late mesozoic bimodal volcanic rocks in the jinniu basin middle lower yangtze river belt yrb east china age petrogenesis and tectonic implications abstract late mesozoic intrusive and volcanic rocks are widespread in the southeast hubei province middle lower yangtze river belt yrb east china detailed in situ zircon u pb and hf isotope elemental and sr nd pb isotopic data are presented in this paper for late mesozoic volcanic rocks from the jinniu basin yrb aiming to constrain their age petrogenesis and tectonic implications the jinniu volcanic rocks show a bimodal distribution in composition with dominant rhyolite and dacite and subordinate basalt and basaltic andesite new shrimp and la icpms zircon u pb ages indicate that the volcanic rocks of three formations in the jinniu basin were erupted at quite a short age range of about 5 ma during the early cretaceous 130 125 ma the mafic rocks are moderately enriched in large ion lithophile elements lile e g ba th u and pb and light rare earth elements lree and are characterized by negative nb ta and ti anomalies and relatively high tio2 0 72 2 06 and nb 9 20 26 5 ppm contents these analyses indicate that the geochemical characteristics of the mafic rocks in the jinniu basin are similar to worldwide phanerozoic nb enriched basalt and andesites neba new in situ zircon u pb ages and field geological relationships demonstrate that neba in the southeast hubei province are not spatially or temporally associated with high silica adakitic rocks but were most likely derived from an enriched lithospheric mantle with assimilation of minor crustal materials and then fractional crystallization during the evolution of the magma overall the felsic rocks in the jinniu basin have geochemical characteristics and sr nd pb signatures and in situ zircon hf isotopic compositions similar to those of the mafic rocks compared with the mafic rocks the felsic rocks are characterized by enriched and variable concentrations of lile and ree e g ba 33 3 1372 ppm y 11 4 33 6 ppm ybc 5 07 18 7 and negative eu anomalies eu 0 22 0 98 as well as a wide range of radiogenic nd pb isotopic values with end t 10 2 to 2 4 206pb 204pb i 17 659 18 705 207pb 204pb i 15 478 15 663 and 208pb 204pb i 37 654 38 935 and in situ zircon hf compositions of ehf t 12 7 to 1 8 these features indicate that the genesis of felsic magma in the jinniu basin is consistent with extensive fractional crystallization and large amounts of crustal contamination from an evolved mafic magma sio2 55 the bimodal volcanic rocks in this study provide convincing evidence that early cretaceous volcanic rocks in the yrb developed in a back arc extensional tectonic regime

geochemical characteristics of biotite from felsic intrusive rocks around the sisson brook w mo cu deposit west central new brunswick an indicator of halogen and oxygen fugacity of magmatic systems abstract the sisson brook w mo cu deposit was formed by hydrothermal fluids likely related to the nashwaak granites muscovite biotite granite group i and biotite granite group ii and related dykes biotite granitic dykes group iii and a feldspar biotite quartz porphyry dyke group iv chemical data obtained using epma and la icp ms data of primary magmatic biotites were used to investigate magmatic processes and associated hydrothermal fluids trace element features of biotite in the group i two mica granite suggest other magmatic processes along with a simple fractional crystallization the k rb ratios and compatible elements cr ti co v and ba in biotite from groups ii iii and iv decrease whereas incompatible elements including ta tl ga cs li and sn increase with magma fractionation no correlation of cu w and mo with k rb ratios is evident suggesting that partitioning of cu w and mo into biotite may not be entirely controlled by magma fractionation halogen fugacity of the parental magma of the nashwaak granites and related dykes calculated from zircon saturation temperature shows that group i has high f hf f cl ratios broadly higher than 0 similar to the plutons at the henderson porphyry mo deposit the f hf f cl ratios of the other groups are generally lower than 0 comparable to the santa rita porphyry cu deposit the f h 2 o f hcl and f h 2 o f hf ratios inferred from biotite in the nashwaak granites and related dykes range from 3 to 5 and from 4 to 5 respectively the inferred oxygen fugacity shows that the dyke phases groups iii and iv have the oxygen fugacity around the nickel nickel oxide buffer the plutonic phases groups i and ii have the oxygen fugacity around the quartz fayalite magnetite qfm buffer at high temperatures and oxidized to nickel nickel oxide buffer at lower temperatures this oxidation process in the plutonic phases groups i and ii could be caused by h 2 release at or near h 2 o vapor saturation at high h 2 o fe 2 the magma associated with the biotite dykes group iii is more likely the source of the hydrothermal fluids at the sisson brook deposit since it has the highest differentiation degree and seems to have formed in an oxidized setting necessary for mo to concentrate in the late stage fluids

copper mineralization prevented by arc root delamination during alpine himalayan collision in central iran contrasting geochemical signatures of copper ore hosting eocene and some barren undeformed miocene diorites to granites in central iran temporally overlap with the alpine himalayan collision and provide key implications on the existence and lack of cu mineralization during collisional magmatism high sr and low y and yb contents of eocene arc rocks in the natanz arc segment reflect thickened andean type orogenic arc crust 45 km whereas barren miocene natanz arc rocks 21 19 ma indicate thin arc crust similar to collisional volcanism in anatolia geochemical modeling indicates a change in the mineralogy of the melt residual from precollisional eocene basaltic garnet bearing 5 30 amphibolite to syn or postcollisional miocene metasomatized mantle peridotite which can be explained by collision induced delamination of the arc lithospheric root subsequent recharge of hot asthenosphere and melting of metasomatized mantle peridotite and lack of interaction with a garnet bearing arc crustal keel explain the low sr and high y and yb contents the relatively enriched initial sr isotope ratios of postcollisional miocene natanz rocks and the lack of copper mineralization in postcollisional miocene natanz arc rocks arc root delamination removes the copper and sulfur enriched metasomatized lithospheric arc root and hydrous cumulate reservoir required to form copper ore deposits lack of the dense melt residues also provides an alternative explanation for the elevated thin crustal iranian back arc plateau 38 km as a result of uplift by isostatic rebound rather than uplift by anomalous shortening miocene arc root delamination implies a minimum age of 21 ma for the alpine himalayan collision in central iran

scouring of gold from the lower crust quartz carbonate lodes have produced a major part of the world9s gold the source for the lodes which were emplaced along shear zones in the upper crust has been enigmatic the bamble belt of south norway is depleted in gold by more than an order of magnitude relative to its crustal abundance other elements present in gold deposits have also been lost gold dissolved and was removed in oxidized sulfur rich fluids rising through this broad ductile shear zone during high grade metamorphism deformation synchronous with metamorphism created the permeability that permitted a pervasive flow of fluids

the giant dexing porphyry cu mo au deposit in east china product of melting of juvenile lower crust in an intracontinental setting the dexing porphyry cu mo au deposit in east china 1 168 mt at 0 45 cu is located in the interior of the south china craton scc made up of two lithospheric blocks the yangtze and cathaysia blocks the cu mo au mineralization is associated with mid jurassic granodioritic porphyries with three high level intrusive centers controlled by a series of lineaments at the southeastern edge of the yangtze block available age data define a short duration 172 170 ma of the felsic magmatism and the mineralization 171 1 ma the deposit shows broad similarities with deposits in volcanoplutonic arcs although it was formed in an intracontinental setting porphyries associated with mineralization are mainly granodiorites which contain abundant phenocrysts 40 60 and carry contemporaneous microgranular mafic enclaves mmes they are mainly high k calc alkaline and show geochemical affinities with adakite characterized by relatively high mgo cr ni th and th ce ratios the least altered porphyries yielded relatively uniform end t values from 0 9 to 0 6 and wide 87sr 86sr i range between 0 7046 and 0 7058 partially overlapping with the sr nd isotopic compositions of the mmes and mid jurassic mafic rocks in the scc zircons from the porphyries have positive ehf t values 3 4 to 6 9 and low 18o values 4 7 to 6 3 generally close to those of depleted mantle all data suggest an origin by partial melting of a thickened juvenile lower crust involving mantle components e g neoproterozoic mafic arc magmas triggered by invasion of contemporaneous mafic melts at dexing the mmes show textural mineralogical and chemical evidence for an origin as xenoliths formed by injection of mafic melts into the felsic magmas these mmes usually contain magmatic chalcopyrite and have original variable contents of cu up to 500 ppm their geochemical characteristics suggest that they were derived from an enriched mantle source metasomatized by proterozoic slab derived fluids and supplied a part of cu au and s for the dexing porphyry system during their injection into the felsic magmas the 171 1 ma magmatic hydrothermal event at dexing is contemporaneous with the mid jurassic extension in the scc followed by 160 90 ma arc like magmatism in southeastern china with respect to the tectono magmatic evolution of the scc the emplacement of cu bearing porphyries and the associated cu mineralization occurred in response to the transformation from a tensional regime related to mid jurassic extension to a transpressional regime related to the subduction of the paleo pacific oceanic lithosphere

cretaceous ridge subduction along the lower yangtze river belt eastern china the lower yangtze river belt is one of the most important metallogenic belts in china the mechanisms responsible for ore genesis and the formation of related cretaceous igneous rocks such as adakite a type granitoid and nb enriched basalt remain controversial mesozoic granitoids in the lower yangtze river belt were mostly formed in the early cretaceous 140 125 ma and three granitoid belts the inner the south and the north have been defined according to petrological and geochemical characteristics previously based mainly on negative end and high initial sr isotope values the adakitic rocks were generally attributed to partial melting of thickened or delaminated lower crust both of which require crustal thickening mesozoic crustal thickening however is not supported by the development of extensional basins in the region from the late jurassic to cretaceous eastern china was closely associated with subduction of the pacific plate in the south and the izanagi plate in the north the midocean ridge mor between these two plates was drifting toward and likely subducting under the lower yangtze river belt a ridge subduction model can therefore explain the distribution of different magmatic rocks and ore deposits in the belt partial melting of subducting young hot oceanic slabs close to the ridge formed adakitic rocks the negative end values of adakitic rocks can be plausibly interpreted by mixing between adakitic magmas and enriched components in the lithospheric mantle and or crustal materials through afc process a slab window opened during ridge subduction as indicated by a type granitoids in the center of the inner belt nb enriched basalt found in the belt was likely formed by partial melting of a mantle wedge metasomatized by fluids released from the subducting slab at shallow depths

a review of the intracontinental porphyry deposits in the middle lower yangtze river valley metallogenic belt eastern china abstract the middle lower yangtze river valley metallogenic belt mlyb is one of the most important metallogenic belts in eastern china and contains many important porphyry deposits these deposits include the tongshankou cu mo jiguanzui cu au chengmengshan cu mo wushan cu mo fengshandong cu au dingjiashan cu yangjishan au shaxi cu au dongguashan cu au shujiadian cu and anjishan cu deposits etc in this review we summarize the geological characteristics including the stratigraphy structure ore bearing porphyry types vein characteristics and wall rock alteration metallogenic ages and petro geochemistry of representative porphyry deposits in the mlyb we conclude that porphyritic magmatism and metallogeny have occurred in three stages the early ca 149 135 ma and late ca 123 105 ma stages comprise mainly porphyry skarn mineralization whereas the middle ca 133 125 ma stage comprises porphyry mineralization ore bearing porphyries in the mlyb are the high k calc alkaline to calc alkaline series with the majority possess adakitic geochemical signature the ore bearing porphyries with adakitic signature may have originated from magma mixing produced by the delamination of enriched lithospheric mantle and partial melting of the thickened lower crust the enriched mantle derived mafic melts component are very important for generating fertile magma and the 34s and 18o values suggest that ore forming materials were magma derived compared with porphyry deposits in typical magmatic arc settings porphyry deposits in the mlyb do not contain advanced argillic lithocaps or high to intermediate sulfidation systems and the magmatic and ore forming material sources are also very different

