origin of decadal el nino southern oscillation like variability in a coupled general circulation model 1 the origin of decadal el nino southern oscillation like variability hereinafter referred to as dev is analyzed in coupled general circulation model cgcm simulations the cgcm experiments test the null hypothesis for the existence of dev that is that dev is linear damped and stochastically forced by atmospheric internal dynamics in order to test this hypothesis we employ the interactive ensemble coupling strategy it is found that the spatially averaged variance of sea surface temperature anomaly ssta and heat content anomaly hca associated with the dev is linearly related to the amplitude of atmospheric internal dynamics this result suggests that the dev is primarily noise forced but that damped coupled feedbacks and or internal ocean dynamics enhance this variability the ssta variability associated with the dev appears to be of a basin type standing mode with a triangular shape however the decadal evolution of the hca associated with the dev shows a systematic westward propagation from the central north pacific and the eastern south pacific both a singular vector analysis and noise variance analysis based on the coupled simulation results support the argument that atmospheric noise in the subtropics leads to the excitation of the dev

ar ar dating of k feldspar in low grade metamorphic rocks example of an exhumed mesozoic accretionary wedge and forearc south island new zealand 1 new 40ar 39ar ages from detrital k feldspars and metamorphic white micas from the eastern province terranes of new zealand have been used to investigate the thermo tectonic history of different parts of an exhumed mesozoic forearc basin and accretionary wedge k feldspars from barely metamorphosed sedimentary host rocks mainly record detrital source area ages whereas those from zeolite and prehnite pumpellyite facies host rocks have textures and argon age spectra that indicate recrystallization during regional low temperature metamorphism the results contribute to a model that genetically links thermo tectonic events across the accretionary wedge and forearc basin elements of the convergent margin and into the median batholith arc probably by the early cretaceous and possibly by the middle jurassic thus even though multidiffusion domain mdd models cannot be used to make inference on cooling histories in such situations the k feldspar argon thermochronometer can provide useful information on the timing of geological events in sub greenschist facies rocks

oxygen isotope studies of carbonaceous chondrites abstract the carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula these isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions we present a comprehensive set of whole rock analyses of cv co ck cm cr ch and ci chondrites as well as selected components of some of these meteorites a simple model is developed which describes the isotopic behavior during parent body aqueous alteration processes the process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition

osmium isotopic homogeneity in the ck carbonaceous chondrites abstract variable proportions of isotopically diverse presolar components are known to account for nucleosynthetic isotopic anomalies for a variety of elements e g ca ti cr ni sr zr mo ru pd ba nd and sm in both bulk chondrites and achondrites however although large os isotopic anomalies have been measured in acid leachates and residues of unequilibrated chondrites bulk chondrites of various groups iron meteorites and pallasites exhibit os isotopic compositions that are indistinguishable from terrestrial or bulk solar isotopic abundances since the magnitude of nucleosynthetic anomalies is typically largest in the carbonaceous chondrites this study reports high precision os isotopic compositions and highly siderophile element hse concentrations for ten ck chondrites the isotope dilution concentration data for hse and high precision os isotope ratios were determined on the same digestion aliquots to precisely correct for radiogenic contributions to 186os and 187os while acid leached bulk unequilibrated carbonaceous chondrites show deficits of s process os components to the same extent as revealed by unequilibrated enstatite ordinary and rumuruti chondrites equilibrated bulk ck chondrites exhibit no resolvable os isotopic anomalies these observations support the idea that acid resistant carbon rich presolar grains such as silicon carbide sic or graphite are major carriers for nucleosynthetic isotopic anomalies of os the destruction of these presolar grains which are omnipresent in unequilibrated meteorites must have occurred during aqueous alteration and thermal metamorphism early in the ck chondrite parent body history the dispersal of ck chondrites along the iiiab iron meteorite isochron on a 187os 188os versus 187re 188os diagram with re os ratios from 0 032 to 0 083 in combination with the observed redistribution of other hse e g pt pd highlights the influence of parent body processes overprinted by effects of recent terrestrial alteration under the oxidizing conditions prevalent on the ck parent body evident from high abundances of magnetite and limited fe ni metal in ck chondrites these parent body processes made all isotopically anomalous os originally hosted in reduced presolar grains accessible the absence of os isotopic anomalies in ordinary enstatite and now also carbonaceous chondrites implies that the carriers of s and r process os must have been effectively homogenized across the region of chondrite formation and possibly even the entire solar protoplanetary nebula as suggested by the os isotopic compositions of iron meteorites and non anomalous ureilites except for a limited number of ureilites the relative proportions of presolar s and r process carriers of os and other elements such as w in chondrites and most other planetary bodies must have remained constant during all subsequent nebular and planetary processes which appears not to have been the case for other siderophile elements including mo ru and pd the existence of mo ru pd and other siderophile element isotopic anomalies thus appears to be in part controlled by the chemical properties of these elements e g volatility their host phase s e g sic graphite metal sulfides and the nature of the nebular or planetary processes experienced in the early solar system

seismic stratigraphic record of transition from mesozoic subduction to continental breakup in the zealandia sector of eastern gondwana abstract the southwest pacific between australia new zealand and new caledonia is a block of continental crust zealandia that moved away from australia and antarctica after a long period of subduction beneath eastern gondwana we use 100 000 line km of seismic reflection profiles to identify intra continental basins related to the gondwana active margin overlain with erosional unconformity by retrogradational strata we interpret this regional scale first order unconformity the eastern gondwana composite surface and seismic stratigraphic megasequence pattern to represent the transition from subduction to continental breakup and separation of eastern gondwana rocks that make up the lower seismic stratigraphic megasequence zealandia 3 permian to early cretaceous have been drilled near new zealand and can be correlated with murihiku supergroup rocks farther north on the lord howe rise we correlate this megasequence with triassic to jurassic rocks of the clarence moreton basin of eastern australia we reinterpret the fairway aotea basin to be underlain by a wedge of zealandia 3 deposits thrust in a retro arc like foreland basin that was active immediately prior to breakup the lower rift and retrogradational megasequence zealandia 2 late cretaceous to eocene we correlate with the pakawau and kapuni groups of taranaki basin new zealand and the formation a charbon and phtanites of new caledonia the boundary with the shallowest megasequence zealandia 1 late eocene to present is the eocene oligocene unconformity which is primarily overlain by pelagic carbonate rocks this regional unconformity likely represents the onset of the modern tonga kermadec subduction system

pacific bidecadal climate variability regulated by tidal mixing around the kuril islands 1 18 6 year period variability has been detected in various aspects of the climate especially in and around the pacific ocean although it is believed to be caused by 18 6 year period tidal cycle no study has directly shown how the tidal cycle regulates such variability using a state of the art climate model we show that the 18 6 year cycle in strong tidal mixing localized around the kuril islands induces 18 6 year periodicity in el nino southern oscillation like pacific climate variability influence of the tidal mixing propagates along the pacific western rim as coastally trapped waves temperature anomaly is generated in the subsurface western equatorial pacific which propagates along the equatorial thermocline and eventually excites 18 6 year periodicity in the equatorial sea surface temperature

discovery of early cretaceous rocks in new caledonia new geochemical and u pb zircon age constraints on the transition from subduction to marginal breakup in the southwest pacific abstract new u pb dating of detrital zircon and geochemical features of permian mesozoic arc derived volcanic rocks and volcaniclastic turbidites graywackes when compared with those of the volcanic rocks associated with unconformable late cretaceous shallow water sediments reveal that subduction in new caledonia once thought to be extinct in the late jurassic ca 150 ma was still active at least from ca 130 to 95 ma the accumulation of volcanic arc derived sediments during the late early cretaceous suggests that as in new zealand active margin activity went on for a short time in spite of the assumed subduction jamming by the hikurangi plateau at ca 100 ma meanwhile the rift related magmatic activity that preceded the marginal breakup migrated eastward from ca 130 ma 130 95 ma in eastern australia to 110 ma 110 82 ma in new zealand and finally to ca 89 ma 89 83 ma in new caledonia and generated large volumes of silicic magma in contrast marginal basins opened synchronously at

long term el nino southern oscillation enso like variation with special emphasis on the south pacific mechanisms for el nino southern oscillation enso like decadal 7 35 years variability are analyzed using observational data when a decadal positive temperature anomaly occurs in the eastern tropical pacific the atmospheric response excites negative wind stress curl in the western tropical south pacific which causes the thermocline to shoal and induce a negative temperature anomaly there the cold anomaly moves northwestward to the western and central equatorial region and then turns eastward along the equator to reverse the original temperature anomaly in the east the eastward propagation of the oceanic signal along the equatorial thermocline correlates with a zonal wind anomaly the cold anomaly in the east grows through tropical air sea interaction and induces a positive wind stress curl in the western tropical south pacific associated with the atmospheric teleconnection in the southern hemisphere subsequent evolution of the negative phase is similar to that of the positive phase the complete scenario for this enso like decadal variability due to the air sea interaction processes within the tropics has a period of 14 years we also discuss enso like variation on the interdecadal 35 years timescale with possible relationship to the 1976 1977 climate regime shift

