oceanwide imprint of large tectonic and oceanic events on seawater nd isotope composition in the indian ocean from 90 to 40 ma 1 we have analyzed four sediment cores from the southern indian ocean odp sites 757 758 1135 and 762 with high carbonate content in order to reconstruct the neodymium isotopic composition end of ancient intermediate south indian seawater from late cretaceous 90 ma to early eocene 40 ma the endvariations are highly consistent and exhibit reproducible patterns over a very large geographic area confirming the seawater origin of the signal combining geochemical constraints with paleogeographic reconstructions we highlight the respective roles of 1 large scale tectonic events 2 continental weathering from surrounding precambrian terrains 90 65 ma 3 oceanic circulation changes 50 40 ma and possibly 4 local volcanism of the ultra fast spreading south east indian ridge seir 60 50 ma on the nd isotopic composition of south indian seawater between 60 ma and 50 ma the regional nd isotopic variations closely mimic changes in seir spreading rate we suggest that the nd isotopic composition of seawater could be influenced by nd of volcanic origin in the vicinity of ultra fast spreading ridges 13 cm yr the india asia collision closed the equatorial seaway between asia and india and drastically changed oceanic circulation patterns in the indian ocean warm and more radiogenic pacific equatorial seawater was diverted to the south by the east indian coast a stronger mixing of this pacific seawater with south indian seawater would explain the rapid shift ofend from 50 ma 11 to 40 ma 8

effects of hydrothermal alteration on the compositions of chromian spinels chromite spinels in hydrothermally altered rocks from fracture zone ultramafic rocks and from both ultramafic cumulate pods and sheeted dikes in the josephine ophiolite california display a wide variety of compositions alteration of the spinel may not be visible in thin section the primary composition changes accompanying hydrothermal alteration are increase in cr cr al and or fe2 fe2 mg in general altered spinel grains associated with hornblende and chlorite show an increase in cr cr al from core to rim altered spinel grains associated with serpentine show an increase in fe2 fe2 mg from core to rim but may not show an increase in cr cr al the compositional zoning in some altered spinel grains appears to result both from reaction of clinopyroxene plus spinel to form hornblende and from reaction of hornblende to form chlorite these observations suggest that subsolidus hydrothermal metamorphic effects need to be considered when interpreting spinel compositions and the compositions should not be interpreted solely in terms of igneous processes further the presence of highly altered spinels may be indicative of hydrothermal alteration in rocks where other evidence of such alteration is absent

discussion of kimberlites and aillikites as probes of the continental lithospheric mantle by d francis and m patterson lithos v 109 p 72 80 article the origin of kimberlites and volatile rich alkaline ultramafic magmas such as aillikites has been a matter of considerable scientific interest and the recent paper by francis and patterson francis and patterson 2009 kimberlites and aillikites as probes of the continental lithospheric mantle lithos 109 72 80 attempts to summarize advances in this research field they introduce new major element geochemical discrimination diagrams and present a petrogenetic model that allegedly has implications for diamond exploration contrary to the statements of francis and patterson we argue that kimberlite bulk chemical compositions are not determined by contamination with lithospheric mantle material alone and cannot be used to predict reliably the diamond grade of new discoveries we dispute their petrogenetic model specifically the proposal that calls for carbonate rich aillikite melts being parental to kimberlite magmas rather we promote the idea of carbonated ultramafic lamprophyre magmas such as aillikites being parental to many carbonatite intrusions in areas of rifted cratonic lithosphere from which archetypal kimberlites appear to be absent furthermore we believe that the geochemical discrimination diagrams si versus k and fe respectively introduced by francis and patterson do not effectively distinguish between kimberlites and aillikites because there is significant data overlap and bias of particular concern is the omission of relevant compositional data for the ultramafic lamprophyre group in this discussion we re iterate that bulk chemical analyses of kimberlites and alkaline ultramafic rocks need to be accompanied by petrographic descriptions and mineralogical data only by the inclusion of such data can the petrogenesis of the rocks considered be discussed

electromagnetic ray trace tomography electromagnetic em tomography can be used to estimate the distribution of electrical rock properties between boreholes for typical oil field well spacings and reservoir electrical characteristics crosswell em measurements are sensitive primarily to the electrical conductivity not the permittivity ray tracing methods normally associated with undamped propagating waves can also be applied to the rapidly attenuated diffusive em waves encountered in the petroleum reservoir environment thermal noise considerations place an upper limit of approximately 20 skin depths on the separation between wells

