lake stock in the centre of the belt has an age of about 2708 ma and was overprinted by younger hydrothermal events that produced monazite 2706 ma titanite ca 2695 2690 ma and rutile the youngest rutile at 2657 ma similar late hydrothermal pulses are recorded by secondary titanite elsewhere in the belt and within the batholiths the protracted magmatic evolution of the belt is typical of that observed in a number of greenstone belts of the northern superior province but is uncommon farther to the south in contrast the structural complications and put of sequence stratigraphy appear to be a quite common tectonic characteristic of greenstone belts of the whole superior province

origin of the silicic volcanic rocks of the early permian panjal traps kashmir india abstract the panjal traps of kashmir india represent a significant outpouring of mafic and silicic volcanic rocks during the early permian and are synchronous with the opening of the neotethys ocean previous studies have suggested that the silicic volcanic rocks are derived by differentiation of mafic magmas dacites and rhyolites collected from the lower portions of the volcanic pile near pampore kashmir are peraluminous anck 1 0 in composition their calculated whole rock i sr values are variable i sr 0 69307 to 0 71825 and indicate open system behavior of either rb or sr or both whereas their nd isotope compositions end t 8 6 to 8 9 are nearly uniform the end t values and trace element th nb pm 4 nb u 8 ratios suggest the rocks are derived partially or wholly from the crust least squares and melts modeling indicate that the likely source of the silicic rocks is the middle crust rather than the lower or upper crust furthermore the silicic panjal traps have trace element compositions similar to some felsic volcanic rocks and a type granitic rocks from other large igneous provinces e g karoo parana and camp the paleoproterozoic t dm ages t dm 1836 to 1937 ma indicate that the rocks were likely derived from an ancient crustal source which experienced multiple episodes of recycling in contrast to silicic volcanic rocks from other lips the silicic panjal traps are unusual in that they did not involve mantle source material the heat required to melt the crust was likely due to the continuous injection of contemporaneous basaltic magmas which formed the majority of the mafic panjal traps

the dynamics of idealized convection schemes and their effect on the zonally averaged tropical circulation in this paper the effect of a simple convection scheme on the zonally averaged tropical general circulation is examined within an idealized moist gcm to obtain broad classifications of the influence of convection on the tropics this is accomplished with a simplified convection scheme in the style of betts and miller the scheme is utilized in a moist gcm with simplified physical parameterizations gray radiation with zonally symmetric slab mixed layer ocean boundary conditions comparisons are made with simulations without a convection scheme i e with large scale condensation lsc only with the moist convective adjustment mca parameterization and with various formulations and parameter sets with a simplified betts miller sbm scheme with the control run using the sbm scheme the tropics become quieter and less dependent on horizontal resolution as compared with the lsc or mca simulations the hadley circulation mass transport is significantly reduced with the sbm scheme as is the itcz precipitation an important factor determining this behavior is the parameterization of shallow convection without shallow convection the convection scheme is largely ineffective at preventing convection from occurring at the grid scale the sensitivities to convection scheme parameters are also examined the simulations are remarkably insensitive to the convective relaxation time and only mildly sensitive to the relative humidity of the reference profile provided significant large scale condensation is not allowed to occur the changes in the zonally averaged tropical circulation that occur in all the simulations are understood based on the convective criteria of the schemes and the gross moist stability of the atmosphere

