zircon u pb age hf isotopes and geochemistry of shuichang algoma type banded iron formation north china craton constraints on the ore forming age and tectonic setting abstract the shuichang iron deposit is an algoma type bif in the north china craton the shuichang bif is interlayered with plagioclase hornblende gneiss indicating that these two lithologies are temporally closely associated we use the content of major elements and their ratios in order to define the protolith of the plagioclase hornblende gneiss sims u pb dating of zircons from the plagioclase hornblende gneiss suggests that the shuichang bif was formed at ca 2547 7 ma and was subjected to metamorphism at 2513 4 ma the major elements and ree data of the ore as well as individual magnetite and chert bands indicate that the shuichang bif precipitated from hydrothermal fluids discharging on the sea floor and that iron and silica may be associated with submarine volcanic activity in situ lu hf analysis of zircons from the plagioclase hornblende gneiss yielded initial 176 hf 177 hf ratios from 0 280903 to 0 281197 and e hf t values from 10 5 to 0 4 with a weighted mean value of 8 72 0 38 the single stage hf model age ranges from 2836 ma to 3249 ma we infer that the protolith of the plagioclase hornblende gneiss originated from the enriched mantle mixed with a small amount of subducted crust materials the shuichang bif formed at 2 5 ga and is coeval with other bifs in north china and in other cratons in the world we propose that the shuichang bif was formed in a subduction related back arc basin or intra arc basin based on the geochemical signatures of the wall rocks we further point out that the 2 5 ga global bif formation peak not only predates the amalgamation of the north china craton but probably also record an ancient supercontinent event

mesoarchean assembly and stabilization of the eastern kaapvaal craton a structural thermochronological perspective 1 understanding the construction and stabilization of archean continental lithosphere has important implications for models of tectonic and thermal regimes in the early earth as well as for the subsequent evolution of continents we provide new constraints for the amalgamation and stabilization of the eastern kaapvaal craton in the vicinity of the barberton greenstone belt circa 3 3 3 1 ga isotope dilution thermal ionization mass spectrometry u pb geochronology and thermochronology are combined with mapping and structural analysis around the margins of this belt in order to constrain movement on major shear zones that separate high grade orthogneiss terranes from low grade supracrustal rocks and to relate this movement to the timing of differential exhumation new and existing data are consistent with accretion at 3 23 ga within an oblique subduction plate boundary manifested in the bgb as an asymmetric flower like structural geometry for 100 ma following terrane assembly transform boundary tectonics manifested partially as transtension on reactivated faults led to large scale juxtaposition of middle to lower crustal basement orthogneiss complexes against upper crustal greenstone sequences and episodic emplacement of granitic batholiths stabilization of this portion of archean lithosphere involved at least a three stage process 1 creation of a thick and rigid mantle lithosphere during crustal growth subduction and terrane assembly from circa 3 30 to 3 23 ga 2 generation of a rigid crust during strike slip and transtensional tectonics coupled with migration of granites and heat producing elements into the upper crust between circa 3 2 and 3 1 ga and 3 erosion and removal of the uppermost crust during regional peneplanation that lasted until circa 2 9 ga

flow and solute transport through the soil matrix and macropores of a hillslope segment subsurface flow from various portions of a soil profile on a steep forested hillslope was evaluated by two sets of step change miscible displacement tests at different application rates and antecedent hydrologic conditions solutions of nacl 1000 mg l 1 cl were applied at steady state rates equivalent to 20 and 30 mm h 1 of standing water over the entire plot area using a line irrigation source located 1 5 m upslope lateral distance from an excavated soil pit subsurface flow and tracer breakthrough from five portions the organic rich soil layer including macropores the mineral soil matrix and three groups of macropores in the mineral soil layer of the soil profile were individually measured and analyzed using a convective dispersive model matrix flow dominated discharge from the soil pit during tracer tests 70 93 of total discharge however during wet periods with upslope drainage macropores including organic rich soil contributed proportionally more flow than during periods when upslope drainage was minimal outflow from macropores during the test with wet antecedent conditions had lower cl concentrations than drainage from the soil matrix suggesting dilution in macropores from upslope drainage effective pore volumes calculated for the flow averaged breakthrough data from the entire profile were much less 40 than the estimates measured by tensiometers of total volume of pore water suggesting that preferential flow significantly contributed to subsurface transport of tracer the pore volume for the entire profile increased only slightly with increasing application rate however the relative proportions of pore volumes calculated for individual portions varied proportionally to antecedent hydrologic conditions these changes are attributed to the expansion of individual macropores with surrounding soil and the lateral extension of macropore networks during wetter conditions