crosswell electromagnetic tomography in steel cased wells the applicability of crosswell electromagnetic em tomography is limited when the boreholes are steel cased steel casing is typically eight orders of magnitude more conductive than the formations around the borehole consequently the high frequency signals which are needed to resolve the formation conductivity distribution in the interwell region cannot be radiated or received by antennas inside the casing introduction of small insulating gaps in the casing eliminates these problems by creating ports where signals can exit and enter the casing making the casing an electric bipole antenna the gapped casing can be operated in a shorted port or open port mode in the shorted port mode the voltage is specified at a source port and the current is measured at all the remaining shorted ports in the open port mode the current is specified at a source port and the voltage is measured at all the remaining open ports for high frequency shorted port operation the effective length of the casing bipole ant

ti phlogopites of the shaw s cove minette a comparison with micas of other lamprophyres potassic rocks kimberlites and mantle xenoliths the two generations of micas in the shaw s cove minette mica potash feldspar lamprophyre of northern new brunswick canada are tio2 rich phlogopites with variable but low silica and potash contents low soda and efectively all their aluminum in tetrahedral sites a majority of the micas have an excess of y cations and a deficiency of x cations there are positive correlations between excess y ions and number of al ions in z sites between k2o and sio2 contents and between k2o and volatile free totals yet the micas optically appear fresh do not respond to hydration or glycolation and x ray diffraction patterns show none of the peaks of talc montmorillonites vermiculite or 7 or l4 a chlorites this suggests that some normally octahedrally coordinated cations and water or hydronium ions are located in the interlayer x sites phenocryst micas are sharply zoned cores are paler colored and have high mg atomic ratio mg mg fe 2 0 810 88 cr2o3 i 0 88 wt vo and nio i 0 08 wt but relatively low tio2 2 93 wt and negligible bao phenocryst rims and groundmass micas are darker reddish brown and have lower mg 0 68 0 79 nil crzor and nio but high tio2 x 5 40 wt and bao x 0 38 wt micas in minettes from other localities 62 analyses are frequently richer in silica and potash than the shaw s cove samples but otherwise are generally chemically comparable chemical zoning or bimodalism is nearly universal in minette micas though the boundary between high zg low tioz phenocryst and low mghigh tioz groundmass groups varies from province to province and even from minette to minette within a swarm comparison of analyses of minette micas with 353 analyses of micas from other mafic largely potassic rocks indicates that micas chemically indistinguishable from those of minettes can be found within some other lamprophyres ultra potassic rocks kimberlites and high pressure xenoliths in alkaline volcanic rocks and kimberlites though each ofthese groups also contains micas unlike those in minettes those kimberlite phlogopites that match minette micas are predominantly secondary rims of phenocrysts or megacrysts or groundmass crystals mainly type ii but some are unzoned pre fluidization phenocrysts while primary primary metasomatic and uaruo suite phlogopites of mantle xenoliths are unlike minette micas higher mg and sioz lower tio2 and alzor some of the secondary metasomatic phlogopites in sheared garnetiferous mantle xenoliths are wholly minettelike the chemical identity of minette mica phenocryst cores and some phenocrysts of diverse mantle derived rocks implies crystallization under similar conditions by analogy with the chemistry of phlogopites produced experimentally in potassic systems at high pressures and studies of equilibration conditions of natural phlogopites it is concluded that phenocrystic phlogopites in minettes may form at temperatures and pressures up to at least 1250 c and 40 kbar and probably under o conditions between the nno and hm buffers higher o than for primary primary metasomatic and uanto suite micas in kimberlites and their included xenoliths

