1 88 ga sao gabriel amcg association in the southernmost uatuma anaua domain petrological implications for post collisional a type magmatism in the amazonian craton abstract in the southernmost uatuma anaua domain central amazonian craton brazil crop out 1 98 ga basement inliers represented by meta leucosyenogranites and amphibolites igarape canoas suite 1 90 1 89 ga high k calc alkaline granitoids agua branca suite a 1 88 1 87 ga alkali calcic a type volcano plutonic system iricoume mapuera tonian sio2 satured alkaline granitoids 1 45 1 25 ga orthoderived metamorphic rocks jauaperi complex and orosirian upper triassic mafic intrusions new data on petrography multielementar geochemistry in situ zircon u pb ages and nd and hf isotopes of alkali calcic a type granites sao gabriel granite mapuera suite and related rocks are indicative of a 1 89 1 87 ga volcano plutonic system integrated to the sao gabriel amcg association its magmatic evolution was controlled by the fractional crystallization combined with magma mixing and cumulation processes nd isotope values endt values 3 71 to 0 51 and nd tdm model age 2 44 to 2 12 ga and u pb inherited zircon crystals 2115 22 ma 2206 21 ma 2377 17 ma 2385 17 ma of the sao gabriel system indicate a large participation of siderian rhyacian crust granite greenstones and granulites and small contribution of rhyacian mantelic magma ehft values 5 2 to 5 8 and hf tdm ages 3 27 2 14 ga also point to contribution of paleoarchean rhyacian crustal melts and small participation of siderian rhyacian mantle melts residual melts from the lower crust have been mixed with basaltic melts generated by partial melting of the subcontinental lithospheric mantle peridotite in a post collisional setting at 1 89 1 87 ga the mafic melts of such a mixture could have been originated through partial melting of residual ocean plate fragments eclogites which ascended onto a residual mantle wedge hornblende peridotite and melted it resulting in modified basaltic magma which by underplating led heat to the anatexis of the lower continental crust this widespread alkali calcic a type magmatism was caused by destabilization and magmatic reactivation in the ventuari tapajos and central amazonian provinces resulting from the ventuari tapajos collision periods younger igneous reactivations have been registered at 1 45 to 1 25 ga 1 0 ga and 100 ma culminating with the production of mafic and felsic alkaline magmas along of the northern border of the amazon basin

ferro potassic a type granites and related rocks in ne poland and s lithuania west of the east european craton the present study of monzodiorite quartz monzodiorite monzonite quartz syenite granodiorite and rapakivi like granite surrounding the suwalki ketrzyn and sejny anorthosite norite and gabbro plutons or forming separate bodies in northern poland and southern lithuania has resulted in the recognition of a specific suite with amcg affinity the bodies belonging to the mazury and veisiejai complexes are aligned to e w trending lineaments in southern lithuania and northern poland with a continuation through the baltic sea into south central sweden in the west and into nw belarus in the east the rocks of the suite form a continuous series ranging from 45 to 75 sio2 with no indication of the classical daly gap between mafic and felsic rocks the mazury and veisiejai complexes chemically belong to the ferro potassic alkali calcic type of rocks and are comparable with the amcg suite e g in rogaland southern norway the most acidic varieties of the granitoids approach the classic rapakivi granites in their petrogenetic characteristics elevated contents of incompatible elements and ree and hence have a type affinities the granitoids are assigned to the post collisional granite field the overall evolution from mafic to acidic rocks is characterized by well defined trends which most probably represent a liquid line of descent fractional crystallization with or without assimilation and hybridization can account for the continuous evolution from mafic to acidic members the formation of the suite is concentrated in the timespan covering almost 50 myr from 1 55 to 1 5 ga the most felsic rocks yield ages of ca 1 5 ga which are very similar to the kabeliai granites further east in southeastern lithuania cooling and local mylonitization proceeded until 1 4 ga hornblende and biotite 40 ar 39 ar ages

boundary lines within petrologic diagrams which use oxides of major and minor elements use of some petrologic diagrams applied to analyses of volcanic rocks is unnecessarily difficult due to lack of data for construction of discriminant lines between rock series coordinates are provided for sufficient points to enable accurate plotting of the boundary lines within seven diagrams viz 1 tas total alkalies na2o k2o vs sio2 2 k2o vs sio2 3 afm 4 jensen 5 ktp k2o tio2 p2o5 6 fms feo mgo vs sio2 and 7 taktip k2o na2o k2o vs tio2p2o5 different versions of these boundaries are collated to indicate their variable position and it is demonstrated that inter laboratory analytical precision suffices to account for almost all of their spread on the tas and k2o vs sio2 diagrams

eastward tectonic migration and transition of the jurassic cretaceous andean type continental margin along southeast china abstract a mesozoic andean type active continental margin is believed to have developed along the southeast china continental margin which has been investigated in detail however the architecture and evolution of its retroarc arc forearc system which is important for us to understand the interaction or connection between continental and oceanic lithospheres are ambiguous using multiple disciplinary data comprising seismic profiles field observations and numerical paleo topographies this study synthetically focused on the jurassic cretaceous evolution and geodynamics of the andean type southeast china continental margin subduction of the paleo pacific plate was initiated during the early jurassic 200 ma generating a nne striking jurassic magmatic arc along the east china sea bounded by imbricate thrust faults on both sides and coinciding with a paleo topographic coastal mountain range while the jurassic arc erupted along an ene striking triassic suture zone in the northern south china sea dominated by the tethyan tectonic domain and overprinted by the pacific tectonic domain the jurassic coastal mountain range began to collapse and transited into a rift basin at 135 ma and then the andean type continental margin gradually switched to the western pacific type during the late cretaceous 100 72 ma accompanied by jurassic thrust faults inverting into cretaceous detachment faults and magmatic arc migrated eastward to the taiwan rukyu areas such eastward tectonic migration and transition is associated with the eastward retreat of the subducted paleo pacific slab then a regional latest cretaceous 72 66 ma compression prevailed southeast china probably related to ridge subduction when the pacific plate replaced the paleo pacific plate to subduct beneath east asia

mesozoic multiple magmatism and porphyry skarn cu polymetallic systems of the yidun terrane eastern tethys implications for subduction and transtension related metallogeny abstract most mineralized porphyries associated with large to giant oxidized porphyry cu deposits show an affinity with relatively high sr y features the mesozoic porphyry skarn cu polymetallic systems of the yidun terrane hosted by the late triassic and late cretaceous intrusions provide chances to investigate the spatial and genetic relationships between subduction and transtension related magmatism and mineralization and determine the petrogenesis and fertility of magmatic rocks zircon u pb ages indicate that the late triassic pre ore quartz diorite porphyries and syn ore quartz monzonite porphyries were emplaced at 225 and 215 ma respectively the late cretaceous syn ore monzogranite porphyries were emplaced at 83 78 ma our new data combined with previously published geochronological data show the spatially overlapping distribution of the multiple mesozoic porphyry systems in the yidun terrane although all the late triassic intrusive rocks share similar geochemical characteristics the pre ore quartz diorite porphyries have normal arc related chemical features with low sr y and la yb n ratios high y and yb abundances while the syn ore quartz monzonite porphyries exhibit high sr y and la yb n ratios low y and yb abundances all samples show similar sr nd hf isotopic compositions 87sr 86sr i 0 7060 0 7117 end t 6 7 to 0 0 zircon ehf t 4 0 to 3 0 suggesting that they were probably derived from partial melting of juvenile lower crust trace element patterns and partial melt modeling indicate that the quartz diorite porphyries were likely formed by partial melting of normal thick lower crust while the causative quartz monzonite porphyries were probably formed by partial melting of eclogitized thickened lower crust we propose that pre ore quartz diorite porphyries were probably generated earlier via the subduction of garze litang oceanic crust and syn ore quartz monzonite porphyries were formed later by partial melting of sulfide enriched thickened juvenile lower crust thus these high sr y quartz monzonite porphyries host several economically important porphyry cu deposits such as pualng xuejiping and songnuo however the late cretaceous syn ore monzogranite porphyries have lower ehf t values 8 4 to 2 9 and end t values 7 5 to 3 8 than the late triassic porphyries indicating that the former mainly originated from ancient crustal materials new dataset and previous studies suggest that the late cretaceous post collisional transtension triggered the asthenospheric upwelling and the underplating of mafic magmas induced the partial melting of garnet bearing amphibolite and thus caused the emplacement of monzogranite porphyries and associated porphyry skarn cu mo deposits