mineral deposit model for porphyry skarn polymetallic copper deposits in tongling ore dense district of middle lower yangtze valley metallogenic belt according to field investigations of major ore deposits along the middle lower yangtze valley metallogenic belt and a detailed study of the data available the authors put forward a mineral deposit model based on the tongling ore district the largest ore cluster in the belt the porphyry skarn cu au mo ore bodies developed around the roof pendants of the high potash calc alkaline granitoids have experienced strong fractionation since there are extensively distributed carboniferous permian carbonates both calcic and magnisian skarn deposits have most important economic significance as components of the porphyry skarn system the skarn and vein like gold deposits and veinlike pb zn ag deposits are distributed outward gradually from the intrusion and the porphyry skarn cu au mo ore deposits because the middle lower yangtze valley belt was a foreland basin during the collision between the south china massif and the north china craton and subsequently a depression belt during the post collision with a lot of decollement and detachment faults especially along the discontinuity boundary which occupied a large space the large ore bodies must have been formed along the large space such as the major ore body in the xinqiao s cu au polymetallic mine the strong retrograde alteration consisting of actinolite tremolite chlorite epidote or serpentine mg chlorite talc tremolite with typical wrigglite and laminated structures along either fractures or discordant boundary replaced the skarn at the contact with the granitoid intrusion there are also a lot of manto or stratabound skarn ore bodies replacing some carbonate layers of different ages this paper also indicates the correct utilization of the model together with some types of geochemical and geophysical technologies for further prospecting in similar tectonic settings

fundamentals of fission track thermochronology fission track ft analysis has developed into one of the most useful techniques used throughout the geologic community to reconstruct the low temperature thermal history of rocks over geological time the ft method is based on the accumulation of narrow damage trails i e fission tracks in uranium rich mineral grains e g apatite zircon titanite and natural glasses which form as a result of spontaneous nuclear fission decay of 238u in nature price and walker 1963 fleischer et al 1975 the time elapsed since fission tracks began to accumulate is estimated by determining the density of accumulated tracks in a particular material in relation to the uranium content of that material chemical etching can be used to enlarge fission tracks that have formed within a mineral in order to make them readily observable under an ordinary optical microscope price and walker 1962 if a host rock is subjected to elevated temperatures fission tracks that have formed up to that point in time are shortened progressively and eventually erased by the thermal recovery i e annealing of the damage fleischer et al 1975 because thermal diffusion basically governs the annealing process the reduction in ft length is a function of heating time and temperature importantly fission tracks are partially annealed over different temperature intervals within different minerals this characteristic allows for the construction of time temperature paths of many different rock types by a plotting ft and other isotopic ages from different minerals versus their closure temperatures which is applicable in the case of a monotonous cooling history e g wagner et al 1977 zeilter et al 1982 and or by b the inverse modeling of observed ft age and confined track length data e g corrigan 1991 lutz and omar 1991 gallagher 1995 ketcham et al 2000 see also ketcham 2005

sierra nevada basin and range transition near reno nevada two stage development at 12 and 3 ma relative and absolute elevations of the sierra nevada and adjacent basin and range province timing of their differentiation and location amount and timing of strike slip movement between them are controversial the provincial boundary near reno developed in two stages 1 at ca 12 ma the 700 km 2 verdi boca sedimentary basin formed across what was to become the boundary probably as a result of a small magnitude but regional extensional episode that affected much of the western basin and range 2 at 3 ma the basin was complexly faulted and folded during a larger magnitude extensional episode that established the modern sierran structural and topographic boundary in this area the boundary is really a transition zone with a western edge along the donner pass california fault zone which is farther west than previously placed both episodes appear to have resulted from east west extension only which suggests that northwest motion of the sierra nevada relative to the basin and range shown by geodetic data began after 3 ma or was taken up farther east

the cretaceous huangdaoshan cu bearing intrusion in chuzhou petrogenesis and implications for the cu mineralization in the middle lower yangtze river valley metallogenic belt eastern china abstract the huangdaoshan mineral deposit in the middle lower yangtze river valley metallogenic belt is located on the northern margin of the yangtze craton eastern china it is hosted by the high k calc alkaline quartz monzonite porphyry and quartz diorite porphyry of huangdaoshan intrusion the molybdenite re os age for the mineral deposit suggests that mineralization occurred at 128 9 2 3 ma and was coeval with the ore bearing intrusion 130 1 ma both porphyries are enriched in light rare earth elements lree and large ion lithophile elements lile depleted in heavy rare earth elements hree and high field strength elements hfse and have positive eu anomalies they also show adakitic affinities with high sr 914 1227 ppm and sr y ratios 125 212 and low y 5 40 9 00 ppm and yb 0 46 0 75 ppm contents petrography micro fabric features and sr nd hf isotopic results suggest that these adakite like magmas were derived from magma mixing between mantle and crustal derived materials the strong ree fractionations as well as the high la sm 6 0 7 1 and intermediate sm yb 4 5 5 6 ratios suggest that hornblende crystallization was the dominant control on fractionation apparent temperatures based on ti in zircon thermometry show that the mineralization related porphyries crystallized at 711 c 790 c the oxygen fugacity fo2 estimated from hornblende mg contents and biotite fe3 fe2 and mg contents indicates that the mineralized magma possessed a high oxidation state nno 0 15 to nno 1 62 the geochemical characteristics of the intrusions enrichment in liles depletion in hfses and nb ta anomalies indicate that the mafic magma was derived from partial melting of the enriched lithosphere mantle which had been metasomatized by slab derived fluids from a subducted oceanic plate therefore the parental magma contained high contents of h2o and metal e g cu with high fo2 the extensive contemporaneous magmatism metallogenic events and volcanic basins in the region suggest an extensional tectonic setting we further correlated this extension regime with slab roll back of the paleo pacific plate

tidal notches in mediterranean sea a comprehensive analysis abstract recent works evelpidou et al 2012 suggest that the modern tidal notch is disappearing worldwide due sea level rise over the last century in order to assess this hypothesis we measured modern tidal notches in several of sites along the mediterranean coasts we report observations on tidal notches cut along carbonate coasts from 73 sites from italy france croatia montenegro greece malta and spain plus additional observations carried outside the mediterranean at each site we measured notch width and depth and we described the characteristics of the biological rim at the base of the notch we correlated these parameters with wave energy tide gauge datasets and rock lithology our results suggest that considering the development of tidal notches the consequence of midlittoral bioerosion as done in evelpidou et al 2012 is a simplification that can lead to misleading results such as stating that notches are disappearing important roles in notch formation can be also played by wave action rate of karst dissolution salt weathering and wetting and drying cycles of course notch formation can be augmented and favoured also by bioerosion which can in particular cases be the main process of notch formation and development our dataset shows that notches are carved by an ensemble rather than by a single process both today and in the past and that it is difficult if not impossible to disentangle them and establish which one is prevailing we therefore show that tidal notches are still forming challenging the hypothesis that sea level rise has drowned them

rapid glacial erosion at 1 8 ma revealed by 4he 3he thermochronometry alpine glaciation and river incision control the topography of mountain ranges but their relative contributions have been debated for years apatite 4 he 3 he thermochronometry tightly constrains the timing and rate of glacial erosion within one of the largest valleys in the southern coast mountains of british columbia canada five proximate samples require accelerated denudation of the klinaklini valley initiating 1 8 0 2 million years ago ma at least 2 kilometers of overlying rock were removed from the valley at 5 millimeters per year indicating that glacial valley deepening proceeded 6 times as fast as erosion rates before 1 8 ma this intense erosion may be related to a global transition to enhanced climate instability 1 9 ma

geochronology and geochemistry of the fe ore bearing zhonggu intrusions of the ningwu basin implications for tectonic setting and contemporaneous cu au mineralization in the middle lower yangzte metallogenic belt abstract the zhonggu ore field is located in the southern ningwu volcanic basin the largest iron ore district within the middle lower yangtze river metallogenic belt mlyrmb of eastern china this area has produced more than 2000 mt of iron ore although comparatively little research has been done on the ore bearing intrusions in this region despite the significance of the mineralization in this area this in turn means that the petrogenesis and the links between these intrusions and the metallogenesis in this area remain unclear this study focuses on the six intrusions that are associated with almost all of the iron deposits within the zhonggu ore field namely the gushan porphyritic gabbrodiorite the longshan gabbrodiorite the hemushan diorite the baixingshan diorite the zhongjiu diorite and the taipingshan monzonite all of these rocks are either high to medium k and calc alkaline or are shoshonitic although the former dominates over the latter zircon laser ablation inductively coupled plasma mass spectrometry la icp ms u pb dating yielded ages of 132 6 1 6 to 131 6 1 6 130 7 2 2 to 129 4 1 9 131 2 0 and 132 3 2 1 ma for intrusions associated with the longshan taipingshan baixiangshan and zhongjiu deposits respectively indicating that all of these intrusions were emplaced in the early cretaceous 132 6 129 4 ma this magmatism and mineralization was contemporaneous with the second stage 135 127 ma of magmatic activity that has been documented elsewhere within the mlyrmb the mineralized intrusions associated with the zhonggu iron ore field have similar chondrite normalized rare earth element ree and primitive mantle normalized multi element variation patterns that are characterized by light ree lree and light ion lithophile element lile rb ba k and sr enrichments and heavy ree hree and high field strength element hfse nb ta zr and hf depletions these intrusions also have total ree ree concentrations that are consistent with the evolution of the magma from mafic intermediate to felsic the magmas that formed these intrusions were derived from an enriched region of the mantle and underwent contamination by the assimilation of continental crustal or lithospheric material the magmatism within the zhonggu iron ore field formed during an early cretaceous period of lithospheric thinning and extension in addition the arc affinities of the intrusions in this region indicative of a relationship to the subduction of the paleo pacific plate a process that was most likely the main factor in the generation of the mineralization within the mlyrmb the fe mineralization related intrusions in the study area are also distinctly different from intrusions in this region associated with cu au mineralization most likely as a result of the heterogeneous distribution of slab derived fluids in this period over time this research also highlights the exploration potential of this region indicating that the 132 129 ma monzonites and diorites in this area and beyond should be considered prime targets for fe exploration but are also unlikely to be related to cu au mineralization

petrogenesis and mineralization of the fenghuangshan skarn cu au deposit tongling ore cluster field lower yangtze metallogenic belt article the fenghuangshan copper gold deposit located in the tongling ore cluster field along the lower yangtze metallogenicbelt lyrb ineasternchina mainlyconsistofskarnoreshostedingranodiorite u pb dating of mag matic zircons from fenghuangshan granodiorite yields a weighted mean 206 pb 238 u age of 143 1 1 6 ma five molybdenite samples collected in the fenghuangshan deposit yield a re osisochronage of 141 7 0 8 ma dem onstrating that the ore formation event is coeval with the fenghuangshan granodiorite intrusion the magmatic zircon hf t values vary from 12 0 to 28 3 corresponding two stage hf model ages between 1 6 ga to 2 4 ga geochemical and isotopic signatures suggest that the fenghuangshan granodiorite resembles adakite which was derived from partial melting of the subducted oceanic crust towards lyrb during the early cretaceous the occurrence of inherited zircons shows the intrusive granodiorite was assimilated by old crustal materials dur ing its emplacement the biotite thermobarometry zircon ce iv ce iii ratios and eu anomalies coincidently demonstrate that the magma source of granodiorite was under high to moderate oxidized condition conducive to cu au mineralization the sulfide ores in fenghuangshan deposit are enriched in pd and pt which could also be a consequence of the high oxidized magma source the high re abundance in molybdenite and platinum group element pge contents of sulfide ores suggest that the ore forming materials are characterized by mixed sources from the mantle and crust and were slightly affected by hydrothermal alteration

