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

geochemical and mineralogical control of different genetic types of deep sea nodules from the pacific ocean deep sea nodules from the northeast pacific nodule belt and the southeast pacific sonne basin being formed in areas bordering the equatorial zone of high biological productivity accumulate by two basically different growth processes a early diagenetic growth by supply from pore water and b hydrogenetic growth by supply from near bottom sea water these growth processes lead to different genetic types of nodules early diagenetic type a hydrogenetic type b and mixed type ab a further type ac very rich in mn is being formed by increasing influence of early diagenesis these types can clearly be distinguished by their shapes surface textures mineral constituents of oxide fraction internal microstructures and geochemistry a genetical classification is being proposed on the basis of statistically computed interelement relationships todorokite very poor in fe is the main mn phase in the early diagenetic substance mno2 intimately intergrown with feooh xh2o is the main phase in the hydrogenetic substance consequently an important difference can be pointed out the metal supply for the growth of the early diagenetic nodules is based on an ionic solution of me2 e g mn2 ni2 cu2 zn2 whereas the supply for the hydrogenetic nodules is caused by transport of colloidal particles mobilization of mn2 and fractionation from fe is controlled by the amount of decomposing organic matter in the peneliquid layer of the sediments the main factor controlling the intensity of early diagenesis is the biological productivity in surface waters the crucial point of reversal at a mn fe ratio of about 5 obtained by hyperbolical regression of the analyses of nodules from the southeast pacific represents best concentrations in ni and cu mn fe quotients greater than 5 cause a decrease of ni and cu content nodules from the northeast pacific nodule belt generally contain higher concentrations in cu than nodules from the southeast pacific this can be explained by an additional supply of cu transported below ccd by siliceous plankton

u th he thermochronology of the ottawa embayment eastern canada the temperature time history of an ancient intracratonic rift basin abstractthe ottawa embayment is an intracratonic rift basin in eastern north america that preserves a unique and eventful history through deep time we report single grain zircon and apatite u th he and biotite 40ar 39ar data from samples collected along a 250 km transect across the crystalline rift flank and through the sedimentary sequences of the embayment the data sets show significant intrasample age dispersions and we investigate the influence of zircon crystallinity and nonideal crystal shapes on he diffusion through the application of raman spectroscopy and x ray microcomputed tomography ultimately we utilize the relationship between radiation damage and helium diffusion to quantify observed age dispersion we integrate our age data from the basement and overlying sedimentary unit of the embayment with regional geology to utilize multisample inverse modeling to reveal viable thermal histories that we then further evaluate by using the forward modeling method to improve our understanding of t

estimating growth rates of ferromanganese nodules from chemical compositions implications for nodule formation processes abstract using available information on the accretion rates and the bulk chemical compositions of oceanic ferromanganese nodules it can be shown that the accumulation rate of manganese is proportional to the square of the accumulation rate of iron this relationship has been used to derive an equation that predicts nodule growth rates from their chemical compositions the equation accurately predicts growth rates up to about 50 mm 10 6 yr but yields incorrect rates for faster growing concretions from this relationship nodules underneath water of high primary productivity grow most rapidly and accumulate transition metals most rapidly however nodules from regions of highest primary productivity do not have the highest concentrations of nickel and copper reduction of manganese within the sediment column and remobilization of a fraction to the surface sediments adds manganese to nodules without substantially augmenting the supply of other transition elements the addition of remobilized manganese to the nodule dilutes the concentrations of nickel copper and iron even though their rates of accumulation are also high

radiochemical observations on manganese nodules from three sedimentary environments in the north pacific abstract decay series isotopes were measured on manganese nodules from three sedimentary environments characterized by substrates of red clay r siliceous ooze s and hemipelagic clay h growth rates of nodules are shown to be site dependent 1 2 mm myr at site r 3 8 mm myr at sites s and 20 50 mm myr at site h correlation between growth rate and the parameter mn fe2 suggests that regional diagenetic variations control the compositions and growth rates of the nodules the frequency of nodule turnover and the period of their growth are assessed from the top vs bottom distributions of several nuclides based on the 230th 231pa and 226ra data turnover times of 103 to 105 years are estimated and they vary with relative size and shape of the specimens at a given site the presence of unsupported 210pb and 228th in the top surfaces but not in the bottom surfaces of the surface nodules suggests active growth during the last decades or years despite their old ages the data also indicate that turnover rates are not more frequent than once every several years or decades the 230th 226ra 226ra 210pb and 232th 228th disequilibrium relationships in the nodules allow the migratory behavior of 226ra 222rn and 228ra and their fluxes to be deduced thus radium leaves the top sides but enters the bottom sides of the surface nodules at sites r and s at site r there is a net loss of radium to the sea the opposite is true at site s surface nodules at site h trap radium from both sides probably due to more intense diagenetic input of radium from sediment pore water the effective diffusivities of 226ra in nodules vary from 3 10 12 to 8 10 14 cm2 s dependent on the textural variation of the nodule material which crudely reflects the growth rate and hence sedimentary environment 222rn diffuses out of nodules from all sides with an effective diffusivity of ca 2 6 10 8 cm 2 s at all sites nodules serve as a more effective source of 222rn to sea water than their adjacent sediments the outward flux of 222rn from nodules relative to that from adjacent sediments tends to be higher in more reduced environments an effect caused by the fact that mn rich nodules from more reduced environment act as a more efficient trap for 226ra

anthropogenic pb component in hydrothermal ochres from marsili seamount tyrrhenian sea abstract recent hydrothermal fe oxyhydroxide precipitates ochres were sampled during two submersible expeditions to the ne part of the marsili seamount summit se tyrrhenian sea the marsili ochres belong to type 1 primary sulfide poor fe oxyhydroxides according to the classification of hekinian et al hekinian r hoffert m larque p cheminee j l stoffers p bideau d 1993 hydrothermal fe and si oxyhydroxide deposits from south pacific intraplate volcanoes and east pacific rise axial and off axial regions econ geol 88 2099 2121 they are x ray amorphous highly metalliferous al al mn fe 0 4 low in si transition metals co ni cu zn pb and rare earth elements ree and enriched in b v and mo their chemical composition and ree distribution patterns indicate precipitation from low temperature hydrothermal fluid mixed with seawater measured pb isotope compositions in the ochres indicate that the pb is dominantly anthropogenic in origin by contrast the pb isotope ratios in the nearby higher temperature hydrothermal deposits from the panarea arc volcano show that the pb is derived mainly from local volcanic rocks the fact that the pb isotopic signature of the marsili ochres is controlled by recent anthropogenic input suggests that the fe oxyhydroxides precipitated from fluids depleted in transition metals the low 206pb 207pb ratios in the ochres reflect the contribution of pb from australian ores indicating precipitation of the ochres somewhere between present day and the beginning of australian pb import to europe the young age of the ochres and the presence of other hydrothermal deposits along the marsili crest suggest that the magmatic chamber beneath the seamount may still be alive this study represents the first observation of anthropogenic influence on submarine hydrothermal deposits

