multiple dating approaches applied to the recent sediments in the yangtze river changjiang subaqueous delta the accumulation rate of recent deposits in a delta environment is critical to the study of delta dynamics and their sustainable management the most commonly used dating approach for recent 100

past present and future of thermochronology in one form or another geochronologists have been practicing thermochronology 1 the use of radioisotopic dating to constrain thermal histories of rocks and minerals for over 40 years building from lessons learned over these four decades thermochronology continues to evolve due to technical developments increasingly sophisticated theoretical models and an expanding range of applications in geologic and planetary science most recently interest in earth surface processes and interactions between tectonics erosion and climate has drawn attention to techniques that can address the timing and rates of processes operating at temperatures below about 300 c the purpose of this rimg volume is to assess the current state of thermochronology as of circa 2005 which is coincidentally the 100th anniversary of the first radioisotopic date rutherford 1905 1906 excellent review papers and books on specific topics within this field have been published but no single volume has yet provided a comprehensive review of current practices basic theory and illustrative examples the motivation for this volume stems from these considerations knowing that in a fast developing field a book like this can quickly become dated we tried to include sufficient review of fundamentals and the literature to offer students and new users a useful introduction to thermochronology that may have some staying power in this chapter we first review the salient points of thermochronology s history before assessing our current capabilities and challenges and then taking the risk of suggesting where the field is headed we do not provide a comprehensive history of the method that does full justice to the work of the large and growing cohort of thermochronologists in this short space we instead opted to give our perspectives on where the intellectual and technological roots of the discipline lie which run deeper and go back farther than is sometimes appreciated

unraveling paraglacial activity on sierra de gredos central spain a study based on geomorphic markers stratigraphy and osl abstract we study the paraglacial activity in gredos gorge a glaciated valley of sierra de gredos central spain using geomorphic markers stratigraphy and an approach based on osl we use luminescence signals from debris flow and fluvial deposits as well as osl dating of three deposits to detect the main paraglacial processes in gredos gorge we identify two major phases of paraglacial activity during and after the retreat of last glacial maximum lgm glaciers the first phase consisted of high discharge debris flows sourced up valley triggered during the deglaciation the second phase started 11 ka and is characterized by two processes 1 the triggering of low discharge debris flows sourced on the flanks of moraines and 2 the reworking of paraglacial deposits by rivers our results of osl signals stratigraphy markers and sediment volume indicate that during and after the deglaciation of gredos gorge paraglacial sediment was depleted as theory predicts however glacigenic sediments have not been transferred to sediment sinks as long as 70 of glacial deposits are still stored in the valley the transition of the environmental conditions prevailing during the lgm to current mediterranean climate seems to play an important role in delaying the exhaustion model of glacially conditioned sediment release we propose that the poor coverage of vegetation driven by the mediterranean climate prevents the stabilization of glacigenic sediment that is only mobilized during high discharge events responding to extreme rainfalls

lenticular shale fabrics resulting from intermittent erosion of water rich muds interpreting the rock record in the light of recent flume experiments lenticular lamination is a fabric that is known from shales of all ages but its origin and paleoenvironmental significance is poorly understood we have successfully reproduced this fabric in flume experiments beds of water rich mud were eroded in a flume and yielded sub millimeter to centimeter size fragments that can be transported in bedload for distances of ten kilometers or more upon redeposition and compaction these deposits have the same textural qualities as lenticular laminated shales from the rock record although accumulation of fecal pellets or abundant burrow tubes in a shale may produce comparable fabrics upon compaction these can be distinguished from erosion produced lenticular lamination via petrographic criteria lenticular lamination in shales that is due to deposition of water rich mud fragments most likely records intermittent erosion and transport of surficial muds by currents

using three different approaches of osl for the study of young fluvial sediments at the coastal plain of the usumacinta grijalva river basin southern mexico we use three different approaches of optically stimulated luminescence osl to study young fluvial sediments located at the main channels of one of the largest fluvial systems of north america the usumacinta grijalva we use the pulsed photo stimulated luminescence ppsl system also known as portable osl reader full osl dating and profiling osl dating in samples extracted from vertical sediment profiles n 9 of riverbanks to detect changes in depositional rates of sediments and to obtain the age of the deposits the results of the ppsl system show that the luminescence signals of vertical sediment profiles highly scattered from the top to the bottom contrast with the luminescence pattern observed on well reset sequences of fluvial deposits where luminescence increase from the top to the bottom of the profile the profiling and full osl ages yielded large uncertainty values on their ages based on the inconsistencies observed in both ages and luminescence patterns of profiles we suggest that these fluvial deposits were not fully reset during their transport as an explanation we propose that in the usumacinta and grijalva rivers the cyclonic storms during the wet season promote the entrainment of large volumes of sediments due to high erosional episodes around the basin resulting from hyper concentrated and turbid flows we conclude that the ppsl profiling and full osl dating of sediments are useful tools to quantify and to assess the depositional patterns in fluvial settings during the holocene these techniques also can yield information about sites where increases in the sediment load of rivers may produce poorly resetting of grains affecting the results of osl dating copyright 2015 john wiley sons ltd

flume experiments with fine grained suspensions with implications for the origin of mud laminites abstract the formation of mud laminites was studied in flume experiments with fine grained suspensions of varying sediment concentration and type a transition from lamina formation to uniform deposition was observed at a concentration of about 1 9 kg m 3 laminae formed during continuous deposition showed gradual contacts whereas breaks in deposition were marked by sharp contacts gradual contacts between laminae deposited from suspensions of concentration less than about 1 9 kg m 3 were more distinct than those separating laminae deposited from denser suspensions

genesis of the au bi cu as cu mo w and base metal au ag mineralization at the mountain freegold yukon canada constraints from ar ar and re os geochronology and pb and stable isotope compositions the genesis of mineralized systems across the mountain freegold area in the dawson range cu au mo belt of the tintina au province was constrained using pb and stable isotope compositions and ar ar and re os geochronology pb isotope compositions of sulfides span a wide compositional range 206pb 204pb 18 669 19 861 208pb 204pb 38 400 39 238 that overlaps the compositions of the spatially associated igneous rocks thus indicating a magmatic origin for pb and probably the other metals sulfur isotopic compositions of sulfide minerals are broadly similar and their 34s vienna canyon diablo troilite v cdt values range from 1 4 to 3 6 consistent with the magmatic range with the exception of stibnite from a au sb quartz vein which has 34s values between 8 1 and 3 1 the 34s values of sulfates coexisting with sulfide are between 11 2 and 14 2 whereas those from the weathering zone range from 3 7 to 4 3 indicating supergene sulfates derived from oxidation of hypogene sulfides the 13c vienna peedee belemnite vpdb values of carbonate range from 4 9 to 1 1 and are higher than magmatic values the 18o v smow values of magmatic quartz phenocrysts and magmatic least altered rocks vary between 6 2 and 10 1 and between 5 0 and 10 1 respectively whereas altered magmatic rocks and hydrothermal minerals quartz and magnetite are relatively 18o depleted 4 2 to 7 9 and 6 3 to 1 5 respectively hydrogen isotope compositions of both least altered and altered igneous rock samples are d depleted from 133 to 161 vienna standard mean ocean water v smow consistent with differential magma degassing and or post crystallization exchange between the rocks and meteoric ground water zircon from a chlorite altered dike has a u pb crystallization age of 108 7 0 4 ma whereas the same sample yielded a whole rock ar ar plateau age of 76 25 0 53 ma likewise molybdenite re os model ages range from 75 8 to 78 2 ma indicating the mineralizing events are genetically related to late cretaceous volcano plutonic intrusions in the area the molybdenite re os ages difference between the nearby nucleus 75 9 0 3 to 76 2 0 3 ma and revenue 77 9 0 3 to 78 2 0 3 ma mineral occurrences suggests an episodic mineralized system with two pulses of hydrothermal fluids separated by at least 2 ma this in combination with geological features suggest the nucleus deposit represents the apical and younger portion of the revenue nucleus magmatic hydrothermal system and may suggest an evolution from the porphyry to the epithermal environments

interpreting luminescence data from a portable osl reader three case studies in fluvial settings optically stimulated luminescence osl is a technique that has been applied from the mid 1980s mainly for sediment dating the osl technique is based on sample stimulation by light to determine the luminescence signal that is stored in the crystal lattices of sediment grains after deposition burial by later sediment and subsequent exposure to ionizing radiation from radioactive elements in the surrounding sediment in such sediment dating two parameters are required the equivalent dose i e the luminescence signal stored in the grains and the dose rate i e the ionizing energy from and radiation emitted by naturally occurring radioisotopes in the deposit plus the effects of cosmic radiation in this research the osl technique is not used for dating the study goal is to analyse only the luminescence signals the total photon counts in polymineral samples obtained after light stimulation in the blue blsl and infrared irsl wavelengths using a portable osl reader designed and built at the scottish universities environmental research centre suerc three fluvial case studies from cambodia australia and mexico are used to illustrate the geomorphological interpretations possible with the portable osl reader data from sediments resulting from a range of different depositional processes the case studies show that aspects of sediment s transport and depositional processes can be inferred from the portable osl reader data providing valuable insights into geomorphological history copyright 2010 john wiley sons ltd