pan african post collisional ferro potassic granite and quartz monzonite plutons of eastern nigeria abstract three pan african hypersthene bearing monzogranitic and quartz monzonitic plutons from the eastern terrane of nigeria have been investigated in detail new major trace and ree data used to constrain their origin and nature indicate that they display chemical features of ferro potassic trans alkaline affinity further trace element discrimination suggests i production of calc alkaline medium k diorite magmas by partial melting of fluid metasomatised mantle wedge possibly combined with melts from the dehydration partial melting of altered oceanic crust ii simultaneously production of the granite quartz monzonite ferro potassic magmas from partial melting of hornblende bearing granodioritic crustal sources iii mixing of the two magmas sr initial ratios of 0 707 to 0 711 witness that the source of the granite magmas is the lower crust ages of the lower crustal granulitic protoliths is bracketed by nd model ages between 1 9 and 2 2 ga pb evaporation ages on single zircons constrain the emplacement of the three plutons around 580 ma 40 ar 39 ar ages of amphiboles at about 560 ma suggest cooling rates around 15 c ma extensive field work has established that pluton emplacement occurred during a regional north south dextral strike slip tectonics following the 630 610 ma stage of oblique continent continent collision in this part of west africa

generation of leucogranites via fractional crystallization a case from the late triassic luoza batholith in the lhasa terrane southern tibet abstract leucogranites are important in understanding intracrustal differentiation and regional tectonic evolution but how these rocks form remains a matter of much debate the luoza batholith in the central lhasa subterrane provides an important opportunity to address these issues as this batholith consists of normal calc alkaline s type granodiorites group 1 and highly fractionated s type leucogranites group 2 laser ablation inductively coupled plasma mass spectrometry zircon u pb dating indicates that these rocks were emplaced at ca 221 205 ma the group 1 samples ca 205 ma have low sio2 content 64 67 wt and low differentiation index values di 75 76 and are slightly depleted in ba p sr and ti compared to the group 2 samples ca 221 ma and 213 ma which have high sio2 content 74 75 wt high differentiation index values 91 94 and are significantly depleted in ba p sr and ti samples from group 1 and group 2 exhibit similar zircon ehf t values 15 6 to 1 4 both of which are significantly higher than melts from the pure ancient basement in the central lhasa subterrane 20 5 to 10 6 the group 1 samples can be interpreted as having been derived from the partial melting of metagreywacke within the ancient basement in the central lhasa subterrane with contributions from mantle or juvenile crust derived components whereas the group 2 samples may have formed via varying degrees of fractional crystallization of different minerals e g plagioclase k feldspar biotite zircon allanite monazite titanite and apatite from the parental magmas represented by the granodioritic samples in group 1 in shallow crustal magma chambers in combination with sedimentary records the high temperature and low pressure conditions indicated by the group 1 samples can be geodynamically linked to a back arc extensional setting in response to the southward subduction of the bangong nujiang tethys ocean seafloor our work implies that fractional crystallization is likely a feasible mechanism for the development of leucogranites and for explaining the compositional diversity of the granite during intracrustal differentiation

an ediacaran back arc basin preserved in the transversal zone of the borborema province evidence from geochemistry geochronology and isotope systematics of the ipueirinha group ne brazil abstract the ipueirinha group is a ca 75 km long by 13 km wide succession of metavolcano sedimentary rocks situated in the westernmost transversal zone borborema province ne brazil it is mostly composed of marine terrigenous sedimentary rocks represented by immature metarhythmites and quartzites local metaultramafites rhyolitic metavolcaniclastic rocks and rare lenses of metamarl the metavolcaniclastic rocks show highly fractionated chondrite normalized ree patterns lan ybn 3 68 8 94 with slight to moderately negative eu anomalies eu eu 0 72 0 94 incompatible trace element signatures similar to those of volcanic arc related rocks including a nb ta trough and negative nd t ranging from 3 4 to 12 2 metarhythmites show lree enrichment lan ybn 4 83 15 32 moderate eu anomalies eu eu 0 68 0 81 and incompatible element signatures consistent with provenance from a continental arc nd isotope data indicate important detrital contribution from juvenile sources for these metarhythmites as reflected by the nd t values between 3 6 and 0 3 detrital zircon la icp ms u pb data reveal that the main sources of detritus for the metarhythmites are neoproterozoic rocks maximum age peak at ca 845 ma and younger zircons at ca 636 ma hf isotope data obtained from detrital zircons show evidence for an important period of juvenile magmatism in the borborema province from 895 to 834 ma hf t 2 0 5 7 and suggest that the neoproterozoic crustal evolution of this province involved mixing between older sources with negative hf t and younger juvenile sources metaultramafites associated with the ipueirinha group show nd t ranging from 1 3 to 8 5 and tdm 1 33 1 64 ga the whole unit was submitted to four deformation phases and to heterogeneous metamorphic conditions from lower to upper greenschist facies additional geochronological data obtained for a granitic sill 578 13 ma zircon u pb along with monazite u pb data from a chloritite sample 595 29 ma indicate that strike slip deformation metamorphism and syn orogenic melt generation coexisted in the ipueirinha group during the late ediacaran we suggest that the ipueirinha group comprises a cryogenian ediacaran back arc basin to the tamboril santa quiteria magmatic arc which is one of the few records of initial convergence tectonics in the west gondwana margin of the borborema province

the cambrian to devonian odyssey of the brabant massif within avalonia a review with new zircon ages geochemistry sm nd isotopes stratigraphy and palaeogeography abstract this study provides an up to date and comprehensive review of the early palaeozoic evolution of the brabant massif belonging to the anglo brabant deformation belt situated at the southeastern side of avalonia microplate it is the only well known part of the northern passive margin of the rheic ocean the cambrian silurian sedimentary pile is 13 km thick with 9 km for the cambrian only the unraveling of this continuous registration reflects the successive rifting and drifting of avalonia from the gondwana mainland followed by soft collisional processes with baltica and finally the formation of laurussia based on recently established detailed stratigraphy sedimentology and basin development on u pb la icp ms analyses of igneous and detrital zircon grains along with geochemical data including sm nd isotopes a new geodynamic and palaeogeographic evolution is proposed brabant megasequence 1 lower cambrian to lowermost ordovician 9 km thick represents an embayment of the peri gondwanan rift from which the rheic ocean has evolved detrital zircon ages demonstrate that the brabant is a typical peri gondwanan terrane with a major pan african neoproterozoic age and a mixed west african and amazonian source palaeoproterozoic archaean and some mesoproterozoic age the transition towards the avalonia drifting is marked by an unconformity and a short volcanic episode the northward drift of avalonia towards baltica is recorded by the megasequence 2 middle to upper ordovician 1 3 km thick the source for mesoproterozoic zircons vanished as the result of the rheic ocean opening and the isolation from amazonian sources the transition to megasequence 3 is marked by a drastic change in palaeobathymetry and an important sub volcanic episode during a tectonic instability period 460 430 ma reflecting the avalonia baltica soft docking as also shown by the reappearance of mesoproterozoic detrital zircons typical of baltica unradiogenic nd isotope signature end 4 5 and tdm model ages 1 3 1 7 ga for brabant magmatic rocks indicate an old recycled component megasequence 3 uppermost ordovician to lowermost devonian 3 5 km thick includes the onset of a silurian foreland basin that reflects the tectonic inversion of the core of the massif brabantian orogeny in response to the baltica avalonia laurentia collision finally the comparison with the strikingly similar cambrian successions of the harlech dome wales avalonia and the meguma terrane nova scotia peri gondwana allows the construction of a new early cambrian palaeogeographic model for the whole avalonia microplate in which the meguma terrane is included