quartz microstructures and c axis preferred orientations in high grade gneisses and mylonites around the morin anorthosite grenville province quartz in deformed rocks from two large high grade shear zones around the morin anorthosite morin terrane grenville province displays distinctive microstructures as well as c axis preferred orientations in the west dipping morin shear zone east of the morin anorthosite four distinct quartz microstructures types 1 4 are identified based on deformation features and grain size the c axis orientations are characterized by a single maximum near the stretching lineation and two maxima in type 1 microstructure and by an asymmetrical single girdle in type 2 microstructure quartz c axes show crossed girdle pattern in type 3 microstructure both quartz microstructures and c axis preferred orientations suggest that crystal plastic slip and dynamic recrystallization are the dominant deformation mechanisms the asymmetry of c axis orientations with respect to the mylonitic foliation as well as the substructures developed in quartz indicates a dextral sense of shear in the morin shear zone type 4 micr

docking of the central metasedimentary belt to laurentia in geon 12 evidence from the 1 17 1 16 ga chevreuil intrusive suite and host gneisses quebec the chevreuil intrusive suite 1 17 1 16 ga represents a chronological field marker of regional extent that intruded the central metasedimentary belt in the western grenville province of quebec after peak metamorphism style and site of magma emplacement and extent of deformation of chevreuil plutons and dykes permit unravelling of the early grenvillian evolution of the belt with respect to cratonal north america the suite comprises a series of vertically layered gabbro stocks and monzonite diorite gabbro sheet intrusions and a swarm of microdiorite dykes that cut across gneisses the dykes display systematic variations in extent of deformation across the belt we targeted u pb geochronology on gneisses within the identified strain windows they preserve the record of a ca 1 20 ga high pressure temperature p t metamorphic event the sheet intrusions define magmatic corridors all along and concordant with the western northern and eastern tectonic boundaries of the belt the concordant and elonga

manganese microchimneys buried in the central pacific pelagic sediments evidence of intraplate water circulation abstract manganese oxide deposits of an irregular tube like shape with unique composition and structure were found within pliocene siliceous sediments from an abyssal hill in the central pacific manganese nodule province effective separation of mn from fe and probably a rapid rate of mn deposition are suggested from the chemical composition a very high mn fe ratio up to 400 and low concentrations of transition metals the ree pattern is similar to other marine low temperature hydrothermal and sub oxic diagenetic mn deposits low total ree abundance and strong negative ce anomaly the deposit consists of major todorokite with minor buserites showing a hydrothermal signature blade like crystals of the minerals typically grow within open tubes several mm thick and lack detrital minerals all data indicate a low temperature hydrothermal or cold seep origin or less likely a sub oxic diagenetic origin this unusual manganese deposit from a pelagic environment is thought to have formed on the sea floor from mn bearing waters that passed through sediments or basement rocks we speculate that intraplate water circulation took place during the late pliocene to pleistocene due to the uplift and or block faulting after the deposition of pelagic pliocene sediments

the lithoprobe abitibi grenville transect two billion years of crust formation and recycling in the precambrian shield of canada we summarize the results of lithoprobe studies in the neoarchean southeastern superior province and the mesoproterozoic grenville province in the southeastern precambrian shield of canada through two composite cross sections based on seismic reflection data which define dramatically different styles of crust formation and tectonic accretion in the neoarchean and mesoproterozoic in the neoarchean the structures at the surface are steep with discontinuous and flatter structures at depth much of the crust appears to be juvenile and the predominant process of crustal growth is inferred to have been subduction accretion of primitive crust in a prograding arc system in the mesoproterozoic surface structures are shallow and the seismic character of the crust is continuous over the entire cross section archean parautochthonous rocks and reworked archean crust comprise a very significant proportion of the preserved crust in the mesoproterozoic and provided the backstop to the grenvillian orogeny result

organic rich and manganese sedimentation during the cenomanian turonian boundary event in the outer carpathian basins a new record from the skole nappe poland abstract upper cenomanian lower turonian strata in the splawa section of the skole nappe outer carpathians poland provide a detailed palaeoenvironmental record of the oceanic anoxic event oae 2 from a deep water basin below the ccd at the northern margin of the western tethys the oae 2 succession consists of black parallel laminated radiolarian shales enriched in organic matter of mainly marine origin toc up to 8 organic carbon isotope variations together with microfossil datum events allowed to correlate the studied organic rich facies with other black shale successions along the outer carpathians and other areas of the western tethys the mean values of sedimentation rate 3 5 5 5 mm kyr and organic matter accumulation rate 0 5 g m2 year calculated for the oae 2 interval in the outer carpathian basins are comparable to the values from other deep water marginal basins in the western tethys the average redox sensitive trace metal contents and their enrichment factors indicate water column anoxia in the outer carpathian basins intensified during the interval of the largest shift in 13c values the periods of bottom anoxia were interrupted by intervals of variable eh conditions with sedimentation of hemipelagic green shales including poor agglutinated foraminiferal assemblages an increase in productivity of organic and siliceous plankton during the oae 2 is documented based on increased values of silica and barium enrichments this closely corresponds to an interval of the largest positive stable carbon isotope excursion related to the beginning of the largest sea level rise linked with intensive coastal upwelling extremely low sedimentation rate or even hiatuses and the increase in deep water circulation causing basin oxygenation resulted in precipitation of two ferromanganese layers their formation was related to changes in hydrodynamic conditions at the basin floor expressed by precipitation of fe mn carbonates some chemical indices seem to suggest that the primary metal enrichments could be related to hydrothermal activity however the concentrations of some elements show also on hydrogenic to diagenetic influences in these metalliferous sediments the precipitation of these fe mn sediments was probably synchronous with the manganese enrichment across the c t transition recorded in other western tethyan basins and in the adjacent epicontinental seas

crustal evolution along a seismic section across the grenville province western quebec results of deep seismic reflection survey along a 375 km long transect of the grenville province in western quebec are combined with a review of geological observations and published isotopic ages the seismic profile offers a remarkably clear image of the crust mantle boundary and a good definition of the various crustal blocks crust about 44 km thick beneath the grenville front zone thins abruptly to ca 36 km southeastward perhaps the result of extension on southeast dipping surfaces extending to the moho other zones of relatively thin crust although less pronounced occur where proterozoic crust overlies archean crust and beneath the morin anorthosite complex the thickest crust is found at the extreme southeast of the transect east of the morin anorthosite from northwest to southeast three main crustal subdivisions are 1 deformed archean rocks with southeast dipping reflectors in the grenville front zone 2 an archean parautochthon with northwest dipping reflectors extending to the lower

metamorphic constraints on the tectonic evolution of the allochthonous monocyclic belt of the grenville province western quebec the tectono metamorphic evolution of grenvillian monocyclic terranes in western quebec has been constrained along a northwest southeast transect from reservoir cabonga to the morin anorthosite by t

