earth s variable rotation recent improvements in geodetic data and practical meteorology have advanced research on fluctuations in the earth9s rotation theinterpretation of these fluctuations is inextricably linked with studies of the dynamics of the earth moon system and dynamical processes in the liquid metallic core of the earth where the geomagnetic field originates other parts of the earth9s interior and the hydrosphere and atmosphere fluctuations in the length of the day occurring on decadal time scales have implications for the topography of the core mantle boundary and the electrical magnetic and other properties of the core and lower mantle investigations of more rapid fluctuations bear on meteorological studies of interannual seasonal and intraseasonal variations in the general circulation of the atmosphere and the response of the oceans to such variations

inner core rotation and its variability from nonparametric modeling 1 we present a new approach for studying the inner core rotation and its variability by separating the underlying structure from its time evolution this is achieved by fitting a large set of existing seismic bc df traveltime data with a smoothing spline analysis which is implemented in the statistics package r this method allows us to separate the time independent mantle contribution from the time dependent core contribution without any a priori constraints and to also estimate the error of the fit we add our newly acquired seismic data from the passcal experiment arctic in northern alaska to pkp differential traveltime measurements previously obtained from south sandwich islands earthquakes and recorded at college col and the alaskan seismic network this nearly doubles the number of measurements to a total of 1165 and increases the data coverage of the inner core structure and our time coverage to about 55 years the large number of measurements allows us to use the standard statistical method of bootstrapping to derive the rotation rate and thus to further separate the core structure from its time evolution this approach has been successfully tested with synthetic data sets that feature both a nonlinear structure and variable rotation rates while sharing the same earthquakes and stations geometry as our real data applying this method to the real data yields an average rotation rate of 0 39 0 090 22 yr 1 at 68 confidence level our results also suggest a nonzero acceleration of the inner core with an apparent change in the rotation rate from 0 24 to 0 56 yr 1 within the last 55 years the minimum torque acting on the inner core is estimated 1 19 1016 n m which could result from the imbalance of the electromagnetic and gravitational torques

seismological evidence for differential rotation of the earth s inner core the travel times of seismic waves that traverse the earth s inner core show a small but systematic variation over the past three decades this variation is best explained by a rotation of the inner core that moves the symmetry axis of its known seismic anisotropy the inferred rotation rate is on the order of 1 per year faster than the daily rotation of the mantle and crust

petrogenesis of monzonoritic dykes in the egersund ogna anorthosite rogaland s w norway trace elements and isotopic sr pb constraints two major monzonoritic dykes occur in the egersund ogna anorthositic massif s w norway the lomland dyke which varies from norite to monzonite and the vettaland ferronoritic dyke they are characterized by high fe ti and p contents low sio2 variable k2o 0 5 4 5 and high fe mg ratios small variations in ree distribution are observed inside the lomland dyke la yb 12 lree ca 150 180 chondrite normalized values neutral to slightly positive eu anomaly part of the vettaland dyke is severely depleted in zr rb and ree and shows a positive eu anomaly all rocks are depleted in u and th and show very low cr and ni contents as well as high sr contents 400 600 ppm variation within the lomland dyke is satisfactorily ex plained through subtraction of an apatite bearing noritic cumulate the role of apatite is predominant in controlling the ree behaviour eutectic partial melting of a fe rich noritic cumulate containing apatite under low ph2o conditions is suggested for the vettaland dyke by ree modelling sr isotopic initial ratios are different in lomland ca 0 708 and vettaland ca 0 706 dykes these values preclude direct derivation from the mantle as well as comagmatic relationship with anorthosite contamination of a mantle derived magma by deep crustal material or anatexis of the lil depleted lower crust is compatible with the low u and th contents and with the pb isotopic ratios the vettaland partial melting process is extended to all monzonoritic types the necessary heat being provided by the high temperature anorthositic crystal mush

the madden julian oscillation and the angular momentum balance in a barotropic ocean model surface wind stresses associated with the madden julian oscillation transfer angular momentum between the atmosphere and the underlying ocean the resulting anomalies in oceanic angular momentum related to either changes in zonal currents or latitudinal redistribution of mass and the torques coupling the ocean and the solid earth are examined for simple zonal stress patterns representing idealized 40 to 50 day fluctuations of pacific winds because the contribution of baroclinic variability to the angular momentum budget is in general small when vertically integrated quantities are considered ponte 1990 only the barotropic response is studied numerical solutions of the shallow water equations with linear bottom friction are found for a constant depth basin centered on the equator and extending over 140 in longitude the angular momentum exchanges between the ocean and solid earth in the model involve the continental torque i e body forces on eastern and western walls due to coastal sea level anomalies and the bottom friction torque solutions yield a dominant balance between the wind and continental torques with the bottom friction torque being negligible the amplitude of the total torque acting on the ocean and the corresponding angular momentum fluctuations are very small compared with the amplitude of the applied wind torque the ocean delivers to the solid earth with no significant time delays the angular momentum anomalies received from the atmosphere in general sea level anomalies are nearly uniform along the eastern boundary and the respective meridionally integrated torque is much larger than the one exerted on the western wall solutions also suggest that coastal barotropic sea level fluctuations as small as 0 5 1 5 cm are sufficient to cause variations in the length of day comparable to observed values in the 40 to 50 day band