quantifying the diffusion kinetics and spatial distributions of radiogenic 4he in minerals containing proton induced 3he apatite titanite and olivine samples were bombarded with a 150 mev proton beam to produce 10 8 atoms mg of spallation 3he high precision stepped heating experiments were then performed in which the artificial 3he and for apatite and titanite the natural radiogenic 4he were measured to characterize the diffusive behavior of each isotope helium 3 diffusion coefficients are in excellent agreement with concurrently and or previously determined he diffusion coefficients for each mineral our results indicate that proton induced 3he is uniformly distributed and that radiation damage associated with a proton fluence of 5 x 10 14 protons cm 2 does not cause noticeable changes in 4he diffusion behavior in at least apatite and titanite proton induced 3he can therefore be used to establish he diffusion coefficients in minerals with insufficient natural helium for analysis or those in which the natural 4he distribution is inhomogeneous in addition step heating 4he 3he analysis of a mineral with a uniform synthetic 3he concentration provides a means by which a natural 4he distribution can be determined

high sr y and la yb ratios the meaning of the adakitic signature abstract the name of adakite is used to describe a far too large group of rocks whose sole common feature is high sr y and la yb ratios however such a signature can be achieved via different processes melting of a high sr y and la yb source deep melting with abundant residual garnet fractional crystallization or afc or interactions of felsic melts with the mantle causing selective enrichment in lree and sr over hree a database of the compositions of adakitic rocks including high silica and low silica adakites martin h smithies r h rapp r p moyen j f champion d c 2005 an overview of adakite tonalite trondhjemite granodiorite ttg and sanukitoid relationships and some implications for crustal evolution lithos 79 1 2 1 24 continental adakites and archaean adakites was assembled geochemical modeling of the potential processes is used to interpret it and reveals that 1 the classical model of slab melting provides the best explanation for the genesis of high silica adakites 2 low silica adakites are explained by garnet present melting of an adakite metasomatized mantle i e at depths greater than 2 5 gpa 3 continental adakites is a term encompassing a huge range of rocks with a corresponding diversity of petrogenetic processes and most of them are different from both low and high silica adakites 4 archaean adakites show a bimodal composition range with some very high sr y examples similar to part of the ttg suite reflecting deep melting 2 0 gpa of a basaltic source with a relatively high sr y while lower sr y rocks formed by shallower 1 0 gpa melting of similar sources comparison with the archaean ttg suite highlights the heterogeneity of the ttgs whose composition spreads the whole combined range of hsa and archaean adakites pointing to a diversity of sources and processes contributing to the ttg suite

vertical deformation associated with normal fault systems evolved over coseismic postseismic and multiseismic periods vertical deformation of extensional provinces varies significantly and in seemingly contradictory ways sparse but robust geodetic seismic and geologic observations in the basin and range province of the western united states indicate that immediately after an earthquake vertical change primarily occurs as subsidence of the normal fault hanging wall a few decades later a 100 km wide zone is symmetrically uplifted the preserved topography of long term rifting shows bent and tilted footwall flanks rising high above deep basins we develop finite element models subjected to extensional and gravitational forces to study time varying deformation associated with normal faulting we replicate observations with a model that has a weak upper mantle overlain by a stronger lower crust and a breakable elastic upper crust a 60 dipping normal fault cuts through the upper crust and extends through the lower crust to simulate an underlying shear zone stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift under the footwall the breakable upper crust is a necessary model feature to replicate footwall bending over the observed width 10 km which is predicted to take place within 1 2 decades after each large earthquake thus the best preserved topographic signature of rifting is expected to occur early in the postseismic period the relatively stronger lower crust in our models is necessary to replicate broader postseismic uplift that is observed geodetically in subsequent decades

4he 3he thermochronometry theory practice and potential complications thermochronometry most often involves the determination of a cooling age from parent and daughter abundances within an entire crystal or population of crystals dodson 1973 complementary information exists in the spatial concentration distribution of the daughter c x y z within a single crystal by combining a bulk cooling age with c x y z on the same sample it is possible to place tight limits on the sample s time temperature t t path techniques for this kind of analysis have been developed for several different parent daughter systems including u th pb and k ar harrison et al 2005 here we describe how this approach is applied to the u th he system the particular attraction of the u th he method is its sensitivity to uniquely low temperatures for example the nominal 4he closure temperatures at 10 c myr for apatite zircon and titanite are 70 c 180 c and 200 c respectively reiners and farley 1999 2001 farley 2000 reiners et al 2002 2004 in the case of apatite we will show that significant diffusive mobility of 4he occurs at temperatures just slightly higher than those of the earth s surface in this chapter we present an overview of the 4 he 3 he thermochronometry technique in which the natural spatial distribution of 4he is constrained by stepwise degassing 4he 3he analysis of a sample containing synthetic proton induced 3he we present the fundamental theory assumptions practical aspects of proton irradiation and stepwise 4he 3he analyses as well as several example applications of 4he 3he thermochronometry in particular we illustrate how the 4he 3he technique can be used to determine the helium diffusion kinetics and constrain the natural 4he distribution within an individual crystal or a small population of crystals and how this information can be

high magmatic flux during alpine himalayan collision constraints from the kal e kafi complex central iran voluminous eocene gabbros to granites of the kal e kafi backarc composite intrusion were emplaced prior to the alpine himalayan collision in the central iranian backarc but the reasons for precollisional high arc and backarc magmatic productivity 60 53 ma are unclear diagnostic geochemical signatures are high k2o sr contents and successively depleted middle rare earth element ree patterns reflecting a highly metasomatized source and an increasing role for amphibole and garnet 0 10 in the relatively younger granites release of concealed k sr rich fluids from oceanic fractures and faults during buckling and bulging of a precollisional choking oceanic slab and melting of phlogopite bearing lithosphere with subsequent interaction of the melt with lower crustal garnet amphibolite of a 40 km thick crust can explain the kal e kafi geochemical and isotopic signatures gravimetric data indicating a 39 km present day backarc crustal thickness are consistent with geochemical results but also imply little if any collisional crustal thickening of the central iranian plateau high eocene arc backarc melt flux prior to collision in this region reflects vigorous thermal convection which may in fact be diagnostic of collisional magmatism explaining the presence of postcollisional shoshonitic melts in this and other collisional orogenic settings

the magma mixing origin of mantled feldspars the key to mantled feldspar genesis is epitaxial nucleation of plagioclase on k feldspar or k feldspar on plagioclase once this nucleation takes place there is a relatively straightforward process of crystal growth yielding rapakivi and antirapikivi textures the most common mantling is plagioclase on k feldspar which occurs in both volcanic and plutonic environments in the volcanic environment the morphology of the plagioclase overgrowth typically is dendritic though in subvolcanic and shallow plutonic environments dendritic growth is followed by a more or less continuous non cellular shell of plagioclase in the plutonic environment early stages of plagioclase overgrowth also tend to be dendritic although with coarser grained characteristics dendritic morphology is thus a common denominator in rapakivi genesis since growth of dendritic plagioclase is clearly related to marked undercooling in silicate melt systems its occurrence in many volcanic rocks is to be expected equivalent quenching in the plutonic environment requires a cooling mechanism independent of conductive heat transfer to wallrock and also independent of effective cooling related to sudden loss of volatile phases that could only occur late in the crystallization of most magmas and therefore after much dendritic plagioclase had already formed internal quenching of portions of magma systems must occur if mafic magma is abruptly mixed with felsic magma such magma mixing yields a heterogeneous system at first one that is in a drastic state of disequilibrium and tending to force nucleation of one feldspar type on the surface of another resulting in epitaxial crystallization of dendritic plagioclase on k feldspar mantling of one feldspar type by another during magma mixing is paralleled by dendritic growth zones in coexisting plagioclase crystals

volcanic signature of basin and range extension on the shrinking cascade arc klamath falls keno area oregon 1 detailed geologic mapping of the klamath falls keno area revealed the complex relationship between subduction crustal extension and magmatic composition of the southern oregon cascade volcanic arc volcanism in the study area at 7 4 ma consisted of calc alkaline basaltic andesite and andesite lava flowing over a relatively flat landscape local angular unconformities are evidence that basin and range extension began at by at least 4 ma and continues today with fault blocks tilting at a long term rate of 2 ma to 3 ma minimum nw se extension is 1 5 km over 28 km 5 high alumina olivine tholeiite haot or low k low ti transitional high alumina olivine tholeiite lklt erupted within and adjacent to the back edge of the calc alkaline arc as the edge receded westward at a rate of 10 km ma at 2 7 0 45 ma the volcanic front migrated east much slower than the back arc migrated west 0 km ma for 6 0 4 ma calc alkaline rocks 0 7 km ma if 6 ma haot lklt is included and 1 km ma if highly differentiated 17 30 ma volcanic rocks of the early western cascades are included declining convergence probably decreased asthenospheric corner flow decreasing width of calc alkaline and haot lklt volcanism and the associated heat flow anomaly the margins of which focused on basin and range extension and leakage of haot lklt magma to the surface this declining corner flow combined with steepening slab dip shifted the back arc west compensation of extension by volcanic intrusion and extrusion allowed growth of imposing range front fault scarps only behind the trailing edge of the shrinking arc

petrogenesis of cretaceous adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china implications for geodynamics and cu au mineralization both adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china are associated with cretaceous cu au mineralization the shaxi quartz diorite porphyrites exhibit adakite like geochemical features such as light rare earth element lree enrichment heavy ree hree depletion high al2o3 mgo sr sr y and la yb values and low y and yb contents they have low end t values 3 46 to 6 28 and high 87sr 86sr i ratios 0 7051 0 7057 sensitive high resolution ion microprobe shrimp zircon analyses indicate a crystallization age of 136 3 ma for the adakitic rocks most volcanic rocks and the majority of monzonites and syenites in the luzong area are k rich or shoshonitic and were also produced during the cretaceous 140 125 ma they are enriched in lree and large ion lithophile elements and depleted in ti and nb and ba and exhibit relatively lower end t values ranging from 4 65 to 7 03 and relatively higher 87sr 86sr i ratios varying between 0 7057 and 0 7062 the shoshonitic and adakitic rocks in the luzong area have similar pb isotopic compositions 206pb 204pb 17 90 18 83 207pb 204pb 15 45 15 62 and 208pb 204pb 38 07 38 80 geological data from the luzong area suggest that the cretaceous igneous rocks are distributed along ne fault zones e g tanlu and yangtze river fault zones in eastern china and were likely formed in an extensional setting within the yangtze block the shaxi adakitic rocks were probably derived by the partial melting of delaminated lower crust at pressures equivalent to crustal thickness of 50 km i e 1 5 gpa possibly leaving rutile bearing eclogitic residue the shoshonitic magmas in contrast originated mainly from an enriched mantle metasomatized by subducted oceanic sediments they underwent early high pressure 1 5 gpa fractional crystallization at the boundary between thickened 50 km lower crust and lithospheric mantle and late low pressure 1 5 gpa fractional crystallization in the shallow 50 km crust the adakitic and shoshonitic rocks appear to be linked to an intra continental extensional setting where partial melting of enriched mantle and delaminated lower crust was probably controlled by lithospheric thinning and upwelling of hot asthenosphere along ne fault zones e g tanlu and yangtze river fault zones in eastern china both the shoshonitic and adakitic magmas were fertile with respect to cu au mineralization

tectonothermal history of the schwarzwald ore district germany an apatite triple dating approach abstract exceptionally large u rich apatite from the schwarzwald ore district germany was triple dated using id tims u pb fission track ft and u th he dating methods the aim of adopting the multi dating approach on a single sample was to i further constrain thermo tectonic evolution of the schwarzwald from the formation of crystalline basement through to cooling and exhumation and ii test potential and limitations of in situ ft u th he double dating the apatite u pb age of 289 5 4 5 ma records the cooling of the basement through the 550 c during the early permian and brackets the age of the apatite hosting rhyolite between 289 5 4 5 ma and 314 6 ma which is the age of rhyolite hosting granite this is in excellent agreement with radiometric ages of related rhyolites and fits with the magmatic evolution of the schwarzwald during variscan orogeny in the eocene between 50 and 40 ma the basement resided at 100 c and then cooled to surface temperatures as revealed by the ft age 37 6 1 3 ma and thermal modelling results based on track lengths during the cooling event the basement was likely exhumed as a rift shoulder of newly formed upper rhine graben rift nine apatite grains yielded u th he ages from 30 7 1 5 to 65 0 2 6 ma mean age 45 7 1 3 ma three possible reasons for the lack of reproducibility are i non homogeneous distribution of parent isotopes evidenced by strong u zoning ii bad neighbourhood causing implantation of extraneous he and iii radiation damage leading to increased he retentivity implied by the high 250 ppm u concentration these problems could not be circumvented by mechanical abrasion of outermost rim of dated crystals which yielded u th he ages from 26 0 1 0 to 56 2 2 2 ma mean age 37 2 1 4 ma in situ ft and traditional u th he double dating of single apatite crystals revealed that the vast majority of u th he ages were younger than indistinguishable from or overlap within error with corresponding ft ages proving the robustness of this approach the results also show that apparent discrepancies between ft and u th he ages reported in the literature may arise simply as a result of statistical misconceptions and conventional data treatment considering the range of single grain ft ages and the oldest single grain ft age in addition to the central ft age may provide an effective basis on which to evaluate the viability of u th he data

