glaucophane schists and ophiolites of the northern california coast ranges isotopic ages and their tectonic implications the geology of a strip of 15 quadrangles across the franciscan complex in the coast ranges of northern california is the basis for interpretation of the significance of potassium argon and fossil ages of glaucophane schists ophiolitic materials and associated sedimentary rocks whole rock and mineral separates of franciscan rocks were analyzed and 69 potassium argon ages were obtained white micas and actinolites from blueschist blocks in melange give apparent ages clustering about 142 and 153 m y but they probably represent a continuum blue amphibole ages from blocks range from 98 to 151 m y the younger ages are from the eastern portion of the central melange belt published u pb ages from the ophiolite belt give crystallization ages from 153 to 165 m y k ar ages extend from 143 to 166 m y whole rock ages from the south fork mountain schist range from 113 to 158 m y but cluster around 124 m y the association of older k ar ages with more coarsely crystalline schist suggests that metamorphism occurred prior to 124 m y ago fossil evidence indicates that the basal sediments of the great valley sequence were deposited upon the disrupted coast range ophiolite within 5 to 10 m y of the oldest crystallization ages for ophiolite fossils within melange units broken formations and unsubducted trench slope deposits provide evidence for melange development by the early cretaceous with youngest melange units generally lying to the west available chronologic evidence is compatible with a tectonic model involving melange formation in a restricted flow channel beneath the accretionary wedge of the subduction complex upflow of melange returned blocks of coarsely crystalline metamorphic rocks that were accreted during the initial stages of subduction when the hanging wall was still hot the viability of this and other proposed tectonic models can be assessed by continued careful field documentation of the nature of contacts between key lithotectonic units and by detailed application of temperature sensitive geochronologic tools

jotunites from the grenville province quebec petrological characteristics and implications for massif anorthosite petrogenesis abstract we report new results on the geology mineralogy and chemical compositions of jotunites mainly pyroxene monzodiorites from the morin st urbain and labrieville anorthosite complexes all in the grenville province of quebec jotunites occur between anorthosite and mangerite as marginal units to anorthosite or mangerite plutons or as fine grained dikes in either rock type some occurrences are probably cumulates but the dikes indicate the existence of jotunitic liquids jotunites consist predominantly of sodic plagioclase an25 an45 clinopyroxene and orthopyroxene having intermediate xmg e g en60 en40 along with significant ilmenite magnetite and apatite most samples contain small amounts of k feldspar locally mesoperthite and quartz it is noteworthy that plagioclase and pyroxene compositions in jotunites lie between those in associated anorthosite and mangerite jotunites from all areas span a similar range in sio2 content 40 55 wt and are characterized by high levels of fe2o3 t 30 wt tio2 6 wt and p2o5 3 25 wt all samples are alkalic with k2o 3 6 wt increasing in the sequence morin st urbain labrieville they contain high sr up to 1400 ppm and ba up to 4600 ppm and concentrations correlate well with those in associated anorthosite in each case jotunites also are high in ga high ga al zr zn y and ree but low in rb high k rb u th ni cr co sc and v high ti v jotunites can be linked spatially mineralogically and chemically with associated anorthosite and mangerite and we interpret them as transitional rocks in a largely comagmatic sequence from anorthosite to mangerite we postulate a model for andesine anorthosite petrogenesis involving early crystallization and accumulation of plagioclase from parental magmas of intermediate sio2 content broadly dioritic in composition resulting in fe ti and p enrichment in the remaining magma leading to jotunite high o2 table causes early crystallization of fe ti oxides which suppresses fe mg enrichment in pyroxene fractionation of fe ti oxides pyroxene and apatite ultimately results in si and k enrichment in residual liquids leading to quartz mangerite significantly liquids follow an initial trend of si depletion fe enrichment followed by a reversal of this trend this view contrasts strongly with current models that regard anorthosite jotunite and mangerite as unrelated products of bimodal magmatism

evidence of arc related svecofennian magmatic activity in the southwestern margin of the east european craton in poland abstract the precambrian basement of northeastern poland forms the western part of the present day east european craton the central part of this area with moderately uniform potential fields of variably oriented magnetic and gravity anomalies has been penetrated by a six boreholes samples from which consist of calc alkaline granodiorite orthogneiss okuniew 1 calc alkaline monzonite rajsk 1 and 2 and calc alkaline orthoamphibolite lomza 1 2 and 3 geochemical features of the most drilled rocks particularly depletion in th u nb p and ti relative to primitive mantle and position on trace element discrimination diagrams y vs nb y nb vs rb hf rb ta and la y nb are consistent with a volcanic arc environment the results of u pb age measurements show that arc related magmatic activity took place between 1 82 and 1 80 ga these data may be compared to analytical results from the transcandinavian igneous belt in the southwestern part of the east european craton where continental crust was formed in several arc systems mainly between 1 91 and 1 86 ga overall the data suggest a general decrease in the age of the intrusive rocks towards the south southwest of the east european craton

the salinity temperature and δ18o of the glacial deep ocean we use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from ocean drilling program cores to reconstruct salinity and temperature of the deep ocean during the last glacial maximum lgm our data show that the temperatures of the deep pacific southern and atlantic oceans during the lgm were relatively homogeneous and within error of the freezing point of seawater at the ocean s surface our chloride data show that the glacial stratification was dominated by salinity variations in contrast with the modern ocean for which temperature plays a primary role during the lgm the southern ocean contained the saltiest water in the deep ocean this reversal of the modern salinity contrast between the north and south atlantic implies that the freshwater budget at the poles must have been quite different a strict conversion of mean salinity at the lgm to equivalent sea level change yields a value in excess of 140 meters however the storage of fresh water in ice shelves and or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level

crustal strain in the southern alps france 1948 1998 active tectonics in the western alps is revealed by a moderate level of seismic activity and geological evidences for quaternary deformation we present new geodetic determinations of the current strain rates in the southern part of the western alps that complement existing results in provence the jura and the subalpine and belledone massifs around grenoble we combined first and second order triangulation data collected in 1948 with global positioning system gps data collected in 1998 we estimate shear strain rates of 0 1 0 2 mrad yr 1 over distances on the order of 30 km significantly diverent from zero in most of the network we obtain nw se to n s compressive shear strain directions over most of the area in agreement with the seismological and geological data these geodetic estimates correspond to long term overall n s to nw se shortening of 2 4 mm yr 1 over the study area on the same order as the far field shortening measured by continuous gps on the grasse torino baseline 2 0 0 5 mm yr 1 that incorporates our geodetic network these results provide new constraints on interseismic strain in the western alps 2000 elsevier science b v all rights reserved

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

detrital zircon constraints on terrane ages and affinities and timing of orogenic events in the san juan islands and north cascades washington detrital zircon geochronology of this report pertains to cretaceous orogeny in northwest washington an event that involved blueschist metamorphism and emplacement of nappes in the san juan islands northwest cascades thrust system and continental arc magmatism and associated barrovian metamorphism in the neighboring coast plutonic complex structurally low in the thrust system quartzose gneiss of the yellow aster complex yields an entirely precambrian suite of detrital zircons with an age pattern that is similar to that of ordovician miogeoclinal rocks and the outboard yukon tanana yreka and shoo fly terranes elsewhere in the cordillera midway in the nappe pile of the northwest cascades sandstone in the bell pass melange has a zircon age population of 110 ma an age that together with the spectrum of exotic materials associated with the sandstone suggests the melange was a major zone of dislocation during mid cretaceous nappe emplacement at a high level in the thrust system are nappes of the fida

mineralogy and phase relations in the blueschist facies of the black butte and ball rock areas northern california coast ranges microprobe study of minerals in rocks of the blueschist facies from the black butte and ball rock areas of the south fork mountain schist northern california coast ranges is the basis in this report for analysis of reactions and phase relations among lawsonite pumpellyite epidote and associated minerals observed assemblages are intermediate in a progression from those observed elsewhere in high p low t schists of the franciscan e 9 panoche pass where lawsonite is present in nearly all lithologies to the relatively low phigh t assemblages of the shuksan blueschist washington where epidote is ubiquitous two successive reactions in this sequence in order of increasing temperature are l lawsonite na amphibole epidote quartz albite chlorite hzo 2 na amphibole pumpellyite quartz epidote ca amphibole albite chlorite h2o the pressure of metamorphism for the black butte and ball rock areas is estimated from the jadeite content of pyroxene and from the stability of aragonite to have been approximately 7 kbar temperature estimates are not tightly constrained by mineral equilibria but are suggested to be in the range of 250 to 300 c

the origin of the palaeoproterozoic amcg complexes in the ukrainian shield new u pb ages and hf isotopes in zircon the ukrainian shield hosts two palaeoproterozoic anorthosite mangerite charnockite granite amcg complexes the korosten and korsun novomyrhorod complexes that intruded palaeoproterozoic continental crust in north western and central parts of the shield respectively we report results of u pb zircon and baddeleyite dating of 16 samples from the korosten plutonic complex kpc and 6 samples from the korsun novomyrhorod plutonic complex knpc fifteen zircon samples from both complexes were also analysed for hf isotopes these new together with previously published data indicate that the formation of the kpc started at c 1815 ma and continued until 1743 ma with two main phases of magma emplacement at 1800 1780 and 1770 1758 ma each of the main phases of magmatic activity included both basic and silicic members the emplacement history of the knpc is different from that of the kpc the vast majority of the knpc basic and silicic rocks were emplaced between c 1757 and 1750 ma the youngest stages of the complex are represented by monzonites and syenites that were formed between 1748 and 1744 ma both ukrainian amcg complexes are closely associated in space and time with mantle derived mafic and ultramafic dykes the hf isotope ratios in the zircons indicate a predominantly crustal source for the initial melts with some input of juvenile hf from mantle derived tholeiite melts the preferred model for the formation of the ukrainian amcg complexes involves the emplacement of large volumes of hot mantle derived tholeiitic magma into the lower crust this resulted in partial melting of mafic lower crustal material mixing of lower crustal and tholeiitic melts and formation of ferromonzodioritic magmas further fractional crystallization of the ferromonzodioritic melts produced the spectrum of basic rocks in the amcg complexes emplacement of the ferromonzodioritic and tholeiitic melts into the middle crust and their partial crystallization caused abundant melting of the ambient crust and formation of the large volumes of granitic rocks present in the complexes

glacial to deglacial changes in north atlantic meltwater advection and deep water formation centennial to millennial scale 14c records from the azores plateau abstract the last deglacial was marked by tremendous changes in ocean temperature and circulation as well as atmospheric co2 and 14c we employed the 14c plateau tuning technique to a centennial scale planktic 14c record of core md08 3180 retrieved s w of the azores islands at 3060 m water depth to establish both a new standard of absolute age control and a record of past 14c reservoir ages of ocean surface waters both 18o minima of g bulloides and high planktic reservoir ages of 1600 to 2170 yr suggest two major melt water incursions that reached from the labrador sea up to the subtropics over heinrich stadial 1 hs 1 in parallel we established a record of apparent benthic ventilation ages that add the planktic 14c reservoir ages together with the benthic planktic 14c age difference at the site and time of deposition a sum finally adjusted to past changes in atmospheric 14c that occurred since the time of deep water formation near the azores apparent deep water ages of the last glacial maximum were as low as 340 740 yr which suggests a lateral advection of young north atlantic deep waters nadw from subpolar regions south of iceland in harmony with recent model simulation and in contrast to a widely assumed major shoaling of glacial deep water formation during hs 1 local benthic ventilation ages increased up to 2200 2550 yr thus suggest an incursion of old southern source deep waters an unstable regime that was interrupted by brief pulses of nadw incursion near 16 15 6 cal ka and most salient near 14 9 14 7 ka