cenozoic thermal evolution and tectonics of the coast mountains of british columbia 1 fission track dating apparent uplift rates and patterns of uplift the high relief of the coast mountains of british columbia has been produced in part by rapid late neogene uplift the relationship of this uplift to the presently diverse and complex plate tectonic regime off the west coast of british columbia however is not clear cut to study this problem the areal patterns rates and total amounts of cenozoic uplift from 50 to 55 n have been determined by using fission track dating of zircon and apatite separated from rocks collected at high and low altitudes along several traverses through the mountains accepting closure temperatures of 105 c 10 c and 175 c 20 c for apatite and zircon respectively and a likely closure temperature difference between zircon and apatite of 70 15 c paleogeothermal gradients have been measured at kemano c km 35 ma ago and near ocean falls king island c km 20 ma ago subcrustal heat flow is suggested to have significantly increased in the late neogene near king island uplift rates in the axial part of the northern 52 55 n coast mountains were 0 1 0 2 km ma from 25 to 15 ma ago this uplift was temporally and tectonically related to part of the subsidence in the adjacent queen charlotte basin uplift rates increased somewhat in the late miocene to about 0 4 km ma probably due to passage of the anahim hot spot beneath the area late miocene recent erosion in the north 52 55 n has reduced summit altitudes and been more extensive than farther south despite this relicts of miocene river valleys and topography are still locally preserved partly beneath 7 10 ma basalts the area of the present southern 50 to 52 n coast mountains was near sea level and experienced very low uplift rates 0 5 km ma of the southern coast mountains the profile of this uplift was broadly plateaulike and this uplift led to the inversion of the miocene coastal topography middle cenozoic uplift from 52 to 55 n was probably the result of denudation and diminishing uplift after the terminal paleocene eocene orogenic episode which grossly thickened the crust this middle cenozoic erosion resulted in the restoration of a normal crustal thickness late neogene uplift in the coast mountains was the result of thermal expansion in the mantle caused by a mantle hot spot near 53 n and changes in the geometry of the subducted slab farther south

coarse sediment connectivity in river channel systems a conceptual framework and methodology identification of coarse sediment connectivity down river channel systems is important for understanding the linkages between river reaches the influence of sediment sources on channel morphology and the mechanisms and liability to propagation of morphological change a conceptual framework is developed in which several types and degrees of connectivity are proposed it is hypothesised that sediment connectivity varies with sediment sources and with stream competence to transport the coarse fractions a method of identifying the status of reaches is developed based on field mapping of morphology and sedimentology the analysis is exemplified by two channels one an ephemeral channel in se spain the other a perennial channel in nw england questions arise over whether reaches that lack channel stores transfer coarse sediment three scenarios are suggested 1 lack of flux due to lack of competence of the reach 2 flushing through of sediment due to high competence and 3 potential transport of coarse sediment but exhaustion or lack of availability changes in connectivity will take place over different time scales depending on the nature of exchange and time scales of storage short term variations in connectivity can be identified by repeated mapping

contemporaneous formation of adjacent porphyry and epithermal cu au deposits over 300 ka in northern luzon philippines there is commonly a close spatial relation between porphyry cu au and high sulfidation epithermal cu au deposits throughout the world although a genetic association has not been proven nowhere is this spatial association better seen than in northern luzon philippines where the lepanto epithermal cu au deposit overlies the far southeast fse porphyry cu au deposit both world class orebodies fresh rock and hydrothermal mineral separates yield k ar ages indicating that premineralization and postmineralization volcanism occurred at 2 2 1 8 ma and 1 2 0 9 ma respectively and that the hydrothermal system was active from 1 5 to 1 2 ma k ar ages of alunite from lepanto have the same range as those of hydrothermal biotite and illite from the fse deposit indicating that both epithermal and porphyry mineralization formed from an evolving magmatic hydrothermal system that was active for about 300 ka this temporal relation strengthens the argument for a genetic link between these two styles of ore deposit and has implications for exploration where one style of mineralization is found there is potential for the other nearby

magmatic and hydrothermal chronology of the giant rio blanco porphyry copper deposit central chile implications of an integrated u pb and 40ar 39ar database the history of hypabyssal intrusion and hydrothermal activity in the northeastern and central parts of the be hemothian sensu clark 1993 rio blanco los bronces porphyry copper molybdenum deposit is clarified on the basis of integrated u pb and 40ar 39ar geochronology isotope dilution thermal ion mass spectrometry id tims u pb dates for zircon separates and id tims and sensitive high resolution ion microprobe shrimp dates for single zircon grains in pre syn and late mineralization volcanic and intrusive host rocks in the rio blanco don luis and sur sur mining sectors provide a temporal framework for interpretation of incremental heating and spot fusion 40ar 39ar dates for respectively magmatic biotite and hydrothermal biotite muscovite and orthoclase the ore deposit is hosted in part by 16 77 0 25 to 17 20 0 05 2 ma andesitic volcanic strata of the farellones formation but the major host rocks are units of the san francisco batholith including the 11 96 0 40 ma rio blanco granodiorite mine terminology the 8 40 0 23 ma cascada granodiorite and the 8 16 0 45 ma diorite hypabyssal dacitic intrusions late porphyries emplaced into the batholith yield 206pb 238u id tims dates ranging from 6 32 0 09 ma quartz monzonite porphyry through 5 84 0 03 ma feldspar porphyry to 5 23 0 07 ma don luis porphyry the late mineralization rio blanco dacite plug yields a shrimp zircon age of 4 92 0 09 ma the 40ar 39ar plateau ages for phenocrystic biotites in quartz monzonite porphyry feldspar porphyry and don luis porphyry as well as the preore diorite range only from 5 12 0 07 to 4 57 0 06 ma all are significantly younger than the corresponding zircons and exhibit no correlation with intrusive sequence the 40ar 39ar ages for hydrothermal biotite and orthoclase veins within the san francisco batholith units fall in a narrow interval from 5 32 0 27 to 4 59 0 11 ma hydrothermal sericites muscovite one associated with chalcopyrite yielded spot fusion ages of 4 40 0 15 ma rio blanco granodiorite hosted and 4 37 0 06 ma don luis porphyry hosted comparison with the id tims and shrimp zircon ages indicates that most of the 40ar 39ar ages even 95 percent plateaus do not record initial magmatic cooling or hydrothermal alteration mineralization events evidence for quasipervasive reheating to at least 300 c by successive intrusions published re os ages for two molybdenite samples range from 5 4 to 6 3 ma and overlap extensively with the zircon u pb ages for the late porphyries they imply that cu mo mineralization overlapped temporally with the emplacement of at least quartz monzonite porphyry and feldspar porphyry units of the late porphyry suite and was therefore contemporaneous with the rise of dacitic melts to subvolcanic levels hydrothermal activity is inferred to have continued until 4 37 0 06 ma following intrusion of the don luis porphyry and the early stages of emplacement of the rio blanco dacite plug complex hypogene cu mo mineralization therefore probably persisted for 2 m y the geochronologic data do not resolve whether ore formation was continuous or episodic but the observed crosscutting relationships between intensely altered and mineralized country rocks and less altered and mineralized late porphyry bodies support a model in which the ascent of metal rich brines from an unexposed zone of the parental magma chamber was periodically stimulated by magma perturbation and hypabyssal intrusion

the interpretation of inverse isochron diagrams in 40 ar 39 ar geochronology abstract the concepts involved in the construction and interpretation of inverse isochron diagrams used in 40 ar 39 ar geochronology are reviewed the diagrams can be useful as a means of recognising atmospheric argon and excess 40 ar incorporated in the mineral lattice which cannot be recognised from 40 ar 39 ar spectra the age established using an inverse isochron plot unlike that yielded by a spectrum is not affected by trapped argon 40 ar 36 ar ratios that are different from the atmospheric argon ratio e g due to excess 40 ar and may contribute to a better age interpretation however a heterogeneous distribution of excess 40 ar or heterogeneous argon loss can cause false isochrons with axial intercepts indicating an incorrect age and an incorrect trapped argon composition inconsistency between the ages from a spectrum and from the associated inverse isochron plot may indicate the degree of inaccuracy of isochrons however it is possible that both the spectrum and inverse isochron yield the same incorrect age the importance of considering all possible interpretations before assigning an age to a specimen is stressed

