ammonium in granites and its petrogenetic significance abstract ammonium is present as a trace constituent in all granites with an average concentration of 45 ppm nh4 equivalent to 35 ppm of elemental n it shows wide variations related to petrography and region but the only significant correlation between ammonium and other geochemical parameters is that it is most abundant in peraluminous granites and least abundant in peralkaline granites these variations can be related to a the amount of sedimentary material in the magmatic source region and b redox conditions in the source region the ammonium content of granitic magmas can also be modified by fractionation or contamination hydrothermal alteration has a major effect on the ammonium content of granitic rocks and variation due to this cause may exceed the magmatic variation most hydrothermally altered granites are enriched in ammonium as a result of the transfer of ammonium from sedimentary country rocks by the hydrothermal fluids

tectonic implications from sapphirine bearing lithologies south west grenville province canada sapphirine has been found in two types of magnesian metabasic lenses from tectonite zones within the central gneiss belt of the south west grenville province canada the first type association i comes from a lenticular mafic lens within highly tectonized anorthosite the second type association ii comes from meta eclogitic pods with foliated amphibolite rims in each case the sapphirine bearing assemblages record a wealth of reaction textures the primary mineralogy in association ii is represented by high alumina clinopyroxene garnet and kyanite plagioclase and records pressures of around 14 16 kbar in association i the primary mineralogy is represented by plagioclase two pyroxenes and possibly olivine but here the equilibrium pressure is unknown the host gneisses equilibrated at approximately 8 to 10 kbar and 700 750 c by continuous cation exchange reactions during and after the culmination of the grenvillian orogeny at 1 16 1 0 ga it is unlikely that the higher pressures recorded in the meta eclogitic pods represent an earlier high pressure metamorphism as the pods are restricted to shear zones a tectonic mode of emplacement into a crust undergoing granulite facies metamorphism is more likely sapphirine formed by discontinuous decompression reactions in association ii this involved a reaction between garnet and kyanite and resulted in the formation of magnesian granulite facies assemblages at the same time primary clinopyroxene became much less aluminous by evolving plagioclase pressures and temperatures from coexisting phases that are believed to have equilibrated at the same time as sapphirine formation are estimated as 11 to 12 kbar and 750 c these probably represent the peak conditions for granulite facies metamorphism in the south west grenville province

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

late holocene formation of lake michigan beach ridges correlated with a 70 yr oscillation in global climate abstract a radiocarbon dated series of 75 beach ridges formed at regular intervals averaging 72 yr over the past 5400 yr provides further support for the existence of a 70 yr oscillation in northern hemisphere climate postulated recently from instrument data representing less than two cycles of this climate oscillation results from this study lend support to the interpretation that internal variations in the ocean atmosphere system are an important factor in climate fluctuations on a decadal centennial time scale a temperature oscillation with a period of about 70 yr has been a previously unrecognized but fundamental part of the global climate system since at least the middle holocene

nature of the elzevir mazinaw domain boundary grenville orogen ontario the mooroton shear zone msz of the metasedimentary belt of the grenville orogen in ontario separates the mazinaw domain to the east from the elzevir domain the shear zone is composed of mafic metavolcanic metaclastic and marble mylonites and is characterized by a subvertical foliation which crosscuts the regional foliation and a near vertical stretching lineation microstructures indicate deformation occurred under crystal plastic conditions and shear sense indicators give movement of east mazinaw side up the geometry of the msz which follows the eastern margin of the elzevir tonalite implies that lithologic anisotropy guided its location garnet biotite and garnet hornblende peak temperatures are juxtaposed across the msz with temperatures ranging from 460 to 530 c in the southeastern elzevir and 490 to 620 c in the southwestern mazinaw conditions in amphibolite facies limiting barometers applied to rocks in both domains show no significant offset petrologic data within the shear zone