sveconorwegian massif type anorthosites and related granitoids result from post collisional melting of a continental arc root article i nfo two magmatic suites were emplaced during the post collisional evolution of the sveconorwegian orogeny an anorthosite mangerite charnockite suite amc suite and an hornblende and biotite bearing granitoids suite hbg suite the amc suite is exclusively located in the westernmost and warmest part of the orogen in granulite facies gneisses whereas the hbg suite intruded in the rest of the orogen but not in the granulite domain new u pb zircon geochronological data confirm previous age determinations 970 932 ma hbg suite and 933 916 ma amc suite the mafic facies of the two post collisional magmatic suites have similar geochemical compositions but the hbg differentiation trend displays higher cao sr u and th as well as lower k2o and feot mgo than the amc differentiation trend the hbg suite is hydrous and has a broadly higher fo2 whereas the amc suite is anhydrous the inferred parent magmas of both suites have overlapping initial sr nd and pb isotopic compositions with increasing differentiation the two trends point towards two different crustal contaminants together with the recent recognition of a major crustal shear zone located just east of the amc suite this difference suggests that the suites were emplaced in two different lithotectonic units using published experimental constraints and geochemical modeling we suggest that the mafic facies of both suites were produced by partial melting of lower crustal sources which were previously underplated probably during the evolution of a long lasting convergent margin later these lower crustal sources were modified by the regional granulite facies metamorphism 1 035 to 0 97 ga prevailing in the westernmost part of the orogen thus producing an anhydrous lower crustal source for the amc suite accordingly we conclude that the sveconorwegian massif type anorthosites result from partial melting of the continental arc root this process if accepted for other amcg anorthosite mangerite charnockite granite complexes was possible in the proterozoic because of a sufficiently high temperature but not in the archean because in subduction zones the main transfer to the crust was then felsic tonalites granodiorites and not basaltic we thus further suggest that the onset of massif type anorthosites at the beginning of the proterozoic may mark the time when plate tectonics began to operate in a similar way as today

8 precambrian geodynamics and ore formation the fennoscandian shield abstract compared with present day global plate tectonics archaean and palaeoproterozoic plate tectonics may have involved faster moving hotter plates that accumulated less sediment and contained a thinner section of lithospheric mantle this scenario also fits with the complex geodynamic evolution of the fennoscandian shield from 2 06 to 1 78 ga when rapid accretion of island arcs and several microcontinent continent collisions in a complex array of orogens was manifested in short lived but intense orogenies involving voluminous magmatism with a few exceptions all major ore deposits formed in specific tectonic settings between 2 06 and 1 78 ga and thus a strong geodynamic control on ore deposit formation is suggested all orogenic gold deposits formed syn to post peak metamorphism and their timing reflects the orogenic younging of the shield towards the sw and west most orogenic gold deposits formed during periods of crustal shortening with peaks at 2 72 to 2 67 1 90 to 1 86 and 1 85 to 1 79 ga the ca 2 5 to 2 4 ga ni cu pge deposits formed both as part of layered igneous complexes and associated with mafic volcanism in basins formed during rifting of the archaean craton at ca 2 5 to 2 4 ga svecokarelian ca 1 89 to 1 88 ga ni cu deposits are related to mafic ultramafic rocks intruded along linear belts at the accretionary margins of microcratons all major vms deposits in the fennoscandian shield formed between 1 97 and 1 88 ga in extensional settings prior to basin inversion and accretion the oldest cyprus type deposits were obducted onto the archaean continent during the onset of convergence the pyhasalmi vms deposits formed at 1 93 to 1 91 ga in primitive bimodal arc complexes during extension of the arc in contrast the skellefte vms deposits are 20 to 30 million years younger and formed in a strongly extensional intra arc region that developed on continental or mature arc crust deposits in the bergslagen uusimaa belt are similar in age to the skellefte deposits and formed in a microcraton that collided with the karelian craton at ca 1 88 to 1 87 ga the bergslagen uusimaa belt is interpreted as an intra continental or continental margin back arc extensional region developed on older continental crust iron oxide copper gold iocg deposits are diverse in style at least the oldest mineralizing stages at ca 1 88 ga are coeval with calc alkaline to monzonitic magmatism and coeval and possibly cogenetic subaerial volcanism more akin to continental arcs or to magmatic arcs inboard of the active subduction zone younger mineralization of similar style took place when s type magmatism occurred at ca 1 80 to 1 77 ga during cratonization distal to the active n s trending subduction zone in the west possibly interaction of magmatic fluids with evaporitic sequences in older rift sequences was important for ore formation finally the large volumes of anorthositic magmas that characterize the sveconorwegian orogeny formed a major concentration of ti in the sw part of the sveconorwegian orogenic belt under granulite facies conditions about 40 million years after the last regional deformation of the sveconorwegian orogeny between ca 930 and 920 ma

geochemistry of the shuksan greenschists and blueschists north cascades washington variably fractionated and altered metabasalts of oceanic affinity the shuksan schist comprises a structurally coherent metabasaltic member of the easton formation the uppermost allochthon shuksan thrust plate in the thrust system of the western north cascades of washington state late jurassic metamorphism at moderately high p t produced interlayering of actinolite bearing greenschist assemblages with blue amphibole bearing rocks major and trace element analyses of twelve greenschist and blueschist samples have been used to establish similarities between the basaltic protolith and moderately to strongly fractionated type i morb to distinguish the effects of seafloor alteration superimposed on the primary igneous chemistry and to evaluate the origin and nature of the chemical controls which produced the two mineral assemblages

re os study of fe ti v oxide and fe cu ni sulfide deposits suwalki anorthosite massif northeast poland the suwalki anorthosite massif located in extreme northeast poland beneath more than a kilometer of phanerozoic cover hosts major fe ti v deposits these deposits discovered in 1962 are contained in fe and ti oxide minerals that coexist with subordinate quantities of fe cu ni and co sulfides in massif style anorthosites norites and gabbronorites accessibility and other considerations preclude development of this natural resource in the present economic climate detailed work by polish geologists during the last 35 years provides a sound geologic framework for this re os study of the age and origin of oxide and sulfide deposits associated with a major but lesser known anorthosite massif rhenium and osmium abundances and os isotopic compositions were measured for nine sulfides and four titanomagnetites from the suwalki anorthosite massif the titanomagnetites are over an order of magnitude lower in re 0 4 1 5 ppb and os 0 036 0 144 ppb concentrations than co precipitated pyrrhotite pyrite and chalcopyrite that yield consistent concentrations for re 30 55 ppb and os 1 6 ppb parallel lines connecting co existing titanomagnetite and sulfides have slopes of 1 on re versus common os concentration plots indicating that both re and os behave similarly during crystallization in their high preference for any sulfide phase over magnetite samples from three deposits within the anorthosite massif were analyzed an age of 1559 37 ma n 10 with an initial 187os 188os of 1 16 0 06 for the jezioro okr gle and krzemianka deposits is essentially identical to an age of 1556 94 ma n 3 for the udryn deposit udryn however yielded a marginally lower initial 187os 188os of 0 87 0 20 the high initial 187os 188os combined with the proterozoic re os age indicates that the source for suwalki oxides sulfides is older crust and hypothetically could involve archean rocks an average crustal value of 50 for 187re 188os yields a 2777 ma age for suwalki source rocks widespread phanerozoic cover severely limits knowledge of basement rocks in poland however and no archean rocks are known in the immediate region more likely 187re 188os ratios may be higher than average continental crust reflecting mafic crust in the source and may move the source age for suwalki anorthosite and mineral deposits toward younger values that easily include 2 0 ga proterozoic rocks this more favorable case also accommodates paleoproterozoic nd model ages regardless of archean or proterozoic source age the high initial 187os 188os ratios derived from the re os isochron indicate that the source for the oxide sulfide mineral deposits is more likely the crust and not the mantle given that these deposits are clearly magmatic the re os results add a new dimension to the long standing origin of anorthosite problem implying a crustal source for the anorthosite as well the 1559 ma suwalki age is compatible with a well exposed east west band of 1530 1660 ma rapakivi granite anorthosite magmatism to the immediate north transecting western russia southern finland estonia and latvia and central sweden in particular the age and isotopic character of suwalki are not unlike those of the well studied salmi rapakivi granite anorthosite batholith in western russia karelia

persistently well ventilated intermediate depth ocean through the last deglaciation during the last deglaciation 18 11 thousand years ago existing radiocarbon 14c reconstructions of intermediate waters in the mid to low latitude oceans show widely diverging trends with some broadly tracking the atmosphere and others suggesting extreme depletions these discrepancies cloud our understanding of the deglacial carbon cycle because of the diversity of hypotheses needed to explain these diverging records for example injections of 14c dead geological carbon mixing of extremely isolated waters from the abyssal ocean or changes in sites of deep water ventilation here we present absolutely dated deglacial deep sea coral 14c records of intermediate waters from the galapagos platform close to the largest reported deglacial 14c depletions together with data from the low latitude atlantic our records indicate coherent well equilibrated intermediate water 14c ventilation in both oceans relative to the atmosphere throughout the deglaciation the observed overall trend towards 14c enriched signatures in our records is largely due to enhanced air sea carbon isotope exchange efficiency under increasing atmospheric p rm co 2 these results suggest that the 14c depleted signatures from foraminifera are likely sedimentary rather than water mass features and provide tight 14c constraints for modelling changes in circulation and carbon cycle during the last deglaciation intermediate depth waters in the atlantic and pacific oceans were well equilibrated with the atmosphere through the last deglaciation according to radiocarbon data from deep sea corals

no signature of abyssal carbon in intermediate waters off chile during deglaciation the rise in atmospheric carbon dioxide at the end of the last glacial maximum has been attributed to the release of carbon dioxide from the deep southern ocean however reconstructions of the radiocarbon signature of chilean margin intermediate waters during the glacial termination do not reflect the influence of such a release

the geochemical evolution of anorthosite residual magmas in the laramie anorthosite complex wyoming olivine and pyroxene bearing fit enriched dioritic rocks in the 1434 ma laramie anorthosite complex are interpreted to represent variably fractionated and contaminated magmas residual after the crystallization of anorthosite geochemical characteristics of this suite include the following high contents ofti02 fe20s and p2o5 high incompatible trace element contents rare earth element patterns with a large range of eu anomalies and isotopic compositions that reflect the geographic location of individual samples with i r increasing and ejy decreasing from south to north after extraction from anorthosite fractionation offerrodioritic residual magmas resulted in secondary residual monzpdioritic melts and complementary oxide rich ferrodiorite cumulates geographic trends in isotopic composition reflect an increasing archean crustal component from south to north dioritic dikes and cumulates with isotopic compositions similar to associated anorthosites were derived locally large isotopic discrepancies between some diorites and their hosting anorthosites reflect preferential contamination of residual magma during ascent and emplacement of mantle derived plagioclase rich diapirs followed by subsequent extraction and isolation of fe enriched interstitial melt strong isotopic contrasts between anorthosite and associated fe enriched rocks in anorthosite complexes do not preclude a direct relationship between them and reflect the diversity and complexity of processes during their petrogenesis