optically stimulated luminescence dating of sediments over the past 200 000 years optical dating of sediment using optically stimulated luminescence has become important for studying earth surface processes and this technique continues to develop rapidly a group of closely linked luminescence methods can be used to estimate the time since grains of quartz and feldspar were last exposed to daylight by detecting their subsequent response to environmental ionizing radiation exposure the technique is well suited to the dating of deposits as young as one year to several hundred thousand years recent technical developments have established a dating protocol with improved precision a high degree of reliability and an in built means to detect incomplete signal removal during deposition this approach has been extended to age estimation for single grains opening up a wider range of potential environments and new possibilities for understanding postdepositional grain movement ongoing research offers the possibility of significant age range extension and novel applications including low t

luminescence dating sediment analysis and flood dynamics on the sabie river south africa abstract floods on sediment rich semiarid rivers often lead to significant geomorphic change but luminescence dating of sediments deposited by past flood events has hitherto been unable to meaningfully inform on past flood dynamics this is important because luminescence dating has commonly been applied to flood sediments but the calculated sediment ages are in almost all cases older than the ages of known floods responsible for sediment deposition correctly interpreting these older ages in the context of flood dynamics is therefore a key problem this study addresses this problem by discussing relationships between luminescence dating sediments and reach scale geomorphology along the semiarid sabie river northeastern south africa twelve luminescence ages were obtained from near surface sediments

thermochronologic constrains on the processes of formation and exhumation of the xinli orogenic gold deposit jiaodong peninsula eastern china abstract the xinli orogenic gold deposit with gold resources of 40 t located in the northwestern part of the giant jiaodong gold province eastern china is controlled by the sanshandao fault and is one of a few deposits hosted by the early cretaceous 129 128 ma guojialing granitoid soon after intrusion the granitoid underwent ductile shearing at 400 500 c marked by recrystallized quartz ribbons and bending of plagioclase lamellae with rapid cooling from zircon crystallization temperature of 750 800 c at 129 128 ma u pb to closure temperature of 300 50 c for biotite 40ar 39ar method at 124 1 ma the ductile deformation lasted 4 million years mineralization was associated with subsequent brittle reactivation of normal movement on the fault indicated by a se plunging downdip lineation on the fault a hydrothermal sericite 40ar 39ar age of 121 ma inferred to date the alteration associated with gold mineralization has been previously obtained for the adjoining cangshang gold deposit also controlled by the sanshandao fault at the xinli deposit the 121 5 1 3 ma and 120 5 1 2 ma 40ar 39ar plateau ages of weakly fractured igneous k feldspar record closely the time of normal faulting and cooling within the range of mineralization temperatures 350 250 c two zircon fission track zft ages of 91 4 ma and 90 3 ma constrain the time of cooling through 240 50 c unimodal distribution of apatite fission track aft lengths with a slightly negative skew and mean fission track lengths of 12 3 0 2 m indicate relative slow continuous cooling through 125 60 c at 60 6 ma the slight acceleration of cooling around 90 ma constrained by the 40ar 39ar zft and aft data and thermal modelling may have resulted from the late normal reactivation of the sanshandao fault in summary extension and normal faulting not only created the channelways for the mineralizing fluids but also gave rise to the subdued topography and post mineralization exhumation that preserved the deposit

the recent history of erosion and sedimentation on the southern tablelands of southeastern australia sediment flux dominated by channel incision abstract as in other regions colonised from europe within the last few centuries australia s vegetation and soils have been dramatically changed by clearing cropping and grazing in southeastern australia particularly on the southern tablelands the impacts of european settlement are clearly manifested by channel incision by using stratigraphic and documentary evidence in conjunction with aerial photographs sediment budgets for the post settlement period have been constructed to define the fluxes and stores of sediment for each of the major geomorphic components of the 136 km2 catchment of jerrabomberra creek near canberra using these budgets and some plausible assumptions it has been possible to approximate the history of both the sediment delivery ratio and sediment yield for this catchment while the quantities estimated in this analysis are approximations the trends through time are credible sediment yield increased rapidly to a peak after european settlement and has returned to a level between the peak and the pre european value the delivery ratio has followed a similar trend the most general conclusion to emerge is that in this landscape both the total sediment flux and the sediment yield of the catchment have been dominated by channel erosion this result is contrary to the findings in many parts of the world where sheet and rill erosion dominates the fluxes the soil conservation implication of these results is clear to control off site effects of erosion the focus must be on the channels

post 10 ma uplift and exhumation of the northern coast mountains british columbia apatite u th he ages reveal three distinct periods in the exhumation history of the northern coast mountains 54 n a well developed helium partial retention zone indicates little or no exhumation between ca 30 and 10 ma beginning at 10 ma and extending to at least 4 ma the range underwent steady but slow exhumation of 0 22 mm yr after which the exhumation rate increased by at least 70 an 85 km long he age traverse across the orogen at sea level shows that vertical offsets on post 10 ma faults are minor furthermore the sea level he ages 14 2 8 ma inversely correlate with local mean elevation along the traverse these data suggest that the coast mountains first appeared as a significant topographic feature only within the past few million years this history is not consistent with suggestions that uplift of the range resulted from formation of the queen charlotte basin in early middle miocene time we speculate that intense erosion by alpine and continental glaciation after 2 5 ma triggered isostatic uplift and creation of the modern topography of the coast mountains

luminescence dating of quaternary sediments recent advances duller geoffrey 2004 luminescence dating of quaternary sediments recent advances journal of quaternary science 19 2 pp 183 192 rae2008

the role of exhumation in the temporal distribution of ore deposits we show here that the temporal age frequency distribution of ore deposits is controlled largely by exhumation the combination of burial uplift and erosion that exposes subsurface rocks and ore deposits exhumation rates calculated from modal ages and emplacement depths for epithermal porphyry copper and orogenic gold deposits of phanerozoic age are 167 158 and 63 m m y respectively these rates agree with rates estimated for continent scale terranes by numerous independent methods thus the scarcity of precambrian epithermal and porphyry copper deposits is probably due to their removal by exhumation archean and pale oproterozoic orogenic gold deposits are more abundant than indicated by the exhumation record of their phanerozoic counterparts suggesting that the precambrian deposits formed in greater numbers recognition of the pivotal role of exhumation requires that the temporal distribution of ore deposits be corrected for this effect before it can be used as an indicator of large scale changes in earth history

pb u and th diffusion in natural zircon zircon zrsio4 is one of the most widely used minerals for determining the age origin and thermal history of rocks by u th pb geochronology but the parameters describing the solid state volume diffusion rates of these elements in natural zircon which are themselves important for establishing the limits on the applicability of zircon for geochronological studies have remained poorly quantified1 this is because of the measurement difficulties associated with the low p p m concentrations and low diffusion rates of these elements in natural zircon and the chemical and physical heterogeneity present in most crystals here we present direct measurements of the uranium thorium and lead loss from a thermally treated gem quality natural zircon and show that lead diffuses much faster than uranium or thorium we find that the u th pb isotopic system in natural zircon will typically have a closure temperature greater than 900 c which explains why zircon is apparently such a robust geochrometer and is capable of remaining isotopically closed through extended periods of high grade metamorphism and partial melting of the host rock

application of apatite u th he thermochronometry to the determination of the sense and amount of vertical fault displacement at the chuquicamata porphyry copper deposit chile chuquicamata is the world s largest porphyry copper deposit notwithstanding the fact that a portion of the orebody has been faulted off by postmineralization movement along the west fault in order to locate the missing portion of the orebody in the vertical dimension a study was designed to estimate the sense and amount of vertical displacement along this major structure by measuring the u th he and fission track ages of vertically distributed apatite samples from each of the crustal blocks fortuna and chuquicamata intrusive complexes bordering the fault apatite u th he ages range from 32 to 16 ma whereas apatite fission track ages range from 33 to 28 ma reflecting the lower closure temperature of the u th he thermochronology method approximately 75 degrees vs approximately 125 degrees c for cooling rates of approximately 10 degrees c m y the u th he ages decrease systematically with depth in both blocks however the age elevation curve for the western fortuna block is shifted vertically with respect to the eastern chuquicamata block indicating that the postmineralization denudation was significantly greater to the west the minimum vertical displacement along the west fault is estimated to be 600 or 100 m implying that the missing portion of the chuquicamata deposit should be located at a present day elevation of at least 3 600 m the new apatite ages combined with previous thermochronometric data rb sr u pb ar ar reveal rapid cooling rates approximately 100 degrees c m y for the chuquicamata deposit following emplacement at about 35 ma thereby indicating that the cu mineralization took place at a depth of less than 4 km

butzer down under debates on anthropogenic erosion in early colonial australia abstract the arrival of europeans in the new world and the rapid deforestation for agriculture and settlement that shortly followed resulted in large and rapid increases in soil erosion and sediment aggradation in australia as in parts of north america and other new world sites this event dates to the last several centuries of the common era a period for which we have surprisingly little historical or scientific data capable of informing debates on the impact of european colonisation on soils and erosion these research themes and debates were central to the work of karl butzer who undertook field and archival research in australia to test existing ideas of the timing and magnitude of landscape response to colonisation in this paper the work and impact of butzer in australia is reviewed as part of ongoing scholarship on the impact of colonisation on landscapes to which butzer contributed butzer and helgren 2005 geomorphic records of soil erosion and historical accounts of land use and impact from eastern australia show that european settlement land clearing and agriculture resulted in rapid and often severe increases in erosion in the late eighteenth and early nineteenth centuries mirroring the experience of anthropogenic soil loss experienced in other parts of the world it is postulated that the geomorphic response to european settlement in australia is more complex than researchers have previously noted that in some contexts continues to influence catchment processes decades and centuries after colonisation