transformation of fe ti gabbro to coronite eclogite and amphibolite in the baie du nord segment manicouagan imbricate zone eastern grenville province fe ti gabbros from the baie du nord segment of the manicouagan imbricate zone metamorphosed under high p t conditions during the grenvillian orogeny have been the focus of a detailed micropetrological study textures and mineral chemistry suggest that the mineral assemblages represent progressive stages of metamorphic transformation resulting in the formation of coronas pseudomorphs after igneous phases transitional and true granoblastic eclogites the transitional and eclogitic samples also have coronas which are developed locally around igneous xenocrysts of plagioclase and olivine the deformed margins of coronitic fe ti gabbros are transformed to amphibolite and contain clinopyroxene bearing leucosomes with garnet poikiloblasts that are indicative of high p t dehydration melting interpretation of garnet zoning and thermobarometry suggest that the highest p t conditions are recorded by coronas around xenocrysts c 720 800 c at 14 17 kbar and garnet clinopyroxene cores in granoblastic assemblages c 740 820 c at 13 17 kbar in the eclogitic samples re equilibration during the early stages of exhumation at high t conditions 700 c affected all samples and is evidenced by the widespread development of pargasite bearing plagioclase collars in the coronitic and transitional metagabbros and by widespread re equilibration of the eclogites giving lower p t estimates at grain boundaries however the difference in calculated pressure conditions between coronite and eclogite samples is consistent with increasing pressure depth from the coronites 11 13 kbar to the eclogites 13 17 kbar the p t conditions recorded by these rocks define a metamorphic field gradient which suggests high heat flow through the lower crust during the grenvillian orogeny

mineralogy of four sandy soils developed under heather oak spruce and grass in the same fluvioglacial deposit in denmark the degree of weathering was investigated in four sandy soils at hjelm hede in northwest jutland denmark previous studies showed that the degree of podzolisation was influenced by vegetation as follows quercus robur oak calluna uulgaris heather picea sitchensis spruce this study shows that the soil under grass is the least podzolized the data show that the particle size and mineralogy of the parent material from site to site are closely similar determination of the mineralogy and chemical composition of five particle size fractions from horizons of each of the four soils indicated an in situ fragmentation of mineral grains and losses of al ca na and k relative to si the apparent degrees of weathering under spruce heather and oak were similar and somewhat more intense than that under grass

seismic images of eclogites crustal scale extension and moho relief in the eastern grenville province quebec seismic images from a 250 km lithoprobe reflection profile in the interior of the eastern grenville province provide important new constraints on the crustal architecture of this part of the orogen prominent upper crustal reflections can be correlated with exposures of high pressure metamorphic rocks in the manicouagan shear belt providing the first direct evidence for eclogite reflectivity in the grenville province the eclogites are cut by major late grenvillian normal faults that penetrate the deep crust and preserve evidence of extensional collapse of the overthickened orogen north to south crustal thinning indicated by a change in moho reflection time from 16 to 13 s correlates well with regional bouguer gravity trends and is accompanied by a dramatic increase in the reflectivity of the lower crust these features underscore the significance of recently recognized along strike variations in tectonic style within the grenville province and point to the internal complexity that characterizes the root zones of collisional orogens