does the oxidation of methane leave an isotopic fingerprint in the geologic record 1 pore water co2 and 13c data are presented for the dysoxic santa barbara and santa monica basins in an attempt to constrain the influence of methane oxidation on the pore water gradients and benthic foraminiferal 13c although these two basins are adjacent to one another santa barbara basin has steeper pore water co2 and 13c gradients methane oxidation could be contributing to the higher gradients in this basin the isotope mass balance for pore water co2 indicates however that the pore water gradients in the upper 2 cm of both basins are controlled only by the rate of photosynthate carbon oxidation and the rate of diffusion methane derived co2 has no discernable influence on pore water or carbonate 13c values at these sediment depths in either basin benthic foraminiferal species inhabiting different depth horizons in the top centimeter incorporate these steep isotopic gradients in their calcite tests and can be used therefore to reconstruct the history of carbon oxidation within the basins on the basis of these modern geochemical constraints a more likely explanation for the apparent 13c excursions recorded in the late pleistocene sediments from santa barbara basin involves enhanced carbon rain and carbon oxidation in the basin sediments rather than clathrate destabilization

ventilation history of nordic seas overflows during the last de glacial period revealed by species specific benthic foraminiferal 14c dates formation of deep water in the high latitude north atlantic is important for the global meridional ocean circulation and its variability in the past may have played an important role in regional and global climate change here we study ocean circulation associated with the last de glacial period using water column radiocarbon age reconstructions in the faroe shetland channel southeastern norwegian sea and from the iceland basin central north atlantic the presence of tephra layer faroe marine ash zone ii dated to 26 7 ka enables us to determine that the middepth 1179 m water depth and shallow subsurface reservoir ages were 1500 and 1100 14c years respectively older during the late glacial period compared to modern suggesting substantial suppression of the overturning circulation in the nordic seas during the late last glacial maximum and the onset of deglaciation 20 18 ka nordic seas overflow was weak but active during the early deglaciation 17 5 14 5 ka our data reveal large differences between 14c ventilation ages that are derived from dating different benthic foraminiferal species pyrgo and other miliolid species yield ventilation ages 6000 14c years while all other species reveal ventilation ages 2000 14c years these data either suggest subcentennial regional circulation changes or that miliolid based 14c ages are biased due to taphonomic or vital processes implications of each interpretation are discussed regardless of this enigma the onset of the bolling allerod interstadial 14 5 ka is clearly marked by an increase in middepth nordic seas ventilation and the renewal of a stronger overflow

the crustal tongue melting model and the origin of massive anorthosites recent detailed field studies in several anorthosite complexes have shown that anorthosites are frequently associated with weakness zones in the crust which may have favoured their emplacement at mid crust levels recent experimental data have shown that the parent magma compositions of various anorthosite massifs lie on thermal highs in the relevant phase diagrams at 10 13 kbar indicating that these magmas cannot be derived by fractionation of peridotitic mantle melts but by melting of gabbronoritic sources in the lower crust at 40 50 km depths in the sveconorwegian province terne boundaries have been traced in deep seismic profiles to moho offsets or to tongues of lower crustal material underthrust to depths higher than 40 km in southern norway we suggest that a lithospheric scale weakness zone the feda transition zone has channelled the rogaland anorthosites through linear delamination asthenospheric uprise and melting of a mafic lower crustal tongue

geochemical constraints of the petrogenesis of the o okiep koperberg suite and granitic plutons in namaqualand south africa a crustal source in namaquan grenville times the namaquan grenville orogeny late mesoproterozoic in the o okiep district is characterized by two tectono magmatic episodes the o okiepian episode 1210 1180 ma with the intrusion of batholitic granites and the klondikean episode 1040 1020 ma which includes the intrusion of the copper bearing koperberg suite and the rietberg granite this study focuses on the geochemistry major and trace elements sr and nd isotopes of intrusive rocks of the o okiep terrane to provide better constraints on their source rock characteristics and on their petrogenesis the o okiepian granites belong to the k rich granite kindred with shoshonitic affinities the concordia granite results from dehydration melting of a pelitic source the rietberg granite shows geochemical similarities with post collisional magmatic series the anorthosites and related rocks of the koperberg suite are cumulates their ree distribution is controlled by their apatite content a new rock type jotunite has been identified in the koperberg suite it is analogous to the rogaland chilled jotunite a characteristic which gives strong evidence that the koperberg rocks belong to the massif type anorthosite suite inversion modelling of plagioclase ree compositions from anorthosite permits the reconstruction of melt compositions and places constraints on the melting process and on the characteristics of the source rocks the occurrence of jotunite in the koperberg suite is strong additional evidence for a crustal source because jotunite is produced by remelting of gabbronorite under dry conditions the various intrusions in the koperberg suite show distinct isotopic signatures which resulted from isotopic heterogeneities of the crustal source and from minor contamination with the country rocks the characteristic negative end 1030 ma values 5t o 11 can be explained by remelting at 1030 ma of a 1900 ma old oceanic crust protolith with an enriched morb ree distribution the large range in sr initial ratios 0 709 0 748 may reflect hydrothermal alteration of the oceanic crust a process which may also explain the cu enrichment the koperberg intrusions were produced by forceful injection of cumulate crystal mush which were differentiated in deeper magma chambers or in conduits

the north eastern polish anorthosite massifs petrological geochemical and isotopic evidence for a crustal derivation deeply buried 1 5 ga polish anorthosites accessible only by bore holes reveal diagnostic features of some massif type anorthosites polybarism jotunitic parent magma diapirically emplaced in the mid crust together with the rapakivi granites of the ew trending mazury complex intruded along a major crustal discontinuity geochemical modelling and isotope data corroborate recent experimental work on the basaltic system in dry conditions the source rock of the parental magma is a gabbronorite necessarily lying in the lower crust since no archaean crust is known in the region high initial 188 os 187 os ratios for sulphide oxide isochrons and negative end values are best accounted for by melting a 2 0 ga mafic crust

geochemical polarity of the early cretaceous gambier group southern coast belt british columbia the gambier group of the southern coast belt was developed on the eastern edge of the wrangellia terrane in early cretaceous time a u pb zircon age determination from rhyolite produced a date of 112 0 0 3 ma consistent with albian fauna in sedimentary units major element geochemistry of volcanic rocks from separate east northeast and southwest volcanic centres displays both tholeiitic and calc alkalic affinities across the axis of the coast belt however assemblages in the east northeast have higher feot mgo ratios highlighting a more pronounced tholeiitic trend and are characterized by high al basalts volcanic rocks in the southwest are enriched in k trace element variations feature a southwesterly increase in ba rb and zr ti towards more alkalic values and a decrease in sr when compared with across arc geochemical trends from numerous other arcs the data may be interpreted to suggest that the gambier arc was east facing above a west to southwest dipping subduction zone such an interpret

oceanic export of relict carbon by small mountainous rivers small mountainous rivers smr export globally significant quantities of particulate organic carbon poc to the oceans the composition of which may be distinct from poc delivered by major world rivers to better constrain the controls on the 14c signatures of poc suspended in smr we examined the temporal variability of 14c and 13c of poc suspended in the santa clara river a smr in california usa our data suggest mixing of bedrock and contemporary soil which can be applied to other smr in contrasting climate zones and with varying land cover the data also suggest that chemical denudation is incomplete but effective to the point that only the most recalcitrant moieties of the parent poc are exported we further propose sediment yield as a potentially useful proxy for the 14c of riverine poc a preliminary analysis of the existing data for a spectrum of rivers supports this hypothesis

a late paleoproterozoic 1 80 ga subduction related mafic igneous suite from lomza ne poland the lomza orthoamphibolites in the crystalline basement of ne poland dated at 1802 9 ma by shrimp zircon u pb are characterized by high incompatible and ree element contents these features the low nb and the position of the rock compositions on la y nb zr nb zr and zr nb y tectonomagmatic discrimination diagrams suggest that the metavolcanics formed in a subduction setting possibly within a continental margin island arc the likely extension of the belt of paleoproterozoic mafic magmatism from latvia and lithuania into ne poland provides convincing evidence for the existence of an active plate margin in that region at that time

petrologic structural and age relations of serpentinite amphibolite and blueschist in the shuksan suite of the iron mountain gee point area north cascades washington part of the shuksan blueschist terrane near iron mountain and gee point north cascades washington has associated serpentinite amphibolite barroisite schist blueschist rare eclogite and blackwall type metasomatic rock field petrographic and microprobe observations indicate that the amphibolite and barroisite schists were metamorphosed in contact with peridotite and suggest that the peridotite may have been a heat source the serpentinite and associated rocks are structurally concordant with the regional blueschists and have been overprinted by blueschist metamorphism isotopic dating gives metamorphic ages of 148 5 to 164 6 m y for the amphibolite and barroisite schist and 129 5 m y for nearby regional shuksan blueschists the origin of the serpentinite amphibolite blueschist assemblage is interpreted to be the result of sequential events in a subduction zone as subduction began oceanic crustal materials underwent high temperature metamorphism along the hot ultramafic hanging wall and were converted to amphibolites materials that were subducted later came in contact with a cooler hanging wall and recrystallized as blueschist this hypothesis may be applicable to the origin of similar rock associations in the franciscan terrane and other orogenic belts

petrogenesis of a mid proterozoic anorthosite mangerite charnockite granite amcg complex isotopic and chemical evidence from the nain plutonic suite the nain plutonic suite nps about 1 30 ga underlies some 19 000 km intruding the boundary between middle to late archean rocks in the east nain province and late archean and early proterozoic rocks in the west churchill province nd isotopic compositions in most igneous units of the nps reflect their geographic position relative to the inferred boundary between the nain and churchill provinces rare exceptions are local intrusions of olivine bearing basic rocks with highest epsilon nd 1 3 ga near 3 0 present in both eastern and western sectors of the nps anorthositic rocks have variable and significant contributions of crustal nd but notably lower i sr than granitoid rocks ferrodiorites are similar isotopically to the anorthositic group and have chemical and mineral compositions more akin to the anorthositic group than the granitoids aluminous orthopyroxene megacrysts in nps anorthositic rocks indicate crystallization pressures of 6 2 to 11 0 kbar consistent with lower cru

structural and metamorphic history of the shuksan metamorphic suite in the mount watson and gee point areas north cascades washington the blueschist facies shuksan metamorphic suite of the north cascades has relict stratigraphy and sediment composition suggesting that it is of oceanic origin broadly defined the first metamorphic event affecting the rocks which probably occurred on the sea floor is a static epidote metasomatism of wide extent the earliest penetrative structures l 1 s 1 formed during latest jurassic early cretaceous blueschist facies metamorphism which is inferred to have occurred during subduction in this event recrystallization and intense penetrative strain were closely linked late metamorphic isoclinal fold axes f 2 and later crenulations l 3 formed at high angles to the l 1 lineation f 2 folds reflect extreme shortening perpendicular to the axis of the shuksan belt microscopic textural relations indicate that ca amphibole not na amphibole was stable during the development of f 2 and suggest that these structures record events related to uplift of the suite l 1 and f 2 structures can be interpreted to indicate either that uplift was the result of a distinct tectonic event or that metamorphism and uplift were part of a continuous tectonic process with no change in the stress field final emplacement of the shuksan suite occurred along a fault system which at least locally is high angle and includes zones of tectonic melange