contribution of mafic melt to porphyry copper mineralization evidence from mount pinatubo philippines and bingham canyon utah usa mount pinatubo in the philippines known for its cataclysmic eruption in 1991 hosts several porphyry copper deposits and active geothermal systems an underlying mafic melt supplied much of the sulphur for the dacitic magma and its injection into the dacitic magma chamber triggered the eruption the eruption caused purging of the sulphur rich fluid from the dacite to the atmosphere and extensive fracturing similar events took place at bingham canyon utah site of the largest copper and gold deposit in north america at 38 ma the bingham canyon mineralization took place beneath an active stratovolcano and pyroclastic flows contemporaneous with the mineralization show evidence for magma mingling ascent of mafic melt supplied sulphur and chalcophile elements to the felsic magma which consolidated to form the bingham stock and its underlying magma chamber injections of the mafic melt caused periodic eruptions of felsic magma to form the stratovolcano and deposition of sulphide minerals in highly fractured rocks in and around the stock

the exhumation history of collision related mineralizing systems in tibet insights from thermal studies of the sharang and yaguila deposits central lhasa abstract the large newly discovered sharang porphyry mo deposit and nearby yaguila skarn pb zn ag mo deposit reside in the central lhasa terrane northern gangdese metallogenic belt tibet multiple mineral chronometers zircon u pb sericite 40 ar 39 ar and zircon and apatite u th he reveal that ore forming porphyritic intrusions experienced rapid cooling 100 c ma during a monotonic magmatic hydrothermal evolution the magmatic hydrothermal ore forming event at sharang lasted 6 0 myr 1 8 myr for cooling from 900 to 350 c and 4 0 myr for cooling from 350 to 200 c whereas cooling was more prolonged during ore formation at yaguila 1 8 myr from 900 to 500 c and a maximum of 16 myr from 900 to 350 c all porphyritic intrusions in the ore district experienced exhumation at a rate of 0 07 0 09 mm yr apatite he ages between 37 and 30 ma combined with previous studies this work implies that uplift of the eastern section of the lhasa terrane expanded from central lhasa 37 30 ma to southern lhasa 15 12 ma at an increasing exhumation rate all available geochronologic data reveal that magmatic hydrothermal exhumation activities in the sharang yaguila ore district occurred within four periods of magmatism with related mineralization significant porphyry type mo mineralization was associated with late cretaceous eocene felsic porphyritic intrusions in the central lhasa terrane resulting from neotethyan oceanic subduction and india asia continental collision

weathering geochronology by u th he dating of goethite nine samples of supergene goethite feooh from brazil and australia were selected to test the suitability of this mineral for u th he dating measured he ages ranged from 61 to 8 ma and were reproducible to better than a few percent despite very large variations in u and th in all samples with internal stratigraphy or independent age constraints the he ages corroborated the expected relationships these data demonstrate that internally consistent he ages can be obtained on goethite but do not prove quantitative 4he retention to assess possible diffusive he loss stepped heating experiments were performed on two goethite samples that were subjected to proton irradiation to produce a homogeneous distribution of spallogenic 3he the 3he release pattern indicates the presence of at least two diffusion domains one with high helium retentivity and the other with very low retentivity at earth surface conditions the low retentivity domain which accounts for 5 of 3he contains no natural 4he and may represent poorly crystalline or intergranular material which has lost all radiogenic 4he by diffusion in nature diffusive loss of 3he from the high retentivity domain is independent of the macroscopic dimensions of the analyzed polycrystalline aggregate so probably represents diffusion from individual micrometer size goethite crystals the 4he 3he evolution during the incremental heating experiments shows that the high retentivity domain has retained 90 95 of its radiogenic helium this degree of retentivity is in excellent agreement with that independently predicted from the helium diffusion coefficients extrapolated to earth surface temperature and held for the appropriate duration considering both the high and low retentivity domains these data indicate that one of the samples retained 90 of its radiogenic 4he over 47 5 ma and the other retained 86 over 12 3 ma thus while diffusive loss corrections to supergene goethite he ages are required these initial results indicate that the corrections are not extremely large and can be rigorously quantified using the proton irradiation 4he 3he method

evidence for early glaciation of southeastern beringia between the klondike plateau and yukon tanana highlands of yukon and alaska respectively current maps explain glaciated alpine locales and periglacial areas in terms of localized pliocene pleisto

how long can a hydrothermal system be sustained by a single intrusive event published numerical calculations show that the convective systems which produce near surface geothermal systems or ore deposits are likely to cool their intrusion heat source in at most a few tens of thousands of years even if the intrusion is large generally hydrothermal circulation near surface geothermal activity and magmatic intrusion should be closely tied in time and space long lived approximately 1 m y hydrothermal activity normally suggests multiple pulses of intrusion with associated pulses of hydrothermal circulation however if the permeability of the intruded environment is just above that which allows convection and the volume of the intrusion is very large calculations presented here show that a single episode of intrusion can sustain hydrothermal circulation and near surface geothermal activity for approximately 800 000 yr for a deep sill heat source these unusually long lived hydrothermal systems can vent through a few very widely separated discharge sites and have the potential to produce isolated massive sulfide deposits of unusually large size

two ages of porphyry intrusion resolved for the super giant chuquicamata copper deposit of northern chile by ela icp ms and shrimp zircon u pb ages measured in situ by excimer laser ablation inductively coupled plasma mass spectrometry ela icp ms and verified by sensitive high resolution ion microprobe shrimp on ore bearing felsic porphyries from the chuquicamata porphyry copper molybdenum deposit northern chile identify two discrete igneous events the volumetrically dominant east porphyry has an age of 34 6 0 2 ma whereas the bench and west porphyries yield ages of 33 3 0 3 ma and 33 5 0 2 ma respectively the age of the east porphyry is indistinguishable from a re os age for early molybdenite mineralization 35 ma and the oldest reported 40 ar 39 ar ages for hydrothermal alteration confirming a genetic link with mineralization previous geological studies and 40 ar 39 ar and re os geochronology identify two main hydrothermal events high temperature potassic alteration with chalcopyrite at 33 4 0 3 ma followed by lower temperature quartz sericite alteration with pyrite at 31 1 0 3 ma the ages of the west and bench porphyries match the ages for potassic alteration younger quartz sericite alteration may reflect an additional fourth intrusion concealed at depth the anomalously large size of chuquicamata appears to be due to a protracted igneous history resulting in the superposition of at least two temporally distinct magmatic hydrothermal systems

using osl to assess hypotheses related to the impacts of land use change with the early nineteenth century arrival of europeans in south eastern australia an exploratory case study from grabben gullen creek new south wales a common explanation for intense soil erosion and gullying in se australia is the introduction by europeans of new land use practices following their arrival in australia in the late 18th century eucalyptus woodlands were cleared to introduce farming and valley bottoms characterized by chains of ponds with organic rich swampy meadow sm soils were subsequently buried by thick deposits of post settlement alluvium psa generated by erosion in the catchment in this study optically stimulated luminescence osl is used to evaluate the source s of the psa in grabben gullen creek ggc australia we use a portable osl reader to measure total photon counts on bulk polymineral and polygrain size samples from nine profiles along the creek we use these luminescence signals as geotracers of sediment source s and transport pathways we obtained higher luminescence signals in the psa than in the sm sediments suggesting different sources and fluvial transport conditions for these two widespread sedimentary units portable osl reader data from soils in the ggc catchment that are potential sources for the sm sediments and psa show that the high luminescence signals recorded in the psa are similar to those from subsoil samples in granite soils suggesting that the psa was derived by gullying of granite subsoils in the sm sediments luminescence signals decrease upwards from the base of the profile as expected in well reset fluvial deposits but with one or more changes in gradient in the profile of photon counts with depth most likely indicating changes in sediment deposition rates to calculate deposition rates in the sm sediments several samples were dated using osl the osl ages produced low scatter in the equivalent doses confirming the well reset nature of the grains composing the sm and indicating a process of sediment transport in dilute flows as is interpreted from the portable osl signals this article is protected by copyright all rights reserved