structural development and petrofabrics of eclogite facies shear zones bergen arcs western norway implications for deep crustal deformational processes caledonian eclogite facies shear zones developed from grenvillian garnet granulite facies anorthosites and gabbros in the bergen arcs of western norway allow direct investigation of the relations between macroscopic structures and crystallographic preferred orientation cpo in lower continental crust field relations on the island of holsnoy show that the eclogites formed locally from granulite facies rocks by progressive development of 1 eclogite adjacent to fractures 2 eclogite in discrete shear zones 2 m thick 3 eclogite breccia consisting of 80 well foliated eclogite that wraps around rotated granulite blocks and 4 anastomosing subparallel eclogite facies shear zones 30 100 m thick continuous over distances 1 km within the granulite terrane these shear zones deformed under eclogite facies conditions at an estimated temperature of 670 50 c and a minimum pressure of 1460 mpa which corresponds to depths of 55 km in the continental crust detailed investigation of the major shear zones shows the development of a strong foliation defined by the shape preferred orientation of omphacite and by alternating segregations of omphacite garnet rich and kyanite zoisite rich layers a consistent lineation throughout the shear zones is defined by elongate aggregates of garnet and omphacite the cpo of omphacite determined from five axis universal stage measurements shows a strong b axis maximum normal to foliation and a c axis girdle within the foliation plane with weak maxima parallel to the lineation direction these patterns are consistent with deformation of omphacite by slip parallel to 001 and suggest glide along 010 the lineation and cpo data reveal a consistent sense of shear zone movement although the displacement was small localized faulting of high grade rocks accompanied by fluid infiltration can be an important mode of failure in the lower continental crust field relations show that granulite facies rocks can exist in a metastable state under eclogite facies conditions and imply that the lower crust can host differing metamorphic facies at the same depth deformation of granulite and partial conversion to eclogite such as is exposed on holsnoy island may be an orogenic scale process in the lowermost crust of collisional orogens

a strand plain soil development sequence in northern michigan usa abstract a practical problem limiting the theoretical application of a soil chronosequence study lies in the difficulty of identifying an appropriate geomorphic age sequence with more than a few surfaces a sequence of approximately 75 strand plain beach ridges located along the northern shore of lake michigan usa overcomes this problem and was used to explore rates of soil development in the initial stages of podzolization well drained pedons were sampled on 24 of the ridges with an age range of 10 to 5200 years chronofunctions were developed using statistical regression techniques for most forms of extractable fe and al both linear and log linear functions adequately describe the changes in property with surface age dithionite citrate extractable fe content however shows little correlation with surface age high r 2 values 0 7 for chronofunctions representing most extractable sesquioxide forms suggest that b horizon sesquioxide content increases with surface age as expected for soils undergoing podzolization visual inspection of chronofunction data suggests that scatter increases on surfaces older than 3000 years possibly because soil spatial variability increases with surface age theory suggests that the log linear form of chronofunctions may be preferable to the linear form for these pedons in general equation slopes are steeper for chronofunctions representing only the initial 1650 years of soil development than for those representing the entire 5200 year sequence suggesting that initially rapid pedogenesis slows over time most chronofunctions for ph and weighted profile organic c are not statistically significant possibly because the temporal resolution of the chronosequence is too coarse to detect valid trends for properties that rapidly approach a steady state

contribution of mineral tunneling to total feldspar weathering in this study we quantified the contribution of mineral tunneling by fungi to weathering of feldspars and ecosystem influx of k and ca we studied the surface soils of 11 podzols across a lake michigan sand dune chronosequence with soil ages between 450 and 5000 years weathering by tunneling was quantified in thin sections by image analysis total mineral weathering was quantified by comparing the mineralogy of the surface soil with the underlying parent material mineralogy was characterized using x ray fluorescence spectroscopy xrfs followed by a normative mineralogical calculation tunnels were observed only in soils older than 1650 years throughout the chronosequence the contribution of tunneling to mineral weathering in the upper mineral soil expressed as tunnel volume divided by volume of weathered feldspar was less then 1 contribution of tunneling to na ca feldspar weathering was higher than the contribution of tunneling to k feldspar weathering feldspar tunneling equals an average ecosystem influx of 0 4 g ha 1 year 1 for k and 0 2 g ha 1 year 1 for ca over 5000 years of soil development intensity of mineral tunneling determined as fraction weathered feldspars was higher than in a previously described north swedish podzol chronosequence the presented data suggest that the contribution of tunneling to weathering becomes more important in older soils but remains low