characteristic variations of sea surface temperature with multiple time scales in the north pacific abstract temporal evolution and spectral structure of sea surface temperature sst anomalies in the north pacific over the last 37 years are investigated on the three characteristic time scales shorter than 24 months hf 24 60 months es and longer than 60 months dc the leading empirical orthogonal function eof for the dc time scale is characterized by a zonally elongated monopole centered at around 40 n 180 the leading eof for the hf time scale is somewhat similar to that for the dc time scale although there are two centers of action with the same polarity at the mid and western pacific the leading eof for the es time scale however exhibits a different pattern whose center of action at the mid pacific is located farther southeastward in the time evolution of the sst anomalies associated with the leading eof of the dc time scale several anomaly periods can be identified that last five years or longer the transition from a persistent period to another with the opposite polarity is gene

microscale oxygen isotopic exchange and magnetite formation in the ningqiang anomalous carbonaceous chondrite we report in situ measurements of o isotopic compositions of magnetite olivine and pyroxene in chondrules of the ningqiang anomalous carbonaceous chondrite the petrographic setting of ningqiang magnetite is similar to those in oxidized cv chondrites such as allende where magnetite is found together with ni rich metal and sulfide in opaque assemblages in chondrules both magnetite and silicate oxygen data fall close to the carbonaceous chondrite anhydrous mineral line with relatively large ranges in 18o in magnetite 4 9 to 4 2 and in silicates 15 2 to 4 5 magnetite and silicates are not in o isotopic equilibrium the weighted average 17o 17o 0 52 18o values of magnetite are 1 7 to 3 6 higher than those of the silicates in the same chondrules the petrological characteristics and o isotopic disequilibrium between magnetite and silicates suggest the formation of ningqiang magnetite by the oxidation of preexisting metal grains by an aqueous fluid during parent body alteration the weighted average 17o of 3 3 0 3 is the lowest magnetite value measured in unequilibrated chondrites and there is a positive correlation between 17o values of magnetite and silicates in each chondrule these observations indicate that during aqueous alteration in the ningqiang parent asteroid the water rock ratio was relatively low and o isotopic exchange between the fluid and chondrule silicates occurred on the scale of individual chondrules

seismic stratigraphy of a buried volcanic arc northland new zealand and implications for neogene subduction abstract for over 6 million years in the early miocene the northland peninsula of new zealand s north island was the site of a volcanic arc comprising north westerly trending twin belts of marine and subaerial andesitic volcanoes approximately 50 volcanic edifices from major massifs to small cones have been newly identified on marine seismic profiles of the western belt which is largely buried the volcanoes were important point sources of sediment and the volcaniclastic deposits of each of the major and intermediate sized volcanoes form distinct seismic sequences the three main elements of the volcanic sequence are i a main body ii a sloping apron and iii a wide almost flat ring plain the downlap of the oldest discernible internal clinoform reflector relative to a known regional marker reflector underlying it indicates the approximate time of onset of activity whereas downlap of the top bounding reflector relative to those of other volcanic sequences provides a relative order of extinction sequence stratigraphic principles and super position determine relative stratigraphic hierarchy the volcanoes studied here were active only in the early miocene with few exceptions most were active by 22 ma and extinct by 16 ma with many extinct by 19 ma there was no pattern in their order of inception or extinction although a few became dominant burying or surrounding their neighbours at the south eastern end of the chain there is a rapid change over a short distance in both age and orientation from the northwest trending early miocene volcanism in the northland basin to north east trending middle and late miocene volcanism in the contiguous taranaki basin the northland volcanoes are interpreted to have been an arc facing the south westwards subducting south fiji basin whereas the taranaki volcanoes are interpreted to have been part of a separate pacific facing volcanic arc the lau colville ridge

oxygen isotopes in magnetite and fayalite in cv chondrites kaba and mokoia we report in situ measurements of o isotopic compositions of magnetite and primary and secondary olivine in the highly unequilibrated oxidized cv chondrites kaba and mokoia in both meteorites the magnetite and the secondary olivine fayalite fa90 100 have o isotopic compositions near the terrestrial fractionation tf line the mean 17o 17o 0 52 18o value is about 1 in contrast the compositions of nearby primary chondrule low feo olivines fa1 2 are well below the tf line 17o values range from 3 to 9 krot et al 1998 summarized evidence indicating that the secondary phases in these chondrites formed by aqueous alteration in an asteroidal setting the compositions of magnetite and fayalite in kaba and mokoia imply that the o isotopic composition of the oxidant was near or somewhat above the tf line in mokoia the fayalite and magnetite differ in 18o by 20 whereas these same materials in kaba have virtually identical compositions the difference between mokoia magnetite and fayalite may indicate formation in isotopic equilibrium in a water rich environment at low temperatures 300 k in contrast the similar compositions of these phases in kaba may indicate formation of the fayalite by replacement of preexisting magnetite in dry environment with the o coming entirely from the precursor magnetite and silica the 17o of the oxidant incorporated into the cv parent body as phyllosilicates or h2o appears to have been much 7 8 lower than that in that incorporated into the ll parent body choi et al 1998 which suggests that the o isotopic composition of the nebular gas was spatially or temporally variable

oxygen isotopes of chondritic components we review the oxygen isotopic compositions of chondrite components refractory inclusions chondrules and matrix and their inter and intra crystalline oxygen isotopic distributions primary oxygen isotopic compositions acquired before planetesimal accretion are easily disturbed by parent body processes such as aqueous alternation and thermal metamorphism primary or original oxygen isotopic compositions of refractory inclusions ca al rich inclusions and amoeboid olivine aggregates distribute along a slope 1 line on the three oxygen isotope diagram over the range of 60 17 o 18 o 16 o rich and 17 o 18 o rich during refractory inclusion formation on the other hand primary minerals of most chondrules have small isotopic variations and are enriched in 17 o and 18 o relative to refractory inclusions suggesting that chondrule formation occurred in 17 o 18 o rich nebular gas however rare 16 o rich chondrules have been found suggesting some overlap in the timing of formation of chondrules and refractory inclusions in the solar nebula oxygen isotopic compositions of matrix grains distribute along the slope 1 line over the same range as refractory inclusions and chondrules the similarity in oxygen isotopic distributions suggests that matrix was originally a mechanical mixture of nebular dusts co generated with chondrules and refractory inclusions presolar grains with oxygen isotopic compositions that are clearly distinct from those of solar nebular materials are a trace component of chondrite matrices based on these oxygen isotopic characteristics more than 99 5 of the solid materials in the nebula formed locally in the solar nebula and the remainder formed in interstellar space the astrophysical setting of chondrite component formation in the early solar system is also discussed refractory inclusions and 16 o rich matrix dusts formed around the inner edge of the solar nebula on the other hand most chondrules and 17 o 18 o rich matrix dusts seem to have formed elsewhere in the solar nebula efficient large scale radial mixing of the solar nebular materials may have been an essential process in the formation of chondritic planetesimals

rhodium gold and other highly siderophile element abundances in chondritic meteorites abstract the abundances of the highly siderophile elements hse re os ir ru pt rh pd and au and 187os 188os isotope ratios have been determined for a set of carbonaceous ordinary enstatite and rumuruti chondrites using an analytical technique that permits the precise and accurate measurement of all hse from the same digestion aliquot concentrations of re os ir ru pt and pd were determined by isotope dilution icp ms and n tims analysis the monoisotopic elements rh and au were quantified relative to the abundance of ir differences in hse abundances and ratios such as re os 187os 188os pd ir and au ir between different chondrite classes are further substantiated with new data and additional rh and au data including new data for ci chondrites systematically different relative abundances of rh between different chondrite classes are reminiscent of the behaviour of re carbonaceous chondrites are characterized by low average rh ir of 0 27 0 03 1s which is about 20 lower than the ratio for ordinary 0 34 0 02 and enstatite chondrites eh 0 33 0 01 el 0 32 0 01 r chondrites show higher and somewhat variable rh ir of 0 37 0 07 well defined linear correlations of hse in particular for bulk samples of ordinary and el chondrites are explained by binary mixing and or dilution by silicates the hse carriers responsible for these correlations have a uniform chemical composition indicating efficient homogenization of local nebular heterogeneities during or prior to the formation of the host minerals in chondrite components excepting rumuruti chondrites and au in carbonaceous chondrites these correlations also suggest that metamorphism alteration and igneous processes had negligible influence on the hse distribution on the bulk sample scale depletion patterns for rh pd and au in carbonaceous chondrites other than ci are smoothly related to condensation temperatures and therefore consistent with the general depletion of moderately volatile elements in carbonaceous chondrites fractionated hse abundance patterns of ordinary enstatite and rumuruti chondrites however are more difficult to explain fractional condensation combined with the removal of metal phases at various times and later mixing of early and late formed metal phases may provide a viable explanation planetary fractionation processes that may have affected precursor material of chondrite components cannot explain the hse abundance patterns of chondrite groups hse abundances of some but not all rumuruti chondrites may be consistent with solid sulphide liquid sulphide fractionation processes during impact induced melting