emplacement ages and exhumation rates for intrusion hosted cu mo sb au mineral systems at freegold mountain yukon canada assessment from u pb ar ar and u th he geochronometers to decipher the thermal history of mineralized systems across the freegold mountain area yukon canada a combined geochronology zircon u pb and hornblende biotite and whole rock ar ar and thermochronology apatite and zircon u th he study was carried out previous u pb data combined with new u pb and ar ar data show that intrusive bodies across the freegold mountain were emplaced during two protracted episodes the first spanning from 109 6 to 98 ma and the second between 79 and 68 ma overprinting of the first intrusive event by a second magmatic hydrothermal event is suggested by a zircon u pb age of 108 7 0 4 ma for a chlorite altered dyke and a whole rock ar ar plateau age of 76 25 0 53 ma zircon u th he data are between 66 and 89 ma whereas apatite u th he data are scattered 38 7 109 9 ma and bracket the two magmatic emplacement events our combined data reveal a complex history of reheating that led to resetting of numerous chronometers in most of the investigated magmatic hyd

brief duration of hydrothermal activity at round mountain nevada determined from ar 40 ar 39 geochronology the round mountain gold silver deposit is one of the world s largest volcanic hosted precious metal deposits reserves plus production total at least 16 million oz 500 000 kg au the deposit occurs in ash flow tuff that is ponded within its source caldera along and overlying the caldera ring fracture host rocks have undergone propylitic potassic and high level silicic and intermediate argillic alteration these are interpreted either as a temporal sequence from early propylitic to late silicic and argillic or as a spatial progression from a potassic core outward to a propylitic halo 40 ar 39 ar ages determined by single crystal fusion of sanidine from host tuff and incremental heating of adularia indicate a most likely duration of hydrothermal activity of approximately 0 1 m y possibly no more than 0 05 m y and a maximum of 0 5 m y eruption of host ash flow tuff and caldera collapse occurred at 26 5 ma a late or postalteration tuff that rests upon mineralized rock is 26 0 ma hydrothermal circulation is unlikely to have been established immediately after caldera collapse so duration was probably considerably less than 0 5 m y eight adularia samples give ages between 25 94 or 0 09 and 26 09 or 0 05 ma and one is 26 20 or 0 05 ma the mean of all nine is 26 03 or 0 08 ma the maximum and minimum values and their uncertainties allows a duration of as much as 0 4 m y but for the following reasons the longevity is probably much less the absolute ages of seven samples that can be placed in the possible temporal alteration sequence do not correlate with that sequence this does not disprove the temporal sequence but does indicate that alteration occurred in a time span which is not resolvable even with precise 40 ar 39 ar dating furthermore all samples show flat age spectra which themselves argue against a long continuously active system kinetic studies of two adularia reveal diffusion domains with ar closure temperatures between approximately 230 degrees and approximately 390 degrees c adularia that crystallized and remained at temperatures of 275 degrees c the maximum temperature inferred from fluid inclusion data would yield age spectra with age gradients spanning the lifetime of the system no spectra are consistent with a thermal history that incorporates sustained 0 1 m y temperatures at or above 275 degrees c episodic activity to account for the one older adularia date cannot be precluded but is inconsistent with most data therefore the hydrothermal system probably was active for less than the uncertainty in the ages of individual samples possibly as little as 50 000 years we conclude that hydrothermal activity at round mountain was a brief event at approximately 26 0 ma and was closely linked to caldera structure and magmatism this activity followed initial ash flow eruption by 0 5 m y and may have been driven by a ring fracture intrusion

age and thermal history of the geysers plutonic complex felsite unit geysers geothermal field california a 40ar 39ar and u pb study abstract sixty nine ion microprobe spot analyses of zircons from four granite samples from the plutonic complex that underlies the geysers geothermal field yield 207pb 206pb vs 238u 206pb concordia ages ranging from 1 13 0 04 ma to 1 25 0 04 1 ma the weighted mean of the u pb model ages is 1 18 0 03 ma the u pb ages coincide closely with 40ar 39ar age spectrum plateau and terminal ages from coexisting k feldspars and with the eruption ages of overlying volcanic rocks the data indicate that the granite crystallized at 1 18 ma and had cooled below 350 c by 0 9 1 0 ma interpretation of the feldspar 40ar 39ar age data using multi diffusion domain theory indicates that post emplacement rapid cooling was succeeded either by slower cooling from 350 to 300 c between 1 0 and 0 4 ma or transitory reheating to 300 350 c at about 0 4 0 6 ma subsequent rapid cooling to below 260 c between 0 4 and 0 2 ma is in agreement with previous proposals that vapor dominated conditions were initiated within the hydrothermal system at this time heat flow calculations constrained with k feldspar thermal histories and the present elevated regional heat flow anomaly demonstrate that appreciable heat input from sources external to the known geysers plutonic complex is required to maintain the geothermal system this requirement is satisfied by either a large underlying convecting magma chamber now solidified emplaced at 1 2 ma or episodic intrusion of smaller bodies from 1 2 to 0 6 ma

quantifying exhumation at the giant pulang porphyry cu au deposit using u pb he dating the triassic pulang porphyry cu au deposit located in the south yidun terrane is the oldest and one of the largest porphyry deposits in the southeastern tibetan plateau the mineralization occurs mostly in the potassic alteration zone of the pulang intrusive complex u pb he triple dating namely apatite u th he zircon u pb and zircon u th he dating together with inverse thermal modeling reveals that the pulang complex was emplaced at a paleodepth of 5 0 to 6 5 km at 215 2 ma the deep level emplacement of the complex coupled with the episodic replenishment of the magma chamber gave rise to the establishment of a prolonged magmatic hydrothermal system at pulang although a range of single grain zircon and apatite u th he ages were obtained on each sample the weighted mean zircon and apatite u th he ages vary systematically with elevation defining a multistage cooling denudation history at pulang specifically three phases of cooling were recognized from inverse thermal modeling including rapid cooling 80 120 c m y in the late triassic moderate cooling 3 5 c m y from the late triassic to early cretaceous and a protracted slow cooling period 50 m y of extremely slow cooling and erosion at pulang could be related to the formation and preservation of a peneplain on the southeastern tibetan plateau since the late cretaceous a relict peneplain thus signifies a favorable tectonic environment for the preservation of ancient porphyry systems worldwide

low temperature thermochronology of the carlin type gold deposits in southwestern guizhou china implications for mineralization age and geological thermal events abstract the dian qian gui area in southwestern china is the second largest concentration of the carlin type gold deposits in the world and the southwestern guizhou is the most important gold producing district of the dian qian gui area dating of the carlin type gold deposits is always a challenge due to the lack of ore stage minerals which are suitable for conventional radiometric dating low temperature thermochronometers including fission track and u th he are temperature sensitive radiometric dating techniques and have been successfully applied to elucidate many aspects of ore deposits including the timing and duration of mineralization processes in this study zircon fission track zircon u th he and apatite fission track dating techniques were applied to the carlin type gold deposits in southwestern guizhou samples for zircon and apatite analyses were collected from mineralized or altered sedimentary rocks in shuiyindong taipingdong bojitian yata and getang gold deposits four groups of thermochronological ages were obtained i e 192 216 ma 132 160 ma 88 ma and 19 40 ma which are considered to be the records of four geological thermal events of them most zircon fission track ages and all zircon u th he ages concentrate in 132 160 ma thermochronological constraints combined with field relationships suggest that the mineralization of the carlin type gold deposits in southwestern guizhou most likely occurred in this period partial zircon fission track ages are in 192 216 ma they may record the cooling timing of a pre ore thermal event caused by the indosinian orogeny which is supported by the paleogeotemperature restoration a few zircon grains with high u content yield fission track age of 88 ma which may record a post ore thermal event associated with the intrusion of local mafic dykes all apatite fission track ages range in 19 40 ma which may record a lower temperature but extensive hydrothermal superimposition in the cenozoic additionally a corresponding relationship between zircon fission track ages and stratigraphic sequences was identified in the huijiabao anticline which is considered to reflect the decrease of temperature and duration of ore forming hydrothermal activity from lower to upper stratigraphic sequences

late quaternary river evolution of floodplain pockets along mulloon creek new south wales australia valley confinement along upper middle reaches of mulloon creek in the upper shoalhaven catchment of southern new south wales australia restricts floodplain development to a series of distinct pockets these pockets comprise a downstream thinning wedge of vertically accreted fine grained deposits atop basal gravels some time before 12500 years ago a bedload dominated river was transformed into a suspended load system in the mid late holocene swamps developed in the middle lower part of each floodplain pocket within a few decades of european settlement of this region circa ad 1820 discontinuous watercourses in some floodplain pockets had incised to form a low sinuosity gravel bed channel wedge shaped units of post incisional alluvium that thicken downstream overlie the swamp and floodplain deposits in the downstream part of these pockets in the downstream most pocket incision commenced prior to colonization while upstream swamps retain a continuous swamp across the valley floor the late quaternary evolution of this variant of discontinuous watercourse is summarized in a schematic model