bicarbonate fluxes and co2 consumption by chemical weathering on the japanese archipelago application of a multi lithological model framework abstract prediction of co 2 consumption by chemical weathering is important to understand the global carbon cycle and island arcs are assumed to contribute significantly to the transfer of atmospheric soil co 2 to the oceans previous work established empirical functions for bicarbonate flux and co 2 consumption in dependence of runoff for five to six lithological classes these functions were applied in global studies however it has remained uncertain if improvements can be achieved by considering further factors or by an enhanced lithological classification scheme this study applies a new lithological map of japan with an enhanced lithological classification a hydrochemical data set representing 382 catchments covering 44 4 of the japanese archipelago and a multi lithological model approach to predict bicarbonate fluxes and co 2 consumption by chemical weathering because of significant carbonate contents in sediments different from carbonate sedimentary rocks acid plutonics and metamorphics firstly a bicarbonate flux model approach is established and secondly silicate and carbonate co 2 consumption is estimated based on the geochemical composition of rocks in accordance with previous studies on the catchment scale the most important factors controlling bicarbonate fluxes are lithology and runoff the anion ratio hco 3 so 4 2 cl is identified as the third most important predictor because anion sources and anion composition of river water have a great effect on bicarbonate concentrations and last but not least potential predictors such as gradient of slope temperature and physical erosion explain some part of the observed bicarbonate flux variation these potential predictors have been discussed in literature but quantification of the effects of these factors remains difficult due to their correlation with runoff and lithology however all tested models reproduce a total of observed bicarbonate fluxes within 10 on the regional scale including the simplest model which recognizes only lithology and runoff as predictors model results suggest that bicarbonate flux from the japanese archipelago is about 6 61 t c km 2 a 1 and co 2 consumption by chemical weathering is about 6 05 t c km 2 a 1 91 6 of bicarbonate flux this co 2 consumption rate is 3 2 times above the global average rate the silicate to carbonate co 2 consumption ratio is comparatively high it amounts to 9 9 which is above the global value the latter one being 1 to 1 5 carbonate sedimentary rocks contribute only 1 3 to bicarbonate fluxes due to their low areal proportion 0 2 acid volcanic rocks va show the lowest bicarbonate fluxes on average while basic and intermediate volcanics vb as well as pyroclastics py are in the range of the japanese average value the carbonate weathering contribution to bicarbonate fluxes from mixed sediments siliciclastic sediments metamorphics and acid plutonics is estimated to be 69 2 23 3 63 4 and 24 8 respectively only an average carbonate co 2 consumption per lithological class is calculated because no function based on typical predictors could be established to calculate carbonate weathering contribution to silicate dominated lithological classes this can be attributed to large spatial differences in carbonate content in rocks and to corresponding contributions to bicarbonatefluxes in the following results are compared to bicarbonate flux models of previous studies and identified differences are discussed in conclusion recognition of carbonate abundance in silicate dominated lithological classes including trace calcite is important to calculate silicate carbonate co 2 consumption ratios presented results are relevant for studies modelling co 2 consumption by chemical weathering in context of the global c cycle

geochemistry and zircon u pb hf isotopic systematics of the neoarchean yixian fuxin greenstone belt northern margin of the north china craton implications for petrogenesis and tectonic setting abstract the yixian fuxin greenstone belt in the western liaoning metamorphic terrane is situated in the middle segment of the northern margin of the north china craton ncc and is composed mainly of plagioclase amphibolites pyroxene amphibolites and hornblende plagioclase gneisses la icpms zircon u pb isotopic dating of three representative samples of hornblende plagioclase gneisses reveals that the magmatic precursors of the yixian fuxin greenstone belt were formed during 2589 ma 2534 ma and subjected to subsequent 2490 ma metamorphism lu hf isotopic analyses of the zircons dated from the three samples yield positive ehf t values of 8 3 to 2 7 and tdm from 2 76 ga to 2 57 ga the youngest tdm value is close to their crystallization ages suggesting that they were mainly derived from partial melting of the depleted mantle materials these zircon chronological data and lu hf isotopic features indicate an important 2 5 ga episode of crustal growth in the western liaoning metamorphic terrane based on whole rock geochemical characteristics these meta volcanic rocks in the yixian fuxin greenstone belt may be subdivided into four groups samples in group 1 show high mgo contents from 7 19 to 7 93 and cr and ni contents of 208 395 ppm and 113 210 ppm with mg numbers mg of 53 4 to 55 1 and are characterized by slight lree depleted to flat ree patterns la sm n 0 77 1 05 flat patterns on the primitive mantle normalized multiple trace elements diagram and nb ta ratios between 12 3 and 15 9 implying that they were derived from partial melting of depleted mantle source samples in group 2 also display higher mgo 7 52 14 51 cr 372 570 ppm and ni 240 320 ppm contents with high mg 53 5 70 2 low tio2 contents 0 52 0 64 high nb ta ratios 15 8 19 9 and have right declined ree patterns with la sm n ratios from 1 73 to 3 6 and negative nb ta and ti anomalies indicative of their derivation from partial melting of a metasomatized refractory mantle source samples in group 3 show mgo content from 1 81 to 3 56 with mg of 35 9 to 43 5 and high cr 1179 1280 ppm and ni 712 721 ppm contents lower y and yb contents 6 7 9 42 ppm and 0 64 0 88 ppm respectively and higher nb ta ratios 18 4 21 8 and are characterized by the highest la yb n ratios 14 91 22 67 and negative nb ta and ti anomalies revealing that they formed from partial melting of garnet bearing oceanic slab and the slab melts were contaminated by mantle peridotite and subjected to crustal contamination during their ascent samples in group 4 exhibit high mgo content 5 98 10 52 with high mg numbers 52 4 70 8 cr 198 376 ppm and ni 112 177 ppm contents and lower nb ta ratios between 12 7 and 14 6 and have la yb n ratios ranging from 4 12 to 6 78 lower than those of the group 3 and strongly negative nb ta and ti anomalies suggesting that they were derived from partial melting of mantle peridotite metasomatized by slab derived fluids thus the yixian fuxin greenstones display geochemical features of the normal mid ocean ridge basalts n morbs group 1 boninite like rocks group 2 adakite like rocks group 3 and high magnesium andesites hma group 4 suggesting that the protoliths of the greenstone belt might have formed in an active continental margin similar to the andean type orogen