quasi periodicity and global symmetries in interdecadal upper ocean temperature variability recent studies find interannual i e 3 to 7 year decadal i e 9 to 13 year and interdecadal i e 18 to 23 year periodicities and a trend dominating global sea surface temperature sst and sea level pressure slp variability over the past hundred years with the interdecadal signal dominating sub el nino southern oscillation enso frequencies we isolate interdecadal frequencies in sst and slp records by band passing with a window admitting 15 to 30 year periods from 1900 to 1989 the rms of interdecadal filtered sst and slp anomalies is largest in the extratropics and eastern boundaries first mode empirical orthogonal functions eofs explain about half the interdecadal variance in both variables with the tropical warm phase peaking near 1900 1920 1940 1960 and 1980 from 1955 to 1994 eof spatial patterns of interdecadal sst slp and 400m temperature t400 anomalies reveals global reflection symmetries about the equator and global translation symmetries between ocean basins with tropical and eastern ocean ssts warmer cooler than normal covarying with stronger weaker extratropical westerly winds cooler warmer ssts in western central subarctic and subantarctic frontal zones safzs stronger weaker subtropic and subarctic gyre circulations in north pacific and north atlantic oceans and warmer cooler basin and global average ssts of 0 1 c or so evolution of interdecadal variability from the tropical warm phase to the tropical cool phase is propagative also characterized by reflection and translation symmetries during the tropical warm phase cool sst anomalies along western central safzs are advected slowly eastward to the eastern boundaries and subsequently advected poleward and equatorward by the mean gyre circulation the latter conducting extratropical sst anomalies into the tropics a delayed action oscillation model is constructed that yields the quasiperiodicity of interdecadal variability in a manner consistent with these global symmetries in both pattern and evolution

ion microprobe analysis of oxygen isotope ratios in granulite facies magnetites diffusive exchange as a guide to cooling history ion microprobe analysis of magnetites from the adirondack mountains ny yields oxygen isotope ratios with spatial resolution of 2 8 m and precision in the range of 1 1 sigma these analyses represent 11 orders of magnitude reduction in sample size compared to conventional analyses on this material and they are the first report of routinely reproducible precision in the 1 per mil range for analysis of 18o at this scale high precision micro analyses of this sort will permit wide ranging new applications in stable isotope geochemistry the analyzed magnetites form nearly spherical grains in a calcite matrix with diopside and monticellite textures are characteristic of granulite facies marbles and show no evidence for retrograde recrystallization of magnetite magnetites are near to fe3o4 in composition and optically and chemically homogeneous a combination of ion probe plus conventional brf5 analysis shows that individual grains are homogeneous with 18o 8 9 1 smow from the core to near the rim of 0 1 1 2 mm diameter grains depth profiling into crystal growth faces of magnetites shows that rims are 9 depleted in 18o these low 18o values increase in smooth gradients across the outer 10 m of magnetite rims in contact with calcite these are the sharpest intracrystalline gradients measured to date in geological materials this discovery is confirmed by bulk analysis of 150 350 m diameter magnetites which average 1 2 lower in 18o than coarse magnetites due to low 18o rims conventional analysis of coexisting calcite yields 18o 18 19 suggesting that bulk 18o cc mt 9 3 and yielding an apparent equilibration temperature of 525 c over 200 c below the temperature of regional metamorphism consideration of experimental diffusion data and grain size distribution for magnetite and calcite suggests two contrasting cooling histories the data for oxygen in calcite under hydrothermal conditions at high p h2o indicates that diffusion is faster in magnetite and modelling of the low 18o rims on magnetite would suggest that the adirondacks experienced slow cooling after grenville metamorphism followed by a brief period of rapid cooling possibly related to uplift conversely the data for calcite at low p h2o show slower oxygen diffusion than in magnetite modelling based on these data is consistent with geochronology that shows slow cooling through the blocking temperature of both minerals suggesting that the low 18o rims form by exchange with late low temperature fluids similar to those that infiltrated the rock to serpentinize monticellite and which infiltrated adjacent anorthosite to form late calcite veinlets in either case the ion microprobe results indicate that two distinct events are recorded in the post metamorphic exchange history of these magnetites recognition of these events is only possible through microanalysis and has important implications for geothermometry

southern hemisphere origins of the 1976 climate shift 1 observations from the tropical pacific ocean identify an abrupt climate shift in 1976 with surface temperatures changing from cooler than normal to warmer than normal in the span of about 1 year model results show that this climate shift originates with subsurface temperature anomalies in the south tropical pacific ocean which propagate first to the western boundary then northward to the equator and finally eastward along the equator to 140 w where they rise to the surface the results suggest that changes in the north pacific respond to changes in the tropical pacific

a clast of bali like oxidized cv material in the reduced cv chondrite breccia vigarano the cv vigarano type chondrites are a petrologically diverse group of meteorites that are divided into the reduced and the ball like and allende like oxidized subgroups largely based on secondary mineralogy weisberg et al 1997 krot et al 1998b some chondrules and calcium aluminum rich inclusions cais in the reduced cv chondrite vigarano show alteration features similar to those in allende metal is oxidized to magnetite low ca pyroxene forsterite and magnetite are rimmed and veined by ferrous olivine fs 40 50 and plagioclase mesostases and melilite are replaced by nepheline and sodalite sylvester et al 1993 kimura and ikeda 1996 1997 1998

south pacific origin of the decadal enso like variation as simulated by a coupled gcm 1 the hypothesis of the south pacific origin of the decadal 7 35 years enso like variation is investigated based on 200 year outputs of the echam4 opa oasis coupled gcm associated with the decadal warm cold sst anomalies in the tropical pacific an anomalous cyclonic anticyclonic circulation which is tilted in a southeast northwest direction appears in the south pacific this results in anomalous upward downward ekman pumping along the northeastern edge of the anomalous circulation and hence shallowing deepening the oceanic thermocline there such an external source of heat content tends to slowly discharge recharge the tropical ocean on the decadal timescale the above result is consistent with the observational study of luo and yamagata 2001 besides the model reproduces amazingly a high lagged correlation between the global land surface temperature and the decadal nino3 sst despite the model biases this suggests a potential prediction skill of the global warming based on the enso like decadal variation

oligocene miocene spreading history of the northern south fiji basin and implications for the evolution of the new zealand plate boundary a tectonic model of the evolution of the northern half of the south fiji basin including the minerva triple junction and cook fracture zone is developed from regional gravity multibeam bathymetry and a new interpretation of magnetic anomalies pinned to radiometric dates of oceanic crust in the basin the geometry and age of a portion of the minerva triple junction and the cook minerva spreading center the connection from the triple junction to the cook fracture zone which accommodated coeval opening of the norfolk basin are resolved with multibeam bathymetry and magnetics the south fiji basin opened from about 34 to 15 ma in an anticlockwise sweep about an euler pole located at the northern end of the present lau ridge this rotation and a rigidly straight southeastward motion of the three kings ridge were accommodated by the configuration of the triple junction changing from ridge fault fault to ridge ridge fault to ridge ridge ridge during this evolution the southeastern arm of the system the julia fracture zone underwent several transformations and the cook minerva spreading center experienced repeated ridge jumps the kinematics of the northern south fiji basin dictate to a large extent the evolution of the southern south fiji basin and the norfolk basin this in turn leads to the interpretation of a complex trench trench double transform fault framework at the northern new zealand margin which explains most aspects of the geology structure and arc volcanic history of the margin and provides a radical new setting for the origin of the northland allochthon

regional implications of u pb shrimp age constraints on the tectonic evolution of new caledonia abstract u pb shrimp ages for zircons from plagiogranites indicate a late carboniferous age of formation for ophiolitic basement of the koh terrane in the central chain mountains of new caledonia samples from ophiolites at koh and koua yielded ages of 302 7 ma and 290 5 ma respectively the similarity of these ages to those of plagiogranites in the dun mountain ophiolite belt maitai terrane of new zealand and the comparable structural positions of the two terranes potentially constrain reconstructions of the cretaceous sw pacific margin detrital zircons from late mesozoic sediments that overlap the koh terrane also provide potential constraints on the location of new caledonia prior to its break up and dispersal from eastern australia

progressive alteration in cv3 chondrites more evidence for asteroidal alteration abstract the oxidized cv3 chondrites can be divided into two major subgroups or lithologies bali like cv3oxb and allende like cv3oxa in which chondrules calcium aluminum rich inclusions cais and matrices show characteristic alteration features weisberg et al 1997 krot et al 1997d kimura and ikeda 1997 the cv3oxb lithology is present in bali kaba parts of the mokoia breccia and possibly in grosnaja and allan hills alh 85006 it is characterized by the presence of the secondary low ca phyllosilicates saponite and sodium phlogopite magnetite ni rich sulfides fayalite fa 90 ca fe rich pyroxenes fs10 50wo45 50 and andradite phyllosilicates replace primary ca rich minerals in chondrules and cais which suggests mobilization of ca during aqueous alteration magnetite nodules are replaced to various degrees by fayalite ca fe rich pyroxenes and minor andradite fayalite veins crosscut fine grained rims around chondrules and extend into the matrix thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures 300 c in the presence of aqueous solutions oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large 18ofayalite magnetite fractionation 20 we infer that phyllosilicates magnetite fayalite ca fe rich pyroxenes and andradite formed at relatively low temperatures 300 c by fluid rock interaction in an asteroidal environment secondary fayalite and phyllosilicates are virtually absent in chondrules and cais in the cv3oxa lithology which is present in allende and its dark inclusions axtell alha81258 alh 84028 lewis cliff lew 86006 and parts of the mokoia and vigarano breccias instead secondary nepheline sodalite and fayalitic olivine are common fayalitic olivine in chondrules replaces low ca pyroxenes and rims and veins forsterite grains it also forms coarse lath shaped grains in matrix secondary ca fe rich pyroxenes are abundant we infer that the cv3oxa lithology experienced alteration at higher temperatures than the cv3oxb lithology the presence of the reduced and cv3oxa lithologies in the vigarano breccia and cv3oxa and cv3oxb lithologies in the mokoia breccia indicates that all cv3 chondrites came from one heterogeneously altered asteroid the metamorphosed clasts in mokoia krot and hutcheon 1997 may be rare samples of the hotter interior of the cv asteroid we conclude that the alteration features observed in the oxidized cv3 chondrites resulted from the fluid rock interaction in an asteroid during progressive metamorphism of a heterogeneous mixture of ices and anhydrous materials mineralogically similar to the reduced cv3 chondrites