geochronology of blueschists from west central baja california and the timing of uplift in subduction complexes a geochronologic study of blueschists from west central baja california has provided constraints on the timing of high pressure low temperature metamorphism and the subsequent uplift of this subduction complex mineral separates from coherent blueschists and blueschist blocks enclosed in serpentinite melange were analyzed by 40 ar 39 ar fission track and rb sr methods 40 ar 39 ar age spectra for white mica separated from four blueschist blocks and an overprinted eclogite block in serpentinite matrix melange show slow cooling gradients between 115 95 ma rb sr apparent ages for one block are concordant with these results 40 ar 39 ar ages of blue amphibole are primarily the result of the degassing of white mica intergrowths as confirmed by microprobe analyses apatite fission track ages indicate a blueschist block and an eclogite block cooled to a temperature below 100 c at 22 ma and 32 ma respectively subduction related metamorphism of the coherent blueschists occurred in la

in situ u pb and lu hf isotopic studies of zircons from the sancheong hadong amcg suite yeongnam massif korea implications for the petrogenesis of 1 86 ga massif type anorthosite abstract isotopic and geochemical characteristics of proterozoic anorthosite mangerite charnockite granite amcg suite have long been used for tracing the mantle crustal source and magmatic evolution we analyzed lu hf isotopic compositions of zircon from the sancheong hadong amcg complex yeongnam massif korea in order to understand tectonomagmatic evolution of the paleoproterozoic amcg suite occurring at the southeastern margin of the north china craton ncc the anorthositic rocks in this complex associated with charnockitic and granitic gneisses were recrystallized to eradicate magmatic features in situ shrimp sensitive high resolution ion microprobe u pb analyses of zircon from a leuconorite and an oxide bearing gabbroic dyke yielded weighted mean 207 pb 206 pb ages of 1870 2 ma and 1861 6 ma respectively charnockitic granitic and porphyroblastic gneisses yielded weighted mean 207 pb 206 pb zircon ages of 1861 6 ma 1872 6 ma and 1873 4 ma respectively these crystallization ages together with our previous geochronological data for anorthosites 1862 2 ma are indicative of episodic amcg magmatism over an 10 ma interval initial e hf t values of zircon analyzed from five anorthositic rocks and four felsic gneisses range from 2 1 to 6 1 and 0 3 to 5 4 respectively zircon hf isotopic data in combination with available whole rock sr nd isotopic data suggest that anorthositic parental magma was most likely derived from a mantle source and variably affected by crustal contamination this crustal component is also reflected in charnockitic granitic magmas produced primarily by the melting of lower crust taken together the amcg magmatism at 1 87 1 86 ga in the yeongnam massif is most likely a late orogenic product of paleoproterozoic ncc amalgamation tectonically linked to assembly of the columbia supercontinent

petrology and isotope geochemistry of the mesoproterozoic anorthosite and related rocks of the kunene intrusive complex nw namibia abstract the intrusion of the large c 18 000 km2 anorthosite body of the kunene intrusive complex angola namibia which is associated with minor marginal granite bodies and syenite syenodiorite dykes marked the beginning of mesoproterozoic igneous activity in nw namibia anorthosites display an igneous mineral assemblage of dominating plagioclase together with minor olivine orthopyroxene or clinopyroxene fe ti oxides whereas biotite and pargasite are late magmatic phases apatite is a common accessory phase in regionally associated felsic rocks k feldspar plagioclase clinopyroxene and or hastingsite crystallized first followed by interstitial quartz hastingsite fe ti oxides and titanite the general geochemical characteristics for the anorthositic rocks of the kunene intrusive complex i e high al2o3 cao sr and eu intermediate to high mg numbers of 0 37 0 74 positive nd t values of 3 0 to 1 0 and initial sr ratios of 0 7028 0 7041 are in excellent agreement with their derivation from fractionated basaltic liquids the 18o values obtained for plagioclase 5 88 0 19 18o support their development from mantle derived magmas relic crustal xenoliths of calc silicate rocks and sr and nd isotope data however suggest that the anorthosite magma underwent minor crustal contamination which was most prominent during the early intrusion stage a u pb zircon age of 1376 2 ma was obtained for a felsic rock associated with the 1385 25 ma anorthosites which suggests that the two suites were emplaced during the same igneous event the geochemical and isotope signatures of the granites syenites and syenodiorites provide convincing evidence against consanguinity of the anorthositic and the felsic rock suites i e 1 a compositional gap exists between the major and trace element contents of the two suites 2 trace element and sr and nd isotopic data of the felsic rocks point to a crustal source nd 2 0 to 0 4 initial sr ratio 0 7024 0 7063 3 the ree patterns of the felsic rocks do not exhibit ubiquitous negative eu anomalies which would be expected from fractionation products of melts that previously formed extensive plagioclase cumulates and 4 18o values of magmatic feldspar from the felsic rock suite fall in a restricted range 7 20 7 92 that is about 1 6 higher than the average igneous plagioclase 18o of the anorthosites and suggests a formation of the felsic melts by anatexis of the lower crust

apparent synchroneity of submillennial scale climate events between greenland and santa barbara basin california from 30 10 ka abstract evidence is presented from odp hole 893a santa barbara basin for possible synchroneity between greenland and california margin submillennial climate change records during termination 1 and the last glacial maximum lgm planktonic foraminiferal isotope and faunal records are compared to the gisp2 18o records greenland for the interval between 30 and 10 ka using a new chronology based on 38 planktonic 14c dates apparent synchronous climatic events include interstadial is events 2 3 and 4 a broad warming trend between 21 and 19 ka and a broad cooling trend between 19 and 17 ka bolling and allerod warm episodes separated by the cooler older dryas event younger dryas cool episode and the preboreal the resulting tight correlation supports an intimate teleconnection between santa barbara basin surface waters and greenland air temperatures differences between greenland and santa barbara basin suggest that some regional variations were superimposed on the global pattern of climate change e g the pre bolling warming

a plate tectonic model for late jurassic ophiolite genesis nevadan orogeny and forearc initiation northern california recently published age and structural data allow the reconciliation of previously conflicting models for late jurassic genesis of the josephine smartville and coast range ophiolites and the nevadan orogeny in the klamath mountains and sierra nevada the resulting model is consistent with the mode of initiation location and geometry of the great valley forearc basin and with the lack of a significant forearc basin west of the klamath mountains the coast range ophiolite formed by backarc spreading west of an east facing intraoceanic arc soon thereafter a remnant arc was calved off the west side of this arc and the smartville ophiolite formed by backarc interarc spreading during this time the sierran phase of the nevadan orogeny began as the intraoceanic arc encountered the west facing continental margin arc of north america an east west trending calcalkaline dike swarm in the sierra nevada foothills may mark the trajectory of the colliding arcs at the initiation of the collision simultaneously a new subduction zone was initiated west of the collision suture zone and this new trench propagated southward thus trapping the coast range ophiolite in the new forearc area south of the klamath area intense deformation in the sierran region resulted from this collision and both magmatic arcs became inactive as the last remnant of intervening oceanic crust was subducted continued westward relative movement of the north american arc was permitted north of the sierra nevada owing to the lack of a colliding intraoceanic arc the result was the westward rifting of the continental margin arc by intraarc spreading which formed the josephine ophiolite in the klamath area the klamath phase of the nevadan orogeny resulted from contraction of the west facing intraoceanic arc and josephine backarc basin beneath the continental margin basal sediments of the great valley forearc basin were derived primarily from the sutured arc ophiolite terranes and were deposited on top of the coast range ophiolite the southern edge of the klamaths and the western side of the sierra nevada a new late mesozoic magmatic arc was superposed across the previously accreted terranes and formed the primary sediment source for the cretaceous forearc basin

ventilation of the deep southern ocean and deglacial co2 rise past glacial interglacial increases in the concentration of atmospheric carbon dioxide co2 are thought to arise from the rapid release of co2 sequestered in the deep sea primarily via the southern ocean here we present radiocarbon evidence from the atlantic sector of the southern ocean that strongly supports this hypothesis we show that during the last glacial period deep water circulating around antarctica was more than two times older than today relative to the atmosphere during deglaciation the dissipation of this old and presumably co2 enriched deep water played an important role in the pulsed rise of atmospheric co2 through its variable influence on the upwelling branch of the antarctic overturning circulation

structural geology and accretionary history of the northwest cascades system washington and british columbia pre tertiary rock units on the western flank of the cascades in washington and southern british columbia constitute the northwest cascades system nwcs this litho tectonic package is characterized by predominantly oceanic lithologies subjected to high p t metamorphism and structurally mixed to form a regional melange although the focus of this report is on rocks of the nwcs as originally defined survey of the regional geology suggests broadening of the limits of this system to include the san juan islands the pacific rim complex and pre tertiary rocks on the western flank of the central and southern washington cascades the shuksan metamorphic suite a relatively coherent and broadly exposed unit of the nwcs contains a regionally consistent stretching lineation which provides evidence of east northeast directed underthrusting subduction during the early cretaceous blue schist metamorphism metamorphic f2 folds are approximately normal to the stretching lineation and appear to have developed late in the same deformational event the melange structure postdates the high pressure regional metamorphism it is characterized by a tectonic assemblage of diverse and unrelated rock units occurring as fragments as much as 10 or more kilometres in breadth and separated by a network of low to high angle north northwest striking faults pre fault restoration is impossible argillaceous or serpentinitic material commonly occurs in deformation zones between more competent lithologies mylonite zones as much as several metres thick are widely developed and display stretched clast lineations indicating a north northwest south southeast transport direction for both low and high angle faults the high angle faults are therefore strike slip in nature shear sense indicators are mixed in thrust fault zones but many indicate dextral movement for the strike slip faults k ar whole rock ages of mylonites range from 20 127 ma but two late cretaceous ages of 87 and 91 3 ma are considered as best representing the time of faulting the inferred shift in direction of tectonic transport from east northeast west southwest during early cretaceous metamorphism to north northwest south southeast during late cretaceous faulting and melange formation is correlated with a mid cretaceous change in plate interaction between the north american and farallon kula plates from high to low angle convergence the nwcs melange is interpreted to have formed during large dextral transform motion along the continental margin and to have reached final emplacement by thrusting against the southern end of wrangellia and the coast plutonic complex

the 40ar 39ar geochronology of the pelona schist and related rocks southern california seventeen 40ar 39ar ages for hornblende celadonitic muscovite and biotite from the pelona orocopia rand and portal ridge por schists range from 39 to 85 ma the 85 ma is from portal ridge consistent with the proposed correlation of that body with the schist of sierra de salinas two muscovites and one hornblende from the rand schist have ages of 72 to 74 ma indistinguishable from the k ar age of 74 ma for hornblende from a posttectonic granodiorite that intrudes the schist but younger than the 79 ma u pb age of the intrusion four muscovite and two hornblende ages for schist and mylonite from the east fork area of the san gabriel mountains range from 55 to 61 ma similar to k ar ages from nearby upper plate rocks a third hornblende has an age of 73 ma but is not well constrained concordance of schist and upper plate ages confirms structural and metamorphic evidence that the vincent thrust in the san gabriel mountains has not undergone significant postmetamorphic disruption ages from the orocopia mountains are 75 ma for hornblende from nonmylonitic upper plate 52 ma for muscovite from structurally high orocopia schist that is mylonitic and 41 ma for muscovite from nonmylonitic orocopia schist these are consistent with field evidence that the orocopia thrust is a postmetamorphic normal fault muscovite and hornblende from the gavilan hills have ages of 48 to 50 ma younger than ages from the san gabriel mountains but similar to schist ages from the orocopia mountains the geochronologic and structural complexities of the vincent chocolate mountains orocopia and rand thrusts imply that previously cited northeastward vergence may not relate to prograde metamorphism subduction of the por schists the 40ar 39ar data indicate substantial uplift of the por schists prior to middle tertiary detachment faulting which confirms other geochronologic evidence of uplift in southern california and southern arizona during the late cretaceous early tertiary