formation age and tectonic setting of the shirengou neoarchean banded iron deposit in eastern hebei province constraints from geochemistry and sims zircon u pb dating abstract the shirengou iron deposit a typical bif deposit located in eastern hebei province in the north china craton is hosted in neoarchean metamorphic rocks the metamorphic rocks include hornblende plagiogneiss plagioclase amphibolite and magnetite quartzite we use contents and ratios of major elements for protolith reconstruction showing that protoliths of the hornblende plagiogneiss and plagioclase amphibolite should be dacite and basaltic andesite respectively based on geology and geochemistry of the hosting rocks we infer that the shirengou bif is an algoma type deposit formed in an arc related basin in the neoarchean constrains from sims u pb dating and oxygen isotopic analysis of zircon from wall rocks and interlayer of the shirengou iron bodies can be summarized as follow 1 igneous zircons from two samples of amphibolite and gneiss yield u pb ages of 2541 21 ma and 2553 31 ma respectively providing the age of the neoarchean protolith because the shirengou bif is an algoma type deposit determined u pb age 2541 2553 ma for zircons from hosting volcanic rocks can constrain the bif forming time 2 metamorphic overgrowth zircons from amphibolite and gneiss give two u pb ages of 2512 13 ma and 2510 21 ma respectively corresponding to the neoarchean matemorphism 3 the zircons with 18o values of 5 9 7 6 also indicate magmatic origin the zircons have 18o values of 6 8 9 9 suggesting that exotic high 18o fluids were involved during metamorphism based on the geology and geochemistry of bif and combing with zircon age and oxygen isotopic systematics we suggest that the shirengou iron deposit was formed in a submarine volcanic setting related to subduction of an oceanic slab

geochemistry zircon u pb geochronology and lu hf isotopes of metavolcanics from eastern hebei reveal neoarchean subduction tectonics in the north china craton abstract the neoarchean metavolcanic rocks of saheqiao occur within the central domain of the precambrian terrane in eastern hebei within the north china craton these rocks consist mainly of garnet two pyroxene granulites garnet clinopyroxene amphibolites amphibole plagioclase gneisses and biotite plagioclase gneisses these metavolcanic rocks are exposed as several kilometers scale of massive blocks or several tens of centimeters scale of enclaves within precambrian granitoid gneisses based on whole rock geochemistry we classify these intermediate mafic volcanic rocks into four groups group 1 exhibits low sio2 yb and nb ta ratios and high ni and cr and shows n morb like normal mid ocean ridge basalts geochemical features suggesting that the magmatic precursors of these rocks were derived through partial melting of depleted mantle compared to group 1 group 2 shows slightly right declined ree and nearly flat multi element patterns with variable negative nb anomalies matching with primitive arc basaltic rocks formed by partial melting of the mantle wedge group 3 exhibits chemical compositions of basaltic and andesitic rocks and is characterized by pronounced lree enrichment but hree depletion and shows distinctly negative nb and ta anomalies and weakly negative zr and hf anomalies these rocks may compare with island arc volcanic rocks and were probably generated by partial melting of the mantle wedge modified by dehydration of subducted oceanic slab the magmatic precursors of the andesites were derived from the crystallization differentiation of the basaltic magma group 4 is characterized by clearly right declined ree patterns and slightly positive or no nb ti anomalies which are analogous to nb enriched basalts neb and originated from melting of hfse enriched mantle sources la icp ms u pb dating of magmatic zircons from five samples from the three groups reveals that group 1 n morb like rocks formed at 2525 7 ma group 2 primitive arc basaltic rocks at 2518 15 ma and group 3 typical arc volcanic rocks at 2523 6 ma to 2614 18 ma zircons from all the dated samples also preserve signatures of 2450 2370 ma metamorphisms or thermal events the zircon lu hf data from the three dated samples in group 3 show ehf t values ranging from 1 4 to 9 0 and tdm values of 2627 ma to 2965 ma suggesting a significant episode of 2 6 2 9 ga crustal growth in this region the 2525 ma n morb like basaltic rocks are younger than the arc related rocks 2614 2518 ma suggesting that the morb like basaltic rocks were generated in a back arc environment on the basis of the rock association of back arc morb basalts group 1 arc related andesites basalts groups 2 and 3 and neb like rocks group 4 we suggest that the neoarchean volcanic rocks of the eastern hebei region formed in a subduction related setting within a convergent plate margin