geochronology and geochemistry of late paleozoic volcanic rocks from eastern inner mongolia ne china implications for igneous petrogenesis tectonic setting and geodynamic evolution of the south eastern central asian orogenic belt abstract here we report new petrography geochemistry u pb zircon geochronology and hf isotope results for volcanic rocks of the dashizhai formation in the dashizhai area keerqin right wing front banner inner mongolia the volcanic rocks have mafic to felsic bulk rock compositions and include basalt rhyolite basaltic andesite andesite dacite and rhyolitic tuff two dacite and rhyolitic tuff samples yield laser ablation inductively coupled plasma mass spectrometry la icp ms 206pb 238u zircon ages of 332 1 ma and 300 1 ma respectively suggesting that the timing of felsic volcanism ranged from the early to late carboniferous mafic volcanic rock samples are enriched in large ion lithophile elements lile and light rare earth elements lree la nb 1 58 4 84 and are depleted in high field strength elements hfse th yb ratios

an evolving magmatic hydrothermal system in the formation of the mesozoic meishan magnetite apatite deposit in the ningwu volcanic basin eastern china abstract the meishan iron deposit contains 338 mt of iron ore reserves at 39 fe and represents the largest magnetite apatite deposit in the ningwu basin of eastern china controversy has long existed about whether this deposit had a hydrothermal or iron oxide melt origin iron mineralization is genetically related to plutons that are composed of gabbro diorite which were emplaced at 130 1 ma these rocks have sio2 contents of 51 72 54 60 wt na2o contents of 3 47 4 04 wt k2o contents of 2 02 2 69 wt and k2o na2o ratios of 0 51 0 73 these rocks are enriched in liles and lrees and depleted in nb ta and ti which indicates that the magma originated through partial melting of an enriched lithospheric mantle source in a subduction environment a pattern of decreasing initial sr isotopic ratios and increasing end t values with time in early cretaceous magmatic rocks of the ningwu basin may indicate incorporation of increasing proportions of asthenospheric mantle material into the source magma which is consistent with the processes of lithospheric thinning and asthenospheric upwelling in eastern china related to mesozoic subduction of the paleo pacific plate two stages of magnetite are found in the gabbro diorite 1 early crystallized magnetite as euhedral subhedral crystals in larger clinopyroxene crystals and 2 later crystallized magnetite and accompanying ilmenite grains in the voids between plagioclase and clinopyroxene crystals the formation of magnetite before clinopyroxene combined with the results of fe ti oxide geothermometry and analysis of magnetite v content indicates that the oxygen fugacity of the source magma was greater than fmq 2 2 at an early stage 640 c but decreased to fmq 2 66 as abundant magnetite crystallized at a later stage 489 c the early crystallization of magnetite at a high oxygen fugacity does not support a fenner evolution trend for the primitive magma and diminishes the likelihood of liquid immiscibility which could have generated an iron rich melt and is thus inconsistent with an iron oxide melt origin for the meishan iron deposit the 34s values of pyrite 6 6 15 1 and anhydrite 15 6 16 9 in the deposit and the occurrence of evaporites under the volcanic rocks likely indicate that the iron ores and alteration rocks of the meishan deposit were formed by the circulation of fluids of evaporitic origin driven by heat from the hypabyssal gabbro diorite intrusives in the late magmatic stage oxygen fugacity decreased to a reducing range triggering the reduction of sulfate to reduced sulfur and leading to local gold and pyrite mineralization

cooling of a late syn orogenic pluton evidence from laser k feldspar modelling of the carion granite madagascar since the late 1980s it has been hypothesized that the wide range of apparent argon ages seen within single k feldspar samples might be due to a distribution of diffusion domain sizes within the mineral to test and apply this idea an analytical technique that combines conventional laboratory degassing experiments resistance heating with numerical inversion procedures has been developed to extract cooling history information from feldspars a key part of the method involves careful control of temperature in the laboratory to constrain the diffusion parameters of the feldspar samples in our study we have k feldspar data from single crystals that mimic the types of data seen in classic resistance heater fusion experiments our step heating data are based on using a continuous argon ion laser with no direct control on temperature however with only a single added free parameter in the model we show that it is possible to analyze this data in the multi domain style and make some simple inferences on the nature of the cooling history of the carion pluton in central madagascar the carion granitic pluton in central madagascar was intruded into warm continental crust following orogenic events related to the final amalgamation of gondwana u pb shrimp dating of the pluton yields an emplacement age of 532 1 5 2 ma followed by relatively slow cooling as constrained by 40ar 39ar ages on hornblende biotite and k feldspar four hornblende samples yielded a mean 40ar 39ar age of 512 7 2 6 ma a biotite sample yielded an age of 478 9 1 0 ma and modeled k feldspar ages show cooling from 350 c at 466 ma to 100 c by 410 ma collectively the data suggest that the pluton cooled from 850 c at 532 1 5 2 u pb zircon ma to 500 c at 512 7 2 6 ma 40ar 39ar hornblende or approximately 18 c ma slowing to 4 c ma between 512 ma and 478 ma and finally to about 3 c ma between 478 and 410 ma

beryllium 7 as a tracer to study mechanisms and rates of metal scavenging from lake surface waters the removal of be 7 from lake surface waters lake lugano switzerland italy was studied from september 1995 to may 1996 during this period the atmospheric input and sedimentary flux of be 7 as well as concentrations of dissolved 1 m be 7 in the epilimnion were measured the separation of dissolved colloidal and particulate fractions of be 7 was carried out using continuous flow centrifugation cfc and tangential flow filtration tff techniques lacustrine colloids log kc 6 were shown to be much more efficient sorbents for be 7 than the suspended particles log kp 4 5 particle concentrations cp ranged from 0 5 to 2 mg l the ratio of colloid 10 kd to particle concentration cc cp was close to 0 09 during winter months when detrital inputs are dominant but was higher 0 16 in summer and in spring after an algal bloom the be 7 data were used to estimate coagulation rates of colloids the highest coagulation rates coag 0 4 d 1 along with the lowest kc log kc 5 2 were found after an algal bloom in spring

geochronology and geochemistry of early cretaceous granitic rocks in the dongqiao area central tibet implications for magmatic origin and geological evolution abstractwe present here new geochronological and whole rock geochemical data for the dongqiao intrusive rocks six samples yield zircon u pb ages of 111 115 ma indicating that the dongqiao granitic rocks are contemporaneous with an early cretaceous 115 110 ma magmatic flare up event in central tibet on the basis of geochemical data granitic rocks from the dongqiao area can be divided into i and a type granites the a type granites contain higher na2o k2o zr hf and zr ce nb y contents than the i type granites the results indicate that i type granites were formed by partial melting of a juvenile mafic lower crustal source while a type granites were derived from a middle crustal source followed by fractional crystallization the formation of a type granites requires broad thermal anomalies indicating that early cretaceous magmatism occurred in a postcollision extensional setting likely related to the upwelling of hot asthenospheric mantle triggered by detachment and sinking of the bango

ancient crustal recycling in modern island arcs a tale of the world s youngest charnockite from sw japan abstract modern accretionary orogens are considered as zones of extensive juvenile crustal growth on our planet with the central asian orogenic belt caob and the western pacific domain as typical examples here we report magmatic charnockites orthopyroxene bearing anhydrous monzogranite from the shikoku island in sw japan intruding the shimanto accretionary belt petrological and geochemical features of the intrusion are identical to archean paleoproterozoic and cretaceous charnockites from various parts of the world and show typical arc magmatic affinity and formation in a convergent margin setting zircon u pb data indicate that the pluton was emplaced at 13 75 ma revealing one of the youngest magmatic charnockite occurrences in the world zircon lu hf data yield epsilon hf t values in the range of 3 2 to 2 8 suggesting that the magma source involved a substantial amount of reworked material in addition to juvenile input the hf modal age tdm shows a major peak at 701 ma suggesting reworking of neoproterozoic basement rocks beneath the young island arc the data confirm the model of the birth of proto japan along the periphery of the cathaysia block in south china the modal age peak corresponds to the timing of magmatism associated with rodinia rifting our study provides evidence for the involvement of both ancient recycled components and juvenile material associated with crust building in a young island arc within an ongoing subduction system

