strike slip faulting thrusting and related basins in the cenozoic evolution of the southern branch of the bolivian orocline abstract the evolution of the cenozoic deformation of the cordillera oriental and of the contact zone with the altiplano in southern bolivia is well documented in the tupiza nazareno and estarca basins the tectonic evolution started at about 29 ma the period between 29 and about 22 21 ma is marked by development of a pull apart basin related to n s trending left lateral strike slip faulting during this period initial deposition consisted of andesitic lavas and detrital sediments breccias matrix supported red conglomerates sands and silts of the catati and tupiza formation deposited in alluvial fan and flood plain environments from 21 to 20 ma the tectonic setting evolved to n s oriented thrusts which had a dextral component this event caused the tupiza basin to evolve into a full ramp basin and triggered the development of two piggy back basins nazareno and estarca both basins record detrital deposition nazareno formation in an alluvial fan environment at 10 9 ma deformation in this area stopped allowing peneplanation during which time the san juan de oro erosional surface was formed and the fluvial conglomerates of the oploca formation were deposited this segment of the andes was then tectonically transported to the east while uplift due to thrusting continued in the eastern andean front and in the subandean zone

use of surface controlled ree sectoral zoning in apatite from llallagua bolivia to determine a single crystal smnd age abstract surface structure controlled partitioning of rees between symmetrically nonequivalent crystal faces leads to sectoral zoning between the 0001 and 1010 sectors of vein filling apatites from llallagua bolivia absolute differences in the concentration of the analyzed rees between these sectors range from a factor of 9 5 in the case of la to a factor of 1 4 for yb the two sectors have different concentrations of sm and nd as well as significantly different sm nd ratios 147 sm 144 nd 0 3558 a sm nd isochron determined from petrographically constrained coeval portions of different sectors gives an age of 43 8 4 7 ma 95 confidence limits we believe that this calculated age represents the time of crystallization of the apatite the application of intracrystalline heterogeneities that formed due to differential partitioning at the crystal surface to dating of minerals is germane for any mineral in which sectoral or intrasectoral zoning is exhibited and may be used with other isotopic systems in which sufficient segregation of parent and daughter nuclides occurs and in which concentrations are sufficient for analysis of small intracrystalline samples

u pb dating of monazite and its application to geological problems monazite is an underutilized mineral in u pb geochronological studies of crustal rocks it occurs as an accessory mineral in a wide variety of rocks including granite pegmatite felsic volcanic a

revised deformation history of the central andes inferences from cenozoic foredeep and intermontane basins of the eastern cordillera bolivia 1 investigation of cenozoic deformation sediment accumulation and provenance in the eastern cordillera of bolivia at 17 21 s indicates major shortening 60 140 km and foredeep development followed by limited internal shortening and intermontane basin development contrasting histories of shortening deposition sediment dispersal and detrital composition distinguish a formerly extensive paleogene foredeep exposed along an eastern belt of synclines from a zone of principally neogene intermontane basins in the central eastern cordillera new 40ar 39ar ages of 25 17 ma for interbedded tuffs reveal latest oligocene early miocene accumulation in intermontane basins at rates 80 m myr several times lower than andean foredeeps although poorly dated foredeep evolution probably coincided with middle eocene oligocene deformation and denudation in adjoining regions to the west a mid cenozoic transition from foredeep to intermontane conditions may be attributable to emplacement of a basement involved tectonic wedge beneath the eastern cordillera in this interpretation wedge emplacement drove flexural foredeep subsidence from roughly 40 to 25 ma whereas subsequent accumulation occurred in localized internally drained basins in elevated intermontane areas regardless of the regional subsurface structural geometry 40ar 39ar ages define a 25 21 ma onset of intermontane sedimentation that signifies the termination of major upper crustal shortening over large parts of the eastern cordillera and possibly the age of initial shortening in the interandean and subandean zones to the east in contrast to several popular models the revised tectonic history presented here suggests significant pre neogene shortening in the eastern cordillera and underscores the large uncertainties in estimates of long term shortening rates in the andes

timing and genesis of cu au mineralization in the khetri copper belt northwestern india constraints from in situ u pb ages and sm nd isotopes of monazite ce the khetri copper belt kcb in northwestern india contains several economically important hydrothermal cu au deposits orebodies in these deposits are locally rich in monazite ce in this study in situ u pb ages and sm nd isotopic compositions of monazite ce are used to constrain the timing of mineralization and to better understand the genesis of the cu au deposits monazite ce crystals were identified in the madhan kudhan and kolihan deposits in the kcb most monazite ce crystals in the two deposits show close textural associations with hydrothermal minerals biotite chlorite and sulfide and have low contents of tho2 mostly 2 wt indicating a hydrothermal origin the hydrothermal monazite ce crystals have u pb ages of 833 5 to 840 6 ma which are interpreted to represent the timing of the mineralization in the kcb another set of monazite ce crystals in the kolihan deposit has relatively high contents of tho2 4 72 wt on average and commonly shows concentric zonation with respect to th they have a weighted average 207pb 206pb age of 1362 29 ma which may record a pre ore metamorphic event in the kcb hydrothermal monazite ce crystals from the madhan kudhan deposit have end t 835 ma values ranging from 4 3 to 16 8 9 6 on average indicating that isotopically heterogeneous materials were in the metal sources or along the flow paths of hydrothermal fluids the ages of cu au deposits in the kcb fall within the age range of the regional ca na metasomatism 830 to 850 ma combining this temporal association with relevant geochemical and isotopic data we propose that circulation of hydrothermal fluids caused widespread ca na metasomatism mobilized certain ore metals and thus facilitated the formation of cu au deposits

timing of skarn gold deposition in the giant beiya polymetallic gold deposit southwest china constraints from in situ monazite sims u th pb geochronology abstract robust dating of hydrothermal deposits is critical to understand ore genesis which depends on judicious selection of mineralization related chronometers especially for complex polymetallic mineral systems the beiya deposit in southwest china is a world class polymetallic gold system 11 9 moz au at a grade of 2 52 g t and the main mineralization is considered as skarn type however available dating results for the gold mineralization give a wide range of ages which in some cases could be inaccurate due to the use of non matrix matched external isotope standards or an equivocal relationship between gold and the dated minerals in this contribution hydrothermal monazite coexisting with gold bearing ore minerals magnetite pyrite and chalcopyrite from high grade massive magnetite sulfide gold ores at beiya was dated in situ using secondary ion mass spectrometry sims the u th pb analyses of hydrothermal monazite yielded a 208pb 232th age of 36 0 0 5 ma 2 mswd 2 0 n 27 which is considered a robust age for the beiya skarn gold mineralization our study supports a genetic link between the skarn gold mineralization and the post collisional quartz monzonite magmatism at beiya based on a new zircon u pb age of 37 2 0 4 ma compared with the previously reported molybdenite re os and sphalerite rb sr isochron ages our monazite u th pb result suggests that the gold deposition was broadly coeval with the formation of molybdenite but probably prior to the local pb zn ag mineralization at beiya

u pb shrimp geochronology of th poor hydrothermal monazite an example from the llallagua tin porphyry deposit bolivia in situ u pb shrimp analysis of hydrothermal monazite virtually free of th and poor in u 0 2 ppm th 40 103 ppm u from the world class llallagua tin porphyry deposit in bolivia defines a mineralization age of 23 4 2 2 ma mswd 0 48 confirming earlier k ar sericite alteration age data these ages are however in contrast with a weighted mean single crystal 207pb 206pb evaporation age of 39 3 6 0 ma and a related pb pb inverse isochron age of 42 4 4 0 ma mswd 0 66 on zircon from a post porphyry dike as well as with an earlier single crystal sm nd apatite isochron age our data points to a significant time gap between emplacement of the ore hosting porphyry intrusion magmatism and its hydrothermal overprint tin mineralization suggesting long lived magmatic hydrothermal activity in this part of the andean back arc crust the decoupling of porphyry magmatism and hydrothermal activity may explain the unusual occurrence of relatively little fractionated felsic rocks together with extensive tin mineralization our study demonstrates the usefulness of the application of the u pb shrimp method to direct age determination of ore mineralization using th poor hydrothermal monazite even when dealing with geological young events the common assumption of synchronous magmatism and hydrothermal ore formation in porphyry systems may not always be warranted

boron in the bolivian tin belt tourmaline alteration and high boron contents are typical features of the magmatic hydrothermal systems of the bolivian tin province the average boron content in melt inclusions of quartz phenocrysts from tin porphyry systems is 225 ppm 1 variation range 110 420 ppm n 12 and suggests a magmatic boron input to the hydrothermal tin systems and not shallow post magmatic leaching of boron from pelitic country rocks boron data from melt inclusions correlate positively with cesium rubidium and arsenic and negatively with lithium titanium and zirconium and define magmatic fractionation trends the generally high b as cs and li contents in melt inclusions suggest involvement of pelitic source lithologies undepleted in these fluid mobile components i e first cycle metamorphic rocks magmatic fractionation modified the trace element contents within a one log unit range bulk rock nd isotope data nd 5 to 10 are in agreement with the dominantly intracrustal geochemical signature of the bolivian tin porphyry systems but also imply a variable but minor mantle input the metallogeny of the tin belt is likely a consequence of intracrustal melting of lower paleozoic pelitic and slightly carbonaceous source material combined with an extended magmatic evolution the long lived thermal preparation of the root zones of the silicic systems is provided by mafic magma which also leaves a chemical imprint in the form of the hybrid dacitic bulk composition of the tin porphyry systems