episodic mantle melting crustal reworking in the late neoarchean of the northwestern north china craton zircon ages of magmatic and metamorphic rocks from the yinshan block abstract the yinshan block in the northwestern north china craton comprises late neoarchean greenstones high grade metamorphic rocks granulite charnockite enderbite and amphibole gneiss diorites sanukitoid and mg adakite and granitoids predominantly trondhjemite tonalite a greenstone terrane comprises a volcanic sequence of predominant basalt and dacite with minor andesite zircons from a high mg andesite and an andesite have weighted mean 207pb 206pb ages of 2533 5 ma and 2510 7 ma respectively which reflect the timing of two distinct volcanic episodes these two either predated or postdated a major volcanic episode that formed a basalt dacite bimodal suite during 2515 10 basalt to 2516 10 ma dacite magmatic zircons from the high grade metamorphic rocks yielded weighted mean 207pb 206pb ages of 2544 5 ma for a mafic granulite 2521 6 ma for a garnetiferous gneiss 2535 5 ma for a charnockite and 2526 5 ma for an amphibole gneiss these ages reflect the minimum emplacement time of rocks that make up the protoliths of the high grade metamorphic complex the metamorphic ages of the high grade complex were determined at 2515 18 ma for mafic granulite and 2503 12 ma for garnetiferous gneiss zircons from a high mg diorite i e sanukitoid have a weighted mean age of 2520 6 ma which is significantly younger than the 2556 14 ma age of a magnesian diorite mg adakite from the same diorite massif these ages reflect distinctive magmatic pulses that generated the diorite massif a tonalite has a zircon age of 2516 7 ma indistinguishable from the 2520 9 ma age of a trondhjemite from the same trondhjemite tonalite dominated batholith a granitic compositional layer in the 2516 7 ma tonalite has zircon ages of 2515 6 ma high u zircon domains and 2512 22 ma low u zircon domains which reflect an intracrustal melting event the presence of an older crustal remnant ca 2600 ma prior to the formation of the yinshan block is indicated by a 2594 4 ma leucogranite xenolith in the diorite massif and by the widespread presence of ca 2583 3485 ma mostly ca 2700 ma zircon xenocrysts in a variety of volcanic and plutonic rocks an undeformed pegmatite dike in high mg andesite has an emplacement age of 2508 17 ma zircon an undeformed trondhjemite dike that cuts the supracrustal greenstone sequence yielded a zircon age of 2502 6 ma similar to that of the pegmatite dike and representing the latest archean magmatic event in the yinshan block these ages of undeformed granitoid dikes delimit the termination of thermo tectonic development of the yinshan block based on these new ages and published geological and geochronological data we conclude that the yinshan block is a typical neoarchean cratonic block not a segment of the so called paleoproterozoic inner mongolia north hebei orogen episodic mantle melting and resultant crustal reworking account for the thermo tectonic development of the yinshan block in a brief period ca 2556 2502 ma in the late neoarchean and based on their regional chronological correlations we argue for their craton scale significance

evaluation of evaporation rate from forested soil surface using stable isotopic composition of soil water in a headwater basin the stable isotopic composition of rain water and soil water was analysed and the soil surface evaporation rate was evaluated using the isotope value of soil water taken from a forested headwater basin in central japan rainfall throughfall soil water groundwater and discharge water were sampled at intervals of one month to determine the isotopic compositions of deuterium d and oxygen 18 18 o therein in addition tensiometric observation of soil water was performed continuously the stable isotopic ratio of soil water was homogenized between the soil surface and a depth of 100 cm by means of active soil water movement above 100 cm in depth the mean 18 o in deep soil water below a depth of 100 cm was 0 24 higher than the volume weighted mean 18 o in throughfall consequently the mean evaporation rate from the soil surface was calculated as 5 of the evapotranspiration rate using the difference between the 18 o in throughfall and in deep soil water based on the rayleigh equation under equilibrium condition

petrology phase equilibria modelling and zircon u pb geochronology of garnet bearing charnockites from the miyun area implications for microblock amalgamation of the north china craton abstract the north china craton ncc was amalgamated through late neoarchean amalgamation of seven microblocks along zones of ocean closure represented by granite greenstone belts ggb typical basement rocks of the zunhua ggb between the qianhuai and jiaoliao microblocks are exposed in the miyun area of the ncc here we report petrology mineral chemistry metamorphic p t estimation and zircon u pb geochronology of newly identified garnet bearing charnockites from the miyun area the prograde mineral assemblages are composed of quartz biotite clinopyroxene plagioclase occurring as inclusions in garnet the peak metamorphic mineral assemblages are identified as garnet clinopyroxene orthopyroxene quartz plagioclase k feldspar ilmenite hornblende whereas the retrograde assemblages are characterized by the breakdown of garnet and formation of quartz biotite association together with k feldspar moats around garnet and magnetite in the matrix the prograde metamorphic p t condition is defined at