gravitational core mantle coupling and the acceleration of the earth 1 gravitational core mantle coupling may be the cause of the observed variable acceleration of the earth s rotation on the 1000 year timescale density inhomogeneities which randomly come and go in the liquid outer core may gravitationally attract density inhomogeneities in the mantle and crust torquing the mantle and changing its rotation state the corresponding torque by the mantle on the core may also explain the westward drift of the magnetic field of 0 2 yr 1 gravitational core mantle coupling would stochastically affect the rate of change of the earth s obliquity by just a few percent its contribution to polar wander would only be 0 5 the presently observed rate

inner core rotation rate from small scale heterogeneity and time varying travel times the time it takes seismic waves to propagate from south atlantic earthquakes through the inner core to station col in alaska has decreased systematically over the past 30 years travel times from three earthquakes in 1991 to an array of 37 seismometers in alaska suggest that lateral gradients in seismic wavespeeds are steep in this part of the inner core this combination of observations can be explained by postulating that the inner core is rotating 0 2 to 0 3 per year faster than the mantle

planet within a planet rotation of the inner core of earth the time dependence of the orientation of earth9s inner core relative to the mantle was determined using a recently discovered 10 degree tilt in the axis of symmetry of the inner core9s seismic velocity anisotropy two methods of analyzing travel time variations for rays traversing the inner core on the basis of 29 years of data from the international seismological centre 1964 1992 reveal that the inner core appears to rotate about 3 degrees per year faster than the mantle an anomalous variation in inner core orientation from 1969 to 1973 coincides in time with a sudden change jerk in the geomagnetic field

tidal despinning of the mantle inner core superrotation and outer core effective viscosity dissipation of tidal energy in the oceans causes a net transfer of angular momentum from the spin of the earth to the relative orbital motions of the moon and sun these torques couple directly to the mantle and cause it to despin viscous coupling across the outer core is an effective means of communicating this change to the inner core the ekman time scale for dissipation of transient fluid motions associated with unsteady torques is much shorter than the time scale for adjustment of inner core and mantle rotational velocities in the steady couette flow regime the relative amplitude and phase of rotational variations in this system with respect to the applied torques are given in terms of core viscosity and torque variation frequency any short period variations in mantle torques will leave the inner core largely unchanged and the influence of long period and secular torques applied to the mantle is efficiently transmitted to the inner core the system response to a steady tidal torque applied to the mantle leaves the inner core with a small excess rotational velocity relative to the mantle proportional to the product of outer core viscosity and the applied mantle torque recent estimates of an inner core super rotation of 1 degree year imply an effective outer core viscosity of 10 3 pa s glacial cycle variations in tidal torques somewhat complicate this picture but do not yield significantly different viscosity estimates however they do imply that the differential rotation velocity varies by roughly a factor of 2 over a 100 kyr glacial cycle the tidal shear strain may also contribute to development of anisotropy in the inner core

late proterozoic and paleozoic tides retreat of the moon and rotation of the earth the tidal rhythmites in the proterozoic big cottonwood formation utah united states the neoproterozoic elatina formation of the flinders range southern australia and the lower pennsylvanian pottsville formation alabama united states and mansfield formation indiana united states indicate that the rate of retreat of the lunar orbit is dxi dt approximately k2 sin 2delta where xi is the earth moon radius vector k2 is the tidal love number and delta is the tidal lag angle and that this rate has been approximately constant since the late precambrian when the contribution to tidal friction from the sun is taken into account these data imply that the length of the terrestrial day 900 million years ago was approximately18 hours