stratigraphy and chronology of upper cretaceous lower paleogene strata in bolivia and northwest argentina integration of sequence stratigraphy magnetostratigraphy ar ar dating and paleontology considerably advances knowledge of the late cretaceous early paleogene chronostratigraphy and tectonic evolution of bolivia and adjacent areas the partly restricted marine el molino formation spans the maastrichtian and danian 73 60 0 ma deposition of the alluvial to lacustrine santa lucia formation occurred between 60 0 and 58 2 ma the widespread erosional unconformity at the base of the cayara formation is 58 2 ma this unconformity separates the upper puca and corocoro supersequences in bolivia and is thus coeval with the zuni tejas sequence boundary of north america the thick overlying potoco and camargo formations represent a late paleocene oligocene foreland fill the onset of shortening along the pacific margin at 89 ma initially produced rifting in the distal foreland santonian campanian eastward onlapping deposits indicate subsequent waning of tectonic activity along the margin significant tectonism and magmatism resumed along the margin at 73 ma and produced an abrupt increase in subsidence rate and other related phenomena in the basin subsidence was maximum between 71 and 66 ma due to the early maastrichtian global sea level high marine waters ingressed from the northwest into this underfilled basin subsidence decreased during the late maastrichtian and was low during the danian it increased again in the latest danian for which a slight transgression is recorded and peaked in the early selandian tectonism between 59 5 and 58 2 ma produced a variety of deformational and sedimentary effects in the basin and correlates with the end of emplacement of the coastal batholith the subsequent 58 2 ma major unconformity marks the onset of continental foreland basin development which extended into andean bolivia during the late paleocene oligocene interval this basin underwent internal deformation as early as eocene time in the altiplano and cordillera oriental these early structures previously assigned to the late oligocene early miocene orogeny probably accommodated observed tectonic rotations in the eocene oligocene

hydrothermal mineral replacement reactions for an apatite monazite assemblage in alkali rich fluids at 300 600 c and 100 mpa mineral replacement reactions are common in the various environments where rocks have undergone re equilibration with geologic fluids replacement reactions commonly take the form of fluid aided coupled dissolution precipitation and often result in pseudomorph formation one class of environment that frequently shows significant examples of mineral replacements is hydrothermal ore deposit systems the goal of this study was to test the simultaneous reactivity of fluorapatite and monazite in na and si rich hydrothermal fluids which partially mimic the mineralogy and fluid chemistry of the llallagua tin deposit in bolivia a series of experiments were performed at 300 to 600 c and 100 mpa utilizing various combinations of monazite fluorapatite and h 2 o na 2 si 2 o 5 reaction products were evaluated using scanning electron microscopy electron microprobe analysis and single crystal x ray diffraction the results of this experimental study show that fluorapatite and monazite are differentially reactive under the conditions studied the reaction products pathways and kinetics have a large temperature dependence the 300 and 400 c experiments show variable amounts of monazite replacement and only minor if any dissolution or reactivity of fluorapatite the high temperature 500 and 600 c experiments are characterized by massive replacement of monazite by vitusite and britholite exclusively at 600 c monazite alteration takes the form of symplectite development at the reaction front as vermicular intergrowths of vitusite and britholite the higher temperature experiments also show substantially more reactivity by fluorapatite which is partially pseudomorphically altered into britholite this is an example of regenerative mineral replacement where both fluorapatite and britholite share the same atomic structure and are crystallographically coherent after the partial replacement the britholite replacement is characterized by the presence of oriented nanochannels which facilitate fluid based mass transfer between the bulk solution and the reaction front the fluorapatite replacement is enhanced by monazite alteration through a self perpetuating positive feedback mechanism between these two reactions which enhance the ree mobility in alkali bearing fluids and further drives bulk re equilibration these results have potential geochronologic implications and may be significant in the evaluation of monazite and fluorapatite as potential solid nuclear waste forms they also give us deeper insights into the mechanism of mineral replacement reactions and porosity development

dating low grade metamorphic events by shrimp u pb analysis of monazite in shales although the u pb isotopic system is widely used to date magmatism and medium to high grade metamorphism dating low grade metamorphic events has been hampered by a scarcity of suitable minerals we show that monazite forms in shales during low grade metamorphism and can be dated by in situ u pb analysis providing precise ages for low temperature thermal events in proterozoic shales from the pine creek inlier of northern australia monazite and xenotime crystals that formed in a contact aureole yield ages synchronous with granite intrusion ca 1830 ma in the pilbara craton of northwestern australia monazite growth 2192 5 m y ago coincided with basaltic volcanism and rifting an event apparently responsible for hydrothermal iron oxide mineralization in a nearby giant iron ore deposit the mineralizing environment was highly oxic and bathed by meteoric fluids thus our results imply the existence of an oxygen rich atmosphere by 2200 ma given the abundance of shales in the stratigraphic record and the likely widespread distribution of monazite in such rocks in situ u pb dating of monazite may become an important chronometer for low grade metamorphic events

high level surfaces plateau uplift and foreland development bolivian central andes newly dated tertiary strata in the bolivian central andean plateau and synthesis of the tertiary record in the adjacent subandean fold thrust belt constrain the age of deformation in both regions age of deformation within the plateau is determined by dated crosscutting relations associated with a regionally extensive high level surface known as the san juan del oro surface new 40 ar 39 ar dates on undeformed strata above the high level surface preclude significant upper crustal shortening within the eastern cordillera after 10 ma tertiary strata within the adjacent subandean region demonstrate that formation of the fold thrust belt occurred after 10 ma on the basis of these data we propose a two stage model of late cenozoic andean growth that links plateau uplift to the development of the fold thrust belt in the first stage early plateau uplift occurred in response to widespread compressional deformation of the plateau eastern cordillera and altiplano during the second stage beginning after 10 ma upper crustal deformation within the plateau terminated and the subandean fold thrust belt developed crustal scale eastward thrusting along the eastern margin of the eastern cordillera drove subandean folding and thrusting the eastern cordillera served as the bulldozer for the deforming subandean wedge

early to middle tertiary foreland basin development and the history of andean crustal shortening in bolivia a 2 5 km thick succession of tertiary strata in the eastern cordillera of southern central bolivia consists of predominantly fluvial and lacustrine deposits the age of the base of the succession is middle paleocene and its upper part which is erosionally truncated is probably late oligocene early miocene the lower 50 130 m of the succession consists of interbedded fluvial sandstone and mudstone including minor paleosols of the santa lucia formation these strata are overlain by up to 50 m of pervasively pedogenically altered mudstone and sandstone in the upper part of the santa lucia formation and lower part of the impora formation that may represent much of late paleocene eocene time above the paleosol zone is a thin zone 10 m of lacustrine carbonate and clastic rocks in the uppermost impora formation and this in turn is overlain by a 2000 m thick upward coarsening succession of clastic fluvial deposits in the cayara camargo and suticollo formations paleocurrent data indicate that fluvial channels that deposited the santa lucia impora and cayara formations flowed mainly westward whereas channels responsible for the camargo and suticollo formations flowed generally eastward modal sandstone petrographic data show a long term evolution from subarkosic during santa lucia deposition to quartz arenitic during impora and cayara deposition to sublitharenitic during camargo and suticollo deposition compositions we argue that the lithofacies and sediment accumulation history of this succession are most consistent with deposition in an eastward migrating foreland basin system e mail decelles geo arizona edu critical to this interpretation is the zone of extreme stratigraphic condensation in the lower impora formation the inferred upper paleocene eocene part of the succession the abrupt decrease in sediment accumulation represented by this zone is difficult to reconcile with the leading alternative model in which continuous postrift thermal subsidence resulted in a gradual continuous decay of early tertiary sediment accumulation rates stratigraphic condensation is however consistent with passage of the forebulge through the region an interpretation that also can be reconciled with the record of foreland basin development in the altiplano to the west and gross sediment accumulation patterns in the subandean zone and modern foreland basin to the east simple flexural modeling and palinspastic reconstruction of the complete cenozoic migration history of the foreland basin system suggest that 1000 km of foreland lithosphere has been underthrust westward beneath the andean orogenic belt at the latitude of southern bolivia the amount of middle and lower crust that would have been added to the andean infrastructure is sufficient to explain the present crustal thicknesses in bolivia

obtaining geologically meaningful 40ar 39ar ages from altered biotite biotite is the most used 40ar 39ar geochronometer yet two significant problems arise from ar ar step heating dating altered biotite can be problematic producing disturbed age spectra that reflect 39ar recoil however unaltered biotite can yield disturbed ages with apparently meaningful plateau ages as a result of mineral breakdown during stepped heating obtaining meaningful ages from such spectra is very difficult because alteration of biotite is common and widespread in nature and because many biotites affected by alteration are nonetheless unique geologically and or representative of key localities the capability to obtain reliable ages from altered material is extremely important in this study the effects of alteration progress on biotite age spectra were tested using both ir laser step heating and uv laser microprobe 40ar 39ar dating techniques our aims were to extract geologically meaningful ages from altered biotite and to identify cases where the ages had been influenced by alteration three variably altered biotites from the precambrian metamorphic terrain of southwestern montana were selected for argon isotopic analysis sample a is an unaltered rock containing pristine biotite sample b is a highly altered rock with chlorite and prehnite interlayers within biotite and sample c contains biotite with only incipient alteration for each sample the biotite ages obtained with ir and uv laser techniques were compared and the validity of the apparent ages was assessed ir step heating analysis of biotite from sample a yielded a well defined plateau of 1776 6 ma uv laser microprobe analysis of the same biotite yielded a concordant weighted mean age of 1771 8 ma based upon 65 spot analyses of eight grains that ranged in age from 1819 54 to 1722 62 ma in contrast ir step heating of biotite from sample b resulted in disturbed spectra with two separate fragments yielding total gas ages of 1505 12 and 1540 16 ma whereas uv laser microprobe analysis yielded 14 spot ages ranging from 1806 72 to 1565 78 ma uv laser analysis of sample c produced apparent ages ranging from 1772 52 to 1359 200 ma detailed analysis of age variations occurring perpendicular to 001 cleavage planes of biotite in sample b was accomplished by depth profiling using the uv laser microprobe depth profiling of single grains revealed considerable age variation among the biotite layers with profiles 1 and 2 yielding apparent ages ranging from 1730 226 to 1511 186 ma and from 1741 290 to 956 230 ma respectively in both samples b and c younger apparent ages correspond to higher 36ar 39ar ratios the youngest ages therefore are believed to have derived from altered layers whereas the oldest ages are related to layers with relatively little or no alteration in summary incremental step heating of altered biotite single grains yields 40ar 39ar age spectra that are compromised by recoil and variable release patterns however extraction of small samples via the uv laser microprobe provides a simpler pattern of apparent ages all younger than the true cooling age yet inversely correlated with atmospheric argon this result suggests that true biotite ages can be recovered from areas of pristine material if they are sufficiently large to be ablated by the uv laser