magmatism and metamorphism in the ladakh himalayas the indus tsangpo suture zone abstract ladakh india provides a complete geological section through the northwestern part of the himalayas from kashmir to tibet within this section the magmatic metamorphic and geotectonic evolution of the northern himalayan orogeny has been studied using petrographic geochemical and isotope analytical techniques the beginning of the himalayan cycle was marked by large basaltic extrusions panjal trap of permian to lower triassic age at the northern margin of the gondwana continent indian shield these continental type tholeiitic basalts were followed by a more alkaline volcanism within the triassic to jurassic lamayuru unit of the gondwana continental margin lower jurassic to cretaceous oceanic crust and sediments ophiolitic melange s s accompany the triassic to cretaceous flysch deposits within the indus tsangpo suture zone the major structural divide between the indian shield high himalaya and the tibetan platform so far no relic of paleozoic oceanic crust has been found subduction of the tethyan oceanic crust during upper jurassic and cretaceous time produced an island arc represented by tholeiitic and calc alkaline volcanic rock series dras volcanics and related intrusives accompanied by volcaniclastic flysch deposits towards the tibetan continental margin subsequent to the subduction of oceanic crust large volumes of calc alkaline plutons trans himalayan or kangdese plutons intruded the tibetan continental margin over a distance of 2000 km and partly the dras island arc in the ladakh region the collision of the indian shield and tibetan platform started during the middle to upper eocene and caused large scale still active intracrustal thrusting as well as the piling up of the himalayan nappes the tectonically highest of these nappes is built up of oceanic crust and huge slices of peridotitic oceanic mantle spongtang klippe in the high himalayas the tectonic activity was accompanied and outlasted by a barrovian type metamorphism that affected triassic sediments of the kashmir nun kun synclinorium up to kyanite staurolite grade and the deeper seated units up to sillimanite grade cooling ages of micas are around 20 m y muscovite and 13 m y biotite towards the indus tsangpo suture zone metamorphism decreases with no obvious discontinuity through greenschist prehnite pumpellyite to zeolite grade remnants of possibly an eo himalayan blueschist metamorphism have been found within thrust zones accompanying ophiolitic melange in the suture zone

zircon u pb ages from the wabigoon manitou lakes region wabigoon subprovince northwest ontario three distinct stratigraphic units have been recognized in the crow lake savant lake belt these are a basal unit consisting of high magnesium tholeiitic flows a middle unit consisting mostly of tholeiitic to calc alkaline pyroclastic rocks and flows and an upper unit of high iron tholeiitic flows a zircon u pb study has been carried out on seven rocks from the wabigoon manitou lakes region of this belt in the manitou lakes area a minimum age of 2755 ma on a porphyry pluton intruded into the wapageisi volcanics gives a minimum age for the high magnesium tholeiitic sequence a trondhjemite phase of the atikwa batholith near wabigoon lake that is dated at 2732 2 2 9 ma has the same age within experimental error as a rhyolite flow from the lower wabigoon volcanics in the same area that is dated at however a trondhjemite phase of the atikwa batholith at eagle lake that is dated at is distinctly younger than a dacite flow collected nearby from the lower wabigoon volcanics that is dated at both thes

volcanism on mercury a new model for the history of magma ascent and eruption 1 we use the identification of volcanism on mercury together with lobate flow front like topography crustal composition information and data on the stress state and history of the lithosphere to derive a new model for the ascent and eruption of magma on mercury we find that extrusion is likely to be dominated by high effusion rate events initial emplacement of dikes in the crust and extrusions to the surface will result in a denser crust favoring even more extrusive volcanism this will be followed by cooling associated with planetary thermal evolution that will rapidly decrease the ability of magma to reach the surface resulting in a decline and termination of volcanism following the emplacement and deformation of regional smooth plains these predictions and the resulting history can be tested with observations from missions to mercury

himalaya the northern frontier of east gondwanaland abstract the himalayan province which represents the northern platform of the peninsular india belonging to east gondwanaland was strongly affected by pan african diastrophism 500 25 ma ago this brought to an end the protracted purana cycle of sedimentation throughout the peninsular india and the lesser himalaya and interrupted basin filling in its northern tethyan domain but the sea returned in the early permian along a narrow depression formed due to rifting of the himalayan crust in what is today the southern lesser himalaya in the rift valley was deposited tillites by glaciers of the gondwana continent under grip of refrigeration along with the glacigene conglomerates were emplaced diamictites generated by submarine slides triggered presumably by earthquakes originating from faults delimiting the rift the diamictities are admixed with lava agglomerate and tuff indicating widespread volcanism in the rift valley the rifting culminated in the breaking away of the tibetan part of the himalaya in the late permian and formation of neotethys between the gondwanaland and the cimmerian microcontinent embodying tibet iran and turkey rivers of the northern peninsular india flowed in the northerly directions since the middle proterozoic through early eocene in the late eocene there was a drastic drainage reversal to south and southeast when the himalaya emerged in the northern front of the gondwanaland