cumulate origin and polybaric crystallization of fe ti oxide ores in the suwalki anorthosite northeastern poland fe ti oxide ores in the proterozoic suwalki massif type anorthosite northeastern poland have been recognized through geophysical exploration and extensive drilling down to 2 600 m depth the fe ti oxide rich rocks from suwalki consist of vanadium poor ti magnetite in lenses varying from the centimeter to the kilometer scale fe ti rich rocks are commonly layered and have gradational contacts with the host anorthosite they do not represent well defined intrusions such as the major tellnes and lac tio deposits based on petrography modal proportions whole rock analyses and liquidus phase compositions of fe ti oxide ores the sequence of crystallization is as follows plagioclase ti magnetite ilmenite followed by orthopyroxene then clinopyroxene and finally apatite the comparatively low v content 0 20 0 67 wt v in ti magnetite results from relatively oxidized crystallization conditions the diapiric emplacement of the anorthositic pluton influenced the crystallization of the fe ti ores and is responsible for the crystal sorting controlled by the density contrast of liquidus phases polybaric crystallization of fe ti oxide ores is evidenced by variable al2o3 ca 1 5 wt content of the associated orthopyroxene polybarism is responsible for the appearance of fe ti oxides before orthopyroxene due to the decreasing stability field of orthopyroxene with pressure

residual liquid origin for a monzonitic intrusion in a mid proterozoic anorthosite complex the sybille intrusion laramie anorthosite complex wyoming the sybille intrusion 100 km 2 is one of three large monzonitic intrusions in the 1 43 ga laramie anorthosite complex of southeastern wyoming the petrographic geochemical isotopic and geophysical characteristics of sybille monzonitic rocks are consistent with an origin by extensive crystallization of liquids residual to nearby anorthositic cumulates ferrodiorites and contamination by archean wall rocks the exposed part of the intrusion is composed mainly of coarse grained monzosyenites with abundant alkali feldspar phenocrysts the monzosyenites preserve mineralogical evidence for high crystallization temperatures 1000 c mid crustal emplacement pressures 3 kbar relatively reduced crystallization conditions 2 log units below the fayalite magnetite quartz fmq oxygen buffer and they crystallized in the presence of a co2 rich fluid phase fuhrman et al 1988 frost and touret 1989 the eastern monzosyenites those adjacent to contemporaneous anorthosite are distinguished by an anhydrous mineral assemblage fo16 fo8 olivine high ca pyroxene lacking modal quartz silica contents of 60 wt and smaller eu anomalies eu eu 1 2 to 1 3 abundant xenoliths of archean wall rocks and anorthosite from the adjacent intrusions in all monzosyenites attest to a stoping emplacement mechanism near the roof of the chamber we propose that the monzosyenites represent a relatively thin 0 5 1 0 km thick roof to a magma chamber dominated by dense ferrodioritic cumulates at depth extensive open system fractionation of a ferrodioritic parent magma residual after crystallization of anorthosite produced fe enriched monzodioritic and or monzonitic magma in the upper part of the chamber and complementary fe and ti rich cumulates in the lower levels we have corroborated the production of monzonitic liquids from crystallization of ferrodiorite through a series of reconnaissance equilibrium crystallization experiments the presence of dense ferrodioritic cumulates at depth is consistent with the prominent positive gravity anomaly associated with the sybille intrusion hodge et al 1973 in the upper parts of the chamber the fractionated monzodioritic and or monzonitic magmas eventually became saturated in alkali feldspar owing to density contrasts the alkali feldspar phenocrysts floated to the roof of the chamber thus producing the exposed porphyritic monzosyenites in addition the roof of the chamber was the site of significant melting of archean gneiss and locally metapelite the sr and nd isotopic compositions of the monzosyenites with sr isotopic ratios becoming increasingly radiogenic from east i sr 0 7059 and initial nd 2 5 to west i sr 0 7092 and initial nd 2 6 are consistent with a 5 to 15 addition of archean orthogneiss to a ferrodioritic parent magma that had isotopic characteristics similar to adjacent anorthositic rocks the stratigraphic and compositional similarity of the sybille monzosyenites to mangerites in the bjerkreim sokndal intrusion of the rogaland anorthosite complex southern norway indicates that similar open system magmatic processes are capable of having produced high temperature k rich monzonitic rocks in other proterozoic anorthosite complexes