chronology and geochemistry of neoarchean bif type iron deposits in the yinshan block north china craton implications for oceanic ridge subduction abstract the dongwufenzi iron deposit is a typical algoma type banded iron formation bif in the yinshan block of the north china craton the iron orebodies occur as layers interlayered with plagioclase amphibolite la icp ms u pb dating of zircons from the plagioclase amphibolite yielded protolith crystallization age of 2538 9 ma mswd 1 01 followed by metamorphism at 2452 7 ma mswd 0 68 the geochemical characteristics of the ores including low al 2 o 3 tio 2 and hfse contents pronounced positive eu anomalies and the y ho ratios 26 37 suggest that the bifs precipitated from hydrothermal fluids discharged on the seafloor the geochemical features of the plagioclase amphibolite suggest the protolith magma to be high fe basalt sm nd analyses of the plagioclase amphibolite yielded end t t 2 54 ga and single stage depleted mantle nd model ages t dm in the range of ca 1 8 to 3 0 and 2 68 to 2 81 ga respectively suggesting an enriched mantle source we link the source of fe in the bifs to the komatiitic complex in the same greenstone belt and the source of si with the high fe basalt integrated geochronological and geochemical data from the other archean rocks in this area suggest that the dongwufenzi bif formed at 2 5 ga coeval with the other bifs in the north china craton ncc as well as similar occurrences in other parts of the world we propose a geodynamic model involving ridge subduction and slab window for the formation of the bifs and the associated rock suites in the greenstone belt

a neoarchean subduction polarity reversal event in the north china craton abstract subduction polarity reversal events following arc continent arc arc or continent continent collisions have been well documented from cenozoic mesozoic and paleozoic orogens but not from the archean we here document a neoarchean subduction reversal event after an arc continent collision between the eastern block of the north china craton ncc and the fuping arc using field geochemical and geochronological data we focus our work on the wangjiazhuang granite in the zanhuang massif located along the eastern margin of the central orogenic belt cob of the ncc and a regional tectonic comparison with other granitic rocks with similar ages geochemical and petrogenetic characteristics the ca 2 5 ga a type wangjiazhuang granite intrudes the neoarchean zanhuang melange belt and contains mafic and felsic inclusions it has positive end t values 0 12 to 1 13 and tdm2 ages between 2784 ma and 2869 ma this work shows clearly from field structural relationships geochemistry and geochronology that the wangjiazhuang granite formed after an arc continent collision between the eastern block which is defined as a continental block and the fuping arc after a subduction polarity reversal event placed a new slab beneath the collisionally modified margin of the eastern block and converted it to an andean type margin the subduction polarity reversal event at ca 2 5 ga resulted in melting of the enriched mantle meanwhile the rising magma induced partial melting of the old and thickened ttg crust leading to the intrusion of ca 2 5 ga wangjiazhuang granite into the neoarchean zanhuang melange there are other granitic rocks with similar ages and geochemical and petrogenetic features in the central orogenic belt and eastern block of the north china craton suggesting that they formed in a similar tectonic setting as the circa 2 5 ga granites across the eastern block the neoarchean subduction polarity reversal event and prior arc continent collision provide strong evidence that plate tectonics was operating by the end of the neoarchean

qingyuan high grade granite greenstone terrain in the eastern north china craton root of a neoarchaean arc abstract the qingyuan high grade granite greenstone terrain is one of the first recognized granite greenstone terrains in the eastern north china craton similar to other archaean terrains its tectonic environment is debated was it an intra continental rift or a modern analogy of arc occurrence and petrogenesis of major igneous series the ultramafic mafic and felsic volcanic rocks 2510 ma and the plutons of the quartz diorite 2570 2510 ma ttg 2570 2510 ma and quartz monzodiorite 2510 2490 ma series in xinbin area are investigated the mafic intrusives and volcanic rocks have high mgo content 5 4 7 5 wt and mg number 48 61 they show slightly depleted to flat trace element patterns the ultramafic rocks serpentinite could be genetically related to the mafic rocks the meta dacite rhyolite is adakitic with enriched light and middle rees and liles but significantly depleted hfses the quartz diorite has high mg number 60 64 moderately enriched light and middle rees and liles the ttg shows distinct light but moderate middle ree enrichment prominent nb ta depletion but zr hf enrichment zr sm 100 the quartz monzodiorite has moderate light and middle ree enrichment significant nb ta depletion and negative eu sr anomalies the ttg has more depleted sr nd isotopes endt 2 6 87sr 86srt 0 700 than all the others endt 0 2 87sr 86srt 0 701 703 their petrogenesis can be explained by an archaean style subduction defined as a mantle wedge absent flat hot subduction with significant vertical tectonism in the overriding slab the ultramafic mafic rocks were originated from primitive mantle the meta dacite rhyolite was originated from the eclogite facies overriding crust the quartz diorite was a mixture of melts from mantle and the overriding crust the ttg was from the subducting slab under amphibolite to amphibole bearing eclogite facies and the quartz monzodiorite was from the subducting slab after the derivation of the ttg the qingyuan terrain represents remnants of the root of a neoarchaean arc its anticlockwise p t path recorded the initiation of the arc to its cession and exhumation cratonization at 2480 ma