synconvergent ductile flow in variable strength continental crust numerical models with application to the western grenville orogen 1 we present results from numerical models for a convergent orogen with laterally variable lower crustal strength representing a simplified orogenic system in which a strong craton flanked by progressively weaker terranes collides with another continent with progressive convergence crustal thickening and thermal relaxation lower crust becomes decoupled from upper and middle crust forming a ductile orogenic infrastructure beneath a stronger superstructure collision with strong external crust results in uplift and expulsion of ductile nappes from the orogenic core creating allochthonous terranes overlying a lower crustal indentor the extent of transport and exhumation of lower crustal nappes over the indentor reflects the amount of convergence and the erosion rate the western grenville orogen displays across strike variations in age tectonic history and protolith association suggesting a systematic variation in precollision crustal strength the laurentian craton margin and accreted terranes were variably reworked at synorogenic depths of 25 35 km during the ottawan orogeny deformation propagated from younger monocyclic rocks in the southeast into older polycyclic rocks flanking the craton on the northwest a comparison between numerical model results and crustal scale cross sections from the georgian bay and montreal val d or transects shows close correspondence between crustal structure and model geometry this indicates that the models produce geologically realistic results and provides a context for interpreting the tectonic evolution of the western grenville orogen contrasts between the results of homogeneous channel flow models and the present ductile nappe models suggest that the effects of different styles of ductile flow can be distinguished in the geologic record

fluxes of metals to a manganese nodule radiochemical chemical structural and mineralogical studies fluxes of metals to the top and bottom surfaces of a manganese nodule were determined by combining radiochemical 230th 231pa 232th 238u 234u and detailed chemical data the top of the nodule had been growing in its collected orientation at 4 7 mm myr 1 for at least 0 5 myr and accreting mn at 200 g cm 2 kyr 1 the bottom of the nodule had been growing in its collected orientation at about 12 mm myr 1 for at least 0 3 myr and accreting mn at about 700 g cm 2 yr 1 although the top of the nodule was enriched in iron relative to the bottom the nodule had been accreting fe 50 faster on the bottom 232th was also accumulating more rapidly in the bottom despite a 20 fold enrichment of230th on the top the distribution of alpha emitting nuclides calculated from detailed radiochemical measurements matched closely the pattern revealed by 109 day exposures of alpha sensitive film to the nodule however the shape and slope of the total alpha profile with depth into the nodule was affected strongly by226ra and222rn migrations making the alpha track technique alone an inadequate method of measuring nodule growth rates diffusion of radium in the nodule may have been affected by diagenetic reactions which produce barite phillipsite and todorokite within 1 mm of the nodule surface however our sampling interval was too broad to document the effect we have not been able to resolve the importance of nodule diagenesis on the gross chemistry of the nodule

growth of a manganese nodule from peru basin a radiochemical anatomy abstract attempts have been made to study the entire growth history of a manganese nodule from the northern part of peru basin in the pacific using radiochemical profiles of 230 th 232 th 227 th 230 th and 10 be 9 be combined with the observations on fe mn contents and textural variation the radiochemical data indicate that the nodule grew more or less concentrically throughout most of its existence since it formed 1 5 my ago receiving mn from both bottom water and pore water this condition appeared to have changed about 180 ky ago when the growth became asymmetric in that the top and bottom sides became fixed in their relative positions on the sea floor since then the bottom side accreted with a fast rate of close to 200 mm my apparently fueled by the supply of diagenetically remobilized mn in pore water from the sediment substrate in the meantime the top side accumulated at about 6 mm my a value which is in the normal range for deep sea nodules having their mn supplied from the hydrogenous source

geochemical and sedimentological studies of a box core from the western sector of the peru basin abstract the distribution of sediments micronodules and manganese nodules which has been studied in a number of cores from the peru basin is clearly related to the proximity of the basin to the c c d and to the equatorial high productivity zone one core from the peru basin has been looked at in considerable detail in this core an extensively bioturbated calcareous siliceous rich upper sedimentary unit is underlain by an overconsolidated dark brown clay characteristic differences in mineralogy and chemistry are observed in the composition of these sediment types with the dark brown clays having higher contents of mn fe co ni cu zn and p than the sediments of the upper horizon in addition these dark brown clays contain montmorillonite as the principal clay mineral whereas the sediments of the upper sediment horizon consist of montmorillonite kaolinite and illite micronodules are much more abundant in the coarse fraction 40 m of the dark brown clay horizon than in the upper sedimentary unit and are characterized by higher mn fe ratios and higher ni and cu contents than those from the upper sediment horizon this reflects the fact that these overconsolidated sediments are well oxidized and that element remobilization from the micronodules has not taken place within this sediment type in the upper sedimentary unit there is a sharp drop in the mn fe ratio and ni and cu contents of the micronodules immediately beneath the sediment surface reflecting the selective migration of mn and other transition elements such as ni and cu from the micronodules buried managanese nodules are found at two horizons within the sediment column these nodules show characteristic differences in their surface texture compared to surface nodules but no marked difference in composition the buried nodules are not associated with any well defined feature such as a sedimentary hiatus it is suggested that nodules are maintained at the sediment surface by bioturbation buried nodules are simply those nodules that have failed to be maintained at the sediment water interface

rheological controls on grenvillian intrusive suites implications for tectonic analysis abstract studies of plutonic suites in western grenville along with the recent advances in understanding magma ascent and emplacement and interactions between magma and their country rock provide insights on the use of intrusive rocks to infer the accretionary history of deeply exposed precambrian orogens in the grenvillian central metasedimentary belt of quebec terrane juxtaposition was inferred to be late based on the distribution of 1 08 ga potassic alkaline plutons this view was questioned however upon recognition that magma ascent by dyke propagation can be stalled to enable the formation of plutons upon intersecting rheologically softer units for example grenvillian marble in this context preferential ponding of magmas in marble rather than tectonics can control regional distribution of plutons the spatial association of plutons with marble and their contact relationships are at the local scale obscured by transformation of marble to skarn and by mechanical excision of marble from the paragneiss wall rock sequence in contrast plutons and dykes of an older 1 17 ga less alkaline magma association are shown by field and remote sensing studies to be evenly distributed across the various lithotectonic domains of the belt their sheet like emplacement along the belt boundary constrains grenvillian tectonic assembly in the region to be early contrasting loci type and degree of deformation of intrusive bodies illustrate that host rock rheological differences influence the final characteristics of an intrusive suite consequently the nature of the host is an important variable in inferring timing relationships and tectonic scenarios from intrusive suites in high grade terranes

thermochronology of the mont laurier terrane southern canadian grenville province and its bearing on defining orogenic architecture abstract convergence during pre grenvillian accretion led to crustal thickening and juxtaposition of shallowly southeast dipping imbricated terranes of the central metasedimentary belt in ontario and its equivalent to the north in quebec known as the mont laurier terrane mlt this investigation focuses on the otter lake region of the southern mlt which is composed of a mesoproterozoic back arc sequence metamorphosed to upper amphibolite granulite facies at conditions of 6 1 kbar and 650 700 c notable peak assemblages include fo bearing marbles and sil kfs migmatites with little to no retrogression the terrane is divided into the marble west and quartzite east domains separated by the east dipping heney shear zone hsz la icpms u pb geochronology on select migmatites from both domains yielded bimodal u pb zircon and monazite age populations at ca 1230 ma and 1180 1140 ma with mineral ages from the leucosomal portions of the migmatites populating the younger age bracket and implying that the metamorphism and anatexis took place during the accretionary shawinigan orogeny directly east of the hsz 40ar 39ar hornblende and phlogopite ages are ca 1145 ma and ca 1150 ma respectively whereas to the west in the marble domain hornblende ages are markedly younger ca 980 950 ma rapid cooling of the quartzite domain at the end of the shawinigan orogeny together with the lack of evidence for any metamorphic overprinting in the southern mlt during the long lived grenvillian orogeny 1095 980 ma is consistent with this region being part of an orogenic lid or suprastructure post grenvillian cooling of marble domain rocks through 500 c nearly 200 m y after cooling of the quartzite domain suggests a protracted middle crustal residence of the marble domain under thermally elevated conditions implying that portions of the orogenic lid remained warm above 500 c during the grenville orogeny moreover the disparate cooling ages on either side of the hsz provide evidence for important late displacement across the hsz comparable to that proposed for terrane bounding shear zones such as the robertson lake and bancroft shear zones these structures may be an expression of vertical orogenic collapse or lateral stretching of the orogenic lid biotite cooling ages are uniformly