inner core anisotropy in three dimensions the purpose of this paper is the investigation of cylindrical anisotropy in the inner core based on the travel time anomalies of the pkikp phase we use the arrival times reported in the international seismological centre bulletins for years 1964 1990 we select only earthquakes which have a good azimuthal coverage and a sufficiently large number of reporting stations the earthquakes are relocated using corrections for lateral heterogeneity computed for our most recent three dimensional mantle model we use a total of 313 422 observations of the df branch of pkp travel time anomalies within the epicentral distance ranges of 120 140 and 150 180 reported by 2335 stations for 26 377 earthquakes we process the data using an averaging procedure which we call cylindrical anisotropy stacking that enhances the effects of anisotropy but is expected to suppress those due to lateral heterogeneity and random errors the processed residuals show a remarkably consistent pattern this confirms the dominance of the cylindrical elastic anisotropy in the inner core with approximately a constant axis of symmetry this axis of symmetry is found to be tilted 10 5 1 from the earth s rotation axis in the direction 160 e 5 in the northern hemisphere in this new coordinate system we determine a four layer axisymmetric model of transverse anisotropy with each layer approximately 300 km thick the model shows that the anisotropy is strongest 3 within the innermost part of the core the travel time anomalies show significant 1 5 s longitudinal variations even when the tilt of the axis of symmetry is considered there is a substantial increase in the amplitude of the longitudinal variations which are dominated by the second and fourth harmonics for rays with bottoming depths exceeding 400 km below the inner core boundary the measurable tilt of the axis of symmetry and the presence of significant nonaxisymmetric signal may provide important clues with respect to the possible causes of anisotropy the increase in the anisotropy in the innermost part of the core departs from earlier inferences that anisotropy may be limited to the outermost 200 300 km of the earth s inner core

investigation of point source pollution by chlorinated solvents in two different geologies a multi layered carboniferous sandstone mudstone sequence and the chalk

the origin of nelsonite and high zr ferrodiorite associated with proterozoic anorthosite abstract a petrological and geochemical major and trace elements sr nd isotopes study of two nelsonite occurrences the kydlandsvatn and hestnes deposits in the rogaland anorthosite province southern norway reveals that both deposits are cumulates but were generated from strikingly different magmas and processes the kydlandsvatn deposit was formed from a primitive jotunite similar to the bjerkreim sokndal parental magma by crystal accumulation by contrast the hestnes cumulate with high ree and zr contents negative eu anomaly cr rich magnetite nb rich ilmenite and high nb ta and zr hf whole rock ratios appears to result from the crystallization of an immiscible fe rich and si poor melt under highly oxidized conditions other jotunites ferrodiorites with high zr contents are typically associated with anorthosites in the rogaland laramie and adirondack anorthosite complexes in rogaland they also have an identical sr nd isotope signature as the hestnes nelsonite these high zr jotunites cannot be produced through extreme differentiation of ordinary jotunite magmas their formation from direct melting of a crustal source or assimilation of a nelsonite cumulate is highly unlikely occurrence of a high zr jotunite at the margin of a quartz mangerite dyke is evidence that immiscibility takes place though furtively along the jotunite liquid line of descent it is suggested here that high zr jotunites in dyke rocks or parental to high zr nelsonites resulted from fractional crystallization of a fe rich immiscible melt formed at higher pressures in the polybaric evolution of anorthosites conditions that are not yet explored experimentally

convection and anisotropy of the inner core estimation of the rayleigh number of the inner core suggests that this region is convecting the flow pattern is likely to produce crystallographic preferred orientation of the elastically anisotropic hexagonal closest packed phase of iron such that compressional wave velocities would be greater in the axial relative to the equatorial direction by roughly 1 percent this result is in agreement with seismological evidence that the inner core is elastically anisotropic

on the structure and origin of major glaciation cycles 2 the 100 000 year cycle climate over the past million years has been dominated by glaciation cycles with periods near 23 000 41 000 and 100 000 years in a linear version of the milankovitch theory the two shorter cycles can be explained as responses to insolation cycles driven by precession and obliquity but the 100 000 year radiation cycle arising from eccentricity variation is much too small in amplitude and too late in phase to produce the corresponding climate cycle by direct forcing we present phase observations showing that the geographic progression of local responses over the 100 000 year cycle is similar to the progression in the other two cycles implying that a similar set of internal climatic mechanisms operates in all three but the phase sequence in the 100 000 year cycle requires a source of climatic inertia having a time constant similar to 15 000 years much larger than the other cycles similar to 5 000 years our conceptual model identifies massive northern hemisphere ice sheets as this larger inertial source when these ice sheets forced by precession and obliquity exceed a critical size they cease responding as linear milankovitch slaves and drive atmospheric and oceanic responses that mimic the externally forced responses in our model the coupled system acts as a nonlinear amplifier that is particularly sensitive to eccentricity driven modulations in the 23 000 year sea level cycle during an interval when sea level is forced upward from a major low stand by a milankovitch response acting either alone or in combination with an internally driven higher frequency process ice sheets grounded on continental shelves become unstable mass wasting accelerates and the resulting deglaciation sets the phase of one wave in the train of 100 000 year oscillations whether a glacier or ice sheet influences the climate depends very much on the scale the interesting aspect is that an effect on the local climate can still make an ice mass grow larger and larger thereby gradually increasing its radius of influence