monazite u pb and th pb geochronology by ion microprobe with an application to in situ dating of an archean metasedimentary rock abstract monazite grains from nine different precambrian rock samples and having concordant isotope dilution u pb and th pb ages were used to develop and evaluate techniques for u pb th pb and pb pb isotopic dating using an ion microprobe operating at high mass resolution r 5500 1 an unidentified isobar at 203 960 amu complicated the determination of 204 pb in the monazites with higher th but it appeared to have been eliminated when using a slight energy offset the 207 pb 206 pb ratios of individual spots were determined in 10 min analyses to 0 3 0 5 1 of the true values using a 20 m wide o 2 primary beam whereas the uncertainty in the mean of several spots on a single generation of monazite was typically 0 1 0 4 2 instrumental bias in the measured pb uo and pb tho values of individual analyses was monitored using linear relationships between 206 pb uo vs uo 2 uo and 208 pb tho vs uo 2 uo the bias appears to vary somewhat with monazite th content requiring the use of compositionally matched standards individual spot measurements of the 206 pb 238 u and 208 pb 232 th ratios in unknown monazites of low to moderate th can be determined to 2 1 the dating technique was applied to in situ analysis of small monazite inclusions hosted in an amphibolite grade metapelite of archean origin both the contextual setting and the morphology of the monazite grains were found to be important factors in interpreting the timing of growth of the host metamorphic mineral e g garnet staurolite plagioclase euhedral monazite grains armoured in low cao garnet and matrix plagioclase yielded an age of 2548 17 ma interpreted as dating an early episode of low pressure metamorphism partially resorbed monazite within a high cao garnet rim yielded ages of ca 2500 ma but are interpreted as inherited from the first event rather than syn genetic with respect to the growth of this garnet an age of 1755 30 ma was obtained for anhedral monazite associated with late chlorite filled fractures apparently reflecting post tectonic retrogression

ion microprobe 232th 208pb ages from high common pb monazite morefield mine amelia county virginia implications for alleghanian tectonics monazite ce th po4 from a pegmatite in the morefield mine of the eastern piedmont of central virginia has unusually high and variable amounts of common pb leading to problematic interpretations of its u th pb ages and how the monazite relates to nearby granite intrusions and faults to address these issues we analyze a single large monazite grain from the pegmatite using electron microprobe analysis empa n 64 laser ablation inductively coupled plasma mass spectrometry la icp ms n 58 and secondary ion mass spectrometry sims n 59 the monazite study grain exhibits compositional variations in proximity to microcracks consistent regions of secondary alteration and recrystallization although the compositions of these regions fit the ideal stoichiometry of monazite they have lower si th u and y and higher p rare earth element ree and ca concentrations compared to visibly unaltered portions of the grain la icp ms and sims analyses demonstrate that common pb as proxied by 204pb is enriched in proximity to microcrack regions and correlates with 137ba sims 232th 208pb analysis from grain regions with lowest contents of common pb 208pb comprises 99 of pb isotopes yields two sets of ages 263 5 3 0 ma 1 mswd 1 7 n 11 and 234 1 3 3 ma 1 mswd 0 4 n 13 regionally the ages are similar to the youngest appalachian pegmatite bodies emplaced during the terminal alleghanian laurentia africa collision however the monazite ages are younger than locally surrounding intrusions the closest intrusive in distance 30 km and age is the petersburg granite 296 33 0 11 ma zircon 238u 206pb the emplacement of which coincided with activity along the hylas fault because the fault experienced a brittle ductile transition in the late permian 262 ma coeval with the older 232th 208pb monazite age group we postulate that the hylas fault may have operated as a fluid migration system between the petersburg granite and morefield mine pegmatite the younger monazite age coincides with triassic normal and or sinistral faulting linked to the development and deformation of local rift basins

ordovician and cretaceous tectonothermal history of the southern gemericum unit from microprobe monazite geochronology western carpathians slovakia the southern gemericum basement in the inner western carpathians experienced a polyphase regional deformation differences in the pre alpine and alpine events have been constantly discussed to address this monazites from metapelites and acid metavolcanic rocks were dated using the th u pb electron microprobe method three monazite generations such as precambrian early paleozoic and alpine have been recognized in the greenschist facies pelites and acid metavolcanic rocks of the southern gemericum basement both inherited magmatic monazite grains in metavolcanites and rare relics of detrital monazites within the polyphase monazite grains in metapelites yielded the precambrian age in the time span of 550 660 ma they prove the provenance and derivation from deeper crustal cadomian fragments high y magmatic monazites of early paleozoic age 444 13 and 477 7 ma have been recorded in the acid metavolcanites and their metavolcaniclastics these ages roughly fit within the previously published magmatic zircon age determinations at 494 1 7 and 464 1 7 ma that clearly indicate two phase volcanic activity in the early paleozoic southern gemericum basin the early paleozoic magmatic monazites were partly overprinted by the low y alpine monazites 133 5 and 184 16 ma at their rims in al rich metapelites the newly formed low y monazites of alpine age commonly occur reflecting the polystage compression geodynamic evolution with three distinct peaks at 100 8 133 5 and 190 16 ma respectively no data as the evidence of the pre alpine metamorphic events were observed in metapelites only some monazites yield the age indications for the permian extensional thermal re heating 260 290 ma the monazite age data from the southern gemericum basement indicate the strong overprinting due to the polyphase alpine deformation at least in the greenschist facies conditions

lower ordovician graptolite biozonation and lithofacies of southern bolivia relevance for palaeogeographic interpretations the interpretation of the lithofacies and basin evolution of the early ordovician of southern bolivia is based on a number of sections on an e w transect lithostratigraphic units are extremely diachronous and only the available data on the graptolite biostratigraphy enabled an interpretation of the basin evolution the newly proposed graptolite biozonation includes the biozones of rhabdinopora flabelliformis adelograptus sp araneograptus murrayi hunnegraptus copiosus tetragraptus phyllograptoides expansograptus protobalticus expansograptus holmi baltograptus minutus azygograptus lapworthi and isograptus victoriae isograptus victoriae is the first isograptid identified from gondwanan south america the early ordovician succession of southern bolivia is the most complete one documented from south america and can be used as a standard for this continent the faunas are most easily correlated with the faunal succession of scandinavia and without doubt belong to the atlantic graptolite faunal province they show distinct differences from coeval faunas of the argentine precordillera referable to the pacific faunal province

the 127 ma gold mineralization in the wulong deposit liaodong peninsula china constraints from molybdenite re os monazite u th pb and zircon u pb geochronology abstract the wulong deposit is a large tonnage deposit 80 t of au characterized by quartz vein style of gold mineralization in the liaodong peninsula china the auriferous quartz veins are mainly hosted by late jurassic gneissic two mica granite 165 157 ma and early cretaceous granodiorite 129 ma and are structurally controlled by nne and nw trending faults previous attempts to date the gold mineralization yielded ambiguous results 135 112 ma here we report the first in situ and direct age constraint for gold mineralization at wulong five molybdenite samples from mo bearing quartz pyrite veins yielded an isochron age of 127 6 2 3 ma in situ sims u th pb dating of hydrothermal monazite that coexists with gold bearing pyrite and quartz yielded a 208pb 232th age of 126 7 3 2 ma these robust ages together with new age data of the wulong host intrusion and post ore dike allow for a better interpretation of the ore genesis of the wulong deposit relative to a well constrained sequence of regional geological events zircon u pb dating of the wulong host intrusion gneissic two mica granite representing the oldest magmatic event at wulong gave a weighted mean age of 159 3 1 4 ma that is interpreted to be the magma emplacement age subsequent magmatic events are recorded by the early cretaceous dikes with zircon u pb ages between 127 and 113 ma a post ore diorite porphyry dike that crosscuts the early cretaceous dikes has a u pb zircon age of 121 5 1 5 ma all the lines of geochronology evidence suggest a distinct genetic link between the gold mineralization and the early cretaceous magmatism in the wulong orefield this episode of magmatism and mineralization corresponds to the lithospheric thinning within the northeastern north china craton which is triggered by the subduction of the paleo pacific plate

delimitation of a cryptic eocene tectono thermal domain in the eastern cordillera of the bolivian andes through k ar dating and 40ar 39ar step heating new k ar ages and 40 ar 39 ar age spectra for samples from granitoid rocks and meta sediments of the cordillera real bolivia reveal a complex mid tertiary tectono thermal history for this segment of the central andean eastern cordillera previous radiometric dating of the cordillera real intrusions defined two areally distinct plutonic domains in the n upper triassic lower jurassic in the s upper oligocene lower miocene our new k ar ages many from deformed intrusions fall between these two episodes for the variably foliated zongo massif there is a marked discordance between biotite and muscovite k ar dates each decreasing consistently from sw to ne across this 8 km wide plutonic centre the age gradients are developed within the foliated and unfoliated facies of the zongo intrusions but do not continue ne into the palaeozoic meta sedimentary rocks for which k ar dates are erratic 40 ar 39 ar step heating analyses of muscovites and most biotites from granitoid rocks reveal that the oldest and youngest micas yield plateaux 210 and 39 ma whereas those with intermediate ages exhibit disturbed spectra a plateau date for a biotite from the ne margin of the zongo massif shows that final cooling through c 300 c occurred in the late eocene the new data reveal that a marked thermal discontinuity existed 39 ma ago at the ne contact of the zongo intrusion additional discordant dates for the yani and illampu intrusions to the nw indicate that the discontinuity was of regional scale there is no direct relationship between this tectono thermal event which affected at least 2000 km 2 and the upper palaeozoic foliation of several of the plutons involved and thus it is cryptic on outcrop and microscopic scales we propose that the thermal discontinuity resulted from late eocene crustal shortening sw verging thrust faulting and attendant cordilleran uplift at the inner eastern boundary of the andean orogen coincident with the incaic deformation defined in peru