time constraints for low angle shear zones in the central rhodopes bulgaria and their significance for the exhumation of high pressure rocks in the central rhodopes of southern bulgaria an eclogite bearing rock sheet belonging to the middle allochthon starcevo unit is over and underlain by eclogite free amphibolite facies rock units along low angle shear zones the borovica shear zone at the top and the starcevo ardino shear zone at the base the age of these shear zones is determined by u pb zircon dating of pre syn and posttectonic magmatic rocks mostly pegmatite veins using la sf icp ms zircons from pre to syntectonic pegmatites within the borovica shear zone yielded ages of ca 45 43 ma indicating that the shear zone was active at that time and zircons from a pretectonic pegmatite and a posttectonic granitoid body within the starcevo ardino shear zone yielded ages of ca 45 and ca 36 ma respectively giving a time frame for the activity of that shear zone which probably rather postdated the activity of the borovica shear zone by combining the ages with the kinematics of the shear zones and the metamorphic history of the rock units the following scenario is sketched soon after the starcevo unit reached peak pressure eclogite facies it was exhumed to a mid crustal level by top to the north west extensional unroofing along the borovica shear zone in a kinematic framework of orogen parallel extension beginning at ca 40 ma the partly exhumed starcevo unit was underthrust from the south west by continental crust of the foreland apulia forming the lower allochthon of the rhodopes along the starcevo ardino shear zone these results underline the significance of orogen parallel extension for the exhumation of high pressure rocks with respect to regional geology of the hellenides and the aegean it is found that the tectonic architecture of the rhodopes is essentially of tertiary age cretaceous syn metamorphic shear zones do exist but are largely restricted to higher levels of the nappe stack upper allochthon the rhodopes do not represent an older essentially mesozoic core of the hellenides but are formed by the internal higher metamorphic portions of the same major nappe systems as occur in the hellenides

the cosmos greenstone succession agnew wiluna greenstone belt yilgarn craton western australia geochemistry of an enriched neoarchaean volcanic arc succession abstract the geodynamic setting of the neoarchaean eastern goldfields superterrane egs of the yilgarn craton is the subject of debate some authors propose plume models while others advocate variants on a subduction accretion model for the origin of mineralised greenstone belt sequences felsic volcanism in the kalgoorlie terrane the westernmost terrane of the egs is considered to have a tonalite trondhjemite granodiorite dacite ttg d geochemical affinity the cosmos greenstone succession which lies in the agnew wiluna greenstone belt awb of the kalgoorlie terrane contains several komatiite hosted nickel sulphide deposits the volcanic footwall to which consists of an intercalated succession of fragmental and coherent rocks ranging in composition from basaltic andesite to rhyolite light rare earth elements lrees and large ion lithophile elements liles are strongly enriched relative to high field strength elements hfses across all volcanic units and the rocks display strong positive pb and negative nb anomalies these geochemical characteristics resemble closely those of modern high k calc alkaline to shoshonite continental arc successions contrasting ree lile and hfse concentrations coupled with assimilation fractional crystallisation afc modelling shows that the intercalated dacitic and andesitic volcanic rocks within the footwall succession are not co genetic xenocrystic zircons within the felsic volcanic lithologies indicate that some assimilation of older continental crust contributed to the generation of the footwall volcanic sequence the geochemical characteristics of the cosmos volcanic succession indicate that parental melts were derived via partial melting of enriched peridotite that had been contaminated by subducted crustal material within the mantle wedge of a subduction zone in contrast two younger felsic porphyry intrusions which cross cut the volcanic succession have a distinct ttg d affinity therefore these intrusions are considered to be generated via partial melting of a subducting slab and are related to local high ca granitoid intrusions the cosmos volcanic succession represents the first extrusive high k calc alkaline to shoshonitic volcanic arc sequence described in the kalgoorlie terrane and coupled with age dating of the stratigraphy is indicative of formation in a long lived volcanic arc setting active from 2736 ma to later than 2724 ma the composition and geochemical affinity of the volcanic footwall succession to the cosmos komatiite hosted nickel sulphide deposits contrasts with the majority of felsic volcanic rocks within the awb and also the wider kalgoorlie terrane suggesting that the overall architecture of this region is more complex than is currently thought our conclusions not only have consequences for recent models of the tectonic evolution of the egs but also contribute to the debate on the operation of plate tectonics during the late archaean in general the arc affinity of the cosmos volcanic succession containing abundant high k calc alkaline andesite lavas provides further support for the operation of plate tectonics in the neoarchaean

trace elemental and sr nd hf isotopic compositions and u pb ages for the kitakami adakitic plutons insights into interactions with the early cretaceous trt triple junction offshore japan abstract we conducted major trace element sr nd hf isotopic and u pb geochronologic analyses of early cretaceous kitakami granitic plutons northeast japan we suggest that these plutons include rocks of adakitic affinity which indicate partial melting of an eclogitic slab the kitakami adakites were mostly derived from juvenile oceanic crustal sources but include inherited zircons with archean to neoproterozoic hf model ages rather than being directly derived from crustal rocks of these ages zircons may have been detrital in the voluminous trench fill sandstone within the jurassic northern kitakami accretionary prism the exhumation of older basement that served as the detrital zircon source may have been triggered by ridge subduction although the plutons show a general southward younging from northern kitakami 120 130 ma southern kitakami 115 125 ma and abukuma 100 115 ma restoration of post crystallization left slip faults inverts this spatial pattern and results in a northward younging pattern this suggests northward migration of a trench ridge transform triple junction that included the izanagi farallon ridge the sambagawa eclogite may be genetically related to the kitakami adakite in time and space if the transform duplexing is restored

geochemistry and zircon u pb hf isotopes of paleozoic intrusive rocks in the damao area in inner mongolia northern china implications for the tectonic evolution of the bainaimiao arc abstract the tectonic evolution of the central asian orogenic belt caob is related to the subduction and closure of the paleo asian ocean pao considerable controversy still surrounds whether when and how the pao subducted underneath the northern margin of the north china craton ncc this study carries out whole rock geochemical and zircon u pb hf isotopic investigations on paleozoic intrusive rocks in both the bainaimiao arc and the northern margin of the ncc zircon u pb dating of gabbroic diorite and diorite in the bainaimiao arc and the granite and diorite at the northern margin of the ncc yielded crystallization ages of 458 2 ma 428 2 ma 326 2 ma and 258 2 ma respectively in the bainaimiao arc the middle silurian diorite as the main body of the arc related intrusive rocks there show geochemical characteristics of continental margin arc magma with negartive hf t values and old hf model ages on the other hand the middle ordovician gabbroic diorite mainly shows typical calc alkaline continental arc geochemical characteristics with positive hf t values and relative young hf model ages indicative of the southward propagating reworking and arc accretion processes thus we interpret these rocks as a consequence of southward subduction of the pao beneath the bainaimiao arc here termed as bainaimiao arc terrane bat the early carboniferous granite and late permian diorite at the northern margin of the ncc show geochemical characteristics similar to post collisional adakites and typical continental arc rocks respectively combined with previous work the early carboniferous post collisional adakite shows limited distribution and corresponds to the subsequent effect of the amalgamation between the bat and the ncc whereas most of the carboniferous permian magmatic rocks ca 342 258 ma at the northern margin of the ncc are arc related and resulted from the continued effect of the southward subduction of the pao moreover the southward subduction in the early paleozoic was transformed from relative high angle subduction beneath the bat to shallow subduction beneath the unity of the ncc and the bat in the late paleozoic which lasted until the late permian ca 258 ma