sedimentological processes in lahars insights from optically stimulated luminescence analysis abstract a lahar is a sediment laden flow capable of major destructive impacts on infrastructure and human life how lahars transport sediment is thus a key issue for understanding lahar sedimentology and behavior especially in terms of the lahar s hydraulic and rheological properties which can be substantially altered as the lahar gains or loses material during its travel in this research we analyze lahar entrainment processes by evaluating luminescence signals total photon counts from lahar sediments using blue luminescence signals blsl a portable osl reader that analyzes several grams of polymineral and polygrain size samples was applied we use data from three lahars in the tenenepanco and huiloac gorges on popocatepetl volcano mexico to elucidate the ways in which lahars may gain lose and transport sediment during flow sediment samples for luminescence analysis were taken through the full thickness of the lahar deposits at eight different sites for two lahars 1997 and 2001 and at one site for a lahar that occurred 500 yrs ago mean luminescence values obtained for the 1997 lahar help to evaluate the relationship between the lahar entrainment processes and the drainage at the different sites for the 2001 lahar this relationship was also established taking into account the channel slope the main conclusion is that luminescence signals total photon counts can be used to detect entrained material in the flow because the bulked materials modify the final osl signals the application of this type of luminescence analysis thus has the potential to provide a better understanding of sediment entrainment in these sediment laden flows

pb diffusion in zircon abstract chemical diffusion of ti under anhydrous conditions at 1 atm and under fluid present elevated pressure 1 1 1 2 gpa conditions has been measured in natural zircon the source of diffusant for 1 atm experiments was a zro2 tio2 zircon mixture with experiments run in crimped pt capsules diffusion experiments done in the presence of h2o co2 fluid were run in a piston cylinder apparatus using a source of ground tio2 zrsio4 and sio2 with oxalic acid added to produce h2o co2 vapor and partially melt the solid source material yielding an assemblage of rutile zircon melt vapor nuclear reaction analysis nra with the resonant nuclear reaction 48ti p 49v was used to measure diffusion profiles for both sets of experiments the following arrhenius parameters were obtained for ti diffusion normal to cover the temperature range 1350 1550 c at 1 atm d ti 3 33 10 2 exp 754 56 kj mol 1 r t m 2 s 1 ti diffusivities were found to be similar for experiments run under fluid present conditions a fit to all of the data yields the arrhenius relation d 1 34 102 exp 741 46 kj mol 1 rt m2 s 1 these data suggest that zircon should be extremely retentive of ti chemical signatures indicating that the recently developed ti in zircon crystallization geothermometer watson e b harrison t m 2005 zircon thermometer reveals minimum melting conditions on earliest earth science 308 841 844 will be quite robust in preserving temperatures of zircon crystallization titanium diffuses somewhat faster in zircon than larger tetravalent cations u th and hf but considerably more slowly than pb the ree and oxygen hence ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost

the dublin gulch intrusion hosted gold deposit tombstone plutonic suite yukon territory canada the dublin gulch intrusion is a member of the tombstone plutonic suite a linear belt of middle cretaceous intrusions that extend across the yukon territory like many of the intrusions in this suite the dublin gulch intrusion is associated with several different zones of gold and tungsten mineralization within and immediately adjacent to the intrusion the eagle zone 50 3 mt 0 93 g t gold located in the southwestern part of the dublin gulch intrusion hosts the most significant concentration of gold in the area the gold occurs in a broadly east west striking steeply south dipping series of sheeted veins the veins consist of early quartz scheelite pyrrhotite pyrite arsenopyrite and are associated with k feldspar albite alteration envelopes these grade out to and are overprinted by sericite carbonate chlorite alteration the same assemblage also occurs in veinlets that refracture sheeted quartz veins and contain the majority of the gold the gold occurs with molybdenite lead bismuth antimony sulfosalts galena and bismuthinite gold correlates strongly with bismuth r 2 0 9 a relationship common to several intrusion related gold deposits but has a poor correlation with all other elements tungsten and molybdenum have a weak inter element correlation r 2 0 55 and paragenetically pre date the majority of gold precipitation lead zinc copper silver antimony and arsenic have moderate to strong inter element correlations 0 58 to 0 93 the change from tungsten bearing mineralization through to gold bismuth rich ores with elevated syn to post ore lead zinc copper silver antimony and arsenic can be grossly correlated with a change in hydrothermal fluid composition early scheelite bearing quartz contains primary co2 rich fluid inclusions which are post dated by secondary inclusions with higher salinities up to 15 wt nacl equiv and less co2 these latter inclusions are interpreted to coincide with the later gold bismuth and base metal mineralization the favored genetic model is one in which early co2 rich fluids exsolved from a magma with an initially high co2 content but progressively became more saline and h2o rich as the system evolved

mineral deposits of canada a synthesis of major deposit types district metallogeny the evolution of geological provinces and exploration methods wayne d goodfellow editor 1 068 pp geological association of canada mineral deposits division special publication no 5 2007 hardcover isbn 13 978 1 897095 24 9 price members cdn 60 00 non members cdn 80 00 following in the footsteps of other landmark reviews of major ore producing countries such as australia hughes 1990 solomon and groves 1994 and south africa anhaeusser and maske 1986 this substantial 1 000 pages monograph is a great achievement that should be in every geologic research library in the world in many ways it sets a new standard most notably in that all figures and photographs are in color and that the entire volume is available in electronic form both as an included dvd and mostly on the gac website it is common in such compendia to have a spectacular cover photo or frontispiece to catch the reader s attention and this book does not disappoint the frontispiece photo is of a 61 8 kg sample from the dome mine timmins ontario and is stated to contain 20 wt percent gold at today s prices the gold alone would be worth 1 5 million dollars

zircon u th he thermochronometric constraints on the mineralization of the giant xikuangshan sb deposit in central hunan south china the xikuangshan sb deposit in central hunan south china is the largest sb deposit in the world which has supplied more than 50 of the world s sb and with total sb metal reserves of about 2 5 mt however the age of this deposit is still not well constrained due to a lack of suitable minerals for reliable radiometric dating which hampered the generation of a generally accepted genetic model of mineralization since the fluid inclusion data suggest that the temperature of ore forming fluids in the xikuangshan deposit is up to 360 c zircon u th he thermochronometry with the closure temperature of 160 200 c was chosen here to elucidate the age of sb mineralization detrital zircons in the altered host rocks from the xikuangshan deposit yielded two u th he age populations of 156 117 and 97 86 ma the older age population 156 117 ma which is well in accordance with previous sm nd dating on hydrothermal calcite 156 124 ma probably represents the timing of main stage sb mineralization in the xikuangshan sb deposit while the younger zircon u th he ages may result from partial loss of he in zircon caused by the distal effect of deep seated intrusions beneath the deposit this study demonstrates that the u th he dating of zircon in altered host rocks can be viable for constraining the timing of low temperature mineralization

ten conceptual models of large scale legacy sedimentation a review abstract considerable interest has been directed toward the recognition and documentation of legacy sediment i e anthropogenic sediment in fluvial systems little has been written however to identify implicit or explicit theories about how these deposits form and evolve over decennial to centennial time scales this review attempts to redress this void by examining conceptual models of the physical behavior and characteristics of catchment scale anthropic fluvial sedimentation events these concepts which are not unique to anthropogenic sediment include cascades sediment delivery ratios waves aggradation degradation episodes residence times budgets connectivity stream power nonlinear dynamical systems and geohistorical geoarchaeological and chronostratigraphic principles a broad definition of legacy sediment as episodically produced anthropogenic sediment is adopted that includes early episodes of large scale human induced sedimentation throughout the world the models apply to a variety of environments so the examples from north america following the introduction of european settlement can be related to other post settlement sedimentation episodes elsewhere during aggradation episodes rates of erosion and sedimentation often increased an order of magnitude in response to land clearance for agriculture timbering or mining these sediments may remain as a lasting geomorphic legacy that provides evidence of anthropogenic change and governs modern rates of sediment production and nonpoint source pollution

the intertropical convergence zone in the south atlantic and the equatorial cold tongue recent observations from the quikscat and tropical rainfall measuring mission satellites as well as a longer record of special sensor microwave imager winds are used to investigate the existence and dynamics of a southern hemisphere partner to the intertropical convergence zone in the tropical atlantic ocean the southern intertropical convergence zone extends eastward from the coast of brazil in the latitude band 10 8 38s and is associated with seasonal precipitation exceeding 6 cm month 21 during peak months over a part of the ocean characterized by high surface salinity it appears in austral winter when cool equatorial upwelling causes an anomalous northeastward pressure gradient to develop in the planetary boundary layer close to the equator the result is a zonal band of surface wind convergence that exceeds 10 26 s 21 with rainfall stronger than 2 mm day21 and an associated decrease in ocean surface salinity of 0 2 parts per thousand