zircon behaviour during crustal anatexis evidence from the tibetan slab migmatites nepal abstract the morphology and internal structures of zircon populations from three distinct types of migmatites from central nepal low zr and high zr in situ migmatites and injection migmatite were studied to examine the behaviour of zircon during anatexis the zircons from mesosomes and melanosomes were all residual zircons characterized by rounded morphologies with little overgrowth and a small elongation ratio suggestive of a detrital or metamorphic origin zircons from the leucosomes showed distinctive features the low zr tonalitic leucosomes we characterized by zircon populations with the same features as those from mesosomes and melanosomes indicative of no or very few transformations during migmatization the high zr leucosome contained euhedral crystals with morphological features typical of magmatic zircons found in crustal peraluminous magmas internal zoning patterns suggested a complex evolution involving dissolution and growth the injected granitic leucosome contained well developed magmatic zircons the role of subsolidus differentiation partial melting and melt composition on the contrasted behaviour of zircons during anatexis is discussed the zircon populations from the tibetan slab migmatites are distinct from those of the manaslu granite therefore suggesting that the migmatite leucosomes are not the unsegregated equivalents to the melts which gave raise to the manaslu type granites

sensitivity of simulated climate to model resolution abstract dynamical measures of the climate e g winds eddy fluxes simulated by a general circulation model are compared at different horizontal and vertical resolutions for the december january and february period the simulations of the troposphere are found to improve significantly as the horizontal resolution increases in the range of spectral truncations from t21 to t63 little sensitivity is found to changes in vertical resolution between about 2 8 km and 0 7 km vertical grid spacing the improvements in the southern hemisphere troposphere are greater than in the northern hemisphere as the horizontal resolution increases the eddy momentum fluxes and kinetic energies in both hemispheres increase monotonically with horizontal resolution at t63 the southern hemisphere winds eddy fluxes and eddy kinetic energies agree favorably with observations while serious discrepancies are present at lower resolutions in the northern hemisphere the eddy momentum flux at t63 is slightly larger than obser

no link between the panjal traps kashmir and the late permian mass extinctions 1 voluminous late permian flood basalt eruptions are contemporaneous with the mid capitanian 260 ma and end permian 251 ma mass extinction events the panjal traps of kashmir are thought to be correlative to the mid capitanian mass extinction however no radiometric age has been determined we report a single zircon u pb laser ablation icp ms date of a rhyolite from the lower middle part of the volcanic sequence twenty four individual zircon crystals yield a mean 206u 238pb age of 289 3 ma the results show that the panjal traps are considerably older than previously interpreted and not correlative to post neo tethys rifting of the gondwanan margin or the mid capitanian mass extinction and are in fact correlative to the opening of the neo tethys ocean in contrast to other similarly size large igneous provinces the panjal traps are not coincident with a mass extinction event and therefore casts doubt on the direct relationship between continental flood basalt volcanism and ecosystem collapse

metamorphic evolution 40ar 39ar chronology and tectonic model for the neelum valley azad kashmir ne pakistan

on the role of planetary scale waves in the abrupt seasonal transition of the northern hemisphere general circulation the role of planetary scale waves in the abrupt seasonal transition of the northern hemisphere nh general circulation is studied in reanalysis data the winter to summer transition involves the growth of planetary scale wave latent heat and momentum transports in the region of monsoons and anticyclones that dominate over the zonal mean transport beginning in midspring the wave dominated regime coincides with an abrupt northward expansion of the cross equatorial circulation and reversal of the trade winds in the upper troposphere the transition coincides with the growth of cross equatorial planetary scale wave momentum transport and a poleward shift of subplanetary scale wave transport and jet stream the dynamics of the seasonal transition are captured by idealized aquaplanet model simulations with a prescribed subtropical planetary scale wave sea surface temperature sst perturbation the sst perturbation generates subtropical planetary scale wave streamfunction variance and transport in the lower and uppertroposphereconsistentwithquasigeostrophictheory beyondathresholdsst atransitionofthezonalmean circulation occurs which coincides with a localized reversal of absolute vorticity in the nh tropical upper troposphere the transition is abrupt in the lower troposphere because of the quadratic dependence of the wave transport on the sst perturbation and involves seasonal time scale feedbacks between the wave and zonal meanflow in theupper troposphere including cross equatorial wave propagation thezonal mean vertical and meridional flows associated with the circulation response are in balance with the planetary scale wave momentumand latentheat meridionalflux divergences the resultshighlightthe leading order roleofmonsoon anticyclone transport in the seasonal transition including its impact on the meridional extent of the hadley and ferrel cells they can also be used to explain why the transition is less abrupt in the southern hemisphere