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

oxygen isotope geothermometry and stability of lawsonite and pumpellyite in the shuksan suite north cascades washington metamorphic temperatures of 330 400 c are inferred for rocks from the shuksan blueschist terrane in the north cascades washington the temperatures are calculated from 18o fractionations between coexisting quartz and magnetite using the equations of bottinga and javoy 1973 pressures of approximately 7 kilobars are indicated by the jadeite content of clinopyroxene coexisting with quartz albite published experimental and theoretical studies of the stability of lawsonite and pumpellyite are consistent with the oxygen isotope temperatures and occurrence of these minerals in the shuksan suite

isotopic evidence for palaeoproterozoic accretion in the basement of the east european craton abstract the precambrian basement in the western part of the east european craton eec consists of a series of arcuate tectonic belts metamorphosed in amphibolite and granulite facies these are separated from each other by crustal discontinuities generally trending nne ssw in conjunction with previously published sm nd and u pb isotopic data the results reported now show that the basement between the baltic and ukrainian shields is palaeoproterozoic in age it was formed between 2 1 and 1 8 ga ago igneous rocks from the various arcuate belts generally have positive initial nd values between 1 and 3 thus they are essentially juvenile and contain little material derived from older continental crust most metasedimentary rocks in contrast contain a distinct component of older crustal materials this is demonstrated by initial nd values ranging from 1 to 3 and by the results of u pb multigrain and single grain sims analyses of detrital zircons the oldest magmatic activity in the region occurred 2 1 2 0 ga ago in the southeast along the margin of the archaean protocontinent of sarmatia two subsequent episodes of volcanism in the tectonic belts farther west have been dated at ca 2 0 and 1 87 ga using the u pb zircon approach the proterozoic volcanic rocks are thus younging towards the northwest away from sarmatia the high grade metamorphism that has been dated employing u pb in monazite and zircon is also younging from the southeast to the northwest its ages range from 1 95 to less than 1 79 ga the available data are explained best by accretionary plate tectonics these involved repeated episodes of generation of juvenile continental crust along and outboard of the margin of the dominantly archaean craton in sarmatia an andean type of geodynamic setting between 2 1 and 2 0 ga ago was succeeded by the formation of several island arcs and accretion of these onto the older continent between 2 0 and 1 8 ga subsequent compression of the newly formed crust lasted until ca 1 7 ga

neodymium strontium and lead isotopes in the maloin ranch pluton wyoming implications for the origin of evolved rocks at anorthosite margins abstract neodymium strontium and lead isotopic data are used in this study to investigate the origin of chemically evolved rocks in the maloin ranch pluton a composite body that borders and intrudes the laramie anorthosite the range of rock types present is similar to that found at the margins of proterozoic anorthosites throughout the world in the maloin ranch pluton these include ferrodiorite at the base of the intrusion overlain progressively by fine grained monzonite monzosyenite and porphyritic granite biotite gabbro and fine grained granitic dikes are present locally at various levels of this sequence the origin of the evolved rocks and their possible relation to associated anorthositic bodies has been much debated in the maloin ranch pluton each rock type has distinct isotopic characteristics which together with trace element data previously reported suggest different source characteristics for each member strontium and neodymium isotopic data for maloin ranch ferrodiorite and laramie anorthositic rocks show considerable overlap consistent with a comagmatic relation biotite gabbro is chemically and isotopically the most primitive rock type in the maloin ranch pluton the data suggest that biotite gabbro has a mantle source but has undergone extensive fractionation in the crust our results suggest that the remainder and bulk of the intrusion formed by partial melting of the lower crust due to the emplacement of the laramie anorthosite maloin ranch fine grained monzonite is chemically more evolved than the underlying ferrodiorite i e lower mg higher silica and alkalis yet has more primitive isotopic characteristics lower isr higher epsilonnd formation of fine grained monzonite by in situ fractionation of ferrodiorite is precluded by both the isotopic data and by mass balance the isotopic data do not rule out formation of fine grained monzonite by fractionation or contamination of ferrodiorite at depth but this model requires that the ferrodiorite is isotopically heterogeneous and that very large volumes of ferrodiorite were present alternatively trace element and isotopic characteristics of the fine grained monzonite are explained by partial melting of mantle derived lower crust added to the margin of the archean wyoming craton at about 1 8 ga neodymium strontium and lead isotope data for maloin ranch monzosyenite and porphyritic granite also suggest a lower crustal source these data indicate a 1 8 ga source component for the maloin ranch monzosyenites but do not require input of archean crust from the wyoming province to the north

ventilation changes in the northeast pacific during the last deglaciation under present climate conditions convection at high latitudes of the north pacific is restricted to shallower depths than in the north atlantic to what extent this asymmetry between the two ocean basins was maintained over the past 20 kyr is poorly known because there are few unambiguous proxy records of ventilation from the north pacific we present new data for two sediment cores from the california margin at 800 and 1600 m depth to argue that the depth of ventilation shifted repeatedly in the northeast pacific over the course of deglaciation the evidence includes benthic foraminiferal cd ca 18o 16o and 13c 12c data as well as radiocarbon age differences between benthic and planktonic foraminifera a number of features in the shallower of the two cores including an interval of laminated sediments are consistent with changes in ventilation over the past 20 kyr suggested by alternations between laminated and bioturbated sediments in the santa barbara basin and the gulf of california keigwin and jones 1990 kennett and ingram 1995 behl and kennett 1996 data from the deeper of the two california margin cores suggest that during times of reduced ventilation at 800 m ventilation was enhanced at 1600 m depth and vice versa this pronounced depth dependence of ventilation needs to be taken into account when exploring potential teleconnections between the north pacific and the north atlantic

reconstructing benthic carbon oxidation rates using δ13c of benthic foraminifers abstract in non bioturbated organic rich marine sediments the concentration and carbon isotope gradient of total dissolved carbon dioxide co2 primarily reflects the rate of carbon oxidation and co2 diffusion within the sediment pore waters here we investigate whether the calcium carbonate secreted by benthic foraminifers that inhabit discrete depths within the sediments record the pore water 13c co2 gradient and hence can be used as proxies to reconstruct a history of carbon oxidation change the distribution and live abundance of bolivina argentea s l bolivina subadvena s l and buliminella tenuata inhabiting the dysoxic marine sediments along the california margin is similar among sites that differ in co2 gradient by up to a factor of three bolivina argentea inhabits the sediments at the sediment water interface whereas b subadvena s l is most abundant at depths of between 2 and 4 mm buliminella tenuata is most abundant at deeper depths of between 4 and 6 mm the 13c of calcite precipitated by these species matches the 13c of the pore water co2 at the depth of their maximum live abundance indicating that each species has a preferred depth for calcification the 13c difference between the species increases as the rate of carbon oxidation increases these results indicate the carbon isotopic difference between these species in fossil assemblages can be used to estimate changes in the rate of carbon oxidation

contribution of ductile flow to exhumation of low temperature high pressure metamorphic rocks san juan cascade nappes nw washington state the san juan cascade sjc nappes were subducted to a depth of 18 km metamorphosed under low temperature high pressure conditions and then exhumed all within 16 m y during exhumation penetrative deformation by solution mass transfer smt resulted in a widespread spaced cleavage strain directions were determined for 27 sandstone samples and absolute strain measurements for a subset of 19 samples z directions generally plunge moderately to the ne and x and y directions are scattered in the plane perpendicular to z smt deformation is constrictional at the local scale but the tensor average indicates plane strain uniaxial shortening at the regional scale with sx sy and sz equaling 1 01 0 91 and 0 58 respectively the average flattening plane xy dips 30 to the ne and the average x direction plunges 20 to the north the large shortening in z was compensated by a mass loss volume strain of 47 we present a simple one dimensional model that illustrates the relationship between finite strain and ductile exhumation for a steady state convergent wedge assuming depth dependent ductile flow and no reversal of principal strain rates with depth this model indicates that ductile thinning of the sjc nappes accomplished only 13 of the total exhumation despite a vertical shortening strain of 36 there is no evidence that normal faulting contributed significantly to exhumation we conclude that erosion operating at an average rate of 1 1 km m y 1 was the dominant exhumation process

orogenic to post orogenic origin for the 1 76 ga horse creek anorthosite complex wyoming usa the age and inferred tectonic setting of the 1 76 ga horse creek anorthosite complex hcac in the laramie mountains of southeastern wyoming place important constraints on the origin of middle proterozoic anorthosite complexes the 100 km2 hcac consists of strongly recrystallized anorthosite and two small intrusions of monzonite and granite u pb crystallization ages from euhedral zircons in anorthosite and monzonite are 1761 5 2 ma and 1754 5 2 2 ma respectively an additional period of zircon growth in the anorthosite occurred at 1753 4 2 ma as represented by a small population of anhedral zircon we attribute the origin of this second morphological variety of zircon in the anorthosite to the loss of zr from ilmenite during reaction with plagioclase to form sphene this reaction took place in response to heat and fluid influx during intrusion of the adjacent monzonite the hcac and the younger 1 43 ga laramie anorthosite complex to the north were intruded along or near a paleoproterozoic suture

paleomagnetic evidence for displacement from the south of the coast plutonic complex british columbia the mid cretaceous spuzzum and porteau plutons of the coast plutonic complex of british columbia have two magnetizations a and b the a magnetization eight sites 83 specimens d 30 3 i 56 7 95 4 9 paleolatitude 37 5 n paleopole 65 0 n 14 9 w a95 6 2 is considered to have been acquired in the age range 105 90 ma this result differs from the field established for cratonic north america in this time range the difference could be caused either by previously undetected tilting about a horizontal axis of the plutons or by their rotation about a vertical axis and lateral displacement relative to the craton previously observed mid cretaceous magnetizations from other rock units from the western canadian cordillera and the cascades of washington united states are similarly discordant with respect to the craton this similarity over such a large area indicates that although local undetected tilting could be partly responsible it is unlikely to be the prime cause and we argue ther