arrested charnockite formation in southern india and sri lanka arrested prograde charnockite formation in quartzofeldspathic gneisses is widespread in the high grade terrains of southern india and sri lanka two major kinds of orthopyroxene producing reactions are recognized breakdown of calcic amphibole by reaction with biotite and quartz in tonalitic granitic gray gneiss produced the regional orthopyroxene isograd manifest in charnockitic mottling and veining of mixed facies exposures as at kabbal karnataka and in the kurunegala district of the sri lanka central highlands chemical and modal analyses of carefully chosen immediately adjacent amphibole gneiss and charnockite pairs show that the orthopyroxene is produced by an open system reaction involving slight losses of cao mgo and feo and gains of sio2 and na2o rb and y are depleted in the charnockite another kind of charnockitization is found in paragneisses throughout the southern high grade area and involves the reaction of biotite and quartz garnet to produce orthopyroxene and k feldspar although charnockite formation along shears and other deformation zones at such localities as ponmudi kerala is highly reminiscent of kabbal close pair analyses are not as suggestive of open system behavior this type of charnockite formation is found in granulite facies areas where no prograde amphibole bearing gneisses exist and connotes a higher grade reaction than that of the orthopyroxene isograd metamorphic conditions of both kabbaltype and ponmudi type localities were 700 800 c and 5 6 kbar lower p h2o in the ponmudi type metamorphism was probably the definitive factor

hydrobiogeochemistry of forest ecosystems in japan major themes and research issues hydrobiogeochemical information on forested watersheds in the japanese archipelago is reviewed to qualitatively summarize the major factors affecting the hydrology and biogeochemistry of this region major features that distinguish japanese forest watersheds from those of north central europe and the northeast united states generally include higher temperature greater precipitation and steeper topography there have been three major themes in hydrobiogeochemistry research on japanese forest ecosystems 1 investigations of nutrient cycles with particular emphasis on the establishment and maintenance of forest ecosystems 2 evaluations of streamwater chemistry as an output from the forest ecosystem and 3 hydrological studies using biogeochemical tracers high precipitation inputs during the growing season affect the seasonality of the streamwater no3 concentration resulting in different temporal patterns than those generally found in north central europe and the northeast united states the high alkalinity and ph of japanese surface waters is due to the rapid weathering of relatively young soils that are generated by steep hillslopes warm temperatures and elevated soil moisture enhance high rates of mineral weathering hydrological studies using biogeochemical tracers have shown that the steep topography contributes to the highly heterogeneous movement of water within japanese catchments copyright 2001 john wiley sons ltd

late neoarchean magmatic and subsequent metamorphic events in the northern north china craton shrimp zircon dating and hf isotopes of archean rocks from yunmengshan geopark miyun beijing abstract the miyun geopark is located in the northern part of the north china craton and includes a variety of archean granitoids and metamorphic rocks shrimp zircon dating documents their emplacement ages at 2567 2508 ma metamorphic events at ca 2 50 ga 2 44 ga and 1 82 ga late neoarchean basement rocks elsewhere in the north china craton document a similar evolutionary history with intrusion of granitoid rocks commencing at ca 2590 ma and reaching three peaks at about 2550 2520 and 2500 ma these rocks then underwent regional metamorphisms at ca 2 50 ga 2 44 ga 1 92 ga and 1 82 ga positive e hf t values of 1 7 to 7 6 with model ages younger than 3 0 ga for magmatic zircons from these late neoarchean intrusive rocks indicate that they are predominantly derived from juvenile crustal sources and suggest that significant crustal growth occurred in the northern north china craton during the neoarchean the intrusive rocks in the miyun area are part of an extensive province of late neoarchean magmatism and appear to be related to mantle plume activity at this time

growth and reworking of the early precambrian continental crust in the north china craton constraints from zircon hf isotopes abstract we synthesize more than 2600 hf isotope data on the archean paleoproterozoic zircons from the north china craton ncc recalculation of the data based on single stage and two stage hf model ages of the eastern block of the ncc shows peak ages of 3902 13 ma and 3978 18 ma respectively and also small peaks at 3 5 4 0 ga the majority of zircon ehf t values are positive suggesting the possibility of the crust and the mantle differentiation at ca 3 9 4 0 ga in the eastern block of the ncc most magmatic zircons from the whole of ncc have their hf model age range of 2 4 2 9 ga and the single stage model ages is cluster at 2698 4 ma whereas the two stage model ages concentrate at 2714 5 ma implying that the protoliths were juvenile crustal rocks the most prominent peak at 2 7 ga indicates that this period marks the most important stage of the crust mantle differentiation and crust formation of the ncc the widespread 2 5 ga rocks in the ncc and the absence of the 2 5 ga peaks in hf model ages are consistent with the partial melting and reworking of the juvenile rocks at 2 5 ga furthermore the 2 5 1 7 ga zircon hf isotope features are also related to the reworking of the crustal rocks our results from the integration of a large database suggest that the eastern block and the trans north china orogen have undergone similar crust mantle differentiation and magmatism leading to the conclusion that the essential cratonization of the north china took place at the end of neoarchean