oxygen isotopic evolution of the solar nebula studies of the three oxygen isotopes in chondrite meteorites demonstrate that diverse o reservoirs characterized by their 17o values were present in the solar nebula the discovery that some chondritic materials have o isotopic compositions that cannot be explained by mass dependent fractionation of an initially well mixed reservoir has important implications for the history of the solar nebula on a plot of 17o versus 18o or 17o 16o versus 18o 16o terrestrial samples with the main exception of stratospheric ozone fall along a single line the terrestrial fractionation or tf line having a slope 0 52 an indication that the parental reservoir was homogenized a convenient measure of o isotopic heterogeneity is the deviation from the tf line 17o 17o 0 52 18o a popular model to explain the evolution of chondritic oxygen compositions during nebular and asteroidal aqueous alteration processes calls for the nebula to have formed from solids having 18o 40 and 17o 41 17o 20 and a gas having a composition roughly estimated to be 18o 30 and 17o 24 17o 9 this model encounters serious difficulties when examined in detail in particular it cannot readily account for the o isotopic compositions of both chondrules and refractory inclusions from individual chondrite groups or for the differences between groups particularly in the compositions of chondrules magnetite fe3o4 is a key phase for o isotope studies because during its formation by the oxidation of ferrous metal or fes all o comes from the oxidant probably h2o it appears that most and possibly nearly all magnetite formed during aqueous alteration processes that occurred in asteroids in all chondrite groups studied to date 17o of the magnetite is greater than or equal to that of the chondrule silicates if the h2o originated in the ambient local nebula then at the time of accretion the 17o of the nebular gas was generally higher than that of the solids an alternative view is that the heterogeneity in the o isotopic composition of chondrites indicates that the nebula formed from diverse batches of presolar materials the precise o isotopic composition of the mix varying during the accretion history of the nebula the large compositional gaps between groups suggest that agglomeration of nebular dust to form chondrites did not proceed at a constant rate but that periods with turbulence levels low enough to allow agglomeration were punctuated by periods of high turbulence during which the composition of the inner nebula sampled by chondrites changed appreciably

propagation of north pacific interdecadal subsurface temperature anomalies in an ocean gcm propagation of subsurface north pacic inter decadal variations is investigated with an ocean general cir culation model forced by observed sea surface temperature anomalies subsurface temperature anomalies subducted in the central subtropical north pacic take a more westward pathway than a passive temperature tracer and reach the western boundary to the north of the bifurcation latitude this prevents them from extending into the equator on the boundary between the subtropical and the subarctic gyres on the other hand the upper 500 m heat content anomaly is found to propagate eastward as high vertical modes of rossby waves advectedbythemean eastward cur rent this notion is supported by a sign reversal in temper ature anomaly underneath

crystal orientation effects in δ18o for magnetite and hematite by sims abstract in situ high precision analysis of oxygen isotope ratios 18 o by secondary ion mass spectrometry sims reveals that instrumental bias in 18 o for magnetite varies due to crystal orientation effects multiple analyses of 18 o have an average precision of 0 4 2sd in single grains of magnetite close to 0 3 that obtained for multiple grains of uwq 1 a homogeneous quartz standard in contrast the average precision is five to ten times worse 2 3 2sd from grain to grain of magnetite due to variation in instrumental bias with crystal orientation electron backscatter diffraction shows that individual grains of magnetite are single crystals and that crystal orientation varies randomly from grain to grain the crystal orientation for each magnetite grain is plotted relative to the incident angle of the sims primary cs beam high values of 18 o are measured when the cs beam is parallel to uv 0 from 110 to 100 preferred channeling and focusing directions for magnetite routine 18 o analysis at wiscsims utilizes a gaussian focused cs primary beam deep pit mode at primary and secondary voltages of 10 kv and 10 kv respectively total impact energy 20 kev four analytical experiments were conducted in attempts to improve the grain to grain precision in measured 18 o for magnetite 1 applying an energy offset of 50 ev 2 using a kohler illuminated beam shallow pit mode 3 reducing the total impact energy and 4 varying the primary and secondary accelerating voltages the best results were obtained in experiment 4 at primary secondary accelerating voltages of 3 kv 10 kv respectively with an incident cs beam angle of 14 the grain to grain precision in measured 18 o for magnetite improves from 2 9 to 0 8 2sd at 10 kv 10 kv and 3 kv 10 kv analysis respectively while precision in single grains is 0 4 for both instrumental bias in 18 o also varies with crystal orientation for hematite at similar levels as is seen for magnetite the grain to grain precision in measured 18 o for hematite improves from 2 1 to 1 0 2sd at 10 kv 10 kv and 3 kv 10 kv analysis respectively while precision in single grains is 0 3 2sd for both importantly crystal orientation effects have not been identified at levels of 0 3 for 18 o in silicates or other minerals analyzed by wiscsims though many minerals remain to be examined

the modern foreland basin system adjacent to the central andes regional variations in sediment thickness internal structures average elevation and bouguer gravity define a four component foreland basin system adjacent to the central andes in the most proximal part of the foreland basin system the eastern subandean zone and westernmost chaco plain 1 3 km of cenozoic deposits overlies active folds and thrusts of the frontal andean orogenic wedge these wedge top deposits pass cratonward into a foredeep depozone containing a 3 4 km thick sedimentary prism that tapers toward and locally pinches out against a broad wavelength forebulge in the central eastern chaco plain the forebulge is underlain by precambrian mesozoic rocks and is largely covered by a thin veneer of quaternary alluvium east of the forebulge a thin 0 5 km saucer shaped accumulation of sediment beneath the pantanal wetland represents a back bulge depozone ancient counterparts of these four depozones can be identified in the central andes suggesting that modern basin architecture is the result of continuous eastward migration of the coupled orogenic wedge and foreland basin system since the late cretaceous paleocene

support for tropically driven pacific decadal variability based on paleoproxy evidence two independent proxy reconstructions of sea surface temperature reflect a common pattern of pacific decadal sea surface temperature variability over the past two centuries since the pattern extends to both the north ern and southern hemispheres this result supports the idea that pacific decadal variability is a basin wide phenomenon originating in thetropics the causes of pacific decadal climate variability here termed pdv are the subject of much debate most work describing pdv has focused on the north pacific where the leading eof of low pass filtered sea surface temperature

low frequency modes of tropical ocean dynamics abstract basinwide very low frequency vlf modes with zonal uniformly deepening and shoaling of the equatorial thermocline are found as solutions of linear shallow water equations with the meridional basin boundaries under an equatorial plane they can be understood as the free heat content recharge oscillations the interannual vlf modes had been recognized as the essential part of the coupled recharge oscillator theory for the el nino southern oscillation it is suggested that the decadal vlf modes may also be transformed into coupled modes relevant to the pacific decadal climate variability through the ocean atmosphere interaction in the tropics

low temperature aqueous alteration on the cr chondrite parent body implications from in situ oxygen isotope analyses the presence of hydrated minerals in chondrites indicates that water played an important role in the geologic evolution of the early solar system however the process of aqueous alteration is still poorly understood renazzo like carbonaceous cr chondrites are particularly well suited for the study of aqueous alteration samples range from being nearly anhydrous to fully altered essentially representing snapshots of the alteration process through time we studied oxygen isotopes in secondary minerals from six cr chondrites of varying hydration states to determine how aqueous fluid conditions including composition and temperature evolved on the parent body secondary minerals analyzed included calcite dolomite and magnetite the o isotope composition of calcites ranged from 18o 9 to 35 dolomites from 18o 23 to 27 and magnetites from 18o 18 to 5 calcite in less altered samples showed more evidence of fluid evolution compared to heavily altered samples likely reflecting lower water rock ratios most magnetite plotted on a single trend with the exception of grains from the extensively hydrated chondrite mil 090292 the mil 090292 magnetite diverges from this trend possibly indicating an anomalous origin for the meteorite if magnetite and calcite formed in equilibrium then the relative 18o fractionation between them can be used to extract the temperature of co precipitation isotopic fractionation in al rais carbonate magnetite assemblages revealed low precipitation temperatures 60 c assuming that the cr parent body experienced closed system alteration a similar exercise for parallel calcite and magnetite o isotope arrays yields global alteration temperatures of 55 to 88 c these secondary mineral arrays indicate that the o isotopic composition of the altering fluid evolved upon progressive alteration beginning near the al rais water composition of 17o 1 and 18o 10 and becoming increasingly 16o enriched toward a final fluid composition of 17o 1 2 and 18o 15