the lower paleozoic nyimaling granite in the indian himalaya ladakh new rb sr data versus zircon typology a granitic batholith in the tso morari culmination of the most internal high himalayan thrust sheets ladakh himalaya india has been investigated by rb sr isotopic methods as well as by typological studies on its zircon population pupin 1980 the good alignment and spread of the single muscovite and the 6 whole rock data points allow the tracing of a fairly good isochron of 460 8 ma which may be considered as the granite s crystallisation age its sr initial ratio i r of 0 7365 2 is very high even in respect to other anatectic granites of this suite known in the himalayas and in continental blocks to the north in terms of the lower cambrian to middle ordovician ages known for this granitic suite the nyimaling granite is among the youngest

cooling and inferred uplift erosion history of the grenville orogen ontario constraints from 40ar 39ar thermochronology stepwise 40ar 39ar degassing experiments of 57 mineral separates of hornblende muscovite biotite and perthitic microcline have been used in conjunction with petrologic observations to place regional constraints on the postmetamorphic cooling and the inferred uplift and erosion history of the grenville orogen in ontario the 40ar 39ar data support an interpretation of slow nearly uniform cooling 1 4 c m y from temperatures of 500 c to below 150 c in the central gneiss belt cgb hornblendes cooled through ar closure between 930 and 1025 ma whereas in the central metasedimentary belt cmb hornblendes record the following range in 40ar 39ar cooling ages 1104 ma in the frontenac terrane 1007 1067 ma in the sharbot lake terrane 919 1026 ma in the elzevir terrane and 972 ma in the central metasedimentary belt boundary zone regional uplift erosion rates of 0 03 0 14 km m y have been estimated for the grenville orogen in ontario based on the 40ar 39ar data a model retrograde p t path for rocks of the cgb and an upper time constraint provided by flat overlying cambrian and ordovician sediments these erosion rates are consistent with rates estimated for other proterozoic or archean granulite terranes but are an order of magnitude slower than active orogens such as the alps and himalayas a regular variation in hornblende 40ar 39ar cooling ages is observed in rocks that traverse highly strained often mylonitic shear zones that separate the four major terranes of the cmb the pattern of 40ar 39ar ages is interpreted to reflect late tectonic extension consistent with field observations in the central metasedimentary belt boundary zone and elsewhere in the cmb up to 13 km of vertical displacement is inferred for some rocks in the cmb between the time they cooled below closure to argon diffusion in hornblende 500 c and their exposure at the surface 25 c

early permian pangea b to late permian pangea a the pre drift wegenerian model of pangea is almost universally accepted but debate exists on its pre jurassic configuration since tedirving introd ucedpangea b by placing gond wana farther to the east by v3000 km with respect to laurasia on the basis of paleomagnetic data new paleomagnetic data from radiometrically dated early permian volcanic rocks from parts of adria that are tectonically coherent with africa gondwana integrated with published coeval data from gondwana and laurasia again only from igneous rocks fully support a pangea b configuration in the early permian the use of paleomagnetic data strictly from igneous rocks excludes artifacts from sedimentary inclination error as a contributing explanation for pangea b the ultimate option to reject pangea b is to abandon the geocentric axial dipole hypothesis by introducing a significant non dipole zonal octupole component in the late paleozoic time averaged geomagnetic field we demonstrate however by using a dataset consisting entirely of paleomagnetic directions with low inclinations from sampling sites confined to one hemisphere from gondwana as well as laurasia that the effects of a zonal octupole field contribution would not explain away the paleomagnetic evidence for pangea b in the early permian we therefore regard the paleomagnetic evidence for an early permian pangea b as robust the transformation from pangea b to pangea a took place during the permian because late permian paleomagnetic data allow a pangea a configuration we therefore review geological evidence from the literature in support of an intra pangea dextral megashear system the transformation occurred after the cooling of the variscan mega suture andlasted v20 myr in this interval the neotethys ocean opened between india arabia and the cimmerian microcontinents in the east while widespread lithospheric wrenching and magmatism took place in the west around the adriatic promontory the general distribution of plate boundaries and resulting driving forces are qualitatively consistent with a right lateral shear couple between gondwana and laurasia during the permian transcurrent plate boundaries associated with the pangea transformation reactivated variscan shear zones andwere subsequently exploitedby the opening of western neotethyan seaways in the jurassic