the vilalba gold district a new discovery in the variscan terranes of the nw of spain a geologic fluid inclusion and stable isotope study abstract this work defines the vilalba gold district a new gold region in the nw of spain comprising three mineralized areas castro de rei valina azumara and arcos and two different types of mineralization 1 w au skarn in castro de rei and 2 au as ag pb zn cu sb vein disseminated mineralization in valina azumara and arcos mineralization is mainly hosted by impure limestone and black slates lower cambrian and spatially related to variscan and late variscan structures rhyolite dikes occur in arcos 299 6 ma and castro de rei both consisting of peraluminous high potassium and calc alkaline rocks these dikes represent the fractionated expression of unexposed post tectonic granitoids located at depth the castro de rei area exhibits a contact aureole with biotite cordierite and calc silicate hornfels prograde skarn consists of garnet pyroxene quartz wollastonite and scheelite the retrograde alteration took place in two stages and mainly consists of amphibole epidote zoisite quartz calcite chlorite and sulfides gold mineralization in the skarn occurs as invisible gold in sulfoarsenides and as electrum related to bi te s minerals the mineralization of valina azumara and arcos comprises two stages the first consists of as rich pyrite and arsenopyrite with invisible gold the second stage mainly consists of base metal sulfides and ag pb zn cu sb sulfosalts hydrothermal fluids involved in the skarn formation are low salinity up to 6 6 wt nacl eq aqueous carbonic fluids h2o co2 ch4 n2 evolving into aqueous fluids during the last stage of gold mineralization stable isotope geochemistry indicates the importance of a magmatic fluid in the early stages 18osmow from 7 5 to 11 34scdt from 2 7 to 5 9 that evolved through interaction with host rocks and mixing with metamorphic and or meteoric fluids the 34scdt values 7 8 10 9 of second retrograde stage sulfides suggest the incorporation of 34s enriched from host rocks in valina azumara and arcos the fluid inclusion and isotope studies indicate similar hydrothermal fluids to those associated with the second retrograde skarn stage taking into account the fluid inclusion study and mineral geothermometry an attempt was made to determine the p t conditions of ore formation the prograde skarn of castro de rei formed at temperatures and pressures ranging from 520 to 560 c and from 1 7 to 2 5 kb the mineralization of valina azumara formed at minimum p t conditions of 1 7 kb and 355 c the estimated temperatures for the arcos mineralization are similar to those of valina azumara up to 383 c but at lower pressures we propose the model of intrusion related gold systems irgss to explain the mineralizations of the vilalba gold district in this model the castro de rei skarn and the valina azumara mineralization represent a proximal and a distal deposit respectively relative to an unexposed granitoid situated at depth we also consider arcos as a distal deposit in relation to another unexposed granitoid located further south in the district

attenuation and velocity structure for site response analyses via downhole seismogram inversion a seismic waveform inversion algorithm is proposed for the estimation of elastic soil properties using low amplitude downhole array recordings based on a global optimization scheme in the wavelet domain complemented by a local least square s fit operator in the frequency domain the hybrid scheme can efficiently identify the optimal solution vicinity in the stochastic search space whereas the best fit model detection is substantially accelerated through the local deterministic inversion results presented for selected aftershocks of the mw 7 0 sanriku minami earthquake in japan recorded by the kik net strong motion network illustrate robustness of the impedance structure estimation by contrast the attenuation structure is shown to be sensitive to the frequency content of seismic input data attributed to the deterministic description of the continuum in the forward model that cannot simulate late arrivals of multiple scattered energy sensitivity analyses illustrate that for the same forward model results can be substantially different based on the definition of the objective function it is concluded that even for engineering purposes inversion should aim to decouple intrinsic and scattering attenuation mechanisms

the significance of mafic microgranular enclaves in the petrogenesis of the dehno complex sanandaj sirjan belt iran abstract quartz monzodioritic and granodioritic enclaves occur in the upper cretaceous paleocene dehno complex nw of isfahan iran they are hosted by hornblende granodiorite and granodiorite monzogranite respectively the presence of xenocrystic plagioclase biotite quartz magnesio hornblende occasionally with relics of clinopyroxene in quartz monzodiorites minor k feldspar and the lack of peraluminous minerals dominate the mineralogy of these rocks and suggest a metaluminous source the plagioclase in the quartz monzodioritic enclaves has higher an content than that of the respective plagioclase of their host hornblende granodiorite indicating crystallization from more mafic magma the quartz monzodioritic enclaves generally contain higher values of fe 2 o 3 mgo cao mno na 2 o transition elements ni cr co v ree and lower values of sio 2 k 2 o p 2 o 5 and zr than their host which are in consistent with occurrence of abundant ferromagnesian minerals in these rocks compare to their host the granodioritic enclaves have higher amount of fe 2 o 3 mgo mno tio 2 p 2 o 5 rb zr y ni cr co and lower concentration of sio 2 k 2 o and ba aside from hornblende granodiorite and granodiorite monzogranite the dehno complex comprises leucogranodiorite and tourmaline leuco granites geochemically the rocks of the complex are metaluminous to strongly peraluminous and are enriched in lile e g rb k sr ba and depleted in hfse e g nb ta p ti zr hf with medium to high k calc alkaline nature these geochemical features are proposed for the volcanic arc granites emplaced in an active continental margin whole rock and quartz 18 o values for all rocks are high 9 7 14 4 and 10 1 14 9 respectively suggesting the interaction of magma with crustal derived components the strongly peraluminous composition can be interpreted in terms of this hypothesis all these mineralogical and geochemical features support the idea that the granitoid rocks of the dehno complex developed through variable degrees of mixing mingling between a basic magma and a supracrustal melt during subduction of the neotethys oceanic crust beneath central iranian microcontenent the quartz monzodioritic enclaves most likely represent the nearest composition to the original more mafic magma the granodioritic enclaves result from the mixing mingling of globules basic magma with host granitic magma

metamorphic sole rocks and their mafic dykes in the eastern tauride belt ophiolites southern turkey implications for oib type magma generation following slab break off the metamorphic sole rocks observed between the pozanti karsanti ophiolite and the melange unit are located on the eastern part of the tauride carbonate platform they consist of ortho amphibolites at the top and metasedimentary lithologies at the base amphibolites from the metamorphic sole rocks are represented by oib morb and iat based on their major trace and ree compositions the isolated dolerite dykes intrude both the metamorphic sole rocks and the ophiolitic unit at different structural levels the dolerite dykes cutting the metamorphic sole rocks are enriched in lile and depleted in hfse enrichment in lile such as th relative to hfse is indicative of the presence of a subduction component flat lying ree patterns of the dolerite dykes also confirm an iat source pyroxenite and albitite dykes also cut the metamorphic sole rocks ree patterns of pyroxenite dykes show prominent lree enrichment similar to that observed in within plate alkaline basalts the alkaline isolated pyroxenite dykes were probably the result of late stage magmatism fed by melts that originated from an oib source shortly before the emplacement of the pozanti karsanti ophiolite onto the tauride carbonate platform a hydrothermal alteration stage is characterized by albitite formation in the joints of the metamorphic sole rocks and by secondary mineralization along the contact zones of dolerite dykes mineral parageneses in the metamorphic sole rocks exhibit amphibolite and greenschist facies assemblages geothermobarometric studies based on a newly recognized mineral assemblage e g kyanite and chemical compositions of minerals in the metamorphic sole rocks indicate that the metamorphic temperature during the metamorphism was 570 580 c and the pressure was around 5 6 kbar