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

cooling and exhumation of the mid jurassic porphyry copper systems in dexing city se china insights from geo and thermochronology the dexing porphyry copper and yinshan polymetallic deposits in dexing city southeastern china are both giant porphyry ore systems located 15 km apart they formed synchronously and share a similar magma source and metallogenic evolution but their metal endowment dominant rock types and alteration assemblages differ significantly in this contribution we investigate the cause of these distinctions through new molybdenite re os ages and zircon and apatite u th he thermochronology data dexing has a molybdenite re os age of 170 3 ma zircon u th he zhe ages of 110 to 120 ma and apatite u th he ahe ages of 7 to 9 ma in contrast yinshan has older zhe ages of 128 to 140 ma and an ahe age of 30 ma viewed in combination with previously published data we conclude that the apparently slow cooling experienced by these bodies is primarily a reflection of their experiencing multiple episodes of thermal disturbance we tentatively infer that both deposits were exposed in the late miocene or more recent time with the dexing deposit more deeply exhumed than yinshan our study has exploration implications for deeper porphyry style ores at yinshan and for porphyry deposits in non arc intraplate settings in general

mesozoic adakitic rocks from the xuzhou suzhou area eastern china evidence for partial melting of delaminated lower continental crust abstract adakitic rocks in the xuzhou suzhou area eastern china consist of dioritic and monzodioritic porphyries and were dated at 131 132 ma by the shrimp u pb zircon method these rocks have high mgo content 1 47 5 73 high mg values 0 49 0 61 and high la yb and sr y ratios these features are similar to rocks derived from partial melting of a subducted oceanic slab however their high initial 87sr 86sr 0 7053 0 7075 and low end t values 4 43 to 13 14 are inconsistent with the origin from slab melting these rocks often contain garnet residual crystals and eclogite garnet clinopyroxenite and garnet amphibolite xenoliths petrographical characteristics and estimated p t conditions of these xenoliths indicate that they were once deeply subducted and subsequently underwent rapid exhumation in the early mesozoic garnet residual crystals from the porphyries show similar chemical compositions to garnets from garnet clinopyroxenite and garnet amphibolite xenoliths ages of the inherited zircons of the xenoliths and their host rocks likely indicate that sources for the adakitic magma and protoliths of the eclogite and garnet clinopyroxenite xenoliths in the study area were from precambrian basement of the north china craton the data also suggest that the lower continental crust in the eastern north china craton was thickened during the early mesozoic and delaminated in the early cretaceous the high mg adakitic magma resulted from partial melting of this delaminated lower continental crust and its subsequent interaction with the mantle during upward transport leaving garnet as the residual phase

effective closure temperature in leaky and or saturating thermochronometers abstract the classical equation of closure temperature t c in thermochronometry dodson 1973 assumed i no storage limitation for the accumulating radiogenic product ii a negligible product concentration at the initial temperature of cooling t 0 and iii a negligible product loss at the final present day temperature t p a subsequent extension ganguly and tirone 1999 provided a simple correction for systems cooling from an arbitrary t 0 at which presence of an initial concentration profile may affect final concentrations here we use a combination of analytical and numerical solutions to derive a general expression for the effective closure temperature in i systems which cool between arbitrary initial and final temperatures potentially still suffering from thermal product loss at t p termed leaky and ii systems which may contain a physical limit on the maximum amount of product that can be stored termed saturating while all conservative results can be easily reproduced an extended use of our formulation provides meaningful effective closure temperatures even when the standard calculation schemes fail for a first order loss radiometric system governed by k t s exp e r t where e j mol 1 and s s 1 are the arrhenius parameters and r is the gas constant we find that the effective closure temperature t c t 0 t p is given by t c t 0 t p 1 t p r e k p ln 1 k p k p e k p k p k 0 1 where k 0 and k p s 1 are shorthand for k t 0 and k t p respectively s 1 the production rate s a time constant and a z the upper incomplete gamma function under conventional conditions our solution reduces to dodson s formula although the solution strictly applies only to systems where 1 t increases linearly with time it is nevertheless a useful approximation for a broad range of cooling functions in systems where closure occurs close to the system s initial final thermal boundary conditions we clarify the use and the meaning of t c t 0 t p by drawing a comparison between i a hypothetical application of apatite u pb dating t c 450 c on venus mean surface temperature of 450 c leaky behaviour and ii the recently introduced thermochronometric application of optically stimulated luminescence osl dating on earth both leaky and saturating behaviour

4he 3he thermochronometry using classical diffusion theory we present a mathematical technique for the determination of 4he concentration profiles in minerals this approach should prove useful for constraining the low temperature cooling histories of individual samples and for correcting u th he ages for partial diffusive loss the calculation assumes that the mineral of interest contains an artificially produced and uniform distribution of 3he obtained by proton irradiation shuster et al earth planet sci lett 217 2004 19 32 in minerals devoid of natural helium this isotope allows measurement of he diffusion coefficients in minerals with measurable radiogenic he it permits determination of 4he profiles arising during ingrowth and diffusion in nature the 4he profile can be extracted from stepwise degassing experiments in which the 4he 3he ratio is measured the evolution of the 4he 3he ratio as a function of cumulative 3he released can be compared with forward models to constrain the shape of the profile alternatively we present a linear inversion that can be used to directly solve for the unknown 4he distribution the inversion incorporates a standard regularization technique to filter the influence of random measurement errors on the solution using either approach we show that stepwise degassing data can yield robust and high resolution information on the 4he profile profiles of radiogenic he are a sensitive function of the time temperate t t path that a cooling sample experienced thus by step heating a proton irradiated sample it is possible to restrict the sample s acceptable t t paths the sensitivity of this approach was explored by forward modeling 4he profiles resulting from a range of realistic t t paths using apatite as an example results indicate that 4he profiles provide rich information on t t paths especially when the profiles are coupled with u th he cooling ages on the same sample samples that experienced only moderate diffusive loss have 4he concentration profiles that are rounded at the edge but uniform in the core of the diffusion domain such profiles can be identified by nearly invariant 4he 3he ratios after the first few to few tens of percent of 3he have been extracted by step heating we show how such data can be used to correct u th he ages for partial diffusive loss

the northwestern margin of the basin and range province part 1 reflection profiling of the moderate angle 30 surprise valley fault abstract seismic reflection profiling demonstrates that the active significant offset surprise valley fault that marks the western boundary of the basin and range province in northernmost california dips at a moderate angle only 30 to 2 km depth a nearby seismic refraction wide angle reflection profile albeit of lower resolution shows the fault plane remains approximately planar to at least 7 km depth variably tilted volcanic strata of known ages within the surprise valley basin demonstrate that 7 km of normal slip occurred along the surprise valley fault within the past 8 4 myr at a time averaged slip rate of 1 2 mm yr and that the fault rotated from an initial dip of as much as 60 to its present dip of 30 the rotation of this isolated fault was not accomplished by domino style rotation as seen elsewhere in the basin and range province but rather by flexural rift shoulder uplift aided by mid crustal flow

the cretaceous duimiangou adakite like intrusion from the chifeng region northern north china craton crustal contamination of basaltic magma in an intracontinental extensional environment abstract zircon u pb ages major and trace element and sr nd and pb isotope compositions of the duimiangou dmg quartz monzonite from the chifeng region on the northern north china craton ncc were studied to investigate its derivation evolution and geodynamic significance laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating yields an emplacement age of 128 1 ma for this intrusion with numerous mesozoic inherited zircons clustering at 219 12 ma and 161 3 ma along with some ancient zircons with ages of 2 5 ga 1 77 ga and 324 ma bulk rock analyses show that this intrusion is characterized by variable sio 2 63 4 69 4 wt al 2 o 3 14 5 16 3 wt na 2 o k 2 o 8 01 8 95 wt and mg 41 3 48 0 they are enriched in large ion lithophile elements and light rare earth elements without significant eu anomalies mostly between 0 89 1 10 and depleted in heavy rare earth elements and high field strength elements with high sr y 63 7 101 7 and la yb n 20 5 31 0 ratios the dmg intrusion formed in an intracontinental extensional setting contemporaneous with the formation of pull apart basins metamorphic core complexes and intense magmatism rather than in a convergent margin it has homogeneous sr 87 sr 86 sr i 0 7059 0 7066 nd e nd t 6 2 to 7 2 and pb 206 pb 204 pb i 17 289 17 375 207 pb 204 pb i 15 359 15 463 208 pb 204 pb i 37 130 37 472 isotope compositions sr nd isotope modeling results plus relatively young nd model ages 1522 1618 ma and the presence of relict zircons suggest that this intrusion could have originated from crustal contamination of newly formed basaltic melts derived from asthenospheric mantle accompanied by fractional crystallization of k feldspar biotite apatite fe ti oxides and minor hornblende and plagioclase thus the dmg adakite like intrusion may record the magmatic event associated with underplating of asthenospheric magma in an intracontinental extensional environment and both asthenospheric magma underplating and lithospheric delamination may have played important roles in the lithospheric thinning of the northern ncc

the reliability of uranium series mollusc dates from the western mediterranean basin abstract fossil mollusc shells from western mediterranean raised beach deposits have been dated using u series techniques sub sampling has allowed intra shell isotopic variability to be assessed although most of the calculated ages appear plausible and some internal consistency exists closer scrutiny of the data reveals that the shells have behaved as geochemically open systems and all the ages therefore must be considered suspect some previously published u series mollusc data from the same region may also contain evidence of open system behaviour and are considered equally unreliable simple modelling suggests considerable variation in isotopic uptake behaviour both within and between shells

two phase neogene extension in the northwestern basin and range recorded in a single thermochronology sample we use a combination of apatite 4 he 3 he u th he and fission track thermochronology to date slip on the surprise valley fault in northeastern california by analyzing a single sample from the warner range in the footwall of the fault this sample a granitic clast from a conglomerate yielded a fission track age of 11 6 2 8 ma and a u th he age of 3 02 0 52 ma geologic relationships indicate that this sample was buried to a depth of 3 3 km prior to exhumation during slip on the surprise valley fault fission track age and length data indicate that the sample was fully reset 120 c prior to exhumation which began sometime after 14 ma a single aliquot of nine apatite grains was step heated for 4 he 3 he analysis modeling of the resulting 4 he distribution indicates that cooling from 80 c to 20 c occurred between 3 and 1 ma interconsistent time temperature t t solutions to the combined 4 he 3 he u th he and fission track data require two distinct periods of cooling consistent with non continuous slip on the surprise valley fault early cooling and fault slip took place between 14 and 8 ma followed by more recent fault slip ca 3 ma this timing is consistent with both local geologic relationships and with the regional timing of faulting along the western margin of the basin and range province these data demonstrate the resolving power of combined fission track u th he and 4 he 3 he thermochronometric data to extract low temperature t t information from a single sample close to earth9s surface