crustal structure of the basin and ridge system west of new caledonia southwest pacific from wide angle and reflection seismic data 1 during the zoneco 11 marine geophysical survey september 2004 two deep reflection seismic profiles recorded by ocean bottom seismometers were acquired in the offshore domain west of new caledonia the northern profile crosses the new caledonia basin the fairway ridge the fairway basin and the lord howe rise the southern profile crosses the norfolk rise south of new caledonia the new caledonia basin the fairway ridge and basin and ends at the foot of lord howe rise on the northern profile the lord howe rise has a crustal thickness of 23 km and exhibits seismic velocities and velocity gradients characteristic of continental crust the crust thins to 12 15 km in the neighboring fairway basin which is interpreted to be of thinned continental origin based on the seismic velocities the crustal thickness of the fairway rise is 22 km and it is also interpreted to be of continental origin the new caledonian basin is underlain by crust of 10 km thickness which shows unusally high velocities between 7 0 and 7 4 uncharacteristic for either thinned continental or oceanic crust on the southern profile the norfolk rise is also found to be of continental nature here the new caledonia basin shows velocities crustal thickness and basement roughness characteristic of typical oceanic crust the crust in the fairway basin shows higher velocities than on the northern profile which could be caused by volcanic intrusions into the crust during extension a deep reflector in the upper mantle was imaged underneath the new caledonian basin on the northern profile

eocene arc continent collision in new caledonia and implications for regional southwest pacific tectonic evolution new caledonia preserves evidence that constrains models for the tectonic evolution of the southwest pacific region onland geology reflects four main tectonic phases 1 early mesozoic development of subduction related terranes and their accretion to the gondwana margin 2 cretaceous passive margin development and sea floor spreading during the gondwana breakup 3 foundering of an oceanic basin and the eocene arrival of thinned gondwana margin crust at a southwest facing subduction zone resulting in collisional orogenesis and obduction of an ophiolitic nappe from the northeast and 4 detachment faulting during extensional collapse resulting in unroofing of metamorphic core complexes the last phase explains supposedly anomalous metamorphic gradients in the northeast of the island

subduction platform subsidence and foreland thrust loading the late tertiary development of taranaki basin new zealand borehole seismic and gravity data are used to investigate deformation of continental lithosphere at a miocene collisional zone deformation is manifested in the three following principal forms a long wavelength 500 km platform subsidence ascribed to mantle convection flexural deformation on a scale of 100 200 km due to crustal thrusting at the eastern boundary of the taranaki basin and a ductile thickening evident on the deep seismic section of taranaki basin that occurs on a scale of 10 km evidence for flexural deformation principally comes from the deep seismic section that shows a 150 km wavelength bending of the moho down toward the major zone of thrusting within the taranaki fault zone paleowater depths however provide evidence for an initial early miocene regional subsidence that is too long in wavelength to be explained by flexure induced from thrust sheet loading instead we propose that this broad platform subsidence was driven by loading from a deep source probably subduction induced flow in the mantle by 22 19 ma 1 2 km of water existed over most of the area now occupied by south taranaki basin by 19 17 ma the water depth in the zone east of the taranaki basin the taranaki fault zone had been replaced by rock due to submarine thrusting and crustal thickening this build up of submarine topography in the taranaki fault zone constitutes part of the load 25 8 mpa that created and maintains south taranaki basin gravity data place further constraints on loading at the thrust front and point to an additional intracrustal loading equivalent to 15 7 mpa over a 50 km wide zone this intracrustal load is explained as being due to thick skinned thrusting bringing denser lower crustal rocks nearer to the surface in the thrust zone the complete load on the taranaki foreland is therefore in three parts the submarine topographic load the intracrustal load and the loading of infilling sediments

opaque assemblages in cr2 graves nunataks gra 06100 as indicators of shock driven hydrothermal alteration in the cr chondrite parent body we have studied the petrologic characteristics of sulfide metal lodes polymineralic fe ni nodules and opaque assemblages in the cr2 chondrite graves nunataks gra 06100 one of the most altered cr chondrites unlike low petrologic type cr chondrites alteration of metal appears to have played a central role in the formation of secondary minerals in gra 06100 differences in the mineralogy and chemical compositions of materials in gra 06100 suggest that it experienced higher temperatures than other cr2 chondrites mineralogic features indicative of high temperature include 1 exsolution of ni poor and ni rich metal from nebular kamacite 2 formation of sulfides oxides and phosphates 3 changes in the co ni ratios and 4 carbidization of fe ni metal the conspicuous absence of pentlandite may indicate that peak temperatures exceeded 600 c opaques appear to have been affected by the action of aqueous fluids that resulted in the formation of abundant oxides fe rich carbonates including endmember ankerite and the sulfide silicate phosphate scorzalite we suggest that these materials formed via impact driven metamorphism mineralogic features indicative of impact metamorphism include 1 the presence of sulfide metal lodes 2 the abundance of polymineralic opaque assemblages with mosaic like textures and 3 the presence of suessite initial shock metamorphism probably resulted in replacement of nebular fe ni metal in chondrules and in matrix by ni rich co rich fe metal al ti cr rich alloys and fe sulfides while subsequent hydrothermal alteration produced accessory oxides phosphates and fe carbonates an extensive network of sulfide metal veins permitted effective exchange of siderophile elements from pre existing metal nodules with adjacent chondrules and matrix resulting in unusually high fe contents in these objects

deuterium enrichments in chondritic macromolecular material implications for the origin and evolution of organics water and asteroids here we report the elemental and isotopic compositions of the insoluble organic material iom isolated from several previously unanalyzed meteorites as well as the reanalyses of h isotopic compositions of some previously measured samples alexander et al 2007 the iom in ordinary chondrites ocs has very large d enrichments that increase with increasing metamorphism and decreasing h c the most extreme d value measured being almost 12 000 we propose that such large isotopic fractionations could be produced in the oc parent bodies through the loss of isotopically very light h2 generated when fe was oxidized by water at low temperatures 200 c we suggest that similar isotopic fractionations were not generated in the iom of cv and co chondrites with similar metamorphic grades and iom h c ratios because proportionately less water was consumed during metamorphism and the remaining water buffered the h isotopic composition of the iom even a h was being lost from it hydrogen would also have been generated during the alteration of ci cm and cr carbonaceous chondrites the iom in these meteorites exhibit a considerable range in isotopic compositions but all are enriched in d as well as 15n relative to terrestrial values we explore whether these enrichments could also have been produced by the loss of h2 but conclude that the most isotopically anomalous iom compositions in meteorites from these groups are probably closest to their primordial values the less isotopically anomalous iom has probably been modified by parent body processes the response of iom to these processes was complex and varied presumably reflecting differences in conditions within and between parent bodies the d enrichments associated with h2 generation along with exchange between d rich iom and water in the parent bodies means that it is unlikely that any chondrites retain the primordial h isotopic composition of the water ice that they accreted the h isotopic compositions of the most water rich chondrites the cms and cis are probably the least modified and their compositions d 25 suggest that their water did not form at large radial distances from the sun where ice is predicted to be very d rich yet models to explain the o isotopic composition of inner solar system bodies require that large amounts of ice were transported from the outer to the inner solar system

oxygen isotopes in separated components of ci and cm meteorites oxygen isotopic compositions have been determined for whole rock and separated components from the ci chondrites alais ivuna and orgueil and from the atypical cm chondrites bells and essebi the composition of ci matrix is in agreement with previous measurements and is systematically different from that of cm matrix probably due to warmer and wetter conditions of aqueous alteration for ci matrix although bells matrix is like that of other cm chondrites the matrix of essebi falls in the ci field essebi also contains abundant magnetite like cis and unlike other cms the isotopic compositions of magnetite in alais ivuna orgueil and essebi define a trend with 17o of 1 3 to 1 8 distinctly out of isotopic equilibrium with the phyllosilicates in each meteorite the magnetite serves as an isotopic tracer for the fluid which brought about aqueous alteration and oxidation and thus provides additional evidence for a gaseous reservoir in the solar nebula which was more 16o depleted than the earth