lower carboniferous post orogenic granites in central eastern sierra de velasco sierras pampeanas argentina u pb monazite geochronology geochemistry and sr nd isotopes the central eastern part of the sierra de velasco sierras pampeanas nw argentina is formed by the large huaco 40 30 km and sanagasta 25 15 km granite massifs and the small la chinchilla stock 2 2 km the larger granites intrude into ordovician metagranitoids and crosscut devonian mylonitic shear zones whereas the small stock sharply intrudes into the huaco granite the two voluminous granites are biotitic muscovitic and biotitic porphyritic syeno to monzogranites they contain small and rounded tonalitic and quartz dioritic mafic microgranular enclaves the small stock is an equigranular zinnwaldite and fluorite bearing monzogranite the studied granites are silica rich sio2 70 potassium rich k2o 4 ferroan alkali calcic to slightly calk alkalic and moderately to weakly peraluminous a cnk 1 06 1 18 huaco granite 1 01 1 09 sanagasta granite 1 05 1 06 la chinchilla stock they have moderate to strong enrichments in several lil li rb cs and hfs nb ta y th u elements and low sr ba and eu contents u pb monazite age determinations indicate lower carboniferous crystallization ages 350 358 ma for the huaco granite 352 7 1 4 ma for the sanagasta granite and 344 5 1 4 ma for the la chinchilla stock the larger granites have similar nd values between 2 1 and 4 3 whereas the younger stock has higher nd of 0 6 to 1 4 roughly comparable to the values obtained for the carboniferous san blas granite 1 4 to 1 7 located in the north of the sierra the huaco and sanagasta granites have a mainly crustal source but with some participation of a more primitive possibly mantle derived component the main crustal component can be attributed to ordovician peraluminous metagranitoids the la chinchilla stock derives from a more primitive source suggesting an increase with time in the participation of the primitive component during magma genesis the studied granites were generated during a post orogenic period in a within plate setting possibly as a response to the collapse of the previous famatinian orogen extension of the crust and mantle upwelling they are part of the group of middle devonian lower carboniferous granites of the sierras pampeanas the distribution and u pb ages of these granites suggests a northward arc parallel migration of this mainly post orogenic magmatism with time

magmatic evolution of the alboran region the role of subduction in forming the western mediterranean and causing the messinian salinity crisis the magmatic evolution of the alboran region westernmost mediterranean contains important clues for improving our understanding of the origin of mediterranean style back arc basins and the desiccation of the mediterranean sea in the messinian we use new laser 40ar 39ar age and geochemical major and trace element and o sr nd pb isotope data from igneous rocks from southern spain the alboran sea and northern morocco to reconstruct the magmatic evolution of the westernmost mediterranean since the eocene lower oligocene dikes near malaga 33 6 0 6 ma and middle to upper miocene volcanic rocks from the alboran sea area 6 57 0 04 to 11 8 0 4 ma can be subdivided into two groups 1 lree depleted relative to n morb primarily tholeiitic series and 2 lree enriched primarily calc alkaline series volcanic rocks both groups are generally enriched in fluid mobile elements e g rb th u k and pb relative to fluid immobile elements e g nb ta lree the lree depleted group has 143nd 144nd 0 5128 0 5130 isotope ratios similar to atlantic morb but higher 87sr 86sr 0 7046 0 7100 in contrast the lree enriched group has less radiogenic nd 0 5121 0 5126 and tend to more radiogenic sr 0 7066 0 7205 isotopic composition pb isotope ratios are surprisingly uniform and have compositions similar to marine sediments analyses of mineral separates show that mafic melts with relatively low 18o 5 6 7 2 had high 87sr 86sr 0 7048 0 7088 7 4 10 6 14 1 and 8 4 40 0 49 3 modeling of the trace elements and sr nd pb o isotopic compositions provides compelling evidence for the contamination of the mantle source with hydrous fluids melts which can be explained through subduction of oceanic lithosphere beneath the alboran basin but not through detachment delamination of lithospheric mantle we present a geodynamic model that reconstructs the late eocene to quaternary evolution of the western mediterranean through westward roll back of subducted tethys oceanic lithosphere slab roll back resulted in a large scale reorganization of the western mediterranean paleogeography causing the closure of marine gateways linking the atlantic ocean to the mediterranean sea isolation of the mediterranean sea led to its desiccation causing the messinian salinity crisis

age of a late quaternary 13 6 cal kyr bp eruption and associated marker tephra of the tengchong volcanoes yunnan province southwestern china abstract the tengchong volcanoes in western yunnan province are some of the youngest volcanoes in china and determining their eruption ages would further our understanding of their genesis and historical activity in this study the age of a late quaternary eruption of dayingshan volcano was obtained by dating organic rich sediments that envelope a 5 cm thick visible tephra layer found in the yubi peat section compositionally the purified glass shards extracted from the layer by density separation are calc alkaline trachyandesite and trachyte trachydacite which is consistent with the composition of the dayingshan lava an age depth model of the yubi section was constructed from accelerator mass spectrometry ams 14c dating of peat samples and poisson models of deposition p sequence functions using oxcal with the intcal 13 database this yielded an age for the tephra layer of 13 642 84 cal yr bp a nearly identical tephra layer occurs in the qinghai crater lake sediments the yubi tephra is now a reliable age and stratigraphic marker layer useful for regional paleoclimate and tephrochronology research

primary magmatic biotite in granitoid intrusions associated with late mesozoic jinchanggouliang erdaogou lode gold deposits north china craton linkage to gold mineralization abstract the late mesozoic jinchanggouliang and erdaogou lode gold deposits in the central segment of the northern north china craton are mainly hosted in late archaean metamorphic rocks of the jianping formation and jurassic volcanic sedimentary rocks these deposits are spatially and temporally associated with a series of i type granitoid intrusions i e the 128 136 ma duimiangou granodiorite complex with a massive margin and a porphyritic center at jinchanggouliang the 161 4 1 1 ma loushang quartz diorite intrusion and numerous syenite porphyry dykes 160 9 1 0 ma at erdaogou and the 227 217 ma xitaizi monzogranite batholith compositions of primary magmatic biotite in these granitoid intrusions have been used to investigate the nature of granitoid magmas and the evolution of magmatic processes and to identify possible linkages between gold mineralization and granitoid magmatism all primary magmatic biotite grains are mg rich in composition xmg mg mg fe 0 41 0 69 the cl contents of biotite 0 09 0 42 wt in the loushang quartz diorite and the duimiangou massive granodiorite correlate negatively with xmg and are consistent with the mg cl avoidance rule the cl contents of biotite 0 01 0 14 wt in the duimiangou porphyritic granodiorite syenite porphyry and xitaizi monzogranite on the other hand remain relatively constant and may be affected by multiple variables such as cl rich fluids and subtle changes in temperature halogen fugacity of the parental magma calculated from biotite shows that the duimiangou granodiorite complex at jinchanggouliang and syenite porphyry dykes at erdaogou have the log fhf fhcl ranges of 0 71 to 0 27 and 2 16 to 1 08 respectively and have similar log fh2o fhcl values from 3 53 to 4 23 oxygen fugacities logfo2 calculated from biotite equilibria for the duimiangou granodiorite complex and syenite porphyry dykes are 13 7 to 7 2 straddling on the nickel nickel oxide and hematite magnetite buffers the xitaizi monzogranite and the loushang quartz diorite have lower log fo2 values from 14 9 to 12 4 between the nickel nickel oxide and hematite magnetite buffers the duimiangou granodiorite complex and syenite porphyry dykes with high oxygen fugacities are similar to oxidized magmas associated with porphyry cu mo au deposits these results suggest that multiple episodes of i type granitoid magmas in the study area were rich in cl and high in oxygen fugacity especially those associated with the duimiangou granodiorite complex and syenite porphyry dykes the i type melts represented by the duimiangou granodiorite complex and syenite porphyry dykes as well as their related cl rich oxidizing fluids were likely efficient in dissolving transporting and precipitating gold for the formation of the jinchanggouliang and erdaogou lode gold deposits