lateral ramps as an aid to the unroofing of deep crustal rocks seismic evidence from the grenville province we suggest that lateral ramps in the basement to orogenic wedges may be important agents in the rapid unroofing of deeply buried continental crust our suggestion is based on a study of the distribution of high pressure metamorphosed continental rocks in the mesoproterozoic grenvillian orogen in eastern quebec these rocks were buried to depths of more than 50 km through crustal thickening during a continental collision and were then rapidly unroofed they are currently exposed in a 100 km 60 km lobate embayment north of the manicouagan reservoir using a combination of surface structural data and seismic reflection data from lithoprobe line 55 we reconstruct the three dimensional form of the high pressure rocks our reconstruct ion methods are based on demonstrable correlations between the attitudes of gneissic layering at the surface and the attitudes of reflectors on the seismic profile they make extensive use of the fact that much of the seismic reflectivity on line 55 comes from outside the vertical plane of the seismic line because of the sinuous nature of the line and its obliquity to tectonic strike the validity of the reconstructions is demonstrated by the generation of a synthetic seismogram from the interpreted geometry that is very similar to the observed seismogram our reconstruction shows that a steep lateral ramp extends to the base of the crust immediately behind the broad lobe of high pressure rocks at the surface the lateral ramp probably provided a favorable pathway for the extrusion of deep seated rocks from the deep crust and their transport onto the foreland

transect across the northwestern grenville orogen georgian bay ontario polystage convergence and extension in the lower orogenic crust the grenville orogenic cycle between 1190 and 980 ma involved accretion of magmatic arcs and or continental terranes to the laurentian craton a transect across the western central gneiss belt georgian bay ontario which crosses the boundary between parautochthonous and allochthonous units at an inferred orogenic depth of 20 30 km offers some insights on the thermal and mechanical behavior of the lower crust during the development of the grenville orogen prior to grenvillian metamorphism this part of laurentia consisted largely of meso proterozoic 1450 ma granitoid orthogneisses granulites and subordinate mafic and supracrustal rocks grenvillian convergence along the transect began with transport of the previously deformed and metamorphosed 1160 ma parry sound domain over the craton sometime between 1120 ma and 1080 ma this stage of transport was followed by out of sequence thrusting and further convergence along successively deeper foreland propagating ductile thrust zones a major episode of extension at 1020 ma resulted in southeast directed transport of allochthonous rocks along the midcrustal shawanaga shear zone the final stage of convergence involved deformation and metamorphism in the grenville front tectonic zone at 1000 980 ma peak metamorphism along most of the transect at 1065 1045 ma followed initial transport of allochthonous rocks over the craton by 15 35 m y regional cooling which postdated peak metamorphism by 70 m y was probably delayed by the combined effects of late stage extension and convergence transport of allochthons at least 100 km over the craton was accomplished along a weak migmatitic decollement further propagation of the orogen into the craton followed partial melting and weakening of parautochthonous rocks below this decollement extensional deformation was associated with distributed ductile flow the formation of regional transverse folds with axes parallel to the stretching direction and reactivation of the allochthon parautochthon thrust boundary as an extensional decollement the extensional lower crustal flow was likely the primary cause of the subhorizontal attitude of many structures and seismic reflectors in this part of the central gneiss belt

crustal architecture and tectonic assembly of the central gneiss belt southwestern grenville province canada a new interpretation the central gneiss belt southwestern grenville province is characterized by parautochthonous crust in the north and allochthonous lithotectonic domains in the south despite nearly two decades of study the basal decollement to allochthonous domains transported from the southeast known as the allochthon boundary thrust has not been precisely located throughout much of the belt between lake nipissing and georgian bay where its surface trace is known it separates 1 24 ga sudbury metadiabase in the footwall from eclogite remnants and 1 17 1 15 ga coronitic olivine metagabbro confined to its hanging wall on the premise that this relationship can be used to trace the allochthon boundary thrust elsewhere in the central gneiss belt we have sought to extend the known distribution of these mafic rock types making use of field petrographic and geochemical criteria to identify them new occurrences of all three mafic types are identified in a region extending from south of lake nipissing to western quebec