multi year predictability in a coupled general circulation model multi year to decadal variability in a 100 year integration of a bmrc coupled atmosphere ocean general circulation model cgcm is examined the fractional contribution made by the decadal component generally increases with depth and latitude away from surface waters in the equatorial indo pacific ocean the relative importance of decadal variability is enhanced in off equatorial wings in the subtropical eastern pacific the model and observations exhibit enso like decadal patterns analytic results are derived which show that the patterns can in theory occur in the absence of any predictability beyond enso time scales in practice however modification to this stochastic view is needed to account for robust differences between enso like decadal patterns and their interannual counterparts an analysis of variability in the cgcm a wind forced shallow water model and a simple mixed layer model together with existing and new theoretical results are used to improve upon this stochastic paradigm and to provide a new theory for the origin of decadal enso like patterns like the interdecadal pacific oscillation and pacific decadal oscillation in this theory enso driven wind stress variability forces internal equatorially trapped kelvin waves that propagate towards the eastern boundary kelvin waves can excite reflected internal westward propagating equatorially trapped rossby waves rws and coastally trapped waves ctws ctws have no impact on the off equatorial sub surface ocean outside the coastal wave guide whereas the rws do if the frequency of the incident wave is too high then only ctws are excited at lower frequencies both ctws and rws can be excited the lower the frequency the greater the fraction of energy transmitted to rws this lowers the characteristic frequency reddens the spectrum of variability off the equator relative to its equatorial counterpart at low frequencies dissipation acts as an additional low pass filter that becomes more effective as latitude increases at the same time enso driven off equatorial surface heating anomalies drive mixed layer temperature responses in both hemispheres both the eastern boundary interactions and the accumulation of surface heat fluxes by the surface mixed layer act to low pass filter the enso forcing the resulting off equatorial variability is therefore more coherent with low pass filtered decadal enso indices e g nino3 sea surface temperature sst than with unfiltered enso indices consequently large correlations between variability and nino3 extend further poleward on decadal time scales than they do on interannual time scales this explains why decadal enso like patterns have a broader meridional structure than their interannual counterparts this difference in appearance can occur even if enso indices do not have any predictability beyond interannual time scales the wings around 15 20 s and sub surface variability at many other locations are predictable on interannual and multi year time scales this includes westward propagating internal rws within about 25 of the equator the slowest of these take up to 4 years to reach the western boundary this sub surface predictability has significant oceanographic interest however it is linked to only low levels of sst variability consequently extrapolation of delayed action oscillator theory to decadal time scales might not be justified

variations in the o isotope composition of gas during the formation of chondrules from the cr chondrites to better understand the environment of chondrule formation and constrain the o isotope composition of the ambient gas in the renazzo like carbonaceous cr chondrite chondrule forming region we studied the mineralogy petrology and in situ o isotope compositions of olivine in 11 barred olivine bo chondrules and pyroxene and silica in three type i porphyritic chondrules from the cr chondrites gao guenie b graves nunataks gra 95229 pecora escarpment pca 91082 and shisr 033 bo chondrules experienced a higher degree of melting than porphyritic chondrules and therefore it has been hypothesized that they more accurately recorded the o isotope composition of the gas in chondrule forming regions we studied the o isotope composition of silica as it has been hypothesized to have formed via direct condensation from the gas bo chondrules constitute 4 of the total cr chondrule population by volume on a three isotope oxygen diagram 17o vs 18o olivine phenocrysts in type i and type ii bo chondrules plot along slope 1 line with the exception of a type ii bo chondrule that plots along slope 0 5 line olivine phenocrysts in type i and type ii bo chondrules have similar but more restricted ranges of 17o values 3 8 to 1 3 and 0 8 to 1 4 respectively than those in type i and type ii porphyritic chondrules 4 6 to 0 3 and 1 8 to 0 9 respectively the observation that olivine grains in type i bo chondrules have similar chemical and o isotope compositions to those of olivine in their porphyritic counterparts argues against the hypothesis that olivine grains in type i porphyritic chondrules are xenocrysts and represent relict fragments of early formed planetesimals the compositional and o isotope data suggest that bo chondrules experienced more extensive but incomplete exchange with the ambient gas than porphyritic chondrules we suggest that cr chondrules formed from relatively 16o enriched solids in the presence of relatively 16o depleted gaseous h2o the o isotope compositions of chondrule olivine likely result from differences in the o isotope composition of both the chondrule precursors and the ambient gas during chondrule formation the inferred o isotope composition of this gas 17o ranges from 3 to 3 is inconsistent with a high abundance of water from the outer solar system which has been predicted to be isotopically heavy

patterns of coherent decadal and interdecadal climate signals in the pacific basin during the 20th century two distinct low frequency fluctuations are suggested from a joint frequency domain analysis of the pacific ocean 30 s 60 n sea surface temperature sst and sea level pressure slp the lowest frequency signal reveals a spatially coherent interdecadal evolution in phase sst and slp anomalies are found along the subarctic frontal zone safz it is symmetric about the equator with tropical sst anomalies peaking near 15 latitudes in the eastern pacific the other low frequency signal reveals a spatially coherent decadal evolution it is primarily a low latitude phenomenon tropical sst anomalies peak in the central equatorial ocean with evidence of atmospheric teleconnections these interdecadal and decadal signals join the enso and quasi biennial signals in determining dominant patterns of pacific ocean natural climate variability relative phasing and location of the sst and slp anomalies for the decadal enso and the quasi biennial signals are similar to one another but significantly different from that of the interdecadal signal

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

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

stratigraphy of the southern norfolk ridge and the reinga basin a record of initiation of tonga kermadec northland subduction in the southwest pacific abstract seismic stratigraphic interpretations of a large new 2d seismic reflection dataset from the reinga basin region northwest of new zealand constrain the history of cretaceous fragmentation of gondwana and cenozoic initiation of tonga kermadec northland subduction the southern norfolk ridge system lay in a proximal location to plate boundaries that were active during both cretaceous and cenozoic events and persistent marine conditions led to a relatively complete record of sedimentation cretaceous extension was followed by regional subsidence and transgression two cenozoic contractional events are separated by substantial 1 km subsidence late eocene contraction led to reverse faulting and folding between new caledonia and the southern norfolk ridge system and topographic highs created in the north western sector were locally eroded by wave abrasion reinga basin was located at the southern tip of this event which had only limited impact in adjacent northern new zealand regional oligocene and miocene subsidence was contemporaneous with late oligocene and early miocene emplacement of nappes in northern new zealand and the onset of arc volcanism early miocene contraction in the reinga basin led to formation of the wanganella ridge these events can be related to calculated plate motions and are shown to be consistent with models of induced subduction nucleation that require c 150 km of convergence the first contraction is associated with regional inception of tonga kermadec subduction whereas oligocene to miocene events and the onset of hikurangi northland subduction were in response to a local change in plate boundary displacement rate and consequent linkage between subduction north of new zealand with alpine fault formation farther south

possible explanation linking 18 6 year period nodal tidal cycle with bi decadal variations of ocean and climate in the north pacific 1 bi decadal climate variation is dominant over the north pacific on inter decadal timescale however the mechanism has not been fully understood we here find that the bi decadal variations in the north pacific climate and intermediate waters possibly relate to the 18 6 year period modulation of diurnal tide in the period of strong diurnal tide tide induced diapycnal mixing makes surface salinity and density higher and the upper layer shallower along the kuril islands and the east coast of japan simple model results suggest that the coastal depth adjustment by baroclinic kelvin waves enhances the thermohaline circulation the upper layer poleward western boundary current and associated heat transport by about 0 05pw this could also explain the warmer sst in the kuroshio oyashio extension regions where positive feedback with aleutian low might amplify the bidecadal variations the 18 6 year tidal cycle hence could play a role as a basic forcing for the bi decadal ocean and climate variations

a delayed action oscillator shared by biennial interannual and decadal signals in the pacific basin 1 biennial interannual and decadal signals in the pacific basin are observed to share patterns and evolution in covarying sea surface temperature sst 18 c isotherm depth z18 zonal surface wind zsw and wind stress curl wsc anomalies from 1955 to 1999 each signal has warm sst anomalies propagating slowly eastward along the equator generating westerly zsw anomalies in their wake these westerly zsw anomalies produce cyclonic wsc anomalies off the equator which pump baroclinic rossby waves in the western central tropical north pacific ocean these rossby waves propagate westward taking 6 12 and 36 months to reach the western boundary near 7 n 12 n and 18 n on biennial interannual and decadal period scales respectively there they reflect as equatorial coupled waves propagating slowly eastward in covarying sst z18 and zsw anomalies taking 6 12 and 24 months to reach the central eastern equatorial ocean these equatorial coupled waves produce a delayed negative feedback to the warm sst anomalies there the decrease in rossby wave phase speed with latitude the increase in meridional scale of equatorial sst anomalies with period scale and the associated increase in latitude of rossby wave forcing are consistent with the delayed action oscillator dao model used to explain el nino however this is not true of the western boundary reflection of rossby waves into slow equatorial coupled waves this requires modification of the extant dao model we construct a modified dao model demonstrating how the various mechanisms and the size and sources of their delays yield the resulting frequency of each signal

the relationship between ck and cv chondrites ck chondrites are highly oxidized meteorites containing abundant magnetite and trace amounts of fe ni metal although the group is predominately composed of equilibrated meteorites types 4 6 in recent years a significant number of new samples have been classified as being either ck3 or ck3 anomalous these unequilibrated cks often display a close affinity with members of the cv oxidized subgroup cks and cvs oxidized subgroup may therefore form a continuum and by implication could be derived from a single common parent body to investigate the relationship between these two groups a detailed study of the oxygen isotope composition opaque mineralogy and major and trace element geochemistry of a suite of cv and ck chondrites has been undertaken the results of oxygen isotope analysis confirm the close affinity between cv and ck chondrites while excluding the possibility of a linkage between the co and ck groups magnetites in both cv and ck chondrites show significant compositional similarities but high ti contents are a diagnostic feature of the latter group the results of major and trace element analysis demonstrate that both cv and ck chondrites show overlapping variation supporting evidence for a single common source for both groups comes from their similar cosmic ray exposure age distributions recent reflectance spectral analysis is consistent with both the cvs and cks being derived from eos family asteroids which are believed to have formed by the catastrophic disruption of a single large asteroid thus a range of evidence appears to be consistent with cv and ck chondrites representing samples from a single thermally stratified parent body in view of the close similarity between cv and ck chondrites some modification of the present classification scheme may be warranted possibly involving integration of the two groups one means of achieving this would be to reassigned ck chondrites to a subgroup of the oxidized cvs it is recognized that a full evaluation of this proposal may require further study of the still poorly understood ck3 chondrites