trace element evidence for growth of early continental crust by melting of rutile bearing hydrous eclogite the early continental crust is composed dominantly of archean tonalite trondhjemite granodiorite ttg gneisses and is generally explained as the product of melting of metabasalts in the subducted crust however whether the melting occurs in shallow level amphibolite facies or in relatively deep eclogite facies is debated here i present experimental partition coefficients ds for 27 trace elements between garnet amphibole and tonalitic melts they are used together with published mineral melt trace element ds to model the melting of metabasalt in order to delimit the conditions for ttg production the results clearly show that model melts with trace element characteristics that completely mimic the ttg are in equilibrium with rutile bearing anhydrous and hydrous amphibole bearing eclogitic residues but not rutile free amphibole dominated residues rutile appears to be a necessary residual phase to account for the characteristic negative nb ta anomaly in the ttg these results thus suggest that the early continental material was produced under eclogite facies conditions based on the modeling results obtained using appropriate partition coefficients and the archean geotherm the preferred process for the ttg production is the melting of rutile bearing hydrous eclogite triggered by the release of h2o from the progressive breakdown of amphibole the pressure temperature p t conditions for ttg production via this process are constrained to 1 5 2 5 gpa 50 80 km and 850 1050 c by the p t stability boundaries of amphibole and rutile in the basalt system

molybdenum and boron isotopic compositions of porphyry cu mineralization related adakitic rocks in central eastern china new insights into their petrogenesis and crust mantle interaction

the northwestern margin of the basin and range province part 2 structural setting of a developing basin from seismic and potential field data abstract surprise valley in northeastern california offers an ideal opportunity to examine the structural setting of a developing extensional basin due to its late miocene to recent activity in isolation from other major normal fault bound basins seismic velocity and potential field modeling help determine the nature of basin fill and identify intra basin faults based on a detailed gravity and magnetic profile we identify shallow subsurface basalt flows and several faults within the valley that may accommodate hundreds of meters of vertical offset possibly cutting and offsetting the 30 east dipping surprise valley fault that rotated during footwall tilting of the adjacent warner mountains some of these intra basin faults correspond with mapped quaternary fault scarps but others have no surface expression these faults may represent the currently active fault system within the basin if so they would indicate that basin development is transitioning away from the main range front normal fault to a new set of steep intra basin faults that are more favorable for accommodating regional transtensional strain

the history of the monti sabatini and alban hills volcanoes groundwork for assessing volcanic tectonic hazards for rome abstract the volcanic rocks of rome provide chronostratigraphic constraint that is of use to geologists archaeologists and paleontologists identifying the areal distribution of these rocks their mode of emplacement and a detailed chronology of the eruptive events also is crucial for assessing local natural hazards in a volcanic tectonic context and for recognizing whether the volcanoes may erupt again in the future we have identified and dated many of the volumetrically significant eruptive units from the monti sabatini and alban hills colli albani and propose a formalized volcanic stratigraphy for rome it is probable that seismic events triggered some eruptions as several ignimbrites from the two volcanoes have statistically indistinguishable ages following a 200 kyr period of dormancy that was coincident with a pulse of regional uplift the alban hills appears to have begun recently circa 45 ka a new eruptive cycle therefore accurate assessment of volcanic tectonic hazards and estimation of possible future volcanic activity is necessary for the safety of the five million people living near these volcanoes

uranium series coral ages from the us atlantic coastal plain the 80 ka problem revisited abstract uranium series coral ages for emergent units from the passive continental margin us atlantic coastal plain acp suggest sea level above present levels at the end of marine oxygen isotope stage mis 5 contradicting age elevation relations based on marine isotopic or coral reef models of ice equivalent sea level we have reexamined this problem by obtaining high precision 230th 238u and 231pa 235u thermal ionization mass spectrometric ages for recently collected and carefully cleaned acp corals many in situ we recognize samples that show no evidence for diagenesis on the basis of uranium isotopic composition and age concordance combining new and earlier data among those ages close to or within the age range of mis 5 over 85 cluster between 65 and 85 ka bp of the corals that we have analyzed those that show the least evidence for diagenesis on the basis of uranium isotopic composition and age concordance have ages between 80 and 85 ka bp consistent with a mis 5a correlation the units from which these samples have been collected are all emergent and have elevations within 3 5 m of those few units where early stage 5 125 000 ka bp coral ages have been obtained the acp appears to record an unusual history of relative sea level throughout mis 5 a history that is also apparent in the dated coral record for bermuda we speculate that this history is related to the regional near to intermediate field effects of ancestral laurentide ice sheets on last interglacial shorelines of the western north atlantic

moderate rates of late quaternary slip along the northwestern margin of the basin and range province surprise valley fault northeastern california 1 the 86 km long surprise valley normal fault forms part of the active northwestern margin of the basin and range province in northeastern california we use trench mapping and radiocarbon luminescence and tephra dating to estimate displacements and timing of the past five surface rupturing earthquakes on the central part of the fault near cedarville a bayesian oxcal analysis of timing constraints indicates earthquake times of 18 2 2 6 10 9 3 2 8 5 0 5 5 8 1 5 and 1 2 0 1 ka these data yield recurrence intervals of 7 3 4 1 2 5 3 2 2 7 1 6 and 4 5 1 5 ka and an elapsed time of 1 2 0 1 ka since the latest surface rupturing earthquake our best estimate of latest quaternary vertical slip rate is 0 6 0 1 mm a this late quaternary rate is remarkably similar to long term 8 14 ma minimum vertical slip rates 0 4 0 5 0 3 mm a calculated from recently acquired seismic reflection and chronologic and structural data in surprise valley and the adjacent warner mountains however our slip rate yields estimates of extension that are lower than recent campaign gps determinations by factors of 1 5 4 unless the fault has an unusually shallow 30 35 dip as suggested by recently acquired seismic reflection data coseismic displacements of 2 4 5 1 m documented in the trench and probable rupture lengths of 53 65 km indicate a history of latest quaternary earthquakes of m 6 8 7 3 on the central part of the surprise valley fault

physicochemical processes in the magma chamber under the black mountain porphyry cu au deposit philippines insights from mineral chemistry and implications for mineralization the black mountain porphyry cu au deposit in the baguio district northern luzon philippines is associated with late miocene to pliocene intrusive rocks that retain primary crystallization signatures providing an excellent natural laboratory to study the details of magma chamber processes each igneous phase contains disequilibrium textures including resorptive textures in plagioclase and distinct core rim textures in amphibole high crystallization temperatures and pressures in felsic 880 c and 2 8 kbar and mafic 1 030 c and 7 7 kbar rocks recorded by amphibole phenocrysts reflect crystallization in the magma chamber amphibole in felsic rocks aged 6 39 0 49 to 2 83 0 23 ma have similar crystallization temperatures and pressures suggesting a long lived and hot felsic magma chamber under the black mountain deposit four independent oxybarometers including amphibole coexisting magnetite ilmenite magmatic anhydrite and zircon consistently show a high oxidation state of nno 1 for the felsic magma and nno 0 7 for the mafic magma element profiles across phenocrystic plagioclase display repeated oscillatory variations of ca fe and sr contents with large anorthite variations and a positive correlation between cao and feo the amphibole is classified as group 1 mg hornblende to tschermakite hornblende in felsic rocks and group 2 mg hastingsite in mafic rocks the group 1 amphiboles show a variety of major and trace element variations from core to rim in disequilibrated grains and transitional compositions to group 2 mg hastingsite both mineral textures and chemistry recorded by phenocrysts of plagioclase and amphibole indicate repeated mafic magma recharge in the felsic magma chamber the common occurrence of rounded or elongated sulfide inclusions in the megacrystic amphibole from the mafic rocks 2 81 0 15 ma suggests a greater enrichment of cu in mafic rocks relative to the ore forming porphyries 2 91 2 83 ma this is also consistent with higher cu contents 3 4 0 9 ppm in the megacrystic amphibole from the mafic rocks relative to amphibole in felsic rocks 1 0 0 2 ppm and may indicate up to 3 4 times higher cu in the mafic magma relative to felsic magma therefore large scale mafic magma recharge particularly at 2 8 ma likely introduced ore forming metals to the long lived felsic magma chamber further contributing to the fertility of the felsic rocks and ultimately to cu au mineralization at the black mountain deposit

thermochronological constraints on the timing and magnitude of miocene and pliocene extension in the central wassuk range western nevada apatite fission track and u th he thermochronological data provide new constraints on the timing of faulting and exhumation of the wassuk range western nevada where east dipping normal faults have accommodated large magnitude ene wsw oriented extension extensional deformation has resulted in the exhumation of structurally coherent fault blocks that expose sections of preextensional mostly granitic upper crust in the grey hills and central wassuk range these fault blocks display westward tilts of 60 and expose preextensional paleodepths of up to 8 5 km based on the structural reconstruction of tilted preextensional tertiary andesite flows that unconformably overlie mesozoic basement rocks apatite fission track and u th he thermochronological data from the fault blocks constrain the onset of rapid footwall exhumation at 15 ma fission track modeling results indicate rapid fault block exhumation occurred between 15 and 12 ma which is in agreement with miocene volcanic rocks that bracket the tilting history in addition fission track and u th he data suggest reduced rates of cooling following major extension as well as renewed cooling related to active high angle faulting along the present day range front starting at 4 ma thermochronological data from structurally restored fault blocks indicate a preextensional miocene geothermal gradient of 27 5 c km the thermochronological constraints on the timing of extensional faulting and the eruptive history in the wassuk range imply a model for extension where crustal heating and volcanism precede the onset of rapid large magnitude extension and where synextensional magmatism is suppressed during the highest rates of extension

geochronology structure and basin range tectonism of the warner range northeastern california the warner range of northeastern california is a north trending horst at the northwest margin of the great basin the 3 000 m thick bedrock section exposed in the southern part of the range is tertiary in age and it dips homoclinally 20 to 25 west southwest much of the section consists of volcanic rocks whose k ar ages range from about 32 m y near the base of the section to about 14 m y at the top rocks older than about 26 m y are principally andesitic lahars those between 26 and 17 m y are andesitic lava flows and rhyolitic welded ash flow tuffs and those younger than about 17 m y are principally basaltic and andesitic lava flows the homoclinal character of the warner section indicates that block faulting responsible for uplift and tilting of the range began after emplacement of the youngest exposed rocks drilling in the deeply alluviated graben adjacent to the eastern face of the range indicates that aggregate vertical offset across the range front fault is at least 3 600 m the difference in elevation between alluvium in the bottom of the deepest bore hole and the crest of the nearby part of the range thus vertical displacement has occurred at a minimum average rate of 26 cm 1 000 yr during the past 14 m y offset of alluvium along the eastern base of the range records the continuation of block faulting into holocene time the onset of block faulting somewhat less than 14 m y ago and the change in character of volcanic rocks from principally andesitic to principally basaltic in mid miocene time are similar to volcano tectonic events of a much broader region proposed by previous workers the warner range is remarkable for the nearly complete record of regional late cenozoic volcanic and tectonic events found within a single horst