terrane accretion in the internal zone of the ungava orogen northern quebec part 1 tectonostratigraphic assemblages and their tectonic implications the tectonostratigraphic record of the ungava orogen contains evidence for the interaction of divergent transform and convergent plate boundaries over a 0 2 ga period in the early proterozoic three principal tectonic domains are recognized 1 autochthonous basement plutonic and supracrustal rocks of archean age 2 autochthonous and allochthonous sedimentary and volcanic units associated with a ca 1 99 1 92 ga rift to drift margin and 3 suspect crustal components of a ca 2 00 ga ophiolite and ca 1 90 1 83 ga island arc terrane domain 1 is the stratigraphic or structural basement to domains 2 and 3 field relationships indicate that domain 2 units were accumulated on or near domain 1 whereas no tectonostratigraphic linkages are known between domain 3 and the others accumulation of continent derived sedimentary rocks continental tholeiites komatiitic basalts and mafic lavas equivalent to modern normal mid oceanic ridge basalts n morb s in domain 2 is interpreted as recording continental rifting leading to the possible formation of oceanic crust pillowed basalts sheeted dykes and cumulate rocks suggest that the crustal portion of an ophiolite is preserved within domain 3 the ophiolite is interpreted as a suspect fragment of oceanic crust which may represent an earlier rifted portion of domain 2 possibly juxtaposed by transform plate boundary motions within domain 3 calc alkaline volcanic and plutonic units and sequences of volcanogenic and siliciclastic sedimentary rocks are thought to indicate the development of a magmatic arc and fore arc basin and thus the establishment of a convergent plate boundary the most internal lithotectonic packages in domain 3 are predominantly crystalline thrust sheets containing i an older intrusive suite interpreted as the plutonic foundation of the magmatic arc and ii younger plutons interpreted as the result of a reversal in subduction polarity the reversal may have followed attempted subduction of domains 1 and 2 beneath the upper plate arc assemblage of domain 3

evolution of the hazelton arc near terrace british columbia stratigraphic geochronological and geochemical constraints on a late triassic early jurassic arc and cu au porphyry belt understanding the development of island arcs that accreted to the north american craton is critical to deciphering the complex geological history of the canadian cordillera in the case of the hazelton arc part of the stikine terrane or stikinia in northwestern british columbia understanding arc evolution also bears on the formation of spatially associated porphyry cu au epithermal and volcanogenic massive sulfide deposits the hazelton group is a regionally extensive long lived and exceptionally thick upper triassic to middle jurassic volcano sedimentary succession considered to record a successor arc that was built upon the paleozoic and triassic stikine and stuhini arcs in central stikinia near terrace british columbia the lower hazelton group telkwa formation comprises three volcanic intrusive complexes mt henderson mt o brien and kitselas that at their thickest constitute almost 16 km of volcanic stratigraphy basal telkwa formation conglomerates and volcanic rocks were deposite

highly alkaline lavas in a proterozoic rift zone implications for precambrian mantle metasomatic processes an occurrence of proterozoic nephelinite and basanite lavas and pyroclastic rocks and associated phonolites indicates that the processes that generate modern alkaline magmas in intraplate settings were operative in the early proterozoic these lavas occur near the top of a 1 9 ga continental margin sequence in the cape smith fold and thrust belt of northern quebec the lavas are classified as nephelinites basanites and phonolites on the basis of high field strength and rare earth element contents although large ion lithophile elements including alkalis appear to have been strongly depleted by greenschist facies metamorphism and alteration certain major elements define trends consistent with low pressure fractionation dominated by clinopyroxene which is the only mafic phenocryst present in the lavas the mafic and felsic lavas have identical 143 nd 144 nd ratios consistent with consanguinity and a lack of contamination by older crust of the superior province values for nd 1 96 ga of 2 represent an enriched mantle source relative to 4 to 5 for the contemporaneous mid oceanic ridge basalt reservoir

paleoproterozoic carbonatitic ultrabasic volcanic rocks meimechites of cape smith belt quebec a 500 m thick lens of carbonatitic ultrabasic lapilli tuffs and lavas interbedded with platformal povungnituk sediments in the foreland of the cape smith belt is its earliest known magmatism and may relate to its initial rifting the sequence comprises tuffs capped in part by effusives accretionary and cored lapilli in the tuffs and pillows in the lavas suggest emplacement in a shallow marine environment its current assemblage of antigorite chlorite talc and in part primary carbonate magnetite ilmenite minor chromite and phlogopite results from probable concurrent hydro thermal alteration and subsequent greenschist regional metamorphism surviving accessory minerals apatite monazite zircon rutile and aeschenite are widespread but scarce carbonate mostly dolomite is a major and integral component of the rock and interpreted as an original albeit recrystallized magmatic constituent magnetite is conspicuous in the tuffs as lapilli and lapilli cores locally as giant crystals and as stringers except in subhedral groundmass crystals its negligible tio2 is evidence of its hydrothermal reconstitution compositions of chromite cores and rare relicts of phlogopite crystals are consistent with mantle derivation rock compositions are low in sio2 25 wt and alkaline the immobile incompatible elements e g zr average 260 ppm nb average 130 ppm and the light rare earth elements are enriched the rocks are compositionally similar to type siberian meimechites and closely resemble the meimechite carbonatite eruptives of castignon lake labrador trough based on experimental evidence lac leclair magmas are interpreted as originating by minor partial melting of carbonated mantle at 100 km depths and reaching the surface via conduits opened by deep rifting that initiated the cape smith segment of the trans hudson orogen