rates of weathering and chemical depletion in soils across a chronosequence of lake michigan sand dunes abstract accumulation of soil organic matter and depletion of base cations and trace metals were measured in surface soils i e o horizon and upper 15 cm of mineral soil across a 4150 year soil chronosequence of dune capped beach ridges bordering northern lake michigan within 400 years of beach ridge formation coniferous forest develops soil c and n accumulate to steady state levels of 40 and 1 3 mg ha 1 respectively and the ph of the upper mineral soil decreases from 8 5 to 4 3 as carbonate minerals dissolve after substantial proportions of ca and mg have been removed an incipient spodic horizon can be observed the upper surface of which progressively deepens with increasing soil age analysis of soil strain of the upper mineral soil showed gradual dilation reaching 121 after several centuries of soil development after accounting for soil dilation quantities of ca mg p zn mn fe and v in the upper 15 cm of mineral soil decreased exponentially to low asymptotic levels representing quantities contained in weathering resistant minerals mass balance modeling indicated weathering and elemental losses in the order of decreasing decay constant as ca mg mn zn p v fe al k na ti this sequence is consistent with weathering of carbonates then ferromagnesian minerals then feldspars p levels are tightly coupled with ca losses in soils older than 200 years suggesting that ca rather than fe or al stabilizes p high concentrations of heavy metals in the organic horizon relative to the upper mineral soil indicate atmospheric inputs of industrial pollutants

paleomagnetism and petrophysics of the janisjarvi impact structure russian karelia paleomagnetic rock magnetic and petrophysical results are presented for impactites and target rocks from the lake janisjarvi impact structure russian karelia the impactites tagamites suevites and lithic breccias are characterized by increased porosity and magnetization which is in agreement with observations performed at other impact structures thermomagnetic hysteresis and scanning electron microscope sem analysis document the presence of primary multidomain titanomagnetite with additional secondary titanomaghemite and ilmenohematite the characteristic impact related remanent magnetization chrm direction d 101 5 i 73 1 95 6 2 yields a pole lat 45 0 n long 76 9 e dp 9 9 dm 11 0 additionally the same component is observed as an overprint on some rocks located in the vicinity of the structure which provides proofs of its primary origin an attempt was made to determine the ancient geomagnetic field intensity seven reliable results were obtained yielding an ancient intensity of 68 7 7 6 t corresponding to vdm of 10 3 1 1 x 10 22 am 2 the intensity however appears to be biased toward high values mainly because of the concave shape of the arai diagrams the new paleomagnetic data and published isotopic ages for the structure are in disagreement according to well defined paleomagnetic data two possible ages for magnetization of jnisjrvi rocks exist 1 late sveconorwegian age 900 850 myr or 2 late cambrian age 500 myr however published isotopic ages are 718 5 myr k ar and 698 22 myr 39ar 40ar but such isotopic dating methods are often ambiguous for the impactites

erratum the high pressure belt in the grenville province architecture timing and exhumation we propose that the grenvillian allochthonous terranes may be grouped into high pressure hp and low pressure lp belts and examine the hp belt in detail in the western and central grenville province the hp belt is developed in paleo and mesoproterozoic rocks of the pre grenvillian laurentian margin and characterized by grenvillian eclogite and co facial hp granulite in mafic rocks pressure temperature p t estimates for eclogite facies conditions in well preserved assemblages are about 1800 mpa and 850 c in the central grenville province hp rocks formed at 1060 1040 ma and underwent a single stage of unroofing with transport into the upper crust by 1020 ma whereas farther west they underwent two stages of unroofing separated by penetrative mid crustal recrystallization before transport to the upper crust at 1020 ma unroofing processes were comparable in the two areas involving both thrusting and extensional faulting in an orogen propagating into its foreland by understacking in detail thrusting episodes preceded extension in the western grenville province whereas in the central grenville province they were coeval resulting in unroofing by tectonic extrusion in the central grenville province the footwall ramp is well preserved but any former ramp in the western grenville province was obliterated by later lower crustal extensional flow continuation of the hp belt into the eastern grenville province is not established but likely on geological grounds however the pattern of deep crustal seismic reflection in the lithoprobe eastern canadian shield onshore offshore transect ecsoot line contrasts with that father west suggesting that if present the hp rocks were exhumed by a different mechanism