formation of wulong mafic dikes via mixing of enriched lithospheric mantle derived and crustal magmas eastern north china craton abstractzircon u pb age and geochemical data are reported for the wulong dike swarms from the liaodong peninsula ne china the studied dikes include diorite lamprophyre and dolerite together with previous dating the diverse rocks have a peak age of ca 120 125 ma they are marked by inversely zoned phenocrysts with mg and cr rich rims and they exhibit mantle like signatures i e high mg cr ni associated with prominent subduction type element enrichments the early diorites have relatively radiogenic sr 0 7143 and less radiogenic nd to 11 0 isotopes coupled with high and variable mgo cr ni contents indicating that they were mainly derived from ancient lower crust with subordinate contributions of enriched lithospheric mantle the transitional lamprophyres are characterized by high rb sr ratios 0 22 0 54 but low initial 87sr 86sr ratios 0 7069 0 7093 moderate negative end t values 14 4 to 12 6 and low promantle elements such as mg cr ni reflecting that juvenile lower crust

numerical investigations of apatite 4he 3he thermochronometry apatite 4he 3he thermochronometry has the potential to constrain cooling histories for individual samples provided that several presently untested assumptions are valid here we simulate the sensitivity of 4he 3he spectra to assumptions regarding geometric model crystallographic anisotropy broken grain terminations parent nuclide zonation and the accuracy of results obtained from analyses of aggregates of multiple crystals we find that 4he 3he spectra obtained from a cylinder with isotropic diffusion are almost indistinguishable from those obtained from an equivalent sphere with an equivalent initial 4he distribution under similar conditions anisotropic diffusion from the cylinder can greatly bias 4he 3he spectra but only if diffusion is 10 times faster in the axial than the radial direction existing data argue against anisotropy of this magnitude we find that analysis of apatites with broken terminations will also bias 4he 3he spectra but not greatly so in contrast we find that zonation of a factor of 3 in parent nuclide concentration produces 4he 3he spectra that deviate substantially from the homogeneous model when parent nuclides are highly concentrated near the grain rim and or cooling is fast the resulting 4he 3he spectra will be readily identified as aberrant however more subtle zonation higher concentrations in the grain interior or samples that have cooled slowly regardless of zonation style can yield 4he 3he spectra that look acceptable but will lead to inaccurate thermochronometric interpretation if parent homogeneity is assumed finally we find that analysis of an aggregate of crystals with identical 4he distributions can yield 4he 3he spectra and diffusion arrhenius arrays that are very different from those that would be obtained on the individual crystals if even small variations in he diffusion exist among the grains overall our observations suggest that modeling tools that assume spherical geometry and isotropic diffusion are appropriate for interpreting apatite 4he 3he spectra however it is essential to analyze only individual crystals and to assess the degree of parent nuclide zonation in those crystals

cenozoic tectonic evolution of the white mountains california and nevada the white mountains represent the westernmost range of the central northern basin and range province they are situated to the east of the unextended sierra nevada and represent a crustal block that is bounded along its western flank by the high angle white mountains fault zone the fault zone accommodates up to 8 km of total dip slip displacement investigation of the structural and thermal history of the white mountains indicates a two stage cenozoic tectonic evolution preextensional miocene volcanic rocks preserved along the eastern side of the range unconformably overlie mesozoic granitic basement and currently dip up to 25 to the east recording the total cenozoic tilt of the crustal block apatite fission track and u th he thermochronological data indicate that the white mountains underwent rapid exhumation and eastward tilting in the middle miocene starting at ca 12 ma geologic mapping 1 10 000 fault kinematic analysis and dating of younger volcanic sequences show that following middle miocene east west extension the white mountains have been dominated by right lateral transtensional deformation related to the walker lane belt the eruption of late miocene and pliocene volcanic sequences in the eastern white mountains postdates the majority of the uplift of the range as evidenced by infilling of paleodrainages and the presence of east directed flow fabrics fault kinematic indicators from the white mountains fault zone are characterized by apparent overprinting of dip slip fault motion indicators by right lateral slickenfibers and fault striations demonstrating that the range bounding fault system along the western side of the white mountains was reactivated as a dextral strike slip fault system at the northern and southern ends of the range pliocene right lateral transtension along this northwest southeast trending fault systems resulted in the formation of northeast trending pull apart basins that truncate the mountain range and transfer strike slip displacement eastward from the owens valley fault zone to the fish lake valley fault zone the inception of strike slip faulting in fish lake valley occurred at ca 6 ma as constrained by late miocene volcanic units right lateral faulting on the western side of the white mountains occurred at ca 3 ma and is distinctly younger than the faulting in the fish lake valley area indicating a westward migration of transcurrent deformation through time

reconstruction of the mis 5 5 5 3 and 5 1 coastal terraces in latium central italy a re evaluation of the sea level history in the mediterranean sea during the last interglacial abstract we present a geomorphological stratigraphical and geochronological study reconstructing a suite of paleo surfaces in a 200 km long coastal sector of the central tyrrhenian sea between argentario and circeo promontories identification of the near shore deposits associated with these paleo surfaces allow us to define corresponding marine terraces and paleo sea levels 40ar 39ar and esr u th geochronologic constraints on key deposits provide correlation with the terraces previously recognized in the coast of central latium refining their correlation with the marine isotopic stages results of this study enable us to propose a re assessment of the ages for the sea level markers of mis 5 5 5 3 5 1 in the central tyrrhenian sea suggest that a continuous tectonic uplift with an average rate of 0 224 mm yr affects the latium coast since 200 ka provide new evidence for a mis 5 5 paleo sea level marker occurring at 35 m a s l on the coastal sector extending from montalto di castro to latina while it possibly drops down and connects to a paleo sea level ranging 10 5 m between monte circeo and gaeta previously attributed to this interglacial discussing possible evidence of similar elevation of the sea level during mis 5 5 5 3 and 5 1 interglacials in the tyrrhenian sea compare this datum with those from the western pacific and several coral reefs where the differences with respect to tectonically stable regions were attributed either to tectonics or to the glacial isostatic adjustment showing that the presented record of sea level markers may have a strong impact on modeling the post glacial effects in the mediterranean sea and on the paleoclimatic and paleoceanographic studies in this region

zircon u pb geochronology and hf isotopic compositions of the mesozoic granites in southern anhui province china abstract mesozoic magmatism is extensively developed in eastern china along the eastern asian continental margin but the geochronological framework is not well understood for each area in this study seventy eight samples were collected from the mesozoic igneous rocks in south anhui province east central china in order to precisely constrain their formation ages and contributions to crustal growth zircon u pb age determination using ion probe and laser ablation techniques indicate that magmatism in the area can be divided into two separate stages at 150 136 and 136 120 ma respectively the first stage of granitic rocks not documented in other areas of eastern china is mostly composed of hornblende bearing i type granodiorite and monzogranite and is considered to be formed by slab tearing during pacific subduction the second stage of magmatism coeval to that in other areas of eastern china is characterized by the occurrence of a type granite and syenite and their volcanic counterparts although i type granitic rocks are also developed locally these rocks are mostly distributed around and within the fault controlled volcanic basins and some are closely related to detachment shearing indicating their formation in an extensional setting zircon hf isotopic analyses indicate that archean material might be present in the area but that the main episode of crustal growth took place during the mesoproterozoic with very little juvenile material in the mesozoic

origin of mesozoic adakitic intrusive rocks in the ningzhen area of east china partial melting of delaminated lower continental crust to the best of our knowledge modern adakites have not been documented in a nonarc environment we report geochemical and isotopic data for early cretaceous anjishan adakitic intrusive rocks that are in a continental setting unrelated to subduction the anjishan adakitic intrusive rocks which are exposed in the ningzhen area of east china have high sr y and la yb ratios coupled with low yb and y as well as relatively high mgo contents and mg numbers mg 0 4 0 6 similar to products from slab melting however low n d t values 6 8 to 9 7 and high 8 7 sr 8 6 sr i 0 7053 0 7066 are inconsistent with an origin by slab melting the tectonics and geochemistry lead us to conclude that adakitic magmas were most likely derived from partial melting of mafic material at the base of the continental crust high sr y and la yb ratios of the adakitic intrusive rocks suggest that garnet was stable as a residual phase during partial melting implying that the crustal thickness exceeded 40 km in the early cretaceous the present thickness of the crust in the ningzhen area is only 30 km and therefore the crust appears to have been thinned by at least 10 km since the early cretaceous the relatively high mgo contents and mg of the anjishan intrusive rocks suggest that adakitic magmas interacted with mantle rocks possibly coinciding with lower crustal delamination which would also account for the observed thinning

uranium series ages of fossil corals from mallorca spain the neotyrrhenian high stand of the mediterranean sea revisited abstract the emergent marine deposits of the mediterranean basin have been recognized as an important record of quaternary sea level history for more than a century previous workers identified what have been interpreted to be two separate high stands of sea in the late quaternary namely the eutyrrhenian thought to be 120 ka and the neotyrrhenian thought to be either 100 ka or 80 ka on mallorca spain both of these named deposits lie close to present sea level implying paleo sea levels slightly above present during both marine isotope stages mis 5 5 5e and either 5 3 5c or 5 1 5a if these interpretations are correct they conflict at least in part with sea level records from far field localities we analyzed corals from the neotyrrhenian beds on mallorca which gave u series ages from 126 ka to 118 ka these ages are consistent with previously published amino acid data that show that the neotyrrhenian and eutyrrhenian deposits are not significantly different in age a fossil molluscan fauna from the neotyrrhenian deposits on mallorca has a warm water paleozoogeographic aspect with nine southward ranging species and four extralimital southern species when compared with sea surface temperatures obtained from planktonic foraminifera and alkenones from odp core 977 in the nearby alboran sea the only time period that shows comparable warmth is mis 5 5 5e consistent with the u series ages of corals from the neotyrrhenian deposits we propose that the neotyrrhenian deposits are a beachrock facies of the same age as the eutyrrhenian deposits this interpretation is consistent with the differences in physical sedimentology of the two deposits explains the u series and amino acid data indicating the same age is consistent with the very slight elevation difference of the neotyrrhenian and eutyrrhenian beds and explains the similar though not identical paleozoogeographic aspects of their fossil faunas

canyon incision and knickpoint propagation recorded by apatite 4he 3he thermochronometry abstract in many regions of the world deeply incised canyons demonstrate the net effects of physical processes active at earth s surface in response to surface uplift low temperature thermochronometry can constrain the timing and rates of bedrock incision which is necessary for relating canyon incision to surface uplift over geological timescales we analyzed four samples from the cotahuasi ocona canyon system in southwest peru using 4 he 3 he thermochronometry and we present a new inversion model to identify continuous low temperature cooling histories that are consistent with the observed data derived cooling histories limit the onset of fluvial incision to 13 to 8 ma this is in agreement with previously reported interpretations based on a three dimensional thermal model interpolation to a much larger set of conventional apatite u th he ages however because 4 he 3 he thermochronometry constrains an independent cooling history for each sample the results also permit testing of landscape evolution models with greater spatial variability in exhumation compared to those models that can be tested by a geographically scattered set of conventional u th he ages the different cooling histories of the four samples require asynchronous incision along at least part of the canyon system that is best explained by headward propagation of fluvial incision by knickpoint migration