u pb ages for magmatism and deformation in the new quebec orogen the new quebec orogen is a paleoproterozoic fold and thrust belt active from 2 17 to 1 77 ga bordering the eastern margin of the archean superior province the orogen developed on a long lived passive continental margin and comprises two volcanic sedimentary sequences the ages presented in this study help to bracket the magmatic and deformational history of the orogen a glomeroporphyritic gabbro from the hellancourt formation was dated at 1874 3 ma and a rhyodacite from the upper murdoch formation yielded an identical age of 1870 4 ma these data allow the correlation of the two units and indicate that they are 10 14 ma younger than the estimated age for the sokoman formation these ages together with already published work indicate that magmatism related to the younger magmatic event occurred at 1884 1870 ma albitized pelites from the murdoch formation contain euhedral detrital zircons 2707 2690 ma old indicating that the source rocks were archean an undeformed monzonitic intrusion occurr

geochemical and tectono magmatic evolution of the volcano sedimentary rocks of pechenga and other greenstone fragments within the kola greenstone belt russia abstract the early proterozoic volcano sedimentary pechenga and imandra varzuga regions form the two larger fragments within the kola greenstone belt a prominent feature of the north eastern baltic shield this belt also contains three smaller fragments at polmak pasvik and ust ponoy the geology of the larger fragments consists of an older northern and a younger southern part separated by prominent conformable deformation zones accordingly the 2350 1850 ma lithological succession of the pechenga greenstone fragment is subdivided into the northern 2550 1905 ma and southern pechenga complexes 1905 1700 ma likewise the imandra varzuga fragment comprises the northern and southern imandra varzuga complexes the relatively better known northern pechenga complex is subdivided into four units which in turn are subdivided into 11 formations in contrast southern pechenga complex comprises only one unit subdivided into four volcano sedimentary and two volcanic formations both the volcanic and volcaniclastic components of these complexes are characterised by magmatic compositions ranging from basaltic andesite to trachybasalt trachyandesite basalt ferropicrite basalt picrite basalt andesite picrite basalt and andesite dacite rhyolite the gabbro wehrlite intrusions hosting the pechenga ni cu sulphide deposits lower down in the stratigraphy are petrogenetically related to ferropicritic volcanics volcanic rocks of the southern pechenga complex extruded from six autonomous contemporaneous volcanic centres the volcanic rocks belong to two geochemical cycles each starting with tholeiitic and ending with calc alkaline magmas these changes reflect magmatic responses to major tectonic phases of crustal rifting and closure changes in the sr and nd isotope ratios indicate that the magmatic melts originated in various deep mantle and mantle crustal source areas a systematic gradual geochemical change is observed between subsequent volcanic formations notwithstanding the fact that the deposition of such volcanic formations is commonly interrupted by sedimentary events changes in the magmatic source were therefore gradual and the magmatic processes were continuous the kola greenstone belt formed as an intracontinental rift kalevian rifting event that has undergone a complex tectono metamorphic evolution during the karelian orogenic megacycle 2550 1700 ma of the northern baltic shield the history of two complete tectono magmatic cycles the lapponian cycle and the svecofennian cycle within this megacycle is recorded in the volcano sedimentary successions of the pechenga fragment the complete lapponian cycle is embodied within the volcanic sequence of the imandra varzuga fragment where the composition of the volcanic and volcano sedimentary rocks range from tholeiitic and boninitic basalts to basaltic andesites calc alkaline rhyodacite boninitic picrite basalts and basaltic andesites subalkalic trachybasalts and trachyandesites here the subsequent svecofennian cycle is represented by tholeiitic basalts and ferropicrites followed al rich basalts and concluded by dacite rhyolites trachyandesites and trachytes during the final phases of the kalevian rifting event tholeiitic and ferropicritic magmas were generated from two distinct mantle sources the tholeiitic magma was derived from a subabyssal depleted mantle source in contrast the ferropicritic magma came from an abyssal metasomatically enriched mantle source the larger degree of mantle contamination in the latter was probably critical in the formation of the ni cu ores of the pechenga gabbro wehrlite intrusions