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

diagenetic mobilization of manganese in peru basin sediments abstract the mn contents and sedimentation rates of two cores from different areas of the peru basin have been determined the southern core is associated with mn nodules of conventional slow accretion rates mm 106 yr while the northern one accompanies nodules with very high growth rates 102 mm 106 yr the depletion of mn observed within the top 40 cm of the cores is interpreted as resulting from a diagenetic remobilization of mn 2 due to the oxidative characteristics of the sedimentary column in both cores the calculated flux of mn provided by the sediment is higher than the total mn recovered in the overlying nodules this indicates that the mn content of the peru basin nodules can be supplied by diagenetic processes from the sediment not only for the slowly growing nodules but also for the extremely fast growing concretions found in the north of the basin

a two stage emplacement for the cabonga allochthon central part of the grenville province evidence for orthogonal and oblique collision during the grenville orogeny the cabonga allochthon central part of the grenville province is a proterozoic unit of high grade metasedimentary and metaigneous rocks resting on top of reworked parautochthonous archean migmatites of the reservoir dozois terrane the geometry and final assembly of terranes in this area result from the following succession of strains and displacements 1 thrusting towards the northwest of a proterozoic terrane 2 northwest southeast shortening of the transported terrane as indicated by large scale northeast trending buckle folds and by coeval development of a decollement within the upper layers of the archean footwall 3 reactivating of this decollement in the form of an east dipping thrust the cabonga thrust piggy back sequence the detached basement and the proterozoic allochthon forming the cabonga thrust sheet 4 northeast trending sinistral wrenching in the parautochthon responsible for the sinuous contour of the overlying cabonga thrust and probably also for the westward thrusting i

anomalous 234 u 238 u ratios in deep sea hydrothermal deposits although hydrothermal ferromanganese deposits often display variable 234u 238u ratios1 5 published values generally do not differ by more than 20 from the seawater value of their hydrogenous counterparts6 here we report very high 234u 238u ratios in hydrothermal manganese crusts recovered from the sanghihe island arc system in the west pacific such ratios about twice that of normal seawater confirm a low temperature hydrothermal supply of uranium which is best explained by leaching of the underlying rocks by the hydrothermal fluids and deposition together with the manganese oxides before mixing with seawater this suggests that the 234u 238u in seafloor deposits may be used as a tracer of low temperature hydrothermal reactions in the ocean crust

ductile thrusting at mid crustal level southwestern grenville province the northwestern boundary zone of the central metasedimentary belt grenville province in the haliburton area ontario is a stack of alternating tonalitic and syenitic crystalline thrust sheets transported toward the northwest on out of sequence upper amphibolite facies ductile thrust zones during the grenvillian orogeny at 1060 ma approximately 100 ma after the initiation of thrusting in the underlying central gneiss belt kinematics of the deformation are complex predominant northwestward thrusting was at least partly coeval with subordinate northeastward thrusting late synmetamorphic extensional shears cut both thrusts and thrust sheets minor late thrusting on discrete ductile shear zones postdates the extensional structures belts of mechanically weak pelite appear to have localised the thrust sheets highly mobile marble behaved as a relatively low viscosity fluid during transport able to intrude and erode more competent wall rock

the influence of suboxic diagenesis on the formation of manganese nodules in the clarion clipperton nodule belt of the pacific ocean abstract polymetallic nodules and a single fe mn crust from the clarion and clipperton zone ccz of the equatorial eastern pacific have been analyzed to determine their chemical and mineralogical compositions icp oes analyses of bulk nodules from the ccz indicate that the nodules formed under oxic diagenetic conditions with typical mn fe ratios of 4 6 ni cu values of 2 3 wt co contents of 0 12 0 17 wt however detail analyses of individual growth layers by electron microprobe analyses empa reveal much larger chemical heterogeneity of individual layers with mn fe ratios ranging from 800 two different genetic types of layers can be distinguished layer type 1 dense layer with average mn fe ratios of 1 80 average ni cu of 0 81 wt co contents of 0 30 wt hydrogenetic metal precipitation from oxic waters these layers consist of fe vernadite mno2 epitaxially intergrown with feroxyhyte feooh nanoparticles layer type 2 growth structures dendritic growth structures and dense layers with average mn fe ratios of 96 ni cu of 3 9 wt co contents of 0 08 wt and a distinct ni cu maximum of 6 51 wt at a mn fe ratio of 56 suboxic diagenetic metal precipitation from suboxic pore waters type 2 layers mainly consist of turbostratic phyllomanganates such as 10 a vernadite 7 a vernadite and todorokite are minor compounds mixed layer type 3 these layers can occur as zones of low reflectivity in the transition from layer type 1 to 2 or build up inhomogeneous growth structures of nm thin layers of low or high reflectivity the mn fe ratios of this material range between 3 and 11 ni cu of 1 4 6 wt and co contents are between 0 02 and 0 77 wt in most cases these growth structures represent a mixture of type 1 and 2 layers x ray photoelectron spectroscopy xps of the recent outermost nm layers of nodules top rim and bottom side indicates hydrogenetic accretion processes under recent oxic conditions both from seawater and pore water the mixed type ccz nodules are interpreted to consist of an oxic hydrogenetic and a suboxic diagenetic end member calculations of the proportions of the individual layer end members show that suboxic layers make up about 50 60 of the chemical inventory of the ccz nodules whereas oxic hydrogenetic layers comprise about 35 40 the remaining part 5 10 consists of incorporated sediment particles occurring along cracks and pores these results demonstrate that suboxic conditions alternate with oxic conditions during the growth of nodules in the eastern ccz this is probably due to fluctuating bioproductivity in the equatorial pacific surface waters during glacial interglacial periods which led to changing organic carbon flux to the sediment and changing oxygen consumption in near surface sediments furthermore reduced ventilation of the deep ocean during glacial periods may have led to suboxic conditions in near surface sediments our investigations prove that bulk chemistry data of whole nodules only provides an average of individual layers that build up the nodules and is inappropriate for genetic interpretation