some phase equilibrium constraints on the origin of proterozoic massif anorthosites and related rocks experimental data in the range of 1 bar to 13 kbar enable us to introduction map the liquidus equilibria relevant to proterozoic massif anorthere is hardly a consensus on the petrogenesis of thosites and related mafic rocks massif anorthosites are widely proterozoic massif anorthosites but many investigators believed to have formed by accumulation of plagioclase into highbelieve in a petrogenetic scheme that involves at least al basaltic liquids mantle derived basaltic liquids fractionating two major stages 1 extensive crystallization asat pressures sufficiently high 10 13 kbar to crystallize the highly similation of a mantle derived magma ponded at or aluminous orthopyroxene megacrysts typically observed in anorthosite near the base of the crust that produces suspensions of massifs reach plagioclase saturation at low normative silica contents plagioclase in fe rich high al gabbroic liquids followed peritectic like equilibria e g liq opx plag cpx sp by 2 intrusion of these suspensions into the mid upper and a thermal divide on the plagioclase pyroxene liquidus surface crust where they form complex magma chambers e g ensure that mantle derived liquids become nepheline normative with duchesne 1984 emslie 1985 ashwal 1993 wiebe further crystallization and crustal assimilation at depth such 1994 a key component of the scheme is the presence liquids cannot produce the full range of troctolitic noritic to trocin most massifs of high al orthopyroxene megacrysts tolitic gabbroic mineral assemblages observed in anorthosite massifs haom emslie 1975 that appear to preserve a record without extensive low pressure granite assimilation conversely the of the high pressure stage maquil duchesne 1984 array of plausible anorthosite parental liquids not only lies along longhi et al 1993 the structures of massifs vary from the trace of the plagioclase two pyroxene cotectic from 10 to 13 those that are composites of multiple diapiric intrusions kbar but also straddles the thermal divide on the plagioclase harp lake emslie 1980 rogaland duchesne 1984 pyroxene liquidus surface this condition requires mafic source to intrusive bodies with well developed layering of regions such as lower continental crust or foundered mafic plutons leucocratic troctolites and leuconorites or leucogabbros for liquids parental to massif anorthosites and associated mafic overlain by masses of anorthosite michikamau emslie intrusions 1970 laramie frost et al 1993 so there may be

correlation of early cretaceous blueschists in washington oregon and northern california the protolith and metamorphic histories of early cretaceous blueschists that occur in washington oregon and california are remarkably similar these blueschists are the shuksan metamorphic suite of northwestern washington the condrey mountain schist of northern california and southern oregon and the pickett peak terrane of northern california and southwestern oregon we suggest that these bodies were coextensive during their formation dispersion of the blueschists occurred in late cretaceous time by lateral translation of up to 900 km along the continental margin in response to oblique plate convergence

radiocarbon age anomaly at intermediate water depth in the pacific ocean during the last deglaciation 1 benthic and planktonic 14c ages are presented for the last glacial termination from marine sediment core vm21 30 from 617 m in the eastern equatorial pacific the benthic planktonic 14c age differences in the core increased to more than 6000 years between heinrich 1 time and the end of the younger dryas period several replicated 14c ages on different benthic and planktonic species from the same samples within the deglacial section of the core indicate a minimal amount of bioturbation scanning electron microscopy reveals no evidence of calcite alteration or contamination the oxygen isotope stratigraphy of planktonic and benthic foraminifera does not indicate anomalously old glacial age values and there is no evidence of a large negative stable carbon isotope excursion in benthic foraminifera that would indicate input of old carbon from dissociated methane it appears therefore that the benthic 14c excursion in this core is not an artifact of diagenesis bioturbation or a pulse of methane a benthic 14c stratigraphy reconstructed from the 14c ages from the deglacial section of vm21 30 appears to match that of baja margin core mv99 mc19 gc31 pc08 705 m but the magnitude of the low 14c excursion is much larger in the vm21 30 record this would seem to imply that the vm21 30 core was closer to the source of 14c depleted waters during the deglaciation but the source of this co2 remains elusive

biotic response to late quaternary rapid climate switches in santa barbara basin ecological and evolutionary implications benthic foraminiferal assemblages from santa barbara basin exhibit major faunal and ecological switches associated with late quaternary millennial to decadal scale global climate oscillations repeated turnovers of entire faunas occurred rapidly 40 400 yr without extinction or speciation in conjunction with dansgaard oeschger shifts in thermohaline circulation ventilation and climate confirming evolutionary model predictions of roy et al consistent faunal successions of dysoxic taxa during successive interstadials reflect the extreme sensitivity and adaptation of the benthic ecosystem to the rapid environmental changes that marked the late quaternary and possibly other transitional intervals in the history of the earth s ocean atmosphere cryosphere system these data support the hypothesis that broad segments of the biosphere are well adapted to rapid climate change

re os isotopic evidence for a lower crustal origin of massif type anorthosites massif type anorthosites are large igneous complexes of proterozoic age they are almost monomineralic representing vast accumulations of plagioclase with subordinate pyroxene or olivine and fe ti oxides the 930 myr old rogaland anorthosite province in southwest norway1 represents one of the youngest known expressions of such magmatism the source of the magma and geodynamic setting of massif type anorthosites remain long standing controversies in precambrian geology with no consensus existing as to the nature of the parental magmas or whether these magmas primarily originate in the earth s mantle or crust at present massif type anorthosites are believed to have crystallized from either crustally contaminated mantle derived melts that have fractionated olivine and pyroxenes at depth2 or primary aluminous gabbroic to jotunitic melts derived from the lower continental crust3 here we report rhenium and osmium isotopic data from the rogaland anorthosite province that strongly support a lower crustal source for the parental magmas there is no evidence of significantly older crust in southwest scandinavia and models invoking crustal contamination of mantle derived magmas fail to account for the isotopic data from the rogaland province initial osmium and neodymium isotopic values testify to the melting of mafic source rocks in the lower crust with an age of 1 400 1 550 myr

arc parallel extension and fluid flow in an ancient accretionary wedge the san juan islands washington structural analysis of the lopez structural complex a major late cretaceous terrane bounding fault zone in the san juan thrust system reveals a sequence of events that provides insight into accretionary wedge mechanics and regional tectonics after formation of regional ductile flattening and shear related fabrics the area was crosscut by brittle structures including 1 southwest vergent thrusts 2 extension veins and normal faults related to northwest southeast extension and 3 conjugate strike slip structures that record northwest southeast extension and northeast southwest shortening aragonite bearing veins are associated with thrust and normal faults but only rarely with strike slip faults high pressure low temperature hp lt minerals constrain the conditions for brittle deformation to 20 km and

geochemical constraints on the genesis of the tellnes ilmenite deposit southwest norway the ilmenite norite of the tellnes fe ti deposit in the aana sira massif type anorthosite is connected to a main dike which varies in composition from monzonorite to quartz mangerite fine grained satellite dikes also occur in the vicinity of the main dike a number of rock samples have been analyzed for 36 major and trace elements an rb sr whole rock isochron 12 samples gives an age of 930 ma initial sr isotope compositions of the ilmenite noritc the main dike and the satellite dikes are 0 7050 0 7069 and 0 7100 respectively thus precluding a comagmatic origin without invoking contamination the evolution of the main dike can be accounted for by a closed system fractional crystallization of a monzonoritic magma that is without progressive contamination which gave rise to a series of liquids prior to intrusion mass balance calculation permits a two stage process in which noritic cumulates were subtracted trace element behavior is also consistent with such a model the satellite dikes represent undifferentiated monzonorites with trace elements and isotopic ratios implying a source material quite different from that of the main dike monzonorite the orebody is made up of ilmenite norite and small amounts of more plagioclase rich rocks which plot on linear trends in variation diagrams it is interpreted as a noritic cumulate which was enriched in dense oxide rich magma before being emplaced as a crystal mush the parental magma was noritic in composition unsaturated in apatite and probably derived from the crystallization of the enclosing massif anorthosite it is not precluded either that it could have given rise to the main dike monzonoritic liquid after being contaminated by lower crustal material nevertheless as an alternative it is not possible to reject two distinct parental magmas for the orebody and the main dike they would have evolved in two separated magma chambers before the tapping of these chambers and simultaneous injection of their contents in the dike the main dike illustrates the process by which a quartz mangerite can derive from a monzonoritic magma and gives support to a comagmatic origin of charnockitic and monzonoritic rocks

significance of 1 5 ga zircon and monazite ages from charnockites in southern lithuania and ne poland abstract the presence of 1 52 1 50 ga charnockites from the anorthosite mangerite charnockite granite amcg mazury complex in southern lithuania and ne poland in the western east european craton eec is revealed by secondary ion mass spectrometry sims and epma geochronology early 1 85 1 82 ga charnockites are related to major orogeny in the region whereas the newly studied charnockites intrude the already consolidated crust the 1 52 1 50 ga charnockite magmatism sims data on zircon was followed by high grade metamorphism epma data on monazite which strongly affected the surrounding rocks the 1 85 1 81 ga zircon cores in lazdijai and 1 81 ga monazite domains in the lanowicze charnockites represent the protolith age of a volcanic island arc the 1 52 1 50 ga charnockite magmatism and metamorphism are likely related to the distal danopolonian orogeny further to the west at the margin of baltica the c 1 52 1 50 ga amcg magmatism and metamorphism in the western eec as well as the paired accretionary rapakivi suites in amazonia may be the inboard manifestations of the same early mesoproterozoic orogeny associated with the juxtaposition of amazonia and baltica during the amalgamation of the supercontinent columbia

direct dating of adirondack massif anorthosite by u pb shrimp analysis of igneous zircon implications for amcg complexes the low abundance of igneous zircon in proterozoic massif anorthosites has presented a major obstacle to the acquisition of direct absolute ages of crystallization for these important rocks indirect dating that relies on zircon ages from associated mangerite charnockite granite granitoids assumes that they have a coeval relationship with anorthosite that requires documentation shrimp sensitive high resolution ion microprobe u pb zircon dating techniques provide a powerful means for directly dating the small populations of zircons in anorthositic rocks and for resolving problems with inheritance within the adirondack mountains 10 samples of massif anorthosite have yielded more than sufficient quantities of igneous zircon to establish directly the ages of the region9s classic anorthosite occurrences e g the marcy and oregon dome massifs in addition a ferrogabbro a ferrodiorite and a coronitic olivine metagabbro all crosscutting massif anorthosite were dated the average age of this suite of 13 anorthositic samples is 1154 6 ma mswd mean square of weighted deviates 0 26 probability 0 99 in addition eight associated granitoids have been dated by shrimp techniques and complement another five previously dated by multi grain thermal ionization mass spectrometry tims methods the 13 granitoids yield an average age of 1158 5 mswd 0 89 probability 0 60 and are broadly coeval with the massif anorthosite the overlapping ages provide evidence that these rocks constitute a single composite anorthosite mangerite charnockite granite amcg suite intruded at ca 1155 ma an age corresponding to the ages of major amcg suites in the grenville province in canada e g morin and lac st jean although rocks of the adirondack amcg suite are now documented as broadly coeval it does not follow that the constituent amcg lithologies were comagmatic field relationships and mineral disequilibria in transitional zones are inconsistent with derivation from a single parental magma moreover the presence of older ca 1 2 1 3 ga inherited cores in some zircons from amcg granitoids conflicts with derivation of these rocks from magmas that formed anorthosite gabbro or ferrodiorite or jotunite in which zircons are highly soluble the slightly older ca 1158 ma average age of the mangeritic and charnockitic members of the amcg suite is consistent with an origin as early lower crustal anatectites that left behind pyroxene plagioclase restites this refractory material then reacted by assimilation fractional crystallization afc with ponded mantle derived gabbroic magmas to produce plagioclase rich crystal mushes with crustal isotopic signatures as proposed much earlier by r f emslie these magmas are considered to be parental to the adirondack anorthosite and upon ascent they were emplaced in proximity to still hot earlier mangeritic and charnockitic bodies where they underwent further fractionation the composite nature of the marcy massif documents that this process was repeated in several sequential pulses