reply to the discussion by mitchell and tappe on kimberlites and aillikites as probes of the continental lithospheric mantle abstract we thank mitchell and tappe for giving us the opportunity to discuss the nature of kimberlite magmas we agree with mitchell and tappe about the importance of mineralogy but the mineralogy of interstitial phases in kimberlites can shed little light on the origin of kimberlite magmas our use of cation units enables the interpretation of kimberlite whole rock compositions in terms of the stoichiometry of their constituent minerals when viewed in this manner the variation in the whole rock compositions of kimberlites clearly indicates that they are mixtures of harzburgitic lithospheric mantle and a carbonate rich liquid aillikites are systematically more fe rich than kimberlites but both contain less silica than olivine such that they would evolve to lower si contents via olivine fractionation the opposite is true of olivine lamproites and meimechites although kimberlite whole rock compositions do not reliably predict diamond grade on a local scale there is a clear correlation between diamond grade and kimberlite composition on a global scale which likely has the same explanation as the correlation between g10 garnets and diamonds considering that there is still no officially accepted definition of kimberlite refusal to even consider the implications of their whole rock compositional variation verges on lack of scientific due diligence

u pb ages from the nimish formation and montagnais glomeroporphyritic gabbro of the central new quebec orogen canada three u pb zircon dates were obtained from two igneous suites associated with cycle 2 sedimentation in the central new quebec orogen labrador trough in the dyke lake area of the western part of the orogen schefferville zone the nimish formation includes a polymictic conglomerate containing quartz syenite cobbles that crystallized at 1877 8 1 3 ma these cobbles are petrographically and geochemically linked to the nimish volcanics which are intercalated with the sokoman iron formation consequently the syenite date gives an approximate age for both nimish magmatism and ironstone deposition in the schefferville zone a date of ca 2 65 ga obtained from a nimish trachyte in the same area indicates that zircons in the sample are xenocrysts farther east at howse lake howse zone a montagnais plagioclase glomeroporphyritic gabbro sill crystallized at 1884 0 1 6 ma the howse lake sill which intrudes turbidites of the menihek formation is considered comagmatic with the basalts that cap the form

upb geochronology of the western cape smith belt canada new insights on the age of initial rifting and arc magmatism abstract the cape smith belt of northern quebec is the foreland to hinterland transition of the ungava orogen a component of the paleoproterozoic trans hudson orogen of north america u pb ages for rift and volcanic arc related units from the cape smith belt are presented and used to evaluate models of its tectonic evolution a gabbroic sill intrusive into the rift related sediments near the base of the povungnituk group is 2038 2 4 ma old indicating that rifting of the superior province was initiated prior to that time 80 m y earlier than previously reported a granodiorite intrusive into the volcanic rocks of the povungnituk group is dated at 1991 2 ma indicating that magmatism associated with the rifting event was active at that time 30 m y earlier than formerly thought the age of parent group arc related magmatism ranges from 1874 3 4 ma the age of a diorite intrusion to 1860 2 ma the age of another diorite intrusion and of a rhyolite a granodiorite intrusive in the parent group yields an age of 1845 6 ma magmatism of the parent group is thought to be related to northward dipping subduction of the superior province margin below the watts group a gabbroic intrusion in the 2000 ma old watts group is dated at 1858 2 ma these ages are consistent with a tectonic model in which the rocks of the cape smith belt formed in a single continental rift to oceanic progression followed by subduction which led to an arc continent collision a comparison of u pb ages for similar events in different sectors of the trans hudson orogen in canada reveals that early events are diachronous and range from 2169 ma to 2038 ma the main collisional events are coeval in the ungava and new quebec orogens and in some of the western sectors at 1830 1860 ma younger ages of 1800 1820 ma are obtained for the late collisional stages throughout the trans hudson orogen

enriched mantle components in proterozoic continental flood basalts of the cape smith foldbelt northern quebec magmatism associated with ca 2 04 ga rifting of the superior province resulted in the formation of a succession of tholeiitic and alkaline basalts as well as minor rhyolites collectively known as the povungnituk group cape smith foldbelt the tholeiites are not typical continental flood basalts cfb as they lack significant negative nb and ta anomalies indicating that crustal contamination has not played a major role in their evolution although crystal fractionation along a gabbroic cotectic can account for much of the compositional variation in the povungnituk basalts it cannot explain the range of observed traceelement ratios which is similar to that from tholeiitic to highly alkaline lavas observed in modern ocean island basalt suites variations of la sm and nb zr indicates the presence of a highly enriched component and that mixing between this enriched component and a non enriched end member can account for the range of trace element ratios in the povungnituk lavas although the most enriched tholeiites are spatially associated with an alkaline volcanic center enriched tholeiites are widely interspersed in the povungnituk group and are also found in other parts of the eastern trans hudson orogen the paleoproterozoic mantle source appears to have contained a dispersed but variable enriched component that was responsible for the variation of degree of enrichment of the povungnituk tholeiitic basalts d 2003 elsevier b v all rights reserved