geochronological constraints on the last stages of terrane assembly in the central part of the grenville province abstract new u pb zircon and monazite ages for syn and post kinematic pegmatites that cut major shear zones within the western quebec portion of the grenville province constrain the timing of deformation and final terrane assembly within this region from the grenville front se along the present section the grenville province consists of a reworked archean promontory partly covered by proterozoic allochthons and two proterozoic metasedimentary and metaigneous terranes which are probably allochthonous the age of the grenville front is still poorly constrained in this area as pegmatites intersecting high grade rocks exhumed some 30 km south of the front have upper intercept u pb ages of 2642 6 5 ma field and geochronological data in this paper however lend support to the possibility of late archean exhumation of high grade terranes along the front south of the front two types of ductile shear zone are responsible for the geometry of terranes in this part of the grenville province the first type corresponds to the boundary of allochthons transported onto the archean parautochthon the corresponding structures are not directly dated but reheating of the parautochthon at about 1020 ma u pb ages on monazite sets a minimum age for thrusting in this area late movement along an east dipping shear zone located within the parautochthon the cabonga thrust ct 998 9 5 ma is rather unique in that it involves rocks of the parautochthon and is characterized by a westerly directed transport the shear zones of the second type are subvertical ne trending generally sinistral and intersect the parautochthon the allochthon or both from the front towards the se these shear zones are the cadgecrib shear zone 998 16 6 ma intersecting the parautochthon the renzy shear zone 1003 4 5 ma involving allochthonous metasediments the baskatong shear zone 1020 2 1 ma which marks the nw limit of proterozoic rocks of the mont laurier terrane the labelle shear zone 1078 6 ma separating the mont laurier and the morin terrane and the taureau shear zone 1074 4 ma bounding the morin terrane to the east all the above timing constraints are from u pb ages on syn to post kinematic pegmatites emplaced within the respective shear zones this age distribution suggests a propagation of transcurrent deformation towards the nw which is responsible for the final configuration of terranes

growth history of manganese nodules and crusts of the peru basin abstract in the nodule field of the peru basin situated south of the zone of high bioproductivity a relatively high flux of biogenic matter explains a distinct redox boundary at about 10 cm depth separating very soft oxic surface sediments from stiffer suboxic sediments maximum abundance 50 kg m 2 of diagenetic nodules is found near the calcite compensation depth ccd currently at 4250 m there the accretion rate of nodules is much higher 100 mm ma 1 than on ridges 5 mm ma 1 highest accretion rates are found at the bottom of large nodules that repeatedly sink to a level immediately above the redox boundary there distinct diagenetic growth conditions prevail and layers of dense laminated mn oxide of very pure todorokite are formed the layering of nodules is mainly the result of organisms moving nodules within the oxic surface sediment from diagenetic to hydrogenetic environments the frequency of such movements is much higher than that of climatic changes two types of nodule burial occur in the peru basin large nodules are less easily moved by organisms and become buried consequently buried nodules generally are larger than surface nodules this type of burial predominates in basins at ridges where smaller nodules prevail burial is mainly controlled by statistical selection where some nodules are not moved up by organisms

archaean cratonic roots mantle shear zones and deep electrical anisotropy the extent to which the mantle participated in the growth and stabilization of ancient cratons is central to our understanding of the evolution of the continents1 the detection of seismic anisotropy beneath precambrian north america for example has been interpreted as showing that strain induced orientation of mantle minerals in subcontinental lithospheric mantle can preserve a record of ancient episodes of deformation2 here we present mag netotelluric measurements from the superior province of the canadian shield which reveal pronounced electrical anisotropy in the upper 100 km of the underlying mantle we argue that this anisotropy is best explained by conducting graphite films oriented within fractures or on grain boundaries and associated with metasomatism of the mantle roots of major archaean shear zones which transect the entire superior province the uppermost mantle beneath the canadian shield has therefore remained fixed to the crust and isolated from significant tectonic reworking since the late archaean

sr and nd isotopic variations in ferromanganese crusts from the central pacific implications for age and source provenance abstract isotopic analyses of two hydrogenetic ferromanganese fe mn crusts from volcanic edifices in the central pacific ocean reveal systematic variations in 87 sr 86 sr and 143 nd 144 nd with both ratios decreasing as a function of depth into the fe mn crusts leaching experiments suggest that sr in the crusts is contained in at least two discrete sites a loosely bound sr dominated by modern marine sr is removed by leaching with a 10 percent acetic acid solution the 87 sr 86 sr ratio of the residue is significantly less than the 87 sr 86 sr ratio of the unleached material the sr isotope ratios of leached samples are compared with the temporal variation in seawater to provide ages for layers within the fe mn crusts these data suggest that the oldest crust layers began to accrete in the early to middle miocene correlated to the 87 sr 86 sr variations 143 nd 144 nd ratios suggest that the nd isotope composition of central pacific ocean seawater also changed systematically over this time interval or that the fe mn crusts simply incorporated nd from various parts of an isotopieally heterogeneous ocean as the crusts were carried along with the oceanic plate in contrast to the layered ferromanganese crust the phosphatized volcaniclastic substrates have sr and nd isotope compositions that are consistent with their volcanic origin

new tectonic divisions of the grenville province southeast canadian shield on the basis of geological geophysical and geochronological data the grenville province has been divided into three first order longitudinal belts the parautochthonous belt pb allochthonous polycyclic belt apb and allochthonous monocyclic belt amb these are set apart by three first order tectonic boundaries the grenville front gf allochthon boundary thrust abt and monocyclic belt boundary zone mbbz the belts are subdivided into terranes based on internal lithological character the gf separates the archean to proterozoic foreland northwest of the orogen from reworked equivalents to the southeast continuous at the scale of the orogen its main characteristic is that of a crustal scale contraction fault the pb although less clearly identified along the length of the orogen in most places represents upgraded and tectonically reworked rocks of the adjacent foreland the boundary between the pb and the apb to the southeast the abt is most clearly delineated in the eastern half of the province it is the locus of major crustal delamination along which high grade mostly middle proterozoic polycyclic terranes were tectonically transported northwest toward and onto the pb the amb comprises two separate areas underlain by the wakeham supergroup and what is currently known as the grenville supergroup respectively its basal contact the mbbz is a decollement zone of variable kinematic significance between older polycyclic rocks and tectonically overlying monocyclic rocks this first order zonation implies a tectonic polarity to the grenville province superimposed on which are second order features evident from contrasting tectonic styles and radiometric ages these characteristics are consistent with a diachronous or oblique collisional model for the grenville orogen

evaluation of biotite garnet geothermometers application to the english river subprovince ontario in recent years there have been numerous calibrations of the biotite garnet fe mg exchange geothermometer the eastern lac seul region of the english river subprovince ontario provides an excellent field area in which to compare these calibrations

texture and elastic anisotropy of a mylonitic anorthosite from the morin shear zone quebec canada a sample of anorthosite from the granulite facies morin shear zone quebec canada was investigated for crystal preferred orientation and elastic anisotropy time of flight neutron diffraction data obtained with the hippo diffractometer at lansce were analyzed with the rietveld method to obtain orientation distribution functions of the principal phases plagioclase clinopyroxene and orthopyroxene texture and microstructures are compatible with the plastic deformation of the aggregate under high t conditions all mineral phases depict a significant preferred orientation that could be related to the general top to the north shearing history of the morin shear zone texture patterns suggest that 010 001 in plagioclase and 110 001 in clinopyroxene are likely dominant slip systems using preferred orientation data p and s waves velocities and elastic anisotropy were calculated and compared with previous studies to explore elastic properties of rocks with different pyroxene plagioclase mixtures p wave velocity s wave splitting and anisotropy increase with clinopyroxene content seismic anisotropy is linked to the texture symmetry which can lead to large deviations between actual anisotropy and that measured along cartesian xyz sample directions lineation foliation reference frame this is significant for the prediction and interpretation of seismic data particularly for monoclinic or triclinic texture symmetries