formation mechanism for isopycnal temperature salinity anomalies propagating from the eastern south pacific to the equatorial region abstract equatorward propagation of temperature salinity or spiciness anomalies on an isopycnal surface emanating from the eastern subtropical south pacific and their formation mechanism are investigated based on a hindcast simulation with an eddy resolving quasi global ocean general circulation model because of density compensating meridional distributions of temperature and salinity the meridional density gradient is weak at the sea surface in the eastern subtropical south pacific with these mean fields cool sea surface temperature anomalies sstas can make the outcrop line of an isopycnal surface migrate equatorward more than 5 and induce warm and salty anomalies on the isopycnal surface subducted warm salty anomalies propagate to the equatorial region over approximately 5 yr and may influence equatorial isopycnal temperature salinity anomalies although the associated effects are unclear if these anomalies could further induce warm eastern equatorial sstas that are positively correlated wit

extremely rapid cooling of a carbonaceous chondrite chondrule containing very 16o rich olivine and a 26mg excess we describe a phenocryst in a co chondrite type ii chondrule that we infer to have formed by melting an amoeboid olivine aggregate aoa this magnesian olivine phenocryst has an extremely 16o rich composition 17o 17o 0 52 18o 23 it is present in one of the most pristine carbonaceous chondrites the co3 0 chondrite yamato 81020 the bulk of the chondrule has a very different 17o of 1 thus the 17o range within this single chondrule is 22 the largest range encountered in a chondrule we interpret the o isotopic and fe mg distributions to indicate that a fine grained aoa assemblage was incompletely melted during the flash melting that formed the chondrule some fe mg exchange but negligible o isotopic exchange occurred between its core and the remainder of the chondrule a diffusional model to account for the observed fe mg and o isotopic exchange yields a cooling rate of 105 to 106 k hr 1 this estimate is much higher than the cooling rates of 101 to 103 k hr 1 inferred from furnace simulations of type ii chondrule textures e g lofgren 1996 however our cooling rate applies to higher temperatures near 1900 k than are modeled by the crystal growth based cooling rates we observed a low 26al 27al initial ratio 4 6 3 0 10 6 in the chondrule mesostasis a value similar to those in ordinary chondrites kita et al 2000 if the 26al 27al system is a good chronometer then chondrule i formed about 2 ma after the formation of refractory inclusions

change of tectono stratigraphic regime in the australian plate during the 99 ma mid cretaceous and 43 ma mid eocene swerves of the pacific the clockwise bend at 99 ma mid cretaceous in linear volcanic chains in the tropical pacific coincides with a change from pre 99 ma head on chilean type subduction of the pacific plate beneath eastern gondwana to 99 43 ma sinistral oblique mariana type subduction and strike slip breakup by simple sea floor spreading between australia and antarctica and by backarc spreading in the southwest pacific the 99 ma breakup of australia from antarctica is documented by a mid cretaceous unconformity this tectono stratigraphic change founded modern australia with a mountain chain along an upper plate margin in the east and lowlands on the lower plate margin in the south the counterclockwise bend at 43 ma mid eocene the emperor hawaiian bend coincides with the onset of structure in the challenger rift of new zealand the eromanga cooper basin of central australia and the oil shale grabens of coastal queensland

oxygen isotope and chemical compositions of magnetite and olivine in the anomalous ck3 watson 002 and ungrouped asuka 881595 carbonaceous chondrites effects of parent body metamorphism we report in situ o isotope and chemical compositions of magnetite and olivine in chondrules of the carbonaceous chondrites watson 002 anomalous ck3 and asuka a 881595 ungrouped c3 magnetite in watson 002 occurs as inclusion free subhedral grains and rounded inclusion bearing porous grains replacing fe ni metal in a 881595 magnetite is almost entirely inclusion free and coexists with ni rich sulfide and less abundant ni poor metal oxygen isotope compositions of chondrule olivine in both meteorites plot along carbonaceous chondrite anhydrous mineral ccam line with a slope of approximately 1 and show a range of 17o values from approximately 3 to 6 one chondrule from each sample was found to contain o isotopically heterogeneous olivine probably relict grains oxygen isotope compositions of magnetite in a 881595 plot along a mass dependent fractionation line with a slope of 0 5 and show a range of 17o values from 2 4 to 1 1 oxygen isotope compositions of magnetite in watson 002 cluster near the ccam line and a 17o value of 4 0 to 2 9 these observations indicate that magnetite and chondrule olivine are in o isotope disequilibrium and therefore not cogenetic we infer that magnetite in ck chondrites formed by the oxidation of pre existing metal grains by an aqueous fluid during parent body alteration in agreement with previous studies the differences in 17o values of magnetite between watson 002 and a 881595 can be attributed to their different thermal histories the former experienced a higher degree of thermal metamorphism that led to the o isotope exchange between magnetite and adjacent silicates

origin and pathway of equatorial 13 c water in the pacific identified by a simulated passive tracer and its adjoint abstract the origin and pathway of the thermostad water in the eastern equatorial pacific ocean often referred to as the equatorial 13 c water are investigated using a simulated passive tracer and its adjoint based on circulation estimates of a global general circulation model results demonstrate that the source region of the 13 c water lies well outside the tropics in the south pacific some 13 c water is formed northeast of new zealand confirming an earlier hypothesis on the water s origin the south pacific origin of the 13 c water is also related to the formation of the eastern subtropical mode water estmw and the sub antarctic mode water samw the portion of the estmw and samw that eventually enters the density range of the 13 c water 25 8 26 6 kg m 3 does so largely by mixing water formed in the subtropics enters the equatorial region predominantly through the western boundary while its interior transport is relatively small the fresher north pacific estmw and central mode wate

stony meteorite characterization by non destructive measurement of magnetic properties four parameters of low field magnetic susceptibility bulk value frequency dependence degree of anisotropy and ellipsoid shape have been determined for 321 stony meteorites from the national collection of canada these parameters provide a basis for rapid non destructive and accurate meteorite classification as each meteorite class tends to have a distinct range of values chondrites show a clear trend of increasing bulk susceptibility from ll to l to h to e within the 3 6 to 5 6 log in 10 9 m 3 kg range reflecting increasing fe ni metal and fe ni sulfide content achondrite values range in log from 2 4 to 4 7 and primitive achondrites from 4 2 to 5 7 frequency dependence is observed using 19 000 hz and 825 hz with variations in strength among meteorite classes and individual specimen dependence ranging from 1 25 6 degrees of anisotropy range from 1 to 53 with both oblate and prolate ellipsoids present the aubrite class is marked by high degrees of anisotropy low bulk magnetic susceptibility and prolate fabric camel donga is set apart from other eucrites marked by higher bulk susceptibility degree of anisotropy and magnitude of oblate ellipsoid shape the shergotty nakhla and chassigny snc meteorites show subclass distinction using frequency dependence and chassigny is set apart with a relatively strong oblate fabric the presence of both strong oblate and prolate fabrics among and within meteorite classes of chondritic and achondritic material points to a complex multi mechanism origin for anisotropy more so than previously thought and likely dominated by impact processes in the later stages of stony parent bodyformation

origin of magnetite in oxidized cv chondrites in situ measurement of oxygen isotope compositions of allende magnetite and olivine magnetite in the oxidized cv chondrite allende mainly occurs as spherical nodules in porphyritic olivine po chondrules where it is associated with ni rich metal and or sulfides to help constrain the origin of the magnetite we measured oxygen isotopic compositions of magnetite and coexisting olivine grains in po chondrules of allende by an in situ ion microprobe technique five magnetite nodules form a relatively tight cluster in oxygen isotopic composition with delta 18o values from 4 8 to 7 1 and delta 17o values from 2 9 to 6 3 seven coexisting olivine grains have oxygen isotopic compositions from 0 9 to 6 3 in delta 18o and from 4 6 to 7 9 in delta 17o the delta 17o values of the magnetite and coexisting olivine do not overlap they range from 0 4 to 2 6 and from 4 0 to 5 7 respectively thus the magnetite is not in isotopic equilibrium with the olivine in po chondrules implying that it formed after the chondrule formation the delta 17o of the magnetite is somewhat more negative than estimates for the ambient solar nebula gas we infer that the magnetite formed on the parent asteroid by oxidation of metal by h2o which had previously experienced minor o isotope exchange with fine grained silicates