oscillatory sr isotopic signature in plagioclase megacrysts from the damiao anorthosite complex north china implication for petrogenesis of massif type anorthosite abstract formation of proterozoic massif type anorthosites is known to be related to polybaric process involving early high pressure crystallization of plagioclase and high al orthopyroxene megacrysts at mantle crust boundary followed by emplacement of plagioclase dominated mushes to shallow level crust therefore the plagioclase megacrysts record important information about the magmatic sources and crystallization process of anorthosites the 1 74 ga damiao complex north china comprises 90 vol anorthosites and leuconorites containing abundant plagioclase megacrysts associated with minor high al orthopyroxene megacrysts haoms the plagioclase megacrysts are generally euhedral to subhedral mostly 1 to 30 cm in diameter and some of them contain very fine lamellae of orthoclase and undefined fe ti rich minerals 1 5 m the haoms occur as subhedral grains or as angular grains with an intercumulus relationship to the plagioclase megacrysts they contain abundant thin regular lamellae of exsolved plagioclase 15 20 vol indicative of originally high al features originally 6 0 7 3 wt al2o3 based on the al in orthopyroxene geobarometry the haoms and associated plagioclase megacrysts are constrained to be crystallized together at pressures of 9 4 11 2 kbar 33 36 km indicative of their crystallization at lower crust depths or crust mantle boundary in contrast orthopyroxene grains from late differentiation phases such as oxide apatite gabbronorites do not contain plagioclase lamellae and have much lower al2o3 contents 1 5 to 1 7 wt indicating final crystallization at

marine radiocarbon evidence for the mechanism of deglacial atmospheric co2 rise we reconstructed the radiocarbon activity of intermediate waters in the eastern north pacific over the past 38 000 years radiocarbon activity paralleled that of the atmosphere except during deglaciation when intermediate water values fell by more than 300 per mil such a large decrease requires a deglacial injection of very old waters from a deep ocean carbon reservoir that was previously well isolated from the atmosphere the timing of intermediate water radiocarbon depletion closely matches that of atmospheric carbon dioxide rise and effectively traces the redistribution of carbon from the deep ocean to the atmosphere during deglaciation

correlation of settler schist with darrington phyllite and shuksan greenschist and its tectonic implications coast and cascade mountains british columbia and washington amphibolite facies settler schist in the southeastern coast mountains of british columbia has long been correlated with chiwaukum schist of the cascade metamorphic core north cascade mountains no

imbricate low angle faulting in uppermost franciscan rocks south yolla bolly area northern california the south yolla bolly area of northern california contains the intersection of the franciscan complex the klamath mountains and the great valley sequence four distinct lithic units among them the south fork mountain schist as well as several subunits have been discerned in the franciscan rocks of this area these units are composed mostly of coherent or semi coherent layered sedimentary and mafic igneous rocks and their metamorphic equivalents rather than melange and are arranged in largely upright parallel imbricate fault slices four major low angle faults have been clearly recognized paleontologic data indicate that at least one fault places older material over younger lithic units exhibit various degrees of differences in metamorphic mineral assemblages textural grade and amount of internal deformation across the faults with more intensely deformed and metamorphosed material occupying successively higher structural positions these contrasts indicate that some of these faults served as surfaces by which deformed rocks were emplaced differentially upward during and or after metamorphism original bedding and compositional layering in all of the coherent units generally parallel the thrust faults two fault bounded units are each composed of a coherent sequence of basalt at the base overlain by bedded chert and further overlain by mudstone and graywacke or their metamorphic equivalents the faults which underlie these two sequences seem to have originated as decollements localized at or near a sedimentary rock mafic crust interface perhaps as discrete underthrust slices the distinct contrasts in original rock composition among these units plus the aforementioned characteristics seem to indicate that these faults had an early history in the accretionary prism apart from their later use as convenient surfaces for differential upward emplacement of metamorphosed material

geochemical and nd hf isotopic constraints on the origin of the 1 74 ga damiao anorthosite complex north china craton abstract the 1 74 ga damiao complex in the north china craton consists of anorthosite 85 norite 10 mangerite 4 and minor troctolite 75 would have been required to form the parental high al gabbroic magma from the lower crust we propose that the crustal rocks were dragged into the upper mantle during amalgamation of the north china craton where the ambient temperature was high enough 1271 c at 12 kbar to cause extensive melting producing a deep seated magma chamber the melt then evolved through polybaric crystallization producing anorthositic magmas with abundant suspended plagioclase that were finally injected at mid crustal depth to form the damiao complex

a new look at old carbon in active margin sediments recent studies suggest that as much as half of the organic carbon oc undergoing burial in the sediments of tectonically active continental margins may be the product of fossil shale weathering these estimates rely on the assumption that vascular plant detritus spends little time sequestered in intermediate reservoirs such as soils freshwater sediments and river deltas and thus only minimally contributes to the extraneously old 14c ages of total organic matter often observed on adjacent shelves here we test this paradigm by measuring the 14c and 13c values of individual higher plant wax fatty acids as well as the 13c values of extractable alkanes isolated from the eel river margin california the isotopic signatures of the long chain fatty acids indicate that vascular plant material has been sequestered for several thousand years before deposition a coupled molecular isotope mass balance used to reassess the sedimentary carbon budget indicates that the fossil component is less abundant than previously estimated with pre aged terrestrial material instead composing a considerable proportion of all organic matter if these findings are characteristic of other continental margins proximal to small mountainous rivers then the importance of petrogenic oc burial in marine sediments may need to be reevaluated 2009 the geological society of america

commingling of magmas in the bjerkrem sogndal lopolith southwest norway evidence for the compositions of residual liquids a detailed re examination of some of the more fractionated portions of the bjerkrem sogndal lopolith bsl has provided evidence for widespread mixing between quartz mangeritic and monzonoritic eia rekefjord magmas the higher temperature monzonoritic liquids are preserved as chilled pillows within quartz mangerite chemical compositions of these and other fine grained monzonorites suggest that they are chilled residual liquids related to the bsl and that they were in equilibrium with the more fractionated cumulates of the bsl the chilled monzonoritic liquids appear to define a fractionation trend of increasing sio2 up to 60 wt the quartz mangerites appear to represent separate partial melts derived from the country rock

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

fe ti v p ore deposits associated with proterozoic massif type anorthosites and related rocks abstract magmatic rocks containing economic concentrations of iron titanium vanadium and phosphorous are commonly associated with massif type anorthosites and related rocks this rock association is part of the anorthosite mangerite charnockite rapakivi granite suites that are restricted to the proterozoic understanding the geochemistry and emplacement mechanisms of ilmenite magnetite and apatite ore deposits is crucial for exploration efficient mining operations and ore processing this review discusses the controlling factors on the grade of an ore its mineralogy and its major and trace element distribution we present petrogenetic models of currently mined deposits lac tio tellnes damiao and discuss the characteristics of minor ore bodies from anorthosite provinces worldwide grenville north china craton east european craton rogaland laramie models of formation of anorthosite and related rocks are presented as well as the nature of the possible parental magmas of the suite a mineralogical classification of fe ti ores is proposed 1 gabbro noritic ilmenite ore apatite magnetite 2 ti magnetite dominated ore 3 nelsonite fe ti oxides apatite and 4 rutile ilmenite ore the stability of ilmenite and magnetite is then critically reviewed and the influence of various factors particularly oxygen fugacity and crystallization pressure is examined we discuss liquidus compositions of fe ti oxides and the behavior of important trace elements such as cr and v both of which are sensitive to fo2 variations post cumulus evolution of both oxides can occur due to re equilibration with trapped liquid re equilibration with ferromagnesian silicates exsolution oxidation reaction between ilmenite and magnetite and metamorphic overprinting these various processes are described and their effects on the oxide geochemistry are emphasized several potential ore forming processes have been invoked and can explain the formation of huge concentration of ilmenite magnetite apatite fractional crystallization can be combined with crystal sorting and plagioclase buoyancy to produce relative enrichment of dense ore minerals silicate liquid immiscibility can segregate conjugate si rich and fe rich melts the latter being enriched in fe ti p magma mixing can produce hybrid magmas located in a single phase field of the phase diagram and precipitate a pure ilmenite cumulate alternative processes are also described such as ejection of fe ti enriched residual melts by filter pressing and compaction solid state remobilization of ilmenite in veins and hydrothermal transport of fe and ti from the host anorthosite followed by concentration in veins and lenticular ore bodies the magnetic properties of fe ti ore deposits present contrasting signatures depending on whether the natural remanent magnetization is dominated by hemo ilmenite or multi domain magnetite micro and macro scale deformation features of ore rocks are intimately correlated with magma emplacement and with ballooning of the anorthosite diapir associated with gravitational sagging of dense ore bodies exploration perspectives show that oxide apatite gabbronorites are interesting targets because ilmenite in these rocks is poorer in cr and mg and because the ti resource may be combined with apatite and vanadiferous magnetite

a neogene structural dome in the klamath mountains california and oregon regional structural doming of neogene age has affected rocks of the klamath and cascade mountains near the california oregon border evidence for this is seen in 1 subannular outcrop patterns of pre cretaceous lithotectonic units 2 a crude pattern of radially oriented high angle faults 3 tilted jurassic plutons 4 tilted cretaceous to miocene strata and 5 various geomorphological features the age of doming is constrained by a major middle miocene to earliest pliocene angular unconformity within the cascade mountains and uplifted upper miocene marine beds on the western edge of the klamath mountains uplift and doming may be the result of shortening in the cascade fore arc region or more speculatively the recent accretion of subducted material to the north american plate beneath the klamath mountains

towards reconstructing ancient seawater mg ca by combining porcelaneous and hyaline foraminiferal mg ca temperature calibrations the temperature of the deep ocean plays a vital role in the earth s climate system paleo reconstructions of deep sea temperatures have traditionally been based on the oxygen isotope composition of deep sea benthic foraminiferal calcite shells although this parameter depends upon polar ice volume as well as temperature more recent reconstructions use mg ca in these shells with temperature calibrations based on empirical relationships observed in present day oceans incorporation of mg dmg into foraminiferal calcite is however not solely dependent on temperature but also on seawater mg ca due to its long oceanic residence time mg concentrations remained relatively constant over time scales of a few hundred thousand years but varied significantly over longer geological time scales accurate reconstruction of past temperatures using foraminiferal mg ca therefore hinges on our understanding of mg ca seawater changes on geological timescales we explore a novel independent approach to reconstructing past seawater mg ca using the temperature dependent offset in dmg between porcelaneous secreting intermediate or high mg calcite abbreviated as imc or hmc respectively and hyaline producing low mg calcite abbreviated as lmc benthic foraminifera we calibrated the mg ca temperature dependence for pyrgo spp one of the few common large sized porcelaneous taxa present in the deep sea since the middle miocene and combined this with an existing calibration of hyaline cibicidoides spp to mathematically solve for changes in mg ca seawater through time we show that changes in mg ca seawater can be reconstructed using the offset between porcelaneous and hyaline foraminifera but absolute values are highly dependent on the species specific offset between mg ca seawater and mg partition coefficients

major right lateral faulting in the franciscan assemblage of northern california in late tertiary time a minimum of 75 km of right lateral fault displacement occurred within the franciscan assemblage of northern california most likely in late tertiary time this displacement is inferred from the present position of two geologically unrelated units the rocks near black lassie california and the redwood creek schist the black lassie rocks show at least 75 km of northward displacement from their source terrane within the coast range ophiolite although no conclusive evidence of northward transport for the redwood creek schist is available the geologic setting of the schist and the nature of the faults that bound it strongly suggest that the redwood creek schist has also been laterally transported many tens of kilometres northward we propose that both these units moved northward by means of one or a few major north northwest trending right lateral faults that were active in the forearc basin off the california coast during right oblique subduction of the farallon plate under the north american plate in late tertiary time