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

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

the urumieh plutonic complex nw iran a record of the geodynamic evolution of the sanandaj sirjan zone during cretaceous times part i petrogenesis and k ar dating the urumieh plutonic complex is located in the northwestern part of the sanandaj sirjan zone iran the urumieh plutonic complex comprises three components i e a dioritic suite a granitic suite consisting of biotite bearing granites and younger stocks i e an alkaline suite alkali syenite and alkali granite and a muscovite bearing granite based on k ar chronology of separated minerals amphibole biotite muscovite and feldspar and field observations the urumieh complex was built during two distinct episodes the diorite and granite suites were emplaced between 100 and 92 ma whereas the younger suites were emplaced between 82 and 80 ma the dioritic suite has sio2 contents in between 56 59 wt and major and trace elements characteristic of mafic i type granitoids a ckn molar ratio 0 81 0 88 this suite is characterized by relatively high mg 49 low na2o content 3 5 wt and a relatively high abundance of lile incompatible elements their chondrite normalized ree patterns are relatively flat la yb n 7 in average and show small or no negative eu anomalies eu eu 0 9 in average some diorites show mingling and mixing textures that may support local crustal contamination of the dioritic melt geochemical features suggest that diorites formed in a subduction setting by partial melting of metasomatized mantle the coeval granites are peraluminous 1 04 molar a ckn 1 37 with sio2 contents between 66 69 wt their chondrite normalized ree patterns are slightly enriched in lree relative to hree la yb n 11 in average with negative eu anomalies eu eu 0 4 in average these granites have biotite as the main mafic mineral and locally contain restitic xenoliths they originated by partial melting of metasediments the younger alkaline syenite and granite are only slightly peraluminous molar a cnk 1 04 in average they show enrichment in hfse high contents of ree and relatively high feo mgo and ga al ratios typical of a type magmas the other younger granite pluton dourbeh granite has peculiar mineralogical and geochemical features none of these late syenite and granites were intruded by mafic dikes and they do not contain any comagmatic mafic enclaves they seem to have been derived only from crustal melting changing of magmatic sources during the 100 80 ma time interval is discussed with respect to the geodynamic context the first magmatic episode 100 92 ma is regarded as subduction related whereas the second one at ca 80 ma likely ocurred during the collision between the arabian margin and the sanandaj sirjan zone

zircon u pb and molybdenite re os dating and geological implications of the shimadong porphyry molybdenum deposit in eastern yanbian northeastern china the shimadong porphyry mo deposit is located in eastern yanbian in the eastern part of the north margin of the north china craton northeastern china here we present the whole rock major and tra

trace element and isotope sr nd geochemistry of porphyry and skarn mineralising late cretaceous intrusions from banat western south carpathians romania geochemical and isotopic strontium neodymium data have been obtained from 24 samples of seven late cretaceous intrusions associated with skarn tincova bocsa ocna de fier dognecea and porphyry copper molybdenum skarn deposits oravi a ciclova sasca and moldova nou in the south carpathians of romania the intrusions cut the supragetic getic nappes and form a 100 km long nne ssw trending lineament in the banat metallogenic province the samples range in composition from gabbro to granodiorite and define in major and trace element variation diagrams a calc alkaline to high potassium calc alkaline trend ranging from 50 to 67 sio2 they are magnetite bearing i type granitoids enriched in lile lree and depleted in nb ta and zr common features for magmas associated with subduction zones the lack of cumulate textures and of positive europium anomalies seems to indicate that the samples represent liquid compositions the observed trend thus approximates a liquid line of descent resulting from fractional crystallisation of parental magmas with similar major and trace element compositions initial strontium isotopic ratios sri vary from 0 7042 to 0 7058 and end t values range from 3 9 to 0 2 variations of sri and end t values with sio2 show minor crustal assimilation the generally positive end t values together with moderate sri indicate that the parental magmas result from partial melting of a rubidium enriched and lree depleted source such as a heterogeneous lithospheric mantle or a young mafic lower crust derived from it selective rubidium enrichment probably occurred during a previous subduction event by metasomatism of the overlying mantle wedge either in the early cretaceous or earlier as suggested by tdm model ages ca 600 ma the cu mo pb zn fe deposits are intimately associated with the intrusions and the banat romania region can be subdivided in two metallogenic zones in northern banat fe cu pb zn skarns occur whereas in southern banat porphyry style copper and molybdenum deposits predominate these differences result from a combination of several parameters 1 magma composition whereby copper and molybdenum rich deposits tend to be associated with calc alkaline compositions 2 an increase of the present day erosion level from south to north as indicated by the presence of large equigranular plutons in northern banat and of porphyritic cupolas and apophyses associated with porphyry style mineralisation in southern banat 3 the nature of the host rocks with skarns preferentially developed in calcareous host rocks and 4 local variations of conditions controlling the infiltration of fluids and the precipitation of ore minerals

petrogenesis geochronology and tectonic significance of granitoids in the tongshan intrusion anhui province middle lower yangtze river valley eastern china abstract the tongshan copper deposit in anhui province is a typical mid sized skarn and porphyry type deposit in the anqing guichi district along the middle lower yangtze river valley eastern china the tongshan intrusion is closely related to this mineralization the intrusion mainly comprises rocks that are quartz diorite porphyry quartz monzonite porphyry and granodiorite porphyry plagioclase in these rocks is mostly andesine an 31 0 42 9 along with minor oligoclase biotite is magnesium rich mg mg fe 0 52 0 67 and aluminum poor al 2 o 3 12 32 14 09 wt and can be classified as magnesio biotite hornblende is tio 2 poor 0 60 and is magnesio hornblende or edenite the shrimp zircon u pb age of the quartz monzonite porphyry is 145 1 1 2 ma which corresponds to the middle yanshanian period whole rock geochemical results show that the rocks are silica rich sio 2 60 23 66 23 wt and alkali rich k 2 o na 2 o 4 97 8 72 wt and low in calcium cao 2 61 5 66 wt trace element results show enrichments in large ion lithophile element e g k rb and ba and depletions in some high field strength elements e g nb ta p and ti the total rare earth element ree content of the rocks is low ree n 10 and small positive eu anomalies average eu 1 16 these mineralogical geochronological and geochemical results show that the intrusion has a mixed crust mantle source the tongshan intrusion was formed by multiple emplacements of crustally contaminated basaltic magma generated by varying degrees of partial melting of enriched lithospheric mantle and lower crust hornblende thermobarometry yielded magmatic crystallization temperatures of 652 788 c and an average crystallization pressure of 1 4 kbar which corresponds to a depth of approx 4 7 km biotite thermobarometry yielded similar temperatures and lower pressures of 735 775 c and 0 6 kbar depth 2 1 km respectively the parental magma had a high oxygen fugacity and was produced in a volcanic arc setting related to subduction of the paleo pacific plate

geochemistry and zircon geochronology of the i type high k calc alkaline and s type granitoid rocks from southeastern roraima brazil orosirian collisional magmatism evidence 1 97 1 96 ga in central portion of guyana shield abstract the understanding of the geological evolution of the uatuma anaua domain in southeastern roraima central region of guyana shield is of major significance in the study of the amazonian craton this region lies between some major paleoproterozoic geological geochronological provinces tapajos parima or ventuari tapajos dominant maroni itacaiunas or transamazon northwest and central amazonian or central amazon southeast and east geological mapping of the northern area of uatuma anaua domain integrated with whole rock geochemistry data and previous and new pb evaporation and u pb zircon geochronology point out for a plutonic collisional magmatic event 1975 1968 ma represented by i type high k calc alkaline martins pereira and s type serra dourada granitoid rocks this magmatism was probably generated from crustal sources by partial melting during amalgamation of the ttg like anaua magmatic arc 2028 ma with transamazonian 2 2 2 0 ga and central amazonian older than 2 3 ga terranes local cumulatic leucogranites fills planar structures of the martins pereira granites these leucogranites show younger ages 1909 ma and several inherited zircons 2354 2134 1997 and 1959 ma suggesting origin from crustal sources