aqueous alteration of opaque assemblages in the ningqiang carbonaceous chondrite evidence from oxygen isotopes chondrules and matrix of the ningqiang carbonaceous chondrite contain numerous opaque assemblages oas these oas are mainly composed of ni rich metal magnetite sulfides phosphates with minor amounts of silicates and trace amounts of pt metal grains their mineral assemblage is very similar to that of oas found in allende refractory inclusions in this study we performed in situ analyses of o isotopic compositions of magnetite and whitlockite in oas and of olivine adjacent to oas from ningqiang o isotopic compositions of magnetite vary by 16 parts per thousand in 618 0 and fall on a regression line with a slope of 0 51 and a mean delta 17o of 2 9 0 3 1 sigma parts per thousand in the three o isotope diagram magnetite grains have consistently higher delta o 17 values than their adjacent olivine grains the mineral chemistry and o isotopic compositions of oas in ningqiang chondrules and matrix are most consistent with the formation of magnetites and whitlockite by aqueous alteration of preexisting metal alloys within a planetary body formation of magnetites and phosphates in oas thus do not constrain processes in the early solar nebula but rather provide information on metamorphism in a planetary environment c 2006 elsevier b v all rights reserved

south pacific eastern subtropical mode water abstract the structure formation and destruction of south pacific eastern subtropical mode water spestmw are analyzed geographic extent and water properties are discussed by using high quality ctd sections collected between 1991 and 1996 defined as having a planetary potential vorticity magnitude of less than 3 10 10 m 1 s 1 spesmtw has a volume of about 1 1 1015 m3 estimated from ctd data the ventilation of this mode water is described by using data from a high resolution xbt section in concert with 30 month time series from profiling ctd floats some of the first argo deployments published subduction rates allow a mode water formation rate estimate of 8 7 106 m3 s 1 combining this estimate with the volume yields a residence time of about 4 years the density compensating covarying patterns of late winter surface temperature and salinity in the ventilation region of spestmw are shown to contribute to the strength of the mode water however while the destabilizing salinity gradient in sp

spiciness anomalies in the upper south indian ocean abstractthis study investigates an isopycnal temperature salinity t s or spiciness anomaly in the upper south indian ocean for the period from 2004 to 2015 using observations and reanalyses spic

control of decadal and bidecadal climate variability in the tropical pacific by the off equatorial south pacific ocean abstractdelayed negative feedback processes determining intrinsic decadal and bidecadal time scales for the tropical variability in the pacific are investigated based on climate model experiments by comparing a control run driven by preindustrial forcing and partial blocking runs driven by the same forcing but with ocean temperature and salinity restored to climatology in selected regions subsurface oceanic signals of south pacific origin are shown to precede sst variability in the nino 3 4 region using a linear reduced gravity ocean model driven only by wind stress changes and an offline tracer model oceanic wave adjustment triggered by changes of wind stress curl in the south pacific extratropics is suggested to be essential for the decadal component of the equatorial sst while slower isopycnal advection of subsurface temperature anomalies from the formation region of south pacific eastern subtropical mode water controls the bidecadal component the intrinsic time scales of the tropical variability

pacific decadal variability the tropical pacific mode and the north pacific mode pacific decadal variability is studied in a series of coupled global ocean atmosphere simulations aided by two modeling surgery strategies partial coupling pc and partial blocking pb the pc experiments retain full ocean atmosphere coupling in selected regions but constrain ocean atmosphere coupling elsewhere by prescribing the model climatological sst to force the atmospheric component of the coupled system in pb experiments sponge walls are inserted into the ocean component of the coupled model at specified latitudinal bands to block the extratropical tropical oceanic teleconnection both modeling and observational studies suggest that pacific decadal variability is composed of two distinct modes a decadal to bidecadal tropical pacific mode tpm and a multidecadal north pacific mode npm the pc and pb experiments showed that the tropical pacific mode originates predominantly from local coupled ocean atmosphere interaction within the tropical pacific extratropical tropical teleconnections although not a necessary precondition for the genesis of the tropical decadal variability can enhance sst variations in the tropics the decadal memory in the tropics seems to be associated with tropical higher baroclinic modes the north pacific mode originates from local atmospheric stochastic processes and coupled ocean atmosphere interaction atmospheric stochastic forcing can generate a weaker npm like pattern in both the atmosphere and ocean but with no preferred timescales in contrast coupled ocean atmosphere feedback can enhance the variability substantially and generate a basin scale multidecadal mode in the north pacific the multidecadal memory in the midlatitudes seems to be associated with the delayed response of the subtropical subpolar gyre to wind stress variation in the central north pacific and the slow growing decaying of sst anomalies that propagate eastward in the kuroshio extension region oceanic dynamics particularly the advection of the mean temperature by anomalous meridional surface ekman flow and western boundary currents plays an important role in generating the north pacific mode

seasonal evolutions of atmospheric response to decadal sst anomalies in the north pacific subarctic frontal zone observations and a coupled model simulation abstractpotential impacts of pronounced decadal scale variations in the north pacific sea surface temperature sst that tend to be confined to the subarctic frontal zone safz upon seasonally varying atmospheric states are investigated by using 48 yr observational data and a 120 yr simulation with an ocean atmosphere coupled general circulation model cgcm sst fields based on in situ observations and the ocean component of the cgcm have horizontal resolutions of 2 0 and 0 5 respectively which can reasonably resolve frontal sst gradient across the safz both the observations and cgcm simulation provide a consistent picture between sst anomalies in the safz yielded by its decadal scale meridional displacement and their association with atmospheric anomalies correlated with sst anomalies persistent in the safz from fall to winter a coherent decadal scale signal in the wintertime atmospheric circulation over the north pacific starts emerging in november and develops into an equivalent barotropic an

mesozoic history of the fairway aotea basin implications for the early stages of gondwana fragmentation the fairway ridge is a buried continental structure that separates the fairway basin from the new caledonia basin the proposed cretaceous age of the fairway basin has remained highly hypothetical to date deep offshore petroleum exploration wells revealed well dated mesozoic carbonaceous sedimentary rocks in the taranaki basin at the southern end of the aotea basin in this paper we use geophysical data to confirm the continuity of the 2000 km long fairway aotea basin connecting new caledonia to new zealand and prove its early late cretaceous age analysis of seismic reflection profiles together with newly compiled gravity and magnetic maps reveals late cretaceous ne sw trending lineaments projecting northeastward from major tasman sea fracture zones and the bellona trough which demonstrate that the opening of the fairway aotea basin predates the opening of the tasman sea this result combined with observations of the mesozoic regional geology suggests that the lord howe fairway and norfolk ridges are part of a remnant late early cretaceous continental arc which was fragmented into three pieces by the late early to early late cretaceous this event might be contemporaneous with a plate motion change between the gondwana and pacific plates and or the arrival of the hikurangi plateau in the subduction zone around 105 ma which caused the cessation of subduction along this plate boundary we interpret either of those two events as being possible trigger events for the post early cretaceous fragmentation of the eastern gondwana margin in a slab retreat process

observed modes of sea surface temperature variability in the south pacific region the south pacific sp region exerts large control on the climate of the southern hemisphere at many times scales this paper identifies the main modes of interannual sea surface temperature sst variability in the sp which consist of a tropical driven mode related to a horseshoe structure of positive negative sst anomalies within midlatitudes and highly correlated to enso and interdecadal pacific oscillation ipo variability and another mode mostly confined to extratropical latitudes which is characterized by zonal propagation of sst anomalies within the south pacific gyre both modes are associated with temperature and rainfall anomalies over the continental regions of the southern hemisphere besides the leading mode which is related to well known warmer cooler and drier moister conditions due to its relationship with enso and the ipo an inspection of the extratropical mode indicates that it is associated with distinct patterns of sea level pressure and surface temperature advection these relationships are used here as plausible and partial explanations to the observed warming trend observed within the southern hemisphere during the last decades

basement geology from three kings ridge to west norfolk ridge southwest pacific ocean evidence from petrology geochemistry and isotopic dating of dredge samples abstract we present new petrographie x ray fluorescence electron microprobe ar ar radiometric fission track and sr nd and pb isotopic data for igneous and metamorphic rocks from 18 dredges from a number of basins and ridges in the southwest pacific ocean the dredge samples can be divided into four groups 1 permian to cretaceous gabbroids granitoids and hornfelses from the west norfolk and wanganella ridges 2 mainly cretaceous mafic igneous rocks from the reinga ridge and vening meinesz escarpment 3 subduction related late oligocene and early miocene basalts and shoshonites from the three kings and southern norfolk ridges and 4 back arc basin and intraplate basalts of early miocene age in the south and north norfolk basins respectively and intraplate basalts of pliocene age in the reinga basin our dredge data combined with regional magnetic and gravity data provide much needed tests of earlier tectonic interpretations of the region correlatives of the permian brook street terrane and mesozoic median tectonic zone of onshore new zealand clearly extend along the west norfolk and wanganella ridges the three kings ridge was active at least in the 19 to 20 ma period and was probably generated above a west dipping subduction zone the norfolk basin was a back arc basin to this arc and had opened by 18 20 ma the oldest cenozoic volcanic rocks in the region are 26 ma subduction related volcanic breccias on the southern norfolk ridge they probably predate opening of the norfolk basin and associated eastward migration of the three kings ridge