time of metamorphism beneath the central metasedimentary belt boundary thrust zone grenville orogen ontario accretion at 1080 ma new u pb zircon and titanite data from the muskoka domain grenville province ontario provide protolith and metamorphic ages for the southwestern central gneiss belt discordant analyses from a migmatitic orthogneiss and its leucosome form a linear array with an upper intercept age of 1457 6 ma and a lower intercept age of 1064 18 ma u pb analyses on metamorphic zircon from an amphibolite yield a set of concordant analyses with an average 207pb 206pb age of 1079 3 ma a weakly migmatitic granitoid rock and a transecting charnockitic vein in the immediate footwall of the central metasedimentary belt boundary thrust zone yielded a discordant array of analyses wth an upper intercept age of 1394 13 ma and a lower intercept age of 1066 8 ma the charnockitic vein yielded concordant zircon ages of 1077 2 ma the upper intercept ages are interpreted in terms of protolith crystallization and the concordant and lower intercept ages as grenviilian high grade metamorphism and associated anatexis we h

feldspars as a source of nutrients for microorganisms phosphorus and nitrogen are essential macronutrients necessary for the survival of virtually all living organisms in groundwater systems these nutrients can be quite scarce and can represent limiting elements for growth of subsurface microorganisms in this study we examined silicate sources of these elements by characterizing the colonization and weathering of feldspars in situ using field microcosms we found that in carbon rich anoxic groundwaters where p and n are scarce feldspars that contain inclusions of p minerals such as apatite are preferentially colonized over similar feldspars without p a microcline from s dakota which contains 0 24 p 2 o 5 but 1 mu mol g nh 4 super was heavily colonized and deeply weathered a similar microcline from ontario which has no detectable p or nh 4 super was barren of attached organisms and completely unweathered after one year anorthoclase 0 28 p 2 o 5 approximately 1 mu mol g nh 4 super was very heavily colonized and weathered whereas plagioclase specimens 0 01 p 1 mu mmol g nh 4 super were uncolonized and unweathered in addition the observed weathering rates are faster than expected based on laboratory rates we propose that this system is particularly sensitive to the availability of p and the native subsurface microorganisms have developed biochemical strategies to aggressively scavenge p or some other essential nutrient such as fe super 3 from resistant feldspars the result of this interaction is that only minerals containing p will be significantly colonized and these feldspars will be preferentially destroyed as the subsurface microbial community scavenges a limiting nutrient

coronitic metagabbro and eclogite from the grenville province of western quebec interpretation of u pb geochronology and metamorphism we present new u pb and metamorphic data on high pressure coronitic metagabbros from three distinct structural settings in the parautochthonous belt of the grenville province in western quebec intrusive ages are i for metagabbro close to the grenville front correlative with the sudbury dykes defined in ontario ii for an eclogitized lens at the base of the highest structural level sl4 a new age for mafic magmatism in the western grenville and iii for metagabbro from sl4 interpreted as correlative with metagabbros from the algonquin and shawanaga domains in ontario metamorphism in all cases is grenvillian with the best constrained age of 1069 3 ma for the metagabbro of sl4 metamorphic grade increases from the grenville front to the south the mafic rocks preserve relict igneous textures overprinted by garnet clinopyroxene that developed as coronas and or pseudomorphs after igneous phases the highest grade metagabbros contain omphacite and some lack primary plagioclase therefore b