magma origins and geodynamic implications for the makran chagai arc from geochronology and geochemistry of bazman volcano southeastern iran abstract bazman is an isolated voluminous 3497 m elevation 300 km2 composite volcano that is located within the western segment of the makran chagai arc this arc obliquely tracks the modern ew trending trench offshore the oman sea coast of iran and pakistan with several quaternary stratovolcanoes bazman and taftan in se iran and kuh i sultan in western pakistan superimposed on a preexisting neogene arc high spatial resolution and high sensitivity u pb geochronology using secondary ionization mass spectrometry sims yielded four clusters of zircon ages for bazman volcanic rocks which range from ca 8 6 ma to 41 ka lava and pyroclastic materials erupted between 8 6 and 5 9 ma forming a thick neogene volcanic succession ngv these deposits were intruded by hypabyssal andesite dacite domes at ca 4 1 ma the next younger group of the quaternary bazman center comprises several eruptive pulses at 1 37 ma 1 13 ma 0 943 ma 0 853 ma and 0 635 ma which constructed the main edifice around a central vent through alternating eruptions of lava and pyroclastic rocks qtv and qa2 subsequently ignimbrite flows also sourced from the main vent erupted at 0 59 and 0 47 ma and covered the earlier erupted deposits the youngest dated eruptive phase qa3 comprises the emplacement of dacitic to andesitic lava around the top of volcano based on uranium series 238u 230th disequilibrium in qa3 zircons model ages of ca 41 ka define a maximum eruption age of these lavas which tapped a long lived magma reservoir with zircon crystallization ages predating eruption by 10 s to 100 s of ka low medium k calc alkaline basaltic andesitic eruptions formed parasitic cones located on northeastern flanks of the edifice as the youngest unit qa4 of bazman both neogene and quaternary rocks from bazman volcano exhibit homogeneous trace element characteristics including enrichments in large ion lithophile elements lile and light rare earth elements lree relative to the high field strength elements hfse and heavy rare earth elements hree respectively high th yb and negative anomalies of ta nb and ti are consistent with an enriched mantle source in a continental subduction zone trace element modeling for the most primitive basalts erupted at bazman suggests an origin of parental magmas through 15 partial melting of an enriched spinell lherzolite mantle whereas the genesis of bazman acidic volcanic rocks with sio2 62 involves partial melting in the middle lower continental crust which became subsequently overprinted through assimilation fractional crystallization afc processes compositional continuity of quaternary bazman volcanic rocks with their neogene precursors implies a steady magma source above the subducted oman slab consequently subduction geometry in the makran chagai arc has experienced little modification over the past few million years

geochemistry of the coastal sonora batholith northwestern mexico new major and trace element and radiogenic sr and nd data from granitic rocks help to characterize the geochemical composition of the coastal sonora batholith which represents the westernmost portion of the laramide magmatic arc 80 40 ma in mexico compared with more inland located regions of the arc in central and eastern sonora inner granites the plutons within the coastal batholith have higher mgo feo and cao and lower k2o contents and tend to be more depleted in nb u and to a lesser extent rb but relatively enriched in sr these rocks display flatter slopes of rare earth elements with la abundances around 80 to 200 times chondrite values and smaller but well developed negative eu anomalies initial 87sr 86sr ratios and end values from a few studied samples of the coastal sonora batholith range from 0 70586 to 0 70679 and from 2 3 to 4 7 respectively these isotopic signatures allow recognition of a more mantle related magma source for this batholith as compared with the inner granite

porphyry cu au mineralization in the mirkuh ali mirza magmatic complex nw iran abstract the mirkuh ali mirza cu au porphyry system in east azerbaijan province is located on the western part of the cenozoic alborz azerbaijan volcanic belt the belt is also an important cu mo au metallogenic province in northwestern iran the exposed rocks in the study area consist of a volcaniclastic sequence subvolcanic rocks and intermediate to mafic lava flows of neogene age the volcanic rocks show a typical subduction related magmatic arc geological and geochemical signature with low concentration of nb ta and ti mineralization is hosted by neogene dacitic tuff and porphyritic dacite situated at the intersections of northeast and northwest faults field observations alteration zonation geochemical haloes and isotopic data of the mirkuh ali mirza magmatic complex show similarities with typical convergent margin cu au porphyry type deposits the following features confirm the classic model for cu au porphyry systems a close spatial association with high k calcalkaline to shoshonitic rock related to post collision extensional setting b low grade cu 0 57 c stockworks as well as disseminated sulfides c zonality of the alteration patterns from intense phyllic at the center to outward weak phyllic argillic and propylitic d the presence of a pyritic halo e accompanied by sheeted veins and low sulfidation epithermal gold f mineralization spatially associated with intersection of structures g genetically related to diorite porphyry stocks at depth h geochemical zonation of cu au ag bi cu mo bi au pb zn as au mo pb zn as ag sb mn ba pb zn hg hg from center to outwards i the range of sulfur isotopic values is approximately zero interpreted to have magmatic source and similar to other subduction related porphyry cu deposits

timing and genesis of the adakitic and shoshonitic intrusions in the laoniushan complex southern margin of the north china craton implications for post collisional magmatism associated with the qinling orogen abstract the nww striking qinling orogen formed in the triassic by collision between the north china and yangtze cratons triassic granitoid intrusions mostly middle to high k calc alkaline are widespread in this orogen but contemporaneous intrusions are rare in the southern margin of the north china craton an area commonly considered as the hinterland belt of the orogen in this paper we report zircon u pb ages elemental geochemistry and sr nd hf isotope data for the laoniushan granitoid complex that was emplaced in the southern margin of the north china craton zircon u pb dating shows that the complex was emplaced in the late triassic 228 1 to 215 4 ma indicating that it is part of the post collisional magmatism in the qinling orogen the complex consists of from early to late biotite monzogranite quartz diorite quartz monzonite and hornblende monzonite which span a wide compositional range e g sio2 55 9 70 6 wt k2o na2o 6 6 10 2 wt and mg of 24 to 54 the biotite monzogranite has high al2o3 15 5 17 4 wt sr 396 1398 ppm and ba 1284 3993 ppm contents and relatively high la yb mostly 14 30 and sr y mostly 40 97 ratios but low yb mostly 1 3 1 6 ppm and y mostly14 19 ppm contents features typical of adakitic rocks the quartz monzonite hornblende monzonite and quartz diorite have a shoshonitic affinity with k2o up to 5 58 wt and k2o na2o ratios averaging 1 4 the rocks are characterized by strong lree hree fractionation in chondrite normalized ree pattern without obvious eu anomalies and show enrichment in large ion lithophile elements but depletion in high field strength elements nb ta ti the biotite monzogranite 228 ma has initial 87sr 86sr ratios of 0 7061 to 0 7067 end t values of 9 2 to 12 6 and ehf t values of 9 0 to 15 1 whereas the shoshonitic granitoids mainly 217 215 ma have similar initial 87sr 86sr ratios 0 7065 to 0 7075 but more radiogenic end t 12 4 to 17 0 and ehf t 14 1 to 17 0 the sr nd hf isotope data indicate that the rocks were likely generated by partial melting of an ancient lower continental crust with heterogeneous compositions as partly confirmed by the widespread presence of early paleoproterozoic inherited zircons mafic microgranular enclaves mmes characterized by fine grained igneous textures and an abundance of acicular apatites are common in the laoniushan complex compared with the host rocks they have lower sio2 48 6 53 7 wt and higher mg 51 56 cr 122 393 ppm and ni 24 79 ppm but equivalent sr nd isotope compositions indicating that the mmes likely originated from an ancient enriched lithospheric mantle the abundance of mmes in the granitoid intrusions suggest that magma mixing plays an important role in the generation of the laoniushan complex collectively it is suggested that the laoniushan complex was a product of post collisional magmatism related to lithospheric extension following slab break off formation of the adakitic and shoshonitic intrusions in the laoniushan complex indicates that the qinling orogen had evolved into a post collisional setting by about 230 210 ma