garnet tourmaline and muscovite bearing leucogranites gneisses and migmatites of the higher himalayas from zanskar kulu lahoul and kashmir

expansion of the hadley cell under global warming 1 a consistent weakening and poleward expansion of the hadley circulation is diagnosed in the climate change simulations of the ipcc ar4 project associated with this widening is a poleward expansion of the subtropical dry zone simple scaling analysis supports the notion that the poleward extent of the hadley cell is set by the location where the thermally driven jet first becomes baroclinically unstable the expansion of the hadley cell is caused by an increase in the subtropical static stability which pushes poleward the baroclinic instability zone and hence the outer boundary of the hadley cell

early permian granitic dykes of alkaline affinity in the indian high himalaya of upper lahul and se zanskar geochemical characterization and geotectonic implications

climate model biases in the width of the tropical belt abstractearth s arid subtropics are situated at the edges of the tropical belt which encircles the planet along the equator and covers half of its surface area the climate of the tropical belt is strongly influenced by the hadley cells with their subsidence and easterly trade winds both sustaining the aridity at the belt s edges the understanding of earth s past present and future climates is contingent on understanding the dynamics influencing this region an important but unanswered question is how realistically climate models reproduce the mean state of the tropical belt this study augments the existing literature by examining the mean width and seasonality of the tropical belt in climate models from phase 5 of cmip cmip5 and experiments from the second phase of the chemistry climate model validation ccmval 2 activity of the stratospheric processes and their role in climate sparc project while the models overall reproduce the structure of the tropical belt width s seasonal cycle they und

reflectance and color variations on mercury regolith processes and compositional heterogeneity multispectral images of mercury obtained by the messenger spacecraft reveal that its surface has an overall relatively low reflectance with three large scale units identified on the basis of reflectance and slope 0 4 to 1 0 micrometer a higher reflectance relatively red material occurs as a distinct class of smooth plains that were likely emplaced volcanically a lower reflectance material with a lesser spectral slope may represent a distinct crustal component enriched in opaque minerals possibly more common at depth a spectrally intermediate terrain probably forms most of the upper crust three other spectrally distinct but spatially restricted units include fresh crater ejecta less affected by space weathering than other surface materials high reflectance deposits seen in some crater floors and moderately high reflectance relatively reddish material associated with rimless depressions

himalayan gneiss dome formation in the middle crust and exhumation by normal faulting new geochronology of gianbul dome northwestern india a general lack of consensus about the origin of himalayan gneiss domes hinders accurate thermomechanical modeling of the orogen to test whether doming resulted from tectonic contraction e g thrust duplex formation antiformal bending above a thrust ramp etc channel flow or via the buoyant rise of anatectic melts this study investigates the depth and timing of doming processes for gianbul dome in the western himalaya the dome is composed of greater himalayan sequence migmatite paleozoic orthogneiss and metasedimentary rock cut by multiple generations of leucogranite dikes these rocks record a major penetrative d2 deformational event characterized by a domed foliation and associated ne sw trending stretching lineation and they are flanked by the top down to the sw normal sense khanjar shear zone and the top down to the ne normal sense zanskar shear zone the western equivalent of the south tibetan detachment system monazite u th pb geochronology records 1 paleozoic emplacement of the kade orthogneiss and associated granite dikes 2 prograde barrovian metamorphism from 37 to 33 ma 3 doming driven by upper crustal extension and positive buoyancy of decompression melts between 26 and 22 ma and 4 the injection of anatectic melts into the upper levels of the dome neutralizing the effects of melt buoyancy and potentially adding strength to the host rock by ca 22 6 ma on the southwestern flank and ca 21 ma on the northeastern flank as shown by a northeastward decrease in 40 ar 39 ar muscovite dates from 22 4 to 20 2 ma ductile normal sense displacement within the zanskar shear zone ended by ca 22 ma after which the gianbul dome was exhumed as part of a rigid footwall block below the brittle zanskar normal fault tilting an estimated 5 10 sw into its present orientation