geochronological constraints on pre syn and postmineralization events at the world class cleo gold deposit eastern goldfields province western australia recent geological and geochronological studies have led to a reevaluation of whether or not the majority of the lode gold deposits of the yilgarn craton formed nearly synchronously during an archean craton wide hydrothermal event as previously proposed the majority of reliable data indicate that gold mineralization took place at ca 2640 to 2625 ma however recent work in the far north of the eastern goldfields province provides structural evidence for instances of earlier gold mineralization and geochronological data for interpreted postore rocks that are considerably older than 2640 ma the documentation of xenotime and monazite in association with ore minerals at the cleo deposit provides a valuable means of determining the absolute age of gold mineralization at the cleo deposit high grade western lodes veins crosscut the sunrise shear zone at a high angle with only centimeter scale offset given that the stratigraphic sequence indicates at least several hundred meters offset across the shear zone the minimal offset of the western lodes veins indicates that gold mineralization was late in the history of movement in the shear zone the absolute ages of pre syn and postmineralization elements in the mine stratigraphic succession have been determined using a variety of geochronological techniques fuchsite micas formed in the sunrise shear zone yield an 40ar 39ar isochron age of 2667 19 ma rhyodacite porphyry dikes postdate the formation of the shear zone but predate the main phase of gold mineralization dike intrusion is constrained to 2674 3 ma by shrimp ii u pb analysis of zircons from these dikes rhenium os analysis of molybdenite from quartz chalcopyrite molybdenite veins that crosscut the porphyry dikes gives an age of formation at 2663 11 ma consistent with their relationship to the porphyry dikes both the dikes and these veins are crosscut by gold bearing western lodes veins mutually crosscutting relationships with ore minerals indicate that microscopic xenotime and monazite grains were deposited during ore formation in the western lodes ore zones shrimp ii u pb analyses of xenotime and monazite grains indicate that western lodes mineralization took place at 2654 8 ma at least 9 m y after the intrusion of the porphyry dikes 95 confidence evidence for substantial temporal separation between intrusive activity and gold mineralization is recorded by other researchers for other deposits associated with granitic intrusions in the leonora laverton area phlogopitic micas from a lamprophyre that crosscuts the whole succession including the sunrise shear zone yield an ar ar plateau age of 2080 4 ma this study constrains the timing of multiple events at cleo including the main phase of gold mineralization during a relatively short span of time however in the context of the larger debate about the existence of a dominant 2640 to 2625 ma period of gold mineralization and the extent of a proposed widespread pre 2660 ma mineralization event in the yilgarn craton the data from cleo are equivocal the 2654 8 ma age for mineralization being significantly older than 2640 ma but not significantly pre 2660 ma even if the maximum possible age is accepted

the miocene pliocene macusani volcanics se peru i mineralogy and magmatic evolution of a two mica aluminosilicate bearing ignimbrite suite

time of formation and peak of variscan hp ht metamorphism of quartz feldspar rocks in the central erzgebirge saxony germany the variscan erzgebirge represents an antiform with a core of gneisses and mica schists surrounded by a phyllitic mantle the gneiss eclogite unit geu in the central part is a composite tectonometamorphic assemblage characterized by a hp ht imprint and comprises migmatitic para and orthogneisses ht mylonites hp granulites eclogites and garnet peridotites it is tectonically sandwiched between two major units with distinctly lower pt histories the geu experienced a characteristic kinked retrograde pt path after hp ht equilibration with 1 strong near isothermal decompression at high temperatures 2 extensive re equilibration at medium pressures followed 3 by rapid cooling during continued uplift we dated zircons pb pb evaporation from granitoid orthogneisses and metapelites of the geu the orthogneisses contain euhedral long prismatic zircons of igneous origin that provided protolith ages between 470 and 524 ma metapelites retain well preserved granulite facies mineral assemblages and contain spherical multifaceted metamorphic zircons that grew near the peak of hp ht metamorphism inclusions of prograde hp phengite 15 kbar and rutile are included in one such zircon metamorphic zircons of three samples from different localities yielded identical 207pb 206pb ages of 340 5 0 7 ma 341 2 0 5 ma and 341 6 0 5 ma respectively consideration of these zircon ages with published 39ar 40ar white mica ages suggests fast cooling and uplift rates in excess of 50 c ma and 4 km ma this is typical for large scale extensional tectonic unroofing of the ultra deep part of a fossil thickened variscan continental crust 60 km during continuing continental collision and orogenic collapse

an improved u th pb age calculation for electron microprobe dating of monazite abstract determination of u th pb ages using the electron probe microanalyser epma is an inexpensive alternative method for dating monazite the method is rapid and reliable both for simple monogenenetic monazite and for complex polygenetic monazite having undergone metamorphic events involving fluid interaction and recrystallization the main limitation of the method is its rather poor precision i e 45 to 120 ma for ages ranging from 300 to 3000 ma calculated on each spot the precision is limited by pb content and by counting statistics which cannot give precision better than 2 for individual determinations on u th and pb even at high levels a procedure that uses the new th pb vs u pb diagram to improve the calculated precision on u th pb ages gives results to within 5 to 15 ma for ages ranging from 300 to 3000 ma with complex polygenetic monazite in which either the points show large scattering indicated by a large mswd or the regression line exhibits a slope very different from neighbour theoretical isochrons the procedure must be applied separately on homogeneous domains only this makes it possible to distinguish between events separated by a gap of 20 to 60 ma according to the range of ages concerned i e 300 to 3000 ma several examples are given to illustrate these systematics

in situ la icpms u pb dating of cassiterite without a known age matrix matched reference material examples from worldwide tin deposits spanning the proterozoic to the tertiary abstract cassiterite sno2 a main ore mineral in tin deposits is suitable for u pb isotopic dating because of its relatively high u pb ratios and typically low common pb we report a la icpms analytical procedure for u pb dating of this mineral with no need for an independently dated matrix matched cassiterite standard la icpms u th pb data were acquired while using nist 612 glass as a primary non matrix matched standard raw data are reduced using a combination of iolite and other off line data reduction methods cassiterite is extremely difficult to digest so traditional approaches in la icpms u pb geochronology that utilize well characterized matrix matched reference materials e g age values determined by id tims cannot be easily implemented we propose a new approach for in situ la icpms dating of cassiterite which benefits from the unique chemistry of cassiterite with extremely low th concentrations th u ratio of 10 4 or lower in some cassiterite samples accordingly it is assumed that 208pb measured in cassiterite is mostly of non radiogenic origin it was initially incorporated in cassiterite during mineral formation and can be used as a proxy for common pb using 208pb as a common pb proxy instead of 204pb is preferred as 204pb is much less abundant and is also compromised by 204hg interference during the la icpms analyses our procedure relies on 208pb 206pb vs 207pb 206pb pb pb and tera wasserburg 207pb 206pb vs 238u 206pb u pb isochron dates that are calculated for a 1 54 ga low th cassiterite reference material with varying amounts of common pb that we assume remained a closed u pb system the difference between the nist 612 glass normalized biased u pb date and the pb pb age of the reference material is used to calculate a correction factor f for instrumental u pb fractionation the correction factor f is then applied to measured u pb ratios and tera wasserburg isochron dates are obtained for the unknown cassiterite analyzed in the same analytical session this allows for u pb dating of cassiterite of any age with no need for an independently dated matrix matched reference material nor assumptions about the isotopic composition of common pb results for cassiterite from tin deposits in bolivia brazil china russia saudi arabia south africa spain and the united kingdom with ages ranging from 20 ma to 2060 ma demonstrate the applicability of this approach across a broad range of geologic time these ages are in good agreement with published geochronology of the host rocks associated with the tin deposits and with previously published u pb ages of some cassiterites from the same deposits thus our in situ la icpms methodology verifies the use of cassiterite as a reliable u pb mineral geochronometer with the advantages of fast and relatively low cost in situ analyses with moderate spatial resolution

detection of inherited monazite in the manaslu leucogranite by 208pb232th ion microprobe dating crystallization age and tectonic implications abstract although leucogranites are among the least petrologically variable of all igneous rocks ironically they are among the most difficult to reliably date the high himalayan leucogranites have been the subject of numerous geochronological investigations because of their interrelationship with the most significant tectonic features of that mountain belt for a variety of reasons linked to the minimum melt composition of these leucogranites these dating studies have not been entirely successful we report results of a new ion microprobe dating method based on the decay of 232 th to 208 pb in monazite that has directly revealed the presence of inherited pb in monazite from the manalsu granite casting doubt on its previously accepted age monazite ages obtained from this leucogranite yield two distinct populations a large number of ages with a normal distribution and mean age of 22 4 0 5 ma 2 s e that we interpret to be the crystallization age and a smaller inherited fraction with an age of ca 600 ma because formation of the granite is thought to be related to slip on the main central thrust both this date and a second less precise result from a structurally similar pluton near mt everest indicate that the main central thrust was active in the interval 24 22 ma but do not constrain its initiation together with crosscutting relationships these data require that movement on the north himalayan fault occurred prior to 22 ma at both locations

metallogeny of tin magmatic differentiation versus geochemical heritage tio 2 sn and rb sr sn variation diagrams for granitic fractionation series from various tin and non tin provinces do not support the concept of geochemical heredity of tin i e the assumption of a primary crustal sn anomaly in tin provinces the controlling factor for the generation of tin granites is a special bulk distribution coefficient of sn probably dependent on the oxygen fugacity of the melt