a tectono genetic model for porphyry skarn stratabound cu au mo fe and magnetite apatite deposits along the middle lower yangtze river valley eastern china abstract the middle lower yangtze river valley metallogenic belt yrb situated along the northern margin of the yangtze craton is characterized by porphyry skarn stratabound cu au mo fe deposits in the areas of uplift and magnetite apatite deposits in cretaceous fault basins following detailed field investigations and a review of published data we recognize two episodes of magmatism and mineralization in the yrb 1 156 137 ma high k calc alkaline granitoids associated with 148 135 ma porphyry skarn stratabound cu au mo fe deposits and 2 135 123 ma shoshonitic series associated with 134 9 122 9 ma magnetite apatite deposits a type granitoids and associated alkaline volcanic have a small age range from 126 5 to 124 8 ma and are temporally spatially and genetically associated with the second episode the geodynamic history of the yrb did not experience the paleozoic to mesozoic lithospheric thickening that took place in the north china craton this process is inferred to be linked to partial melting of the delaminated lower crust at high pressures resulting in the development of c type adakitic rocks the petrochemical and sr nd isotopic data show that both the shoshonitic series and a type granitoids are quite different from adakites with only some of the k calc alkaline granitoids having adakitic signatures previous ore genesis models were established based on an assumed relationship with adakites and a continuous tectono thermal evolution from 150 to 100 ma all data obtained for the middle lower yangtze river region consistently show that the tan lu regional strike slip fault zone initiated at 233 6 to 225 6 ma from the collision between the north china and yangtze cratons and was reactivated at ca 160 ma the tan lu fault was caused by the oblique subduction of the izanagi plate which along the yrb the low angle subducted slab and the overlying crust was disrupted or broken due to the disharmonious movement of the two blocks the high k calc alkaline granitoids magmas were derived from melting of the subducted slab with some input of crustal material these magmas were emplaced at the intersections between ne and ew trending faults and formed porphyry skarn stratabound cu au mo fe deposits between 156 and 137 ma after 135 ma the subducted plate changed its direction of motion to northeast now running parallel to the eurasian continental margin and leading to large scale continental extension the shoshonitic series and subsequent a type granitoids magmatism and the development of magnetite apatite ores in the yrb took place in both fault basins and ne trending rifts between 135 and 124 ma

magma mixing in the kalaqin core complex northern north china craton linking deep lithospheric destruction and shallow extension abstract the widespread mesozoic magmatism in the north china craton ncc has received considerable attention as a trigger for large scale lithospheric destruction here we investigate the early cretaceous jiguanzi adamellite from the northern part of the ncc which is contemporaneous with shallow extensional deformation and deep lithospheric destruction this intrusion emplaced at ca 133 ma is located in the foot wall of the kalaqin metamorphic core complex mcc and occurs as a synextensional ring complex with numerous magmatic equigranular group 1 and porphyritic group 2 enclaves hornblende and plagioclase from the host adamellite and xenocrysts of group 2 enclaves show distinct inverse zoning with mg and ca rich mantle the group 2 enclaves are characterized by plagioclase xenocrysts hosting hornblende biotite and apatite inclusions quartz ocelli with fine grained rim enriched in biotite and hornblende and poikilitic biotite surrounded by hornblende geochemically the host intrusion is calc alkaline to alkaline and metaluminous with variable contents of sio 2 60 70 72 20 wt al 2 o 3 14 19 17 22 wt na 2 o k 2 o 6 16 9 42 wt and mg values 28 0 47 7 whereas the group 2 enclaves exhibit low sio 2 54 05 55 55 wt high fe 2 o 3 8 18 8 64 wt and tio 2 2 08 2 28 wt and moderate mg 44 0 44 1 both the host intrusion and group 2 enclaves are enriched in large ion lithophile and light rare earth elements and depleted in high field strength elements and heavy rare earth elements except that the latter has lower ba and high nb ta and ti contents the major and trace element contents of the group 1 enclaves are broadly similar to those of the host intrusion analyses of sr nd hf isotopes in the host intrusion and in group 1 and group 2 enclaves show 87 sr 86 sr i host 0 70600 0 70618 e nd t host 8 2 to 9 6 t 2dm nd host 1592 1706 ma e hf t host 9 2 to 12 0 87 sr 86 sr i group 1 0 70590 0 70635 e nd t group 1 9 6 to 10 4 t 2dm nd group 1 1705 1775 ma 87 sr 86 sr i group 2 0 70586 0 70587 e nd t group 2 0 6 to 0 7 t 2dm nd group 2 971 978 ma and e hf t group 2 4 5 to 10 0 the mineralogical and geochemical features suggest that the host jiguanzi adamellite and group 2 enclaves were generated through synchronous mixing and fractional crystallization accompanied by mechanical and chemical exchanges the group 1 enclaves showing cogenetic affinity with their felsic host represent the mechanical concentrations of mafic minerals and accessory phases from evolved hybrid host magma magma sources of the host jiguanzi adamellite and its group 1 enclaves are dominated by lower crust lcc components whereas those for the group 2 enclaves are dominated by metasomatized lithospheric mantle the magma genesis involved complex multi stage crust mantle interaction processes including 1 lithospheric mantle modification induced by triassic subduction of the paleo asian ocean slab and or triassic cretaceous asthenospheric melt underplating and 2 melting of the ancient lcc and lithospheric mantle and hybridization of mantle and crust derived melts in conjunction with regional geological and geochemical data we argue that the late jurassic early cretaceous shallow extension events represented by the kalaqin mcc triggered deep seated multi stage magmatism and lithospheric destruction and the continuous generation of magma further strengthened the extension and result in more extensive lithospheric thinning

retracing the quaternary history of sea level changes in the spanish mediterranean atlantic coasts geomorphological and sedimentological approach abstract this study analyses coastal geomorphic responses to the various sea level changes that occurred throughout the quaternary period in the mediterranean and atlantic coasts of spain particular emphasis is paid to the geomorphic and stratigraphic record of the changes in amplitude duration and frequency associated with the major gradual climate changes observed in marine cores and ice oxygen isotope records during the early and middle pleistocene ca 2 6 myr ca 1 4 0 8 myr ca 0 4 0 2 myr and also with the rapid and abrupt late pleistocene and holocene climate changes with this aim the best preserved and most complete sedimentary sequences known in the spanish mediterranean and atlantic coasts covering diverse geodynamic and climatic contexts were selected and analyses this study is mainly based on field investigation of geomorphic sedimentologic and stratigraphic features of mapped morphosedimentary units combined with reliable chronological data the analyses include the interpretation of sedimentary environments the 3 d reconstruction of facies and morphosedimentary unit arrangement paying special attention to the lateral geomorphic relationships between marine and terrestrial morphosedimentary units developed during interglacials under sea level highstand scenarios the interglacials occurred during four key quaternary periods might be related with major gradual changes associated with glacial climate cycles reported from marine and ice oxygen isotope records almost coeval changes in geomorphological styles are reported from all studied areas regardless of their specific geodynamic context results from the mediterranean realm suggest that this area is more sensitive to climatic and sea level variability than the spanish atlantic coast particularly in the case of rapid and abrupt changes

early cretaceous low mg adakitic granites from the dabie orogen eastern china petrogenesis and implications for destruction of the over thickened lower continental crust it is generally accepted that the low mg adakitic rocks were derived from the partial melting of metabasalts eclogites in this study we demonstrate that the early cretaceous low mg adakitic granites in the north dabie complex ndc were generated by the partial melting of the ndc orthogneisses here we present in situ u pb and lu hf isotopes in zircon with whole rock geochemical and sr nd isotopic compositions were carried out for the tiantangzhai porphyritic monzogranites from the dabie orogen eastern china the monzogranites are characterized by high sr 576 988 ppm low y 7 3 19 0 ppm and depletion in hree yb 0 50 1 78 ppm thus resulting in high sr y 34 3 135 2 and la yb n 17 0 105 2 ratios without a negative eu anomaly they also exhibit high sio2 66 5 73 5 wt and k2o 2 7 4 7 wt and low mgo 0 4 1 6 wt or mg 28 2 45 3 mostly 40 values whole rock geochemical compositions suggest that the monzogranites represent low mg adakitic rock with high si and rich k features equilibrated with residues rich in garnet sr nd isotopic compositions end t 16 2 to 20 3 87sr 86sr i 0 707798 0 708804 tdm2 nd 2 3 2 6 ga of the monzogranites are distinct from that of the eclogites and amphibolites in the dabie orogen but similar to that of the neoproterozoic 700 800 ma gneisses in the ndc u pb dating of zircons gives a consistent age of 130 0 3 4 ma with discordia upper intercept age of 716 34 ma for inherited cores identified by cl imaging correspondingly in situ lu hf analyses of early cretaceous young age spots from zircons yield initial 176hf 177hf ratios from 0 281898 to 0 282361 ehf t values from 28 1 to 17 6 and two stage crust hf model ages tdm2 from 2293 89 to 2949 108 ma which are generally in agreement with values of 0 281891 to 0 282218 28 2 to 11 7 and 1927 87 to 2963 92 ma for the pre mesozoic inherited cores respectively as for individual core rim pairs in zircon th u ratios increase from the inherited cores to the young growth rims possibly due to variable degrees of partial melting whereas 176lu 177hf ratios greatly decrease because of the garnet effect in residues thus we suggest that the early cretaceous low mg adakitic granites were derived from the partial melting of the ndc neoproterozoic 700 800 ma gneisses and the foundering of the garnet bearing residues could have caused the destruction of the over thickened lower continental crust

magma differentiation and mineralisation in the siberian continental flood basalts new major trace element and sr and nd isotope data are presented for selected lavas from the three uppermost formations in the siberian trap and on over 60 samples of the associated intrusive rocks the lavas from a 1400 m section are remarkably homogeneous and apart from four samples of basaltic andesites sio2 48 4 49 6 mgo 8 1 6 3 and mg 54 58 tio2 1 05 1 6 sr 1 7 and nd 3 8 1 3 there is no significant depletion in ni and cu or coupled increase in sio2 and la sm which so characterise the underlying nadezhdinsky formation rocks the intrusive rocks are considered in 5 groups following naldrett et al the alkaline rocks group 1 dolerites with a range of ti contents groups 2 and 3 and differentiated intrusions not associated with ore junctions group 4 all exhibit restricted initial sr and nd values of 3 32 and 3 5 to 3 2 respectively in contrast the intrusions related to ore junctions noril sk and lower talnakh types 5a and 5b trend towards higher sr and lower nd with sr 17 59 and nd 2 9 to 3 4 in the noril sk type and 41 66 and 3 7 to 6 2 respectively in the lower talnakh type the roles of crustal contamination and partial melting in the continental mantle lithosphere are briefly reviewed a minimum of three components are required to explain the basalt data which are therefore inconsistent with simple mixing between plume derived magmas and crustal material rather magmas were derived from both the mantle lithosphere and the underlying asthenosphere and crustal contamination modified the composition of specific magma types the minor and trace element characteristics of the contaminant appear to have been similar to those of an inferred deep seated crustal melt rather than an upper crustal melt or a bulk sediment the between suite variations in the intrusions are similar to those in the lavas but in addition there are within suite variations attributed to late stage open system differentiation within the noril sk and lower talnakh type intrusions in the preferred model in which sulphide precipitation occurred in response to the crustal contamination processes responsible for the elevated la sm and lower nd of the lower talnakh and nadezhdinsky rocks sulphide precipitation took place before the crystallization of the silicate phases currently preserved in the intrusive rocks

faulting in a propagating continental rift insight from the late miocene structural development of the abert rim fault southern oregon usa abstract new geological mapping and 40ar 39ar ages reveal a temporal progression of faulting along a major extensional fault the abert rim fault at the active margin of the basin and range province in the western u s the onset of extensional deformation near lake abert coincided with widespread basaltic volcanism fault cross cutting relationships and tilt of volcanic layers demonstrate that nw striking faults formed between 8 9 and 7 5 ma and were subsequently cut by the nne striking abert rim fault sequential restoration of cross sections indicate that the abert rim fault south of 42 40 n latitude had 250 m of stratigraphic separation prior to deposition of the rattlesnake tuff at 7 ma low values of net extension 4 and long term rates of geologic deformation 1 mm yr suggest that regional extension since 10 ma has occurred primarily by diking we model province wide along and across strike expansion within the margin of the basin and range province as regional dilation accompanying northward propagation of the walker lane transform the growth of this extensional province is superimposed on a previously unrecognized early miocene volcanic landscape marked by volcanism between 21 4 and 22 3 ma dike orientations within one of these early miocene volcanoes and evidence for the existence of as much as 500 m of paleo topography prior to widespread deposition of the steens basalts at 16 ma suggests that late miocene faults near lake abert may reactivate an older structural fabric