detrital zircon constraints on grenville sedimentation at the margin of laurentia abstract the southern grenville province is made up of metaigneous and metasedimentary rocks that were formed and metamorphosed as part of the mesoproterozoic active margin of laurentia grenville supergroup quartzites from the adirondack highlands new york the morin terrane quebec and new jersey highlands were analyzed to determine detrital and metamorphic zircon u pb ages and to help constrain mesoproterozoic tectonics these grenville quartzites have broadly similar detrital age populations as each other suggesting similar sedimentary source regions and depositional settings in back arc basin environments at the laurentian margin during geon 12 all samples contain detrital zircon with 1 45 1 25 ga ages consistent with proximal grenville source regions they also contain detrital ages that point to derivation from the mazatzal 1 7 1 6 ga yavapai 1 8 1 7 ga and penokean 1 9 1 8ga orogens of the north american midcontinent and have a diverse population of archean ages these results and published data from adirondack lowlands metasediments chiarenzelli et al 2015 2017 show distinctly laurentian sources and the related and likely connected nature of the sedimentary histories of the adirondack highlands and lowlands morin terrane and new jersey highlands metamorphic zircon formation is common in high grade quartzites and ages are variable between samples depending on the metamorphic history of each terrane and the melt productivity of different rocks peck et al 2010a adirondack highlands samples experienced metamorphic zircon grown during the shawinigan orogeny and anorthosite suite emplacement 1 19 1 14 ga morin terrane samples are from the morin shear zone which was active and caused metamorphic zircon growth during the ottawan phase of the grenvillian orogeny 1 09 1 02 ga the new jersey highlands sample has metamorphic zircon formed during the rigolet phase of the grenvillian orogeny 1010 980 ma

oxygen isotope constraints on terrane boundaries and origin of 1 18 1 13 ga granitoids in the southern grenville province granitic rocks related to 1 18 to 1 13 ga anorthosite mangerite charnockitegranite plutonism stitch three terranes in the southwestern grenville province adirondack highlands morin terrane frontenac terrane elzevir terrane because of the refractory nature of zircon zrn analysis of oxygen isotope ratios of dated igneous zircon from these rocks allows calculation of 18 o values of original magmas even if the rocks were subjected to late magmatic assimilation postmagmatic alteration or metamorphism documented variability in 18 o zrn for these granitic rocks corresponds to their geographic location seven plutons from the central frontenac terrane ontario have a high average 18 o zrn 11 8 1 0 which corresponds to 18 o magma values of 12 4 14 3 in contrast twenty seven other plutons and dikes of this suite new york ontario and quebec average 18 o zrn 8 2 0 6 with a typical igneous range of 8 6 to 10 3 for 18 o magma values high 18 o values in the frontenac terrane are some of the highest magmatic oxygen isotope ratios recognized worldwide but these plutons are not unusual with respect to whole rock chemistry or radiogenic isotope compositions such high 18 o values can result from mixing between paragneiss 18 o 15 and hydrothermally altered basalts and or oceanic sediments 18 o 12 in the source region we propose that high 18 o hydrothermally altered basalts and sediments were subducted or underthrust to the base of the frontenac terrane during closure of an ocean basin between the frontenac terrane and the adirondack highlands at or prior to 1 2 ga

carbon isotopic variations on glacial to interglacial time scales in the ocean modeling and implications downcore variations in the deep sea 13c signal as recorded in benthic foraminifera are a function of past changes in global organic carbon inventory and ocean circulation thus the carbon isotopic composition of fossil benthic foraminifera constitutes a valuable geochemical proxy for reconstructing paleooceanographic conditions this study examines the mean ocean 13c 12c variations due to the climatically induced changes in the size of the two organic carbon pools terrestrial biomass forest soil and continental shelf sediment through modeling the paired foraminiferal 13c 18o data in the literature it is estimated that during the past several hundred thousand years in late quaternary transfer of organic carbon between these two pools and the ocean in response to glacial interglacial climate and sea level changes has resulted in global oceanic 13c fluctuations with a mean amplitude of about 0 32 the transfer has accounted for about two thirds of the observed carbon isotopic shift in the deep eastern pacific ocean circulation accounting for the remaining one third of 13c amplitude variations in the deep north atlantic ocean it has accounted for about one third of the shift of the two organic carbon reservoirs forest soil is roughly 2 5 times more responsible than shelf sediment in altering the mean carbon isotopic composition of the quaternary oceans destruction of organic matter from the shelf sediment reservoir is responsible for raising the oceanic nutrient inventory during glacial times by about 4 relative to the present interglacial level a level which is difficult to be assessed by the cadmium proxy marine deposition of organic carbon in glacial oceans increased by 3 10 in spite of a reduction in terrestrial biomass during ice ages isolating out the global climatic signals in 13c records shows that since about 300 kyr ago there has been a trend of increasing organic carbon accumulation toward the present at least in the equatorial e pacific it also shows that the contrast between the 13c values hence nutrient content of deep water in the atlantic and pacific observed in today s ocean was smaller during glacial periods in the northwestern indian ocean the global climate corrected 13c results reveal interglacial intensification of the monsoon driven upwelling and productivity back to at least oxygen isotopic stage 11 circa 400 kyr b p

crustal scale shortening and extension across the grenville province of western quebec a deep seismic reflection survey shot in 1993 crosses almost the full width of the grenville province in western quebec the seismic transect provides a very clear image of the crust mantle boundary and the most precise definition to date of the various grenvillian terranes the crust is around 44 km thick beneath the grenville front but thins rapidly to 36 km some 60 km to the southeast it is also notable that the greatest crustal thickness of 50 km occurs at the southeast end of the transect far from the inferred location of the main grenvillian collision the grenville front zone in which nw directed thrusting at about 1 ga was followed by se directed extension is defined by discontinuous se dipping reflections which extend down to the moho to the southeast the overlying migmatitic archean parautochthon almost half of the transect is characterised instead by nw dipping reflectors extending into the lower crust these reflectors are in turn truncated to the southeast by a 12 km thick zone of intense se dipping reflections the baskatong crustal ramp the base of the allochthonous terranes allochthon boundary thrust is likely located at this ramp which flattens out at around 30 km depth into the base of the relatively transparent intermediate crust a highly reflective upper crustal deck corresponding to rocks of the mont laurier terrane was thrust over the baskatong crustal ramp and is represented further to the northwest by the klippelike cabonga allochthon the synformal transparent morin anorthosite charnockite complex belongs to the same upper crustal level ramp anticlines and the overriding basal thrust of the upper allochthons demonstrate the nw directed propagation of tectonic transport during the grenvillian orogeny involving deformation and displacement along the baskatong ramp with a relay into the grenville front zone postaccretional extension appears to have been primarily accommodated along the latter two crustal discontinuities thinning the crust immediately south of the grenville front and affecting the crust up to 350 km away from the front