a tale of two eras pliocene pleistocene unroofing of cenozoic and late archean zircons from active metamorphic core complexes solomon sea papua new guinea u pb ion microprobe analyses of zircons from gneisses and granodiorites exposed in the d9entrecasteaux islands and from conglomerate sections of the goodenough no 1 well in the adjacent trobriand basin provide constraints on the age of magmatism peak metamorphism and nature of rocks unroofed during initial stages of metamorphic core complex formation in the solomon sea the youngest populations of zircons from felsic gneisses and granodiorites indicate late pliocene 206 pb 238 u ages no inherited zircons were identified in the granodiorites and the 206 pb 238 u ages 1 65 0 18 ma 1 98 0 08 ma 2 are interpreted as crystallization ages these synkinematically emplaced granodiorites intruded into actively extending continental crust are some of the youngest known granitoids currently exposed at the earth9 surface zircon ages from felsic gneisses 2 63 0 16 ma 2 72 0 28 ma 2 are interpreted to date zircon growth subsequent to eclogite facies metamorphism felsic gneiss samples also contained zircon xenocrysts from cretaceous miocene protoliths in striking contrast zircons from igneous and metamorphic clasts from the goodenough no 1 well indicate a single population with a 207 pb 206 pb age of 2781 9 ma 2 we speculate that they are derived from basement rocks unroofed during initial stages of development of the d entrecasteaux metamorphic core complexes these results provide the first direct evidence for the existence of archean protoliths in the basement rocks of southeastern papua new guinea

geochemical and isotopic study of metasomatic apatite implications for gold mineralization in xindigou northern china abstract the 0 7 moz xindigou gold deposit lies on the north margin of north china craton the orebodies are controlled by nww trending shear zones and hosted by an archean metavolcanosedimentary sequence these host schist amphibolite and marble rocks were intruded by late paleozoic granites and mafic dikes two independent magmatic hydrothermal assemblages were identified based on petrographic evidence a pre ore magmatic hydrothermal magnetite apatite pyrite zircon assemblage and an ore related potassium feldspar muscovite sulfide minor monazite assemblage apatite that has undergone later alteration shows significant intracrystalline spatial variability with respect to the concentrations of rare earth elements rees si and sr scanning electron microscope backscattered images and statistical interrogation of the compositional data acquired by la icp ms indicate that apatite grains in the pre ore magnetite apatite assemblage are homogeneous and enriched in rees and si ap1 where sulfide related alteration of mineralization stage was overlapped these apatite grains display a distinctive texture of homogeneous cores and turbid rims this dissolution reprecipitation process preferentially transported elements from the original apatite rees and si gradually decrease from the core ap1 to the altered rim ap2 ap3 whereas sr increases localized leaching of rees especially lrees from apatite was followed by precipitation of secondary monazite grains in the metasomatic apatite rims and the muscovite sulfide quartz phosphate sequence in situ sr isotope analyses of the apatite show the 87sr 86sr ratios varying from the lowest value 0 707874 in unaltered ap1 to the highest 0 714160 in altered ap3 zircon grains from migmatite display a peak metamorphic age at 2512 9 ma whereas zircons from the early magnetite apatite association formed near 1776 12 ma and late hydrothermal monazite yields a th pb age of 301 0 1 7 ma these geochronology results show that the mineralization occurred during the late paleozoic orogenesis long after neoarchean regional metamorphism and late paleoproterozoic rift related magmatism the typical hydrothermal features of orogenic gold deposit could be inferred from the fluorapatite the elemental patterns of fluorapatite grains indicate that a carbon and sr enriched acid slightly oxidized and low salinity hydrothermal system was responsible for apatite metasomatism and gold mineralization strontium isotopes further reveal that the fluid related to gold deposition was derived from mafic lower crust with extensive radiogenic sr accumulation during fluid rock interaction this study demonstrates the potential application of apatite in exploration for orogenic gold deposits and its use in tracking hydrothermal ree re mobilization during metasomatism

pb pb and u pb zircon dating of subvolcanic rhyolite as a time marker for hercynian granite magmatism and sn mineralisation in the eibenstock granite erzgebirge germany considering effects of zircon alteration tin mineralisation is closely related to rhyolite stocks and dykes which occur in the endo and exocontact of the eibenstock granite erzgebirge germany the same structures which cut the granite control the rhyolite emplacement and the location of ore bearing greisen bodies albitisation and greisenisation related to tin mineralisation as well as sericitisation and argillic alteration may be traced by changes in chemical and mineralogical composition of both rhyolite and granite wall rock comprehensive zircon studies by scanning electron microscopy secondary and backscattered electron as well as cathodoluminescence imaging edx measurements reveal that zircon from rhyolite and from the enclosing granite shows significant changes in chemical composition and crystallinity including distortion of the u pb isotope system when affected by greisenisation single evaporation analysis of zircon from rhyolite with little or no greisenisation gave a 207pb 206pb age of 290 5 ma whereas zircon from little altered granite gave a 207pb 206pb age of 320 8 ma the single evaporation age of zircon from rhyolite is confirmed by 238u 206pb shrimp ages of 297 8 ma the significant time gap of at least 20 ma between granite intrusion and rhyolite formation suggests that the late magmatic evolution of the eibenstock granite cannot be regarded as a source for tin ore forming fluids as previously assumed

a textural and geochemical guide to the identification of hydrothermal monazite criteria for selection of samples for dating epigenetic hydrothermal ore deposits hydrothermal monazite is one of the most reliable geochronometers for u pb dating of epigenetic or hydrothermal ore deposits because its blocking temperature at ca 700 c is higher than that of most metamorphic conditions although igneous monazite is routinely used for age dating igneous rocks only a few ore deposits have been dated by hydrothermal monazite this is due to the similar morphology of hydrothermal and igneous monazite which prevents the reliable distinction of hydrothermal monazite in particular we demonstrate that hydrothermal monazite can be distinguished from igneous monazite by its unique geochemical signature its local abundance and to common association with hydrothermal mineral assemblages our data and the data of others reported in the literature suggest that the low tho 2 content of hydrothermal monazite 0 1 wt is distinct from that of igneous monazite 3 to 5 wt and may be used to determine their genesis

magmatic and metallogenetic episodes in the northern tin belt cordillera real bolivia new k ar determinations for granitoid rocks and ores from the northern bolivian segment ca 15 18 s of the central andean cordillera oriental eastern cordillera confirm that this region displays a remarkable repetition of magmatic activity and associated lithophile metal mineralization intrusion of monzogranites in part peraluminous and granodiorites took place in the mid to late triassic apparent age range 225 202 ma and late oligocene early miocene 28 4 ca 19 2 ma the two plutonic domains are juxtaposed with little or no areal overlap along an essentially linear belt defining the inner boundary of the central andean magmatic arc there is no conclusive evidence of granitoid intrusion during the intervening period although at least two centres of upper cretaceous basic intermediate hypabyssal volcanic rocks are known whereas the triassic episode simultaneously affected ca 200 km of the belt the oligocene miocene domain experienced a longitudinal southeastward migration of activity which in its later stages 22 19 ma coincided with the initiation of widespread volcanism and intrusion on the altiplano to the west of the granitoid belt

physico chemical control on the ree minerals in chloritoid grade metasediments from a single outcrop central alps switzerland this study assesses the effects of fluid whole rock composition and oxygen fugacity on the texture and composition of monazite allanite and xenotime for this purpose these were investigated in 13 mono metamorphic metasediments from a single locality of the central alps switzerland which record greenschist facies conditions t 400 450 c two of the samples contain hydrothermal veins dominated by quartz and calcite quartz respectively in metasediments devoid of veins the light rare earth elements lree are concentrated in allanite in all samples except for one metamarl ga06 allanite formation is texturally coeval with apatite chloritoid and xenotime during the main tectono metamorphic stage allanite formation implies significant mass transfer of ca and p via a fluid phase which is not clearly related to advective transport in ga06 elongate monazite grains have a detrital core rimmed by newly formed monazite significant arsenic contents are found in newly formed monazite xenotime and apatite monazite texture and composition suggest re crystallization by pressure solution at an oxygen fugacity sufficient to partly oxidize as s u and fe whether or not monazite is preserved appears to be but weakly dependent on the ca al ratio and thus whole rock composition at greenschist facies conditions samples with veins show peculiar features along carbonate bearing veins allanite occurs as porphyroblasts overgrowing the main foliation of the host rock as similar allanite porphyroblasts occur in calcite bearing metamarl their formation is attributed to environments rich in co2 bearing fluid a new generation of monazite is found in and along retrograde quartz veins this study demonstrates that at least in metasediments up to chloritoid grade ree minerals record fluid rock interaction that occurred at different deformation stages arsenic concentrations in ree phosphates appear to reflect conditions of elevated oxygen fugacity in cases where such conditions are not inherited from the sedimentary protolith the oxidation reflects a hydrothermal event the age of which may be directly datable by u th pb of as rich monazite

an extended episode of early mesoproterozoic metamorphic fluid flow in the reynolds range central australia the products of metamorphic fluid flow are preserved in zones within the marbles and metamorphosed semipelites of the upper calcsilicate unit in the granulite portion of the late palaeoproterozoic reynolds range group northern arunta block central australia the zones of retrogression characterized by minerals such as wollastonite grossular and clinohumite local resetting of oxygen isotopic compositions and local major element metasomatism were channelways for water rich fluids derived from granulite facies metapelites u th pb isotopic ages measured by the shrimp ion microprobe on zircon and monazite from a granulite facies semipelite an early semiconcordant aluminous quartz rich fluid flow segregation and a late discordant quartz rich segregation record some of the extended thermal history of the area zircon cores from the semipelite show its likely protolith to be an igneous rock 1812 11 ma old itself derived from a source containing zircon as old as 2 2 ga low th u overgrowths on the zircon grew during granulite facies metamorphism at 1594 6 ma monazite cooled to its blocking temperature at 1576 8 ma zircon cores from the semiconcordant segregation are dominantly 2 3 ga old indicating that the source of the fluids was not the particular metamorphosed semipelite studied two generations of low th u overgrowths on the zircon give indistinguishable ages for the older and younger of 1589 8 and 1582 8 ma respectively the monazite age is the same 1576 12 ma zircon from the late discordant segregation gave 1568 4 ma fluid flow occurred for at least 18 3 ma and ended 26 3 ma after the peak of metamorphism suggesting a very slow cooling rate of 3 c ma 1 the last regional high grade metamorphism in the reynolds range occurred at 1 6 ga not 1 78 ga as previously thought the high grade event at 1 78 ga is a separate event that affected only the basement to the reynolds range group