from coseismic offsets to fault block mountains in the basin and range extensional province of the western united states coseismic offsets under the influence of gravity display predominantly subsidence of the basin side fault hanging wall with comparatively little or no uplift of the mountainside fault footwall a few decades later geodetic measurements gps and interferometric synthetic aperture radar insar show broad 100 km aseismic uplift symmetrically spanning the fault zone finally after millions of years and hundreds of fault offsets the mountain blocks display large uplift and tilting over a breadth of only about 10 km these sparse but robust observations pose a problem in that the coesismic uplifts of the footwall are small and inadequate to raise the mountain blocks to address this paradox we develop finite element models subjected to extensional and gravitational forces to study time varying deformation associated with normal faulting stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift which is predicted to take place within one to two decades after each large earthquake thus the best preserved topographic signature of earthquakes is expected to occur early in the postseismic period

a new age within mis 7 for the homo neanderthalensis of saccopastore in the glacio eustatically forced sedimentary successions of the aniene river valley rome abstract field observations as well as borehole sedimentological and geochronologic data allow us to reconstruct the geologic setting of the aniene river valley in northern rome framing it within the recently recognized picture of temporally constrained glacio eustatically forced aggradational successions of this region the sedimentary successions cropping out in this area include those described in the literature of the early 20th century in saccopastore where two skulls of homo neanderthalensis were recovered based on the geometry elevation and sedimentologic features of the investigated sedimentary deposits the stratigraphic record of saccopastore is correlated with the aggradational succession deposited in response to sea level rise during glacial termination iii at the onset of mis 7 i e 250 ka corresponding to the local vitinia formation as opposed to previous correlation with the mis 5 interglacial and a locally defined tyrrhenian stage 130 ka this previous attribution was based on the interpretation of the sedimentary succession of saccopastore occurring between 15 and 21 m a s l as a fluvial terrace formed around 130 ka during the riss wurm interglacial ca 6 m above the present day alluvial plain of the aniene river in contrast to this interpretation a 40ar 39ar age of 129 2 ka determined for this study on a pyroclastic flow deposit intercalated in a fluvial lacustrine sequence forming a terrace 37 m a s l near the coast of rome constrains the aggradational succession in this area to mis 5 precluding the occurrence of an equivalent fluvial terrace at lower elevation in the inland sector of saccopastore we therefore interpret the stratigraphic record of saccopastore as the basal portion of the aggradational succession deposited in response to sea level rise during mis 7 whose equivalent fluvial terrace occurs around 55 m a s l in this region we also review the published paleontological and paleoethnological records recovered in saccopastore and demonstrate their compatibility with the faunal assemblages and lithic industries occurring in the sedimentary deposits of the vitinia formation while we show the lack of any unequivocal late pleistocene mis 5 affinity we therefore propose that the chronostratigraphic position of the saccopastore deposits containing the two skulls should be around 250 000 years as opposed to a previously preferred age of 130 000 years the revised age makes these skulls the oldest italian occurrences of h neanderthalensis and provides evidence for a substantially coeval appearance and evolutionary path with respect to central northern europe

the early paleozoic xitieshan syn collisional granite in the north qaidam ultrahigh pressure metamorphic belt nw china petrogenesis and implications for continental crust growth abstract syn collisional magmatism produced by partial melting of subducted oceanic and continental crust during the continental collision plays an important role in understanding the orogenic evolution and crustal growth this contribution reports zircon la icpms u pb ages and hf isotopic compositions whole rock major and trace elements and sr nd isotopic compositions of syn collisional xitieshan intrusion within the north qaidam ultrahigh pressure metamorphic uhpm belt to study its petrogenesis and contribution to continental crust growth la icpms zircon u pb dating of the xitieshan granite yields magmatic crystallization ages of 441 2 ma and 442 2 ma which are consistent with the peak age of ultrahigh pressure eclogite facies metamorphism in the xiteishan terrane the temporal correlation between them confirms that the xitieshan granite was products of syn collisional magmatism during the continental collision between qaidam and qilian blocks these granites show high k calc alkaline and slightly peraluminous signature low zirconium saturation temperatures and high contents of k2o with the s type characteristics they have rare earth element and trace element patterns resembling those of bulk continental crust with strong fractionation of light and heavy rare earth elements la yb n 19 26 moderately eu negative anomalies eu 0 65 0 71 and the obviously nb ta p and ti negative anomalies the xitieshan granite also exhibits remarkable sr nd isotopic differences initial 87sr 86sr 0 70920 0 71080 and end t 4 54 4 11 from the contemporaneous granites within north qaidam uhpm belt combined with the positive ehf t 0 5 5 3 and ages of inherited zircons 475 518 ma the magmatism is best explained as resulting from melting of subducted oceanic and continental crust during continental collision isotopic mixing calculations suggest that ca 28 35 ocean crust and ca 65 72 continental materials contribute to the origin of the xitieshan granite thus the syn collisional felsic magmatism represents juvenile crust with input of oceanic crustal materials derived from the depleted mantle and the hypothesis continental collision zones are primary sites for net continental crust growth is applicable in the north qaidam

hematite fault rock thermochronometry and textures inform fault zone processes abstract minerals on fault surfaces record fluid rock interaction strain and or heat during fault slip fault hosted hematite is amenable to u th he he thermochronometry hematite he dates reflect fault related processes or exhumation depending on hematite growth above or below the grain size controlled closure temperature and processes that promote open system behavior deconvolving these phenomena requires multi scale hematite textural characterization and constraints on the ambient thermal history from conventional thermochronometry two examples of this approach include investigations of hematite coated fault surfaces from exhumed damage zones in the seismically active wasatch fault zone wfz ut and painted canyon fault pcf paralleling the southern san andreas fault mecca hills ca wfz fault mirrors preserve sub m scale polygonal grain textures and hematite he data patterns that together with host rock apatite he data are consistent with localized friction generated heat hematite he loss and hematite recrystallization during damage zone seismicity

contrasting geochemical and sm nd isotopic compositions of archean metasediments from the kongling high grade terrain of the yangtze craton evidence for cratonic evolution and redistribution of ree during crustal anatexis abstract twenty three clastic metasediments from the kongling high grade terrain of the yangtze craton south china were analyzed for major trace and rare earth elements and sm nd isotopic ratios associated dioritic tonalitic trondhjemitic dtt and granitic gneisses as well as amphibolites were also analyzed in order to constrain provenance the results show that the clastic metasediments can be classified into 3 distinct groups in terms of mineralogical geochemical and sm nd isotopic compositions group a is characterized by having no to slight negative eu anomalies eu eu 0 82 1 07 being high in cr 191 396 ppm and ni 68 137 ppm and low in th 3 3 7 8 ppm and ree ree 99 156 ppm these characteristics are similar to those of metasediments from archean greenstone belts in addition the group a metasediments have the value of the chemical index of alteration ciw close to felsic gneisses their sm nd isotopic ree and trace element compositions can be interpreted by mixtures of the dtt gneisses and amphibolites dating of detrital zircons from 2 group a samples by shrimp reveals a major concordant age group of 2 87 3 0 ga which is identical to the age of the trondhjemitic gneiss these results strongly suggest that group a was principally the first cycle erosion product of the local kongling dtt gneiss and amphibolite moreover the higher than amphibolite cr content and slight eu depletion exhibited by some samples from this group infer that ultramafic rocks like komatiite and granite of probably 3 0 3 3 ga in age also played a role group b is characterized by the presence of graphite and shows a more evolved composition similar to post archean shales with a prominent negative eu anomaly eu eu 0 48 0 77 and high ciw on paired cr th vs la co and co th plots group b samples conform to a two end member mixing line of the kongling granitic gneiss and amphibolite however data on nd model age and ciw suggest that the granite component should be younger than the sampled granitic gneiss and derived from a distal source both groups a and b exhibit a clear positive correlation between ciw and tdm and a negative one between ciw and eu eu these correlations point to the crustal evolution of the yangtze craton towards coupled increasing ciw and eu depletion with decreasing age this in turn reflects the change of granitoid magmatism from local na rich dioritic tonalitic trondhjemitic rocks to widespread k feldspar granite the change led to the intracrustal differentiation stabilization and growth of the craton group c is restite and contains abundant sillimanite and garnet and unusually high ilmenite 7 11vol which can be seen to be dehydration melting products of biotite under the microscope this group shows extremely varied ree distributions from lree enriched to depleted and from negative to strong positive eu eu 1 63 eu anomalies compared to groups a and b group c is severely depleted in na2o k2o lree rb and ba whereas tio2 co v sc and hree and y are considerably enriched this is accompanied by anomalous high sm nd 0 21 0 28 147sm 144nd 0 1361 0 1738 and 143nd 144nd 0 511589 0 511958 ratios tdm correlates clearly with sm nd ratio and 2 out of 3 samples give significantly older to unrealistic tdm 3 9 4 9 ga the results document redistribution of ree and an open behavior of the sm nd isotope system during the biotite dehydration melting of metasediments

evolution of the hongzhen metamorphic core complex evidence for early cretaceous extension in the eastern yangtze craton eastern china we conducted structural and geochronological studies on the hongzhen metamorphic core complex in the eastern yangtze craton the hanging wall of the hongzhen metamorphic core complex consists of neoproterozoic to permian unmetamorphosed strata which were folded during nw se shortening in the middle triassic and cretaceous terrestrial basins the exposed paleoproterozoic dongling complex in the footwall is widely overprinted by a detachment ductile shear zone which has consistent sw plunging mineral elongation lineations and top to the sw shear indicators analysis of the mesostructures microstructures and quartz c axis fabrics indicates that they formed within a low angled sw dipping extensional shear zone at midcrustal levels four muscovite grains separated from mylonites within the shear zone yielded 40 ar 39 ar plateau ages ranging from 128 5 1 0 ma to 126 1 1 1 ma they are interpreted as cooling ages of the shear zone associated with the hongzhen metamorphic core complex we propose that the hongzhen metamorphic core complex was initiated as a midcrustal low angle extensional shear zone with top to the sw shear sense at ca 145 ma and the shear zone was then warped and uplifted by the emplacement of the hongzhen granite at 122 ma brittle normal faulting and basin rifting in the hanging wall also developed during the formation of the hongzhen metamorphic core complex but these processes continued until the late cretaceous this study of the hongzhen metamorphic core complex demonstrates that the eastern yangtze craton was also involved in the early cretaceous extension widely occurring in the eastern china continent a ne sw extensional direction during the early cretaceous is indicated by the hongzhen metamorphic core complex

high sr y arc magmas and porphyry cu mo au deposits just add water porphyry cu mo au deposits are commonly associated with intermediate composition arc related igneous rocks with high sr y and la yb ratios and such rocks are equated by some researchers with melts derived from subducted oceanic crust undergoing eclogite facies metamorphism adakites however similar geochemical characteristics are readily developed in normal asthenospheric mantle wedge derived magmas by fractionation of amphibole and or garnet and or by interaction with crustal materials during ascent through the upper plate lithosphere while there is widespread evidence for such fractionation and contamination processes in porphyry magmas there is little direct evidence for an origin by slab melting the enhanced fertility of arc magmas relates primarily to their high water content which is required for the formation of magmatic hydrothermal systems upon shallow crustal emplacement magmatic water contents 4 wt percent h 2 o cause abundant amphibole garnet fractionation but suppression of plagioclase crystallization at deep crustal levels resulting in increasing sr y and la yb ratios with differentiation commonly into adakitic ranges but not reflecting slab melting additional factors that affect arc magma fertility are relatively high oxidation states and sulfur content but these are secondary to the requirement for sufficient water thus arc magmatic suites with high sr y ratios and evidence for the presence of hydrous phenocryst phases hornblende and or biotite are indeed prospective for porphyry cu mo au deposits but only because these parameters indicate high magmatic water content