rare earth element geochemistry and strontium isotopic composition of a massif type anorthositic charnockitic body the hidra massif rogaland sw norway abstract the hidra massif rogaland complex sw norway mainly consists of plagioclase cumulates anorthosites and leuconorites which grade progressively into a fine grained 200 m locally porphyritic jotunitic rock towards the contact with the granulite facies gneisses the massif is cross cut by thin 10 cm up to 1 m charnockitic dykes the petrographical and geochemical evolution of the hidra massif can be explained by fractional crystallization of a jotunitic parental magma major and trace element constraints indicate that mafic phases are underabundant in the exposed levels of the massif most likely as a result of plagioclase flotation in the early stages of solidification partitioning into the cumulate minerals mainly plagioclase and orthopyroxene governs the trace element contents of the leuconoritic adcumulates however the trace element geochemistry of the apparently early formed anorthositic orthocumulates largely depends upon the amount of a trapped intercumulus liquid on the basis of trace element abundances high ree rb th u negative eu anomalies the silicic charnockitic dykes can be considered as the residual liquid of the anorthositic fractionation trend the higher initial 87 sr 86 sr ratios 0 7086 0 0006 vs 0 7055 0 0004 for the plagioclase cumulates and jotunites point to contamination of the charnockitic liquids by surrounding gneissic material

deformational history and regional tectonic significance of the redwood creek schist northwestern california structural petrologic and geochemical data support the correlation of the redwood creek schist of northwesternmost california with the south fork mountain schist of northern california and the colebrooke schist of southwestern oregon metamorphism to lawsonite albite chlorite facies and development of secondary structures recording two penetrative deformations are shared by all three units a later deformational event recorded by the redwood creek schist but absent in the south fork mountain schist consists of differential rotation of domains several kilometres in size within the schist belt this deformation is significant because it records an event that occurred after the separation of the schist bodies the rotation most probably occurred in conjunction with northward strike slip movement of the redwood creek schist

a 190 drop in atmosphere s δ14c during the mystery interval 17 5 to 14 5 kyr reconstructions of atmospheric 14c for the deglacial period reveal a 190 10 drop between 17 5 and 14 5 kyr before present during the mystery interval while it appears that the major contributor must be the mixing between an isolated low radiocarbon abyssal reservoir and the remainder of the ocean a combination of 14c measurements on coexisting benthic and planktic foraminifera shells and 13c 12c measurements on benthic foraminifera make it difficult to identify a sufficiently large volume for this reservoir an alternative scenario based on higher 14c production rates between about 38 and 18 kyr ago would escape the need for a large isolated reservoir prior to the mystery interval but instead would call for a better ventilated ocean afterwards the addition of 14c deficient sedimentary carbon appears not to be an important contributor while the unlikely explanation that the half life of 14c is 15 greater than the accepted value 5730 yr would eliminate the steady decrease in the 14c c over the last 40 kyr it would not explain the steep drop which occurred between 17 5 and 14 5 kyr

early cretaceous transition from nonaccretionary behavior to strongly accretionary behavior within the franciscan subduction complex 1 during subduction at the franciscan trench beginning at 170 160 ma and continuing to the present marine sedimentary and lesser volcanic rocks have been underthrust accreted and metamorphosed to form the franciscan accretionary wedge the south fork mountain schist sfms forms the eastern margin and structural top of the wedge and so was apparently the first unit of substantial size to accrete into the franciscan new u pb ages of detrital zircons and 40ar 39ar ages of metamorphic white micas indicate that the sfms accreted surprisingly late in the time span of franciscan subduction probably at ca 123 ma at least parts of the valentine spring formation and yolla bolly terrane accreted soon thereafter therefore accretion of the sfms apparently marks a fundamental transition from virtually nonaccretionary behavior to strongly accretionary behavior in the franciscan forearc about 75 of modern forearcs are nonaccretionary so recognition of an early nonaccretionary period is consistent with modern examples the franciscan mafic high grade exotic blocks and related very small slabs which yield ca 132 to 169 ma metamorphic ages are the only well documented rock record of the early 40 m y long nonaccretionary period and represent very sparse accretion during that interval the transition into an accretionary regime at ca 123 ma was essentially synchronous with the end of the late jurassic early cretaceous magmatic lull in the sierra nevada magmatic arc with the waning of early cretaceous faulting and warping within the great valley forearc basin and possibly with changes in motion vectors of the pacific and farallon plates

carbon isotope geochemistry of the santa clara river the santa clara river is a prototypical small mountainous river with a headwater height greater than 1000 m and a basin area smaller than 10 000 m 2 although individual small mountainous rivers export trivial amounts of sediment and carbon to the ocean as a group these rivers may export a major fraction as much as 50 of the total global river sediment flux milliman and syvitski 1992 making their geochemistry relevant the study of the ocean s carbon cycle in addition many small rivers export sediment in a few high flux events causing massive sporadic discharge of carbon onto coastal shelves discharge conditions very different from those of large rivers this class of rivers is an end member of the river ocean carbon exchange system opposite the earth s largest river the amazon the carbon mass and isotopic properties of the santa clara river are significantly different from previously studied large rivers during the 1997 1998 winter all santa clara carbon pools were old with flux weighted average l4c values of 428 76 for particulate organic carbon 73 31 for dissolved organic carbon and 644 58 for black carbon the age of exported carbon is primarily due to the deep erosion of old soils and not to inclusion of fossil fuel carbon additionally the 13c signatures of exported carbon pools were high relative to terrestrial carbon bearing a signature quite similar to marine carbon average particulate organic carbon poc 13c 22 2 0 8 the santa clara s estuary is small and drains onto the narrow eastern pacific coastal margin exporting this old soil organic matter directly into the ocean if the santa clara export patterns are representative of this class of rivers they may be a significant source of refractory terrestrial carbon to the ocean

the age of the lac saint jean anorthosite complex and associated mafic rocks grenville province canada u pb analyses of zircon and baddeleyite from the south central and southeastern parts of the lac saint jean anorthosite complex lsja give an igneous crystallization age of 1157 3 ma parts of the anorthosite were deformed in the solid state and subsequently intruded by a diorite megadyke which also gives a crystallization age of 1157 3 ma indicating that crystallization and deformation of the anorthosite were essentially synchronous the diorite megadyke was intruded into a north northeast trending shear zone and deformed by sinistral strike slip movements emplacement was followed by intrusion of a subparallel leucotroctolite megadyke that again gives the same crystallization age and hence dates movement of the shear zone at 1157 3 ma this short history of crystallization and synchronous deformation rules out slow diapiric rise as the emplacement mechanism for the anorthosite instead anorthosite parental magmas probably rose up offsets in subvertical strike slip shear zones to their present

resolving the cause of large differences between deglacial benthic foraminifera radiocarbon measurements in santa barbara basin 1 to better understand the deglacial upwelling pattern in the east pacific we have made radiocarbon 14c measurements on benthic foraminifera and macrofauna from a 3 5 m long interval in odp core 893a from santa barbara basin california representing early deglaciation this work serves to investigate the source of apparent disagreement between radiocarbon data sets from leibnitz laboratory kiel university kiel and carbon center for accelerator mass spectrometry lawrence livermore national laboratory llnl these data sets are based on measurements of mixed benthic and mixed planktonic foraminifera interlaboratory 14c results are similar for the planktonic foraminiferal analyses however kiel measurements on mixed benthic foraminifera are much older than mixed benthic measurements from equivalent depths measured at llnl our new results show distinct 14c differences between taxa with pyrgo sp giving ages consistently older than kiel measurements on mixed benthic taxa while ages for nonionellina sp buliminella sp uvigerina sp and benthic macrofauna were much younger even younger than the llnl mixed benthic data the new data supports benthic planktonic age offsets of no more than 300 years indicating that bottom waters within the basin remained significantly younger during early deglaciation than some previous results have suggested and are thus consistent with sedimentary and faunal evidence for well oxygenated conditions

radiocarbon variability in the western north atlantic during the last deglaciation we present a detailed history of glacial to holocene radiocarbon in the deep western north atlantic from deep sea corals and paired benthic planktonic foraminifera the deglaciation is marked by switches between radiocarbon enriched and depleted waters leading to large radiocarbon gradients in the water column these changes played an important role in modulating atmospheric radiocarbon the deep ocean record supports the notion of a bipolar seesaw with increased northern source deep water formation linked to northern hemisphere warming and the reverse in contrast the more frequent radiocarbon variations in the intermediate deep ocean are associated with roughly synchronous changes at the poles

the specific case of the mid proterozoic rapakivi granites and associated suite within the context of the columbia supercontinent abstract rapakivi granites and the associated suite anorthosite mangerite and charnockite that developed during the mid proterozoic escape the global rules that control usual granitic magma formation about 40 points that characterise the proterozoic magmatism confirm the originality of the magmatism rapakivi granites developed without a global orogenic context within the supercontinent columbia the intrusions extend from the east european shield to the western us through fennoscandia greenland and labrador other occurrences in the amazonian shield australia or south china are less well documented they show no definite trend in age or chemistry that would explain large scale mantle plume effects a mantle upwelling of material is contradictory with the re assembly of a supercontinent because it occurred before this magmatic episode 1 9 1 8 ga at 1 7 ga the supercontinent columbia amalgamated with the collision of the yapavai and mazatzal provinces a model is suggested that takes into account the supercontinent re assembly defining a downwelling flow in the mantle that anchors the continent above it in contrast to a material flow heat is still delivered to the base of the continental lithosphere and is focused toward the juvenile suture zone the base of the crust must reach 1200 1300 c before producing anorthosite magmas under such a high temperature gradient lasting over a long time magmas are transferred toward the upper crust giving the thin 5 km and square shape 100 km that the intrusions presently have heat delivery is essentially conductive leading to long time spans for intrusions the presence of the supercontinent immobile over a descending cell poloidal mode of convection developed a tangential force toroidal mode of convection that partly split the continent through strike slip deformation due to plate rotation it developed progressively between 1 57 and 1 3 ga starting from fennoscandia and then passing to amazonia western us and labrador in a clockwise sense the associated rotation induced sinistral shear manifested by small scale shear zones and the orientation of late magmatic facies topaz bearing granites in each province the proterozoic magmatism appears to be unique because it requires a supercontinent with a zone of juvenile crust surrounded by older cratons the present moho still shows remnants of this process having bumpy undulations that may reach 22 km in amplitude over a distance of 200 km

the southern ocean s role in carbon exchange during the last deglaciation changes in the upwelling and degassing of carbon from the southern ocean form one of the leading hypotheses for the cause of glacial interglacial changes in atmospheric carbon dioxide we present a 25 000 year long southern ocean radiocarbon record reconstructed from deep sea corals which shows radiocarbon depleted waters during the glacial period and through the early deglaciation this depletion and associated deep stratification disappeared by 14 6 ka thousand years ago consistent with the transfer of carbon from the deep ocean to the surface ocean and atmosphere via a southern ocean ventilation event given this evidence for carbon exchange in the southern ocean we show that existing deep ocean radiocarbon records from the glacial period are sufficiently depleted to explain the 190 per mil drop in atmospheric radiocarbon between 17 and 14 5 ka