late pleistocene environments of the central ukraine the vyazivok loess sequence from the dnieper plain ukraine documents regional environmental changes during the late pleistocene and holocene pedological and palynological analyses and low field magnetic susceptibility document changes from dense temperate forest during the last interglacial maximum to open harsh loess steppe during the latest pleistocene the vyazivok section overlies hillwash derived from a lower pleistocene terrace and consists of two stratified soil complexes kaydaky and pryluky marine isotope stage mis 5 equivalent separated by a layer of eolian dust tyasmyn silt the lower soils in both complexes formed within forest these soils are overlain by the uday mis4 and bug mis2 loess units which are separated by boreal soils of the vytachiv mis3 complex the coldest conditions within the record occurred in the youngest loess holocene soils cap the bug loess the vyazivok section shows remarkable similarities with other classical loess sequences in western europe the czech republic and austria the kaydaky pryluky and vytachiv deposits correlate with the pkiii pkii and pki soil complexes respectively of the czech republic the tyasmyn and prylyky silt layers correspond to marker horizons from central europe c 2001 university of washington

a review of shallow ore related granites textures volatiles and ore metals shallow texturally complex granites can be associated spatially introduction and temporally with hydrothermal alteration and mineralization granite related ore deposits include porphyry and skarn the formation of a granite related ore deposit represents the confluence type ores and other hydrothermal deposits that are of many chemical and physical geological factors including magma spatially and temporally associated with granitic sensu composition e g concentrations of ore metals chlorine and water lato rocks in this paper i emphasize characteristics magma oxidation state the relative timing of crystallization magma found in porphyry style cu mo au deposits and some ascent magmatic volatile phase exsolution and the depth of em related systems however my treatment here is not meant placement early magmatic crystallization of ore metal rich minerals to cover the full range of granitic rocks and mineralization coupled with late exsolution of the magmatic volatile phase is that make up the granite related ore systems the forpromoted by deeper emplacement levels and lower magmatic water mation of granite related ore deposits by orthomagmatic concentrations and leads to low eyciencies of removal of compatible hydrothermal processes is dependent upon many physical elements from melts into the magmatic volatile phase s water and chemical magmatic factors including but not limited concentrations in the melt and pressures of crystallization can be to the composition and evolution of the associated estimated from phase equilibria and textural relationships of horn magmas the rate of magma ascent the depth and blende in some felsic systems physical factors avect the dynamics geometry of magma emplacement and the local temof fluid magma melt and volatile phase movement which in turn perature and stress fields at the site of magma emavect the size of zones of alteration and mineralization granite placement detailed studies of the igneous rocks textures can record the partial history of some dynamic processes associated with ore deposits can therefore yield critical miarolitic cavities are good evidence for magmatic volatile phase information regarding the source of metals and ligands exsolution both miarolitic cavities and pegmatitic texture exhibit in the ore generative hydrothermal solutions that are evidence for external nucleation of crystals nucleation controlled operative in the formation of granite related ores in this phenomena expressed as variations in granite textures can result review i will present a series of narratives consistent in from a multiplicity of causes including undercooling of the melt my view with prevailing field and experimental data on textural elements such as pegmatite aplite skeletal crystals and the orthomagmatic hydrothermal theory for the genesis graphic textures can form as a result of undercooling interconnected of some granite related deposits volumes of the magmatic volatile phase allow for advection of some high level granites i e those that are emplaced hydrothermal ore fluids through the magma in shallow granitic at depths of 8 km or less represent the crystallized systems miarolitic cavities can be interconnected consistent with remains of magmas that were associated with subvolcanic this hypothesis ore generative hydrothermal systems therefore studies of shallow granites aimed at understanding magmatic evolution and volatile phase exsolution at shallow levels are necessary if we are to understand ore genesis and the deep inputs to present day geothermal systems as well as evaluate hazards associated with the volcanic

boron isotope composition of melt inclusions from porphyry systems of the central andes a reconnaissance study quartz hosted melt inclusions from latite dykes of the eocene el salvador copper porphyry system in northern chile display wide ranges in both boron concentration 15 155 p p m b and isotope composition 11b 7 to 12 n 10 likely reflecting slab derived fluid input from seawater altered oceanic crust in contrast the major miocene tin silver and tin porphyry systems in the bolivian back arc region cerro rico de potosi chorolque llallagua have distinctly different melt inclusion compositions with 11b of 11 4 2 7 n 10 and magmatic boron enrichment up to several hundred p p m b the seawater signature in the el salvador melt inclusions explains the oxidized mineral assemblage of the copper porphyry system as opposed to the more reduced nature of the bolivian tin porphyry systems which reflect intracrustal melting of pelitic rocks

evolution of continental crust in the central andes constraints from nd isotope systematics periods of crustal reworking and of crustal growth can be distinguished within orogenic belts through nd isotope studies of both igneous and sedimentary samples the active continental margin of the central andes has been the site of magma genesis since at least 300 ma during the late paleozoic orogenesis was virtually an intracrustal reworking event resulting in late proterozoic nd model ages during the jurassic a marked decrease in model age indicates a critical change in tectonic style and the onset of crustal growth younger model nd ages are restricted to the 180 30 m y period of andean tectonics consistent with active crustal growth through mantle input over the past 30 m y elevated model nd ages from volcanics and sediments record a return to intracrustal processes in the central andes synchronous with tertiary crustal thickening these results imply that crustal growth is not a continuous process at active continental margins and may progressively decelerate during orogenic evolution

syn deformation fluid assisted growth of monazite during renewed high grade metamorphism in metapelites of the central rhodope bulgaria greece abstract we present textural chemical and u th pb age data on monazites from garnet kyanite grt ky metapelites from the chepelare shear zone bulgaria and the nestos shear zone greece in the central rhodope samples from both locations have experienced two stages of high temperature metamorphism during alpine times the first event involved mid mesozoic granulite facies dehydration melting the second event involved mid cenozoic lower grade fluid assisted partial melting the latter is well expressed in adjacent felsic rocks but had limited impact on the grt ky metapelites most samples display evidence for strong ductile shearing in the presence of fluids monazite is present in the highly foliated matrix and as inclusions in garnet and kyanite unlike the inclusions matrix monazites display features of fluid assisted dissolution recrystallization y poor domains with u th pb ages of between ca 115 and 165 ma represent the largest part of the grains y rich domains with mid cenozoic ages occur as rims or as small satellite grains surrounding the mesozoic grains the cenozoic monazite domains crystallized at the expense of the mesozoic ones and simultaneously incorporated y provided by the fluid assisted resorption of garnet an age of ca 36 ma is obtained for the samples of both shear zones interpreted as dating the main episode of monazite growth during the cenozoic similar ages exist for the crystallization of leucosomes and pegmatites in the adjacent migmatitic gneisses indicating that the fluids responsible for the precipitation of the cenozoic monazites were probably released during the crystallization of nearby anatectic melts together with associated rutile and biotite many newly grown monazites show a preferred orientation paralleling the matrix foliation this supports the hypothesis of dynamic dissolution precipitation as an efficient mean to promote renewed monazite crystallization during ductile deformation of the host rock at ca 36 ma

uthpb zircon dating of the 13 8 ma dacite volcanic dome at cerro rico de potosi bolivia abstract the temporal relationship between the extrusion of the miocene dacite volcanic dome at cerro rico de potosi bolivia and the associated ag sn mineralization has an important bearing on the heat and metal sources for this world class mineral deposit the highly altered nature of the volcanic rock however has prevented previous efforts from definitively determining the emplacement age of the dome rather than subsequent episodes of alteration the present study uses u th pb dating of sparse zircon contained in the dacite to demonstrate that at most only several hundred thousand years separate dome emplacement from main stage mineralization the dacite contains a morphologically heterogeneous population of zircon with considerable variation in size shape and color preliminary analyses revealed the presence of a significant component of inherited zircon most likely as older cores that were overgrown by rims during the crystallization of the dacite magma morphological distinctions shape size color within the zircon population provided the basis for separating the zircon into fractions that reduced or enhanced the inherited component in composite grains by analyzing the tips of zircon with very large length to width ratios it was possible to constrain the crystallization age of the dacite to 13 8 0 2 ma the dispersion of data on a concordia diagram indicates at least two ages of inherited zircon one mesozoic associated with yellow grains and another proterozoic associated with colorless grains such xenocrystic components have useful petrogenetic implications for the source and travel path of the magma