fluid flow monitoring using electromagnetic probing high frequency electromagnetic probing is used to monitor the rate and direction of flow of fluids injected into the ground this method shows the potential for providing more detailed information than procedures presently used the experimental technique and the test of concept experimental results are discussed this technique has applications in oil reservoir engineering and in hydrology studies concerning storage of chemical wastes

age and tectonic implications of paleoproterozoic mafic dyke swarms for the origin of 2 2 ga enriched lithosphere beneath the ungava peninsula canada abstract mafic dyke swarms represent short lived magmatic events that carry important temporal and chemical constraints for the evolution of the lithospheric mantle five baddeleyite u pb isotopic analyses of paleoproterozoic mafic dyke swarms intruding the ungava peninsula yielded ages of 2508 6 2220 1 2212 3 2199 5 and 2149 3 ma these ages fall within the 2 5 2 0 ga period previously defined by five other swarms which together comprise a magmatic record of more than 500 ma the similar age composition and surface area of two 2 51 ga swarms along with the lack of coeval supracrustal rocks suggest they correspond to failed rifts an important magmatic hiatus of 280 ma follows but ends with the intrusion of numerous dykes between 2 23 and 2 20 ga in the thinnest lithosphere of the northern ungava peninsula these dykes exhibit chemical signatures that vary from enriched older 2229 2212 ma dykes nd t 4 to relatively depleted 2209 2199 ma voluminous younger dykes nd t 1 4 la yb ca 2 21 2 20 ga later dykes emplaced ca 2 17 ga within a rejuvenated paleoproterozoic lithosphere also have depleted chemical compositions and map the extent of rifting coeval with the emplacement of early basalts in the labrador trough dykes emplaced in the 2 15 2 00 ga period further to the south are proximal to coeval continental basalts with which they share enriched isotopic compositions nd t 1 5 to 7 and a positive correlation between la yb and zr nb la yb 4 10 zr nb 7 20 that suggest assimilation of an archean crustal component a progressive decrease in the nd t values of these magmas with decreasing age further implies increasing contamination until the archean lithosphere failed ca 2 0 ga and permitted the eruption of isotopically depleted basalts the ca 2 2 ga depleted northern dykes and the 2 1 1 9 ga povungnituk basalts of the cape smith foldbelt share a negative correlation between zr nb and la yb that is expected for the incorporation of an enriched lithospheric component this component is represented by the alkaline rocks comprised in the circum ungava supracrustal belts carbonatites lamprophyric lavas alkaline basalts and by the lac aigneau lamprophyric dykes 1941 3 ma intruding the ungava peninsula these alkaline magmas collectively have 2 2 2 1 ga depleted mantle nd model ages t dm similar to a 2 15 ga sm nd isochron defined by the basaltic rocks of the supracrustal belts although these nd t dm ages and isochron are 100 300 ma older than magmatic ages they are identical with the ca 2 2 ga mafic dykes of the ungava peninsula this time correlation along with the similar chemical signature of the northern dykes and younger povungnituk basalts suggest that the composition of younger lavas and alkaline magmas was influenced by an enriched component associated with the pervasive metasomatism of the lithosphere coeval with the emplacement of the many ca 2 2 ga dykes

petrology of the abloviak aillikite dykes new quebec evidence for a cambrian diamondiferous alkaline province in northeastern north america a dozen ultramafic lamprophyre dykes have been identified in the eastern part of ungava bay quebec the dark grey dykes are composed of macrocrysts of olivine and phlogopite featuring tetraferriphlogopite rims these minerals are included in a matrix consisting of fine grained phlogopite olivine spinel and interstitial carbonate the geochemical composition mineral assemblage chemical analyses of the xenocrysts and phenocrysts and sm nd isotopic signature indicate that these rocks are carbonated ultramafic lamprophyre dykes the chemical zonation of the micas and the presence of andradite suggest a complex sequence of crystallization an ar isotope correlation analysis indicates an age of approximately 550 ma the dykes have intruded the tasiuyak gneiss a suite of paleoproterozoic metasedimentary rocks this unit occupies the torngat orogen collision zone between the rae province and the nain province the dykes are considered to have been emplaced within tension gashes during reactivation of major