on the likelihood of tropical extratropical cloud bands in the south indian convergence zone during enso events abstractthe southern hemisphere subtropical convergence zones are important regions of rainfall in the subtropics the south indian ocean convergence zone sicz has the strongest seasonality and exhibits substantial interannual variability in strength and position during austral summer on synoptic time scales the sicz is a preferred region for the formation of tropical extratropical te cloud bands with local maxima over the southern african mainland and madagascar this study investigates how the seasonality in satellite observed cloud band frequency emerges from the interplay between the asynchronous seasonal cycles in convective instability and upper level flow as represented by reanalysis data these atmospheric mean states are diagnosed with a gross convective instability metric and a method to distinguish between subtropical and eddy driven jet axes month by month analysis of these diagnostics elucidates how mean state perturbations during enso events modify cloud band likelihood typically 1

the origin and pre cenozoic evolution of the tibetan plateau different hypotheses have been proposed for the origin and pre cenozoic evolution of the tibetan plateau as a result of several collision events between a series of gondwana derived terranes e g qiangtang lhasa and india and asian continent since the early paleozoic this paper reviews and reevaluates these hypotheses in light of new data from tibet including 1 the distribution of major tectonic boundaries and suture zones 2 basement rocks and their sedimentary covers 3 magmatic suites and 4 detrital zircon constraints from paleozoic metasedimentary rocks the western qiangtang amdo and tethyan himalaya terranes have the indian gondwana origin whereas the lhasa terrane shows an australian gondwana affinity the cambrian magmatic record in the lhasa terrane resulted from the subduction of the proto tethyan ocean lithosphere beneath the australian gondwana the newly identified late devonian granitoids in the southern margin of the lhasa terrane may represent an extensional magmatic event associated with its rifting which ultimately resulted in the opening of the songdo tethyan ocean the lhasa northern australia collision at similar to 263 ma was likely responsible for the initiation of a southward dipping subduction of the bangong nujiang tethyan oceanic lithosphere the yarlung zangbo tethyan ocean opened as a back arc basin in the late triassic leading to the separation of the lhasa terrane from northern australia the subsequent northward subduction of the yarlung zangbo tethyan ocean lithosphere beneath the lhasa terrane may have been triggered by the qiangtang lhasa collision in the earliest cretaceous the mafic dike swarms ca 284 ma in the western qiangtang originated from the panjal plume activity that resulted in continental rifting and its separation from the northern indian continent the subsequent collision of the western qiangtang with the eastern qiangtang in the middle triassic was followed by slab breakoff that led to the exhumation of the qiangtang metamorphic rocks this collision may have caused the northward subduction initiation of the bangong nujiang ocean lithosphere beneath the western qiangtang collision related coeval igneous rocks occurring on both sides of the suture zone and the within plate basalt affinity of associated mafic lithologies suggest slab breakoff induced magmatism in a continent continent collision zone this zone may be the site of net continental crust growth as exemplified by the tibetan plateau c 2012 international association for gondwana research published by elsevier b v all rights reserved

seasonal to multidecadal variability of the width of the tropical belt 1 an expansion of the tropical belt has been extensively reported in observations reanalyses and climate model simulations but there is a great deal of uncertainty in estimates of the rate of widening as different diagnostics give a wide range of results this study critically examines robust diagnostics for the width of the tropical belt to explore their seasonality interannual variability and multidecadal trends the width based on the latitudes of the maximum tropospheric dry bulk static stability measuring the difference in potential temperature between the tropopause and the surface is found to be closely coupled to the width based on the subtropical jet cores on all time scales in contrast the tropical belt width and northern hemisphere edge latitudes based on the latitudes at which the vertically averaged stream function vanishes a measure of the hadley circulation s poleward edges lag those of the other diagnostics by approximately 1month the tropical belt width varies by up to 10 latitude among the diagnostics with trends in the tropical belt width ranging from 0 5 to 2 0 per decade over the 1979 2012 period nevertheless in agreement with previous studies nearly all diagnostics exhibit a widening trend although the stream function diagnostic exhibits a significantly stronger widening than either the jet or dry bulk stability diagnostics finally gps radio occultation observations are used to assess the ability of the reanalyses to reproduce the tropical belt width finding that they better situate the latitudes of maximum bulk stability versus those of the subtropical jets