vegetation and climate in the early and pleni weichselian in northern central europe analysis of numerous pollen diagrams from north and central germany and from the adjacent lowlands of the netherlands denmark poland and belarus have facilitated a regional comparison of the vegetation and climatic evolution from the beginning of the early weichselian glaciation to the weichselian pleniglacial data from geological studies and analysis of fossil beetles and plant macroremains have been used to supplement the palaeoclimatic reconstruction up to the end of the oerel interstadial the palaeoclimate was characterised by increasing continentality the winter temperatures in particular tended to fall continuously during the stadials and the interstadials of the early weichselian and early pleniglacial in the brorup and odderade interstadials summer temperatures where sufficiently high to enable boreal forests to grow whereas in the oerel interstadial summer temperatures were such that tree growth was inhibited it is probable that falling sea level and the consequent extension northwards of the north sea coast were the main causes of increasing continentality in the latter part of the pleniglacial peat accumulation frequently took place and humic silts were deposited under lacustrine conditions correlation between various sites is extraordinarily difficult pollen diagrams from the so called interstadials of the glinde moershoofd complex hengelo and denekamp are similar to those of the known early weichselian stadials it is proposed therefore that these interstadials should be called intervals and that the term interstadial be reserved for climatic variations that result in distinctive pollen assemblages and which in turn reflect distinctive vegetation dynamics interstadials should be capable of being characterised on a biostratigraphical basis and it should be possible to establish correlations over considerable distances according to this definition the first three warm oscillations of the weichselian glaciation in the central european lowlands are the brorup odderade and oerel interstadials all other pleniglacial peat layers should be assigned the rank of interval copyright 2001 john wiley sons ltd

constraints on fluid evolution during metamorphism from u th pb systematics in alpine hydrothermal monazite abstract the timing and duration of hydrothermal activity during orogenesis are difficult to constrain because such systems are open and multistage using mm sized monazite crystals from two alpine clefts from the central alps switzerland we demonstrate that combined u th pb isotopic systematics of hydrothermal monazite can constrain both timing and fluid evolution during crystallization our data highlight four major characteristics of the cleft monazites i extreme th u ratios ii significant common pb in the u system up to 39 206 pb iii excess 206 pb up to 54 and iv precise and reliable th pb ages comparison of our results with literature data indicates that th u in monazite is a remarkable discriminant of geological conditions capable of distinguishing metasedimentary magmatic and hydrothermal origin hydrothermal monazite crystals are characterized by th u ratios up to 629 among the highest values ever reported extreme th u ratios in monazite enhance incorporation of 230 th a short lived intermediate product in the 238 u 206 pb decay chain generating 206 pb excess which if not accounted for results in 206 pb 238 u ages that are too old for example in the samples investigated here by as much as 300 for the two zoned monazite crystals studied in detail 208 pb 232 th ages are reliable for the different compositional domains visible in back scattered electron bse images 232 th 208 pb ages for the older domains 15 2 0 3 ma and 14 1 0 3 ma respectively are consistent with the structural relationships of the hydrothermal veins indicating early retrograde genesis the youngest rim age at 13 5 0 4 ma for the blauberg crystal marks termination of monazite precipitation the resolvable age difference is interpreted to reflect pulsed monazite growth over an extended period of hydrothermal activity in both crystals the outer rims have the highest 206 pb excess confirming a two stage crystallization two scenarios are envisaged to account for the 206 pb excess evolution in the first increasing 206 pb excess is caused by a modification of the th u fractionation between monazite and fluid due to an evolution of the fluid towards more oxidizing conditions that favor partitioning of hexavalent u into the fluid alternatively it is possible that 230 th increased with time in the fluid in this second case monazite growth would have occurred in a closed system from a fluid that was initially in disequilibrium with the 238 u 206 pb decay chain and progressively equilibrated t

late oligocene early miocene major tectonic crisis and related basins in bolivia recent advances in biochronology geochronology magnetostratigraphy structural geology and basin analysis make untenable the traditional correlation of the first major andeanage deformational episode in bolivia with the middle eocene incaic tectonic phase defined in central peru and instead demonstrate that the episode took place in late oligocene and early miocene time this major tectonic crisis resulted in contemporary development of the subandean external foreland basin and altiplano intermontane basin which were separated by the initiation of thrusting in the present cordillera oriental area the deformation suggests that the bolivian orocline began to develop at that time it is likely that this tectonic upheaval is genetically linked to the marked increase in rate of plate convergence produced by the contemporaneous breakup of the farallon plate

whole grain evaporation for 207 pb 206 pb age investigations on single zircons using a double filament thermal ion source a technique has been developed and tested to analyse 207pb 206pb apparent ages by thermal evaporation of radiogenic lead directly from untreated whole zircon grains 0 3 mm the evaporation analyses are performed in the double filament arrangement of a thermal ion mass spectrometer thims the method is a powerful tool to distinguish between different lead components occurring in the same grain because differing activation energies of the competing lead components cause their sequential evaporation from the zircons the evaporation of test samples results in 207pb 206pb apparent ages in good agreement with u pb ages known from literature single zircons from a granite of the marble mountains california yield an age of crystallization of 1 410 30 ma ceylon zircons from heavy mineral bearing gravels yield 560 40 ma as age of crystallization of the pegmatitic gravel sources individuals from a heterogeneous zircon population of a diatexite from the southern schwarzwald sw germany indicate metamorphic zircon formation around 500 ma and the existence of middle proterozoic relics 1 95 0 05 ga

precise electron microprobe age determination in altered uraninite consequences on the intrusion age and the metallogenic significance of the kirchberg granite erzgebirge germany an integral method of data evaluation for chemical dating of accessory uraninite by electron microprobe analysis and electron microscopy is proposed the internal structure of uraninite grains the contents of si ca and fe and tests for loss or gain of pb and u are suitable criteria to decide whether or not a given crystal area was affected by secondary alteration the method was applied to uraninite from the kirchberg granite erzgebirge germany and an age of 330 5 ma 2 was constrained this result supports earlier assumptions that there were at least two events of hercynian granite magmatism separated by a time gap of about 40 ma and that the magmatic evolution of the kirchberg granite is not related to the formation of the w mineralisation developed in the endocontact of this granite secondary alteration of uraninite is probably closely related to the formation of u deposits in the vicinity of the kirchberg massif which was extensively mined in the past

growth of the central andean plateau by tectonic segmentation is controlled by the gradient in crustal shortening abstract crustal deformation orocline formation and growth of the central andean plateau as well as the mutual relations of these processes with climate are a matter of international debate earthquake focal mechanism fault kinematic paleomagnetic and cross section balancing data are paramount for understanding the morphotectonic evolution of this noncollisional orogen but collectively await an explanation in terms of a comprehensive kinematic model we offer such a model that approximates simple shear in plan view and that predicts the kinematics of first order fault zones in the southern central andes the model indicates that segmentation of the upper crust into rhomb shaped domains confined by transpressive ranges resulted from the decrease in crustal shortening with distance to the central bend of the andes an anastomosing network of kinematically coupled reactivated orogen parallel and newly formed ne trending deformation zones encompassing components of sinistral and dextral strike slip res

timing of diagenesis and very low grade metamorphism in the eastern sector of the sierra de cameros iberian range spain a u pb shrimp study on monazite the sierra de cameros is an intracontinental orogen and represents the north western part of the iberian range in northern spain it comprises a thick sequence of syn rift continental sediments mainly sandstones and carbonates deposited during lower cretaceous times a unique characteristic of the sierra de cameros in relation to the rest of the iberian range is the presence of low grade metamorphism in certain parts of the basin an event that predates basin inversion this paper describes the presence textural relationships and geochemical aspects of authigenic and or metamorphic monazite within different lithologies from the deepest parts of the basin sensitive high resolution ion microprobe shrimp u pb dating of monazite records the presence of two age populations the first with 206 pb 238 u ages ranging from 122 to 116 ma which is considered as diagenetic in origin whilst the second is dated at 99 2 ma and postdates the metamorphic climax

environmental changes in the crimean mountains during the last interglacial middle pleniglacial as recorded by pollen and lithopedology abstract lithopedological and pollen successions of multilayered paleolithic sites have been studied in the foothills of the crimean mountains the kabazi ii and buran kaya iii sites and they demonstrate multiple environmental changes in the area during the late pleistocene the late temperate and post temperate stages of the last interglacial are palynologically recorded in the kaydaky chernozem mollisol at the base of the upper pleistocene sequence two early glacial interstadials are indicated by pollen data in the overlying pryluky pedocomplex which is separated from the kaydaky soil by colluvial sediments of the tyasmyn cold unit the first interstadial represented by a luvisol derivative had a warmer and wetter climate the second interstadial identified by a rendzina soil and dated by esr between 74 and 85 000 yr was drier and cooler boreal environments existed during the stadial detected between the two early glacial soils the climate became much colder during the early pleniglacial uday non soil unit overlying the pryluky pedocomplex the middle pleniglacial is represented by the vytachiv pedocomplex it consists of three warm interstadials cambisols and their derivatives and two stadials non soil beds the upper cambisol yielded radiocarbon ages of 28 30 000 14 c yr bp and the middle interstadial was esr dated at 44 000 yr ago a cooler interstadial 38 36 000 yr occurred between them the elements of broad leaved vegetation spread from refugia during the middle pleniglacial interstadials whereas the stadials had dry boreal climates particularly during the second stadial 35 31 000 yr bp

versatile monazite resolving geological records and solving challenges in materials science generalizations about monazite implications for geochronologic studies with the advent of techniques that preclude mineral separation ages from specific compositional domains in monazite ce la th po 4 have provided a wealth of information regarding the timing of the geologic evolution of numerous regions however confusion can arise when single grains show large differences in age that fail to correlate to chemistry or location within the monazite generalizations that lead to incorrect age interpretations include that monazite zoning in y th and or the rare earth elements ree always identify 1 distinct tectonic events 2 environment of crystallization and 3 provenance of detrital grains increasing th contents in monazite do not always reflect 1 increasing grade in metamorphic grains 2 changes in silicate melt composition in igneous grains 3 make the mineral more susceptible to alteration nor 4 control the mineral s uptake of ree metamorphic monazites from himalayan garnet bearing rocks with coexisting allanite show no relationship between th content and ree instead chondrite normalized ree patterns of the allanite mirror those of the monazite indicating the variations are related to the reactant that formed the mineral generalizations about pb behavior in monazite remain problematic incorporation of pb into monazite has thus far been precluded by experimental studies yet common pb has been measured in many studies of natural monazite a clear understanding about controls of monazite composition and the role of the chemical and or pressure temperature p t environment of the rocks in which it forms is required to correctly interpret the meaning of the mineral s age s