charnockite geobarometers based on coexisting garnet pyroxene plagioclase quartz numerous geothermometers based on compositions of coexisting minerals have been calibrated experimentally or theoretically during the past 10 yr in contrast few continuous reaction geobarometers exist which have had wide application one based on the reaction of cordierite to garnet sillimanite and quartz is limited by a relatively narrow pressure range of application and also by conflicting calibrations1 2 because the mixing relations of mg and fe and the role of h2o in cordierite3 are not understood another successful barometer uses the assemblage garnet plagioclase al2sio5 and quartz4 5 continuous geobarometers based on the reaction of orthofer rosilite to fayalite plus quartz6 and on the aluminium content of enstatite in equilibrium with garnet7 have been used to a lesser extent the former barometer is limited by rarity of the requisite assemblage and the latter by uncertain experimental calibration for crustal rocks we calibrate here two mineralogical geobarometers from measured thermodynamic data the participating minerals pyroxenes garnet plagioclase and quartz are frequently associated in high grade metamorphic rocks calculation of pressures for several terrains show that the geobarometers yield reasonable and consistent results for the entire range of crustal pressures

microblock amalgamation in the north china craton evidence from neoarchaean magmatic suite in the western margin of the jiaoliao block abstract the archaean earth is considered to have been characterized by microcontinents that formed dominantly through the accretion of oceanic arcs and plateaus the north china craton ncc provides a typical case where at least seven ancient microcontinental nuclei with distinct lithological features and independent tectonic histories were amalgamated into the cratonic framework at the end of the archaean here we investigate a suite of magmatic rocks developed at the periphery of one of these microblocks the jiaoliao block that forms part of the composite eastern block of the ncc we present petrological geochemical and zircon u pb geochronological data from the taipingzhai charnockite suite and associated amphibolites metagabbros and orthogneisses from the qianxi complex geochemically the rocks show a wide range of sio 2 charnockite suite 52 57 75 50 wt metagabbro 43 71 wt amphibolite 50 24 wt garnet bearing biotite 63 73 wt and mgo charnockite suite 0 89 5 01 wt metagabbro 3 99 wt amphibolite 6 23 wt garnet bearing biotite 2 08 wt the composition of the felsic units straddle from diorite through syeno diorite to granite with both alkalic and subalkalic affinity with dominantly magnesian composition and arc related features their immobile trace element relationships suggest calc alkaline affinity they show positive pb ba la nd and gd and negative nb ta sr th and ti anomalies with slightly negative anomalies of ce and y attesting to arc related features in tectonic classification diagrams the rocks plot in the vag syn colg field or the vag area suggesting subduction related origin the dominant population of zircons in all these rocks displays magmatic crystallization features including high th u values with core rims textures indicating subsequent thermal events the zircon u pb data yield upper intercept ages of 2587 10 ma to 2543 17 ma and 207 pb 206 pb mean ages of 2578 7 3 ma to 2536 8 ma for the charnockite suite marking the timing of emplacement of the arc magmas the overgrowth rims as well as discrete neoformed grains are interpreted as dating subsequent metamorphism and yield 207 pb 206 pb ages between 2533 ma to 2490 ma zircons in the metagabbro preserve upper intercept ages of 2556 20 ma representing the crystallization age of this rock the younger ages of 2449 58 ma upper intercept age and 1845 25 ma 207 pb 206 pb spot age are interpreted to represent subsequent multiple thermal events in this area zircons in the amphibolite preserve the 207 pb 206 pb mean age of 2539 9 ma representing the crystallization age of this rock the garnet bearing biotite gneiss shows an upper intercept age of 2562 10 ma mswd 0 66 n 36 and the 207 pb 206 pb mean age of 2561 9 ma mswd 0 63 n 33 which is taken to represent the crystallization age of this rock some inherited zircons are also identified with 207 pb 206 pb ages of 2664 26 ma and 2628 26 ma zircon lu hf data show dominantly positive ehf t values and combined with crustal residence ages the results suggest mesoarchean to neoarchean juvenile crust formation in the ncc we interpret the data presented here to represent a phase of major late neoarchaean arc magmatism along the western margin of the jiaoliao block related to the birth of microcontinental nuclei within the ncc our data suggest that the western and eastern blocks might not have existed as discrete crustal blocks and that the construction of the ncc is a result of the assembly of several microblocks or terranes at the end of archaean similar archean cratonic nuclei in other regions of the world might have formed part of a primitive supercontinent in the early earth

deglacial meltwater drainage and glaciodynamics inferences from laurentide eskers canada abstract this paper evaluates current knowledge of laurentide eskers in canada in the light of developments in glacier hydrology and glacial sedimentology questions regarding the morpho sedimentary relations of eskers the synchroneity and operation of r channel systems the role of supraglacial meltwater input and proglacial water bodies the controls on esker pattern and the glaciodynamic condition of the ice sheet at the time of esker formation are discussed a morphologic classification of eskers is proposed five types of eskers are identified and investigated type i eskers likely formed in extensive synchronous dendritic r channel networks under regionally stagnant ice that terminated in standing water type ii eskers likely formed in short subaqueously terminating r channels or reentrants close to an ice front or grounding line that may have actively retreated during esker sedimentation type iii eskers plausibly formed in short r channels that drained either to interior lakes in or tunnel channels under regionally stagnant ice type iv eskers may have formed as time transgressive segments in short subaerially terminating r channels or reentrants that developed close to the ice margin as the ice front underwent stagnation zone retreat or downwasted and backwasted regionally stagnant ice however formation in synchronous r channels cannot be discounted on the basis of reported observations type v eskers may have formed in h channels that terminated subaerially the spatial distribution of these esker types is discussed the factors that determined laurentide r channel pattern and operation were likely a complex combination of i supraglacial meltwater discharge ii the number and location of sink holes iii the ice surface slope thickness and velocity and iv the permeability topography and rigidity of the bed these factors cause and respond to changes in ice dynamics and thermal regime over the glacial cycle