the black lake shear zone a boundary between terranes in the adirondack lowlands grenville province abstract the black lake shear zone has been proposed as a potentially important tectonic boundary between the frontenac and adirondack lowlands terranes based on geologic and isotopic evidence we present new structural geochronologic and anisotropy of magnetic susceptibility ams results from the black lake area that constrain the location kinematics and timing of deformation in the region both structural and ams results document a northeast trending zone of high strain between black lake and the saint lawrence river within this zone strain is heterogeneous and includes a strongly developed sub vertical northeast trending foliation less commonly two orthogonal lineation sets are present one that is sub horizontal and another that is down dip the foliation and granitic dikes are locally folded forming tight to isoclinal northeast trending folds kinematic indicators show thrust deformation in areas of down dip lineation but are mixed in areas of sub horizontal lineation with a slight majority suggesting left lateral shear these results suggest major northwest directed shortening accommodated by flattening and ductile thrust faults possibly with a component of sub horizontal shear the two lineations may have formed during discrete episodes or synchronously during transpression u pb shrimp geochronology on igneous titanite from deformed dikes in combination with previous geochronology show that significant deformation occurred from ca 1170 1100 ma this deformation likely occurred during the late stages of the shawinigan orogeny and may record accretion of the adirondacks to the margin of laurentia during terrane assembly

aeromagnetic signature of an exhumed double dome system in the sw grenville province canada analysis of aeromagnetic data in the grenville province reveals the presence of two regional scale unmapped structural domes the morin and mekinac taureau domes with an oval shaped magnetic pattern bounded by regional scale shear zones and a geometry that is similar to that produced in crustal flow models under extension which predict two upright domes of foliation double dome separated by a steep shear zone the mekinac taureau dome a metamorphic core complex and the morin dome may have been exhumed by channel flow exhumation occurred by a combination of thrust normal sense and wrench shear zones the preservation of paragneisses in the morin dome suggests that it underwent a lesser degree of exhumation than did the mekinac taureau dome this study shows how the integration of local field information with magnetic data in a regional tectonic setting can reveal and delineate concealed gneiss domes and highlights a role for strike slip tectonics in the creation of regional structures involving the exhumation of deep crust this article is protected by copyright all rights reserved

structure of the lac nominingue mont laurier region central metasedimentary belt quebec grenville province the lac nominingue mont laurier region of the central metasedimentary belt grenville province of quebec comprises the granulite facies bondy gneiss complex core of the bondy gneiss dome and overlying sourd group metasedimentary rocks a metamorphic foliation transposed compositional layering s1 host to peak pressure parageneses has been folded by isoclinal folds f2 and f3 crosscut by leucosomes that host peak temperature assemblages the orthopyroxene isograd cuts obliquely across f3 folds indicating that 1 20 1 18 ga granulite facies metamorphism post dated d3 d3 structures are cut by ductile shear zones and boudinaged in d4 and are folded by regional scale open upright north south folds f5 folds with shallowly dipping axial surfaces f6 are subsequently developed in the sourd group f5 and probably f6 developed prior to intrusion of the ca 1165 ma chevreuil suite in the nominingue cheneville deformation zone ncdz east of the bondy gneiss dome chevreuil intrusions contain nort

sedimentary processes and manganese nodule formation in the korea deep ocean study kodos area western part of clarion clipperton fracture zones northeast equatorial pacific abstract in the southern part of the korea deep ocean study kodos area the western part of the clarion clipperton fracture zones abundant nodules occur in the oligocene to miocene radiolarian bearing smectitic clay the nodules are generally concentrated in patchy pavements more than 5 kg m2 on the hilly seafloor with sediment waves they are either rare or abundant on the seamounts and are generally rare in the abyssal plain the nodules can be classified into three types based on distinct surface texture the s type nodules occur in intensely bioturbated sediment of the abyssal hill and seamount areas in the abyssal plain the r type nodules are dominant embedded within the topmost quaternary sediment layer in the southeastern part where pliocene sediment occurs they are in an incipient stage of growth the s type nodules are rich in fe and co in columnar structures of mno2 whereas the r types contain abundant mn ni cu and zn in dendritic and massive 10a manganate layers the t type nodules occur together with either the r or s type showing intermediate composition regardless of the type and shape the bottoms of nodules contain more abundant mn ni cu zn and 10a manganate than the tops as the mn fe ratio increases in the nodules the abundance of ni cu and zn increases up to a constant value about 11 of mn southward in the underlying sediment however it decreases northward manganese and these minor metals are concentrated in the lowermost tertiary sediment as much as 2 to 3 times than those in the topmost sediment layer which is intensely bioturbated iron and co are relatively uniform downcore manganese ni and cu are abundant in micronodules whereas fe is concentrated in smectite redistributional processes of bottom currents seem to be most responsible for the re generation and concentration of nodules in patchy pavements by excavating buried nodules these processes result in an inverse relation of nodule abundance to the thickness of uppermost sedimentary layer which comprises the radiolarian ooze of clipperton formation in the seamount areas sediment slumping has also contributed to the concentration of nodules the fragmentation of old nodules also enhances the nodule re generation activities of benthic animals cause the nodules to be lifted upward onto the seafloor mostly during the quiescent periods of bottom currents the growth of nodules by resedimentation processes results in the large discrepancy in composition not only between the types but also the tops and bottoms controlled by the burial rates of nodules within the topmost sediment layer where the diagenesis takes place diagenetic growth of nodules occurs by utilizing mn and minor metals remobilized from micronodules during biomixing and decomposition of organic materials within tertiary sediment nodule growth is more active southward toward the equator latitudinal variations of nodule size distribution abundance and composition result from the change in surface water productivity and the timing of nodule nucleation as the pacific plate migrates northwestward

fine scale study of major and trace elements in the fe mn nodules from the south china sea and their metallogenic constraints abstract many marine fe mn polymetallic nodules may contain high concentrations of mn cu ni zn co and rare earth elements plus yttrium rey to determine the occurrence and enrichment processes of these metals in the fe mn nodules we conducted high resolution mineralogical and geochemical studies on the fe mn nodules collected from the south china sea in situ epma and la icp ms analyses and elemental imaging were performed on individual microlayers of the nodules to reveal the major and trace element distributions the whole rock mineralogical and chemical compositions of the fe mn nodules indicate a hydrogenetic origin the mn mineral phases are mainly composed of nanocrystalline vernadite with interlayered 10 a and 7 a phyllomanganates such as todorokite birnessite and buserite fe ti oxides hydroxides are intergrown and essentially x ray amorphous feroxyhyte and goethite we recognize two main types of microlayers type a layer suboxic diagenetic precipitates containing a high mn fe ratio and high concentrations of cu ni zn ba li and mg and type b layer oxic hydrogenetic accretions with low fractionation of mn and fe and high contents of co rey ti sr and pb furthermore elemental mapping indicates that the enrichments of co and rey are mainly associated with fe mineral phases rather than mn ones which are enriched in mg cu ni zn li and ba two mineralization processes and metal distributions in the individual microlayers are identified in the fe or mn mineral phases the occurrence of 10 a and 7 a phyllomanganates in type a layers are commonly enriched in trace metals such as ni cu zn li ba and mg whereas the metals for the type b layers include co ti pb sr rey which may be carried by the intergrowing fe ti oxyhydroxides and vernadite thus hydrogenesis and diagenesis facilitate the enrichment of fe co ti sr pb rey and mn ni zn cu li ba mg respectively during the mineralization of the south china sea nodules