the chronology of early mesozoic arc magmatism in the yerington district of western nevada and its regional implications the yerington district west central nevada is underlain by arc volcanic sedimentary and plutonic rocks ranging in age from middle triassic to middle jurassic twenty three u pb radiometric dates from eight igneous units have been determined for zircon from both plutonic and volcanic rocks in the district which establish two distinct periods of voluminous intermediate to silicic high k calc alkaline magmatism the earlier period is constrained by zircon dates of 232 and 233 ma on a quartz porphyry and a metadiorite respectively which intrude and are possibly comagmatic with andesitic to rhyolitic volcanic rocks the second period of arc magmatism is constrained by 5 concordant zircon dates that define an approximately 4 m y period 169 165 ma in the middle jurassic during which as much as 4 km of volcanic and volcaniclastic strata accumulated and two major batholiths were emplaced middle jurassic magmatism began with eruption of the volcanics of artesia lake they were intruded by the probably comagmatic 250 km 2 yerington batholith which was differentiated emplaced and crystallized within approximately 1 m y 169 4 168 5 ma granite porphyry dikes 168 5 ma are the latest phase of the yerington batholith and are synchronous with porphyry and skarn copper mineralization disconformably overlying the artesia volcanics is a second volcanic suite consisting of as much as 2 km of latitic volcanics of fulstone spring 166 5 ma the volcanics of fulstone spring were subsequently intruded by quartz monzodiorite porphyry dikes 165 ma and the shamrock batholith 165 8 ma the triassic through lower jurassic stratigraphic column was contact metamorphosed and folded adjacent to and at least in part contemporaneously with emplacement of the yerington and shamrock batholiths 169 4 165 8 ma we interpret the early 232 233 ma period of magmatism to represent a minimum age for the establishment of a west facing triassic volcanic arc within west facing triassic volcanic arc within west central nevada following the permian triassic sonoma orogeny the timing of middle jurassic arc magmatism and deformation in the yerington district and surrounding regions is strikingly similar to the timing of magmatic and tectonic events documented in the klamath mountains region of northwestern california we suggest that the similar record of arc magmatism and deformation in these two regions is not fortuitous but reflects a common tectonic evolution within a single west facing arc constructed along the western edge of north america

anatomy of a world class epizonal orogenic gold system a holistic thermochronological analysis of the xincheng gold deposit jiaodong peninsula eastern china abstract xincheng is a world class orogenic gold deposit hosted by the early cretaceous guojialing granitoid in the jiaodong peninsula eastern china a zircon u pb age of 126 1 4 ma together with previous data constrain the emplacement of the guojialing intrusion to 132 123 ma the granitoid underwent subsolidus ductile deformation at 500 c following its intrusion the small difference in age between the youngest zircon u pb age of unaltered granitoid 123 ma and the ca 120 ma 40ar 39ar ages of sericite associated with breccias and gold mineralization within it indicate initial rapid cooling from magmatic temperatures to those prevalent during brittle deformation and associated gold mineralization at 220 300 c evidence of a direct association between granitic magmatism and gold mineralization such as at least localized near magmatic depositional temperatures and metal zoning evident in undoubted intrusion related gold deposits is absent the 40ar 39ar age of 120 ma coincides with the mineralization age of many other orogenic gold deposits along the jiaojia fault sixteen zircon fission track zft ages across the ore and alteration zones range from 112 9 3 4 to 99 1 2 7 ma the long period of cooling to the 100 ma zft closure temperatures recorded here suggests that ambient temperatures for hydrothermal alteration systems lasted to 100 ma possibly because of their focus at xincheng within the young guojialing granitoid as it cooled more slowly below approximately 300 c to 220 c however the restricted number of auriferous ore stages combined with the presence of cross cutting gold free quartz carbonate veins indicate that gold itself was only deposited over a restricted time interval at 120 ma consistent with studies of orogenic gold deposits elsewhere this highlights the complex interplay between magmatism deformation and the longevity of hydrothermal systems that cause genetic controversies based on apatite fission track aft ages the xincheng gold deposit was then uplifted and exhumed to near the surface of the crust at 15 ma probably due to movement on the crustal scale tan lu fault recognition of such exhumation histories along gold belts has conceptual exploration significance in terms of the probability of discovery of additional exposed or sub surface gold ore bodies as discovery is as much a function of preservation as formation of the deposits

large scale coast parallel displacements in the cordillera a granitic resolution to a paleomagnetic dilemma abstract resolution of the paleomagnetic dilemma the discrepancy between large paleomagnetically determined dextral displacement of outboard portions of the northern cordillera and much smaller offsets implied by mapping and stratigraphic correlations is fundamental to understanding the tectonic evolution of the cordillera this paper presents structural orientation data from the middle cretaceous dawson range batholith of west central yukon and its wallrocks and suggests that some of the missing displacement may be found in intrusions the elongate northwest trending batholith has a margin parallel foliation a sub horizontal stretching lineation and records syn intrusive dextral shearing in country rocks adjacent to the batholith north trending lineations are deflected clockwise into near parallelism with the batholith s margins lineations from wallrock screens within the batholith are all aligned parallel with the batholith s long axis the big creek strike slip fault forms the north margin of the batholith and accommodated a minimum of 20 km of dextral slip these observations imply that the batholith invaded an active dextral shear zone accommodated shearing while crystallizing and focused post crystallization fault development the batholith is conservatively estimated to have accommodated 45 km of syn intrusive shearing collectively middle cretaceous intrusions of the northern cordillera may account for 400 km of previously unrecognized dextral displacement

response of a landscape to tectonics using channel steepness indices ksn and osl a case of study from the jalisco block western mexico abstract rapid tectonic uplift is known to increase river incision rates and to trigger the propagation of knickpoints along a river profile augmenting local relief thus the topography of mountainous landscapes records long term interactions between tectonics and climate we evaluate the geomorphic response to differential rock uplift with topographic analysis of 16 river basins including the normalized channel steepness index k sn our study focuses on rivers incising the northern and western sectors of the jalisco block western mexico a crustal unit bounded by plio quaternary extensional faulting we use osl signals from 17 riverbed samples to assess erosion rates the results indicate that basins in the northern sector have higher rates of rock uplift and erosion mean k sn 111 18 m 0 9 than those in the southwest mean k sn 77 23 m 0 9 in spite of the plio quaternary lavas that cap large areas of the northern sector the development of plio quaternary grabens and half grabens along the northern boundary of the jalisco block has increased the erosion rates augmenting the local relief by contrast the topography of the basins in the southwestern sector has resulted from a long erosional history controlled by the migration of old tectonic signals farther upstream in this region the landscape seems to have reached the steady state and is currently experiencing the propagation of knickpoints due to the increase in the rate of rock uplift in the coast of jalisco during the holocene

identification characterization and statistical analysis of mudstone aggregate clasts cretaceous carlile formation central alberta canada abstract while clastic mudstones and shale were traditionally interpreted to have been deposited in quiet water settings recent flume experiments and studies have shown that mud can be transported in and deposited by traction currents as migrating ripples of mud aggregates despite these recent advances mud aggregates have rarely been adequately described in the rock record these mud aggregates and the sedimentary structures they form in mudstone successions are difficult to observe in the rock record due to compaction which often obliterates the aggregates and flattens bedforms this paper documents unambiguously identifiable sand sized mudstone aggregates in thin sections and sem transported in traction and deposited in a series of prograding clinothems these aggregates were sufficiently indurated to locally preserve shelter porosity significantly improving the hydrocarbon reservoir properties grain size analysis of the aggregates was performed on thin sections as well as disaggregated samples measured by a laser diffraction grain size analyzer for comparison these analyses showed that sand sized aggregates often comprise more than half of the sediment volume while the clay rich composition of the carlile formation would suggest that it is a mudstone statistical analysis of these grain size measurements show that it could alternatively be described as a silty sandstone these findings potentially change how we think about mudstone classification fine grained sedimentation and mudstone dominated petroleum reservoirs

landscape antiquity and cenozoic drainage development of southern yukon through restoration modeling of the tintina fault the impact of tintina fault displacement on the development of the yukon river and drainage basins of central yukon is investigated through geophysical and hydrological modeling of digital terrain model data regional geological evidence suggests that the age of the planation of the klondike plateau is at least late cretaceous rather than neogene as previously assumed and that surprisingly there has been little net incision in the region since the late mesozoic the tintina fault has been previously interpreted to have experienced 430 km of dextral displacement primarily during the eocene however the alignment of river channels across the fault at specific displacements coupled with recent seismic events and related fault activity suggests that the fault may have moved in stages over a longer time span topographic restoration and hydrological models show that the drainage of the yukon river northwestward into alaska via the ancestral kwikhpak river was only possible at restored displacements of u

alluvial sedimentation rates from southeastern australia indicate post european settlement landscape recovery increased catchment sediment yields are common following the introduction of european style agriculture to relatively undisturbed landscapes catchment erosion rates generally increase immediately after disturbance and then decline over time consequently where a catchment currently sits along this disturbance recovery sequence will strongly influence future catchment sediment yields and river morphology in this study field stratigraphy optical dating and hydraulic modelling are used to investigate changes in catchment sediment yield and storage in the lake burragorang catchment in australia with emphasis placed upon changes occurring since european settlement in a d 1820 on the southern tablelands and the upper cox s river subcatchment a large volume of sediment was liberated by gully erosion early in the post settlement period much of which was deposited at break of slope positions below the catchment s headwaters or stored in alluvial benches adjacent to the channel but within the confines of older holocene alluvium a lack of substantial sediment deposition over the last 20 to 40 years is evidence that catchment sediment yields have strongly declined this is consistent with both reduced erosion rates and re aggradation of the incised gullies that in their erosive phase dominated the catchment s post settlement sediment flux collectively these characteristics indicate the catchment is undergoing a phase of landscape recovery