the age and thermal history of cerro rico de potosi bolivia cerro rico de potosi bolivia is the world s largest silver deposit and has been mined since the sixteenth century for silver and for tin and zinc during the twentieth century together with by product copper and lead the deposit consists primarily of veins that cut an altered igneous body that we interpret to be a dacitic volcanic dome and its underlying tuff ring and explosion breccia the deposit is compositionally and thermally zoned having a core of cassiterite wolframite bismuthinite and arsenopyrite surrounded by a peripheral lower temperature mineral assemblage consisting principally of sphalerite galena lead sulfosalt and silver minerals the low temperature assemblage also was superimposed on the high temperature assemblage in response to cooling of the main hydrothermal system both the dacite dome and the ore fluids were derived from a larger magmatic hydrothermal source at depth the dome was repeatedly fractured by recurrent movement on the fault system that guided its initial emplacement the dome was extruded at 13 8 0 2 ma 2 based on u th pb dating of zircon mineralization and alteration occurred within about 0 3 my of dome emplacement as indicated by a 40ar 39ar date of 13 76 0 10ma 1 for sericite from the pervasive quartz sericite pyrite alteration associated with the main stage high temperature mineralization the last thermal event able to reset zircon fission tracks occurred no later than 12 5 1 1 ma 1 as indicated by fission tract dating minor sericite and magmatic steam alunite veins were episodically formed around 11 ma and between 8 3 and 5 7 ma the younger episodes occurring at the time of extensional fracturing at cerro rico and wide spread volcanism in the adjacent los frailes volcanic field none of these younger events appear to be significant thermal mineralizing events the exceptionally flat thermal release pattern of 39ar from sericite and the results of the fission tract dating of zircon show that none of the younger events was hot enough and lasted long enough to cause significant loss of ar or annealing of zircon fission tracks u th pb dating of zircon cores indicates a precambrian progenitor for some zircons and ree analyses of dated samples of hydrothermally altered dacite show the presence of a prominent positive eu anomaly which constrains interpretations of the origin and evolution of the magmatic hydrothermal system

zircon morphology geochronology and trace element geochemistry of the granites from the huangshaping polymetallic deposit south china implications for the magmatic evolution and mineralization processes abstract the huangshaping polymetallic deposit is a large scale deposit located in the central nanling region south china different types of mineralization have been classified in the area which are attributed to three types of granitoids from the composite granitic pluton quartz porphyry granophyre and granite porphyry in order to study the magmatic genesis and evolutionary process as well as constrain the crystallization and mineralization events 100 zircon separates from different intrusive stages of the pluton have been analyzed for trace element contents and u pb isotopic concentrations the results show that zircons from the huangshaping granitoids are enriched in th u hf ti ree and other trace elements indicating hydrothermal fluid alteration and transformation additionally there is a large variation between different types of granitoids in terms of trace element concentrations compared to the zircons from the quartz porphyry and the granophyre zircons from the granite porphyry are more enriched in th u hf ti and p but strongly depleted in eu this suggests that the magma that formed the granite porphyry possessed higher temperatures possibly experienced stronger crystal fractionation and originated from a more evolved complex magmatic source region with higher degree of crustal maturity combined with characteristics of crystal morphology and internal texture hydrothermal zircons were distinguished from magmatic zircons in each granitoid to reveal mineralization processes the u pb geochronology results show that there are two major stages of mineralization 190 ma weak cu pb zn mineralization related to the quartz porphyry and the granophyre and 155 ma strong w sn mo pb zn mineralization associated with the granite porphyry compositions of these hydrothermal zircons suggest that the earlier stage mineralization could be close to single relatively cold reduced and quickly ascended fluids whereas the later stage might be related to hot oxidized strongly fractionated and highly evolved mixed fluids this study also indicates that hydrothermal zircons from typical composite granitic plutons could be a good tool to reveal the multi stage magmatic and mineralization process in middle to late jurassic south china

upb pbpb and smnd dating of authigenic monazite implications for the diagenetic evolution of the welsh basin abstract authigenic monazite nodules from silurian turbiditic rocks in the central welsh basin are zoned with respect to nd isotope composition the cores are relatively radiogenic and the rim to core trend projects toward the composition of associated very early authigenic apatite concretions these authigenic phases therefore equilibrated with changing fluid composition as they formed the apatites and the monazite nodule cores may have included significant nd from organic matter or seawater whereas the rees in the outer parts of the monazite nodules were derived from clastic detritus the apparent sm nd age obtained from these phosphates is a mixing line which gives an ordovician age for these silurian rocks the u pb isotope system does not show similar trends and shows promise as an alternative method for dating such phosphates a date of 417 11 ma 2 mswd 107 agrees well with recent estimates of the time of the diagenetic smectite illite transition in the rocks of this study a pb pb isochron gave an age of 422 24 ma 2 mswd 0 9 this shows that the pb is in isotopic equilibrium and is undisturbed and that the elevated mswd of the u pb regression is caused by slight subsequent mobility in the u pb system the event dated by the monazite is probably compactional dewatering during accelerated mid silurian sediment loading in the central welsh basin

geological geochemical and geochronological characteristics of weilasituo sn polymetal deposit inner mongolia china abstract the recently discovered weilasituo sn polymetal deposit is located in the southern part of the great xing an range of inner mongolia ne china which is belonged to the eastern part of the central asian orogenic belt caob sn polymetal mineralization is closely related to the emplacement of the early cretaceous fine to medium grained quartz porphyry three types of mineralization have been recognized at weilasituo with the disseminated and stockwork sn polymetal mineralization mainly hosted by the quartz porphyry the vein type sn polymetal mineralization hosted by ne trending and we trending fractures and faults in the upper and outer part of the porphyry and breccia mineralization occurred within a steep cryptoexplosive breccia pipe the ore related alteration typically consists of na ca sr alteration and greisen in order to understand the petrogenetic link between the sn polymetal mineralization and the host quartz porphyry this paper presents new whole rock geochemistry for the quartz porphyry epma analysis of ore and gangue minerals and in situ u pb dating of cassiterite the laser abrasion multiple collector inductively coupled plasma mass spectrometer la mcicp ms cassiterite u pb dating yields two well defined isochron ages of 138 6 ma for disseminated ore and 135 6 ma for the vein type ore which could be regarded as the ore forming age the cassiterite u pb ages ca 138 135 ma determined in this study together with previous data reveals the close temporal and genetic relationship between the mineralization event and the emplacement of the quartz porphyry the quartz porphyry is characterized by high sio2 na2o and a cnk values 1 09 1 21 ree tetrad effect combined with extremely high rb sr k ba ratios and low k rb zr hf la nb la ta and eu eu ratios indicate that the quartz porphyry is a highly fractionated peraluminous i type granite that is hydrothermally altered low end t values of 4 27 0 28 and the two stage depleted mantle nd model ages t2dm ca 1279 908 ma for the quartz porphyry are similar to granites in precambrian microcontinents of the eastern part of the central asian orogen caob this suggests that the quartz porphyry was derived from the remelting of juvenile crust and precambrian rocks in an extensional setting therefore the highly fractional crystallization and magmatic hydrothermal interactions of the quartz porphyry have contributed to the formation of the weilasituo sn polymetal deposit

resolving poly metamorphic paleoarchean ages by chemical dating of monazites using multi spectrometer u th and pb analyses and sub counting methodology abstract chemical u th total pb dating method is a low cost and reliable technique to estimate the age of monazites of detrital and diagenetic origin or those found in low to high t metamorphic or magmatic rocks using electron microprobe emp analyses the method has been commonly applied for age estimation in phanerozoic and proterozoic rocks and less commonly in neoarchean rocks monazite dates from the paleoarchean era are rare and the associated error of spot age 2 error absolute age 100 is high i e between 2 and 26 the errors associated with chemical dating of monazite are significantly larger compared to isotope methods which impede precise age estimation and age resolution in polygenetic monazites of neoarchean and older rocks in this study simultaneous element analyses in multiple spectrometers and the sub counting method of analyses are employed to obtain precise estimates of u th and pb concentrations in monazite using vanadinite pb 5 vo 4 3 cl as the pb standard instead of pbs the method yields an age of 3118 28 ma with mount narryer mesoarchean monazite thermal ionization mass spectrometry tims age 3132 1 ma and 516 12 ma with moacyr monazite tims age 509 1 ma emp monazite age 497 10 ma as the reference samples the modifications led to 40 reduction in spot age errors in the mount narryer sample relative to those obtained by conventional monazite dating method the reduced errors in spot ages helped in resolving statistically un mixed age populations 3152 16 ma 3322 15 ma and 3420 140 ma in polygenetic monazites within muscovite quartz schists from the singhbhum craton eastern india the significance of these dates is briefly discussed

upper pleistocene loess palaeosol and vegetational successions in the middle dnieper area ukraine abstract the loess palaeolsol successions of the middle dnieper area provide high resolution records of the last interglacial glacial cycle in the paper the palaeoenvironmental information is based on the results of pedostratigraphic and pollen studies the last interglacial is recorded by pollen succession of the mikulino eemian type in the kaydaky pedocomplex overlying the deposits of the dnieper glaciation the soils of the pryluky pedocomplex are correlated with the early glacial interstadials and the tyasmyn loess and the silt beds of the pryluky unit are compared with the stadials of the early glacial two main loesses of the pleniglacial are separated by the middle pleniglacial vytachiv pedocomplex it includes three interstadials boreal soils and two stadials silt beds formed in subperiglacial environments the bug loess corresponds to the first half of the late pleniglacial it documents frequent oscillations in humidity at the beginning of the interval and strong stable loess input during the second half of the bug time the dofinivka pedocomplex of subarctic soils separates the bug and prychernomorsk loesses the last one corresponds to the end of the late pleniglacial the last strong loess input and to the late glacial stadials and interstadials