origin of the giant allard lake ilmenite ore deposit canada by fractional crystallization multiple magma pulses and mixing abstract the late proterozoic allard lake ilmenite deposit is located in the havre saint pierre anorthosite complex part of the allochtonous polycyclic belt of the grenville province presently the world s largest fe ti oxide deposit it had a pre mining amount in excess of 200 mt at grades over 60 wt hemo ilmenite the main ore body is a funnel shaped intrusion measuring 1 03 1 10 km and 100 300 m thick two smaller bodies are separated by faults and anorthosite the ore is an ilmenite rich norite or ilmenitite made up of hemo ilmenite hem22 6 29 4 66 2 wt on average andesine plagioclase an45 50 aluminous spinel and locally orthopyroxene whole rock chemical compositions are controlled by the proportions of ilmenite and plagioclase orthopyroxene which supports the cumulate origin of the deposit ore forming processes are further constrained by normal and reverse fractionation trends of cr concentration in cumulus ilmenite that reveal multiple magma emplacements and alternating periods of fractional crystallization and magma mixing mixing of magmas produced hybrids located in the stability field of ilmenite resulted in periodic crystallization of ilmenite alone the unsystematic differentiation trends in the allard lake deposit arising from a succession of magma pulses hybridisation and the fractionation of hemo ilmenite alone or together with plagioclase suggest that the deposit formed within a magma conduit this dynamic emplacement mechanism associated with continuous gravity driven accumulation of fe ti oxides and possibly plagioclase buoyancy in a fractionating ferrobasalt explains the huge concentration of hemo ilmenite the occurrence of sapphirine associated with aluminous spinel and high alumina orthopyroxene 7 6 9 1 wt al2o3 lacking exsolved plagioclase supports the involvement of a metamorphic overprint during the synchronous ottawan orogeny which is also responsible for strong textural equilibration and external granule of exsolved aluminous spinel due to slow cooling

differentiation of nelsonitic magmas in the formation of the 1 74 ga damiao fe ti p ore deposit north china the 1 74 ga damiao anorthosite complex north china is composed of anorthosite and leuconorite with subordinate melanorite mangerite oxide apatite gabbronorite perthite noritic i e jotunitic and ferrodioritic dykes the complex hosts abundant vein pod and lens like fe ti p ores containing variable amounts of apatite 10 60 modal and fe ti oxides in addition to fe ti p ores there are also abundant fe ti ores which are closely associated with fe ti p ores in the deposit most of fe ti p ores are dominated by fe ti oxides and apatite devoid of silicate minerals mineralogically similar to the common nelsonites elsewhere in contrast fe ti ores are dominated by fe ti oxides with minor apatite 5 modal the parental magma of these ores estimated from olivine and apatite compositions using mineral melt partition coefficients has composition similar to the ferrodioritic dykes fe ti p ores have variable fe ti oxides and apatite proportions indicating that they are cumulates their simple assemblage of fe ti oxides and apatite and local net texture suggest that the fe ti p ores in damiao have formed from nelsonitic melts immiscibly separated from the ferrodioritic magma during late stage differentiation fe ti ores are also cumulates and have mineral compositions similar to fe ti p ores the close association between fe ti and fe ti p ores indicates that the fe ti ores may have also formed from the nelsonitic melts we proposed that differentiation of nelsonitic melts accompanied by gravity settling is responsible for the formation of fe ti and fe ti p ores such a differentiation process in nelsonitic melts is well supported by variations of sr y th u ree and eu eu of apatite in fe ti p ores using oxides apatite ratio of 2 1 and compositions of apatite and calculated primary oxides we estimate the composition of the nelsonitic melt as 52 0 wt fe2o3t 18 5 wt cao 14 2 wt p2o5 8 7 wt tio2 4 0 wt al2o3 and 1 1 wt mgo with minor sio2 k2o na2o and f such a nelsonitic melt is suggested to be possibly conjugated with si rich melts compositionally similar to the damiao jotunitic dykes 50 wt sio2 and 15 wt fe2o3t which may subsequently evolve to mangeritic rocks in damiao our modeling also indicates that the onset of immiscibility occurs at a time when the evolved melt has 44 wt sio2 21 wt fe2o3t 3 0 wt tio2 and 2 6 wt p2o5 high oxygen fugacity and phosphorous content in magmas may play important roles in the immiscibility of nelsonitic magmas including promoting iron enrichments and widening the two liquid field