the mont laurier quebec earthquake of 19 october 1990 and its seismotectonic environment on 19 october 1990 at 07 01 ut a magnitude mblg 5 0 earthquake occurred approximately 9 km southwest of mont laurier quebec canada latitude 46 47 n and longitude 75 59 w this earthquake is the largest to have occurred in the western quebec seismic zone since the 1944 magnitude 5 6 cornwall massena earthquake the mont laurier earthquake was widely felt up to distances of 500 km and caused some minor damage in the epicentral region intensity modified mercalli mm v during the week following the earthquake a field survey recorded 23 aftershocks magnitudes were all less than ml 1 5 analysis of the mainshock and its aftershocks indicates focal depths in the range 10 to 12 km of the two east west oriented nodal planes given by the predominantly thrust mechanism of the mainshock the steep northerly dipping one probably represents the fault plane as indicated by the trend of aftershock hypocenters the last 10 yr of recording have confirmed that most western quebec earthquakes including the mont laurier earthquake occur in a northwest southeast trending zone inside the central metasedimentary cm belt with most focal depths varying between 7 and 25 km although some northwest trending structural features are known correlating these with the epicentral trend is premature the mid crustal hypocentral depths of many earthquakes the east west trend of the fault plane of the mont laurier earthquake and variations in regional focal mechanisms all suggest reactivation of deep structural features which may not have a surface expression inside the central metasedimentary belt most earthquakes occur along the eastern side where the activity seems to correlate with the labelle shear zone and the morin anorthosite body which may act as a stress concentrator the western side of the activity does not end with the central metasedimentary belt a fact that implies that even though the factors controlling seismicity lie predominantly within the central metasedimentary belt the adjacent geologic domains are also seismogenic

magnetostratigraphy of hydrogenetic manganese crusts from northwestern pacific seamounts abstract fine scale dating is crucial to understanding the growth and environments of formation of marine manganese deposits the paleomagnetic method of dating of manganese nodules and crusts has been attempted but with no success so far we measured remanent magnetization rm on up to 75 mm thick hydrogenetic crusts at intervals of 2 5 mm after mineralogical and chemical examination careful separation and alternative field demagnetization stable sharp rm and well correlated polarity change patterns between four samples made it possible to identify the pliocene quaternary magnetic chrons in them these data show that the three crusts have grown continuously at rates of 14 17 mm m y since the early pliocene this is three or four times faster than those for central pacific seamount hydrogenetic crusts estimates of growth rate based on determination of co flux are within this range magnetostratigraphy therefore appears to be a powerful method for dating hydrogenetic manganese crusts when supported by conventional dating methods these results encourage finer scale investigations which promise more detailed paleoceanographic reconstruction

evolution of p t conditions during a high grade metamorphic event in the maniwaki area grenville province pelitic and basic rocks of the grenville supergroup in the maniwaki area 100 km north of ottawa were selected for a detailed investigation of the metamorphic history of the central metasedimentary belt of the grenville province mineral assemblages suggest metamorphic conditions of the granulite facies with local and irregular persistence of the amphibolite facies chemical analysis of minerals reveals a lack of equilibrium on the thin section scale systematic variation of mineral compositions is explained as the net result of several mineral equilibria established at different stages during the metamorphic evolution of the area peak temperatures obtained by biotite garnet thermometry cores of isolated grains are between 760 and 860 c whereas clinopyroxene garnet thermometry gives 740 820 c retrograde temperatures as estimated by various thermometers range between 550 and 750 c biotite garnet 498 and 670 c cordierite garnet and 690 and 720 c clinopyroxene garnet peak pressures were 6

40ar 39ar thermochronology along a western quebec transect of the grenville province canada ar ar thermochronology on 24 hornblendes 3 biotites 2 muscovites and 2 k feldspars collected along a 400 km long nw se geotraverse through the grenville province in western quebec is employed to provide time constraints on the intermediate and low temperature stages of cooling of part of the grenville orogen in the grenville front zone the c 1000 ma time of exhumation previously established from thermobarometric and isotopic studies is supported by the hornblende age data presented here from 60 km to 160 km se of the front reworked archaean migmatites of the parautochthonous reservoir dozois terrane rdt 1004 ma old metamorphic monazites contain hornblendes with 972 950 ma cooling ages assuming metamorphic geotherms between 25 and 30 c km 1 calculated cooling and unroofing rates are about 6 c ma 1 and 0 33 km ma 1 in the p t range 725 c 800 mpa and 450 c 400 mpa hornblendes from monocyclic rocks of the mont laurier and morin terranes mlt and mt monazite ages c 1165 ma give ages of about 1040 and 1010 ma respectively calculation of cooling unroofing rates from peak metamorphic conditions in this area is hampered by thermal perturbations associated with the still poorly dated grenville collision which took place approximately between 1060 and 1020 ma cooling ages of c 900 ma for muscovite and biotite and 860 810 ma for k feldspar show that cooling rates decreased to around 1 5 c ma 1 under retrograde greenschist facies conditions in the mlt on a time vs distance diagram the hornblende data define several distinct age ranges suggesting that each terrane had a characteristic thermal history thus cooling was diachronous and probably non homogeneous throughout this segment of the grenville orogen the time lag between the cooling history of the parautochthon 972 950 ma and the allochthons 1040 1010 ma is compatible with an earlier pre 1040 ma peak of metamorphism in the allochthons the reservoir cabonga allochthon was transported toward the nnw from its probable root zone in the mlt during the 1060 1020 ma grenvillian collision as a partially cooled slab the remobilization of the archaean parautochthon is attributed to this collision in the grenville front zone slightly older cooling ages and cooling rates initially faster than in the remaining part of the parautochthon are probably as a result of rapid tectonic exhumation shortly after collision the minor delay 20 30 ma in unroofing of the mt compared to the adjacent mlt is most likely related to post 1040 ma extensional displacement along the labelle shear zone in terranes like those described above where metamorphism is diachronous determination of cooling rates and the history of exhumation may be meaningless without a firm control on the regional structure however identification of contrasting cooling histories contributes to unravelling the independent movement of terranes

methane seasonal cycle at gale crater on mars consistent with regolith adsorption and diffusion a strong repeatable seasonal cycle in the background methane mixing ratio has been observed at the gale crater landing site of the mars science laboratory rover with the tunable laser spectrometer of the sample analysis at mars instrument however as of yet no physical process has been proposed that can explain both the timing and amplitude of the observations here we show that a one dimensional numerical model considering adsorption onto and diffusion through the regolith can reproduce the variation including a phase lag if the regolith is impregnated with methane from a prior plume or supplied from below by microseepage combining the model results with geological constraints we estimate that the amount of microseepage at gale is at most 3 10 5 tonnes km 2 yr 1 gale s unique dynamical environment makes such seeps easier to detect in surface sampling measurements over most of the martian surface atmospheric mixing is stronger or atmospheric transport more effective and we expect the amplitude of the seasonal cycle to be smaller for the same strength of seep the seasonal cycle in the methane mixing ratio observed at gale crater on mars can be explained by adsorption onto and diffusion through the regolith suggests a one dimensional numerical model with geological constraints