two neoarchean supercontinents revisited the case for a rae family of cratons abstract a variety of early paleoproterozoic supercontinents or supercratons have been proposed including kenorland superia and vaalbara improved geologic knowledge of the churchill province canadian shield suggests that the classical kenorland configuration with linked rae and hearne cratons is invalid and represents a younger ca 1 9 ga nuna configuration we review the early paleoproterozoic tectonic history of the rae craton and propose that the ca 2 55 2 50 ga macquoid and 2 50 2 28 ga arrowsmith orogens represent critical piercing points for supercontinent reconstruction utilizing the stratdb and dateview databases we have identified nearly two dozen regions worldwide that show effects of these orogenic events including the rae gawler mawson peninsular india west africa amazonia north china and sask crustal blocks we propose that these cratonic blocks form a distinct rae family lineage utilizing new time space plots for the rae family and components of the superia and vaalbara supercratons we demonstrate that the rae family lacks the distinctive early paleoproterozoic depositional and glaciogenic record characteristic of superia and vaalbara but has an important contemporaneous record of juvenile crust formation and contractional orogenesis we propose the collective history of the rae family is best reconciled if it represents the now dispersed blocks of a third earliest paleoproterozoic supercraton that we term nunavutia in this model the magmatic and tectonometamorphic record of these cratons includes an early 2 55 2 45 ga period of interior collisional orogenesis in which the supercraton amalgamated and a later phase of long lived peripheral orogenesis 2 45 2 28 ga prior to its partial break up at ca 2 05 ga forming within an otherwise globally quiescent period the history of the rae family is important for assessment of constrasting models of early paleoproterozoic geodynamic activity

calculation and application of clinopyroxene garnet plagioclase quartz geobarometers recently published thermodynamic and experimental data in a variety of chemical systems have been evaluated to derive gibbs free energies for hedenbergite and pyrope these were used to calculate the geobarometric equilibria

granitoid evolution in the late archean wutai complex north china craton abstract two temporally discrete episodes of granite magmatism have been identified in the wutai complex of the north china craton based on shrimp u pb zircon dating of all major granitoid bodies in the area the older period is latest archean and ranges in age from 2560 to 2515 ma whereas the younger episode is paleoproterozoic with magmatism at 2170 and 2120 ma archean magmatism can be further separated into two pulses based on geochemistry and the association of the younger plutons with extensive coeval volcanic activity in the wutai complex the early phase of archean activity is represented by the lanzhishan ekou and portions of the chechang betai granites with ages ranging from 2560 to 2540 ma the lanzhishan granite is the only one at wutaishan that contains inherited zircon with a number of cores and individual grains giving ages in excess of 2700 ma these are relatively evolved granitoids interpreted to be derived from older basement of the eastern block of the north china craton the shifo guangmingshi the main grey phase of the wangjiahui granite and the major components of the chechang betai granite have ages of 2540 2515 ma and are coeval with felsic volcanism in the wutai complex which is a consequence of subduction and related arc magmatism the dawaliang granite and pink phase of the wangjiahui granite are considerably younger with paleoproterozoic ages of 2170 and 2120 ma respectively these are also evolved granitoids most likely derived by partial melting of the older basement although we have found no evidence of inheritance the petrogenesis of the granitoids reflects the precambrian amalgamation history of the north china craton indicating derivation along the western edge of the eastern block during development and amalgamation of the wutai arc and prior to collision with the western block of the craton 1 8 ga ago

an overview of charnockite abstract charnockite a quartzfeldspathic rock containing orthopyroxene is an important component of high grade deep crustal terrains the origin of charnockite by both igneous and metamorphic processes not yet clearly defined has major bearing on the evolution of continents

hydrological flow paths controlling stream chemistry in japanese forested watersheds water sources and flow paths contributing to stream chemistry were evaluated in four japanese forested watersheds with steep topography slopes 30 stream chemistry during periods without rainfall and during events with less than 100 mm of precipitation was similar to seepage water chemistry but markedly different from that of soil water which had higher concentrations of no 3 and ca2 and lower concentrations of na and hco 3 also stream cl concentrations in a cl treated watershed did not increase either during events with less than 100 mm of total rainfall or at baseflow conditions even three years after the cl treatment these results suggest that groundwater within bedrock fissures of paleozoic strata had a long residence time and was a major contributor to steam water under baseflow conditions and even during small precipitation events 100 mm in contrast for large precipitation events 100 mm stream chemistry became more similar to soil water chemistry especially within the steepest watershed also for large precipitation events stream cl concentrations in the cl treated watershed increased markedly these results suggest that soil water was a major contributor to stream waters only during these large events copyright 1999 john wiley sons ltd