apatite u th sm he thermochronology of rapidly cooled samples the effect of he implantation apatite u th sm he ahe thermochronology is increasingly used for reconstructing geodynamic processes of the upper crust and the surface results of ahe thermochronology however are often in conflict with apatite fission track aft thermochronology yielding an inverted age relationship with ahe dates older than aft dates of the same samples this effect is mainly explained by radiation damage of apatite either impeding he diffusion or causing non thermal annealing of fission tracks so far systematic age inversions have only been described for old and slowly cooled terranes whereas for young and rapidly cooled samples too old ahe dates are usually explained by the presence of undetected u and or th rich micro inclusions we report apatite u th sm he results for rapidly cooled volcanogenic samples deposited in a deep ocean environment with a relatively simple post depositional thermal history robust age constraints are provided independently through sample biostratigraphy all studied apatites have low u contents 5 ppm on average while aft dates are largely in agreement with deposition ages most ahe dates are too old for leg 43 where deposition age of sampled sediment is 26 5 29 5 ma alpha corrected average ahe dates are up to 45 ma indicating overestimations of ahe dates up to 50 this is explained by he implantation from surrounding host u th rich sedimentary components and it is shown that ahe dates can be corrected by mechanically abrading the outer part of grains we recommend that particularly for low u th apatites the possibility of he implantation should be carefully checked before considering the degree to which the alpha ejection correction should be applied

the mineralization age of the banxi sb deposit in xiangzhong metallogenic province in southern china abstract the banxi sb deposit is one of world class sb deposits located in the xiangzhong sb au metallogenic province in southern china however the mineralization age of this deposit is still not well constrained due to a lack of suitable minerals for reliable radiometric dating since the fluid inclusion data suggest that the temperature of ore forming fluids in the banxi deposit is up to 330 c zircon u th he thermochronometry with the closure temperature of 160 200 c was chosen here to elucidate the timing of sb mineralization of this deposit detrital zircons within three samples of altered host rocks in the banxi deposit yielded u th he dates of 132 113 ma weighted mean 121 12 ma 132 124 ma weighted mean 129 3 ma and 142 113 ma weighted mean 125 10 ma respectively which are broadly consistent with the rb sr and sm nd isochron ages of hydrothermal sulfide minerals 130 ma combining with the reported ages of adjacent sb deposits we propose that sb mineralization in the banxi deposit may have primarily taken place during 130 120 ma

reverse engineering mother nature shale sedimentology from an experimental perspective abstract experimental study of the sedimentology of shales can take a variety of forms at its simplest one can experiment with suspensions in a glass jar and try to understand their settling behavior or one can manipulate mud in a tank or bucket to gain insights into its rheology this approach was championed over a century ago by sorby and the insights gained can be quite profound more recently tank and settling tube experiments of animal sediment interactions compaction behavior and sediment unmixing via re suspension have proven to be highly informative in spite of their simplicity flumes can be used to obtain quantitative information about depositional and erosional parameters and to generate fundamental bedforms in flume experiments however it is of critical importance that the flume be designed in a way that flocculated materials move under shear stress conditions that would be reasonable in natural environments although much flume work on muds has been conducted by hydraulic engineers the transfer of that knowledge to sedimentology is hampered by the fact that engineers and sedimentologists are interested in different though not mutually exclusive products from such experiments engineers and hydrologists are commonly concerned with quantifying fluid flow properties whereas sedimentogists are particularly interested in the sedimentary products that result from a variety of flow conditions recent sedimentologically oriented flume studies have shown that muds can form deposits at flow velocities and shear stresses that would suffice to transport and deposit medium grained sand mud suspensions are prone to flocculation and the resulting floccules travel in bedload and form ripples that accrete into beds the latter finding suggests that many laminated shales were deposited from currents rather than by settling from slow moving or still water there are many other sedimentary features in shales that can potentially be reproduced in flume studies and in the future serve to provide a quantitative basis for shale sedimentology

confirming geomorphological interpretations based on portable osl reader data portable optically stimulated luminescence osl readers are increasingly being used in geomorphological and archaeological investigations but information regarding data reproducibility and the reliability of interpretations based on portable osl reader data has not yet been presented to the wider geomorphological community this letter addresses these two issues by returning to grabben gullen creek in the southeastern australian tablelands where we remeasure a sediment profile that was first measured by other researchers 3 years earlier we also compare portable osl reader data measured on sediment interpreted to have been deposited in swampy meadow wetlands and flood alluvium settings with data measured on known swampy meadow and flood deposits our data show that portable osl reader data are reproducible moreover we confirm the earlier interpretation that stratigraphies commonly exposed in southeastern australian tablelands valley bottoms reflect pre european swampy meadow wetlands and flood alluvium copyright 2015 john wiley sons ltd

fluorite u th he thermochronology constraints on the low temperature history of yucca mountain nevada abstract fluorite is one of the secondary minerals precipitated in pore spaces at the future nuclear waste repository site at yucca mountain nevada the authors have conducted u th he dating of this fluorite in an attempt to constrain the temperature and timing of paleo fluid flux into the site repeated analysis of colourless fluorite yielded a weighted average age of 9 7 0 15 ma 2 younger than previously determined sanidine 40ar 39 ar ages 12 8 ma for deposition of the tuff laboratory he diffusion experiments conducted on the yucca fluorite yield a preliminary he closure temperature tc of 90 10 c cooling rate of 10 c ma and previous studies have determined that the fluorite precipitated from warm fluids 65 80 c at depths of it was observed that the purple coloured outer portion of the fluorite nodule yielded non reproducible and invariably older ages than colourless fluorite several possible reasons are suggested

characteristics and osl minimum ages of relict fluvial deposits near sossus vlei tsauchab river namibia and a regional climate record for the last 30 ka the present end point of the tsauchab river is at sossus vlei 30 km into the namib sand sea interdune deposits in three depressions west and southwest of the vlei include channel and interdune lithofacies associations but no deposits typical of river end points or of groundwater seepage into interdune areas the two lithofacies associations show that the tsauchab river extended further into the sand sea in the past it had a well developed channel and a higher flow than today that caused flooding of adjacent interdune areas osl 4 mm aliquot minimum ages indicate that the tsauchab river reached 2 3 km beyond its present end point at ca 25 ka and ca 9 7 ka and that the river was more active from 0 9 0 3 ka the eastward migration of the river end point since ca 7 ka suggests a reduction in flood magnitude accompanied by the gradual invasion of the sossus vlei area by dunes the regional data indicate an additional wet interval at ca 15 ka that is so far not recorded in the sossus area copyright 2006 john wiley sons ltd

human and natural impacts on fluvial and karst depressions of the maya lowlands abstract this paper begins to differentiate the major drivers and chronology of erosion and aggradation in the fluvial and fluviokarst landscapes of the southern and central maya lowlands we synthesize past research on erosion and aggradation and add new data from water soils radiocarbon dating and archaeology to study the quantity timing and causes of aggradation in regional landscape depressions geomorphic findings come from many excavations across a landscape gradient from upland valleys karst sinks and fans into the coastal plain floodplains and depressions findings from water chemistry show that sources in the uplands have low quantities of dissolved ions but water in the coastal plains has high amounts of dissolved ions often nearly saturated in calcium and sulfate we found significant geomorphic complexity in the general trends in upland karst sinks in a few instances sediments preserve late pleistocene paleosols buried 2 3 m though many more have distinct middle to late holocene paleosols buried 1 2 m after c 2300 bp maya early to late preclassic from 2300 1100 bp late preclassic to classic periods the landscape aggraded from five main mechanisms river flooding climatic instability accelerated erosion ancient maya landscape manipulation and gypsum precipitation from a rise in a water table nearly saturated in calcium and sulfate ions evidence exists for two or three high magnitude floods possibly driven by hurricanes moreover lake core and geophysical studies from the peten lakes region have shown high rates of deposition of silicate clays maya clays starting and peaking during the maya preclassic and continuing to be high through the late classic the main driver on upland karst depressions the peten lakes upland valleys and fans was accelerated soil erosion but water table rise probably driven by sea level rise was the main driver on the wetlands of the coastal plain because the aggraded sediments here are dominantly composed of gypsum precipitated from the groundwater this latter mechanism represents a little recognized mechanism of aggradation over a large region these large scale environmental changes occurred during periods of intensive ancient maya land use and climatic instability both of which may have contributed to erosion by increasing runoff despite these geomorphic changes ancient maya farmers adapted in several key cases